Time and distance in a photon's frame of reference

Disclaimer, not a physicist. When I look at the sky I can see the star Rho Cassiopeiae. In my frame of reference, the photon hitting my retina has traveled for 4000 years and 3.78x10^16 km. In the photon's frame of reference, there's no time elapsed and my retina and the surface of the star are at the same place (no distance traveled). Is that a correct understanding of time dilatation and space compression at relativistic speed?


Ok so first off a bit of background. I've been working professionally three years in a software engineer position after my BSc. in Mathematics and Physics. At some point I realized I missed doing true research so I enrolled in Masters in Financial Mathematics, which seemed to me the ideal trade off between maths, programming and well finance which is quite interesting.  So now, here I am, first year, with full time lectures. My first reaction was to be disappointed by the amount of team work, since in my BSc days all homeworks were individually graded. For some mathematics courses it's fine, since there's a single good answer. However, there are some instances where it's definitely more research-like, almost like a lab report actually.   What however is unnerving is that I'm stuck with teammates with whom I don't exactly share the same work ethic. For instance, I had to insist on writing formal proofs. Anyway, I just feel that if it wasn't for me we'd keep to the bare minimum. AFAIK this is quite different from the industry where, if a team screws up, then either someone is going to get fired or at least the team is going to be split by the management. Here, the prof just won't care and will assign a global grade and go on to the next team.   So I'm not sure what's the right path. On one side, I really want to make sure our team performs well, this is quite a big move I made here, but on the other side, I just don't want be bossy with them, yet here I am writing emails where I detail clearly what I'm awaiting from each of us. Also, well, I haven't talked openly with them about this issue, I'm not certain how I can bring it.


Create a Python list with multiple instances of a data class

I'm new to Python, and need to create a list with multiple instances of a data class.  I tried using list multiplication to do this, because I figured it would be faster since I'd have to 'append' thousands of individual instances of my data class.  However, my list multiplication seems to create objects that all reference the same instance of my data class, rather than to multiple independent instances of my data class. Here's the simple example that I tried: class Test:                 # define data class "Test".    def __init__(self, a):       self.a = a  test = Test(1)              # define an instance of data class "Test".  tests = [test] * 2          # define a list called "tests", with 2 instances of "test". print(tests[0].a)           # both instances of 'a' in the list show that "a = 1". print(tests[1].a)  tests[0].a = 2              # change the first instance of 'a' in the list to "a = 2". print(tests[0].a)           # first instance of 'a' properly changed to "a = 2". print(tests[1].a)           # but, the second instance of 'tests.a' ALSO changed from 1 to 2!  I had expected that changing one instance in the list wouldn't affect the other instance, but it looks like what I actually have is multiple copes of the same instance.  So, how can I create a list with multiple, independent instances of my data class "Test"?


This is my code  \begin{enumerate}[(i)] \item  $\frac{1}{2}$  \text{VS}  \displaystyle \frac{1}{2}\\ \item $\sum_{k=0}^{n} f(k)$ \text{ VS }  \displaystyle \sum_{k=0}^{n} f(k) \\  \item  $\int_{1}^{2} f(x)dx$ \text{ VS } \displaystyle \int_{1}^{2} f(x)dx  \end{enumerate}   And it ends up like this   How can I fix it?


Be $S^1$ the unit circle in the plane, that is, $S^1=  \lbrace (x,y)  : x^2+y^2=1 \rbrace$ with the subspace topology. Show that $S^1 - \lbrace (1,0)\rbrace$ is homeomorphic to the open interval $(0,1)$.  I have an idea. Using this theorem:  Let $f:(X, \tau_1) \rightarrow (Y, \tau_2)$ be a homeomorphism. Let $a \in X$, so that $X - \lbrace a \rbrace$ is a subspace of $X$ and has induced topology $\tau_3$. Also, $Y-\lbrace f(a)\rbrace$ is subspace of $Y$ and has induced topology $\tau_4$. Then $(X - \lbrace a \rbrace, \tau_3)$ is homeomorphic to $(Y-\lbrace f(a)\rbrace, \tau_4)$. (Morris, "Topology without tears", remark 4.3.6)  My idea is to make $X=S^1$ and $Y=(0,1) \cup ?$ so, with the respective topologies using the theorem, $S^1-\lbrace (1,0)\rbrace$ is homeomorphic to $(0,1)$.  But I'm stuck in the part of defining $Y$ and find the homeomorphism $f$ between $X$ and $Y$.  PD. Sorry about my English, but it is not my native language.


Multi Armed Bandit and Price Optimization

I obtained a model fit: Sales = 1020 -8.8*Price +2.1*online reputation  after substituting the value of online reputation, I came out with following demand equation: 1036.8-8.8*Price Now to take out the revenue (sales*Price) I converted it to revenue function: 1036.8*Price - 8.8*Price^2  Now can I implement MAB for finding the price in order to maximize the revenue


In C, I know that int main() returns an int where void main() does not. Other than that, is there a difference between them? Is the first better than the second?


Verify XPath is valid with developer tools in Internet Explorer 8

I'm writing Selenium tests, and I need to support Internet Explorer 8.  I want to use Developer Tools in Internet Explorer 8 to verify that Internet Explorer 8 can find certain elements by their XPath expressions. I can do this easily using Chrome of Firebug with Firefox, but I can't figure out how to do it with IE Developer Tools -- it feels very clunky, foreign, and unintuitive for someone coming from Chrome and and Firebug with Firefox.  I'm not trying to get an element's XPath expression with Developer Tools. (The web has plenty of links for how to do that.) I'm trying to verify that XPath expressions which I already have will work in Internet Explorer 8 using Developer Tools.  If I want to verify that an XPath expression finds an element in Chrome, I would:   Navigate to the page I want to verify Press F12 to bring up Chrome debugger Press Ctrl + F to bring up find Type or paste in the XPath expression that I want to test See if the XPath expression found an element.   Here is an image of what it looks like in Chrome:    I would like to do the same thing in Internet Explorer 8. How can I do this?  I have seen  which tries to get the XPath expression from the webelement. I'm trying to do the opposite: get the webelement from the XPath expression to verify the XPath expression is valid in Internet Explorer 8.


Wave-particle duality seems like an obvious example of a contradiction that people refuse to accept. What am I missing?

We state that electrons are subatomic particles with no known subcomponents. We discover that these electrons behave as waves. We also discover that sometimes, these electrons behave as point-particles. We conclude that they're the both at the same time. This, to me, sounds nonsensical. If this happened in math, and one discovered that 1 = 2, one would not go around saying that we have one-two duality, would we? No, we would question the axioms that we used to perform our calculations. If one-two duality is an outcome of those axioms, we should not accept one-two duality, rather we should reject the axioms! Yet, in physics, this does not seem to be the case. Why? Why is wave-particle duality accepted, rather than the axioms rejected? And what are the axioms in this case? Well, it's the first line in this question. We assumed electrons have no known subcomponents. Well, clearly our experimens show we're wrong. They do have subcomponents, and when the wave-like behavior of electrons occurs, it occurs precisely because of interactions between those subcomponents that we are not familiar with and therefore cannot understand. So what am I missing? It seems like physicists have accepted this bizarre notion of wave-particle duality that even Einstein thought was an embarrassment of physics,  rather than consider that some premises may be wrong and it is those wrong premises that lead to the wave-particle duality.


How do I tell my daughter the only dad she's ever known, isn't her biological dad?

I had my oldest daughter very young,  with a man that chose to not be involved at the time (Who now has two more children by two different woman)  we split up when my oldest daughter was about 1. Not to long after,  I met my current spouse who I have been with for years now.  He has been by my side,  and being a dad to her since as long as she can remember. ( she is now four and has become very curious) We have since had my second daughter (who is now 2). Since she was born she ofcourse called him dad,  and although I never suggested it my oldest begun to call him dad as well.  He is the only dad she's ever known.    Anyways,  recently her biological dad has been trying to reach out,  (he has never called or made an effort since the break up) and I don't know how to bring it up to her.  She's four,  and is an amazing,  happy kid,  and although she's smart I don't want to hurt her.  But I also don't want to keep her from her real dad and later in life have her spiral out if control because if it.  How do I bring this up and explain it?  Should I at all?  Has anyone else ever had experiences with it?  I am totally lost,  and just want to save my daughter from dissapointment.


Through The Witcher 3 is it possible at some point of the game to reset my skill tree; in case I made a mistake or want to re-spec? If there is please answer with no spoiler about how to obtain this if spoilers are evident to know, just answer saying yes/no and how far into the story.


Is this set dense on the positive half of the real line?

We know a positive rational number can be uniquely written as $m/n$ where $m$ and $n$ are coprime positive integers. Particularly, we can pick out those numbers with $m$ and $n$ both prime.  The question is, is the collection of all such numbers dense on the positive half of the real line?


A word that describes a person who has to fight against a more powerful opponent on a regular basis?

I'm looking for a word that describes a person who has to fight against a powerful opponent on a regular basis. This does not involve a competition, like some kind of sport.  Example :   Lawyers willing to take on powerful companies are hard to find, however James from the law firm  Crane & Schmidt, regularly lock horns against major companies.  So in the above example what would someone like James be called, who has to regularly fight against companies/entities that are much more powerful than him?


Is a character on a motorcycle-like vehicle considered "mounted"? What about a larger vehicle?

Does a character using a Devil's Ride, the motorcycle-like vehicle from BG:DiA, count as "mounted" for the purposes of using a lance or the Mounted Combatant feat? If so, what about a larger vehicle; would a character be able to hang off the side of a Scavenger with his lance, or poke it from the gunwale of a galleon? Must a character be mounted astride a creature, RAW? A creature a size larger than its rider and with the proper anatomy "can" serve as a mount, but are mounts exclusively creatures? How is "mounted" defined in 5e terminology, as it is not a condition?


What's the difference between the following sentences?      (a) I wish they wouldn't make so much noise.   (b) I wish they were not making so much noise.    (c) I wish they did not make so much noise.   I'd appreciate your help.


I'm studying for a test in quantum mechanics and I'm having a hard time understanding how to use . There are no examples in my text book, only definitions that I can't understand how to use, so I hope you can help me instead.  So, there's an assignment where you're supposed to calculate first order correction to the ground state using ladder operators. In the right answer they say that  $$E_0^1 = \langle 0|H'|0\rangle$$  where does the zeros come from? I understand that they're coming from the wave function $\psi$. But I don't really understand the theory behind this.  Then, after some calculations it's written in the right answer  $$ \langle 0|aa^\dagger a^\dagger|0\rangle +\langle0|aaa^\dagger a^\dagger|0\rangle =\langle0|aa^\dagger a|1\rangle +\langle0|aaa^\dagger|1\rangle$$  What are the mathematical rules of these ladder operators? How did these zeros become ones?  I would really appreciate if someone could help me understand this a little bit better.


difference between `for i in {1..$N}` and `for i in $(seq 1 1 $N) `

I have the following in a script:  #!/usr/bin/env bash  ... for i in {1..$N}    <loop content>   The above doesn't work and is only executed once where i has the value {1..5}  (if 5 was provided as argument).  If I replace the above with:  for i in $(seq 1 1 $N)   .. then things work as expected. Why is that?


Visually impaired friend wants to try Ubuntu

I've got a friend who is using Windows 7 and I "sold" him the benefits of open source, and he actually wants to try Ubuntu 16.04 LTS (that's the good news)! The bad news are: he is visually impaired and he has some problems with his hands/fingers.  Are there some packages that can help visually impaired people?   Like a zoom shortcuts with his mouse … I don't know … And also packages that can write with voices? He uses accessibility stuff in his phone doing that, so it might be good on his PC as well.


How can I change the MAC adress in Android 2.2. HTC desire wifi mac address?


I'm confused with the terminology. What is the difference between shell, console, and terminal?


Proper way to use LaTeX fonts in XeLaTeX

What is the proper way to use LaTeX fonts, for example calligra or other fonts from the  in XeLaTeX.   Something like   \usepackage{fontspec} \setromanfont{Calligra}   doesn't work. However using it just like in pdflatex via  \usepackage{calligra} and \calligra works. So what's the best way to use LaTeX fonts from the Fonts Catalogue in XeLaTeX?


Make left-hand pages' `\marginpar` text right-aligned

\marginpars only appear on the right margins of right-hand pages of my manuscript. For left-hand pages, they are are so far to the left that they aren't even on the page.  The reason is because the text of \marginpars are left-aligned.  How do I make the \marginpars of left-hand pages right-aligned so they are next to the body text?  \documentclass{svmono}  \usepackage[paperwidth=15.5cm, paperheight=23.5cm]{geometry}  \begin{document}  Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in \marginpar{[245]} reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.  Another page: Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum. \marginpar{[246]}  \end{document}


I am a non-UK & non-EU citizen. I am travelling on the Eurostar from London to Paris. I have a UK visa & a Schengen visa issued from Switzerland, not France.  Would the UK immigration in London allow me to board the Eurostar to Paris if my Schengen visa first entry is France, not Switzerland?


In the Thor movies, why can only Thor lift his hammer?

In the Thor movies we have seen that only Thor can lift up his hammer Mjolnir. In The Avengers/Avengers Assemble The Hulk attempts to pick it up on the Helicarrier and cannot even move it.  What is the scientific reason behind the fact that only Thor can lift his hammer and not others?


Is deleting a down-voted answer to preserve my reputation points bad?

Let's say I'm trying to answer a lot of questions just to up my reputation (even if I generally don't know what I'm talking about).  Then, whenever I get downvoted, I just delete my answer so that nobody sees that I've posted stupid answers, and so I don't lose reputation points.   Is this frowned upon? Do I lose reputation points on downvoted answers if I delete them?


Did Spock warn of disasters in the new Star Trek universe?

Did Spock Classic (in the new timeline universe) warn NuSpock of upcoming natural disasters? i.e. V'ger, the whale probe, Praxis and explosion, the Borg, violent first contacts, the wave from Generations, etc?


Proving inequality with fractions using induction

I'm trying to prove the inequality below using induction: $\dfrac{2^{2n}}{n+1} < \dfrac{(2n)!}{(n!)^2} \,\, (n > 1)$ The base case is ok, but I'm not able to see how I can proceed in the induction step. I'm reaching a dead end, either multiplying by 2 or adding $\dfrac {1} {k + 1}$ to both sides of the inequality. Any tips?


Problem books like I.E. Irodov for advanced physics

I really enjoyed doing problems from Irodov while learning introductory physics. But I am not able to find a book like that for Graduate level physics. Can you suggest me a book which has good (and hard) problems from advanced topics like Quantum Theory, QFT, Relativity, etc?


Would upgrading to a full frame Camera be worthwhile with just one lens?

I'm in the Canon system. Would you buy an entry level full frame camera like 6D II having only one FF lens (50 1.8 prime)?   I don't have money to buy both the body and the lens at the same time, but later on I'd like to get the wide angle EF L 16-35 f4. Apart from portraits, I shoot mainly architecture and landscapes for microstock sites, so in the long term they will pay for themselves to some degree. Just one prime lens is limiting, but I thought that buying a FF body now would "commit" me to high image quality photography, and next year I would buy that wide angle lens to really switch to full frame. I know FF is not a solution for every problem with image quality, but 6D II pictures are just crisper, sharper etc. not to mention low light photography. As I said I sell pictures on stock sites, so this expense will be partly covered by royalties.   Another possibility is to wait another year for the EOS R price to come down and then invest in the future-proof RF system, especially since I could then use my EF-S lenses.


Iterating over an array or a list that has no element, foreach seems very slow compared to for. Running below code, the result I got is:  3ms  143ms  7ms  Is foreach really slow or am I doing something wrong?   var l = new List<int>(); var watch = new Stopwatch(); var test = 0;  watch.Start(); for (int i = 0; i < 10000000; i++)      if (l.Count > 0)          test = 1; watch.Stop(); Debug.Log(watch.ElapsedMilliseconds);  watch.Reset(); watch.Start(); for (int i = 0; i < 10000000; i++)      foreach (var item in l)          test = 1; watch.Stop(); Debug.Log(watch.ElapsedMilliseconds);  watch.Reset(); watch.Start(); for (int i = 0; i < 10000000; i++)      for (int j = 0; j < l.Count; j++)          test = 1; watch.Stop(); Debug.Log(watch.ElapsedMilliseconds);


Calculating the limit of $\sqrt[n]{n!}$ as $n \rightarrow \infty$

Some may consider this a duplicate, but the only similar question I have found make use of Stirling's identity and then conclude the result. I would like to try and avoid this and so would like a more elementary approach of solving the problem.   This is my progress so far:  I think the following is true (and the limit I'm trying to calculate would follow immediately):     For every $k\in\mathbb{N}$, for sufficiently large $n$ we have $n! > k^{n}$    I'm not sure how to prove this result, but it would be equivalent to proving that     For sufficiently large $n$, $\sum_{i=1}^{n} \log_{k}i > n$ for any $k \in \mathbb{N}$.    Would somebody be able to provide a hint on how to proceed, and whether or not my method could be fruitful?


The existence of the empty set is an axiom of ZFC or not?

I found in the Wolfram MathWorld page of the  that this is one of the Zermelo-Fraenkel Axioms, however on the page about these  I read that it is an axiom that can be deduced from the Axiom of Subsets and the Axiom of Foundation (or Axiom of Regularity), so, the existence of the Empty Set is an axiom of ZFC or not?


How to make a bib entry appear also in the main document

I have a reference which has a bib entry and appears in the bibliography. I want to be able to include the entire entry, exactly as it appears in the bibliography, somewhere else in the document.   Is there any way to do that other than to manually write it and format it to look similar?


I'm using using algorithm2e package with the following settings:  \usepackage[ruled,vlined,linesnumbered,noresetcount]{algorithm2e}   But for some subset of algorithms in the same document, I want to use this setting:  \usepackage[boxed]{algorithm2e}   Is there a way to override the default setting just for a subset?  I found a similar question:  Here newenvironment is used to override the default setting of an option. But I want to override the option itself.  I wish there was a way to load a package several times with different options for each instance.


How do I delete photos from JUST my iPhone 6s when using iCloud Photo Library?

Whenever I got to delete a photo, it says "This photo will be deleted from iCloud Photo Library on all your devices." I don't want it deleted from my iCloud Photo Library, only my iPhone 6s. What I want to do is import photos and videos from my iPhone to my MacBook Pro and then delete them from my iPhone. If I import those photos and videos to my Mac and then delete them from my iPhone (ignoring the warning) will they also be deleted from my Mac?


How to make dark gray background on TIF image transparent or white in QGIS

see also:   That question addresses why the TIF imported into QGIS has a dark gray background when the color set is set to 4096 when exported from PDFCreator.   That file's gdalinfo shows NBITS=4  Here, in this question, I would like to know if there is a way to render the dark gray transparent, much in the way that entering a "0" in  properties->transparency->no data value->additional no data value will make the black lines transparent.  Alternatively, is there a way to have QGIS render the dark gray as white?


Algorithm for computing the plane that passes through three arbitrary points

I'm writing a computer graphics library, and I'd like to compute the plane that passes through three arbitrary points, $p$, $q$ and $r$. I'm defining the plane in the form of $Ax + By + Cz + D = 0$.  My algebra is rather rusty, but I suspect this is a job for some simultaneous equations I'll need to solve a system of equations:  $$0 = \begin{cases} Ax_p + By_p + Cz_p + D \\ Ax_q + By_q + Cz_q+ D \\ Ax_r + By_r + Cz_r + D \end{cases}$$  How would I efficiently find the values of $A$, $B$, $C$ and $D$ with respect to $p$, $q$ and $r$?


How to implement zoom in Preview screen of iOS app

My colleague developer and I cannot find how to implement double-tap or pinch-zoom in the Preview screen on iOS when 'from camera' image import option is used.  We are using standard camera to take a picture.  Once the round button is clicked, the next screen displays the taken picture and two options "Retake" and "Use Photo".  I would like to allow the user to double-tap or pinch-zoom on this screen. Current default behavior does not affect picture zoom in any way.  The screen looks like , but in the latest iOS7 UI.  Please advise if this is possible and what specifically do I need to do to enable zoom in this screen?  Thanks.


How to typeset asymmetrical confidence level limits / uncertainties?

Below is an example of an asymmetrical limit (or uncertainty)  How can I typeset this in a \LaTeX equation? Such pair of numbers should be vertically stacked while being vertically center-aligned with rest of the equation. Solution $X^{+Y}_{-Z}$


I've used TikZ Editor for some time to make my TikZ drawings. I've really appreciated the live-rendering features. Now, I'm wanting to make some graphics using the pst-optexp package, and I'm having a hard time finding an application that does what TikZ Editor does for pstricks. Theoretically, TikZ editor should do the trick... it allows me to change everything in the preamble, etc... except for allowing me to change the \begin{tikzpicture}.   Does anyone know of a way to:   Install software that allows live-reload of pspicture environment? Modify the code in TikZ Editor such that I can compile pspicture in this application?   For the record, I'm running OS X El Capitan. I'm thankful for the link to the other stack exchange question with a list of apps that people use for editing. However, most of those are either click-and-drag, or are for windows/linux. I'm not interested in a click-and-drag application. I'm more interested in something very similar to TikZ Editor. Is there any such editor that allows live preview of PSTricks on Mac?


Some user interfaces feature titles such as:   My documents My photos My previous orders   While others opt for:   Your documents Your photos Your previous orders   Are their any guidelines addressing which is more suitable to pick in different situations? Is one more preferable than the other?


Changing A Windows 10 Account Name With A Batch File

I've been looking around and can't find an answer to this. i want to change an account name with a batch file


How to avoid matching numeric string that has # at the beginning?

I'm using below regular expression to match numbers that includes decimals, negative numbers inside quotes ("). What changes should I be doing so that it does not match "#1200"?   \"(-?\d*.?\d+)\"  "1200"     ---> matches as expected "1200.67"  ---> matches as expected "-1200"    ---> matches as expected "-1200.67" ---> matches as expected "#1200"    ---> I'm not expecting this to match. As you can see It has # at the beginning.


How do I switch using my AirPods between my Mac and my iPhone?

I have AirPods that I often need to switch using between my Mac and my iPhone. I never do this during a conversation, but often I'll have used them on my phone for a phone call, and then need to use them on my Mac; or vice versa. Doing this involves multiple steps on both ends (whatever is required for an explicit BT connect) and even then, doesn't seem to "stick" until the APs disconnect and reconnect to the switched-to end several times (often interrupting whatever I've started doing there).  How is this supposed to work?    Note that I'm aware of  that this should be a seamless process. But it doesn't work that way for me, or any of the dozen or so other people I know in similar situations.


Is it ok to extend/straighten legs fully while pedaling and will it give me maximum power?

When I first got my bike, I had the saddle too low and I experienced some pain in my right knee while riding.  I seem to have "fixed" this problem by raising it some.  However, that got me thinking... what would happen if I raised it even more so that my legs would be straight (not bent at the knee) when the pedal was at the bottom?  Would this give me increased power?  Have power tests been done to verify what level of leg extension produces the most power?  Are there any problems allowing your leg to fully extend (straighten)?  I may try this sometime but wanted to get some info here first.  I asked someone at the local bikeshop and they told me there is a chance of hyperextending if I do that but I asked myself how if the position is fixed?  I think the general rule is to have a little bit of knee flex while the pedal is at the bottom but maybe that is a guideline and not a "hard" rule.   I wanted to add that I don't use any fancy riding shoes or any clips.  Just regular "street" shoes. Also, my typical longest ride in a single day is only about 10 miles max.  That translates into about a little over 1 hour at an average speed of less than 10 MPH.  Also, I am not sure why some people might say it is "bad" to straighten your leg totally when riding cuz when we walk we have alternating straight legs so why not the same when we ride a bike?  When we lift a heavy object off of the  floor, the hardest part is when our legs are bent the most, indicating that is the most inefficient position.  When our legs are nearly straight it is much easier for us to lift weight such as a heavy box that is already at waist height for us.


Which best practice for using gedit as root?

gksudo seeming to be somehow depreciated since 2017 as I see on the , is there an environment and version agnostic best practice allowing to use gedit as root?  (excluding vim, nano or tee: the use case being a GUI amendment of sources.list for instance)  My researchs brought me these proposals, are they equivalent or to be rejected :   pkexec env DISPLAY=$DISPLAY XAUTHORITY=$XAUTHORITY gedit gedit admin:///path/to/document sudo -i gedit sudo -H gedit   Any other ?


Who can edit "on hold" questions? My guess is users with more than 2K reputations and OP himself, is that correct?


How come 18.04 python3 package doesn't have latest security release?

The version of python3 in 18.04 is 3.6.9, missing out on the security issues fixed in 3.6.10 back in Dec 2019. I thought that since python3 is in main it would get all security updates for the life of the LTS? Am I wrong about that?


Can neutrinos really travel faster than the speed of light?

A few years ago scientists found that neutrinos were going faster than the speed of light. Then they found some problem with the calculations. I read an article that was made this year about faster than light neutrinos. I'm not sure if the journalist is ignorant or if they found that the neutrinos really were going faster.


Is there any way to show the number of selected vertices in Edit Mode?


How to find the prime factors of a number in Python?

I just started to open for myself programming in python. I know how to find factors for example of 30. I will get [1,2,3,5,6,10,15,30]. But I need this output 30 = 2 * 3 * 5. Thank you in advance!


Is there a web-based stock query service that allow me to look up for Stocks that match certain criteria?  E.g. I want to find ALL stocks that are on 52-week high, with an Avg-daily volume greater than 1 million, and that cost between 5 and 10.  Thank you.


Dual boot with Ubuntu 11.04, OpenSUSE 11.4 and/or Fedora 15 beta. Does the order matters?

I'm planning to have an Ubuntu 11.4 / OpenSUSE 11.4 or maybe an Ubuntu 11.4 / Fedora 15 beta dual boot (or the three of them).  Will they dual boot just after installation? or I have to install them in a certain order or do some special configuration?  (Right now I'm using Ubuntu 10.10)


how to export Bezier curves control points?

How does one export a file containing all the control points of the bezier surface in a Blender object?  Here is an image showing my work.  The .obj file I export unfortunately doesn't contain those.  I am pretty new to  blender. I don't know any python.  Blender 2.7


Why did Walt give up 1.5 million to work with Jesse?

In Breaking Bad, Walt had the opportunity to work with Gale and earn 3 million dollars. Instead he insisted on working with Jesse and split the money with him. He claimed it was because he didn't have chemistry with Gale but that seems like an unlikely excuse. What are the other reasons that Walt would give up 1.5 million in order to work with Jesse?


Looking at the truth table, they're equivalent:  A   B      (A+B)  (A+A'B) ------------------------------- 1   1       1       1 1   0       1       1 0   1       1       1 0   0       0       0   But what manipulation can one do using basic identifies and laws to show that they're the same?


I know it's probably due to some sort of rounding technique, but clearly 6.53 + 8 should only equal 14.53. My questions are, why is this happening, and how can I get an accurate sum?  var x = 6.53 + 8; console.log(x);// 14.530000000000001


How to get the result of difference between two date using php?

I have this php code  $today_date = date('d/m/Y H:i:s'); $Expierdate = '09/06/2017 21:45:03'; $remaindate = date_diff($today_date,$Expierdate);        echo $remaindate;   and i need result from difference between two date.


Driver for TP-Link Archer T2U for Kubuntu 20.04

Just realized the TP-Link Archer T2U (ID 148f:761a) I just bought does not plug and play on Kubuntu 20.04 Exact product is  The box specifically says linux support is for kernel 2.6-3.16 while Kubuntu 20.04 is far advanced with 5.4.x Is there some sort of solution that can be applied to make this dongle work on this old machine which currently does not have internet access so sudo apt-get ... is less comfortable. if I could only download a thingy/driver and put it on a thumb-drive and plug that thumb-drive into the kubuntu 20 machine and install that thingy/driver and things would work, that would be awesome.


Sed - replace with variable first occurrence only

I have a file app.spec with the string:  Version:  1.0.0   I want to replace 1.0.0 with the variable version e.g. 1.0.1.  The regex below which matches this but how can I replace only the first occurrence?  sed -i -E "s/[0-9]+\.[0-9]+\.[0-9]+/$version/" ./app.spec  I tried but it didn't work.  sed -i -E "0,/[0-9]+\.[0-9]+\.[0-9]+/$version/" ./app.spec


Is there a mathematical relationship between time and entropy?

If there is a relation between time and entropy, what is it? Are there limitations for this equation?  Or if there is no relationship between them, what is the current state of research?


Partial sum of the series $\sum\limits_{r=1}^{\infty} \frac{1}{r(r+1)}$

An  which I am not able to solve.  Let $\mathsf{S_{n}}$ denote the $n$-th partial sum of the series: $$\sum\limits_{r=1}^{\infty} \frac{1}{r(r+1)}$$  Prove that for every integer $k>1$, there exists integers $m$ and $n$, such that $$s_{m}-s_{n} =\frac{1}{k}$$


How to get maxium Levels for a Multidimensional array in PHP

I have a such array   <?php      array(          'CHILDRENS' =>  array(         array(              'CHILDRENS' =>  array(                 array(                      'CHILDRENS' =>  array(                         array(                              'CHILDRENS' =>  array(                             )                         )                     )                )            )         )     ),     array(          'CHILDRENS' =>  array(             array(                  'CHILDRENS' =>  array(                 )             )         )     ),     array(          'CHILDRENS' =>  array(             array(                  'CHILDRENS' =>  array(                     array(                          'CHILDRENS' =>  array(                             array(                                  'CHILDRENS' =>  array(                                     array(                                          'CHILDRENS' =>  array(                                             array(                                                  'CHILDRENS' =>  array(                                                     array(                                                          'CHILDRENS' =>  array(                                                         )                                                     )                                                 )                                             )                                         )                                     )                                 )                             )                         )                     )                 )             )         )     ) )   I would like to know how to get the maxium deep of this array.  I tried this :     and    It that last case, it return only first array depth  Thanks for help.


My bike's chain broke, so I have to replace it now. The question is - how can I tell what size chain do I need to buy so it fits the bike? It's a 5 gear internal-hub bike.


javascript prototype chain Object vs function Object

I probably did not make the title correctly but please someone explain why I can't create prototype for person object? Only works when I put hit to Object.prototype chain.  const person = {   isHuman: false,   printIntroduction: function () {     console.log(`My name is ${this.name}. Am I human? ${this.isHuman}`);   } };  //person.prototype.hit = function(){ //    console.log("hitting me"); //}  Object.prototype.hit = function(){     console.log("hitting me"); }  const me = Object.create(person);  me.name = "Matthew"; // "name" is a property set on "me", but not on "person" me.isHuman = true; // inherited properties can be overwritten  me.printIntroduction(); me.hit();   (UPDATE) . Why does THIS work?? Not sure what the differences are actually from this example but this code works.  function person {   isHuman: false,   printIntroduction: function () {     console.log(`My name is ${this.name}. Am I human? ${this.isHuman}`);   } }();  person.prototype.hit = function(){      console.log("hitting me"); }  /* person.prototype.hit = function(){     console.log("hitting me"); } */  Object.prototype.hit = function(){     console.log("hitting me"); }  const me = Object.create(person);  me.name = "Matthew"; // "name" is a property set on "me", but not on "person" me.isHuman = true; // inherited properties can be overwritten  me.printIntroduction(); me.hit(); // expected output: "My name is Matthew. Am I human? true"   update 2  Ok, so I make it work like below but clearly prototype doesn't work the way I expected.. so I am clearly confused about prototype  function person(){     console.log(`My name is ${this.name}. Am I human? ${this.isHuman}`); }  person.prototype.hit = function(){     console.log("hitting me1"); }  Object.prototype.hit = function(){     console.log("hitting me2"); }  const me = Object.create(person);  me.hit();   UPDATE 3.  thank you.. this is the explanation that I got from below.. thank you and this is clear now.  function person(){     console.log(`My name is ${this.name}. Am I human? ${this.isHuman}`); }  person.prototype.hit = function(){     console.log("hitting me1"); }  Object.prototype.hit = function(){     console.log("hitting me2"); }  //const me = Object.create(person); const me = new person;  me.hit();


Local homeomorphisms which are not covering map?

I am trying to find examples of maps between topological space which are local homeomorphism but not covering maps. Especially, how twisted has to be such a counterexample : can it be a local diffeomorphism between connected manifolds which is not a covering map ?   I found here() a nice proposition which state that a local homeo from a compact space to a connected Hausdorff space is a covering map.   I am interested in all type of counterexamples, from non-Hausdorff spaces to surfaces, to get a better picture of the differences between covering maps and local homeomorphisms.  Thank you !


how to create a kinetic energy kugelblitz in theory?

Black holes form when enough mass gets packed so close together that its gravity gets so strong that even light cannot escape it. Mass and energy are equivalent, so theoretically it is possible to create a black hole by bringing enough energy in a different form than mass together, for instance in the form of photons. This is called a .   Now, is it possible to create a kugelblitz by giving a small amount of mass enough kinetic energy? As far as I know, that should work, but I'm not a trained physicist. But that leads me to my second question: a particle's speed depends on the frame of reference that is used to describe it. A particle that is at rest in one frame of reference is traveling at relativistic speed in a different frame of reference. So, why does not all mass collapse into black holes? Or is there one frame of reference that is 'special' in this regard?


How do i get all classes within a package?


An interesting video:   But how is it possible for a metal tank to implode?  Even if one can vacuum it, it is subjected to 1 external atmospheric pressure maximum which is around 1 bar or 14.6 psi. How could 14.6 psi crush a metal tank?  Please correct me if I am wrong.


Is there a way to know the current (or average power consumption) on OS X (a Mac Mini without battery). Preferred would be a command line tool but anything is OK.


set on beamer,how to get same shade on footline?new to latex,watch out for greek characters

\documentclass{beamer}  \setbeamertemplate{navigation symbols}{}     \usepackage[utf8]{inputenc} \usepackage[english,greek]{babel}  \usepackage{alphabeta} \usepackage{multicol} \newcommand{\en}{\selectlanguage{english}} \newcommand{\gr}{\selectlanguage{greek}} \author{\textlatin{author}} \usepackage{array,amsmath} \usepackage{amsthm}  \definecolor{UniBlue}{RGB}{83,121,170} \definecolor{frame}{RGB}{2,0,0} \setbeamercolor*{frametitle}{fg=frame}   \useoutertheme{shadow} \usepackage{tikz} \usetikzlibrary{shadings} \colorlet{titleleft}{cyan!75!black} \colorlet{titleright}{UniBlue}  \makeatletter \pgfdeclarehorizontalshading[titleleft,titleright]{beamer@frametitleshade}{\paperheight}{%     color(0pt)=(titleleft);     color(\paperwidth)=(titleright)} \makeatother       \title{}  \begin{document}       \begin{frame}{\textlatin{frametitle}}  \end{frame}  \end{document}


Issue: I have a car that requires Win.XP Pro 32-bit OS to access and update the software.   Is it possible to install Win.XP Pro 32-bit OS on a MacBook Pro running Mojave 10.14.2?


Conflict of domain and endpoints in Noether's theorem and energy conservation

In the derivation of energy conservation, there is the transformation $q(t)\rightarrow q'(t)=q(t+\epsilon)$, whose end points are kind of fuzzy. The original path $q(t)$ is only defined from $t_1$ to $t_2$. If this transformation rule is imposed, $q'(t_2-\epsilon)=q(t_2)$ to $q'(t_2)=q(t_2+\epsilon)$ is not defined in the original path. Then how could the Lagrangian be integrated?  On P.98 of Jakob Schwichtenberg's book Physics from Symmetry, he stated that $\delta q(t_1)=\delta q(t_2)=0$ whereas Kleinert stated in his Particles and Quantum Fields $\delta q_s(t_a)$ and $\delta q_s(t_b)$ are not necessarily $0$. Who's correct?  This question is different from the endpoint questions since it is already clear that $q(t_2+\epsilon)\neq q(t_2)$.


I was just wondering, when you put a straw in water and block the top, water doesn't get out from the bottom when you lift it up.   What about alcohol like Vodka ( ethanol )? I am trying to make a straw such that when you block the top, the alcohol actually does get out from the bottom. I just have no clue what diameter, shape, or modifications I should make into the straw in order to achieve this.   As i know the surface tension of Ethanol is 22.1 mN/m


How to formally prove: if $d\mid da+b$, then $d\mid b$?

How would I formally prove that for the integers $a$, $b$, and $d$, if $d\mid da+b$, then $d\mid b$? Would a direct proof be the best option? If I do a direct proof I seem to get stuck pretty quickly... in fact I don't even know how to start...   Assume $d\mid da+b$ ... ?  This might look like a HW dump but I honestly just don't know how to continue...


What does the C value for LC_ALL do in Unix-like systems?   I know that it forces the same locale for all aspects but what does C do?


In Vista file explorer, how can I use the search to find only directories matching my input?  The find is quite useful and convenient, but I cannot find a way to restrict the result list to directory items as I could in XP.


Installing Ubuntu 13.10 alongside Windows 8.1

I have a Dell Inspiron 5520 (8GB Ram, 1TB HDD) and I have installed Windows 8.1 x64 on it. I want to install Ubuntu and dual boot Windows 8.1 with Ubuntu but I can't (my problem isn't the dual booting process, which I can fix later using EasyBCD), Ubuntu won't install.  When I boot from the live CD I have no option to "Install Ubuntu alongside Windows 8" and when I choose "Something else..." it shows me my partitions which are all used by Windows (System reserved, reserved, etc..) and the one partition that I wanted to install Ubuntu on is "unusable". My disk is MBR and I think the problem is having more than 4 partitions. I created another Local Disk from inside Windows but Ubuntu just sees that drive and the drive I shrinked to make it as one partition.   So, right now I want to install Ubuntu without killing my Windows (if it's possible). Perhaps there is some way I can make an extended partition and use that but I don't know how to (I can shrink one of my drives but that wouldn't make a new partition would it?).  Here is a screenshot of GParted in Ubuntu:     I don't know why the 800 GB is unallocated, in Windows, it is consisted of 2 drives (I've named them Local Disk E:\ and L:)   Also, when I right-click on that 800 GB partition and click on "New..." it gives me this error:    Which makes sense and is exactly what I'm trying to do but I don't know which partition I can remove so that my Windows doesn't break. Also, I don't know how to create an extended partition as I haven't done it before so I guess I would need help with that.  EDIT: Here's a screenshot of the Warning descriptions beside the partitions:    For the NTFS partitions the description is the same apart from that last part which instead has written:  The following list of software packages is required for ntfs file system support: ntfsprogs / ntfs-3g  Thank you!


How to interpret multiple regression coefficients

I'm running multiple linear regression with 6 variables. For one of the variables D, the correlation coefficient between D and the response Y is - 0.34. But in the regression output, the coefficient for D is +8.9.   What is the best way to interpret D's influence on Y? Is it safe to assume that there's some confounding going on so I can ignore the fact that the correlation coefficient is negative and thus say increasing D will result in increasing Y?


I'm new to Ubuntu and am running an old unsupported release and would like to gain some understanding of how the release schedule works.   What the difference is between an  end of life and a supported release is and how I can go about moving to a supported release?   Here's the extent of what I know: Windows executables don't run natively on Ubuntu and my update manager says the Ubuntu I have is no longer supported.


For my study design: When to log-transform data vs. when to use a non-parametric approach

Edit Purpose of my study  I have weather stations collecting data inside and outside low-tech greenhouses. Four of the weather stations are inside, and one is outside. They are collecting temperature, humidity, solar radiation, wind speed, etc. I am testing to see if the differences between the weather station data inside and outside is statistically significant.  Because I have an unequal number of replicates inside and outside the greenhouses, I calculated the difference for each variable between each weather station inside each greenhouse and one weather station outside. This gives me a sample size of 4. Sometimes 3 because I lost a replicate for part of the study. I was hoping to test the significance of the differences from zero rather than the original weather station data.  The shapiro wilk test in R finds that none of my data are from a normal distribution. I am debating whether or not to transform the data and use a t-test or use a non-parametric test. I am leaning towards the latter.  Question Should I log-transform the data and run the t-test or should I find another non-parametric test to use? What are the pros and cons of each? I have done a bit of research, but I'm still unclear on the best approach. Or is there another approach I haven't thought of.  *The post  talks about transformations, but it doesn't compare and contrast them to not transforming your data and using a different test.


How to calculate an integral involving square roots and trigonometric functions?

I am waiting for the response since 2009. This question was asked by my teacher.  $\displaystyle \int \mathrm{\sqrt{\sin{x}}}\,\mathrm{d}x$


I wonder how idle games, games where players only make a few clicks to get a game progress, work. These games appear to be running in the background, even when the app is closed. Therefore these games may be implemented on the server side and run on it accordingly. I'm interested in the kind of implementation.   Is there a program running on the server that creates a separate instance for each player and performs the actions accordingly? Or is this realised via a database?   Furthermore I ask myself where the data is stored, on the client (susceptible to manipulation) or on the server (high memory requirements).  Maybe one of you has experience in this area and can give me more information, insights or explain how it works. I am also happy about further reading or links.


Cuban going to London. Transit visa at Madrid required?

I am a Cuban. I am traveling to London and acquired plane tickets from Air Europa, which goes through Madrid. Do I need a transit visa to switch planes at Madrid?


how to validate file upload in drupal means,  in my form allowed only txt file, but now user also can upload image file also after change the extention .jpg -> .txt  function oz_workbench_moderation_buttons_form_alter(&$form, $form_state, $form_id) {   dpm($form);   if ($form_id == 'catalog_node_form'  )     {     $form['#validate'][] = 'upload_validate_function';           return $form;     } }  function upload_validate_function(&$form, $form_state){ $extensions = array('txt' => 'text/plain; charset=us-ascii','doc' => 'application/msword; charset=binary','pdf' => 'application/pdf; charset=binary','xls' => 'application/octet-stream; charset=binary','docx' => 'application/vnd.openxmlformats-officedocument.wordprocessingml.document; charset=binary'); $uploadedfile=count($form_state['values']['field_application_document']['und']);         for($i=0;$i<$uploadedfile-1;$i++){                 $file_name=$form_state['values']['field_application_document']['und'][$i]['fid'];                  $file_handler = file_load($file_name);                 $file = $file_handler->uri;                 $filename = $file_handler->filename;                 //echo $file;                 $finfo = new finfo(FILEINFO_MIME);                 $type = $finfo->file($file);                 //echo $type;                     if (!in_array($type, $extensions) )                     {                     drupal_set_message(t($filename.' is not valid file'), 'error');                     }          } }


I'm reading Nano: The Essentials by T. Pradeep and I came upon this statement in the section explaining the basics of scanning electron microscopy.     However, the equation breaks down when the electron velocity approaches the speed of light as mass increases. At such velocities, one needs to do relativistic correction to the mass so that it becomes[...]   We all know about the famous theory of relativity, but I couldn't quite grasp the "why" of its concepts yet. This might shed new light on what I already know about time slowing down for me if I move faster.  Why does the (relativistic) mass of an object increase when its speed approaches that of light?


If I have the plane $\pi:x+y-z-1=0$ and the two points $A:(1,1,1), B:(2,1,2)$ as two vertices of an equilateral triangle in the plane $\pi$. How can I find all (I'm assuming only 2?) sets of coordinates for the vertex $C$. Note that $A,B,\text{ and }C$ lies in $\pi$.  I've noted that $\vec{AB} = (1,0,1)\iff ||\vec{AB}||=\sqrt2$     Let $Q$ be midpoint for $\vec{AB}$, i.e. its coordinates are $\frac{1}{2}(A+B) = (\frac{3}{2},1,\frac{3}{2})$. The plane has the normal vector $\vec{n} = (1,1,-1)$   $\therefore$ The line which goes through $Q$ and $C$ is orthogonal to $\vec{n}$ and $\vec{AB}$. We call this line $L$.  $$\vec{n} \times \vec{AB} = (1,-2,-1)$$   Using this and that the point $Q$ lies on $L$ we get the equation for $L:$   $$L = (\frac{3}{2}+t,\,1-2t,\,\frac{3}{2}-t)$$  So combining this with the fact that $||\vec{QC}||=\frac{\sqrt{3}}{2}||\vec{AB}|| = \sqrt{\frac{3}{2}}$ as $||\vec{AB}|| = \sqrt{2}$. We can now put $||L(t)|| = ||\vec{QC}||$.  $$||L(t)|| = \sqrt{\left(\frac{3}{2}+t\right)^2 + \left(1-2t\right)^2 + \left(\frac{3}{2}-t\right)^2} = \sqrt{6t^2-4t+\frac{11}{2}} = ||\vec{QC}|| = \sqrt{\frac{3}{2}}$$  $\therefore 6t^2-4t+\frac{11}{2} = \frac{3}{2}$  This equation has no real solutions for $t$. What am I to do with this result? Did I do something wrong, or must the solutions contain imaginary units?


Add a suffix string to end of each line?

I have two files:  file01:  line1 line2 line3   file02:  A B C   And I want to get  line1 A line2 B line3 C   I could possibly write a Perl script but it is better if I don't need to.   I have tried using the obvious  grep -o  '^' file02  >> file01   But this produces   line1 line2 line3 A B C   It should be a simple thing to do, but have not found it in the "man grep" (manual for grep).


When I am reading a machine learning book I came across the following notation  $$||\theta||^2_2$$  What does the $||.||^2_2$ stand for? I know its magnitude but what is the 2,2 for?


MultiThreading for time delay in WinApp Form C#

I have a problem with This code in C# :   main class { var trick = new Object(); } ....... public void AddTabWithCheck(List<Urls> url) {  //Some Code   foreach(Urls link in url){      var thread = new System.Threading.Thread(p =>         {             lock (trick)             {                 Action action = () =>                 {                     addTab(link);                 };                 this.Invoke(action);                 if(link.Host == "google")                     System.Threading.Thread.Sleep(5000);             }         });         thread.Start(); } }   I had problem to do a Time Delay in winapp form.   I coudnt use thread sleep , while(withDatetime) or similar becouse inside the WinAPP there is a WebControl Browser and i wish add some page in a loop with some delay time without freeze the UI. Neither timer is a good solution cause it's hard to handle for my situation.  So a User suggests me to use this Solution (the ones with Thread). I thought that it worked without problems but only now i realize that if i put in my loop it's take only last element (of loop)  and create X threads all with the same element.  For a better explanation :  i have this List<Urls> url ;   with this Class   public class Urls {             public string Host { get; set; }             public String url { get; set; } }   Now i cant understand why if i add that code inside a simple Foreach , when the threads start all use the last element of loop.  I already checked if the List is correct ,  adding a MessageBox to show the current Object   before the thread code , and it change properly.


What is the difference between a proxy and a VPN?

There are several service providers out there that allow a user to circumvent firewalls or anonymize their web access.  Some of them use proxies, some use VPNs. Most people say that VPNs usually work better than proxies. They are also generally more expensive.  For example, a proxy will grant an international user access to Pandora.com, but not Hulu.com. A VPN will work for both.  How does a proxy work differently than a VPN and why does that make a difference?


Log4Net: set Max backup files on RollingFileAppender with rolling Date

I have the following configuration, but I have not able to find any documentation on how to set a maximum backup files on date rolling style.  I know that you can do this with size rolling style by using the maxSizeRollBackups.  <appender name="AppLogFileAppender" type="log4net.Appender.RollingFileAppender">     <file value="mylog.log" />     <appendToFile value="true" />     <lockingModel type="log4net.Appender.FileAppender+MinimalLock" />     <rollingStyle value="Date" />     <datePattern value=".yyMMdd.'log'" />     <layout type="log4net.Layout.PatternLayout">       <conversionPattern value="%d %-5p %c - %m%n"  />     </layout> </appender>


i need help with this exercise.     If $\mathbb{H}$ is a finite field and $a\neq0, b\neq0$, are elements   of $\mathbb{H}$ then exists $u,v\in\mathbb{H}$ such that   $1+au^{2}+bv^{2}=0 $   I don't have idea of how attack this exercise. Can someone help me?


The book is about alien birds that must dock and flap their wings to keep islands afloat on their home planet. All of a sudden aliens attack them and slaughter most of them. The birds have at least one space ship, and a few escape on that.   The birds find a water planet, and decide to explore it. They notice a large object under water; when they try to check it out, they crash. Only one bird survives the crash; he finds some sort of tentacle monster (?), and survives off it.  The bird eventually leaves the water planet, becomes part of a space ship, and battles other aliens. Both sides have powerful ships which end up destroying galaxies.  The birds in the beginning also play a VR game about being god. They try to help one race become more powerful. A more detailed bit of the game is they main protagonist, the bird, has these animals that cannot lookup so he clears the sky so that they can look up which leads to the enemy destroying them because the enemy can finally see a race to kill (all in the simulation VR game). The game is something the birds have on their homeworld; I think it's implanted in their heads. It's an activity for them to do while they're docked, keeping the islands afloat.  As far as I can recall, the birds were presented as looking much like actual birds here on Earth, with wings and talons (no hands, for example).  I read the book in 2017; I'm not sure how old it was then, and I don't remember anything about the cover.  Extra detail: There might have been crystals on the islands crystals that helped keep them floating.


Prove/Disprove: Find $a\in S_4$ that is not a power of $b$ such that $ab=ba$ while $b=(123)$   What I did:  I think this statement is false.  So we need to find $aba^{-1}=b$, we know that $id\in S_4$ will surely $id*b*id^{-1}=b$ but we get $id^k=b$, I wonder if there are more elements such that $ab=ba$, how to find them?   Any help will be appreciated.


Which version of Perl should I use on Windows?

The  web site provides references to several Perl distributions for MS Windows.  For a long time I have been using ActivePerl from   but recently I switched to  .  IMHO The only advantage that Active Perl still has over Strawberry Perl is the fact that it comes with Perl Tk which means its easy to install   the graphical debugger. Other than that, I think Strawberry Perl has all the advantages.


how do i set up a virtual box shared folder in an Ubuntu 18.04 VM on a windows 10 host?

i added a folder to the machine in VirtualBox, but from inside Ubuntu i can't get to the shared folder.  host: windows 10 guest: ubuntu 18.04


Is it technically illegal for US citizens to visit Cuba?

There is a belief that US citizens would be doing something illegal if they were to visit Cuba.  I remember hearing years ago while in Mexico where lots of people go on sidetrips to Cube that it's not illegal for Americans to visit Cuba but that if they spend any money there they would technically be breaking the law of "dealing with the enemy"?  So what's the real story? Is this all outdated or is it illegal for people from USA to go to Cuba? Or is the thing about them spending money there true? What are the real legal ramifications, if any?


Cloud solution that doesn't take up disk space

I'm on a macbook running macOS Sierra with a hard drive capacity of 256gb and I'm running out of storage. I bought iCloud storage thinking that this would free up some disk space, but soon discovered that it just copies the files to the cloud and still keeps a local copy on my computer.  Is there any other solution where I can upload files to "the cloud" and not store them locally to free up disk space?


Where do you report serious flaws with iOS7?

I now have a list of over twenty serious flaws with iOS7. It is driving me nuts that this new iOS is so riddles with flaws it should never have been released in this state, and Steve Jobs wouldn't have permitted it so. And this site just helped me resolve the mystery of why all my contacts vanished this morning. (thank you!) when the iOS decided to suddenly and for no apparent reason turn off contact syncing sometime overnight. I've hesitated to do a blog post as I'm sure no one at Apple would read my blog though it is a high trafficked blog in my market and would certainly hurt Apple sales, which isn't my desire, I'm a mac fan boy - but frustrated with all the problems and it seeming like after 4 updates, they aren't fixing them.  Thanks! I'd happy list them here if this is the place. If not, just delete this post. But I'd like to be helpful and note a complainer, but at a dead end on how/where to post up to 25 critical flaws that are hindering the practical use of the iPhone now. (despite the fact I still prefer it over the other options)  How do you get Apple to hear and address these things?


In a certain list of exercises, contained the question     $$\int_{0}^{\infty}{\left(x^3\cdot(e^x-1)^{-1} \right)}dx$$   How do you solve?


What happens to lightning spells underwater?

As the old adage goes "water and electricity don't mix" because in real life water has impurities in it that make it super conductible. So what would happen in D&D if, for instance, a sorceress cast  on a creature underwater?  Would the spell not work? Would it affect the caster as well? Would it spread and hit everything under water?   Shocking grasp in particular specifies that "You have advantage if the target is wearing metal armor" which indicates that they are taking conductivity into account.  What about  or , would casting a higher level spell change the outcome?


Return a Function With Expanded Variables

This is a simplified example, but the goal is to have a function that returns a function given a set of arguments, and the returned function should have those arguments expanded into numbers/strings.  The example here returns a function that checks whether a set of coordinates are within a rectangle:  function createFunction(startX, startY, width, height) {     return function(x, y) {         if (x >= startX && x <= startX+width && y >= startY && y <= startY+height) {             return true;         }         return false;     }; }  var myFunction = createFunction(5, 10, 200, 100);  console.log(myFunction); //startX and the other arguments aren't expanded   The problem described in the comment above is that the arguments from the "createFunction"  function aren't expanded into values, and if one used the returned function it would create an error because startX and the other arguments aren't globally defined.  How do I return a function with the variables expanded?


I have read that when matter and antimatter collide they just cancel out each other with the emmision of bright light. But doesn't it violate law of conservation of mass? If the the atoms dissapear into nowhere?


Why isn't this sudo mv operation with wildcard working?

I think there must be simple answer to this, but I can't figure out why this isn't working!  I have a folder in my home directory (well, a few levels down) called installed-plugins. I want to transfer all the contents of that folder (about 15 .jar files) to a different folders, also called installed-plugins.  This is what I am trying:  $ sudo mv /home/jira-plugins/installed-plugins/* /var/atlassian/application-data/jira/plugins/installed-plugins/                                                                                mv: cannot stat `/home/jira-plugins/installed-plugins/*': No such file or directory   What is my error?  The folder is definitely not empty. Here is the ls output:  $ sudo ls /home/jira-plugins/installed-plugins analytics-client-3.15.jar                                  plugin.2223138796603023855.jira-importers-plugin-6.0.30.jar atlassian-chaperone-2.0.3.jar                              plugin.330169947367430109.jira-fisheye-plugin-6.2.8.jar atlassian-client-resource-1.0.jar                          plugin.4363048306537053933.jeditor-2.1.7.2.jar atlassian-pocketknife-api-commons-plugin-0.19.jar          plugin.4438307615842123002.jira-ical-feed-1.0.4.jar atlassian-pretty-urls-plugin-1.8.jar                       plugin.461510159947098121.jira-issue-collector-plugin-1.2.5.jar base-hipchat-integration-plugin-7.8.24.jar                 plugin.5630909028354276764.atlassian-universal-plugin-manager-plugin-2.7.8.jar base-hipchat-integration-plugin-api-7.8.24.jar             plugin.6920509095052318016.atlassian-bonfire-plugin-2.9.13.jar hipchat-core-plugin-0.8.3.jar                              plugin.6952408596192442765.atlassian-bonfire-plugin-2.8.2.jar hipchat-for-jira-plugin-1.2.11.jar                         plugin.7079751365359230322.jira-importers-bitbucket-plugin-1.0.8.jar jira-email-processor-plugin-1.0.29.jar                     plugin.7451827330686083284.atlassian-universal-plugin-manager-plugin-2.21.4.jar jira-fisheye-plugin-7.1.1.jar                              plugin.7498175247667964103.jira-importers-redmine-plugin-2.0.7.jar jira-ical-feed-1.1.jar                                     plugin.7803627457720701011.jira-importers-plugin-3.5.3.jar jira-issue-nav-components-6.2.23.jar                       plugin.7977988994984147602.jira-bamboo-plugin-5.1.6.jar jira-servicedesk-2.3.6.jar                                 plugin.8372419067824134899.jira-importers-plugin-5.0.2.jar jira-workinghours-plugin-1.5.5.jar                         plugin.9081077311844509190.jira-fisheye-plugin-5.0.13.jar plugin.1260160651631713368.stp-3.0.11.jar                  plugin.9128973321151732551.jira-fisheye-plugin-6.3.10.jar plugin.2076016305412409108.jira-fisheye-plugin-3.4.10.jar  plugin-license-storage-plugin-2.8.jar plugin.218965759549051904.jira-importers-plugin-6.1.5.jar  querydsl-4.0.7-provider-plugin-1.1.jar plugin.2211202876682184330.jira-ical-feed-1.0.12.jar       stp-3.5.10.jar


Does anybody know how to solve the following differential equation?  $$w^2\cdot r+\frac{dw}{dt}\cdot r+\frac{dr}{dt}\cdot w=3g$$  where w and r are a function of time so $w(t)$ and $r(t)$. $g$ is a constant  This equation came from a thought problem of mine which I will now explain since I still do not know how to approach the problem.  Basically I want to design a spiral track in which a vehicle will accelerate. However the total acceleration needs to be constant.   The vehicle will have 2 acceleration components, a radial component ($a_r$) and a change in speed component ($a_s$). Since we want constant acceleration: $a_r + a_s = constant$  From circular motion we know that $a_r = \omega ^2 r$ where $r$ is the radius, and $\omega$    Further we know that $v=\omega*r$, therefore: $$a_s=\frac{d}{dt}(\omega r)$$  For constant acceleration $a_{total} = a_r + a_s = \omega ^2 r + \frac{d}{dt}(\omega r) =constant$  Further usefull information: Length of the track covered at a certain time $$l=v\cdot t=\omega r t$$  With all this the radius will be a function of time, $r(t)$ and the angular velocity will be a function of time, $\omega (t)$  Boundary conditions: $$r(0)  = 0$$  $$\omega (0) = 0$$  Now I would like to find a possible set of solutions to create a track by implementing end boundary conditions that i choose e.g. $v(t_{end})=100 [m/s]$ and $l(t_{end})=5000 [m]$  Here is a diagram for clarity:


Javascript function not defined but it does

My page's code is:  <!--Custom JavaScript --> // --> This Script contains the initLoadMore function <-- <script src="/static/js/custom.min.js"></script>      <script src="/static/js/moment.min.js"></script> <script src="/static/js/material-datetimepicker.js"></script> <script>    $(function(){       initLoadMore("btnLoadMoreEvents","events-list");    }); </script>   the Script custom.min.js contains:  $(function(){ function initLoadMore(btnLoadMore,container){     let num_page = 2;     $("#"+btnLoadMore).click(function(){         $.get("?p="+num_page).done(function(data) {             $("#"+btnLoadMore).prop("disabled",true);             if(data.last_page == true){                 $("#"+container).append(data.content);                 $("#"+btnLoadMore).remove();             }else{                 $("#"+container).append(data.content);                 num_page = num_page + 1;             }        }).fail(function(xhr){             swal("Error", "Ha ocurrido un error al cargar m\u00E1s contenido. Por favor, int\u00e9ntalo de nuevo.", "error");        }).always(function(){            $("#"+btnLoadMore).prop("disabled",false);        });     }); } });   The console says Uncaught ReferenceError: initLoadMore is not defined. The function only works if I delete the $(function(){ ... });(document ready) in the custom.min.js Script.  Why does this happen?


Is it possible to store variables into arrays? What is the correct way of doing it? I can't seem to be able to store it in this way.   var fxVal = '<?php echo $fxVal;?>'; var equitiesVal = '<?php echo $equitiesVal;?>'; var boVal = '<?php echo $boVal;?>'; var balance = '<?php echo $account_balance;?>';  var myData = [fxVal,equitiesVal,boVal,balance];


I have JRE installed on my PC, however in chrome Java plugins are missing, it was working fine, since today, Java plugin is missing from Chrome browser.  I have installed JRE, but problem still persists.   What could be the reason and how can I resolve this issue?


Short story that takes place off planet, involving sun and rain

I read this short story about 20 years ago, and I'd love to find the title and author. This is what I can recall about the story:   It takes place in a classroom full of kids (around 10 years old?) The planet always gets rain The kids lock the main character (a girl, I think) in the closet during the very rare occurrence of sunlight and she misses the entire event.    I know it's not much to go on, but I hope it rings a bell for someone!


Not using second leg of flight with Aer Lingus

I have a flight booked from San Francisco > Dublin > Manchester later this year. I have to be in Dublin for business the day after I get to Manchester so rather than flying on I'd prefer to just stay in Dublin.  Is it possible to ditch the second leg of my flight and stay in Dublin with Aer Lingus?


Does group inverse commute with multiplication for all groups?

Is the following a property of $\textbf{all}$ groups?  $a^{-1} \circ b^{-1} = (a \circ b)^{-1}$  As far as I can tell it is true for addition and multiplication, but in the notes that I have come across, I have not seen it stated as a property.


I have a tar.gz file. I was extracting the original from it but tar command gives following error:   where numeric off_t value expected   While gtar runs perfectly.  Tar.gz was made using gtar command. I have other tar made with same process but they are fine.   Can anyone tell me what might be the cause of this. I have googled a little, but cannot find a satisfying answer.


Sapling tree add on, can edit the trees after doing something else?

I'm working with the blender-version v2.77 and I'm making one of my first trees with the sapling tree add on. Does anyone of you know if you still can edit the trees after doing something else? So for example you made the tree, and than modeled something else. Can you still edit the tree than (for me the leafs)?


How to duplicate an existing Cognito form

Is it possible to duplicate an existing Cognito form? If so, how?


I know that in League of Legends, if I try to have two items which are both unique with the same effect, that only the earlier purchased item's effect applies. ()  My question is in regards to stacking named Unique items with different effects.  Titanic Hydra and Ravenous Hydra both have "UNIQUE - Cleave" effects  but each Cleave effect does something different.  Does this mean that both Hydra's effect will be applied or will the same rule of which came first apply?


Prove that if $\sum{a_n}$ converges absolutely, then $\sum{a_n^2}$ converges absolutely

I'm trying to re-learn my undergrad math, and I'm using Stephen Abbot's Understanding Analysis. In section 2.7, he has the following exercise:  Exercise 2.7.5 (a) Show that if $\sum{a_n}$ converges absolutely, then $\sum{a_n^2}$ also converges absolutely. Does this proposition hold without absolute convergence?  I'm posting about this here because my answer to that last question about whether the proposition holds without absolute convergence is "Yes", but my suspicions are raised by him merely asking the question. Usually questions like this are asked to point out that certain conditions are necessary in the statement of propositions, theorems, etc. I just want to see if I'm missing something here.  Anyway, here's how I prove the absolute convergence of $\sum{a_n^2}$, and note that I never use the fact that $\sum{a_n}$ is absolutely convergent:  Proof: Let $s_n = \sum_{i=1}^n{a_n^2}$. I want to show that $(s_n)$ is a Cauchy sequence. So, let $\epsilon > 0$ and $n > m$, and consider, \begin{equation}   \begin{aligned}     |s_n - s_m| &= |(a_1^2 + a_2^2 + \cdots a_n^2) - (a_1^2 + a_2^2 + \cdots a_m^2)|\\                 &= |(a_{m+1})^2 + (a_{m+2})^2 + \cdots + a_n^2|\\                 &= |a_{m+1}|^2 + |a_{m+2}|^2 + \cdots + |a_n|^2\\   \end{aligned} \end{equation} Now, since $\sum{a_m}$ converges, the sequence $(a_m)$ has limit 0. Therefore I can choose an $N$ such that $|a_m| < \sqrt{\epsilon/n}$ for all $m > N$. So for all $n > m> N$,  we have, \begin{equation}   \begin{aligned}     |s_n - s_m| &= |a_{m+1}|^2 + |a_{m+2}|^2 + \cdots + |a_n|^2\\                 &< \left(\sqrt{\frac{\epsilon}{n}}\right)^2 + \left(\sqrt{\frac{\epsilon}{n}}\right)^2 + \cdots + \left(\sqrt{\frac{\epsilon}{n}}\right)^2\\                 &< \left(\sqrt{\frac{\epsilon}{n-m}}\right)^2 + \left(\sqrt{\frac{\epsilon}{n-m}}\right)^2 + \cdots + \left(\sqrt{\frac{\epsilon}{n-m}}\right)^2\\                 &= \epsilon   \end{aligned} \end{equation} Therefore $(s_n)$ is Cauchy and $\sum{a_n^2}$ converges. And since $\sum{a_n^2} = \sum{|a_n^2|}$, the series $\sum{a_n^2}$ is absolutely convergent. ∎  Am I doing something wrong here? Am I right in thinking that $\sum{a_n}$ need not be absolutely convergent for $\sum{a_n^2}$ to be absolutely convergent?


When removing unused kernals (to make space on /boot) I get this message:   The following packages were automatically installed and are no longer required:   gnome-mplayer hardinfo libgda-5.0-4 libgda-5.0-common libgmlib1 libgmtk1   libgmtk1-data libmusicbrainz3-6 libwxsqlite3-3.0-0 linux-headers-3.19.0-30   linux-headers-3.19.0-30-generic lubuntu-default-session   lubuntu-software-center lxappearance-obconf lxsession-default-apps mtpaint   python-gudev python-pysqlite2 sylpheed-plugins transmission xpad Use 'apt-get autoremove' to remove them. 0 to upgrade, 0 to newly install, 0 to remove and 47 not to upgrade.   I don't understand the last line, and when I use the autoremove command as suggested I get:  E: Could not open lock file /var/lib/dpkg/lock - open (13: Permission denied) E: Unable to lock the administration directory (/var/lib/dpkg/), are you root?   What do I do?


Add "Main site reviews" button in meta sites queue

Main sites have button to open meta site queue.        But meta's queue page doesn't have button to go to main site queue.        Could you add it?


jQuery event handlers always execute in order they were bound - any way around this?

It can be anoying that jQuery event handlers always execute in the order they were bound. For example:  $('span').click(doStuff1); $('span').click(doStuff2);   clicking on the span will cause doStuff1() to fire, followed by doStuff2().  At the time I bind doStuff2(), I would like the option to bind it before doStuff1(), but there doesn't appear to be any easy way to do this.  I suppose most people would say, just write the code like this:  $('span').click(function (){     doStuff2();     doStuff1(); });   But this is just a simple example - in practise it is not always convienient to do that.  There are situations when you want to bind an event, and the object you are binding to already has events. And in this case you may simply want the new event to fire before any other existing events.  So what is the best way to achieve this in jQuery?


What terminal emulators are available for heavy terminal users?

I spend a lot of time at the command-line during the workday and at home too since I run Ubuntu exclusively.  I've been using the default gnome terminal but I've reached a point where I'd really like to get my terminal tricked out so that my common tasks are as easy as possible. Specifically, I find that I spend of lot of time browsing code in the terminal and working in config files.  On my wish list would be:   Ability to have multiple screens, tabs, windows (I don't have a preference at this point) that I can easily switch between. Color coding for everything Easy to modify the aesthetics of the terminal (is it vain to want my terminal to look nice?) such as transparency, borders, etc.


Some textbooks I came across, and a homework assignment I had to do several years ago, suggested that the reason we can skate on ice is the peculiar $p(T)$-curve of the ice-water boundary. The reasoning is that due to the high pressure the skates put on the ice, it will melt at temperaturs below $273 K$ and thus provide a thin film of liquid on which we can skate. It was then mentioned as fun fact that you could ice-skate on a planet with lakes of frozen dioxide because that gas has the $p(T)$-curve the other way round. My calculations at that time told me that this was, pardon my french, bollocks. The pressure wasn't nearly high enough to lower the melting point to even something like $-0.5$ degrees Celsius. I suppose it is some other mechanism, probably related to the crystal structure of ice, but I'd really appreciate if someone more knowledgeable could tell something about it.


I have a notebook with dual boot (Windows 8.1 & Ubuntu 16.04). I'm trying to merge an unallocated partition with an ext4 (sda8) partition.Is this possible?    I'm using a LiveUSB for all the procedure.  I really appreciate any help you can provide.


The following fascinating formula appears in the paper  by M.Chamberland and A.Straub (see page 9): $$\prod_{n=2}^\infty\left(1-\frac{1}{n(n-1)}\right)=-\frac1\pi\cos\left(\frac{\sqrt5}{2}\pi\right).$$ Unfortunately, it's given without any reference or explanation. Could anyone give one?


How to prevent system applications (like the Software Center) from asking for password?

I'd like Software Center, Update Manager and some other system management applications to work without asking for password (like sudo does if configured with NOPASSWD) but only asking for a confirmation instead, or even without any confirmation. At the same time I wouldn't like to use no user password at all. Is this reachable?


Let $A$ be an infinite set. For each $a \in A$, let $x_a$ be a non-negative number. Let the value of the series $\sum_{a \in A} x_a$ be the value of the supremum of its finite partial sums, i.e.:      $$\sum_{a \in A} x_a = \sup_{n \geq 0} \sup_{(a_1, \ldots , a_n) \subset A} \left(x_{a_1} + x_{a_1} + \ldots + x_{a_n}\right)$$   (Supremum is well defined even when its value is infinite)       If $\sum_{a \in A} {x_a}$ is finite, prove that the set $A' = \left\{{a \in A | a > 0}\right\}$   is countable.   My guess is that we have to write $A$ as a union of finitely many sets.


Keyboard shortcuts to launch GNOME calculator in Ubuntu 18.04?

Is there are predefined keyboard shortcut for fast launch gnome-calculator?  When I try set custom (For example Ctrl+Alt+5) from settings they doesn't work for me:


How to prevent spiders from making webs on my bike?

I really hate spiders and I'm afraid of them so this is really a problem for me. I use bike every day to get everywhere - to work, to shop etc. These nasty things can make a web in a matter of a few hours here (Cambridge, UK) - almost every morning when I want to get to work there is a web, almost every afternoon when I want to go home there is a web. Sometimes there is even a spider. It's really annoying and terrifying. I found this:  but it wasn't really helpful. I was thinking about spraying my bike with Raid or something, or maybe spraying it with some kind of water solution with washing liquid and essential oils (I read that some of them repel spiders). Do you have any advice on this? Or maybe at least some advice on dangerous fluids for my bike that I shouldn't use for this? (Like water makes my bike rusty)


Does "apropos" take a preposition? How do you use this word, anyway?

Which is more correct:     Apropos of your earlier comment, I decided to....   or      Apropos your earlier comment, I decided to...   Actually, apropos is so fancy a word, even I, a word maven if I do say so myself, am not entirely sure when to use it.  If I may add to my preposition question, are there any constructions where it would be appropriate to use something like with regard to and not apropos?


For my banked road I sort of managed to make it look like it is a racing track.  I am really stuck with the pink part that is completely flat. I have a road texture and want to apply it to that, so that it follows the road   I think it should be easy but I don't know how to do it. I have searched but can't seem to find the right tutorial for this.


At the moment I have example.com that my colleague bought from GoDaddy which was first purchased via Google Work. The purchase did not include a hosting plan. We do not plan to host our website on GoDaddy since we have a less expensive option using another host.  We still want to keep the Google Work services, and the domain in GoDaddy. However, we are trying to point the address to the new hosting. I have minimal understanding of DNS & its records, so please correct me if I am wrong.  At the moment the A record for example.com has the following records: 1. 50.xx.xx.xx 2. 216.239.32-38.21 which is from Google.  These are the following actions that I have taken to address this: 1. Add the hosting's IP to the A record 2. Edit CNAME record for www to example.com (it was previously @)  Now, the changes do not seem to do anything, when I try to access example.com it still redirects to Google's 404 page (the same as before the changes). I realize DNS changes may take up to 12-48 hours, but since I am not 100% confident in what I am doing I might as well ask the community if this is correct.  Question: 1. Am I doing this right? What additional steps do I need to do? Is it okay to keep those Google A records? Do I need to remove anything? 2. Is @ the same thing as example.com?


Is any way to continue executing try block if an exception is raised? I think that the aswer is no, but I think that the following code is ugly.  def preprocess(self, text):     try:         text = self.parser(text)     except AttributeError:         pass     try:         terms = [term for term in text if term not in self.stopwords]         text = list_to_string(terms)     except AttributeError:         pass     try:         terms = [self.stemmer.stem(term) for term in text]         text = list_to_string(terms)     except AttributeError:         pass     return text   There is another way to do this in a pythonic form?


Java Override Super Class Method Null Exception

I'm having troubles finding out why my code is displaying a null pointer exception error when it runs the getScale () method from the subclass "Weather". The getScale method in the subclass is suppose to change the private variable (scale) depending on the short form in to the long form (return Celcius instead of C).  *PS this is a school computer science inheritance exercise  Thanks for any feedback.  Main Method      Temperature number = new Temperature ();     Temperature scale = new Temperature ();      System.out.print ("Enter temperature: ");     number.setNumber (Double.parseDouble (stdin.readLine ()));     System.out.print ("Enter scale (C/F/K): ");     scale.setScale (stdin.readLine ());      Weather windSpeed = new Weather ();     Weather windDirection = new Weather ();     Weather visibility = new Weather ();      System.out.print ("Enter wind speed (km/h): ");     windSpeed.setWindSpeed (Double.parseDouble (stdin.readLine ()));     System.out.print ("Enter wind direction: ");     windDirection.setWindDirection (stdin.readLine ());     System.out.print ("Enter visibility (m): ");     visibility.setVisibility (Double.parseDouble (stdin.readLine ()));      System.out.println ("\nTemperature: " + number.getNumber () + " " + scale.getScale ());     System.out.println ("Wind Speed: " + windSpeed.getWindSpeed () + " km/h");     System.out.println ("Wind Direction: " + windDirection.getWindDirection ());     System.out.println ("Visibility: " + visibility.getVisibility () + " m");      Temperature scaleFull = new Weather ();      System.out.println ("\nTemperature: " + number.getNumber () + " " + scaleFull.getScale ());     System.out.println ("Wind Speed: " + windSpeed.getWindSpeed () + " km/h");     System.out.println ("Wind Direction: " + windDirection.getWindDirection ());     System.out.println ("Visibility: " + visibility.getVisibility () + " m");   Temperature Class (superclass)  private double number; private String scale;     public void setNumber (double number) {     this.number = number; }   public double getNumber () {     return number; }   public void setScale (String scale) {     this.scale = scale; }   public String getScale () {     return scale; }   Weather Class (subclass extends Temperature)   private double windSpeed; private String windDirection; private double visibility;  public void setWindSpeed (double windSpeed) {     this.windSpeed = windSpeed; }   public void setWindDirection (String windDirection) {     this.windDirection = windDirection; }   public void setVisibility (double visibility) {     this.visibility = visibility; }   public double getWindSpeed () {     return windSpeed; }   public String getWindDirection () {     return windDirection; }   public double getVisibility () {     return visibility; }   public String getScale () {     if ((super.getScale ()).equals ("C"))     {         return ("Celcius");     }     else if ((super.getScale ()).equals ("F"))     {         return ("Fahrenheit");      }     else if ((super.getScale ()).equals ("K"))     {         return ("Kelvin");     }      return (" units");  }


For example: $$7x \equiv 1 \pmod{31} $$ In this example, the modular inverse of $7$ with respect to $31$ is $9$. How can we find out that $9$? What are the steps that I need to do? Update If I have a general modulo equation: $$5x + 1 \equiv 2 \pmod{6}$$ What is the fastest way to solve it? My initial thought was: $$5x + 1 \equiv 2 \pmod{6}$$ $$\Leftrightarrow 5x + 1 - 1\equiv 2 - 1 \pmod{6}$$ $$\Leftrightarrow 5x \equiv 1 \pmod{6}$$ Then solve for the inverse of $5$ modulo 6. Is it a right approach? Thanks.


How does a one-sided glass work on atomic level?

What does the description of the phenomenon at atomic level look like? I assume that atoms absorb and emit a wave with a changed amplitude. What is responsible for dividing the amplitude level and direction of division?


how to convert a string to an object in Javascript?

I would like to know how to convert the string below to an object in Javascript:  var string = '{"id":"50","actor":"1","subject":"1","object":"18","message":"a ajout\u00e9","status":"unseen"}'   In fact, I would like that after converting the string above to an object, I will be able to access to any element of that object. For example, if I convert the string to an object called "obj" I will be able to access to the value of the element "id" (which is "50") in such way: obj.id  Thanks in advance.


User Reputation count mismatch while searching user

If I search for user in  page it displays old reputation of the user.  Example :        But original reputation is :


We're building an app that allows people to upload or record their voice or video using HTML5 (not flash). We've run into a problem where users can't seem to find the button to allow the app to use a microphone or webcam. On chrome it's a little topbar that slides down when an app requests permission to use hardware.  The users that we're working with are very low -> low in technical literacy.   Has anyone had a similar problem? how did you guys handle the communication?


How to set backround image in Blender 2.8

I am trying to set a background image in Blender 2.8 Beta.   The image is what I have right now for nodes. I set it to world node and it has a background when I render it but it is all mixed up.Do you know what I am doing wrong? (I am a beginner with Blender).   Thanks for your help.


A simple series $\sum_{i=1}^\infty \frac{i}{2^i} = 2$

I don't do math a long time, so I completely don't remember how to prove that: $$ \sum_{i=1}^\infty \frac{i}{2^i} = 2 $$  Can anybody help me?


In the show they often allude to the history between Guinan and Picard but, to my knowledge, there has never been anything more than allusions.  What exactly happened that created this bond between the two?


How Do I Configure Automatic Updates in WordPress 3.7?

WordPress 3.7 added automatic updates. How does this work, and how can I configure this feature?


"Amint I" is this correct? Would you use it? If not, I welcome suggestions

First question, am I seeing this slang correctly? amint I Second, is there an alternative way I should say it? And if not, how would you write it? "Well yeah, I’m standing here amint I?"


Creating non-rectangular hotspots and detecting clicks

Say for a game with irregular hotspots (say Risk, or a strategy game like Paradox's Hearts of Iron or Crusader Kings), how do you   Define a non-rectangular hotspot of irregular shape (much like a territory on a map?), in code? What tool can you use to trace out the hotspot and import into your game? What is the algorithm for detecting if someone has clicked within such a hotspot?


A basic marinade is acid, oil, herbs/spices.  I understand the herbs and spices are for taste, the acid helps meat absorb by breaking down the tissue and taste.  What is the oil for?


How do we define interior and exterior of a geometric figure?

I was thinking about this today. And although I've made some trials to answer it, none of them seem to fit. So, how do we define interior and exterior of a geometric figure? I guess that perhaps there might be some connection with the idea of open/closed sets in topology. But I'm not sure.


Freedom fighter versus evil space empire

I'm looking for a pair of YA science fiction books from the 90's about a rebellion against an evil space empire. I remember reading these books in primary school, in the 90's, but don't remember a lot about them.  As is often the case, I can recall only some details about the book, not the main plot itself.  • The protagonist had a metal coated spine.  • Pretty sure the name Legionnaires was involved.  • The rebellion had a base inside a hollow meteorite.  •It was a two book series, both in hard cover, they were also quite popular for years in the second hand bookstore & library market, but I haven't seen a copy for years.  •They had quite distinctive cover art that covered both the front and back of the book. It was an almost 1980's sci fi comic book look to the cover art, with our hero fighting human soldiers in identical green military uniforms, but not modern military space uniforms, they had that Blake Seven evil empire look to them, but in green.


Is there a way to find the derivative of an equation where I cannot separate the independent variable from the dependent variable. For example, what is $dy/dx$ given  \begin{equation*} \cos(y) = \dfrac{x}{x+y} \end{equation*}


Why 401k contribution as % of salary vs. fixed amount per pay check?

I am wondering why some companies do not let their employee choose a fix amount per pay check as a 401K contribution. In my all jobs it has been always a % of my salary, so I will chose a percentage high enough to at least get the maximum employer contribution.   I was chatting with a colleague in my company, and in their previous jobs it was also the same way.  What is wrong with letting people chose a fix amount, so suppose some one wants to maximize they can just divide the maximum annual salary divided by pay frequency?


"Accountsd wants to use the 'iCloud' keychain"

I, too, am suddenly getting this message.  I don't see a Keychain First Aid option in Keychain, and the two Login Keychain Settings were already unlocked.  Any other ideas for what the error message is all about, and what I should do about it?


Can virtual particles be thought of as off-shell Fourier components of a field?

I just found  blog post, which gives an interpretation of virtual particles I haven't seen before.  Consider a 1D system of springs and masses, where the springs are slightly nonlinear. A "real particle" is a regular $\cos(kx-\omega t)$ wavepacket moving through the line, where $\omega$ satisfies the dispersion relation $\omega = \omega(k)$. When two real particles collide, the region where they collide temporarily looks really weird, as they interact nonlinearly, pulling and pushing on each other.  Formally, we can write this weird region as the sum of a bunch of $\cos(kx-\omega t)$ waves, but there's no guarantee they'll have the right dispersion relation. Thus, each term in the resulting expansion is a off-shell "virtual particle". If you add up all the virtual particles, you get the actual intermediate field state, which is just a weird ripple in the field where the two particles are interacting.  As another example, consider the statement "a static EM field is made of virtual particles". Under this interpretation, what that really means is, "a static field (e.g. $1/r^2$) is not equal to $\cos(kx-\omega t)$, but may be expanded in terms of such sinusoids", which is much less mysterious sounding. In fact, this is exactly what we do when we consider scattering off a potential in normal QM, e.g. in the Born approximation.  The above gives some intuition for what a 'virtual particle' means in classical field theory. They are the Fourier components of the field with $(\omega, k)$ not satisfying the dispersion relation, and they are useful in classical perturbation theory. However, they are not propagating degrees of freedom, so they only appear during interactions.   The picture above is entirely classical. Does this picture generalize to quantum field theory, giving a physical intuition for virtual particles there?


Do posts have to be in English on Stack Exchange?

Otherwise known as  必须用英语吗？(is English required?) ¿Necesito hablar en inglés? ?האם אני חייב לכתוב באנגלית Muss ich auf Englisch schreiben?  Do I have to use English when posting a question, an answer or a comment on a Stack Exchange site?


An exercise on isomorphic groups of order 24

I am a beginning learner of group theory.  Which of the following are isomorphic:$$\mathbb{Z_{24}}, D_{4}\times \mathbb{Z_{3}},A_{4}\times \mathbb{Z_{2}},\mathbb{Z_{2}}\times D_{6}, \mathbb{Z_{12}}\times \mathbb{Z_{2}},D_{12}, S_{4}$$  I know $\mathbb{Z_{24}}$ is cyclic and none of $\mathbb{Z_{12}}\times \mathbb{Z_{2}},D_{12}, S_{4}$ are cyclic since none has an element of order 24. I also know $D_{12}$ and $S_{4}$ are not isomorphic because $S_{4}$ has no element of order 12. Finally, I know $A_{4}$ and $D_{6}$ are also not isomorphic because $D_{6}$, unlike $A_{4}$, contains an element of order 6.  Other than this I don't know how to proceed. Any hints are appreciated. Please allow me to do the work.


In a function declaration, what's the difference between void fun(const string& a) and void fun(string a)?

I know (correct me if I'm wrong) that const string& a is an lvalue reference and string a is a simple string variable, but I'd like to know if, in this context, there's a difference between the two, because in some tutorials I saw people using const [type]& var instead of the simple [type] var.  What's the purpose of using one of the two declaration?  Thanks


Is it possible to be admitted to a masters in Germany with a 3-year bachelors from another country?

I am a Nepali citizen and I have completed a 3 year bachelors from my country. I am planning my masters degree in Germany. Can I directly start my masters or do I have to do some courses?


I got multiple entry schengen visa issued by Greece.. Can I directly travel from India - Qatar - Romania or through schengen state

I got multiple entry schengen visa issued by Greece.. Can I directly travel from India - Qatar - Romania or should I have stamping in schengen state?


What heroes should Mercy damage boost versus shooting herself?

In FuriousPaul's , he recommends damage boosting Lucio if there is no other hero around, but Mercy's blaster plus Lucio's gun combined does more damage than 130% of Lucio's shots. So it should be a higher DPS for both of them to shoot and not worry about damage boosting.  For which heroes is the total DPS higher when Mercy damage boosts them compared to when she shoots her blaster alongside them?


I have following scenario: I have set up an ad-hoc network with wicd on my server, and use dnsmasq as an dhcp- and dns-server. The network works very well, I can connect, get an ip address, and on all clients the nameserver is set to the IP of my server. But I want that all dns request of the clients are resolved to my local server which runs an apache webserver. Is this possible with dnsmasq?


Confused about voltage due to a point charge

If we have a point charge $q$ then at any point around $q$ we have an electric field due to our source charge $q$. We have a certain value of voltage or potential at this point, which is nothing but the work done by $q$ in moving a charge of $+1C$ from my reference point to infinity.   Is my understanding correct?


Thunderbird - remove unused dictionaries from menu

I use Thunderbird with two sets of dictionaries: English and Spanish. In the spell checker menu I find about 30 localized dictionaries (all Spanish-speaking countries, and for English: US, England, Canada).  It's quite annoying that every time I need to look for the single proper dictionary, I see all this heap of other dictionaries (useless for me).  Is there any way to remove the unused dictionaries from the menu and leave 2 or 3 that I really use?