why does Matthew only name 5 women in his genealogy?

Question: In the genealogy Matthew names 5 female ancestors of Jesus, the first 3 were Gentiles and the fourth was married to a Gentile. Why would this have been important for Matthew's community?
Answer: Matthew's book portrays Jesus Christ with regard to a particular aspect. The book has a purpose and its content reflects that purpose. The kingdom of heaven features particularly strongly in the pages of Matthew as do the several parables describing the kingdom of heaven being 'like' or 'likened to' something that is less than what is outwardly apparent.
The book is a matter of contrasts, as are the parables of the kingdom which contrast that which is inherently spiritual against that which is outwardly more (apparently) glorious.
The genealogy which Matthew records is the royal line of succession and features the omissions that are a result of God's judgements on the kings of Judah.
But among the ancestors recorded, there stands out Tamar the Canaanite, Rahab the harlot of Jericho, Ruth the Moabitess, and Urijah the Hittite.
Gentiles ?
Yes, gentiles, in the providence and wisdom of God who is not willing that any should perish but that all should come to a knowledge of the truth.
Right from his opening page, Matthew is declaring that God's purposes never were restricted to one nation - albeit he, himself, favoured that nation in order to proclaim something on earth to all the nations.
The remarkable stories of Tamar, Rahab and Ruth stand out in the genealogy, along with the reminders - in the kings - of the terrible failures of Israel to live up to their inestimable privilege.
Then, increasingly, Matthew - by specifically recording certain items, chosen parables, distinct events - weaves a narrative that displays the purpose of God to be heavenly, not earthly, to be for an entire world (to come) not just one nation, to be for ever (not just the duration of a natural kingdom on earth).
The climax, after the events of the crucifixion of Jesus and his resurrection from the dead, is the sending forth of the eleven to the whole earth, to every creature under heaven - to teach all nations :

Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: Matthew 28:19 KJV.

The significance of the women mentioned is their origin and it is not Bathsheba that is mentioned but Urijah and his Hittite origin that is drawn attention to.
They are specifically mentioned because of their individual (and remarkable) stories as they were brought in within the skirts of Israel, despite being of gentile origin - as would be gathered multitudes from the nations to join - as one - with those of Jewish origin to form one church.
Answer:
In the first verse, the words Abraham and David are close, this, for a Jew, brings to mind Mount Moriah, the Jewish Temple in Jerusalem and the Sacrifice of the Lamb.

Jewish genealogies were always male and the social behaviors that allowed the enslavement of relatives and it was extremely insulting to Jewish culture to quote women... In this part the Jews are "nervous on edge"...

Contextualized, all atypical plot of the first verses was to justify the 18th verse of the first chapter, if the Jews do not believe in the story or story of the virgin birth of Jesus Christ, respect his birth in a natural way, because the Jewish matriarchs according to the Hebrew scriptures had moral problems of a sexual nature.
.
The genealogies of the Jews rarely mentioned women, especially not women of questionable character. Nevertheless, Matthew reports four women with a dubious reputation in the lineage of the Messiah. Why?

Tamar (Mt 1:3): Genesis 38 tells the story of how she ended up pretending to be a prostitute and became pregnant by her father-in-law, Judah. A sordid tale indeed. Tamar was the wife of Judah's eldest son, Er, a wicked man whom "the Lord put to death" (Gen 38:7). This left Tamar a young widow with no children. At Judah's request, Tamar then married Onan, Judah's second son. He also proved to be wicked, and thus, the Lord "put him to death" (Gen 38:10). More sorrow for Tamar. She was now twice widowed, young, and childless.
When Tamar realized that Judah would not send Shelah, the youngest son, to be her husband, she decided to take matters into her own hands. Tamar knew that Judah was going to Timnah to shear his sheep. So, Tamar dressed as a prostitute and waited until he appeared, agreeing to have intercourse with him for a certain price. She became pregnant and then confronted Judah, revealing that he was the father. When Judah realized what he had done, he said, "Tamar is more righteous than I, since I wouldn't give her to my son Shelah" (Gen 38:26). Nevertheless, what she did was still questionable. She was a woman with a complicated past. Matthew did not need to mention her name; he could have simply written, "Judah fathered Perez and Zerah, Perez fathered Hezron..." He intentionally included her name.
Rahab (Mt 1:5a): Next, we encounter a genuine prostitute. Joshua 2 tells us that she showed hospitality to the two spies Joshua sent to Jericho, saving their lives. Joshua 8 informs us that when Joshua destroyed Jericho, God spared Rahab and her family. Rahab is called a prostitute in Joshua 2:1; 6:17, 25. She is also called a prostitute in Heb 11:31 and James 2:25. Scripture does not tell us if and when she stopped practicing prostitution. Many who comment on her suggest that she came to faith and was born again before marrying Salmon, and that she never practiced prostitution again. But it is true that she was not a person of high moral character before embracing faith. Rahab was not Jewish, although she married a Jew. Matthew could easily have left her name out of Christ's lineage. He could have written, "Salmon fathered Boaz, Boaz fathered Obed..." The Holy Spirit wanted her name in Jesus' official genealogy.
Ruth (Mt 1:5b): The next woman on the list has a questionable reputation only because of her birth. She was not Jewish but married a young Jewish man when he and his family were in Moab. She was born and raised in Moab. The Moabites had mistreated Israel when they entered the land and were not a blessed people. The Moabites, though close relatives to the Jews, were nevertheless Gentiles. Her husband died, as did her brother-in-law. This left her mother-in-law, Naomi, a childless widow with no prospect of having children. Naomi decided to return to Israel and bid farewell to her two daughters-in-law. Orpah returned to her family, but Ruth clung to Naomi and went to Israel with her. Ruth followed Naomi's instructions and ended up finding a husband in Boaz. They had a son named Obed, bringing great joy to Naomi, Ruth, and Boaz. The Book of Ruth is one of the most beautiful books in the Bible. She is clearly a woman of great character. However, an orthodox Jew might have questioned why God allowed her to be the grandmother of King David and why she would be included in a genealogy.
The wife of Uriah (Mt 1:6): Matthew does not mention her by name. He writes, "David fathered Solomon from her who had been the wife of Uriah." Bathsheba committed adultery with King David, as recorded in 2 Samuel 11. Some think Bathsheba was an innocent victim. However, there is no indication that David took her by force. The account in 2 Samuel 11 indicates that she was a willing participant in the adultery. David was a man after God's own heart, but he was not without sin. David committed adultery and had Uriah killed to cover up his sin with Bathsheba. Only when God confronted him through the prophet Nathan did David repent (2 Samuel 12). Nevertheless, she is also mentioned in Jesus' genealogy. However, we may wonder why she is not mentioned by name. Tamar, Rahab, and Ruth were all mentioned by name.
Why were these four women mentioned?
The teaching is that orthodox Jews, when reading the Genealogy of Jesus and not believing in the virgin birth by the Holy Spirit, might at least respect Mary as a common mother when looking at the preceding women.
Comment: I have learned a lot through your insightful answer. Just want to share with you this perspective that may add to the narrative of non-Israelites in the royal blood line of Judea and Jesus https://hermeneutics.stackexchange.com/a/85984/44739


Sensor size of Sony HDR-HC7e

Question: I want to motion track a shot from my Sony HDR-HC7e camcorder and I am not quite sure about the horizontal sensor size(width).
I set the focal length to minimum and the recording to HDV 16:9
This manual (HC7e and HC7 are basically the same) states it is a 1/2.9" sensor with a diagonal of 6.3mm (page 101). But if I do my calculations and multiply (1/2.9) with 25.4 to convert it to mm I get 8.75862069?
The camcorder outputs a 1440*1080 interlaced .m2t file. The image in this file is squeezed by a factor of 1.33. as seen in this example.
So I suppose that the sensor has an aspect ratio of 4/3(1.33) So I did some math:

$$a^2 = b^2 +c^2$$
$$
\begin{matrix}
a_1 &=& 6.3\\
a_2 &=& 8.75862069\\
b &=& x\\
c &=& 1.33x\\
\end{matrix}
$$

$$6.3^2 = x^2 + (1.33x)^2$$
$$
\begin{matrix}
x &=& 3.78605\\
1.33x &=& 5.0354465\\
\textrm{horizontal 1} &=& 5.0354465
\end{matrix}
$$

$$8.75862069^2 = x^2 + (1.33x)^2$$
$$
\begin{matrix}
x &=& 5.26359\\
1.33x &=& 7.0005747\\
\textrm{horizontal 2} &=& 7.0005747\\
\end{matrix}
$$
So I thought because there always is a relation between sensor size and focal length, I just take the sensor size horizontal 35mm and the corresponding 35mm focal length equivalent of 49mm (manual page 101) and get the ration: 35 / 49 = 0.714285714 then multiply the true focal length of 5.4mm by that and get a horizontal sensor size of 3.857142856
So now I have got 3 possible horizontal sensor sizes. Now I want to calibrate my lens with a set of images like the linked one. Should I leave them with the 1.33 aspect ratio and where would I specify that in the OpenCV camera calibration or do I unsqueze them and then calibrate? And do I even need the sensor size and focal length for OpenCV camera calibration?
Comment: You might have a better time asking about this on [Photography.SE](photo.stackexchange.com), I'd guess they will know more about camera sensor geometry. This is a bit out of our bailiwick here at CGSE.
Answer: Answer over in Photography:
https://photo.stackexchange.com/questions/119761/sensor-size-of-sony-hdr-hc7e/119764#119764
It turns out to be Vertical: 3.74 horizontal 4.98 and diagonal 6.23

Sensor size of Sony HDR-HC7e


Should answers to homework questions be available to future readers?

Question: If I understand correctly the current policy is that if the poster admits that hers is a homework question and also shows her own effort then help should be given. This may be a hint so that they can arrive at the solution themselves or in some cases a full answer. However future readers might have the same homework question (for example the students in next years class). If the answer is already posted they can read or even copy paste it without any effort.
Is there some way to improve the current policy in this respect?
For example:
Answers could perhaps be moved chat. The drawback of this is that the same answer would have to typed in every time someone posts the question and shows effort.
Should the policy be improved, and if yes in what manner?
Answer: Yes, answers should absolutely be available to future readers
The idea of Stackexchange is to generate a stack of questions for future visitors to read. Questions that have no use to future visitors are off-topic everywhere. As a corollary, every question should be phrased such that other users can benefit from it.
So what about the future-homework-copiers?
The solution is simple: Do not solve homework questions for others. I have always tried to keep answers similar to answer keys: A hint on how to solve the question, but leave the main work for the OP to do.
Comment: I meant to include another question but it got lost in editing:
Should we encourage people who post homework questions to post their answers once they figure it out?
Either the gain to others with similar problems outweighs the 'loss' caused by future copypasters or it does not, it should not really matter who gave the answer.
Comment: Both answers had helpful insights. Alas I could only accept one.
Answer: I strongly support @FooBar. We are a reference resource. If the professor asks a question that can be answered by searching Google, that's their problem, not ours. Our role, like any reference resource, is to provide quality, relevant information in an accessible format.
The same argument could be made against plagiarizing Wikipedia, but again, it's not Wikipedia's problem if students copy and paste their answers, it's up to their teachers and professors to ask questions that can't be plagiarized, or at least have basic Google-Fu and check to see what the most likely plagiarized sources are.


What is the correct current in the datasheet for the LED-Matrix?

Question: If I understood correctly the maximum DC Forward Current for one LED is 30mA (Page 2). So if I wanted to drive an entire column (5 LEDs) I would need 5 times the forward current. If I don't take the maximum but something like 20mA it would result in 100mA per column. Is that correct? Basically I'm wondering if the 30mA is for one LED or for a column.
Datasheet
Answer:
So if I wanted to drive an entire column (5 LEDs) I would need 5 times
  the forward current.

There are 5 columns and 7 rows intersecting with each column: -

So if you want to drive a full column at 20 mA per LED the column current in total will be 140 mA.
Comment: I'm just using the data sheets references of rows and columns. If you swapped them around it would of course be 100 mA!
Answer: The 30 mA is the ABSOLUTE MAX per diode. The normal recommended maximum is 20mA in the section before the absolute max. See the Vf line.
If you want to power 5 leds in parallel, then yes you need 5 times the current.


USB drive not in my boot list, cannot boot from usb

Question: my problem is very simple. Although I can use my flash drive to move files, I am not able to boot from it. Actually, usb drive is not even listed in my bootable device list (along with cd, hdd) in the BIOS. How can I fix this in order to be able to boot from it ?
Comment: Could you post a snapshot of the Boot To category in the BIOS? Is your BIOS the latest version? What model is your computer and what version is your BIOS?
Answer: You need to make it bootable first. You can write a bootable image file to your drive or install GRUB2 on it and use GRUB2 to boot an ISO file from the USB storage.
If you don't know where to start, you can take a look at unetbootin to install GRUB2 and configure it to boot your ISO file from a GUI
Comment: Not entirely true. The "bootable" bit, yes, but the question says the device doesn't appear with CD etc so I would assume BIOS doesn't show device. Check your BIOS to see if there is another option to enable booting to USB. Your BIOS might not be capable of booting to USB. If it can't then you won't be able to boot to USB without a stub-booter via CD. You might as well put your files on CD in that case.
Comment: YES, the BIOS doesn't show the usb device. That's what my question refers to .
Answer: If the BIOS is the latest version (go to your computer manufacturer's site to download) and still doesn't have the option, then you can follow this method:
I'm assuming your computer has an optical drive, and you have a blank CD.

Download PloP Boot Manager image
Use any iso burning software to burn the Boot Manager iso to the blank CD. The iso is located at the root of the zip file and it is named plpbt.iso.
Enter your BIOS and set it to boot from the optical drive. Insert your CD and reboot, then from there you can boot from the USB.

Source. Demonstration.


How is the attacked fleet selected?

Question: When there's more than one hostile fleet of the same faction at a system, and one of my fleets chooses the attack option in that system, the game always picks the attacked fleet for me. How is the attacked fleet determined? Is there anything I can do to affect this?
Comment: It's been a while since I played this game, but I think I remember it being the fleet with the most MP.
Comment: @DCShannon so far that's my impression as well. Can you add this as an answer so I could accept it?
Answer: I have more than 500 hours of playtime on Endless Space.
I haven't played the game in a while, so haven't explicitly tested this, but I recall that the fleet with the highest MP is selected.
As some kind of evidence, note that you have to destroy all fleets with any MP before being allowed to attack the AI's invasion fleets, even it's just one scout ship.

How is the attacked fleet selected?


Variant of principal components analysis where only the variance of a single variable counts

Question: Principal components analysis finds the axis(/es) along which the variance of some dataset is maximized. What if I'm in a situation where I have a single dependent variable $v$ that is dependent on $n$ independent variables $v = f(x_1, x_2, \dots, x_n)$ and I would like to know "what principal components of $\mathbf x$ cause the most variance in $v$?" Is this an answered question already? I feel like it would be just a small modification of the PCA algorithm..
Comment: The answer is that none of the PCs of $X$ may be associated with $v.$  Ordinary least squares regression can be interpreted as finding a linear combination of columns of $x$ that maximize the correlation with $v.$
Comment: @whuber is it exactly the same problem as iterated OLS then?
Comment: @whuber also, to clarify a possible misunderstanding - by "principal components of $\mathbf x$" I do not mean the p.c.s as identified by PCA, rather I mean "set of axes that give directions that drive the most variance of $v$". This is probably related to the output of ordinary least squares regression.
Answer: If I got your question correctly (and I am not sure), the solution is that you have to take the spectral decomposition $VDV^{T}$ where V is the orthonormal matrix of eigenvectors and D is the diagonal matrix of eigenvalues. Then you transform the set of dependent variables by multiplying the original matrix of predictors $X^{*}$  by the eigenvectors $X=X^{*}V$. Then you can regress y against the new transformer predictors X that are now uncorrelated. Since they are uncorrelated, the total explained variance of y will be the sum of variances of $\beta x$ where each x is the vector representing each column of X (so each transformed variable) and $\beta$ denotes its corresponding beta estimated at previous step. The PC variable $x^{max}$ such that $\beta^{2}_{x^{max}} Var(x^{max})$ is maximum among all the pc transformed variables is the one explaining the highest portion of the variance of $y$.


triangular matrix and linearly independence

Question: Let $T$ be a triangular matrix where $t_{ii}\ne 0$ for all $i$. Show that the rows and the columns of $T$ are linearly independent.  I think it is obvious from the structure of $T$. But I do not know how to prove.
Comment: Note that $T$ and its transpose are invertible.
Answer: The argument is basically the same for upper / lower triangular matrices. For an upper triangular matrix, use the bottom-right entry to clear all the entries above it. Now repeat this process until your matrix is diagonal, and has no zero entries. Then manifestly the rows and columns are linearly independent.
Comment: can you make it an answer?
Answer: Consider the lower triangular case and let's deal with the row case. If $\sum_{i=1}^{n} \lambda_{i} r_{i} = 0,$ and not all $\lambda_{i}$ are $0,$ then choose $j$ as large as possible so that $\lambda_{j} \neq 0.$ Then $\lambda_{j}r_{j} = -\sum_{i=1}^{j-1} \lambda_{i}r_{i}.$
The right hand expression has $(j,j)$-entry $0,$ but the left hand side doesn't, a contradiction. (Strictly speaking I should have also said that there is more than one non-zero $\lambda_{i}$, which there is).


`C-x C-c` closes all windows on OSX

Question: In OSX, pressing C-x C-c closes all Emacs windows instead of only the selected one. This isn't the bahavior I've come to esxpect from using Emacs on Windows, Ubuntu,or CentOS. What's up?
Comment: `C-x C-c` exits Emacs, i.e. it closes all open frames. It works the same on all operating systems. If you just want to close the current frame, use `C-x 5 0`.
Comment: @Lindydancer On other systems opening a new file from outside creates a new instance.
Answer: C-x C-c is for Kill Emacs (save-buffers-kill-terminal).
Maybe on other systems you are using emacsclient, then

C-x C-c behaves specially if you are using Emacs as a server. If you type it from a client frame, it closes the client connection.

Or maybe you run multiple instances of Emacs?
To close only one frame use C-x 5 0 or s-w.
This command delete current frame or kill Emacs if there are only one frame:
(defun close-frame-or-kill-emacs ()
  "Delete frame or kill Emacs if there are only one frame."
  (interactive)
  (if (> (length (frame-list)) 1)
      (delete-frame)
    (save-buffers-kill-terminal)))

Comment: @Aido, in the absence of the client/server feature, `C-x C-c` has *always* been for quitting the Emacs instance -- which means closing all of its frames.  If you are not using `emacsclient` then the only explanation which makes any sense is that, rather than using multiple frames of a single Emacs instance, you are running multiple instances of Emacs (in which case `C-x C-c` would close only the one you were using at that time).
Comment: @Aido Added `close-frame-or-kill-emacs` command to answer. Bind it to `s-w` so it will "close" the last frame.
Comment: Darn, that's really annoying. `C-x 5 0` and `s-w` won't close the last frame either.

On other systems I just use the default `emacs` or `emacs.exe`, however it comes.
Comment: @phils Yeah, it looks like that. I've got a script from my dad that randomizes the background color of each instance, and on OSX they're all the same until you close and reopen every window.
Comment: @muffinmad Good idea, thank you!

`C-x C-c` closes all windows on OSX


What are the different types of solder used for?

Question: How do I know when to use lead, flux-core, lead-free, or any other kind of solder out there? Do you have any tips on solder gauge for specific applications?
Answer: A great question, and since a textbook could probably be written to answer it, there's probably not going to be any single answer.  I want to provide a general answer tailored to hobbyists, and hope that people more knowledgeable can come in and tie up specifics.
Summary
Solder is basically metal wire with a "low" melting point, where low for our purposes means low enough to be melted with a soldering iron.  For electronics, it is traditionally a mix of tin and lead.  Tin has a lower melting point than Lead, so more Tin means a lower melting point. Most common lead-based solder you'll find at the gadget store will be 60Sn/40Pb (for 60% tin, 40% lead).  There's some other minor variations you're likely to see, such as 63Sn/37Pb, but for general hobbyist purposes I have used 60/40 for years with no issue.
Science Content
Now, molten metal is a tricky beast, because it behaves a bit like water: Of particular interest is its surface tension.  Molten metal will ball up if it doesn't find something to "stick" to.  That's why solder masks work to keep jumpers from forming, and why you see surface-mount soldering tricks.  In general, metal likes to stick to metal, but doesn't like to stick to oils or oxidized metals.  By simply being exposed to air, our parts and boards start to oxidize, and through handling they get exposed to grime (such as oils from our skin).  The solution to this is to clean the parts and boards first.  That's where flux cores come in to solder.  Flux cores melt at a lower temperature than the solder, and coat the area to be soldered.  The flux cleans the surfaces, and if they're not too dirty the flux is sufficient to make a good strong solder joint (makes it "sticky" enough).
Flux Cores
There are two common types of flux cores: Acid and Rosin.  Acid is for plumbing, and should NOT be used in electronics (it is likely to eat your components or boards).  You do need to keep an eye out for that, but in general if it's in the electronics section of a gadget store it's good, if it's in the plumbing section of a home supply/home improvement store, it's bad.  In general, for hobbyist use, as long as you keep your parts clean and don't let them sit around too long, a flux core isn't necessary.  However, if you are looking for solder then you probably should pick up something with a rosin core.  The only reason you wouldn't use a flux core solder as a hobbyist is if you knew exactly why you didn't need the flux in the first place, but again, if you have some solder without flux you can probably use it for hobbyist purposes without issue.
Lead Free
That's pretty much all a hobbyist needs to know, but it doesn't hurt to know about lead-free solder since things are going that way.  The EU now requires pretty much all commercially-available electronics (with exceptions for the health and aerospace industries, as I recall) to use lead-free components, including solder.  This is catching on, and while you can still find lead-based solder it can lead to confusion.  The purpose of lead-free solder is exactly the same: It's an evolution in the product meant to be more environmentally friendly.  The issue is that lead (which is used to reduce melting point of the solder) is very toxic, so now different metals are used instead which aren't as effective at controlling melting point.  In general, you can use lead-free and lead-based solder interchangeably for hobbyist uses, but lead-free solder is a bit harder to work with because it doesn't flow as nicely or at as low a temperature as its lead-based equivalent.  It's nothing that will stop you from successfully soldering something, and in general lead-free and lead-based solders are pretty interchangeable to the hobbyist.
Tutorials
There are plenty of soldering videos on YouTube, just plugging in "soldering" to the search should turn up plenty.  NASA has some old instructional videos that are great, because they deal with a lot of through-hole components.  Some of these are relevant because they discuss the techniques and how the solder types relate.
In general, if you got it at the electronics hobby shop, it's good to use for hobbyist purposes.
Comment: two things 1: [tin whiskers](http://en.wikipedia.org/wiki/Whisker_(metallurgy)) are something to be aware of when using Lead Free solder.  2: 60/40 solder has a _lower_ melting point than either [tin or lead alone](http://en.wikipedia.org/wiki/Eutectic_point)
Comment: @Logan Yes, for high volume manufacturing SMD components are arranged on the PCB with a pick and place machine. Reflow soldering is preferred for SMD parts and is required for most BGA packages. Through hole components are placed by hand and wave soldering attachs them to the board. Russel McMahon provided a good answer about the diffrent types of soldering here: http://electronics.stackexchange.com/questions/27573/why-and-when-to-use-reflow-soldering
Comment: Would you agree that if an electronic is manufactured in mass quantities, and contained microchips that are almost impossible to solder by hand (you know with thin solders, many and close to each other) they would be most likely done by machine soldering? And would it be more likely to be using a solder with high melting point temperature for products that are made in mass quantities? I'm just trying to understand if this is a common thing to see, and if most companies use machine soldering or something... I have this guitar pedal that my soldering iron can't desolder easily..
Answer: Lead vs Lead-free
60/40 lead solder melts at around 191°C (376 °F) (and is commonly worked with at around 300°C (570 °F)) and takes about 1.5 seconds to melt and form a bond, aka "wet".  Good bonds are shiny and shaped like a "tent", not a ball.  With just a little practice, you can get good or at least very competent using lead solder.
However, lead is a toxic heavy metal, so extended skin contact isn't good for you (and terrible for the environment if disposed of improperly).  I like to wear very thin cotton gloves while soldering (but I don't always).  Note that lead does not "evaporate" during soldering.  The smoke you see is the flux.  But you shouldn't be breathing flux either.  I use a fan and filter when soldering.  There is also the "breath out" technique to avoid the fumes, which is fine for small jobs.
Lead-free solder melts at 220 to 300°C (430 to 570 °F) (depending on the formula), and takes about 4 seconds to wet.  Good bonds are not shiny, and it is harder to visually detect a bad joint, at least at first.
Simple answer: unless you are planning to sell the device you are soldering to someone in the EU, stick with lead-based solder.  Lower soldering temperature and faster wetting time of lead-based solder means less chance to thermally damage your board and parts (and its cheaper).  Electrically, you can use either.  You can even use lead solder to rework a lead-free board.  Of course, then it won't be RoHS.
Diameter of solder
Very thin solder, 0.020" (0.51 mm) dia or less, gives you a lot of control over how much solder you are putting down, and melts a bit faster.  But you have to "feed" the solder into the joint at the right speed, and unrolling another foot from the roll every couple joints gets old.  I sometimes don't get enough solder into the joint with thin solder because I don't/can't feed it fast enough.  Good for hand-soldering fine SMT parts.
Thick solder, 0.050" (1.3 mm) dia or more, is good for making big joints, like heavy gauge wire or leads on a TO-220 regulator.  But it is easy to put down too much solder, and seems to melt slower as the solder itself acts as a heat sink.
I generally prefer "mid sized" solder, 0.025 - 0.031" (0.64 - 0.78 mm) dia, for most work.  It gives me a balance of controlling how much I put on a joint, without the hassle of feeding the hair-thin stuff.
Flux
Electronics flux can be rosin, water-based, or no-clean.  All are about the same quality as far as de-oxidizing the copper so a good solder bond can be made.
Rosin flux leaves an ugly, sticky residue.  Cleaning it off takes either a LOT of water, or a (nasty) chemical solvent.  You shouldn't leave it on, as it is slightly corrosive, and can also be somewhat conductive.  This is falling out of usage due to the environmental impact of cleaning.
Water-based (aka Resin) flux is less ugly, not sticky.  The stuff I have used leaves a white film behind.  I have heard this film can cause problems with long term reliability.  Some people just leave it on, but removal takes only a moderate amount of water.
"No-clean" flux is resin flux that burns or boils off, leaving almost no residue.
Comment: I found several references indicating 60/40 solder melts at 375ºF/191ºC, not 599ºF/315ºC. Perhaps you can edit this bit.
Comment: Everything evaporates a little bit, even solid objects.  The vapor pressure of lead at 327.6°C is 4.21E-07Pa, though, which seems pretty low.  Here's a chart: http://www.powerstream.com/z/vapor-press1-big.png
Comment: Excellent answer, thanks! Helped me picking my wire gauge and flux type too!
Comment: As of today (2015) more laws and directives similar to RoHS are being enacted in several countries (not only the EU) restricting the use of lead on electronics. So, if you plan to sell what you are soldering, you may be required to use lead-free solder.
Comment: OMG, "Rosin Core" and "Resin Core" just blew my mind.
Answer: "60/40 lead solder melts at 315C"
Not true.  60/40 Sn/Pb solder has a pasty range of a few degrees C and solidifies at 183 deg C.  A eutectic solder such as 63/37 Sn/Pb melts and solidifies at 183 deg C.
"However, lead is a toxic heavy metal, so extended skin contact isn't good for you"
Again, not true.  Lead cannot propagate through the skin.  It can only be ingested by transference from fingers to food or cigarettes, or through inhalation if atomised.
"Lead-free solder melts at 340 to 370C"
An alloy such as 96.5Sn/3.0Ag/0.5Cu is liquidous at 217 deg C.
"Electronics flux can be rosin, water-based, or no-clean. All are about the same quality as far as de-oxidizing the copper so a good solder bond can be made."
Wrong.  Different fluxes have different levels of activity and will help wetting and coalescence to different degrees.
"No-clean" flux is resin flux that burns or boils off, leaving almost no residue."
These are commonly synthetic fluxes that do not "burn off' but remain after the joint has solidified and are inert so do not pose any long-term risk to the circuit from hygroscopic action or ionic contamination.
Comment: "Lead cannot propagate through the skin."

Not quite true. Organic lead compounds can be absorbed through the skin (see http://is.gd/dsVou). Also, powdered lead can enter the body through the skin but it appears to be contained to sweat and saliva (see http://is.gd/dsVuJ). You can probably see that if you absorb some lead at work (despite washing your hands), head home and then swap saliva as you kiss your wife/husband this could be a problem. In fact, the increased concentration of lead can remain for days!

Also, I think you mean aerosolised, not atomised.

apologies for the paywall links.
Comment: It can certainly get into the body through cuts or other small injuries.  I know I've been punctured by through-hole components or solder spikes many times over the years.  :/
Comment: @penjuin 'organic lead compounds' are not metallic lead, any more that organic carbon compounds are carbon. It's equivalent to saying your body can absorb a lump of charcoal (the solid element) as easily as it can alcohol (an organic compound containing the element).
Answer: It's a tricky topic to get good information on, but lead-free solder's supposed to be worse for you, overall.

The transition to lead-free soldering
  has reduced strain on the environment,
  but for the operator, the hand
  soldering process has become more
  dangerous. The lead in the solder is
  gone, but to get the solder wire to
  flow properly, substantially more flux
  must be used.
The temperature needed to create a
  good solder joint using lead-free
  solder is also higher, causing a
  stronger reaction within the flux and
  creating more solder smoke with a
  greater number of particles. Lead-free
  soldering produces up to 250 % more
  particles between 0.5 and 1.0 microns
  in diameter, the size that is the most
  dangerous to inhale. In addition to
  particles, solder smoke can contain
  isocyanates, aldehydes, and other
  unhealthy substances.

http://www.wellerzerosmog.com/health_risk/

Recent research has suggested that the fumes and vapours emanating from lead-free solders may be even more dangerous to workers and the environment than those emitted by traditional lead containing solders
  And it is these fumes that seem to pose the most immediate risk. Many of these lead-free solders use rosin as a fluxing agent. Tin-lead solders melt at around 180°C, whereas lead-free solders melt at temperatures 30-40°C higher. The fear is that that the higher temperatures required for lead-free soldering will significantly increase the amount of fume produced. As solder fume is one of the top eight causes of occupational asthma, Britain's Health and Safety Executive is very concerned about workers breathing in fumes from solders containing rosin-based fluxes, also known as 'colophony fume'. Anyone soldering with rosin-based fluxes is at risk of developing asthma.

http://dataweek.co.za/article.aspx?pklArticleId=3959
Yet Wikipedia claims

The use of lead-free solders and components has provided immediate health benefits to electronics industry workers in prototype and manufacturing operations. Contact with solder paste no longer represents the same health-hazard it did before.

You also have to worry about tin whiskers


Equivalence of bounded gradient flow solutions and uniformly bounded gradient descent trajectories for definable functions

Question: I am reading paper [1] by C. Josz regarding the global convergence of the gradient method. The main result is the following:
$\textbf{Theorem}$: For a definable differentiable function $f : \mathbb{R}^n \rightarrow \mathbb{R}$ with locally Lipschitz gradients, the following statements are equivalent:

For all initial conditions $x_0 \in \mathbb{R}$, there exist $\bar{\alpha} > 0$ and $c > 0$ such that the sequence $(x_k)_{k \geq 0}$ defined by $x_{k+1} = x_k - \alpha_k x_k $, where $\alpha_k $ are arbitrary in $[0, \bar{\alpha}]$ satisfies $\| x_k \| \leq c, \forall k \geq 0$.
For all $ T \in (0, \infty]$ and differentiable solution of the gradient flow $x^\prime(t) = -\nabla f(x(t)), \forall t \in (0, T)$, there exists $c > 0$ such that the solution is bounded, i.e. $\| x(t) \| \leq c, \forall t \in [0, T)$.
For any $X \subset \mathbb{R}^n$ bounded, there exist $\bar{\alpha} > 0$ and $c > 0$ such that for any $x_0 \in X$, the sequence $(x_k)_{k \geq 0}$ (defined as in 1.) satisfies $\sum_{k=1}^\infty \| x_{k+1} - x_k \| \leq c $.

In order to prove this theorem, the following Lemma is used:
$\textbf{Lemma}$: If a locally Lipschitz definable function has bounded continuous gradient trajectories, then continuous subgradient trajectories initialized in a bounded set have uniformly bounded lengths.
While I do understand the proofs, I would like to convince myself of the necessity of o-minimality of $f$ for obtaining the conclusions of the theorem by finding some counter-examples of the implications when $f$ is not definable. However, I have trouble coming up with such counter-examples.
For example, I agree that 3. is stronger than 1. and there is no reason why the implication 1. $\implies $ 3. would be generally true. I think that the existence of a counter-example might be shown using a strategy similar to the one from [2], namely design a $C^k$ convex function by specifying some of its level sets. I think that maybe one could design a convex function such that the gradient descent iterates are bounded, but the lengths of the gradient descent paths are unbounded (this could be achieved with a function for which $(x_k)_{k \geq 0}$ has more than one accumulation point; while boundedness of the iterates might be achieved through the specification of some level sets of the function). But I'm not familiar enough with the techniques used in [2] in order to judge if this would indeed work.
As another example, for 2. $ \implies $ 1., I cannot imagine how all solutions of gradient flow would be bounded and yet gradient descent with however small step size might have unbounded iterates. Intuitively, I would expect this to be true in general.
When it comes to the Lemma, however, I have a clear counter-example: if one looks at the Mexican hat function [3] (which is $C^\infty$, but not analytic; and non-definable, I would assume), then continuous gradient trajectories remain
bounded, but the lengths of the trajectories can be unbounded, since the solution might end up rotating around the unit circle infinitely.
Any thoughts or references are appreciated! Thanks!
[1] Global convergence of the gradient method for functions definable in o-minimal structures by C. Josz
[2] Curiosities and counterexamples in smooth convex optimization by J. Bolte and E. Pauwels
[3] Convergence of the Iterates of Descent Methods for Analytic Cost Functions by PA. Absil, R. Mahony and B. Andrews
Comment: When you quote someone's work, please consider using `>`
Answer: Regarding $1\Longrightarrow 3$, by [1,Corollary 3.9] the discrete trajectories of convex functions have finite length. So I don't think you can find a counterexample among convex functions.
[1] Böhm, A., Daniilidis, A.: Ubiquitous algorithms in convex optimization generate self-contracted sequences. J. Conv. Anal. 29, 119–128 (2022)
Regarding $1\Longrightarrow 2$, it is not necessary for $f$ to be definable. It suffices for it be $C^{1,1}_\mathrm{loc}$ (i.e., differentiable with locally Lipschitz gradient).


why do you need to update a whole operating system to get updated php version? (debian)

Question: I am mostly a windows guy. I have a debian 9 VM with OMV and wanted to update the php version.
I read and realised that you need to update the whole os to get the latest php version?
Why do you need to update a whole OS just to get the latest php version; I assume this is true for other software too?.
Comment: no, you dont need to, you can for example build from source, or you can add repository with latest php for debian, look for  PHP 7.3 PPA repository
Comment: how difficult is it to build from source?
Comment: you just install required packages for build and you build it. You need ./configure script options, you can make them yourself or you can copy from system php source package. Try ./configure --help in php source folder
Answer: Why?
This is well explained in the official documentation on Choosing a Debian distribution. Debian has chosen to value stability over new features. That's why some of its software is quite old. I'd recommend also reading Advice For New Users On Not Breaking Their Debian System, especially:

Don't suffer from Shiny New Stuff Syndrome
The reason that Debian Stable is so reliable is because software is
extensively tested and bug-fixed before being included. This means
that the most recent version of software is often not available in the
Stable repositories. But it doesn't mean that the software is too old
to be useful!
Don't blindly follow bad advice
Unfortunately there's a lot of bad advice on the Internet. Tutorials
found on blogs, forums and other sites often include instructions that
will break your system in subtle ways. Don't simply follow the first
advice you find, or the tutorial that seems the easiest. Spend some
time reading the documentation and compare the difference between
tutorials.
It's better to take the time to figure out the correct way to do
something first than spending even more time fixing a broken system
later.

You don't need to upgrade whole Debian...
Once you have acknowledged the warnings from the previous section, it actually is possible to upgrade PHP without upgrading whole Debian. The most Debian way of doing this without using the official repositories is probably adding DEB.SURY.ORG's Debian DPA repository to your APT sources.
The tutorial on Ryan Erwin's answer seems quite reasonable, but keep in mind (from the same DontBreakDebian article) that...

Blog and forum posts don't expire. Instructions that might have been
safe a couple of years ago might not be safe to follow any more. When
in doubt keep researching and read your version's documentation.

This is true for any answer on a Q/A site, too. What's written here may work differently with future releases.
Answer:
I read and realized that you need to update the whole os to get the latest php version?

Updating the whole OS is one option, and it's a good one.
Debian 10 is now stable, and will bring lots of enhancements and security updates to your entire system.

Why do you need to update a whole OS just to get the latest php version; I assume this is true for other software too?

What is a Linux Distribution to begin with? What has to change for it to be a new version? Perhaps you've read of the Ship of Theseus... If you replace every part a piece at a time, is the original thing now a new thing? :-)
So when you upgrade you Debian 9 to Debian 10, you're not upgrading only PHP, you're upgrading everything that's tested with the system... However, even then you won't have the latest version of many programs because new versions of something come out everyday. If you upgrade to Debian 10, you'll just get a relatively new version of PHP (and everything else).
So if you really want to get the very latest version of PHP, you need to build it yourself from source, or find a place that's already done that, preferably a place that will keep the binary updated so that you can automatically grab the security updates.
Here's a good guide to building PHP on Debian 9, based on the DEB.SURY.ORG packages:
Install PHP 7.4 on Debian 10 / Debian 9
Follow the steps covered below to install PHP 7.4 on Debian 10 & Debian 9 Linux distribution. The latest builds of PHP for Debian are available on SURY PHP PPA repository. We'll add the repository as prerequisite then install PHP 7.4 on Debian 10 / Debian 9 from it.
Step 1: Update system
Ensure your system is updated:
sudo apt update
sudo apt upgrade -y && sudo reboot

Step 2: Add SURY PHP PPA repository
Download and store PPA repository in a file on your Debian Server/Desktop. But first, download GPG key.
sudo apt -y install lsb-release apt-transport-https ca-certificates
sudo wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg

Then add repository.
echo "deb https://packages.sury.org/php/ $(lsb_release -sc) main" | sudo tee /etc/apt/sources.list.d/php.list

Step 3: Install PHP 7.4 on Debian 10 / Debian 9
The last step is to Install PHP 7.4 on Debian 10 / Debian 9. Before installation, update system package list on added repositories.
sudo apt update

Then install  PHP 7.4 on Debian 10 / Debian 9:
sudo apt -y install php7.4

Answer yes when prompted to complete installation of PHP 7.4 on Debian 10 / Debian 9 Linux system.
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following additional packages will be installed:
  apache2 apache2-bin apache2-data apache2-utils libapache2-mod-php7.4 libapr1 libaprutil1 libaprutil1-dbd-sqlite3 libaprutil1-ldap libbrotli1
  libcurl4 libgdbm-compat4 libgdbm6 libjansson4 libldap-2.4-2 libldap-common liblua5.2-0 libnghttp2-14 libpcre2-8-0 libperl5.28 librtmp1
  libsasl2-2 libsasl2-modules libsasl2-modules-db libsodium23 libssh2-1 perl perl-modules-5.28 php-common php7.4-cli php7.4-common php7.4-json
  php7.4-opcache php7.4-readline psmisc ssl-cert
Suggested packages:
  apache2-doc apache2-suexec-pristine | apache2-suexec-custom www-browser php-pear libsasl2-modules-gssapi-mit | libsasl2-modules-gssapi-heimdal
  libsasl2-modules-ldap libsasl2-modules-otp libsasl2-modules-sql perl-doc libterm-readline-gnu-perl | libterm-readline-perl-perl make
  libb-debug-perl liblocale-codes-perl openssl-blacklist
The following NEW packages will be installed:
  apache2 apache2-bin apache2-data apache2-utils libapache2-mod-php7.4 libapr1 libaprutil1 libaprutil1-dbd-sqlite3 libaprutil1-ldap libbrotli1
  libcurl4 libgdbm-compat4 libgdbm6 libjansson4 libldap-2.4-2 libldap-common liblua5.2-0 libnghttp2-14 libperl5.28 librtmp1 libsasl2-2
  libsasl2-modules libsasl2-modules-db libsodium23 libssh2-1 perl perl-modules-5.28 php-common php7.4 php7.4-cli php7.4-common php7.4-json
  php7.4-opcache php7.4-readline psmisc ssl-cert
The following packages will be upgraded:
  libpcre2-8-0
1 upgraded, 36 newly installed, 0 to remove and 7 not upgraded.
Need to get 15.0 MB of archives.
After this operation, 76.9 MB of additional disk space will be used.
Do you want to continue? [Y/n] y

Use the next command to install additional packages:
sudo apt-get install php7.4-xxx

Example:
sudo apt-get install php7.4-{bcmath,bz2,intl,gd,mbstring,mysql,zip}

PHP configurations related to Apache is stored in /etc/php/7.4/apache2/php.ini
Using PHP with Nginx:
The installation of php on Debian configures Apache. For users interested in running Nginx and PHP, you need to stop and disable Apache service.
sudo systemctl disable --now apache2

Then install fpm extension and nginx packages.
sudo apt-get install nginx php7.4-fpm

PHP FPM configuration files are located in the directory: /etc/php/7.4/fpm/
The nginx and php-fpm services should be running.
$ systemctl status php7.4-fpm nginx
● php7.4-fpm.service - The PHP 7.4 FastCGI Process Manager
   Loaded: loaded (/lib/systemd/system/php7.4-fpm.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2019-09-19 17:32:26 UTC; 14s ago
     Docs: man:php-fpm7.4(8)
 Main PID: 12151 (php-fpm7.4)
   Status: "Processes active: 0, idle: 2, Requests: 0, slow: 0, Traffic: 0req/sec"
    Tasks: 3 (limit: 2377)
   Memory: 14.7M
   CGroup: /system.slice/php7.4-fpm.service
           ├─12151 php-fpm: master process (/etc/php/7.4/fpm/php-fpm.conf)
           ├─12152 php-fpm: pool www
           └─12153 php-fpm: pool www

Sep 19 17:32:26 deb10 systemd[1]: Starting The PHP 7.4 FastCGI Process Manager...
Sep 19 17:32:26 deb10 systemd[1]: Started The PHP 7.4 FastCGI Process Manager.

● nginx.service - A high performance web server and a reverse proxy server
   Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2019-09-19 17:32:27 UTC; 12s ago
     Docs: man:nginx(8)
 Main PID: 12362 (nginx)
    Tasks: 2 (limit: 2377)
   Memory: 3.2M
   CGroup: /system.slice/nginx.service
           ├─12362 nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
           └─12363 nginx: worker process

Sep 19 17:32:27 deb10 systemd[1]: Starting A high performance web server and a reverse proxy server...
Sep 19 17:32:27 deb10 systemd[1]: nginx.service: Failed to parse PID from file /run/nginx.pid: Invalid argument
Sep 19 17:32:27 deb10 systemd[1]: Started A high performance web server and a reverse proxy server.

Enjoy your websites and Web Applications development with PHP 7.4 on Debian 9 Linux system
Answer: Packages in a particular OS version (stretch, buster) stay at a particular version for the life of the OS version.  Security updates will typically be backported, even after the upstream maintainers have stopped supporting a PHP version to ensure still supported versions of Debian aren't security nightmares.
This ensures that you can deploy a site with a version of PHP and even if features or functions are deprecated and removed in later versions, your site stays up and working.  It is only when you decide to jump to a new version of the OS that you risk breaking your site because of features removed from your platform stack.
That said, you don't have to upgrade everything.  You can install a few packages from the next release or even the pre-release "testing" repository or the not-ready-for-production "unstable" repository.  (Pro tip: test them in a staging environment before you install in prod.  I wish I didn't have to say that out loud.)
There is an excellent ServerFault answer explaining how to do this:
How can I run Debian stable but install some packages from testing?
If you're wondering what versions of a particular package are available for any OS release or pre-release, mosy over to https://packages.debian.org/ or https://packages.ubuntu.com/.
Comment: Forgot to mention, there are also "backports" repositories for each release (e.g., buster-backports.)  If the package you want happens to be in there, that will be better tested against an OS version than the "testing" repository.


Who is flying the vertibirds?

Question: With the Brotherhood of Steel being wiped out in Appalachia, who is flying the random vertibirds that appear throughout Fallout 76?
Comment: I thought Fallout 76 wasn't canon?
Answer: Fallout 76 starts on October 23 2102. This is much earlier in the timeline compared to other Fallout games, for example Fallout 4 starts October 23, 2287.
So at the time of Fallout 76 the BoS has not yet been decimated. Important to note is also that the Brotherhood has several chapters on the West and East coast so chances are big that they have not been completely wiped out.
The BoS is also not the only operator of the Vertibirds, the Enclave also uses them.
In Fallout 76 specifically there are automated Vertibirds flying around, known as Vertibots.
Sources:
Fallout Timeline
Vertibird on the Fallout wiki
Comment: I don't know about Fallout 4 or 76, but BoS is certainly around during Fallout 1, 2, 3 and New Vegas, which take place between 2161 and 2281. As is Enclave (well, post-FO2, to a degree; but they certainly do have vertibirds). I don't remember the timeline regarding BoS, but I think Enclave at least was active all the time after the war.
Comment: *Project: Safehouse*, aka the *Societal Preservation Program*, tasked the Enclave to oversee the vaults; active since before the war for 23y. – [Space program in Fallout universe](https://scifi.stackexchange.com/questions/105849/space-program-in-fallout-universe). Given that one of your tasks in F2 is to steal plans for the BoS, the SF faction doesn't have any yet, as of the end of F2, circa 2241.
Comment: Ah, Vertibots are also the large aircraft. I thought that name referred to only the small cargo drones.
Answer: Nobody is flying them, the larger craft are Vertibots, the smaller drones are Cargobots. See time 01:20:54 in the Oxhorn live stream "Day 16 of Fallout 76 Part 2" here:

Who is flying the vertibirds?


Peltier wiring diagram

Question: im just an electronic enthusiast #1?  Is it posible to power the peltier with a motor speed controler 220vac input and varable output. If no, why? What  are the remidies #2? And if i use a 48vdc power supply stack it in series What will b the power consumption. Thank u for any answer
Comment: Would you be able to tell us what you're cooling?  How to use a peltier depends greatly on application.
Comment: Im trying to make a small freezer w20in x L27in x H24in. I will use tec1-12715. How will i reduce the power consumption without sacrificing the performance of the peltier
Answer:
Is it possible to power the peltier with a motor speed controller
  220vac input and variable output. If no, why?

Sure it's possible, is it safe? No.
Does the above circuit risk electrocution? If the motor controller does not have galvanic isolation, then yes.
The other problem is the output of the controller shows 220V, which is above the 48V rating of the peltier modules and is sure to exceed the maximum ratings and burn them up.
Find a DC power supply with voltage control at minimum. Also running peliters at full power can be bad because the heating from resistive losses in the peliters causes them to heat up and gives you less cooling
Comment: The output of the controler can be adjusted to 0v to 220v dc so i will fixed it to 48v. And also use step down dc-dc converter with cc/cv output 48vdc.
Answer: No, you shouldn' t do that.
For the following reasons:

The possible output voltage of 220 V is much higher than the maximum voltage the peltier elements are meant for (if the output ist controlled with phase cutting, than this applies even to dimmed output)
Peltier elements should not be driven with alternating current as this will cause thermal stress, whitch is harmful to them
You should implement a galvanic isolation to protect yourself.

So you will have to look for a PSU that is rated for 4×12V×6A = 288 W at 48 V.
Comment: Also To transfer as much Q heat as possible use the lowest thermal resistance interface that fits with high velocity cooling (3m/s) on hot side to reduce the temperature drop on Peltier interface.
Answer: There is a long list of things which are not variacs! Motor  speed controllers are on that list.
OP wants a variable  voltage. What varies an AC voltage is a variac.  they are heavy, bulky and expensive, which is why there is a long list of things which are not variacs.  Those other things use tricks which are appropriate for the particular things they are driving -- lamp dimmers use leading or trailing edge triacs, fan speed controllers do what they do, motor controllers use VFD, etc.  None of these things are designed to produce a sensibly varying voltage.
What OP really needs is a variable voltage DC power supply, and the best tech for that is electronic buck conversion down to a practical voltage for his project. Such power supplies which are UL listed (or to be more precise RU listed) are readily available at your friendly mail-order electronics supply house.

Peltier wiring diagram


Traveling Outside USA as a visitor

Question: I'm from Mexico and planning a trip to Japan, and so me is a few thousand dollars cheaper and way faster to do it from LAX, than from my own country.
I do have an American Visa B-2 type (Tourist).
What problems could there be regarding my situation?
and
Are there any extra steps in me taking an international flight within the US as a foreigner?
Thank you so much in advance, I really don't want to have an issue and have never done a flight like so.
Answer:
What problems could there be regarding my situation?

You could be denied entry into the US. Since you already have a B visa, this is probably rather unlikely.

Are there any extra steps in me taking an international flight within the US as a foreigner?

Not really.  The airline will report your departure to the US government, so you might have to show your US visa when you leave for Japan, but otherwise the process will be essentially the same as it is for a US citizen.
Comment: The airline is unlikely to check the OP's USA visa upon departure from the USA. The USA visa is just permission to apply for admission. It holds no value once a passenger has already been admitted. They will be more interested in the required visa (if any) for Japan.
Comment: @greatone I know that.  But when I flew on Delta from JFK to Dakar a couple of years ago, the airline required my wife to scan her US visa at the checkin kiosk.  I don't know what specific condition triggered this requirement, but it succeeded in convincing me to use my US passport instead of my other one.  We normally leave the US on European carriers, where there has been no such requirement.
Answer: You want to transit through the USA using a B2 visa. You are unlikely to have any problems.

If you already have a valid visitor (B) visa, you may be able to use it to transit the United States. If you are a citizen of a participating country, you may be able to transit the United States on the Visa Waiver Program.

https://travel.state.gov/content/travel/en/us-visas/other-visa-categories/transit.html

Traveling Outside USA as a visitor


Pull data from Salesforce Chatter into a SharePoint list?

Question: We're looking to query data driven within Salesforce Chatter and pull relevant information into a SharePoint list. Does anyone know if this is possible and how to do it?
Answer: Salesforce has an connected app architecture where you can register an app which will give an access uri and key to the required resources.
you can now write a custom solution using the oath via the generated key and then get the access token.
now pull the chatter information and store them in to sharepoint via onject model or CSOM
Answer: Yes you can,check this video Sharepoint Salesforce.com Integration
Or use the 3rd party App Chatter for SharePoint – the leading solution for integrating your SharePoint collaboration platform with SalesForce Chatter


What is the vector form of Taylor series expansion?

Question: What is the expression for expansion of $\phi(\vec r+ \vec l)$ where $\vec r$ is variable and $\vec l$ is a constant vector. I think it can be expanded as a vector form of taylor series as $\phi(\vec r+\vec l)=\phi(\vec r)+\vec l.\vec \nabla\phi(\vec r)+....$ in analogy with general taylor series expansion of $f(x-a)$=$f(a)+xf'(a)+\frac {x^2}{2!}f''(a)+....$. But I can't be sure about it. I have seen this formula in a book. If that vector formula is true, (for further reference I denote this formula $f(x+a)$=$f(a)+xf'(a)+\frac {x^2}{2!}f''(a)+....$ as formula 1) then why the constant vector $\vec l$ is multiplied with the gradient of $\phi$ and why the gradient is evaluated at $\vec r$ where $\vec r$ is variable in oppose to formula 1 where variable $x$ is multiplied with derivative of $f(a)$ and derivative of $f(x)$ is evaluated at $a$ where $a$ is constant? And isn't it obvious that $f'(x)$ is evaluated at $a$? if a was a variable, then how could we evaluate $f'(x)$ at $a$? If r is variable then how can we get a value of gradphi at r? the left hand side is symmetric but $\vec l$ is a constant here and $\vec r$ is variable, so should we not write the vector formula as $\vec r.\vec \nabla\phi(\vec l)$ instead of $\vec l.\vec \nabla\phi(\vec r)$ in analogy with the scalar one?[I want to mean the value of $\vec \nabla\phi(\vec r)$ at point $\vec l$ by writing $\vec \nabla\phi(\vec l)$]
Answer:
Your vector formula is correct whereas the scalar one is wrong (should be $+$ instead of $-$).
The left-hand side is symmetric in the two variables, so it doesn't matter which one you consider "constant". Also, $f'(a)$ does not mean "derivative of $f$ w.r.t. $a$" but "derivative of $f$ evaluated at the point $a$".
Comment: Sorry for that wrong formula, I did not notice it, actually messed with the formula of f(x)=f(a)+(x-a)f'(a)...sorry for that and I know that f'(a) means derivative of f at the point a but in that vector formula grad is operating on phi evaluated at the vector r which is variable, that makes me confused. if r is variable then how can we get a value of **gradphi** at r? the left hand side is symmetric but l is a constant here and r is variable, so should we not write the vector formula as **r.gradphi(l)** instead of **l.gradphi(r)** in analogy with the scalar one?
Comment: I don't quite understand what you mean. It is an asymptotic formula, i.e. an approximation to the left-hand side with error bounds that can be computed. If you have an analytic function, you can even write down the infinite series and it will give you back your analytic function. In any case, this holds pointwise, so you can plug in whatever you want, no matter if you consider it "constant" or "variable". It is exactly the same as in the one-dimensional case.


Well breaker tripped we ant reset it

Question: I was in the shower and water just shut off. The breaker tripped we tried resetting it all it does is hum then its off again. We have no water. What can we do
Comment: Sounds like the well pump has died.
Answer: Assuming the humming sound is your well pump (were you able to hear it when it was working?) then it either has something stuck inside or it has simply seized up.
If you cannot normally hear the well pump, and the humming sound comes from the breaker itself, that means it's definitely seized and is drawing a LOT of power until the breaker trips. Stop doing that.
Either way, time for a new pump.
Changing a well pump is one of those things where if you have to ask how, you need to call someone. Electricity and water don't get along very much and mistakes can be costly. Like ruining the new pump and having to buy a third one, causing the well sides to collapse and therefore needing to re-dig the hole, or someone getting electrocuted and dying.
Any plumber in your area will know exactly what you need, and will likely be able to fix it the same day.
Comment: Any plumber? I rather  doubt that. Would be better to say "Find a plumber that specializes in wells and water pumps...".
Comment: @MichaelKaras I think he means "any plumber in an area where lots and lots of people have wells, because it's a big part of what they deal with day by day, especially because lots of homeowners in well country can solder a pipe themsleves".   If you are one of the 6 houses in the county of San Francisco who were somehow omitted from the City of San Francisco, you might have trouble finding a local well expert.

Well breaker tripped we ant reset it


How to debug inapp billing in android?

Question: I would like to debug the whole in app billing process of my app.
But unfortunatly, everytime i try to buy some products of my app when i am in usb debugging mode and error occurs, telling me, that the app is not signed and that's why i can't buy anything. When i upload the app on google play, the purchasing works, so it obviously solves the problem, but that's basically not what i want.
So what do i have to do, to test the in app billing locally when i am debugging the app. is it even possible?
Comment: You need to upload (at least a beta version) to Google Play to use it, however you should be able to debug locally if you already did that. Are you testing while having at least one APK there?
Comment: Yes that's the point, i have already uploaded my app on play store and it's available since 2 months with the in app functionality. But i can't debug my inapp billing code with usb debugging using android studio.
Answer: If you try to upload a debugable apk on google play you'll get this error:

Upload failed You uploaded a debuggable APK. For security reasons you
  need to disable debugging before it can be published in Google Play.

So you can't debug an app downloaded from google play.
Instead you can upload the release undebuggable version to google play then build a debuggable release signed apk of the same app with:
buildTypes {
    release {
       minifyEnabled false
       debuggable true
    }
}

install resulted apk through adb
adb install -r name.of.your.apk

and then you can easily debug inapp billing app.
Comment: Interessting. For me as the developer, the most appropriate solution would be a direct way to debug this, without having to wait until the new update is published to the store. But thanks anyway, i didn't know this way either :)
Comment: Actually that didn't work for me. Has anything changed?
Comment: I tried reinstalling the debuggable release signed apk and I got an error: "_adb: failed to install releases/consumer/release/app-consumer-arm64-v8a-release.apk: Failure [INSTALL_FAILED_UPDATE_INCOMPATIBLE: Package  signatures do not match previously installed version; ignoring!]_". Should I uninstall and try again?
Comment: Uninstall first and then install the debuggable signed apk did worked.
Answer: 1) Upload it to developer console and wait 2-3h
2) Download this app from play store
3) Connect app with android studio (only OPEN the source code)
4) In android studio select "attach to debugger"

How to debug inapp billing in android?


Is my Roth-IRA still valid after if the business no longer exists?

Question: I have a Roth-IRA from my company that is no longer in business. Is it still valid for me to contribute to it or do I need to change it?
Answer: The Roth-IRA or for that matter a regular IRA is generally not connected to your place of employment.
Now a 401(k) is linked to your place of employment. If the business no longer exists, they should have turned over the 401K. The US department of Labor has information regarding plans that have been abandoned.

I suspect my plan is abandoned, but I have never received a notice of
  plan termination. How could I find out if a QTA has elected to
  terminate and wind up my 401(k) pension plan?
EBSA has developed an Abandoned Plan searchable database to help
  participants and beneficiaries find out if a particular plan is in the
  process of being, or has been, terminated. The site is searchable by
  plan name or employer name and will provide the name and contact
  information for the QTA, if one exists.  If you do not have access to
  a computer to conduct the search, you may contact one of EBSA's
  Benefits Advisors to assist you by calling toll-free, 1.866.444.EBSA
  (3272).
Answer: In general, Roth IRAs, are associated with the individual.  Unlike 401(k)s for which the business holds the retirement account in the name of the individual.  So, although the company may have helped you set up the Roth it is in your name and you can continue to contribute to it.  Wikipedia has some helpful information here.
It should be noted, however, that sometimes businesses set up special deals with retirement service companies or brokers that hold Roth IRAs so you should check with the particular company/broker that holds your Roth.


Dotted quarter rest vs. eighth note rest + quarter rest

Question: Is it ever appropriate to use a dotted quarter rest vs. an eighth note rest along with a quarter rest?
Comment: Related: [Dotted rests and rhythm](https://music.stackexchange.com/questions/58482/dotted-rests-and-rhythm)
Answer: There are various opinions about this.
The "ultra-orthodox" view is that dotted rests are not even a thing. They don't exist. So you can't use them anywhere! The fact that people write music using them (and computer music notation software permits them) just demonstrates that many people don't know (or don't care) what they are doing. But you don't need to go around correcting their mistakes all the time, because some deity or other will probably have special punishments reserved for them in the afterlife :)
A slightly less extreme position is that dotted rests can only be used for complete beats (or multiple beats) in compound time signatures like 6/8 or 9/8.
That may seem extreme, but it does have some practical common sense to support it, because with hand copied music and/or in poor lighting conditions, dotted rests can be hard to read. Many music publishers followed that convention up to about 1900.
A more mainstream opinion today would be that dotted rests can be used if they are at the start of a beat, or a subdivision of a beat for short rests. For time signatures with an even number of beats the situation where a dotted rest starts on a beat in the first half of a bar but extends into the second half is not allowed.
So in 4/4 time you can write a bar of music as a dotted half rest + quarter note, but not a quarter note + dotted half rest. The second case should be quarter note, quarter rest, half rest. And similarly you can write a dotted 8th rest + 16th note (starting on a beat) but not a 16th note + dotted 8th rest.
That rule usually makes it clear where the beats are in complicated rhythms.
The most permissive opinion is that you can write whatever you like, of course - and that is true, but don't expect other people to read it without getting the rhythm wrong.
Incidentally, Glorfindel's second example is generally considered to be wrong, because when a beat is divided into 3 parts, the second and third subdivisions should not be combined into one rest. Again, the practical reason for this is to help show where the beats are in a compound time signature - a quarter rest will always be at the start of a beat. In the example, the visual appearance of "quarter rest + 8th rest" suggests a whole beat's rest, but it doesn't start on a beat.
Comment: To sum it up: In essence you use dotted rests the same way you use dotted notes.
Answer: We are currently in the middle of a progression from 'NO!' to 'same rules as for dotted notes'.
(There's actually a similar progression in thinking about notes.  We all know the 'show the beat, show the half-bar' rules.  But a more linear approach is becoming acceptable in some styles.)
In an examination situation, I suggest you play safe and reserve dotted rests for whole beats in compound time.   In real life check which way the wind is blowing in your particular musical style!
Answer: Yes; rests aren't any different from notes here. There are situations where a dotted quarter is preferred; there are situations where a quarter + an eighth (or the other way around) is the more natural notation.
I don't have a concrete example from existing music, but consider the following example, a 6/8 time signature, where the rhythm is such that (most) measures are divided into two parts of 3 eighth notes. A dotted quarter rest is appropriate if it starts at beat 1 or 4; if it starts at beat 2, a quarter + an eighth is more natural:
<code>X: 1
M: 6/8
K: C
L: 1/8
CEGFDB,|CEGz3|CEGFDB|Cz2zEG|A6||
</code>
Comment: "rests aren't any different from notes here": actual practice of professional music engravers and copyists does not reflect that statement.
Comment: The second last measure should be 3 eighth rests in a row. "Large" rests symbols should only start on strong beats.
Comment: @ElementsinSpace in 6/8, the fourth eighth note in the measure _is_ a strong beat.  It should either be a quarter rest plus an eighth or a dotted quarter rest, if you go in for that sort of thing
Comment: @phoog No, in 6/8 you can have a quarter rest (or dotted quarter rest) on beat 1 or beat 4, but *not* on beat 2. See Gould pp. 161, 163.
Comment: @ElementsinSpace from the example image it's obvious that Glorfindel is counting dotted quarters, so "beat 2" means "beat 2 of 2" rather than "beat 2 of 4."  Except now that I've tried that, I see that the example has 5 bars, bitte 2, and that you were talking about bar 4 whereas I was talking about bar 2.
Comment: @phoog Oh, right.  I'm happy with bar 2.  It's just bar 4 that I was suggesting is incorrect.
Answer: Basically, the short answer is that dotted quarter rests are more natural on the first and fourth beats of a compound time signature. On simple time signatures, not so much. Hope this helped!
Answer: Generally, dotted rests are used in metres with three-beat units when the whole unit is silent. So you will see dotted quarter and dotted half rests in 12/8 metre.

Like this.
You aren't likely to see things like a dotted half rest paired with a quarter note in a 4/4 bar.

This is likely to be denoted as two undotted rests.
I wouldn't call it a hard and fast rule, but this is how it's typically handled.


When removing Tefillin, why do we start by taking off the finger, hand, and two windings of the forearm before removing the shel rosh?

Question: When removing Tefillin, why do we start by taking off the finger, hand, and two windings of the forearm before removing the shel rosh? The shel yad needs to be on first and last. So why not simply remove the shel rosh right away with none of the shel yad? It's obviously not an "earth-shattering" matter. I'm just curious if there is a special reason for this. When I ask such questions, I generally learn that there is indeed a reason for the procedure. Many thanks. CHODESH TOV! CHAG SHAVUOT SAMEACH!
Comment: I daven nussach Ashkenaz and take off my tefillin this way.
Comment: Yes, I should have specified that, to the best of my knowledge, that is the Ashkenaz manner.
Comment: I'm not sure everyone does this. What nusach takes off their tefillin this way?
Comment: In Heidenheim's siddur it's explicitly written: _Beim Ablegen der תפלין, nach עלינו, werden zuerst die drei Ringe vom Finger entfernt, dann wird erst של ראש und hiernach של יד ausgezogen._ You are just doing exactly the opposite way as you put it on.
Comment: Thanks very much. Most interesting and helpful. (posting from Israel)
Answer: From the Dirshu halacha email Daf HaYomi B'Halacha Daily Email - 28 Iyar/May 29
"According to the teachings of Kabbalah, the proper way to remove tefillin is by first removing the straps which are wrapped around the middle finger. Then -- because it is forbidden to wear the shel rosh without the shel yad -- the shel rosh is removed, followed by the shel yad. To show the wearer's reluctance to remove his tefillin, the shel rosh should be removed with the left hand. In certain ways, the tefillin should be removed in the manner that they were put on."
[שו"ע כח, ב, מג"א ב, ומשנ"ב ה-ו]
also from 11 Iyar/May 12, "Upon removing the tefillin, one must be careful to remove the shel rosh before the shel yad." [סעיף ו, ס"ק כב, וביה"ל ד"ה פגע]
Comment: The source seems to be the magen avraham there quoting a גלי רזיא which I assume is this kabbalistic work https://www.hebrewbooks.org/pdfpager.aspx?req=24580&st=&pgnum=4 but I can't find anything about tefillin in it
Comment: Thank you VERY much, rosends. That is most interesting and helpful. I greatly appreciate your response and assistance. Chag Sameach!


An exact sequence of abelian groups

Question: Consider an exact sequence of abelian groups
$$
0 \to A \to \mathbb{Z} \oplus \mathbb{Z} \to \mathbb{Z} \to B \to 0,
$$
where we make no assumption on the map $\mathbb{Z} \oplus \mathbb{Z} \to \mathbb{Z}$. Is it possible to determine $A$ and $B$ up to isomorphism of abelian groups from this data?
Answer: No, $A$ and $B$ depend on the map $\phi:\mathbb{Z}\oplus\mathbb{Z}\to\mathbb{Z}$.
If $\phi$ is trivial then $(A,B)=(\mathbb{Z}\oplus\mathbb{Z},\mathbb{Z})$ and if for example $\phi$ is the projection onto one copy of $\mathbb{Z}$ then $(A,B)=(\mathbb{Z},1)$ (where $1$ is the trivial group).
These are not the only possibilities, we can take any homomorphism $\phi$, then $A\cong\ker(\phi)$ and $B\cong\mathbb{Z}/{\rm im}(\phi)$
Comment: This is correct and $B$ can be any cyclic group
Comment: ker$(\phi)$ is a subgroup of $\mathbb{Z}\oplus \mathbb{Z}$, does this imply that it is necessarily free abelian of rank at most two? In that case, the kernel is either $0, \mathbb{Z}$, or $\mathbb{Z} \oplus \mathbb{Z}$. It can't be $0$ since the  kernel of $\mathbb{Z} \to  B$ would have to be $\mathbb{Z}\oplus \mathbb{Z}$, which is not a subgroup of $\mathbb{Z}$.

An exact sequence of abelian groups


Convert road bike mechanical disc brakes to hydraulic

Question: Im relatively new to road bikes, i was a mtb user my whole life. So i wanted to ask if its possible to change my road bike mechanical disc brake to hydraulic disc brake. I currently have the sora r3000 brake and shifter combo.
Answer: It is possible using special convertors that have a hydraulic fluid reservoir that is controled by the cable from your brifters. Giant makes such an upgrade kit https://www.giant-bicycles.com/gb/conduct-hydraulic-disc-brake-upgrade-kit There are also brakes that have hydraylic fluid only in the caliper itself such as TRP HY/RD.
Otherwise, the same limitations I discussed at https://bicycles.stackexchange.com/a/72522/21133 apply. Shimano only.makes brifters from 10 speed above and those different cable pull ratio for shifting.
Answer: You can't just "connect" a mechanical cable to a hydraulic system. You'd have to upgrade the shifters/brake levers ("brifters") to ones which are made for hydraulic brakes. Unfortunately brifters are the most expensive part of road groupsets, so this would be quite an expensive upgrade. The least expensive is Shimano Tiagra 4700. However it's also 10 speed instead of your 9 speed so you'd have to upgrade the derailleurs, chain, cassette etc. as well.
There used to be "adapters" (TRP Parabox, Trickstuff Doppelmoppel) before hydraulic brifters became available. These were mounted somewhere on your handlebars, and through some pistons allowed you to "convert" from mechanical cables to hydraulic. However they are quite expensive and I'm not sure how well they worked.
What's your issue with mechanical disc brakes? Maybe new and properly routed cables (+cable housing) is all you need.
Comment: Compressionless housing as well, e.gl yokozuna
Answer: Mountain bikes are easier to convert to hydraulic as the brakes are often separate from the shifters on the handle bars. This makes upgrading brakes straightforward and reasonably cost effective as you can keep your old shifters. Most road bikes are have integrated brake/shifter units, this means upgrading the brakes also means you must upgrade the shifters which adds substantial to the cost.  Furthermore hydraulics have been difficult to fit into the small space available in a road brake/shift lever so they tend to be found on higher end component lines. In your case this would mean having to upgrade to a system with a higher number of gears which means also replacing the derailleurs and potentially the chainrings/cranks depending on how high end you go.
This may seem ridiculous just to upgrade the brakes and it is, but it is also the result where development went.  Road set ups used to separate the brakes and shifters, but there were serious advantages to integrating the brake and shifter. Next time you are climbing out of the saddle and seamlessly grab a different gear, long ago you would have had to sit down, swipe at a downtube shifter, then stand back up to make the same shift. Integrating the two components have made fitting hydraulics difficult due to the limited space and complexities of the mechanisms. This has delayed the entry of hydraulic braking into road cycling for quite a while, about 15-20 years behind mountain bikes.
You can find some brake only hydraulic levers (TRP) but you are left with figuring out shifting. Most road frames no longer support downtube shifters so you are not left with many options.


jQuery UI Collision - detect divs that are NOT collided

Question: I'm very new to JavaScript so forgive me if this question is naive/obvious. I'm using jQuery UI drag and drop (and the jQuery Collision Detection library from this site: http://eruciform.com/static//jquerycollision/jquery-collision-drag-collision-example.html). Although I have no problems detecting which divs are colliding with each other (and doing things to said divs with ($(this).collisions(".collisionclass")).each(function() ...)), I haven't been able to find this list of divs that have NOT collided with each other or the target collider, at least not an elegant solution (and the reason is I wanted to do other actions on those remaining, uncollided divs).
Does anyone know of an elegant way to find which divs have not collided without resorting to brute force (e.g., add all such divs to a collection and every time there is a collision event check which ones from original collection are not in the resulting collision collection)? The example source code via the link above seems to simply add and remove dynamic div overlays on portions of original divs that are collided, but that doesn't tell me how to detect not-collided divs...
Answer: You can use the jquery not method.
<code>var not_collided = $(".item").not(".collisionclass")
</code>
Technically this will check all the items if they have the "collisionclass" class, however it is still efficient until you get to huge numbers of items.
Comment: Thanks, Nal -- however, I'm not sure how this would work...here's my (limited) understanding of the situation:

1. Whenever a div start to get dragged, is dragging, or stopped dragging, a "handleCollision" function (that I write) is called, because I bound that function to those drag events.

2. The handleCollision function uses the jQuery Collision Library to look at all the divs and returns a collection of divs that have collided with each other. It doesn't assign any ".class" to those divs.

3. Therefore, not sure how using class filter could do this...
Comment: Pass the collection of divs to the .not() method.  It can take more than just a class selector.
Comment: Genius! Thanks a ton, Nal! You saved me probably a week of trial-and-error. :)


How can I install Ubuntu onto a 16GB USB and run on Pi?

Question: I have a Raspberry Pi 2 model B V1.1 and I want to download Ubuntu onto the Pi with it's existing 8GB SD card or with an 16GB USB. Can someone please help me?
Comment: If you are going to answer this question can you try find a way to do it with the USB not sd card because my PC does not have a SD card port
Comment: Ubuntu or Ubuntu Mate. For Ubuntu Mate look here:https://ubuntu-mate.org/raspberry-pi/ On site it's written that you need 6 GB SD, but not long ago there was a problem and you needed 16 GB. I do not know if this is corrected. Transfering the image depends if you have Windows or Linux home computer.
Comment: Then you're going to need to buy an adapter for your SD card. There is no way to setup the RPi without doing at least the bare minimum with the SD card.
Comment: I use windows 10 pro and I also have a MacBook with a sd card slot.I don't mind about ubuntu and ubuntu mate I just want the one that performs best.
Comment: @Kyle if you want the best performing, use Raspbian. It's specifically created for the pi and should not have issues.
Answer: Ubuntu Mate:
Download Ubuntu Mate for RPi 2 from here. As you said that only your MacBook has SD card slot you will have to do it there (or buy SD card adapter to use it on Win 10 computer). The downloaded file is compressed (zip) so it has to be un-ziped first (I do not own Apple, but I was told that by double-clicking on the zip file it should automatically unzip it into the same folder). Than insert your SD card (make sure that write-protection pin is not on). You need to know what "name" has been given to SD by your computer (diskN, where N is a number). Write to command line:
diskutil list

Find your SD card. Be sure that this is SD. If you get this wrong you could write the image to your system disk and make your MacBook a brick).
Unmount the SD with:
diskutil unmountDisk /dev/diskN ... change N to the number you found from above command.
And now transfer the unzipped Ubuntu Mate image to SD card:
dd if=/path/to/ubuntu-mate-mage-for-raspberry-pi.img of=/dev/diskN bs=1m

Again, change N to the number you found in diskutil list
Note that it can take a while.
Look at this, this or this link for help.


Pass SIGINT through bash script to application

Question: I have a Linux application, written in C++, which traps the SIGINT interrupt in order to do some final cleanup before exiting. I call this application within a bash script. Now, when I type control-C with the bash script running in the foreground, the script terminates as does the program it invoked but without running the final cleanup code. How can I have the interrupt pass through the bash script, directly to the application, resulting in the final cleanup and then a normal exit which then causes the script itself to exit?
Answer: bash also has the ability to trap SIGINT. It would be feasible to trap the signal so the script doesn't die, and then in the trap handler, use kill to pass the signal off to your application.
Answer: #somecommand has to be a unique substring of the command being run

trap "kill -3 %?somecommand" sigint

somecommand&
wait %?somecommand


Can a base runner steal during an appeal play?

Question: Can a player steal a base during an appeal play of another runner missing a bag?
Comment: Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
Answer: Runners are allowed to advance at their own risk when the ball is in play (time out has not been called).
Different leagues have different rules about the specifics of the appeal process.  But for MLB, runner appeals are made when the ball is live, so a runner on base may attempt to steal during an appeal play.


It is a 'fair use' of trademark if a book's advertising refers to a famous book series?

Question: For instance can a book based on (or about) ancient mythologies be advertised as 'for fans of the Percy Jackson books'?
Answer: This is legal
Trademark infringement occurs when confusion would be created by the use of the trademark - this is not the case here. It seems to be a type of comparability fair use.
Furthermore is the book went on to compare and contrast the Percy Jackson use of mythological figures with their historical or other fictional representations this would be copyright fair use as literary criticism.


Input impedance of common-collector configuration

Question:
We have been asked to find the input impedance of the given circuit (above)
I've done the small signal representation of the circuit which is as follows
The question is :
I tried to solve it i'm getting this result :
Rin= ( rR2+[(R3//R4//R5)(B+1)R2])÷R2+r
Answer: Just a short hint:
Are you familiar with the MILLER-effect (which drastically reduces the input resistance)? Here we have the opposite effect - BOOTSTRAPPING via C2. This method drastically increases the effective dynamic resistance of R2 because the emitter signal voltage is nearly identical to the base signal and is in phase with the base signal voltage.
Hence, there is only a very little signal current through R2, which is needed, of course, for establishing the necessary DC bias at the base node.


Is there somewhere to complain about offensive moderator behaviour?

Question: Is there anywhere or anyone to complain to about the behaviour of moderators? I've been "spoken" to offensively by a moderator, and I'm unhappy about it.
Answer: Yes, there is. It's right here. You already found it!
Alternatively, if it's a sensitive issue that you'd prefer not be discussed out in the open, you can email email@example.com about it, citing all relevant details, and someone will contact you in private. The advantage of that versus raising another moderator flag is that it's guaranteed to be handled by one of the Stack Overflow employees, rather than a community-elected moderator.
But please remember: moderators are people, too. They sometimes make mistakes and/or have temporary lapses in judgement. Just because they were harsh with you once or made a decision that you disagree with doesn't mean that they're bad moderators, that they'll hold a grudge against you, or even that they'll make the same decision a second time.
Comment: In fact, we can't even be guaranteed to make the same decision the _first_ time thanks to our super spiffy quantum moderator tools.
Comment: They *absolutely* respond to emails, assuming that you've sent them an email worth responding to. If you start out being confrontational and insulting, I imagine you are less likely to get a response.
Comment: "Right here" made sense a very long time ago, but nowadays you'd want to post on the per-site meta of the relevant site. Meta Stack Exchange is rarely the right place to post, since many questions require domain knowledge or privileges only held by members of the relevant site.
Comment: I think this is a good rule to live by in life generally, online, as well as offline: no matter how perfect a person seems or pretends to be, never forget that human beings are ***flawed***. Even the "perfect" ones. Given that, it's important to forgive sometimes, too. Sometimes, you just have to let things slide, especially the little ones (in the "grande scheme of things" sort of way).
Comment: They do not respond to emails.
Comment: Note that this answer was posted when this site was the Meta site specifically for Stack Overflow. There was no such thing as a network-wide Meta Stack Exchange. As Laurel says, the advice would be different today.
Answer: Right here! If it's something you prefer not to be made public, you can always email firstname.lastname@example.com.
Comment: Are there similar email addresses for other forums of stack exchange?


Calculating the bit period

Question: I want to calculate the bit period in my RF packets that I transmit them with 50Kbaud (Symbol rate=bit rate in my case) , how can I calculate the bit period?
Comment: The bit period is the time duration of one bit-- if the symbol rate is the bit rate, then the symbol rate is the inverse of the time duration. Is that what wasn't clear to you or something else?
Comment: @DanBoschen Yes exactly that's wasn't clear , you mean that 1/(50Kbaud) gives me the bit period .. ? but per what second or ms?
Answer: 50 KBaud means the symbol rate is 50 KHz (and in the OP's case the bit rate with 1 bit per symbol). The units of Hz is 1/sec. So the duration of each bit (the bit period) is simply
$$t_p = \frac{1}{50,000} = 20 \mu\text{s}$$
Comment: APPRECIATED! and one more thing that's confusing me which it's really not making me to progress ! , I send RF packets in frequency 868MHZ and symbol rate 50KHZ (symbol rate=bit rate) , deviation is 100kHZ , so once I transmit by cc1350 hardware of texas instrument, and Im sampling those IQ SAMPLES DATA (raw data) by a sampler called SDR dongle.
Comment: Im sampling over frequency 868MHZ and  sample the radio At 2048000 , the IQ samples data I save them to a file type of dat, I enter that file into matlab and I see the packets , Im trying to detect the start of my packets by xcross corelation with my syncword(syncword is constant for every packet) , I did a demodulator (two matched filter) for detecting the data at 868khz with given deviation 100khz
Comment: see here please https://dsp.stackexchange.com/questions/68347/find-syncword-pattern-in-signal-using-correlation
Comment: what should I do in order to detect the start of my every RF packet? Im trying to find xcross corelation according to my syncword(it's constant) but not succeeding to see the peak of corelation where there's syncword, I guess my two matched filter(demodulator) isn't good .. so could you help me what should I do in order to detect the start of my packets in matlab? thanks alot!!
Comment: Hi Ryan- We are encouraged to not have a back and forth discussion in the comments, and your comments are specific to another question so better if you just put those details in your question not here. Thanks!

Calculating the bit period


Need help on a simple circuit LM317T

Question: I want to make a Lm317 4.5a output circuit. So I want to know that- do I need any resistor on point 3 & 4? And which capacitor will be best for point 1 & 2. Pls help me.
Comment: See page 16 in the [TI datasheet](http://www.ti.com/lit/ds/symlink/lm317.pdf) for LM317.
Comment: I don't have all components from datasheet. Pls help me what I asked for.
Comment: Lacking components, use one LM317 in the short shoulder (KCS) variety of TO-220 and clamp its bottom side to a big cooler looking like this: https://images-na.ssl-images-amazon.com/images/I/811Jg0bp8eL._SL1500_.jpg
Answer: Here is the circuit you should be using from the LM317 data sheet! You'll notice your resistors at 3 and 4 are there to protect the individual supplies from slightly different outputs.
In this example they're using an OP Amp to set the adjust voltage but you could actually just set them all the same (with fixed resistors) assuming you don't want it variable.
In any case you'll need a nice big heatsink to get this much current out of the chips. Id suggest using a large metal plate if you've got nothing else.
Hope that helps!
Comment: Only the last lm317 getting hot. Is that normal?
Answer: Have a look at the first circuit in LM317 High Current Voltage Regulator
Naturally TI prefers you to buy more TI circuits, but this solution is simpler and cheaper => better.

Need help on a simple circuit LM317T


Exception raised when invoking MembershipUser.ResetPassword() using OracleMembershipProvider

Question: In some cases, MembershipUser.ResetPassword() raises an exception. This only happens for some users, and it's not clear why. There are no inputs to the method, so it seems like a problem internal to Oracle's membership provider implementation.
The exception text: The provider returned an error that is not described by other MembershipCreateStatus enumeration values.
The traceback:
<code>at Oracle.Web.Security.OracleMembershipProvider.ResetPassword(String username, String passwordAnswer)
at System.Web.Security.MembershipUser.ResetPassword(String passwordAnswer)
at System.Web.Security.MembershipUser.ResetPassword()
...
</code>
Any idea what could be happening here?
Answer: Today I were having the same issue.
Answer is very simple. User account is LOCKED. Execute MembershipUser.UnlockUser() before password reset.


Is there a user manual for the Specialized bike serial number WSBC618222729N

Question: I was just trying to find a manual for my bike the brand is Specialized and all i could see was the serial number WSBC618222729N.  Been searching online but no success, any suggestions?
Cheers
Comment: What do you need help with? Most bicycle parts are from component manufacturers and the same between bike brands, and the rest are usually quite similar between brands.
Comment: Hi, welcome to bicycles.  I'm afraid serial numbers are rarely useful for anything, and bikes don't normally come with manuals.  You should ask about the specific problems/concerns you have rather than asking about an unknown bike in a general way.
Answer: Most bicycle sellers, including Specialized, don't have a manual that is specific to any one bike. The "manual" that sometimes comes with a bike is designed to cover a broad range of bike types so that one document can be used for many types of bikes.
As the comments indicate, the best thing to do is to ask specific questions with pictures.
Here is a link to the web page for the Specialized Support Center
The page has a list of links for information for the different models of bike Specialized contracts other companies to make with their branding.
Each link takes you to information for that model. For example, the Allez link looks like this:

The link to "Manuals" takes you to a PDF with lots of warnings and generalized instructions for safety, fit, and a section called "Tech" that has generic instructions for a variety of components that let them have one document for many different bikes in many different languages.


How to get Uniswap V3 price range by given tickUpper and tickLower?

Question: For example, there is an add uniswap v3 pool operation
The tickerUpper is -115000, the tickLower is -138000
What is the price range?
Answer: In Uniswap V3, the price range for a given tick range can be determined using the formula P = 1.0001^T, where
P represents the price ratio of token1 to token0, denoted as token1/token0, which aligns with the representation used for sqrtPriceX96 in the UniswapV3Pool, and T is the tick value. This formula was also correctly pointed out by @quentinadam
For the specific tick range in your question, [-138_000, -115_000], the calculation can be performed as follows:

For tickLower (-138,000), the price is calculated as P_{lower} = 1.0001^{-138,000} = 1.016332451797928e-06
For tickUpper (-115,000), the price is calculated as P_{upper} = 1.0001^{-115,000} = 1.0135919688900418e-05

These calculations yield the price range in terms of token1/token0
If you'd like to get the price in the context of solidity you can use the OracleLibrary.getQuoteAtTick function from Uniswap's v3-periphery. The example contract below implements a getPrice(int24 tick) function that returns the price for a given tick with 18 decimal precision:
import "@uniswap/v3-periphery/contracts/libraries/OracleLibrary.sol";

contract Price {
    function getPrice(int24 tick) external pure returns (uint256 priceU18) {
        priceU18 = OracleLibrary.getQuoteAtTick(
            tick,
            1e18, // fixed point to 18 decimals
            address(0), // since we want the price in terms of token1/token0
            address(1)
        );
    }
}

Using this contract, the prices for the ticks -138_000 and -115_000 as returned by getPrice was found to be 1016332451796 and 10135919688887 respectively, which aligns very closely with the previously calculated values after decimal scaling.
Answer: You need to take 1.0001 to the power of the tick to get the price.
For instance, for the tick -115000, the price would be 1.0001^(-115000) = 0.0000101359.
Please note that you need to take into account the number of decimals of each token, because the Uniswap price is expressed in units of token.
For instance, if the pool was WETH/USDC, a price of USDC 2000 for WETH would actually be expressed as 2000 * 1e-18 * 1e6 = 0.000000002, because WETH has 18 decimals and USDC has 6 decimals.