I know next to nothing about electric engineering, so I got the Arduino Uno R3 and a bunch of LEDs to play around with and hopefully learn something. I have no idea about the proper terminology or anything here, so bear with me ...  When I connect an LED to a normal pin, it works fine. When I connect it to 5V or 3.3V with a 220 ohm, it works fine. Without the resistor, the LED gets cooked. My question is, why does it work with the digitals without resistance and not the 3.3V or 5V? Are they hooked up to onboard resistors? What is their output?  And finally, where can I learn more about my shiny new microcontroller without diagrams that I can't make head or tail of?  Edit: I think this is different from the related question I noted in my comment, but tell me if I should remove it anyway.
I'm just trying out Arduino Uno for the first time with 2 blinking LEDs on a breadboard. All the tutorials on the Internet seem to use a resistor. I do know the function of resistors, but does it really matter here? These LEDs are working just fine without a resistor.
Background image shows in front of 3D objects, not behind them. I've done a quick 3D track in blender and I'm trying to render my output, but the plate I used to track is showing up over my 3d objects.  I want to render the objects in the scene with an alpha channel and comp them over the plate I tracked. My renders however, are covered by the aforementioned plate.  Un-checking "Background Images" in the camera properties (only removes it from the viewport) isn't doing it for my render outputs.  Working on some production tests and am not really proficient with the software yet, my apologies in advance. I am trying to install Wordpress on Lubuntu. I followed the instructions . Including PHP Apache and MySQL setups. Apache and MySQL appear to be running fine.  However, when I go to http://localhost/blog/, I get the following error:     Neither /etc/wordpress/config-localhost.php nor /etc/wordpress/config-localhost.php could be found.   Ensure one of them exists, is readable by the webserver and contains the right password/username. We have a job that is set to run Monday thru Friday. Up until two weeks ago, it ran fine 5 days a week. For the last two weeks it has failed on Monday. I am unable to locate where to find the point of failure.   ### Example Scripts 0 2 * * 1-5 /admin/scripts/example.exp 1&gt;/dev/null 2&gt;&amp;1   We run AIX 7.1.  I've looked in the /var/log/ and there is no cron file there. Looking for advice to add to this so we can troubleshoot.   I found that the log is located in /var/adm/log. Further we are getting this error repeatedly ever since this date/time. How do I clear this max limit?  c queue max run limit reached Fri Nov 25 21:52:00 2016 ! rescheduling a cron job Fri Nov 25 21:52:00 2016 I'm running Apache2 in a docker container, and want to write nothing to the disk, writing logs to stdout and stderr. I've seen a few different ways to do this (,  ) but these seem like hacks. Is there no way to do this by default?   To be clear, I do not want to tail the log, since that will result in things being written to the disk in the container. Short, Politically Correct word for Native Americans No more than four syllables, more PC than Indians.  EDIT: I arbitrarily chose four syllables because any more seemed like a mouthful. I like to be PC and not have to stumble over 6+ syllables. Can I buy (liquid) duty free at Dublin airport, before going through pre-clearance? Following on from my , I've been watching the  from the Dublin airport website. That mentions that after checkin, passengers clear normal Irish security checks, then proceed (via optional shopping) to a TSA-style security check before reaching the CBP juxtaposed border control. It also mentions that duty free shopping is available after immigration and customs.  That leads me to wonder - can I buy duty free liquids in the main bit of Dublin Airport, before reaching the US pre-clearance area? Or must all duty free liquids (eg alcohol) be purchased in the smaller duty-free shop after US pre-clearance just before boarding? Some websites and textbooks refer to $$\Delta x \Delta p \geq \frac{\hbar}{2}$$ as the correct formula for the uncertainty principle whereas other sources use the formula $$\Delta x \Delta p \geq \hbar.$$ Question: Which one is correct and why?  The latter is used in the textbook "Physics II for Dummies" (German edition) for several examples and the author also derives that formula so I assume that this is not a typing error.  This is the mentioned derivation:     $\sin \theta = \frac{\lambda}{\Delta y}$      assuming $\theta$ is small:      $\tan \theta = \frac{\lambda}{\Delta y}$      de Broglie equation:      $\lambda = \frac{h}{p_x}$      $\Rightarrow \tan \theta \approx \frac{h}{p_x \cdot \Delta y}$      but also:      $\tan \theta = \frac{\Delta p_y}{p_x}$      equalize $\tan \theta$:      $\frac{h}{p_x \cdot \Delta y} \approx \frac{\Delta p_y}{p_x}$      $\Rightarrow \frac{h}{\Delta y} \approx \Delta p_y \Rightarrow \Delta p_y \Delta y \approx h$      $\Rightarrow \Delta p_y \Delta y \geq \frac{h}{2 \pi}$      $\Rightarrow \Delta p \Delta x \geq \frac{h}{2 \pi}$   So: Which one is correct and why? Is it time to be rid of automatic down votes on certain closed questions? Right now,  carry automatic downvotes.  The  for this was largely to enforce specific quality bans in part because people were not down voting questions. Now that question down votes are free on questions and it seems to be pretty commonplace for question quality bans to trigger, even without the automatic votes from closure, and we have completely revamped the closure system. Is it time to reevaluate whether or not these automatic votes are still a good idea?  What benefits do the automatic votes provide and have they effectively run their course? "In" vs. "after" for future talk The class will be over in 10 minutes. The class will be over after 10 minutes.  I know the first is correct but why? What, exactly, is transferred along supply lines? What are the differences between Desktop, Server, and Alternate Installs? Why this javascript regex doesn't work? "Learn More" link on tags broken in latest Chrome stable Note: This is identical to , but that bug was declined because Chrome 30 was in dev. Chrome 30 has now been released, and still has this issue.   The "Learn More" link for tags is broken in the latest release of Google Chrome.    If I right-click and open in new tab, I get the tag's page, but just clicking doesn't work.  I'm using Chrome 30.0.15599.69, the latest stable release: Can I fetch the value of a non-standard CSS property via Javascript? I am trying to read a custom (non-standard) CSS property, set in a stylesheet (not the inline style attribute) and get its value. Take this CSS for example:  #someElement {   foo: 'bar'; }   I have managed to get its value with the currentStyle property in IE7:  var element = document.getElementById('someElement'); var val = element.currentStyle.foo;   But currentStyle is MS-specific. So I tried getComputedStyle() in Firefox 3 and Safari 3:  var val = getComputedStyle(element,null).foo;   ...and it returns undefined. Does anyone know a cross-browser way of retreiving a custom CSS property value?  (As you might have noticed, this isn't valid CSS. But it should work as long as the value follows the correct syntax. A better property name would be "-myNameSpace-foo" or something.) In almost all proofs I've seen of the Lorentz transformations one starts on the assumption that the required transformations are linear. I'm wondering if there is a way to prove the linearity:  Prove that any spacetime transformation $\left(y^0,y^1,y^2,y^3\right)\leftrightarrow \left(x^0,x^1,x^2,x^3\right)$ that preserves intervals, that is, such that  $$\left(dy^0\right)^2-\left(dy^1\right)^2-\left(dy^2\right)^2-\left(dy^3\right)^2=\left(dx^0\right)^2-\left(dx^1\right)^2-\left(dx^2\right)^2-\left(dx^3\right)^2$$  is linear (assuming that the origins of both coordinates coincide). That is, show that $\frac{\partial y^i}{\partial x^j}=L_j^i$ is constant throughout spacetime (that is, show that $\frac{\partial L_j^i}{\partial x^k}=0$).  Thus far all I've been able to prove is that $g_{ij}L_p^iL_q^j=g_{pq}$ (where $g_{ij}$ is the metric tensor of special relativity) and that $\frac{\partial L_j^i}{\partial x^k}=\frac{\partial L_k^i}{\partial x^j}$. Any further ideas? R's lmer cheat sheet "Baggage" versus "luggage" Can a shell script set environment variables of the calling shell? I'm trying to write a shell script that, when run, will set some environment variables that will stay set in the caller's shell.  setenv FOO foo   in csh/tcsh, or  export FOO=foo   in sh/bash only set it during the script's execution.  I already know that   source myscript   will run the commands of the script rather than launching a new shell, and that can result in setting the "caller's" environment.  But here's the rub:  I want this script to be callable from either bash or csh.  In other words, I want users of either shell to be able to run my script and have their shell's environment changed.  So 'source' won't work for me, since a user running csh can't source a bash script, and a user running bash can't source a csh script.  Is there any reasonable solution that doesn't involve having to write and maintain TWO versions on the script? Can my spouse receive an emergency UK visa to visit a funeral? I'm a British national. My grandmother just passed. My wife is Chinese. In general it's a major pain to get my wife a visa to visit the UK, we have never been before.  Is there any way to get an emergency visa to attend the funeral?  What sort of documents would we need? (Fitzpatrick Advanced Calculus 2e, Sec. 2.4 #12)  For $c \gt 0$, consider the quadratic equation $x^2 - x - c = 0, x &gt; 0$.  Define the sequence $\{x_n\}$ recursively by fixing $|x_1| \lt c$ and then, if $n$ is an index for which $x_n$ has been defined, defining  $$x_{n+1} = \sqrt{c+x_n}$$  Prove that the sequence $\{x_n\}$ converges monotonically to the solution of the above equation.  Note: The answers below might assume $x_1 \gt 0$, but they still work, as we have $x_3 \gt 0$.    This is being repurposed in an effort to cut down on duplicates, see here: .  and here: .