Wikipedia:Reference desk/Archives/Science/2011 May 16

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May 16[edit]

Waterford Nuclear Generating Station[edit]

How is Waterford Nuclear Generating Station impacted by the 2011 Mississippi River floods? It looks like it might be under 20 feet of water, or fine depending on where one draws inferences. Can anyone tell for sure? Should we call the public affairs telephone number and ask? 99.39.5.103 (talk) 04:12, 16 May 2011 (UTC)

This CNN story says: "A nuclear unit in Louisiana may have to shut down if Mississippi River levels are too high, according to the Nuclear Regulatory Commission. The Waterford Steam Electric Station Unit 3, about 25 miles west of New Orleans, was back online Thursday after being shut April 6 to refuel and replace the main generator. Entergy Louisiana, which owns the plant, said flooding is not expected with the opening of the Bonnet Carre Spillway. But if the river exceeds 27 feet, the plant would be forced to shut down because a circulating water system that drives the turbine would not be able to operate." --Mr.98 (talk) 11:38, 16 May 2011 (UTC)
Thanks; added to article. 99.39.5.103 (talk) 18:28, 16 May 2011 (UTC)

being awake like a zombie[edit]

after get awaken by a family member in the middle of REM sleep... why is that?, and what can i do to cancel this zombie feelingness after that happened?.

THX —Preceding unsigned comment added by 109.67.5.122 (talk) 04:22, 16 May 2011 (UTC)

A normal person can be awakened from any stage of sleep. But it isn't REM sleep that gives rise to that "zombie" feeling, it's probably stage IV sleep, the deepest level. REM sleep is actually pretty light. People in it are hard to awaken because they are "cut off" from the world, but they pretty frequently awaken from it spontaneously. The best way I know to get rid of that drugged feeling is to go back to sleep. For me, if I can't do that, I generally feel shitty all day, or at least all morning. Looie496 (talk) 05:48, 16 May 2011 (UTC)
I'm curious about this also. Everything I read about sleep talks about cycles, but that's not how it seems to me. To me it feels like there are two different kinds of sleep, which I think of as "liver sleep" and "brain sleep". "Liver sleep" seems to have a lot to do with eating or sleep-conducive activities like nodding off in an audience or (God forbid) while driving, and is distinguished by my ability to sleep through noises like a TV going in the background that would immediately bother me in the other version. As a result, sometimes I doze off for an hour or two and then wake up from the background noise. I call it "liver sleep" because sometimes when I've been awoken from it, I've literally felt as if the "center of consciousness" is somewhere far down, even as far as my liver, and my head towers confusedly above it. The other kind, the brain sleep, is where I have all the good dreams. But I've never seen anything about two different kinds of sleep in the literature. Wnt (talk) 09:26, 16 May 2011 (UTC)
Because the literature is scientific, rather than just anecdotal. :-P There are volumes and volumes and volumes about sleep research being done; we don't have to make it up as we go along anymore... --Mr.98 (talk) 11:41, 16 May 2011 (UTC)
Hypnagogia includes a lot of different phenomena which affect people between sleep and wakefulness.--Kateshortforbob talk 10:40, 16 May 2011 (UTC)

Plant survival[edit]

just wondering can a plant (given the appropriate conditions such as light,water etc) survive on the moon?

Let's see how the conditions differ. A day on the moon lasts about a month, so artificial light and dark may be required for some species - though there are multi-day and multi-month days and nights on the Earth too, near the poles, and many plants do just fine. There is no atmosphere (actually the Moon does have one, but it is so thin as to be hardly noticeable) so we'll need to give the plant some carbon dioxide and whatever gases the species in question needs. We'll need to give it soil that has the nutrients that the plant needs. Gravity is 1/6th of Earth gravity, and some plants might suffer, while others might thrive - if we insist, we could put the plant in a centrifuge for artificial gravity. The Moon is outside the Van Allen radiation belt, and therefore receives more radiation than the Earth's surface - we may need to build our greenhouse underground for protection.
I think we should be able to grow plants on the Moon. Not outside, though, as plants do need an atmosphere at the very least to get carbon dioxide for photosynthesis. And there are delicate species that require more carefully monitored conditions than more robust plants. 88.112.59.31 (talk) 13:52, 16 May 2011 (UTC)
The centrifuge suggestion seems rather impractical, especially in the case where we want to grow plants on the Moon to generate food. However, I'd think 1/6th normal gravity would be sufficient, although you might see different growth patterns (perhaps tall, gangly plants would result). StuRat (talk) 16:17, 16 May 2011 (UTC)
You have specify "appropriate conditions", because all inclusive conditions effectively renders the moon irrelevant to your question. It is like asking whether you can breathe (given the appropriate conditions such as a personal air supply) in a vacuum. Plasmic Physics (talk) 13:57, 16 May 2011 (UTC)
If you're asking if a plant could survive outside on the Moon if you dumped enough water on it, I seriously doubt it. Not any multicelular organisms you'd normally recognize as "a plant", anyway. For one thing, the water wouldn't stick around, most of it would boil off in the low pressure, and some of it might freeze if it was in shadow. That alone would kill the plant. But the super low pressure would also suck moisture out of the plant, so even if it did manage to absorb a little water, it wouldn't be able to hold onto it. There's bound to be other complications from the low pressure, but let's not worry about that, another major problem would be oxygen and CO2. Plant's typically need access to large amounts of both, with no air, that's not going to happen. So not only is the plant dehydrating, it's also suffocating! Most plants would also have trouble with the sharp temperature differences between sun and shade.
I think unless you cover the moon in air, the plants on the Moon will have to be indoors. At that point you could make it almost entirely Earth-like except for the gravity if you wanted to put enough effort into it. APL (talk) 06:29, 17 May 2011 (UTC)
Inclussive appropriate conditions include atmospheric pressure, adjusted humidity (soil and atmospheric), protection from ionising radiation, carbon dioxide rich atmosphere, soil nutrients, and controlled temperature. Anyone, please add if I missed anything. If these conditions are met then yes, a plant could survive on the Moon given that it is completely isolated from the Moon, and under controlled conditions. Plasmic Physics (talk) 12:34, 17 May 2011 (UTC)
Well, there's light, of course. It might be possible to use sunlight, but, in addition to the month-long cycles, the UV is likely to be rather excessive without an ozone layer. Would that be a problem ? If so, perhaps UV resistant glass could be used on the "greenhouse". Or, if the monthly sunlight cycle just won't work, then artificial light could be used, instead.
Also, I bet plants need some gravity, to know where to put the stems and where to put the roots. I would think that the Moon's gravity would be sufficient for this, but I'm not positive.
Finally, I don't think soil is required, as plants can grow hydroponically. StuRat (talk) 05:28, 18 May 2011 (UTC)
I think that a lower gravity shouldn't be detremental, it should result in taller plants. Nutrients and water should be easilier transported in the upward direction. Plasmic Physics (talk) 06:01, 18 May 2011 (UTC)
Has any experimentation been done growing plants in 1/6 (or 1/3) gravity in large centrifuges on the ISS to see how they do respond? -- 110.49.227.79 (talk) 06:32, 18 May 2011 (UTC)
I understand why you asked about 1/6th, since that matches the Moon. But what's the significance of 1/3rd ? StuRat (talk) 18:38, 18 May 2011 (UTC)
Mars. APL (talk) 22:34, 18 May 2011 (UTC)

When do chlorine in a solution evaporate?[edit]

  • Water that is heavily chlorinated (with NaOCl I believe)can be left in a bucket over night, letting the dissolved chlorine 'evaporate' from the water. Though the speed depends on the type of bleach and other factors [1].
  • Saltwater, which contains dissolved NaCl can be left for as long as you like, the dissolved chlorine will not, to my knowledge, disappear.

What chemical effect is behind the difference? EverGreg (talk) 13:53, 16 May 2011 (UTC)

A solution emmanates chlorine gas when it contains chemically unstable, chlorine-containing compounds. These compounds decompose into free chlorine and other products. Hypochlorite in bleach is one example of unstable chlorine compounds, chloride is not, hence it does not decompose to chlorine. Plasmic Physics (talk) 14:10, 16 May 2011 (UTC)
Cl2 + NaOH NaOCl + HCl
Since this reaction is reversible, if the Cl2 is gradually removed from the equation by evaporation, the equilibrium will eventually lie fully to the left, leaving no NaOCl remaining. There is no comparable reversible reaction involving NaCl because it is so stable, as Plasmic Physics notes. —Preceding unsigned comment added by 148.177.1.210 (talk) 18:18, 16 May 2011 (UTC)
The reaction is a bit more complicated; for clarity:
2 OCl- 2 Cl- + O2
OCl- + Cl- + H2O Cl2 + 2 HO-
Or the net reaction is:
4 OCl- + 2 H2O 2 Cl2 + O2 + 4 HO-

Plasmic Physics (talk) 03:48, 17 May 2011 (UTC)

Thankyou. But with my very limited knowledge in chemistry, I'm left with a question: The equation 2 OCl- 2 Cl- + O2 describes a reaction involving Cl-. Why does this reaction take place in a solution with NaOCl but not with NaCl? It looks like O2 and Cl- should be available in both cases. Or does table-salt NaCl in fact not 'dissolve' into Na+ and Cl-? EverGreg (talk) 10:57, 18 May 2011 (UTC)
What the net reaction is telling me is that OCl- is the key reactant. Thus the first reaction cannot take place for a NaCl solution as it does not contain OCl- in anything but trace quantities. In any case, this is not the determining reaction that produces chlorine gas, the second reaction is. Plasmic Physics (talk) 11:08, 18 May 2011 (UTC)
In theory, if you take a heaped teaspoon of salt and stir it into a cup of bleach, it should generate a fair amout of chlorine gas. Plasmic Physics (talk) 12:32, 18 May 2011 (UTC)
I think EverGreg is making a different (and very valid!) point: the first reaction of the "complicated; for clarity" reaction pair is , so "add products and reaction gets pushed backwards": reversibility is the very heart of equilibrium. If you were to mix oxygen gas and chloride, it says you get hypochlorite. So we need to know the equilibrium constant (which direction and how strongly a certain direction is favored for this reaction). A second interesting question is whether the hypochlorite produced could react with more (unreacted) chloride and water to produce chlorine and hydroxide (another net reaction by combining the two originals is 4 Cl + O2 + 2 H2O 2 Cl2 + 4 HO). This is possible but definitely not the "likely" direction so it would be hard to push the reaction in the strongly disfavored direction. DMacks (talk) 13:18, 18 May 2011 (UTC)

Space shuttle booster rockets[edit]

The booster thrust appears to be off-center, so what keeps the shuttle from rotating ? (I see that they also fire the shuttle engines, but those certainly appear to provide far less thrust than the boosters.) It occurs to me that the mass of fuel in the boosters must move the center of gravity towards them, when full. However, when nearly empty, this effect would be minimal. Do they steadily alter the relative thrust to provide more from the shuttle as the tanks empty out and the COG shifts ? StuRat (talk) 16:50, 16 May 2011 (UTC)

The SRB nozzles are gimballed through up to 8 degrees[2]; the orbiter's engines gimbal too. As with any launcher (with gimballed thrust, which is almost all), the flight control system continually tweaks the direction of these to keep the spacecraft flying in the intended direction. Failure of this authority is typical of those "somersault into launchpad" accidents that fill space programme blooper reels. -- Finlay McWalterTalk 17:30, 16 May 2011 (UTC)
See space shuttle solid rocket booster#thrust vector control. It seems concievable that a constantly adjusted mass/thrust imbalance may be desirable to avoid a null control default situation.190.56.125.48 (talk) 17:49, 16 May 2011 (UTC)
The SRBs and external tank weigh about 20 times more then the actual shuttle, so there doesn't need to be nearly as much thrust under it. Vespine (talk) 00:12, 17 May 2011 (UTC)
I assume that's when they are full of fuel. What's the ratio when empty ? StuRat (talk) 07:59, 17 May 2011 (UTC)
Looking roughly at the figures, it's close to 2:1 tanks:shuttle; the shuttle it self about 110 tons at lift off, the SRBs are 90 tons each and the tank is 26 tons empty.. I should have added "at lift off" in my above post, the SRBs detach before the main tank and which would complicate things a little further. Actually, Space_shuttle#Launch has a pretty good write up of the sequence of events. Vespine (talk) 01:39, 18 May 2011 (UTC)

How long does it take to test DNA?[edit]

In the case of bin Laden it took 6 hours, in the case of Dominique Strauss Kahn it will take 5 days.Quest09 (talk) 17:34, 16 May 2011 (UTC)

Our lengthy article DNA profiling discusses several DNA profiling methods, but nowhere discusses how long they each take — when someone finds the answer, please be sure to add the information to the relevant sections of that article. Comet Tuttle (talk) 18:14, 16 May 2011 (UTC)
(ec)And in the case of Alan Newton in New York City, it took 12 years.[3] I think that for ordinary, non-"priority" defendants, it is typical to wait months for a result[4] - probably in a cell because someone without the money for special consideration doesn't have money for bail either. Wnt (talk) 18:20, 16 May 2011 (UTC)
Any reason to think that article from 2005 indicates what's typical nowadays? The article itself mentions one crime lab so badly backlogged as apparently acknowledged by all involved, that people are now trying to use other resources and the lab themselves see the need to double their resources. Not exactly what you would expect if the situation is typical and accepted as the norm. (It wouldn't surprise me if many crime labs are backlogged [5] for example mentions something like that but that doesn't mean the situation as as bad as the Indiana lab or that it's typical to wait months for a result particularly when there is a clear cut purpose for the test, as opposed to just profiling a criminal in case something pops now or in the future or doing a test on a 20 year old case from before DNA in the hope you find a 'cold' suspect.) Nil Einne (talk) 01:47, 17 May 2011 (UTC)
The answer to the question is that it will take 6 hours to run the test in the lab. It will take 5 days or so for the full procedures regarding evidence custody and documentation to be followed. We covered this before a few months ago, the time it takes to run the test itself does not take into account the fact that there is a several-months-long backlog of evidence at just about any forensic science lab in the nation. On top of this, its not like someone walks into the lab with a few test tubes, hands them to a lab tech, and waits around in the waiting room for it to be done. There's a principle called Chain of custody, which requires certain standardized procedures regarding how evidence is handled, so as to minimize tampering or other issues. 5 days is likely a massive "rush" case; i.e. it was moved to the top of the list; i'd imagine that's roughly the time it would take to process, do the test, and return the test results to the prosecutors. --Jayron32 04:39, 17 May 2011 (UTC)
See also the takes on this by the xkcd and piled higher and deeper webcomics. – b_jonas 16:51, 17 May 2011 (UTC)

Eye color changing with mood.[edit]

My new g/f claims that her eyes change color with her mood. This seems spectacularly unlikely to me - but before I go stomping over this rather beautiful idea with big scientific boots on - I thought I should check with you guys. She claims her (normally brown) eyes turn greenish or golden depending on mood. My kinda suspicion is that her perception of herself changes with her mood and that her estimation of their color changes accordingly. But since this is a potential relationship minefield...yeah, exactly. 216.136.51.242 (talk) 18:09, 16 May 2011 (UTC)

See Iris (anatomy) — as one photo caption claims, the exact color of some eyes are "often perceived to vary according to its surroundings". You can either tell her "Pics, or it didn't happen", or you can arrange a carefully controlled scientific experiment, or you can agree, or you can tell her you need to closely examine her Crypts of Fuchs. Comet Tuttle (talk) 18:18, 16 May 2011 (UTC)
It is not uncommon for the appearance of eye color change to happen as the pupil dilates (or contracts). If you look very closely at your iris, you will see many different colors. Some people have uneven distribution of the color. She probably has a lot of brown near the pupil and more hazel around the edge. When the pupil dilates, the brown is dampened, allowing more of the hazel to appear. That is just a biological factor. Light sources also cause eye color changes. My eyes are a very different shade of blue under fluorescent lights compared to sunlight. Also, clothing/makeup can reflect off the eye, making the iris appear to change colors. Maybe she likes to wear green blouses when she's happy, making her eyes appear green. -- kainaw 18:19, 16 May 2011 (UTC)
I wonder if blood pressure, due to stress or anger or excitement, might make the eyes look more red. Also, does more oxygenated blood make them look redder, and less oxygenated blood make them look bluer ? StuRat (talk)
It is quite well documented that trauma to the surrounding area can result in the iris becoming brown because of the trapped blood leaking therein. See David Bowie as an example. (I also have a colleague who was in a RTA, and whose eyes went brown from blue as a result.) --TammyMoet (talk) 18:35, 16 May 2011 (UTC)
Mine also went from brown to blue after a severe motorcycle accident. -- kainaw 18:54, 16 May 2011 (UTC)
Really ? That's the opposite of the expected direction. StuRat (talk) 19:02, 16 May 2011 (UTC)
Eye color#Changes in eye color has some info, as does this "Ask a Geneticist" article and Snopes' forum. 99.39.5.103 (talk) 18:39, 16 May 2011 (UTC)

titration endpoint[edit]

I'm titrating solutions that contain two pH indicators, methyl red and bromocresol green. I'm not sure exactly what color I'm looking for as the end-point of the titration. I found a description of this indicator combination in an old paper (Stancil Cooper. Mixed Indicator Bromocresol Green-Methyl Red for Carbonates in Water, Industrial & Engineering Chemistry Analytical Edition 1941 13 (7), 466-470). It lists these color changes:

pH of Solution -- Color

  • 5.2 and above -- Blue with trace of green
  • 5.0 -- Light blue with lavender gray
  • 4.8 -- Light pink gray with cast of blue
  • 4.6 -- Light pink
  • Below 4.6 -- Pink or rose

So which of these colors indicates the end-point? Thanks, ike9898 (talk) 19:23, 16 May 2011 (UTC)

Equivalence point says stop as soon as a color change can be seen, but for these particular indicators, "The endpoint of 2:3 methyl red:bromocresol indicator is light pink to light green. The complete transition is from light pink (sometimes tannish) to light green to light blue (acidic solution to basic solution). It is sometimes difficult to see the green endpoint since one-half a drop over will give the blue color without observation of the light green intermediate."[6] Dualus (talk) 00:06, 17 May 2011 (UTC)
I'm going the other way - I start with a blue solution and titrate with acid. Where would you stop in that case? ike9898 (talk) 14:20, 17 May 2011 (UTC)
Ideally, you should probably pick a different indicator. Back up a minute and think about what you want to achieve - that is, what quantity do you want to measure with this titration? Most commonly it is the proton equivalents that it would take to bring the solution from where it is to neutral (how far off of neutral it is). So in those cases what you want to do is keep adding protons (or hydroxyls) to the solution until the pH indicator tells you you've hit 7.0. In this case, you're starting above 7.0, and you don't get any feedback until you've reached 5.0. Now if you have a solution with only strong base, you should be fine, as your titration will only be off by about 10-5 M protons, or 0.01 mM. However, if your solution also has a buffering agent with a pKa between 5.0 and 7.0, your titration won't just capture what it takes to bring the solution to 7.0, but also the buffering capacity of that agent as you go from 7.0 to 5.0. That said, not all titrations are attempting to reach neutrality. Often you'll want to find out how much acid/base a buffering system can handle before it loses its buffering capacity. In that case you don't want an indicator which changes around neutral, but you want one which changes (just) outside the operating range of your system, so it will tell you when you've gone "over the edge". -- 174.31.219.218 (talk) 15:57, 18 May 2011 (UTC)

disease detection by dogs[edit]

A recent coversation triggered a years old memory of when I had badly injured my foot from a conflict with a power tool. The foot healed up fine but about a year later my little dog freind started insistently licking my foot close to the scar tissue. A couple of days later I noticed small points poking through my skin in the same place. It turned out that these were small chips of wood which were being expelled from my foot. My dog had clearly detected these before I could. Similarly I used to suffer migrain headaches and my little dog would come and lick my forehead and temples where the pain was. I've also heard stories about dogs being used to detect cancers. If I had not experienced this myself I might have poo-pooed it as misinterpretation, but my dog's unusual attention to the affected spots was undeniable. I'm not given to mystical explanations, and this should be scientifically verifiable. "Desease detection by dogs" only turned up deseases of dogs. Anybody know anything about this please?190.56.125.48 (talk) 19:39, 16 May 2011 (UTC)

"Dogs Smell Cancer in Patients' Breath, Study Shows", National Geographic (lung and breast cancer); Dogs 'sniff out' bladder cancer, BBC News (bladder cancer). The latter article also discusses self-reported claims of dogs detecting skin issues. But these news stories may just be the usual "a study says" stuff that popular science news coverage loves so much (much more than "a better study says that a previous exciting study was wrong, and in fact we know nothing"). -- Finlay McWalterTalk 19:47, 16 May 2011 (UTC)
Dogs can do a lot of very impressive things with their noses. There's a wonderful account in Temple Grandin's Animals in Translation about dogs that have been trained to detect when epileptics are about to have seizures and things like that. They have remarkably good rates at being able to be trained to sniff for cancers and other things. It's not mystical in the slightest — they have extremely powerful sensory organs and they are interested enough in humans to use them in ways that happen to be useful for us. --Mr.98 (talk) 20:56, 16 May 2011 (UTC)
The migraine example doesn't seem to match, though, because I see no reason for the affected area to release a smell through the skull. I suspect your dog either noticed a warm area or saw you were rubbing at it, and decided to give it "special attention". StuRat (talk) 21:04, 16 May 2011 (UTC)
We had a dog that was a brilliant early warning system if my brother and I were up past our bed time when our parents were out. When our dog would get really restless and run around the yard we knew we had a minute or two to kill the tv and lights and get in bed. It could obviously hear the car from a mile away. There was also a fantastic mythbusters episode on sniffer dogs, if I didn't trust mythbusters was genuine, i'd suspect foul play, it's almost unbelievable what they can do. Vespine (talk) 23:02, 16 May 2011 (UTC)
StuRat, their "smell" capacity is truly uncanny. There are stroke dogs that can smell strokes long before they happen. There's obviously some kind of delicate chemical release (hormones or whatever) involve that is well beyond really obvious chemical releases. Who knows what migraines (or their side effects) put into one's sweat or other glands? I would hardly be surprised by it unless one were truly an expert on these sorts of things. --Mr.98 (talk) 02:14, 17 May 2011 (UTC)
Humans have a sense of smell orders of magnitude less acute than that of dogs, but I can "smell" when I have pneumonia, so it should be quite easy for dogs to sniff out a variety of infections and other maladies. Training them to indicate clearly what they have smelled is the real challenge. Edison (talk) 02:18, 17 May 2011 (UTC)
Instead of having a single dog trained to sniff out multiple things and then try to communicate what they smelled, the usual approach is to train each dog to sniff out just one thing. That way, if the dog "goes on point" or otherwise alerts, you know it smelled that thing. This would mean you'd have to have several dogs sniff over each patient, though. StuRat (talk) 06:19, 17 May 2011 (UTC)
Dogs can detect when a diabetic's blood sugar is getting low. source I knew a family whose kid had such a service dog. Not sure if they smell the insulin (or lack thereof) or a difference in the person's body because of the surplus/deficit of insulin. 20.137.18.50 (talk) 21:15, 18 May 2011 (UTC)

Aberration[edit]

According to http://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html, it is possible that a light from a star behind an observer can reach the eyes in front of the observer [if the observer is moving at a high fraction of the speed of light (forgot to write this initially)]. How is this possible? 74.15.138.241 (talk) 20:32, 16 May 2011 (UTC)

It happens when the speed of the observer is higher than the component of the speed of light along the direction of the motion of the observer (The component can be smaller than c since it's only one out of three components). Dauto (talk) 20:55, 16 May 2011 (UTC)
(ec) The obvious answers are a reflection or being bent 180° around a massive object, like a black hole, but that article seems to be talking about the effects on a traveler moving at (near) the speed of light. StuRat (talk) 20:59, 16 May 2011 (UTC)
Our articles on this are relativistic aberration and relativistic beaming, and this external page[7] has a good explanation. Red Act (talk) 21:02, 16 May 2011 (UTC)
From what I understood of the articles, from the observer's perspective the moving stars will emit their light in thin cones along their line of motion...but the stars will still be behind the observer, so how does the light reach them? 74.15.138.241 (talk) 02:05, 17 May 2011 (UTC)
With respect to the instantaneous inertial rest frame of the receiver at the time of reception, the angles are correct: the stars were in that direction at the time they emitted the light. They aren't in that direction "now"; they're farther behind the receiver than they used to be. In order to have a homogeneous distribution of stars "now", most of them must have been in front of you when emitting the light. It is pretty confusing.
I don't recommend the "C-ship" web site. The images are not accurate. The animations here are mathematically accurate, but not necessarily very helpful. -- BenRG (talk) 03:52, 17 May 2011 (UTC)
What if you were initially at rest with all the stars evenly distributed, and then you accelerated very quickly to a high speed?
And why are the images inaccurate? Is it because they don't include all effects? 74.15.138.241 (talk) 04:45, 17 May 2011 (UTC)
What happens in the situation you describe is that although the star starts out behind you, the star has been emitting light for a very long time, and some of that light that the star has been emitting is in front of you. So if you move very quickly forward, you basically run into the light that's in front of you, even though the star is never in front of you in this scenario. It's possible to catch up to and overtake the light that's in front of you, because the light that you catch up to isn't traveling in exactly the same direction you are, so the component of the light's velocity in the direction you are traveling is less than c, as Dauto pointed out. Red Act (talk) 06:46, 17 May 2011 (UTC)
Of course, if you're moving in the +x direction on the x axis in your inertial frame of reference, and the star is in the -x direction exactly on the x axis, then it would be impossible to catch up to the light in front of you, because the light in front of you on the x axis is in that case moving away from you at speed c. In order for it to be possible to run into the light ahead of you, the star has to be somewhere off of the x axis, so that the light it produces crosses the x axis at a nonzero angle. Red Act (talk) 07:25, 17 May 2011 (UTC)
Ah, that makes sense. Is there a way to calculate the change in angle? 74.15.138.241 (talk) 01:23, 18 May 2011 (UTC)
The relativistic aberration article has the pertinent formula. Red Act (talk) 04:08, 18 May 2011 (UTC)

Cervical spondylosis/hypertrophy, neural foraminal stenosis - parts of the body affected[edit]

C5-6 bilateral uncovertebral hypertrophy causing narrowing of neural foramen bilaterally.

C6-7 asymmetric right neural foraminal stenosis while left neural foramen preserved secondary to posterolateral osteophyte.

Upper discs and C7-T1 unremarkable. Facet joints and vertebral body alignment normal.

I am wondering what parts of the body might be affected by the compression of the affected nerve roots; and if this condition can cause compression of the spinal cord itself. Many thanks in advance. bcatt (talk) 22:02, 16 May 2011 (UTC)

It appears that you are asking us to interpret the results of an individual's imaging study, which would be inappropriate for us to do. This is really a situation where "clinical correlation is recommended," meaning that the person's doctor can explain what it means and whether any part of that person's body could be affected. We do have articles on spondylosis and cervical vertebrae that may help with general questions, but any specific information related to an individual's condition would violate our rules on giving medical advice. --- Medical geneticist (talk) 23:06, 16 May 2011 (UTC)
Agreeing that we're in no position to do amateur diagnoses based on text results of an unspecified exam, I've taken the liberty of Wikilinking some of the structures you mentioned - as you see, Wikipedia isn't completely terrible with anatomy. Our article on the spinal cord offers a generalized breakdown of the main innervations. Wnt (talk) 04:11, 17 May 2011 (UTC)
Thanks for the responses. I was worried this might be mistaken as a request for medical advice, but I have had it interpreted by a GP (it's going to be a long wait to see the specialist), and have been doing some research myself on all the terms so that I know the mechanics of what's going on so I can identify, prevent and manage symptoms in the meantime (based on what I learn in my research and what information I was able to get from the GP), but was having trouble finding info and diagrams of the involved nerves. Brachial plexus, and cervical spinal nerve 6 and 7 were what I was after. However, I am still having difficulty understanding the term "uncovertebral", or where exactly "posterolateral" is referring to, which is why I am not sure if the spinal cord is involved. I'm sure the info I'm asking for is somewhere in one of the articles I've read, but I'm having trouble finding layman-friendly explanations. bcatt (talk) 04:36, 17 May 2011 (UTC)
Well, as usual WP has an article about uncovertebral joints. 'Posterolateral' is the indication of a position of any part of the body, for example skull, trunk, or spine where posterior means 'at the back' and lateral means 'at the side'. So 'Posterolateral' would be not quite at the back and not quite at the side. The term can be further qualified as left or right. Richard Avery (talk) 07:19, 17 May 2011 (UTC)

Nonlethal weapons for use on large animals[edit]

Are there any ? I suppose mail carriers have mace, etc., to deal with dogs, but I'm more concerned about rangers in animal reserves which occasionally have to shoot bears, wolves, tigers, lions, elephants, rhinos, etc, when they attack. This seems to run counter to their mission of preserving those species. Perhaps mace could still work, but you'd need the ability to spray it much further. Then there are stun guns which shoot electrodes at the subject. Loud sounds (air horn with a parabolic "cone" ?) and lights (lasers ?) might also work, but it seems like inflicting pain is important to teach those animals to avoid people from then on (both for the sake of the people and the animals). There are tranquilizer darts, of course, but those are too slow to stop a charging animal. So, I'd like to know if anybody is working on this niche market. StuRat (talk) 22:27, 16 May 2011 (UTC)

Brown bears can be repelled with pepper spray; that article says that spray cans designed for use against bears can be effective as far as 8m away. Personally I have my doubts about pepper spray, as in lower concentrations it seems more like a garnish than a deterrent, like a fish releasing a cloud of lemon juice and cream cheese to defend itself against humans. That article also talks about thwacking the bear's arse with wooden pellets from a slingshot (but do we really want to annoy it?) -- Finlay McWalterTalk 22:37, 16 May 2011 (UTC)
I agree. We need a method guaranteed to protect the human. StuRat (talk) 00:08, 17 May 2011 (UTC)
My understanding, from a relative's trip to Africa, is that the rangers there are extremely canny and know pretty well how to avoid trouble 99% of the time with said animals. They carry a gun for that 1%. I'd say that's a pretty good tradeoff — it's easier to avoid having an animal charge at you in the first place (because you know how the animal will act, because you work with them on a regular basis) than trying to engineer some sort of way to stop said animal non-lethally. --Mr.98 (talk) 02:12, 17 May 2011 (UTC)
Even if rangers only shoot animals 1% of the time, that still might have an effect on their numbers. It would be nice if they had a non-lethal option. StuRat (talk) 06:15, 17 May 2011 (UTC)
One of the problems is there is unlikely to be any way guaranteed to protect humans. It's not like less lethal weapons are guaranteed to work against humans. There are plenty of stories of people being shot or whatever after less lethals weapons like tasers are deployed but fail. With situations involving humans, given the usual ability to communicate, the greater importance given to human life, the fact multiple officers may be involved, the speed of advance, how quick lethal options are likely to work and other factors this is often an acceptable trade-off with officers or whatever usually making a decision when they have both less lethal and lethal options available (and the possibility of being charged if they make the wrong decision). With endangered animals it seems less likely the trade-of would be accepted. BTW I don't see any reason to think bears would particularly like pepper spray even in lower concentrations (in other words you're more likely to annoy them) Nil Einne (talk) 06:44, 17 May 2011 (UTC)
Of course, lethal weapons don't always stop an attacker, either. Gunshots in certain areas may not stop an attacker, whether human or animal, even if they later prove to be fatal. Since bullets aren't specifically designed to cause severe pain or otherwise distract or disable an attacker, there might even be nonlethal weapons with more "stopping power' than lethal ones. StuRat (talk) 07:56, 17 May 2011 (UTC)

A one-legged companion. Cuddlyable3 (talk) 08:52, 17 May 2011 (UTC)

? StuRat (talk) 15:41, 17 May 2011 (UTC)
He's referring to the old joke about outrunning bears. You don't need to outrun the bear, you really only need to outrun your slowest companion. On the serious topic, I agree that the concerns mentioned above are probably why people continue to have lethal weapons available when in areas with dangerous animals. Try the pepper spray, sure, but have a very large gun on hand in case it doesn't work. Friday (talk) 15:59, 17 May 2011 (UTC)
I'm not sure if pepper spray has the range to stop an animal before it gets to you. Perhaps a single weapon with both lethal and nonlethal options would be best, where it can quickly be switched between the two. StuRat (talk) 16:13, 17 May 2011 (UTC)
There's a joke about what you need to know in bear country. First, it says, you should always carry pepper spray, and wear little bells to avoid surprising the bears. Then, you need to be able to tell the difference between the scat of black bears and grizzly bears. Black-bear droppings are full of roots and berry seeds. Grizzly-bear waste has little bells in it, and smells like pepper. --Trovatore (talk) 21:42, 18 May 2011 (UTC)