Stability of BJT circuit using Re resistor

Question: This is a post I found on Quora. I don't understand why decreasing Vbe decreases the current.
Vbe=Vb-Ve
To decrease Vbe you could increase Ve, Vb doesn't necessarily have to change, so neither Ib....
Comment: "Vb doesnt necessarily have to change, so neither Ib" - Wrong conclusion. V[be] *is* what matters. I[b] depends on V[be], not on V[b] alone.
Comment: Why does increasing Ic increase the voltage drop across the emitter?
Comment: You are misreading the explanation.  It's the transistor that's controlling \$I_C\$, but it's subject to changes in temperature.  ).  Re-read, *carefully*.  Consider that \$R_E\$ is 'trying' to keep the emitter current constant, and if the emitter current is constant, so is the collector current.
Comment: Michael_a general recommendation: Do not rely too much on Internet contributions.Here you are quoting Quora ...and in other contributions you have found some information in Wikipedia. I know Quora ....a lot of garbage!! Try to find a good textbook - that is the best knowledge source for beginners. Even in this forum, you can find wrong information.
Comment: Your base voltage is not fixed because the base does not have an important resistor to ground making a voltage divider. Then there is hardly any negative feedback from the emitter resistor.
Answer: To bias a bipolar transistor at 1milliAmp collector (emitter) current, you'll need approximately 0.600 volts Vbe.
For 10X less, at 100 microAmps, expect Vbe to be 0.600 - 0.058, or 0.542 volts.
For 100X less, at 10 microAmps, expect Vbe to be 0.600 - 2*0.058,
or 0.600 - 0.116 = 0.484 volts.
For 1,000X less, at 1 microAMps, expect 0.600 -3*0.058 = 0.600 - 0.174 = 0.426 volts across Vbe.
For 10,000X, at 100 nanoAmps, expect 0.600 - 4*0.058
This relation, where each 0.058 volt reduction in Vbe causes a 10:1 reduction in collector (emitter) current, comes from the exponential equation long trusted to describe behavior of a junction.
Vdiode = 2.718...^[(Q * Vdiode)/(K * T * n)]
where "n" is result of the abruptness (or lack of abruptness) of the transition from N doping to P doping in the base-emitter junction (Or the "diode" junction).
Note this equation has a strong factor of Temperature (Kelvin).
Classically, at a constant current the Vbe changes by 2 or 2.2 milliVolts per degree C (Kelvin). This behavior is crucial for most voltage references.
Answer: To decrease Vbe you can either lower Vb or increase Ve or both. Decreasing Vbe reduces base current because the base-emitter junction acts as a forward biased diode and lowering the forward voltage across a diode (Vbe) also reduces the current flow through it.
Answer: when someone analyses the temperature, they talk about a small phenomenon and then check that is positive feedback or negative feedback effects.(positive feedback generate instability)
For a simple example,
if you drop a fixed voltage on NTC(a resistor with a negative temperature coefficient) then the temperature is raised( even 0.1 degrees), then a small delta(T) even 0.1 degrees, generate a new R that is smaller than before:
R_new = R_old - NTC_Coef * delta-T
In fixed voltage, decreasing R, make current higher(V_fix/R) and then R*i^2 make the temperature higher than the last step, then makes R smaller -> increase temp -> R is smaller -> increase temp ... .this called positive feedback and not good, and you should avoid instability.
But for your example:
With temperature rise, we know the Beta and Ic will be raised, if Ic is raised even a small value,
V_emitter ~ Re*Ic
will be increased and then
Vcc_fixed = RB * IB + Vbe + Ie * Re ~ constant + Vbe + IC * Re
The equation shows the Vbe should be decreased and this decrease Ib(even pico amp) then Ic decrease,
inc temp -> inc Ic -> inc Beta -> decrease ic -> decrease temp injunction -> ...
This is a stable region for a circuit(all parameters microvolt, 0.1 degree, pico amp, ... )
It is a negative feedback effect, the circuit tries to work on a bias point, even changing the environment temperature.


Where can I download a large sample bibliography collection in BibTeX?

Question: I'm developing an application that works with BibTeX files, and I'd like to test it with a large collection produced not by myself, to be sure that the application will handle it correctly and to assess its responsiveness (with large I mean at least a thousand of entries). But I cannot find any such collection available for download, even though there are many resources that provide bibliographies for queries online via html-pages. Does anyone know where I can download a large .bib file? (The topic of the collection is irrelevant.)
Answer: For your purposes, I would highly recommend you to use The Collection of
Computer Science Bibliographies by Alf-Christian Achilles. This extensive collection contains 3M+ references on the various CS subjects (grouped in about 1500 collections) and, besides offering search and browse interfaces, allows one to download the actual bibliographic data in BibTeX format - just select a particular bibliography and you will see the links to the source files - uncompressed and/or zipped.
P.S. Don't forget to acknowledge the value of this resource to the maintainer of this meta-collection (a thank you note will do) and, perhaps, even attribute the source, if your software will be citable.
Comment: @jakebeal: Thank you! That's a long tail of the Web, I guess... :-)


Is it faster to print PDF or PS?

Question: Say I compiled a .tex file into ps and pdf. Will there be a difference in printing speed between pdf and ps?
Comment: If printing speed is your main concert, you'd be better off buying the fastest printer you can find. The time difference between printing PS and PDF files is likely to be trivial compared to the time it takes the pages to roll off.
Comment: Yep, usually the bottleneck is the printer, but for high-end operations PDF versus PS will actually matter.
Answer: The short answer is PDF will print faster.
According to Adobe:

So why is PDF more advanced than
  PostScript? A PDF file is actually a
  PostScript file which has already been
  interpreted by a RIP and made into
  clearly defined objects. These objects
  are viewable on screen not in code,
  but in visual objects that everyone
  can see. Because these files are
  already interpreted by the RIP, they
  can be more reliable than an EPS or a
  .PS file when printed. Additionally,
  because EPS files and .PS files can be
  easily converted to PDF and viewed on
  screen, print service providers can
  benefit from seeing the file after
  interpretation but before they send it
  to their printing devices. This may
  allow them to see errors in a file
  before wasting paper, film, or plates.
  This can be a terrific timesaver for
  people who run service bureaus or
  operate printers, and the result is
  that files print faster, more
  accurately, and with fewer errors.
Comment: But, if I print a PDF to my PostScript printer, wouldn't it be slower than just copying the PS file in?  Doesn't it have to convert PDF to PS, then send it out?
Comment: You're right! ;-)
Comment: thanks! surely i am neglecting actual paper roll off time as David M mentioned.
Comment: and if a PDF prints faster, then it will take longer to generate. You see the dilemma?
Answer: While the other answer is right, that the PDF-to-paper stage is faster (because the RIP stage is done already), if the original posting user is considering whether to generate  a PDF and then print to the printer, or generating postscript which they then just dump to the printer raw, then the same amount of work will be done, in total.   In fact, there may be some extra overhead with the creation of a much larger PDF file, which is them compressed, and which then includes more information (including fonts etc).
The difference is merely whether the RIP stage happens in printer or on PC.    It is possible that, measuring from the time that the user clicks "print", if you were both generating the PDF, and then sending it to the printer, versus just outputting your document directly as postscript, that it might even be faster (in some configurations) to print postscript, if your PC/operating-system PDF library of choice is less performant on your system than the dedicated RIP in your printer.
In short, it is not always an optimization, to have your application (if this is what you wanted to do) generate a PDF then send that to the printer.  If you don't need the PDF end product, and don't want to launch a preview (and save a tree) before comitting to paper, then skip the PDF generation, and you may not find any speed difference.
Of course, the smarter thing, rather than asking, would be to test your actual scenarios.
Answer: If your printer is able to consume PDF (accepts PDF as an input format for printing), then PDF printing is probably a bit faster. I say probably, because some PDFDirect printers do secretly convert incoming PDFs to PostScript first, fooling users to believe they contain a PDF RIP when that is untrue.
If your printer cannot consume PDF (even if it can consume PostScript), then you cannot tell in advance. It depends on your

operating system,
exact printer model,
printer driver you use for printing,
the currently used driver settings.

Depending on these factors, your OS' print subsystem and driver setup will convert the jobfiles (PDF/PostScript in your case) through a chain of converters/filters, and it is unpredictable how fast/slow that will work for each case. How do you open a PostScript file for printing? Or will you send it from the commandline to a non-PS printer? If so, how will it be converted to the real format your printer understands?
You should clarify your exact requirements and your environment, before you can expect any useful answer.
Answer: I'm pretty sure it depends on how your printer is set up: if you are going through ghostscript to a consumer-grade printer, it probably doesn't really make a difference; if you're printing directly to a smart printer which supports both, you'd best ask your printer manufacturer; if you are printing to a printer that can handle PostScript but not PDF, then the PDF will need some kind of translation -- this might be doable by with a PostScript program running on the printer, but whether that costs more than running application-generated PostScript code probably depends on what kind of code the application generates.
Personally, I tend to use PDF because this makes it so much easier to preview on (or print from) Windows machines, which are usually what I end up sitting at when I'm working on my LaTeX documents -- especially since I unplugged the monitor and keyboard from my Linux machine.
The only way to be sure which way is faster for your setup is to time the printing of a sufficiently-large document each way. (Does dvips time count? How about latex/pdflatex time?)

Is it faster to print PDF or PS?


Does ethstats.net include blocks with 0 transactions?

Question: Does the The Ethereum network status monitor (ethstats.net) include blocks with 0 transactions?
Thanks in advance.
Answer: Yes, blocks with 0 transactions are still valid blocks, and add to the security of the chain. There would be no reason not to show them, given that a block with 0 transactions potentially has other important characteristics, such as uncles.
Edit:
Note that transactions and uncles are stored separately from one another in the main body of the block, in two different lists. Block explorers, including ethstats.net (and etherscan.io), subsequently report them in two separate columns. Note also that when 0-transaction blocks are reported, they're reported with other useful attributes, such as block difficulty, block time, and network hashrate.
Comment: Hi Richard, doesn't an uncle count as a 'transaction"?  I would be grateful if you could clarify that part of your answer.


Turning Major to Minor

Question: I'm changing a song (When I Was Your Man) from a C major to C harmonic minor. I am not quite sure what to do with the Dm Em and Bb that exist in the major key. I have been using Ddim which has worked fine enough, but I have no ideas on how to handle the Em and Bb. What chords might work best in their place?
Answer: I'd generally substitute E♭ chords for the Em chords, since both correspond to mediants of their respective keys (C minor for E♭ and C major for Em).
I'd leave the B♭ chords well alone since they're common in C minor; I do not recommend using harmonic minor alone when changing tunes from major to minor.
If you insist you must use harmonic minor, then E♭ augmented and B° are your only options.
Answer: Don't worry too much about whether it's in the melodic, harmonic or natural minor scales. You don't have to stick to diatonic chords.  The original version didn't - it was in C but included Bb!
Modify the melody to have flattened 3rds and maybe flattened 6ths.   It seems there are some flattened 7ths there already.   You may not have to change as many chords as you imagine.   You're giving the song a different flavour, that's all.
Answer: Those basic chords in minor would be iio III VI or d diminished, Eb major, and Bb major.
As @LaurencePayne pointed out the Bb major is already used in the original form of the song.
I imagine you are getting stuck when trying to use III+ (Eb augmented.) If so, that's understandable, because the mediant chord in minor is normally a major chord not an augmented chord. (Minor key harmony isn't based simply on one form of minor scale, but that's another story.)
If the iio is working OK, great. You could also try the minor iv.

Turning Major to Minor


High VIF after removing intercept in R

Question: I'm doing a regression using R.Initially I used the fit=lm(data).Got all of my variables are significant including intercept.I checked the VIF using vif(fit) & got maximum VIF as 2.5. But my customer wants model without intercept and I don't have any option other than removing intercept. So I used following line of code
fit=lm(A ~ B+C+D+E+F-1,data=data) , I'm just coding the variables as it is client data & I can't share that.The data set I used in first model is same as the data set used in second model with same set of variables.Only in second model I removed intercept forcefully.
But after running the model I'm seeing my maximum vif is coming 2079.30. I'm not able to understand the reason for such high vif as I used to think that VIF determines how much the variance of a coefficient is "inflated" because of linear dependence with other predictors & it does not depend on intercept.
Can you expert please help me understand why VIF is drastically changed after removing intercept in R
Comment: It's generally (outside very specific cases) [not sensible](http://stats.stackexchange.com/a/7950/11849) to exclude the intercept. If the client forces you to do something like this it doesn't make sense to care about further statistical issues. In fact, if they know best how to do the statistical analysis, what is your role there?
Comment: The function `car::vif` provides an informative warning, "No intercept: vifs may not be sensible" when you try to calculate VIFs on models without an intercept.
Comment: Thanks a lot for your response. But how does intercept helps determining VIF? Can you please share with me some link(/s) so that I can read?
Answer: VIF depends on the intercept because there is an intercept in the regressions used to determine VIFs as described in "Step 1" here. When the intercept is out, then $R_i^2$ is not meaningful because it may be negative, in which case one can get VIF < 1, implying that the $s.e.(\beta_i)$ would go up if predictor $i$ were uncorrelated with the other predictors. You don't need to keep the intercept in the original model, but keep it for VIF computation.
Comment: Could you please explain the upward movement of se (beta i) when it is uncorrelated with the other predictors? Idealy, when two predictors are uncorrelated, their se must be low allowing them to be significant if their estimates are high enough.
Comment: How would the ratio of two sums of squared numbers ever become negative?

High VIF after removing intercept in R


Are introns conserved among cells?

Question: To elaborate on the title: Among somatic, post-mitotic cells, would the same intron on a given chromosome have the same sequence among all cells descended from a progenitor cell?
Comment: Could you perhaps edit your query to include those details with any appropriate references as comments are ephemeral in nature and we want to questions to be self-contained and last over time. Please also take our [tour] and refer to the [help] for guidance as to our ways.
Comment: Sorry for being unclear. I meant the same intron, on the same chromosome, in different cells. Also changed the question to reflect this.
Comment: Welcome to SE Biology! See [here](https://biology.stackexchange.com/help/how-to-ask) for some advice on ways to ask questions that are likely to get a helpful answer. Have you looked at any examples of introns on the same chromosome? Can you cite any sources suggesting what you ask is the case?
Comment: Hi I'm just asking out of curiosity. Not sure how, if I got a sequence, I would know whether that would be the same for each cell in a sample, given that genomes are assembled from several reads and sometimes individual bases are averaged, right? Just off the top of my head, I figured that since introns are not coding for proteins but do regulate gene expression, there would be less of a force for their sequence conservation between divisions from a stem-like progenitor, but that's why I'm asking.
Comment: I think that ignoring genome assembly for now may clarify the issue. I still don't understand the question. Are you referring to the _same_ intron across different cells, or _different_ introns on the same chromosome? Your comment makes it sound like the first, but your question makes it sound like the second.
Answer: I believe that the kind of mutation that you are interested in is somatic mutation, as opposed to germ-line mutation.
Any given genomic locus (intron, exon, intergenic region) probably doesn't mutate most of the time. In the case of somatic mutation, it is yet more likely that no mutation happens.
Nonetheless, such mutations do happen, in all of those different regions. For example, here is a study that catalogs somatic mutations in introns that lead to a particular phenomenon called intronic polyadenylation; here is another that catalogs intronic mutations that mess up splicing.
The same is true for protein-coding somatic mutations, one can find similar catalogs of mutations for those.
Such mutations in different regions (intronic, exonic, and otherwise) are all of interest as events that can lead to cancer.
None of this should distract us from that fact that usually mutations don't happen at any given site. But it's a question of probabilities, not of absolutes.
Comment: OK humor me this. What if you were trying to engineer, using some DNA editing technology, several cells in a sample at once, and wanted to precisely introduce a double-stranded break at some intronic site. Would the risk of somatic mutation ever be a concern? Thanks
Comment: @UD22022 Somatic mutation is always a possibility. But, frankly, the efficiency of gene editing technologies is (at a guess) a 2-3 orders of magnitude higher than the rate of somatic mutation. You could not exclude the possibility without recovering and analyzing the edited cells. But you generally have to isolate, select, and culture edited cells anyways. I would say that it is a theoretical concern worth keeping in mind examining data, but likely not a regular practical concern for gene editing compared to e.g. the rate of off-target effects of editing.

Are introns conserved among cells?


500 Internal Server Error on PHP Image Load

Question: This problem happened all of a sudden after Magento was working for 2 years.
When I load a page, a thumb.php GET request is made to load 6-7 images. Now most of them are loaded fine with a 200 response from thumb.php, but there is always 1 image that doesn't load right away and seems to be giving 500 internal server error. If I refresh the page it will load all the images without problem. It's very weird since some of the pages are loading all the images right away without any problem. Any suggestions?
Answer: You need to reset the permissions on your media folder and files.
run this from your Magento installation folder
find . -type f -exec chmod 644 {} \;
find . -type d -exec chmod 755 {} \;

If this fixes the problem you should then review the permissions of your Magento installation according to best practice. Further info here What permissions should I give /var and /media?
Also enabling error reporting within php will give you further information to the exact nature of the error instead of the unfriendly 500 Internal Server Error.


Pickling cars with simple management system in Python

Question: This is my first Python program (before that I've been just poking around with the interpreter itself). I took this opportunity to do some user input and play around with pickle.
I tried to made a system that reads input from the user (a car's name, year of launch and price), and then gives the power of exporting or importing it to an external file.
Is there any way to make this looks better (something that bothered me was my printing function and my super simple regex)? Is there any way that I can make this more pythonic? I've read many articles with this "pythonic" idea, and as I'm moving from Java, I'm afraid I might be losing something.
Made with python 3 in mind.
Example of input is:

add
Mitsubishi Eclipse
1999
1300.00

Here is the code.
import re
import pickle

class Car():
    def __init__(self, carName = None, year = None, cost = None):
        self.carName = carName if carName is not None else "undefined"
        self.year = year if year is not None else "undefined"
        self.cost = cost if cost is not None else "undefined"

cars = []
canImport = True #can only import if has already exported before or at program start

def addNewCar():
    """ Reads input from user and adds a new car to the current collection of cars.
        Year/Cost numeric validation are deliberately ommited """

    usr_input = input("Enter the car's name : (protip: if can enter the whole object by typing name/year/cost)\n-> ")
    match = re.search(r"\w+/\w+/\w+", usr_input)
    if match:
        name, year, cost = splitCarAttributes(match)
    else:
        name = usr_input
        year, cost = getCarAttributes()
    cars.append(Car(name, year, cost))

def splitCarAttributes(attributes):
    return attributes.group(0).split("/")

def getCarAttributes():
    year = input("Enter the car's launching year:\n-> ")
    cost = input("Enter the car's cost:\n-> ")
    return year, cost

def printCars():
    for i, car in enumerate(cars):
        print("Car #{:d}\n{{\n\tname:{:s}\n\tyear:{:s}\n\tcost:{:s}\n}}\n---\n".format(i+1, car.carName, car.year, car.cost))

def importCars():
    if not canImport
        print("You don't have anything to import.\n\n")
        return

    fileObject = open('cars', 'rb')
    importedCars = pickle.load(fileObject)
    for car in importedCars:
        cars.append(car)
    canImport = False
    printSuccess()

def exportCars():
    fileObject = open('cars', 'wb')
    pickle.dump(cars, fileObject)
    cars = [] # clears cars
    canImport = True
    printSuccess()

def printSuccess():
    print("\n\n--- Great success!\n\n")

def main():
    opt = ""
    while (opt != "exit" and opt != "q"):
        opt = input("Would you like to:\n- import all data\n- export all data\n- print all cars\n- add a new car to the collection?\n-> ").lower()
        if opt == "import":
            importCars()
        elif opt == "export":
            exportCars()
        elif opt == "add":
            addNewCar()
            printSuccess()
        elif opt == "print":
            printCars()

if __name__ == '__main__':
    main()

Edit: I just realized I'm calling printSuccess() in different contexts. Not gonna change the code now, just a heads up to clarify that I should move all to main() and maybe do some exception handling, but that's no the point right now.
Answer: def printCars():
    for i, car in enumerate(cars):
        print("Car #{:d}\n{{\n\tname:{:s}\n\tyear:{:s}\n\tcost:{:s}\n}}\n---\n".format(i+1, car.carName, car.year, car.cost))

cars is a global variable: that should be avoided.
Use dictionaries
    if opt == "import":
        importCars()
    elif opt == "export":
        exportCars()
    elif opt == "add":
        addNewCar()
        printSuccess()
    elif opt == "print":
        printCars()

should be a dictionary.

Also I feel like all your methods should be inside the car class as they are logically connected to it.


WF 3.5 stateful activities

Question: I'm using WF 3.5 and looking for a way to develop an activity preserving its state among different iterations of the standard WF "while" activity. The problem is that normally the Execute() method of an activity should return the "Closed" execution status. Once it did that - it cannot get back to the "Executing" state and in the next iteration a new clone of the activity is used and thus we lose the state of the first one. For example, I want my activity to sample the next line of an input file in each iteration. It requires maintaining a cursor for this file or in other words it requires a state. How can I achieve this functionality?
Answer: Why do you need to close your workflow? It seems it has not finished yet :) Consider have a loop and not closing until you have finished with it.
If you must close it and need to store the line number of the file for the "next run". Perhaps store that on the enitity it's running from.
Or having two workflows a controler that stores the file line number and calls the child workflows to do the processing.

WF 3.5 stateful activities


How can I force Thunderbird to download all emails by IMAP?

Question: I just created a new Thunderbird profile. Unfortunately Thunderbird only downloads recent messages. I need to get all my messages and subfolders. Any idea?
Comment: Worked for me out of the box when switching to offline mode. Only spam|junk|trash folders needed to be manually activated.
Answer: Go to Tools/Options/General/Config Editor or in more recent versions Edit/Preferences/Advanced/General/Config Editor.  This may vary between operating systems.
If presented with a

This might void your warranty!

dialog, click on the button "I'll be careful, I promise!".
Type folders_for_new in the filter box.
Look for an option called mail.check_all_imap_folders_for_new or on newer versions mail.server.default.check_all_folders_for_new.
Change this setting to true.  This has the effect of not treating inbox as special, but all folders are "inbox", so all folders will be checked and downloaded.
If this key does not exist, then add it (right click / new) exactly as it is written above as a boolean preference.  When you add the preference, you will be asked for the initial value.  Choose true.
Next, in Account Settings/the account you are referring to/Synchronisation & Storage ensure that "Synchronise all messages locally regardless of age" and "Keep messages for this account on this computer" are selected.
Comment: @EchtEinfachTV "Keep messages.." won't achieve what the OP is after, if the key isn't present, it needs to be added.
Answer: There should be a menu or button to "go offline"
In my current Thunderbird 17.0.2 (on Ubuntu 12.04), the button is at the lower-left corner of the whole application.
Clicking the button will start the download and if everything is configured correctly (i.e. has keep all messages regardless of age local) then that is what it will download
Comment: This is the key. Hitting the button in the bottom left corner will take you to offline mode and will give you the chance to force Thunderbird to download everything.
Answer: You have to check a box called "Keep messages for this account on this computer". Have a look at this tutorial for keeping IMAP messages in Thunderbird.
[
Comment: This option is already set. The main issue is that it doesn't get subfolders.
Comment: Have a look at the tutorial, they write about this, too.
Comment: I read that part as well. It seems that Thunderbird is not able to see subfolders. I am going to try with another mail client.
Answer: In the list of your accounts in the main window, and right click on the account name and click the "Subscribe..." option. You will then see the list of (sub)folders on the server, check the ones you want. They will now be synced with everything else.
Answer: To retrieve all messages in all folders and subfolders, regardless of age and whether the messages are new/unread or not:
From Thunderbird version 115 and later:

Right-click on the account and select 'Settings'.

In Synchronization & Storage, ensure Synchronize all messages regardless of age is selected.  By default, it is already selected.

Edit (ALT+E) -> Settings -> General -> (scroll to the bottom and select) Config Editor

Type '_folders' into the search bar.

Double-click on the entry, mail.server.default.check_all_folders_for_new to set the value to true. If the entry does not exist, create it.  By default, the entry already exists and is set to false.

6.  Click the online/offline icon in the bottom-left corner of the main reader pane/window.  This will start to get all messages not already got.  The status bar at the bottom will indicate it's getting messages from each folder.

Step 6 is the most important.  Previous answers focus on the mail.server.default.check_all_folders_for_new setting, but that is only part of the solution.  The clue is in the text - it only gets new/unread messages, not older ones.  You need to go into offline-mode to get the older/read messages.
Comment: I think the client being online is a reasonable assumption. Others already note making sure the client is set to download messages regardless of age.


Boot straight to grub without holding 'Option' on Macbook?

Question: I am dual-booting Lucid and Snow Leopard on a Macbook Pro 5,3. I have uninstalled rEFIt, and I am wondering if there is a way (without reinstalling rEFIt) to boot automatically to the GRUB menu without requiring me to hold Option and select the "Windows" partition at each boot. Since there is actually no Windows installation on my computer, I can't access the Boot Camp Assistant to tell OS X to boot to the Windows partition by default.
Comment: You may get an better answer from http://apple.stackexchange.com/ .

I'm just curios why do you need Ubuntu on a mac?
Comment: because the hardware is nice, but OSX sucks.
Answer: In OS X there is the Startup Drive section in System Preferences. Ideally you should be able to select Ubuntu as the default drive there. I wasn't able to, I just set refit to only show up for one second in the config file (not difficult to do). I only see refit for a split second so it doesn't really bother me.
Also if you only want to use GRUB, I'm assuming you still want access to OS X. Without chainloading GRUB you can't boot directly into OS X from the grub menu. The option is there but it won't work properly, so that's another reason to see refit for a second at bootup.
Comment: I didn't think of modifying the rEFIt config file to make it go away quickly---great suggestion! Maybe I'll just reinstall rEFIt and do that. I also wasn't aware that the option in GRUB to boot to OS X didn't work. Thanks!
Comment: Not a problem, good luck!
Answer: Hold down option while booting, but when the drives appear hold down the left control key before you click on the Windows drive.  That will change the appearance of the icon beneath the drive to a circular arrow, and if you click on that it should set that as the default selection for future boots without holding down option.  I'm not sure if that will help, but that is how it works on my Macbook Pro 5,2 dual booting OSX and Grub/Linux.


Getting usability issues in Google Search Console for the responses of API calls

Question: Today I found an error that appeared in GSC recently.
The URL of the affected page is not a page actually.
That's a example.com/api/v2/getcurrentuser API call that the JS is requesting to retrieve an active user.
When you go to that URL directly, it says:
{"type":-2,"msg":"You are not logged in"}

Just a blank text on a white screen.
GSC is returning 2 issues for the page:

Viewport not set
Text too small to read

We did not have such an issue a few days ago!
How to fix this?
Should we just decline robots?
Gev
Answer: API endpoints are usually not useful to have in Google Search Results, so the best thing to do would be to block them using robots.txt as you suggested.
These API endpoints are not supposed to be viewed directly by an end-user, so usability issues like "viewpoint not set" and "text too small to read" are nonsensical. I'm not sure how Google decided to try to index these API endpoints. There is no reason for Google to try to crawl them, so block them using robots.txt.
Someone else may suggest using a noindex HTTP header on these endpoints instead of using robots.txt, however that's not quite what we want. A noindex header tells Google "this is a page that we don't want in the search index" whereas a robots.txt disallow tells Google "there isn't any human-readable content at this URL so don't even try to parse it". So robots.txt is a better choice in this situation.


How actually an integral transformation(Fourier and Laplace) works?

Question: After seeing a question on one of the posts I got this confusion in my mind. Here I'm not much interested in just mathematical explanation but I would like
to know how a transformation actually turns a time domain signal to frequency domain. And what frequency domain representation actually means.Since the signal say a unit step has 0 frequency.
Is it just a plot of magnitude of signal with frequency parameter or there is more to it?
Comment: *After seeing a question on one of the posts I got this confusion in my mind*. Which question was it?
Comment: Laplace transform and the idea of frequency domain analysis
Comment: For info,the question OP is referring to is [here](http://electronics.stackexchange.com/questions/208458/laplace-transform-and-the-idea-of-frequency-domain-analysis).
Answer: I can only explain why they work mathematically, b/c the way time-domain functions get turned into s-domain functions is mathematically-based.
Fourier and Laplace Transforms are based on a mathematical concept known as an integral kernel. An integral kernel is defined to be the \$f(x,t)\$ term in an integral of the form:
$$
F(x) = \int_{t_0}^{t_1}f(x,t)g(t)dt
$$
\$f(x,t)\$ defines a family of functions parameterized by x, such as \$e^{-jxt}\$, for example. There are an infinite number of functions that take this form one for each (uncountably!) infinite number of values of \$x\$ from, for instance, \$-\infty\$ to \$\infty\$.
Let's assume we're given a value of \$x\$, call it \$x_0\$, and a function \$g(t)\$ that we want to analyze. Let's assume the domain is \$\pm\infty\$. The above integral can be written as:
$$
A = \int_{-\infty}^{\infty}f(x_0,t)g(t)dt
$$
The above integral is known as an inner product, analogous to the concept for vectors in linear algebra. Informally, an inner product produces a number \$A\$ which measures "how similar in shape is \$f(t)\$ to \$g(t)\$?".
It turns out by summing every single function of the family \$f(x,t)\$, each with a constant multiplier \$A\$ obtained by evaluating the inner product with \$g(t)\$ at each \$x\$, one can get the original \$g(t)\$ as a result.
Now, to answer your question, Fourier Transform decomposes a function \$g(t)\$ into a set of complex exponentials \$f(x,t)\$ of the form \$e^{-jxt}\$. These are very closely related to sinusoids of an angular velocity \$x_0\$ by taking the magnitude of the resulting complex number.
Laplace transforms are similar, but of the form \$e^{-xt}\$, where \$x\$ is a complex number, and \$t\$ is limited from 0 to \$\infty\$ (\$x\$ is normally called \$s\$ in this transform. I am using \$x\$ for consistency). They don't have as nice an intuitive interpretation that I'm aware of. Wikipedia says the Laplace Transform decomposes functions into moments. Analyzing the values of the Laplace transform for values of \$x\$ of the form \$jx_0\$ gets you back to the sinusoidal interpretation as above.
As Lorenzo also points out, there are convenient properties of integral transforms that appear in the frequency domain, such as convolution of two functions \$f(x_0, t)\$ and \$g(t)\$ become a multiplication in the s-domain.
Comment: @manav.tix The frequency domain can be thought of as sums of sinusoids that extend in time from \$-\infty\$ to \$\infty.\$ We trade information about time (since the sinusoids don't have a well-defined beginning and end) for information about sinusoidal content. Obviously, we can't create sinusoids like that in reality, but the model is still very useful.

Real signals are generated in the time domain, as a function of time, not as a function of infinitely-long sinusoids.
Comment: Thank for support, now I understand use of transforms, and their basic theory but I still have some confusion on what frequency domain representation implies in physical terms.
Comment: If you integrate over t, there won't be any t remaining in the result.
Comment: @ThePhoton Fixed my integrals. Not sure what I was thinking there.
Comment: @cr1901 Plz correct me if my assumption is flawed but then transformation changes entire signal and its properties but energy remains conserved thus the information stored too is saved. And we analyze the signal as a sum of sinusoids for various frequency value to see its amplitude variations.
Comment: I would rather say: the transformation changes the signal to another form that makes certain properties more readily apparent compared to the initial form. Every else you say is correct; the transformation doesn't create/destroy information (_or properties_), just converts the signal to an alternate form for the sake of analysis.
Answer: Well, from what you say it is not clear what you mean by "how the transform works", since you don't want a mathematical explanation. How transforms work is something mathematical.
Anyway, I guess you are interested in the rationale behind their application in the circuit engineering fields and the like.
In that respect you can view transforms as a way to represent a circuit or a signal in a different way, but a way that preserves (apart from pathological cases) the "information" of the original circuit/signal.
For example, when you apply Laplace transform to a circuit to perform transient analysis in the s-domain you are exploiting the math properties of the L-transform to simplify your work. And when you use it to compute the transfer function of a linear time-invariant system you are using the math properties of the L-transform to represent that system in a different, equivalent way. This equivalent representation can be advantageous, for instance, if you are interested in the stability of the system, since this property is related to the position of the poles of its transfer function.
To summarize, it is all about choosing the right representation that helps you analyze or design a circuit/system/signal in the easiest possible way. As an analogy, think of a civil engineer designing a building. He can choose different representations for the building according to what he is going to design: he must use technical drawing to represent the exact measurements for walls and other structures, but he may resort to 3D modeling (either real scaled-down models or CAD simulations) to see the impact of the building on the surrounding environment.
Comment: dear friend I from the line "I'm not much interested in just mathematical explanation" wanted that I would like its maths to be explained along with its physical applications. If you can make your answer more informative with maths then please go ahead. It would be great.
Answer: A Fourier transform is essentially the infinite period time (\$T\to\infty\$) limit of the Fourier Series. This means applying the transform will transform a time-dependent signal to it's frequency spectrum. Because \$T\to\infty\$ , the difference between the harmonic frequencies approaches zero, and the spectrum becomes continuous. By adding all the frequencies in the spectrum mathematically together again, you also get the inverse transform.


How to limit jobs in an indicated queue in SGE

Question: I have two queues in SGE for different purposes. Each of them has a limit in slots. What I want is to have only a certain number of jobs submitted to a queue waiting even when the other queue is idle. However, what I found is the additional jobs were assigned to the second queue.  How should I change the configuration?
Comment: I'm not sure I understand your question. You want jobs to wait for a queue to become available, up until you reach a certain number of jobs, and only then utilize the other queue?
Answer: You need to specify the queue name when submitting:
qsub -l qname=<queue name> ...
Then the other queue will not be used.


Subscriptions in PayPal

Question: I am working on integrating Recurring Payments functionality in Asp.Net based application where people can subscribe to a Service where they will be paying a monthly amount. I am trying to achieve the same using PayPal's Subscription APIs. One another aspect is where people will be making payments using their Credit Card instead of PayPal's account. I have tried to search for a sample code where I can see that Credit Card information is passed to the Subscription API but unable to find the same. Can anyone points me to a sample code where this is implemented or guide me on how I can do this?
Answer: PayPal does provide a Subscription only API for PayPal payments or Guest Checkout where buyer's prompt to create PayPal personal account. To achieve a Credit card subscription I'd reckon to refer to Braintree Vaulting functionality wherein you can have both Credit Card & PayPal.
Braintree Vault Overview:
Our Braintree Vault securely stores customer information – including payment method information – so you can safely keep customers on file.
The Vault is used to process payments with our recurring billing feature, and can also be used for non-recurring transactions so your customers don't need to re-enter their information each time they make a purchase from you.
https://articles.braintreepayments.com/control-panel/vault/overview
Thanks.

Subscriptions in PayPal


Geoserver, PostGIS and Postgres setup better on which web server?

Question: Is it better to have Jetty or Apache as a Webserver for GIS stack?
Answer: you can find very detailed information about Jetty and Apache httpd (from http://wiki.eclipse.org/). i think you should decide what you want from a web server more precisely according to the expectations.

Apache httpd is a HTTP server written in C, that is often used to
  front other web services. Jetty is a full functional and optimized
  HTTP server and has no need of an apache httpd instance between it and
  the internet. However, deployers often want to place an instance of
  apache between Jetty and the internet for some of the following
  "reasons":
Performance. Apache Httpd does have slightly superior performance to jetty for pure HTTP request handling. However, for dynamic response
  generation, apache must pass the request to another process and the
  resulting double handling reduces the total throughput to less than
  direct requests to Jetty. More over, with the advent of comet style
  web applications, long held requests are common and the apache thread
  model assigns a thread per outstanding request, so apache does not
  scale to large numbers of comet connections.
Static content. Apache Httpd is very good at serving static content fast. However, Jetty is no slouch either as it can use direct
  memory mapped buffers for static content, so that only kernel space is
  used for the data transfer. Besides, if your application has a lot of
  static content, then you will get much better results by either
  ensuring good client caching or serving the content from an CDNS edge
  cache.
Security. Some believe that apache gives them a more secure solution as there are no TCP/IP connections terminating on Jetty.
  However, since Jetty is written in Java, it is not vulnerable to the
  class of security exploit that a server written in C is. Jetty has a
  good security record, but has had some past issues, but mostly of the
  nature that would not have been helped by a fronting instance of
  Apache.
Load Balancing. Apache has several options for load balancing between multiple servlet servers. These solutions are reasonable, but
  there are better software and appliance load balancers available. The
  main limitation of apache as a load balancer is that it's threading
  model is not-asynchronous, so scaling is limited (specially for comet
  traffic).
Administration. Often an enterprise has staff who are very familiar with apache and thus have a strong preference to deploy
  everything behind apache. This can be a good reason to avoid chaos in
  a deployment environment, so long as some of the performance and
  scalability limitations do not affect your web application.

i hope it helps you...
Comment: As aways your answer is clean and detailed. Thanks @Aragon.
Comment: you're welcome. my only wish to share something useful for people. :)
Comment: So nither are superior than other, however Apache seems to attract more crowd then Jetty I guess. :) I will go with Apache and setup my GIS stack. Thanks Aragon!
Answer: I only find sense in using Jetty, Tomcat or the like when the middleware you are going to use is Java based (GeoServer). Otherwise, a HTTP server like Apache is, in my opinion, a better solution.
As pointed in another response, one of the pros of Apache is that in many workplaces there is staff already used to work with this HTTP server. In case you have the freedom to choose another HTTP server, I would give a try to nginx or lighttpd, both open source and ready to be used in heavy-load production environments.
These HTTP servers typically demand much less RAM memory and CPU than Apache. Another advantage is that they are easier to configure; I find Apache configuration barroque.
Personally I have used lighttpd to set up several GIS based on MapServer, and the results have been satisfactory.
Comment: Thanks dariapra. Nice insights and notes for my future GIS  setups :)
Answer: Jetty is way better in performance and concurrency serving.


Cant unlock phone after using Google's Find my Device

Question: I forgot my phone's pattern lock, when I used Google's Find my Device, it just locks my phone and I don't know what to do. How can I get back in to my phone?
Answer: I don't know how new your phone is, but some of the older builds allow you to do a factory data reset, and it clears off the password. If you were lucky and had USB debugging enabled at the time of locking it up, you could do a backup of your stuff to your computer before you do the factory reset. I use Mobogenie, although some people say it's buggy, and it does have a lot of adware. I'm fairly sure you should be able to use Mobogenie on it even if the device is locked.
By the way, as far as i know, Google's Find My Device is for only if it's lost or stolen and you want to find it, or lock it up so a thief can't access it.
EDIT: To unlock your phone via ADB without factory reset(if you had USB debugging enabled), read this answer to another post here.


Arrangement of elements in the reactivity series

Question: I have seen a variety of reactivity series of elements online and also have consulted some books regarding the arrangement of the elements. I understand that the arrangement of elements is based on degree of reactivity of elements with cold water, steam, oxygen, dilute acids etc.
Lithium is less reactive with respect to the criteria mentioned above yet it is placed on the top of more reactive elements in the reactivity series that I have observed.
What is the reason for the position of Lithium above let us say potassium and sodium which are more reactive.
Link to one of the references:
https://kaiserscience.wordpress.com/chemistry/metal-reactivity-series/
Comment: The electrode potentials in water, really aqueous acid, are free energy deltaG[0] changes of the reaction with H2 or H+ ions Everything in their standard states, to equilibrium. If it sounds complicated it is because it is complicated. It takes into account all the various heats and entropies. What is of limited importance is the apparent reactivity. Li reacts more sedately than Na or K or frightenly reactive Cs[The differences really are very small] but seems to go farther when done. The relative energies will change if products change by changes in solubility or by complexation
Answer: The reason that lithium is on the top of the activity series is due to its behavior in aqueous reactions with water and acid. Due to the lithium atom's very small size (only two energy levels), the lithium ion interacts well with water forming ion-dipole interactions.  The lithium atom's small size compared to sodium and potassium is more entropically favorable in the formation of ion-dipole interactions with water and consequently so are reactions involving lithium ion formation favored to to other alkali metals.
The reasoning behind this is that reactions favor a greater state of entropy (disorder) in the universe. With larger cations, more water molecules have to become ordered around the cation to form the appropriate ion-dipole interaction.  However, due to the lithium cation's small size, less water molecules are required to form the ion-dipole interaction, thus less order, being more favorable in terms of entropy.


Unreal Engine and Simple Animation

Question: I am creating a card based game and I am stuck on an animation detail.
My question is I need an animation to shuffle the deck, a animation for dealing and  an animation for drawing.
My question is should I create the animations in Unreal Engine or would I create them in blender. I know traditionally with characters and other animations you would create them within blender. However I am unsure in this instance as we are talking about simply shuffling, dealing, and drawing cards.
Comment: How the animations should look like ? - dealing for instance could be just a "tweening" animations.
Answer: I guess that should not make much of a difference you obviously can import animations from blender so that wont be a problem.
Answer: If you are already familiar with unreal, animation/modeling and simple, I think you could use it.
Especially if you are going to do a simple animation (just moving the cards with simple moves).
Now if you want something more refined, with the cards rotating on some axis, I think it would be easier for the blender. Because I believe that if you need help you will find it easier, both here in the forum and on youtube.

Unreal Engine and Simple Animation


Java/Android: anonymous local classes vs named classes

Question: I would like to ask what is the good practice on using anonymous classes vs. named inner classes?
I am writing an Android application, which includes many UI elements (buttons, text fields, etc). For many of them I need some kind of listeners, so in onCreate of the application I have bunch of quite small anonymous classes like:
someButton.setOnClickListener(
    new View.OnClickListener() {
        public void onClick(View v) {
            // do something...
        }
    }
);

Each of of such anonymous class is 5 - 20 lines big - small enough and fits good for recommendations from Java™ in a Nutshell book:

In general, you should consider using an anonymous class instead of a local class if:

The class has a very short body.
Only one instance of the class is needed.
The class is used right after it is defined.
The name of the class does not make your code any easier to understand.

But the problem, IMO, is that onCreate becomes quite big and the code becomes more complex to read and understand by quick looking in to it. It is still easy to understand, but simply too big.
So what would be better practice in such case - have bunch of small inner sub-classes, where each of it is nicely separated , but used just once or better keep using anonymous classes instead?
Comment: my experience: keep continue using anonymous class but, try to move some part of your code to one (or more) private method(s) and call it (them) from onCreate method.
Answer: I don't think there is a clear answer one way or the other.  Both styles work fine, its really just what you prefer.
Another option is to have
the contents of each onClick by a single function call, which will keep the anonymous classes very short.  I.e:
someButton.setOnClickListener(
    new View.OnClickListener() {
        public void onClick(View v) {
            doSomeButtonClick();
        }
    }
);

private void doSomeButtonClick() {
  // do something
}

Answer: Refactor the onCreate() into separate methods grouped by common functionality so you have logical units.  If the GUI is complex then it will help you later.
EDIT:
Also, since you are by default indented more by a code formatter when inside an anonymous class your lines need to be shorter to avoid being broken over several lines by the formatter making it longer.  This is usually the thing that make it clear that it would be a good time to extract the class and give it a name.
Answer: I do Desktop/Swing applications, but I think the concepts are the same.
I prefer to handle all of the events in one class, so I create a Controller class and implement all of the listeners I need in that one class.  Then, I create a method on the panel for each type of listener.  It adds the listener to each component in the panel that it needs to listen to.  I pass the panel as the first argument to the Controller class's constructor and have it call each of those add listener methods on the panel.  Then I instantiate the controller when I instantiate the panel.
This gives me several advantages:

All of the event handling code is in one class.
Any crossover in functionality between events is easily caught and handled.
Any state that's affected can be stored and controlled in one class.
All event handling code is separate from the component layout code.
The View layer (Panel) doesn't know anything about the Controller layer.

That being said, if the events you're hooking up all do simple things, and these things don't conflict with other events, then it's not wrong to use anonymous classes.
Comment: This is great technique you're using. I think, it is very useful when you have many interactions between UI components. Although Mayra suggestion probably fits more for my needs, but still - really good idea. I'll keep it in my mind for future, thanks!
Answer: I don't know if it's considered by the community as a best practice, but when this sort of class gets too big, I create a package listener and create my class in it. Why use inner class or anonymous class if it gets in your way later in your code.
But most of the time, if this kind of class gets big, it's because you didn't delegate enough. Maybe other classes should have methods that help your listener to be lighter.
Answer: As the quote suggests, this is something that is subjective. You need to figure out what counts as "very short" and "easier to understand" for yourself, to determine at what point the code size crosses the line from something that makes sense as an anonymous class to something that makes sense to be it's own unit.
Any answers anyone would give you on this is based on their own subjective measures of what "short" is and how many lines of code it takes to no longer be "short".
Answer: You have several advantages to putting these items in named classes.
The first is the one you mention--it will make the onCreate() method more concise and understandable.
The second is that the name should quickly identify which logic goes with which button, which will make the code cleared
The third is easier separation of duties.  If you should decide to go to an IoC model, you'll have a much easier time injecting named implementations of the listeners.


Something similar to MBA, but with support?

Question: If someone can't afford to go to school for an MBA, but wants to train to be a manager, is there some compatible Master's, which has a reasonable level of support (teaching assistantships)?
Comment: Seeing from your profile that you're American - most MBA students in the US are people who already have some business experience at a junior level and are going back to school for more education and networking.  I would suggest you apply for management trainee positions at large chains or conglomerates, junior investment banking positions, and junior consultant positions at consulting companies.  Most people hired in these positions are arts/sciences graduates without business degrees.  Companies will frequently (partially) fund MBAs for their most promising junior managers.
Comment: @AlexanderWoo - Thanks.  I'm not asking for myself.  Your comment is very helpful -- why don't you put it in an answer?
Answer: I would definitely suggest the Chartered Financial Analyst program (aka, the CFA exam, https://www.cfainstitute.org/pages/index.aspx) for learning the few "hard" skills I would expect a business manager to have -
 such as, accounting, basic finance, elementary quantitative/organizational skills, etc.
Not only is it basically free compared to the cost of an MBA - total cost = $4000 is possible - it is, with regard to the relevant, real, demonstrable skills and knowledge base, far more rigorous and comprehensive than probably any MBA program (explanation below).
While I am not exactly sure what you mean by "a reasonable level of support (teaching assistantships)", if interpreted as "a desire to obtain requisite knowledge", I believe this is the best route available regardless of how much money you have. If that interpretation is incorrect, then hopefully the following will help out a bit.
While the CFA program is considered to be a graduate level program, it is not an actual university "Master's". This may be of concern when considering the culture of management and, more generally, business today.
First of all, you can get an MBA in about 2 years. Furthermore, you can do so while applying very little effort. Of course this all depends on the school, whereas the CFA takes at least 4, if you make it through. (Last I saw, success rates for the level 1 exam were 33% - has there ever been an MBA program that failed 2/3's of their freshmen class in any given year? Levels 2 and 3 have rates slightly higher, somewhere around 45-50%)
Combined with the notion that university education, especially in these related fields, has been transformed almost completely into an instrument for class division and social hierarchy (and away from learning and education), it may be (and I am certain it is) that an MBA is not for training, knowledge, skills, performance, etc, etc. but rather as a prerequisite for acceptance into the management/business class/social structure.
For evidence of this see the growth in the administrative body of universities compared to faculty and combined with absurd growth in the costs of it and ask yourself what this does to the society at large and why it is necessary. Not satisfied? Need a stat?
According to the article by Andy Beckett in a recent Guardian publication, "In 2017, half of recent UK graduates were officially classified as "working in a non-graduate role."[1]
Combine those tidbits with the fact that evaluating the success, merit or performance of managers, or of the tatics/skills/curriculum generally associated with their education is extremely difficult if not impossible. And the idea that what you are really paying for with an MBA is the acceptance into a social class may at least seem plausible.
Now, it is apparent that I am not a fan of the whole business world and the state of higher education but, I think it is hard to argue that the value in the MBA program is not, at least in some material way, dependent on what it means for one's social status. And this value must be accounted for when accessing the CFA program which is void of such factors.
Another commonly referred to source of business school value is that of "networking". I'd love to trash that idea as it is literally the opposite of what university education purports to be (pursuit of knowledge, anyone?) but, it does in fact hold some value somehow, and that source of value is absent from the CFA.
And, in demonstrating evidence for my claims against b-school and management and to back up the idea that we cant even be sure if any of it or its teachings have any value or truth at all, don't forget that the business/MBA led world recently failed to predict, understand, or even recognize the complete collapse of the system they were suppose to understand and were completely in charge of.
If you can ignore the emotions such a statement and its content may invoke and realize that my goal is to compare the program I suggested as an answer to your question, then it should be evident that while the points I have made may be debatable, hold some amount of truth. Because of this and that I don't think I fully understand what you are looking for, I think these points are relevant when considering alternatives.
Anyways, this got long, point is, if you are seeking to learn management principles you would be fine in buying maybe a couple hundred bucks worth of books. This is essentially the CFA is combined with a difficult exam to validate yourself with. Whatever the case, best of luck.[2]
[1] https://www.theguardian.com/news/2018/jan/19/post-work-the-radical-idea-of-a-world-without-jobs
[2] Full disclosure,I passed the first 2 levels of the exam before focussing on software development. But I can attest the fact that it is pretty difficult but definitely achievable.
Comment: Crap, I should have mentioned, if by "teaching assistantships" you mean a program that provides instruction and access to teachers and other experts, the CFA is NOT what you are looking for as it is totally self-study - you literally get like 40 pounds of books in the mail one day and a date and location to show up at to take a 6 hour long exam a year later. I know that there are a lot of courses and other 3rd party related things you could optionally attend if you need further assistance. This will raise cost, but compared to MBA, itd still be cheap.


Group isomorphism between $D_3$ and $S_3$

Question: If one wants to prove that $D_3$ is isomorphic to $S_3$, would it be sufficient to define a homomorphism $\psi: D_3\to S_3$ and argue that it is well-defined since $\psi(sr^i)=\psi(s)\psi(r)^i=\sigma_i\sigma_j = \psi(r^{-i}s)=\sigma_j^{-1} \sigma_i$ (where $\sigma_i$ is a transposition and $\sigma_j$ is a 3-cycle)? And then show that this homomorphism is injective and surjective.
Answer: I would show more generally that $D_n \leq S_n$. When their orders are the same, they are isomorphic. The trick is to find permutation representations of $r, s$, the generators for the Dihedral group.
Comment: It appears that $s$ can be represented by any 2-cycle in $S_3$ and $r$ can be represented by any 3-cycle.


I installed anaconda and since then I am getting (base) in the terminal, and it has slowed the system down

Question: I know it will go away when I type in
conda deactivate

but that is not it, I have also seen that my system has slowed down since I installed Anaconda. It was because of this, I have been fiddling with it just to get rid of slowdowns.
I downloaded it using
wget http://repo.continuum.io/archive/Anaconda3-2020.02-Linux-x86_64.sh

After downloading that I installed it in again by
supreetsingh@zeppelin:~/Downloads$ bash ./Anaconda3-2020.02-Linux-x86_64.sh

Changed the location of the install to
[/home/supreetsingh/anaconda3] >>> /home/supreetsingh/dodge/anaconda3

Did this
Do you wish the installer to initialize Anaconda3
by running conda init? [yes|no]
[no] >>> no

Conda was installed and the command conda was working.
I updated all the packages
supreetsingh@zeppelin:~/Downloads$ conda update --all

Did this to initialise conda
supreetsingh@zeppelin:~/Downloads$ conda init bash

After that, as the instructions asked me to run this command then I did this
supreetsingh@zeppelin:~/Downloads$ /home/supreetsingh/dodge/anaconda3/bin/conda shell.bash hook

Everything is working fine, I just want to remove the (base) that comes every time when I start the terminal and it is slowing down the terminal. Also would like to know if there is a better way to install Anaconda.
 (base)supreetsingh@zeppelin

Answer: Just do after activating conda
conda config --set auto_activate_base false


Code for Degrees not

Question: Using Audrino Nano and MKS SERVO42 42 Stepper Motor With Driver Board Closed Loop with the LCD. I have got the motor going by using the menu on board. Now able to run Code1 https://github.com/makertut/Arduino-Closed-loop.git out of GitHub and it runs as it is designed. Line 5 int numstep = 1030; cc runs the number of steps indicated and changing this number will determine the movement.
I can do the math to calculate the degrees for number of step for a particular stepper. I would like to use degrees instead of steps for my program. Does anybody know how to code this?
Thanks Greg
Comment: convert the angle to step count
Comment: You can find the number of steps per revolution in the specification of the stepper motor. Then just calculate the angle from the steps. Simple rule of three
Comment: If you can calculate the number of steps per degree you can calculate the number of degrees per step. It's high school math. Not even high school math. It's bordering on preschool math...
Comment: Thanks for reply. I said I could do the math in my question. Maybe I wasn't clear in my question or didn't supply enough info. I going to monitor multiple sensors, When one sensor is detected I want the stepper to turn to a certain degree such as 45, If another, different sensor is detected it would move to that place say 90.  Every sensor would be assign a specific degree or position.  Will steps act the same as degrees?  If  the stepper is at 90 degrees (or 50 steps) and the first sensor is then detected will it move to the 45 degree position (or 25 steps) position.   360/1.8=200
Answer: This is basic algebra 1.
Say steps / degree = 5
So write that as 2 fractions:
steps   5
----- = -
degree  1

Then take the reciprocal of both sides:
degrees   1
------- = -
step      5

Code for Degrees not


Work done by friction in pure rolling

Question: I just want a clarity about work done by friction in pure rolling when external force is acting. So suppose we have a ring and an external force is applied at the centre, the ground has friction. After some time pure rolling starts such that $a = r* alpha$. After this is work done by friction still zero. Because although the point of contact is at rest but rotational speed is increasing due to angular acceleration so there should be a rotational work done by friction? Please if anyone can clarify
Comment: [Is work done in rolling friction?](https://physics.stackexchange.com/q/158878/37364), [How can friction do no work in case of pure rolling?](https://physics.stackexchange.com/q/465017/37364)
Comment: Because pure rolling happens when point of contact is not getting displaced with respect to ground if body is pure rolling on ground which means displacement of point of application of force is zero and hence work done by friction is zero
Answer: If you want to write work in two parts,
$$W_{tot} = \int \vec{F}\cdot d\vec{s}_{trans} + \int \vec{\tau}\cdot d\theta$$
Then yes, the part due to torque will be non zero. However, first term will be negative to make sure that the total work is zero.
To evaluate the first term, recall that we only have to consider translational motion. Accounting for translational motion of the ball and assuming constant friction force,
$$dW_{trans} = - f_{fric} ds$$
Where ds is small translational displacement of the ball. Now, for the rotational work,
$$dW_{rot} = f_{fric} r d\theta$$
But remember that for pure rolling, $ds=rd\theta$. So,
$$dW_{rot}= f_{fric} ds$$
Thus, $$dW_{tot} = dW_{trans} + dW_{rot} = 0$$
Comment: Thank You! Just one more thing, So if the lower surface was also moving. Let's say this ring was pure rolling on a moving plank, then the net work done by friction would not be zero right? because there is displacement of the plank with respect to ground!
Comment: No, it'd still be zero. If a ring is pure rolling on a moving plank, it actually means that the ring is in pure roll with respect to the plank. So, application point of friction on the plank still has no velocity and thus 0 work.
Comment: But with respect to the ground, the point is moving and it is getting displaced as well. With respect to the plank the point is at rest but not with respect to ground and if we calculate work done in ground frame then friction is there and there is also displacement with respect to ground !!
Comment: The application point of the force is moving with the body as well
Comment: Exactly the application point is moving! So then work done by friction should not be zero because it has a displacement right?
Comment: But I do understand it if we will take whole ring and plank as a system then net work done by friction is zero because f is doing negative work for ring and same positive work for plank so as a system it should be zero but if we talk individually on ring I think it should not be zero in this case.

Work done by friction in pure rolling


Android Fragment Active on Opening

Question: I am using ViewPager. I have 3 fragments (A,B,C) and two of them(A & C) are populating ListView from the server, so it will take a few seconds for that. And I am showing a ProgressDialog. B is the fragment which is set to show first and its is not having any background process, having a few buttons only.
So the problem is that the ProgressDialog will always show upon creating that activity,that is all the Fragments are loaded always.
So I wonder if I can load the specific Fragment only (A or C) when I open it (Slide) so that the user who want to use the Icon menu (B fragment) should not need to wait for the other fragments (A & C) to load. I am not sure whether its possible or not. Can anyone suggest me any code snippets or references to achieve it. Any help regarding this will be really appreciated.
Answer: Nevermind, I had done it easily with AsyncTask and the Fragments are updated in background

Android Fragment Active on Opening


Closed questions

Question: Once a question is closed, shouldn't any comments also be closed? The "is there a way to design a realistic religion" question is turning into a debate forum completely inappropriate to SE.
Comment: It doesn't matter that the question was closed. That discussion should have been migrated to chat.
Comment: I agree. It's not a proper use of SE to debate opinions.
Answer: No, comments should not be closed. This is because questions being closed is a temporary measure. If and when the question has had the problems with it fixed (if that is possible) then it can be opened and the comments are a vital part of that process.
If there is specific abuse of comments happening in one question then that should be dealt with there. Looking at the question though I only see 4 or 5 new comments in the last day, not enough to worry about yet although it would be better taken to chat and if the number of comments does explode a moderator will most likely step in and enforce that.
Comment: The question was closed as too broad. If your reasoning is correct, comments not specifically aimed toward narrowing the question should be flagged as inappropriate. Yes?
Comment: @CAgrippa Why? The comments pointed out reasons why the question should be closed, which could be useful in the future. There was no debate. I agree that chat was a possibility, though.

Closed questions


Start without any sound?

Question: How can you disable the startup-sound? I mean the drums when you login.
Edit: I have tried disabling Gnome Login Sound, but it keeps drumming.
And also set the volume to muted so that it sticks? Now when I press mute on keyboard the first keypress seems to lower the volume instead, and thus plays a sound. Second keypress works.
I would like to start without any sound at all.
Thanks
Answer: Just log out, then click on the little speaker icon in the upper right hand corner of the login screen.  Set the volume here to Mute.

Start without any sound?


Am I exercising out too much?

Question: So I am a 17 year old fat boy with a height of 5'9" and weigh around 183 pounds. I can't change my eating habits, I just love fast food and could't resist. So I decided to exercise as much as possible. Currently, per day, I cycle 14 klicks daily on a flat road and cycle around 7 klicks in the gym. I walk 4 klicks on a flat road and jog for around 1 klick on a treadmill. I spend around 10-12 minutes on an elliptical, burning about a hundred calories. Is this too much? I feel very tired sometimes. P.S: I don't lift weights.
Comment: It's easier to just not eat calories than burning them off. Having that said, many people jog/cycle to work as their commute much farther than you exercise every day. You can do it, but you need to build up endurance.
Comment: Here's a good [video](https://www.youtube.com/watch?v=UQbuzsY_34Q) to illustrate diet vs exercise.  You may want to reconsider your fast food.
Answer: Apart from what @Boris and @Josaur said, I would like to suggest you some tips as you are only 17 years old.

Durability and quality of structure always depends on the raw materials that has been used for its construction. So, to start with you can't just think about having a healthy body without following proper healthy diet.
As you are just 17 years old and consuming cold drinks daily along with junks 2 times a week, its not good for your body in longer run. May be you wont feel the difference for next 7-8 years but gradually it'll take its toll.
For losing weight, this exercise in not that much sufficient given that you are having junks, chocolates and cold drinks so often. Reduce junks to once in a week at least along with cold drinks. Bro, you should watch out for the heavy amount of sugar that you are taking. It will surely hit your body hard and bad in long run inviting several diseases.
There are 2 things because of which you might be feeling tired:

You are not taking taking proper rest (7-8 hrs is a must if you are involved in physical exercises)
Your body is not getting proper energy from the food you are eating. You can't expect a bike to run on water , it needs petrol. Similarly you need to consume protein & carbs rich diet to fuel your body

So, give utmost respect to your body because you can change everything but your body
Answer: So in total, you cycle/run 22km, plus 12 minutes on the elliptical (5km I guess).
Is it too much? That depends on what your goals are.

If you want to lose fat, that's not enough, given that you eat junk food (every day?). And you don't tell much about the intensity of your training, which also plays a role in that. As said by @cbll, the first step to lose weight is your diet. Unless you train like an athlete several hours per day (more than 5 hours), don't expect to burn more calories than your fast food provides
If you just want to do cardio, it might be a bit too much, because you don't give your body enough rest, that's why you feel tired. But it is also linked to your diet : if you don't eat well, you won't rest well. Your body needs good "fuel" to perform.
Comment: Umm.. No, actually, I dont eat junk food everyday, it's more like once every three days..
Comment: Eat chocolates and drink cold drinks everyday, though..
Answer: Are you exercising too much? If you have no rest day in your week then yes. Otherwise, no (assuming you are getting 7-8 hours of sleep a night).
Is your diet making you tired? Yes, lots of junk food is not providing your body with fuel it needs to recover, eventually you will just be tired and fat.

Am I exercising out too much?


What is causing my brand new tankless water heaterto knock?

Question: I just had a Navien tankless water heater installed. It works fairly quietly when in use, but there is a knocking sound from the unit or the copper pipes hours AFTER it has been used (typically in the middle of the night).  It usually makes 3-4 quick knocks in rapid succession.
Comment: So this noise does not occur every time, only when it's used at night?
Answer: Most likely, that is just the sound of the pipes contracting again after expanding from the heating cycle.  With an on-demand water heater, the difference in temperature in the water lines is much more drastic than with a tank-style heater with 50 or so gallons of liquid to act as a buffer.
Some of that is probably never going to go away, but to reduce the noise, you could try slightly loosening any pipe clamps near the heater that you can access.  It's possible that the installer snugged them down really tight and they are binding as the pipes expand and contract.


aluminum foam capacitor

Question: Sorry if this question is in the wrong community but anyway, why don't people use foam aluminium for capacitors? Its got a large surface area to my understanding (however probably not as much surface area as activated carbon) which should give it a good capacitance, right? Thanks for reading.
Comment: It's not just about large surface area. You need a large surface area between two conductors that are very close, but slightly separated by a dielectric. Getting another conductor close to the aluminium foam will probably be challenging, compared to a flat aluminium foil that can be anodized and rolled up.
Comment: Interesting question. Tantalum capacitors make use of a similar idea where the high surface area of a volume of sintered tantalum provides high capacitance. The sintered tantalum is the anode, and the cathode is either an electrolyte that saturates the bulk or a conductive layer chemically built up throughout the porous bulk. Perhaps it's hard to make foam aluminum with a sufficiently fine structure; perhaps aluminum foam has been tried but was unsuccessful for other reasons -- but maybe you have an idea that's worth investigating further.
Comment: I don't know the answer but I can make some guesses. 1. What is the characteristic size of the voids in aluminum foam? Many capacitors have dimensions measured in fractions of a mm. 2. Does aluminum foam maintain some conductivity through the bulk? Because if it does that would defeat the purpose of using a capacitor in many situations.
Comment: Thanks for the feedback, honesty, I never thought of having to roll it up :). And only some aluminium foam is closed cell, you can get open cell.
Answer: Because only a small fraction of that surface area woyld be exposed to the other plate of the capacitor. A way would have to be found to coat the foam in an insulating substance then in another conductive substance throughout its whole volume. Also, it would not be as efficient as an electrolytic capacitor which has an insulating layer molecules thick, which is chemically formed after assembly.

aluminum foam capacitor


Main Dial stops working on Canon EOS 7D

Question: The main dial on my Canon 7D has started to intermittently stop functioning.  Powering it off for several minutes has always brought it back.  Am I the problem or do I have a camera problem?
Answer: You may just have a slipping Main Dial. It can be fixed yourself if you are just a little "handy".
Fixing a Slipping Main Dial on a Canon DSLR

In recent months, the main dial on one of my Canon 50D DSLR cameras would slip when attempting to rotate it.
The slipping occurs more frequently in one direction than the other
  direction, and also appears to be weather-related, occurring more
  frequently in hotter weather.
This was particularly annoying, as most of my photography sees my
  camera mode set to aperture priority, and without a fully functional
  main dial, it was difficult to quickly adjust the aperture.
It turns out this appears to be a relatively common issue with some of
  the Canon DSLRs, including the 30D, 40D and 50D.
Getting the dial assembly replaced by Canon will apparently cost you
  about USD$150.
On closer inspection, it was clear that the rubber grip on the dial
  was slipping on the inner plastic wheel. Rather than sending the
  camera into Canon for repairs, I decided to try a DIY repair by
  applying some glue between the rubber grip and the plastic wheel.
I lifted up the rubber grip on the main dial with my finger (as shown in the photo below), and used a toothpick to apply some glue to the plastic wheel. The rubber grip was released back into position, I rotated the main dial by approximately 180 degrees, and repeated the process with some more glue.
  If necessary, use a toothpick or paperclip to assist in lifting up the rubber grip on the main dial.
I used some Tarzan's Grip General Purpose Glue, as I happened to have
  some handy, and the specifications indicate it will bond to rubber and
  plastic.
Be careful not to apply too much glue, as that could result in the
  glue squeezing out the sides when you release the rubber grip back
  onto the plastic wheel. That could result in the main dial being glued
  to the outer case of the camera, which would prevent it from being
  rotated!
The DIY glue repair has been successful, with no more splipping of the
  main dial, and was certainly a lot cheaper than sending the camera to
  Canon for repair.
Answer:
Am I the problem or do I have a camera problem?

Sounds like a camera malfunction. There's no real trick to using the dial, so if it doesn't work the way it should then something is wrong.
Before sending it in for service I'd try to make as fresh a start as you can. Reset the camera to factory settings (there's a menu option for that). Insert a memory card (with no photos that you want to keep) and format it in the camera. Install a fresh battery. If the problem keeps happening, then you should take it to a reliable camera store or send it back to Canon for service.
Answer: Something similar happened to my old D60: the main wheel just suddenly stopped working. I found out, after opening up the camera and reaching the wheel, that the fork-type contacts that touch the wheel contacts were bent. So I carefully straightened them and everything worked again.

Main Dial stops working on Canon EOS 7D


How to determine which process sends UDP packets periodically to an IP address?

Question: I tried looping with netstat and  but the packets are small and not frequent so do not get caught (can still see them with tcpdump). Need to know which process sends those packets.
Comment: Have you tired iptables --log-uid option?
Answer: Check tcpdump for the source port number of the packets.  Then run
sudo netstat -a -u -n --program

Look for the PID/Program name matching the source port number.
This assumes that the sending process is leaving its socket open between sends, which is what any normal program would do.  If you are dealing a program that is deliberately trying to hide itself, that's whole different story.
Answer: I guess it should be possible with QUEUE target in iptables. But you'd need to write an userspace application to "check" those packets (and this appication could help you to know which process sends those packets). Sorry, I haven't got more details.


ColorBox JQuery Form Plugin Post To Same ColorBox

Question: I have been trying for two days to get ColorBox to return post results back to the same open box but it just will not do it.
I am using Jquery Form Plugin to Post from a ColorBox. It seems to work in IE 8, but not Safari or FireFox.
In IE 8 it returns the result from the post page "action" and returns the result in the same ColorBox but in FF and Safari it closes the box and sits on the load page (i.e. process1.php)?

I have a page say "process1.php" which loads the ColorBox onLoad (it does this no problem)

Load Page ColorBox Code For process1.php:

var $j = jQuery.noConflict();
$j(document).ready(function() {
    $j.fn.colorbox({
        href:"process2.php",
        escKey: false,
        overlayClose: false,
        width: "60%",
        height: 350,
        title: "Process Secure Order",
        open:true
    });
 });

Upon Page Load it will load the "process2.php" displaying a form for the user to submit data.

This is my JQuery Form Plugin Code:

var $j = jQuery.noConflict();
$j(document).ready(function() {
    var options = {
        beforeSubmit: showSpinner,
        success: showResponse,
        //resetForm: true,
        timeout: 3000,
        target: '#output1'
    };
    function showSpinner() {
        $j('#sterms, #accept, #decline, #side-cart').hide();
        $j('#working').show().html('Please Wait');
        return true;
    };
    function showResponse(){
        $j('#working').hide();
        $j('#result').show();
        return true;
    };
    // bind form using 'ajaxForm'
    $j('#secure_process01').ajaxForm(options);
});

It posts fine and then just tries to reload the same page with out the ColorBox opening on Load.
It has me stumped why it works in IE and nothing else, any help would be appreciated.
Using JQuery 1.5.2 (JQuery Form Plug In is not working with anything higher has permission issues)
Reference For JQuery Form Plugin http://jquery.malsup.com/form/#ajaxForm
Answer: This issue has been solved.
It turned out that the Jquery Form Plugin did not like the 1.6.1 JQuery version so I did the code using Jquery Post and it worked in all browsers.
ColorBox plugin big rap, great and easy.


Why does an authoritative name server not DNSSEC-validate its own results?

Question: If I query a name server a record it is authoritative for it seems the answer does not get DNSSEC validated:
$ dig cloudflare.com @ns3.cloudflare.com

; <<>> DiG 9.16.22-Debian <<>> cloudflare.com @ns3.cloudflare.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 28361
;; flags: qr aa rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;cloudflare.com.                        IN      A

;; ANSWER SECTION:
cloudflare.com.         300     IN      A       126.96.36.199
cloudflare.com.         300     IN      A       126.96.36.199

;; Query time: 3 msec
;; SERVER: 184.108.40.206#53(126.96.36.199)
;; WHEN: Sat Nov 20 15:29:00 CET 2021
;; MSG SIZE  rcvd: 75

There is no "ad" flag returned, hence the answer is not DNSSEC validated. If I ask a non-authoritative server the same query, an "ad" flag is returned:
$ dig cloudflare.com @220.127.116.11

; <<>> DiG 9.16.22-Debian <<>> cloudflare.com @22.214.171.124
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 23361
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;cloudflare.com.                        IN      A

;; ANSWER SECTION:
cloudflare.com.         145     IN      A       220.127.116.11
cloudflare.com.         145     IN      A       220.127.116.11

;; Query time: 3 msec
;; SERVER: 188.8.131.52#53(18.104.22.168)
;; WHEN: Sat Nov 20 15:35:35 CET 2021
;; MSG SIZE  rcvd: 75

Could you please tell me:

Is this a correct and well defined behavior?
What is the reason no validation is done?
Could I change this behavior with ISC bind9 in the configuration? How?

(If this behavior is intentional one should never configure a name server to use its own name server software to resolve, because for some client software it makes a difference whether an answer gets validated or not: I was wondering why SSHFP records did not work doing ssh -o VerifyHostKeyDNS <host> from the name server itself).
Answer:
Why does an authoritative name server not DNSSEC-validate its own results?

Because it can't, not without being a recursive nameserver itself, which would be bad.
To fully validate DNSSEC, you need to start from the root and go through the whole link of DS/DNSKEY records, and the authoritative resolver you consult is not authoritative on all of that, just its part down the link.
See for example section 6 of RFC 4033, "Resolver consideration":

A security-aware resolver has to be able to perform cryptographic
functions necessary to verify digital signatures using at least the
mandatory-to-implement algorithm(s).  Security-aware resolvers must
also be capable of forming an authentication chain from a newly
learned zone back to an authentication key, as described above.  This
process might require additional queries to intermediate DNS zones to obtain necessary DNSKEY, DS, and RRSIG records.  A security-aware
resolver should be configured with at least one trust anchor as the
starting point from which it will attempt to establish authentication
chains.

And RFC 4035, section §3.2.3 "The AD Bit" under "Recursive Name Servers":

The name server side of a security-aware recursive name server MUST
NOT set the AD bit in a response unless the name server considers all
RRsets in the Answer and Authority sections of the response to be
authentic.  The name server side SHOULD set the AD bit if and only if
the resolver side considers all RRsets in the Answer section and any
relevant negative response RRs in the Authority section to be
authentic.  The resolver side MUST follow the procedure described in
Section 5 to determine whether the RRs in question are authentic.
However, for backward compatibility, a recursive name server MAY set
the AD bit when a response includes unsigned CNAME RRs if those CNAME
RRs demonstrably could have been synthesized from an authentic DNAME
RR that is also included in the response according to the synthesis
rules described in [RFC2672].

As for:

it makes a difference whether an answer gets validated or not

Of course it does, that is the whole purpose of DNSSEC. But end clients do not consult authoritative nameservers directly during the course of normal operations. They use a recursive nameserver, which in turns iterate over various different authoritative nameservers to get the final reply, and which can validate DNSSEC if configured to do so.

I was wondering why SSHFP records did not work doing ssh -o VerifyHostKeyDNS  from the name server itself

Whatever problem you have here is not related to anything above. ssh should use whatever OS level resolver is configured to get the data.
See https://github.com/openssh/libopenssh/blob/05dfdd5f54d9a1bae5544141a7ee65baa3313ecd/ssh/dns.c#L191 which is inside the verify_host_key_dns function:
    result = getrrsetbyname(hostname, DNS_RDATACLASS_IN,
        DNS_RDATATYPE_SSHFP, 0, &fingerprints);
    if (result) {
        verbose("DNS lookup error: %s", dns_result_totext(result));
        return -1;
    }

    if (fingerprints->rri_flags & RRSET_VALIDATED) {
        *flags |= DNS_VERIFY_SECURE;
        debug("found %d secure fingerprints in DNS",
            fingerprints->rri_nrdatas);
    } else {
        debug("found %d insecure fingerprints in DNS",
            fingerprints->rri_nrdatas);
    }

and getrrsetbyname is defined in https://github.com/openssh/openssh-portable/blob/2dc328023f60212cd29504fc05d849133ae47355/openbsd-compat/getrrsetbyname.c and is basically a wrapper around res_query which is the low level libc binding to do DNS queries.
I have found at https://weberblog.net/sshfp-authenticate-ssh-fingerprints-via-dnssec/ some details on ssh behavior between a validated (DNSSEC) SSHFP record or not.
Comment: I don't have a problem with ssh/SSHFP, I just saw it didn't work on one of my name servers: This particular server had set itself as the resolver in /etc/resolv.conf which was the reason, why it didn't work: Hence my questioning here. Thank you for your answer.
Comment: The cited RFCs do mention not to validate authoritative zones. At least bind and probably at lot of other name server software are able to recursively validate, so they indeed could validate their own zones.
Comment: "so they indeed could validate their own zones." Not without being a recursive nameserver themselves to fetch all the data they don't have. `bind` can have both roles (authoritative and recursive) but it is recommended not to. If you use other software like `nsd` or `yadifa` they are authoritative only, without any recursive logic...


Letters of Recommendation for economics grad school for non-economics majors?

Question: I understand there are many people who major in math or physics and get into elite economics graduate schools. I'm sure that I will be able to find math professor who will with letters of recommendation that say I can successfully do research in math, but it would be hard for me to come up with such letter from economics professors. What do non-econonomics majors generally do for letters of recommendation?
Answer: Most committees are happy to see letters from mathematicians, although they might like at least one from an economist (and you probably should have at least one upper division course in economics if possible).
Just be careful. One eminent mathematician once wrote "X is not smart enough to be a mathematician, so I suggested he study economics." I don't think we admitted him.
Comment: Are the letters generally tailored to economics (i.e. suppose I wanted to apply to both economic and math grad schools. Would I need different letters?)
Comment: I think they should be tailored differently, although it wouldn't have to be much.  Instead of recommending "Graduate program in math" it should recommend  you for the "Graduate program in economics".


Discrepancy Between Results of Cosmological Observations & the Assertions of Quantum Mechanics

Question: Quantum mechanics requires a vacuum energy 40 orders of magnitude higher than that indicated by cosmological observations. Which side is most likely to be right,& when the truth is finally established beyond doubt,as one day it will be,won't this be extremely embarrassing for whichever group turns out to be wrong? Forty orders of magnitude is not a trivial error.
Comment: Nobody on the "quantum mechanics" side thinks the "vacuum energy = extremely high value" calculation is correct -- it's obviously wrong. The debate is about *why* it's wrong, and why it's not exactly zero (as naive cancellation arguments might suggest) but is instead a very small, positive value.
Comment: I can't see the now deleted comments(s) before yours. But I think the problem is that they don't understand your question. Please give much more details. You might also try https://physics.stackexchange.com .
Comment: @peterh Just to clear things up, there are no deleted comments here.
Comment: Orthogonally to that, though, this question is too opinion-based, for two reasons: First, we have no idea as to what future theories of physics and cosmology will arise, or even which current ones will stand up to even more stringent tests at high energies and exotic conditions. Second, whether a result is embarrassing boils down to an individual's personal feelings. For all of these reasons, the question unfortunately isn't a good fit for the site in its current form.
Comment: Virtually all questions are opinion based;it is someone's opinion that there are fractional charges within the nucleus,that there are WIMPs which explain dark matter,& so on. Whether or not one side or the other would feel embarrassed if the view they have championed were discredited is a matter of opinion.but don't tell me that the side which is finally proved right won't be feeling triumphant. Scientists love to prove their rivals wrong,& well you know it.
Answer: I'm not sure the language of "sides" really applies here. There is a model, one of the predictions seems to be wrong, so we will try to find a better model.
By way of analogy, look at the model of black-body radiation developed in the 19th century, one of its predictions was that an infinite amount of energy should be radiated at very short wavelengths. That prediction was ridiculous, so over the early part of the 20th century, people developed a better model, that "better model" became known as quantum mechanics.
There's nothing embarrassing about a model being wrong. All models are wrong, buts some are more useful than others. QM is a very useful model of reality in many many situations but seems to give some surprising values. So physicists try to find something better. There aren't "groups". This isn't a school playground. Being wrong isn't embarrassing, it just means the theories (or the observations) are incomplete.
Comment: Sides, factions,groups? According to Shakespeare,a rose by any other name would smell as sweet. As for 'embarrassing',embarrassment is in the mind of the beholder. Some people,psychopaths for example,are never embarrassed at their lies & shortcomings being found out,likewise with politicians,some of whom are psychopaths.