Wikipedia:Reference desk/Archives/Science/2011 October 14

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October 14

Is this a viable method for calculating two-body tension?

Hi. This is not a homework question. I have looked at some force-tension calculations, and determined the following method for calculating tension. For a (simplified) scenario involving two objects connected via a tensile non-elastic tether (ie. steel or nylon), in which an applied force (horizontal or gravitational) is exerted on object A, and object B is being accelerated solely by the rope or tether connected to object A; the entire system is accelerating at the same magnitude:

• First, find friction on mass A by multiplying the kinetic friction coefficient on object A by the mass of object A, multiplied by the normal force acceleration on mass A. For objects in free fall (ie. when object A is held vertically), the frictional force is zero (negating air resistance and tension via mass B).
• Subtract this frictional value from the applied force exerted on mass A. This is the net force on mass A (F_netA).
• Divide the F_netA by the mass of object A, to determine the "unimpeded" acceleration of the mass, without the attachment to object B. For object in free fall, this value is ~9.8 m/s².
• Next, multiply the total mass of both objects by the frictional coefficient (unless of course, only object B is experiencing a frictional force, in which case only the mass of that object is used), then multiply by the normal force acceleration (equal to gravitational acceleration perpendicular to surface). This is the total frictional force (...actually, skip this step when only mass B has friction).
• Subtract the total frictional force (unless ignored) from the applied force exerted on mass A, and also subtract any vector applied force (including gravity) exerted on mass B that counteracts the applied force on mass A. This is the total net force (F_netT), and will likely differ from F_netA.
• Calculate the acceleration in the entire system, via dividing the F_netT by the total mass (m_T), assuming the tether is weightless. This is the net effective acceleration, the acceleration in the direction of object A at which the system is actually moving, or "a_net".
• Subtract a_net from the "unimpeded" acceleration of mass A. This will be called the "tensional acceleration" (a of F_T, or the effective acceleration that prevents mass A from accelerating at its "unimpeded" acceleration after friction. This tensional acceleration is caused by the inertia from mass B.
• Multiply the "tensional acceleration" by the mass of object A, that is, removing the (shared) tensional force solely from object B. This is a tensional force.
• Finally, for systems that only have friction upon mass B, add the frictional force from that mass to the previously calculated force, to determine Tension (F_T).

How well does my method work? Moreover, are there circumstances in which this method is invalid, and does it also apply to pulley systems? Thanks. ~AH1 ^(discuss!) 00:11, 14 October 2011 (UTC)

I think you have essentially described the calculation of net force on each body (though, your explanation implicitly assumes certain characteristics, such as a particular model for friction). (And, with all due respect, I think your explanation is a bit convoluted, because you are not treating each body separately, yet you are not using a convenient formulation that would make coupled motion analysis very easy - e.g., modal analysis or eigenfunction decomposition for the system). Setting up the net forces on each body is the first step in setting up a statics problem. In the general case, you must define, and then solve, a system of equations that specify all the constraints you are modeling. More sophisticated modeling of physical scenarios require the solution of more simultaneous constraint equations; and each individual equation is more complicated; until finally you reach, say, the complexity of finite element modeling that requires a computational solution.

I think you may benefit from reading our article on the Free body diagram. This is a conceptual and pedagogical tool to help introduce the formulation of statics problems, without requiring any difficult mathematics. Nimur (talk) 00:47, 14 October 2011 (UTC)

Will the two giant stars of Capella merge?

Capella consists of 4 stars, two of which are on their way of becoming red giants, and these two are orbiting around each other at a distance of just 100 million km. Count Iblis (talk) 01:16, 14 October 2011 (UTC)

They may simply temporarily share an envelope. Dauto (talk) 01:51, 14 October 2011 (UTC)

(ec) Roche lobe and Binary star#Configuration of the system are two good articles to start with. --Dr Dima (talk) 01:53, 14 October 2011 (UTC)

Would the merging of such a system be an exceptionally bright event? How would it compare to supernova? —Anonymous Dissident^Talk 07:07, 14 October 2011 (UTC)

The sharing of gas will depend largely on the timing of their transition to red giants or supergiants. FWIW, Type Ia supernovae are caused by the accretion of an giant star's gas upon a white dwarf star, which can occur if timing differs greatly. When a binary star system spirals inward, collision sometimes occurs resulting in a supernova or perhaps hypernova, but most of these are theoretical speculations. ~AH1 ^(discuss!) 22:17, 14 October 2011 (UTC)

A type 1a supernova at the Capella system would have an apparent visual magnitude of -18.7, about 250 times brighter than the full Moon. Count Iblis (talk) 23:31, 14 October 2011 (UTC)

Of course, one would need to factor in the radial velocity and extrapolate Capella (or any other exploding star)'s position to determine future (or past) distance. ~AH1 ^(discuss!) 22:09, 16 October 2011 (UTC)

Neurosurgery questions

I watched This video of cyst removal on youtube. I have a few questions.

• What tool did they use to cut the skull? How did they put the skull back together (adhesive-wise)? Does the fact that the patient was a child affect what they use?
• What will happen to her brain? Will it expand to fill the cranial cavity? How does that work?
• Most likely cause of infection is drinking dirty water, right?

Thanks. --70.122.122.218 (talk) 09:44, 14 October 2011 (UTC)

I don't know the surgical details, but from the title this is a hydatid cyst. I marvelled at the willingness of the surgeons to simply allow the cyst to fall out of the skull - looking at the little pink patch stuck to the rear end of it, I was thinking, "No, no, no, don't tug on that. You never know what it might be attached to."^[1] But (neglecting that little bit of pink) in theory this cyst is actually the parasite, not the body's reaction to it! (Contrast arachnoid cyst, etc.)

The brain is capable of growth, but it is slow and pretty limited.

From the article, the infection is from eggs in the feces being ingested. Wnt (talk) 14:10, 14 October 2011 (UTC)

Levers

Hi. Our article on levers says that they work by multiplying force. However, this force must actually come from somewhere, since this force can't just appear "from the void", can it? What is the origin of the additional force of levers? Thanks. Leptictidium (mt) 13:49, 14 October 2011 (UTC)

It isn't creating new force. It is changing the work done. If you want to lift something heavy, you do a little work over a large distance and the lever concentrates that work over a small distance. The result is that the force is multiplied because the total work (unchanged) is concentrated. Knowledge of levers predates written history, so any date when they were first discovered is pretty much a guess based on archaeology. -- kainaw™ 13:54, 14 October 2011 (UTC)

(ec) Kainaw's answer is essentially correct, but one should be careful in using the term work, as it has a specific meaning in physics. (Our article is pretty thorough, though it might get a bit dense at times. For the purposes of this discussion, you won't go wrong if you just think of 'work' as the total amount of energy transferred from one body to another.) As Kainaw says, the amount of work done is the same at both ends of the lever—the work done by you on the lever is equal to the amount of work done by the lever on whatever object you're lifting. To be absolutely clear, when he says that a lever "[changes] the work done", he means that the way that work is accomplished is different, not the total amount. A small force over a large distance (your end of the lever) represents the same amount of work done as a large force over a small distance (the object's end of the lever). There isn't any magic here; it makes intuitive (and mathematical) sense that lifting a bowling ball an inch or two is the same amount of work – consumes the same amount of energy – as lifting a tennis ball over your head. TenOfAllTrades(talk) 14:18, 14 October 2011 (UTC)

There is no "law of conservation of force". There is, however a "law of conservation of energy". Work is basically energy (the distinction is semantic for the level of discussion we are having here; some physicist will come by immediately below and explain, in details unnecessary to understanding the concepts to answer this question, how very wrong this is, but go with it for now), work = force x distance. Thus, for the same amount of work, force and distance are inversely related: if you increase the distance over which you apply a force, you can multiply the effect of a certain "input force" to produce a proportionally greater "output force". All simple machines operate this way. For the lever, if you want to lift an object that weighs 100 newtons a distance of 1 meter, but you can only exert 50 newtons of force yourself, you position your lever so that you can push down on the lever at least 2 meters, and you will only need to exert 50 newtons of force. The work output = the work input (100 x 1 = 50 x 2), but it is functionally easier for you to do that work because the limiting factor in this case is how hard you can push; you effectivly reduce that by using the lever. You can't gain without losing something, and what you lose here is that you need to move the lever farther. --Jayron32 14:14, 14 October 2011 (UTC)

It is instructive to consider the question of "where the force is coming from", directly. When all acceleratons are zero, the total force exerted on any arbitrary region of the system is zero. This means that you do have "conservation of force", so forces do come from somewhere in such cases. In the case of the lever, to account for the force exerted on the large mass, you need to take into account the force exerted by the suspension at the pivot point on the lever. Count Iblis (talk) 15:25, 14 October 2011 (UTC)

It's strange that levers seem so magical, when other similar situations are so intuitive. For example it's obvious that carrying heavy buckets of water for a short time = carrying small buckets of water for longer. Wnt (talk) 01:52, 15 October 2011 (UTC)

Using that as an example in the article probably helps a lot. Joepnl (talk) 00:12, 17 October 2011 (UTC)

Transplanting external human body parts

I just finished watching the latest episode of Grey's Anatomy (because I like watching things crash and burn) and they were doing a penile transplant. They don't normally do external transplants, so this got me wondering. How long does the pigmentation of such donor parts take to change to the same color as the lost appendage would have? Is it at least partially dependent on the number of capillaries? Dismas|^(talk) 15:34, 14 October 2011 (UTC)

OT and OP complained Nil Einne (talk) 17:11, 14 October 2011 (UTC)

I don't see much use on a penile transplant. Wouldn't they try to reconstruct a lost appendage with tissue of the patient? Quest09 (talk) 15:52, 14 October 2011 (UTC) The TV show claimed that reconstructed versions aren't sexually responsive, and that trying to restore normal function was the motivation for trying a transplant. They also admitted that transplants risk rejection, etc., unlike traditional reconstructions. I don't know whether real doctors would ever try such a thing, but this is a fictional show that likes drama. Dragons flight (talk) 16:05, 14 October 2011 (UTC) Neither of you checked Penis transplantation then? I also found a recent mini-review of the ethical issues here [2]. That source notes that the hospital which performed the first and only attempt, now have a guideline which amongst other things (now added to our article): recommended that the procedure be restricted to individuals with severe injuries who are unwilling to undergo traditional reconstructive surgery It doesn't really discuss why someone may reject traditional reconstructive surgery but it does note some of the social, emotional, pscychological and cultural issues in China. I guess such considerations (whether in China or elsewhere) could lead to a patient rejecting a reconstructed penis even with significant counciling etc, but willing to take the risk with a transplanted donor one one. BTW, earlier back it mentions Penile reconstruction using microsurgical techniques is feasible and can result in the preservation of sensation and sexual function I checked out one of the refs for that statement and found it says reported the successful development of erogenous and tactile sensation in all of 12 patients in whom coaptation of flap nerves to the pudendal nerve was completed. Reading more careful, I realised it's not clear if this is referring to reconstructions needed due to trauma or female to male reassignment, but a brief check of [3] confirms some of the patients were reconstructions following trauma. This makes the Grey's Anatomy claim seem a bit questionable, although I don't think anyone here would be surprised by that. However Phalloplasty isn't quite so rosy, but it isn't sourced directly so it's difficult to check. P.S. Am I the only one confused by "participate in a multifaceted rehabilitation program (for example, physiotherapy, speech therapy)" in the first source? Nil Einne (talk) 16:37, 14 October 2011 (UTC)

I don't see where any of the links provided answers my question. Thanks, Dismas|^(talk) 16:57, 14 October 2011 (UTC)

Sorry for the confusion, I was referring solely to Df's and Quest09's statements (hence the 'neither' rather then a 'none') which I appreciate are OT to your question, as it doesn't really concern penile transplatation per se anyway. I was going to mention the ethical mini-review source doesn't say anything about any colour or pigmentations issues but neglected to as I decided it may be obvious. Nil Einne (talk) 17:11, 14 October 2011 (UTC)

Back to the original question, while this is more of a guess since I can't find many sources discussing the issue, is there any reason to think the donor part will change to match? Since basically the entire structure and definitely the epidermis is going to come from the donor, it seems likely the structure will largely remain the same pigment. Even more so if it's something not exposed to the sun much (therefore sun exposure of the structure between the donor and recepient isn't going to vary much).

In other words, it would seem to me this is more of a 'choose the best pigment match available (well combined with the best matching in other relevant areas)', 'hope for the best' (there's probably some risk of unpredictable pigmentation changes) and then manage any hopefully minor mismatches via cosmetic procedures as best as possible (at the very least you'd have to consider how to manage scarring). [4] notes the need for a pigment match for hand transplants although in that case there are significant functional advantages which likely help reduce concerns about cosmetic issues. Can't find any discussion for face transplants. Slightly relevant, even for skin autografts [5] getting a good pigment match is suggested. I presume that's more for full-thickness grafts as [6] notes with split-thickness grafts, pigmentation can be a problem.

Edit: Sorry at some stage I stopped searching for 'colour'. Anyway perhaps not surprisingly [7] [8] note the need for similarity of colour in choosing face transplant donors. BTW, I hope my understanding is correct you're referring to the colour being similar to the patient, not the colour looking like living tissue (many sources coming soon after transplantation mention how the transplanted structure has started to take on a healthy pink colour).

Edit2: Also came across [9] which may be of slight interest as it mentions how a new experimental technique of spraying on skin for a (auto)graft, enabling a better colour match since you only need a small piece of skin. All in all, these seem to support my original conclusion, your best bet for a good match is to ensure you get the right match in the first place.

Nil Einne (talk) 18:10, 14 October 2011 (UTC)

Skin color is caused by local production of melanin at the cellular level. Human skin color It doesn't spread around or people would not have freckles or other more obvious coloration issues. Chose the color of your penis donor carefully. μηδείς (talk) 18:33, 14 October 2011 (UTC)

I see. Thanks all! To answer the assumption question that was posed back at me, I figured that as cells die off and get replaced that they would be replaced with cells with the DNA of the... erm... donee? (seems to be a word!) And as they have the donee's DNA, the skin color would match the lost appendage. But apparently I misunderstand how these things work. Dismas|^(talk) 01:27, 15 October 2011 (UTC)

There are a few hormonal influences, such as POMC (melanocyte stimulating hormone) which might lead to a slight trend toward color matching in a transplanted body part. Whether they matter enough to actually notice, I can't say. I just read that skin donation for burn victims doesn't require color matching, ^[10] presumably because that involves an uppermost layer; but of course the entire skin thickness is involved in this question. Really, apart from a few high profile hand transplants and face transplants of late, I can't really think of many real world transplants where this kind of boundary between full-thickness donor and recipient skin would be visible. Maybe going through photos from some of these famous cases something interesting might turn up - I wouldn't be surprised if melanocytes turned out to be more mobile than expected. Wnt (talk) 01:49, 15 October 2011 (UTC)

My guess from the sources I provided above in particular [11] (while referring to autografts) is that one of the reasons they may not bother with matching for split thickness skin allografts is because there's no point. Such grafts tend to end up abnormally pigmented anyway but since they are some important functionally it's an acceptable tradeoff in many cases. Also from [12] and looking at the site you linked to, it's not clear to me if the intention is for the allograft to be kept for ever or if it's just used as temporarily for protection and to allow for healing etc until autografts can be carried out. (Obviously if the allograft is just temporary, matching is even less important.) Nil Einne (talk) 13:25, 15 October 2011 (UTC)

BTW I realised no one properly clarified this but the structure will largely remain cells with the donor's DNA forever. Yes cells in the structure will die, but new cells in the structure will generally come from cells in the structure so will of course remain cells with the donor's DNA. This is why the recepient will need to take Immunosuppressive drug for life and one of the reasons why such transplants are very serious procedures with life long risks. Nil Einne (talk) 04:34, 18 October 2011 (UTC)

Photons in an empty universe

I believe the editor Dauto mentioned in a previous answer that from the point of view of a photon, the universe is flattened into a 2D pancake, with the photon being emitted and absorbed at the same moment. That is pretty amazing. My question, however, is what would it "look like" from the point of view of a photon in an otherwise empty and boundless universe, with no place for it to be absorbed? --Goodbye Galaxy (talk) 16:13, 14 October 2011 (UTC)

You might be interested in Penrose diagram where an infinite time is scaled to something finite - and you can then stick another infinite amount after it. But as to your question how can it 'look like' anything without time, what do things look like to you when you are asleep? Dmcq (talk) 16:50, 14 October 2011 (UTC)

Things don't "look" like anything to a photon. We humans use our brains to perceive visual stimuli - photons - that bounce off of things in coherent, focused ways, forming images.

Photons are localized perturbations of electromagnetic fields. They don't see anything - they can't perceive anything - they either interact with the outside world, changing the values of the electric- and magnetic- fields, or they don't. So, in an empty universe, I think the best we can say is, "the electromagnetic fields would behave in a way described by the unforced Maxwell's equations." Nimur (talk) 17:38, 14 October 2011 (UTC)

Humans use their brains to perceive visual stimuli!? Thank god for the science desk! Kidding aside, we can also use our brains to imagine travelling alongside a photon, and can attempt to visualize the experience, just like we can visualize neutrinos, even though there's no way to actually see them. --Goodbye Galaxy (talk) 20:35, 14 October 2011 (UTC)

You may be interested in extinction. ~AH1 ^(discuss!) 22:08, 14 October 2011 (UTC)

For any finite length of time, it still "looks" like a flat pancake - the photon is just emitted, not absorbed. For an infinite length of time, the pancake has thickness infinity/infinity (the inverse of 0/0, I suppose) ... unless the photon reaches an energy of precisely zero due to redshift in a less infinite period of time, that is. Really though, we're not so good at calculating infinitely far forward in a universe where all is finite and changing. Wnt (talk) 14:12, 15 October 2011 (UTC)

When your maths is giving you infinity/infinity or 0/0, you need to stop. That means something has gone wrong. Basically, the usual methods don't apply to massless particles. There simply is no meaningful proper time for a photon. Trying to describe what happens from the perspective of a photon isn't going to give meaningful answers (although, as the story goes, it was such a thought experiment that first gave Einstein the idea for special relativity, so it isn't without some use). --Tango (talk) 00:51, 16 October 2011 (UTC)

First: The proper time for a photon is not given by 0/0, it is given by t*0 which is perfectly fine

Second: 0/0 is meaningless, true. But the limit A/B can often times be calculated even when both A and B are zero at the limit. For instance, that's what is done when calculating a derivative. Dauto (talk) 01:40, 16 October 2011 (UTC)

Ach, you take me too literally. But a limit was what I was hinting when I said it would have thickness zero for any finite time. And yes, of course, the math breaks down. Wnt (talk) 21:26, 16 October 2011 (UTC)

The photons in the empty universe may collectively experience something similar to what you are experiencing right now sitting in front of your PC. The universe will after all evolve toward a state in which there are only photons and neutrinos in the far future. This means that there exists a unitary map from such a future state back to the current state. Now, the principle of functional artificial intelligence says that for subjective experiences it doesn't matter on what type of hardware the program that renders that subjective exprience is run or on exactly how it is run. Because the future state can be re-interpreted as the current state via the time evolution map, it then follows that our subjective states also exist in that future state. Count Iblis (talk) 01:47, 16 October 2011 (UTC)

According to relativity theory, an observer travelling at the speed of light should see all relative clocks to be frozen in time, except for their own clock. Thus, a photon perceives a universe, through field interactions, to be frozen in time. A photon in itself does experience the passage of time between emmision and absorption. Plasmic Physics (talk) 02:10, 16 October 2011 (UTC)

That's not right. From the point of view of the photon it is emitted and absorbed simultaneously at the same place. No time elapses between emission and absorption. Dauto (talk) 14:29, 16 October 2011 (UTC)

So, photons don't exist, they just an illusion? Plasmic Physics (talk) 22:15, 16 October 2011 (UTC)

I'm just saying, that if something is created and destroyed with no time passing, then is equivalent to saying that it never existed in the first place. It should mean that a photon is an abstract and imaginary particle, it is simply a way to measure the time it takes for a quantum of energy to be exchanged over a distance that connects two points along a path. This in turn means that from the moment of emmission to absorption, the energy quantum does not exist, yet it's final coordinate where it is absorbed still affected. It sounds like energy teleportation to me, there should be no experimental way to prove that the photon doesn't exist between points event E and event A, since any attempt to observe the photon will result in event A. I'm saying that this is a logical theoretical conclusion from your above statement. Plasmic Physics (talk) 09:43, 17 October 2011 (UTC)

Look, at some point, your question ceases to be scientific and becomes purely teleological. What do you mean by "illusion"? Photons are one particular model of the physical phenomenon we call light; they represent spatially-localized, quantized packets of energy in the form of a propagating disturbance of interacting electric and magnetic fields. Are they an illusion? I mean, I don't think so - you can see them - so, they are "real..." but the definition of "real" is pretty arbitrary. In physics, all we care about is "repeatability" and "quantifiability," which are arguably distinct, philosophically, from "real." Nimur (talk) 18:54, 17 October 2011 (UTC)

Read the latter paragraph, it explains the former question. Plasmic Physics (talk) 23:05, 17 October 2011 (UTC)

Dingoes vs. rabbits in Australia

Yikes.

Why haven't dingoes been a significant way to help control the Rabbits in Australia problem? Comet Tuttle (talk) 16:57, 14 October 2011 (UTC)

Because they have no reason to preferentially target rabbits as opposed to other prey. Might be able to get some giant toads to help, though.μηδείς (talk) 17:28, 14 October 2011 (UTC)

Well, one reason might be that it appears you can't walk ten meters in the outback without tripping over twelve rabbits, judging from the Rabbits in Australia article. Comet Tuttle (talk) 18:33, 14 October 2011 (UTC)

Shirley a large number of the rabbits in that picture are dead by now. μηδείς (talk) 20:38, 14 October 2011 (UTC)

• Who is Shirley? And what has she to do with the whole thing? Quest09 (talk) 21:32, 14 October 2011 (UTC)

White farmers thought dingoes were a pest right from the start, and shot them close to extinction very early on. Rabbits were actually introduced as a positive thing. HiLo48 (talk) 20:42, 14 October 2011 (UTC)

It's duck season! Clarityfiend (talk) 20:58, 14 October 2011 (UTC)

Another perspective - dingoes don't breed like rabbits. HiLo48 (talk) 21:21, 14 October 2011 (UTC)

Dingoes limit the population of rabbits, but, as an apex predator in nature (that means, excluding humans, who tend to hunt dingoes down), also the population of other predators like foxes and feral cats. Consider also that since dingoes prey on rabbits, a decrease in the number of rabbits will also imply a decrease in the number of dingoes, and therefore, an increase in the number of rabbits. Wikiweek (talk) 22:50, 14 October 2011 (UTC)

What surprises me more is that people don't limit the number of rabbits. After all, rabbit is theoretically edible - I'd have thought some companies would have started netting them and processing them into at least pet food, if not a new flavor of SPAM, and (barring protective legislation) hunted them to extinction. ;) Wnt (talk) 12:59, 15 October 2011 (UTC)

During the Great Depression rabbits were extensively hunted for food and became known as "underground mutton". Didn't drive them to extinction though. HiLo48 (talk) 00:32, 16 October 2011 (UTC)

Hmmm, upon reading the article it's apparent why. Australia may be overrun by excess rabbits, but the Chinese apparently still farm them and produce cheaper exports! Wnt (talk) 14:07, 15 October 2011 (UTC)

Tack-on question: I've heard that the AU rabbit population has fallen dramatically in the last 5-10 years, following the introduction of a rabbit pathogen. The story goes that the official release of the pathogen was politically contentious, so some vigilant type just released a few infected bunnies and let nature take its course. Anyone have info on the veracity of this story, or the disease in question? SemanticMantis (talk) 14:59, 15 October 2011 (UTC)

I think you're talking about myxomatosis. --Tango (talk) 00:48, 16 October 2011 (UTC)

No, myxo was officially and formally released by the government, Frank Fenner did a lot of work on myxo. The illegal pathogen release was Calcivirus: Rabbit_haemorrhagic_disease#Australia. Fifelfoo (talk) 00:54, 16 October 2011 (UTC)

After reading up on that a bit, it sounds like the release was an "accident", in the sense that trusting that a 300 meter rabbit free zone and picking up carcasses within a day will keep crows from spreading it to outside the site - after it's already gotten out once before - is an accident. But shortly afterward it was determined to be a new form of a non-pathogenic virus already widely distributed in the wild rabbits.

While disturbing, it looks like the species specificity is pretty tight for that virus. What is more worrisome is that it very abruptly went from non-pathogenic to a lethal plague ... and the norovirus spreading around on cruise ships is related to it. There's a vaccine in early clinical trials for that, but I didn't see anything about a phase III study... Wnt (talk) 12:43, 16 October 2011 (UTC)

I'm not disturbed by dead bunnies, but rather by an uncontrolled release schedule. My assumption (from being a young tyke at the time, and the media reports) was that Calcivirus wasn't present in Australian rabbit populations—therefore the lethal plague. Same reasons why myxo didn't exist here. If they held Calcivirus back while finding a second pathogen, the double knock would be much more effective at killing bunnies than the single pathogen release. Now I'm imagining if Calcivirus and Myxo were released simultaneously... Bunnies in Australia are bad. But as seen with Cane toads attempts to import biological control mechanisms without policy lead by science result in horrors. Fifelfoo (talk) 01:01, 17 October 2011 (UTC)

Wnt: they also don't limit the number of dogs here in Europe, even thoguh strays are available for no cost, and you could even sell ones that people feed for a few months then throw out. Why? – b_jonas 17:25, 15 October 2011 (UTC)

Shuttle launch camera footage

Where can I get footage from individual cameras for Nasa shuttle or rocket launches? Is it available for download online? I can only find edited versions. Thank you. 200.89.138.70 (talk) 19:21, 14 October 2011 (UTC)

NASA is just ... it's just darned huge. There are hundreds of millions of images, videos, and technical data downloads. There are loads of ways to get loads of videos. Let's put it this way: even Google can't handle the sheer volume of imagery that NASA makes available. Here are some of the most useful places to start looking:

• NIX - the NASA Image Exchange search engine
• NASA Video Gallery
• Imagery released by the NASA Photography Office (typically geared towards "press" or "media" style images)
• Spaceflight.NASA.GOV, where you can search by individual mission. Usually, you can link to both image archives from individual cameras on science platforms, and a large "data dump" from all (or most of) the handheld cameras the astronauts used on a mission.

It's pretty rare that you want a photo from a specific camera - most of the time, you want a photo of a specific event or view. But, every so often (especially if you're a camera nerd), you may know of a specific camera (like the infamous Apollo Hasselblads) and you can use NASA's webpages to search for those images from that specific camera.

For example, I wanted to get some photos from the pair of iPhone 4`s that flew on STS-135; so I went to the Flight Day 14 gallery for STS-135. So far I have only been able to find images from the D3s and a few of the other hand-helds. It is not clear whether any images were ever captured from the iPhones on that mission. Most of the time, the really good imagery from the more recent shuttle flights comes out of the Nikon D3s the astronauts carried around inside the orbiter. NASA's mission page aggregates all the different photos; you can get individual camera and image names, and then waltz over to NIX and search for more.

Hopefully this points you in the right direction. Nimur (talk) 22:13, 14 October 2011 (UTC)

p53 damage and its frequency in cancers

A question I don't seem to be able to find an answer to, though it should be relatively easy. This is a question for my own curiosity--in the new movie 50/50 which came out recently (no spoilers) tumor protection gene p53 was referred to as a rare/medically surprising cause of cancer. I thought that this was not rare, it was one of the most common genetic etiologies of cancer (hence it's "larger than life" nicknames, like "Guardian Angel gene"). However, I don't seem to be able to find etiological information as to the prevalence of p53 damage being involved in cases of cancer. Anyone out there have sources? Or their own knowledge, for that matter?

Peace and Passion ☮  ("I'm listening....") 23:21, 14 October 2011 (UTC)

Our article notes under p53#Role in diseae that more than 50% of human tumors contain a mutation or deletion of p53, citing this article (free abstract, subscription required for full text). The exact number will depend on the type of tumor and the population studied.TenOfAllTrades(talk) 01:27, 15 October 2011 (UTC)

I haven't seen the movie, but note that while p53 mutations are common in tumors, they are commonly not the first cause of the tumor, but an important part of its progression to lethal malignancy. Li-Fraumeni syndrome in which one copy of p53 is mutated from the beginning, and multiple cancers arise, is much less common. Wnt (talk) 12:54, 15 October 2011 (UTC)

Prions

I read the article on prions, and I have to admit, I'm not afraid of germs, but those things on the other hand are a pretty terrifying concept. They seem to be much more dangerous/lethal than all but the worst "normal" infectious agents (at least in modern times), but I had never heard of them specifically until I stumbled upon the article and no one I mentioned them to had heard of them, leading me to wonder just how concerned should people actually be about prions? Ks0stm ^{(T•C•G•E)} 23:37, 14 October 2011 (UTC)

I find prions much less scary than viruses or bacteria. They are primarily transmitted through eating things. That's a rather limited mode of transmission and one that can be countered with strict food regulation practices. Viruses and bacteria can often be transmitted through simply being in the vicinity of someone who is infected. I find that a lot more disturbing, personally. Anyway, I don't know why you'd think them to be more infectious than other forms — Creutzfeldt–Jakob disease has killed less than 200 people worldwide, that's probably less than the number who get killed by elephants, and an order of magnitude smaller than those who get killed by influenza even in a non-pandemic period. What makes prions disturbing, I guess, is that we don't have any form of treatment for them. That's not good, but there are a lot of ways to die in this world, and that's not the most prominent of them by far. --Mr.98 (talk) 23:59, 14 October 2011 (UTC)

Um, not sure where you get your figures, but CJD has killed MANY more than 200 people worldwide; according to Creutzfeldt–Jakob_disease#Epidemiology there is about 1 case per 1 million people who get the disease worldwide each year; it is fatal 100% of the time, often within less than a year of contracting the symptoms. That's about 5000-6000 people per year who die from it, give or take. (On a personal note, I had a family member die of it recently, so I did a bit of research on it before). --Jayron32 03:06, 15 October 2011 (UTC)

I imagine that Mr98 is talking about vCJD, which is the variety of the disease linked to beef, mainly in the UK. The numbers are about right for that, although there is a suggestion that this infection route is also responsible for an increase in cases of the 'Sporadic' form of the disease. Figures for the UK are available here. Mikenorton (talk) 13:05, 15 October 2011 (UTC)

Mmm, yes, that might be right. In any case, it is still quite low as far as diseases go. That doesn't mean it's a great thing — and my apologies to your loss, Jayron32 — but when one is making comparative threat/risk assessments, things that are pretty rare (which 5000 people a year is) and don't spread rapidly rank a lot lower than many much more mundane things (traffic deaths, alcohol deaths, smoking, influenza, malaria, etc.). --Mr.98 (talk) 15:16, 15 October 2011 (UTC)

And this is an even nastier prion disease than Creutzfeldt–Jakob disease :( . Count Iblis (talk) 04:06, 15 October 2011 (UTC)

There are also much more nasty viruses than influenza (ebola, anyone?) but the fact that they are relatively rare makes one rank them lower in the grand view of threats. Again, there are a lot of really lousy ways to die, but your odds of dying from many of them are quite low. The diseases that keep me up at night (figuratively speaking) are the ones like the Spanish flu which don't have very exciting symptoms (you get a fever and then you die) but spread rapidly and kill huge numbers of otherwise healthy and low-risk people (e.g. not just the very old and the very young). The exotic and the horrific are only of particular concern if they are also combined with having great possibility for spreading. --Mr.98 (talk) 15:16, 15 October 2011 (UTC)

Are these all beef diseases? Dualus (talk) 07:37, 15 October 2011 (UTC)

No: see scrapie. --TammyMoet (talk) 09:46, 15 October 2011 (UTC)

The transmissible spongiform encephalopathies are all caused by a misfolded form of the same protein, inventively named the major prion protein (PrP) in the scientific literature. All mammals have a version of this protein, though not all are susceptible to disease. In cows it causes 'mad cow disease' (bovine spongiform encephalopathy: BSE); in sheep and goats it goes by scrapie, in deer and elk it's called chronic wasting disease. Minor variations in the PrP sequence from one species to another generally make transmission between different species a bit slower than it is between animals of the same species; some species are apparently completely immune. A very small number of humans carry a mutated form of PrP which is particularly prone to spontaneous misfolding; it causes the autosomal-dominant inherited disease fatal familial insomnia. TenOfAllTrades(talk) 18:02, 15 October 2011 (UTC)

Jerks and mental illness

Are the symptoms of people who are popularly called jerks considered a mental illness? (jerk: An insensitive, selfish, ignorant, cocky person who is inconsiderate and does stupid things.).Quest09 (talk) 23:47, 14 October 2011 (UTC)

In Australia we call such people bogans or ferals, and blame the parents. HiLo48 (talk) 23:50, 14 October 2011 (UTC)

Yes, but times change. Maybe it's a similar case of naughty children: now they have ADHD and even get drugs from their parents. Quest09 (talk) 23:55, 14 October 2011 (UTC)

See bullying, narcissism and impulsivity. ~AH1 ^(discuss!) 23:54, 14 October 2011 (UTC)

No, these people are metally superior to us, that's why we find them annoying and complain about them. Count Iblis (talk) 23:58, 14 October 2011 (UTC)

According to User:Count_Iblis, you are superior to us, so you (User:Count_Iblis) are a jerk. Wikiweek (talk) 00:03, 15 October 2011 (UTC)

Do you mean he's mentally ill? Quest09 (talk) 00:06, 15 October 2011 (UTC)

I divide them into two categories: "mere assholes," and the higher category of "screaming assholes," with the "screaming" being more likely manifested among the victims than among the assholes. Edison (talk) 00:44, 15 October 2011 (UTC)

Several of the categories in the sidebar I just added could be considered "jerks", in particular people who show so-called sadistic personality disorder (which is not, however, an officially recognized condition). Looie496 (talk) 00:55, 15 October 2011 (UTC)

Lateral question: The OP refers to "people who are popularly called jerks". I'm guessing that's in the USA. I am familiar with the word, although it's rarely used here in Australia. Is it still a relatively common term in America? HiLo48 (talk) 02:22, 15 October 2011 (UTC)

It's not extremely common, given that most people who are really displeased tend to use stronger language, but it's common enough in situations where stronger language might arouse the ire of the nanny brigade. SDY (talk) 02:44, 15 October 2011 (UTC)

Mental disorder is an unfortunate condition. Be thankful rather than critical - you'll never know.hydnjo (talk) 02:27, 15 October 2011 (UTC)

I think they would more likely fall into either of two categories: psychopaths or sociopaths. Not mentally ill, just "bad and dangerous to know". --TammyMoet (talk) 09:45, 15 October 2011 (UTC)

A robust exemplar of a psychopathic manipulator boss should be able to use a classic double bind, so you are in the wrong whatever action you take. Their style of mentorship covers the full spectrum from threat to warning. Edison (talk) 04:52, 16 October 2011 (UTC)