Wikipedia:Reference desk/Archives/Science/2006 October 18

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October 18

How many seagulls...

...would I need to get to stand very close together in order to create sufficiant mass to form a black hole? --Kurt Shaped Box 00:36, 18 October 2006 (UTC)

Posting on behalf of User:Ziyi_cai841117: let me count...one, two three, four, five...two hundred billion one thousand and one...two hundred billion one thousand and two...four hundred billion...four hundred trillion...four billion billion billion... --Bowlhover 03:28, 18 October 2006 (UTC)

How heavy is a seagull? 500 grams? If so, you'd need about 1.2 x 10^31 seagulls (see Tolman-Oppenheimer-Volkoff limit). By the way, why are satirical questions about seagulls often asked? How did this joke originate? --Bowlhover 00:57, 18 October 2006 (UTC)

Your average gull weighs about a kilo - the biggest gulls weigh up to 3kg. As for the questions about gulls - I think I started that one off. I have an interest in gulls and started asking a few questions about them. A few people saw this and started taking the mickey... :) --Kurt Shaped Box 01:01, 18 October 2006 (UTC)

Ah I remember that --froth^{T C} 16:34, 18 October 2006 (UTC)

But would you have to compress them as well? There are plenty of stars more massive than 6 x 10^30 kg (~3 solar masses) which are not black holes. There are stars around 20 times as massive. How about an upper bound for the problem. A rough back of the envelope calculation shows that a sphere of radius ~ 2.68 AU at the same density of water would be roughly the same size as its Schwarzschild Radius. That's a mass of about 2.7×10³⁸ kg.Richard B 22:17, 18 October 2006 (UTC)

I think you could make a black hole with just a few. But to be on the safe side, I would gather the complete worlds population, and pack them together rather tightly. THen you need to surround the gull mass with a very powerful exploding (or imploding) mechanism. Say an H bomb. Under the massive compressive forces, its just possible you could get a very small BH. On the positive side tho, that would be the end of ANY future gull questions on WP 8-)).--Light current 01:28, 18 October 2006 (UTC)

A H bomb is not at all powerful enough. You'd just be creating a very big mess. In order to create a black hole, you'd have to overcome the strong nuclear force, which is very strong. --Bowlhover 02:09, 18 October 2006 (UTC)

You're not related to L. Ron Hubbard by any chance, are you? ;) --Kurt Shaped Box 02:04, 18 October 2006 (UTC)

You gather a bunch of gulls together. Then surround them with a flock of swallows (African or European - your choice) and get them to throw the coconuts they're carrying at them at close to the speed of light. Voila! Clarityfiend 02:40, 18 October 2006 (UTC)

Yeah but you forgot that the swallows have swallowed the coconuts thus rendering them useless as missiles 8-) --Light current 15:28, 19 October 2006 (UTC)

Interesting question. I've often likened the "big crunch" scenario to the mannerisms of a large group of seagulls converging wildly on a stray piece of bread on the ground.  freshofftheufoΓΛĿЌ  05:07, 19 October 2006 (UTC)

What kind of bird is this?

This bird flew out of a bush in the middle of Manhattan. What is it? grendel|khan 00:46, 18 October 2006 (UTC)

It's a common starling. In my homeland we have many. --Kurt Shaped Box 00:50, 18 October 2006 (UTC)

Blame Eugene Schieffelin. MeltBanana 02:38, 18 October 2006 (UTC)

You can send some of yours back over here if you like - they've started to decline in the UK. Also, has anyone ever considered trapping for the pet trade? Check out those talking starling videos on YouTube... ;) --Kurt Shaped Box 05:55, 18 October 2006 (UTC)

Nice photograph. —Bromskloss 09:15, 18 October 2006 (UTC)

Time machine

How can two teenagers build a time machine? --Bowlhover 03:24, 18 October 2006 (UTC)

You'll need some paper clips, a piece of string, and tachyon-enriched uranium. —Centrx→talk • 03:29, 18 October 2006 (UTC)

It's easier when you find a guy named Rufus who will lend it to you, preferably disguised as a phone booth. ---Sluzzelin 03:43, 18 October 2006 (UTC)

It's really easy [1]. Clarityfiend 04:37, 18 October 2006 (UTC)

A police box would do nicely as well. – ClockworkSoul 04:38, 18 October 2006 (UTC)

Eat some mushrooms and all will become clear. Vespine 05:01, 18 October 2006 (UTC)

Forget the paper clips and uranium. You can find out all about time machines here. B00P 05:46, 18 October 2006 (UTC)

Or, alternatively, you could buy the plans on the Internet. Just be careful not to injure your vital organs in the process :) --Robert Merkel 07:07, 18 October 2006 (UTC)

It's quite easy ready... 1. Get a cardboard box, old circuit boards, egg time and some glowing fuel (tip: Paint rock with glow-in-the-dark paint). 2. Set up box and glue on circuit boards and 'fuel' 3. get inside cardboard box and set egg timer for the amount of time you wish to travel into the future. 4. Wait for egg timer to countdown, and only then exit your time travel box. 5. You've now sucessfully travelled the set time into the future. Benbread 08:30, 18 October 2006 (UTC)

Don't forget to write "TIM MASHIN" on the side! Confusing Manifestation 12:04, 18 October 2006 (UTC)

How about deciding that when you build the machine you will come back to today from the future and give yourselves the plans. If you don't want to risk meeting yourselves then you can work out where you can leave the plans so that you will find them. Write it on your calendar now so that you won't forget ! Now go and look for those plans ! Gandalf61 08:35, 18 October 2006 (UTC)

Make sure you bring it to the 24 hour all you can eat car wash. --Russoc4 18:13, 18 October 2006 (UTC)

Ask yourself. The yourself that already built it and went back into the past to tell you about it, that is.  freshofftheufoΓΛĿЌ  05:02, 19 October 2006 (UTC)

Funny.. Im starting to get deja vu on this thread! Does that mean Im already in the future, or does it mean this is a FAQ?--Light current 15:36, 19 October 2006 (UTC)

You guys have all got it wrong. Just reach the Planck heat and you've got everything all set! — X [Mac Davis] (SUPERDESK|Help me improve)05:52, 20 October 2006 (UTC)

dirigibles

designs for commercial use; design principles; performance and capacity. Thanks. SKalmutz--Skalmutz 03:52, 18 October 2006 (UTC)Bold text

See WP's article on airships, and also the external links mentioned there. Have a look at the P-791 for a recent example of design.---Sluzzelin 04:18, 18 October 2006 (UTC)

Regarding Earth rotation and revolution

If gravity is a force towards centre of sun, why doesn't the earth fall straight into sun instead of rotating around its own axis and revolving around sun? One explaination given by stephen hawkins in brief history of time says that actually earth is travelling strainght in space-time but in 3 dimensional space it looks curved as a result of removal of time dimension.Does somebody have any simpler answer to understand?

If the earth were to stop moving through space for an instant, it would indeed start moving in a straight line directly towards the sun. And if the sun's gravity stopped for an instant, the earth would continue moving in a straight line instead of orbitting. But you know that neither of those "if"s happen...the earth is in orbit, always tending to move "sideways" relative to "directly towards the sun" and the sun's gravity keeps pulling it closer. These effects are balanced--the gravitational pull is strong enough to keep the earth curving around instead of zooming off but not strong enough to overcome the earth's inertia and pull it any closer. See centripetal force and planetary orbit, and remember that actually the earth and sun orbit each other (but the sun is so much more massive, that result is as if just the earth is orbitting a virtually stationary sun). DMacks 09:05, 18 October 2006 (UTC)

(edit conflict) Hi! Please sign your comments with "~~~~" at the end. We can forget about the earth rotating around its own axis since that is not related (or its impact is at least very small). An object doesn't have to move in the direction of the force that is acting on it if the object is already moving in another direction. Think of a car that rolls past you. If you give it a nudge, it doesn't immediately change its movement and start moving in the direction you pushed, right? If you continue to push it in the same direction for a long time, however, with nothing holding against, it would more an more in that direction. But the sun does actually not pull the earth in the same direction all the time because toward the sun is not the same direction all the time – it depends on where the earth is at the moment. A more familiar example is when you have an object in a string that you swing around in a circle. Let's say you do it in empty space so we don't have to think about air resistance. The only force on the object is the string pulling it and that force works toward the center, where your hand is. Still, the object don't end up in your hand, but continues in a circle. —Bromskloss 09:08, 18 October 2006 (UTC)

Just to expand on things a little, there are two answers to your question. The first is based on Newtonian gravitation - that gravity is a force, which pulls the Earth to the Sun. But, as pointed out above, the Earth is travelling in another direction, so the force acts to change that direction. Imagine you've got a big cannon on top of a big hill. If you fire the cannon with a small charge, the cannonball will go forwards a bit and fall at the same time, making a parabolic path. If you use a lot more charge, it will go further and further. If, theoretically speaking, you used a massive amount of charge, you could shoot it so fast that by the time it's fallen a certain distance, the curvature of the Earth means it's still at roughly the same height. As long as it keeps falling down as fast as it's moving forwards, it will track out a circular path around the Earth. This is a (very much) simplified way of making something orbit the Earth, like a satellite. Now, imagine that on a bigger scale, and you have the Earth orbiting the Sun.

Unfortunately, it turns out Newton didn't get things perfectly right, and when Einstein came along and invented General Relativity he made the universe look a whole lot different. In particular, in GR gravity isn't a "force", it's a distortion in the shape of spacetime. Think about standing on top of a sphere, like the Earth. From our scale, it looks like the Earth is flat. But if you tried walking straight forwards, eventually you'd come back to where you started, because in fact the Earth is curved. Now imagine space is like that - curved, but in more complicated ways. Anything moving in space that doesn't have a force acting on it (and remember, gravity isn't a force any more) will move forwards in its little bit of spacetime, which will always look flat on a small scale (and in the universe, the scales get pretty big), but whenever you have something massive, like a star, that makes the overall shape of spacetime curved, so even though you may think you're going straight forward, someone standing far away will watch you trace out a curved path - in particular, spacetime around the Sun is shaped so that the path the planets make is roughly circular - i.e. an orbit. Confusing Manifestation 12:03, 18 October 2006 (UTC)

I could have sworn this was only a theory... --Wirbelwind 02:32, 20 October 2006 (UTC)

Well yes, Einstein's theory of general relativity is only a theory in the same way that most all of science is only a theory. It's a convenient way to explain why gravity can act at a distance, seemingly instantaneously. It also happens to hold up to the empirical evidence we've been able to gather so far.sthomson 19:15, 24 October 2006 (UTC)

.

sinisoidal RC phase shift oscillators

how does a sinusoidal RC oscillator prodduce a sinusoidal output??? I know that an oscillator produces a out put signal even withought a input signal bcause it amplifies the noise signals but noise signals are not always sinosoidal are they?

An oscillator consists of gain more than unity to compensate for losses.So the noise automatically gets amplified,and due to resonant nature of circuit only a particular frequency gets amplified causing suistained oscillations.

The RC produces 60 deg phase shift, so Supposing the output of the amp is 180 out of phase, three such RC networks would eventually produce zero phase shift or in phase oscillations for feedback,thus positive feedback in short.

See Wien bridge oscillator for one answer. Another is the "Twin-T" oscillator, described briefly at RC oscillator.

Atlant 17:03, 18 October 2006 (UTC)

How can I study theoretical physics in one of the US universities?

I want to study theoretical physics (Quantum mechanics) in one of the US universities. I am nineteen years old. I live in Egypt. What shall I do? How much will this cost me? Is there a way I can get a free scholarship? I have an account under the name Meno25 talk. I sent this message from a public computer because my computer is currently broken down. By the way, I am currently having a wikiholiday.

--196.218.105.36 11:32, 18 October 2006 (UTC)

First of all, you cannot study just theoretical physics. The canon of undergraduate physics is more or less the same everywhere, and usually contains, within in the first three years (in many conuntries, that is up to the Bachelor of Science degree) courses in: calculus, linear algebra, general physics, mechanics, electrodynamics, lab practices, a bit of quantum mechanics and relativity. If you are then thrilled by it, you'd contnue your studies up to an Honours degree, a Master of Science, or even a PhD, depending on the country and your stamina. But I'm afraid I am not an expert for your main question, because I studied physics in Germany and currently work as physicist in Austria, so I do not know much about scholarships in the USA. But I could tell you about Germany or Austrai, of course, in case you are interested. Simon A. 11:56, 18 October 2006 (UTC)

Here are some types of scholarships:

• Academic scholarships for exceptional students. If you are at the top of your class and score extremely well on tests, you might be able to get one of these.

• Athletic scholarships for excellent athletes. Somehow I doubt if many physics majors have athletic scholarships, but there may be a few.

• Need-based scholarships. These provide money to those who are poor. Generally speaking, they are only for those of the same nationality as the scholarship fund.

• Special group scholarships. You get these by being a member of some class (blind, deaf, black, etc.) or organization.

As for the cost, that will vary widely. However, I would say US$10,000-$20,000/year would be a bare minimum for tuition and expenses. Some are far more expensive. One option is to take the first two years at a community college, which can be much less expensive.

As for getting into the US, you would apply for a student visa, at the American embassy. So long as nobody in your family is a member of a terrorist organization like the Muslim Brotherhood, you can probably get one. However, if you ever overstay your student visa, you are likely to be deported and banned from ever entering the US again.

StuRat 14:02, 18 October 2006 (UTC)

I don't know about the US, but in the UK, plenty of universities, including some prestigious ones such as Imperial College London and University of St Andrews, offer theoretical physics as a possible course[2]. It tends to overlap normal physics but with some modules changed (more maths, less lab work). It's probably too late to apply to a UK university this year (the 2006 UCAS application season is now in full swing), but registration for 2008 should start up soon, and with physics application rates so low, universities will be competing to accept you! As far as scholarships and bursaries are concerned, unfortunately UK universities tend to ask that overseas students sustain themselves (for more info, see International Students on the UCAS website). Laïka 15:27, 18 October 2006 (UTC)

Well I'm paying 28000 USD per year here in america. I was a geek child so no scholarships for me I'm afraid :) If you do decide to study in america you'll be paying it off for many many years. IIRC britain has free higher education (or was that canada?) but you might have to be a citizen. --froth^{T C} 16:24, 18 October 2006 (UTC)

Canada does not have free higher education (it has severely reduced higher education but international students have to pay twice the amount domestic students do. However becoming a citizen is easier in Canada.) Sweden and other socialist countries do have free higher education but I forget the requirements. ColourBurst 16:43, 18 October 2006 (UTC)

The UK did have free Uni education. The universities can now charge up to £3000 (~$5000) per year in Top-up fees, but that still sounds a heck of a lot cheaper than a lot of countries. But an international student would have to pay full fees (Cambridge, Leeds and Imperial all charge around the £10,000 (~$18,000) mark for scientific courses to international students). Laïka 19:02, 18 October 2006 (UTC)

Doesn't cambridge have like individual dorms and fireplaces and leather furniture in the rooms? At 18 grand? Geez what am I doing in the US? --froth^{T C} 19:16, 18 October 2006 (UTC)

Some of the rooms are pretty sweet; the best room at Corpus Christi College, Cambridge has ensuite and a private living room! Of course, you need to get at least a first to even be entered into the lottery to earn the room... Laïka 20:39, 18 October 2006 (UTC)

As you asked on my Talk page, some infor on German universities: University education used to be free, but this year, most Länder have introduced fees. Their amount is not too clear yet but it should settle below €1000 per year. But note that, as you are not a EU citizen you will AFAIK be required to prove that you own enough money to afford living in Germany in order to get a student visa. Maybe I point out a few differences between German and US universities. Many other countries in northern continental Europe (Austria, Switzerland, Benelux, Scandinavia, ...) are comparable to what I say about Germany.

• German universities have no entrance exams, and besides the most popular subjects (which does not include physics) anybody with an Abitur may start studying at any university. Foreigners have to show that they finished secondary education (i.e. high school) at a level comparable to a German Gymnasium.
• To compensate for the lack of entrance exams, in physics, the exams after the first and second year are designed to sieve, i.e. to let only those pass who are good enough to study physics. More than a third of the freshmen leave physics after failing these exams!
• In US universities most undergrads start with one or two terms of general studies before deciding on a major. German universities require you to decide for your major at the beginning. Also, the starting level is higher due to the longer high school time and our three-tier school system.
• While the US has a few elite universities and many medicore ones, the quality of education differs not that much from one German university to another one, and lies below the top US universities but clearly above the average US university. Still, the physics departments of some German universities are much better than average.
• Undergrad courses are taught in German! Most foreigners need a year of full time language courses before thay can really start to study. But as every German physicist is usually more or less fluent in English, some universities are considering to offer undergard courses in English. I don't know whether this has already left planning stage.
• German freshmen are older than US freshmen and treated more as adults. You are expected to organize your live and your studies yourself. While there is counseling offers you have to actively seek them -- nobody will notice if you are left behind. And few universities have a campus with on-campus housing,
• Traditinally, physics studies take five to six years and finish with the Diplom degree, which is comparable to the Master of Science of British or US universities. However, due to the Bologna process, this is now being changed to a two stage scheme: three years to a Bachelor of Sciene, than two years to a Master of Science degree. The PhD is considered not as a part of the studies but as the first employment of a physiscist at university.

If you have more questions or need pointers to information, just ask. And have a look at the web site of the German Academic Exchange Service (DAAD), which represents German universities abroad: [3] Simon A. 21:19, 18 October 2006 (UTC)

In the U.S. top private colleges it will cost $40,000 to $45,000 per year for tuition, housing, food, books, fees and other expenses, not including airfare. There may be restrictions on you working if you have a student visa, but perhaps some part time work is allowed. You might check on that. Many foreign governments have sponsored their top students or those related to the people in power to study in the U.S. Some foreign students get the general education courses at a cheap community college, whole they also polish their English. There are tests of English proficiency (TOELF) required by many colleges. Check with your government for possible sponsorship. Good luck! Edison 23:24, 18 October 2006 (UTC)

I believe the guys on Wikiversity can probably help you out to, (more once the site gets running better). — X [Mac Davis] (SUPERDESK|Help me improve)05:49, 20 October 2006 (UTC)

To learn before you get to the university, try "Opencourseware at MIT". Lecture notes, videos of classes, etc. Free. http://ocw.mit.edu/ --GangofOne 20:08, 20 October 2006 (UTC)

Science, I think

I am a Marine currently in Iraq. I found a Phillips PYE Unicam PU 4023 Refractive Index Detector, a PYE Unicam LCXP gradient Programmer, and a Hitachi 150-20 Data Processor. I have researched the 3 items and found that they are most likely used together. What I am trying to figure out is what would the owner use the items for.

Sounds like HPLC. DMacks 15:36, 18 October 2006 (UTC)

Kill you and your mates most likely if he had a chance. DirkvdM 18:32, 18 October 2006 (UTC)

orbital plane

Are planets in other solar systems on a parallel orbital plane to our planets? Also why is it that pictures of multiple deep space objects (like that hubble deep field scan) seem to show everything scattered about helter-skelter? If planets and moons form in the same plane then why don't universe-level objects like galaxies? --froth^{T C} 16:19, 18 October 2006 (UTC)

1. No.
2. Because they are scattered about.
3. Your question betrays a misunderstanding. While the planets of the Solar System revolve around the Sun in (pretty much) the same plane, their axes of rotation are all different (Earth's being tilted by 23½°). So why shouldn't galaxies be oriented in any direction?
B00P 07:04, 19 October 2006 (UTC)

Formation and evolution of the Solar System should clear this up. Essentially, the process that forced everything onto the same plane at the formation of the Solar System was a completely local process, neither affected by nor affecting other star systems, and not controlled by any larger order. In the absence of a reason for things to line up, they don't. Melchoir 16:49, 18 October 2006 (UTC)

I'm not sure, but I assume it's because the planets' rotation around the Sun and the moons' rotation around the planets forming at the same time, in the same protoplanetary disk, caused them to be in the same plane. Why that disk is not in the same plane as the milky way, I don't know, but what I said suggests that the two disks did not form at the same time. Just the other night I saw in a documentary that the Sun bobs up and down through the Milky Way's disk, almost as if it rotates around something else in the disk (at least, that's what the visualisation loked like). As for larger structures, it's still a mystery why they formed in the first place. What caused structure in the Universe after the Big Bang that resulted in the accretion that resulted in galaxies and such. Sorry to have asked more questions than given answers. :) DirkvdM 18:50, 18 October 2006 (UTC)

It has been noted that the arrangement of galaxies resembles the arrangement of a pile of bubbles, with clumps of galaxies where the "bubbles" come together, more sparsely placed galaxies along the "skins" of the bubbles, and inter-galactic voids in the center of the bubbles. To me, this implies that something at the center of the bubbles repels normal matter. This would also help to explain why the expansion rate of the universe is accelerating. StuRat 19:09, 18 October 2006 (UTC)

Or that there's something near the skins that pulls other bubbles to it, like the Great Attractor or something.. hmmm --froth^{T C} 19:18, 18 October 2006 (UTC)

But that wouldn't explain why the expansion rate of the universe is accelerating. StuRat 20:33, 18 October 2006 (UTC)

I think the OP has asked an interesting question. Planetary systems and spiral galaxies (the most common type of observed galaxy) exhibit preferred orbital planes, due to the interaction between conservation of angular momentum and gravtitational attraction. Are there any signs of preferred orbital planes in larger scale structures, such as groups, clusters and superclusters ? If not, why not ? Gandalf61 08:34, 19 October 2006 (UTC)

Flu vaccine

The university I work for is providing flu vaccines for all employees, with no foreseen shortages. Should I as a healthy, fit, not-very-flu-susceptible, 24-year-old male get the vaccine?

My concerns are:

1. People in more at-risk groups ought to go ahead of me, even though the uni says they have enough (if they have spare, would the spares go back to the hospital?)
2. If I'm not at risk, I don't want to put unnecessary medicine in my body
3. I believe in letting my body's own immune system do the work, and hopefully become stronger.

So obviously I'm leaning towards not getting one (I've never gotten one before), but I am wondering if

1. My beliefs are mistaken or out-dated
2. I am selfishly allowing flu to spread by not vaccinating myself.

What do people think?

Thanks! -Sam

You don't seem to be a member of any priority group defined by the ACIP. So basically do as you wish. Don't do so thinking that getting the flu will make your immune system "stronger", though, that's just silly. And yes, by not getting the vaccine you are making it ever-so-slightly more likely for others, especially those you live with, to get flu, but it's a marginal difference. - Nunh-huh 17:39, 18 October 2006 (UTC)

The defined priority groups are:

People at high risk for complications from the flu, including:

Children aged 6 months until their 5th birthday,

Pregnant women,

People 50 years of age and older, and

People of any age with certain chronic medical conditions;

People who live in nursing homes and other long term care facilities.

People who live with or care for those at high risk for complications from flu, including:

Household contacts of persons at high risk for complications from the flu (see above)

Household contacts and out of home caregivers of children less than 6 months of age (these children are too young to be vaccinated)

Healthcare workers. - Nunh-huh 17:39, 18 October 2006 (UTC)

Right: my question was based on the fact that the university said that they would have no shortages, and so wondered whether non-priority groups ought to also get the vaccine. --Sam

Yes. You should if you don't want to get the flu, with the risks that entails, risks which are greater than those caused by the vaccine. If you don't care whether you get the flu, or spread it to others, you needn't get the vaccine. - Nunh-huh 17:48, 18 October 2006 (UTC)

There is a shortage of flu vaccine for the nation, (the US, but probably in other countries as well), and it is a real problem. Companies and individuals with the necessary funds purchase huge amounts of vaccine and then resell it to anyone who has money, regardless of risk factors, in "flu clinics" all over the place. This year, the entire stock of flu vaccine made by Sanofi Pasteur was purchased within the first 14 hours it was on sale. Out of the many units, only about 10% went to actual medical facilities (I'm sorry I can't give exact numbers here). This year, in the city I live in in the US, we have 7,500 DPH-appropriated units for the entire priority population (about 20,000 individuals). Some will seek immunization outside of DPH-funded clinics, others will get sick, some of them will die... and their care will cost the city much more than a few vials of vaccine. That said, your university has said that they have a surplus, and they probably do. If I were you, I would ask them where the extra units will go if they are not used at the school. If the answer is "the trash" then I would get one. Otherwise, I would probaly not. And if you do happen to get sick, stay home if you can. In any case, I would tell them that it is not cool that they purchased so much vaccine. It is certainly unfortunate, Sam, that more people are not as thoughtful as you when they are asked if they want a flu shot, then we might just have enough for the people that need it.Tuckerekcut 22:18, 18 October 2006 (UTC)

There is no flu vaccine shortage. 40 million doses have been shipped to date, the most ever at this point in the season. [4] [5]. There may be distribution problems, which will be corrected. But just like eating all the food on your plate won't do anything to alleviate the suffering of children starving in Africa, foregoing a flu shot when it's available won't do anything to make it available to others elsewhere. - Nunh-huh 00:54, 19 October 2006 (UTC)

I regularly get flu shots and I'd suggest you do the same. People who have to interact with lots of people on a regular basis (like at your uni) have a vested interest in doing everything they can to prevent the flu from climbing aboard their body. On the one hand, you'll be in contact with people from over a wide area in a somewhat cramped environment, making it very very likely that you will come in contact with some bugs. On the other hand, lots of people from all over will be coming in contact with you - while you're shedding viruses, you'll potentially infect a lot of the folks around you. My understanding is that the one good reason not to get the shot is if you're allergic to eggs, which are used to incubate the vaccine. See our article for more details. To answer your specific question, yes, I think your views are a little out-dated, but asking questions is the best way to reverse that! If it's the shot that's really bothering you, there's also a nasal mist, which is apparently more effective. Matt Deres 01:24, 19 October 2006 (UTC)

There is no flu vaccine shortage this year. I just got the annual brochure from the DOH and it makes it very clear that there is no shortage and that it should be given to everybody who wants it. -THB 02:22, 19 October 2006 (UTC)

membrane capacitive current?

Hello. I can´t understand exactly what is meant by a capacitive outward current across a cell membrane, apparently in the opposite direction of an ionic inward current. Is it because of the departure of positive ions from the extracellular space into the intracellular space, that one defines the "lack" of positive charges outside the cell as a current "across" the membrane? Or is capacitive current a real, physical current from the intracellular space to the extracellular one? Thank you for any help. Christian, medical student, Denmark

Take a look at this. If you still have questions, please return. --JWSchmidt 01:20, 20 October 2006 (UTC)

Thanks a lot. Anyway, I understand that the membrane has the ability to store charges on its surface area, but in my textbook it is written as if there is a specific "current" in opposite direction of the ionic one (ex. in opposite direction of the inward Na+ current in nervecells about to unleash an actionpotential). It is the nature of this "current" that puzzles me.

Any biological membrane has many charges that part of the molecules of the membrane. Under most physiological conditions, a biological membrane is a "fluid mosaic" and some of the charges that are in the structure of the membrane can move in response to a change in the electric field that exists across the membrane. This shifting of charge is very fast and fairly symetrical, as shown here (compare panels A and B). --JWSchmidt 02:20, 24 October 2006 (UTC)

What bs. Christian is absolutely right in his assumptions, and you're just puzzling him with reference to diagrams that show action potentials, not the fluid mosaic model you brazenly say you know of. Tag radet fran en svensk och ignorera herr Schmidt. Han ar ingen hjalp.

 Hello,I  had the same question and it even led me here now I think I can shed some light.You must first know that  a capacitor after charging has the same voltage of the source that charged it without  decreasing the voltage of that source,so the batteris in the RC circuit of the memrane must first charge the memrane by actually moving charge from one side of the memrane to the other and this charging doesn't drain these batteries(the electro chemical gradients of the ions)this is the capacitive current .Then the batteries (e.g the Na ion gradient)can start the ionc current that will eventually drain the battery when the membrane potiental approaches the equilibrium potential of Na(reversal potential)  

DFT bins

I often read terms like transform bin or DFT bin in papers concerning DFT and other transforms.. Can you explain me the meaning?

I think you want to see discrete fourier transform. --Kainaw ^(talk) 20:03, 18 October 2006 (UTC)

I did, but on en.wiiki I found that therm in Goertzel Algorithm only, without definiton

When you're doing a transform from the time domain to the frequency domain, you need a way to represent the output data. One conventional way is to define a series of "frequency bins" into which you allocate the spectral energy of the waveform being analyzed. For example, you might define 256 frequency bins that are centered on 0 Hz, 1 Hz, 2Hz, ... 254 Hz, and 255 Hz. So when you do the transform, any energy that the transform produces that occurs from >=0.5Hz to <1.5Hz is dumped into the "1 Hz" frequency bin, >=1.5Hz through <2.5Hz is dumped into the 2Hz frequency bin, and so on.

Naturally, the more samples you have, the more finely you can resolve the frequency of the spectral components and the narrower you can make your bins (at least, if you wish).

Atlant 13:10, 19 October 2006 (UTC)

More specifically, the "bins" are because you're using the DFT rather than the analogue fourier transform - by its very nature, the DFT requires that the output data comes in discrete packages, which are your bins. (And as Atlant pointed out, the size and number of the bins is mostly based on what you want them to be.) Confusing Manifestation 00:38, 20 October 2006 (UTC)

Thank you! --Ulisse0 08:55, 20 October 2006 (UTC)

Look at [Z-transform] as well. That's a sampling transform that has discrete time points as well. A key point of the bins is that the summation of the bins over the same frequency range should equal the analog continuous transform. This makes it look like you can lower the noise floor by increasing the number of bins but that is incorrect. --Tbeatty 06:16, 24 October 2006 (UTC)

Spacetime

One interesting interpretation I heard about relativity is that as you move faster through space you move slower through time. So photons dont actually move through time at all, and if you are stationary in space you are moving at maximum rate through time. Another way to look at, albeit from my laymans viewpoint, is that you have to apply energy to 'brake' your progress through time. Anyway, does this mean that everything travels at the same rate through spacetime, and if so what is that rate mmatt 20:09, 18 October 2006 (UTC)

Yes: in a very real sense, everything travels at the speed of light through spacetime. (The proper dimensions of spacetime are somewhat hard to define; it really makes just as much sense to say that time and space are the same thing and call the speed of light 1. This makes sense, because for a stationary object, the only speed is "time-speed", and it seems only fair to call that "one second per second" or just 1.) Of course, the very notion of "speed" when time is relative to the observer is somewhat odd; perhaps you'd like to read about proper time, which is one sort of realization of the "constant speed" idea. --Tardis 20:14, 18 October 2006 (UTC)

According to Einstein, everything is always going at the speed of light it just happens to be that most of that speed is through the fourth dimension (time). When one travels at significant portions of the speed of light through space (say in a fast rocket ship), it's simply transfering some of this speed away from time to space so that you're still going at the speed of light. No faster, no slower. Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 21:01, 18 October 2006 (UTC)

I'm not sure Einstein would have subscribed to this version of his theory.  --Lambiam^Talk 11:30, 19 October 2006 (UTC)

I am truly confused at what you two have said. Rest mass never moves at c. Photons experience no time, tardyons and luxons, together, travel at many different speeds. — X [Mac Davis] (SUPERDESK|Help me improve)05:44, 20 October 2006 (UTC)

Male marsupial nipples ?

Male placental mammals have nonfunctional nipples, so do male marsupials have them, as well ? In the females, those nipples are inside the pouch. Do males also have a partial pouch which contains the nipples ? StuRat 20:18, 18 October 2006 (UTC)

Better ask User:JackofOz from marsupial land! 8-)--Light current 02:41, 19 October 2006 (UTC)

I'm flattered, but I have no idea, sorry. What I do know is that marsupials are also found in New Guinea and some adjacent islands; South America; and North America. JackofOz 07:16, 19 October 2006 (UTC)

I would be very flattered too if another man asked me a question about nipples. — X [Mac Davis] (SUPERDESK|Help me improve)05:40, 20 October 2006 (UTC)

Yeah, but you could go and check. Don't you have koalas hanging around in your back yard? Or are you afraid that groping in their pouches to feel their nipples would be seen as sexual harrassment? DirkvdM 08:32, 19 October 2006 (UTC)

You've been here, mate, so you know that isn't true. Maybe they do things differently in Bundaberg, but the last time I saw a koala was years ago, in a zoo. Mind you, I have plenty of possums in my garden. And in a couple of weeks I'm moving to a place in the country, where kangaroos and wombats are frequently seen, so I'll be sure to keep an eye out.  :) JackofOz 08:35, 20 October 2006 (UTC)

If nobody can find out, I know some people in the marsupial lab at uni and can ask them. I may see them tomorrow, but otherwise next Wednesday. So remember to check this post then. Thanks. --liquidGhoul 08:14, 19 October 2006 (UTC)

Darwin had something to say about this:

[...] long after the progenitors of the whole mammalian class had ceased to be androgynous, both sexes yielded milk, and thus nourished their young; and in the case of marsupials, that both sexes carried their young in marsupial sacks.

Everything I can find on the internets tell me that male marsupials should have nips too, but I can't find anyone saying "YEP, IT'S TRUE, MR. WALLABY HAS LITTLE BOOBS JUST LIKE YOU AND ME", so I guess you're going to have to take this one on faith.  freshofftheufoΓΛĿЌ  09:59, 19 October 2006 (UTC)

Do I get a prize for having stumped the professors ? :-) StuRat 14:41, 19 October 2006 (UTC)

For god's sake, all marsupials are mammals. Mammals are called mammals because they have mammary glands. All of them. Even the males. All of them. End of story. -THB 21:03, 19 October 2006 (UTC)

The question remains, where are the nipples on a male marsupial ? Are they in a pouch or not ? StuRat 22:22, 19 October 2006 (UTC)

Point of order, THB. Monotremes are mammals and possess mammary glands, but they don't have nipples (either gender). Whether marsupial males have nipples is still a legitimate question. I can't think of a single reason why they wouldn't have them (since the females do), but nature is under no constraints to meet my expectations. Matt Deres 01:46, 20 October 2006 (UTC)

Why the hell would they have mammary glands but no nipples? — X [Mac Davis] (SUPERDESK|Help me improve)05:40, 20 October 2006 (UTC)

Marsupials are very strange, in many parts of their biology (have you seen the shape of their sperm?). The female nipple changes in size during the development of the offspring, and, depending on the species, each nipple can be at a different state. I wouldn't be surprised if the males don't have nipples. Having said that, my guess is that they will have small ones in the same place, just without the pouch. --liquidGhoul 12:46, 20 October 2006 (UTC)

Monotremes are the branch of mammals most like the earliest proto-mammals. The mammary gland/milk/nipple situation had to evolve somehow and I guess monotremes show that the nipple was the last part to develop. The milk just kind of seeps out (I believe milk glands are homologous to sweat glands) and the young suck it from the fur. Matt Deres 01:06, 21 October 2006 (UTC)

electromagnetic interaction and contact for force fields?

I have read recently in a book called "a brief history of pretty much everything" it calimed that all physical interactions are actually electrons repeling each other, would it be at all possible at least in theory if not in practice at this stage in technology to create a field or beam of electrons with the same properties as matter to move or repel matter like a force field? is this why we cant make one coz we cant make a powerfull enough or dense enough electron cloud? hopefull

I think you would be more likely to melt it than move it.mmatt 21:00, 18 October 2006 (UTC)

In the absense of atomic nucleii, the electrons tend to fly apart from one another. They can be kept together temporarily, as in a television with a cathod ray tube. --Gerry Ashton 21:04, 18 October 2006 (UTC)

but if you could make them group them together in the right way they would form a solid force, like a stream or solid force? hopefull

cathode ray tube. Xcomradex 21:16, 18 October 2006 (UTC)

That didnt answer my question about if electrons could be arranged to form a force that is solid like normal things are if electron repulsion causes things to be solid? Hopefull

The usual way that electrons are "arranged to form a force that is solid like normal things are" is to, well, use normal things, like, say, a forklift. If you could somehow arrange electrons to make a smooth surface, you could perhaps push on objects with it. But the objects would push back, so you'd have to hold the electrons in their formation somehow. What better way to do that than to stick a bunch of nuclei in with them (to bind them to a spot) and let the resulting atoms bond together to hold a shape? (This, of course, is once again "use normal matter".) It is not unreasonable to charge a piece of metal and then manipulate it with an electric field, or run a current through it and then manipulate it with a magnetic field. The latter is more common since you don't need to keep anything charged, and is the principle behind all sorts of things like rail guns and magnetic levitation. Does that help? --Tardis 22:22, 18 October 2006 (UTC)

I think so , so the answer is "yes you could make a solid electron field if you could keep them charged and stationary" this would move stuff if it touched it, or stop things moving towards it? is that much correct? would it be possible to make a stronger repulsion than normal, so instead of just pushing it repulses away, like magnets? sorry to ask another question on top of that Hopefull

I think you're right -- but realize that tissue paper has the same qualities. If you can keep it stationary (or move it as you like), you can move things around with it or stop objects from passing through it. The problem is that there's no way (short of backing it with steel) to keep it "stationary" (including intact, since parts of it must move if it breaks) when it's called upon to stop, say, a bullet. The same thing is true of the electron sheet: you've no way of holding it in place, except reinforcing it with something stronger (here, the rest of the steel). In fact, it's worse with the electron sheet because they repel each other, so can't hold up against even 0 force without assistance (fortunately, the same rest of the steel is also positively charged and serves to cancel this effect.) As far as increasing the repulsion, no: in fact, uncharged objects will be attracted to a big sheet of electrons (see electrostatic induction, and think about where the separated charges would go). It's only at very short range (this is the definition of "contact") that you can repel anything, and even then the force falls off so strongly that it is again like a wall instead of like a "flow of force" that could accelerate anything away from the electrons. Once again, since normal matter interacts through the very mechanism you're describing, you can't expect (although it's not inherently impossible for) applying this mechanism to be unlike using normal matter in any way. --Tardis 15:50, 19 October 2006 (UTC)

Ok then so if one could find a method for groupiing electrons together, without a nucleus, and keeping them together [stop them repelling each other , depending on how many and how closely grouped the electron sheet would act like normal matter. with the more electrons per space in the sheet the stronger it will be, so you could vary from tissue paper consistancy? would it be possible to make it stronger than this? wioth more electrons or closer together, also would it be possible to create the charge the electrons build up that repel each other some other way? from a source other than electrons? Hopefull

If you can suppress electrostatic repulsion ("stop them repelling each other"), you can probably do a lot better than simply making an "electronic broom"; see Niven's Wunderland Treatymaker. As far as lots of electrons, remember the bit about normal matter being attracted to charge; with enough of them, you'd be pulling strongly on everything nearby that wasn't actually in contact with the broom. Your remark about "tissue paper consistency" is confused: the whole point of this discussion is the equivalence of all normal matter and your electron sheets. In both cases you can push on things, but need some variety of material-like strength to maintain your pusher's integrity (more in the case of self-repelling electrons). As for other sources of negative charge, there are plenty: antiprotons, some pions, down quarks, etc. — but they tend to be harder to deal with than electrons. --Tardis 18:52, 20 October 2006 (UTC)

Domestic Poultry

Why do they loose lose their pigments in captivity and turn white? (ie: chickens, turkeys, ducks, flamingos, etc). --Russoc4 22:39, 18 October 2006 (UTC)

Their loose pigments fall off ? :-) StuRat 23:36, 18 October 2006 (UTC)

Ah, you got me. --Russoc4 23:41, 18 October 2006 (UTC)

I think there are multiple answers. Flamingos lose their colour because they get their colour from the food they eat; when they eat different micro-organisms, they lose their pink-ness. ISTR that zoos and other places actually introduce a reddish dye to their food so that they look 'right'. For the others, I'm not sure if there's an actual trend to whiteness, if it's just happenstance that white happened to be bred in barnfowl, or if some of the same answer applies as with flamingos. Matt Deres 01:32, 19 October 2006 (UTC)

Flamingos need carotenoids in their diet to develop their pink/red color. This is mentioned in the Flamingo article under "color". It is possible that there are similar effects for other birds. Though, I would consider this more likely to be an effect of breeding. I.e. I've seen brown chicken in captivity. There are different chicken types/races. Lukas 01:47, 19 October 2006 (UTC)

Perhaps white poultry has been intentionally bred because they are easier to find if they get loose. StuRat 01:52, 19 October 2006 (UTC)

Right. Anyway, the question is still unanswered. Also, is there a reason why lab rats are white? --Russoc4 02:11, 19 October 2006 (UTC)

If StuRats are white, why shouldn't lab rats be white ? :-) StuRat 23:33, 20 October 2006 (UTC)

I also don't think they 'lose' their pigment, I think they've been bread that way. Maybe because brown chickens camouflage better, so are harder to find if they escape the coop, as opposed to white birds which would stand out more. Also, white feathers are more aesthetically pleasing to use as stuffing for pillows and duvets. There are probably more reasons. Vespine 02:14, 19 October 2006 (UTC)

Is the poultry bred to be breaded poultry ? :-) StuRat 02:25, 19 October 2006 (UTC)

Follow on: As for lab rats my guess is to tell them apart from wild rats? Vespine 02:15, 19 October 2006 (UTC)

So...they're white "bread". So I guess the brown ones are whole wheat? Clarityfiend 02:27, 19 October 2006 (UTC)

haha actually, can I say the pun was intended? No, it was a typo;) read:bred ;) Vespine 02:34, 19 October 2006 (UTC)

Aren't lab rats albinos? Lab animals are often bred to have specific deficiencies. About poultry, there are plenty non-white domesticated ones and there are white wild birds. But there do seem to be more white domesticated ones, so you still have a point. DirkvdM 08:46, 19 October 2006 (UTC)

With the exception of flamingos and some amphibia (which obtain their colouring from their food), the reason that we have albino or leucistic) domestic animals is simply from selective breeding. There are naturally found albino and leucistic animals of pretty much every species, although they are pretty rare. For whatever reason - probably aesthetic - humans have selected these and bred them so the are more common in domestic species (check out the number of white dogs around, for example). Lab animals are a slightly different story. Contrary to popular belief not all lab rats and mice are white, plenty of different strains are used that are brown (or "agouti"), black and white. There are good technical reasons people used different strains and different colours in experiments, and the genes that cause the differences in pigmentation are a very good model for studying genetics. Rockpocket 18:09, 19 October 2006 (UTC)

Alas! My question has finally be answered! --Russoc4 22:21, 19 October 2006 (UTC)

Glad i could help. Rockpocket 05:57, 20 October 2006 (UTC)

To celebrate, go and rent Pink Flamingos. Actually, no, don't, you would regret it. Seriously. JackofOz 08:27, 20 October 2006 (UTC)

Electromagnetic Pulse

How does an electromagnetic pulse short-circuit electronic devices? Note: I am not planning on building an E-bomb. There is just something about being arrested for terrorism that scares me. THL 23:38, 18 October 2006 (UTC)

See induction. Basically, the EM field induces currents in the circuitry, which can cause a number of different problems, particularly when components are exposed to a greater-than-intended voltage, reverse-biased voltage, or an SCR is switched on (see latch-up).

Over voltages and excessive currents basically destroy the electronic components and devices.--Light current 02:02, 19 October 2006 (UTC)

EMP rapidly releases the magic smoke from electronic devices over a very wide area.

Atlant 13:13, 19 October 2006 (UTC)

I should really have said that in all cases electromagnetic energy causes failure by dissipating itself in the component and causing all the magic fumes to escape. Just like letting the genie out of the bottle: you can never get it back in 8-(--Light current 15:42, 19 October 2006 (UTC)

There is of course another, maybe more satisfying way to destroy a component that has (partially) failed. THis technique is called Widlarizing named after the semiconductor circuit genius and father of the op amp (I thikn) Bob Widlar.--Light current 15:46, 19 October 2006 (UTC)