Added custom attribute not triggering a script

Question: I am using a script src which makes it possible to open a lightbox frame when a custom attribute is added to an element.
An example looks like this
<button data-custom-attr="123"> </button>

It works when I add it manually, however first I must replace a similar script that is already in place, by removing some attributes first.
I'm using jQuery to select the element, remove the attributes, and to add new ones. However when I add them to an element, clicking it doesn't trigger the lightbox pop-up. I have also tried creating a new element and replacing current one with it, but it didn't work either.
What can be the possible reason? Is it possible to achieve this using jQuery?
The code I'm using:
<button class="mybtn" data-prop='1'></button>

javascript
jQuery(".mybtn").each(function (index, object) {

  $(this).removeAttr('data-prop');
  $(this).attr('data-custom-attr','123');

});

(the attribute is added to the element when I inspect it)
Comment: We can't really help you to debug code that you aren't showing us.
Comment: Pls post your code :)
Answer: I believe, the lightbox script is running once on DOM-Ready. If you manipulate the DOM after maybe the script doesn't notice that. Is it possible to rerun the script?
Comment: Correct. what solved the issue was adding
$.getScript('myscript');  at the end of the replacement script
Answer: Try to trigger the event by binding the click on the body, not on the button itself, ex:
$('body').on('click', '[data-custom-attr="123"]', function(){
    // the code when button is clicked
}


Lost preferences when upgrading Blender, how can I get them back?

Question: I downloaded the latest version, and I made a huge mistake and I did not copy the UI from the previous version.
Now the 123 keys change my camera and they do not select vertices, edges or faces.
Do you know how I could fix it or reassign it?
Thank you
Answer: If you still have the old version installed, you can still find the preferences saved. Go to: C:\Users\ <your username>\AppData\Roaming\Blender Foundation\Blender\ <old blender version>\config
Comment: And, if you delete the config of the new version, next time you open Blender you'll have the option to transfer settings from the old version.


Creating Android App builds

Question: How do I create Android app builds similar to Windows code builds? I have my Android app code base checked in to Tortoise SVN. But I also have the binaries checked in - i.e the apk file etc. and not just the source code. Everytime there is a change I am building it manually on Eclipse and then updating the apk and the code folders. Is there no mechanism to create builds like on Windows where you run a batch file running the visual studio exe to create builds and binaries. I need this because otherwise it s just replacing the apk's everytime. Its very frustrating that I dont know this simple detail so please help!
Answer: Actually you have to just checkin your project to SVN. The other team member or even you when loading it in another working space (another PC or diff Eclipse WorkSpace), Eclipse will throw error.
Simply clean the project it should rebuild the app and APK files for you again. Nothing much to worry. Me and my friends have done it several times.
Correct me if I'm wrong.
Answer: You can use ant building scripts (details at http://developer.android.com/guide/developing/building/building-cmdline.html).

Creating Android App builds


List installed packages that are no longer installable via repository?

Question: This question is in reference to another question that has not been answered. When I upgraded Ubuntu, all my PPAs were removed (which I'm ok with). Is there a way to list all the packages that no longer have a repository associated with them?
Answer: APT refers to these packages as "obsolete".
Evidently there is no direct way to list these, but you could do:
aptitude search '~o'

Or alternatively:
apt-show-versions | grep 'No available version'

Source: How do I get a list of obsolete packages?
If you want a GUI tool you can do this with Synaptic by using the built-in "local or obsolete" filter.
Comment: Really thanks for posting the Synaptic solution. For some reason, aptitude is not listing all of the packages without a repository.


Rivest Cipher 6 (RC6) Key Scheduler

Question: I am trying to understand the Key Scheduler used in RC6 and I have a total of 3 questions. The RC6 Wikipedia page says that the only difference between the RC5 and RC6 key scheduler is that more words are produced from the key in RC6. In my application, I am using w=32bits, r=20rounds and b=16bytes.
My first question is are these are two separate for loops or is the second for loop that iterates from s-1 to v inside the first for loop that iterates from 1 to 2r+3?
My second question is why are we setting A=B=i=j=0 and is this command and the v=3xmax{c,2r+4} inside the first for loop?
The RC6 paper also supplies this pseudo code:

Input: User-supplied b byte key preloaded into the c-word array L[0... c - 1]
Number r of rounds
Output: w-bit round keys S[0... 2r + 3]
Procedure: S[0] = Pw
for i = 1 to 2r + 3 do:
S[i] = S[i - 1] + Qw
A = B = i = j = 0
v = 3 x max{c,2r+4}

for s = 1 to v do:
{
A = S[i] = (S[i] + A + B)<<<3
B = L[j] = (L[j] + A + B)<<<(A + B)
i = (i + 1)mod(2r + 4)
j = (j + 1)modc
}

My third question is on how to preload the word array L with my 16byte key. The RC5 paper says:

The first algorithmic step of key expansion is to copy the secret key K[0...b-1] into an array L[0...c-1] of c=b/u words where u= w/8 is the number of bytes/word. This operation is done in a natural manner using u consecutive key bytes of K to fill up each successive word in L, low-order byte to high-order byte. Any unfilled byte positions of L are zeroed.

And the pseudo code for this operation is:
for i=b-1 downto 0 do:
    L[i/u] = (L[i/u]<<<8)+K[i];

To elaborate on my third question, if i is going from 15 down to 0, and my u = 32/8=4, how can I use a decimal to index L? For example, when i is 15 we have L[15/4]=(L[15/4]<<<8 + K[i]);
Answer:
The loops are disjoint. In other words, the first loop completes and then the second loop starts.

A=B=i=j=0 are explicitly initialised to zero as in many languages failing to specify an initial value can lead to unspecified behaviour (e.g. setting the variables to random values lying in old memory). This initialisation and the initialisation of v occur outside of the loops.

The expression i/u should be interpreted as C-like integer arithmetic that returns an integer value (in this case by taking floor). Thus in your example L[15/4]=L[3].

Rivest Cipher 6 (RC6) Key Scheduler


Sci-fi book series about an ex-soldier who's kidnapped from Earth by a spaceship-stealing robot, and goes on to create a mercenary band

Question: A series of multiple books (recent; still writing more in the series). An ex-soldier living in their parents' cabin stumbles on a damaged spaceship in the woods, is kidnapped by the robot captain (who himself stole the ship) and taken to a slavehold, where the ex-soldier frees several other creatures and a robot (later named Lucky). They steal the ship from the first robot and become mercenaries, get lots of jobs, and eventually have to save the Earth from the original robot.
Comment: Hi, welcome to SF&F.  Please split this into two separate questions, so they can each be answered.
Comment: @DavidW - _"Rewriting the question to fit [my] answer"_ is a rather loaded way to put it. The edits I performed did two things: 1) removed the description of the second work, for which no answer has yet been submitted, and 2) improved the grammar in the description of the first work. I didn't fundamentally alter the meaning of anything that was written, and aside from removing the description of the second work, it was a standard, run-of-the-mill edit like dozens of similar edits I've performed in the past.
Comment: @Varikk - I've edited your question to focus on the book series only, as story-ID questions should only ask about a single work or series of works. If you still want the other book identified, please do go ahead and post that as a separate question. You can copy your description of the other book from the [revision history](https://scifi.stackexchange.com/posts/259654/revisions) of this question.
Comment: @LogicDictates I think you are taking a bit too much liberty here in service of your answer.  Yes, we're all impatient to answer questions, but I think rewriting the question to fit your answer goes a bit too far.
Answer: The first series might be the Omega Force series by Joshua Dalzelle. There are currently thirteen books in the series, with the first book having been published in 2013, and the most recent in 2020.
Here's the Goodreads synopsis for the first book, Omega Rising (2013).

Jason Burke was a man hiding from himself in a small cabin high in the American Rocky Mountains when his simple, quiet life was shattered one night by what he first assumed was an aviation mishap. But when he investigates the crash, what he finds will yank him out of his self-imposed exile and thrust him into a world he could have never imagined.
He suddenly finds himself trapped on a damaged alien spacecraft and plunged into a universe of interstellar crime lords and government conspiracies, along the way meeting strange new friends… and enemies. As he struggles to find his way back home he is inexorably drawn deeper into a world where one misstep could mean his death. Or worse. He desperately wants to get back to Earth, but it may be the end for him.
… or is it just the beginning?

This review mentions "a lone synth named, Deetz, who runs the ship" (i.e. a robot captain).

Omega Rising is an interesting account of a guy, Jason Burke, who has moved away from the big city (and his problems) to a solitary existence of an isolated cabin. It's not the setting you would expect when you pick up a science fiction book. It's not long before he sets off to investigate an unexpected event, and stumbles aboard an alien spacecraft. His life takes a major turn as the cargo bay doors close and he finds himself trapped and then launched into the depths of space. It's an adventure that he had no choice but to accept.
Jason soon meets a lone synth named, Deetz, who runs the ship. He's a mysterious fellow who quickly accepts his new stowaway (or is he a captive?), after recognizing there was potential to gain benefit from him. The plot is a switch on the standard – who is the alien question. Normally it's those other than human who are alien, but in this book, Jason the human is the alien.
After agreeing to help Deetz with a 'job' in exchange for being returned to Earth, they head to the far reaches of space. Things are going well until they're attacked when collecting a mystery cargo from a distant planet. In the process, another alien is wounded and saved by Jason, and ultimately ends up onboard the ship just before they escape.
Just imagine being thrown into something completely different to your normal environment. You'd need to learn how to use and react to everything you come into contact with. Dalzelle has covered that off with some clever ways to get past the communication barrier, and there's a rather ingenious method of giving Jason the skills required to function in his new environment. Tick.
With an escape under their belt and bonding underway, Deetz still has some debts to settle, so they take on a mission to deliver a cargo to a place called The Vault. It's a place where things can get very dangerous. Jason and his new alien buds soon discover that not all friends are really friends. There's an overthrow, then there's a plan, which leads to another plan etc. (Trying not to reveal too much here).
We are hit with some teasers about something that spells doom for the future, and there's promise of plenty of dramas for the crew to solve. It's enough to spark interest for readers to jump on-board for future instalments of the series.
This first Omega book is an origins story of how a bunch of random beings are brought together. With their initial mission completed, they realise that they all have a common past and a common goal for the future. So… Omega Force is born.

This reader review mentions a synthetic warrior dubbed 'Lucky 7', and states that the protagonist had recently served in Afghanistan.

Jason Burke is an American, age 26, who recently served in Afghanistan. When a damaged spaceship lands near his lonely cabin in the Rocky Mountains, he offers help. Next thing we know, he's Commander Burke, leading a crew of five benign aliens (including an artificial intelligence /Battle Synthetic) across galaxies on a quest to free slaves and put a stop to illegal genetics manipulation.
Feels like Firefly, but not so sophisticated, and there are no female crew members and so far, no special abilities.
Feels like Guardians of the Galaxy, but there is no cassette recording of best hits.
Main Characters:
Commander Jason Burke.
Blue skinned engineer / mechanic Twingo
Doctor Jorven Ma'Fredich (Doc)
A 4-armed computer hacker, code slicer named Cage
Wolf-man warrior named Crusher
An AI, a fully armed Battle Synthetic warrior dubbed Lucky 7.
A synthetic named Deetz
A slave-trading snake-man mobster named Bondrass.
Comment: @Varikk - If you want someone to identify the second book, you'll need to post a separate question for that one, as we don't ID multiple books within a thread here.


How to redirect verbose garbage collection output to a file?

Question: How do I redirect verbose garbage collection output to a file?  Sun's website shows an example for Unix but it doesn't work for Windows.
Answer: From the output of java -X:

    -Xloggc:<file>    log GC status to a file with time stamps

Documented here:

-Xloggc:filename
Sets the file to which verbose GC events information should be redirected for logging. The information written to this file is similar to the output of -verbose:gc with the time elapsed since the first GC event preceding each logged event. The -Xloggc option overrides -verbose:gc if both are given with the same java command.
Example:
    -Xloggc:garbage-collection.log

So the output looks something like this:

0.590: [GC 896K->278K(5056K), 0.0096650 secs]
0.906: [GC 1174K->774K(5056K), 0.0106856 secs]
1.320: [GC 1670K->1009K(5056K), 0.0101132 secs]
1.459: [GC 1902K->1055K(5056K), 0.0030196 secs]
1.600: [GC 1951K->1161K(5056K), 0.0032375 secs]
1.686: [GC 1805K->1238K(5056K), 0.0034732 secs]
1.690: [Full GC 1238K->1238K(5056K), 0.0631661 secs]
1.874: [GC 62133K->61257K(65060K), 0.0014464 secs]
Comment: "-XX:+PrintGCDetails" seems to work with -Xloggc. I don't know why the Sun page has a - instead of a +.
Comment: java --Xloggc:firstgen.log -Xloggc:secondgen.log doesn't seem to work by the way.
Comment: Also, this doesnt increase the output, as I expected.  There are no additional details after using these arguments:

-Xloggc:gc.log -XX:-PrintGCDetails
Comment: that worked. thanks!  now, i use these options:   set JAVA_OPTS=%JAVA_OPTS% -Xloggc:logs\gc.log -XX:+PrintGCDetails -XX:MaxPermSize=128m
Answer: If in addition you want to pipe the output to a separate file, you can do:
On a Sun JVM:
-Xloggc:C:\whereever\jvm.log -verbose:gc -XX:+PrintGCDateStamps

ON an IBM JVM:
-Xverbosegclog:C:\whereever\jvm.log

Comment: If you use -Xloggc, you don't need -verbose:gc.
Answer: Java 9 & Unified JVM Logging
JEP 158 introduces a common logging system for all components of the JVM which will change (and IMO simplify) how logging works with GC. JEP 158 added a new command-line option to control logging from all components of the JVM:
-Xlog

For example, the following option:
-Xlog:gc

will log messages tagged with gc tag using info level to stdout. Or this one:
-Xlog:gc=debug:file=gc.txt:none

would log messages tagged with gc tag using debug level to a file called gc.txt with no decorations. For more detailed discussion, you can checkout the examples in the JEP page.
Comment: With JDK 16 you even get a warning if you use the old `-Xloggc` instead of `-Xlog:gc:...`
Comment: How can I append the log to an existing file?
Answer: To add to the above answers, there's a good article: Useful JVM Flags – Part 8 (GC Logging) by Patrick Peschlow.
A brief excerpt:
The flag -XX:+PrintGC (or the alias -verbose:gc) activates the "simple" GC logging mode
By default the GC log is written to stdout. With -Xloggc:<file> we may instead specify an output file. Note that this flag implicitly sets -XX:+PrintGC and -XX:+PrintGCTimeStamps as well.
If we use -XX:+PrintGCDetails instead of -XX:+PrintGC, we activate the "detailed" GC logging mode which differs depending on the GC algorithm used.
With -XX:+PrintGCTimeStamps a timestamp reflecting the real time passed in seconds since JVM start is added to every line.
If we specify -XX:+PrintGCDateStamps each line starts with the absolute date and time.


How to increase output power of pre-designed USB-PD fast charger?

Question: The circuit in the link is providing 45 W output. How to increase output power to 50 W? Which component should be changed?
Comment: The reason it's designed for 45W is that's the maximum standard amount of USB power at 15 volts. There is no USB 15V 50W mode.
Comment: The component you linked to is not capable of negotiating a higher PD profile than 15V/3A with a connected load.
Comment: Are you asking how to get the power anyway? there's a good chance a converter designed for 45W can output 50W with no changes needed; if it triggers the over-current protection there's a good chance you can tweak a resistor to make it think it's running at 45W when it's actually 50W; of course this is all off-label use. Of course if you're using this to power a laptop or something, the laptop will still only take 45W because it knows what I just told you in the last comment.
Comment: You both are right. I just need 50 W, but it is not capable for 15 V. But I see that it can be redesigned for 20 V to get 50 W. At 20 V, it can support 45-100 W.
Answer: It requires a redesign and many components would need to be changed. So there's no simple answer. At the very least it would need a new transformer, and changes to the configuration of the chip that speaks over the CC line.
And anyway: are you in the business of making USB-PD chargers? If you need one, you buy one, and that will always beat the cost of anything you can come up with yourself. So perhaps you'd need to say what exactly is the application, and why are you using that eval board to begin with.
Such eval boards are usually aimed at high-volume manufacturers, and those manufacturers usually have experienced staff on hand. So, from your question I gather that you're not working for a high volume manufacturer. Thus my point that it's very unlikely that you'd want to design such a supply yourself as a supply that works from the mains: it will not be cost-efficient to do so... But perhaps we don't know something you know, so please amend the question to clear this up.
That eval board costs more than USB-PD 50W-capable supplies, even from high-end brands (!). A 96W Apple USB-C power supply is about $60 - less than the board you look at. The best I can figure, every second you look at that eval board for purposes other than self-education is a second wasted :)
Comment: Eval boards are targeted at anyone learning to use the chip or prototyping with one. You don't have to be in the high-volume business. However, *for a USB charger* I do agree you may as well go to the mall and get one from Apple or Samsung for cheaper - *if* one of those is good enough for you.
Comment: @user253751 *Eval boards are targeted at anyone learning to use the chip or prototyping with one.* And I agree! However, if one wants a standard wall-powered USB PD supply, there's no beating commercial high volume products.
Comment: I am engineering student and that is my graduation project, not doing it for my own pleasure :). My consultant asked me to design and simulate a fast charger rated at 50 W, and I have to do.
Comment: @FurkanAdıgüzel That's an important bit of info :) You won't be able to "modify" that board, but it can be an inspiration.
Answer: You can't change it, because USB has a predefined voltage and current profiles.
As this product is limited to 3A current and to 15V, it can't advertize being capable of outputing 50W and no product would be able to request 3A.
To go above 45W accoding to PD protocol voltage would need to go up from 15V to 20V instead of current going above 3A limit.
Comment: I saw the USB profile table, thank you for your explanation.


Air conditioner upstairs

Question: My downstairs ac unit stopped working. My upstairs unit is still running. Will my upstairs unit work harder? Upstairs is smaller unit. Downstairs is the main unit
Answer: Here's the thing. Cooling is not equal on a building. The heat you're trying to remove doesn't come from "outside"... it comes from 3 places.

Solar Gain. Every square foot of sunlight hitting your house adds 150-300 BTU/hour of heat to your house that your A/C must remove. (depending on angle and paint color). The worst is roofs, which have an albedo of about 5% (95% absorbed so adding 320 BTU/hr to your house.
Humidity leaking in from outside.  Because of the way humans sweat, humidity feels like heat and dry air feels like air conditioning. That means if air leaks are letting humidity into the house, it will feel warmer than the thermometer says, and removing that humidity will steal capacity from the A/C. (970 BTU per pound of water removed).
outside air warming the outside of the house, and that heat working its way through insulation.  This will be a problem even on the north side of the house, but all in all this is not as big a problem as the others.

So it depends on your house's layout. If most of the solar gain falls on the upstairs, it could be that most of the important air conditioning happens up there.
Answer: Without knowing what kind of AC or what capacities, and the square footage of the building, who can say?
Most likely, the upstairs unit is not sufficient to cool the entire place, or else you wouldn't have 2 ACs. So it's quite unlikely that the upstairs AC is going to cool both floors.
If you limit the airflow from upstairs to downstairs, it shouldn't have to work much harder, since it's still only trying to cool the upstairs. Though heat from the now hot downstairs will rise upstairs and it'll have to work a bit harder. If there's no doors in the way blocking hot air from rising upstairs, it may have to work a lot harder, or just not be able to keep up and cool the place sufficiently.
Answer: Not really work harder.
It usually works at maximum capacity anyway.
But it will work longer since the thermostat upstairs' will not report cool down.
It just means you will use more electricity.
Let's talk about the AC that is not working.
Could be just the thermostat, or just the circuit breaker.
Testing the circuit breaker is easy.
Testing the thermostat is bit more complicated. It depends what kind is it.
Comment: Thank you. I was just worried the ac upstairs will break down too.
Comment: No it wont, it should be fine running all the time.
Comment: @CynthiaWilliams lets try some easy fix for the AC, find and trip the circuit breaker (off/on)
Comment: @CynthiaWilliams listen to your Thermostat very carefully, then change the dial. Do you hear a click? If they are one of the modern one, you can unplug without removing wires, exchange it with the upper thermostat.

Air conditioner upstairs


Pecan trees growing from Roots

Question: I have several pecan trees that were planted too deep. If I cut them back to the root and let a new tree grow up, will it it be any good, either for shade or nuts? One tree has already done this and looks pretty healthy, but it's only 4 or 5 years old.
Comment: I dont get, it will still be too deep. Or are you transplanting, or replanting.
Answer: If I understand your question correctly, what you are doing should result in one of 2 things:

New growth from the rootstock
A dead plant

Without knowing what rootstock was used for your pecan trees, it is not possible to know in advance what will grow. You might get a pecan tree, but you might get some other compatible rootstock. Whether or not the tree yields something edible is also not predictable.
Generally, when planting any kind of orchard tree for food production, if you have trouble with the initial planting and need to know what you're growing, you should just pull the trees and plant new trees of known variety.
If you are growing the trees as a pastime and curiosity and don't mind tending an unfruitful tree for a while, then you can just wait to find out.
Lastly, if you are feeling adventurous, or know how and/or are willing to learn, you can grow the rootstock until it reaches thumb thickness or so, and then graft a desired variety of pecan onto it. Then you have a good rootstock that has survived and grown healthy roots, and you can predict what will happen on top.
Comment: Do you have any idea if there will be an issue with the root stock being planted too deeply?  Is that something it can overcome in time, or will this plant always be at a disadvantage?
Comment: If you've actually buried the rootstock too deeply, I would expect it to fail or struggle. If it continues to send up new shoots from the roots, you probably would be better to start over, in my opinion. But growing plants is an adventure, too, so maybe you just want to keep pruning root shoots and trying to nurture a single central start from the rootstock to graft onto later. Your call. You can't know until you give the plant time to adapt. But you may find it fails, anyway. You have to accept the risk, I think.

Pecan trees growing from Roots


A condition for uniqueness of solution

Question: Assuming that $f$ is a continuous real function and $f(0)=0$ , $f(x)>0 $ when $x\neq 0$, prove that the differential equation $x'= f(x)$ with the initial value $x(0)=0$ has a unique solution if and only if $$\int_0^c \frac{1}{f(x)}dx$$ is not defined for all $c\in \mathbb{R}$. That is $$\int_0^c \frac{dx}{f(x)}= \infty.$$
Comment: Nice problem. What's your attempt for to solve the problem?
Comment: This sounds to be a classical exercise. I suspect we should use epsilon approximations to the solution in some way.
Answer: I am sharing a solution for one direction :
We note first that since $f$ is positive the integral $\int_0^c \frac{dx}{f(x)}$ can only be $+\infty$ when $c>0$ and $-\infty$ when $c<0$ as $\int_c^0 \frac{dx}{f(x)}= +\infty $ , moreover $\frac{1}{f}$ is continuous over $\mathbb{R}\setminus\{0\}$ and $\lim\limits_0 \frac{1}{f}= +\infty$
Let $y_1, y_2$ be two solutions of the differential equation, we seek to prove that $y_1= y_2$ under the hypothesis $\int_0^c \frac{dx}{f(x)}= \infty $  :
We have $y_1(0)= 0= y_2(0)$ and $$y_1(t)= \int_0^t f(y_1(s))ds \ \ ,\ \ y_2(t)= \int_0^t f(y_2(s))ds $$ for all $t$ in an interval $I= [-a,a]$ centered at $0$
The function $t\mapsto |y_1(t)- y_2(t)| $ is continuous and satisfies
$$\max\limits_{t\in I} |y_1(t)- y_2(t)| = \max\limits_{t\in I} |\int_0^t (\ f(y_1(s))- f(y_2(s))\ )ds|\leq \int_0^{|t_0|} |f(y_1(s))- f(y_2(s))|ds $$
for some $t_0 \in I$ as the maximum is reached.
By the hypothesis we have $\int_0^a \frac{dx}{f(x)}= +\infty$ , the divergence of this integral implies that $\forall M>0\ \exists\ x_0\in (0,a] $ such that $(\min\limits_{(0,x_0]} \frac{1}{f} )\times x_0> M$ (we can show it by considering first the limit of $\frac{1}{f}$ then the fact that $\int_\delta^a \frac{dx}{f(x)}$ can be as large as desired and taking the mean value)
So we can transform this to $(\frac{1}{\max\limits_{(0,x_0]} f})\times x_0> M \quad$ or  $\quad \max\limits_{(0,x_0]} f < x_0/M $
Using this in the previous inequality $$\int_0^{|t_0|} |f(y_1(s))- f(y_2(s))|ds \leq |t_0|\max\limits_{[0,t_0]} |f(y_1(s))- f(y_2(s))| \leq a\times 2\max\limits_J |f(s)|$$
where $J$ is the union $y_1([0,t_0])\cup y_2([0,t_0]) $ , $J$ is an interval (why?).
Now take $M$ to be $2a^2 N$ so that $\exists\ s_0\in J\setminus \{0\}$ for which
$ \max\limits_{(0,s_0]} f(s) < a/M= \frac{1}{2aN}$ and the inequality becomes
$$\max\limits_{I} |y_1(t)- y_2(t)|\leq 2a\max\limits_{(0,s_0]} f(s)< 1/N$$
As this hold for all $N>0$ then it can only be true when $\max\limits_{I} |y_1(t)- y_2(t)|= 0$ and we deduce that $y_1= y_2$ over the existence interval $I$.
Comment: There are some obvious gaps. At first $t_0=\pm a$ is easy to see. Second, $x_0\cdot\min_{(0,x_0]}\frac{1}{f}>M$ is also wrong. An example is $f(x)=x.$ Thus $x_0\cdot \min_{(0,x_0]}\frac{1}{f}=1.$
Comment: Thanks for pointing that out, I'm not sure if $\max\limits_{(0,a]} f<x_0/M$ will do the trick, anyway there is a way simpler answer to that problem which is here in stack

A condition for uniqueness of solution


replicability and statistical significance

Question: Data for two nearly identical clinical trials.  Study A had 750 pts, 374 placebo and 376 drug.  Study B had 752 pts, 376 placebo and 376 drug. Same protocol for both. Study A showed mean change from baseline of -0.17 indicating improvement in sign, p<0.05 and 95% CI <0 while Study B showed mean change from baseline of -0.03, p>0.05 and 95% CI >0. 95%.  CIs overlap for both studies and mean for Study A is within the CI of Study B and vice versa.  Each Study has a capture percentage of 83.4% for the mean of the other study.
It seems the probability that neither study captures the mean of the other is the product of each individual failure to capture the mean of the other study... i.e., (1.00-0.834) X (1.00-0.834)= (0.166) X (0.166)= 0.0276.  Might this demonstrate statistically significant replicability in capture percentage despite failure of one study to reach p<0.05?
Comment: If studies A and B would have st. error of the mean of e.g. 0.07, then A would be significant (0.17 > 2*0.07), B would be non-significant (0.03 < 2*0.07), but A and B would not be significantly different (0.17-0.03 < 2*0.07*sqrt(2)). That's a normal situation.
Answer: Although it's not completely clear what "replicability in capture percentage" is intended to mean, the question itself is interesting.  It appears to ask about the utility of comparing the mean effect of one experiment to the confidence interval of the mean from another experiment, and vice versa.  This can be done.
As the following analysis shows,

At least approximately, the chance that neither experiment's confidence interval includes the other's mean--the chance of "overlap"--does not depend on the experimental outcomes.
Conceptually, this chance depends only on the true underlying distribution: it cannot possibly depend on the outcomes.  This is analogous to asserting that the chance of a coin landing heads does not depend on the result of just one or two flips (or even any finite number of flips).  The coin's chance is what it is;  the flips merely reflect, quite indirectly, that underlying chance.
The chance of non-overlap is appreciably large.

In the situation posited in the question, the chance of non-overlap when both experiments are run at a size $\alpha=0.05$ (that is, 95% confidence) is approximately
$$2\Phi(-Z/\sqrt{2}) = 2\Phi(-1.96/ \sqrt{2}) \approx 16.6\%$$
where $1.96 = Z_{1-0.05/2}$ is used for computing two-sided $95\%$ confidence intervals.
Finally, since this chance says nothing whatsoever about the true effect size, studying overlap is really a way of assessing whether the experiments concern the same underlying distribution or not.
A closely related analysis (comparing confidence intervals) appeared earlier at https://stats.stackexchange.com/a/18259/919.  It examined the case where two confidence intervals do not intersect at all.

To get a sense of what non-overlap might tell us, let's adopt assumptions that--although not entirely realistic--are close enough to how many experiments work that the results will be informative.  Namely, suppose that experiment $i\in\{1,2\}$ collects a sample of size $c_i$ from a distribution $F$ for its control group and a sample of size $n_i$ from a distribution $G$ for its treatment group.  Let $\sigma_F^2$ be the variance of $F$ and $\sigma_G^2$ that of $G$.
The variances of the experimental effects $m_i$ (the differences between treatment and control group means) therefore are
$$\operatorname{Var}(m_i) = s_i^2 = \frac{\sigma_F^2}{c_i} + \frac{\sigma_G^2}{n_i}.$$
Let's assume the $c_i$ and $n_i$ are large enough that the sample distributions of the means can be approximated by Normal distributions.
Finally, let us suppose $\sigma_F^2$ and $\sigma_G^2$ are known (so we can simplify the analysis while still capturing its essence).
A symmetric two-sided confidence interval for the mean effect in experiment $i$ will therefore have endpoints close to $$m_i\pm Z s_i$$ where $Z$ is a number depending on the confidence level.  The event that each CI fails to cover the other experiment's mean is equivalent to the difference in the means exceeding the larger of the interval radii, $Z\max{(s_1,s_2)}$; namely
$$\mathcal{E}:m_2 - m_1 \notin [-Z\max{(s_1,s_2)},Z\max{(s_1,s_2)}].$$
We can compute this because the random variable $m_2-m_1$ is Normal with mean $0$ and (since the experiments are independent) its variance is $s_1^2 + s_2^2$.  Writing $\Phi$ for the standard Normal distribution, this chance is
$$\Pr(\mathcal{E}) = 2\Phi\left(-Z\frac{\max{(s_1,s_2)}}{\sqrt{s_1^2 + s_2^2}}\right).$$
When the experiments use groups of comparable sizes, as in the question, $s_1 \approx s_2$, and therefore we may approximate the ratio easily by writing both variances as $s$ and computing
$$\frac{\max{(s_1,s_2)}}{\sqrt{s_1^2 + s_2^2}} \approx \frac{s}{\sqrt{s^2+s^2}}=\sqrt{1/2}\approx 0.7.$$
Therefore
$$\Pr(\mathcal{E}) \approx 2\Phi\left(-Z/\sqrt{2}\right).$$
Since $Z$ is a value for which $\Phi(-Z)\approx \alpha/2$ and $0 \lt Z/\sqrt{2} \lt Z$, the non-overlap probability will always be greater than the test size $\alpha$.
Answer: I think "statistically significant replicability" is a rather strange idea. With statistical significance, the null hypothesis is usually that there is nothing going on and you usually want to reject that null.  Here, you would be happier if the null was true (that is, the improvement is the same in the two trials).  If you want a statistical test of this, look into tests of equivalence.
But, really, I think the important bit is not statistical significance but, rather, whether -0.17 is meaningfully different from -0.03.  We have no way of knowing that - it depends on what is being measured.
Comment: Apologies on error
Comment: Apologies on error. I will look into tests of equivalence. There is no statistically significant (two-sided alpha < 0.05) difference in the mean change from baseline for Study A (-0.17) and Study B (-0.03).


Non-surjective coordinate transformation

Question: Is coordinated transformation which is not surjective (so it's inverse remove some region on spacetime) allowed in general relativity?
Answer: A coordinate chart does not need to cover the entirety of spacetime. So coordinate charts do not need to be surjective.
A coordinate transformation ( I.e. the map relation to coordinate charts) only needs to be valid on the part of the spacetime covered by both charts. This means that a coordinate transformation does not have to be valid on the entire domain of the original coordinate chart, nor does its image have to cover the entirety of the domain of the new coordinate chart, i.e. it does not have to be surjective.


Is all matter made of virtual particles?

Question: This article in New Scientist says that all matter is actually virtual particles popping in and out of existence and nothing more. is this correct?
Comment: It is much,much more complicated than stated in the article. So much that the main article line is completely wrong.
Comment: A disturbingly large proportion of that article is either wrong or grossly misleading, from the title, to the closing sentence "So if the LHC confirms that the Higgs exists, it will mean all reality is virtual"
Comment: There is no sharp dividing line between a virtual particle and a real particle; it's not true that every particle is clearly one or the other. However, calling the electrons and nuclei that make up a physical object *virtual* is really very misleading.
Comment: Just because a proton is made up of virtual particles, why should that mean that it's virtual itself? The chair you're sitting in is made up of microscopic charged particles called electrons, protons, and neutrons, but it's not microscopic, and it's not charged.
Comment: can I get this right then, in quantum field theory, electrons and quarks are not completelty virtual particles?
Comment: but peter, we are told that its unknown if virtual particles exist? if they dont, that means normal particles aka field quanta dont exist because virtual and not virtual are the same?
Comment: peter my point is, QFT says that ALL quarks are constantenly being created and annihilated all the time from the vacuum of inside the hadron very quickly, this would make them virtual particles and hence the proton/field quanta is a virtual particle, am I right or wrong? advice please
Comment: http://www.physicsforums.com/showthread.php?t=658412   thats the link that says it
Comment: ok, but you are confirming protons are made up of virtual particles only and not real particles. Field quanta are virtual particles not real particles...
Answer: The terminology "virtual particle" comes from quantum field theory.
Note the third word in QFT, theory. Theory means that it is a mathematical model for calculations which will, if the theory is valid, describe concrete measurements and behaviors  of physical reality. The basic building block of QFT is the Feynman diagram: a mathematical prescription that will give integrals which will describe the cross section and angular distributions and phases in experiments with elementary "particles". By "particles" we refer to the standard model particles assumed to be elementary.

Some of the lines that you see in this image are  called virtual particles and some are called on mass shell particles. The two electron lines are on mass shell, the gamma, the quarks and the gluon are virtual, in this diagram. It is incomplete because although it has as input on mass shell particles, the right side has only virtual ones.
The following decay of a Kaon

shows input real and output real particles, i.e. particles we can measure with our instruments and get their lifetimes, their cross sections etc and check against the theory as exemplified by the Feynman diagrams.
We observe that input is a pair of quarks and output are three pairs of quarks. It is the pairs that are real. The quarks, the gluon, the W exchanged  are virtual, i.e. off mass shell particles: with the quantum numbers from the table of SM particles but an off shell mass.
Now one can say that the K meson is composed of virtual particles if one makes a one to one identification of the guess, a good guess, of how the Kaon is built up, but the Kaon itself is real, as are the pions which are the end products. Real because we measure them with our instruments. Virtual particles are a very useful mathematical tool that simplifies our view of particle interactions, that is all.
In some sense asking about "is everything virtual" is like entering a clock shop with its hundreds of clocks and say " are all clocks  gears". Clocks are made up with gears but are much more than gears. Thus protons are made up with quarks and a sea of gluons, all virtual particles, but a proton is much more than the virtual particles.
Edit: I will incorporate the content of my reply to the comments here.
Electrons  and all leptons are real particles when on the mass shell, i.e. on external Feynman lines. The same is true for photons and Z and W bosons when on mass shell. Quarks and gluons can never be free and measured individually, because of the nature of the strong force. So quarks are always virtual and have to appear in pairs(mesons) or triplets (protons) in the external legs of the diagrams, and it is the pairs and triplets that can be on the mass shell. Gluons cannot be on their mass shell either, and their only externally measured evidence is in hadronic jets.
The nucleus is a more complicated grouping, it contains off the mass shell protons neutrons gluons photons, but all together, the nucleus is on the mass shell  when isolated. When surrounded by electrons it becomes an atom, the atom then is the one that is on the mass shell and contains  electrons +nucleus off the mass shell. When observing a  molecule, the molecule is on the mass shell and contains off mass shell atoms. When observing  a crystal, the whole crystal is on the mass shell and the molecules are off mass shell.
All microscopic quantum mechanically defined items can be sometimes virtual and some times real ( except quarks and gluons which are always virtual). Virtual  is in the contained level and real is the total group that is under measurement and observation.
There is always a real level riding on virtual particles, nuclei, atoms, molecules depending on the magnification one looks at in the microcosm. Our reality rests  on nested levels of virtuality and reality ascertains itself on the level we are examining.
In the classical world we live and move in the underlying levels of virtuality are immaterial, because in addition to the nesting process  described above there is also something called "decoherence"

decoherence is the mechanism by which the classical limit emerges out of a quantum starting point and it determines the location of the quantum-classical boundary. Decoherence occurs when a system interacts with its environment in a thermodynamically irreversible way. This prevents different elements in the quantum superposition of the system+environment's wavefunction from interfering with each other.

It statistically transforms all quantum mechanical substructures to the level we measure and describe  with classical physics and certainly call real.
Answer: Virtual particles exsist for short time. They do not observe conservation of energy. Heisenberg uncertainity principle applies here.
Answer: a better way to say it would be to say that all matter is created from ENERGY.
the term virtual particle seems to mean something different to everyone.
i have seen folks refer to virtual particles as quantum foam, and i have seen others call virtual particles simply a way to describe field fluctuations.
also beware that many so called "science mags" are clickbait and not real science backed by real experiments.
so, you can think of "solid" matter (things with mass) as being built with elementary particles, that are made up of quarks, that are made up of energy. (vibrating strings of energy is a popular model)
Answer: Although the New Scientist requires readers to subscribe in order to read the entire article, this is very much the answer I was looking for.  An agreement of 2% of the proton mass with QCD-based calculations is indeed impressive, and a big improvement over previous attempts (and from which I was actually sourcing some of my much less popular responses).
The energy that causes the gluons and quarks to get pumping, dancing, color changing, and whatever else they do, is driven by the relentless popping in and out of existence of other quark-antiquark pairs, as well as other virtual particles.  I'd like to know the details of the analysis they did, but it will need to be published somewhere I don't need to subscribe in order to read.
Although it could not be said when this article was published, the other 2% is no doubt the contribution of the Higgs mechanism with the quarks.  Murray himself should be pleased, as much as figuring out such things seem to have tortured him.
This is a beautiful theory, and it makes a lot more sense than the previous nonsense I read about having "perfect vacuum" in confines of the constantly changing flux tubes.   Now I can finally understand why everyone else at the physics stack exchange is so jazzed about QCD in general.   It makes perfect sense to me now.  Thanks for sharing.
Answer: New Scientist is a frightfully un science like mag.
the pretend to be science when they are clueless.
"New Scientist says that all matter is actually virtual particles popping in and out of existence and nothing more. is this correct?"
the quick answer is NO.
i will try to give a better answer than that however.
first off, all matter is composed of atoms that are themselves made from subatomic particles.
those subatomic particles are made from quarks in different combinations.
what are quarks made from ?
string theory says they are made from BRANES (short for membranes) of vibrating strings of energy.
New Scientist should not have used the word "virtual particle" to describe objects with mass, like a proton.
while one can say all matter comes from energy, it is wrong to suggest that the mass you have in your hand will all the sudden pop out of existence.
The proton decay hypothesis was first formulated by Andrei Sakharov in 1967. Despite significant experimental effort, proton decay has never been observed. If it does decay via a positron, the proton's half-life is constrained to be at least 1.67×1034 years.
so the matter that you see and believe to be "real" is not going anywhere.
the term VIRTUAL PARTICLE is best suited for describing force carriers, like how virtual photons mediate the electromagnetic force.


color specific days in different background in org agenda

Question: a weird question. I want to be able to color specific days in different background in the Org-agenda buffer (created with org-agenda-list). I want it to be lets say every Monday and Wednesday. The aim is to get a nice visual queue to not schedule meeting during theses days so i can focus on actual work :). Ideally i would like the day header and all the time slots to get a different background on these specific days.
any clue if that's possible?
Comment: Are you only referring to an `*Org Agenda*` buffer created with `org-agenda-list` -- i.e., *not* `org-tags-view`, and *not* `org-search-view`?  Are the specific days to be arbitrarily determined by the user, or programmatically determined based upon a certain criteria (if so, what)?  Will they be every Monday and Wednesday, or will they be the 1st, 8th, 9th, and 25th of *only* November, 2016?  Is it just the divider line containing the date that should change color, or is it the task itself (e.g., the title *only* of the task)?  Please give some specific thought as to the new feature request.
Comment: thx and sorry for not being more clear, i edited the original post :)
Answer: The following is a custom function, set with the built-in variable org-agenda-day-face-function, that controls the colors of the date header in the *Org Agenda* buffer generated by calling org-agenda-list.  In the context of the function calendar-day-of-week, Monday is 1 and Wednesday is 3.
If another forum participant would like to tackle the entries that appear underneath this date header, please feel free to write up an alternative answer.
(defun my-org-agenda-get-day-face-fn (date)
"Return the face DATE should be displayed with."
  (let ((day-of-week (calendar-day-of-week date)))
    (cond
      ((or (= day-of-week 1) (= day-of-week 3))
        '(:background "red"))
      ((org-agenda-todayp date)
        'org-agenda-date-today)
      ((member day-of-week org-agenda-weekend-days)
        'org-agenda-date-weekend)
      (t 'org-agenda-date))))

(setq org-agenda-day-face-function 'my-org-agenda-get-day-face-fn)

Comment: thx that already an cool improvment :)


If multiple sources are parallel with the diode, why does the one with a higher voltage turn on?

Question:
I've found this combination in many devices—for example, power supply redundancy modules, Ethernet-powered devices (PD of PoE), and RTC in circuits. In this circuit, the voltage source with a larger voltage only supplies current, but the other does not. Can anyone explain why?
Comment: If you add a voltage probe at the common node (left side of R1), you will see that the  voltage there is 23.3V.  So D2 is in the reverse bias region (cathode more positive than anode).  Current will be negligible.  If you put in "real" diode models, you may see a small amount of reverse current flow here.

Things get more interesting if the difference between the input voltages are closer together:  say 24 and 24.1V.  With ideal diodes, all the current will flow through one diode.  With actual diodes, more current will flow through the one with a higher voltage.
Comment: Not "the diode" (singular) but rather two diodes, here in common cathode configuration or when speaking of multiple voltage sources, OR configuration.
Answer: Let's say we have 2 ideal diodes, to make it easier to understand:

simulate this circuit – Schematic created using CircuitLab
You know that a diode passes current when its anode is positive relative to its cathode, and it blocks current when its cathode is more positive than its anode.
In this ideal case, if only the 23V source is turned on, we will have +23V where the 2 diodes are tied together (at their cathodes).
But when we turn the 24V source on, the +24V passes through the diode D1 because its anode is at +24V while its cathode is at +23V, and the +24V  appears on its other end.
This will make the D2 reverse polarized and it will block and prevent the +24V passing through it towards the +23V side.
In the case of real world diodes, there will be a small voltage drop across them, but the higher potential side will be more positive and thus its diode will conduct.
Below is the same circuit with 2 separate loads (and real world diodes) to make it easier to see what is going on:

simulate this circuit
As you can see, the 24V side will have a potential higher by 1V relative to the +23V side, which would make the diode D2 reverse polarized and thus blocked if we connect their cathodes together.
In order for the D2 diode to conduct, its cathode would have to be at about 0.7V lower potential than its anode, which is 23-0.7=22.3V, which would happen when the +24V side drops to about +23V, in which case ideally equal currents would flow through both diodes. Any lower than that, and the D1 will keep going into a turn-off state sharply.
This kind of a circuit is useful, for example, in the case of a line adapter supplying a circuit with a backup battery. As long as there is line power coming in, there is no current going from the battery, but as soon as the adapter voltage drops below the battery voltage, the battery will automatically start supplying all the power.
Except for the small voltage drop across the diode(s), this is the simplest and most effective backup power circuit, which also has practically zero delay in switching between the two power sources.
This kind of a circuit is also useful in similar situations where there are two or more redundant or spread out power supplies on the line to both reduce the voltage drop between supplies and loads (if placed on different ends of the line) and to ensure the power remaining on if one of the supplies fails.
P.S.: I've used standard silicon rectifier diodes as a practical example. Different types of diodes will have different forward voltage drops, for example about 0.3-0.4V for a Schottky diode vs. about 0.7V for a standard rectifier diode.
Comment: Nice story about the famous diode configuration...
Answer: Because the diode 'blocks' it, think about it. On D2 you have 24V on the blocking side and 23V on the other side (or ~23.3V for a non ideal regular diode), so the current wants to go from high to low voltage, but the diode blocks the current.
In reality there is a bit of leakage current, but it is very small and negligible in most applications
Answer: It's called diode OR-ing or auctioneered power.  If the voltage at the "central node" between the cathodes of the diodes and the resistor is higher than the voltage at the anode of a diode, it will be in reverse bias and no current will flow.
Answer: I will add a few more ideas to the other answers to expand on this diode configuration.
Basic idea
Connecting diodes in series to voltage sources eliminates conflicts between them. This makes them unidirectional, preventing current from being passed through them in the opposite direction.
Diode as a "comparator switch"
In these applications, diodes work as "comparator switches" that close when the voltage drop across them is positive and open when it is zero or negative. This can be illustrated by the circuit of an "ideal" diode made by an op-amp driving a transistor.

simulate this circuit – Schematic created using CircuitLab
As you can see, the circuit is very intuitive and gives a functional idea of what the diode does when we apply a positive or negative voltage to it. We can make sure that it is almost perfect from the graphs below of a DC sweep simulation...

... and time domain simulation.

We also see that the diode switch cannot be absolutely perfect (VF = 0 V) because it will not work; it needs some, albeit very small, voltage difference across its terminals to be able to switch.
More applications
Below I have added more applications of this famous diode configuration. Since my schematics are conceptual, I have used ideal diodes.
Maximum voltage selector
If we connect more diodes and voltage sources with different voltages, the highest voltage will appear at the output.

simulate this circuit
Diode OR gate
Here, the input voltages have only two values - 0 V and 5 V. It is enough that only one of the sources has produced a high voltage (5 V or connected to Vs), and it appears at the output.

simulate this circuit
Diode AND gate
The dual diode gate works as a "minimum voltage selector" - it is enough that only one of the input sources has produced a low voltage (0 V or connected to ground), and it appears at the output. But here there is a peculiarity - because the diodes are reversed but the input voltages are positive, something has to provide the high output voltage.  For this purpose, we connect a "pull-up" resistor R to an additional 5 V voltage source.

simulate this circuit
Diode AND as OR gate
A typical application of the diode AND gate acting as an OR gate with active zero voltage can be seen in the input circuits of car security systems. Diodes isolate the inputs by preventing them from influencing each other.

simulate this circuit
It is enough to open a door, front engine cover or rear trunk, and a signal with an active zero level is applied to the input of the alarm system (but the other lamps will be not turned on).
Isolating diodes
Diodes play a similar role in the outputs of the alarm systems controlling the turn signals and side lights of the cars. They call them all kinds of names - isolating, blocking, separating, decoupling, etc.

simulate this circuit
Switching without diodes
Sometimes some of the diodes are not needed.
Diode rectifier:
For example, the rectifier below has diodes (D3 and D4) that block the battery current; therefore a diode is needed only for the backup battery.

simulate this circuit
Try the simulation for two values of the input AC voltage - 10 V (there is a mains supply) and 0 V (there is no mains supply).
Emitter-coupled pair:
In this configuration, two "voltage sources" - the emitter followers Q1 and Q2, fight to drive the common load R3. But there is no need for isolation diodes because the "pull-up" transistors can only source current.

simulate this circuit
Try the simulation for two values of the input voltage V1 - 100 mV (Q1 supplies R3) and -100 mV (Q2 supplies R3).
Diode switching
Finally, in addition to switching voltage sources, diodes can switch themselves. The rule is similar:
If we connect two or more diodes with different voltages in parallel, the current will flow through the diode with the lowest voltage; the other will simply be turned off.

simulate this circuit
This effect can be used to switch LEDs, Zener diodes and others, using simple SPST (ON/OFF) switches instead the more sophisticated SPDT ones.

simulate this circuit
Generalization
A relationship between the first and last configuration can be seen. In the first, strings of voltage sources with different voltages and diodes with the same VF in series, are connected in parallel; in the latter, only diodes with different VF are connected in parallel. Connecting a voltage source (V) in series with a diode (VF) can be seen as artificially increasing its VF to V + VF (like a Zener diode).
Comment: The circuit with Mains is a nice application, but instead of 1 kHz I would rather think of 50 Hz (or 60 Hz). What is a diode of 1V, or 3V? How to get a reading of 1.000V, that is an unrealistic accuracy. A voltage source of 0 V is just a short circuit, or a straight copper wire, so two of your diagrams are identical. Nice elaboration, but I prefer the short answer of Spike
Comment: @Roland, I take your comments and explain. These are conceptual diagrams with selected convenient values (1 V, 1 mA, 1к...) without details. About the mains frequency, yes... I can fix it. 1.000 V is what the simulator shows me and I don't know how to rough it; it annoys me too. I am a practical person but for the purpose of an intuitive explanation I have simplified quite a few things; for example the elements are not specifically labeled and their values are not always standard. My goal is to show the general idea, not the specific implementation.
Comment: Also, I agree that a voltage source with zero voltage is just a piece of wire but I suppose that readers will experiment with the simulation by changing the voltage.


Why do non-orphans leave during Yizkor?

Question: In all the Shuls (Synagogues) I've Davened in over the years, I noticed that all those whose parents are alive leave the shul during Yizkor. Why is this so?
Comment: In recent years, in synagogues I've davened in both in the US and in Israel, the rabbi has pleaded with his congregants for everyone to remain in the shul for Yizkor, arguing that the minhag to leave is shtus, everyone can say yizkor for martyrs and Israeli soldiers and grandparents or great-grandparents, and it is divisive to abandon fellow community members when they are reciting yizkor. I'm not sure if this trend is catching on, but I have noticed it in a number of places.
Comment: The situation described in the question used to be our custom, however in recent years, our Rabbi has asked everyone to remain for the yizkor for martyrs and Israeli soldiers, and then they can leave when we do the personal yizkor.
Answer: Taame Haminhagim (589–590) explains (in free translation):

If he remains there, he might say it with them, and there's a covenant made with the lips [that what they say is true comes true]. Another reason is that everyone's busy saying Yizkor and he's silent, and it says in B'rachos that it should not be the case that all are busy etc. There's a slight concern of ayin hara in such a case (as in Y'vamos 106, "Do you have parents in town?" ―"Yes", and he set his eye upon them and they died).

As Alex (thank you!) points out in a comment, the B'rachos quotation, from 20:2, is "so it should not be the case that everyone is busy [praying] and he's sitting idle" (in another context of someone who would not be praying with the community [but would, I assume, be in the synagogue]).
Comment: I guess we assume no one gives Ayin Haras while watching 80% of the shul leave to go have a break and schmooze for 10 minutes.

Why do non-orphans leave during Yizkor?


tire bubble on audi

Question: I have an Audi Quattro with 29000 miles on the tires.  One has developed a bubble and tire shop said I need to replace all 4 because of 4 wheel drive could damage differential.  Is this true?
Comment: tl;dr Yes. Change all 4 tires.
Comment: Tony, see the previous question. Yes, running mismatched tires can damage your car.
Answer: I'm not an Audi mechanic, so I can't say for sure that you could harm your car over the next 20K miles with the imbalanced tires, but this is the foundation for the warning.
The differential is designed to allow the wheels to spin at different speeds when cornering, and also designed to (along with other systems) detect when one wheel is losing grip (spinning at a different rate) so power can be transferred to other wheels.
Normal operation assumes that all wheels are the exact same size and spinning at the same rate. When you put one new tire on a car with three worn tires, it will put extra work on the differential.  The new tire will be rotating slower than the others because it will have a larger circumference.
Tires with 29,000 miles are probably more than half gone in terms of wear.  If it was 10,000 miles, the size difference might be negligible, but with well worn tires, it's probably a valid warning.
Please comment if you know how severe the situation is.
Answer: If the car has limited slip diffs, the constant slight difference in wheel speed can cause wear of the friction plates, fairly quickly wearing them out.  If the diffs are normal open diffs, this is not quite so important, but if you look at how the planetary gears work in a differential, you will see that the difference in wheel size will cause some of the gears that normally only turn when going around corners to be turning slowly all the time, which will add a little wear.  As I said before, this is much more important for limited slip diffs.

tire bubble on audi


Music too Distracting and Loud in the Workplace

Question: I work in a mail processing plant and the music is too distracting and loud. Every night it feels like I'm walking into a dance hall. I informed my supervisors and Health and Safety representatives took their cell phones around to each speaker/radio and came back and said the noise level was 30 decibels below the unacceptable level. They told me to wear ear plugs. Every night I dread going to work because of this and I've had migraines on 2 occasions. I've complained on several occasions and nothing is being done. What do I do next?
Comment: Possible duplicate of [Distracted by loud music](https://workplace.stackexchange.com/questions/113723/distracted-by-loud-music)
Comment: "They told me to wear ear plugs." What happened when you wore the ear plugs? Did they work?
Comment: Who plays the music? Other coworkers? Do you have an employee handbook?
Comment: Also, do you know how your co-workers on the floor feel about the music? If they also want it quieter, that's an easier situation than if they like it this way.
Comment: Also, what is your location?
Answer: If ear plugs are unacceptable to you, you could invest in a good set of noise cancelling headphones.
You don't need to listen to music through them. If you play some white noise then a decent pair can drown out a surprising amount of background noise.
Answer: The next step is to wear the earplugs.
A lot of people have to deal with distractions and noise. If it wasn't music, it may be mail processing machines. Would you demand the machines be turned off while you work?
The simple fact of the matter is, your employer is trying to improve the enjoyment of the environment for people. There is an easy thing you can do to make sure everyone is happy. I don't see any justification on why you don't think this solution is suitable.


What is BIOS and why do we need it?

Question: I have tried reading about BIOS on Wikipedia and other websites, but I couldn't understand much. Can anyone please tell me what is BIOS and why do we need it? Also is BIOS present in every electronic device or just computers and smart phones?
Comment: A simple question that solicits a thorough answer. Hmm... *the rep is strong with this one*.
Comment: Just a note (that the current answers don't seem to address) - the original IBM PC BIOS and variants has been mostly superseded by UEFI. It's basically a newer specification with better support for newer hardware and is more extensible.
Comment: @ps06756 In case you want to learn a little bit more about BIOS, boot sequence and memory types used during the booting process, perhaps you can have a look at [this answer about booting](http://superuser.com/a/689894/279815). Might be helpful. Nice question, +1.
Answer: PCs are run by complicated programs, called Operating Systems (OSes). They are hosted in RAM memory, which is volatile, i.e., it loses its content when you turn power off.
So the question arises: when the pc power is turned on, since the RAM will be empty, how will the pc start?
The BIOS is what makes this possible. It is a very small program, hosted on Read-Only-Memory (=ROM) which is non-volatile, i.e., it does not vanish when you turn the power off. It is automatically loaded onto the pc from the ROM by special circuitry, so that the pc can start its boot-up process.
Since the amount of ROM memory is small, it is a small program, which can do a limited number of things, basically three:

It performs a self-test;
it checks that peripherals (disk, video, keyboard, ...) work correctly, and initializes them;
determines a list of places where a more advanced stage for the inizialization might reside (your hard drive, a cd-rom disk, a USB stick, the network), and tries to pass control to this new stage. If it succeeds, the start-up process continues, otherwise it halts with some hard-to-fathom error messages.

I was vague about the second stage: basically, the new stage is located in a special location of the hard drive or cd-rom, or USB stick, called a Master Boot Record (MBR). This is a tiny (446 bytes) section of the disk, for instance, which tells the pc how the disk is divided (partitioned is the technical term) in slices, and on which of these slices the next stage of the power-up process can be found. This last stage is the final stage, which will be responsible for loading the true Operating System (Windows, Mac Os, Linux, Unix,...) into the pc's RAM. And, from then on, it is business as usual.
Answer: Good question.
When I took my first programming job back in 1978 we had a room sized mini computer.  An HP2100.  When it would crash we would need to carefully set 16 switches on the front panel, then toggle a switch to load that memory word in, and repeat this about 20 times.  If you made even the smallest mistake you would have to start over.
What had to be programmed in by hand was an extremely simple program called a boot loader.  Once it was loaded we would click the run switch to execute this code and a program would start up the paper tape reader and read punch holes in a long paper tape into memory.
On this paper tape was another more complicated program which was a simple BIOS, or Basic Input/Output System.  This program knew how to access the hard disks, e.g. it new how to move the read write head back and forth, and how to swoop up a sector of data which contained another program, a bigger one, the operating system.  And if something went wrong it had a very simple command line tool to interrogate what was in memory and to hand edit it.
So it's a three step process and that hasn't changed in all of these years.
Now back with these early PCs the BIOS on microcomputers was a little different than  it is today.
When you typed a command on the command line, like dir to list the files on a disk, the operating system would compute where to look based on a file system, but then ask BIOS to actually do the work of making the hardware move and spin the disk to get a specific block of data.  Similarly the BIOS provided the low level interface to  the serial ports used to display information on your screen and get keystrokes, and to send data to the printer, etc.  So DOS (the Disk Operating System) would deal with the command line, but once it was figured out that a character needed to be sent to the screen, that job was handed to BIOS which knew how to operate the serial i/o circuit.
So the BIOS was an abstraction layer which made it possible to run CPM and MSDos on different hardware, e.g. different size, and type of hard and floppy disks.
Today BIOS is similar but once your operating system is loaded most operating systems replace the BIOS hardware drivers with drivers more tightly integrated into the operating system.  This is done to get better performance, i.e. do the same thing faster.
IBM published the source code for it's BIOS for the IBM PC so engineers could study and modify it.  One winter I also disassembled MSDos, the whole darn operating system, not something that one is licensed to do today, to see how it worked.  It took a couple of months, and some clever basic programs to disassemble it, and a lot of head scratching to try and understand what the code was doing, but in the end it gave me a solid understanding of what exactly an operating system does and how it does it.  It's not magic.  It's just a bunch of carefully written functions to take high level commands and convert them into hardware actions.  And the BIOS is no different.  It has a bunch of things you can request it to do, and ways it can be configured for various hardware.
I thought a little history of where all of this stuff came from might help you better understand this modern magic.  Today this code is proprietary so most engineer's can't ever know how it works.
Comment: +1 The reason modern operating systems replace the BIOS drivers is that its hard to call 16-bit BIOS drivers from "protected-mode"-- 32 bit mode. Cheers.
Comment: +1 Thanks! For sharing your experience, Never expected computers to be so complicated.
Answer: So, in a few words.
BIOS mean Basic Input/Output System, it's the most essential program in programable devices, like main boards in computers (PCs, laptops, mainframes and other computers, also in phones and other electronic toys, like tablets) and all another sort of hardware, like DVDs, BDs, etc.
BIOS is stored directly in device and control it behaviour. Main board BIOS has simple interface to configure board.
Comment: BIOS in optic drives is also called firmware.

What is BIOS and why do we need it?


how to add New device for testing and make a new certificate for testing

Question: I have a exiting certificate for testing on device but i have added a new device for testing so how may create a new provisioning so that i can test the app on new device also
Answer: If you need to add a testing device, you should go to developer.apple.com -> Member Center -> iOS Provisioning Portal -> Select Devices on the left tab menu-> Press Add Device button -> insert test device UDID and save this new device.
After that you need to go to Provisioning section (on the left tab menu) and create new or edit existing development and distribution provisioning profiles. After that download new development and distribution provisioning profiles on your development Mac, add this profiles in Xcode Organizer to your test devices (iPhones of iPods) and update Target settings of your application project for Code signing (Select your Target -> Build Settings -> Code signing Identity option).
Thats all - now you can run your app on test devices. I would also recommend you to look at TestFlight service, which can provide you a useful way of over-the-air application builds distribution.
Hope that will help you! :)
Answer: Try to follow instruction for add new device for testing:
This worked for me:

Login to your iphone provisioning portal through developer.apple.com
Add the UDID in your iphone device Go back to XCode, open up the Organizer and
select "Provisioning Profiles", ensure that "Automatic Device
        Provisioning" is checked on the top right pane, then click on the
        "Refresh" button, and magically all your devices set in the
        provisioning portal will be automatically added.

Thanks...!
Comment: Listen i have already a provisioning profile on whici i am testing on iPhone i have new device i have added that in developer now i have to make a new provisoning or not for testing on it
Comment: if your phone connected in xcode show's your iphone name in simulator selection option?
Comment: my device is not connected to mac i have made new provioning profile how to save it on mac in which folder


Bubbling sound from the cooliant area when I turn the engine off

Question: I drive a 2002- Chrysler PT Cruiser. I hear this bubbling sound when I turn the engine off. It occasionally registers at hot so I put more coolant in and it seems OK for a while. The coolant is not on the ground. I don't see any leaks. What could this be?
Comment: Hi it seem as if my hose as a tiny hole because i check everything and still cant find the problem
Answer: Bubbling probably means that air pressure is building in the coolant. This is often caused by a blown head gasket, where coolant leaks into one or more cylinders in the engine, and is simply burned off, so you don't see any leaks or coolant on the ground, as it's leaking internally. Compression from the cylinder forces air back through the head gasket into the coolant system, and the air makes its way up to the overflow tank where you hear the bubbling and may see foam on top of the coolant. The engine will not run as well, as the compression will be lower as the cylinder has lost its seal, the coolant seeping into the cylinder will affect the burning of fuel, and the loss of coolant will increase risk of overheating. The coolant lost into the cylinder can also damage the exhaust components, particularly the catalytic converter, which can further hinder performance and efficiency of the engine.
Answer: If you're lucky like I was, it simply means there's a leak in one of your pipes or the coolant bottle is cracked. This would allow air to escape, meaning you lose pressure, which in turn allows the coolant to boil. Look for a tiny leak in the pipes or bottle somewhere. When the engine is hot and the coolant is boiling, open your hood and have a look around. DO NOT try to open the coolant bottle, it will blast you in the face with hot, poisonous gases.
Answer: When you start your engine and it runs up to operating temperature most of the air in the system is let out of the rad cap. When the engine cools down some air is drawn back into the cooling system. The amount of involved is accomodated by the volume of the cooling system in total. The full mark is used on a cold engine to minimise this air activity to a once only event. If you are having to top up your system every short while then you do have a water leak. This can be an external leak, and can be seen by water/antifreeze stains or drips on the engine or cooling system parts. The engine can also leak internally, and this is more usually the case when you have a boiling and bubbling event in the water reservoir that you fill with coolant. Never remove the rad cap on a hot engine. A further possibility is the water pump on your engine has a failed impeller and is not circulating the water through thr rad for cooling. Have the vehicle checked at your favourite repair shop to avoid any engine damage.


Cycles Render Engine on but still no Surface Option

Question: I am having a problem. I am following a tutorial for a Minecraft animation in blender but the person wanted to change the sky color so he used the surface tab to do so once background was enabled.
I enabled mine but no surface option to change the background.
I looked around saw that you needed cycles render on but I already had it enabled.
Answer: You will find the surface option in the "world" tab.


What is the difference between gcloud and gsutil?

Question: I want to know difference between gcloud and gsuitl. Where do we use what? Why certain commands begin with gsutil while others with gcloud?
Answer: The gsutil command is used only for Cloud Storage.
With the gcloud command, you can interact with other Google Cloud products like the App Engine, Google Kubernetes Engine etc. You can have a look here and here for more info.
Comment: For additional "color", first came App Engine then Cloud Storage. At that time, there were service-specific CLIs for each (`gsutil` for Cloud Storage). By the time `gcloud` (Cloud SDK) provided a framework for any Google Cloud Platform service, `gsutil` was so embedded|familiar, that it was not (and still hasn't been) unified under `gcloud` (e.g. `gcloud storage ...` does not exist). Generally this isn't a problem although it begs the OP's question *and* it sometimes adds complexity when trying to script `gcloud` and `gsutil` when dealing with e.g. authentication.
Comment: As of recent gcloud releases (402.0.0) `gcloud storage` exists in GA and lets you do the basic file operations (cat, cp, mv, ls, rm) which previously were only available using gsutil. It is [advertised](https://cloud.google.com/blog/products/storage-data-transfer/new-gcloud-storage-enables-super-fast-data-transfers) to be faster-by-default than equivalent gsutil commands
Answer: The gsutil is a Python application that lets you access Google Cloud Storage from the command line. You can use gsutil to do a wide range of bucket and object management tasks, including:
Creating and deleting buckets.
Uploading, downloading, and deleting objects.
Listing buckets and objects.
Moving, copying, and renaming objects.
Editing object and bucket ACLs.
The gcloud command-line interface is the primary CLI tool to create and manage Google Cloud resources. You can use this tool to perform many common platform tasks either from the command line or in scripts and other automations.
For example, you can use the gcloud CLI to create and manage:
Google Compute Engine virtual machine instances and other resources,
Google Cloud SQL instances,
Google Kubernetes Engine clusters,
Google Cloud Dataproc clusters and jobs,
Google Cloud DNS managed zones and record sets,
Google Cloud Deployment manager deployments.
Answer: "gcloud" can create and manage Google Cloud resources while "gsutil" cannot do so.
"gsutil" can manipulate buckets, bucket's objects and bucket ACLs on GCS(Google Cloud Storage) while "gcloud" cannot do so.
Answer: With gcloud storage you can do now everything what you can do with gsutil. Look here: https://cloud.google.com/blog/products/storage-data-transfer/new-gcloud-storage-cli-for-your-data-transfers and also ACL on objects: https://cloud.google.com/sdk/gcloud/reference/storage/objects/update
Comment: Whilst this may theoretically answer the question, [it would be preferable](//meta.stackexchange.com/q/8259) to include the essential parts of the answer here, and provide the link for reference.


Why are distant type Ia supernovae dimmer than expected?

Question: Why are the (extremely) distant type Ia supernovae dimmer than expected?
Relative to what? Their cosmological red shift? Well, what else.
Please don't just say "Because the expansion is accelerating".
Of course I accept that but what's the actual mechanism?
Is it simply because the CRS\z increases linearly and
the intensity decreases as the inverse-square with distance,
so it gets affected more, by the increased distance?
Comment: Very closely related if not a duplicate https://astronomy.stackexchange.com/questions/35847/why-dimmer-high-redshift-supernovae-means-the-expansion-is-accelerating-if-the
Answer: The supernovae are observed at some fixed redshift. Their peak brightness will depend on how far away they are. Changing the cosmological parameters changes the relationship between redshift and distance. In this case, introducing the cosmological constant, means the supernovae are further away, compared to the expectations of a decelerating expansion, for a given redshift and are hence dimmer.
A point of confusion here is that redshift is only directly related to proper distance now. The Hubble "constant" in fact changes with time in a complex way (it was bigger in the past) depending on the values of the matter and dark energy densities.
If we estimate the distance to the supernovae using Hubble's law and the vale of $H_0$ today then we overestimate the light-travel distance to the supernovae if the expansion has been slowing down. On the other hand, if the expansion has accelerated over the last few billion years then that brings the estimated light travel time back up towards the naive Hubble's law value and even exceeds it for redshifts of $z\sim 0.5$. Thus when we say the distant supernovae are dimmer than expected, we mean they are further away than expected for a decelerating universe containing only matter.
Comment: U are right. The C/RS\z and I/ntensity\d do not disagree. It is simply relative to what was expected, which was a decelerating expansion.


How to add/ change meta tags specific to the Contacts page?

Question: I have a shopping store (www.goorganics.us) in Magento using the "Magento ver. 22.214.171.124". Please guide me how to update the Title and other Meta Tags (for SEO) of my Contacts page?
Answer: The contact page comes from the module Mage_Contats.
To change the meta data you need to add this in local.xml layout file of your theme or inside the contacts.xml in the same theme.
<contacts_index_index>
    <reference name="head">
       <action method="setTitle" translate="title" module="contacts"><title>YOUR META TITLE HERE</title></action>
       <action method="setDescription" translate="description" module="contacts"><description>YOUR META DESCRIPTION HERE</description></action>
       <action method="setKeywords" translate="keywords" module="contacts"><keywords>YOUR META KEYWORDS HERE</keywords></action>
    </reference>
</contacts_index_index>

Comment: Just to note: if you choose to include this snippet in local.xml, it will break the layout of the contacts page. Best to do it in contacts.xml
Comment: I tried the above xml in my contacts.xml in my current theme (1.9.1) but its not updating, the title and meta.
Answer: For Any CMS Page in Magento This is how you should update Meta Tags
Go to CMS -> Pages in Magento Admin
Click on the Page for Which you want to Update the Meta Tags from list  (Contact Page in Ur Case)
On The Left you Have Page Information Block ,
For Meta Title - Update your Page title. (Thats it)
For Keyword and Description tags
Switch Meta Data Tab.
Here you have the Requisite Fields you can easily update.
 Keyword and Description by default.
Its that easy. Cheers !!
Comment: What if there're pages where this isn't working? What would you suggest?
Comment: @versedi can you explain what are those pages ?? maybe in ur case.
For any cms page, what i suggested would work, for module pages Marius' solution http://magento.stackexchange.com/a/35867/9676  will do
Comment: Yes you're right, I've accidently had override from System Configuration option turned on in my testing environment. So it's worth mentioning that you can't have a global description or it will not be overwriten by page's description. (P.S. Why isn't it working that way?)
Comment: @echoashu. It is required to verify website on  merchants.google.com after add meta ?
Comment: @SanjayGohil Meta Title & Descriptions will be auto fetched by google when it wud next crawl your website.
I wud say it is not required to "re-verify" after updating meta-descriptions / title as they wud keep updating.


How to send MQ message with correct format via Jmeter

Question: We're building a new project where we need to inject message in IBM MQ via Jmeter. We've installed the relevant mq jars & configured the script with Java request in jmeter. The connection was successful but then we found the XML we're sending is going in text format including CDATA. How to configure proper message format using this configuration?
Answer:
We don't know what format is "correct". As per Wikipedia

The design goals of XML emphasize simplicity, generality, and usability across the Internet.[6] It is a textual data format with strong support via Unicode for different human languages.

so XML is text hence your "expectations" are quite unclear

We don't know what is the format your plugin is producing

We don't know what is the plugin you're using.

If this is mqmeter - you can reach out to the plugin developers via Github or raise an issue
Another option is using JSR223 Sampler where you will have full freedom regarding what, where and how to send, see IBM MQ testing with JMeter - Learn How article for more details if needed
Comment: The format here we need to send is MQSTR. Like we use http header manager for providing the header for http request, here also we need to send some header. But we don't find any filed to provide the value for the header. Also this is the error received at the mq end while we are sending the request: Caused by:org.xml.sax.SAXParsexception; unexpected element CDATA


How does GR treat centrifugal force/acceleration?

Question: We know GR turns gravitation induced acceleration into curvature in spacetime.
But in GR, what happens to the acceleration due to the centrifugal force?
And similarly, the acceleration due Euler or Coriolis force?
Comment: You should check how it works in classical mechanics eg. Lagrangian point of view. I suppose even, that studying GR without such background is completely counterproductive
Answer: The law of inertia can be stated by saying that the covariant derivative of the velocity vector is zero for a free particle. The covariant derivative with respect to a certain coordinate differs from the partial derivative by a term involving a Christoffel symbol. In a rotating coordinate system, these terms can be interpreted as describing the centrifugal and Coriolis forces. No curvature is involved, so this is not really GR.
The answer by Constantin is wrong. His example of the bike inside the cylinder presupposes a centripetal force, but we can observe the centrifugal and Coriolis forces regardless of whether there is a centripetal force. The centrifugal and Coriolis forces exist in any rotating coordinate system.
Comment: Hi user261328, thank you for your first post, I completely agree! If you want to improve your answer further, it would help to increase readability e.g. by inserting equations instead of just text ("covariant derivative of the velocity vector is zero" etc.).
Comment: @user261328, In a heuristic sense I see your point. I am surprised though with all possible coordinate transformations available in GR, why GR is still sensitive to the difference of the inertia frame vs a particular kind of non-inertial rotation frame.
Comment: Speaking as a GR-outsider: imho it is a matter of choice to describe the experimental physical phenomena, i.e. the laws were chosen to be constructed that way.
Answer: If the movement is due to a gravitational phenomenon then the particle will "fall" along a geodesic trajectory and the study of this trajectory will describe the movement and will take care of what we experience as acceleration and therefore forces on the object. You would need to use the geodesics to calculate how we can experience that as a centripetal force or any other (it GR is more complicated and there are other phenomena such as frame dragging problems).  For Example, you can check the calculation for a "free" moving object in a Schwarzschild space-time, along the geodesics, and recover the planetary or any other conic trajectory and even profound non-Newtonian corrections. If you want to consider Coriolis you would need to use a more complicated metric. In this free article you find discussions which might help with this:
http://articles.adsabs.harvard.edu//full/1975AcC.....3...97H/0000101.000.html
Answer: In GR, objects follow the geodesic(allowed path induced by energy/matter) only in free fall. In the centrifugal force case(say biker circling in a big cylinder) objects follow the restricted path. And this is not a free fall.
Comment: So you are saying the physics of centrifugal phenomenon does not apply in GR? How then can we consider GR being a more useful physics when the Newtonian machines can treat centrifugal phenomenon but GR can't?
Comment: Also, with all possible coordinate transformations available in GR, how it is possible that GR can still miss centrifugal way of motion?


Can NH4Cl react with HNO3 to give NH4NO3?

Question: I assume that the reaction would be
$\ce{HNO3(aq) + NH4Cl(aq) -> HCl(aq) + NH4NO3(aq)}$
But will this reaction really happen?
Answer: Be aware that all 4 compounds, dissolved in water, are dissociated to respective ions. E.g. $\ce{NH4Cl(aq)}$ is just a shortcut for $\ce{NH4+(aq) + Cl-(aq)}$.
So it is not combination of $\ce{HNO3}$, $\ce{NH4Cl}$, $\ce{HCl}$ and $\ce{NH4NO3}$, but of (hydrated) ions $\ce{H+}$, $\ce{NO3-}$, $\ce{NH4+}$ and $\ce{Cl-}$.
Ammonium nitrate cannot be formed even by crystallization of the less soluble salt:
$$\ce{NH4Cl(s,aq) + HNO3(aq) -> NH4NO3(s) + HCl(aq)},$$
because it is more soluble than ammonium chloride.
OTOH, if the mixture has minimum of water, there can be reaction like:
$$\ce{NH4Cl(s,aq) + HNO3(l,aq) <=> NH4NO3(s,aq) + HCl(aq,g)}$$
But, in such high concentrations, there would be significant oxidation of chlorides, forming nitrogen oxides, chlorine and nitrosyl chloride.
Comment: As a comment to Poutnik's message, it should be mentioned that the original $\ce{HNO3}$ reacts with the $\ce{HCl}$ produced in a second reaction like $\ce{HNO3 + 3 HCl -> NOCl + Cl2 + 2 H2O}$, which occurs in the solution called *aqua regia*.
Comment: It was already said, by other words.
Answer: Dissolving those two compounds in water would lead to four species of ions floating around (without discussing solvation and oxidation).
To get the solid compounds back again would require removing the water, e.g., with a vacuum pump, to get the anions and cations to link (crystallize) again. Then the question arises, which of the resultant compounds are least soluble, and would precipitate first?
In this way, brines are separated into (relatively) purer substances through fractional crystallization. For example, solar evaporation ponds are used commercially to separate $\ce{NaCl}$, $\ce{K2SO4}$, and $\ce{MgCl2}$ from the mix of ions in Utah's Great Salt Lake brine.
Answer: Redox reactions aside, the reaction would tend to go the other way, precipitating ammonium chloride.
Below, we note the solubilities of a few ammonium salts in water at 20°C, translated into moles of ammonium ions per kilogtlram of water. Mass solubility from which the molar solubilities are computed are given in the linked sources.
$\ce{NH4Cl}: 6.8$ (https://en.wikipedia.org/wiki/Ammonium_chloride) (interpolated between 0 and 25°C)
$\ce{NH4HSO4}: 10.0$ (https://www.scbt.com/p/ammonium-bisulfate-7803-63-6) (it is assumed that in the acid solutions described below sulfate ions would be converted to bisulfate)
$\ce{NH4NO3}: 18.7$ (https://en.wikipedia.org/wiki/Ammonium_nitrate)
Thus given sufficient salt concentrations, the addition of $\ce{HCl}$ would precipitatethe less soluble ammonium chloride from solutions of the other salts listed:
$\ce{NH4HSO4 + HCl -> NH4Cl(s) + H2SO4}$
$\ce{NH4NO3 + HCl -> NH4Cl(s) + HNO3}$
As described by Maurice in a comment, given the high solute concentrations required plus the formation of nitric acid, the reaction with ammonium nitrate would likely be accompanied by oxidation of the ammonium and chloride ions. With sulfuric acid the oxidizing action is not as strong, so the (bi)sulfate reaction would be cleaner.
The reduced solubility of ammonium chloride may be attributed to its relatively efficiently packed lattice structure. This salt has a caesium chloride type simple cubic structure, with ammonium ions oriented so that their protic hydrogen atoms are facing alternating chloride ions. With this arrangement both ionic bonding and hydrogen bonding serve to stabilize the solid. The bisulfate and nitrate, with bulkier and nonspherical anions, do not offer as good a fit in the solid lattice and thus the solid is more easily attacked by the water solvent.


Multiple Authentication

Question: I am creating a web-page/website that integrates all my accounts into one spectrum, as in, from this page I want to use this page to log into my mail box online or any other site that requires authentication. All i want is a central login panel. enter my unname&passwd and get redirected to my mail. Is that an impossible question to ask?
Answer: It sounds to me like you want to consider using OpenId, which is a standard, fairly widely adopted form of single sign-on. Used by this very site, in fact, and supported by at least two of the three companies you mentioned: yahoo and google. Hotmail does not currently support it.
Answer: It completely depends on the individual service. You'll have to investigate each service  to see if they even allow you to authenticate against their servers remotely. In the event that they do allow it, it's still up to the service whether or not you'll be able to retrieve any kind of information from them after logging in.
Banks in particular are very unlikely to give you any way to interface with them and the ones that do will likely require a monthly access fee.
Comment: in the case with the bank i might just put up the link and a logo
Answer: You want to look into SAML, an XML-based standard for exchanging authentication and authorization data between security domains, that is, between an identity provider (a producer of assertions) and a service provider (a consumer of assertions). SAML is a product of the OASIS Security Services Technical Committee.
With SAML, you can communicate between the major single sign on (SS0) technologies like CAS, OpenID, Shibboleth, AD/LDAP...

Multiple Authentication


Recruiting from a specialized pool

Question: We're trying to create a database of users that we can contact for our future UX needs. But the pool is small and specialized (doctors). Can you offer any advice for how to encourage sign-up from a pool of people who may not be motivated by money?
Answer: How about offering the incentive money as a donation to a charity or cause of their choice?
Specialized professionals are the hardest to recruit since they have no time even if you offer to compensate them. Might also be a conflict of interest if they receive compensation in the case of doctors. If your user group is interested in giving feedback on the user experience but have no time for lab testing, you could offer to schedule sessions at their workplace (if possible) or remotely and after work hours.
I also find that keeping the pool engaged by keeping them updated of features/changes that were implemented as a result of their feedback and testing, really works. People like to be involved and see the results of their contributions. Too often, in UX research, we forget or don't have time to share our findings with participants.
Side note: Participants who aren't receiving compensation tend to give better feedback and are more motivated to complete tasks (or try to complete them) compared to paid participants.
Answer: Well if it is not money (which usually works), then it has to be a cause they care about or a promise to improve their user experience. I've heard many complaints from doctors and pharmacists working at hospitals having bad experiences with the software they use and the way the whole process of documenting their work flows.
In addition to that, I recommend keeping the money option offered but in different forms if cash is not working. By knowing more about users, you could find out what would work better for them ... Think about providing the money in forms like trips, subscriptions, discounts, gift cards...etc.
Just an example from personal experiences, some people would much prefer A Visa gift card than paper cash. Although the card is mainly cash in a card but it feels different...
Answer:
... how to encourage sign-up...

Many users (including physicians and pharmacists) would gladly participate in usability studies if it would improve the software they use, as Mo'ath notes.
You can organize testing at times and locations that are convenient to subjects, as Ling suggests. For instance, many hospitals have educational lunch seminars.
Doctors may simply not know that you are seeking participants for usability studies. How are you reaching out to them?
Consider involving residents. They haven't yet bought into any particular system, so they tend to be more interested in their future options.
Demonstrating that feedback is taken seriously by making real changes would also be helpful, as Ling notes.
You can gather data with surveys and opt-in metrics. Include sign-up for usability studies with your surveys.

... who may not be motivated by money?

I would leave money out of it. If you want to give to charity, that's fine, just keep it separate – Do not let your left hand know what your right hand is doing. Doctors can be motivated by money, just like anyone else, but there are social and legal factors that make monetary incentives problematic. Reporting requirements. Conflicts of interest. Even just providing free pens is frowned upon. It's simply easier to stay away from the controversy.
Also, as Ling states:

Participants who aren't receiving compensation tend to give better feedback and are more motivated to complete tasks (or try to complete them) compared to paid participants.

Recruiting from a specialized pool