What should I do when I am stuck on names during freewriting?

Question: If I get hung up choosing a name for a character, should I come back to it later? Or should I try to figure one out? I feel like sometimes I have some momentum going forward and taking too much time to select a name stops said momentum.
Comment: Not really an answer to your question, but the [Everchanging Book of Names](http://ebon.pyorre.net/) has been a very useful, easy-to-use resource for me.
Comment: [I'll just leave this here](https://i.stack.imgur.com/aoffO.jpg)
Comment: Welcome to Writing.SE *Luke*! If you have a moment please take the [tour] and visit the [help] to learn more about the site. Have fun!
Comment: I don't know if this counts as an answer, because it seems like you're looking for quick ways to generate _meaningful_ names. I've always taken inspiration from cryptography: Alice, Bob, Carol, David, Eve.
Comment: I find that unusual/uncommon names work really well (depending on your story though). Like I prefer names like Jade/Freya/Obadiah/Xavier to ones like Bob/Alice. Also, it helps to name your character around their character i.e if I have a time traveller,I would call him Decade. On top of this, I would then go on to cast him as a Christian coloured man because that's the sort of image you get from the name.
Answer: I always feel that names are a big problem for me and coming up with some meaningful names that sound pleasant is one of the hardest parts of writing for me. That's why I never stop to come up with a name.
Before starting to write I normally have a plan for the next few pages at least and I know which characters will come up and what they will basically be doing. Then I use one of their main character traits or characteristics to come up with a name by using Google Translator with different languages until something interesting comes up. You can read more about my technique in my answer to What are good resources to get fantasy names?. That way I have an interesting name that I can use and that is likely so unique that I can relatively easily replace it later if I find a better name.
"Search and Replace" of your word processing software is likely a big help in this, but you have to be careful. For example in German saying "Tims Antwort ist gut" ("Tim's answer is good") and replacing "Tim" with "Secespitus" would yield "Secespituss Antwort ist gut" - which is wrong, as it should say "Secespitus' Antwort ist gut".
Furthermore the name can be part of a bigger name, like "Tim" could be part of "Timothy" and if you only want to replace "Tim" with "Dean" you would end up with "Deanothy" - which might be an interesting name, but not your originally desired result. Especially when you have a lot of different characters you should be careful. And at the same time you should be careful that if you want "Tim" and "Timothy" to be the same person you would have to rewrite the parts where for example the longer name is used - it might be a rhetorical device, like an angry mother calling her child by its full name, and you might want to preserve this when changing the name.
You should only replace each instance individually and not all at the same time to not run into these problems.
If you are writing and suddenly you introduce a new character that you haven't thought of you shouldn't stop - just use the first thing to make a placeholder that is easy to find later. ShadowMan, MagicLady, CreepyGrandma, BigFurryMonster, NiceButCreepyBoy, ... - everything is fine as long as it's easy to find.
That way you can stay in the flow and continue with the important stuff to know how your characters act and behave - which will allow you to more easily come up with a useful name for them. You have to learn about your character first before you can give him a fitting name. And to learn about your character you have to write something that he is part of. It's completely normal to leave the naming for later, for example the first revision.
Comment: In the UK at least "Secespitus's" is fine. In Newcastle,  there is a stadium called St. James' Park and in London a tube station (and park) called St. James's Park. No one has any trouble comprehending meaning in either case.
Comment: @Strawberry It seems like I confused a few German and English rules there. Thanks for pointing it out, I updated the example.
Comment: If your composition software supports macros (LaTeX, microsoft Word) you can define one for a character's name. Then you can change the macro at will - faster and safer than search/replace, though possessives may still be a problem. So will short versions other characters use in dialog.
Comment: @Strawberry Yes, that is grammatically correct. According to the [Oxford Dictionary](https://en.oxforddictionaries.com/punctuation/apostrophe) "*With personal names that end in -s: add an apostrophe plus s when you would naturally pronounce an extra s if you said the word out loud: He joined Charles's army in 1642.*"
Comment: @Secespitus: Don't worry - it's a very common misconception amongst native English speakers anyway; I was actually taught at school that you'd write things like "Jesus' cows" (and, as pointed out by Strawberry, this form finds its way into "official" usage) even though it's not strictly correct (and, IMO, not preferable).
Comment: Be sure to add those protonyms to your _Dramatis Personae_ so that you can look for them later.
Comment: Your text editor software ought to enable you to do a search-and-replace which operates only if the string you're searching for starts at the start of a word and ends at the end of a word. Then searches for Tim won't see occurrences of Timothy (or Time).
Comment: @Strawberry Did you know that there's also a "St James Park", home of Exeter City FC, just to confuse matters?
Comment: Who are they? ;-)
Comment: @Strawberry The characters. (I am not sure what you are trying to tell me with your comment.)
Answer: I often face the same problem with finding names, not just for characters, but also for places, titles, etc. In such cases, I use a temporary name, and specific markup, to make those temporary names easy to find later. For example

{Alpha} and {Bravo} lived in {TownName} town, {X} leagues from {CapitalName}. {Alpha}'s parents...

When I find a name, this system makes it easy to find and replace, without accidentally replacing something I don't want to. And I can easily go over a document, search for { tags, to see what I still need to name.
Another thing I do is I keep around a list of names that sort of work for my setting, and for minor characters, at least, I pick one at random. I can always change it later, right? Where do I get the list? Names I come across, and like the sound of. I do research for whatever I'm writing, I run across relevant names, I write them down.
The thing you don't want to do is sit around for days, not continuing your story because you can't find a name. Like you say, it kills momentum completely.
Answer: This is a useful book, Writer's Digest Character Naming Sourcebook. Each name comes with its original translation of meaning (although some are just 'mythical mother of Jason', or a few per page 'unknown origin'.)
This is a useful website of many links to online naming resources, baby names, character naming apps, etc. Writing World Links to Naming Resources.
With or without a book or online assistance; start a note page for your names with the Alphabet listed, one letter per line. This is both to remember the names you have used, and help you come up with new ones.
A,B,C,D etc.
When you need a name, look at your existing list of names.
For "important" characters (those appearing in more than one scene), try to pick an unused starting letter, or if that is not possible, at least be sure to get a name that sounds (out loud) and looks (in print) distinct from other names starting with the same letter, whether male or female. If you have "Dean", don't use "Deana" or "Diane" or "Dana" or "Dino". But "Drake" would be fine, or "Dimitry". No pair from "Tory" and "Tony" and "Troy".
Star (*) the names of your "important" characters.
Less important for reader memory is minor characters that they only need to remember for the scene (if they have names at all). For minor characters, it is best if they have unique names, but less important if they happen to be similar to a main character name. I always avoid ANY character name starting with the same letter as my main character, which I also aim to give a fairly rare name. If I name her Alicia (I never have), no other character has a name starting with "A", even if it would sound completely different.
Comment: @DarrenRinger Just my opinion, but statistical realism is not really important to me, nothing trumps clarity for the reader. I would not do this except for comic effect: *"This is Darryl, this is my other brother Darryl."* [Bob Newhart sitcom]. I expect 99.999% of readers will never notice that, *Golly, all these characters have different names! Does Amadeus* ***really*** *expect me to buy that?* Clarity first. "This really happens" is never an excuse for putting something in a story. It is only something to be ***checked,*** e.g. if the story is realistic, char cannot run a 3 minute mile.
Comment: I like this advice for breaking out of mental ruts, but see https://en.wikipedia.org/wiki/Birthday_problem - it may help realism if you pick one or two first names and use them for more than one person.  The same is true of starting letters - one or two might be used for a plurality.
Comment: +1 for keeping a notebook with a list of names - add to it whenever you come across a name in real life, or think of some interesting name, or read one in a book, or whatever.
Answer: As a GameMaster in pen&paper roleplaying games, I have to come up with names all the time, and unlike a writer don't have the luxury of pondering over it for some minutes (or hours).
The best method I found so far is this:

For major characters draw up your cast including names beforehand. There are many reasons for this, one of them being that all their names should be easy to remember and recognize and not similar to each other (unless intentionally so).
For minor characters have a list of names nearby. There are dozens of name generators or name lists on the Internet, use any. However, randomly sort the list before printing. Then check off names as you use them, to avoid duplicates, and write a few words behind the name which character you used it for (e.g. "prison guard", or "suspicious merchant at the marketplace"). This way you get both unique names with zero effort and a list of minor characters to reference in case the players (in my case) or the story (in your case) ever comes back to them.
Answer: My suggestion is to do what you would do every time you're stuck on something: make anything up, and move on. A name, more than any other words, is often nothing but a place marker. Once you come up with a good name, you can make a search-and-substitute across the whole document with one single operation.
I generally try to come up with names based on the sound they have in the sentence, the way they change the pace and musicality of the sentence. My point being: if you don't have anything in mind, just go for the sound and pace, to make the passage sound smooth.
Another great criteria for names is their meaning: if in your world names have meanings, or etymology, go for it. References are also a smart idea: in The Name of the Rose, Eco calls his protagonist "Guglielmo da Baskerville" as a reference to Sherlock Holmes.
Finally, a software like Scrivener includes a tool to randomly generate coherent names, where you can specify the letters in it, the initials, the length, etc.
Answer: I believe there are two ways to deal with the problem you describe:
1) use a temporary name to be replaced later
If it doesn't bother you to give the character a random name, whether it's Alice or blonde girl, go with this option.
If you prefer a descriptive name (eg. blonde girl), great.
If you prefer a more normal name, I suggest creating a list of names, similar to the list for naming storms, and then just use the first name of the list and so on. Although, obviously, you may want to have two lists, for male and female names. You don't even have to spend much time on it. Just google something like 'filetype:pdf 100 popular names USA' (obviously, you may want to change the country to fit your setting) and then print out the result.
You can even have a third list for unisex names, in case you're naming a character you haven't yet decided if it will be male or female.
Of course this approach has the problem of how to replace the temp name with a definitive one in as efficiently and quickly as possible. @Secespitus answer, though, has the only solution I know of.
2) use a definitive name
This approach is more problematic, but I cannot write on if a character I've just created does not have their own name. It's one of those 'writing blocks' I have to deal with. If this is not a problem for you, ignore this approach. If you must have the right name... here is how I go about it.
Do you know the lists I advised above? I added such a list into an excel file. I have first names and surnames, and I added information about whether their female, male or unisex. I also added information about their meaning and origin/language. Then I further specified whether their modern, traditional or dated. Then I put together some formulas to choose random names.
Now, when I need to name a character, I simply choose gender, origin/language and whether it's modern/traditional/dated (or leave those categories blank) and click a button. If I need to have a character whose name is related to a specific meaning, I can  write, say, 'white', and get a relatively short list that can go from Blanche to Alvina. These categories are separate for first name and surname, so that I can choose whether the specific theme I want is present in both or in only one of the names. I can also choose to have two first names or two surnames (handy for other cultures where people have more names) and I can freeze one name I like while keeping on searching for a surname. I know, it's a rather complex name generator.
I spent a lot of time on this generator but I cut down from spending one hour or more searching for the right sounding name to five minutes (in the worst case scenario; it's usually a matter of seconds). I had to name a team of ten background characters, and they were all 'perfectly' named in less than ten minutes.
If you are less picky, you can just copy&paste a list of names, identify the gender, and add a number for each name. Then just use a RANDOM function to create a basic generator.
Answer: In addition to Dan Clarke's answer, I would suggest using names you've decided in advance, i.e. Alice, Bob, Carol, etc. This will make it easier for you to remember which names need to be replaced later.
Comment: Welcome to Writing.SE *Defiant_Kitsune*! This is an important addition and I think it's good as its own answer, but in general each answer should stand on its own. I'd suggest [edit]ing your answer to talk about the stuff Dan mentioned in your own words a bit (and removing the last sentence, which looks like this should be flagged as "comment, not an answer" and might therefore lead to your answer being deleted if enough community members think so). If you have a moment please take the [tour] and visit the [help] to learn more about the site. Have fun!
Comment: It's a good addition that I hadn't thought of. Try to expand it a bit and you're golden.
Answer: I know a good many writers spend an inordinate amount of time perfecting the names of characters. This is similar to the nine months or so that parents frequently spend selecting the name for a single child. As writers, we have entire worlds to populate so we cannot afford to do that.

I feel like sometimes I have some momentum going forward and taking too much time to select a name stops said momentum.

In my opinion, anything that reduces writing momentum is bad. There is no one strategy for moving past name selection and what works for one writer may not be good for another.
If you can skip this point and come back to it later, it may be more productive (or not).
Here are some strategies that I have known writers from my local writing circles employ.
Strategies
Placeholder
I've seen several good writers say that if you get stuck for a name or a description type a character string that never occurs naturally and move past it.
I have often typed something like:

## This guy needs a name ##

or

## Description goes here ##

If you wanted to get advanced you could use:

##[CHAR-1]##

Which would stand out as wrong in a finished manuscript but would allow for easy search and replace when you are finished.
No names, please
I have read stories where the characters are simply known by distinctive elements.

The man with the blue hat
The woman with the red hair
The old guy
The girl with the blue dress
The man with the shaggy beard
The homeless dude
etc..

This works for short stories and for characters that are just passing through but gets old really fast for significant characters.
My name is...
I've known more than one (discovery) writer that will put the character "on the stage" in a scene, maybe describe them a little, and then have another character ask their name.

"My name," said the boy, "is #The first thing that comes to your mind#"

For some writers, they feel the characters already know their names or at least what they want to be called. So they just ask them. Don't judge, it works for those writers.
Re-use friends and family
When I was very young (pre-teen), my stories would be written using the names (and middle names) of family and close friends. I often renamed them later but I found it helped to have a person I could imagine and knew well.
Prepared name list
Quite a common strategy is to maintain a list of setting appropriate first and last names. I know more than one writer that will make sure the list has only one of each for any given letter of the alphabet.
When a character needs a name they pick the next name from the list and just roll with it.
One time I write a PHP script to generate a name with a given letter. It was basically just a really big list of names (first and last) which picked one of each at random. For the benefit, the effort was not worth it. If that works for you, there are random name and even identity generators online.
Pre-filled character biographies
This one is popular with planners. I have used it more than once.
The strategy is to create a side of A4 with details about the character, their name, their background, and the journey they will go through during the story. That way when I am writing the issue never comes up.
This works for me because I can take the time to come up with names while I am not worrying about story, plot, or anything else. By the time I come to write the story, I feel I really know the characters. I've even used family tree software before to work out how they were all related to each other. But then again, I am the type of person that will write a setting bible for a big project.
Work from a book of names
I have several books of names and their meanings on my bookshelf. I have also used baby name websites for those times when I absolutely have to have the right meaning for some reason.
If you name characters on the fly one or both are invaluable.
Let your local writer's group name them
I have mixed feelings about this approach. However, it seems common for a person to ask for a name for a character that (insert short bio here). Some people seem to enjoy the discussion that follows. Your mileage may vary.
The most important thing
What matters most - more than names - is telling the story. If you have to call your characters Bob, Jane, and Fred to get to the storytelling, then that is what you should do. Names take on significance because of what we know about the person that has the name.
As you have rightly realised, don't let anything stop the writing momentum.
Answer: Keep a list of names
Early in Time Clare's writing podcast Couch to 80k he sets the reader a task of spending 10 minutes inventing names.
I loathe and detest coming up with names, and was dreading it. But I found that approaching the job as an end in itself, with no particular goal in mind, very liberating, and I easily jotted down a page full.
He then invites the listener to look over the list and see if any of them suggest a character. But he also points out that such a list is extremely useful to have around if you're writing and suddenly need the name of an incidental character.
So: write a list. Keep it around. You might find it more fun and more useful than it sounds.
Answer: Pick one that sounds interesting and easy to spell. Once you find a name you like use a basic "Search and replace" on your writing program and switch it around. It only adds a few minutes to your time, and it keeps things moving.
This method has let me change some characters names 5 or 6 times until I found one I liked.
Answer: I sometimes look up information on sporting events of the past and change the first names  and surnames e.g. Look up an FA Cup Final and use the first name of the goalkeeper from team A with the surname of the goalkeeper from team B.
Failing that, have a wander round any cemetery and pull a few names from there.
If a character was born in a particular year, which actors were around then?
Answer: An issue I occasionally encounter in my DnD games is naming NPCs... Typically I have to consider race and region, but for when I'm writing (usually short stories and aborted epics, lol) I tend to drop in the first name that comes to mind with a vowel tacked to the end, and when I proofread I make sure I'm not duplicating a name. If not, I drop the vowel, if I am, I take time to consider something else then. Saves my momentum for the actual writing.
Answer: Have a separate process for writing names:
This is only a suggestion.  But an answer to your question, nonetheless.  With a separate process, you can spend your energy on writing and focus later on the editing process.  Name creation can be seen as an editing process.
Here's an idea to help you:
Yes, you should come back to it later.  That's the first thing.  As mentioned in other answers, use a temporary name (or some kind of descriptive tag) so that your momentum isn't disrupted by trying to come up with an appropriate name.
Second, think of a simplified meaning for that character.  You can use an adjective, attribute, or even the type of person they are or what they represent (a king, a lion, a snake, etc...).  Find something that suits them based on who they are in your story.
Third, look up the meaning online.  Let's say your character is a regal type.  Maybe a name that means "king."  You'll get many names to choose from, and also the place of origin for that name.
Fourth (optional), if you really want it to sound different for whatever reason, change it a little.  Perhaps the meaning might be difficult for the reader to find out, but you're the author.  You can do whatever you want.
Again, this is just one idea, but it is one way to not get stuck when free writing.  You can look at it as a tool you can use later and not have to worry about or ruin your momentum in the meantime.
Here's a couple sites that I've found helpful:
https://www.behindthename.com
http://www.meaning-of-names.com
Answer: You could always consider adjusting the flow of your story to accommodate the unknown.
Either make it so that the person's name is not necessarily revealed just yet,

The woman with the red dress simply turned her back to me and said, with not even a turn of her head, "You'll need a better shirt first."
Maybe.  Through the din of the crowd, she could've said something else.

Or, the person gives themself a colorful or silly autonym which is later superseded by another.

"You can call me 'Al'."

In effect, you can use your indecision to your advantage and be slightly more spontaneous.  This seems like a good recommendation because you'd probably already have a name for a person if you were planning their introduction.
Answer: Most people are answering the implicit question of "How do I generate a list of names", instead of the title question.
If that's what you want, could you edit the title to fit?

I'd say, if you don't need a name immediately, give them a placeholder, like "{A}", then just keep describing their actions or whatever, and fill in the name later, going progressively down the alphabet when you need more names.
But if you're choosing meaningful names, then a name change would change the course of your story, so it may be best to pick it before continuing.
Then again, once you know what they do in your story, a meaningful name may be easier to find.
Events are usually the same, no matter what the names of things are...
Answer: Use a name generator which you can get from Google play or Apple store for free. Just like the password generators.
Answer: I use to think well chosen character names were uber important. When I noted that a famous American playwright gave character names from A to Z in order of appearance, I thought he was making a statement to put your creative energies into good writing and not pondering good names. Unfortunately I can't recall the screenplay. Anyone know?
Answer: I seems to me that no one really took into account that we are talking about freewriting.
The whole point of freewriting is that you don't stop to reflect, but write down your stream of consciousness without editing it in any way.
From the rule that, while freewriting, you shouldn't correct orthography, find the right words, or even force yourself to stay on topic, but write whatever comes into your mind, it follows that regarding names you should also use whichever label comes to your mind first: a name ("Peter"), a characterisation ("the man"), or a placeholder ("M") – and then write on. You will know who you refer to, even if that label changes in the course of writing, and you will remember who you thought of when you revise your text later.


Cognitive Techniques to train Working Memory?

Question: What are some practical techniques/methods which can be used to train/improve your working memory and what studies have been done on this subject?
Answer: There are a few commercial packages that provide training for verbal and visuo-spaital working memory. The most well-known is CogMed (http://www.cogmed.com). Another popular one is Jungle Memory (http://junglememory.com). Both of these packages have been used in research studies (comment about these results below) There is also a myriad of online working memory games that promise to improve working memory, e.g. some games in Luminosity (http://www.lumosity.com). The content of these games is very similar, but there are fewer independent scientific studies of them as far as I'm aware.
As a caveat, the scientific evidence about the benefit of WM training is mixed at best. Training on WM tasks improves performance on them. This improvement also transfers to similar tasks (near transfer). However, there is currently little evidence for transfer to other tasks or improvements in everyday function (far transfer). For example, have a look at this report from a randomised control trial of working memory training in children: http://onlinelibrary.wiley.com/doi/10.1111/desc.12068/full
Answer: In recent news, Lumosity has paid a $2 million fine to the FTC for unsubstantiated claims about the benefits of its training. I've heard CogMed recommended by practicing neuro rehab professionals. Apparently, there is science to back its claims. It gets a bit pricey, however.


What is the jutsu that ninjas use to appear/disappear instantly?

Question: Some users of the jutsu are Kakashi, Gai, Genma, Kabuto, etc. It can often be seen when Anbu members are dismissed.
Comment: Can you expand your question a little bit? like add references to manga/anime(where you see it happen)
Comment: iKlsR has given the correct answer.
Kakashi uses that technique during Chunnin exam Preliminary round and Gai uses it to appear infront of Rock Lee to punish him for using a forbidden move against Sasuke.
Answer: The most common one I know of and I think you are talking about is the Body Flicker Technique (also known as Teleportation Jutsu, or Shunshin no Jutsu).

The Body Flicker Technique is a high-speed movement technique,
  allowing a ninja to move short to long distances at an almost
  untraceable speed.*
To an observer, it appears as if the user has
  teleported. A puff of smoke is occasionally used to disguise the
  user's movements. It is accomplished by using chakra to temporarily
  vitalise the body and move at extreme speeds. The amount of chakra
  required depends on the overall distance and elevation between the
  user and the intended destination.
Answer: It could also be a shadow clone.
Comment: It seems very unlikely that it'd be a Shadow Clone. Do you have anything that could back up your opinion?
Comment: Meh. There is no jutsu that make one appear/disappear. It's only shadow clones that disappear. I remember an episode where naruto had to master his wind nature energy, and talked with asuma sensei. It was a shadow clone who was talking with azuma, when they were done talking, naruto undid the shadow clone and azuma mentioned it was a shadow clone. it was episode 56, minute 7:35.


For a given bitrate, what video resolution is perceived as the highest quality?

Question: I'd like to achieve certain approximate bitrate for video encoding. If I use higher resolution like 720p, I'll get more fine-grained image, but more encoding artifacts. If I use smaller resolution like 480p, I'll get less detail and more coarse image, but higher image quality. Naturally, if the resolution is too high or too low, the result will be bad. Is there any research or information based on experience, what's the optimum resolution, given a desired bitrate and codec (in my case libx264)?
Comment: There's a piece of the puzzle missing: what's the target display size? After all, for a given bit rate, 320x180 would give you more bits per pixel, but the cost in quality when upscaling that to a 1280x720 display would far outweigh any benefit.
Comment: @JimMack Good point. The target display size would be a standard 24" computer screen.
Answer: In case of H.264 codec, you can use YouTube recommendations.
Here's Vimeo video compression guidelines
Answer: No, such a thing does not exist.  You can get some very rough guidelines in terms of things like suggested recording profiles for Youtube, Vimeo, or bitrates used by Netflix, Hulu and Amazon Instant Watch, but at the end of the day, the bitrate needed for a given resolution is entirely content dependent as well as dependent on how much time you can spend encoding.
It is a complex field and far too in depth to detail everything here, but in general, the slower you encode, the fewer noticeable artifacts you will have.  Additionally, the less motion (or more predictable motion) that your footage has, the less bitrate will be needed to display a high resolution image.  Conversely, if you are using fast software encoding options, there will be lots of artifacts or wasted bitrate for the level of quality you get.
Video compression is a complex field and each video needs to be calibrated a bit for best results.  Alternately, you can use a quality based encoding which will vary the bitrate as necessary to preserve a given level of quality (lack of artifacts.)  This would then be independent of the resolution of the file, it would just impact how much bitrate is consumed.  More active videos would consume more bitrate and more static or predictable videos would use less.  Additionally, slower encodings would use lower bitrates while faster encodings would use higher bitrate.
Answer: You're right, at some point it visually looks better to downscale and have a lower rez but less artifacty video.  The bitrate where this happens depends strongly on how compressible your content is.
One way to judge this for x264 might be to look at the rate-factor.  For 2-pass, the x264 output includes the rate-factor.  For CRF mode, the CRF value you set IS the rate-factor.  Just guessing off the top of my head, a rate-factor of maybe 30 or higher might be the point where you would be better off downscaling.  That might still be content dependent; e.g. if you have some very detailed but very static backgrounds, you might prefer to have the moving parts of the picture blocked/blurred, but the background high rez and crisp.  (IIRC, play around with AQ strength and/or psy-rd to control distribution of bits between long-displayed static parts of the image vs. parts that are changing.)
In the extreme case of using way too high a rez for your bitrate, a lot of the bits are just per-macroblock overhead (headers and so on), with little room for motion vectors and DCT coefficients.  Newer codecs like h.265 have bigger macroblocks (coding units in h.265 terminology), and also just higher coding efficiency (better rate-distortion tradeoff), so they push down the point at which you should start downscaling.
Visually, modern codecs will start to blur things themselves when there aren't enough bits to look sharp.  So once things start to blur as much as they would if you just downscaled, you might as well downscale.
For more discussion about encoding stuff, look around on forums.doom9.org.  Especially http://forum.doom9.org/showthread.php?p=1691228#post1691228, which is the discussion I was thinking of when writing this.


How to find the greatest value of the function?

Question: $$ f(x, y)=x^2+y^2,\quad x,\;y \ge 0,\quad 3x+2y \le 6$$
The max value is in the point $(0, 3)$, but how do I prove it? I may be able to prove that the function decreases on the curve $x(t)=2t,\; y(t)=3-3t$, but I don't know how.
Comment: Clearly the maximum occurs on the boundary $3x+2y=6$. Plug it in, solve for $y$, take a derivative and set it equal to 0.
Comment: It does, but not in a stationary point.
Comment: Ah, you also have to check the boundaries $x=0$ and $y=0$.
Comment: In general, the sledgehammer here is to use the method of Lagrange multipliers, which will always work. But by recognizing properties of the problem (ie, that the objective function is radial and has no local maxima) you can save yourself a lot of work.
Answer: As always, pictures provide a great way to see what is happening. I will let you fill in rigorous arguments to make this into a proof.

EDIT
There are many ways to make this into a rigorous proof. Below is one way. Say the maximum of $x^2+y^2$ is $a^2$. Then we have that $x = a \cos(\theta)$ and $y = a \sin(\theta)$. The constraint enforces that $\theta \in [0, \pi/2]$ and
$$3a \cos(\theta) + 2a \sin(\theta) \leq 6 \implies a (3 \cos(\theta) + 2 \sin(\theta)) \leq 6$$
Since, we want to maximize $a$, we want to minimize $ (3 \cos(\theta) + 2 \sin(\theta))$ in the domain $\theta \in [0, \pi/2]$. Now this is a simple calculus problem in one variable. Find the derivative and set it equal to zero and check the boundary points to figure out the minimum of $ (3 \cos(\theta) + 2 \sin(\theta))$. This will give you that the minimum occurs at $\theta = 0$. Hence, the maximum value of $a$ is $3$. Hence, the maximum value of $x^2 + y^2$ is $9$.
Comment: It states what I mentioned, that $(0,3)$ is the maximum. But how to prove it?
Answer: Since
$$
f(x,y) \ge 0=f(0,0) \quad \forall\ (x,y) \in \mathbb{R}^2,
$$
the function
$$
f: \mathbb{R}^2 \to \mathbb{R},\ f(x,y)=x^2+y^2
$$
has a global minimum at $(0,0)$, therefore the maximum of $f$ on the compact set
$$
K=\{(x,y) \in \mathbb{R}^2:\ x,y \ge 0,\ 3x+2y\le 6\}
$$
is on its boundary
$$
\partial K=\{0\}\times[0,3]\cup[0,2]\times\{0\}\cup\{(t,-\frac32t+3):\ 0 \le t\le 2\}.
$$
We have
\begin{eqnarray}
f(x,y)&\le&9=f(0,3) \quad \forall\ (x,y) \in \{0\}\times[0,3]\\
f(x,y)&\le&4=f(2,0) \quad \forall\ (x,y) \in [0,2]\times\{0\},
\end{eqnarray}
and for every $t \in [0,2]$ we have
\begin{eqnarray}
\phi(t)&:=&f(t,-\frac32t+3)=t^2+\Big(-\frac32t+3\Big)^2 \le \max\{\phi(0),\phi(2)\}=9=\phi(0).
\end{eqnarray}
Hence
$$
\max_{K}f=9=f(0,3).
$$
Answer: $f$ is critical when the gradient is $(0,0)$; that is,
$$
\nabla(x^2+y^2)=(2x,2y)=(0,0)
$$
$(0,0)$ is on the boundary of the triangle $x\ge0$, $y\ge0$, and $3x+2y\le6$.
An extremum can also be attained on the boundary where the gradient is perpendicular to the boundary.
On $x=0$, where the boundary is parallel to $(0,1)$ so we are looking for a point where
$$
(2x,2y)\cdot(0,1)=0
$$
Again, we have $(x,y)=(0,0)$.
On $y=0$, where the boundary is parallel to $(1,0)$, we are looking for a point where
$$
(2x,2y)\cdot(1,0)=0
$$
Yet again, we have $(x,y)=(0,0)$.
On $3x+2y=6$, where the boundary is parallel to $(2,-3)$, we are looking for a point where
$$
(2x,2y)\cdot(2,-3)=0
$$
$3x+2y=6$ and $4x-6y=0$ intersect at $\left(\frac{18}{13},\frac{12}{13}\right)$.
The other points are the singular points of the boundary (the vertices of the triangle): $(0,0)$, $(2,0)$, and $(0,3)$.
Checking each of these possibilities, we get
$$
\begin{align}
f(0,0)&=0\\
f\left(\frac{18}{13},\frac{12}{13}\right)&=\frac{36}{13}\\
f(2,0)&=4\\
f(0,3)&=9
\end{align}
$$
Therefore, $f(0,3)=9$ is the maximum.


Has LEGO Made A Minifigure-Scale Shopping Cart Piece?

Question: For the current MOC I am working on, I am going to need a LEGO Minifigure-scale shopping cart. I thought I had seen one in an official set, but after searching Bricklink extensively, I am now not sure they have. Has LEGO produced a shopping cart piece or will I just have to make my own?
Comment: There is one Friends scale shopping cart. But that is probably not helpful I guess.
Comment: @Aziraphale On the contrary, that is actually quite helpful!
Comment: @Aziraphale why not?
Answer: The 41118 Heartlake Supermarket contains a Friends scale shopping cart. This is how it looks like:

There is, however, a cute little MOC design with Window 1 x 2 x 2 2/3 Pane Lattice Diamond with Rounded Top on both sides and 1x2 tile modified grilles. This is, I think, a perfect shopping cart:

@MindS1 This is how far I got with it. The panes bend the grilles quite a bit. I would consider this an illegal building technique. I also don't see how the droid arms connect to the wheels and to the basket part.
Comment: The Friends shopping cart is most likely the one I've seen before. That design is perfect! I guess I'm finally going to be able to put my Lattice Windows to good use! :D
Comment: That is a really excellent design. It's so hard to find good solutions at that scale!
What is the minifigure holding onto in that picture? And how is it attached to the grille?
Comment: The grills are the other way around on the MOC...
Answer: LEGO heard the wishes, and finally put one out new this year (2019).

Part #49649 Minifigure, Utensil Shopping Cart Frame.
Part #2496 Wheel Skateboard / Trolley.
Is this for a Fortnite project?


Proxy for a home network

Question: What would be a good proxy for a home network?

I'd like to install the software proxy on 1 machine and to share it across my LAN
how can I configure my Linux Ubuntu machines to use the proxy just for specific domains? (e.g. www.gravatar.com)
Answer: Firstly, How many users are we talking about?
As suggested by Arcath, Squid is the de factor standard these days for open source caching proxies.  Various add-on packages allow content filtering and several programs have been make to do fancy reporting against Squid's logs.
A good lightweight caching proxy is Polipo.  It's not the fanciest thing in the world, but it's small, fast, and should work well enough for a handful of users.
Concerning your second question, Squid's ACL functions can be used for caching only certain sites.  I'm not sure why you'd go through the trouble of setting up a proxy but not want the clients to take full advantage of it, though.
Answer: Squid is a rather good proxy, the wikipedia article might be a good resource http://en.wikipedia.org/wiki/Squid_%28software%29
Answer: If you want a proxy for apt updates, look at apt-cacher-ng.  I used that on my cluster at work.
The other answers are for general-purpose HTTP proxies that don't specifically know about Packages.gz, Releases, and .deb files.  apt-cacher-ng uses that for cache staleness decisions.
Answer: I believe you can use the Firefox add-on, FoxyProxy, to cause Firefox to use the proxy just for certain domains.

Proxy for a home network


What is the difference between memo writing and business letter writing?

Question: What is the difference between memo writing and business letter writing? Memo and business letters both are informal reports, so what is the main difference?
Comment: I think the problem is in your given. I would not define a *business letter* as an "informal report." A business letter is a letter you write to someone with whom you are, or may be, doing business, or possibly have done business with. It could be an invitation, a cover letter, a summary of a meeting, a threat, a request for information, a confirmation or rejection of a deal, etc. Only one of those could be considered an "informal report."
Comment: Welcome to Writing.SE *Hajra*! If you have a moment please take the [tour] and visit the [help] to learn more about the site. Have fun!
Answer: A business letter is written to someone outside your company. Letters in general and business letter especially follow certain national (or international) conventions and norms. For example, the formatting and placement of dates and addresses may be prescribed by industry standards and the form of address follows social conventions. Besides these culture specific norms and conventions, most companies have style guides that require their employees to use certain formats when they communicate outside the company. For example, often there is a company letter paper, with the company logo in a specific color, size, and placement.
A memo(randum) on the other hand is a document that records events or decisions and is used internally, within the company. A company may or may not have a certain formatting requirement for a memorandum. Most distinctly, unlike the letter, it is usually not addressed to someone specific.


Are there any _severe_ drawbacks of bitcoin justifying all the alternatives?

Question: There exist quite some alternatives to bitcoin that are partially based on it, and I'm sure their creators all are convinced they improve upon something. But are there any serious drawbacks in bitcoin that can or will probably never be fixed?
Comment: Related [Why do we need alternatives to Bitcoin?](http://bitcoin.stackexchange.com/q/8114/5406)
Answer: I don't think there are severe drawbacks of Bitcoin. Certainly none that other coins are solving.
However, Bitcoin has certain properties that could be replaced with some other. Most altcoins to just that. Popular properties that altcoins change are:

replace PoW with something else

Some altcoins do not use a PoW mechanism or use a hybrid mechanism. PeerCoin (originally named PPCoin) was the first altcoin to use the Proof-of-Stake mechanism, which basically requires miners to hold a certain amount of currency in order to mine new. PeerCoin uses a hybrid of PoS and PoW. Nxt is an altcoin that uses pure PoS.

the PoW algorithm

Bitcoin uses SHA-256, which is a hash algorithms that almost entirely requires CPU cycles to calculate. This means that it is easy to create custom hardware to perform this calculations. There are many altcoins that use Scrypt as the PoW algorithm. Scrypt is more memory-intensive and therefore harder to implement in custom hardware. The first altcoin to implement Scrypt is Litecoin. Primecoin requires miners to calculate large prime numbers as a PoW mechanism.

the total amount of coins that can be mined

Bitcoin has a 21 million coin limit. Some altcoins raise this limit, such as Dogecoin, others lower it, such as 42.

the rate at which new blocks are created

Bitcoin blocks are mined at an average rate of one block every 10 minutes. Many merchants require that a transaction has been confirmed by several blocks before they accept it. With a confirmation time of 10 minutes (in fact, the recommended amount of confirmations to wait for is 6) can be quite cumbersome in certain use cases. Litecoin has a confirmation time of 2.5 minutes.

the time it takes before the maximum amount of coins is created

Block rewards usually have a halving time. Every halving time the block reward halves until it is too low to represent using the maximum precision and it becomes zero. With Bitcoin it will take until 2140 until the block reward becomes zero. Some coins shorten this period. Sometimes they shorten it so much that the creator (who mines first, of course) is accused of pre-mining because he can mine very fast and easy in the beginning of the existence of the coin.
Comment: Thanks! PoS sounds interesting, and I like the idea of primecoin trying to calculate something actually (slightly) useful instead of brute-hashing. Personally, I consider changing the amount of total coins nonsense though, since that is equivalent to changing the scale (apart from, maybe, changing for how long miners get a reward in addition to fees).
Comment: Well, take care with PoS though. I once read a post from one of Bitcoin core devs (yeah I lost the post and can't find it anymore) that PoS is not at all as safe as PoW is. And about increasing the amount, the Dogecoin community quite enjoys talking in big numbers :) It sounds better that you can say I own 10k doge instead of 1 BTC, right?
Comment: Well, I could say I own a billion nano-Satoshi :P But PoS alone does indeed sound a bit risky - if one party _does_ manage to hold the majority of altcoins they'd most likely increase their lead forever, and there seems to be no mechanism to prevent that. Though, I start having an idea - one could track which part of a given transaction was already "used" as PoS (via it's history) and only unused parts, to be included (in the respective fraction) in the coinbase transaction, would count
Comment: I think that's somehow the principle of how it works. But I thought the main issue was that there was much less incentive for minders to only work on the current branch. The way of gaining your PoS share is by being lucky to be picked and you will get your stake * the time you are holding it without PoS share. But because no "work" is involved, it would make sense to keep trying to append your self after any recent block to try having more luck there. It was something like that. Could result in regular forks and orphaned blocks.


Square bracket notation for dimensions and units: usage and conventions

Question: One of the most useful tools in dimensional analysis is the use of square brackets around some physical quantity $q$ to denote its dimension as
$$[q].$$
However, the precise meaning of this symbol varies from source to source; there are a few possible interpretations and few strict guidelines. What conventions are there, who uses them, and when am I obliged to follow them?
Comment: Thanks to LaRiFaRi for sparking this post, and providing the BIPM and ISO references, in [this question](http://physics.stackexchange.com/q/77641/8563).
Answer: I had an extensive look around, and I turned up four conventions. This included a short poll of google, other questions on this and other sites, and multiple standards documents. (I make no claim of exhaustiveness or infallibility, by the way.)

 Using $[q]$ to denote
commensurability
 as an equivalence relation.
That is, if $q$ and $p$ have the same physical dimension $Q$, one might write $$[q]=[p]=[Q],$$ but no bracketed quantity is ever shown equal to an unbracketed symbol. Thus, if $v$ is a speed one might write $[v]=[L]/[T]$ or $[v]=[L/T]$ or $[v]=[L\,T^{-1}]$ or some equivalent construct. You can see $L$ and $T$ as denoting the dimension or just "some length" and "some time". To see how you would work without evaluating braces, here is a proof that the
fine structure constant is dimensionless:
$$
[\alpha]=\left[\frac{e^2/4\pi\epsilon_0}{\hbar c}\right]=\frac{[F\,r^2]}{[E/\omega][r/t]}
=\frac{[F r][\omega t]}{[E]}=\frac{[E]}{[E]}[1]=[1]
,$$
so $\alpha$ and $1$ are commensurable. Some examples are
this,
this,
this, or this.

 Using $[q]$ to denote the dimensions of a quantity. Thus if the physical quantity $q$ has dimension $Q$, one writes $$[q]=Q.$$ A velocity would then be written as $[v]=L\,T^{-1}$ or its equivalents. This seems to be the leading candidate on Google, closely followed by the convention 1. Some examples are
this,
this,
this,
this, and this. This is my personal favourite, as I find that it permits the most flexibility without horribly formalizing the whole business (though I will often skip the actual evaluation of the braces, essentially using convention 1).

 Using $[q]$ to denote the units of a quantity. Here if $q$ can be written as a multiple of some unit $\text q$, you write $$[q]=\text q.$$ This is contingent on what unit system you choose but different units for the same dimension are of course equivalent. When this approach is used, the notation $\{q\}=q/[q]$ is sometimes used to denote the purely numerical value of the quantity. A speed would be written, for example, as $[v]=\text m\,\text s^{-1}$. This use is endorsed by the
NIST
Guide to the SI,
section 7.1,
the
IUPAC guide
 Quantities, units and symbols in physical chemistry, the IUPAP guide Symbols, units, nomenclature and fundamental constants in physics, as well as the
ISO standard
ISO 80000-1:2009, section 3.20. (That document is very paywalled, but chapters 0-3 are available for free preview
here.)

Google results seem relatively scarce, with
this and
this
 as examples, although that could simply be poor representation. (There is also
this document, which uses the notation $[\text W]=[\text V][\text A]$, but I think this is quite uncommon as well as not very useful.)

 Using $\operatorname{dim}(q)$ to denote the dimensions of a quantity. This is the notation set as standard by the
 Bureau International des Poids et Mesures
in the
SI Brochure
 (8th edition, chapter 1.3, p. 105). This also sets roman sans-serif as the standard for physical dimensions, so $\mathsf{Q}$ would be the dimension of $q$ and you write $$\operatorname{dim}(q)=\mathsf Q.$$ (To typeset roman sans-serif in TeX or MathJax, use \mathsf; note that this is distinct from \operatorname, which is used for $\operatorname{dim}$ and would produce $\operatorname{Q}$ through \operatorname{Q}.)

A real-world usage example is thus $\operatorname{dim}(v)=\mathsf L\,\mathsf T^{-1}$ for a velocity.

This use is set as standard by
ISO 80000-1:2009, section 3.7, and it is also endorsed by the NIST Guide to the SI,
section 7.14.
(NIST also reproduces the BIPM text in p. 16 of
The International System of Units.)

Examples of this online are
this,
this,
this and
this; I note, though, that most examples I found are technical, while pedagogical examples tended to use conventions 1 and 2. (This also feels less common, but that's hard to judge.)

I also find it important to add that few academic journals impose standards in this area. As a working physicist in academia, the style guidance of one's chosen journal is often the only style standard one is really obliged to follow. The style manuals of the American Physical Society, the Institute of Physics, Reviews of Modern Physics, Nature Physics and several Elsevier journals have no mention of which convention should be used in their publications.
As was made clear in Should we necessarily express the dimensions of a physical quantity within square brackets?, the choice of what the symbol $[q]$ means is entirely a matter of convention. The most important thing is that your usage is consistent. Do not jump conventions within a document. If your work is closely allied to other resources (e.g. textbooks) that use a particular convention, it is best to stick to that, to avoid confusing your students. If you are presenting an exam, use the notations used in your course to avoid confusing your examiner, or - at the very least - define all non-standard notation you use.
So, what convention should you use? There is really no requirement to use any one of the above (and you can even make up your own notation, as long as you define it appropriately and don't overdo it). This is really less of an issue than it looks, as there's actually rather rarely a need to use this notation in print except in pedagogic settings. (That's not to say that professional physicists don't use it in practice: we do use it, often, in everyday life, but it's mostly informal work used on the side to keep calculations straight or as exploratory scaling arguments when starting work on a problem, for example.)
If your work is a commercial report, or similar document, and it could potentially have legal repercussions, then you should check whether there is a legal standard you should be using, which will then probably be conventions 3 and 4. Academically, you are typically free to choose the conventions you find most convenient as long as you use them properly and you avoid conflicts with other allied resources. If you are publishing in a journal or as part of a bigger work, you should check if they provide style guidance on this, though as I said journals rarely take stances on this. (You should really be reading the style guidance anyway as part of your submission process, though.) For your informal work, you should use whatever you're most comfortable with!
Finally, if you have questions about the typesetting of these notations in LaTeX, you should go to How should I typeset the physical dimensions of quantities? on TeX.SE.
Comment: Am I the only person in the world who writes $[t]=\text{s}$? Maybe this is just an artifact of the way I teach the topic, but I teach my students to write out an expression like $m\cdot a$ in terms of the SI base units like $\text{kg}\cdot\text{m}/\text{s}^2$. If you think of the algebra of units as a vector space, then this corresponds to fixing a basis. Of course "a gentleperson never fixes a basis," but for freshmen, abstraction is hard and anything concrete is easier.
Comment: @Emilio I am having problems to understand the first point. If $q$ and $p$ have the same dimension, it is the same as point 2. If $[q]=Q$ and $[p]=Q$ than $[q]=[p]$. But in the examples for point one, you actually write $[q]=[Q]$. I hope, you understand what I mean. I am getting a bit confused on all my "dimensions-research" :-)
Comment: To the examples in 1: The second one is of type 2. $[q]=[p]^\alpha [r]^\beta \dots$. The third and fourth is of type "The dimension of $q$ is $[Q]$". The first one is strange and like the one, you explained further. $[q]=[Q]$ which I find very confusing.
Comment: @BenCrowell Sure, that's convention 3. It's not that common online but my feeling is people _do_ use it. It's also the recommended standard in as much as there is one.
Comment: @BenCrowell: I am also using convention 3.
Comment: Also see my answer about DIN 461 and DIN1313 here: https://hsm.stackexchange.com/a/14059/16002
Answer: It may also be worth mentioning another shorthand convention that appears in the field theory literature and some textbooks (e.g. A. Zee, Quantum Field Theory in a Nutshell, Chapter III.2). This is essentially a modified version of the second convention on Emilio's list. If one is working in the "natural" units of the problem then often everything can be expressed in terms of a single dimensionful quantity. For example, particle physicists usually set $\hbar = 1$ and $c = 1$ so that all quantities carry the dimension $\mathrm{mass}^x$ for some power $x$. In that case, one can simply write
$$[q] = x.$$
To give an example, with $\hbar = c = 1$ a length $l$ would be assigned a mass dimension $[l] = -1$.


Closing down the old site?

Question: In follow-up to this previous question, shouldn't the old askaboutprojects.com site be closed now that this one is running?
Answer: Could we keep it open until this site survives Public Beta?  Could the Admin of AskAboutProjects put up a system message pointing people to here for now?
I heard the old site might close for financial reasons, so if we can help point existing users here first, I feel like that might be more helpful.
However, it's not a good idea to migrate questions during a public beta, so for now redirection might be best.

Closing down the old site?


Is a Titan-like planet with Earth-like gravity plausible?

Question: For my hard sci-fi story, I would like to have a planet similar to Titan (very cold, nitrogen atmosphere, methane seas) but with a surface gravity in the region of 1g. Could this occur, or would the greater gravity result in a significantly different atmosphere?
Answer: Based on this chart

with Earth escape velocity and Titan temperature your planet should be able to keep nitrogen and methane, like you ask, but also water, ammonia, oxygen, helium, carbon dioxide and xenon. Hydrogen might be borderline.
If you don't have photosynthetic life forms it is likely that all the oxygen will be chemically bound to other atoms, due to its reactivity, and you will have no free oxygen.
Comment: Venus reaches the temperature of 650K, not 350K. But that is not so important. The chart is simply senseless. Any atmosphere will run away at any temperature and any gravitation (save black holes). The difference is in TIME only. The chart must have a comment about what time interval of escaping half of the atmosphere is meant.
Comment: as far as life in a non-polar sea, some people have worked out a membrane prototype, but no mention of a metabolic framework: https://www.popsci.com/heres-what-methane-based-life-titan-could-look
Comment: This is a fantastic answer. Would the atmosphere be *primarily* nitrogen, water or ammonia? (or some combination thereof)
Comment: @Megalonychidae, I suspect that strongly depends on the composition of the cloud condensing to form the stellar system
Comment: @Gangnus, there is no way to escape a gravity well with a velocity below its escape velocity. I don't know where you get your statement from.
Comment: @L.Dutch From school and univ. physics. The speeds of molecules is distributed statistically. There are always some fraction that have velocities above the second cosmic. And that fraction, in higher heights will be dissipated into space.
Comment: @KJO The acceleration on the surface and second cosmic velocity are different things. Saturn has same acceleration as the Earth, but much higher second cosmic. And it is the last that define the speed of gas evaporation into space.
Answer: That depends on if the planet is sole or a satellite of a giant planet.
The presence of different chemical stuffs in the atmosphere or on the surface are defined:
For simple stuffs: by second cosmic velocity from one side and temperature and molecule weight from the other.
For complex stuffs: by second cosmic velocity from one side and temperature, atomic weight of the lightest component of the molecule and the radiation level in the exosphere  from the other.
For both variants the speed of input of the stuff into the atmosphere is utterly important, too.
The processes are:
for simple stuffs: The speeds of molecules is distributed statistically. (https://www.khanacademy.org/science/physics/thermodynamics/temp-kinetic-theory-ideal-gas-law/a/what-is-the-maxwell-boltzmann-distribution) There are always some fraction that have velocities above the second cosmic. And that fraction, in higher heights will be dissipated into space. That defines the speed of output of the stuff. The speed of input and output are balanced.
For complex stuffs: The radiation makes molecules fell apart. And if they can, they are joining back. That can be prevented by the loss of a component.
For example, water is divided into hydrogen and oxygen. The first is lighter and has much higher speeds of molecules. And speed of losing water is defined by the fraction of hydrogen in water vapor (defined by radiation) and fraction of hydrogen molecules, free atoms or ions, having second cosmic speed (defined by temperature). The speed of oxygen is 256 times smaller (gases have same temperature/energy and H2 is 16 times lighter than O2, so lesser mass should be compensated by 16^2 times higher speed), so its losses are negligible in comparison and it is always enough oxygen to restore the water molecule back.
Again, the speed of coming and losing the stuff are balanced.
So:
1. It is not acceleration that is important for gas keeping in the atmosphere, but the second cosmic speed. For example Saturn has same acceleration as the Earth, but much higher second cosmic (35m/s2), and does not lose even hydrogen. The question is undefined in this part. Let us say, you need a planet that is more Earth-like and the second cosmic is the same as ours (11m/s2).

Titan on its place does not lose nitrogen. Neither would the Earth there. The water is frozen and lies as rock. The same would be on the Earth. Titan has some methane as liquid. Not much, for it escapes by radiation dissipation and hydrogen losing. The Earth would lose less hydrogen, so, much more methane will be left. Seas will be larger.
At its place, the Earth significantly loses only hydrogen and helium. The question is, what will be with them if the Earth will have the Titan temperature. For much H in atmosphere will cause reaction with N and ammonia will snow onto the surface, leaving no N in gas state.

(https://geosci.uchicago.edu/~kite/doc/Catling2009.pdf) - look for explanation below the chart on the 4th page.
According to the chart, if the planet will have the radiation and temperature as on Titan and second cosmic speed as on the Earth, the planet will NOT lose its hydrogen and as a result, it will have ammonia/hydrogen/helium atmosphere instead of the nitrogen one. Ammonia fells as snow and only H/He atmosphere remains. It will be so, if the planet will be separate one.
But if it will be the satellite of a giant, the giant and Earth magnetospheres will react, thus greatly heating up the exosphere layers (look at the Earth and giant planets temperatures on the chart). And it WILL lose its hydrogen and helium and mainly nitrogen remains.


Lebesgue non measurability in the plane

Question: Suppose A is contained in the unit square of R^2, and the projection of A on any line outside the unit square is not Lebesgue measurable in R. Does that imply that A is not Lebesgue measurable in the plane?
Comment: OK, we have an example where every projection is non-measurable, and an example where all but one projection is non-measurable.  Can we do others?  Say: (a) All projections but two are non-measurable?  Or:  (b) Projections in uncountably many directions measurable and projections in uncountably many other directions non-measurable?
Answer: No, it doesn't. Take a non-measurable set $S$ on a line segment, and make this line segment to be a side of $A$. Then $S$ as a subset of the plane is measurable (it is of measure zero), while its projection on the line segment (i.e. itself) is not.
EDIT: As Pietro Mayer says one needs a union of a few isometric copies of my $S$ to yield an example whose projection on every line is non-measurable.
Comment: This subset $S$ of the x-axis has also the property that its projection on *every line but the y-axis* is not measurable. To make an example of a measurable subset of R2 whose projections on every line is non-measurable one can take three copies of $S$, on three segments starting from the origin and at 120 degrees from each other.
Comment: @Pietro: thanks a lot! I read the question and responded to it in a hurry.
Comment: Pietro Majers does give a full and nice answer. I would like to ask further, what happens if we add the demand that A is not a union of less than $2^\aleph_0$-many lines. Does this assumption, plus the assumption that the projection of A on every line outside the unit square is not Lebesgue measurable, ensures that A is not measurable in the plane?
Comment: @simon: Pietro's example is not a union of lines. In fact one can choose my $S$ and Pietro's variant so that it contains no line or line segment. Probably you wanted an example which cannot be covered by less than continuum many lines. I think such an example is given by taking a non-measurable $S\subset[0,1]$ and mapping it to the unit circle via $t\mapsto e^{2\pi it}$.
Answer: This is an answer to Gerald Edgar's question (a) (see comment just after main question). To produce a set such that all but two projections are non-measurable, take a subset X of [0,1] that's not measurable in any interval and put a copy of X into the segment from (0,0) to (1,0) and a copy of the complement of X into the segment from (1,0) to (1,1). If we project to the Y axis we get two points, so it's measurable. If we project to the X axis, we get the interval [0,1], so it's measurable. If we project in any other direction, then the images of the two segments are intervals of positive length that do not share their endpoints, so by the local non-measurability of X the resulting projection is non-measurable. My guess is that similar tricks can be used to do other things but I haven't thought about this.
Edit: I also have a very silly answer to Gerald Edgar's question (b), which is that the existence of such an example is consistent with ZF. It is known that there can be non-measurable sets of cardinality less than the continuum (of course, this means that CH fails). Let $K$ be such a set and let $X=K\times\mathbb{R}$. Now let $Y$ be the union of uncountably many rotations of $K$, but not continuum many. Finally, let $Z$ be the complement of $Y$ in the plane. If one of the rotates of $K$ is through an angle of $\theta$, then the projection of $Z$ on to the line $L_\theta$ that makes an angle of $\theta$ with the x-axis misses all points in $K$ (or rather the obvious copy of $K$ along that line). It also contains each point not in $K$, since if P is such a point, then we have removed fewer than continuum many points from the line perpendicular to $L_\theta$ that goes through P. Therefore, this projection is just a copy of the complement of $K$ and so non-measurable. If $L$ is any line that is not perpendicular to one of the $L_\theta$ for which $\theta$ is one of the angles we chose, then again we have removed fewer than continuum many points from $L$. Therefore, if we project onto $L_\phi$ for some $\phi$ that is not one of our chosen angles, then we obtain the whole of $L_\phi$, which is of course measurable. So we have uncountably many measurable projections and uncountably many non-measurable ones.
I don't know what happens if we ask for continuum many measurable projections and continuum many non-measurable projections ...
Answer: The subset S is not as required.
Its projection on the X-axis is not measurable, but it certainly does satisfy it for every line segment outsides the unit squrae. For instance, its progection on a line parallel to the y-axis is a single point, which is measurable in R.
Comment: See Pietro Majer's comment below. I think it deals with your objection.
Answer: Partial answere (anyway I guess no).
Take $S\subset [0,1]$ non mesaurabile and let $A:=S\times ${0}$\cup${0}$\times S, \ B:=\mathbb{R}\times ${0}$\cup${0}$\times \mathbb{R}$, then $A\subset B\subset \mathbb{R}^2$  and $A$ and $B$ have measure 0. If the projection is  bijective is a  omeomorphism from  $B$ to the line, then the image of this proiection is no measurable:
we have that  $A\subset B$ isnt measurable (on $B$ consider the linear lebesgua measure, if we suppose $A$ measurable the also $A\setminus (0\times \mathbb{R})=S\times 0$ is measurable, absurd)
further a projection is   continuous, then  meaurable i.e. the inverse image of a measurble subset is still measurable. If a  projection is a  omeomorphism  then establishes an identification (or bijection) between the measurable sets.
THe some   follow  if the line is vertical or horizontal (the image of prjection is essentally $S$).
Let now $f: B\to l $ a projection , no  injective and $l$ no vertical or horizontal.
then $f(S\times 0)$ and $f(0\times S)$ are a homothetic (dilatate or traslate) copies of $S$.
Then the problem reduces to finding a no-measurable subset $ S $ such that the union of two of its homothetic images is  no-measurable.
Comment: Note that Pietro Majer's example deals with all projections, not just to the coordinate axes.  In your case you would have to argue why no "skew" projection of the set is measurable either.
I think this is actually true, but it requires a more complicated argument as in Pietro's example.
Comment: I edited  my answere.

Lebesgue non measurability in the plane


Why contribute to Android if it has an Apache license?

Question: Why do commercial firms contribute to Android open source project if they are not bound to. They can build their own version of android and use it with their products under any license. Samsung uses Tizen in its products but at the same time contributes to Android. Why? What is the benefit of doing so?
Answer: There a few benefits I can imagine in making such contributions.
First, from a practical point of view, I'm guessing such companies have their own patches they'd want to rebase on top of the upstream as it moves forward, in order to consume new features, performance improvements, and bugfixes. The larger these patches are, the harder this rebasing is - so it may sometimes (often?) make sense to donate a patch upstream instead of creating it behind your closed walls.
Second, it's important to support the community. Even if a company has it's own Android fork, it's customer probably don't use just its software - they install third-party apps and games. These third-party apps are usually developed by developers who develop apps for Android, and not for a specific company's Android fork (although they probably test it on several models of the main manufacturers). To ensure this community continues growing, it's important for these companies to make sure the Android market, as a whole, gets a steady stream of new features and bugfixes - and the way to do so is to contribute to the upstream Android.
Third, I can assume there's an HR component here. A lot of developers [this one included] like contributing to open source - it's often a fun experience, it allows for a lot of professional growth (as you're able to get feedback on your work from a wider circle than your immediate coworkers), and it improves your own visibility and personal brand. Companies may recognize this and allow some of the work to be done upstream as a type of benefit for the employee.
Comment: @Rahul As a simple example, suppose mainline Android has a `getLocation` function that uses available physical sources and guesses the device's physical location. Foo Corp has a modified version that improves `getLocation` with their own additional logic. Later, Android eliminates the `getLocation` function and replaces it with `getGeneralLoc` and `getPreciseLoc` -- Foo Corp cannot update to this new version of Android until they figure out how to apply their change to the old `getLocation` to the new set of functions. If they had shared their changes, this would have been solved already.
Comment: Since I am a student of social sciences I do not fully  understand the first point. could it be elaborated in a simpler form.Second and third points are well taken.
Comment: @Rahul in short - a company with it's own "flavor" of Android takes the upstream Android and applies a series of changes (patches) to it. Each time a new version of Android is available, it needs to take that newer version of Android and apply the these changes (or a modified version of them that are appropriate for the new version). The less changes it needs to apply (since these change were incorporated in the upstream Android), the easier this task is.


can I only replace only 3 tires on a FWD van?

Question: I have a Toyota van  FWD- had to replace one tire last year (nail in sidewall).
new tire - P225 / 60R17 Michelin Defender ( warranty 145,000km).
 It now has about 12km
The other 3 tires need replacement!!
Is it ok to just replace the other 3 with the same Defender tire ???
Comment: Are you using "FWD" as Four Wheel Drive? FWD usually specifies Front Wheel Drive, so I'm just making sure.
Comment: It is front wheel drive ..
Answer: Since this is only a two wheel drive vehicle, placing three new tires should not pose any issues for you if they are the same type/model as the ones which are coming off. Ensure you put two new tires on the front so that the drive tires are exactly the same (same wear amount). Not that it would create a huge issue, but different rolling widths may cause the differential in your transaxle to work a little harder than it would normally. Make sure you explain this to the tire shop as they will want to put two new tires on the back end ... just tell them, "I want two new tires on the front, with the used one in the rear."
There is one issue which may occur depending on the amount of tread difference between the new/old tires. That problem would be the wheel speed sensors. If the tread difference between the new/old tires is enough, it may trip the sensors and flash a fault on the dash (CES light). You won't know until it comes on though, if it's going to be an issue.


How do moderators update custom off-topic reasons for their site?

Question: Now that the on-hold/close chane is live, how do site moderators update their off-topic reasons?  Our list is rather sparse, and we are starting to get complaints questions about which to use.
Comment: For advice before you start changing things, read [What do site moderators need to do to support the new custom question close reasons?](http://meta.stackexchange.com/questions/184637/what-do-site-moderators-need-to-do-to-support-the-new-custom-question-close-reas)
Answer:
Go to a question on your site and click the "Close" link.
Select "A community-specific reason" from the list.
At the bottom of the list of close reasons, there will be a link to edit the list.
From there, you can add a new custom close reason or deactivate close reasons that other moderators have added.

Alternatively, you can go to "Mod" -> "Links" -> "Manage community-specific close reasons", where you'll see the current reasons and an "add" button.
It will require another moderator to approve your edits to make sure that at least two people approve of the changes being made. This review and approval is done from "Manage community-specific close reasons".
Comment: I don't see an option to Edit, only to Deactivate and 'Add Custom Reason'.
Comment: @Emracool You should definitely run on the "incomprehensible gibberish close reason" platform in the next moderator election.  ;)
Comment: New plan: become a moderator and add "This question is off topic because sbarble gribble wubblepumpus."
Comment: @JonW From what I can see, only the default (generic) close reason and custom close reasons can be edited by diamond moderators. (Updated my answer.)
Answer: Open the close dialog on any question, and click "off topic". Then click "edit these reasons"

Initially, you'll see a default OT reason, possibly with some custom ones.  The default OT reason does not show up in the close menu, unless you currently have no active custom reasons. However, the default OT reason can show up on posts if:

Close voters have used the custom (freeform) reason
The post had outstanding close votes from before the overhaul

The custom ones can be deactivated. Deactivated close reasons cannot be seen in the close dialog, but will still be shown on closed questions (which have in the past been closed with that reason) and can be easily reactivated. To reactivate, click the "show deactivated" button, and then "reactivate".

To propose a new custom reason, click the "add custom reason" button and write one.

As you can see, it is editable and can be deactivated, but it needs another moderator's approval to show up in the close dialog.
Note that these close reasons1 cannot be edited once approved. Make sure the reason is good -- it should clearly explain the problem (with links to relevant help center or meta posts if necessary), and if possible explain how to fix it. Try to collaborate with the community on these.

You can also reorder the close reasons by dragging them. Only 3 close reasons can be active at any given time.
1. Except the default; this one is always editable.
Comment: @MPD No. Deactivating _only_ removes it from the close dialog
Comment: Snap.  The non-editable thing is a drag.
Comment: @MPD Deactivate and create new ones (get consensus on meta and fetch an extra mod for the activating). This isn't supposed to be something you do daily; so not really a pain.
Comment: If you deactivate a reason, does that wipe out / change any posts that already have that reason?  We have been discussing this on our meta, but there isn't consensus on a few, so I anticipate more-than-the-average editing the first few weeks.
Comment: @MPD Please hold while I do some SCIENCE on one of my pet science sites.


In my homemade electrolysis setup, only the negative end bubbles?

Question: I've created an electrolysis setup by connecting a $6~\mathrm{V}$ battery to a cup filled with saline water via pencils; I am confused as to why only the negative pencil bubbles though. After running the setup for longer than five minutes, the water turns brown but so far that information has not been useful. Why is the negative pole the only one bubbling and if possible, why is the water turning brown?
Answer: Your setup, using table salt ($\ce{NaCl}$ plus additives) will initially electrolyse according to the following two reactions, separated by cathodic reduction and aniodic oxidation:
$$\ce{2 H+ + 2 e- -> H2 ^}\tag{CatRed1}$$
$$\ce{2 Cl- -> Cl2 + 2 e-}\tag{AnOx1}$$
These reactions assume no counterions. However, you don't have dissolved protons in your solution because you aren't electrolysing hydrochloric acid. Instead, the proton is taken from water molecules and if we include them (and sodium counterions) we get the following improved cathodic reduction equation:
$$\ce{2 Na+ + 2 H2O + 2 e- -> H2 ^ + 2 NaOH}\tag{CatRed2}$$
This still displays the hydrogen gas bubbling away at the cathode but chlorine gas at the anode should also bubble after some time (or at least evolve noticeably). However, with the increase of $\mathrm{pH}$ due to the generated hydroxide, the chlorine produced at the anode will react further:
$$\ce{Cl2 + 2 OH- -> Cl- + OCl- + H2O}\tag{AnOx2}$$
And both of these are soluble ions. The overall reaction of your electrolysis setup is:
$$\ce{NaCl + H2O -> H2 ^ + NaOCl}\tag{RedOx}$$
There will be hydrogen evolution at the cathode but no gas evolution at the anode. The browning will likely be due to a number of side reactions induced by the oxidant hypochlorite anion.
In case you're wondering why water's oxygen is not oxidised, this is due to its higher standard electrode potential.
Comment: are there any books you would recommend reading to learn about this sort of stuff?
Comment: @JakeWickham I generally don't recommend books because I never use them, but there is a question here on chem.SE about good books for certain topics.
Comment: I've done this experiment using steel clips (from a car battery charger) and got a brown colour due to the steel being reduced to Fe3+ salts. After the experiment you could clearly see where the clip had been corroded.
Answer: Depends a bit on your voltage, but you might just be making chlorine at the anode. It's pretty soluble in water. I've always used sodium sulfate as the electrolyte.
Answer: Try collecting the gas at the negative electrode and testing it. Hold a match to the gas and my guess is that it will go pop. (Positive test for hydrogen)
If there is a group 1 metal salt in your solution like $\ce{NaCl}$ the ions would be Na+ and $\ce{Cl^-}$.
When the Na+ is reduced to Na by accepting the electron from the cathode (negative terminal) it becomes the metal atom.
$$\ce{Na+ + 1e^- \rightarrow Na}$$
This then reacts with the water in the solution to release hydrogen bubbles at the negative electrode.
$$\ce{2Na + 2H2O \rightarrow 2NaOH + H2}$$
This is probably why you have bubbles at the negative electrode.
If the cup vessel you are doing the experiment in has any imperfections in the ceramics or has any metals in the surface then there is probably a displacement reaction from the Na ions or the Halide ions floating around.
There could also be displacement of other ions from inside the saline (saline is a mix of different salts)
That's my best argument for your observations
Comment: This is incorrect. Sodium shall not even touch the cathode as long as species exist that can be reduced more easily (such as hydrogen in water)!
Comment: Re first comment: Wrong. Please go back to your books!
Comment: It's saline. Salts (ionic substances)would be reduced far more easily than water (simple covalent structure).
Comment: Add indicator the negative electrode would show the presence of an alkali.
Comment: I'll agree with you on the presence of a base near the cathode; see my answer as to how this is formed.


How to tell if a roll of film has been exposed?

Question: I have found film reels some with tails of film others not. Is there a way of telling if they have been exposed/used in a camera? Film types are for 35mm and one Kodak Advantix.
Answer: As for the Advantix (APS) film, check for a white circle on one side of the roll.
If only a half circle or an X appear in white, there'll likely be some pictures already taken: in the former case you'll be able to insert it into a camera supporting this feature and have it automatically start after previously exposed frames.
While this technique isn't foolproof (resetting this indicator was in fact a requirement to replace the film at any time with cameras not supporting the resuming of a roll) it should be a significant tipoff; with standard 135 film there is no such option and position of the film as it leaves the camera tells nothing about its contents, with no practical way of checking.
If you hold any expectations on their contents, have them developed at your local place (empty rolls are generally charged at a relatively low nominal price, since there'll obviously be nothing to print).
Comment: I would recommed the same. Having them all developed and ending up with blank film is better than to be sorry with unusable double exposures. Anyway, nice reading about all this here, flamewars and whatnot. I bought my b/w film in 30 meter long rolls and wound the cassettes myself :)
Answer: The only sure way to tell if film has been exposed or not is to develop it. Any light used to examine undeveloped film will fog it.
It is probably safe to assume the rolls with no leaders extended out of the cartridge have been exposed. The rolls that still have film showing are another matter. Some cameras with motorized winders, such as my EOS film camera, would wind all of the film back into the cartridge after the roll had been shot. Some other cameras with motorized winders had an option in the settings that allowed you to leave the leader out. With manual film rewinders, the decision was up to the operator. Most folks would wind all the film back into the cartridge, but some would watch the exposure number indicator and stop when it got down to "0".
Comment: My Pentax MZ-6 has motorized rewind, and leaving the leader out is an option in settings (useful if you'd like to switch between films).
Comment: If the leader's out check to see if it's crimped. Many/most film cameras reverse-roll the film and that will often leave a mark or crease on the leader where it fits into the take-up slot.
Comment: Many, but certainly not all, film cameras left a crimp in the leader. Neither my Rebel II nor Konica FS-1, for example, did. They both had motorized winders and large take up spools. The Konica's spool had teeth that caught the perforations on the edge of the film. Especially during the last years of film's heyday, many cameras had built-in winders that didn't leave a crease in the leader.
Comment: Having been gifted a roll of film which looked pristine, I'd assumed it was unshot. As it happens, it had been shot on a Fujica ST605, which normally puts a very obvious crimp in the leader, yet in this case, it didn't. Sadly, there's no foolproof way other than developing it, although if you do end up reshooting the roll, you can end up with some very odd double exposures!
Comment: This is why I always used to make sure to wind my rolls in even if my camera didn't.  So glad I don't have to deal with film any more.
Answer: If you know what camera the film might have been exposed in, take a look at the takeup spool in the camera. Many cameras have a winding mechanism that involves some kind of slot in the spool into which you stick the film leader, and this bends the leader as film winds onto the spool. If the exposed leaders have a discernable bend or crease, that's a telltale sign that the film was in a camera at some point. If the leader is smooth you really can't say for sure -- IIRC cameras with integrated motor drives grabbed the film a different way and may not bend the film.
Answer: So I just found this thread and discovered a way to solve the problem actually. My Nikon L35af (I think...) leaves a little bit of the roll out when it rewinds. This is awesome when you want to shoot double exposures but a bummer if you forget whether or not you shot the roll yet. I compared the number of sprocket holes to a brand new roll of the same film - exactly the same. I looked at the end of the lead but there was no bend.
Finally - I noticed that the roll had very tiny scratches on it in the glare from my bedroom light, I compared the glare to a brand new roll and it was completely smooth. When in doubt try this method and see if it works for you. :)
Answer: Unused Kodak 35mm rolls have the tail, plus the ramp, right up to the full width of the film, exposed for three sprocket holes.
In my experience, auto rewind cameras set to "leave tail" will either rewind until all of the upper row of sprockets are within the canister, or with a longer length of the full width of the film than three sprocket holes. (IIRC, it was an option to choose between tail-out styles on some cameras, as the "more lightproof with film in slit vs. more lightproof with tail fully rewound" was a favorite flame war of the primordial pixel-peepers back in the day.)
You may have run into a roll of film where the photographer fiddled with it until there were exactly three sprockets exposed, or the film may have expanded or contracted on the spool over the years so there's two or four sprocket holes exposed, but it's a good guideline.
A GIS for "Fuji 35mm film roll" indicates that either 2 (Fuji Pan) or 4 (Velvia) sprocket holes are exposed for that company's product. I think it's a good bet that anything less than 5 or greater than 0 means it's unexposed
Answer: I use Fujifilm and Ilford, and I find that they have the tab, ramp and about 2 sprocket holes of the full width film outside of the casing, as new.  This is a good indication that the film is 'new'.  It is a million to one that you rewound a film just exactly to the point that the manufacturer sets!  Once, I had a film that I was sure I had not used, albeit, it only had the tab exposed (strange: I know I have not used it, but it doesn't look like a new roll): Carefully, with my fingertips, I pulled out some of the film so that the ramp and a couple of sprocket holes of the full-width film were exposed.  Had a look and saw fingerprints that would not have occurred in the factory.  So it had been exposed after all!
Answer: Better photo labs will offer a service called a "clip test". This is where they extract just the first few inches of the film from the cassette and cut (clip) off that portion. They'll develop just that portion, and in an ideal world, it will give you an indication of how to proceed. Note that this can also destroy a frame, because they might cut right through the frame.
If you are getting a lab to do a clip test in order to determine if the film has been exposed or not, do tell them – it could be useful to know the purpose of the clip test in advance.