Which one is grammatically correct sentence and why?
How to ‘guess’ if a noun is countable or uncountable?
What is / how can I get a student-safe power supply for electronics projects?  I'm looking for a student-safe power supply for solder less breadboard.  I'm developing a course to teach electrical engineering to grade school students as an after-school program.  I'm wrapping up the first course and I've learned a lot, including that I need to find a safer power supply.  We're mostly using 9V batteries and connecting them to the breadboard via alligator clips.  After lots of searching, I'm realizing that I need to turn towards the expert community for guidance.  I hope that with the rise of the Makers  this question will become increasingingly relevant with time as more kids get into electronics.  Inextricably linked to this question is what is the minimum power source to use.  I've liked using 9V batteries since we can connect to them using alligator clips; but I worry that they are just a little too powerful.  I can imagine them somehow starting a fire with them.  My #1 priority is to keep the students safe.  Kids just have no concept that they can cause damage to themselves and property.  When I ask "where is that smoke coming from?" I'll get a gleeful response from the student that is seeing how many batteries he could hook together and short out.   I really need to limit the damage they can do.  I mainly don't want anyone electrocuted or anything to catch fire.  Kids will routinely attach LEDs backwards, leave them like that and then act surprised when they explode.   After safety, I want to protect the equipment.  Kids will hook up a LED backwards all the time.  After protection, I want to give the kids feedback as to what is going on.  A light that indicates power is on would be awesome.  A light or siren or circuit break that indicated a short would be awesome too.  Battery powered supplies are slightly preferred, just to keep upfront costs low and to avoid having to run outlets to each table.  Boundaries:   We are only using simple LEDs, BJT transistors, resistors and maybe a timer IC.    Similiar Questions:       References:  Course details are here:   We currently sometimes use  from the Squishy Circuits Store and/or a 9V battery with alligator clips.  Epilogue  I found it tougher than expected to find a suitable wall wart, so I'm listing what I finally found for future reference.  I'm about to test the following combination:         Epilogue 2  A year-plus in, I've decided to drop the in-line power switch since it wasn't obvious when it was 'on' vs. 'off'.  I'm instead relying upon the students to unplug the rat-tail from the supply, which is quick and easy.  Also, since I'm primarily using this for a squishy-dough project, I'm experimenting with with using two button batteries instead of a wall power. Creating fishnet grid with specified rotation angle in ArcGIS Desktop? I'm working on this project and I need a grid with a certain rotation, at about 60 degrees, for example.  Starting from that I need to make a block of 20mx50m, and the last thing is that inside each block there must be a small set of sub-blocks.   The result is this:    Of course it's been done manually, but I was thinking of a way of making it done automatically because I must do 30 blocks like this one, maybe more, and it is consuming a lot of my time. Suffixes indicating people and language of country vary by country:  _an: American, German, Italian, Belgian, Australian, Russian, Ukrainian, Korean,  Mexican, Brazilian, Chilean, Argentinean, Indonesian, Malaysian, Iranian, Egyptian, Somalian, Palestinian  _sh: English, British, Polish, Danish, Swedish, Turkish,    _ch: French, Dutch  _ese: Chinese, Taiwanese, Japanese, Vietnamese, Portuguese  _no: Filipino, Latino  _i: Israeli  _: Thai  Among the above, _an seems to outnumber other suffixes.  Are there any simple rule to govern appropriation of suffix turning a country name into adjective, indicating people and language of countries in the world in terms of say, region, race, or cultural background? Or is it just discretional? I have the following reference:  @MISC{EX2012,   author = {{S}ingle {A}uthor {O}rganization},   year = {2012},   title = {Example} }   A citation for this is breaking after "Author", but extending beyond the margin, as shown in the following example layout in the PDF:  Demo text demo text demo to margin Demo text which cites it (Single Author Organization, 2012) and flows over the margin.   How can I solve this? I am using natbib and citing with \citep{EX2012}. What's a recommended alternative to Quickbooks pro? I've just installed Ubuntu to replace Windows. I can't seem to find a good alternative to  to run on Ubuntu. Any help would be appreciated. Non-blocking Synchronous AJAX Which arena do free and crown chests use when determining the cards you will get? If I am in arena X when I collect my tenth crown for the crown chest, or a free chest becomes unlocked, then proceed to climb to arena X+1 before opening the chests, which arena will be used to determine the cards I get? Will it use the arena I was in when I unlocked the chests in, or the arena I opened them in? Can I travel after visa's intended travel date? I just finished applying for my visa and had originally planned to travel on the 30th of September, so I put that as my intended date of travel. But now I will not be leaving until close to the second week of October.  How does this work, will I still be able to travel with this visa even though it says I intended to arrive on September 30th? How do I make Windows 10's File Explorer open "This PC" by default? I know how to do that on Windows&nbsp;Vista and Windows&nbsp;7, and I know how to do that on Windows&nbsp;8 and Windows&nbsp;8.1, but neither of the ways work with Windows&nbsp;10; it always defaults into the "Home" view.  (I am basically reposting  for Windows&nbsp;10.) Deleting my own question At least two questions (, ) on this site indicate that in more than a few isolated cases at least, letters of recommendation are in fact written by the applicant and only signed off (or perhaps rephrased somewhat) by the recommender, who would actually be responsible for writing the letter.  Is there any evidence about the prevalence of this practice that goes beyond anecdotes? I realize that cross-country (cultural) difference may play a role. How to print all printable ASCII chars in CLI? Run a shell script as another user that has no password I would like to run a script from the main ubuntu shell as a different user that has no password.  I have full sudo privileges, so I tried this:  sudo su -c "Your command right here" -s /bin/sh otheruser   Then I have to enter my password, but I am not sure if that script is now really running under that user.  How can I confirm that the script is really running under that user now? Travelling from London, Heathrow to Lusaka, via Jo'burg, how much time should we allow for the international connection in Jo'burg?  Is it a matter of arriving at one gate and leaving at another, or do you have to go through passport control, customs, security? By considering:  $$\lim_{n\to\infty}\frac{\sum_{k=1}^n k^1}{n^{2}} = \frac 1 2$$ $$\lim_{n\to\infty}\frac{\sum_{k=1}^n k^2}{n^{3}} = \frac 1 3$$ $$\lim_{n\to\infty}\frac{\sum_{k=1}^n k^3}{n^{4}} = \frac 1 4$$  Determine if this is true: $$\lim_{n\to\infty}\frac{\sum_{k=1}^n k^m}{n^{m+1}} = \frac 1 {{m+1}}$$  If it is, prove it.  If it is not, evaluate $\lim\limits_{n\to\infty}\frac{\sum_{k=1}^n k^m}{{m+1}}$. Does the Great Old One warlock's telepathy from the Awakened Mind feature take an action? Does the Great Old One warlock's telepathy from the Awakened Mind feature take an action?  It doesn't seem too clear to our group and we have basically ruled it as equivalent to talking. How to create meaningful relationships with NPCs How do I help the PCs to create meaningful relationships with NPCs?   Maybe it is a result of my group playing too many one-dimensional adventures trying to find whatever MacGuffin they are after each week, but most of the time my PCs don't tend to value NPCs too much. Every time they meet an NPC they quickly evaluate what immediate values the NPC can give or tend to ignore them.  What I would really like is to have some good relationships where the PCs actually go out of their way to help NPCs without selfish motivation or even just to try to think of NPCs more and how their actions affect others.  I am not looking for a specific game rules solution to this, but instead techniques to get the players to feel attachment to these fictional characters. What is the fastest car in Saints Row 4, and where can I find it? I found an Attrazione in Salander, which has traditionally been fastest in previous games, but I don't like sinking upgrades money into a car unless it's for keeps. What car is fastest in Saints Row IV (before and after upgrades), and how can I get it? Is there any way to get stats on the car in-game? Problem to launch java at Debian: "error while loading shared libraries: libjli.so" Vortex in liquid collects particles in center At xmas, I had a cup of tea with some debris at the bottom from the leaves.  With less than an inch of tea left, I'd shake the cup to get a little vortex going, then stop shaking and watch it spin.  At first, the particles were dispersed fairly evenly throughout the liquid, but as time went on (and the vortex slowed, although I don't know if it's relevant) the particles would collect in the middle, until, by the time the liquid appeared to almost no longer be turning, all the little bits were collected in this nice neat pile in the center.  What's the physical explanation of the accumulation of particles in the middle?  My guess is that it's something to do with a larger radius costing the particles more work through friction...