Can you please explain the statement in the David Morin's Classical Mechanics?
Can a massless rope accelerate?
Is GNOME Terminal a type of non-login shell? Using QGIS3 Processing algorithms from standalone PyQGIS scripts (outside of GUI) I'm writing a script which must work outside of QGIS GUI. I call some API functions from qgis.core but I'd like to use the processing plugin.  I'm able to import processing with sys.path.append() but I can't run any process. Moreover, all "native" algs are missing in QgsApplication.processingRegistry().algorithms()  So is it possible to run processing that way ? What am I missing ?  import os, sys from qgis.core import * QgsApplication.setPrefixPath('/usr', True) qgs = QgsApplication([], False) qgs.initQgis()  sys.path.append('/usr/share/qgis/python/plugins') from processing.core.Processing import Processing Processing.initialize() import processing  layer1 = QgsVectorLayer('data/ROUTE_PRIMAIRE.SHP') layer2 = QgsVectorLayer('data/ROUTE_SECONDAIRE.SHP')  processing.run('qgis:union', layer1, layer2, 'test.shp') # returns nothing   I'm on QGIS 3.0.1 - Debian 9 Where can I get a Thunderbolt hub or splitter? Apple has just announced the new MacBook Airs, Mac mini, and Thunderbolt display. One of the features of the Thunderbolt display that caught my eye was its ability to daisy-chain two displays together from one Thunderbolt port (on a MacBook Pro).  I already have two 24" monitors and I don't feel like paying for two £900 displays. I worked out that all I need is a Thunderbolt hub/splitter so that I can plug the two cables that emerge into mini DisplayPort-to-DVI adapters.  Does anyone know of any Thunderbolt hubs or splitters? Or does anyone know of an alternative method? A result of Erdős on increasing multiplicative functions Erdős proved that if $f(n)$ is a monotone increasing function from the natural numbers to the positive reals, and $f(n)$ is completely multiplicative, then there exists some constant $C$ such that $f(n)=n^C$ for all $n$.  I have not been able to find a nice proof of this online and was hoping someone could provide a proof. I would like to cook frozen chicken breasts in a pressure cooker for shredding and making chicken mole.  I do not want to add anything except water, but I'm having a hard time finding specific guidelines on the time to cook frozen meats with no added ingredients or steps.   In my case, I have 3 pounds of frozen chicken breasts to cook.  What are the general rules to follow for frozen meats and, in my case, how long and at what heat should I cook this for? Install Windows 7 with Bootcamp on OS X Yosemite with USB Key I have an iMac (bought in 2011) and I recently upgraded it with Yosemite. I am trying to install Windows 7 on it via Bootcamp.  However, its optical drive does not work, so I chose the USB key solution using the trick of modifying the file info.plist of Bootcamp (type 'usb bootcamp youtube' in google to see a video of this trick).  So I follow the process religiously and end up with the classic and famous boring screen 'No bootable device -- insert boot disk and press any key'.  So I tried to use Unetbootin (  ) to make my USB Key bootable, and tried to boot on it through the screen that appears when you maintain the Option key (Alt button) while starting the mac. Result: I never managed to have my Unetbootin-formatted USB key appear on this screen :(  I read some stuff about reFit (  ) and GParted, but I just don't know how to use them...  If someone managed to install Windows 7 on his/her iMac with Yosemite using a USB Key, please help me understand why I can't see the USB as a boot option. I recently bought myself a pack of four YN560 IV's and a YN560-TX for my Canon camera, and apparently I got ahead of myself and didn't realise I should make sure the flashes support HSS.  I tried them out yesterday at home, and even on 1/128 and 1/250s on the camera, they were overexposing here and there. Unfortunately, I don't really have the space to move the flashes much further from my subject, so I was wondering if there is any way to trick them into HSS? I should mention that I also own a Canon 580ex II, which does support HSS. I was thinking I could perhaps use that mounted on the camera to trigger the Yongnuo's, but as far as I can tell that would render the 560-TX useless as the flashes can't be controlled wirelessly when in S1 or S2.  I guess I could buy an ND filter, but as I have lenses with differing sizes, this feels like more of a pain in the ass.  Is there any hack I can pull off here that you guys know of?  Thanks! Possible Duplicate:     Which one of these is correct?  It is I who am at fault. It is me who is at fault.  The word &quot;is&quot; is a conjugation of &quot;be&quot; which is a linking verb. I also want to know the same for 2nd person.  It is you who are at fault. It is you who is at fault. java.io.IOException: An existing connection was forcibly closed by the remote host Upon entering any given minecraft server, after a minute or two I am forced out of the server, and I'm given the following error:  java.io.IOException: An existing connection was forcibly closed by the remote host.  What does this mean, and how can I prevent it from happening again? How would you make a comma-separated string from a list of strings? I use XeTeX, Version 3.1415926-2.4-0.9998 (TeX Live 2012/W32TeX).  I am using the crop package to add bleed and crop marks to a document. This works fine for pages with white background, but how do I achieve this for pages which have another colour in the bakckground?  I tried the pagecolor package, and see that it somehow extends the pagecolour to around 2 to 3 mm into the bleed but not beyond. How do I make the entire bleed region of the same colour as the page?  \documentclass[12pt]{article} \usepackage[dvips=false,pdftex=false,vtex=false,paperwidth=138mm,paperheight=216mm]{geometry} \usepackage[noaxes,noinfo,cam,dvips,pdftex,center,width=168mm,height=246mm]{crop} \usepackage{xcolor} \usepackage[english]{babel} \usepackage{blindtext} \begin{document} \pagecolor{orange} \blinddocument \end{document} 12.04.3 can start only after I press "resume" in rescue mode (every boot) - problem with Nvidia driver I've tried to install maybe ten Linux distros on my new PC, and every time I have problems with video drivers: black screen or visual artefacts.  I was able to install only Ubuntu 12.04.3 64-bit, but also with problems: black screen on startup (sometimes all was normal when I used Live mode before install, sometimes I was not able to load Live Mode - Ubuntu says that I have problems with video and gives me a choice with four elements, one of them "use safe graphics mode", but I even can't choose this - the system is frozen).   In tty I installed nvidia-current, but it didn't help me. Every boot I need to press ESC and enter rescue mode and just press Resume and after this the system boots normally. If I try to do a normal restart I get a black screen after Ubuntu logo again.  I tried switching nvidia driver in the options - I have version 319-updates and version 319 [Recommended], but neither works.  I have Palit GeForce GTX650, all updates. Why can "trans" be replaced with an x? I can't think of an example, so I may be wrong about this, but I think I've seen people replace the prefix "trans" as in transport with an x. "Cross" makes sense, as in "railroad crossing", and I guess "chris" is sort of a punny extension, the extension being like "chris cross" and the example being "xmas", but why trans? How do I build a TRRS headphone jack with a jack that is detectable by an iPhone I have a circuit and I am trying to integrate it with an iPhone via a TRRS headphone jack's microphone input. I have a generic TRRS cord and am trying to send a signal through it. However, the iPhone does not detect that a mic is even plugged in. However, if I plug it into my Mac via line-in and record, I can record the signal I am sending perfectly.   I have read online that it needs to detect resistance between the ground and mic, which I have. Are there any other things I need to do? It seems like this is an issue that stems from Apple's proprietary technology, as the earbuds are from a Windows Phone before they were spliced.    Thanks so much! Prevent Mac Terminal from reverting to default theme I can't find any way to change the Terminal theme and have that theme applied permanently.  I want to change to another darker theme other than the default 'basic' theme, and (most importantly) have it remain as the theme every time I open Terminal. Is it correct to say "I write children books" (not possessive case)? Although Children's books is what everybody says, I would like to understand why the genitive case is applied in such case.  If I write books for children, children is an adjective here; not the owners of my book! The word "children" just defines or characterizes the type of books I write. Therefore, it's an adjective.   So, I understand that genitive/possessive case ("I write children's book")  is incorrect grammar.  My question is: is the genitive case here really accepted as right? If I use "I write children books" (following the grammar principle) as as I say "I write pets books" (books about pets, and not possessions of pets) - would I be incorrect? Why? How do you associate the .exe file extension with a program in Windows? Why do I get "Required key not available" when install 3rd party kernel modules or after a kernel upgrade? This issue happens only on UEFI systems with enabled Secure Boot.  When I try to install DKMS modules like VirtualBox, Nvidia, or Broadcom drivers, they do not install and I get Required key not available when I try to modprobe them.  VirtualBox complains that vboxdrv is not loaded.  Broadcom wl driver is shown in lspci -k as a kernel module but is not in use. sudo modprobe wl throws Required key not available.  Also this issue may happen when I install some kernel modules from git sources.  This issue may appear after a kernel update as disabled wireless adapter, black screen after a reboot, etc.   How can I fix it? Would depositing large cash amounts cause problems? I saw  recently where a man withdrew $600,000 USD in cash from his bank.  I'm sure many folks here would advise against this move for obvious (and perhaps not-so-obvious) reasons.   My question: suppose you did this and then, some months later, changed your mind and wanted to re-deposit with a bank.  I assume the gent cannot simply walk into a bank with $600,000 USD and deposit it, right?  Wouldn't money-laundering alarms be raised?  Wouldn't the IRS like to know where the money came from? I have read both two uses:   The combinations of a, b and c, taken two at a time, are ab, bc, ac. We can not help but noticing a harmonious combination between classic and contemporary.   Are both uses interchangeable? Perhaps substitute combinations among for combinations of in the first sentence? Any idea is appreciated.