Do partial derivation respect to velocity and total derivation respect to time commute?
Total time derivatives and partial coordinate derivatives in classical mechanics
Cannot Delete Item "Could Not Find This Item" issue A friend sent a long a file (a .rar) he wanted me to check out for him before he installed it.  I downloaded it and unrared it with no problems, but it was full of .exe's instead of the intended contents (fonts) so I advised him to delete it immediately and not use.  I then proceeded to do the same, but the folder simply will not delete. Oddly the files went fine, and I never ran anything, but this is what I'm seeing:   Could not find this item  This is no longer located in C:\Users\This_User\Desktop. verify the item's location and try again.   I've tried the following things with no help:   Using "Unlocker" to Unlock and delete Using move on reboot and rebooting Using PendMoves (from sysinternals) and rebooting Elevating a cmd line, doing a dir /x to get the short name of the folder, and then del 'shortna~1' Moving the folder to a new folder and then trying to delete the parent folder   I'm on Windows 7 RTM, very fresh install. Any thoughts?  Update: Just to confirm, I've run Hijack this and half a dozen other malware detectors, and everything came back clean (no extra processes, no other obvious badness). Rebooting in safe mode didn't help either. My HDRI doesn't appear on Cycles Render Where in the registry does Windows store with which program to open certain file types? After installing Adobe PDF reader, it opens files with the .PDF file extension. Ones' default web browser opens .html files and notepad opens .txt files, etc.  Where exactly in the registry are these filetype - program associations stored in the registry?   In other words, how does Windows know with which software/program it must open a certain file(type)? Can a black hole absorb photons whose wavelengths are greater than the BH horizon size? I have just booted my clean Ubuntu 18.04 LTS VM and tried to install some application with sudo apt install.  But got error message:     E: Could not get lock /var/lib/dpkg/lock-frontend - open (11: Resource temporarily unavailable)       E: Unable to acquire the dpkg frontend lock (/var/lib/dpkg/lock-frontend), is another process using it?   What process created the /var/lib/dpkg/lock-frontend file in Ubuntu? How to gently stop it and take manual control on APT? Determine Whether Two Date Ranges Overlap Schengen refusal formulae can be difficult to understand sometimes.  Sometimes an applicant receives a refusal with:       Justification for the purpose and conditions of the intended stay was not reliable.     often accompanied by:       Your intention to leave the territory of the Member States before the expiry of the visa applied for could not be ascertained.   What is meant by this refusal reason?  What are they trying to say? In Windows 10 how can we change the name of this folder under C:\Users? I'm using Windows 10 on my personal computer (HP Pavilion Laptop) and you can see in the Screen Shot under C:\Users there are two folders.    The name of the first folder is C:\Users\SINGHA, however, the correct spelling of my last name is SINHA.  I need to change the name of this folder to C:\Users\SINHA so that it shows the correct name.     Under User Account, the spelling of my name is correct - it's only under C:\Users\ where the name is spelt incorrectly. Consequently, if I open/edit a Word or Excel document, the name of the owner being shown is the incorrect one (i.e it's shown as C:\Users\SINGHA instead of C:\Users\SINHA)   If I right-click on this folder, I won't get the Rename option; How can I change the name of this folder? How long should a temporary notification (toast) appear? I sometimes hear stories where people compare their feelings in winter in different places in the world.  It goes like     in city X the temperature was the same as in city Y, but the humidity made me feel much colder...   or      oh well, -20°C would be cold, but the humidity was low, so it felt OK   so it implies that humidity somehow makes it feel colder. I am talking about temperatures below freezing (-30...0°C).  Does this have any physical explanation, or is it some sort of ? How do i know which wheels will fit my bike? my bike is:  and everything I have came with the bike, only now the axle of the rear wheel bent and the skewer has lost its grooves.  and I would like to replace the rear wheel with the 12 x 142mm version of:   I want to reuse the old casettes and disc break. I was told to buy new rotor bolts, will these do?   Will I be able to migrate all my previous parts onto this new wheel and will the wheel fit onto my bike?  update: A replacement axle would be prefered. What axle would work for my bike? If an email message contains an email address in the body, Gmail automatically converts it into a mailto: link, which is helpful.  And many times each day I've enjoyed being able to right-click a mailto: link in an email (within Gmail) and then click "Copy email address" in the context menu.  Then I can paste that email address into a program (such as when I want to search a database).  However, within the past month or so, I've noticed that I can't right-click and click "Copy email address" without Gmail then popping open a "New Message" panel and changing my current URL to have ?compose=new at the end.  I wonder if it's related to .  How can I disable it?  I'm tried of having to click the "Discard draft" trash can button so many times throughout the day. I'm currently a beginner when it comes to 3D modelling but doing okay so far. I'm struggling a bit when it comes to the final renders of my scene, specifically on the camera view I want. Sometimes its to zoomed in and sometimes to zoomed out that it's gone out of the environment of the blender. I realized the settings for the camera on blender are for actual cameras / photography and I'm no expert on that too. A tip on how to control them precisely would be nice. Thank you. Is it possible that my laptop shut down because my mobile is too close? If I put my phone on my notebook's left corner, it shuts down. Can anybody give me reliable explanation as to why this is happening?? homemade chilli oil I am making chilli oil using light olive oil, crushed chilli, dried garlic, dried fennel seeds and parsley.  I have been making this for years. I am concerned about this Botulinum business. Should I be concerned? And what can i do to avoid this?  Currently, I heat the olive oil before putting it into the mixture, jar it, and normally keep it in the cupboard for months, with no problems with taste.  Another thing I am wondering is, how does one measure the expiry date on homemade chilli oil? Can someone help? How to import Illustrator swatch libraries into InDesign - Adobe Indesign Mac? I have a very reach swatch library in adobe-illustrator like food colors and.... But in adobe-indesign I don't have many colors. Why? Can I import them to indesign? What Happened to The Latex Symbols In the Libreoffice-Texmaths Equation Editor? How to change/rewrite the lost password url? I used iThemes Security (formerly Better WP Security) hide back-end functionality to change the login url to /signin however clicking the lost password link /wp-login.php?action=lostpassword now generate a 404  Manually going to /signin?action=lostpassword works.  I came across the following code below which is suppose to make the change to however after some testing it doesn't seem to work  //******************************************************* //Function to change to lost password url //******************************************************** add_filter('site_url',  'wplogin_filter', 10, 3); function wplogin_filter( $url, $path, $orig_scheme ){     $old  = array( "/(wp-login\.php)/");     $new  = array( "signin/"); //this can be change to login or whatever or may remain there     return preg_replace( $old, $new, $url, 1); }   add to .htaccess  RewriteRule ^signin$ wp-login.php   How can i modify the above code in order to change the url for the lost password? With arrays, why is it the case that a[5] == 5[a]? I would like to read in a number of files and pipe their output to subsequent programs while still maintaining them as individual pipelines of data.  program1 *.txt | program2 | program3 folder   I know what the above syntax can accomplish for single streams of data, but I am looking at keeping the files separate throughout the entire operation. The above would translate to the following:   program1 reads text files and pipes to program2 program2 processes data individually and pipes to program3 program3 writes data to files in folder with the same file names as the original   This kind of operation is currently the domain for build tools like Gulp, but I am trying to see if a shell can fully replace them. Since programs are written to handle only one stdin, it doesn't seem feasible.  The reading and writing of multiple files isn't an issue as I will just handle that within the programs themselves.  I have looked into the following, but they don't seem like the correct solution:   the tee command file descriptors substitutions   One possible way is to create a process for each individual file, and maintain a list of file names somewhere, but I am hoping for something more elegant.