According to the doppler effect , if my source is faster than sound , will I hear the sound backwards?
Hearing a sound backwards because of Doppler effect
Ubuntu 18.04: switch back to /etc/network/interfaces Starting sometime around Ubuntu 18.04, the Ubuntu devs stopped using the classic /etc/init.d/networking and /etc/network/interfaces method of configuring the network and switched to some thing called . This has made a lot of people very angry and been widely regarded as a bad move. Is it possible to remove netplan and use the correct /etc/network/interfaces method for configuring the network? How is offside determined in football? The offside rule on the pitch is often unclear and called suddenly. How do I know if a player is offside? Opt in "mentor" privilege at 7.5k I am suggesting a Mentor privilege at 7.5k. It would be on a per-user per-site opt in basis.  At some reputation level (perhaps 7.5k) there could be an opt in "mentor" privilege.  If someone opts in then when a new user signs up, they become their Mentor. The new user is the Mentee.  They will get notified of any posts or suggested edits they make, and can help and support them.  While this would by no means help everyone (I'm sure there are more new people signing up than there are 7.5k people willing to help them), it could help mitigate the "new user's bad posts" and such like.  By no means would being someone's mentor mean you are the only person who can edit and help them, and you aren't obliged to do so - but if you have opted in then you should help.  How would this work?   Any Mentor would have no more than 5 active Mentees at once. Once the Mentee gets to 125 rep, the downvote privilege (or any other level deemed sensible) they are no longer a Mentee. If they aren't active for a month, they are no longer a Mentee. If the Mentor has 5 Mentees (i.e. cannot mentor anyone else) then any Mentee not active for 2 weeks is no longer a Mentee. The Mentee can opt out at any time, the Mentor can opt out, but if they opt out a lot (say 5 people in 2 months) they are blocked from the privilege for 2 weeks. The Mentor gets no extra rep. They can still get rep from answering their Mentee's questions and similar. Once the new user gets 20 rep on the site, a chat room is created for them to talk. No user with the association bonus will become a Mentee. This would (maybe) be opt in for sites. For example, this might not be at all useful for this site, or for , but on  or  I imagine this could be quite good.    appears to be asking the same thing, based on the title, but that is asking about people who know each other offline mentoring each other.    Every single one of these suggestions (especially the numbers) is open to discussion. Maybe 125 is to low to stop being mentored, or maybe it's too high. What do you think? proving topological equivalence How would I show that $$d_E = \sqrt{\sum_{i=1}^n(x_i-y_i)^2}$$ and $$d_\infty= \sum_{i=1}^n|x_i-y_i|$$ and $$\sup\{|x_1-y_1|,|x_2-y_2|,...,|x_n-y_n|\}$$ are topologically equivalent on $\mathbb{R}^n$? I can do it for $\mathbb{R}^2$, but I'm not sure how a generalization looks like. Search and replace registry entry value using powershell If $A^2 = I$, $B^2=I$ and $(AB)^2=I$, then $AB = BA$ Matrix Question  If $A^2 = I$, $B^2=I$ and $(AB)^2=I$, then $AB = BA$  Basically, got up to $A(BA-AB)B = 0$ (by cancelling and equating terms from $I^2 = I$ and to $A^2B^2 = A^2B^2$ and using distributive laws), but that doesn't work out too well!  Thanks for help in advance! In my document, I will write something like this (using natbib, but that shouldn't matter too much):  \citet{reference} show that .....   which would render as     Jones et al (1990) show that....   (\citet in \natbib creates an 'author-list (year)' reference style)  Of course if {reference} was a single individual, I should have written  \cite{reference} shows that ....   rendering as     Jones (1990) shows that....   Since I'm lazy and can't take the extra 5 seconds to search the reference to see if it's a single author or not, is there conceivably an automated way to do pluralization ? Or some relatively simple macro that would look like   \IfRefIsPlural{reference}{show}{shows} I understand what the game already tells you in the general sense... it changes enemy damage, resistances, and chance of legendary monsters appearing.  But, specifically, how does the difficulty level affect the game? Is going from Normal to Hard a 5% increase in damage? 50%? 200%? Are there any additional things changed that aren't mentioned. Does Survival mode add any extra mechanics, or is it just even bigger numbers than Very Hard? When does $120$ divide $n^5 - n$ Find n such that $n^5 - n$ is divisible by $120$. (*Here $n$ belongs to the natural number set)  Seems a trivial problem, but the answer mentioned in the text book seemed incomplete to me so I'm here just to ensure whether approach to this problem is correct or not.  So my approach is as follows: We know that $n^5 - n$ can be written as $n^5-n = n(n-1)(n+1)(n^2 + 1)$  Now since it's product of three consecutive natural numbers so it's divisible by $3! = 6$. Now using Fermat's Little theorem we can prove that $n^5= n \mod5$ hence $n^5 - n$ is divisible by $5$ as well. So $n^5 - n$ is divisible by $30$. Now to ensure their is another factor of $4$ in the term we need to ensure that $n^5 - n$ is divisible by $8$. I found that all odd natural numbers and multiples of $8$ makes $n^5 - n$ divisible by $8$, hence $n^5 - n$ is divisible by $120$. But in the text book they have only mentioned odd natural numbers as answer, which seemed incomplete to me.  Thanking everyone in advance:P Finding a formula to sum natural numbers up to $n$ Possible Duplicate:          I got this question in homework:  Find an expression for the sum ‫‪     $\sum k = 1 +\cdots + n‬‬$.    and prove it using an induction.   I'm not even near finding the expression. What I did notice is that if $n$ is (for example) 5 then the sum would be   $5^2 - 4^2 + 3^2 - 2^2 + 1^2$  So the first number is always positive and from there on the sign changes.  Any tips on how do I contintue from this point on, assuming I'm in the right direction?  Thanks! I've removed the poll style answers in favour of open discussion.  I realise now this isn't the best way to have a proper discussion about this issue - sorry to anyone who commented/voted.    This is mostly a followup on this question:    As I've answered, the reason this is happening is that the root database (in the production Stack Exchange database server) is still called StackExchange.Programmers - a database name that propagates to SEDE and through it to the data dump.  The question here is what to do about it - the current situation is somewhat broken for users of the data dump.  These are the options we have:   Do nothing Update the root database name (requires downtime - so very undesirable) Update the update scripts so the SEDE database name is the new name, change will flow to the data dump export (breaks any queries using the old name) Update the export to the data dump so only it gets the new name Something else we haven't thought about   I have added all of these options as answers below - please vote on the one you most prefer, we will try to accommodate the top voted answer. Book set underground everyone lives in pods woman wants to see her son Can anyone help me identify this book please? I read a book in the 80s about a woman living underground in a pod. Everyone had a big tv which gave them news etc (but it was starting to go wrong) and their food was delivered direct to their pod.  They weren't allowed to go to the earth surface as it was supposedly contaminated (post-war?). She gets a message from her son on the other side of the world and she takes the tube train from outside her pod and then some sort of aircraft to see him and eventually gets onto the surface of the earth and breathes the air and meets free people. Upper bound for $\sqrt[n]{n!}$ How to use proxy for Transmission? How to add “jQuery” onclick functionality for a column each row in jQgrid to display different popups for different rows I want to make it so I always have 50 entities in an area. So when 1 dies/despawns/leaves the area I want it to detect that and summon in a new entity, and yes I do want them to die/despawn/leave the area so preventing those things is not an option. How does "proof of effort" make a question better? It seems like many questions by new users are downvoted immediately.  Sometimes there is a comment to the tune of "lacks research", "we're not here to do your homework", or "show us some effort".  Now I wonder, what does it matter how much work someone has done before posting?  If someone can ask a good question in 5 seconds, more power to them.  To illustrate this point, look at how you could "improve" a question to include proof of effort.  You could put in 5 failed code snippets and their in- and output.  This would make for very long questions with a high noise ratio.  Another suggestion is to add "research".  By "research", I suppose most programmers mean "Google".  So this is basically a suggestion to add a list of fruitless Google queries.  That doesn't sound interesting either.  How can "proof of effort" turn a bad question into a good one? A proof that $1=2$. May I know why it’s false? While accepting an offer to grad school, one is basically entering into a lasting relationship with one's adviser - most likely, someone whom the applicant has never met before, and the only exposure has been through the potential adviser's website/publications. It is in the interest of both parties to ensure (to the greatest possible extent) that there are no personal/professional traits of either that hamper the formation of a pleasant working relationship - no-one would want to go through the ordeal of having to change advisers midway!  While the faculty has a chance to have a good look at the applicant's profile as well as his motivations (through his grades and SOP), the applicant doesn't have a similar opportunity. So, I'm interested to know what parameters can be used to gauge a potential fit. I've thought of the following:   Past students:  Did anyone ever drop out/change advisers midway, and if so, for what reasons? These would be a bit hard to find though, as I don't expect the faculty concerned would list them on their website. It would be great if anyone could let me know how to find out the list of incoming students to a department for any year. Publication rate, taking into account the venues where they were accepted. Time taken to graduate - though I accept this is more dependent on the student, a median figure should be telling ... What they did post Ph.D. - did anyone get tenure if they went into academia, or is almost everyone unable to break out of being a post-doc?  Tenure status: I'm a bit unsure about this, so wanted the community's opinions about it. Just so that I'm clear, I'm only trying to calibrate the applicant's expectations about the working style of his potential adviser - and hence need to know to what extent are the following "typical" assumptions valid.  Tenured professor  A full professor is more likely to get grant funding, hence less time spent on TAship - but could also mean less time/effort spent on interactions with students (either being busy with other projects/talks, or due to more commitments to family at that age).  Tenure-track faculty (Assistant profs)  More likely to be young and energetic, and could translate to more time spent on one-to-one discussions with grad students - but funding may prove to be an issue, and may have to be on TA for a longer period.   What other factors would be relevant in this matter, and to what extent am I correct/incorrect in either the factors considered, or for undertaking this exercise at all? Prove $P(x,y)$: If $x$ and $y$ are odd integers, then the product  $xy$ must also be odd.   I need a direct proof of this.  I know that $ x $ and $y$ both have to equal to $2n+1$ in order for them to be odd. But that's all I have. Any help will be appreciated.