Wikipedia:Reference desk/Archives/Science/2007 May 9

= May 9 =

stress transfer theory
you do not talk about stress transfer theory in plate tectonics —The preceding unsigned comment was added by 68.72.3.2 (talk) 01:47, 9 May 2007 (UTC).


 * I encourage you to be bold and add information you feel is lacking from articles, keeping in mind the necessity of adding verifiable content. I see that the plate tectonics article is currently protected from editing by unregistered users (a measure to deal with repeated vandalism), so your best course of action would be to explain what is missing (in detail, preferably) on that article's talk page.  That way an established editor can add the missing information to the article. -- mattb 02:01, 9 May 2007 (UTC)

Pulse
Why is the heart a double beat whereas the pulse is a single beat? What is the most prominent pulse in your body and does anyone know what chamber initiates the pulse?

-I choose to remain anonymous


 * Might want to take a look at our Cardiac cycle page. The first part of your question is an interesting one! Think about what part or parts of the whole "double beat" cycle actually involve moving blood through the vessels you're feeling. DMacks 04:38, 9 May 2007 (UTC)

My pulse is often a double beat, especially if I measure it from my chest :) You usually only feel one beat as the other sends blood just to the lungs :) And I am quite sure it is the left ventricle that creates your pulse :) And you don't have to say you are anonymous, noone here knows who you are anyway, and signing will give just a munber, from which almost nothing can be found out about you :) HS7 11:59, 9 May 2007 (UTC)
 * ...and which is already given in the history anyway. Getting a username here actually makes you more anonymous in some senses.  --Tardis 13:06, 9 May 2007 (UTC)

motion in universe
Is it possible to stop moving? Say I take my spaceship and go to the least occupied part of the universe. Is it possible to just not move? If so, would I recognize that I've stopped moving? —The preceding unsigned comment was added by 69.42.16.90 (talk) 04:58, 9 May 2007 (UTC).


 * What you could do is cease all acceleration. There is no such thing as "not moving" as all motion is relative per special relativity.  As in, you can only measure your motion relative to other objects, there is no absolute reference frame to judge one's motion.  Someguy1221 05:49, 9 May 2007 (UTC)


 * I'm sorry, but what do you (and others) mean by "cease all acceleration"? It's bugging me. BTW, I'm not a physicist, so that's partly why I ask. It would seem to me that acceleration is subject to the same provisions as motion in terms of its measurements. Root4(one) 19:26, 9 May 2007 (UTC)
 * And the question I should have been asking is, what does "all acceleration" mean? Root4(one) 19:29, 9 May 2007 (UTC)


 * As i understand it, there is no least occupied part of the universe. And what you will find at any point in the universe is that objects will tend to be moving away from you as the universe is  expanding.  --Tbeatty 06:39, 9 May 2007 (UTC)

It's a meaningless question. There is no such thing as absolute motion - you can only ever measure your speed with respect to something else. Einstein, relativity, all that stuff. If you aren't actually accelerating - you can consider yourself to be stationary at any time and in any place - it simply has no meaning to say that. SteveBaker 14:55, 9 May 2007 (UTC)


 * Note, acceleration != motion. In Newtonian physics, a = dv/dt.  if a=0, v can be anything (including 0).   The earth is not accelerating (much) with respect to distance to the the sun (hopefully!) but it is moving at quite a speed.  The problem is the definition of motion and lack thereof. Motion can only be observed with (at least) two entities and is meaningless to describe it otherwise.  I'm having trouble seeing that Relativity really has anything to do with the concept of motion discussed here.  To make some definition where "motion" is observed in only one entity X of would require some sort of God's-eye-view coordinate system of the universe and the entity X moving with respect to it (which we cannot see, and even if we could see, if we only had that fact -- motion with respect to the God's eye view -- in mind, and not position or any other fact on the God's eye view, we couldn't derive anything about anything else in the universe, so for all practical purposes this is meaningless).   I also have trouble seeing how motion could be defined for three entities, if I try to define it, it appears to become something other than motion, or it doesn't fully describe the situation with respect to how the three entities are interacting. So how could I describe it for motion relative to everything in the universe?


 * If I'm hurdling to a brick wall at 100 mph, I could just as well say the brick wall is hurdling to me at 100mph! But if I remain at an equal distance to that wall for some time period, I remain "motionless" to that wall (and likewise the wall to me).  I think that's all that any concept of motion can tell you.


 * Root4(one) 18:39, 9 May 2007 (UTC)


 * Acceleration means a change in direction or velocity. You can feel a real force when doing that (though it is equivalent to a fictional gravitational field, but let's not get into that!), unlike with inertial motion (i.e. motion at a constant speed/direction). So you can definitely not be accelerating (not changing in direction or speed) but you can always be said to have inertial motion. In any case the relevant article is principle of relativity (the reason why it matters in the article that the physical laws are the same in all frames is because if that can be shown to be the case then there is no physical way to tell who is moving and who is not. you can, however, tell who is accelerating and who is not) --24.147.86.187 01:24, 11 May 2007 (UTC)
 * Thank you! That was a much more eloquent explanation than I gave. SteveBaker 03:32, 11 May 2007 (UTC)


 * Thank you 187. That article's quite useful. Root4(one) 03:45, 11 May 2007 (UTC)

Questions about birthmarks
I have an area of abnormal pigmentation covering most of the back of my left hand. I have always described it as a birthmark. It's red and blotchy and much warmer than the surrounding skin; it looks a lot like the burst blood vessels you get with love bites. It is much lighter than a port wine stain. I read the Wikipedia article on birthmarks and mine doesn't seem to belong to any of the types of birthmarks listed. Are there other categories? Also, it appeared one day when I was six years old, but the doctor said it is still a birthmark, and they sometimes do appear that late. However, I can't find any information about this phenomenon online. I'm interested to know why a birthmark would suddenly appear, and how common it is. --Grace 06:11, 9 May 2007 (UTC)


 * From your description, it sounds like the blood vessels are closer to the surface of the skin than normal, causing the color change and the increased heat. Does this sound correct ? StuRat 06:41, 9 May 2007 (UTC)
 * Yes, that does sound right. Does that mean something? --Grace 12:18, 9 May 2007 (UTC)
 * It sounds most like a Macular stain (about which we don't have a specific article), but the timing of its appearance isn't really consistent with that. Birthmarks, by definition, don't just appear in children aged six. However, a doctor may have described it as being like a birthmark (in that it is essentially harmless). If you want to know for sure, a dermatologist would be likely be able to tell you. Rockpock  e  t  06:54, 9 May 2007 (UTC)


 * I asked about this a few months ago. I was told it is a mongolian spot. --Kainaw (talk) 13:47, 9 May 2007 (UTC)
 * But Mongolian spots are very uncommon in white people (I'm white) and almost always disappear before puberty (I'm 23 and it has not faded). Also, those are blue to brown, and this is red, and the texture is different (based on google image search). It is not raised, but looks more like a rash than a solid area of color. I'm still confused... --Grace 23:51, 9 May 2007 (UTC)


 * Mine are (and have always been) red. They look like bruises and are not raised.  I had them from the back of my head all the way down my spine as a child.  Now, they are just on the back of my neck.  My son has them also - just red.  His are only on the back of his head.  I'm mostly white, 1/4 Blackfoot (hence, the use of the nick that sounds like Kainah). --Kainaw (talk) 00:26, 10 May 2007 (UTC)


 * 1/4 Blackfoot, does that make you a Lightgreyfoot ? :-) Could either of you have rosacea ? StuRat 07:22, 10 May 2007 (UTC)


 * Actually, I think I do have rosacea. I'm not sure if the birthmark could be related because my rosacea symptoms are confined to my face and I have only had them for a year or so. I suppose a dermatologist appointment is in order! --Grace 12:06, 10 May 2007 (UTC)


 * Yes, the dermatologist can tell you if both conditions are related. StuRat 14:51, 10 May 2007 (UTC)


 * I know that mine (and my son's) is not rosacea. First, it is on the back of the neck and down the spine - not on the face.  Also, it does not come and go from one day to the next.  It is a constant red splotch. --Kainaw (talk) 19:43, 10 May 2007 (UTC)

What's the L in L-ascorbic acid?
If you buy plain ascorbic acid (vitamin C) in the store, is that the same thing as l-ascorbic acid? Sorry for being dumb - I can't find anything in the vitamin C article that addresses the meaning of the L. --Grace 06:29, 9 May 2007 (UTC)


 * I believe that means levorotary (as opposed to dextrorotary). StuRat 06:35, 9 May 2007 (UTC)


 * The fairly comprehensive Enantiomers article where StuRat was is a good source, as is the "Naming conventions" section of our Chirality (chemistry) article. Need to be very careful here—are we talking about a lower-case letter "l" (levorotary, a physical property involving how the molecule interacts with light) or the unrelated capital "L" (a structural geometry, not a physical one)? The "L" form of ascorbic acid—the biologically active one—has a positive optical rotation, therefore it's "d" not "l". Assuming you're buying "plain ascorbic acid" in the context of a vitamin supplement or nutrient, it's probably almost certainly that L one. DMacks 06:50, 9 May 2007 (UTC)


 * Thanks for the clarification. StuRat 07:15, 10 May 2007 (UTC)

Life on(to) Mars
What sort of precautions, if any, are taken to make sure that bacteria and other small organisms aren't carried to Mars on the probes and rovers and such that we send there? Dismas |(talk) 08:43, 9 May 2007 (UTC)


 * They bake the spacecraft to sterilize them prior to launch. It's never perfect though. And Mars and Earth exchange rocks anyway; some bacteria may have taken a natural ride during the last 4.5 billion years. We could all be one big happy family, Martians, us, and the rest of the universe. Weregerbil 12:29, 9 May 2007 (UTC)


 * I can see how Mars rocks get to Earth, but wouldn't any Earth rock dislodged from Earth be vaporized in the process and burn up before it escaped from Earth's atmosphere ? StuRat 23:15, 9 May 2007 (UTC)


 * Here is an interesting article on space.com relating to this question. --LarryMac 18:12, 9 May 2007 (UTC)

See also planetary protection. Icek 10:54, 13 May 2007 (UTC)

Mobile phones
Can mobile phones damage your brain. I have one and use it quite alot. —The preceding unsigned comment was added by HappyEater (talk • contribs) 09:03, 9 May 2007 (UTC).


 * See Mobile phone radiation and health. --Shantavira 11:52, 9 May 2007 (UTC)


 * Executive summary: we don't have a lot of reason to believe that it does, but we don't really know. -- mattb 05:27, 10 May 2007 (UTC)

Hot air balloon speed
Settling a dispute between a buddy of mine and I. In a hot air balloon, in say, 25 mph of wind, how fast would you be traveling? My understanding of it is, since any energy transfer (kinetic energy of the wind -> kinetic energy of the balloon) includes loss due to entropy, drag, all that, you'd never attain the same speed as the wind, while he contends that the balloon travels at the exact same speed as the wind (or effectively the exact same, the difference would be minimal). Thoughts? Especially with links to back it up? - M  ask?  10:52, 9 May 2007 (UTC)
 * Thought: Balloons are less dense than the air surrounding them (or in approximate equillibrium) and have immense surface area. They would be very responsive to changes in the wind.--138.29.51.251 12:16, 9 May 2007 (UTC)


 * Any drag the balloon experienced would tend to raise or lower the balloon's speed to exactly match the wind speed (at which point there would be no more drag). The experience on the ballon in a steady wind is "dead calm".


 * This is slightly different than for a sailboat running downwind; the sailboat contacts the water (which imposes a different drag force vector on the boat than does the air) so a sailboat typically approaches but does not quite match the wind speed.


 * Atlant 12:53, 9 May 2007 (UTC)


 * Yeah - I agree. At the point you launch the balloon, it's moving at 0mph relative to the ground - but 25mph relative to the air.  It'll very rapidly gain speed (relative to the ground) and lose it relative to the air - until it's going very close to 25mph relative to the ground and is almost stationary relative to the wind.  In a sense you are both right. As your buddy says: If you measure the speed of the balloon after it's been up there for 10 minutes, it'll be so close to 25mph that there is no instrument you'd be likely to have that would tell you any different - especially given that the air is a little turbulent and will vary depending on the terrain you are crossing so in reality this isn't an exact science.  However, you are also technically correct - in an idealised perfect world with perfectly smooth airflow - the balloon would never quite reach 25mph - it'll be 24.999999999999 mph or something.  Let your buddy win this one - you are being ridiculously pedantic! SteveBaker 14:50, 9 May 2007 (UTC)


 * If it's in a steady wind for an extended period of time, it's speed relative to the ground will be the exact same as the speed of the air relative to the ground, for all practical purposes. Adam2288  T  C  17:59, 9 May 2007 (UTC)

if, however your talking about convayences in general, it is easy to go above the wind speed in a sailboat.--Hacky 20:41, 9 May 2007 (UTC)


 * Dead downwind?


 * Atlant 23:21, 9 May 2007 (UTC)


 * Yes - dead downwind. We should be rigorous and replace every instance of the word "speed" in the previous answers with "velocity" - which expresses "speed and direction". SteveBaker 11:03, 10 May 2007 (UTC)


 * Steve, I couldn't understand the "polarity" of your answer. AFAIK, a sailboat can only approach and never even equal the velocity of the wind when the sailboat is sailing dead downwind. There's no way it can exceed the velocity of the wind.


 * Atlant 12:32, 10 May 2007 (UTC)
 * (Sorry - I missed the 'topic switch' to sailboats - I was still talking about balloons). SteveBaker 21:18, 10 May 2007 (UTC)

Yes, but at an angle of about 100° to the wind, it can easy go faster see sailing "Some extreme design boats are capable of traveling faster than the true windspeed." --204.234.208.164 16:45, 10 May 2007 (UTC)


 * Right. If you represent the sailing ship by a ball sitting in a groove that it can roll up and down and represent the wind by a long straight-edge at 45 degrees to the groove.  As you move the straight-edge forwards, the ball (because it's constrained to roll along at 45 degrees to "the wind") moves about 1.4 times faster than "the wind".  The trouble for sailboats is that there is no "groove" for them to sit in.  But the long, deep keel sticking down under the boat effectively forces it to move through the water in whatever direction it's facing instead of sliding sideways parallel to the direction of the wind.  So if the keel works well enough - the boat can theoretically move at almost any speed.  However, in reality, the keel doesn't keep the boat "in the groove" very well at all - so you can only beat the wind speed if you get the angle just right and everything is set up optimally.  But our balloon can't do that - unless it has something dangling down and fixed on the ground somehow - there is no way for it to stay "in the groove" - so it just moves parallel to the wind and at the same speed. SteveBaker 21:18, 10 May 2007 (UTC)


 * See Leeway for a discussion of the problem that sailboats face in trying to stay "in the groove".
 * Atlant 22:18, 10 May 2007 (UTC)


 * Meh - that's a pretty terrible article. SteveBaker 23:55, 10 May 2007 (UTC)


 * Many article improvements have arisen from Reference Desk discussions... (hint, hint)


 * Atlant 13:29, 11 May 2007 (UTC)

Converting alcohol to alkene
There was an exam question that asked for a way to convert an alcohol to an alkene without using dehydration or elimination. Does any body know any other methods with which such a conversion can take place?Bastard Soap 12:16, 9 May 2007 (UTC)
 * Apparently not. 209.53.181.172 21:35, 9 May 2007 (UTC)
 * I don't know, but I'd bet that nature has found a way using [enzymes]... Aaadddaaammm 01:27, 10 May 2007 (UTC)
 * What level of academia are we talking here—isn't "dehydration" just a specific type of "elimination"? How about oxidize to a ketone/aldehyde, then Wittig or Julia coupling? Or convert that carbonyl to an enol triflate and reduce off the oxygen functionality? Or cheat: convert the alcohol to a tosylate and displace with allyl Grignard:) DMacks 02:26, 10 May 2007 (UTC)

I have no idea of what you just said... so I guess you are at a much higher level than I am. What would happend if you passed a current through the alcohol? Bastard Soap 11:14, 11 May 2007 (UTC)

Own sweat smells nice.?
Okay weird question. As my understanding goes, we find other people's smells attractive because their genes are different to ours. The more genetically different they are, the better they smell. However, I tend to find my own smell attractive... or at least not offensive. Where by my logic I would assume that my own smell should be the least attractive to me, as I have the exact same genes to me, and so I should be attracted to someone who is the same as myself, as this offers no advantage from the point of view of genetic mixing. More worrying, does this mean that i will find someone with similar genes to me more attractive in this sense? Or, is it just the case that I am familiar with my own smell? Or is it that the gene-smell test only works in the case of early encounters - but you can get used to an offensive smell and find it comforting?? Will be glad to hear your thoughts.. Or even if we have an article on the topic. 213.48.15.234 13:18, 9 May 2007 (UTC)


 * Your assumption is flawed. It is just as common for a person to find another person's smell attractive as it is to find the other person's smell offensive.  Much of a person's odor comes from what they eat.  Use of deoderants and perfumes also have a huge effect.  I work in a highly mixed group of people.  I have heard many complaints of the "stink" of others because they eat too much fish, or they don't use deoderant, or they use too much hair straightener, or they wear too much flowery perfume... --Kainaw (talk) 13:45, 9 May 2007 (UTC)

I saw a program once where they got a group of men, halve very attractive and have very unattractive, to do vigorous excercise. They then wrapped dolls in the mens t shirts and got 4 female models to come and smell the dolls, choosing which ones they prefered the smell of. every model chose the smell from the unattractive men. So your theory sounds right to me. And of course from an evolutionary point of view things like perfume and hair spray have been around a lot shorter time than we have been smelling each other. Anya Fox89.241.20.220 14:11, 9 May 2007 (UTC)


 * I think the pheromones in sweat have nothing to do with genetic difference. [' Mac Δαvιs '] ❖ 17:01, 9 May 2007 (UTC)
 * Buzzer word : think. As for myself perhaps their is an influence from the genome of someone on the pheromone emitted in sweat, but that's entirely an personal opinion on my side and I don't have any scientific paper on the subject to show you. -- Esurnir 17:51, 9 May 2007 (UTC)


 * The facts are that the situation in humans are not fully understood. Seperating the innate response to odors from the associative response is extrememly different. Also, most human societies have strong pressures to mask natural odors with sweet smelling perfumes or deodorants, therefore we have been socially conditioned from a very young age. Nevertheless, there are some studies that suggest humans do (or once did) use odors as social cues. For example, the Yanomami people will rub the body of someone they have encountered and then sniff their fingers (Schaal & Porter 1991).
 * T-shirt tests (as described above) seem to suggest that we can distinguish between those who have a similar or dissimilar Major Histocompatibility Complex class (MHC) to ourselves, a mechanism that would permit us to find a mate that is genetically distinct based on their odour. Interestingly, females on the contraceptive pill appear to find those with a similar MHC class attractive while those not on the pill find those with a dissimilar MHC class attractive (Wedekind, 1995). The classification of what is considered visually "attractive or unnattractive" in men (as described by anon above) was linked to facial symmetry. Woman only preferred the odour of "attractive" (symmetrical) men in the period of fertility during ovulation. During periods of low fertility, they showed no preference. However, between a quarter and a third of people can repeately identify their own body odour from a choice of 10. A similar proportion can detect their sexual paterner's odor in a similar test. Women tend to be better at this than men (Schleidt, 1980). So seperating a previous association with an odor which results in a conditioned preference, from an innate preference, is near impossible in humans, which is why scientists use animal models.
 * There is so much data on animal pheromones in the literature, most of it crappy, but some reputable studies have shown that mice do distinguish between MHC class peptides in an innate, non-learned manner. They do so via a specific receptor expressed in their vomeronasal organ (VNO). The problem with interpreting this data with regards to humans, is that humans do not have a functional VNO, and thus this mechanism seems unlikely to be conserved. The Holy Grail of olfaction research is to demonstrate that humans do have a mechanism for pheromone detection and then to find the pheromone compound that activates it. If you wish to learn more about this, a really nice overview can be found in Pheromones and Animal Behaviour by Tristram D. Wyatt. Rockpock  e  t  18:20, 9 May 2007 (UTC)

yeast
how can you tell whether yeast cells are dead? Basically I need to conduct an experiment in which I will need to know whether any cells in a sample of yeast are still alive. I thougt just putting them underwater and waiting for the bubbles to stop, but I suppose they would produce ethanol then, and all get drunk and die. Are there any other reasonably easy and feasible ways to see if the cells are alive?


 * See Wikibooks Cookbook: Yeast. If you add yeast to warm (110 degree F) water with sugar added, it will foam in a few minutes if the yeast cells are alive. The process is described better at Ochef.com.. The temperature is critical, so if you are doing an experiment, this is an independent variable you should control accurately. Guessing whether the water is warm versus hot is not as easy as one might assume. Edison 15:13, 9 May 2007 (UTC)


 * Expanding on what Edison said, this process is called proofing (or maybe proving) the yeast. Bakers who aren't certain their yeast is still fresh routinely do this.


 * Atlant 16:18, 9 May 2007 (UTC)

actually temperature is the variable I am measuring.


 * You could use a stain that only stains dead yeast cells. And look at it under a microscope. 62.194.90.107 16:10, 9 May 2007 (UTC)


 * If you happen to have access to a fluorescence microscope, there are several yeast-specific Live/Dead staining kits available. A couple of those are listed on this page. --mglg(talk) 18:55, 9 May 2007 (UTC)

Really what I wanted was something that would show whether the yeast was alive or not. I have to cook them until they are all dead, and have no idea how to tell. I expect looking at them under a microscope will be too complicated and take too long.


 * What grade are you in? I think people are being a bit too tricky here.  It's easy to massively overheat the yeast, and then prove that they don't 'proof'.  --Zeizmic 20:03, 9 May 2007 (UTC)


 * I agree. Boil them for 5 minutes, and they'll be dead as Dillinger, guaranteed.  --TotoBaggins 20:14, 9 May 2007 (UTC)

How about using the yeast to make bread ? If it's alive, you have a nice loaf of bread. It it's dead, you have matzo bread. StuRat 22:18, 9 May 2007 (UTC)

Are therre any chemicals I can pour into the yeast that will make them look different if they are alive than if they are dead?

I've given up on this and gone for the easy option of using a respirometer.

Zip line speed
I need to make a zip line for a show I'm doing and I need to know A) pythagorus theorum so I can work out the height from the ground to the zip line, at any given point on the zip line, so that things can pass under it. and B) the equation to work out the speed that an 8 stone person will travel over a given distance and height. My two towers are roughly 7 metres and 5 metres tall across a 50 metre distance thank you Anya Fox89.241.20.220 14:05, 9 May 2007 (UTC)


 * The formula you asked for is simply a2+b2=c2. However, that will not help you.  You will likely only have the distance of an object from one of the towers.  So, you only know one of the variables.  Instead, you know that the ratio of the height to run is 2/50.  So, to calculate the height at another run (distance from the 5 meter tower), you use H/D = 2/50 or H = (2D)/50 where D is the distance from the 5 meter tower and H is the height from the top of the 5 meter tower to the line.  Add 5 to H and you have the height from the floor to the line.
 * Keep in mind that this will not be accurate. 50 meters is a long run for a zip line.  It will sag a lot.  Add a person to it, and it will likely drop below 5 meters a good 2/3 way from the 7 meter to the 5 meter tower.  Of course, that means that the speed of the person will be zero since he will only drag about 30 meters across the line and then stop. --Kainaw (talk) 14:14, 9 May 2007 (UTC)
 * Assuming a completely rigid zip-line (ie; that it won't sag: not exactly true, but I can't find any more accurate models of the situation), the acceleration of a person zipping down the wire would be $$a = sin(\frac{2}{\sqrt{{2}^{2}+{50}^{2}}}) \times g$$, where g is the acceleration due to gravity, roughly equal to 9.8 and the $$\sqrt{{2}^{2}+{50}^{2}}$$ comes from Pythagoras theorem (given above). It looks ugly, but as the angle in your zip wire will be only very slight, so only the acceleration of the object will only be slight, and can be worked out at 0.39 ms-2. However, the speed can then be calculated by $$v = \sqrt{2as}$$, where s is the distance travelled by the person in metres (the angle in the wire is so slight, you can simply assume that s is the distance from the bigger pillar). This eventually works out that, when the person reaches the end of the wire, their speed is 6.24 metres per second, or 13.95 miles per hour; that's still pretty fast! Laïka  16:01, 9 May 2007 (UTC)
 * For the idealized expression above, a simpler equivalent is $$a = tan(2/50) \times g$$. However, this will not be useful in practice for the reasons given below. --Anonymous, May 10, 06:06 (UTC).

You are neglecting both air resistance and friction. Air resistance would be pretty negligable at those speeds - but friction in a zipline isn't. Te effect of a slightly saggy cable ought to be beneficial since it'll make the cable steeper to start with (more accelleration - more speed to start with - hence more excitement) - and will then make it level out and perhaps even head uphill slightly at the end - which will help to decelerate the rider before the big "kersmack!" at the end. That being the case, if the zipline does seem to fast at the end, it may be worth slackening off the cable a bit to simultaneously make the ride more exciting - and slow it down where you need it to be slower. SteveBaker 19:20, 9 May 2007 (UTC)

The hang of cables without any additional weight follows that of a Catenary. As far as how a a cable hangs with something hanging from it, that sounds a little bit like one method to draw an Ellipse (see figure drawing on article). Root4(one) 20:04, 9 May 2007 (UTC)

I wonder how heavy the cable is? If it's nothing compared to the rider - then you're right - a section of an ellipse would be a better model than a catenery. But if this is a heavy steel cable, it might easily be much heavier than the rider - which would make the catenary curve a better model. SteveBaker 22:42, 9 May 2007 (UTC)

Olive plants
Just curious: can I grow an olive tree from the core of an olive? From green olive in brine that are sold as food? Does it require some dormace breaking? 84.160.229.65 15:20, 9 May 2007 (UTC)


 * Since salt is toxic to land plants not accustomed to it, like olives, I would very much doubt if you could get it to germinate once it has been soaked in brine. StuRat 22:11, 9 May 2007 (UTC)


 * I doubt that salt affects seeds, at least not in general. The olives are not supposed to germinate while in the brine. Some other seeds have to endure bush fire or the inside digestation of varius animals to break dormancy. After all the olives have not been put with pizza in the oven. 84.160.220.235 19:15, 10 May 2007 (UTC)

Anti missile defense in Europe and Booster phase ICBM interception
I was wondering, reading an article about the freezing relation between Europe and Russia that it was mainly based on the decision of eastern country to accept base of ABM.

While I see the use of those interceptor for intercepting (official reason) nuclear ballistic missile from Iran heading toward Europe. I was wondering if abm placed at the most eastern part of Europe (think baltic country, Poland, Ukraine) could intercept ICBM during their booster phase ?

Note the booster phase of an icbm is the phase where the icbm is still a "rocket" and is the easiest (due to the low speed of the icbm during that stage) place to intercept it.

I was asking this question as I'm a total noob in the icbm ballistic trajectory. If the trajectory is like "firing a shell" a nice parabolic curve, then it would be "doable" to intercept the icbm during the booster phase. But perhaps the trajectory would be more "square" like with a missile going nearly straight up to make it toward space then the warheads go ballistic during a flat trajectory before rentering the athmosphere and drop like a thermonuclear anvil

I assume the trajectory of an icbm is on middle ground between those two projection. So intercepting an icbm during booster phase with abm in eastern europe "doable ? Or not doable ?" -- Esurnir 17:47, 9 May 2007 (UTC)


 * As far as I know about the trajectory, the ballistic missiles follow an elliptic path having the center of the Earth as a focus. This site seems to have some interesting infos about missile defence. --V. Szabolcs 18:27, 9 May 2007 (UTC)


 * Shells don't really follow a parabolic path; that's a simplification based on (1) ignoring air friction and (2) treating the Earth as flat. If you continue to ignore air friction, but allow for the curvature of the Earth (so that the direction of gravity changes over the flight of the shell), then the path is really an ellipse.  And the same applies to a rocket once it stops thrusting, i.e. when it is "ballistic".


 * The problems with intercepting a missile during boost are, first, that's when it's farthest away, so you would need a really powerful launcher on your ABM to cover the distance to the launch site in a short enough time; and second, whatever you use to detect it has to be able to detect it that much faster. Having said that, I have no idea of the capabilities of military systems in these areas today. --Anonymous, May 10, 06:15, copyedited 08:15 (UTC).


 * But during launch, the target missile is going at its slowest - that gives you the best chance to hit it - and it can't deploy multiple independent re-entry vehicles and decoy balloons as it can on the way back down again - so the risk of you shooting down a bunch of decoys is eliminated. Also, your anti-missile missile ought to be a lot lighter than the target vehicle - it doesn't have to have enough fuel for a long range trip - and it can have a vastly smaller payload - this ought to give it much better accelleration than the target - and hence in a race, the anti-missile ought to be able catch up with the target fairly swiftly.  Best of all, if you blow a nuclear weapon apart on the way DOWN, you shower the target area with radioactive junk - but if you smash it to bits on the way UP, it's the launch site that gets showered with radioactive debris - and I suspect you'd greatly prefer that scenario!  If I were designing such a system to counter threats from relatively low-tech places such as North Korea, I'd mount my anti-missiles on high altitude helium balloons or on satellite-based launchers (although the latter would be illegal under international law). SteveBaker 23:02, 13 May 2007 (UTC)


 * The best place to learn, of course, is The Missile Defense Agency, since they will be overseeing any such construction. In general, different types of interceptors are effective for each of the phases of ICBM flight - boost, mid-flight, and re-entry/detonation.  So in the most practical sense, the engineers will tell you that a mid-course interceptor is "not designed" for boost interception.  This may mean that the radar can not track the target fast enough, or that the interceptor kill vehicle can only destroy the ICBM in certain configurations (many are kinetic kill vehicles which do not use explosive, and this puts some limitations on where it will be effective).  Any numerous other engineering issues could naturally come up; you will get a better perspective if you learn about the basics of ballistic missile defense.  This site gives a pretty decent introduction to the technology in use today. Nimur 08:12, 10 May 2007 (UTC)

Last night's episode of House - medical question
Last night's episode of House featured a particularly gory scene where an 'infection' (never actually specified) caused the back of a young woman's skull to spontaneously split open, exposing the brain - following only a very brief period of agony with no related symptoms beforehand. As I understood it, the back of her head just 'popped'.

So, is this just an example of medical/body horror - or is there really an infection out there that can do this?

I'm aware that there are infections that consume flesh and bone - but surely they cause *pain*, or have other symptoms (that would be noticed in a patient in a large, well-equipped hospital under the care of The World's Greatest Doctor(tm)) before it gets to the stage of cracking open heads?

I am also aware that the writers of House have not always strictly been 'medically accurate' with their scripts - but AFAIK, they've never actually gone as far as 'making shit up because it looks cool/gross'. --Kurt Shaped Box 20:45, 9 May 2007 (UTC)


 * Not an explosion, but a massive and disgusting insult to the brain that the patient was unaware of: a man ... suffering from an unusual form of cancer which had eaten away at the upper portion of his skull and scalp but who had not sought any medical treatment because the condition was not causing him pain. Link.  --TotoBaggins 21:45, 9 May 2007 (UTC)


 * Hmmm - "No pain, no brain" eh?! Well, you don't actually feel pain from trauma in the brain - so the "no pain leading up to it" makes a certain kind of sense. SteveBaker 22:37, 9 May 2007 (UTC)


 * I don't think that there was actually any brain trauma. They patched her up (metal plate?) and she was physically fine eventually, once the underlying condition been correctly diagnosed and treated - it didn't seem to actually come from the brain, rather the skull itself. --Kurt Shaped Box 22:48, 9 May 2007 (UTC)


 * It wasn't an infection, it was cleaning fluid, remember? [' Mac Δαvιs '] ❖ 00:05, 10 May 2007 (UTC)


 * Na, it was downing the cleaning fluid in a gel-cap that caused the infections - the scar tissue in her stomach made a bridge between a vein and an artery, allowing various bacteria to go where they shouldn't in her body. --Kurt Shaped Box 00:10, 10 May 2007 (UTC)

Suger on paper
Im a clutz and I dropped a beaker full of a .1 Molar souluton of sucrose in water all over some papers. it was boiling on a hot plate. The papers are very important, and I would like to know if anyone knows of a solvent that can be used to take the glossy/sticky resedue off them, without damaging the paper itself. the paper is standerd lined notebook paper, written in pencil. I have acsess to many chemicals. —The preceding unsigned comment was added by Hacky (talk • contribs) 20:51, 9 May 2007 (UTC).


 * Er, boiling water got it on, how about boiling (or at least warm) water to get it off? Pencil-writing isn't usually water-soluble. DMacks 20:55, 9 May 2007 (UTC)


 * Note that boiling water has a nasty habit of turning paper into pulp, however. TenOfAllTrades(talk) 21:07, 9 May 2007 (UTC)


 * Glucose is apparently soluble in 2-methyl-2-butanol at 30°C, which should allow a quick washing of the sheets without them being damaged (adding Dimethyl sulfoxide makes the solvent even more effective, but be warned that it has the odd effect of triggering a taste reaction of oysters on skin contact, and it may also strip the graphite off the page!). I'd recommend if possible making up some fake sheets, just with some scribble, and testing the solutions on these before using them on the real thing. Laïka  21:54, 9 May 2007 (UTC)

How about if you enclose each page in two sheets of clear plastic (overhead projection floppies should work), so they don't stick to anything else. You can then keep the papers like that, or, if you prefer, you can photocopy them and toss the originals. (This might be a good idea, as sugar-coated pages could attract vermin and varmints.) StuRat 21:59, 9 May 2007 (UTC)

Photocopy the papers and use the copies, notarized if necessary?

Atlant 23:27, 9 May 2007 (UTC)

Encyclopedia of Life
The Encyclopedia of Life is up and running for anyone who does not know. 71.100.2.43 21:37, 9 May 2007 (UTC)


 * Well, it is and it isn't. There isn't actually an encyclopedia there in any shape or form yet. Skittle 21:46, 9 May 2007 (UTC)


 * No it's not, and even if it was, this reference desk isn't the place to advertise such projects, even cool ones. --TotoBaggins 21:48, 9 May 2007 (UTC)

I just hope it has a Wikipedia-compatible license. —Pengo 23:48, 9 May 2007 (UTC)


 * So much for wikispecies. --Russoc4 03:22, 10 May 2007 (UTC)


 * .... or is it? Apparently "The Wikimedia Foundation is a member of the Encyclopedia’s Institutional Council."   Perhaps there will be a merger... Nimur 08:16, 10 May 2007 (UTC)

Liver Cleansing/Detox Foods???
Is anyone familiar with changes that can be made to your diet to help cleanse the liver? So far the only things that I can come up with that seem credible are 1. lots of water 2. lots of 'whole foods' like fruit and veggies and 3. have a low fat diet. Any insight would be great! Thanks ~ Ashley604  ~


 * Um, I'm not sure why the liver needs "cleansing", or how changing your diet will do that. Talk to a medical practitioner for medical advice. Splintercellguy 23:54, 9 May 2007 (UTC)
 * Actually, yeah, I used to think the detox thing was a good idea and made sense, but I've been reading more and more that it's just a big commercial scam. There is no such thing as cleansing or detox, toxins don't build up and doing a detox doesn't get rid of them and doesn't mean you start from scratch. If you go back to your old eating habits you will be exactly where you started before your detox. Generally, a healthy diet is healthy for your liver too, I don't know of any specific diets to target the liver, but I do know it's definitely NOT Atkins diet. :) Vespine 00:28, 10 May 2007 (UTC)


 * Still, for completeness you may want to see the article on Sandra Cabot, which includes some details of her version of the liver cleansing diet. Confusing Manifestation 01:07, 10 May 2007 (UTC)

Do not talk to a "medical practitioner" about this. Talk to a "folk medicine practitioner". What you are asking about has nothing to do with what doctors and scientists mean when they use the word "liver". You don't expect an MD to adjust your chakras, do you? Most of us wish the quacks would make up their own words instead of using ours for entirely different concepts. alteripse 02:53, 10 May 2007 (UTC)
 * Next you'll be telling me I don't have 40 year old cornflakes in my colon! - Nunh-huh 03:55, 10 May 2007 (UTC)

Any of these "cleansing" diets will all have one thing in common: they tell you to drink large, large quantities of water. Guess what actually wicks toxins out of your body? That's right! Most toxins are exuded through sweat or passed out of the body through urine. Thus, drinking the FDA recommended amount of water every day is the best "cleansing" technique. Any of these fads that proscribe this food or that pill are just taking money from you in exchange for a placebo. -- Kesh 05:31, 10 May 2007 (UTC)

I like to cleanse it under running water and fry it with some onions. A nice chianti and some fava beans finishes it off.


 * It isn't normally necessary to "cleanse the liver", just eat a healthy diet and you will be fine. There are exceptions, however, requiring emergency medical care, such as the chelation therapy used if you ingest poisonous heavy metals. StuRat 07:12, 10 May 2007 (UTC)


 * As several people have said lots of water is the universal body cleanser. That being said, is certainly possible to cleanse the gallbladder and indirectly the liver.  Clearing the gallbladder allows anything that is backed up in the liver to come out into the gallbladder.  You can find several procedures here.  The prodecures mostly boil down to this:


 * 1. Eat extremly low fat for a couple of days in order to have bile build up in the liver / gallbladder.
 * 2. Drink nothing but juice the day of the cleanse.
 * 2.5 You may like to flush with epsom salts a couple of hours before the next step. (1 tablespoon mixed  with 1/2 cup water + drink about a quart of water extra.)  Tastes nasty, but will flush through your system
 * 3. Evening of Cleanse drink 1/2 - 1 cup of olive oil (you may mix with fresh lemon juice). Lay down on your right side so the oil can penetrate the gallbladder.  The oil will stimulate the bile and lubricate gallstones so that they will be expelled.
 * 4. The morning after you should pass gallstones. If you flushed with epsom salts then you shoould have very little stoolo, and the stones will float on the water in the toilet.  They may be rice to bean  sized or larger, colored vivid green to yellow or black.


 * There are more detailed procedures listed on the site referenced above. I can tell you from personal experience that this does really work, you should pass gallstones, unless your gallbladder is seriously blocked.  Also, I had no pain involved, although I didn't like the taste of the epsom salt flush.  Personally all of the stones I passed were rice to pea sized, but I would rather pass them now than have to have my gallbladder removed when they are the size of eggs.-Czmtzc 12:36, 10 May 2007 (UTC)


 * Wow, never heard of that. But wouldn't drinking a cup of olive oil give you pancreatitis? Anchoress 12:53, 10 May 2007 (UTC)


 * I would want to be sure I actually had gallstones before putting myself through that, and would also check with a doctor before drinking large quantities of olive oil and/or Epsom salts. This treatment may also give you temporary diarrhea. StuRat 14:46, 10 May 2007 (UTC)

Crap. Just crap. Drinking olive oil results in formation of fecal globules by a process of saponification. It comes on through, and is vastly interesting to fools who are taken in by this nonsense. I am sure if you ask, czmtzc will offer you a cure for the evil eye as well. alteripse 23:52, 11 May 2007 (UTC)

Question on Humanities Desk
I asked a question on the humanities desk, here. However, while the question fits the humanities desk, I think most of the people who are likely to know the answer frequent the science desk. So I hope it's okay to link like this :-) Skittle 23:01, 9 May 2007 (UTC)

Darwin's Domestic Pigeons
The  first chapter of Charles Darwin's hugely significant book The Origin of Species discusses Darwin's hobby of pigeon breeding and domestic pigeon breeds such as the English carrier and the short-faced tumbler. I recently came across a drawing of just a few pigeon breeds (1.8 MB jpeg) and found, like Darwin, "The diversity of the breeds is something astonishing".

Wikipedia is sorely lacking in images (or articles) on the vast majority of pigeon breeds, and it's a pity that we don't even have the breeds mentioned specifically by Darwin as articles, photos or drawings. I suspect that the drawings in the book linked to above have fallen into the public domain, but the book lacked a source. However, there must be a large number of public domain drawings, at the least, of the breeds around in Darwin's day, and I'm sure there must be some pigeon fanciers around today?

This is a call for photos, drawings, etchings, etc, and for anyone interested in writing articles on the animals which launched Darwin's thesis on natural selection, which has become the cornerstone of biology today.

And finally the question: are these breeds still around today? —Pengo 23:46, 9 May 2007 (UTC)


 * There are still pigeon fanciers today though I'm not sure it is as popular as it was in Darwin's day. There are a number of pictures of specific breeds of pigeons in Darwin's The Variation of Animals and Plants under Domestication which is now wholly in the public domain. --24.147.86.187 00:30, 10 May 2007 (UTC)
 * And available from Project Gutenberg: http://www.gutenberg.org/etext/3332  Rmhermen 03:05, 12 May 2007 (UTC)
 * Gutenberg's scans really aren't that brilliant, but it's a start: —Pengo 16:40, 12 May 2007 (UTC)