Science desk
< May 21	<< Apr \| May \| Jun >>	May 23 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

May 22

Types of wave through wall

How come that radio waves (lower side of the frequency spectrum) can cross walls, light (in the middle) can't, but X-rays (upper side) can cross walls too?

And regarding mechanical waves, why do sound waves can cross walls (somehow), but ultrasound (starting at a certain frequency - don't know which) is blocked? If ultrasound has more energy, shouldn't it be able to cross walls? --Hofhof (talk) 01:05, 22 May 2018 (UTC)[reply]

This guy thinks he has an answer to part of your second question.[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:30, 22 May 2018 (UTC)[reply]

And this guy says X-rays only partially penetrate walls, and it depends on the density of the wall.[2] And you know from personal experience that reception of radio waves also varies depending on various factors, including the structure of whatever wall you're within, if any. Like if you go through a tunnel and lose the signal. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:33, 22 May 2018 (UTC)[reply]

The tunnel has a mash of steel, it's not really the walls proper that are blocking the radio waves. But the point it, brick walls block 100% light, a little radio waves, and some x-rays. So, the blocking is not proportional to the wave frequency. Hofhof (talk) 01:49, 22 May 2018 (UTC)[reply]

The radio waves have a very low energy per photon, so they do not interact in quantum ways, instead they interact with electrical and magnetic properties of what it encounters. If there is no iron or steel the magnetic interaction is simplified, and it is more effected by dielectric constant and electric eddy currents. The waves can still penetrate bricks, plaster, and wood, but some will reflect off, and a little will be absorbed. As the frequency rises into the high microwaves, more and more will be absorbed. In the sub-millimeter range there are many molecular absorption bands, which extend into the infrared. With things like bricks and plaster, they are composed of tiny crystals just a bit bigger than the wavelength of light. These will scatter the light, as each time it goes into a crystal or comes out, some light will be reflected, and soon none makes it through. But if you had a thin sliver of brick, you will be able to see some light coming through diffusely. Graeme Bartlett (talk) 07:45, 22 May 2018 (UTC)[reply]

Sounds very similar to what one of my high school science teachers said - that if you had a sheet of normally-opague metal that was sufficiently thin, it would be translucent. ←Baseball Bugs ^{What's up, Doc?} carrots→ 08:43, 22 May 2018 (UTC)[reply]

This is why thin metallic (usually aluminium) coatings on mylar plastic film or on glass can be used as filters on camera and telescope lenses to directly view and to photograph the Sun safely. {The poster formerly known as 87.81.230.195} 2.221.82.140 (talk) 17:03, 22 May 2018 (UTC)[reply]

The rule of thumb in linear physics (which includes most common waves) is that everything is a low-pass filter beyond a certain frequency, so that very high frequencies always get blocked by everything. You can expect exotic effects close to resonance frequencies though, and the meaning of "very high" can vary.

GB above has answered the radio vs. light vs. X-rays question, but here are a few more links for the many modes of EM-matter interactions, depending on which frequency (or energy or wavelength) the photon has compared to matter: close to molecular bond energy, close to Zeeman effect spin coupling, above atomic radius, below atomic radius.

For mechanical waves across walls, first of all ultrasound has more energy is a bit misleading. You would not say that "blue light has more energy than red light". Similarly to light, you have more energy per "particle" (phonon) at higher frequencies, but it does not mean that the whole excitation is higher-energy. See Sound_energy_density#Mathematical_definition for the math (v/c is essentially frequency; sound pressure can vary between your typical ultrasound and your typical sound, though).

Finally, wall-ultrasound interaction can get tricky because we still have resonance effects, not at the molecular level but with the micro-structure of the material (example of ultrasound spectroscopy). Tigraan^{Click here to contact me} 09:12, 22 May 2018 (UTC)[reply]

VOR/DME approaches

What are (or were) some real-life examples of VOR/DME (or TACAN) approaches where (1) the DME arc extends all the way to the missed approach point, and/or (2) the approach course begins on one VOR radial and then sidesteps onto another radial from the same VOR station (without crossing it)? 2601:646:8A00:A0B3:EDA1:77AF:46A8:7B5 (talk) 06:44, 22 May 2018 (UTC)[reply]

turmeric with black pepper vs crcumin with piperine

This is a layman's question. The benefits of turmeric are said to be unavailable when consumed raw due to rapid metabolism of curcumin. Curcumin compounded with piperine is said to increase absorption of the former many times over. Do raw turmeric powder/paste mixed with raw black pepper powder provide any considerable beneficial results? --Skillguru (talk) 09:22, 22 May 2018 (UTC)[reply]

No. Count Iblis (talk) 11:00, 22 May 2018 (UTC)[reply]

@Count Iblis: That paper makes some very strong statements, and whenever one paper says that thousands are wrong, we should be cautious. To be sure, it is true that curcumin sticks nonspecifically to things and is fluorescent, which can make many false positive results. However, there is at least some indication [3] that curcumin really influences a subject animal. Studies on animal models and patients suggest real effects. The most impressive effect is its effect on liver toxicity from something like an injection of carbon tetrachloride -- see [4] for example, but there are dozens of papers like this on PubMed. Nothing in Figure 1 looks like it is due to nonspecific activity or autofluorescence. To be clear, I'm not making a case here that it is known to be beneficial (or not) for a human, but the results should not all be discarded just because the research has a few known obstacles. Wnt (talk) 14:43, 22 May 2018 (UTC)[reply]

In my opinion this question is a request for medical advice. Looie496 (talk) 13:16, 22 May 2018 (UTC)[reply]

Can the question be answered completely without providing a diagnosis, prognosis, or treatment advice? Yes. It's just a request for information about a combination of substances, not one bit related to diagnosis, prognosis, or treatment of anything. Nyttend (talk) 00:25, 23 May 2018 (UTC)[reply]

Everything in some way provides something considered a "beneficial result." To ask this question, you must define what a "beneficial result" might be and then define what level of result is considered "considerable." For example, hemlock provides a considerably beneficial result if your goal is suicide. 209.149.113.5 (talk) 15:42, 22 May 2018 (UTC)[reply]

Fat

According to this video on Youtube saturated fat contains only 6 calories per gram instead of the 9 calories which is traditionally stated for fat. Dude sounds like he knows what he's saying. Can anyone prove to me if he is telling the truth? Couldn't find any references myself on this one. Thanks bros. — Preceding unsigned comment added by 177.43.154.145 (talk) 16:17, 22 May 2018 (UTC)[reply]

edit: he says it at 5 mins 15 seconds into the video — Preceding unsigned comment added by 177.43.154.145 (talk) 16:20, 22 May 2018 (UTC)[reply]

He says cocoa butter is 6 calories per gram. This site says "there are 248 calories in 1 oz. of cocoa butter" There are 28.35 grams in an ounce, so this works out to 8.7 calories/gram. Pretty close to 9. Why would you believe one site more than the many sites that give an approximation of 9? Seems to be the "dude" needs to present some sources if he wants to be believed, rather than merely making an assertion. - Nunh-huh 22:30, 22 May 2018 (UTC)[reply]

Since butter is an emulsion of water in fat, it's reasonable that it's calorie content per gram is somewhat lower than that for pure fat. 202.155.85.18 (talk) 03:34, 23 May 2018 (UTC)[reply]

The dude thinks that smoking is good for you, even arguing that "smoking causes cancer" is a conspiracy to make money. I'd call him a quack, but it's more accurate to say that Barry Groves is to healthy living what neo-Nazis are to Judaism. Ian.thomson (talk) 00:56, 23 May 2018 (UTC)[reply]

Actually, it's more like Barry Groves is to healthy dying.... He died of a heart attack in 2013 at the age of 77. - Nunh-huh 02:33, 23 May 2018 (UTC)[reply]

All mimsy were the Barry Groves... and remindful of this item:[5] ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:33, 23 May 2018 (UTC)[reply]

The truth on this statement is the ketogenic diet. See the liver as a "metabolic converter", only. When eating sugar, it directly feeds. Depending on the sugar, glucose does immediately, other sugars less fast. In the intestine, carbohydrates were converted to sugars and transferred into the blood, rising the blood sugar level. Sugar addiction, we are already suffering on it. Beginning a ketogenic diet or traveling in a region without availability of convenience food, we feel about 3 day of nearly permanent hunger, not caused by the stomach, but caused by the liver which tries to avoid getting forced into ketosis. The Hay diet (separating fats from carbohydrates) has a similar effect, but returns the body to the sugar addiction. See also the list of diets. A ketogenic diet also requires interrupted by consuming carbohydrates when stopping loosing weight or power when the body turns into an energy saving mode like starvation response when food is not avail. Beginning such diet, diabetes affected people get the problem of controlling the blood sugar levels. Usually drinking more water will be necessary, least to avoid problems on blood and kidneys, also when eating more proteins. With reducing weight and consuming of sugar containing food, sometimes blood sugar levels and blood pressure can more normalize when not caused my other disease or malfunction. A critical overweight can be normalized by such or similar diet. An increase of weight, is such diet usually does not happen, least when walking enough or having sports. A further loose of weight, sometimes requires the HCG diet or Hollywood Diet. This also can be found in the paleolithic diet as refinated sugar did not already exist. About or misunderstanding about sugar and metabolism, read about the Sugar Lie. [6] We are storing sugar, converted into fat. Converting the fat back to sugar as ketones, we feet uncomfortable when not longer being a sugar Junkie and decide for food, not made to keep customer being a sugar junkie. But no one will start such business due loosing customers. --Hans Haase (有问题吗) 16:47, 24 May 2018 (UTC)[reply]