Signal-to-noise in inverse angstrom for spectroscopy?

Question: In a paper I came across the description of the signal-to-noise ratio (SNR) for observations with a spectograph. This was reported as $10\:1/\mathring{A}$. I am rather new to spectroscopy, so could someone clarify these units for me? Why is it used and how should I read it?
Comment: Can you link the paper or else provide the relevant text?
Comment: I can't provide a full answer, but it seems to me the source of the inverse angstrom is because the noise is calculated over a band or wavelength regime. See for example [this description on wiki](https://en.wikipedia.org/wiki/Signal-to-noise_ratio#Optical_SNR).
Answer: A spectrum imaged onto a CCD or other detector consists of photons spread out along a wavelength axis. Signal-to-noise (S/N) depends on how many photons you have from the source, how many from the background, intrinsic noise from the electronics, etc. -- and what kind of bin you're adding up the photons in. If you summed up all the photons across the spectrum (over all wavelengths), you'd get one number with a very high S/N, but no spectral information. If you divided the spectrum into N different wavelength bins, you'd get a lower S/N per bin, but more spectral information.
What the S/N ratio you mention means is that if you divided that spectrum into bins that were 1 Angstrom wide, you'd have enough photons in each bin for a S/N of 10 in each bin (at least for some region of the spectrum, probably near the central wavelength). You can then have some idea how the S/N would improve for bins larger than 1 Angstrom in size, or how it would get worse for smaller bins. S/N per Angstrom is conventional for optical spectroscopy, both because Angstroms are traditional and because moderate resolutions spectrographs often have scales of a few tenths to several Angstroms per pixel along the wavelength direction.
Answer: Warning: I never worked with spectra, and I don't have a complete answer. Anyway, here's how I understand it:
A spectrograph has a resolution $R = \Delta \lambda / \lambda$ that tells us how well it can distinguish light of different wavelengths. VIMOS from the paper has a resolution from 200 to 2500. With the same flux from the source and for a low-resolution spectrograph, you get more photons per wavelength bin than for a high-resolution one. This means you'll also get better SNR. So, giving SNR / wavelength makes inherent sense.
Here's where I'm very unsure: giving a SNR / $(0.1$nm$)$ should be equivalent to a magnitude limit, if the spectral energy distribution is the same. Or it could be a minimum quality criterion on the spectrum - stop taking data as soon as the SNR is reached.
Comment: "With the same flux from the source and for a low-resolution spectrograph, you get more photons per wavelength bin than for a high-resolution one." -- Actually, it's the opposite way around: low-spectral resolution means *more* photons per wavelength bin.
Comment: I thought that's what I wrote. Low resolution -> more photons per bin.
Comment: Oh, yes, that is what you said! My apologies...


How can a drawish opening be fashionable?

Question: dfan's answer to this question suggested the following. Why would a specific opening become popular as the method of choice to play for a draw? Wouldn't it be better to select an obscure out-of-fashion variation that leads to a draw? That way you always have the chance to catch your opponent unprepared and score an extra 1/2 point.
Comment: If you choose an out-of-fashion 'drawing' opening, your opponent may miss the fact you're looking for a draw. This negates the benefit of selecting a 'drawing' opening.
Answer: If I choose a well known drawish opening, it sends two messages to my opponent:

Offer me a draw and I'll accept it
If you play for a win, you'll just smash against my rocks.  If you try too hard, you'll lose.  If you don't, you'll probably just get a draw anyway.

Of course, some opponents won't care and will fight for the win while others will be more than ready to throw in the towel, especially if there's a rating difference in the opponent's favor.
This really only applies to master play.  Amateurs make enough mistakes that nothing is drawish, nothing is safe.
Answer: Because an obscure variation is just that -- obscure. It is far less understood and analyzed, and so you cannot be confident in your ability to play lines that lead to the outcome you want. In a well known opening, you can play the lines that you know most likely lead to certain positions.
In response to your edit:
In order to be confident in playing the lines of an opening, you would have to be well-studied in it. If you are playing at high level chess, your opponent most likely will know that you play these lines, and will prepare for it.
Answer: It's difficult to give a general answer why one opening is more popular than another. I can try to give some reasons in the specific case of Berlin vs Petrov that prompted your question.
In the Petrov the following line is popular for white.
<code>[fen ""]
1.e4 e5 2.Nf3 Nf6 3.Nxe5 d6 4.Nf3 Nxe4 5.Nc3 Nxc3 6.dxc3
</code>
This might be theoretically fine for black, but from a practical point of view white is very much in control. White may have prepared a dangerous novelty to use at a later stage in the opening, and black has to react over the board. There is almost no upside for black as white can play for a win with little risk.
The Berlin
<code>[fen ""]
1.e4 e5 2.Nf3 Nc6 3.Bb5 Nf6 4.O-O Nxe4 5.d4 Nd6 6.Bxc6 dxc6 7.dxe5 Nf5 8.Qxd8+ Kxd8
</code>
on the other is much more flexible. Black has almost as many different possible set-ups as white has. Compared with the Petrov, here it is much more difficult for white to prepare specific lines. White frequently goes wrong even at the highest levels. I think Aronian once commented that he sometimes plays the Berlin when he wants to win with black.
Answer: Specific openings become popular as a way to play for a draw (among grandmasters!) because those openings tend to lead to very drawish position (few unbalances).
Playing less popular lines is a different subject, with pros and cons -- the opponent may not remember too much about it and that may be an advantage, on the other hand you won't have much experience with them either, and unpopular openings are usually unpopular for a reason -- they're often worse than the popular ones. In fact your opponent may well know the exact reason why it's unpopular.
But those are trade-offs associated with playing unpopular openings at all -- not of playing them when trying to achieve a draw. Your question boils down to "why play popular openings at all?" Well, if one line is seen as having the biggest chance of success at the moment, then that line is going to be popular.
People don't choose a line based on popularity, but based on how good they think they can do with the positions they lead to.


How to find all item files in Minecraft Bedrock Edition

Question: I can't seem to find any of the Minecraft Bedrock Edition item files.  Specifically, I am looking for the bow.  I need it to create a behavior pack with it.  The template behavior pack contains all food/farming items, but no others. Hours of looking up how to find them lead me nowhere.  I watched a few tutorials on how to get the bedrock game files, and in all of them there was a "vanilla" file in the com.mojang folder.  I checked every sub-folder in com.mojang and didn't find them either.
Answer: It looks like you're thinking that addons for bedrock work like mods in java. They don't. Most of the things you see in Minecraft are not possible in the JSON/JavaScript Bedrock API. You can't make a bow, sorry. The items in bedrock are limited to the following behaviors: blocks, seeds, ordinary items, foods, potions, or a combo of food and potions (like a gapple), and maybe some other random thing I forgot.


Blog not indexed

Question: my blog is 6 months old, with frequently updated content. Yet, not a single page is indexed by Google. Why is that so? isn't wordpress set up for SEO by default?
Answer: Actually your site is indexed all 176 pages.  It would probably help your search results if you changed your permalink structure to something other than default.
You should also get a yourself a Google Webmaster Tools account so you can see how your site gets indexed and crawled.
Answer: I have to ask the obvious here; have you changed your privacy settings to allow the blog to be accessible by search engines.  Blogs in general and WordPress blogs are typically well crawled by Google and the other search engines.  If you have already made the blog visible, you may want to create a sitemap and submit it to the search engines.  You can use the plugin Google XML Sitemap to create the sitemap with almost no configuration.  The plugin is available here http://wordpress.org/extend/plugins/google-sitemap-generator/.  Hope this helps.
Comment: +1 for sitemap generator. Awesome plugin. Within 6 months of using it, my site was fully indexed and being crawled by Google. Though, my keyword strength was not strong. :-/
Answer: Check under Settings/Privacy. Is the site marked as private by accident? It's happened to me.
I'd also suggest installing the Google XML sitemaps plugin which will update your sitemap as well as ping relevant services when content is updated.
It's probably also worth checking your robots.txt file to see if you're excluding the whole site for some reason.
Comment: thanks guys. i did install an SEO plugin a week or so back. Could it have been because of that that my blog is now indexed suddenly? Besides, I want to understand how wordpress is structured in the first place with regard to search engine friendliness. Isn't it set up for SEO by default? Is the SEO plugin necessary then? and to what extent does post name in the url make a difference as against the standard numerical format of wordpress urls?
Comment: By default does give you a bunch of help with SEO friendliness but it also comes down to the theme you're using. Does it wrap you post title in h1 and your site title in h2 when on posts? Does it provide proper titles on the page? Really SEO is SEO WordPress just makes it easy to write a theme that search engines want to see.

Blog not indexed


Stage of my personal practice

Question: This  time when  the controller  of the  breath  disappears  thoughts  too disappear cittarupa  stop by presenting  a line across  and the top of it there is a picture  of a person. After a minute breath  appeared. And there was no observer  too at that time. What is the meaning of the cittarupa  which appeared and what is the stage?
Comment: My first teacher always said, don't worry about stages. Thinking about stages is bad for your progress.
Comment: It's kinda like an orgasm.  If you have to ask, you probably didn't have one.  Keep at it!
Comment: What observed this? Did you lose consciousness?
Comment: I don't know stages, but the mind presents images when it does not have words for what it experiences, or when discursive thought is not operating. The image might be meaningful, or random.
Comment: In a session last week, Ronald McDonald hung himself. Naturally, I hesitate at deducing meaning from this. In fact, this has been my approach for images in meditation for two years. I once saw a beautiful 3 dimensional image of the Buddha sat on a white elephant. My friend said this was auspicious - I wasn't interested. Just carry on.
Answer: You can find some advice from Ajaan Fuang on this page:

§ When Ajaan Fuang taught meditation, he didn't like to map things out
  in advance. As soon as he had explained the beginning steps, he'd have
  the student start sitting right in his presence, and then take the
  steps back home to work on there. If anything came up in the course of
  the practice, he'd explain how to deal with it and then go on to the
  next step.
Once a layman who had known more than his share of meditation teachers
  came to discuss the Dhamma with Ajaan Fuang, asking him many questions
  of an advanced nature as a way of testing his level of attainment.
  Ajaan Fuang asked him in return, "Have you had these experiences in
  your own meditation yet?"
"No, not yet."
"Then in that case I'd rather not discuss them, because if we discuss
  them when they're not yet a reality for you, they'll just be theories,
  and not the real Dhamma."
§ One meditator noticed that his practice under Ajaan Fuang was making
  quick progress, and so he asked what the next step would be. "I'm not
  going to tell you," Ajaan Fuang said. "Otherwise you'll become the
  sort of amazing marvel who knows everything before he meets with it,
  and masters everything before he's tried his hand. Just keep
  practicing and you'll find out on your own."
§ "You can't plan the way your practice is going to go. The mind has
  its own steps and stages, and you have to let the practice follow in
  line with them. That's the only way you'll get genuine results.
  Otherwise you'll turn into a half-baked arahant."
§ "Don't make a journal of your meditation experiences. If you do,
  you'll start meditating in order to have this or that thing happen, so
  that you can write it down in your journal. And as a result, you'll
  end up with nothing but the things you've fabricated."
Answer: When you meditate you can see weird visions of many kinds, unless you make them intentionally for meditative purposes like attaining some jhana ala Visudhimagga style or as in MN 128 Upakkilesa Sutta - Imperfections, you should not attach to them much significance in general. This i say based on teachings on imperfections of insight.
You should remember what is happening to the body imagination, postures, behavior, feelings & sensations. If you are going to discern some other things you should focus on these or others from Satipatthana Sutta that i did not mention here:

... [1] "There is the case where a monk remains focused on mental
  qualities in & of themselves with reference to the five hindrances.
  And how does a monk remain focused on mental qualities in & of
  themselves with reference to the five hindrances? There is the case
  where, there being sensual desire present within, a monk discerns that
  'There is sensual desire present within me.' Or, there being no
  sensual desire present within, he discerns that 'There is no sensual
  desire present within me.' He discerns how there is the arising of
  unarisen sensual desire. And he discerns how there is the abandoning
  of sensual desire once it has arisen. And he discerns how there is no
  future arising of sensual desire that has been abandoned. (The same
  formula is repeated for the remaining hindrances: ill will, sloth &
  drowsiness, restlessness & anxiety, and uncertainty.)
...
...
  ...
[4] "Furthermore, the monk remains focused on mental qualities in & of
  themselves with reference to the seven factors for Awakening. And how
  does he remain focused on mental qualities in & of themselves with
  reference to the seven factors for Awakening? There is the case where,
  there being mindfulness as a factor for Awakening present within, he
  discerns that 'Mindfulness as a factor for Awakening is present within
  me.' Or, there being no mindfulness as a factor for Awakening present
  within, he discerns that 'Mindfulness as a factor for Awakening is not
  present within me.' He discerns how there is the arising of unarisen
  mindfulness as a factor for Awakening. And he discerns how there is
  the culmination of the development of mindfulness as a factor for
  Awakening once it has arisen. (The same formula is repeated for the
  remaining factors for Awakening: analysis of qualities, persistence,
  rapture, serenity, concentration, & equanimity.) ...

Stage of my personal practice


How to cut a thick glass block at home?

Question: Due to pandemic, there are a lot of machine shops closed and delays in getting something custom made. I was wondering how to cut a triangular glass prism (~5cm hypotenuse) in the middle so I have two half slices? I was originally thinking of ordering some glass cutters that can cut up to 20 mm thick glass, but I'm pretty sure I won't be able to cut it into smaller pieces with just that. Are there any home made conventional ways of cutter thicker than normal glass? Or is there any specific tool I can order to cut thicker glass?
Comment: Note that glass dust is relatively hazardous to breathe in, so if you are using a sawing method, it should be continuously flooded with water to prevent the dust from becoming airborne.
Answer: Here is one way, used to drill holes through the plate glass wall of an aquarium.
Imagine a thick brass shim. we cut slots along one edge so that it looks like a saw blade with oddly square teeth.
We set this "blade" reciprocating against the glass piece we wish to cut in half and smear the "teeth" with diamond polishing paste, which loads the kerf cuts along its "cutting" edge.
The back-and-forth action embeds diamond particles into the surface of the soft brass shim, transforming it into an abrasive machining tool. it begins very slowly sawing through the prism.
We replentish the diamond paste from time to time so as to keep the cutting edge "fresh" until the brass shim has abraded its way all the way down through the prism.
If needed, we use a trickle of water as saw lube during this process.
Comment: +1 for this answer. A similar method is used for drilling holes in glass of almost any thickness. A brass (sometimes copper) tube is used with the teeth created in the described manner. With a modeling clay dam around the work area, an abrasive powder can be added to water to improve the cutting action.

How to cut a thick glass block at home?


Using same account in two phones

Question: If two phones use the same google account, can I log in while other person is already playing ? Is the other person kicked out?
Comment: By *other person* do you mean two users at two different locaions using the same google account?
Answer: Yes you can and none is kicked out.
I have configured it currently on both of my Android phones. The data is saved on the server, and syncs after some time in cases where you catch a Pokemon on one phone. No data is saved locally except your login info.
I have never tried giving one of the phone to another person and access the game at different location with same google account. That might bring down a Ban situation.
More Info - Reddit
Answer: My son and i use the same account on different phones. we can't both collect pokestops at the same location but he can use it at one location while i use it at another at the same time. anything i catch appears in the caught pokemon on hos phone and vice versa. Same with pokeballs and items collected from pokestops.
Answer: Me and the wife both have the same account on the phone. while shes is park and grabbing pokestop farm i walk around to grab further pokestop. The items are shared and if one of us catch a pokemon the other wont be able to catch the same. its a great team effort in a way.
you also cant flip the same pokestop. so there is not really abuse because someone has to walk/move and you cant double dip on anything.

Using same account in two phones


How to keep track of mysql database table entries by chronological insertion in php

Question: I had originally wanted my alarmID value to be the primary key and to be Auto incremented. But I have decided to make my Title value as so.
How can I manually auto increment alarmID so that every time I insert values, the alarmID value gets incremented by exactly 1.
I want a way to keep track of entries by when they were inserted to be display chronologically later on.
Here is how I have my php code.
<code>$sql = "CREATE TABLE IF NOT EXISTS alarms (
    alarmID INT NOT NULL,
    PRIMARY KEY (Title),
    Title CHAR(30) NOT NULL,
    Description TEXT,
    DT DATETIME
    )";
</code>
Answer: Something like this should work, you still get a unique indexed title and the auto increment alarmID, it's much more subtle than using a mysql function / proc.
<code>CREATE TABLE IF NOT EXISTS alarms (
    alarmID MEDIUMINT NOT NULL AUTO_INCREMENT,
    Title CHAR(30) NOT NULL,
    Description TEXT,
    DT DATETIME,
    PRIMARY KEY (alarmID),
    UNIQUE KEY title (Title)
);
</code>
Comment: This worked, although I was getting errors with the single quotes.. removing the single quotes removed the errors.
Comment: I was testing it directly on the mysql console, my bad.
Answer: Your best bet here would be to make alarmID an auto incrementing primary key and, if Title has to be unique, place a unique constraint on it.
Manually computing the new incremented ID could in fact lead to issues if multiple users use your system, so it is better to leave the job to the DBMS itself.


How did "like" change from a noun meaning "body" to the modern verb?

Question: As pointed out here, saying "I like X" in old English would have to be formulated as "X pleases my body" and the word "like" would represent "body" in that sentence. But it's not clear to me how "like" became a verb in modern English.
Comment: ***Like:*** Old English lician "to please, be pleasing, be sufficient," from Proto-Germanic likjan ....., "to suit," Old High German lihhen, Gothic leikan "to please"),***from  lik- "body, form; like, same."***

***The sense development is unclear***; perhaps "to be like" (see like (adj.)), thus, "to be suitable." Like (and dislike) originally were impersonal and the liking flowed the other way: "The music likes you not" ["The Two Gentlemen of Verona"]. The modern flow began to appear late 14c. (compare please).  (Etymonline)
Comment: Even in Old English, "I like X" would use _like_ as a verb, I believe.
Answer: Just because you found it in a YouTube video doesn't mean it's true. Even if the video was made by a professor. Like became a verb in modern English from the Old English verb lician, which wouldn't have been translated as "pleases my body" but as "is pleasing".
The OED says that the original root word was lich, which can mean body, but also form or appearance. Thus one thing was like another if it had the same appearance. Perhaps the semantic connection to pleasing is through suitable appearance, but that connection is likely lost in the misty beginnings of the language over a millennium ago.
Comment: @Josh As far as I can tell, this is a linguistic Just-So story. The professor is saying that *like* made its passage from Old English *lich* (body) to English  *like* (to be pleasing to) to valley-girl speak (said) as in "She was like I think he's cute." But a thousand years ago there was already an Old English verb *lician* meaning to be pleasing, and the valley girl is saying nothing more startling than "She was saying something like 'I think he's cute.'"
Comment: The YouTube professor is saying  what you are saying and what other etymological sources suggest. Body in the sense of form, a form that resembles mine. From there, after a thousand years, lik ( body, form) became like as we know it today. The process is unclear but the origin appears to be from lik/lich.


Storing passwords online using Gmail documents

Question: Following this discussion about "Online Passwords Managers" I wonder whether it is a good idea to store the passwords using a spreadsheet inside Gmail documents? I mean, it seems to me that these password will be as safe as my Gmail account which I consider to be safe enough. Is my assumption correct, or this way of storing passwords is not recommended?
Comment: The google spreadsheet is not encrypted thus it is stored in plain text.  Which means anyone with acces to your Google account can access the file.
Comment: I typed out all my passwords and then saved as a PDF, stored it in an innocuous named folder on gmail. How safe is that?
Comment: What's the up-to-date thinking about this (now in 2021)?
Answer: I have done that before and it is a fairly good solution when you need to share certain password lists with other administrators. Yes, your gmail account can be somewhat safe if you use it correctly. On the other hand, gmail is also a pretty big target, is susceptible to government subpoenas, and you have to be VERY careful that everything that connects to your gmail account uses a trusted SSL connection. It is very easy to take over a gmail account just by sniffing unencrypted traffic.
My preferred solution, other than an online password manager, is to place a password-protected excel spreadsheet on a shared cloud storage folder.
Comment: Wouldn't it make more sense to use an offline password manager && save the resulting archive to the cloud?
Answer: Many of the javascript attacks have come through advertising circulated via google.com.  Mitigate that by creating a dedicated firefox profile just for password management blocking all other sites besides docs.google.com.
It is better to encrypt on the client side so what is stored online is not reversible.  If google supports a way to encrypt at the client in javascript, then google docs may be ok.
ClipperZ is an open source project that you could host yourself on a private server only accesible via your vpn.  Passwords are encrypted in the browser before being sent to the server.
Comment: Password best practices are still important.
Comment: In the past, there were many cracking programs to crack an Excel spreadsheet password.  Not sure if that has changed much in the last few years.
Answer: I would suggest a personal encryption technique,
like for example whenever you save passwords, alter some letters at specific positions personally known to you, ( e.g may be the first and second last).
For example you are storing password foo762. don't save as "foo762" instead alter first and last by next digit-letter, like "goo772".
trick, you must know positions and addition/subtraction by 1,2 etc, of your choice.
Comment: Don't be a dave: http://security.stackexchange.com/questions/25585/is-my-developers-home-brew-password-security-right-or-wrong-and-why


Android: Cannot refer to a non-final variable inside an inner class defined in a different method

Question: I know this question has been asked several times before, but I upon reading many answers, I haven't found something which suits me. First, please look at the following code, which is supposed to open an AlertDialog once an image is clicked (this works perfectly). The AlertDialog hosts an EditText field - this is where the problem arises:
    ImageView scissorsImage = (ImageView) findViewById(R.id.scissorsImage);
    scissorsImage.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view)
        {
            AlertDialog.Builder alert = new AlertDialog.Builder(context);

            alert.setTitle("Apply a Coupon");
            alert.setMessage("Enter the coupon amount (i.e. 25 for $25)");

            // Set an EditText view to get user input
            final EditText couponAmount = new EditText(context);
            alert.setView(couponAmount);

            couponAmount.setText(couponAmountString);

            alert.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int whichButton) {
                    String couponAmountString = couponAmount.getText().toString();
                    System.out.println(couponAmountString);
                }
            });

            alert.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int whichButton) {
                    // Canceled.
                }
            });

            alert.show();
        }

    });

Now, this bit of code is inside my onCreate method, and the variable couponAmountString is outside the onCreate method. So the code executes just fine, the only problem is that the line couponAmount.setText(couponAmountString); does not work as I want it to.
What I am trying to do with it is that when the user puts a value in the dialog box, and closes it by pressing OK, the value gets stored in couponAmountString - so far so good. When the user touches the image again to re-open the dialog box, I am trying to have the EditText field pre-set with the last value they entered, hence couponAmount.setText(couponAmountString);. But this isn't working, because I have to declare the EditText field as final. Which is why I get the error Cannot refer to a non-final variable inside an inner class defined in a different method when I click on the image the second time.
So is there any way I can accomplish what I want?
Thanks!
Answer: Silly, silly me. It turns out that I was re-initializing couponAmountString inside the method as you can see. I just had to take out String and it's working now!


Should I redirect non-existing m.example.com links if they are appearing in Google search results?

Question: I was wondering if it is worth it to redirect non existing m.example.com links that are being displayed in Google, or if it is better to just delete these from Google (if that is possible)?
Answer: Redirect them only if there is a suitable/corresponding page to redirect to. Otherwise, if these pages literally do not exist anymore then it is better to return a meaningful 404 message, perhaps guiding them to pages they might find useful.
Providing you are returning a 404 status then, in time, Google will drop these pages from its index.
Comment: I'd only add that these links will fall out of Google eventually no matter what you do.    Google will stop indexing redirects, 404 not found, or 410 gone pages.   It will usually happen in a few days, but it could take a few weeks.
Answer: If you think content is really related than do 301 redirection. Do not redirect to homepage, instead create meaningful 404 Error page.
Yes, you can remove those results from search result by using 410 code. I did not recommended to use 404 pages, because Google think, may be this content will be back, may be user redirect this pages to another URL. So Google do not immediately remove 404 pages from search result.
So, if you place some content in your site, and further you just remove it, and if you think, it will never come again, then I strongly recommended to use 410 against 404, because it remove those pages fast from search result compare to 404.


How to restore last El Capitan/Safari session manually with Time Machine backup?

Question: I am using Safari version 9.0.3 on Mac OS X El Capitan version 10.11.3.  I had dozens of Safari windows and tabs open when it became unresponsive.  In the past I could force quit and then the session would automatically restore at the next launch of Safari.  However, this time Safari was still unresponsive after force quitting and relaunching (the whole system was having difficulty at this point), so I force quit Safari a second time.  Now the last session windows are gone, and the history menu option to restore it is greyed out.
In an earlier version of the system a few years ago I used to manually restore Safari sessions by simply replacing the ~/Library/Safari/LastSession.plist file with a backup.  That is no longer working.  I have also tried restoring ~/Library/Preferences/com.apple.Safari.plist and deleted the ~/Library/Saved Application State/com.apple.Safari.savedState folder since it did not exist before the issue; I might have caused creation of the folder by fiddling with the General pane System Preference setting to close all windows when quitting an app (I unchecked and checked it back on), and the Safari > Preferences... > General > Safari opens with: setting (changed from "A new window" to "All windows from last session" and then back again).  Any further ideas of how to restore the session?  The History option to restore the session is greyed out no matter what files I restore from the backup.
Answer: I don't know what you are talking about, since I just restored a lost session using Time Machine following the usual steps: quit Safari, restore the ~/Library/Safari/LastSession.plist file from a backup, launch Safari, hit "restore last session" menu option. (Safari 11, El Capitan)


How can I include video in an eBay auction listing?

Question: Is it possible to embed or link to video in an eBay auction listing?  I'm following instructions found online to try to embed a YouTube video by checking the "use old embed code" box, which everyone seems to think I need to do because iframes aren't allowed, but I'm still getting a warning from eBay that I won't be able to post my listing because it includes "non-clickable links".  Now I'm wondering if eBay changed their link policy to disallow embedded videos sometime after the instructions I'm finding were written, or if I'm just doing it wrong, or what.  What's my best option here, and how do I make it work?
Answer: I ended up ignoring the warning about not being able to post my listing and clicking the "List it" button anyway, and it seems to have gone through.  So maybe the warning was displayed by mistake, and everything is fine?  If I discover otherwise, I'll follow up here....
Comment: FWIW, the auction completed and the (sizable) payment cleared without incident.
Answer: From a policy standpoint, you're likely in the clear.
Navigate to the "Links from an eBay listing" tab in eBay's Links Policy.
http://pages.ebay.com/help/policies/listing-links.html


Does submitblock require the wallets private key?

Question: I would like to know if invoking the submitblock RPC is supposed to work if the daemon that handles the RPC does not have the private-keys for to the coinbase output address?
Answer: submitblock is not a wallet RPC so it does not need private keys nor is it related to anything in the wallet. It can be used even if the wallet is disabled.
Comment: So submitting a block to a node on behalf of your "real" wallet controlled by another node is a supported use case?
Comment: Yes. Block's aren't tied to wallets... You don't need a wallet to create a block, and a block does not need to be created by a wallet.
Comment: I ran into this issue https://github.com/vergecurrency/VERGE/issues/646 but hey that's VERGE /sigh


I need ethernet controller driver, PCI bus for Presario 6010US

Question: Hi I am unable to connect to the internet.  ,Just installed the OS XP Pro and the device manager has a yellow question mark  for controller driver, PCI bus.  My network connection shows I am connected to a firewalled network with zero packets sent and received.  I checked HP.COM, with no luck.   Please advise what I should do.
thank you very much
Answer: Looking at the page on HP for that model it uses an nVidia nForce chipset.
It is likely that the LAN chip will not be recognized properly until you have installed the nVidia chipset software first.
Then install the LAN driver


Half wall supporting 18" overhanging counter -- can this be done?

Question: As part of an upcoming kitchen remodel we plan on knocking down a (non-load bearing) wall between the dining room and kitchen. We are thinking of converting a portion of the existing wall to a half wall and placing an overhanging quartz countertop on it to create a peninsula. See attached Sketchup screenshot. This layout was suggested to us by a professional designer and my question is whether it makes sense structurally. Normally there would be a row of cabinets on the other side of the half wall, and the total amount of overhang would be ~1/3rd the overall width of the slab. Unfortunately there is no room for this in our 1950's-era, 10'x10' kitchen so the entire piece would need to be supported by the 4" half wall. I could perhaps see this working with enough reinforcing but I wanted to see whether anyone else has attempted such a feat and what the outcome was.
Comment: Are you opposed to having corbels underneath the countertop providing support? And what is the thickness of the quartz?
Comment: Not opposed to corbels, but invisible braces would be preferable (though probably unrealistic here.) standard 3cm countertops.
Comment: There are pretty thin metal corbels that can be used, both in L shape and as flat bars that are attached to cutouts in the knee wall. You'd need to verify with the counter installer if that would be compatible with the countertop. (here's a good example: https://www.amazon.com/Hidden-Granite-Bracket-Counter-Support/dp/B00S35LE7C/ref=asc_df_B00S35LE7C/?tag=hyprod-20&linkCode=df0&hvadid=198104726338&hvpos=1o2&hvnetw=g&hvrand=9970581360409591396&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9052229&hvtargid=pla-350792079588&psc=1)
Comment: Corbels only solve the secondary problem. The primary torsional force is at the floor joint. The wall would need to be securely fastened to the floor framing at multiple points.
Comment: I did something similar by firmly mounting the subcounter mdf then embedding steel https://diy.stackexchange.com/questions/20862/can-i-support-a-granite-countertop-overhang-with-embedded-steel-bars
Answer: For countertops, 3 cm is fine  but that's thin for something free-hanging. To avoid the stone breaking, the slab needs even support in a lot of places.  You don't want a long unsupported area that people will lean on or that might have something dropped on it.  You can do it with a lot of full-width supports, like Eli Iser links to in a comment.  But you need support near all of the edges and at regular intervals in between.
An easier way to accomplish that is to have the slab sit on a solid top (like 3/4" plywood), which also provides a place for fastening all of the support.  It should be as big, or almost as big, as the slab.  You can cover the edge for appearance.  That would also serve as the top surface of the half wall.
To avoid torsion forces, you need to support the free corners.  At the back wall, you can fasten a horizontal support board to the wall that the top rests on.
For the outer corner, That's a lot of weight and a lot of leverage.  I wouldn't trust hidden braces fastened to the half wall, or even the half wall attachment to the floor or the half wall framing staying square and plumb.  Use a leg that rests on the floor.  It should also be fastened to the floor, perhaps with a tie-back to the half wall.  You could even make the half wall an "L", creating a cubby hole under the overhang.  If that would eat too much of the length, you could use something like a wrought iron railing that would provide support but only consume a few inches (instead of a leg).
That will still leave a very heavy 4' span that needs support.  Put some type of brace in the middle that fastens to the half wall (ensure there's a stud in that location when the wall is built) and provides support to a point most of the way to the outside edge of the overhang.  You can avoid knee interference with a right-angle or curved brace.  But it should be something that is seriously strong and rigid, not something like the utility brackets used to put up garage shelving that sag under load.
Keep in mind that the issue isn't so much that the half wall will fall over. The issue is any part of the slab support structure sagging or twisting even a little.  If that happens, you're still holding the slab off the floor, but some part of it won't be supported.  Then it doesn't take much for the slab to break.


Migration to security by default too?

Question: I've seen several questions recently where one very reasonable reason for closing would have been that they are more generic security questions, not really Unix specific. Is it possible to add migration there as a close reason?
Comment: @Wildcard On [security.se], the about page is actually a bit scarier than the reality: questions from non-professionals are usually accepted there, as long as the asker is willing to learn (i.e.. not "sendmetehhackz"). But only questions about security are on-topic there, not questions about configuring tools for ordinary users and administrators such as antivirus, SSH, firewalls, etc.
Comment: One issue is that security.stackexchange.com is for information security *professionals*.
Comment: Links? I rarely see questions that would be on-topic on Sec.SE, let alone also off-topic here.
Answer: Users with 10k rep can see a history of outgoing migrations and recent statistics.
There was a single migration in the last three months.
Even accounting for the fact that some migrations may be missed because nobody thinks of flagging, this is very far from warranting adding a new target to the migration dialog.
In addition there's a risk that questions will be migrated even though they're on-topic here, or worse, even though they're off-topic on the proposed destination. Questions about, say, configuring Apache for HTTPS or public key authentication for SSH, or setting up a firewall, are off-topic on Security.SE (because they're about configuring some tool, not about achieving a security objective), but Sec.SE frequently gets such question and has to migrate them away. If there was a migration path, I'd expect some of our community who are unfamiliar with the scope of Security.SE to see trigger words like "key" and "SSL" and migrate questions away even though they're on-topic here and off-topic on Sec.SE.
I am a regular both here and on Sec.SE. My subjective perception is that we do get the occasional question that would be on-topic on Sec.SE, but those are rarely off-topic here; when I see a question that is on-topic on both sides but would be better served on Sec.SE, I leave a comment suggesting that if the asker wishes they may have their question migrated. In the very rare cases when the question is actually off-topic here, I flag to migrate. I'm sure that I'm not the only one who does this. I doubt that many questions fall through the cracks, considering that I read more than half the questions here and I'm very likely to read a question if it's related to security.
In summary, no, we should not have a migration path to Security.SE, because it would be misused more often than useful.

Migration to security by default too?


Can pilots turn off warning alarms? Re: Aeroperu Flight 603

Question: I just watched the Mayday S1E4 episode concerning Aeroperu Flight 603.  Gut wretching to see the pilots in that situation.  On listening to the recording tape, alarms were blaring constantly, some for maybe as long as 15 minutes straight.  I can only imagine that that constant blaring adds stress and confusion to the cockpit.  So I wanted to ask if pilots have the ability to silence alarms after a certain period of time?
Answer: Sometimes they can sometimes they cant, how to do it varies by aircraft but generally alarms can often be silenced by acknowledging they are going off and pressing some kind of button. On my little Piper Archer the alternator under volt it just a light and can't be shut off but if my G430 throws an alarm or warning it can usually be silenced.
On the 737 some alarms cant be silenced and some can

Cockpit aural warnings include the fire bell, take-off configuration
  warning, cabin altitude, landing gear configuration warning,
  mach/airspeed overspeed, stall warning, GPWS and TCAS. External aural
  warnings are: The fire bell in the wheel well and the ground call horn
  in the nose wheel-well for an E & E bay overheat or IRS's on DC. Only
  certain warnings can be silenced whilst the condition exists.

A lot of aircraft display failures on some kind of annunciator panel or glass cockpit equivalent. These lights typically can not be turned off until the error is addressed (fire suppressed, breaker pulled etc.). Master Caution lights (and audio warnings) can typically be shut off through the use of a Master Caution Reset switch.

Once notified, the pilot may cancel the master caution, but a
  dedicated system or component annunciator light stays illuminated
  until the situation that caused the warning is rectified. Cancelling
  resets the master caution lights to warn of a subsequent fault event
  even before the initial fault is corrected.

The FAA's full advice on warning and caution light design can be found here.
They shed more light on the topic in this AC

Clearing and Recalling Visual Alert Messages. Clearing visual alert messages from the current warning, caution, and advisory display
  allows the flightcrew to remove a potential source of distraction and
  makes it easier for the flightcrew to detect subsequent alerts. a. The
  following guidance should be applied for clearing and recalling or
  storing the visual alert messages:

(1) If a message can be cleared and
  the condition still exists, the system should provide the ability to
  recall any cleared visual alert message that has been acknowledged. 11
  12/13/2010 AC 25.1322-1
(2) Either through a positive indication on the display or through
  normal flightcrew procedures, a means should be provided to identify
  if alert messages are stored (or otherwise not in view). b. The visual
  alert message must be removed from the display when the condition no
  longer exists (§25.1322(a)(3)).

In short, if a message can be cleared you should be able to pull it back up easily and if the problem goes away the alert should clear as well.
Answer: Some alarms, like those announced by the Master Warning System like fire bells, can be silenced by pushing the Mater Warning light and you do it as part of the memory procedure to deal with the warning.  Other alarms, like ones for configurations that are wrong for the conditions, can only be silenced by correcting the configuration.  Think gear warning horns or flap overspeed clackers.
I used to complain about the gear warning horn in the CRJs which has a dual tone that sounds almost exactly like a TV station off-the-air test pattern.  It is extremely easy to blend into the background when the stress level is high and you are becoming mentally saturated. Fortunately, the GPWS announcement "Too Low, Gear" comes on as you get close to the ground to hopefully wake you up.  Hopefully.... some years back a Britair CRJ200 crew landed wheels up in spite of the warnings because they were landing flapless and were mentally saturated by the stress of landing at 160kt (and I believe the GPWS callout may have been inhibited; not sure).


Error reaching public extensions directory

Question: I receive this error:  Extension download error
The CiviCRM public extensions directory at https://civicrm.org/extdir/ver=4.7.9|cms=Drupal could not be contacted - please check your webserver can make external HTTP requests or contact CiviCRM team on CiviCRM forum.
However, from the browser I can go to that page and see a listing of extension.xml files. I'm trying to get the twilio sms extension installed.
Drupal 7.5 CiviCRM 4.7.9
Answer: In this situation, some possibilities to evaluate:

There is a problem on civicrm.org, but it only occurs on a subpage. For example, in v4.7.x (and maybe 4.6.x), it fetches the subpage /single (e.g. https://civicrm.org/extdir/ver=4.7.9|cms=Drupal/single).
There was a problem on civicrm.org and the failure got somehow cached. You could wait a while and try again -- or clear the caches. (Maybe use the "Support => Developer => API Explorer" to run Extension.refresh or System.flush.)
Something in the web server environment is preventing it from making the request, e.g.

A security system (such as a firewall, suhosin, or php ini setting) interferes with outgoing requests.
The curl/http layer has a broken HTTP/SSL configuration.

In this particular case, I believe there was a change on civicrm.org which prevented it from correctly reading several of the XML files needed for /single, but that issue is now resolved.
(See also: https://issues.civicrm.org/jira/browse/CRM-19090 )
Comment: Confirming that the issue has indeed been resolved.
Comment: I have used it and it works well for me.  Do we know why this would happen about once a week?
Answer: There have been intermittent connectivity issues with our civicrm.org server this week. We've observed this ourselves as well for a number of our projects.
Answer: It is working fine today. Must have been a temporary access issue.


How to operate on HF if an AM transmitter is only 540 feet away?

Question: I'm a General Class Licensee, and due to pulmonary disease I cannot operate voice. I am also about 540 feet from a 24/7 1 kW AM station. The signal is so pronounced that most audio devices in the house pick up the station. Every shortwave receiver I've tried overloads (without an antenna) from 1-30 MHz. Any suggestions?
Comment: I've seen high-pass filters being sold to solve that issue. They'll attenuate LW and MW and let most of SW through.
Comment: Wow, I wouldn't have assumed it was possible to live so close to an non-ham transmitter that basically all audio devices experience harmful interference. Not going to lie to you: That doesn't sound good.
Comment: I am sure this can be solved. First, what shortwave receivers have you tried? If they were amateur band, please describe them, as well as all the wiring and coax connections.
Answer: First, find a transceiver which is properly shielded. When connected directly to a dummy load, there should be no breakthrough on any frequency (except the MW transmitter itself). Portable broadcast radio receivers are completely out of the question, but fairly recent ham gear should be ok.
Then, try a highpass filter to reduce the impact of the MW. I'd suggest starting on one of the higher bands, 15 m or 10 m.  A simple highpass filter can be made with a quarter wavelength short circuit stub. On 15 m that's about 2.2 m of coax.  Ideally for the stub you should use double screened coax like RG223, RG400 or hardline etc. Solder the stub into the radio end of a short jumper lead. A better filter can be made with more stubs or with discrete components.
Finally, take some precautions to reduce the pickup of the RF in the shack. Keep loop areas small - run coax, 12 V and power cables close to each other. Make a filter or trap for common-mode currents on both coax and power lines that enter the rig. Ground the coax shield to shack ground as it enters the shack. (forget about ground stakes, you're trying to keep differential voltages to a minimum). Use a horizontal dipole antenna, broadside to the MW source,  as the MW fields are mostly vertical, and still somewhat radial as you're so close. Use a balun with good choking well below your HF frequency.
You may still be in  trouble, if there are any non-linear effects in any gutters, downpipes, fences or electric cables outside anywhere near the transmitter. They could cause significant harmonics and intermods on your HF frequency, which cannot be filtered out.
Comment: Thanks. I can't take down the aluminum gutters or the steel fences my neighbors have. My Alinco overloaded without an antenna. I guess I'll have to go to VHF or UHF and find an SSB transceiver if I want to legally operate as a ham.
Comment: @GordonC I wouldn't give up hope quite so quickly: "overloaded without an antenna" is different than Tom's "connected directly to a dummy load"! I'd expect an uncapped UHF connector to pick up strong signals. Shielding that input — and addressing any other power supply/mic/accessory leaks — might reveal a situation where either well-shielded filters or a narrow band antenna (like a resonant small loop) could let you proceed.
Answer: This is not necessarily an impossible problem. You might approach the problem iteratively, with a simple monoband receiver and expand from there as you see what works.
Assuming you are able to solder, you could start with a 40m SoftRock receiver kit for $21, which plugs into your computer line-in sound card input for decoding of digital modes. On 40m (7MHz) you'd receive stations hundreds to thousands of kilometers away with a simple outdoor antenna, particularly on sensitive digital modes like WSPR and JT65.
I would build that receiver inside a metal box, and start with a few meters of wire as an antenna.
If you don't have interference with no antenna and short antennas, but longer antennas bring interference, consider building a medium-wave bandstop filter, like these demonstrated to attenuate AM broadcast by over 50 dB.
Finally, consider that after filtering the fundamental on-channel AM transmitter, the N-th harmonics of that transmitter will be present and will have N times the bandwidth of the fundamental channel.
If the AM transmitter was on 1000 kHz, it will have significant modulation energy from about 995-1005 kHz (more if using HD Radio transmission). The second harmonic will spread from 1985-2015 kHz and so on.
Answer: Assuming the AM station doesn't wipe out your internet connection, how about setting up a remotely operated HF rig far offsite (friend or relative's house, etc.)?], and operating it from your home computer (laptop, et.al.)?
Answer: Why not try a good small transmitting "magnetic loop" (like LNR's W4OP Loop, the AlexLoop, the AlphaLoop, etc.) along with some RFI protection around your transceiver? A narrowband directional antenna like that should help with half the problem, so you can focus on cleaning up the other power/data/microphone "inputs" on your transceiver.
While your situation definitely sounds dire, with a careful station design it should not be insurmountable.
Consider that a typical 2m repeater shares one single antenna between its transmitter and receiver. That is, it is simultaneously pumping a 25–100W transmission into the antenna over the very same coax used to receive the teeny tiny signal from a handheld in the next town. Not to mention, those two signals (the 25W output and the picowatt-level input) are half a percent away from each other, frequency-wise!
[Aside: If you changed the tuning of a guitar or violin the same relative amount, you'd barely hear the difference. If we kept track of notes up that high, the difference between 146.2 and 146.8 MHz would be only 7 musical cents. This is hardly past the average audible threshold of five cents. Put another way, there's about 100 cents between a piano's middle C and the black key right next to it — the entire US 2m allocation could fit twice within that musical half-step and the 0.6MHz offset just a tiny offset within.]
All that to say, in many ways a repeater inherently deals with much more severe interference than what you face. It's true that expensive duplexers and often additional filters are needed there, but in your case you have the benefit of signals that should be several octaves apart! It's a whole lot easier to keep a 550m or a 175m signal apart from a 40m signal, than keeping a 2.044m signal separate from a 2.052m one.
There's two things you need to avoid:

signals overloading within your receiver
passive intermodulation around your house

The first is completely within your control:

You need a well-shielded receiver, which will hopefully be designed against RF signals coming in via the power supply or accessories but may need some "shoring up" in those regards due to your situation. Troubleshoot this via a dummy load or cap on the antenna port.
Then you need to make sure interference doesn't come in via your antenna system. The most obvious way is that your antenna itself will pick up the signal. Adding a good filter (shielded and capable of handling the broadcast power levels) should help in the case of a broadband antenna. There are also some antennas that are inherently very "narrow band", such as a resonant small loop.
A less obvious way can enter your antenna system is if your antenna is unbalanced.

This and more is all described in a much more authoritative way in "A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing" by Jim Brown K9YC. I've been trying to learn this stuff for a couple years now, and I still find that reference somewhat intimidating — when he says "You should study this tutorial thoroughly" he means it! — but he ends up boiling things down to practical actions. That guide is a perfect fit for your situation, though!
The other part is a bit out of your hands:
Even with a good station design, you'll still need to avoid that "Rusty bolt effect" of passive intermodulation. This one isn't as much in your control, since you may have little "transmitters" on all sorts of frequencies sprinkled throughout your neighborhood. A directional antenna will help here, and/or some additional "notch" filters for signals that are "in your way" on a particular band.
You might also try strike up a friendship with the broadcast engineer of the station. He might be just as interested in tracking down strong sources of intermodulation around their transmitter, or at least have more advice. His radio shack is 540 feet closer to the broadcast than you are!


How do we know to refer to the Holy Spirit as He?

Question: Another question really got me to thinking about the Holy Spirit.  I thought it better to  open a new question rather to divert the focus of that thread.  So growing up, I also thought of the 1st Person of the Trinity as Father and the 2nd Person of the Trinity as Son but never really came away with the overwhelming feeling of Holy Spirit as He.  "It" would certainly be quite wrong, after all the Holy Spirit is the 3rd Person of the Trinity.  What support is there for referring to the Holy Spirit as He?
Comment: This may help: http://en.wikipedia.org/wiki/Gender_of_the_Holy_Spirit
Answer: There is never any indication in the New Testament that the Holy Spirit is a "he". In Greek, gender for normal nouns like "spirit", "rock" or "bread" is a grammatical thing, not a sex thing. This is common in the romance languages as well, if you are familiar with those. The fact that it is neuter does not tell you that it is an "it" as we think in English. The word "day" is feminine, but there is nothing feminine about the daytime. "Death" is masculine, but both males and females die. "teknon", one of the Greek words for child, is neuter, etc... So the fact that the word "spirit" is neuter (and it is, despite what was said in one of the other answers) actually doesn't tell you anything.
People often appeal to things like John 14:16 and 16:7 to prove that the Holy Spirit is male, but this is inaccurate. The word "helper" is masculine grammatically (like the words above). This is why pronouns that refer to "helper" like the "auton" in 16:7 are masculine. To do otherwise would be to commit a grammatical foul.
If you wish to say that the Holy Spirit is a "he", realize that this is an English thing you are doing, not a Greek. Orthodoxy states that the Holy Spirit is a person, so speaking of him/her/it personally entirely makes sense and is appropriate, but personhood in the Godhead need not imply gender. So, theologically, feel free to call him a person. But by arguing about gender you are taking this question beyond what the writers of the New Testament apparently felt like discussing.
Edit 9/11/2015 in response to comments because the response is too long to put in the comments themselves
@bruisedreed I can see where that could be confusing. Let's change the verse to something non-controversial to see my point. In John 19:23, it refers to Jesus' tunic with the statement ἦν δὲ ὁ χιτὼν ἄραφος..., translated by the ESV as "But the tunic was seamless". In the next verse it says μὴ σχίσωμεν αὐτόν... "let us not tear it". Grammatically speaking, αὐτόν/"auton" in John 19:24 is just as masculine as the αὐτόν/"auton" in the case we're discussing. Yet there is no debate on the personhood of the cloak and people would question the sanity of the ESV translators if they translated that last bit "let us not tear him". Unless it's one of those cases where we used a gendered pronoun when it isn't actually necessary but is idiomatically okay (e.g., "My boat, she's a sinking!"), in English we would generally choose "it" if something doesn't have an obvious gender and/or agency. So here "it" is appropriate because it would be weird in English to call a cloak "him". But in Greek that's not the case. If someone said μὴ σχίσωμεν αὐτό in reference to the cloak, he/she might be chastised for bad grammar because using the masculine is normal for the language in this case. John 16:7 is parallel. Greek has the pronoun as masculine because the noun it refers to is grammatically masculine. That in and of itself implies no gender or even agency. Jesus (or his translator into Greek) essentially had no more choice in the gender of the pronoun than whoever it was that said "let us not tear it (masculine pronoun)."
Now if παράκλητος/parakletos implies gender or agency, that's something else. That is meaningful. It clearly implies agency but it is debatable that it implies gender.
@warren you say "so saying it's merely an English thing to assign gender to persons of the Godhead is false". I agree. However, what I said was "need not imply gender", not "does not imply gender". Perhaps I should have said "doesn't necessarily imply gender".
@Susan That's really interesting. So here's the question I have about this. Idiomatically speaking, when referring to an agent and substantized, is this adjective/noun always masculine? If it is, then there isn't really a choice that can be made here (grammatically speaking) and the "choice" of gender isn't a choice at all and just what is expected in the language. If it isn't, then a masculine παράκλητος here might be useful for arguing gender, which could be useful for those concerned with giving the Spirit a gender. I was hoping the Philo reference in De opificio mundi would be helpful but I don't think so :( I don't know the answer to this but I think it's an interesting question. More usages of the word would be helpful. The form you mention clearly shows that there can be a feminine (in both grammatical and sex senses) παρακλήτρια. But is there enough data to prove that παράκλητος is a dude? Somebody get us all the references to the term in Greek literature and we'll figure it out :)
Comment: Glad I could help :)
Comment: @Mallioch While I appreciate your (on the whole) well reasoned response, I fail to see how you are not contradicting yourself between paragraphs 2 & 3 - specifically: 'This is why pronouns that refer to "helper" like the "auton" in 16:7 are masculine'  &  'this is an English thing you are doing, not a Greek' - is it possible to clarify this at all?
Comment: "Father" is distinctly "male", as is "Son" - so saying it's merely an *English* thing to assign gender to persons of the Godhead is false.
Comment: I agree about grammatical gender != sex. However, in most languages, including Greek, adjectives and certain nouns that refer to people are inflected according to sex. Παράκλητος (derived, as it is, from a participial=adjectival form of παρακαλέω) behaves (or at least *can* behave) this way. Thus you will find in LSJ [an entry for the fem. παρακλήτρια](http://stephanus.tlg.uci.edu/lsj/#eid=80615&context=lsj&action=hw-list-click), used in classical lit., e.g., to encourage Hecuba to ["sit a παρακλήτρια at the knees of Agamemnon"](https://books.google.com/books?id=9_ZbAAAAcAAJ&pg=PA37&lpg). :-)
Answer: Jesus calls the Holy Spirit "him":

John 14:16

I will ask the Father, and He will give you another Helper, that He may be with you forever

John 16:7

But I tell you the truth, it is to your advantage that I go away; for if I do not go away, the Helper will not come to you; but if I go, I will send Him to you.
Comment: I'd want to know that in the original languages the pronoun was masculine, and that there was a gender neutral alternative that the writers discarded in favour of "he". Otherwise this could be simply an arbitrary choice by the writers, not intended to imply actual gender information.
Comment: So to summarize the comments, this answer is completely wrong! Jesus did not call the Holy Spirit "Him". The biblical translators had to pick a pronoun to make the sentence grammatical, and choose "him" as probably the best alternative.
Comment: In John 14:16, there is no pronoun - it's just paraklatos, which is masculine.
Comment: @DJClayworth it is actually arbitrary, to a point. The gender used is masculine because "paraclete"/"helper" is masculine. The word choice itself was not arbitrary because he meant to say what he said, but the gender of the word is. So this line of reasoning is not accurate.
Comment: Yes. The gender of the word is not indicative of anything. Otherwise the Hebrew ruach would be a feminine spirit and then we're all theologically messed up.
Comment: The answer ignores the fact that the Greek language uses gender specific words


dismissViewControllerAnimated sends message to zombie object

Question: I have two UIViewControllers, VC1 and VC2. VC1 has a button that invokes a triggered Modal segue to VC2. This segue is defined in the storyboard. In VC2, the user can return to VC1 using a pan gesture that executes this line of code:
[self.presentingViewController dismissViewControllerAnimated:YES completion:nil];

This code has worked for a long time. However, all of a sudden when this line runs, the app crashes. I enabled zombie objects and I can see this error:

-[VC2 retain]: message sent to deallocated instance 0x7f843a81e200

I've run the zombie profiler and here are the results:

UIClassSwapper initWithCoder seems to be where the app crashes, and there appears to be a an over retained object there, but I can't get any further. When I set an exception breakpoint, I just get into the assembly code, and this isn't of any apparent help.
So, there are a couple of questions here. The first is simply what am I doing wrong in how I am presenting and dismissing this view controller? After that, I don't know how to crack into the event history to figure out how to handle this zombie object.
Any help is appreciated. Thank you!
Answer: It seems that you use ARC project. Please provide more code:
1. How you initialize presentingViewController property (and declare). Is it (nonatomic,strong)?
2. How do you put this ViewController to the screen. Is it a kind of modal view controller etc?
-- added after comment.
ARC based project decides automatically if the object is needed or not and removes it from the stack automatically. So, the only one useful recipe to avoid this problem is to add NSNotification observer and post there notifications time after time. It will keep view controller in the stack and avoid automatic release.
Another solution - check if the controller is still in the stack:
    if (!self.presentingViewController) [[THECONTROLLER alloc] init];

The third one - is to use some object to declare VC1 and VC2 as class variables, and present them as modal view controller when needed. In this case, object and its variables will be kept untouched as long as any of VCs presented.
In any case, the Exception happens because ARC considers that VC is not needed anymore and releases it atomatically.
Comment: Thanks for the reply. Yes, this is an ARC project. There is no explicit reference to the presentingViewController in the code. Both `UIViewController`s are defined in the storyboard, as is the segue between the two. As I mentioned, this segue is a Modal segue. That segue gets executed as a triggered segue also defined in the storyboard. Does that answer your question?
Comment: It answered the question and reply is corrected. Hope it helps


What is the purpose for the tag "saw"? Should it be replaced on questions?

Question: I just called up the tag "saw" to review info on its tag wiki and discovered that it has been used 13 times and has no descriptive tag wiki.  There are also a lot of other "saw" related tags such as hand saw, table saw etc.  My thinking is that this tag is not useful and in each case the tag could be replaced with a more specific and useful one.  I would be inclined to review all of the related questions and retag them more appropriately, but wanted some feedback before doing so.
Answer: I agree, given "saw" is such an incredibly broadly-applicable and generic term.


Can I hide some applications from menu, but leave it searchable?

Question: I want hide some applications from menu, but leave it searchable from search field in app menu.
This beheavior is similar to Onboard application. Which icon not visible on menu, but may be find with search field.
Answer: You can achieve this by editing the corresponding *.desktop files, or the easiest way is to use an app called AppEditor, you can find it in appCenter. Just uncheck 'show in launcher' and save.


In the US, how can a federal law be prevented from being made?

Question: I often hear about measures that both major parties employ to prevent laws they do not like from passing, but in asking this question I would also like to know what a third party could potentially do to that end. Both in case of specific laws and all legislation in general.
Comment: As far as I can tell, this question is just asking how a bill is turned into law?
Comment: **Jury Nullification** is always an option.
Comment: @user1873 - Jury Nullification doesn't prevent the law from being made. Merely from being applied in one, specific, court case.
Comment: This question needs some clarification. Are you talking about the process prior to a bill being passed as a law? Or are you talking about repealing existing laws? (in either case, however, the process would be the same for everyone--regardless of the political party they belong to)
Comment: I am talking about the process prior to abill being passed as a law.
Answer: So, assuming you mean: in Congress, before a bill is passed, how can a party prevent a bill from passing:

Obviously, vote against it, on the full floor of either House
Kill(vote against) or pigeonhole(take no action on) it in the Committee
In the House of Representatives, in the Rules Committee, pass a restricting rule or schedule for a non-in-session date

Out of Congress, before a bill becomes law, obviously you have the Presidential Veto, which in the vast majority of cases kills the bill.


How did Dr. Brand decelerate when reaching Edmunds' Planet?

Question: At the end of Interstellar all fuel from main engines of the Landers and Rangers was used to escape Gargantua's (the black hole) gravity well. They accelerated enough to break free. So how did Dr. Brand slow down when she got to Edmunds' Planet? The ship would have been traveling at a high speed.
Comment: Aerobraking does not require much, if any, fuel.
Comment: @AndrewThompson it does require air. OP is asking about Endurance in space, not the rangers or landers in atmosphere.
Comment: The novelisation says that they've enough fuel (and velocity) to "scrape" to orbit around Edmunds. That would imply that they wouldn't be moving it a high velocity and could simply move directly into a parking orbit without the need for a retro thrust.
Comment: (De/A)cceleration is like one big plothole in this movie. Thorne thought about medium sized accompanying black holes they could use for gravity assists but they weren't included.
Answer:
They only used Lander 1 and Ranger 2's main thrusters. Other thrusters, including maneuvering, retro or deceleration thrusters, were not used. The Endurance was still blasting it's engines even after Coop had detached Ranger 2.

They calculated what was needed, and either saved some fuel for the deceleration, or the burn was calculated to minimize any needed deceleration. Ideally, it was calculated to put the Endurance into orbit at the perfect speed.
Brand placed Endurance in high orbit, using Edmunds' Planet to decelerate.
Endurance has it's own fuel and drive sections. Lander 1 and Ranger 2 were used as a boost, emptying their tanks, but Endurance did not burn everything. In fact, the Endurance only had 3 engines left after Mann destroyed one.

Brand uses Lander 2 to land on Edmunds. Lander 2 hasn't had all of it's fuel burned off.

According to the wikia:

Lander 2 was later used by Brand and CASE to reach the surface of Edmunds' planet. With the amount of fuel available after delivering supplies to Mann's planet and pushing the Endurance out of [Mann's planet] orbit, only two cargo pods could be delivered to the surface of Edmunds. It remains capable of atmospheric flight, but has insufficient fuel to return to orbit. -Interstellar, The Official Novelization

Each of the sections of the Endurance are modular sections. Four are specifically designed to be detached from Endurance, and ferried down to the surface with the Lander ships. Since Brand had to (could only) bring two down, that means Lander 2 had enough fuel for one or two orbital launches. The Landers are only big enough to carry one pod at a time. (Assuming she went down for recon, up then down for Pod 1, then up for Pod 2, and finally down for good. Or she immediately took down Pod 1 and only came back up once.) For this, Endurance had to be in some form of stable orbit.

The Landers could only take one pod down at a time.

Notice the ones on Edmunds' Planet are significantly bigger, much like the modules on the Endurance.
Answer: Taking the film's official novelisation into account, it's not especially clear that Brand would need to use any fuel to decelerate the Endurance once it gets to Edmunds' planet. All signs point to her being able to maneuver straight into some sort of orbit once she gets there, not forgetting that since the Endurance is lost to her (it's explicitly stated that she only has enough fuel to make a single trip to the planet's surface, delivering one of the cargo pods (which presumably contains the two individual hab modules seen at the campsite), it therefore doesn't really matter whether the orbit is totally stable, just as long as it's sufficiently stable for her to locate the landing site from space, then loop back around at least once to make the final trip down.

Please excuse poor quality of diagram
Coop tells Brand that with the amount of speed they'll lose exiting the black hole's enormous gravitational field and even with a full burn (and the dropping of the Ranger) to boost them, they'll still have barely have gained enough velocity to make it to the planet. That would strongly suggest that they're not going to be moving at an especially high speed once they arrive:

He stopped within arm's reach of her. They were both sealed in their spacesuits, yet it felt very—personal.
  "The navigation mainframe's destroyed," he said, "And we don't have enough life support to make it back to Earth.
  "But…" he added, "We might scrape to Edmunds' planet."

Coop also makes it clear that that she'll have fuel enough for course corrections but makes no mention of a retro burn, again strongly suggesting that the plan it to take the ship directly into a stable orbit without the need to lower its speed.

But when he considered everything she would have to accomplish, and
  all on her own, just to reach Edmunds' World — the course corrections,
  placing the Endurance into a stable orbit. Loading the population bomb
  onto the lander—along with anything else she would ever need, since
  there wasn't enough fuel to go back up once the lander had descended.


Reference for the number of samples needed to distinguish two probability distributions

Question: I am looking for a reference (and/or a full proof) for this statement:

$O(1/\epsilon^2)$ samples suffice to distinguish any two probability
  distributions with variation distance $\epsilon$.

I would be very grateful for any pointers.
Answer: So here, you only have two options: either your samples come from $p$, or from $q$ (and you know explicitly both).
By definition of the statistical/total variation distance, we have
$$
d_{TV}(p,q) = \sup_S( p(S)-q(S))
$$
where the supremum is taken over all measurable sets $S$. I haven't looked at the paper, but assuming all is nice (finite), the $\sup$ is a $\max$ and achieved for some particular set $S^\ast$, that you can compute given $p,q$.
So at this point, you have an explicit set $S^\ast$, the values $p(S^\ast)$, $q(S^\ast)$ which by definition satisfy
$$
p(S^\ast) = q(S^\ast) + \varepsilon
$$
and you know that the unknown distribution $h$ is either $p$ or $q$. So to distinguish between the two cases, it suffices to estimate $h(S^\ast)$ up to an additive $\frac{\varepsilon}{2}$, which can be done straightforwardly with $O(1/\varepsilon^2)$ samples.

Side remark: this can be improved a little if both $p(S^\ast), q(S^\ast)$ are both $O(\varepsilon)$ themselves. In which case, distinguishing between the two cases only requires $O(1/\varepsilon)$ samples. (The "hard case" basically is to distinguish $1/2$ from $1/2+\varepsilon$, which requires $\Omega(1/\varepsilon^2)$ samples.)

Second remark: usul refers,in his answer, to a harder problem, composite hypothesis testing. In this problem, you only have one distribution $p$, and want to distinguish between (i) $h=p$ and (ii) $d_{TV}(h,p)>\varepsilon$ (that is, the second option is not a singleton $\{q\}$, but the much larger set of all distributions that are $\varepsilon$-far from $p$). In this case, you need a lot more samples: as a function of the (explicitly known) $p$, this will be basically* $\lVert p^{-\max}_{-\Theta(\varepsilon)}\rVert _{2/3}/\varepsilon^2$ (see [VV14]), where $\lVert p^{-\max}_{-\Theta(\varepsilon)}\rVert _{2/3}$ is a functional of the distribution $p$ (equal to $\Theta(\sqrt{n})$, for instance, when $p$ is the uniform distribution on a set of $n$ elements). See also [BCG16] for an alternative, also tight* characterization of this quantity in terms of another functional.
$*$ The two characterizations are tight in most cases, except some pathological/strange ones.

[VV14]  G. Valiant and P. Valiant. An automatic inequality prover and instance optimal identity testing. In Proceedings of FOCS, 2014. [full version]
[BCG16] E. Blais, C. Canonne, and T. Gur. Alice and Bob Show Distribution Testing Lower Bounds (They don't talk to each other anymore.)
Manuscript, 2016. [ECCC TR16-168]
Comment: Incidentally, here is a writeup (nothing fancy, basically just the argument above) on it: https://github.com/ccanonne/probabilitydistributiontoolbox/blob/master/testing.pdf
Answer: Edit I misinterpreted the problem! See Clement's answer instead.
I don't know the context of this paper (not having read it), so I'm not going to address the paper at all, but I can talk about sampling from classical probability distributions which seems to be the question.
In that context, the statement you give is only true fixing the support size of the distribution. The more precise statement was shown in [1], see also [2]. The right bound is $O\left(\max\left\{\frac{n^{2/3}}{\epsilon^{4/3}}, \frac{n^{1/2}}{\epsilon^2}\right\}\right)$ samples suffice when support size is $n$. If you fix $n$, then this is $O(1/\epsilon^2)$ as $\epsilon \to 0$ (as the second term in the max is larger). I think for a proof you have to see those papers, maybe my comments below are also helpful.
If the question is just to tell whether a distribution is uniform or far from uniform, which sounds relevant for the paper you mentioned, then the complexity of this is simply $O\left(\frac{n^{1/2}}{\epsilon^2}\right)$ whose upper bound goes back I'm not sure how far -- it is the idea of birthday paradox -- and whose lower bound was shown by [3].
To show the $\sqrt{n}/\epsilon^2$ upper bound (which is $O(1/\epsilon^2)$ if support size is fixed) is pretty easy: Draw $O(\sqrt{n}/\epsilon^2)$ samples and check the number of collisions. It will be much higher than expected if the distribution is nonuniform. I think you can find something like this in these lecture notes[4], which also mentions the distinguishing-two-distributions problem where similar ideas can be used. (I also have the uniformity-testing case written up in a paper I could reference if wanted.)
To get an idea of a counterexample when support size is not fixed, suppose $\epsilon < 0.5$ and imagine a distribution on support size $n$ where each probability $p_i = \frac{1}{n}\left(1 \pm 2\epsilon\right)$, where say a random half of the coordinates get probability $\frac{1}{n}\left(1 + 2\epsilon\right)$ and the other half get the lower probability. The total variation distance between such a distribution and the uniform distribution is $\epsilon$. But imagine trying to tell whether you have this or the uniform distribution. You can learn nothing if every sample you draw is unique -- you need a "birthday collision". But the chance of a birthday collision gets smaller and smaller as $n$ grows. This construction was used by Paninski to prove the lower bound in [3].
[1] "Optimal Algorithms for Testing Closeness of Discrete Distributions" by Chan, Diakonikolas, G. Valiant, and P. Valiant, 2013. https://arxiv.org/abs/1308.3946
[2] "A New Approach for Testing Properties of Discrete Distributions" by Diakonikolas and Kane, 2016. https://arxiv.org/abs/1601.05557
[3] "A Coincidence-Based Test for Uniformity Given Very
Sparsely Sampled Discrete Data", Paninski, 2008. http://neurotheory.columbia.edu/pdfs/Paninski_2008.pdf
[4] http://www.wisdom.weizmann.ac.il/~oded/PDF/pt-dist.pdf


Vintage MTB, mounting new v brakes

Question: I'm installing deore v brakes on a 1988 Bridgestone mb2.
The front brakes installed fine.
On the rear, the pin on the v brakes that is inserted into the frame to set spring tension does not align with the hole in the frame. It's misaligned by a mm or two.
This is my first v brake setup, could be missing something obvious.
I definitely have rear brakes. Also tried installing a front brake in the rear, with the same misalignment.
Not sure if this is an issue with standards that have changed over the years? Strange that the front pins insert perfectly.
Comment: Hello and welcome to the website! To get a higher chance for help or advice, a picture of the rear brake so that pins/holes are visible will help. You can edit your question and add pictures to it any time. Noting (exact) models of old brakes that were present on the frame and the new ones you try to install might also help.
Answer: I find the v-brake on the front fork, which often times has just one hole for the spring pin, is a smoother install. Idk why.  There is no difference in "front" or "rear" v-brakes except the direction of the pads.
Typically at the rear, the frame's tabs where the brake bosses are threaded or brazed on will have three holes per side drilled in them from which to choose the insertion of the brake arm's spring pin. Each arm's spring pin should be placed in the same relative hole (if the left spring's pin is in the middle hole, the right spring should also be in that side's middle hole).  Spring tension is highest when the upper most hole is used. Typically the middle hole is chosen.
One way to ease getting the pin into the desired hole is loosen the brake pad's nut enough so the pad can be rotated parallel with the arm. In this position the whole side of the brake can freely rotate on its boss without the pad bumping into the seat stay.   This way allows easier access and placement of the spring pin into your desired hole.  This may be the crux of the problem. Is the brake pad blocking the movement of the arm before it's pin is sufficiently lined up with the hole?
Park Tool has a great tutorial on installation of linear pull brakes.  V-brakes is a term coined by Shimano and is a linear pull brake system.
Comment: Thanks for the response! I've updated the post with pictures. I tried your trick of loosening and rotating the pad, no luck. Also watched the Park Tool video. I have some old cantilever brakes (unbranded), and these installed fine. The bike was sold with cantilever brakes back in 1988. Perhaps the frame or linear pull pin require some persuasion, the misalignment is quite small. I'll leave that to a mechanic! I'll also try visiting a LBS with old parts bins & see if I can get a linear pull brake to fit. I'd rather not use cantilevers over the wet winter here.
Comment: @ Ted Lewis Is the misalignment one in which the receiving hole seems a little too far outside from where the pin can fall?  In other words, the distance between the center of the bike's brake boss to the receiving hole is greater than the distance between the caliper arm's mounting hole center and the spring pin. Enlarging picture #2 and examining the pin hole, there's a notable wear notch from previous spring pin(s). It's in the area you'd expect from a slight discrepancy between the aforementioned distances. Previous spring pins were barely clearing the distance to be received by the hole.
Comment: Good eye Jeff. You're correct about the direction of the misalignment. Turns out the right rear will fit the new linear pull brakes with some persuasion. It's just the left rear where the pin is too far from the hole.
Comment: I brought the bike to my LBS. The mechanic had more balls than me & simply tightened the brake & the pin found its way into the hole. I'm sure the pin bent along the way, but it's on. Thanks to those who responded!
Comment: Way to persevere, Ted.

Vintage MTB, mounting new v brakes


Derivation of gravitational potential energy

Question: Change in potential energy is $$\Delta U = -\text{Work Done} \, .$$ While deriving the equation for potential energy we just equate the work done by gravitational force with the potential energy and do not consider $\Delta U$, i.e. $U(r) - U(\infty)$, where $r$ is the distance of the object from the gravitating source. If we do that then the gravitational potential energy would come out positive. Why is that we don't take $\Delta U$ in this case?
Comment: I'm not sure what you mean by $U(r)$. Potential energy isn't absolute, i.e. you can only define it relative to a reference point. Often, we take a point infinitely far away from the system of interest as the reference point. Then we *define* the potential energy at point $p$ as the work needed to move a particle from infinitely far away to the point $p$. Is this what you're asking about?
Comment: Yes exactly. Why is the work done equated with potential energy. What's the logic behind. If it's something related to "storing energy" then what about the change in kinetic energy due to that work?
Comment: More on [sign convention for gravitational potential energy](https://physics.stackexchange.com/search?q=is%3Aq+sign+%5Bconventions%5D+%5Bpotential-energy%5D%5Bnewtonian-gravity%5D).
Answer: I think you're a little bit confused. $$\Delta U = \text{-work done BY the object} = \text{+work done ON the object}$$
This is critical! So, if you push a block, you're losing your "potential" to do work, and the block is GAINING said ability. (Friction aside, of course). You need to differentiate between work done BY and work done ON. In fact, in some sense, potential is the total amount of work done ON an object; once the object "gains" that energy, it can release it. So the potential energy is kind of the work done by "God" (or your teacher, or some angry really bored person who's been around since the dawn of time) on your object to get it the way it is.
As you know: $$\text{Work done BY object}=\int_a^b F dx$$
As I mentioned earlier, you can see potential as the work done by the universe to get an object into the state that it's currently in.
Since it's stupid to say "let's measure gravity relative to a distance exactly 37.6 AU from some random object", we might as well just say "let's measure compared to being infinitely far away", because it's way more useful and easier to work with.
Well, now everything is easy:
$$\text{Force exerted by gravity} = -\frac{GMm}{r^2}$$
Now we shove that into our integral:
$$\text{- Work done ON object}=\text{Work done BY object} = \int_\infty^{r_{0}}{-\frac{GMm}{r^2}dr}=[\frac{GMm}{r}]^{r_0}_\infty= \frac{GMm}{r_{0}}$$
And we're done! Since potential energy is work done ON object ("by the universe" is implied), and that's negative work done BY the object, so our potential is negative, which it intuitively should be!
Answer:
Change in potential energy is $\Delta U =$ -Work Done

is to be read as
Change in potential energy is $\Delta U = -$Work Done by gravitational forces
So imagine that you have two point masses as the system that you are considering and define the gravitational potential energy to be zero when their separation is infinite, $U\infty) = 0$
The separation of the masses is then decrease to $r$ and so the gravitational potential energy of the masses is now $U(r)$.
In going from infinity to separation $r$ the change in gravitational potential energy of the system of two masses is $\Delta U = U(r) - U(\infty) = U(r)$
So that is the left hand side of your equation dealt with.
The gravitational force is attractive and along the line joining the two point masses.
Imagine that something (you?) is holding the masses apart but allows them to start at rest when at an infinite separation and finish at rest when the separation is $r$.
Whilst the separation is decreasing the gravitational forces are moving and doing work.
This work is positive because the direction of the gravitational forces and their direction of movement are the same.
So minus the work done by the gravitational forces is negative which means that the change in gravitational potential energy of the system is negative ie the gravitational potential energy has decreased.

Another way of defining the change in gravitational potential energy is $\Delta U = $Work Done by external forces
Now the external forces are opposite in direction to the gravitational forces so the direction of the external forces is opposite to the direction of movement of the external forces.
Hence the work done by the external forces is negative as is the change in gravitational potential energy of the system.

If the system os two masses is isolated then the centre of mass of the system cannot move.
This means that if the masses are allowed to move closer together due to their mutual attraction their centre of mass does not move.
This in turn means that both masses move towards the centre of mass and the gravitational forces (equal in magnitude by Newton's third law) on both bodies do work.
However in the case of a system like the Earth and an object on the Earth with the mass of the object being very much less than that of the Earth the movement of the Earth towards the centre of mass of the system is negligible compared with the movement of the object.
The Earth is assumed not to move at all.
Answer: I don't know where you're getting your signs from, but the procedure you're considering is exactly what is done in practice.
If you let a particle of mass $m$ fall in from rest at infinity to some radius $r$, it will pick up some kinetic energy and speed: this means that it goes from kinetic energy 0 to positive kinetic energy, so positive work was done on it.
Since the change in potential energy is the negative of the work, the potential energy must have decreased, not increased. So the change is negative, not positive.
Comment: So the work done $W=U(r)-U(\infty)=\int_{\infty}^r\frac{GmM}{r^2}dr=-\frac{mMG}{r}$ is the work done by the gravity force, to bring $m$ from infinity to $r$. The work done on the mass $m$ is the negative of this. Therefore the potential energy of $m$ has decreased. In other terms, $m$ gains kinetic energy on the expense of potential, and the balance is zero. The total energy remains unaltered. Right?
Comment: @AlexanderCska almost; I would take issue with saying that the first expression is "the work done by the gravity force to bring $m$ from infinity to $r$," that is the exact opposite of what your next sentence says, which I would regard as correct. A work is a force *on an object* integrated over distance, which by the work-energy theorem is also a change in the kinetic energy *of that object*. So there is no difference between "the work done on the mass $m$" and "the work done by the gravity force".


Differential Privacy and appropriate noise distribution

Question: In differential privacy solutions and more specifically for queries that they do entail counting the proposed solutions define the Laplace distribution that is best calibrated for low error. Other solutions for non-numerical queries propose exponential distribution. However, it is not clear why noise from a Laplace distribution is chosen for numerical? What is the special property that best suits the Laplace distributrion?
Answer: In order to bridge the gap between two worst case scenarios to produce similar distribution of privatized answers certain noise is added. For example the salaries of a CEO (max) and a line worker or who ever gets minimum wage (min) may not be produce similar distribution without the noise.
Random values taken from Laplacian distribution with standard deviation is large enough to cover the gap.
This link has a good beginners tutorial with detailed explanation. Around 15.33 minutes in the video the speaker discusses about the issues like Global Sensitivity and Laplacian Noise.  Subsequently she discusses the proof too.
Comment: yes but why laplacian and not gaussian for example??What is the special property that makes laplacian suitable for differential privacy
Comment: I thought the second line "Random values .." answers the same. For detailed explanation please follow the excellent video link i gave
Answer: The Laplace mechanism is a symmetric exponential distribution, which works particularly well with the differential privacy guarantee: when you compare two Laplace distributions of the same scale, with a different mean, the ratio between the tails stays the same. For example, in the following graph, the Laplace distribution has a parameter of $1/ln(3)$, so the ratio between two distributions is bounded by $3$ and $1/3$.

The Gaussian distribution, on the other hand, doesn't have this nice property. It's not as straightforward to find out the maximum ratio between two Gaussians with the same standard deviation and different means. Let's compute the ratio of density functions of two Gaussians, centered respectively in $0$ and $1$. Getting rid of the constant factor, we have:
\begin{align}
  \frac{e^{-\frac{(x-1)^2}{2\mu^2}}}{e^{-\frac{x^2}{2\mu^2}}}
    & = e^{\frac{x^2-(x-1)^2}{2\mu^2}} \\
    & = e^{\frac{2x-1}{2\mu^2}}
\end{align}
This is unbounded when $x$ increases. So you can't get true differential privacy with a Gaussian. You can use it to obtain relaxations of the definition though, like $(\varepsilon,\delta)$-differential privacy or Rényi differential privacy.


Same redirect URL for Approve and Reject

Question: Why, when I'm requesting /oauth/dialog and selecting either of the options I get redirected to the same URL with different hash values? It's not a bug per-se, just an observation I made while developing an app.
Answer: This is just how OAuth 2.0 indicates rejection, you get different values on the redirect (either in the hash for the implicit client side flow, or in proper query string parameters for the explicit server side flow).
Instead of code or access_token (depending on the flow the app is using) you get error and error_description.  When a user rejects you get error=access_denied.
Comment: @Eimantas - nope, not if it's a compliant OAuth 2.0 implementation.  Responses should be 302's (redirects) or 200s (pages displayed as normal to *users* saying an error was encountered).
Comment: but shouldn't it return different status code (sorry if it already does) or get redirected to different URL (`login_failure` instead of `login_success`)?


Filefield with IMCE browse server

Question: I am having rather strange issue. I have created custom CCK with image upload field. To browse a server folders I've installed a CCK Filefield and configured it to work with IMCE , however I can't see images (uploaded with FTP), unless I upload them through IMCE itself. The strange thing is that in Description field I have also IMCE file browser wich "see" correctly all images. What am I missing? Thanks
Comment: What users are owners of files uploaded via FTP? And who's owner of those uploaded with IMCE?
Comment: "Administrator" is the owner of those uploaded with IMCE. I've read about this isue in some posts but, if this is the case than why I see them correctly in IMCE file browser which is located in Description field ?
Comment: one owner does not help, as we can't compare it to anything. The point is to find a difference between these 2 kind of files. Only then we can try to find out why that difference matters. Tell us how these files are different. My guess was file system owner recorded for them, but it may be something else.
Comment: I cant find the owner of the file in CPANEL it just show the user which is the same for all files
Comment: Have I told you I don't love cPanel? Guess not. Sorry, I can't help you if I don't know what's the difference between files, and it's probably in uid, gid or mode. Don't think cPanel is going to tell you them.
Comment: I've cheked file owners via FileZilla and it seems they are the same for all files (Owner:10059 Group:505)
Comment: So my usual solutions just went down the drain. At least you avoided most common configuration errors.
Comment: As I said this is a very strange while it works in CKEditor and not in Filefield
Answer: To overcome the above problem, I have installed the IMCE for FileField module; everything started working.
Answer: Make sure you reference the files directory as "." NOT as "sites/default/files" in your IMCE profile settings. (Per the Directory instructions below: "To specify file system root, just enter .(dot) character.")

Filefield with IMCE browse server


Why are transaction fees sometimes higher than what I'm transferring?

Question: Transferring from my wallet to another baffles me prior to the transaction charges. Please someone help. The charges are sometimes higher than what I am sending.
Comment: What wallet software are you using to send?  If you are sending very small amounts, then this is normal; fees are based on the number of bytes in the transaction, not the amount in bitcoins.  Bitcoin is not designed to allow people to efficiently send very small amounts.
Comment: Possible duplicate of [How to calculate transaction size before sending](http://bitcoin.stackexchange.com/questions/1195/how-to-calculate-transaction-size-before-sending)
Answer: Transaction fees are not in relation to the amount of value transferred, but in relation to the amount of block space they'll take. Therefore, it is relatively cheap to send large amounts of value in Bitcoin but uneconomical to send micro-payments.
Answer: It doesn't matter how much bitcoin you send, it matters on the size off the transaction. For example, inputs are about x bytes, outputs are y bytes, and a transaction is z bytes. If you add them all together (Let's say in one transaction, I have two inputs and one output, 2x+y+z), you will get the size of the transaction.
I use cointape.com for this. It tells me the best Satoshi/byte rate to use. Currently the network is congested, and takes about 70 sat/byte for a fast transaction. Usually it's around 20-30.