Wikipedia:Reference desk/Archives/Science/2017 April 19

= April 19 =

ISO classification of materials
I some times see non-ferrous metals being referred to as "ISO N". There's a corresponding one letter ISO code for most common materials. Which specific ISO standard is this defined in? ECS LIVA Z (talk) 01:29, 19 April 2017 (UTC)


 * Here are the ISO codes for metallurgy - https://www.iso.org/ics/77/x/ - they are entirely numeric. I can locate no use of the letters you refer to except by the company website you linked to. It may be an older system that they have retained, even though no longer official. Wymspen (talk) 12:02, 19 April 2017 (UTC)
 * Thats a very special ISO exclusively dedicated to categorize hard cutting materials! Its called ISO 513 and it has infact a Group "N". Sandvik is a producer of the Inserts for metal cutting which are usually made from Cemented carbide material as categorized in ISO 513. Unfortunately Sandvik got a little "sloppy" with their ISO description and its a shame they dont mention ISO 513 anywhere on that page or they fear they would have to pay the very hefty licences all ISO authorities ask for any printed ISO-page or part. I could only find some foreign pictures of the list that usually is used for study or reminder by professionals. Just check out what pictures google offers when you search "ISO 513" and you will find your "N". --Kharon (talk) 21:32, 19 April 2017 (UTC)
 * Thank you so much!! ECS LIVA Z (talk) 22:14, 22 April 2017 (UTC)

Moving across the monkey bars
Is there an easy way to move across the monkey bars? For some reason, I have never acquired the ability to move across the monkey bars. I can just hang on one bar with both hands until my hands burn, and I fall down. If I release one hand, then I will fall down quicker. How do I train my arm muscles to become stronger? 50.4.236.254 (talk) 01:49, 19 April 2017 (UTC)


 * Search "train for monkey bars" on Google. You will find sites like this, this, this, and this.  In short, you're just going to have to spend more time on monkey bars or else do lots of pull-ups.  Push-ups train an opposing group of muscles that should be balanced with the pull-up group but do not directly help with monkey bars.  As this illustrates, your natural build will also affect things.  Ian.thomson (talk) 02:11, 19 April 2017 (UTC)
 * There is no article written for children? Does that mean or imply that children have an intuitive sense of moving across monkey bars and then losing this ability due to forfeiting recess time during middle school and high school years? 50.4.236.254 (talk) 02:21, 19 April 2017 (UTC)
 * Outside of very early childhood, your weight generally increases faster with age than your strength. So a 10 year old will typically have an easier time lifting his own weight than an out-of-shape adult. Someguy1221 (talk) 02:51, 19 April 2017 (UTC)
 * Um, but I never acquired the ability to move across the monkey bars. As an 8-year-old, I couldn't do it. As a 10-year-old, I couldn't do it. Even as an adult, I can't do it. I don't think I am out-of-shape, because my legs seem to be more powerful than my arms. I just can't lift my own weight. 50.4.236.254 (talk) 03:15, 19 April 2017 (UTC)
 * Strength in one muscle group bears no relationship to other muscle groups, especially when it's legs and arms. Ian.thomson (talk) 03:27, 19 April 2017 (UTC)
 * The problem may be technique more than muscles, specifically, starting from a static position. There's typically a ladder on one side, and you can climb it on the inside, turn around so your back is to the ladder, then grab the first of the monkey bars with one hand only, and your inertia should carry you forward enough to grab the second bar with your other hand.  When you reach that bar, you let go of the first, and your inertia carries you on to the next bar, etc.  With practice it gets easier. StuRat (talk) 02:13, 19 April 2017 (UTC)


 * A scaling law is also involved. Your strength is (vaguely) proportional to the area of muscles, i.e. the square of your linear size, but your weight is proportional to volume, thus the cube of linear size. So "a child" of "equal fitness" as they grow larger starts out able to pull themselves up and around monkey bars, but becomes less so as they grow - not because they are lazier or weaker, but simply from this scaling.  To pull up on monkey bars at adult sizes, you will need to train and build a little more physical strength than is typical - although not an unachievable amount. Andy Dingley (talk) 12:12, 19 April 2017 (UTC)

Why the mixing of DNA is prohibited in human by law?
Why the mixing of DNA is prohibited in human by law? — Preceding unsigned comment added by 110.34.22.169 (talk) 04:12, 19 April 2017 (UTC)


 * Eh? I have no idea what you are talking about. Can you talk about the context? 50.4.236.254 (talk) 04:23, 19 April 2017 (UTC)


 * It isn't. How do you think babies are made? MarnetteD&#124;Talk 04:26, 19 April 2017 (UTC)


 * Something involving a bird, a bee, a seed, a stork? EdChem (talk) 04:29, 19 April 2017 (UTC)


 * I've seen a number of Sci Fi films covering those :-) MarnetteD&#124;Talk 04:33, 19 April 2017 (UTC)


 * The Asilomar Conference and this link from the article should at least give some background information on your question.--Wikimedes (talk) 04:50, 19 April 2017 (UTC)


 * I would guess they are asking about genetic engineering of humans to include animal DNA. I believe the scientific consensus is that this is a bad idea, but I don't know if it's actually illegal in most places. StuRat (talk) 04:53, 19 April 2017 (UTC)
 * Another possibility - at least some jurisdictions have made it illegal to carry out human germline genetic manipulation, though many of these permit non-germline gene therapy. Agricolae (talk) 15:32, 19 April 2017 (UTC)


 * I agree that the OP is asking about genetic engineering of humans with non-human DNA. I'm not sure whether it's specifcally prohibited by law anywhere, though any kind of DNA manipulation of an embryo is prohibited some places. I'm sure I've read about ethical views on this, but I can't think of where. The only mention I can find in Wikipedia is in Genome editing, which says According to a September 2016 report by the Nuffield Council on Bioethics in the future it may be possible to enhance people with genes from other organisms or wholly synthetic genes to for example improve night vision and sense of smell.[59][60] You might check references 59 and 60 and see where that leads you.


 * Note that there is a distinction between inserting non-human genes into a human embryo to prevent disease and inserting them into an adult to cure disease. Loraof (talk) 15:39, 19 April 2017 (UTC)


 * ManBearPig, First, do no harm, Frankenfood. μηδείς (talk) 19:16, 19 April 2017 (UTC)


 * Could it be a trolling reference to miscegenation? There are (or were) anti-miscegenation laws. Bus stop (talk) 19:30, 19 April 2017 (UTC)
 * Maybe, though he asked why it's prohibited, as opposed to why isn't it prohibited. ←Baseball Bugs What's up, Doc? carrots→ 22:04, 19 April 2017 (UTC)

Winged ants
A few of these have been poking around the last few days. The smaller tick marks are millimeters, so the small ant is about 3.5mm long and the large one about 7mm, though slightly curled up. I'm generally curious about them, and any information would be welcome, but I have a few specific questions: 1) Are they ants or termites?  2) What species are they? (or whatever clade you can narrow it down to.) 3) Are they a male (smaller) and female (larger, queen?) of the same species?--Wikimedes (talk) 04:38, 19 April 2017 (UTC)
 * According to Ant, the male (drone) and the breeding female (queen) age generally both winged, while the non-breeding females (workers) are usually not. These may all be drone ants of different species.  -- Jayron 32 12:16, 19 April 2017 (UTC)
 * These are definitely ants, not termites. This is the time of year in which winged males (generally smaller than queens, but often a bit larger than the non-winged and infertile female workers) and winged females/potential queens will emerge from their colonies and engage in their nuptial flight; they fly quite remarkably high in the air, in large numbers so as to overwhelm avian and insect predators (if these are in or near your home, keep an eye out for woodpeckers, jays and such as they really go for this annual no-hassle feast) and then mate at the apex of their ascent.  They then return to the ground where the males die and the females lose their wings and begin their own colonies (or in particularly eusocial species, new satellite annexes of megacolonies).  Given the morphology of these particular specimens, the location, and the timing, I'd say you are looking at some variety of Tapinoma, very possibly Tapinoma sessile; if they give off an offensive little odor if you disturb them and find any source of sugar left out instantly, you have a ballpark ID.  If not, this source may be of further use to you.  If not a species of Tapinoma, Formica would be next best bet.  With some extra photos, I may be able to make a more definitive identification.  S n o w  let's rap 20:07, 19 April 2017 (UTC)
 * Thank you for your help. The sniff test was negative, both for agitated live ants and squished dead ones.  I've been using a dissecting scope to work through the key you linked, and although I'm uncertain about some of the steps, the ants have a single-segmented petiole and no discoidal cell.  Given the size of the ant and the shape of the marginal cell (which you probably can't see in the picture), I think it's prenolepis rather than camponotus.  Does this make sense?  (The smaller ants have claspers, so definitely male.)--Wikimedes (talk) 05:44, 21 April 2017 (UTC)


 * Good eye! Yes, as it happens, those two genera can be a little hard to tell apart, because of their common lineage and similar morphology. Carpenter ants, as you note, are generally on the larger side, and though there are a handful of widely-dispersed North American species small enough to align with your specimens, the features don't seem quite right for any of them, as best I can make out from the pictures.  Rather, I think you are quite right that prenolepis is more likely; in fact, reviewing the photos in light of your smaller-scale observations and your educated guess, I think I have a good candidate: Prenolepis imparis:, , .  Size, behaviour, distribution, colouring, and all anatomical features that I can make out are consistent.  However, workers are most ideal for making a truly reliable identification; I'm not sure what kind of resolution you can get on them for a photo, as they are likely only a few millimeters in length, but you can find some comparative images and a lot of further information at the following links: , , , .  Someone even has video up on youtube if you care to compare the close-ups and their responses to environmental stimuli:.


 * Note also that there is another reason to suspect that these are P. imparis, other than the close match of morphology and appearance; we are in the mating season for ants at your latitude generally, but just barely. Most species will not be taking their nuptial flights until May, especially in a region that stays as cool and wet as Western Oregon does for as long as it does.  However, this species is known for being a relatively cold-loving ant (one of its colloquial names is actually the "winter ant"), and its breeding population actually overwinters in their colony from the previous summer (unlike most species, in which these members of the colony develop during spring itself).  Between those factors, the nuptial flights of this species occurs a little earlier than most species in a given region. In fact, the one reference I could find to their breeding habits in Oregon in particular noted that they undertake their flights during early-to-mid April.  All in all, these seem your gals and guys.   S n o w  let's rap 10:03, 22 April 2017 (UTC)


 * Thank you again. It's been a pleasure.--Wikimedes (talk) 20:11, 23 April 2017 (UTC)


 * Glad to be of assistance! :)  S n o w  let's rap 21:10, 23 April 2017 (UTC)

== Feynman Lectures. Lecture 52.Ch.52-5 Reflection symmetry 2. archive==

According to the Lecture 20 we have the coordinates of a vector product and the rule to build it (the right-screw rule). Suppose we have $$\mathbf{r}$$ and $$\mathbf{p}$$ coordinates png. We draw the vector product by the coordinates. Then if we change the coordinate system to left-handed and again draw the vector product it will be built by left-screw rule png. How is it possible? So what should we use right-screw rule or coordinates? . dwg1dwg2

Username160611000000 (talk) 07:23, 19 April 2017 (UTC)


 * I think Feynman is saying that L = rxp is only true in a right-handed co-ordinate system. If you switch to a left-handed co-ordinate system (by inverting the z-axis, for example) then the rule becomes L = - rxp i.e. a right-hand rule in a right-handed co-ordinate system becomes a left-hand rule in a left-handed co-ordinate system - see right-hand rule. Another way of expressing this is to says that angular momentum is a pseudovector. Gandalf61 (talk) 08:53, 19 April 2017 (UTC)
 * Feynman mentioned that in lecture 20 :


 * So it's no matter what the coordinate system we have, sign of z-coordinate is chosen arbitrary, and for right-hand system and left-hand system the formulas for x- and y- coordinates become the same.
 * Username160611000000 (talk) 13:56, 19 April 2017 (UTC)

And second question: Where should we stop the reflection operation ? Here (just going to left-hand system) or here (redrawing in usual form)? If first, then I don't understand the figure 52–3, because in left-hand system vectors ω must be opposite. If second, then I don't understand why should the vector product $$\mathbf{r \times p}$$ become $$-\mathbf{(r \times p)}$$Username160611000000 (talk) 14:32, 19 April 2017 (UTC)

Would effervescent vitamin c tablets still be usable after 20 years?
In my kitchen cupboard I found an unopened fully shrink wrapped box of "Redoxon Effervescent Vitamin C" with an expiratory date of November 1996. I am NOT going to use them but I just wondered out of curiosity whether or not they would still actually contain Vitamin C that is usable to the body. Or would the Vitamin C have broken down after 20 years? The ingredients are listed as "Vitamin C (ascorbic acid BP), Sodium Tartrate, Sucrose, Flavourings, Colours Apo-Carotenal, Riboflavin, Artificial Sweetener Sodium Saccharin, Sodium Chloride. Thanks for your time
 * This is more of a materials science question than a pharmacological one. Vitamin C has a very long storage life in dry conditions - decades. In these typical tablets, the usual "failure mechanism" is by the effervescent agent (the sodium tartrate) absorbing moisture from the air. This gives the typical soft, spongy and slightly expanded appearance of most old Vit C tablets.
 * The question is how well hermetically sealed they were. "Box" and "shrink wrappped" just aren't enough - those materials are permeable to moisture over a timescale of years. If your kitchen cupboards are at all damp, I'd expect the box itself to start looking damp-affected by now. Usually though, effervescent Vit C is packed in a plastic tube, either polyethylene or polypropylene, and with a dessicant pellet inside the lid. Even then though, LDPE is water permeable - certainly on this decades timescale. A serious problem if you're laying telephone cables, and why polyethylene cables also have moisture barriers of aluminium foil and an internal grease packing or dry air pressurisation. If these tablets were packed for long-term storage, they'd instead be in aluminium tubes with a screwed cap. Those can easily be rated for 50+ years. Andy Dingley (talk) 09:10, 19 April 2017 (UTC)


 * Rather than just guess, it is easy to purchase some 2,6-Dichloroindophenol Sodium Salt and then assay it for oneself. Youtube even has some demos to show how you can do it in one's own kitchen. Vit C is also heat liable. So it depends on the storage temperatures also. Aspro (talk) 11:21, 19 April 2017 (UTC)

The predictability of humans
I remember that there was an online game, in which the artificially intelligent algorithm tried to compete with the human player. As time moved forward, the algorithm learned the human patterns and began winning games, because the human was becoming more and more predictable. However, the algorithm also displayed its own "thinking process" and "prediction" of the human's next move, so the human, with that knowledge, could make a choice in contrast to the algorithm's prediction. At that point, isn't the algorithm pushing the human to become truly random or unpredictable? Biologically, do humans manifest a greater degree of randomness than other animals to the extent that it appears as though humans are harder to predict? So, in order to defeat other humans, a human must be able to observe the biases that govern other humans while trying to hide his own biases by misleading other humans? 50.4.236.254 (talk) 13:59, 19 April 2017 (UTC)
 * I'm not really sure where you're going with your question, but the concept in your last question about "observe the biases that govern other humans while trying to hide his own biases by misleading other humans" is a level of cognition known as metacognition, which literally means "reflexive thinking" and refers to the ability of a person to understand their own thought processes and to control them. There is also what is known as theory of mind which is a related skill, and refers to the ability of a person to understand another person's thought processes; that other people have minds like yours, which are also distinct from yours, and further how to understand how their minds are likely working.  -- Jayron 32 14:13, 19 April 2017 (UTC)


 * In a non-cooperative game in which opponents can change their strategy - whether the players are human or machine - the strategies can continue to evolve each time you play the game, until all players finally reach the Nash equilibrium strategy. That is the point in the game at which no further strategy-change, by any player, will yield a statistical improvement in the chance of winning for any participant.
 * In a simple, constructed game that is designed to study game theory, we can use mathematical formalism to describe the equilibrium strategy "exactly." This also works for real games like blackjack.
 * In sophisticated games, where the decision space is quite enormous, it can be hard to formalize the strategy, and it can be mathematically intractable to solve for the provably-optimal strategy; but the concept still applies: in broad brush-strokes, a strategy can account for an opponent who may make "unpredictable" choices. There does exist a "best" strategy: even if the "best" strategy sometimes loses (e.g. when it guesses wrong about its opponent's plan), it is statistically more likely to win.
 * Intelligent data-driven humans and computers can use methods of statistics to model the opponent's behaviors, in the pursuit of playing with an optimal strategy.
 * Nimur (talk) 15:19, 19 April 2017 (UTC)


 * The OP asked whether the given scenario is pushing the human to behave randomly. A random strategy is called a mixed strategy. Loraof (talk) 15:59, 19 April 2017 (UTC)


 * It's not all that difficult to make people make precisely those "random choices" that you want them to make. Count Iblis (talk) 20:19, 19 April 2017 (UTC)
 * Which observation raises the even deeper epistemological inquiry of whether a human being (or any entity based on physical laws) is capable of doing anything that can be accurately described as truly "random"; hard determinism suggests this is a tautological impossibility.  S n o w  let's rap 21:19, 19 April 2017 (UTC)
 * A buddhist carries that enquiry to the extreme of all-encompassing determinism known as Pratītyasamutpāda or interdependent origination: all things arise and exist due to certain causes (or conditions), and lose their existence once these causes (or conditions) are removed (see Idappaccayatā). However the enquirer must be prepared to discover himself or herself is no more than such an illusory thing, constantly re-imagining themself in a cycle of samsara. A physicist however, typically insists that physical phenomena such as the nuclear decay of atoms, can drive decisions that are truly random. Schrödinger speculated about the confusion such unpredictability might cause between one or more cat(s). Blooteuth (talk) 23:03, 19 April 2017 (UTC)


 * No offense, Blooteuth, but I wasn't really talking about mysticism, but rather the variety of metaphysics informed by hard science and natural and empirical (rather than religious) philosophy. I'm not saying these aren't interesting topics in their own way, but they are not really the same subject I was bringing the OP's attention, and are related only in the most tangential manner.  As to the uncertainty principle, it also really has little to do with the question of determinism as it relates to human behaviour.  For starters, uncertainty, as the term applies to complementary variables, is not the same thing as the abstract concept of "randomness".   One is a product of mathematical and physical systems with a precise (if complex) function, while the other, as you use it, is more of a vague mental construction.   And even if we were to theorize a truly "random" effect at the subatomic level, there would be no clear manner by which this effect would propagate "up" to play a consequential role in the biomolecular mechanisms which give rise to human behaviour--not withstanding the psuedoscientific wonkery of quantum mysticism nonsense.  If it were as simple as you are suggesting, the very profound debate about determinism would have been over a long time ago.  But you're actually comparing apples and oranges (and meaning no offense, but also describing both the apples and the oranges incorrectly).  S n o w  let's rap 02:47, 20 April 2017 (UTC)
 * I enlist the Buddhist "B" and the Physicist "P" as generic proponents of their respective World views who may yet share a constructive dialog. They find agreement in the term "uncertainty" when each recognizes the scope of the other's understanding of "random", which I shall summarize. P can prescribe hardware that detects subatomic events that are individually unpredictable, though statistically bounded, such as a Geiger counter that detects a Beta particle and thereby seals the random fate of Schrödinger's cat. B reminds S that the demonstration asks us to accept on trust alone someone's report on the state of the cat, which itself introduces the covert vagueness of an Argument from authority. With insight into the myriad ways that consciousness can play tricks on a person, S himself must, if not claiming divine infallibility which is anathema to B who doesn't accept dogma, admit his own imperfect sight, interpretation or memory as further sources of random error. The disputed view that Hard determinism nullifies existence of free will is suspected by P who cannot verify it, but B may, depending on his specific practice, choose Noble Silence rather than be drawn into unproductive debate on questions that cannot reach closure. Blooteuth (talk) 14:57, 20 April 2017 (UTC)
 * It is not randomness but newness that is pursued by each entity, whether that entity be man or machine. Each entity gains an advantage by requiring the other entity to learn something new and to make educated guesses about what makes the other entity tick. Bus stop (talk) 18:33, 20 April 2017 (UTC)
 * The question is asked "isn't the algorithm pushing the human to become truly random or unpredictable?" No. The algorithm is simply pushing the human to do things that the human has not done before. Randomness would serve no purpose. Of course the new things that the human is doing would have to be things that are acceptable to the human or which would lead to outcomes, several steps removed, that are acceptable to the human. Bus stop (talk) 22:34, 19 April 2017 (UTC)
 * A game in which the human's opponent reveals its "thinking process" and "prediction" is an entirely different game from one in which it is not displayed. The human will be evolving a new strategy to deal with the new rules, not becoming random. - Nunh-huh 02:21, 20 April 2017 (UTC)
 * The optimal strategy according to game theory is not the optimal strategy against a person who has biases. One would still win as much or more than one would playing a person who played according to game theory - however the biases make it a new game where a different strategy could make a lot more. So yes it is right that if both sides learn their strategy will get more random. Dmcq (talk) 09:39, 22 April 2017 (UTC)

Distinguishing phytoplankton from zoo plankton
Is there any easy way to distinguish phytoplankton from zoo plankton without using a microscope?? Georgia guy (talk) 15:56, 19 April 2017 (UTC)
 * How good is your eyesight? Assuming you mean unicellular life, then no, there isn't.  If you mean plankton under the more formal definition, which is just "aquatic life that cannot navigate on its own", then yes, some plankton are clearly visible without a microscope.  You'd need a large microscope to even fit a Portuguese man o' war on it; you can tell readily it is zooplankton, whereas seaweed is sometimes classified as a phytoplankton; it too is quite identifiable to the naked eye.  -- Jayron 32 16:04, 19 April 2017 (UTC)

1.0x magnification lens - what is the purpose?
[This head-mounted magnifie]r comes with a 1.0x lens. What could possibly be the purpose of a 1.0x magnification lens? Isn't that an oxymoron? --78.148.99.149 (talk) 18:24, 19 April 2017 (UTC)
 * In this one case, so you can use the head torch without any magnification. -- Jayron 32 18:36, 19 April 2017 (UTC)
 * That make no sense because the headtorch doesn't need a lens in place to function? --78.148.99.149 (talk) 22:59, 19 April 2017 (UTC)
 * I'd guess it's so they can increase their profits by selling you a part you'll never need. --76.71.6.254 (talk) 23:05, 19 April 2017 (UTC)
 * Just because you would never use doesn't mean someone else wouldn't. The world doesn't consist only of you and people whose needs and wants and preferences match exactly yours.  -- Jayron 32 03:01, 20 April 2017 (UTC)
 * Of course. Among others, it also includes people who want to increase their profits by selling you parts you'll never need. --76.71.6.254 (talk) 02:53, 21 April 2017 (UTC)


 * Could they function as safety glassess ? StuRat (talk) 02:31, 20 April 2017 (UTC)


 * These are not just magnification lenses. They are used to help a person focus on something close up. Most humans lose the ability to maintain focus close up when they get older. Therefore, they wear some form of 'reading glasses.' You may want the assistance in focus without magnification. So, you get 1.0x magnification lenses. They help you focus without making everything huge. 209.149.113.5 (talk) 14:54, 20 April 2017 (UTC)
 * I can't tell from that how the lenses are supposed to be changed. Depending on how it works, switching to a 1x lens might be easier or quicker than removing the headset.  Iapetus (talk) 15:03, 20 April 2017 (UTC)


 * The lens screen unclips and you clip a new one on. So, no, it would be work to remove the 2x and put on the 1x. As I mentioned above, if I am trying to work with something really small and it is close to me, I might want a 1x lens to help bring what I'm looking at into focus without magnifying it. Another example... I used to have bifocal lenses. They were set for different focal lengths, but both lenses were 1x magnification. 209.149.113.5 (talk) 18:02, 20 April 2017 (UTC)
 * I don't think that works. A 1x lens is not a reading lens, it's just a pass-through. Reading glasses have some degree of magnification to them. (Just as glasses for nearsightedness have some degree of reduction to them.)  Usually between 1.5x and 2x.
 * This is mentioned briefly in the article for Corrective lens.
 * The 1.0x lens must just be a place-holder. Why you'd need a place-holder, I don't know. ApLundell (talk) 20:08, 20 April 2017 (UTC)


 * Did you search for 1.0x reading glasses before you stated that 1.0x reading glasses don't exist? 71.85.51.150 (talk) 22:42, 20 April 2017 (UTC)
 * Yes. I did search. The only examples I found were either place-holder lenses, or situations where someone had confused 1.0x with 1.0 diopters. (which is roughly 1.25x magnification.) Confusing diopters with magnification factor seems to be a common mistake in the realm of reading glasses. ApLundell (talk) 14:12, 21 April 2017 (UTC)


 * Reading glasses do not require magnification. Mine do not magnify. They aren't even 1.0000000001x magnification. They adjust the focal length so things that I cannot focus on anymore are now in focus. It appears that most people answering this question are under 50 and don't understand what it is like to have old eyes. 209.149.113.5 (talk) 12:02, 21 April 2017 (UTC)
 * I'm under 50, but I absolutely understand what it is to have weak eyes, don't worry about that.
 * You could have "reading glasses" that only correct for astigmatism, but they wouldn't actually be correcting for farsightedness which is how the term "reading glasses" is usually understood.
 * I understand that they don't look like they're magnifying because they're compensating for a fault in your own built-in lenses. Just like glasses for distance don't look like they're reducing. At least when you're wearing them. If you hold your bifocals over a sheet of graph paper, it's clear that the distance lenses reduce and the reading lenses magnify.
 * I promise you, all glasses that correct for farsightedness (aka "reading glasses") are Converging lens. The point isn't the magnification, that's a secondary effect, but it is a real effect. ApLundell (talk) 14:12, 21 April 2017 (UTC)
 * As a side note, it always bugs me when TV shows or books feature a nearsighted character starting a fire with his glasses. That's not really possible. You'd need reading glasses to start a fire. Unusually strong ones, too.ApLundell (talk) 14:12, 21 April 2017 (UTC
 * Yes, that error in Lord of the Flies destroyed the credibility of William Golding for me at age ll. How could an author who had not noticed such an easily observable, checkable (ask any spectacles-wearer) and correctible (he could easily have made Piggy long-sighted) fact about the material world be trusted on other matters? I also have a memory of him mentioning a crescent moon rising at sunset, but haven't subsequently re-found the passage – I may have conflated LotF with another work in this respect. {The poster formerly known as 87.81.230.195} 90.217.249.244 (talk) 02:21, 23 April 2017 (UTC)
 * I don't think those kinds of details were the point of the book. ←Baseball Bugs What's up, Doc? carrots→ 03:00, 23 April 2017 (UTC)


 * Dear goodness. It's been so much fun watching people stumble through this discussion without any research or providing actual sources.  Sorry to ruin everyone's good time by actually finding sources that answer the question, but here is one.  -- Jayron 32 14:33, 21 April 2017 (UTC)
 * What are we supposed to learn from that source? That the advertised power of a lens is 1 plus the magnification?
 * That's what prompted the question. A 1x power lens has 0 magnification. ApLundell (talk) 14:55, 21 April 2017 (UTC)
 * This is a better reference. 209.149.113.5 (talk) 18:13, 21 April 2017 (UTC)
 * Saying it is 0 magnification is not useful and could be confusing. What magnification then would a lens that halved the size have? -1? -1/2? I think just saying 1x for no magnification is fine. Dmcq (talk) 19:31, 22 April 2017 (UTC)

Jellyfish evolving into land creatures
What would jellyfish look like if they evolved into land creatures? Has anyone speculated? I tried doing a Google search but I didn't come up with muchUncle dan is home (talk) 20:23, 19 April 2017 (UTC)
 * Surely this question is inviting only speculation - not appropriate for a ref desk in my opinion. DrChrissy (talk) 21:23, 19 April 2017 (UTC)
 * There are at least potential sources for similar questions - see The Future Is Wild. Speculative evolution seems to be a field, so while there is speculation evolved, it's not necessarily speculation by the refdesk. --Stephan Schulz (talk) 21:27, 19 April 2017 (UTC)
 * Agreed, it is perfectly reasonable in these circumstances to link to published speculation as a reference on prior (presumably informed) speculation. SemanticMantis (talk) 22:46, 19 April 2017 (UTC)
 * Jellyfish need a fluid so they can float. If they where big they might float in air if they could produce and contain a gas lighter than air but then how would their offspring manage that? Maybe they could rise from a lake. Anyway they would not work as land creatures. --Kharon (talk) 21:45, 19 April 2017 (UTC)
 * Such creatures have featured in several science fiction stories and novels set on alien planets. The terrestrial (in the planetary sense!) Portugese man-o-war looks as if it's part of the way there. {The poster formerly known as 87.81.230.195} 90.217.249.244 (talk) 02:48, 20 April 2017 (UTC)
 * Portugese men-o-war regularly become land animals, if the wind's in the wrong direction for them. They're not very good at it, and die quickly.
 * A "jellyfish" has the characteristics that it relies on buoyancy for support, some sort of environmental current for locomotion and similar currents (and prey) for food and its passive capture hunting. This might work out of water, especially on other planets with other gravities, but we can establish some boundaries for density and Reynolds number for an environmental medium in which such a creature could survive, and where it definitely couldn't. On Earth, only water is plausible. A hydrogen-filled "sky jellyfish" might work on Earth, but it would need to develop a gasbag membrane, also a greater number of flying insects or small birds to feed upon - or maybe chloroplasts. Jellyfish don't have great tensile strength, they don't make good balloons.
 * I'm also unaware of any freshwater jellyfish. I'm guessing that there's also an osmotic limit on them? Andy Dingley (talk) 09:20, 20 April 2017 (UTC)
 * Just to make it clear for the reader, the Portuguese man o' war is not a jellyfish, but a siphonophore. DrChrissy (talk) 17:59, 20 April 2017 (UTC)


 * And they will be preyed on by big birds that pierce them with their sharp beaks. Sagittarian Milky Way (talk) 12:49, 20 April 2017 (UTC)
 * See Olindiidae, especially craspedacusta sowerbii . -165.234.252.11 (talk) 17:35, 20 April 2017 (UTC)
 * Oh yes, thanks - they're invasive and currently of concern, aren't they? Andy Dingley (talk) 17:42, 20 April 2017 (UTC)
 * I want to see octopuses​ evolve into land animals. And gain sentience and see what their chairs look like. Sagittarian Milky Way (talk) 22:07, 19 April 2017 (UTC)
 * Octopi can work on land. There was a video a year or so ago showing an octopus crawling up on a rock and grabbing a crab. Also, see SPECTRE. ←Baseball Bugs What's up, Doc? carrots→ 22:12, 19 April 2017 (UTC)
 * Well I better not speculate so I'll just point to where the ideas here have been investigated :) How about jellyfish not just on land but in space? And don't Pastafarians have a deity rather like a very intelligent octopus with lots more arms? I believe it resides on a plate rather than sitting in a chair. Dmcq (talk) 22:35, 19 April 2017 (UTC)


 * This seems related to some other questions. Typically, I would think a route to land should begin in fresh water, because salt water will no longer be available to an organism that strays much from the beach.  Which brings me to discussions like https://www.reddit.com/r/explainlikeimfive/comments/2r32xb/eli5why_are_there_no_freshwater_corals/ .  I mean, we see with coral a remarkable lack of options biologically speaking, to the point where the Great Barrier Reef is or soon will be no longer a viable environment for them.  It is hard for me to understand really why there is so little evolvability there, why the corals can't just throw some ATP and enzymes at any problem and grow in battery acid if they have to.  But the limitations seem undeniable. Wnt (talk) 12:05, 22 April 2017 (UTC)

Why does Defibrillator has two stickers to attach the chest of a victim?
Why does Defibrillator has two stickers to attach the chest of a victim? Is one is not enough in order to deliver dose of energy / electricity? 93.126.88.30 (talk) 22:02, 19 April 2017 (UTC)
 * See Defibrillation. An electrical current must flow between two points. In general this cannot happen if you have a single electrode. -Arch dude (talk) 22:13, 19 April 2017 (UTC)
 * In an electric circuit, current flows between two electrodes, the cathode and the anode. Electricity isn't some kind of fluid that you can just pump into a person.  CodeTalker (talk) 22:15, 19 April 2017 (UTC)
 * For a layerson's description of how a defibrillator works see https://www.howequipmentworks.com/defibrillator/ Richerman    (talk) 22:27, 19 April 2017 (UTC)
 * By the way the person being treated with a defibrillator is usually called a patient rather than a victim. Dmcq (talk) 22:39, 19 April 2017 (UTC)
 * Heheh, the original poster never said the person using it would be a doctor ;) Wnt (talk) 17:11, 21 April 2017 (UTC)
 * Interestingly, if a person is laying on the ground it would be possible to use only one electrode as the earth itself would complete the circuit (thinking to why people can get electrocuted from power lines where birds do not). But completing the circuit with two pads gives you much more control of where the energy goes (through the heart), along with reducing resistance which can cause burns which is why they typically use a conductive gel. Drewmutt ( ^ᴥ^ ) talk  22:47, 19 April 2017 (UTC)
 * the person may be grounded, but the portable defi isn't, so coming in contact with just one pad should be safe (insert disclaimer.) IOW, it's not about having a definite return path (instead of through the person's shoulderblades, bum etc), it's about having any return path at all. Asmrulz (talk) 05:32, 20 April 2017 (UTC)
 * Yeah you wanna make sure the current is through the heart not from the chest to ground. The term 'victim' (by another poster really made me laugh though). Keep it up RD posters: (its the best comedy channel on the internet, especially with some of the regulars posting their 2 cents worth). 31.109.117.25 (talk) 00:11, 20 April 2017 (UTC)
 * Just to understand and to make it clear, I would like to know if in AEDs normally there is a pad for right and a pad for left or it doesn't matter? [Regarding to using of "victim", it may-be mistake but it may-be a meter of difference between the AmEn to BrEn and AUen and CaEn. I don't belong to one of them but still I found it a lot in what called "high education" lectures or official sites, books, Googling (AED + victim) can show a plenty of examples).] 93.126.88.30 (talk) 03:30, 20 April 2017 (UTC)
 * perhaps they don't want to imply a doctor-patient relationship or something, AEDs being one of those apparatus that may be used by laypersons Asmrulz (talk) 05:32, 20 April 2017 (UTC)
 * Probably they are referring to a person who suffers a heart attack as the victim of a heart attack. I don't go in for personifying illnesses but lots of people do. Dmcq (talk) 10:42, 20 April 2017 (UTC)


 * Back to the important bit: Yes, AEDs have a left and a right pad. There's a drawing on the pads indicating where to place them. They have clear instructions since it cannot be expected that the user would have ever used one or even been told how to use it. They are foolproof. Hofhof (talk) 10:45, 20 April 2017 (UTC)
 * Never underestimate the ingenuity of fools. -- Jayron 32 12:05, 20 April 2017 (UTC)
 * I always thought it's on the off chance that you encounter a time lord as they have two hearts and the current needs to pass through them both, hence one on the left and one on the right. Better to have a one size fits all machine than risk a premature regeneration. Polyamorph (talk) 12:49, 20 April 2017 (UTC)
 * Well, some AEDs have distinct left vs right pads, and maybe all did on older equipment. But not strictly true any more. I just verified that CardiacScience G3 in my building has non-polarized pads. I *think* the cable is polarized, but the pad instructions are clear that they can go in either location. DMacks (talk) 15:29, 20 April 2017 (UTC)

Near Earth object flybys and statistical oddities
This shows a best fit power law of 19 absolute magnitudes of size cutoff reduction resulting in 9 orders of magnitude higher frequency of hitting the Earth. Or 2.97635144 times more asteroids per 1 absolute magnitude dimmer size cutoff. The nearest might be sqrt(2.97635144) times closer to the center on average and thus 2.97635144 divided by the 1 astronomical magnitude (2.51 times) dimmer asteroid still makes it 1.184 magnitudes brighter from the center and even more from parts of the Earth closer to it than Earth's center. So does that mean the brighter (apparent magnitude) a near Earth asteroid flyby is (from either Earth's center or the best place in the world), the more likely it is to be smaller and closer than bigger and farther? Are apparent magnitude 10 asteroid flybys more likely to be less wide than expected through the expedient of higher albedo? But if so the chart seems to say the power law holds for both width and absolute magnitude. Is there a name for this statistical oddity? Sagittarian Milky Way (talk) 23:24, 19 April 2017 (UTC)

P.S. Can someone explain why the apparent magnitude link doesn't lead to the apparent magnitude article? Sagittarian Milky Way (talk) 23:29, 19 April 2017 (UTC)
 * so why dont you bledinmg well link it then??? — Preceding unsigned comment added by 31.109.117.25 (talk) 00:16, 20 April 2017 (UTC)


 * Cause if our universe is a computer simulation and I'm being screwed with I don't want to know. Sagittarian Milky Way (talk) 01:38, 20 April 2017 (UTC)


 * The apparent magnitude link works for me, but when I cut and paste yours, it doesn't. I would guess you have an unprintable character in there. StuRat (talk) 00:28, 20 April 2017 (UTC)


 * The original "apparent magnitude​" link has a U+200B zero-width space at the end. PrimeHunter (talk) 01:26, 20 April 2017 (UTC)


 * Yep, that'll do it. How did you find it ? StuRat (talk) 02:20, 20 April 2017 (UTC)


 * I copy-pasted the string including brackets to the "Characters" field at http://r12a.github.io/apps/conversion/ and clicked "View in Uniview". Also, when I hover over the red link in Firefox the url at the bottom of my window includes . When I click the link I see the less informative (to me)   in the address bar. But at least it confirms there is something unwanted. PrimeHunter (talk) 15:34, 20 April 2017 (UTC)


 * OK, thanks. StuRat (talk) 05:14, 21 April 2017 (UTC)