Wikipedia:Reference desk/Archives/Science/2008 October 7

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October 7

Quantum: Difference between an operator and a measurement

Suppose there is a qubit whose state is

$|\psi \rangle ={\frac {1}{\sqrt {3}}}|0\rangle +{\frac {\sqrt {2}}{\sqrt {3}}}|1\rangle ={\begin{bmatrix}{\tfrac {1}{\sqrt {3}}}\\{\tfrac {\sqrt {2}}{\sqrt {3}}}\end{bmatrix}}$

After we measure the qubit, the state of the qubit will change from $|\psi \rangle$ to $|1\rangle$ with probability

${\big |}\langle 1|\psi \rangle {\big |}^{2}=\left({\frac {\sqrt {2}}{\sqrt {3}}}\right)^{2}={\frac {2}{3}}\approx 0.666\dots$.

This process is called wave function collapse. If $|1\rangle$ is observed after the measurement, the qubit becomes

$|\psi \rangle =|1\rangle$

Instead of measuring the qubit, a Hadamard gate

$H={\frac {1}{\sqrt {2}}}{\begin{bmatrix}1&1\\1&-1\end{bmatrix}}$

operates on the qubit will be

$H|\psi \rangle ={\frac {1}{\sqrt {2}}}{\begin{bmatrix}1&1\\1&-1\end{bmatrix}}{\begin{bmatrix}{\tfrac {1}{\sqrt {3}}}\\{\tfrac {\sqrt {2}}{\sqrt {3}}}\end{bmatrix}}={\frac {1}{\sqrt {2}}}{\begin{bmatrix}{\tfrac {1+{\sqrt {2}}}{\sqrt {3}}}\\{\tfrac {1-{\sqrt {2}}}{\sqrt {3}}}\end{bmatrix}}={\frac {1+{\sqrt {2}}}{\sqrt {6}}}|0\rangle +{\frac {1-{\sqrt {2}}}{\sqrt {6}}}|1\rangle$

as I know, the process of the operation is 'not' a wave function collapse.

My problem is why an operator acts on a qubit doesn't cause a wave function collapse? As I know, any subtle interaction with the qubit will cause the wave function to collapse. The Hadamard gate operator, which should be an apparatus, when acts on the qubit should also interact with the qubit. So how an operator can circumvent the wave function collapse? - Justin545 (talk) 05:28, 7 October 2008 (UTC)

I'm a little rusty in my quantum theory, but if I remember correctly, it's not all interactions that cause wave-form collapse, only those actions that generate information. It is entirely possible to transform a wave-function without actually observing (i.e. gaining information from) said wave function. Take for example the most basic quantum experiment, the double-slit experiment. The slit certainly interacts with the beam of particles; as the beam hits the slits, an interference pattern immerges, this is a result of the slits "transforming" the beam of particles via interaction. The wave function collapse occurs only when you try to gain information about the particle's location, for example, by placing a charge detector at one of the slits. As long as no information is obtained on the system, it goes on behaving as an uncollapsed wave function. Once the detector is placed, information is extracted, and the wave function collapses, resulting in an uninterferred double beam... The Hadamard gate must operate in the same way; it performs a transformation on the qubit blindly (that is, without observing the state of the qubit). Such an action is not philosophically that hard to understand. Imagine a blind man turning coins over. You hand the man a coin, and he simply reverses the face of the coin. He can perform the operation (turning heads to tails and tails to heads) perfectly every time, even if he doesn't know which states the coins are in before he flips them. To take this on a quantum scale, he's able to perform a transformation on the wave function, without causing any waveform collapse. He's made no observations of the bits of information he's transforming, he's just doing the transformation. A Hadamard gate must work on this level. --Jayron32.talk.contribs 05:47, 7 October 2008 (UTC)

It could be difficult to define the term 'gaining information from'. Cite form the article Quantum computer:

One major problem is keeping the components of the computer in a coherent state, as the slightest interaction with the external world would cause the system to decohere. This effect causes the unitary character (and more specifically, the invertibility) of quantum computational steps to be violated. Decoherence times for candidate systems, in particular the transverse relaxation time T2 (terminology used in NMR and MRI technology, also called the dephasing time), typically range between nanoseconds and seconds at low temperature.

I think the 'decohere' is actually the wave function collapse. It seems that even the 'temperature' is also a way to interact with the qubit and it is not clear to me how an environmental temperature makes information gaining... maybe what you mean is that a measurement is an irreversible operation whereas a gate operation is a reversible operation. Indeed, the action of a Hadamard gate is a reversible operation since there is no information lost during the operation of the Hadamard gate. And saying that a measurement is an irreversible operation is just my suspicion since some information is lost and gained by the observer during a measurement. By thinking the gate operation as a transform as you said make it more understandable to me. And now I know there are some interactions don't collapse the wave function. - Justin545 (talk) 07:23, 7 October 2008 (UTC)

Unless the qubit is lost due to interaction with other particles; at high temperatures there are bound to be more particles moving faster and thus more interference on the qubit; there may be some threshold temperature where the system becomes so inefficient due to losses that it stops "working." --Jayron32.talk.contribs 11:29, 7 October 2008 (UTC)

Definitely some interactions don't collapse the wave function, otherwise a proton, for example, couldn't be a quantum particle since it consists of more fundamental particles constantly interacting with each other.

See quantum decoherence for more on that subject. It is effectively the same thing as wavefunction collapse and people are likely to use the terms interchangeably.

Measurement/decoherence is all about copying. An example of copying is a transition from $\alpha |0\rangle +\beta |1\rangle$ to $\alpha |0\rangle |0\rangle +\beta |1\rangle |1\rangle$. This is different from cloning, which would take $\psi$ to $\psi ^{2}$, e.g. $(\alpha |0\rangle +\beta |1\rangle )^{2}=\alpha ^{2}|0\rangle |0\rangle +\cdots$. Cloning isn't possible, but copying is possible. The key difference between them is that copying is basis-dependent. The example I gave above was copying with respect to the computational basis $\{|0\rangle ,|1\rangle \}$. Copying with respect to the dual basis $|{\pm }\rangle ={\tfrac {1}{\sqrt {2}}}(|0\rangle \pm |1\rangle )$ takes

$\alpha |{+}\rangle +\beta |{-}\rangle$ to $\alpha |{+}\rangle |{+}\rangle +\beta |{-}\rangle |{-}\rangle$,

which is the same as taking

$\alpha |{0}\rangle +\beta |{1}\rangle$ to ${\tfrac {\alpha }{\sqrt {2}}}(|00\rangle +|11\rangle )+{\tfrac {\beta }{\sqrt {2}}}(|01\rangle +|10\rangle )$,

if I calculated right—at any rate it's a different operation. If you copy a qubit (with respect to a basis) and put the copy somewhere where it's unavailable to you, the effect on the original qubit is exactly as though you'd measured it (with respect to that basis). But if the copy ever becomes accessible to you again, you can use it to "undo the measurement," so it's not a real measurement. Measurements only become definite when they can no longer be undone, e.g. because the copy has been amplified into a macroscopic thermodynamically irreversible state change like a flash from an LED.

Reply composed in a hurry and I may not be able to reply again for a few days. -- BenRG (talk) 11:44, 7 October 2008 (UTC)

A short mathematical answer: Self-adjoint operators correspond to measurements. Unitary operators correspond to state changes without any wave function collapse. Icek (talk) 21:32, 8 October 2008 (UTC)

Noisy laptop fan

Why do they (fans) do it (noise)? Is a silent laptop fan possible?Mr.K. (talk) 11:06, 7 October 2008 (UTC)

A (laptop) fan moves air, using an electric engine. Air flow creates sound, and the engine can't be perfectly silent either, so: no, a silent laptop fan isn't possible. There are however some new, interesting ways of cooling coming about, some of which may be silent. Someone please fill me in here :) -- Aeluwas (talk) 11:08, 7 October 2008 (UTC)

There is liquid cooling, but that would be for rack-mount mega-chips (stacked processors have a higher power density than a nuclear reactor), not laptops; and the liquid would still need cooling. See this Economist article (and I can email it if you can't see it). Franamax (talk) 22:13, 8 October 2008 (UTC)

Actually, there are ways of generating air flow without any moving parts, for example see Air ionizer; it operates similar to a mass spectrometer; air molecules can be ionized via say, a negatively charged plate, and accelerated via a pair of positively charged plates. Many air molecules will simply gain electrons at one plate and lose them back at the other (or visa-versa; I am not positive on the specific mechanics of the situation), however, some will "overshoot" the second plate, and also drag many "non-charged" molecules with them, resulting in net air flow. However, the method is quite innefficient, especially on a scale small enough to fit into a laptop, and I suspect that in terms of net air flow for, for both its size and wattage, a simple mechanical fan is far more efficient. --Jayron32.talk.contribs 11:24, 7 October 2008 (UTC)

The engine could be so silent like the HDD. Moving air doesn't have to be noisy. I suppose it is noisy only if it generates turbulence right? So, a silent laptop fan should be possible... Mr.K. (talk) 11:38, 7 October 2008 (UTC)

But laminar airflow may not be terribly efficient at moving heat around, as it may not move all the air and probably wouldn't move fast enough. 130.88.64.189 (talk) 12:29, 7 October 2008 (UTC)

The other common means of making a fan quieter is to spin it at a lower RPM. Of course, the direct consequence is that you move less air, reducing the cooling effectiveness. In a desktop system, that just means that you make the fan larger to compensate. With space at a premium in laptops, this solution is less effective. — Lomn 12:59, 7 October 2008 (UTC)

A related option is to reduce your CPU usage, which reduces the laptop's need for cooling, which should let the fan run slower and less frequently. Plasticup ^T/C 15:15, 7 October 2008 (UTC)

Often, reducing the CPU usage is not an option, since I use the laptop with a purpose. Mr.K. (talk) 15:24, 7 October 2008 (UTC)

Amen to that! Plasticup ^T/C 00:28, 8 October 2008 (UTC)

To remove a particular amount of heat per minute, you must move a particular amount of air per minute, often measured in CFM. A fan with a smaller diameter must spin faster for the same CFM. The higher speed results in a higher amount of vorticity at the blade ends, and this is where most of the noise is generated. A laptop cannot accomodate a large-diameter fan, so the fan must spin very fast and is therefore very noisy. The same is true for 1U rack-mount servers. As an example of the difference diameter makes, consider the difference between a 20" diameter window fan and a 3" diameter "muffin" fan in a desktop computer. The window fan at its lowest speed moves much more air than the muffin fan at its normal niosy speed, but is virtually silent.The motor contributes very little noise in either case. -Arch dude (talk) 00:41, 8 October 2008 (UTC)

Question (Goliath Beetle)

What is the main predator to the Goliath Beetle? —Preceding unsigned comment added by 204.210.238.42 (talk) 11:54, 7 October 2008 (UTC)

I'm not sure it has a main predator. There are more than enough predators and omnivores in tropical Africa that would not think twice before dining on a huge delicious beetle larva. Mandrill comes to mind as a very likely predator, but I couldn't find any specific data. Besides, Mandrill habitat extent is much smaller than that of Goliathus sp. . Sorry. --Dr Dima (talk) 17:13, 7 October 2008 (UTC)

How does fruit get "bruised"?

Just curious how fruits like apples and bananas get "bruised"? Aren't they dead? How does impact against the surface affect the fruit below the skin? --70.167.58.6 (talk) 16:00, 7 October 2008 (UTC)

I'm not sure it's accurate to say they're dead. They are still chemically active, otherwise they wouldn't be able to ripen after being picked. I think the bruising is caused by breaking the cell walls so the individual cells die, but I can't guarantee it. I'm sure a botanist will be along shortly. --Tango (talk) 16:07, 7 October 2008 (UTC)

Not a botanist, but Tango has the right idea. Inside of plant cells are chemicals which oxidize upon exposure to air. If the cell remains intact, nothing happens. However, cutting the fruit or striking it can cause the cell walls of the cells to break, exposing the chemicals to air, and causeing a change in both color and texture. Incidentally, bruised fruit is perfectly healthy and there's nothing at all wrong with eating it. You abuse the fruit much more when you chew and swallow the fruit anyways; the color change is not a sign of bacterial growth in any way, its merely a sign of physical damage. --Jayron32.talk.contribs 16:47, 7 October 2008 (UTC)

You may want to look at this. --Dr Dima (talk) 19:18, 7 October 2008 (UTC)

Fresh animal products consists of all dead cells when you buy them but fruits fruits and vegetables are all alive. The "bruise" consists of plant cells that are dead. Sjschen (talk) 03:51, 8 October 2008 (UTC)

So is it possible for bruises to grow? Will a bruise "infect" undamaged cells making it more unattractive? Do bruised areas rot faster? --71.158.222.207 (talk) 03:59, 8 October 2008 (UTC)

Yes, bruises will grow - the lysed cells burst in the original insult will release oxidizing enzymes which will continue to degrade the contents of the fruit, in part by lysing more cell membranes. And yes, as more cells contents are spilled out, they will be more susceptible to bacterial invasion. This is why the little bruise spot on your tomato when you bought it gets bigger and gets a grey mold at the centre. Franamax (talk) 05:54, 8 October 2008 (UTC)

Unquestionably the best resource on this is On Food and Cooking: The Science and Lore of the Kitchen H. McGee ISBN 978-0-684-80001-1.[1] It explains all this stuff and tells you how to get your eggs right! :) Franamax (talk) 06:18, 8 October 2008 (UTC)

Grass Seed Lifespan

I have had a bag of lawn grass seed in my garage for over 4 years. Over that time it has been exposed to -20C to +35C degrees. Would it still be alive and able to grow after all? —Preceding unsigned comment added by 151.123.128.250 (talk) 16:40, 7 October 2008 (UTC)

Quite possibly. Many kinds of seeds are quite resilient. There are some seeds that have been shown to germinate after hundreds of years of dormancy. The best thing to do is to run a little experiment. Take a cup of dirt, put a small pinch of seeds in it, keep it moist and in direct sunlight (like the windowsill) and see what happens. The seeds, if still viable, should germinate within a few days. If they do, you probably have good seed. If it just sits there for a week and nothing happens, then you probably need to pitch them. --Jayron32.talk.contribs 16:44, 7 October 2008 (UTC)

The normal rule is: If at least 75% of the seeds germinate, use as directed. If 50%-75% germinate, use double the normal amount. If less than 50% germinate, toss it and get a new bag. --Stephan Schulz (talk) 17:41, 7 October 2008 (UTC)

calorie consumption per hour/ mile (cycling)

Hello Everyone,

i've been trying to work out how many calories I burn on my cycle to work but i'm struggling to get some relevant info (i've been on a few forums but they use 40 year olds as reference points -i'm not even sure if one burns more or less calories as one ages so this is less than helpful.) Anyway, i'd be grateful if any one has any ideas - its about 4.7 miles (according to google maps anyway) each way, along reasonably flat terrain -stopping and starting for traffic lights often. It takes me about 30 minutes on average. Also i'm a (reasonably fit) 24 year old man... Any help, or even some starting data, would be great...

Thanks, 82.22.4.63 (talk) 19:09, 7 October 2008 (UTC)

While caloric intake is relatively easy to calculate, based on the nutritional content of the food in terms of ammounts of proteins, fats, and carbohydrates, its a different story for caloric output, in terms of exercise. Its going to vary WILDLY depending on how hard you are pedaling, your current body weight, your personal body chemistry and metabolism, the ambient temperature that day, your muscle mass, yada yada yada. The variables are almost too great to even think of all of them. Calculators that purport to determine how many calories you burn (for example, those found on treadmills or stationary bikes) are likely just WAGs. They may be based on, for example, the 50th percentile human, but variation from that ideal is likely so large that there is no way to assure they will be accurate for you. The easiest way to tell is to see if it has an effect on your own body: If you are losing body fat over time, you are likely burning more calories than you take in. If you are gaining body fat over time, you are likely consuming more than you burn. Take Michael Phelps for example. It is widely reported that he consumes 10,000 calories per day. That's roughly the amount of food 4 people would eat. And yet, he has almost no body fat, which means his level of activity has him burning at least that much. The funny thing is, another person, performing the same workout regimen as he does, may find himself gaining fat at that level of intake. Isolating WHICH activities are burning which calories is entirely a guessing game. The best thing that can be said is more activity always burns more calories, so more is always better. --Jayron32.talk.contribs 20:21, 7 October 2008 (UTC)

Human feet vs. Chimp feet

Chimps' feet have thumb like digits on them so they can grab objects with their feet in a similar way to how we can grab things with our hands correct? So I was curious if our feet which do not have that ability, have any advantages over their feet. 98.221.85.188 (talk) 19:51, 7 October 2008 (UTC)

Chimp feet are great for walking on branches, too. But they're lousy for running. (See achilles tendon not what I expected.) See Persistence hunting. Saintrain (talk) 20:07, 7 October 2008 (UTC)

Chimps are also not bipedal like humans. Like some other animals (bears, for example) they can, relatively easily walk on two legs, but their preferred method of ground locomotion is "knuckle walking" on all fours, generally as a sort of side-shuffle. Chimps are not very efficient at walking flat footed, however, as noted above, they are VERY efficient at traveling in trees, having evolved in a forested habitat. Modern humans largely evolved in a savannah habitat, with few trees, and thus flat-footed walking gave them an advantage in that environment. Thumbs are an impediment to flat-footed walking, and so proto-humans with "modern human" style feet tended to predominate in that environment. --Jayron32.talk.contribs 20:26, 7 October 2008 (UTC)

To expand on Jayron32, the human foot is specifically adapted to walking upright. The big advantage we have over chimps (for the bipedal environment) are the two arches of the foot which act --like springs-- as shock absorbers, distributing weight and allowing us to easily run upright. --Shaggorama (talk) 20:56, 7 October 2008 (UTC)

I was talking a while back to someone who lost their big toe in a lawnmower accident and they said the loss of the toe made walking quite bit more difficult. So it looks like the toe might have been actively evolved to help with walking. Dmcq (talk) 00:30, 8 October 2008 (UTC)

Fizzy drinks.

The aqueous carbon dioxide in fizzy drinks makes the drinks acidic (for some reason that I have forgotten), couldn't you just add an alkaline solution to the drink to neutralise it. Fizzy drinks are critisised for being bad for your teeth because they're acidic, this would get rid of that problem. Thanks.92.2.212.124 (talk) 20:02, 7 October 2008 (UTC)

Except that acidic compounds have a generally pleasant "sour" flavor. Alkali compounds have a bitter, soapy flavor. Eat a bar of soap, or drink some lemonade. Which do YOU prefer? --Jayron32.talk.contribs 20:31, 7 October 2008 (UTC)

Also, its not the acid in sodas that is damaging to your teeth per se since it does not remain in contact with your teeth for very long. However, bacteria, which DO remain in contact with your teeth for a long time, will feed on the sugar in the soda, and produce an acidic waste product. Since these bacteria are essentially always there, the more sugar you give them, the more acid they make. Its this acid, which is held directly against the tooth for a long period of time, and not the acid that washes over the tooth which causes decay. Its the sugars in the soda that cause the decay, not the acid inherent in the carbonic acid. --Jayron32.talk.contribs 20:31, 7 October 2008 (UTC)

Thanks92.2.212.124 (talk) 20:43, 7 October 2008 (UTC)

It is not carbonic acid that is responsible for the sour taste and the tooth weakening, it is phosphoric acid (Cola) or citric acid. Cacycle (talk) 03:28, 8 October 2008 (UTC)

From this article, it's due to a combination of acidity, buffering capacity (titratable acidity) and sugar content. Axl ¤ [Talk] 17:40, 8 October 2008 (UTC)

The grayed tip of a banana

As a child I was told to bite off the usually grayed tip of a banana before eating it. What is it, though? Thanks. Imagine Reason (talk) 20:03, 7 October 2008 (UTC)

Greyed tip? I assume this means pre-peeled bananas, but i wouldn't bite the peel of a banana. If this means a peeled banana, what grey tip? Anyway, I've never heard that.92.2.212.124 (talk) 20:30, 7 October 2008 (UTC)

I'm pretty sure it's banana. --Shaggorama (talk) 20:38, 7 October 2008 (UTC)

Yes, it's the tip of a just-peeled banana. It's usually not white. C'mon, I thought that were the common experience. Imagine Reason (talk) 21:19, 7 October 2008 (UTC)

See vascular bundle and, specifically for bananas, phloem bundle (What!? No article!?). What you are referring to is the part of the banana where the bundles (strings) join and invert into the center of the fruit. -- kainaw™ 21:49, 7 October 2008 (UTC)

You mean the dark bit at the far end from where you open it? I don't bite it off, it comes off very cleanly on its own if you push it sideways slightly. --Tango (talk) 23:17, 7 October 2008 (UTC)

Systemic bias! Seriously, you don't open a banana at the stem end? Weird. --Sean 22:43, 8 October 2008 (UTC)

This sounds like bruising as described not far above. When the cells are damaged, they release enyzmes which oxidize the surrounding tissue. Damage could occur at the stalk end due to wrenching when the banana bunch is pulled of the stem, at the bottom end when the bunch hits the container, and anywhere else the bananas get bumped in transit. If you're getting bananas with brown on them, consider yourself lucky, the only bananas I ever see are very far from ripe - thank you very much, modern commercial food distribution system. Franamax (talk) 03:33, 8 October 2008 (UTC)

My dad used to bite out the bruised bits of bananas before slicing them onto his breakfast cereal. (I don't know whether he still eats breakfast cereal.) The texture may be icky to some, but it won't hurt you, if that's what you're asking. —Tamfang (talk) 06:44, 8 October 2008 (UTC)

Nobel Prize winners

Have there been any Nobel Prize winners whose work has since been completely discredited or otherwise found to be useless/incorrect? -Elmer Clark (talk) 20:41, 7 October 2008 (UTC)

Interesting question! Since you posted in Science, I assume you're less interested in the Nobel Peace Prize, where Rigoberta_Menchú and Henry Kissinger come to mind. --Sean 21:45, 7 October 2008 (UTC)

If this were about Nobel laureates generally, I'd mention Paul Heyse, who won the 1910 Literature prize. One of the judges said "Germany has not had a greater literary genius since Goethe" - but history has been rather less kind to Heyse. -- JackofOz (talk) 01:12, 8 October 2008 (UTC)

Off the top of my head, the closest I could come up with is Neils Bohr, who won the Nobel Prize in Physics for devising the Bohr model of the atom. Its not that the Bohr model was wrong, in fact it is perfectly accurate for any two particle system. The problem is, in practical terms it means it predicts the electronic structure of the Hydrogen atom (which has an electron and the nucleus) and nothing else. The Bohr model breaks down for any atom with more than one electron in it; so while it works for the He⁺¹ ion, it doesn't work for the He atom. It was an important step in the modern understanding of the electronic structure of the atom, but other more recent models, such as the wave mechanical model of the atom as derived by Erwin Schrödinger, Paul Dirac, Louis de Broglie, and others is far more useful, and as a model it contains the Bohr model as a special case. Still, Bohr is important as a key step in our understanding of the atom, and his contributions should not be deminished merely because better models came along later. --Jayron32.talk.contribs 21:37, 7 October 2008 (UTC)

Bohr's idea of quantization of angular momentum also inspired de Broglie whose's work latter inspired Erwin Schrödinger so that he came up with Schrödinger equation. I believe that the modern quantum theory couldn't exist without Bohr's breakthrough. - Justin545 (talk) 00:35, 8 October 2008 (UTC)

Johannes Andreas Grib Fibiger is an interesting case, especially in light of this week's award to Harald zur Hausen. --Arcadian (talk) 09:47, 8 October 2008 (UTC)

Argh - the guy's name escapes me for the moment. There is at least one case where someone made a seemingly great discovery - and it was disproven shortly before the Nobel was awarded - so they gave him the prize anyway but changed the citation from that very specific discovery to some kind of vague lifetime-achievement award...but the guy's name escapes me right now. SteveBaker (talk) 13:55, 8 October 2008 (UTC)

In 1912 the swedes awarded the physics prize to one of their own, for the invention of an automatic lighthouse. Useful but trivial on the nobel scale. In 1949 the Nobel Prize in Medicine was awarded for an advance in Lobotomy. EverGreg (talk) 20:48, 8 October 2008 (UTC)

Times sure do change and science advances. Now, that 1949 choice seems unlikely, but at the time it was a no-brainer. DMacks (talk) 21:05, 8 October 2008 (UTC)

Ba-da-bomp! And the Nobel Prize for today's best joke goes to...DMacks. :) Franamax (talk) 22:00, 8 October 2008 (UTC)

Interesting answers, thanks - Fibiger at the very least certainly seems to qualify. -Elmer Clark (talk) 12:44, 9 October 2008 (UTC)

honey locust spines: poisonous?

I just tore an enormous (23 centimeter long) spine off of a honey locust near here and in the process my left hand got jabbed. It didn't break the skin or draw any blood, but there's a small, red raised bump there like an insect bite that itches a little and the area around it is somewhat red and feels sore. I heard that honey locusts have some sort of toxin in their thorns that can be dangerous, but I can't find any information on it at all. Is this true? If so, do I need to seek medical attention? Can this get infected?

Any help is appreciated. Thanks. 63.245.144.77 (talk) 20:44, 7 October 2008 (UTC)

Sorry, we can't give medical advice. Please contact your doctor's office. The nurses there will be able to tell you what sort of medical attention (if any) you need. Also, note that some locations have a poison control telephone number - they are usually staffed with medically trained people, and are very helpful with "is this plant poisonous" type questions. -- 128.104.112.147 (talk) 23:39, 7 October 2008 (UTC)

Holt Biology

What is a phospholipid layer that covers a cell`s surface and acts as a barrier between the inside of a cell and the cell`s environment? —Preceding unsigned comment added by 75.68.106.206 (talk) 21:14, 7 October 2008 (UTC)

Your Holt Biology book should have the answer. Please post all your homework questions at once so we don't have to repeat multiple times that we are not here to do your homework. -- kainaw™ 21:22, 7 October 2008 (UTC)

See comments below on the plant cells. Be aware that while Wikipedia has an article on Cells, which I recommend that you read, your Holt Biology book is likely much easier to follow, and if you read it, it will give you the answer. --Jayron32.talk.contribs 21:23, 7 October 2008 (UTC)

Hearing

Hi all,

Hypothetically, and I do mean hypothetically because I’m not asking for medical advice, how does one increase the results of a hearing test (only a temporary basis, not permanently).

I’ve heard that: 1. One’s hearing is better in the morning (so take the hearing test in the morning) – there will be a slight benefit. 2. Wear headphones (like the headphones for ear protection with firearms) prior to the hearing test. This will allow one to “rest” the ear drums so they’ll be more “sensitive” during the hearing test.

Any other thoughts (again, not seeking medical advice). Thx! Rangermike (talk) 21:15, 7 October 2008 (UTC)

I had an uncle (until my aunt divorced him) who was practically deaf from working on jet aircraft. He needed to pass a hearing test to stay in the Navy Reserve or National Guard (don't remember which). What he did was wear ear plugs for a week or two before the test. Then, he would barely pass. He never tried it without the earplugs before the test, so I can't make a claim that it actually helped. -- kainaw™ 23:39, 7 October 2008 (UTC)

Fully off-topic - what is that guy called now? Ex-uncle? Uncle infinitely-removed? Former uncle (is this one best)? And for that matter, how do I refer to events that occured when my ex-wife was still just my girlfriend? SciRefDesk is probably not the best place to ask, I suppose... Franamax (talk) 05:45, 8 October 2008 (UTC)

Um - he is called "the ass who tried to stay in the reserves so he could spend one weekend a month in another city where he married another woman and, eventually, couldn't keep the two wives apart, got caught, and got dumped by both of them", or "the ass" for short. -- kainaw™ 13:16, 8 October 2008 (UTC)

Wait, seriously? Plasticup ^T/C 04:20, 10 October 2008 (UTC)

I was thinking that too - good God man, two wives? I had enough trouble with just the one. OTOH man in unhappy marriage meets woman fresh out of unhappy marriage - Franamax results and mummy/daddy live happily together 'til death do them part. I suppose that "the ass" is always a relative term (though Kainaw seems to have identified the type specimen). Franamax (talk) 07:25, 10 October 2008 (UTC)

Holt Biology

what is an organelle found in plant and algae cells where photosynthesis occurs? —Preceding unsigned comment added by 75.68.106.206 (talk) 21:17, 7 October 2008 (UTC)

You know, if you read your Holt Biology book, you may find the answer very easily. I bet you wouldn't have to look for more than 2 or 3 minutes. As an aside, you should also read the disclaimer at the top of this page, where it mentions that we aren't here to answer your homework questions. If reading your textbook is too much, you may want to read the Wikipedia article on Plant cells. Toodles. --Jayron32.talk.contribs 21:20, 7 October 2008 (UTC)

Really you'd get a much faster answer by typing photosynthesis into the search box than we could ever provide, I just don't get it. -- Mad031683 (talk) 22:07, 7 October 2008 (UTC)

What is, "I'll take chloroplast for 200, Alex"? - Nunh-huh 06:47, 8 October 2008 (UTC)

An acceptable phrasing for choosing a 200 dollar question on the subject of chloroplasts on the show Jeopardy? —Preceding unsigned comment added by 82.120.232.170 (talk) 19:56, 8 October 2008 (UTC)

And always remember, google is your friend. Sjschen (talk) 03:51, 9 October 2008 (UTC)

steam rockets

I am interested in steam rockets. What can you tell me about them? I specifically wanted to know about heating the steam. The small steam rockets I've seen are preheated with a torch and then released. Is it possible to have an onboard heating system on a relatively small rocket? What would that be? Any additional information would be very helpful. Thank you.Wizardh2o (talk) 22:43, 7 October 2008 (UTC)

We have an article on hot water rockets. While it's possible to do an onboard heating device, it's inefficient -- you're burning fuel to heat water not just to "steam" but to "very hot steam" (to ensure sufficient pressure) when you could just be burning fuel for the pressure of the initial combustion and leaving the weight of the water out. So while it's possible, it's going to be rare. — Lomn 23:09, 7 October 2008 (UTC)

One exception occurs in science-fiction: fusion reactors produce heat, but nothing much you could expell directly, so the writer imagines a tiny super-storng nozzle through TINY amounts of insanely super-heated water are expelled. (This is a space ship). Can't remember who the writer was, someone famous like Asimov... —Preceding unsigned comment added by 82.120.232.170 (talk) 18:00, 8 October 2008 (UTC)

This is the basic idea behind the nuclear thermal rocket, except that for an NTR, Very Bad Things can happen if you expel the fuel. --Carnildo (talk) 21:50, 8 October 2008 (UTC)

I think you mean Nuclear salt-water rocket, and the rocket doesn't expell fuel, it expells propellent (aka reaction mass). 98.221.85.188 (talk) 04:21, 9 October 2008

I meant nuclear thermal. A nuclear salt-water rocket *does* expel the fuel -- that's what the uranium salts in the water are. --Carnildo (talk) 20:05, 9 October 2008 (UTC)

No, you meant Nuclear salt-water. And what the salt-water rocket expells is reaction mass. Sometimes fuel can be used as reaction mass, but if it's being expelled, it's called reaction mass, not fuel. 98.221.85.188 (talk) 14:44, 10 October 2008 (UTC)

No, I mean "nuclear thermal". As in a solid-state nuclear reactor ("nuclear") that heats ("thermal") water, expelling it out the back of the rocket at high velocity. --Carnildo (talk) 22:17, 10 October 2008 (UTC)

Isn't that what the ip is talking about? You mentioned fuel being expelled as uranium salts in the water, so presumably, you indeed are talking about what he is saying. ScienceApe (talk) 00:12, 11 October 2008 (UTC)

What about those new racing motorcycles that have rockets? they must have on board heating. How do they work? And what about those mini helicopters with rockets on their blades? Or that car that went 260 mph for a quarter mile? It had rockets also, that I'm pretty sure were steam. I really could use the information. 74.71.203.132 (talk) 17:54, 9 October 2008 (UTC)

Putting car in park

Is it a good idea to shift my car (a 2004 automatic) into park when I'm at a long light or waiting for a left turn? Can doing this alot damage my car? Does it save any gas?97.118.170.250 (talk) 23:08, 7 October 2008 (UTC)

For an automatic? It's not likely to affect the car negatively, though in many cases it'll burn more gas -- my auto, and most I've driven, idle faster in park/neutral than in drive. There's an advantage to shifting to neutral in a stick shift so as to reduce wear on the clutch. — Lomn 23:11, 7 October 2008 (UTC)

Is there much wear on a clutch when it's fully disengaged? --Tango (talk) 23:19, 7 October 2008 (UTC)

According to the Car Talk guys, keeping the clutch pedal fully in causes wear on the throw-out bearing. They recommend shifting to neutral. — Lomn 00:02, 8 October 2008 (UTC)

The only advantage of shifting to park that I can think of is to avoid putting your foot on the brake. The disadvantage is that you'll need to ensure you shift into drive (not neutral and definitely not reverse) when the light turns green. As for the transmission (it's automatic, so you aren't manually messing with the clutch), each car I've owned has run just fine for at least 10 years without transmission problems. From my experience, people I know with automatic transmission problems are those who gun it and race from light to light - which has nothing to do with sitting at a light. My sister-in-law has two foot settings: all the way down or all the way up. She goes through a transmission a year. -- kainaw™ 23:36, 7 October 2008 (UTC)

But will it save me any gas?97.118.170.250 (talk) 23:41, 7 October 2008 (UTC)

Did you read Lomn's response above? He states that his experience is that it will burn more gas, not less. -- kainaw™ 23:45, 7 October 2008 (UTC)

Re Lomm's observation: isn't the idling speedup due to removing the transmission load from the engine rather than increasing the fuel supply? -hydnjo talk 00:40, 8 October 2008 (UTC)

It is difficult to say in modern vehicles where a computer controls the fuel supply. In the good old days, shortly after we had to use our feet to make the car move, the gas pedal actually increased/decreased the amount of fuel to the engine. So, regardless of what else was happening, not having your foot on the pedal would make it consume fuel at the idling rate at all times. The OP said this was a 2004 car, so it is one of those newfangled computer-controlled ones. -- kainaw™ 01:53, 8 October 2008 (UTC)

In re the above:

• Switching an automatic transmission into Park should alert the computer to select the most economical fuel mode possible. At certain times, it could select "curb idle", which is a higher idle rate to maintain alternator output. If you aren't running your A/C, there's no particular reason I can think of that the computer would choose to send more fuel to the engine. However, given the same amount of fuel, shifting to Park would stop your motor from pumping liquid around the transmission torque converter, so I'd expect the engine to rev a little higher without that load.
• And for a manual transmission, shifting to neutral is always good, not least because your leg doesn't get tired. However, I think Lomn's Car Guys link is a piece of semi-crap. Their piece ends with an appeal to send them $3 to find out the rest of the mysteries, which is a little suspicious. Keeping your clutch depressed means there is a constant load on the throw-out bearing, but there is no other load - the bearing is not rotating, it's just sitting there with the incredibly hard steel of the bearing-balls and bearing-races subject to the pressure of - your foot! Contrast keeping the clutch fully disengaged though with riding the clutch, or keeping your foot lazily off the floor, so that the throw-out bearing is under pedal pressure and is rotating the partially-engaged clutch - that's definitely not good! But I've gotten 14 years and 440,001 km out of a single clutch (1992 VW Golf), and I never worried that much about shifting to neutral. The Car Guys might be right though, maybe the clutch would have blown at 600,000 km... :) Franamax (talk) 04:08, 8 October 2008 (UTC)

Keeping your foot on the clutch in a stick-shift car does indeed wear out that bearing prematurely (it's sometimes called the "thrust washer"...same thing). But in a modern car, with a typical driver, it's pretty unlikely that that'll wear out before the clutch itself - so while it's a good idea to shift into neutral and take your foot off the clutch when stopped - it's not a really critical thing. On an automatic, it's irrelevant because there is a fluid coupling clutch. There are many cases though where it's DANGEROUS to leave the car in gear with your foot on the clutch - for example, if you are stopped at a junction and you get rear-ended, your foot will almost certainly slip off of the clutch and you'll be launched forward into oncoming traffic - turning a minor fender-bender into a life-threatening situation. If you are in neutral with your foot on the brake (either in an automatic or a manual, then if your foot should happen to slip (eg as a result of a rear-ending or wet shoes or something) then at least you'll only roll rather gently forwards. Best of all is to put the car in neutral and put on the parking brake. In an automatic, putting it in park should have the same effect - but I have heard that the pin that slips into the transmission when you put the car in park can get worn out from excessive use...so I'm still going to say "Neutral with the parking brake on" is the best option and "In park" as the second best. I would be very surprised indeed to discover any difference whatever in gas consumption with any of the above techniques so long as you aren't revving your engine to keep your turbo spooled up in preparation for an impending burn-out when the light turns green!

Rather the contrary, if you're sitting in (manual transmission) neutral and get rear-ended, you will be launched into the intersection if your foot slips off the brake. If you're in gear with the clutch down, when your foot slips off the car will stall and engine braking will prevent you from being shoved into the intersection. Neutral with parking brake on would be best though. Franamax (talk) 21:31, 8 October 2008 (UTC)

I disagree about the stalling thing. I know of one person who had this happen - the car didn't stall and she ended up being side-swiped by a Jeep that was going about 40 to 50mph - which rolled the Jeep - totalled her car and might have killed her had it not been for her side-impact airbag and door reinforcement. If you think about it, that's not surprising. The engine stalls when you are at a dead stop and dump the clutch too suddenly - but if you've just been propelled forwards by the force of a rear-ending, the RPM may well be efficiently matched to the speed of the wheels when the clutch bites - and far from stalling - the car may actually accellerate into the intersection. A lot will depend on the car - my MINI Cooper'S is pretty hard to stall like that - it has a pretty flat torque curve so you tend to get a bit of tyre squeak and then it's perfectly happy. Personally - I don't recommend taking that bet. If that's your driving style - you should change it ASAP. In neutral with the parking brake on - or possibly in gear with the clutch down AND the parking brake on - are the only safe possibilities with a stickshift car. SteveBaker (talk) 02:14, 9 October 2008 (UTC)

Steve, I quail at the thought of ever disagreeing with you, what with you being pretty much completely always right and all (I mean that!) - but I have to disagree here. Yes of course using the parking brake is always the best solution, and by that we probably both mean the handbrake available to hand in a small car. Even then, most people will not engage the handbrake at a common driving stop. Consider now a traffic stop where the parking brake is not engaged, and the only variable is whether or not the manual transmission is engaged in gear, or in neutral (the driver's feet disengage from all pedals on impact). In the neutral case, the car will accept the momemtum transferred on impact (minus energy of deformation) and (almost) immediately adopt a forward velocity. In the case where the transmission is engaged, regardless of whether or not the engine stalls, the rotating/translating mass of the engine will participate in the collision energetics. Unless you were sitting there revving the engine, including the inertial moment of the engine elements into the energy equation can only slow the car down. Remember that you are not feeding extra fuel to the engine - whacking the car from behind may cause the auto with an engaged gear to move slowly forward making a "putt-putt" sound from the idling engine, but I see no possible way it would cause sufficient velocity to participate in an intersection crash. Smacking a car in neutral gear though - think about billiard balls, and the pocket is on the other side of the intersection.

As far as changing my driving style, I'll let you know when I've completed ny second million kilometres, the first has gone pretty well. (FD - 2 accidents - early 20's [age, not year!] - one, making a U-turn without looking back, the other looking for something in my back seat) I've in the past read advice about sitting still in a manual auto, it's uniformly to stay in gear with the clutch down. You are absolutely right that the parking brake is the way to go, but in abeyance of that advice - keep it in gear. Franamax (talk) 03:28, 9 October 2008 (UTC)

Actually, I'm not sure - there may be no pockets in billiards. So instead, think of it as a snooker ball or a pool ball. I know how to play and lose at both of those. :) Franamax (talk) 03:33, 9 October 2008 (UTC)

When the engine is idling, there is fuel going into it. You put a car in gear and take your feet of all the pedals it will move forwards (assuming it doesn't stall, and the fact that it's already moving slightly from the impact will help there as Steve says). I'm not sure the velocity imparted by the impact would be enough to prevent the car stalling, but it could well be - remember the engine is disengaged at the time of the impact (since your foot is on the clutch) so there is no engine braking in that first fraction of a second. I guess it all depends on how quickly your foot falls off the clutch pedal. That said, I don't think I know anyone that puts their car in neutral every time they stop at lights, and my driving instructor never told me to. Of course, if you have your feet on both the clutch and the foot brake, you should be fine - the brake will stop you moving forwards from the impact even if your foot does then fall off it, so then the engine will stall when you lift the clutch. --Tango (talk) 20:50, 9 October 2008 (UTC)

Just think about the dynamics. You've been rear-ended and your feet have been knocked off all the pedals. If you're in neutral, your car is free to move forward with all the imparted momentum. If the car is in gear, part of the momentum is dissipated into accelerating the engine. The idle fuel feed is immaterial - how fast does your car go when your foot's not on the gas pedal? Chugging forward into the intersection is not the problem, getting shoved forward is. If you get rear-ended hard enough to knock your feet off the pedals, you want every possible means to stay out of that intersection.

If I take my car out of gear whilst sitting on the active road area, I pull the handbrake - always. But usually I hold the clutch in, with the other foot on the brake pedal. I also do the left-turn thing where you pull out and crank the wheel left to get a good sight-line, then turn the wheel back so you don't get rammed into oncoming traffic. And the left-turn thing where you hang back until at least one other car is behind you, then move forward a bit. There's also the best practice thing where you stop 20 feet behind the next car at a stop-light, wait 'til at least one other car stops behind you, then move up - I don't do that though, since I've paid for an airbag I didn't ask for, meant to save the life of an overweight American male who isn't using his seatbelt. :) I actually spend most of my driving time evaluating threats - and enjoying my machine. Franamax (talk) 07:17, 10 October 2008 (UTC)

I've never actually measured the speed a car goes when idling, but I heard 8mph given as a figure once, which is plenty fast enough to cause a problem at a junction. --Tango (talk) 21:15, 10 October 2008 (UTC)

And if you're sitting in neutral and get rear-ended by a car moving at 30 mph, what is your resulting velocity? More or less than 8 mph? Franamax (talk) 01:06, 11 October 2008 (UTC)

Difficult to say, but probably about the same. If we assume your cars are of similar masses, then the maximum you could be going is 15mph, but quite a lot of energy will be absorbed by deformation (cars have crumple zones which can and do absorb a lot of energy). Also, most cars rear-ending you will be going slower than that, since they will have just started braking too late rather than not at all. --Tango (talk) 11:36, 12 October 2008 (UTC)