# Wikipedia:Reference desk/Science

Welcome to the science reference desk.

Main page: Help searching Wikipedia

How can I get my question answered?

• Provide a short header that gives the general topic of the question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Post your question to only one desk.
• Don't post personal contact information – it will be removed. All answers will be provided here.
• Specific questions, that are likely to produce reliable sources, will tend to get clearer answers,
• 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 are not a substitute for actually doing any original research required, or as a free source of ideas.

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

Choose a topic:
 Computing desk Entertainment desk Humanities desk Language desk Mathematics desk Science desk Miscellaneous desk Archives

# August 13

request for medical advice, user wishes to take a drug and wants to know how it will affect him
The following discussion has been closed. Please do not modify it.

I'm curious what nicotine addiction feels like so I plan on doing e-cigarette's. I'm fine with the crash I'll experience for a few weeks after quitting but I'm wondering if it'll be like low-level craving it for years/rest of my life? I don't want to wake up everyday forever thinking damn I wish I had some nicotine. 2.102.184.47 (talk) 03:44, 13 August 2017 (UTC)

Please read the instructions at the top of the page, we cannot make medical predictions or speculate on the future. μηδείς (talk) 04:05, 13 August 2017 (UTC)
I think dismissing this is an unjustifiable cop-out. Nicotine is not a prescribed medication, and sources on the rapid onset of addiction are available: [1] [2] [3] Note these sources all agree that one can become addicted within two days, though it may not happen that fast. As in Charlottesville, there is more harm to be done by suppressing discussion than by permitting it. Wnt (talk) 12:05, 13 August 2017 (UTC)
The FDA has regulated all nicotine products since August 2016 https://www.fda.gov/tobaccoproducts/labeling/rulesregulationsguidance/ucm394909.htm. This is a request for personal advice on how the use of a drug will affect the individual, a classic no-no. μηδείς (talk) 15:24, 13 August 2017 (UTC)
I tried smoking as a youth, but it just made my heart pound, so I could not achieve the habit. Alcohol and caffeine worked better. It might be genetics. Edison (talk) 02:44, 14 August 2017 (UTC)

## identify an insect

Triangular shaped bug about 5-7 millimetres long. I think it is initially translucent, then green and finally brown (not sure though). Dozens of this insect are present on the stalks of a bean plant. It is not feeding on the leaves, but probably on the stalk. Not found on nearby plants until the bean stack was cut down / pruned. Ants seem to interacting with it a lot (I think). Google reverse image search wasn't helpful.

unknown insect about 5-7 mm long found on bean plant.

— Preceding unsigned comment added by Cplusplusboy (talkcontribs) 07:04, 13 August 2017 (UTC)

These look like larvae of some species of Cicadellidae or leafhoppers, sap sucking insects that probably produce honeydew which accounts for the opportunistic (or farming) ants. There are very many species and some specialist sources will probably be required to establish the exact indentification. Compare with this image http://www.ozanimals.com/Insect/Leafhopper-larvae/Cicadllidae%20family/spp2.html. Richard Avery (talk) 10:18, 13 August 2017 (UTC)
The thorn shape reminds me of a treehopper - for example, [4] reviews that this shape is pretty representative, and involves a much modified pronotum... the setae do make it seem more like a nymph, though early treehopper stages apparently don't have the thorn shape. this photo of Acanthuchus trispinifer looks similar but not identical to me. Our resources, including Wikispecies, seem almost entirely deficient on any kind of Terentiini other than this species. Wnt (talk) 11:56, 13 August 2017 (UTC)
The pictures in the landcareresearch.co.nz link are the ones (unless this shape and colour are commonly found in other species). The green photos with the pyramid shaped head and curved tail I posted are nymphs and the brown ones not posted here is the adult tri-horned treehopper as per the website. Thanks Cplusplusboy (talk) 16:37, 13 August 2017 (UTC)
Do the ants actively protect these from predators? I want to know whether I can get these pests to get eaten by predators if I get rid of the ants. The ants seem to have made a colony under the soil very close to the plant on which these insects were found Cplusplusboy (talk) 16:46, 13 August 2017 (UTC)

## Pressure during gravitational collapse

How much pressure approximately (say, in GPa) is generated by gravitational compression during gravitational collapse of a star (also in cases of black holes)? Thanks.--212.180.235.46 (talk) 14:46, 13 August 2017 (UTC)

If I haven't lost a decimal place, I believe the sun's core is roughly 34 million GPa, which should give a representative idea of the pressures involved. Dragons flight (talk) 10:44, 14 August 2017 (UTC)
Well, according to our neutron star article the pressure near the center of a typical one is on the order of 10^35 Pa, or 10^26 GPa, which is, um, a bit higher than your figure. (This already appears in the "orders of magnitude" list.) Looie496 (talk) 19:45, 14 August 2017 (UTC)

## Fat

What is the maximum dietary fat intake per day and over what time period to cause rabbit starvation? Does the type of fat make any difference (animal vs plant)? The article is vague on the specifics. Thanks — Preceding unsigned comment added by 134.213.208.187 (talk) 18:56, 13 August 2017 (UTC)

Rabbit starvation occurs when there is excessive protein and too little fat in the body.[5] This study suggests that there is no difference between lentil-based protein and animal-based protein on nitrogen absorption and thus hints that the lentil-based protein can be used to feed moderately malnourished children.[6] Dr. Michael Greger reports that eating a high-fat, high-protein animal-based diet faces a much higher mortality rate than eating a high-fat, high-protein vegetable-based diet here and the Standard American Diet. SSS (talk) 19:35, 13 August 2017 (UTC)
Looking at Vegetarian nutrition, I see no problems with plant-based fats (...Yummmm. Avocados...). Vegitarians and vegans have to take some extra care to avoid nutrient deficiencies, but millions and millions of people do it and live healthy lives without eating animals. Note: I am not a vegetarian; I am just reporting what the science says. --Guy Macon (talk) 21:36, 13 August 2017 (UTC)
Presently the US government suggests that a person who needs 2000 kcal per day consume no more than 65 grams of fat a day and of those that no more than 20 grams be saturated fat. If the total energy need is 2500 kcal then the corresponding numbers are 80 g fat and 25 g saturated fat. See also [7]. The nanny state worries about us consuming saturated fat, sugar, and caffeine.Edison (talk) 02:40, 14 August 2017 (UTC)
• Here is a current headline about a woman who died from a high-protein diet. μηδείς (talk) 21:34, 15 August 2017 (UTC)

## Tunnel, sea

Are tunnels crossing the sea, like the euro tunnel, a tube over the sea bed or are they dig under the ground like a subway? — Preceding unsigned comment added by 31.4.149.201 (talk) 22:22, 13 August 2017 (UTC)

The Channel Tunnel was dug through the sea bed.. You can see a cross-sectional diagram at that article. Rojomoke (talk) 23:28, 13 August 2017 (UTC)
I think in general, laying a tube over the sea bed but deep under water has the problematic aspect that a rupture would make immense quantities of water enter at once. A tube beneath the sea bed can be dug like any tunnel beneath the water table (including tunnels on "land") - to be sure, it is immersed, but the permeability of the rock determines how rapidly water can enter. Wnt (talk) 23:44, 13 August 2017 (UTC)

Both techniques are possible. As noted, the Channel Tunnel (or Eurotunnel) was bored below the seabed, but on the other hand, the Transbay Tube is indeed "a tube over the sea bed". However, note that while both are under arms of the sea, the English Channel is a good deal deeper than San Francisco Bay.

By the way, note that subways are not always "dug under the ground". Another common technique is to dug them into the ground as open trenches which are then then covered over. See Tunnel#Cut-and-cover. --69.159.60.147 (talk) 06:19, 14 August 2017 (UTC)

I've often wondered, if the Transbay Tube were ruptured, how many stations in the City would be flooded! —Tamfang (talk) 05:34, 16 August 2017 (UTC)
That article links to Undersea tunnel but it doesn't really discuss construction methods that much. However it does link to our article on the Immersed tube tunnel. From there, you'll find a link to the article on the theoretical Submerged floating tunnel. Nil Einne (talk) 07:20, 14 August 2017 (UTC)
BTW those articles claim without sources that Marmaray is the deepest immersed tube tunnel in the world, and per our article its deepest point is around 60m. Busan–Geoje Fixed Link is said to be the deepest road immersed tube tunnel and our article suggests it could be the second deepest, being 48m at its deepest point. By comparison, our article says the Channel Tunnel is 115m below the sea level at its deepest point although it's also 75m below the sea bed. Going back to the earlier articles, we find Eiksund Tunnel which is said to be the deepest overall and is 287m at its deepest point. However it seems Rogfast is probably going to be 390m at its deepest point. Nil Einne (talk) 07:32, 14 August 2017 (UTC)
• Wikipedia has an article titled Tunnel construction which may be a good place to start your research. --Jayron32 11:01, 15 August 2017 (UTC)

I believe that the Washington DC Subway system has used both. I believe the Tunnel on the Blue/Orange/Silver line under the Potomac was dug under the ground, the one on the Green Line under the Anacostia is in a tube sitting on the bottom.Naraht (talk) 19:43, 15 August 2017 (UTC)

## DIY crappy chokes for VGA cables?

The VGA cables I have don't have chokes on and I think there is some interference between them or them and something else. Is there something I can use to make a choke that I can apply to the cable? I have a few ferrite toroids but I can't get them around the cable without cutting the cable first (not doing that, obviously). I have some strips of thin steel I could wrap around and maybe magnetise first if that would make a difference. --145.255.246.8 (talk) 23:26, 13 August 2017 (UTC)

A ferrite choke, scored with a file, snappped in half and then superglued back together is still a reasonably efficient choke. There are also ferrite rings made in two pieces, ground smooth on the mating surfaces, and held in a snap-lock plastic housing. You can often find these on old cables: monitor or keyboard. I habitually recycle these when scrapping old keyboards, they're often useful for ad hoc suppression tasks. Andy Dingley (talk) 09:26, 14 August 2017 (UTC)
https://www.amazon.com/dp/B01MRIKIJX/ref=asc_df_B01MRIKIJX5121726 Also see: http://palomar-engineers.com/ferrite-products/snap-on-split-beads --Guy Macon (talk) 09:31, 14 August 2017 (UTC)

## Industrial uses of seawater

Here in the non-coastal US, we always have enough water for drinking and other non-agricultural uses (the only significant effect of droughts is that farmers who can't irrigate may lose their crops), and when non-potable water is needed for ordinary industrial purposes (firefighting, power-washing, dust suppression, etc.), we routinely use water from the mains or from a river if it's available. Can seawater generally be used for similar purposes? Geography of Singapore notes that their freshwater needs surpass what they get from rainfall, and I'm left wondering if they're able to use seawater in such contexts (i.e. if they couldn't, they'd have to import far more water than they do now), or if for some reason it's impossible and they have to import water for industrial purposes as well. Nyttend (talk) 23:47, 13 August 2017 (UTC)

PS, I'm familiar with fireboats; I'm wondering if it's practical to set up water mains for seawater for the sake of firefighting that's not near the shoreline. Given Singapore's numerous high-rises, I doubt they'd want to rely on tanker engines, and obviously they can't use long fire-hoses to pump water for non-shoreline fires. Nyttend (talk) 23:50, 13 August 2017 (UTC)

Bad idea, contaminating all the waste water with salt (if you recycle waste water for drinking etc). Also, what proportion of the ciy's water usage is fire fighting - not much i'd guess rather negating my first point. Greglocock (talk) 01:57, 14 August 2017 (UTC)
It suggested to use seawater for cooling in Singapore [8]. I suspect it happens in practice but am lazy to search for sure but it definitely happens elsewhere although this does require careful consideration of the cooling system design, and also leads to concerns over the local marine environmental effects of tie discharge [9] [10] [11] [12]. A particularly common user is power plants but again there's a lot of controversy over the effects of such practices on the local marine enviroment, especially with once through systems [13] [14] [15] [16]. Nil Einne (talk) 07:14, 14 August 2017 (UTC)
[17] discusses using sea water in mining operations but although it does mention the possibility of using it straight, all the examples cited seem to involve some desalination. Nil Einne (talk) 07:35, 14 August 2017 (UTC)
When I lived in Hawaii, the university installed seawater cooling for multiple buildings. It isn't really use of seawater. They take a coolant (not seawater) and pump it down deep into the ocean. The coolant gets cold. It is pumped back up and circulated through the walls of a building. It cools down the building. It is then pumped back down into the ocean. I would call it deep-ocean cooling, not seawater cooling. 209.149.113.5 (talk) 14:56, 14 August 2017 (UTC)

For clarity are you referring only to the system you encountered or are you claiming this applies to all systems? If the later, I suggest you read the links carefully as some of them explicitly talk about using sea water for the purpose, including the problems of designing the piping as well as other structures, as well as pumping it around building for heating to reduce the environmental impact of warm seawater discharge. Another issue is the addition of materials like chlorine to reduce biofouling and the impact of this when the sea water is discharged. Likewise while technically the system you described is similar to a once through cooling system I guess, AFAICT, the term only applies to systems where the sea water is taken in and directly discharged after use.

I did come across some sources which seemed to refer to directly using the ocean for cooling, but intentionally didn't link to them. I did just notice we have an article Deep water source cooling which seems to mostly discuss systems which directly use sea water although it isn't always clear.

I also just came across this system in Honolulu which is a little different from the one at the university you mentioned [18]. If I understand the diagram and description correctly, it doesn't use the seawater for cooling buildings, but also doesn't directly cool in the ocean. Instead seawater is taken to a cooling station and there used to cool freshwater. The seawater is returned to the ocean and the freshwater used to cool buildings. So sort of an intermediate. I presume freshwater is used as the refrigerant for cost, environmental and safety reasons. (Any system which cools directly in the ocean especially if it uses some semi hazardous refrigerant would need to consider such issues, as well as maintenance and construction costs.)

Nil Einne (talk) 13:49, 15 August 2017 (UTC)

Salt water is not very gentle on whatever you put it into (pipes, etc.). Also, in some of the example applications you gave, the water will then evaporate and leave the salt behind, which is usually undesirable. Reclaimed water systems are what is generally used to produce non-potable water and reduce water usage. --47.138.161.183 (talk) 08:10, 14 August 2017 (UTC)
Salt doesn't tend to come out of solution until the seawater is quite concentrated. At high temperatures, the bigger problem is sulphates, as these form a hard scale that's hard to shift. Provided that brine isn't concentrated more than three times, and doesn't exceed 60ºC, it's not a big problem (see Evaporator). Andy Dingley (talk) 09:44, 14 August 2017 (UTC)
The salt doesn't need to come out of solution to be a problem. It acts as a catalyst to increase corrosion, such as iron rust. Also, there's the smell. Sea water often smells like fish, and many may find that unpleasant. StuRat (talk) 20:26, 15 August 2017 (UTC)
That's a vast over-simplification. It depends on the type of steel used. It depends hugely on the remaining oxygen content. Brine is typically (as the process that concentrated it usually deoxygenated it too) not a problem for corrosion in closed piping. Andy Dingley (talk) 17:03, 16 August 2017 (UTC)
• [19]. [20]. [21]. --Jayron32 12:11, 14 August 2017 (UTC)
• Sea-water can be used for flushing toilets; assuming that the sewage system can cope with saline water. However, that means having two sets of water entering the properties, and is probably only worth it for new-build estates. LongHairedFop (talk) 18:12, 15 August 2017 (UTC)
• A better solution may be implementing a gray water system. For example, the shower water can be used to flush the toilet. I have such a system myself. See the WikiHow page: [22]. No additional plumbing needs to be run to the house (for sea water) or from it (to desalinate waste water). StuRat (talk) 20:28, 15 August 2017 (UTC)
• Another disadvantage to using sea water is that it implies the use of pumps, while freshwater from a higher elevation can often be gravity-fed. The cost of all those pumps and electricity is substantial. StuRat (talk) 17:09, 16 August 2017 (UTC)

# August 14

## Trying to find a video footage of Albert Einstein

A few years ago, in some TV scientific program, a short & rare footage was shown, with Einstein. The impression made by it is immense - 'looking' at you, surveying you from top to bottom, as if you were completely transparent. Chilling. Unforgetable. I'll be very glad to hear about this movie and how to get it. I need it also for psychophysical research. בנצי (talk) 08:08, 14 August 2017 (UTC)

You can look at this but there is many videos on Youtube. Ruslik_Zero 20:26, 14 August 2017 (UTC)

## Is this clickbait real?

https://www.youtube.com/watch?v=-Cto1DXXHAc for something as easy to test as this, I'm sure professional labcoats have done it 1,000,000,000 times already. Is it real? I've never even heard of any alien looking life form. Money is tight (talk) 11:09, 14 August 2017 (UTC)

It is a real video packed full of ads. It is designed to get as many people watching as possible so the ads pay off. As for the content, it is not real. You have to be very very ignorant to think that there is anything remotely real about the video. See Fertilisation. 209.149.113.5 (talk) 11:35, 14 August 2017 (UTC)
Yea thought it was fake. I've never even heard of something like this and its such a simple test. What is that thing though? Some kind of flatworm? How did he get it in the egg? Money is tight (talk) 11:44, 14 August 2017 (UTC)
Your initial query triggered my clickkbait monitor, and I'm certainly not looking at it now I know it is packed with ads. But II'm still interested how did they manage to get you to watch it??— Preceding unsigned comment added by Dmcq (talkcontribs) 12:03, 14 August 2017 (UTC)
Given your propensity to point out videos without explaining anything [23][24] I am afraid I also have to discount you as a spammer. Wnt (talk) 12:09, 14 August 2017 (UTC)
Money is too tight, maybe... —PaleoNeonate – 12:14, 14 August 2017 (UTC)
I wasn't thinking of the OP as a spammer, I was just interested in how they got sucked in when even their description shouts trashy video made to get clicks and incidentally destroy a few minutes each of millions of lives. Enough of that and they'll spend eight hours a day watching mind-numbing nonsense. Dmcq (talk) 13:24, 14 August 2017 (UTC)
Wow spammer? You think that's my video? It's called ad block, I see 0 ads on youtube. I was intrigued, never saw anything like it. You people are arrogant and paranoid. Money is tight (talk) 02:27, 15 August 2017 (UTC)
You people? μηδείς (talk) 02:52, 15 August 2017 (UTC)
I consider using an ad blocker a form of theft. The price for watching the stuff is those ads. I think it is acceptable to switch off javascript which cuts down the chances of viruses too. Dmcq (talk) 10:29, 15 August 2017 (UTC)
I whitelist tech sites I visit, but youtube has far too many ads and many without a 5 second skip, I've seen ads where they force you to watch for 2 minutes, and these ads cost time unlike normal display ads on other sites. If they give even 10 second skip option I wouldn't be blocking it. Money is tight (talk) 13:12, 15 August 2017 (UTC)
Are the clickbaiters paying my monthly internet access fees? No? I didn't think so. Ad blockers are no more "theft" than is call-blocking on your telephone. ←Baseball Bugs What's up, Doc? carrots→ 14:16, 15 August 2017 (UTC)
Copyright infringement then at best. I hardly think you have a real need to visit clickbait sites and you can always close them down again having spotted you've gone onto one by mistake. Dmcq (talk) 14:42, 15 August 2017 (UTC)
What copyright infringement? ←Baseball Bugs What's up, Doc? carrots→ 15:45, 15 August 2017 (UTC)
Copyright owners have exclusive rights on the performance of their works. That is one way they get their money. An ad blocker is a way of subverting those rights. If someone videos a movie and shows you the result the movie maker does not get the money they might otherwise get from the performance watched by you. There is no essential difference in your watching of clickbait videos. Dmcq (talk) 16:17, 15 August 2017 (UTC)
You're not required by law to actually watch advertisements. You can close your eyes, get up and take a piss, and there's no law against that! --Jayron32 16:28, 15 August 2017 (UTC)
The point here is that there are ads *in* the video. Ad blockers don't block those ads. Youtube inserts them while you are watching the video. It is easy to see because the progress bar below the video shows yellow where advertisements are inserted. 209.149.113.5 (talk) 18:31, 15 August 2017 (UTC)
No, DMCQ seems to think that the authorities are going to bust down my door if I get up to get a beer during a commercial, because not watching commercials is theft. --Jayron32 19:33, 15 August 2017 (UTC)
I'm glad YOU understand where DMCQ is coming from. Keeping ads away from one's sight is not copyright infringement. I have the right, as the owner of the PC and the payer of the monthly fee, to block anything I want to. Or, as you say, to simply not watch it. Or at least to turn the speakers off until the spam is done. ←Baseball Bugs What's up, Doc? carrots→ 21:18, 15 August 2017 (UTC)
You are entitled to not watch the ads, however you are not entitled to remove the ads. You are breaking the conditions of use and that is copyright infringement. Pay for YouTube Red if you want their ads gone or badger them for the service in your country if it isn't supported there. Dmcq (talk) 21:37, 15 August 2017 (UTC)
How would you even be able to remove ads embedded in a youtube video? I still don't understand your premise. ←Baseball Bugs What's up, Doc? carrots→ 06:29, 16 August 2017 (UTC)
Google's lawyers believe they enforce advertisements in YouTube videos by this Terms of Service wording:Third-Party Rights. You and your API Client(s) will not, and you will require those acting on your behalf and your users to not, infringe or violate third-party rights, including intellectual property rights and other proprietary right, confidentiality, privacy right, or right of publicity. (My underlining.) Blooteuth (talk) 22:29, 15 August 2017 (UTC)
That's for people directly using the API. An ad blocker should follow that but of course doesn't. For the general public the terms of use of the YouTube site are at [25] which has terms like 'You agree not to alter or modify any part of the Service' and 'You agree not to access Content through any technology or means other than the video playback pages of the Service itself, the Embeddable Player, or other explicitly authorized means YouTube may designate'. Dmcq (talk) 11:07, 16 August 2017 (UTC)
A specific terms of service agreement is quite different from a general legal principle requiring that you MUST watch advertisements lest you break the law. Your initial statements did not include such nuance, and instead seemed a general condemnation of ad avoidance in general. Saying "a specific website has a specific term of service that prohibits a specific use of their materials" is leagues away from saying "avoiding ads is illegal". --Jayron32 11:34, 16 August 2017 (UTC)
I never said you had to actually watch the advertisements. As I said above 'You are entitled to not watch the ads, however you are not entitled to remove the ads'. Do you think you are entitled to exploit other people? Dmcq (talk) 15:20, 16 August 2017 (UTC)
────────────────────────────────────────────────────────────────────────────────────────────────────@Dmcq: Absolutely. But first, I should add that I don't understand your position. I typically use NoScript - is blocking Javascript from one site listed on a page but not another a "theft"? Is it a theft only to block an ad, or also to block a spy script or tracking cookie? Is it a theft to clear your cookies routinely to hinder cross-site tracking? So many things a person can do on his computer, so many "thefts".
But I say copyright is a peculiar institution directly comparable to slavery, which holds that you can own a part of a man's mind or a part of his expressions or a part of his freedom to block advertisements. Abolitionists were widely referred to as nigger-stealers in period literature like John Fennimore Cooper's The Illini, because slaves represented a large chunk of the South's overall wealth, and they unabashedly supported stealing it. I support stealing intellectual property, because it is a tyranny over the mind of man, a form of tax farming, a government granted monopoly coupled with a funding program that could be funded in other more efficient ways comparable with freedom of expression. Because copyright cannot be enforced without tracking literally every communication and contact between every two people and having censors hovering over them waiting to punish.
That said, my opinion, like yours, is quite off topic for this thread, and properly speaking both ought to be hatted. Wnt (talk) 23:39, 16 August 2017 (UTC)

It's been debunked, https://www.youtube.com/watch?v=DBQdAsDtTio, he used clay with magnets inside, drilled a hole in the egg and put it in (he doesn't show you the egg had no holes before he cracked it). Money is tight (talk) 03:08, 15 August 2017 (UTC)

# August 15

## How many hours after aphelion could "the moment of the year you're furthest from the Sun" be?

Without exceeding airliner speed/altitude. What's the approximate path? It seems like it'd involve avoiding the antisolar point from >12 hours before to >12 hours after then flying over the antisolar point (actually you cannot fight the Earth's orbit all the way to the antisolar point since you'll eventually fly too perpendicular to the "Earth-to-Sun" line to overcome Earth's (increasing) inward orbit motion so you're done before actually reaching the point). Sagittarian Milky Way (talk) 00:38, 15 August 2017 (UTC)

I'm not quite sure how to interpret your Q. I thought you were asking for a particular point on the surface of the Earth, when is it farthest from the Sun. The path would approximately be an epicycloid. Whether the Earth's rotation is more significant than the Earth's distance from the Sun I'm not sure of. So, it could either be the point nearest aphelion where that point on the Earth is rotated farthest from the Sun, or it could be at the exact moment of aphelion (somehow I doubt this, though, unless you are close to a pole).
But then you introduced the possibility of flying in a plane, which confused me. In that case, you would just fly to the point of the Earth furthest from the Sun at aphelion, in advance, and then aphelion would be the moment. StuRat (talk) 01:32, 15 August 2017 (UTC)
Well a stationary point that's noon when Earth's center is furthest and with the Sun underfoot on the midnights of that day should have one or both the adjacent midnights be the time it's furthest (I can look up how many miles Earth moves in during this time but from dividing how much Earth moves in in the inward orbit half by 365 half days I doubt it isn't under an Earth radius) If the point can also move at Mach 0.85 then you should be able to extend the disparity to over 12 hours with the right path. Sagittarian Milky Way (talk) 04:36, 15 August 2017 (UTC)
Earth's center is only moving 3.something meters per second away from the Sun 12 hours after aphelion. Sagittarian Milky Way (talk) 05:47, 15 August 2017 (UTC)
OK, by comparison, the Earth's rotation moves a location on the equator a max of about 296 meters per second toward or away from the Sun. Of course, the minimum movement drops to an instantaneous 0 right at the nearest and furthest points on Earth from the Sun. So, based on that, including the Earth's rotation in the calcs would likely be worth the Earth itself not being directly at aphelion. StuRat (talk) 18:01, 15 August 2017 (UTC)
• There is an instant in time when the earth's center is farthest from the Sun in a given year: this is the instant of aphelion. at this instant, there is a subsolar point where the Sun is at zenith. for a spherical Earth, the antipodal point of this subsolar point is farther from the Sun than any other point on the Earth's surface, and is farther from the Sun than any other point will be during this year. The geoid is not exactly a sphere, and the earth's surface has mountains, etc., but without doing the math I suspect that these will not affect the exact point by much at all. -Arch dude (talk) 23:58, 16 August 2017 (UTC)
Right but the center only gets 1 Earth diameter closer in the first week. So if your top speed was infinity you could be furthest ~July 11 while Earth's center was furthest ~July 4. (by staying at the subsolar point for ~2 weeks centered on aphelion then teleporting to the antipode). The question is how much more than 12 hours can you make the disparity if your top (air)speed was ~Mach 0.85? Sagittarian Milky Way (talk) 00:41, 17 August 2017 (UTC)

## Electrical Engineering question, Therevin reduction

Two questions. I have an example in my textbook of a step by step Therevin equivalent circuit, from a few series and parallel connections, given the per unit (pu) values. I believe that the rule for parallel circuits is:

${\displaystyle {\frac {1}{Z_{\mathrm {total} }}}={\frac {1}{Z_{1}}}+{\frac {1}{Z_{2}}}}$

And the pu for a parallel circuit is ${\displaystyle Z_{1}=0.032+j0.958}$ and ${\displaystyle Z_{2}=0.042+j0.610}$. Their solution was ${\displaystyle Z_{\mathrm {total} }=0.021+j0.373}$, but when I put this sucker in my calculator I get ${\displaystyle Z_{\mathrm {total} }=0.018+j0.373}$. They are awfully close, and maybe some significant digits were rounded somewhere, but I'm worried I am using the wrong equation or using my calculator wrong or I'm skipping a step. What I'm doing:

${\displaystyle Z_{\mathrm {total} }={\frac {1}{({\frac {1}{.032}}+{\frac {1}{.042}})}}+{\frac {1}{({\frac {1}{j0.958}}+{\frac {1}{j0.610}})}}}$

As you can see, I get the imaginary portion correct. The real portion is close, but off. So am I doing something wrong?

One more question, they have this equation in the text:

${\displaystyle I_{\mathrm {FAULT} }={\frac {1}{\left\vert 0.021+j0.623\right\vert }}=1.605\mathrm {pu} }$

And I have no idea how they did that. What steps are between that? Maybe I don't know what the vertical lines mean, but taking a reciprocal of a complex number in rectangular form somehow can be reduced to a real number? -12.38.236.194 (talk) 04:10, 15 August 2017 (UTC)

Re the first bit, that's not how I'd do the reciprocal of a complex number. Re the second bit, vertical bars mean the magnitude of the complex vector. Greglocock (talk) 09:10, 15 August 2017 (UTC)
See reciprocal of a complex number. When z = a + bi,${\displaystyle {\frac {1}{z}}={\frac {a}{a^{2}+b^{2}}}-{\frac {b}{a^{2}+b^{2}}}i.}$. Blooteuth (talk) 12:32, 15 August 2017 (UTC)
Yes, for #2, I googled magnitude of complex vector, and came up with Pythagorean theorem, which totally makes sense (convert rectangular to polar, and ignore the angle), and I put that in my calculator and got 1.6042, which is very close to the answer given.
However, for #1, I don't exactly follow, and don't understand where to utilize the reciprocal formula given. I'm using the rule for parallel circuits, which formula I gave above. Is that not the correct formula? Or did I combine the numbers wrong when I went to do the math, or do I have order of operation wrong? Like I said, my method did give me the exact same number for the complex portion, but the real portion is slightly off. So would you mind explaining a little more detail where I went wrong, or show your work (if you agree the book answer is correct, and my value which is .003 lower, is wrong). Thanks for your help so far. -50.95.197.232 (talk) 13:14, 15 August 2017 (UTC)
here's the answer with a few too many sig figs 0.0205157+0.372802j . Hopefully that will help you debug your method. Greglocock (talk) 18:54, 15 August 2017 (UTC)
Here is what I was getting from my formula above with a few too many sig figs 0.018162 + j0.372691. I provided the formula above that I am entering into my calculator, but it seems that is the wrong formula. -50.95.197.232 (talk) 02:09, 16 August 2017 (UTC)
Problem #1:
1. Apply the reciprocal formula to Z1 to get 1/Z1. I used i instead of j and hope that didn't confuse you, here they both mean the same imaginary unit (and not electric current). Do it right and you find 1/Z1 = .034828 - 1.04268 j. Keep working with 5 decimal places.
2. Apply the reciprocal formula to Z2 to get 1/Z2.
4. We have used the textbook formula to get 1/Ztotal.
5. Take the reciprocal of 1/Ztotal and bingo, you have Ztotal
6. Round your answer to 3 decimal places and have the correct textbook solution.
Problem #2:
You are correct, your calculator is correct, but your sloppy textbook has wrongly rounded the answer 1.604225319 ! Blooteuth (talk) 22:12, 15 August 2017 (UTC)
Here is what I got using your method .020515 + j.3728085, but I had a negative sign at some point, so that part is still confusing me. This was a lot of steps, and using the (bad) formula above got me pretty close answers to 3 other questions, but this one was off more than the others. Not sure why this bad formula gets me so close. And I wonder if there is a way to reduce or simplify your method: ${\displaystyle Z_{\mathrm {total} }={\frac {1}{({\frac {a_{1}}{a_{1}^{2}+b_{1}^{2}}}-{\frac {b_{1}}{a_{1}^{2}+b_{1}^{2}}}i)+({\frac {a_{2}}{a_{2}^{2}+b_{2}^{2}}}-{\frac {b_{2}}{a_{2}^{2}+b_{2}^{2}}}i)}}.}$ Doing the reciprocal formula 3 times is a hassle.. But it worked, and I appreciate you giving me step by step! -50.95.197.232 (talk) 02:09, 16 August 2017 (UTC)
Your result differs a little from Greglocock whom I find to be correct to 6 decimal places, so something is not quite right. The formula for the reciprocal of a complex number definitely introduces a negative sign (and the link shows why). The real and imaginary parts of the reciprocal both have the same denominator so you can simplify a program or minimise calculator keysteps by storing (a2+b2) for the 2nd time it will be needed. Blooteuth (talk) 16:52, 16 August 2017 (UTC)
The vertical lines represent the modulus = absolute value of the complex number. It is the hypotenuse per Pythagorean theorem, so the modulus of (1+i) = sqrt(2) for example. In general, when you multiply any two complex numbers, you can add their angles and multiply their absolute values to get the product. (See [26] for an explanation) Anyway in this case you get that 1.604, then just invert that real number. Either the author rounded wrong or he figured (almost correctly) that when you have a vector that goes 0.623 in one direction and only 0.021 in another, its length is basically 0.623 because the square of 0.021 is so small, and never bothered doing the Pythagorean calculation at all. Almost, but it's still off. Wnt (talk) 02:04, 16 August 2017 (UTC)

## From genes to organelles, bones, organs, their parts and shapes

In the college biology textbooks that I have read, there is an explanation of how genes are transcribed and translated into proteins but not how one goes from genes to shapes and parts of organelles (during the synthesis of organelles before mitosis), organs, and bones. Exactly how are the structures of organelles and organs encoded in the DNA and expressed during development? VarunSoon (talk) 09:11, 15 August 2017 (UTC)

This is the realm of the study of ontogeny, especially the subfield known as organogenesis. While the Wikipedia articles seem a bit light on the details, that will provide you some search terms and some initial starting points to begin your research. --Jayron32 11:07, 15 August 2017 (UTC)
This field is still a big miracle for todays science. Its known that the Stem cells are the core of this. I believe some are busy for quite some times now to understand and eventually copy the stunning regrow of lost bodypart (Regeneration (biology)) some amphibians are capable of. --Kharon (talk) 11:24, 15 August 2017 (UTC)
Another aspect which is growing in the field of research here is the role of epigenetics. It turns out that there are aspects of development which cannot be explained directly by DNA, and yet still involve heritable traits. DNA is very important, but it is likely not the only factor in determining growth and development as described above. --Jayron32 12:46, 15 August 2017 (UTC)
You may enjoy our page on EvoDevo, and look for textbooks in that area, here [27] is a reading list. SemanticMantis (talk) 16:16, 15 August 2017 (UTC)
The pages on hox genes and homeotic genes may also be useful. --OuroborosCobra (talk) 19:22, 15 August 2017 (UTC)
Some organelles are explicable - for example, microtubules form from known protein structure, and small microtubule-based organelles like centrioles can thus be put together. Others can be deduced to some extent from various known factors - it looks like [28] might be worth an interlibrary loan from Sci-Hub. I am certainly not an expert on all these scattered and detailed topics, but I think at this point much is known but it is not so clear how much is unknown. Wnt (talk) 01:48, 16 August 2017 (UTC)

## ketosis

When a person fasts (eats absolutely nothing at all) how long after their last meal does it take for their body to enter ketosis? — Preceding unsigned comment added by 52.8.172.72 (talk) 10:56, 15 August 2017 (UTC)

According to Ketosis#Diet, it takes the brain about 48 hours before the process of using ketone bodies for energy begins. --Jayron32 11:05, 15 August 2017 (UTC)
The liver starts producing ketone bodies for other organs long before the brain starts consuming them, though. I'll check my biochem textbook at uni tomorrow. Adrian J. Hunter(talkcontribs) 09:55, 16 August 2017 (UTC)

## power supply

I have a 12v DC power source at 20 AMPS. I want to adjust the voltage from 1V to 12V whenever I want. What is the best way to achieve this? How would I build a voltage adjuster? Thanks for your time. Okiaoa1 (talk) 11:01, 15 August 2017 (UTC)

The best way is to use a thyristor chopper (I can't tell you how to make one, though, because I forgot). 2601:646:8E01:7E0B:1C44:225C:6039:189C (talk) 11:16, 15 August 2017 (UTC)
Buy a new, better power source. --Kharon (talk) 11:33, 15 August 2017 (UTC)
That's just about what I was going to say. Dmcq (talk) 11:43, 15 August 2017 (UTC)
Yes, and I believe the logic is that the new adjustable voltage PS may cost less than the equipment to make your existing PS adjustable, plus you will then have 2 PS's, which is presumably better than 1. Also, if you can describe the reason you need it, then other solutions may apply as well, such as a device which rapidly opens and closes the circuit, providing the average voltage you want. This approach is good, for example, to power a dimmable light bulb and has the advantages of not wasting electricity (particularly important if running off a battery) and generating heat. StuRat (talk) 12:29, 15 August 2017 (UTC)
The article Voltage regulator covers a wide range of technologies. There is no simple "best" choice because it depends on the load. This tutorial is helpful. Begin by establishing the maximum output current you need. Review Voltage_regulator#Comparing_linear_versus_switching_regulators since this choice will dictate the complexity and power dissipation (i.e. heat production) of your solution. If you need only very low currents (a few mA = amps/1000) and not exact regulation, a single Potentiometer can serve as a voltage reduction device. A component to consider is a wirewound 100 ohm (linear taper) potentiometer rated at 3W or more. Another alternative, not necessarily a recommendation, is you can add a variable transformer or "Variac" at the mains input to your power supply; however this is an expensive component and is only workable if your supply is mains powered and a linear, not a switching type. Blooteuth (talk) 12:24, 15 August 2017 (UTC)
• 20A? 240W? Buy one ready made from someone who knows how to make 20A power control circuits. Andy Dingley (talk) 12:31, 15 August 2017 (UTC)
• You appear to want to vary the DC output. Purchase a PWM dimmer or "motor speed controller". These are inexpensive (less than \$20.00 on Amazon.) You cannot use a Variac: these are transformers and only work for AC, not DC. You can in theory use a potentiometer, but these work by consuming the power your circuit is not using, so they are wasteful and they get hot. A PWM works by turning the 12V on and off very, very quickly, then using a capacitor to smooth out the output. This presents a lower average amperage to the 12V supply while presenting the selected voltage to the load. Since the PWM controlelr is on the output side of the 12Vdc power supply, it is indifferent to the AC input of the 12V power supply. -Arch dude (talk) 23:46, 16 August 2017 (UTC)

## Does "Absolute Colorimetric" intent do any good under uncontrolled light?

In color management, when even the proofs of a printed item are to be viewed under uncalibrated lamps, and/or natural light filtered through uncalibrated window glass (and where the weather at viewing time may or may not be predictable at printing time), is there any benefit to using the "Absolute Colorimetric" intent versus the "Relative Colorimetric" one? NeonMerlin 12:29, 15 August 2017 (UTC)

I believe it comes down to a question of whether the image will be viewed on a light-emitting device such as a monitor or on a passive medium such as paper. On a monitor the "absolute" intent will (if properly done) produce defined RGB outputs, which you might or might not desire. On paper it isn't even possible to render "absolutely" under undefined lighting conditions. Etc. Looie496 (talk) 14:04, 15 August 2017 (UTC)

## Are there any receptors that detect fat?

Glutamate receptors detect umami. Glutamate is also an amino acid. So, what detects fat? For example, one reason why the avocado is tasty is that it is mostly fat, giving a creamy flavor. 140.254.70.33 (talk) 16:46, 15 August 2017 (UTC)

For some time, most science in this field held that fat was primarily identified by mouthfeel rather than taste, specifically. However, in just the past 2-3 years, research has turned up a "fat taste" [29] [30] called by some "oleogustus". See Taste#Fattiness_.28oleogustus.29, which discusses the involvement of a possible fatty taste receptor. --Jayron32 16:50, 15 August 2017 (UTC)
You can actually do a test of this at home. Get some beef and pork, and carefully separate the fat from the lean. With a meat grinder, make some ground beef with pork fat and some ground pork with beef fat. Cook up a couple of patties. You will find that they taste like the meat the fat came from. Or, as one source[31] puts it, "What gives meat its flavor is the fat". --Guy Macon (talk) 20:48, 15 August 2017 (UTC)
It's not that simple, since many sensations, including mouthfeel and smell, get mixed up with taste. Actually figuring out which portions of the eating experience are sensu stricto taste and which are arriving via other senses such as touch or smell is way more complex than just "try it out yourself". The OP asked about specific taste receptors. They are unlikely to discover those eating burgers on their own.--Jayron32 21:02, 15 August 2017 (UTC)

## In quantum mechanics an electric current can move in opposite directions simultaneously. Where can I find the Wikipedia article?

In quantum mechanics an electric current can move in opposite directions simultaneously. Where can I find the Wikipedia article? Antonquery (talk) 23:15, 15 August 2017 (UTC)

Flux qubit. Count Iblis (talk) 23:26, 15 August 2017 (UTC)

Thanks!

# August 16

## Can foil dissolve in stomach?

Could a piece of aluminium foil be expected to be dissolved in the stomach and poison a person? I'm not seeking medical advice but I do figure that with a lot of chocolate wrapped in foil around the world, some people must end up eating a bit here and there and it used to be thought that aluminium absorption was correlated with Alzheimer's so maybe chocolate shouldn't be wrapped in foil. --145.255.246.8 (talk) 06:32, 16 August 2017 (UTC)

See: Aluminium poisoning. --47.138.161.183 (talk) 08:42, 16 August 2017 (UTC)
That article is amusing. It says that doses of 40 mg/kg per day may cause problems. For an average size person that's a lump of aluminium about the size of a sugarcube. Every day. My fillings cringe. Greglocock (talk) 11:11, 16 August 2017 (UTC)
People do consume aluminum. It used to be that most consumption came from using aluminum cookware and utensils. Now, most consumption comes from using aluminum cans. A single can of drink will contain less than 1 mg of aluminum, so while it is a primary source of aluminum, it is still considered safe. 209.149.113.5 (talk) 12:38, 16 August 2017 (UTC)
Relevant is the dose makes the poison. --Jayron32 13:53, 16 August 2017 (UTC)
Some antacids also contain aluminium. —PaleoNeonate – 15:02, 16 August 2017 (UTC)

## gluconeogenesis

Does during ketosis does gluconeogenesis using protein replenish glycogen stores in the liver? Would eating too much protein cause gluconeogenesis to produce so much glucose that ketosis comes to an end? FatWater2 (talk) 10:30, 16 August 2017 (UTC)

Not sure, but it seems unlikely, as the same fasting conditions that produce gluconeogenesis also induce the body to undergo glycogenolysis, i.e. the body is breaking down glycogen faster than it can produce it. Remember, even under extreme ketosis, one's blood glucose levels never drop to zero; glucose has other roles besides just producing energy, and a blood glucose level of strictly zero sounds a lot like dead to me. Still, I can't find any definitive answer, other than reading the articles I linked, which hints that is not the case. Someone else may be able to direct you to better reading materials on the subject. --Jayron32 10:50, 16 August 2017 (UTC)
Found something. According to this: [32] no, you cannot generate enough glucose through gluconeogenesis to override ketosis. In short, that article states that it is a "demand-driven rather than supply-driven process", in other words the body only uses gluconeogenesis to meet its bare minimum needs for glucose, and dumping extra protein into your system does not cause it to ramp up. --Jayron32 10:54, 16 August 2017 (UTC)
To elaborate: note that "ketosis" just means your body is burning ketone bodies for energy, which it generally doesn't do if you're in a well-fed state. If you're in ketosis (assuming there's no medical abnormality), your blood insulin is low and glucagon is high. Low insulin tells cells to reduce glucose uptake from the blood. Glucagon tells the liver to dump glucose into the blood, which it gets from breaking down glycogen and gluconeogenesis. But then as blood glucose rises, glucagon levels go down and insulin levels go up, which then downregulates glycogenolysis and gluconeogenesis in the liver. It's a negative feedback loop; the liver (again, normally) will never produce so much glucose that insulin and glucagon levels return to the "well-fed" state and the liver starts storing glucose again. If you eat lots of protein, excess amino acids are burned for energy, or converted into fat, or glycogen in the muscles, and stored. (Gosh, some of those words are a mouthful!) --47.138.161.183 (talk) 02:53, 17 August 2017 (UTC)

## Do computer weather models take eclipse insolation drop into account?

Variation in sunlight brightness caused by Earth's elliptical orbit? The solar cycle? Sagittarian Milky Way (talk) 23:34, 16 August 2017 (UTC)

In my experience, the typical answers are no, yes, and sometimes (if the same model is intended for both weather forecasting and long-term climate studies, as some more recent models are). Dragons flight (talk) 07:40, 17 August 2017 (UTC)