Where do virtual particles come from?

Question: Do I understand correctly that for the existence of virtual particles, a single physical object is needed - a quantum field? And virtual particles are excitations of this field that fills all space. In this case, what are virtual strings, because in string theory there is no "string field" from which they could be born?
Answer: The virtual particles are not really existing objects. They are the entities, which emerge in the Feynman diagrams, when evaluating the amplitudes of a certain process in a perturbation theory.
There is a large program, led by Arkani-Hamed, Trnka, Cachazo, and other authors to define the scattering amplitudes without the need to refer to the spacetime and Feynman diagrams. The whole scattering is defined in terms of the canonical form, living on the positive geometry, such that all the particle poles correspond to the singularities on the boundary of this geometry. In this approach the notions of locality and unitarity are manifest.
The drawback is that, by far this theory is applicable in rather limit scope : $N = 4$ Super Yang-Mills theory, $\phi^3$ bi-adjoint scalar field theory, and some non-linear sigma-models and string theories.
Comment: @ChiralAnomaly thanks, yes it seem that it can be shown that quantum fields are Lorentz invariant. This is probably lecture one in any quantum field course.
Comment: @ArmanArmenpress the existence of a field is a subtle question, as far as our beliefs on the nature are and at the modern level of understanding of physics, they do exist, and their properties describe the Universe we know
Comment: @boyfarrell I am not an expert in this field, in the recent works Arkan-Hamed with collaborators have reinterpreted it in terms of some quivers, with the relation of cluster algebras. And the positive geometries emerge as a certain sequence of the mutations of quivers. A beatiful science, although hard to comprehend
Comment: it is a philosophical question - from the point of view of QFT, I would say that fields are more primary and the particles follow from them. But from the S-matrix point of view, the particle is well-defined notion, whereas the field is more obscure
Comment: @spiridon_the_sun_rotator getting slightly off topic. But how is an all pervasive quantum field different from the classical aether theories? Somehow they must be consistent with relativity and not provide an absolute frame. Probably phrased that question poorly.
Comment: @boyfarrell what does one mean by the Lorentz invariance of the fields? Lagrangian is constructed in Lorentz invariant way, but the particle content transforms under a certain represantations of the Lorentz group
Comment: Do quantum fields exist?
Comment: Arkani-Hamed is such a great presenter too. Are you referring the amplituhedron? https://youtu.be/WGNZEZcO3bo
Comment: @boyfarrell yes, and also there is a more modern story of **Associahedron** i
Comment: @spiridon_the_sun_rotator I probably cannot follow the full details, but what's the latest with amplituhedron?
Comment: And what is more primary? Fields, the excitations of which are particles, or particles, from which fields are formed?
Comment: I'm very much out of my depth with terminology. What I'm trying to express is somehow "relativity is baked in".
Comment: What about computing things that are not scattering amplitudes, like correlation functions?
Comment: @correlation functions in this approach are not defined, only boundary observables. But the correlation function is something that cannot be measured directly by the experiment.
Comment: @spiridon_the_sun_rotator I disagree. Correlation functions can be measure by external sourcers, e.g. very heavy particles that couple with the field in question.
Answer: String fields indeed exist. It is usually stated in introductory courses in string theory that string fields do not really exist because off-shell string amplitudes are incompatible with world-sheet symmetries.
Heuristic argument: I will give an example to illustrate how worldsheet symmetries force string states (via the operator-state map) to be on-shell.
Consider the vertex-operator for a closed string tachyon  $$ \int d^{2}{\sigma} \sqrt{g} :e^{ikX}:$$
In locally flat coordinates we have the replacement $$\int d^{2}{\sigma} \sqrt{g} e^{ikX} \rightarrow \int d^{2}{z}  e^{ikX}$$ where we can turn $d^{2}{z}:e^{ikX}:$ into a tensor of type $(0,0)$ by noticing that $d^{2}{z}$ is of type $(1,1)$ and choosing $k^{2}=-m^{2}=\frac{4}{l_{S}}$. Notice that this latter choice is the only consistent with worldsheet Weyl invariance and is precisely the light-cone mass-shell condition.
See chapter 3, section 3.6, page 103 of Polchinski's textbook (Vol. 1) for an argument for general vertex operators. The idea is the same, namely that worldsheet symmetries fix the conformal dimension of general vertex operators forcing them to be in the mass-shell.
Conceptual argument: See the excellent blog post Observables in quantum gravity or my answer to String amplitudes for finite times and string wave-functions.
What virtual strings are? Despite the arguments from above. It is actually possible to define string fields. Although not the clearest conceptual way, I recommend the discussion on second quantization in the book of Polchinski (chapter 9.6 in Vol. 1).
The answer to your actual question is that virtual strings are the off-shell strings that appear in finite time process in string field scattering amplitude computations.
For an spectacularly marvelous introduction to closed string field theory see  String Field Theory – A Modern Introduction.
For an overview see the talk developments in perturbative string theory.
UPDATE:
@Nogueira Has correctly pointed that my rough argument just works for strings that scatter from infinity. In presence of $D$-branes my argument is no longer valid, off-shell string states can be exchanged between branes and the masses of stretched strings between $D$-branes are proportional to the separation between those branes (and in particular not fixed by perturbative dynamics).
Comment: What about stable - and even untable - D-branes? The boundary state is on-shell? As far as I understand, only strings coming from the infinity should be on-shell. Strings that comes from D-branes must be in boundary states, and these are the only off-shell objects that I know off.
Comment: Thanks for your pertinent and interesting clarification @Nogueira. You're completely right, the rough argument I shown only works for perturbative string theory; the strings that come from infinity are the only ones allowed to be on-shell. When we choose a background with $D$-branes things become different. Off-shell string states can be exchanged bewteen any two branes.
Comment: @Nogueira I will edit my answer to take into account your valuable observation.
Answer: One way of looking at it is that in any scattering event there is an amplitude for the strings to have a topology where for equal-time slices they seem to split and join. The intermediate strings are the virtual ones.
In this picture we may choose the time coordinate to point straight up, and so this would look like two incoming strings joining together to form a virtual string, who splits into two virtual ones, who join together, and split to two outgoing strings.

If you are already comfortable with the field-theory formalism, then you may view string theory a a field theory. This formalism is called String Field Theory.
Comment: @Rd Basha This answer is completely wrong and disinformative. It's totally false that the the intersection of equal time slices and the worldsheet are virtual strings. See the topic "Off-shell amplitudes?" in chapter 3.6, page 103 of Polchinski's textbook (Vol. 1) in string theory to understand why the answer of Rd Basha is wrong. And chapter 3.5 for the correct interpretation of the string scattering diagrams.
Comment: @ArmanArmenpress I'm writing an answer ;)
Comment: Do I understand correctly that for the existence of virtual particles, a single physical object is needed - a quantum field?
Comment: I'm not sure what you mean by "existence". Virtual particles are part of a model that we give to explain the world. There could very well be a model without them.
Comment: Do quantum fields exist?
Comment: Again, I'm not sure what you mean. We might as well ask if the classical electric field exists. It's a good model for describing the world. There might be a good model without the electric field.
Comment: @ArmanArmenpress Be careful with this answer. It's totally wrong.
Comment: @RamiroHum-Sah What's the correct answer? what are virtual strings, because in string theory there is no "string field" from which they could be born?

Where do virtual particles come from?


Varnish or Squid as cache server with IIS

Question: Can we setup a Varnish or Squid server as web cache server for IIS server?
I did not find much information anywhere. Please let me know where can I get information
Answer: Of course you can! You probably found the varnish and squid web sites and googled for some tutorials as a starting point. The question is; what do you want to cache? How is your website (not) cachable? Are you comfortable with linux (varnish only works on unix/linux/posix systems)? Why not stick with some Microsoft cache solution if you run IIS?


Physical/pictoral interpretation of higher-order moments

Question: I'm preparing a presentation about parallel statistics. I plan to illustrate the formulas for distributed computation of the mean and variance with examples involving center of gravity and moment of inertia. I'm wondering if there is a physical interpretation of the third or higher central moments that I can use to help illustrate the general formula.
Comment: If you must preserve the interpretation of $x$ as a length, then anything above third moments will require too many dimensions to illustrate!  In spirit, your question and comment are like the Ancient Greek drive to cast all arithmetic in terms of geometry.  That indeed provides insight, but it also limits the scope of what can be done to a small number of dimensions (0 through 3).  Creative use of graphics can help us visualize higher dimensions (and therefore, perhaps with higher moments).  Thus I think you shouldn't dismiss graph-based illustrations out of hand.
Comment: Closely related: http://stats.stackexchange.com/questions/132914, http://stats.stackexchange.com/questions/17595.
Comment: Wow, this is a truly old question.

I asked this question over a decade ago when I was a software-engineering intern at a hedge fund. I know there was demand from the traders to compute the kurtosis of large datasets; for what purpose, I was not privy. The audience of the talk would have known better than I did what the applications were.
Comment: For what purposes would the distributed computation of higher moments be useful? I'd say better to show those applications than to show physical analogies. (I would see applications easily enough for paralllel computation of quantiles, but there may not be so many applications with theee higher moments.)
Comment: That relates the properties of moments to graphs of PDFs, but is not useful for visualizing computations done on moments.

I'd like to be able to, for example, write Welford's algorithm (http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance#On-line_algorithm) on the board, and then draw a picture and say "This is $x_n-\overline{x_n}$" and have the equality become somewhat obvious.

Also at that link is a streaming algorithm for the mean. It takes a few seconds to see why the formula works, but becomes immediately obvious if I draw it as a center of gravity problem.
Comment: I'm not sure what you mean by physical interpretation. (Perhaps it's that I don't think about mean or variance in terms of physical quantities).

If you're just trying to to reprise the Welford algorithm, is it mathematically anything more than the insight that to compute statistics of the form $T = \frac{1}{N} \sum_{i=1}^n f(x_i)$, you can always compute them recursively via:

$\;T_1 = f(x_1)$, and

$T_i = ((N-1)\cdot T_{i-1} + x_i) / N \;\;$

?  Raw moments can always be computed this way, and formulas for centered moments can (presumably) be derived from these?
Comment: I show pictures on https://stats.stackexchange.com/a/324197/99274 higher moments also explained.
Comment: We used 3rd and 4th moments for input features in this image classification paper using Hermite and Laguerre neural networks ( http://bol.egr.uh.edu/sites/bol/files/files/publications/IJKESDP010304-PETERSON.pdf ).
Answer: If by graphical representation you meant histograms, I gather this is the best approach to provide a visual display of the moments. Please be aware we cannot specify any value for kurtosis. But there is a formula to provide kurtosis under random simulations.
Being k = kurtosis, sk = skewness, the formula is: k > sk^2 +1.
Below, a histogram with the specifications.
Comment: This is being automatically flagged as low quality, probably because it is so short.
At present it is more of a comment than an answer by our standards. Can you expand
on it? We can also turn it into a comment.


What does a database component in a UML diagram represent?

Question: Sometimes the UML component diagram contains a database component. Does this database component represent a class that programmers create (which includes host, username, password, port... DB connection with PDO, SQLI... etc.) or does it represent the real, entire database?
Answer: It depends on the level of abstraction on the diagram.
A component on a component diagram usually represents more than just a single class, but that doesn't mean that it can't represent a class. A component identified as a "database component" could be the class or classes used to represent a connection to a database. It could also be the database itself and the interfaces provided by a database client library or even the database server itself.
Ideally, it would be able to tell based on the diagram itself. The component could be annotated with information about what the component represents or a note element can be used to provide more information. If it's not clear based on context clues, you'd have to ask the author and hopefully have them update the diagram or provide explanatory text around the diagram to make it clear to future readers.
Answer: UML is an object oriented modeling language so components do represent classes but they will be course level descriptions lacking detail. The point is to outline the big chunks and communication routes between them, to show what entity talks to what other entities and to get a high level overview of the entire system.
So it does represent the entire database but it is more a service identifier then a description of the thing.
Comment: Classes are not represented on all UML diagrams. Deployment diagrams, Component diagrams, and Object diagrams don't necessarily represent classes.


How to fade in and out light bulb(220V) (Arduino)

Question: I have relay conected with arduino and high voltage bulb, now how can I control voltage to fade in and out bulb? I know that a relay is an on off device so maybe a triac or IGBT would be needed?Would an optpcoupler be good for isolation? Should I use a PWM output on the arduino?
Answer: With a relay? You can't.
The relay contacts are either open (lamp fully off) or closed (lamp fully on) and can't switch a relay fast enough to give a dimming effect.

simulate this circuit – Schematic created using CircuitLab
What you're looking for is a triac controlled dimmer.

simulate this circuit
In this case an opto-coupled triac is used. Your micro would switch the LED D1 on at the appropriate point in the mains half-cycle turning on the triac. The triac stays on until the next zero-cross of the mains and then turns off. At 100 (50 Hz) or 120 (60 Hz) half-waves per second the flicker is not noticeable.
Your code would have to monitor the mains zero-cross somehow, ramp the delay in triggering the triac and pulse the optoisolator at the right time. Plenty of examples on a web search.
Answer: +1 for the opto-coupled triac.
Opto-couplers are nice because you can "drive" the circuit as if you were controlling an LED. Throw a resistor in series and you can separate your arduino from the high voltage.


How do we walk?

Question: I know I am asking a very basic question but still I wanted to make my understanding clear. Please correct me if I am wrong about what I know so far. Whenever someone starts to walk , he/she pushes the ground backward, since there is no sliding between the shoes and the ground, so static friction is acting which enable us to walk as it acts in the direction in which we want to walk . But my question was , that eventually , when we lift our leg , does our leg starts to slide over the surface , has it overcome the static friction and kinetic friction starts to act or is it just that , we just lift our leg and broke the contact between the leg and the surface. Moreover , I wanted to know , if friction is the cause of our motion , then there must be certain limit above which we cannot accelerate and that is the limit when we start slipping . Is all this of correct?
Comment: Welcome to PhysicsSE. Feel free to take a [tour] of this site to get a good understanding of how this site works. Hope you get an answer soon.
Comment: see http://aplusphysics.com/community/index.php?/blogs/entry/1275-the-physics-of-walking/.  Although not directly related to your question, the energetics are discussed here: https://www.europhysicsnews.org/articles/epn/pdf/2008/05/epn080505.pdf
Comment: Your picture is not complete. We're also falling forward as we walk, which also places a limit on the maximum speed, check: https://en.wikipedia.org/wiki/Walking#Biomechanics
Answer: Practically speaking, one can think of it as simply breaking the contact between the foot and the surface.  If one dives deeper into the milliseconds as the foot is becoming unweighted, the maximum force of friction that can be applied to our foot becomes smaller and smaller, so there's technically going to be some slipping.  However, it is very minor.
When Ninjas learn the art of walking on rice paper, they're developing awareness for these tiny forces.  They are learning to transfer their weight such that the back foot has very little lateral forces on it as they lift it.  This sort of awareness is very useful for them.
For a more close-to-home example, we can answer your second question by considering someone walking on ice.  When people slip and fall, quite often it's because their back leg slides out from beneath them.  This is proof of the conjecture you had.  On ice, the maximum force of friction you can attain is quite low.  As people walk, they typically issue one last quick correction with their back foot before letting it rise off the ground.  If this movement is too forceful, the back foot can slip.
Answer: Yes, all your statements are correct and for each one all of us have real-life experience.
On a very slippery, that is low-friction, surface you can move by pushing and sliding. Indeed, this is how people naturally cross any slippery surface: Keeping both feet on the ground and slowly sliding forward. However, this is not how you walk. Instead, you lift your foot off the ground and move it through the air. This is much more efficient as you experience less friction moving your feet through the air than sliding over the ground.
There also is a maximum acceleration and conversely a maximum deceleration. We all know this from slippery surfaces where you can't just stop, but continue to slide for a few meters.

How do we walk?


How to use IDA Pro debug Android Application?

Question: Any person can give some examples or resources about how to use IDA Pro debug Android Application?
Comment: Hi and welcome to RE.SE! Please edit your question to include what you want to know specifically. As it stands your question is too broad. Once you edited your question you can then simply ask for it to be reopened (both are links right below your post).
Answer: (Although IDA lets you reverse .class files, there are tools that convert the Java byte code back to source code and are preferred for this)
It's pretty common nowadays to compile libraries and use NDK to develop a part of your app in C/C++.
Those parts will be compiled to an .so files, which can be invoked using the java code.
You can reverse those files, they should even contain some symbols in a form of package_classname_method to know who can invoke them.
Other than that, I don't think ida can offer something to reverse android apps.
The point is - Ida is not a general app reversing tool, it has a specific use.
That being said, here are examples:

IDA Dalvik debugger: tips and tricks
Reverse-Engineering-and-Tampering
Remote debugging using IDA Pro


2005 Toyota Camry Auto Headlights stay on about 20 minutes

Question: I have a 2005 Toyota Camry. The auto headlights stay on about 20 minutes after turning the car off. This MAY have started when I replaced the alternator, but I can't say for certain. Any ideas on what I should try to do?
Comment: Is this happening every time you exit the vehicle? I've read some posts elsewhere which was stating if the driver side door is not opened after the key is removed, the lights will stay on indefinitely. Also, there should be a setting which would allow you to adjust the timer for how long the lights stay on. This, I believe, would be done through the dash. Just throwing it out there.
Answer: Your best friend, the owner's manual, has the answer. Page 102 in this case.
You have the headlight switch in "position 2 Auto" and the car thinks that a door or the trunk has been left open. It's leaving the headlights on because it thinks you're loading / unloading the car or something, but to preserve the battery it's cutting the lights off after 20 minutes as promised in the manual.
If a door or the trunk are not actually ajar, you may have a defective door or trunk switch. Check your dome light when all doors are closed. Have someone close the trunk with you in it so you can see if the light stays on. (Be careful who you trust to let you out . . . .)
If you replaced your alternator because your battery kept dying, the issue may have been this all along. A continuous drain from a dome or trunk light can certainly kill a battery over time, especially if the car is driven infrequently.
2005 Toyota Camry manual excerpt here, pp 102 - 103.
Comment: Thank you. To add to the context, the trunk was damaged a few years ago in an accident. Recently the trunk would not latch shut and I had to remove the bulb in the trunk because it would not go off. Next time I will read the manual first! :-)
Comment: @BigRedBettaFish If you can find the trunk lid switch and disconnect it, that should solve the problem.


What can I do about slow running water in my Whirlpool refrigerator?

Question: We have a Whirlpool refrigerator that's 2 years old which has always had slow running water since new. I noticed that when we remove the water filter water runs nice and fast, but with a filter installed, even a new filter, water runs slow. We discovered that some friends of ours actually have the same fridge and it suffers from the same problem. What can I do?
Comment: +1 all around. Bypass and live with it, improve the valve and/or supplement an inline filter.
Answer: The filter will definitely restrict the flow, but it might be made worse if there is already a flow issue present.
Many DIY waterline install kits come with self-piercing saddle valves.  Compared to the 1/2" pipe they are fitted on (and even the 1/4" supply line), the hole they make is relatively small which reduces water flow to the fridge.
Your best bet is to not use these types of valves at all and instead solder in a tee fitting with a new 1/4 turn ball valve.  If you can't do this, an alternative is to remove the saddle valve and carefully drill a larger hole in the pipe, and then re-install the valve.
Comment: There's actually not a saddle valve - just a hose like this that connects directly from the supply valve in my house to the fridge's inlet: http://cdnroot.filtersfast.com/ProdImages/Whirlpool-8212547-Filter-PLAIN.jpg
Comment: how does it connect to your supply? no valve, just a tee with a compression fitting?
Comment: There's just a typical looking shutoff valve coming from the wall - something like this: http://s1.hubimg.com/u/1997596_f260.jpg
Comment: Verified it's fully open?
Answer: Perspective :)
Look at it this way: with the filter installed, everything is okay, but without the filter, water runs extremely fast because it isn't being filtered.
Better slow and safe than fast and unfiltered, I say.
But seriously, unless the water you're feeding your fridge is pre-filtered and the pipes are all perfectly clean, you need that filter.
Of course, if you're going to filter your water anyway after it's cooled by the fridge (I can't see why, really), it's probably okay to not use a filter.
Comment: It's not that we don't need the filter, it's that water just seems slow even with the filter - perhaps 11 seconds for 8 ounces. Our old fridge, even with a filter, was twice that fast. Perhaps the filter was not as good?
Comment: It may also be that your water inflow to the refrigerator is slow by itself, and the filter only ads to that... May be this combination's causing the slow flow you're seeing.
Comment: I tested the water line that comes out of the wall and that thing is rocketing water. Once it comes into the fridge I'm not sure what happens, but the filter being in certainly slows things from when it's not in.
Answer: All water filters restrict flow to some degree. Generally, the more filtration/treatment the more flow restriction. If you are using an in-line filter, there are many types available. If you want to just filter out sediment you could switch to a simple (and cheap) particulate filter and probably see better flow. The ones that remove chlorine and some chemicals (charcoal activated) restrict the flow more; "residence time" of water contacting the filter media is required for the filter to perform as advertised, so restriction is required.
Like @alt said, bypass the filter if you want flow and don't care about the water quality/taste.


When two continents crash against each other, mountains arise, right?

Question: In the background of my world it happens that two continents crash against each other. Now that I've done some research, do I correctly understand that this would create a mountain range? Or did I get something wrong?
Comment: What exactly you mean by crash? Speed like India crashing into Asia? Or something faster, something that would be a "common sense" crash?
Comment: Possible duplicate of [How quickly can I form a mountain chain?](https://worldbuilding.stackexchange.com/questions/73842/how-quickly-can-i-form-a-mountain-chain). The question is different, but the answer (mine) answers this question fully, and then some. If not a duplicate, then this question belongs on Earth Science, and is a dupe there, check out https://earthscience.stackexchange.com/questions/5332/is-there-a-reason-most-mountain-ranges-seem-to-run-parallel-to-coastlines, or https://earthscience.stackexchange.com/questions/13509/how-did-the-ural-mountains-form
Comment: Welcome to Worldbuilding.SE!  We're glad you could join us!  When you have a moment, please [click here](https://worldbuilding.meta.stackexchange.com/questions/6388) to learn more about our culture and take our [tour].  Thanks!
Answer: Mountain building, or Orogenesis, occurs in two main tectonic settings. One is, as you rightly describe, where two continental plates are pushing against each other (e.g. Himalayas). The other major setting where orogenesis occurs is where an oceanic plate is subducting under a continental plate (e.g. Andes, Rocky Mountains).
There are other less common settings which can cause orogenesis, but these are the ones you should be most aware of.
Comment: Could we add more detail to this?  Can two plates collide without subduction?  Can the local edge of the non-subducting plate be flexible?  What if it's rigid?  Can subduction occur without mountain building?  This is darn close to the right answer, it just needs some more detail.  Remember, you're not just answering the OP's question, you're informing the rest of us (and the future), too.
Comment: @JBH I am wary of muddying the waters by adding extraneous detail. The answer I have given does answer the question asked. Ultimately, subduction is not really relevant to the question of a continent-continent collision, so adding detail on that process I would think is not required.
Comment: @JBH I'm not sure how rigid you're talking about here, and on which scale. When it comes to large portions of plates, I think it's already fair to view it all as thin, slightly hardened top layer of liquid. It can always bend, flex, stretch, tear and mount up (to a certain height, after which it starts to sink too fast).
Answer: Yes. Two continents crashing into each other create folded mountains, which is what it's called when two large landmasses collide and the land in between them gets crumpled upwards.


Eclipse\Aptana code completion is unreadable

Question: I'm having an issue where the text in the code completion dialog is unreadable. For whatever reason the foreground is the same as the background. I have tried finding the right colors to change in the preferences but with no success.
Comment: I have the same problem and found this here.  Any luck fixing it?
Answer: It was pulling the colors from the default system theme selected in Ubuntu. It appears that Aptana doesn't allow one to override the system colors for that dialog.
Answer: Actually, there is a solution for this problem. The first possibility is to change the Aptana theme at Window - Preferences - Aptana Studio - Themes. IMHO, the "Bespin" theme's quite nice. The second possibility is to change the colors system-wide using Ubuntu's appearance settings for tooltips:


If entropy decreases for cold systems, isn't the heat death of the universe a state of low entropy?

Question: Entropy is a consequence of heat. The heat death of the universe results in an approach to absolute zero temperature. Does this mean the end of the universe is low entropy?
Answer:
If entropy decreases for cold systems,

There is some misunderstanding in this statement, using the verb "decreases".
from the three laws of thermodynamics entropy either remains constant on increases.
If one compares a cold system, to the same system at higher temperatures, the entropy is higher in the hotter system , but in order to get a hot system to a cold state a larger combined system is needed in order to obey the thermodynamic law 2:

Second law of thermodynamics: In a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases. Equivalently, perpetual motion machines of the second kind (machines that spontaneously convert thermal energy into mechanical work) are impossible.

Entropy as a variable is connected to temperature through differential equations, not linear ones, so it does not necessarity mean "low temperature"= " low entropy" as you assume
It can be demonstrated that all definitions of entropy are equivalent mathematically.
You ask

isn't the heat death of the universe a state of low entropy?

The useful definition of entropy for cosmological purposes , comes from statistical mechanics

Specifically, entropy is a logarithmic measure of the number of states with significant probability of being occupied

You ask:

Entropy is a consequence of heat. The heat death of the universe results in an approach to absolute zero temperature. Does this mean the end of the universe is low entropy?

Consequence and linear dependence are two different concepts. Heat generates microstates and thus increases entropy, but it is not the only variable that can increase entropy.
So it is possible to have a system of particles in a very large volume with very small kinetic energy ( which is directly connected to temperature) to a huge number of states occupied by these particles, so that the entropy is large but the temperature close to zero.
Comment: How many states are there at the heat death of the universe?
Comment: @Hierarchist  a very large number, all of the quantum mechanical permutations in addition to all the space permutations of the particles involved.
Answer: First of all, I agree with @anna v answer. I just want to expand (no pun intended) on the last paragraph.
Entropy is related to the dispersion of energy. In that sense, it is related to the universe gradually moving to its most probable state on order that all the energy is equally dispersed throughout the universe. At the present time energy is concentrated in particular areas (you might some of them "hot spots") but as the theory goes it will eventually spread out all over the universe (whatever all over means) because that is the most probable state.
Now as the temperature of the universe goes down there is less energy available to do work. A the present time we take advantage of temperature differences and the fact that heat flows from high to low temperature by taking some of that heat from the high temperature body and doing work in a cycle, while necessarily rejecting some of it to the lower body due to the second law. The energy rejected to the low temperature body is no longer available to do work in the current environment. We would need to take our heat engine and operate it between the lower temperature body and yet another even lower temperature body. Each time we do this we have less of the original heat energy available for work since our engine can never be 100% efficient. What's more we need to continue seeking lower temperature bodies to reject heat to.
Eventually as we approach absolute zero we will no longer be able to find a lower temperature body. In other words, the temperatures will be equal and we will no longer be able to do work.
Hope this plus anna v's answer helps.
Comment: So at the heat death of the universe, there will be no other possible state to transition to, thus there is only one state of the heat death?
Comment: @Hierarchist If the universe is in thermal equilibrium there are no differences in temperature between regions. Heat is energy transfer due solely to temperature difference. Without temperature difference there  can be no energy transfer in the form of heat and therefore no heat flow to drive heat engines to do work.
Comment: So it's in a single state.
Comment: @Hierarchist OK, but I think I would call it the single most probable state.
Comment: But anything else would be not the heat death, and there are infinitely more not-heat deaths than there are the one heat death, right?


Asp.net 3.5 forms authentication timeout

Question: I have this codes in
<code> <authentication mode="Forms">
  <forms loginUrl="/Login" timeout="180" name="__Auth"     slidingExpiration="true" />
</authentication>
</code>
And Plesk panel Session  settings are as below :
   Authentication mode : Forms
   Sesion Timeout(minutes) : 180
And this settings automatically adding a line to web.config aas below:
<code> <sessionState timeout="180" />
</code>
Everything seems good.
But session ends too early (about 10 min)
I could not find reason.
Answer: Please include following code in web config in your application.
<code>  <session State timeout="30" mode="In-proc" />
</code>
and also check time in

But you remove space in between session state and remove - in In-proc...
Answer: Please include following code in your web.config file and try.
<code><httpRuntime maxRequestLength="102400" executionTimeout="3600"/></httpRuntime>.
</code>
Comment: I had .
Now changed.I'am trying.I will write with results.Thank you
Comment: Could you please explain the issue in detail that you were facing while logging .


Is there an android shell or adb command that I could use to get a device's IMEI/MEID?

Question: Is there some adb or android shell command that I could run that would return a device's IMEI or MEID number? Preferably that's all that would be returned.
Comment: There are a few answers here that run `adb shell ...` and pipe the output into `awk` and then into multiple `sed` and `tr` commands and then maybe into `awk` again.  That isn't necessary, `awk` can do everything `sed` and `tr` can do.  e.g.  `awk -F"'" 'NR>1 { gsub(/\./,"",$2); imei=imei $2 } END {print imei}'`
Answer: I figured out how to do this. You need to run adb shell dumpsys iphonesubinfo in a shell. It will give you a bit more than you need, but it will also return IMEI or MEID number.
Edit (2017): In Android 5.0+ you'll need to use the service call command. More info about that can be found here.
Comment: adb shell dumpsys iphonesubinfo command is not working Android 5.0 lollipop on all devices. Specially which are not rooted device.
Comment: Sometimes, I don't know why, I've seen `adb shell dumpsys iphonesubinfo` display null as the IMEI. The correct IMEI was restored by rebooting the device.
Comment: I added another solution here: http://stackoverflow.com/a/37940140/1140682 that should work for nearly all Android devices.
Comment: the first part of the answer is relative at old android versions.
Answer: For IMEI you can use:
adb shell service call iphonesubinfo 1 | awk -F "'" '{print $2}' | sed '1 d' | tr -d '.' | awk '{print}' ORS=

Comment: this one, and 'cas' comment to mitesh' answer, are the only ones that worked for me (Galaxy s8+, Android 8.0, adb version = Android Debug Bridge version 1.0.40, Version 4797878
Answer: The following ADB command works for me to get the IMEI:
adb shell "service call iphonesubinfo 1 | cut -c 52-66 | tr -d '.[:space:]'"
Answer: For ESN you can do
service call iphonesubinfo 16
at least it gives me the right one on Motorola Photon Q.
To clean it up (assuming you have shell on the device and have a capable busybox there, if not I highly recommend one):
    service call iphonesubinfo 16 | busybox awk -F "'" '{print $2}' | busybox sed 's/[^0-9A-F]*//g' | busybox tr -d '\n' && echo

For MEID with cleanup:
service call iphonesubinfo 1 | busybox awk -F "'" '{print $2}' | busybox sed 's/[^0-9A-F]*//g' | busybox tr -d '\n' && echo

Comment: This solution works on Android 6.0, whereas the `dumpsys` solution does not.
Answer: This works for me on my nexus 5 and moto 5G.
output:
[build.id]: [M4B30X]
[build.version.release]: [6.0.1]
[build.version.sdk]: [23]
[build.version.security_patch]: [2016-10-05]
[product.brand]: [google]
[product.manufacturer]: [LGE]
[product.model]: [Nexus 5]
[product.name]: [hammerhead]
[serialno]: [05xxxxxxxxxxx4]
[device.imei]: [xxxxxxxxxxxx]
[device.phonenumber]: [+xxxxxxxxxx]

Script: get.deviceinfo.bash
#!/bin/bash
# Get the device properties
adb shell getprop | grep "model\|version.sdk\|manufacturer\|ro.serialno\|product.name\|brand\|version.release\|build.id\|security_patch" | sed 's/ro\.//g'
# get the device ime
echo "[device.imei]: [$(adb shell service call iphonesubinfo 1 | awk -F "'" '{print $2}' | sed '1 d'| tr -d '\n' | tr -d '.' | tr -d ' ')]"
# get the device phone number
echo "[device.phonenumber]: [$(adb shell service call iphonesubinfo 19 | awk -F "'" '{print $2}' | sed '1 d'| tr -d '\n' | tr -d '.' | tr -d ' ')]"

It requires:

UBS debugging ON (developer options)
adb (Android SDK Platform Tools)
Comment: This is the complete solution, work perfectly.
you can execute scripts one at a once or all together running them by .sh file
Answer: For the IMEI, maybe this command is easier to understand
db -s <device id> shell  service call iphonesubinfo 1 | cut -c 52-66 | tr -d '.[:space:]'

db -s <device id> shell  service call iphonesubinfo 1 gets the full result, for example

Result: Parcel(
      0x00000000: 00000000 0000000f 00350033 00340037 '........126.96.36.199.'
      0x00000010: 00350032 00370030 00310032 00390039 '126.96.36.199.188.8.131.52.'
      0x00000020: 00370034 00000032                   '4.7.2...        ')

cut -c 52-66 trims away all columns except 52-66, using the above example

........220.127.116.11
18.104.22.168.184.108.40.206
4.7.2...

and tr -d '.[:space:]' trims off any '.' and white space, using the example above

357425072199472

Warning
A downside of this approach is that it is brittle, in the sense that the output must always be in the same format, having the exact same columns. I verified it on CentOs and OS X, but an update to the adb version could break this command simply by adjusting the whitespace in the output.
Answer: As the iphonesubinfo 1 command does not work on many devices, here is a little workaround that should work consistently on most Android versions and on rooted and unrooted devices:
If you already have an own app that you can install on the device that you want to know the IMEI from, add this BroadcastReceiver to your app:
public class GetImeiReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        String imei = ((TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE)).getDeviceId();
        setResultData(imei);
    }

}

and to the AndroidManifest.xml:
<receiver android:name=".GetImeiReceiver">
  <intent-filter>
    <action android:name="com.myapp.GET_IMEI"/>
  </intent-filter>
</receiver>

Call your receiver over ADB:
adb shell am broadcast -a com.myapp.GET_IMEI

...and the output will be something like:
Broadcast completed: result=0, data="000000000000000"

...where data is the device IMEI.
If you have don't have an existing app to integrate this solution into, I created this simple one which includes the required code:
https://github.com/saschoar/android-imei-getter (also includes the APK and full instructions).
Comment: where and how to write this command adb shell am broadcast -a com.myapp.GET_IMEI . Downloaded your code but does not work
Comment: I need to find imei for real device, just java code does not works for me
Comment: This is an irresponsible implementation, as it allows any app on the device to query for the IMEI or MEID. You should add `android:permission="android.permission.READ_PRIVILEGED_PHONE_STATE"` to the receiver in order to close this security hole, since that permission is required by `getDeviceId`, and the android shell will already have been granted this permission by default.
Comment: Note: Older API levels only require `READ_PHONE_STATE` instead of `READ_PRIVILEGED_PHONE_STATE` in order to call `getDeviceId`, but `READ_PRIVILEGED_PHONE_STATE` is safer and should work as far back as Android 4.0. Using only `READ_PHONE_STATE` will leave a security hole open for Android 10 and later.
Answer: IMEI-
adb shell service call iphonesubinfo 1 | awk -F "'" '{print $2}' | sed '1 d'| sed 's/.//g' | awk '{print}' ORS=''
Android ID=
adb shell settings get secure android_id
Comment: good idea but that awk|sed|sed|awk pipeline is horrible - awk can do it all.  Try `adb shell service call iphonesubinfo 1 | awk -F"'" 'NR>1 { gsub(/\./,"",$2); imei=imei $2 } END {print imei}'`
Comment: Nice... this is a small edit for running on Mac OSX, the backslash before the "." prevents matching anything [outputting nothing] and instead matches the actual "."'s, and the END will add a linefeed to make the output stand out alone: adb shell service call iphonesubinfo 1 | awk -F "'" '{print $2}' | sed '1 d' | sed 's/\.//g' | awk '{print} END {printf("\n");}' ORS=''


What is a Galactic Eclipse?

Question: It is said that when our solar system passes through the dark rift of galaxy (what is it exactly?), a phenomenon named 'Galactic Eclipse' happens, when our solar system witnesses 3 days of darkness. Is it possible even in this case that there would be no light in the night sky, as there are many stars in the night sky. (don't consider city lights and other artificial human interference)
Comment: The "galactic eclipse" is a hoax.
Comment: [oncubamagazine.com/science/the-lies-of-the-galactic-blackout/](http://oncubamagazine.com/science/the-lies-of-the-galactic-blackout/)
Comment: Someone did Asimov's **Nightfall** backwards: https://en.wikipedia.org/wiki/Nightfall_%28Asimov_short_story_and_novel%29
Answer: Definitely a hoax as other commenters have said.
Dark rifts exist in the galaxy - large clouds of dust, several can be made out by eye, overlapping the milky way, in ideal conditions.  See for example the Great Rift.  However these are so large it would take far longer than three days for a solar system to pass through them.  Probably thousands or millions of years.  So this is definitely incorrect information.
Comment: Even if we were inside such a dust cloud, there would be no noticeable effect on the brightness of daylight. Even the densest clouds rarely exceed an extinction in visible light of $A_V \sim 100$ magnitudes per parsec ([Kitchin, 1987](http://adsabs.harvard.edu/abs/1987snim.book.....K)), or $5\times10^{-4}$ per AU (the distance from the Sun to Earth). Thus, the fraction of the Sun's light that would still reach us would be $\exp(-\tau)\sim\exp(-A_V)=99.95\%$. But the night _would_ be starless.

What is a Galactic Eclipse?


The expression "I'll take it as take out"

Question: If I order a coffee and want to take it out. (To go..) The expression "I'll take it as take out." makes sense? And use that in common?
Comment: The repetition of 'take' is awkward. 'I'll have it as take out' is better. Why don't you just say 'I'll have it to go'?
Answer: The repetition of "take" is awkward, so your example is not the best choice.
When it comes to ordering food, sometimes you can just tack on a short phrase which is not a full sentence:
"to go"
"for take-out"
"for take-away" chiefly British
Adding the word "please" at the end is a good idea.
Of course, full sentences are also possible:
"I'd like it to go please."
"I'll have it to go."
"I'll have it as take-out."
"I'll take it to go."
Comment: I would not hyphenate "to go" unless using it as an adjective: "a to-go order"

The expression “I'll take it as take out”


How does the dpi setting affect the image exported from Lightroom

Question: If I export an image from Lightroom (as a jpeg) I can specify to resize it to particular dimensions, or keep it as it is. But regardless of that there is also a dimension field as in dots per inch but surely this is just a decision made at printing time I don't understand what effect it has on the exported image.
Comment: I'm not sure but maybe it Affects the settings of the sharpening applied during export (if activated)
Comment: It sort of is the same answer but they are different questions, and different questions to the same answer help users to find the correct answer.
Answer: In general, dpi is the conversion from pixel dimensions (image size) to inch dimensions (on paper... X number of pixels per inch determines inches of paper coverage).
When we resample an image, we can specify its new size dimensions, like say 1800x1200 pixels.
Or, we can specify its new printed size, like 6x4 inches at 300 dpi, which computes the same 1800x1200 pixel dimensions (6x300 = 1800, 4x300 = 1200).
Specifying both dpi and inches of print size normally does this resample computation (computes new size of resampled pixel dimensions - to fit that declared paper size).
But merely specifying only dpi (called scaling, to fit the paper inches) merely stores that number in the image file somewhere (and we might then see some new corresponding print size numbers in inches, but the pixels are unaffected, NOT resampled due to the number).   Dpi serves no other purpose, or has no other effect, on digital camera images. Only important at the time of actually printing (and deciding paper size).
The Photoshop resample box allows either method.
I think you are saying Lightroom export does the second method, which merely saves a dpi number for future reference.  Any dpi number has no effect on the image or pixels, until possibly the time you may be actually printing it, and decide paper size, when you will surely address it again then.
Comment: dpi also affects the size of an image when imported into a pagesetting application such as InDesign or a word processor. The application will apply the dpi number in the EXIF info and size the photo on the page at that many ppi.
Comment: Yes, agreed, because that "page" is a "printing on paper" job, and paper is dimensioned in inches.  That is what dpi is for (inches).     The real exception is of course scanners, which use dpi to define the resolution of the  area of the inches of Paper it scans, which does then define the pixels it creates.    But if speaking of digital cameras, dpi is a "who cares?" which does not affect the pixels. Dpi is not important until time of printing on paper, at which time some new value is likely determined instead.
Answer: DPI information is only relevant when the pixels are projected to a device that have defined metric dimensions, so you can measure the size of the projection of one sample (pixel).
Traditionally, computer screens have only a fictitious DPI scale, which is considered something like 72, 96 or 120 etc. dpi, as those are the most probable actual size of the monitors available on the market; and since operating systems usually don't know the metric scale of the actually attached destination screen, this DPI setting is kept as a user setting.
This fictious current DPI setting in OS is used to implement scaling of the font and user controls, or to implement a "display a printable document in actual size" function. But for displaying on a computer's screen, which has it's own intrinsic DPI as a raster device and at the same time can display content in different scale on user's demand, this setting in the image is irrelevant. The best rule in pre-retina era was - use the size in pixels which matched the screen's resolution. Oversampling did not provide any benefit, as a slightly scaled down image looked worse than perfectly fit to screen's resolution, event if it's effective DPI was higher.
But when you are working with a publishing software such as InDesign this setting, embedded in the images would allow you to size the placed image when editing the pages.
The same (in pixels) image with different DPI settings would occur at different scale when placed on a page initially, depending on the tool you use to place the image.
The same applies to word processing software, such as the Microsoft Word.
Actually, it could be used by any software having a concept of physical canvas size as well.
So, if you export with different DPI setting, you can find that it's obeyed by different software systems when initially placing the image on a canvas, or in a sort of "display in actual size" function.
Actually, I found this setting very useful, because it affects the imagery placed in InDesign when you are placing many images of the same size. In my case, tuning this setting alowed to create an image gallery almost automatically, instead of scaling each image individually.
Answer: I don't know why Lightroom gives you the ability to select DPI. As per definition DPI is "the number of individual dots that can be placed in a line within the span of 1 inch" (Wikipedia). So the DPI is directly pending on your resolution and print out size.
Also, if you export an image with e.g. 300 DPI and 1 DPI, you will see that both file sizes are equal.
Maybe, the selected DPI would tell the printer how big your image shall be printed, if you do not tell it any size...


Scripts to calculate ionic diffusivity

Question: I found several AIMD analyzers to estimate mean square displacement and ionic diffusivity such as pymatgen, mo, vaspkit. I tried some tests and found that the same data set might result in different MSD slops by using different analyzers. The ways of calculating MSD are not similar (I do not see vaspkit source code). I wonder which way/script is reliable and its obtained results are accepted?
Answer: Short Version
The differences have to do with possible discrepancies in the order of operations when computing MSD's, or with lengths of trajectories in different studies.
For software packages, in addition to the ones listed in the question, there is also kinisi. There is also CHAMPION, which is not published but possible to reverse engineer, and is nicer for complex fluids. See especially Figure 7 in the CHAMPION paper for an example of where differences between approaches come from.
Personally, I would bias towards verifying the underlying physics over trusting any code which does not show it to me.
Long Version: Computing MSD Properly
Nomenclature:

$\bar{x} = \frac{1}{\Delta} \int_0^\Delta x(\delta) d\delta$ for time-averaging single-ion quantities over multiple starting points in the simulation trajectory of length $\Delta$. We are interested in the displacements over time intervals $t$, $x_1(t,\delta) = r_i(t+\delta) - r_i(\delta)$, and squared displacements, $x_2(t,\delta) = (r_i(t+\delta) - r_i(\delta))^2$. Here, little $\delta$ is the integrand of the time averaging.
$\langle x \rangle = \frac{1}{N} \sum_1^N x$ for the ensemble averaging over all ions $i$ in the simulation.

There are three operations to keep track of: taking the square of the displacements for a given interval $t$ and starting point $\delta$, taking the time average, and taking the ensemble average.
The proper way of computing the self diffusivity is to first compute single-ion MSD's, then average them over the ensemble of the ions in a simulation, i.e. $\Big\langle \bar{r^2} \Big\rangle$ - bar inside the brackets. I'll call this quantity tMSD. When this quantity is linear with time interval (not simulation length), Fickian diffusion can be assumed and the self diffusion coefficient extracted.
Computing tMSD properly requires custom code because simulation engines pack trajectories by time point ($\delta$), not by ion. Hence all the packages. I have tried to understand what exactly pymatgen and others compute, but in finite time was not able to for layers of abstraction. Hopefully some of the developers can comment in more detail.
Sometimes the computation is done either in reverse order, i.e. take the square, then the ensemble average, then time-average, or skipping the time-averaging. This makes built-in methods such as the computes msd and msd/nongauss in LAMMPS not give reliable answers: they only sample one starting point. I would not recommend using either.
A third order of operations, i.e. first computing the ensemble center-of-mass displacement, then its square, $\langle r \rangle^2$, and then averaging over times, gives the "jump" diffusion coefficient, which yields conductivity rather than diffusivity. Both for real physics and for having effectively one particle, this takes a very long trajectory to converge. I am bringing this up because often from AIMD a unity Haven ratio is assumed, and the self diffusion coefficient used in place of the jump one - which is not always a good assumption.
Long Version : How Long is Long Enough?
Besides possible errors in the order of operations, sometimes the (AI)MD trajectories are simply not long enough, and the results will vary with changing the length of the trajectory. So how does one tell whether a trajectory is "long enough" and a long-time limit is reached? There are a few ways.

The one used most often for self diffusivity is to verify linearity of tMSD (if done correctly) on a log-log plot vs the time interval $t$. That involves human judgement over when the long-time linear regime starts, i.e. how close to 1 is "good enough".
The maximum-entropy distribution with the constraints of a mean and a variance is a Gaussian. This means that distributions of tMSD's over longer and longer time intervals will asymptotically tend towards Gaussians. So an indirect test for "long enough" is whether the distributions of tMSD's are Gaussian. This is why the non-Gaussian parameter (NGP) is sometimes used. It has the same drawback: it does not go to zero at finite interval $t$, but approaches it asymptotically.
Next, there is the ergodicity breaking parameter, $EB(t,\Delta)$, which is the relative variance of the tMSD, very similar to Mandel's Q parameter. This is typically computed for a fixed small-ish $t$ over increasing trajectory lengths $\Delta$. The benefit of using $EB$ is that it can have a well-defined cutoff for a long-time limit, i.e. you can tell when a trajectory is "long enough".
Fourth, there is the correlation of the diffusion kernel $C_D$, which is another test loosely based on when nonlinear path-dependent effects, which are represented by higher-exponent averages of displacements, become negligible relative to tMSD. Like the $EB$, it has a well-defined long-time limit, and reaches that limit at finite time intervals. The drawback is that it involves a Laplace transform and an inverse Laplace transform, which may need to be tuned numerically.

The python code I wrote for a recent paper is far from great, and is not a package. But as of the time of this writing (July 31, 2022), it is to my knowledge the only one that implements the three metrics above (NGP, $EB$, $C_D$) for verifying that the "infinite-time" limit has been reached in the simulation.
References

Song et al. Transport dynamics of complex fluids. PNAS 2019, 116 (26), 12733.
He, Burov, Metzler, Barkai. Random Time-Scale Invariant Diffusion and Transport Coefficients. PRL 2008, 101, 058101.
Jeon et al. Protein Crowding in Lipid Bilayers Gives Rise to Non-Gaussian Anomalous Lateral Diffusion of Phospholipids and Proteins. PRX 2016, 6, 021006.
Lanoiselée, Grebenkov. A model of non-Gaussian diffusion in
heterogeneous media. J. Phys. A. 2018, 51, 145602.
Poletayev, Dawson, Islam, Lindenberg. Defect-driven anomalous transport in fast-ion conducting solid electrolytes. Nat. Mater. 2022.
Comment: Thank you for your answer and congratulation on your new publication in Nature Material. I found you prepared an analyzer for LAMMPS. It will be very convenient if there is an option for VASP users.
Comment: Hi @BinhThien! I have since used the same math scripting for VASP trajectories (unpublished). The difference is in going from the XDATCAR to the single-ion trajectories, not in the subsequent statistical analyses. Once the XDATCAR is re-parsed into single-ion trajectories, everything else becomes the same. Happy to discuss further - please feel free to contact at the corresponding-author email on the paper.
Comment: Thank you. I also wonder about the time consumption for MSD estimation since we have to deal with several hundred or billions of structures for long-time sampling. In addition, how the crystallographic coordinates are treated is also my concern. I think the shortest distances would be taken in the summation due to periodic supercell. I take a look at your analyzer, but not sure which file is for MSD calculation. Can you let me know the file name in your python code?
Comment: @BinhThien the most time-consuming part is re-parsing, esp. on 100-GB LAMMPS trajectories. VASP XDATCAR's are generally not that big. You have to unwrap the coordinates in any case, and subtract the host-lattice center-of-mass motion. Each atom's MSD ("bar") is computed with the `hop_utils.multistart_r2r4()` function called in parallel from `parse-r2a2.sh` via `sherlock_multistart.py`. They are averaged ("brackets") with `sherlock_combine_restarts.py` also called from `parse-r2a2.sh`.

Scripts to calculate ionic diffusivity


FFMPEG for frame interpolation ala Twixtor

Question: Can any FFMPEG experts tell me if FFMPEG can do any sophisticated frame interpolation similar to the Twixtor plugin in After Effects?
If so, what would be some suggested settings to try?
I'm trying to create ultra slow motion HD footage from a 60fps source. ie Convert to 120fps and interpolate the frames.
Answer: The libavfilter library has a filter called minterpolate, which is available since November 2016. According to the fitler's description, its purpose is to:

"Convert the video to specified frame rate using motion interpolation."

Example usage:
<code>ffmpeg -i input.60fps.hevc -filter "minterpolate='fps=120'" output.120fps.hevc
</code>
I do not know which settings to use in order to achieve the best possible result. From my experience, the default settings provide acceptable quality of the motion interpolation itself. But there are some very noticeable visual artifacts introduced occasionally. I was not able to find a combination of settings which would completely eliminate them.
The filter is very slow at the moment. It can output around 2 motion-interpolated frames of 1080p video per second on a modern, high-end x86 CPU. I have noticed that the interpolation utilizes only a single CPU thread, which is probably the main reason for such a slow speed.
In order to speed up the filter on a multi-core CPU, it may be advisable to split the input video into several chunks of equal length and apply the motion interpolation to all of them in parallel.
Comment: Here's a script to make parallel minterpolate just as you suggested: https://gist.github.com/majal/1e63a511b41faeae188083777f8e4b46
Answer: Months after update:

ffmpeg -i input.mp4 -movflags +faststart -filter_complex "[0:v]minterpolate='fps=60:mi_mode=mci:me_mode=bidir:mc_mode=obmc:me=ds:vsbmc=1'" -preset ultrafast output.mp4

Original post:
I am able to achieve such effects (not perfect though), with
tblend filter

ffmpeg -i source.mp4 -filter:v tblend -r 120 result.mp4
Comment: The new minterpolate filter should be a better fit.
Comment: On one hand `tblend` doesn't create any artifacts; on the other, the result is indistinguishable from simply altering speed with `setpts` (to my naked eye). Maybe changing its defaults will have more of an effect.
Comment: It unavailable at rpm-fusion distribution, thanks for advice!
Answer: FFmpeg cannot do this.
There were some discussions about implementing such a feature a couple of years ago, but so far they haven't released anything similar to frame interpolation in the project.
You could of course use a similar free tool like slowmoVideo which is also hosted on GitHub if you want to take a look at the source.


How to create 3-elements dragon?

Question: I'm mixing dragons with 2 elements for a long time, but each time I got the 2-element dragon. How it is possible to create a dragon with 3 elements? I'm level 19. Is it level-dependent?
Answer: One way you can get a 3 element dragon is to breed War and Mud. You have ~20% of getting a Quake dragon which is War, Terra, and Water. You have to breed it in the Breeding Sanctuary lvl 2
Answer: yes lvl is dependent and it also depends on what device your playing on and on what lvl the breeding sanctuary is
I suggest you lvl up on of the parent dragons you're going to breed to lvl 15 and one could be at 10 or higher but one must be at lvl 15. that's how I got the apocalypse. and your sanctuary might breed differently if you play on facebook or on mobile and usually mobile gives the best results when bred directly
so mud/waterfall + war would give you a better chance of getting quake on mobile than on facebook which requires a lot of different elements and I usually never get the quake by breeding directly so mobile is better
Answer: It is possible to get a three-element dragon without using the breeding sanctuary(which is locked by your level by the way). However, you have to use a lvl 20 dragon parents to breed those dragons, such as the poo dragon, the angry dragon, and the crystal dragon.

How to create 3-elements dragon?


How to uninstall Ubuntu 11.10 in netbook

Question: I have installed Ubuntu 11.10 on my Acer netbook as a dual boot with the default Windows XP on said netbook. Now I need only Windows XP and want to completely uninstall Ubuntu 11.10, there is no cd drive in my netbook. Any help would be greatly appreciated.
Comment: I've been trying to find ways to do this for the last 20 minutes and it seems the sticking point is restoring the Windows bootloader without a CD. With a CD, it's easy (recovery console, startup repair). Whatever you do, don't delete the Ubuntu partition until the Windows bootloader is back, or GRUB will probably stop working and you'll be left with no bootable OS.
Comment: Does this answer your question? [How to remove Ubuntu from dual boot system with Windows 7?](https://askubuntu.com/questions/152812/how-to-remove-ubuntu-from-dual-boot-system-with-windows-7)
Comment: How did you install it in the first place? Wubi, or something else?
Comment: as "Caesium" said just restore the windows boot loader and remove the ubuntu partition this will solve your problem
Comment: possible duplicate of [How to remove Ubuntu and put Windows back on?](http://askubuntu.com/questions/133533/how-to-remove-ubuntu-and-put-windows-back-on)
Answer: Follow the instructions regarding easybcd as described
How to reinstall windows bootloader to the MBR
After you reinstalled the windows bootloader you can delete the ubuntu partion using a live cd/usb and running gparted.
Answer: If you have a Wubi install then you can just remove it from the Windows 'Add/Remove programs' tools (or whatever it's called these days).
If you installed it some other way (USB?) as a full dual-boot system, then you can probably restore it using a USB CD drive - but I'm sure you already thought of that. (Maybe you could put a Windows CD image on a USB drive, but I don't know?)
If none of that works then you could try using a virtual machine. If your machine can't handle real VMs (and many netbooks won't be able to), then kvm can simulate a machine the hard way, slowly, as long as you have enough memory.
Within Ubuntu, kvm will boot from an iso image of a Windows CD (or maybe a network mounted CD drive, slowly), and you can set your virtual hard drive to be your real hard drive /dev/sda (or whatever it's called on your system - you'll need to be root to access it), and then you can let it do a repair. IF THIS GOES WRONG BAD THINGS WILL HAPPEN, so wait until somebody has found the obvious flaw in my plan and posted it in the comments.
Don't ever try to do a full install this way though: a) bad things happen if you wipe the drive your OS is running from, and b) Windows detects hardware at install time, not run time, and the virtual hardware won't match your real hardware, so the result won't boot. (Although, I have actually used this technique to install Linux on a drive that I had physically removed from another machine that had no CD or boot-from-USB feature.)
Once the Windows boot loader is restored, you can reboot into Windows, and use normal Windows tools to rearrange/reformat/delete/extend the drive partitions to your taste.
Comment: Setting the virtual HD to be your currently live mounted real HD sounds incredibly dangerous. Does that even work?
Comment: It works as long as you don't touch the partitions you are running from. In particular, if you're running Linux, you can touch the Master Boot Record and Windows partitions 'safely' (as in, it won't crash now - you can easily prevent it from booting again, but then that's true for any installer).


How does SSD achieve wear-leveling when disk is near-full?

Question: I'm trying to understand this. Say I have a 256GB SSD, 180GB of which are already occupied by permanent files (OS, installed programs etc.). The remaining 70GB or so gets new files created and deleted. Doesn't this mean the the NAND chips of that portion will get weared out earlier than the area whose files are not modified? Or does SSD move the non-changing files too over the course of time?
Comment: The short answer is that SSDs move blocks around all the time, and don't really care if the data is actively referenced or not. Consider that deleting files normally only removes the pointer to the blocks from the file system, it doesn't actually clear the data blocks. I don't have enough time to compose a proper answer right now, but that'll most likely be the gist of an answer also with references.
Comment: If your OS does use the TRIM command from time to time, it will certainly clear the data blocks after you deleted a file. At least periodically. And even if it doesn't: the blocks need to be cleared the next time you want to write to it.
Comment: The same way it always does just with the cells that are not marked as having data on them by the filesystem.
Comment: I would say that the correct answer is 'it depends' ... mainly on the SSD, or more specifically its controller and firmware. Wearleveling algorithms will differ for different sillicon and different manufacturers.
Answer: The SSD moves non-changing files around over the course of time.
First of all, you have the virtual sectors that are exposed to the operating system (not to be confused with file system clusters), and then you have the physical cells in the flash chips.  As the flash controller allocates/deallocates cells, it remaps the virtual sectors accordingly so it is transparent to the operating system (the same virtual sectors may appear at different locations in the flash cells at different times).
Second of all, SSDs actually have spare cells that are not usable as free space.  They're specifically set aside for the purpose of wear leveling, mitigating write amplification, and remapping dead cells.  That way, even if your SSD has zero bytes of free space on it, the flash controller still has room to perform wear leveling.
Let's say you have a 500 GB SSD that is 100% full.  Now let's say that 499 GB of that data is a file that never changes, but you have a 1GB file that changes all the time.  If you delete that 1GB file and then copy over another 1GB file, the flash controller will do one of two things at that moment:

All or some of the new data will be allocated to spare cells, leaving the old cells in a still-trimmed state.
1 GB worth of cells within the 499 GB of data that never changes will be copied to other available cells.  The old cells will then be erased and rewritten with the new data.

In both cases, the virtual sectors presented to the operating system never change, so the OS is unaware of what's actually happening.  The flash controller keeps a mapping table of memory cells to virtual sectors.
The wear leveling algorithm's goal in life is to try and exercise all the cells evenly, even if that involves moving data around to achieve it.  This process does slow the drive down, and it does (ironically) cause additional wear to the flash cells.  It's called write amplification and it's a significant problem with SSDs.  The actual wear leveling algorithms employed by SSDs and the ways they mitigate write amplification are proprietary trade secrets among SSD manufacturers, so this is just a general descripton of the process.
Comment: "The SSD moves non-changing files around over the course of time." Or at least they are *supposed* to, but it depends on the controller of course. If SSDs *always* moved stale data around (like say installed OS and program files), then we should've never encountered the Samsung 840 Evo slow-down issue.
Comment: Not necessarily. It does depend on the controller, but we'll never know the details about how the firmware makes its reallocation decisions. If the drive spends most of its time doing reads (as is the case with an OS drive), very little wear-leveling needs to occur. Presumably, the firmware knows the cycle count of every cell, and it's logical to assume that the firmware would prefer to use a "fresh" cell rather than a used, but trimmed one. For a large SSD, it's conceivable that it could be years before a reallocation needs to happen, depending on use of course.
Comment: The 840 EVO problem was caused by a firmware bug. As we discovered, voltage drift over time causes cells to become weak and they need to be refreshed occasionally whether there's data to be written or not. Samsung's problem was that the wear-leveling algorithm *wasn't* reallocating cells when it needed to -- probably because the voltage drift was happening faster than Samsung predicted it would.  Of course, this is a guess, because Samsung isn't getting into the gritty details of the bug, and it only affects that model drive (other TLC-based drives are unaffected).


What is the difference between "the door opened" and "the door was opened"?

Question: What is the difference between "the door opened" and "the door was opened"?  Are there subtle differences?
Comment: Yes, there are subtle differences, though they can both mean the same thing as well. _The door opened_ is the **inchoative** use of _open_; this means "came to be open; became open", and it's intransitive -- _open_ has no object, and nothing is said about why it opened. _The door was opened_ is a passive sentence, with the past participle of _open_ (not the past tense, as in _The door opened_) preceded by a form of _be_. This is the **causative** use of _open_, which means "cause to be open" -- with a passive, in this case, "was caused to be open", by some unknown agent. But deliberately.
Comment: @JohnLawler Why post as a comment and not an answer? That looks like a fine answer to me.
Comment: What did your previous research tell you? You have to tell us so that we do not recreate an entire academic text.
Answer: active voice: the door opened
passive voice: the door was opened
Comment: Welcome to ELU.SE. While this answer is technically correct, have a look at answers on the linked question to see the sort of thing which gets upvoted as useful.
Comment: Your answer is misleading, in that this doesn't give the normal active – passive transformation: active voice: _John opened the door_ <==> passive voice: _the door was opened_ [_by John_]. In both renderings here, the agent is the same (John). With the inchoative use, there may not even be an agent (and none can be mentioned).


Where can I find GPS-device-compatible maps of Georgia?

Question: I am looking for Georgia maps for supported for Garmin device. Especially I'm interested in Svaneti and Kazbegi regions. Is there any place I could find such maps?
Answer: The Openstreetmap wiki has an overview of downloadable maps for Garmin devices.  If you're interested in hiking, you may want to look at their hiking maps page; those services may include more information of interest to hikers and some include contours as well, but most are not (easily) downloadable for offline use on Garmin devices.  In general I used to recommend Garmin Openstreetmap, but this service is often down.  These days I use userbeam for downloadable maps (but right now I get a certificate error here).  When it works, in the drop-down list, just select Europe -> Georgia (they classify Georgia as Europe, even though it's mostly Asia).  Otherwise check out other sources on the linked overview.
Note that it does not cover topographic information, so it is not enough for hiking.  For Georgia, I would print out some old soviet maps, which probably cover Georgia pretty well.  If you're lucky enough to be in a highly frequented area, there are probably commercial topographic maps as well.  I've also had some luck on downloading Soviet topo maps to my Garmin device, but they were very slow to load, they're (naturally) not routable, and therefore not great as a sole solution.
Comment: It doesn't have the download option. Are you sure this site allows you to download the maps?
Comment: @Ostati It does have this option, there is a link *Download map now!* that appears when I select *Europe -> Georgia*, pointing to [this download link](http://osm.pleiades.uni-wuppertal.de/garmin/generic/01-03-2020/daa1db254f44ca1c980a0806e06ef33f).  I've downloaded there many times and it's working for me right now.
Comment: I got it. It just didn't work due to site being down at that moment. Thx
Comment: @Ostati You're right, it's a frequently unreliable site.  I've edited the answer to refer to a list of other options.
Comment: @gerrit I thought it did, at least with newer devices, but looking further maybe I'm wrong.  There is now non-android (e.g. Windows) software that it works with, but the converters don't extend to Garmin (previous comment deleted)
Comment: Openstreetmap now has contour-line (topographic) data for Georgia.
Answer: The Garmen GPS maps do not show detail in the regions such as Mtskheta where Kazbegi is located. I used and still use the free app maps.me in Mtskheta, Kakheti, Shida Kartli, Samtskhe-Javakheti, Imereti, Guria, and Adjara. To get this, you have to first download the app to your iPhone, then the Georgia specific map. It works offline, shows your location, maps directions, and has the pin points for some sites of interest.
Answer: Quite good maps you can download http://garmin.opentopomap.org/
If you want to get some GPS coordinates of Georgia Svaneti area, some trek coordinates for GPS device: http://www.zmidloch.com/outdoor-blog/svaneti-trek-georgian-caucasus/


Is there a formula to find a rational number between $x$ and $\sqrt{2}$

Question: Is there a formula to find a rational number between $x$ (where $x$ is rational and  $x^2>2$) and $\sqrt{2}$? I'm not looking for an existence proof, but a formula that can give the result.
Answer: Let $x$ be a positive rational with $x^2>2$. Then $(2/x)^2<2$ and the
average $y=(1/2)(x+2/x)$ of $x$ and $2/x$ should be nearer $\sqrt2$ than
either. By AM/GM actually $y>\sqrt2$. As $2/x<x$ then $y<x$ too.
Answer: Take $n\in\mathbb N$ such that $\left(x-\frac1n\right)^2>2$. Such a $n$ exists, since$$\left(x-\frac1n\right)^2>2\iff x^2-\frac2n+\frac1{n^2}>2\iff x^2-2>\frac2n-\frac1{n^2}.$$Then, take the number $x-\frac1n$.
Answer: just take $x-f(x)$ where $f:(\sqrt{2},\infty)\rightarrow \mathbb R$ is a function that is small  and always rational if $x$ is rational.
How small? Smaller than $(x-\sqrt{2})$
We propose $f(x)=\frac{(-(x-\sqrt2)(x+\sqrt2))}{(x+2)\times(\text{favorite big number that makes us confident)}}$


Push changes from Eclipse PDT to production server with EGit (FTP like)

Question: I'm totally new to Git, so I figured I'll have more luck with EGit since I'm using Eclipse PDT. I'm the only programmer on the project. Here's what I'm doing right now:

I have two identical copies of website on my local machine and server
I'm making changes to the local version, testing, debugging etc.
When I'm satisfied with the code, I open FileZilla and upload each and every file I have changed

What I would like to do is:
...
3. Commit changes
4. Push changed files (those I have dragged to Staged Changes) to the production server
So, this looks like very simple request. I don't want Git installed on the server, .git folder on the server etc. I just want to push new and changed files to the server, overriding those that are already on the server. I suppose this is possible, because when I right click the project and go to Team > Remote > Push..., there is a sftp option for the Protocol.
How can I achieve this? What would the input on the form I've mentioned (Team > Remote > Push...) look like? Or am I wrong, and I must install Git on the server?
Can EGit be used as SFTP client?
My only knowledge of Git is from this tutorial: http://www.vogella.com/articles/EGit/article.html. I've searched StackOverflow, but every topic is way to "Git specific" and way beyond my knowledge, so I don't understand most of it.
Thanks in advance.
Answer: I'm not sure if it will work but maybe you can use export feature (File->export->Remote System->Remote file system). I think to use this feature you have to install RSE (Remote System Explorer). This should export clean project, without .git folder.
Answer: The sftp protocol you see is just a protocol for git to connect to another computer having a git repository. So no luck for that.
You cannot achieve that workflow with only a git command. When creating a git server, called a bare repository, the layout on the filesystem does not reflect the files of your project but git's internals.
So when you push your changes to the bare repository, you indeed send the files to the it but in order to "see" those files, you need to clone it.
The easiest way to do step 3 would be to create a script to upload your files using ftp, instead of doing the procedure manually. So no git bare repository on the server is needed.
There are also other nice workflows involving installing git on the server FYI.


What is the line here?

Question:
A game I just played at chess.com, in the analysis, it was a missed win at a point. My mind is saturated right now, and I can't think of the line. Can you help me out?
Answer: The obvious tactic is
1) ... a6 2) Na3 Nxd4 3) cxN Qxd4 4) QxQ BxQ and you are forking the two rooks on a1 and g1
Disclaimer: I haven't checked this with an engine but it would be my first thought during the game. The engine may find a hole in this
Answer: First, a6 to kick that knight away.  Assuming they don't want to lose it, it has to go to the horrible square a3.
Second, Qxf3.  It takes a pawn, puts more pressure on the pinned e2 knight, and also threatens c3 now that the b5 knight is gone.
After that, it really depends how they reply, but you're certainly winning.  They're down a pawn, they're poorly developed, their king is in the center (which is partially open), and their knight is pinned.  Perhaps one plan would be to double the rooks on the e-file to exploit the pin.
Comment: I don't see how this makes the difference between -0.46 and -3.06. I think it's the tactic mentioned by Brian Towers.
Answer: I believe that the missed win text refers to the score going strongly in your opponents favour after that move. I have noticed it in my own analysis after a blunder and since I have premium, i recall the line shown not resulting in a mate but just a maintained advantage which i had blundered.

What is the line here?


'Whether or not' VS 'whether'

Question:
He wants to know whether we want dinner.
He wants to know whether or not we want dinner.

What is the difference between two sentences above?
Answer: There's no grammatical difference or difference in meaning: the "or not" is just an informal addition to the sentence, often seen in colloquial and informal language.
It's similar to the "at" added to the end of "Where's the dog at?" - it's not necessary and the entire meaning could be conveyed with a simpler "Where's the dog?"
In both examples, the question is "Do you want dinner, or not?". The word "whether" incorporates the "or not", but sometimes people choose to be more explicit. Over time, it just becomes part of the language, and is more of a turn of phrase than a grammatical necessity.
You could, perhaps, assign a slight semantic difference in meaning. For the purposes of this example I'll simplify the scenario to a "One person asking another", but it applies to your example too.
The sentence

Do you want dinner?

Is more likely to be seen as an open-ended "Do you want to eat?", eg "Should we make dinner?" or while

Do you want dinner, or not?

Is more akin to "I've made some dinner, do you want some of it?"
That's very minor and certainly isn't a grammatical rule, it's just a difference in the context they are most likely to be used. This is also likely to be dependant on your locale: in some areas this difference is more pronounced, in others the two would have identical meanings
Answer: He wants to know [whether (or not) we want dinner].
The inclusion of "or not" is entirely optional here, though one might say that it's redundant.
The bracketed expression is a subordinate interrogative clause (embedded question) functioning as complement of "know".
The meaning can be glossed as "He wants to know the answer to the question 'Do we want dinner (or not)?'"
Answer: Semantically, there is no difference. There is a difference in how they tend to be used, I believe, though I suspect it is dialect-dependent.
In my experience (native British English speaker), we would tend to use the first when it's simply an offer. The second is used when there's a possible expectation that dinner will be provided. Depending on tone and context, it might be that everyone knew he would be feeding you and something has happened that calls it into question. It might also be used if you're going to be spending the evening at someone's home and it unclear if good manners mean they should be expected to provide dinner.
The second would also be used, as in many "whether ... or not" cases, when someone is impatient for an answer.

‘Whether or not’ VS ‘whether’


Upgrade PostgreSQL 9.1 to 9.3 and server no longer starts

Question: Technically, I didn't upgrade from 9.1 to 9.3, I built a new server with Ubuntu 14.04 and used my old 9.1 config files. PostgreSQL wouldn't start:
* Starting PostgreSQL 9.3 database server
* The PostgreSQL server failed to start. Please check the log output.

but the logs were empty.
Eventually, after comparing the stock 9.3 postgresql.conf file and my 9.1 file I figured out that, at some point, the config variable unix_socket_directory had been changed to unix_socket_directories (not that easy to pick up in a diff with many changes and comments after each line).
Posted because I couldn't find anything on the net about this (until after I already knew what the issue was).
Answer: The config variable unix_socket_directory has been changed to unix_socket_directories in 9.3 - found in postgresql.conf


Notification of media inserted to DVD tray in FreeBSD

Question: I would like to create a script that automatically copy the dvd to a folder in my FreeBSD box (copy back DVD archives).
I would need a notification from the system when the DVD tray has been closed. I haven't found any start point which subsystem should provide this. I was look for hal, but I can't see how can it help me.
Answer: Take a look at the sysutils/automount port.
It's config file has a parameter FM where you could launch your script.


Assumptions of the Ordered Probit model

Question: What are the assumptions of an ordered probit model that must be met?
What are the tests to check these?
Answer: There are some distributional assumptions about the error, but these cannot be tested in a formal way (as far as I know).
There is also a parallel regression assumption, which is frequently violated. Long and Freese's categorical dependent variables book describes an approximate LR and a Wald (aka Brant) test (and provides Stata code).
Answer: The error term needs to be normally distributed to justify the ML estimation of the model. This assumption can be tested using the LM test developed by Johnson (1996) "A Test of the Normality Assumption in the Ordered Probit Model," Metron, LIV, 213-221. The issue is further discussed by Giles at  https://davegiles.blogspot.com/2015/06/specification-testing-in-ordered-probit.html.

Assumptions of the Ordered Probit model


PyQt app looks different when run via sudo

Question: I have a PyQt4 application that looks really nice when run as a normal user (on Ubuntu 12.04). But this application needs root access to bind to TCP ports below 1024, so I'm using this trick ( https://stackoverflow.com/a/5222710/95083 ) to relaunch as root if necessary.
However, when my application is run now, it looks horrible. I'm not sure what is making it look that way.
Answer: Try gksu/gksudo instead of sudo (Ubuntu help - about graphical sudo)


What is this effect called and How Do I create this?

Question: The part where the human is shown. I have the original image in color and want to convert it into the red effect. What is the effect called and what technique is used.
Comment: Please try to describe the effect in the title or at least the body of the question. Otherwise, it will be useless for anyone else in the future, cause it wont be searchable.
Comment: Thats why I said "describe" not "name" :)
Comment: I do understand that, but if you read the question carefully I am not very much aware of what the effect is called.
Answer: The image you have attached was not created using an effect - this is actually a well-executed vector illustration. You may achieve similar look in Photoshop but the outcome will be nowhere near the provided illustration in terms of quality.

Create a new layer above your original photo, fill it with the color you wish (red in your case), and set the blending mode of this layer to Screen.
Select a layer with your photo, choose Image > Adjustments > Threshold and drag the threshold slider until you achieve a satisfactory result.
Comment: If we were to do it in Illustrator, how should we proceed. Though the method shown by you is also satisfactory
Comment: This method of colorizing in Photoshop (Step 1) is applicable to any b/w image (just paste your vector illustration below the red layer instead of photo). If you want to do it completely in Illustrator, you may follow the steps suggested by @Yisela (works in Illustrator as well, just substitute *layers* with *objects*) and then just draw a large red rectangle underneath your vector work.
Answer: For a more detail result, you would have to redraw the image. You can do it in Photoshop, but it'd be much easier in Illustrator.
Steps in Photoshop:

Open the original image and duplicate the background layer,
Hide the original one, and bring the new duplicated one to 30% opacity or so (at this stage you can play with your adjustments to bring more contraste to the image. This will make the next step easier),
Create a new blank layer on top of you image,
Using the Pen Tool, draw the darker parts of the image.

The process will kind of look like this, excuse my poor execution, but hopefully the idea is clear!:


Mountain Pass theorem for minimization problems with constraints

Question: Let $I[u]$ be a functional on a (possibly infinite dimensional) Hilbert space. Then, under some conditions, the Mountain Pass theorem guarantees the existence of a saddle point (see http://en.wikipedia.org/wiki/Mountain_pass_theorem for the precise statement of the theorem). I wonder if there is a generalization of this theorem for minimization problems with constraints.
Comment: There are generalisations of the theorem: see for example references [17] and [24] in master's thesis of Eero Ruosteenoja: https://jyx.jyu.fi/dspace/handle/123456789/41049
Comment: Linking theorem might be useful. The aforementioned references should contain relevant material.
Comment: Mountain pass theorem finds saddle points. What are you precisely looking, a minimum of the functional or a saddle point?
Comment: Roughly speaking, consider a constrained minimization problem with two distinct minimizers. Can we generalize the mountain pass theorem to find a third critical point (a saddle point) for the constrained problem?
Answer: You can generalize the mountain pass theorem if the constraints consist of a Banach manifold.
This is because you can construct a pseudo gradient flow on a Banach manifold, which is required in the proof of the theorem.
Check Chapter 27 of 'Nonlinear Functional Analysis' by K. Deimling.
For example, in the paper 'Standing waves of some coupled nonlinear Schroedinger equations' by A. Ambrosetti and E. Colorado (2007), the authors used the mountain pass theorem on a Nehari manifold.


Rpi zero w is not recognized as com port

Question: When I connect my Rpi zero w to my PC (windows 10 via usb cable, I cannot see it under com port devices of PC. I am connecting micro usb side to the socket labeled as USB on Rpi. I want to establish a serial communication between my PC (windows 10) and Rpi. Is not this such a normal thing that should work? What is wrong?
Comment: What have you done on the software side?  Bare minis to add something like modules-load=dwc2,g_serial into command line...
Comment: @Andrew from raspi-config I enabled serial interface, other than that, I have not modified anything. I can ssh into it by the way. I wonder why my w10 pc does not even see/list rpi under com ports when it is connected via usb.
Answer: The default serial port on the Pi is presented on the GPIO pins BCM 14 and 15 not over usb.
To create a serial port over USB you have to:

Set up the Pi operating system first on the SD card
When booted enable serial gadget mode on the Pi
Reboot the Pi

To enable gadget mode issue the following from the Pi command line:
<code>echo dtoverlay=dwc2 | sudo tee -a /boot/config.txt
echo 'dwc2' | sudo tee -a /etc/modules
echo 'g_serial' | sudo tee -a /etc/modules
</code>
After the rebootyou will have a device /dev/ttyGS0 that is the USB port.
Comment: Thank you for your answer, I will try these. However I am confused for one thing, I could make raspberry pi communicate with another microcontroller through that usb connection port. Rpi sees a device attached at /dev/ttyACM0 and I could use screen command to establish the connection. Is it normal to be able to do that with the microcontroller but not with the pc?
Comment: it worked... though I have not completely understand the reason why I could use the serial port to communicate with a mcu before doing your suggested settings but not with pc.
Comment: "understand the reason why" - because USB OTG
Comment: Controllers are configured to act as serial ports (normally in firmware on the chip) and have to be told how to act as a USB port in software.  The zero range is a Linux computer and brings full USB support from boot and has to be told its a serial port, Ethernet network etc.  To see more capabilities see https://gist.github.com/SeanMollet/67e2d3c7f49cdfee9c57542693e172f6  BUT note the os discussed is out of date


What is the definition of Data Scout?

Question: I am looking for a definition of Data Scout.
what is the difference between Data Mining and Data Scout?
Comment: Never seen that term before. Do you have any citations that use it?
Answer: Copying from the abstract I found here - read the paper for more insights:

In the year 2011, the CMS collaboration introduced the novel concept
of data scouting, allowing to take data that otherwise would be
rejected by the usual trigger filters. This special data flow, based
on event-size reduction, was created to maintain sensitivity to new
light resonances decaying to jets or muons, with very small online and
offline resources allocated to it. The challenges implied by this new
workflow and the solutions developed within the CMS experiment are
shown. This technique is now a standard ingredient for CMS data-taking
strategy. The present status of data scouting in CMS is presented.

I do not come from a Physics background, and hence I could not completely understand the context while reading the paper in the larger scheme of things. But atleast this gives you a heads up about what it is.
Coming to Data Mining, there are plenty of definitions you can find. My definition would be using raw data to find patterns or insights from large datasets. This could be done with the use of many algorithms from math, computer science or statistics.
Some data mining algorithms are k-nearestneighbor, k-means, naive bayes, and so on.
So what is the difference between data scouting and mining? In mining, you consider raw datasets and perform some operations. In scouting, if I am not wrong, you take the data discarded by some filters (do not know what these filters are) while performing some operation, and then considering that data to perform additional operations.
Answer: In business, there is little time to look through the data that has been eliminated before a specific analysis project so I put that data in an elim_bin (project code#, project date) I ALWAYS attach data source & date pulled for each eliminated.
Later, I can "scout" that data with an algorithm to see if something could be useful/learned.
This is how I use "scout" data. Hope this helps.

What is the definition of Data Scout?


can vs could in an informal request

Question: Could anyone help me with can vs could in a request? I know 'can' is used in an informal way 'Hi bro, can I use your pen?' and 'could' in a formal way 'Excuse me, could I use your pen please?' But when a mother asks her son to turn down the music, it is an informal setting but 'can' doesn't seem right and 'could' does 'Could you turn down the music, I'm on the phone.' Thank you in advance. I couldn't find this specific request in previous tags.
Answer: Could is considered more polite than can when making a request. But IMO, in most cases, the politeness of the request has more to do with tone than actual wording.  If you sound hot and bothered when using could, your request will sound impolite regardless.
There's nothing wrong with using either in the family context you described.
Comment: Thank you for this. As I am not a native speaker, I sometimes find it difficult to make a distinction between two almost similar words. And as you pointed out correctly, the tone of voice can be important as well!

can vs could in an informal request


What's the adjective used to qualify a software that's available on your first boot?

Question: What's the adjective used to qualify a software that's available on your first boot? By that, I mean a software that's available on a machine as soon as you boot the system. Is there an adjective for it? There has to be some word for it, because they are annoying and people uninstall them often whether on smartphone or their PC.
Answer: "Pre-installed software", or "bundled software" (because it comes in a "bundle" with  the operating system)
But you don't mean "available on boot", you mean "available from when you purchase the computer".  Booting is the process of starting up the computer. You boot the computer many many times. Every time you turn off the computer you need to boot it when you start it again.
Answer: I think you mean something different by 'boot' than I would assume; for me, booting refers to every time you start the system, whether you just purchased the device or whether it's already a few years old.
Such software is called pre-installed software, bundled software, or if you want a term with negative connotations, bloatware.

Pre-installed software (also known as bundled software) is software already installed and licensed on a computer or smartphone bought from an original equipment manufacturer (OEM).

(source: Wikipedia)


How to eliminate parallel 5ths with chordal skips

Question: This is kind of the opposite of my other question Can 16th notes cause parallel octaves?. If chordal skips are able to cause parallel intervals then surely they are able to eliminate them as well. In fact I know this is true because it is written in my textbooks but I'm not sure to which extent it is true. In this example I've written a descending 5th sequence and there are blatant consecutive parallel 5ths on every beat but I have used chordal skips to remove them. Would this be acceptable voice leading?
Answer: This would be hidden parallels. While these are acceptable to some extend you should try to avoid overusing this. This will still have a bit of the character of parallel fifths and will sound quite blunt and unelegant (even if it was considered acceptable by some theories).
Comment: ok so what you are saying is that it doesnt break any voice leading rules it just sounds bad?
Comment: @armani It sounds bad if you do it to frequently. Generally one should be careful with having "parallels" over prominent beats, because you will easily get the same character as actual parallels (like two voices being in fifths on each 1 and 3).