Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

July 14

Penis in vagina

Why is "penis in vagina" sex so ubiquitous in nature compared to fertilizing eggs externally or other methods of non-preventative procreation?

Cause it's a lot more fun. Contact Basemetal here 17:31, 14 July 2015 (UTC)

That reply is of course completely and utterly backwards. It is 'fun' because if it wasn't, animals wouldn't engage in it, and would thus fail to reproduce. AndyTheGrump (talk) 17:39, 14 July 2015 (UTC)

And of course many animals don't need to do anything of the sort. Penis-in-vagina sex is in no way necessary for a viable population, as demonstrated by my many refs below. SemanticMantis (talk) 18:59, 14 July 2015 (UTC)

There is obviously a benefit to letting a baby grow in the womb for a while instead of laying an egg. So, in that case, how else do you expect the egg to be fertilized? 209.149.113.136 (talk) 17:38, 14 July 2015 (UTC)

As noted below, the male can just hand the female a sperm packet (an entirely different way to deliver one's package). StuRat (talk) 20:11, 14 July 2015 (UTC)

You're really missing out on the wide wide world of sex! In fact, the way humans procreate not the norm. First let's get plants out of the way - pollination uses no penis nor vagina, and often involves a second species pollinator as an intermediary.

For animals - did you know that squid use a special arm called a Hectocotylus to inseminate females? And then there's many things that use Spermatophores - a salamander puts a little sac of sperm down, then does a mating display, and if the female likes it, she'll take it in to her body. Of course most bony fish use external fertilization, as do many amphibians, corals, protozoans, etc.

The Bdelloid rotifer has some of the weirdest "sex" - they have no males, only females, and they can incorporate DNA of their dead sisters when rejuvenating after dessication! Discover magazine couldn't resist a little anthropomorphic language, and called them Lesbian Necrophiliacs [1]

Then there's the bedbugs and other invertebrates that use traumatic insemination - the females don't have anything like a vagina, and a male just sort of stabs in to the abdominal cavity. And while we're on the topic of insect genitals, they don't have penises, they have Aedeagus, which is a rather different thing altogether.

Every male hymenopteran is born from an unfertilized egg! That's part of the fun of haplodiploidy.

The Amazon_molly reproduces solely through gynogenesis - a male (of a different species) is required, but his sperm do nothing! Then there's the very common Parthogenesis, which leads to things like many female aphids being born pregnant with another female - no sex required.

There are many other strange tales of sex and nonsexual reproduction in the living world, but hopefully this gives you a better feel for the variety of things out there that can get the job done just fine. While there are many benefits to internal fertilization and live birth that result from penis in vagina copulation, that form is not the norm, neither by number of species nor by number of practitioners. SemanticMantis (talk) 18:57, 14 July 2015 (UTC)

It might be the most common, if you look at total biomass of animals that engage in internal fertilization (since that would be "heavily weighted" towards larger animals) versus other forms of sexual reproduction (since that leaves out most microbes). StuRat (talk) 20:10, 14 July 2015 (UTC)

Nope. Good thing to think about, but terrestrial insects have more biomass than terrestrial vertebrates, and they don't have penises. Just ants alone have about the same biomass as humans do. And that's not even mentioning huge amounts of bony fish and marine invertebrates, compared to the very few marine animals that practice internal fertilization. Biomass_(ecology)#Global_biomass has some info, but could use some expansion. I'll buy that PIV copulation is the most common method of fertilization among terrestrial vertebrates (by species number, individual number, biomass, etc), but that's about it. SemanticMantis (talk) 20:36, 14 July 2015 (UTC)

More variety that I should mention - most birds don't have anything like a mammal penis - see Pseudo-penis and cloaca. Spiders use another type of specialized "arm" for insemination - the Pedipalp. SemanticMantis (talk) 21:25, 14 July 2015 (UTC)

MAF sensor disconnection

Most cars (for some time now) are equipped with a mass air flow sensor I know some cars have a MAP sensor but my question is only in regards to vehicles with MAF sensors. Some vehicles will still run with the MAF sensor disconnected while others will not run at all with the MAF sensor disconnected. Why is this? Void burn (talk) 13:57, 14 July 2015 (UTC)

The MAF is used to tell the computer how much air is coming in. If it is disconnected, the computer gets no signal. So, the computer could be programmed to assume "average" air flow and then send an "average" amount of gas to the engine. Or, the computer could be programmed to assume "no" air flow and then send "no" gas to the engine. It is really up to the engineers to decide what to do when the MAF sensor isn't sensing anything. 209.149.113.136 (talk) 15:35, 14 July 2015 (UTC)

I would imagine that it would be better engineering to program the computer to assume "average" Stoichiometry so that in the event the MAF sensor stops working the vehicle will still drive until the MAF can be repaired. Seems like this should be an industry standard if reliability is desired. Void burn (talk) 17:16, 14 July 2015 (UTC)

In the interests of robustness the engine will attempt to estimate the MAF from the throttle plate angle and the rpm, if the MAF sensor fails. Greglocock (talk) 01:05, 15 July 2015 (UTC)

How can you determine the percentage some feature is determined genetically?

What scientific methods besides comparing twins are useful to tell the percentage that genes plays in a feature? For example, what's the % of our height, intelligence, that's genetically determined. Or how do genes increase the chances we develop some illness like Parkinson or Alzheimer's.--Scicurious (talk) 23:12, 14 July 2015 (UTC)

You're right that twin studies are an important tool. Other than that see Disease_gene_identification - now heavily influenced by genomics. There's some info and refs at Nature_versus_nurture#Advanced_techniques, but it's not a very good section. Make sure you read the section on IQ in that article and we have a whole article on Heritability of IQ. Lots of work is also done with model organisms - Knockout_mouse is a very common and popular tool. SemanticMantis (talk) 00:29, 15 July 2015 (UTC)

Those are some general methods; for your specific questions, see Parkinson's_disease#Genetics and Parkinson's_disease#Genetics. The "percent influence" of genetics is hard to quantify, and my understanding is that each research project will operationalize that concept for each specific question, but there are some general approaches discussed at Heritability#Estimating_heritability. The claims in those disease articles both have refs to the academic literature, if you don't have access you can often find reprints by googling the title, or you can ask for a copy through WP:REX. You may also be interested in List_of_genetic_disorders. SemanticMantis (talk) 00:39, 15 July 2015 (UTC)

You must have an inherited tendency to repeat Parkinson's_disease#Genetics. :-) StuRat (talk) 00:46, 15 July 2015 (UTC)

Right, Alzheimer's_disease#Genetics. SemanticMantis (talk) 01:02, 15 July 2015 (UTC)

Some evidence can be gleaned by looking at two large and genetically similar populations in different environments. For example, comparing cancer statistics within China to cancer statistics amongst Chinese immigrants to the United States, as was done in this study. It's conceptually similar to a large-scale twin study. Someguy1221 (talk) 02:56, 15 July 2015 (UTC)

"For example, what's the % of our height, intelligence, that's genetically determined." Is it true that the characteristics of genes (or the characteristics that give rise from genes) are largely determined by environmental variables? Void burn (talk) 17:16, 15 July 2015 (UTC)

The phrase "explained by" is sometimes seen in popular literature that presents statistical arguments. I view such vagueness with great suspicion. One of the meanings it might have is discussed in Cross Validated. Jim.henderson (talk) 17:55, 15 July 2015 (UTC)

Oh. We do have an article "Explained variation" with appropriate criticism. Jim.henderson (talk) 18:00, 15 July 2015 (UTC)

July 15

bainbridge reflex

wanna know about bainbridge reflex05:52, 15 July 2015 (UTC) — Preceding unsigned comment added by 36.252.1.148 (talk)

Have you tried Bainbridge reflex? Richard Avery (talk) 06:14, 15 July 2015 (UTC)

Mononucleosis

Is kissing the only way mononucleosis is transmitted? 90.192.122.101 (talk) 07:34, 15 July 2015 (UTC)

And sexual intercourse. As the article says, "A person becomes infected with this virus by direct contact with infected body fluids", including saliva, urine, blood, and tears, so any licking and spitting would do it, and sharing food etc.--Shantavira|^{feed me} 08:01, 15 July 2015 (UTC)

then why isn't it more common if it can be pretty much transmitted through all of those? That's almost daily human contact. Surely everyone should get it then. 90.192.122.101 (talk) 09:04, 15 July 2015 (UTC)

Our article says, "About 95% of the population has been exposed to this virus by the age of 40, but only 15–20% of teenagers and about 40% of exposed adults actually become infected." You're correct that almost everyone gets it eventually. The terminology can be a little confusing. Let me try to summarize. Mononucleosis has multiple causes, but the overwhelming majority of cases are caused by the Epstein–Barr virus. However, only a minority of people who contract the virus will develop mononucleosis. In the majority of people it causes no or only minor symptoms. Epstein–Barr is a member of the Herpesviridae, which also includes among other viruses the chicken pox virus and the viruses that cause herpes simplex (usually simply called "herpes"). The Herpesviridae are adapted to evade the immune system and establish a latent infection that persists for the rest of your life, essentially "hiding" inside some of your cells. The viruses sometimes simply lay dormant indefinitely, but they can become reactivated and cause a new outbreak. Herpes is well known for repeated cycles of active and latent infection, and reactivation of the dormant varicella (chicken pox) virus in previously infected persons is what causes herpes zoster, commonly known as shingles. Because they usually persist indefinitely in infected hosts, cause relatively limited symptoms, and are easily transmitted, many of the Herpesviridae are near-universal in the adult human population. This ties into what's called optimal virulence; pathogens tend to become less damaging to their hosts over time. Pathogens want to reproduce, and relatively healthy hosts can spread them better than really sick or dead ones. These viruses are quite evolutionarily successful! As a personal demonstration, I am cytomegalovirus positive, but I've never had anything worse than a typical cold, so I probably had an asymptomatic infection. The only reason I know I'm infected with the virus is because I donate blood, and all donors are tested for the virus, because CMV positive blood can't be given to pregnant women, newborns, or immunocompromised people. Anyway, I hope that was informative! If you liked my explanation, I have one request: donate blood regularly if possible! It saves lives! Thank you. --108.38.204.15 (talk) 12:26, 15 July 2015 (UTC)

Look at virulence and optimal virulence. Diseases do best the longer their hosts live and the better those hosts spread their germs to others. New pathogens like HIV usually spread at first because they are highly communicable. But if they cause quick morbidity and death, they don't pass on to as many hosts as possible. Over time, strains that stress the host the least tend to become the most common (although their are other factors involved which can counteract this). Many viruses like herpes viruses ("everyone has herpes") become widespread but cause fewer obvious symptoms. For example, my mother gets cold sores, but none of the rest of us in my immediate family do. I got shingles while in the hospital, but the case was so mild I thought I had a mosquito bite. Of my clique at college, only one of us "got" mono (i.e., symptoms), and that led to hospitalization for jaundice, but none of the rest of us did, although there was some intimate contact within the group. As long as a disease has any easy time of spreading (promiscuity, large classrooms) it will tend to become less and less symptomatic while it becomes ever more prevalent. μηδείς (talk) 21:13, 15 July 2015 (UTC)

Saved shark? Looked pretty dead to me.

There've been some reports (for example here) of a stranded juvenile great white that was supposedly "saved" yesterday in Cape Cod. In the footage that I've seen it looked utterly dead and I have not seen any footage showing it swimming away. Does it look like websites just repeated the story without checking it? How do they know it was saved? Does anyone here have any source that can prove it swam away? Is it at all credible that a shark that was beached for hours can survive the ordeal? Contact Basemetal here 14:28, 15 July 2015 (UTC)

Did you not see it move its mouth and tail at ~5 seconds, and everybody cheers? Later, in the water, a guy says something like "see the gills pumping"? and if you look closely you can see that too. The shark certainly doesn't look dead to me in that video, though I admit it's not clear or certain that it will still be alive next week (I guess that goes for all of us ;) For further video evidence, see here [2] - the second video shows the shark clearly swimming under its own power - apparently they dragged it about a mile out. Probably took a while to recover from the shock and get more oxygen in to its blood. SemanticMantis (talk) 14:47, 15 July 2015 (UTC)

I did see it move at the beginning but then by the time they towed it into the water it looked pretty dead. But you're probably right. Here's another video. It seems to show footage of the shark finally moving in the water and it confirms that it took a long time to bring it back. Now as to my more general question: How long can a shark stay out of the water and still remain capable of being brought back? Incidentally this reminds me of a scene (having to do not with a shark but an octopus) in the Japanese movie Departures (about 18 m 30 s into the movie) where the woman (Ryōko Hirosue) brings home an octopus for dinner. But then suddenly the octopus starts moving on the kitchen floor. The couple (husband played by Masahiro Motoki) rush to release it in Tokyo harbor but the guy's already dead. How long can you keep an octopus out of the water before it dies for good? Contact Basemetal here 18:06, 15 July 2015 (UTC)

See here [3] for a discussion of the octopods. Several people are reporting survival out of water times on the scale of hours. Given that many of them have a natural behavior of moving over land between tide pools, it's not so surprising that they can survive out of water for a while, especially if kept moist. SemanticMantis (talk) 18:43, 15 July 2015 (UTC)

Maybe this will turn out to be like the lion and the mouse, and the shark will refrain from munching on swimmers. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:01, 15 July 2015 (UTC)

Yeah right I wouldn't count on it. Now if you wanna get in the water, be my guest A shark's brain is pretty small. They're superefficient killing machines but I doubt they can remember anything. Killer whales would be better candidates, but they don't munch on swimmers to begin with. At least there's no recorded case in the wild and what happened in Florida a few years back was clearly an accident. (In fact the guy didn't munch on anything but it did drown its trainer) Contact Basemetal here 18:06, 15 July 2015 (UTC)

"At least there's no recorded case in the wild" - in other words, they make sure not to leave any witnesses. Iapetus (talk) 10:45, 16 July 2015 (UTC)

Without getting into the realm of legal advice, it's still interesting to imagine that if someone is attacked by a shark, and it could be proven to be the one that was put back in the ocean, whether those who did so could be held liable for the attack. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:27, 15 July 2015 (UTC)

There should be a big "if" attached to the "it could be proven". I'm not sure anyone took a DNA sample that would stack up in court, nor did anyone attach a tracker. It's possible there are sufficient high resolution photos showing the dorsal fin or other unique markings, and despite these being from a juvenile [4] [5] they could be used to uniquely identify the shark later (bearing in mind the standards acceptable for tracking are likely to be different from that for a court case) but this seems unlikely. Noting you'll also need to be able to use the same method for the attacking shark. Nil Einne (talk) 02:55, 16 July 2015 (UTC)

If you tie a rope around a shark's tail, and drag it into the ocean with a boat as these people did, how then do you get the rope off the tail?Edison (talk) 03:13, 16 July 2015 (UTC)

Using hands? Maybe a knife or safety scissors. I can't tell from the video how they tied it on, but I'd probably use some sort of quick release knot, perhaps some variant of the Highwayman's_hitch [6] or some other slipped knot. SemanticMantis (talk) 14:20, 16 July 2015 (UTC)

From comments I've seen the bystanders could have dragged it into the water with their bare hands (assuming they had the physical strength to do it) with no danger to themselves as the shark in the position it was beached in couldn't hurt them (unless they were foolish enough to go stick their hands in its mouth) but that alone would have been pretty pointless as the real hard thing was to induce it to start breathing again, to restart its gills. Apparently, even in the water, if a shark doesn't keep moving, it suffocates. Other species of fish have the ability to breathe while staying put but not sharks. So, after they had dragged it into the water, the shark had to be towed alongside the boat to revive it and that took some time. In any case you couldn't do that by dragging it from its tail. They had to tie a rope around its trunk or whatever that part of the body is called. I suppose that makes the problem of getting back your rope a little easier to solve, if that's what you're worried about. Contact Basemetal here 15:41, 16 July 2015 (UTC)

July 16

What's the name of this rock formation

Please, what's the name of this kind of rock formation ?

The “teepee fountain” in Thermopolis, WY

As far as I understand, it works almost like a stalagmite/tite, but water/sediments come from the inside, no ?! Thanks in advance. Blump007 (talk) 04:35, 16 July 2015 (UTC)

It's called a flowstone. --Jayron32 04:36, 16 July 2015 (UTC)

Thanks. I previously searched flowstones but they seem to be only inside (caves), don't they ? Blump007 (talk) 04:40, 16 July 2015 (UTC)

Not necessarily. Travertine is a common flowstone that is found deposited at the surface. The only requirement for forming flowstone is mineral-rich waters that flow over the same area slowly for very long periods of time, to allow for precipitation and lithification of the minerals. They are often found in caves because the environment of a cave is often left undisturbed for millennia, but they can form in other environments. --Jayron32 04:48, 16 July 2015 (UTC)

Thanks a lot, that's very informative (+ I added the name of the one pictured) Blump007 (talk) 05:43, 16 July 2015 (UTC)

@Blump007: Thanks for uploading this unusual image to Commons. But please - can you confirm for the description that it was taken in Thermopolis, Wyoming, and when it was taken? We ought to illustrate that article with this photo. I can almost, but perhaps not quite, confirm it is the same one from something like [7]. Wnt (talk) 15:03, 16 July 2015 (UTC)

This is the official website of Hot Springs State Park in Thermopolis, and has pictures of the above formation as well. --Jayron32 00:51, 17 July 2015 (UTC)

Does ESP8266 has an hardware AES engine or not?

ESP8266[8] is a popular wifi-enabled SoC. I'm trying to figure out whether it has a hardware accelerated AES engine or not.

Evidence point to YES:

1. Googling "ESP8266 AES engine" yields dozens of sites saying the affirmative, though most of them likely just copy and pasted that information from somewhere else.

2. ESP8266 contains an ARM Cortex-M4 core. Googling "Cortex-M4 aes" suggests that most manufacturers pair a hardware AES engine with their Cortex-M4 SoCs, so it's likely that ESP8266's manufacturer has done the same.

Evidence point to NO:

1. This reposity[9] contains a purely software implementation of AES, would seems to suggest that there's no hardware AES engine, at least not one that's available to the user. My other car is a cadr (talk) 14:07, 16 July 2015 (UTC)

This might be better answered at Wikipedia:Reference_desk/Computing. shoy (reactions) 14:28, 17 July 2015 (UTC)

Thanks. Moved.My other car is a cadr (talk) 03:14, 18 July 2015 (UTC)

July 17

What happens when the inputs to a phototransistor is shorter than its response time?

Please see this drawing[10]. The first frame is my (admittedly poor) understanding of a phototransistor's response time. Please correct me if there's any mistake.

My question is, what happens when the duration of the input is shorter than the phototransistor's response time? Is there still a delayed response, or is there no response at all? (The latter case being like your car, if you don't turn the key long enough, it doesn't start at all)

Assuming there's still a response, what happens when the input is shorter than even the rise time? Would there still be a cut-off triangular-shaped rise? What would the response waveform look like?

Lastly, is there a minimal input duration below which the phototransistor makes no response at all? My other car is a cadr (talk) 06:36, 17 July 2015 (UTC)

I think you are correct in assuming that you will get a smaller output. You may be able to see this in a frequency response chart. At high frequencies the output will be reduced. Graeme Bartlett (talk) 08:33, 17 July 2015 (UTC)

Electromagnetic radiation vs particle radiation

The quantum of electromagnetic radiation is photon. Then why is electromagnetic radiation not considered to be a particle radiation? --IEditEncyclopedia (talk) 06:46, 17 July 2015 (UTC)

It is, you use the theory that is most useful to you. Graeme Bartlett (talk) 08:16, 17 July 2015 (UTC)

In our article Radiation, three types are described in the lead paragraph: electromagnetic radiation, particle radiation and acoustic radiation. EM radiation is not included in particle radiation. --IEditEncyclopedia (talk) 08:37, 17 July 2015 (UTC)

My reading of that lede is that what are being give are examples, which are neither exhaustive nor necessarily mutually exclusive. Notice that examples given of particle radiation include β radiation which comprises electrons, but electrons can also be interpreted as waves. These phenomena are neither "pure" particles nor "pure" waves, but something else that appear to be either, depending on how you look at/detect them: see Wave-particle duality. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 12:57, 17 July 2015 (UTC)

half life

Why is half life in first order reaction independent of initial concentration but not other order reaction? — Preceding unsigned comment added by 36.252.1.178 (talk) 08:28, 17 July 2015 (UTC)

In first-order reactions the rate of reaction is proportional to the concentration, and the rate of change of the concentration is the same as rate of reaction. You can see from the formula that the left over is proportional to the initial amount. This results in an exponential decay of the initial product. SO for half life look at the t for e^-kt=⁠1/2⁠. With other orders of reaction the relative rate will change on concentration. You can reverse the formula so C=C_i×⁠1/2⁠ after a half life for each C_i. Take the derivative of this. You will get rate of change of C is then proportional to C_i and not C_i² or any other power. Graeme Bartlett (talk) 08:39, 17 July 2015 (UTC)

In case of first order reaction, if initial concentration is $a$then after first half life time it will become ⁠1/2⁠a and after same time it will become ⁠1/2⁠ *⁠1/2⁠a and so on.

Then what is the similar physical interpration for other case (for those dependent on initial concentration)? Does it change continously for a same rxn with time or not? 36.252.1.178 (talk) 09:04, 17 July 2015 (UTC)

for second order the reaction rate is proportional to the square of concentration, for example sulfur monoxide reacting to form disulfur dioxide. Then the rate will drop off much more rapidly. But for zeroth order the rate is constant no matter what the initial concentration (within limits). Graeme Bartlett (talk) 12:53, 17 July 2015 (UTC)

Supermassive black holes

I was looking at the supermassive black holes article and I see no mention of the contribution of dark matter to their size. Has anyone estimated how much WIMPs would contribute to them, would it just be in proportion to the amount of dark matter in the galaxy or quite different? Dmcq (talk) 09:42, 17 July 2015 (UTC)

It is normally thought that black holes form almost entirely from barionic matter. Ruslik_Zero 19:26, 17 July 2015 (UTC)

Thanks I'd have thought after getting large a black hole would grow by the amount proportional to the density of matter in the neighbourhood times average speed by the area of the black hole. And there's lots more dark matter and it probably goes a bit faster if it forms a halo. I guess though the density of dark matter near the center of the galaxy must be low compared to the visible matter there which would explain why only the visible matter matters. Dmcq (talk) 21:00, 17 July 2015 (UTC)

Basically in order to fall into the black hole, matter of any type has to lose angular momentum by interactions with other matter -- otherwise it will just orbit around the black hole indefinitely. But the ways that dark matter interacts with itself or with normal matter are essentially not understood at all. So it is impossible to predict the rate at which it will fall into the black hole, even within orders of magnitude. Looie496 (talk) 13:45, 18 July 2015 (UTC)

I thought those orbits also caused the organised orbits as in the disc of the galaxy. In that case if the dark matter has very littler interaction it should just be in a blob rather than form nice orbits, so instead of orbiting the black hole nicely it would just approach it at random perturbed by the gravitation as it goes out to the halo and back. But then again it looks from the articles that spiral galaxies are younger than the elliptical ones so they must start off going in nice orbits and later get mixed up which is rather strange. It's not what I expected. Dmcq (talk) 14:48, 18 July 2015 (UTC)

Why doesn't the B2 Stealth Bomber need a rudder to control yaw?

How does it do vertical stabilization/control with no rudder? 20.137.7.64 (talk) 15:29, 17 July 2015 (UTC)

There is a general discussion of the problems of yaw control in flying wing aircraft at flying wing#yaw control. Not sure which specific solution is used in the B-2. Gandalf61 (talk) 15:45, 17 July 2015 (UTC)

The B2 has a drag rudder and a very complex computer. 209.149.113.45 (talk) 15:46, 17 July 2015 (UTC)

The aircraft is actively controlled for stability. Here's an Air Force website that explains: "The outboard wing trailing edge has split (drag) rudders which provide yaw control. Three sets of elevons (outboard, mid, inboard) provide pitch and roll control."

Nimur (talk) 16:13, 17 July 2015 (UTC)

Here's a document produced by a senior aerodynamicist at BAE, available on DTIC, Stability and Control of UCAV Configurations. It's not about B-2; but it expounds several options for unconventional yaw control on blended body and flying wing aircraft. Among the options: thrust vectoring, reaction control systems, symmetric split drag control surfaces (as used on the B-2 drag rudder). Here's an aerodynamic engineering lecture note from Virginia Tech on the topic of B-2 aerodynamic control specifically. Its author calls out numbers for CG and CP as well as details of the control surface.

Nearly all technical information about B-2 is confidential - even though the aircraft is a few decades old - so a lot of what you will find is analysis by way of reverse-engineering; and little snippets of facts that are officially released to the public. It is difficult to verify the accuracy of such details. Nimur (talk) 16:25, 17 July 2015 (UTC)

I feel obliged to remind the non-aviators: bank turns the aircraft - not yaw! It took a while to find a good reference to clarify this point using only illustrations and non-technical language, and finally: here is Banking Turn, from the NASA Glenn Research Center's Beginner's Guide to Aeronautics.

This is one of those things that's a little bit unintuitive to the non-pilot: you don't (normally) turn the aircraft using the rudder. You control yaw using the rudder, but you turn by rolling into a bank and holding attitude. This causes aerodynamic lift generated by the wings to act as a centripetal force, pulling the aircraft into the turn. In coordinated flight, the pilot also controls yaw to ensure passenger comfort and aircraft stability. For the B-2, where yaw control is marginal, passenger-comfort and aircraft stability are also marginal.

Furthermore - B-2 aircraft operate out of only specific military airfields, where they won't have to contend with serious crosswinds. This eschews the need for very effective cross control. We probably cannot find exact numbers for the maximum demonstrated crosswind capability of the B-2 - but it's probably lower than the published procedures for the U-2 - which can safely land with crosswind component in excess of 15 knots! (This is to say nothing of a conventional landing gear aircraft like the Citabria, where rudder authority means everything: the manufacturer advertises the 7GCAA with a maximum demonstrated crosswind component of 17 kts!)

Nimur (talk) 18:18, 17 July 2015 (UTC)

What does "authority" mean here? Is it part of aviation controlled vocabulary, or are you just using it in a fairly normal metaphorical sense to indicate the large effect of the rudder in the control system? SemanticMantis (talk) 22:38, 17 July 2015 (UTC)

In the context of steering a vehicle, or controling a vehicle, the word authority is used qualitatively to describe the responsiveness of the vehicle to the actions taken by the person steering or controling the vehicle. For example, if a yachtsman applies a large force to move the tiller through its maximum deflection but the yacht changes direction only slowly, it is reasonable to say this type of yacht does not provide its helmsman with adequate directional authority. Conversely, if a small force and a small deflection of the tiller cause the yacht to make a prompt change of direction at a satisfactory rate, it is reasonable to say this type of yacht provides its helmsman with excellent directional authority. Dolphin (t) 07:20, 18 July 2015 (UTC)

This phraseology - "rudder authority," "control authority," and variants - is very common. It appears in both the Airplane Flying Handbook and in the Pilot's Handbook of Aeronautical Knowledge, among many other great resources. I'm not certain what you mean by "controlled vocabulary"; a different resource (the Pilot/Controller Glossary) standardizes terminology for use between airmen and air traffic controllers, and still another resource (the AIM) standardizes radio phraseology; but "rudder authority" isn't in these resources - it's sort of a different scope.

So, although "control authority" shows up in a lot of training manuals, none of the major book resources actually define it! I can provide my ("non-authoritative") definition: "authority" means that when you operate the controls, the aircraft actually responds. In plain English: when you hit the stick, the airplane pitches and rolls; when you kick the rudder pedal, the airplane yaws.

Maybe the surprising thing is that not all aircraft have great control authority in all operating conditions. For example, at low speeds in some aircraft, you might find poor aileron effectiveness: pushing the stick left and right may not actually roll the airplane very much at all. The ailerons, for example, need lots of fast moving air flowing over the wing in order to exert a strong torque and cause a roll. Intuitively, you expect that when you manipulate the control, the aircraft should just move - but that's not how aerodynamics works!

This intuitively-simple behavior requires many things:

• The aerodynamic forces must not be too powerful for the pilot (or the hydraulic system, or whatever else moves the control surface). In plain English: if the wind pushes the control surface so hard, forcing it back to equilibrium with such great pressure that the pilot can't operate it, that constitutes poor authority. This plagued the Mitsubishi Zero, and it recently killed a Mustang pilot (and many spectators) at the 2011 Reno Air Race - a trim tab became damaged, and the stick pushed back against the pilot's manual input with hundreds, perhaps thousands, of pounds force. No human pilot - conscious or otherwise - could have pushed the stick with enough force to control the aircraft.
• It also means that the deflection of the control surface is within its maximum limitations. In plain English: if the stick is all the way to the right and the plane is not rolling as much as you need, that constitutes poor authority - and defective aircraft design!
• It means that aerodynamically, a deflection of the control surface actually causes the aircraft to maneuver as expected. The magnitude of the effect should be commensurate to the pilot's input. The actual amount of control authority depends on all the engineering details for any specific airframe and the mechanism of its control surface actuation (the size and position of the control surfaces; the mechanical advantage of any cables, push-rods, or hydraulics; the operation of any electric motors, aerodynamic spades; the effects of any software and electronic interlocution; or whatever else is designed into the aircraft). It depends on messy details of fluid dynamics, laminar flow, slipstream effect, and so on.

I checked another one of my books - Conventional Gear, expecting to find an excellent definition... but to my surprise, author David Robson does not appear to ever use the phrase "rudder authority." Instead, he always uses the term "power" - which I find a little bit erroneous (power has a specific meaning in physics). For example, in his section on flight dynamics, he writes: on the design of aircraft forIncreased Rudder and Elevator Power:

"...Since the taildragger is designed to land at the stalling angle of attack, there must be enough elevator power at minimum airspeed to still pitch the nose up. Thus the taildragger has more elevator power than the trike. Similarly, at this minimum airspeed it must have sufficient rudder to provide positive directional control. This control power is invaluable, but can cause departure from controlled flight or overstress if misused at low or high speed respectively."

In this case, he refers to "power" where I would say "authority;" nonetheless, he accurately describes that tailwheel aircraft tend to have more of it than their trike counterparts.

Bringing it all back to the original question: the B-2 has poor rudder authority compared to some hypothetical, differently-designed flying wing with a large vertical stabilizer and rudder; but that's okay, because B-2 is operated in conditions where this doesn't affect safe and effective flight.

Nimur (talk) 08:10, 18 July 2015 (UTC)

Thanks, I hadn't heard the usage. I guess it's a little less formal than being part of a controlled vocabulary, but a little more specialized than a regular metaphor. Perhaps term of art covers it. SemanticMantis (talk) 14:59, 18 July 2015 (UTC)

Big bang(s)?

Since our Big Bang is supposed to have happened out of nothing in a zero spacetime complete non-entity, what is the probability of other big bangs having occurred or going to occur in completely separate unlinked non-entities? Also, can non entities ever get connected to each other before or after they have had their bangs?? Also, when we've already had one big bang, is there anything to stop another big bang occurring in our existing universe?--81.147.170.83 (talk) 19:11, 17 July 2015 (UTC)

You will probably enjoy reading about the Multiverse. Probability is ontologically weird in this context, it's not clear to me that any of the Probability_interpretations would make sense.

Ultimate_fate_of_the_universe outlines some possibilities of some things that are sort of like Big Bangs, but not. The Cyclic_model suggests that we could have a Big Crunch followed by another Big Bang. SemanticMantis (talk) 19:37, 17 July 2015 (UTC)

There are times when you just have to admit you don't know... even if you're a physicist. It is still up in the air what cosmic inflation really means, whether it is a model that makes any testable predictions. Anything before that seems to be pure speculation (I welcome anyone to differ!) So what happened before the Big Bang, multiple Big Bangs and all that... we don't know. Also, AFAIK, since there were (apparently) more and more collisions and interactions at higher and higher energies the closer you look back toward the Big Bang, there is in a sense an infinite amount of "history" in that finite interval as measured by our definition of time (also feel free to correct me there; I'm speaking out of my depth). Wnt (talk) 23:38, 17 July 2015 (UTC)

"In the beginning God created the heaven(s) and the earth." Replace "God" with "the forces of nature" and "the heavens and the earth" with "the universe", and the bottom line is that the writers of the Bible knew as much as the physicists know (and vice versa). ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:52, 18 July 2015 (UTC)

All we know is that the universe has expanded and cooled from a very uniform, dense plasma. That state might have resulted from inflation, in which case we have no idea what started the inflation or what the universe was like before, or it might have arisen in some other way, in which case we know even less. There's absolutely no evidence that the universe came into existence 13.7 billion years ago or at any other time. Though modern cosmology still uses the name "big bang cosmology", it doesn't have a big bang in it. -- BenRG (talk) 07:20, 18 July 2015 (UTC)

I hope some real physicists reply here and school you trolls. I'm sure the writers of the bible knew all about Particle Physics time dilation special relativity the photoelectric effect radiation periodic elements and so on etc etc etc.. evidence for the age of the universe redshift CMBR Void burn (talk) 17:48, 18 July 2015 (UTC)

July 18

Air conditioning

Hi all - I live in a two-story apartment with central air conditioning. However, the second floor (where the two bedrooms and the bathroom are) is a converted attic, so it has no A/C vents. The result is that my downstairs level gets air conditioned perfectly, but the upstairs remains practically as hot as if I had the A/C turned off - it's basically a sudden transition right at the top of the stairs. Basically, I'm looking for some MacGyver-esque solution to circulate the A/C to my upstairs as well. Unfortunately, the circumstances make a couple of the more obvious solutions impossible or suboptimal:

• Each of the upstairs rooms only has one window, so I don't really want to get a window unit and lose all window functionality in one of them
• There is no overhang over my windows, so I can't do anything that involves leaving windows open without risking getting everything drenched when it rains

So far, the best I've come up with is to buy a really big box fan and place it on the stairs facing upward, hoping it will circulate enough cold air to the upstairs to make a difference. Does this seem likely to work? And are there any other options I'm not thinking of? Thanks. -Elmer Clark (talk) 06:00, 18 July 2015 (UTC)

Not very MacGyver, but they do sell portable AC units that sit inside and have only a minimal window footprint (e.g. [11]). That wouldn't obstruct much of the view. They also start with an okay window opening shield and with a little MacGyver-ing you could improve that. If you really want full-on MacGyver, running some interior duct work could help (more than a fan at the base of the stairs anyway). Ducts that runs along the interior ceiling of the stairwell might work. Assuming your construction options are limited (e.g. rented apartment), you'd probably end up with some fairly obvious and ugly looking exposed ducts, but depending on taste, that might be acceptable. Dragons flight (talk) 06:44, 18 July 2015 (UTC)

What else do I need for a virtual way to touch a dragon?

I'm throwing a party for my nephew. He's a fan of dragons. So I have an idea to set up an impressive show for his birthday party where he'll be able to touch a dragon. I know that touching pressurized air can feel like a solid object, when a hand makes contact with it. So in addition to pressurized air, what else do I need for the virtual touching of a dragon? NPham2005 (talk) 07:32, 18 July 2015 (UTC)

pipeline spill

Regarding Long Lake oil line spill,why doesnt the flow detection system stop the pumps before 5 milion litre,s has gone by — Preceding unsigned comment added by 70.69.144.57 (talk) 07:43, 18 July 2015 (UTC)

Magnitude 9 megaquake

According to the New Yorker, if there was a magnitude 9 earthquake, a tsunami would hit Seattle and Portland afterwards. How is that possible, given that Portland is inland? Also, wouldn't Seattle be shielded by puget sound? Wouldn't the puget sound be too shallow for huge tsunamis to occur?— Preceding unsigned comment added by 24.207.79.50 (talk) 11:23, 18 July 2015 (UTC) I also saw an online video from fox about this. — Preceding unsigned comment added by 24.207.79.50 (talk) 11:45, 18 July 2015 (UTC)

Neither place would see significant harm from a tsunami, but both cities would have issues with soil liquefaction and collapse of unreinforced masonry buildings, as well as transportation and utility disruptions. See this article [12] in Slate for a critical discussion of the New Yorker article. Acroterion (talk) 12:05, 18 July 2015 (UTC)

The New Yorker article discusses the possibility of a magnitude 9.2 or larger earthquake on the Cascadia subduction zone. Our article gives a good description of the processes that would come into play. Note that such an earthquake would be twice as strong as the 2011 Tōhoku earthquake and tsunami. Portland is on the Columbia River, with the lowest parts barely above sea level. If you have seen Youtube videos of the tsunami flowing up Japanese rivers, you can get some sense of what could happen. Looie496 (talk) 13:38, 18 July 2015 (UTC)

Space time creation

If I alone suddenly popped up out of nowhere/nothingness into my own empty universe, How much spacetime would I create on my own?--81.147.170.83 (talk) 17:14, 18 July 2015 (UTC)

What a bizarre question. HIGHLY hypothetical and lacks real valid substance. To answer your question: "you would create the amount of space-time that you displace relative to your mass". I am not qualified but thought I'd give it ago. Who knows maybe the great nimur or jayron will take some time to answer this. Void burn (talk) 17:35, 18 July 2015 (UTC)

What units of space and time do you want the answer in? AndyTheGrump (talk) 17:42, 18 July 2015 (UTC)

Richard Owens west Canada expedition

19:00, 18 July 2015 (UTC)66.192.172.132 (talk)What is known of Owens west Canada expedition? What is known of M.W.Bartlett who was an agent for Owens on the west Canada expedition?