If we are standing on earth, then some force (gravity of earth) is pulling us down. Can't we make a force which can oppose gravity? Can't we make an object of zero mass?
Electromagnetic waves can be shielded by a perfect conductor. What about gravitational fields or waves?
Find $\sum_{n=1}^\infty \frac{n^3}{n!}$. Should north, south, east and west be capitalised? Should cardinal points be capitalised? Please give a reason why they should or should not. Which airlines allow in-cabin pets on transatlantic flights? Show that $11^{10} \equiv 1 (\mod 100)$ $11^{10} \equiv 1 \pmod{100}$  I tried to solve by using euler's theorem, But I got stuck.  $\gcd(11, 100) = 1$  $11^{φ(100)} \equiv 1 \pmod{100}$  $11^{40} \equiv 1 \pmod{100}$  I don't know how to go on as $11^{40}$ is bigger than $11^{10}$ Create a tar archive split into blocks of a maximum size I need to backup a fairly large directory, but I am limited by the size of individual files. I'd like to essentially create a tar.(gz|bz2) archive which is split into 200MB maximum archives. Clonezilla does something similar to this by splitting image backups named like so:  sda1.backup.tar.gz.aa sda1.backup.tar.gz.ab sda1.backup.tar.gz.ac   Is there a way I can do this in one command? I understand how to use the split command, but I'd like to not have to create one giant archive, then split it into smaller archives, as this would double the disk space I'd need in order to initially create the archive. Storable Action - System.LimitException: Too many DML statements: 1 @AuraEnabled(cacheable=true) public static String  deleteContacts(List&lt;String&gt; contactIds) {     List&lt;Contact&gt; returnList = new List&lt;Contact&gt; ();     String query = ' SELECT Id,Name, LastName,Department,MobilePhone, Email FROM Contact WHERE id IN : contactIds ';     for (Contact thisContact:  Database.Query(query)) {          returnList.add(thisContact);     }     try {       delete returnList;       return'deleted successfully';     }     catch(Exception ex){        return 'Problem occoured';     }  }  JS Method deleteSelected(){     deleteContacts({         contactIds :this.selectedIds     })      .then(result =&gt; {         this.dispatchEvent(             new ShowToastEvent({                 title: 'Success',                 message: result,                 variant: 'success',             }),         );         return refreshApex(this.getContactList, { searchKeyWord: '$searchKeyWord' });     })     .catch(error =&gt; {         this.error = error;     }); How can I change my VPN connection settings in Windows 7 from the command line?  I know how to do it using the GUI but I really need to do it from the console.  I need to change the user, password and internet address and then restart the connection. It doesn't matter if I have to install some third-party software in order to do this (from the command line). pdfx: incomplete CIDset in some fonts I try to compile a document as pdf/x and pdf/a with pdfx under LuaLaTeX, and I am already quite successful. One thing still poses problems though: With some fonts I get the following error if I check the resulting pdf/a file with Acrobat: "CIDset in subset font is incomplete (font contains glyphs that are not listed)" (VeraPDF gives the same error, so the issue seems to be real).  Here's a MWE:  \RequirePackage{filecontents} \begin{filecontents*}{\jobname.xmpdata} \Title{Test}       \Author{Simon Spiegel}       \Language{de-DE} \end{filecontents*} \documentclass {article} \usepackage{fontspec} \setmainfont{Palatino Linotype} [Ligatures={TeX,Common}, Extension = .ttf, ] \usepackage[a-3b]{pdfx} \begin{document} Test \end{document}   I realise that not everyone will be able to compile this MWE due to the proprietary font, but since the problem only occurs with specific fonts, I had to use this example.  The pdfx manual mentions this error, but only in relation to XeLaTeX. According to the manual, it should not occur with LuaLaTeX.  From what I understand, this seems to be at least to some degree a problem of this specific font, but since I am relying on it, I am looking for a way to fix it.  EDIT  Here's a new MWE with a bunch of fonts which are hopefully more common (the paths have to be adapted of course).  \RequirePackage{filecontents} \begin{filecontents*}{\jobname.xmpdata} \Title{Test}       \Author{Simon Spiegel}       \Language{de-DE} \end{filecontents*} \documentclass {article} \usepackage{fontspec} \setmainfont{Georgia} [Ligatures={TeX,Common}, Extension = .ttf, ]  \newfontfamily\fontone{Verdana} [Ligatures={TeX,Common}, Extension = .ttf, ] \newfontfamily\fonttwo{Cambria} [Ligatures={TeX,Common}, Extension = .ttf, Path = {/Users/simi/FontExplorerX/C/Cambria/} ] \usepackage[a-3b]{pdfx} \begin{document} Test  \fontone Test  \fonttwo Test \end{document}   All these fonts give me the same error. I wonder if this only happens with .ttf OpenType fonts. I am trying to build a custom Adventure Island. At this moment I am trying to limit the allowed items on this island. I'm trying to do this by filtering on a certain enchantment which is not item-specific.  For example.   When you want to filter an wooden sword with a custom name, you use this command:  /testfor @p[r=5] {Inventory:[{tag:{display:{Name:"Custom Sword"}}}]} &lt;   When you want to filter a wooden sword with a custom name and specific enchantement, you can use:  /testfor @p[r=5] {Inventory:[{tag:{display:{Name:"Custom Sword"},ench:[{id:16,lvl:1}]}}]} &lt;   But how can I filter on items with a specific enchantment on ANY item? I tried:  /testfor @p[r=5] {Inventory:[{tag:{ench:[{id:16,lvl:1}]}}]} &lt;   But this ain't work. Does anyone know how to solve this issue? I am going through Shankar's Principles of Quantum Mechanics and am having trouble finding the free particle propagator $U(t)$ that satisfies $$\lvert\psi (t)\rangle = U(t)\lvert\psi (0)\rangle$$ due to the degeneracy of the $E$ eigenkets. Shankar says that if the Hamiltonian has degenerate eigenvalues, we change the propagator equation from $$U(t) = \sum_{E} \lvert E\rangle\langle E\rvert e^{-iEt/{\hbar}}\tag{4.3.13}$$ to $$U(t) = \sum_{E} \sum_\alpha \lvert E, \alpha\rangle\langle E, \alpha\rvert e^{-iEt/\hbar} $$ where $\lvert E, \alpha \rangle $ are the orthonormal eigenkets for the $E$ eigenspace. This makes sense to me, because it seems like whenever we deal with degeneracy to use a projection. He also says for a Hamiltonian with no degeneracy to change the sum into an integral, so I imagine that for a Hamiltonian with a continuous, degenerate spectrum we would have this propagator: $$ U(t) = \sum_\alpha\int_\Re dE\lvert E, \alpha\rangle\langle E, \alpha\rvert e^{-iEt/\hbar}$$  I tried applying this to the free particle and had some trouble. In the book, after solving for the eigenkets and eigenvalues, $\lvert E\rangle = \lvert p\rangle$ and $p = \pm\sqrt{2mE}$, he chooses the propagator as a function of the momentum eigenvalues $p$ so that $$U(t) = \int_\Re dp\lvert p\rangle\langle p\rvert \exp(-ip^2t/2m).\tag{5.1.9}$$ I understand how he got to this, but I'm having some trouble because this doesn't appear to be the same expression that I have above. Splitting the integral up, we have $$U(t) = \int_{-\infty}^0dp\lvert p\rangle\langle p\rvert \exp(-ip^2t/2m) + \int_0^\infty dp\lvert p\rangle\langle p\rvert \exp(-ip^2t/2m)$$ The left integral can changed to an integral over $-p$, and the bounds switch from $0$ to $\infty$ such that: $$U(t) =  \int_{0}^\infty d(-p)\lvert -p\rangle\langle -p\rvert \exp(-ip^2t/2m) + \int_0^\infty dp\lvert p\rangle\langle p\rvert \exp(-ip^2t/2m)$$ Now we can substitute and interchange $\lvert p\rangle = \lvert E, + \rangle$,  $\lvert -p\rangle = \lvert E, - \rangle$, $E = p^2/2m$, and $dp = \pm mdE/\sqrt{2mE}$ to get: $$U(t) = \sum_{\alpha = \pm} \int_0^\infty dEm/\sqrt{2mE}\lvert E, \alpha\rangle\langle E, \alpha\rvert e^{-iEt/\hbar}. $$ This is the result that we are asked to prove in Exercise 5.1.1. Why is this not the same as the first expression for the propagator? Where did the extra $ m/\sqrt{2mE} $ come from? Am I just wrong in assuming that that is the general expression for a Hamiltonian with continuous and degenerate eigenvalues? Maximal ideals of polynomial rings in infinitely many variables Let $k$ be an algebraically closed field. Nullstellensatz states that the maximal ideals of the polynomial ring $R=k[X_1,\dots,X_n]$ are precisely those of the form $\langle X_1-a_1,\dots,X_n-a_n\rangle$, with $(a_1,\dots,a_n)\in k^n$.     What if we are working with infinitely many variables, say $\{X_i\}_{i\in I}$, being $I$ an infinite set? Again, the ideals of the form $\bigl\langle\{X_i-a_i: i\in I\}\bigr\rangle$, with $(a_i)_{i\in I}\subseteq k$ are maximal (even if $k$ is not algebraically closed), but what about the converse? Should I write "X and I", "X and me", "I and X", or "me and X" in a conjoined object? "Where will you go" vs. "Where you will go" Which sentence is correct between these?      Where will you go?     Where you will go? Use Outgoing SSH to receive incoming SSH My ISP does not allow me to have a static IP address. As such I am unable to remotely SSH in my home machine. Is there a way I could SSH from my home machine to a server and SSH into the server from my remote laptop and bridge the two connections?  Cheers! Is it possible to insert arguments into functions when they're used like Function@ or //Function? Having trouble setting up a nginx web server on Amazon EC2 Can we have threaded comments? The conversation often continues in the Comments and important information is held in the comments. I'd like to have threaded comments there. This is my first question.   Let $a_1, a_2,\ldots, a_k$ be natural numbers $\leq n$ with $m$ prime factors.  Let $p_1, p_2, \ldots, p_r$ be the prime numbers $\leq n$.   Let $$C_{m,n} = \frac{\sum_{i=1}^{k}a_i}{\sum_{i=1}^{r}p_i}$$ Does the following limit exist when $m\geq 2$? Obviously, when $m=1$,  $C_{1,n}=1$.  $$\lim_{n\to \infty} C_{m,n}$$  I have some guesses but not defendable enough.  My best,  The FM. Efficiently storing query-affecting settings in a database I want to know how to efficiently store query-affecting settings in a large analytical database (MS SQL Server). By efficiency I mean no hardcode (1) and fast/optimal query processing (2).  My example  I've got a massive table of sales orders. Let's simplify it to two columns:  SalesOrder  OrderID      int      Primary Key  OrderDate    date   I need to retrieve the list of orders for the last X days and this X should be configurable. That's why I introduce a table of settings where I define it:  Admin_Configuration  SettingName   (PK)|      SettingValue  ------------------|------------------  DaysBack          |          30      It allows me not to hardcode this "30" in query definitions. Then I would run queries like:  SELECT OrderId   FROM SalesOrder as S   JOIN Admin_Configuration as A     ON A.SettingName = 'DaysBack'   WHERE [OrderDate] &gt; DATEADD(DAY, -A.SettingValue, GETDATE());   Performance  It avoids hardcoding, but leads to a performance problem. This query runs much slower than it would've, had I simply hard-coded 30 in the WHERE clause.  My understanding is that optimizer doesn't know how large my SettingValue is and assumes the worst - that all rows would be retrieved from the SalesOrders table, thus leading to a suboptimal query plan.  Trying a scalar function yielded even worse results. I'm desperate enough to have a separate view which stores these hardcoded settings but I've been refraining from it with hopes for a better solution.  Here is the original query plan (with a join): 4 seconds elapsed   Here is the plan with subquery, as :  SELECT orderid FROM [SalesOrder] as s WHERE s.OrderDate &gt; dateadd(DAY,    (SELECT -NumValue    FROM Admin_Configuration where SettingName = 'DaysBack'   )     , getdate())   7 seconds elapsed, slightly slower   As for the ideal performance: I just hardcoded 20, the query took 2 seconds. It needs mentioning that the Admin_Configuration table contains only 18 rows, hence it shouldn't affect performance.  SELECT OrderId   FROM SalesOrder as S   JOIN Admin_Configuration as A     ON A.SettingName = 'DaysBack'   WHERE [OrderDate] &gt; DATEADD(DAY, -20, GETDATE());   Using parameters would mean that I'd have to replace views (that I use now) with stored procedures/table-valued functions, which is unacceptable in my case replacement wood threshold insert for metal door I have some late 70's doors and one is missing a threshold insert (the adjustable wood kind), anybody know of where one could by just the "wood strip" that goes in and screws down (there is a metal piece that sticks up into the wood, though you can't see it)?    They have about 4 screws that go down into them?