Is our galaxy colliding with Andromeda, or is Andromeda colliding with our galaxy? (i.e. Which is moving less / staying still?)

Question: ...Or does this question not make sense because of Relativity?
Comment: Related to MW+M31 collisions: http://physics.stackexchange.com/questions/26745/, http://physics.stackexchange.com/questions/14657, http://physics.stackexchange.com/questions/49799
Answer: Andromeda and the Milky Way belong to a group of galaxies called the Local Group. The two galaxies are the largest galaxies in the group, so to a pretty good approximation their interaction can be treated as a two body problem, with the other galaxies in the group producing only minor perturbations to their motion.
So as you suspected, it isn't the case that we are moving towards Andromeda or Andromeda is moving towards us. Both galaxies are moving towards their mutual centre of mass, which is somewhere on the line joining the two galaxies.
If you go by visible matter then Andromeda is about four times heavier than the Milky Way, but as BillOer mentions some studies have suggested that including dark matter reduces the difference and may even make the Milky Way heavier than Andromeda. Whatever the case, it seems clear that neither galaxy is so much heavier than the other that it dominates the motion.
As Bob mentions, the Local Group as a whole is moving relative to the cosmic microwave background, and the average speed of the group is around 630km/sec. The relative speed of the Milky Way and Andromeda is about 125km/sec, so it's small compared to the overall speed of the Local Group.
Answer: Strictly speaking, the universe has no rest frame (that we know of). If you want to set the rest frame of the CMB to be stationary, (which is reasonable in many applications), you may compare the velocity of the Milky Way and the velocity of Andromeda with respect to the CMB rest frame. (I don't know if anyone has ever done this, however.)
The CMB dipole should consist of two factors: the dipole due to our peculiar velocity (our motion through space) and a primordial dipole. However, there two would be near impossible to disentangle from each other, and as far as I know, nobody even considers this as an answerable question (at least among the CMB people I know).
Answer: Their mutual gravity will pull them towards each other, with the more massive galaxy causing more acceleration on the smaller. According to this article the more massive is the Milky Way, so it will cause Andromeda to accelerate more than the Milky Way, not that it really matters. Since interstellar space is mostly empty (i.e. there is a lot of distance between stars), other than possibly being ejected from the combined galaxy, very few will be affected.


I have a 20 watt UV light, how long do I have to expose my screen?

Question: I tryed exposing for 10 minutes and my design doesn't wash out. I used Emulsion for beginners. And I used a uv light and stand from Amazon.
Comment: Does this answer your question? [How do I determine exposure time for a silkscreen?](https://graphicdesign.stackexchange.com/questions/13576/how-do-i-determine-exposure-time-for-a-silkscreen)
Comment: This can not be answered, theres no info on emulsion used nor what the light is like (wavelength, spread, light producing method;  20w lightbulb is way different from a 20w led, would be better to know lumens on surface). That said there are people who feel this question does not fit here.
Answer: The only way to know is that you make a controlled test. I am assuming the emulsion actually works.

The first step would be reading the instructions for the product.

But on your specific setup you can do a test strip.

Cover for example 80% of the area of the emulsion (and design) with thick flat cardboard (It is better if it is painted black on the side of contact) and put some weight on it. 20% will be exposed.

Expose X amount of time. Let's say 5 mins. But as you already have tested 10 mins, start with that time.

After time X, uncover 20% more. The first strip will be exposed 2X.

You can now test 1X to 5X time and see which exposure works best for your combination of exposure, light intensity, light distance, temperature, and other variables.

The test strip will tell you not only which time is enough to harden the emulsion, but also if the design gets too hard to wash because the borders of the design, especially on thin lines got also burned.

I don't know what is the power of the lights you have, or quality, etc.
If 25-30 mins is not enough, I would make a strip test on sunlight, to see if the emulsion actually works, then I can discard 1 variable. Probably you can do the sun strip test first. The base time X can be different depending on the product.

A variation on the times of the first test can be using squares. So the first strip will be exposed double the time incrementally. For example:
In minutes: 1, 2, 4, 8, 16
So the exposure will be 31, 15, 7, 3, 1.
Then you can have a rough idea and refine it later with a linear change. This is especially useful for example the sun test because some products could be fast enough to be ready on the first strips.
Comment: I added this answer to the other question.


play sound on receiver phone when message from custom app is send

Question: I am building android app where i need to send message to some contacts and that receive must read that message immediately.I want to play some music when i send message from my app at receivers place even if his mobile is in silent mode.
Any help will be appreciated
Comment: If I have my phone in silent mode, I really don't want to hear a sound from any kind of app... I'm pretty sure that android will never let you do this. (Maybe I'm wrong)
Answer: I suggest Google Cloud Messanging or a service wich does Poling on the server looking for new messages.
the first one is better.
On message received create a notification that plays a sound and shows the message.
If the receiver keeps the device with no sound, you shouldn't force it to play the sound


What does it mean when an oil is labeled with an ISO range rather than a single ISO value

Question: I am a layperson, not an engineer. After reading some articles on what ISO viscosity grades mean, I do not understand what it means for an oil to be labeled with an ISO viscosity range, e.g. "ISO 32-46".   I thought the ISO number translated to a specific flow rate under a defined set of circumstances relating to temperature and orifice.
Comment: Tolerances are a thing. You might be concerned with just one bottle of oil, but the manufacturer needs to deal with hundreds or thousands over multiple batches.
Comment: @DKNguyen  :  Are you saying the oil so labeled would be "close enough" to 32 and close enough to 46 (i.e. somewhere between them) that it could be used when either viscosity was called for?
Comment: Yes in that it might vary from bottle to bottle. No with regards to "close enough to use." Whether you can use it depends on how tolerant or sensitive your application is. You can probably get away more with a lawnmower than a race car. Ratings generally do not tell you how to use the product. They tell you what the product is.
Answer: In the US, motor oils are sold with viscosity ranges ascribed to them if they contain additives that flatten the viscosity-versus-temperature curve (so-called "multi-viscosity" oils). Is the ISO rating you are citing here describing a multi-vis product?
Comment: Multi-vis oils retain their low-temperature viscosity at high temperatures  (the slope of the viscosity-versus-temperature curve is decreased). so they do not lose lubricity when running hot. I do not know if the oil in question is such an oil.
Comment: The oil in question is pneumatic oil.  The tool calls for ISO 46.  When searching for a small quantity of that oil, I found products labeled ISO 32-46 and I didn't know what that range signified versus the simple designations ISO 32 and ISO 46.  In practical terms, what does it mean "to flatten the viscosity-versus-temperature curve"?  Does it mean that the viscosity of such treated oil remains relatively constant despite changes in temperature, and if so, where in the range does the viscosity lie?  Does ISO 32-46 have a relatively constant viscosity of about 39 across a temperature gradient?
Comment: ...across a given temperature gradient?  (ran out of characters)


delete a file on my local branch using git

Question: I have some changes in some of my files which were already there. Then I have added a new file in it using
git add newfilename

I didn't commited yet, Now I want to delete this new file. I can't do the reset as it will reset all other file changes also which I don;t want.
I tried git checkout newfilename and usual guesses delete and rm also but not helping.
Answer: git reset newfilename will remove it from the index and then you can delete it as usual.
Answer: Try a
git rm --cached newfilename

To at least remove it from the index.
Answer: Just you can remove a file from your branch by using this command:
$git rm file_name


I'm trying to create this model for 3d printing. Blender says I have zero faces even though they have area. How do I fix this?

Question: I started off with a plane and applied the solidify modifier to it so that it was 1.5 mm thick. I used plane cut to cut off some corners and now blender says I have zero faces made from those cuts. What are zero faces and how do I fix this?
Answer: I believe that is telling you there are zero area faces present, and that tool will  highlight them if you click on the actual button that is reporting them . You can probably simply delete the faces it has highlighted and all will be well.
Maybe a better approach would be to select all of the faces in the object (in edit mode) and then go to Mesh -> Clean Up -> Degenerate Dissolve, which will dissolve all zero area faces and zero length edges ....
Comment: The thing is, those aren't the only faces marked that way. of the other pieces you see in the screenshot, those are all marked zero faces. I'm not sure what or how I created these zero area faces so I have no idea how to make the rest of the geometry if I don't know how to avoid it. I noticed that they seem to all be from places that I separated the mesh at and either filled holes or joined meshes at but I'm not sure then how I could do those things without creating a zero face


Canon PIXMA MP230 doesn't work with Ubuntu 20.04

Question: I have a problem with my Canon PIXMA MP230.
The problem is that when I want to print a file, it goes to the print queue, but it does not print, printing appears stopped.
I clarify that I have the drivers installed but it still does not work.
Answer: I had a similar problem with a Canon printer (Pixma IP7250), which worked fine with Ubuntu 18.04 and 19.10. But with kubuntu 20.04, it did not work at all. I finally found help in this forum, in the terminal I typed in
    sudo apt install cups-backend-bjnp

This installation worked quickly. After I could choose a driver which worked for my printer in the system settings, the printer worked properly with this driver!
Comment: Saved my life.  Set this up like 3 times on a ODROID XU4 for AirPrint and I could not remember for the life of me how to get the network part to work.  Fixed!
Comment: This solution also worked great for installing my Canon Pixma MG5300 on Ubuntu 22.10
Answer: I have had the same problem for a long time after upgrading to Ubuntu (Xubuntu/Ubuntu studio in my case) 20.04: my Pixma mp230 accepted print jobs, proudly announced "rendering complete" (in the log file) and just as proudly refused to print. I have tried to fix it a couple of times, but it failed miserably and was not a great priority these past few months.
This is the simple solution, which I found on distrowatch.com' s user rating page of Ubuntu 20.04  (the review dated 2020-08-19):

remove ippusbxd (sudo apt remove ippusbxd in terminal)
delete and reinstall the printer using the normal GUI printer utility
Print a test page. Worked for me!

The proposed theory behind it is that ippusbxd "creates" a "ubuntu"-printer which interferes with the original printer/printer drivers (in the reviewer's case a Brothers printer, in my case a Canon Pixma mp230).
I am incredibly thankful to the original problemsolver for this simple solution and thought I would pay it forward here, where more people might see it.
You might also want to read these related questions where more knowledgeable people than me explain how all printers now are "network printers" or something like that. Apparently removing ippusbxd isn't the most elegant solution, but as long as it works I'm happy :-)

Getting HP DeskJet 3700 working with Xubuntu 20.04
Comment: This answer seems totally appropriate here, as it's the same model printer. For other models, I'm not so sure it will work, so I would hesitate to post the same answer. At the moment, I'm not sure whether all these questions about being unable to print after upgrading to 20.04 should be closed as duplicates even though they are about different printer models. In general we prefer to link questions that are essentially the same and have the same answer rather than posting the same answer to all of them. If your answer works for all these questions, they should probably be closed.
Comment: I fail to see how it would be inappropriate. People looking for a solution for this specific printer (including me) will end up on this page and until now didn't 't get an answer. As a bonus, the solution seems to work for several models, as described in my answer. I also documented where I got that answer.
Comment: I leave it to others to decide if all these seemingly similar questions should be merged, isn't the important thing that there is an answer or link to an answer after each question?
Comment: I would tend to agree with you on the whole, it's just that duplicate answers get automatically flagged and what tends to happen to them here is that they all get deleted except one, regardless of the situation with the questions. I don't support that as a rule, but I would like to figure out if these questions should be closed. I'll try to find some time to look into it.
Answer: This solution 'seemed' to partially work as I was able to find my MG2900 Canon listed in the GUI as a new, available printer, in Ubuntu 20.04, Mate desktop.
But...it still didn't print. So I unplugged it so as to reset the Wifi. The light was blinking. That stopped that, but still didn't print. So 'Delete'd it from the GUI with the intent of reinstalling it automatically again, like it had done a few seconds before. AND now, it doesn't show up in the listing of available printers attached to USB like it had the first go round.
I'd already installed sudo apt install cups-backend-bjnp
I'm going to reboot and see if that makes a difference.
Nope. Canon printer no longer shows up at all. Going to uninstall/reinstall in term now.


Limit user profile on specific OU using Group Policy

Question: We have a host that will be used for creating VM clones from time to time for testing purposes.It is used actively for testing and users tend to keep a lot of files in their profiles.We would like to limit users profile size to avoid cloning unnecessary files to new VMs.
Is there way to impose limit on user profile on OU level without introducing roaming profiles?
Comment: What Windows OS would this be?  You could possibly just set disk quotas for the user profiles, but the method to do this can vary.
Comment: Sorry, this would be Windows 2k3 server.
I am not sure that 2k3 can have per directory quotas though
Answer: One solution would be to create a logoff script that deleted the usual locations where users store things in their profiles or on c:\temp or wherever. Just create a GPO, link it into the OU where the users live and create a WMI filter to apply it only to that machine (the VM). Then it only runs for users if they logoff from that machine.


Display Network analysis route service in India

Question: I am working on ArcGIS JavaScript API, I need to display route from one point to another.
Thats why I need any Network Route Service for India. Is there any?
Comment: There in no such service exists in India..please be specific..
Answer: Apart from what has been mentioned already, you might consider using Bing Routing service that should be available in ArcGIS API for Javascript. I have personally seen the sample working with ArcGIS API for Silverlight though. The Bing Maps seems to cover India geographically, so the routing service should be available there even when accessing programmatically.
Some other alternatives are consuming the routing services from Nokia or TomTom (TomTom might not cover India though) with their APIs and then parsing and visualizing the response in JS API since it comes back what I've seen so far in JSON with the geometry and such.
If you will plan to build your own network analysis services, consider using OSM Planet, for example, available for download for free from http://market.weogeo.com. This will give you access to the roads in India you might use then in ArcGIS for building own network datasets.
Answer: Yes, please take a closer look at http://resources.arcgis.com/en/help/arcgis-online-network-analysis-rest-api/#/Overview_of_Network_Analysis_Services/02s500000007000000/ and http://resources.arcgis.com/en/help/arcgisonline/index.html#//010q000000pt000000.
Answer: At the time of writing, no such routing service exists from Esri for India.
Option 1 - Build your own:

Obtain the datasets you need for creating a Network Analysis Layer.  Might be worth asking a separate Question on obtaining data for India, I am not familiar with what datasets are freely available.
Publish this layer within a dynamic map service and enable the network capability.
Consume the service within your JS application and make use of the RouteTask to enable routing within your application.

Option 2 - Use Google
The above might be hard work depending on the data availability.  Perhaps an alternative option would be to use the Google Maps API (read terms of use).

Overlay your services from ArcGIS Server using this library.
Use the directions service to make use of routing within your application.


ambient air temp. sensor reading -40 on 2004 Jeep Grand Cherokee Laredo

Question: The old sensor got broken during a accident with a deer. I've replaced the sensor and it's reading -40 deg. Is there a reset on this unit? The sensor worked about a year after the wreck until the plastic end finally broke off. What's the secret to getting it to read at all?? Is it in the computer chip or do I have a wire that is shorted out?? Any help would be appreciated.
Comment: If you give the engine size, and 2 vs 4 wheel I can provide more detailed troubleshooting to my answer.
Answer: The wire going to the sensor is not connected (most likely) or is grounded out somewhere. It's also possible that the switch is bad, but you said you have replaced it.
-40 is the lower limit, it will read -40 when it's unplugged or grounded depending on how it's set up, most are set up for the former.
Comment: Thanks Larry. My neighbor has three Jeeps and after talking with him he agrees with you. So I'll have to find a new harness and install it. I appreciate your info. Oh the engine is a 4.0 six cylinder and it's a 4WD. Just saw the second part of your note.


What happens when pixels cover almost all the area of the sensor?

Question: I think, in this question, one who give an answer has to consider 'pixel size vs pixel pitch'.
I read that in some sensors, pixels don't cover the whole sensor and my question is, when the pixels cover almost the entire area, will the pixel size and the pixel pitch be equal?
And what can be said about sensor that is related to pixel size and pixel pitch?
Comment: Are you referring to spacing between two adjacent photon receptors? As in: "no spacing <=> cover all the complete area"?
Comment: @MartijnCourteaux Yes
Answer: With conventional CMOS sensors the issue isn't so much the spacing between photosites (pixels). It's all of the circuitry on top of them (usually on the edges of each photosite) that blocks light from getting through to the semiconductor layer. What microlenses do is redirect light that would otherwise fall on the edges of photosites where the circuitry blocks some of that light and aims it to the center of the photosite where there is no circuitry etched on top of the semiconductor layer.
By redirecting the photons that would otherwise not make it down a pixel well the microlenses help make the sensor more efficient because more of the photons that strike the sensor actually make it down a pixel well and are counted by the sensor.
Comment: So, is it for the 'pixel size vs pixel pitch' case you said about the circuitry?


Who should write summary papers and what are the pros and cons of doing so?

Question: My advisor has suggested that I write a survey paper. I am concerned because neither my advisor nor I are know for, or are knowledgeable in, the topic my advisor is suggesting. We would be starting completely from scratch. I am concerned this will be an exercise in futility as our combined lack of experience would make our credentials questionable at best and make publishing our work in a quality journal either hard or not possible. Even if we can create a publishable work, I am concerned about how many PhD students undertake such a project. From my (admittedly) limited experience it seems like survey papers require an exorbitant amount of time and may not offer as high of a return on investment as research papers can for PhD students. I am in the computer science PhD program at my school if that helps. Are my concerns irrational? What are the pros and cons of a PhD student writing a summary paper? Thank you!
Comment: Is the suggested topic relevant for your PhD thesis?
Comment: yes, it is relevant
Answer: In my field survey papers are highly cited. If the same is true in your field than the low chance of success may be ofset by the high reward if you succeed.
Regardless, you need an overview of what has happend in your field concerning your thesis. Making it an article forces you to really think through the relationships between the articles. For me it is quite common for me to read articles and think "well, it is kinda like that" and when I force myself to sit down and really write that argument down it does not work. So even if your overview does not get published, it is still a great investment in your subsequent articles. And who knows, maybe you are lucky.


In The Belgariad, where did Errand come from?

Question: In the book Magician's Gambit, the 3rd book of The Belgariad, they come across a boy whom they name Errand.  Who was he really, and where did he come from?
Comment: [Wikipedia has a paragraph on this](http://en.wikipedia.org/wiki/List_of_The_Belgariad_and_The_Malloreon_characters#Eriond), do you think there's a lot more to say about him?
Comment: The [Belgariad](http://en.wikipedia.org/wiki/Belgariad) article links "Errand" to [`#Eriond`](http://en.wikipedia.org/wiki/List_of_The_Belgariad_and_The_Malloreon_characters#Eriond).
Comment: @Gilles - I never found that...probably because I didn't remember that errand = eriond.
Answer: It sounds like you haven't read the Malloreon, the sequel series. Errand is explored a lot more in that series, and in the two followup books about Belgarath and Polgara, which are stories set after the end of the Malloreon, where they talk about their personal histories. I'd very strongly recommend you read those books, as they really are as good as the first series, if not better.
I'll mark this with spoiler tags, as it would kind of ruin the reading of the Malloreon to know this stuff going in. It's been a year or two since I last read the books, so I apologise if the details are a bit fuzzy.

 The prophecies, and the killing or Torak, are all a buildup to fixing a great cosmic accident, which happened millions of years ago, millions of light years away. As a result of the accident, Torak was born as one of the 7 gods, which was never meant to happen. When Belgarion killed Torak, he was clearing out the old mistake, and leaving the path open for the originally intended God of the Angaraks to step forward: Errand (or as UL gives him his true name: Eriond). Errand's role in stealing the Orb was essentially to move the prophecy forward, so that Torak could be killed and he could become the God of the Angaraks. However, Errand himself is ignorant of most of this until most of the way through the Malloreon.
   So that's who Errand really is. As to his origins and where he came from, Zedar's story about finding him in a city he can't remember is the truth. This is the first memory Errand has. Belgarath and Beldin theorise that Errand was brought into being specifically so that Zedar could find him, and the prophecies deliberately made Zedar's memory of the incident fuzzy. As such, we never explicitly find out exactly where Errand came from, but we do know that the Gods and/or the Light Prophecy had a hand in his creation. His origin certainly isn't a natural one.
Comment: "really as good".  No.  Not by far.  They are even worse than the tail end of the Belgariad.  Of course, this is about taste.  I *did* devour the Belgariad like a hungry wolf (got the first book "by accident" while on a trip to England, ordered the other two back home in Germany, couldn't wait to get them).
Comment: Thanks!  I actually did read the Mallorean, but it was millions of years ago as well, and for some reason it didn't stick with me as well as the Belgariad did.  I didn't even recall that it was something of a continuation...my memory was that it was a completely unrelated story with the same characters.  Huh.
Comment: "There was no father. I carried him, I gave birth, I raised him, I can't explain what happened." :-D


What, if any, is the point in demanding to copy-paste an entire Reddit page?

Question: Where to buy a judo uniform (judogi) in Tokyo this was word-by-word asked on Reddit, which I found and left a link to it. Then you idiots forced me to copy-paste a good 80% of it. What's the point? Reddit archives pages after six months, they do not change and the chances of Reddit disappearing off the Internet is incredibly small and the discussion in question was quite on point with perhaps one comment being irrelevant. I tried to make it shorter but there is some information lost unless I do copy the whole thing.
Comment: Steady on old mate, link only answers are shunned for whatever reason and it's just part of WHAT IS.  I upvoted your answer anyway also because WHAT IS. Take the good with the bad and crack on :)
Comment: StackExchange wants people to visit their site, not some other random page on the Internet.
Comment: @pnuts The question here was at first...erm...not so well asked. But if you don't mind, you can outline as own answer under what circumstances a link-only answer would be acceptable. Being in the Fortress of Commonality can be a bit boring, a voice of cool dissent could be refreshing.
Answer: Keep cool.
The question itself was something I would have voted to close because it resembled too much a shopping question. But ok, let's let it be valid.
I can understand that you want to link to it because it is a completely
self-contained answer and reddit archives them. So copying an answer
from it seems to be a pointless exercise, accepted.
The problem is that the point of stackexchange is not linking to answers,
but giving answers at once so that the person asking the question
does not need to browse the web. And reddit can still be DDos'ed and
yes, it can vanish from the internet (Millenials, do you know what "Netscape" is ? No ?)
I also want to point out that stackexchange is voluntarily, nobody
forces you to copy-paste 80% of a question.
I would advise that you take some time and sleep over the business.
We could still talk over linked-only answers, but it seems currently
your blood is a little bit boiling.
Comment: I laughed out when I saw the mention of Netscape. Yes, I'm a millenial and I do, though ;)
Comment: @Jan how about Lynx?
Answer: Quite simply: Stack Exchange's model is questions and answers. Note that is says answers — not counterquestions, not links to answers, not 'yes I need that, too' comments, not saying thank you but answers.
There are a number of reasons why somebody might want an answer right below the question. Maybe their internet is tediously slow, incredibly expensive, or both. Maybe some sites are blocked but <code>*.stackexchange.com</code> isn't on their machine. Maybe they trust voting here but not there.
Also note that nobody is forcing you to copy and paste. You can also quote and summarise. You can condense that page with information you get elsewhere. You can delete your post. (You can wait until it has an absolute value score of 3 to win a badge while doing so.)


Who decides precisely when a film will be released?

Question: Who decides when a film is released? We know that the director and producer work in tandem, but who specifically, job role would be preferable here, decides precisely when a film will be released into the wild? For some reason, I had in my head that there was a large meeting, where they would decide exactly when a film was released into cinemas - what person, with what job role, decides this, and does this person work as someone who has nothing to do with the films production in the first place?
Comment: That would be the studio executive.
Comment: Please make this an answer so I can mark this as complete.
Answer: For a major studio, there is likely no single individual who makes the call - not even the CEO, who is ultimately responsible to a board of directors. For the most part, a studio is going to look at market conditions and other competing releases to determine the best date to maximize box office revenue.
This is illustrated by recent statements by Disney's CEO on the controversial decision to release Black Widow simultaneously in theaters and on streaming due to the ongoing COVID-19 pandemic.

Bob Iger and I, along with the leaders of our creative and distribution teams, determine this was the right strategy because it would enable us to reach the broadest possible audience.

So, the largest and most profitable studio in the industry makes this decision carefully after input from stakeholders who are deeply involved in the process and only after carefully weighing alternatives. Other studios very likely have similar processes in place for their releases.
Comment: Another example - Dune, being released in various markets on September 15th, US and UK Oct 22nd, and Australia Dec 2nd due to the ongoing lockdowns in the country which are anticipated to be over by that point.
Answer: While there is an accepted answer to this question, I will post an additional one here, as I can answer specific parts of the original question that have not been answered yet.
Usually the director/s, producer/s, studio/s will agree on a theatrical (cinema) release window. This will be determined by the completion date of the production. The bigger the film is, the narrower the window of the theatrical release. Big blockbusters have their dates locked when the initial production agreement is signed and any release date change will require approval from a number of parties.
Then the Theatrical Distribution teams will work on the cinema release of the title around the world. They will decide on specific release dates. For the vast majority of the titles they will have the ability to move the release date of this title in any country, within a few weeks/months.
The distribution teams are typically split into two groups, the Domestic (US & Canada) and the International distribution teams. The International team is further divided into EMEA (Europe, Middle East & Africa), Latin America & APAC (Asia Pacific).
So, for example, for the release date of a film in Peru, the local Managing Director of the distribution company who will release the film and his/her team will have a release date recommendation based on the instructions (e.g. film delivery date, contractual obligations, global release strategy, talent touring availability etc.) they received by the head office. Their recommended release date will be reviewed and approved/rejected by the LATAM regional distribution team.
For some releases the recommendation goes the other way, from top to bottom. This is usually for bigger titles, with the local teams only making counter-proposals if it is absolutely necessary.
Key factors to take into consideration:

The US release date (aka Domestic date)
The competitive landscape ( i.e. other films that may get released around the same time, this includes local titles)
Major local holidays, sport events, elections etc., that may affect the availability of the target audience
Piracy: in markets with rampant piracy, you need to release the film as close to the domestic date
Weather: In some markets, weather dictates how people will spend their time. The first hint of summer-like weather in spring, may mean barbecues instead of cinema visits in some markets. We cannot predict the weather of course months in advance, but distributors do avoid periods where the weather can literally destroy the release of a film.
Talent availability for PR. If your main actor/actress is willing and/or contractually obligated to support the film's marketing campaign, then he/she will go to premieres and other events around the world. Clearly this helps the film's release and requires additional planning, that takes into account the talent's availability.
Some films will be award contenders. Depending on the potential awards, there are further restrictions in terms of when a film can be released.
And last by definitely not least, the target release date for the other, and much more profitable, revenue streams: this was TV and video in the past and streaming in our times. Die Hard had a Christmas theme and was released in July 1989, as the studio was aiming to have an appropriate 1989 Christmas release for home entertainment (video rentals/purchases).

This is just a brief list of some of the many factors that need to be taken into consideration when the distribution teams around the world work on a theatrical release date.
In the 35mm film era, another important consideration was the cost of the reels. The set of reels required for a film to be shown in one cinema would cost $2-3k or more. In these times, a reel would first play in the bigger cinemas of a major market (US) then move a few months later in another English-speaking country (UK, AUS, SA) and then finally move to subtitling markets where they would chemically etch the subtitles on the 35mm print. For example, Die Hard opened in July 1988 in the US, in February 1989 in the UK and in December 1989 in Hungary. Today, practically all cinemas play digital copies, so this is not an issue.


Vorticity and angular momentum

Question: In Taylor-Couette flow, the interior fluid becomes fully turbulent if the relative angular velocity of the cylinders is high enough. The turbulent fluid has a vorticity distribution, and each of the (time-averaged) vorticity vectors must point along the rotation axis. If one increases the relative velocity even more, the strength of the turbulence (and its vorticity) also increases, as does the total angular momentum of the fluid. What is the quantitative relation between the two?
Answer: Around each vortex of vorticity $n$ the rotor of velocity is:
$$
\oint v \ dl = 2 \pi \kappa
$$
Where $\kappa$ is some constant ( in case of superfluids $\frac{n \hbar}{m}, n \in \mathbb{Z}$). At the same time, using $v = \Omega \times r $, $\Omega$ - angular velocity, and $\text{rot} v = 2 \Omega$. Let us consider some circle of unit area, on one hand taking the integral around this circle:
$$
\oint v \ dl = 2 \pi \kappa \nu
$$
Where we $\nu$ denotes the average vorticity of the fluid. And at the same time
$$
\oint v \ dl = 2 \Omega
$$
Where we have applied the Stokes formula. So finally one gets:
$$
\Omega = \pi \kappa \nu
$$
Comment: I understand there is a relation between vorticity and the local angular speed. I am asking about something else. Given the vorticity distribution in a 2D fluid, what is the total angular momentum content of that fluid?

Vorticity and angular momentum


Performing join on simultaneous spatial and attribute criteria in ArcGIS for Desktop in Modelbuilder?

Question: A similar question was posted here, but I have an additional problem that seems to make the answers there unlikely to work.  I am interested in performing a spatial join between point feature class A (target) and point feature class B in order to get the feature in B that is closest to each feature in A.  However, I would like it to be the case that a feature in B must be in the same country as feature in A in order for it to be joined.  The difficulty, is that the closest feature in B to feature in A may in fact be in a different country, but the next closest feature in B may be in the same country, and this is the feature I'd like to have the spatial join return.  While model builder seems to allow me to iterate through selection of one feature class (the "feature selection" iterator), it does not seem to allow me to iterate a feature selection that draws on attributes for two feature classes, so that I could set the country fields equal before performing the spatial join.  (I'd like to avoid using python since I don't have any experience with it).
Comment: Have a look at http://gis.stackexchange.com/questions/185673/arcgis-near-by-group/185718#185718
Comment: This is wonderful! Thank you - this tool seems to work really well (so long has the relevant field of attributes has the same name in both feature classes).
Comment: Also, just to let folks know:  It looks like for some reason you can only perform this tool once on a given feature class. I've tried to do it by changing field names so the NearOID does not become a non-unique descriptor, but I have been unable to do this model twice on the same feature class (with different corresponding "near" features).  The work around I did was to copy the feature class (before performing the "near by attribute" function), then perform it separately on each copy, joining it back together after the fact.
Answer: If you want to use model builder probably the simplest approach would be to expose some of your inputs as parameters and turn your whole model into a tool.
If it were me:

I would expose the the whereclause of a select by attribute tool which allows you to enter the code for a county. Apply this selection process on feature class A and B.
You now have two featureclass each with points select for a specific county, run the spatial join with these.

Most tools honour selections so only these points will be processed.


Can anyone tell me what this is

Question: I took this about a week ago, its always green and it very hearty  It is in Kentucky, I noticed it when I bought the house, I have even tried to mow it down but its very tough
Comment: Can you give us a clue?  Like, where is it?
Comment: What plant/tree is the trunk behind it? Because it looks like this growth is coming off the base or roots of whatever it is...
Answer: I have a feeling that looks like a young pampas grass. If it is, the edges of the long leaves are very sharp so be careful handling it as it can leave painful paper cuts. They can germinate from seeds blown on the wind from the fluffy plumes it produces in summer, when established, and can grow very big and wide.
Comment: The grass looks too coarse to be pampas grass (*Cortaderia* genus). I initially thought it might be Chinese Silver Grass (*Miscanthus sinensis*) or one of its cultivars because that grass is listed as invasive in Kentucky, but then I noticed that the characteristic white central vein was missing. My next thought is tufted hair grass (*Deschampsia*), which is at the southern limit of its range in Kentucky. About the only way to know for sure is to wait for flowers this summer.
Comment: It is some type of yucca, re the loose 'hairs' on the leaves visible in the photo.

Can anyone tell me what this is


Fingering for black key pentatonic scales

Question: I have noticed that everything I play on the black keys sounds "oriental".
I want to know the standard fingering for this pentatonic scale?
Comment: It can also sound African. I highly recommend this video about the "black keys": http://www.youtube.com/watch?v=DMF_24cQqT0
Comment: Does this answer your question? [What are the pentatonic scale fingering for piano?](https://music.stackexchange.com/questions/43311/what-are-the-pentatonic-scale-fingering-for-piano)
Answer: The black keys do indeed form a pentatonic scale, with the major mode starting on Gb and the minor mode starting on Eb. Here's the full list of modes for this scale. Personally, I wouldn't call the pentatonic scale particularly oriental in sound since it lacks the most commonly associated intervals (minor second, diminished fifth) for that sound.
One common fingering for the major pentatonic starting on Gb would be 1-2-3-1-2 (thumb is 1). Another (that involves less third skips on the thumb tuck) would be 1-2-1-2-3.
Here's a very interesting jazz improvisation over a pentatonic scale to get your creative juices flowing: http://www.youtube.com/watch?v=KkpQbjkRbzs
Comment: The mode build on Db provides a rather interesting sound, for instance. The mode built on Ab is called "egyptian". Major and minor pentatonic sound decidedly non-oriental to me :)
Comment: I've cleaned up the comments here, I think they got a little away from the point of the question :P
Answer: A basic fingering like R.H. 123 12 for a major pentatonic makes sense. But I seem to naturally do 123 13, 123 13 because then the 3 13, 1 portion uses the same 3 1 for the minor thirds between scale degrees ^3 ^5 and ^6 ^1.
I find playing a pentatonic scale literally on all the black keys - F# major pentatonic - is not very comfortable for the hand. Normally a complete major scale on F#/Gb would start with finger 2 rather than 1 so 123 12 feels kind of awkward. I've tried 231 21, 231 21 so that it starts with 2 like a major scale and the thumb doesn't need to pass under for the minor thirds. But I don't like that either.
Just in case, be aware you can play a pentatonic scale starting on any tonic. Ex. tonic on A would be A B C# E F# for major, or for a minor pentatonic on B would be B D F F# A, etc. A mix of black and white keys usually allows some better fit to the hand.


Why don't very many HTTPS websites supply ownership information in their certs?

Question: Why don't very many HTTPS/SSL websites supply identity information in their certs?
Comment: I think they do. All of the commercial SSL certificates issued by any of the major CAs will, at a minimum, include the domain name of the server. The domain name is exactly the identity information the HTTPS client has to verify. The HTTP client attempt to connect to a server with a specific DNS name. The SSL/TLS layer authenticates that the entity providing the content has been authenticated using that specific DNS name.
Comment: I think CAs charge extra for identity verification and since browsers don't display it prominently (unlike extended validation), few site operators bother with it.
Answer: Ownership information requires an actual human to look at documentation submitted and verify that it's correct; you can't automate verifying a human-level concept like ownership. If a certificate needs a human to look at and manually approve it, that costs money. Since ownership information isn't something that's very visible to users except for EV certs, and most users don't care almost all of the time, there's no reason to spend the extra money for an ownership-verifying certificate.
(edit: It's not enough for the site to just put it in a cert: for ownership verification to be done in the cert, the CA has to verify the ownership themselves; no CA is willing to sign something claiming to be a person or company unless they verify that that's actually true).
Comment: Extended Validation. Go to http://bofa.com and see the green bar saying "Bank of America" in the URL. That's an EV cert, which has extensive ownership verification and clearly displays it to the user.
Comment: What are EV certs?
Comment: Oh, yes, I was just reading [the Wiki page on EVC](https://en.wikipedia.org/wiki/Extended_Validation_Certificate). So, my question amounts to: "Why doesn't everyone use EV certs?" I think you've answered that. thanks


Difference between drawing via CGContext functions(CGContextAddArc, etc) vs CGPath functions(CGPathAddArc, etc)

Question: I know that if you draw with CGPath functions you would have to add that CGPath to CGContext in the end anyway(CGContextAddPath), but is there any advantage/disadvantage choosing first method over the second? And yes, I know that you can draw with UIBezierPath as well, and I know the difference between CGPath.
Answer: So, going through the documentation on UIBezierPath I bumped into one of the advantages of drawing via CGContext functions:

The advantage of modifying the graphics context (as opposed to the path object itself) is that you can easily undo the transformation by saving and restoring the graphics state. UIBezierPath documentation

Another one I came up with is that you don't have to release the path(CGPathRelease) if you draw via CGContext functions.


For swapping should i approve 0x contract address or address from function 'getTransformerDeployer' or 'getTransformWallet'

Question: I am building a middleware contract to interact with 0x protocol. so for swapping tokens
should I approve(erc20 function) directly 0x address for transferring asset or the address from the function 'getTransformerDeployer'. In other words should i transfer assets from user address to 0x contract address or the address from 'getTransformerDeployer' or 'getTransformWallet'
Answer: You approve the 0x exchange proxy address, 0xdef1c0ded9bec7f1a1670819833240f027b25eff. This is returned in 0xAPI responses as allowanceTarget.


What lead screw to use for specific torque and speed requirements?

Question: The setup: I'm trying to mount a leadscrew powered by this motor Tetrix Max Torquendado Motor on a 40ish pound robot, in order to lift it 4" off the ground. I already have the linear motion, latching mechanism, etc. I'd like it to go as fast as possible, but for now, let's just say that it can take 4 seconds to lift the robot. There will be 40ish pounds of tension acting on the screw when the robot is hanging, and minimal compression. Also, resolution is unimportant. It seems like there's a simple way to calculate the pitch/diameter leadscrew needed based on the torque, motor, and time requirements. What leadscrew should be used, and generally how could I calculate this sort of thing?
Comment: You may be able to simplify the system to a pair of gears with a ratio of the the pitch to the mean circumference. Given that for every rotation the thread will move it's pitch. But I'm not sure how to get it from torque to linear force and make the units balance without making stuff up. This would allow you to calculate a maximum pitch to diameter ratio required to lift a load with a certain torque, which you then need to compare to the material strength to minimise the diameter. This also doesn't consider friction, but you may be able to get away with grease and a fudge factor in real life.
Answer: The relationship between torque and force for a frictionless single-start leadscrew is [1]:
$$
\frac{F}{\tau} = \frac{2 \pi}{p}
$$
where $F$ is linear lifting force, $\tau$ is torque, and $p$ is pitch.
You can choose a suitable torque which that motor is best operated at, you know the force is the weight of the robot, so you can calculate pitch.
The speed of lifting is determined by the power delivered by the motor. So you can get maximum speed by operating the motor at a torque that maximizes its power output. That's typically half its stall torque (700 oz-in) so choose $\tau$ = 350 oz-in.
[1] https://en.wikipedia.org/wiki/Screw_(simple_machine)#Torque_form
Comment: What units should force and pitch be in? Also, does the diameter of the lead screw mater?
Comment: You can use any units as long as you carry them through the calculations (see high school physics textbook for how to do that). Or, to take a shortcut, choose a consistent system like (in, lb_f, lb_f-in) or (m, N, N.m). Diameter turns out not to matter at this level of idealization (frictionless, static, weightless rod).


Maximum size of data Bitcoin OP_RETURN tx can handle?

Question: I was wondering, it's possible to do proof of existence with the blockchain. How many bytes can we put in the 'OUT' of the transaction? Is there a limit? If yes, how many?
Answer: As intended by design, you can fit 80 bytes of arbitrary data in an OP_RETURN ( (I think originally proposed as 80, then set to 40, then set to 80, and it has been there for years.)
The script length is up to 83 bytes, but the first bytes are used up identifying the output as an OP_RETURN.
IIRC, the bytes are:
1: Output sequence number
2: OP_RETURN code
3: Number of bytes of data to follow (up to 80)
4-83: data

You can theoretically put a large amount of data in an OP_RETURN, but only if you mine it yourself (easier if you happen to be a big mining pool.) This is because if you put more than 80 bytes of data in there, other nodes will not, by default, relay your transaction, so it will never reach a miner's node and thus never get into a block.
In the past, miners have included some rather long OP_RETURNS in blocks. There's an example of a long output from November of 2013 in transaction d29c9c0e8e4d2a9790922af73f0b8d51f0bd4bb19940d9cf910ead8fbe85bc9b in block 268060.
This site decodes the output of the OP_RETURN to human-readable text, read it and you'll see it's over 1000 characters:
https://bitcoinsays.com/d29c9c0e8e4d2a9790922af73f0b8d51f0bd4bb19940d9cf910ead8fbe85bc9b
Comment: Please note that the `up to 80` part is misleading: one data push can handle up to 75 bytes. Therefore OP_RETURNs with 76-to-80 bytes need special handling: encoded with OP_PUSHDATA1 with 1-byte length. More details: https://bitcoin.stackexchange.com/questions/116080/tx-with-op-return-with-77-bytes-of-data-refused-by-node/116083#comment132105_116083
Answer: Using the OP_RETURN script you can put up to 80 bytes of data on the blockchain in exchange for paying a small transaction fee.  Some miners will let larger data through.
More details here: https://developer.bitcoin.org/devguide/transactions.html#null-data
Answer: According above link https://developer.bitcoin.org/devguide/transactions.html#null-data, since Bitcoin Core 0.12.0 you can put up to 83 bytes.


"Chained" relations (1:n:m) with Mongoid and Rails

Question: I'm trying to achieve a really simple "multiple relationship" in Rails (3.2.12) with Mongoid (3.1.2). I got three models:
class User
  include Mongoid::Document
  field :name
  has_many :collections
end

class Collection
  include Mongoid::Document
  field :name
  belongs_to :user
  has_many :things
end

class Thing
  include Mongoid::Document
  field :name
  belongs_to :collection
end

So basically there is a user who has collections and there are collections which have "Things".
Well ... first question: Is this even possible? And if not: Why not? ;-)
I can create users now (from a rails console or via web), and I can create collections belonging to users. But when I try to create a "Thing" now ... well it just doesn't get created:
2.0.0-p0 :014 >   u = User.first
 => #<User _id: 514b2b32e05658e1f1000005, name: "test">
2.0.0-p0 :015 > c = Collection.create!(name: "somename", user: u)
 => #<Collection _id: 514b30f0e05658ca67000001, name: "somename", user_id: "514b2b32e05658e1f1000005">
2.0.0-p0 :016 > t = Thing.create!(name: "a thing", collection: c)
 => #<Thing _id: 514b3120e05658ca67000002, name: "a thing", collection_id: "514b30f0e05658ca67000001">
2.0.0-p0 :017 > Thing.first
 => nil

The "Collection" gets created just fine:
2.0.0-p0 :018 > Collection.first
 => #<Collection _id: 514b2b65e05658e1f1000006, name: "test", user_id: "514b2b32e05658e1f1000005">

Comment: What happens if you change the Collection model name to something else, say to 'Stockpile'.
Comment: Jason ... perfect hint! That seems to be the problem. I renamed my model and it just works as expected. Now how can I mark your comment as answer?
Answer: Change the Collection class name to something else, say to 'Stockpile'. MongoDB uses 'collection' as part of it's terminology, so it may not play well with your models.


Is it permitted to use nicknames on jersey in international matches?

Question: I have seen that Dinesh Karthik from team India wears his jersey in the recently concluded Asia Cup 2014 with his name as DK. Is it permitted? I have seen players who use their nicknames in county games but not in international games.
Comment: i think they can have it.beacause i see a sometimes players wearing another one's jersey.so that's not a problem i think....
Answer: Not sure about ODI matches but in T20I match it is allowed to use nicknames. Here is a photo of a T20I match between Australia and India played at Melbourne on 1st Feb. 2008. In this match, IIRC all Aussie players used their nicknames instead of surnames e.g. Brett Lee used Binga instead of Lee, Michael Clarke used Pup instead of Clarke.

Again this may be allowed only in bilateral series and not in big tournaments like World T20.
Edit:
In ODIs too it is allowed to use nicknames on jersey. Parvez Rasool in his debut match against Bangladesh used "Parry" on his jersey. And some comments regarding this was posted on Cricinfo:

"It may well be a storm in a teacup but am not a big fan of using shortened names or nicknames in your T-shirt when you are representing your country - the case in question being Parvez Rasool's t-shirt carrying the name Parry. "
Comment: Yep! Have you seen Uthappa , his name in the jersey like ROBBIE
Comment: @Sukan - Nope, I didn't notice him.


Why do people use bouncycastle instead of Java's built in JCE provider? What is the difference?

Question: Why do people use bouncycastle instead of Java Cryptography Extension? What is the difference?
Comment: JCE is a standard API that any crypto algorithm can implement to allow for it to be accessible without coding dependencies on the provider. In other words, using the JCE APIs, you can switch ciphers and cipher providers without changing your code (in many cases). BC is a provider which means they implement ciphers that can be accessed through the JCE APIs. If another provider comes along that implements the algorithm you want better than BC or a newer, stronger algorithm, you can switch without changing your code (probably).
Answer: BouncyCastle has many more cipher suites and algorithms than the default JCE provided by Sun.
In addition to that, BouncyCastle has lots of utilities for reading arcane formats like PEM and ASN.1 that no sane person would want to rewrite themselves.
Comment: Sun never intended to be an exhaustive provider of ciphers. It's why JCE uses the provider framework which BC supports http://bouncycastle.org/specifications.html#install . Any users of BC would be wise to use it through the JCE APIs when possible.
Answer: Bouncy Castle is Australian in origin, and therefore is not subject to the Export of cryptography from the United States.
It is useful if you are outside the United States and you need to manage key sizes grater than permitted by such that restriction. In that case you are not permitted to use software from United States for that.
Comment: I wonder how many restrictions that actually remain, anno 2016 ?   As far as I understand there's no longer a restriction on key size as long as you register with US Department of Commerce's Bureau of Industry and Security (BIS), something I guess Oracle is already doing. But the regulations are cryptic (pun intended).
Comment: Ugh, if I am outside of USA I don't need to be permitted anything. The project may need to be permitted to ship something.
Comment: Most of the restrictions in the western world are based on where it's exported to rather than key size these days.  The key size limitation was one of the things relaxed at the end of the '90s.  As for current Australian regulations, it's not quite as lax as this answer implies, but it's not as bad as as the fearmongering of a few years ago was concerned of either (unless you invent a new algorithm and one or two other things.  In general it's covered by the Wassenar Arrangement and the ITAR regulations (via AU DoD).
Comment: An addendum to the above comment and which might indicate what can be done from Australia; I completed the DoD ITAR checks without tripping a single point (all of which were just "call us for clarification" type responses anyway) and so there's no barriers to my FOSS crypto work, though none of it is in Java.  This is because AU concerns are more with new and innovative cryptography developments, not things that are well known everywhere anyway (also the AU DoD definition of "public domain" is **not** the usual copyright one, they use it to mean that it's not classified or restricted).
Answer: On server or desktop, I don't see any reason to use BC unless you have to deal with some legacy ciphers or formats not supported by Sun JCE.
However, many JREs don't come with a JCE provider, like on mobile or embedded environments. BC comes handy in such cases.
Comment: On server there definitely is a reason, if your server is using TLS and you care about security (if you don't, why are you using TLS at all?). The cipher suites included with JCE only includes AES in CBC mode, which has a couple of known problems: http://googleonlinesecurity.blogspot.dk/2013/11/a-roster-of-tls-cipher-suites-weaknesses.html.
Comment: FYI This not true Java8 (From Oracle) at least.


How do I dynamically control animations in PowerPoint 2010?

Question: I'm playing around with PowerPoint creating a trivia game. When the user clicks on a tile on the main slide it advances to another slide with the question. When the user clicks the return button, they should return to the main slide (simple enough), but the tile that they had previously clicked on should disappear so that they cannot click on it again. It's a simple matter to make the tile disappear, but when returning to the title slide, all tiles reappear. I cannot figure out how to save the state of the animation so that they are not on the screen any more. I'm guessing this will need to be done with VBA, but my VBA knowledge is a bit limited. Any advice would be greatly appreciated.
Comment: A friend of mine, David Marcovitz, has written a book about this kind of thing and includes a LOT of useful examples on his web site: loyola.edu/edudept/PowerfulPowerPoint/index.html
Answer: An ugly, brute force solution that may lead to a maintenance nightmare
is to have an obscene number of copies of the page.
(And I guess that probably means an obscene number of copies of each page.)
For example
<code>X a     X a     X a     X a     X a     X a     X a     X a
X b     X b     X b     X b     X       X       X       X
X c     X c     X       X       X c     X c     X       X
X d     X       X d     X       X d     X       X d     X
</code>
would be the first 8 of the 16 (24) copies that you would need
if you have four tiles.
Using VBA would probably be a more scalable approach.
Comment: My VBA experience/knowledge is also severely limited; I might be able to grind out something that would help you, but there are probably people here who could do it in their sleep.  I suggest that you edit your question.  (1) Put in a bit more detail, like maybe mock-ups of what you want your slide to look like, before and after.  Consider changing the title; e.g., "How do I dynamically hide elements on a PowerPoint slide?"  And (2) tag it [vba] (and maybe mention VBA in the text of the question).  That might attract some more attention.
Comment: Right, I considered the page approach, but that's too intensive. VBA would be fine, but my VBA experience is too limited to know what to do. I'd still need advice there.
Comment: @SteveRindsberg: Thanks for contributing, but your comment might be more effective if you attached it to the question, rather than my answer.  Consider: since the OP has, essentially, rejected my answer, I might just delete it.  (I probably won't, but I *could*.)  Also, if other people who have similar problems find this question, they aren't likely to read all the comments *on my answer*.
Comment: @scott  Thanks, you're right. I've added it as a comment to the original.  Delete away, if you wish.
Comment: @SteveRindsberg: I was going to explain that I don't have the power to delete *your* comments,, but you do — but it looks like you already figured that out.


Stop command blocks on clock when sign clicked?

Question: I am making a one command creation which means that the command blocks are on a constant clock, I can make a sign on the front of it and I was wondering if there was a way to make it so if that sign is clicked they don't work until it is clicked again.
Answer: It's possible if your sign do a setblock to make appear a redstone_block next to one of the commands witch make the fill clock work. By keeping the clock command block activated it won't be able to continue looping.
But you will have to do many tests to find the good relative coordinates in the setblock and whenever you add a new command in your one command creation it make not work anymore since your sign may be at a different place so be shure to add it only when you have finished your one command.
To reactivate the clock you must add 3 commands on the sign:

make disappear the redstone_block you made appear earlier to deactivate the clock.
Make appear a air block between the 2 command blocks which makes the fill clock work.
Make appear a redstone_block again between the 2 command blocks which makes the fill clock work.

Here is an example of the json needed to add multiple commands in 1 sign:
<code>/give @p sign 1 0 {
    BlockEntityTag: {
        Text1: "{text:\" \\\/ \",color:\"gold\",bold:true,clickEvent:{action:\"run_command\",value:\"/setblock ... air\"}}",
        Text2: "{text:\"Click\",color:\"blue\",clickEvent:{action:\"run_command\",value:\"/setblock ... air\"}}",
        Text3: "{text:\"Here\",color:\"blue\",bold:true,clickEvent:{action:\"run_command\",value:\"/setblock ... redstone_block\"}}",
        Text4: "{text:\" /\\\ \",color:\"gold\",bold:true}"
    },
    display: {Name: "Custom Sign"}
}
</code>
It's almost the same if you want to do it with a /setblock or /blockdata command.


How do you convince an atheist that Islam is the true religion?

Question: How can you convince an atheist that Islam is the true religion and that Allah exists using proofs from the Quran?
Comment: As-written, this is hardly answerable; if atheists were so easy to convince as all that, fourteen-hundred-odd years of dawah would've make short work of whatever atheists were left by now. All you'll attract here is speculation and guesswork rather than practical *answers*, which is not what this site is geared for (see: http://islam.stackexchange.com/help/dont-ask)
Answer: An atheist does not believe in Quran so how would you convince him from Quran. First you have you make him believe that this world is run by a very complex and very orderly program which is beyond capacities of a human or human like thing. And there is one who regulates this program, there is one who has written the script of this program and this authority who has written code of this program has the ability to manipulate any part of this code at any time at will and we call this authority as Allah or God. Only when one believes on this reality then you can come to Quran or Prophet etc.
There are more plausible reasons to this, for that one should strive and reflect.


do squirrels chew lead-coated copper flashing boots on rooftop plumbing vent pipes

Question: I've seen pictures of damaged lead pipe boots where squirrels had chewed on them. Does the same damage risk exist with lead-coated copper?
Comment: The risk is low in either case. I live in squirrel heaven and they've never touched my plumbing. I think it's only a concern if they get the impression that there's something interesting in your attic.
Comment: I live in Squirrel Hell. Supposedly they chew on these flashing boots over the four-inch vent pipes because they like the taste of lead, or want to wear their teeth down.
Answer: Squirrels can cause many thousands of dollars in damage trying to get inside then if they do the mess and insulation both thermal and wiring they chew on and make nests out of. In the Pacific Northwest (the area I live) metal roof jacks and boots are the best to reduce damage but if they think they can get in they will really work hard at making a hole to enter. I have not seen much difference with copper or galvanized both are better than the PVC type that the little varmints can go through in a day. The best defense I have found is to make sure the jacks are sealed down with asphalt sealer (I don't think they like the taste). Lead and lead coated materials are getting tough to find in my area because of the push to remove lead from building materials. With that said if there is a small section that is loose they will try no matter what the material is or that is what I have observed. A good nasty tasting sealer and metal is the best option I have found with asphalt working the best for me.


Strange Feature? of Ruby Arrays

Question: I came around this strange feature(?) of arrays in Ruby and it would be very helpful if someone could explain to me why they work the way they do.
First lets give an example of how things usually work.
a = "Hello" #=> "Hello"
b = a #=> "Hello"
b += " Goodbye" #=> "Hello Goodbye"
b #=> "Hello Goodbye"
a #=> "Hello"

Ok cool, when you use = it creats a copy of the object (this time a string).
But when you use arrays this happens:
a = [1,2,3] #=> [1,2,3]
b = a #=> [1,2,3]
b[1] = 5 #=> [1,5,3]
b #=> [1,5,3]
a #=> [1,5,3]

Now thats just strange.  Its the only object I've found that doesn't get copied when using = but instead just creates a refrance to the original object.
Can someone also explain (there must be a method) for copying an array without having it point back to the original object?
Answer: Actually, you should re-examine your premise.
The string assignment is really b = b + " Goodbye". The b + " Goodbye" operation returns an entirely new string, so the variable b is pointing to a new object after the assignment.
But when you assign to an individual array element, you are not creating an entirely new array, so a and b continue to point to the same object, which you just changed.
If you are looking for a rationale for the mutating vs functional behavior of arrays, it's simple. There is nothing to be gained by modifying the string. It is most likely necessary to allocate new memory anyway, so an entirely new string is created.
But an array can be arbitrarily large. Creating a new array in order to change just one element could be hugely expensive. And in any case, an array is like any other composite object.  Changing an individual attribute does not necessarily affect any other attributes.
And to answer your question, you can always do:
b = a.dup

Answer: What happends there is that ruby is treating the Array object by reference and not by value.
So you can see it as this:
 b= [1,2,3]
 a= b

              --'b' Points to---> [1,2,3] <--'a' points t---

So as you can see both point to the same reference, that means that if you change anything in a it will be reflected on b.
As for your question on the copying the object you could use the Object#clone method to do so.
Comment: .clone, doesn't seem to work for a two demential array.  I'm assuming it clones the outer array, but keeps the inner arrays pointing to the original objects.  Any ideas what I would do there?
Answer: Try your Array case with a String:
a = "Hello" #=> "Hello"
b = a #=> "Hello"
b[1] = "x" #=> "x"
b #=> "Hxllo"
a #=> "Hxllo"

Strings and Arrays work the same way in this regard.
The key difference in the two cases, as you wrote them, is this:
b += " Goodbye"

This is syntactic shorthand for
b = b + " Goodbye"

which is creating a new string from b + " Goodbye" and then assigning that to b. The way to modify an existing string, rather than creating a new one, is
b << " Goodbye"

And if you plug that into your sequence, you'll see that it modifies both a and b, since both variables refer to the same string object.
As for deep copying, there's a decent piece about it here:
http://ruby.about.com/od/advancedruby/a/deepcopy.htm

Strange Feature? of Ruby Arrays


Is there any way to improve the gross CC/cycle gained from exploited systems?

Question: Right now, Arissa Lavigny Duval isn't doing so hot. We may have overextended a little bit, discovering that CC overheads don't increase on a linear scale. My theory is, that the best way to contribute to the power, would be to increase the gross CC gain from exploited systems. Is there any way to increase the profit margins of systems we already exploit, and already have no upkeep cost for?
Comment: It seems turning systems to your favorable government type is helpful, but this may only be for fortification purposes (for example: ALD favors Patronage governments)
Answer: No. CC/cycle is based on the population of all exploited systems. Since there is no way to increase population of a system, and one cannot create more systems, there is no way to increase this number. The only thing that can be done with these sort of deficit-causing systems is to shed them through turmoil by not fortifying them.


setsockopt with SO_SENDBUF/SO_RECVBUF is not working

Question: I was using setsockopt with SO_SENDBUF/SO_RECVBUF for setting the send/receive buffer of TCP with 256*1024 bytes.
But when I see in wireshark, I can see that the TCP's "Window Size" is shown as only 1525.
Also wmem_max and rmem_max are set with values 131071(126 kb).So ideally I was expecting it to be at least 128 kbps.
can anyone please help with this ?
Is this can also be a problem of wireshark where it is showing wrong "Window size".
Answer: You need to set that size on the listening socket at the server, before any accepts(), and at the client you need to set it on the socket before you connect it. That way you are allowing TCP's 'window scaling' option to take effect, which can only happen during the connect handshake. After the connection is established it is too late. That way the TCP receive window can be as large as the receive buffer, assuming various other conditions hold.
However unless you have an extraordinarily high-latency network with extraordinary bandwidth, 256k may be too large a size. There is no point whatsoever in setting it higher than the bandwidth-delay product, which can be calculated as the bandwidth in bytes/second times the delay in seconds, giving a result in bytes.
Comment: It's a *high* latency network that requires a larger window, not low.  As you then say, it's the bandwidth-delay product.


Can I tell ggpairs to use log scales?

Question: Can I provide a parameter to the ggpairs function in the GGally package to use log scales for some, not all, variables?
Comment: Have you tried using the aes() function for this purpose? I see nothing in the help pages that suggests there is any special log capability in ggpairs, but maybe it was assumed you would use typical ggplot conventions.
Answer: You can't provide the parameter as such (a reason is that the function creating the scatter plots is predefined without scale, see ggally_points), but you can change the scale afterward using getPlot and putPlot. For instance:
custom_scale <- ggpairs(data.frame(x=exp(rnorm(1000)), y=rnorm(1000)),
upper=list(continuous='points'), lower=list(continuous='points'))
subplot <- getPlot(custom_scale, 1, 2) # retrieve the top left chart
subplotNew <- subplot + scale_y_log10() # change the scale to log
subplotNew$type <- 'logcontinuous' # otherwise ggpairs comes back to a fixed scale
subplotNew$subType <- 'logpoints'
custom_scale <- putPlot(custom_fill, subplotNew, 1, 2)

Comment: Thanks for the solution, it's good to know how to manipulate the charts. I will try it later; for now, introducing new log'ed variables appears easier.
Answer: This is essentially the same answer as Jean-Robert but looks much more simple  (approachable).  I don't know if it is a new feature but it doesn't look like you need to use getPlot or putPlot anymore.
custom_scale[1,2]<-custom_scale[1,2] + scale_y_log10() + scale_x_log10()
Here is a function to apply it across a big matrix. Supply the number of rows in the plot and the name of the plot.
scalelog2<-function(x=2,g){  #for below diagonal
 for (i in 2:x){
    for (j in 1:(i-1)) {
      g[i,(j)]<-g[i,(j)] + scale_x_continuous(trans='log2') +
scale_y_continuous(trans='log2')
                        } }
 for (i in 1:x){  #for the bottom row
      g[(x+1),i]<-g[(x+1),i] + scale_y_continuous(trans='log2')
                       }
 for (i in 1:x){ #for the diagonal
      g[i,i]<-g[i,i]+ scale_x_continuous(trans='log2')  }
  return(g) }

Comment: this code does not work for me for values other than 2. and why "g[(x+1),i]", not just "g[x,i]"?!?
Comment: Just to clarify, this option works as of ggplot2 versoin 2.0.0 and GGally version 1.0.1
Answer: It's probably better use a linear scale and log transform variables as appropriate before supplying them to ggpairs because this avoids ambiguity in how the correlation coefficients have been computed (before or after log-transform).
This can be easily achieved e.g. like this:
library(tidyverse)

log10_vars <- vars(ends_with(".Length"))             # define variables to be transformed

iris %>%                                             # use standard R example dataframe
  mutate_at(log10_vars, log10) %>%                   # log10 transform selected columns
  rename_at(log10_vars, sprintf, fmt="log10 %s") %>% # rename variables accordingly
  GGally::ggpairs(aes(color=Species))

Can I tell ggpairs to use log scales?


the real part of a holomorphic function on C \ {0, 1}

Question: Let $h$ be a real valued harmonic function on the twice punctured plane $Ω = \text{C \ {0, 1}}$. Show that there exist unique real numbers $a_0$, $a_1$ such that
$u(z) = h(z) − a_0 \log |z| − a_1 \log |z − 1|$
is the real part of a holomorphic function on $Ω$ .
I tried to show that $u$ has a harmonic conjugate. I assumed there exists such a conjugate $v$ exist, then used Cauchy Riemann equations on $u$ and $v$. After integrating two equations, I tried to use the result to find $a_0$ and $a_1$. However, I failed to cancel out the extra terms. Is there any other direction I should go?
Answer: Define a function $g = h'_x - ih'_y$. Since $h$ is harmonic (and hence $C^2$), $g$ satisfies Cauchy-Riemann's equations on $\Omega$. Indeed:
$$
(h'_x)'_x = h''_{xx} = -h''_{yy} = (-h'_y)'_y
$$
and
$$
(h'_x)'_y = h''_{xy} = h''_{yx} = -(-h'_y)'_x.
$$
In other words, $g$ is holomorphic on $\Omega$. Assume for a moment that $g$ admits an anti-derivative $G$ on $\Omega$. If $G = U+iV$, Cauchy-Riemann shows that $G' = U'_x-iU'_y$, but $G' = g = h'_x-ih'_y$, so $\nabla U = \nabla h$, i.e. $U=h+C$, and we may as well take $C=0$ by adjusting our choice of $G$. Hence $h = U = \operatorname{Re} G$.
Now, the problem is that $\Omega$ is not simply connected, so we can't guarantee that $g$ admits an anti-derivative. On the other hand, we know that $g$ has an anti-derivative on $\Omega$ if and only if $\int_\gamma g(z)\,dz = 0$ for every simple closed curve in $\Omega$, and it's not difficult to see that this condition is equivalent to the fact that the residues of $g$ at $0$ and $1$ should both be $0$.
Let $a_0 = \operatorname{Res}\limits_{z=0} g$ and $a_1 = \operatorname{Res}\limits_{z=1} g$, and put $u(z) = h(z)-a_0\log|z|-a_1\log|z-1|$.
Repeat the above argument to get a holomorphic function $f=u'_x-iu'_y$ on $\Omega$. It's straight-forward to verify that
$$
f(z) = g(z) - \frac{a_0}{z} - \frac{a_1}{z-1}
$$
so by construction, the residues of $f$ at $0$ and $1$ vanish, and from the discussion above, we are done.
This takes care of existence. For uniqueness, assume that $u(z) = h(z)-a_0\log|z|-a_1\log|z-1|$ and $\tilde u(z) = h(z)-\tilde a_0\log|z|-\tilde a_1\log|z-1|$ are two such functions. Then $u(z) = \tilde u(z) = (a_0-\tilde a_0) \log|z|-(a_1-\tilde a_1)\log|z-1|$ is the real part of a holomorphic function on $\Omega$. It's a standard exercise to check that this can only happen if $a_0 = \tilde a_0$ and $a_1 = \tilde a_1$.


I have not verified my ISO...is there anything I can do other than reinstall?

Question: New to Linux. Short story is I didn't bother verifying my ISO due to it being downloaded directly off of Elementary's site and now I'm wondering if this was a mistake. Post installation is there any way to verify the integrity of this install? Thanks in advance.
Answer: If your installation is working, then there is probably little point in verification. The point of verifying the file is usually to check the iso file hasn't been corrupted during download. Corrupted downloads usually result in installation failures, so if you've managed to install elementary successfully, the iso file was probably valid.
Realistically, you'll only be able to verify post-installation if you kept the original iso file you downloaded, and follow the steps as documented.
If you didn't keep the iso file; in theory, depending on how you wrote the iso to your installation media, it may be possible to turn that back into an iso and then verify it. But there are a lot of potential ways that could go wrong and give you a false negative result, so I won't document that here.
Comment: Appreciate the response David but I tried Ubuntu 20.04 with the 5.8 and 5.11 kernel to no avail as well as Fedora which lead me to the conclusion that Linux doesn't support OLED displays currently at all. I didn't intentionally purchase an OLED display so I'm returning this XPS for the model that doesn't have it.


Dropbox like the old gDrive?

Question: I really like Dropbox. I also liked the old gDrive a lot. Now that computers are using SSDs, and so far the cost for big SSDs are still high (at least for countries outside US, like Brazil), is there any way to use Dropbox like the old gDrive? I will try to explain what I want:
With Dropbox, a folder is created on your PC/MAC and every file inside this folder will be synchronized with Dropbox. But the problem in this scenario is that a file is still consuming space in your hard drive. The old gDrive used to create a Drive in your PC/MAC, and every file inside it was not in your hard drive. For me, gDrive was like a network shared folder, and it allowed me to have files that look like they were in my hard drive but they were not.
I know that I can tell Dropbox to no sync certain files or folder, but I want to use it completely online so no file will be on my hard drive (despite the fact that it looks like it is).
Answer: Dropbox probably is not good for this. On the other hand OwnCloud (http://owncloud.org/) is perfect for this. You can mount your files with WebDav (native support on Gnome/KDE/Windows/Os X). You can host it yourself or find free/cheap providers.
Answer: You can use Expandrive for storing your files on a server that would sync your files to dropbox. It's not free, you can try it for 7 days, and after that upgrade pricing is $19.95.
From the website:
Seamless Access to Cloud Storage
SFTP/FTP, WebDAV, S3, OpenStack Swift, Dropbox, Google Drive and more.
Just like a USB Drive, in any application.
Cloud storage in every application
ExpanDrive acts just like a USB drive plugged into your computer. Open, edit, and save files to remote computers from within your favorite programs—even when they are on a server half a world away. ExpanDrive enhances every single application on your computer by transparently connecting it to remote data.
Finder & Explorer is your user interface
With ExpanDrive, you can securely access any remote file server directly from Finder and Explorer, or even the terminal. No need to open a separate transfer client just for file transfer. ExpanDrive extends the way all applications can access data.
Available for Mac & Windows. : Linux version coming mid-2014
Expandrive Screenshot : Windows

Expandrive Dropbox Screenshot : Online via Browser

If this option is not valid, then I'd suggest you read THIS PAGE on dropbox, where this question has been asked. My answer to your question is based on a comment from this page as well. Apart from this answer, most of the posts are requesting the same feature for dropbox. According to the few answers, dropbox doesn't support this, but you can get this done via the Expandrive.
Comment: Wow!ExpanDrive is perfect for me! It also allows me to do the same thing with google and box! I really appreciate your answer!
Answer: I'm 99% sure this can't be done using plain Dropbox. You might find some extension to Dropbox that would do that, but it would be so complex to the point where it won't even make sense to use Dropbox for it anymore.
Answer: I don't think Dropbox is designed to work this way, but you can upload files to dropbox rather than sync them.
Log into the site, then choose the option to upload files. You should probably put them all in a folder that you will not sync.
So the files will be on Dropbox, but not on your computers. You can access them anytime through a web browser.
I know this is not exactly an answer to your question, but I think it is the closest Dropbox can get to doing what you want.
Answer: It seems you can backup to dropbox via (s)ftp. Wordpress has a plugin to backup the site to dropbox. So I guess that means you can use FTP or SFTP, and why wouldn't this work from your local computer? I just thought of this, know it works in wordpress, but don't know how to get it working on your computer. I hope this helps you in the right direction!

Dropbox like the old gDrive?


Battery Cable Replacement 1987 Chrysler 5th Avenue

Question: The negative battery cable on my 1987 Chrysler 5th Avenue is two-wire and very old and brittle.  The 4 ga cable connects to alternator; smaller lead to frame of car.  Both are about 20 inches in length.  Aftermarket cables are 20 inch with  6 in pigtails, butt splice connector.
Prefer not to extend the pigtail the required 14 in to frame. Can the old cable be replaced with two separate cables--- a 20 in  ground strap from the negative battery terminal to the frame; and a 20 in 4ga negative from the negative battery terminal to alternator?
Thank you
Ann
Answer: Yes, your solution is electrically equivalent, which is all that matters.


What is the difference between a public and private subnet in a Amazon VPC?

Question: When I launch a server with a security group that allows all traffic into my private subnet, it displays a warning that it may be open to the world.
If it is a private subnet, how can that be?
Comment: It means that if you were to add an EIP to the instance and the default route were an IGW it would be accessible from the world. The SG would not block the access.
Comment: A subnet being "public" or "private" is not a simple attribute check, but rather a high-level description of the subnet based on its routes. AWS probably can't run a comprehensive accessibility check (or it doesn't want to), so it gives a general warning instead
Answer: The main difference is the route for 0.0.0.0/0 in the associated route table.
A private subnet sets that route to a NAT gateway/instance. Private subnet instances only need a private ip and internet traffic is routed through the NAT in the public subnet.  You could also have no route to 0.0.0.0/0 to make it a truly private subnet with no internet access in or out.
A public subnet routes 0.0.0.0/0 through an Internet Gateway (igw).  Instances in a public subnet require public IPs to talk to the internet.
The warning appears even for private subnets, but the instance is only accessible inside your vpc.
Comment: @committedandroider - External traffic can only reach the instance if: It has a public IP assigned, it is on a subnet with the default route for 0.0.0.0/0 pointed at an internet gateway (aka 'public subnet'), the assigned security group allows the incoming traffic on the specified port from 0.0.0.0/0, and if the network ACLs allow the ip/port.  If ANY of these are not set correctly, public traffic will not reach the instance.
Comment: what makes it so that the instance is only accessible inside your vpc? if i put an instance in a private subnet, what's stopping traffic from outside the vpc to reach it. I saw that by default the vpc network acl permits all traffic
Comment: thanks @JasonFloyd this is still helpful 3 years later!
Answer: The Topic of this question is different from the actual problem which is described above. This topic is also important and highly searched over the Internet, and just because of this, other websites have much higher views of the same topic as it is not well defined here, if both Public and Private Subnets can go To the Internet to download updates and packages then what is the difference between them? Both should be Public then, but let me clear this and add my answer from AWS point of view, as well as a conceptual, practical point of view.
Answer of the Topic:

Public and Private Subnets are the name of the concept, not actually a separate entity.

Answer of the Actual Problem which is being asked

The warning is Correct technically, I am assuming you are talking
  about Inbound Traffic, not Outbound, because if you wanted to download
  software, packages, updates so you have to add every single IP in the
  Outbound which is practically not good and time consuming., so, the
  warning is about other networks and Private classes
For example: if you are adding a rule in Private Subnet security group like Inbound 0.0.0.0/0 so it doesn't mean that it is available
  for Public and someone can send a request to that Instance/service/machine, what
  actually it means that other Private Subnets or Private networks can
  communicate with your instance or services, like 192.168.x.x,
  172.16.x.x, 10.0.0.0 Private classes, which is only possible if your routes are allowed to do that. Other than this, you can ignore that warning and
  not worry about it. Here you have to understand the difference between From the Internet and To the Internet, so as per Security Group rules and help info, it will show you that warning which can be misunderstood by anyone.

The Confusion

When you create a Subnet in AWS VPC, there is an option Auto-assign
  Public IPv4 This is the main problem which makes confusion to the
  people if it is set to Yes, then your Subnet is Public, no matter what
  name or key-value you tagged to the Subnet, which means, at the time of Subnet creation, if you use a name like Private Subnet-A so it doesn't mean its Private Subnet, it depends on your use case and configurations (Auto-assign Public IP option).

Difference between Public and Private Subnet:

Instances in Public Subnet can be accessible From the Internet, which means traffic From the Internet can hit a machine/Instance/Service in Public Subnet. You normally keep things like Load Balancers, Web Servers in Public Subnet. So when you create them, you add name Public in front of them to keep them separate from others and, it doesn't matter you enabled Auto-assign Public IPv4, but every time you choose the Public Subnet that you marked Public, you have to check or enable Auto-assign Public IPv4 option when you launch an instance of EC2 or RDS/Service. But it's better if you enable Auto-assign Public IPv4 at Subnet level to make it properly Public because this is the reason you are making difference and using Public-Private concept, so whenever you launch any service/Instance/machine in Public Subnet, it will be able to accessible From the Internet and To the Internet, means, You can hit the service/Instance over the Internet and can download updates and packages in the service/Instance as well. You can check who is going To the Internet by simply typing the command curl wgetIP.com, you will see your Instance/machine Public IP in results.
"Because, when you launch an instance into a Subnet that has this attribute enabled, a Public IP address is assigned to the primary network interface (eth0) that's created for the instance. A Public IP address is mapped to the primary Private IP address through network address translation (NAT).".....said, AWS.
Instances in Private Subnet can not be accessible From the Internet. E.g. you can put Database Server, Redis Server or these kinds of other services in a Private Subnet and no one can access it From the Internet. It would be accessible only via Instances/machines/Services in Public Subnet (Web server, ELB, etc). Because it doesn't have Public IP enabled option and also we marked it as Private for the specific use as explain, for security and unwanted access over the Internet. This is good for architecture level security to avoid loopholes. To access this Private Subnet services/Instances, you have to add allow rule in Security group and add proper routes in the route table.

Now the question is,
Can Private Subnet go To the Internet?
So, answer is by default no,
If you wanted to access To the Internet through a Private Subnet or a Subnet having no Public IP or a Subnet having disabled Auto-assign Public IPv4, you need to create NAT instance or a NAT-gateway, and that NAT-gateway must have Public IP so, your service/Instance with Private IP will go to the Internet and can download updates,software and packages.
Private IP will route traffic to NAT-gateway and NAT-gateway will route to Internet Gateway. Then your communication from Private Subnets to Internet can start, you can check your IP by simply running command curl wgetIP.com, it will give you NAT-gateway Public IP, because NAT-gateway will go to the Internet for you and Internet gateway is a path of outside communication to the world and its a term in networking as well to pass the traffic from inbound to outbound. You can simply understand its main gate of the building for the exit.
Conclusion
The instances in the public subnet can send outbound traffic directly to the Internet, whereas the instances in the private subnet can't. Instead, the instances in the private subnet can access the Internet by using a network address translation (NAT) gateway that resides in the public subnet. The database servers can connect to the Internet for software updates using the NAT gateway, but the Internet cannot establish connections to the database servers.".....said, AWS
Links:
Internet Access: https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Internet_Gateway.html
VPC & Subnets Basics: https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Subnets.html
VPC with Public and Private Subnets (NAT): https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Scenario2.html
Comment: Great answer.  Thank you.
Answer: As documented here
PUBLIC SUBNET If a subnet's traffic is routed to an internet gateway, the subnet is known as a public subnet.
PRIVATE SUBNETIf a subnet doesn't have a route to the internet gateway, the subnet is known as a private subnet.
Answer: The distinction between "public" and "private" subnets in AWS VPC is determined only by whether the subnet has an Internet Gateway (IGW) attached to it. From the AWS docs:

If a subnet is associated with a route table that has a route to an internet gateway, it's known as a public subnet. If a subnet is associated with a route table that does not have a route to an internet gateway, it's known as a private subnet.

The IGW allows network traffic from the internet to reach endpoints inside the subnet.
To answer your second question:

When I launch a server with a security group that allows all traffic into my private subnet, it displays a warning that it may be open to the world. If it is a private subnet, how can that be?

It appears AWS does not check whether your chosen subnet has a route table with an IGW or not, when displaying that warning. It's a blanket warning they always show when you set up an instance with a security group allowlisting all inbound traffic. They use "may be" (as opposed to "will be") in there to cover their butts, but the warning is only relevant if you are on a public subnet.
Answer: The problem we are trying to solve is to make some resources "private", that is deny inbound traffic from outside your VPC, but still allow those private resouces to access the internet for e.g. updates.
There are a couple of ways to do this:

You could try to use Network Access Control Lists (NACL) but these affect inbound- and outbound traffic the same way ("stateless"). Therefore, you cannot deny inbound traffic while allowing outbound traffic. Also, they seem to be rarely recommended anyhow (see second comment of this SO post).
You could use security groups associated with each resource. This would work well but seems the less popular solution (maybe because it's easy to forget adding a security group to a resource?)
At last, you could setup a separate subnet without a connection to the internet gateway but instead a connection to a NAT gateway. That NAT gateway is usually (always?!) placed in another subnet which has a connection to the internet gateway. You'd then call these two subnets private and public, respectively. In other words, the terms "private subnet" and "public subnet" are really just names for this specific setup (as the other posts here state) and do not describe an inherent feature of the subnet.


What is the cause of wooden flooring gaps?

Question: We have gaps in our wooden birch floors. Some quite large. We are told that the cause of this was due to nail spacing and inadequate glue. I'm baffled as to why nailing and glue would prevent hardwood floors from shrinking and staying shrunk. We live in CO and had the floors acclimatize for 30 days before installing. Are there reports/tests that show that floor shrinkage is caused by incorrect nail spacing and insufficient glue - I can't find any... seems to be caused by the manufacturer not drying the wood sufficiently before production.
Comment: What glue? Flooring type would be good information to have. You're probably right, though. This is due to moisture loss. How was it acclimated?
Comment: The manufacturer may have dried the wood according to some standard, but if your location is drier then it will shrink further...
Comment: Just a guess, but wood, over time, dries more and more, this causes shrinking of material.  But also humidity causes expansion, so in essence the floor is always moving in expand/contract mode.  Gaps form and the repair is not hard just manually intensive.  If you pull boards out an reset you get a better fit, but the gaps could all return.
Answer: The flooring was probably mis-milled.
Wood flooring has to be cut, dried, accumulated, fit, nailed, etc. perfectly or you'll have big gaps.
Often the manufacturers point the finger at installers, when actually it's their problem.
The way to check is to hold two boards up and push them together. If one slips through then it's too loose a fit between the tongue and groove. There's no amount of acclimation or nailing that can fix that.
We've had many gymnasiums floors removed and replaced because it doesn't meet grade. (You can see the manufacturers cry when it's chainsawed out of there.)
Follow the Western Woods Use Flooring guise (National guide).
Hint: test a zillion boards to make sure all the tongues fit tight in the grooves and doesn't slip...even if you shake the board while in the groove.
Answer: Wooden floor gaps are usually caused by the change of temperature. Wood has natural moisture so in the winter time, when the air is dry and homes are heated, it loses its moisture and shrinks. Thus, the gaps. Wait until the spring because they might expand back once they regain moisture. To avoid dirt and gunk going in those gaps put a rope (natural not synthetic) in between. If the gaps still show, you can apply wood fillers using your fingers or with a putty knife.
Comment: But beware that if you fill the gap, the filler will be spat out when the wood expands again.
Answer: Some of those floors are better left to 'float', meaning that each board is not attached to the floor joist. I have never glued tongue-and-groove flooring together. The boards will shrink and expand according to temp and humidity. The gaps will be larger when it is cold and when it is dry. They will get smaller when it is humid and when it is warm. If the gaps are too big when it is warm and humid, then I would loosen the nails, close the gaps, and just nail the perimeter.Sometimes i add finish screws to attach squeaky boards more tightly to the subfloor
Answer: If they are real wood planks, they may not have been installed tightly enough next to each other with an appropriate expansion gap along the walls. If they were installed in the summer after acclimating for 30 days, they probably needed to be installed tightly so when the humidity dropped in the winter and caused the wood to contract, the gaps would have been minimal. Vice versa if they were installed in the opposite season. Or the installer may have used incorrect fasteners to allow the wood to expand and contract with the grain of the wood. The wood will move more on the long side edges (assuming the wood was cut correctly in the direction of the grain).