What security threats does the SA account and other known account names pose to security?

Question: Does an known account name like sa, pose a security threat to database? When using windows authentication on SQL Server does it impose the same password policy(if it was set to say account lockout after 5 times)?
Comment: Can you improve your question? 1) Make the title a question. 2) Can you narrow down the scope of the question? Are you interested about brute-forcing attacks, or the vulnerablies of known accounts. What *area* of security are you interested in?
Comment: I talk about this more in a book that I wrote that should be published in about a month.  I put this separately as buying the book isn't part the answer.  http://www.amazon.com/Securing-SQL-Server-Protecting-Attackers/dp/1597496251/ref=sr_1_1?ie=UTF8&qid=1294447009&sr=8-1
Comment: @Mrdenny could you give us some useful quotes from the book? It may help to answer your question, and citing it as a source is quite acceptable :)
Comment: @Brian I'll have to check the contract to see if I can do that.  I may have to paraphrase, but I'll see what I can do.
Answer:
Does an known account name like sa, pose a security threat to database?

A "god" user account with a known name is generally considered a worse idea than a god user with a less well known name. It makes brute force attacks that bit easier as the attacker only has to guess the password and not the username and the password.
Also having a god user anyway can be dangerous. You are generally better off having specific users with specific rights for what they need to do. This sort of privilege based security is easier to implement from scratch than it is to retrofit into your environment later.
Disabling sa and giving specific users specific admin rights as needed in SQL server is essentially the same recommendation as disabling root and handing out admin rights as needed via sudo under Linux and similar. You can always re-enable sa once directly connected to the machine with adequate privileges should anything go wrong and you end up dropping all the rights your users need to operate (and fix the issue) just the same as you can engineer root access to a Linux box if you have physical access to the box - so disabling the account is no magic bullet (but once an attacker has physical access to your machine, or full Administrative access via RDC or SSH, all bets are off anyway).

When using windows authentication on SQL Server does it impose the same password policy(if it was set to say account lockout after 5 times)?

When using Windows Integrated Authentication SQL server has no control over account lockouts and such - it just maps a Windows user to an SQL user and asks the OS to vouch for the fact that the user has provided appropriate credentials. For interactive human users this means any lockout would occur as the user attempted to authenticate with Windows, not as they logged in to SQL Server.
Answer: It's not a bad idea to make it so that the default admin user (admin/root/postgres/sa/etc) don't actually exist in your system.  You can always create a privileged account under a different name.
If nothing else, people trying to exploit your system don't have quite as easy of a time as if they're working blind (eg, sql injection without having some interactive shell nor being able to see direct output from their commands)
As for account lockouts -- if someone's managed to get far enough to even be able to attempt to log into your machine, unless you specifically allow direct login from users, you've already lost the battle.  Personally, I'm not in favor of lockouts for the most part, because it gives someone the ability to create a denial of service if they manage to get the name of any of your users.  (and having them lock out the super user?  not fun).
I'd recommend looking over the CIS Benchmarks ... they don't have them for every database, but they have recommendations for Oracle, MS SQL, DB2 and MySQL.  If you're running something else, it's still worth looking over the general sorts of things they recommend.
Answer: I didn't see anyone else mention this so I'll add it.
With SQL Server 2005+ if your server is part of a domain and the domain has a password policy you can enable the password policy to be enforced on SQL logins. This includes password complexity requirements and the ability to force password changes at login.
Note that this can at times cause problems with some software installers that haven't been updated to work with SQL 2005+ and create SQL logins with insecure passwords.
Answer: There are two authentication modes used in SQL Server: Windows authentication and mixed mode (enables both Windows authentication and SQL Server authentication)
The first mode is less vulnerable to brute-force attacks as the attacker is likely to run into a login lockout (the Account Lockout Policy feature) after a finite number of attack attempts. Every production environment, if using Windows Authentication mode, should utilize the lockout policy feature, as it makes brute-force attacks impossible
When it comes to SQL Server authentication brute-force attack vulnerability, the situation is not so favorable. SQL Server Authentication has no features that allow detecting when the system is under a brute-force attack. Moreover, SQL Server is very responsive when it comes to validating the SQL Server authentication credentials. It can easily handle repeated, aggressive, brute-force login attempts without negative overall performance that might indicate such attacks. This means that the SQL Server Authentication is a perfect target for password cracking via brute-force attacks
Also, brute-force methods are evolving with each newly introduced encryption and password complexity method. For example, attackers that use rainbow tables (the pre-computed tables for reversing the cryptographic hash values for every possible combination of characters) can easily and quickly crack any hashed password
In order to protect your SQL Server from brute-force attacks, you should consider the following:

Don't use SQL Server Authentication mode - force the attacker to hit the login lockout via Windows Authentication
In case you need to use SQL Server Authentication mode, disable or remove the SA login – that way the attacker must guess and pair both the user name and password
Answer: The sa account, when enabled can do anything on the SQL Server.  If an attacker were to get into this account they could do anything on the SQL Server instance (and possibly the host OS) that they wanted.
Answer: The SA (and other well known account names) are well known points that hackers can attack. Some of the Oracle ones were poorly documented and thus the default passwords were not always changed. Once you've got control of the SA account in SQL Server, you control the server it is running on and can run any code or install anything you wish. In my more cowboy days, I remember not being allowed (it needed paperwork I wasn't going to fill out) to install an ActiveX control on a webserver that was also hosting the SQL Server - so I used xp_cmdshell to copy and install the control.
Comment: The default Oracle SYS password is change_on_install and you would be surprised how many people don't!


What is the difference between XLR and JACK out?

Question: Hi I was just wanting to know what the difference is between XLR and JACK out is.  I'm sort of new to this sort of thing. (So if someone could explain it as simple as possible would be great!)
Answer: XLR typically gives you a 'balanced' connection, whereas the Jack connection is unbalanced.
An unbalanced connection is very susceptible to electromagnetic interference - the mains hum you get from a guitar plugged into an amp, for example. For a high signal level instrument, like a guitar, this is often not a problem, but for a low level signal like a microphone it could significantly degrade the sound quality, so balanced connections are used.
From Wikipedia:

A typical balanced cable contains two identical wires, which are twisted together and then wrapped with a third conductor (foil or braid) that acts as a shield.
The term "balanced" comes from the method of connecting each wire to identical impedances at source and load. This means that much of the electromagnetic interference will induce an equal noise voltage in each wire. Since the amplifier at the far end measures the difference in voltage between the two signal lines, noise that is identical on both wires is rejected.

Over on Music Stack Exchange we have some useful posts on balanced audio, including this one.
Comment: @Tetsujin Mono balanced TRS is actually very common in studio monitors. I think a more accurate answer would be "Jack can be either TS or TRS. There's no difference between TRS and XLR, both can carry stereo or balanced mono signals (most commonly the later). The difference between TS and XLR is that TS is unbalanced mono." or something around those lines.
Comment: Isn't a TRS cable a balanced "Jack" connection?
Comment: only if it's mono; not just by default of it being a TRS. It could be either, but balanced TRS is not common. Not impossible [I have one device that can use it] but just not common. Conversely, I'm not about to see how much my Rikki stereo would appreciate 48v ;-)
Comment: Interesting, & fair point - can't say I've noticed on studio monitors, as I almost never see round the back. My own are XLR actually, Dynaudios.
Answer: In addition to Rory's answer, it is also important to remember that XLR is a locking connector (though the lock isn't always utilized) where as 1/4" (the more common term for what I assume is being referred to as JACK) is a non-locking connector.  It is susceptible to accidentally being pulled out.
It also has some inconsistency in application.  1/4" cables are used both for instrument cables, some line level signals and amplified signals from amplifiers to loud speakers.  This is dangerous as plugging the wrong line in to the wrong device can result in damage since there are 3 different levels of signal being sent over the same kind of connection.
For safety and reliability sake, more well built systems will often use XLR connections for mics and line level signals (and convert instrument cables to XLR in a direct box early on).  They will also use speakOn connectors such as Neutrik NL2 or NL4 connectors on amplifier connections (a different type of connection which locks and won't fit with the lower power connectors.)  NL4 has the added advantage of keeping tweeter and woofer feeds reliably separated (incorrect wiring can cause speaker damage.)  This ensures that cables can't be pulled out accidentally and also helps prevent incorrect connections that could cause damage to the system.


ShareKit : Facebook connection issue in iOS

Question: getshrekit.com : Yesterday I was facing problem in Facebook. I was register App on Facebook and that keys are incorporated in ShareKit when I was click the Facebook button I was getting error Screen shot attached.
Please provide your feedback.!
Answer: Whenever you use ShareKit, you need to first check updated version of it. You can follow this link and i hope it will certainly help you. http://getsharekit.com/docs/


How can a signal be both periodic and random?

Question: Do any examples of such signals exist where the signal is both periodic and random? Because as I see it, if a signal is periodic then the randomness kinda goes away because you know what the signal will look like after some time.
Comment: White noise, pink noise and brown noise come to mind.
Comment: Counterquestion: Is Gaussian noise truly random? Because, if you know the mean value and the variance, you kinda know what the value is going to be when you look at it. Same with stochastic signals: a periodicity in the time-dependent probability density function might really look like periodicity (think of Gaussian noise, just that its variance is $\sin(2\pi f t)$-modulated). Or,think of the joint probability density function of that random var $X$ for two time instants $t_1$ and $t_2$, $f_{X(t_1),X(t_2)}$: pdf can be very periodic,and you'll learn a lot about these when discussing receivers.
Answer: An example you run typically across in a text book (Papoulis as an example) is the sine with random phase
$$
x(t)=\sin(2\pi f + \phi)
$$
where $\phi$ is a random variable, distributed uniformly, over $0$ to $2\pi$.
Any realization will have $\phi$ take on a particular value, but it's random, just like a 6 on a dice after a throw. You could not predict it would be 6 before the throw or in this case you could not predict $\phi$ before you received the signal.
At the other extreme, you can construct a very "random" looking waveform using something like randn() in Matlab. It will pass several statistical tests for randomness but if you use the same seed, the waveform is perfectly repeatable (deterministic).
Every waveform has a story ( a context ) and the story is how you judge if something is random or not.
Comment: Also, in the long term the random sixes have a reliable period of one in six throws. Hence, a random signal with a predictable period.
Answer: Most realistic signals are both random and periodic.
For example, you can modulate a harmonic oscillator with a slow enough random signal that moves its frequency around a $\mu_{f}, \sigma_f$. This looks like:
$$y= \sin \left( \frac{2 \pi \mathcal{N_s}(\mu_f, \sigma_f) n}{Fs} \right )$$
Where $\mathcal{N_s}(\cdot)$, denotes a normally distributed random variable that evolves much slower than once every sample.
For short segments, this signal is approximately periodic but because of the random phase, it never quite is periodic.
In fact, the signal does not even have to have any resemblance to trigonometric functions.
The Electrocardiogram (ECG) for example is approximately periodic for an average human being at rest. However, the heart modulates its function at every beat. Therefore, in the long term, while there is some structure in this signal, its period is random.
And finally, taken to the extreme, the signal does not even have to have any resemblance to "periodicity" and yet still be periodic. These are chaotic signals. These can appear to look like noise, like the output of a laser for example but careful examination of their state space reveals some form of regularity.

...the randomness kinda goes away because you know what the signal will look like after some time.

The key phrase here is "...after some time" and the question is "How much time"?
Consider for example a binary sequence of length 3. It has 8 distinct states ($000, 001, 010, 011, ...$). This means that it will "run out of combinations" very quickly and its patterns would have to start re-appearing. But in reality, the phenomena that give rise to signals do not have to occur in "small finite batches". If you were to start looking for subsequences of length 3 you would find that even they tend to appear in more complex batches of pairs of sequences of threes...And then what about pairs of pairs of subsequences and so on.
Therefore, yes, periodicity, but at what timescale?
Hope this helps.
Comment: Also, if anyone is interested in the non-dsp viewpoint of this, google for  "yule-slutsky" or "slutsky-yule" effect.
Comment: Hi: I can't find links where you can get them ( I may have them somewhere in non hard-copy. I found only hard copies ) but here are two you would like. ( especially second one ). 1) The Spectral Theory of Discrete Stochastic Processes and 2)  The Oscillatory Behavior of Moving Averages. I'm sorry that I can't provide links. Both are by P.A.P Moran.
Comment: @markleeds I did not know about this, thank you. I feel that it is worthy of a answer on its own as yet another possible pathway to periorandomic signals.
Comment: Hi: youre quite welcome and am glad you liked it. I always find it interesting to see what these giants were doing in the early days. Truly unbelievable if you ask me. The comment is fine I think, particularly because it's a DSP list. If you are interested in the connection, check out a paper by Moran. I'll try to find the link to it. He takes the yule-slutsky finding and uses DSP to derive an interesting DSP like property. Let me find it and atleast provide the  title.
Answer: If you are talking about a given signal as "a deterministic realization of a phenomenon", it can be periodic, but not really random.
However, some physical systems are prone to produce randomness and periodicity, like rotating machines, gears, cyclic engines, that produce signals similar to:

Naturally rotating bodies (stars, planets) also produce random periodic events (sunspots, daily temperatures).
A whole branch of digital processing is devoted to those. In terms of processes (that may generate realizations in terms of signals), then there exists notions that combine stochasticity and periodicity, like:

random periodic processes,
cyclostationnarity, or periodically processes.

A stochastic process $x(t)$ with expectation $\operatorname{E}[x(t)]$  and autocorrelation $R_x(t,\tau) = \operatorname{E} \{ x(t + \tau) x^*(t) \},$ is said wide-sense cyclostationary for $T_0> 0$ if

$\operatorname{E}[x(t)] = \operatorname{E}[x(t+T_0)]$,
$R_x(t,\tau) = R_x(t+T_0; \tau)$.


Is it reasonable to write patent documents on your own?

Question: Obviously all agents and lawyers will vote to work with them.
How hard is it to write patent documents on your own?
Answer: I am not a patent agent or attorney, yet I believe patent agents and attorneys' help is extremely valuable for filing patent applications because of their experience. You can do large parts of the filing yourself, yet you should better seek help for writing the application and the arguments during prosecution.
It is quite easy to obtain a patent entirely on your own. If you invented something worth patenting, and have some experience in writing say scientific papers, you can get a patent on this invention eventually. It requires quite a fair amount of work, quite a long time, but it's doable. However, the patent you will get might be worth nothing at all from an IP point of view. It might even be counter-productive as it will publicly disclose your invention.
The description is filed initially, and mostly cannot be changed. It sets the priority date. If you realize you missed something in your description, you might need to file a new patent application and added matter will get a new priority date. Since patent prosecution is long, you will typically realize this during examination, several years later, and your invention will not be so fresh and will therefore be less patentable.
Patent agents and attorneys will help you get the description right initially. They can ask you to write a description of your invention and will transform it to make it a great patent application. For example, they know about subtle elements that must be present the description, especially in the difficult field of software patents. They know this because they are aware of appeals decisions and they acquired experience from past cases with other clients. You could read about appeals and other decisions, learn from blogs (and pass the exam to become an agent yourself), yet there are things you will only learn from experience of prosecution. Besides, if you plan to seek patents internationally, you will need help from agents or attorneys who are aware of usage abroad.
Patent agents and attorneys will also help for writing claims. Part of this help comes from not being the inventor and understanding the value of the patent application. Part of this help also comes from their experience of prosecution. Also, they know the usage for writing claims, but you can figure this out yourself.
Patent agents and attorneys also know how to argue with examiners. This is less critical than getting the description right initially, yet it is both a time-saver and a way to get a patent as broad as possible. Examination is often tough and office actions are not always easy to understand. Besides, not being the inventor helps them react rationally. They also know the usage for writing amendments, but you can figure this out yourself.
Patent agents and attorneys know how to file forms and design figures that respect the requirements. This is the less critical aspect and will only save time. If you do it wrong, the office will usually give you a chance to fix the forms or the figures.
Eventually, patent agents and attorneys know about the timing. They typically use software or some tool to perform all operations in time. Most offices will tell you about acceptable delays for procedure, and in many cases you can do things late with a financial penalty. Yet failing to respect timing can invalidate your application.
Comment: Very insightful answer.
Comment: It's not just the claims. I see many inventors who don't really understand what makes their inventor different from the prior art, so they leave out small details that would make the issued patent stronger and more valuable. Inventors tend to miss the "written description' requirement, because "everyone knows what they mean."
Answer: You might consider writing a patent using this analogy:  writing a critical app using a new coding language that is vaguely related to the language you presently prefer, but that has a few interesting type conventions which, if you don't know about them, will lead to significant bugs.
You get one chance to compile and debug, after the code is written.  The compiler may produce recoverable errors, or it may produce unrecoverable errors.  The recoverable errors will cost $1000s to fix, while the unrecoverable ones will not be fixable.
How do you feel about writing a patent document on your own?
Comment: And the syntax and semantics of the language are changed slightly every few months between when you wrote it and when it is first complied 2 years later. The rules on editing at that point do not permit "new matter".
Comment: With that description, I don't fancy anyone's chances of writing a patent document successfully ;o)
Comment: Now you know exactly how patent agents and attorneys feel....
Answer: There are inventors who do a reasonable job of drafting a provisional application that has some value. If they understand the limits of the value they are getting and do not get a false sense of security from it, they will probably be better off than if they had done nothing. Although I do not recommend writing your own patent application, I do highly recommend reading Patent it Yourself by David Pressman. It is updated every year and he has a web site covering errata and changes in the law. If you study the book, do not skip the complex parts or the boring parts and feel confident you could write a regular patent application then you might be able to write a provisional application without shooting yourself in the foot.
The more abstract and complex your invention is the lower the likelihood is that you, or anyone, will get it right. But there are prolific inventors who follow courts cases, attend the annual USPTO independent inventor conferences in D.C. and faithfully read the PatentlyO blog every day. If you consistently have 10 good ideas a year and are willing to learn enough so you could almost pass the patent bar exam (you can find old ones on-line) and to play the percentages of winning and loosing, getting better at it as you go, then have at it.
I am a relative newbie, having passed the patent bar five years ago in order to get into a second career as a patent agent after being an engineer, technical manager and entrepreneur for 20+ years. I was always the person interfacing between the outside patent attorneys and the engineer/inventors and I thought I had a pretty good handle on the topic. I didn't.
The first step in becoming a registered patent practitioner is filling out a form and sending it with your college transcript to the USPTO. I got the form back with a letter: "Please fill out and submit the form again. You included your name on line 1a, thank you, but you neglected to fill in your name as it appears on your government issued ID in line 1b." Just the tip of the iceberg of nits to get right or your patent goes abandoned.
After studying for and passing the patent bar (it has a 50% pass rate), I decided to take one of my own (lame) ideas and do a patentability search and then write an application before I hung up a shingle to take on anyone else's project. Every week for three months I announced to my wife that "Last week I thought I knew what I was doing but I was wrong, now I really do know what I am doing."
Answer: 80% of a patent you can write yourself.  I have written over 50.  The process is very straight forward as long as you understand how to organize it.  I have probably saved over $100,000 writing my own.
The part you absolutely want to have a lawyer do (keyword: absolutely!) is drafting your claims. This language is key to obtaining your patent and getting your claims accepted.  It is an "art form" few master with out considerable experience.  I would also advise having a lawyer submit your patent as the submittal, and follow on correspondence, can be tricky.
Answer: I agree completely with Ken S (the above poster), and couldn't put it better.  I have also drafted my own patent application, and my lawyer has had to change very little.
Writing the claims is something else.  It seems to require a different, more strategic approach, than the descriptions.  Those are truly just technical documents detailing your invention and illustrating the novel aspects.
Still, going it alone might not always be a bad choice.  The claims I had written, but not shown, to my lawyer were nearly identical to her wording and substance as well.  Either she is a bad lawyer or I've grasped something about the process.
Studying approved patents, and also what happened to those products, is great practice whether you lawyer-up or not.


When should I plant an apple tree in the UK?

Question: Can anyone tell me what the best time is to plant apple trees in the UK? These trees will be on a trellis and will be spread wide not high.
Answer: Doesn't matter whether you're fan training, espalier or cordon growing, the best time for planting trees in the UK is September or October. If they're container grown plants, you can plant at other times, like February or March, if the ground is neither waterlogged nor frozen, but you will need to pay careful attention to watering during the first and second year, especially the first summer.
UPDATE
As requested, I'll expand the answer. In the UK, the soil is still warm up to end of October, but the heat of summer is well past and we're usually pretty wet during autumn, which is why autumn planting is recommended for long term, woody specimens such as trees and shrubs. The weather here supplies sufficient moisture during autumn and winter, and because the soil is still warm, roots settle in quicker. Bare root trees and shrubs are best planted October, not September, through to early November at the latest,  for similar reasons, though the timing varies somewhat depending on which part of the UK - in the south, planting is best in October, in the North, September.
Comment: @GiacomoCatenazzi see expanded answer, but I mentioned September because the person does not live in the southern part of the UK. Here in the South, September planting isn't great, its usually very dry here during that month, often into October as well, now, because of climate change.
Comment: Already in September? I was thinking in autumn, but just after falling leaves (so dormant plant). But so I never really understood why autumn is much better then late winter. Could you expand the answer. It is in any case one of the most important topic (IMO).
Comment: Sorry, that should say 'might not' live in the southern part...


Can't get internet working in Ubuntu 12.04 guest virtual box

Question: I cannot get internet working at my work place, may be because of proxy. At home internet works perfectly fine. Virtual Box is using NAT for network connection. I had also tried changing the connection to Bridged and didn't work either. I have seen a lot of posts on this and none of them have solved my issue. Unless this one works I cannot connect to CVS from Eclipse.
eth1      Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx
      inet addr:10.0.2.15  Bcast:10.0.2.255  Mask:255.255.255.0
      inet6 addr: xxxx::a00:27ff:fe4a:f961/64 Scope:Link
      UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
      RX packets:372126 errors:3 dropped:0 overruns:0 frame:0
      TX packets:173506 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:1000
      RX bytes:446759931 (446.7 MB)  TX bytes:10066402 (10.0 MB)
      Interrupt:10 Base address:0xd020

 lo        Link encap:Local Loopback
      inet addr:127.0.0.1  Mask:255.0.0.0
      inet6 addr: ::1/128 Scope:Host
      UP LOOPBACK RUNNING  MTU:65536  Metric:1
      RX packets:710 errors:0 dropped:0 overruns:0 frame:0
      TX packets:710 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:0
      RX bytes:66411 (66.4 KB)  TX bytes:66411 (66.4 KB)

This is what I have in /etc/network/interfaces/
auto lo
iface lo inet loopback

I tried appending below settings, didn't work for me
auto eth1
iface eth1 inet loopback

Can someone help me how to get this working. Virtual Box with Windows 7 Guest working perfectly fine, but not Ubuntu. This problem is it fixed in later versions of Ubuntu, so that I can update it or any suggestions on fixing this
Answer: As far as I know it will only work with bridged mode.
Also you might have to set the proxy of Ubuntu too.
What is the ifconfig output when you use bridged mode?
To set a proxy try:

export http_proxy=ip.or.hostname:port
Comment: Network is always trying to connect, it doesn't connect in bridge mode. Ubuntu doesn't even start quickly, I get `Waiting up to 60 more seconds for network configuration`. /etc/network/interfaces doesn't even show the `eth1` config. It just shows `lo`


version control for small team

Question: We are bootstrapping a new team of very small size (say 2-5) my question is:
 which type of version control works best for these kind of teams, either centralized or distributed.
Comment: What dó you want to write, and what platforme?
Comment: Try SVN http://tortoisesvn.tigris.org/ This is best 4 you.
Answer: Distributed all the way, there is really no point for centralized anymore IMHO, specially if you are talking about team development.
Another vote for Mercurial, no hassles to setup under windows and bitbucket.org has free repositories (that can be private) with unlimited space.
If you are planning to work on a open source project, git and Github seem to be more adequate/popular. However, if you haven't ventured into DVCSs, I recommend you start with Mercurial and this awesome guide.
Comment: Even as a lone developer Mercurial makes perfect sense.
Comment: +1 for that awesome guide from Joel Spolsky.  Great stuff.  Also, even if you are very small now, like @dukeofgaming says, there is no point for starting out centralized anymore.  Even if you're only planning slightly ahead.
Comment: For projects caring about software freedom, gitorious is probably better than github.
Comment: @Lars: What do you mean by "software freedom"?
Comment: amen @Helper Method, that is how I started to use it
Comment: +1 for mentioning bitbucket.  I wasn't aware of that one.  Private repos are neat.
Comment: @Richard Ev: http://en.wikipedia.org/wiki/Software_freedom should get you started
Answer: the one that you will all use consistently
[personally, i like Mercurial]
Comment: As long as it's not SourceSafe.
Answer: Probably the best answer is "whatever you're comfortable with." Even when working on personal stuff, I use Git. It seems to do a pretty good job of scaling both up and down and my limited experience with Mercurial is about the same.
Comment: Msysgit works nicely if you are familiar with a Shell prompt.
Comment: From my limited experience with Git -- if you're on a Windows platform, Git tools are not ready for prime time there yet.  Stick with Mercurial (or Kiln).  On other platforms, Git is probably fine.
Comment: @Mark you are certainly correct if folks don't want command line. However, Git command line (with a shell as Thorbjorn points out) is fine. I only program on Windows and am using Git for VS projects. There's certainly nothing that approaches TortoiseSVN and AnkhSVN for Git though.
Answer: I think you should choose whatever you are comfortable with. In a small team, you will not have different code-trees (like the Linux-kernel), so a central repository is OK. But you can have this setup also with distributed VCS. So I would go with popularity and personal experience. Popular are SVN, git and Mercurial. You should decide, which o them is best used with your team (experience, tool-support in your choosen IDE etc.).
Answer: It really depends of whether or not your developers are going to develop a lot of code offline or not, but only to choose between a distributed or centralized repository, since this is the first thing you should decide. Then, if you decide that a centralized approach works better than SVN is all you need. On the other side if you go for a distributed approach than go for git, even on windows it's good enough since now you have tortoise git (the same interface that also exists for svn). Also, don't count so much on the IDE support because you might get a nasty surprise if you ever use that, and you might find that files that shouldn't be commit do get committed in your behalf by the IDE.
Answer: Ask your team, if some one want to take care of it. It is much better to have stable system, and responsible person, than good system when none care about it, and none able to restore it from backup.
If there is such person - he will already know what to use, so just accept his decision. If not - get some hosted solution. It would be very stupid try GIT (one of the best) if all of developers never touched Shell/Linux.
It also depends of number of "nontechnical" people, that need to read/contribute. Just make sure that they could use it, and there are tools available.
Answer: SVN is widely supported in tools. Tooling is the key; different people will have different skill sets. Some will prefer command line, some will prefer IDE based tools, some will prefer graphical tools. At the moment SVN seems to be the most widely supported tool.
Other than that Mercurial or Git.
Answer: I think that in small companies there are arguments for having certain things centralized. (Think for example about offsite backup. When you only have 2 persons working on a project and they are housing in the same building and there is a fire, decentralized to all of two computers might not be enough.)
However: having a partly centralized solution doesn't limit you to a centralized system. You can just push to an outside server with something like git or mercurial.

version control for small team


Mail.app Bug -- Keeps Showing Messages

Question: I'm running Mail.app on my Mac (Snow Leopard).  Two GMail accounts are linked to it using POP.  There is an annoying bug which causes certain messages from one of the account to show up in my Inbox.  They are always messages I sent to a certain account, and are 6-7 messages from one thread.  If I delete them, they just show up again if I restart Mail.app or switch to a different mailbox and back, although the number of messages goes down, until it reaches one, and goes back to six-seven.  The only solution I have found is to delete the offending thread from within GMail, except that then another thread takes its place and starts annoying me.
Any solution?
Comment: Are you using POP or IMAP?
Answer: I had a similar problem with GMail constantly showing several messages as inboxed messages. It was like it eternally received the exact same messages. Your best bet would be to contact the GMail team at email@example.com.
Comment: Did they resolve your problem?
Comment: Yes. I'm not sure what they did, but it stopped happening.

Mail.app Bug -- Keeps Showing Messages


Reinstall Ubuntu with encrypted home directory?

Question: I have Ubuntu 10.04 installed with encrypted home directory. /home is on a a separate partition. Can I just boot from a 10.10 CD, reformat / and install as usual? Should it work if I use the same password? Is there anything else to keep in mind?
Answer: I have previously done this on Ubuntu and Mandriva.
This will work and you will be able to mount your existing /home partition even if it is encrypted as long as you know the passphrase.
Thing to keep in mind is to set up the mount points correctly and don't accidentally format your /home partition.
Comment: Will the installer ask for the passphrase or will it be asked on first login? Or do ineed to enter it manually somewhere?
Comment: Actually you don't need to know the passphrase, just the password that will be asked when you first login after the installation.
Answer: You should take a note of your mount passphrase. This is covered on the page
https://help.ubuntu.com/community/EncryptedPrivateDirectory - "Recovering Your Mount Passphrase"
Answer: It will work as long as you use the same username and password.
Actually you won't need the passphrase, just the password that will be asked when you first login after the installation.


On the paper "On the asymptotic  linearity of Castelnuovo-Mumford regularity"

Question: I have posted this question on MSE, however it seems not to be interested by member there, so I decided to post it here. I am sorry if you feel it is not appropriate for MO.
I am now reading the paper on Castelnuovo-Mumford regularity of Ngo Viet Trung and Hsin-Ju Wang, which can be found
here
In this paper, the authors gave the concept of flat extension of ring, and in my opinion, they gave an example of it (in the lemma 1.2):

Let $A$ be a Noetherian ring, $R$ be standard graded finitely generated $A$-algebra, $R_{+}$ be its irrelevant ideal, $M$ be a finitely generated $R$-module.
  Let $Q$ be a $M$-reduction of $R_+$, generated by linear form $x_{1},...,x_{s}$. For $i=1,...,s$, put $z_{i}=\sum_{j=1}^{s}u_{ij}x_{j}$ where $U=\lbrace u_{ij}|i,j=1,...,s\rbrace$ is a matrix of indeterminates. Put $A'=A[U,\text{det}(U)^{-1}], R'=R\otimes_{A}A', M'=M\otimes_{A}A'$ then $A'$ is a flat extension of $A$.

As I understand $A'$ is a flat extension of $A$ if regarded as $A$ module, tensoring a exact sequence with $A'$ will give us an exact sequence.My questions are

How can we prove that the ring $A'$ constructed above satisfies the above property ?
From a commutative ring $A$, how can we construct its flat extension ?

I also have questions in the proof of the proposition 2.1 in that paper

Let $S=A[X_{1},...,X_{S}, Y_{1},...,Y_{v}]$ be a polynomial ring over a commutative Noetherian ring $A$. This ring can be viewed as a bigraded ring if we associate the degree for $X_{i}$ and $Y_{j}$ as $\text{deg}(X_{i})=(1,0), i=1,...,s; \text{deg}(Y_{j})=(d_{j}, 1), j=1,...,v$
Now, let $\mathcal{M}$ be a finitely generated graded module over $A[X_{1},...,X_{s}, Y_{1},]$. For a fixed number $n$, put $\mathcal{M}_{n}=\oplus_{a\ge0}\mathcal{M}_{(a,n)}$. Then $\mathcal{M_n}$ is a finitely generated graded module over the naturally graded polynomial ring $A[X_1,...,X_s]$. If $s=0$ then $\text{reg}(\mathcal(M_{n})$ is the invariant : $a(\mathcal{M_{n}})=\text{max}\lbrace a|\mathcal{M_{(a,n)}}\neq 0\rbrace$

3-Question : Why $\text{reg}\mathcal{M_n})$  is equal to $a(\mathcal{M_n})$ ?
As I understand , in $\mathcal{M_{(a,n)}}$, the index $a$ is graded for the variables $X_i$ and the index $n$ is graded for the variables $Y_{J}$ and then $\mathcal{M_{n}}$ is graded module over $A[X_1,…,X_s]$  but it is not a graded module over $A[Y_1,…,Y_v]$. So if $s=0$, and $n$ is fixed then we get nothing on $\mathcal{M_n}$.  So, what is the point here ?
Proposition 2.1 in that paper says that

Let $\mathcal{M_n}$ be a finitely generated bigraded module over the bigraded ring $A[Y_1,...,Y_v]$. Then $a(\mathcal{M_n})$ is asymptotically a linear function with slope $\leq d_v$

Here is the argument in the proof :

The case $v=0$ is trivial.Consider the exact sequence :
  $0\rightarrow [0_{\mathcal{M}}:Y_{v}]_{(a,n)}\rightarrow \mathcal{M}_{(a,n)}\xrightarrow{Y_{v}}\mathcal{M}_{(a+d_{v},n+1)}\rightarrow \mathcal{M/Y_{v}M}_{(a+d_{v},n+1)}\rightarrow 0$
Since $0_{\mathcal{M}}:Y_{v}$ and $\mathcal{M}/Y_{v}\mathcal{M}$ can be viewed as bigraded modules over $A[Y_1,...,Y_{v-1}]$, using induction we may assume that $a([0_{\mathcal{M}}:Y_{v}]_{n})$ and $a([\mathcal{M}/Y_{v}\mathcal{M}]_{n})$ are asymptotically linear functions with slope $\leq d_v$. As consequence :
  $$a([0_{\mathcal{M}}:Y_{v}]_{n})+d_v\ge a([0_{\mathcal{M}}:Y_{v}]_{n+1})$$
  $$a([\mathcal{M}/Y_{v}\mathcal{M}]_{n})+d_v\ge a([\mathcal{M}/Y_{v}\mathcal{M}]_{n+1})$$
  for large $n$.

My question for this part is :
4- How did the author use the induction ? If they use the induction on $v$ then why can they get the above two inequalities, since I think we can get the inequalities if we use induction on $n$.

Since $a(\mathcal{M}_{n})\ge a([0_{\mathcal{M}}:Y_{v}]_{n})$ for all $n$, we only need to consider the case that $a(\mathcal{M}_{m})> a([0_{\mathcal{M}}:Y_{v}]_{m})$ for infinitely many $m$. Putting this condition into the above exact sequence we get :
  $$a(\mathcal{M}_{m+1})=\text{max}\lbrace a(\mathcal{M}_{m})+d_{v},a([\mathcal{M}/Y_{v}\mathcal{M}]_{n+1})\rbrace $$

My question for this part is :
5-How can the author get the above information from the exact sequence ?
Here is my argument : We have : $Y_{v}\mathcal{M}_{n}=\oplus_{a\ge 0}Y_{v}\mathcal{M}_{(a,n)}:=\oplus_{a\ge 0}\mathcal{N}_{(a+d_{v},n+1)}$. Then :
$$a(Y_{v}\mathcal{M}_{n})=a(\oplus_{a\ge 0}\mathcal{N}_{(a+d_{v},n+1)})$$
$$=\text{max}\lbrace a+d_{v}|\mathcal{N}_{(a+d_{v},n+1)}\neq 0\rbrace$$
$$=\text{max}\lbrace a+d_{v}|Y_{v}\mathcal{M}_{(a,n)}\neq 0\rbrace$$
$$=d_{v}+\text{max}\lbrace a|\mathcal{M}_{(a,n)}\neq 0\rbrace$$
$$=d_{v}+a(\mathcal{M_{n}})$$
Since $Y_{v}\mathcal{M}_{n}\subseteq\mathcal{M}_{n+1}$ then $a(Y_{v}\mathcal{M}_{n})\le a(\mathcal{M}_{n+1})$ or $a(\mathcal{M}_{n+1})\ge d_{v}+a(\mathcal{M}_{n})$.
6-Am I wrong anywhere ?
7-What is the aim of the authors in the rest of the proof ?
I know that my questions are very long and may be hard to follow. If you have any question on this or this kind of questions are not appropriate with MO please let me know.
Thank for reading!
Comment: For (1) and (2), do some background reading on the concept of flatness, e.g. in Matsumura's book.  In particular note that a given ring generally has many flat extensions, not just one.
Answer: The flatness has nothing to do with the module or even the gradedness of the ring. If you take any ring and adjoin a matrix of indeterminates and the inverse of their determinant, you get a flat extension. This is because adjoining indeterminates is flat, adjoining inverses is flat, and a composition of flat morphisms is flat. All these facts are obvious from the definition.
Comment: @William Sawin : Thanks. I really appreciate that. What about the other questions ?


Why after only one week of not working out my body gets so sore?

Question: Two weeks ago I got sick and could not workout at all for a whole week.
After the week I felt that I really needed to do a workout, I took it easy and started by doing yoga.
A day after doing yoga I felt good and decided to do an aerobic workout that combines strength and endurance. The day after I felt so sore! I Haven't felt that sore in a long time.
I could barely more I was in so much pain.
Is that normal?
Comment: It's possible you were still ill, but didn't really feel it. So your body also couldn't recover as well as it normally would. This is especially true if you lost any weight while you were ill and/or wern't eating. you also mention that you took some time off, as the saying goes the first session back after a break is always the hardest. I'd say go again when you have recovered from this workout and if the abnormal pain is still persisting consider seeing a professional.
Comment: Thank you for answering, I am back to normal now with no abnormal pain.
Answer: Sometimes illnesses stir up different detoxifying mechanisms in our body. Yoga practices offer a gentle and systematic way to continue that detoxification and elimination from the body. More strenuous physical exercises can flush the elements through our system and our body can sometimes respond in the ways you described - pain, aches, ...
A week without movement can also allow for atrophy of the muscles since they are not being used. Jumping back into a strenuous workout would require muscle fibers to be rebuilt, sometimes experienced as soreness from the lactic acid and/or overworking or overstretching. Did you recall being well hydrated before, during and after?


Mizrachim saying Avinu Malkeinu on Shabbat

Question: I would like to turn around these two questions. We saw that it is problematic to ask personal requests on Shabbat, and certain verses of Avinu Malkeinu correspond to the blessings of the weekday Amidah. However, our Mizrachi brothers do say it on Shabbat. What is their reasoning, what sources do they have?
Answer: The Ra'van on Yuma writes:
( ראב"ן יומא ד״ה
ובמוצאי של יוה"כ )

וגם אומרים אבינו מלכינו לערב שבת ושבת שבין ר"ה ליוהכ"פ
  And we say Avinu Malkeinu on Friday and on Shabbos between Rosh Hashana and Yom Kippur

(Indeed while the Rama (OC 602) sounds like Avinu Malkeinu is said on Friday afternoon before Shabbos Shuva, the Yad Ephraim in 554 says the custom in his locale was not to. In any event it seems some Eidos Mizrach communities do say it even on Shabbos Shuva itself.)
I haven't seen a reason for allowing this. Perhaps the reasoning of the Baal HaTanya can be applied here, since Shabbos Shuva is an Eis Ratzon, and if not when?
In the Eidus Mizrachi Siddur I have with the Haskama of HaRav HaGaon Ovadia Yosef ztz"l they mention saying Avinu Malkeinu on Shabbos Shuva, they omit three of the lines (they're written smaller).
Comment: https://www.sefaria.org/Siddur_Edot_HaMizrach%2C_Shabbat_Shacharit%2C_Amidah.51?lang=bi
Comment: I don't see the relevance of the discussion of Friday afternoon. Moreover, isn't ראב"ן from Ashkenaz?
Comment: Which page in Yoma has those words?
Comment: In most Ashkenazi communities Avinu Malkeinu is not said on Friday Afternoon.  So we see a precedent that Ashkenazi Communities don't say it then, but some do, and we see therefore that this is probably down to minhag.  The Ravan is a Rishon.  What does it matter where he is from, he is a Rishon that supports this view.  In any case the Ravan was born in Provence ([according to Wikipedia][1]).  He then moved around the Ashkenazi centers, before settling in Toledo, Spain. [1]: https://he.wikipedia.org/wiki/אברהם_בן_נתן
Comment: One must remember that the minhagim of Sefardim vs. Ashkenazim were being developed during this time, and locations are not necessarily indicators of minhagim.  Whereas later on (by the 16th Century) they do become indicators.


Disappearing questions

Question: Over the last few months I have noticed that the counter of the number of questions I asked went from 125 to 122. Any idea why? Are questions being purged?
Answer: Do (did) you have any closed questions with 0 or negative score and no answers? There is an automatic cleanup of such questions.
There's also the "roomba" which deletes low-scoring, unanswered, low view questions after a year.
Also, if you have anything migrated to another site, the "stub" would be eventually deleted on the original site.
Comment: Feature request on meta: [Notify the OP when a question is about to be removed by Roomba](http://meta.stackexchange.com/q/250816/178179)
Comment: I don't think so. Is there anyway I can check? I don't see anything in "deleted recent questions" (except 2 questions I deleted myself).
Comment: I wasn't aware of this Roomba. I am really disgusted: I'm going to lose many of my questions. Stack Exchange has totally no respect for user content.
Comment: So I counted. This March,  around 10 questions of mine will be deleted by Roomba: 2 have already been deleted, 1 has just been saved by AI E, and the others are waiting for silent deletion: http://webapps.stackexchange.com/q/58876/18147 ; http://webapps.stackexchange.com/q/58854/18147 ; http://webapps.stackexchange.com/q/58765/18147 ; http://webapps.stackexchange.com/q/58427/18147 ; http://webapps.stackexchange.com/q/58423/18147 ; http://webapps.stackexchange.com/q/58315/18147.
Comment: I Moderator might be able to tell you. (I was just about to suggest you ensure that the "recently deleted posts" checkbox was checked.)
Comment: I started using webapps around 1.2 year ago so roomba is indeed most likely the cause. Questions that are 365 days old + no upvote + less than 365*1.5 = 547 views is quite common. E.g. [this question](http://webapps.stackexchange.com/q/58004/18147) should be deleted in 2 days if nobody upvote it or leave a comment... I am still interested in the answer!

Disappearing questions


iso download fails Ubuntu Server 12.04.1 LTS 32bit

Question: I have tried downloading Ubuntu Server 12.04.1 LTS 32bit but it fails at 156.790kb image file at start of download says 645mb it will only download 156.790kb then finishes. where can I download this image to receive the full download? I have tried to download it in different browsers same problem.
Answer: Open this as a text file.
You will able to see all links. Maybe you will be able to use them. Try each one, one by one.
Answer: I can download the Ubuntu Server 12.04.1-i386 image just fine, but it appears to be a bad ISO. No matter which computer I use to download the image I am unable to read it. I am also unable to find a link back to the previous version ISO (12.04 without the .1).
I've tried this using Mac OS X v10.8.2 (Mt Lion), Windows XP SP2, and VMware ESX.
UPDATE: Also, the amd64 appears to have the same problem. Perhaps it's the mirror that the web site is pointing me to by default that has the bad images? I guess I'll start trying links from Xiokang's response...
UPDATE: Doesn't seem to matter which mirror I use. The MD5 checksum verifies that the image I'm downloading matches what Canonical thinks I should have. However, I still can't do anything useful with the images, nor can VMware read it.
Checksums:

ubuntu-12.04.1-server-i386.iso  = 3daaa312833a7da1e85e2a02787e4b66
ubuntu-12.04.1-server-amd64.iso = a8c667e871f48f3a662f3fbf1c3ddb17

These match what Canonical has listed here.
SOLUTION: Ok, apparently these images are SUPPOSED to be broken, as they are using some kind of hybrid multi session layout or something. OS X is not able to verify or read these images without extra help from some shell commands. Also, VMware, when using EFI mode, will not be able to boot from the images as well. Apparently these images are intended for applications (like Roxio Toast) to burn directly to physical optical media. Hence why they have the unusual hybrid configuration, which works fine when being read from a CD. Follow the instructions for creating a USB thumbstick in order to use the images on a Mac. For VMware, make sure that your ESX virtual machine is set to use BIOS rather than EFI.
Answer: first of all, if you can download torrents which is the preferred way to download big files then use this
http://releases.ubuntu.com/precise/
if you don't want torrents. Then take my advice: Never download big files using the default downloader of the browser, they are so bad, do not support stopping and resuming, and you will often end up with a corrupted image. Use an independent download manager. If you're on windows use FDM, if you're on Linux download uget.


Can I partially bake a pie?

Question: I am planning on making a pie for my dad for father's day. I know when you buy most pies at the grocery store, you have to pop it in the oven for a few minutes to heat it up. Is it possible to do a similar thing with a homemade pie - bake the whole pie (not just the crust) most of the way one day, and then finish it off the next? I don't want to fully bake it and then heat it in the oven because I am afraid it will burn or overbake, but I also don't want to underbake it and have it go bad.
Comment: Out of curiousity, why would you say that?
Comment: In berry season we would make lots of pies and freeze them to be thawed and cooked during the winter. Partially cooking a pie is just a recipe for disaster.
Answer: I'd avoid the whole reheating issue altogether and simply keep the uncooked pie in the fridge, covered in plastic wrap, then bake it as normal when ready. The only issue you might have is if your filling is very runny, in which case you could par-bake it a little before filling to help it 'seal'.
Answer: The butter or shortening should never slowly become warm between the time the crust is mixed to the time the time the pie is finished baking. This is why you use iced water and cold shortening to mix the crust and place the crust after rolling back into the fridge before filling.
Imagine the example of bread. If you have uncooked bread dough and pour water on top of it the water will run down the side and if the water sits in the bowl with the dough only a little will be absorbed into the raw dough. Now if the bread dough is cooked and water is poured onto it the bread will absorb all the water. The same concept is true for pie dough that is about to be frozen. The uncooked dough will repel the moister better than partially cooked or fully cooked dough.
Also if the dough is fully covers the filling, the dough has a lot of fat in it which acts like a layer of protection in the freezer. Freezing pies is great at the height of berry season when they can be bought in bulk super cheap to preserve the fruit for when it's cold.
I doubt that if the pie filling is super runny it's a good idea to freeze it, otherwise just having uncooked dough works quite well for freezing pies for later.
Answer: You didn't mention which type of pie you would be freezing, so all I can offer is what I do. Apple pie can be frozen before or after baking; I prefer after, and if you sprinkle some turbinado sugar on it before you bake it, it will keep a nice, crispy top crust after the thaw and second bake.
For me, berry pies are best frozen after baking. Use tapioca starch in your filling instead of cornstarch, and it won't turn runny on the second bake.
Meat pies are best frozen before baking if they are just meat pies. If they contain potato, either pre-cook the potato before it goes into the pie, or bake before freezing, because uncooked potato will either disintegrate or assume a very peculiar, spongy texture.
Fish pies I recommend baking the crust before filling, and then freeze it without baking the filling. I learned the hard way to only cook the filling once, so it goes into the baked shell unprocessed; a second bake of the filling usually creates a truly spectacular (and fishy-smelly) mess for me, and it takes days, plus sometimes a wall-washing, to get the smell out of my kitchen.
Quiches, cream pies and pies involving curd or custard, do not freeze at all. They either disintegrate or they adopt a grainy, unpleasant texture and lose most of their taste.
Comment: I figure they must do something. The only reason I tried to freeze quiche was because I saw it and figured it\s perfectly fine to do it. That was definitely not the case. What came out of the oven was pretty disgusting, and it was a colassal waste of lobster, crab and shrimp. If you discover the secret, I would love to have it,
Comment: I've never done it, personally, but I see frozen quiche all the time in grocery stores... and they usually taste just fine. Do you know if they do something differently to make them freeze well?

Can I partially bake a pie?


Can you use the same 24 word seed from other wallets like ledger nano s to generate a monero address?

Question: Is the generated 24 word seed from a ledger nano s compatible with monero core wallet?
Comment: What makes matters worse is while the older Electrum v1 list had 1626 words, the list of new Electrum v2 words is the same as the list of 2048 BIP 39 words.  This will confuse end users even more.
Answer: The list of English words available to create a bitcoin seed is not the same as the list of English words available to create a monero seed.
For example, the first few words of the former are "abandon ability able about" whereas the first few words of the latter are  "abbey abducts ability ablaze".
Monero only considers the first three letters of each seed word (for English, four for other languages) - in this case abandon, for example, would result in aba which is not the beginning of any valid monero seed word. That is not going to work well...
And the number of words in each list is not the same either so you could not even convert the words into indices and back.
Comment: If this answer is indeed correct, an implication is that three letters of uniqueness from the 2048 BIP 39 words maps cleanly to 1626 words used by Electrum v1 list of words. I find this to be a far reach due to the amount of error prone time to confirm this is fact.
Answer: The short answer is Yes, but until Monero wallet hardware support is out of alpha testing and is supported by two or more wallets consistently the answer to this question is a work-in-progress.
For example BIP 39/44 technology can be used to seed the synthesis of 25 Electrum Words, see Example 10 that uses a shortened m/44'/128'/0' path that works with 12, 15, 18, 21 and 24 BIP 39 seed words. An older deprecated alpha Monero Trezor hardware support never attempted to harmonize BIP 39 technology with Electrum words, which mentally itched me enough to write and share https://github.com/skaht/XMR around 18 months ago. I believe the recent Nano S body of work uses a path such as m/44'/128'/0'/0/0.
FYSA - The Brainwallet JavaScript code at https://github.com/bholben/seaweed (in alpha) should harmonize brainwallets, BIP 39, and Electrum wallet technologies across the board.
Comment: This question is ultimately related to question of how does one transform 24 BIP 39 seed words and a passphrase to the 25 Electrum v1 seed words used by Monero.  The question posted some time ago at https://monero.stackexchange.com/questions/9815/support-for-a-ledger-nano-s-recovery-plan-b remains unanswered.
Answer: If I'm not mistaken monero uses a 25 word seed.
And do you really want to use the same seed on all/multiple wallets?
Comment: The 25th Electrum v1 word used to restore a Monero wallet is always one of the previous 24 words.  There are 1626 Electrun v1 English words that are located within https://github.com/monero-project/monero/blob/master/src/mnemonics/english.h that do not correspond to the 2048 BIP 39 English words posted at https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt.  The issue is to map the 24 BIP 39 words with a potential passphrase to configure a Ledger to the 25 Electrum v1 words used to restore a Monero wallet without the need to use a Nano device.


Mnemonics to distinguish popular airplane models

Question: When in the airport I'd love to be able to distinguish most popular aircraft from each other, how can I say that a plane I am looking at is say a320 or 737 etc? They look so similar. I can detect 747 for 4 huge engines, but that's as far as I can go.
Comment: See https://www.airlinerspotter.com/
Answer: https://aviation.stackexchange.com/a/2742/1084
The easiest thing is looking at the fin for small types! The A320 from Airbus doesn't have a dorsal fin, the B737 from Boeing has dorsal fin and the vertical- and horizontal stabilizer reaches to the far end of the fuselage.
The big ones are generally easy because the B747, A380, A340 and MD11 are distinguished by the number of engines and the hump (B747) for the half, full (A380) or none upper deck (A340).
The A350 is similar to the B787, but it helps that A350 wears a "black mask" around the cockpit. Therefore the A350 looks like Räuber Hotzenplotz or Zoro or whatever you prefer in your part of the world.
The landing gear is barley visible and different and swapable engine types are also difficult. The nose of Airbus planes is more round, while a nose from Boeing is usually more pointy.
For me the problematic ones are the A330 which is shorter than A350 and B777 which is longer. But there are also the B757 (small body) and B767 (wide body). For this ones you need probably take a close look and it helps if a different type is next to them, to get an impression of relative sizes.
A350 - Callsign Bandit?
Comment: Number of doors is also a good one. The A330 wing tips are shared only between A330, A340 and 747-400 (and since the latter two are explained above, anything with an upward kink in the wingtip that has two engines must be an A330). Also, for widebodies, to my eyes it's the Airbusses which have the pointy noses and the Boeings with the blunt noses.
Comment: Wingtips are a good hint for the A330! Thanks.


Differential equation for log-returns

Question: I have a question that might be trivial to most of you, but somehow I'm not able to solve it by myself. I have a disagreement with my colleague on the distributional properties of a Geometric Brownian Motion: my point of view is, that if you estimate the parameters $\mu$ and $\sigma$ on log return (and assume that they are normal), the GBM at point $t$ has indeed an expected Value of $X_0\exp{((\mu+\sigma^2/2)t)}$ (properties of log-normal) and not $X_0 \exp{(\mu t)}$ as found in the literature, since there $\mu$ is the drift term of the differential equation of the stock price process itself, not of its log-returns.
I tried to confirm my view via several derivations and numerical examples. My colleague though is still not convinced, cause I use $\text{d }{\ln{\!X}}$ in Ito's Lemma for the log returns, but he argues that they are $\ln{(X_t/X_{t-1})}$. Apparently, my knowledge of differential equations is too limited to find the step from the log-returns to their corresponding SDE. In the literature I only find derivations where they start with the sde of $X$. I'm looking foward to your hints.
Answer: If you consider $X_1$ a random variable which is normally distributed with mean $\mu$ and variance $\sigma^2$ them $S_1 = \exp(X_1)$ is log-normally distributed with mean $\exp(\mu + \sigma^2/2)$ and variance $(\exp(\sigma^2)-1)\exp(2\mu+\sigma^2)$. This follows from the definitions of the normal distribution and the log-normal distribution and deriving the expectation and variance from these definitions and you can find it here.
If you define a process $X_t$ by
$$
dX_t = \mu dt + \sigma dB_t,
$$
then the process has expectaion $\mu t$ and variance $\sigma^2 t$ by basic SDE theory.
If you consider the process $S_t = \exp(X_t)$ then you get by Ito's lemma
$$
\frac{dS_t}{S_t} =  \mu dt + \sigma dB_t + \sigma^2/2 dt = (\mu + \sigma^2/2) dt + \sigma dB_t.
$$
and because of considerations above we have $E[S_t/S_0] = \exp(\mu t + \sigma^2/2 t)$ and variance $(\exp(\sigma^2 t)-1)\exp(2\mu t+\sigma^2 t)$. Thus a drift of $\mu$ in the process of the log-returns gives you a drift of $\mu + \sigma^2/2$ in the process of geometric returns. Now you can define $\tilde{\mu} = \mu + \sigma^2/2$ and rewrite the processes with $\tilde{\mu}$ then you have drift $\tilde{\mu}$ for the geometric returns and $\tilde{\mu} - \sigma^2/2$ for the log-returns.
EDIT: After having written this, I found nice lecture notes by Karl Sigman about this in the web.
Comment: I know how to apply Ito's Lemma here, my question was more on how to show that dlnX is the corresponding SDE for ln(X+dt/X), thus the change of the log of the ratio of X, and not of the log of X itself.
Comment: I'm aware, of course, that $ln(\frac{X_{t+dt}}{X_{t}}) $ equals $ln(X_{t+dt})-ln(X_{t})$, but is that equal to $dln(X)$?
Comment: $ln(X_t)$ can be written in integral form as $ln(X_0) + \int_0^t d ln(X_u)$. So if you are interested in $ln(X_u) - ln(X_v)$ for $u>v$ then this is $\int_u^v d ln(X_u)$.
Comment: Thank you very much! I knew I couldn't get around the integral notation...
Answer: To complete the perfect answer of Richard, I would add that pretending that the expected value of the GBM at $t$ is $X_0\exp(\mu t)$ amounts to claim that $E(exp X) = exp(EX)$ which is wrong "because the exponential is not linear."  This is why there is this $\sigma^2/2$ term popping up, it is sometimes known as the "convexity correction"—the exponential being convex you have $E(exp X) \ge exp(EX)$ and you may find a more precise statement in Jensen's inequality.
This could provide you with an argument which is easier to grasp as a mathematical derivation. This topic is adressed in Hull's classical book on derivatives (12.3 The expected return in the 5th. edition).
Comment: Nice addition, "Jensen" is an important key word I was missing.

Differential equation for log-returns


No activity showing for Tor exit relay

Question: Ive been testing a run of a tor exit relay on a vps which has been active for a few hours however, when using nyx to show traffic stats it shows little to no usage.
Ive also tried searching for my relay on torstatus but no results are shown for the ip.
when running <code>/usr/sbin/tor --verify-config</code> it shows the configuration was valid and that its running as an exit node.
I have also ensured that the default accept out and forward policy is enabled. ports 9001 tcp & 80 tcp are also accessible from the outside, verified through a qucik nmap scan.
the traffic for both upload nor download has gone above 1 -2KB

How long do I have to wait to see any activity on my relay? and is there anything im missing?
Answer: So ive been looking into the lifecycle of a tor realy and this seems to behave as you would expect. https://blog.torproject.org/lifecycle-new-relay

No activity showing for Tor exit relay


Graphing Continuous Functions

Question: My question is How do I graph a continuous function when I am only given restrictions?
For example, Sketch the graph of a function that is continuous everywhere except at x=3, and
is continuous from the left at x=3. I have another problem to solve, but if I can get help with this one, I am sure I will get the other one as well.
Answer: The first thing to realize is that there are infinitely many different correct answers. Instead of drawing a sketch, I'll give a couple explicitly. Let's start with a function $f(x)$ that's continuous at every real number. It doesn't matter what $f$ is, so let's make it very simple: $f(x)=0$ for all $x\in\Bbb R$. Now we want to make it discontinuous at $x=3$; one simple way to do that is to make it jump at $x=3$. For instance, we could set
$$g(x)=\begin{cases}
0,&\text{if }x<3\\
1,&\text{if }x>3\\
?,&\text{if }x=3\;.
\end{cases}$$
This function $g$ will certainly be discontinuous at $x=3$ no matter how we fill in the question mark, because
$$\lim_{x\to 3^-}g(x)=0\quad\text{ and }\quad\lim_{x\to 3^+}g(x)=1\;;$$
if $g$ were continuous at $x=3$, the two one-sided limits would have to be equal.
Now what about $g(3)$? We want $g$ to be continuous from the left at $x=3$, which means that we want
$$g(3)=\lim_{x\to 3^-}g(x)=0\;.$$
Thus, the desired function is
$$g(x)=\begin{cases}
0,&\text{if }x\le 3\\
1,&\text{if }x>3\;.
\end{cases}$$
Note that I could have pulled the same trick with any continuous function $f$ by defining
$$g(x)=\begin{cases}
f(x),&\text{if }x\le 3\\
f(x)+1,&\text{if }x>3\;.
\end{cases}$$
Answer: In order to sketch such a function, you need to come up with a function with this property.
I suggest the function $f : \mathbb{R} \rightarrow \mathbb{R}$ defined by
$f(x) = \begin{cases}
1 & \quad x \leq 3 \\
-1 & \quad x > 3
\end{cases}$
It is clear that the function is continuous everywhere except $3$. It is continuous from the left since $\lim_{x \rightarrow 3; x\leq 3} f(x) = 1 = f(3)$. It is not continuous at the $3$ since the right limit $\lim_{x \rightarrow x; x > 3} f(x) = -1$.
Comment: Actually, one **can** produce a sketch without having an explicit function. Just draw something that's continuous on $(\leftarrow,3]$ and $(3,\to)$ and has a jump at $x=3$; this is typically indicated by making a heavy dot at the righthand end of the left half of the graph and an open circle at the lefthand end of the right half.

Graphing Continuous Functions


How to measure food acidity

Question: I am asking about a method or a trick to measure (or guess) how acidic is food.
Please don't suggest any expensive tool; this will be for home usage only.
Answer: Litmus paper is quite inexpensive. Edmund Scientific has 100 strips for US$1.95.
Comment: It's unfortunate that even Edmund Scientific describes that as "litmus paper" - litmus is really a specific pH indicator, that classic red/blue acid/base test that you might've used in your high school chemistry class.
Comment: Does it harm the food or I have to use it on a sample of the food?
Comment: @mmonem: My wife, a chemist, doesn't think there should be any problem putting it directly into the food.  They require very small samples, so using it on a sample of a food should work as well.  Dipping a spoon in, and rubbing the paper across the back of the spoon should be fine.  The only problem I could see is if you food has a deep color (tomato sauce, blackberries, etc).  It might be hard to tell the color of the strip through the food coloring.
Comment: @mmonem: If you're in the US, you can order them at the link I gave. Otherwise just search in Google Shopping for litmus paper. [Here](http://www.wikihow.com/Make-Homemade-pH-Paper-Test-Strips) is a page which gives instructions more making pH test paper of various types yourself.
Comment: Where can I find this? On supermarkets?
Comment: @mmonem: online, or wherever you might buy chemistry supplies.
Answer: Some less precise methods using common ingredients:
Anthocyanin-containing foods (red cabbage, blueberries...) tend to turn blue in an alkaline, red in an acidic environment. Turmeric goes more lemon-yellow in acidic, more orange in very alkaline environments.
Baking soda can indicate strong acidity, it will activate and foam.
If there are green vegetables in a dish, their cooked colour gives you a hint about the cooking liquid (effect is not instant!)- if their color tends to go in the direction of olive drab, you are quite acidic; if they are unnaturally green your cooking liquid is rather alkaline.
Also, browning behaviour, especially of protein rich foods, gives you a hint - if it is hard to brown, your marinade might be just too acidic.

How to measure food acidity


Why Did Qui-Gon Accept Shmi's "No Father" Birth Story So Easily?

Question: When Qui-Gon asks Shmi about Anakin's Father, she tells him there was never a man involved.  Why is Qui-gon so quick to accept such a miraculous story?  He didn't even bat an eye, but took her at her word from the start.  Why didn't he even question it and try to verify it was true instead of accepting it as a given?
Comment: Quibble: I don't think there's any indication that she was a virgin, just that there was no father for this particular conception.
Comment: @KeithThompson: Did I say something about her being a virgin?
Comment: It's in the title.
Comment: @KeithThompson: Funny.  I was being so careful to avoid that term, and then when I wrote the title, I was trying to make it short enough to be easy to read.
Comment: I'm pretty sure it's because he know of the prophecy of The One, and had perhaps even foreseen part of his own role in finding said savior. However, the movies don't mention this, and I haven't read enough EU stuff, so I have no proof. (Hence comment, not answer.)
Answer: There are a number of reasons.
First of all, he doesn't accept it as truth, only plausible. When he is talking to other Jedi, he mentions only a "possible" birth through midichlorians.
Secondly, he very well could have been using Jedi tricks to learn that she at least thought it was true. If she thought it true, there wouldn't be much he could gain.
Lastly, Jedis are in complete control of their emotions. He must have realized that reacting would not help him, so he didn't.
Comment: #4: he was aware of a prophecy of "The one to bring balance to the force". Given the Midichlorian count, it's NOT implausible that he was willing to believe anything
Comment: Qui-Gon Jinn was particularly adept with [the living force](http://starwars.wikia.com/wiki/The_Force#The_Living_Force). While he couldn't read her mind, he would be able to pick up on her emotions and general intentions.
Comment: @HNL: Maybe I'm mixing different stories, but it seems to me that a Jedi could tell if someone was being truthful...
Comment: I think he dismissed it out of hand until he saw Anakin's midichlorian count. As for Jedi mind tricks: they don't work in the reverse direction (i.e. receive information) do they?
Answer: Maybe he noticed that he had touched a very sensitive point. Shmi was a slave and lived in a very harsh planet visited everyday by pilots, bandits and all sorts of people. What if Ani was the result of a forced intercourse? I say that because I always see some embarrassment both in her answer and in Qui-Gon's expression  - as much as you can see expression in a Jedi - right after he asks the question. Anyway, my guess is that Palpatine has something to do with that, maybe he made her believe there was no intercourse just to make the Jedi believe Ani was the one of the prophecy.
Comment: +1 While we saw what Anakin did for Watto, Shmi's role remained a mystery.  She could have been a prostitute.
Answer: Darth Plagueis "influenced life" in Shmi Skywalker and created the most powerful jedi to have ever existed. BOOM. Check out Star Wars Episode 3, the scene to look for is the one where Darth Sidious talks to Anakin while he is trying to entice him to join the dark side. It took me one snow day and all 6 movies in a single day to understand this.


Should I convert my JPEG images to DNG in Lightroom 3?

Question: I am new to LR3 and have decided to convert RAW images to DNG on import. However, I have about 8000 or so JPEG images that I have brought in to LR and I am on the fence as to whether to leave them in JPEG format or to convert them to DNG. I know DNG will take up more space and I think I can live with that. The question is how much is gained by going to DNG from JPEG and should I do it. As I understand it, the XMP data for a DNG resides in the file where the JPEG data is in a sidecar. My photos are mainly family memories and I want to preserve them. Appreciate any comments/suggestions.
Comment: I didn't think this was possible. I have my Lightroom 3 set to auto-convert to DNG on import, but it only does that for RAW files - JPG files stay as JPG.
Answer: Benefits or disadvantages aside, you can't import JPEG as DNG in Lightroom (to my knowledge). If you import a JPEG file in "Copy as DNG" mode, LR will prompt an error dialog saying, in substance: "Non-raw files were not converted to DNG". What you can do, however, is select your JPEG file in LR, and export it as DNG, then re-import that DNG file.
DNG is really designed for RAW sensor data. For instance, your typical DNG file doesn't contain a color space. Its data structure, bit depth and format are very different from the RGB pixels found in a JPEG file. Think of a JPEG file as a "baked" version of a RAW file.
There is a "Linear DNG" variation that can store a demosaiced RGB image data arranged in a rectilinear format. It is supported by LR and is used for cameras with Foveon sensors for example. However, you do not increase the quality of your JPEG file by converting it to Linear DNG. Everything you can do with a Linear DNG you can already do with a JPEG file in the Lightroom UI.
As far as metadata and develop adjustments are concerned, they are stored in Lightroom's catalog file, unless you tell LR to export them automatically, or do so manually by selecting "Metadata -> Save Metadata to file". If your photo is a JPEG file, LR will create a XMP sidecar. If it's a DNG file, LR will be store these settings directly within the file itself. At this point, yes, you can say DNG is a bit more convenient, especially if you want to share these settings with somebody else. Personally, I do not let LR export metadata automatically for performance reasons, and I rarely save the metadata back. What I make sure to do, however, is to carefully backup my catalog so that these memories we are preserving are not lost. Look for "lightroom backup" on this site (or check this one specifically).
Answer: The only real gain is the ability to apply non-destructive edits to the image and to reset them inside the file, as you noted in your message. Bear in mind that it can't totally put you in the same position as the RAW source format since the actual sensor data is lost along with anything discarded during the JPEG compression phase. Beyond that, there really isn't an advantage since JPEG, itself, is a well known and massively supported format (much more so than DNG).
Anyways, I would suggest that if you do want to convert to DNG, that you only do it on an as-needed basis. There's probably not a lot of value in mass converting the whole 8000 up front.
Answer: XMP (sidecar files) are optional in lightroom. The benefit to using them is that any application that can parse them can make use of them, as opposed to the default behavior of storing edits and meta data inside lightrooms database.
Since you don't need to use XMP files, necessarily, the question is whether it makes sense to move to DNG.
In my opinion, there is no real advantage to moving to DNG. The file size is larger and sidecar files aren't that big (they may be irksome (especially on an SSD)). DNG really makes sense if you're looking to "archive" your raw files.


A tool to export images (photos) in a folder hierarcy on iOS

Question: I've tried to import photos from my computer to my iPad (Air 2), and they just end up in an album, all together. But in my computer they're all in different folders nicely organized. I would like to keep this organization in albums.
Correct me if I'm wrong, but it's not possible to do that with iOS ?
If not (because I couldn't I'm asking here and not somewhere else) : is there a tool, an app, that would make me able to do that?
A very simple file explorer that would allow me to browse pictures, only pictures, saved locally on the ipad, that I have previously imported. The app/tool has to work offline.
If I have that I'm 100% happy, I won't mind extra features from the app.
Also if you know how to do this with the classic "Albums" then i'm all ears, but then this question wouldn't be relevant on this stackExchange website.
Answer: I use Readdle's Documents 5. Its free and feature full not just for photos but all kind of documents. Also works as extension to other apps and with cloud when you want to.


What Kind of Outlet Allows 1 In-Wall Light Switch w 2 Outlets to Control 2 Sconces w Semi-Independent On/Off Buttons & Outlets on Each?

Question: I have a bathroom light switch with two outlets and one light switch. The switch turns on/off two wall-mounted sconces. Both sconces have their own on/off buttons and an outlet. The buttons on the switches will not turn the lights on unless the wall switch is flipped on. If a sconce's button is set to off, flipping the wall switch will not turn it on. Neither of the sconce's outlets will work if their light is turned off by button or switch. Neither sconce's button can control what happens with the other sconce. What kind of in-wall outlet/switch is this? How many poles and ways is it going? What would I need to buy to just replace the in-wall switch with two outlets? Thx
Comment: How serious are you willing to get?  $100?  $200?  You know how in almost every room in every residence, there's always a wall switch in a standard location that you kind-of-expect to be there? That's because building codes absolutely require that. Does your local building code allow you to **not** have that in a bathroom?
Comment: Huh...Okay, no, didn't realize that was a legal requirement rather than design choice. This outlet/switch is not on a wall on either side of the doorframe. It's on the wall to left of the door, aside the medicine cabinet. The house is 115 years old and there's really nothing standard anywhere, everything appears to have been eyeballed & the walls are all brick & plaster.
Answer: Your switch sounds like a normal single pole switch.  Someone basically wired up the switch to the sconce which already had switches so they could leave the sconce switch on all the time and turn both sconces on with the wall switch only.
So nothing fancy - you should be able to just get a standard outlet to replace the wall switch and run the line to the sconces as "load" from the new outlet.  However since this is a bathroom you might want a GFCI outlet as extra protection.
Comment: Hold on though. Building code may require a light switch at a wall location next to the door (with additional restrictions like height).
Comment: There are height restrictions? What if you want a kid or a little person or someone in a wheelchair to be able to reach the switch? There's no one who meets those criteria living here, but it's a private residence not a place of business.
Comment: The Code is so those people can reach the switch.  You may not have any in your family *today*, but the Code requirement isn't for you *today*.  It's for when you sell the house, get a kid, get disabled, have a houseguest, have a First Responder call, you name it.  If you're lying there coding,do you really want the EMT spending your golden minute trying to find the light switch?
Answer: This is effectively impossible to do with parts from Home Depot. 3-way switch wiring will act very weird and have states where throwing the door switch will only exchange which light is on. That's not what you want.
You can do exactly what you want with two GE RR7 relays, a tiny transformer, and the switches used with RR7s.
They are special switches that are SPDT momentary switches.  These are available in a wide variety of formats.  You have one switch at the door which commands both lights on or off.  Then you have a switch on each light that commands that light on or off.
The door switch must be DPDT momentary. It can be hooked up woth simple 5-wire thermostat cable instead of heavy electrical cable.
It works exactly as intended, that being the job of the relays.

An RR7 relay is essentially a switch which can be electrically thrown.  Imagine if a common light switch had a little solenoid coil above and below the switch, and either one can throw the switch.  .  Apply power to one coil for a second, and it throws the switch (assuming the switch wasn't already that way).  After you remove power from the coil, the switch stays where it is,
This is how the RR7s work.  Pushing a lamp's on switch makes the "on" coil throw the RR7 into the "on" position (it may have already been on).  Pushing the "off" switch makes the "off" coil thrn the RR7 off.  The door switch is wired to throw both relays "on".
The wiring is somewhat complex, and is beyond the scope of this answer.
Comment: This is interesting because the switches I originally wanted to buy (for aesthetic reasons) are momentary switches. Can you link me to a diagram of what you've described? Where would the transformer need to be placed? This sounds fairly complicated for a novice, but drawn out maybe it'd be easier to grasp. Thanks.
Comment: The transformer could live right next to the relays, which could all be in the fixture. Mains could come into the fixture, and a 5-wire thermostat cable could leave it to go to the room switch.


What is the correct water to pasta ratio?

Question: I have heard one should use a lot of water when cooking pasta; how much water should I use?
Comment: @roux, @attila, I disagree that it is a repeat question. It turns out that the **answer** to this question exists in another Question (thanks, roux), but the question itself is different. If I were looking for how much water to use, I would not check a question about water temperature for that answer.
Comment: possible duplicate of [Pasta: Simmering Water or Rolling Boil?](http://cooking.stackexchange.com/questions/3949/pasta-simmering-water-or-rolling-boil)
Comment: i don't think they travel very different ground, but i'm not going to get bolshy about it.
Answer: This question was answered to some extent in another Pasta cooking question by Roux. This answer, which is basically just a link to a series of experiments by an MIT grad / Chef, dispels a number of myths about cooking pasta. For instance:

Water will return to a boil in the same amount of time regardless of how much is in the pot prior to pasta being added.
Pasta won't get sticky with smaller amounts of water. It only gets sticky because of reactions in the first few minutes of cooking, and the solution is to stir it. This is necessary even with lots of water.
You do not need a lot of water to cook pasta.
Water does not need to be boiling to cook pasta. It simply needs to be above 180°F/82°C.

Some really interesting stuff in the article that debunks quite a lot of kitchen lore about cooking pasta. I have tried this at home with great success.
So in answer to your specific question:

No, you do not need a lot of water, it simply has to cover the pasta.
The amount of salt is heavily dependent on the amount of pasta, the amount of water, and your own taste. You need to find a consistent way to cook pasta and then experiment.
Comment: It is important to note that the article you link to states outright that for fresh pasta or for long-shaped pasta (such as spaghetti), the "less water is fine" rules do not apply.
Comment: @Tim: But the reason given is that the long pasta won't be completely submerged. It only takes 20-30 seconds to get full-length spaghetti to soften enough to bend and submerge. I've cooked plenty of long pasta in minimal water. (You may want to *start* with the water boiling rapidly, but you can reduce the heat half a minute later with no problems.)
Comment: I have been using the no-boil method for several month, even for long strand pasta like angel hair. I use cool tap water that will cover the amount of pasta I'm intending to cook, add salt, put on stove on high and stir throughly. I do snap the long pasta in half before throwing it in, to make sure it's entirely covered. Often the water will have just come to a simmer when my pasta is done, which uses less energy and keeps my kitchen cooler in the summer. I can't believe it works, but it totally does.
Comment: The only other argument for using more water is that less water is more likely to cause the pot to boil over.  Basically the starch in the pasta makes it easier for the water to form bubbles that collect and spill over when not paying attention.  I've found that with a very low pasta to water ratio can end in a messy kitchen.
Answer: I prefer to use more water than is likely necessary, simply because when you add the pasta to the water, the temperature will drop some.  The less water you have, the lower it will drop/the faster it will take to bring it back to a boil.  Edit: This very likely may be a disproven myth, please read comment below.
Unfortunately I eyeball it based off how much pasta I have, so I can't give you an exact ratio.  But I would err on the side of too much.  Edit: I just eyeballed and then measured a pot, it looks like I use about 5 quarts of water for a lb of pasta.  I still recommend erring on the side of too much, but now only because you don't want to lose too much to evaporation and end up running low on water halfway through cooking.  Just enough to cover the pasta a little bit seems to work fine at our house.
Comment: Wow, I think you just made my head explode a little.  I guess I never sat and thought about it before, but based on simple physics that makes perfect sense.  Great comment!  Updated my answer.
Comment: This isn't actually true. It takes the same amount of time to come back to a boil. However, the larger pot will have a smaller temperature decrease than the smaller pot. They'll both get back to a boil at the same time though. Think about it: the pasta has a certain amount of energy to exert to decrease the temperature. It's the same for both pots. The difference in volume affects how far the temp swings. But the burner also exerts a fixed amount of energy to heat it. Because the smaller pot has less volume it increases temp faster. The total energy change to both pots is exactly the same.
Comment: I thought the exact same way you did, but the article that Roux linked a while back that is the basis for my answer in this thread dispelled that. It makes perfect sense, but I'm not sure it's obvious. I hope you didn't get any exploding head on your keyboard.
Answer: I have found that enough so that upon evaporation, you don't run out is the correct amount.  But then again, using too much takes longer to boil.  I try to find an optimum based on these two factors.
Answer: My rule of thumb is 4 qt. of water per 1 lb. of pasta.  This comes from a Cooks Illustrated article (I think from around '00) that suggested that this was the best way to keep pasta from sticking to itself.
Answer: That is nonsense. The more water per pasta ratio will result in less recovery time, which is more desirable.
It's simple. Boil a gallon of water and add an ounce of pasta. The water will not stop boiling. Boil it again and ad a pound of pasta. The water will take time to recover.
For dried pasta, every manufacturer recommends rapidly boiling water.
Aldente reqires high heat to cook the outside of the pasta, leaving the inside slightly undercooked. This is were the "snap" comes from.
Comment: First, it's not nonsense, and second, you're not entirely wrong. If you've got a 100 gallons of boiling water and add one noodle, then you're right the change in temperature is going to be negligible on a thermometer. However, if you have a 100 gallons at temp x and 1 oz at temp x, and you add a noodle to each, then the change in temperature will be much greater in the second case. The first case may not stop boiling at all. However, the time to get back to temp x (given the same heat source) will be identical in both cases, even if the larger pot doesn't lose it's boil.
Comment: Basically, in both cases, you've got a fixed amount of negative energy in (heat loss from the pasta) and positive energy in (heat increase from the burner). The amount of energy is fixed on both the in and out side, so the amount of water makes no difference in time to regain a certain temperature. What changes is the swing in temperature during the time period. While your example about an ounce vs a pound is probably correct, I don't think that it will make any appreciable difference once you start talking about realistic cooking quantities and the amount of water required (for either method)
Comment: To be honest, I was skeptical of the approach I outlined when I first heard it. I mean, it makes sense, but I didn't quite believe it. So I tested it. I noticed zero difference in outcome. Seeing is believing.
Comment: As I'm re-reading my comment, I notice a slight error. Boiling water is boiling water, but the difference between a strong and slight boil is the amount of energy in the system, not the absolute temperature. Adding the pasta decreases the energy in the system which may or may not be enough to decrease the temp from a boil. So, given enough water, you could add your pasta without ever killing the boil. However, if you read the article I referenced, it points out that you only need 180F to cook pasta, so a boil isn't even necessary. You just want to stay about 180 for the course of cooking.
Answer: 1 cup of water to 4 cups of pasta.
Comment: This makes absolutely no sense.
Comment: I think that's the other way around, no?


How much SQL knowledge do I need to learn Selenium Testing

Question: I have just started learning Selenium.
I'd like to know how much knowledge of SQL I should have in order to be able to learn Selenium.
Answer: For writing Selenium tests itself, none. Selenium does not use SQL.
Now if the application under test uses SQL, maybe you need a bit of knowledge to setup test data for your tests. For basic SQL knowledge have a look at the free SQL course at Codecademy. This should probably be enough.
Answer: For Data Driven testing / Validation I used SQL Queries. It depends on your test scenario, Few Examples

You perform a UI operation. Results are listed. You can perform the
same query from DB and check records count match
When you add a new user / delete a user from front end. You can perform DB query and validate records updated / deleted
For multipage search results sql record count is easier to verify count of records in GUI / DB Query

Decent knowledge of SQL select query and joins is good enough for automation.
Answer: The key part of your question is "to learn selenium"
To learn selenium you don't need SQL knowledge inh order to be able to write good selenium test cases.
However a broader answer includes the following scale:
Junior Developer on a small system, tightly defined role using Selenium IDE with other frameworks available for querying data (e.g. RubyOnRails ActiveRecord).  Here you would have a limited use for SQL and it would not be a requirement for learning this 'flavor' or usage of Selenium.
Mid-level developer on more complex systems that have several components and other systems that are interacted with, e.g. a service orientated architecture will find it hard to know what's really going under 'under the hood' without being able to do SQL queries to look at the records they are creating and updating through the web interface.  They may my using the seleniumIDE with patterns such as Page Object or they may be using web driver in conjunction with programming languages such as C, Ruby, Python, Java, etc.
Senior Developers on complex system will find SQL knowledge and access essential to doing their job and being able to perform backend queries on complex data sets and conditions that are not exposed through the application interface.  They use selenium with web driver and run cases both locally and remotely on test server providers.  They understand workflows and how the back end data model is implemented in a Relational Database Management System and how it records transactions and state changes.
Answer: Unless you are doing any database or backend testing, you dont need any SQL knowledge for selenium. Selenium is a UI automation tool.
In case if your test data is separated by any Database, you may require SQL queries to retrieve data from the DB; that would be only plain language + DB connection.


Everything about a very disturbing movie Martyrs (2008)

Question: After watching Martyrs (2008), I kept on thinking about the motive or the message behind that movie. My question is, why was the skin peeled off the entire body of that girl, and what did she tell to the old woman which led the woman to commit suicide?
Comment: I've flagged to close for now, as there are two separate questions here. Can you edit your question to focus on one or the other, then open a new question for the second part?
Comment: title of my question is "everything about the movie", it would be unnecessary to ask two questions, which are related in some sense.
Comment: @DarrickHerwehe, I got my answer.
Answer: In Martyr, Mademoiselle  was the head of secret philosophical society seeking to discover the secrets of the afterlife through the creation of "martyrs". Their experiments inflict systematic acts of torture upon young women in the belief that their suffering will result in a transcendental insight into the world beyond this one. It include that peeling of the skin etc.
For you second question why Mademoiselle commit suicide?
Answer is in the last lines of Mademoiselle

Mademoiselle: Keep doubting. IMDb

They kept it ambiguous intentionally. There are various theories on reddit about it but they are just plain speculation form the side of viewer.


Give me some tips for testing Email client mobile application

Question: I am not familiar with e-mail but I need to test Email client for mobile platform. I suppose that there are some test engineers which can help me to define tricky use cases and well-known problems which could occur. And which articles and standards do I need to learn for better understanding?
Comment: You aren't familiar with email?
Comment: Yes, I am not an expert. I need to test email app for mobile platform and I can do it basically like a common user but how can I guarantee quality?
Answer: A partial answer: email rendering is very important.  Many emails, like newsletters, marketing materials, etc put a lot of effort to make their emails beautiful.  Having the HTML render properly on a mobile client takes effort.
One type of test is the acid test: http://www.email-standards.org/acid-test/
You could also do side-by-side comparisons for many marketing emails, from well known email providers like mailchimp, etc...
Good luck.
Answer: Your question is rather vague. There are different types of email protocols, and your overall test strategy depends on which protocol(s) your client supports.
But, some basic areas for testing email clients on a mobile device include

Setting up client on device
Compose card
Read card
List view
Send/receive Attachments,
Message encodings (Unicode support),
Performance,
Rendering text / attachments
how much of the msg is downloaded,
first sync
other mail sync'ing options,
search on device,
search on server,
SSL (incoming/outgoing)
conversation view
copy/paste
folders
tagging emails
linked inbox
sharing
etc.

Of course this list assumes that you are very familiar with email functionality, and email protocols.