Wikipedia:Reference desk/Archives/Science/2019 June 3

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June 3

Cat scan

What procedures are needed to prepare a patient (or a cat) for a cat scan? About how much time do they take? How about for MRI? 2601:646:8A00:A0B3:E143:3EF:8DB:B5B7 (talk) 02:20, 3 June 2019 (UTC)

You will normally get a set of instructions from the scan facility about what to do. See also for example here. That showed up immediately with a web search. 173.228.123.207 (talk) 02:41, 3 June 2019 (UTC)

[anecdotal] I recently had about a half dozen cat scans in conjunction with emergency surgery.For at least three of them (including one in the emergency department) there was no preparation at all.    → Michael J Ⓣ Ⓒ Ⓜ 21:34, 3 June 2019 (UTC)

As in the anecdote above, the scan itself involves just putting someone in a scanner. For an MRI, it's also necessary to verify the patient doesn't have anything that would be affected by strong magnetic fields, including medical implants. However, many non-emergency CAT and MRI scans involve administration of a contrast agent to produce a better image. In these cases, the agent needs to be administered, and then waiting may be necessary to allow the agent to distribute in the body. Another type of medical imaging used less frequently is a PET scan. This always involves administering a radioactive drug; the scan involves measuring the radiation emitted by the drug as it decays. Again, a delay between administration of the drug and the scan is often necessary. --47.146.63.87 (talk) 00:01, 4 June 2019 (UTC)

Thanks! So, other than taking the patient's medical history and injecting the contrast, there is no preparation? One last question: if contrast is used (as will be the case in my screenplay), about how long is the waiting time between the injection and the scan? 2601:646:8A00:A0B3:E143:3EF:8DB:B5B7 (talk) 01:15, 4 June 2019 (UTC)

Different agents have different time-courses based on the route of administration, the target area, and the pharmacokinetics of getting it to where it needs to be. I think this is about as far as we can go here per the Wikipedia:Medical disclaimer. Only your physicians know what is right for your specific situation. DMacks (talk) 02:41, 4 June 2019 (UTC)

Per the medical disclaimer, I have just specified that I am NOT seeking personal medical advice -- I am doing research for my screenplay. 2601:646:8A00:A0B3:E143:3EF:8DB:B5B7 (talk) 05:24, 4 June 2019 (UTC)

Whatever you are doing, these are questions about medical procedures, and other readers may take them as medical information, dangerously close to a medical advice. That's why answers here must stop at some level of generality. Any detailed answer may depend too much on a detailed situation of a patient (be it a real ill person or an imagined novel or game character) and only professionals can make such answers true, precise and reliable enough. --CiaPan (talk) 08:04, 7 June 2019 (UTC)

Artemia Salina

Also known as and sold as Sea Dragons or Aqua Dragons are a "pet" advertised on UK television. I have bought these for my son, upon request, and just like my wife's hamster before our son's birth, (I had to clean the cage, feed, water and exercise it) I have ended up having to feed them, air them and provide sunlight. It has been several months now and I have a few questions. A. How long will the little bastards live for?! B. At what point will they reproduce? We went away and came back to maybe 15 left alive. Some appear to have grown testicles?! C. If they do breed, how many can I reasonably expect to have? My most important question, D. What is the humanitarian way of getting rid of them, I don't want to kill anything, hire a whale? Can I flush them, will they live? Can I drop them in the local river? I can't see myself caring for these things much longer but also don't want to kill anything. E. Our article on these guys discussed them as being a salt water creature yet the Sea Monkeys we have are thriving in normal filtered tap water, how is this possible? Is the article wrong? Thanks Anton 81.131.40.58 (talk) 10:39, 3 June 2019 (UTC)

Our article indicates that the "starter kit" includes salt (both the "water purifier" and the "instant life eggs"), so maybe your water is actually sufficiently saline to allow them to survive. Mikenorton (talk) 11:58, 3 June 2019 (UTC)

I found some more about the biology here. Apparently the prominent sacs ([1][2] are called a brood pouch or uterus. Note that oviparity and ovoviviparity are both modes of reproduction here - the female can either give birth to free-swimming larvae, or release eggs in which the larvae are securely encysted, depending on conditions.

Brine shrimp are essentially fish food that can hide out in environments too salty for fish. Disposing of them "most appropriately" should involve finding a friend with a fish, so that whatever happens next, you can wash your hands of it. You remind me it's been too long since I boiled a lobster... :) Wnt (talk) 12:42, 3 June 2019 (UTC)

why don't you return them to their original state, that is, "powder"? You just need to dessicate those Sea-Monkeys back to induce Cryptobiosis. They survive, so you are happy, aren't you? Gem fr (talk) 17:08, 4 June 2019 (UTC)

I believe the eggs survive dehydration, but not the adults. SinisterLefty (talk) 13:58, 5 June 2019 (UTC)

I believe the opposite, that's the whole point of cryptobiosis (and explains why you don't need to wait the eggs to hatch). Gem fr (talk) 16:28, 5 June 2019 (UTC)

Diamonds in The USA

I have been told and have not been able to confirm or dispute the claim that there are no Diamonds or economically viable diamond mines in the United States of America. There are in South America and there are in Canada but not on the Mainland USA. Please confirm, our article does not discuss this under distribution. Thank you. Anton 81.131.40.58 (talk) 11:40, 3 June 2019 (UTC)

This USGS page only mentions industrial diamond production in the US and natural diamonds are not mentioned here in the list of all commodities. This USGS page compares natural diamond production globally and gives the US production as less than half a unit (500 carats of gem diamond) in both 2017 & 2018, suggesting that US diamonds do exist, but in very small quantities. Mikenorton (talk) 12:07, 3 June 2019 (UTC)

https://www.msn.com/en-gb/news/uknews/21-incredible-accidental-treasure-discoveries/ss-BBN8cEv?ocid=spartandhp&parent-title=chess-piece-bought-for-%C2%A35-and-kept-in-a-drawer-for-50-years-is-missing-treasure-worth-%C2%A31m&parent-ns=ar&parent-content-id=AACjDrG&fullscreen=true#image=2 was the article that re-ignited the discussion. Kindly clarify. Anton 81.131.40.58 (talk) 14:25, 3 June 2019 (UTC)

See Uncle Sam (diamond) and Crater of Diamonds State Park for the full story. See also Kelsey Lake Diamond Mine for what appears to be the only other commercial diamond mine to operate in the US. Mikenorton (talk) 15:02, 3 June 2019 (UTC)

There are or were a lot of synthetic diamonds (including gem sized) made in the US. Gemesis was a well known manufacturer. I don't know if that helps you. 173.228.123.207 (talk) 02:59, 4 June 2019 (UTC)

The claim "there are no economically viable diamond mines in the United States of America" is probably explained by a mixture of opportunity cost (you can earn money by mining diamonds in USA, but you would earn more by mining them elsewhere, so, why bother?) and monopsony/monopoly (you have to sell your diamonds to some broker, which would be De Beers or similar company with no interest in your product since they can earn more from other sellers, so, they would reap you off in a deal). (this is worth 2 cents, as I have no special knowledge of this market). Gem fr (talk) 17:38, 4 June 2019 (UTC)

I know the Crater of Diamonds State Park in Arkansas produces some diamonds but not sure how many carats is produced or the quality of the diamonds or weather they are commercially sold or not. 64.222.180.90 (talk) 15:34, 6 June 2019 (UTC)

Are there primary colors of light?

For some reason I never tried searching for an article by that name. When I do, I get redirected to Additive_color.

Some of the responses here suggested there was no such thing as primary colors of light. Also, I found an actual photo of what I meant, while in the other question I showed a Venn diagram to illustrate what I meant.— Vchimpanzee • talk • contributions • 20:53, 3 June 2019 (UTC)

You are correct that light uses additive color, in which the primaries are considered to be specific frequencies of red, green, and blue. (See RGB color model.)   → Michael J Ⓣ Ⓒ Ⓜ 21:43, 3 June 2019 (UTC)

• No, there still aren't, same as when you asked a similar question last week about darkroom safelights. "Primary" colours only exist because of the way the human eye works. Andy Dingley (talk) 22:15, 3 June 2019 (UTC)

• Primary color is an article. Primary colors redirects to it. Let's see, primary colour and primary colours... nay, they go the same place. There must be something about the search interface that is confusing you. Note by the way that primary "colors" are not single frequencies of light, as that article shows, but sometimes complicated mixtures of frequencies (look at that red! I had no idea!) that happen to trigger one photoreceptor more, and the other two less. Wnt (talk) 23:28, 3 June 2019 (UTC)

The search interface isn't confusing me. It's what people have chosen to include and not include in Wikipedia that suggests I am confused.— Vchimpanzee • talk • contributions • 15:17, 4 June 2019 (UTC)

• Just to be absolutely clear in case it wasn't: color is NOT a phenomenon of light. It is a phenomenon of psychology. Everything you perceive of color is an interaction between color receptors in your eye and your visual processing systems in your brain. There are some tenuous connections to light properties, but the process still mostly goes on in your brain. See qualia, which is one common theory of such phenomena.--Jayron32 00:28, 4 June 2019 (UTC)

laser pointers

• That's a bridge too far. You can program an AI drone to drop a bomb on any green car, without it having the same mental image of "green" as you do, since it doesn't have a mind. Color is a processing of frequency data but a relatively simple one. Wnt (talk) 02:22, 4 June 2019 (UTC)

  But that's recognising a particular wavelength as "a primary colour", despite the drone otherwise having no concept of it. A planet of sentient drones (the humans having followed the bees into extinction) wouldn't develop similar concepts of some colours being "primary". In fact, they might do - they might recognise 520nm green line as being a "convenient" colour standard to produce and would prioritise it alongside 635nm red, 445nm blue and 405nm violet as the "obvious" four primary colours. But they're not the same as the human-perception colours. Andy Dingley (talk) 10:05, 4 June 2019 (UTC)

  Color perception is how our brain interprets the complex mixture of wavelengths of light. DMacks (talk) 02:35, 4 June 2019 (UTC)

Why does it have to be a pedantic argument? For average humans, eyes pick up on red, green, and blue wavelengths and, therefore, humans perceive those as primary colors of light. Why? Because you can use those three colors of light in combination to create all other colors of light that humans can perceive. Similarly, red, green, and blue cannot be created from other colors of light for humans. That is why we say "primary". They cannot be a secondary color caused by mixing two other colors of light. It is also important to note that ink is different. Cyan, Magenta, and Yellow (also referred to as Blue, Red, and Yellow for simplification) are the primary ink colors because you can't create those with other colors of ink. For humans, those are the primary color. Now, if we were discussing primary colors for mantis shrimp, it would be a completely different answer. They have at least 12 primary colors, and possibly a total of 16. 68.115.219.130 (talk) 12:08, 4 June 2019 (UTC)

"you can use those three colors of light in combination to create all other colors of light that humans can perceive" is untrue. See Gamut. DroneB (talk) 12:43, 4 June 2019 (UTC)

To achieve complete chromaticity, you must have pure primary colors. Most displays don't have have pure colors, so they cannot produce complete chromaticity. Instead, they produce a gamut of the complete chromaticity. But, that is an entirely different topic. 68.115.219.130 (talk) 13:17, 4 June 2019 (UTC)

Just to elaborate, gamut (in the purest case of monochromatic light) mostly involves the green photoreceptor, which covers frequencies sandwiched between blue and red (actually it seems closer to red, but this seems to make surprisingly little difference). A single frequency of "pure green" light will activate green and red and blue receptors. A single frequency off to one side will activate the green nearly as much, but less of the red or the blue receptors. As a result, if you add "pure green" to a red or a blue, you'll always get something that has green plus some red and blue and therefore looks whiter than the pure frequency. (Actually, I can't believe nobody has figured out some odd way to strobe, polarize, or cohere light in a way that registers as a negative, allowing imaginary color to be real.) Wnt (talk) 13:25, 4 June 2019 (UTC)

This isn't about psychology or perception. There have to be three real primary colors. RGB color model seems to explain it. It does say the exact three colors vary from situation to situation, but there has to be a standard for TV to work, and I think that article comes the closest to explaining it.— Vchimpanzee • talk • contributions • 15:32, 4 June 2019 (UTC)

• There is no single "RGB colour model". There are many RGB colour models, depending on technology. They vary somewhat. In particular, some are additive, some subtractive. But all of them are still based on the human colour model. There's no Platonic colour model, as an aspect of physics.

Your answer to the original question can be "yes" or "no", whichever you prefer. It just depends on how you chose to phrase the question. Andy Dingley (talk) 16:11, 4 June 2019 (UTC)

Our article does say that RGB is additive. The subtractive system used in printing is explained at CMYK. 2A00:23C4:5D0C:D500:305F:D789:20A:9B8 (talk) 16:17, 4 June 2019 (UTC)

That is still all based on human perception. TVs work the way they do because our eyes (and visual cortices) work the way they do. Your statement that "there have to be three real primary colors" is the equivalent of saying that "feet are the shape they are so that our shoes will fit". --Khajidha (talk) 16:45, 4 June 2019 (UTC)

But someone had to decide which three colors would make TVs and computer monitors work, even if it is based on human perception. For TVs and monitors, those are the primary colors. If the technology has changed, fine.— Vchimpanzee • talk • contributions • 16:52, 4 June 2019 (UTC)

I believe your confusion is about the word "primary". Secondary colors are produced by mixing two or more other colors. The primary colors are ones that cannot be produced by mixing other colors. With light, the primary colors are red, green, and blue. With ink, the primary colors are cyan, magenta, and yellow. Nobody "chose" those colors. The reason they are primary is because of how the light receptors in our eyeballs work. If we had different light receptors in our eyeballs, we would perceive different colors as being the primary colors. For example, if we had only "orange" and "green" receptors in our eyeballs, we would consider orange and green to be the two and only two primary colors. But, we have red/green and blue receptors in our eyeballs. So, our eyes made the choice, not some random person who designed the first monitor. 68.115.219.130 (talk) 17:44, 4 June 2019 (UTC)

I'm not confused. You are admitting there are primary colors of light. The reason is not important. Because of how our eyes work, there are primary colors.— Vchimpanzee • talk • contributions • 18:35, 4 June 2019 (UTC)

Light comes in a range of frequencies. Your eyes and your brain together see different colors from subsets of those ranges. Not everyone can see those colors, being partially or totally color-blind. There have also been stories about people who could see a little bit beyond the edges of the normal color vision that you and I have. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:23, 4 June 2019 (UTC)

AFAIK, after some fairly intensive searching, there are no humans who can see "beyond the edges of the normal color vision". This has been claimed a few times by charlatans, but always debunked.

There are though some rare cases, although robustly demonstrated, of human tetrachromats, who have a "four channel" vision system. But this still gives only a more specific form of perception, with a different physiological model, and yet it doesn't extend beyond the normal human range, either to infra-red or ultra-violet. Andy Dingley (talk) 21:56, 4 June 2019 (UTC)

Ultraviolet § Visibility: UV is not perceived by most people because the human cornea and lens block it. If your eyes lack lenses, or if they've been replaced with a lens implant that doesn't block UV, you can see some UV wavelengths. Of course, as noted, human eyes don't have a specific UV receptor, so it's perceived as whitish violet. --47.146.63.87 (talk) 23:38, 4 June 2019 (UTC)

Recent experiments with mice have enabled them to see near infrared for up to a few weeks. In principle the same could be done with humans, although safety concerns make it unlikely that this will be attempted for a while. {The poster formerly known as 87,81.230.195} 2.122.177.55 (talk) 02:11, 5 June 2019 (UTC)

Well you can 'smell' infrared, if it's directed up your nose, as a sort of DIY synesthesia, but that (or lens removal) are hardly the sense organs we're talking about here, in their usual context. You might as well say that frogs have legs just so they can use them as galvanometers.Andy Dingley (talk) 08:00, 5 June 2019 (UTC)

You may be interested in infrared sensing in snakes Gem fr (talk) 09:51, 5 June 2019 (UTC)

The above link is real; it leads to [3]. For more about this link, ask Alexandra Elbakyan; apparently the results are locked up from casual examination, which makes me think this isn't NIH-funded research. The direct ocular injections sound like an obstacle, but how much of one? Special forces may be a lot more 'special' coming up. Wnt (talk) 06:02, 6 June 2019 (UTC)