Why would a recipe use both Light LME and Light DME?

Question: I just brewed a clone of Belhaven Scottish Ale using the extract recipe from the book, Clone Brews.  The recipe calls for both light LME and light DME.  Why would it use both?  It does specify brands of each to use.  Might the recipe be taking into account the particular flavor of each extract from the different brands, or is there something more obvious I'm missing?
Comment: Northern Brewer's Kolsch extract kit uses DME and LME in the same recipe, too. No indication as to why. http://www.northernbrewer.com/brewing/recipe-kits/extract-kits/extract-ale-kits/kolsch-extract-kit.html
Comment: What are the brands it asks for?
Comment: What other extracts does the recipe call for?
Comment: I realize I've been cagey about the recipe.  I didn't want to put a commercially-available recipe that's published in a book on here.  But since I found it online, here it is:  http://www.homebrewtalk.com/f12/belhaven-scottish-ale-5418/
Comment: Most of the extract recipes I have seen call for both LME and DME. No idea why and honestly I kinda doubt the creators know why either ;)
Answer: Theory the First
Since the recipe lists specific brands of extract the author could be looking for some esoteric flavor differences in the two.
Theory the Second — The Texas Two-Step Method
The liquid extract is intended to be added near the end of the boil, around the 10 or 15 minute mark.  (See Brew Your Own magazine, October 2003.)
Extract brewers normally do not do a full-wort boil (all 5.5 gallons).  High concentrations of extract decrease the hop utilization rate.  The higher gravity wort you boil, the less hop extraction you'll get.  Boiling all the extract at once in a small volume will probably throw off the hopping rate.
It has also been shown that beer tastes better when hops are boiled with some extract.  Just boiling hops straight up extracts undesirable flavors.
So, you boil some extract for the full 60 and add the rest near the end just to sanitize.
Why the dry first & liquid second? Probably because LME will dissolve quicker.
Bonus
To check the first theory: mix up two equal gravity worts of each extract. Taste for differences.
Comment: Theory 1 was my first inkling.  It calls for 6.6 lbs of John Bull light LME  (John Bull isn't available anymore) and 2.75 lbs of M&F (now Munton's) light DME.  That's two parts John Bull to one part Muntons.
Comment: Theory 2 would make a lot of sense... if the recipe called for the LME to be added as a late addition.  But it doesn't.  The recipe calls for all the malt extract to be included in the full 60 minute boil.
Comment: Theory 2 would apply for the recipe I mentioned.  It's dry at the beginning and liquid late addition.  Late addition is also intended to minimize darkening due to boiling highly-concentrated malt extract solutions (often erroneously referred to as caramelization, but actually due to Maillard reactions between proteins and sugars, like browning a steak).
Answer: LME is usually cheaper, but harder to measure and store if you don't use the full package.  Sometimes recipes add on DME if you aren't using even 1 pound increments.  Light LME and light DME are interchangeable, as long as you take into account the higher extract per pound of DME (since it has less water it has more fermentables per pound).  Also, don't switch out something like wheat LME for light DME.  They aren't the same.
Comment: Thanks, this is a good answer given that I didn't specify the amounts the recipe called for.  However, the recipe isn't using DME to avoid using a fraction of a can of LME.  It calls for 6.6 lb LME (that's two 3.3lb cans) and 2.75 pounds DME (that's equal to one more can of LME).  The could have easily called for 3 cans (9.9 lbs) of LME and had the same amount of fermentables.
Answer: DME has a higher chance of instigating a boil-over, doesn't it?  It might just be a mechanical choice to save you having to continually shut the heat off, particularly if there are multiple hop additions.
Of course, LME has you shutting the heat off to prevent scorching.
Comment: That's a good thought, and I'm upvoting your answer, but I'm not sure that's it, either.  Adding 8.25 lbs of DME (the equivalent of 9.9 lbs of LME) would be a lot of powder, but another recipe in the same book does just that - all DME and no LME.
Answer: Another totally different, and more plausible answer, in the case of Northern Brewer's Kolsch recipe is that it's difficult to divide liquid extract to get the exact right gravity.  For that recipe, 1 lb of DME early gives enough for hop extraction, and 6 lbs late gives the rest of the OG. With their raw materials, which are generally 3.15 lb and 6 lb LME jugs, and 1 lb DME bags, it's possible they want to fill in a little more gravity with the DME, without going so far as adding another full or half jug of LME.  The recipe you've posted, though, does not fit with this explanation.  2.75 lbs of DME is not all that far from 3 lbs of LME, which is a pretty standard size, so still not explanation for the specific case you mention.
Answer: I doubt this is the reason, but you may want to consider the water profile of the final beer.
If you use all LME then you get the chance when using distilled water to get a beer that has the exact profile from where the extract was made.  Because the minerals in their water are still in the LME.  When using DME, much of that mineral profile was lost in "ringing" out the last of the water to make the powder.
So you can use distilled water for the LME portion and your "house" water with the DME addition and get something in between the two locales.
Like I said, no one at the brew shop really gave it that much thought, but I just point out the opportunity that it presents to you the brew now at home.
Answer: I realize this is five years old, but I came across it while searching for the same question, so I'll throw in my two cents in case it helps.
First thing, most LMEs are hopped and most DMEs are unhopped, so you might use both to dial in the bittering.
Second thing, it seems it's easier to find lighter DMEs than LMEs, so you might use LME for the bulk of your malt and then a light DME to round out your OG without making your final product too dark. I came across this making a recipe for a light American pilsner in Brewsmith, actually, which is what led me here.
Answer: I think using both LME and DME is all or mostly about marketing. These kits like to showcase the liquid and dry malts, different hops and specialty grains to draw you into buying more of their sponsored products. I've bought kits that required DME to be put in late.
My supplier used to sell Brewers Best kits, but discontinued them in favor of kits they put together themselves. They make different styles using different specialty grains to steep with the DME/LME that they also stock on the shelves. It's just there to lure you in toward all-grain brewing. It's their bread and butter.
I know because it happened to me. Not that it's a bad thing, I'm full on with it and having loads of fun brewing all-grain now. These kits really helped me to learn the products.


Treating underscore as delimiter in SharePoint search results

Question: What is the best way to treat an underscore "_" as a delimiter in a SharePoint 2007 environment (MOSS2007 Enterprise)?
For example, if we have got files that are named PricingConditions_UK_2011.docx, PricingConditions_Germany_2011.docx, 2011_France_PricingConditions.docx, I want to be able to find these files through their filename by searching for PricingConditions.
While I would agree that in a perfect world there'd be spaces here and lots of appropriate metadata, this is not a solution that is feasible for us. So we really want to treat the underscore as a delimiter. I was hoping to find a simple word breaker solution that we could implement, but either I didn't find it or there seems to be none?
Answer: afaik no there isn't :( but I'm not Bruce AlMighty


How does a Buddhist care for others' suffering?

Question: Please forgive me, I know really little about buddhism. From what I heard, the Buddhist will try to find relief from suffering by meditation and trying to be selfless. But what about others that are suffering? Does the Buddhist value more attaining enlightenment for himself or helping others in need? Also what if others do not have the skills to practice to go towards enlightenment? Is the Buddhist concerned?
I'd like to understand more the relationship between the Buddhist and the suffering of other people.
Comment: What one learns one can teach it. Teaching others to understand suffering and dissatisfaction can be the greatest gift.
Comment: The [bamboo acrobat](http://accesstoinsight.eu/en/tipitaka/sut/sn/sn47/sn47.019.than) may answer the question.
Answer: When a person is sick, due to knowing they are sick, they act to visit a doctor. To be a doctor, a person must study medicine at university for at least 5 years, before they can help sick people.
Similarly, a person who is suffering must, via their own initiative, seek out a solution. Similarly, to be a Buddhist that can help others end suffering, a person must train for enlightenment.
An enlightened Buddhist makes themselves available to help others. However, others must learn to help themselves by following the advice of Buddhism.
Answer: I guess it broadly happens in three ways.

There's a focus on behaving ethically or virtuously -- keeping the precepts (or monks have stricter rules). These include no killing, no stealing, no lying, and more (e.g. no seducing their family).
That protects other people from misbehaviour.
More broadly there's some degree of emotional control as well as behavioural control. So "no anger" and "no coveting" as well as "no killing" and "no stealing".
And IMO that helps protect other people from emotional contagion (of afflictive emotions).
There's helping people in mundane ways. Being a good member of the family and of society, friend and employer. Earning an honest living. Being prudent, being generous, being thrifty not dissipated.
In that way you're able to help people in some worldly ways.
You're better able to help other people find their own liberation, perhaps by formal teaching or more generally perhaps by simply behaving (practising) as a good example.

There may be a step beyond that i.e. "bodhisattva" -- which is not a feature of the form of Buddhism which I've studied so far, maybe the three ways listed above are at least a good beginning, possibly sufficient.
Does the Buddhist value more attaining enlightenment for himself or helping others in need?
That question might assume things about identity which may be non-obvious from a Buddhist perspective -- Buddhism identifies selfishness as a problem, a cause or even the cause of "suffering".
Someone might answer that enlightenment is helping all beings (i.e. that the question is a false dichotomy).
Some of the doctrine in the suttas is like,

Even as a mother protects with her life
      Her child, her only child,
  So with a boundless heart
      Should one cherish all living beings;
  Radiating kindness over the entire world:

There's also What is the difference between 'compassion' and 'pity'?
Buddhism also mentions intention (what you're trying to do) and skill (how well or successfully you do it).
I think some of the elementary doctrine includes "skillful virtue results in lack of remorse" -- and "helping others in need" might belong to the category of actions which you don't regret -- and therefore helping someone is a little taste of enlightenment.
Together with "selfishness", "greed" is a problem (there are other problems too). I think that generosity is recommended even as part of the elementary training in virtue.
Also what if others do t have the skills to practice to go towards enlightenment?
I'd like to hope that everyone has the skill.
I'm not sure everyone has the right environment or circumstance (or society), though, maybe history (training) too -- perhaps their environment is part of what you affect (improve) by your own practice.
Answer:
"We're going to have depend on one another. And one way to make sure that other people will be happy to help you is that you help them. You keep them in mind. Here's why I keep saying: At the end of the day when you've done what you have to do, don't just think about what you want to do now. Ask yourself: "Do I have a little energy to do at least one more thing for someone else's well-being?" Make that a habit. That kind of habit then becomes something you can depend on."
~ Thanissaro Bhikkhu "Owners of Our Actions" https://www.dhammatalks.org/Archive/Writings/CrossIndexed/Published/Meditations10/200405_Owners_of_Our_Actions.pdf


Is it possible to read a device's firmware or internal programming in computer's RAM?

Question: Let us say I want to reverse engineer a PCIe-based FPGA device. Can I read or extract the IP core or any firmware in the computer's RAM or by trying to communicate with the device in some way?
Answer: The firmware for these devices is typically not directly connected to the computer, and the FPGA reads the data itself upon startup through a dedicated connection not accessible to anything else.  There would be no need to connect the memory chips to the computer, as it would add unnecessary complexity to the device.
The device may implement functions that let you read and write memory (e.g. to reflash the firmware) but often they don't implement read functions as it would make reverse engineering the firmware easier, and isn't needed for the device to function.  Plenty of devices still do however, so you can back up the firmware before reflashing it.
FPGAs often have dedicated memory chips connected to them, so there's a good chance you could just physically attach an EEPROM reader to that chip and dump the data as you would for any other standard flash memory chip.


Taylor Expansion of the 1/2th Derivative

Question: In trying to solve the problem $\sqrt D f(x)=g(x)$ I tried to expand the derivative as a Taylor series, and have encountered a lot of problems. Is there some reason that this shouldn't be possible? The Taylor series for the $1/2th$ derivative seems to be: $\sum\limits_{n=0} {1/2 \choose n} (D-1)^n $ with $D$ being $\frac{d}{dx}$. The one is there because if you center the Taylor series around zero it will acquire a lot of sums of infinities. Because $D$ is really a matrix, and therefore $\sqrt D$ is also a matrix, so I think that 1 should really be the identity matrix. Any help would be appreciated.
Comment: @vonbrand It's a linear operator on some function space, so I suppose you can think of it as an (infinite-dimensional) matrix.
Comment: Why do you say that $D = \frac{d}{d x}$ is a matrix? Where did you get the expansion for $\sqrt{D}$?
Answer: You have two ways to solve this problem:
1) You can integrate both sides of the equation $f(x)=D^{\frac{1}{2}}g(x)$. But for performing this option, you need that the resultant function is of the form $D^{\frac{1}{2}}g(x)=x^{\lambda}\eta(x)$ where $\eta$ is an analytic function and $\lambda\leq\frac{3}{2}$.
It would be to long to give you all the details that justify this argument. But you can find them in "An introduction to the fractional Calculus and Fractional Differential Equations" by Miller and Ross, Theorem 3 page 105. Basically is a more complicated version of the Fundamental Theorem of Calculus that you know.
2) If you lack the hypothesis of 1) you could try to apply the Laplace transform to both sides of the equation, solve it algebraically (will be easy in general for this equation unless $g$ is very ugly), and reverse back with the inverse transform. But you are going to get an special function as an answer in most cases, no matter if $g$ is simple.
(All this assuming you use the Riemann Lioville definition of fractional calculus. I would forget about Taylor.)
Hope it helps.
Answer: We want $D_x^{1/2}$ to be an operator (we shall forget uniqueness a bit) such that $D_x^{1/2}\left(D_x^{1/2}f(x)\right)=f'(x).$ We also want it to have some reasonably nice properties, such as linearization and the product rule. Let's try to find out $D_x^{1/2}(a_nx^n)$  first, so we can take advantage of the linear properties and study a more general case, $D_{x}^{1/2}\left[\sum_{k\geqslant 0}a_kx^k\right]$. First, show by induction that $$D^{r}_x(a_nx^n)=\frac{n!}{(n-r)!}a_nx^{n-r}\tag{$r\in\mathbb{N}$}$$ and assume it can be extended for fractional $r$, using the $\Gamma$-function. Using linear properties, $$D^{r}_x\left(\sum_{n\geqslant 0}a_nx^n\right)=\frac{r!}{x^r}\sum_{n\geqslant 1}{n\choose r}a_nx^{n}$$ Since you are looking for a Taylor expansion, write it: $$D_{x}^{r}\left[f(x+a)\right]=\sum_{n\geqslant 0}\frac{x^{n-r}}{(n-r)!}f^{(n)}(a).$$ Let $r=1/2$ and we're there. However, this answer is sketchy; there are another issues, such as convergence and existence of these operators. Consider also negative cases (antiderivatives).


How to update the LG GT540 Optimus to the lastest stable Android version?

Question: How can I update my LG GT540 Optimus to the latest stable Android? Is if safe to update, or I could brick my phone? Or it does it by auto? How are the installed softwares (from Android Market) updated? I have to do manually  or is it done automatically?
Comment: It doesn't look there is (nor will be) an official update. If so, you're only remaining option is a custom ROM. See: http://android.stackexchange.com/questions/11882/how-to-install-custom-rom-in-lg-gt540
Answer:
Backup your phone

this is important if you wish to keep any data from your phone. You will have to restore backed up data (such as apps) after you update. The only way to update to the latest software is to erase your device, so backup whatever you do not want to lose.

Extract the .zip file, which you can download from this AndroidForum thread or this XDA thread. Open the folder and install MSXML 4.0 SP3 Parser (msxml.msi).
Once that has finished, install LGAndroidDriver_WHQL_ML_Ver1.0_All_Win7.exe which are the drivers so your computer will recognize your phone. Windows XP Users download this driver, extract the contents anywhere (e.g. desktop), right-click on the 'android_usb.inf' file and click 'Install'.
Next, open KDZ_FW_UPD.exe
(i) Change 'Type' to '3GQCT' THIS IS A MUST, THE UPDATE WILL NOT WORK OTHERWISE AND YOU MAY BRICK YOUR PHONE
(ii) Make sure 'PhoneMode' is set to 'DIAG'
(iii) Browse for the 'V20B_00+Fastboot.kdz' file.
Prepare the phone by enabling USB Debugging by going to Settings>Applications>Development>Enable USB Debugging and connect the phone to the computer via USB cable and wait for the drivers to install for the phone. Sometimes the computer still won't recognize the phone, if this is the case, try this: Windows Vista and Windows 7 users press start and type device manager (Windows XP users right click 'My Computer' and click properties, then click the Hardware tab and click Device Manager) then locate LGE Android Platform Modem, right click it and click disable. Accept any warnings that come up. Also, make sure you've disabled Mass Storage Mode on your phone. To do this, go to Settings>Storage>Enable Mass Storage, and untick the box.
Click 'Launch software update' and do not use your computer until the update is complete. The update will take roughly 10-20 mins to complete.

This method was found in the AndroidForums. There is also a Youtube tutorial on rooting the GT540.
Bricking is always a possibility when modifying software that doesn't come directly through the intended channels
That said, the methods here have been proven to work and your risk is significantly less if you perform these steps correctly.
Let us know if you need any help!
Comment: This is the exact same answer you left on [another question](http://android.stackexchange.com/questions/11882/how-to-install-custom-rom-in-lg-gt540). This question, I don't believe, is asking about custom ROMs.
Comment: i just added this answer to that question because it seemed the same question (it has been tagged as a possible duplicate). And i found this answer most appropriate, as i do not believe there is a LG GT540 2.3 update without using a custom ROM.
Comment: see note on other answer.
Comment: While the answer might (ultimately) be the same, I think they're different questions.
Comment: i'll agree with that. i have modified the other post to fit that question better.
Answer: You probably need download and install LG tools and drivers from lg web site. And follow the software instructions.
Also this is the site for ireland http://www.lg.com/ie/android/index.jsp, mentioning  Upgrade of GT540 to Android 2.1 Eclair.
You may also check these two references:
- http://forum.xda-developers.com/showthread.php?t=1032744
- http://forum.xda-developers.com/showthread.php?t=803695
I learned a lot from xda forums and beware most of things in xda are on your responsibility, meaning yes, there is a chance you can brick your phone.
Comment: there is no offical way to update android without the risk bricking it?
Comment: no, you have to wait lg to release an official update. even official update procedures can brick your phone, there is no absolute guarantee


2007 Kia Spectra engine temperature fluctuating

Question: what would cause my kia's engine temperature to start fluctuating. it never gets hot but it will rise 2 bars on the temp gage and when it rises to the second bar over where it normally reads my ac will quit blowing cold air. if I turn the car off and turn it back on it will start blowing cold air again but only for a few seconds if the temperature doesn't start to go down. if the temperature goes down below that that second bar it will keep blowing cold air. the temperature will go back to its normal reading then back up then back down and like I said it never gets over 2 bars higher than normal. I hope I've explained my problem to where it makes sense.
Answer: Is the temperature getting higher only when it is warm out or is it a constant problem the just started?
With it being several years old can you advise as to last time your had the cooling system flushed and new antifreeze added.  The cooling system clogs with age and can reduce the effectiveness causing a rise in operating temperature.  Some engines have a thermal switch to stop the AC system to prevent overheating the engine.
Another area could be the thermostat is starting to fail and not opening proper when temperature gets to the operating zone.
Have your system flushed, coolant changed and pressure tested.
Answer: It was my thermostat! Hope this helps somebody else one day


Is there an MAC emulator?

Question: I really like the wine, a complete .exe emulator.
But I would like to use an Mac OS X theme, so, I would like to use the "Made for Mac" programs.
Where can I download this emulator - if it exists?
Thanks
Gabriel
Answer: Yes there is a  compatibility layer that can run Macintosh binaries On Linux and it is called Darling.  You can get it by this command in the terminal (Note this is only for the source code)
<code>git clone --recursive git://github.com/LubosD/darling.git
</code>
and you need you compile it also, where is link telling you how http://darling.dolezel.info/en/Build.
Note this project is early in development, there aren't many Apple programs that can run on this compatibility layer.  There is more Apple programs that can  run on Darwin OS than this compatibility layer that said I think you will be better off running Darwin in a VM!.

Sources:
http://darling.dolezel.info/en/Download
http://www.phoronix.com/scan.php?page=news_item&px=MTI0Njc
Comment: I hope it can help me.
Answer: I think there is no "emulator", as there are for example nes-emulators. Also, Wine isn't really an emulator.
So, I think the best solution for you would be virtualbox, a program which allows you to install several other OSs in Ubuntu. Install it from the softwarecenter. Open it and put the OSX-DVD in your mashine (This is the only non-free part of this solution). Create -New- and follow the wizard. Your operating system will be installed and you can use it inside Ubuntu, as if it was on a separate computer. Everything inside a window, a little Mac.

Is there an MAC emulator?


Apache2 redirect URL to another internal server

Question: Our home setup consists of two Linux webservers on a single static IP. My server currently uses the standard HTTP(S) ports. My friend's server uses non-standard ports to get around this. Both of us have URLs set up.
I'm curious as to whether I could configure Apache on my server to redirect or proxy any connections heading to my friend's URL (on standard ports), to his server, transparently. I know I could rewrite the URLs but I'm not good with the rules, so I'm wondering if I could use mod_proxy to send the connection to the other machine through my server. I've done something similar, but that involved proxying all incoming connections.
Is it possible? Thanks, and sorry if this has been answered; I wasn't sure what to search for.
Answer: You could also do this using virtual hosts and setup Apache as a reverse proxy. This is how I have it setup where I work.
a.domain.com -> ProxyPass http://192.168.1.101
b.domain.com -> ProxyPass http://192.168.1.102

Checkout the documentation for ProxyPass and ProxyPassReverse.
If you just do a name based virtual host for both then you could add something like this to your virtual host definition (or replace localhost for your IP if your box will be hosting apache):
<Location />
    ProxyPass http://192.168.1.101
    ProxyPassReverse http://192.168.1.101
</Location>

Then in your friend's virtual host config
<Location />
    ProxyPass http://192.168.1.102
    ProxyPassReverse http://192.168.1.102
</Location>

You can also add ports to the ProxyPass directive if you don't want your friend to change firewall rules, service setting etc. Or you can even be a reverse proxy for another external IP address too.


Is it safe to use a battery charger to test the capacity of a non-rechargeable battery?

Question: I have this battery charger at home. It has a voltage test function. I also have a lot of non-rechargeable batteries lying around. Is it possible and safe to use the charger's test function on non-rechargeable AAA or AA batteries?
Answer: That charger device clearly states that it is for NiCd and NiMH rechargeable batteries only. It would be a risky proposition to put other batteries in that unit whether they be lithium or alkaline types. I think it would be just too easy to put the unit into the wrong mode.
What you want to do instead is get yourself a digital multimeter that can measure voltage of any battery that you may have laying around. These days you can pickup a suitable device that would fulfill your needs for a surprising low cost. Check out offerings on Amazon for example. The good thing about this approach is that you will find other uses for a digital multimeter once you have it and learn how to use it.
Comment: A digital multimeter is a very worthwhile investment. Specifically with batteries though, my understanding is that a test-under-load is superior to a simple voltage check, and a good battery charger/tester would hopefully do that. But since the relevant curve varies by battery chemistry, using the wrong type of charger (unless it specifically says it can test other types) doesn't make sense.
Comment: It is worth knowing that what a charger does is convert one chemical compound into another by applying voltage in reverse.  The "Negative" element actually grows back so that it can release electrons in the normal way. Because the negative compound does not reform into its original efficient shape, over time rechargeable batteries will no longer take a charge. While non-rechargeable batteries will also reform, it does not do it fast enough to absorb the energy and must therefore release the excess as heat, which expands the interior and causes a nice boom
Answer: I have a suspiciously similar LaCrosse charger that I have used for testing alkaline batteries.  My charger spends a few seconds detecting and displaying the voltage before it begins charging, so if you're a bit quick, yes, you can use it to test voltage.
Answer: No. It is made for NiCd and NiMH batteries only, which happen to work at the same voltage.  The charge indicator will be useless for any other type of battery, which by nature operate on different voltage.
Buy a real DVM, measure the actual voltage, and google up a table that shows voltage vs. state of charge for that battery type.
Comment: If you go look at the charger, it outputs voltage. Doesn't have anything to do with the "type of battery". Still not sure that it would be a good idea, but it does show voltage.


What is the common way to type in Hebrew for this site?

Question: Is there a recommended approach to entering Hebrew text?  I see lots of it, and some questions/answers will require it (as transliterating into English works poorly).
Comment: @AviD - I think, in the spirit of "think of this site as asking a crowd of your friends", pronunciation need not be standardized. Sometimes there are nuanced meaning differences between two pronunciations from the same source and other times it is simply natural variation in dialects. Either way, I don't see the need to standardize unnaturally - just maximize comprehensibility.
Comment: @AviD @jake, if the site can decide on a single standard transliteration scheme, then someone who's aware such a scheme exists (it can be advertised) will be better able to search, yes. based on my experience at [another site dealing with transliterating Hebrew](http://en.wiktionary.org/), I doubt that we'll come to such agreement. But one can always hope. Most people have a way to search for Hebrew characters. Perhaps all questions (including old ones) should have any relevant Hebrew (or other Hebrew-script) words included in Hebrew characters to aid findability?
Comment: Also related, what "form" of Hebrew should be used: Proper grammatical Hebrew, Yiddish/Hebrew, American Hebrew, "Yeshivish"... I pretty much prefer strict use of proper Hebrew (e.g. Shabbat, not Shabbos, Shabbes, sabbath, etc...)
Comment: @WAF, On the other hand, though, standardized transliteration can make it much easier to search on the site, if your search contains hebrew word(s).
Comment: I've posted this (my comment above) as [a new question](http://meta.judaism.stackexchange.com/questions/40).
Comment: @WAF, @jake, I agree with all the above comments: *if* there were a standard, it would definitely help searching; however we are unlikely to achieve that. We do need to take into account that this *will* harm searches, but what ya gonna do... We can at least *try*, however, to aim for and encourage correct "pronounciation", at least, and then (hopefully) transliteration won't diverge as much. Don't forget, you would also have to account for word forms: e.g. kashrut vs. kosher vs kasher vs kashering vs... this would only get much worse if we also have to deal with non-standard pronounciation...
Comment: Related to the comments above is http://judaism.stackexchange.com/questions/9870.
Answer: Modern versions of MS Windows, Mac OS X, Ubuntu, and, I'm guessing, other (at least modern) OSes have a "character map" program that will allow you to select Hebrew letters (and vowels) one at a time and copy the lot. Windows also has an on-screen keyboard and you can add a Hebrew keyboard layout; I'm guessing other OSes have the same.
Some instructions can be found here.
Adding  (for the left-to-right mark) (and sometimes  (for the right-to-left mark)) as necessary helps.
Comment: For the record, those instructions you've linked to aren't for using the character map program, rather they're for installing Hebrew as a second language. This solution is actually much much better than using a character map app where you would have to point and click on each letter you want to "type". Installing the language into the OS lets you just switch back and forth seamlessly and type naturally with your keyboard. So +1 for the awesome link - that really is the way to do it.
Comment: @Bachrach44 yes, see the second half of my first paragraph.
Comment: @msh2010 - Maybe the instructions at the link have changed since you posted it 3 years ago, but that's not instructions for an on screen keyboard - that's to actually use your current physical keyboard. You will simply have to learn that to write an 'א' you type 't'. As I said if you really have to type in Hebrew a lot this is the way to go - It actually takes a lot less time than you think to learn touch typing in another language.
Comment: @Bachrach44 Perhaps I should learn to touch-type in my first language first. `:-)`
Answer: I may be mis-understanding this question, but as far as I can tell it is about typing Hebrew characters for use on the site. If so, the best method which exists (if you don't have native Hebrew support and keyboard stickers) is Mikledet and amazing online Hebrew keyboard emulator which allows you to type with your keyboard and see the Hebrew on-screen.
Additionally, I would recommend pasting Hebrew text which is copied from elsewhere (eg. Bar Ilan, Mechon Mamre) into Google Docs first to format and then moving it over to this site. This is simply because Google Docs has very good RTL support and encoding so it clears most of the formatting issues you mayb have with RTL text. (For instructions on using RTL in Google Docs see here: https://docs.google.com/support/bin/answer.py?hl=en&answer=65166)
Answer: My personal policy is just to transliterate to the best of my ability and italicize. It makes it readable to the most people, which is the point of posting in the first place, and usually doesn't detract from the meaning. When transliteration loses some of the intended meaning (such as in questions about Hebrew letters or the like) I put in the original Hebrew.
Answer: A Hebrew keyboard is now built into Mi Yodeya, based on a script originally written by @HodofHod.
In the editor, click on the circled button:

to get this keyboard:

Clicking on keys on the Hebrew keyboard produces Hebrew.  Typing on your keyboard continues to produce English.  Mix and match as needed.
Use the  key after punctuation that appears at the end of a Hebrew phrase to make the punctuation appear at the end of the word.
Answer: On my Android device, I enable a Hebrew keyboard and switch to it whenever I need to enter Hebrew characters.

Open Settings and tap on Language & Input. Tap on the settings icon next to Google Keyboard. Tap Input Languages at the top. Deselect "Use System Language" and then select any keyboard languages you wish to use.
Comment: The same works for iOS. (Slightly different instructions for how to get to the appropriate setting, obviously.)
Answer: If your native language is English and you want to type in Hebrew or Yiddish, you should go to https://www.google.com/inputtools/try/ instead.
How about using google tranlitrate? This link is only useful for native Hebrew speakers.
At the bottom of the page there is a bookmarklet you can add to your links and clicking on it will tranlitrate what you type in the page you are viewing.
Comment: That looks like a way to generate Hebrew characters, but not necessarily the specific ones you want.
Comment: Dear Arjang: Google Transliterate is now part of the Google Input Tools suite. Your link is only useful for native Hebrew speakers. If your native language is English and you want to type in Hebrew or Yiddish, you should go [here](https://www.google.com/inputtools/try/) instead. Please edit your post and repoint the link.
Comment: @IsaacMoses: It's been improved since six years ago, and it's quite useful now.
Comment: @unforgettableid : thank you for the info, I'll update it , please check.
Comment: @Arjang: Better, thank you.


Intermittent error 404 during higher loads. (nginx/php/apc/mysql)

Question: I have a 4 cpu core VPS with 4GB ram. It is running Ubuntu 10.04 with nginx/0.7.65, PHP 5.3.2, and MySQL. I use php5-fpm for the communication to nginx. I also have php5-apc complimenting with php caching.
This system runs four sites and shows approximately 2.5 million page views per day.
Introduction to problem - The sites will intermittently show error 404 when loading a page. It potentially happens on every page, and I can sit there and refresh over and over and it will happen on average once in every seven to ten times.
What I've tried - Updating Ubuntu and nginx, playing with php and nginx configurations. this problem has been replicated on Ubuntu 11.10 and nginx/1.0.5.
Notable logs - Nginx error.log and access.log show nothing out of the ordinary, but do report when a 404 is issued. php5-fpm.log displays:
Nov 20 21:47:45.640003 [ERROR] [pool www] unable to retrieve process activity of one or more child(ren). Will try again later.
but I am not convinced that is related to this issue, as i've seen it in previous setups.
Configurations (links to images to save space) -
* APC settings, note Fragmentation: 0% and Cache full count is 0. https://i.stack.imgur.com/i0TrK.png
* nginx.conf
user www-data;
worker_processes  4;

error_log  /var/log/nginx/error.log;
pid        /var/run/nginx.pid;

events {
    worker_connections  1024;
    use epoll;
# multi_accept on;
}
http {
include       /etc/nginx/mime.types;
server_names_hash_bucket_size 64;
access_log off;  #/var/log/nginx/access.log;

sendfile        on;
#tcp_nopush     on;

keepalive_timeout  0;
#keepalive_timeout  65;
tcp_nodelay        on;

gzip  on;
gzip_disable "MSIE [1-6]\.(?!.*SV1)";

include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;
}

typical site configuration included in nginx.conf https://i.stack.imgur.com/I3Y4N.png
my php5-fpm.conf is default, except pm.max_children = 30 from pm.max_children = 10.
my php5 config is default, only edits are sendmail/postfix related
ulimit -n shows 1024

What helps - The only relief I have had from this is by moving one of the two busier sites to its own VPS. Obviously I would love to have all the sites on one vps, as the system has more than enough resources. Am I hitting open file limit somewhere? I'm suspicious it may have something to do with something php related.
Pretty confident that this is a config issue somewhere. Not confident what it could be though, and have spent 48 hours attempting to research before posting this question.
Answer: Upgrading to PHP >=5.3.4 should help, as it seems you've been bitten by this bug: https://bugs.php.net/bug.php?id=53028
Comment: I have this issue with PHP 7.1. I think the cause may be session_start() taking over 30 seconds due to a write-lock by another php process, and so nginx times out. I think I'll find more info in the logs


Articles- Sound Design in comedy

Question: I wonder if you guys have read great articles or have book referees about sound design for comedy (which tricks are used and how the sound helps the movie/tv show/etc to be funnier) that you could tell me about! I would really appreciate :)
Answer: There's an article in The Soundtrack from a few years ago (Volume 1, Number 1) that I think would be well worth reading.  It's called "The Sound of Coen Comedy: Music, Dialogue and Sound Effects in Raising Arizona," by Randall Barnes.
That particular edition is available for free download here: http://www.atypon-link.com/INT/toc/tst/1/1?cookieSet=1
but here's a direct link to the article in .pdf format: http://www.atypon-link.com/INT/doi/pdf/10.1386/st.1.1.15_1
Answer: Holy crap, there's a girl in our midst!
Now that I got that out of the way... I haven't read anything about comedy specifically, but I have seen it mentioned in texts about sound design for animation. (I'm looking for a reference... when I find it, I'll let you know.)
In the mean time.. this is a similar question (fixed): What makes a sound funny?
Comment: @Dave -I'd argue that's not necessarily the same question. Many things can make a sound funny, but a serious sound can make a visual funny. The sound itself does not have to be funny, but it can provide commentary for a visual/action/scenario the creates humor. That's a different technique of sound design that shares the same goal.
Comment: Point taken, and I agree.
Answer: There are no rules. There are only lessons to be learned from watching the movies that made you laugh!
At the risk of repeating some of what @Ryan wrote, there is no formula for making a soundtrack "funny" -- just the idea of that doesn't make much sense since the same sound to two different people will elicit different reactions. Making it funny is partly about timing, partly about context. Some techniques I've found useful and effective:

Use your sound moment to make a
statement, whether it be over-the-top
or understated
Try to tell the story with a sound
that is unexpected
Try to tell the story with a sound
that is completely expected (and
perhaps cliché)
Use timing to your advantage
If the film is a remake, sequel or
reminiscent of another film, try
using sounds from those films as an
homage

Articles- Sound Design in comedy


My chicken soup always ends up with bones

Question: I'm an avid crock pot-ter. My favorite recipe by far is my dad's famous chicken soup. It calls for bone-in chicken. I usually use drumsticks because that is what my dad uses, but I ALWAYS end up with a ton of little pieces of bone in my soup and it makes this amazing soup kind of disgusting. I'm wondering if I'm doing it wrong? I always get out the big bone, but those little ones are hard to find once the soup is made and everything is just falling off the bone. Is there a better cut of chicken that I can use to minimize the bones I have to fish out of it? I've tried it with boneless chicken and it isn't near as good.
Comment: I'm confused.  Drumsticks have only *two* bones, one large and one small.  Where are "*those little ones*" coming from?
Answer: I generally make chicken soup in two phases. Phase 1 is chicken stock, simmering (roasted) bones with aromatics for a long time (often, overnight), followed by straining. Phase 2 is chicken soup, combining the strained stock with chicken meat, vegetables, and other ingredients.
Because the stock is strained, it has no bones, big or small. There can be vegetables in the stock as well, which will be cooked until they are mushy, giving up their flavor but no longer something you want to eat; they are also strained out. If you're using very meaty bones, or even whole birds, you can salvage the meat by picking it off the bones, and adding it to your soup (though most of the flavor will be cooked out of it.)
The bones and the meat don't have to come from the same bird. You can take bones leftover from a roast chicken or other meal, and make stock out of that. You can even save the bones in the freezer, accumulating them from a number of projects, then make one big batch of stock. Freezing the stock means you'll have it on hand any time.
Then you could make chicken soup by buying drumsticks (or whatever part you like), and removing the meat. That will turn into soup fairly quickly: it will take just half an hour or so to cook vegetables to the right point, and just a few minutes to incorporate the meat. The bones you removed can go into the freezer, and the process continues.
Answer: Welcome! I would suggest using bone-in chicken thighs. You would still have the dark meat and the flavor is pretty much the same as drumsticks.
Additionally, the thighs do not have the additional small bone that can separate and they usually have have less gristle or cartilage at the ends of the bone. And none of the nasty tendons that you sometimes see in the larger drums.
Note that if you decide to try thighs, buy them without the back portion or remove the back portion. The back bones can be worse than anything you get from drumsticks.
Answer: BOIL IN CHEESECLOTH, works great and I still strain liquid into cheesecloth AGAIN JUST to MAKE SURE there aren't bones or anything.  Also REMEMBER to pick meat BEFORE BOILING for Stock.  Or the meat has no flavor.  Add meat AFTER the first round after carcass is taken out and remake with new meat and fresh veggies.....YUMMMMM
Answer: Here's the thing - you want the bones and chicken parts when making the soup because it adds so much flavor.  However, I generally don't use the keep the meat from that process for my soups, because all the flavor from the meat has been extracted into the liquid.  That makes things much easier.  You can avoid the pieces you don't want by:

Straining everything through a mesh strainer or through a collander lined with cheesecloth.  This also allows you to squeeze a bit more liquid from the vegetables/carcass melange.
Wrap the meat parts in cheesecloth (spread out the cheesecloth, put it in, wrap the cloth around and tie a knot in the end of it) or a muslin cloth bag before putting it into the pot.  This allows you to remove it all at once.  Bay leaves, parsley and any other things just for flavoring the stock, to be picked out and discarded later (or, if they aren't currently included, they can be flavor-adding enhancements now that you have an easy way to remove them when it's done), can all go in there.

Then, when you've taken it out, have some cut up leftover chicken meat ready to go back in.  The meat will have more flavor than the stuff used to make the stock, and you'll have a more flavorful end result.
This might run contrary to the whole point of using a crockpot (simplicity and less steps for preparation), which I normally don't do for soups.  Another option -

Do some knifework before adding the chicken - cut away most of the meat, chop it up, throw it into the crockpot, and then wrap the bones, gristle, cartilage and skin, separately, into a cheesecloth packet as mentioned in option #2.  Then you don't have to bother with having a separate bunch of meat ready to add, but you can remove the stuff you don't want in one step.
Answer: roast the chicken first, then let it cool. This will make stripping the meat off the bones easy, and if you take the time give you a great amount of meat. then take the bones and boil them with an onion, a couple of carrots a stick of celery all roughly cut for 2hours or so. strain off the liquid into a crockpot and add your roasted chicken, and whatever veg ,herbs and dumplings ect, cook on a low heat  for another 40 to 50 mins.
this may seem to be a lot of bother and it is but it does give you the best stew.
Answer: The marrow in the bones add the flavor that boneless is missing. My mom had the same problem you are having. You are right about it being disgusting. It kept me away from making crockpot meals for two decades.
The disgusting part isn't that the taste is funky...for me. My disgust comes from the thought of accidentally swallowing a small bone that sticks in my throat. That, and the thought of biting into gristle...had that happen once and I never ate crockpot chicken soup again unless it is made with boneless chicken.
First, I would ask your dad what he does to eliminate the small bones. I suspect he is cutting those pieces out so they are not a problem. Or, maybe he cooks them into the broth(I've heard that this can be done, but since I use boneless, I don't know for sure).
Answer: When making chicken soup, I use the carcass of a whole chicken. I put the carcass, onions, celery, peppercorns and fresh dill into a soup sock! The best at keeping it all together. Soup socks are made from cheesecloth. They are pretty big. You can use two if needed. You just have to check the kitchen stores, or large grocery stores. They lesson a lot of work for me!!!!!!


Inode Usage on Joomla Website

Question: I have a joomla website on shared hosting at siteground.com
in the control panel, i see this message that i have exceeded my inode usage of 150,000.
any tips to reduce this?
Comment: Hey Vivek, did either of those answers help you out?
Answer: This question on Stack Overflow suggests that deleting files should help. If you have multiple WYSIWYG editors, remove all that you don't need. Some of the editor plugins (like fckeditor) have an unbelievable number of files.
However, since it's shared hosting it's likely that the message is caused by the number of files across all the sites on the server. I would contact your host about it; they probably have too many sites on one server.
Answer: You may want to consider changing the cache settings of your Joomla! website as well to reduce the number of inodes. For an interesting case study on how the number of inodes was reduced dramatically for a shared hosting site that has a maximum of 150,000 inodes, see:
http://www.test.developmentwork.net/data-recovery/joomla-test-sites/35-using-a-subdomain-as-a-joomla-test-site
By changing the cache settings and clearing the cache regularly, the number of inodes was reduced from over 450,000 to some 80,000.
By managing your cache settings effectively, you may be able to run up to 10 subdomains with Joomla! installed if traffic is not too heavy and you do not run too many scripts on a shared hosting account with a maximum of 150,000 inodes.
Gregory
Answer: I suggest you change your hosting... Joomla files already exceed 9000+ and with adding new extensions and files it will be hard to keep removing files like that
Answer: It is the total number of files. Just reduce your files by removing unnecessary modules, templates and reducing cache clean up time.

Inode Usage on Joomla Website


Shamir's Secret Sharing of modular inverse

Question: Given a secret $K \bmod q$ which is shared among entities $E_1,…,E_n$ using polynomial Shamir's Secret Sharing, how can the inverse of $k$ be shared without revealing $k$ and $k^{-1}$?
Answer: I'm assuming $q$ is prime.
Note that $k^{-1}\equiv k^{q-2}\bmod{q}$.
We can compute $k^{q-2}\bmod{q}$ via a multiparty computation protocol such as the one outlined in this paper ($\S3.1)$. Or, since $q$ is likely a public parameter, you can even do the simple square-and-multiply algorithm (for example, VIFF provides this capability).
You might also be able to compute the modular inverse via the extended euclidean algorithm implemented using general MPC techniques. The reason I say might is that the extended euclidean algorithm does have a conditional branch in it. While this is technically not a problem for MPC, it could leak information in the real world that you wouldn't want to leak.
Answer: All this happens in your prime field q:

Use a secure DKG algorithm to distribute shares of a random number
Each party computes secret_share[i] * dkg[i]
Use a secure degree-reduction protocol (aka: redistribution) on those shares
Each can then reconstructs secret_share * dkg == SD
Each can then compute inverse(SD) * dkg[i], which are shares of the inverse

You should be very aware that this protocol is protected solely by the quality of the random numbers used, and the correctness of the DKG.
(Also, it's been tested and works fine)
Comment: Assuming $secret\_share[i]$ as the initial shares? Then it should be $inverse(SD) * dkg[i]$. Also it should be mentioned that this requires $2*t + 1$ shares instead of $t + 1$.
Comment: Thanks but why does it require 2T + 1?  Degree reduction protocol should handle that right?
Comment: The reduction is the final result, but the first multiplication results in a polynomial of degree $2*t + 1$.


Is there any reason for doing back face culling in software?

Question: I, a newbie, have been doing back face culling in javascript for my WebGL app because I didn't know gl.cullFace() existed. Is there any reason to use software-based culling instead of just passing all faces to GPU and let it do the culling?
Answer: No.  The GPU has dedicated hardware for the purpose, so it will be far faster, especially compared to Javascript.  (I wouldn't do anything that iterates over individual verts / faces in JS!)
Answer: Sometimes, but it depends on your use case and data structures.  You can still get a win if your data is set up so that you can cull groups of faces per test, and if doing so doesn't require you to break a batch.  Otherwise just let the GPU do it (especially if you have VBOs available).


Testing Java performance

Question: There are a handful of different standard desktops and laptops at my company that I could choose from for developers on my team.  Each is from a different company and comes with different load-outs of CPU, RAM, OS, etc.  I'd like a test to determine which one of them will run Eclipse most quickly with some sort of impartial test.  Since the task most critical to our team is running Java programs, I was considering using SciMark 2 scores.  Is this a relatively good rough idea of how Eclipse will perform of this machine, or is there a better way?
Answer: I don't understand why you even need to test for this.  You should know generally which is faster than what.
OS shouldn't matter, since you should be reformatting everything to be the same.
Just pick the fastest (non server) CPU, and then max out ram.  Simple.
You'll also want to read this:
http://www.codinghorror.com/blog/archives/001198.html
Answer: It all depends what kind of Java development your team is about to do. If all they do is console based number crunching, sure SciMark might do the trick as far as I can tell, since it is benchmarking just that: number crunching. And in this case, that would be CPU first, then memory. On the other hand, if they're developing JEE applications with an ant/maven deployment and, say, a local database for tests, disk access and memory would be number one factors. And if they are developing graphical interfaces with for examples a 3D rendering, you might want to take care of the GPU.
Best test for you, if the project already exists, would be to load up Eclipse and run builds and tests for your application being developed. No generic benckmark can really help you there unless it matches your exact needs.
Answer: Eclipse is very memory hungry.  Assuming the CPU's are roughly in the same range, I would try to give them the ones with the most memory.
The best way to test for Eclipse would be to run Eclipse:-)  I don't think any sort of benchmark would help that much.
Answer: The best test is the user frustration test. Make then use Eclipse for work for a given duration and then ask them what was better. Alternatively, use a stopwatch to record time spent twiddling their thumbs waiting for a compile/refresh/deployment operation.

Testing Java performance


Would it help if you jump inside a free falling elevator?

Question: Imagine you're trapped inside a free falling elevator. Would you decrease your impact impulse by jumping during the fall? When?
Comment: @Earwicker: Nope, the elevator is very important. The falling human cannot change the total momentum of the system, but by jumping, he can *transfer* momentum to the elevator in the hope of reducing his own momentum. If there is no elevator, the human can't do anything (except drop his shoes, perhaps.) Instead of an elevator, imagine that the human has a jetpack. Now it is conceivable that he could reduce his own momentum at the expense of the ejected fuel.
Comment: Another way to approach this: suppose shortly after the fall began, the elevator miraculously disappeared. Now it's just you in free-fall. I find this makes the outcome more intuitive. The elevator is not the problem, and so the problem cannot be solved by breaking your contact with the elevator.
Comment: @Greg Graviton - or alternatively, simply wait until you're in reach of the ground and use your leg muscles to push against it, thus transferring momentum to the Earth. Problem solved.
Comment: @Earwicker: Sure, but the disadvantage of this "method" is that it's very difficult to efficiently transfer muscle energy onto the ground in this situation. Then again, weightlessness in the falling elevator doesn't make it easy either.
Comment: Your actual, literal answer to your actual question is "Yes, you would decrease your impact impulse".  Your relevant answer is given below.
Comment: Depending on how far the elevator is falling, you would expect some terminal velocity so that there would be a gravitational force keeping you on the floor.You could push against the floor in that case.
Answer: While everyone agrees that jumping in a falling elevator doesn't help much, I think it is very instructive to do the calculation.
General Remarks
The general nature of the problem is the following: while jumping, the human injects muscle energy into the system. Of course, the human doesn't want to gain even more energy himself, instead he hopes to transfer most of it onto the elevator. Thanks to momentum conservation, his own velocity will be reduced.
I should clarify what is meant by momentum conservation. Denoting the momenta of the human and the elevator with $p_1=m_1 v_1$ and $p_2=m_2 v_2$ respectively, the equations of motion are
$$ \dot p_1 = -m_1 g + f_{12} $$
$$ \dot p_2 = -m_2 g + f_{21} $$
Here, $f_{21}$ is the force that the human exerts on the elevator. By Newton's third law, we have $f_{21} = -f_{12}$, so the total momentum $p=p_1+p_2$ obeys
$$ \frac{d}{dt} (p_1 + p_2) = -(m_1+m_2) g $$
Clearly, this is not a conserved quantity, but the point is that it only depends on the external gravity field, not on the interaction between human and elevator.
Change of Momentum
As a first approximation, we treat the jump as instantaneous. In other words, from one moment to the other, the momenta change by
$$ p_1 \to p_1 + \Delta p_1, \qquad p_2 \to p_2 + \Delta p_2 .$$
Thanks to momentum "conservation", we can write
$$ \Delta p := -\Delta p_1 = \Delta p_2 .$$
(Note that trying to find a force $f_{12}$ that models this instantaneous change will probably give you a headache.)
How much energy did this change of momentum inject into the system?
$$ \Delta E = \frac{(p_1-\Delta p)^2}{2m_1} + \frac{(p_2+\Delta p)^2}{2m_2} - \frac{p_1^2}{2m_1} - \frac{p_2^2}{2m_2} .$$
$$ = \Delta p(\frac{p_2}{m_2} - \frac{p_1}{m_1}) + (\Delta p)^2(\frac1{2m_1}+\frac1{2m_2}) .$$
Now we make use of the fact that before jumping, the velocity of the elevator and the human are equal, $p_1/m_1 = p_2/m_2$. Hence, only the quadratice term remains and we have
$$ (\Delta p)^2 = \frac2{\frac1{m_1}+\frac1{m_2}} \Delta E .$$
Note that the mass of the elevator is important, but since elevators are usually very heavy, $m_1 \ll m_2$, we can approximate this with
$$ (\Delta p)^2 = 2m_1 \Delta E .$$
Energy reduction
How much did we manage to reduce the kinetic energy of the human? After the jump, his/her kinetic energy is
$$ E' = \frac{(p_1-\Delta p)^2}{2m_1} = \frac{p_1^2}{2m_1} - 2\frac{\Delta p\cdot p_1}{2m_1} + \frac{(\Delta p)^2}{2m_1}.$$
Writing $E$ for the previous kinetic energy, we have
$$ E' = E - 2\sqrt{E \Delta E} + \Delta E = (\sqrt E - \sqrt{\Delta E})^2 $$
or
$$ \frac{E'}{E} = (1 - \sqrt{\Delta E / E})^2 .$$
It is very useful to estimate the energy $\Delta E$ generated by the human in terms of the maximum height that he can jump. For a human, that's roughly $h_1 = 1m$. Denoting the total height of the fall with $h$, we obtain
$$ \frac{E'}{E} = (1 - \sqrt{h_1/h})^2 .$$
Thus, if a human is athletic enough to jump $1m$ in normal circumstances, then he might hope to reduce the impact energy of a fall from $16m$ to a fraction of
$$ \frac{E'}{E} = (1 - \sqrt{1/16})^2 \approx 56 \% .$$
Not bad.
Then again, jumping while being weightless in a falling elevator is likely very difficult...
Answer: As an addition to already posted answers and while realising that experiments on Mythbusters don't really have the required rigour of physics experiments, the Mythbusters have tested this theory and concluded that:

The jumping power of a human being cannot cancel out the falling velocity of the elevator. The best speculative advice from an elevator expert would be to lie on the elevator floor instead of jumping. Adam and Jamie speculated the attendant survived because the tight elevator shaft created an air cushion. This together with spring action from slack elevator cable could have slowed the car to survivable speeds.
(This myth is fueled by the story of an elevator attendant found alive but badly injured in an elevator car that had fallen down a shaft in the Empire State Building after a B-25 Medium Bomber crashed into it in 1945.)
Comment: Right, and the only reasonable fall you could survive that way is where the elevator's speed (after your jump is subtracted) isn't enough to kill you. Like that old joke about falling off the first step of a ladder.
Comment: Another important point to point out is that even if your jumping power was super powered and COULD cancel the downward velocity, it would still not save you: while you will now be at rest with respect to the ground, the TOP of the elevator car will still be rushing down at you at fall velocity and you will be smashed -- from your HEAD down, not your feet up!
Comment: @mike4ty4 This may be the reason why the suggestion includes jumping near the end of the fall — then you won't be crushed from above if the cabin stays intact.
Answer: The reason that jumping can make a relatively large difference is that the kinetic energy is proportional to the square of the velocity. Thus relatively small changes to the velocity can result in relatively large changes to the kinetic energy. In addition, the velocity which a human can achieve in jumping is a substantial percentage of the velocity of fatal falls.

Let the human weigh $m$, let him jump with upward velocity $v$ and let the elevator fall from a height $H$. Then the human's initial potential energy will be $10mH$. What fraction of this potential energy can he avoid having turned into kinetic energy?
At any given point before jumping, the human's kinetic energy and potential energy add up to $10mH$. If he jumps at a height of $h$, his potential energy will be $mgh$ and his kinetic energy will be $mg(H-h) = 0.5mV^2$ where $V$ is the elevator (and human before jumping) velocity, taken as a positive number so that $V=\sqrt{2g(H-h)}$.
At the moment of jumping, he will not reduce potential energy, but instead will decrease his velocity. So his kinetic energy decreases from $0.5mV^2$ to $0.5m(V-v)^2$. Therefore his total energy will become:
$$mgh + 0.5m(V-v)^2$$
$$= mgh + 0.5m(\sqrt{2g(H-h)}-v)^2$$
$$= mgH +0.5mv^2 - mv\sqrt{2g(H-h)}.$$
The terms have a simple interpretation. $mgH$ is the energy in the absence of any jumping. $0.5mv^2$ is the energy of the jump (in the frame of reference of the human). And the remaining term is the reduction in energy due to the reference frame conversion.
We wish to make the third term as negative as possible. This occurs when h is small so we put $h=0$ (as our intuition suggests, indeed, the best time to jump is just as the elevator impacts). Then the remaining kinetic energy is:
$$mgH +0.5mv^2 -mv\sqrt{2gH}.$$
An example of a height $H$ which is generally fatal for a human is $H=10m$. A maximum velocity for a very athletic human jump is on the order of $v=3.64$ m/s. Such a jump would give a maximum height of 0.66 meters. See: Vertical Jump Test calculator for data on human jumping capabilities by sex, age, and athletic ability. Using $g=10$ and $m=50$, the kinetic energy before and after jumping are:
$$mgH = 5000J$$
$$mgH+0.5mv^2-mv\sqrt{2gH} = 2757J$$
Thus, in fact, jumping could reduce the kinetic energy suffered by a factor of two. The final collision with the floor would be reduced from a height of 10m = 32.8 feet, to a height of 5.5m = 18 feet.
Comment: I don't understand the third term in your equation where you mentioned it's the reduction in energy due to reference frame conversion. How do you arrive at that?
Answer: From the question of simple reduction of velocity, the answer's already been given (yes, but not enough to make a significant difference) ... but there's one other issue at play here -- how the forces are transfered to the body.
If you're standing upright, it'd all be transfered through your legs;  as Flaviu mentioned, laying down so the force is spread across a larger area would be a better option to this.  But, if you could manage to jump at just the right time, and you knew how to take a fall (bend your knees, roll into it, etc.), it might be possible to spread the force over a greater time and distance, therefore reducing the impulse, and thus the actual damage to your body.
Unfortunately, I don't think the chances of timing it correctly would be very good, so it wouldn't be particularly advisable.  You'd have to weigh the risk & benefit of this strategy vs. just lying down.
Comment: What if you jumped at exact moment when the elevator started to fall? Then you'd actually gain energy and would worsen your chances.
Comment: But if it's all transferred to your legs, won't the impact mostly break your legs and hips, rather than damaging vital organs?
Comment: @Jerry : it's a matter of force over distance (and time) ... You have additional distance and time to decelerate if you can control the fall, which would significantly reduce the force (the impulse would remain the same, but the time is increased).
Answer: It's not about whether or not you can jump up fast enough to cancel out a 60mph impact. If you could jump up at 60 mph, you wouldn't need to because passively absorbing the impact (60mph deceleration) would be less stressful than actively accelerating upward to 60 mph (total impact cancellation), because you would be subjecting yourself to the same-if not greater-'g' forces. It seems more practical to jump up at 30 mph (partial impact cancellation) which can effectively cut down the 'g' forces by distributing the braking distance, sort of like the last second "braking" rockets of cosmonaut space craft that fire just before a parachute landing.
Impact severity is largely defined by the shortness of stopping distance. There's little-if any-substitution for distributing stopping distance in alleviation of impact. So, the question is more one of whether or not jumping up is ever the wisest option.
Suppose you're in an elevator that's headed for an uncushioned landing at twice the velocity you can jump up. You're coming down at 10 mph, and can jump up at 5mph. If your feet leave the floor at the precise moment you reach 5 mph, the  deceleration would be a 2X5mph impacts, each with 1/4 the kinetic energy of an unmodified 10 mph impact, which equals half the impact. The main problem is, you reach your highest (and lowest) speed of 5 mph at the critical part of your upward jump where you're in the worst position to absorb the balance of the impact by rolling into it. You might be safer ONLY doing that-namely flexing your knees, and rolling into what skydivers refer to as a parachute landing fall, or plf.
Answer: No you cannot survive if you are in an elevator that is in free fall.
While it is true that everything in a falling elevator will float like in a space capsule but the moment you hit the ground and acceleration of the elevator reduces from "g" to zero, the impact will be fatal.
Let us say you start accelerating down from top floor of a building. The forces that are in play are - one, the gravitational force on you (mg) in downward direction and the push of the elevator floor on you in upward direction (let us call this "W"). If the elevator was stationery, this downward force mg and upward force by the floor would have been equal (hence no acceleration).
However, the fact that there is acceleration in downward direction means there is a net downward force and this is the absolute value of difference between W and mg. If we take any vector pointing in downward direction as negative and upward as positive and plug all forces in Newton's 2nd law of motion equation
F net = ma, what we get is
W-mg = m(-a)
(a is negative since it is in downward direction. Remember acceleration is not always positive and deceleration is not always negative. It depends on the sign notati )
or W = m (g-a)
If you were on weighing scale in the elevator, W would be your weight. You can see that if the acceleration is "a", your weight is getting reduce since (g-a) is less than g.
Now if the elevator is in free fall, a = g. If this happens W = 0 and you will feel weightless, quite like conditions in space. But as I said earlier, the moment the free fall of the elevator stops, your flotation will stop and the impact will be fatal
Watch these 2 videos I have made for a better understanding
Forces inside an Elevator - Part 1
Forces inside and Elevator - Part 2
Answer: If you jumped just before impact, your speed towards the bottom of the elevator shaft would go down a little bit.  But consider that the elevator falls tens of meters, while you jump about one meter.  Your jumping ability is quite small and probably won't make a noticeable difference
Comment: For example, you jump 1 metre, but fall 9, that's 9 times as much, the difference in the velocities is the square root of this, so the elevator's falling speed is 3 times as much as the speed of your jump.
Comment: "the elevator falls tens of meters, while you jump about one meter" - how does this difference of distance relate to a difference in speed? You're not saying they're proportional are you?
Comment: They're not proportional.  I'm just pointing out that one is much larger than the other.
Comment: There is a relationship. Assuming falling from rest, constant gravitational acceleration and no air resistance, the square of your final speed is proportional to the distance fallen.
Answer:
Would you decrease your impact impulse by jumping during the fall?

Yes

When?

Soon enough that it's before impact, late enough that you don't hit the ceiling of the elavator.
Beyond that I don't think it matters much.

Would it help if you jump inside a free falling elevator?

Probably not. Indeed I expect it would make things worse.
The consequences of a fall cannot be adequately explained by rigid body models. What matters is the peak force delivered to critical parts of your body.
If you don't jump then the elavator and you experience the crash as a system. Some elevators have explicit buffers at the bottom of the shaft. Even if they don't it is likely that there will be some compression of the elavator car and of whatever happens to be at the bottom of the shaft which will limit the peak force delivered to your body.
If you jump at the "right time" then you reduce your "impact impulse" but the elevator and you crash at different times. So the elavator can no longer help in spreading the impact over time.
If you jump two early then you hit the ceiling of the elevator. This gives you the worst of both worlds. You experience the original "impact implulse" and the elevator can no longer help in spreading it out over time.


Should I repair or replace a wheezing circular saw?

Question: I have a hand-me-down Craftsman circular saw that is probably from the 1970s. It mostly works fine, but makes a grinding wheezing noise when decelerating after power has been cut (finger taken off trigger). Knowing my dad, if there were multiple 7 1/4" Craftsman saws available at the time, this was the cheapest one. Is it wiser to just replace it, or is it worth repairing? If it's time to replace it, what are your thoughts on corded vs. battery?
Answer: Repairing small hand tools is rarely economically feasible (even thought the thought of built in obsolescence/landfill overload is distressing).
It sounds like a bad bearing, but the cost of the labor involved in changing would probably exceed the cost of a new saw.
I would get a new one.
Cordless tools are great, even in a shop. But circular saws need a good deal of power, and most cordless ones are seriously underpowered. Unless you will be away from outlets a good deal or limited to a few cuts in light materials, I would opt for a corded circular saw.
Comment: If there's nothing about saws from a previous generation that makes them better than current ones, I guess I'll keep running this one into the ground, and then replace it with another corded one--the truth is that I'm never that far from an outlet, and it sounds like the extra power will sometimes come in handy. Makes sense.
Comment: When you're ready, a cordless is an excellent choice as an _additional_ saw. There are many times that not having to drag out the extension cord for a couple of quick cuts is super handy.
Answer: Chances are either 1) the brushes are shot, in which case it may be a cheap fix, or 2) the motor itself (bearings, windings) is just wearing out. In the latter case it's probably not worth the cost and effort to have a repaired very old saw.
As to what you should buy, I have no idea what your needs are. I like Makita 5007 corded saws. A number of brands make nice Lithium cordless saws.


Why do different countries have different currency?

Question: Why do different countries have different currency?

I have this question because I want to know why to divide it? If it's not divided then we can easily use the money anywhere and we won't need to use currency exchange.
Comment: Downvote because this question shows little thought and no attempted research.
Comment: If you are asking about possible advantages and disadvantages, it's worth looking at the theory of the optimum currency area.  An outline with some references to the literature is here (https://en.wikipedia.org/wiki/Optimum_currency_area).
Comment: Why do different door locks have different keys? I have this question because I want to know why to divide it? If it's not divided then we can easily use the key anywhere.
Comment: Why not? Historically they had, so why should it be different now? Anyway you can easily use the money anywhere, just convert it to local currency before using it.
Comment: @9ilsdx9rvj0lo In effect, everything about the question except the title is unclear.
Comment: This is why bitcoin borned. ;)
Comment: Because they do not have the same currency.
Comment: So you made another account to provide the bounty to yourself? How is a Quora based answer consistent with the bounty message, which was looking for "authoritative source"?
Comment: @spacetyper it's funny that your comment has more upvotes than the question has downvotes.
Comment: This might be of interes: https://economics.stackexchange.com/questions/4951/what-would-happen-if-the-world-switched-to-a-single-currency
Answer: Two reasons: history and ability to control the money supply.
History: paper-money started by being issued by trustworthy agents from kings/governments, as a way to be able to transfer the ownership of gold without moving the gold physically. This looked something like "This paper is exchangeable for 10 gold coins at this location". This meant you had to go to that specific kingdom to get the paper (bill) converted into gold. These papers evolved into what we now call banknotes, and kept tied to a specific country.
Money supply control: having your own currency allows governments to fund themselves by producing more money, or stimulate exports by devaluing their currency. Look at the euro-zone difficulties with the government debt of Greece: this could be solved (with consequences, of course) if they had their own currency.
Comment: The "trustworthy agents" were noted to be private, not public, in your source I quoted. Of course it's history and it can be tough to untangle but you should follow your source. There's no doubt that governments have offered paper notes through history but the earliest known recorded instances were not governmental. Why add the "from kings/governments" at all if it contradicts those sources?
Answer: I will focus on some economics reasons not mentioned explicitly so far. There are economic benefits to having your own currency. Your question essentially raises the question of so-called "Optimum Currency Areas" (OCAs). There was a lot of interest in the question of what areas should have the same currency. It is in general not immediately obvious that different countries should have the same currency, or even that the same country should have the same currency everywhere.
Your question boils down to asking whether the whole world is an OCA - and the short answer is no.
The pros of having different currencies are that you can use monetary policy to offset shocks. Especially for trade shocks, because monetary policy can change the exchange rate of a currency to affect trade. For example if Germany and France are hit by different shocks, then they will want to conduct different monetary policies, which they can't if they share the same currency. The main cost of different currencies are transaction costs of exchange, which can hamper things like trade and tourism.
Therefore an area should have the same currency (is an OCA) if it is subject to the same shocks or other factors are present, such that those shocks are absorbed without monetary policy. This thinking leads us to the four most important criteria for an area to be an OCA. You can use these criteria to evaluate whether countries should have the same currency and to answer your question.
It is worth noting, that the pioneer in this literature was Robert Mundell with his 1961 paper. The other two most important works are Kenen (1969) and Mckinnon (1963). The criteria are:

The regions should have similar business cycles. As mentioned, if the countries tend to experiene similar shocks, then they will require the same monetary policy. In that case there is no reason for them to have different currencies!
Openness of the economy (Mckinnon). This can be divided in two parts:

2.1. High labor mobility across regions. If there is a recession in one region and people can move to another one as a response, then monetary policy is less important in adjusting to the shock, as labor itself adjusts. This is a reason why countries can usually have the same currency within their whole territory. For example, people who lose their job in one U.S. state often move to another. If that wouldn't be possible, then adjusting to the recession with monetary policy would be more important. That is why the freedom of movement agreement is so important for the Euro to be sustainable. Note that wage flexibility would be required here as well.
2.2. Capital mobility. The reasons are similar as for labor mobility. If a region becomes less developed, then returns to capital there will increase. If markets are free, then capital can travel from the more prosperous region to the one hit by the shock, thereby mitigating the negative effects of the shock. Note that price flexibility must be given here for these effects to occur.

A risk sharing system, such as fiscal transfers. Since monetary policy can't be used, we would need fiscal policy. Fiscal transfers from unaffected areas can help with negative shocks in another region. The Eurozone has a no-bailout clause, so this condition wasn't given during the Greek crisis. However, this was de facto abandoned. This is unsurprising to those familiar with the theory of OCAs.
Product Diversity (Kenen). Trade shocks, which monetary policy can help with, usually occur to certain industries and not the whole economy. If countries produce a variety of products, they will be less likely to suffer from large demand shocks. Hence, more diverse economies will face fewer trade fluctuations and see smaller increases of unemployment if shocks occur to one industry. This also reduces the need for monetary policy stabilization, since any given shock has a small impact on the overall economy.

Sometimes further criteria are also given, but they are less important. These include "solidarity" as well as homogenous preferences across regions, for similar reasons as the condition of similar business cycles.
So you can use these criteria to evaluate whether certain countries or areas should have the same currrency or not. All these criteria are definitely not fulfilled for the whole world, so there is a role for different currencies. An issue with the theory of OCAs is that it is unclear how much weight we should give to each criterium. So it could be unclear how to evaluate whether two countries who partially fulfill some of the criteria should have the same currency or not.
Comment: You have made a good case for London to have a different currency from the rest of the UK......
Answer: There are also many countries without their own currency. For example, Ecuador and Panama both use the US dollar as their official currency. See this list for more examples.
There are several reasons why you might like to adopt another country's currency, but common factors are

high inflation: the domestic currency loses value against foreign ones. Therefore, people start more and more to use foreign currency for transactions (e.g. dollars in Venezuela today). Therefore, one solution is simply to get rid of your own currency and adopt a foreign one. This immediately stabilises prices, as the central bank can no longer print money.
high levels of trade with one country: for example, if you trade very much with the US (as many small Caribbean islands do), you would rather adopt the US dollar. This will give much more certainty to exporters and business in general.
Answer: You might also want to think about

If it's not divided then we can easily use the money anywhere.

Is that positive and desirable for everyone in all situations? If you want to control the flow of money and people, different currencies are helpful.
JoaoBotelho also pointed to control of the supply and historical reasons, I would also add that everyone would have to agree, what the currency of the world is supposed to be. Different countries have (and have had) very different ideas as to how a currency should behave.
Like:

gold- or silver-backing, or fiat money?
how independent should the central bank be?
general monetary policy - this will never fit all of the world at the same time
what is the right amount of inflation?
Comment: Also, do you *want* one single country or governing entity be the sole determiner of how much money exists? Money is power much like armies are; most sovereign nations won't give up control over theirs to *anyone* else no matter how well they get along otherwise.
Comment: Your last two points are one of the biggest difficulties of the euro zone challenge faced by the southern countries
Answer: Ultimately, a complete answer has to deal with the history of money. Here I just provide a very brief attempt to answer the question. There are dedicated books on the topic, of which the most authoritative source might be Glyn Davies' book. The analysis here is based on that book and Wikipedia.
What is money?
Davies defines money as:

Money is anything that is widely used for making payments and accounting for debts and credits.

As Davies states, money have a variety of economic functions:

Unit of account
Common measure of value
Medium of exchange
Means of payment
Standard for deferred payments
Store of value

These functions are important because they tell us why later on official authorities would like to "produce their own money".
Origin of money
Given the above functions, it would seem simple to believe that money came to exist because its economic benefits, for example, to replace barter as a method of commerce. However, as Davis state:

Money originated very largely from non-economic causes: from tribute as well as from trade, from blood-money and bride-money as well as from barter, from ceremonial and religious rites as well as from commerce, from ostentatious ornamentation as well as from acting as the common drudge between economic men.

In other words, money originated from social customs. Davies does acknowledges that "the clumsiness of barter" gave an economic impulse to the spread of money, but it was not the cause of it.
Coins
Yet, as civilisations became more complex and trade among nations grew, the economic functions of money became more relevant. Davies notes that many physical items have been used as money:

Amber, beads, cowries, drums, eggs, feathers, gongs, hoes, ivory, jade, kettles, leather, mats, nails, oxen, pigs, quartz, rice, salt, thimbles, umiacs, vodka, wampum, yarns, and zappozats (decorated axes).

But with the advance of ancient civilisations, coins became the most common item to function as money. Pretty much every major civilisation or group had its own coins (e.g. Roman Empire denarius, Etruscan empire Shekel, Persian daric, Chinese myriad of round-with-middle-hole coins, just to name a few; notice that the Incas had no money). Coins normally represented a form of commodity money, in that the coin itself had value because it was made of a valued metal like gold or silver.
As such, Roman emperors, Etruscan Kings, and other civilisations, pretty much until the end of the middle ages produced their own coins in order to foster commerce, facilitate taxes payment, and so on. Money usually had the stamp of a royalty or emperors, and minting was usually a monopoly of the state.
In fact, one of the first schools of economic thought was mercantilism, which considered the accumulation of species (gold, silver, etc), primarily via trade surplus and mining as the chief economic objective of a government. As such, each country producing its own money via minting became a core state objective. Why would you then use another country's money? Why would the English Kings give up their capacity to control their currency and instead adopt that of e.g. the Kingdom of France? The most sensible option was the sovereign control of the monopoly of money.
Paper Money
The above already explains why different countries had different money systems. The "natural" transition from commodity money to fiat money simply reproduced national differences into banknotes and eventually, to modern currencies.
Simply put, different bank notes emerged in the late middle ages (although its used has been recorded earlier in China), often as a simple mechanism to store and transfer money. Instead of you giving a load of heavy coins to someone, you simply used a bank to keep that physical money in exchange of a note that credited that ownership. You can then simply transfer the note and thereby the ownership of the load of coins. Many times there were many competing bank notes, but eventually the state and kings, not the least because of some economists recommendation pursued the monopoly of banknote issuance, leading to what now are central banks.
Currency replacement
Yet, in more recent times, some countries have gave up their own currencies. Notably is the case of the Euro, which replaced many national currencies like the Deutsche Mark, the Lira, the Peseta, etc. This was already commented by BB King in another answer. Myself also commented on why some countries have adopted the US Dollar (or other major currency). Most of the factors are economical, but political factors cannot be discounted too (e.g. Euro as part of a wider political integration process, not the least to avoid further war in the continent).

In summary, different countries have had different currencies because of historical reasons, ranging from non-economic to economic ones. In the beginning, the production of competing forms of money by different civilisations and kingdoms was mainly a cultural issue, but with the growth of commerce and the growing complexity of societies, money became a powerful tool to foster economic activity and why not, military capacity. The state soon realised that controlling the monopoly of money production was beneficial for their interests. In this context, having no money and using other countries money was a totally irrational option. In modern times, economic motives has been the primary factor defining whether countries have or not their own currency.
Answer: So they can set their own monetary policy for good reasons such as to improve macroeconomic stability.
So they can set their own monetary policy for bad reasons such as to print increasingly devalued money instead of engaging in better macro management.
So corrupt people can print and/or otherwise control monetary within their country.
So other countries will not control the value of the monetary instruments used in the country.
Because they don't like Uncle Sam or the Fed.
Because they don't trust EU bankers.
Answer: If I go down to the border with Mexico and step over the line that separates the two countries, what has changed? The air is the same. The sunshine is the same. There is only one thing that is not the same. The laws. I am now under a different legal system. If I commit a crime, I am arrested by Mexican police and face a Mexican judge who applies Mexican law to my case.
Money is legal tender. It's what the law recognizes as the unit that holds value for all economic activity occurring under the jurisdiction of the body that prints it. It's what the law itself uses to impose fines, enforce contracts, levy taxes, and so on. The entity that makes the laws also issues the currency and declares it the legal tender and guards its integrity.
Comment: Are you not arrested under the German law rather that under the French law if you commit a crime in Germany? And yet, they have the same currency. Likewise, in Ecuador you are not arrested under the USA law, and yet, they use the US dollar.