Is the exchange of momentum between two interacting objects always the same?
Deriving Newton's Third Law from homogeneity of Space
Schengen visa validity start date My Chinese in-laws intend to visit us in one month from now. Their visa is valid from Nov 23rd. Would it be possible for them to take the airplane on November 22nd in China and arrive in Schengen area on November 23rd?  Or does the visa already have to be valid upon departure?  In our particular case, they still need to transfer in Beijing first. The actual flight to Schengen zone effectively only departs on the 23rd so I guess that should be completely fine then? The entire answer is moving when hovering the bounty button It's just a minor CSS issue. See the following gif: Is there a 'rule of thumb' on the upper limit of how many related records in related objects an object should have to avoid slow page loading? Typically, each record in Salesforce will be 2kb large: .   However, let's say in an extreme example, the Opportunity object is related to 40 custom objects, each which has 100,000 records. The page would load much slower, especially in an older browser version.   1) Is there a 'rule of thumb' as to what the upper limit of how many related records an object should have?   2) Also, , there's an indication that there's some sort of tier-tuning per org based on the volume of data it has. Is that correct? And if so, are the volume ranges and respective tier-tuning capacity available? Python: list items are not changed in for loop Closed-Form Solution to Infinite Sum I often hear about subatomic particles having a property called "spin" but also that it doesn't actually relate to spinning about an axis like you would think. Which particles have spin? What does spin mean if not an actual spinning motion? Why would a company care about the price of its own shares in the stock market? There are a number of services that will scan a website for vulnerabilities and allow the display of a trustmark image if the site passes their tests.  This allegedly increases the level of trust a potential client feel toward the website and therefore makes them more likely to complete a purchase.    McAfee claims it has studies which show significant increases in sales. Should I take their word for it?  What sort of increase should I really expect, if any?  Are these types of services worth the prices they charge? How to prevent nginx redirecting from HTTPS to HTTP on AWS? I have a website served by nginx behind an AWS ELB Load Balancer. Only HTTPS is enabled on the load balancer.  Requesting individual files, or directories with a trailing slash, work fine. However, requesting directories without a trailing slash don't work.  The reason is, when I request the directory without the trailing slash, nginx does a redirect to the path with the trailing slash (that's OK), but it also changes from HTTPS to HTTP. The load balancer is configured to only allow HTTPS, so that doesn't work (timeout).  On the nginx logfile, I can see that the request reaches nginx, and that it's nginx that responds with the 301 Permanent Redirect (so it's not e.g. a problem with the load balancer setup).  10.100.10.15 - - [24/Nov/2017:15:41:08 +0000] "GET /admin HTTP/1.1" 301 178 "-" "Wget/1.18 (darwin16.0.0)"   When I request the URL via curl I see the redirect:  $ curl -v https://example.com/admin *   Trying 1.2.3.4... * TCP_NODELAY set * Connected to example.com (1.2.3.4) port 443 (#0) * TLS 1.2 connection using TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 * Server certificate: example.com * Server certificate: Amazon * Server certificate: Amazon Root CA 1 * Server certificate: Starfield Services Root Certificate Authority - G2 &gt; GET /admin HTTP/1.1 &gt; Host: example.com &gt; User-Agent: curl/7.54.0 &gt; Accept: */* &gt;  &lt; HTTP/1.1 301 Moved Permanently &lt; Date: Mon, 27 Nov 2017 09:19:05 GMT &lt; Content-Type: text/html &lt; Content-Length: 178 &lt; Connection: keep-alive &lt; Server: nginx &lt; Location: http://example.com/admin/ &lt; X-UA-Compatible: IE=Edge &lt;  &lt;html&gt; &lt;head&gt;&lt;title&gt;301 Moved Permanently&lt;/title&gt;&lt;/head&gt; &lt;body bgcolor="white"&gt; &lt;center&gt;&lt;h1&gt;301 Moved Permanently&lt;/h1&gt;&lt;/center&gt; &lt;hr&gt;&lt;center&gt;nginx&lt;/center&gt; &lt;/body&gt; &lt;/html&gt; * Connection #0 to host example.com left intact   My nginx config file is just   server {     root /var/www; }   The /etc/nginx/nginx.conf is .  I have tried server_name_in_redirect off but it did not make any difference.  I would like to avoid putting the hostname in the config file, because this is packed into a Docker image which is then deployed on different hosts (QA, Prod, etc.).  I would like nginx to do this redirect, but stay on HTTPS. What can I do? Strange bug with "MessageName[a,b] is not of the form symbol::name ", Debugger & cursor location How to fetch the columns of the synonyms for linked servers in SQL server I am using two servers local (SQL Server running on my system) and remote (SQL Server running on another system). I have created synonyms in my local server for a table which is located on the remote server.  Synonym used- CREATE SYNONYM [dbo].[test] FOR remoteserver_name .[database_name].[schema_name].object_name  Requirement   I need to fetch the columns of the synonym.  I can retrieve the columns of the synonym using below query in SQL server.  select * from dbo.test   where  dbo is synonym created schema name (local server schema name) and test is synonym name.  I have tried to retrieve the columns of the synonyms using below query, but I cannot fetch the columns  SELECT sys.schemas.name   AS SCHEMA_NAME,        sys.synonyms.name  AS view_name,        sys.columns.name   AS COL_NAME,        sys.types.name     AS data_typename FROM   sys.columns        INNER JOIN sys.synonyms             ON  OBJECT_ID(sys.synonyms.base_object_name) = sys.columns.object_id        INNER JOIN sys.schemas             ON  sys.schemas.schema_id = sys.synonyms.schema_id        LEFT OUTER JOIN sys.types             ON  sys.columns.system_type_id = sys.types.system_type_id WHERE  sys.types.system_type_id = sys.types.user_type_id        AND sys.schemas.name = N'scehmaname'        AND sys.synonyms.name = N'synonymname'   Can you please suggest some other way to retrieve the columns of the synonym or correct the above query? Why couldn't Bond have backup at the battle of Skyfall? I think I am missing a key plot point here.   Bond had to fake-kidnap M and bring her to Skyfall in order to lure Silva there for one last stand. Why did this have to be a secret from his colleagues at MI6? Why couldn't there have been other agents there to help defend the house and take down Silva?  Also, why did he have to have Q lay a fake trail to get Silva to follow him to Skyfall when he was actually going there, and he wanted Silva to follow him? What are logic gates? So from what I understand transistors are one of the most important electronic elements for computers because of TTL (Transistors-Transistors Logic).  Is this true? If so, how exactly does this work? I have heard the terms "logic gate" and "logic block" tossed around. Nesting block level elements inside the  tag... right or wrong? I'm trying to wrap my head around this for a while now. It's a simple question for what I think will be a not so simple answer. How would you go about modeling one leg of this stool? I would like to do it without using sculpt mode because I can't get things quite clean enough. The following code  number=1 if [[ $number =~ [0-9] ]] then   echo matched fi   works. If I try to use quotes in the regex, however, it stops:  number=1 if [[ $number =~ "[0-9]" ]] then   echo matched fi   I tried "\[0-9\]", too. What am I missing?  Funnily enough,  suggests this should work.  Bash version 3.2.39. I want to compute the Galois group of some polynomials, but I want to see some examples first. For example this proposition could be helpful. I don't know how to prove it &lt;.&lt;  Let's consider a polynomial $f(x)= x^4+ax^2+b \in \mathbb{Z} $. Let $ \pm\alpha , \pm\beta$ denote the roots of $f(x)$. Note that $f$ is irreducible iff $\alpha^2, \alpha\pm\beta \notin \mathbb{Q}$. So let's suppose that $f(x)$ is irreducible. Let's denote $G$ the galois group of $f$ (the Galois group of the splitting field $\mathbb{Q}(\alpha,\beta)/\mathbb{Q}$)  $i)$ $G\cong V$ the Klein 4-group iff $\alpha\beta \in \mathbb{Q}$  $ii)$ $G\cong \mathbb{Z}_4$ iff $\mathbb{Q}(\alpha\beta)=\mathbb{Q}(\alpha^2)$  $iii)$ $G\cong D_8$ the dihedral group of order 8, iff $\alpha\beta \notin \mathbb{Q}(\alpha^2)$  I need help with the proofs of this propositions... Well I'm very lost with the computation of Galois group, some care must be exercised, I don't have it. For example I know that Galois group acts transitively, in the sense that $u\in K/F$ a galois extension, the other roots of the minimal polynomial of $m_u(x)\in F[x]$ are precisely the elements $ \sigma(u)$ , where $\sigma \in Gal(K/F)$. And clearly any automorphism, is determined by only the value of a basis. In this case we are working on $\mathbb{Q}(\alpha,\beta)$, so I have to know the values of both. But I have to respect the algebraic relations involving $\alpha , \beta$ I proved that in $i),ii)$ $\mathbb{Q}(\alpha,\beta) = \mathbb{Q}(\alpha) $ So I have to know the values on $\alpha$.   My first question is: If in both cases $i),ii)$, I have an extension of degree 4 (so $|G|=4$) I have to map $\alpha$ to determine the automorphism, but I have also to map $\alpha$ to all of it's four roots. Why the galois group in this case are different?  My second question is about $iii)$ I have no idea How to attack it. I'm writing a sports management simulation game. Like most sport management games, it makes heavy use of statistics. I would like to use real players, teams and league names.  i) Am I running the risk of getting into legal battles if I should use the real names? ii) Also what about team colours and emblems etc?    Update Much thanks for all the input! When a 0-1-matrix with exactly two 1’s on each column and on each row is non-degenerated? [1] Logins with only HTTP - are they as insecure as I'm thinking? Recently I was thinking about how websites like gmail and amazon use HTTPS during the login process when accessing your account. This makes sense, obviously, since you're typing in your account username and password and you would want that to be secure. However, on Facebook, among countless other websites, their logins are done with simple HTTP. Doesn't that mean that my login name and password are completely unencrypted? Which, even worse, means that all those people who login to their facebooks (or similar sites) at a wifi hotspot in public are susceptible to anyone getting their credentials using a simple packet sniffer (or something similar)? Is it really that easy? Or am I misunderstanding internet security?  I'm a software engineer working on some web related stuff, and although at the current time I'm not too involved with the security aspect of our software, I knew I should probably know the answer to this question, since it's extremely fundamental to website security.  Thanks!