Robotics Location Following and Tracking?

Question: I am building a robot that will follow a target as the target moves around. I would like some help with the setup for tracking the target. The most obvious solutions are Ultrasound or Infrared sensors, but for this application, they won't work. Imagine that the robot is placed into a crowded area and asked to move towards a particular person in the area (for the sake of simplicity, assume the person is less than 5 meters away). Is there some kind of radar or radio solution to this, or anything?
Comment: We really need a bit more information to answer this properly.  Solutions to robotics problems are heavily dependent on the environment and what you are trying to achieve.  Information like what type of robot (does it fly, is it land based at eye level, ankle level?) would help.  How do you acquire the target (a controller manually selects the target, rule based classification, can the target be physically tagged with something, etc).
Comment: Right away, I am thinking of an RF solution where the person to be followed has an emitter. The robot could have a couple of tuned detectors mounted to scanning servos to help determine which direction the signal is coming from, following it based on signal strength, but this could have a lot of complications. I agree with @anorton - this should be migrated to Robotics.SE to get a good answer; it's not the best fit here.
Comment: @KurtEClothier "I am thinking of an RF solution where the person to be followed has an emitter" Right, so clearly, we need to build an ... emitter follower.
Answer: In a broad sense, there are a couple of ways to do this, but they basically boil down to the problem of how do you know what person you're going towards?
If it's feasible to give the person a flashlight or some light source (IR or visible), you could use light sensitive elements to determine where to go.
Magnetic fields could also be used, by giving the person in question a strong enough magnet.  (But it would have to be pretty strong, so I don't think this is as feasible...)
A final resort would be to attempt some form of a vision system.  For instance, if you gave the person a lime-green ball, a vision system could pick up on that, and treat it as a target.
Comment: It's a rather large misconception that magnets _destroy_ sensitive electronics. At most, you'll get interference, and that's in rare cases. In fact, most modern electronics aren't affected by magnetic fields of reasonable strength, with the exception of spinning hard disks.
Comment: Ideally, the person being followed could carry something like a transmitter to have the robot follow them. It would NOT be ideal for that person to be followed with a vision based approach, because I would not want the robot to be distracted if, for example, someone walked between it and the target. Magnets are no good, because of their propensity to destroy sensitive electronics.
Answer: The tricky part with what you want to do is that matching a person to some electronic representation of their "signature" is a very difficult task to do. Outside of some advanced facial recognition software, or tweaked vision software that could recognize a lime green shirt for example, there isn't much you can do.
I thought of something I haven't seen suggested elsewhere so I don't know if something like this exists or not but it seems like it could work for you with development. Perhaps using an thermal infrared camera to calibrate a thermal image of you putting in your height dimensions would work. Ultimately you are still getting into a vision based solution but a thermal camera would auto-greenscreen your whole body so to speak so you wouldn't have to worry about wearing the right color clothes or vibrantly colored clothes. It also wouldn't matter which direction you were facing. One caveat would be if you sat down or bent over, you wouldn't be properly height matched so something would have to account for that.
Anyways, just thought I'd throw that idea out there. It wouldn't work in a crowded area as well as you being the only one wearing vibrant green and color matching with a vision solution. Perhaps a combination of the two? Two cameras are better than one.

The issue with any kind of field based approach is that the robot wouldn't know in which direction it was coming from without enough resolution which might force one to get expensive high resolution equipment. Also, the smaller the robot, the more expensive and higher res equipment one would need to triangulate a point of origin.
Alternatively, sound signatures could work. Sound waves are slower than electromagnetic waves and so would be easier to triangulate. You could also use a frequency that humans/animals cannot hear. You wouldn't need very high end equipment I don't think if you orient mics at appropriately far angles apart. Imagine a "follow my voice" kind of scenario.
Perhaps RF would work here too as mentioned but it does depend on the size/equipment.


Can I limit IIS to use one rather than two processors?

Question: Our ASP.NET app uses a component that is licensed by the number of processor cores. Unfortunately, our customer wants to deploy the app onto a multi-function server (IIS, SQL Server, file server, etc.) that exceeds the number of processor cores for which the customer is licensed: they are allowed four cores but have two processors with four cores each. Can I configure IIS 6 on a Windows Server 2003 machine to use only one processor?
Answer: You can set processor affinity (and thus limit to 1 processor) per application pool, which would effectively limit the app that runs in that pool to use one processor.
This will limit the w3wp process to only use one processor, which is hopefully all you need to comply with this licence.
The other IIS services (admin service etc) will still use both CPU's
You can find the details on how to do so here.
Comment: doh, you beat me to it
Answer: Firstly you should put the app in it's own application pool, you can then set affinity for each app pool in the metabase.  Allowing you to limit that one web app without limiting anything else.
http://www.microsoft.com/technet/prodtechnol/WindowsServer2003/Library/IIS/529588d3-71bc-45ea-a84b-267914674709.mspx?mfr=true
Answer: Set processor affinity.  I think that may do what you're looking for.
Answer: You can configure Windows to use only a specified number of processors in the boot.ini file via the /numproc switch. Of course this disables those processors for the whole OS, not just IIS.


Why Frequency Domain conversion is Important in Digital Image Processing?

Question: Any Image enhancement technique can be easily applied to the normal images. Still, most of the folks say that frequency domain conversion of the images can lead to better enhancement. Why do we need to view images or apply enhancements in frequency domain when they can be easily used in spatial-domain? Can someone please explain this in plain and simple English rather then mathematical equations for the sake of simply understanding the concept.
Comment: Some distortions like periodic noise can only be observed and  removed in frequency domain and in some cases fourier is faster O(NlogN) vs conventional filtering.
Answer: Not sure if frequency domain is necessarily better for image processing but frequency domain does give you an advantage for certain types of problems because it is more quantitive.
First you need to understand what frequency domain of an image means as it is intuitively difficult to look at frequency domain of an image and make sense out of it. Topic is beautifully handled here : What does frequency domain denote in case of images?
Basically frequency domain represents the rate of change of spatial pixels and hence gives an advantage when the problem you are dealing with relates to the rate of change of pixels which is very important in image processing. For example :high frequency in the frequency domain represents rapidly or sharply changing pixels such as boundaries or edges in an image. A high pass filter can be extremely helpful in identifying or removing these edges easily but the same problem is much more difficult in spatial domain (x-y domain).
Similarly a simple low pass filter can be used to get a smoother image. As you can guess images can be easily made sharper or smoother by manipulating different parts of frequency domain.
Some points on why it is so powerful :

Frequency domain gives you control over the whole images, where you can enhance(eg edges) and suppress (eg smooth shadow) different characteristics of the image very easily.
Frequency domain has a established suit of processes and tools that be borrowed directly from signal processing in other domains.
Some tools used for even image recognition such as correlation , convolution etc are much simpler and computationally cheaper in frequency domain.
Answer: Let me first balance some of the assertions. Because of the non-stationarity of many image features, frequency (on the whole image) is not so informative in some cases.
Then, some processings are easier, or faster, in the space domain, some in the frequency domain. For instance, homomorphic filtering, a breed of linear (frequency) and not linear enhancement is done in frequency.
If one focuses on linear filtering, as several patches with a similar content can be located across the image, all these patches "gather" in the same regions of the frequency domain, and the global effect of the filtering is seen more easily in this domain. Especially if you want to modify the relative importance of oscillations, or frequencies, their quantitative alteration are perceived in a simpler way in the Fourier domain.


Alternative to WScript.Sleep

Question: I'm using WhatsUpGold to monitor the uptime of services and one of them is a MySql server. Since there's no explicit support for MySql, I'm forced to write a VBS script to do it. Unfortunately, WhatsUpGold doesn't support WScript.Sleep. The alternative that is on their forum is this one but it seems like a dirty hack. Are there any alternatives to the two of these that I can use? I'd really prefer not to have to copy/paste functions around.
Answer: Ooh, now that is a hacky trick. It'll work though, if the user the app is running as isn't locked down such that it can't use wshell.run. I think I actually like it...
If the app is running on a box that you have admin access to so that you can register a COM DLL, then when I want a sleep in classic ASP code for testing (it is sometimes useful to insert artificial delays) I use a simple free DLL that is unfortunately not longer available from the original source (see here for some discussion). If you want to give it a try I've put a copy in here. To invoke, use something like Dim WaitObj: Set WaitObj = Server.CreateObject ("WaitFor.Comp"): WaitObj.WaitForSeconds 10
No doubt that library is just a wrapper around the sleep API call, so you could make your own if you don't want to trust some random library from some un-vetted 3d party (trusting anonymous code from un-vetted sources is not something I would not recommend, and I count as an un-vetted source). For VB6 the call would be declared as Private Declare Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long).
First thing I would do at this point though, before trying either of the above, is ask over in StackOverflow to see what other people use for non-busy waits in classic ASP. You might find there is another library out there that is still supported by its creator, or a better technique altogether. As the ping trick is using CreaetObject I suspect that anything usable in a classic ASP context will be usable from your app.
Answer: Ugh! I haven't used any of the "WhatsUp" software in years, so I've lost familiarity. A quick review of their forum and a search with my friend Gooogle confirms the ugly hacks you've mentioned.
I'd go for abusing PING like we do in batch files sometimes to get a delay. It's clever, but ugly.
The alternative to being ugly would be to come up with code that doesn't need any "sleep" functionality at all. How are you monitoring MySQL? Are you connecting to it with ODBC and running a query to judge its "aliveness"?
Answer: The ping -n X 127.0.0.1 trick is a hack, but not particularly dirty. It is widely known and used in all sorts of Windows batch scripts since the last century ;)
Answer: have you tried SleepCMD
Answer: Why not just use a a setTimeout method?  Look at the following "Hey, Scripting Guy" columns:
http://blogs.technet.com/heyscriptingguy/archive/2006/03/30/how-can-i-temporarily-pause-a-script-in-an-hta.aspx
http://blogs.technet.com/heyscriptingguy/archive/2006/08/18/how-can-i-minimize-or-hide-an-html-application-for-30-seconds.aspx

Alternative to WScript.Sleep


05 Mustang electrical problems

Question: I have a 05 Mustang base V6 auto. Headlights won't stay on. Sometimes high beam works. Everyday it's different. Last night when the fans turned on the lights would come on the off again when the fans turned off. Today I can't  get them to stay on more than 2 seconds while the car is running. If the car is off they will stay on as long as you need them to. I've checked fuses and wiring. And replaced the headlight switch. While the car is running, if you turn the headlights on they will stay on for a couple of seconds then go off, turn the headlight switch off then back on they'll come back on for a couple of seconds. Also, occasionally the windows won't work, interior light and the car won't shift out of park (does this all at once) I don't know if the problem is all one thing or not. Any ideas trying to avoid the dealer.
Answer: Might be a possible alternator failure. You can check the battery voltage. It should be ~12V when not working and ~14ish on idle. This kind of faulty alternator causes something like that.
Comment: I forgot the solution. At the circumstane you have alternator replacement is the only solution I guess. And then you might need to charge the battery with this new part.
Comment: Radio and everything else works i just cant get the lights to stay on. Everything reads 13 volts. The car has aftermarket halo headlights in them i unplugged the headlights from the harness this morning i had brake lights for 25 mins then all the lights (brake, dash, and interior) shut off. I had to start the car up a couple of times before they would turn back on then 15 mins later i lost all my lights again.
Comment: Improper voltage signs faulty alternator in general but not that situation it seems. However I still doubt on alternator. Thanks for the feedback
Answer: First, remove the illegal, substandard, and defective "aftermarket halo headlights" and the ballasts that came with them, and replace with the OEM lights.
Then repair the damage the ballasts did to the rest of your system when they back-fed your wiring harness with high voltage discharges.

05 Mustang electrical problems


find route distance & time taken to travel between two points using leaflet

Question: I am able to find route between two points using cloud mode & leaflet using this.
CloudMade Routing with Leaflet: route is not displayed
But I also want to find distance & time taken to travel from first point to last point.
Answer: Looking at an example of route : http://routes.cloudmade.com/8ee2a50541944fb9bcedded5165f09d9/api/0.3/47.25976,9.58423,47.26117,9.59882/car/shortest.js
You can adapt the function given on the post CloudMade Routing with Leaflet: route is not displayed to retrieve response.route_summary : there you will find total_distance and total_time.


.25" bleed on an irregular shape

Question: How would I go about adding in a .25" bleed on the shape attached? The magenta line is the final shape. These will be diecut so I'm hoping it won't matter too much but I'm struggling to figure out the best way to extend the shape. The top and bottom edge are simple but where the rectangular shape meets the circle, things get awkward. What am I not thinking of?
Answer: Bleeds do not have to follow shapes exactly. They simply need to be a minimum distance from the artwork.
Factor .25" outside the circle and then run the bleed as a rectangle to that distance. It will be greater in the area of the vertical strip, but that won't matter.
In this case, just extend the strip edges making certain the circle cuts into the strip properly. Since the circle isn't printing, you merely need to ensure the curved edges around it are correct for the bleed.

I would probably consult the print house with the 3 options above and ask them which one they feel is best suited to meet the bleed requirements for their die cutter. without consultation, I'd run with the rightmost option (that shows the cursor on it).
The primary issue is, you have to imagine a hairline variance. So, if there is a variance, which would you prefer... a little curved white cutting into the strip, or a little blue cutting into the circle? I feel the right option eliminates these factors as much as possible should there be a variance.
Comment: So glad you showed me that third option because that's exactly what I did after reading the answer before you edited it, I'm going to run it by them now. Thanks, Scott!
Comment: I would never print options 1 or 2. Those are simply incorrect. You'd never hit a perfect white with those. I'd edit your answer to include only your third option since it's the only correct one.
Answer: Select the outside path and choose Object > Path > Offset Path and experiment with the setting. It will give you a replica of the path that will allow you to hold bleeds.

.25" bleed on an irregular shape


Should I use real pedal for making the best sound or using virtual amplifier is enough?

Question: I am currently deciding whether I should buy a real pedal for overdrive/distortion or just stay with virtual pedals in my Guitar Rig 5. What are the pros and cons of using one or the other?
Comment: It seems like you are asking for an opinion here, which is off topic. An objective response is that the analog versus virtual effects will sound *different* from each other, and it's up to you to decide which kind you prefer and fits the sound you are going for best.
Comment: @ToddWilcox I did not know whether it is subjective or not, I am sorry. You may answer with this comment, I'll accept it. Or I may delete this question if necessary.
Answer: The answer to this will very strongly depend on the quality of your gear.  Most often, I find that an amplifier with built-in effects ends up not being of very high quality.  This tends to be the case with other types of products as well, such as a TV with a built in DVD player.  When a company chooses to build in more than one thing and keep the price relatively low, the quality of both is sacrificed.  This is not a hard and fast rule but if you are buying anything on the lower end of the pricing scale, it's significantly more likely.  I have had and have played with people who had built in effects that they were very satisfied with but these were relatively expensive.  The other issue that comes of this, is that if your amp decides it doesn't want to work anymore, you have no effects.  In the case that you are playing a gig when this happens, you may be able to borrow someone else's amp to get through your show but then you don't have all the effects that you are used to and potentially can't accomplish your desired sound.  A lot of gigs that have multiple bands playing throughout the night will end up having shared gear, so if you were playing such a gig, you may not able to share amps with others, which can be logistically annoying.
One thing that is particularly nice about a pedal board is that you have independent control over each effect, allowing you to turn on or off any pedal at any time, where a virtual setup will likely have a preset that you can only dial in through the amp.  On the other hand, having presets can be helpful because you only have to hit one button to change all of your effects for another sound, where a pedal board may require that you turn off multiple pedals and turn on several others, so there is some practicality.
With all that said, if you are just learning and not gigging yet, getting everything built in may be easier for you to work with and a lot of the concerns don't apply.  You can always buy pedals later if you find the quality is too low or start gigging and it becomes an issue.
Comment: I just reread your question and realized that you are likely not talking about an amp with built-in effects but an application for computer or phone with a virtual setup.  Is that accurate?
Answer: I use both sim software on my IPad/Mac and physical pedals, depending on my mood and situation.
I use Bias FX on my IPad, Amplitube on my Mac; I use this when I am on the move, or sitting at home noodling in front of the TV, no need to worry about leads, batteries, and takes up very little room.  In addition, you have a whole range of effects and amps that you would never have physically, however you can spend more time playing with your settings than actually playing.
However, when playing with friends or even just practicing in front of my amp (loudly) I prefer to make things VERY simple.  An amp, a pedal (fuzz rather than distortion at the minute) and guitar.  I enjoy how physical it is, more tactile and I get more out of my single effect than I ever would if it was virtual.
In the end its down to personal taste, and the quality of amp and effect sims are fantastic, however its just as easy to get a bad sound out of a virtual pedal as it is a physical one.
Answer: While Todd Wilcox is right in his comment that they will sound different and it's your opinion that matters, I think there are some points that most would agree upon.

Many people prefer real pedals and real amps as far as sound and dynamics.
Many people use virtual/digital amps and FX anyway because they are convenient and economical (low volume, many sounds for a cheaper price, easily recallable settings saved digitally, etc).

Opinions differ—and yours might—but if you polled a bunch of guitarists that have used both, you'd start seeing that pattern emerge.
So for you it probably comes down to whether you are happy with the sound you are getting and if not weighing that against the cost/convenience of software.
PS. If you meant staying with software for an amp but adding a gain pedal in front before your interface/DI, I'd be wary. I've never had very good results with using pedals in front of amp sims. It doesn't hurt to try it though.
Answer: I don't do gigs and I have been using a PC for a number of years now. I was using an old stereo amp with a decent size "2.1 speaker" setup which got loud enough and didn't color the sound too much. I also have bass and an electronic drum kit so I have a mixer I use to switch inputs and attenuate etc. That amp has since died, so I am now using my old Spyder2 amp.
I put together a reamper kit box (L2A/Line2Amp) which matches impedance for high-z guitar amp input.
Right off the bat, using a guitar amp means not using any of the cab and amp sims, as they sound pretty awful.
I have been using wah, compressor, gain, and fuzz sims and the main problem with all of them is that you need to be especially careful about the gain or volume. Virtually none of them have db meters or any kind of guidance regarding reference levels, and the software often has input and output gain knobs, preset knobs, knobs on the ADC (analog-digital converter "soundcard"), knobs on the PC volume.
So you need to do a lot of work taming the signal path.
If your sim software has any sort of metering (like built into a compressor sim), try using that to visualize the signal. I also found it helpful to toggle pass-through mode to ensure the guitar amp is receiving something very close to what it would see without the PC in the middle.
I don't play around too much with different pedals and sounds so I am actually pretty happy with the result, but I think that the distortion and fuzz tends to be kind of thin and cold sounding compared to real pedals. The basic overdrive and compression kick along with the real amp overdrive is not bad.
So TLDR; volume/loudness saturation; potentially excessive re-re-re-amplification (the wrong kind of distortion); cold & thin.
One other thing: this stuff is fragile and may not travel well without headaches or excessive fiddling on site.


Using TFT with hardware SPI and speaker with tone()

Question: I want to make a device with a TFT screen and a speaker that uses the builtin tone() function. However, according to the documentation, using tone() interferes with PWM on pins 3 and 11. On the Arduino Uno, the MOSI pin is default on pin 11, and it seems like defining another pin for MOSI disables hardware SPI, which, according to the module page, slows down the device. As well, the examples are written for hardware SPI and the SD card is only available with hardware SPI. What should I do here? Is there a way to redefine the default MOSI pin without disabling hardware SPI?
Comment: It is no problem. The tone function uses timer2 which is the same timer when using pwm for pin 3 and 11. The tone function does not interfere with pin 3 and 11, it only uses timer2 for a software interrupt to create a tone on any pin. The tone function does not use the pwm capabilities of the microcontroller.
Comment: short version : "interference with PWM", not with SPI
Answer: You are getting your wires crossed in your brain and imagining a problem where there is none.
Both PWM on pins 3 & 11, and tone(), use the Timer2 device. Only one of those can use Timer2 at a time, and they both want to use it in different ways, so there is a conflict between them.
Timer2 has nothing to do with SPI. So tone() has no effect on SPI, and nor does PWM have any effect on SPI (other than the fact that only one can come out of pin 11 at any time), since there is no internal resource conflict.


How should we abbreviate the tag for "Affordable Space Adventures"?

Question: This question was asked, but with the inappropriate tag. I tried to add the tag affordable-space-adventures, but that is 27 characters long. I'm not sure how to abbreviate the gamename (or remove the dashes, but then it becomes unreadable), so that is fits into the tag.
Comment: [tag:affordable-space-adv] maybe?
Comment: cheap-space-trips?
Comment: @Ktash I think something like that will work. If someone want to ask a question about it, they first type in 'afford-'. If that tag pops-up, it will be used
Comment: That would do the trick. However, the findability and usability is not very high, I suppose :P
Comment: Only real way I can think about shortening it and still getting that. I searched around but didn't see any abbreviations for it in use on any other pages.
Answer: I edited the question, and took @Ktash's suggestion. The new tag is now affordable-space-adv. When one enters the first few characters of the gamename, then this tag will pop-up.
Comment: With cases like this, please feel free to edit the tag wiki blurb for the game with the proper name so it shows up on hover. It helps to disambiguate the game when we have cases where the title won't fit within the tag limit.
Answer: status-completed
Now that the tag length was increased to 35 characters, I've went ahead and retagged both questions with the full title.
The tag name is now affordable-space-adventures.


Is Jihad Al-Nikah (جهاد النكاح) an Islamic rule?

Question: I heard about Jihad Al-Nikah in television and radio, especially in the Syrian war which Saudi cleric gave a fatwa about it. Does it exist in Islam?
Answer: There is nothing in Islam as Jihad un-nikah. I bring you the history of this story.
Firstly, this Fatwa was issued by a news network called Al-Jadid in Lebanon on December 2012. It had claimed that Saudi sheikh Al-Arifi has issued a Fatwa about Jahad-u-nikah and made it Halal. But After this news, Al-Arifi and his companions  rejected it.
Then in march 27, 2012, Pan-Arabist newspaper called Al-Hayat from Lebanon issued an article about Tunisian girls, who leave their countries to attend Jahadu-Nikah because of Mr. Al-Arifi's Fatwa. But the report provided no evidence that this Fatwa was issued officially by Al-Arifi or other Muftis.
The next propaganda was in July 2013. In that time, Some news network such as Al-Arabia and Associated press issued several article about jahadu-Nikah of Egypt Akhmatova-Muslimin women just on the basis of a Facebook post. And Russia today in those days Have a report from the women who got pregnant and left Syria.
Roth Michelson, Author and journalist who spent some time in Syria in September 2012, is one who has written extensively about the war in Syria and sexual abuses, however, he highly doubts this rumor is correct, and says that widespread dissemination of this story is owe several thoughts called racist and Orientalism as they are hidden in this.
Answer: There is nothing in Islam called Jihad An-Nikah (sex Jihad).
It was propaganda made by some people and was widely spread by those who hate the Saudi cleric.
Here is a video of him denying it and then stating that the tweet that he sent was photoshopped to make it look like he has issued Jihad An-Nikah fatwa.
Here is the photoshopped image (205 characters which Twitter doesn't allow)
Comment: I declare it in my answer


How does one memorize a chess game?

Question: I study games from books, and would like to retain some of them in my memory, especially the opening part. I also want to remember my own games (I play about 5-10 tournament games - mostly against >2000 ELO rated players, and some rapid ones here and there). Are there any particular techniques or tips?
Comment: How do you memorize a song? You can just read it until you can repeat it, or you can try to understand it. Lyrics, melody, chorus verse and bridge. The deeper your knowledge about what makes music beautiful to you, increases your ability to remember beautiful pieces effortlessly. Same applies for chess.
Answer: In my experience, memorization of chess games simply came from improvement. I first realized that I could remember the games of past tournaments when I was around 1600 ELO, and as I improved my visualization became sharper and I could recall games played years ago. My advice to you is to have the games notated and not just read, but play through them regularly. This repeated process of playing the moves of a game will help you retain the information necessary for you to recall the game in the future.
Comment: +1 I agree.  I just want to add that playing through the game on a physcial board helps memorization more than playing through the game on a computer.  This probably has something to do with your brain not just remembering the moves but also remembering moving your arms.
Comment: I'd add to this that stronger chess players need to memorize fewer moves to accurately remember a game, as some parts of it will just "feel natural"
Answer: Memorizing things move by move is very hard indeed. There's evidence that masters use something called chunking. Google chess masters chunking to see various links. A basic example would be instead of Nxd5 Bxd5 Bxd5 cxd5, you might think "everything is exchanged on d5." Masters might think "OK, we set up the King's Indian formation."
https://www.chessprogramming.org/Chunking
Once you understand basic structures and motifs, memorization will be easier. Until then, it may feel like studying for a test in a class you don't like.
Comment: the link is broken... the correct link is https://www.chessprogramming.org/Chunking
Answer: In chess, memory is related to learning. The deeper you study, the easier it is to remember the most important points. Its about quality not quantity. You can "cram" openings, but unless you understand the position you'll start making mistakes. You'll play better if you focus on the types of positions that interest you.
Answer: There are a few techniques to remember openings -

In the beginning, stick to a single opening. Ex: play only 1.e4
Choose an opening that has fewer variations or that has (more or less) standard set of moves. For ex: King's Indian Defense or Sicilain Dragon variation. You can mostly play standard moves without worrying about white's moves.
Study common traps in your opening
Last (but not the least) - practice. Study more games and play often.
Answer: I found that flashcards are a great tool to help memorize complete games and game openings. They allow one to implement in practice many concepts mentioned in earlier answers.
There are many flashcard software available, including free ones. Some allow to schedule future reviews based on the difficulty of a recall. The idea is to drill difficult moves more often then easier ones.
A single flashcard could be created by taking a screen shot of a particular game position and inserting it in the question part of a flashcard.
The answer part will contain the screen print of the next position of a game.
One potential drawback of this method is that it can be time consuming. A game containining 70 moves will require 140 screenshots.
There are ways to streamline it and even fully automate it.
For example this website will create chess flashcards automatically out of a game saved in Portable Game Notation (PGN) file. Full disclosure: I am the author of this website.
Answer: Maybe just write the openings and some games down and read them very often. Just hang them up on some mirror, for example in the bathroom and then every time you brush your teeth, you see it and will remind it. You could probably also hang some post its on your cupboard / desk.
On the openings part, just play your opening often and then you will automatically remember it.
Answer: As trivial as it sounds, learn the board first. To the point where you can instantly identify any square just by randomly pointing at it. This will make memorizing easier by abstracting the board component while trying to "burn" a game into your brain.
Answer: Understand why the moves have been made. Once you have gotten a notion of the game, then memorization becomes much easier.

How does one memorize a chess game?


number of elements on a finite vector space

Question: I know that there is no vector space over any field $\mathbb{F}$ having precisely $6$ elements. I would like to know if there is a theorem which characterizes those $n's \in \mathbb{N}$ such that there is a vector space having exactly $n$ elements over a field $\mathbb{F}$. For example: $n=p^{k}$ where $p$ is a prime number and $k\in \mathbb{N}$ ($k\neq 0$).
Comment: Infact, the prime-powers are the only $n's$ for which you can find a vector space with those many elements!
Answer: I think you can put a proof together from the following ingredients.
If $F$ is a finite field with $q$ elements, then $q$ is a power of a prime.
If $V$ is a finite vector space over a field of $q$ elements, then it has a finite basis, which we'll call $\lbrace\,b_1,b_2,\dots,b_r\,\rbrace$, and every element has a unique expression as a linear combination of basis elements, and the number of such linear combinations is $q^r$.
Are the "ingredients" things you already know?
Answer: Let V be a finite vector space over a field F.
Since any two distinct scalars multiplied to a non zero vector will give distinct vectors,and since V has only finite number of elements, F must be finite. Hence the number of elements of F must be the n-th (say) power of some prime p.
Since V is finite, it must be m- dimensional for some m. So V is isomorphic to the direct sum of m copies F. So the number of elements of V must be the mn-th power of p.
Therefore, the number of elements of a non zero finite vector space also must have the number of elements a power of a prime number.
Answer: You cannot have vector spaces with finite elements. Even if the field is finite having just finite elements
consider a vector space with basis $\{e_1, e_2, e_3,\ldots\}$
where
\begin{align}
e_1 &= (1,0,0,0,\ldots)\\
e_2 &= (0,1,0,0,\ldots)\\
e_3 &= (0,0,1,0,\ldots)\\
\vdots & = \vdots
\end{align}
Comment: Any vector space of finite dimension over a finite field has finitely-many elements: http://en.wikipedia.org/wiki/Examples_of_vector_spaces#Finite_vector_spaces.


How do I get seasoning to stick to home-popped popcorn?

Question: I've been popping my own corn and I want to season it with salt, but when I sprinkle it over the popcorn it just ends up at the bottom of the bowl without taking to the popcorn. How could I get the seasoning to stick to the popcorn?
Comment: Almost-duplicate (that person was already using oil): http://cooking.stackexchange.com/questions/6865/how-can-i-get-salt-to-stick-better-to-buttered-or-oiled-popcorn
Answer: If you want dry seasonings to stick to popcorn, you will probably need to add a liquid to adhere them with. You could try adding butter or oil to your popcorn while it is hot, then adding the salt and tossing it together. If you're avoiding extra fat, a few spritzes of a non-stick spray (like Pam) might do the trick without adding significant fat.
Comment: I use one of the misting pump sprayers filled w/ olive oil.  A little spritz, sprinkle with popcorn salt, maybe a second spritz if I made a large batch, then toss some more.  The salt that doesn't stick falls through to the bowl, so it's the oil that actually affects how much ends up on the popcorn.  And if you can't find popcorn salt, look for pickling salt, which is another fine grind (but also iodine free)
Comment: I bought some expensive organic olive oil spray and thoroughly sprayed the popcorn but my nutritional yeast didn't really stick despite being ground fine. I saw a You Tube of someone called Mareko (I think) advocating Tabasco sauce or lime juice. Will try that next. Interested in hearing from any one who has done that.
Answer: I air pop my popcorn and then I spray it with Dr. Bragg Liquid Aminos.  It has a salty flavor and if you spray it lightly it doesn't make the popcorn soggy.
If all you want is the salty flavor then this will do it but it also has the added advantage of allowing other spices to stick as well.
Answer: In addition, as Sourd'oh says, to using some fat as glue.  Water will also work if you don't want calories, but will soften the popcorn somewhat.
Use popcorn salt.  This is salt that is very, very fine, so that it sticks more easily to popcorn.
Additionally, applying the salt immediately after popping when the popcorn is very hot will help.
Comment: I had wondered if you could perhaps mist the popcorn with a brine while it's still hot to minimize the sogginess. Time for experiments!
Comment: Be careful when you use the ground salt. My family and I ground up the salt into a fine powder to where it resemble confectioners sugar and poured it on the hot popcorn. It sticks but when you eat the popcorn, you also inhale the tiny salty particles and cough up a storm. We continue eating but it is annoying and leaves a slightly salty feeling in your throat as if you had stayed outdoors on a boat for too long.
Answer: Put the salt in a spice grinder (such as this one)! My grinder has several options for granule size. Unfortunately, it has no markings or logos on it so I can't tell you what the exact type it is else I'd highly recommend it.
Answer: The problem is not liquid. The problem is the size of the salt. You have to grind the salt. If you don't have a spice grinder, (I use a mortal & pestle) you can put a cup of salt in a blender :) and use it in the future.
Comment: This is already in the Aug 2013 answer.
Answer: Why not add the salt to the oil while it is heating up - or otherwise mix with the kernels before throwing them into the oil?  I have done this both with sugar and salt and it works well for me (and the salt does not appear to burn or damage the saucepan...  If you shake everything up (as you should do) while cooking, then the popcorn gets evenly coated.  However, no-one else seems to suggest this, so there may be something I am not considering...


Since Garbage Collection is non-deterministic, why isn't it used for secure random number generation?

Question: I get that /dev/random is a good source of entropy, and is what is usually used-- It's just as I'm reading up on GC, at least in Java, it seems accepted that the garbage collection daemon executes non-deterministically.  If this it true, why don't we use the timing of the garbage collection as a source of entropy instead of the variable /dev/random?
Comment: something nondeterministic can still be highly predictable
Comment: take a look at some of the docs for rand() functions in standard C-library. They specifically call out that while they give you what appears random numbers, they cannot be used for security.  Your typical garbage collector probably would fall into the same category. If you are going to use one for security, you've got to make sure you use a cryptographically secure garbage collector.
Comment: In this case "non-deterministic" is a poor description.  A garbage collector is a completely deterministic system and if you have full knowledge of its state and the state of the program that uses it, you can deterministically predict the results.
Comment: "Any one who considers arithmetical methods of producing random digits is, of course, in a state of sin." - John von Neumann
Comment: @DXM do you know of a good implementation for a cryptographically secure garbage collector? ;)
Comment: For one thing, if the first thing a program needs to do is generate a random number, odds will be excellent that the garbage collector won't have run yet and will have contributed nothing to the pool.
Answer: "Unspecified" and "random" are two entirely different concepts.
The exact workings of a garbage collector are not specified and are up to the garbage collector (usually implemented by a VM of sorts, but not necessarily).
Therefore, you have no specified (i.e. deterministic) time at which garbage will be collected.
However any given implementation will follow some rules and there is a high chance that two subsequent runs of the same program will have very similar garbage collection patterns.
Therefore the actual entropy provided by a garbage collector would be very low (and finding out which parts you can actually use as entropy will be tricky).
As a comparison: A HashMap in Java doesn't guarantee any order of retrieval for its members (basically because guaranteeing it would add an overhead that's not worth paying, most of the time). However for a given implementation and a given set of insertions/removals you can definitely calculate the resulting order. Just because there is no guarantee for any given order, doesn't mean that the order is random.
Comment: I think it would be a fair statement to say that if a computer ever does something that's actually non-deterministic, that computer is broken.
Comment: @Schilcote: Some modern CPUs have non-deterministic (true) RNG's implemented in hardware. These are truly non-deterministic down to quantum level physics.
Comment: @Schilcote Even without specialized RNG instructions (Intel's RDRAND and RDSEED) a computer isn't completely deterministic. Some timings aren't completely specified and can depend on external factors like temperature.
Comment: Non-deterministic could also mean that it relies on some state external to the program at hand, which itself may be deterministic, but will be completely unrelated to the program itself and so can be different each time the program runs.
Comment: @asmeurer I don't think I've heard these terms in any such context. In fact, I'm not even sure what you mean: Every program that takes external input (that is, most useful programs) "relies on some external state", but that doesn't make it non-deterministic.
Comment: @CodesInChaos Well, barring timing I suppose. But even with true random number generators, the computer is still operating entirely predictably; it's just reacting predictably to inputs that are (hopefully) not known to someone who is trying to break your encryption.
Comment: @us2012 non-deterministic in the sense that multiple runs with the same input result in different outputs. If you think about it too hard then everything in the universe is "deterministic", assuming you believe in fate :)
Comment: @asmeurer: Quantum physics says that not everything is deterministic. And personally I do believe in quantum physics, but I'm still on the fence about fate ;-)
Answer: Firstly, we have to be careful not to fall into the trap of reasoning by manipulation of mere words. For instance, we could ask, since a NFA is a "non-deterministic finite automaton", why don't we use it to obtain random numbers? In that case, it would be because that's not what "non-deterministic" means in an NFA; in fact, when we simulate an NFA, on a given input, the behavior of the simulation is perfectly deterministic.
"Deterministic" is a loaded phrase. To a computer programmer or computer scientist, non-deterministic behavior just means "determining the exact behavior is complicated to think about", and depends on too many factors, including the program input.
However, that doesn't mean it's not deterministic to someone motivated to attack a cryptosystem.  Sometimes environmental factors and inputs can be pinned down, and repeatable patterns emerge from "non-deterministic" behavior.


Mucking hand face up

Question: Need some help here please
heres the scenerio Seat 4 and seat 5 are all in..2 pair on board. Seat 5 says to seat 4 you win you have the ace and shows his hand but does NOT table the hand.He then throws the card to the muck actually hitting the muck with one and the other is next to the muck.I immediately fold the hand and award the pot. As he was throwing his hand toward the muck he was half out of his seat. It was clear he thought he lost and intended to muck although he mucked face up. He left the room them came back a few minutes later saying he won the hand with pocket 10s..Should I have stopped him,should I have read the hand
Answer: It doesn't matter whether he thought he actually mucked his hand, misread his hand, or believed he was beaten. If both his cards were face-up after he threw them (whether that was toward the muck or not), that is a showdown and his hand is alive. Your job as a dealer is to read his hand and declare the winner accordingly. That's the beauty of a "misread". players might throw their cards face-up saying: "nice hand, I only got ace high", it's the dealer's job to find out whether the player actually hit a billy buster straight on the river without being aware of it.
Having said that, it's ok to call "throwing the cards face-up toward the muck" a "bad etiquette", but not a dead hand.
Answer: WSOP rules state that "once all players are all in and action is complete, all hands must be turned face up". All in players are generally required to show their hand to prevent collusion.
The dealer should have protected the muck and required both players to table their hands.
Comment: There's no indication that this is a tournament. This rule doesn't apply to cash games in most rooms. There's also no indication that any of these players were all in, so it wouldn't apply even in a tournament.
Comment: To your second point, the first sentence reads "seat 4 and seat 5 are all in". So both players were clearly all in. But citing tournament rules was incorrect on my part. That said, most cash games would require the dealer in this situation to protect the muck and read the hand, determining the winner.
Comment: Oh, that's true.  Good point.  I'm not sure how I missed that.

Mucking hand face up


Are the Trappist-1 planets close enough to be tidally heated?

Question: According to the NASA press release, the Trappist planets are close enough (only a few million kilometers) that "the tidal forces between the planets are not negligible".  The speaker says that this could cause ocean tides on the planets.  Are they close enough that the tidal forces could heat the interior of the planets?
Answer: This is a complicated question that would really require a full physics simulation and better knowledge of the system to accurately answer. But let's try a few back of the envelope calculations to see what we get.
Calculating tidal forces from TRAPPIST-1c on TRAPPIST-1b
I'm going to calculate the tidal effects of TRAPPIST-1c on TRAPPIST-1b (simply because, a priori, this seems likely to be where the strongest tidal heating will be induced). See the figure below which describes the parameters.

The tidal force of 1c on 1b is defined as the differential force of gravity across 1b, that is, the difference of the force of gravity on the side of 1b facing towards 1c and the force of gravity on the side of 1b facing away from 1c. Mathematically, we get.
$$F_{tide,c-b} = F_{g,-R_b} - F_{g,+R_b} = \frac{GM_bM_c}{(D-R_b)^2} - \frac{GM_bM_c}{(D+R_b)^2} = 4GM_bM_c\frac{DR_b}{(D^2-R_b^2)^2}$$
We can presume that $R_b << D$ (for this case $R_b/D = 1\%$) and reduce this to
$$F_{tide,c-b}(D) \approx 4GM_bM_c\frac{R_b}{D^3}$$
But this isn't enough to determine the amount of tidal heating that may occur. Tidal heating only occurs when the tidal force changes. It is this constantly changing tidal force which results in tidal flexing of the planet and thus creating heat through tidal friction. Fortunately, for these two planets, the tidal force will be changing since $D$ will be constantly changing. So let's calculate $F_{tide}$ for the two extremes where these planets are as close as possible and as far as possible and difference them.
$$\Delta F_{tide,c-b} = F_{tide}(0.004\:\mathrm{AU}) - F_{tide}(0.026\:\mathrm{AU})$$
If I plug in numbers to this, I find that
$$\Delta F_{tide,c-b} \approx 3.7\times10^{20}\:\mathrm{N}$$
Okay, but what do we do with this number? It's somehow a metric of the change in tidal forcing that 1c imparts on 1b, but is it negligible? To determine this, we have to compare it to something. Let's compare this to the tidal forcing that TRAPPIST-1b would receive from the star.
Calculating tidal forces from TRAPPIST-1 on TRAPPIST-1b
I've already set up the math, so we don't need to go over that again. But first, let me discuss where this tidal forcing is actually coming from. Quoting an article from space.com, the paper's author, Gillon, states:

Because the seven alien worlds orbit so tightly, they're probably all tidally locked, Gillon said. That is, they likely always show the same face to their host star, just as Earth's moon only shows the "near side" to us.

As I said above, the only way to produce tidal heating is to have changing tidal forces. These planets are likely synchronized and always present the same side to the star. It's marginally possible these planets aren't perfectly tidally locked, but rather have some higher spin-orbit resonance. That is, their spin orbit resonance might not be 1:1 (as it would be if they were tidally locked) but instead could be something like 3:2 (which is what Mercury has). I'll ignore that complication though and just assume 1:1 resonance. So if they're tidally locked, they can't experience differing tidal forces through their own rotation. Instead, the differential tidal forcing comes from the orbit's ellipticity. Sometimes the planet will be closer and sometimes it will be farther, causing a differential tidal force on TRAPPIST-1b from the star as it orbits. This is exactly what occurs in the tidal heating of Io. Let's calculate $\Delta F_{tide,*-b}$ by using the varying distances TRAPPIST-1b will have from the star. I found that TRAPPIST-1b will orbit between $0.0101\:\mathrm{AU}$ and $0.0119\:\mathrm{AU}$1. This means the differential tidal force is:
$$\Delta F_{tide,*-b} \approx 4GM_bM_*R_b\left(\frac{1}{(0.0119\:\mathrm{AU})^3} - \frac{1}{(0.0101\:\mathrm{AU})^3}\right) = 1.8\times10^{23}\:\mathrm{N}$$
Is planetary tidal heating non-negligible?
The back of the envelope calculations show that the differential tidal force on TRAPPIST-1b from TRAPPIST-1c is about $0.2\%$ of the differential tidal force due to the star. Whether you consider this negligible or not is up to you. I'd personally consider it a pretty small effect and say that most of the tidal heating these planets experience comes from the star itself.
Could the inter-planetary tidal heating still contribute to the tidal heating of the planets enough to heat the interior?
This is a remarkably hard question to answer and I can't even really do a back of the envelope calculation without making wild, unjustifiable assumptions. The calculations above simply determined the maximum tidal force variation over time. That doesn't tell us anything about how much tidal heating this may induce though. That requires knowing more about the planet itself, in particular the planet's Love numbers which define the rigidity of the body and thus how easy it is to stretch via differential tidal forces. You can vary your tidal forcing as much as you want, but if your planet is pure iron (and thus very rigid) you're unlikely to have as much of an effect as if it were primarily silicate (and thus much less rigid). The paper produces the plot below which defines the potential constituents of each planet. This would be a first step in determining the planet rigidities, but as you can see from the error bars, it would be highly uncertain.

Overall, and this is entirely opinion based and from my calculations above, but I'd say the chances of the inter-planetary tidal heating having significant effects on the interior heat of of these planets is negligible. More than likely the biggest contributing factor is radioactive decay, followed by tidal heating from the star (but this is amplified by the eccentric orbits induced by planetary gravitational perturbations)

1 Note that this calculation involves using the eccentricity and the paper only provides an upper limit. These distances then represent an upper limit as well and the final answer will also be an upper limit. It may be less.

Values used in calculations:

$G = 6.67\times10^{-11}\:\mathrm{m^3 kg^{-1} s^{-2}}$
$M_b = 5.075\times10^{24}\:\mathrm{kg}$
$M_c = 8.239\times10^{24}\:\mathrm{kg}$
$M_* = 1.604\times10^{29}\:\mathrm{kg}$
$R_b = 7.34\times10^{6}\:\mathrm{m}$
Comment: While long, this answer is not quite correct. Rather than downvote, I'll post an alternative.
Comment: @DavidHammen What about this is not quite correct? I believe I explained everything in my answer that you put in yours. Particularly the point about the eccentric orbit being induced by other planets, causing tidal heating.
Comment: It ignores orbital resonances, which are a primary driver in the tidal heating of the Jovian moons, and it ignores that a tidally locked object in a perfectly circular orbit about the primary would undergo zero tidal heating from the primary.
Comment: @DavidHammen I don't specifically mention orbital resonances, but I do have a whole paragraph describing the effects of the planets on each others ellipticities (and in fact mention and link to the case for Io). I also explicitly say "if they're tidally locked, they can't experience differing tidal forces" and "the differential tidal forcing comes from the orbit's ellipticity". This is equivalent to saying no tidal heating occurs for circular orbits. I don't believe I said anything incorrect as you suggest, I just didn't mention all the exact points you might have.
Answer: What drove the comment that "the tidal forces between the planets are not negligible" was the Jovian moons. The three innermost of the Galilean moons of Jupiter, Io, Europa, and Ganymede, are in a 4:2:1 orbital resonance. Io would not exhibit any tidal heating if its orbit was circular.
Io's orbit is not circular, thanks to those orbital resonances. One of the consequences of these resonances is that Europa and Ganymede act to pull Io's orbit out-of-round; i.e., more elliptical. The elliptical nature of Io's orbit results in time-varying tidal stresses on Io, which makes Io geologically active. Those tidal stresses by Jupiter in turn act to circularize Io's orbit.
The tidal stresses become less severe as Io's orbit becomes closer to circular. Io cools down, resulting in an increase in its tidal qualify factor Q. This makes it less susceptible to further circularization. The competing forces from Europa and Ganymede can then make Io's orbit more eccentric. Tidal stresses eventually come into play again, warming up Io and decrasing its tidal quality factor. Now Jupiter is the driver. This makes for a rather nice hysteresis loop.

What prompted that comment that the TRAPPIST-1 planets may be subject to tidal heating is that some of those planets appear to be in an orbital resonance, with periods being very close to small integer multiples of one another.
Comment: I understand how tidal heating works, especially with the Jovian system.  My question was more about if the planets of the Trappist system were close enough to their star and to each other to be tidally heated.


How can I extend partition into free space that is not directly before or after the partition?

Question:
I want to add free space (323.69GB) to my Ubuntu file system (242.62GB). But as you can see I can't do this via GParted. How can I do this?
Answer: Yes.  You can combine partitions, by using GParted.  You can install it from the Ubuntu Software Center, or click the image below.
Remember that gparted won't work on a mounted partition. First you have to unmount .
NOTE: You might want to consider doing this from a live/bootable CD or USB, to be safe.  Also keep in mind that anytime you deal with partitions, there is risk involved in doing so.
NOTE: When dealing with partitions, always make sure that a backup is available in case something goes wrong.  You may consider Clonezilla
Answer: As Mitch has said you will need to do this from a live environment so that sda1 is not mounted. Also make sure that swap is not being used - if necessary right click on the swap partition and swapoff.
You'll then need to move the partition with the install (sda1) to the left so that the unallocated space is to it's right.
Then you can expand sda1 to use the unallocated space.
It could take a long time - do not use battery - do not assume it has hung and turn it off. Ensure you have backups of data you can't afford to lose.
It would be easier in my mind to just create a new partition in the unallocated space and add it to fstab so it is mounted on boot.


Kohen as Chazzan During Birchas Kohanim

Question: Can a kohen serve as chazzan for mussaf on days when there is birchas kohanim? If so, what is the proper procedure for him to follow?
Comment: I'd note that this would apply to shacharit in Sephardic  (and Israeli) minyanim too, and there it applies every single day.
Answer: If I'm reading Shulchan Aruch 128:20, 22, 25, with Mishna B'rura, correctly, the rule is as follows. But contact your local, orthodox rabbi for any practical cases.
Is the shatz (leader, "chazan") the only kohen, or are there others?

If he's the only one, and he has a sidur, he should step toward the duchan at "r'tze", go on the duchan for birkas kohanim, do birkas kohanim facing the congregation, return to his place, and complete the amida.
If there is another kohen, then no one should tell the shatz to wash his hands or to do birkas kohanim. Did anyone?

If so, he should do as described above in the "If he's one only one" paragraph.
If not, he should not do birkas kohanim.

In all cases, someone not a kohen should prompt the kohanim and say "kohanim" (though not "elokenu..."); however, if no one present is able to who's not a kohen then the shatz should prompt the kohanim and say the introduction, unless he's doing birkas kohanim.
Comment: I seem to recall a preference for a Yisrael (as opposed to a Levi) to be the prompter.
Answer: The Sephardic mesora is that the Sha"tz who is a Kohen covers his eyes and stays silent for the duration of the prayer, as he is essentially taking himself out of the room. Then a non-Kohen calls out "Kohanim!" and leads the entire Birkat Kohanim.
I am not sure what happens when the sha"tz is the ONLY Kohen in the room. He probably says the "Barekhenu baBerakha..." as the Ashkenazim do.
Comment: Most Israeli Shuls, even Askhenazi ones, go by this minhag.

Kohen as Chazzan During Birchas Kohanim


Determine the values of $r$ for which the differential equation $y'+8y=0$ has solutions of the form $y=e^{rt}$

Question:
Determine the values of $r$ for which the differential equation $y'+8y=0$ has solutions of the form $y=e^{rt}$.

We have never done a problem like this in class. We've only done direction lines and separable differential equations.
Answer: If you plug $y = e^{rt}$ into the given differential equation, you get
$$re^{rt} + 8e^{rt} = 0,$$
or
$$(r + 8)e^{rt} = 0. \tag{$\ast$}$$
Now $e^{rt} \neq 0$ for all $t$, so you can divide both sides of $(\ast)$ by $e^{rt}$ to get
$$r + 8 = 0.$$
This tells us that $r = -8$.
Comment: I think this is the most appropriate answer to the question.
Answer: Hint:  $y^\prime+8y=0$   $$\frac{y'}{y}=-8$$  Integrate  both sides to get
 $$\ln y=-8t+c$$ $y=\exp(c)\exp(-8t)$
Answer: This equation is separable:
$$\frac{dy}{dt} = 8 y \implies \frac{dy}{y} = -8 \, dt$$
Now integrate both sides:
$$\int \frac{dy}{y} = -8 t + C$$
where $C$ is a constant.  The integral on the left is a natural log:
$$\log{y} = -8 t + C \implies y = e^{-8 t+C} = A e^{-8 t} $$
so $r=-8$.
Answer: $$y'/y=(\log(y))'\implies y'/y=-8 = (\log(y))'.$$ Integrate both sides to get $$-8x + C=\log(y)\implies y(x)=e^{-8x+C}=C_0 e^{-8x}.$$ Setting $C_0=1,$ we see that $r=-8.$
You can easily turn this into a separable equation and avoid the trick $y'/y=(\log(y))'.$ Here's your equation: $$\frac{\mathrm dy}{\mathrm dx}=-8y\\\implies\int\frac{\mathrm dy}{y}=-\int 8x\,\mathrm dx$$ and I think you know what to do next: find the solution of the from $C_0 e^{kt}$ and compare it to $e^{rt}.$


Flat-file PHP issue tracker

Question: I need a self-hosted issue tracker that

is written in PHP,
doesn't require a database, and
is free/libre/open source.

Required features

An issue can have a category ("bug", "feature request", "support") and a status ("closed", "open", "on hold").
An issue can be commented.
Issues and comments can have image attachments.
Email notifications for new issues and new comments.
The list of issues can be filtered by category and status.

Nice-to-have features

When referencing issues/comments internally, the links should be relative (or there should be a config option to change the hostname) so that switching domains is hassle-free.
Answer: You should have a look at Traq. It runs with the file based "database" Sqlite (look at the travis configurations).
It has a nice user interface and all the features you are looking for.

Flat-file PHP issue tracker


What is the theory behind scales?

Question: My question is the following:
Scales are The backbone of quite everything in western music.
Does anybody know if there is some sort of backbone behind scales?
A number, something like that?
Or do some scales sound better than others because its culture-related?
I have truly no idea. I can't find anything about this subject. anywhere. on. the. internet.
I'm very curious.
Comment: Some have argued that scales derive from the harmonic series (https://en.wikipedia.org/wiki/Scale_of_harmonics) Schoenberg seems to suggest this in his Harmonielhere. That said I'm not sure of how much practical value this hypothesis is. At some point a particular selection of scale tones (as well as tuning system) "stuck" to a musical culture and people living in such a culture are grow up to be conditioned to it.
Comment: There are other important elements that are central to Western music besides scales. But I like your question, as it seeks information about "how" and "why" scales work as they do.
Comment: http://music.stackexchange.com/questions/8173/the-major-scale-why-and-how
Answer: If you're looking for a magic number upon which scales are based, take a look at 1.5, which can also be expressed as a ratio of 3:2 (the same as multiplying by three and dividing by two). That's the ratio of an interval called a pure fifth. It's also called a just fifth; the terms are interchangeable. (They are not necessarily the same as a perfect fifth, however. And if you're wondering why they're called fifths at all, don't get hung up on that just yet. Hopefully, it will be clear later. If you already know what a fifth is, my apologies; I don't mean to insult you.)
If you start with a note of a particular frequency and multiply its frequency by 1.5, you've found a higher note which sounds consonant with the first. (Consonance is the opposite of dissonance.) If you graph the waves of these two notes, you'll find they meet up on a regular basis. In the image below, the lower blue note completes two wavelengths while the higher red note completes three. There's your 3:2 ratio. The waves cross zero together at every 1.5 wavelengths of the higher note.

This regular meeting of the waves is what gives them consonance. The simpler the ratio, the more consonant the interval. There are two intervals which are more consonant than a fifth: unisons and octaves. Their ratios are 1:1 and 2:1 respectively. One may wonder if a stack of fifths and a stack of octaves ever line up and meet at a particular frequency. (Unisons, while very consonant, won't get you far.) Spoiler alert: no, they will never line up, at least not the way you might wish they would.
But let's see what happens if you try. If you start with a frequency, find its pure fifth, take the pure fifth of that fifth, and so on until you've done it 12 times, you end up at a frequency which is just over 7 octaves. If you say, "close enough" and adjust the interim notes by repeatedly halving their frequencies until they all fall into a range of one octave, you've got the 12-note chromatic scale you know and love. This is shown in the chart below. I believe this answers your question and tells you why an octave is divided into twelve notes. (You asked the latter in a follow-up comment to another answer which was deleted.)

Supplementary information regarding the chart
The difference between 7 octaves and 12 fifths, the one you could say was
  close enough, is called the Pythagorean comma. We often fudge this
  difference and take some portion away from each fifth so that 12
  fifths line up perfectly with 7 octaves. So perfect fifths are
  always less than or equal to the just/pure fifths which are shown on the chart, but your ear generally
  accepts that they are slightly off. (You're much more sensitive to octaves
  being off.)
Note that the Pythagorean comma is not a specific number of Hertz, but a ratio.
  It's 12 fifths to 7 octaves:

If you do the math, you get 1.0136432647705078125. This is the math:

The various schemes we use to fudge the fifths are called
  temperaments. Today, we use a temperament called Equal Temperament,
  which takes the same amount away from each fifth. Not all temperaments
  do. In fact, what we call Pythagorean tuning doesn't adjust anything
  at all. The tradeoff is that some intervals sound positively awful
  because the Pythagorean comma must be accounted for somewhere. These
  intervals are called wolf tones. Each progressive key becomes more and
  more off, so you are limited in what you can do with modulation.

Let's say we decided to build a scale from the first 7 notes derived by stacking fifths. (To avoid accidentals, I will begin with F, but it works no matter where you start.) When we chain fifths from F to C, C to G, G to D, D to A, A to E, and E to B and we reduce them to the same octave, we find that, regardless of the starting note, they line up in an alphabetical order which wraps around. Instead of F C G D A E B, they could line up as C D E F G A B. Notice that the G (in this example) lines up into the fifth spot of a scale that starts with C. The choice of C as the scale's starting note gives us the major scale, but this choice is essentially arbitrary. If we left F as the starting note (F G A B C D E), we'd get the Lydian mode. Pick A (A B C D E F G) and we'd get the Aeolean mode, which is the same as natural minor. In every case but one, the fifth scale degree is the perfect fifth of the starting note. That is, of course, why fifths are called fifths. (The exception occurs when we begin with B, which gives us the Locrian mode. The fifth is still a fifth, but it's a diminished fifth instead of a perfect fifth. That is because, when we stacked fifths, we stopped short of including B's perfect fifth, F♯.)
Now, you could say all of this is arbitrary and yes, culture has trained our ears to hear the major scale as "normal" and anything else as more exotic to some extent. But it does have its basis in physical phenomena.
Answer: Everything in trw's answer is true, and the next to last paragraph really does answer the question.  (Finally!!!)  But I would like to add a bit more historical perspective to why the seven note scale came to be so important.
Almost all primitive cultures have at most a pentatonic (five tone) scale.  I'm sure if you go back far enough in the Western Tradition (that is, European), you'll find they were into pentatonic scales as well.
But musicians, especially performers, are very aware of 'gaps' in things.  For example, there's a 'gap' in a so-called perfect fifth, that keeps it from having a 'flavor.'  That is, it's neither major nor minor.  If you're a primitive musician and all your bone flute can do is octaves and fifths, you notice this gap and so you invent the pentatonic scale, which provides the missing interval of a third, thereby determining major or minor.  (Note that the smallest interval in the pentatonic scale is what we call the whole step.)  But that new pentatonic scale also has gaps.  There's an obvious gap after the first three notes, and another one between the last note and the octave.  So you invent the half-step, and now suddenly you have modes, including the two that will eventually become known as Major and Minor.  Thus one aspect to the importance of scales in this culture is the insatiable curiosity of the musician, who wants to know 'what else' there is beyond what is given.

What is the theory behind scales?


Quarter Wave Transmission Line transformer

Question: Can someone explain to me exactly how a quarter-wave transmission line transformer is put into action? I mean, how does it operate and what values are usually taken into consideration, calculation wise?
Comment: This question is too broad. Please include context and your research so far.
Comment: I have included this is in my answer to your other question on Stub Impedance Matching
Answer: A quarter-wave transmission line makes some load appear to the source on the other end look like the load's dual impedance. The most common case is that the impedance at the end is a short or an open, and the quarter-wave transmission line makes it look to the source (V1 or V2) as the opposite:

simulate this circuit – Schematic created using CircuitLab
This is pretty weird. In the case of V1, it looks like it's connected to a short: a huge (theoretically infinite) current flows. But if you stick an ohmmeter on the same terminals where V1 is connected, it will tell you there's no connection between them.
In the case of V2, it looks like it's connected to nothing: no current flows. Yet if you measure with your meter again, it will tell you there's a dead short.
Since it seems like this is logically impossible, it bears mentioning that a short "looks like" an open (or vice versa) only at equilibrium. If you were able to slow time such that the speed of light were observable, you'd see that in both cases, which V1 is initially connected, some current does flow. Once that initial wave has reached the end of the transmission line, and then reflected back (maybe several times), does the system reach equilibrium.
In the more general case, the load on the right end doesn't have to be a short or an open: it can be any impedance:
"Quarter wave impedance transformer" by Courtesy Spinningspark at Wikipedia. Licensed under CC BY-SA 3.0 via Wikipedia.
In this case:

$Z_\text{in}$ is the impedance something will see, looking into the transmission line,
$Z_0$ is the characteristic impedance of the transmission line, which is commonly $50\:\Omega$, and
$Z_L$ is the impedance of the load at the end.

These three parameters are then related by the equation:
$$ {Z_\text{in} \over Z_0} = {Z_0 \over Z_L} $$
Since these are complex numbers the math can be a little unintuitive, so some consequences, in plain English:

inductors look like capacitors
capacitors look like inductors
small resistors look like big resistors
big resistors look like small resistors


Brainiac has a twelfth-level intellect. What level intellect does Superman have?

Question: Lex Luthor increased Brainiac from a tenth level to a twelfth-level intellect. What level intellect does Superman have?
Comment: Brute-level intellect!
Answer: Given Superman's/Kal-El's parents being considered as 8th level intellects, Superman must at least possess the POTENTIAL to be an 8th level intellect and even untrained would still likely possess the intellectual capacity to be one of the most intelligent beings living on the DCnU Earth.
The DC Universe has never really known how to address their descriptions of intellectual capacity in an objective level. The DCnU is littered with a variety of geniuses at varying levels of intellectual capacity and development.
One such measuring tool was the use of the "genius levels of intellect" scale rated from one to twelve, with twelve being the maximum. Yes, there are rumors of a 16th level intellect but canon writings only take the scale to 12. Given the difficulties in determining how such intellects are rated:

There is no objective scale that has been clearly determined
The five known measures are still highly subjective

The five markers set down by DC in the previous continuities of the DC Universe were:

Highest level of genius intellect currently defined is a 12th level intellect.

this has been displayed as the ability to consciously have 12 simultaneous thought processes at a genius level of intellect being performed concurrently. Intellectual capacity at that level is capable of developing sciences and concepts beyond the comprehensions of even other known geniuses and associated with the potential to master an unlimited number of disciplines. Such intellects are capable of memorizing entire libraries of information, multitasking and building entire mental simulations with the speed and accuracy of supercomputers. It has been hinted, however, that intellects at a level greater than ten are inherently unstable and prone to erratic behavior.
Brainiac 5 of the Legion of Superheroes, and the original planetary computing machine Brainiac are considered to be at this level.

The entire 31st century Earth's population is considered to be at a 9th level of intellect.
The scientist Jor-El of Krypton was individually considered at the 8th level of intellect.
The average citizen of Colu is individually considered to be at the 8th level of intellect.
The entire 21st century Earth's population is considered to be at a 6th level of intellect.
One last marker: Lex Luthor has been estimated of being a 8-9th level intellect and the smartest human on the DC Earth.

Given these ratings and the recent reveal that Jor-El is at least an 8th level intellect and considered by "The Collector" to be Krypton's leading scientific mind, and Lara was also considered a first rate scientist on Krypton, this means Kal-El has the genetic potential to be considered a genius of that order. Assuredly with his mind's enhancement under a yellow sun, he is certain capable of being one of the most intelligent beings on the DC Earth. His greatest weakness is likely a lack of significant exposure to information and education to challenge his intellect to achieve its greatest state.
This page clipped from Action Comics #3, page 4 is shown quoting Jor-El's considerable intellectual capacity.

You can also see: "Does Superman's super-speed affect his thinking" for further ideas on the subject of Superman's intellectual capacity.
Comment: Based on the average Internet forum, negative intelligence may not be that far off.
Comment: If the average Earthling is a 6th level, that doesn't say much for the 6th level.
Comment: @Omegacron I took that to mean that the *combined* intellect of everyone on Earth was a 6th level intelligence. After further thought, that means that a lot of people would have negative intelligence, since at least one person (Lex Luthor) has intelligence above 6th level...
Comment: In fact Grax was a twentieth level intellect, that I think appeared in at least two stories, see http://supermanica.superman.nu/index.php/Grax
Answer:
DC Adventures is an officially licensed RPG based upon DC comics.  It is based upon a heavily modified version of the D20 system.  One of the modifications is the ability scores - D20 has ability scores (which range from 3-18 for a normal human, average is 10) and ability modifiers (calculated as (ability score - 10)/2, rounding down).
DC Adventures (also known as Mutants and Masterminds 3rd edition) instead uses your modifier as your ability score, to better handle characters with enormous abilities (the D20 system has an unnecessary level of detail for stories where characters routinely lift tanks or throw others for miles).
In the DC Adventures Heroe's Handbook there are stats for Superman and Braniac.  The stats in the books are for the 'iconic' versions of the characters, essentially the core character.  They include notes for modifications for different versions (such as Aquaman with the harpoon hand, or when he heavily used magic).
In that book, Braniac is given an Intellect score (replaces the D20 'Intelligence' score) of 12.
Superman's Intellect is given as a 2.  (His strength, on the other hand, is 19)
For comparison, Batman has an 8 Intellect, and Lex Luthor has an 11.
An average human, in DCA, has a 0 Intellect.  Superman is about 10% smarter than an average human (your score is added to a D20 roll for checks related to that ability, so Superman will succeed roughly 10% more often than an average person).  Batman is 40% more likely to pass an Intellect check than an average person, and Lex Luthor is 55% more likely.  Braniac just beats him by being 60% more likely to pass that same check.
The game is officially licensed and the material was approved by DC, who paid close attention to the character builds, so it's as close to an official word as we will get.
Comment: @SteveJessop: That's just his raw Intellect, *without* considering his super powers.  He also has Quickness 10 (limited to Mental things) which lets him think roughly 1200 times faster than a 'normal' person.  So he can make 1200 Intellect checks (each 60% more likely to succeed than a normal person's) in the time it takes an average person to make one.
Comment: As it's D20 based, that means he could Take-20 on those checks (taking twenty times the normal time required) if there is no consequence for failure other than failing itself. Those 1200 checks become 60 discrete tasks, all of which he automatically counts has 20 on the die.
Comment: @T.J.L.: Indeed.  Brainiac also has Expertise (essentially, a combination of Knowledge/Profession/Craft) in History and Known Space with +11 bonuses to each (total +23).  So for a pure Int check, he can take 20 as a free action to get a 32 ('Heroic' difficulty) to come up with solutions or remember facts.  If he can apply one of his Expertise skills (or his similarly-bonused Technology skill) the result is instead a 43 ('Nigh-Impossible' difficulty).  So he can solve nearly-impossible problems ~60 times per second.
Comment: More clearly it seems to wildly underestimate Brainiac's. It's not all that uncommon an effect in RPGs, I don't think it's reasonable to assume that DC is unusually good at making the outcomes from its system reflect its hand-crafted background material.
Answer: In the finale of Season Two of "Justice League Unlimited" Lex Luthor states that he is "overqualified" to pass a obstacle requiring a '12th level' intellect...
Quoting from Wikipedia;

The Source Wall appears in the final episode of Justice League
  Unlimited, "Destroyer". Metron takes Lex Luthor there to find the
  Anti-Life Equation. Metron himself is unwilling or unable to take him
  any further, and warns Luthor that only a "twelfth-level intellect"
  has a slightest hope of surviving such an experience. Luthor dryly
  states that he is overqualified then leaps into the wall. He is
  seemingly correct, as shortly after, he appears again on Earth in
  possession of the Anti-Life Equation. Dwayne McDuffie when asked what
  happened to Lex Luthor and Darkseid when they seemingly exploded from
  the Anti-Life Equation stated that they were fused with the wall, as
  all living things that solve the equation are. As a subtle homage to
  Jack Kirby, Galactus image can be seen on the wall.

Superman-Prime also manages to pass a Source Wall (albeit by destroying it) which would suggest that by definition he has also at least a level 12 intellect;
Comment: This is not an answer to what intellect level Superman has. Therefore it is not helpful. I'm not sure what "they prove I" means, but it doesn't sound like a helpful addition. The bits about Lex and Brainiac only further distract from the question. I also wanted to edit your post but was not quite sure what you were trying to say.
Answer: The reason that much of this information is muddled is that it combines PreCrisis and PostCrisis versions of Superman, Lex, etc.  In the PreCrisis continuity, Superman and Lex were both 9th Level.  The Post-Crisis Superman was not much smarter than the average human.
Comment: Welcome to the stack exchange.  If you could add some examples with links, it would improve your answer.
Answer: Superman only does not reach brainiac and lex level of intelligence(but is capable of lexs and even more) because he does not really study or make findings , well as u sud know superman brain is capable of great feats he could read billions of world and assimilate without problem and tell u every bit of it any time. Again superman brain is much more advanced than lex(es) ,he is just human while superman brain is capable of much more. If superman had studied like lex he would have being one of the most intelligent beings, but he spends time on ...... U all know. So i would rate superman on the intellectual he is capable of and not is intelligence 90% upwards and brainiac intelligence (well thats because he is a computer and contains many database of galaxies aliens ...name it) 95% upward. Lex well just a genius and for that he is going to also have a slighlty different brain(not in structure)a 80% upwards he is just human. This sud clear it up with all the explanation.                                                        By, Akala Ayodeji.
Comment: Also, punctuation and grammar.
Comment: This could be much improved if you gave some references for these assertions.


Young adult novel about a girl with a robot housekeeper on an Alien Planet

Question: I read this book roughly 4 years ago, and got it from a library. The sequel was actually about to come out when I had finished the book, but I never got to read it.
I don't think it was old enough to be made in the 90's. I remember thinking it was quite new, not a "classic" yet so I didn't expect much of it. The story felt Wizard of Oz-esque.
The girl, I believe her name was similar to Alice (maybe a spelling variation) was living in this type of small, electronic home. The robot maid took care of her, but she really wanted to leave to the outside world and try to find other humans. I think what happened was an alien creature came and tried to raid their hut, and possibly damaged the robot. She ended up leaving with the robot after that with an alien companion. The alien was akin to the Gungans from Star Wars, though that could solely just be my memory and how I imagined them.
The main points I remember is that the robot gives her a chip in her throat to speak to aliens (technology!), but she needed to be in close proximity to the robot for it to work. She thought the robot died, and she couldn't understand anyone after that, but then all of a sudden she started to understand people again and the robot returned!
Also she carried around a slip of paper that was slightly burnt and illegible save for a few letters, and at the end, she reaches a library that had the same paper on a book that was The Wizard of Oz (or some variation of it) even though the entire time I thought it was going to be Alice in Wonderland.
The sequel, from the snippet at the end, was about a colorfully haired human boy coming from the sky to "return her to her people".
Comment: I think they were described as lanky and long-jawed. There were pictures strewn into the pages every so often and I THINK they looked mildly similar as well. Sorry I don't remember them very well- I didn't care for them that much lol. And thank you!
Comment: Hi, and welcome! Do you recall why the aliens made you think of Gungans? Was it described as having floppy ears or being moronic? Or was it more or less just a random way of imagining it?
Comment: hmmm, I read this, and relatively recently.  It's a recent children's novel.  I think the title of it alludes to the book.
Answer: The Search for WondLa by Tony DiTerlizzi

Eva Nine had never seen the actual sun before, or walked outdoors. In fact, she had never even seen another living person in all twelve years of her life. That changes when a marauding huntsman destroys her underground home and sends her fleeing for her life. She is desperate to find someone else who is like her, and a single clue gives her hope: a crumbling picture of a girl, a robot, an adult, and the word "WondLa".

Matches:
Timeframe:  published in 2010
Small, electronic home: "underground Sanctuary"
Robot maid: "Muthr"
Slip of Paper = Wizard of Oz: YES
Alien companion: YES
Human boy comes to take her home at the end: YES
Comment: Thank you so much, kind stranger.


Replace nylon strings with steel ones on a guitar made for steel strings

Question: I recently bought a guitar from a friend and it has nylon strings. He said it originally came with steel strings, but for some reason he replaced them with nylon.
I'd like to know if it will bring any problems to my guitar if I replace the nylon strings with steel again, since the guitar is already used to the nylon strings tension.
Comment: Nylon Guitar strung with steel strings. I did it, you shouldn't. Makes an explosive sound at 2:00 am and ticks off the wife. Don't do it!!
Answer: Hold on here. If this particular make and model of guitar was indeed originally designed for steel strings, but your friend put nylon strings on it, then it would indeed be okay to put steel strings on it instead.
However, we need more information. What is the exact make and model of the guitar? What modifications have been made to the guitar to accommodate nylon strings? Were they ball-end "folk"-style nylon strings inserted into the original steel-string-style bridge and bridge plate? Or was some other arrangement made?
Please post the exact make and model of the guitar. Some detailed photographs of the headstock, nut, and bridge would be helpful.
It would be a good idea to take the guitar to a reputable guitar repair technician, have them inspect the guitar, and ask them about the feasibility of switching to steel strings.
If the guitar technician says this is OK, you would expect to need to pay for modifications and adjustments to be made to the guitar so that it is properly set up for the new strings and so that it plays in tune. Steel strings have more than twice as much tension as nylon strings, and they are different thicknesses and diameters, so modifications or adjustments will probably need to be made to the nut, the truss rod (I hope this guitar has a truss rod) and possibly to the bridge saddle and bridge.
You could try to do these things yourself, but in my opinion, paying money to a professional would result in a guitar that is more playable.
Answer: Guitars designed for steel strings are made completely different from guitar's designed for nylon strings.  Putting steel strings on a guitar made for nylon strings could ruin the guitar.  Putting nylon strings on a guitar made for steel strings is not a good idea either.
A picture of the guitar might help me determine which type of guitar you have.  But there are some clues you can look for.
Guitars designed for steel strings will almost always have a truss rod to compensate for the very high tension that steel strings exert on the neck.  If your guitar does NOT have a truss rod, you should not put steel strings on it.
A truss rod is adjustable with a special wrench (often an allen wrench) and exerts counter tension on the neck to prevent the string tension from warping it.  Truss rods run through a channel in the guitar's neck and are accessible either through the sound hole or by removing a small plate on the headstock directly behind the nut.
Some nylon string guitars also have truss rods, so the existence of a truss rod does not automatically mean the guitar is designed for steel strings.  But the absence of a truss rod definitely means you don't want to put steel strings on the guitar!
If you put nylon strings on a guitar with a truss rod, you would want to loosen the truss rod so that it does not warp the neck by exerting tension that is not adequately counter balanced by the string tension.
Another significant difference between guitars meant for nylon vs. steel strings would be that the string slots in the nut would be much wider for nylon strings, especially the treble strings, given their larger diameter.
The bridge on a guitar designed for steel strings will usually be reinforced more to handle the extra tension.  Putting steel strings on a guitar with inadequate bridge reinforcement could result in the bridge pulling loose from the top of the guitar.
Most steel string guitars have bridge pins and the ball end steel strings are inserted through the bridge itself into the body and held to a bridge plate on the inside of the guitar by the bridge pins.  This transfers most of the string tension to the bridge plate on the inside of the guitar, allowing the bridge to withstand the greater tension of the steel strings.  Nylon string guitars are often strung by tying the nylon strings around the bridge as opposed to through the bridge into the body.
The tuning mechanism and gears are more robust in guitars designed for steel strings as well.
Bottom line - if your guitar was built for and designed for steel strings, you should change the strings back to steel and adjust the truss rod for the correct amount of counter tension and desired amount of relief.  If the guitar was designed for nylon strings or does not have a truss rod, you should not put steel strings on it.
Again - several pictures from different angles including close ups of the headstock and bridge might help us determine which kind of guitar you have.
Comment: Maybe I'm weird, but I really really like the way my Ovation (hollow-body electric designed for steel) sounds and plays with nylon strings.  I used strings 1-3, 5-6 from a normal set, and use the unwound third string from an extra-heavy set as the fourth string.  Since I use a modified G-D-d-f-g#-b tuning, every chord can use one of the two wound strings as the bass, and the four unwound nylon strings have a "harp-like" quality.
Comment: @supercat - your experience with your custom string set proves that the choice of strings can have a huge impact on the way a guitar sounds.  I admire your willingness to think outside the box and experiment with non standard string combinations as well as non standard tunings.  Sounds like you discovered a formula that works well for your purposes and preferences.  That's great!
Comment: My custom tuning came about because I couldn't wrap my head nor my fingers around the chord shapes for standard tuning, and so figured I'd try to come up with something I could play that wouldn't sound too wimpy.  In fact, I'd say it sounds better than Standard for a lot of purposes.  All chords except the open-D chords and the seldom-used open-G chords are moveable (in most contexts, a fifth-fret G-g-b-d'-g' sounds better than the open G-D-d-g-b-d'), and "voice leading" often works better than Standard (e.g. when playing an E7-A transition in Standard, the 7th of the E7 is nowhere near...
Comment: ...the 3rd of the A chord; in Flat Finger Tuning, all V7-I transitions place the 7th a half step above the 3rd of the next chord (sometimes an A7 chord is played A-E-e-g-c#'-e', and sometimes A-a-c#'-e'-g', but a D chord (D-f#-a-d'-f#') will provide a half-step resolution for the 7th in either case.
Comment: @supercat  Interesting!  Apparently there is a method to your madness.  I am going to copy and paste your comments into a word document so when I have time to experiment, I can tune one of my acoustics using your method and try it out.  Thanks.
Comment: You'll probably want to swap the 5th and 6th strings, since tuning anything but a really heavy A string down to D will make it really floppy and twangy, and tuning anything but a really light E up to G might be a dangerous stretch.  Any major or minor triad or 7th chord can be played by barring across the fretboard with the first finger, and then placing one or two of the remaining fingers flat across some or all of the top three strings.
Comment: Awhile ago I created some web stuff to try to promote Flat Finger Tuning, but it sorta fell by the way side.  Check out http://casperkitty.com/guitar/temp/guitar1.html if you want to see some chords (it's set up for FireFox; other browsers may be quirky).  The top row of red buttons selects a strum pattern, the next row moves a selected chord up or down, and the big grid of red buttons lets you select and hear any chord from a huge collection.