I have two-step verification (via Google Authenticator) enabled for almost all of my accounts on the Internet. I somehow feel safe with that.  I have enabled two-step verification for almost all my accounts since I have read these news:      I want hate remembering passwords, allow me to use 12345 (just kidding) everywhere and let two-step authentication take care of security for me. I wish to enable two-step authentication for all my Stack Exchange sites. How would I do that?  I Googled, but I couldn't find a way to enable it. So, may be it's a feature request (correct me if I am wrong).
Is there any possibility of setting up two factor authentication (2FA) for Stack Exchange OpenID authentication?  I could just use my (already 2FA-enabled) Google account for Stack Exchange, but I would prefer to continue use Stack Exchange OpenID.  After  (which, I appreciate, didn't affect Stack Exchange, as you use IIS and Schannel, not OpenSSL), there have been a lot of recommendations to change passwords and to enable 2FA where possible.  So, what are the chances of a text-messaging-based or Google-Authenticator-based 2FA for Stack Exchange?
Integrating $\int_1^2 \int_0^ \sqrt{2x-x^2} \frac{1}{((x^2+y^2)^2} dydx $ in polar coordinates I'm having a problem converting $\int\limits_1^2  \int\limits_0^ \sqrt{2x-x^2}   \frac{1}{(x^2+y^2)^2}  dy dx $ to polar coordinates.  I drew the graph using my calculator, which looked like half a circle on the x axis.  I know that $\frac{1}{(x^2+y^2)^2}  dydx$ turns to $ \frac{r}{(r^2)^2}drd\theta$, which would be $ \frac{1}{r^3}$  The region of integration in  $\theta $ is I guess $0 \leq  \theta  \leq  \frac{1}{4}  \pi $, but I'm stuck for r. The lower boundary is $x=1=rcos\theta \rightarrow r=1/cos\theta=sec\theta$, but what is the upper boundary?? Is it  $\sqrt{2rcos\theta-r^2cos^2\theta}$? I tried this but I couldn't integrate my equation...  Could someone please help me out?  Also, how can I draw the graph of $y= \sqrt{2x-x^2} $? I could only know how it looked like by using my calculator... Can you concentrate on a special ability while also concentrating on a spell? There exist several abilities that have the text similar to, this effect lasts while you maintain concentration (as if you were concentrating on a spell). One such example is the Bard College of Glamour: Mantle of Majesty ability.     At 6th level, you gain the ability to cloak yourself in a fey magic   that makes others want to serve you. As a bonus action, you cast   command, without expending a spell slot, and you take on an appearance   of unearthly beauty for 1 minute or until your concentration ends (as   if you were concentrating on a spell). During this time, you can cast   command as a bonus action on each of your turns, without expending a   spell slot.   Another example is the Cleric Trickery Domain: Channel Divinity: Invoke Duplicity ability.     Starting at 2nd level, you can use your Channel Divinity to create an   illusory duplicate of yourself.      As an action, you create a perfect illusion of yourself that lasts for   1 minute, or until you lose your concentration (as if you were   concentrating on a spell).   While you are concentrating on maintaining such an ability would you also be able to maintain concentration on a spell that requires concentration?  There does not seem to be any RAW that limits this however the limitation around concentrating on a second spell exists which may suggest that the intent is that a character cannot concentrate on 2 effects at the same time unless explicitly stated. I'm trying to generate a secret key to be used for HMAC SHA-256 signature processing. I've seen many sample of keys with variable length from 32 characters to 96 characters.  What is the ironclad rule for this key size? I'm trying to install the  IDE in my Ubuntu and in the process it's asking for my root password which I don't remember. I know my  user password. How can I recover my root password? One who has potential, but never gives the effort to show it.   What would be the best word or words that match this description? biblatex and new line for DOI, URL and Eprint half sine and half cosine quaternions How to show bibliography alphabetically with biblatex? I'm looking to implement a phase lock in an FPGA without using any external components (other than the ADC). For simplicity locking to a simple binary pulse is adequate. The frequency of the signals is ~0.1-1% of the clock. I can't use the onboard clock PLL's because they are typically:   Not configurable (set during synthesis). Jittery. Don't support the frequency I need.   I've been sorting through the literature and found a few binary phase locked loops. Most notable a "pulse steal" design that I can post a link to if desired. I have implemented and synthesized with some success, but its jitter and lock range was not as good as advertised. I've also had success using a external DVCO, but I would prefer if I can implement everything on chip.  A digital circuit design or even a hint in the right direction would be helpful (I've been banging my head against this for a while), a proven FPGA implementation would be wonderful but not expected.   ADDED 10-27-2010   The actual DPLL design that I used has a "Random Walk Filter" as the loop filter (not the "pulse steal" described earlier, going through my notes that didn't work to well), which then drives the clock pulses to the DCO. The lock-in range is set via divider in the DCO. The sensitivity of the loop is established by varying the length of the random walk.   The paper in which this is found is cited at the end of this post. After implementing parts of it myself, I found that it was actually already implemented on OpenCores, however it turns out that in the last few months the project was deleted but I have the Verilog files saved if anyone wants them.  Yamamoto, H.; Mori, S.; , "Performance of Binary Quantized All Digital Phase-Locked Loop with a New Class of Sequential Filter," Communications, IEEE Transactions on , vol.26, no.1, pp. 35- 45, Jan 1978  doi: 10.1109/TCOM.1978.1093972  URL: How to synchronize systemd stop order from one service? Suppose I have a.service which I cannot modify, and b.service which I can modify, I want to see this stop order:  Stopping b.service ... Stopped b.service Stopping a.service ... Stopped a.service   instead of this:  Stopping b.service ... Stopping a.service ... Stopped b.service Stopped a.service   Assume that b.service may take at least 20 seconds to finish. I'd like to work on a bbcode filter for a php website. (I'm using cakephp, it would be a bbcode helper) I have some requirement.    Bbcodes can be nested. So something like that is valid.  [block]       [block]       [/block]       [block]           [block]           [/block]       [/block]   [/block]     Bbcodes can have 0 or more parameters.     Exemple:     [video: url="url", width="500", height="500"]Title[/video]   Bbcodes might have mutliple behaviours.     Let say, [url]text[/url] would be transformed to [url:url="text"]text[/url] or the video bbcode would be able to choose between youtube, dailymotion....  I think it cover most of my needs. I alreay done something with regex. But my biggest problem was to match parameters. In fact, I got nested bbcode to work and bbcode with 0 parameters. But when I added a regex match for parameters it didn't match nested bbcode correctly.   "\[($tag)(=.*)\"\](.*)\[\/\1\]"  // It wasn't .* but the non-gready matcher  I don't have the complete regex with me right now, But I had something that looked like that(above).  So is there a way to match bbcode efficiently with regex or something else.  The only thing I can think of is to use the visitor pattern and to split my text with each possible tags this way, I can have a bit more of control over my text parsing and I could probably validate my document so if the input text doesn't have valid bbcode. I could Notify the user with a error before saving anything.  I would use sablecc to create my text parser.   Any better idea? or anything that could lead to a efficient flexible bbcode parser?  Thank you and sorry for my bad english... How to run "sudo apt-get update" through proxy in commandline? In my office i want to update and download through (wget) and here they are using proxy?  How can i do this by commandline? As stated in the question, I am looking for a Noetherian ring over which the Euclidean algorithm is not valid.  I am trying to construct non-trivial examples of Noetherian rings.  Thank you. Constructing a HoTT proof term of 1≠0 As an exercise in HoTT basics, I am trying to construct a term that has the type $Id_{Nat}(S(O),O)\to\bot$. If this were a Coq proof, I'd be done after a single inversion on the premise, as the impossible identity would leave zero cases to consider. I guess I could do something similar here, but I'm not sure how. What would be an HoTT term that has the type? Let $C_k$ be the set obtained in the $k-$th stage of building the Cantor set, where  $$C_1=[0,\frac{1}{3}]\cup[\frac{1}{3},\frac{2}{3}]$$  $$C_2=[0,\frac{1}{9}]\cup[\frac{2}{9},\frac{1}{3}]\cup[\frac{2}{3},\frac{7}{9}]\cup[\frac{8}{9},1]$$  $$\dots$$  So we have   $$C_k=\bigcup_{j=1}^{2^k}I_{k,j}$$  where $I_{k,j}$ are pairwise disjoint closed intervals of length $3^{-k}$ in $[0,1]$, let  $$[0,1]\setminus C_k=\bigcup_{j=1}^{2^k-1}J_{k,j}$$  where $J_{k,j}$ are pairwise disjoint open intervals and each $J_{k,j}$ are located between intervals $I_{k,j},I_{k,j+1}$  define  $$F_k:[0,1]\to[0,1]$$  where  $$F_k(0)=0,F_k(1)=1,F_k(x)=\frac{j}{2^k}\quad x\in J_{k,j}$$  and $F_k$ is linear on each subinterval of $C_k$. We can show that $F_k$ converges to the Cantor function $F:[0,1]\to[0,1]$. Moreover, it can be shown that  $$|F_k(x)-F_k(y)|\leq\frac{3^k}{2^k}|x-y|$$  How can we show that $F$ is Hölder continuous of order $\log_32$ ? Most efficient way to append arrays in C#? I am pulling data out of an old-school ActiveX in the form of arrays of doubles. I don't initially know the final number of samples I will actually retrieve.  What is the most efficient way to concatenate these arrays together in C# as I pull them  out of the system? I use this program in Windows that's one-box and searches all of my drives. By default it lists all files, everywhere, in a single list. Is there a Linux graphical utility that does this? Is kinetic energy a relative quantity? Will it make inconsistent equations when applying it to the conservation of energy equations? How to alter touchpad settings on Ubuntu GNOME 16.04? After upgrading to Ubuntu GNOME 16.04 with GNOME 3.20 I have found that if I tap my touchpad it clicks which is something I do not want due to a faulty touchpad, previously I was able to disable this through the gnome-control-center, but seemingly there is no way to do this any more through there, so how do I do it? Also, even though it is set to false in gsettings and the dconf-editor seemingly for some reason somewhere in the system it is also set to true as it is behaving as such. I am also unable to set natural scrolling or any of the other touchpad settings seemingly, why not? How can I have an SPF record longer than 255 characters?