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June 22

basic physics question about inertia, riding the bus, balance, etc.

When I ride the city bus I stand perpendicular (facing out the window) to the direction of movement (forward). Knowing that we will soon be approaching a stop, I shift my weight to my rear (nearer the back of the bus) leg. Then, as the bus rapidly decelerates, I gradually shift my weight to my front (neared to front of the bus) leg and thereby disperse the change in inertia? velocity? momentum? in a controlled fashion. Done properly, I never need grasp a handrail no matter how abruptly the bus stops. At no time am I off-balance.

What I want to know is: from a Physics standpoint, what exactly is going on here? How can I properly describe this sequence of events? As a layperson, I can sum it up by just saying "shifting my weight and maintaining my balance" but I'm very curious to hear a detailed explanation of the physics involved. Any takers?

Thank you! —Preceding unsigned comment added by 218.25.32.210 (talk) 01:14, 22 June 2010 (UTC)

You are making sure the reactive force on your feet from the floor (well, the total of the forces on each foot) points through your centre of mass (by moving your centre of mass), so that it does not produce a torque. The direction of that force will usually simply be "up", but when the bus accelerates/decelerates the direction changes. You can think of this simply as a change in the direction that is "up", since the equivalence principle tells us that acceleration is indistinguishable from gravity (without external reference, so let's assume the bus's windows are so dirty you can't see out - not a big assumption on the buses I use!). --Tango (talk) 02:05, 22 June 2010 (UTC)

When the bus is not accelerating (bus stationary or moving at constant speed) there are only two forces acting on your body – your weight acts downwards, and the floor of the bus exerts an upward force equal to your weight but opposite in direction. The vector representing the upwards force passes through your center of mass.

When the bus is accelerating there is an extra force – a horizontal force exerted on your feet by the floor of the bus. (If the floor of the bus was slippery with water or ice this horizontal force would not exist. When the bus accelerated you would slide towards the rear, and when the bus stopped you would slide towards the front.)

The horizontal force exerts a torque about your center of mass. When the bus stops, this torque tries to make you rotate (fall forwards.) When the bus is increasing speed, the torque tries to make you rotate in the other direction (fall backwards.) You prevent this from happening by leaning forwards or backwards so that the upwards force exerted on your feet is no longer through your center of mass and exerts a torque on your body. By adjusting the position of your center of mass you can ensure that the torque exerted by the horizontal force on your feet is equal and opposite to the torque exerted by the upward force on your feet. When the two torques cancel you do not rotate (neither fall forwards nor backwards.) Dolphin (t) 02:41, 22 June 2010 (UTC)

I'm not sure that you'd need an external reference (clear windows). All you need to keep from falling over is that the total force vector (gravity + other acceleration) points from your center of gravity to some point on the floor between your feet. This is certainly made easier by seeing the relative motion of a fixed reference frame, but theoretically, at least, it wouldn't be necessary. -- 174.24.195.56 (talk) 15:30, 22 June 2010 (UTC)

You misunderstand me. The external reference is required to tell the difference between the bus accelerating and gravity changing. (Obviously, you know it's the former, but there is no experiment that could actually demonstrate it.) You don't need to know which it is in order to remain upright. --Tango (talk) 16:53, 22 June 2010 (UTC)

Another way to think of this is that when you consider gravity and acceleration to be equivelant, when the bus accelerates forwards, and gravity pulls straight down, the vector sum of those two things is a vector that's as some angle to the vertical. (If the bus accelerated at 1g, it would be a 45 degree tilt). So standing without falling in an accelerating bus is just like standing on a hillside. When you stand on a hillside, you have to put your weight on the 'topmost' foot and brace yourself with the 'lower' foot...and that's exactly what you instinctively do when the bus accelerates. SteveBaker (talk) 19:46, 22 June 2010 (UTC)

A few more questions on quantum mechanics.

Is the observer effect a basic part of quantum theory or a particular interpretation of it? Is the observer effect falsifiable? Is the ensemble interpretation incompatible with the observer effect? And is quantum entanglement a possible explanation for why individual photons might still exhibit interference in a Mach-Zehnder interferometer, regardless of whether they're being observed? ☯  Zenwhat (talk) 02:43, 22 June 2010 (UTC)

To answer your first question: it depends what you mean by "observer effect". If you mean the effect in which observing a system disturbs it (or, in more QM terms, any interaction between two initially isolated systems leavs them in an entangled state) then yes, I think this is a basic part of quantum theory. If you mean wavefunction collapse then I think this is interpretation dependent - in the many-worlds interpretation, for example, there is no objective wavefunction collapse - the apparent collapse of the wavefunction is an illusion due to the fact that an observation implicitly selects one out of a multitude of universes. Gandalf61 (talk) 09:36, 22 June 2010 (UTC)

Another way to look at that is using the classical Schrodinger's cat thought experiment - but without the observer having "special" status:

• The poison gas container became entangled between being closed and being open when it "observed" the quantum event that set off the trap.
• The cat became entangled by "observing" the poison gas canister and is simultaneously dead and alive.
• When the outside experimenter opens the box to look at the cat (and thereby "collapses the wavefunction"), he/she merely becomes a part of the entanglement - and is now the entanglement of an experimenter who is sad for the loss of the cat with an experimenter who is pleased that the cat is OK.
• When the experimenter phones the cat's owner to tell of the sad/happy news - that person on the other end of the line also becomes entangled.
• The telephone system also became entangled between two states where more or less electricity was used for the phone call - the air in the laboratory is entangled between one set of sound vibrations and another - the photons of light reflecting off of the cat and the experimenter are entangled between the two states and head outwards through the laboratory windows entangling other things that they interact with.

In this view, wave functions are not collapsed by some special "observer" - they merely entangle the observer along with everything else. The observer has no special status - which is a much more comfortable position than proposing that human brains are somehow "special". The entanglement ripples outwards (in truth, at the speed of light), affecting more and more things. Since every quantum scale event in the universe is simultaneously entangling different parts of the universe into different states, you effectively have the many-worlds interpretation where every possible quantum event creates an entire new copy of the universe that is an 'entanglement' of all of the other copies. SteveBaker (talk) 10:47, 22 June 2010 (UTC)

It is important to caution that the observer effect is not the same thing as the uncertainty principle. The latter is an intrinsically quantum mechanical effect that is anavoidable. The former can be present in quantum mechanics, classic mechanics, and any other theory for that matter, and is avoidable in principle though it may be hard to avoid it in some experiments. Dauto (talk) 23:10, 22 June 2010 (UTC)

Fossil fish

Hello, does anyone know what kind of fish this is? Thanks, --The High Fin Sperm Whale 03:25, 22 June 2010 (UTC)

It tells you right in the file description. TheGoodLocust (talk) 03:46, 22 June 2010 (UTC)

He's the one who uploaded the file, so I think he wants a more specific answer than the file description. ☯  Zenwhat (talk) 03:57, 22 June 2010 (UTC)

I would imagine that HFSW knew that, since it is his photo. "Ray-finned fish" is not a very specific description. There are more species of ray-finned fishes than all other vertebrates put together. Anyway, I'm certainly not an expert, but it looks very generic to me. Looie496 (talk) 04:00, 22 June 2010 (UTC)

Yes, I would like to know the order, genus, or, preferably the species. --The High Fin Sperm Whale 04:03, 22 June 2010 (UTC)

Have you tried at Wikipedia:WikiProject_Fishes#Related_WikiProjects eg fishes, biology or tree of life.87.102.66.101 (talk) 12:52, 22 June 2010 (UTC)

One would almost certainly have to know the location / geological formation from which the fossil came to assign it to a particular genus or species. Do you have that information? Deor (talk) 15:03, 22 June 2010 (UTC)

I'm afraid not. I guess this is hopeless then. --The High Fin Sperm Whale 16:39, 22 June 2010 (UTC)

It's similar to a knightia alta, such as this one [1]. Mikenorton (talk) 18:13, 22 June 2010 (UTC)

Geophysics survey

Following up on the question about "Faraday cage from water": Would the electromagnetic sensors used for geophysical surveying (such as ground-penetrating radar, or induction-based electromagnetic sensors) be useful for detecting magnetic/conductive materials (e.g. iron ore deposits, manganese nodules, or the occasional Electra 10-E) underwater? 67.170.215.166 (talk) 03:55, 22 June 2010 (UTC)

Perhaps in freshwater, but I think it is unlikely to work at sea. I imagine some advanced form of sonar would be necessary for the latter. TheGoodLocust (talk) 07:08, 22 June 2010 (UTC)

read magnetotellurics which can detect material of different conductivities in the earth. Careful measurement of the magnetic field with Aeromagnetic surveys can reveal iron ore deposit below water, but it would not be economical to mine. Your ground penetrating radar would suffer too much attenuation in water to be useful. Graeme Bartlett (talk) 10:59, 22 June 2010 (UTC)

Specifically Controlled source electro-magnetic or CSEM is being used to identify the presence of relatively resistive hydrocarbons in hydrocarbon exploration offshore. Most potential reservoir rocks contain brine, which is low resistivity, except where the pores are filled with oil or gas when they become much more resistive causing an anomaly on the CSEM data. The technique is still somewhat experimental - identifying that depth at which the anomaly is located remains problematic AFAIK. Ground penetrating radar has almost no penetration into low-resistivity materials and even under the best conditions can only penetrate a few 10s of metres. Mikenorton (talk) 17:56, 22 June 2010 (UTC)

Yes, I was wondering when I wrote that if magnetic measurement could do such a thing but it seemed a bit iffy to me and I wasn't sure how well it'd work on some metals. That's why I thought sonar, specifically ultra-high frequency sonar (which might limit the range?) for its penetrating effects, would be more useful since I imagine veins of various materials would have fairly distinct sounds. TheGoodLocust (talk) 21:56, 22 June 2010 (UTC)

Seismic reflection surveys are the main geophysical tool used in hydrocarbon exploration. They're also used to in coal mines and deep gold mines. All you need is a significant contrast in acoustic impedance and you should be able to image it. The frequencies used are generally rather low - 20–40 Hz is pretty normal although special kinds of acquisition can get up to 1000 Hz, but such high frequencies are attenuated very quickly in the earth and so the depth of penetration is limited. Mikenorton (talk) 22:09, 22 June 2010 (UTC)

The OP has asked for solutions to different problems. Metal ores, mineral deposits, and hydrocarbon reservoirs occur (usually) deep below the seafloor. A crashed airplane or a sunken ship should be near the seafloor - depending on the depth of water, there will be minimal to severe buildup of new sediments. But, there will still be a "bump" on the sea floor. When searching for Titanic, the crew from WHOI used a side-scan sonar to detect a "bump". But, Titanic was on the bare edge of detectability (many years ago - presumably the resolution has improved with new technology). In any case, it's not likely that a small aircraft would be detectable at great depths by any technology currently available. On the other hand, streamer-based seismic reflection surveys operate at very low frequencies (as low as even 5 Hz, and up to ~40 Hz as Mike Norton pointed out). These surveys can operate in much deeper water; but they are specifically intended to survey the deep subsurface (below the seafloor). At such frequencies, it would be very unlikely to detect a small bump on the seabed due to a ship, aircraft, or other anomaly on the surface. After significant post-processing and analysis, you might be able to discern a surface static, but that could be due to anything - geological anomaly, rocks on the seafloor, variations in the bathymetry, even choppy water at the sea surface. Nimur (talk) 15:46, 23 June 2010 (UTC)

Site surveys for locating exploration wells offshore use a mixture of high-frequency seismic reflection and side-scan sonar data. This is is intended to look out for any obstructions on the seafloor at the proposed well location that might get in the way of the rig - such as shipwrecks. This data of course is only acquired in a small area around the proposed location, you couldn't do it over large areas. Mikenorton (talk) 18:01, 23 June 2010 (UTC)

Potato battery

A recently published article has been making the rounds on the Internet lately, with bold claims of "The treated potato battery generates energy that is five to 50 times cheaper than commercially available batteries". But reading the study I did some calculations and with the 225cm² of Zn surface area in their potato cell at ~1.2mWh/cm² (their data) the total power capacity of their potato cell is only 270mWh, less than half of the most basic Zinc-Carbon AA battery, yet they proclaimed "at maximal performance the treated Zn/Cu-potato cell is markedly more economical than a typical 1.5 V AA alkaline or D batteries." Is my calculation correct? Can anyone decipher how they arrived at the cost analysis and conclusion? Is this article (at least its claims) completely hogwash? --antilived^{T | C | G} 06:50, 22 June 2010 (UTC)

I think the idea is that you have more than one cell, and their combined cost is lower than a regular battery. That said, the idea is nonsense anyway. There were people talking about how much potatoes cost, and sorts of other nonsense. The power comes from the metal. NOT the potato. The potato does nothing. Just replace it with some salt water. Ariel. (talk) 06:53, 22 June 2010 (UTC)

You'd have to pay for the metal rods and wires and cost your time too. By the way can I interest you in some stone soup?, a couple of potatoes now would give it some body. Dmcq (talk) 10:29, 22 June 2010 (UTC)

50 times cheaper - I cannot disagree with this claim - the cost of the battery is that of the metal plates they are using, plus the boiled potato - compare with convention batteries - they don't just use zinc plate - but specially prepared zn powder, plus MnO2, plus construction costs - to what is a quite sophisticated finished product - the potato battery just uses the raw materials - it will without doubt be much cheaper. I don't know if they've included transportation costs...

They also compare against $1.89 AA batterys - not only is this overpriced, but a poor comparison - D cells are much cheaper per Joule. —Preceding unsigned comment added by 87.102.66.101 (talk) 15:41, 22 June 2010 (UTC)

Second claim more economical - no idea what 'economical' means in this context - probably a repeat of the above correct claim.

Summary: Not hogwash (but getting close) - but not actually a practiable energy source. (see below)

Note: This battery would be fine for a digital watch, but I'm fairly certain that it would have serious problems driving a substantial load - eg radio loudspeaker, or even tiny electric motor. A led is not a demanding load. They tested at loads of less than 0.01Amp Otherwise it's interesting to note the suitability of boiled plant matter as a ion conudctive material.87.102.66.101 (talk) 13:11, 22 June 2010 (UTC)

monofilament cutting string

In SciFi stories sometimes they have monofilament strings that are just one atom wide and can cut through anything. But wouldn't the material that was cut just immediately vacuum weld back together again? (You don't get a better vacuum than that, and the cut piece are exactly in the right spot to join right back together.) I'm guessing metals would do that? But would more complicated molecules? Say a piece of wood? Would it depend on what kind of bond the molecule used? Ariel. (talk) 07:12, 22 June 2010 (UTC)

Yes, this idea pops up in Sci-Fi books/comics/manga/anime/movies/cartoons a lot; see this partial (but very impressive) list. A "monofilament" (a molecule, really) one atom thick makes no sense, however, as it has a strength of a single molecule. The work needed to tear it is about the same as the work required to move a couple of electrons from one orbital to another, that is, something of order of 10^-18 Joule. So no, that won't cut anything. If you take a bunch of, say, nylon molecules side by side, however, then you have a fishing line. The thicker it is, the stronger it is. And yes, you can get some nasty cuts from the fishing line if you are not careful. --Dr Dima (talk) 08:24, 22 June 2010 (UTC)

I'd imagine having such low mass would be a major hindrance as well. If one could increase the strength of the electromagnetic force in the filament then that should get rid of the strength issues (it is sci fi after all), but that would still leave the mass problem, which I suppose could be countered by increasing the acceleration of the weapon. TheGoodLocust (talk) 08:37, 22 June 2010 (UTC)

Yes, you can do that, but the cutting implement will not be a monofilament string anymore; rather, it would be an ion beam. Yes, an ion beam can cut solid materials. --Dr Dima (talk) 08:52, 22 June 2010 (UTC)

Why would it be an ion "beam"? I'm saying increase the electromagnetic force to increase the strength of the molecular bonds, sure you could do that with ions, but would that have to be a beam? TheGoodLocust (talk) 21:39, 22 June 2010 (UTC)

By the way, if we return to the original idea of a very thin monofilament string, you can see that it is unlikely to work by doing a simple dimensional analysis. Note that, for a given force applied to the filament, the pressure it exerts on the surface you are trying to cut is proportional to the force applied to the filament divided by the filament diameter to the first power. However, the maximal force the filament can withstand is roughly proportional to its cross-section, so to its diameter squared. Assuming you pull on the filament with the maximal force it allows without breaking, then, for the same cutting configuration, the pressure will increase as the first power of the diameter. That is, the larger is the filament diameter the higher is the pressure it exerts on the surface you are trying to cut. Indeed, I've never heard of anyone getting cut by walking into a spiderweb; but a snapping steel cable will cut a person clean in two. --Dr Dima (talk) 09:04, 22 June 2010 (UTC)

...and to finish that thought: Spider's web is gram-for-gram stronger than steel...so if the idea of thinner (being "sharper") is better - then spiders web ought to cut more easily than a cheese wire - which in turn ought to cut better than a steel cable. SteveBaker (talk) 10:24, 22 June 2010 (UTC)

In the stories the monofilaments are made of unobtainium. So assuming they are strong enough - what about the vacuum weld part of my question? Would molecules reconnect? Ariel. (talk) 03:21, 23 June 2010 (UTC)

Sounds feasible, but I guess you don't know until you try. If it is a problem then perhaps heating the monofilament, causing evaporation as it cut, would solve such a problem - the only problem with that is that it would have to be pretty hot and good at conducting heat to work since it'd have such a small contact area. In this imagining it'd essentially be a strong and flexible heating element - and would probably look a lot cooler than a simple monofilament. TheGoodLocust (talk) 06:52, 23 June 2010 (UTC)

If you've removed molecules with the (abrasive?) monofilament then there's a gap -a gap remains a gap even at 1 atom wide.77.86.123.157 (talk) 12:57, 23 June 2010 (UTC)

Again, it is more complicated than that. Some of the molecules (proteins, genetic material, structural elements of the cell wall) in the living cells are fairly large. If they get cut or dislocated, some of them may reconnect (see e.g. our very extensive article on DNA repair), and some may not; especially unlikely to reconnect are the structure elements under tensile stress. If the damage is extensive, the cell will go into necrosis or apoptosis. Perforation of the cell wall alone is usually a good enough reason for a cell to promptly die. So no, the cell will not necessarily repair itself, but there will not be a 1-atom gap left, either. Here is a good example: when you stick a glass microelectrode in a nerve cell, and you are careful enough, the membrane seals itself around the electrode and the cell keeps functioning, at least for a few hours. If you are not careful enough, and the membrane damage is too big, the cell dies within seconds. --Dr Dima (talk) 22:11, 23 June 2010 (UTC)

Inner asteroid belt?

Is there any reason there is no asteroid belt within the Mars, Earth, Venus, Mercury and the Sun? Just chance, or some does physical principal exclude this possibility?80.1.88.13 (talk) 08:00, 22 June 2010 (UTC)[Trevor Loughlin]

Well, I'm totally guessing here since I've never taken any astronomy classes, but I'd imagine that as matter accretes into planets they'll move closer to the sun. Once this happens I think the complex gravitational interactions between the planets, sun, and asteroids would tend to throw the remaining asteroids in the core of the system into each other to make more planets, into the existing planets to increase their mass or into the sun. The outer asteroid belt wouldn't be subject to such chaotic gravitational forces as frequently and should remain relatively stable. TheGoodLocust (talk) 08:32, 22 June 2010 (UTC)

Jupiter perturbs orbits and makes planet-formation difficult. Being further away allows the asteroids to accrete into planets. So implies our Asteroid_belt#Origin article, anyway. Vimescarrot (talk) 10:36, 22 June 2010 (UTC)

In this close the planets will muck up the orbits and make them unstable, even though Mars etc are smaller, they would be much closer to an inner belt and have a huge impact. Graeme Bartlett (talk) 10:54, 22 June 2010 (UTC)

There are small groups of asteriods in these regions: Atens, Apoheles, etc. (See also List of minor planet groups.) There are no known Vulcanoids, whose orbit would be between Mercury and the Sun, though. 75.41.110.200 (talk) 17:08, 22 June 2010 (UTC)

As far as I know, one of the most accepted theories of the formation of the asteroid belt is that the huge mass of Jupiter stopped them to form a planet (or destroyed the emerging new planet via its tidal forces). The other planets are just not big enough to do this. --131.188.3.21 (talk) 01:19, 23 June 2010 (UTC)

Ferrofluid heart assist jacket?

Some researchers have created experimental powered jackets surrounding the heart to give about 10% assistance in the case of heart failure. Could the power limitations be overcome by using a ferrofluid filled jacket (surrounding the heart, as before) powered by superconducting magnets external to the patients body?[Trevor Loughlin]80.1.88.13 (talk) 08:20, 22 June 2010 (UTC)

I can't comment on the physics, but I doubt the FDA would approve such a device with that kind of liquid in it. Perhaps someone qualified can comment on the FDA's views on the chemicals used in ferrofluids.--mboverload@ 09:28, 22 June 2010 (UTC)

Ferrofluids tend to be things like oil or water with nano-scale particle of iron, magnetite or hematite suspended in it. Certainly stuff like that would be pretty disasterous to have inside your body if the surrounding container leaked. I think the toughest problem would be to find a material flexible enough to pump the heart millions of times without breaking - that is also biologically tolerated. For a short-term emergency, it ought to be OK - but not for long-term use. SteveBaker (talk) 10:17, 22 June 2010 (UTC)

A superconducting electromagnet has significant size, weight and power consumption. Besides its non-portability it raises safety issues, see MRI#Safety, and it would be unacceptable for a patient with a medical implant such as a pacemaker. Cuddlyable3 (talk) 10:31, 22 June 2010 (UTC)

If I had tubes of magnetic fluid wrapped around my heart I don't think I'd want to go anywhere near a superconducting magnets. APL (talk) 15:21, 22 June 2010 (UTC)

Metal mesh interfere with WiFi signal?

Could a laptop stand fashioned from this mesh interfere with the laptop's WiFi signal? --89.243.136.23 (talk) 09:35, 22 June 2010 (UTC)

If it is just a stand it won't have much effect, but if the mesh blocks the line of sight to the wireless router it could well seriously degrade the signal. Graeme Bartlett (talk) 10:50, 22 June 2010 (UTC)

power electronics

what's the difference between a volotage regulator and voltage stabilizer? —Preceding unsigned comment added by K.saikishan (talk • contribs) 10:53, 22 June 2010 (UTC)

A voltage stabilizer appears to be the name of a finished product (ie a box with inputs and outputs). A voltage regulator is a more general term which can refer to a single component, integrated chip, or finished product.87.102.66.101 (talk) 13:15, 22 June 2010 (UTC)

See Voltage regulator and Voltage regulator#DC voltage stabilizers. The article does not make a consistent distinction between voltage regulator and voltage stabiliser. For me a voltage stabiliser uses a non-linear component in parallel with the load to conduct i.e. waste current as required to prevent the voltage exceeding a specified voltage, while a voltage regulator has a more complex circuit with feedback that employs a voltage reference separate from the load. Cuddlyable3 (talk) 22:05, 22 June 2010 (UTC)

The term voltage stabilizer usually applies to an ac source, whereas voltage regulator usually applies to control of a dc source.--RampantHomo (talk) 21:03, 27 June 2010 (UTC)

Cheetah attacks

Have there ever been any reports of Cheetahs attacking humans? Your article on the Cheetah doesn't give any details on this. 202.129.232.194 (talk) 13:41, 22 June 2010 (UTC)

Yes http://www.google.co.uk/search?hl=en&q=cheetah+human+attack&meta= eg [2] [3]

87.102.66.101 (talk) 15:20, 22 June 2010 (UTC)

saltation velocity vs choking velocity

What is the rough numerical difference between choking velocity and saltation velocity for fine particles? How reliable is the rizk correlation for saltation velocity compared to the equation: slip velocity at saltation=terminal velocity? Can anyone suggest an accurate correlation for particle velocity? Thanks —Preceding unsigned comment added by 122.172.201.6 (talk) 15:36, 22 June 2010 (UTC)

First question. Try [4] p4.12

This book also has numerous models for both which might be useful to you [5] 87.102.66.101 (talk) 15:53, 22 June 2010 (UTC)

Dense phase flow vs dilute phase flow

In pneumatic conveying which uses more power, dense phase flow or dilute phase flow? Thanks —Preceding unsigned comment added by 122.172.201.6 (talk) 15:40, 22 June 2010 (UTC)

Petroleum detergent in Dawn

There was an NPR story[6] this morning about the use of Dawn dish detergent in the BP oil spill. The story mentioned that Dawn contains a petroleum product itself and alluded that is why it works so well. Any idea what type of compound that would be? --70.167.58.6 (talk) 15:52, 22 June 2010 (UTC)

A lot of surfactants are made from alkanes and paraffins as chemical feedstocks. It's like saying hydrochloric acid is water-based and that's why it works so well. John Riemann Soong (talk) 16:00, 22 June 2010 (UTC)

They mentioned that Dawn was composed of about 1/7th petroleum ingredients. One of the theses in the story was that Dawn was "eating it's own tail" by being a super-cleaner used to combat a spill of the very parent material it's derived from. They brought up the fact that petroleum-free soaps do exist but are ignored by anyone on cleanup duty because they lack effectiveness. The other telling part of the story was that the cleanup process for marine life is actually kicked off by coating them in cooking oil, as a way to displace the crude oil that's grown very thick and sticky from it's time in the sun. Seems to me that the basic premise behind Dawn is that it's so effective because it can totally displace so many other oils, and rinses away completely when diluted. Interesting, all around. --144.191.148.3 (talk) 16:27, 22 June 2010 (UTC)

Depending on the type of 'dawn' [7] ? The active ingrediants are/will be anionic surfactants and non-ionic surfactants msds There's a list at Surfactant#Classification

Without knowing 'dawn' (I assume it's similar or near identical to Fairy Liquid) [8] likely major constituents are Sodium lauryl sulfate, Sodium laureth sulfate. The non-ionic components include Lauramine oxide [9] , C9-11 pareth-8 link shows C12 version 1,3-Cyclohexanedimethanamine [10] , polypropylene glycols and Dimethyl aminoethyl methacrylate/hydroxyproplyl acrylate copolymer citrate , which are also detergents/surfactants/dispersants and reduce the harshness of the formulation in terms of degreasing of hands etc.

All of these will contribute to its activity.87.102.66.101 (talk) 16:23, 22 June 2010 (UTC)

There must be something special about "Dawn" as opposed to other brands of washing up liquid. It's common for particular applications to specify Dawn in particular...for example, when I put vinyl rally stripes on my car, the instructions were very specific that the area where the decals were to be applied had to be washed with water with a few drops of "unscented Dawn" - and NOT any other brand. I also had some rubber grommets to fit into a row of tight holes through which electrical wiring has to be threaded - and again, the instructions were to lubricate the grommets with "Dawn". I suspect (without proof) that Dawn has very little in the way of non-detergent stuff in it so it's more pure than the stuff that's usually sold with hand softeners, scents and who-knows-what other junk in them. SteveBaker (talk) 19:35, 22 June 2010 (UTC)

Isn't it just another fuzzy example of a Genericized trademark? I'm even going to go crazy and say that there is no such thing as 'unscented dawn' as a product .. what they mean is 'plain normal dawn'. 87.102.66.101 (talk) 21:07, 22 June 2010 (UTC)

Dawn (brand) and Fairy (brand) are both brands owned by Procter & Gamble. Here is video documentation] of the former compound's ability to maintain the resilence of an adult female's epidermis during culinary utensil cleansing duties. Cuddlyable3 (talk) 21:38, 22 June 2010 (UTC)

I'm more interested in SteveBakers admission "..when I put vinyl rally stripes on my car.." - was that a long time ago steve? 1970's much ? 87.102.66.101 (talk) 22:01, 22 June 2010 (UTC)

Once a year ago (white stripes on my British Racing Green '63 Mini), then 2 years ago (black stripes on my Orange MINI Cooper'S convertible) then 3 years ago (white stripes in my British Racing Green MINI Cooper'S)...between those, my Yellow MINI got crushed before I had time to put the (Black) stripes on it - and my present Red MINI came with stripes from the factory. MINI's just look good with stripes...other kinds of cars...not so much. Evidence: [11], [12], [13], [14] SteveBaker (talk) 23:40, 22 June 2010 (UTC)

Sorry to here about your yellow mini - we used to have one of those .. long time ago..87.102.66.101 (talk) 23:46, 22 June 2010 (UTC)

I heard the NPR story, and as I recall, the reason for the use in cleanup is that it's a strong detergent which is able to break up oil, but will not unduly strip oils from hands and skin. This was attributed to the particular *mix* of surfactants used by Dawn. (Online lists include sodium lauryl sulfate, sodium pareth-23, sulfate C-12-14-16, dimethyl amine oxide, undeceth-9, cyclohexandiamine, and polyacetate. P&G somewhat reasonablly keeps the exact formula secret.) -- 174.24.195.56 (talk) 05:05, 23 June 2010 (UTC)

Clarify - All liquid hand washing detergents are formulated to not unduly strip oils from hands and skin - not doing so would result in tens or thousands of people suing the producer for induced dermatitous or similar. The ingrediants in dawn/fairy liquid are commmon to all liquid hand washing detergents. One of dawn/fairy's main selling points is the higher concentration they use - "more dishes per bottle" - Their formulation is a good one (and probably the original and best, from which others copy), but any innate advantage isn't there - that's all due to the millions Procter and Gamble spend on advertising and marketting every year - the rival products are so similar - the only way to differentiate is consumer awareness.77.86.123.157 (talk) 13:05, 23 June 2010 (UTC)

You'll find similar brand loyalty for "Ludwig" in Poland, and for "Pril" in Germany. The article http://de.wikipedia.org/wiki/Pril is interesting in it's description of an early advert for Pril.77.86.123.157 (talk) 13:42, 23 June 2010 (UTC)

arent surfactants toxic to fish ?

any way to get plant cells to grow along a surface?

Plant cells with intact plasmodesmata behave a little differently than protoplasts....anyone have a technique for culturing cells only at max a few cells thick on a microscope slide? John Riemann Soong (talk) 15:59, 22 June 2010 (UTC)

well here's what I roughly have in mind -- I'll take a sample from an explant, sonicate it in some solution to make a suspension culture; then add it to an polylysine-treated slide and let the slide incubate.

I'm thinking if I control the incubation time, the plant cells will grow along the surface than against gravity. (Okay someone help me -- I don't know that much about plant cell division.) I was thinking that if I even control the culture medium I leave on the slide as it incubates, I could get a thin layer rather than a thick callus. I'm thinking that if I leave part of the slide barely immersed, even if the medium evaporates the cells can still pull water through the plasmodesmata; the strong osmotic forces might even help the gold particles I will eventually insert on the liquid-rich side travel faster? John Riemann Soong (talk) 16:32, 22 June 2010 (UTC)

Can't answer your specific questions but how about using the skin found between layers of onions - it is already one cell thick. 86.7.19.159 (talk) 23:58, 24 June 2010 (UTC)

terminal velocity of flour?

Hi Can anyone tell me what the terminal velocity of flour is? Thanks —Preceding unsigned comment added by 122.172.201.6 (talk) 16:04, 22 June 2010 (UTC)

Loose flour? I suspect it is going to depend on how finely it is ground. Googlemeister (talk) 16:31, 22 June 2010 (UTC)

Wheat flour having a rough particle size of a little over 0.1mm —Preceding unsigned comment added by 122.172.201.6 (talk) 16:48, 22 June 2010 (UTC)

I don't think it's meaningfull to talk about the terminal velocity of such small particles. They will be suspended in the air for a long time before settling. That isn't because they are falling very slowly, it's because they are moving around randomly (see Brownian motion). We considering terminal velocity, we don't think about individual molecules of air, we average them all out because there are so many hitting the falling object. For a single particle of flour, though, there aren't many molecules hitting it (well, there's probably still a big number by every day standards, but it's a small number relatively speaking) so we can't ignore the fact that they are all moving around at random. The particle will be pushed in different directions by different molecules, which makes its movement unpredictable. --Tango (talk) 17:04, 22 June 2010 (UTC)

There is an equation at Terminal_velocity to use to calculate it. You can use the density of flour and an assumption of light packing to calculate the mass of a 0.1mm flour object.87.102.66.101 (talk) 17:14, 22 June 2010 (UTC)

Tango, two problems. A) 0.1 mm isn't very small. From the spherical approximations in terminal velocity you can estimate a velocity of order 1 m/s. For very fine particles, the second equation in Stoke's Law actually gives a better estimate of the settling velocity. At this particle size however, it also predicts ~1 m/s. B) Brownian motion in air (as opposed to water) is almost always overshadowed by turbulent motion. You'd need an exceptionally still volume of air to be able to appreciate Brownian diffusion, rather than eddy diffusion. You're right that other effects can become important when the particles are small enough, but the natural scale for observing solids suspended in air is ~1-10 microns rather than the 100 microns in this question. Dragons flight (talk) 17:42, 22 June 2010 (UTC)

Well, I don't know the maths of it, but I've spilt flour before and it doesn't fall at a steady rate. It gets suspended in air and gets blown around randomly. (You are right that the motion is more turbulent than Brownian, I apologise for that mistake.) --Tango (talk) 17:59, 22 June 2010 (UTC)

Judging from the questioneer's previous I think they're looking at transportation of fine powders using air blowers. eg Conveyor_system#Pneumatic_Conveyor_Systems 87.102.66.101 (talk) 18:10, 22 June 2010 (UTC)

I hope the OP is aware that transporting fine combustible powder suspended in air is a recipe for a disaster. See Dust explosion. --Dr Dima (talk) 19:30, 22 June 2010 (UTC)

Thanks a lot guys. I was hoping for some experimental confirmation of the equations... as the above includes a drag coefficient which again depends on some correlation. Anyway I was also expecting a velocity of around 1 m/s so this confirms my calculations in a way. Thanks. —Preceding unsigned comment added by 122.166.161.184 (talk) 04:15, 23 June 2010 (UTC)

I am sure that you will get a mixture of sizes and a variety of speeds. The dust you see suspended in the air when you drop flour is likely the finer bits. Graeme Bartlett (talk) 12:07, 23 June 2010 (UTC)

Latitude

Which latitudes(geodetic or geocentric) are shown on the topographic maps of a country? —Preceding unsigned comment added by 113.199.191.33 (talk) 16:34, 22 June 2010 (UTC)

It's going to depend on the map/mapper surely - did you have a map series in mind?87.102.66.101 (talk) 16:45, 22 June 2010 (UTC)

Any accurate map from the mid-nineteenth cenury onwards will show geodetic latitudes, that is latitudes that take account of the fact that the Earth is slightly "flattened" at the poles. The difference is small, except at high latitudes where few people live or work, but, for the most accurate work, one needs to be aware that there are several different geoids and to check which one is used for the map in question. Physchim62 (talk) 19:10, 22 June 2010 (UTC)

Excuse me, but the question isn't whether you take account of the shape of the earth, it's how. Both geodetic and geocentric latitudes are well defined for any particular geoid. --Anon, 21:22 UTC, June 22, 2010.

Indeed. See Geodetic system#Geodetic versus geocentric latitude for details. If I understand it correctly, the difference is greatest around 45 degrees latitude. At the equator and the poles, they should agree. --Tango (talk) 01:34, 23 June 2010 (UTC)

RDA percentage for calories

Is there a reason that food labels (in the USA) contain % recommended daily amount for many nutrients such as fat, protein (sometimes), carbohydrates, etc, but never do they provide a percentage for calories? There is always a caveat on the label proclaiming that it is "based on a 2000 calorie diet" but then the calories are never expressed as a percentage of that basis. It would be easy to read a conspiracy into this; the manufacturers don't want you to think "oh this 350 calorie soda is 17% of what I am allowed to have all day!" but maybe there is a more rational explanation? Is the 2000 calorie diet just not meant to be taken literally? --144.191.148.3 (talk) 17:25, 22 June 2010 (UTC)

The 2000 calorie guideline is an approximation. The number of calories you need varies widely depending on your size and level of activity. The other requirements probably don't vary as much (they probably still vary by size, not so much by activity), so giving percentages for them probably makes more sense. --Tango (talk) 18:07, 22 June 2010 (UTC)

The psychology of hog drivers

You know those incredibly loud motocycles that people drive around on? Can anyone offer an explanation for why people do that? I mean, it's just plain rude, but I'm thinking that's kind of the point. In fact there's a lot of people in my community that do this even with their regular vehicles -- they rev them so hard, it's like every day is an existential crisis for them, and doing that is their only way of balancing their mental books. But I'm interested in other people's explanations. Especially anyone who actually owns and drives a noisy vehicle. What can I do to see a decline in this behaviour, besides moving towns or deafening myself? Vranak (talk) 17:34, 22 June 2010 (UTC)

It may be cruel of me to link this, but perhaps this Tom the Dancing Bug cartoon is apposite: [15] darn I can't find it on the real TtDB website-- Finlay McWalter • Talk 17:41, 22 June 2010 (UTC)

Yeah, I feel that you're on to something. Vranak (talk) 17:52, 22 June 2010 (UTC)

it's like every day is an existential crisis for them  :) Yeah. I think from their point of view they like the sound of the engine, and the ability to control it.. Give me an electric motor and power supply and I'll happily spend hours revving it from 0 to 1500rpm. For me it's relaxing for everyone else it's annoying. Buy a drill.87.102.66.101 (talk) 17:59, 22 June 2010 (UTC)

People often don't see motorcycles. Making them annoyingly loud is thought to improve safety by making them harder to miss. As for cars, well, a free-flowing exhaust can slightly improve efficiency... but I suspect some people just like the sound. Why you most frequently see this on cars that sound like chain saws, I'm not sure. I suspect they think the exhaust sends a message saying "look at me, my car is fast".. altho, if you're driving fast, the LAST thing you want is for people to notice this. I prefer going fast in a way less likely to draw law enforcement attention. Friday (talk) 18:21, 22 June 2010 (UTC)

You need to have a passion for cars, bikes or engines in general to appreciate it. Your comment about "existential crisis" is way off the mark, it's simple enjoyment. Me? I love the sound of a Honda S2000 screaming to 9,000 rpm in 3rd gear, especially when overtaking trucks or driving through a tunnel ;) Zunaid 20:28, 22 June 2010 (UTC)

Ok, fair enough. Let me approach this from a different angle then. Do hog drivers get off on the fact that their engine noise bothers everybody else? Because I find it intolerable, and it in fact puts thoughts into my head about acquiring a Glock to take matters into my own hands. Our local government periodically talks about making such noise illegal, but all they ever do is talk. Vranak (talk) 20:40, 22 June 2010 (UTC)

Well that could be because it is very difficult and costly to enforce such issues. Googlemeister (talk) 20:45, 22 June 2010 (UTC)

I'm not sure it would be. Install a few listening devices around the neighborhood to triangulate offenders, find out where they are coming from, install a few more, and find out where they live. Then execute a search warrant, run a test of the machinery to see if it falls within acceptable parameters, and if not, prosecute. I mean, we're basically talking a few microphones and a bit of software, and a bit of analysis. It's no great feat. I wonder if perhaps we let these guys get away with it because if they couldn't express their hatred of the world that way, they'd be committing even worse crimes. Vranak (talk) 20:56, 22 June 2010 (UTC)

Riders ride for a wide range of different reasons, I used to have a 100 mile commute each way and riding it was far quicker and more fun than driving it. Born Agains and wunday riders have their own reasons, but largely people ride because it's a huge amount of fun. I suspect that you'd find that most really don't give too much of a flying f**k what other people think.

All that said there isn't the same culture here in the UK around bikes, most riders are on sports bikes, sports tourers or big trailies. There are a lot of tarts handbag riders, but proportionately far fewer than elsewhere.

There is a noise limit in the UK, and janitors can, and do, enforce it. Stopping a rider is a judgement call, and the bike is taken into the workshop to have the noise output assessed. There are practical reasons for that, largely around emissions regulation.

Riders don't hate people, although we do tend to get very p!ssed off with cagers and their SMIDSY approach to road safety.

ALR (talk) 21:11, 22 June 2010 (UTC)

Yeah, this is exactly my point of contention -- people not giving a flying fig what people think. I mean, the general rule is that if you piss people off, then you live in a community of pissed off people, which is fun for no-one, right? It just seems so short-sighted. Make a loud horrible noise and make the whole world around you a little angrier. But maybe these guys, at least where I live, are angry to begin with and so want to bring everyone else down to their level. I really wish there were a more palatable explanation but this seems to be what I arrive at again and again. Vranak (talk) 02:50, 23 June 2010 (UTC)

I think you missed my point. It's highly unlikely that anyone is doing it with the intention of p!ssing you, or anyone else, off. It's just not worth it, there are more important things to concern oneself with.

Anyway, the sound does depend on the engine type. A single cylinder has a wonderfully antiquated thump, hence thumper, I'm not keen on twins, triples make a wonderful singing sound as they rev, four cylinders and it starts getting a little anonymous.

In practice engine efficiency is quite badly affected by opening up the baffles as it reduces the backpressure on the cylinders. So it's counterproductive to mess around with them.

ALR (talk) 08:09, 23 June 2010 (UTC)

Perhaps it makes Conspicuous consumption more conspicuous? Perhaps they're worried that if they had a proper muffler some people might tragically not notice how awesome, manly, and American-made their bikes are. APL (talk) 21:26, 22 June 2010 (UTC)

More importantly, there is a significant issue of noise pollution here. Although it is annoying to encounter these sounds during the day, hearing them before eight in the morning and after nine at night can interfere with sleep patterns. I think the effects of noise pollution are considerable and may have a role to play in human health. What is so interesting (and sad) about this, is that in many cities and urban areas, people live in and swim through an ocean of noise from the moment they wake until they sleep again at night. Viriditas (talk) 22:17, 27 June 2010 (UTC)

Absorption of sugars and carbs

does the rate of how long the sugars and carbs are absorbed effect your blood sugar level? For example if I took a pill with a piece of chocolate cake and that pill slowed the absorption up to seven hours for the carbs and sugar of that cake to be absorbed, would the same number of sugar and carbs be absorbed if I hadn't taken that pill? Would your blood sugar spike more if the sugars and carbs were instantly absorbed rather than more slowly over a longer time period? How does that work? —Preceding unsigned comment added by 71.137.241.251 (talk) 18:23, 22 June 2010 (UTC)

For the record, carbohydrates are sugars. I can't answer your question, though, sorry! Regards, --—Cyclonenim | Chat  20:37, 22 June 2010 (UTC)

Your citation is invalid. I can't find that anywhere in Regards going all the way back to 1932. 71.100.2.16 (talk) 15:06, 27 June 2010 (UTC)

I think you mean, sugars are carbohydrates, not the reverse. For example, starch is a carbohydrate, but not a sugar. --Trovatore (talk) 08:17, 27 June 2010 (UTC)

Eating chocolate cake would indeed spike your blood sugar. Bodybuilders and some diets promote the concept of eating low [GI] foods and other techniques to avoid blood sugar spikes, which also lead to spikes in insulin, may lead to diabetes and will cause food cravings later on. To answer the first part of your question, if you had a pill which slowed the absorption of the chocolate cake then theoretically you might get more calories from the same amount of food. This is less clear with regards to something as easily digestable as chocolate cake, but with something like meat if you eat a massive amount of food all at once your body won't digest it as efficiently and you'll get less calories. In general, as I said, it is better to keep blood sugar at stable levels by avoiding simple sugars, eating fiber with your meals to slow digestion, and, on a related subject, mixing proteins (e.g. casein, egg, etc), which digest at different rates, will provide your body with a constant stream of amino acids necessary for maintaining and building muscle. TheGoodLocust (talk) 21:29, 22 June 2010 (UTC)

what is a "thin cell layer explant"? (TCL)

People in the literature keep talking about this technique (with some modifications) as some promising way for growing whole plants... which is not what I want. I just need to observe a layer of plant cells (with plasmodesmata intact) under a DIC microscope! Can someon help me find a protocol just how to MAKE a TCL culture, straight up? John Riemann Soong (talk) 19:14, 22 June 2010 (UTC)

Well, here is a recent review of the technology and its applications, for what it's worth. Looie496 (talk) 22:26, 22 June 2010 (UTC)

Wait I think I read that one already...John Riemann Soong (talk) 22:41, 22 June 2010 (UTC)

human brain and language

Is it possible for a person through brain trauma to completely forget their own language and have it replaced with a different one? I am not talking about foreign accent syndrome, but actual language change. Even incomplete would be of interest, perhaps a single word is always replaced with a foreign word? Like an English speaker who lost the ability to express the word "air", even in thought, and it came out as the German word "Luft" instead? Or perhaps they completely forget English and are unable to relearn it, but are able to learn German as a substitute? Googlemeister (talk) 19:28, 22 June 2010 (UTC)

You can't suddenly learn a language you didn't previously know following a bump on the head, if that's what you mean. I believe there are forms of aphasia (that's the article to read for everything on this subject) where you might sound like you are speaking another language, but it is actually nonsense. I believe there are also conditions where patients revert to their mother tongue and lose the ability to speak foreign languages they had previously known. I'm not aware of any condition where you can learn a new language but not relearn a previously known one, nor can I see how that could occur. --Tango (talk) 19:37, 22 June 2010 (UTC)

I don't think OP means that the person would suddenly start speaking another language, but instead have the person replace certain words of say English with other languages that they know (for example I know hello in English and bonjour in French). Could that happen? Regards, --—Cyclonenim | Chat  20:35, 22 June 2010 (UTC)

That is quite common, even without any sort of brain injury! As a "serial ex-pat", I've seen it many times; when I used to live in France, it was not uncommon for me to switch unconsciously from English to French while talking to my parents on the phone. Physchim62 (talk) 22:37, 22 June 2010 (UTC)

The "incomplete" type definitely occurs -- "pathological mixing" is a common result of bilingual aphasia. It is also possible for the native language to be more seriously impaired than the second language. I couldn't find any mention of cases where the native language is completely lost and the second language remains fully intact, though. Search Google Scholar or Pubmed for "bilingual aphasia" if you want to get into the literature on this topic. Looie496 (talk) 21:42, 22 June 2010 (UTC)

See the article Glossolalia. Cuddlyable3 (talk) 22:22, 22 June 2010 (UTC)

Glossolalia usually involves the person speaking in a previously known, unknown (by the speaker) or "holy language", but any inability of the speaker to use their own language would be temporary. ~AH1^(TCU) 15:19, 23 June 2010 (UTC)

Fiber Optic Duplex Communication

Can an optical fiber carry optical information in opposite directions at the same time when both light beams are the same frequency or will they interfere?--74.67.89.61 (talk) 20:12, 22 June 2010 (UTC)

Yes. One needs an optical directional coupler or "hybrid" at each end to separate the forward and reverse signals. Cuddlyable3 (talk) 22:18, 22 June 2010 (UTC)

An Optical circulator can do the job. They work at a specific wavelength such at 1550 nm. Alternatively you can have different wavelengths going in each direction. Graeme Bartlett (talk) 10:55, 23 June 2010 (UTC)

So full duplex communication along one optical fiber with the same wavelenght is possible, you just need special equiptment to seperate the signals from any reflections? —Preceding unsigned comment added by 74.67.89.61 (talk) 14:08, 23 June 2010 (UTC)

Asked and answered. Cuddlyable3 (talk) 13:07, 24 June 2010 (UTC)

culturing pollen tubes

Are pollen tubes capillaries of many cells or just a single cell? The article says that sperm cells are carried in them....so cells get carried within a single cell?

I am thinking of culturing some pollen grains....it may be promising to have them germinate long shoots along a microscope slide (treated with polylysine if necessary to help the cells "stick" to the slide).

Also how far back the plant lineage are plasmodesmata present? Are they present in bryophytes or even plants' algae ancestors? John Riemann Soong (talk) 22:26, 22 June 2010 (UTC)

Plasmodesma says: "Species that have plasmodesmata include members of the Charophyceae, Charales and Coleochaetales (which are all algae), as well as all embryophytes, better known as land plants". Pollen tube says they are a single cell, from what I understand, the pollen grain germinates forming the pollen tube and this allows the two sperm cells to move down to the ovary and fertilise the egg. So yes, two sperm cells are transported inside another cell. You must need to use something to initiate pollen grain germination - otherwise they would germinate if they got wet which doesn't happen. 86.7.19.159 (talk) 16:03, 23 June 2010 (UTC)

Does sulfuric acid ignite matches?

I think so but I haven't actually tried it. Any other common chemicals that would ignite matches without setting off gasoline? TheGoodLocust (talk) 23:40, 22 June 2010 (UTC)

yes I believe so - the explanation is that strong acid converts Potassium chlorate to HClO₄/Cl₂O₇ (both very unstable)

Quote Mixtures of potassium chlorate and a fuel can be ignited by contact with sulfuric acid and this reagent should be kept away from potassium chlorate (from the wiki article) , probably other strong acids would do the same. Other compounds and elements are also very unstabel with potassium chlorate - more detail in that article.

I'm not sure about lighting the match and not setting off gasoline - usually the two are related..87.102.66.101 (talk) 23:52, 22 June 2010 (UTC)

It doesn't form perchloric acid; it forms the highly reactive chloric acid. --Chemicalinterest (talk) 10:57, 27 June 2010 (UTC)

Not necessarily, 87 IP -- sulfuric acid is indeed inert to gasoline, it's even used as a catalyst for petroleum refining. The reason it ignites matches is because of the aforementioned reaction with potassium chlorate. FWiW 67.170.215.166 (talk) 02:49, 23 June 2010 (UTC)

Que? "I'm not sure about lighting the match and not setting off gasoline" is what I said, what are you talking about?77.86.123.157 (talk) 13:08, 23 June 2010 (UTC)

Oh I see now - something that lights a match and does not ingnite gasoline.. As a cheat answer how about sandpaper, or the strips on the box that is used to light the match?77.86.123.157 (talk) 13:19, 23 June 2010 (UTC)

The point is to ignite on impact. The bottle shatters, letting out both the acid and the gas, the acid sets off the match and that ignite the gasoline. I'm also rather curious how sulfuric acid would react with some of the other things added to molotov cocktails like coal/charcoal dust, various thickening agents (e.g. egg whites) and oil/tar. I'm assuming it wouldn't react with the charcoal/oil stuff (I could be wrong), which makes me most interested in which method of gelled gasoline would be best for an impact fire grenade. TheGoodLocust (talk) 17:14, 23 June 2010 (UTC)

Can you expand on what you are talking about - your original question was about matches and sulphuric acid - now you seem to be talking about some sort of incendiary device - what is this ? 77.86.123.157 (talk) 17:36, 23 June 2010 (UTC)

I'm basically talking about a modified (easier to make and use) version of this. This device is commonly described in a lot of books, but I've never seen a description that uses matches instead of sugar/KClO3 for ignition . TheGoodLocust (talk) 20:21, 23 June 2010 (UTC)

I see. The strike anywhere match will almost certainly ignite on contact with conc sulphuric acid. The safety match might, or may not, or the combustion may be delayed or weak due to the relative lack of reactive combustable material in the head (excluding the wood of the match itself); the remainder in a safety match is sulphur - I'm not sure hwo readily it reacts with acidified chlorate - but think it won't be spontaneous. An experiment would check this.77.86.123.157 (talk) 21:11, 23 June 2010 (UTC)

Well, I think the only confounding factor is that I believe there is a coating on matches that covers up the potassium chlorate (not sure what it is). Anyway, homemade incendiary grenades are basically bottles filled with sulfuric acid and gas and (after cleaning the outside of the bottle of course) they tape/tie on cloth that is soaked in a sugar/potassium chlorate solution (going off of memory here). It just seemed like taping on matches would be a more accessible method for creating such a device and would last longer. TheGoodLocust (talk) 00:01, 23 June 2010 (UTC)

You can check out the article on Molotov cocktail for more info. Clear skies to you 67.170.215.166 (talk) 02:51, 23 June 2010 (UTC)

Yes, I hadn't looked at it, but it looks like the version I described is close to the Polish Home Army version. However, that article doesn't mention the ignition system that I'm proposing, which is to tape matches along the outside of the bottle. The match on the one in the article is supposed to be lit before throwing, which is inferior in several ways - time, environment (wind/rain), and stealth (a light storm match at night would tell people where the bomb came from, which is why impact ignition is preferable). TheGoodLocust (talk) 03:29, 23 June 2010 (UTC)

Guys perchloric acid may be very thermodynamically unstable, but it takes a lot to get it going. John Riemann Soong (talk) 16:11, 23 June 2010 (UTC)

Also as I recall, perchloric acid is a stronger acid than sulfuric acid. There is no way sulfuric acid will completely protonate perchlorate. John Riemann Soong (talk) 16:12, 23 June 2010 (UTC)

The nice thing about sulfuric acid is that anyone can get a hold of it pretty easily (concentrate it from battery acid). TheGoodLocust (talk) 17:16, 23 June 2010 (UTC)

I think concentrated sulfuric acid will ignite a matchstick — no need for the matchhead at all. But I haven't actually tried it. --Trovatore (talk) 21:13, 23 June 2010 (UTC)

I think it will just char the wood - but not burn .. in fact matchsticks are coated in paraffin/wax - which would protect it from reaction with the acid. A small piece of untreated wood would be converted roughly to carbon, but with no flames - a similar reaction to the sugar/sulphuric acid reaction (see youtube), but slower since the wood is not finely divided.77.86.123.157 (talk) 21:17, 23 June 2010 (UTC)

Well, I was thinking that I might have to scrap off the coating on the head, but I wasn't sure how difficult it would be and wouldn't want to do it if it wasn't necessary. I suppose the nice thing about soaking something in a sugar/chlorate solution is that you could take something like a bottle of Snapple brand ice-tea, soak the label in such a solution and let it dry. That'd be a nice little covert weapon. TheGoodLocust (talk) 21:52, 23 June 2010 (UTC)

Yeah, that's a good idea, but you have to be sure to use a strike-anywhere match, not a safety match -- the latter doesn't contain KClO₃ in the matchhead, only in the matchbox. Seriously, though, what do you need this info for? First you ask about extracting arsenic from microchips for use as a poison, next about igniting matches with sulfuric acid, and now this? 67.170.215.166 (talk) 01:35, 24 June 2010 (UTC)

KClO3 is in the matchbox for safety matches? The matches article says it is in the head? As for your question, I have nothing nefarious planned, but I suppose the information would be handy in a Red Dawn or V for Vendetta scenario - I just have an interest in improvised and/or stealthy weaponry. I probably should re-ask my question about how to poison someone with microchips (or if it is even feasible) since it was posted so far up. TheGoodLocust (talk) 01:54, 24 June 2010 (UTC)

Oh yeah, I must've confused the potassium chlorate with the phosphorus -- it's the phosphorus that's in the matchbox, and the chlorate is in the head (that's what makes safety matches {relatively} safe). As for the microchip question, I'll repeat what I already said: you could extract the arsenic by melting the microchip in an inert atmosphere (which would sublimate the arsenic), but the quantity of arsenic extracted in this way would be too small to be useful. Good luck with your writing :-) 67.170.215.166 (talk) 02:31, 25 June 2010 (UTC)

June 23

Dingman mouth gag

Good people; I am doing a bit of research on a surgical tool used in cleft palate surgery. The Dingman Mouth Gag is used by plastic surgeons to hold the jaw open, repress the tonque, and spead the cheeks for the surgeon to work on the roof of a patient's mouth. I would like to read an article on the history and development of this device. My interest lies in how it might be improved upon slightly.

Thank you, Rick Waltonsmith —Preceding unsigned comment added by Waltosmith (talk • contribs) 00:23, 23 June 2010 (UTC)

What about the current device makes it in need of improvement? When performing surgery in the oral cavity, a number of anatomical regions must be properly retracted (lips/cheeks, tongue), access must be appropriate (and so mouth props + ratchets come into play) and sufficient lighting and suction must be employed to facilitate visualization of the surgical field. While all of these things might not be necessarily employed simultaneously for the full duration of the procedure, cleft palate surgery is one of those surgeries in which a) occlusion of the teeth must not be checked, and so closing of the jaws is unnecessary during the surgical procedure and b) the surgery is of a type and duration such that patients are put under general anesthesia (or at least moderate or deep sedation). The latter offers one greater breadth of tools that may be used that would normally not be tolerated by the awake patient. From what I can see from a google search of the device you mention, it seems that it may be very well suited for lip/cheek and tongue retraction, and in a surgical operatory with adequate lighting and suctioning devices, what else can one expect from your improved device? It would have to be significant enough for all the hospitals to throw out their old Dingman and purchase the Waltonsmith-modified Dingman, and for over $1000USD, it had better be worth their time, effort and expense to follow through. DRosenbach ^{(Talk | Contribs)} 01:57, 23 June 2010 (UTC)

No offence but if everyone was such a cynic, no one would ever invent or improve anything! And even if the OP can't improve on it, the information he seeks might lead him to this discovery on his own, which would still be a worth while endeavor IMHO. However I will grant that only someone intimately familiar with the device and its use, which the OP is eveidently not, will likely be in a position to improve on it. Vespine (talk) 00:36, 24 June 2010 (UTC)

No offence either but the kind of critical realism that DRosenbach offers is exactly what can help someone such as the OP and your claim that it would prevent all future inventions is ridiculous. Cuddlyable3 (talk) 12:54, 24 June 2010 (UTC)

Alkyd Resin Paint

what is Alkyd Resin Paint what type of resin do they use ? do they use formaldehyde resin ? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 01:58, 23 June 2010 (UTC)

Alkyd resins are derived from polyols and dicarboxylic acids or fatty acids by esterification, and are a completely different type of resin from the phenol-formaldehyde resins such as Bakelite. Clear skies to you 67.170.215.166 (talk) 02:56, 23 June 2010 (UTC)

Temperature of water in Kettle

I was wondering how the temperature of the water in a kettle changes over the course of its boiling. Unfortunately I cannot find values on the internet. Can someone give me these values?

Thanks, 110.174.151.109 (talk) 06:28, 23 June 2010 (UTC)

Doesn't it stay at ~100 Celsius until it's all boiled away?... --mboverload@ 06:47, 23 June 2010 (UTC)

I mean, for example 20 seconds from the time the kettle is turned on the water temp is (just guessing) 50C or something like that. 40 seconds is 60C or something. 110.174.151.109 (talk) 09:56, 23 June 2010 (UTC)

It'll depend on how much water you've got (more water takes longer), where you are (mains power in some countries is a lot weaker than it is in other countries, resulting in water taking twice as long or more to boil), and no doubt, the design of the kettle. Vimescarrot (talk) 11:34, 23 June 2010 (UTC)

(ec) The water temperature will not be uniform across the whole volume of the kettle or whichever item you use to store the water. The temperature will be rising first in the bottom section (assuming a kettle placed on a stove), and only then further up. Now, taking this further - boiling will be setting in quite quickly for tiny amounts of water adjacent to the bottom of the kettle, but the bottom will at the same time be kept cooler by all the colder water lying further up.

Now that we know this, we can discard this for simplicity and use mean temperature values for the entire volume of the water as physics classes in secondary schools assume. The (mean) temperature of the volume of the water will be rising steadily and (I guess) arithmetically until the boiling point. The ratio of temperature increase depends on the amount of water, heat transfer capacity of the kettle (material the kettle is made of; say a stone kettle will take longer to boil than a metal one), energy (right?) applied to raise the temperature (i. e. larger flame vs smaller flame), ambient temperature, ambient air pressure (water will not reach 100 degrees C at Mount Everest). It's not as simple as You suggest, you have to know your settings precisely to be able to tell the exact (mean) temperature of the volume of water at any given time.

After all this theory, it was enough for me to type "water boiling curve" into Google to find this. Hope I was helpful. --Ouro (blah blah) 11:44, 23 June 2010 (UTC)

It won't be entirely linear. Temperature transfer depends (quite strongly - by the fourth power, if memory serves) on the difference in temperature, so the transfer will tend to slow down as the water heats up and gets closer to the temperature of the heating element. I'm not sure how hot the elements typically get in kettles and how that temperature varies as the water temperature changes, so I'm not sure how significant a factor it will be. --14:23, 23 June 2010 (UTC)

Hence my I guess in the brackets. That was the part I was unsure of most. Seems logical what You write, though. --Ouro (blah blah) 14:58, 23 June 2010 (UTC)

If I recall correctly, the heat-transfer rate by conduction is linear in the difference in temperature. I suspect that the unsigned contributor is thinking of the black-body law, which is about the rate at which heat radiates rather than conducts. --Trovatore (talk) 21:19, 23 June 2010 (UTC)

Photon exists? or just a Concept?

Hi, I would like to know if photon really exists or is just a concept?--Capim Dourado (talk) 06:56, 23 June 2010 (UTC)

Yes, it really exists (inasmuch as anything "really exists").--Shantavira|^{feed me} 07:33, 23 June 2010 (UTC)

See Virtual particle. Ariel. (talk) 07:59, 23 June 2010 (UTC)

I'm just curious. Where did that idea that photons might not really exist come from? Can you give us an example of something that only exists as a concept so we can better understan the back ground of your question? Dauto (talk) 17:41, 23 June 2010 (UTC)

Maybe he was wondering whether it was a fictional particle, like a phonon. There are concepts that are 'fictional', e.g. centrifugal force. John Riemann Soong (talk) 18:48, 23 June 2010 (UTC)

Centrifugal force is not "fictional" - that's nonsense put out by high school math/physics teachers. See this for a coherent explanation. ;-) SteveBaker (talk) 21:58, 23 June 2010 (UTC)

There's a difference between "fictional" and "fictitious". Centrifugal force is not fictional in that it is a measurable phenomenon which actually exists. It is, however a fictitious force, as it arises not from fundamental interactions per se, but due to a particular way of looking at the system. Similarly, one could perhaps call phonons "fictitious particles", as they don't arise from clusters of fundamental particles directly, as "traditional" particles like alpha particles do, but rather from looking at the system as a whole in a particular way. To answer the original question, in all theories of physics I've heard of, photons are considered real, non-fictitious particles, or at least as real and non-fictitious as alpha particles and billiard balls. BTW a web comic, even one as cool as xkcd, doesn't really count as a reliable source. -- 174.24.195.56 (talk) 03:42, 24 June 2010 (UTC)

Phonons are not fictional either. They are as real as a particle can be. Individual phonons have been experimentally produced and detected. It doesn't get more real than that. Dauto (talk) 00:32, 24 June 2010 (UTC)

I agree with the above answers however I don't think the question is as ridiculous as some of the answers seem to suggest, for someone who's not familiar with particle physics anyway. Higgs Boson is an example of a particle which possibly does not exist. Standard model is a good article relevant to this question. Vespine (talk) 03:43, 24 June 2010 (UTC)

It's important to keep in mind that answers like "as real as an alpha particle" or "as real as a particle can be" is not necessarily quite as real as most observers would expect. It is quite difficult to reconcile quantum mechanics with realism. See the article on the two-slit experiment for a first indication of why someone might want to consider particles to be fictional — you get the interference pattern if both slits are open, but you don't if you close one of them off, even if the particles are released slowly enough that only one should be going through at a time. So which slit did the particle go through, if there really was a particle?

More sophisticated arguments involving the Bell inequality, which is experimentally confirmed (e.g. by the Aspect experiment), place actual hard limits on certain sorts of realistic interpretations of quantum mechanics.

That's not to say there can't be realistic accounts, but they all have other difficulties that most people are also hesitant to accept, such as backwards causality, or some sort of superdeterminism that is very hard to distinguish from "God decided that the experiments would all come out that way". --Trovatore (talk) 03:59, 24 June 2010 (UTC)

A little self-correction here: What's confirmed experimentally is the violation of the Bell inequality, not the Bell inequality itself. I had forgotten that detail. --Trovatore (talk) 05:07, 24 June 2010 (UTC)

Part of the problem is that we can only conceive of the particle realm in terms that our minds can handle. so, put technically, some phenomenon surely exist which produces the effect that we have tried to capture in the concept 'photon'; but whether our 'photon' conception is actually anything close to a good description of that phenomenon is an entirely different question. --Ludwigs2 04:06, 24 June 2010 (UTC)

I would be careful in this context with words like phenomenon, which someone might think you're using in its technical philosophical sense. Actually I'm not quite sure you aren't, though I don't think you are, because it wouldn't make much sense as far as I can see. --Trovatore (talk) 04:08, 24 June 2010 (UTC)

Suppose that starting from the Theory of Everything you can do approximate calculations by introducing fictitious fields described by a fictitious Lagrangian that happens to be the Standard Model Lagrangian. Note that in any real process, the external lines in a Feynman diagrams start and end at sources. Just like the internal lines representing virtual particles or ghosts are not real, we can't be sure if the external lines represents things that are real. Count Iblis (talk) 14:58, 24 June 2010 (UTC)

Well, as you're reading this, something is affecting your retinas to produce a discernable image. Generally, we call these things photons. You don't have to though. It's certainly something though, so they are certainly real. Vranak (talk) 18:18, 24 June 2010 (UTC)

Sorry but I think the above is very poor reasoning. Easy to say with hindsight, but by the very same reasoning, "cold" and "heat" were once thought to "real" too. Vespine (talk) 00:00, 25 June 2010 (UTC)

Well, they do refer to real phenomena. And what shall we call those phenomena? How about, photons, heat, cold, etc. Vranak (talk) 04:39, 25 June 2010 (UTC)

Ok but cold existing as a "phenomena" is a long shot from it existing as some sort of fluid called frigoric. Darkness also exists as a phenomena. That's more like the distinction I think the OP was referring to. Vespine (talk) 06:23, 25 June 2010 (UTC)

There is no such thing as "a phenomena". --Trovatore (talk) 08:52, 25 June 2010 (UTC)

Ontology is a slippery subject. Which of the following "really exist", and which are "just a concept": gravity, temperature, energy, democracy, pain, the colour blue, the sky, the number 17, aleph-null, Robin Hood, Homer Simpson, the Invisible Pink Unicorn, next week's lottery winner, the first female President of the United States ? Nevertheless, in any system of shades of reality photons will be placed near the "really real" end of the spectrum. Gandalf61 (talk) 09:38, 25 June 2010 (UTC)

Probability in Quantum Mechanics

Why do we assign probabilities to states in quantum mechanics? Is it because we presently lack the knowledge to determine the state of an elementary particle, and can only assign statistical probabilities from empirical observations? Or has it been shown that it is physically impossible to know for certain the state of a particle? —Preceding unsigned comment added by 220.253.96.217 (talk) 07:29, 23 June 2010 (UTC)

See uncertainty principle and Heisenberg, for starters. The short answer is: with a "God's-eye" microscope (so to speak), it would still be impossible to specify BOTH the position and velocity of, say, an electron; the more exact you are for one, the less so for the other. It's a fundamental property, not a product of technological limitations. 63.17.50.124 (talk) 08:12, 23 June 2010 (UTC)

Also take a look at the Quantum Zeno effect. ~AH1^(TCU) 15:04, 23 June 2010 (UTC)

While the answers above are essentially correct, they miss the mark. In fact, a state can be precisely determined in quantum mechanics. For instance the state of an electron in a hydrogen atom is precisely determined by four quatum numbers. Not only that but the evolution of a quantum state is described by an unitary quantum operator which makes it completely deterministic! The problem arises when you make the wrong kind of question such as "What's the precise position and momentum of that electron?" Thap happens because of the wavy nature of the quantum state. Dauto (talk) 21:50, 23 June 2010 (UTC)

Cr-V

An alloy is composed of vanadium (V) and Chromium (Cr), how the two can be separated from the metal alloy of it? This alloy is particularly weak magnetic and suction are Iron and Iron powder. I know the nature of the two metals are very similar, separating it from the alloy is probably a bit difficult!--אנונימי גבר (talk) 08:00, 23 June 2010 (UTC)

Very difficult unless you do a chemical reaction to dissolve the alloy, (or vaporise the alloy).77.86.123.157 (talk) 13:11, 23 June 2010 (UTC)

Were you interested in a chemical method? 77.86.123.157 (talk) 13:16, 23 June 2010 (UTC)

---

>I give a solution of Sodium Hypochloride and Sodium hydroxyde, and the effect of Chromium alloy - Vanadium is obtained a brown black precipitate, which I think may be Chromium (III, II) oxide. But what is it with you?--אנונימי גבר (talk) 10:23, 25 June 2010 (UTC)

I personally think this reaction is due to the Sodium Hypochloride liberated oxygen atoms that make up the alloy oxidized

Zombies

Are zombies real ??? —Preceding unsigned comment added by Galaxyboy93 (talk • contribs) 08:51, 23 June 2010 (UTC)

No. Someguy1221 (talk) 09:03, 23 June 2010 (UTC)

But see Tetrodotoxin. Ariel. (talk) 09:50, 23 June 2010 (UTC)

you are right ariel, plus see Clairvius Narcisse

Not according to our articles. Tetrodotoxin specifically says that the symptoms don't match those of voodoo-zombieism - and the Clairvius Narcisse article says that the story has "met with some criticism" from the scientific community. That's a very polite way of putting it...the truth is that neither of these things are remotely anything to do with zombies - which are pure fiction. SteveBaker (talk) 21:56, 23 June 2010 (UTC)

Don't forget about catatonic state, depersonalization and vegetative state. ~AH1^(TCU) 15:02, 23 June 2010 (UTC)

BRAINS --Ludwigs2 04:07, 24 June 2010 (UTC)

Yes, Galaxyboy93, there is a zombie. He exists as certainly as mindless wandering with outstretched arms and grey skin marked by enormous bloody gashes and brain-eating while being blasted with a shotgun but not being killed exist, and you know that they abound and give to your life its highest beauty and joy. Alas! how dreary would be the world if there were no zombies. It would be as dreary as if there were no Galaxyboy93s. 63.17.32.100 (talk) 09:34, 24 June 2010 (UTC)

Zombie computer? Googlemeister (talk) 13:20, 24 June 2010 (UTC)

The Zombie Alert that was prominantly displayed on emergency signs in Austin, Texas last year was easily dealt with by local construction workers armed with nothing more than jack-hammers and chainsaws. Warnings of Nazi Zombies in the area turned out to be an early overreaction and the grass-roots Keep Austin Zombie Free campaign has paid off well and I, personally, have not been even slightly inconvenienced by Zombie invaders since my morning commute in January last year, and evne then, the biggest problem was people blatently ignoring the instructions to "RUN!!!" so clearly displayed on roadside signage, and instead stopping to take photos. SteveBaker (talk) 15:05, 24 June 2010 (UTC)

Bioavailability of iron

Irn Bru contains ammonium ferric citrate. Is the iron in this accessible for the human body to use? I've had a look at Human iron metabolism and it just confused me on this point. It says "To be absorbed, dietary iron can be absorbed as part of a protein such as heme protein or must be in its ferrous Fe2+ form. A ferric reductase enzyme on the enterocytes' brush border, Dcytb, reduces ferric Fe3+ to Fe2+." Does this mean the body can absorb ferric ions, by converting them to ferrous ions? Does the citrate confuse this? or the ammonium? 86.164.66.4 (talk) 11:09, 23 June 2010 (UTC)

The body can't absorb Fe(II) ions? :S I thought they were water soluble. Plus, citrate can't reduce Fe(III) to Fe(II)? John Riemann Soong (talk) 18:52, 23 June 2010 (UTC)

I don't know: that's why I'm asking. 86.164.66.4 (talk) 19:06, 23 June 2010 (UTC)

This seems to answer your question [16] also here in full - yes citrate prevents the iron being absorbed a bit, but not totally.

Yes ferric iron is absorbed by first converting to ferrous iron.

It seems that ferric reductase is present in the duodenum amongst other places.77.86.123.157 (talk) 00:11, 24 June 2010 (UTC)

Cool, thanks! That's both helpful and interesting :D 86.164.66.4 (talk) 00:17, 24 June 2010 (UTC)

Does this mean Fe(III) ions induce oxidative stress? (I suppose the body wants to reduce Fe(III) in order to prevent unwanted Lewis-acid-catalysed reactions?) John Riemann Soong (talk) 16:06, 24 June 2010 (UTC)

Attracting flies to my fly paper

I hung up some fly paper to catch flies, but they're not interested in it. I managed to catch one manually, by pressing the paper against it, but that's not the idea! I sprinkled sugar on it, to try to lure them towards it but still, they buzz around the house, mocking me. What ought I to do to make the paper more attractive to these cheeky little flies? --78.148.140.94 (talk) 15:32, 23 June 2010 (UTC)

Flypapers are good for catching those smaller flies that make little zig-zaggy flights around the light in the centre of the room but for those bigger guys who buzz from one room to the other like they've left something somewhere then they are less good. My suggestion is to experiment with positions, like near the entrance where they..er, enter or in a window where the light is more likely to attract them. 86.4.183.90 (talk) 18:21, 23 June 2010 (UTC)

I like the way you write very much, you must be a very nice young woman. 92.230.69.146 (talk) 21:42, 23 June 2010 (UTC)

Is this some sort of in joke? Otherwise this is possibly the creepiest post I've ever read on the ref desk.. If the OP hasn't been scared away for life already I'd like to state that the above unregistered user does not represent the view of Wikipedia or the majority of ref desk regulars.. You may or may not be nice, young and/or a woman however the ref desk regulars would mostly refrain from judging you based on any of those factors.. Well unless you are particularly not nice, then we might. Vespine (talk) 23:16, 23 June 2010 (UTC)

lol... If I was a very nice young woman, then I don't know what I would've made of it, but I'm actually a nice young man, so I find it pretty funny. I like to think of myself as a brilliant combination of feminine and masculine characteristics; a few days ago, I baked some really moist blueberry and strawberry muffins and today, I rendered a garden wall (well, started it, anyway). Sometimes I write like a nice young woman, other times like a cantankerous old man :D goodnight; much love (Oh, I just noticed that my IP has changed! I'm the OP with the pest-control problem!) 92.28.83.178 (talk) 00:20, 24 June 2010 (UTC)

Commercial flypaper is usually yellow which is apparently the most attractive colour for flies. Also hang it up high, an it will be a natural landing space. Instead of sugar you can put prawn paste. This will attract flies as it decomposes. Graeme Bartlett (talk) 06:59, 24 June 2010 (UTC)

Yellow? As I recollect, most fly paper is brownish where I come from, distributed in rolls (picture something like an old 35 mm camera film roll container) and hung from convenient objects, usually in the kitchen by the ceiling lamp. These things seem to be pretty damn effective - my girlfriend's parents use these and there are usually dozens of flies (all sizes, not just the little ones) stuck to them. Creepy. AFAIK, flypaper is meant to be attractive to insects, not just sticky, through smell and/or special chemicals. Experiment with other brands, I suggest. Last year we assaulted our food moths (these guys) with something similar (pieces of specially-coated cardboard stuck to shelves) and I think we got most, if not all, of them, and I do hope to think it was not just coincidence that they wandered onto the paper. We repeated the process until the last sheet was left untouched, which we saw as a sign that the colony was no more. Sorry for the excessive talkativeness. Yes, that WAS a creepy answer up there by 92.230) --Ouro (blah blah) 08:27, 24 June 2010 (UTC)

A type of memory disorder

Its funny. I'm trying to remember the name of a type of memory disorder, but I can't remember. It sounds sort of odd. It is defined by an occurrence where you are doing something that you do regularly like drive a car, or shoot a basketball, etc; but you feel like it is the first time you have done it. You may well realize this isn't the first time I have ever driven my car, but there is at least a portion of the activity that suddenly feels unfamiliar and new. It sounds similar to the Choking Under Pressure phenomenon, but not related to sports necessarily.Mrdeath5493 (talk) 16:33, 23 June 2010 (UTC)

not really a disorder but sounds like Jamais vu --Digrpat (talk) 17:09, 23 June 2010 (UTC)

That seems to describe it quite well, but I'm not sure it is the term I'm looking for. Maybe you could call it a temporary impairment? I read about it in a medical text in a section about absence seizures. Nevermind. A quick Ctrl+F found that to be exactly it. Thanks, Digrpat.

Mrdeath5493 (talk) 17:33, 23 June 2010 (UTC)

sodium borohydride and hydrogen peroxide

Thermodynamically I know the reaction is spontaneous; but what about kinetically?

What about sodium perchlorate and sodium borohydride under strongly basic conditions? John Riemann Soong (talk) 18:57, 23 June 2010 (UTC)

First reaction - you might get peroxoborates (mostly stable, but some very unstable)+ hydrogen, rather than reduction of the peroxide, this is what I would expect to be the kinetic product.

note the reactivity of hydrogen peroxide is increased in many reactions by a lewis acid, even a weak one. Thus the reaction of LiBH₄ might be different due to Li+ activation (speculation) —Preceding unsigned comment added by 77.86.123.157 (talk) 21:43, 23 June 2010 (UTC)

Second. No reaction in ice cold water. No kinetic pathway I'm aware of. At some temperature a reaction will start - but this would just lead to thermal runaway and destruction of both reagents to the most stable products.

The second is a reaction not to try in the solid phase + heat , or in concentrated solutions, even if it is expected not to react.. unless you take special (ie remote) precautions.

more Searching http://www.google.co.uk/search?q=perchlorate+borohydride+reaction&hl=en&ei=HH0iTMyXNoWi0gTw2Oj4BA&start=20&sa=N shows that perchlorate is a stable counter ion in many borohydride reductions, as far as I'm aware strongly basic conditions reduce the activity of both - so no reaction. 77.86.123.157 (talk) 21:22, 23 June 2010 (UTC)

Delayed death after serious injury

Why do some people die some time after receiving a serious injury? I would have imagined that if you survived the injury, then your body would start healing and you should not die. Is it due to a build up of toxins that the injured body cannot clear? 92.15.3.0 (talk) 19:55, 23 June 2010 (UTC)

Sometimes it can be toxins. Sometimes it can be internal bleeding. Sometimes it can be organ failure. Sometimes it can be an infection. Googlemeister (talk) 19:58, 23 June 2010 (UTC)

I suppose it depends on the timeline - shock can easily kill someone after they are seriously injured. TheGoodLocust (talk) 20:22, 23 June 2010 (UTC)

Sepsis and/or shock (and, um, septic shock) often play a role in "finishing off" someone who has survived the initial injury. Matt Deres (talk) 20:36, 23 June 2010 (UTC)

Depends on the sort of injury. Blunt force injuries can sometimes appear benign and then the patient may deteriorate due to bleeding. If you have a sharp injury wound and lose a lot of blood, there is no guarantee that you will receive the blood in time to combat the effects of hypovolaemia. As mentioned above, toxins are sometimes unapparent and when they do kick in, it can be too late to start reversing the effects. Sepsis plays a big role in open wound injuries and sometimes the risk of death by infection outweighs the risk of dying from the initial injury. Finally, it should be noted that some injuries are unrepairable. Brain and other nerve injuries are very hit and miss with recovery; some may recover and others may not. In summary, our bodies are amazing and can recover from remarkable injuries, but they're not perfect. Sometimes things appear fine and then other factors come into play and it's too hard to combat them. Regards, --—Cyclonenim | Chat  21:01, 23 June 2010 (UTC)

Oh, I forgot that sometimes after the injury things inside the body will move and cause problems, such as a fat embolism. Googlemeister (talk) 21:15, 23 June 2010 (UTC)

While I can't be sure, in terms of timeline I'm guessing the OP is thinking of the sort of thing where you here of someone e.g. surviving a plane crash or car crash or falling down a cliff or being shot or stabbed or whatever but dying in hospital (not from life support being turned off as the patient is brain dead where in some ways the patient was already dead) a few days, weeks or months later, rather then someone dying a few hours after the injury occured. Nil Einne (talk) 21:21, 23 June 2010 (UTC)

Yes, I was thinking of days weeks or even months later. 92.15.3.0 (talk) 21:53, 23 June 2010 (UTC)

An injury to the head can create an opening which allows leakage of Cerebrospinal fluid fluid into the sinuses. This leakage can continue without symptoms (other than a "runny nose") for months, until bacteria, viruses or fungus make their way into the CSF around the brain and cause Meningitis, which, if not treated promptly, is often fatal. Edison (talk) 22:32, 23 June 2010 (UTC)

I was also thinking of people being treated in hospital. 92.24.191.32 (talk) 22:58, 23 June 2010 (UTC)

I think infection is the most likely explanation of a death that long after an injury. Open wounds, especially burns, are very good ways for infections to get in. If you are in a hospital, then there is always a risk of things like MRSA. --Tango (talk) 23:26, 23 June 2010 (UTC)

I would offer than a reasonably healthy human body has all sorts of mechanisms that can help mitigate immediate death. Only after all options have been exhausted does a human expire. Vranak (talk) 18:17, 24 June 2010 (UTC)

Identify wasp or insect

Wasp ? Click to expand

Can anyone identify this wasp (UK) slightly squashed - it's quite red, line spacing is 5mm 6mm. Sf5xeplus (talk) 23:54, 23 June 2010 (UTC)

Looks like a kind of Ichneumon wasp. If you tell us where you saw it (country, area, etc.) it would probably help. Matt Deres (talk) 00:38, 24 June 2010 (UTC)

Found it in England, Kingston upon Hull. (I've still got it if more info is needed, but I'd like to bury it quite soon..).77.86.123.157 (talk) 00:45, 24 June 2010 (UTC)

Could be Ophion sp. Those are found in England, look about right, have large ocelli and short ovipositor. This is just a guess, though, so it's quite likely that I'm dead wrong on this one. There are many ichneumonid species found in UK, and I am unfamiliar with most (I'm not from UK). --Dr Dima (talk) 01:29, 24 June 2010 (UTC)

Thanks - most in commons under Ophioninae look close to me. I'm worried that you decribe the ovipositor as short - it looks absolutely massive to me (3mm) - I hope there's no chance one of these would mistake me for a caterpillar.

Q.? Do they have a sting or not - the thing I think is a sting in the tail is not? Is that right? I read the article

Q. ? Because it has an ovipositor this must be a female then? 77.86.123.157 (talk) 01:56, 24 June 2010 (UTC)

For what I know, Ophion can actually sting a human (most ichneumonids can't). Regarding the ovipositor size, some Ichneumonidae (namely Megarhyssa) sport the longest ones in existence. If you see one, you will be impressed. The ovipositor of Ophion is relatively short for an Ichneumonid. --Dr Dima (talk) 02:29, 24 June 2010 (UTC)

And regarding your last question: yes, sure enough, males lack an ovipositor. --Dr Dima (talk) 02:32, 24 June 2010 (UTC)

ok thanks, that's enough info for me.

Resolved

June 24

Thrust vectoring

Does thrust vectoring have any disadvantages? Since it makes an airplane much more maneuverable, one would think it would be used on more fighters.

There's a relatively small amount of extra weight for the equipment, plus the additional complexity.

Additionally allowing a jet engine to provide it's thrust in a direction other than in the direction of flight means that the 'airframe' must be able to support/resist that thrust - ie the vectored thrust must be able to be transmitted to the plain without the plane snapping into bits.. This could mean addition weight due to extra trusses etc needed - especially since the torque is different to that due to the mass of the engine in manouvers - ie the trust vectoring force is not coaxial with the centre of the mass of the engine (I've assumed that the thrust vectoring force is transmitted though the engine assembly - this might not be the case) - in short additional reinforcement may be needed.77.86.123.157 (talk) 01:23, 24 June 2010 (UTC)

You also need the power available to redirect the thrust, which is power that isn't available for other purposes (such as speed). Physchim62 (talk) 01:42, 24 June 2010 (UTC)

Personally, I think that the reason why we don't see it on fighters is because it's still a pretty new concept, plus the fact that on fighter planes (crammed as they are with fuel tanks, weapons and electronics) it's often not clear where one could stick the extra ducting and equipment. That said, the F-22 and F-35 both incorporate a form of thrust vectoring where the rear-mounted jet nozzles pivot up/down to give a super-fast response in the pitch plane. As for Physchim's point, it's completely irrelevant because the power to redirect the thrust is the power supplied to the actuators, not the power taken from the jet exhaust, and in any case it's only a small fraction of the power generated by the engine. Clear skies to you 67.170.215.166 (talk) 01:52, 24 June 2010 (UTC)

How is it a new concept? It's a completely obvious one as soon as you have jet engines. What's new is the ability to actually put it into action efficiently and effectively. The OP's question is what was stopping this being done sooner, and what is stopping being done more widely? --Tango (talk) 02:07, 24 June 2010 (UTC)

Well it might not be a new concept, but the way it is applied to fighter aircraft is fairly new. The article even states at first thrust vectoring was only envisioned for VTOL and STOL capability. I imagine just the fact that it is substantially more complex and therefore expensive and more difficult to maintain is probably the main reason you don't see it on more aircraft as yet. Vespine (talk) 02:32, 24 June 2010 (UTC)

There's at least two more reasons why it's not as good an idea as it might appear:

1. The ability to suddenly change direction eg pitch of an aircraft means that the wings will experience massive forces - ie the wind force at mach 1+ on a couple of square meters will probably just rip the wings off.. If the wings are strong enough the pilot has to survive the acceleration too. There's a limit to how fast you can turn at high speeds for both these reasons.

2. Aerial combat is quite missile based - the missile doesn't need a direct hit, and are very maneouverable - even with thrust vectoring the mass of the plane is likely going to prevent it from being able to evade a missile even if 1. can be avoided.

On the other hand thrust vectoring does raise the possibility of a plane with fewer control surfaces, and thus a simplified wing (numerous advantages). You can yaw, roll and pitch with suitable thrust vectoring. landing control might be a problem.77.86.123.157 (talk) 03:09, 24 June 2010 (UTC)

The Sukhoi PAK FA has thrust vectoring too. I think modern fighters do in fact have thrust vectoring; but soon there might not be any modern fighters, because the sixth generation might all be UAVs... at least some of which will have thrust vectoring [17]. 213.122.59.238 (talk) 15:24, 24 June 2010 (UTC)

Every additional moving part you add to a propulsion system (in fact, any change at all to an existing design) brings an additional risk of failure. The people who design propulsion systems for aircraft tend to be very paranoid about that sort of thing. Nimur (talk) 03:25, 24 June 2010 (UTC)

The first practical jet engines weren't really around until the 1940's - and the first practical vectored-thrust jet was the British Hawker Siddeley P.1127, which started development in 1957 and first flew in 1960. So given the problems with pushing out new technology during WWII - there really wasn't much of a lag between the time when people were able to start seriously considering jet engines and the time when thrust vectoring was first used. SteveBaker (talk) 14:51, 24 June 2010 (UTC)

I disagree with the above, thrust vectoring in the Hawker and later the harrier were developed specifically for VTOL, It's a very different thing. The concept of thrust vectoring to improve combat maneuverability is a completely different paradigm and a relatively new one. Vespine (talk) 00:05, 25 June 2010 (UTC)

And thrust vectoring would work with prop aircraft as well. I think the older airships (USS Akron (ZRS-4) perhaps?) were able to use some degree of thrust vectoring with their engines back in the 30s, but I do not know if we mention such capabilities in our article. Googlemeister (talk) 15:00, 24 June 2010 (UTC)

Difference of animals

What is the difference between cheetah and leopard? --Extra 999 (Contact ^me + _contribs) 01:15, 24 June 2010 (UTC)

If you mean on how to recognize the difference, then look at the size. Cheetahs (Acinonyx jubatus) are much smaller and slimmer, whereas leopards (Panthera pardus) are more robust and heavyset. Also, the spots on a leopard are rings, called rosettes, whereas on a cheetah they are spots. Cheetahs can also run much faster - up to 65 mph. If you mean what makes them separate species, I suppose it's the fact that they can't interbreed. --The High Fin Sperm Whale 01:23, 24 June 2010 (UTC)

One has evolved itself into a specialized and therefore vulnerable evolutionary niche while the other has retained more general abilities that will allow it to survive future bottlenecks. TheGoodLocust (talk) 02:05, 24 June 2010 (UTC)

Grebe

File:Grebe swimming with young.JPG

I am fairly sure that this is a grebe, but does anyone know what species it is? It could possibly be a Red-necked Grebe (Podiceps grisegena), but I don't think Red-necked Grebes have a red head, only a red neck. Thanks, --The High Fin Sperm Whale 03:34, 24 June 2010 (UTC)

merganser

looks more like a merganser to me. Particularly note the hooked bill and the spiked crest (not features of grebes) --Ludwigs2 04:14, 24 June 2010 (UTC)

I concur. Look up 'merganser' on Google images and there is plenty of evidence. Richard Avery (talk) 07:10, 24 June 2010 (UTC)

A female Common Merganser (Mergus merganser), known in Britain as Goosander. Ghmyrtle (talk) 07:22, 24 June 2010 (UTC)

Piezoelectric body armor?

The idea would be similar (and perhaps incorporate) body armors made from non-Newtonian fluids, but I'm basically wondering if you could make a body armor with a bunch of microscopic crystals (similar to how some warriors use to soak their armor in brine), which, upon impact, would generate an electric charge to power an electromagnetic reaction to harden a magnetorheological fluid? I'm not sure how much of a charge could be generated in this manner or if it would require specially designed materials rather than something common like quartz. Properly designed I'd think armor like this would protect from tasers/stun guns too. TheGoodLocust (talk) 04:29, 24 June 2010 (UTC)

No. You're writing fantasy - a piezoelectric material that stops bullets without breaking doesn't exist. Have you don e any research on this at all - or are we expected to comment on every scheme you dream up? 77.86.123.157 (talk) 13:19, 24 June 2010 (UTC)

I thought it was pretty clear I was wondering about microscopic crystals that are either incorporated into the fluid itself or which use a conductive fabric as a substrate - not giant sheets of the substance. The actual stopping of the bullets would be done by the magnetorheological fluid. Also, such crystals would be harder than anything coming out of a gun (not that it really matters that much). TheGoodLocust (talk) 16:34, 24 June 2010 (UTC)

And a cool defense would be emitting an EM field so that your supercommandos will be frozen solid in their armor for easy capture. Googlemeister (talk) 14:52, 24 June 2010 (UTC)

Yes, I suppose that could be a problem even with current concepts for magnetorheological armor, but current power/range limits would, i suspect, limit the practicality of such a device.TheGoodLocust (talk) 16:34, 24 June 2010 (UTC)

A related idea is dilatant based body armours such as Liquid Armor or d3o which exist. The set-up you describe seems to require nano-engineering and would be years away if ever practicable, also see Magnetorheological_fluid#Military_and_Defense. You also might want to consider using a material that thickens with an electric field eg Electrorheological fluid.

Also http://www.memagazine.org/backissues/membersonly/sept06/features/narmour/narmor.html

And especially this patent (UK patent 2460493):

An impact protection device comprises a web of piezoelectric fibres and an electrorheological fluid suspended by said web. In response to an impact event, the piezoelectric fibes generate an electrical signal, This is used either directly or indirectly to apply a second electrical signal to one or more electrodes, in response to which an electric field is applied to the rheologolical fluid. This causes the fluid to stiffen, providing protection against the impact event.[18]

it's possible that similar patents exist similar to your idea too. 77.86.123.157 (talk) 18:44, 24 June 2010 (UTC)

Yes, I referred to such substances in my initial post as non-Newtonian fluids. I was unaware that electrorheological fluids exist (makes sense though) and that would be a better method of implementation. Nanotech might be a requirement, but I suspect in this application it wouldn't be terribly difficult to grow large amounts of small crystals. The big question is whether it would be cost effective and superior to current body armor technologies. The article on ER fluids states that under compressive stress they become solid or nearly solid, which seems to indicate some potential in this application. Cheers. TheGoodLocust (talk) 19:00, 24 June 2010 (UTC)

Ah yes, it looks like people are already looking into this. This isn't surprising since it is a pretty basic concept. TheGoodLocust (talk) 19:00, 24 June 2010 (UTC)

TO220 heat sinking

While designing a circuit, I had a bit of a fleeting thought: suppose you had a board with plenty of space parallel to the plane of the board (i.e. horizontally), but little space perpendicular to it (i.e. vertically), and you need to use a TO220 package under conditions requiring a heat sink (such as an LM7805 pulling 800mA with V_CC=12V). If, then, you were to use solder paste to solder the heat sink tab directly to a large, exposed copper plane on the PCB (bending the pins at the vias so it lies flat on the board, of course), would that be a viable alternative to a tall, bulky heat sink? (I'd imagine so considering D²PAK packages often have similar specs to TO220s, but don't usually have a vertical heat sink - but I'm still not certain.) Also, if you were to do that, would that have a (much) more significant parasitic thermal effect on nearby semiconductors than a vertical heat sink? And one more: if you used Arctic Silver 5 instead of solder paste and then bolted the tab to the board instead of soldering it, how would that compare (in terms of heat dissipation) to the previously described way of soldering it (assuming an otherwise identical board)? Thanks! (And forgive me for the amount of parentheses I used. (I'm rather addicted to them, you see.)) --Link ^(t•c•m) 06:39, 24 June 2010 (UTC)

Your LM7805 dissipates (.8A x (12-5)) = 5.6W. Here are some TO220 heatsinks. For example the twisted vane type has thermal resistance 9.9 degC/W so the LM7805 temperature would increase 5.6 x 9.9 = 55 deg C. The PCB copper plating being so thin and insulated on one side would have much higher thermal resistance. A rule of thumb I remember is that a semiconductor device's lifetime is halved for every 10 degC rise. Tip: you can pass the minimum output current through a resistor in parallel with the regulator thereby sharing the 5.6W dissipation between two devices. Cuddlyable3 (talk) 12:16, 24 June 2010 (UTC)

I agree that the thickness of copper in a standard pcb would not make a suitable sink. If vertical space is limited why not use a horizontal copper or Al plate above the surface of the PCB (ie bend te package the opposite way so that the thermal contact area is pointing up) - you could if necessary cut holes in the plate to both allow air circulation to/from other components, as well as allowing large vertical components (eg big caps and inductions etc) to poke through?? (No idea above comparison between artic silver and solder paste ) 77.86.123.157 (talk) 14:36, 24 June 2010 (UTC)

Interesting. It was a purely hypothetical question so it won't matter either way, but thanks for the replies! A custom-cut heat sink with TO220s attached face-down is a very interesting idea. It might even double as a form of casing or mounting bracket. Would make for a funny-looking board, that's for sure. --Link ^(t•c•m) 16:47, 24 June 2010 (UTC)

Here is a project I did recently that has horizontal mounted to220 with heatsinks. The pictures aren't great but you can see it to the right of the bottom board and also see it in the assembled picture from the side. HTSSOP package relies on using the board as a heatsink and a trick I saw recently was to have a patch of closely packed vias which the bottom of the package is soldered to. The vias carry away more heat then just a patch of copper, but these were just LED drivers, not voltage regulators. Vespine (talk) 00:28, 25 June 2010 (UTC)

If you can get your hands on them you can also use one of the 5V switch mode regulators, which gets rid of the issue completely. --antilived^{T | C | G} 05:29, 25 June 2010 (UTC)

astrophotography with the webcam

i have bought a webcam to use it in the astrophotography, i dismounted its lens and then i assembled a small plastic cylinder in its place. after that, i tried to picture the Moon by the webcam through a binocular, but i pictured just a scattered white light. is this method in the astrophotography don`t work with the binoculars? or i did a something wrong? --Abbad Dira (talk) 09:28, 24 June 2010 (UTC).

Maybe the position is out of focus? Have you tried at different depths? 77.86.123.157 (talk) 14:38, 24 June 2010 (UTC)

thank you all for the answers.

• i looked through the binocular before taking the picture and everything was right --Abbad Dira (talk) 19:56, 24 June 2010 (UTC).

You have to make sure that the image plane of the camera (the little silicon chip that picks up the light) lies at the focal point of the binoculars. You'll need to vary the distance between the camera and the binocular eyepiece to get it in focus. Remember also that the binoculars are designed to focus light THROUGH the lens of your eye to form a sharp image onto your retina - in the case of your lens-less camera, the distance will be different than from the eyepiece to your eye. I think you need to experiment with different lengths of the plastic cylinder, fine tuning it with the focussing controls of the binoculars to get the most accurate focus. SteveBaker (talk) 14:40, 24 June 2010 (UTC)

• i tried now, but i couldn`t find a good thing to set the binocular on it and in the same time i can observe a bright and enough distant object from its place. however, i tried with a faint and non-celestial object, and i could see just a white light with a scattered black-points on it. i will try to experiment a different lengths --Abbad Dira (talk) 19:56, 24 June 2010 (UTC).

I don't think the setup you're trying is going to work. The page you linked to discusses removing the lens from a webcam and using it in place of the eyepiece of a telescope. A binocular is like a telescope with a permanently attached eyepiece. With a binocular, I think you need to do afocal photography, which would mean the webcam's lens should remain attached. (Basically, if your "telescope" is something you can look through with your eye (that is, one that produces a virtual image), you need a camera with a lens. If your "telescope" is something that can project a real image onto a piece of paper or film, you need a sensor without a lens.) -- Coneslayer (talk) 14:50, 24 June 2010 (UTC)

• so why i don`t use a digital camera?! what i should to do with the lens of the camera?! --Abbad Dira (talk) 19:56, 24 June 2010 (UTC).

Astrophotography is a very challenging and potentially expensive hobby! I think you'd be much better off finding a forum specifically on the subject, rather then trying to work it out on the ref desk. My fav forum is iceinspace.com.au, don't let the fact that it's Australian put you off, it's one of the best astro photography forums I've ever found. Lots of beginners and amateurs, and several people so good they get their pictures on NASA APOD. Vespine (talk) 00:19, 25 June 2010 (UTC)

Strange parrot behaviour

Can anyone suggest what the parrot in this: http://www.youtube.com/watch?v=DWYv-R5x9Cw video is actually doing and why? My guess would be that he's, for some reason, trying to seduce the dishwasher, but that's just a guess. --95.148.107.169 (talk) 10:11, 24 June 2010 (UTC)

Perhaps it has fleas or an itch from some other source? Either that or drugs and/or calisthenics. TheGoodLocust (talk) 16:39, 24 June 2010 (UTC)

Is the dishwasher perhaps blowing some air out through the lower vent, e.g. from heating cycle perhaps? I know my cat loves to sprawl in front of the kitchen heat register because the heat is blowing towards him rather than up into the room.

On the other hand, there's a reason someone coined the term "birdbrain", too! DaHorsesMouth (talk) 00:00, 25 June 2010 (UTC)

It may be Anting (bird activity) or having a Dust bath, without any ants or dust. 92.28.242.52 (talk) 16:37, 25 June 2010 (UTC)

finite element

where commercially used this process —Preceding unsigned comment added by Dhirajsharma89 (talk • contribs) 10:46, 24 June 2010 (UTC)

Are you referring to the Finite element method? --Ouro (blah blah) 11:50, 24 June 2010 (UTC)

Spacetime and diverging timelines - not really a question, just a request for more information

Okay, so the speed of light seems to be the upper limit for speed in the universe, which means that nothing can accelerate above this velocity.

This means that:

• nothing which happens in the Moon will affect us before 1.28 seconds.
• nothing which happens in the Sun will affect us before 499 seconds.
• nothing which happens in Córdoba, Argentina, will affect Wuhan, China before 0.066 seconds.

Since no phenomena can propagate above the speed of light, for all intents and purposes, these locations are not only in different points of space but also in different points in time. In effect, the Moon is 1.28 seconds out of synch with the Earth, the Sun is 499 seconds out of synch, and antipodal points in the world are 0.066 seconds out of synch with each other.

Therefore, when I take an airplane to see my girlfriend, I am not only covering 1,400 km in space, but I'm actually synchronising her timeline and my timeline by 0.005 seconds.

Please, could you direct me to articles, either here or off-Wikipedia, which deal with the subject of travelling in time by travelling in space?--83.38.102.61 (talk) 13:33, 24 June 2010 (UTC)

I think you have slightly the wrong idea. The problem is that you are still clinging to the idea of 'absolute time'. The moon isn't 1.28 seconds "behind" the Earth - because if you were standing on the moon, you'd see events from Earth delayed in exactly the same way - so it's just as easy to say that the earth is 1.28 seconds "behind" the moon. Ignoring the teeny-tiny effects of relativity, the timeline of someone on the Earth is the same as that for someone on the moon - the speed of light only limits how information gets from one place to another. Relativity adds a much larger and harder concept - which is that the idea of two events being "simultaneous" at all is a fairly meaningless concept. However, the lack of the concept of "simultaneity" is really only an issue when things are moving very fast relative to each other. Here on Earth, you can say that two events happened "simultaneously" in Cordoba and Wuhan - but that the person in Cordoba can only possibly find out about a simultaneous event in Wuhan 66 milliseconds later...but that delay doesn't represent a 'time shift' as you seem to be implying because an event that happens in Cordoba isn't somehow magically known to have happened 66 milliseconds EARLIER in Wuhan...they still only know about it 66ms AFTER it happened in Cordoba. So in 'normal' situations where relativity is a negligable effect, you don't have to "synchronise timelines" at all...all you are doing is reducing the communications delay by getting closer. SteveBaker (talk) 14:35, 24 June 2010 (UTC)

The article you want is Relativity of simultaneity but be aware than it's not an easy concept, and you'll probably need other sources besides wikipedia to help you understand it. Ariel. (talk) 14:37, 24 June 2010 (UTC)

This is also interesting to think about Count Iblis (talk) 14:44, 24 June 2010 (UTC)

Also technically, no two points on earth can be more the 0.043 light seconds away. You have to consider going straight through the earth, not traveling on the surface for the correct distance. Googlemeister (talk) 14:51, 24 June 2010 (UTC)

As are light cones. 86.164.66.4 (talk) 18:55, 24 June 2010 (UTC)

The Rietdijk–Putnam argument is complete nonsense; please ignore it. It confuses an arbitrary way that special relativity is taught (and probably shouldn't be) with the actual physical content of the theory. -- BenRG (talk) 09:58, 27 June 2010 (UTC)

Hmm? From the WP article on it, the argument doesn't appear to be about the physical content, but the metaphysical content — questions about whether the future and the past really exist. If you want to criticize it, fine, but you have to do so in its own context. --Trovatore (talk) 10:10, 27 June 2010 (UTC)

how many g's can a gourmet salad be subjected to without being ruined?

How many g's of acceleration can a gourmet salad be subjected to without being ruined? (e.g. cherry tomatoes in it popping and so on). I don't mean for a very long time, just long enough to get to the other side of the earth in a vacuum tunnel. 2) at that, most-crushing-but-without-being-ruinous g of acceleration and deceleration, how long would it take to get from the one side of the earth to the diametrical opposite side of the earth along a great circle (e.g. along the equator) in a vacuum tube at sea level? Thank you. 85.181.145.173 (talk) 19:54, 24 June 2010 (UTC)

The answer, my friend, is blowin' in the wind.... --Trovatore (talk) 19:55, 24 June 2010 (UTC)

(The more serious answer is I don't know; maybe someone else will. But you know, it's always a good time for Dylan.) --Trovatore (talk) 19:59, 24 June 2010 (UTC)

Maybe it depends on the salad's GI index. :) -- Jack of Oz ... speak! ... 20:02, 24 June 2010 (UTC)

I'll take a stab at a serious attempt to find a lower bound. Salad can survive being in a salad spinner. Salad spinners go at, perhaps, 10 revolutions per second and are, perhaps, 30cm in diameter. The centripetal acceleration required to make something go in a circle is $a=r\omega ^{2}$ where r=15cm and $\omega =20\pi \mathrm {s^{-}1}$, so a=9.4 m/s or just under 1g. Since it is also under 1g from gravity, the resultant acceleration is ${\sqrt {2}}$ g or about 1.4g. So that's the best lower bound I can offer you. --Tango (talk) 20:17, 24 June 2010 (UTC)

tangent

judging from the responses so far, perhaps I've hit on an "inherently funny" concept (like a salami sandwich). I know there are clown colleges, perhaps someone could refer me to a researcher at one with whom I could apply for a grant to study and refine the material along these lines. This is basic research, so it might never lead to comedy or a joke, but pure research has a calling of its own for me. 85.181.145.173 (talk) —Preceding undated comment added 20:08, 24 June 2010 (UTC).

Try here http://www.clownsforhire.com/clownschools.html : "Most "clown schools" hold clown classes when there are enough students to fill or justify having a class" 77.86.123.157 (talk) 21:39, 24 June 2010 (UTC)

I don't know about funding for this kind of research, but the Ig Nobel Prizes are awarded for it. --Tango (talk) 20:11, 24 June 2010 (UTC)

Well if you want it to be somewhat fresh when it arrives, it would probably have to average 6,000 km/hr on its trip. It will be 2 hours old by then, but if refrigerated, might not be a disaster when it arrives. Granted, a gourmet chef would probably prefer it to be fresher then that. Googlemeister (talk) 20:21, 24 June 2010 (UTC)

I'd like it to arrive within 7 minutes, as parts are hot/freshly roasted. Looking at it from that end, how many g's of acceleration must it endure to go through a vacuum tunnel clear around the Earth (to the other side) along the equator at sea level in 7 minutes? 85.181.145.173 (talk) 20:26, 24 June 2010 (UTC)

I did a rough calc and got 22g, but that did not allow time to slow down at the end, so I hope you like your salad served at mach 12. Googlemeister (talk) 21:08, 24 June 2010 (UTC)

I'm getting mach 120 ?77.86.123.157 (talk) 21:20, 24 June 2010 (UTC)

I did not actually calculate arrival speed, I just stated a big number. Technically there is no speed of sound in a vacuum in any case. Googlemeister (talk) 13:04, 25 June 2010 (UTC)

(edit conflict) ok so the equations. v=ra/t where v= velocity, r=radius of earth, a=angle you want to travel through (use radians ie 180 degrees = pi radians), and t is the time.

and the acceleration is v²/r

so the acceleration is a²r/t² _{r=6000000m, t=420sec answer ~36g ??}

77.86.123.157 (talk) 21:09, 24 June 2010 (UTC)

um, it should be at the destination at rest at the end of the journey, not flying through it at mach 120 or whatever.

Now, what do these answers, e.g. 36g mean?

Does it mean that a cherry tomato will feel like it just has 36 cherry tomatoes sitting on top of it? 85.181.145.173 (talk) 21:46, 24 June 2010 (UTC)

yes. 77.86.123.157 (talk) 22:13, 24 June 2010 (UTC)

No. 35 other cherry tomatoes, not sitting on top but connected at the midriff. That's if tomatoes have midriffs and can feel. Which they don't. Instead you will get this. Cuddlyable3 (talk) 23:06, 24 June 2010 (UTC)

Have a look at g-force#Acceleration and forces Dolphin (t) 11:10, 25 June 2010 (UTC)

breakup/thinning of plant calluses into solution via ultrasound/high-frequency sonication

I'm trying to image strips of plant cells connected by plasmodesmata by Differential interference contrast microscopy. Of course my hand isn't that precise, so I've used ultrasound sonication as a strategy.

I've been a little unrigourous in my methodology (just trying to figure out what seems to work), but I've been using a combination of surfactants, vortexing, centrifugation slicing and grinding. Ideally I want majority intact cells and a slight minority of injured/broken cells (for nanoparticles to enter through). What combination should I use?

I was thinking of flattening the callus and then slicing into tiny strips/squares, dissolving it a little in water (should I add osmolarity/pH buffer?) and sonicating it. Should I go for low-amplitude, long term sonication (5-15 mins maybe?) or short, powerful bursts? What about adding a little bit of surfactant, alcohol or detergent? I'd also like to thin the cell wall a little -- not totally remove it, but rather make it more permissive to DIC microscopy.

I have access to a few good centrifuges, so I could probably repeatedly centrifuge solutions to remove debris and excess water. I already attempted this once (with lots of sonication) with lots of what I think is cellular debris (I hope it's not microbes) and clumps of intact cells that I can image to some degree. (It's very hard to see the nucleus -- though you normally can). The clump is several cells thick -- from two to four cells I think. Which isn't bad. I'd just like to have suggestions on how to improve it. John Riemann Soong (talk) 20:38, 24 June 2010 (UTC)

Are there any enzymes that you can use to selectively digest the cell wall, such as xylanase or cellulase? Graeme Bartlett (talk) 04:02, 25 June 2010 (UTC)

I could borrow some from another group. Do these enzymes resist degradation by sonication? John Riemann Soong (talk) 20:36, 25 June 2010 (UTC)

pros and cons of immortality

what are the pros and cons of immortality. note: not asking for medical advice, just curioujs —Preceding unsigned comment added by 85.181.145.173 (talk) 22:09, 24 June 2010 (UTC)

have you seen Immortality#Ethics_of_immortality 77.86.123.157 (talk) 22:14, 24 June 2010 (UTC)

Don't expect a pension if you're going to be immortal... Physchim62 (talk) 22:17, 24 June 2010 (UTC)

That's not necessarily true, you just wouldn't get as good a pension. You would need an endowment, rather than an annuity. (Obviously unfunded pensions wouldn't work - they require a constant ratio of working people to retired people, and people working for a finite amount of time and then having eternal retirement would result in an ever decreasing ratio.) --Tango (talk) 22:28, 24 June 2010 (UTC)

Also at the top of this page it states "the reference desk does not answer requests for opinions .. do not start a debate" - this question can't really be answered scientifically without 'opinions'. Think for yourself. Have you made the slightest attempt to answer the question yourself? 77.86.123.157 (talk) 22:18, 24 June 2010 (UTC)

I don't agree with shouting this question down, and I think the link you provided before the shout-down was helpful and useful. Comet Tuttle (talk) 22:20, 24 June 2010 (UTC)

The article Immortality notes that the jellyfish Turritopsis nutricula has developed biological immortality one consequence of which is a worldwide population explosion of the organism. Mark that down as a con if you are considering biological immortality. However that can happen only in fiction so it seems we are being asked to brainstorm about a story plot. Immortality can also describe a person's reputation of which there are good and bad examples. Cuddlyable3 (talk) 22:54, 24 June 2010 (UTC)

You can't answer it meaningfully...even hypothetically...there just isn't enough information. For example:

1. Are people somehow immune from accidents? Since your chance of dying in an accidental manner is around 10 to 13 percent, you wouldn't actually live forever.
2. Are people somehow immune from absolutely all diseases? If the only thing this miracle process helps you with is not dying of old age, you should realize that maybe only 50% of people survive disease and accident to actually die of "ageing" (although that's a pretty fuzzy definition - you never really die of "old age" - it's always something specific like heart stoppage). If you have a 50% chance of making it to 80 years old then you only have a 25% chance to make it to 160 years, a 12% chance to 240 years and so on. Living forever means never fighting in a war, never driving a car, never crossing the street, never choking on a fishbone, never catching any kind of nasty virus, no cancer, etc.
3. Are you still fully fit and alert through this vastly extended life? Can you still work? If we have a lot of people with failing faculties and inability to do heavy work then society is in horrible trouble...if they are all fit and alert - then that's a different matter.
4. Are people still able (and willing) to bear children at those ages? Again, this makes an immense difference to population growth rates (which would be serious in any case).
5. Can we assume that the other problems of over-population (global warming, water and food shortages, etc) would also be solved? If not, then the answers are vastly more dramatically serious than if those things too have magically "gone away".

In short, this is a speculative question - and we shouldn't attempt to answer it because our remit here at the ref desk says that we don't do that.

SteveBaker (talk) 23:04, 24 June 2010 (UTC)

I totally believe people will be able to live forever, or at least increase their lifespans by 5 or 10 times, possibly not in my lifetime, but within 100 years or so I think it's very plausible. So I believe this kind of thing will need to be worked out. But yeah, at this stage, it's still pretty much a speculative debate. Vespine (talk) 00:12, 25 June 2010 (UTC)

But just think about what you're saying! To have people live forever, you don't just have to solve the 'shortening telomere' problem of aging. You also have to cure ALL diseases, end ALL wars, eliminate ALL causes of accidental death - oh and by the way: eliminate famine and resource/living-space limitations AND somehow take away people's ability to murder, commit suicide, etc. If you plan to live forever then how do you avoid car accidents? What are the odds of you surviving for more than a couple of hundred years without getting involved in a war or being murdered or choking on a fishbone or catching ebola or being struck by lightning or attacked by a rabid dog? Without the technology to prevent all of those things, immortality is impossible. As fast as we fix problems of aging, so diseases that you'd rarely live long enough to suffer from (cancer induced by normal background radiation, for example) become significant killers of the population. Fixing all of those things to provide even a small probability of living (let's say) for 2000 years is a crazily impossible thing! So sure, lifespans will probably continue to increase as our medical technology advances - and as it has done for the past several hundred years - but immortality takes a much more drastic step that seems unreasonably difficult. SteveBaker (talk) 13:52, 25 June 2010 (UTC)

I sure hope we've mastered space-based resource and energy harvesting before then!! APL (talk) 02:43, 25 June 2010 (UTC)

There is a huge body of science fiction work where the underlying theme can be roughly summarized as "I've achieved immortality, but it turns out that it sucks." See this TVTropes link for an incomplete, but long, list.

Frankly, I've always thought that these stories are a form of sour grapes. APL (talk) 02:34, 25 June 2010 (UTC)

Immortality cannot be experienced because there are only a finite number of states a brain can be in. So, even if you have a brain that exists forever, it can only generate some large but finite number of conscious experiences. In each of these subjective experiences, you have a finite memory of past events. What will happen if the brain survives forever is that some of these conscious experiences will be generated infinitely often. Count Iblis (talk) 03:11, 25 June 2010 (UTC)

I think that The Lord of the Rings tackles this issue in a serious and sober manner. Can't think of any others. Vranak (talk) 04:42, 25 June 2010 (UTC)

Maybe not exactly serious or sober, but the description of the Struldbrugs in Gulliver's Travels raises some issues about immortality. AndrewWTaylor (talk) 12:00, 25 June 2010 (UTC)

Immortality does not imply that the brain "survives forever". For example, nothing on this planet is more than 5 billion years old, and nothing will remain after another 5 billion years when the Sun becomes a red giant. A biologically realistic notion of immortality implies that the immortal being does not age (like many single-cell organisms that can divide indefinitely), or ages but continuously renews itself (like an aspen grove), or reverts to larval stage and starts again (like some jellyfish). All of those are immortal in the sense "not aging"; however, no living being is immortal in the sense of "cannot die". Anything that lives can die. --Dr Dima (talk) 07:11, 25 June 2010 (UTC)

If it is the immortality of the Struldbrugs I certainly don't want it. Imaging getting more and more aged and decrepit for ever. Dmcq (talk) 12:08, 25 June 2010 (UTC)

Immortality could cause "life" (which is by definition finite) to lose its meaning, as new experiences get less interesting and the level of variety approaches 0, and one would not be able to experience an afterlife if there is one and eventually there would be enough memories to cause brain inflammation. ~AH1^(TCU) 02:22, 26 June 2010 (UTC)

KSR's Mars trilogy addresses some of these issues -- not precisely with immortality, but with a drastic increases in longevity. One proposed solution to the population question was to award everyone a 0.5 right to bear a child, so that a couple could pool their rights and have one child. This child would also receive such a right, and this way everyone would be permitted one child, but the population would at most double. -- 58.147.52.85 (talk) 11:58, 26 June 2010 (UTC)

June 25

Probability distributions in Quantum Mechanics

How do scientists derive probability distributions in quantum mechanics? ? ––115.178.29.142 (talk) 03:09, 25 June 2010 (UTC)

Solve the Schrödinger equation. For one example see Particle in a box or List of quantum-mechanical systems with analytical solutions for others. Graeme Bartlett (talk) 03:57, 25 June 2010 (UTC)

To expand that answer somewhat: solving the Schrödinger equation gives the wavefunction of a system as a function of time, ψ(t). To find the probability distribution of an observable A at a given time t, you express the wavefunction ψ(t) as the sum of eigenstates of A; there will be an eigenstate ψ_a corresponding to each observable value a of A. The "co-ordinate" of ψ(t) along the "dimension" ψ_a will be a complex number φ(a, t) called a probability amplitude. The probability that a measurement of A at time t gives a value a is then the square of the magnitude of the probability amplitude, |φ(a, t)|². Gandalf61 (talk) 08:38, 25 June 2010 (UTC)

A 'perfect solution' is difficult, so sometimes iterative (but approximative) methods like Hartree-Fock are used. John Riemann Soong (talk) 20:38, 25 June 2010 (UTC)

scientific name of the plant( ?or substance?) called "Lapland sesame" in the Wikipedi- article about hand of glory

Please give me to know a botanical name of this thing, if it be a plant; if it be something else, please give me a reas'nably precise definition of that thing. In case past monetary support of {Wikipedia} be of any importance concernin' your-all decision, whether yeah or not to respond unto this query, i mention, that i donated ninety USDollars unto {Wikipedia} in May of this year. —Preceding unsigned comment added by Stig weard (talk • contribs) 04:54, 25 June 2010 (UTC)

Hmmm... Unless there are two Laplands, or some unrelated plant also called sesame, it seems unlikely that there is any sesame native to (or even grown in) Lapland. See sesame and this map which shows where Sesame is cultivated. Sesame is an exclusively tropical plant, while Lapland (northern Norway and Finland) is one of the coldest inhabited places on earth. I did a google search for Lapland Sesame, and turned up almost nothing other than references to the candle recipe already found in Wikipedia. --Jayron32 05:25, 25 June 2010 (UTC)

Agree. It seems that nobody really knows what this is supposed to be, but there is some speculation that it is a bad translation from a French original that meant "sesame and horse dung". Looie496 (talk) 05:28, 25 June 2010 (UTC)

I have corrected the links for you. this is one of those questions that shows just how useless Google can be. There are six hundred-odd links but they are almost circular in source with no answer evident. This seems to have been a 15th century scam but the real identity (if ever there was one) of the plant has been lost. Caesar's Daddy (talk) 15:52, 25 June 2010 (UTC)

I don't know if this is relavent here, but many alchemical/witchcraft recipes usually have ingredients that are either unobtainable, or the name obscured.77.86.123.157 (talk) 15:58, 25 June 2010 (UTC)

Measurment change by interacting

Hi. What's the name of the process, when we measure something, and by measuring we change the properties of this body or thing? 83.31.79.94 (talk) 12:23, 25 June 2010 (UTC)

Heisenberg uncertainty principle.

ALR (talk) 12:35, 25 June 2010 (UTC)

That is incorrect, the Uncertainty principle states that we can't know the exact location and vilocity of a particle at the same time, not that a measurement changes the particles properties, that is a seperate principle. —Preceding unsigned comment added by 74.67.89.61 (talk) 13:03, 25 June 2010 (UTC)

From a pure physics perspective you are indeed correct as it applies to sub-atomic entities. It is, however, used as the basis for a more practical problem in instrumentation and control, measurement impinges on the system and changes the characteristic.

I'd make the observation that I very rarely hear the issue described as observer effect, far more frequently we'll discuss uncertainty, although that does pre-suppose an understanding of the concepts in advance of the discussion.

ALR (talk) 17:42, 25 June 2010 (UTC)

The correct principle is the observer effect. The uncertainty principle's got nothing to do with it. Dauto (talk) 13:37, 25 June 2010 (UTC)

Frequently the Heisenberg uncertainty principle is explained in terms of the observer effect. This is based on Heisenberg's original explanation of the principle (Heisenberg's microscope). However, recent interpretations of the uncertainty principle hold that the principle is a fundamental property of the universe and always valid, and is not simply a result of trying to measure the system. -- 140.142.20.229 (talk) 17:07, 25 June 2010 (UTC)

Yes, we do see that interpretation quite often but it is simply wrong. Dauto (talk) 17:35, 25 June 2010 (UTC)

DIY inspection camera

Is there a way to put together a home-made inspection camera using inexpensive parts? By "inspection camera" I mean something that can feed through a hole no more than an inch in diameter. You can use it to check the plumbing or wiring inside a wall, or to check the condition inside an an air duct. What can you adapt or repurpose for the camera component? --98.114.98.48 (talk) 12:40, 25 June 2010 (UTC)

This is a tiny $13.99 webcam - with LED lighting and infrared capability! All you need is a long enough USB cable and a laptop and you're in business. I'm pretty sure the case is under 1" - but it might be a tight fit. If that's a problem then you might need to remove the pretty plastic casing and make something smaller using electrical tape!

SteveBaker (talk) 13:39, 25 June 2010 (UTC)

Check the articles Borescope and Endoscopy. Cuddlyable3 (talk) 21:17, 25 June 2010 (UTC)

paint and primer in one

does Behr Ultra latex paint and primer in one contain surfactants such as sodium Lauryl sulfate to make the paint mix with the primer ?

the paint im talking about is seen here:

http://www.homedepot.com/Paint-Interior-Paint-Stain/Behr-Ultra/h_d1/N-5yc1vZ1xilZbbbpZ528/R-202182650/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053 —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 14:26, 25 June 2010 (UTC)

It doesn't appear to be just a mixture of paint and primer, so the answer is no. Conventional paint and primer are similar enough to probably not required surfactants to mix (you can try this at home!). However surfactants are widely used in paints anyway.

The lack of requirement for a primer appears to be due to nanoparticles that reduce the porosity of the surface to be painted - I think, the company documentation is not that clear.77.86.123.157 (talk) 14:51, 25 June 2010 (UTC)

I'm guessing that the Aluminium hydroxide and diatomaceous earth are part of the active ingrediantes that make the paint an 'all in one' - mentioned on the MSDS [19], these should be carried by the acrylic (latex) binder just like the pigment. 77.86.123.157 (talk) 15:17, 25 June 2010 (UTC)

i thought oil and water dont mix? primer is oil based and latex paint is water based. does adding surfactants make them mix? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 15:16, 25 June 2010 (UTC)

No, primer can be water or oil based. If you were applying a water based paint you'd 100% certainly use a water based primer. ok maybe not, some people avoid oil based becuase of the solvents, bur water based still stinks, plus oil based paints are gradually being banned. An emulsion of oil/water based paints wouldn't work as planned though - there's no way for the oil component to know to be the undercoat. 77.86.123.157 (talk) 15:20, 25 June 2010 (UTC)

so does it have a water based primer in it ? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 18:16, 25 June 2010 (UTC)

Is the product water based or not? It depends what you mean by primer - a primer is just something that treats a surface before painting - this is a primer and paint in one: A primer is a product not an ingredient.77.86.123.157 (talk) 19:26, 25 June 2010 (UTC)

Is it possible to clean a pool with just Baking Soda and Bleach?

I heard a rumor about this. Anyone know anything about it? 148.168.127.10 (talk) 14:46, 25 June 2010 (UTC)

What sort of cleaning do you mean? (algae maybe?) - eg I can clean a pool with a scrubby, some cif and a bucket of water..77.86.123.157 (talk) 14:52, 25 June 2010 (UTC)

oh you must mean this http://wetheadmedia.com/how-to-clean-a-green-pool/ I thought you meant clean the sides.. Both chemicals are replacements for commercial formulations, but you need to know what you are doing, andwill probably still need test kits.77.86.123.157 (talk) 15:46, 25 June 2010 (UTC)

query regarding B.TECH

what does mechanical & electronic-communication{EC} engineering mean? —Preceding unsigned comment added by Spooky92 (talk • contribs) 16:45, 25 June 2010 (UTC)

Can you give more details, it might mean nothing. It might mean a combined course of two disciplines. Which BTECH? 77.86.123.157 (talk) 17:56, 25 June 2010 (UTC)

Big cases of correct theories largely ignored because they came from amateurs

What are some of the big cases where someone without status/credentials/contacts in the scientific community puts out a paper, the paper is largely ignored, and later it is discovered that the paper was right in what it stated? 20.137.18.50 (talk) 16:47, 25 June 2010 (UTC)

Marjorie Rice might qualify, though I don't know if she published her findings. --Sean 17:00, 25 June 2010 (UTC)

I don't think that one counts. Her discoveries were accepted by the main stream mathematitians as soon as they came to their knowlege. Dauto (talk) 17:06, 25 June 2010 (UTC)

I notice that Gregor Mendel wrote a paper describing what he is now known for that was ignored for 35 years. 20.137.18.50 (talk) 17:13, 25 June 2010 (UTC)

One of the best-known cases is John Garcia, who discovered the so-called Garcia Effect, also known as conditioned taste aversion. He had a Ph.D. and worked as a postdoc at Berkeley, but he didn't have any reputation, and his discovery, which now is considered a major part of the history of psychology, was at the time considered so bizarre that he was unable to publish it in any reputable journal. Looie496 (talk) 18:18, 25 June 2010 (UTC)

I have trouble imagining that the theory could be considered "bizarre" — it seems almost obvious. Is there anyone to whom this sort of taste aversion has not happened? Wouldn't you just say, "oh, yes, of course I know that; that happened to me when I was eight years old, even if I don't know why"? --Trovatore (talk) 01:25, 26 June 2010 (UTC)

Can someone with a PhD be considered an amateur? Dauto (talk) 21:28, 25 June 2010 (UTC)

Yes, sure (just having a PhD by itself does not actually make you a member of any particular academic community, much less the one you are innovating in), but probably not somebody working at a postdoc at a major research university. --Mr.98 (talk) 22:27, 25 June 2010 (UTC)

A similar case is Alfred Wegener, whose theory of continental drift was rejected by orthodox science for many years, but is now accepted as the basis of plate tectonics. Ghmyrtle (talk) 21:45, 25 June 2010 (UTC)

Wegener's theory was rejected because it was impossible. It is not the "the basis of plate tectonics"; it posited a different and impossible cause (mechanism) producing the same effects at the surface of the earth. (Cite: Asimov's New Guide to Science, p.174) It is true that scientists wrongly disbelieved that those effects existed, but that was because no possible mechanism was known. If Aristotle had encountered a radioactive substance and theorized that it was warm because it contained the element fire, that would not mean that his theories were "the basis of nuclear physics". Credit is due to Wegener for being partly right, but only for that. --Anonymous, 00:17 UTC, June 26, 2010.

Note, A. Wegener: The hypothesis of continental drift (ca. 1915), evolved to seafloor spreading (ca. 1962), and more recently to the theory of plate tectonics (ca. 1967). He based his publications on cartography, paleontology, glacial striations and old orogenic uplifts. But paleomagnetism, reflection seismology, sonar survey and gravity anomaly survey were needed to etablish the hypothesis. There was a lack of sound data... --Chris.urs-o (talk) 07:03, 26 June 2010 (UTC)

Keep in mind—as has been pointed out by the likes of Carl Sagan and others—that the cases of "amateurs who were totally wrong or actually just cranks" vastly overweighs the extremely limited number of times that an amateur was judged a crank and turned out to be brilliant. Quoth Sagan: "They laughed at Columbus, they laughed at Fulton, they laughed at the Wright Brothers. But they also laughed at Bozo the Clown."

Two really famous cases (depending on how you define "amateur") are Wegener and Albert Einstein (came up with the special theory of relativity while working at the Swiss patent office). If you go back historically, of course, the line between professional and amateur is quite blurry until the strong professionalization of science in the 19th century, and even then some fields (like astronomy) still often have a strong history of contributions from amateurs. (Even today, many astronomical discoveries—e.g. comet Hale-Bopp—are done by amateurs pointing telescopes at the sky.) --Mr.98 (talk) 22:27, 25 June 2010 (UTC)

It's worth noting that in Einstein's case his Annus Mirabilis papers were accepted for publication in a prestigious journal (Annalen der Physik), and that his work – particularly the special theory of relativity – were generally widely and rapidly accepted by the scientific community. TenOfAllTrades(talk) 22:43, 25 June 2010 (UTC)

Well, it's worth noting that the papers were accepted for publication largely through the influence of a single person (Max Planck), who acted as his sponsor, more or less. It was nothing like the expectations of modern peer review and there is little doubt that Einstein's papers would have been rejected had the standards been a bit higher. If you read his classic SR papers through the lens of what "physics in his time" was considered to be, they are extremely unusual, very amateurish in many ways (they read more like an exercise in logic than a work of physics, even theoretical physics, and have horrible citation practices). As an experiment give "On the Electrodynamics of Moving Bodies" a read without considering that the author is Einstein and obviously correct and you'll see what I mean—it's a very odd paper and if it had the name "Joe B. Crank" attached to the top of it you'd probably dismiss it as nonsense.

And to say that SR was rapidly accepted is an exaggeration. Most physicists did not regard it as "physics" at all in the traditional sense (they considered it philosophy or simply irrelevant), with the exception of the photoelectric effect, which they did find to be a rather convenient explanation. By the time Einstein put together GR it was considered something that needed to be known about but not at all unambiguously true. After the GR experiment of Eddington, relativity as a whole got a lot of attention but was still considered extremely scientifically controversial. Even after Einstein was generally recognized as a great scientist (say, in the 1920s and 1930s) by many (i.e. the newest physicists) it was still a pretty controversial theory. It was not until the 1940s and 1950s that it really became considered one of the gold standards of physics. Now one can say that many of the physicists we now consider to be the "winners" in history (e.g. Bohr and Eddington and even Planck) thought Einstein was pretty brilliant from the start. But they are not actually representative of the larger scientific community as a whole in Einstein's time, and depending on what one defines as your community, the up-take was really quite different (e.g. the physics communities in Germany, France, England, USA, Russia, and Japan all received relativity pretty differently). I'm not saying this to be pedantic, but studies on the reception of relativity are sort of a "canonical" topic amongst historians of physics and it was anything other than straightforward. (For a nice overview, Helge Kragh's Quantum Generations is great, and has an excellent graph of the early distribution of scientific publications on relativity and a great section discussing it, which you can see in Google Books. You'll notice it takes about 5 years for even the Germans to really start to get interested in the subject.) --Mr.98 (talk) 23:57, 25 June 2010 (UTC)

My aim here was mostly to respond to the original poster's question — specifically, to note that Einstein doesn't really qualify under the terms given. The fact that his work was supported and endorsed by Planck by itself suggests that he was not without academic contacts. And whatever else may be said about his papers, they certainly weren't 'largely ignored'. (To be fair, Einstein was far from the only scientist to benefit from the much laxer variety of peer review practiced a century ago.) I'll grant that his work wasn't universally and completely accepted for years (sometimes decades) and that there were geopolitical factors which hampered its acceptance in some countries (particularly France), but that's not unusual even for non-crank science published by well-known scientists. Consider the Higgs boson. It was first postulated in 1964, it's part of the Standard Model, but it's still not totally accepted — and it's still possible to have a career as a respectable scientist developing Higgs-less models. (One of those models might even be correct!)

The graph you've linked to is interesting. The figure legend observes that (on the subject of relativity) there is a "...decrease in the total number of publications between 1910 and 1915..." and notes that this feature "...probably reflects that, by 1911, the special theory of relativity was widely accepted among physicists and was no longer considered to be at the cutting edge of physics." I would tend to argue that five years is actually not a long time for a major new theory to gain prominence (if not predominance) in physics, particularly one for which experimental tests are difficult — and in an era when publications had to be distributed on paper and interpersonal communications tended to travel by snail mail. TenOfAllTrades(talk) 02:27, 26 June 2010 (UTC)

I think Einstein qualifies, even though he was shepherded in by someone "inside" the institution. I don't think "amateur" is meant to mean "totally ostracized". Einstein was an outsider. The only reason he got taken seriously at all is because an insider decided he wasn't a crackpot.

The graph and the accompanying chapter make it a bit more clear what is going on, especially if you recall that Einstein wasn't the first (or only) person talking about relativity theories (he was entering into a field already populated by the likes of Poincaré, Lorentz, etc.). Einstein's own specific take on things—that there is no such thing as universal time, for example—was really not accepted as true for quite a long time. By the time Einstein started work on GR, the idea of relativity and Einstein's contributions (again, because of Planck's sponsorship, in part) was enough of a topic that it warranted some attention from other theorists, but it was still a very, very minor part of how physics was thought of at the time, and considered irrelevant by most. It was not until 1919—for both scientific and political reasons—that it really became something that people had to grapple with (because of the immense attention given to it, and the huge implications saddled on it), and even then it was certainly still considered extremely controversial, often incorrect, by most "established" physicists.

Anyway, in the end, I don't think Einstein is a bad case study for this kind of question, even if he is obviously a rather singular historical figure. He's definitely an outsider, and he definitely had a struggle in getting his work accepted, in part because he was not in synch with the priorities or methods of the predominant physical community, and because the conclusions he proposed were seen as very out of step with how contemporary physics was developing. (Today we always refer to aether theory as the "classical" view, but this is quite ahistorical—it was considered a radical, unifying theory for the late-19th century and early-20th century, a real vanguard composed of really quite sophisticated mathematics. It was wrong, of course, but it was as "revolutionary" as what replaced it.) He also illustrates the way an outsider can get a "shortcut" into the mainstream discussions: get a major sponsor who can't be dismissed, weasel your way into mainstream journals, follow up some rather vague theories with really quite striking experimental reports. (And while you're at it, become a major international icon. ;-) --Mr.98 (talk) 12:12, 26 June 2010 (UTC)

As a chemist, my own favorites are John Dalton and Amadeo Avogadro. The former was excluded from university because of his religious beliefs; he wasn't exactly an "amateur", but he described atomic theory while earning his money as a schoolteacher and his theory would not be fully accepted for many decades. Avogadro is a more flamboyant character, an ecclesiastical lawyer but part-time revolutionary... still, he found the time to imagine Avogadro's Law, for which he never received credit during his lifetime: now, it is considered one of the bases of modern chemistry, hence the Avogadro constant named in his honour. Physchim62 (talk) 23:29, 25 June 2010 (UTC)

See http://www.environmentalgraffiti.com/sciencetech/the-5-most-important-amateur-scientists/940. I do not know how quickly their discoveries were accepted.—Wavelength (talk) 00:31, 26 June 2010 (UTC)

It's an interesting stab at a list, for something that gets caught up in real definitional issues, anyway. Faraday, for example, was certainly an outsider when he started, but he apprenticed under Davy before doing his really fundamental work. Does that make him an amateur? (Or just of low class in a highly stratified society? Is there a difference in 18th century British science?) Mendel was not so much an "amateur" as in a parallel profession, one that did value agricultural research and had cross-overs to mainstream academic biology (though Mendel himself was pretty much at the fringes). He wasn't denounced as a quack or anything, but he was ignored, mostly because his work just didn't have much exposure and even Mendel didn't think it was a general theory of heredity. His work was "rediscovered" many years later and translated into a somewhat different framework. Edison pushes that nice boundary between "inventor" and "scientist," wherever we want to try and draw that line. Evans and Leavitt I don't know enough about to comment, except that again there is a long, rich tradition of amateur astronomy, one that continues to this day. --Mr.98 (talk) 01:18, 26 June 2010 (UTC)

SeeHistory of radio. Discovery of the ability to transmit and detect high frequency electromagnetic radiation which Thomas Edison called "etheric force" in 1875, and which separately was discovered in 1878 by David Hughes, were rejected as "mere electromagnetic induction" by leading scientists of the day. When Hertz in 1886-1888 did similar experiments more mathematically based on Maxwell's theory the results were accepted. Hertz was better credentialled, and had a systematic mathematical and theoretical basis for the observations. Edison similarly discovered and wrote up Thermionic emission, the basis for diode vacuum tubes, but scientists of the 1880s rejected it as merely charged bits of carbon coming off the filament, and decades later Fleming used the same tubes with improvements to invent the diode valve or vacuum tube, with a better physical explanation, after the discovery of the electron by others circa 1897. Scientists of the era considered Thomas Edison and Hughes to some extent to be mere amateurs/tinkerers/inventors. Edison (talk) 04:23, 26 June 2010 (UTC)

In the 18th century, Kant realized that some of the "stars" are actually galaxies. In the 19th Century, a lot of bad science "discredited" this brilliant conclusion. Not till the 1920s was it established beyond doubt. 63.17.62.100 (talk) 06:53, 26 June 2010 (UTC)

Ants in my vacuum cleaner

If I use my vacuum cleaner to suck up an ant trail, will they survive the journey up the tube to the filter bag, or do I have to empty it to prevent further infestation? Hemoroid Agastordoff (talk) 17:04, 25 June 2010 (UTC)

The ants will survive (at least a good majority will). I remember reading that if you want to kill the ants, you could vacuum up some kind of dust right after you get the ants, but I can't remember what it was. Talc maybe? Or diatomaceous earth? Googlemeister (talk) 18:19, 25 June 2010 (UTC)

I think diatomaceous earth will work -- it has a dehydrating effect on insects (including ants). FWiW 67.170.215.166 (talk) 02:36, 26 June 2010 (UTC)

Disposing of the bag promptly is a good idea. Edison (talk) 04:07, 26 June 2010 (UTC)

Ant dust. Mitch Ames (talk) 13:17, 26 June 2010 (UTC)

Urologists

How many urologist are there in new jersey68.236.210.120 (talk) 17:19, 25 June 2010 (UTC)

I've added a section header for this question. Comet Tuttle (talk) 17:31, 25 June 2010 (UTC)

428 [20] 77.86.123.157 (talk) 17:51, 25 June 2010 (UTC)

How many urologists does it take to change a lamp bulb? Cuddlyable3 (talk) 14:17, 26 June 2010 (UTC)

Dunno. Tell us/--RampantHomo (talk) 20:15, 27 June 2010 (UTC)

Memory

I have heard there is one memory condition where one is unable to forget out anything and everything you experience is remembered forever. The advantages are obvious: One would never forget one's in-laws' birthdays for example ;). But What Would be some disadvatages to having such a permanent memory? Would it be harder to recall things? 76.229.149.7 (talk) 17:59, 25 June 2010 (UTC)

I think you're looking for hyperthymesia. An interview with the first identified case suggests that she doesn't find it harder to recall things; rather, things are recalled whether or not she wants to. She certainly expresses disadvantages to the condition in the interview. In particular, the inability to forget (and moreover, the inability to avoid remembering) tragedy is pretty lousy. Having a merely eidetic memory has a lot more practical upside. — Lomn 18:06, 25 June 2010 (UTC)

There is no such condition. There are people with extraordinary memory for events, but not perfect. There is however a well-known work of fiction by Jorge Luis Borges describing such a person, called Funes the Memorious. The most common problem for people with extraordinary event memory is difficulty in seeing patterns -- when somebody remembers every detail of every event, they have trouble seeing what the events have in common. The Russian psychologist Alexander Luria wrote a wonderful book called The Mind of a Mnemonist] about such a person. Looie496 (talk) 18:10, 25 June 2010 (UTC)

I've heard of people with such a "condition"...while not a medical condition, persay, the phenomenon does exist...I remember it being mentioned in a National Geographic article. [21] Ks0stm ^(T•C•G) 21:42, 25 June 2010 (UTC)

Perhaps not that relevant, but Gene Wolfe's The Book of the New Sun has a protagonist with an Eidetic Memory. The condition is a prevalent theme in the book, and is explored in several ways. Zigorney (talk) 19:14, 25 June 2010 (UTC)

You may want to read this book (http://www.amazon.co.uk/Delete-Virtue-Forgetting-Digital-Age/dp/0691138613) it is all about the virtue of forgetting and how useful it is (for society as well as individuals). It's an interesting area but whilst I have this book I must admit it's not the best read (a bit repetitive and a bit woolly in terms of their proposed solutions) but it has a lot about the disadvantages of never forgetting (that you wouldn't be able to escape ones past being a major issue). ny156uk (talk) 20:32, 25 June 2010 (UTC)

Some neurobiologists and cognitive psychologists think that once something makes it from short term memory into longterm memory (via attention being paid to it, through analysis and study, through rote rehearsal), it doesn't really go away, but we just lose the ability to access it. If I've forgotten someone's name, recognition is far better than recall. Same for "forgotten" addresses or phone numbers. The right prompt can cause it to be right there. But memory can be reconstructive, and we can be fooled into "remembering" things that never happened, by the right instruction [22]. An electrical stimulus in the temporal lobes of the brain during brain surgery, as reported by Wilder Penfield, can supposedly cause random forgotten incidents from the distant past to be relived in vivid detail in some individuals. Or maybe the "memories" are created out of fragments like dream experiences. Alexander Luria wrote "The Mind of the Mnemonist" about Solomon Shereshevsky, who could remember amazing amounts of detailed information. He sounds much like the mnemonist in The 39 Steps (1935 film). Some of us can probably recall a lifetime of factual information, but fail to recognize someone they were introduced to 5 minutes ago. Edison (talk) 23:15, 25 June 2010 (UTC)

since we're onto novels, try Black Milk by Robert Reed. interesting view on the topic.

The problems with excessively high retention are mostly social: (1) being able to remember accurately events which others have revised is uncomfortable (most people's memories are inaccurate and revised in various self-serving ways, and do not like being reminded that things were not as fun and noble as they remember them to be). (2) if the retention includes emotional states as well as simple factual recall, one may be left re-experiencing a lot of unpleasantness. consider being forced to remember how you felt (in full detail) whenever you think about high school. --Ludwigs2 03:56, 26 June 2010 (UTC)

It would be so easy to win at Trivial Pursuit and similar trivia games that either such a person would have to throw games by "not knowing the answer" or people would hate them. Edison (talk) 04:06, 26 June 2010 (UTC)

I think that it may be hard to focus on a task at hand if you are continually bombarded with vidid memories of yesteryear. Vranak (talk) 18:02, 26 June 2010 (UTC)

Silicone solvent?

I'm trying to remove some 3-year old 100% silicone caulk from a textured glass panel. The textured glass prevents me from using razor blades. When I try to peel or rub the silicone off, it just comes off in bits. Is there any chemical method to removing silicone? —Preceding unsigned comment added by 70.167.58.6 (talk) 18:11, 25 June 2010 (UTC)

In short, no. There is no simple way to chemically remove silicones from glass. You can sometimes remove them physically, if you're lucky, but it's usually not worth the bother (as you seem to be discovering). What do you want to do with the glass afterwards? Physchim62 (talk) 18:26, 25 June 2010 (UTC)

It's glass from the 40's in an old office. The previous occupants thought it would be neat to affix acoustic foam to the windows using silicone glue. The foam was easy to tear down. But all these islands of silicone remain on the glass. Would a heat gun help to peel it off? Or would it just make a gooey mess? --70.167.58.6 (talk) 18:33, 25 June 2010 (UTC)

A heat gun might crack the glass, be careful.

My local DIY store sells silicone remover. Just Google it. --Heron (talk) 18:38, 25 June 2010 (UTC)

The problem with "silicone remover" is that it sticks to the glass itself, making it very difficult to get anything else to stick there. You can't see it, but it's there to prevent any other putty from sticking. If you must keep the glass plates, the best bet is patience and a judicious use of sandpaper (the cheapest works best, just don't scratch any visible bits of the glass) Otherwise, replace the glass. Physchim62 (talk) 18:58, 25 June 2010 (UTC)

Potentially, depending on how aged the sealant is you could used wd40/diesel/other oil (also consider nitromors or equiv) to try to soften it - it wont' remove it but it might make your job easier.

Disposable plastic knives (or even bluntish metal knives), as well as rotary brass brushes may be helpful tools in getting it off.77.86.123.157 (talk) 19:39, 25 June 2010 (UTC)

There's a technical paper here [23] it suggests

• tetramethylammonium hydroxide (TMAH) in alcohol - you probably can't get this
• solvents such as CH2Cl2 and DMF (again "nitromors" is a CH2Cl2/MeOH mixture - it might work)

as well as fluorides

A home grown version might be caustic soda in methanol, or isopropanol - but this also is very dangerous to work with in terms of burning your hands or face off.77.86.123.157 (talk) 19:50, 25 June 2010 (UTC)

You could also try DMSO. I had a professor that used to say "If it doesn't dissolve in DMSO, it wasn't meant to dissolve". Accodring to our article, it is safer than DMF and other similar compounds. --Jayron32 17:08, 26 June 2010 (UTC)

Silicones tend to form chemical bonds with glass (the tubes of silicon contain chemicals that polymerise) - that's why hydroxide or fluoride is needed to debond it. DMSO could make a good solvent for these, but probably won't work on its own. —Preceding unsigned comment added by 77.86.115.159 (talk) 17:19, 26 June 2010 (UTC)

A word of warning here: Fluoride in DMSO will enter the body via skin contact, and will have toxic effects similar to those of concentrated hydrofluoric acid (deep burns, etc.) So if this is what you plan on using, make ABSOLUTELY sure that you wear nitrile gloves and clothing (these are impervious to DMSO). Clear skies to you 67.170.215.166 (talk) 05:38, 27 June 2010 (UTC)

Why nitrile gloves? They will just dissolve. See Dimethyl_sulfoxide#Safety. --Chemicalinterest (talk) 18:23, 27 June 2010 (UTC)

June 26

Cobalt (III) oxide

What is the oxidation state of cobalt in Co₃O₄? --478jjjz (talk) 03:04, 26 June 2010 (UTC)

Both +2 and +3 as the article title suggests ie Co₃O₄ links to Cobalt(II,III) oxide , the II and III are roman numerals - it's Stock nomenclature. 77.86.115.159 (talk) 03:26, 26 June 2010 (UTC)

If cobalt's oxidation number is +2, then Co₃⁺² O₄^-2; so the net charge is 6-8 = -2. However, this can't be because the net charge is supposed to be 0.--478jjjz (talk) 03:37, 26 June 2010 (UTC)

--- For cobalt (III) oxide

If cobalt's oxidation number is +3, then Co₃⁺³ O₄^-2; so the net charge is 9-8 = +1.--478jjjz (talk) 03:46, 26 June 2010 (UTC)

Seriously, read the article - Cobalt's charge is 2 and 3 - that is one third have charge 2, and two thirds have charge 3 - ie it's Co²⁺(Co³⁺)₂ (O^2-)₄ . It has the spinel structure, the spinel article has more information.77.86.115.159 (talk) 03:52, 26 June 2010 (UTC)

I didn't know that one element could have 2 different oxidation states in one compound. Thank you. "Co²⁺(Co³⁺)₂ (O^2-)₄" was extremely helpful.--478jjjz (talk) 04:06, 26 June 2010 (UTC)

N₂H₄O₃ or NH₄NO₃ might be an example for nitrogen.--Stone (talk) 07:58, 26 June 2010 (UTC)

Other well known examples are magnetite, Fe²⁺(Fe³⁺)₂ (O^2-)₄, and Prussian blue, (Fe³⁺)₄([Fe^II(CN)₆]⁴⁻)₃. Prussian blue, or iron(III) hexacyanoferrate(II) is particularly interesting because there is another compound, traditionally called Turnbull's blue, which is iron(II) hexacyanoferrate(III), (Fe²⁺)₄([Fe^III(CN)₆]⁴⁻)₃. It turns out that the two compounds are the same: you cannot tell which iron atoms are iron(II) and which are iron(III) in the compound. Physchim62 (talk) 10:50, 26 June 2010 (UTC)

That Turnbull formula looks weird: hexacyanoferrate(III) would be a 3− not 4− anion? Iron(II) hexacyanoferrate(III) would be (Fe²⁺)₃([Fe^III(CN)₆]³⁻)₂ The prussian blue#Composition section is an interesting example of how important it is to document the experimental method:) But it also does state not that so-called Turnbull's blue (the preparative method) is iron(III) hexacyanoferrate(II), but instead that it rapidly converts by electron exchange to become it (from the other oxidation-state form). And that there is good evidence which iron oxidation state is in the cyanide complex and which is the counter-cation. DMacks (talk) 16:57, 26 June 2010 (UTC)

Alpha Centauri at 1 G acceleration

How long would it take to reach Alpha Centauri on a ship that accelerated at one G (about 9.8 meters per second per second) for half the trip then spent the last half decelerating at that same rate. Would it even be possible to maintain that rate of acceleration for that long without crossing the speed of light?

I ask this because this would be a convenient way to make "artificial gravity" during the transit. Seems like it would make life a lot easier for the passengers.

63.245.168.34 (talk) 03:25, 26 June 2010 (UTC)

The speeds and distances associated with continuous 1G acceleration in space have been frequent topics on the Science Reference Desk. At [24], for instance, I linked to a site with a relativistic calculator. It sems to be defunct. but the Internet Archive Wayback Machine lets us regress in time (so to speak) to a version from May 2008 which lets you input variables and derive the info you seek.Alpha Centauri is 4.365 light years away (per the Wikipedia article. The webpage says 4.3 light years). The calculator says the trip would take just under 6 years to an observer left behind on Earth, but only 3.58 years as experienced by a traveller on the ship, which would reach a max speed of .952C. Sure the artificial gravity would make life easy for those on board, but figuring out how to build an engine to provide 1G acceleration for 3.58 years would make life a living hell for the engineers assigned the task of designing it and the persons required to pay for building it. Edison (talk) 04:02, 26 June 2010 (UTC)

As far as "crossing the speed of light", it would take an infinite amount of energy for any particle to reach the speed of light. See Speed of light#Upper limit on speeds. Comet Tuttle (talk) 05:30, 26 June 2010 (UTC)

Okay, this leads to a point I've been confused about for a while. When you think of a normal "constant acceleration", you think of an acceleration due to a constant force. At low speeds, a constant force will yield a constant acceleration as expected. However, when you approach relativistic speeds (as you do in this case), it requires a larger and larger force, and eventually becomes impossible, to maintain a constant acceleration. So the question of "constant 1g acceleration" is not really all that simple. I don't understand how the calculator that Edison linked to accounts for this; can anyone shed some light on this?-RunningOnBrains^(talk) 06:40, 26 June 2010 (UTC)

I presume it doesn't. It isn't a 'practical relativistic calculator' just a 'relativistic calculator'. It presumes you are capable of building a ship capable of reaching '.952C' (or whatever maximum speed for your distance), in other words capable of accelerating at a constant 1G for your travel distance, and surviving that travel. Whether it's likely to be possible is besides the point of the calculator Nil Einne (talk) 07:11, 26 June 2010 (UTC)

Edit: In fact as I somewhat expected it says "Note how the kinetic energy becomes extremely large. Besides this, there are many other practical problems in realizing a star ship (such as hitting small dust particles while moving at relativistic velocities)" and the site does in fact show the maximum kinetic energy as one of the results which in this case is 202430223928 megajoules per kilogram. Nil Einne (talk) 07:14, 26 June 2010 (UTC)

Actually, it doesn't require a larger and larger force (if you deplete fuel, it actually takes less force). What you're thinking of is what's required to maintain a constant 1g acceleration in the original frame of reference. But that isn't possible; that would eventually put you over the speed of light.

In this context, when we talk about a "constant 1g acceleration", we mean in the ship's frame of reference. Assuming the ship's (rest) mass remains constant, that requires only constant force (again, force as measured in the ship's frame).

So if you had some magical source of constant force, you could indeed do this, ignoring as Nil says the hazards of your environment.

But no one knows of any such source. If you carry fuel with you, you'll run out. The Bussard ramjet is an idea for getting fuel from surrounding space, but apparently the current consensus is that it probably won't work (though I tend to be skeptical of that sort of prediction when the limitations all appear to be "engineering difficulties" rather than genuine physical limits). Even with the Bussard ramjet, though, you eventually hit some sort of limit, because the fuel keeps coming at you faster and faster, and eventually the force you have to apply to it to keep it in the reaction chamber is going to equal the outgoing thrust. --Trovatore (talk) 07:28, 26 June 2010 (UTC)

How much matter would have to be converted to energy to produce the calculated 202430223928 megajoules per kilogram of kinetic energy? It should be E/C² but units can be a stumbling block. Dividing 2.02 E17 joules by (3E8 m/sec²)², I get 2.24 kilograms. Then double that, because you have to decelerate, so 4.48 kg of mass would have to be converted to energy to accelerate a 1 kg payload over the specified voyage. How long would it take the Sun to produce enough energy to accelerate that one kg if all the Sun's output were used to drive the spacecraft? Sun says it converts 4.26 E6 metric tons of mass to energy per second. A tiny fraction of the Sun's output from departure to midpoint would produce the specified acceleration over that timespan. It looks like .024 kg per second of matter converted to energy would power the voyage of a million kilogram spacecraft. (Maybe the folks at Alpha Centauri would power the deceleration after the midpoint turnaround). (Note:All calculations are subject to large and careless errors and should be checked). Edison (talk) 20:04, 26 June 2010 (UTC)

Ballistics calculations done with energy are usually misleading. You usually can't get anything but a tiny tiny fraction of the energy you use as kinetic energy of the craft, because almost all the energy is carried away in the other direction by the reaction mass. If you use a solar sail, the "reaction mass" is the photons bouncing off the sail (note that it doesn't help to absorb them instead; you get worse results that way). Solar sails do get better from this perspective as you approach the speed of light away from the light source, because the reflected photons are red-shifted and therefore don't carry away as much of the energy. --Trovatore (talk) 20:30, 26 June 2010 (UTC)

But, if you're relying on the last effect to bail you out once you get near the speed of light, keep in mind that this is giving you improved increase in kinetic energy per unit time in the Sun's frame of reference, not the ship's. From the perspective of the ship, the light from the Sun is red-shifted, and is therefore providing less thrust. --Trovatore (talk) 20:35, 26 June 2010 (UTC)

You could also consider using a laser-driven solar sail. With no reaction mass having to be stored on-board, you don't have any of those nasty restrictions. You can use just one solar sail for the first half of the journey - then when you are halfway there, you release the connections between craft and sail and deploy a second solar sail behind you. The laser light from back home must then hit the original (now disconnected) sail - uselessly accelerating it towards your destination at ever increasing speeds. However, if the first sail is mirrored, the light can bounce off of that and back towards your craft and its second solar sail. That allows you to decelerate throughout the second half of your trip...and perhaps even return home again. Additionally - instead of using a true laser - you could build a gigantic lens system and focus sunlight directly onto your craft. The lens would have to continually and microscopically adjust its focal length as the vehicle gets further away. There are undoubtedly vast problems with building large enough lasers, lenses or mirrors, but those are not issues of fundamental science - they are engineering and financial issues that could probably be overcome given the willpower to do so. However, it's hard to imagine anyone funding such a crazy effort. SteveBaker (talk) 05:57, 27 June 2010 (UTC)

There are some similar questions here, question 7.5 on page 13 is actually about a mirror propelled by a laser. I'm wondering though about how to deal with the fact that a laser beam will always diverge. If the initial beam of the photons appearing out of the laser is L, then the uncertainty in the momentum of the photons perpedicular to the beam direction will be of order hbar/(2L) at best. Dividing this by the momentum in the direction of the beam of h/lambda, gives an angle of divergence of lambda/(4 pi L). You can think of this as giving the width of the peak of the inteference pattern if you were to shine the laserlight on a far away screen. I don't see how one can make this angle arbitrarily small. Count Iblis (talk) 15:01, 27 June 2010 (UTC)

There has been some distinction between "physical impossibility" and "engineering limitation" - this is a valid distinction to draw. However, we need to make clear that we do not know about some physical possibilities and impossibilities until our engineering capabilities bring us into the regime where those physical laws will start to manifest, so that we can do controlled experiments. For example, it would not have been possible to know that the speed of light was finite until we were able to build machinery precise enough to measure it. So, our ability to develop correct physical theories (and deduce physical impossibilities) was limited by our engineering capability. After we started measuring that the universe behaved in certain bizarre ways, we developed consistent equations and physics to describe those behaviors. I think it is fair to say that there may be as-yet-undiscovered limitations (and possibilities) related to interstellar travel that we currently have no physics to describe. Once we start building giant lasers and spacecraft, we may learn new details about relativistic phenomena. Material properties, fundamentals of energy transfer, and so on, all plausibly might need to be rethought and re-understood in this new regime. Nimur (talk) 20:49, 27 June 2010 (UTC)

Production of Mn oxide

What is the chemical equation if you heat Manganese oxalate hydrate in a crucible in the presence of oxygen?

--478jjjz (talk) 04:11, 26 June 2010 (UTC)

• I have done this experiment. The product is Mn (II) Mn (III) oxide = Mn Mn₂ O₄ I just need to use mass % to figure out the coefficients.--478jjjz (talk) 05:33, 26 June 2010 (UTC)

Manganese(II) oxalate hydrate is Mn(C₂O₄).2H₂O (or sometimes Mn(C₂O₄).3H₂O)

The first step is dehydration:

Mn(C₂O₄).2H₂O → Mn(C₂O₄) + 2H₂O

The decomposition in air gives Mn₂O₃ without any carbon monoxide (see [25])

Mn(C₂O₄) +¾O₂ → ½Mn₂O₃ + 2CO₂ (equation 1)

Manganese(II,III) oxide is formed when Mn₂O₃ is heated, some oxygen is lost:

3Mn₂O₃ → 2Mn₃O₄ + ½O₂ (equation 2)

Combining equations 1 and 2 gives:

3Mn(C₂O₄) + 2O₂ → 6CO₂ + Mn₃O₄

So the overall reaction is

3Mn(C₂O₄).2H₂O + 2O₂ → 6CO₂ + Mn₃O₄ + 2H₂O

77.86.115.159 (talk) 14:18, 26 June 2010 (UTC)

I kowtow before thee. Your response was thorough and simply phenomenal. Thank you.--478jjjz (talk) 02:53, 27 June 2010 (UTC)

No need, we are here to serve .. 77.86.115.159 (talk) 03:05, 27 June 2010 (UTC)

In a vacuum it will form manganese(II) oxide. --Chemicalinterest (talk) 18:25, 27 June 2010 (UTC)

Ion nomenclature

In Manganate#Permanganate, manganate, hypomanganite, and manganite, shouldn't hypomanganite and manganite be switched? Because it should go hypo-ite, -ite, -ate then per-ate, like the chlorine oxoanions.--Mikespedia is on Wikipedia! 07:26, 26 June 2010 (UTC)

This is most likely a typo in the article! Thanks! I will change it.--Stone (talk) 08:06, 26 June 2010 (UTC)

Wait...then is potassium manganite a typo?--Mikespedia is on Wikipedia! 09:59, 26 June 2010 (UTC)

Manganate(V) is hypomanganate, not hypomanganite. The potassium manganite article is just plain wrong, I'll try to fix it in a moment. Physchim62 (talk) 11:08, 26 June 2010 (UTC)

Actually, it was only one sentence which was obviously wrong in potassium manganite, removed now. Physchim62 (talk) 11:32, 26 June 2010 (UTC)

Manganites can also refer to mixed oxides of manganese and other metals (eg [26]). The mineral manganite is MnO(OH), a slightly hydrated form of Mn₂O₃. Physchim62 (talk) 11:32, 26 June 2010 (UTC)

So now what are the correct names?--Mikespedia is on Wikipedia! 12:36, 26 June 2010 (UTC)

IUPAC proposes permanganate, manganate(VI) and manganate(V), along with the systematic names tetraoxidomanganate(1−), tetraoxidomanganate(2−) and tetraoxidomanganate(3−). Physchim62 (talk) 12:58, 26 June 2010 (UTC)

So how about the trivial name?--Mikespedia is on Wikipedia! 13:26, 26 June 2010 (UTC)

Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. p. 1222. ISBN 978-0-08-022057-4. give "hypomanganate" as a trivial name for managanate(V), as does Cotton, F. Albert; Wilkinson, Geoffrey (1980), Advanced Inorganic Chemistry (4th ed.), New York: Wiley, p. 746, ISBN 0-471-02775-8. The latter reference (which I've only just looked up) also refutes the potassium manganite article: apparently, the compound formed by the dissolution of manganese dioxide in concentrated potassium hydroxide is K₃Mn^VO₄ (by disporportionation), ie potassium hypomanganate. Physchim62 (talk) 13:35, 26 June 2010 (UTC)

I've corrected potassium manganite, which now redirects to potassium hypomanganate. Physchim62 (talk) 15:29, 26 June 2010 (UTC)

... manganite is a IV species, I've put Potassium manganite up for speedy deletion. Potassium hypomanganate seems fine.77.86.115.159 (talk) 16:17, 26 June 2010 (UTC)

Mixed metal oxide manganites do exist - I've created a temporary hat note from manganite.

These are quite notable eg [27] - if anyone wants to create an article about these compounds please do. They appear to be of interest due to their magnetic properties ie Computer hard disk=$$$ eg [28] There really should be an article on these...Sf5xeplus (talk) 17:03, 26 June 2010 (UTC)

Lanthanum strontium manganite already exists, although it's not in wonderful shape. Physchim62 (talk) 18:28, 26 June 2010 (UTC)

Mixed-valence is currently a redirect to inner sphere electron transfer, an article that does talk about mixed-valence compounds. Seems the relevant section or two could split out into its own article and extended on this topic. DMacks (talk) 17:17, 26 June 2010 (UTC)

(edit conflict) Yes, indeed. Those mixed valence manganites seem to be based on manganese(III) compounds which are doped to give some manganese(IV). Interesting, there is a potassium compound, K₆Mn₂O₆, which contains discrete Mn₂O⁶⁻
₆ anions [29]: I would call that compound potassium dimanganite. The lithium and sodium manganites, MMnO₂, are mixed oxides with a distorted NaCl structure. Physchim62 (talk) 17:19, 26 June 2010 (UTC)

So now they go permanganate, manganate, hypomanganate and hypomanganite?--Mikespedia is on Wikipedia! 02:47, 27 June 2010 (UTC)

And how about manganate(IV)?--Mikespedia is on Wikipedia! 02:50, 27 June 2010 (UTC)

Not quite:

+7 permangante

+6 manganate

+5 hypomanganate

+4 would be manganite - if we had a good example..

+3 would be hypomanganite ... These are for oxo-anions - for metal oxides in general people call them manganates or manganites irrespective of oxidation state.. (sometimes they get it right, and call Mn3+ a hypomanganite, but not often..)

Or just use manganate(n)

It's all described here [30]

77.86.115.159 (talk) 03:08, 27 June 2010 (UTC)

Eating late leads to weight gain?

I know it's repeated a lot by non-scientific sources (cover of magazines) but can anyone point me towards some scientific sources, or something similar, that discuss if eating before going to sleep increases weight gain (than eating the same diet, but only at a different time)? Shadowjams (talk) 07:39, 26 June 2010 (UTC)

I don't know of any such sources, but I'm butting in just to point out that this is not, in my opinion, really the right question. The right question is, if you schedule your evening meal early vs late, will that make a difference in your weight? You can't assume that your dietary intake will be the same in the two scenarios. It's possible that one of them will make you overall hungrier than the other. --Trovatore (talk) 07:43, 26 June 2010 (UTC)

I understand the distinction you're making, and my question is the original one. I'm interested in the nutritional / metabolic question rather than the public health considerations. You bring up a good point though: that though may be the reason for so much popular culture repetition of that statement. From a public health perspective the causation is less important than the correlative effect. Shadowjams (talk) 08:34, 26 June 2010 (UTC)

Oh, no, it's still causation. Just with an extra link in the causal chain. Correlation could be an indication of causation in the other direction, or a common cause for the two effects; that's not what I'm talking about. --Trovatore (talk) 09:16, 26 June 2010 (UTC)

Here's a BBC article [31] which is about breakfast size. It makes it sound like a behavioral thing, as you say. But wait! Here's a more recent one [32] about eating late at night, which makes it sound metabolic (and highly speculative). 213.122.29.174 (talk) 11:16, 26 June 2010 (UTC)

I remember hearing that there was a study that claimed people who ate more at night were fatter than people who didn't, but then subsequent investigation showed that the study hadn't properly looked at how much people were eating the rest of the time, so really all the study showed was that people who ate more tended to be fatter. I can't find this story, however. 86.164.57.20 (talk) 14:32, 26 June 2010 (UTC)

Well, a lot of bodybuilders will have a late night shake since they believe it'll prevent muscle breakdown. TheGoodLocust (talk) 17:38, 26 June 2010 (UTC)

Thank you all. That BBC link seems to sum up my instinct, "At this stage, the results could still be interpreted as controversial when applied to humans." Maybe I need to spend some quality time on pubmed. Shadowjams (talk) 09:18, 27 June 2010 (UTC)

Sensing colours

What causes the difference between sensing colours in a coloured material and in coloured light? For example, to me, a reddish violet colour reflected from some material looks delightful, but exactly the same colour being displayed by a computer screen looks very different, even some disgusting. Is that a matter of a colour system or does the brain perceive the information differently? --87.95.51.116 (talk) 13:22, 26 June 2010 (UTC)

By "exactly the same" colour you mean that you perceive the same colour whereas colours can have very different spectra but seem the same. The colours on a computer screen have to be made from the 3 available primary colours and they limit the range of possible colours. In the case of a material one's perception is affected by knowing that the surface has a texture that can be touched. Cuddlyable3 (talk) 14:05, 26 June 2010 (UTC)

Other factors that may explain the difference you perceive are that the screen image flickers, and the material is lit by ambient light of a certain colour for which you unconsciously compensate. Cuddlyable3 (talk) 14:11, 26 June 2010 (UTC)

See gamut for the technical details of how our eyes respond to colour, and the limited range most monitors have. CS Miller (talk) 16:05, 26 June 2010 (UTC)

When you look at a colored material, the light reaching your eye is determined by a combination of the color of the material and the color of the illumination, but your visual system automatically subtracts the color of the illumination, to such a high degree of perfection that we are generally not even aware of the process. When you look at a colored monitor, the visual system again attempts to compensate for illumination, but the result is very different. Thus you really aren't seeing the same thing at all in the two cases. In fact it isn't ever correct to say that a material has the same color as a light unless the lighting conditions have been precisely calibrated, and even then a small change in lighting will cause the appearances of the two to diverge. Looie496 (talk) 04:18, 27 June 2010 (UTC)

Some considerations are:

• The aesthetic effect of a slight texture.
• Shiny reflections (particularly highlights). On hard, rough surfaces such reflections will be fragmented, but still present.
• The reflection of light (which may be strongly coloured) from other nearby objects. 3D artists know this as radiosity, and it is important to realism and prettiness.
• Related to this is that parts of the object further away from other objects (or walls) will be more brightly lit. This has an effect even when the object is viewed close-up. Outside of computer screens, we rarely encounter objects which present areas of flat colour of a single tone (and just as well, because it would be confusing.) We don't tend to be conscious of this, though, and I think it might be the effect most important to your question - surfaces which appear to be a single tone really aren't. You can verify this by taking photographs and inspecting them digitally.
• In artificial light, the parts nearer the light source are more brightly lit (because of the spread of the light).
• Internal illumination of a surface can make the whole thing glow (this would tend to make it more similar to a flat colour on a computer screen, though). Transparency and refraction may matter.
• Oddities of various materials which cause tone and hue variations depending on the angle of the surface (or a local part of it) to the eye. The pile of velvet produces an effect similar to lenticular printing. Some materials are iridescent.

213.122.13.154 (talk) 11:02, 27 June 2010 (UTC)

toxic to fish ?

There was an NPR story[6] this morning about the use of Dawn dish detergent in the BP oil spill.

arent soaps toxic to fish ? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 17:49, 26 June 2010 (UTC)

This does not directly address your question, but presumably the soap is used to clean aquatic birds, like pelicans, and aquatic mammals, rather than fish. --Jayron32 17:56, 26 June 2010 (UTC)

Yes. Conventional soaps (soap bar) are harmful because they reduce the level of oxygen in the water. Liquid detergents are similarly harmful; they also damage the fishes gills, as well as they eggs, and make the absorption of toxic chemicals more likely.

Old fashioned detergents, and laundry detergents are also toxic to fish for other reasons - lowering pH and presence of phosphate causing algae blooms. (not all algae blooms are harmful, but some are)

It's summarised here [33] in the third section. that's about freshwater, but it's similar for marine as well

Also see http://www.sciencedaily.com/releases/2009/03/090316101430.htm 77.86.115.159 (talk) 18:13, 26 June 2010 (UTC)

If you are refering to this NPR story, Dawn dish detergent is used more on birds and turtles and such, an example being the Pelican pictured here.

"Dawn spokeswoman Susan Baba says [[...]] the reason Dawn is so good at cleaning birds without hurting them is that it was designed to erase grease from dishes without harming hands. The exact formula is a secret, but she says the key is balancing the surfactants — the chemicals that cut the grease." Dunno if that helps clarify anything. :) ^Avicenna_sis @ 18:49, 26 June 2010 (UTC)

It's important to note that there are 2 types of detergent being used here:

• Dawn : used to clean birds etc - this is being used (I assume) on land, and may not come into contact with fish
• 'Oil dispersants': these are the 'detergents' that are used at sea to disperse the oil slick, they are toxic to fish (as is the oil, fundamentally)

'Dawn' isn't being poured directly into the Gulf of Mexico as such.77.86.115.159 (talk) 19:16, 26 June 2010 (UTC)

Life expectancy in the UK

A newspaper says "He [UK politician] pointed out that in 1940, when the retirement age was set at 60 for women and 65 for men, life expectancy was 72. Today it has soared to 89 for men and 90 for women". Is there any truth in the latter claim in particular? Thanks 92.15.5.103 (talk) 19:56, 26 June 2010 (UTC)

Seems No. See http://www.statistics.gov.uk/cci/nugget.asp?id=168, there is more detailed data in the links on that page.77.86.115.159 (talk) 20:03, 26 June 2010 (UTC)

It's possible that this is a statistical balls up (where did you read it)?

eg http://www.independent.co.uk/news/uk/politics/mens-pension-age-up-to-66-from-2016-2009087.html appears to be confusing percentage expectancies of reaching 65 years and life span - ie 90% of women live to be 65? Is that what you got? 77.86.115.159 (talk) 20:09, 26 June 2010 (UTC)

City AM, 25th. June 2010, page 9. 92.15.5.103 (talk) 21:40, 26 June 2010 (UTC)

Doesn't look like misreporting - the govermental site gives the same words.77.86.115.159 (talk) 22:19, 26 June 2010 (UTC)

http://www.dwp.gov.uk/newsroom/ministers-speeches/2010/24-06-10.shtml repeats similar - looks like the minister's speech contains an error if the goverment statistics are to be believed - I'm fairly certain someones balls up their table.77.86.115.159 (talk) 20:13, 26 June 2010 (UTC)

Having had a quick look at the data it definately seems that ~90% of people can expect to live to 65 in the UK .. this appears to be the truth (though the male female difference appears to be ~5% not 1% ..as of 2006-8 see interim life tables). 77.86.115.159 (talk) 21:04, 26 June 2010 (UTC)

On BBC World the figure of 89/90 years was also mentioned, but it was said that some who is 20 years old now can expect to live that long. Count Iblis (talk) 00:12, 27 June 2010 (UTC)

That seems rather optimistic and assumes the UK's economy and technology will progress at the same rate - much less regress.TheGoodLocust (talk) 01:11, 27 June 2010 (UTC)

Actually, it probably assumes no progress at all. Any attempt to factor in future progress involves lots of guesswork, so it usually isn't done. They calculate these probabilities by assuming that the chance of the person in question dying during the year when they are X years old is the same as the proportion of people that were aged X a year ago that died during the last year (actually they usually average over 3 years or so, but that isn't important). So, it's how long you could expect to live if stuck in a time loop living the last year again and again. The figure is wrong, though. The Office of National Statistics (see the interim life tables linked to above) says a man aged 20 can expect to live to 78 and a woman to 82 (that's less than a year older than expectancy at birth, since we've all but eliminated infant mortality in the UK - the chance of a child dying before turning 20 is tiny). I don't know what BBC World was talking about. --Tango (talk) 13:38, 27 June 2010 (UTC)

Perhaps for this purpose (finding a good argument for increasing the pension age), the government asked the people doing to calculations to be less conservative and make some reasonable assumptions about progress in medicine? Count Iblis (talk) 14:32, 27 June 2010 (UTC)

It's possible, but if it were possible to make such reasonable assumptions why wouldn't they always be used? Life tables are mostly used for determining fair values for pension schemes and life insurance policies, and people doing such calculations would have exactly the same requirements from their data as people wanting to work out a fair retirement age. --Tango (talk) 16:20, 27 June 2010 (UTC)

Calcium Hypochlorite

I have about 10 kg left of dry powder bought as Calcium Hypochlorite three years ago. It is in a non air-tight (but child proof) plastic container and seems to have lost its zing. So does this slowly decompose to CaO in air? The WP article only lists reacting with CO2 and I cannot believe enough of that has got through the container lid. Roughly how long can I keep it if I get some more (so how much should I buy)? The large compact tablets of presumably the same thing were airtight sealed and seem to have lasted better. --BozMo talk 21:13, 26 June 2010 (UTC)

This book [34] page 523 mentions that the stabilily is reduced by absorbed water content, and that typical compositions loose about 3-5% effectiveness per year. This [35] states that it 'rapidly decomposes on exposure to air' and 'liberates chlorine with water' - so a non air tight container, especially in a damp enviroment will go off eventually.

It seems unlikely that 10kg has gone off.. I recommend removing some from the top of the container, and seeing if it's better lower down.77.86.115.159 (talk) 21:48, 26 June 2010 (UTC)

The decomposition in air at room temperature is not totally straightforward, some chlorine will be evolved, but not all - roughly Ca(OH)Cl 'basic chloride' is roughly what is left over from:

4Ca(OCl)₂ + 2H₂O >> 4Ca(OH)Cl + 3O₂ + 2Cl₂

though a variety of reactions can occur including a slow reaction which increases the acidity, which in turn increases the above decomposition

3Ca(OCl)₂ >> 2CaCl₂ + Ca(ClO₃)₂

So once the stuff starts to go off, it tends to go off faster and faster.. The best bet is to keep it in a dry place, out of light and heat, and keep it dry.77.86.115.159 (talk) 22:07, 26 June 2010 (UTC)

Relatively high incidence of lactose tolerance in Spaniards

Why do Spaniards have relatively high lactose tolerance in comparison to their neighbors? --Belchman (talk) 21:50, 26 June 2010 (UTC)

I wasn't aware that they do. In various group studies I've seen, the southern French and Portuguese populations have had higher percentages of lactose intolerance. [36] [37] [38]. As with most things generically related, I suspect fluctuations in prevalence is a result of how often those genes are used. In populations where lactose intolerance is higher, it's reasonable to assume that either lactose was less available to them, or they didn't have it quite as much. Regards, --—Cyclonenim | Chat  21:58, 26 June 2010 (UTC)

The article Lactose intolerance describes what is known about its cause and distribution. Cuddlyable3 (talk) 22:01, 26 June 2010 (UTC)

automotive question

What is minimum PSI cylinder compression pressure for 1275cc engine in a MG Midget?

Thanks . . . Joe

<removed email address>

I removed your email address so you don't get spammed. Ariel. (talk) 04:10, 27 June 2010 (UTC)

Opal vs clear in old incandescent bulbs

What difference did 'opal' or 'clear' finish make to the light in old incandescent bulbs? Was one more white than the other? --78.148.142.76 (talk) 22:25, 26 June 2010 (UTC)

clear was more efficient, but a pain to look at so you would want it in a light fitting. Whereas the opal did not blind eyes seeing it, so it is more suitable for the bare globe. Strangely Incandescent light bulb does not mention it. Graeme Bartlett (talk) 22:30, 26 June 2010 (UTC)

Yes, the 'opal' is/was just a Diffuser (optics) - didn't really affect the colour.77.86.115.159 (talk) 22:37, 26 June 2010 (UTC)

I never heard of diffuse white bulbs being called "opal". Must be a UK thing. If someone gave me an "opal" bulb I would probably be expecting it to be pink or something. --Trovatore (talk) 23:14, 26 June 2010 (UTC)

I've generally seen it as short for opalescent, rather than a direct reference to opals. If that helps at all... 86.164.57.20 (talk) 01:57, 27 June 2010 (UTC)

The first incandescent light bulbs were clear glass, but were often placed in frosted glass fixtures to decrease the glare. "Ground glass" had a surface which had literally been made rough by sanding or etching. "Frosted" was a term used more commonly than "opal" for early light bulbs which diffused the direct glow of the filament as in this 1904 citation. Here is a 1902 description of "opal glass" as then used in shades for gas lights: [39].Here [40] is a 1913 House and Garden article about opal or frosted glass shades around lights. Here is a 1911 engineering article which discusses frosted, etched and opal glass to diffuse illumination. They likely used a clear bulb in a diffusing globe. They were probably slightly less efficient than clear bulbs. A later term was "soft-white." Modern frosted or soft white bulbs are likely to have a water-soluble white coating inside the bulb, rather than it being actually etched by acid or sandblasting as in early frosted bulbs. The color temperature of the light would have been somewhat independent of the forsted or clear bulb, and would have been related to the design efficiecy and lifetime of the filament. I expect that the frosted or clear light bulb would not have been tinted blue as in modern "full spectrum" bulbs, but would have had a typical somewhat yellowish appearance of incandescent bulbs. Edison (talk) 03:24, 27 June 2010 (UTC)

Probably a UK thing as trovatore says - opal or clear over here .. google shopping.77.86.115.159 (talk) 03:48, 27 June 2010 (UTC)

I don't know where "over here" is to you but in the States, we generally have a choice between clear and "soft white" which I think is what everyone seems to be calling "opal". Dismas|^(talk) 08:51, 27 June 2010 (UTC)

UK, should have been clearer - thought link to google.co.uk would be obvious, but on second thoughts, it's not —Preceding unsigned comment added by 77.86.115.159 (talk) 12:10, 27 June 2010 (UTC)

Tip: If you click on the first link in an IP signature, it takes you to the contributions page for that address. At the bottom of that page there's a link called "Geolocate", which will show you where the post comes from (well, usually and approximately; there are a few gotchas). --Trovatore (talk) 10:14, 27 June 2010 (UTC)

Power supply to the town sewage works

Today I took a stroll down to my local sewage works (life in the fast lane, huh), and the overhead electrical supply to it caught my attention. I've taken a couple of photos of the utility pole outside - photo A and photo B. I have two questions:

• Firstly, what are the characteristics of that electrical supply likely to be (this is in the UK). It's surely three-phase, and of a fairly high voltage (the pole is ~25ft tall, with some serious anti-climb measures and lots of warning signs about carrying high objects nearby). I believe high-users like this in North America get either 13kV or 4kV - what would such a facility typically get in the UK? (It's a pretty big site, with several acres of tanks, serving a town of around 10,000 people).
• Secondly, what that is that little light thing, that's best seen in photo B? It's about ten feet off the ground, it carries the legend P360-alpha, and there's no cable running to it. I'm guessing it's a warning light - that somehow being near the pole with a conducting thing like a ladder causes enough flux for this thing to light up as a warning. Frankly it's not in a place I'd feel happy about visiting in the dark, so I can't discount that it's simply a solar-powered lamp (or somehow powered by the field of the transmission line) so that it illuminates the "danger of death" signs at night.

Any ideas? Thanks. -- Finlay McWalter • Talk 23:14, 26 June 2010 (UTC)

A. Three phase obviously 11 or 33kV are standards [41]

Images from geograph.org 11kv 33kv lloks like yous is 11kv, though that is an uneducated guess - there should be standards for UK power line construction somwhere on the web. Haven't found them yet. (It seems there are some other voltages used 6.6kv as well).

this link has some typical images. [42]

B. why don't you get a lightweight aluminium ladder and have a closer look at the light just kidding. If it's solar powered then you should be able to see the solar cell using a mirror attached to a fishing rod Maybe not. A safe way to see it to attach a video camera to a kite and then fly it above the device No. Sorry can't help myself. Don't know.77.86.115.159 (talk) 23:58, 26 June 2010 (UTC)

The "little light thing" has a wide-angle globe, so it looks like an illumination lamp to illuminate the warning signs and/or light up the area for linesmen to work at night. I can't tell how it's powered, but if we're talking about an 11-kV 50-Hz power line, then there's no way you could get enough flux through the air to power the lamp, not even with a bucket truck nearby for conductance -- so it can't be a warning light like you say, nor can it be powered by the field of the power line. FWiW 67.170.215.166 (talk) 05:50, 27 June 2010 (UTC)

The "P360 Alpha" gadget is lightly built and poorly attached to the pole, with one screw per side. It has no wires going to it. If it were a solar light I would not expect it to put out much of a light overnight, or after a few overcast days. It looks like a plastic cylinder, with a lid to keep rain out (can't rule out a solar collector on the top, but is is not optimally aimed for any latitude but the equator). At the resolution available, the bottom looks like it might be a basket with fine openings, which would keep out birds but let in bugs and air, so I wonder if it might be a non-utility gadget used on the pole with permission of the utility for sampling what bugs are in the area, or for air quality monitoring. They would periodically come along and collect the sticky paper inside or see what wandered into an internal trap, or what passed through filter paper. Edison (talk) 20:45, 27 June 2010 (UTC)

Along those speculative lines - maybe it's designed to trap bugs that might otherwise eat the wooden pole? (I sense this is far from likely)83.100.183.236 (talk) 20:49, 27 June 2010 (UTC)

I doubt that. Poles are usually treated with serious preservatives. If my speculation about a trap for studying what the insect population is (rather than eradication) it might have a solar powered UV led to attract insects at night. Some insect study traps are triangular paper prisms with sticky paper inside, others are plastic cylinders with an attractant inside and a funnel trap to prevent escape. Edison (talk) 20:53, 27 June 2010 (UTC)

Applying Occam's razor, it seems likely that the light was installed but wires were never connected to it (or were removed later) so it is not operational. On the other hand, other photos of the P360 Alpha also lack wires. Maybe the light is battery-operated. Nimur (talk) 21:01, 27 June 2010 (UTC)

As it appears to have a transparent lid, I'd suggest that it is solar-charged darkness-activated light. —Preceding unsigned comment added by Csmiller (talk • contribs) 21:11, 27 June 2010 (UTC)

June 27

endocrine disruptors

Are all nitric substances endocrine disruptors or just potassium nitrate? for example, are amyl nitrate and nitric acid endocrine disruptors? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 01:21, 27 June 2010 (UTC)

Nitric acid is too darn corrosive to be an "endocrine disruptor" -- if you get some of it inside your body, it will burn you from the inside out before any endocrine disruption can take place. Don't know about amyl nitrate, though. FWiW 67.170.215.166 (talk) 02:39, 27 June 2010 (UTC)

To the OP: can you please cite the sources of the statement that potassium nitrate is an endocrine disruptor? I'm not being negative, I'm just curious. Potassium nitrate is routinely used as a food additive, and has LD50 of several g/kg weight, comparable to that of the table salt. How does it affect the human endocrine system? --Dr Dima (talk) 06:34, 27 June 2010 (UTC)

to dr. dima: http://pubs.acs.org/doi/abs/10.1021/es032437n —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 08:25, 27 June 2010 (UTC)

It says that nitrates are suspected, not proven, to be endocrine disruptors. 67.170.215.166 (talk) 09:04, 27 June 2010 (UTC)

For a direct reference, one could look at this article which finds no evidence that nitrates have an endocrine disrupting effect during male rat embryogenesis. It's a pretty limited scope of investigation, but you could track down any references they cite that have shown evidence for nitrates as endocrine disruptors. --- Medical geneticist (talk) 11:57, 27 June 2010 (UTC)

This ref, for example, shows in vitro endocrine disruption by inorganic nitrate (with all due caveats, what happens to mouse tumour cells in a Petri dish might not necessarily happen in the human body). But to answer the question posed, all the studies we're citing are looking at inorganic nitrate, so sodium nitrate would be equivalent to potassium nitrate. The hypothesis is that endocrine disruption comes from production of nitric oxide in inconvenient places, so that would imply that you'd get similar results from amyl nitrite (or amyl nitrate, but fewer people sniff amyl nitrate!). The big difference is the exposure profile: if you're going around sniffing enough amyl nitrite to cause serious endocrine disruption (assuming the hypotheses are correct), you would have many, many other health problems first! Inorganic nitrate, on the other hand, is a well known contaminent in drinking water around the world, and people exposed literally from the day their born until the day they die. As such, it's potentially a much bigger problem, and several groups have looked for effects on human reproduction, without much success from the studies I've seen. Physchim62 (talk) 16:17, 27 June 2010 (UTC)

what about Nitric acid in water ? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 20:09, 27 June 2010 (UTC)

Fan curve derivation

How is the fan curve - pressure vs volume flow rate - derived? In other words how is it related to the specifics of the fan (no of blades, blade angle, blade length etc)? Also how is the efficicency curve of the fan derived (if it can be derived - Im not talking about the friction loss in bearings etc but the hydraulic losses which depend on geometry)? If the answers to the above are not available, can someone tell me how the efficiency varies with fan rpm? Im not talking about ways to calculate/measure the above but get an equation for it. Thanks

'Metallic conduction' in non metals

Hi. Any examples of metallic conduction (and hence metallic appearance) in non-metals other than poly(sulphurnitride) eg eg, excluding heavily doped polymers such as poly-enes? (ie from a pure compound). Not semiconductors please. ie conductivity better than 100 Ω^-1cm^-1 or thereabouts. 83.100.183.236 (talk) 14:27, 27 June 2010 (UTC)

Carbon nanotubes are good thermal conductors. --The High Fin Sperm Whale 16:59, 27 June 2010 (UTC)

Metallic appearance

Similar to above question, excluding metal (and metal based powders) are there any pigments or other compounds that have a metallic appearance (specifically - any used as a metallic pigment) ? Thanks. 83.100.183.236 (talk) 14:30, 27 June 2010 (UTC)

Can woodlice breath underwater?

82.43.90.93 (talk) 14:51, 27 June 2010 (UTC)

Certain types can as they live in water! But regarding the more common land species, I'm not sure. Regards, --—Cyclonenim | Chat  15:45, 27 June 2010 (UTC)

No, terrestial types can't. They will drown if put in the water. --The High Fin Sperm Whale 16:57, 27 June 2010 (UTC)

oysters

af2ter opening some oysters from the delaware bay I have found what appears to be some sort of a crab living inside the shell.Can someone identify the creature & provide some info (does it spend its entire life there,how does it get there etc...) ? —Preceding unsigned comment added by Dvp56 (talk • contribs) 15:57, 27 June 2010 (UTC)

Oysters do snap shut if disturbed. The crab could have crawled into the oyster, and the oyster would have closed its shell, trapping the crab. --The High Fin Sperm Whale 16:53, 27 June 2010 (UTC)

Switching mobile phones while flying.

Is it really necessary to turn our mobile phones off while flying in airplanes, as instructed? Or it is just a fear of new technology like putting off our shoes from the room where computers were used.I myself have never turned off my mobile phone while travelling in airplanes, but just put it in silence mode.This is just to check what will happen and nothing has happened.I am a very frequent flyer. —Preceding unsigned comment added by 113.199.218.23 (talk) 16:06, 27 June 2010 (UTC)

A relative who is a pilot tells me that mobile phone signals can mess with the navigational equipment — if I remember rightly, the VOR, among other things. While flying light aircraft, he is permitted to send text messages (there are plenty of times when he has a minute to type the message), because the text is just a quick burst of signals, while talking on the phone involves several minutes of constant signals. The point of turning your phone off is to ensure that you don't talk on it: having the phone on isn't by itself a problem. Nyttend (talk) 16:12, 27 June 2010 (UTC)

In addition to interfering with the plane's equipment (which isn't really a problem on modern passenger jets - they all have appropriate shielding), it can cause problems with the phone network due to you being a similar distance from lots of cell towers (since the distance between the cell towers is small compared to your height above them). Two non-neighbouring towers will assume that no phone will be communicating with both of them, so they will often use the same channels. Your phone will realise there is a low signal and boost power (flattening your battery quite quickly) and at that higher power will be able to communicate with both towers, causing lots of confusion. --Tango (talk) 16:26, 27 June 2010 (UTC)

We have a pretty lengthy article on this: Mobile phones on aircraft. Comet Tuttle (talk) 17:45, 27 June 2010 (UTC)

Superoxide reactivity

I was under the assumption that superoxide reactivity is a result of the superoxide having such a great affinity for electrons that it grabs electrons from surrounding molecules (DNA, membrane phospolipids, etc.), thereby contributing to the danger to biologic viability in the immediate area of superoxide concentration. Is this accurate? How does the electron affinity of the deficient valence shell of a single oxygen atom (as in a superoxide) differ from the deficient valence shells of two oxygen atoms (as in binary oxygen) to produce such a reactive substance? DRosenbach ^{(Talk | Contribs)} 16:59, 27 June 2010 (UTC)

Yes I think that as an oxidizing agent it snatches electrons from reducible substances, creating lots of havoc. --Chemicalinterest (talk) 17:38, 27 June 2010 (UTC)

It's also a radical (chemistry), which gives it a direct method of attack on just about any inorganic substance eg:

R-H + O₂^-· → R· + HO-O^- (forms peroxide and a radical)

It's it's radical nature in addition to the oxidising properties that makes it particularly harmful. This can be put another way by showing its reaction with water:

O₂^-· +H₂O → HO₂^- + HO·

ie hydrogen peroxide anion and a hydroxyl radical

Didn't understand the second part of your question, the electron affinities of O, and O₂ are given at Electron affinity (data page). I think the answer you are looking for is "molecular oxygen is less reactive since the bond dissociation energy is high.." O^-is even more reactive than O₂^- - a reason why it isn't usually found. 83.100.183.236 (talk) 18:15, 27 June 2010 (UTC)

Ants

When a queen bee dies, the female workers start to lay their own eggs as the queen isn't producing the pheromone anymore. Does the same happen in an ants nest when the queen ant dies? 82.43.90.93 (talk) 17:02, 27 June 2010 (UTC)

According to E. O. Wilson's wonderful article/story "Trailhead", the answer is basically "yes". "Soldier-queens" begin laying eggs, no longer inhibited by the queen's pheromones. However, the eggs are unfertilized and are thus all male drones, which can then go aid the beginning of new colonies, but their original colony will eventually die out after the queen has died. --Mr.98 (talk) 18:05, 27 June 2010 (UTC)

I'm only really familiar with honey bees (my grandfather is a bee-keeper), so other bees may be different, but that isn't my understanding of how it works. The workers don't start laying eggs (I don't think they are capable of laying). Rather, they start feeding royal jelly to existing larva (there is always some brood in a hive, I believe) so they become queens. It is also possible that there will already be a virgin queen in the hive who will simply take over as queen. I have no idea how it works with ants. --Tango (talk) 19:38, 27 June 2010 (UTC)

Scientific term for species who don't take care of their young.

Hi, I'm writing a story, and I want an adjective that means the species does not take care of their offspring. Is there a term for that? --Ye Olde Luke (talk) 19:33, 27 June 2010 (UTC)

I don't have a term to describe the species, but I know there is a range of altricial to precocious to describe birds depending on the level of maturity they possess at the time of hatching. The terms are defined by such things as whether the young hatch naked or with feathers already developed and what type of feathers are present, whether the eyes are open or closed, etc. Perhaps you can take a spin on that and term the species a precocious one if the young do not need the parents' attention. DRosenbach ^{(Talk | Contribs)} 20:04, 27 June 2010 (UTC)

There you go -- you can term the species precocial. DRosenbach ^{(Talk | Contribs)} 20:05, 27 June 2010 (UTC)

From the parental investment article, the term is r-selected, as opposed to K-selected. CS Miller (talk) 20:54, 27 June 2010 (UTC)

or as a made up term "non-incubatory" ?? 83.100.183.236 (talk) 20:55, 27 June 2010 (UTC)

Thanks all! For the species introduction, I think I'm going to use "non-incubatory," but I plan to mention all of these terms at leter parts in the story, since it would get redundant to just keep using "non-incubatory." --Ye Olde Luke (talk) 21:24, 27 June 2010 (UTC)

The common cuckoo is an example. 92.28.242.168 (talk) 21:25, 27 June 2010 (UTC)