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March 3

How does a GPS know its precision?

How can a GPS know if the precision of a result is 10m, 15 or 30m? Many results of mine are shown with this caveat. How can it calculate how wrong it can be? --Scicurious (talk) 02:29, 3 March 2016 (UTC)[reply]

There's actually an entire article on this, Error analysis for the Global Positioning System. -- BenRG (talk) 03:01, 3 March 2016 (UTC)[reply]

The most widely-used specific technique is called RAIM. Our article explains how RAIM works, and exactly what type of accuracy it provides. Fundamentally, the scheme works because we have extra satellites - we designed and built redundancy into the global navigation satellite system. As that redundancy degrades - for any reason, including weather, natural or artificial radio interference, satellites below the horizon, satellite or equipment malfunction, and so forth - the confidence in the signal is reduced.

If you use a GPS for, say, aeronautical navigation, there is a RAIM flag that is visible somewhere on the device. For example, the GNS530 will flash a yellow INTEG or a red WARN label when the GPS precision is not suitable for navigation. From the more detailed operator's manual, the vendor says that the device uses "certain software algorithms" including "Receiver Autonomous Integrity Monitoring (RAIM) and Fault Detection and Exclusion (FDE)." The device also offers a software tool to predict whether satellite coverage will be suitable at some other time and location, to assist in planning. The position of satellites can be predicted long in advance - you can download them manually, receive them from a radio link, or buy a device that contains those data in an up-to-date software database. Nimur (talk) 03:47, 3 March 2016 (UTC)[reply]

I do wish the GPS in a camera or camera phone would fill in the GPSDOP attribute in EXIF so the map could show a fuzzy circle when a hard little dot is misleading. Jim.henderson (talk) 19:23, 3 March 2016 (UTC)[reply]

Cross-correlation is done on received signals form satellite. The 1st generation of the SiRF chip was depending on wheel sensors and a compass was needed. The 3rd generation of the SiRF chip returned the lane of the road you are using. --Hans Haase (有问题吗) 17:26, 5 March 2016 (UTC)[reply]

Does mitosis occur in both somatic cells and sex cells?

According to what I know mitosis takes place in somatic cells while meiosis take place in sex cells only. But mitosis can be also in sex cells? in which stage? it's not clear to me. 93.126.95.68 (talk) 03:44, 3 March 2016 (UTC)[reply]

If by "sex cells" you mean the gametes (sperm and ovum) then they are produced by meiosis, and do not then divide again. The process by which they are generated will involve several divisions by mitosis, and then one by meiosis as the final stage. After that they must either combine with another gamete of the opposite gender, or die.109.150.174.93 (talk) 11:56, 3 March 2016 (UTC)[reply]

Under the typical definition of "sex cell," that term is synonymous with "germ cell," not with gamete, so let's not confuse the issue. Germ cells are a particular type of differentiated cell. Like other kinds of differentiated cells, they themselves arise from totipotent cells that have formed via mitosis. Once differentiated, sex cells (like most other differentiated cells) do not undergo mitosis again. The meiosis process is unique to sex cells and is the method by which gametes are produced. Evan ^{(talk|contribs)} 07:32, 4 March 2016 (UTC)[reply]

What does it mean "condensation" in context of chromosomes?

From here: "Meiosis I begins with the condensation of the chromosomes (B) in the leptotene during prophase I. During the pachytene (another stage of prophase I) (C) the pairs of homolog chromosomes align to form tetrads in a process called synapsis. Corresponding segments of DNA of sister chromatids of two homolog chromosomes twist and cross, forming so-called chiasmata. In these regions exchange of DNA between homologe chromosomes (C) can occur: crossing-over). Crossing-over (or crossover) requires that the chromosomes break and reconnect to the other chromosome." — Preceding unsigned comment added by 93.126.95.68 (talk) 04:25, 3 March 2016 (UTC)[reply]

DNA condensation is an article on this subject. DMacks (talk) 07:08, 3 March 2016 (UTC)[reply]

Ice skate friction

Quite obviously, the isotropic model of having a uniform coefficient of friction cannot correctly describe the action of figure skates, which clearly have different friction depending on relative motion to the ice. So I have been thinking that perhaps we need a "friction tensor", with two different coefficients of friction as its eigenvalues (one for the friction when the skate is oriented exactly parallel to the direction of motion, and another for when it is oriented orthogonal to the direction of motion; the "friction tensor" should operate on the skate orientation (vector) and current velocity vector, and so probably is not a true tensor). But I am not sure of how to construct this generalized friction formula and Googling "friction tensor" doesn't yield many useful results.--Jasper Deng (talk) 06:33, 3 March 2016 (UTC)[reply]

Tires have their own problems with the schoolkid version of friction, the keyword to search for is 'friction circle', which describes some of their behavior. In the case of figure skates that is still not very helpful,in all probability. Greglocock (talk) 07:54, 3 March 2016 (UTC)[reply]

We have an article about that: Circle of forces (Wikipedia:WHAAOE!) - although it goes by many names. In car racing circles, I've always called it the "traction ellipse" - but it's the same basic idea. It allows you to more easily visualize why it's dangerous to try to apply the brakes on your car while you're turning sharply - or why turning sharply while accelerating can cause fish-tailing. But even that doesn't adequately describe the full complexity of the situation because (for example) a quick touch of the brakes causes the car to pitch forwards, transferring more pressure onto the front wheels - and providing more traction for cornering.

The classical description of friction is only an approximation - and an extremely bad one in many real-world situations. For example, the classical description claims that the surface area of the contact zone doesn't alter the frictional force...which is true in some situations - but obviously untrue in others. Try dragging a large rug across the floor when it's unrolled versus when it's rolled up! Formula one race cars use smooth "Racing slick" tyres to increase the contact area - but switch to grooved tyres in the rain...the classical rule would say that the grooved variety should be perfectly adequate in all conditions...and very clearly, that's untrue!

With ice skates, the pressure of the blade is sufficient to melt a thin layer of ice - so you have a layer of water acting as a lubricant between ice and steel. Describing these things adequately with a nice, clean piece of mathematics is not always easy. Ice skates are the perfect example of that failure.

In order to develop a decent model for the dynamics of ice skates, you'd need experimental data that might be extremely difficult to obtain. However, for a reasonable approximation, using the "traction ellipse" approach would doubtless be a good model to start with - although in the case of ice skates, it's probably a very long, narrow ellipse. SteveBaker (talk) 13:36, 3 March 2016 (UTC)[reply]

This is a myth; the pressure is insufficient to melt water under typical skating conditions. It is, however, a good example of "things aren't that simple", as claimed! --69.159.61.172 (talk) 22:59, 3 March 2016 (UTC)[reply]

However, the melting action most definitely is not due to pressure alone. Also, in practice, indoor rinks have their temperatures maintained basically at freezing (the exact temperature distribution is the subject of my pet math problem as a solution of the heat equation).--Jasper Deng (talk) 03:42, 4 March 2016 (UTC)[reply]

In reality physics or in this case Tribology are bit more complicated and as dynamic proces it's far away from being as static as simple models suggest. Friction is based on "additional" mechanics and forces like a plane needs a starting speed for the wings to establish a lift force and thus to take off. Friction needs such an starting speed too! --Kharon (talk) 03:14, 6 March 2016 (UTC)[reply]

@Kharon: My question explicitly states that the current velocity of the skates relative to the ice needs to be taken into account.--Jasper Deng (talk) 04:13, 6 March 2016 (UTC)[reply]

Excuse me for my poor attempt, i wanted to point you to the complexity of real physics in comparison to its reduction on factors in mathematical models. Such models are set up to make one causality approachable for relieable analysis and synthesis. Like in a Testbed you try to establish same conditions for all your tests, else you never know what realy caused your results. Science and Engeneering use this reduction because a complex approach usually fails. So ofcourse you can take a more complex approach like adding a "friction tensor" to some simple friction model. Will that help you approach real physics, an engeneering project? I doubt that. Maybe thats the reason why you can not find anything about "friction tensor" on google. --Kharon (talk) 18:03, 6 March 2016 (UTC)[reply]

@Kharon: I'm sorry, but I have to say that you are not being especially helpful here. I'm already making lots of simplifying assumptions when I mention a "friction pseudo-tensor", namely that friction is still a linear function of the normal force. I knew all of what you are saying when I posted my question. None of that is relevant to the actual science of my question. Friction is a very complex phenomenon, and clearly, the simple isotropic friction model fails spectacularly for this system.--Jasper Deng (talk) 18:27, 6 March 2016 (UTC)[reply]

OK, sorry for the distraction then. Search on then. In case you fail you may want to try what all the other Engeneers with such projects always do: Get a nice Workstation, some CAD and Simulation software and try something with all the parameters you see fit. --Kharon (talk) 11:04, 7 March 2016 (UTC)[reply]

Is there such a thing as one replicate?

If an experiment is performed without replicates, is there one replicate or is that an oxymoron? ----Seans Potato Business 10:43, 3 March 2016 (UTC)[reply]

My impression is that "replicate" is indeed generally used to mean the total number of copies, i.e. "one replicate" means n=1. Some papers like [1] use this definition. That said, "no replicates" is also common usage, which would be in line with the idea that a replicate is a replica, rather than any old sample. Though grammar, or at least etymology, may be on their side, I think these usages are less formal and less common. The point remains unclear enough that I think people sometimes try to clarify using other language (n=1, "one sample per condition" etc.) rather than count on the "one replicate" language being taken correctly. For this reason, I think "one replicate" is relegated mostly to theoretical discussion of what to do with different numbers of replicates. Wnt (talk)

It's a linguistic minefield...I might say "I own three copies of this photograph" - implying that I have three actual photographs. But then I might tell someone "I need three copies of this photograph" - expecting to own four photographs at the end - or "There are no copies of this photograph in existence", meaning something entirely different depending on whether I have a photograph in my hand or whether I'm describing a long lost photograph that exists only in people's memories. I'd be very careful to clarify what I meant in cases where it matters! SteveBaker (talk) 13:43, 3 March 2016 (UTC)[reply]

If you're down with descriptive linguistics, then yes, it's easy to demonstrate that there is such a thing as a single replicate. Here's a whole list of books (mostly about math or experimental design for sciences) [2] that have "single replicate" in them. The second hit has a whole chapter dedicated to "More on single replicate factorial designs". SemanticMantis (talk) 19:47, 3 March 2016 (UTC)[reply]

Deadly biocontainment

In works of fictions such as Andromeda Strain and the Walking Dead, research facilities dedicated to the study of severe biohazards are designed with extremely lethal fail-safe mechanisms that are intended to sterilize / destroy the entire facility in the event of containment failure. In the real world, I'm pretty sure the CDC building in Atlanta isn't rigged to blow itself up in the event of a prolonged power failure. Among other problems, using explosives seems about as likely to spread infectious agents as to eradicate them. But I was wondering, are such fail-safe mechanisms pure fiction, or is there some nugget of truth to them? Maybe in a smaller scale, perhaps some high hazard labs monitor the air and respond to risks by automatically locking down and spray disinfectant over all surfaces? Dragons flight (talk) 13:39, 3 March 2016 (UTC)[reply]

Biosafety level makes no mention of any of that sci-fi stuff. The diagram of a level 4 containment unit (the highest designation there is) shows no explosives, nuclear weapons or racks of automatic weapons for dealing with zombie outbreaks. SteveBaker (talk) 13:48, 3 March 2016 (UTC)[reply]

Also, of note, additional containment failures in fictional works may be shown in works like The Stand (a person looking out for their own self interest accidentally lets the disease out) or 12 Monkeys (deliberate bioterrorism). I just wanted to add those just for sake of completeness. --Jayron 32 14:34, 3 March 2016 (UTC)[reply]

As far as what could be used, if they choose to do so, bleach in a high enough concentration is cheap and effective at killing a broad range of microbes, so some type of fire sprinkler system modified to spray bleach would get the job done. Of course, that would be deadly to any people in the area not wearing full containment suits and oxygen masks (would bleach damage those ?). You might also be interested in Halon, which is used to extinguish fires in critical area, like computer rooms. People are advised to evacuate the area before a Halon dump occurs, however, it's not nearly as dangerous as bleach spray would be. StuRat (talk) 17:23, 3 March 2016 (UTC)[reply]

You're worried about whether the people who are already wearing full positive-pressure/independent-air suits because they're in a BSL-4 are wearing full containment suits with their own air? DMacks (talk) 03:12, 4 March 2016 (UTC)[reply]

Yes, because I am imagining a situation where containment has already been seriously breached. For example, the little nasties have escaped the lab and are now in the office/administrative area of the building. It would be nice to be able to spray bleach throughout the entire building, but killing all the office workers would be a bad thing. Perhaps they could first be evacuated to a portable containment unit, and then be watched and treated for disease, while the office is sprayed down with bleach. This would also destroy all the office equipment, but if it would help to avoid unleashing a plague, that would be a small price to pay. StuRat (talk) 18:19, 4 March 2016 (UTC)[reply]

The whole idea of the containment lab is to contain stuff. All you're suggesting is adding yet another layer of containment - and if you're going to do that then putting the extra layer just around the lab area is better than trying to contain it inside the entire building. That's a far better idea because then you don't risk killing a whole bunch more people and leaving yourself with a bigger space to decontaminate if things go wrong. Moreover, the staff in that wider area won't have been trained in the correct protocols. In the end, they'll have added as many layers and backups to the lab area as is considered safe, affordable and necessary - and there is therefore no justification for adding yet another. SteveBaker (talk) 21:01, 4 March 2016 (UTC)[reply]

I would hope anyone who works in a biohazard facility would have some training on dealing with a leak (for the office workers, presumably that would be how to evacuate safely). StuRat (talk) 23:04, 4 March 2016 (UTC)[reply]

I'm not sure we can rely on any normal sources here. Legitimate biological facilities are meant to contain pathogens for study and treatment, but the hypothesis in sci-fi may be that the facility is or was a secret bioweapons facility. (How secret? Secret enough that nobody on the Refdesk can find any references about it!) Given the extreme political fallout that can occur when such a program is revealed, and the potential that attackers may be leaving with weaponized systems, it might make sense to have a contingency for attacking the site, and perhaps even to build some of that in. Basically ... it's hard to debunk a work of fiction. :) Wnt (talk) 17:57, 6 March 2016 (UTC)[reply]

can Vasectomies and tubal ligations be performed easily on cats

I would have a deep objection to having my cat castrated, if I owned one. Part of this is me anthropomorphising, no question. But also, once you remove a tomcat's testicles, you "knock him off his perch" in terms of his position in the hierarchy of the local cat population (he gets pushed right to the bottom). Similar concerns have been raised in places in Europe where it's accepted practice to "catch, neuter, and release" stray cats, (as opposed to those countries which euthanize them or put them up for adoption). If you neuter the tomcats, you potentially disrupt the whole social order of the colony.

My question is, how difficult would it be, from a veterinary perspective, to perform a Vasectomy on the tomcat instead, which obviously would not cause these issues? How much more expensive and time-consuming a procedure would it be?

Similarly, with female cats ("queens"), how much more difficult (veterinarily speaking) would it be to perform a Tubal ligation rather than the standard practice of "spaying" - in other words, so that the queen would still have her cycles and come on heat and mate, but would be extremely unlikely to get pregnant? (yes, I'm aware that tubal ligations can, in extremely rare cases, spontaneously reverse themselves, but the risk is so low, let's put it aside, and stick to the question of the difficulty of the veterinary procedure, and any side effects of each option). Eliyohub (talk) 14:59, 3 March 2016 (UTC)[reply]

Here is a discussion of the issues with performing such procedures on pets, while this page makes it clear such procedure can be done, though it is harder to find a veterinarian that does them. --Jayron 32 16:30, 3 March 2016 (UTC)[reply]

Adult cats, especially toms, that haven't been neutered exhibit extremely obnoxious behavior, like spraying urine all over to mark territory, fighting, and caterwauling, in the middle of the night. They really don't make good pets, and their lifespan is likely to be shorter due to the need to go out at night and prowl. StuRat (talk) 17:29, 3 March 2016 (UTC)[reply]

One veterinarian, whose name I do not remember, has written that animals that retain their gonads (but have been sterilized) have a longer life expectancy than ones that have had their gonads removed, because the hormones have a beneficial effect. This differs from what StuRat says. I haven't researched the issue. Robert McClenon (talk) 17:57, 3 March 2016 (UTC)[reply]

To the OP. I would not be overly worried about a tom-cat falling in the dominance hierarchy after castration. Cats mediate much of their communication using olfaction. Where there are multiple cats in one area, the cats patrol and mark their territory with pheromones. It is often the interpretation of these pheromones alone which conveys the dominance - the cats might never meet. As the pheromones degrade, other cats can tell how long it has been since the marking cat was there and will avoid patrolling the shared territory at the same time. By the way, many cat screams at night are due to mating. Cats are induced ovulators. The male has backwards pointing spines on his penis and it is the sensation (pain, hence the scream) of withdrawal that induces the female to ovulate. DrChrissy ^(talk) 17:59, 3 March 2016 (UTC)[reply]

By the way, a tom-cat that has been castrated by a vet using appropriate anaesthesia and analgesics has had it lucky! I defy any male reading this to now read the elastration article without wincing or crossing their legs! DrChrissy ^(talk) 18:06, 3 March 2016 (UTC)[reply]

I once read a study where they investigated (in part) cats screaming during copulation. They inserted smooth glass rods into female cats, and the cats still screamed. The conclusion was that female cats do not scream due to the spikes on the penis. This not to say that the copulation is not painful, it may be, but it does show the screaming is independent of the spikes. It's also conceptually possible that the screams indicate pleasure. Here is a photo of a textbook [3] describing the study, and the citation seems to be-- "W. Greulich Artifically-induced ovulation in the cat (Felis domestica) Anat. Rec., 58 (1933–1934), pp. 217–224 --, though I cannot find an online copy. Finally, Sexual_conflict#Spiky_genitals and Penile spines are our relevant articles. Anyway, the point is we shouldn't jump to conclusions about pain. It's hard to study, and the parsimonious assumption is generally that animals enjoy copulation. SemanticMantis (talk) 18:29, 3 March 2016 (UTC)[reply]

Interesting study with the glass rods - perhaps it is the dilation of the vagina by the rods/penis that causes the female cat to scream. Note I avoided suggesting pain to describe the motivation. You are correct to indicate the cat could be screaming with pleasure. Having said this, that would not be the most parsimonious explanation. The most parsimonious explanation is that cats do not experience pain and the female is screaming simply because she is motivated by a stimulus-response association. (please note, I do not believe this for one second, so you could very easily see me arguing against myself in my next post here!) DrChrissy ^(talk) 23:53, 3 March 2016 (UTC)[reply]

I don't know about cats - but when we investigated neutering for our dog, the research said that doing it at a very early age (as has historically been the common practice) does indeed shorten the animal's life, and has several other unfortunate outcomes. But that's because the natural growth into adulthood is disrupted. But neutering at the beginning of adulthood doesn't have that deleterious effect on lifespan and avoids most of the other problems. That said, there is sometimes a period of adjustment right after the neutering during which there can be some short-term issues. SteveBaker (talk) 20:09, 3 March 2016 (UTC)[reply]

Not buying the shortened lifespan thing given the evidence that it actually increases it ([4], last sentence of intro paragraph here, [5]). Some mixed findings for dogs ([6]). A few quotes:

The behavior of most sexually intact male cats makes them undesirable or dangerous as pets. Because castration substantially reduces these sexually dimorphic behaviors, it is recommended that all male cats not intended for breeding be castrated prior to puberty and that all breeding males be castrated as soon as their use as a breeding male has ceased.
— Kustritz, Margaret V. Root. 2007. “Determining the Optimal Age for Gonadectomy of Dogs and Cats.” Journal of the American Veterinary Medical Association 231(11):1665–75

Most studies evaluating lifespan suggest that neutered animals live longer than intact animals (Kraft 1998; Greer et al. 2007). Increased lifespan in castrated male dogs may be due to a decrease in risky sexually dimorphic behaviours such as roaming, or to increased owner investment in the animal’s care (Bronson 1982; Michell 1999; Moore et al. 2001). Castrated cats have reduced mortality compared with intact cats (Kalz 2001).
— Root Kustritz, M. (2012), Effects of Surgical Sterilization on Canine and Feline Health and on Society. Reproduction in Domestic Animals, 47: 214–222. doi: 10.1111/j.1439-0531.2012.02078.x ([7])

It seems generally that there are possible complications from the surgery and some related disorders, but afaik most vets suggest spay/neutering your pets. The evidence seems especially strong for male cats. If you really want to increase your cat's lifespan, keep it indoors. EvergreenFir (talk) Please {{re}} 00:31, 4 March 2016 (UTC)[reply]

Displacement of the SS Badger

Hello!

I am currently working on a draft of said article for the German Wikipedia. As it is customary to give the displacement of a ship, I would use the numbers given on the homepage of 6650 "tons". But: what kind of ton? Metric (tonne) at 1000kg? British long ton at 1016 kg? Or short ton at 907kg? Can someone help me on that point? Kind regards, Grand-Duc (talk) 22:32, 3 March 2016 (UTC)[reply]

SS Badger operates in the United States, so it seems like the U.S. Coast Guard rules would apply. I found this brochure, Documentation and Tonnage of Commercial Vessels, on the Coast Guard's website (although note that the informational pamphlet is aimed at operators of smaller vessels, less than 79 feet). Tonnage is reported using one of the standardized systems of measurement - none of which are trivially converted to units of mass.

More references and reading material: Tonnage related links.

Nimur (talk) 23:06, 3 March 2016 (UTC)[reply]

Ok for the tonnage as size measurement, but, as I understood Badger's website, it's clearly a fact about weight ("Weight: 6650 tons displaced"). So, how could you put that in a definitively metric kind of unit? Kind regards, Grand-Duc (talk) 23:14, 3 March 2016 (UTC)[reply]

See ton and tonnage for additional information as to the complexity of the concept of the "ton" as applied to ships, where it is a unit of volume rather than of weight or mass. Robert McClenon (talk) 01:49, 4 March 2016 (UTC)[reply]

I had a look on the German Wikipedia (despite being unable to read or speak German) it appears that older ships like de:Bismarck (Schiff, 1939) show their displacement in tons. Newer ships like de:Explorer (Schiff, 1969) use an SI unit "BRZ" and "NRZ", linked to this page, which may explain things if you can read what's written there (I did try "Teach Yourself German" some years ago, but didn't get beyond "The landlady loves the policeman"!). Alansplodge (talk) 11:20, 4 March 2016 (UTC)[reply]

The Bismarck as battleship was subject to other politics than merchant marine ships, their displacement is indeed calculated using British long tons, but this was/is IIRC not mandatory for civilian vessels. The abbreviations BRZ and NRZ stand for Bruttoraumzahl and Nettoraumzahl, units of volume that are the follow-ons to the deprecated BRT/NRT (Brutto-/Nettoregistertonne = gross / net tonnage). To add to the confusion, I checked Badger's IMO number and a new number popped up, the dead weight (DWT) at seemingly 3058 tons (a bit small for a 125m icebreaking ferry, isn't it?). Well, it still does not state if it's a metric or imperial unit. :-/ I guess I simply have to let this value out of the infobox. Thanks for all ideas given! Kind regards, Grand-Duc (talk) 18:25, 4 March 2016 (UTC)[reply]

Deadweight tonnage is the measure of the cargo capacity of the ship - it does not include the weight of the ship itself. Rmhermen (talk) 19:39, 4 March 2016 (UTC)[reply]