Wikipedia:Reference desk/Archives/Science/2017 June 14

Science desk
< June 13	<< May | June | Jul >>	June 15 >

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.

June 14

Watermelon rind

A good way to get the most of the watermelon is to eat the pink flesh raw (sweet) and the green rind (cooked). Usually, the sweet flesh is scooped out and eaten. Then, the outer skin is peeled or shaven off. But the rind is kept to be sautéed or stir-fried with spices. My family always eats this way. Look it up; it's a real dish. Anyway, watermelon rind isn't listed on the Food Tracker of ChooseMyPlate, so I'm curious if it would be considered as a fruit or vegetable. Maybe it's both? 50.4.236.254 (talk) 01:31, 14 June 2017 (UTC)

Watermelon is a fruit, and this includes the rind. StuRat (talk) 02:11, 14 June 2017 (UTC)

When I was young we fed the watermelon rinds to the chickens, then ate eggs and chickens. Edison (talk) 22:40, 14 June 2017 (UTC)

My dog when I was a boy, a big black-coated German Shepherd, used to absolutely go crazy for watermelon rind. He would wolf it down and want more. I never understood why. --Trovatore (talk) 22:43, 14 June 2017 (UTC)

You don't even try to understand dogs' eating preference. My previous dog loved arugula. The current dog won't touch vegetables of any sort. Shock Brigade Harvester Boris (talk) 01:23, 15 June 2017 (UTC)

Zero calories

Is water the only ingestible substance that has zero calories or are there others (discounting things that are 99% water)? — Preceding unsigned comment added by 152.92.200.66 (talk) 07:53, 14 June 2017 (UTC)

Cellulose? For humans, anyway. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:03, 14 June 2017 (UTC)

Cellulose is a subset of a group that we can't digest, called insoluble fiber: Dietary_fiber#Fiber_and_calories. StuRat (talk) 13:31, 14 June 2017 (UTC)

Salt is an obvious example; there's also gold. AndrewWTaylor (talk) 09:08, 14 June 2017 (UTC)

The homologous potassium chloride and silver respectively would also meet the criteria; the former is commonly used as a salt substitute. Double sharp (talk) 10:52, 14 June 2017 (UTC)

Beeswax can be safely eaten, but is not digestible by humans. - Lindert (talk) 10:35, 14 June 2017 (UTC)

As with cellulose. Note the OP said "ingestible", not necessarily "digestible". That is, consuming it won't kill you. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:58, 14 June 2017 (UTC)

Given that grass is mostly cellulose except for the grain, I think a good way to lose weight and starve yourself to death is to eat grass. Not only will your humanly digestive tract fail to absorb any nutrients, but also you will spend a lot of energy in moving and chewing and attempting to digest. I prefer the supermarket, though, mostly because I can't really recognize safe plants from non-safe plants. The money transacted at the supermarket for food is the money that goes to other people's work of bringing the food to me. 50.4.236.254 (talk) 11:06, 14 June 2017 (UTC)

Seemed to work for Enkidu. {The poster formerly known as 87.81.230.195} 2.217.208.38 (talk) 12:06, 14 June 2017 (UTC)

Somewhat more appetizing and practical than the previous suggestions is olestra. SpinningSpark 18:42, 14 June 2017 (UTC)

The heat produced by bacteria breaking down fibers in your gut must be counted, because it doesn't matter whether bacteria in your gut or cells in your body are producing heat. Count Iblis (talk) 22:37, 14 June 2017 (UTC)

True. Zero-calorie or extremely-low-calorie substances like water and grass can even effectively have negative calories, though actually digestible and nutritious food generally does not. Related article: Negative-calorie food. --Florian Blaschke (talk) 22:14, 17 June 2017 (UTC)

Improvement of Hipparchic cycle

Is there any known improvement to the Hipparchic cycle in Antiquity or the Middle Ages ? The error of this cycle with regard to the lunar phases amounts to one day in over three millennia. I ask this because a far simpler cycle, equating 49 lunations to exactly one Julian cycle minus a fortnight (or 1447 days) has an error of about one day in three-and-a-half millennia. By comparison, Hipparchus' cycle equates 752 lunations to 22207 days. Though the errors are comparable, the figures involved in the latter are much larger. (The Octaeteris, Metonic and Callippic cycles involve, of course, numbers much smaller than those of Hipparchus, but their errors are, by comparison, between ten and fifty times larger. On the other hand, though about five times more accurate than Hipparchus, the Hebrew calendar, based on computations done by Ptolemy in his Almagest, features even more astronomic values, no pun intended, equating 25920 lunations with 765433 days). — 79.113.239.167 (talk) 14:12, 14 June 2017 (UTC)

The Hebrew calendar doesn't use a cycle. It's true that the new moons regress by 14.00109 days every four years, but that's not a cycle either. Clavius, in his book on the Gregorian calendar, calculated the solar and lunar elements forward for 200,000 years and claimed them to be completely accurate. That may be overoptimistic, but according to Gregorian calendar (note 12) it's practically spot on. 86.176.19.17 (talk) 10:07, 15 June 2017 (UTC)

Magnetic stirrer

With Magnetic stirrers you always have a magnet of some sort in the vessel. At least that's what I thought. But I youtubed "magnetic stirrer" in order to see one in action and in this video[1] I don't see the moving magnet anywhere. The video is from a reputable manufacturer so it's not one of those troll/special effects/magic youtube videos with some video editing/tricks behind it.

So what's going on here? Does this company's product use a different operating principle than other magnetic stirrers? Scala Cats (talk) 18:55, 14 June 2017 (UTC)

Review the product brochure - some of those products are magnetic stirrers, and some are only hot-plates (without a stirring feature). Nimur (talk) 19:42, 14 June 2017 (UTC)

Right, but in the video, they clearly show the liquid swirling around, and even demonstrated that the liquid is constantly moving by adding blue dye to it. And yet no where do I see a magnetic stirring rod in the vessel in the video. Scala Cats (talk) 20:45, 14 June 2017 (UTC)

Look more carefully - I spotted it spinning at a couple of points in the video. Wymspen (talk) 21:32, 14 June 2017 (UTC)

Is the liquid electrically conductive, like water with a bit of salt or acid in it? If so a magnetic stirrer might be able make it swirl like an Electromagnetic pump could make it flow through a tube, due to varying electromagnetic fields created under the baseplate. Would not work for, say distilled water. Such electromagnetic stirring seems common for metal casting, but I could not find a description of its use with water or other common liquids. I don't see why someone would find it necessary to avoid the little ceramic-covered magnet used in lab stirrers for many decades. The video linked by the original poster does not show a stirrer bar in the swirling liquid, but possibly one is there. Edison (talk) 22:36, 14 June 2017 (UTC)

I briefly looked and the stir bar was obvious. Because of refraction it might not be quite where you expect to see it, and the liquid is blue, but there's no doubt in my mind. Wnt (talk) 23:14, 14 June 2017 (UTC)

Quantum cryptography in commercial environment

I've been reading about quantum cryptography. There are many descriptions but they mostly discuss ongoing projects and plans. That includes the Wikipedia as well. However I found one site[2] which talks about this method of communications as if it were a reality. This is what I mean. If I decided to purchase a commercial two way communication system for practical purposes can I do it today? However, why did they shut the system down? --AboutFace 22 (talk) 23:00, 14 June 2017 (UTC)

From Quantum computing: "As of 2017, the development of actual quantum computers is still in its infancy, but experiments have been carried out in which quantum computational operations were executed on a very small number of quantum bits.[7]" Loraof (talk) 23:29, 14 June 2017 (UTC)

A pitfall when quoting from Wikipedia articles is to carry over a superscripted reference without its functioning link. In general, a quantum computer with $n$ qubits can be in an arbitrary superposition of up to $2^{n}$ different states simultaneously. The "[7]" in Loraof's quote here is only a non clickable ghost of a reference and it must not be misinterpreted as a number of qubits. Blooteuth (talk) 21:31, 15 June 2017 (UTC)

I made it clear in my OP post that I am not interested in quantum computing but in quantum communications. --AboutFace 22 (talk) 01:35, 15 June 2017 (UTC)

Maybe I'm wrong, but it seems to me that if we can only compute on a very small number of quantum bits, then we cannot quantum communicate. Loraof (talk) 01:39, 15 June 2017 (UTC)

I may be wrong too but that Swiss system I provided the link for, seems to have been operational on a reasonable level of communication but after two years they shut it down. Why? There are two avenues for quantum communications, one with photons and entanglement and this pretty much matches your objection. There is another way with fiber optic and this is how the Swiss system worked and from what I gathered it is easier to set up and more practical. --AboutFace 22 (talk) 12:38, 15 June 2017 (UTC)