Have there been multiple time wars?

Question: They mention "The Last Great Time War" in Doctor Who.  Assuming that the one they talk about is the last, have there been other time wars in Doctor Who? Have they ever been mentioned in the classics?
Comment: The Time Lords had multiple temporal conflicts over the length of the species' existence. The first time war fought by Gallifrey was the Black Sun War, starting when the Order of the Black Sun sent a time-travelling assassin to prevent Gallifrey from gaining time travel. While the televised shows often called the Time War with the Daleks "The Last Great Time War," it was called this because after this war, the Time Lords were removed or isolated from the rest of the temporal flow of the Universe and became inaccessible even to people who may have had a TARDIS, like the Doctor.
Comment: Given that Enterprise turns out to have taken place entirely on the Holodeck, it is obvious that the Temporal Cold War never happened, or happens, or will happen.
Comment: @Gaius Doctor Who, not Star Trek. But that would be fine too.
Comment: A "first" can also be a last. Maybe it was called the "Last Great Time War" because the Timelords were thought extinct in its conclusion, and without them, there can't be another Time War. Thus, it was the FIRST and LAST Time War.
Answer: Yes, the Time Lords have had (will have) multiple cross-temporal conflicts or "time wars" over the length of their species' existence. The first time war fought by Gallifrey was the Black Sun War, starting when the Order of the Black Sun sent a time-travelling assassin to prevent Gallifrey from gaining time travel.

 (COMIC: Star Death, 4-D War)

The Order of the Black Sun itself existed 30,000 years in the future, and launched a second attack in the Question Hall twenty years after the initial attack.
  (COMIC: 4-D War)
The Time Lords had been viewed by the Order as striking first in the present, after the Sontaran ambassador Brilox used a psy-snare to make the parahuman Millenium assassinate the Black Sun Elder in an attempt to secure the uranium on Desrault for the Sontarans while Gallifrey and the Black Sun were "at each other's throats". (COMIC: Black Sun Rising)

While the televised shows often called the Time War with the Daleks "The Last Great Time War," it was called this because after this war, the Time Lords were rendered nearly extinct, and removed/isolated from the rest of the temporal flow of the Universe.
Comment: Incredible answer. Love the level of detail here :)
Comment: Aren't comics in Doctor Who considered at best secondary canon?
Answer: No canonical mention of any other temporal conflict has ever been mentioned on screen.
The BBC 8th Doctor Novel range described a series of events beginning with a "Last Contact" between the Time Lords and an unnamed Enemy. Several of the novels in that series depicted paradoxical events, including an alternate death-and-regeneration event for the Third Doctor. These in turn fed a third power, Faction Paradox, originally an offshoot from the Time Lords, which seemed to be taking advantage of the situation rather than actually the Enemy. Faction Paradox has since enjoyed its own series of spin-off media.
Big Finish have depicted a series of temporal conflicts in its Gallifrey range of audio plays. These stories depict Lord President Romana's efforts to navigate the treacherous politics within Gallifrey, and between Gallifrey and other Temporal Powers.
On the one hand, none of these things are really canonical, based on the usual definition of canon for a television series.
On the other hand, Steven Moffat is more or less on record as saying that there's no such thing as continuity in a show about a time traveler, which means that none of these events are really mutually exclusive with the Last Great Time War.
Answer: A "Time War" in essence exists across all of time and space meaning that there was really no end to the war, making any conflict involving the daleks, time lords, or other notable time-traveling species would be considered part of the Time War.
Comment: I can see how "_a_ time war" _could_ mean that, but the question is asking about what the show means when they say, "_The_ Time War" or "The Last Great Time War".

Have there been multiple time wars?


Sorting almost sorted array using Insertion Sort

Question:
Regarding insertion sort on almost sorted arrays, it takes linear time. But that is only after we have an if condition in our implementation to break out of loop if array is sorted, right??
For insertion sort on small data sets, why is insertion sort preferrable? Because of the fewer amount of compariosns/operations comapred to quicksort and mergesort?
Answer: Yes, it takes linear time on almost sorted arrays because you break out of the comparison loop very early. Once you insert the element in the right place, there is no need to go through the rest of the sorted array.
I guess it's because you're utilizing the knowledge about the already sorted array, whereas in quicksort, you get each element to the right place and then sort the remaining elements.


How can two different domains map to the same range in a function?

Question: How can two different domains map to the same range in a function? I'm honestly trying to become better at math, so sorry if I come off as ignorant. A function must have every domain value associate to only one y-value. Ok, that makes sense. But then, in a function, one y-value IS able to map to 2 different domains. Why? This puzzles my logic. A function has a rule, so if, per say, my rule is f(x)=x+1 , then I can have the following set: {(1,2),(2,3)}. This set follows the function, however, I am unable to have a set such as: {(1,2),(1,3)}, ok so that makes sense according to my rule. However, a function CAN have a relation of the following: {(1,2),(2,2)}, this is allowed in a function, however, I don't see how this could ever follow my rule? Is there an example where my brain could be proved otherwise? lol Thanks guys!
Comment: Here is another example of a function which is not one-to-one:  Denote the function "$\text{First}$" with domain being the set of words in the English language and range the set of letters used in the English alphabet defined as taking a word as input and outputting the first letter of that word.  We have $\text{First}(apple)=a=\text{First}(ant)$.  Written in set form we have $\text{First}=\{(aardvark,a),(aarnet,a),\dots,(first,f),\dots,(zulu,z)\}$.  We don't even need our functions to have "rules" that "make sense" in the first place, $\{(1,\pi),(potato,5)\}$ can be a perfectly valid function
Comment: The most basic example that comes to mind is a constant function such as $f(x)=5 , x \in \mathbb{R}$.
Comment: $f~:~\{-1,1\}\to\{1\}$ given by $f(x)=x^2$ satisfies $(-1)^2=1$ and $1^2=1$ is an example of where $f(-1)=f(1)$.  Perhaps you are only trying linear functions of the form $ax+b$ with $a\neq 0$.  As for $\{(1,2),(2,2)\}$, we might call such a function a "constant function" and might be written simply as $f(x)=2$, or if you insist on a more convoluted way, how about $f(x)=|x-1.5|+1.5$ where one has $f(1)=f(2)=2$.
Comment: Nice way to prove the point @JMoravitz
Answer:
I think intuitively the idea is A function takes its input and follows a rule to produce its output. Sometimes, following the rule for different inputs leads to the same output result.
You may be used to functions where different inputs always produce different outputs. For example, "adding one to a number" is a function where different inputs produce different outputs. Or "doubling a number".
However, some rules can behave differently: even if you start with two different inputs, the rule may transform them into the same output.
Here's an example: a function like $f(x)=x^2$ sends every number to its square. So, for example, $f(3)=3\cdot 3 = 9$. Because (-3)(-3) = +9, we know that $f(-3)=9$ as well. So, squaring -3 and squaring 3 end up as the same result.
So, the function is built of the tuples $(3,9)$ and also $(-3, 9)$.
Or you can consider  the rule $g(x)$ which takes in a number and tells you whether it's odd or even. Then $g(2)=g(4)=g(6)=\ldots = \mathsf{even}$ and  $g(1)=g(3)=g(5)=\ldots = \mathsf{odd}$. Many inputs lead to the same result.
Functions can even deal with things other than numbers. Imagine a function whose inputs are people and whose outputs are numbers— the person's age. Then this rule may associate two different people with the same age.
Answer: Functions are designed to model specific relationships, where we associate with each input ("element of the domain") exactly one output ("element of the range"). There is a certain amount of asymmetry in this definition; nothing prohibits a function from sending several inputs to the same output (but fear not, we have such a concept in mathematics as well! Functions that do send different inputs to different outputs are called "one-to-one" or "injective").
It is not an accident that (given a function $f$, and an element $x$ in the domain of $f$) we generally say "$f$ of $x$" when we see $f(x)$. Lots of relationships in the real world are functions in the mathematical sense, and this is especially clear if we can say "the $\_\_\_$ of $\_\_\_$".
For example, "the (biological) mother of $x$" is a function from the set of all people to the set of all people, that associates with a person $x$ that person's mother. Any person has exactly one biological mother, and so it satisfies the definition of a function (each input person gets paired with exactly one output person).
If we denote this function by $f$, then for a given woman $y$, the equation $f(x) = y$ may have many different solutions; a woman may have more than one child, and for any child $x$ of mother $y$, "the mother of $x$ is $y$" is true (symbolically, $f(x) = y$). This is an example where different inputs (people) may get sent to the same output (their mother).
Here again we see asymmetry: If we had tried to define our function by "the child of $x$", that sends to each biological mother her child, this would not be a function: A given input (biological mother) may correspond to several outputs (that mother's children). It certainly constitutes a relationship between biological mothers and people, but in general, we haven't specified any criteria that makes the outputs unique.
Comment: Both functions (single output for every input) and relations are useful, and I don't really have a great answer to your question. But, functions eliminate choice. We like deterministic things, and functions are deterministic: You give a function the same input, and it'll always give you the same output. But for a relation, we might have to choose between several "outputs" for a given input. The first way is more "streamlined" in that we don't have to make choices, we just follow a single path. But the second way allows us to model more things.
Comment: Awesome explanation! Thanks @pjs36
Comment: Nice! Hmm, thanks to all who have chimed in! I was wondering, my notion of equations has changed, lol. At first I saw functions ONLY as equations which take input and give an output, which is not wrong, but I did not understand the conceptual constraints on such. Now that I do, I'm left wondering at what the significance of splitting off equations such as f(x)=y^2+3 (non-function relation), and f(x)=x(0)+3 (function relation)? What is the purpose/importance/practice of a function vs a non-function. Why prefer a function over just a relation and vice-versa?


MOOC's certificates on graduate admissions

Question: Do departments look at MOOC's certificates favorably during the graduate admissions process? Will it give me any advantage over students who don't have them if I am trying to enter a PhD program?
Answer: You're free to mention the certificate in your application.  How much weight to give to it is presumably up to individual committee members.  I think unless the certificate pertains to a specific skill that's in demand for the program, you shouldn't expect to get much of a boost from having one.  At the moment, people don't have much experience with such certificates, and will be more inclined to look at indicators they know better, like grades and GREs.  It's possible this will change a bit in the future, but it will likely move pretty slowly.
Answer: What sort of advantage do you have in mind?  MOOCs could help a little in addressing weaknesses in your application: if there's a standard course you were unable to take, then it could be helpful to be able to say you learned the material by other means, and a MOOC certificate might carry a little more weight than completely independent reading.  However, on a scale from saying you read a book to getting a strong letter of recommendation, a MOOC certificate is much closer to saying you read a book.
Beyond that, it can't hurt to list MOOC certificates on your CV, but I doubt they'll make any difference.  If you're going to graduate school, you should have spent time on many different sorts of learning: lots of formal classes, extensive discussions with peers, independent reading, and ideally working with a faculty member on something (a senior thesis, undergraduate research, etc.).  Adding a few online classes is just not a big deal, especially if people are unsure of what the standards are.  Compared with things like letters of recommendation or research experience, MOOCs disappear in the noise.
Answer: If the MOOC certificate is in a closely related field, it will help. If it is in something like "Underwater Basket Weaving", it may not give you an advantage over anyone else, unless of course you are entering a program in Underwater Basket Weaving. Or something similar, such as Underwater Knitting.
Comment: What? I honestly don't think a certificate from any computer science MOOC would help in my department, or in any strong CS department. Graduate admissions is largely based on building a convincing case for future success as a researcher; a MOOC certificate doesn't provide evidence of research potential.  But if you have evidence that relevant MOOC certificates help in graduate admissions, say in the form of a citation, I'd love to see it.
Comment: _If the MOOC certificate is in a closely related field, it will help._ - [citation needed]
Comment: I see the trolls are out


ios different image sizes for UIActivity subclass

Question: iOS documentation describes that UIActivity subclass should return image for 'activityImage' with different sizes for iPhone, iPad and iOS 6, iOS 7.

For iPhone and iPod touch, images on iOS 7 should be 60 by 60 points;
  on earlier versions of iOS, you should use images no larger than 43 by
  43 points. For iPad, images on iOS 7 should be 76 by 76 points; on
  earlier versions of iOS you should use images no larger than 60 by 60
  points. On a device with Retina display, the number of pixels is
  doubled in each direction.

What is the correct way to return the image:

Create if/else block following the device iPHone/iPad and iOS6/iOS7 to return. I think this not the best way.
Name the images following the naming convention (such as suffix ~iPHone, ~iPad, ....), then we just create the image with one name in coding. The system automatically match the correct image file. I think this is the best way, but I don't know the naming convention.

Which is the way should I use? Thank you!
Comment: I answer your question, Did it help you?
Answer: The best way to do that is always follow the Apple standard:
For iPad:
 - someIpadImageIcon@2x~ipad
 - someIpadImageIcon~ipad
For iPhone:
 - someIphoneImageIcon@2x
 - someIphoneImageIcon
Hope it helps you


HP Elitebook Revolve 810 trackpad not working

Question: I just installed the newest version of Ubuntu today and the trackpad will click, but will not right click or scroll. I'm fairly new to Linux so any help would be extremely helpful.
Answer: You might have some luck altering the options for the trackpad's driver (if it is Synaptics).  Open a terminal, and take a look at the output from the following command
synclient -l
(which gives options and corresponding values for the trackpad if the Synaptics driver is being used).  I have a different machine (MacBook Pro) so my options are probably different from what you need, but for what its worth my value for the VertTwoFingerScroll option is 1, TapButton = 2, and ClickFinger2 = 3.  Not sure if these are the appropriate options, but they may help.
(To set an option, use synclient option=value, for example synclient TapButton=2).


Securely tell the user his password in new WHM/Cpanel account creation?

Question: I understand it's not safe to send passwords via email but when accounts are created via WHM/Cpanel, I have to let the user know what password I created for them. How can I relay the password safely?
Answer: Don't transmit a password at all. Set the password to something completely random, then automate a password reset. This will create a one-time link that allows them to log in, and forces them to change the password immediately.
Benefits of this scheme:

A valid password is never sent in cleartext.
The one-time link is useless after one use, so an attacker stealing the link later isn't a problem.
The user is prompted to create a password immediately, so the account is secure the instant they start to use it.
You know when a user has logged in successfully for the furst time, which allows you to send them an email thanking them for their custom. Furthermore, you could send out an email to any unactivated account after 12 hours or so, reminding them to use the link to set up their password.
Comment: I'm assuming the difference between sending an expire-on-login password and a one-time-link is that the link can be used _only_ once, and would have to be re-requested, whereas the user might decline to create a new password (forgoing the ability to use the site, but leaving the password eligible).  Or have I missed something here?
Comment: Pretty much, yeah. The point is that once the link is used, it's used, and the user has set their own password. With a one-time password, you are transmitting a token that is usable for more than one login.


Looking for a Book about people Called Talents

Question: I remember something about people gaining powers from areas that were once inhabited by dragons. The main character can talk to animals and is followed around by a wolf; her brother can influence others. They meet a noble later on who can see into the future through skin contact. There was also something about a draft for the "Talents" to send them off to war.
Comment: Do you remember about how long ago you read it?
Comment: possible duplicate of https://scifi.stackexchange.com/questions/4549/novel-about-a-dragon-lord-who-has-to-wear-gloves-at-all-times
Answer: I was just looking for a book that meets this description too. I think it's The Secret of Dragonhome by John Peel. I also just discovered that he wrote a sequel (The Slayers of Dragonhome) to this book in 2011. Hope this is what you're looking for!

Melayne and her young brother Sarrow are Talents, hunted by the King's relentless Seekers. If their Talent is discovered, they will be sent to their death. So they must hide...or die.
  Melayne and Sarrow find refuge at Dragonhome, the mysterious estate of the shadowy Lord Sander. Lord Sander also has something to hide--a dark and fantastical secret that haunts his every move. In order to save herself and her brother, Melayne must confront forces much stronger than her talent--tempests of magic, desire, and betrayal. If Melayne is not careful, her truth will be revealed.
  Melayne must unlock the secrets of Dragonhome. As danger approaches, it will be her only hope

From one of the reviews:

The protagonist, a girl named Melayne, has a magical ability called a Talent that allows her to communicate with animals.
Comment: That's definitely the book. I enjoyed reading it growing up. I finally managed to contact the author a few years ago to ask him about a sequel, because the original is left on a cliff hanger for year. He said he was just about to release the sequel and that the final words were "to be continued". This indicated a 3rd book. I re-read the first book and it stood up fairly well for what it was. I didn't like the writing of the second book at all, but was glad to know what happened after the 2nd book. I'll read the 3rd if it comes out, but I really hope it's better written than the 2nd.
Answer: Perhaps you are thinking of the Xanth series by Piers Anthony? The magic system is based around "talents" that many people have, that allow them to do things such as seeing into the future, and a plethora of other things. In the over 30 books in that series, it is possible a main character is followed around by a wolf, but I can't remember.
As for dragons being the source of their magic, in the Xanth series the source of magic is a demon. However, he occasionally appears in the form of a dragon, perhaps that is what you thought of?
Comment: Xanth was my first thought too, but none of the details besides Talents match; also IIRC all most of the animals in Xanth could talk _anyway_ so being able to talk to them wouldn't really be much of a talent, though I will admit I never read much past Dragon on a Pedestal.
Answer: Might be way late, but I'm pretty sure you're talking about Assassin's Apprentice by Robin Hobb
The magic is passed down by bloodlines, it's called The Talent. And the protagonist has a rare combination of The Talent and an ability to connect with animals. The rest of the trilogy goes well into the dragon lore.
Comment: Hi, welcome to SF&F!  Interesting thought, but you should also disclose how it doesn't match; Fitz is male, not a "her," and he can only talk to Nighteyes.


Is there any way to use chown/chgrp without modifying the last modified date?

Question: I'm recovering files from an old hard drive and I need to keep the last modified date from the drive. The reason they are updating is because I need to change the ownership of the files to a new user.
Comment: This would be suspicious. Imagine a hacker or a rootkit disguising its accesses.
Answer: The mtime (file modification time) shouldn't change when the owner is changed (nor should the atime or access time).  That would be a change in the inode information, reflected in the ctime field.
If you find that on your system, chown(2) (or chown(1) and chgrp(1)) do change the mtime or atime and you're concerned about preserving both mtime and atime, then you'll need to write code to collect the current times (using stat(2) or stat(1)), and reinstate them (using utimes(2) or touch(1)).
AFAIK, you cannot control the setting of the ctime.  If the inode changes, the system records the time it changed and doesn't allow you to change that.
Comment: When I just used FTP to copy a file between machines (default options), the modification time of the file on the target machine was set to the current date, not to the original date. So FTP does not preserve mtime and atime timestamps by default. This isn't very surprising; FTP is more general than Unix with its mtime and atime. Put another way, FTP is not TAR. Maybe you should consider using TAR to package the files on the source machine, use FTP to transfer the (compressed) tar file, and then use TAR on the target to restore with the correct time stamps. You can then adjust ownership later.
Comment: Hmm, interesting. I assumed that the chown and chgrp commands would be the modifiers on the time. The only other action performed on the files was a transfer from a hard drive to a server using ftp via Filezilla. Would this cause the time change?


Borderline off topic questions / alternative forum recommendation

Question: Often we see a question which is not really handled on Arduino Stack Exchange because, for example, a solution may involve some electronics in addition to Arduino know how or, in some other way, is not regarded as a pure Arduino matter. Usually, such questions would be a good candidate for forum.arduino.cc . The question is, is it good form to say so so explicitly to the OP ?
Answer: Personally I have no problem with people being politely referred to a place which may be able to help them better, such as Electronics Stack Exchange, Stack Overflow or the Arduino Forum.
Bear in mind that beginners may not know what it is that they don't know (for example, it is fairly common for them not to know the Arduino is programmed using C++).
Plus, the idea of things being "pure" Arduino are a little hard to quantify. After all, most problems have some elements of programming in them, some elements of electronics, and some elements of simple debugging and problem solving.
My personal approach is to help people as much as I can, even if a question is largely about C++ or electronics, unless the question doesn't seem to have any relationship at all to the Arduino. And I don't try quite so hard for questions that seem to be "here is my homework assignment, please do it for me ... and I'm in a hurry, it is due tonight".

Step-by-step debugging where the OP gets asked dozens of questions, given things to try, and report the results are better suited to a forum than Stack Exchange. If a question is heading down that path it could be a good time to suggest that the forum format is better suited to solving their problem.
Answer: Very few questions will not be "borderline off-topic". I have to agree with @NickGammon that whether we're hobbyists, experimenters, engineers acquiring a new skill-set, etc., very few problems fit compactly into "Arduino" or "not-Arduino". Can't we just try to be helpful before - or instead of - looking down our noses at the newcomer? Are we here to help our them? Or to posture before each other? Are we a community, or a collection of egos showing off what we know? Should ASE to be a welcoming place for people to learn or a group of elitists who might tolerate a newcomer if they figure out The Right Way to ask a question? I see a lot of responses to newcomers, even to knowledgeable ones that didn't write a question in the One True Way. that could send anybody walking, muttering to themselves about how unfriendly ASE is.
It doesn't have to be this way. But it will need the mods setting a friendly example and taking a firm stance on unfriendly & unhelpful replies toward newcomers by ASE members. Sure, if a question is a better fit for another SE (or non-SE) group, by all means, suggest it and in a helpful way. But why not welcome newcomers with a more friendly stance (yes, some do, but not all) and a more liberal interpretation of what fits here?
Comment: My belief is that the problem here is that the primary goal of ASE is to build a searchable question and answer database. If users are helped here, then that is only a side effect of this primary goal. This concept works very well for a well structured domain like say the C++ language but does not work so well IMHO for Arduino which can be a very broad area and often cannot yield a good clean question and answer pair. . . .
Comment: . . . Having said that, I agree, however, that more effort could be made to help users who are, after all, creating content on this site even if their issue is of no general interest and therefore does not contribute much to the primary goal of the site. This could be achieved, while still maintaining the site quality, by simply marking the question down and giving the user sufficient information to send them on their way.


Delta potential, negative energy, quantum particle

Question: I was solving a task involving bound states of an electron : We have a delta potential $V(x) = -\lambda \space \delta(x)$, find the energy of the only bound state. So I get $\sqrt{k}e^{i k x} , \space  x<0 $ and $\sqrt{k} e^{-i k x},\space x>0$, where I used normalisation and the continuity condition. And then I integrate the stationary Schrödinger equation $H\psi=E\psi$  to get the only eigenvalue - bound state energy $E=- \frac{\lambda ^2 m}{2 \hbar^2}$. What is the physical interpretation of the negative energy, since the potential energy is equal to zero, except at origin, does this imply that the kinetic energy is negative ($H=T + V$)? There are some similar examples on this, but they are all done with tunneling, where there is a potential present.
Comment: The negative energy implies that what you have found is a bound state. Meaning, the particle will be bound inside the delta potential.
Comment: Can I think of this as taking a normal square potential well with width **a** and then letting **a** go to 0 ?
Comment: That is exactly how delta function potential is thought of asymptotically.
Answer: For your confusion about whether kinetic energy is negative, just do this. You have the total energy $E$ = $-\frac{\lambda^2 m}{2\hbar^2}$. Find $\langle V \rangle$, the expectation value of the potential. Subtract that value from the energy $E$. What you get is the expectation value of kinetic energy $\langle T \rangle$, which is positive (try it out). Finding $\langle T \rangle$ directly for the wavefunction of delta function potential is nasty.!
Answer:
What is the physical interpretation of the negative energy, since the
  potential energy is equal to zero, except at origin?

First, we need to understand that Energy is relative, both in Quantum and in Newtonian mechanics. This means that different reference frames will determine different values for the energy of a given object at a given point in space and time.
In this case, we are allowing to have negative Energy values for delta potential energy by the following.

()=− () (where  is a positive number)

This means, in this reference frame we consider all Energy values with minimum () value that is negative infinity. Therefore, we are allowed to solve the Schrodinger Equation for all the negative and positive values of Energy.
In contrast, for the free particle problem's reference frame, we consider minimum () value is zero and all the Energy values should be positive for well-defined solutions.
However, the conservation of energy holds in any reference frame. This means that, in a single reference frame the total energy (KE + PE) will be constant over time.


distinguish single-block vs multi-block reads in Oracle explain plan

Question: If I am looking at a query plan in Oracle 11g, is there any way I can tell which operations will result in single-block reads and which will result in multi-block?
Answer: TABLE ACCESS FULL and INDEX FAST FULL SCAN use multi-block I/O, other kind of access paths use single-block I/O.
Answer: FULL INDEX SCAN reads the index a block at a time, from start to finish, It uses single-block.
FAST FULL INDEX SCAN reads the entire index, unsorted, as it exists on disk, And use multiblock I/O and read all the leaf, branch, and root blocks.
the same thing happen too in TABLE ACCESS.


Notation of Affine space.

Question: I am following Fulton's book on Algebraic curves.It starts with the notion of affine spaces denoted by $\mathbb A^n(k)$ where $k$ is a field.The author defines the affine space $\mathbb A^n(k)=k^n$ the $n$-fold cartesian product of the field $k$ and there is no additional structure on it.So,my question is about the notation.Why cannot we simply denote the affine space by $k^n$.Why we denote it with a more complicated notation $\mathbb A^n(k)$?Algebraic curves is almost new topic to me and I have no idea why this is defined by such a notation.Can someone clarify?
Answer: If you write $k^n$ it will most likely be interpreted as the $n$-dimensional vector space over $k$. The $n$-dimensional affine space over $k$ is a different object, it's not a vector space, and although both objects can be identified as sets they belong to different categories and have different morphisms (affine space is commonly thought as a scheme). So the notation $\mathbb{A^n}(k)$ is preferred because it is less ambiguos, and it is consistent with the notation $\mathbb{P}^n(k)$ for projective space.
Answer: Yes, $\mathbb A^n(k)$ is just $k^n$ but Fulton's motivation for the notation is probably to distinguish the set of $n-$tuples of members of $k$ from the projective space $\mathbb P^n(k)$, which is $k^{n+1}\(0, ... ,0)$ modulo the equivalence relation of scalar multipication by a non-zero member of $k$.

Notation of Affine space.


Careers links in mega menu

Question: I am designing a corporate website career page. Should I use a mega menu for the career page? Here are some of the items related to the career page:

Who we are!
What we do?
Life at Our Company!
Reasons to join us?

compensation
benefits
work/life
Answer: Welcome Naveed to UXStackExchange.
I think a megamenu is a bit of an overkill with the options you are currently listing.
Here is an article from NN/G with a quote

Mega menus (sometimes spelled "megamenus") are a type of expandable
menu in which many choices are displayed in a two-dimensional dropdown
layout. They are an excellent design choice for accommodating a large
number of options or for revealing lower-level site pages at a glance.

Now, if you plan on adding more options in the future. Like top-level job categories or more resources, then it might indeed be a good idea to go for a mega menu and make it a tad future-proof.
Another thing to consider is the overall aesthetic of your website and what type of users you expect to visit. Will a mega menu perhaps be useful in other aspects of your website? Then you could implement it as a common design/aesthetic component.
Or, will your users be mostly visiting via mobile? Then maybe again a megamenu can work instead of a fiddly dropdown.
Whatever you choose consider the options you are currently offering, the ones you will offer in the future, and the behaviour you expect from your users. If in doubt, it sounds like the perfect excuse for some A/B testing ;)
Answer: This decision could arrive after looking at information architecture of the whole website. But, looking at the content you plan to put, it appears that can come on single page instead of links in mega menu
Comment: thank you @Sujit Devkar for you quick response, so mega menu issue for any specific page?
Answer: Yes you can only if you have multiple list of job or multiple jobs in different categories then you can show categories in individual columns.

Careers links in mega menu


PHP Cache Security: File caching vs memory caching

Question: Are there any relevant security issues in using a file cache (i.e. PEAR Cache_Lite) to hold data (serialized arrays, objects) in PHP? Is a data cache more secure in memory, i.e. using memcache or APC?
Comment: security from hackers trying to access the data cache
Comment: wouldent thay have to get access to the server first in either case?
Answer: Since you mentioned: Security from hackers, the answer would be no..
If somebody is able to access your filesystem or system in general, they will have access to pretty much everything, including your mysql data.
When it comes to caching, the main extra worry you have is if you are sharing the server with other people.
If you are using memcache, you do want to make absolutely sure that nobody can access the memcache server from outside. Do you have a firewall? Do you only keep the ports open that you must?
If the answer to those is yes, then your biggest security problem is your own application.
Answer: When using a file cache, you at least get the built-in security of the underlying file system.  I don't believe Memcached or APC have any kind of privilege separation, so other users on the same system could in theory access whatever you had stored in one of the aforementioned memory caches.


Ctrl+Break on Apple keyboard

Question: I usually use ctrl+break to break the compilation in visual studio, and now my new apple (macbook pro) laptop does not have break key. Is there a shortcut that I can use on an apple laptop?
Answer: I don't know if there is a Fn or some other key combo that duplicates a PC Break key, but you can assign any hot key you like to the Build.Cancel command from with Visual Studio. Just go to the Options dialog (available under the Tools drop menu), find the Build.Cancel command and assign a new shortcut for that command.
Answer: yes ctrl+F14 (on mac full keyboard) :
Also you can use virtual keyboard for somethings in windows.
ctrl+F14 is interpreted by windows as ctrl+scrlLock, F14 on full mac keyboard is in the same position as scrl-lock key on windows full keyboard.
Comment: Welcome to Stack Overflow! Thank you for your answer. Please provide more details about your solution. Code snippets, high quality descriptions, or any relevant information would be great. Clear and concise answers are more helpful and easier to understand for everyone. [Edit](https://stackoverflow.com/posts/77045362/edit) your answer with specifics to raise the quality of your answer. For more information: [How To: Write good answers](https://stackoverflow.com/help/how-to-answer). Happy coding!

Ctrl+Break on Apple keyboard


Are There Specific CSS Selectors Targeting IE10?

Question: Since IE is getting rid of conditional comments in version 10, I'm in dire need to find a "CSS hack"  targeting IE10 specifically. Note that it has to be the selector that's getting "hacked" and not the CSS-properties.
In Mozilla, you can use:
@-moz-document url-prefix() {
  h1 {
    color: red;
  }
}

While in Webkit, you usually do:
@media screen and (-webkit-min-device-pixel-ratio:0) {
  h1 {
    color: blue;
  }
}

How would I do something similar in IE10?
Comment: IE10 will probably be standards compliant enough to not need any hacks. And Tyler, the question said it doesn't support conditional comments.
Comment: @BoltClock Unfortunatelly there are some weird variations even among the standard compliant web browsers (Webkit/Firefox/Opera) thus a selector such as @-moz-document really helps out, when attempting to create a pixel perfect experience across all browsers. Even though I'm a big fan of allowing browsers show a slightly different experience for their users - my client doesn't.
Comment: I'd just use IE conditional commenting. Besides, none of my friends or family even know about IE 10.
Answer: The following example shows how to do this
/*
 #ie10 will only be red in MSIE 10,
 both in high contrast (display setting) and default mode
*/
@media screen and (-ms-high-contrast: active), (-ms-high-contrast: none) {
   #ie10 { color: red; }
}

Warning: will probably work in IE11+, too.
Comment: That is dangerous thinking. Even if it is a long time before IE11 comes out, that means the code will be less fresh in your mind and perhaps harder to fix. Also, no one really knows when the next version of IE will come out, or the bug you are working around will be fixed. I'd only use a hack like this for something that won't break if the bug is fixed in a later version.
Comment: Just tried using this method. Only works in the dev environment, not production.
Comment: Thank you for your input, I accepted this as an answer. Wether it will target IE11 or not is something I don't think any of us should worry about, for some time :-)
Answer: Using the css browser selector from http://rafael.adm.br/css_browser_selector/ you can add a simple + to the code and call out IE10 from your CSS.
Look for /msie\s(\d)/ and change it to /msie\s(\d+)/.
Now in your CSS just add .ie10 before your selector like so:
.ie10 .class-name { width: 100px; }
.class-name { width: 90px; }
You should now see IE10 rendering the 100px width and all other browsers rendering the 90px width.
Answer: As far as I know, no such CSS selector exists. If you want to target IE10 specifically, why not just write a bit of javascript to set a class on the body element called ie10, then create a specific styles for IE10?
Answer: I'm not sure if this fits your selector vs property requirements but I came up with the following method while trying to fake text-shadow in IE7-9 and then turn off the hack in IE10. The key is to use the new -ms-animation stuff in IE10.
.header {
    /* For browsers that support it to add a little more punch to a @font-face */
    text-shadow: rgba(100, 100, 100, 0.5) 0 0 2px;

    /* Make IE7-9 do faux bold instead and then turn down the opacity to match */
    *font-weight: bold;
    font-weight: bold\9;
    *filter: progid:DXImageTransform.Microsoft.Alpha(Opacity=75);
    opacity: 0.75\9;

    /* Uh oh! We've also caught IE10 in our above hack */

    /* But IE10 supports CSS3 animations. Will a high duration keep CPU usage down? */
    -ms-animation: text-shadow 60s infinite;
}

/* Define the animation */
@-ms-keyframes text-shadow {
    0%, 100% {
        font-weight: normal;
        opacity: 1;
    }
}


What was the political impact of the 'Daisy' election campaign commercial?

Question: I can see why the Johnson Campaign's Daisy was controversial. I also know that Johnson won the 1964 United States presidential election. However, how much of a political impact did Daisy really have? Wikipedia tells me "Jack Valenti, who served as a special assistant to Johnson, later suggested that pulling the ad was a calculated move, arguing that "it showed a certain gallantry on the part of the Johnson campaign to withdraw the ad."" This doesn't make clear the real implications and seems hypothetical.
Comment: VTC as opinion based. There's no objective way to assess the impact of a single 1964 presidential campaign advertisement. The current answer discusses how widely seen it was, but the effect it had is not quantifiable 55 years later.
Comment: I wonder if anyone would have understood those two characters 55 years ago.
Answer: The sentence right before the one you quote in the wiki article is instructive:

The ad was immediately pulled, but the point was made, appearing on the nightly news and on conversation programs in its entirety.

The commercial became widely known and seen because ABC News and CBS Nightly News broadcast it a lot due to the controversial content, and the nature of the content makes it hard to not form some kind of an opinion on it.
In other words, the impact was widespread awareness of the ad and the controversy.
To make this a tiny bit more relatable: consider the uproar whenever Trump or someone in his team make a controversial tweet or statement. For instance, the frenzy that erupted when Kirstjen Nielsen falsely blamed Congress and the courts for the Trump administration's policy of child separation.
Comment: @Jontia: To me, the impact is widespread awareness of the ad and the controversy. Which seems fairly significant.
Comment: This doesn't address the impact, just the profile and distribution. Though to be fair I don't really know how you would address the impact in a concrete manner.
Comment: @J.D: no idea about long term effects, but in the short term there's research to support the idea that there was awareness convinces. See e.g. https://en.wikipedia.org/wiki/Mere-exposure_effect


How can I rename long file names?

Question: I was told I can rename and shorten file names that have more than 255 characters (including file pathway entries) using Ubuntu. How can I do this?
Comment: Are you currently running Ubuntu?
Comment: No offense but I would not be on this forum if i was not using Ubuntu. Yes I use Ubuntu 18.04.2
Comment: The wording in your question lent itself to "I have a problem with Windows..."
Comment: i said absolutely nothing about windows
Comment: I didn't intend to offend - there are a lot of questions on this site related to Windows - people starting to use Ubuntu, or having problems with dual-boot, or using WSL.
Answer: Most of this will be done using a terminal window, and typed commands, often referred to as CLI, for command line interface.

The first way that you might try to shorten your fully defined path and filename, is to move the files in question to a shorter path.
Using a terminal window, this is done with the mv command as outlined below.
1st, open a terminal window (press ctrl+alt+t)
Let's assume that the full pathname to a file is
/This/Is/The/First/Part/Of/A/Long/Path/And/Here/Is/My/file.name
where the first part log the long pathname is not of interest.  You must first create a destination directory to store the files of interest.  First let's make sure that you are in your home directory
cd ~
Now lets create a directory to store the renamed files:
mkdir ./Shortpath
Now we could move just the one file to the new Shortpath directory:
mv /This/Is/The/First/Part/Of/A/Long/Path/And/Here/Is/My/file.name ./Shortpath/
Now the file file.name is in the Shortpath directory in your home directory.  The full pathname to the file is /home/<username>/Shortpath/file.name where <username> is your user name.
That's fine for a single file, and a little modification makes it move entire subdirectories:
mv /This/Is/The/First/Part/Of/A/Long/Path/And/Here ./Shortpath/
moves the directory named Here from the long path, to the Shortpath directory, so the full name for the file would now be /home/<username>/Shortpath/Here/Is/My/file.name
So, by using mv (see man mv) you can move files, or directory structures, from the end of long paths to shorter paths.

This is all well and fine if you want to permanently move the files from a long and unwieldy path, to a short path permanently.  Sometimes you just want to do it for a little while, and for that I'm going to use mount (see man mount) to create a short path to the files, that will go away the next time you reboot.
Again lets assume that the long path is
/This/Is/The/First/Part/Of/A/Long/Path/And/Here/Is/My/file.name
and the part you are interested in begins at the Here
Using mount with the --bind option, we can add a new directory structure to your linux system, so that the path tot he file is much shorter.
First, make sure that a directory we will use as a mountpoint exists:
ls -ld /mnt
should return something like
drwxr-xr-x 2 root root 4096 Apr 16 11:59 /mnt
if it does not, the command sudo mkdir /mnt will create the directory.  You need to use sudo for this, as regular users can't create directories at the root level.
Now we can connect the directory structure of the long path, starting at Here to your file system with the command
You might try using
sudo mount --bind /This/Is/The/First/Part/Of/A/Long/Path/And/Here /mnt
Now a path to your file is /mnt/Is/My/file.name
Please note that the file has not been moved - there a are now two fully valid paths to the file:
/mnt/Is/My/file.name and /This/Is/The/First/Part/Of/A/Long/Path/And/Here/Is/My/file.name point to exactly the same place on the disk.
When you are done manipulating files, and you don't need the path mounted anymore, you can execute the command
sudo umount /mnt
which will disconnect the path, or you can reboot.  Either way, the mount will be gone.

Some useful information:
In a terminal window, information about commands can be found in the Manuals which are  installed in Linux:
man mv show the manual pages for mv
Other commands used here were ls, mkdir, mount, umount, sudo.  All of these also have pages in the manuals.
Comment: I have no idea what you are trying to say, I am relatively new to this. could you explain how step by step in greater detail? @Charles Green
Comment: @MikePeterson Sure - but I think I should ask are you just trying to find the files, access the files, or move them to a shorter directory path?
Comment: I want to move them to a shorter directory path.
Comment: @MikePeterson OK, I'll expand the answer, and provide details for two methods.

How can I rename long file names?


Sync between Adobe and Texniccenter

Question: I am using TeXnicCenter and Adobe Acrobat Pro 11. My problem is whenever I compile my article in TeX -> PDF profile, it produces the output PDF and give me back from the first page, it does not navigate to the place where I have done changes or the page where I left. Please help me out for this.
Comment: The preferred viewer for TXC2 is [Sumatra PDF](http://blog.kowalczyk.info/software/sumatrapdf/). In opposite to the Ad0be products it supports SyncTeX for forward and inverse search between source and PDF output.
Comment: Don't use adobe. Use e.g. sumatra if you need good syncing.
Comment: A suggestion: Do us a favour and change your username to something more telling than "user1234".
Answer: What you want to achieve is not possible with Adobe Acrobat or Reader. You have to use another PDF Viewer. The preferred alternative is SumatraPDF. For configuration see How to configure TeXnicCenter 2.0 with Sumatra (2013--2016 version).
From SumatraPDF you will have the opportunity to open the active document in Adobe Reader (or another installed PDF viewer) for documents with more complex contents, that will not be displayed with all features in SumatraPDF, but you are responsible then to close them by hand in the other viewer.
Comment: @Sunit_gupta: No, you cannot sync with Adobe. I also do not see your problem with a second _free_ PDF viewer, where you have the possibility to open the document in Adobe Acrobat.
Comment: The problem is i have license version of adobe, so i dont want to use another pdf viewer for it. So does it mean that we can sync adobe and TeXnicCenter.

Sync between Adobe and Texniccenter


Problem installing java in Ubuntu 20

Question: i tried to install java using the following :
apt install default-jre

but when i want to see the version using :
java -version

it says :
apt install default-jre              # version 2:1.11-72, or
apt install openjdk-11-jre-headless  # version 11.0.8+10-0ubuntu1~20.04
apt install openjdk-8-jre-headless   # version 8u265-b01-0ubuntu2~20.04
apt install openjdk-13-jre-headless  # version 13.0.3+3-1ubuntu2
apt install openjdk-14-jre-headless  # version 14.0.1+7-1ubuntu1

i run the installation command again it again :
Reading package lists... Done
Building dependency tree
Reading state information... Done
default-jre is already the newest version (2:1.11-72).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

and when i try to run the following :
sudo update-alternatives --config java

i got this :
There is only one alternative in link group java (providing /usr/bin/java): /usr/lib/jvm/java-11-openjdk-amd64/bin/java
Nothing to configure.
update-alternatives: warning: forcing reinstallation of alternative /usr/lib/jvm/java-11-openjdk-amd64/bin/java because link group java is broken
update-alternatives: warning: not replacing /usr/bin/java with a link

and the same keep happening over and over .
i had no problems during installation and all ok when i run a program that depend on java or run the java -version it is not working .
regards
Answer: Problem was solved by going to the path:
 /usr/bin/java

and there  i found a file with the name
 "jdk-14.0.2_linux-x64_bin.deb"

removing the java folder form there fixed the issue and now everything is ok .
Regards

Problem installing java in Ubuntu 20


Arduino printer emulation

Question: I'm working on a project in which an arduino should emulate a thermal printer.
I'm currently using an Arduino UNO R3 board with ATmega16U2 controller to handle the communication between USB and the ATmega328 microprocessor.
I used the FLIP suite from ATMEL to erase the firmware in the ATmega16U2 and reprogrammed again with the arduino firmware.
Which are the steps to take in order to make the board appear in the computer as a USB printing support? Is there any firmware available? What I need is basically to be able to use the arduino board with a standard windows printer driver and to catch the messages sent to the emulated printer.
I checked out the LUFA library but I do not have it clear how to use it.
Comment: If you can find a driver for a simple serial printer, you likely won't need to change anything about the Arduino's USB-serial interface.  Given that thermal printers often go in dedicated/embedded systems like point of sale setups, I'd think that those with serial (rather than proprietary USB) interfaces would be fairly common - at least far easier to still find than modern desktop printers with a serial interface.  Conversely, if you must emulate a *specific* thermal printer, you will need the details of its USB protocol which you might glean from the manual, or a Linux driver (if available)
Comment: Also, there's a fundamental problem with your question.  You claim, for unstated reasons that you cannot use a serial printer's driver.  That seems to say that you must use a specific USB printer's driver, but then your question would be unanswerably incomplete due to the failure to state which printer that is.
Comment: I'm aware about the possibility of using a serial interface with the windows driver, but unfortunately this is not possible. I really need to use a USB interface and the arduino should appear like the printer itself. I need to emulate a specific printer. What do I need to know about the USB protocol? Would it be enough if I could obtain the original firmware of the printer and I would flash it into the ATmega16U2?
Comment: No, the printer firmware will almost certainly not work on your board.  You will have to understand most of how the computer talks with the printer.  Often this is poorly documented - that's why I was suggesting trying to find the source code of a linux driver, to take advantage of someone having already figured that out, often by reverse engineering.  However, if you are using the OEM windows driver, you may have to implement even more of the original functionality in your firmware beyond what an open source driver might use.  Needless to say, this is *not* a beginner project.
Comment: @Francesco Hi, have you made any progress on this? I am looking for the exact same thing and I would really appreciate it if we could discuss it in person!
Answer: edited to add: related question
You need to change the USB ID from the Arduino to match the code that Windows would expect to see from your printer. Here is a sample list. And an example from that list:

03f0  Hewlett-Packard
    0004  DeskJet 895c
    0011  OfficeJet G55

03f0:0011 appearing on the USB means the device appears to Windows as a HP OfficeJet G55. You can determine this number easily if you have one of the printers physically. Plug it into windows and Computer -> Properties -> Device Manager find the device, open it, click the Details tab, select Hardware Ids dropdown and the manufacturer ID and device ID are in the "Value" window.
The next part (and hard part) is to then program the Arduino to do what you need/want with the data once attached to Windows. Oh, and how to program the Arduino when Windows thinks it is a printer. THAT, I can only say what I already have and no more, as I haven't done this before. Normally, when I would dev USB or serial like this, there's an ethernet back door I use for programming the target system.
Sounds fun, please update with your progress, I'd like to learn from this.
Comment: @David - the Arduino model in question does not use an FTDI chip.  Those were superseded a few years ago, though other vendors still sell clones and derivatives of the old boards using that part.  The USB interfaces on the newer Arduinos are based on a USB-enabled member of the ATMEGA family and are reprogrammable, though there's still the gaping challenge of figuring out what exactly it is going to have to do to emulate the unspecified printer needed.
Comment: Ah, my mistake; the last Arduino I used was the Duemilanove, so I shouldn't have assumed that the hardware was still the same. Good to know that they've made it more flexible.

Arduino printer emulation


finding Morse index for the following functional

Question: not sure if this meets the standards here in this forum. I was dealing with the following functional $I(u)=\frac{1}{p}\int_{\Omega}|\nabla u|^{p}dx-\frac{1}{q}\lambda\int_{\Omega}|u|^qdx$ for $p \geq 2$ and $p-1<q<p^*$, $p^*=\frac{Np}{N-p}$, $p<N$, $\Omega$ is a bounded domain in $\mathbb{R}^N$. I was interested to check the Morse index of $I$. Towards this, I computed the double derivative which is as follows. \begin{eqnarray}I''(u)(w,w)&=\int_{\Omega}\{|\nabla u|^{p-2}|\nabla w|^2dx+2(p-2)|\nabla u|^{p-4}(\nabla u.\nabla w)^2\}dx\nonumber\\
&-\lambda \int_{\Omega}(q-1)|u|^{q-2}|w|^2dx.\end{eqnarray}
I wasn't able to figure out what will be the largest dimension of a subspace of $W_0^{1,p}(\Omega)$ such that $I"(u)$ is nonnegative?. Is it at least possible to do so?.
Comment: You may consult the paper ''Morse index and uniqueness for positive solutions of radial $p$-Laplace equations" by Aftalion and Pacella in Trans of AMS (2004).
Comment: same question on MSE https://math.stackexchange.com/questions/3483440/finding-the-morse-index-of-the-following-functional
Answer: I guess you mean "the largest dimension of a subspace of $W_0^{1,p}(\Omega)$ such that $I''(u)$ is negative"? Otherwise, the largest dimension equals infinity, due to the spectral theory of the linearized $p$-Laplacian, see, e.g., Theorem 1.1 in [Castorina, Esposito, Sciunzi; 2011].
Moreover, the choice of $W_0^{1,p}(\Omega)$ doesn't seem to be optimal for $p \neq 2$, see again [Castorina, Esposito, Sciunzi; 2011].
Finally, in general, the Morse index depends on $u$. E.g., if $u$ is a local minimizer of $I$ (i.e., in the case $p-1<q<p$), then the Morse index equals $0$.
On the other hand, if $p=2$, $q>p$, and $\Omega$ is a ball, then the Morse index of the positive radial solution is $1$.


Why in Joomla 3.0.1 installation sql script ENGINE=InnoDB is used?

Question: Can someone please explain why in Joomla! 3.0.1 installation sql script for MySQL is used ENGINE=InnoDB !?! Is there a particular reason !??!?
Answer: The 2 major types of table storage engines for MySQL databases are InnoDB and MyISAM. To summarize the differences of features and performance,

InnoDB is newer while MyISAM is older.
InnoDB is more complex while MyISAM is simpler.
InnoDB is more strict in data integrity while MyISAM is loose.
InnoDB implements row-level lock for inserting and updating while
MyISAM implements table-level lock.
InnoDB has transactions while MyISAM does not.
InnoDB has foreign keys and relationship contraints while MyISAM
does not.
InnoDB has better crash recovery while MyISAM is poor at recovering
data integrity at system crashes.
MyISAM has full-text search index while InnoDB has not.
In light of these differences, InnoDB and MyISAM have their unique
advantages and disadvantages against each other. They each are more
suitable in some scenarios than the other.

Advantages of InnoDB
InnoDB should be used where data integrity comes a priority because it inherently takes care of them by the help of relationship constraints and transactions.
Faster in write-intensive (inserts, updates) tables because it utilizes row-level locking and only hold up changes to the same row that's being inserted or updated.
Disadvantages of InnoDB
Because InnoDB has to take care of the different relationships between tables, database administrator and scheme creators have to take more time in designing the data models which are more complex than those of MyISAM.
Consumes more system resources such as RAM. As a matter of fact, it is recommended by many that InnoDB engine be turned off if there's no substantial need for it after installation of MySQL.
No full-text indexing.
Advantages of MyISAM
Simpler to design and create, thus better for beginners. No worries about the foreign relationships between tables.
Faster than InnoDB on the whole as a result of the simpler structure thus much less costs of server resources.
Full-text indexing.
Especially good for read-intensive (select) tables.
Disadvantages of MyISAM
No data integrity (e.g. relationship constraints) check, which then comes a responsibility and overhead of the database administrators and application developers.
Doesn't support transactions which is essential in critical data applications such as that of banking.
Slower than InnoDB for tables that are frequently being inserted to or updated, because the entire table is locked for any insert or update.
The comparison is pretty straightforward.
InnoDB is more suitable for data critical situations that require frequent inserts and updates.
MyISAM, on the other hand, performs better with applications that don't quite depend on the data integrity and mostly just select and display the data.
Read more
Comment: Thank you for the analysis! Still, I don't understand why it had to be by default InnoDB?
Answer: Considering the fact that they aren't using any foreign key constraints it's actually a really good question.
Since they are not using foreign constraints themselves there are a couple of reasons that come to my mind why they might use InnoDB over MyISAM which are:

They have some future plans to stricten data integrity at some point in time.
They want to allow people who write extensions for Joomla to refer to existing data and make hard constraints if that's what the creator desires. I.E.: Let's imagine a component that stores notes for users in Joomla system. An author could then create a table like so:
<code>CREATE TABLE IF NOT EXISTS `#__notes` (
  `id`    INT(11) UNSIGNED NOT NULL AUTO_INCREMENT,
  `note`  VARCHAR(255)     NOT NULL,
  `owner` INT(11)          NOT NULL,
  PRIMARY KEY (`id`),
  INDEX (`owner`),
  CONSTRAINT FOREIGN KEY (`owner`) REFERENCES `#__users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
</code>
then the author could be sure that an owner for the notes actually exists and he won't have any garbage leftover in case a user is removed from the system as all the notes that belongs to a certain user would be removed as well due to set CASCADE on delete action which is very convenient if you don't want to maintain clean database manually which would not be possible if databases you would want to refer to would use different engine, namely MyISAM.


Which Qt DLL's should I copy to make my program stand-alone?

Question: I'm trying to make a distribution directory with my application. I've copied several Qt DLLs to that directory, and the program seems to be working, with one exception: it doesn't seem to find SQL plugin for SQLite. Copying qtsqlite.dll to the directory, doesn't allow my application to open or create SQLite files. What must be the direcotry structure or which additional files need to be copied so that the program can read the database?
Answer: you can use depends.exe to see exactly what the dependencies of your exe are and make sure they're all included.
Also, read this page about qt plugins. they are supposed to be in a specific directory called "plugins" and not in the main directory with all the other dlls.
Comment: By default the application will use its start-up directory as the plugins directory; you need to put the drivers in a base class directory name:  e.g., app_dir/sqldrivers.
Answer: Most probably, the qtsqlite.dll itself depends on original SQLite DLL's which you probably need to copy as well.
Don't forget to include an LGP license copy in your distribution as well as pointers to the original download ressources of the libs you include and their sources. To stay with the law :-)
Answer: Thanks to the link @shoosh provided, I was able to fix the problem. I needed to create sqldrivers subdirectory in the distribution dir with qsqlite.dll library inside. But that was just step one. Do you have any tips and resources on creating a full-blown Windows installer? I'm mainly a Linux programmer so this area is unknown to me.
Comment: Perhaps NSIS is a good starting point for you: http://nsis.sourceforge.net/
It is open source and scriptable. Good for Linux programmers :-D


Is it possible with Import Activity to clear data extension if salesforce report is empty?

Question: Hi I have created an automation to import data from saleforce report to overwrite data in a data extension. This is working fine when salesforce report is not empty, however, if the report is empty it should clear data in data extension. I use Overwrite as update type in my import activity. Please help how can I achieve this. TIA.
Comment: I am not 100% certain, but I think, Salesforce can enable this feature for you :)
Answer: This indeed is something which is not enabled by default. You will need to ask Salesforce Support to allow allow blank file processing - a setting which is managed by a business rule in the backend of Marketing Cloud.


Who did Jesus preach to in 1 Peter 3:19?

Question: 1 Peter 3:19 says that Jesus preached unto spirits in prison; are these spirits associated with the angels of 2 Peter 2:4 and Jude 1:6? If not who were the spirits that He preached to?
Comment: You may want to check out the related question, "[Does Peter suggest Jesus "descended into hell"?](http://hermeneutics.stackexchange.com/q/413/2215)".
Comment: Mark, I don't see where you accepted the answer by @MarkEdward which I find to be extremely cogent (and the answer I would have given if he had not first). Did you not consider it to be the answer? If not, can you indicate why not? And if so, please mark it as the answer.
Answer: The Passage in Question

1 Peter 3.18-20, NRSV
For Christ also suffered for sins once for all, the righteous for the unrighteous, in order to bring you to God. He was put to death in the flesh, but made alive in the spirit, in which also he went and made a proclamation to the spirits in prison, who in former times did not obey, when God waited patiently in the days of Noah, during the building of the ark, in which a few, that is, eight people, were saved through water.

Overlap Between 1 Peter, Jude, and 2 Peter
I've highlighted a set of key elements of 1 Peter 3.19–20 from the NA28 Greek text:

ἐν ᾧ καὶ τοῖς ἐν φυλακῇ πνεύμασιν πορευθεὶς ἐκήρυξεν ἀπειθήσασίν ποτε, ὅτε ἀπεξεδέχετο ἡ τοῦ θεοῦ μακροθυμία ἐν ἡμέραις Νῶε κατασκευαζομένης κιβωτοῦ εἰς ἣν ὀλίγοι, τοῦτ' ἔστιν ὀκτὼ ψυχαί, διεσώθησαν δι' ὕδατος

1 Peter 3.19–20
What we have here are:

Spirits (πνεύμασιν)
Who disobeyed (ἀπειθήσασίν)
In prison (ἐν φυλακῇ)
During the days of Noah (ἐν ἡμέραις Νῶε)

Jude 6
As noted in the original question, this is remarkably similar to a passage from Jude:

Angels (ἀγγέλους)
Did not keep their first [dwelling], but abandoned their own home (τε τοὺς μὴ τηρήσαντας τὴν ἑαυτῶν ἀρχὴν ἀλλ' ἀπολιπόντας τὸ ἴδιον οἰκητήριον)
Are kept in eternal chains under darkness (δεσμοῖς ἀϊδίοις ὑπὸ ζόφον τετήρηκεν)

2 Peter 2.4–10
Critical scholars are in general agreement that the author of 1 Peter was not the same author of 2 Peter, but that the author of 2 Peter had a copy of 1 Peter (referenced in 2 Peter 3.1). Second Peter also shows extensive dependence on Jude (cf. this related answer), and appears to combine the ideas present in 1 Peter and Jude:

Angels (ἀγγέλων)
Who sinned (ἁμαρτησάντων)
Delivered to chains of gloomy darkness in Tartarus (σειραῖς ζόφου ταρταρώσας παρέδωκεν)
Related to 'the ancient world' of 'Noah' (ἀρχαίου κόσμου … Νῶε)

1 Enoch 1–36: The Book of the Watchers
First Enoch, along with a few other texts from the Second Temple period, interpreted the 'sons of God' from Genesis 6.1–4 as angels, and expanded on the account. This large crowd of angels, called 'the watchers', conspired to leave heaven in order to marry human women on the earth:

1 Enoch 6.1–2
And it came to pass when the sons of men had multiplied in those days, beautiful and comely daughters were born to them. And the watchers, the sons of heaven, saw them and desired them. And they said to one another, "Come, let us choose wives for ourselves from the daughters of men of earth, and let us beget children for ourselves."

The narrative describes how the watchers taught humans forbidden things, and the children the of the watchers were giants. The four archangels in heaven raise a complaint to God about the violence the watcher's offspring have brought on the earth. In response, God sends the archangel Sariel to inform Noah that he must build an ark, Raphael is sent to imprison Azazel the leader of the watchers, Gabriel is sent to destroy the watchers' giant offspring, and Michael is sent to pronounce judgment over the other watchers. (1 Enoch 9–11)
Then Enoch is enlisted by God:

1 Enoch 12.4, 13.1
"Enoch, righteous scribe, go and declare to the watchers of heaven who forsook the high heaven, the sanctuary of their eternal station, and have defiled themselves with women. … And, Enoch, go and say to Azazel, 'You will have no peace. A severe sentence has gone forth against you, to bind you. …'"

In other words, Enoch proclaims to imprisoned spirits shortly before the days of Noah.

Who Proclaims in 1 Peter 3.19–20?
The text in question, 1 Peter 3.19–20, doesn't actually identify 'Jesus' as the one preaching. Instead, Jesus, the subject of the previous verse, is inferred by readers because of the phrase ἐν ᾧ καὶ τοῖς ('in which also he'):

ἐν ᾧ καὶ τοῖς ἐν φυλακῇ πνεύμασιν πορευθεὶς ἐκήρυξεν ἀπειθήσασίν ποτε, ὅτε ἀπεξεδέχετο ἡ τοῦ θεοῦ μακροθυμία ἐν ἡμέραις Νῶε κατασκευαζομένης κιβωτοῦ εἰς ἣν ὀλίγοι, τοῦτ' ἔστιν ὀκτὼ ψυχαί, διεσώθησαν δι' ὕδατος

It has been suggested that the opening of verse 19 originally referred to Enoch. This conjecture takes two forms, either emending ἐν ᾧ καὶ as Ἐνώχ καὶ by suggesting the restoration of a single χ, which was misheard or misread with the following κ in καὶ, or as ἐν ᾧ καὶ Ἐνώχ by suggesting Enoch's name was dropped entirely.
A.T. Robertson (Word Pictures of the New Testament) comments on the verse, summarizing the speculation as follows:

In which also (εν ωι και). That is, in spirit (relative referring to πνευματι). But, a number of modern scholars have followed Griesbach's conjecture that the original text was either Νωε και (Noah also), or Ενωχ και (Enoch also), or εν ωι και Ενωχ (in which Enoch also) which an early scribe misunderstood or omitted Ενωχ και in copying (ομοιοτελευτον). It is allowed in Stier and Theile's Polyglott. It is advocated by J. Cramer in 1891, by J. Rendel Harris in The Expositor (1901), and Sidelights on N.T. Research (p. 208), by Nestle in 1902, by Moffatt's New Translation of the New Testament. Windisch rejects it as inconsistent with the context. There is no manuscript for the conjecture, though it would relieve the difficulty greatly.

The passage in 1 Peter 3 definitely seems to be referring back to the familiar story about the watchers, the flood, and Enoch. If such conjecture is correct, the passage would be something like this:

For Christ also suffered for sins once for all, the righteous for the unrighteous, in order to bring you to God. He was put to death in the flesh, but made alive in the spirit, in which also Enoch went and made a proclamation to the spirits in prison, who in former times did not obey, when God waited patiently in the days of Noah, during the building of the ark, in which a few, that is, eight people, were saved through water.

In other words, Enoch proclaims to imprisoned spirits shortly before the days of Noah.
However, for as desirable an emendation like this may have, there is no textual evidence for it. For this reason, most scholars have rejected it. Dalton (Christ's Proclamation to the Spirits, p. 144) heavily criticizes the theory:

For a period this conjecture was in favour among a number of scholars. However it has now been abandoned, and with good reason. A pure conjecture, with no support at all in the manuscript tradition, could only be justified if the text were really incomprehensible. The text of 1 Pet 3:19-20 is indeed difficult, but not incomprehensible. In addition, such a conjecture should make the text intelligible. But the conjecture fails to do this. If Enoch is the person who makes the proclamation to the spirits, then the transition from 3:18 to 3:19 is abrupt in the extreme. In any case, it is hard to see how this ancient story about Enoch bears on the situation of the persecuted Christians.

Manuscript evidence notwithstanding, I think Dalton may be overstating his position. First Peter 3.19-20 displays too much overlap with the 1 Enoch-version of angels being imprisoned shortly before the time of the flood. That this version of the story makes explicit appearances in the related letters of Jude and 2 Peter seems to corroborate that the hypothesis has some merit.

tl;dr:
Angels who were imprisoned for their sins (the 'sons of God' from Genesis 6.1-4) are the ones being proclaimed to.
Possibly, Enoch, not Jesus, is the one doing the proclaiming, based on intertextual dependence and conjecture.
Comment: You could also mention that "angels" (ἄγγελοι) are equated to "spirits" (πνεύματα) in Psa. 104:4 (cp. Heb. 1:7).
Comment: I disagree with the Enoch points in the above answer. Especially when 1 Peter is speaking of Christ in this whole chapter and Enoch is not mentioned AT ALL in the book, let alone the chapter. The focus is on Christ, and it is incorrect to imply that the scripture here is talking about anyone else.
Comment: I agree that this passage is not referring to Enoch, neither are the spirits here referring to angels, for one seemingly obvious reason: the book of Enoch days the angels descended and sinned during the days of Jared, not Noah. The spirits were disobedient while the ark was being prepared. If you do the timeline math, the days of Jared comd way before the building of the ark! Thus disqualifying the angels referenced in 2 Peter from being the spirits referenced in 1 Peter. The spirits in prison are human beings who were disobedient while the ark was being prepared.
Answer: The question as I understand it is,"Are pneuma the same as aggelos"?
To answer that question, one must understand the triparte being that man is:(1 Thess. 5:23)

And the very God of peace sanctify you wholly; and I pray God your
  whole spirit and soul and body be preserved blameless unto the coming
  of our Lord Jesus Christ.

We 'live' in a body-our earthly tabernacle, we manifest our life through our soul, our 'pneuma' is the life of God(Gen. 2:7):
"And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul."
Therefore, men are living "spirits"(pneuma), who express their life through their souls, and are housed in a physical body until they die.
An "aggelos" is not an heir of salvation:(Heb. 1:14)
"Are they not all ministering spirits, sent forth to minister for them who shall be heirs of salvation?"
They 'dwell' in God's Presense continually-therefore, they are not needing 'salvation', they are ministers of salvation to those who believe.
'But what about those who rebelled, isn't that what this text(1 Pet. 3:19) refering to?
Matt. 25:41 says,
"Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels."
Hell(everlasting fire) was prepared for Satan(the devil) and his angels-their judgement was immediate, there was no "waiting" for a Great White Throne Judgement. It's the souls w/the 'pneuma' of God who await their destiny at the Great White Throne Judgement.(Matt. 25:31)
Comment: I haven't downvoted, but this answer relies on these different texts (1 Peter, 1 Thessalonians, Genesis, Hebrews, Matthew) using the same definitions for the relevant words. That falls under a  systematic approach that needs to be shown, not assumed.
Comment: @MarkEdward-I'm not contesting your linguistic analysis but the evidence lies within the context of how the words are used. One cannot reconcile Heb. 1:14 and maintain that "spirits in prison" are in fact "angels" who according to Jude 1:6,"And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day."
Answer: In addition to 3:19, we also have 4:6:

For this is why the gospel was preached even to the dead, that though judged in the flesh like men, they might live in the spirit like God.1

The preacher is Jesus and those being preached to are those from Old Testament times who had been consigned to Sheol (Gr. Hades).  I lay out my support for this below.
πνεύματα and ἄγγελοι
The spirits (πνεύματα) being preached to in 1 Peter 3:19 are not the same beings you refer to in 2 Peter 2:4 and Jude 1:6.  The latter are fallen angels (ἄγγελοι) - in other words, demons. (See the end of this answer to What's the difference between demons and devils?)
The Enoch Conjecture
I don't think that interpreting ἐν ᾧ καὶ as a typo derived from Ἐνώχ καὶ is very credible.  Metzger argues against this in his Textual Commentary on the New Testament:

Several scholars have advocated the conjectural emendation that introduces the subject "Enoch" (ενωκαιενωχ). Instead of improving the intelligibility of the passage (as a conjectured reading ought to do), the word Ἐνώχ breaks the continuity of the argument by introducing an abrupt and unexpected change of subject from that of ver. 18.2

The facts that (1) not a single of the available hundreds of Greek manuscripts has any "Enoch" variant and that (2) no commentator in antiquity seems to have ever commented on the passage in this context weigh heavily against the conjecture. (I am happy to be corrected on either point).  It also would beg the question why Enoch in particular should suddenly appear out of context to preach the Gospel (1 Peter 4:6).
Related Scriptures
In all of the surviving ancient commentaries, Jesus was universally understood to be the one preaching.  The spirits that the passage speaks of were those souls captive in Hades (Hebrew Sheol).  The Gospel texts that allude to Christ's descent into Hades include:

Matthew 12:40

For as Jonah was three days and three nights in the belly of the whale, so will the Son of man be three days and three nights in the heart of the earth.3

also foreshadowed in the Old Testament:

Job 38:17 LXX

And do the gates of death open to thee for fear; and did the porters of hell quake when they saw thee?

Hosea 13:14

Shall I ransom them from the power of Sheol? Shall I redeem them from Death? O Death, where are your plagues? O Sheol, where is your destruction?

Other New Testament Scriptures relate to Christ's descent and His victory over death:

Ephesians 4:12

In saying, "He ascended," what does it mean but that he had also descended into the lower parts of the earth?

1 Corinthians 15:54-57

When the perishable puts on the imperishable, and the mortal puts on immortality, then shall come to pass the saying that is written: "Death is swallowed up in victory." "O death, where is thy victory? O death, where is thy sting?" The sting of death is sin, and the power of sin is the law. But thanks be to God, who gives us the victory through our Lord Jesus Christ.

Colossians 2:14-15

... having canceled the bond which stood against us with its legal demands; this he set aside, nailing it to the cross. He disarmed the principalities and powers and made a public example of them, triumphing over them in him.

Patristic Understanding
In the patristic interpretation, those spirits in Hades were those of the Old Testament times who had died.  Irenaeus (130-202), having recounted the sins of such figures as David and Solomon, explains:

It was for this reason, too, that the Lord descended into the regions beneath the earth, preaching His advent there also, and [declaring] the remission of sins received by those who believe in Him. Now all those believed in Him who had hope towards Him, that is, those who proclaimed His advent, and submitted to His dispensations, the righteous men, the prophets, and the patriarchs, to whom He remitted sins in the same way as He did to us, which sins we should not lay to their charge, if we would not despise the grace of God. For as these men did not impute unto us (the Gentiles) our transgressions, which we wrought before Christ was manifested among us, so also it is not right that we should lay blame upon those who sinned before Christ's coming. For all men come short of the glory of God,4 and are not justified of themselves, but by the advent of the Lord5

Hippolytus (175-235) also wrote of Christ's descent into Hades:

For this reason the warders of Hades trembled when they saw Him, and the gates of brass and the bolts of iron were broken.  For, lo, the Only-begotten entered, a soul among souls, God the word with a human soul.  For his body lay in the tomb, not emptied of divinity; but as, while in Hades, he was in essential being with his Father, so was he also in the body and in Hades.  For the Son, just as the Father, is not contained in space and he comprehends all things in himself.  But of his own will he dwelt in a body animated by a soul in order that with his soul he might enter Hades, and not with his pure divinity.6

Addressing 1 Peter 3:16 directly, Hippolytus writes:

He showed all power given by the Father to the Son,7 who is ordained Lord of things in heaven, and things on earth, and things under the earth, and Judge of all:8 of things in heaven, because He was born, the Word of God, before all (ages); and of things on earth, because He became man in the midst of men, to re-create our Adam through Himself; and of things under the earth, because He was also reckoned among the dead, preaching the Gospel to the souls of the saints, (and) by death overcoming death.

The overall patristic understanding of 1 Peter 3:19 has been summed up:

In addition to the broad significance of the salvation of the world here indicated, the death of Christ and His subsequent descent into hades (I Peter 3: 19– 20, 4: 6; Eph. 4: 8– 10) signify in a narrower sense the deliverance from hades of the souls of the reposed first ancestors, prophets, and righteous ones of the pre-Christian world; and thus they express the special significance of the Cross of the Lord for the Old Testament world, a significance which comes from the death of Christ accomplished upon it: for the redemption of the transgressions that were under the first testament (Heb. 9: 15)9
The deliverance from hades testifies also to the lifting of the curses which were placed in the Old Testament: (a) the curses in the third chapter of the book of Genesis, which were joined to the deprivation of life in Paradise of Adam and Eve and their descendants; 19 and then (b) the curses placed by Moses, in the book of Deuteronomy (chap. 28), for the stubborn non-fulfillment of the laws given through him.10

(Much of the material included in this answer is based on Hilarion Alfayev's Christ the Conqueror of Hell: the Descent into Hades from an Orthodox Perspective, especially Chapters 1 and 2.)

1. RSV
2. See also Metzger, Journal of Religion, xxxii (1952), pp. 256 f.; Metzger, The Text of the New Testament, p. 185, n. 1; Dalton, Christ's Proclamation to the Spirits; a Study of 1 Peter 3:18–4:6 (Rome, 1965), pp. 135 ff.
3. New Testament and Masoretic Text translations taken from RSV.  Septuagint translations taken from Brenton.
4. Romans 3:23
5. Against Heresies, IV.XXVII.2
6. Fragment III cited by Nicetas the Deacon; in Hyppolitus Werke (Leipzig, 1897), p.268
7. Matthew 28:18
8. Philippians 2:10
9. Therefore he is the mediator of a new covenant, so that those who are called may receive the promised eternal inheritance, since a death has occurred which redeems them from the transgressions under the first covenant.10. M. Pomazanski, Orthodox Dogmatic Theology (3rd ed.),
pp.205,206
Comment: Yes, the linguistics and patristics carry this answer.
Comment: The problem is not the atonement or rescue of the saints but he says the atonement of the disobedient who died rejecting Noah.
Answer: Who were the spirits that He preached to?
There are several interpretations of 1 Perter 3:19. I won't go into detail on each view but let me list them here and then I will explain which one I hold.

St. Augustine held the view that the spirits are unbelieving contemporaries of Noah, to who the spirit of Christ in Noah, preached, or to whom the pre-incarnate Christ himself actually    preached.
Christian Reformation and Enlightenment(Thomas Belsham) beliefs held    the view that the "spirits in prison" were simply Gentiles in the    "prison of ignorance (darkness)" to whom Christ is preached by the    Apostles.
When Christ died, he went and preached to people in hell:
sub-view 1: offering them a second chance of salvation.
sub-view 2:    proclaiming to them that he had triumphed over them and their    condemnation was final.
sub-view 3 (fallen Angels - not people):    proclaimed triumph over the fallen angels (the Nephilim, i.e. Giants    in the days of Noah) who had sinned marrying human women in the days    before the flood.
sub-view 4: proclaimed release to the people who    had repented before they died in the flood, and took them from    purgatory into heaven.

It is my stance that the verse is most clearly interpreted by cross-referencing Isaiah, looking at the context in which Peter wrote (i.e. specifically to whom did he write this to) and trying not to tie in the interpretations of (2 Peter 2:4, and Jude 1:6) which uphold sub-view 3 most strongly.
The key to me is the preceding verse in 1 Peter 3:18 (emphasis mine):
For Christ also hath once suffered for sins, the just for the unjust, that he might bring us to God, being put to death in the flesh, but quickened by the Spirit:
The use of the word us in "that he might bring us to God" signifies the object, the human object, not fallen-angels of the next statement. Peter, a Jew, was still living in a world view held by the Jewish communities that God was for the Jews and no one else. It was still hard for the Jewish mind to let go of their selfish exclusivity on God and even the Gospel not to mention the Laws they lived by. He was reaching out to both Jewish and Gentile "elect" as we see in the first of his letter to whom it was addressed "…to the strangers scattered throughout Pontus, Galatia, Cappadocia, Asia, and Bithynia…"
This letter encourages the Elect in the audience — the mainly "gentile" audience — of these areas of the world. The gospel is preached to these folk who were by Jewish eyes those people who were "unclean" and sat in "outer darkness" of the ignorance of the true God.
Finally, let's look at Isaiah who many years before prophesied of this exact occurrence in which Peter and others were bringing about through the preaching of the Gospel to the Gentile world.
Isaiah 42:6-7
I the LORD have called thee in righteousness, and will hold thine hand, and will keep thee, and give thee for a covenant of the people, for a light of the Gentiles;
To open the blind eyes, to bring out the prisoners from the prison, [and] them that sit in darkness out of the prison house.
This is the best example of God's grace being shed upon the unbelieving world at large which sat in ignorance obeying their lusts which imprisoned them. This gospel should bring together all people regardless of ethnicity and at that time of Peter's writing it was still a radical idea to think that Gentiles were worthy of hearing or could even hear the good news.
I hope this helps you and you can consider this view and hopefully it makes sense. Blessings.
Comment: Welcome to Biblical Hermeneutics Stack Exchange! Be sure to take our [site tour](http://hermeneutics.stackexchange.com/tour) to learn more about us. [We're a little different from other sites.](http://meta.hermeneutics.stackexchange.com/a/803/423)
Comment: Augustine's view makes most sense to me. Just as Christ preaches to men today by His pastors and teachers as they proclaim the Gospel,  so He did in Noah's day through Noah.


Motivation for using moment about mean versus moment about the origin

Question: When calculating moments of probability distributions, what would motivate you to take the moment about the mean (called "central moment") versus the standard moment about the origin?
Comment: Related: https://stats.stackexchange.com/questions/132914/what-exactly-are-moments-how-are-they-derived/132968#132968 and https://stats.stackexchange.com/questions/17595/whats-so-moment-about-moments-of-a-probability-distribution
Comment: Related question with interesting comments: https://stats.stackexchange.com/questions/448209/what-does-the-second-moment-tell-us-that-variance-does-not
Answer: These uncentered moments are sometimes called "raw" or "crude" moments:  https://mathworld.wolfram.com/RawMoment.html
One practical difference between centered moments and uncentered (raw) ones is their estimation from data. For example, estimating $E[X^2]$ is trivially done in an unbiased manner via: $\frac{1}{n} \sum_i^n x_i^2$.
However estimating the 2nd centered moment, ie. $\text{Variance}[X]$, involves first estimating the expectation to do the centering. To estimate the variance in an unbiased manner, one has to account for the fact that the expectation was also estimated from data, leading to a subtle difference in the denominator term: why sample variance has has n-1 in the denominator?
The raw moments are intimately related to the Characteristic function and Moment-generating function of the distribution:
https://en.wikipedia.org/wiki/Characteristic_function_(probability_theory)#Moments
Characteristic functions are very useful for studying theoretical properties of distributions, cf:
What is the purpose of characteristic functions?
Similar representations of distributions like characteristic functions have many practical uses in Machine learning: https://en.wikipedia.org/wiki/Kernel_embedding_of_distributions
Regarding centered or raw moments, it is not the case that one should inherently prefer one over the other, it all depends on what you want to use them for. The centered moments have more common uses than the raw moments. For instance, the second centered moment is the variance, which used to quantify the spread of a distribution. The third centered moment (technically a normalized version thereof) is the skewness, which is commonly used to quantify the lopsidedness of a distribution (how asymmetric it is). The fourth centered moment is the kurtosis, which is commonly used to quantify how heavy-tailed a distribution is.
Centered  moments are useful to measure properties of distributions in a location-invariant manner. Random variable $X$ and $X + c$ (for any constant $c$) have the same centered moments. Also the $k$-th centered moment of $c \cdot X$ is equal to $c^k$ times the $k$-th centered moment of $X$. Finally for independent random variables $X$ and $Y$, the $k$th moment of $X+Y$ is equal to the $k$th moment of $X$ + the $k$th moment of $Y$ -- but only for $k = 1, 2, or 3$ (not higher moments).
Comment: @psyguy yes thank you, let's get some more answers
Comment: (Welcome to CV!) Thanks for your reply, you provide a good overview of how the raw and centered moments differ. If I'm understanding correctly, you suggest the raw moments are to be preferred over centered moments, though I think the OP had asked why/when the latter are (or should be) preferred over the former.
Comment: updated my answer to reflect the advantages of centered moments over raw moments. I originally thought the question was to list some advantages of raw moments, since centered moments are encountered much more commonly.


How do I set a different default place when I click on 'files' in the sidebar?

Question: This is another question all about the usability of unity, which is proving to be not as easy to customise as I'd like. Using Ubuntu 14.04, When I click on the files icon, it immediately takes me to $HOME. However, I would like to set it it to, for example, $HOME/Desktop/folder. This would make my navigation much better.
Comment: "which is proving to be not as easy to customise as I'd like" It is a work in progress ;-)  What is "files"? I do not have that in Nautilus left pane. (I assume that's why it is tagged nautilus?)
Comment: 'files' is the application you launch from the sidebar (they've stopped calling it Nautilus as far as I'm aware. Hover over the icon and you'll see that's the name that comes up in 14.04). So I was wondering whether, when launched from the sidebar, you can get it to default to a particular place
Answer: You can make your own launcher.
1) On a terminal: gedit ~/.local/share/applications/mylauncher.desktop
Then paste this into the file:
#!/usr/bin
[Desktop Entry]
Version=1.0
Terminal=false
Type=Application
Name=Nautilus Desktop
Exec=nautilus Desktop
Icon=nautilus

2) Mark as executable:  chmod +x ~/.local/share/applications/mylauncher.desktop
3) Logout and log backin.
4) Open the dash (press Super) and search nautilus. When you find it, drag it to the launcher.
Enjoy.
Answer: To change the default directory of the Files icon:

Copy the default nautilus.desktop file to your local directory:
cp /usr/share/applications/nautilus.desktop ~/.local/share/applications/nautilus.desktop

Open the file with gedit (open gedit, go to ~/.local/share/applications, drop the file on to the gedit window)

Edit the (first!) Exec= line of the file to open the alternative directory to Exec=nautilus /path/to/your/directory. However, I would prefer not to do that:
It would be better to add a directory to the nautilus ("Files") icon permanently,  accesible by right-clicking the icon:

Copy the default nautilus.desktop file and open it with gedit like above,
Paste the following at the end of the file:
[Desktop Action Desktop]
Name=Desktop
Exec=nautilus /home/yourname/Desktop
OnlyShowIn=Unity;

Then look for the line starting with Actions=, add the name of your new mention (in this case Desktop) + ;, so the complete line should look something like Actions=Window;Desktop;
After logout / login it works.
Alternatively, you can use a quicklist editor to add or remove items to the launcher items.
Another tip Last but not least: whenever you are in a directory (in nautilus) and you add the directory as a bookmark, it will appear in the "Files" icon as well when you right-click on it.
I would not create another .desktop file (launcher) calling nautilus. Creating multiple .desktop files, calling the same application in their "native" command causes inconsistency in the way the application appears in the launcher.


Are a lot of highly logical people (such as mathematicians) prone to depression?

Question: In my mathematics and physics classes, half the students are seeing, or have seen, psychologists because of depression. Based on my experience, I feel that there is a huge correlation between logical people doing mathematics, physics, informatics, programming, making computer games and depression. Is this just a personal opinion or is it more widespread? Does anybody have an explanation for this?
Comment: do you have any evidence of this or is it entirely anecdotal?
Comment: hum, this is a constatation that I made by seeing and comparing student in my school and in other school,  and people in general
Comment: Because this question is based off your personal experience it is considered off-topic. However, if you were to change it to generally asking if those with more logic-based employment are depressed, it would be a reasonable question.
Comment: Only it it were shown that "more logic-based employees" actually are depressed.
Comment: @n0tis:

    "Our work shows that the price of higher intelligence and more complex behaviours is more mental illness."
 http://cogsci.stackexchange.com/questions/5333/is-the-price-of-higher-intelligence-and-more-complex-behaviours-more-mental-illn
Answer: Overall, based on my limited research it appears there is no evidence that people who are more logical are more likely to experience depression. There is a theory that people who see the world more accurately (of which rationality would be a component) are more likely to become depressed. It is called depressive realism {1}. However, the theory doesn't seem to be well researched or supported.
Rather that high levels of logical thinking supporting depression it may well be that factors that predict logical thinking also predict depression. One of these is introversion which, based on some research {e.g., 2}, may be correlated with intelligence (which is related to logical thought) and appears to be correlated with depression {3}.
Also, and this is just my opinion, I think that it is possible that the relationship that between maths, physics and programming students and depression might actually be explained by link between introversion and depression as all of these types of careers are probably more commonly associated with introverts.
References
{1} Ackermann, R. and R. J. DeRubeis (1991). "Is depressive realism real?" Clinical psychology review 11(5): 565-584.
{2} Furnham, A., et al. (1998). "Personality and intelligence." Personality and Individual Differences 24(2): 187-192.
{3} Janowsky, D. S., et al. (2002). "Myers Briggs Type indicator personality profiles in unipolar depressed patients." The World Journal of Biological Psychiatry 3(4): 207-215.


How to disable pen mode change on slow motion?

Question: If I try to draw something carefully in OneNote, my pen stops drawing.
I.e. when I start to draw and move pen slowly, some guesture triggers, round circle appears and the line I drew turns to selection border and pen starts to continue selecting process. I.e. my work is dropped as Microsoft likes to do.

How to overcome?
How to disable this specific reaction?
I have all checks on in OneNote setup

Disabling last option does not help.
My press and hold options are set to longest

My pen is Wacom Bamboo Pen CTL-470
My OneNote is 2010.
Answer: Unchecking "enable press and hold for right-clicking" in the Press and Hold Settings worked for me.
Running windows 7 pro, OneNote 2013, Wacom Bamboo Capture tablet.


Broken 12V connector on USB cable

Question: Did not see it but someone must have had this problem.  My 12v (cig) connector is BROKEN.  The center terminal came out and is LOST. I want to replace it with another connector (or do I?). .  but unsure of the wiring from the output of the cig connector to the USB cable until I cut it.  I want to be sure I get the 5volts to the correct USB line and dont get it to the other signal lines in the USB line.
Comment: You have a hot, exposed 12VDC line that was fused high enough to power a cig lighter lost somewhere behind the dash and **that isn't your most immediate problem**?
Comment: I hate the cigarette lighter as a power adapter, it just needs to die.
Comment: @GaryBak it is a simple device, common and convenient. There are other plug&socket systems that are relevant, but getting agreement by every manufacturer and all the device manufacturers may be challenging.
Comment: As far as I can tell, the OP talks about the adapter tip and not about the socked in the dashboard being broken.
Answer: The centre tip of the cigar lighter is positive, so would be connected to the red wire.
But, and it is a big but, cheap cables may not have red / black as pos & neg...
So, be sure and check with a multimeter what goes where.
From what I have seen the outer cables are power, inner pair data...
Answer: I believe you are referring to the power outlet of your car. If so then you can get to buy the power outlet socket. It is easy to fix with just one connector.
Answer: If you have a multimeter you would be able to check the polarity of the cigarette lighter before reconnecting USB devices.

Broken 12V connector on USB cable