Wikipedia:Reference desk/Archives/Science/2011 February 7

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February 7

What happens when black holes collide?

I thought that there would be an almighty bang, with cosmic rays galore, and local solar systems devestated. Because I was thinking of a sun being sucked into a black hole. As it spiraled in, it would be spaghettified, ripped apart, and there would be an extremely powerful radiation that would be seen for galaxies around. But then I thought, with black holes, NOTHING can escape, not light, matter, nothing. So even the most powerful collision between two of them would hardly matter. Consider a technology superior to ours which, instead of sending two atomic particles on collision courses in something like the Large Hadron Collider, they sent two massive black holes, both at nearly the speed of light directly at each other. What would happen? No explosion. Maybe one would bounce of the other, or they would just integrate, like two blobs of paint. Much less dramatic than the collision of two suns. And no one around would notice, let alone be obliterated. Is that right? Myles325a (talk) 06:43, 7 February 2011 (UTC)

Although a collision of black holes doesn't give off matter or light, it does give off energy in the form of gravitational waves. In the most realistic case of a collision that isn't exactly head on, the two black holes will inspiral for a short time before they coalesce into a single black hole, and the gravitational waves produced will carry away angular momentum. The gravitational waves produced by the merger of two black holes also carries away linear momentum, producing a recoil on the merged black hole. In the case of the merger of two supermassive black holes, the recoil can be huge enough to wind up kicking the merged black hole out of its host galaxy. The ejected black hole can rip some stars away from the galaxy when it leaves, producing a hypercompact stellar system. See Gravitational wave#Energy, momentum, and angular momentum carried by gravitational waves. Red Act (talk) 07:58, 7 February 2011 (UTC)

The aftermath of two black holes colliding is formidable. During the inspiral, you'll have a moderate set of waves coming out, which increase somewhat exponentially with time. They reach their peak during coalescence, which is a short period of time where the two black holes become one. Then, there will be a dumbbell shaped black hole, which will 'ring down' into a sphere, emitting more waves. This pattern of waves (inspiral, coalescence, ringdown) is quite distinctive, and is one of the ways we can detect (colliding) black holes. The nature of the coalescence waves can give us an insight to black hole physics. In fact, there's a very large experiment called LIGO going on, which attempts to detect these waves as they reach Earth. ManishEarth^{Talk • Stalk} 16:06, 7 February 2011 (UTC)

How does the black hole decide which way to move, relative to the center of mass of the two colliding precursors? Wnt (talk) 16:46, 7 February 2011 (UTC)

If the collision is a head on collision between two non-rotating black holes than there is no recoil. A more realistic collision wouldn't be so symmetric and there might be "some" recoil. Dauto (talk) 19:13, 7 February 2011 (UTC)

The recoil encountered during the merger of two black holes can be huge. In the paper I reference below, describing calculations of the mergers of two black holes with spins of magnitude S/m²=0.8 under various initial conditions, the recoil came to more than 1000 km/s in all but one case. That's about 1/300 of the speed of light, and about 33 times faster than the orbital speed of the Earth around the sun. The merger of even non-spinning black holes of unequal mass can have a recoil of up to 175 km/s, which is still more than 5 times faster than the orbital speed of the Earth. When black holes merge, the resulting black hole goes flying off at a very high speed relative to the initial center of mass, in a hard-to-predict direction. Gravitational waves carry away a huge amount of linear momentum when black holes merge. Red Act (talk) 22:08, 7 February 2011 (UTC)

I know. That's why I put the word some within quotation marks. Dauto (talk) 03:24, 8 February 2011 (UTC)

Oh, OK, I understand now. I mistook the quotes as connoting downplaying, instead of connoting ironic understatement. Sorry. Red Act (talk) 04:42, 8 February 2011 (UTC)

In realistic cases, a precise head-on collision isn't going to occur, and the black holes are going to be a binary system for a while before they merge. The merger of non-spinning black holes of equal sizes produces no kick (a.k.a. recoil). For the merger of two non-spinning black holes of different sizes, the kick direction (which of course must be in the orbital plane, due to mirror-image symmetry) is mainly determined by the relative positions of the two black holes before their very last orbit and merger. The net radiated linear momentum before then is small, because it's fairly close to being equal in all directions over time when the orbits of the two black holes are nearly circular. However, much larger kicks occur when the merger is between two spinning black holes, in which case the initial spin orientations play a crucial role in the kick direction, and the kick direction is no longer even confined to the orbital plane. As in the case of non-spinning black holes, almost the entire kick is accumulated during the final merger phase, so the kick direction is highly sensitive to initial conditions, and there isn't some simple formula for it. For more information, see this paper. Red Act (talk) 19:58, 7 February 2011 (UTC)

Scientific name etymology

Hi. Several sources (including Wikipedia) state that the scientific name Leptictidium means "graceful weasel". However, this etymology seems to correspond to Leptictis (lepti+ictis) rather than to Leptictidium. So what does Leptictidium actually mean? What's the difference in meaning between Leptictidium and Leptictis? Thanks. --79.89.248.158 (talk) 07:17, 7 February 2011 (UTC)

The suffix '-idium' is from the greek suffix '-idion' meaning smaller or lesser. Mikenorton (talk) 07:55, 7 February 2011 (UTC)

Why don't we have pneumatic tubes?

It seems people in the past (like end of nineteenth century) thought that by now -- in the 21st century -- we would have pneumatic tubes everywhere, for fast delivery. Why don't we? Is there something wrong with the idea after all, that makes it impractical, etc? I can't get a homecooked meal in my house any faster than either making it, going to go get it myself, or having someone deliver it. Whereas with tubes, I could just get one as from a buffet... Is there some reason the idea doesn't actually work? (even though more than a hundred years ago, people were convinced it would). 109.128.127.87 (talk) 12:01, 7 February 2011 (UTC)

Such pneumatic tube systems were quite widely used in the 20th century in industrial and commercial settings, such as factories, banks and department stores, and even across cities, to transport packages of documents, cash, postal items, etc. They remain in use in a variety of specialist settings - my local Tesco supermarket, for example, uses such a system to send containers of cash from tills to a central cashier's office. Although our article is not explicit, my guess (as someone professionaly experienced in Facilities management) is that the necessary servicing and maintenance required to keep them working is relatively impractical in a domestic setting, making rival technologies or methods more economical. 87.81.230.195 (talk) 12:39, 7 February 2011 (UTC)

Document distribution has become overwhelmingly electronic, information is no longer the prisoner of sheets of processed dead tree. The need to transport a specific piece of paper within a single physical facility has become relatively rare.

I know some large hospitals use pneumatic systems to transport laboratory specimens and urgent medications.

City-wide "public utility" systems ran into scalability problems. What works well in a single building gets hopelessly snarled up in a city-wide system - the information and communication technology of the late 19th - early 20th century simply could not do the job economically. Roger (talk) 13:16, 7 February 2011 (UTC)

Rival technologies - there is none. If I want piping hot food in my house, I have to make it, or someone has to walk it to my doorstep (probably me). There is nothing that replaces it. Dodger67, I understand about late 19th - early 20th century limitations. My question is: what about today? 109.128.127.87 (talk) 13:18, 7 February 2011 (UTC)

Using magnetic levitation and propulsion would get over some of the difficulties of long distance operation -if it can be made to work economically.A visionary idea for modernising the goods-distribution network --Aspro (talk) 13:57, 7 February 2011 (UTC)

The infrastructure needed would mean that there would be high start up costs, which would make it a risky investment, and probably high running costs. The Royal Mail had a narrow gauge railway under London which they closed in 2003 due to running costs. -- Q Chris (talk) 14:14, 7 February 2011 (UTC)

I'm not sure that pneumatic tubes are ideally suited to food delivery. The acceleration and deceleration, not to mention the sudden twists and turns would thoroughly scramble most food items.

A pizza would be disastrous, and the wrong shape anyway. Some Chinese-food items would be OK, but some would not survive. Grinders would be the ideal shape of course, but I think that even tightly wrapped in wax paper they'd be pretty badly damaged. I'll bet all the meat would wind up bunched up at one end and the bread would be soaked from the obliterated tomato. I'll bet a burger would be just as bad, but with more grease.

Maybe some systems go a lot slower than I'm imaginingAPL (talk) 16:20, 7 February 2011 (UTC)

"I'll bet all the meat would wind up bunched up at one end and the bread would be soaked from the obliterated tomato." It's a sacrifice I'm willing to make. 109.128.127.87 (talk) 16:32, 7 February 2011 (UTC)

Well if it was spag bol, it wouldn't matter. But in other cases, the food could be vaccuum sealed in a heavy plastic wrapper, which would prevent it from moving around. Myles325a (talk) 00:44, 8 February 2011 (UTC)

Actually I would think unmanned aerial vehicles would offer a rival technology, when appropriately optimized for the task. "All hail the Pizza Bomber!" But unless you teach a parachutist pizza how to ring a doorbell, you'll need some specialized slot in your hose for the planes to dock, deliver their cargo and take off again. Conceptually, the friction of moving air in a sufficiently long pneumatic tube should eventually exceed the necessary lift and drag of a tiny airplane. Wnt (talk) 16:55, 7 February 2011 (UTC)

NOW you're talking. Smart Quadrocopters could flit all over town carrying precious fast-food take out. They could use cel-phones to alert buyers when they're about to land. I wonder how much you have to tip a delivery robot. APL (talk) 17:26, 7 February 2011 (UTC)

OK, now for a list of shortcomings of pneumatic tubes:

1) As Wnt mentioned, friction is more of a problem the longer the tubes are (and the more bends). You would need to put more and more pressure in the tubes, the longer they are, to get them to work. This would require that the tubes be thicker and better sealed, and the container would also need to seal more closely with the tube, to prevent air leakage, which in turn would also increase friction. Perhaps powdered graphite or some other lubricant would be needed along the inside of the tubes, which would, unfortunately, tend to blow out black dust at the ends. Also, at such pressures you could no longer have the tubes be open at the end. While this results in a harmless puff of air for short lengths, for the lengths you are talking about, the air pressure blast would blow your ear drums out. Instead, you'd need to have the pipe open up to a chimney on the roof, and would need special baffles or maybe use active electronic noise reduction methods, to prevent it from making loud sounds.

2) As APL mentioned, food might get messed up by the forces involved. Soda, even if well sealed, would likely explode when you opened it.

3) Switching systems would be needed, as a single tube from every fast food restaurant to every home wouldn't work. This is another opportunity for air to leak out. I suppose an automated system using bar codes could be used.

4) There could be a security concern, as somebody could send bombs this way, or stop your food and poison it. StuRat (talk) 18:31, 7 February 2011 (UTC)

Now for some places where it could work:

A) Hotels. Rooms service would no longer require that you put your robe on. As for scrambling the food, the relatively short distances would mean that they could move it rather slowly. Another way to do the same thing would be with dumb waiters. The latter wouldn't allow going around corners, but you would need a vertical shaft between every pair of rooms (or maybe every 4 rooms, if the halls are on the outside, as in a motel). The dumb waiter system might be quieter and allow a full tray of food, but either system would need to control the door at the room end, so people couldn't just steal food sent to another room.

B) Skyscraper apartment buildings.

C) Hospitals.

D) Retirement homes. StuRat (talk) 18:44, 7 February 2011 (UTC)

Bellamy in 1887 wrote "Looking Backward", a sort of time travel or futurism forecast of what the world of 2000 would be like. He forecast an underground delivery system, whereby you could order and get automatically delivered food, clothing, or whatever. Picture the Denver Airport luggage handling fiasco. Such a system would likely cost more to set up and maintain than just getting stuff delivered by car from the pizza place, or by FedEx from internet merchants for books or clothes. Edison (talk) 19:59, 7 February 2011 (UTC)

It might also be useful to list some of the alternatives:

- For horizontal transport (or slight angles): Conveyor belts.

- For downward transport: Chutes. No power required.

- For upward transport: Elevators.

The additional flexibility of pneumatic tubes to transport in any direction apparently doesn't make up for the other short-comings of such a system.

Incidentally, it might interest you to know that the first New York Subway and an early London Underground were both pneumatic. StuRat (talk) 23:32, 7 February 2011 (UTC)

We currently use a pneumatic tube system at the hospital where I'm employed. It's primarily for sending samples to the lab, and medicines to various floors. We used to use a dumb waiter for moving large charts up to Medical Records, but most charting is electronic now, so that's obsolete. Suffice to say, I don't see much use for pneumatic tubes outside our current implementation. — The Hand That Feeds You:^Bite 23:45, 8 February 2011 (UTC)

In fairness to the tubes, you shouldn't really need to have the entire tube powered by an end-to-end difference in air pressure - you could e.g. have pistons at regular intervals which pull out as the package approaches and push in after it passes; this creates a gradient of air pressure only over a shorter interval. That said, pneumatic propulsion is (as with the railway) simply an alternative to an engine power, and eventually it still makes sense to have one engine that goes with your package rather than dozens or hundreds along the way. (Unless you have a whole lot of packages?) Wnt (talk) 00:53, 9 February 2011 (UTC)

How do the birds "print" spots on their eggs?

Guillemot eggs

Do they have "printers" in the cloaca? -- Toytoy (talk) 14:40, 7 February 2011 (UTC)

I found this in the article eggshell:

In an average laying hen, the process of shell formation takes around 20 hours. Pigmentation is added to the shell by papillae lining the oviduct, coloring it any of a variety of colors and patterns depending on species. -- Toytoy (talk) 15:04, 7 February 2011 (UTC)

You seem to have answered your own question in part, but in case you're also interested in why you might like to read this. This book also has more details on the how. SmartSE (talk) 16:30, 7 February 2011 (UTC)

capillary

what is capillary action? —Preceding unsigned comment added by 59.92.106.164 (talk) 14:52, 7 February 2011 (UTC)

See Capillary action. Red Act (talk) 15:11, 7 February 2011 (UTC)

the environment.

Does nuclear energy destroy the environment? — Preceding unsigned comment added by Drloic (talk • contribs) 15:10, 7 February 2011 (UTC)

See Environmental effects of nuclear power. Red Act (talk) 15:14, 7 February 2011 (UTC)

If it is released all at once, it has a very negative impact on the local environment. Googlemeister (talk) 16:05, 7 February 2011 (UTC)

There are some rather spectacular products of nuclear energy that could adversely affect the environment, however we'd all die without it. -- JSBillings 16:16, 7 February 2011 (UTC)

Short version: if there are no accidents, the net pollution is probably a couple of orders of magnitude less than coal. The "long version" explanation would include the probability of accidents (never non-zero, but lower than most people think; but the consequences of them are high), and the question of whether coal is the appropriate alternative to compare it to (whether that comparison creates a false dichotomy or not). You have to compare it to something, because all forms of energy generation have some environmental effects. --Mr.98 (talk) 16:36, 7 February 2011 (UTC)

I agree - coal power actually releases more radiation into the environment than nuclear: [1] [2] and the waste from coal can lead a very nasty mess [3] which is worse than anything proven about nuclear waste AFAIK. SmartSE (talk) 16:41, 7 February 2011 (UTC)

Note that nuclear decommissioning hasn't really been done that often, and until it is done we don't know whether the radioactive components inside will really be disposed of neatly in some small underground place we agree never to go to again, or dispersed all over the countryside during war or civil unrest as accidental discharges or dirty bombs. Wnt (talk) 17:05, 7 February 2011 (UTC)

I think the most important detail is that nuclear fission power stations produce a small, solid waste-product (which I can admit is fairly hazardous). But unlike any fossil-fuel power plant, the waste is not tons of gas that is just vented to the atmosphere. Nuclear waste can be safely carried to a secure location for disposal, while carbon dioxide, other noxious gases, and the soot and particulate pollutants of fossil fuel plants (especially coal) are just haphazardly thrown to the wind. Nimur (talk) 17:06, 7 February 2011 (UTC)

Yes, this is a very important thing to keep in mind. Containment is much easier for solids than gasses. SemanticMantis (talk) 21:21, 7 February 2011 (UTC)

An appropriate syllogism is "Nuclear power is to coal power as air travel is to car travel". As in, air travel is orders of magnitude safer than car travel, and yet when we have plane crashes they are Major Events, whereas someone dies of a car crash so often, no one notices (someone, right now in fact, is probably dying in a horrific car crash). In the same way, nuclear is far and away safer and more environmentally friendly than coal, but coals effects are more insidious, while nuclears is more disasterous. Thus, we overemphasis the danger of nuclear and underemphasize that of coal, much as plane crashes are big news, and car crashes are ignored. --Jayron32 22:07, 7 February 2011 (UTC)

There are several problems with nuclear energy. Apart from the fact that we have not yet found a proven solution for long-term treatment and/or storage of nuclear waste, the overall CO2 footprint is not that small. The power plant itself does not emit much CO2, but mining, transporting, and refining uranium is, at the moment, fairly CO2 intensive. A study a few years back found that nuclear power plants are better than coal (big challenge...), but slightly worse than natural gas in total CO2 production. The major snag for nuclear is, however, that it does not scale. Even now, people are not happy with Iran and North Korea expanding their nuclear capabilities. And I really don't want to see 10 reactors each in Nigeria, Eritrea, Colombia, Burma, Syria and Yemen. It enormously increases the risk of proliferation, and it's very uncertain if politically unstable countries can operate nuclear plants safely and securely. If we do not develop an energy solution with global reach, fossil fuel burning will simply shift to other countries. --Stephan Schulz (talk) 23:53, 7 February 2011 (UTC)

I would just like to note that theoretically the reactor problem does not have to be a big proliferation problem. There are types of reactors that are relatively proliferation resistant and would require really a lot of obvious effort to make a weapon out of. Extracting plutonium from spent fuel is not something that can be done in your basement.

The real proliferation problem is the fuel cycle. If you permit enrichment, then the proliferation problem is huge. If you permit recycling, it is not only monumentally huge, but you also raise the very real possibility that material can be stolen. (The "material unaccounted for" at a recycling plant the size of Rokkasho Reprocessing Plant, for example, is around 50 kg a year or so. That means that there is really no way for them to know whether a missing bomb's worth of plutonium is just lost in the pipes somewhere, or has been smuggled out by an employee.) --Mr.98 (talk) 01:04, 8 February 2011 (UTC)

Don't forget that in assessing the carbon footprint of a power station you need to do a life-cycle analysis from construction to decommissioning, not just a snapshot of consumption in normal use. Nuclear power stations are made of many tons of concrete, and manufacture of cement requires a very high energy input. Itsmejudith (talk) 12:29, 8 February 2011 (UTC)

Somehow that logic doesn't seem to add up. If a nuclear power plant really needs that much fossil fuel input than the energy prices from those plants wouldn't be competitive in the market place. We know that nuclear power is fairly competitive. Dauto (talk) 16:11, 8 February 2011 (UTC)

"We know that nuclear power is fairly competitive" - um, yes, once the government provides heavily subsidised risk insurance and waste disposal, not to mention the fact that governments underwrote most of the R&D to begin with. I don't think nuclear has ever competed fairly in a open market. --Stephan Schulz (talk) 21:28, 8 February 2011 (UTC)

Neither has coal, really. And I'm speaking as a Kentuckian. — The Hand That Feeds You:^Bite

It's hard to get raw economic numbers that are unbiased by politics on any infrastructure project, especially if the order-of-magnitude investment is going to be a few billion dollars. Thorough study of the reported costs will require parsing through thousands of analyses of construction, operation, labor, and technology costs; and it's naive to assume that a straight answer is available from every single contractor, who will act in good faith, provide correct numbers, and act selflessly to make sure the best technology wins (irrespective of individual profit potential). That's why the issue is so murky. For example, I hear the "concrete carbon footprint argument" a lot. I don't think nuclear plants require that much concrete, proportional to the energy they deliver. Remember: we're talking about an energy production system that can power an entire city for a thirty to fifty year lifespan. How much electricity and gasoline does one concrete factory use up, even accounting for all the embedded energy inputs in the mining and transportation? I'm astonished at the assertion that the amount of fossil fuel required to construct one building is even relevant. How can that amount of energy possibly compare to the amount of coal that is not burned as a result - literally an entire city's worth of fossil fuel, over a time-span of decades? A nuclear plant, at full capacity, produces about a gigawatt - that's one billion joules every second. Nimur (talk) 00:06, 9 February 2011 (UTC)

Isn't the comparison between nuclear and natural gas not nuclear and coal? Nil Einne (talk) 06:52, 9 February 2011 (UTC)

(EC)n the history of nuclear power plant operation, the radioactivity released to the environment has been at trace levels, except for Chernobyl type accidents. Coal contains Uranium and Thorium, which are released up the smokestack when the coal burns. See a paper from Oak Ridge National Laboratory, a nuclear think tank, which has a graph indicating about 12000 metric tons of Uranium and 3000 metric tons of Thorium released into the atmosphere from coal combustion in 2000. It says people living downwind from a coal plant are exposed to more radioactivity from the combustion of coal than if they lived downwind from a nuclear plant operated per regulations (again, excepting major accidents). It says the radioactive elements released from coal combustion far exceed the radioactive fuel used in nuclear reactors. Edison (talk) 16:16, 8 February 2011 (UTC)

"In the history of nuclear power plant operation, the radioactivity released to the environment has been at trace levels, except for Chernobyl type accidents." Didn't Marion Barry once say Washington, DC was safe except for murders? -- Mwalcoff (talk) 03:39, 10 February 2011 (UTC)

The nuclear pellets and other nuclear waste represent a storage and disposal problem as the involved radioisotopes often have a long half-life, as is the case for Uranium-238 which eventually decays to toxic lead. ~AH1^(TCU) 22:54, 11 February 2011 (UTC)

density

A NEEDLE IS IMMERSEDIN WATER BUT A HEAVY SHIP IS NOT. WHY —Preceding unsigned comment added by 122.179.85.65 (talk) 15:29, 7 February 2011 (UTC)

From Buoyancy: "A ship will float even though it may be made of steel (which is much denser than water), because it encloses a volume of air (which is much less dense than water), and the resulting shape has an average density less than that of the water". -- Q Chris (talk) 15:36, 7 February 2011 (UTC)

(EC) See Archimedes' principle, which should help. Mikenorton (talk) 15:37, 7 February 2011 (UTC)

Actually, a needle can also float, even though it's denser than water, due to a different reason than why a ship can float, namely surface tension. Red Act (talk)

Motor oil LD50

What is the LD50 of 10W40 motor oil? I saw the Quantum Solice James Bond where a guy was thinking about drinking it and wondered how toxic the stuff actually was. Googlemeister (talk) 16:23, 7 February 2011 (UTC)

You need to improve your google skills! This says the LD50 varies on the route of ingestion. Inhalation = 2.18 to >4 mg/l (Rat) Dermal = 2 gm/kg (Rabbit) and orally = 5 ml/kg (Rat). SmartSE (talk) 16:34, 7 February 2011 (UTC)

As an indication of how toxic it is compared to other oils though, it looks similar as they all seem to have similar LD50s. SmartSE (talk) 16:37, 7 February 2011 (UTC)

But does an LD50 of 5 ml/kg on a rat mean it is the same 5ml/kg on a human? I mean the metabolism is very different between a human and a rat and the digestive systems aren't quite the same etc... Googlemeister (talk) 17:34, 7 February 2011 (UTC)

Well I doubt anyone is going to feed engine oil to people and see how much it takes to kill them... Rat and human metabolism is very similar and tbh I doubt that engine oil is going to be metabolised anyway. SmartSE (talk) 17:54, 7 February 2011 (UTC)

Fair enough, but what specifically in the motor oil is toxic to people and how does it cause the harm? Does it paralyze muscles, or does it block neural signals or does it cause ruptures in the digestive tract or what? Googlemeister (talk) 20:01, 7 February 2011 (UTC)

"Symptoms of motor oil ingestion are depression, lethargy, paralysis of hind legs, staggering, vomiting and coma, in very severe cases." They're talking about dogs by the way. SpinningSpark 20:29, 7 February 2011 (UTC)

Sounds like a muscle relaxant then. Googlemeister (talk) 21:54, 7 February 2011 (UTC)

I do not believe that 5ml/kg is a sensible LD50. I would imagine anyone could drink 250ml. Meanwhile, fatty mc fatterson at 150kg could never finish 750ml. Just doesn't sound right to me. No source! Egg Centric (talk) 21:43, 11 February 2011 (UTC)

Veinal sins

The site where blood is removed and replaced in the veins and arteries, for dialysis, seems to deteriorate over time, such that they need to periodically change the location. What's the name and cause of this problem ? StuRat (talk) 18:04, 7 February 2011 (UTC)

Scar formation. Roger (talk) 18:23, 7 February 2011 (UTC)

Right, but what about dialysis causes the veins and arteries to scar ? Is it due to pressure, infections, some type of chemical imbalance, or something else ? StuRat (talk) 18:48, 7 February 2011 (UTC)

I presume it's just due to the repeated breaking of the vein wall by the insertion of the needle (or whatever the proper word is) and the resultant healing. I have a similar problem as a result of having donated blood many times: the staff sometimes have trouble finding a suitable spot to stab. AndrewWTaylor (talk) 18:54, 7 February 2011 (UTC)

In patients that are undergoing hemodialysis, there is usually a surgically created arteriovenous fistula or shunt. The various alternatives and some of the complications of this process are discussed at Hemodialysis#Access. --- Medical geneticist (talk) 19:16, 7 February 2011 (UTC)

Thanks. That said "The catheter is a foreign body in the vein and often provokes an inflammatory reaction in the vein wall". Doesn't medical science have any catheter material which doesn't provoke an inflammatory reaction ? StuRat (talk) 23:18, 7 February 2011 (UTC)

Dicrocoelium dendriticum or Dicrocoelium dentriticum?

Is it: Dicrocoelium dendriticum or Dicrocoelium dentriticum? I see sources for both. Is one simply a typo, or are both valid? Ariel. (talk) 21:59, 7 February 2011 (UTC)

Google scholar shows sources using both, but over ten times as many using the d, and many that use the t appear to be from non-native-English speakers. In short, the t form appears to be a relatively common error, but an error nonetheless. Looie496 (talk) 22:08, 7 February 2011 (UTC)

Chromatid is to sister chromatid as chromosome is to what?

What's the associated chromosome that every chromosome typically has in humans, among others? Not sister chromosome? --90.213.111.224 (talk) 22:21, 7 February 2011 (UTC)

Homologous chromosome? Not sure I understand what particular "association" you have in mind. DMacks (talk) 22:39, 7 February 2011 (UTC)

Life span of cut dogwood

I have some dogwood branches from a florist that I bought about a week ago. They've been sitting in my car (I live in Canada, it's pretty much been below freezing thus far). If I put them in a bucket of water now will they be okay? Or has it been too long and the branches are likely dead? Thanks. --生け花 23:23, 7 February 2011 (UTC)

There doesn't seem to be much cost to trying. One suggestion, cut the last bit of the branches off, under water. This will hopefully remove the dead, dried out portion, without introducing air bubbles into the circulation system of the branches, which would tend to prevent the uptake of water. StuRat (talk) 23:36, 7 February 2011 (UTC)

My grandmother could grow pants from cuttings such as a rose bush from cut flowers. Perhaps one has to be something of a "plant witch" to achieve such success. Edison (talk) 03:23, 8 February 2011 (UTC)

Were they in leaf, in bloom, or dormant? If they were already dormant, they still may well take root and sprout. As StuRat point out, it's a low-risk experiment. Good luck! SemanticMantis (talk) 04:17, 8 February 2011 (UTC)

They're..."dormant", I guess, since they are no leaves or flowers on them. I've placed them in water...hard to tell if it's having any effect though. :P --生け花 22:27, 8 February 2011 (UTC)