Throwing out bread or Challah

Question: In todays generation when there is leftover bread or Challah we often discard it. As bread is the food for life there are those that either feed it to the birds, make kugel, breadcrumbs, etc. instead of discarding it. Is there an Issur of throwing bread away?
Comment: Similar: http://judaism.stackexchange.com/q/6785
Answer: Destruction of any object or food that is still usable falls under the catagory of Lo Sashchis (Rambam Melachim 6:10)
I sometimes leave the bread out until it stales and is no longer edible to the norm of society.  Alternatively, I throw it in the garbage inside a bag so that the bread is preserved in its state.
Answer: I don't know from where I remember this:
The bread part that is less then כזית could be thrown away.
Comment: This comes from the idea that pieces less than a kazais are not fit for human usage.  Firstly, it is dependent on societal norms.  Secondly, if you are normally strict about the size of a kazais, remember to be strict the other way.  I assume the reasoning is that throwing the pieces away doesn't make less fit for animal consumption, but throwing away larger pieces renders them unfit for humans and significantly lowers their level of usage (to only fit for animals) which qualifies for the issur of lo sashchis.
Answer: From the following sources I see that it is forbidden to destroy a kezais (olive size) of bread
and it is permitted to destroy bread less then a kezais as long as it's done in a respectful way
Talmud
Brochois 52b

... the crumbs which are as large as an olive and leaves those which are smaller than an olive. This supports the dictum of R. Johanan; for R. Johanan said: It is permissible to destroy willfully crumbs [of bread] smaller than an olive. *7 ...
*7 In spite of the prohibition against wasting food.

Toisfos Shabbos 143 פירורין שאין בהן כזית אסור לאבדן ביד.

... may be wantonly destroyed, the deduction being from the statement, BECAUSE THEY ARE FOOD FOR ANIMALS, which may be destroyed.

Rambam Sefer Ahavah » Berachot » 7 » 11

...[This practice should be followed] lest pieces [of bread] the size of an olive be found on the floor. It is forbidden to walk or wash over [pieces of this size]. If, however, the pieces are smaller than an olive, it is permissible to destroy them intentionally.

Shulchan Aruch HaRav Orach Chaim 180.5

אע"פ שמותר לאבד פירורים שאין בהם כזית בידים לא יזרקם במקום דריסת רגלי בני אדם מפני שקשה לעניות כשדורסים על פירורי לחם ולא התירו אלא לאבדם כגון להשליכם למים וכיוצא בזה
even though it is permitted to destroy crumbs that do not have a kezais (size of an olive) with your hands, do not throw them in a place that people walk, since it is bad (euphemism) for poverty when they are stepped on, they did not permit it only (they only permitted) for example to throw them into water and similar things.

Maybe it is permitted to cut the bread into pieces less than a kezais and then to destroy them, and maybe it is forbidden since by cutting it you are destroying it (making is useless).
Answer: If it is good it should not be thrown away.
However, I have seen that some people dump such bread in public places, allegedly to feed birds, causing a mess and possibly unhealthy conditions. They should only do that on their own property or in a place where they have permission to do so.
Comment: What is your source?

Throwing out bread or Challah


Internet connection to a VM running inside of an Internet-free computer?

Question: Is it possible to have a VM directly speak to, say, a USB modem device on a computer that does not have an Internet connection, thus providing Internet access to the VM, but ONLY inside of the VM? Is this a sensible security measure for a box that should have extremely limited Internet services?
Answer: It's quite possible, technically. However, I'm pretty certain that if your IT-security guys got wind of it, they would scream out loud, depending on what your IT policy says. I know that where I work, such a thing would be impossible to get approved if I want it to work on a classified system.
The best way would simply to use a stand alone computer where you don't have to worry about security.
Answer:
Is it possible to have a VM directly speak to, say, a USB modem?

No. It is not possible.
A Virtual Machine is just that; a virtual non physical machine that runs on top of a host physical system. If your host (physical) system cannot see or use the USB device in question, then the virtual machine will have no idea about the hardware either. If the host (physical system) has no drivers present to run the hardware (USB Modem) then the guest system generally cannot access or use it either.
What you can try doing however, is plug in your USB device and install the drivers for it in the guest system. Enable the device as a network interface in the host, and set up your virtual machine connection as 'bridged'. Your traffic is still going over the physical machine, through the hardware bus and to the device , but should skip the other network layers.
Explanation of different network nodes for VirtualBox or Oracle diagramming.

Is this a sensible security measure for a box that should have extremely limited Internet services?

No.
Use SSH or a VPN with HTTPS for website and keep network traffic secure.


Ubuntu not booting from usb

Question: So today my hard drive on my desktop decided to fail... I am trying to launch ubuntu via USB flash drive and I am getting several errors, I used the universal USB installer to get ubuntu 12.10 desktop amd64 iso onto the usb, I prioritized it to launch from the USB and once it does I get a screen saying   boot:
  If I press enter the message will appear as:  initial menu has no LABEL entries
It then quickly disappears. I tried using Ubuntu 12.4 iso however it had a different error, where it says:
  unknown keyword in configuration file: niciar &
unknown keyword in configuration file: ubuntu &
No DEFAULT or UI configuration directive found
  Please I have no idea what to do, I've searched but I couldn't find a solution to this problem. One result I found said:
Open the the syslinux folder in the root of the flash drive.
Inside is a file called syslinux.cfg you'll want to edit that.
Find the line "ui gfxboot bootlogo" and simply remove the "ui ".
Save and try booting again.
I opened the cfg file in notepad, and some spanish writing came up, I'm not sure if that is the problem... Any help would be appreciated, thank you!
Answer: Ok so I managed to get ubuntu to boot from my usb flash drive by using UNetbootin http://unetbootin.sourceforge.net/ as someone suggested on this website, I had previously tried the LiLi program as well as universal usb installer but both gave me the errors I discussed above. I used the UNetbootin program and it miraculously worked, so if anyone is experiencing the errors I was getting, try out UNetbootin and hopefully it works.
Comment: Mark your answer as accepted(click on the grey tick to the left of this answer), as it seems to have solved your problem.

Ubuntu not booting from usb


How does Russia have so much foreign exchange reserves?

Question:
Source
Russia is under U.S. sanctions. How does Russia have so much foreign exchange reserves?
Answer: russia uses its oil revenue to setup russia stabilization fund in 2004. The money in that fund is used to pay for national budget deficit. The foreign exchange reserve of Bank of Russia is not affected by the US led sanctions.
Comment: Hi! Can you add sources of your answer? :)
Comment: @LimonadaPT   use your common sense, no country will put their forex exchange outside the country. Unless you live inside a Banana Republic.
Answer: Russia has been ramping up its production of oil since late 1990s after it defaulted on its debt. It has been maintaining positive trade balance since then.

Also, notice in the above graph, Russia has had current account surplus for a long time. It is somewhat similar to saying that Russia has been a net lender to the rest of the world. The current account surplus has increased Russia's net foreign assets, this situation puts Russia among the top countries with the highest foreign reserves.
Also, the sanctions did not target oil and gas industry as much as the financial, agriculture, weapons and other industries.


How to test battery consumption of mobile app?

Question: I want to test mobile app battery consumption on android. I am new to this. Is there anyone who can guide me about this?
Comment: What does the app do? What modes does it have? Are there things you would logically expect to consume more battery than others? Without the answer to these questions, there isn't much of a plan that can be made.
Comment: Very similar. Check out the link [Here](http://stackoverflow.com/questions/7566910/testing-battery-usage).
Answer: You can use adb to get battery consumption of your app by
adb shell dumpsys batterystats [your.package.name]
The result is very detail, so you may need to use grep to fine grain information you want and then import result into your continuous integration.
If you only need to know an over view of battery usage for all your tests in a controlled environment, adb shell dumpsys battery should be enough. You can grep the battery level by adb shell dumpsys battery | grep level
You can have further information from The Android official site
Answer: Go to Settings -> About Phone -> Battery Usage.
Answer: Go to Settings > About phone > Battery Usage

The top battery drainers:

Mobile apps are going to use battery, but some take it to the next level, and there is a common thread between those specific apps.

Power-saver modes:

Check power saving mode in your mobile friends or foe..?

Low battery Performance:
Mobile app development and testing teams must also be aware of how an app performs on devices that do not throttle battery use when the tank is running on empty.


How to avoid knee pain/injury during Shikko waza?

Question: In Aikido there are suwariwaza techniques which are done on the ground and one should walk on knees or sometimes pivot on one knee for tenkan. Some schools make the students walk in shikko like 10 times around the mats to train it. However it could be really painful for knees especially if the tatami is hard. Are there any good tips to prevent knee pain or injury? Is it better to avoid shikko completely?
Answer: Bad knees
If you have bad knees, as in medical professional has told you they are bad, then you should avoid any exercise that damages them further. Your coach/teacher should modify the exercises so you still can do them standing up. You will miss some of the subtleties of suwari waza but nothing drastic.
Good knees
If your knees are fine… There are a few things you can do to mitigate the pain.
First, make sure your dogi is re-enforced in the knees. This means that you have some extra padding to protect your soon-to-be sore flesh. Your knees are not used to being threaded on so the padding will help. You could use some light bandage or knee pads. The former is an extra layer of protection but does cut into the back of your knee. The latter exacerbates the cutting and can be counter productive in the long run. However, if your knees are bleeding because you ripped the skin off them, they are essential!
Second, lose weight and increase your flexibility. The former is kinda obvious: the heavier you are, the more pressure you are going to put on your knees. So, the more they are going to hurt even before you do shikko or suwari waza. Clearly, if you are a lean mean machine already, this might not matter. The latter is a little less obvious. Flexibility will help make the posture of kneeling easier and thus allow you to do it more often. Which nicely brings me to…
Thirdly, do less more often. This will get your knees more used to being used as feet and therefore less painful. This is kind of lazy advice: do more dhu! The trick there is to do little a lot rather than a lot once in a blue moon.
Lastly, try to minimise the time you spend on your knees. You can site in seiza or cross your legs. You can get up and walk instead of using shikko to go to your partner. You can (and really should) make sure your knees are not stiffening up.
Do yourself no harm!
The most important advice I can give you is do yourself no harm!: If it hurts, stop doing it.
Your knees are super important1 and once they break, they never go back to a good state. You should be in martial arts for the duration, not a few years. No one will care in a dozen years how macho you were doing laps in shikko and leaving blood trails on the mat because you will not be there training. Or they might tell this as a warning to others.
Martial arts all claim to teach self defence: this is a prime example. You should know when to stop to protect your own body and not be ashamed of it.

1: This is the understatement of the year. ☺
Answer: This is not to take away anything that Sardathrion said, as it is largely correct (wait for it...)
However, Aikido is not knitting class (nor are most of the other martial arts). There is discomfort, and there is pain. There is "hurt" that denotes damage, and there is hurt that is merely the triggering of some neurons that really should learn to shut the >ahem< up and let you get on with things.
I was a Marine subject to reveille at one point in my life, and I didn't learn that lesson for a LONG time. Now I have arthritis in several joints (including both my big toes!), a fused vertebra and a moderately high pain tolerance. I have learned to stop when it starts hurting more than momentarily.
As in one of my martial arts instructors in the past said "Damn. You have a high pain tolerance".
We study martial arts for different reasons--I have no idea what "yours" are (and no idea who "you" are), but martial arts are, inherently about fighting. In a fight you will experience both mental (at least the first few times) and physical discomfort, you will likely get hit, which will hurt, and you might get damaged.
Part of martial training is experiencing some of that discomfort in class so that when it happens outside of class you don't get your OODA loop interrupted.
If your knees are in really bad shape you need to discuss this with your instructor.
But unless your instructor is is having you do suwariwaza races on concrete (go find another instructor) it's going to be uncomfortable at first, but I don't think it's something that will damage healthy knees of a healthy individual. Hell, we do similar techniques (different art) and the biggest problem I have is that I'm not flexible enough.
To recap:

Learn the difference in feeling between discomfort and damage.
Suwariwaza should not be painful, but until you learn how and gain
the requisite flexibility it will be uncomfortable.
Embrace the suck, it makes you a better person. Modulo the issues in 1.
Comment: That the pain is a part of martial arts training is clear. What I was expecting as an answer was more like, small tips to do suwariwaza/shikko correctly or better. @Sardathrion has provided such recommendations in his answer. Thank you anyway.


Putty SSH, can't log into Raspberry

Question: Heyo, I use my raspberry pi zero as an rgb strip controller behind my desk, I have a simple http/php server running on it so I can change the color from my web browser, it is powered by a phone charger and also connected directly to my pc via the second usb port, and that's how it gets it's internet. Thing is, every morning I have to go into putty, log in with the default pi/raspberry username and password and type in sudo pigpiod so I can start controlling the strip online... This takes about a minute and I thought I'd just shorten it 2x by removing the login bs, tried finding any results on how and didn't have great luck, but I did find this post: How can I deactivate the login password on my Raspberry Pi? .
I followed it's instructions and made sure to set those settings to no, restarted my pi and putty. And now when I try to log in putty still asks for a username, and if I type anything in at all it brings me this message: "disconnected: no supported authentication methods available (server sent: publickey)" and I can't get into my pi through putty... the equipment I used to set it up (keyboard/mouse/usb hub/ 5 adapters for all the connections) is who knows where in the attic so I'll just leave it be and live without rgb if there is no simple solution within putty >_>
Comment: Try writing in paragraphs
Answer: There is a solution to start automatically pigpio :
<code>wget https://raw.githubusercontent.com/joan2937/pigpio/master/util/pigpiod.service
sudo cp pigpiod.service /etc/systemd/system
sudo systemctl enable pigpiod.service
sudo systemctl start pigpiod.service
</code>
So when you start your raspberry pi, pigpiod start automatically and so you don't have to connect to your raspberry pi with putty.
Hope this will help you :).
Comment: Isn't the service already installed on Raspbian and just needs enabling? Option Remote GPIO in `raspi-config`
Comment: Here is the link where I found that solution : https://github.com/guymcswain/pigpio-client/wiki/Install-and-configure-pigpiod

Putty SSH, can't log into Raspberry


Which comments got me the Pundit badge?

Question: I just got a Pundit badge, so I must have 10 comments — somewhere — with 5 votes each.  I'm curious what they are, since I have been leaving more comments lately, except that none of my recent ones has more than one or two votes.  Of course, looking at my comments under the "activity" tab of my page shows only the title and not the votes.  Is there any way to figure this out short of doing a linear search?
Comment: http://data.stackexchange.com/tex/query/71678/my-most-popular-comments (current data there is from June 27)
Comment: Similar: http://data.stackexchange.com/tex/query/71222/whats-my-pundit-badge-progress
Comment: These are both good suggestions (though I am not sure what the difference is).  Though since they do used cached data, I still needed to trawl through the 4-point comments to figure out what put me over the edge.
Comment: @RyanReich: They are pretty much the same. There are probably quite a few more equivalent queries to be found on the data explorer (and you can write your own too).
Answer: As said in the comments, there are SQL queries on data.SX for this, for instance:

http://data.stackexchange.com/tex/query/71678/my-most-popular-comments
http://data.stackexchange.com/tex/query/71222/whats-my-pundit-badge-progress

The data are cached so the votes appear there delayed. I'm afraid it's not easily possible to get the up-to-date information instantly since caching is necessary to avoid server overloads.

Which comments got me the Pundit badge?


Is a proton collision (collisions like in the LHC) visible to the human eye?

Question: I was curious if a proton collision is visible to the human eye.
(This might sound like a really basic question and forgive me if it is.  I am very inexperienced in Physics and just wanted an answer to my curiosity)
Comment: Someone has (inadvertently) tried this! http://en.wikipedia.org/wiki/Anatoli_Bugorski
Comment: Interesting, but one should realize this was a beam, i.e. ten to the something protons, not "a proton". I knew people who would center a beam from the cerenkof light left in the eyeball, but those were very weak beams.
Comment: @charliehorse55 the comment was on your link
Comment: @annav It's relevant, but not exactly what the question was asking. That's why I put it in a comment instead of an answer.
Answer: This is actually a really good question.  (And I'm not one of these people who insists that there's no such thing as a dumb question; I just think we shouldn't be embarrassed to ask dumb questions.  Anyway, this isn't a dumb question.)
As you may know, collisions between two protons (like those the LHC usually does) can produce many different types of particles, some of which are Higgs bosons, but most of which are more familiar.  Photons are definitely among the familiar types of particles that get created, and since humans can see photons, it's at least possible in principle that we might be able to see the flash of light that results.  The question is whether that light is bright enough and has the right "color" so that we could see it.
Now, the "color" has to do with the energy of the photon.  The preferred unit of energy for particle physics is the electron-volt (eV), and in these units, we see photons with energies between about 1.65 and 3.27 eV.  So only if a photon produced by the proton-proton collision has an energy in that range could we even possibly see it.  The LHC is designed to collide protons with energies totaling 14 TeV (equivalently $1.4 \times 10^{13}$ eV, or 14 million million eV), and most (but not all) particles that result from a collision will have comparable energies.  So we can expect that most photons produced by those collisions will have energies well over a million times too large for us to see.  They can happen, but they'll be very rare.  So that's color; what about brightness?  Well, in those rare cases, we'll get one or maybe even two photons produced with the right energy for us to see.  And this link suggests that we would need five to nine of them from a single event.  So it would be very unlikely for a single collision to do this; they won't generally be bright enough.
On the other hand, these are just the direct results of the proton-proton collisions.  High-energy collisions like this typically produce showers of other particles as soon as the products of the collision enter some matter (like an eye).  It's kind of like a bowling ball hitting a bunch of pins.  The energy of the ball gets distributed to the pins, each of which moves at lower energies, and can hit other things that will move at even lower energies, and so on.  So such a thing would dump a lot of energy into your eye, much of which would be in the form of visible light.  And this isn't just possible, it's downright likely.  Of course, the many things produced in such a particle shower include various forms of radiation that would kill a human pretty quickly if that human were exposed to the entire power of the LHC.  But in principle, yes the human eye could perceive the results of a single proton-proton collision.
A related topic is that of cosmic-ray visual phenomena, in which astronauts can see flashes of light, which are presumably due to individual cosmic-ray particles interacting with their eyes.  A relatively recent study (behind a paywall) suggested that the protons produce a shower of particles, including visible photons, within the various structures of the eye.  The authors suggest that heavier cosmic rays may directly stimulate the retina itself.  There's also a nice little (free) overview of the study here.
Comment: As I was reading the entire post, I was thinking "I hope he mentions the flashes of light astronauts see in space..." You made me wait for it though!
Comment: Well, the reasonable reader would immediately click off and start reading about that because it's so interesting.  I just wanted my post to be read.  :)
Comment: Hi Mike, do you have a more quantitative estimate why it's "unlikely" that a generic pp collision would produce more than $O(5)$ relatively soft photons in the eV range? It seems like that would be a very inclusive observable, although of course it doesn't have a huge phase space available. And getting 10 of them in a small solid angle is of course a different story...
Comment: I think 14 TeV is 14 trillion eV, not 14 billion
Comment: @Sahuagin That depends on whether you're e.g. in the USA (where they have millions = $10^6$, billions = $10^9$, trillions = $10^{12}$) or e.g. Germany (where there are millions = $10^6$, milliards = $10^9$, billions = $10^{12}$) - one more reason why people should stop using ambiguous words when they could just mention the relevant power of ten (See https://en.wikipedia.org/wiki/Long_and_short_scales). Either way, the [SI prefix](https://en.wikipedia.org/wiki/Metric_prefix) [tera-](https://en.wikipedia.org/wiki/Tera-) means $10^{12}$.
Comment: +1 for a great post, with enough detail to answer the question for a general audience, without talking down or bogging down.
Comment: @Mike That's no brain fart, that's continental thinking :-P Why don't you skip the ambiguity and write $10^{12}$ or million million (which I personally don't like) instead?
Comment: @Vibert: I don't actually.  There are way too many possibilities for me (at least) to even attempt any calculations, and I can't find any convenient references for this.  I was mostly just thinking of the phase-space argument.
Comment: @Sahuagin: Oh god, you're entirely right.  I'm American; it was just a total brain fart.  Corrected in the answer.  Thanks!  [That's embarrassing...]  :/
Comment: @TobiasKienzler Yeah, I like that suggestion.  Thanks.
Answer: These collisions don't produce significant amount of light in the visible range, so the easy answer is "no".
They also take place in a vacuum, inside a beampipe which is itself buried in a detector apparatus that is ten meters plus on a side and packed full of stuff with no room for a human.
That said, there are several ways in which a high energy ionizing particle could---in principle---make light in the visible range. In particular a electromagnetic shower impinging on the eye itself might produce enough Cerenkov light to pass the simple filters the brain imposes on retinal output and be consciously registered as a blue flash. (Each flash would represent a small fraction of the--considerable!--ionizing radiation dose which you would be exposed to in the course of this stunt.)
If we assume a interaction region without a detector and a physicist dumb enough to be in the hall while the beam is on (having carefully bypassed both hardware and administrative interlocks designed to prevent this) who then put his head near the interaction region beam pipe, you might be able to say "I saw one!" every once in a while.
But you won't catch me trying it: I plan to die of something other than radiation poisoning or cancer.
Answer: It all depends on your definition of visible.
Elementary particle collisions have been made visible since the time of cloud chambers and bubble chambers. A good site for bubble chamber pictures exists . Unfortunately proton scattering is not as photogenic as scattering by other particles  so I was unable to find a photo of a proton proton scatter in a bubble chamber though thousands must exist.
Here is one kaon from the beam hitting a proton in the bubble chamber  and creating a number of new particles from its excess energy ( go to "would you like to see" for a list of particles).

Due to the kaon having interacted with a proton in the hydrogen, the rightmost beam track produces a spray of 4 tracks. The longer highlighted track is clearly dark – it has produced a higher number of bubbles per centimetre than, say, the beam tracks; this tells us that it is moving more slowly. (For details, click here.) Such tracks are a common feature in bubble chamber pictures and usually signify protons.

In the link there exists an explanation of how a bubble chamber works to make visible charged tracks coming from an interaction.
For LHC energies the detectors become more complicated and depend on electronics and computer outputs to get the same visibility. Vertex detectors and other track  chambers  give accurate images of the interactions, though the high multiplicity of vertices makes life more difficult.
Answer: Hmm, interesting question at least.  Visible as in see two balls crash into each other; no, visible as in see the light emitted from the collision; probably not.
The emitted photons are of the order of $\rm{}MeV$, around $10^{-13}\rm{}$ joules.  The human eye works at around $10^{-5}$.  So individual collisions no.
Answer: A spinthariscope is a simple device consisting of a minute amount of an alpha-emitter and a zinc-sulphide screen.  It often includes a magnifier to view the screen.  The amazing part is that a dark-adapted eye can clearly see the flashes of light produces as individual alpha-particles hit the screen!  There's probably multiple visible-light photons from the collision, but the eye can detect the light produced by the energy of a single nuclear decay.
Comment: The point, however, is that a scintillator/fluoror is used to make that happen. The energy is not at question. The way the energy is produced *is*.


Xdebug only writes to /tmp

Question: I've installed Xdebug on Centos 6.2. It writes cachgrind files to /tmp just fine, But I want it to write to /tmp/xdebug instead.
I've added this to my php.ini:
xdebug.profiler_output_dir = /tmp/xdebug

and changed the owner of the folder to apache:apache and chmode it to 777.
But, it is not writing any files. When I configure it back to:
xdebug.profiler_output_dir = /tmp

It does write files. How can it be fixed ? thanks.
Answer: If I recall from my other reading correctly, the folder on CentOS for xdebug output needs to be owned by the "nobody" account, not apache.

Xdebug only writes to /tmp


Enable scroll by dragging my stylus?

Question: How can I configure my Wacom Bamboo Pen&Touch stylus to scroll when I hold one of the buttons on the stylus and drag with it? This is a standard supported operation on the Mac, but I can't find how to configure it in Ubuntu?
Answer: I've got absolutely no experience with the Wacom tablet but looking through many sites it is supported well in Ubuntu and can be configured to do many things.
One of the most comprehensive sites to look at is the Ubuntu Community Wiki page for the Wacom tablet - it has many useful suggestions and workarounds as well as links to forums and other sites for development of the drivers in Ubuntu to support the tablet.

Enable scroll by dragging my stylus?


What would keep Dyson Swarm reflectors in place?

Question: I've been reading a bit about the concept of a Dyson Swarm and how one of the more plausible routes would be to disassemble Mercury to construct ~1km hematite mirrors as the swarm reflectors. The basic concept is that the mirrors would be un-powered and simply reflect sunlight to a central processor that would extract the energy and beam it wherever we need. But that got me wondering; in such a scenario, wouldn't that simply turn the mirror elements into solar sails? Wouldn't they need an equivalent amount of energy in the opposite direction simply to keep them in place?
Edit: Additional links about the swarm idea here and here
Comment: @kimholder I've added a couple, sorry for the omission.
Comment: So you don't have a link to where you read that version, right? Can you mention an author or a book it was in?
Answer: If each 'mirror satellite' in the swarm could at least keep the same face towards the sun, then it wouldn't need to expend energy to stay in its orbit. This is because of a handy cancellation.
The force of gravity scales as $-m_{sat}/r^2$ and the force of the photon pressure scales as $+A_{sat}/r^2$ where $m_{sat}$ is the mass of the satellite (which might change a little if it has propellant for attitude control) and $A_{sat}$ is the effective area of the satellite. Since they both vary as $1/r^2$ the photon pressure just feels like the gravity of the sun is a little weaker.
Here are the full equations. For Radiation Pressure of a flat reflector with 100% reflectivity (no absorption/re-radiation):
$$P_{rad} = \frac{2E_f}{c} cos^2\alpha $$
where $E_f$ is the incident energy flux density of the sun's photons on the satellite (and $E_f/c$ is the incident momentum density thereof) and $\alpha$ is the tilt angle away from 'straight back towards the sun'. The factor of 2 in momentum comes from the reflection - you reverse the sign of the momentum $p$ of the photon so the mirror gets $2p$.
The force is then just pressure times area:
$$F_{rad} = A_{sat} P_{rad} $$
The energy flux density at the satellite's distance $r$ is just the total radiation power of the sun $\mathscr {P}_{sun}$  divided by the area of a sphere at that distance:
$$E_f = \mathscr {P}_{sun} \frac{1}{4 \pi r^2}  $$
All together, assuming normal incidence (setting $cos^2 \alpha = 1)$:
$$F_{rad} = \frac { \mathscr {P}_{sun}}{2 \pi c} \frac{A_{sat}}{r^2} $$
The gravitational force comes from the 'modern form' of Newton's law of gravitation:
$$F_{grav} = -Gm_{sun}\frac{m_{sat}}{r^2} $$
So the same $1/r^2$ dependencies are in both forces, and since the signs are opposite, it simply "feels" like slightly weaker gravity.
side note: the cancellation sort-of works for elliptical orbits too, except for the libration. As the mirror orbits (revolves) around the Sun once, it also rotates around its axis once so that it points towards the sun all the time. But if it's in an elliptical orbit, it is sometimes moving faster and sometimes slower, but the rotation of the mirror around it's axis is constant. For very small eccentricities this 'periodic pointing error' will be 'very very' small (since $cos^2 \alpha$ is quartic about $\alpha = 0$ ), but it's not zero.
However if you can somehow keep the mirror pointed directly back at the sun, then the cancellation works just fine.
A graphic example of libration - the moon is rotating about its axis pretty much uniformly, but because of its elliptical orbit around the earth, it appears to be tilting back and forth. When it's farther away, it appears to be turning to the right faster, when it's close, it can't keep up and appears to move to the left.
Lunar Libration image from here

At a given circular orbital radius, a shiny flat mirror pointing back towards the sun has a slightly lower orbital velocity that a diffuse white thing that scatters in many direction, and that has a slightly lower velocity than a dark thing that soaks up the power then re-radiates it isotropically. But they all just continue in their stable orbits (unless of course they rotate then it's a total mess!)
But the problem is that the satellites may change reflectivity due to damage, or effective area and reflection direction due to attitude changes, and the mass may change, and of course they all have gravitational effects on each other.
The ring can accommodate some of those, if they all behave identically. But the more complicated multi-ring orbits will perturb each other both gravitationally and by blocking each other's photon pressure, and that may require some much fancier orbits.
Comment: Thanks for the detailed explanation! So given ideal conditions, it shouldn't be too hard (relatively speaking) to get the forces to cancel out for an orbiting ring of reflectors?
Comment: @thanby well for anyone who can "disassemble Mercury", keeping the radiation pressure constant or at least only slowly decreasing should be fine. As the mirrors degrade, their reflectivity will decrease. but if it's over a long time, they would just very slowly spiral out a tiny bit, but remain pretty much circular. There might be issues with instabilities due to gravity between the mirrors in the right, but that should be a separate question.
Answer: In the Wikipedia article you referenced, the Dyson Swarm constructs orbit around the star - standard orbital mechanics would apply, but traffic management might be interesting.
Further down in the same article, the Dyson Bubble has non-orbiting (& extremely lightweight) constructs that balance the solar sail pressure with gravity.
Comment: How in the world... So to "deploy" this swarm, you'd have to orbit around the sun, stop completely, deploy the sail, then move on. You'd need some crazy propulsion systems to pull that off. I wonder what the size of the solar sail would need to be as well to keep it completely stationary (if we'd assume a couple tons for each mirror).
Comment: @MagicOctopusUrn Since you're using solar sails anyway, you could probably start by deploying them, then have them propel themselves towards the Sun and settle into the desired position. And according to Wikipedia, each square metre of sail needs to weigh no more than 0.78 grams, so that's a maximum of 0.78 tonnes for each square kilometre.


How do I get LinkedIn to email my new primary email address?

Question: I've recently changed the main email address I use.  I put the new address into LinkedIn, confirmed it, and made it primary.  But LinkedIn still sends me all its email on the address that I had first joined it with (which is still active, so I don't want to remove it.)  How do I get LinkedIn's messages to come to my new primary email address?
Answer: You could try unsetting your message receiving settings and then setting them back. I changed my email not too long ago also, and have email still going to my old address (which is not a problem for me). I did notice upon joining a new group that the group digests go to my new email address.
Answer: Unfortunately, you seem to have followed the correct process.
I assume that you can distinguish the emails. So it is not possible that you have a forward set-up outside of LinkedIn.
Otherwise, as you say you have multiple active emails, I would suggest changing the primary email back to your original one (that still gets the emails).  Wait for "1 day" then try again.  ( Wait 1 day if this is not urgent, otherwise an hour should be plenty for back-end systems... assuming that there is actually some kind of lag )
Comment: I tried this, and unfortunately, it did not work.  Emails still come to the old address.
Answer: Are you having this problem 24 hours after you changed your primary email address?
According to the LinkedIn suport site, changes to your primary email address should take effect within 24 hours.
Comment: It's been weeks since I changed the primary email address, and the emails are still coming to my old one.


What's the difference between 64-bit and 32-bit dxdiag?

Question: I'm doing some logging and noticed that on 64-bit platforms I can use the /64bit switch to run 64-bit dxdiag.  I assume there must be some reason for doing this, namely additional functionality in the 64-bit version (or incorrect/insufficient functionality when using the 32-bit version on x64).  What exactly are the differences?
Comment: One is a 64-bit process the other is a 32-bit process.  So the only differences would be in how a 64-bit Windows installation would treat a 32-bit process.
Answer: From personal experience, dxdiag can also be used to determine if there is a problem with the 32 or 64 bit portions of the drivers.  For example, running dxdiag in 32 bit might show no acceleration for DirectDraw or D3D; yet running DXDiag64 might show everything as fine.
This is useful when trying to figure out video issues, particularly since most games execute in x86 (32 bit) mode only.
Answer: No, there is nothing "extra" when running DXDiag in 64-bit mode, it simply runs the native 64-bit executable files instead of the 32-bit files. The 64-bit ones will not need to be emulated or done in compatibility mode and will be able to make the maximum usage of the system, so they (should) be able to run faster and more reliably.
(That said, it would be possible that in 32-bit mode, it has to skip some tests that would only be possible in 64-bit mode, similar to how a game can have "extra" content in the form of special graphical effects that are only available with a fancier video-card that supports them. However, that doesn't really apply to DXDiag; speed and stability are really the only "extras" you get.)
Answer: Yes there is "extra" info, all drivers show their driver date.  In a laptop that has dual GFX adapters only the primary would show it's driver daye and the secondary that is buried further down wouldn't have a driver date.
Answer: besides the driver info, the 32-bit dxdiag has a video memory limited to 4095, while the 64-bit dxdiag has a not easily reachable limit (I couldn't find it).


Why are my Ohm Robots not using Teleporters?

Question: In the game Universe At War, the first race in the campaign has teleporters to warp any of your units across the map, but my Ohm Robots do not seem to use them at all. Is this a bug?
Answer: To get your units to use the rapid transport towers, double right click somewhere. This will cause all your units to move as fast as possible, instead of them all going at the speed of the slowest in the group.


Continuity of the mutual information

Question: The mutual information $I(\mathfrak A_1;\mathfrak A_2)$ of two complete $\sigma$-algebras $\mathfrak A_1$ and $\mathfrak A_2$ in a Lebesgue probability space $(X,m)$ is the integral of the logarithm of the Radon-Nikodym derivative $dP/d(P_1\otimes P_2)$, where $P_i$ are the quotient measures on the factor-spaces $X_i$ determined by the $\sigma$-algebras $\mathfrak A_i$, respectively, and $P$ is the joint distribution on $X_1\times X_2$. If $\mathfrak A_i$ correspond to countable measurable partitions $\alpha_i$ of the space $X$, then $I(\mathfrak A_1;\mathfrak A_2)$ are expressed in terms of the associated entropies as $H(\alpha_1)+H(\alpha_2)-H(\alpha_1\vee\alpha_2)$. I need an explicit reference for the following fact (I know how to prove it): if $\mathfrak B_n$ is a decreasing sequence of $\sigma$-algebras converging to a limit $\mathfrak B$, and $\mathfrak A$ is another $\sigma$-algebra such that $I(\mathfrak A;\mathfrak B_1)<\infty$, then $I(\mathfrak A;\mathfrak B_n)$ converges to $I(\mathfrak A;\mathfrak B)$.
Answer: The last proof of this continuity property (and of its analogue for increasing sequences) is given in this paper by Harremöes and Holst. It also contains a pretty comprehensive list of references to earlier work. Apparently, first this property was established by Pinsker in his 1960 book "Information and Information Stability of Random Variables and Processes".
Answer: Mutual information is weak-* lower semicontinuous, because it is Kullback-Leibler divergence. For this see Pinsker's book or Dupuis-Ellis. This gives you the desired liminf. For the other direction (which is usually easy because I haven't used your monotonicity condition yet), maybe you have some monotonicity or convexity argument.
Comment: Thank you - I know how to prove it. My question was about a reference.

Continuity of the mutual information


Can gynecomastia breast tissues be dissolved?

Question: If one takes zinc and vitamin D then the T levels increase.
So oestrogen must decrease and thus gynecomastia goes away.
But this site says that the breast tissues can never be dissolved even if the hormones are balanced. Is it true?
Comment: Possible duplicate of [How to get rid of gynaecomastia?](https://health.stackexchange.com/questions/16804/how-to-get-rid-of-gynaecomastia)
Comment: @ChrisRogers His first question was a blatant request for medical advice. It shouldn't be reopened. This question is okay.
Comment: Does this answer your question? [How to reduce weight-caused man boobs (psuedogynaecomastia)?](https://medicalsciences.stackexchange.com/questions/7630/how-to-reduce-weight-caused-man-boobs-psuedogynaecomastia)
Comment: Please edit your original question on gynaecomastia with this question.  You can then flag the original question to morderators for re-opening.  The re-opening will go to a vote and if you follow this advice you would get my vote to re-open
Answer: No, it's not true that the breast tissue caused by gynecomastia can never go away. According to the Mayo Clinic (emphasis mine):

Most cases of gynecomastia regress over time without treatment.
  However, if gynecomastia is caused by an underlying condition, such as
  hypogonadism, malnutrition or cirrhosis, that condition may need
  treatment. If you're taking medications that can cause gynecomastia,
  your doctor may recommend stopping them or substituting another
  medication.

So the first step in dealing with gynecomastia is to identify and treat the factor causing it. That may mean treating an underlying condition or it may mean stopping or changing medications. Once that's been addressed all that's needed is time, and the time needed can be measured in months or even years.
If the breast tissue doesn't go away despite appropriate treatment and the sufferer finds the tissue intolerable, two options remain: medication and surgery. Again, according to Mayo:

Medications
Medications used to treat breast cancer and other conditions, such as
  tamoxifen (Soltamox), raloxifene (Evista) and aromatase inhibitors
  (Arimidex), may be helpful for some men with gynecomastia. Although
  these medications are approved by the Food and Drug Administration,
  they have not been approved specifically for this use.
Surgery to remove excess breast tissue
If you still have significant
  bothersome breast enlargement despite initial treatment or
  observation, your doctor may advise surgery. Two gynecomastia surgery
  options are:
Liposuction. This surgery removes breast fat, but not the breast gland
  tissue itself.
Mastectomy. This type of surgery removes the breast
  gland tissue. The surgery is often done endoscopically, meaning only
  small incisions are used. This less invasive type of surgery involves
  less recovery time.
Answer: First, vitamin D supplementation does not seem to increase testosterone levels. Most high quality trials see either no increase, or a very very small one:
https://pubmed.ncbi.nlm.nih.gov/32446600/
Second, zinc might negate a transient exercise-induced decrease in testosterone. There is no evidence this is clinically meaningful:
https://pubmed.ncbi.nlm.nih.gov/17984944/
And (short-term) zinc deficiency might decrease testosterone. So in case you're zinc deficient, supplementation is (of course) wise.
https://pubmed.ncbi.nlm.nih.gov/1609752/
Treating gynecomastia is a whole different ball game. This is either done by surgery or sometimes off-label with endocrine treatment. Endocrine treatment refers to drugs that counteract estrogenic action. Since estrogenic action lies at the root of gynecomastia development.
Several of such drugs have been tested in clinical research, including: Tamoxifen (Nolvadex), clomiphene (Clomid), raloxifene (Evista) and Anastrozol (Arimidex).
Of these drugs, clomiphene and anastrozol don't seem so effective against it. Of raloxifene only one trial is available which suggests good results. However, it's a low quality trial.
Finally, a lot of research demonstrates that tamoxifen (Nolvadex) is effective against gynecomastia.
More details can be found here in case you're interested: https://peterbond.org/post/endocrine-treatment-of-gynecomastia


Can we show through simple geometry rather than formulae or graphs that the best glide ratio occurs at the maximum ratio of Lift to Drag?

Question: For an unpowered glider, can we show through simple geometry involving force vector diagrams, rather than mathematical formulae or graphs, that the best still-air glide ratio is achieved at the angle-of-attack that gives the maximum ratio of Lift to Drag?
Comment: That's a pretty tall order for engineering types lol.
Comment: Highly related: https://aviation.stackexchange.com/q/80731/4108
Comment: This one is also related, but a bit different-- https://aviation.stackexchange.com/questions/3610/how-are-the-glide-polar-and-l-d-ratio-charts-related?rq=1
Comment: Re "Highly related: https://aviation.stackexchange.com/q/80731/4108 -- had not come across that one before, and probably wouldn't have posted this one if were aware of it. Arguably not quite a duplicate because of the specification not to use formulae, but very close; answers to the present question will also fit that one.   I would consider deleting the present question if there weren't already answers to it (other than my own).
Comment: We could consider "migrating" all answers to this question to the other one (https://aviation.stackexchange.com/questions/80731/why-is-the-l-d-ratio-numerically-equal-to-the-glide-ratio ) -- if all posters wish to post their answers there and delete them here, I will delete the question.  However since we have an answer here with three upvotes already, that might not be a palatable solution to all...
Answer: Let's start with a Lift/Drag/Weight diagram, and draw the velocity vector as well:

Since no thrust is involved, Lift+Weight+Drag must sum to zero. Let's shift the origin of these vectors around a bit:

Now, let's finish the velocity triangle, drawing a (horizontal distance), and b (vertical distance). The ratio between a and b is by definition the glide ratio.

The key idea here is to notice that the triangles L-W-D and V-a-b are similar, that is, they are the same triangle up to a scale.
The similitude goes: W <-> v, D <-> b, L <-> a.
This means that the ratio between a and b is the same as the ratio between L and D. The latter is of course the Lift-To-Drag ratio.
So, in any condition, the glide ratio is the same as the Lift-To-Drag ratio.
It then follows that the best glide ratio is achieved for the best Lift-To-Drag ratio.
Comment: Please ignore the unrealistically high angle of attack, I used the first plane image I found on google search.
Comment: your diagrams are excellent.  Now, what is moving the glider horizontally? Consider an iceboat, being pushed by the wind from the side (glider sinking), yet moving forward *faster than the wind* (lift).  Vertical drag (caused by altitude loss) is glider fuel.  V min sink may have a lot to do with air pressure underneath the airfoil assisting lift, but pushing the plane forward more slowly.  100% agree with your rate of descent/ horizontal speed triangle.  This is where Vbg is proven more efficient. (Your glider nose should be below the horizon).
Comment: The answer is perfect, exactly the same points that I was making, just nicer diagrams and more concise language.  Obviously there are some unspoken assumptions built in-- for example, still air (as specified in the question).  PS @RobertDiGiovanni I'm sure we can find some examples of an aircraft in an unpowered glide with a *nose-up pitch attitude* though it may not be the norm for efficient sailplanes.
Comment: Not to worry, the lift vectors are correct.
Comment: You might consider also posting this answer here https://aviation.stackexchange.com/q/80731/34686 .  You might initially get a downvote or two for posting the same answer twice but in the long run it is a nice concise answer and likely will be appreciated wherever it goes.
Answer: First a caveat-- please keep in mind that this answer is focussed on steady-state linear gliding flight.  Throughout this answer, when we talk about what happens when we change the angle-of-attack and L/D ratio, we're assuming that we've waited long enough for the glider to settle back into equilibrium at whatever airspeed is appropriate for the new angle-of-attack and L/D ratio.
All three of the vector diagrams below represent the exact same physical situation-- sustained, steady-state gliding flight along a linear flight path in still air. We've represented the aerodynamic forces in black, and the gravitational force-- the weight vector-- in green. The left-hand and right-hand diagrams are easier to understand than the middle diagram, because the force vectors are arranged into a closed polygon (a triangle in this case), which shows us instantly that the net force is zero. On the right-hand diagram, we've also included the airspeed vector, and its horizontal and vertical components.

Lift is defined as acting at right angles to the relative wind, i.e. the undisturbed apparent airflow created by the aircraft's path of travel through the airmass.  I.e. lift is defined as acting at right angles to the flight path through the airmass.  Drag is defined as acting parallel to the relative wind, i.e. parallel to the aircraft's path of travel through the airmass.
Note that K is the glide angle, and note that on the right-hand diagram, the triangle formed by the force vectors and the triangle formed by the velocity vectors are similar triangles.  This is why the still-air glide ratio -- the ratio of horizontal speed to sink rate in still air -- is identical to the ratio of Lift to Drag.
The still-air best glide ratio -- i.e. the best ratio of horizontal distance travelled to altitude lost in still air -- must coincide with the best ratio of Lift to Drag.
Note that in a steady-state glide, Lift is less than Weight by the same proportion that horizontal speed is less than airspeed.  For many calculations, it is a close enough approximation to assume that Lift and Weight are the same, and that horizontal speed and airspeed are the same.  However, our vector triangle is very sensitive to this distinction -- overlooking it forces our vector triangle to collapse into a straight line, which forces the sink rate to be zero and gives us a glide angle of zero, i.e. a glide ratio of infinity.
Also note that the geometry of the triangle is such that the maximum Lift to Drag ratio also coincides with the minimum Drag value, and the maximum Lift value.
Note that the minimum Drag value does not coincide with the minimum value of the Drag coefficient.  The Drag coefficient is minimized at very low angles-of-attack, i.e. at very high airspeeds.  So we need to be careful about what we mean when we say we want to minimize Drag in order to maximize the glide ratio.  This is only true when we are speaking about Drag as an actual force, not as a coefficient.  The same is true for Lift.  While (for reasonably high L/D ratios) Lift varies much less than Drag as we change the L/D ratio, it is still true that in gliding flight, Lift is slightly higher at the point of max L/D ratio than at any other L/D ratio.  But the Lift coefficient is not maximized at the point of max L/D ratio-- rather, it is maximized near the stall angle-of-attack.  Yet in spite of all this, it is an arithmetic fact that when we maximize the L/D ratio, we also maximize the ratio of Lift coefficient / Drag coefficient -- even though we are not individually maximizing either the Lift coefficient or the Drag coefficient.
Warning: do not mistake the right-hand diagram for an indication that to minimize the sink rate, we simply need to minimize the drag vector.  The force vector triangle and the airspeed vector triangle are geometrically similar, but  they are not identical.  As airspeed changes, the entire airspeed vector triangle scales up or down in size, while the force vector triangle is locked in size by the fact that the Weight vector is constant.  If we miss this relationship, we may tend to assume that the minimum sink rate airspeed must coincide with the airspeed for minimum Drag, which is also the airspeed for the maximum L/D ratio.  This is not the case-- as we'll see below, the airspeed for the minimum sink rate is lower than the airspeed for minimum Drag, which is also the airspeed for the maximum L/D ratio.
Every possible angle-of-attack of the wing is associated with a specific lift coefficient, a specific drag coefficient, and a specific Lift / Drag ratio. If we ignore effects due to changes in Reynolds number associated with changes in airspeed, we can make the approximation that the same angle-of-attack of the wing will always be associated with the same lift coefficient, drag coefficient, and Lift / Drag ratio regardless of whether the aircraft is heavy or light-- a change in weight is expressed as a change in the airspeed associated with any given angle-of-attack, but no change in the lift coefficient, drag coefficient, or Lift / Drag ratio associated with any given angle-of-attack.  If we increase weight, any given L/D ratio-- including the maximum L/D ratio-- will now occur at a higher airspeed.  The increase in airspeed will be proportional to the square root of the increase wing loading.
If the still-air best glide ratio occurs at the same angle-of-attack that gives the best L/D ratio, then it clearly follows that we can minimize the sink rate by increasing the angle-of-attack to slow down slightly, even if this degrades the the L/D ratio and the glide ratio a bit.  In other words, if we fly more slowly down a slightly steeper glide path, we can minimize the sink rate.  Obviously there is a limit to this process-- as we continue to increase the angle-of-attack and degrade the L/D ratio, then at some point well before we reach a full-blown stall, we'll reach a point where the increased steepness of the glide path is too much to be offset by the decreased airspeed, and the sink rate will start to increase again.
In fact, the highest L/D ratio occurs at the angle-of-attack that gives the highest ratio of Cl/Cd, while the minimum sink rate occurs at the angle-of-attack that gives the highest ratio of (Cl^3) / (Cd^2), which is also the highest ratio of ((L^3) / (D^2)) / airspeed.  It's clear that when we want to minimize the sink rate, we gain more by maximizing the lift coefficient than by minimizing the drag coefficient, so we should choose an angle-of-attack that is somewhat higher than the angle-of-attack for the best L/D or Cl/Cd ratio.  This means that the airspeed for the minimum sink rate is always slower than the airspeed for the best glide ratio in still air.
Vector diagrams like the ones included in this answer are surprisingly rare in books about soaring flight.  Materials published by the FAA sometimes attempt to include such a diagram, but they are invariably badly botched, with the length of the various force vectors altered so that they could not possibly form a closed vector triangle, thus eliminating any possibility for the reader to understand the relationship between the force vectors and the glide ratio.  (One might optimistically hope that they are trying to make the point that a glider is not always flying in a straight line with no acceleration?)  (See for example figure 3-1 on page 3-2 of the FAA's "Glider Flying Handbook" (2013) -- here they've even included a Thrust vector!)  Even a theory-rich book like "New Soaring Pilot" by Welch, Welch, and Irving (3rd edtion, 1977) is entirely lacking in any presentation of the Lift-Drag-Weight diagram for steady-state gliding flight.  However, see page 233 of that book for a "polar curve" clearly showing that the max L/D ratio occurs at a higher airspeed than the minimum sink rate.
A couple of additional notes--

Our vector triangles also show that the maximum value of (horizontal speed / sink rate) and the maximum value of (airspeed / sink rate) both occur exactly at the maximum L/D ratio, so we can also find the airspeed for maximum glide angle by looking at the plot of (airspeed / sink rate) versus airspeed and picking the airspeed where (airspeed / sink rate) is maximized or (sink rate / airspeed) is minimized.  Naturally, this will not be the airspeed for minimum sink rate.  The airspeed for minimum sink rate will clearly always be lower than the airspeed for minimum (sink rate / airspeed).

Occasionally one encounters a suggestion that the best L/D speed or the minimum sink rate speed has something to do with the point where Induced Drag is minimized.  The vector diagrams above demonstrate that as long as Weight is fixed, when we maximize L/D, we also minimize Drag.  So at the best glide-ratio airspeed, where the L/D ratio is maximized, Drag is minimized.  Since Induced Drag decreases with airspeed and Parasitic Drag increases with airspeed, it follows that at the point of max L/D -- i.e. at the point of minimum Drag -- half the drag must be Induced Drag and half the drag must be Parasitic Drag.  This is the only point where Drag can be at a minimum.  Clearly, the point of best L/D is cannot be tied to a minimum in Induced Drag or a maximum in Lift / Induced Drag.  The ratio of Lift / Induced Drag is highest at very low angles-of-attack, i.e. at very high airspeeds.

For more on L/D ratios and gliding flight and powered flight, see this related A.S.E. answer, and other linked answers-- 'Gravitational' power vs. engine power
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/115370/discussion-on-answer-by-quiet-flyer-can-we-show-through-simple-geometry-rather-t).
Comment: This is a lot of text for a question asking for "simple geometry"...
Comment: @Sanchises -- the question is fully answered by the end of the fifth paragraph (third paragraph under the diagram), the rest addresses other topics of related interest.  Do you think the answer would be improved by simply deleting everything after the end of the fifth paragraph?
Comment: @quietflyer I think it would but I thought It'd be rude to suggest :) Especially as you asked the question yourself, you probably know best what you wanted to know, and my preference for short & concise answer is definitely a personal one. (It wasn't my downvote here)
Comment: related-- derivation of why min sink occurs at max Cl^3 / Cl^2 -- https://aviation.stackexchange.com/a/82201/34686


What tools do you use to answer questions?

Question: If you have useful tools to help you when you are writing an answer on a WPSE question, please list them here so we can all benefit from them!
Answer: I wrote a small script that creates a new plugin, based on the question ID. It uses the Stack Exchange API to get the question info, puts that in the plugin header, and opens the file in an editor.
I created a local setup with all WP versions since 1.5, with a plugin dir that has a symlink called wpse to a common plugin folder. I just need to go to this plugin folder, type wpse/create 1234, and it creates a plugin for question #1234 in the common folder, and a symlink in this version's plugin folder. If I want to try it out in another version I just create an extra symlink.
#!/usr/bin/env php
<?php
// This file is called `create`, in the common folder, and made executable
function createWPSEPlugin( $idQuestion )
{
    $questionInfo = getWPSEQuestionInfo( $idQuestion );

    if ( ! $questionInfo ) {
        exit( "Cannot get question info\n" );
    }

    $questionSlug = strtolower( preg_replace( '/[^\w\-]/', '', str_replace( ' ','-', $questionInfo->title ) ) );

    $pluginDir = $idQuestion . '-' . $questionSlug;

    $baseDir = dirname( __FILE__ );

    if ( is_dir( $baseDir . '/' . $pluginDir ) ) {
        exit( "Plugin already exists here!\n" );
    }

    if ( ! mkdir( $baseDir . '/' . $pluginDir ) ) {
        exit( "Cannot make plugin dir!\n" );
    }

    $pluginFilename = 'wpse-' . $idQuestion . '.php';

    $fh = fopen( $baseDir . '/' . $pluginDir . '/' . $pluginFilename, 'w' );

    if ( ! $fh ) {
        exit( "Cannot create plugin file!\n" );
    }

    fwrite( $fh, <<<EOF
<?php
/*
Plugin Name: WPSE {$idQuestion}
Plugin URI: http://wordpress.stackexchange.com/questions/{$idQuestion}/{$questionSlug}
Description: {$questionInfo->title}
Version: 1.0
Author: Jan Fabry
*/
EOF
    );

    fclose( $fh );

    $currentDir = getcwd();

    if ( 'plugins' == basename( $currentDir ) ) {
        // Educated guess: we are in a WP plugin dir
        symlink( $baseDir . '/' . $pluginDir, 'wpse-' . $idQuestion );
    }

    // Extra: open plugin file. Change this to suit your situation
    exec( 'open ' . $baseDir . '/' . $pluginDir . '/' . $pluginFilename );
}

function getWPSEQuestionInfo( $idQuestion )
{
    $urlAPI = 'http://api.wordpress.stackexchange.com/1.0/questions/';

    // This is probably not the best way to do this...
    $compressedResponse = file_get_contents( $urlAPI . $idQuestion );
    $jsonResponse = file_get_contents( 'compress.zlib://data://text/plain;base64,' . base64_encode( $compressedResponse ) );

    $arrayResponse = json_decode( $jsonResponse );

    return $arrayResponse->questions[0];
}

createWPSEPlugin( $argv[1] );

Comment: wow, very cool -- consider listing this on meta.so as well
Comment: @Jeff: As a WordPress-specific "question", or make it more generic, so people can post stub generators for other languages too?
Answer: I modified Jan Fabry's plugin above and created a mini-app of sorts that spits out a plugin file based on the question ID.
Here's what the front-end form looks like:

Here's a sample of what is generated.

All you need to do is:

Download the files here: https://github.com/inspectorfegter/WPSE-Plugin-Generator
Dump the contents onto your local server
Configure the plugin-generator.php defaults to insert your name and WPSE profile URL.
Answer: Here's a simple workflow I use to identify answers to difficult questions that aren't obvious in the Codex or from previous experience: http://3-3.me/eMTF
Here's my local setup for researching/testing/etc...

Standard local installation of WordPress setup to create and test answers
I use my IDE's 'find in files' function to search WordPress core for functions, HTML class names, or any other clue I can find on the DOM to help locate functionality
My IDE is also setup to track WP phpdocs and functions. This allows me to easily traverse the core by simple shift-clicks on the convenient links to the original functions.
I use Twenty Eleven with no plugins activated for testing answers as it is a good sanity check against rogue code in custom themes/plugins.

As a caveat, if difficult questions pertain to specific plugins, I rarely answer them and usually direct users to the plugin author via the WordPress.org forums. I am also careful not to do the entire work for the user, but give them a functional proof-of-concept.
Answer: We already had a related question about creating screenshots. Skitch was recommended for Mac users.
Comment: **@Jan Fabry:** Yes, I would love to see more people providing screenshots with Skitch or another tool that provides shadows; they make for a much more pleasing view.


Should I recapture the queen with my king or knight in the Scotch Game?

Question: I watched the following video on the Scotch Game by NM Dereque Kelley, and he clearly points out that 3...d6 is not a good move on Black's part because it causes all sorts of problems, especially coming from 4. Bb5 pinning the knight.  But if Black does play 3...d6 and 4. dxe5 dxe5 5. Qxd8+ follows, we arrive at a position that I have been in many times as White and as Black.  As Black, I normally would play 5...Nxd8, but in the video, Dereque says that this is not an option because it leaves the e5 pawn hanging, so Black must capture with 5...Kxd8 and give up castling rights.  Is this really the best move given that castling is a fundamental part of the opening?  I understand that 5...Nxd8 does leave the e5 pawn hanging, but what is more important here, holding on to the e5 pawn or maintaining the ability to castle?
Comment: I'm just an 1800 player but I can tell you (without watching the video mind you) that NM Kelley was, if not wrong, at least incomplete in opining 3...d6 is not good due to 4. Bb5.  Black handles this with 4...Bd7 and a transposition to the Steinitz defense to the Ruy Lopez (http://en.wikipedia.org/wiki/Ruy_Lopez#Steinitz_Defence) has been reached
Comment: @GeorgeJempty - NM kelley did not say the only reason why `3...d6` was a bad move was because of `4. Bb5`, he just didn't go into the the details of the other moves.
Answer: As you say, each of the options 5. ... Nxd8 and 5. ... Kxd8 has its own drawbacks: the former drops a pawn and the latter gives up castling rights. In this situation Kelley is right that losing the pawn is significantly worse than giving up the right to castle.
In a typical middlegame that features a lot of firepower on board for both sides, a king stuck in the center of the board can be in a great deal of danger of facing a mating attack. But in this case, the king gets stuck in the center only after the queens come off the board, which means Black has much less to worry about in terms of facing an attack. This queenless middlegame is not so far removed from an endgame, in which centralization of the king is generally a plus rather than a minus. Now there are still a lot of pieces on the board, so it's not a walk in the park for the Black king; I'm just saying it's not as dire as things can be with the ladies still around.
This particular position still has certain problems for Black (which is one reason why 3. ... d6 isn't the best choice); for instance, the king having been pulled to d8 means that the f-pawn is undefended, so with something like 6. Bc4 White develops the bishop, and the Black either must waste a tempo moving the king back to defend the f-pawn, or play 6. ... Be6 to defend the pawn, allowing White the chance to give Black doubled, isolated pawns by 7. Bxe6 fxe6. That's not the end of the world, and in this kind of position those pawns do at least help control some central squares. The main point: Black will probably end up with some structural problems, or lag behind in development for a bit, but this is better than the alternative.
Losing a pawn isn't the end of the world either, it's true, but here it's much closer. After 5. ... Nxd8 6. Nxe5, White is a clear pawn up without any compensating factors in Black's favor; in fact White has a lead in development as well. This is something Black definitely shouldn't allow, especially since we really are getting toward the realm of the endgame, where having an extra pawn is of crucial importance. Going this route puts White in the enviable situation of "playing for two results," meaning that from here either a White win or a draw are nearly certain, with a loss for White being very unlikely (barring a big mistake later of course). That's one of the worst things Black can do to herself in the opening.
Answer: Often losing the right to castle is OK for Black if queens are of the board. Take the Berlin Defense for example:
rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1
[StartPly "16"]

1.e4 e5 2.Nf3 Nc6 3. Bb5 Nf6 4.O-O Nxe4 5.d4 Nd6 6.Bxc6 dxc6 7.dxe5 Nf5 8.Qxd8+ Kxd8

Kramnik used this opening to win the title from Kasparov in 2000.
Comment: One thing the answers have in common is once the queens are off the board, castling is not as important.
Answer: Capture with the king and hang on to the pawn. The value of the "right" to castle is greatly reduced after queens are exchanged. If it goes into an early "endgame" (with the exchange of a couple more pieces), having the king in the middle of the board would even be an advantage.


What language should the questions be written in?

Question: I was about to ask a question on the main website, but was not sure if we are supposed to ask questions in English, or in German, or a mixture, or even both. My guess would be that most questions will get asked in English. But I wanted to be sure before posing my question!
Comment: I agree with both languages being allowed; and it seems that most others do too---so it's all good.
Comment: What about the header?
Answer: I think on Area51 it was suggested that we accept both English and German as question language, and I quite agree with that. While it might be a bit messy later on, that way we can make sure that everyone is able to ask about anything.
After all this page is not limited to people that are not native, right? I mean native German speakers should be allowed to ask questions too.
Comment: But it might be possible, that a native speaker wants to ask a question but is not able to communicate that well in English.
Comment: If we do not allow German questions, native speakers will still be allowed to ask questions, just not in their native tongue. I am a native speaker by the way.
Comment: Or it might be possible that a non native speaker wants to train and improve his/her German skills, like me. :D Of course, being sure that the question is grammatically correct. I wouldn't ask something in German if I thought it was THAT wrong.
Comment: Please note, that non native Geman speakers are automatically better in English. Think of Syrians, Turkish, Afghanistan, Chinese and Indien people.
Answer: Either English OR German question should be acceptable.
Many of the questions will be about difficult-to-translate phrases or really subtle nuances that would get lost in translation. There will be German users who I hope will use this site in much the same way English speakers use "English Language & Usage". Asking native speakers to "think in English" would remove much of its usefulness.
Stack Exchange sites are fundamentally for experts and avid enthusiasts in the subject. It's not unreasonable to expect the participants here to at least understand the subject matter.
This site is the first of the (non-English) "language" sites to get created, so we're going to have to work our way through some of the issues raised by a multi-lingual site.
Answer: I fully agree with the free use of German and English.
What is less clear to me is the language on meta and the language in answers to question.
I propose that ideally answers use the same language as the question, but to maximize participation, if people fall short of the ideal, someone can just add a translation.
Comment: I think reading questions in German is good practice. I think maybe ideally, answers would be in both languages, however otherwise I think answers being in the same language as the question is the way to go.
Answer: I totally agree that questions in both languages should be accepted. What I'm not sure about is how effective searching this site might become - you could extensively search for a term in one language and not find a question written in the other.
How big a problem is that going to be? Other than writing each question and answer in both languages, I'm not sure how to get around it.
Answer: Nach mehrfachem Nachdenken komme ich zum Schluss, dass Fragen, Antworten und Tags ausschließlich auf Deutsch sein sollten.
Natürlich können sie englische Inhalte behandeln und fragen:

Was wäre das dt. Äquivalent für "think outside the box"?, aber die Kommunikation sollte auf Deutsch stattfinden.

Gründe:

Es ist absurd, dass ein Chinese, Inder oder Franzose Englisch lernen muss, um den meisten Fragen hier zu folgen. Die Annahme, dass die meisten Menschen Englisch können, ist schon fragwürdig - eine Minderheit, selbst Muttersprachler, werden hier ausgeschlossen, was große Teile weniger gut gebildeter junger Menschen betrifft, und viele Ältere aus dem ehemaligen Osten, die zur Schulzeit Russisch gelernt haben.
Meines Wissens ist es allgemeine Praxis, dass Sprachunterricht in der Zielsprache stattfindet. Die Kommunikation über die Sprache findet auch in dieser Sprache statt.

Eben wurde ein dt. Tag, "Redensart" aus meiner Frage gelöscht. Jetzt habe ich Beiträge zu "Language" und "Tag" gesucht, und von dt. Synonymen gelesen, die im Hintergrund werkeln sollen. Eine Suche nach "Redensart" bringt aber 0 Treffer zu Tage.
Es ist absurd, dass dt. Muttersprachler die Seite nur richtig benutzen können, wenn sie Englisch benutzen.
en_US
Questions, answers and tags should be in German.
Of course, they might deal with English content and ask:

Was wäre das dt. Äquivalent für "think outside the box"?, but the communication should happen in German.

Reasons:

It's absurd, that a Chinese, an Indian or French have to learn English, to follow most of our discussions. The idea, that most people know English, is questionable – a minority, even native German speakers are left behind: People without much education in general and older ones from the eastern part of Germany, who were taught Russian instead.

It is common practice to teach a language by using it. So I expect that most people, trying to learn German, are done a favor by teaching them German in German.

The tag "Redensart" (idiom) was deleted from one of my questions recently. So I searched for meta entries to language and tag, and read about German synonyms, which act in the background, but a search for "Redensart" yields 0 results.
It's absurd, if Germans can't use the page without good English knowledge.
Comment: Ich bin auch der Meinung, dass Tags auf Deutsch sein sollen. Das Meta muss aber auf Englisch beschrieben sein, weil die Leute von StackExchange unsere Grundsätze verstehen müssen.
Comment: I support this point of view. It doesn't make sense to require that everything is written in English in a forum dealing with *German language*.  I do not have any problem reading questions and answers in English, but it would not be acceptable if German would be banned.
Comment: @StrixVaria: Ja, ein entsprechendes Posting mit einem Link nach Französisch.SE, wo ein Moderator im Namen von SE Englische Metadiskussionen verlangt hat, habe ich gefunden, und bin widerwillig bereit mich daran zu halten. Ich schreite also sogleich zur Übersetzung meines Beitrags.
Answer: I think that both languages should be allowed, for questions as well as for answers. I suggest some rules on how to meet a decision:

Language of a question
Use German if ...

... you are a German native speaker
... your German is excellent, even when you are an English native speaker
... your native language is not English, and your skills in German are equal or better than your English skills.
... you are an English native speaker with mediocre German skills and want to give your best to write a question using absolutely correct German language. (Users with enough privileges will edit your question to correct minor mistakes.) (also note item 1 in "use english if...")

Use English if ...

... your English is better than your German and you think that your question is mainly of interest for English native speakers who are learning German as a foreign language.

Language of an answer
When ever possible try to give an answer in the same language as the question was asked.
Some reasons why you might use the other language:
German answer to an English question

Your English is way worse than your German and you think, that the question's topic deals with something that is more interesting for people with high skills in German language (for example: Questions on regional aspects of German language or questions on language styles in old poems)

English answer to a German question

Your German is way worse than your English, but good enough to understand the question. So it's much easier to write your answer in English.
Answer: I think accepting German questions will just divide the site into people who speak German well enough and people who don't. Thus we should accept only English questions. Almost all Germans I know speak English well enough to make themselves understood. The rest can be fixed with editing.
Comment: I have to disagree that Germans should be asked to "think in English" to discuss the finer points of the language. Many of the questions will be about difficult-to-translate phrases or really subtle nuances that would get lost in translation. Stack Exchange sites are fundamentally for experts and avid enthusiasts in the subject. It's not unreasonable to expect the participants here to at least understand the subject matter.
Comment: I guess I won't be using this site then.
Comment: I totally disagree. This site should also be for expert question on the usage of German and for German speakers who search for the right phrase in English.
Comment: Why? We could introduce tags to indicate the language of the question and you can filter out all the German questions. The equivalent option is not open to me if you forbid German questions.
Comment: If you ban German, you will only reach a limited audience.


What is a kermesse race?

Question: I heard about a local club holding a kermesse race, and I was wondering what exactly they were?
Comment: Just finished some Kermis racing there myself - I have two more posts about the final two races (last one was best, cobbled climbs/descents, crap weather - great fun). http://ryansherlock.blogspot.com/search/label/kermis Races on everywhere, everyday and is aggressive from start to finish.
Answer: Not a big fan of this type of answer, but wikipedia has a pretty good definition of it.

The races are usually 90-140
  kilometers in total length. While some
  are longer or shorter, most are about
  120 kilometers. The race is comprised
  of a set distance and number of laps
  over the established course[2]. There
  are typically 10 to 20 laps, of
  between 5 and 10 kilometers. The race
  usually begins and ends in the center
  of the town which is hosting the day's
  race. The race will occupy the roads
  in town as well as the roads
  surrounding, either city streets or
  farmland.
The course usually has a rolling
  enclosure. This means that while the
  race is not passing through, the
  streets are open to traffic. A
  designated car, usually with a caution
  sign and a red flag, leads the riders
  and close the cross streets to
  traffic. A following car, usually with
  signs and a green flag, open the
  streets back up to traffic.
[...]
The kermesse is similar to the
  criterium but differs primarily in
  total course length and lap length.
  While a criterium traditionally last
  60-90 minutes, a kermesse will often
  take 120-180 minutes. A single lap in
  a criterium is usually less than 5
  kilometers while the kermesse is
  usually 5-10 kilometers per lap.

See the link for info on payouts and UCI information.
Comment: @domsterr - It's StackExchange policy for an answer to be reasonably self-contained, links are great for providing additional information or references. Theres a question about this on Meta Stack Overflow: [Are answers that just contain links elsewhere really "good answers"?](http://meta.stackexchange.com/q/8231/149375).
Comment: So I cited the good bits and encourage going to see the rest. Is that an improvement?
Comment: About that downvote to whoever did it, is it really necessary to re-write something up when a link provides the necessary information?
Comment: @domsterr: yes, significant improvement
Comment: So, basically, it's like a crit but with laps about twice as long and overall race also about twice as long?
Comment: This also came up in our own meta - http://meta.bicycles.stackexchange.com/questions/28/avoiding-just-buy-a-new-one-or-heres-a-link-answers - but a downvote with explanation would have been helpful so domsterr would know why/what to fix.
Answer: The answer by domsterr is a really good summary of what a kermis is. Here's some additional info:
They have these almost every day in towns across Belgium (and Holland) through the cycling season. (I stayed in Gent and there was always one within 30k of there.) They begin at 3 usually. The top 20 pays. First place usually receives 150 Euros. On our team, as with others, the first place rider in addition to the winnings from the race got 200 Euros from the team. This money was explicitly for bargaining. Often these races come down to a small group of guys. At which point you have to be measurably stronger than your breakaway companions, or do some politicking. You can either pay off the guys in the break, or enough to have them work for you while you attack. This is always part of the racing. The guys who are strong enough just ride away, the rest pay off the guys in the break, then ride away.
The races begin with 40-150 guys and get whittled down to roughly 15. The guys at the front attack non-stop, each time whittling down the group. As the riders fall off, they are given a 1 lap to go warning and then they sprint for whatever place that is. The guys who actually finish kermis races, as in they last the entire race without getting pulled, are strong enough to race and win some PRO/1/2 races in the U.S. Often you will see national teams bring their riders to kermis races for training. Most national teams have bases in Belgium for the summer so their riders can race locally. Also, there are riders from professional development teams as well. Guys who are technically PRO, riding for a real team, but making no money. In one race I entered (I was always dropped very quickly) Iljo Keisse was racing--a track legend.
Here's my post from the first kermis I went to. The posts after this are all from ones I entered.
http://hummushead.blogspot.com/2009/08/my-first-kermis-race.html
If you're interested in racing in Belgium let me know. I have friends there still and there's, no joke, a bike house where you can pay 200-300 Euros a month and race.
Comment: I changed "The above" to "The answer by domsterr". (Stack exchange pages aren't static, they're sorted either by date or the number of votes given, depending on what the user has selected.) Thanks for the answer, and welcome to the site!

What is a kermesse race?


How does sensitivity on teeth heal?

Question: When teeth become sensitive I suppose it's because of enamel wearing away. Isn't this permanent? If so, then how come sensitive teeth eventually 'heal'?
Answer: What Causes Sensitive Teeth? - WebmD
Things that cause this usually break down your teeth so that other things reach your pulp or tooth root which cause pain when touched.

Dental cleaning
Tooth Grinding
Tooth Decay
Age
Tooth whitening products, etc

So it is wear, as explained here:

You get it when your gums pull back and expose the surface beneath,
  called the dentin. This soft layer has thousands of tiny tubes that
  lead to the tooth's nerve center (the pulp). They allow the hot, cold,
  or sweet food to reach the nerve in your tooth, which kicks off your
  pain.

While the above is just one scenario of how it can happen, the way your nerve reacts is not specific to that. Tooth sensitivity can be stopped by several methods depending on circumstance. Flouride can be used to help build the enamel of the tooth back, root canals can be used to eliminate problems in your root canal and are one of the most successful treatments for this. Also, there are grafts which cover the exposed root canal desensitizing root canal by applying resins. Using desensitizing toothpastes also help and preventing further wear of enamel is always on the treatment plan. The reason why sensitive teeth can get better is because the root canal is exposed and recovering enamel or desensitizing the nerve fixes the problem or makes it less sensitive to pain.
While in this answer I may have used different terminology the word pulp, root canal and root are referring to the nerve in your teeth.
Comment: @CareyGregory I realized that to, thanks for the suggestion. I'll try to edit accordingly.
Comment: The term "root canal" was confusing for me initially because that's the name of a specific dental procedure. Since the quote uses the word "tubes" I might consider using that instead.
Comment: so for example, if you have a sensitive edge on your tooth, the flouride in toothpaste can cover up the exposed dentin?

How does sensitivity on teeth heal?


My 3 year old just refuses to listen to me

Question: I have a 3 year old little boy. Me and his father are both ADHD and my son's doctor says he shows signs of being ADHD too. We don't really want him to be on medication because meds messed me and his father up when we were younger and we just don't want the same thing for our son but I'm on the last straw at this point. We ask him to do something and he just ignores us, tells us no or just cries. We have tried everything. Behavioral therapy along with speech therapy but once they said he was finished he went back to doing the same things we took him for. We have tried whooping him, hand swats, time out, being kind and gentle, just simply telling him that what he is doing is a no no. It's like it goes in one ear and out the other. Recently we started potty training and he has peeing down but when we get him in a pull up at night or during the day he removes it and poops and pees on the carpet and puts it on walls. I'm at my end I just really need some advice.
Comment: Note that giving lots of different responses, while it's a tempting path to find a solution, results in less structure and trust in what he can expect when he behaves or misbehaves. Predictably is a virtue in training.
Comment: I feel your frustration. Our 2.5 year old also has a habit of selectively listening to us (only hearing what he wants to hear), but fortunately we don't have those potty problems.
Answer:
Behavioral therapy along with speech therapy but once they said he was
finished he went back to doing the same things we took him for.

Family therapy is not to change the KID's behavior. It's to change YOURS. The behavioral therapy worked, until you went back to your old behavior. You need to practice the behavior that worked. Then keep doing it.
One reason kids act out is to MAKE the family get help. The kid may be relatively healthy, and the parents need more help than they do.
There's a substantial overlap between ADHD and bipolar spectrum, and frankly the label isn't much help. If both you and your husband have behavior problems, work on those AND work with a psychopharmacologist for better medication solutions. Stimulants may not be the answer, but lithium and other mood stabilizers may be.
Hitting kids happens because parents are frustrated, not because it works on changing kids behavior except in the crudest, least effective ways.
How does the kid behave when left with others?
You need help.
Start with family therapy for you and your husband. If your moods are so out of control you can't help hitting the kid, the RIGHT medications may help.
Comment: to be clear, your last paragraph is suggesting the parents get on medications?
Comment: Hi Adam, they have substantial issues. Parents MAY do better w meds, but the first thing they need is an accurate diagnosis. Medications should make them MORE functional, not less. Diagnosis for mental health is notoriously delayed, leading to lots of suffering.
Answer: Edit:  In another answer Autonomy Support Parenting was suggested.  After researching this topic I feel it is not appropriate or relevant the the matter at hand.  However, I concede my perspective and experience is in the United States and our cultural experience is different than other countries.  I do not support breaking the law and if anything I mentioned below is contrary to your state or countries laws then please disregard.
Original Post
There is hope for your situation, and it is a good thing you are asking for help now.  You must first stop being inconsistent and come up with a pre-planned response to dealing with your child not listening and doing the wrong thing.  Things to keep in mind

Be kind and respectful to them
Be emotionally detached, never act out of anger, only love for them and their development
Do what you you planned, nothing more or less, unless you change your plan itself
Your plan should have progressive steps that are clear.

At the end of the day your individual child will react better to some things over others. I'm not against spanking, but it is a double edged sword as you can easily fall into frustration and use it wrong, and without enough love and attention you fall into the trap of being authoritarian and ruining your future relationship and development of your child.
Remember that acting out is normal for children, it is normal for adults too.  Here are some age appropriate tips that I reviewed and think are valid. Source: An age-by-age guide to disciplining your kid
• Ask once nicely ("Please put your toys away").
• Ask a second time, but warn of a negative consequence if your child doesn't listen ("I asked you to please put your toys away. If you haven't done it by the time I count to five, I'll have to keep them from you until tomorrow evening"). Avoid making unrealistic threats like "Slam that door and you'll never watch TV again!"
• Apply the negative consequence, if necessary. "If you don't make good on your promise of discipline," says Radcliffe, "you lose credibility."
Your plan of action needs to be kind, to the point, and something you and your spouse can do repeatedly without losing your cool.
Avoid
• Long drawn out battles
• Emotional outbursts by adults
• Demeaning your child
Do
• Have a plan you stick to
• Communicate what is happening each step to your child
• Follow through with your established consequences
• Reconnect and show them they are still loved after the event is over without rewarding their bad behavior
• Spend quality time with them at other times so your only interactions are not during discipline times.
Comment: Adam, I agree with your outline, but IMO this family needs more than self-help. They skirt it, but I think there's enough loss of temper and physical punishment going on so I'm concerned about abuse. And the kid is clearly acting out in ways that DEMAND they do something.  I'm also concerned bc they say 'when we did this, it worked, but we stopped.' They need more training. Also concerned re poss bipolar in one or both parents-untreated leads to lots of suffering. I dunno why you got downchecked. I +1.
Answer: This is a phase during normal child development where the child starts to develop their autonomy. We are not able to give advice on medical issues, but from your description, there is nothing that hints to me that this should be especially related to the use or non-use of ADHD medication. This is normal behaviour in any child.
Typically, obedience will decline from here on, as obedience is the antithesis of autonomy. If your goal is to raise an obedient child, you may persevere, by doubling down on authoritative measures, and you may see that your child eventually yields to your will, but such success is usually temporary, and backlashes are common.
If, instead, you wish to raise an autonomous child, this is where you should dial back expectations of obedience, and start working with the child. Role model cooperation, so that the child will be encouraged to cooperate with you. The description that your child "doesn't listen" reveals an expectation of obedience. Think instead that he is listening, but having a different opinion / choosing not to cooperate.
Seen in that light, "we ask him to do something and he just ignores us" is no longer a problem per se. It is just the child being autonomous. It may cause problems to you, downstream, but that's a more workable situation. Now you do not have a problem with disobedience (since you're not aiming for obedience). Instead of trying to get your child to comply, you are now in the position of trying to work with your child to find solutions collaboratively, that accommodates the child's needs in a manner that doesn't cause problems for you.
Comment: I think this is a dangerous suggestion and detrimental to the well being of the child.  Parents and children are not equal in authority and establishing such a relationship is not healthy.  I do agree that they are equal in value, but you don't seem to make such a distinction.  In many life areas we are expected to listen to authority and further there are safety reasons to do so.  Think of holding hands while walking in a parking lot, or keeping your child next to you in sight while in a store.  These are potentially life threatening and only the tip of the iceberg to the value of obedience.
Comment: @Adam: Conversely, I think imposing your will in life threatening situation has more clout if you don't also always impose your will in less important situations. The case for autonomy supportive parenting stands on rather firm scientific ground. See for instance Ross W Greene's CPS model.
Comment: Another point - I work with children in groups, i am a parent of 3, and my wife is a 20 year teaching vet, my mother has 40 years teaching and my sister 15.  To be frank, self-discipline is completely lacking and I have serious doubts about any 'modern' and 'contemporary' theory on childhood development.  On the ground floor kids are less capable and self secure then every before.  Theory is great, but practice is the sword the divides truth from fiction.  I am not blowing smoke when I say it is unreasonable to expect a society to function and kids to grow and respect adults when you have ...
Comment: We've already concluded this discussion in chat, but for completeness, if anyone's reading here: my view is that you can only teach self-discipline by letting the child *practice* self-discipline. Imposing external discipline defeats that purpose. If the kids succeed anyway, it is - I hold - *despite* that manner of parenting. On a personal note, yes, you win in experience. Luckily, the views reflected above are not derived from my own personal guesswork, nor are they unrooted in practice.
Comment: if you have direct links to support your viewpoint you should include them in your answer.  On a side note, I have seen a high number of parents with out of control teenagers ruining their lives and one root issue is lack of self-discipline.  This type of theoretical research is worrisome as it's practical outcomes don't match the theory.
Comment: ... to come to a personal understanding with all of them.  It simply doesn't work.  I also still stand by my previous examples and can add any number of new examples from supporting illicit activities, to addictive drugs, driving and following the rules of the road.  Seriously the list is long and the truth is kids don't get it, their brains are literally and scientifically not developed for many things.


What is a Birdseye Maple Neck?

Question: Where does it come from or how is it chosen over regular Maple Necks - is there a tonal difference?
Answer: Birdseye maple is a cut of wood from one of several types of hard maple, most commonly  Acer Saccharum. The only real difference between birdseye and regular hard maple is the figure, which doesn't really do anything to the tone of the wood. It's still as bright as any other type of maple. Scientists really have no clue as to why the figure occurs, but we guitarists are sure glad it does ;).
I would simply consider it an aesthetic benefit--and what a benefit! Under gloss it looks beautiful!
Comment: What's interesting/curious, is that the figured maples were considered junk wood for many years, and used for furniture like school desks and chairs. You can find old school furniture with highly flamed and quilted tops, or nice birds-eyes. My mom had one for years that made me nuts because it would have made a beautiful guitar top.
Answer: The name "maple" for wood is very ambiguous (there are many subspecies and also other species sold under this name). If one stays with the "commercial" names, on an aesthetic level there is plain maple, flamed maple, quilted maple and birdseye maple.
It can have really complex figures that reveal themselves fully after varnish. The effect and shapes are very diverse from one example to the other. Here is an example of a guitar neck (found at 1.bp.blogspot.com):

Plain maple can be very nice in its simplicity (image taken from the Gibson Website).

As jduv said, there is probably no impact on sound but it may require special care when carving and finishing.
There are so many things to look for such as the quality of the neck shape itself, hardness, drying process, etc. as explained in other questions here.
Comment: Interesting. By simplicity, do you mean the sound?
Comment: @neilfein: Not in a first approach. I first mean the visual aspect. I remember seing and hearing a plain maple Les Paul (which sounded also very nicely). I will add this image to my post.

What is a Birdseye Maple Neck?