Wikipedia:Reference desk/Archives/Science/2009 March 28

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March 28

Antibiotic deodorant

Would making deodorant with a liberal dose of some antibiotic work? I've read that underarm odor is not really you exactly, it's waste from bacteria living under your arms. So an antibiotic deodorant makes great sense to me. However, I also see a very real problem and possible *danger*. You would quickly evolve antibiotic resistant strains right? Is that possibly the main reason it's not done? Because it would only be effective (maybe really, really effective!) but only for a short time period until you bred and released yet more multi-antibiotic bacteria on the world? I have some erythromycin sitting around I may just grind it up and smear it on. Good idea? (not serious).♥70.19.64.161 (talk) 03:27, 28 March 2009 (UTC)

You've listed one reason it's a bad idea. Another is that an antiseptic can kill off helpful bacteria which control nastier things which would otherwise grow in that warm, moist, dark environment. Adult diapers treated with hexachlorophine allow fungus to grow, for example. StuRat (talk) 04:21, 28 March 2009 (UTC)

The link above should be to Hexachlorophene. --NorwegianBlue ^talk 14:13, 28 March 2009 (UTC)

Thanks, that explains the red link. I'll add a redirect, in case others misspell it the same as I did. StuRat (talk) 15:44, 28 March 2009 (UTC)

For a decade or more I've been spritzing my pits with alcohol each morning. It does a fine job of keeping odor down, much cheaper than antibiotics(!), with no ill effects other than occasionally making the skin uncomfortably dry. —Tamfang (talk) 01:05, 29 March 2009 (UTC)

Yes, the drying effect would be an issue for most people. If you have oily skin to begin with, perhaps you can get away with it. StuRat (talk) 17:31, 29 March 2009 (UTC)

In contrast to our current article layout, where deodorant and antiperspirant redirect to the same article, they are slightly different things (e.g. Speed Stick sells "deodorants", "antiperspirants", and "deodorant/antiperspirants"). An antiperspirant stops sweating, most commonly via aluminum salts. A deodorant, in contrast, functions by stopping the growth of bacteria which produce most of the noxious body odor. Usually this is through making the underarm inhospitable to the bacteria, by increasing the salt concentration, or increasing/decreasing the pH. Sometimes alcohol is used to kill bacteria directly, or broad spectrum antibacterial compounds like triclosan or hop extract are added. While an antibiotics like erythromycin or penicillin might kill the bacteria (while usually effective on a range of bacteria, most antibiotics are still somewhat specific - c.f. gram positive and gram negative), you're right in that resistance would likely occur rapidly in such an uncontrolled setting. -- 76.204.102.79 (talk) 18:01, 29 March 2009 (UTC)

Hm, do unscented deodorants exist? —Tamfang (talk) 22:46, 30 March 2009 (UTC)

Yes: [1]. StuRat (talk) 04:59, 31 March 2009 (UTC)

How do pet parrots perceive humans?

It's an oft-quoted 'fact' on bird-keeping discussion forums/newsgroups that when a pet parrot sees a human, it supposedly only identifies the face and hands as an individual 'fellow creature' with which it can interact and sees the rest of the body as some sort of strange, wobbly, walking tree. I've got no idea where this theory comes from - but it seems to be 'common knowledge'. Can anyone tell me if there's any actual, real scientific evidence behind it?

I appreciate that the answer to this may simply be 'you'd have to be able to read the parrot's thoughts to know' - but from my own interaction with parrots, I don't personally believe it to be the case (why would a parrot nip at a person's feet when desiring attention if it believed that the feet were just 'roots' and not a part of the person they were trying to attract the attention of, for instance?). --Kurt Shaped Box (talk) 03:37, 28 March 2009 (UTC)

I agree that that description seems rather silly for a parrot. That might apply to an insect which can't see all of you, but only the part near them. StuRat (talk) 05:05, 28 March 2009 (UTC)

I read that dogs see humans as peculiar three-headed creatures - with our hands being seen as 'mouths' - and actually - when you see how the dog interacts with you - that makes a lot of sense. But obviously, we can't really know what they think...particularly with birds, which are so far from us, genetically. SteveBaker (talk) 12:14, 28 March 2009 (UTC)

The identify us how they identify us. Not how we identify us. Not how we identify trees. Not how they identify parrots. Not how they identify trees. It's sort of like asking if light is a particle or a wave. It is what it is, independent of how we think. If they do think of our bodies in a similar manner as trees, that doesn't mean that they wouldn't be able to understand that it's part of us. A lot of people think their monitor is their computer, but it doesn't stop them from turning on their actual computer. — DanielLC 15:34, 28 March 2009 (UTC)

Perhaps they could do one of those experiments they do to test cognition of very young humans, where they make a ball disappear somehow, and at a certain age the infant gets noticeably befuddled. They could use some kind of trickery to hide the "strange, wobbly, walking tree" and see if the bird gets weirded out. I've noticed with my dogs that when I lift another human onto my shoulders they seem to think the people have left the room and some bizarre creature has appeared in their place. --Sean 21:37, 28 March 2009 (UTC)

That test is used tell if the baby understand that objects don't disappear when it can't see them anymore. It shows nothing of how the baby thinks of the object. I don't see how that test could be used here. — DanielLC 20:19, 29 March 2009 (UTC)

Mechanism of Copper (II) Sulphate on the iodine clock reaction

I am writing an investigation on the iodine clock and am confused as how the copper ions increases the rate of the reaction. I understand the mechanism of iron ions as:

2Fe2+(aq) + S2O82-(aq) 2Fe3+(aq) + 2SO42-(aq)

Fe2+ ions act as reducing agents to reduce the Peroxodisulphate ions to sulphate ions, in turn, being oxidised themselves to form Fe3+

2Fe3+(aq) + 2I-(aq) 2Fe2+(aq) + I2(aq)

The Fe3+ ions produced then act as oxidising agents to oxidise the Iodide ions to Iodine whilst themselves being reduced back to Fe2+.

But I understand the mechanism with copper (II) sulphate is different,I would like to know how.I also understand that the copper is not regenerated so it's not exactly a catalyst in that respect. —Preceding unsigned comment added by 82.27.37.30 (talk) 06:47, 28 March 2009 (UTC)

iodine clock reaction does not mention copper. Is this a part of the reaction? Graeme Bartlett (talk) 21:04, 28 March 2009 (UTC)

The original reaction doesn't but i'm investigating the effect of adding copper to the reaction and my results show a much faster rate with the addition of copper.82.27.37.30 (talk) 00:01, 29 March 2009 (UTC)

Copper makes numerous complex ions with even moderately good Lewis bases. My guess is that there is some sort of Copper (II)-Iodide complex ion formation going on here which is affecting the reaction in some way. Since we don't know all the details of your particular iodine clock reaction (such as all reagents, pH, amounts, etc. etc.) it is hard to tell exactly what is going on here, but my guess is that there are some complex ions forming... --Jayron32.talk.contribs 03:49, 29 March 2009 (UTC)

Neuro Behcet's disease

I just looked at the article on Behcet's disease (Silk Road Disease) but it appears to be solely a dermatological condition. My nephew has "Neuro Behcet's disease" which seems an outgrowth of cereberal meningitis. My sister (she's 58, he's in his early '30s) is forced to care for him because of government cutbacks to long-term care facilties and his behaviour's become erratic/violent, I'm trying to find researchers involved in that field in the hope of finding alternative therapy/programs that could help him, and her. Because of the stress, she had a collapse from a pelvic infection last year, meanwhile his condition worsens. I just today found out the name of the syndrome as she'd posted something in facebook to Oprah's blog, as Dr. Mehmet Oz had discussed hyperbaric chamber therapy, but the doctors in the local medical system (in British Columbia) say there's no evidence it works. Any help/advice appreciated as to where to look/who to ask greatly appreciated.Skookum1 (talk) 13:13, 28 March 2009 (UTC)

This question was a request for medical advice, which we cannot provide here. This removal can be discussed here, on the RefDesk Talk page. I am sorry we cannot provide assistance. --Scray (talk) 19:25, 28 March 2009 (UTC)

Because this question is not clearly a request for medical advice, I have restored it. It is being discussed here, on the RefDesk Talk page. --Scray (talk) 20:30, 28 March 2009 (UTC)

HER2/neu

Hi I am doing some research into breast cancer and after reading some articles I have a couple of things I am a bit unsure about. After reading the article on HER2/neu I was a little confused as to whether or not there is difference between HER2/neu and HER2? Or is HER2 simply a shortened version of writing HER2/neu? Also, the article on estrogen receptors says that a theory of why over expression of oestrogen receptors can cause cancer is that the metabolism of oestrogen produces 'genotoxic waste.' Is 'metabolism of oestrogen' refering to breaking down oestrogen once it has bound to the receptors or producing oestrogen or something else? And finally what do over expressed oestrogen receptors do? Cause cell division? Thanks. —Preceding unsigned comment added by 139.222.241.27 (talk) 13:35, 28 March 2009 (UTC)

"HER2" and "neu" are synonyms, as explained in the second paragraph of the section on HER2/neu and cancer. Estrogen is a steroid hormone, and there are many breakdown products with a variety of effects. The metabolism (breakdown) of a hormone can occur before or after it has bound its receptor. Some of your other questions are answered in the section on estrogen receptors and cancer, but in short you are correct that over-expression of estrogen receptors is thought to facilitate cell division. I hope this helps. --Scray (talk) 16:44, 28 March 2009 (UTC)

Frequency in physics

With reference to previous question, March 9, titled “The meaning of Frequency in physics” , this is a new attempt to clarify the concept(/-s?) of “frequency” in physics.

To me frequency is the number of occasions of an event per unit of time (area, volume etc.).

I’m informed in the answers to my previous question, that this is “emission frequency”.

So I ask: What kind of frequency is represented by the rules c=(ny)•(lamda) and E=h•(ny)=h/(lamda) ?

Did Planck have reason to believe, that all emission sequences from the same emitter have maximal emission frequency ?

Does this latter convention arise from frequency spectrography ?

And why not give it another name ? Suggestions are welcome !

Rolf —Preceding unsigned comment added by 83.226.97.246 (talk) 16:53, 28 March 2009 (UTC)

Monochromatic light is an electromagnetic wave. As such, if you were to plot an electric field component perpendicular to the direction of propagation of this light, vs. time, you would get a sine. It is the frequency of this sine that is used in the formulas you speak of. —Preceding unsigned comment added by 81.11.162.104 (talk) 19:36, 28 March 2009 (UTC)

To help you conceptualize, the electric and magnetic field vectors have spatial locations; and as vectors, they have spatial positions and a direction. However, the quantity they measure is Electric field or magnetic field, so there is no "spatial extent" for the arrows - they exist as a magnitude and a direction at each point in space. As such, if you plot the magnitude vs. time for a specific location in space, you will see a sinusoidal signal as described above. Alternatively, if you take a snapshot of a single time, for a large range of spatial values, you will probably also see a sinusoidal wave in space as well. These "plots" will depend on what exactly your light signal is doing - if it is similar to a plane wave with long duration, these statements are valid; if it is more pulse-like, you might see wave packets or other frequencies as well when you plot the magnitude of the fields vs. either time or space. Nimur (talk) 22:30, 28 March 2009 (UTC)

Rolf: – I perceive ‘a wave’ as a ‘shower ‘ of wave packets ≈ photons/phonons, the intensity of which varies as ‘a wave’. So, what is the frequency of a single photon/phonon ? / Rolf

Rolf, your understanding of the electromagnetic wave as a particle shower of varying intensity is not correct. In a plane wave for instance, the wave intensity is the same everywhere at all times. What's varying over time with frequency ν is the electromagnetic field. Even with a single photon you still will have the same frequency ν. That single photon still propagates according with the wave equation and can be subject to interference, diffraction, refraction, etc. The energy of that single photon is related to its energy content through Planck's equation E=hν. Planck didn't know that at the time, but that relation is a consequence of the fact that position and momentum are not compatible and cannot both be established with zero uncertainty according with Heisenberg's uncertainty principle. Dauto (talk) 13:18, 29 March 2009 (UTC)

Certainly our OP's mental model of how light 'works' is wrong - but actually, so are other models too. The problem is that light is neither a wave nor a particle because there are times when it behaves entirely unlike a wave and other times when it behaves entirely unlike a particle. Rolf's model fails because it doesn't explain any of these behaviors. The mental models of wave and particle merely serve to help us to apply math to the problem of light - they don't get you far as mental 'pictures'. FWIW, I offer the "wave packet" image at right as a better way to envisage things...but it's still not a true picture of what's going on. SteveBaker (talk) 22:06, 29 March 2009 (UTC)

Yes, SteveBaker is right. The wavepacket model isn't the whole story. The main problem with the wavepacket picture by itself is that it does not give a theoretical reasoning (beyon fitting experiment) behind Planck's equation E=hν which is simply added to the model 'by hand'. This is sometimes described as a semi-classical (or semi-quantical) picture. It took a quarter of a century after Planck's work for a more consistent picture of quantum mechanics to arise. The Canonical commutation relation was the essential element missing in the old quantum mechanics. Dauto (talk) 05:19, 30 March 2009 (UTC)

I don't think there is any connection between a wavepacket and a photon at all. One photon is simply a certain amount of energy in the electromagnetic field. Transfers of energy into and out of the EM field are localized and always happen in discrete units (one photon's worth of energy). That's the one and only context in which the particle picture of light makes sense. The EM field itself is as continuous as the classical EM field. It doesn't have a discrete structure of wavepackets the way matter has a discrete atomic structure. (At least not in quantum field theory. The field might have a discrete structure in quantum gravity, but I don't think that structure would be directly related to the number of photons in it. I know almost nothing about quantum gravity, though.) -- BenRG (talk) 13:06, 31 March 2009 (UTC)

Rolf: Gentlemen! Sincere thanks for Your efforts! Being embarrassingly ignorant of 'electrics', I can't even express myself intelligibly (specifically with reference to my use of the word wave). Thus,I found the initial comment easiest to 'swallow'. My perception of a wave packet coincides with the image "Wave_packet_(dispersion).gif.". This I had equivalenced with photon/phonon. I have read 'popu-loosely' about the dicotomy between packet and photon/phonon but don't feel I have real understanding. Some of what You've written is way over me, but I will enjoy returning to it and further comments from You. Keep well! / Rolf

What would actually happen if you used a defibrillator on yourself?

There is a scene in the latest episode of Terminator: The Sarah Connor Chronicles where Sarah places defibrillator paddles to her own chest and gives herself a jolt (in order to destroy a radio tracking device that has been implanted into one of her breasts, FWIW). Before doing so, she asks a doctor if doing this will kill her and is told "no - but it'll hurt a lot". So she shocks herself, falls over and is momentarily stunned - then gets up, kills a nameless henchman (by defibrillating his temples with the same machine!) and seems perfectly fine and healthy afterwards.

So, in the boring world of Real Life, and mammary tracking devices aside, autodefibrillating (heh!) on a normal heart rhythm would pretty much guarantee a cardiac arrest or another extremely serious heart-related 'event', right? --Kurt Shaped Box (talk) 17:24, 28 March 2009 (UTC)

We have an article on defibrillators that has interesting information related to your question. Any response beyond that, particularly with regard to the prognosis of someone who uses a defibrillator outside of established guidelines, would violate our prohibitions regarding medical advice. --Scray (talk) 17:33, 28 March 2009 (UTC)

Seriously? Do I need to specify that I'm not planning to defibrillate myself, nor advise others to defibrillate themselves in order to get an answer? ;) If so, I do specify that (honestly). I was merely curious about something I saw on a TV show that seemed rather unlikely to me... --Kurt Shaped Box (talk) 17:55, 28 March 2009 (UTC)

Defibrillators are available in many public places, and they are designed for exclusively medical purposes. I didn't delete your question, I just gave a limited answer. Further discussion should probably happen on the RefDesk Talk page. --Scray (talk) 19:08, 28 March 2009 (UTC)

The defibrillators available in public places are, or should be, automated ones that read the heart rhythm before delivering a shock, so in the TV show situations described by the original poster, they probably wouldn't do anything at all. Defibrillators designed for use by doctors, who (unlike us here) are supposed to have actual medical knowledge, are different. --Anonymous, 19:36 UTC, March 28, 2009.

It would depend on exactly where she placed the paddles and what she set the defibrillator to. If the current is low enough, and/or it doesn't go through the heart, then it shouldn't kill you. A high enough current through the heart runs a high risk of stopping it (although I doubt it is guaranteed). --Tango (talk) 22:42, 28 March 2009 (UTC)

(post e.c.) "Burns are often complications of using a defibrillator, especially on repeated defibrillation. They are mostly mild, but may be uncomfortable for the patient." (ref is http://www.healthhype.com/sudden-cardiac-death-scd.html) Mythbusters, though definitely not a reputable source, decided that it was "plausible" that defibrillation of patients with underwire bras and nipple piercings could cause burns. Taking that into account, the presumably conductive radio tracker could possibly cause internal burns. I also found the following quote from the NYT: "because shocking a healthy person or someone with another type of heart problem could be dangerous or even fatal." I couldn't find anything regarding nonfatal outcomes of defibrillating someone with a normal heart rhythm, but that may be due to the tendency for extreme outcomes (i.e. accidental death) to be the most widely disseminated. As Anonymous mentioned above, a lot of public access external defibrillators automatically sense the different abnormal heart rhythms and will not shock people with a healthy rhythm. Accidental defibrillation of people who don't need it may be pretty rare because of automated defibrillators. Sifaka ^talk 22:50, 28 March 2009 (UTC)\

AEDs can shock a healthy rhythm. Movement interferes with the rhythm analysis, and shivering or seizure activity can be interpreted as ventricular fibrillation. Also, pulseless ventricular tachycardia is a shockable rhythm, but the device is unable to distinguish between that and sinus tachycardia, i think they are set to shock any rate above 180 beats per minute or so. You are only supposed to attach AED leads to unresponsive and pulseless patients.—eric 00:16, 29 March 2009 (UTC)

Resuscitation, the Official Journal of the European Resuscitation Council, printed the results of research into what happens to healthy people who receive secondary shocks. Not good, but not lethal. There are several cases, easily found using Google, where direct defibrillation of a healthy person caused that person's death. One example: the U.S. State of Virginia found a person guilty of manslaughter for the death of a coworker after he (ahem) 'playfully' shocked her with a defibrillator. 152.16.16.75 (talk) 09:45, 30 March 2009 (UTC)

Just a note that low defib intensities are actually more dangerous than high intensities. A strong pulse, at least if applied to the right spot, will reliably reset the heartbeat, but a marginal pulse has the potential to perturb it just enough to produce an arrhythmia. Looie496 (talk) 23:45, 30 March 2009 (UTC)

And another note that George Ralph Mines, who did some of the basic research on defibrillation, is widely thought to have accidentally killed himself by self-experimentation with an electrical heart stimulator. Looie496 (talk) 23:55, 30 March 2009 (UTC)

Dweller's thread of the week. It's an 'out of the box' idea.

This shocking thread wins this the newly rescucitated, and possibly no longer weekly, and certainly unlucky for some 13th Ref Desk thread of the week award. Mammaries, like the corners of my mind... --Dweller 14:18, 6 November 2007 (UTC)

When does a square become a rectangle (Psychology)?

I'm looking for the height-width ratio that differentiates when a human perceives an object as being a square vs a rectangle. I know that technically, anything other than 1-1 is not a square, but I think that human perception is different than the mathematical definition. I've tried some google scholar searches but have not found any thing. Thanks AmitDeshwar (talk) 23:00, 28 March 2009 (UTC)

If the visual field is black-and-white with no other details or depth cues then one sees small deviations from squareness, though I can't quantify that. I think we are more sensitive to distortions of circles than squares. Added details or textures can however distort perceived dimensions so that a true square seems rectangular, as in various optical illusions. A related issue is the distortion that seems to be well tolerated by viewers of widescreen television when a movie made with 4:3 picture format is "stretched" to fit the screen. Cuddlyable3 (talk) 00:53, 29 March 2009 (UTC)

Though... keep in mind that most widescreen TVs these days allow you to adjust how the movie is displayed, so it doesn't have to distort. (For example, on mine you have "Widescreen", "Normal", and various "Zoom" options. By fiddling with them you can come up with a setting that has no black space but doesn't cut off too much.) --98.217.14.211 (talk) 02:05, 29 March 2009 (UTC)

It is relative. If you put a square next to a rectangle, the square may lose its squareness. There are many of those optical illusions in which humans see straight lines as being bent, elongated, or parallel when they aren't. -- kainaw™ 02:37, 29 March 2009 (UTC)

Gestalt psychology seems to be the relevent bit here... Others have hinted at it, but it bears repeating that it will depend a LOT on context. The entire viewing environment of the rectangle and the square will alter our perceptions of it. Depending on the viewing environment, a true square may be made to look rectangular; a rectangle may be made to look square, etc. etc. There is a lot more to perception than quantifiable data. Even personal psychology will play a part here. --Jayron32.talk.contribs 03:22, 29 March 2009 (UTC)

I think the point is this: If you have a smallish rectangle (sufficiently small that perspective isn't playing much of a part) - but it's held at an angle to the eye such that the long sides are fore-shortened - then it can appear to be perfectly square. However, our brains are very good at compensating for effects like this - so if there is (for example) a subtle texture to the paper that it's printed on - or if the edges of the paper are within your visual field - then there are enough cues to let you know that this supposed-square is really a rectangle that's not parallel to your plane of vision - and your brain says "Nope! It's not a square!". But if the lighting conditions are set up just perfectly and all cues as to the nature of the surface are removed - then it's impossible to tell the difference. So while we're very attuned to the precise ratios of sizes - we can be fooled. However (as others have suggested) when you view a 4:3 aspect-ratio broadcast TV show on a 9:5 aspect-ratio widescreen TV - then (for example) the circular wheels on cars are compressed into ellipses - but we really don't notice it. However, if presented with a similarly distorted white ellipsoid on a black background - you can see easily that it's not a circle. What this means is that a precise answer to the question is really not possible. There is no single number like 1.3% that says how far off of 'perfect' a square can be without our brains yelling "Rectangle!!!" - it all depends on context.

In this image (which I just drew to illustrate the point) - the red shape on the left looks rectangular - the shape on the right looks square. They are neither quite parallel to the eye - and perspective comes into play here. However, (of course - because this is always the answer with optical illusions) the two red shapes are identical. What changed is the background grid. On the right side of the image - the grid is also made of perfect squares - with identical perspective to the red square. On the left side, the underlying grid is 7:8 aspect ratio rectangles - also with identical perspective - and that red shape is still a square. Our eyes/brains prefer to see the grid on the left as being at a steeper slope than the one on the right (even though the angles are identical) and therefore are forced to deduce that the square on the left is really a rectangle. Of course if you measure either red shape - neither have parallel sides or equal length sides. SteveBaker (talk) 14:03, 29 March 2009 (UTC)

I think you may have distorted the picture a little too much to illustrate your point; I saw them both as trapezoids first and only later noticed that they looked different from each other (in comparison to the background). It didn't help that WP shifted the picture to the right, ruining the symmetry of their positions. Matt Deres (talk) 14:34, 29 March 2009 (UTC)

It is interesting that a Go board is traditionally printed as a rectangle in order for it to look like a square when seen at an angle from the perspective of the players. Dauto (talk) 15:38, 29 March 2009 (UTC)

Go boards are weird - some of the very best traditional ones are made with a grid that's just slightly SMALLER than the go-stones you play onto it. This is because traditionalist players prefer the slightly irregular 'jostled' look when the stones don't line up in neat, straight lines. SteveBaker (talk) 18:02, 29 March 2009 (UTC)