Wikipedia:Reference desk/Archives/Science/2010 May 30

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May 30[edit]

Ammonium hydroxide and sodium hypochlorite[edit]

What is formed when these two reagents react? I reacted them and I got some bubbling (very slow). --Chemicalinterest (talk) 00:48, 30 May 2010 (UTC)

Dude, you mixed ammonia and bleach? That's like the one thing that everyone's told not to do with cleaning chemicals. Our Ammonia article says that Chloramines can be formed. Our Bleach article also has some of the reactions possible, including the possibility of making Hydrazine. I hope you're being careful. Buddy431 (talk) 02:02, 30 May 2010 (UTC)
That is a reaction that definitely requires a fume cupboard! The OP survived long enough to ask the question, so must either have been careful or lucky. --Tango (talk) 02:41, 30 May 2010 (UTC)
Or a gas mask. I own one rated for chlorine, I bought it in a local hardware store. Ariel. (talk) 02:50, 30 May 2010 (UTC)
I absolutely agree with Buddy (and others). Did you really have to mix these together yourself to see what happens? There is plenty of stuff on the internet telling you what will happen. After reading a bunch of your questions and answering them (under an IP address, I have since signed up with an actual user ID) I should warn you that all of these exotic reactions and metals (chromium, lead, mercury) can be very dangerous. If you are doing this at home, what sort of apparatus do you have for these experiments? What do you do for waste disposal? My apologies if you are already doing this in a safe environment.
Don't get me wrong, I think that it is great that you want to learn about chemistry, and experiments can be a great way to understand something, but be careful! I'd recommend asking your science teachers, but I seem to remember from a previous post that your chemistry teacher is a dolt - don't ask him/her. Maybe someone else in the department can help you get some background material on your proposed experiments, or even let you use some equipment at school. I am a chemist myself, so I think that it is absolutely awesome whenever students are interested in chemistry, but there is a lot more to it than pretty colours, funny reactions and party tricks. To answer your original question, Buddy is right, chloramine will be produced and this may or may not be the gas observed. It could be chloramine, or it could be ammonia evaporating if the reaction is exothermic.Pmdove (talk) 03:04, 30 May 2010 (UTC)
I totally agree, but the bleach/hypochlorite reaction is almost universally presented totally wrongly in all internet discussions - the reaction is actually used to treat water, and is nothing like the hazard presented someplaces online. Nevertheless Chloramine is produced in considerable quantities.. Be Safe. (talk) 14:12, 30 May 2010 (UTC)
Actually chloramine is likely to remain in solution, and the gas is likely to be nitrogen. Both NHCl2 and NCl3 are not stable in alkaline solutions and will not be present in the very basic NH3 / NaOCl mixture to any significant extent (except as intermediates) (They are formed in acid solutions) (also MSDS reports present a worse case scenario - not what will typically happen). This thesis gives some of the background [1] intro upto p.10 (the internet is full of worst case 'mis-information' that does not apply in strogly alkaline solutions.) All the reactions are exothermic, so de-gasing of NH3 is also a possibility as stated above.
Nevertheless the reaction is still not advisable due to Chloroamine produced, and the heat produced (which could be considerable with concentrated NH3 and bleach). (talk) 14:02, 30 May 2010 (UTC)
see also [2] The reaction is used in water treatment - and called "Breakpoint chlorination" Breakpoint chlorination involves the use of chlorine (in the form of gas or sodium hypochlorite solution) to chemically oxidize ammonia and convert it to nitrogen gas. p.2 (14th page adobe reader count) (talk) 14:07, 30 May 2010 (UTC)
There's some additional info at Bleach#Chemical_interactions - whether you get predominately NH2Cl or N2 depends on which way round you added the solutions, and the relative amounts of each reagent. (talk) 15:16, 30 May 2010 (UTC)
Look on my user page to see what my equipment is. I just reacted about .1 mL of household bleach and .1 mL of household ammonia in a test tube (didn't sniff it). --Chemicalinterest (talk) 18:42, 30 May 2010 (UTC)
Impossible to say without the concetrations... (talk) 18:52, 30 May 2010 (UTC)
BTW I also reacted bleach and acid. --Chemicalinterest (talk) 18:45, 30 May 2010 (UTC)
I've got the same pliers as you. (talk) 18:52, 30 May 2010 (UTC)
I got a whole set of them. --Chemicalinterest (talk) 12:03, 31 May 2010 (UTC)

What complications may arise if Athlete's foot gets left untreated?[edit]

Here, *Athlete's Foot would apparently lead to complications if left untreated. The user didn't say what the complications were. Therefore, could you tell us instead, please? Thanks in advance. --Let Us Update Wikipedia: Dusty Articles 02:54, 30 May 2010 (UTC

See this article for a technical explanation of complications. Check down about 5 or 6 blue headings until you come to "Complications". Bielle (talk) 03:05, 30 May 2010 (UTC)
For a humourous, unscientific, and very, very gross take on this, check out The Stinky Feet ExperimentQuietmarc (talk) 18:47, 31 May 2010 (UTC)

Birth Defects[edit]

An Anonymous editor ( asked at the New contributors' help page; "What are possible birth defects to a baby that can be caused by the mother being morbidly obese while pregnant? Thank you" ;"Could you please inform me of what birth defects can arise?" -- wiooiw (talk) 02:57, 30 May 2010 (UTC)

I know of Spina bifida. wiooiw (talk) 03:02, 30 May 2010 (UTC)
From the abstract of “Maternal obesity and morbid obesity: the risk for birth defects in the offspring” found here comes:
Maternal prepregnancy morbid obesity was associated with neural tube defects OR 4.08 (95% CI 1.87-7.75), cardiac defects OR 1.49 (95% CI 1.24-1.80), and orofacial clefts OR 1.90 (95% CI 1.27-2.86). Maternal obesity (BMI > or = 30) significantly increased the risk of hydrocephaly, anal atresia, hypospadias, cystic kidney, pes equinovarus, omphalocele, and diaphragmatic hernia. CONCLUSION: The risk for a morbidly obese pregnant woman to have an infant with a congenital birth defect is small, but for society the association is important in the light of the ongoing obesity epidemic.
Now all we need is for someone to explain what it says, although the conclusion is clear enough. Bielle (talk) 03:17, 30 May 2010 (UTC)
An "OR" is an odds ratio. A "CI" is the confidence interval. Simply put, there is about a 4-fold (range from 1.87 to 7.75) increased chance for an obese woman to have a baby with a neural tube defect. The "odds ratio" can be multiplied with the baseline odds of having a baby with a neural tube defect to calculate an actual risk, which is usually still quite small for the individual (as noted above), but when considering millions of births the increased risks amount to an important public health problem. --- Medical geneticist (talk) 11:46, 30 May 2010 (UTC)
OK? Caesar's Daddy (talk) 07:49, 30 May 2010 (UTC)
One additional risk is that obese women often don't seem to notice they are pregnant as soon and those around them may not notice all all. They might just normally have an irregular period and figure that's what's happening, since the "baby bump" isn't as apparent. This could lead to consuming alcohol, smoking, or taking drugs which should be avoided during pregnancy. In extreme cases (probably with some denial tossed in), obese women may not even know they are pregnant until they give birth. StuRat (talk) 03:36, 30 May 2010 (UTC)
I'm not sure that's true. Having a bump is a relatively late symptom; the woman is more likely to be concerned with no period and morning sickness, which come before the bump. By your logic we'd have loads of women not knowing they were pregnant until the bump came, and that comes later than the missed period or morning sickness. Regards, --—Cyclonenim | Chat  19:17, 30 May 2010 (UTC)
It's not common - but just Google for "gave birth didn't know pregnant" and you'll find that it's not exactly unknown either! SteveBaker (talk) 02:13, 31 May 2010 (UTC)
Obesity can be associated with all sorts of endocrine dysfunction, such as polycystic ovarian syndrome, so the woman may be having such irregular menstrual periods that she really doesn't notice missing her period. The morning sickness, who knows... it's so variable between women that it isn't really a reliable clue about pregnancy. Anyway, SteveBaker is right, this is not unheard of. There's even a Discovery channel television series about it. --- Medical geneticist (talk) 03:15, 31 May 2010 (UTC)
Fair point, I stand corrected. Regards, --—Cyclonenim | Chat  11:21, 31 May 2010 (UTC)

Luna Moth[edit]

When a Luna Moth hatches does it normally just lay eggs? Aren't they supposed to mate?

As far as I know all lepidoptera (moths and butterflies) strictly engage in sexual reproduction. That is, the adults mate, the female lays eggs, they hatch as caterpillars that then pupate to form a cocoon/chrysalis, from which the adults emerge. StuRat (talk) 03:29, 30 May 2010 (UTC)
Females of Saturniidae moths will start laying unfertilized eggs a few days after eclosion if they cannot find a mate by then (note that the imago stage of Saturniidae has a typical lifespan of only about a week). Nothing will hatch from unfertilized eggs, though, since (as StuRat said already) Saturniidae are incapable of parthenogenesis. --Dr Dima (talk) 06:12, 30 May 2010 (UTC)

Drew Brees Sports Science[edit]

I had some questions about what I thought was some spurious science in a video I saw today, To begin with, the whole football player/archer comparison is quite silly in my opinion, but the questions I had concern the physics at the end. First off, while my physics may be a little rusty, the term "gyroscopic torque" seems like a load of bull to me. Then they talk about gravity inducing a torque, but isn't the only torque on the ball caused by aerodynamic influences and the like? They also mention that the ball wobbles at an "ideal" rate of three wobbles per five spins. But isn't the rate of precession for a small angle of wobble always fixed? And can anyone give a reason why a small wobble would be better (as opposed to no wobble)? And while I'm at it, what causes the ball to dip with its nose always pointing to where it's headed? I might have asked this question a while back, and the answer involved the Magnus effect, but how does this make the dip so perfect? Thanks. (talk) 03:58, 30 May 2010 (UTC)

First of all, Olympic archers shoot from 70 meters - this guy was throwing from 20 yards - so let's keep that all in perspective for that video (though still impressive). They did confuse the torque a little bit: The ball is a gyroscope, as you probably know, and therefore exerts resistance to anything trying to change its axis of rotation. The force of gravity is trying to do just that, so a "gyroscopic torque" is exerted to preserve the ball's direction (I wouldn't use that term - they were just using it to sound all-sciencey). As for the wind going around the ball, there is a airfoil effect for sure and that probably acts in concert to counter gravity. At the end of the day, the "equations" are best worked out by the feedback in distance and grace that the athlete feels.
I'm not familiar with the Magnus effect until reading the article, after which I remember us playing around with that in grad school when we were discussing table tennis with the Chinese students (and we derived most of it ourselves). So when a football spins on the axis on which it's thrown, it should curve a bit like a sliced golf ball, which is definitely not desirable. My guess is what the previous people told you is that the precession (wobble) is a way to counteract that slice effect. It would make sense to me, sorta, without doing the math. Sports physics is very interesting, but I really hate trajectories. SamuelRiv (talk) 19:13, 30 May 2010 (UTC)
Sorry, I don't see why gravity would be trying to change the axis of rotation...doesn't gravity not exert a torque? (talk) 22:12, 30 May 2010 (UTC)
Sorry, you're of course absolutely correct - gravity is not important in this case. The air flow causes the torque (it blows the nose upward because of the shape of the ball) but the ball stays in the same direction by a gyroscopic effect. The "gyroscopic torque" is about the "odd" axis of the ball going through the fat middle.
The reason, again, this is all necessary is because the ball is an airfoil, so it's generating lift by its upward pitch (the nose is higher than the tail, like a climbing airplane). But the air going by is trying to destabilize it, and since the ball doesn't have any of the fins or wings of an actual airplane, it has to spin to remain stable. Thanks for pointing out the error though - gravity exerts no torque on this system. SamuelRiv (talk) 05:47, 1 June 2010 (UTC)


what is the purpose of cutting vents into a attic? wouldent it just make it very cold up there? (i live in a cold place) —Preceding unsigned comment added by Tom12350 (talkcontribs) 05:03, 30 May 2010 (UTC)

One purpose of having attic vents is to vent the smoke out of the attic in case of a house fire -- or else the flammable pyrolysis gases would build up in the attic and form an explosive mixture with the air, which could cause a dangerous smoke explosion or flashover as soon as the firefighters open a door or window in the attic (not to mention that it could choke someone up if not properly vented). (talk) 05:29, 30 May 2010 (UTC)
Another purpose is that houses have to "breathe". If houses are so well sealed that air can't escape, you get a build up of mildew. See Ridge vent. Dismas|(talk) 05:45, 30 May 2010 (UTC)
Warm, moist air which permeates up from the house in winter can cause condensation within the cold, uninsulated, attic space. This condensation then encourages the growth of fungi and moulds which may be harmful to the wooden structure of the roof. In extreme cases moisture may drip back onto the ceiling and cause watermarks. Ventilating the attic/roof space keeps the space dry. Caesar's Daddy (talk) 07:42, 30 May 2010 (UTC)
Here in Texas, the heat that builds up in the attic space is enough to dramatically increase your air conditioning costs in the summer even when the attic floor is well insulated. Venting the attic (and even using a fan to get airflow through there) is a huge help. SteveBaker (talk) 15:29, 30 May 2010 (UTC)
The chief purpose of attic ventilation is to remove moisture that escapes from the interior of the house through poorly-sealed penetrations in the ceiling membrane that can be found in even a well-constructed house. Once it reaches the attic, it will condense on cool surfaces like the roof sheathing. There is no practical reason to keep an unoccupied attic warm in winter - the insulation above the ceiling is supposed to be of sufficient thickness and provided with a vapor barrier. If moisture builds up, it will compromise the insulation's effectiveness, grow mildew and rot the structure. I've never seen any reference to smoke ventilation - the small scale of typical vents would have no practical effect on even a small fire. In warm climates or in summer, roof ventilation will help keep the attic a few degrees cooler, although the effect in most cases is marginal unless you've installed a fan or are using light-colored roofing. Insulation deals with a warm-cold transition better than a cool-hot gradient (it gets heat-saturated), so any cooling of the attic, however slight, will help the air conditioning system.
Even if the attic is occupied, in most cases it is wise to have a ventilated airspace between the insulation and the roof sheathing. Exceptions would be found in a well-installed sprayed insulation installation, or in construction using structural insulated panels, which won't transmit water vapor. Acroterion (talk) 15:48, 30 May 2010 (UTC)

container ship[edit]

If the crew of a container super ship spotted a person floating on a raft in the middle of the Pacific would they be obligated to stop and pick the person up? (talk) 05:19, 30 May 2010 (UTC)

Comment by User: removed.
I have removed an offensive remark from previous poster. Caesar's Daddy (talk) 07:32, 30 May 2010 (UTC)
Now what the hell is so offensive about me saying that I would probably stop to help, except in certain cases? I bet it's a lot more that what most of you would have done if you saw someone in a lifeboat! (talk) 05:28, 1 June 2010 (UTC)
Primer on sailing the high seas. Super container ships, run at speeds of -teens up to approx. 20 knots. While this is not technically fast on land (1 kt is ~1,852 km/h), it causes their braking distance to amount to around a kilometer (give or take) on sea. So in the simplest case it would take them a while to stop/turn/whatever. An immediate stop is not possible.
Such a ship, however, in a situation just like the one described by the OP, is obliged by maritime law to help directly (i. e. by lifebuoy or whatever, time permitting) or indirectly (i. e. by sending out a distress call or informing vessels nearby that a person is in distress) anybody who may be out on sea in distress. Apart from strictly legal requirements, seamen are often plain helpful to each other in what goes just a little bit beyond simple human readiness to help. Father's a sailor, that's how I know. HTH. --Ouro (blah blah) 05:52, 30 May 2010 (UTC)
Ouro is correct about the distance required to stop or turn a large vessel such as a container ship. To reverse direction and return to a point previously passed, such as when rescuing a man overboard, requires careful maneuvering and navigating. See Man overboard rescue turn. Dolphin (t) 11:00, 30 May 2010 (UTC)
Surely they'd have a lifeboat or some kind of zodiac inflatable that they could use to pick up the survivor without the need to stop the container ship? SteveBaker (talk) 15:26, 30 May 2010 (UTC)
Imagining the situation you described, I am seeing a lost sailor trying to reach the released lifeboat and the mother ship disappearing behind the horizon ;) I suppose they could release a lifeboat on the spot, but should at least stop and wait for the guy to reach the ship in order for the rescue to be complete, provided the floating person had enough stamina left to reach the vessel in the first place, seeing as they could have been lost at sea for days without proper food... I guess it depends on the exact situation, i. e. if the person is spotted ahead (like, if the vessel had not passed by them yet, and on seagoing ships lookout is usually maintained via radar and binoculars during watch so as to notice everything, because a radar will probably not pick out a person floating in the water), then the ship could react more quickly by stopping and could probably be able to come to a full stop somewhere around where the person is. A person spotted far off would require much more manoeuvering. If you're worried about delaying the ship that's delivering important cargo, do not - afaicr, delayed ship arrivals aren't all that extraordinary, especially on longer routes. --Ouro (blah blah) 15:53, 30 May 2010 (UTC)
Freefall lifeboat
Usually there aren't traditional lifeboats, or a semi-rigid inflatable in a state of instant readiness. Lifeboats on bulk carriers and tankers, which are prone to sudden, catastrophic failure, and some container ships, are usually freefall-style, and aren't suitable for going out and picking somebody up. Acroterion (talk) 15:58, 30 May 2010 (UTC)
Good photo. However, there are usually others as well, though, which pop out on contact with water and can be recovered, and as such ships usually have at least a small crane or something to hoist things like i. e. crates on board, it is not impossible. I have work and I'm sitting here. --Ouro (blah blah) 16:07, 30 May 2010 (UTC)
Holy Mackerel Batman, do the rescuers get in that thing before or after it is fired at the water? (talk) 02:48, 31 May 2010 (UTC)
They sit inside all the time, Robin, always ready, because nobody ever knows when they will be needed to take action. --Ouro (blah blah) 11:11, 31 May 2010 (UTC)

In fact, there has been just such a rescue by a container ship within the past month. Looie496 (talk) 16:20, 30 May 2010 (UTC)

I believe any ship that can't stop quickly enough to deal with a MOB (either someone from their own ship falling over the side, or someone else they just happen to pass close to) is required by international law to carry a powered boat suitable for such rescues. It wouldn't take too long for that smaller boat to catch back up with the larger ship, assuming the larger ship started slowing down straight away. (In fact, WP:WHAAOE: MOB boat - it's very short and doesn't mention legal requirements, though.) --Tango (talk) 16:27, 30 May 2010 (UTC)

Meditation and sleep[edit]

Can you sleep less if you meditate? The guy who told me this, also told me you can levitate through meditation, so I am not quite sure I should believe him on this point. On the other hand, it sounds plausible that you might need less sleep if you have less stress along the day. -Mr.K. (talk) 12:47, 30 May 2010 (UTC)

Regarding levitation, I read that the monks in Tibet and elsewhere sit cross-legged in their cells, and with a lot of practise they can jump into the air while maintaining that posture, leading to stories and photos of levitation. (talk) 13:42, 30 May 2010 (UTC)
That's a really funny image; somehow I doubt that it would look like levitation, as opposed to a bizarre form of hopping. Anyway, concerning the question, it would make sense, and there are claims by proponents that that happens, but I couldn't spot much in the scientific literature to support it. A more common report is that meditation increases sleep in some people by reducing stress-related insomnia. Looie496 (talk) 14:37, 30 May 2010 (UTC)
The flying bit is described at TM-Sidhi_program#Yogic_Flying Youtube is a good source: search for "yogic flying" eg [3] Stupid and strangely beautiful. (my opinion). (talk) 15:23, 30 May 2010 (UTC)

Levitation revealed, ScienceApe (talk) 17:56, 30 May 2010 (UTC)

Meditation might temporarily make you less tired even given the lack of sleep, but I wouldn't count on it over longer periods as sleep deprivation sets in. Stress can contribute to either insomnia or hypersomnia. Techniques like yoga and taichi may lower your stress, but again any reduced need for sleep is probably only temporary. ~AH1(TCU) 18:11, 30 May 2010 (UTC)
You'd probably feel better using the meditation time to sleep, if you are short of sleep. (talk) 19:39, 30 May 2010 (UTC)

Ecological implications of eradicating malaria-carrying mosquitoes[edit]

What would be the ecological implications of eradicating Anopheles mosquitoes, particularly Anopheles gambiae, which are responsible for transmitting malaria? I don't mean from the huge decrease in human mortality, with the population pressures that would be likely to result, but in terms of the effect on whatever else (apart from malaria itself) which relies on these mosquitoes for its life. DuncanHill (talk) 16:40, 30 May 2010 (UTC)

Cracked has you covered. No specifics of course, but may be of interest to you. Vimescarrot (talk) 17:27, 30 May 2010 (UTC)
Thanks, I was really looking for something more detailed. DuncanHill (talk) 09:07, 2 June 2010 (UTC)
Any mosquito (larval stage, specifically) tends to be an important food source for water borne organisms. Indeed, some organisms subsist entirely on mosquito larvae. Then again, the average area in Africa that permits mosquito habitation tends to support more than one species, so the annihilation of one species may not be that big a problem in the long run (and better yet, the malaria bearing mosquitos form only a very small subset of the total set of mosquito species). There's aren't that many scientists studying total (but species specific) erradication. I looked at the most recent good paper on this, but they didn't really mention environmental impact [4]. An earlier paper from another group considered population replacement with a non-malaria-bearing, but otherwise identical species, to avoid the environmental issues [5] (unfortunately, they only got it to work in fruit flies, which as you may be aware, is not exactly a major source of malaria). Someguy1221 (talk) 09:26, 2 June 2010 (UTC)

Setting up a fishtank[edit]

I had many a fishtank when I was a kid and now as an adult, I just bought a 20 gallon for my family to enjoy. As a kid, I completely ignored pH, ammonia/nitrogen and everything else that relates to "water management" and everything always went great -- I did, however, worry about chlorine and made it a rule to use 1-day-old tap water when adding/exchanging. So my question is now that I'm starting again, was it dumb luck that things worked out or is it really not such an issue assuming one has a good filter and does exchange water about once every 2 months (and to give you an idea of the hardiness/sensitivity of the fish that I will include in my tank, it will most likely consist of danios, gouramis and catfish).
And then as a follow up, the fishtank article has a bunch of photos -- about halfway down is one of a sad looking tank while the upper most photo in the article displays a beautifully decorated tank. Would I only be able to get all those plants in there and keep them alive if I take care of the pH, salinity, ammonia, etc. or what? DRosenbach (Talk | Contribs) 17:46, 30 May 2010 (UTC)

You'd need to watch the nitrate and ammonia levels in the tank, as those are the biggest killers of aquarium fish. Cleaning the feces from the tank by vacuuming the substrate regularly should do the trick. ~AH1(TCU) 18:02, 30 May 2010 (UTC)
With the caveat that I know absolutely nothing about tropical fish, my experience in the areas that I do know something about is that most of the advice you read on any given topic is aimed at getting you to spend money on stuff. Looie496 (talk) 23:40, 30 May 2010 (UTC)
That question is a whole book in itself ..
  • firstly what sort of filter did you use/are you planning to use
  • secondly you might be lucky with plants (I wasn't)
  • thirdly for having a successful planted aquarium the conditions and set up can change considerably compared to conditions for a successful non-planted equation
  • fourthly - no it doesn't need to be an exercise in water testing and chemistry , (but it can be if you want)
  • fiftly - one big factor that must be considered is the requirement for CO2 for plant growth - luckily fish breath out CO2 - unluckily strong filtration can de-gas the water of CO2
  • sixthly - your fish might eat the plants... especially if the plants are soft leaved and the fish are omnivores - one of the more successful experiences I had was with carnivorous and heavy eating catfish and soft leaved plants - the fish made the fertiliser, and the plants grew in it...
  • seventhly - some plants are easy, others are hard to grow - just like fish.
I'd like to recommend a book - in fact most I've seen contain about the same info - in general the tricky bit is growing both fish and plants in the same aquarium. (talk) 23:42, 30 May 2010 (UTC)
I used to run 2 tanks and am now running one - a Rio 300 (about 3x larger than yours). When we initially set up our first tank (about the size you're talking about) I knew nothing about the chemistry of tanks and my initial fish (mostly guppies) pretty much all died fairly quickly. I then learnt about the chemistry, and it became clear that the probably died of ammonia poisoning. The best way to avoid this is to start with few fish and add them slowly, so the bacteria in the tank can grow to accommodate the larger ammonia load. You need 2 types of bacteria - ones that convert the ammonia to nitrite, and others that convert nitrite to nitrate. You don't need to add them - they grow of their own accord. I would recommend testing for ammonia in a new tank if you do nothing else. If it gets too high, change some of the water. You can use tap water but you must use a additive to remove the chlorine. You should also count on making regular water changes in order to keep the nitrates down - I change about 4 to 5 gallons of water each week and would recommend you do the same. --Phil Holmes (talk) 11:31, 31 May 2010 (UTC)

Controlled burns on oil and hurricanes[edit]

Hi. Let's say that a medium-sized hurricane was threatening the Gulf Coast, and was heading directly for the Deepwater Horizon oil spill. If controlled burns were set over a large portion of the oil, what if any effect would that have on the hurricane? Would the extra heat fuel the hurricane, or would it cause the storm to expand and unravel, or expand to have a dangerous storm surge, or disrupt its eyewall, or cause it to change direction, or would the surge of the storm cause the oil to pool underneath the eye, or would it cause upwelling that cooled the oil, or would it create more shear and tornadoes, or would the storm plow the fires into the coast? Thanks. ~AH1(TCU) 18:00, 30 May 2010 (UTC)

There is no way to really predict what would happen. Weather is chaotic by nature, so the hurricane would react differently for different sizes, shapes, orientations, temperatures, durations and positions of fires. We know large fires can create storms; there was a large vortex—called a tornado by some—caused by an oil tank fire in California in 1926 that killed two people after traveling almost a mile away from the fire. Pyrocumulus are a well-documented phenomenon whereby clouds and even thunderstorms can be created by large fires. However, I feel it would be impossible to predict the effects, and they would probably not be good. Hurricanes are basically a giant heat engine; adding more heat just isn't a good idea. Not to mention that, with the amount of rain and waves generated by the average hurricane, it seems likely that the fire would just go out.-RunningOnBrains(talk) 20:22, 30 May 2010 (UTC)
On top of which modelling the burning oil is hellish tricky. Rough waves mean the oil forms a moussy emulsion with sea water: when we tried (twenty years ago) replicating the mousse to try to burn it we found the characteristics were incredibly sensitive to how well mixed the emulsion was, as well as the exact crude characteristics including how long it had been on the surface losing volatiles. We even looked at floating wicks in it etc but it is not going to be burning well in a storm, not so much because of the rain but from the breaking waves. The only good news is that oil is basically biodegradable; in a decade all traces will have gone eaten by bugs and the sensitive nature sites will be mainly back and happy. Of course some Corals and some oil companies might not survive the "obvious" solution of time. --BozMo talk 21:14, 30 May 2010 (UTC)
Hurricanes are FAR bigger than that (than tornadoes or pyrocumulus). The heat from fire would have no measurable affect at all. The change in the water/air interface might have an affect, but I don't think it'll be big. The energy released in a hurricane is on the scale of hundreds of nuclear bombs. Ariel. (talk) 21:44, 30 May 2010 (UTC)
Would the huge fire generating a pyrocumulus storm be likely to cause rotation and gradually become a tropical depression (and then tropical storm, followed by hurricane)? Falconusp t c 23:41, 30 May 2010 (UTC)
Unlikely. Ariel is correct in that it would be very unlikely to have any effect at all; pyrocumulus storms are on the order of a few kilometers. Hurricane formation depends more on large-scale features than storm-scale features. I was just playing devil's advocate in saying that if you managed to make a fire big enough to affect a hurricane, it might only serve to strengthen the storm. Careful using that "nuclear bomb" analogy though...nuclear bombs are near-instantaneous events, while hurricanes can last weeks.-RunningOnBrains(talk) 00:59, 31 May 2010 (UTC)

new LED lightbulbs[edit]

I've heard that a new generation of LED light bulbs are coming out soon. Will they come on quickly (the main problem with compact flourescent bulbs is the time it takes them to get bright.) Bubba73 (You talkin' to me?), 21:07, 30 May 2010 (UTC)

It depends what you mean by 'new generation of LED light bulbs'. LED are continually improving, and light bulbs for existing fixtures already exist. In other words, there are what could be called new generations of LED light bulbs probably every year. One of the biggests problems is probably cost particularly for bright lights. There should be some decent replacements for 60W incandescent lightbulbs coming out at the end of this year or early next year (some decent ones may already exist), these were demonstrated at the recent Light Fair in the US. [6] [7] Expect them still to cost quite a bit though. Sorry misread the question, see the next answer. Nil Einne (talk) 21:33, 30 May 2010 (UTC)
Yes, all LEDs come on instantly. (talk) 21:38, 30 May 2010 (UTC)
Thanks, and the links were informative too. Bubba73 (You talkin' to me?), 23:58, 30 May 2010 (UTC)
LED lightbulbs are already here - I have three of them in my home and I'm typing by the light from one of them right now! They don't need any time to 'warm up' like CFL's do. They use less electricity than any other type of light - are longer-lived than any other kind - and they are actually made of clusters of LED's so when they do fail, they tend to do so one LED at a time - so they rarely just go black like a failed incandescent or CFL. However, they are still hideously expensive - and unless you want one as a gimmick or you are a fanatical tree-hugger, you should probably wait for the prices to drop. They aren't close to being cost-effective yet. Mine are cool because you can adjust the color to any RGB value, remotely from your PC...I like a slightly yellowish light - but...hold the light is blue-ish...and now pink! LED Xmas tree lights were in most stores last Christmas - and specialized lighting for swimming pools and hot-tubs have been using LED's for at least 10 years (my 10 year old hot-tub has LED lighting). SteveBaker (talk) 02:09, 31 May 2010 (UTC)
What kind of bulb is it? Can you give a link to a store or vendor, Steve? --Ouro (blah blah) 16:00, 31 May 2010 (UTC)
I don't want one as a gimmick but I do want to save money and energy. I have mostly CFLs in our house. Color is an issue - I like daylight color. Bubba73 (You talkin' to me?), 02:37, 31 May 2010 (UTC)
Like CFls, LEDs can come in a variety of colour warmths - like CFLs the common type seems to be warm white ie 3500K rather than daylight 6500K+ , but you can get daylight type too. (talk) 14:01, 31 May 2010 (UTC)
(EC with both above) I originally thought you asked 'are the next gen LEDs coming out soon' but then realised I was mistaken. Glad that it was still of interest. I've been following this area recently, more from a torch/flashlight angle but I've of course read or thought of things related to LEDs that may be of interest even from a lightbulb perspective.
Another interesting this is that Cree (who were mentioned in some of the above links in other areas) are also going to release the XM-L LED in (Northern hemisphere) Autumn of this year [8] [9]. This is supposed to be rated to output 750 lumens from a single die emitter (in other words a single continuous LED) which they say is equivalent to a 60W incandescent (although based on our Incandescent light bulb, they probably mean a 60W 220V bulb rather then a 110V one). I suspect the 750 lumens is the maximum of the LED bin at the time of their release, in other words the LED they release might only be rated for something like 675-750 lumens (there is always variance, LEDs are sold as bins and guaranteed to output something in that range at whatever the maximum rated current for the LED) however I still find it an interesting development.
I don't however know whether it will actually be used much in replacement bulbs for incandescent lightbulb types (like the E27), there are already multi-die LEDs (basically they stick 4 or more LEDs on a package and connect them, somewhat similar to some earlier dual core and quad core CPUs) like the Cree MC-E & SSC P7 which are rated for slightly higher output [10] and have been available since early 2008 but don't seem to be used much for this purpose that I could find (of course most manufacturers don't say what LEDs they're using).
It may be because they tend to have poor Colour Rendering Index compared to what people are releasing for other LED light replacements. (Also the maximum output is usually those with the colour temperature of the cool white/bright daylight variety which don't tend to be so popular in the West.) Also these LEDs aren't necessarily the most cost effective from a $/lumens area. Or other factors, I don't really know much about (as said, I don't really know that much about light bulb replacement designs).
BTW, there's also the Luminus SST-50 and SST-90 which are also already available but again don't seem to be used light bulb replacement that I've seen. These use what's called a photonic lattice so can also be called a single die but are somewhat different from more traditional emitters. If you looked at the earlier DealExtreme link you may notice the currently available best bin of the SST-90 outputs when driven with (the maximum rate) 9 A, 2350-2820 lumens! According to our incandescent light bulb article, the minimum is equivalent to a 135W 110V bulb.
But even so, don't expect those sort of outputs to be done in a typical light bulb replacement anytime soon (meaning perhaps within the next year or so). One of the things I didn't mention above is for such high outputs, temperature really starts to become a problem which will not only kill the LED if it gets too hot but reduces effiency too (i.e. light output). (In addition to the heat output from the LED, the driver/regulator of the LED also can output a fair amount of heat since it's unlikely to be close to 100% efficient.) Incandescents and even CFLs can get quite hot, but they can survive such temperatures, LEDs can't. You need good heatsinking and I don't think from what I've read you're likely to be able to provide sufficient heatsinking for something like a E27 to do that (perhaps particularly given the variety of fixtures, including some enclosed, that may be used). Well unless you have some active cooling which is obviously unlikely to be considered suitable for household usage. Of course the fact the heat is a problem means effiency (lumens/watt) is important. See also some discussion [11].
Of course all these are obviously used for general/fixed lighting purposes, flashlights are clearly only a tiny proportion of what they're used for, this mentions a few. Other custom light fixtures (perhaps also fluorescent tube replacements) can obviously better accomodate the heatsinking/cooling requirements then having to design for existing bulb types. [12]
P.S. To avoid confusion, the current draws are at the forward voltage of the LED which is likely to be something in the 3-4 V range.
P.P.S. As a brief mention of cost. For the P7, you can get an LED with some sort of driver suitable for a torch for about US$15 with shipping from China/HK (i.e. this is a retal price). However the optics, heatsinking, driver suitable for main voltage are obviously going to add a fair bit. A cheap P7 based torch which uses rechargable lithium ion batteries is about $30 from China/HK (again with shipping). However these often don't draw and therefore use the maximum rated 2.8A for the P7. I would guess $40+ is likely for a light bulb replacement.
Nil Einne (talk) 02:52, 31 May 2010 (UTC)
I don't understand your use of "bin." Is it a technical term, or do you just mean "a bin of light bulbs?" Thanks. Edison (talk) 15:11, 31 May 2010 (UTC)
It's a form of grading - 'best bin' means those which performed the best. (talk) 15:28, 31 May 2010 (UTC)
If you look at [[13]] it looks like LED's are currently about as efficient as CFLs. There is still a lot of room for improvement in terms of luminous efficiency though. (talk) 13:45, 31 May 2010 (UTC)

Lawn Mowers[edit]

This is not a medical question, more just looking for confirmation of what seems common sense to me. The other day, my friend informed me that I should stop using my gas powered lawn mower and buy an electric one; he told me that I could get carbon monoxide poisining from using it to cut the grass. Being that I would be using it outside, this sounds rather unlikely to me. So, in short, is there any possible validity to what he is saying? (talk) 21:58, 30 May 2010 (UTC)

If you cut the grass with a gasoline-powered mower in a small enclosed room with no ventilation, carbon monoxide poisoning is a real hazard. Edison (talk) 22:07, 30 May 2010 (UTC)
I don't know exactly, but of all of the people that use gasoline lawnmowers responsibly (i.e. not in the living room of their house), I haven't heard of any cases of CO poisoning. Millions of people presumably use them, so if it was a serious risk, I suspect that it would be a very well-known thing. Falconusp t c 23:43, 30 May 2010 (UTC)
I have a hard time imagining getting much exposure to CO outdoors, even with a typically fume spitting lawnmower engine; people just don't spend that much time mowing lawns, and outdoors, the risk is greatly diminished. Most of the Google hits relate to not running the mower in a shed or garage, for example. All that being said, lawnmowers (and other gasoline powered yard tools) are notorious for not having very clean or well filtered engines. See, for example, [14], as well as a source from the epa: [15]. So even if it's not a health risk, your mower may be hurting the environment. Buddy431 (talk) 00:43, 31 May 2010 (UTC)
(edit conflict) Carbon monoxide poisoning is only a hazard in encloses spaces, or in some extreme circumstance that I can't think of right now. It is metabolized quickly, and exposure to oxygen is the antidote, so it has no cumulative effect such as those seen with methyl mercury and other environmental contaminants of concern. Thus there really is no reason I could think of that gas mowers would be dangerous.-RunningOnBrains(talk) 00:51, 31 May 2010 (UTC)
Here is one such extreme circumstance, a ghost town caused by CO and CO2 poisoning from a smouldering underground fire. (talk) 11:20, 31 May 2010 (UTC)
That and when the coal is burned, part of the ground unexpectedly collapse. Googlemeister (talk) 13:15, 1 June 2010 (UTC)
There are lots of reasons to consider getting an electric lawnmower (gas mowers are horribly polluting, noisy, heavy and a pain in the neck to maintain as they get older) - but I agree that if used in a reasonable way, carbon monoxide poisoning isn't one of them. SteveBaker (talk) 02:00, 31 May 2010 (UTC)

Time reversibility[edit]

How can you show mathematically that a law of physics, like gravity, is time reversible? (talk) 22:32, 30 May 2010 (UTC)

The hows are explained at Time reversibility - for gravity (ie 'newtonian' gravity) the following section applies: "If a deterministic process is time reversible, then the time-reversed process satisfies the same dynamical equations as the original process, AKA reversible dynamics; the equations are invariant or symmetric under a change in the sign of time"
The last sentence above gives the simple way to tell. eg consider motion under gravity as a function of time.
Ask if you need more explain. (talk) 23:30, 30 May 2010 (UTC)
OP here: I would think this means that any time derivative changes sign, and hence a second time derivative preserves sign. So for something like gravity, where d2r/dt2 = (GM/r3)r, nothing changes when time changes sign, so the motion is identical, except the velocity changes sign so the particle will travel in the opposite direction. Is this right? (talk) 02:56, 31 May 2010 (UTC)
I think so. (talk) 13:33, 31 May 2010 (UTC)
Cool, thanks. (talk) 22:24, 31 May 2010 (UTC)