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

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[edit] April 7

[edit] neighbor's dog and silent whistle

My neighbor has a very annoying dog. Specially when the dog is alone it is very loud. I thought I could buy a dog whistle to 'train' the dog so it can let me alone. As it starts to bark I could blow the whistle as loud as I can. Does this training method will work? 217.168.3.246 (talk) 00:08, 7 April 2008 (UTC)

It would have to be loud enough to bother the dog. I suspect that dogs have far more tolerance for loud noises and vocal strain than we do. Therefore, you would get tired of blowing the whistle long before the dog would shut up. Perhaps some type of automated system similar to an air horn could work, where you just press a button and it sends out a deafening sound at dog-ear frequencies until he gets the idea and shuts up. Of course, other dogs in the neighborhood will also be affected, and may actually start barking as a result. You'd need to aim the horn right at the target dog to try to limit this side-effect. I'm assuming the dog is left outside, I can't imagine this having the desired effect on a dog inside a house.
At this point I should probably point out that these While E. Coyote schemes are less likely to work than just informing your neighbor politely of the problem. Perhaps then he would leave the dog inside the house where it can hopefully bark until it's throat bleeds without bothering you. StuRat (talk) 03:06, 7 April 2008 (UTC)
Dog whistles seems to be both capable of attracting dogs and inflicting pain. On the contrary, a dog's hearing is more sensitive than a human's. That is why they get scared easily by fireworks as they would sound like grenades to them. My dog almost hanged herself in her leash during the New Year celebration. Anyways, I think inflicting pain to the animal to make it get the point is a bad idea. As StuRat said, it is better to inform your neighbor about the problem--Lenticel (talk) 09:36, 7 April 2008 (UTC)
To actually get the dog to behave (versus just locking it in a sound-proof room), you probably would need to use pain, or at least discomfort, in some form. The use of a choke collar is one technique used in obedience schools, for example. This may seem cruel, but if the alternative is to put down a dog that just won't behave properly, isn't a brief period of pain a better choice ? StuRat (talk) 14:01, 7 April 2008 (UTC)
Choke collars don't actually choke the dog—a dog's esophagus is in the middle of their neck, and is well insulated from such a collar (unlike a human's neck). They just add a lot more control to the collar. Pain and discomfort play a minor role in training; usually it is based around rewards. And there are usually more alternatives than putting down the dog because it doesn't behave "properly" in minor ways. In any case, you should not try to inflict pain and discomfort on someone else's dog—it's a bad idea, and it's possibly illegal. --Captain Ref Desk (talk) 15:21, 7 April 2008 (UTC)
I can't think of a way to train dogs not to bark by giving them a reward. If they are silent and you reward them, how would they know they are being rewarded for their silence ? On the other hand, if they experience pain or discomfort each time they bark, they could likely figure that link out. StuRat (talk) 01:44, 8 April 2008 (UTC)
Dogs, like most animals hate getting soaked. A sudden downpour or even the threat of a good soaking can sometimes divert the attention of a dog away from whatever is making it bark. A perimeter can be established using agricultural, landscape or golf sprinkler heads, which typically have ranges of 30 to 50 feet or more. Neighbors will usually complain that your water is crossing the property line and landing on their property. When the neighbor complains simply ask if the rule of not letting water cross the property line applies to sound as well. If the answer is "yes" then an agreement may be possible to eliminate the cause to the water crossing the property line. If the answer is "no" then complaint should be ignored until the answer changes to yes. (Disclaimer: This is not legal advice.) Mimus polyglottos (talk) 13:11, 7 April 2008 (UTC)
That's a dopey approach and the water/sound comparison doesn't work out at all. Why not just talk to the neighbor about it? --Captain Ref Desk (talk) 15:21, 7 April 2008 (UTC)
...ever succeed in licking your own elbow? 71.100.160.37 (talk) 16:47, 7 April 2008 (UTC)
This question has also been posted on the Miscellaneous Desk. Gandalf61 (talk) 13:15, 7 April 2008 (UTC)
Most cities have rules about dogs barking too much. Bark collars are effective and not cruel as far as I know. They're certainly less cruel than sending a dog to the pound for annoying the neighbors too often. I use one for one of my beloved dogs who loves a good yap. I would definitely avoid any solution where you're molesting the dog in any way, as that could lead to a conflict where you're in the wrong. --Sean 13:59, 7 April 2008 (UTC)
I think that's why he wanted to use a "silent whistle", so he can molest the dog privately, without triggering the wrath of the owner. There is some president for using such sounds on humans for this effect, such as the Mosquito, an annoying high-pitched sound that only kids and teenagers can hear, which keeps them from congregating in businesses' parking lots and scaring off customers. StuRat (talk) 14:06, 7 April 2008 (UTC)
The difference there is that the teenagers can easily leave the (presemuably private if the sound is coming from a private device) area. However the dog is basically locked up and can't leave the place and would probably have no idea why someone is blowing a whistle at it Nil Einne (talk) 16:03, 7 April 2008 (UTC)
Sean is right—talk to the owner, suggest a spray bark collar. I have seen them used very effectively on dogs with barking issues. They are humane and cheap. They just release a little bit of citrus when the dog barks (dogs hate citrus), and quickly the dog learns that when the collar is on, they shouldn't bark. They don't always make this a universal rule (probably depends on how smart the dog is—I knew a very smart dog that knew that the second the citrus ran out he could bark again), but it's a workable solution for a barking dog. If your neighbor objects, tell him that it is his responsibility to make sure his dog is not a nuisance when he leaves the house; not only is this part of being a pet owner, it's likely a requirement of local code.
Any of the other approaches are very bad ideas. You don't have any experience training dogs (obviously). You shouldn't be trying to train your neighbor's dog without their knowledge and permission. You could find yourself in legal hot water for harassment of their dog. But from a simply ethical point of view, you wouldn't want them doing something like that to a pet of yours, would you? You'd probably rather they talked to you about it in a civilized way and you could come up with an acceptable solution, wouldn't you? --Captain Ref Desk (talk) 15:21, 7 April 2008 (UTC)
If for whatever reason you are really unable to talk to the person about this, you could send a polite computer printed anonymous note informing the person of the problem through the mail. Presuming you have other neighbours, your neighbour likely won't know who sent it. Provided you ensure your note is polite and not in any way threatening, I'm doubtful you'd get in legal trouble in most jurisdictions (but this is not legal advice and I could easily be wrong). However I would strongly recommend you approach the person directly. If they refuse to do anything about it, you may be able to get your local animal control or council to do something about it depending on where you live (e.g. http://www.ccc.govt.nz/Animals/DogBarking.asp & http://www.waitakere.govt.nz/cnlser/aw/dogs.asp). Nil Einne (talk) 15:34, 7 April 2008 (UTC)
According to the Madrid City Council website [1] and Babelfish, dog owners have an obligation "To adopt the measures that are precise to avoid that the animals can instill fear, to suppose danger or threaten, or to cause annoyances to the people." It sounds to me like persistant barking would be counted as "cause annoyances to the people" so it's easily possible the Madrid council will do something about it if the owner doesn't/refuses. If you indeed live in Madrid and understand Spanish, you could probably find out more by looking through the website. If you live in Viladecáns or somewhere else, look for the appropriate website. In any case, as I mentioned earlier, it is vital you inform the owner first since the council is far less likely to take action if the owner isn't aware of the problem (at best, they will inform the owner which will likely mean he or she will just be more annoyed that whoever it was didn't tell them directly) Nil Einne (talk) 15:53, 7 April 2008 (UTC)
It would be great if it were that simple in all cases. Consider a Jewish store keeper from NYC who moved into a suburban area in the the Deep South. His neighbor is outraged by the presence of a Yankee Jew living next door. According to the neighbor the only thing the Jew had going for him is that he is not Black. The neighbor has dogs. Fortunately they are not big dogs. Unfortunately their bark is louder than big dogs. The neighbor also has chickens, being originally from a rural area. The suburb being a block from a river is frequented by raccoons and possums looking for a meal. Chickens are a favorite item along with left out dog food. The neighbor leaves his dogs outside all night to guard the chickens. The shop keeper's mother is dying of cancer in the back bedroom, 8 feet from the fence that separates the properties and 16 feet from the chicken coop. She is awakened by the ruckus every night. After 20 or 30 minutes it tapers off. Finally it stops. Just as she is falling asleep, same thing. This pattern repeats itself over and over again until daybreak. The shop keeper complains to animal services with audio/video evidence. Animal services says it can't help him without his first obtaining signatures from families living close but at separate addresses. The test case for the soundness of the law was a mother who worked for the county and her daughter who lived in a rear apartment of the same house. Since their addresses were not the same they qualified for help from animal services to issue citations under the law. They attested to the soundness of the law. The shop keeper's case was not addressed, however, because there were no other families in the neighborhood willing to go against his neighbor. The shop owner was finally forced to find another residence for his mother. The rear bedroom was not usable and had to be shut off. The other bedrooms and living spaces had to be sound proofed. 71.100.160.37 (talk) 16:14, 7 April 2008 (UTC)

Don't talk to your neighbor. If he doesnt't cave in and you have to go on with plan B (silent whistle) or execute plan C (killing it), he will know who it was. —Preceding unsigned comment added by 80.58.205.37 (talk) 16:52, 7 April 2008 (UTC)

How would he know about the silent whistle ? StuRat (talk) 01:37, 8 April 2008 (UTC)
He'll find out that his neighbor's house has a lot of stray dogs. The silent whistle will attract hordes of stray dogs and they will camp near it.--Lenticel (talk) 03:32, 8 April 2008 (UTC)

What ever happened to talking to one's neighbor? To go on wikipedia asking for advice on how to covertly train someone else's dog is ridiculous. I would respect this question if it were hypothetical or an exercise.

[edit] Galaxies

Hi. Do you know what the farthest galaxy from the Milky Way that we know of is?Thanks! —Preceding unsigned comment added by 208.54.14.121 (talk) 00:24, 7 April 2008 (UTC)

Hi. Well, the farthest galaxies that are visible with any type of telescope are about 13 - 17 billion light-years away. They're in the Hubble Deep Field or maybe the Hubble Ultra Deep Field, if I'm not mistaken. However, the universe is believed to only be about 12 - 15 billion years old, and beyond that boundary, the galaxies' light did not have time to reach us and you're looking at them before they existed. I think some of their distances might be calculated by redshift. Remember there might be galaxies an infinite distance away from us, they're just too far to be in the observable universe from our location. Hope this helps. Thanks. ~AH1(TCU) 00:48, 7 April 2008 (UTC)
"that we know of" limits this to an answerable question. In 2004, galaxy Abell 1835 IR1916 was discovered to be 13,230 million light-years away. I haven't read about any further ones in the last few years. -- kainaw™ 01:39, 7 April 2008 (UTC)
One possible answer is IOK-1, discovered in April 2006. According to the discussion at Galaxy#Formation, Abell 1835 IR1916 has been claimed to be even more distant than IOK-1, but its distance and nature (is it in fact a galaxy?) are less well characterized. --mglg(talk) 01:50, 7 April 2008 (UTC)
The universe is now believed to be 13.7 billion years (discovered February 2003). So you can't have galaxies > 13.7 billion light-years. Textbooks before February 2003 would reflect the 12-15 billion year universe age. This was discovered by NASA with 1% error. Check the almanacs out for the sources. Neal (talk) 16:53, 7 April 2008 (UTC).
It depends on the distance measure used. Comoving distances, for example, can exceed 13.7 Gly without implying an object age older than the universe. See Distance measures (cosmology) referenced by Icek below, along with Observable universe#Misconceptions and Dltt is Dumb. Really, you should all be comparing redshifts, because that is the directly measurable quantity, and has no dependence on cosmological parameters or choice of distance measure (comoving, light-travel-time, etc.). If you insist on comparing distances, make sure you're talking about the same distance measure (e.g. comoving) and that the distances were obtained using the same assumed cosmological parameters. -- Coneslayer (talk) 18:11, 7 April 2008 (UTC)

Note that these "distances" are "naive Hubble" distances, the comoving distances are larger. Icek (talk) 13:57, 7 April 2008 (UTC)

[edit] --172.134.250.18 (talk) 02:24, 7 April 2008 (UTC)

--172.134.250.18 (talk) 02:24, 7 April 2008 (UTC)if i exposes myself to cosmic rays will i get super powers like in the fantastic 4

No, you'll get radiation poisoning or even death if the radiation is strong enough. --antilivedT | C | G 05:27, 7 April 2008 (UTC)
Quite the opposite – losing weight, muscle weakness, no hair – so unfantastic. How did the 4 get away with it? Mutation! Julia Rossi (talk) 08:51, 7 April 2008 (UTC)
Uh, they're in the comics?--Lenticel (talk) 09:28, 7 April 2008 (UTC)
Ah, the "s" has been moved. Julia Rossi (talk) 23:10, 7 April 2008 (UTC)

[edit] speed/long skis and skateboards

Long skis go faster than short skis. Long skateboards go faster than short skateboards (I think). What is the reason (physics) for this phenomena.~ davidwinkelaar —Preceding unsigned comment added by Davidwinkelaar (talk • contribs) 03:16, 7 April 2008 (UTC)

The long ski can spread the load and displace less snow. I don't know about the long skateboard though, it may be you can stoop lower to reduce wind resistance. Graeme Bartlett (talk) 05:47, 7 April 2008 (UTC)
The length of high-speed skateboards is primarily a result of laying down on them. It is not specifically because the long boards inherently go faster. -- kainaw™ 18:22, 7 April 2008 (UTC)

[edit] sunscreen

Does sunscreen have an expiration date? I was told that old sunscreen could do more harm than good. Is this true? —Preceding unsigned comment added by 74.138.241.13 (talk) 04:25, 7 April 2008 (UTC)

I would assume that all cosmetic products will eventually decay/emulsify, rendering them unusable. In the case of sunblock, I would expect the titanium dioxide to stay unchanged, so it may have sunscreen properties. You probably wouldn't want to use it, though.18.96.7.121 (talk) 04:55, 7 April 2008 (UTC)

It's possible that it may do more harm than good if it gives people a false sense of protection, and end up spending lots of time in the sun. - Akamad (talk) 11:49, 7 April 2008 (UTC)
Hi. Yes, sunscreen can be harmful, if you put it that way. Let's say that you put on sunscreen and inscect repellent at the same time, which I recomend you do not do. Sunscreen goes under the skin, while insect repellent, which contains poisonous deet, should stay on top of the skin. So, if you apply both at the same time, the two can mix, and the sunscreen can bring some of the deet into the bloodstream. Sunblock, however, should be fine, as the chemicals stay on top of the skin. Remember that sunscreen contains a lot of chemicals that we might not be used to. Also, remember that even "water-resistant" sunscreen only stays for about 40 minutes, and "waterproof" sunscreen only stays about 80 minutes while underwater. Also, remember that the eyelids, lips, ears, and the neck are most sensitive to sun exposure. Hope this helps. Thanks. ~AH1(TCU) 21:14, 7 April 2008 (UTC)

[edit] Video card adhesive

What sort of adhesive is typically used when glueing something onto a video card? A part fell off, and I know exactly where it goes, but I'm not sure what glue to use. --AtTheAbyss (talk) 12:41, 7 April 2008 (UTC)

If it is the heat sink, you need a thermal interface material. If it is something else, you would have to connect all the small wires which have been broken, without getting a larger resistance than the original one, and without getting a larger capacitance between the wires (a larger capacitance could be caused by conducting parts being closer to each other than they were before). Icek (talk) 14:15, 7 April 2008 (UTC)
I'm not really sure what it is. It's a small silver-colored piece of metal with a textured grid surface. It's about an inch long I think; I'm not sure how wide. There are no wire involved. It was just glued to the surface. I have an ATI Radeon 9800XT. --AtTheAbyss (talk) 14:33, 7 April 2008 (UTC)
Sounds like a heat sink to me, but maybe you should ask at the Computing Desk? --Captain Ref Desk (talk) 14:46, 7 April 2008 (UTC)
Looking at pictures of that card, it looks like it may very well be a capacitor. They are surface mounted - silver on both ends and have a textured wrap covering the middle. You need to solder them back on if they come off. -- kainaw™ 18:24, 7 April 2008 (UTC)
This should go without saying, but if you have capacitors dropping off your video card, you probably have bigger problems than just getting them stuck back on. That said, I'd strongly suspect the part in question is indeed a heat sink. If it isn't, or if you're not sure of your skill at applying thermal adhesive, I'd recommend taking the card (and the loose part) back to the store you got it from. If it's fixable, they'll fix it — if not, they can sell you a new card. If it indeed "just fell off", it may even be covered by the warranty. —Ilmari Karonen (talk) 22:04, 7 April 2008 (UTC)
Actually, there's a good chance the card is not covered by warranty any longer. THe 9800XT is quite an old card and it's easily possible the editor bought it more then 2 maybe even 3 years ago. Nil Einne (talk) 12:27, 8 April 2008 (UTC)
I doubt this helps, but I can see the little rings of dry adhesive (on the part and on the card) where it was attached.--AtTheAbyss (talk) 12:10, 8 April 2008 (UTC)


Just Google for "heatsink glue". Most electronics spares shops sell it. Make sure you obey the instruction about not spreading it on too thickly. --Heron (talk) 17:42, 8 April 2008 (UTC)
I'm not sure it's the heatsink. THe piece is less than half an inch thick, if that. I appreciate all the help so far guys and gals.--AtTheAbyss (talk) 12:07, 9 April 2008 (UTC)

[edit] Cog Railway System

how is the energry transfer from engine to wheels to enable it to climb such steep gradient( going up and coming down)? it must be facing a lot of friction, how does it overcome that? what are the advantages and disadvantages of this system compared to a normal railway track? Nathelly wee (talk) 14:11, 7 April 2008 (UTC)

Your question looks a lot like it might be a physics homework problem—perhaps you could start by sharing your thoughts on the question, and we might be able to help you over the rough spots? TenOfAllTrades(talk) 14:16, 7 April 2008 (UTC)
Here's a hint: In a cog railway system, there may not be any significant energy transferred to the wheels.
Atlant (talk) 16:01, 7 April 2008 (UTC)

[edit] Telescopes

Hello,

Just for information, could you tell me wich telescope is the brighter (for visual observation of galaxies, nebulae, clusters, ...) : a Newton 200mm/1000mm (focal ratio=5) or a Schmidt-Cassegrain 305mm/3048mm (focal ratio=10) ?

Thank you very much. —Preceding unsigned comment added by 91.177.21.100 (talk) 14:55, 7 April 2008 (UTC)

The 305mm telescope is brighter. Since it has a larger aperture, it can collect more light, and the amount of light collected is the apparent brightness of the object being viewed. The focal length is simply how quickly the light converges; it has no effect on brightness.
The reason photographs taken at higher focal ratios are dimmer is because cameras shrink the aperture to increase the focal ratio. The only other way to increase the ratio, increasing the focal length, would zoom in the camera. --Bowlhover (talk) 20:41, 7 April 2008 (UTC)
Hi. Also, remember that larger telescopes are harder to store, heavier and harder to carry around, and more difficult to set up. The focal ratio is more important to the magnification rather than the light collection, and too much magnification will spread out the light from deep-sky objects. With the 200 mm telescope, using a 20 mm eyepiece, for example, will give 50x, while using the 305 mm telescope will produce 152x. However, sometimes a higher magnification can be a good thing. Remember however, that a higher magnification will produce a smaller field of view. So if the 20mm eyepiece had an FOV of 50 degrees, using it on the 200mm will produce a 60-arcminute FOV, which is good for observing the Orion nebula, most large galaxies, and large globular clusters, while using it on the 305 mm will give a 20-arcminute FOV, which is 9x smaller in area and better for smaller globulars, galaxies, and nebulae. Remember, however, that you can often get many different eyepieces for different magnifications, often ranging from about 5mm to about 40 mm for 1.25-inch barrels, and up to about 50 or 60 mm for 2-inch barrels (especially common on Schmidt-Cassegrains), and you can also also use barlow lenses to double or triple the magnification, which both these telescopes should be able to handle. Remember that the effects of aperture and magnification are squared, so a 305mm telescope should have about 2.3x more light-gathering capability, or about 130% better, ignoring the size of the secondary mirro. Try comparing these parameters on a telescope simulator or calculator. Hope this helps. Thanks. ~AH1(TCU) 21:29, 7 April 2008 (UTC)

[edit] Cell cycle analysis with brdu and 7-aad

[In this diagram http://www.icms.qmul.ac.uk/flowcytometry/uses/cellcycleanalysis/diagrams/DNAse.jpg], how is the 7-aad being used to stratify the populations of cells? I thought 7-aad detection meant dead cells, but there must be more to it than that. Thanks in advance. --145.29.23.38 (talk) 15:26, 7 April 2008 (UTC)

It's probably a one-shot technique that they're using. The cells (or an aliquot of cells) are taken at a single timepoint and fixed. 7-AAD will easily penetrate what's left of a cell's plasma membrane after fixation in cold ethanol, methanol, or acetone. TenOfAllTrades(talk) 20:12, 7 April 2008 (UTC)

[edit] Dog skeleton curiosity

My adult pointer/whippet mix has a strange feature at the very tips of her last (or near to last) floating ribs: the end 1/2" or so of rib seems to be jointed, such that I can flip it back and forth like the tip of my index finger. This feature is the same on both her left and right, and twiddling it causes her no discomfort. What is this? Are the ends of dog ribs made of cartilage? I've looked for dog skeletons online, but not found anything useful. Note that this is a general question about dog anatomy, and not a request for veterinary advice as there is no problem. --Sean 16:49, 7 April 2008 (UTC)

It's definitely not a bone joint. Ribs do have a lot of flexibility to them, to accomodate breathing, etc., both in human and dogs, but I wouldn't go so far as to call them cartilage. Perhaps your dog's ribs are even more flexible than most. StuRat (talk) 19:27, 7 April 2008 (UTC)
This is not uncommon in young dogs. The ventral part of the dog's rib is made of cartilage. This is true in other animals, including humans, I think.
The darker part of the rib is cartilage
The darker part of the rib is cartilage
The cartilaginous part of the rib meets the bone part in a costochondral junction known as the knee or genu. Only the last rib (the 13th) (or no rib at all) in the dog is a floating rib. In young dogs, the cartilage in the ribs is flexible. It calcifies and stiffens with age. That flexibility is what saves a lot of young dogs' lives when they are hit by cars.
With this condition, the flexibility of the cartilage in a floating rib allows it to flip back and forth. I'm not sure if this happens at the junction or further down. --Joelmills (talk) 15:20, 8 April 2008 (UTC)

[edit] organic chemistry(Catenation)

Carbon and silicon both have the same electronic configuration yet only carbon shows the property of catenation Why??Diya 16 (talk) 17:37, 7 April 2008 (UTC)Diya

The catenation article seems a good place to start reading. DMacks (talk) 17:48, 7 April 2008 (UTC)
Or at least now that I added some information that silicon can form bonds to other silicon atoms. Not sure your question is completely correct in its premises:) DMacks (talk) 18:10, 7 April 2008 (UTC)
are you sure you don't mean the formation of unsaturated bonds, such as double bonds and triple bonds? There is a bit of a shortage of compounds like HsiSiH or H2Si:Si2. Graeme Bartlett (talk) 05:24, 8 April 2008 (UTC)

[edit] Feed back Amplifiers

How to say which Feed back is applied , if a circuit is given?Raeez (talk) 18:09, 7 April 2008 (UTC)

Have you read Negative feedback amplifier as well as Amplifier and Electronic amplifier? Edison (talk) 18:33, 7 April 2008 (UTC)
Its not easy, without a great deal of experience, to identify all the feedback paths in any circuit. For instance even a simple emitter follower has unity voltage feedback. —Preceding unsigned comment added by 79.76.170.42 (talk) 00:11, 8 April 2008 (UTC)

[edit] safety issues with oxiding agent

Solid magnesium nitrate is apparently somewhat hazardous because it is an oxidizing agent. I am wondering if it would be any more or less hazardous when it is dissolved in water (saturated solution). I am mainly interested in the context of workers or consumers that might come into contact with such a solution in a hypothetical situation. ike9898 (talk) 19:22, 7 April 2008 (UTC)

Dissolving in water will reduce fire hazard, but increases the risk that a breakage or spill will result in your substance going somewhere you don't want it. Graeme Bartlett (talk) 21:19, 7 April 2008 (UTC)
What about skin contact? Is skin contact with a saturated solution any more of less dangerous than skin contact with the solid? ike9898 (talk) 13:32, 8 April 2008 (UTC)
This seems like the sort of thing you can find on a Material Safety Data Sheet. You can find these from a chemical supplier, such as [2]. Nimur (talk) 14:35, 9 April 2008 (UTC)