Wikipedia:Reference desk/Archives/Science/2010 April 15

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April 15

Caustic size variation with temperature

I've noticed that you can see how cold a swimming pool is when it is lit by sun and the water is not still by simply noting the pattern of light dappling the bottom. Cold water has smaller sharper looking caustic patterns while warm water has large soft and slowly moving caustic patterns. Why? -Craig Pemberton 02:09, 15 April 2010 (UTC)

It may not be the overall temp that's directly important, but rather the range of temperature variations within the pool, as each temperature change has an associated change in density, and thus a refraction occurs at the boundary layer. Perhaps a pool which is overall colder but also in sunlight tends to have more temperature variations, and thus more refraction ? StuRat (talk) 02:14, 15 April 2010 (UTC)

To test this I drew a scalding hot bath in a cold tub. The caustics were relatively small. -Craig Pemberton 00:20, 19 April 2010 (UTC)

ISS EVA Capabilities

Hey everyone and thanks in advance for reviewing my question. The bottom line of my question is: does the staff stationed at the International Space Station have the ability to do EVAs (spacewalks) when there is no visiting mission (NASA Space Shuttle or otherwise). In response to the current valve failure in the nitrogen/ammonia tank assemblies, a lot of talk is heard about whether an EVA could be done during this shuttle mission or the next, however I hear no talk about whether the station crew could do a spacewalk during the interim. Obviously, it would be preferable to do spacewalks during visiting Shuttle missions, because the astronauts going up have the ability to train for the exact procedure in advance, but in a more urgent situation, is it possible (with standard equipment kept on the Station, etc.) for the station crew to do a spacewalk during a time when there is no docked mission vehicle? --Nick—^Contact/_Contribs 04:25, 15 April 2010 (UTC)

Sure, They've got both the Quest Joint Airlock and the Pirs docking compartment, though the later is apparently only compatible with Russian suits.

This has been done a number of times. Check out the List of spacewalks since 2000. I believe that all the space walks where "Expedition [number]" is listed as the "Space craft" were based from the space station when no shuttle was docked. (This list is not terribly clear on this point.) APL (talk) 05:15, 15 April 2010 (UTC)

I notice the quest airlock says it allows both kinds of suits, however the Pirs only allows the russian Orlan suits. What is the factor that prevents a US suit being used in the Pirs airlock? Some sort of coupling? I didn't think you had to be coupled during EVA. Vespine (talk) 06:02, 15 April 2010 (UTC)

I'm guessing - but I know that you have to pre-breathe pure oxygen for quite a while before you go outside in order to purge nitrogen from your system to avoid getting "the bends" in the lower pressures used in the spacesuit. That takes a long time - and it has to be done in the airlock because the pressures have to be gradually reduced while you do it. You wouldn't want to be using your limited supply of suit oxygen for that - so if the issue is one of suit couplings, that would explain the problem. SteveBaker (talk) 13:26, 15 April 2010 (UTC)

Car trick

I was looking at the following video: http://www.youtube.com/watch?v=qKxgNOR5QnY&feature=related, and I had some questions about the physics. First, how stable is the car in this situation? It seems precariously close to falling over, but often looks can be decieving. I would imagine that, for the trick to have any reasonable chance of success, the car has to be somewhat stable. But from what I can see, the center of mass seems to be nearly over the the wheel. Do you think weights were added to the left side of the car to make it appear less stable than it actually is?

Second, would it be possible to use the gas in this situation, what with the wheel not being flat on the ground? Thanks 173.179.59.66 (talk) 09:34, 15 April 2010 (UTC)

Oh, and how do you think they would return the car back to its original position? I would think a sharp right turn would do the trick, but is turning right really and option when only two wheels are on the ground? 173.179.59.66 (talk) 09:36, 15 April 2010 (UTC)

Here's the Wikipedia article on it Ski (driving stunt). 194.221.133.226 (talk) 10:03, 15 April 2010 (UTC)

though i'm not convinced by the article - my understanding was that you needed specialist work done to the Axles as otherwise they basically just snapped...That said maybe what I head was a load of cr@p. 194.221.133.226 (talk) 10:05, 15 April 2010 (UTC)

A lot depends on the weight of the vehicle. Something as heavy as the vehicle in the video might well need stronger axles - but I've seen the stunt done with lightweight vehicles that have definitely not been modified ([1], [2], [3], [4], etc). The difficulty lies in getting the vehicle in that position in the first place - you have to hit the ramp at a fairly exact speed to get it to that position without tipping over. However, once it's up there (I'm told), keeping it there is relatively easy - and the larger the vehicle, the easier that is. This is one of the more easily done car stunts - you just have to practice the "getting it up to that position without rolling it over" part. The moment of inertia of a car is huge - it responds fairly sluggishly and you have plenty of time to react to keep it up on two wheels. Steering is done much like on a bicycle...and again, I'm told that isn't difficult. SteveBaker (talk) 13:21, 15 April 2010 (UTC)

as in you haven't ridden a bycycle SteveBaker or as in the steering isn't difficult (much like riding a bike isn't). 194.221.133.226 (talk) 14:47, 15 April 2010 (UTC)

Russ Swift is a well-known stunt driver who regularly appears on Top Gear episodes doing stunts such as these (amongst many others). He also showed Jeremy Clarkson how to do the ski in one of Clarkson's motoring specials. Zunaid 14:55, 15 April 2010 (UTC)

The car in that trick is about as stable as a bicycle. In both cases keeping balance is by a combination of leaning one's body and steering. Having power steering may help. It looks like the stuntmen are not too stressed to wave to the onlookers. I don't think any weights were added to the car. Higher air pressure in the tires might help. The car in the video is probably not the first one in which the driver has tried the trick because it looks undamaged. It is unsurprising to see the trick done by arabs with enough disposable income to play with new vehicles, insignificant fuel price and wide open flat roads without much traffic regulation. Ancestral skill at balancing on lurching camels may help too.
@Second, yes the driver uses the engine to keep the car moving because otherwise it would slow to a stop and become harder to keep balanced when one loses the gyroscopic effect of the rotating wheels. Like on a bicycle. I think the car drivetrain needs to have an LSD or 4WD to sustain the trick.
@Last I'm sure it is easier to come down with a bump than it is to go up. Getting up seems extra risky when done without a ramp but I never saw an example of a car overtoppling on youtube. Cuddlyable3 (talk) 16:47, 15 April 2010 (UTC)

One of the finest articles on Wikipedia is Bicycle and motorcycle dynamics - it says that the idea that some gyroscopic effect is responsible for the stability of a bicycle is discredited. It's all to do with the angle of the front forks. However, the geometry of the steering mechanism of most cars confers similar stability in this case. SteveBaker (talk) 23:29, 15 April 2010 (UTC)

Thanks for the quick replies! Quick question about the stability though. On a bike I'm abe to stay upright by shifting my weight. If the car were to start falling one way or another, how could the driver compensate?173.179.59.66 (talk) 05:22, 16 April 2010 (UTC)

By turning the wheel left/right which will move the car in the (hopefully) opposite direction in which it is falling. Ariel. (talk) 12:48, 16 April 2010 (UTC)

The driver will shift his body weight too. I don't think anyone does the trick while wearing a seat belt. Cuddlyable3 (talk) 23:13, 16 April 2010 (UTC)

Wolverine vs Honey Badger

In a hypothetical fight to the finish, which one would most likely be left standing? Exxolon (talk) 10:02, 15 April 2010 (UTC)

Quite clearly the wolverine. The wolverine often takes prey such as reindeer calves. While both are omnivores, the wolverine can grow heavier than 20-23kgs, whereas a honey badger will not become much more than 14kg (this according to their respective articles). Badgers in general will far more often dine on animals lesser in size than themselves. 88.90.16.251 (talk) 12:20, 15 April 2010 (UTC)

Are you sure? I've seen a video of a honey badger seeing off a lion. Zzubnik (talk) —Preceding undated comment added 13:30, 15 April 2010 (UTC).

Lions tend to be non-confrontional, and regularly back down from fights with smaller animals. Hyena are often observed chasing lions off. Lions would win if they fought such an animal, but they tend to not want to. --Jayron32 14:58, 15 April 2010 (UTC)

Well, not to be overly pedantic or anything, but if the lion backs off, the lion loses the fight, right? He's disqualified himself out of sheer cowardice. Comet Tuttle (talk) 18:17, 15 April 2010 (UTC)

I think if the lion and the honey badger were locked in a cage, and had to fight to the death, the lion could tear it to shreds. If forced to fight, the lion wins. If it doesn't have to fight, however, why bother? --Jayron32 18:54, 15 April 2010 (UTC)

Predatory animals don't generally like to engage in fights against opponents where there is a non-insignificant chance of injury. Injuries, even small ones, tend to add up over the years, you see - and affect the predator's ability to hunt. Impaired hunting ability = death in the cold, hard, brutal indifference of nature. So they will only tend to go after what they consider to be 'soft targets' - unless the situation is extremely dire. --Kurt Shaped Box (talk) 20:59, 15 April 2010 (UTC)

Indeed in such circumstances both win. The larger animal who could have won the fight but would have suffered unnecessary injury doesn't suffer that injury and the smaller animal who would have lost the fight lives another day. One might argue similar things for most human fights where generally the outcome for both is better if they just don't fight. It's usually unfair to say the person who backed down 'lost' just because they avoided a silly fight which would have benefited no one. Nil Einne (talk) 07:42, 16 April 2010 (UTC)

now result

i am very angry to use this web page but could not have any result pattaining to my search —Preceding unsigned comment added by 41.202.199.4 (talk) 11:36, 15 April 2010 (UTC)

If you can let us know what you were searching for, we might be able to help you find it. Karenjc 12:22, 15 April 2010 (UTC)

A little atitude adjustment is likely in order as well. Dauto (talk) 14:19, 15 April 2010 (UTC)

I was assuming that, since the OP's first language doesn't seem to be English and his IP address geolocates to Cameroon, what he meant could have been closer to "I feel bad about coming here asking, but I can't find what I need by searching". Karenjc 14:36, 15 April 2010 (UTC)

Also a little spelling adjustment?--79.76.228.211 (talk) 14:59, 15 April 2010 (UTC)

Could you be looking for something called "NOW", such as the National Organization for Women ? StuRat (talk) 14:21, 15 April 2010 (UTC)

What do these symptoms lead to?

I have been given a fake "patient" with the following symptoms: fever, dizziness, vomiting and diarrhea, a diffuse maculopapular rash on all limbs, puffy edema of the face and extremities, and raised temperature, pulse, blood pressure, and respiration. What do these symptoms lead to? At first, I thought it was meningitis, but he doesn't have a stiff neck ... I'm completely lost.

Also, we found through Gram-Staining that he has numerous PMNs (polymorphonuclear cells) and many gram-positive cocci as single cells, in pairs, and in clusters. A blood test was negative. —Preceding unsigned comment added by 69.16.95.123 (talk) 11:39, 15 April 2010 (UTC)

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

Ah, come on, he has "attempted to solve the problem himself", and is stumped. What more can we expect him to do, other than looking through some medical reference book or browsing through random wikipedia articles or something. It seems like an appropriate step to ask for help on-line. I am a bit worried about giving medical advice though, even for a "fake patient". I'll start a thread on the talk page. Buddy432 (talk) 15:00, 15 April 2010 (UTC)

Here's the thread I started. Buddy432 (talk) 15:08, 15 April 2010 (UTC)

(from talk page) Ask, Were thy on any medication prior to admittance? I'm thinking along the lines of discounting any adverse drug reaction, especially the rarer ones caused by to or more drugs. --Aspro (talk) 15:16, 15 April 2010 (UTC) —Preceding unsigned comment added by Buddy432 (talk • contribs)

Has Dr House told you what he thinks yet? He is usually wrong on the first couple of tries. Googlemeister (talk) 16:03, 15 April 2010 (UTC)

... and don't forget that it's never lupus - except when it is. Gandalf61 (talk) 16:38, 15 April 2010 (UTC)

I'd not discount meningitis just on the absence of one symptom. It's too severe an infection to discount like that. Also, there are symptom sorters available online (yourdiagnosis.com) or in written form. Have you also ruled out measles or rubella?

Your first paragraph includes symptoms that could result from a range of diseases, including infections, vasculitis, and systemic inflammatory processes. However the presence of numerous gram positive cocci is a giveaway. This is almost certainly either Streptococcus or Staphylococcus. The clusters are more suggestive of Staphylococcus; the most likely cause is Staphylococcus aureus septicaemia. Axl ¤ [Talk] 20:22, 15 April 2010 (UTC)

You make a very good point; the previous post makes a very good point also, about not discounting meningitis just on the absence of one symptom. It goes therefore, without saying that ”Time is of the essence”, and this is not the time to discuss the evils of over proscribing antibiotics. BUT what does one do (now, at this very moment)? The word 'many', as in “many gram-positive cocci as single cells, in pairs, and in clusters” is not a truly objective, any more than anything else said - (pictures would have been nice). So does one give a gram antibiotic? Time may be running out.--Aspro (talk) 21:19, 15 April 2010 (UTC)

Well, I thought that the OP was asking for help on the (fake) diagnosis. So you want to know about treatment? Axl ¤ [Talk] 07:45, 16 April 2010 (UTC)

So taking into account Axl's putative diagnosis of Staphylococcus aureus septicaemia, test for methicillin resistance in case this is MRSA: if so, find an antibiotic that works and start therapy pronto! --TammyMoet (talk) 21:00, 16 April 2010 (UTC)

But what about the unlikely chance that this is a real patient, or that these exact symptoms will be used for a real diagnosis in the future? ~AH1^(TCU) 16:20, 17 April 2010 (UTC)

DNA Bases

Why are the bases in DNA/RNA said to be hydrophobic if they can form hydrogen bonds? —Preceding unsigned comment added by 67.177.181.221 (talk) 14:06, 15 April 2010 (UTC)

Are they hydrophobic? Do you have a source for that. Looking at the structure, I would think they would be fairly hydrophilic; their presence in the cytoplasm (which is mostly water) would indicate that they aren't. Indeed, if they were hydrophobic, I would expect them to cluster or agglomerate in such a way as to make them not work as they do; the fact that they exist free-floating in the cyctoplasm indicates to me that they aren't hydrophobic. I could be proven wrong, but where is the assertion that they are? --Jayron32 14:56, 15 April 2010 (UTC)

When 67.177.181.221 refers to the hydrophobicity of nucleotide bases, that may be a reference to the sides of the base, not the edges. As the bases are aromatic, the flat bits (the top and bottom) are covered by a poorly polarizable (at least in the direction normal to the plane of the rings) delocalized electron cloud. While pi-pi stacking interactions readily occur, all of the hydrogen bonding and polar interactions happen "edge on" in the same plane as the rings. -- 174.24.208.192 (talk) 07:23, 17 April 2010 (UTC)

Electrolysis

I understand the concept of electrolysis, but what does it mean to apply a voltage? Say a cell that has a net voltage of -2V as indicated by potentiometer (and since -2 is negative, the redox reaction is nonspontaneous.) My textbook says you need to apply -2V to drive this reaction. But shouldn't you apply +2V? I totally don't understand the concept of applying a voltage. —Preceding unsigned comment added by 142.58.43.216 (talk) 16:31, 15 April 2010 (UTC)

Some people like to think of electricity in terms of the Hydraulic analogy where voltage (or "potential difference") is compared to pressure of a fluid. One connects anything that might pass current to a voltage source (such as a battery) by two wires, just like in the analogy one connects to a pump by two pipes for forward and return flows. The negative terminal of a voltage source is the one where there is a surplus of electrons. Cuddlyable3 (talk) 17:02, 15 April 2010 (UTC)

Yea, the sign doesn't really matter. 2V just refers to the differential between the two wires. Depending on which wire is positively charged and which is negatively charged, the electrons will flow one way or the other, and this is what the + and - show. However, the anode and cathode should be made of different materials for electrolysis, so you do need to know which gets connected to the positive and negative terminals. StuRat (talk) 18:42, 15 April 2010 (UTC)

No, the materials need to be of different materials if you are making a galvanic cell. For an electrolytic cell, just about any inert conductor will do fine. They can be the same material. --Jayron32 19:08, 15 April 2010 (UTC)

My question is still not answered. Why does it not matter if you apply a + or - voltage? In electrolysis, it should matter because the natural voltage between two nonspontaneous redox reactions should be negative. My incomplete understanding of this is making it hard for me to further understand the basics of voltammetry. —Preceding unsigned comment added by 142.58.43.94 (talk) 19:31, 15 April 2010 (UTC)

In electrolysis, the two electrodes are in the same solution. So it doesn't matter whether the electrode in your left hand has the higher voltage or the one in your right one does. The process will happen the same either way; the only difference will be at which electrode the oxidation process goes on and at which one the reduction process goes on. However, the sign of the voltage is merely directional. It only tells you whether electrons are flowing in or out of that particular electrode. The actual process will occur regardless of the direction; the only difference will be which half-reaction will take place at which electrode. --Jayron32 19:56, 15 April 2010 (UTC)

(after edit conflict) ::::A voltage is just a potential difference between terminals. Whether you call it +2V or -2V depends on how you measure it. As mentioned above, for electroysis, the + side of your voltage source goes to the anode, and the - to the cathode. The anode is +2V with respect to the cathode, or you could say that the cathode is -2V with respect to the anode. If anode and cathode are the same material, then it doesn't matter which is which, but the direction of the electrolytic separation will depend on the direction of the current, and this depends on which side is positive and which side is negative. Traditionally, current flows from + to - but negatively charged ions will flow the other way. Dbfirs 20:05, 15 April 2010 (UTC)

sodium carbonate

does sodium carbonate (soda ash) degrade when exposed to air? or does it remain corrosive? —Preceding unsigned comment added by Jonny12350 (talk • contribs) 18:41, 15 April 2010 (UTC)

It depends on which sodium carbonate you mean. Sodium carbonate exists naturally in several different hydrated forms, see Sodium_carbonate#Occurrence. I am pretty sure they are all fairly stable for any reasonable amount of time. Pure, unhydrated sodium carbonate is likely somewhat hygroscopic, so you can likely generate one of the hydrate forms if you leave it out on a humid day for some time. And acid will tend to degrade the sodium carbonate first to sodium bicarbonate then to carbonic acid; the latter of which is metastable and decays quickly to carbon dioxide and water. But if kept dry and in a sealed container, I think that sodium carbonate can keep indefinately. --Jayron32 18:59, 15 April 2010 (UTC)

im talking about the kind you buy in the store for cleaning. its not in a sealed container but rather in a pile on the counter —Preceding unsigned comment added by Jonny12350 (talk • contribs) 19:45, 15 April 2010 (UTC)

In that case, its cleaning properties are largely because it is abrasive and not corrosive. In other words, its gritty, and so tends to break dirt and stains up into smaller bits to make them easier to wash away. It is slightly alkali in nature, so it will saponify any oil-based dirt, to a small extent, which also helps. Due to the ion exchange effect, it can, like all ionic salts, speed the corrosion (rusting) of iron much like ordinary table salt (sodium chloride) does, so I would rinse it off any metal surfaces you cleaned with it; but by itself it isn't usually very corrosive. Douse with water and follow with several wipes with a damp sponge, and your metal surfaces should be fine. --Jayron32 20:04, 15 April 2010 (UTC)

It may react with atmospheric carbon dioxide to form sodium bicarbonate, but that shouldn't affect its cleaning or water softening abilities. --98.221.179.18 (talk) 00:37, 17 April 2010 (UTC)