Wikipedia:Reference desk/Archives/Science/2007 August 11

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August 11

Questions about hydrogen/oxygen ratio in Eternal Tank, Kourou launch site and inclination

Hello,

I have a couple of questions :

1. I was taught (or maybe I misunderstood) that two hydrogen molecules and one oxygen molecule combine to make two water molecules. Now from this I conclude that 1 kilogram of hydrogen and 8 kilograms of oxygen give you nine kilograms of water. But when I check this official site : [1], it turns out that they have a 616/102 ratio). Does anyone understand why?

Probably has something to do with the fact that hydrogen is the lightest element. If you had a kilogram of ping pong balls and a kilogram of tennis balls, would you expect the numbers to be the same? Matt Deres 00:16, 11 August 2007 (UTC)

I don't see where you got the ratio from. Two moles of hydrogen masses 2.01g. One mole of oxygen masses 16.00g. When they meet, you should get 18.01g of water. The mass can't change, but the volume -- the amount of space it takes up -- can change. --Mdwyer 00:27, 11 August 2007 (UTC)

The ratio comes from the weight/weight ratio given on Nasa's website. Someguy1221 00:34, 11 August 2007 (UTC)

I thought two moles of hydrogen would mass 4.02 g or something like that? I still don't understand the ratio though?Evilbu 00:42, 11 August 2007 (UTC)

I suspect they rely on natural oxygen in the atmosphere. It makes sense to take more hydrogen than necessary to burn all the oxygen since it is very heavy to waste oxygen. Also any burn from the atmosphere is free. --Tbeatty 04:40, 11 August 2007 (UTC)

You are right in your mass calculations - the data I found on the site was

Liquid oxygen:

616,496 kilograms

(1,359,142 pounds)

Liquid hydrogen:

102,619 kilograms

(226,237 pounds)

that's about 6:1 (not 8:1) as you find - I can't explain the descepancy.87.102.5.144 09:39, 11 August 2007 (UTC)

The 8:1 ratio of Oxygen:Hydrogen for combustion is correct (ignoring Isotopes). So there are IMO only two possible explanations for the 6:1 ratio in the external tanks:

• Atmospheric oxygen is pulled-in mid-flight (very unlikely)
• There is unburned hydrogen either remaining in the tank, or expended due to incomplete combustion.

Note that the NASA website states, "The now nearly empty tank separates and falls", so I vote for the second option. Speculation: One reason for the tanks not being "completely" empty could be that the fuel intake system for the shuttle's engines requires the oxygen/hydrogen to be available at a particular partial pressure, which cannot be maintained once a certain % of the fuels have been consumed. Calculation of how much fuel remains unused will depend upon detailed design specs. of the tank, "fuel-injection-system" and engine. Abecedare 12:00, 11 August 2007 (UTC)

Let me rephrase the answer as I don't think I was clear. 8:1 is the theoretical limit with a perfect burn. Perfect burns are impossible. So they have a choice: they can stack the equation to either burn all the hydrogen or burn all the oxygen. Since oxygen weighs significantly more, it makes sense to add more hydrogen to consume all the oxygen. It is a huge waste to expel unreacted oxygen, but not nearly the amount of waste to expel unreacted hydrogen. They are engineering the combustion to consume all the oxygen by carrying extra hydrogen. By mixing in a 6:1 ratio, they make sure all the heavy item is burned. As an added benefit, the excess hydrogen will burn in normal air and provide additional thrust. Simply doing the math of increasing the oxygen to get to 8:1 (~200,000 kg) vs. the amount of hydrogen that brought it to 6:1 (25,000 kg) shows how effective it is to scale with excess hydrogen --Tbeatty 06:40, 12 August 2007 (UTC)

Tbeatty, I agree with everything you said, but I did not understand how the burning of the excess hydrogen in the atmosphere provides additional thrust.

That aside, the unburned hydrogen in the rocket engine exhaust may also have the additional benefit of reducing the average molecular weight of the exhaust gases -> increasing the speed of sound in that medium -> allowing for higher exhaust velocities (i.e. greater thrust) as mentioned in the rocket engine and choked flow article. I am no rocket scientist, so I can't say if this effect is quantitatively significant, especially since the unburned hydrogen will also reduce the average temperature of the exhaust. Abecedare 07:11, 12 August 2007 (UTC)

2. I read that many critics complain that the inclination of the ISS is too high, raising costs each time something is launched by NASA from Cape Canaveral. But why is the inclination 51.6 degrees? The Baikonur Cosmodrome lies at a latitude of about 46 degrees, so why the unnecessary five degrees?

3. Am I correct that nothing has been launched to ISS from the Kourou base? I was just wondering about the costs and others problems. Does ESA have lots of experience when it comes to docking in low earth orbit? And won't the it be really expensive to give their Automated Transfer Vehicle a huge inclination like that, while they are situated near the equator?

Thanks,Evilbu 23:42, 10 August 2007 (UTC)

The oxygen might reacte with the rocket combustion chamber, and additional hydrogen will create a reducing condition and might protect the wall.--Stone 16:33, 11 August 2007 (UTC)

I would assume that those numbers are maximums for each tank. After the rocket is fuelled, it's got to sit there on the laumch pad for hours before launch. During this time the tanks are often vented to atmosphere for various reasons (pressure/temperature control perhaps). Our article on Space Shuttle external tank also mentions some venting that happens after launch. Maybe they need to vent more of one gas than the other under some complicated set of conditions - and therefore one tank is larger than would be expected. SteveBaker 17:38, 11 August 2007 (UTC)

What is the fate of insulin molecules in the body?

What happens to a typical molecule of insulin after it has been produced in the pancreas? It circulates in the blood and attaches to an insulin receptor to do its job, and then what? Thanks, AxelBoldt 02:43, 11 August 2007 (UTC)

Insulin enters the cell after binding to its receptor, and is rapidly degraded by insulin-targeting cytosolic enzymes[2]. Someguy1221 03:16, 11 August 2007 (UTC)

name of Middle Eastern herb?

I'm trying to figure out the English or preferrably Latin name for this Arabic herb: مرمية

Another name is wild miramiya, meramiya, mariamiya, as in in mariam.. or meryam .. virgin Mary. They say she had tea made from this herb while pregnant with baby Jesus. It's calming to drink, soothes the body, and if you take a lot you can for sure sleep like a baby. It can be used to alleviate stomach pain. Or it can be put in baby's milk bottle when he's teething to reduce pain.

I Googled it and it showed pictures of common sage, but I'm told by my informant that the herb in question is definitely not common sage, nor is it rose of Jericho, which were my two first guesses. Apparently it's popular in Israel and in the Levant.

Picture: http://www.kisa.ca/lj/herb.jpg

--Sonjaaa 03:46, 11 August 2007 (UTC)

I created the stub Salvia libanotica, because this might be it. But I'm not positive.--Sonjaaa 04:46, 11 August 2007 (UTC)

From living in Egypt I believe it's actually another member of the mint family, marjoram. Bendž|Ť 09:53, 11 August 2007 (UTC)

Although after looking it up it seems the dictionary gives مريمية (with an extra ي, so pronounced mariamiya, "belonging to Mary") to mean "sage" while marjoram is ṣa3tar sha2i3, which, if you can read that awkward transliteration, you could ask your informant about. If it turns out to be a different sage species, it may also be Salvia lanigera, "wrinkle-leaved sage," which makes sense looking at your picture. Bendž|Ť 10:18, 11 August 2007 (UTC)

Toe Nails

Can anyone hazard a guess as to the growth rate for a complete "cycle" of a typical toe nail? In other words ... say, you are examining the "newest" portion of the toe nail (the section closest to the skin from which it has protruded). How many days/weeks/months will that part of your toenail take to grow out to where it is at the "end" of the toenail -- i.e., ready to be clipped? Thanks. (Joseph A. Spadaro 04:04, 11 August 2007 (UTC))

A study of 70 individuals suggested an average toenail growth rate of 0.050 mm per day, with significant variation from person to person. The "cycle" time would then depend on the size of your toenail. [3] Someguy1221 04:10, 11 August 2007 (UTC)

So... if your toes are 1 cm long, it takes about six months. —Keenan Pepper 19:49, 11 August 2007 (UTC)

biology --- moth question

Why is there no Wikipedia page about the moth genus(?) Phalaena ? Is it an outdated term? If so, what is the modern equilavent(s)? What did it originally mean or span?--Sonjaaa 04:22, 11 August 2007 (UTC)

Phalaena was originally a subdivision of lepidoptera, created by Linnaeus, and included moths in general. It is now obsolete, having been replaced by the various families currently under lepidoptera (shown below). Someguy1221 04:32, 11 August 2007 (UTC)

So Phalaena means all lepidoptera? Or only certain subgroups of lepidoptera?--Sonjaaa 04:48, 11 August 2007 (UTC)

To my knowledge it included only identified moth species (not sure if it contained all of them). This classification has not been used in contemporary taxonomy in two centuries though, to my knowledge, and the distinction between moths and other members of lepidoptera has changed significantly in that time. Finding a comprehensive, internet-ready source for this may be a difficulty, but I'm going to search trough entomology journals right now. Someguy1221 05:04, 11 August 2007 (UTC)

Correction, I have found papers using this term in their title as late as 1910 (needless to say, these might be somewhat difficult to actually find and read). However, it's use in more recently printed papers (last 40 years) seems to be only as an historic artifact of the original taxonomy, and these papers make no attempt at actually defining the term. Someguy1221 05:10, 11 August 2007 (UTC)

nano tech

Is it possible to synthesise nanoparticles of CuS

Almost certainly - probably by preciptiation with a copper (II) salt and a sulphide salt - it may be neccessary to introduce additives into the mix to prevent the CuS agglommerating - I can't give more details.87.102.5.144 09:41, 11 August 2007 (UTC)

Here http://nanotechweb.org/articles/news/1/5/7/1 shows nanowires have been made - do nanowires count as nanoparticles?87.102.5.144 09:43, 11 August 2007 (UTC)

or here http://www.informaworld.com/smpp/content~content=a759267176~db=all but chains again87.102.5.144 09:47, 11 August 2007 (UTC)

Or just do a search for "copper+sulphide+nanoparticles" http://ww.google.co.uk/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=copper+sulphide+nanoparticles&spell=1 - which gives syntheses in the first few results. 87.102.5.144 09:55, 11 August 2007 (UTC)

AC Adapter

I ordered a Linutop, which of course came with a europlug. I live in the US, so the europlug won't work. However, it says on the back that the output is 9V 1.5A. I've looked through my AC adapters, even universal ones, and they only go up to 300mA. Where would I be able to get a 1.5A one? Can I find one in this country? 172.135.153.217 04:52, 11 August 2007 (UTC)

You'd want a switching power supply here, most adapters your looking at are probably just plain old transformers (although a switching power supply doesn't have to be able to supply a high current of course, most mobile phone chargers are switching nowadays). Your best bet would be to look at the kind of adapters suitable for laptops and stuff. However are you sure the power supply isn't universal? Many are so all you would need is a passive plug adapter. Check the ratings carefully of course before you try anything Nil Einne 09:50, 11 August 2007 (UTC)

When I accidentally left my adaptor behind on one trip, I found a 'univeral' adaptor at Fry's for my laptop that provides that amount of power - they definitely exist - but they aren't cheap (I think mine was about $45) and most places like WalMart and Radio Shack don't carry them. One thing though - read the label on the thing REALLY carefully - some of them only provide that much current at lower voltages.

Bit does the existing adaptor work at 110v/60Hz? If it's designed to work in Europe, it should - 110v/60Hz is what they use in France (for example). If that's the case then all you need is a different plug - you can just cut the old one off and put a new one on. Screw-on plugs are not exactly common in the USA - but I've found them in DIY stores (the one I found was for garden tools - it's huge and bright orange - but it works). Alternatively, there are adaptors that accept a Europlug and plug into a US-standard wall socket. I've only ever seen those on sale at airports though - they might be kinda hard to find. SteveBaker 17:15, 11 August 2007 (UTC)

Where did you get the information that France uses 110V/60Hz? As far as I know and according to various "voltage charts" I can find it uses 220V/50Hz (or 230V/50Hz, which, I think, is the official value these days), just like the rest of Western and Central Europe. And I second Nil Einne's question: perhaps the AC adapter is universal? My laptop's power supply is rated "100-240V 50-60Hz", and has a Schuko plug; with a simple adapter, I could easily use it in the US. --Dapeteばか 10:54, 12 August 2007 (UTC)

IF your adapter is rated for "universal voltages" (120 volt operation as well as 230 volt operation), then any Radio Shack in the United States can sell you the adapter you need to plug a Europlug into an American NEMA 5-15 outlet. And if you will be mostly using this in the United States, any hardware store, Home Depot, or Lowe's home center can sell you any of ten different types of plugs that you could rewire onto your adapter's power cord (assuming it has a cord and doesn't plug directly into the wall).

Atlant 12:05, 13 August 2007 (UTC)

Intracranial pressure

My EEG revealed a slightly high intracranial pressure. However IMHO after downing the pressure to normal I will a bit more passive and slow. Does it make much sense? --Vado

Wikipedia cannot offer medical advice, please ask your doctor. However, did your doctor tell you why you had high ICP? Or could you tell us how it was reduced? Knowing these might allow us to offer you some insight. Someguy1221 06:17, 11 August 2007 (UTC)

I've responded to your question here: [4]. StuRat 04:13, 12 August 2007 (UTC)

anxiety disorders

im having a habit of impressing everybody since childhood..this is leading me to a variety of problems such as social phobia and gynophobia..what can be done to overcome this?

Find a psychiatrist. I got over my own social phobias by deciding the whole world could go fuck itself if it didn't like me. I think it's a good personal philosophy ;-) WP:DGAF. Someguy1221 06:17, 11 August 2007 (UTC)

Or, with mad skills like that, you would fit in perfectly among the Ref Desk regulars ;) But seriously, impressive as we are, we can't give medical advice, you should ask a mental health professional for direction. Rockpocket 06:53, 11 August 2007 (UTC)

Given the difference between psychiatrists and psychologists, it follows that you probably need to see a therapist (which could range from anything from a counsellor, to a psychologist, to a pschiatrist, etc). To my knowledge the psychiatrists are more the ones that dispense medication, so a psychologist is probably the one to see. You probably just need to talk to someone (in addition to talking to a professional). By "Gynophobia" do you mean "fear of women", or "fear of women's sexual anatomy"? Articles you should probably look at include Genophobia and Erotophobia and definitely have a read through of Social Anxiety - a great article which should really help you analyse yourself (even you're going to be paying for someone like a psychologist).

Other than that my personal advice is to definitely consider seeing a psychologist, and socialisation is extremely important (even if you feel that you "don't get it right" or "aren't comfortable" in social situations, maybe keep trying because through socialisation you learn a lot about yourself, and you observe how everyone else behaves, you can put forward and develop whatever 'personality' or 'persona' that you want to. In life you should have a variety of friends that feed different aspects of your personality. For example there might be friends that really make you laugh, and other friends that think everything you say is funny, or you have friends where you are always serious with and have very mature and 'deep' conversations, and other friends that seem to be unable to talk about anything of seriousness or importance. Through these you learn to develop certain social skills. Mirroring for example is where you mirror the behaviour of the person you're with - if they put their hands in their pocket, do the same, or if you're both at a table and they lean forward, copy them, or they lean back, so do you, or if they talk and use a lot of expression, don't answer back in a monotonous voice (unless of course you're tryin to specifically not mirror them). Another piece of advice is to try maintain self esteem. Spending time in the sun for example helps me a bit. Getting a good haircut helps a lot of people. Meditation can keep you focus on yourself and your objectives. Seeing a movie can really help motivate you.

Finally, as for the gynophobia, that's something you and your therapist can try and find the cause of. However in my persuit to try and help, here are some ideas: befriend a female (i.e. become friends with a female not because you're interested in her romantically, but rather as someone you feel relaxed with - and by befriend it can be anything you're comfortable with); consider whether you want your therapist to be male or female (note that Tony Soprano of The Sopranos had a female therapist) on the one hand you might feel very embarassed imparting your personal feelings to a woman, on the other hand it might be just what you need to get honest feedback from a woman and perhaps break through your problem.

If you like you should check if there are any newsgroups on the web of other people with social phobia or social anxiety, other people with gynophobia, and I know for sure that there are mens groups out there that discuss mens issues where some people could talk to you about it.

Good luck! Hope this helpsRfwoolf 15:18, 11 August 2007 (UTC)

First thing to do is go discuss it with your normal doctor. He/she will then prescribe something and/or refer you for further treatment to psychologist etc.--SpectrumAnalyser 23:15, 11 August 2007 (UTC)

I'm wondering what the OP meant by "impressing". —Tamfang 23:54, 14 August 2007 (UTC)

How to find out the caffeine content thropugh experiment

Hello

Im a student and i have tried to find out about how to detect caffeine in coffee and tea. I know that we require sulphuric acid and chloroform but havent found the way to find out how much caffeine a particular tea has or which of the provided samples have more caffeine 122.163.203.2 14:12, 11 August 2007 (UTC)Tarush

Feed it to a spider and observe the web it builds. See Spider_web#Spider_webs_and_drugs - the photograph is even of a cafeine-induced web. Funny thing is, I made this up and the short section actually mentions this as a method of determining the toxicity of substances. Every now and then I find out my thoughts aren't as weird as one (including myself) might think. :) DirkvdM 19:09, 11 August 2007 (UTC)

There is a funny video about spiders on various drugs on youtube [5] I have no idea how much, if any of it is true. Theresa Knott | The otter sank 07:55, 12 August 2007 (UTC)

Except the spider trick doesn't measure the quantity of caffeine. I've also got to remind Tarush that there is a lot of argument about tea not actually having any caffeine. Some argue that tea instead has a similar chemical called theobromine, most often discussed with chocolate, which is gentler than caffeine. --Mdwyer 22:52, 11 August 2007 (UTC)

I have no personal direct knowledge of the caffeine content of tea, but I have trouble believing that there can be an argument about it -- any decent lab should just be able to take a sample of tea and assay it, and find out. If tea really contained no caffeine, that ought to be common knowledge; since it isn't, I much doubt that it's true. --Trovatore 23:02, 11 August 2007 (UTC)

Yeah, it sounds kind of sketchy to me, too. But I came across it when I was doing some research earlier. A quick google found this and this which seem to contradict each other somewhat. 'Course now I'm getting tea and chocolate confused... --Mdwyer 03:40, 12 August 2007 (UTC)

It could be less simple than that if (for example) the theobromine is metabolized into caffeine in the body. I don't think this reaction actually occurs, but similar things confound food science when studying many complex transient phenomena (like browning reactions). --Sean 13:37, 13 August 2007 (UTC)

I don't know if it counts as "experimental," but I think that caffeine content is typically determined quantitatively using something along the lines of HPLC. For both quantitative and qualitative determination, maybe something along the lines of LC-MS. Although I'm sure there's a titration of some sort for a non-instrumental determination. --Bennybp 00:40, 12 August 2007 (UTC)

This is from my recollection of a school science project from a long time ago. I cannot attest to the safety of the procedure or the accuracy of the results. (In general, I recommend against trying it.) The procedure goes like this: the content of several (e.g. 10) teabags are emptied onto a container; the net weight is measured accurately using an electronic scale. Concentrated tea solution is obtained by boiling in water and filtering. Residue of the first filtration is boiled a second time to allow more of the remaining constituent compounds to be extracted. Lead acetate solution is then added to the solution to cause tannins to precipitate. The precipitate is removed by filtration. Solvent extraction (using chloroform) is performed to extract caffeine (and possibly other organic compounds) from the aqueous solution. The chloroform is evaporated in a hot water bath (and recovered, for safety reason). The solid that remains is supposedly mostly caffeine and is weighed using an accurate electronic scale. (Warning: This experiment involves fire, explosion, lead poisoning, and other hazards. Do not attempt unless the experiment has been cleared for safety, authorization, and regulatory compliance. And do not attempt without adequate safety precautions, and expert guidance and supervision. The information here may be incomplete or inaccurate, and is not to be relied on.)

There is a slightly different method in my organic chemistry lab book. I think it's a common experiment for undergraduate organic or separations lab. It basically involves boiling tea bags in hot water with sodium carbonate (to help keeps the tannins water soluble), extracting the solution with dichloromethane (I'm guessing this is used as a slightly safer replacement for chloroform), boiling off the dichloromethane, and recrystallization of caffeine in hot acetone and ligroin. That would extract it, but would only probably give a rough idea of how much is in the tea, due to some impurities and yields. The details should be in any undergrad lab book (This is in "Macroscale and Microscale Organic Experiments", 4th edition, by Kenneth L. Williamson, pg 148). But again, this should not be attempted without the proper safety equipment (fume hood, hazardous waste collection, etc) and supervision by a professional. --Bennybp 17:19, 12 August 2007 (UTC)

Term for an aggressive signal used by animals

My girlfriend has a bird (Quaker parrot) that doesnt really like me, and times moves its head side to side. I'm the type of person that likes to explain behaviors with psychology and evolution. So I figured him doing this meant some kind of signal of being aggressive.

What's funny is while my girlfriend would hold him, I would make the same signs (such as turning head side to side, and making bird calls) and he would respond right after I did with the same thing I used. So right there I figured that those signals had something to do with a competition to show ability to fight.

Last night, around 6 AM, I watched the Science channel, and in one of the documentaries it showed that the side-to-side behavior being done by a chameleon right before fighting with another. And that it was done to show off its swiftness and the like to intimidate the competitor. It was a very small part, so it didnt go into details, which I wanted. But when I saw that, I thought "Eureka!"

I want to know if there is a term for that. And I also want to know if I was right about my assumption, and also if that signal is used for anything else, such as a normal social reason. I looked around on a few pages and couldnt find a mention of it. I looked it up on google and they only said the signal, and hardly on why it'd done. Sorry for the long explanation, but I thought you guys would appreciate the story. =) PitchBlack 16:33, 11 August 2007 (UTC)

When an animal puts on a show without necessarily acting on it, this is called a "display" (as you suspected, here an "agressive display"), which is a part of its inherited evolutionary stable strategy. This theory explains behaviour from an evolutionary perspective. In this case, the bird is sizing you up as an opponent rather than taking a lunge at your eye straightaway as it realises you may be capable of doing more grievous harm to him than he to you. Where fighting for dominance does occur within a species, it is rarely "red in tooth and claw", as the mutual costs in terms of injury and time are too great and the outcome can be decided with restraint. Needless to say, his jealously is misdirected (or is it?), and when harmless, the neuroticism of an animal outside of its natural environment is a big part of the fun in keeping a pet. Don't take it personally! Bendž|Ť 17:38, 11 August 2007 (UTC)

Thank you for the response! I have some responses myself though. If my girlfriend were to actually let the bird down on the couch, it would come to me and bite/attack me, it TRIES to attack me if I touch or hug her (starts chirping like hell too). So its not just sizing me up, I think it might be using its signals cause it really wants to do something. And when I let it bite me, I put on a little show and everyone starts laughing. And when my girlfriend takes it away and picks it up, the bird actually laughs with her. Can you tell me if maybe the bird is doing this not only for a jealous/territorial reason, but maybe a humorous reason too? And can you explain more about how an animal can be jealous? PitchBlack 19:01, 11 August 2007 (UTC)

I think that bird is trying to steal your girlfriend, dude. Someguy1221 07:39, 12 August 2007 (UTC)

Sure, displays often indicate intent, but you can see the difference between the show that is swinging its head back and forth (unless its trying to hypnotise you) and actually biting you, a more utilitarian action; it's taking aggression to the next level. Many beaks are designed primarily to crack nuts and seeds rather than disembowling adversaries. Nevertheless, among polygynous chickens, where the stakes are much higher (all the females or none), fighting is wanton and beaks are used to their full capacity, leaving the loser to choose his final resting place. You can take it on good faith that your girlfriend's parrot is actually being quite gentle with you really and that there's still a signaling element to its behaviour. Many parrots pair up for life, so you can imagine how in the absence of a conspecific (member of its own species), it's grown quite attached to your girlfriend. As a seeming loner arriving on the scene, you're clearly a threat. I'm quite positive birds experience a wide range of emotions, including jealousy, although self-pity is a luxury only humans seem to indulge in. Humour, also, is a fairly recent innovation that is probably only shared in a true sense with some of our closest relatives. Remember parrots are talented mimics, and laughing may not be something they do in the wild. A book you may be interested in is Alexander F. Skutch's The Minds of Birds. A good chunk of it can be sampled on Amazon. (I should say that no, I'm not the author, nor have I even read the book myself.) Bendž|Ť 09:47, 12 August 2007 (UTC)

Oh, ok. Yeah, I know theyre great mimics, that's why I asked if it was doing it for a humorous reason. I didn't know if it was actually laughing or just mimicing (sp?) the others laughing. Thanks for all the answers, but I have one more question. The bird was biting her cusion for a while, but then stopped. Why? Also, when my girlfriends presence around the bird is gone (like in vacation) it'll be much nicer to the people around. PitchBlack 03:44, 14 August 2007 (UTC)

New fish in an ecosystem

Oftentimes when people create artificial pools or lakes, I know a whole ecosystem can move in - frogs, birds, insects, subsequently tadpoles, etc. However have there not be times when fish have somehow shown up? Or how could fish migrate from one pool to another pool without water as a medium? Or do these ecosystems just make do without fish? Any input is appreciated Rfwoolf 17:18, 11 August 2007 (UTC)

I don't have a source for this, but I remember being told that fish eggs are transported between ponds on birds' legs. 80.169.64.22 17:45, 11 August 2007 (UTC)

Flooding also can help fish to migrate.

Also when an artificial lake is created it's almost inevitable that a human will put fish fry in there..87.102.8.162 21:29, 11 August 2007 (UTC)

I read that as "fried fish". Oops. It is also somewhat conceivable that the ecosystem was already there, just dormant. Cryptobiosis explains that some organisms stay dormant until water appears. Sea monkies are an example. --Mdwyer 22:46, 11 August 2007 (UTC)

And some fish can walk using their fins. They can cross land from one pond to another. Graeme Bartlett 10:47, 12 August 2007 (UTC)

I’ve heard the fish eggs on birds’ legs explanation as well. I’m pretty sure it’s a standard ecological phenomenon. Most ecology text books should have it. --S.dedalus 21:04, 12 August 2007 (UTC)

Slow vcr power-up

More of a technology question, but I suppose the science community is most likely to have an answer.
My old vcr has started to develop the problem that when I turn it off for a while, it takes a long time to power up again. When I leave it off for a few days I have to hold the power button down for a minute or so until it 'comes alive'. When I left it off for about a month recently it even took several days (in case you're wondering - I kept the power button down with sticky tape). On stand-by there is no problem, but in power-save mode I get the same problem. Now this isn't too much of a problem if it remains the same (though still annoying), but if it gets even worse (as seems to have happened over the last year or so), it might not power up at all if I turn it off too long. I only occasionally need it when I play an old tape, but then I do need it. And I don't want to have it powered up all the time just for that. DirkvdM 19:34, 11 August 2007 (UTC)

Leaky electrolytic capacitors?--SpectrumAnalyser 20:27, 11 August 2007 (UTC)

Sounds like a good reason. Heat causes some electronics -- especially capacitors -- to slowly degrade. Once they get to a certain level, they no longer function at the ranges they are supposed to. A few years ago, there was a problem where a particularly bad set of capacitors were manufactured and turned up in a great number of consumer goods. I personally had these show up in computers, DVD players, and cable modems. If the VCR was built in the last few years, it might contain these capacitors. In that case, unless it is still under warantee, there is probably very little you can do about it, I'm afraid. --Mdwyer 22:43, 11 August 2007 (UTC)

If you have a soldering iron handy you can still replace the capacitors with a blown cap. --antilived^{T | C | G} 02:46, 12 August 2007 (UTC)

I've got a soldering iron, but I don't know which one to replace - there are about seven capacitors near the power inlet section (assuming a code like 'C904' means a capacitor). Btw, there is a writing saying 'HOT' between two capacitors - a big round one (400 V 120 μF) and a small blue 'blobby' one. Notice that I barely have a clue what I'm talking about. But then again, if the alternative is to give up on the vcr then that is a wonderful excuse to completely take it apart (ignoring the 'shock hazard' warning :) ).

Another thing is, how do I find out how much power it consumes in the various states it can be in. If it consumes less than 1 W on standby then I'll just do that. 1 W would cost me less than 2 euro per year (at today's electricity prices).

Or, more importantly, is there a chance that if I disconnect the power and try to start it up again in 10 years, it will not? DirkvdM 09:09, 12 August 2007 (UTC)

If this is indeed a leaky electrolytic, you can probably distinguish it from the non-electrolytic capacitors because electrolytics are normally marked with a '+' at one end and a '-' at the other - where non-electrolytics are not. Electrolytics are generally bigger, and cylindrical rather than disk-shaped - but that's not such a 'for sure' thing as the +/- markings. Hopefully, that will narrow it down to a small number that you could replace one at a time. SteveBaker 04:23, 13 August 2007 (UTC)

You can distinguish them by plugging them in backwards. The electrolytic ones will explode.  :) --Tbeatty 04:28, 13 August 2007 (UTC)

Can you see any cylindrical capacitors with some goo on the top or its cap is not flat? Those are the faulty ones and you can try replace them with approximately same spec'd ones. Remember to discharge the capacitors (shove some maybe scissors across the two pins and wait for the spark) first. --antilived^{T | C | G} 06:04, 13 August 2007 (UTC)

Ah, so that's what you meant with 'blown cap'. I thought you meant 'broken capacitor'. :) No, I don't see any blown caps or goo. But now I hear a ticking sound coming from the power section, with a frequency of just over 1 Hz. IT'S A TIME BOMB! :) Or rather, it sounds like something a capacitor might do - build up a charge, not able to hold it and then discharging it somehow, resulting in a tick. Of course, that would happen at very regular intervals. QED. I hadn't noticed that tick before, so I assume it wasn't there.

Anyway, accessing the big capacitor (which might be the faulty part) from the top is a bit tricky because I'd have to dismantle the recorder-section, which is rather delicate, and I couldn't figure out how to remove the bottom plate, so I cut out a section (right next to the 'Warning: shock hazard, do not open' sign :) ) and when I put the blade of my knife across the prongs I got the fireworks you promised. Strangely, all the electronics parts shops are at the other side of town - where I work, so I'll look for a replacement tomorrow. Thanks for the help so far. DirkvdM 08:28, 13 August 2007 (UTC)

Oh, and something I had forgotten to mention so far - at the top of the cylindrical thingies, which I assume to be capacitors, there is a symbol that looks like a 'K'. Or a 'V' with a line at the bottom. Which looks rather like the symbol for a diode, which I find rather confusing. The '+' and '-' are on the circuit board, though, as indicated. And there appear to be only two connectors to the board, which isn't very diodish. :) DirkvdM 08:37, 13 August 2007 (UTC)

(Diodes also have two pins). The term 'blown cap' does mean 'blown capacitor' - but frequently, when they blow, the contents (which is a nasty chemical paste) may boil - either forcing some of the contents of the capacitor out of one end or actually bending the metal can. Similarly the term 'leaky electrolytic' doesn't necessarily mean that it's leaking fluids - it means that it's leaking voltage. But it's perfectly possible for the capacitor to fail in ways that don't cause those obvious signs - and since your VCR does EVENTUALLY turn on, I doubt the capacitor has completely failed - it's just leaking voltage and therefore not charging as fast as it should. If you can't completely remove the dead capacitor - perhaps you can just solder a wire across it's pins to short it out - then cut one of the tracks leading up to it and solder the new capacitor across the gap you made (making sure the +/- of the new electrolytic are in the same order as the old one!) - you can use a couple of short lengths of wire to connect your new capacitor to the circuit board so you can position it someplace more convenient. SteveBaker 12:11, 13 August 2007 (UTC)

Why would you want to replace a cap with a blown one? 68.39.174.238 23:04, 13 August 2007 (UTC)

Yeah, that had me puzzled for a moment too, but of course he didn't mean replace the capacitors with others with 'a blown cap', but replace 'the capacitors with a blown cap' with a good one. Which led me to think that 'blown cap' meant something other than 'blown capacitor'. As per above. DirkvdM 07:39, 14 August 2007 (UTC)

Digital vs Analog Television Broadcasting

What are the real CURRENT facts regarding the alleged discontinuance of analog television broadcasting in favor of analog by 2009? What is the now-intended timing of this change if revised? What does it mean for the future of our fifteen year old TV (without HD capability, of course)?----Bob

You didn't specify the country. Your WHOIS information points to the US, however (I live in the UK, and so know nothing at all about the US switch off, and post this merely for the sake of someone else who might) Angus Lepper^{(T, C, D)} 21:20, 11 August 2007 (UTC)

For the time being at least, TVs do not need to be high-definition to receive a digital service; the UK offers Freeview (terrestrial), Sky Digital (satellite) and Virgin Media (cable) digital services which will work just fine on any TV with just a small set-top box to show for it. The US offers similar services, although they are currently slightly less advanced; according to our article on digital television "The FCC has determined that an external tuning device can simply be added to non-digital televisions to lengthen their useful lifespan. [Although] external tuning devices are not widely available, are relatively expensive, and require bulky AC power supplies, starting in 2008, the government will take requests from households for up to two coupons to reduce the price of some converter boxes by $40". These will make your TV perfectly digital compliant if you live in the US. Laïka 22:07, 11 August 2007 (UTC)

On the point of switchoff, the FCC will switch off the analogue signals on 17 Feb 2009 and sell the old analogue stations to other companies; this will render your TV screen completely blank on this date onwards, although analogue cable will continue for the forseeable future. Laïka 22:10, 11 August 2007 (UTC)

(Assuming USA/FCC NTSC, etc) Well, sort of. The stations will still exist, they'll just have moved to digital signals. The frequencies are being sold off -- mostly to cell phone companies. The FCC intends to have a voucher program, that will put money towards a new TV or an adaptor. You'll still be able to use your 15yo TV, assuming the correct adaptor. Your picture may even be better, since problems like ghosting will go away. But depending on where you are, you might have to invest in a UHF antenna, instead of a VHF antenna. --Mdwyer

However, don't expect an old analog TV with a converter to give a picture anywhere near as good as an HDTV, especially one with 1080i resolution. I'm personally planning on upgrading rather than spend more money on bad TV, but I am waiting and hoping the HDTV prices will come down first. StuRat 02:11, 12 August 2007 (UTC)

Note though, that correlating the analog switch off to the advent of HDtv is far from necessary. StuRat's approach to this makes the whole thing seem like a major cost and investment to households, and may very well create far more opposition to the switch than what's really warranted. Yes, digital terrestrial tv will not be as good as HDtv, but the existence of HD does not mean you need it. The cost to continue watching tv if you use an old tv set and your own antenna for reception can be as low as $30 US. ([6] Swedish appliance store, 1 USD = 7 SEK)/Kriko 08:21, 12 August 2007 (UTC)

In Australia the government keeps delaying the switch off, of analogue TV, as very few viewers have changed to digital. Only in the last year or so have TVs with a digital tuner been available as standard. It is now difficult to buy a plasma or LCD screen with only an analogue tuner. The set top box has been getting cheaper and cheaper. Graeme Bartlett 10:53, 12 August 2007 (UTC)

Health,

Has anyone heard about the study being done at the Mayo clinic using DNA testing to have a extremely early detection of cancer throughout the body? Cory Nelkin 21:06, 11 August 2007 (UTC)Cory Nelkin

Are you sure it's all cancers? Or is it a particular cancer? Recurring dreams 23:49, 11 August 2007 (UTC)

The Mayo clinic offers many types of screening for many types of cancer. You'll have to be more specific. Someguy1221 03:55, 12 August 2007 (UTC)

Enzymes releasing products after the reaction.

Whenever I read about enzymes things talk about substrates being brought together, reactions happening, and then the product is released. Nowhere have I found a description of what chemical/structural changes occur that cause the product to be released.

My assumption is that the product somehow changes the enzyme shape so that it can no longer hold the product. Is this correct? Additionally in competitive inhibition how does the inhibitor get out of the active site (and when)? Thanks Caffm8 22:35, 11 August 2007 (UTC)

(Oy, where are my Bio notes when I need them) The enzyme generally returns to its original conformation after catalyzing a reaction (the product cannot hydrogen bond or ionically bond to the enzyme exactly as the substrates did, being a different chemical), and in doing so the product unbinds. As for competitive inhibitors, these can just randomly bind and unbind from the reaction site (as hydrogen bonds and ionic/ionic or ionic/polar bonds can form and break in solution quite easily). It's also possible that it can't be removed, and the enzyme is rendered useless (mode of action of penicillin and similar antibiotics). Some substrates involved in signal transduction (such as acetylcholine and insulin) are removed from their receptor enzyme through another enzymatic reaction. It's possible some products and competitive inhibitors must be also, but I know of none. Someguy1221 23:55, 11 August 2007 (UTC)

Funny thing is that the product doesn't so much change the comformation of an enzyme. It's the change of conformation of the enzyme that produces the product. An enzyme will have a certain affinity for a substrate but an even higher affinity for the transition state (the state between substrate and product). So as the enzyme is catalysing the reaction it will take on a conformation that is ideal to match the transition state. But because the transition state is unstable it won't last very long, leading to a product. Of course the enzyme has a very low affinity for the product, so it is released. If an enzyme would have an extremely high affinity for either the substrate or the product no reaction would ever occur. Because either de product or the substrate would be permanently stuck to the enzyme. PvT 18:44, 12 August 2007 (UTC)

CO2 levels

Is there a simple way to measure the level of CO2 in a given gas sample that would be accessible to the at-home scientist? I don't need to know the exact quantity, just compare one sample with another. 69.123.113.89 23:52, 11 August 2007 (UTC)

Do you have sensitive balance? CO2 is heavier than air for example.--SpectrumAnalyser 23:57, 11 August 2007 (UTC)

That wouldn't really work in this situation (I should have been more specific). I need to measure the CO2 in a sample, and then measure the same sample again at a later time. 69.123.113.89 00:02, 12 August 2007 (UTC)

I think I've thought of a way to do what I need, but I'm not sure it will work. My Idea: I pass the gas sample through a tank of water to which a pH indicator, like Red Cabbage juice, has been added. Hopefully, some of the CO2 will disolve and form Carbonic acid, which will cause a pH change. Then, later, I can pass the gas sample through a second tank, and compare the pH changes of the two.
My Question is - will this work? 69.123.113.89 01:25, 12 August 2007 (UTC)

The basic concept sounds good, but the problem is that the sensitivity of the cabbage juice indicator probably isn't up to the task of detecting the minute changes in atmospheric carbon dioxide levels. It would also be critical to bubble the exact same quantity of air through the cabbage juice both times. StuRat 02:00, 12 August 2007 (UTC)

The CO2 would be absorbed by a strong base like NaOH.. if you can get that to happen then the amount of gas would be reduced by the fraction of CO2 present in the air - you'd need to be able to measure the volume - not easy for small amounts of CO2 though.87.102.1.234 10:36, 12 August 2007 (UTC)

Or you could attempt to measure the increase in weight of the NaOH. Although it would absorb water as well. A more exotic method may be to grow a seed and see how much dry weight the final plant ends up with. Graeme Bartlett 10:57, 12 August 2007 (UTC)

In high school chem lab, we looked at absorbing CO2 from a given amount of air in a given amount of water. You could use an indicator directly but you'd need to standardize it against known amounts (how dark or what color corresponded to how much CO2). See [7] for a way that might work for you. Alternately, you could titrate the dissolved CO2. Finally, you can measure the turbidity after passing the air through lime water. DMacks

The conventional grade school test for CO2 is to bubble the gas through Kalkwasser/Lime water (a saturated Calcium hydroxide solution). Carbon dioxide gas will precipitate as calcium carbonate. You may be able to quantitate the precipitate either volumetically, or by dry weight. Alternatively, here's a NASA webpage that may help: [[8]] -- 20:33, 12 August 2007 (UTC)

There's a commercial gadget that measures CO2 content in gas by the reduction in the temp of a target heated by IR beamed through the gas. Sort of a reverse greenhouse effect. Gzuckier 15:50, 14 August 2007 (UTC)