Wikipedia:Reference desk/Archives/Science/2016 September 29

= September 29 =

Identifying a plant
Hi refdesk,

I took a picture of this plant in San Francisco a couple months ago and for some reason I'm having a tough time identifying it. File:Unidentified plant on the beach in San Francisco 1.jpg. Anyone have a good lead? :) &mdash;  Rhododendrites talk  \\ 02:58, 29 September 2016 (UTC)


 * What's the scale? Are those flowers about the size of a US penny? Is the photo of an area of few square feet, taken from a few feet up? Is the plant succulent? How tall was the mat? I have hazy guesses and memories but this info will help. In the future, three photos are a good basis for plant ID, a closeup of one flower, a closeup of one leaf/stem, and a distance shot like this. In the mean time, good resources for this would be CalFlora and the California Native Plant Link Exchange database . SemanticMantis (talk) 14:48, 29 September 2016 (UTC)


 * Here's a link to Google Streetview for where [I'm pretty sure] I took it (within a hundred feet). Streetview is a different time of year, but I think you can see this plant in context. It was maybe 2 feet tall. Flower [clusters] maybe dime sized? Hard to remember because it was sort of just snapped in passing. Image was taken from probably a foot and a half up? There's another picture from a different angle here: File:Unidentified plant on the beach in San Francisco 2.jpg. Might help with scale a bit more? Sorry, I know that's not a lot more to go on. I took a look at Calflora -- it seems to want more information than I'm able to provide (thousands of hits). Thanks. &mdash;  Rhododendrites talk  \\ 02:08, 30 September 2016 (UTC)
 * Update: has added the images to Category:Unidentified Asteraceae, which gets us part of the way there, I suppose :) &mdash;  Rhododendrites  talk  \\ 03:11, 30 September 2016 (UTC)
 * I'm not entirely convinced it's an Asteraceae, but I guess it could be. Are the leaves actually succulent, or do they just appear to be? Knowing it was on the Presidio helps: here is fairly long list of the plants found there. At a skim: I can find similar flowers, and similar leaves, but haven't found the total package. As for further references/resources, Reddit's /r/whatsthisplant  will probably give you a species-level ID faster than we can. They have far more readers/contributors, and focus only plant ID. SemanticMantis (talk) 15:42, 30 September 2016 (UTC)
 * Eureka! Baccharis pilularis! I just started scrolling through however many hundreds of hits there were in the Cnplx link above and came across one that looked kind of close. So I googled it and found this picture, which was promising, so looked through the rest of the species in that genus, Baccharis. Narrowed it down to: Baccharis patagonica, Baccharis magellanica, Baccharis macraei, and Baccharis pilularis (Coyote brush). The last one is the one listed at Cnplx and in the picture, and is also the only Baccharis that comse up on that Presidio list, so I think we have a winner. :) &mdash;  Rhododendrites talk  \\ 16:49, 30 September 2016 (UTC)
 * Cool, great team effort! They annoying thing is I *thought* I knew coyote brush, but I guess not that well. I think I might have gotten it eventually but I was looking in the wrong parts of the Presidio list because 1)couldn't tell it was woody shrub, as I misinterpreted the waxy/sclerotic leaves as succulent. Also FYI it will have a much more upright habit in the Chaparral (which I'm more familiar with), and the squat coastal format of the coast threw me off Cheers, SemanticMantis (talk) 17:48, 30 September 2016 (UTC)

Why do people fear the long process of dying?
According to here, Old age, they did a study saying that most old people didn't fear death but welcomed it. However, nearly all the people in the one study feared the long process of dying. Why would people in old age fear dying slowly but prefer dying in their sleep or on their feet? — Preceding unsigned comment added by Uncle dan is home (talk • contribs) 06:54, 29 September 2016 (UTC)


 * Have you ever visited a hospice? Someguy1221 (talk) 07:22, 29 September 2016 (UTC)
 * That is not a question for the science reference desk. We try to give factual facts, or scientifically established hypotheses about these. We have an article about death anxiety with secondary sources, but by its very nature, the subject invites a lot of speculation. Tigraan Click here to contact me 07:44, 29 September 2016 (UTC)
 * ... more specifically, see the article Death anxiety (psychology).   Ghmyrtle (talk) 07:53, 29 September 2016 (UTC)


 * Disagree with Tigraan, think this is a worthy question for ref desk. By the time most people get to experience the end stages of life they have personal experience of what awaits them, from having close friends and family slowly die. They know they may well become unable to look after themselves and become incontinent. They may have cancer and know that involves experiencing pain 24/7. Ironically, Nixon's war-on-drugs also mean that many can not receive appropriate opiate pain management in-case the get addicted – would you believe, as cancer produces pain that only opioid can relieve. If cancer gets to the brain they can experience horrifying hallucinations, which the 'old people' you refer to,  may have witnessed friends and relatives experiencing. . If they are fortunate, they may be able to afford good medical care were they are kept alive with the aid of tubes and things. Yet may have well seen friends and relative in the same situation and have ringing in their ears the words of desperation as they say " this is no life ". They beg for release. Yet the medics keep resuscitating them, not from the desire to improve the patients quality of life but because health-care is a business and the longer you keep the patient alive the more money the care-home/hospice receives.--Aspro (talk) 17:48, 29 September 2016 (UTC)


 * Stroke doesn't look like a picnic either. There's more than one way to skin a cat, but none it's gonna like. Wnt (talk) 02:12, 30 September 2016 (UTC)


 * In the last few years I've experienced both a close friend and a parent undergoing a lingering departure from cancer and in both cases, our creaky National Health Service, working in combination with charity organisations were quite wonderful. Despite all the drugs and care, it was a thoroughly unpleasant experience for both of them and I sincerely hope that there's a legal way of terminating the process quickly when I get to that stage. Alansplodge (talk) 10:24, 30 September 2016 (UTC)
 * A bit off topic. A new editor Francesmawson (talk) (aka:109.231.192.149) has been trying to add  new sections to Macmillan Cancer Support.Read: Help_desk. May well have a COI but we can allow one step at a time for a newbie. By all means, help this new editor if you can.--Aspro (talk) 16:01, 30 September 2016 (UTC)


 * There's always Dignitas (Swiss non-profit organisation). Palliative care for cancer looks okay but I'd hate the thought of being dead but walking around with alzheimers ruining my relatives lives. Dmcq (talk) 12:43, 30 September 2016 (UTC)

Practical Heatsink calculation
sir, please guide where can i find mathematical calcuolations done in this site https://www.heatsinkcalculator.com/demo.html Please give me books name or research paper thanks in advance SD — Preceding unsigned comment added by Sameerdubey.sbp (talk • contribs) 09:23, 29 September 2016 (UTC)
 * Joule heating describes how electric currents inside semiconductor devices (diodes, transistors and integrated circuits) release heat energy that will raise the device's temperature; if the heat is not removed quickly enough the device could be damaged by overheating. Heat passes out of the device by a combination of Thermal conduction (through the chip package and parts in mechanical contact with the package) and thermal convection (from mechanical part(s) such as a heatsink exposed to the air). The latter article includes performance equations for heatsinks; engineers who are familiar with Ohm's law that explains current as a function of voltage and resistance will recognize that heat flow is a similar function of temperature difference and Thermal resistance. This link describes the improvement over natural convection of forced air cooling i.e. using a fan. AllBestFaith (talk) 13:06, 29 September 2016 (UTC)


 * This is a difficult problem to model in detail. It requires finite element analysis to model the heat flow through a non-linear heatsink. At one time it used to be modelled with an analogue model, using Teledeltos paper.
 * The example here probably uses an approximation for the heatsink. Chop the heatsink into two sets of parts, a "base" and multiple "fins". By some approximation here, treating each fin as a long parallel strip with heat flowing in only one direction along it, then modelling the base similarly (ignoring the gaps between fins, as if the fins were wide enough to touch) then these can be modelled analytically. Andy Dingley (talk) 13:44, 29 September 2016 (UTC)
 * I agree it's difficult to model, and that Teledeltos paper is neat! But sure there are other schemes for modeling PDE for heat flow that are not finite element analysis? For example I can't see any reason why finite volume method or finite difference method couldn't be applied. (It may well be that FEM is widely used and considered the most appropriate in this context, but my point is more about the distinction between the PDE and the computational method used to solve it). SemanticMantis (talk) 14:53, 29 September 2016 (UTC)
 * The usual method (throughout the industry) is "that looks about right" in the heatsink factory, then to physically measure performance and tabulate the results as equilibrium temperature / heat rejection rate for the combinations of ambient temp. / heat input / fan airflow rate. Then the grunts do a simple lookup.
 * It is rare to _design_ a heatsink. Mostly this is done when it isn't "a heatsink" (as an added component), it's using the existing superstructure of the satellite / missile as a design, then trying to predict its performance. Those people tend to like FE, simply because it's a tool they're already familiar with for the structural aspects and, these days, computation is cheap. Andy Dingley (talk) 15:24, 29 September 2016 (UTC)
 * Manual methods were used to design boilers long before computers were available. Any decent thermo book will take you through boiler design (which is actually trickier than a heatsink). Rogers and Mayhew for example. Greglocock (talk) 02:52, 30 September 2016 (UTC)

Bio-degradable polymer banknotes
With reference to this article, is it true that the Bank of England has deliberately made the new polymer banknotes quick to bio-degrade so that people who keep money in a safe or under their mattress will find their money turns to dust so they can't spend it? Secondly, how long does it take for the breakdown to happen? Months? Years? — Preceding unsigned comment added by Leteoot (talk • contribs) 10:27, 29 September 2016 (UTC)
 * No - "the new notes are not biodegradable," but apparently can be recycled into flowerpots.   The article to which you linked seems to confuse "green" production methods with biodegradability - they are not the same thing.   Ghmyrtle (talk) 10:34, 29 September 2016 (UTC)


 * The Bank of England will freely replace damaged banknotes, so it wouldn't be much of a scheme. They also claim that the notes are more durable than paper (since paper is after all relatively easy to tear) - you can read the detailed life cycle assessment, which estimates that a heavily paper note survives 2 years of use on average, while a polymer one survives 5, and a rarely used paper note survives 40 years while a polymer one survives over 100. Unless they're lying, there's no way this could be used to sneakily reduce money supply. Smurrayinchester 10:56, 29 September 2016 (UTC)
 * As far as I can tell, there's nothing particularly special about the Bank of England's polymer notes. They're using Guardian (polymer) same as pretty much everyone else    including Australia who've been using them since 1988. They have I suspect been changes over time, still you can try asking any Australian, Kiwi, Malaysian etc whether their notes are biodegrading in mattresses. Nil Einne (talk) 12:52, 29 September 2016 (UTC)
 * I think that the publication date and the footnote identifying the source "close to the Bank of England" are clues to how much you should worry about your banknotes biodegrading in your wallet. Sjö (talk) 13:02, 29 September 2016 (UTC)


 * No-one seems to have spotted the date on the article quoted by the OP - 1st April 1914. It is a fairly clever April Fool! Wymspen (talk) 07:50, 30 September 2016 (UTC)


 * See Banknotes of the pound sterling.  On 1 April 1914 the Bank of England was just thinking about issuing paper banknotes as a temporary wartime measure.   It wasn't until 1 April 2014 that it started the move to plastic ones. 80.44.164.18 (talk) 14:33, 1 October 2016 (UTC)
 * Hmmm... The Currency and Bank Notes Act 1914 was rushed through Parliament on 6 August 1914, two days after the UK had declared war on Germany, according to Timeline of the United Kingdom home front during World War I. There was no inkling of war on 1 April. Alansplodge (talk) 16:40, 1 October 2016 (UTC)
 * On the subject of changing the currency, it amazes me that people still hand in ten shilling notes at the Bank of England and get just fifty pence in return.  Collectors pay a fortune for them.   The initial reaction to the polymer fivers is unfavourable.   Once folded they don't lie flat and can't be stacked when counting.   We're getting a new pound coin in March - why can't we have a five pound coin? 80.44.164.18 (talk) 13:43, 3 October 2016 (UTC)
 * The outbreak of the First World War had been expected for most of the twentieth century.  Everyone knew that Europe was a tinderbox waiting to explode - all it needed was for someone to light the fuse.   As usual the culprit was the Balkans, the fault line where Catholicism, Islam and Orthodoxy meet. 80.44.164.18 (talk) 13:55, 3 October 2016 (UTC)

Angular velocity on a spiral
What is the expression of the angular velocity for a motion a spiral? Does the ordinary relation v = ω r hold? Is angular velocity constant in the previous equality? Thanks.--5.2.200.163 (talk) 13:55, 29 September 2016 (UTC)


 * Do you mean assuming constant linear velocity of a point moving along the spiral? If so, do you mean a Archimedean spiral or a logarithmic spiral or some other spiral? SemanticMantis (talk) 15:09, 29 September 2016 (UTC)
 * Yes, that is what I initially considered: the case of constant linear velocity of a point moving along the spiral.--5.2.200.163 (talk) 10:50, 30 September 2016 (UTC)


 * Linear velocity in term of angular? Or angular velocity in terms of linear (just the reciprocal of that)?
 * Your spiral is defined somehow, probably as a function for radius in terms of angle. So convert that (with Pythagoras and differentiation) to an expression for the change in position, i.e. linear speed, in terms of angle. It may not be constant, for some spirals. Andy Dingley (talk) 15:19, 29 September 2016 (UTC)
 * Of course, if the linear velocity along the planar spiral is constant, one can expect that given variable radius, angular velocity be not constant. Are there some spirals where angular velocity can be constant along with linear velocity?--5.2.200.163 (talk) 11:00, 30 September 2016 (UTC)
 * In many scenarios where you find spiral motion - like an electron gyrating as it travels along a simple magnetic field - you can completely decompose and separate the transverse, linear velocity from the gyro or circular velocity. Then, you're back to simple algebraic kinematics.  This works because of the physics of electromagnetics that cause the spiraling motion: the Lorentz force has a cross-product, so when you work the math, the circular- and linear- motion don't couple at all.  The forward velocity is inertial, and the gyration is a simple circular motion.
 * In more complicated situations - like a non-ideal magnetic field - things get tricky.
 * If you had a different scenario, like a marble rolling down a spiral slide under the influence of gravity, or an airplane conducting a standard aileron roll, we'd have to write out equations of motion and constraint-force equations, and solve. In the case of the marble rolling down a spiral slide, you will find that angular velocity is non-constant, and that's an interesting conundrum: where does the angular momentum come from?  This is a great chance to consider graduating from Newtonian mechanics and to start using the Hamiltonian or Lagrangian mechanics.
 * Here's an example of a worked problem from MIT's 13.385: Bead, on an horizontal rotating hoop. As you can see, it only took 11 pages of calculation to write out this case, because the bead was constrained in two dimensions to the position of the rotating wire.  If the test particle were to spiral freely, under its own dynamics and without position constraint... well, that would be a totally different kind of problem!
 * Nimur (talk) 15:24, 29 September 2016 (UTC)
 * Interesting aspect about the suggested transition from Newtonian mechanics.--5.2.200.163 (talk) 13:40, 30 September 2016 (UTC)
 * What is understood by non-ideal magnetic field?--5.2.200.163 (talk) 14:45, 30 September 2016 (UTC)
 * In the first textbook introductions to magnetic fields, you will study a uniform magnetic field: all the field lines are parallel, and the field strength is the same everywhere.
 * Simple electron gyroresonance occurs if the magnetic field is spatially uniform: the field lines have the same strength and same direction at all points. This ideal field is a good approximation if you're looking at very small sections of space, far from the poles of the magnet; or if you're looking at the region directly between the poles of a horseshoe magnet; but in almost any other case, magnetic field lines rapidly vary in direction and magnitude.
 * See the diagrams in magnetic field? Anywhere the lines look mostly parallel to each other, that's a region where the simple, uniform field approximation might be valid.  As you can see, most places around a magnet don't satisfy this ideal assumption: those are all the places where the magnetic field is non-ideal.
 * We can use the simplified idealization in lots of applications, as long as we understand its limits.
 * For example, if you study geomagnetism, you can often assume that the field is uniform and parallel, because you're a tiny human and you are usually far from Earth's magnetic poles. That's why you expect a magnetic compass to work!
 * But if you study more geomagnetism - like its association with the van Allen radiation belts or the deep geological structures inside Earth described by Dynamo theory, you can no longer consider our planet's magnetic field "ideal." Here's a website from Goddard Space Flight Center: Magnetic Fields and Mars.
 * Nimur (talk) 15:36, 30 September 2016 (UTC)

Universe and subatomic particles
As a kid, I used to imagine that all subatomic particles in our universe are themselves small universes, and that our universe itself is a subatomic particle in a large universe. I once found out that my brother -- with whom I had never talked about this -- had imagined the same thing. Has there ever been any real scientific hypothesis bearing any (remote) similarity to that, even if it has been rejected by mainstream science? --Pointe noire (talk) 16:08, 29 September 2016 (UTC)
 * Is there any scientific theory that hypothesizes about complicated sub-structure inside of the smallest particle we currently know about?
 * I think a good way to start answering this is to take apart the etymology of the word atom. When first proposed, atoms were the thing that scientists believed was most fundamental: it was the smallest entity and it was not sub-dividable.  This is in itself a hypothesis - using the name "atom," early scientists hypothesized that the atom had no substructure.  It was the literal, actual, smallest thing possible.
 * That hypothesis began to be discredited during the 19th and 20th century as the first sub-atomic particles were discovered. We now know, of course, that atoms are made of an atomic nucleus and an electron cloud.  Further, we know that atomic nuclei are composed of nuclear particles - protons and neutrons.  And even more recently, we discovered that nucleons have structure: they are composed of quarks.
 * Here is where we reach the limit of our knowledge. We know that nucleons have substructure, and we also know that atomic nuclei can be split: the name "atom smasher" was used to describe experimental devices that could split atoms apart.  But individual nucleons cannot be split easily!  Although we know that a proton has quarks "inside" it, we can't "get the individual quarks out."
 * In our quest for ever-smaller fundamental particles, we have constructed a standard model of physics. These are the smallest things we know about.  Using today's methods, we can not sub-divide those fundamental particles any further.  An even stronger statement: we can not even discern whether those particles have any structure at all.  Yet, physicists continue to look: we know how to look for sub-sub-atomic structure, and we have looked, and so far, we have not seen it.
 * If entire "micro-universes" existed inside subatomic particles, that would be "structure" - immensely complicated structure! - and so far, our best experiments do not even find simple structure there. To continue probing, we will need dedicated physics laboratories with unique capabilities - specifically, high-energy particle accelerators.  This avenue of physics research is actually giving way: historically, we have already slammed incredibly high energy particles together, and we saw nothing interesting, so we stopped looking further.  That doesn't mean we could never find something if we kept looking: it only means that our best scientific institutions have switched their resources over to pursuing other interests.
 * At most major labs, recent experiments in high-energy physics have not been looking for substructure, but have instead focused on other areas of interest. For example, CERN's top research priorities are listed on their website.  Here in the United States, our top particle accelerators are more interested in high-time-resolution, rather than high space-resolution: just this week, SLAC's public lecture was on the emerging applications of their X-ray laser for studying atomic-scale dynamics in material science applications.
 * Nimur (talk) 16:43, 29 September 2016 (UTC)


 * The fact that quantum particles have quantum statistics means that they are all identical, and, in particular, they don't evolve over time. So they can't be universes, at least if change over time is part of the definition of a universe. They could still be strings, or bound states of preons, or have some other arbitrarily complex substructure in principle, but that substructure has to be in a ground-state configuration that's exactly the same for all particles of a given type. -- BenRG (talk) 19:08, 29 September 2016 (UTC)


 * how certain can we be of that? I'm thinking specifically of something like a black hole. Wherein every black hole with identical mass/charge/spin is "identical", regardless of its internal structure (recognizing it may not even be meaningful to talk of internal structure of a black hole). Is it at all possible for there to be a variable internal structure of a quark that is simply unobservable? Or is that precluded by known physical laws? Someguy1221 (talk) 20:18, 29 September 2016 (UTC)
 * How do we know that particles obey any type of statistic? How do we know if any mathematical theory describing our universe is valid?  We know this because we conduct experimental physics, and those experiments provide data that informs our root knowledge about theoretical quantum mechanics.  This position is empiricism.  I can acknowledge that some people do not consider it to be the ultimate theory of human knowledge; perhaps BenRG and others believe that mathematical theory is more fundamental than experiment.   Nonetheless, I assert that experimental physicists believe that knowledge based on experimental results trumps knowledge based on theory, in all cases.  We're very lucky to live in a time in which our experimental results largely agree with our theories, so in this century, we have no severe existential crisis of scientific epistemology.
 * But, we've reached the limits of resolution that can be provided by experimental physics, within the present constraints of technology and budget. We do not see any sub-structure; our theory does not predict any substructure; as BenRG points out, one can make the case that our present theory precludes substructure.  But, if that line of reasoning is true, then our current theory would have to change if we ever - somehow - did observe substructure.
 * Nimur (talk) 21:30, 29 September 2016 (UTC)
 * I guess I'm trying to think entirely inside the confines of the standard model, and not ask about the consequences of proving it wrong. Ok, let me explain a bit more. Before Hawking radiation was proposed, and we had the no hair theorem, it appeared that general relativity rendered the structure of a black hole irrelevant - it would impact no experimental measurements made from outside the event horizon. What I'm asking is whether, given currently understood laws of quantum physics, if such a thing is possible inside a quark. Is it possible to have a condensed pocket of particles whose structure is invisible to the outside. Someguy1221 (talk) 22:15, 29 September 2016 (UTC)


 * Quantum mechanics doesn't preclude substructure. For example, strings have in principle infinitely many degrees of freedom, and string theory seems to require the Standard Model fundamental particles to be extremely complicated states of strings. However, every electron has to be the same (complicated) string state. If there were even two "isomers" of the electron string configuration with the same observable properties, then the Pauli exclusion principle would permit four electrons in each atomic orbital instead of two, and chemistry would be completely different. The second electron type could be rare for some reason, like antimatter is, but it would still be pair-produced at the same rate as ordinary electrons in cosmic rays and particle accelerators.
 * It's theoretically possible for particles with identical measurable properties (mass, charge, spin) but different internal "identities" to exist, and black holes could be a real-world example. But you can always (in principle) detect this by the violation of bosonic/fermionic statistics, and in the case of Standard Model fundamental particles we've actually done those experiments.
 * Quantum mechanics could be wrong, but it has a unique mathematical structure and a uniquely fundamental role in physics (Scott Aaronson describes it as the "operating system" on which the rest of physics runs), so any alteration of it would have enormous repercussions. -- BenRG (talk) 23:07, 29 September 2016 (UTC)
 * I am glad to hear that you believe quantum mechanics does not preclude substructure to our known standard-model particles! I was never aware of any such constraint either - only that we've never yet found substructure - but I interpreted your earlier commentary to imply that you might know of some way to demonstrate that substructure is mathematically impossible!  I was finding that to be ... an implausible assertion, but on occasion, things turn out to be true even when I find them implausible!  In any case - it seems that I misinterpreted your comment, and you were not asserting any such statement. Nimur (talk) 23:45, 29 September 2016 (UTC)
 * Maybe the combination of black hole baby universes and elementary particles being a kind of black hole would give you something of this sort. Vaguely similar ideas include bootstrap models where there is no distinction between elementary and composite particles, 't Hooft's unparticles which have a self-similar structure, and conformal cyclic cosmology. All of these are considered highly unlikely, though, even by their inventors (except bootstrap theory which was taken seriously for a while but isn't any more, and elementary particles being black holes which seems likely to be true).
 * You didn't ask, but this has a long history as a romantic idea. "Recursive Reality" at TV Tropes says "A rather famous Russian poem from 1922 Atom, later republished as The world of an electron, by Valery Bryusov starts with 'What if those electrons // are worlds with five continents, // arts, knowledge, wars, thrones // and memory of 40 centuries?' The idea seems to have been quite widespread back then." (Quantum mechanics requires that electrons have no knowledge/memory, though: see my reply to Nimur.) -- BenRG (talk) 19:08, 29 September 2016 (UTC)
 * As BenRG says, though never a scientific theory, the idea has been used repeatedly in literature. Another famous example that springs to mind are the stories 'The Girl in the Golden Atom' (1919) and 'The People of the Golden Atom' (1920) (combined into a novel in 1922 under the first's title) by Ray Cummings. {The poster formerly known as 87.81.230.195} 90.202.211.191 (talk) 17:43, 30 September 2016 (UTC)