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September 2

Thrust vectoring

Does anyone know of a flat, rather than round, thrust vectoring system that can vector in the yaw besides the X-36? And does anyone have a picture of the X-36's thrust vectoring system? --The High Fin Sperm Whale 03:00, 2 September 2010 (UTC)

Some scant pics here. --Sean 18:24, 2 September 2010 (UTC)

Shrinking helium

In last Sunday's Ask Marilyn article, Marilyn vos Savant discussed helium escaping from balloons. I understand the microscopic porous nature of the balloon, but I'm skeptical of the following statement: "Helium contracts as the temperature drops, which allows gas to slip through the pores of a balloon more easily."

I know that the gas as a whole would contract with decreasing temperature (assuming a constant pressure), but is this true at the atomic level? -- Tom N (tcncv) talk/contrib 04:39, 2 September 2010 (UTC)

It's a complex process. When a gas contracts because of temperature dropping, the molecular density increases; that is there are more molecules per unit volume of the gas, which may mean more collisions with pores. Of course, as the temperature drops, so does Root mean square speed of the molecules, which may mean less collisions with the pores. Of course, under a first approximation (ideal gas), these effects should exactly cancel. Since real gases behave slightly differently than ideal gasses, its quite more complex, and one effect may predominate over the other. The relevent discussions could be found in the articles Effusion and Graham's law, though the effusion article seems to lack some. --Jayron32 04:52, 2 September 2010 (UTC)

• Minor nitpick: you're talking about helium atoms; helium doesn't form molecules. --Anon, 04:08 UTC, September 3, 2010.

Speaking in general terms, its tough to choose a term which readers will recognize, and which is a stand in for "atoms and/or molecules and/or other particles". Chemists use the term "moety" sometimes to mean this, but its not a term in widespread use. When speaking in general terms over the behavior of something like gases in general, given that there are about 7 gases which exist as lone atoms, and about 1 billion that exist as molecules, just using the term molecule is, statistically atleast, close enough. --Jayron32 04:41, 3 September 2010 (UTC)

I know; in fact I just used "molecule" myself that way in answering another question, below. But on this question we're talking specifically about helium. No big deal. --Anon, 06:42 UTC, September 3, 2010.

The rubber around the balloon also contracts, and presumably, so do the pores. The walls should actually be slightly thicker as the balloon contracts. Gas transmission rate through the balloon-wall is much more complicated than a simple application of the ideal-gas law. I'd stake my bet on an empirical measurement of gas escape rate as a function of temperature; there are so many relevant factors (gas thermal velocity; pore size; collision rate; rubber material properties, etc) that trying to model them from fundamental physics is unlikely to be accurate. Nimur (talk) 05:35, 2 September 2010 (UTC)

Also, Helium is about as close to an ideal gas as you can really get, so ideal gas laws are pretty relevant. Googlemeister (talk) 13:05, 2 September 2010 (UTC)

Energy from pressure difference

How do you calculate energy from a pressure difference?

For example a hurricane has an eye 100km by 1km high, so a volume of 1.6×10^11 cubic meters, and a pressure of, say, 950 millibars, compared to 1013 millibars for the air around it. How much energy is contained in that pressure difference? Ariel. (talk) 05:40, 2 September 2010 (UTC)

You need a volume and a pressure to determine energy stored by a gas; and it simplifies if you assume an isothermal process for the energy release. Nimur (talk) 20:19, 2 September 2010 (UTC)

There is a discussion at Potential_energy#Relation_between_potential_energy.2C_potential_and_force which, while it focuses more on gravity, does deal with the mathematical relationship between forces and potential energy, but not in a simple "Here's a nice equation to use to calculate this." --Jayron32 05:49, 2 September 2010 (UTC)

Another related idea is Elastic_potential_energy#Elastic_Internal_Energy_in_Compressible_Gases_and_Liquids. Remember that the Gas constant can be expressed in Volume*Pressure OR as Energy, Joules and pascal*cubic meters are (I think) equivalent units. I think the relevent issue is that the potential energy is proportional to either PdV or VdP; that is under a constant pressure changes in volume represent a change in energy; while under a constant volume, pressure differential would be the relevent relationship to energy. So, I think (and I could be wrong here) that this is as simple as volume of the eye * pressure differental across the eyewall; corrected for units. Since m³*mbar is technically an energy unit, you could leave it as that, or you can do the dimmensional analysis, and change it to joules or kilojoules or whatever. --Jayron32 06:00, 2 September 2010 (UTC)

Doing that gives me an energy of 1×10^15 joules (about a quarter of a megaton of TNT), which seems low (this says hurricanes release 6×10^14 J/second, and hurricanes can last at least 2 or 3 days on land). But I'm surprised that it doesn't depend on the density of the air. Wouldn't a heavier fluid contain more energy? Moving a given volume of water takes more energy than moving a given volume of air. Maybe not - I guess with a heavier fluid you need to move fewer atoms to produce a given pressure? Ariel. (talk) 06:07, 2 September 2010 (UTC)

The actual masses of the particles are irrelevent for this particular calculation; pressure and temperature already account for mass in their inherant formulation. The pressure is merely the force acting on a surface; that force doesn't care whether its a smaller particle moving fast or a heavier particle moving slow; its the same force so its effect on the energy should be the same. Also, that potential energy you have is instantaneous potential, that is the energy of the storm right now Besides dissipating energy, a storm also accumulates energy over time; that 1E15 Joules of energy you just calculated is not the total energy availible to the storm, since it will continue to gather energy even over land. On the balance, the storm loses more energy than it gains over land, but that's only because the rate of dissipation is greater than the rate of accumulation; the rate of accumulation is not zero. --Jayron32 06:22, 2 September 2010 (UTC)

I thought the rate of accumulation over land was zero since the energy source is latent heat of condensation of water. Ariel. (talk) 06:27, 2 September 2010 (UTC)

Tropical_cyclone#Mechanics and Tropical cyclogenesis discuss this in detail. There's even numbers in there. Yes, the primary source of energy is condensing water vapor. However, the process is far too complex to declare that this primary source of energy accounts for 100% of the energy in the storm... --Jayron32 06:34, 2 September 2010 (UTC)

That page says "When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly." Seems to me that hurricanes must store energy somewhere else besides the pressure gradient, maybe in all the moisture they carry with them. Ariel. (talk) 06:39, 2 September 2010 (UTC)

Again, that doesn't mean that the energy accumulation over land is zero, only that it is much smaller than the energy accumulation over water. The energy is stored in both the pressure gradient, and in the internal energy of the gasseous water molecules, as compared to the internal energy of liquid water. If you want to know ALL of that energy, you'd also need to know the temperature of the air in the defined volume; that temperature should equal the dew point (the air should be saturated) so you can then compare that to the vapor pressure of water at that temperature, which can then be used to find the partial pressure of the water vapor, which can be used to calculate the total mass (or moles, whatever) of water vapor in the air. You can then use that to calculate the energy differential between the gasseous and liquid water; i.e. the latent heat of vaporization. However, your question only dealt with the energy stored as the pressure gradient. --Jayron32 06:48, 2 September 2010 (UTC)

Yes it did because I thought that was all of it. I'm going to try calculating the water energy tomorrow (unless someone wants to do it for me :) BTW thank you for the replies. Ariel. (talk) 06:56, 2 September 2010 (UTC)

Another idea (just popped into my head); a third, probably non-negligible source of energy is gravitational potential energy. After all, you just raised a HUGE mass of water rather high into the air, this height differential should itself be a possible source of potential energy. --Jayron32 07:00, 2 September 2010 (UTC)

Indeed it is. This gravitational potential is extremely significant. It is responsible for things like flash-condensation - which you might know as a lenticular cloud or a mushroom cloud (things with real wide, flat-bottomed layer structures). As air masses convect and are forced to different altitudes by fluid-dynamics (e.g. by momentum and viscous forces), they are working against an energy gradient, and they must cool rapidly to account for this energy-change. Rapid temperature decreases will lead to a change of state, and vaporous water will condense. That can result in a flat-bottomed cloud - this represents a gravitational equipotential surface (perturbed by local changes in humidity and temperature); but you can often see very sharp, crisp "bottom layers" when this occurs. Nimur (talk) 20:15, 2 September 2010 (UTC)

Pressure-volume work is defined as the integral of $\int {PdV}+\int {VdP}$. So, to calculate the work capability of a system with a pressure gradient, you can assume the hurricane is a giant carnot engine; the pressure gradient defines the limits of pressure in a thermodynamic cycle; and the volume can be estimated based on geographic scale of the hurricane. If there is net energy influx from solar radiation (or indirectly via ground or water re-radiation of heat), you can account for this by moving the adiabat. The work done (rather, the energy released by the hurricane), is the difference between two curves (just like any other heat engine). This work done is released as energy; it takes the form of kinetic energy of wind and water; as state-changes as water evaporates and re-precipitates; as changes to the temperature of massive volumes of air, water, and land, and so on. Nimur (talk) 20:06, 2 September 2010 (UTC)

It's only the first of those two integrals: if V is constant, no work is done because no interface is moving, regardless of the (change in) pressure. --Tardis (talk) 20:30, 2 September 2010 (UTC)

Well, it's not in a confined area like a piston cylinder; but the volume doesn't have to be fixed. The air-mass could be expanding. But you're right, you can make simplifying assumptions. Trying to model a hurricane from first-principles will require "some approximation." Nimur (talk) 21:26, 2 September 2010 (UTC)

The $\int VdP$ term is simply wrong and should be dropped; my example of constant V was just to prove that. --Tardis (talk) 22:35, 2 September 2010 (UTC)

Are you saying that the total derivative $dW=d(PV)$ does not equal $P\partial {V}+V\partial {P}$ ? Or that the term $V\partial {P}=0$ for this case? In either case, I don't understand your reasoning. (The former is a mathematical fact; the latter is because pressure can change in weather systems, and volume is non-zero, so V dP is not negligible). There is additional discussion about path-independent work in our article. Increasing the pressure for a fixed volume requires work; I don't know why you would say "no work is done." Nimur (talk) 23:04, 2 September 2010 (UTC)

Falling stick

A straight vertical rod of length l, when pushed, slides for a little while and then topples from the vertical position. What will be the velocity of the upper end when this end hits the ground?

My approach was to use the work due to torque (∫τdθ = (1/2)Iω²) about the end touching the ground, but I don't think this is right. If axis I'm using is accelerating (and if there's friction, it should be accelerating), then won't I have to take into account ficticious torques? But that would mean knowing something about the friction, no? 74.15.136.172 (talk) 10:45, 2 September 2010 (UTC)

To me this looks like a much simpler question. The horizontal component seems to be neglected, what with the "push" and the "sliding" and all. But for the vertical component, you know that the stick starts with the potential energy g*(l/2)*m (m=its mass, irrelevant) and no kinetic energy (neglecting horizontal). When it hits the ground it has zero potential energy and (neglecting any energy dissipated in friction) kinetic energy 1/2 m v^2. So v (on average) = sqrt ( 2/m * m/2 * l * g) = sqrt (lg). If one end is stationary, then the other end should be twice that. Unless I forgot something. Wnt (talk) 14:10, 2 September 2010 (UTC)

Well, I think you forgot about rotational kinetic energy...but anyways, if I were to ignore friction, then what I wrote above would be right, except that I don't think that friction can be ignored; otherwise, why mention that it slides for a little while? 74.15.136.172 (talk) 20:37, 2 September 2010 (UTC)

I don't believe I have to take rotational versus translational into account, if I simply average up the energy in all the particles of the rod. However, when I said "twice that", I think I needed to consider more carefully just what was twice what, since kinetic energy goes according to the square of the velocity... Wnt (talk) 00:55, 3 September 2010 (UTC)

OK. To take this your way, the rotational kinetic energy = 1/2 I ω². For a rigid rod spinning around its center, I = 1/12 m L². But here let's look at it spinning around one end, so all the kinetic energy is rotational. Using the integral from that page, I work out that its I = 1/3 m L². So Lgm/2 = 1/6 m L² ω². So ω²=3g/L, and ω=sqrt(3g/L). The top of the rod moves at speed sqrt(3gL) --- note that this differs from the 2 sqrt(gL) I said before because of the error in averaging kinetic energy I mentioned above. Hope I'm right this time... Wnt (talk) 01:24, 3 September 2010 (UTC)

Both our ways give the same answer, so I guess they're equivalent...but the question seems to suggest that we take friction into account. Any thoughts? 74.15.136.172 (talk) 01:51, 3 September 2010 (UTC)

I think the implication of "slides for a little while" is that the stick must have been pushed at its base. It stayed vertical until it came to stop. Then it toppled from stationary, meaning that there is no trace momentum of the original push. I think we have to assume the stick is very thin and ignore air friction, although that maeans the base is a point which makes sliding difficult. So we also assume the surface is frictionless. But then the stick would never stop sliding. I am not here and did not think any of this. Cuddlyable3 (talk) 13:16, 3 September 2010 (UTC)

Mathematical sequence

Hello PPL, whats the best approach for solving mathematical sequences like 1 4 17 54 145 368 945 ___? , the ones that are in IQ tests?Is there any kind of logical one? Or just trying blindly? TY much and sorry for my english.194.138.12.146 (talk) 12:41, 2 September 2010 (UTC)

For integer sequences, taking forward differences is a good place to start. If you don't see a pattern in the first forward differences, take forward differences again, rinse and repeat. Or, if you get impatient, you can look up the sequence at OEIS. Gandalf61 (talk) 12:55, 2 September 2010 (UTC)

I didn't see the pattern in the forward differences, even after looking at the entry - maybe I needed to compare something other than adjacent terms? But the ratios tell you something is up that is more complicated than an x_n+1=ax_n+b sort of thing:

4 4.25 3.17 2.68 2.53 2.56 ...

I'm actually surprised that this "Titan test" is so public. And to think the UK newspapers are griefing us over posting the ending to The Mousetrap! Wnt (talk) 14:18, 2 September 2010 (UTC)

Sounds interesting. Got a link? Vimescarrot (talk) 16:27, 2 September 2010 (UTC)

Assuming you mean the Mousetrap thing, see User_talk:Jimbo_Wales/Archive_64#Cyclopia.27s_unexpected_promotion_to_.22spokesman.22_for_Wikipedia_by_journalists_of_the_Independent, with lots more links. - Jarry1250 ^{[Humorous? Discuss.]} 18:34, 2 September 2010 (UTC)

Cheers! Vimescarrot (talk) 19:42, 2 September 2010 (UTC)

Actually I was asking the question from work, was not signed in, after 5 hours and 5 papers I solved it. After a while I began to try combinations with 2^, as it didnt work I tryed 3^, and there I saw a pattern, the algorithm is n^3+3^n but I was not following any rule for solving it.And its not "that" public, I was looking specifically for"Titan Test"DSTiamat (talk) 16:08, 2 September 2010 (UTC)

These sorts of sequences can be fit by an infinite number of functions, so there is not one "correct" pattern. Providing several integers and asking to fit "any" function leaves a null space of infinite size - there is literally no limit to the number of different, unique solutions that can yield those numbers. Typically, there's an implicit "integer-coefficients" assumption; there is usually the assumption that the sequence will be a linear sum of simple terms (like a polynomial in n), but unless these requirements are formally laid out for the sequence, there is no correct answer. Proper IQ tests do not use "guess the next number in this sequence" questions, because there is no objective way to define "correctness." If you have smarter and smarter participants (especially those who have formal training in mathematics, but not necessarily), they will solve the problem more effectively than the test-provider intended; and the test becomes invalid; so well-structured IQ tests will never ask this kind of question. Nimur (talk) 19:59, 2 September 2010 (UTC)

While there are indeed an infinite number of functions that'll work, it's generally clear that what is required is the simplest function that'll do the job - and it's usually very clear what that is once you find it.

Of course some sequences are tougher:

• 0,1,2,5,8,11...is the first N numbers that look the same if viewed upside down on a calculator display.
• 3,3,5,4,4,3,5,5,4,3,6...is the number of letters in the English word for 'N'.

If someone is using a criterion like that then no amount of messing around with numerical stuff will get you the "correct" answer you really do have to just have the answer pop into your head. But some are completely ambiguous:

• 4,8,12,16,20,24,28,32... has got you thinking 4N - when in fact I was thinking of the years in our calendar that were leap years and you wouldn't have had a hope in hell of realizing that until I said...92,96,104,108,112 and you were forced to figure out why I skipped '100'. Of course if I'd said 2004,2008,2012,2016... then you might have jumped at "Leap year" immediately rather than 2000+4N - but if I'd said 1234,1238,1242,1246,...then again, you might not have thought "leap years" and would have gone back to 1230+4N.
• Even if the answer is "simple" and "numerical", you might never find it other than by luck - but I bet you get: 3,1,4,1,5,9,2,6,5,3,5... which is certainly "simple" and numerical/arithmetic - but trying to fit a function to it would take you forever!

(10^n*pi)%10-(10^n*pi)%1 That wasn't so hard. —Preceding unsigned comment added by DanielLC (talk • contribs) 18:36, 4 September 2010 (UTC)

This clearly isn't about mathematics so much as the very human idea of "simplicity".

SteveBaker (talk) 06:13, 4 September 2010 (UTC)

What's funny is that all these sequences are in OECD. It actually lists four other answers for the 0,1,2,5,8,11 sequence! Wnt (talk) 17:49, 4 September 2010 (UTC)

Ant?

What is this? It looks like a queen ant from the species Myrmica rubra. Is it the ant flight time of year for this species in the UK? 82.44.55.25 (talk) 15:16, 2 September 2010 (UTC)

It's a bit hard to tell for sure but yes, it looks like a Myrmica rubra queen. AntWeb is your friend in all things ant and Wikipedia's too since they have released all of their images under CC-BY-SA. I guess it's still nuptial flight time in the UK for these guys, yes. Sean.hoyland - talk 16:22, 2 September 2010 (UTC)

". . .for these guys"?!! Richard Avery (talk) 19:40, 2 September 2010 (UTC)

Does "guys" not refer to a group consisting of either/both genders? 82.44.55.25 (talk) 19:55, 2 September 2010 (UTC)

It can, loosely; most people will understand it correctly. --jpgordon^{::==( o )} 19:59, 2 September 2010 (UTC)

guys, plural noun used to address people: used to address a group of people of either sex Hey, guys, where are you off to?

Microsoft® Encarta® 2009. © 1993-2008 Microsoft Corporation. All rights reserved. --Chemicalinterest (talk) 20:37, 2 September 2010 (UTC)

Yes, "guys" as in "Hey guys, let's watch Sex in the City and talk about why the liquids in sanitary napkin adverts are never red". Also, I believe Myrmica rubra males have long campaigned for a move to grammatically genderless semiochemicals. Sean.hoyland - talk 03:20, 3 September 2010 (UTC)

Microsoft Encarta? Why not Collins or Chambers or Oxford. They support the case, and I stand a little wiser. Up the workers!! Richard Avery (talk) 06:59, 3 September 2010 (UTC)

End organ

In your discussions of cutaneous senses and mechanoreceptors, reference is made to the "end organs" (e.g. Pacinian Corpuscles end organ[s]). What does that mean: "end organ" in terms of these sensory cells? I know cell body, and terminal buttons (at the synapse gap) and dendrites (on the receiving cell). I do not understand what "end organ[s]" is/are. Please explain this to me. (I am studying Neuroscience and have used the text and many web searches. Thank you.97.126.243.41 (talk) 17:07, 2 September 2010 (UTC)

As you stated, Pacinian corpuscles (together with Merkel discs, Ruffini endings, Meissner's corpuscles, end bulbs of Krasue and others) are examples of modified dendrite tips known collectively as special cutaneous receptors. There are also free nerve endings. DRosenbach ^{(Talk | Contribs)} 19:29, 2 September 2010 (UTC)

(after EC) They call the cutaneous sensory receptors "organs" because they are generally complex arrangements of different types of cells that together serve the purpose of transducing a given sensation to the nerve ending. Take a close look at the pictures in the Pacinian corpuscle, Meissner's corpuscle, organ of corti, olfactory bulb, and taste bud articles -- these structures are complicated collections of nerve fibers, connective tissue cells, blood vessels, etc. and they clearly meet the definition in organ (anatomy): "a collection of tissues joined in structural unit to serve a common function". The structures you are listing (cell body, terminal boutons, and dendrites) are all integral parts of the neuron itself, enabling communication of the sensory reception into the nervous system, but the overall process of sensory reception requires the more complex "end organ". Does that help? --- Medical geneticist (talk) 19:38, 2 September 2010 (UTC)

Where find actuarial statistics?

Where could I find data to answer questions like what percentage of woman lived past age 50 circa 1850? RJFJR (talk) 17:07, 2 September 2010 (UTC)

Which country do you want data on? --TammyMoet (talk) 17:57, 2 September 2010 (UTC)

Try life table. 92.29.120.223 (talk) 19:37, 2 September 2010 (UTC)

lifting an average passenger train car

I am not sure how heavy the average North American passenger train car is, but I am wondering if one were to want to lift said vehicle off the ground (say even 10 feet) using a helium-style balloon, how big would this balloon need to be? How would this compare to the Hindenberg in size?

Related to this, if one were to fill all available space (except where passengers sit, of course)with helium, how significant would this lighten the train car? 142.46.225.77 (talk) 17:54, 2 September 2010 (UTC)

You're going to need about a cubic meter of helium per kilogram of train car (And per kilogram of balloon!)

So if you imagine a 75ton train car, you're going to need about 70,000 cubic meters of helium.

So, Maybe a spherical balloon 110 meters across? Very roughly. APL (talk) 18:05, 2 September 2010 (UTC)

Our article suggests the Hindenberg had a volume of about 200,000 cubic meters, but then again it did weigh a significant amount in itself. I have no idea how much that is. - Jarry1250 ^{[Humorous? Discuss.]} 18:17, 2 September 2010 (UTC)

Our article also gives a "useful lift" of 10,000 kg, well below that of a rail car. On the other hand, I'm sure that you could build an airship comparable in size to the Hindenburg both much lighter, and that actually had light gas envelopes filling more of the volume. Buddy431 (talk) 18:59, 2 September 2010 (UTC)

Also, the Hindenburg (famously) used hydrogen rather than helium as its lifting gas - so it would have had a somewhat higher payload than a helium balloon. SteveBaker (talk) 05:40, 4 September 2010 (UTC)

I also see that a company known as CargoLifter wanted to construct an airship capable of carrying 160 tons, which would have had a volume of 550,000 cubic meters. Perhaps unsurprisingly, the company no longer exists. You can visit their former hanger, though, as the Tropical Islands resort in Germany. Buddy431 (talk) 19:06, 2 September 2010 (UTC)

First, if an Amfleet car is taken as the typical passenger car today, it weighs 116,000 pounds (58 short tons or 52.6 metric tons) according to Wikipedia. (Traditional passenger cars were often heavier, up to 70-80 tons, while subway cars are often lighter, under 40 tons.)

In the book The Golden Age of the Great Passenger Airships: Graf Zeppelin & Hindenburg by Dick and Robinson, details are given of the loading of the Hindenburg for its first transatlantic flight, a year before the disaster. I may as well reproduce the entire table for interest. All weights are in kilograms; divied by 1,000 for metric tons.

         2,960   37 passengers
         1,840   23 engine personnel
         1,680   21 deck crew
           800   10 stewards
           600   passenger baggage
         1,080   crew baggage
         3,000   provisions
         1,269   freight
            84   mail
        55,230   fuel oil
         4,000   lubricating oil
         1,200   reserve parts
         1,400   reserve radiator water
         1,150   drinking water and liquors
        11,300   trim ballast
         3,000   emergency ballast
         1,120   miscellaneous
         2,500   bedding, utensils, etc.
         1,000   moisture
         1,000   lightness
        96,213   SUBTOTAL
       118,000   dead weight (approx.)
       214,213   TOTAL

Clearly a bunch of these items apply only because we're talking about a passenger airship. And likewise for some of the "dead weight" -- if it wasn't carrying passengers you wouldn't need passenger cabins and all the things that go with feeding the passengers. And you could also go with a lighter structure (a blimp rather than a dirigible) if you were willing to have a less capable airship. So in short I think it's fair to say that while a Hindenburg-size airship wouldn't be quite big enough, it's too small by not all that large a margin.

Of course, the Hindenburg was inflated with hydrogen; with helium you get about 8% less lift, so you need a slightly bigger airship for that reason. (The calculation is (29-4)/(29-2) = 0.926, where 29, 4, and 2 are the respective average molecular weights of air, helium, and hydrogren.)

On the other question, the enclosed volume of a passenger car is something like 70 x 10 x 8 feet, which is 5,600 ft³ or say 160 m³. That is less than 1/1,000 of the gas capacity of the Hindenburg, so you can see that even if you were willing to suffocate the passengers by filling it with helium, you would not get any significant lift.

--Anonymous, 04:45 UTC, September 3, 2010.

Earth's Atmosphere

Coming back to wake you up again! If Earth had no atmosphere and we were still alive somehow; how can we see things around us look like, including the sky, horizon, sunset, sunrise, ..etc?--Email4mobile (talk) 21:55, 2 September 2010 (UTC)

The sky looks blue due to Rayleigh scattering - without an atmosphere it'd just be black. It doesn't answer any of your other questions, though. (I don't know whether you'd be able to see the stars during the day, but I doubt it.) Vimescarrot (talk) 21:58, 2 September 2010 (UTC)

You'd surely be able to see the stars so long as your eyes were dark-adapted at all (which would just involve being in a hole behind a wall). --Tardis (talk) 23:08, 2 September 2010 (UTC)

There would be no pre-dawn brightening of the sky. It would be completely dark until the sun first appeared over the horizon. Similarly at dusk, the sky would go dark as soon as the sun had set. Rojomoke (talk) 23:36, 2 September 2010 (UTC)

If it's not obvious, it would be exactly what it is like on the moon. One more thing I would add to the above is that shadows would be much sharper and darker because there would be no light scattering from the atmosphere or clouds. Vespine (talk) 23:49, 2 September 2010 (UTC)

However, contrary to popular belief, shadows would not be pitch-black. There's still diffuse interreflection to light things up. --Carnildo (talk) 01:20, 3 September 2010 (UTC)

While you might be able to see the stars, they wouldn't twinkle as that is caused by turbulence in the atmosphere. Confusing Manifestation(Say hi!) 01:56, 3 September 2010 (UTC)

No mirages. No Aurora. No Meteor showers to see until they make craters around you. No Rain, Snow, Wind or Weather at all. During a Lunar eclipse the occluded area of the Moon would be black not dark reddish. Your Barometer pointer is hard against the stop. You might notice that the tires of your bicycle and car are bulging because they are over-inflated, though I don't know where you got the gas to pump into them. If you had anything held by a Suction cup, well it isn't held. You would see neither the Space Shuttle nor parachutists land more than once (painfully). If you break an ordinary lamp bulb it may still work. Anyway everybody without a space suit would be dead which makes it a horrible idea. Cuddlyable3 (talk) 12:37, 3 September 2010 (UTC)

We didn't cover sunrises and sunsets. In both cases, the sun would appear as a sharp white circle - there would be no change in the color of sky or sun as it rose or set. Also no rainbows (because no rain). Kinda boring really. SteveBaker (talk) 05:38, 4 September 2010 (UTC)

The Sun would also be a sharp white circle at all the other times of the day. Without the sky scattering the blue, it wouldn't be yellow anymore. Also, the stars and planets would look a bit bluer. The oceans would freeze dry, and it would look like it's boiling and freezing at the same time. Not really an optical effect, but it's still cool. — DanielLC 17:11, 4 September 2010 (UTC)

Theory of Relativity and Time Travel

How does Einstein's theory explain time travel, and more importantly Grandfather's Paradox ?  Jon Ascton  (talk) 23:46, 2 September 2010 (UTC)

It doesn't, really. There are various interpretations of Special and General Relativity that seem to allow backward time travel from some reference frame (see Time_travel#In_physics), but they are pretty speculative and my understanding is that most physicists think they wouldn't have much of a chance of working. Relativity certainly has nothing to say in particular to say about the grandfather paradox. --Mr.98 (talk) 00:08, 3 September 2010 (UTC)

See however tachyonic antitelephone. If it were possible to send information faster than light by a frame-independent and direction-independent process, it would also be possible to send information backwards in time. That gets you the grandfather paradox. --Trovatore (talk) 00:15, 3 September 2010 (UTC)

See closed timelike curve, especially Tipler cylinder. Wnt (talk) 00:51, 3 September 2010 (UTC)

Right, but my point is, there are clever (and probably not workable ways) is come up with some kind of possible backwards time travel using SR/GR, but SR/GR itself doesn't say anything about how the paradoxes would be resolved, if they would be. --Mr.98 (talk) 12:09, 3 September 2010 (UTC)

September 3

Xyliooligo saccharide

Xyliooligo saccharide —Preceding unsigned comment added by 220.136.107.152 (talk) 01:50, 3 September 2010 (UTC)

Does this help? hydnjo (talk) 02:30, 3 September 2010 (UTC)

What is protium hydroxide?

Is it the same stuff as dihydrogen monoxide? --81.96.185.94 (talk) 05:37, 3 September 2010 (UTC)

Yes. Someguy1221 (talk) 05:46, 3 September 2010 (UTC)

(edit conflict) Yes. Compare protium, hydroxide, water. It's just water, and someone is trying to be silly. --Jayron32 05:47, 3 September 2010 (UTC)

Cheers.--81.96.185.94 (talk) 05:49, 3 September 2010 (UTC)

Wrong. If you actually look at the protium article you will see that it means hydrogen-1, the most common isotope of hydrogen. In normal water, most of the hydrogen is protium but there is a small amount of deuterium, forming molecules of heavy water. Protium oxide would be water without any deuterium in it. "Dihydrogen monoxide", or simply hydrogen oxide, on the other hand, is just water. --Anonymous, 06:48 UTC, September 3, 2010.

What happens when you mix diprotium oxide with dideuteriuum oxide? (heavy water) entropy is increased, but is there any temperature effect? Graeme Bartlett (talk) 11:14, 3 September 2010 (UTC)

I don't have my tables handy, so I can't tell you which way the temperature would go, but there should be a small change. The protons and deuterons are labile, so there will be a rapid equilibration reaction converting some H₂O and D₂O into HDO. TenOfAllTrades(talk) 14:10, 3 September 2010 (UTC)

OK, but for most practical purposes, are they the same? By the way: what's the difference between "protium hydroxide" and "protium oxide"? Was that a typo, or are those the same? (I abandoned chemistry when I was 14.)

You know, something named "protium oxide" could be a great spoof miracle drink!--81.96.185.94 (talk) 11:06, 3 September 2010 (UTC)

Protium hydroxide implies ¹H-O-H, i.e. one of the hydrogen atoms is definitely protium (no neutrons in its nucleus) but the other hydrogen atom may be any one of protium (¹H or just H), deuterium (²H or D), or tritium (³H or T), that is to say, the other hydrogen may or may not have neutrons in its nucleus.

Seen another way, protium oxide is ¹H-O-¹H, whereas protium hydroxide encompasses three isotopomers:

• ¹H-O-¹H, i.e. H₂O
• ¹H-O-²H, i.e. HDO
• ¹H-O-³H, i.e. HTO

Heavy water covers:

• ¹H-O-²H (aka semiheavy water, deuterium protium oxide, HDO)
• ²H-O-²H (aka heavy water, deuterium oxide, D₂O).

Tritiated water covers:

• ¹H-O-³H (aka tritium protium oxide, HTO)
• ³H-O-³H (aka super-heavy water, tritium oxide, T₂O)

Ben (talk) 11:17, 3 September 2010 (UTC)

water, water everywhere, yet not a drop to drink... --Ludwigs2 16:27, 3 September 2010 (UTC)

You guys put WAY too much effort into analyzing a joke. The person who introduced the OP to the words "protium hydroxide" wasn't expressing a scientific concept, they were using a marginally accurate bit of obfuscation to mask the fact that they are talking about ordinary water. The DHMO joke made its first run through the internet like 15 years ago, this is just another minor variation on it. --Jayron32 02:54, 4 September 2010 (UTC)

Well, if you know what that person's motivation was, fine. The fact is that "protium" does not mean the same thing as "hydrogen", and it was necessary to say that to answer the question. --Anon, 04:19 UTC, September 4, 2010.

Yes, that was my motivation - trying to obfuscate what I had suspected to be the effective nature of the aforementioned subject.--81.96.185.94 (talk) 18:28, 7 September 2010 (UTC)

Quantum mechanics

Niels Bohr said about this theory that those who are not shocked by it don't understand it ! What I want to simply know is that - is there any implication in this theory that says that an electron, proton or photon starts behaving differently when it is under observation  Jon Ascton  (talk) 06:35, 3 September 2010 (UTC)

The simple answer is no! Particles are not aware when they are under observation. Dolphin (t) 07:33, 3 September 2010 (UTC)

... but, of course, the act of observation can change behaviour. Dbfirs 07:43, 3 September 2010 (UTC)

In quantum mechanics, an observation collapses the particle's wave function. So, yes, an observation affects a particle's future behaviour, in the sense that it changes the future shape of its wave function and so changes the probability that it will be observed in a given state at some time in the future. For example, in the double-slit experiment, observing the particle as it passes through the slits affects the interference pattern observed on the screen. Gandalf61 (talk) 09:07, 3 September 2010 (UTC)

If you're a follower of the Copenhagen interpretation, that is. If, on the other hand, you prefer the Many-worlds interpretation, then a wave function never really collapses, and we just observe one of all possible states. The math's all the same, but there are different ways of viewing the rules of quantum mechanics. Buddy431 (talk) 13:17, 3 September 2010 (UTC)

I would like to see that example in practice. I have my lamp, slits and screen set up with the expected interference pattern showing. What may I do that will change the pattern on the screen? Cuddlyable3 (talk) 11:40, 3 September 2010 (UTC)

Block out one of the slits ;) That might seem trivial, but imagine an experiment where the photons are going through one at a time (this can be done practically, although probably not at home). You note where each photon arrives on the screen, and repeat the experiment a few thousand times. When you look at the number distribution of the photons, you have exactly the same pattern (to within experimental error) as you have from a classic Young's slits experiment. So either an individual photon goes through both slits at once or it somehow "knows" that the second slit is there... Physchim62 (talk) 12:41, 3 September 2010 (UTC)

If you want to see very weird things, look up Wheeler's delayed choice experiment. There are some very odd results that seem to imply some very weird violations of causality, for example. --Mr.98 (talk) 12:54, 3 September 2010 (UTC)

For Bohr, the heart of quantum mechanics was Complementarity. Give it a read. It is not just about things looking different when you look at them differently. It is about, in Bohr's formulation, the ultimate limits of what meaning means in the physical world. Not all physicists, especially modern ones, do QM in the same way that Bohr did. The best individual experiment that gives an indication of the kinds of "shocking" things Bohr is talking about is Wheeler's delayed choice, linked above, which was dreamed up to specifically show how "shocking" this could be, where very weird things happen that make very little sense using macroscopic (non-quantum) logic.--Mr.98 (talk) 12:54, 3 September 2010 (UTC)

I think we should really state what "observation" actually means in physics. We actually have an article about quantum observations, but I can summarize briefly. Let's say you want to observe a flower - you look at it, right? But what is "looking" at something? Light is involved - photons from the sun hit the flower and an amount proportional to the size of the flower hit your eye, thus giving it a nice image against everything else in your field of vision. But the key here is that, if there was nothing that actually hits that flower, there'd be no way to see it, feel it, smell it, etc. Something physical must happen to the flower, and in quantum mechanics, this physical interaction is "observation". It doesn't matter if you are a conscious being or not - when a quantum particle interacts with something, it must collapse into a definite space and time to actually make a cause-and-effect billiard-ball interaction. Once it's done interacting, it rapidly becomes the wavy cloudy quantum-uncertainty thing it was beforehand again. All it has to do is hit something - anything - to be observed. SamuelRiv (talk) 20:46, 3 September 2010 (UTC)

The simple answer is yes. A crucial prediction of quantum mechanics is that any act of observing a particle perturbs it, and there is a limit to how small the perturbation can be. Looie496 (talk) 22:52, 3 September 2010 (UTC)

ISOMERISM

What is D and L designations in organic isomers? and also what is meant by Racemic mixture??Rohit.bastian (talk) 08:25, 3 September 2010 (UTC)

See chirality and racemic mixture, respectively, and if these don't answer your questions then come back. HTH. --Ouro (blah blah) 08:36, 3 September 2010 (UTC)

mass and charge

what is mass and what is charge? I mean other than trivial attributes attached to different particles, what is it that is actually responsible for them? --91.103.185.230 (talk) 09:57, 3 September 2010 (UTC)

In the Standard Model of particle physics, charge (assuming you mean electric charge) measures the strength of a particle's interaction with the electromagnetic field and with its force carrier, the photon. There are various theories as to the origins of mass; one that has wide acceptance, although it is not yet experimentally proved, is that mass measures the strength of a particle's interaction with the Higgs field and the (hypothetical) Higgs boson. Gandalf61 (talk) 10:28, 3 September 2010 (UTC)

cheers for replying, youre a fucking legend mate. --91.103.185.230 (talk) 11:11, 3 September 2010 (UTC)

Hurricane disruption

If a nation were to detonate a 1Mton nuclear device in the eye of a hurricane (for example a cat 3), would the hurricane be weakened, strengthened or not notably affected? Googlemeister (talk) 13:28, 3 September 2010 (UTC)

Our Tropical Cyclone article says

"Scientists at the US National Center for Atmospheric Research estimate that a tropical cyclone releases heat energy at the rate of 50 to 200 exajoules (10¹⁸ J) per day, equivalent to about 1 PW (10¹⁵ watt). This rate of energy release is equivalent to 70 times the world energy consumption of humans and 200 times the worldwide electrical generating capacity, or to exploding a 10-megaton nuclear bomb every 20 minutes.

So an extra 1 Mton is not going to make much difference. Rojomoke (talk) 14:22, 3 September 2010 (UTC)

That logic doesn't quite work. The energy that the Sun transmits to the surface of the Earth is like exploding god-knows-how-many megatons every few seconds (the Tsar Bomba was only some 1.4% of the power output of the Sun), but the fact that it is dispersed over a great area means that it doesn't, you know, destroy us totally. Raw energy release is meaningless unless you take into account the scale. Nuclear bombs are impressive because they release a lot of raw energy in a very localized area. --Mr.98 (talk) 14:46, 3 September 2010 (UTC)

NOAA discusses it here. --Sean 14:23, 3 September 2010 (UTC)

Yeah, it's a really bad idea. Aside from the fact that it probably wouldn't affect the storm (storms are not just a "thing" you can blow up, but a complicated system made up of tiny parts — it's the not the kind of thing a nuke is good against!), you'd spread fallout over a huge area. The worst way to deal with fallout is to have it be taken up by some kind of weather system and rained down on everybody, rather than having it dilute in the upper atmosphere to safe levels. It would be a catastrophic disaster. --Mr.98 (talk) 14:46, 3 September 2010 (UTC)

A hurricane is a heat engine that feeds on high surface water temperatures and favorable atmospheric circulation to produce a rotating storm system over a scale of hundreds of kilometers. In order to disrupt a hurricane you must disrupt these fundamental conditions. A nuclear weapon, apart from making the storm into an efficient fallout spreader, is but a pinprick. Since a cyclone makes its living by transporting heat into the upper atmosphere from the ocean's surface, you could argue that any large production of heat would actually feed the storm (rather doubtful that enough heat could be generated to make a difference). Acroterion _(talk) 15:09, 3 September 2010 (UTC)

Wouldn't the pressure wave disrupt the eyewall? Googlemeister (talk) 15:28, 3 September 2010 (UTC)

Not in a meaningful way. It would be of short duration. Also, pressure shock fronts from explosions are "zero-mean" - loosely speaking, this means that an exactly equal amount of wind blows in and then blows back out. So the effect is no net change on the pressure (after the transient pressure shock dies away). For an entity that operates on the size- and time-scales the size of a hurricane, these momentary pressure spikes would be negligible. Nimur (talk) 18:12, 3 September 2010 (UTC)

Lets look at it from another angle then. If we wanted a weapon that could maximize casualties, all we would have to do is detonate a dirty bomb like a cobalt bomb inside of a hurricane, and that would assist in delivering casualties than just detonating the bomb alone? ScienceApe (talk) 15:39, 3 September 2010 (UTC)

Well, it sounds sort of plausible, but I doubt anyone here really knows. Or more to the point, anyone here who does really know, is probably not allowed to say. --Trovatore (talk) 18:40, 3 September 2010 (UTC)

Don't despair; User:Rocketshiporion will be around momentarily to simulate it for us... Nimur (talk) 21:05, 3 September 2010 (UTC)

But don't confuse a dirty bomb with a salted bomb... anyway, fallout effects are very hard to predict, even under ideal conditions. I think blowing up a cobalt bomb inside a hurricane would be a pretty good way to contaminate a large area. Whether it would increase the acute causalities much, I don't know. If you want raw casualties, just detonate a hydrogen bomb over a densely populated area. It's hard to beat that for raw numbers. If you were really going for mayhem, what you'd want to do is detonate a very dirty H-bomb over, say, New York, under conditions that would spread the fallout plume along the BosWash corridor. Castle Bravo transposed along the north east. Bleh. --Mr.98 (talk) 02:39, 4 September 2010 (UTC)

The more I think about this, the more I think that detonating an H-bomb in a hurricane would probably not increase the acute deaths at all, but would increase the clean-up costs, and possibly the long-term cancers, etc. The issue here is that you are diluting the fallout pretty considerably. That means less acute problems, more long-term problems (though at presumably lower exposures), and basically an impossible cleaning job. It would be a good way to make an entire region moderately radioactive, in other words. Whereas if you wanted megadeaths, what you want to do is detonate the H-bomb over a populated area under conditions that would spread the fallout only over other populated areas. --Mr.98 (talk) 13:38, 6 September 2010 (UTC)

• Interesting question. Theoretically, what would happen if a warm bubble were to be placed into the eye of an idealized tropical cyclone? Assuming the bubble is initialized at ~700mb, my intuition is that it would weaken the storm because the updrafts caused by the warm bubble would decrease the natural downdrafts in the cyclone, and thereby reduce the secondary circulation. As others have mentioned above, the effects would likely be very small. -Atmoz (talk) 23:06, 3 September 2010 (UTC)

Now, if you have a storm, category 3 or higher(a major hurricane), instead of detonating a nuclear bomb, why don't NOAA or the DOD try a hydrogen bomb? That would probably freeze the water, if not drop the tempature well below the minimum needed to sustain the power of a hurricane? Yeah, so sea life will die, but in the long run, won't that save lives and billions of dollars?

Novichok agent

According to the article, this nerve agent is a fine powder instead of a gas or vapor. As a weapon, would that be an advantageous trait or a disadvantageous trait? ScienceApe (talk) 15:05, 3 September 2010 (UTC)

According to this, "the nanopowder can bypass most of the chemical weapons detectors commonly used in the modern armies. The nanopowder can, however, firmly attach to the skin and the toxic compound directly penetrates into the body." --jpgordon^{::==( o )} 15:54, 3 September 2010 (UTC)

What is the standard reduction potential for ascorbic acid

I have used ascorbic acid to reduce iodine to iodide, copper(II) oxide to a red powder that could be copper(I) oxide or copper, and chlorine to chloride. I am curious as to what the reduction potential of ascorbic acid is compared to stannous ion, for example? --Chemicalinterest (talk) 15:17, 3 September 2010 (UTC)

chicken

what is the breed of chicken found here

File:Industrial-Chicken-Coop.JPG —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 15:56, 3 September 2010 (UTC)

White leghorn, one of the most popular in the United States. They might also be bantys, based on their combs. See also, chicken breeds. Nimur (talk) 16:35, 3 September 2010 (UTC)

They wouldn't be Bantams - Bantam hens are too small to be decent egg layers, except for boutique/niche markets. (i.e. they have small eggs and wouldn't be raised industrially). -- 174.21.233.249 (talk) 02:24, 4 September 2010 (UTC)

Question about being born brain dead

Are there some people who are born brain dead? What happens to them, are they kept alive? Prize Winning Tomato (talk) 18:55, 3 September 2010 (UTC)

Someone who is born brain dead usually does not survive, but not always. What happens to them if they do survive is usually up to the parents. They can be kept alive by machines, but (I believe) more often they let them die (by not providing any medical intervention). See also Anencephaly for a more extreme case. The bottom of that article also discusses the subject of their survival (see Baby K (which BTW does not have a NPOV). Ariel. (talk) 20:13, 3 September 2010 (UTC)

Ariel, just out of curiosity, what part of the Baby K article did you see as not having NPOV? I just read the article myself and it seems to have a disinterested tone, presenting basically just the facts. Perhaps since I'm reading the article from my own POV, it seems sufficiently neutral, but I would truly be interested to know if there were parts that you found not so neutral. --- Medical geneticist (talk) 00:31, 4 September 2010 (UTC)

"despite the fact that being born without a brain is not curable or treatable" has kind of a POV tone to it — a snipey sort of thing that doesn't really have anything to do with the argument that the mother made about it. If it were up to me, I'd maybe word it a little more neutrally: "despite there being no medical chance for an improvement in condition" or something like that. --Mr.98 (talk) 00:59, 4 September 2010 (UTC)

Thanks, I can see how that phrase was a little slanted; it looks like someone has already made some changes to the article! But overall, would you agree that the article handles a touchy subject pretty well? --- Medical geneticist (talk) 10:49, 4 September 2010 (UTC)

The article kept mentioning futile care and no chance of improvement, when those things don't really matter. Cancer patients are happy to get an extra year, this baby got 2 and a half. Doesn't seem futile to me. But the two quotes in "Significance of Baby K. case" were the real problem. "allocation of scarce resources"?? Medical care is not so scarce that this matters. And "right of physicians to make sound medical decisions"? So implying that killing the baby is the right decision, when maybe it's the wrong decision? Not to mention that the physician has no right to decide this at all, only the parents do. Ariel. (talk) 02:12, 5 September 2010 (UTC)

Thanks for the reply, Ariel. It seems that you have pretty strong feelings about the issue and I won't argue your points, which are covered in the article on futile medical care. But please recognize that your phrase "killing the baby" is highly inflammatory and misrepresents the decision to remove life support or withhold extraordinary measures. When a discourse becomes charged with this kind of terminology it's hard to imagine any meaningful interchange happening. --- Medical geneticist (talk) 12:24, 5 September 2010 (UTC)

(ec)You may be interested in our articles on anencephaly (note: disturbing images) and Baby K. Matt Deres (talk) 20:19, 3 September 2010 (UTC)

Brain death is the standard criterion for declaring a person dead, so somebody who is born brain dead is already not alive. Looie496 (talk) 22:45, 3 September 2010 (UTC)

But note that brain death has a very restrictive definition. Baby K specifically was apparently not brain dead, because she had a brainstem that controlled autonomic functions. Mere absence of all correlates of cognitive activity is not enough. I suspect that when a fetus experiences brain death, more conventional sort of death follows very quickly, so brain-dead-but-not-all-dead births are probably quite rare. --Trovatore (talk) 22:55, 3 September 2010 (UTC)

Existence precedes essence Smallman12q (talk) 23:58, 3 September 2010 (UTC)

I would be wary to draw too many conclusions about what a "brainstem" can or can't do, when we're speaking of the product of a completely abnormal pattern of development. This may not the same as if you took an ordinary brain and chopped off everything but the tail, and how much do we know about that? In ordinary meditation, a person may try to focus all attention on breathing, heartbeat, such simple functions as Baby K concerned herself with; and who can say whether this awareness is a higher-order interpretation of the actions of the brainstem, rather than a perception that occurs in the brainstem itself? It may be inefficient, even intransigent, for the religious to insist on trying to save a doomed child, but how tiny this inefficiency and intransigence truly is, beside the similarly dogmatic and hidebound traditions of the medical bureaucracy, which transform such a simple pump as a mechanical ventilator into a mysterious, all but religious implement that can only be used in a certain building by certain people under such conditions as to make the formal expense rival a lifetime's wages, and demand the right to decide whether a child lives or dies based on this. Wnt (talk) 14:03, 6 September 2010 (UTC)

How to calculate the north pole right ascension and declination of Mars

Does anybody know how to calculate the north pole right ascension and declination of Mars using axial tilt, inclination, argument of perihelion, and longitude of ascending node? The north pole right ascension of Mars is 317.681° and declination +52.887°. The axial tilt is 25.19°, inclination to ecliptic 1.85061°, argument of perihelion 336.04084°, and longitude of ascending node 49.57854°. I couldn’t figure it how to get that answer. BlueEarth (talk | contribs) 21:56, 3 September 2010 (UTC)

The information you list is not enough, you need e.g. the argument of Mars' northern vernal equinox. In the Martian spherical coordinate system analoguous to our (Earth-centric) ecliptic coordinate system the Martian north pole's direction is (right ascension = 270°, declination = 90° - (axial tilt)). Now it's a matter of converting this direction to other spherical coordinate systems: Convert it to the system which is still in Mars' orbital plane but uses the ascending node as the zero point of the right ascension; then convert it to the (Earth-centric) ecliptic coordinate system; and finally convert it to Earth's equatorial coordinate system. You can derive the conversion from one spherical coordinate system to another by trigonometry, or use the formulas in the article on celestial coordinate systems (I haven't checked if they are correct). Icek (talk) 19:42, 4 September 2010 (UTC)

I saw that there are no such formulae in celestial coordinate system, so the only formulae I saw is converting equatorial to horizontal coordinate system. I believed in ecliptic coordinate system has good formulae, but I tried to calculate it but couldn't get it. So I'm not sure if they're right formulae to calculate the north pole coordinate of Mars. So can you show me the formula how to calculate it between spherical coordinate systems? I think that the simplest formula I can think of to calculate the north pole right ascension of Mars is simple, 270+Ω, which I get 319.57854°, but close to the actual value of 317.681°. So we need a better formula. I also believe to calculate north pole declination is simply use axial tilt and inclination, so 90−25.19−1.85061=62.96°, but the actual value is +52.887°. It also need a better formula for that. So do I have to use SOHCAHTOA to calculate the north pole right ascension and declination of Mars. I tried to search in google to look for good formulas but I couldn't find it. BlueEarth (talk | contribs) 21:28, 7 September 2010 (UTC)

The general way of transforming from one spherical coordinate system to another one on the uni sphere is this: The vector to the unit sphere with the angles $\theta$ and $\phi$ (in the geographical and astronomical convention that $\theta$ = 90° at the north pole) is:

${\vec {k}}={\begin{pmatrix}cos(\theta )\cdot cos(\phi )\\cos(\theta )\cdot sin(\phi )\\sin(\theta )\end{pmatrix}}$

For transformations "in the same plane" (i.e. the "equator" of the system is the same) you only need to subtract the new zero point from $\phi$ (e.g. you want a coordinate system where instead of Greenwich Paris is at 0° longitude you subtract 2° 21′ from the old $\phi$ to get the new $\phi$). For transformations with a different "equatorial" plane but with the same zero point of $\phi$, you can use the following equations:

$sin(\theta _{new})={\vec {k}}(\theta _{old},\phi _{old})\cdot {\vec {k}}(\theta _{N},\phi _{N})$

$cos(\phi _{new})={\vec {k}}(\theta _{old},\phi _{old})\cdot {\vec {k}}(0,0)$

where the product of vectors is an ordinary dot product; $\theta _{N}$ and $\phi _{N}$ together are the position of the north pole of the new system: $\theta _{N}$ is (90° - (inclination or axial tilt)) and $\phi _{N}$ is 90° or 270°, depending on the convention (think of the particular system geometrically).

Using these two transformations, starting with ($\theta$ = 90° - (axial tilt), $\phi$ = 270°) you can chain together your way from Mars' orbital coordinate system to Earth's equatorial system: same-plane transformation into the ascending-node Martian system using the argument of the vernal equinox; then a transformation to an ecliptic system using Mars' orbital inclination; then a same-plane transformation to the standard ecliptic system using the argument of the ascending node times minus one; then the transformation to Earth's equatorial system using Earth's axial tilt. Icek (talk) 13:49, 14 September 2010 (UTC)

Why can we see stars?

I understand that some stars are very large and very bright, but they are also so unimaginably far away that my instinct tells me that they should not be visible to the human eye. Of course, they are visible, so I wonder, is it simply because they are so large and bright, or is there some other "effect" or "phenomenon" that makes them more visible than they would otherwise be. Thanks in advance for any input. Francis78 (talk) 22:21, 3 September 2010 (UTC)

Stars are not all the same distance away. Some very large, very bright stars are so distant that you can't see them. Some small dim stars are near enough to see.

The further away a star is, the dimmer it is. This fact is used at times to gauge the distance to other galaxies, for example by looking for the spectra of cepheid variables, which are a class of "standardized" stars with known luminosity.

The light receptors in your eyes are sensitive to photons hitting them. One or two photons won't register, but above some threshold, you will perceive light. Stars that you can see simply happen to emit enough photons that a sufficient number get into your eye, allowing you to see them. The closest star, our sun, isn't especially big or bright as stars go, but it's so close that you get a huge dose of photons when you look at it, sufficient to burn out your optic receptors.

You are correct to imagine that stars are so far away that they should not be visible. Starlight is, actually, quite faint. That's why you can't see stars during the daytime, because the light from our own star illuminates our atmosphere to drown out the faint light from other stars. ~Amatulić (talk) 22:30, 3 September 2010 (UTC)

Light from a star never "wears out", no matter how far away it is, any light that is emitted will keep going. So as long as a couple of the light photons hit your eye you can see the star. The light from the star does spread out, but stars make enough photons, that even when they spread out, enough of them remain next to each other for several of them to enter your eye at the same time. Ariel. (talk) 22:46, 3 September 2010 (UTC)

(Edit conflict with Ariel) You're quite right that we can't see most stars in the sky. Most stars in our galaxy are red dwarfs, which are very dim, even when quite close. In fact, the closest star to our solar system, Proxima Centauri is a red dwarf, and has an Apparent magnitude of about 11, well below the threshold that you can see with the naked eye. But even though there are lots of stars that we can't see, there are some that are big enough, bright enough, and close enough to us that we can see them. Some stars that we see are comparable in size to our sun, and are close enough that we can still get enough of their light to see with the naked eye; things like Sirius, Alpha Centauri, Epsilon Eridani, and others. See List of nearest stars. The ones with their apparent magnitude in light blue are bright enough to be seen with the naked eye. Notice that even among the stars closest to us, though, most cannot be seen. When you consider stars further away, it's only the largest and brightest stars that we can see: stars like Canopus, Rigel, and Betelgeuse are really enourmous, atypical stars, but it's only atypical stars that we can see at distances of hundreds of light years. I'm not sure what the farthest individual star that can be seen is, but I bet it's "only" a couple thousand light years away, easily still inside the Milky way galaxy. The Andromeda Galaxy is often cited as the furthest object that can be seen with the naked eye (at 2.5 million light years), and, while not strictly true (people have seen claimed to have seen Messier 83, for example), that's about the limit. And that's literally billion's of stars that can just barely be seen under good conditions. The point is, the vast, vast, vast majority of star's aren't visible from Earth (with the naked eye), but there are just a few (about 6,000 under good viewing conditions) that happen to be big enough, bright enough, and close enough that our eyes can (just barely, in most cases) make them out under very dark conditions. Amatulic also makes a good point: we can only just barely see even the stars that we can; we can't see them during the day, many we can't see when the moon is out, and a good deal of them we can't even see when there's any sort of light pollution at all. Buddy431 (talk) 23:04, 3 September 2010 (UTC)

So how many photons does it take to trigger our receptors? Clarityfiend (talk) 02:48, 4 September 2010 (UTC)

It depends on a lot of variables - but under ideal conditions, just one photon is enough to trigger a rod cell to fire. SteveBaker (talk) 05:29, 4 September 2010 (UTC)

And not many for it to be treated as signal rather than noise, see Can a Human See a Single Photon? and Optimization of Single-Photon Response Transmission at the Rod-to-Rod Bipolar Synapse. Sean.hoyland - talk 05:42, 4 September 2010 (UTC)

Also keep in mind that even the best star viewing conditions do not come close to these experimental conditions; if nothing else, light from other stars ruins the total dark that was used. I don't know how bright a star actually has to be to be visible, but it's certainly a couple order's of magnitude greater than these experiments suggest (Which is still very, very dim). Buddy431 (talk) 14:58, 4 September 2010 (UTC)

It's been remarkably hard to find out how much energy a given star actually deposits on the Earth (its flux). If we could find that, then it should be easy to calculate a number of photons/second/square cm, or whatever. Flux is used directly to calculate apparent magnitude, so obviously there are a table of star fluxes somewhere, but I can't find them anywhere. If we even found the flux from a single star, we could calculate it for any other stars, based on the widely reported apparent magnitudes. That's odd that the apparent magnitudes are so widely reported, but the underlying, physical data that is used to calculate them is not. Buddy431 (talk) 15:15, 4 September 2010 (UTC)

It's easy! We know the flux deposited by one star...the sun! That's a pretty typical star and there is tons of that kind of data in sun and sunlight. Then you just have to figure the ratio of the distance of your chosen star to the distance to the sun - square that number and divide the insolation flux by that number. I'd do it for you...but I'm kinda busy right now. SteveBaker (talk) 23:26, 4 September 2010 (UTC)

The Sunlight article only appears to have total flux at Earth (1.3 KW/m², give or take), while we need information for just the visible range. Mr. 87.81, below, is probably right that we need to be careful what we actually want, and at this point, I don't care enough to figure it out. However, if we user the entire luminosity, then we find that a magnitude 3.2 star (easily seen under most conditions) would give a flux of only one 10¹⁰th that of the sun. Using the sun's total flux (rather than visual) of 1300 W/m², that would give the magnitude 3 star a flux of only 1.3x10^-7 W/m², or 1.3x10^-11 W/cm² (the approximate size of a dilated eye). Assuming a wavelength of 500 nm (right in the red/orange region), each photon of which has 4x10^-19 J of energy (someone might want to check my math there), that gives 3x10⁷ photons per cm² per second. Obviously, not all starlight is in the visible region, and I've made some huge assumptions and approximations, so that number should be taken with a large grain of salt. Buddy431 (talk) 01:15, 5 September 2010 (UTC)

(Edit Conflict) That's probably because, historically, apparent visual magnitudes were not calculated from instrumental flux measurements, but estimated directly by human observations. This might sound rather imprecise but actually it easily yields figures accurate to 1/10 1/100 [belated correction - apologies] of a magnitude, by repeatedly comparing several stars in a single telescopic field of view, some with already established magnitudes, and judging their relative brightnesses. More precise visual photometric measurements were made using photographic plates (once these were available), though care in interpretation was needed because the logarithmic response of the human eye is not equivalent to the geometric(?) way in which photographic images form, and different plates respond differently.

Once we became interested in total flux, aka Luminosity, (i.e. all wavelengths, not just the visual ones) absolute flux measurements became more useful, but because measured values depend on variable elements - such as the momentary local 'seeing' or transparency of the atmosphere, the altitude of the star above the horizon and the altitude of the observatory above sea level (and hence the thickness of atmosphere the star is being viewed through), whether the instrument is in fact in orbit and outside the atmosphere entirely, and the characteristics of the individual instrument - raw data has to be carefully calibrated anyway and the results are generally thought to be of interest mainly to the academic specialists, but you should be able to track such data down. You may find searching on Stellar Luminosity (rather than 'flux') helpful. 87.81.230.195 (talk) 23:35, 4 September 2010 (UTC)

This is an interesting question: if a star is infinitesimally small, why can the retina perceive it? Of course, stars twinkle, the eye vibrates with each pulse, the lens is imperfectly focused... yet my feeling is that all of these things decrease, not increase, the ability to see the stars. So my attention would focus on the photoreceptor cell, i.e. the rods. Now consider that looking up at a hemisphere of sky, about 3000 stars are visible, and there are 120 million rods; thus for any given star, on average about 40,000 rods deal with a sector of sky containing that one star and no others. That's the square of 200; and so, roughly, a line of 200 rods should separate any two visible stars in the sky. Now "retinal ganglion cells respond quite reliably to single rhodopsin isomerizations (R*) with two to three spikes"[1] Bear in mind that a star's image is sitting atop not a single membrane to detect it, but a tremendous stack of disklike membranous projections of the rod cell, each with its own chance to detect the light. And from that source, about 15-20 rods send signals to a rod bipolar cell, and about 26 rod bipolar cells send signals to an amacrine cell. So the perceived size of a single detected photon covers a territory of about 500 cells, or a line of about 22 rods. The neural size of a star should thus be about 22/200 of the distance to the next one, which seems plausible in a perfectly dark night sky. Its faint light, focused on a single point, is actually sufficient to set off a rod cell over and over again* to produce the image seen. Wnt (talk) 13:44, 6 September 2010 (UTC)

* - as explained above,[2] it takes about 9 detected photons to perceive the light consciously, or 90 photons reaching the eye. The figure above that stars can be measured to 1/100 of a magnitude is interesting, though, because magnitudes differ by a factor of 2.512, and the 100th root of this is 1.00925, so a 1% difference in brightness is visible. So if that number extends to the dimmest visible star, that would mean that a one-photon difference in brightness can be seen! But it would be nice to see the source for this, to see whether it applies to very dim stars. Wnt (talk) 19:28, 6 September 2010 (UTC)

Looking at Fundamentals analytically

Can one define a fundamental concept analytically, or will this always lead to a circular definition?Smallman12q (talk) 23:24, 3 September 2010 (UTC)

I don't understand the question. Do you mean defining the term fundamental concept, or do you mean defining particular fundamental concepts such as energy? And what do you mean by "analytically"? Looie496 (talk) 23:57, 3 September 2010 (UTC)

I mean fundamental concepts such as though pertaining to Quantum mechanics and classical mechanics. By analytically, I mean separating into relevant constituent parts.Smallman12q (talk) 00:03, 4 September 2010 (UTC)

Well, I'm not a philosopher, or a scientist. But it's of note that some of the definitions of fundamental concepts have definitely led to potentially productive circular definitions. I'm thinking of Einstein's basic work in redefining things like "distance" (what a ruler measures) and "time" (what a clock measures). Those are superficially pretty unsatisfying definitions, but the point is to refocus attention less on metaphysical definitions and more on practical definitions, and from there, a very useful theory falls out rather nicely. Anyway, I don't think this resolves your question, but I offer it up as a possible contribution in thinking this through. --Mr.98 (talk) 00:46, 4 September 2010 (UTC)

Relevent related information to this question would be the idea of the axiom, that is a concept which is taken as absolutely true but unproven (or unprovable), and Axiomatic system, which are the backbone set of axioms (fundemental concepts) of a system. Also the theorems of Kurt Gödel, which are closer related to mathematics but still germaine to the OP's question, especially Gödel's incompleteness theorems, and the philosophy of Ludwig Wittgenstein, dealing with the relationship between language and reality. --Jayron32 02:45, 4 September 2010 (UTC)

Wittgenstein -- meh. He may have had something useful to say on something; I've never read him closely enough to be sure. But when he wrote on mathematical logic, specifically on Goedel (and Cantor) he made absolutely elementary errors. The word crackpot is not too strong for his take on these things. --Trovatore (talk) 23:43, 4 September 2010 (UTC)

Yes - Axioms are the key here. Mathematically, one can take a set of arbitary axioms (which may or may not be "true" - in the sense of them being a true representation of the real world) and make some deductions from that - perhaps even prove some interesting theorem or other. But when you do that, you are always saying: "This thing that I've proved is 'true' providing that the axioms that I started with are 'true' - otherwise, all bets are off".

In the world of science, things are a little different. Rather than taking 'axioms', you'll generally be taking observations of experiments or of nature. You may go through the same process of logic, mathematics, reasoning - and you'll come up with some result. Then you can say "on the basis of this pile of observations - I deduce the following". The observations are kinda like axioms in mathematics in that your conclusion is only valid so long as those observations are correct. What Einstein did was a little different. He noted the results of some experimental observation - things like the Principle of Invariant Light Speed which had been established by the Michelson–Morley experiment and others. But he also picked some axioms (in the mathematical sense). He supposed things like "The Principle of relativity" - which is (roughly) that the laws of nature are the same over all time that they are the same regardless of the person experiencing them. His subsequent deduction of the Theory of Special Relativity is rock solid - but only if the laws of nature are the same everywhere and only if Michelson-Morley (et al) didn't screw up their experiments. But if either of those two things are untrue - then all bets are off. SteveBaker (talk) 04:59, 4 September 2010 (UTC)

Axiom is the term I was looking for. ThanksSmallman12q (talk) 22:49, 4 September 2010 (UTC)

It is of note that there is considerable scholarly debate as to whether Einstein cared much about experimental results when establishing his theory. The work of Gerald Holton in particular argues against this. By contrast, the work of Peter Galison emphasizes the importance of the technological-cultural-philosophical context of Einstein's work at the patent office. Anyway, I'm just putting out there that the "Einstein saw an experimental result and ran with it" theory is not actually held by most historians of physics. It's more like, "Einstein had a number of reasons for believing in the invariance of light, and didn't totally trust experimenters anyway, and ran with his theory because it aligned with his Machian positivist inclinations, and seemed like the only intuitive way out of the complicated aether theories," and so on. --Mr.98 (talk) 14:23, 5 September 2010 (UTC)

Blow hole flap?

Is there an anatomical name for the flap that covers a cetacean's blow hole? - or does it just clench shut? Adambrowne666 (talk) 23:41, 3 September 2010 (UTC)

My understanding is that it doesn't have a cover. It is surrounded by a ridge called the "rostrum" that acts as a splash guard, but it closes by squeezing shut. Looie496 (talk) 00:02, 4 September 2010 (UTC)

I'm not so sure about that. Sources say 'rostrum' apparently refer to the animals snout! See Rostrum (anatomy), also see the diagram here, which is supposed to be sourced from Seaworld. From the Seaworld website here under HEAD, 2. "In front of the melon, a bottlenose dolphin has a well-defined rostrum (snoutlike projection)." I can't find a specific name for a flap over the blowhole.
• A search on Wikipedai for "blowhole flap" give only one result at Bottlenose dolphin, which is referenced back to the same page on Seaworld as above. "6. A single blowhole, located on the dorsal surface of the head, is covered by a muscular flap. The flap provides a water-tight seal." 220.101 talk^\Contribs 11:38, 4 September 2010 (UTC)

This Scientific American article [3] describes the blowhole as a muscular flap, which is normally closed unless contracted. Perhaps the right analogy to make is to the anus or urethra - there might not be a separate (scientific...) word for the hole as opposed to the structure that defines the hole. But I know little of cetaceans... Wnt (talk) 07:44, 6 September 2010 (UTC)

September 4

Snoring = Collapsed Trachea?

I've often seen in videos of riots or so forth that people who are assaulted and take severe blunt damage to their face/head start to make a very distinct and audible 'snoring' sound when they are down. They appear to be conscious (though sometimes barely) while doing this. I looked at various reasons why people snore and generally found an indication of a difficulty/blockage of the airway. Does anyone know what happened to them to cause this? I assume a collapsed trachea but I'm not particularly adept in anatomy or biology. Robots.by.hand (talk) 01:03, 4 September 2010 (UTC)

A truly collapsed trachea is a very serious event that's likely to lead to death without immediate intervention. I rather think you heard stridor due to someone being winded, a very unpleasant but hopefully very temporary event frequently caused by one's lungs being used as a dudelsack. -- Finlay McWalter ☻ Talk 01:25, 4 September 2010 (UTC)

The people I've seen in this condition did not sustain serious blows to their chest/stomach/back. And some of the people were fine after a short while (stood up/walked off after a paramedic/police officer instructed them to breath through in their nose and out through their mouth while they were on the ground for a few minutes in some videos) so it seems it wasn't a collapsed trachea. Robots.by.hand (talk) 01:42, 4 September 2010 (UTC)

My experience is that it's when I sleep in the wrong posture. Sleeping directly on the back or certain stuff where some flappy body organs do flappy things relaxed and causing the snoring. Are you ready for IPv6? (talk) 07:29, 4 September 2010 (UTC)

World War III and Alein invasion

HOw likely is WWIII and alein invasion? Like is it for certain that WWWIII will never happen ever again and there won't be any more world wars? If it isn't and if WWWIII happens, will there be conscription reinforced in lots of countries where it's abolished? What about the US and selective service?

And how about alein invasion? If aleins do invade Earth and exterminate everyone how likely is it? What about meteors? Do people know when the next meteor will hit Earth. Lastly, will humans be extinct by the 25th century? Or sooner? HOw do people predict the Earth will be like in the 25th century.

I've read the above guidelines so don't say please that these questions ask for opinions. I'm not asking for opinions just to be clear. I'm asking for reliable sources or information that gives evidence for any of the above phenomena and past experience that could back up the occurence of the above phenomena.

thanks guys ... —Preceding unsigned comment added by 114.72.206.160 (talk) 08:33, 4 September 2010 (UTC)

You have asked five seven (by my count) separate questions above; at least one of them requires prediction of unforseeable future events, which the Reference Desks do not (and cannot) undertake. Trying to ask all of them under one heading will lead to confusion and unwieldiness: I suggest you repost your questions one at a time (waiting for each to be dealt with before posing the next one) so that each can be addressed (or not) separately. 87.81.230.195 (talk) 10:52, 4 September 2010 (UTC)

Unfortunately you won't get any reliable sources on the above phenomena. All we can give you are opinions, so here's mine.

"How likely is WWIII and alien invasion?" - We don't know. No one does, but I'd speculate that the former is more likely than the latter (given we've already have two!).

"Like is it for certain that WWWIII will never happen ever again and there won't be any more world wars?" - It is by no means certain that there won't be another World War. I'd say it's unlikely unless we get into another severe paranoia, power-bent struggle like the Cold War but we can't predict the future.

"If it isn't and if WWWIII happens, will there be conscription reinforced in lots of countries where it's abolished? What about the US and selective service?" - I'd say conscription is unlikely in Western countries, at least to the extent it was present back in World War I & II. Most warfare in modern technological countries is carried out almost in proxy with aircraft, ships and bombs. Of course troops are still necessary, but not to the same level as was required by trench warfare.

"If aleins do invade Earth and exterminate everyone how likely is it?" - If aliens invade Earth and exterminate everyone then obviously it's 100% likely. Sorry, I'll stop joking around, I know what you meant. How likely is it that aliens will invade our planet and kill everyone? Who knows. We're still trying to figure out whether aliens exist, let alone are they violent or peaceful. If they exist, they could be either.

"What about meteors? Do people know when the next meteor will hit Earth?" - Not for certain. Most meteor impact predictions are just that, predictions based on probabilities! I can't remember the specific examples off my head but there are predicted close-encounters in the near future, but none are predicted to be close enough to cause concern.

"Lastly, will humans be extinct by the 25th century? Or sooner? HOw do people predict the Earth will be like in the 25th century?" - Again, you're asking us to answer (with reliable sources?! ha!) a question which no one can know the answer to. It depends on too many factors. Do we stop climate change? Do we survive it even if we stopped emitting all ozone depleting gases now? Will a meteor actually hit Earth that we've missed? Will there be a global, nuclear war? It's impossible to predict. As for how people supposedly predict what life will be like in the 25th century: they're guessing. No one knows. We take predictions on technology by extrapolating how we've progressed/how we're progressing, but it's not very reliable in the long term. Regards, --—Cyclonenim | Chat  11:09, 4 September 2010 (UTC)

Our article on meteorites says that "an estimated 500 meteorites ranging in size from marbles to basketballs or larger do reach the surface each year" - so there will probably be one or two meteorite impacts somewhere on Earth in the next 24 hours. NASA has catalogued around 1,000 Potentially Hazardous Objects with diameters of 150m or larger which could potentially impact the Earth at some remote time in the future, but none has ever scored above 4 on the 10-point Torino Scale of impact hazard, and none currently scores above 2. Gandalf61 (talk) 12:41, 4 September 2010 (UTC)

poisoned letter

what is a poisoned letter like that that killed

http://en.wikipedia.org/wiki/Ibn_Al-Khattab —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 10:48, 4 September 2010 (UTC)

I don't think any details are available about that or about the many other reported cases of Chechen rebels being a poisoned by the FSB other than that in the more recent cases using food, the poison was slow acting. Sean.hoyland - talk 11:15, 4 September 2010 (UTC)

Whilst I doubt we can say for certain, it's likely to either be an airborne toxin contained within the envelope, such as anthrax, or a toxin coated on the letter that, when touched, is absorbed through the skin. Regards, --—Cyclonenim | Chat  11:50, 4 September 2010 (UTC)

Also, you may be interested in Laboratory 12. Sean.hoyland - talk 12:37, 4 September 2010 (UTC)

I found a FAS report [4] which says "The Chechens claim that the agent coated a letter to Khattab with a fast-acting nerve agent, possibly sarin or a derivative." A number of sources seem to agree at least that it was fast-acting.

What is so mysterious about the Russian poisonings is that usually they use some exotic element - thallium, polonium, mercury - something so obvious and undegradable that if you dug the corpse up ten thousand years from now you could still tell the victim was poisoned, and, in the case of the polonium, allowing the murder suspects to be tracked by their exposure. I don't know why a secret agency would use such unsecret tools, especially if they have something as devastating as a "contact nerve gas" in their arsenal. Wnt (talk) 17:22, 4 September 2010 (UTC)

With the case of the polonium, a lot of analysts saw it as a calling card. "We don't care if people know it was the Russians who did it," and so on (since access to polonium is pretty restricted). Who knows, though. --Mr.98 (talk) 19:08, 4 September 2010 (UTC)

Alexander Litvinenko poisoning describes what happened when the Russians poisoned someone with Polonium. It's pretty obvious that they wanted to be found out. They were sending a message: "If you mess with us, we can kill you even if you think you're safe." Polonium is only formed in few nuclear reactors in the world - the 'signature' of the isotopes formed made it a trivial exercise to figure which one it came from. They must have realized that when picking such an exotic poison. SteveBaker (talk) 23:21, 4 September 2010 (UTC)

I can't find anything online linking the two, but I should add that the properties of this apparent contact nerve gas sound like what you might expect from the solid skin-absorbable dust described for the Novichok agent in a discussion here a week or so ago. Maybe this answers both questions... Wnt (talk) 21:53, 6 September 2010 (UTC)

Where does the ink from whiteboards go when you erase them?

This may sound like a silly question, but what happens to the ink when you clean a whiteboard (like this) with an eraser (like this)? I used to think it went into the eraser, but when I tried to clean mine, which must have been used hundreds of times, with water and soap, I noticed no ink would come out of it.

Does it pulverize and go into the air (ready to be inhaled), or does it somehow magically diffuse deeply into the eraser where it can't be washed out? Is it even real ink in those pens, or something else?

Thanks for your ideas, --Sven Eberhardt (talk) 13:00, 4 September 2010 (UTC)

From personal experience, the `ink' is not absorbed in to the eraser at all, the eraser just provides a source of friction. Flaky dust can settle into the tray at the bottom of the whiteboard if you have one, or disperse into the room. SemanticMantis (talk) 15:10, 4 September 2010 (UTC)

Yes, a thick layer of dust can accumulate under the whiteboard if it is not cleared up. A small amount might go into the air, but this is much less dangerous than chalk dust. Dbfirs 16:29, 4 September 2010 (UTC)

Our whiteboard article is in horrible shape. The statement there that the inks are less toxic has been {{cn}}-tagged for ages. I know some professors with specific allergy/reaction to chalk, but in general calcium sulfate is pretty benign from a chemical standpoint. DMacks (talk) 06:26, 5 September 2010 (UTC)

Thanks for your replies. I find it hard to believe that pen ink is less toxic than chalk as well. But I didn't have any problems with either yet ;) --Sven Eberhardt (talk) 18:01, 5 September 2010 (UTC)

From experience, most ends up on your hands. -Atmoz (talk) 02:25, 5 September 2010 (UTC)

Looking at the sun

If someone looks at the sun with the naked eye on a clear day with no clouds, would it damage their eyes? I assume not...and no this isn't medical advice I don't intend to go out looking at the sun and besides it's cloudy.--92.251.223.71 (talk) 13:50, 4 September 2010 (UTC)

Looking directly at the sun is very likely to damage your eyes if done for any, even a short, length of time. Human eyes are not designed for that intensity of light. It is probably as stupid a thing to do as looking into a Laser It could very easily burn your retina.
Do Not Do It! 220.101 talk^\Contribs 14:10, 4 September 2010 (UTC)

See Solar retinopathy "Vision loss due to solar retinopathy is typically reversible, lasting for as short as one month to over one year." 220.101 talk^\Contribs 14:15, 4 September 2010 (UTC)

See also this advice from NASA SpinningSpark 14:12, 4 September 2010 (UTC)

Eclipses are especially dangerous, because the pupil will dilate in response to the darkness, making damage more likely. See Solar eclipse#Viewing. I'm not saying it's safe to look at it any other time, but usually the brightness makes it very difficult to look at; the pupils contract, they eyes close, and there is a strong reflex to look away. These responses are attenuated during an eclipse, making prolonged exposure (and thus possible damage) more likely. Buddy431 (talk) 14:54, 4 September 2010 (UTC)

As always, Wikipedia has an article on it..Sungazing --Aspro (talk) 14:15, 4 September 2010 (UTC)

But humans and their ancestors have been around for millions of years. Surely we would have evolved to tolerate looking at the sun? It would have been vital to look in the direction of the sun for hunter gatherer peoples stalking prey. If they could go blind that easily wouldn't they have died out? I know your eyes can be sunburned temporarily, but I can't imagine going blind. To take your wording 220.101, the human must be "designed to look at the sun", musn't it?--92.251.223.71 (talk) 14:19, 4 September 2010 (UTC)

Perhaps the ones that looked at the sun couldn't find a mate or were eaten by the prey they were stalking that avoided detection by having a blinding light behind them leaving only the ones that don't look at the sun. Sean.hoyland - talk 14:46, 4 September 2010 (UTC)

(edit conflict)'92' I challenge your assertion "It would have been vital to look in the direction of the sun for hunter gatherer peoples stalking prey." If so, then the sun would be low in the sky and significantly less intense due to coming through a thicker section of atmosphere. People get cataracts, Pterygium (conjunctiva) and similar at least partly by exposure to sunlight. This link here to a PDF actually shows on (p.2) the damage caused by staring at a solar eclipse. Please read the references and links you have been given. N.b Your IP address indicates you are in Ireland, so the intensity of your light will be far less than where I am in Australia, but it is still a bad idea to stare at the sun! 220.101 talk^\Contribs 14:50, 4 September 2010 (UTC)

This all depends on how long you look for, and it'd be pretty damn hard to stare at the sun long enough without instinct kicking in and making you look away. This is similar to trying to suffocate yourself by holding your breath. The sun is not magic; one quick look won't damage your eyes forever RECYCLED FIRE (talk) 15:02, 4 September 2010 (UTC)

It depends on a number of factors, not just how long. As I mentioned your local latitude is a factor, as is how high the sun is in the sky. But the fact remains (read the references supplied please!) that it is possible to cause damage to you eyesight by looking at the sun. 220.101 talk^\Contribs 15:24, 4 September 2010 (UTC)

It's faulty reasoning to think your "instinct" or "reflex" would be good enough to keep you safe from harm. For example, if you touch a hot stove, your reflex will pull your hand back quickly - but you still may suffer a third degree burn! The same applies for the eye - it is well known in optics labs that your blink reflex is too slow to prevent damage if a powerful laser shines in your eye. The same caution is warranted with regard to the sun. Do not trust your reflex to be fast enough to prevent permanent damage. It is known from prior documented experience that your reflex will not be fast enough. Nimur (talk) 16:37, 4 September 2010 (UTC)

Holding your breath is an incredibly poor example too. A better (but still far from perfect) example would be holding your head under water Nil Einne (talk) 16:45, 4 September 2010 (UTC)

A great deal of eye damage was suffered by early sextant users due to the design requiring the sailor to look directly at the sun.[5] SpinningSpark 17:29, 4 September 2010 (UTC)

Looking at the diagram of one from that book, it shows a small telescope as part of the design. But where the naked eye is concerned, this is starting to sound a little silly. The Sun just sits there in the middle of the sky - there's no way not to look at it now and then. The article cites photochemical damage rather than a burn, but either way, I assume the retina takes time to cook - though I didn't quickly find data on short exposures. And, in one of the most pathos-tinged experiments I've ever read of, it is apparent that staring at the sun for a full hour does not greatly reduce vision in the short term, though significant damage is apparent histologically. (PMID 1209815) Apparently sungazing can be used therapeutically, under bizarre circumstances. (PMID 3428072) Wnt (talk) 17:42, 4 September 2010 (UTC)

it shows a small telescope as part of the design, no it doesn't, the diagram I linked is a pre-1590 sextant. The telescope was invented in 1608 so not likely, try reading the text. Anyway, my apologies, I must have got it completely wrong (along with NASA and the medical profession) it is perfectly safe to stare at the sun, do it as much as you want. SpinningSpark 22:54, 4 September 2010 (UTC)

Sorry, Google is subjected to the "restricted page" thing, and apparently the two of us were issued different restricted pages and weren't looking at the same picture. Does it specifically say that pre-1600 sextant users were suffering permanent eye damage? Wnt (talk) 07:33, 6 September 2010 (UTC)

The NASA article refers specifically to eclipses, which, as I explained above, have a number of factors that make them more dangerous than looking at the sun under normal circumstances. Surely staring at the sun, intentionally, can cause damage, sometimes permanent. But as for unintentionally, briefly glancing at the sun, I think it's a lot less clear. Maybe Nimur's right that our reflexes aren't fast enough to prevent damage, but the sun and a powerful laser are much different beasts. I don't know the answer, but I tend to agree that a lot of the danger is over-hyped for incidental exposure. People do look at the sun (sometimes intentionally, for long periods of time), and they don't just go blind. There's damage, to be sure, but we're constantly wearing out our bodies, and in many cases, the damage is at least partially temporary (see Solar retinopathy). It's also interesting that that article describes the damage as being photochemical, rather than thermal (where a laser generally causes thermal damage, if I'm not mistaken). Buddy431 (talk) 00:43, 5 September 2010 (UTC)

Electric vehicles

When do you estimate that 50% of automobiles in Canada/US will be electric? —Preceding unsigned comment added by 76.68.167.110 (talk) 14:36, 4 September 2010 (UTC)

2050, when the oil runs out. See Peak oil and Oil depletion. RECYCLED FIRE (talk) 14:59, 4 September 2010 (UTC)

That's very pessimistic! See this. --76.68.167.110 (talk) 15:25, 4 September 2010 (UTC)

There is a fundamental misunderstand of economics here. Oil will never run out. It will just get more expensive until alternatives become viable to develop. There is no need to worry. I think stuff like hydrogen is the most promising and would be more likely than electricty.--92.251.223.71 (talk) 18:08, 4 September 2010 (UTC)

Neither hydrogen nor electricity are source of energy - they are methods of distribution. See our article primary energy and our very thorough energy development article. Nimur (talk) 18:48, 4 September 2010 (UTC)

We're talking about cars, not electricity generation.--92.251.213.233 (talk) 20:36, 4 September 2010 (UTC)

We can't answer this question. It's possible (for example) that the hydrogen economy takes off with hydrogen filling stations popping up all over the place. If that happened then there might not ever be 50% of electric cars. On the other hand, if the infrastructure for hydrogen doesn't happen and a political will to attack global warming seriously somehow kicks in - then it could probably happen in 10 to 20 years. That "political will" thing is a tricky business. One major disaster somewhere in the world that could be definitely attributed to climate change - or one Disney-style documentary about the plight of the cute baby Polar Bears - could take a hold of the public imagination and make it be so socially unacceptable to buy a non-green car that we'd flip over in about the time it takes cars to get too old to keep on the roads...10 years. But it's unfounded speculation...and we don't do that here. SteveBaker (talk) 22:34, 4 September 2010 (UTC)

We dont speculate here.--88.104.91.225 (talk) 23:14, 4 September 2010 (UTC) —Preceding unsigned comment added by 88.104.92.244 (talk)

Predicting the future isn't always speculation. Since there are already electric cars lined up for market roll-out in 1-2 years (Nissan leaf), I'm not surprised if we have 50% electric cars by 2020. —Preceding unsigned comment added by 76.68.167.110 (talk) 00:49, 5 September 2010 (UTC)

To redirect this line of inquiry - are there reputable, freely-available market predictions from scholars or business analysts that predict electric car adoption rates over the next decade? These could be suitable and encyclopedic sources to base predictions on; they would be grounded in actual analytic process and data, instead of idle speculation. Nimur (talk) 01:52, 5 September 2010 (UTC)

Do you mean electric motors powered by onboard gas generators? Because I think those will become more and more popular. But if you mean electric cars powered by the grid, I don't think they ever will reach 50%. If we run out of oil we'll make gasoline from coal, via the Fischer–Tropsch process. Hydrocarbons are likely to always be the power source for cars, hydrogen has too many problems to be likely. Ariel. (talk) 02:22, 5 September 2010 (UTC)

Wild plant with large purple snapdragon flowers, serrated leaf edge

About four or five feet high growing in damp streamside conditions in southern England. Non-woody stem. The purple snapdragon-like flowers were about an inch across. Does anyone know what it is please? It was not foxglove nor was it Rose Bay Willow Herb. Thanks 92.29.127.175 (talk) 17:53, 4 September 2010 (UTC)

Sounds like Himalayan Balsam to me. --TammyMoet (talk) 19:14, 4 September 2010 (UTC)

That's it, thanks. I had guessed that it was'nt a native British species. 92.29.116.238 (talk) 20:36, 4 September 2010 (UTC)

Forward-sweeping wings

Does anyone know of an aircraft with variable sweep wings that sweep forward? I am not talking about aircraft with wings that sweep forward to make a delta, like the Northrop Switchblade, I am talking about something that sweeps forward to make a wing like the Sukhoi Su-47 or the Grumman X-29. Thanks, --The High Fin Sperm Whale 18:55, 4 September 2010 (UTC)

Just from a quick read, I would think not. The forward-swept design increases performance but also increases torsional stress on the wings; since variable wing aircraft would naturally be structurally weaker than fixed-wing aircraft, such a design would be an engineering nightmare. --Ludwigs2 02:00, 5 September 2010 (UTC)

Wouldn't the Northrop Switchblade then be an engineering nightmare? --The High Fin Sperm Whale 04:22, 5 September 2010 (UTC)

Not my field by a long shot, but since the plane exists, I'd guess not. I was merely noting (well, opining, really) that the swept-forward design seems to put more stress on the inner joint of the wing - the articles on the two planes of that design say that more lift is generated by the inner part of the wing, and that the forward design tends to cause the wing to twist (which I am assuming means a rotation parallel to the plane of movement). the variable wing design requires some kind of joint near the plane body (which is right where the extra stress develops in the wing forward design), and a movable joint is always going to be weaker than a rigid structure - hence the nightmare. I'm not suggesting it's impossible, but the planes are already designed to within a fraction of the limits of the materials (the sukhoi article notes that the plane's top airspeed is limited by the materials). but that's all an educated deduction - I'm willing to be corrected by someone more knowledgable on the subject. --Ludwigs2 04:51, 5 September 2010 (UTC)

Apart from the Northrop Switchblade I don't know of any such aircraft. It is very likely there will be no such aircraft, for the following reason. Variable-sweep is a highly-specialised and expensive solution to a niche problem - namely the need to travel at high supersonic speeds at high altitude but also to have moderate takeoff and landing distances. (The GD F-111 was originally conceived as a carrier-borne aircraft that could travel around Mach 2 at high altitude. The variable sweep allowed both of these requirements to be met.) Forward-sweep is a highly-specialised and expensive solution to a different problem - the need for high agility in combat. No air force would attempt to solve both these problems with one aircraft design - if an air force did attempt to solve both with one design it would be a compromise and so would be vulnerable to enemy aircraft and missiles.

The high Mach number of variable sweep aircraft like the F-111 and F-14 seems not to be such a high priority now as it was forty years ago. The USAF no longer operates either of these aircraft types. I think its only variable-sweep aircraft is the B-1 bomber. The current generation of fighter aircraft have fixed-sweep, less sweep-back and lower wing loadings than their predecessors because less importance is placed on Mach number at altitude, and more importance is placed on rate of climb and maneuverability.

Forward sweep is better than aft sweep for reasons of aerodynamics, handling qualities and agility. That begs the question why weren't all the early supersonic aircraft equipped with swept-forward wings? The answer is the nasty way in which swept-forward wings twist so that when they deflect tips upwards they also twist so the angle of attack increases. Not nice! However, with modern composite structures, which can be given different stiffness in one direction than at ninety degrees to that direction, it is possible to reduce or reverse the way in which swept-forward wings increase their angle of attack when they deflect their tips upwards. So an aircraft with variable sweep and swept-forward wings would be a strange bird indeed. People would look at it and say What is the designer trying to achieve? Is he trying to design a high Mach number aircraft, or a highly agile combat aircraft? The Switchblade is also intended to be a highly-specialised solution to a niche problem. I don't know what its role is to be, but it certainly isn't simply to be very fast and/or very agile. It is presently an experimental aircraft rather than one which has a clearly-defined role. Dolphin (t) 08:44, 5 September 2010 (UTC)

radio

Resolved

If someone talks about "breakthrough" when referring to radio equipment, what are they talking about? 82.44.55.25 (talk) 19:17, 4 September 2010 (UTC)

It's probably a generic jargon-y term to refer to finally getting signal out of static. This could be by changing signal parameters, moving the transmitter/receiver, aligning the antenna, and so on. I don't think I've ever heard "breakthrough" in reference to a specific phenomenon. Nimur (talk) 19:39, 4 September 2010 (UTC)

Adjacent-channel interference is a brakethrough of sorts. Can you give more info? --Aspro (talk) 20:35, 4 September 2010 (UTC)

Here is a Radio Ham thingy on brakthrough. [6] It can include things like when you set up a PA system and the local cab company swamps your amp, so that you can here their calls and all.--Aspro (talk) 20:52, 4 September 2010 (UTC)

Thanks! 82.44.55.25 (talk) 22:16, 4 September 2010 (UTC)

raining oil

Is it possible for a hurricane too rain oil thats on warm tropical oceans during hurricane season or will it only take the warm water under the oil. --86.41.140.251 (talk) 19:58, 4 September 2010 (UTC)

No. Even Popular Mechanics considers it unlikely, and that publication has a reputation for spreading sensationalized semi-truths to sell copy! In reality, oil does not evaporate easily, (well, crude does contain a tiny quantity of light alkanes that could evaporate, but in small proportions); and the minuscule quantities that could get "dragged up" by wind and evaporation of water would be insignificant compared to other airborne pollutants. Pollution can affect rainwater quality; but usually the relevant pollutants are particulate matter and gaseous pollutants like nitrous oxide, not heavy liquid hydrocarbons from an oil slick. Nimur (talk) 20:03, 4 September 2010 (UTC)

Do you have a better source? It is not unlikely for evaporated paraffins to precipitate with rain, especially if they have had time to glom to dust.

"Small patches of non-evaporated oil and tar balls could be carried great distances by the currents and other smaller eddies, especially if strong winds are introduced during storm/hurricane situations."Accuweather.com

The answer to the question is clearly, "Yes." Why Other (talk) 22:07, 6 September 2010 (UTC)

A large enough oil slick might kill a hurricane. Hurricanes depend on moisture evaporating from the ocean, and an oil slick prevents that from happening.

However our article on Weather_control#Storm_prevention, says that scientists now believe that a hurricane would churn the ocean so much that the oil wouldn't be able to prevent evaporation.

In either case, the oil will not evaporate and become part of the storm. APL (talk) 20:05, 4 September 2010 (UTC)

Do you have a citation for the assertion that an oil slick could kill a hurricane? Does it assume that storm swells would be shorter than the depth of the slick? Why Other (talk) 22:07, 6 September 2010 (UTC)

The National Hurricane Center published this document on what would occur if a hurricane were to strike an oil spill (specifically the Deepwater Horizon oil spill, but it could apply in most situations). Ks0stm ^(T•C•G) 20:23, 4 September 2010 (UTC)

tryn to find out what killed my mom in 1992

Aloha, I'm tryn to figure out what killed my mom at the age of 39. In 1992. She was healthy and worked for OSHA, drank a beer now and then but drug free and just liked to stay at home after work. On her death certificate it states the following: Cause of death~ Encephalopathy, probably from Hypoglycemia, due to Pulmonary Emboli, due to Cellulitis. I found her in her bed after looking for her for 2 days when she did not show up to work, medi vaced her to Providence in Anchorage,Alaska and she remained in a coma for 2 months after we decided to let go. She was breathing on her own. There was no autopsy done but my aunt told me that they took brain slices and came up with a Metabalical Catashpe, what ever that means~ I still don't know. For that matter my aunt could not be telling the truth because like i said there was no autopsy done.

I was 19 when i lost my mom and have been looking for answer ever since. we were best friends, and mother and daughter. I now have had my first daughter and know the feeling of love,from a mother to a daughter. This has been killing me for almost 20 years now and im telling my daughter stories of my mom and i cant tell her what exactly happened. She did have a cold at the time. Any help would be great on my mind and my soul~ Please email me @: @aol.co or @hawaiiantel.net (email addresses removed to discourage spam) I really appreciate all the helpful hints, mahalo for all the help! Jennifer L. Miller —Preceding unsigned comment added by Meandmonkey (talk • contribs) 20:10, 4 September 2010 (UTC)

I'm not so sure the reference desk is a good place for this question... Ks0stm ^(T•C•G) 20:20, 4 September 2010 (UTC)

Sorry to hear about your loss, but this is not the place to find the answer you want. I would add that doctors are generally very, very good at what they do, and autopsies are generally very, very accurate. The diagnosis on that death certification is quite specific and I would venture to trust the pathologist report. If you have more questions, these need to be addressed with those responsible for dealing with your mother. Sorry again for your loss. Regards, --—Cyclonenim | Chat  20:48, 4 September 2010 (UTC)

Um. I can't agree with the statement about doctors. At the refdesk we don't give medical advice and tell people instead to see doctors, but that's because (1) we don't have enough information, (2) there's no quality control, and (3) we don't want to get sued. (Not necessarily in that order.) It's not because the doctors are necessarily reliable either; it's good to keep a healthy skepticism in their regard, and do your own inquiries if a doctor's advice seems off.

Jennifer, my sympathies. I can't say whether the death certificate is accurate or not. But short of a full-scale forensic investigation, I can't imagine how you're going to get anything more reliable. Maybe for your own peace, the best thing to do is accept the explanation given. --Trovatore (talk) 21:00, 4 September 2010 (UTC)

Do you want to see encephalopathy, hypoglycemia, emboli, cellulitis? --Chemicalinterest (talk) 21:03, 4 September 2010 (UTC)

So you disagree that doctors are generally well trained and the most informed people to trust in this situation? Who else can give you a better answer, if not a pathologist? Regards, --—Cyclonenim | Chat  21:21, 4 September 2010 (UTC)

What I disagree with is the attitude of treating medical doctors like priests. The way to think of them is like mechanics. Yes, your mechanic probably knows more than you do about how to fix your car. Probably, though maybe not; it depends.

But in any case if you have a reason to think your mechanic has missed something, you mention it, right? It's your car that's at stake, not his.

As for there likely not being anyone available who can be trusted more than the pathologist, you might notice that I actually agreed with that in my response. But saying that a more reliable answer isn't available isn't the same thing as saying that that answer is very reliable. --Trovatore (talk) 22:59, 4 September 2010 (UTC)

(ec) Wikipedia has articles on encephalopathy, pulmonary embolism, hypoglycemia, and cellulitis, which you may find helpful. For a specific guidance in interpreting the death certificate, you should speak to a trusted medical professional — perhaps your own doctor. At that point, if you have unanswered questions then you might consider approaching your mother's physician, the physician who cared for your mother in hospital, and (if necessary) the pathologist(s) who handled any tissue samples. Bear in mind that it may take time to locate people and records, and that some of the physicians involved may have retired or even died in the last eighteen years. TenOfAllTrades(talk) 21:06, 4 September 2010 (UTC)

(ec) Respecfully, I am the one who referred her here. This is not a request for medical advice per se; it's a request for an explanation, in lay terms, of what some of that stuff means. For example, look at the post on her talk page -- it may be helpful if someone could explain what a "metabolic catastrophe" is, since we do not have an article on the topic. Thanks, Antandrus (talk) 21:10, 4 September 2010 (UTC)

A metabolic catastrophe is where the energy in demand by your body cannot be fulfilled by the supply. It's a very general term, though, and it's more of a symptom than a diagnosis. There are multiple causes. Regards, --—Cyclonenim | Chat  21:23, 4 September 2010 (UTC)

In layman's language, this would be something like Brain damage, probably due to low blood sugar, which was in turn a result of a blockage in the arteries of the lung caused by a skin ulceration. In other words, her brain did not get a sufficient amount of glucose, which caused a fatal amount of tissue damage. The low blood glucose level was caused by a blood clot in the lungs, a clot which likely originated in a bad infection in her extremities (most likely a leg) and migrated to the lungs. I'm no doctor, but was your mother diabetic? hypoglycemia (low blood sugar) can result from insulin usage, and cellulitis is associated with diabetes. --Ludwigs2 21:35, 4 September 2010 (UTC)

Assuming we can believe the death certificate - and I can see no reason to think it's wrong - then if what you are looking for is an explanation, then we should just look at what the words mean. We can't make a diagnosis - but we can take the diagnosis you have and tell you what the words mean. You should probably read the articles yourself - but my quick reading suggests:

• Cellulitis - an inflammation of connective tissue and skin. Cellulitis happens when bacteria that should normally be on the outside of the skin get inside. There are a bunch of possible causes, the elderly, those with diabetes and those with compromised immune systems are at greater risk. Open wounds, sores and such are a way for the bacteria to get where they shouldn't be. This can cause all sorts of symptoms ranging from a simple rash to really nasty diseases of the "flesh eating" kind.

• Hypoglycemia - Not enough sugar in the blood. It's implicated in cellulitis because diabetics and the elderly are prone to getting both conditions. But laying in bed for days without food would also do that. It sounds like a symptom rather than a cause.

• Pulmonary embolism - A blood clot or some other solid lump (and embolus) formed somewhere in her body and came loose, flowing along a major artery and eventually lodging in one of the arteries in the lungs. Since oxygen is carried by that artery - suddenly there is a dramatic drop in the amount of oxygen in the blood.

• Encephalopathy - Her brain stopped working - that happens when it's not getting enough oxygen and/or not enough sugar to power its metabolism. Clearly that is why she was in a coma - the rest of her body was functioning - but evidently her brain was too damaged to do anything more than keep heart and lungs functioning.

So the immediate causes are reasonably clear. The embolism presumably happened very quickly - days before you found her...probably while she was asleep. Even if she was awake, this is one of the better ways to die.

My father died of a similar way - he was perfectly fine eating dinner, feeling OK...then he said he suddenly felt a bit 'woozy' and within 30 seconds fell off his chair and never regained consciousness. He was a heavy smoker - so his cause in his case was pretty obvious. Presumably the embolism (in his case, a blood clot) cut off the oxygen to his brain - causing brief dizziness - then brain-death. He was still breathing and his heart was still beating when the ambulance came - but he never showed any signs of consciousness - and within several hours he was finally pronounced dead. But he didn't suffer, for him it was all over in seconds. It's reasonable to assume that your mother didn't suffer either.

The hypoglycemia was to be expected if the body has been laying in bed with no food and the brain not functioning for days. Bedsores and pressure-point problems could have caused the cellulitis - but that hardly matters. She was already dead.

Why did this happen? That's hard to tell without knowing a lot more about her lifestyle.

The question you perhaps should be asking is why the embolism formed in the first place. If she was a smoker or had some other issues to make her prone to this - then you probably need to look no further. However, our embolism article lists a dozen kinds of embolism and perhaps three dozen possible reasons. Some of them look like "just plain bad luck" things - others would be due to other injuries. After all of these years have passed, you can probably only guess which of those things it was. Read the article - see if any of the causes ring any bells.

What I think you should take away from this is that your mother's brain probably died very quickly, probably while she was asleep. All of the horrifying grief that you must have gone through after finding her is a terrible thing - but it's clear that she was effectively already dead.

SteveBaker (talk) 22:25, 4 September 2010 (UTC)

I'm no expert but it looks to me like the things listed there may be results of being in a coma for two months, lying in bed without moving. I would not necessarily take them as indications of what caused the coma in the first place. The most common cause by far of events like this is a stroke, but there really is no way of knowing without more information. Looie496 (talk) 01:15, 5 September 2010 (UTC)

I'm really sorry to hear about these issues you are having. I am only going to add that your aunt was talking about a metabolical catastrophe which is medical speak for her system being overwhelmed by a number of things going wrong. It is used in a number of different ways and needs to be understood in the circumstances in which it is used. Richard Avery (talk) 07:43, 5 September 2010 (UTC)

Okay, here goes... This my first, posting, editing etc on wiki, so there are bound to be a lot of mistakes. sorry. Sorry to hear about your mom. I think her death must have really devastating for you (guessing from the fact that it has been 5 years and you now have children of your own. I graduated in medical science 10 years back, but i grew up and still reside in an obscure state in India, a 3rd world country, as it is known. Getting back on track - you did not give a lot of information that could have helped. From what i analyse the important information answers only lead to more questions: 1. OSHA, i take it pertains to Occupational Health etc, so if your mom was working for the OSHA, Alaska, it is likely that she would have been diagnosed as Diabetic. But you made no mention of her having diabetes. 2. People do not go into a Hypoglycemic Shock or coma even if they are diabetic (many of the drugs like Insulin and OHA or Oral hypoglycemic agents used to control the disease/bring down the blood sugar will result in hypoglycemia). The body stores excess glucose as glycogen that can be converted back to glucose as and when needed by the body The human body also has a warning system that tells a person that his blood sugar is below the normal threshold. Most of us start shivering with excessive sweating and palpitation etc. when the blood sugar is ~ 60 to 70 mg/100ml. 3. Pulmonary embolism, in most cases does not lead to loss of consciousness nor does cellulitis, not over several hours anyway. 4, Encephalopathy takes several days to manifest as coma, and the causes are varied (liver failure being common) My apologies, but i just don't accept the cause of death (even if i am from an overpopulated 3rd world country) A more plausible explanation would be a stroke/CVA (cardiovascular accident). It may have been hemorrhagic or embolic, whichever the case, it often is life threatening without immediate intervention (hours not days). A CAT scan or MRI, if done will confirm the case. Again my sympathies, and sorry about the mess (my reply, i mean) Ralte, 6th September 0130 hrs IST —Preceding unsigned comment added by Ralte (talk • contribs) 21:14, 5 September 2010 (UTC)

I agree with Steve Baker's answer above. Any comorbid infection during a cold could cause a blood clot and and embolism if it inflamed an artery, and it was a bad embolism near the brain so she probably went very quick from painless hypoxia to the brain. If it had hurt she probably would have been able to get out of bed and would have been much more likely to have been found by a telephone or a door. Please rest assured that she probably had no idea she was dying, and that such freak accidents only happen to a small percentage of the population. Most of us have much more painful cancers and heart disease to look forward to, where we will be very aware of a sense of impending death. You might try explaining to your daughter that your mom was just very lucky.

Working for OSHA is unlikely to have any bearing on diabetes. Why Other (talk) 22:21, 6 September 2010 (UTC)

Distance required to see planet Earth from space?

In most reports or photographs from space, I have seen only parts of our planet. What distance is required to view our planet as a complete sphere? With Earth's diameter of ca. 12750 km, can that required distance be calculated mathematically? Thanks. —Preceding unsigned comment added by 66.183.191.95 (talk) 22:44, 4 September 2010 (UTC)

Well you could get the whole Earth in the picture from any distance if you use a wide-angle lens of the right focal length. Photographers reckon that a 50mm lens on 35mm film gives an image similar to the image produced in the human eye. Using that set-up 35mm/Earth diameter = 50mm/distance, or a distance of 1.4 Earth diameters or about 11,000 miles. SpinningSpark 23:04, 4 September 2010 (UTC)

Strictly speaking the required distance is infinite. From your eye or camera (for simplicity reduced to a point, but you need an eye at least as large as the Earth in order for the distance not being infinite) you can calculate the cone which has your eye at the tip and touches the Earth - the diameter of the circle where it touches the Earth is (diameter of Earth)*Sqrt(1 - (radius of Earth)²/(distance from Earth's center)²), if Earth is a sphere.

Icek (talk) 23:46, 4 September 2010 (UTC)

I think the question is really "how far away do I have to be such that Earth looks like a circle", which, as Spinningspark pointed out, is pretty meaningless if we allow any type of lens. It would be really cool to see a picture taken from, say, a balloon pointed straight down with a wide enough lens to capture the whole horizon. I suppose you'd need a lens that could capture over 180 field of view, but such lenses certainly exist. Buddy431 (talk) 00:30, 5 September 2010 (UTC)

Yes, Imax has indeed produced such shots. Re Icek, I don't understand your point, you seem to be saying that one has to stand at infinity to see the full diameter of the earth - true, but you will still only be seeing half the earth, the opposite side is obscured. If you are reading "complete sphere" to mean the entire surface area is visible then your answer should have been "it can't be done". However, as Buddy431 pointed out, the meaning of the question is that the whole earth is in frame, not the whole earth is visisble. SpinningSpark 00:50, 5 September 2010 (UTC)

Maybe I can rephrase the original question - how far do you need to be to see the (or an entire) equator? Ariel. (talk) 02:37, 5 September 2010 (UTC)

You'd have to be infinitely far away. (See my more complete answer below) SteveBaker (talk) 22:21, 5 September 2010 (UTC)

Assume the Earth has radius r and that your field of view is θ. Also assume that your field of view is a perfect cone and the Earth is a perfect sphere. In a two-dimensional space your field of view can be thought of as two rays secant to the circle of the Earth. So you are looking for the distance from you (the point from which both rays originate) and the center (or alternately, the point on the circle perpendicular to the line connecting it and you) where your field of view is greater than the radius of the Earth. I think. My calculations are probably wrong at this hour, but I came up with any distance greater than tan(θ/2)/{r cos(θ/2)) + (r - r sin(θ/2)) 76.199.167.204 (talk) 03:24, 5 September 2010 (UTC)

See: Horizon#More exact formula for the required height to get the horizon to the radius. Hcobb (talk) 03:33, 5 September 2010 (UTC)

Technically - these kinds of 360 degree photos: [7]...are photos of the entire planet - and they are circular (well, very approximately!) - but the deal is that because of perspective, seeing the entire world as a circular thing leaves most of it hidden. You aren't seeing a "hemisphere" - just a tiny circular patch that ends at the horizon. The higher you get, the further away the horizon is - and the larger the circular patch that you can see becomes.

But mathematically, you never can see an entire hemisphere. You have to be infinitely far away from a sphere to be able to see that much. The rays of light coming from the planet form a cone with it's apex at your eye. Since the sides of the cone are never parallel - they always meet the sphere just a little short of the full hemisphere. So if we're allowed to pick any lens - then at any height/distance at all, the earth can be pictured as an approximate circle...and there is no height (short of infinity) that'll let you see a full hemisphere. So we can't answer your question without saying what "lens" or what "field of view" we're considering. SteveBaker (talk) 16:02, 5 September 2010 (UTC)

I think Spinning Sparks first answer is pretty good. Consider this example which might clear the situation up a little. The astronauts on the space station. They can certainly see "the earth" against space from about 370km up if they look around, but it would be too big to see in "one go" and they are still only seeing to a particular "horizon" from their height. If they had a wide enough angle lens, they could easily take a photo of the "whole earth" against a background of space and stars but they would still only be seeing a fraction of the entire hemisphere facing them. As you get higher and higher you would see more and more of the planet until you go to a point where increasing your distance by a lot was only increasing your "view" by a little. One significant milestone for traveling away from the earth which might be worth describing is when the earth will take up 90 degrees of your field of view, (imagine looking forward and seeing one edge and then looking left and seeing the other edge) you would need to be about 2600km (1600mi) above the surface. I did this calculation just by drawing a circle then drawing a square where two of the sides are radius lines seperated by a right angle and the two other lines are tangents of those which cross at the last corner outside the circle. You the observer at the point outside the circle has a view of the earth described by the tangents. The distance to the center from opposing corners of this square is root 2 of the radius, so the section of distance that is NOT in the circle (between you and the circle) is root 2 of the radius minus one radius. Even at this point, you are only seeing "half" of the "half of the earth" that faces you.. So to see considerably more then 50% of the hemisphere facing you, you'd need to be considerably more then 2600km above the surface, 18000 km(11000mi) doesn't sound unreasonable. Vespine (talk) 04:24, 6 September 2010 (UTC)

Shorthand notations for nuclear decays

What is the shorthand notation for the alpha and beta decay? For fusion reactions it is ^aA(^bB,xn)^a+b-xC. Is there something similar for simple decays? Nergaal (talk) 23:09, 4 September 2010 (UTC)

You mean like ⁶Li(n,α)³H? Physchim62 (talk) 01:27, 5 September 2010 (UTC)

more like ⁵He(,α)¹H with no trigger required, or ³H(,e)³He. But you can write ³H→e+^-+³He. Graeme Bartlett (talk) 06:56, 5 September 2010 (UTC)

Sweet! Thanks guys! Nergaal (talk) 20:59, 5 September 2010 (UTC)

September 5

Is it possible for grass to ferment?

Topic says it all. ScienceApe (talk) 00:01, 5 September 2010 (UTC)

See Silage Rojomoke (talk) 00:10, 5 September 2010 (UTC)

I wouldn't recommend drinking it, though. silage martinis don't have a kick worthy of the effort it takes to choke them down. --Ludwigs2 01:50, 5 September 2010 (UTC)

Silage is indeed fermented grass - which proves that grass can be fermented. However, it's particularly nasty smelling stuff and for sure a 'silage martini' would be an incredibly nasty thing! But that doesn't mean that you couldn't make a nice grass-based wine. After all, if you leave a pile of grapes to rot - what you get isn't 1992 vintage Chablis...it's a rather nasty pile of rotten grapes. So presumably, if the right amount of care was taken, it might be possible to get something drinkable by humans out of fermented grass. Maybe. SteveBaker (talk) 15:42, 5 September 2010 (UTC)

It might be worth pointing out that grass ferments inside the rumen of grass-eating animals such as cows and horses. Looie496 (talk) 16:51, 5 September 2010 (UTC)

Science (dark matter and black holes)

What is the "dark matter"? And how black hole can absorbed the time? —Preceding unsigned comment added by Seonti (talk • contribs) 05:56, 5 September 2010 (UTC)

See dark matter, and black hole plus event horizon for the second question. Does this help a bit? I also expanded the heading. --Ouro (blah blah) 06:02, 5 September 2010 (UTC)

A very short explanation of dark matter is: We know there is a lot of mass out there that we can't detect, but shows itself by means of its gravitational effects. We don't really know what it is. Because we can't detect it, we call it "dark". There are different theories as to what it might be. Nobody is really sure at the moment which one is correct. --Mr.98 (talk) 14:14, 5 September 2010 (UTC)

Basically we can observe how fast galaxies are rotating, and how they orbit each other. We can infer the mass of the stars from their brightness. There seems to be too little mass for the speed the galaxies are rotating. IIRC we can only account about 10% of the mass. Therefor either -

1. Our understanding of physics of galaxy rotation is wrong.
2. Our understanding of the relation between the brightness and the mass of stars is wrong
3. Our understanding of the distance to the galaxies is wrong (and thus the distance between the stars is wrong).
4. There is more mass in galaxies, which we can't see.

The first three have been discounted. 2 and 3 are related to standard candles. Thus only the last one remains. The main candidates for the missing mass are -

1. Massive compact halo objects (MACHOs). These are brown dwarfs, black holes and other large collections of normal matter which is too dark for us to see.
2. Weakly interacting massive particles (WIMPs). These are isolated particles such as neutrinos and large hypothetical particles, that only interact with gravity (and the weak force).

Currently WIMPs are in favour over MACHOs, but there is not enough evidence to decide either way.

CS Miller (talk) 15:50, 5 September 2010 (UTC)

There are constraints on the total amount of baryonic matter from Big Bang nucleosynthesis. If there had been significantly more protons and neutrons (which MACHOs would be made of) around in the early universe, then BBNS would have produced a different abundance of light elements to that which we observe in the universe (roughly 75% H, 25% He, and a smattering of Lithium). The dark matter can't all be MACHOs without chucking this out of the window. That's part of the reason WIMPs are favoured. (Obviously, brown dwarfs and black holes and such do exist, just not in large enough quantities to explain the rotation curves etc.) --81.158.2.129 (talk) 16:05, 5 September 2010 (UTC)

It's Dust in Lyra's world. 67.243.7.245 (talk) 18:53, 5 September 2010 (UTC)

if the universe is in black hole we feel the flip of the arraw of time in the age and gravity start to push . thanks . —Preceding unsigned comment added by 77.124.170.151 (talk) 15:07, 6 September 2010 (UTC)

Why can't I just get a local orthodontist to readjust braces installed in India?

Here, I asked about why we can't just fly to India to get braces, since they're far cheaper there than in the US.

Someone thinks I have to fly back every few months for a readjustment. What kind of aggravating joke is that? It's like buying an SUV at the Little Apple Toyota Honda dealership in Manhattan, KS and if it breaks down in Seattle while on a vacation, it has to get towed all the way back to Manhattan to get fixed. It doesn't work that way; the vehicle gets fixed at the closest local service center.

So why didn't somebody think that we can readjust our Indian-installed braces at the orthodontist nearest me? --70.179.165.170 (talk) 07:12, 5 September 2010 (UTC)

There are plenty of confused people in this world, and people say plenty of silly things on the internet for a large variety of reasons. In other words, there's no way we can tell you why the person said what they said. Your best bet is to ask them if you really want to know. In any case, it's possible you misunderstood what the person was saying. Perhaps they were suggesting that braces aren't necessarily a one time thing but rather may require ongoing support and adjustment. Therefore you will need to go to someone for this, either the person who installed them or someone else. In any case, this will add to the cost and if you do go to someone else, I would guess it not unusual you will be charged extra. Also if the braces are a different kind and the dentist isn't used to dealing with them, this may also add to the cost. In other words, your cost savings may not be as big as you think from a simplistic analysis Nil Einne (talk) 11:35, 5 September 2010 (UTC)

Carbon steel

is carbon steel magnetic —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 08:59, 5 September 2010 (UTC)

I think it is magnetic, but the answer must be somewhere on this page [8] --Stone (talk) 09:15, 5 September 2010 (UTC)

Carbon steels display ferromagnetism. Dolphin (t) 11:33, 5 September 2010 (UTC)

Quarks

many sources i have read includes mass of QUARK in Mev which is hopefully unit of charge.Kindly anyone having knowledge of this subject answer. thanks in advance sameer,india 59.93.129.150 (talk) —Preceding undated comment added 09:59, 5 September 2010 (UTC).

MeV is mega electron-volt which is a unit of energy, not of charge. Mass is related to energy through Einstein's E=mC². Energy is often used as a measure of mass by particle physicists since this is the energy that they must impart to a collision in order to create the particle in question. SpinningSpark 10:08, 5 September 2010 (UTC)

In atomic physics mass and energy are freely mixed. 1 electron-volt is the amount of energy need to move one electron against 1 Volt. 1 Joule (or watt-second) is the amount of energy need to move 1 Coulomb of electrons against 1 Volt. The typical energy of a photon of light is around 2.5 eV. 1 MeV is around 0.001 atomic mass units, where the mass of 1 carbon atom is 12 amu. CS Miller (talk) 15:59, 5 September 2010 (UTC)

... and, in case you were wanting to know about quarks and haven't read our article, the charge of a quark is either one-third or two-thirds of the charge of a proton, and the mass of a quark is only a tiny fraction (0.4%) of the mass of the proton that it is part of. The remainder of the mass of the proton comes from the "kinetic energy" of the gluons that keep the quarks together, and from their binding energy. Dbfirs 16:48, 5 September 2010 (UTC)

In physics, we have very well defined units for measuring all kinds of things. And, we have very effective applicable physical laws that relate different quantities together. So sometimes experimental physicists muck up the works by using the "wrong units." But rest assured - their weird units are okay given two things: (1) knowledge of the physical relationships between parameters; and (2) knowledge about any assumptions in the experimental apparatus.

In the simple case of, say, weighing a person, we want the person's mass; but we can really only measure their weight (in a reasonable classroom kind of setup). So, we put the person on a spring scale (on Earth and subject to one unit of Earth gravity, g. In this specific case, we can say that "force=mass⋅acceleration" with very little loss of accuracy or correctness. So, we often find people describing their weight or their mass interchangeably - because under "normal laboratory conditions" (for the specific scenario we care about), [pound]]s are directly related to kilograms by a simple relationship. And, we find it convenient to use "pounds" as a unit of "mass" - even though it's not technically right - but that's what the scale reads off to us (and we all know that we can perform the conversion).

We can go a step farther. The scale can't actually measure a force - we're really measuring a compression of the spring inside the scale! By Hooke's law, we know that spring force is linearly related to the distance displaced; and we can simply relate spring force to mass; and we could have a standard spring-scale - so we could actually measure a mass in meters - even though mass is not measured meters! What we would do is measure how many meters (Δx) the person deflected the scale; and then multiply by the spring constant (k_spring) of the scale; and then assume they were on Earth; and say their mass exactly equals Δx*k_spring/g. Or we could say "the mass was Δx meters" - a bit of sloppy shorthand and not really correct; so we can invent a unit called meters-standard-spring-constants-per-Earth-gravity (m k_s/g). Now we can read standardized-scale deflections Δx and mark the scale in m⋅k_s/g. In fact, this is more "correct" than reading off the scale units in kilograms or pounds - because we're directly observing a displacement in meters, and this unit reminds us that our conversion to mass depends on all the implicit assumptions above. If our spring-scale changes, we can keep using the same units and just change the conversion factor from meters to mass.

In subatomic physics, we have similar relationships - for example, mass-energy equivalence. This is a special property that (under certain conditions), mass and energy can be converted. In the case of experimentation with quarks, we don't have a lab scale: we have sophisticated experiments called deep inelastic scattering probes inside a machine called a Linear Particle Accelerator - and it so happens that the results of these scattering experiments will be read off in units of energy. In analogy to the way that we can measure a person's force on a scale to infer their mass, given the conditions of "standard Earth gravity" - we can measure an energy release to infer a mass, assuming a perfect "E=mc²" style conversion. So, we can use the units of Energy and Mass interchangeably. It so happens that the way we will measure "energy" in a high-energy particle accelerator is by measuring a voltage - say, on an avalanche photodetector or a BaBar - so it makes perfect sense to measure "energy" in units of "electron-volts" (it makes the job a bit easier for the semiconductor physicist who has to do the instrument design). We use derived units, like the electron volt (and in fact, even the volt - which is a kilogram-per-couloumb times a meter squared per second squared), to make the mess easier to read. And, while in the simple laboratory experiment, we never have to worry about the 9.81 m/s/s "changing" - in high-energy physics, we might need to consider what happens if a new discovery "recalibrates" the coulomb, or the joule, and so on - so it's nice to be able to handle that complexity with our choice of units. Nimur (talk) 18:07, 5 September 2010 (UTC)

Silicone Caulk

why is Silicone Caulk not typically paintable? what happens if you paint it? —Preceding unsigned comment added by Tomjohnson357 (talk • contribs) 11:05, 5 September 2010 (UTC)

I'm pretty sure the paint will just fall off as soon as it dries. Looie496 (talk) 18:04, 5 September 2010 (UTC)

In order to paint it, the paint has to stick, and silicone caulk is just not sticky. Another option is a textured surface, so the paint fills little holes - but silicone caulk is very smooth. So you can't paint it (with ordinary paint anyway). Ariel. (talk) 18:25, 5 September 2010 (UTC)

What kind of spider is this?

Hi. I just wondered if anybody could help me identify spider please? It was found in a house in London, and I think that it might possibly be a False Widow, judging by the markings on its back. However, I am not sure that the body shape and legs are quite right for a False Widow. Any help would be greatly appreciated. Thanks Spider788 (talk) 11:28, 5 September 2010 (UTC)

I have posted a second video here. Thanks Spider788 (talk) 16:09, 5 September 2010 (UTC)

Looks like a Tegenaria species to me - see [9]. And it's a male (you can tell by the pedipalps - the two little "clubby" things at the front), out looking for a female - it's the mating time of year. -- Boing! said Zebedee (talk) 21:03, 5 September 2010 (UTC)

If not Tegenaria, most likely something in the Araneomorph_funnel-web_spider family. SemanticMantis (talk) 02:40, 6 September 2010 (UTC)

Does http://tineye.com ever help with these sorts of questions? Why Other (talk) 22:26, 6 September 2010 (UTC)

Development of the insulin unit (copy request)

Request Moved to: Wikipedia Resource Exchange/Resource Request.
--Seren-dipper (talk) 17:35, 5 September 2010 (UTC)

Estimate of number of generations since origin

Has there ever been made an estimate of the number of generations that has happened since the origin of life?

I would guess that the Last universal ancestor would have an extremely low reproductive age, and from the linked article it seems like the length of a generation for the LUA could not be determined with any accuracy. Still, has anyone tried? Xelnaga diku (talk) 15:58, 5 September 2010 (UTC)

I doubt it's even meaningful. For 3 billion years of the 4 billion year history of life there was nothing more than bacteria, archaea, and protista of various sorts, which can reproduce in less than a day but can also generate spores that lie dormant for potentially thousands of years before reproducing. The best one can say is billions of generations at minimum. Looie496 (talk) 16:12, 5 September 2010 (UTC)

We can put some bounds on the estimate with a few assumptions. It is believed that LUCA lived 3.5–3.8 billion years ago. So for our upper bound on the numer of generations, let's take 3.8 billion years ago and a reproductive cycle of one hour: that makes 33×10¹² generations. For the lower bound, let's take 3.5 billion years ago and a reproductive cycle of one day (much longer than most modern bacteria): that makes 1.3×10¹² generations. So we can say with reasonable confidence that the number of generations since LUCA is in the fairly low trillions, but quite possibly in the low tens of trillions. Physchim62 (talk) 18:56, 5 September 2010 (UTC)

A number like that is kind of hard to relate to. Is there any estimate on the number of human generations on average, in some more recent stretch? For example, in my ancestry tree, who has been traced about 400 years back, there are about 13 or 14 generations, or about 30 years per generation. I just wonder if 25-35 is a good rule of thumb for the last 2,000 years, perhaps? ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:10, 5 September 2010 (UTC)

Yes - although our article surprisingly doesn't mention a rule-of-thumb length. Ghmyrtle (talk) 19:24, 5 September 2010 (UTC)

 Added Wikiscient (talk) 21:26, 5 September 2010 (UTC)

25 years is a reasonable rule-of-thumb scale for a human generation, although it is impossible to define a "generation" across a whole population. On that basis, Homo sapiens came into existence about 200,000 years ago, so that makes 8000 generations. Physchim62 (talk) 21:06, 5 September 2010 (UTC)

Confusion regarding electricity

Hello, I am currently somewhat confused as to what "electricity" actually is. I will attempt to explain my current level of understanding which contains a ridiculous amount of contradictions, so that you can perhaps see why I am so confused and explain it a little better.

• It's a type of low-frequency radio wave, yet it is apparently made of protons.
• It is a mysterious force which looks like blue-white fire, and yet cannot be seen.
• It moves forward at the speed of light... yet it vibrates in the AC cord without flowing forwards at all.
• It's totally weightless, yet it has a small weight.
• When electricity flows through a light bulb's filament, it gets changed entirely into light. Yet no electricity is ever used up by the light bulb.

Regards, --T.M.M. Dowd (talk) 17:49, 5 September 2010 (UTC)

It would be encouraging if you would give some indication that you had tried to read our electricity article. Looie496 (talk) 18:00, 5 September 2010 (UTC)

Yes I have read through the article previously. Upon viewing it again, the phenomenon I am having difficulty in understanding is "electrical potential". My apologies for having not been clear about this earlier. --T.M.M. Dowd (talk) 18:08, 5 September 2010 (UTC)

It's not a radio wave, and it's not made of protons, but rather electrons (but of course telling you the name doesn't tell you what it is.) It does NOT look like blue white fire. Blue white fire is the color of hot AIR. If you heat air by any means, it will look like that, a lighting bolt in space has no color at all. The flame of a natural gas stove is also blue - for the same reason: it's hot.

Here is the main source of your confusion (I think): Electricity is carried by electrons, but it is not the electrons themself! So when electricity goes through a filament, the electrical energy gets converted to light, but the electrons, which carry the energy are unchanged. In an A/C current the electrical energy travels at the speed of light from one electron to the next - but the electrons hardly move. This energy can be considered weightless, and it can change direction quickly (but not infinitely quickly, but let's skip that for now). The electrons, which carry the energy do have weight. (Technically the electrical energy has weight too - E=MC2, but let's skip that too.) Did I answer everything? Feel free to ask again. A lot of wikipedia articles are written by in a way that is hard to understand unless you already understand the topic. It's hard to write an encyclopedic article any other way since you don't know the level of the student. Ariel. (talk) 18:16, 5 September 2010 (UTC)

On your user page, you say you have an A* in GCSE Science and a B in AS Physics. Did you seriously not cover any basic concepts like voltage and current? --81.158.2.129 (talk) 18:21, 5 September 2010 (UTC)

Of course those topics were covered. We learned how to use equations such as Ohm's law and the resistivity equation, but not really what electricity was in its most fundamental form. --T.M.M. Dowd (talk) 18:36, 5 September 2010 (UTC)

If you connect light bulb to light bulb so one uses the other one's waste electrical current, they both will be very dim. All of the energy was used up. --Chemicalinterest (talk) 18:22, 5 September 2010 (UTC)

"Electricity" in common parlance loosely refers to both the actual flow of electric current, and to the use of electric current to deliver energy to devices. Because electric current and energy are both invisible (we only see their effects, like incandescence), many people incorrectly think they are the same.

In fact, what you need to know is that there are small particles called electrons, that carry electric charge. Other particles, called ions, can also carry charge, but this doesn't happen inside a copper wire. When charge-carriers move, we call this electric current. We can use and control this motion to carry energy from place to place - to power devices like lightbulbs. We can also use this energy to create electromagnetic waves that carry information - and use this to transmit data, sound, pictures, and so on.

Another common misconception is about the speeds. Electrons do not move at the speed of light (in fact they move very slowly when inside a copper power-cord). But the energy that they are conveying does (or can) move as fast as the speed of light. Again, this is because energy is not the same as electric current. The way that energy and electric current are related is explained by Maxwell's equations and the Lorentz force equation; it requires some complicated math, but what you need to know is that the energy can move at a different speed than the individual particles that are conveying it. In fact, it is even possible to convey energy without any current - because electromagnetic waves can travel through vacuums - they do not need electrons to carry them. We use copper wires (and therefore, electric current) to guide the electromagnetic energy to the place we want it to go - like to your lightbulbs.

"Electric potential" is a measure of the relation between energy and current - when a potential exists, it means that individual electrons have the energy to move from one place to another - this is what drives them through a wire or a circuit. Nimur (talk) 18:25, 5 September 2010 (UTC)

I'm trying to decide whether electricity can be seen as a guided electromagnetic wave, as you suggest above, and I think the answer is no. In a steady-state DC circuit consisting of a battery driving a lamp, there are no time-varying fields. To the extent that electrons are quantum particles, I suppose there is a tiny time-varying field, but electricity still works in the classical limit where it's carried by a continuous fluid. -- BenRG (talk) 00:55, 6 September 2010 (UTC)

Hm. That's a very good point. In the case of DC current flow, how exactly is power transferred? The battery produces a voltage; and the voltage entices a current to flow across a resistance; and power is transferred from the battery to the load. The individual charge-carriers are doing work on the load - e.g., by adding thermal energy to it, in the case of a light-bulb. But in this case, all of the energy is actually carried by the charge-carriers, and none of the energy is carried in the form of a wave (I think.... Could a DC or "zero-frequency" wave convey energy?). I think the case of the AC current has some energy carried by the charge-carriers, and the rest carried by the electromagnetic wave; and the final case, an electromagnetic wave in free space, has all the energy in the wave, and none in the form of moving charge carriers. I have to think about this some more; but I think the answer is that energy can be conveyed by either the moving electrons, or the electromagnetic wave, or both. Nimur (talk) 07:17, 6 September 2010 (UTC)

I had to think about it too, but I'm pretty sure this is the answer: in the half of the circuit where the charge carriers are heading from the battery to the load, they're under pressure and hence a bit closer together than they would otherwise be, so there's a small net charge on this half of the wire, which produces a radial electric field. There's also a magnetic field, of course, and the cross product of the two (the Poynting vector) is parallel to the wire and points in the direction of the load. In the other half of the circuit the charge carriers are under tension, so there's a slight charge of the opposite sign, and the current is also in the opposite direction, so the Poynting vector again points toward the load. So the energy is carried by the EM field (outside the wire!), even though it's static. Maybe this does deserve to be called an EM wave. -- BenRG (talk) 08:41, 6 September 2010 (UTC)

You might find the hydraulic analogy useful. In short, electrons (or other charge carriers) are like water, wire is like a pipe, voltage (or potential) is like pressure, current is like current, a battery is like a pump, and a light bulb is like a paddlewheel driving a mill. It's a close analogy. If you start a pump at one location in a sealed loop of pipe, a paddlewheel at another location will start turning almost immediately, even though it takes much longer for the water that was initially in the pump to reach the paddlewheel. What gets transmitted quickly is the pressure, not the water itself. If you run the pump alternately forwards and backwards, the paddlewheel will turn alternately forwards and backwards and that can also be converted into useful work (by a slightly more complicated mechanism) even though the water in the pump never reaches the paddlewheel in that case. The water remains in the pipe and is not produced by the pump or consumed by the paddlewheel. -- BenRG (talk) 18:35, 5 September 2010 (UTC)

Truck with a 3d picture on it - is it possible in reality ?

Perhaps you`ve seen those images with truck photoshoped so that it appears to be transparent with large three dimensional object inside (if not just google 3d truck [10]) Last year I had a course in advertising and in oe class we were asked to find good ads vehicles, I offered these as currious example, but most people thought it wouldn`t be usable as acctual ad because the ilusion would work only in this one angle. I`ve seen some videos with 3d street paintings that look crap if not viewed from certain angle. However I wonder if there might be some instances when this would work (like the pepsi boxes or those with ilusion only on side of the car) i.e. it would look 2d from other angles, but wouldn`t be misshaped ? Also from what viewpoints would this illusion be visile ? ~~Xil (talk) 19:55, 5 September 2010 (UTC)

If you are talking about pictures that create a 3d appearance by leveraging optical properties (like sidewalk pictures) then those would only work from one narrowly defined angle. you might be able to leverage some of the old-school multi-image effects (the kind used on kids' playing cards, where tilting the card displays a succession of images), but I've never seen it done using 3d images. You could always, obviously, produce a hologram. --Ludwigs2 20:53, 5 September 2010 (UTC)

No, I specificly mean practical application on trucks, certainly nothing like those cards, please see the pictures in question. I mentioned street painting only because it looks distorted from other angles - 2d look would be acceptale, distorted would not ~~Xil (talk) 21:35, 5 September 2010 (UTC)

You can't do it for an arbitary viewpoint without some tricks. I've seen U-Haul trucks where the tailgate is painted with a fairly convincing picture of the interior of a truck - and it works well when you're driving along behind one. They've obviously set up the perspective of the thing to make it look right from that most common situation. If you watch the back as you overtake it - it looks distorted.

There are a few (very few) tricks that might get you a little further - but almost all 3D view tricks are either sensitive to your position - or require the viewer to wear some kind of headgear (like the 3D glasses in movie theatres). The only tricks I know of that work without glasses are:

• Autostereoscopy - which relies on tiny lenses molded into the surface of the picture to (typically) direct the light from alternate thin vertical strips of the underlying image off in different directions. By drawing the picture as corresponding alternating thin vertical strips from multiple pictures you can arrange for viewers to see different images depending on where they are standing. Done carefully, this works to a degree - but not perfectly. There are places you can stand where you'll get some light from one image and some from the next one along - and you get a blurry double-image that's not too convincing. You see this trick used in a lot of cheap children's toys - and it used to be popular for making "3D" postcards.
• Holograms - these are expensive to make in large sizes. They also only work well when the lighting is good. Worst of all, they don't work in color very well. So I can't imagine them being much use on a truck.
• There are some odd tricks that rely on the fact that your eyes focus different colors at slightly different depths. I've seen some moderately effective tricks done using this technique - but they are very viewer-position dependent - and the 3D effect is at best rather mild.
• There is a theoretical possibility that some kind of system could recognise where the human viewers heads were and using (for example) multiple lasers, send a tiny rasterized image directly into that persons eyes. Each image would be calculated using computer graphics to be just the right view of the object for each eye. It would take a lot of lasers to convince a whole crowd of people though - and the precision of the head tracking software would have to be amazingly good. This is still more in the realms of science fiction than actually real.

So - I think the answer is "No" - you can't do this. What you've been seeing is either a carefully posed single-person view - or a highly faked movie! SteveBaker (talk) 22:14, 5 September 2010 (UTC)

The images Xil is talking about are obviously photoshopped (and Xil knows it). They all show the same truck from the same angle against the same background. At most one of them might be real. -- BenRG (talk) 00:42, 6 September 2010 (UTC)

I think the OP is talking about images like this, right? Similar to what Steve mentions having seen on U-Hauls. Looks "real" to me (from that angle)! And, clearly, yes, someone is using that as an advertising gimmick -- don't know why the OPs classmates would have wanted to shoot down such a thing -- the (non-"gimmick") advertising is still effective from any angle. Wikiscient (talk) 05:39, 6 September 2010 (UTC)

Here are other photoshopped versions of that same image: [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32]. Apparently they are all submissions to the Rhino Rolling Advertising Award. -- BenRG (talk) 07:24, 6 September 2010 (UTC)

Even if the image only worked from one angle, it would still be an amusing novelty. An early example is The Ambassadors (Holbein). See anamorphosis. 92.15.7.161 (talk) 09:44, 6 September 2010 (UTC)

protein

In vegetarian stuff where does the protein come from? Calm Minds (talk) 20:45, 5 September 2010 (UTC) Calm Minds (talk) 20:45, 5 September 2010 (UTC)

Often from any variety of legumes (beans, peas, etc.) ···日本穣^? · 投稿 · Talk to Nihonjoe · Join WikiProject Japan! 20:51, 5 September 2010 (UTC)

Nuts HiLo48 (talk) 21:04, 5 September 2010 (UTC)

see Vegetarianism#Protein RJFJR (talk) 21:08, 5 September 2010 (UTC)

All plant material contains protein. The problem is with the kind of protein. Proteins are made of amino acids - the human body can consume 22 different amino acids - of which 8 are 'essential' to maintaining your bodies structures and biochemistry - and the other 14 are mostly broken down for energy. You can't live long without having adequate quantities of all 8 of the essential ones. You can live without the unessential ones providing you have enough carbohydrate and fat to provide the necessary energy input.

And that's the problem. There is protein in all kinds of plants - but only a few kinds contain all 8 of those essential amino acids. Meat, fish and eggs have all eight - so people who are not vegetarians (or those pseudo-vegetarians who eat fish, eggs or dairy product) have easy ways to get all they need without taking too much care of it. But for a 'pure' vegetarian, it would be perfectly possible to come up with a diet that was missing one or more of the those essential building blocks - and that would be "A Bad Thing". So the trick is to come up with enough of those rarer foods that have all 8 - or to devise a diet that has a suitable combination of plants that covers those 8. SteveBaker (talk) 21:51, 5 September 2010 (UTC)

That's basically right but let me make a couple of small corrections. Human proteins are made of 21 amino acids. Eight of them must be obtained in the diet; the other 13 can be synthesized by the body. They are just as necessary, and aren't broken down for energy unless they are present in excess quantities -- it's just that they don't need to be eaten. See our article on essential amino acid for more information. Looie496 (talk) 22:23, 5 September 2010 (UTC)

For example, Lysine is typically not very abundant in grains, so people getting most of their calories from cereal crops are typically deficient in it. This can occur in people who choose to be vegetarians and aren't very smart about it, but it's also a problem for people in (generally poorer) parts of the world whose diets are limited by poverty to consist primarily of cereal crops. Vegetarians who are smart enough to realize this often eat Legumes, which contain plenty of lysine (but generally lack some of the other essential amino acids, like Methionine). Buddy431 (talk) 23:27, 5 September 2010 (UTC)

I should note that I've never heard of a multicellular species that could do without at least the "standard" 20 amino acids in its cells. When plants are described as a poor source of essential amino acids, it doesn't meant that any of these are entirely absent, only that they're not available in the most efficient amounts for nutrition. Wnt (talk) 07:19, 6 September 2010 (UTC)

Eating too much protein may be bad for you, see Protein_(nutrient)#Excess_consumption. I believe most adults in the West consume more protein than they need, and it is converted to energy. It used to be thought that you needed to consume cereals and legumes in the same meal, but now that is thought not to be true. See http://www.ajcn.org/cgi/reprint/59/5/1203S.pdf 92.15.7.161 (talk) 10:01, 6 September 2010 (UTC)

Hilarious cupcakes

Vegan bacon french toast cupcakes. Just the concept might make you laugh, SpinningSpark 23:28, 5 September 2010 (UTC)

Are there any foods which induce laughter? Fiorsless3 (talk) 21:32, 5 September 2010 (UTC)

This would require the food to contain some substance that causes laughter, some might be listed here, mix them in cupcake dough and see what happens ~~Xil (talk) 21:43, 5 September 2010 (UTC)

How about Lime Jello Marshmallow Cottage Cheese Surprise? Looie496 (talk) 22:27, 5 September 2010 (UTC)

I don't know about food, but see Inherently funny word. Ariel. (talk) 23:52, 5 September 2010 (UTC)

Obviously magic brownies come to mind... ;) Wnt (talk) 07:30, 6 September 2010 (UTC)

Whipped cream made with nitrous oxide? Or maybe anything at thisiswhyyourefat.com. Smartse (talk) 16:53, 6 September 2010 (UTC)

The pictures at thisiswhyyourefat.com made me want to vomit, not laugh. -Atmoz (talk) 19:28, 6 September 2010 (UTC)

van't Hoff factor problem

A solid consists of a mixture of NaNO3 and Mg(NO3)2. When 6.50 g of the solid is dissolved in 50.0 g of water, the freezing point of the solution is lowered by 5.15 degrees C. What is the composition by mass of the solid?--74.232.4.49 (talk) 22:16, 5 September 2010 (UTC)

How many grams are there of NaNO₃ and Mg(NO₃)₂?--74.232.4.49 (talk) 22:19, 5 September 2010 (UTC)

We won't do your homework for you, sorry. Regards, --—Cyclonenim | Chat  00:52, 6 September 2010 (UTC)

You might find inspiration at Freezing point depression. Dolphin (t) 04:13, 6 September 2010 (UTC)

You have to find out the decrease in temperature that each solid gives. Then use an equation to figure out by all the data. --Chemicalinterest (talk) 10:58, 6 September 2010 (UTC)

September 6

Skyscrapers

I was reading the articles Mile-High Tower and Dubai City Tower. Dubai City Tower will be 2,400 m high with 400 flrs which will be a remarkable achievement. I was wandering whether it will be possible within next 30 yrs to build a building which will be the tallest structure on Earth, i.e. taller than Mt Everest? I'm not expert of skyscraper technology, do those who are knowledgeable in this area see such progress in the near future? --Galactic Traveller (talk) 02:07, 6 September 2010 (UTC)

Highly unlikely. Skyscrapers become feasible when the value of land (such as in a central business district) becomes so high that it is economically feasible to construct a very high building. The cost of a skyscraper increases in proportion to its height to some exponent greater than one. (For example, perhaps the construction cost is proportional to the height to the exponent five. That would mean doubling the height of a proposed building would increase the construction cost thirty-two times.) So a super-skyscraper would only become feasible in a district where the value of land was extremely high. And when the cost of doing business in one business district becomes conspicuously high, another business district emerges nearby, with much lower costs. Probably no business district on Earth would justify a skyscraper approaching 2400m, and certainly not one as high as Mt Everest.

So that begs the question Why do architects do preliminary designs for super-skyscrapers? I guess it is an interesting design study. Getting your plans published would do good things for your reputation if you were an architect. But would anyone be willing to finance one of these super-skyscrapers? Unlikely. I notice the X-Seed 4000 and Dubai City Tower are presently nothing more than eye-catching ideas. Dolphin (t) 03:36, 6 September 2010 (UTC)

Building a super tall is to some extent also a way to show off and announce your presence to the world hence why it tends to be more common in developing countries recently. However it remains difficult to imagine anyone would build a 2400m building in the near future. I have no idea if the DCT was ever really intended to be a serious design proposal or just a design idea (like the X-Seed 4000 was), but notably the design was released in August 2008 which was still the early days of the current economic problems (most of the work of course likely been a while before) and notably before Dubai's problems which resulted in them effectively being bailed out by Abu Dhabi several times [33] [34] which is generally believed to be a key reason the largest supertall they do have was renamed from Burj Dubai to Burj Khalifa. BTW did you read the X-Seed 4000 article which notes "Unlike conventional skyscrapers, the X-Seed 4000 would be required to actively protect its occupants from considerable air pressure gradations and weather fluctuations along its massive elevation." Nil Einne (talk) 04:08, 6 September 2010 (UTC)

I presume the question is basically whether it will be technically feasible, not whether anybody will have a reason to do it. My impression is that theoretically it is feasible, but it would have to make use of exotic materials quite a bit stronger than steel per unit weight, materials such as carbon nanotubes or even diamond. Looie496 (talk) 05:45, 6 September 2010 (UTC)

The existence of Everest, (or, for a greater challenge, Mauna Kea) is proof that it is possible to construct such structures from ordinary rock... if a large enough footprint is permitted! We'd need a more stringent set of specifications to determine how tough a material is actually required. Wnt (talk) 07:25, 6 September 2010 (UTC)

My understanding is the the lithosphere underneath Everest is unusually thick, and Mauna Kea is located over a mantle hotspot. It wouldn't necessarily be possible to place something like that at an arbitrary location without it sinking into the earth. Looie496 (talk) 18:42, 6 September 2010 (UTC)

I'd also suggest that as well as the sheer technical challenge there is a physiological aspect. Even if the building could be built, would it be usable? Altitude sickness could be a real issue, as could regular compression/ decompression.

ALR (talk) 15:48, 6 September 2010 (UTC)

Not exactly related, but you might enjoy reading the Space elevator article. APL (talk) 20:23, 6 September 2010 (UTC)

MOSFET?

I have an electronic component labelled K3797. I think it's a n-type MOSFET transistor. The resistance between the source and drain terminals decreases to nearly 0 immediately after I apply 9V to the gate, but takes about 10 seconds to return to its previous value after I replace the 9V with ground. In fact, for the first 3 seconds, the resistance doesn't even change measurably. Why does this happen? I always thought transistors responded immediately, not after 10 seconds. --99.237.234.104 (talk) 03:14, 6 September 2010 (UTC)

Is the ground rail really at ground or is it just a copper track that does not connect to anywhere or is it via a capacitor etc?--Aspro (talk) 08:43, 6 September 2010 (UTC)

Could you please post a picture of the component next to a ruler? Why Other (talk) 22:30, 6 September 2010 (UTC)

Killing the pain

Endorphins are constantly referred to as "nature's painkillers." If they are the body's natural way of stopping pain, why do we take artificial substitutes instead of some kind of endorphin pill for our various aches? Or endorphin injections for people with chronic pain, etc. 71.104.106.143 (talk) 07:37, 6 September 2010 (UTC)

At a brief scan, I don't see the answer in the endorphin article, but my guess would be that they probably can't cross the blood-brain barrier. Maybe they would work if you injected them into the spinal column, but that seems extreme.... Trovatore (talk) 07:40, 6 September 2010 (UTC)

The article touches on this, noting that hypothalamic neurons release beta-endorphin directly into the brain; there is some question about whether or not endorphins circulating in the bloodstream are capable of crossing the blood-brain barrier in sufficient concentrations to be meaningful. Meanwhile, oral administration of peptides like beta-endorphin are plagued by technical difficulties. This article gives a good outline of the the major problems: digestion by gastric enzymes in the stomach and peptidases in the intestinal lumen; hydrolysis and denaturation by stomach acid. (Be aware that the article is written by a company seeking to market products that purport to circumvent some of these problems, and take their assertions about how they have been 'solved' with a large grain of salt.)

In addition to the relative ease of delivery, the simpler synthesis, purification, and storage of synthetic small-molecule painkillers are not to be overlooked. The synthetics are generally much smaller molecules, and are apt to have a much longer shelf life (particularly when unrefrigerated). TenOfAllTrades(talk) 15:16, 6 September 2010 (UTC)

There's also the issue that endorphins tend to be fast-acting (ie., to have quickly dissipating neuronal effects). Which is why chronic pain sufferers need pain management in the first place, of course. (Chronic pain is a problem which our natural physiological responses don't deal with as well as modern medicine perhaps because it just wasn't too much of a problem in our evolutionary history (if you were hurt bad enough to have it, you'd probably just die before it got too bad?), whereas pain itself is very evolutionarily advantageous (subject to various trade-offs and exceptions, which endorphins are "designed" to deal with even more evolutionarily advantageously:). Wikiscient (talk) 17:18, 6 September 2010 (UTC)

I'd also be a bit worried about addiction issues. Endorphins aren't merely pain killers, they are euphorics; opiates, for instance, are close mimics of endorphins, and use of opiates can rapidly lead to psychological dependency. Access to 'the real thing' might have some fairly nasty repercussions. --Ludwigs2 17:53, 6 September 2010 (UTC)

It's a bit puzzling why our teeth have evolved to be capable of generating so much pain given that we haven't been able to do much about it until recently. It's pretty easy for a primate to crack a tooth and end up in a world of pain sometime later. Seems odd. This struck me as I was having a tooth pulled last week having lost patience with the tooth's not at all helpful approach to telling me that there was a problem. Sean.hoyland - talk 19:03, 6 September 2010 (UTC)

That might be because you have someone to pull the tooth. Otherwise... how are you going to be goaded into doing it yourself with your bare hands? But more to the point, I suspect that our species first evolved in regions with very high flouride levels in the water. Wnt (talk) 21:59, 6 September 2010 (UTC)

Could Gene Therapy help in the removal of scars?

I know I asked a similar question a while ago, only with the extracellular matrix with a cool video:

http://news.bbc.co.uk/2/hi/7354458.stm

but after reading this from http://curezone.com/forums/fm.asp?i=837983 :

"Have you ever wondered why scars persist on the skin even though the skin is by far the most regenerative organ that we have?

I have read some very interesting information lately on scarring. Contrary to popular belief on this site, scars are really not sites of incomplete healing or sites still in the process of healing. These areas of skin have healed. It's just that they have healed with scar tissue. Scar tissue is the glue that fixes the wounds.

A new generation of skin cells migrates from the basal cells (often called dermal stem cells) within the subcutaneous layer of tissue every 30-40 days. These cells will produce cells based upon the genetic information encoded within their cells that dictates the specific charachterics of each cell that slowly migrates to the epidermis (surface layer of skin). When tissue becomes scarred, the genetic information (DNA) within these basal cells actually becomes radically altered. In essence, the genetic formula for skin cells then becomes reprogrammed according to the scarred skin. The DNA of these basal cells now contains the information that instructs these cells to produce skin cells that are scarred. The scarring literally becomes locked within our DNA. It as if we were born with them.

This is why scars are perpetually on the skin even though the skin cells replace themselves every 20-40 days. Scars, as some would have you feel, are not areas of incomplete healing. These areas have healed and they have healed with scar tissue.

This is why scars are so difficult to change. You would have to figure out how to reprogram the DNA of these basal cells once again. Unfortunately, no one has been able to do this. Although scarring is easily programmed into the genetic information through the aquisition of a traumatic wound, it is impossible thus far to reprogram a lack of scarring.

Anybody who can figure out how will be the personal saviour of millions that suffer from scarring, especially facial scarring."

So after reading this, I am wondering if someone gets the reprogramming right, will it be possible to remove a scar for good?

I know the wikipedia scar article says it can't currently be done but it is does not address the applications in gene therapy and is quite old. I am also suggesting that a new article on scars be created so that new break thorughs in the medical world so that major breakthroughs like the one about the extracellular matrix can be incorporated into wikipedi and will be recognized and will give hope to millions upon millions of people who read the wikipedia article on scars and think that scar removal is impossible and give up hope.

Also, I was wondering if the article has a valid point on reprogramming scars

So thank you all very much.— Preceding unsigned comment added by 139.62.86.190 (talk • contribs)

I am very doubtful of the claim "When tissue becomes scarred, the genetic information (DNA) within these basal cells actually becomes radically altered". There is no mention of this in our scar article. I am sure that traumatic injury and subsequent inflammation triggers biochemical processes that lead to scarring, but I would like to see a reliable source for the claim that this actually modifies the DNA of the surrounding skin cells. Gandalf61 (talk) 09:36, 6 September 2010 (UTC)

They are probably talking about changes in gene expression profiles due to epigenetic changes in the cells around the wound (i.e. not altering the genetic information itself but changing the way in which different genetic programs are carried out). Basically, every cell type has a characteristic transcriptional profile that defines what that cell type does. A deep skin injury would cause a variety of different responses, from the blood clotting cascade to degranulation of platelets and various immune cells, to local production of signaling molecules like transforming growth factor. These conditions could set up the types of biochemical signaling pathways that would alter the gene expression of the skin cells and convert them from "normal replacement mode" to "repair mode". That being said, I would expect that once the scar has been formed, the dermal cells would revert back to "normal replacement mode".

Finally, the scar article says:

"Scar tissue is composed of the same protein (collagen) as the tissue that it replaces, but instead of a random basketweave formation of the collagen fibers found in normal tissue, the collagen cross-links and forms a pronounced alignment in a single direction."

Basically what this means is that the repair process creates an imperfect solution that persists in the form of a scar. This isn't necessarily something that could be fixed by gene therapy, it requires remodeling of the extracellular proteins themselves. --- Medical geneticist (talk) 11:40, 6 September 2010 (UTC)

Gene therapy is unlikely to become useful in cosmetic surgery although stem cell therapy#Wound healing may find common ground between the two. Chemical peel may also be of interest. Why Other (talk) 22:36, 6 September 2010 (UTC)

Faith

Why is there such a division between those who believe in god and those who don't - what factors influence whether someone has faith? And is there any way people could do some big research project and prove the issue once and for all? TheFutureAwaits (talk) 12:52, 6 September 2010 (UTC)

Is there really "such a division" ? Althought there are clearly vocal extremists on both sides of the debate, I suspect the majority of people are more moderate and either don't feel the need to impose their own beliefs on others, or don't have a firm belief either way, or just plain don't care. Gandalf61 (talk) 13:02, 6 September 2010 (UTC)

Indeed. And what sort of a research project would be appropriate for proof of answers to such a question? ("After six hours, the fleece was found to have retained 30ml/m³ of water as measured by psychrometer.") Also, is this really appropriate for the Science desk? It sounds like more of a Humanities problem. Marnanel (talk) 13:18, 6 September 2010 (UTC)

Perhaps you've heard of a discipline called Sociology? I hear they even use statistics these days... ;-) --Mr.98 (talk) 14:16, 6 September 2010 (UTC)

There have been some studies on religiosity and genetics; I don't have the references at hand and am not up to date as to whether they are seen as likely or crackpot. Just putting that out there as one of the proposed influences I have seen bandied around. There is a lot of work on Religiosity and intelligence, and religiosity and education, as well. --Mr.98 (talk) 14:16, 6 September 2010 (UTC)

We also have articles on faith and rationality and Relationship_between_religion_and_science for an overview. --- Medical geneticist (talk) 16:21, 6 September 2010 (UTC)

Do you mean "a big research project" to decide whether what some people have "faith" in (eg. "God") is really "real" or not, FutureAwaits? Because that's a big project that has been around for a long time: see eg. Existence of God. But understand that "belief" becomes "knowledge" whenever faith does get settled that way, so there will always be room for faith as long as knowledge is incomplete. Wikiscient (talk) 19:11, 6 September 2010 (UTC)

Wasn't there also a large double blind trial on the power of prayer ? Didn't it show that hospital patients who knew that people were praying for them recovered more slowly from illness (possibly due to performance anxiety) ? I'm not sure whether it has been published yet. I recall it being mentioned in a Dawkins book. Sean.hoyland - talk 19:12, 6 September 2010 (UTC)

If the patients knew they were in the group being prayed for, the trial wasn't double blind. Unilynx (talk) 20:48, 6 September 2010 (UTC)

It would be if they knew someone may be praying for them, but didn't know for sure if they really were or they were getting the placebo (i.e. no prayer) 22:08, 6 September 2010 (UTC)

You're probably thinking of the STEP project. -- BenRG (talk) 21:19, 6 September 2010 (UTC)

It is misleading to try to determine the existence of God by the effectiveness of intercessionary prayer. Some might believe in the existence of God without prayer, or that mundane magic is not the purpose of prayer. Perhaps the purpose of prayer is not to inform an omniscient God of one's woes and wants, but to allow the pray-er to address his faults and nobler desires within himself, or to feel the friendly companionship and love of the maker of the universe when all others fail, or to receive gentle guidance or divine inspiration, or to track through the words and logic of the ancient formulae to be able better to understand what is the right thing to do, or to strive toward Heaven regardless of the suffering on Earth. Or, perhaps most likely, something I don't understand. ;) Wnt (talk) 21:36, 6 September 2010 (UTC)

Faith is defined in terms of doubt, and most faiths see the others as superstition. Given that any fact can be proven from a contradiction, the pattern is clear. Why Other (talk) 22:38, 6 September 2010 (UTC)

Plasma-powered cannon

I was looking at this article, and found it fascinating. Would the plasma created leave behind any chemical residue that would have to be cleaned as is the case with traditional propellant based firearms? ScienceApe (talk) 14:15, 6 September 2010 (UTC)

From the article, it looked like it "plasmized" the air, so only air would be a residue. Maybe some oxidation of the bullet would happen, but not much. --Chemicalinterest (talk) 21:09, 6 September 2010 (UTC)

Cost of building road tunnels

In an ideal world, cars would travel in underground tunnels, leaving the noise- and pollution-free surface to humans. In reality, it is usually too expensive.

What makes up the greatest costs in building shallow road tunnels? Is it labour, or energy for example? Or the cost of materials, or the cost of disposing of the waste? Thanks 92.15.11.248 (talk) 16:25, 6 September 2010 (UTC)

dig —Preceding unsigned comment added by 77.126.131.222 (talk) 17:12, 6 September 2010 (UTC)

What is that supposed to mean? 92.15.19.57 (talk) 19:30, 6 September 2010 (UTC)

see the Big Dig article, which discusses the costs and problems encountered when they did this in Boston. --Ludwigs2 17:55, 6 September 2010 (UTC)

It gives overall figures, but I cannot see any answer to my questions. 92.15.19.57 (talk) 19:30, 6 September 2010 (UTC)

sorry, I thought a breakdown would be in there. you might do some googling and improve that article, because I know this has been discussed extensively in newspapers (it was a controversial project). My guess it would be mostly materials and equipment - tunnel boring machines, for instance, are exceedingly expensive to rent (if I remember right, it can get to 4 or 5 figure bills per day) - so project slowdowns can cause rapidly mounting overruns. Waste disposal would not be overly expensive since the material is non-toxic earth - I think Massachusetts used it for land fill to expand one of the bay islands. --Ludwigs2 19:48, 6 September 2010 (UTC)

As a side note, I disagree about tunnels being ideal. A lot of the enjoyment of driving is the scenery. Also, tunnels don't magically get rid of pollution - it just gets out, one way or another, into the open air. Clarityfiend (talk) 20:22, 6 September 2010 (UTC)

And depending on the material you will be digging through, the cost of repairing all the damage caused above ground, as they found out with the North/South Line (Amsterdam metro). As far as the pollution is concerned, for the 3 billion being spent on that tunnel they surely could build a few 30 meter high pipes to at least get the pollution out of the city. Unilynx (talk) 20:57, 6 September 2010 (UTC)

I don't know the answer, so I'll add a question: How about at least roofing/walling limited access roads with solar collectors, to achieve the same as above (and put an end to snowplowing), and to provide that "area the size of Massachusetts" that solar naysayers are always asking about? Wnt (talk) 21:20, 6 September 2010 (UTC)