Wikipedia:Reference desk/Archives/Science/2008 March 31

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March 31

Something semi-interesting about Cockatiels...

Anyone here have experience with keeping large numbers of Cockatiels? I was told today by someone who does that in aviary conditions, the birds form a loose social hierarchy based upon how 'natural' their plumage appears. In other words, the birds with wild-type plumage tend to dominate birds of alternate colour mutations when it comes to feeding, mate selection, choice of nest box, etc.. Apparently, the more grey feathers and the closer its resemblance to a wild 'tiel, the more 'respect' the bird gets from its flockmates. Pieds/whitefaces/pearls are somewhere in the middle and the lutinos and albinos are at the very bottom of the pile.

I'd never heard of this before (I've never noticed anything similar with the various shades of budgie I own) but it sounds absolutely fascinating (to me, at least - maybe not to you). Does this sound familiar to anyone? Any link to writings on the subject? Thanks. --Kurt Shaped Box (talk) 00:41, 31 March 2008 (UTC)

In support of what you were told, there's cockatiels and pecking order here[1]. Male vocals or "song" count for something, apparently even more than colouring. Females can mate downwards and out of the family until they have chicks. Complicated little network, aren't they. Budgie pecking order would be an interesting search. Julia Rossi (talk) 22:41, 31 March 2008 (UTC)

Thanks for that. When I hear about bird breeders who place a particular chosen genetically suitable male and a particular chosen genetically suitable female together in an artificial environment and just expect them to reproduce, it makes me of the opinion that sometimes we, as humans just don't 'get it'. I just leave my birdies to as they wish. When it comes to my flock, I can't say that I've noticed a particular pecking order forming, unless the dominance of adults over recently-fledged youngsters counts. The hens can get a bit snippy with each other in the spring when it comes to nesting box selection but that seems to be first come, first served (as long as there are sufficient boxes for all). --Kurt Shaped Box (talk) 21:43, 1 April 2008 (UTC)

You're welcome. Breeders just don't 'get it' because they have market priorities as in the article. Maybe pecking order is more obvious when there's a limit at stake. Nests (and other things such as space, roosts etc) for all would take the pressure off probably. A spider person told me about the pecking order of daddy long legs spiders. The important thing was once the webs are set up, the pressure is gone and they become very tolerant. Julia Rossi (talk) 00:49, 2 April 2008 (UTC)

Sharing genes with bacteria

What percentage of our genes, approximately, do we share with bacteria? And what other species do we have such information for? Is there a table I could see somewhere? Thanks!

James 01:12, 31 March 2008 (UTC)

For the second part of your question, the chimp is the best example for genetic similarity - about 95%. See here. Wisdom89 _{(T / ^C)} 01:26, 31 March 2008 (UTC)

The human genome consists of about 30,000 human genes; about 1,000 of these are nearly identical to analogous genes in bacteria. I don't know of a table; as far as I know you'd have to look at each organism's genome individually. - Nunh-huh 01:34, 31 March 2008 (UTC)

Be mindful though, that there isn't really a true consensus on the actual number of human genes (protein encoding). I've seen estimates range from 25,000 to 80,000. This is a good link [2]. Wisdom89 _{(T / ^C)} 01:45, 31 March 2008 (UTC)

Thanks for the interesting replies. I'm surprised by Nunh-huh's reply that we share about 1/30th of our genes with bacteria. After writing this question, I was able to come up with a little more research, and found that we have about 3 billion base pairs, while many bacteria have only a few million base pairs, which would put the upper-bounds of our similarity at under 1%, but I guess there is probably large variation in the size of bacteria DNA. — James 13:18, 31 March 2008 (UTC) —Preceding unsigned comment added by 63.138.152.238 (talk)

There's a difference between the number of base pairs and the amount of genes that are expressed (or at least, are currently known to be expressed). Bacterial DNA tends to have a lot less non-coding DNA in it than humans. The important point here is that a while humans differ a lot from, say, yeast, we both need to be able to convert sugar to energy and perform other metabolic functions, and those genes are highly conserved. -- JSBillings 15:24, 31 March 2008 (UTC)

There used to be such a table in WP. After a bit of guesswork and searching through page histories I found it in this old version of Genomics. It was deleted on 10th October 2006. --Heron (talk) 20:52, 31 March 2008 (UTC)

DIY Lab hood

I am trying to make a DIY laminar flow hood. I have already built the the hood and have used a plenum coupled with a furnace blower and HEPA filter to create the laminar flow stream. I would like to add a UV light for sterilization. I want to just buy a UV bulb and put it in a standard fixture (Like so: Fixture and Light but none of these lights appear long enough! Am I going about this improperly? Is there a special fixture I need to use a UV light?

Thank you!

Ebenbayer (talk) 02:08, 31 March 2008 (UTC)

I'm fairly certainly that any UV fixture you purchase does not have to extend the entire length of the laminar cabinet. My experience with such hoods is 1.) The UV light isn't really that effective at sterilization when the hood is not in use and 2.) A small fixture is enough to illuminate everything behind the UV protective shield. You might want to try contacting NuAire, which is where my laboratory purchased their flow hood. I'm sure they sell accessories for them. Wisdom89 _{(T / ^C)} 02:19, 31 March 2008 (UTC)

Thank you for the response, the problem I am having is that the light bulb length appears to short for the fixture, not that the fixture is to short for the hood (sorry to not be more clear). I just seem unable to find a site that sells a fixture that would interface with the germicidal bulbs I referenced. —Preceding unsigned comment added by 128.113.36.116 (talk) 12:57, 31 March 2008 (UTC)

You can get away without one if the hood is used a lot. I have two commercial ones in my lab and neither have a UV light fixture. Just clean everything regularly with >70% ethanol. —Preceding unsigned comment added by 82.36.27.228 (talk) 17:38, 31 March 2008 (UTC)

I'd just like to point out that "laminar" does not really mean clean or sterile. When used in this sense, laminar flow is in contrast to turbulent flow. This is important for hood design in that if you have turbulent flow, there is a higher likelyhood that dust and bacteria will make their way in from the outside. Having a laminar, nonturbulent flow means that all the air passing over the samples has passed over the HEPA filter. So while the HEPA filter will make the airflow clean, it will not make it "laminar". (Although how necessary a truly "laminar" airflow is depends on your application. You may not need it.) -- 128.104.112.85 (talk) 18:21, 2 April 2008 (UTC)

Dosage of medication

What's the term for giving someone a larger dose of a medication when starting them on the drug and then cutting it back to a smaller dose once they've ramped up the dosage in their body? I'd like to read the article on it so that I can understand why this needs to be done with some meds but I don't know the term. Thanks, Dismas|^(talk) 02:58, 31 March 2008 (UTC)

Loading dose. The article needs expansion and probably won't be of much help. - Nunh-huh 09:42, 31 March 2008 (UTC)

Yeah, thanks. That took me less than a minute to read and I'm still not any closer to knowing why a loading dose is necessary. At least now I have a term for it though. Thanks! Dismas|^(talk) 09:53, 31 March 2008 (UTC)

It depends on the pharmacokinetics of the drug in question. Some drugs are cleared from the body relatively slowly. In order to maintain a constant concentration of these drugs within the body, only small doses need to be taken—but if one only administers small doses, it can take a long time for the drug to reach a useful concentration in the body after starting therapy.

Consider the hypothetical drug foosporin. Suppose it has a long lifetime in the body, and only ten percent of it is cleared from the blood each day by the liver and kidneys. Suppose also that the drug works best when the total amount in the body is exactly one gram. So, your maintenance dose of foosporin is 100 milligrams (100 mg) per day—just enough to offset the amount cleared.

Suppose you just started taking 100 mg of foosporin every day. On the first day you'd have 100 mg in your system; your body would clear 10, leaving 90 mg. On the second day you'd have 190 mg in total; your body would clear 19 mg, leaving 171 mg. On the third day, you'd be up to 271 mg total; your body would clear 27 mg, leaving 244 mg. As you can see, it will take many days for the total amount of drug within the body to come close to 1 gram (1000 mg) and achieve its full therapeutic effect.

For a drug such as this, a doctor might prescribe a loading dose of one gram to be taken on the first day. That immediately gets the drug's concentration in the body up to the therapeutically-useful level. First day: 1000 mg; the body clears 100 mg, leaving 900 mg. On the second day, the patient takes 100 mg, bringing the level back to 1000 mg; the body clears 100 mg overnight, still leaving 900 mg...and so forth. TenOfAllTrades(talk) 19:00, 31 March 2008 (UTC)

I've taken the liberty of incorporating your example above into the article. Thanks! —Ilmari Karonen (talk) 21:54, 31 March 2008 (UTC)

Cool! Thanks for that! Dismas|^(talk) 22:08, 31 March 2008 (UTC)

Nanoparticles

Size (nm)	Number of atoms	Fraction on surface (%)
0.5	1	-
1	8	100
2	64	99
5	1000	50
10	8,000	25
20	64,000	12
40	512,000	6
80	4,000,000	3

Is the above table (approximately) accurate? I extrapolated (and rounded) the last few entries. It is for spherical particles isn't it? (I may insert this into nanoparticles) Cheers, Shniken1 (talk) 04:01, 31 March 2008 (UTC)

The percentage on the surface doesn't appear to be quite correct. Using a cubic structure, you could use the formula 100-[100(N^1/3-2)³/N] to find the percentage given N atoms. This gives me the following results:

Number of atoms...	Fraction on surface (%)
8	100
64	88
1000	49
8,000	27
64,000	14
512,000	7
4,096,000	4

StuRat (talk) 05:04, 31 March 2008 (UTC)

hair loss

hi, it is said that it is normal to lose 50-100 hairs a day, but how come we don't go bald as i am quite convinced that the rate of hair growth is much slower than the rate of loss. thanks :) —Preceding unsigned comment added by 218.250.158.232 (talk) 10:39, 31 March 2008 (UTC)

If the rate of hair growth were much slower than the rate of loss, we would all go bald. Perhaps you are going bald, if this is the case for you? For those of us who are not going bald, the rate of hair growth cannot be much slower than the rate of loss and you shall just have to unconvince yourself :) Skittle (talk) 11:51, 31 March 2008 (UTC)

Another way to look at it: On average, people have about 100,000 hairs on their head.[3] Each hair grows at a rate of about 1/2 inch per month. So your total hair growth is 50,000 inches per month, or 1643 inches per day. As long as your total hair loss (including haircuts) is less than 1643 inches (or 136 feet) per day on average, you should be holding steady against balding. jeffjon (talk) 12:47, 31 March 2008 (UTC)

Buffer solutions

Hello. Do you think you could offer a brief explanation of how buffer solutions work? I (think) I get what they are, as in what they're overall effect is, but how they work has never made sense to me. For example, if you add HCl to water, the water molecule splits into H+ and OH- (or really into H3O+ and OH-, if I recall?) and the OH- accepts the H+ from the HCl, neutralising it. But surely just as many protons are donated by the water as are accepted, so why would this have a neutralising effect? What have I misunderstood? Skittle (talk) 12:00, 31 March 2008 (UTC)

Water isn't a buffer solution, so yes, if you add HCl to water you get an acid. Algebraist 13:36, 31 March 2008 (UTC)

Really? It was always used as an example of a buffer solution that could buffer both acids and alkalis, at A level. Skittle (talk) 16:05, 31 March 2008 (UTC)

Water can act as an acid or a base, as it is amphoteric. It's a relatively poor buffer. Wisdom89 _{(T / ^C)} 17:48, 31 March 2008 (UTC)

For water alone, there exists an equilibrium between three species:

2H₂O ←→ H₃O⁺ + OH^-, often written in simplified form as

H₂O ←→ H⁺ + OH^-

This dissociation is spontaneous, but tends to sit well to the left—at room temperature only about 1 of every ten million water molecules is dissociated into charged species. When hydrogen chloride gas dissolves in water, it dissociates as well:

HCl ←→ H⁺ + Cl^-

This reaction proceeds essentially to completion, elevating the concentration of hydrogen ions (H⁺) in solution. By Le Chatelier's principle, this pushes the equilibrium from the first two equations back to the left—some of the excess hydrogen ion in solution reacts with hydroxide (OH^-) to re-form water. This still leaves a surplus of hydrogen ions, rendering the final solution acidic. TenOfAllTrades(talk) 18:19, 31 March 2008 (UTC)

It's not 1 in 10 million molecules, but one ten millionth mole per liter - about 1 in 555 million molecules. Icek (talk) 12:03, 1 April 2008 (UTC)

Buffers work by soaking up the excess proton (hydroxide) ions. Buffers are weak acids (weak bases) - this means that they can exist in both the acid form and the conjugate base forms in significant amounts. Now, if you look at the chemical equation for the reaction, you'll notice that where the equilibrium lies is affected by the pH (i.e. the amount of protons):

Acetate buffer: CH₃COOH <=> CH₃COO^- + H⁺

When you add in H⁺ ions to the solution (say from dissociated HCl) you add to the right hand side. By Le Chatelier's principle, that means that the reaction moves to the left, removing free hydrogen ions from solution. If there is a drop in the number of protons (say from adding base), the equilibrium then moves to the right, and the acid form of the buffer dissociates into conjugate base and hydrogen ions, reducing or "buffering" the loss of protons. The pH stays stable with large perturbations because buffers usually are used in large concentrations (milimolar), as compared to the amounts of free hydrogen and hydroxide (picomolar at pH 7). Now, this only works when there are significant amounts of both the acid and base forms of the buffer. The pH at where both forms are equal is called the pKa, and this is where the buffer is most effective. Now away from the pKa (about 1 pH unit in either direction), there is not much of the other form, and the buffer doesn't work too well. This is just a consequence of simple equilibrium principles - the Henderson-Hasselbalch equation may look magical, but it's just the K_eq equation rewritten. Now for water, one may be tempted to think that the pKa of water is 7, but that's not quite right. Remember that pKa is where the concentration of the two forms are equal. At pH 7, there is 10^-7 M H⁺, but ~55 M H₂O - You need to get well above pH 14 or below pH 1 before water even begins to become a decent buffer. -- 128.104.112.85 (talk) 18:13, 2 April 2008 (UTC)

Excellent. That actually makes sense! It also reveals that my textbook was at least a little misleading :) Thanks. Skittle (talk) 22:51, 3 April 2008 (UTC)

Pain of death

Do people dying of congenital heart desease Congestive heart failure experience unbearable pain and if so what is the cause of the pain? 71.100.4.126 (talk) 13:05, 31 March 2008 (UTC)

Have you read Congenital heart disease? I'm not quite sure if you have the right disease. Are you sure you don't mean Coronary heart disease or Congestive heart failure? Nil Einne (talk) 17:23, 31 March 2008 (UTC)

Sorry, Congestive heart failure is right. 71.100.4.126 (talk) 18:50, 4 April 2008 (UTC)

Commercial aviation \ Airports: Penalty box

ORD airport layout.

What is it for? It is provided at O'Hare International Airport nearby A 5 (around 87° 55' W 51° 59' N). Thanks, --Scriberius (talk) 17:46, 31 March 2008 (UTC)

The 'penalty box' is just a (somewhat whimsical) name given to an area in which aircraft can be temporarily parked, usually either while waiting for a gate to open up, or after boarding to free up a gate for another aircraft. (Notes: [4], [5].) TenOfAllTrades(talk) 18:25, 31 March 2008 (UTC)

OK thanks. Looks like this parking space is a unique word just justed in Chicago. --Scriberius (talk) 20:31, 2 April 2008 (UTC)

I notice they also have a "Scenic Hold Pad". --LarryMac | Talk 20:46, 2 April 2008 (UTC)

Thermoregulation

A mother complains that her 3year old child's head is hot while the extremeties are cold. What are the physiological mechanisms responsible for this symptoms--82.128.29.40 (talk) 20:55, 31 March 2008 (UTC)Oyinmart

A doctor's primary concern would be to determine whether the temp difference is noteworthy. It's quite common for someone's head to feel warm relative to hands or feet (irrespective of age); I would hazard a guess that the distinction is a function of blood flow (heat in) versus surface area (heat out). — Lomn 21:08, 31 March 2008 (UTC)

Architects in construction project

Are architects in most major "design and build" construction projects appointed by the client or by the main contractor? Thanks in advance. Clover345 (talk) 21:09, 31 March 2008 (UTC)

Fancy buildings will have the arcitect employed by the client, and then give the concept to the construction company. Graeme Bartlett (talk) 05:33, 1 April 2008 (UTC)

My wife is an architect and this is what I have gleaned. Normally the client hires an 'architect of record'. These guys do the 'big picture design'. If the architect of record doesn't have the capacity to handle all the work, they will get a 'design architect' firm to help do the mountains of detail, documentation and project management. I believe the client separately gets the contractor to build the thing. From what I understand, this is the normal set up in big commercial projects in the US, but there are many variations. ike9898 (talk) 16:42, 1 April 2008 (UTC)

Radio waves, microwaves, cancer

Just today on MSNBC there was a story about some Australian neurosurgeon claiming that mobile phones are more likely than cigarettes to give you cancer - similar to claims we've seen countless times in the past. But how could radio waves and microwaves give you cancer when they are less energetic than visible light - that is, not nearly energetic enough to ionize, like UV light, X-rays or gamma rays - and when there are so many studies like the ones here that show no link? And yet how do you explain studies like the ones cited here that do purport to show a link? I'm not a high-frequency cell phone user, but I still need to know if my wireless MacBook is going to kill me. --Lazar Taxon (talk) 21:10, 31 March 2008 (UTC)

We have an article on Electromagnetic radiation and health. Basically, there have been studies that purport to show a link and many that don't, but there is also a weighty little pile of organizations that don't believe in a link, such as the WHO, the American Medical Association, and the NIH. Someguy1221 (talk)

Regardless of the merit of the claims, it is not sufficient to rule out all health effects just because the emissions do not cause ionization. Ionization is only one form of energy transfer from electromagnetic waves - there are many potential effects of radiation at various wavelengths. For example, microwave heating does not occur by ionization; instead it excites a molecular resonance. Undoubtedly, dielectric heating can occur at mobile-phone frequencies, but as Someguy1221 mentioned, many reputable institutions do not consider this to be a health hazard at the power levels in use. Nimur (talk) 14:59, 1 April 2008 (UTC)

Nitpick: it's not molecular resonance, it's just plain old dielectric absorption. It says so in microwave heating.

Anyway, if anybody here is worried by Dr Khurana's findings, then at least take a look at denialism blog, which picks a few holes in his research. I particularly liked the bit about hot water bottles. --Heron (talk) 12:21, 2 April 2008 (UTC)

Bekenstein Bound

How would the Bekenstein bound work in a universe without a surface, such as a 3-sphere? Thanks *Max* (talk) 21:32, 31 March 2008 (UTC).

The Bekenstein bound should still work as you will have volumes of space that you can surround with a surface, and the bound will apply to that surface and volume. You can expect that the volume will be a blackhole if you reach the bound! Graeme Bartlett (talk) 00:53, 1 April 2008 (UTC)

But bekenstein bounds are proportional to surface area, not volume, so they don't add (except in the special case when the regions are disconnected and at least a certain distance apart). *Max* (talk) 01:09, 1 April 2008 (UTC).

Sorry, I did not fully explain myself. Since the universe is finite, how would you find the bound of the entire universe? Thanks, *Max* (talk) 01:44, 3 April 2008 (UTC)

In this case you can still cut up the universe into several volumes that add to the whole, and then look at the surface on each. This could only work on a finite universe. Graeme Bartlett (talk) 21:42, 3 April 2008 (UTC)

I thought Bekenstein bounds don't add; the uncertainty principle implies that bigger region measured = less average precision. Also, the bound of an infitnite universe would just be infinite, so there's no point unless it is a finite universe (with a 3-sphere being the simplest case). *Max* (talk) 02:12, 5 April 2008 (UTC).