tom@tom-pc:~$ ls -lrta .Xa* -rw-rw-r-- 1 tom tom  0 May 23 23:45 .Xauthority.RM2HXW -rw-rw-r-- 1 tom tom  0 May 24 09:06 .Xauthority.CS6HXW -rw-rw-r-- 1 tom tom  0 May 24 16:51 .Xauthority.BYMIXW -rw-rw-r-- 1 tom tom  0 May 24 23:22 .Xauthority.F13LXW -rw-rw-r-- 1 tom tom  0 May 25 23:55 .Xauthority.FWY3XW -rw-rw-r-- 1 tom tom  0 May 27 18:52 .Xauthority.Z936XW -rw-rw-r-- 1 tom tom  0 May 28 08:54 .Xauthority.IGGQXW -rw-rw-r-- 1 tom tom  0 May 28 22:41 .Xauthority.874LXW -rw-rw-r-- 1 tom tom  0 May 29 08:49 .Xauthority.LQQWXW -rw-rw-r-- 1 tom tom 51 May 29 18:02 .Xauthority   From looking at the timestamps, a new one seems to be generated every time I turn off my computer (or log off). Where are they coming from? How can I stop these from being generated? I'm running xubuntu 13.04. Thanks
I'm using Ubuntu 13.04 on a Lenovo X220.  Why do I have so many .Xauthority.* files in my home directory? I.e  .Xauthority .Xauthority.0JW6UW .Xauthority.2HWRVW .Xauthority.2TA6VW .Xauthority.49F8VW .Xauthority.4E27UW .Xauthority.7CLTVW .Xauthority.8JGGXW .Xauthority.96SAVW .Xauthority.AOUFVW .Xauthority.ASDOVW .Xauthority.CGVJXW .Xauthority.E0ZSVW .Xauthority.E5VZWW .Xauthority.FE64UW .Xauthority.FIHDWW .Xauthority.HL45VW .Xauthority.HYCCVW .Xauthority.ILUEWW .Xauthority.JXJHVW .Xauthority.K1QJXW .Xauthority.KXSOVW .Xauthority.LEKEVW .Xauthority.M48WVW .Xauthority.M6QTVW .Xauthority.MW6NWW .Xauthority.N57TWW .Xauthority.O5HAWW .Xauthority.OIC5VW .Xauthority.P2RPVW .Xauthority.Q0FRVW .Xauthority.QW01WW .Xauthority.RDW5WW .Xauthority.T0TLWW .Xauthority.TSO4WW .Xauthority.U6R9VW .Xauthority.V3KAWW .Xauthority.W8Z1WW .Xauthority.XDLGVW .Xauthority.XOOHWW.Xauthority.XUICVW  They are all zero bytes except the first, with timestamps all over the place.  What are these, and are they safe to delete?
What are the various physical mechanisms for energy transfer to the photon during blackbody emission? By conservation of energy, the solid is left in a lower energy state following emission of a photon.  Clearly absorption and emission balance at thermal equilibrium, however, thermodynamic equilibrium is a statement of the mean behaviour of the system, not a statement that the internal energy is constant on arbitrarily short timescales.  The energy has to come from somewhere during emission, and go somewhere during absorption.  Energy in a solid can be stored as kinetic and potential energy of electrons and nuclei, either individually or in collective modes such as phonons and plasmons.  In thermal equilibrium energy will be stored more or less in various forms depending on the temperature and material.  However, even if most of the thermal energy in a particular solid at temperature $T$ is stored in the form of phonons, it could be that phonons primarily interact with light indirectly via electrons, e.g. a phonon excites an electron in a phonon-electron interaction, which can interact with light via the EM field.  Given that light is an EM field, it makes sense to me that it is emitted and absorbed by charged particles.  The electron-photon interaction is probably dominant for visible and ultraviolet light, given that metals are opaque, while semiconductors and insulators are transparent to (visible and UV) light with energy lower than their bandgap. However, once you get into energies in the IR and below, or X-rays and above, other mechanisms apparently take over.  For example, on the high-energy end of the spectrum I've heard that gamma rays can interact directly with nuclear degrees of freedom, which is reasonable considering that gamma rays are emitted during a lot of nuclear reactions.  A review of  might give clues to important light-matter interactions over a broad range of wavelengths.  Whether all of the these processes are involved in blackbody emission is a somewhat different question.  What physical processes mediate energy transfer during blackbody emission, and in which energy ranges are the various processes dominant? Why does this excerpt say that unbiased estimation of standard deviation usually isn't relevant? I was reading on the computation of the unbiased estimation of standard deviation and the source I read stated      (...) except in some important situations, the task has little relevance to   applications of statistics since its need is avoided by standard   procedures, such as the use of significance tests and confidence   intervals, or by using Bayesian analysis.   I was wondering if anyone could elucidate the reasoning behind this statement, for example doesn't the confidence interval use the standard deviation as part of the calculation? Therefore, wouldn't the confidence intervals be affected by a biased standard deviation?  EDIT:  Thanks for the answers so far, but I'm not quite sure I follow some of the reasoning for them so I'll add a very simple example. The point is that if the source is correct, then then something is wrong from my conclusion to the example and I would like someone to point how how the p-value doesn't depend on the standard deviation.  Suppose a researcher wished to test whether the mean score of fifth graders on a test in his or her city differed from the national mean of 76 with a significance level of 0.05. The researcher randomly sampled the scores of 20 students. The sample mean was 80.85 with a sample standard deviation of 8.87. This means: t = (80.85-76)/(8.87/sqrt(20)) = 2.44. A t-table is then used to calculate that the two-tailed probability value of a t of 2.44 with 19 df is 0.025. This is below our significance level of 0.05 so we reject the null hypothesis.  So in this example, wouldn't the p-value (and maybe your conclusion) change depending on how you estimated your sample standard deviation? Should the top navigation be frozen (optional)? In Excel, the window can be frozen in place in such a way that you can always see the name of the column even though you go way down below the 'fold' of the screen.  On SE, when you scroll, the whole page goes up (or down). This means the top navigation bar is scrolled off screen. I'm not sure if it would be a good idea or not to fix the top navigation to the top of the screen and let the rest of the content scroll.  What do you think about this, in terms of pros and cons?  [Update]  With the new Top navigation bar, kudos to the design team, I think this question becomes relevant again. I'm aware of the busload of downvotes, but still.  The top navigation bar doesn't occupy much space and has two notification areas:   Inbox Achievements   Having these two notifications visible at all times would be nice, IMO.  [Update]  I've just noticed that I haven't used the word "optional" in this discussion... My bad. In Excel, the Freeze function is controlled by the user. You can optionally Freeze part of the interface, and you can eliminate the Freeze at will. Find $\int \frac{x^3}{x^2-1} \:\mathrm{d}x$ Find $\displaystyle \int \dfrac{x^3}{x^2-1} \:\mathrm{d}x$.   I think there are a few ways to do this. We could just break this up using long division or break it up into partial fractions then use long division. My homework says to break this up into its roots so that's why I brought up partial fractions. Is that the best way to do it here? I have an entry-level Nikon DSLR, and I cant decide if I should upgrade my camera body or upgrade from a  AF-S DX Nikkor 18-200mm to whatever else might be recommended? I eliminated a computer player that had a strong religion (Buddhism). My religion was weak, whereas this other one was taking over the continent quickly. Now that I have him overrun, I want, well wanted, to work on converting cities to mine, but I see now that all of the cities period have his religion! I tried making an Inquisitor just to test, but he is ineffectual at removing Buddhism, being that I can only buy him in Buddhist cities. (Because all of my cities are Buddhist and my religion, Shinto, has been wiped out.   Is there no way to recover your religion in such a situation? Windows 98 on a modern computer? This is a  about CNAMEs at the apices (or roots) of zones   It's relatively common knowledge that CNAME records at the apex of a domain are a taboo practice.  Example: example.com. IN CNAME ithurts.example.net.  In a best case scenario nameserver software might refuse to load the configuration, and in the worst case it might accept this configuration and invalidate the configuration for example.com.  Recently I had a webhosting company pass instructions to a business unit that we needed to CNAME the apex of our domain to a new record. Knowing that this would be a suicide config when fed to BIND, I advised them that we would not be able to comply and that this was bunk advice in general. The webhosting company took the stance that it is not outright forbidden by standard defining RFCs and that their software supports it. If we could not CNAME the apex, their advice was to have no apex record at all and they would not provide a redirecting webserver. ...What?  Most of us know that  insists that A CNAME record is not allowed to coexist with any other data., but let's be honest with ourselves here, that RFC is only Informational. The closest I know to verbiage that forbids the practice is from :     If a CNAME RR is present at a node, no other data should be   present; this ensures that the data for a canonical name and its aliases   cannot be different.   Unfortunately I've been in the industry long enough to know that "should not" is not the same as "must not", and that's enough rope for most software designers to hang themselves with. Knowing that anything short of a concise link to a slam dunk would be a waste of my time, I ended up letting the company get away with a scolding for recommending configurations that could break commonly used software without proper disclosure.  This brings us to the Q&amp;A. For once I'd like us to get really technical about the insanity of apex CNAMEs, and not skirt around the issue like we usually do when someone posts on the subject.  is off limits, as are any other Informational RFC applicable here that I didn't think of. Let's shut this baby down. Units in gravitational $N$ body simulations When & how did Yoda come to know about the Rule of Two? Computing: $\int_0^1 \sqrt[3]{x\log{\frac{1}x}} \, \mathrm dx$ Compute the integral $\int_{A} x^m y^n z^p (1-x-y-z)^q dx dy dz$ Multiple domains for different products? I have a website with software applications. Is it good for SEO to choose one keyword rich domain name for each of our software products or should we stick to a single domain?  From a user's perspective I think it would be easier to remember a domain that is keyword rich as the user will instantly know what this product is for.  But I have read articles that the latest trend in SEO is to stick to one domain for all of your products and invest on this single domain website.  Is that true? What do you advise? Should I register a separate domain for each of our products or should I use only one single domain?  Should I do a 301 redirect with a .htaccess to a single domain? And what about the sitemaps? Should I register all sites in Google Webmaster Tools and post a separate sitemap for each one of them? should my main site sitemap include all pages or should separate domains have their own sitemaps? How should we deal with duplicate answers? Prove that: $(f(x))^{2} + (f'(x))^{2} \leqslant \max(a,b)$ where $(a,b) \in \mathbb{R}^2$ Let $f\in C^2(\mathbb{R},\mathbb{R})$.   Assume there exist  $(a,b) \in \mathbb{R}^2$ such that  $\forall x \in \mathbb{R}, (f(x))^{2} \leqslant a$ and $(f'(x))^{2} + (f''(x))^{2} \leqslant b$.   Prove that: $$(f(x))^{2} + (f'(x))^{2} \leqslant \max(a,b)$$ for all $x \in \mathbb{R}$.   I tried to use taylor lagrange with the integral form of the remainder but I did not succeed.  Ì really don't know how to tackle  the problem.   Any suggestion, Hint (or Answer) will be very helpful,  Thank you in advance, Generate a comma-separated list of cell contents, excluding blanks To concatenate a certain four cells, I'd use:  =CONCATENATE(A2,",",C2",",D2,",",F2)   This would make it so that...   A2 = "Matthew" C2 = "Mark" D2 = "Luke" F2 = "John"   would result in Matthew,Mark,Luke,John.  But we run into problems with something like...   A2 = "Jesus" C2 = "" D2 = "Mary" F2 = "Joseph"   which would result in Jesus,,Mary,Joseph.  Here, the extra comma is undesired. Is there a way to gracefully handle this so that all non-blank cells are included in the comma-separated list, while avoiding the addition of unnecessary commas when some cells are blank?  Certainly, this can be done with a fair number of nested IFs, but I really want to avoid that if possible. Can it be done with native Excel functions, or perhaps an array formula? Or would one have to resort to VB Script for something like this? What is the format for e-mail headers that display a name rather than the e-mail? If "No One" uses a face from the Hall of Faces to become someone then how did he do this Tags are not showing up on the right side of the screen This is on Stack Overflow. On Meta I'm able to see what the tags are on the right side of the screen. In fact, I think yesterday or some point earlier today I saw tags on the right side of the screen (I can't screenshot or remember correctly).  It's right above the asked and active heading.  I know this is minor but what happened to it? It might be useful for browsing instead of having to look at the bottom of the question post.    Found an image on Google and it shows the tags on the right side of the screen: Forcing Subdivide to create non-zig-zag edges