Wikipedia:Reference desk/Archives/Science/2015 September 30

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September 30

What compound is it?

When reading Chemistry of the Elements (second edition) by N. N. Greenwood & A.Earnshaw, I saw a strange conpound in a chemical equation in page 692 - $(SbF_{3})_{3}SbF_{5}$. What structure does it have? I went through the section of antimony's halides but found nothing about it. --WhitePhosphorus (talk) 03:03, 30 September 2015 (UTC)

There is apparently a crystal structure for this, but I can't download it myself [1]. Someguy1221 (talk) 04:21, 30 September 2015 (UTC)

[2] gives a little more info & crystal unit cell dimensions, but not bond lengths or anything. I don't have journal access anymore but I'm sure someone else at WP:CHEMS does, if you want to ask there. shoy (reactions) 13:56, 30 September 2015 (UTC)

This article does give atom coordinates in the unit cell, angles and bond lengths. There is also a Raman spectrum. The structure has SbF₆⁻ anions, and parallel chains of (Sb₃F₈)⁺. Le me know if you need more detail. Graeme Bartlett (talk) 12:16, 1 October 2015 (UTC)

Thanks to all of you. I've approximately known the struture already but I'm still confused about the bond angle of Sb-F-Sb in (Sb3F8⁺)_∞ - is it 180°? --WhitePhosphorus (talk) 12:38, 1 October 2015 (UTC)

That (Sb3F8⁺)_∞ is quite complicated. It forms a double strand wobbling up and down. There are two different angles subtended of the F atoms in the chain, 147.4° and 150.2°. On the Sb atoms the angles to two F atoms along the chain are 155.2° and 83.4° (the last where the wobble kinks in). Three Sb atoms outline a hexagon with the bottom bent in, with 3 F atoms making the other vertexes. Then each bent hexagon is linked by 2 F atoms to the left, and 2 to the right. An extra F atom is inside each hexagon and sticking out sideways from the chain on the other Sb atoms. Graeme Bartlett (talk) 22:03, 3 October 2015 (UTC)

Record number of daily seizures

There's currently a campaign in Ohio to permit the use of marijuana in certain cases, and some of the proponents have been running atelevision advertisement featuring a mother who says that medical marijuana improved her daughter's epilepsy. According to the advertisement, the girl "was having over 1,000 seizures in a day" before they started using marijuana. I've tried and failed to find any even-close-to-reliable sources that attempt to guess the record highest number of seizures in a 24-hour period; the highest numbers I'm seeing are from news results, e.g. this one stating that a boy had approximately 100 per day. Does anyone know where I could find a reliable source that might attempt to identify the highest recorded number of seizures in a 24-hour period? Nyttend (talk) 03:26, 30 September 2015 (UTC)

PS, please note that no discussion of medical marijuana is intended or desired; I'm solely looking for information about epilepsy symptoms, not methods of relieving it. Nyttend (talk) 04:09, 30 September 2015 (UTC)

Can't really help with that, but can add some thoughts to consider. Remember not all "seizures" are the same. Nor are they the same duration. Which is worse, 3 seizures that last a total of 2 minutes, or 1 seizure that lasts 3 minutes? Note also that Addyson Benton, the child featured in the commercial, isn't having grand mal seizures or tonic/clonic seizures. She has myoclonic epilepsy, which consist of muscle jerking without loss of consciousness. In terms of numbers, I suspect simple absence seizures (which manifest outwardly only as staring) can occur very frequently during the day without even being noticed.- Nunh-huh 06:16, 30 September 2015 (UTC)

There are a range of epileptic disorders and seizure types, as Nunh-huh indicates. If you include simple partial seizures (seizures restricted to one or a few parts of the body), the maximum will be much more: for an Epilepsia partialis continua study I saw, the selection criterium was: 10 seconds or less between seizures; that's at least 8640 per day (assuming they continue during sleep).

For severe disorders, the mortality will depend on the frequency and severity; children with more seizures die younger. So it's hard to come up with a maximum, it varies with type and with age.

Some of the generalized types with high frequencies:

• West syndrome: has an onset between 3 and 12 months, with seizures peaking after 5 months. At it's peak, a child can have up to 30 clusters per day, with 20 to 150 seizures per cluster. 5% mortality at age 5 Source
• Lennox–Gastaut syndrome: combination of a variety of seizures, including sometimes hundreds of tonic seizures at night, onset 2 to 8 years, prognosis poor.
• Atypical benign partial epilepsy: (not really partial) onset 2.5 to 6 years, multiple types, hundreds per day.
• Ohtahara syndrome: onset within first 3 months, tonic seizures, independent of sleep cycle, can be hundreds per day. 50% mortality at age 2, may transition in West S and later in Lennox G S.
• Childhood absence epilepsy: as mentioned by Nunh-huh. can occur hundreds of times per day without others noticing.

Had a similar problem a while ago, when I came across idiopatic insomnia (child age onset, often at birth, persistent and life-long). One source writes that they included some of the worst forms of insomnia ever recorded in a sleep laboratory. But I couldn't find any source saying how much (or little) those people slept (not for lack of trying, my browser history now has 1027 searches and webpages containing the words "sleep" or "insomnia" ((+_+)) ). Found only one notable case report: long-term (19 year) opiate therapy for a woman who slept 0 to 3 hours nightly before treatment. Ssscienccce (talk) 10:26, 1 October 2015 (UTC)

This Watch

Can someone please tell me about this watch.These don't seem to be "hot digits", or are they? If not,what is the actual system. How it works? 27.255.203.64 (talk) 03:36, 30 September 2015 (UTC)

That to me looks like a static prototype. i.e. those digits are molded and painted onto the band, it's not a "functional" watch. I'd need to see a video of the digits changing to convince me otherwise. I'm not an expert but I am somewhat familiar with LEDs and various displays, I've built LED cubes and clocks from VFDs and Nixie tubes amongst other things. Vespine (talk) 05:43, 30 September 2015 (UTC)

Ok, i take that back, it's just a terrible photo which has probably been "retouched". I did a reverse image search to find a supplier and given the price AND the fact you have to press a button to display the time (as opposed to "on all the time") these are almost certainly just regular hot digits. The reason it looks fake is probably the digits don't photograph well so they've been "shopped" in.Vespine (talk) 05:48, 30 September 2015 (UTC)

Vespine, For the sake of the rest of us, as neither Googling nor searching on WP finds any results, what exactly are "hot digits"? Rojomoke (talk) 12:32, 30 September 2015 (UTC)

Well, I have to admit I made a little bit of an assumption on my part too, but I expect the OP was just talking about regular old LED segment displays. I actually did a google image search for hot digit display and confirmation bias took me the rest of the way. I realize now that even though that gave me the result I was expecting, it wasn't for the right reason. Vespine (talk) 22:57, 30 September 2015 (UTC)

Meaning of elemental mass

In an old German physics paper, the author used the term "Elementarmasse" (literally "elemental mass").

This term does not appear in any of the physics textbooks (English) I have.

The whole sentence translates as something like:

Here, K is the gas constant of an electron, T is the absolute temperature, ε is the elementary charge of an electron in electrostatic units, and μ its elemental mass and the i in electrostatic units, measured current per unit area.

What exactly is "elemental mass"? What is its standard value? 124.178.135.7 (talk) 03:31, 30 September 2015 (UTC)

It would really help if you gave us more context, including the equation. Literal translation of German physics is a notorious problem, as I have previously remarked!

Going from the limited context we have, this is probably referring to the "elementary mass" - not "elemental." in English, we would typically say "rest mass." Contrast this to the reduced mass, the relativistic mass, or any of the various other masses we might care about. In this case, it would be the m_e constant, 9.1×10^-31 kg, or, about 1/1800th of an atomic mass unit.

Nimur (talk) 04:50, 30 September 2015 (UTC)

Thanks, Nimur. The subject involves assuming the electrons have near zero speed, so there is no reason why the author had to indicate it was not under any sort of relativistic effect. I had thought that it should simply be the mass of an electron. But why not just simply say so? Other aspects of this paper had tricked me, so I thought I had better not assume too much. Unfortunately the formula makes no sense dimensionally, so I am looking for an error. 120.145.150.244 (talk) 08:32, 30 September 2015 (UTC)

Could it be the mass in Dalton (5.485799*10⁻⁴)? Ssscienccce (talk) 06:20, 1 October 2015 (UTC)

Gravity and Hubble's constant

According to metric expansion of space, special relativity allows spacetime curvature to change at superluminal speed, meaning that space's expansion goes faster than speed of light. If this is so and if gravity cannot propagate faster than light, there should be regions in space unaffected by gravity. Yet it's typically stated that gravity has infinite range. How to reconcile that?

Also, does it mean that due to accelerating universe Hubble's constant technically isn't a constant value anymore and is changing? Brandmeister^talk 08:40, 30 September 2015 (UTC)

"Gravity has infinite range" and "gravity propagates at the speed of light" are not incompatible in theory, though they may be incompatible in reality. In the actual universe, it could be the case that certain objects will never experience one another's gravity due to constantly increasing distance. You may be interested in reading Cosmological horizon and hubble sphere. And you are correct, hubble's constant is not required to be constant. Someguy1221 (talk) 09:23, 30 September 2015 (UTC)

(EC) When people say that gravity (or electromagnetism) has infinite range, what they mean is that the force never "stops". A photon or a graviton/gravitational wave keeps propagating forever (a gluon, by contrast, will decay into a quark/antiquark pair if you stretch it too far, which is why the strong force does not have infinite range), regardless of what spacetime is doing around it. Smurrayinchester 09:24, 30 September 2015 (UTC)

"special relativity allows spacetime curvature to change at superluminal speed" isn't true, and I don't think the article says that. It's true that the rate of change in cosmological distance per unit cosmological time can be larger than c. But that's a different notion of speed, where c has no special role to begin with. (Other examples of that are closing velocity and the "superluminal scissors".) The special-relativistic rule that nothing can go faster than light (meaning that worldlines don't leave the light cone) is not violated in cosmology. I don't think it's accurate to describe a rapid increase of cosmological distance as a rapid change of curvature. Cosmological distance is not directly related to curvature, and the way it's defined is somewhat unphysical.

As far as we an tell, the universe is homogeneous: the big bang happened everywhere, and there are galaxies everywhere. So there needn't be any part of the universe that is unaffected by gravity. But it's true that in an exponentially expanding universe, local perturbations of matter will never be detectable beyond a certain distance, and in that sense you could say the range of gravity is limited. The cosmological constant, if it is really a constant of nature, sets a gravitational distance scale of ~18 billion light years that you could perhaps reasonably call "the range of gravity". But I can't remember hearing a physicist call it that.

Hubble's "constant" changes with time in any big-bang cosmology. It's normally written H(t), with H_o = H(t_now) being the current value (which will not detectably change for millions of years at least). H(t) was much higher in the past (it goes to infinity at the big bang singularity). In the exponentially expanding ΛCDM future, H(t) approaches a constant positive value. H is constant only in an exponentially expanding, exponentially shrinking, or static universe. -- BenRG (talk) 21:10, 30 September 2015 (UTC)

The limited range of gravity only prevents it from reaching all space if mass-energy can truly be created or destroyed. Otherwise the mass has always existed, from the time of the Big Bang; the response to changes in its position might merely be out of date, to be corrected later by gravity waves and such. But while once the conservation of mass-energy seemed like fundamental law, in these days of dark energy and tired light, I'm no longer nearly so clear on the concept. Wnt (talk) 15:55, 1 October 2015 (UTC)

Dark energy doesn't contradict conservation of mass/energy. The basic idea is simply that the universe contains a field that exerts a repulsive effect. There isn't any energy being expended to cause this effect; it's just there. Similarly, the Earth doesn't "use up" energy to maintain its gravitational attraction, and a magnet doesn't "use up" energy to attract or repel things magnetically. For extra measure (and because it's really neat), consider the Casmir effect, or more generally vacuum energy. Disclaimer: I'm not a physicist, just an interested layman. --71.119.131.184 (talk) 21:34, 1 October 2015 (UTC)

Superconducting DC transformer

When I was searching for superconducting transformer I found this explanation: https://van.physics.illinois.edu/qa/listing.php?id=2372 . Then, in the follow up 2, Mike W claims that a superconducting transformer can also use DC and AC instead of normal transformer that can only uses AC. Is this true? If this is true, will the equations for normal AC transformer apply? What happens if the primary winding is connected to the DC source without any load connected to the secondary? Will it short-circuit? 139.228.134.204 (talk) 12:05, 30 September 2015 (UTC)

You can read this. Ruslik_Zero 20:24, 30 September 2015 (UTC)

Domesticated but not by choice

Do cockroaches, rats and the like count as domesticated? I mean animals that live around humans and are dependable on us somehow. Is there a name for such niche? They are not really wild, but also not like my dog Simba.--Denidi (talk) 13:28, 30 September 2015 (UTC)

The live in amensalistic or commensalistic relations with humans. Domestication implies deliberate action by humans to derive benefit, which is not the case. Brandmeister^talk 13:51, 30 September 2015 (UTC)

(By "dependable" I assume you meant "dependent".) Note that cats and dogs likely started being domesticated in that way. Cats would hang around human grain stores to catch the mice they attracted, and thus be dependent on the humans, before they moved in with people. The people, noticing fewer mice and less missing and contaminated grain, let the cats stay. Dogs probably started as wolves hanging around the perimeter of human encampments to eat any hunting scraps left behind. Humans, noticing the value of the wolves making noise whenever a dangerous or huntable animal was nearby, similarly allowed them to stay. StuRat (talk) 13:58, 30 September 2015 (UTC)

No. They are not domesticated. But yes, there are terms for it. I actually mentioned it just recently for the spider ID request above. For organisms that usually live near or around human habitations, the term is synanthropy. For organisms which specifically prefer human habitations or animals which prefer humans as a food source (for instance some mosquitoes and parasites), the term is anthropophilia. -- OBSIDIAN†SOUL 14:21, 30 September 2015 (UTC)

Then the spider is domesticated if I choose not to kill it so it captures more mosquitoes??216.178.82.218 (talk) 18:18, 30 September 2015 (UTC)

No, domestication sensu stricto implies selective breeding. If you were to breed spiders selectively to look cute, and/or to not bite people, and/or to catch flies better than their wild-type ancestors, and/or to spin curtains for your window instead of a regular spider-webs; - then they would be domesticated. OTOH, the term domestication used in a broad sense may imply any stage of domestication process, which is continuous and spans many generations of the animal being domesticated. Dr Dima (talk) 18:38, 30 September 2015 (UTC)

@Dr Dima: Not to quibble too much, but selective breeding isn't exactly the same as animal husbandry. Killing spiders around the house vs. letting them live can in principle form a selective pressure. While we have certainly selectively bred dogs with extreme intention for certain traits over the past few centuries, the origin of the domestic dog is still disputed, with Origin_of_the_domestic_dog#Self_domestication currently leading among other theories. In that line of reasoning, a selective pressure came about wherein wolves that didn't fear humans had an adaptive benefit compared to those that did fear humans. The point being, that the domestication of the dog may well have not involved "selective breeding" in the strict sense, but rather a more general exertion of human-derived selective pressure. I don't want to say that tolerating spiders is "domestication" per se, only to point out that there is serious room for debate in how these terms apply. OP may be interested in this Wired article [3] detailing changes in behavior and perhaps evolution of animal species due to unintentional effects of human commensalism/synantrhopy. I can find more scholarly refs on that topic upon request :) SemanticMantis (talk) 22:46, 30 September 2015 (UTC)

Most definitions of domestication involve taming the animal [4] [5]. Richerman (talk) 01:06, 1 October 2015 (UTC)

Here are some "cute" spiders, if anybody was wondering how that works. InedibleHulk (talk) 07:07, 1 October 2015 (UTC)

Salticids are not only cute, they're smart too. They're some of my favorite animals. That said, that "family portrait"? I hate to break it to you, but... that's not her baby. And she's not carrying it, she's um... :[ -- OBSIDIAN†SOUL 08:57, 1 October 2015 (UTC)

what if we catch flies and put them in spider's web so that it doesn't have to hunt?66.87.83.109 (talk) 13:54, 1 October 2015 (UTC)

Keeping something around the house as a "pet" of sorts, or as something with a practical use, is not necessarily the same thing as domestication. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:47, 1 October 2015 (UTC)

A Simple Amplifier

Can one build a simple amplifier using a transistor, microphone, and small-speaker? 27.255.203.64 (talk) 14:11, 30 September 2015 (UTC)

Wouldn't you need a power source ? (An unpowered megaphone doesn't actually amplify sound overall, it just concentrates it in one direction.) StuRat (talk) 14:16, 30 September 2015 (UTC)

Well, not exactly. You'll need to add at least a resistor and a capacitor - possibly more depending on precisely how much amplification you need. If you google "one transistor amplifier" - you'll find a ton of information - including circuit diagrams and component values. SteveBaker (talk) 14:19, 30 September 2015 (UTC)

If you want to actually amplify the sound wave power -- that is, to get more sound energy per unit time from your speaker than the sound energy per unit time arriving at your microphone --then you will certainly need a power source other than the sound itself. If, on the other hand, you want to simply demonstrate the operation of an amplifier circuit, without actually increasing the sound power, then you can use your microphone as a power source. Many microphones do not require an electric power source; rather, they convert the sound power to electric power by inductive, piezoelectiric, etc. mechanisms. Most loudspeakers, too, can work both ways - convert electric power to sound power when used as speakers, or sound power to electric power when used as microphones. However, you can never get more sound energy out than the sound energy that goes in, unless you use some additional source of energy. If you can clarify your question, we can give you a more specific answer. Dr Dima (talk) 19:14, 30 September 2015 (UTC)

Assuming you have connected a power supply, a single transistor stage as posed in the question will not work until the transistor is biased on so that it conducts current. Transistors are always off until biased on. The normal (and easiest) way to bias the transistor on is with a single resistor, as SteveBaker said above, and it should be connected from power source to the transistor's base. There also needs to be an audio transformer connected in the transistor's collector circuit to transfer audio to the speaker, or a load resistor with large value capacitor to transfer audio while blocking DC from harming the speaker. If you use a carbon microphone (high output voltage), there will likely be enough signal to drive the transistor into producing some audio, which may be low level or distorted or both until you take some measures that may involve more components. Any other type of microphone will not produce enough audio. The short answer to the question, 'Can one build a simple amplifier using a transistor, microphone, and small-speaker?' is no, there are at least two other components needed and even then, the results may be very unsatisfactory. Akld guy (talk) 21:43, 30 September 2015 (UTC)

Good old carbon microphone, wouldn't even need a transistor, simply put power, microphone and speaker in series. Like the first telephones. Or how about this: Sound-powered telephone, doesn't even need a power supply. Ssscienccce (talk) 14:26, 1 October 2015 (UTC)

OP: As others have remarked, you need at minimum a few resistors, a power source, and 2 capacitors. However, it is very doubtful that you get enough amplification for it to be usable. Your output depends on the microphone output and the transistor's beta (h_FE). At most you'll get a weak signal when someone shouts in the microphone. I'm assuming that the micro is a little electret or capacitor microphone: the energy it can pick up from the sound waves is directly proportional to the surface area, so the electric signal it produces is also small (unless they have a pre-amplifier built-in, that's possible). A (small) speaker has a much larger surface area and can also work as a microphone, so if you have a second speaker, you could use it as microphone to increase the output. Even then, output would suck. This page may provide some tips if you want to try. With a few components more you get acceptable quality: A simple two transistor amplifier Or here: fig 13 or 27. Ssscienccce (talk) 14:26, 1 October 2015 (UTC)

Single transistor wideband amp.

Use a amplifier in an integrated circuit. This device needs additionan basic passive components only. If your need is a problem of energy consumption, temperature, needed space or weight, look for a class-D or class-T amplifier. Quality would not be an issue using this. Reliability is the price of passive components and manufacturing quality. Amplifiers with a single transistor have a high lost, are not really linear, and are used as preamplifiers only. --Hans Haase (有问题吗) 10:37, 1 October 2015 (UTC)