Follow-up 2: Copy File, remove spaces in specific lines

Question: This is an iterative review: The Original Question | Follow up 1
Differences to Follow up 1
This iteration tries to take the previous review to heart and see how it turns out. It sacrifices the flexibility to easily exchange sourceReader/sinkWriter classes that may read/write from different sources/sinks and specify that they read/write as BufferedReader/PrintWriter from/to files specified in the arguments in order to make the program less bulky. I'm unsure how to evaluate this change because I see reasons pro flexibility/bulky program as well as contra flexibility/bulky program. For the magnitude of this program and its actual task, I guess it might have been overkill.

Here the relevant sections of the previous questions:

The task itself is to go through a large .txt file that contains lines with ">" as their first character and to remove all spaces in
  these lines. I am using this program to modify files in FASTA format,
  a format often used in biology.
Algorithm

Read next line from input file and store in "line"
If "line" contains ">" as first character, remove all spaces in "line"
Print "line" to output file
If next line is not null, go back to Step 1

Changes to Argument Handling
In the process I also updated the argument handling process with my custom-written classes. Argument handling is still done by an ArgumentHandler, custom for every program, and an ArgumentCollectionImplementation class that implements the interface ArgumentCollection.
The ArgumentCollectionImplementation contains a List of all flags possible for this program upon instantiation (including a default String to print if -h is called) and gets the arguments of these flags added to it during argument parsing. It contains methods to receive and change one or all arguments of a given flag as well as methods to add and test arguments for int/double.
Setting default values of arguments, throwing errors if mandatory flags don't have an argument and similar tasks are all handled by the ArgumentHandler, implementing interface Configuration (of which I see very little use outside of this program) that provides the necessary methods getSinkFile()and getSourceFile() for the Client. Since the ArgumentHandler is program specific, it makes only sense to include it as private static class of the Client RemoveSpacesClient.

Client - including ArgumentHandler
public class RemoveSpacesClient {
    private static class RemoveSpacesArgumentHandler implements Configuration {
        private ArgumentCollection arguments;

        RemoveSpacesArgumentHandler(String[] args) {
            /*- Define all allowed Flags in the ArgumentCollection and add text for help flag:
             * -i: input flag
             * -o: output flag
             * -h: help flag*/
            String[] argumentList = { "-i", "-o", "-h", "Text to display if -h is called" };
            arguments = new ArgumentCollectionImplementation1(argumentList);

            /*- Parse arguments and add them to their associated flags in the ArgumentCollection*/
            arguments.parseArguments(args);

            /* Test mandatory flag -i for arguments */
            if (!arguments.flagHasArguments("-i")) {
                throw new RuntimeException("Mandatory flag -i was not specified");
            }

            /* Add a default argument to flag "-o" if it has no argument */
            if (!arguments.flagHasArguments("-o")) {
                arguments.addFlagArgument("-o", 0, arguments.getFlagStringArgument("-i") + ".nospace.txt");
            }
        }

        public File getSourceFile() {
            return new File(arguments.getFlagStringArgument("-i"));
        }

        public File getSinkFile() {
            return new File(arguments.getFlagStringArgument("-o"));
        }

        public void printArguments() {
            arguments.printArguments();
        }
    }

    private static void printProgramProgress(int i) {
        if (i % 1000000 == 0) {
            System.out.println(i / 1000000 + " * 10^6 lines written.");
        }
    }

    public static void main(String[] args) throws IOException {
        Configuration arguments = new RemoveSpacesArgumentHandler(args);

        System.out.println("Starting Program with the following arguments: ");
        arguments.printArguments();

        BufferedReader sourceReader = new BufferedReader(new FileReader(arguments.getSourceFile()));
        PrintWriter sinkWriter = new PrintWriter(arguments.getSinkFile());

        /*
         * Write every line from source-file to sink-file. If the line is a
         * sequence name (first character is ">"), remove all spaces in it
         * before writing.
         */
        int i = 0;
        for (String line = sourceReader.readLine(); line != null; line = sourceReader.readLine()) {
            if (line.charAt(0) == '>') {
                line = line.replace(" ", "");
            }
            sinkWriter.println(line);
            printProgramProgress(++i);
        }
        sourceReader.close();
        sinkWriter.close();
        System.out.println("Finished!");
    }
}

In a seperate class "CustomInterfaces" I have also Configuration
public interface Configuration {
    /**
     * Returns the name and path of a file to read from in form of a String.
     */
    File getSourceFile();

    /**
     * Returns the name and path of a file to write to in form of a String.
     */
    File getSinkFile();

    /** Prints all arguments */
    void printArguments();
}

Requests

Am I correct in my assessment that a Configuration interface here is somewhat unnecessary, seeing as I think I would hardly be able to reuse the interface.
The Client code throws 4 places where Exceptions can occur:

When sourceReader is instantiated (FileNotFoundException),
when sinkWriter is instantiated (FileNotFoundException),
when sourceReader reads a line from source (IOException),
when sourceReader is closed (IOException).

I came to the conclusion that there is not a lot the Client can do in case any of these occur, baring terminal-User-interaction that force the user to re-enter incorrect arguments until the input no longer causes exceptions. As such I let main throw an IOException. Was that wrong?
Answer: In the following code :
    BufferedReader sourceReader = new BufferedReader(new FileReader(arguments.getSourceFile()));
    PrintWriter sinkWriter = new PrintWriter(arguments.getSinkFile());

    /*
     * Write every line from source-file to sink-file. If the line is a
     * sequence name (first character is ">"), remove all spaces in it
     * before writing.
     */
    int i = 0;
    for (String line = sourceReader.readLine(); line != null; line = sourceReader.readLine()) {
        if (line.charAt(0) == '>') {
            line = line.replace(" ", "");
        }
        sinkWriter.println(line);
        printProgramProgress(++i);
    }
    sourceReader.close();
    sinkWriter.close();
    System.out.println("Finished!");

if an exception occurs at any point, files may not be properly closed.
I won't show the java 6 idiom for managing this case (because it's ugly and if you are still using java 6 you really should upgrade your version) but if you are using java 7, you should use try-with-ressources to avoid all the unnecessary closes.
This is how it looks like :
try (BufferedReader sourceReader = new BufferedReader(new FileReader("yolo"))) {
    // do some stuff here
} // no need to close sourceReader

If you are using java 8+, you should take a look the new static methods in the Files class (nio package) and how to manipulate Stream objects.
About your Configuration interface, yeah... it's better removed, because it is so coupled to the rest of your code you will probably never have another implementation besides RemoveSpacesArgumentHandler.


Is it okay to post a one-line answer, or would those be better as comments?

Question: I always find it difficult to differentiate between a comment and an answer when I feel like the question can be "answered" in one line. But I'm generally reluctant to post an answer because I feel like I'm not being detailed enough. If you look at blackcompe's answer here, it is technically correct as it stands. But should it have more detail to actually qualify as an answer and not a comment?
Answer: If your proposed response can stand alone and actually answers the question, then it's perfectly okay to post it as an answer. Otherwise, you should post it as a comment.
Of course, obviously the better answers will generally be longer than one line. To bulk up the content, you might consider doing things like:

linking to the appropriate documentation
including a code sample
suggesting a superior alternative approach
cautioning against some things that people in the same situation commonly do wrong
adding superfluous bulleted lists

I will frequently post a comment instead of an answer when I'm either guessing at a solution, providing only a hint or a link, or otherwise unable/unwilling to write a complete answer. Ideally, someone else (including, potentially, the asker) will come along and expand my suggestion into a full answer.
Comment: +1 superfluous bulleted lists. noted. thanks :)
Answer: I think the policy of demoting simple answers to comments is hiding good, terse, answers in the comments section. I know at least I skip over them, because they rarely have good information.
So to answer your question: Yes, they need to be more complete to get past the moderators, even though they are technically fine without the unnecessary explanations.


Dimensional transmutation in Gross-Neveu vs others

Question:
Firstly I don't know how generic is dimensional transmutation and if it has any general model independent definition.

Is dimensional transmutation in Gross-Neveau somehow fundamentally different than in say massless-scalar QED or QCD?
I mean in the later two cases it shows up in doing perturbation theory - as in QCD, you calculate the 1-loop beta function and try to integrate it to get the flow of the coupling and in the answer you see that its possible to tradeoff the bare-coupling and the renormalization scale in terms of a fictitious mass scale.

But doesn't it happen in a fundamentally different way in Gross-Neveau?

In here because of chiral symmetry isn't it guaranteed that nothing will diverge in perturbation theory and no mass scale will appear perturbatively?
So the dimensional transmutation happens only when you try to exactly try to do the path-integral (..which only works may be in the limit of large number of Fermions..)
I mean - in general shouldn't one be surprised if no scale appears in doing perturbation theory?

Also if the above is true then what is exactly so special about Gross-Neveu comapared to say QED with massless Fermions? Why is it that in the former the masslessness is perturbatively stable but so is not true for massless QED?
How well do we know or can prove that RG flow will not break any symmetries of the classical Lagrangian?
Answer: Dimensional transmutation is of course not generic and is shown by few models, Gross-Neveu being one of those.
I guess fundamentals are the same, the theory has dependence on a dimensionless parameter which transforms into a dimensionful parameter.
All you have to find is the dependence of coupling constant on renormalization scale, which is also the case in Gross-Neveu (if you are reading Coleman).


Question about flagging topics that are a valid Q but also have a seperate main topic...

Question: If you ask how to add a quicklist to a launcher and get it answered (Case in question) and it then gets included into a main topic with several examples of how to add quicklists to a myriad of other launchers (Case in question 2) would that merit flagging the question? As a dupe or as a 'more complete topic'(?) Even though the question by itself is valid.
Answer: The question is not only valid, it is the source of the quicklist. IMHO, the best option would be for the posts in lists such as the quicklist one to link back to their sources where applicable. They are also good for searches, as the question solving your exact query (in the case of 'deadbeef quicklist') comes before the more generic list in the search result. If you go by the generic list, you have to search in the list as well.
Not to mention that other possible solutions would be left out if the original question was closed.
Answer: An alternate view of this would be to close the First question as a duplicate, then merge the answer into the quicklist question. Thereby giving the original answerer credit for the work via upvotes.


How to constantly see highlighted targets in Arma 2?

Question: Every time you exit the Esc menu, targets and objectives are highlighted briefly. I can't find the shortcut to do the same. Is there one?
Answer: This is depending on your difficulty settings.
There is no key, that you can use to show them directly.
While "veteran" or "expert" won't show you these overlays, "recruit" will show them every time. On "regular" they'll only show if you hit escape and get back into the game.
However I think you're playing Arma3 nowadays anyway. But it's really the same there. :)


Why was the close button moved to the left side in Ubuntu?

Question: I was using Ubuntu 9. After automatically updating it to 10, the minimize, maximize and close buttons that used to be on top right were moved to the top left. Among the three buttons, close was moved to the far left. Close is below Applications and above File. You have to look to the close button to close windows now. Why?
Answer: Mark Shuttleworth explains the reasoning behind this change on his blog.
The Ubuntu team wanted to gut the notification area (a.k.a. system tray) and add notification indicator menus instead.  They also added window indicators which function similarly to notification indicators, but for windows.  In order to add window indicators on the right side of the window bar, mirroring the notification indicator location, they needed to move the close/restore/minimize buttons to the left.  The plan is that by Ubuntu 11.04 the notification area will be completely phased out.
There is an API available so applications may start using the indicators soon.  If you can't stand this change, the buttons can be moved back by following tutorials online.
Answer: To switch it back follow these directions:

Press Alt+F2, then type gconf-editor
  and press enter. That's for opening
  the configuration editor.
Once on this editor, in the item tree
  at the left, you have to look for this
  path  app -> metacity -> general and
  you doubleclick on the field named
  button_layout.
Then, you have only to change the
  value field and put this:
menu:minimize,maximize,close

Edit: As far as "why?", see Trey's Answer.
Answer: If you want to change it, go to System -> Preferences -> Appearance and select a different theme
Comment: Which theme was the original?
Comment: Try Clearlooks.
Comment: Tried, but it was Ambience.
Answer: If you want to keep using this theme there's a solution here: http://www.junauza.com/2010/05/move-ubuntu-1004-window-buttons-from.html
I tried and worked fine here. Not sure how to move then back tough.


How can I paint walls properly without sanding due to possiblity of lead based paint?

Question: My husband and I are buying our first home. During the inspection, our inspector said there could be lead-based paint (due to the age of the house) under the several layers of existing paint, and although nothing is chipped or flaking, NOT to sand the walls (the sellers don't know if lead paint exists under the current paint, and I'd rather not sand the walls and take chances). To save money, we want to repaint the interior ourselves and I'm not quite sure how to do it properly without sanding the walls first. The walls are in good condition, with no holes or cracks, and are a cream color, and we intend to paint over it with another light color, but don't want it to look like we cut corners. What's the best way to paint over the existing paint and still have good results without sanding?
Comment: Has anyone actually tested to see if there is lead paint?  It is easy and cheap to test for, and either way it would probably be best for you to know if there is lead or not.
Comment: No, it was not included in our inspection, but it would be good to know, especially once we have kids in the house.
Answer: If the walls are in good condition then why would you even have to anticipate sanding?
Prepare the surfaces by cleaning them well using a bucket of hot water and TSP (trisodium phosphate) cleaner. Make sure to wear protective rubber gloves. This will get years of dirt and gunk off the walls to make it a good place for new paint to adhere. The TSP will even help to dull glossy surfaces.
I have also found that the cleaner "409" will also help to dull especially glossy paint surfaces but they do also produce products especially for the purpose.
Comment: You can tell I've never owned a home, or painted anything. Thanks, that was my thought-as long as we have nothing to patch over, I think a good cleaning,  priming, and paint job will suffice. Thanks!
Answer:
lead-based paint under the several layers of existing paint

Planning on attacking the walls with a belt sander? The lead paint will only be an issue if you actually sand the lead-based layer. Since most paint jobs don't require a complete strip you'll be fine. The point of sanding is to remove surface dirt and glossy finishes - a few passes with a hand sander is all you really need to do.
There will probably be places in the wallboard that need attention - in this case use a knife to open the crack up and patch it. sanding the patch material flush is the same idea - you will not be touching any old paint.
Comment: Nope, no attacks planned. Our inspector did mention it should not be an issue unless the walls are sanded, since nothing is cracked or chipping, so I think we'll be ok. Thanks for the advice!
Comment: I think you misunderstood. Paul means it should be OK to sand it lightly.


Why does coffee taste better out of ceramic cups compared to a paper cup?

Question: I usually drink double espressos and they always seem to taste much better out of a ceramic cup compared to take-away paper cups. I ordered 2 back to back from the same shop within half an hour yesterday, one in a ceramic cup and one to go (I have a coffee drinking problem...) and the difference was still there - so same barista, machine, beans etc. Why is this? For sushi you are told not to eat it with a metal fork since it will supposedly taint the taste, so could this be similar?
Comment: Hello and welcome to [coffee.se]! Is this a small, conventional, waxed paper cup, or is it something special? What kind of difference do you notice between the cups -- e.g., mouthfeel/astringency, bitterness, sourness? Despite the similarity of the situation (same barista, etc.) you might still be getting a slightly different product from one pull to the next. Separately, you use the sushi tainting clearly as just an analogy, but I haven't heard that; you could probably roll *that* into a question at [cooking.se]! :)
Comment: Hi, it's a standard paper cup you get at most places serving take away beverages. I'm assuming it's waxed but I'm not 100% sure . I've experienced this many times, the situation where I ordered 2 drinks back to back was only an example. The sushi example seems reasonable as you can take a fork and lick it and you'll taste metal. I've been advised not to do it in several restaurants so far (eating sushi with forks, not licking them) :) I don't know whether this reasoning is true though or whether it's just an etiquette thing.
Answer: Both cup material and temperature are in play here, I think.
A big part of the coffee taste (and experience as a whole) is the aroma. I personally find that paper cups (not surprisingly) smell and taste like paper. Ceramic (or glass, porcelain, etc.) should be practically neutral. Any smell you get from the cup could affect the perception of taste of the contained beverage. If the cup has a plastic lid, that could contribute both to its own smell, or holding-in / reducing the coffee aroma that you smell, also. (Aside: there are some interesting links to the physiology of smell and taste interplay at the Wikipedia article on taste.)
The very experience of drinking from a paper cup versus a ceramic cup is different; heft, shape, handle, other aesthetics, etc., though this probably reduces to personal preference.  For example, I find sometimes that my lip sticks to the outside of the paper cup, which is unpleasant (to me, anyway :). A plastic lid could be a factor here as well.
Temperature may also be a factor. For example, temperature can affect the perception of bitterness. A properly pre-heated ceramic cup/demitasse will help the brewed coffee be at a consistent temperature (without shocking it after pull) and keep it warmer for longer (so it doesn't cool down too quickly). Such temperature changes could result in a difference in taste; keeping brewed coffee at a consistent temperature is recommended -- that and some other general properties are listed here. Temperature stability of the brew will probably be different between paper and ceramic.
Comment: Thanks, especially for the coffee faq link :) I had no idea that temperature fluctuations were that important but this makes a lot of sense. Also the smell, I definitely smell paper while drinking as well. One thing I forgot to mention was that the cups at my coffee dealer are brown, and according to [this](http://www.flavourjournal.com/content/3/1/10) that might make a difference as well.
Comment: Temperature can affect, for example, the perception of bitterness (link added above). Interplay between things like smell, taste, and temperature is (to me) fascinating. In that vein, the link you sent is fantastic -- suggesting that the *color* of the vessel influences the perception and experience -- thanks for posting!
Comment: It is, it also seems to be a science on its own :) Also if you check the references section of that article you'll see that there is quite a lot of work on this topic apparently.
Answer: Keep in mind that paper cups are manufactured. I have been in industrial plants my whole career.  There are odors, vapors and minute particles in the air that get packaged with the product.  They are not harmful per say but are released into the hot beverage on contact and could likely impart a flavor.
Comment: Makes sense, I guess that's what they are trying to avoid by waxing the cups. I think it's strange though that serious coffee shops (this one offers, courses on coffee history, prep, barista techniques etc.) don't mention this anywhere.
Answer: We at Delpac manufacture paper coffee cups.  The inside of the paper is PE polyethylene coated (not wax).  There should not be a taste per se from this material but there is a different "experience" from using a ceramic cup or mug.
Comment: I guess the question was **why** there is a difference.
Comment: I guess it could be subjective, but for me the taste differs. The "experience" could have an effect though.


What does this sentence mean "Mes amis sont légers mais la situation n'a rien d'une blague."

Question: I know what it means, however, I don't know how to phrase this. I know it says my friends are, but then in "légers" I'm confused a bit. I just get stuck on the word légers since I know it means something along the lines of light or slight. I know what the phrase is saying, however, I don't know how if I'm right. The best thing that I've come up with is "My friends are making light of the situation, but it's not a joke".
Comment: "my friends are easy-going, but this situation is no joke". My guess is: It could be for example, you made a joke that is extremely offensive about your friends, and you think they'll not make a big deal about it because they are easy going but they are taking the joke seriously.
Comment: Or the situation is tragic, but the friends can still make light of it
Answer: It is rare to see this kind of sentence with this acception of légers in everyday life. People would usually describe the situation as: Mes amis prennent la situation à la légère, instead of characterizing their friends as légers (that would certainly make it less confusing).

Léger : Qui manque de sérieux, qui fait preuve d'imprudence

French people will say: Mes amis prennent la situation à la légère. This means their friends are not putting unnecessary pressure on themself whereas the situation shoud be taken seriously. Translation: taken lightly.
Answer: This sentence is not that easy to understand, even for a native speaker. I have an interpretation, but it depends on the context.
Could you maybe provide some context for your sentence? Where did you read it? What was the speaker talking about before?
Anyway, here's my interpretation: léger can be used in the phrase "un ton léger", meaning "a light tone", or "light-hearted", when you're not too serious about something.
The sentence would then mean something like:

My friends are light-hearted [when talking about it], but the situation is no joke.

I assume the text is from a book or a play, because omitting the part about the ton would then be a stylistic figure of speech. It needs the reader to make some effort to understand the sentence, making it more subtle and interesting.
Does that make sense in the context of your sentence?


How to Recover from a Spin in Cessna 172?

Question: How to recover from a spin in a Cessna 172 ? What are the different maneuvers that a pilot would have to use to to do so?
Comment: The C172 recovers very easily from spins - in fact you usually have to force it to enter one and then hold it there - so [this question](http://aviation.stackexchange.com/q/11246/62) might also be interesting
Comment: In a 172 just let go of the controls, it'll fly itself out. Just recover from the steep spiral without over-g or over speeding.
Comment: Isn't it described in the operating handbook? Nevertheless, in the aircraft I've received instruction: C-152, Piper Cherokee, Piper Tomahawk, all the same: (1) full opposite rudder until rotation stops, (2) lower nose to regain airspeed, (3) recover from dive and apply power.
Comment: Some of the above answers-in-comments show why it's a good idea to go to the POH for an answer.
Comment: A few of these coments omits (forgets?) the most important part of PARE, power off!  IRL the same applies, it is not uncommon to forget pulling power to idle.
Answer: The memory aid is PARE:

POWER to idle
AILERONS neutral
RUDDER on the floor opposite the direction of spin
ELEVATOR nose-down to break the stall

You will want to read the full explanation in the Pilots Operating Handbook or POH for an understanding of the steps and why you need to take them. Commit the sequence above to memory and better yet get spin training from a qualified instructor.
The POH for the 172N model reads (caps and boldface in original):

Should an inadvertent spin occur, the following recovery procedure should be used:

RETARD THROTTLE TO IDLE POSITION.
PLACE AILERONS IN NEUTRAL POSITION.
APPLY AND HOLD FULL RUDDER OPPOSITE TO THE DIRECTION OF ROTATION.
JUST AFTER THE RUDDER REACHES THE STOP, MOVE THE CONTROL WHEEL BRISKLY FORWARD FAR ENOUGH TO BREAK THE STALL. Full down elevator may be required at aft center of gravity loadings to assure optimum recoveries.
HOLD THESE CONTROL INPUTS UNTIL ROTATION STOPS. Premature relaxation of the control inputs may extend the recovery.
AS ROTATION STOPS, NEUTRALIZE RUDDER, AND MAKE A SMOOTH RECOVERY FROM THE RESULTING DIVE.

NOTE
If disorientation precludes a visual determination of the direction of rotation, the symbolic airplane in the turn coordinator may be referred to for this information.

Other Spin Recovery Methods
The methods below may or may not recover from all spins. Seek out a qualified instructor for spin training — or, better yet, avoid spins altogether!
Finagin

Finagin advocates a four-step recovery technique for unintentional spins and departures from controlled flight that pilots can put to use without hesitation — and without fear of making the situation worse — even when they're confused or disoriented by the unusual attitudes and strange sensations that can accompany spins.

Rip the power to idle.
Forcefully neutralize the stick and rudder pedals.
Look at the airspeed indicator, and once it shows 100 knots or more (roughly 1.4 times the airplane's stall speed) …
Pull out of the dive.

Source: AOPA
Beggs-Mueller

Power – Off.
Remove your hand from the stick.
Apply full opposite rudder until rotation stops.
Neutralize rudder and recover to level flight.

Source: Spins in the Pitts Special by Gene Beggs
Hands In Your Lap
Some advocate the "hands in your lap" method of pulling power, taking your hands (and feet) off the flight controls, and waiting for the airplane to fly itself out of the spin. This may work for certain airframes but not all. Catherine Cavagnaro of Ace Aerobatic School says she likes to perform spin training in a Cessna 152 because that airplane will not self-recover from a spin.
Comment: I don't know if its just me... but I've found the many "memory aids" in aviation to be more difficult than just rote memorization... when trying to recall,  is it PAIR? or PARE?  What exactly is TOMATO FLAMES?  A FAST MOOSE? APES? RAW FAT?  These aren't helping me. :)
Comment: That's the NASA answer. It works in many but not all airplanes. In particular, some airplanes need a very swift push forward on the stick to break the stall while in the spin. Neutral elevator won't do it.
Comment: Once I found myself in that situation, and got so scared, that I forgot which pedal should be pushed... Fortunately, I had enough altitude, kept pushing the stick, and the plane flew out of the spin by itself...
Comment: A key point here is `If disorientation precludes a visual determination of the direction of rotation, the symbolic airplane in the turn coordinator may be referred to for this information.` I've heard if you haven't been in a spin before (or very often) it is hard to tell what direction you are actually spinning, so looking at the turn coordinator can help you figure that out.
Answer: I always taught my students the acronym PARE:
P: Power idle. This reduces the airflow over the tail. This may seem counterintuitive, but it's about helping to lower the nose and break the stall. The less airflow over the tail, the lower its downward lift component will be. This will in turn allow the aircraft's nose to drop, helping to break the stall.
A: Ailerons neutral. This may also seem counterintuitive, as your natural urge will be to put opposite aileron in to level the wings. But in a stall, one wing is more stalled (higher angle of attack) than the other. Let's say it's the left wing. If you were to add right aileron to bring that left wing back up, that means that the left wing's aileron will go down in an attempt to create more lift on that wing. But by lowering the aileron on that wing you will actually be increasing the angle of attack on that wing, which in turn will only deepen the stall on the wing and worsen the spin.
R: Rudder full opposite the spin. This is the key step, and in most Cessnas will be enough on its own to dampen or end the spin pretty fast. It counteracts the yaw and roll of the spin.
E: Elevator nose down to break the stall (after applying the opposite rudder). This will be like an exaggerated stall recovery, as you will likely have a very nose low attitude. However, this step is key on some aircraft to break the stall.
All aircraft have different stall and spin characteristics. Some are certified for spins, some aren't but will recover easily, and some will not recover well at all. Consult your aircraft's POH to learn about your aircraft's characteristics and certifications, and don't attempt to learn by yourself; always fly with an instructor if you intend to practice spin recoveries.
Answer: First lesson from my CFI to recover from a spin:  Feet on floor, hands in your thighs.  This is called the Beggs/Mueller recovery technique.
The 172 is a "stable" plane.  So, as i understand it, if it were dropped from upside down or on its side from a cargo plane, it will right itself.
Comment: I wonder if what was stated in this answer really works for all allowable CG positions for this aircraft.  Two people in front may be a world of difference than lots of weight in back too.  I would trust the POH advice more than this recommendation.
Comment: Well, this goes against what the Pilot's Operating Handbook says. I'm not saying that a Cessna 172 *won't* recover from a spin if you just take your hands and feet off the controls, but I'm wary of any advice that contradicts the POH.
Comment: From someone who has done it in a 172, this is a stable plane.  If you stall, just let go of the yoke but KEEP THE NOSE STRAIGHT WITH THE RUDDER PETALS.  You still have control of your rudder, work those petals.  The nose will gently drop (with maybe a little shudder), nose down with elevator and recover,  Do not apply ailerons until you are flying.  You can work on power on and power off stalls with your instructor.  Use PARE.
Comment: Hi Bill, welcome!  I've added a link to the technique to your post.


How does tire pressure vary with altitude?

Question: How does measured tire pressure vary with altitude?  If I inflate a tire to the recommended cold pressure of 30 PSI in Yellowstone (elevation 8000 feet), then drive to Big Timber (elevation 4000 feet) and measure the pressure the next morning at 26 PSI, does this mean I have a slow leak, or is this due to the change in atmospheric pressure?
Answer: I won't go into a whole lot of detail, but read this article here. http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=167
Pay special attention to this part as it pertains directly to your question.

Since a tire mounted on a wheel essentially establishes a flexible airtight (at least in the short term) pressure chamber in which the tire is shaped and reinforced by internal cords, it retains the same volume of air molecules regardless of its elevation above sea level. However, if tire inflation were set with a tire pressure gauge at sea level (where the atmospheric pressure of 14.7 pounds per square inch is used as ambient atmospheric pressure by the gauge), the same tire pressure gauge would indicate the pressure has increased at higher elevations where the ambient atmospheric pressure is lower. Those measured at the 5,000-foot level (where an atmospheric pressure of only 12.2 pounds per square inch is the ambient pressure) would indicate about 2-3 psi higher than at sea level. On the other hand, traveling from a high altitude location to sea level would result in an apparent loss of pressure of about 2-3 psi.

With that being said, your tires should be fine. If you're worried about it, just inflate your tires to the recommended pressure at the altitude that you spend most of your time at. The differences in altitude will cause varying readings on your gauge, but the pressure inside of the tire itself is contained and has a constant volume.
Answer:
How does measured tire pressure vary with altitude? If I inflate a tire to the recommended cold pressure of 30 PSI in Yellowstone (elevation 8000 feet), then drive to Big Timber (elevation 4000 feet) and measure the pressure the next morning at 26 PSI, does this mean I have a slow leak, or is this due to the change in atmospheric pressure?

The important thing to notice is that tires (sans leaks and temperature changes) have a constant absolute pressure inside, but what any gauge tells you is the pressure difference.
Example: I have a fat-tired bicycle that uses around 0.5 bar pressure (gauge reading). If I inflate it at room temperature to 0.5 bar (gauge reading), it actually has 1.5 bar. Pressure is proportional to temperature so 22 degrees Celsius room temperature (295.15 Kelvins) reduces to -10 degrees Celsius (263.15 Kelvins) so pressure is now 1.5 bar * 263.15 / 295.15 = 1.3374 bar. The pressure difference is thus 0.3374 bar. So for these kinds of bicycles, you have to be precise what your intended working temperature is. Inflating the tires at some other temperature is a problem.
A similar problem occurs with altitude. If you have 30 PSI at 8000 feet, it's at 10.91 PSI ambient pressure. Thus the pressure is actually 40.91 PSI. Then lowering to 4000 feet (12.68 PSI) you have 40.91 PSI absolute or 28.23 PSI relative.
Thus, the possibilities are as follows:

Your tire had 30 PSI relative, it reduced due to altitude to 28 PSI relative and then you lost 2 PSI due to a leak.
Your measurements are not precise and the apparent 2 PSI leak was due to imprecise measurements
Temperature had an effect. For example, if the 30 PSI was measured when the tire was hot, and the 26 PSI was measured when the tire was cold, it is very well possible that of the 4 PSI difference, 2 PSI was due to altitude and the remaining 2 PSI was due to temperature. (See the fatbike example -- car tires have a far higher pressure than fatbikes so the problems are not as prominent as for fatbikes, but the problem is that temperature still has an effect on tire pressure.)

The apparent 2 PSI leak can for example be caused by 15 degrees Celsius reduction in the tire temperature. If the ambient temperature reduced by this amount, there's your problem! If not, it could be that the 30 PSI was measured when the tires were warm from driving, and the 26 PSI was measured when the tires had not been driven for a long time and were thus cold.
Answer: True enough, but the author does not also factor in Temperature which also affects psi.  So as the ambient temp increases 10 degrees, tire pressure will increase 1 psi, assuming no change in altitude.  But that increase in psi is off set if you are increasing in altitude because atmospheric pressure decreases as altitude increases.
So if your psi is say 40 at sea level, it will be almost 46 psi at 8,000 feet above sea level.  But it will also probably be colder at 8,000 feet than at sea level.  So assuming ambient drops from say 80 at sea level to 40 at 8,000, temp alone would drop your psi about 4 psi, so adjusted to altitude, your net change in psi is only 2 psi more after factoring in BOTH temp and altitude.  And in the winter, ambient at 8,000 feet could easily drop to 20, so your net change in psi would be 0.


Stopping criteria for iterative linear solvers applied to nearly singular systems

Question: Consider $Ax=b$ with $A$ nearly singular which means there is an eigenvalue $\lambda_0$ of $A$ that is very small. The usual stop criterion of an iterative method is based on the residual $r_n:=b-Ax_n$ and regards the iterations can stop when $\|r_n\|/\|r_0\|<tol$ with $n$ the iteration number. But in the case we are considering, there could be large error $v$ living in the eigenspace associated with the small eigenvalue $\lambda_0$ which gives small residual $Av=\lambda_0v$.  Suppose the initial residual $r_0$ is large, then it might happen we stop at $\|r_n\|/\|r_0\|<tol$ but the error $x_n-x$ is still big.  What is a better error indicator in this case?  Is $\|x_{n}-x_{n-1}\|$ a good candidate?
Comment: You may want to think about your definition of "nearly singular".  The matrix $I \cdot \epsilon$ (with $\epsilon\ll 1$ and $I$ the identity matrix) has a very small eigenvalue, but is as far from singular as any matrix could be.
Comment: Addendum: I think the following paper pretty much adresses the ill-conditioned systems you worry about, at least if you are using CG: Axelson, Kaporin: Error norm estimation and stopping criteria in preconditioned conjugate gradient iterations. DOI: 10.1002/nla.244
Comment: Also, $||r_n/r_0||$ seems like the wrong notation. $||r_n||/||r_0||$ is more typical, no?
Comment: What about $\| b - Ax \| / \| b \|$? and what is your algorithm, exactly?
Comment: Yes, you are right, Bill! I will correct this mistake.
Comment: Thanks, Martin! I use GMRES. For your method, there could still be some error in the nearly null space of $A$, could not?
Answer: Please never use the difference between successive iterates to define a stopping criteria. This misdiagnoses stagnation for convergence. Most nonsymmetric matrix iterations are not monotone, and even GMRES in exact arithmetic with no restarts may stagnate for an arbitrary number of iterations (up to the dimension of the matrix) before converging suddenly. See examples in Nachtigal, Reddy, and Trefethen (1993).
A better way to define convergence
We are usually interested in the accuracy of our solution more than the size of the residual. Specifically, we might like to guarantee that the difference between an approximate solution $x_n$ and the exact solution $x$ satisfies $$|x_n - x| < c$$ for some user-specified $c$. It turns out that can achieve this by finding an $x_n$ such that $$|A x_n - b| < c\epsilon$$ where $\epsilon$ is the smallest singular value of $A$, due to
$$\begin{align}
|x_n - x| &= |A^{-1} A (x_n - x)| \\
& \le \frac 1 \epsilon |A x_n - A x| \\
& = \frac 1 \epsilon |A x_n - b| \\
& < \frac 1 \epsilon \cdot c \epsilon = c
\end{align}$$
where we have used that $1/\epsilon$ is the largest singular value of $A^{-1}$ (second line) and that $x$ exactly solves $A x = b$ (third line).
Estimating the smallest singular value $\epsilon$
An accurate estimate of the smallest singular value is usually not directly available from the problem, but it can be estimated as a byproduct of a conjugate gradient or GMRES iteration. Note that although estimates of the largest eigenvalues and singular values is usually quite good after only a few iterations, an accurate estimate of the smallest eigen/singular value $\epsilon$ is usually only obtained once convergence is reached. Before convergence, the estimate will generally be significantly larger than the true value. This suggests that you must actually solve the equations before you can define the correct tolerance $c\epsilon$. An automatic convergence tolerance that takes a user-provided accuracy $c$ for the solution and estimates the smallest singular value $\epsilon$ with the current state of the Krylov method might converge too early because the estimate of $\epsilon$ was much larger than the true value.
Notes

The above discussion also works with $A$ replaced by the left-preconditioned operator $P^{-1}A$ and the preconditioned residual $P^{-1} (A x^n - b)$ or with the right-preconditioned operator $A P^{-1}$ and the error $P (x_n - x)$. If $P^{-1}$ is a good preconditioner, the preconditioned operator will be well-conditioned. For left-preconditioning, this means the preconditioned residual can be made small, but the true residual may not be. For right preconditioning, $|P(x_n - x)|$ is easily made small, but the true error $|x_n-x|$ may not be. This explains why left-preconditioning is better for making error small while right-preconditioning is better for making the residual small (and for debugging unstable preconditioners).
See this answer for more discussion of norms minimized by GMRES and CG.
The estimates of extremal singular values can be monitored using -ksp_monitor_singular_value with any PETSc program. See KSPComputeExtremeSingularValues() to compute singular values from code.
When using GMRES to estimate singular values, it is crucial that restarts not be used (e.g. -ksp_gmres_restart 1000 in PETSc).
Comment: ''also works with A replaced by a preconditioned operator'' - However, it then applies only to the preconditioned residual $P^{-1}r$ if $P^{-1}A$ is used, resp. to the preconditioned error $P^{-1}\delta x$ if $AP^{-1}$ is used.
Comment: Good point, I edited my answer. Note that the right-preconditioned case gives you control of $P\delta x$, unwinding the preconditioner (applying $P^{-1}$) typically amplifies low-energy modes in the error.
Answer: Another way of looking at this problem is to consider the tools from discrete inverse problems, that is, problems which involve solving $Ax=b$ or $\min ||Ax-b||_2$ where $A$ is very ill-conditioned (i.e. the ratio between the first and last singular value $\sigma_1/\sigma_n$ is large).
Here, we have several methods for choosing the stopping criterion, and for an iterative method, I would recommend the L-curve criterion since it only involves quantities that are available already (DISCLAIMER: My advisor pioneered this method, so I am definitely biased towards it). I have used this with success in an iterative method.
The idea is to monitor the residual norm $\rho_k=||Ax_k-b||_2$ and the solution norm $\eta_k=||x_k||_2$, where $x_k$ is the $k$'th iterate. As you iterate, this begins to draw the shape of an L in a loglog(rho,eta) plot, and the point at the corner of that L is the optimal choice.
This allows you to implement a criterion where you keep an eye on when you have passed the corner (i.e. looking at the gradient of $(\rho_k,\eta_k)$), and then choose the iterate that was located at the corner.
The way I did it involved storing the last 20 iterates, and if the gradient $abs(\frac{\log(\eta_k)-\log(\eta_{k-1})}{\log(\rho_k)-\log(\rho_{k-1})})$ was larger than some threshold for 20 successive iterations, I knew that I was on the vertical part of the curve and that I had passed the corner. I then took the first iterate in my array (i.e. the one 20 iterations ago) as my solution.
There are also more detailed methods for finding the corner, and these work better but require storing a significant number of iterates. Play around with it a bit. If you are in matlab, you can use the toolbox Regularization Tools, which implements some of this (specifically the "corner" function is applicable).
Note that this approach is particularly suitable for large-scale problems, since the extra computing time involved is minuscule.
Comment: @HuiZhang: it isn't _always_ an L. If the regularization is ambiguous it may be a double L, leading to two candidates for the solution, one with gross featurse better resolved, the other with certain details better resolved. (And of course, mor ecomplex shapes may appear.)
Comment: Thanks a lot! So in loglog(rho,eta) plot we begin from the right of the L curve and end at the top of L, is it? I just do not know the principle behind this criterion. Can you explain why it always behave like an L curve and why we choose the corner?
Comment: You're welcome :-D. For an iterative method, we begin from right and end at top always. It behaves as an L due to the noise in the problem - the vertical part happens at $||Ax-b||_2=||e||_2$, where $e$ is the noise vector $b_{exact}=b+e$. For more analysis see Hansen, P. C., & O'Leary, D. P. (1993). The use of the L-curve in the regularization of discrete ill-posed problems. SIAM Journal on Scientific Computing, 14.  Note that I just made a slight update to the post.
Comment: Does the L-curve apply to ill-conditioned problems where there should be a unique solution?  That is, I'm interested in problems Ax = b where b is known "exactly" and A is nearly singular but still technically invertible. It would seem to me that if you use something like GMRES the norm of your current guess of x doesn't change too much over time, especially after the first however many iterations. It seems to me that the vertical part of the L-curve occurs because there is no unique/valid solution in an ill-posed problem; would this vertical feature be present in all ill-conditioned problems?
Comment: At one point, you will reach such a vertical line, typically because the numerical errors in your solution method result in ||Ax-b|| not decreasing. However, you are right that in such noise-free problems the curve does not always look like an L, meaning that you typically have a few corners to choose from and choosing one over the other can be hard. I believe that the paper I referenced in my comment above discusses noise-free scenarios briefly.


I am having orgasms while sleeping, specifically when i don't recite duas before sleeping

Question: I remember when my Arabic tutor told me girls who do not recite duas before sleeping are visited by jinns and they can cause physical harm if they have intercourse with them. For the past few days, due to some school related stress i couldn't recite duas and i started to have orgasms frequently in my dreams, now i am fearing something bad has been happening to me all those nights, i just want to know if this is actually true, that jinns can have intercourse with the women who do not recite Allah's verses before sleeping. And this specifically happens when i don't recite duas, as told before, and i noticed one night when i recited them and i had no trouble sleeping. Plus i am a teenager so is there any chance that puberty and hormones are causing all of this? I'd really appreciate if someone answers my question.
Answer: We may read in the sunnah:

Anas b. Malik reported:
  Umm Sulaim who was the grandmother of Ishaq came to the Messenger of Allah (ﷺ) in the presence of 'A'isha and said to him: Messenger of Allah, in case or woman sees what a man sees in dream and she experiences in dream what a man experiences (i. e. experiences orgasm)? Upon this 'A'isha remarked: O Umm Sulaim, you brought humiliation to women;may your right hand be covered with dust. He (the Holy Prophet) said to 'A'isha: Let your hand be covered with dust, and (addressing Umm Sulaim) said: Well, O Umm Sulaim, she should take a bath if she sees that (i. e. she experiences orgasm in dream).
  (Source Sahih Muslim, see also these versions in Sahih al-Bukhari, al-Muwatta', Jami' at-Tirmidhi and in Sunan abi Dawod etc.)

A bit off-topic:
Umm Sulaim is also the mother of the sahabi Anas ibn Malik.
This hadith in first place explains why the 'Aishah () uttered the statement:

'A'isha said: How good are the women of Ansar (helpers) that their shyness does not prevent them from learning religion.

Which one may find in another version of the hadith in Sahih Muslim, Sunan abi Dawod and Sunan ibn Majah.
Therefore it is a bad habit in Islam to remain silent and not ask if one has doubt or don't know about a manner it is even sinful and it is also a bad manner in Islam to accuse or denounce somebody who asks something that might be regarded as shameful in order to get knowledge.
We must all be aware that:

"All the sons of Adam are sinners, but the best of sinners are those who repent often."  (See for example in Bulugh al-Maram)

so accusing or hating somebody because of his sins is wrong.

The hadith shows that:

this is a natural thing and that women may also have nocturnal emissions.
anybody who has nocturnal emissions must perform ghusl in order to be able to pray and worship Allah.
Having these emissions is not sinful nor has any relation to jinn,

The Pen is lifted from the minor, the insane person and the sleeper."
  (See for example in Sunan ibn Majah)

but ghusl is required to reach the state of taharah (ritual purity) again.

Nevertheless as this happens while sleeping and is caused  by dreams we know also from the sunnah that:

"A good dream is from Allah, and a bad dream is from Satan; so, if anyone of you had a bad dream which he disliked, then he should spit on his left and seek refuge with Allah from it, for it will not harm him."
  (See for example in Sahih al-Bukhari and Sahih Muslim)

Therefore it is recommended to seek refuge from satan and perform the recommended du'a's before sleeping etc. further it is recommended to avoid watching at anything that may cause sexual arousal.
Comment: Thank you so much for clearing out my confusions, may Allah shower us all with His blessings.


Does drag increase with increasing bypass ratio in turbofan engines?

Question: Does drag increase as the bypass ratio increases in turbofan engines? Is there an analytical expression describing the increase in drag related to an increase in the fan duct diameter? How else might one consider this effect?
Comment: To me the bypass path seems to be a lower drag path than it would if it were going through the compressor, so it would (maybe I'm completely wrong) that increasing the bypass ratio wouldn't increase the drag vs the same size duct and a lower bypass ratio.
Answer: According to this 1975 NASA report on the effects of turbofan engine bypass ratio, the drag does increase for increasing bypass ratios. In the report, they use the following drag coefficient equation:
$$
C_{D,prop}=C_{D,nacelle}\cdot \frac{A_{nacelle}}{S} = \frac{D_{nacelle}}{\rho_\infty A_{nacelle}} \cdot \frac{A_{nacelle}}{S}
$$
As shown below, the nacelle drag coefficient initially increases for increasing bypass ratio.

Since $\frac{A_{nacelle}}{S}$ also increases with bypass ratio, the propulsion system drag will increase as well. So drag is closely related to the frontal area of the engine.

(images taken from report linked above)


Are there food combinations that are dangerous?

Question: Is there a combination of ingredients that will chemically interact to create poison?  I am interested in whether this possible with any common preparation method (e.g. via cooking, blending, whisking, microwaving) but not by burning the food or leaving the food out to be contaminated by bacteria.  I am interested in any ingredients that on their own are approved by some country's government as safe.
Comment: @Jolenealaska, a tiny bit too simple, see answer below. We discussed that in chat last fall, iirc.
Comment: Not a poison : but acids + bases might make for some discomfort.  (along w/ poprocks + soda)
Answer: Basically everything at all normal is safe.
There is a mushroom that gets toxic if combined with alcohol, but alcohol itself isn't 100% safe and if you're gathering wild mushrooms you need to be safety conscious, so it's not really something you could run into by accident or with storebought ingredients.
Relevant paragraph from Wikipedia

Consuming Coprinopsis atramentaria within a few hours of alcohol results in a "disulfiram syndrome". This interaction has only been known since the early part of the twentieth century. Symptoms include facial reddening, nausea, vomiting, malaise, agitation, palpitations and tingling in limbs, and arise five to ten minutes after consumption of alcohol. If no more alcohol is consumed, they will generally subside over two or three hours. Symptom severity is proportional to the amount of alcohol consumed, becoming evident when blood alcohol concentration reaches 5 mg/dL, and prominent at concentrations of 50–100 mg/dL. Disulfiram has, however, been known to cause myocardial infarction (heart attack). The symptoms can occur if even a small amount of alcohol is consumed up to three days after eating the mushrooms, although they are milder as more time passes. Rarely, a cardiac arrhythmia, such as atrial fibrillation on top of supraventricular tachycardia, may develop.
Comment: I've edited this to present the overall picture rather than just the one example, so that it's potentially helpful for folks being paranoid about accidentally poisoning themselves with routine cooking.
Comment: That's the case for the whole coprinus family to various degrees and a few others. Also note that this is not a poison per se, but that coprine stops the metabolism of alcohol.
Comment: To be fair, alcohol on its own is only sometimes safe, and you always have to be careful with wild mushrooms, so this still leaves us with no examples in which both ingredients are thought of as completely safe.
Comment: @Jefromi, although I would have liked an answer that uses food that is safer than alcohol, this answers the question as it is stated, hence I accepted it.  (On second thought, most countries do not rate alcohol as safe for children to drink, so it is debatable whether this answers my question).
Comment: @StrategyThinker I think it's a useful answer too, I'm mostly just saying that, if this is the best we can come up with, then the overall answer is basically no, nothing you mix will be poisonous.


Why is Russia considered a tricky destination for European football cup ties?

Question: In the light of Liverpool being drawn alongside Rubin Kazan in the Europa League, most news websites are terming it as a difficult or tricky tie. Similar things have been said in past for the Champions League when teams are drawn alongside any Russian club. But very few Russian league players are ever signed on by top sides. So why are Russian clubs considered to be tough teams to play compared to other European clubs?
Comment: I think that the insane salaries paid in Russia may very well have to do with why Russian league players are rarely signed by top clubs: they hardly have any financial reason to make a transfer to any but the absolute top clubs, for which most of them are just not good enough for.
Answer: It is tricky fixture. Because of many reasons,

A long travel for the away fixture is a headache.
The long travel doubles the headache, as the UCL or Europa fixtures will be played during the Mid-Week. Its too hard for the team, as they'll be too tired
And most importantly, it in Russia. It'll be very very cold. They might even have to play in snow.
Comment: Another reason (not only for russian teams, also for scandinavian teams) is that most of them are playing on artificial ground (or a mixture of artificial and natural ground).
Answer: It's a bit of an opinionated question actually, but I'll give it a go.
Niranjan's answer focus is with the practical side of the story, in the end it will be decided on the pitch so I'll stick to the game part.
Teams are divided in 4 drawing pots based on their UEFA club coëfficient, Rubin Kazan was in Pot 1, Liverpool in Pot 2. This means the average performance of Kazan over the last 4-5 seasons was better than Liverpool's.
Rubin Kazan has 45.576 points where as Liverpool has only 32.006.
Now, these coefficients tell more about the past than the present to be honest, but it gives a fair view on their performances in Europe.
You have England, Germany and Spain. Below them you've got France, Italy closely followed by Portugal and Russia. Russian teams like Kazan will lose to Chelsea, City,... Liverpool is not on the same level, so Kazan at home will make it very difficult for them.
Will most people say Liverpool has a better team than Rubin Kazan if you put each player from both sides next to each other? Probably. But that does not make it true. Same thing goes for what you read in the media btw.
As to why Russian league players are rarely signed by European top flight clubs, I'm going with money. Russian clubs pay very good money for their star players. Besides the money not many Russian players seem to be attracted to go play abroad.
Comment: Note that the system has changed a bit this year: the teams in pot 1 were the champions of the "top 8" leagues, independent of their UEFA coefficients.
Comment: True, just seven I think btw + CL winner, but as Barcelona won both PSV grabbed the open spot. But not so for Europa League if I'm not wrong.
Comment: Its not just the case for Liverpool this time... some time back in 2006 Arsenal were also worried about being drawn against CSKA Moscow in group stages of CL, that was when Arsenal had just reach champions league final in previous season (and they subsequently lost 1-0 to CSKA)... It was a similar situation when the then in form Manchester United were drawn against CSKA in 2009... I guess there is really something about english teams travelling to Russia for play...
Comment: The travelpart is mentioned by niranjan, as said, I focused elsewhere. I'm not denying it, I just saw no need to repeat it. ;)
Comment: @PhilipKendall Note: Liverpool is playing in the Europa League. The cup with the domestic champions are set in pot 1 is the Champions League.


Why did none of the neighbors call the Police despite the traps?

Question: In Home Alone 2: Lost in New York, despite of all the commotions caused during "Operation: Ho Ho Ho" (i.e. Marv getting hit with bricks in the street, a large kerosene explosion on the second floor, and the hail of varnish cans out by the front patio), why did none of the neighbors appear concerned enough to call the police?
Answer: This may be listed as goof on IMDb, but there is an explanation for this.
It seems no neighbor was concerned about calling the police, because probably no one saw it.
Remember it's midnight on Christmas. Everybody must be at either Church, or enjoying festival treats at sofa, or sleeping. If you look at the street where that house was located at was completely empty. No one was walking through the street at that time.
During winter time, we tend to stay inside at night unless we got some work to do. Nobody really pays attention to what happening outside unless it is too noisy which leads to the question why they didn't hear the kerosene explosion.
The kerosene explosion was too short to live. If it might have alerted any neighbor, they won't see anything because it didn't do any damage to the house from outside and since it's under-construction and all of them were inside the house, nobody would have really paid attention to it.
The other trap of varnish cans was too loud. But the people in the adjacent buildings seem to be sleeping or absent. Even if they were present, it'd take time to understand what happened and take a look outside. If they will look outside, they won't really see anything because all cans were in that section below the ground level. If they had come outside to look, both crooks had already left by then.
Comment: would be helpful to have some kind of source listed to back this answer up. I'm not saying this answer is wrong, but at this point it seems like this is just an opinion. Maybe someone could find something backing it up. I tried, but all I found was IMDB admitting it was just a plot hole.
Comment: If a question can be answered from the movie itself, then there is no need to add a source. It may be good to add if there is any, but it's not compulsory.
Answer: This is an admitted plot hole in the movie. Basically the neighbors don't call the police because it would ruin the rest of the movie by resolving it too quickly. You could get imaginative and think up reasons. But it is just a bad plot hole. One of many in this movie along with an unusually large number of "Goofs, Mistakes, and Errors" as can be seen at the website listed below. Some are actually quite interesting.
http://www.imdb.com/title/tt0104431/goofs


Why was question about PostGIS spatial functions closed?

Question: Why was the question Finding holes in proposed districts (Polygons/Multipolygons) closed?
Answer: It was closed as Off Topic because:

When seeking help to debug/write/improve code always provide the desired behavior, a specific problem/error and the shortest code (as formatted text, not pictures) needed to reproduce it in the question body. Providing a clear problem statement and a code attempt helps others to help you.

If you feel it was closed wrongly, vote to reopen it.
Answer: That question starts:

Thinking through something that I seek some SQL on:

so the question is seeking SQL code.
When I voted to close the question did not include anything like a code snippet that illustrated what they had tried and where they were stuck.
We are a little different from other sites. We are a Q&A site, not a discussion forum.  For questions that involve code we ask that users show us where they are stuck with their own code by including a code snippet in their question.  There is an edit button beneath their question which will enable them to do that and a <code>{}</code> button that enables them to format any highlighted code nicely.
We placed this requirement on coding questions here, and created a custom close reason for it, to prevent us becoming a code request service.  The discussions that led to that close reason include:

Guiding authors of code related questions to post actual code?
Shortest code to reproduce GIS programming problems
Tweaking custom close reason for poorly framed code debugging/writing/improving questions?

As soon as the user edited their question to provide more details the review queue introduced 7 new close/re-open voters to the question, and of those, 2 voted to still leave it closed, and 5 voted to re-open, and so it is now open.


What are the maximum number of pieces that can be checking a king at once

Question: Was just thinking about this. It's easy to have two pieces checking the king via a discovered double check, but three is where it gets interesting. Finegold said in a video he was TDing for a game and a player's king was in check from five different pieces. Sounds like an exaggeration, but I'm curious what input people have.
Comment: Finegold makes these sort of exaggeration five million times in every video
Comment: Can you post a link to the video, if it is publicly accessible? It would be interesting for context. Quintuple check is impossible unless illegal moves were made, which I suppose might happen with sufficiently clueless players, although even that seems unlikely (or maybe players playing a prank?)
Comment: @Phonon Would't call it a duplicate since my questions generalized to n checks
Comment: @itub actually an illegal position makes sense, since he was TDing for beginners.
Answer: If you have an unlimited number of pieces to place, and ignore the mechanics needed to get them there in actual gameplay, it's easy to show you can surround a king with eight queens and eight knights for a total of sixteen checks.
In actual gameplay, however, you have only fifteen non-king pieces to use, and there are serious difficulties in getting more than two pieces to an attacking position in the same move, remembering that the opposing player cannot leave his king in check after his own move.  Answers to this question even claim that triple check is impossible in standard chess, never mind quintuple.
Under standard rules, a double check can result from a move giving both a direct and a discovered check.  In the case of an en-passant capture, it is even possible to invoke a double discovered check, but the moving pawn is then not in position to give a third direct check.
It is also possible to consider more than two pieces to be "attacking" the opposing king, in the form of batteries (which would need to be set up via discovered check) or absolute pins.  However, these do not directly count as checking pieces, only as complications to the problem of getting out of check.
Do you have a link to Ben Finegold's video?  He's a respected player, so I'm sure there's some context being missed here.
Comment: He said something along the lines that he specifically wasn't joking, but since he was TDing for a beginners' tournament an illegal position makes sense. For some reason I never assumed that :)


When preparing a ristretto shot, should the brew time remain the same as a normale?

Question: I have heard that a ristretto shot is in the realm of 1:1.1-1.5  bean to coffee yield ratio here. Is the brew time to remain the same? I have used about 25s as a rule of thumb for my espresso shots. If so, the flow of coffee from the machine is very slow, but if not the shot can be completed very quickly. I have tried both preparations and prefer keeping the shot time constant. Is this the prevailing wisdom?
Comment: Thanks I edited it to keep the link and my post consistent!
Comment: I am not sure to understand the "coffee to bean" ratio? The link mentions "coffee to yield", which is different, if not mistaken.
Comment: How do you think about rephrasing the question title? It seems the real question is "Is the brew time to remain the same?". I was answering when I noticed that, and scrapped my tentative (for now).
Comment: Very true. My question and title did not match. I've updated as well.
Answer: The time could absolutely stay the same for both your ristretto and normale shots. But - for that to happen your grind is certainly going to have to change, and obviously your yield (since you are now pulling a smaller / ristretto shot).
An example:
If you pull a shot that's:
20g in | 25s | 20g out
And then you decide to pull a larger/normale shot, but you want to keep the time constant. Then you are basically forced to loosen your grind to a coarser grind size.
Then you could pull your normale at:
20g in | 25s | 30g out
Hopefully that answers your question!
Comment: I appreciate the analysis on how to keep the brew time constant, but my question really wanted to address if you should in the usual preparation. Saying that I could was a little unsatisfying as a definitive answer.
Comment: Ah I understand. Yes, the time should certainly be around the same exact length.


What are the pros and cons of using live CDs vs VMs for malware analysis?

Question: I'm planning on doing some malware research for a research project, and I was wondering what would be a better option for keeping my system safe from viruses accidentally infecting it.  I'm only planning on analyzing the binaries, not running them, but an errant click could happen.  Should I be trying to do this analysis in a VM?  Should I use a Live CD/Live USB boot (with some sort of forensic OS like Kali)?  I know some viruses can break out of VMs, so would that make the Live CD approach be better?  Or are there other things I'm not considering that makes the VM approach better?
Comment: As long as you will do analyz binaries, both options would work. Live or VM.
If you were to run them in a safe env. then neither would work because nowadays malwares tend to act differently on VM's and Live's than they do on the actuall device. Sometimes they don't run, and sometimes they run "differently", which makes you think oh these malwares are not so bad, but when you run them on primary OS, BOOM!
Comment: Related thread: [Is it safe to install malware in a VM](http://security.stackexchange.com/q/12546/32746).
Answer: The main two things that come to mind are the threats that can compromise you when using them.  In both cases, the threats are fairly rare.
For a VM, the main threat to your system is a virus that is able to exploit the hypervisor.  Such a virus would be able to escape the VM and infect your system.  VMs also have the benefit of being able to do a closer comparison to the state change caused by the virus to determine exactly what it does.
For a live CD, such a virus would be a hardware resident virus that is able to corrupt the hardware in such a way that it survives a reboot to your normal environment and is then able to spread.
Both are pretty unlikely to be problems from all but the best attackers, however, a hardware resident virus is a far bigger (if much rarer) threat than any software virus since it would be basically impossible to remove. Because of this, I would personally lean towards VMs, however the most truly paranoid individual could use a VM running off a live CD.
Comment: I don't know AJ Henderson's plan for using "a VM running off a live CD". But I am rather paranoid ;) One can install VirtualBox on Debian, add Crunchbang VM, and then use bootcd to create a LiveCD. With enough RAM, that will boot in a diskless machine.
Answer:
I was wondering what would be a better option for keeping my system safe from viruses accidentally infecting it. I'm only planning on analyzing the binaries, not running them

To summarize the simple answer:
Get a hex editor or whatever other tools you plan to use on an ARM-based NON-Windows smartphone or tablet to analyze Windows x86 binary malware.
The more complex options:

Look at the application (malware) you don't want to run on a processor that doesn't use the same machine code in the first place; i.e. look at an ARM or Power executable on a PC, look at an x86 or x64 virus on a Power or ARM chip, look at anything at all printed out on paper.

Watch out for cross-platform applications (malware) like Javascript, Java, Flash, and the like.

As John Deters said, (also) use an OS they don't run on.

Again, watch out for cross-platform applications (malware) like Javascript, Java, Flash, and the like.

Don't have any devices they can infect, i.e. have the virus on one read-only CD-ROM, and boot from a LiveCD on a machine with two x-ROM drives, one for the OS and one for the malware, or use a LiveCD on an x-ROM that can be removed easily afterwards (perhaps Puppy Linux or Parted Magic; Kali likely works too)

AFTER removing all floppies, hard drives, USB sticks, external drives, x-RW's, etc. etc. from the machine.
AFTER making sure that both the LiveCD and the x-ROM are 100% full, particularly in the case of Puppy Linux
AFTER doing your best to ensure that the malware you're using cannot infect BIOS at all (or at least not on the system you're using it on.

Alternately, if you're really really paranoid and have even a small budget (or friends who upgrade), use a used 100% throwaway machine (preferably from cast-off, ancient, useless parts), remove or destroy all the networking capabilities, and use x-ROM's to perform one-way transfers (except for printing on a throwaway printer).  Write malware and investigation tools to x-ROM's, load them in the throwaway machine,

Shred the x-ROM's after loading
You are allowed to print output.  Nothing but paper, light, and scraps comes from that setup machine ever again.
Use a sledgehammer on the hard drive(s) after you're done.
Triple-bag it in Ziplock bags with a layer of cheap towel in there; you want to watch out for glass shards.
Use the sledgehammer on the motherboard's BIOS after you're done.
If you're truly paranoid, sledgehammer the printer after you're done, too!
Dispose of it all after you're done.
Enjoy the fruits of your research and the bliss of hammering an infected machine into scrap!

Essentially, the paranoid goal is to prevent infection and to prevent spreading the infection you assume you got despite preventing it.
Answer: You can analyze them in an incompatible OS. Nothing says you have to study a Windows virus on a Windows machine. This keeps the risk of accidental infection of your test environment lower.
I've tested some malware in a virtual machine with no ill effects, but my experience is limited to some not-very-aggressive code. I suppose it's possible that you could make a mistake and infect your host. Code intended to attack a specific USB device could break the boundaries, too.
A LiveCD is also a good choice. Configure it to be write-locked so it won't mount writeable media unless you explicitly tell it to.
Comment: Some kind of modern virus are multi-platform...


'Companion Planting' Logic Puzzle - Is there an elegant solution?

Question: Problem: You're a vegetable gardener planning to plant out seedlings in a new garden bed, however your farmer's almanac has outlined a system of rules about what plants can and cannot be placed next to each other. Your job is to map out a garden bed/s that will provide the most benefits to the plants within.

Each Plant has 5 classes of companion plant associated with them, ranging from mutually beneficial plantings to stunting or being stunted by neighbour Plants.

For example, the rules for planting Carrots state;
i)  Mutually beneficial to Tomatoes and Leeks..
ii ) Receives Benefits from Onions and Rosemary.
iii) Provides benefits to Peas and Radishes.
iv) Has growth stunted by Dill and Coriander.
v) Stunts growth of Parsnip.

While Tomatoes state:
i ) Mutually beneficial to Carrots and Asparagus.
ii ) Receives benefits from Basil and Mint.
iii ) Provides Benefit to Gooseberries and Coriander.
iv ) Is stunted by Leeks, Onions, Fennel and Cabbage.
v) Stunts growth of Corn.
---

Each plant has a 'sphere of influence' that encompasses all plants with 2 spaces of it - Left, Right, Up, Down, Diagonally - so benefits or detriments affect those plants within those spaces. A plant does not have any effect on itself.

Graphically; o is the Primary plant, all x's around that plant are influenced by that plant's companion rules, all _'s are unaffected.
__________________
| _ | _ | _ | _ | _ | _ | _ |
| _ | x | x | x | x | x  | _ |
| _ | x | x | x | x | x  | _ |
| _ | x | x | o | x | x  | _ |
| _ | x | x | x | x | x  | _ |
| _ | x | x | x | x | x  | _ |
| _ | _ | _ | _ | _ | _ | _ |

Plants can be planted in rows, columns or clusters. There is a limit of 10 rows and 100 columns per plant bed. There are 50 sets of plants with associated rules (as per Carrots and Tomatoes above).  No limit to number of Plant Beds. You are required to lay out the maximum number of types of plants with the highest benefit scores (i.e - not just alternating rows of Carrots and Tomatoes and ignoring everything else).

So that's the basics of the rules. This is obviously not a complete problem for solving - I'm not looking for a 'solution' as such, for that you'd need to know all 50 plants and rules etc. What I'm looking for is more of a theory or problem solving logic that will help me create a 'map' of these plants. While I know it's possible to brute-force an answer through 'seating chart mayhem', I'd like to believe there's a more elegant mathematical/logical solution, I'm guessing something kinda like a venn diagram meets a weighted decision matrix - but... cleaner.

Full disclosure; This is not a homework question or logic puzzle. I'm actually looking to begin Organic Market Gardening myself, but after years of working in marketing all of the useful high school and college maths that works for problems like these has been replaced by analytics formulae, acquisition rates and social network models. I had to reach down into the depths of my mind just to bring up SOHCAHTOA so I could build an angled garden frame.

What I'm saying is, Any and All help is appreciated before I start cutting up pictures of plants and adding little score discs of 2+, 1+, 0, -1, -2 on a grid while constantly consulting rules that occasionally almost contradict each other.

Thank you all immensely in advance.
Comment: Did you mean "[...] with*in* 2 spaces of it"?
Answer: I think the answer is probably no.
Here's a much simpler but related problem. You have just two kinds of plants, carrots and tomatoes, on a square grid. Each cell in the grid either prefers carrots (you score +1 for planting carrots there, -1 for planting tomatoes) or prefers tomatoes (other way around). Each adjacent pair of cells either prefers to have the same kind of plants (score +1 if same, -1 if different) or prefers to have different kinds (other way around). Your goal is to maximize your score. The end.
Well, this is the problem of "finding a ground state of a 2d Ising spin glass with an external field" and it's NP-hard, meaning that (1) no efficient way to solve it is known and (2) if you found an efficient way to solve it, that would enable you also to solve a huge variety of other problems for which no efficient solution is known. (Here "efficient" has a technical meaning, namely that for some $d$ the time it takes to find the solution for a problem instance of size $n$ grows no faster than $n^d$.)
The problem becomes efficiently soluble if we take away the per-cell preference between carrots and tomatoes (leaving only the "interactions") -- but becomes hard again if we now, as in your problem, allow closer-than-nearest-neighbour interactions, even if it's just "next-but-one neighbour".
This doesn't prove that your problem is hard, because there are still plenty of differences between your problem and this one. But it's suggestive.
Rather than cutting up pictures of plants, I would suggest doing this on a computer, which can try things out much faster than you can. The simplest thing would be to make it try lots of random configurations and choose whichever one does best. Next simplest would be: after picking a random configuration, repeatedly try making small simple changes (e.g., change just one plant, or maybe swap a neighbouring pair) until you can't find any that make things better. Next simplest (which might actually be simpler, because there might be software out there that already does lots of the work) would be something like simulated annealing.
Comment: _"The problem becomes efficiently soluble if we take away the per-cell preference..."_

Ok - so we can make it simpler by saying that these plants are only sown in 'rows', rather than cells. That's an easy fix, but the 'Neighbour Row + 1' still makes it too messy to be 'efficient'?

From what I understand then, the best way to go about this would be to grid all plants against each other, and where they intersect, assign a score (-2 to +2)  based on their interaction, then choose the highest scoring interactions and work down through the interactions? Not 'elegant', but logical, I guess?
Comment: The "greedy" approach of always choosing the highest-scoring things first (if I'm understanding you correctly) surely can't be guaranteed to give the best results, but it might give pretty good ones, which may well be enough.

Making the problem one-dimensional by only planting in rows certainly makes it simpler. (I don't know exactly how much it helps in the case of the Ising spin glasses, when you have the distance-up-to-2 interactions, but it doesn't really matter because that's only an analogy anyway.)
Answer: I think there is a perfect solution to your specific query.
Knowing that there are overlaps of pros and cons (benefits/stunts and benefited by/stunted by) you can easily plan your garden.
I'll give an example of 5 plants :
+2 = Mutual benefits
+1 = Benefited By
0 = No Effect
-1 = Stunted By
-2 = Mutual Stunting
Plant A  |+2 B|+1 C | 0  |+1 D|-1 E|-2  |
Plant B  |+2 A|+1   | 0 C|+1 E|-1 D|-2  |
Plant C  |+2  |+1 A | 0 C|+1  |-1  |-2 E|
Plant D  |+2 E|+1 B | 0  |+1 C|-1  |-2  |
Plant E  |+2 D|+1   | 0  |+1 B|-1 A|-2 C|
Instead of 10 rows and 100 columns, I'll use a smaller grid of  5 rows and 10 columns to demonstrate a layout
|C|C|A|A|B|B|E|E|D|D| C and E are outside of each others influence [-2]
|C|C|A|A|B|B|E|E|D|D| A and B are paired as they have [+2]
|C|C|A|A|B|B|E|E|D|D| E and D are paired as they have [+2]
|C|C|A|A|B|B|E|E|D|D| B is buffered by E [+1] from D [-1]
|C|C|A|A|B|B|E|E|D|D| C gets no benefit from D [+1]
Should we increase the grid to 12x5 to demonstrate the repetitive pattern, then C does benefit from D [+1]
|C|C|A|A|B|B|E|E|D|D|C|C|.
Note:
Your crops are aligned for optimum growth and ease of harvest.
The numbers are arbitrary for demonstration purposes as plants also have different requirements such as water, temperature, season, etc.
Should you increase the number of plants and the benefit/stunt variables, you'll be looking at a different chart ;)
Regardless of what the variables are, you will need to group your beds according to the different requirements above, so you already have predefined sets which you are restricted to when formulating your tables.
A cluster structure using the same settings would look something like this:
|C|C|C|C|C|C|C|C|C|C|C|C|
|C|C|A|A|A|A|A|A|A|A|C|C|
|C|C|A|A|A|A|A|A|A|A|C|C|
|C|C|A|A|B|B|B|B|A|A|C|C|
|C|C|A|B|B|B|B|B|A|A|C|C|
|C|C|A|B|B|B|B|B|A|A|C|C|
|C|C|A|B|B|B|B|B|A|A|C|C|
|C|C|A|A|A|A|A|A|A|A|C|C|
|C|C|A|A|A|A|A|A|A|A|C|C|
|C|C|C|C|C|C|C|C|C|C|C|C|
Hope this helps.
I would like some literature regarding your almanac. Could you point me in the right direction?
Answer: As Gareth McCaughan says, there probably isn't a good method to solve this problem.
However, you might be able to find a sufficient solution by using so-called evolutionary algorithms (or other algorithms with the same principles).
For example, by randomly swapping crops each generation you obtain either a better or worse crop-layout and by doing this multiple times can increase your overall score.
The algorithm would not need to brute-force all possible solutions, but might find a nice solution in reasonable time.
Also you would probably be able to set it up in less then an hour if you have experience with evolutionary algorithms.
Answer: You don't provide quite enough info-- you say that you are required to layout the maximum number of types with the maximum benefit, but you need to specify more.  For example, of the 50 types, if some, say 5, have more detrimental effects, can you ignore or minimize those?  If you have to plant all 50, do they have to be in equal numbers?  If so, then it's a somewhat simpler problem.  Similarly, if you could pick only the best 50%, that would also be simpler.
If there were no minimum requirements, you could do it recursively-- start with one, then randomly select from the most beneficial neighbors, move along, repeat.  If there were more minimum requirements, you could track the total number of each type planted, and use that to weight the values of potential neighbors, so that eventually types not planted would have scores high enough.  That is, the higher percentage of the total a type had, the lower the relevance of its benefit.


Blood circulation - How to expand blood capillaries?

Question: Do blood capillaries expand? If yes, through what means can it be done? And can warm water also be used to expand blood capillaries?
Comment: It's considered a requisite on biology.se that at least some reading/research is carried out and presented with your question. For example, have you read about vasodilation and capillaries? Otherwise it will be closed as *homework*. The [site tour](http://biology.stackexchange.com/tour) and the [help center](http://biology.stackexchange.com/help)  provide guidance on how to use this site. Please take a few minutes to read about the kind of questions which are on topic here
Comment: @paul What do you mean by "expand"? Do you mean "increase the number of capillaries by angiogenesis" or "vasodilate"? Given the warm water example, I'm guessing it is the latter?
Answer: Capillaries are the smallest blood vessels. They are unique in that:

They don't have any muscular component like arterioles or venules do.
They are lined by a single layer of endothelium  (cells lining blood vessels are called endothelial cells) overlying the basement membrane.

Due to these reasons the capillaries are very permeable facilitating nutrient and gas exchange.
The capillaries don't expand as they do not have muscular or elastic components. However exposure to heat do increase the circulation. This is due to the following facts:

Exposure to heat dilates the pre-capillary arterioles - this would inevitably cause improved capillary circulation in capillaries that are already open.
Increase in pre-capillary flow opens up collapsed capillaries. In the human body roughly only one-fourth of the capillaries are open during rest1. As the pre-capillary arterioles dilate, the collapsed capillaries open up thus further improving circulation.

To improve capillary perfusion:

Temporary improvement can be achieved by activity (exercise), exposure to warmth, emotions (flushing is due to vasodilation), even exposure to cold causes vasodilation after the initial vasoconstriction
Permanent improvement of capillary circulation can be achieved by increasing capillary density. Capillary density refers to the number of capillaries present in 1 cm2 area. Capillary density can be increased by consistent anaerobic (isometric and to some extent isotonic) exercise.

References:
1: Boron and Boupaep text book of medical physiology, 2nd Edition, p.467
For more:

http://corporate.dukemedicine.org/news_and_publications/news_office/news/6597
http://www.ncbi.nlm.nih.gov/pubmed/8852622
Answer: Yes, some blood vessels change their diameter, they dilate or constrict. This is termed 'vasodilation' and 'vasoconstriction'. Large and mid-sized vessels contain smooth muscle in their walls. The walls of arteries tend to be stiffer than those of veins, to withstand high pressure coming from the heart.

Smooth muscle, when stimulated by the nervous system, can sustain contractions for long periods of time, and often with fine control. When smooth muscle in the walls of your blood vessels relaxes, those vessels will dilate.
Small capillaries do not have smooth muscle in their walls, but the flow of blood through them can be controlled by the larger vessels that feed them. When arterioles constrict, the capillaries they feed can have reduced flow.

Our nervous system takes in a lot of signals relevant to controlling blood pressure and flow, and controls these smooth muscles. Flow can be increased or decreased to individual organs when needed, like the intestine (after a meal), the muscles (during exercise), the skin (for heat exchange).
The question about warm water is actually quite interesting. Placing your arm in warm water will cause vasodilation in your other arm (the one not in the water), in order to lose some heat to the cold air and maintain your core temperature. Normally, the blood vessels in our 'extremities' (our hands and feet) are kept quite constricted to reduce heat loss with the cold air.
If we exercise or take a hot bath our core temperature will rise, some people will notice their skin gain a red hue after these activities, due to vasodilation.
Comment: Very little of this answer addresses the OP's question. Can you expand on what, exactly, increases capillary flow and how?
Comment: OP asks "by what means [can capillary expansion] be done?". As C Rags says capillaries don't have muscular or elastic components to their walls, but I (and he) have answered that the flow through them is controlled by contraction and relaxation of the smooth muscle of the arterioles that feed capillary beds. Flow resistance is inversely proportional to the diameter to the power 4 - decreases of diameter increase resistance steeply.

Are you asking what environmental stimuli & nervous input causes increased capillary flow? I can't answer that - there's many (google), and OP didn't ask that imo.
Comment: As I said (I did not miss the above), very little of your answer was a direct response to the OP's question. That remains a fact.
Comment: You're right. Honestly, I don't see much point in improving it: OP ought to read a textbook, as you commented. I tried to give some background since it can't be assumed from the question.
Comment: On 2nd thought, I disagree with you. All paragraphs of the answer contribute, having assumed OP knows little:
-Larger vessels have smooth muscle
-This smooth muscle changes their diameter
-Precapillary vessels control capillary flow
-Circulation is influenced by many things
-Warm water is one

The issue is purely that the question lacks any background awareness of vasodilation. I think the answer is an appropriate one for a bad question, but is not a good read for yourself. :)


Why doesn't using the @ mark always highlight users?

Question: When I am commenting on other posts, I use @ to ping other users. Sometimes when I type @ and the user's name, it auto-generates their full name if I type in the first few letters. But other times it does not, and I have to type the full name. I don't know if they are actually being pinged.
Answer: See also: How do comment @replies work?
If you're commenting on a question or an answer post, the poster is automatically notified and the @ method is redundant.
If a user (including the question/answer poster) comments on the post. You will be able to use the @ method to ping the user and the username will be auto-generated.
You will be unable to use the @ method to ping users that have not left a comment on a post.
If you're posting in chat, the @ method works on those that have recently left a message in chat.
You can also reply to a specific message by clicking on the option tab on the left of the message and selecting "reply to this message" Or use the shortcut on the right of the message.
Comment: @kandy ^ そそ・・ ^^
Comment: Related? https://meta.stackexchange.com/q/43019/309033
Comment: This comment is an example. I typed @ and began to type your username but it did not generate it automatically. Is that because you are pinged automatically? If user "12345" comments under this, and I type @12 will it automatically generate 12345 as it does at other times?