Public IP for my PC through XFINITY gateway router/modem

Question: Question: It is possible have public IP for my PC hooked up to XFINITY gateway (the router/modem combo) through wifi?
My home network has several PCs connected to the XFINITY gateway through wifi. Each one has it's own private/local IP address of course. My PC has a web server running on it with web apps I'm developing (unlike my spouse's and kids PCs). So I'd like to be able to access my PC through a public IP to test my devel web apps without having to pay to third party for this service since I'm already paying Comcast for our Internet service at home.
I've been developing for awhile, but new to networking as most of my development was done on workstation at work which already has public IP.
Any help and suggestions will be greatly appreciated.
Comment: @Ramhound Comcast doesn't use carrier grade NAT. Comcast XFINITY customers always get a public IPv4 address.
Comment: If  Comcast only assigns NAT ip address then you are out of luck unless you pay them for a public ip address.  You have not given enough information to determine if they assigned only NAT ip addresses.  Furthermore it is against the Terms of Service to host a website on your home connection.  Additionally if you are  assigned a NAT ip address it won't be possible to forward your domain to your ip address for obvious reasons.  But you don't need to forward ports, or have a "public ip address", to do web development work.  You just use localhost instead.
Comment: The author wasn't very clear.  The author most likely only has one ip address anyways.
Answer: You could put your "web server" PC on a static private IP address and then configure the NA[P]T gateway feature inside your router to make that IP address be the "DMZ" (a.k.a. "default host", "bastion host", "default server", etc.). Or, since you maybe only care about web development, you could just make a small handful of port forwarding rules (port mappings), for TCP ports 80 and 443, and maybe also 8000, 8080, or whatever, if you have multiple websites you're developing in parallel.
You could then point a DNS hostname at your cable gateway's public IP address. In my experience, Comcast doesn't change my public IP address very often, so since I'm only "hosting" experiments and not real public websites that need serious uptime, that's good enough for me. I haven't looked into paying for a static public IP address. If Comcast changes your public IP address a lot, you could use a Dynamic DNS solution like Dyn.com (dyndns.org) to keep your public domain name pointed at your public IP address even when your public IP address changes.
Please note that for this to work well for you, your NAT gateway needs to support "NAT Loopback" (a.k.a NAT Hairpinning), which not all NAT gateways do. NAT Loopback is for when you're running, say, a web browser on one of your machines on your home LAN, and you go to the public domain name or public IP address of your website. Your NAT gateway has to do "outgoing NAT" on that packet, and then realize that the packet needs to turn right around and go through "incoming NAT" to get to your server on the private side of the gateway.
The reason people using port forwarding or DMZ features for this is because it's more likely to be supported in home gateways. The ability to do NA[P]T for some addresses, but bridge or route other addresses, is less common. The networking layer of Linux is almost infinitely configurable, so if you can put an aftermarket Linux firmware distro on your gateway, you might be able to configure it to do "NAT for some addresses, bridging for other addresses" like your were initially envisioning, but I've never set that up myself so I can't quite vouch for it.
Comment: Thank you. I'll try this approach. That is a lot of information to take in and explore since I'm new to networking.
Answer: I think this worked for me with an X1 gateway.

Go to http://ip4.me/ to find the public IP of your router
Go to https://internet.xfinity.com/network/advanced-settings/portforwarding
Click Add Port Forward and then forward the ports you want to the device you want

For more info https://www.xfinity.com/support/articles/port-forwarding-xfinity-wireless-gateway
Comment: The Xfinity link no longer works.
Answer:
I'd like to be able to access my PC through a public IP to test my [development] web apps without having to pay to third party for this service since I'm already paying Comcast for our Internet service at home.

This can be done with Comcast.

It is possible have a public IP for my PC hooked up to XFINITY gateway (the router/modem combo) through wifi?

Yes.
Gateway Caveats
Per anecdotal experience, Comcast gateways are not always reliable or easily configured. As a suggestion, rather than just using the gateway itself, a better option might be to simply put the gateway in "bridge" mode (so it effectively acts only as a modem) and buy a router with hairpinning (NAT loop back) as mentioned by @Spiff.
I personally use this setup (Bridge Mode + External Router) and have been extremely happy with it.
Note that if you do use the "bridge mode" method above, you might have to change the external router from using 192.168.1.x to use 10.0.0.x internal addresses (which is what the gateway will likely be using). If necessary, this usually a very simple process on most routers.
Setting Things Up
Port Forwarding
While you can set up a default host (which might be better for a number of reasons), port forwarding should be sufficient for most development needs.
The exact method of setting up port forwarding will depend on the gateway or router, but if you do so, you will want to forward port 80 (HTTP) at minimum and you will likely want port 443 (HTTPS) as well (for basic web development at least).
You can also forward ports for any other services you wish to be publicly available (e.g. DNS, SMTP, FTP, SSH, etc.) or non-standard ports (e.g 8080 for "alternative port" access to a web server).
Regardless, any forwards should point to the local IP (e.g 10.0.0.x) of the server handling the request (e.g where Apache or whatever program is installed).
Getting Your Public IP
Getting your public IP is fairly simple. You can just search "What's my IP?" on Google and it will return your current Comcast address.
Test Things In The Right Order

Ensure the server/service is working on localhost if possible.

Ensure that the server/service is available to the local network (e.g you can access your web server with a local IP from another device on the network.)
This usually will inform you of firewall issues.

Test that you can access the server/service from the local network via your Comcast public IP. This will help inform you of any hairpinning issues.

Test that you can access the server/service from a non-local network (e.g with your phone over 3G/4G) via your Comcast public IP. This should tell you whether or not the server/service is truly available publicly.

If you picked a non-standard service port (e.g 8080), you will need to append that to the IP (e.g 10.0.0.10:8080 or  22.214.171.124:8080). For standard ports, this should not be necessary (e.g a web server on port 80).
Domain Names
While IPs are all well and good, if you don't want to use them (or need to test something that relies on domain names), you can register a domain name and point the DNS at your server (via your public IP).
Another cheap option is to use a dynamic DNS provider, such as No-IP or afraid.org, which have clients that periodically sync your public IP to a domain name.
Note that (currently) Namecheap FreeDNS will provide free dynamic DNS services with any registered domain you own (not just Namecheap) if you need that kind of setup.
Comment: Thank you for the thorough explanation. That's a lot of valuable explanation. The XFINITY modem/router i have already assigns the local IPs in the 10.0.0.x format. From the Test Things In The Right Order - the numbers 1, 2 and 3 all checked out already. I do know my public IP and can access the web server through it when on the local network (connected to my wifi). However, the number 4 doesn't. That is I cannot access my web server/gateway while on non-local network. Is it possibly because of the firewall settings or something else? Any suggestions?
Comment: Glad to help. I hope you get everything working to your satisfaction.
Comment: It could be the gateway settings. I would double-check any firewall settings on the gateway as well as any port forwarding settings.
Comment: Just to be clear, on the port forwarding, you need something like "HTTP TCP 80 80 10.0.0.10" and make sure the blue "Active" button is checkmarked. 10.0.0.10 is an example of course and should correspond to the webserver's local IP.
Comment: Welcome and please do.
Answer: AHare- Your current assumptions and testing have been spot on for what I have experienced as well. And unfortunately, Comcast has set up their modem/router access points with minimal functionality and have implemented a sort of "dummy mode" where in even the average tech idiot (or well for the most part) can simply just set up their WiFi, make a password, control the devices on it in some comical scheme...not allowing one to wander off into any advanced section (although yes said advanced section essentially only allows port forwarding)
They have configured it to be unable to do any hosting in the way you describe, they do this I can only assume because they want you to have to pay more and upgrade to some Business Tier package which will allow some sort of functionality in this way (although most likely still limited) and it will certainly not be cheap.
Now...it may be possible to put your modem/router into bridge mode (essentially turning it back into just a modem and also stopping the Xfinity WiFi signal to be broadcast for others to use...which is not a security risk but more so a speed, QoS, and performance issue...just think about it I mean if another Comcast customer who pays for internet is connected to your gateway via the Xfinity Wifi and chewing up data its not going to show up as you using it...However you better believe that it is slowing down your connection. As much as I love connecting to this Xfinity Signal to save mobile data when I am out...I choose to nix it on my gateway. Besides it really only is of impact if you live in an urban setting (my brother actually went without an internet plan for 10 months in his apartment because the neighbors upstairs had their gateway right above his place most likely on the floor and he could just connect to the XFinity signal at all times even on Xbox and other consoles. I digress...
Comcast also changes your WAN IP more often than you would think...although it can be somewhat random. So if you bridge mode your gateway and then buy a router which supports some sort of hosting feature. I personally like to flash routers and just install DD-WRT firmware to unlock all the features of the router which many times are hidden by Linksys or Netgear etc etc. Set up your port to connect via when out and any other settings. And then it MAYYYYY be possible to do what your trying. I stress may because your still having to route through the modem which may have some features to specifically stop this even when placed in bridge mode. Or it may work perfect until they change your WAN and then you just might need to figure that small fix out. Bottom line...Comcast is only concerned with the most basic of features that 99% of their customers are worried about...which is essentially just make that darn internet work and make it easy for me to name my WIFI network and set a password...


PHP wrapper for XML/SWF charts

Question: Anyone know if there is a PHP wrapper for the latest version (5.X) of   XML/SWF charts
Answer: http://www.maani.us/charts/index.php
"As of version 5.0, there isn't a dedicated PHP interface for this charts tool. However, PHP or any other scripting language can still be used with XML/SWF Charts (the XML version of the same tool)."
There are examples how to use XML version with PHP:
http://www.maani.us/xml_charts/index.php?menu=Reference&submenu=Scripting
Answer: As part of another project, I developed an open-source CodeIgniter library for generating the XML required by XML/SWF Charts: http://milktek.com/XML-SWF-Charts-for-CI
However, looking over the code in this library, I believe it will work outside of CodeIgniter as well. Just create a new Maani_xml_swf_charts object and call the various available methods. It should work because there is no CodeIgniter dependent code in the library.
$mxsc = new Maani_xml_swf_charts();
$mxsc->chart_type("stacked column");
$mxsc->chart_data(
                   array("sales","non-sales"),
                   array("Clothing","Food","Toys"),
                   array(
                          array("100","145"),
                          array("34","54"),
                          array("84","21")));
$mxsc->chart_label(array(
                          "shadow"=>'low',
                          "color"=>'ffffff',
                          "alpha"=>'95',
                          "size"=>'20',
                          "position"=>'inside',
                          "as_percentage"=>'true'));

Answer: I don't know about the XML/SWF charts software, but if you feel like hand coding it, you can use PHP's XML classes and Ming to dynamically create charts. You would simply parse the xml data from the file, and pass it to a Ming object for processing. then include the swf when done.
Simple!
;-)
Comment: avoid comments as answers, add a comment itself instead.

PHP wrapper for XML/SWF charts


How do I chain vert and street tricks in Tony Hawk's Pro Skater 1/2/HD?

Question: I've never really played the first two "Tony Hawk's Pro Skater" games - I've only began to obsessively play it from the third game onward, but Tony Hawk's Pro Skater HD brought me back to the first two games. So, it might be a newbie question, but here goes: is it possible to chain together street and vert tricks without using the Revert which was added in THPS3?
Comment: You have to jump into a manual to keep the combo going. That is one of the only things I remember from back then.
Comment: In the first two games, it was practically impossible to continue your combo off of a vert ramp (a `revert`) unless you could somehow land in a grind.  But since you don't level off, you couldn't do it.  You might be able to if you shot off the ramp at a close-to-horizontal angle toward a rail/ledge, I don't think that ever worked though.
Comment: I haven't played the new release, but have you tried a manual? Can't remember if it was possible in the first two games or not, but it should be up and down ( or down and up) on the control stick to go into a manual.
Comment: I have. Unless something in my timing is off, it just ends the combo and starts a manual.
Comment: so... when coming down from the pipe - jumping + manual? Doesn't have to do a No Comply for that?
Comment: ok, the jump+manual doesn't really work. @JeffMercado - "It's impossible" is a legit answer. :)
Answer: Back in Tony Hawk Proskater 1(original game, not hd), you were unable to perform a manual. In the second game, they added the manual, but you are still unable to manual after performing a tick from a pipe. Even if you pressed down/up, up/down before landing off a pipe, you cannot combo  that trick. Street tricks/rails can be chained with manuals by pressing up/down, down/up as mentioned in the other answer.
I have played all three games mentioned and I am also finding inconsistencies with chaining using manuals in the updated HD game. It seems as though the HD re-make is not polished enough to consistently record a manual after performing excessive grinds/street tricks. Also, it is impossible to chain a manual to a vert trick in THPS HD, unless you buy the Revert DLC Pack, and then it is possible to chain the tricks using a revert move.
Answer: Revert was given free in a patch before the DLC was released. You do not need to buy the DLC revert pack in order to receive the code adding revert to the game.


Why would hot water pipes be smaller than cold water pipes?

Question: Just bought a house and am finding the hot water pipes are smaller than the cold water pipes. Why?
Comment: What type of water heater do you have? What size are the cold pipes? What size are the hot pipes? What material are the pipes?
Answer: Hot water delivery times are highly dependent on the size of the pipe. It will take more than twice as long for hot water to reach the fixture travelling through a 1/2" pipe than a 3/8" pipe (because there is roughly twice as much cold water sitting in the pipe), and more than twice as long through a 3/4" pipe compared to a 1/2" pipe. Thus, using the smallest supply lines possible for hot water plumbing to fixtures will supply hot water much faster, saving water and energy, and making occupants happy.
With cold water supply lines, there's no similar issue. Instead, our only concerns are about supplying enough water for good flow rates, and stable pressure (so output doesn't noticeably fluctuate when someone flushes a toilet, for example). So for the same fixture where a 3/8" hot water supply line makes sense, it also makes sense to use a 1/2" cold water supply line.
Answer: For  part of the system this may make perfect sense - i.e. the main cold feed line into the house, which is carrying all the cold and "will be heated to become hot" water at the same time, so it should be larger than the individual feed lines to fixtures.
If it's extended all the way to individual fixtures with larger cold water and smaller hot water lines, it makes less sense and is tending to make things unbalanced, though again, it can make sense for a "bathroom set" where the hot line is feeding the tub/shower and sink, but the cold line is also feeding the toilet. A larger cold line there might make "flush-scald" where the cold water pressure drops and the shower is suddenly hot less likely, or less severe.
Why? You'd have to dig up whoever plumbed it and ask...many things in houses don't make a lot of sense unless you are the guy who chose to do it that way, for whatever inscrutable-after-the-fact reason.
Comment: There is also the possibility that a cold water feed across part of the dwelling ends up going to an outside water hookup at say the back yard, sprinkler valve manifold or to a swimming pool. These usages can demand larger volumes of water than the typical indoor fixtures and possibly be in use for longer periods of time. Larger diameter piping helps to meet these demands without as much pressure drop within the dwelling.
Answer: It is completely normal to have your cold and hot water lines be different sizes. Your boiler or your water heater probably has a smaller output size than the main coming in.
Even though the water pipes differ for the most part, the size of the water supply pipes to your fixtures would be the same for both hot and cold lines. Standard sinks and tubs would use 1/2" supply lines, and toilets use a single 3/8" line.
As long as there is enough volume and pressure in your system, you shouldn't have any issues.
Answer: It may also be that the hot water lines are CPVC and the PVC. In case you're wondering what the difference maybe: CPVC is a smaller diameter than PVC. It is used specifically for potable hot water.
Comment: This post doesn't appear to be finished.
Comment: I was referring to the _"and the PVC"_ part at the end of the first sentence.


X-Mirror on weight paint doesn't work

Question: I've heard that x-mirror option is supposed to mirror the weight paint that I do on one side to the other. But it isn't working with my mesh for some reason, it still only paints on side at a time. Any help why?
https://drive.google.com/file/d/1neePPk9PlKjhpp8AIbUOF94m1KHws7hX/view?usp=sharing
Answer: The mesh is not a perfect mirror so it can't find the opposite side. You could try to use the "Topology mirror" option and see it that helps.
Comment: The bone rotation is probably unrelated but when rigging you need to take control over the bone roll and not leave that to chance. Use Recalculate Roll and make sure that your rotational axises match up. It will be horrible to animate if you don't.
Comment: You should also make sure that your origin is in the right position. Don't assume that centre of weight will get it right. The mesh object shouldn't have any scaling done to it when rigging.
Comment: Thank you. I presume its because of the book item on his back. Could it also be because the bones on the right side shoulder and arms are slightly rotated compared to the ones on the left? That's another problem I had when trying to duplicate to the other side
Comment: Thank you for the help again. I found that the easier solution was to right click on all my left side selected bones, right click, then symmetrize. Must be a new option in 2.8, I don't remember it being in 2.79. However, no we're back to square 1. I removed the object that was making my mesh uneven, and everything I've worked on on the mesh was done in mirror, then applied. However I'm still not getting the proper x-mirror results.

X-Mirror on weight paint doesn't work


How do you move a tile in OpenTTD

Question: Can you move a tile in OpenTTD 1.5.2 (depot, station, etc)? If so, how do you do it? I don't want to demolish it.
Comment: Can you specify clearly what you mean by move? In general everything you do in the game, including construction and purchasing of vehicles is permanent. The game explicitly does not allow you to undo anything, so barring destroying and rebuilding I'm fairly sure moving something isn't allowed.
Comment: I don't see what the down vote is for. The question is as clear as daylight. Anyway, you answered it.
Answer: You cannot 'move' any structure you have constructed. The game does not allow you to undo any action, be it construction or purchases.
To move something, you have to build the structure somewhere else, then remove the original. For stations, as long as the new station is within a certain radius of the original and you construct the replacement first, the new station will be grouped together with the original. This may also work for other structures, but further testing is needed.
Comment: With stations, so long as the new station is on a directly adjacent tile (not diagonally adjacent) it will be linked to the existing one. It's not determined by radius.
Comment: @KingJ Nope - https://wiki.openttd.org/Distant-join_stations
Comment: That only applies if you hold control when placing though, if you're just placing normally it won't join unless it is directly adjacent. I read your answer as saying that you could place normally within a given radius, rather than needing to hold control.

How do you move a tile in OpenTTD


Will installing Ubuntu to dual boot with Windows slow down any OS or my laptop?

Question: I am going to install Ubuntu to dual boot with Windows 8 soon, but one of my friends warned me that partitioning my hard drive will slow my computer down. I run on a 500GB HDD and 8GB of ram if that helps at all. Is that true if I do it?
Answer: There are several factors to take into account but generally speaking, Ubuntu normally is at disadvantage when installing. This is because Windows is normally at the beginning of the disk, and Ubuntu (or any other distro) is at the end. Disks are faster then closer they are to the start, hence Windows will have shortest seek times, that will give it a boost opposed to Ubuntu.
Another thing is that Windows will not run at the same time that Ubuntu, nor the reverse. Hence while you are running Windows, only your system inherent performance is taken into account. I have not seen (nor imagine) any circumstance that Windows will slow down because you installed Ubuntu.
Bottom line, Windows normally will have the advantage on the hardware, but Ubuntu (Linux) will use it more efficiently. That's all.
Comment: Thank you for the answer, it was the most explanatory and detailed of all of the other ones.
Comment: Disks (or in this case partitions) are not faster when they are closer to the start. It's the opposite. Here is an useful related post: http://superuser.com/questions/159890/does-the-order-of-partitions-matter
Comment: @YuppieNetworking did you really read the link? To put it simply, the first 125GB are faster than the later 250GB and the speed is less and less the further you go. I don't know what are you referring with *"start"*, but *my "start"* is the start of the disk which is normally the outer edge of the disk.
Comment: @Braiam - I would like to know weather reinstalling ubuntu and giving it the primary partion which is 1TB help me with speed issues, because right now I am having 100Gb ubuntu parition dual booted with Win 7 (500 Gb partition). Reinstalling would affect system performance?
Comment: @Creator ask another question, and primary partition isn't what you think it is. https://en.wikipedia.org/wiki/Disk_partitioning#Primary_partition
Comment: @Braiam-  I asked a new question as you told me  http://askubuntu.com/questions/641423/how-to-increase-ubuntus-performanceoverall
Answer: Partitioning will decrease the current size of your Windows partition. This will affect storage capacity, not speed.
Answer: It would not slow down your machine because you're not firing it up all together :)
The fact that only one operating system will run in a dual-boot setup, hardware resources like CPU and memory is not shared on both Operating Systems (Windows and Linux) therefore making the operating system currently running use the maximum hardware specification. Regarding the disk issue, well unless the windows partition run out of free space which eventually can be fixed by removing some files.
Answer: It will slow down your computer in one case: if you have too small amount of free space on your Windows partition. Thus Windows will show drive C: (or D:) with red bar and will prompt you for cleaning. Just remember that you need to keep ~10 GiBs free space on your Windows hard drive and ~40 GiBs for Ubuntu.
Answer: While all ten other answers are correct that there will be no noticeable difference in running time.  Boot time will plummet on modern PCs as you will not be able to enable bios caching (at least none of my systems will bios cache to grub) and grub will have a pause and select time of it's own which will slow down boot time (configurable).
Bottom line do it but be aware that you can no-longer boot to windows in under 5 seconds (assumes ssd and bios caching)
Comment: Eh? He is trying to see if there will be any difference in the runtime, not the boot time. Some people don't even shutdown their PC and the GRUB delay is something they can change whenever they want.
Answer: I would just like to add to this that I have noticed a significant performance decrease in my Windows 7 after repartitioning my Windows drive to create space for Ubuntu, although I did screw around with the partitioning quite a bit (created partition to install Ubuntu to, had some issues, repartitioned, more issues) before actually installing Ubuntu to unpartitioned space.
So I checked on Windows whether the drive might be fragmented because this is the only logical reason that I could think my Windows is running slower after the dual boot installation and only came up with a 1% fragmentation. Still not 100% sure why Windows is running slower now though. I might just re-install Windows to see if that helps (note if anyone else tries this, remember to reset your grub).
Could be that I'm just so used to working on a lightning fast linux machine that Windows feels slow now :P
Answer: Nobody here has addressed the issue of the windows page file. If you rely on the page file currently and reducing the space available to windows decreases your page file size, it can lower the total memory consumption (hardware + paged) available to Windows.
Really a minor issue though.
Comment: Err... and how the installation of Ubuntu affects the pagefile? IMHO, Windows >6 (Vista, 7, 8) have the `pagefile.sys` size dynamically, and is independent of the disk space left but depends on the total physical memory available using the Memory×2 formula for the page file, and it grows whenever it needs.
Comment: @Braiam but how can it grow past the partition size? It cannot


Setup Ad-hoc WIFI from terminal in OS X

Question: Is it possible to create a Ad-hoc Wifi network in OS X using the command line? Without using Apple Script to do it through the UI.
Answer: I've used sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -i[<arg>] to do the job.  Take a look at /usr/sbin/networksetup to round out the solution.
Answer: As a newer answer for making an ad hoc network that works in Mojave without a internet connection, while searching online, I finally found an answer!
Smoooosher's answer only works with an active connection to share.
To create your own "active" network, in terminal run the 2 following commands.
sudo networksetup -createnetworkservice Loopback lo0
sudo networksetup -setmanual Loopback 172.20.42.42 255.255.255.255

This creates a new network conection that although it looks inactive, it can be shared from the internet sharing preference pane to wifi.

Setup Ad-hoc WIFI from terminal in OS X


Canasta - picking up stock pile

Question: My partner and I had a canasta of 9s and I had a pickup which contained three 9s which I held in my hand to use as fairly safe discards because the pack was frozen.  I used one of them and then my opponent threw a 9.  Could I pick up the pile with the pair of 9s I had in my hand?
Answer: Yes, you can do that. From the rules:

UNFREEZING THE DISCARD PILE

A frozen discard pile is unfrozen only by being taken. When the discard pile is topped by a wild card or a black three, at least one natural card must be discarded on top of the pile before the pile may be taken. Then, a player may take that card (and the pile) only with a natural pair of the same rank from his hand. Before touching the discard pile, the player should show the pair (together with any additional cards if needed to meet the minimum count of an initial meld).

As long as you have a natural pair in your hand, it doesn't matter what else you have on the table. In fact, it is a common strategy to not add to an existing meld (even if it would form a Canasta!) to make your opponent think that a particular rank is a safe discard on a frozen pile.

Canasta - picking up stock pile


Ring without zero divisor

Question:
Does there exist a ring $R[x]$ without a zero divisor but the ring R is having a zero divisor.
Comment: I know the the theorem that states if R is a ring without zero divisor, then $R[x]$ is a ring without zero divisor. Is the converse true?
Answer: No, because $R\subseteq R[x]$.  Hence, if $a,b\in R$  with $a,b\neq 0$ and $ab=0$, then also $a,b\in R[x]$ with $ab=0$.
Comment: very good answer :-)
Answer: Indeed $R[x]$ has zero divisors of every degree; for if
$\exists a, b \in R, \; a, b \ne 0 \mid ab = 0, \tag 1$
then setting
$f(x) = \displaystyle \sum_0^n a x^i \in R[x], \tag 2$
and
$g(x) = \displaystyle \sum_0^m b x^j \in R[x], \tag 3$
we have
$f(x)g(x) = \displaystyle \left ( \sum_0^n a x^i \right) \left (\sum_0^m b x^j\right ) = \sum_{k = 0, i + j = k}^{m + n} ab x^{i + j}  = 0. \tag 4$
As for the question our OP Atul Anurag Sharma posed in his comment to this question, it is easy to see that if $R[x]$ has no zero divisors, then neither does $R$, since $R \subset R[x]$ as the ring of polynomials of degree zero:
$(ax^0)(bx^0) = abx^0, \tag 5$
$ax^0 + bx^0 = (a + b)x^0, \tag 6$
etc.  Thus the existence of zero divisors in $R$ forces their existence in $R[x]$; if there are none in $R[x]$, there are none in $R$.
Answer: This is a trivial result since any zero-divisor of $R$ is still a zero-divisor of $R[x]$.  This is the more interesting result: McCoy's theorem.  If $f(x)\in Z(R[x])$, then there is a non-zero $r\in R$ with $rf(x)=0$.  See Zero divisor in $R[x]$
Comment: Zero-divisors of $R[x]$.  I think McCoy's theorem needs commutativity.  Polynomials over non-commutative rings seem like they would be nasty.
Comment: By $Z(R[x])$ do you mean the set of zero divisors in $R[x]$, or the center of $R[x]$?

Ring without zero divisor


I can't delete worlds

Question: I have Minecraft on my Kindle Fire, but it won't let me delete certain worlds. I go to edit, click on the x next to the world, but it still stays there! Is there a different way to delete worlds? Or is it a glitch?
Comment: I play on my kindle and it works fine. In fact, it works so fine I accidentally deleted my favorite world, and it took me months to finish my hotel!
Answer: For my Nexus 7 Android, I could plug the device to my computer, browse to This PC\Nexus 7\Sisäinen tallennustila\games\com.mojang\minecraftWorlds and delete a folder called My World, which was the name of the world. Apologies for localized folder name.

I can't delete worlds


Parallel Process is not updating WPF Collection List

Question: In my WPF application, I have a Data Grid which populates with a ObservableCollection collection. Suppose I have such 10 student data in the grid. Each student is capable of doing 2 long running works or process and updates the status of the process back to the grid. I want to do those 2 process simultaneously. So I used Task and Parallel.Invoke methods. The work flow is as follows.

I populated the Student data collection in the Grid.
I clicked on a start button.
In the click event of the start button, i did the following code.
<code>   foreach (Student stud in StudentLists)
    {
        stud.Status = "started..";
        Task.Factory.StartNew(() => StartProcess(stud));
    }
</code>
In the StartProcess,
<code>Parallel.Invoke(() =>
    {
        MarkService ms = new MarkService(stud_data);
        Student s = ms.GetMarkProcess(); // This will return the stud_data in the above line

        Student studitem = StudentLists.Where(x => x.RollID == s.RollID).FirstOrDefault(); // find the student in the grid
        if (studitem != null)
        {
            studitem.Status = "Mark Got it";  // if find, updating the status
        }
    },

    () =>
    {
        SentMarks(poll); // this is another method to be executed parallel
    }
    );
</code>

When executing all the 10 students process, each student in the grid became the same data.
Or only 2 or 1 student in the Grid is showing Status "Mark Got it". Other rows show "started.." status only.
Why this is not updating the collection.
I have used INotofyPropertyChanged and raisng the event when property updated.
In the XAML, each binding is used in Two way mode.
There is no error. But the 1 or 2 items in the student collection is updating some times. Sometimes the collection contains the last students data for all the 9 items.
It is not updating the exact student object in the Grid. what is wrong in my code ?
Any help in this case ???
Answer: The problem here is that your referencing a UI control from another thread. You should create an in memory data structure that a grid can use as DataSource (anything that implements IEnumerable). I would suggest using the ConcurrentBag data structure for parallelized code (http://msdn.microsoft.com/en-us/library/dd997305.aspx). Once you've updated each of the student records in the ConcurrentBag you set the grid's datasource to that bag.


Wood burning stove pipe through the ceiling and roof

Question: I have a 16 x 22 cottage in Minnesota. Bought a small wood burner. Only one place inside to put the small wood burner. But, it is directly beneath a horizontal stud/joist of the truss. Would have to cut 14 inches of it out for square support box. Is there a way to block it in or not. Will I compromise the truss completely? Again, small cottage 16 ft wide and 2x4 run across the width. 24 in on centers in the ceiling. Bob
Answer: Yes you will compromise the truss.
Each pipe supplier, if not, the stove supplier should have the allowable amount of elbows and the distance it can be offset with the elbows. Although I have only seen this with the insulated pipe behind walls and with additional supports. What you need may not look the best, but if it is allowed, it will keep your truss from failing should it be cut.


Apple ID Verification (iPod touch)

Question: I did not receive any verification email for my Apple ID. I already repeated the procedures more than twice. What am I going to do?
Comment: Is the email address correct, are you able to receive emails from other sources, did you look into your spam folder?
Answer: Contact the iTunes Store, let them know you are trying to verify your account and are not receiving any email. Also make sure to mention [if you did] that you checked the spam/junk folder and that your email on the account is correct [make sure it is].
They will provide further assistance from there and they'll most likely be able to enable it for you with some verification information.
Comment: They still **need** verification via email. Else, in the future you end up with no password restore option for example plus very critical info is sent (example on other device) for example.
Comment: This comment was from 2012, of course things have changed since and yes **NOW** they need verification via email.

Apple ID Verification (iPod touch)


Black screen on startup Ubuntu 20.04

Question: I have a Lenovo g50-70 with Intel i3 4th Gen, Intel HD Graphics 4400, 8 GB RAM and a 1TB HDD. I installed Ubuntu 20.04 recently, and the installation and the first boot up went fine. But afterwards, whenever I boot the computer from a shut down state, the screen stays black. It does not show any vendor logo or errors. If I force shut down the computer and then power on, the computer starts normally. I have tried installing other distros like elementary OS, Manjaro etc., but the problem remains the same. What could be the problem, and how to solve it?
Answer: From what I can gather, it could be a few different bugs. Please read and follow the instructions. I listed them in descending order from easiest to hardest.
1. Updates

Problem: If there's ever an issue, by habit, updating and upgrading might help it, especially with new releases having bugs.

solution:
Run in your terminal. autoremove will remove any unused packages files. Might be an incompatibility issue with 20.04 that you weren't even aware of.
sudo apt-get update
sudo apt-get upgrade
sudo apt-get autoremove

2. GRUB bootloader

Problem: the GRUB boot loader may have been overwritten (MBP), preventing Ubuntu from booting

Solution:  check is whether you can access the GRUB2 boot loader. Boot your computer while holding the Shift key. If you see a menu with a list of operating systems appear, you've accessed the GRUB boot loader.
If you see the Grub boot menu:
 Select the "Advanced options for Ubuntu" then select the "Ubuntu (recovery mode)" option. Checkout the 1st URL in the appendix for which menu option to use.
If you don't see the Grub boot menu: Make sure you have working wifi then following below.

If you have the media you installed Ubuntu from, insert it into your computer, restart, and boot from the removable drive. If you don't, download a Ubuntu live CD and burn it to a disc or create a bootable USB flash drive.
When Ubuntu boots, click "Try Ubuntu" to get a usable desktop environment.
Open a Terminal window from the Dash and run the following commands:
This will install and launch Boot Repair to scan your system.
sudo apt-add-repository ppa:yannubuntu/boot-repair
sudo apt update
sudo apt install -y boot-repair
boot-repair

Choose recommended repair and follow the instructions.
Restart your computer. It should  boot up normally if that was the issue.
Note: if you want the original walk-through or another way check out the 2nd URL in the appendix.

3. Reinstall Ubuntu while keeping files and programs

Problem: Might be a problem with Ubuntu 20.04. I currently use 20.04 version without this bug. It might be that it wasn't downloaded properly.

Solution:
Follows instructions from the 2nd and 3rd URL in the appendix.
From the least aggressive to the most. Follow these terminal commands:
to update the snap store to was recently switched.
sudo apt update
gnome-software
// if you don't have it then run:
sudo apt install gnome-software

to reinstall Ubuntu software -shouldn't erase your files but if you want, make a backup of your files
sudo apt install --reinstall ubuntu-software

appendix:
https://www.howtogeek.com/196740/how-to-fix-an-ubuntu-system-when-it-wont-boot/
https://www.howtogeek.com/114884/how-to-repair-grub2-when-ubuntu-wont-boot/
How do I reinstall Ubuntu Software in Ubuntu 20.04 LTS version?
Comment: Oddly for me booting into linux (recover) from inside Grub boot menu and then just selecting the "resume boot" option fixed the black screen for me. Rebooting worked as normal after that.
Answer: I had a similar problem. I seem to have fixed it by changing from lightdm display manager to gdm3 display manager. I did this by using the command sudo dpkg-reconfigure lightdm and following the prompts (using the enter key and the up/down arrow keys.)
Answer: This will solve the problem:

Code:

sudo setpci -s 00:02.0 F4.B=00

Re-type:

sudo setpci -s 00:02.0 F4.B=00

in the terminal.
  Then lets edit the file:

gedit ./etc/pm/sleep.d/9_lcd_backlight.sh

(if not gedit then any other text editor) this will create the file 9_lcd_backlight.sh. 9 is the priority you can put any number through 99.

Paste the following in your file.

Code:
#!/bin/bash
    case $1 in
        thaw)
        setpci -s 00:02.0 F4.B=0
            echo "oh, suspend to disk is over, we are resuming..."
        ;;
        resume)
        setpci -s 00:02.0 F4.B=0
            echo "hey, the suspend to RAM seems to be over..."
        ;;
        *)  echo "here we GO!."
        ;;
    esac

With the bash file in place you now need to make the file executable. Make sure you are in the directory ./etc/pm/sleep.d/ and type this in the terminal:
chmod +x 9_lcd_backlight.sh

Once the bash file is now executable lets make sure the back-light turns on when you boot up. Input the next 2 lines in ./etc/rc.local file at the bottom line. So type in the terminal:
gedit ./etc/rc.local

This will open rc.local file. Now at the bottom make sure it looks like below and save.
sudo setpci -s 00:02.0 F4.B=00

exit 0

You should be fine, reboot and check it out.
  Leave a like, comment , thanks.
Comment: This is the same instructions found in the link that I posted in the previous comment.
Answer: The solution to the problem, in my case, was very simple.
In my BIOS, the boot mode was set to legacy.
I just changed it to UEFI and turned off the secure boot option.
Now the problem is no more!
Answer: Full root drive!
Before you throw your hands up and reinstall Ubuntu, check if your kernel disk is out of space. That seems to interfere with full graphical boot (though ssh still works).
Moral of the story: any time you run rsync backup jobs, make sure your destination disk is mounted successfully. You are one unsuccessful mount away from filling your root disk.

Black screen on startup Ubuntu 20.04


I am getting the sign up screen whenever I open the Pokemon GO app. What's wrong?

Question: Whenever I open Pokemon GO, I get the screen I would get if I had just downloaded the game. It's asking me to sign up with a google account or if I have Pokemon trainers club. There is nothing I can press other than those buttons. What's wrong and how can I fix.
Comment: I don't see this problem as one of the potential problems in the list on the other question. If this is going to be marked as a duplicate, shouldn't this problem be added to the list?
Answer: I would get this issue myself when the connection timed out. If you signed up via Google, clicking the Google account button will sign you in again rather than create a new account. I assume the same would happen via the Trainers Club.


data store with a "get or block" operation?

Question: I'm looking for a data store that has a "get or block" operation. This operation would return the value associated with a key/query if that value exists or block until that value is created.
It's like a pub/sub message queue but with a memory to handle the case when the subscriber connects after the publisher has published the result.
This operation allows unrelated processes to rendezvous with each other, and it seems that it would be a very useful architectural building block to have - especially in a web environment - i.e. a web request comes in which kicks off a backend server process to do some work and the web client can get the results via a future AJAX call.
Here is an blog post I found on how to accomplish this sort of operation with mongodb:
http://blog.mongodb.org/post/29495793738/pub-sub-with-mongodb
What other solutions are in use today? Can I do the same thing with redis or rabbitmq? I've looked at the docs for both, but it's unclear exactly how it would work. Should I roll my own server with 0MQ? Is there something out there specifically tailored for this problem?
Answer: Your are correct both Redis[1] and rabbitmq[2] have pub/sub capabilities.
[1] http://redis.io/topics/pubsub
[2] http://www.rabbitmq.com/tutorials/tutorial-three-python.html


How do I "End a round in under 10 seconds"?

Question: How do I "End a round in under 10 seconds"? What's it mean by "round"?
Answer: A round is a the whole level. A round starts when you enter "in-game", flying over the play area. Typically a round ends when you can no longer defend the base from zombies.
The only way to end a round that quickly (10 seconds) is to intentionally fail. The easiest way (only way?) to do this is to kill civilians. You'll likely have to kill three civilians in one shot.
Additionally, remember you can always use coins to bypass these challenges if you're having too much trouble with them.


Does Skip Gram output differently for each context word?

Question: I was following a youtube lecture about the topic and came upon this diagram (40:48) of the skip gram model which shows different outputs for each context word although also stating that the context word matrix is the same for every context word. It was my understanding that the output for each context word would be the same probability distribution and the loss would be calculated differently, but different online sources that I read say different things. If the context word matrix is the same how are different outputs produced?
Answer: In the paper word2vec Parameter Learning Explained by X. Rong, it is mentioned that "Each output is computed using the same hidden→output matrix" and each of the context word output will be calculated with this same matrix so, your understanding is correct that each word should have same probability distribution and loss will be calculated differently depending on the 1-hot vector for each context word.


Durbin-watson test for autocorrelation

Question: Also Durbin Watson test showed to be: Durbin-Watson D=1.672, Number of Obs=171, 1st order autocorrelation=0.162 Do I have autocorrelation problem?
Answer: The Durbin-Watson $D$-statistics tests the first order autocorrelation. For a discussion on higher order autocorrelation, see this post.
In order to test for auto-correlation, you need to understand how the test works.
The $D$-statistics is obtained as: $D=\Sigma_{t=2}^T(e_t-e_{t-1})^2/\Sigma_{t=1}^Te^2_t$ where $e$ are errors.
This $D$-statistics is bounded by $0$ and $4$, because, in large samples, $D=2-2\hat{\rho}$ where $\hat{\rho}$ is the coefficient in the regression: $e_t=\alpha+\hat{\rho}e_{t-1}+\eta_t$
If $D$ is lower than $2$, then we test positive autocorrelation (a positive residual is followed by a positive residual, in general) whereas we test negative autocorrelation when $D$ is larger than $2$.
The question now, as in every statistical test, is "Is my statistics far enough from my null hypothesis such that I can reject the latter with a certain amount of certainty ?". That is, is the statistics that I obtain beyond the critical value ?
The particularity of the Durbin-Watson test is that you do not have one critical value, but two: a lower bound $D_l$ and an upper bound $D_h$. Since the test is symmetric, you also have the equivalent $4-D_h$ and $4-D_l$.
The test works as follows, if I am between $0$ and $D_l$ or between $4-D_l$ and $4$, then I can reject the null hypothesis of no autocorrelation. If I am between $2$ and $D_h$ or between $2$ and $4-D_h$, then I cannot reject. What happens when I am between $D_l$ and $D_h$ or between $4-D_h$ and $4-D_l$ ? The test cannot conclude on the presence of autocorrelation. It is an indetermination area.
To run the test, you need two things: the number of variables used in your regression and the number of observations. With this, you can find $D_l$ and $D_h$ given in statistical tables like this one. Then you can conclude on the presence of autocorrelation or not.
You do not provide the number of variables used in the estimation, I therefore cannot answer your question, although I have a hunch that it is Ok because of the first order autocorrelation value which is quite low and the value of $D$.

Durbin-watson test for autocorrelation


Approximations using Poisson and Binomial distributions

Question: The probability of a bit error in a communication line is $10^{-5}$ per bit. Suppose we examine a string of $1000$ independent bits. Calculate the probability of $0$, $1$, $2$, and $3$ errors in the string using Poisson theory and using binomial theory. Compare the results.
Comment: What have you tried ? Why can't you compute $P_0 + P_1 + P_2 + P_3$ in the specified ways ?
Comment: I think I got it, I did what I explained below in my reply to calculus' answer. If I am supposed to add the probabilities together, however, I've probably done it wrong.
Answer: Hints:
binomial distribution: $P(X=x)={n \choose x}\cdot p^x\cdot (1-p)^{n-x}$
$n=1000; p=10^{-5}, 1-p=1-10^{-5}$
poisson distribution: $P(X=x)=e^{-\lambda }\cdot \frac{\lambda ^x}{x!}$
$\lambda=n\cdot p=10^{-5}\cdot 1000=\frac{1}{100} $
Both distributions can be approximated by the normal distribution. In the case of a binomial distributed variable: $$P(X=x)=\Phi \left( \frac{x+0.5-n\cdot p}{\sqrt{n\cdot p \cdot (1-p)}} \right)-\Phi \left( \frac{x-0.5-n\cdot p}{\sqrt{n\cdot p \cdot (1-p)}} \right)$$
$\Phi(\cdot )$ is the cummulative function of the standard normal distribution
In the case of a poisson distributed variable: $$P(X=x)=\Phi \left( \frac{x+0.5-\lambda}{\sqrt{\lambda}} \right)-\Phi \left( \frac{x-0.5-\lambda}{{\sqrt{\lambda}}} \right)$$
There are some conditions for approximation. They are only rule of thumbs.
Binomial distribution:  $n\cdot p\geq 10$ and $n\cdot (1-p)\geq 10$
Poisson Distribution: $\lambda >10$
Comment: Thank you very much. It makes sense once you know what the values of the parameters are. Then I just replaced $x$ with $0$, $1$, $2$, and $3$ and calculated the values with the pdf formulas of the Poisson and Binomial distributions, getting basically the same answers. I think the factorials in the Binomial distribution became too big for my calculator so I had to use Wolfram Alpha for it. Is that why the Poisson is used to approximate the binomial? Because it is much easier to compute values?
Comment: Yes, you are right, that´s why you have to approximate the binomial by the poisson distribution. This works only for "small" x. $x!$ is hard to calclulate, if x is "large"
Comment: Ok, I think I understand. Because only if $p$ is small will the mean of the exponential distribution be large and the $e^{\lambda x}$ small, so that they balance each other out. So is it possible to approximate any distribution with another distribution as long as the curve shapes of the pdf look similar, regardless of whether one is a discrete distribution and one a continuous distribution?
Comment: The expoenential distributioin was not a good idea. I have made an edit.
Comment: You don't have to compute $1000!$ to compute $1000 \choose k$.  For say $k=3$ it is just $1000*999*998/3!$.  The factors in the denominator cancel most of the factors in the numerator.


"stagger to one's feet"

Question: I've come to see my favorite online dictionary in my native tongue says that "stagger to one's feet" means "to come up to standing position in staggering way (this is my translation so might not be so good)", but is this true? I thought it means totally opposite and come to sitting position in staggering way. No?
Answer: To get to one's feet means to stand up or to get into a standing position.
You can use other verbs in place of get:

He rose to his feet.
He jumped to his feet.
He sprang to his feet.
He struggled to his feet.

Those are just some examples of different ways that someone could stand up (or get to their feet).
If someone staggered to their feet, then they got to their feet—that is, they stood up—but they did it while staggering.
Answer: one of the meanings of "stagger" is :
to walk in an uncontrolled way, as if you are going to fall over
The man staggered to his feet and ran away.

"stagger to one's feet"


Having trouble going from the menu I created w/ Android normally to my LibGDX game file

Question: So I wanted to use Android Studio to create the menu for my game so I created a button with an onClick method that included the Intent i and startActivity(i) but when I clicked the button the app would just crash on me
Comment: What is the exception that causes the crash? Is there more details in logcat?
Comment: "Caused by: android.content.ActivityNotFoundException: Unable to find explicit activity class {com.mygdx.game/com.mygdx.game.bantz}; have you declared this activity in your AndroidManifest.xml?" I'm not sure if this is the reason why. Do all activities have to be in the manifest for them to be able to run?
Comment: Ok yeah I had to add it to the manifest, but not the exact libgdx java file but rather the AndroidLauncher java file that's in the android java folder instead of the core libgdx folder
Answer: LibGDX has an AndroidLauncher file that's located in the Android java folder that opens up the game file in the core folder but you have to add it to the android manifest for it to work


Compact and connected

Question: Let $\mathbb{J} :=\{1/n: 0< n\in \mathbb{Z}\}$
Let $T_{ir}$ be topology of $\mathbb{R}$ generated by $$\{(a,b)\subset \mathbb{R}:a<b\}\cup\{(a,b) \setminus \mathbb{J}\subset \mathbb{R}:a<b\}$$
(a)Discuss the compactness of a closed interval $[a, b]$ in $(\mathbb{R}, T_{ir})$.
(b)Show that $(\mathbb{R}, T_{ir})$ is connected but not path connected.
For (a), I know that if $0<a$ or $b\le 0$, then $[a, b]$ is compact. How about the case: $a=0<b$?
For (b), I have no any idea about connectedness. I want to show it is not path connected by considering  path joining $0$ and $1$ but I want give a rigorous proof.
Please give me all detail. Thank you.
Answer: $\frac{1}{2}(\text{Hint}+\text{answer})$: For compactness, let's consider for instance $[0,1]$. The only thing that can go wrong for compactness is if we try to include our new open subsets in our covering, so let's do that and see what happens. To get almost all of $[0,1]$ we could start by including $I = (-1,2) \setminus \mathbb{J}$. Of course, to include the points $[0,1] \cap \mathbb{J}$, we need to use some of our regular open sets. We don't want them to be so big that it's easy to find a finite subcover, so let's use open intervals $I_n$ that include the point $1/n$ in $\mathbb{J}$ but no other points from $\mathbb{J}$ (you can construct such intervals explicitly if you like). So now, by construction $I \cup \bigcup_n I_n$ will be a covering of $[0,1]$. Does it have a finite subcover?
For connectedness, what have you tried?
For non-path-connectedness, you're on the right track. The only way such an argument would not instead show path-connectedness would be if your path was not continuous, so that's what you want to show. So, what do preimages of open subsets look like? In particular, what about preimages of the new open subsets you've added?
Comment: For connectedness, I have tried:
Let $U$,$V$ $\in T_{ir}\setminus \{\emptyset,\mathbb{R} \}$ s.t. $U \cup V=\mathbb{R}$. I want to show $U \cap V \neq \emptyset$. Suppose not. If $U$,$V$ $\in T_{std}$, done. WLOG, assume $U\in T_{ir}\setminus T_{std}$. If $ 0\notin U$, then $U\in T_{std}$. So, $0 \notin V$ and hence $V\in T_{std}$. There exist $n$ and $\epsilon$ s.t. $(1/n-\epsilon,1/n+\epsilon)\setminus\{1/n\}\subset U $but $1/n\in V$.(otherewise $\mathbb{J}\subset V$ and $U\in T_{std}$)
Comment: But $V\in T_{std}\implies $there exist open interval $I$ s.t.$\emptyset \neq I\cap (1/n-\epsilon,1/n+\epsilon) \subset U\cap V$.Contradiction.But I am not sure if this answer is correct

Compact and connected


Variable-width non-breaking space in Word 2016 (including a possible solution)

Question: I'm using Word 2016 to write articles that must keep certain words on the same line. Therefore, I work with a lot of non-breaking spaces. The articles eventually go to print (or PDF), meaning there must be absolutely no visual difference between a regular space and a non-breaking space. I sometimes also send them as Word documents to editors, so there has to be no difference between the spaces when the file is opened in Word, either.
Word 2013 mostly eliminated fixed-width non-breaking space, meaning that when you typed Ctrl+Shift+Space, you got exactly what I need: a variable-width non-breaking space, which behaved just like a regular space. That's logical: a space is a space, and a reader looking at a page has no reason to get a different visual result when it's a non-breaking space. It was different for purely historical reasons, but Word 2013 at least partly fixed that.
Word 2016 reverted to fixed-width non-breaking space, which is precisely what we are trying to avoid. This occurs not just when typing Ctrl+Shift+Space, but also when inserting any Unicode character of this family, including U+00A0, U+2009 and U+202F. These either don't work (the line breaks), or they are fixed-width. Similarly, U+2007 is too wide (also fixed-width).
So far, I found a single solution: typing U+FEFF, then regular space, then U+FEFF again. U+FEFF is "Zero Width No-Break Space", so it does not produce a space itself, but keeps on the same line what's before and after the regular space. Visually, this produces an identical result to a variable-width non-breaking space.
The problem is, first, it's cumbersome to type; and, second, when the file is edited in Word, you get a strange, interruptive feel - it's three characters instead of one, two of which are invisible, etc. If it was possible to merge this character sequence into a single keyboard shortcut, that would be helpful, but still wouldn't resolve the second problem.
I read the other threads online for the last few days; none helped (expectedly, many resort to the historical parables). So, what is a streamlined way to get a variable-width non-breaking space in Word 2016? Either a Unicode character I haven't yet discovered, a compatibility setting that would make Word 2016 behave like Word 2013 in this regard, or any other solution. Many thanks for the help.
Answer: There is no better way than yours. However, you can combine typing U+FEFF, then regular space, then U+FEFF again and make it into a shortcut on your keyboard.
Add a macro in Word with the following code: <code> Selection = ChrW(65279) & " " & ChrW(65279)</code>
ChrW adds a Unicode character, 65279 is the decimal code for U+FEFF.
Comment: My Word program (version 16.46 on macOS) complained about the parentheses around the number `65279` constituting invalid syntax.


Why is the docking bay locked?

Question: I was just trying to get to my seamoth when the docking bay said "locked" when I hovered over it. I then tried to go in from the side to investigate, but it was locked too. Why can't I access my seamoth (I put it in the Cyclops by the way)
Comment: Screenshots would be helpful
Comment: not my screenshots but its the exact thing that's happening to me https://imgur.com/a/otHXG
Comment: On the 2nd floor, there are doors that lead under the seamoth/prawn
Answer: I encountered the same issue. The reason was that there was not enough space between my Cyclops and the ground. Just needed to elevate a little bit the Cyclops.

Why is the docking bay locked?


Passing data between threads (non main thread to OS main thread) in GTK4

Question: I am building a GTK application using GTK4. I am stuck with the problem on how to pass some data between threads in GTK. To be specific, I am presenting the problem in detail.
I have a Server and a Client module, where the Client displays the UI based on the data received from Server. The UI related operations happen on the OS Main thread where the GTK event loop runs. Whereas the communication with the Server happens on a non main thread. At some point, Server may send some update to the Client. The update will be received on the communication thread i.e. the non main thread. Since the intention is to update the UI (either modify the UI or Create a new window) based on the information received, somehow the information shall be passed to the OS main thread where event loop is running.
In GTK4 how to pass the information between threads (main to non-main or vice versa)?
I am deliberately avoiding g_idle_add / g_idle_timeout because it keeps running the function continuously or at regular intervals. I am looking for some GTK supported message passing mechanism without building my own message passing system.
Answer: The callback you pass to g_idle_add needs to return TRUE/G_SOURCE_CONTINUE or FALSE/G_SOURCE_REMOVE. The latter will remove the function from the main loop after the first invocation so it won't be run continuously.


Unexpected behavior using Autolayout with NSSplitView

Question: I have the following implemented with springs and struts along with several NSSplitViewDelegate resizing and constraint methods and it all works as desired.  I am now trying to adopt autolayout for this same scenario by replacing all of the setFrame messages and NSSplitViewDelegate methods with proper autolayout constraints.
My main window's view contains a vertical split view (I call OuterSplitter) with the top, bottom, left and right leading and trailing space constraints set to zero for OuterSplitter to its superview.
The right pane of OuterSplitter contains (among a few other things) another vertical split view (I call InnerSplitter)  which also has the top, bottom, left and right leading and trailing space constraints set to zero for InnerSplitter to its superview (i.e. OuterSplitter's right pane).
I have set nominal minimum width constraints for OuterSplitter's left pane, and also for both the left and right panes of InnerSplitter.
When the main window is being resized, the desired behavior is for all (or most) of the expansion and contraction to be applied to InnerSplitter's left pane, unless one of the minimum width constraints takes effect. Therefore, I have set the split view Holding Priority for OuterSplitter's left pane to 260 (highest) and 250 for the right pane. Also, the Holding Priority for InnerSplitter's left pane to 245 (lowest) and 255 for the right pane.
I have watched the video for session 232 from WWDC 2012 and thought I was on the right track. My autolayout constraints work mostly as desired, but there is one very strange behavior that does not occur with my springs and struts version.
If the split bar of the InnerSplitter is as far right as it will go (InnerSplitter right pane is at its minimum size) AND the OuterSplitter split bar is NOT as far left as it can go, then if you try to drag InnerSplitter's splitter bar farther to the right, then unexpectedly the OuterSplitter's split bar moves to the left causing the InnerSplitter's Left pane to grow and OuterSplitter's left pane to shrink.  My expectation is that no resizing should take place in that case.
It is possible to stop the OuterSplitter's split bar from moving when tugging on the InnerSplitter's split bar that is pinned to the right?  If so, what constraints should be added? Or are some of the NSSplitViewDelegate methods still required? Thanks.
BTW, I'm using Xcode 4.6.3 and targeting OSX 10.8.
Comment: Here is a barebones demo: https://github.com/Whiffer/Test-Autolayout
Answer: I had the same problem and got around it by using NSViewControllers within each split view pane so that I didn't directly have split views embedded in split views. It's more code and more complex but it does seem to work.
I never found a solution for when split views are embedded in split views so I'll be interested if anyone has an answer.
Comment: I finally gave up and added a third pane to the outer split view and eliminated the inner split view.  I was not able to achieve all of my desired UI behavior, but at least it works without any strangeness.
Answer: To fix this, you could add an explicit width constraint on -mouseDown: in the NSSplitView before calling through to super, then remove it immediately after.

Also, it looks like this is fixed in the 10.11 beta!


Information about Apply mining pool rewards ERC-20 Smart Contract

Question: I was contacted from a girl of Singapore,she told me to join a website,with 1k of buying USDT erc-20,every day I withdraw 30 dollar,but today I accept this partecipation for the claim the reward but nowhere was written that one time you accept if you don't put the rest of money in my case 3674, they blocked for 180 days my money, how I to réclame my money, I contact them from the customer service of the website and send me to a telegram number service and they say I had to wait 180 days if I don't put the rest of the money,what I have to do for to take back my 1325 USDT ? Help me
Comment: Sounds like pig butchering scam: https://ethereum.stackexchange.com/questions/155862/what-is-pig-butchering-scam
Answer: You were not contacted by a girl from Singapore. You were contacted by a computer program pretending to be a girl from Singapore. The scammer operating the program then took over the conversation.
You cannot reclaim your money. Consider it lost. You've been scammed.
Beware, they will try to get more money out of you. They have added you to a list of victims and you will be contacted by more scammers, including people pretending to be able to get your money back. That's a scam too.
In the modern world you cannot assume that a person you haven't met even exists, let alone trust them to give you investment advice.
Sorry this happened to you.


Zend Framework Controller with action as steps

Question: I am working on a register controller to create a account. I send the user to a special url:
www.name.com/activate/1/fdafdsafdasfdsa where 1 is a id en fdafdsafsda is a hash. I check these in the public function init. If the id and hash are right the init does a forward to step1: <code>$this->_forward('step1', null, null, array());</code>
Step 1 is a form and if this is posted and correct step 1 does a forward to step2. But now the problem is in step 2 there is also a form. But I don't want to change the url so I use forward. But when posting on step2 he send the user back to step1. What is a good solution to fix this problem?
Thanx
Answer: You can use an extra parameter in your form to indicate which step is the current. Then, in your "Controller > predispatch", you can "select" the right method.
But for my personnal use, I prefere to change the URL to point the differents steps (and I implement a check to ensure the user follow the sequence of step).


Logistics data sources for data analysis work

Question: Where can I find logistics data sets?
I look for data for my student to analyse in a bachelor thesis.
Answer: Transport and Logistics Case Study Data Set (Cargo 2000)
The case study data comprises tracking and tracing events from a forwarding company's Cargo 2000 system for a period of five months. From those Cargo 2000 messages, we reconstructed execution traces of 3,942 actual business process instances, comprising 7,932 transport legs and 56,082 service invocations. Each execution trace includes planned and effective durations (in minutes) for each of the services of the business process (introduced in Section II), as well as airport codes for the DEP ("departure") and RCF ("arrival") services. Due to the fact that handling of transport documents along the business process differs based on whether the documents are paper-based or electronic, we focus on the flow of physical goods, as our data set did not allow us to discern the different document types.
-Transport Tracker Solution | Google Developers
https://developers.google.com/maps/solutions/transport-tracker/
-GIS in logistics and vehicle routing applications - Geospatial World
https://www.geospatialworld.net › Articles
-Mapping for Transport & Logistic Professionals | MapData Services
https://mapdataservices.com/industries-transport-logistics
-UCI Machine Learning Repository: Data Sets
Lafifi, Mohamed-Mourad. (2019). Re: Transport and Logistics dataset?. Retrieved from: https://www.researchgate.net/post/Transport_and_Logistics_dataset/5c54a4244f3a3e4b096edf76/citation/download.


Does there any non discrete metric space in which closure of an open ball is not closed ball?

Question: In other words does there exist a non discrete metric space in which Closed balls are subset of the closure of open balls?
Answer:
The rectangle pictured above, with the Euclidean metric restricted from the plane, gives an example where the closure of an open ball of radius $r$ is not the same as the closed ball of radius $r$.  The segment inside the pictured circle (not including endpoints) is an open ball, and its closure is the segment including the endpoints.  However, the closed ball with the same radius includes the point where the circle is tangent to the rectangle.
Because closed balls are closed, the closure of an open ball of radius $r$ is always contained in the closed ball of radius $r$, so the only way for the two to not be equal is for the closed ball to contain points not in the closure of the open ball.
Comment: To be explicit:  by rectangle you mean the green segments shown, not the interior.
Comment: Ross: That's right, thanks.
Answer: To construct an example as in the title (the text doesn't say the same thing): remove from $\mathbb R^2$ the intersection of the open unit disk and the rectangle $[1/2, 1]\times [-1,1]$. In the new space (with the induced metric), the closure of the open unit disk is strictly smaller than then the closed unit disk (we miss a portion of the circle).
Comment: right ..thank you very much
Answer: Maybe the OT would mean: the closure of the open ball is a subset of the closed ball (not the converse). Here is another simple example: $(\mathbb R,d)$, with $d(x,y)=\min\{1,|x-y|\}$.
The condition that the closed balls are the same as the closure of the balls is known to be equivalent to the following condition: for all $x\in X$, the mapping $y\rightarrow d(x,y)$ has a unique propert minimum at $x$. This is why metric spaces verifying this property are called pitless in http://arxiv.org/abs/1111.0268. They verify also a general property, which generalizes amenability to any metric space, called property SN.
Answer: None of the explicit examples given so far seem to be important as anything other than "weird counterexamples" (similar to the examples one may create to test ideas in general topology). It would be good to have an answer to the question using a metric space that is of serious interest. One such example is the $p$-adic numbers ${\mathbf Q}_p$, which form a metric space in which any open ball is already a closed set. For example, the open unit ball $\{x \in {\mathbf Q}_p : |x|_p < 1\}$ is a closed set, so its closure is itself. The unit circle $\{x \in {\mathbf Q}_p : |x|_p = 1\}$ can't be approached closely by any point in the open unit ball. Another example is the $X$-adic metric on the formal power series ring ${\mathbf R}[[X]]$, which can be used to justify some formal manipulations with formal power series by checking the case of polynomials and then appealing to continuity.


Why is there a very long 6 second delay in start of Curl

Question: I did a full install of Cygwin on my Windows 7 x64 machine. After each machine reboot, Curl can take around 6 seconds to start (even if no command line options were specified). On subsequent uses of Curl there is no delay. It looks like a DLL is being initialized or ? Has anyone else seen that and is this normal?
Comment: Could be the Cygwin DLL initializing itself, if no Cygwin processes have been previously started. How are you invoking curl -- from the Windows shell, or from Cygwin bash? Do you have any Cygwin services enabled, or any Cygwin commands that run on startup or login?
Comment: I am invoking it from the Windows cmd prompt (not from bash). I haven't configured any other services to start. I have reproduced the problem on other machines including 32 bit Windows XP so I am thinking it might be the normal time to startup but I want to confirm this.
Answer: This is normal; the first time the Cygwin DLL runs, it performs several initialization steps, which can potentially be time-consuming, to set up the Cygwin environment. This initialization occurs the first time after system boot that a Cygwin process is created, and there is unfortunately no real way around it.
The best recommendation I can offer is to modify your system startup scheme, or your login scripts, to create a Cygwin process, so that the initialization time gets "rolled in" at a point when you're already expecting to be waiting on the system, rather than occurring later on when you're expecting a quick response. For example, you might add something like the following, as a batch file, to C:\Users\<your username>\AppData\Local\Microsoft\Windows\Start Menu\Programs\Startup:
c:\cygwin\bin\run.exe '/bin/bash -c "ls > /dev/null"'

This will launch a Cygwin bash process which fairly quickly does nothing and then exits, without displaying a window on your console -- thus forcing the Cygwin DLL to load and initialize itself, without producing any side effects, and so that when you finally open a command prompt and run curl, the initialization time will have already occurred, and you won't be annoyed by it while running interactive commands.
Comment: Thanks for the link, that explains the delay I was seeing.


Diffuse Maps and DirectX

Question: How would I load two diffuse maps onto one mesh. I have a mesh with multiple sub meshes but each one of those sub meshes has a vertex buffer and I don't think that's very efficient. How could I have two diffuse maps on one mesh without having to go into 3d modeling software and merge the Uv coordinates of the two objects. I'm using directX and C++.
Comment: Why wouldn't you do this in 3D modeling software exactly? That's the normal way of solving this problem.
Comment: "I don't think that's very efficient" - have you actually benchmarked this?  Until you have hard evidence that it's actually not very efficient, you're indulging in premature optimization.
Comment: Just wanted to know if there was another way to go about it to minimize vertex buffer switches.
Comment: @AndrewWilson Why do you need to switch vertex buffers?  Do the submeshes have different input layouts?
Comment: @MooseBoys May be out of inexperience. But I thought for each distinct mesh you should have a separate vertex buffer?
Answer: The only way I can even think of accomplishing this would be to add some sort of selector data to the vertex information that would allow a custom shader to select between the two textures to be applied. This technique can be applied with a little custom code to rewrite/combine the two vertex buffers, and of course the custom shader to take the new vertex format and the two textures to be used.

Diffuse Maps and DirectX


Is there a way to back up all the keybindings in Ubuntu (the ones in "Keyboard Shortcuts" UI)?

Question: Is there a way to back up and restore (from the command line) all the keybindings that are shown in the "Keyboard Shortcuts" UI? I'm not talking about just the custom ones that a user creates (which would be pretty easy), but the whole sh-bang.
Comment: http://askubuntu.com/questions/101226/where-does-ubuntu-store-its-keyboard-shortcut-configuration
Answer: Check out: <code>/usr/share/gnome-control-center/keybindings</code>
Comment: Close, but no cigar. :D  Commenting out the xml for a keybinding removes the keybinding from the list, but does NOT actually stop the keybinding from existing.  For example, I set the "Run Terminal" shortcut to ctrl-r, then comment out the xml for that keybinding.  While the keybinding for Run Terminal is no longer in the list when I run the gui, and the Run Terminal shortcut is no longer displayed, but I can still use ctrl-r to open a terminal.
Comment: I'm not sure we have the same understanding for the words "backup" and "restore". For me backing up means creating a tarball of the directory and sending it somewhere safe. For you it seems it means editing the files by hand and expecting it to work without actually forcing gnome itself instead of that applet to re-read the file. (P.S. CTRL-R already has a more useful usage in bash :( )
Comment: Backing up by copying the directory somewhere (by tarring or otherwise) is *exactly* what I'm trying to do.  I want to be able to do.  In particular, I want to do a fresh install of Ubuntu, bring in whatever I need, and blow away the fresh install keybindings with the set of keybindings that I have backed up.  And ctrl-r was arbitrary :P  :D


How to fix windshield washer pump in Yaris Verso

Question: My windshield washer pump in my Toyota Yaris Verso has stopped working. The fuse seems to be fine, so either it's due to a loose connection, or the pump is broken. What is the likely cause, and how can I access the pump?
Comment: @MarkJohnson: thanks for getting back to me. Yes - the pump motor had to be replaced, as simple as that.
Answer: The pump is usually mounted to the bottom of the tank.
Common causes of failure:

Disconnected or clogged hose with the engine off can you hear the motor running under the hood? If so could be a clogged or disconnected hose.
Wax or other debris in the jets, if the jets are located on the hood they can get clogged with wax or dirt, if you hear the pump motor running and there are no disconnected or clogged hoses this may be your problem.
Bad motor, check for voltage at the terminals connected to the motor
If no voltage to the motor you may have a bad wiper switch
Comment: Thanks! I don't hear the pump so I guess it's either a bad motor or a bad switch. I'll have to access it first, which isn't easy without lifting the car.
Answer: I've had a faulty windshield washer pump motor changed in my Yaris once. This one is not so easy to access. The mechanic replaced it via front right wheel area after removing front guard. He said this way is better other wise he'll have to remove front bumper, headlight then washer water tank to get to motor. Hope this helps
Answer: Remove front right tire, remove plastic guard, remove wiring connection and water tube from washer pump, then remove washer pump. Going through the bumper is more tedious.
Answer: I have also a faulty front washer yaris 2013... But better check first before you buy a replacement..mine stop woking  because of rusty connectors because water leakage.. I try clean it with wd40... brushed it then test it now its working..
I believe pump motor is sealed so 95% its still good


Is a hydrogen bond considered to be a van der Waals force?

Question: Is a hydrogen bond considered to be a Van der Waals force?
Answer: According to the IUPAC gold book a van der Waals force is:

The attractive or repulsive forces between molecular entities (or between groups within the same molecular entity) other than those due to bond formation or to the electrostatic interaction of ions or of ionic groups with one another or with neutral molecules. The term includes: dipole–dipole, dipole-induced dipole and London (instantaneous induced dipole-induced dipole) forces.

Hydrogen bonding is a type of dipole-dipole interaction, so it would fit the definition of a van der Waals force.
The way I think of it is: van der Waals forces are anything that make a gas non-ideal, since that's how they were originally discovered and defined.
Comment: The provisional IUPAC recommendation for the definition of hydrogen bond requires "evidence of bond formation" and refers to "partial covalent bond formation".  This would seem to exclude the "other than those due to bond formation" requirement of the van der Waals definition. http://media.iupac.org/reports/provisional/abstract11/arunan_prs.pdf
Comment: But doesn't hydrogen bonding contain a rather sizable covalent component which would mean it doesn't fall under the IUPAC definition?
Comment: I agree with @DavePhD and the source he cited (maybe make it an answer for a more permanent record?). The [goldbook](http://goldbook.iupac.org/H02899.html) however recommends, to regard an Hydrogen bond as an "electrostatic interaction", which would make it fall under the mentioned vdW description. This is one of those topics, where a pure classification is not possible - in some cases the covalent character would outweigh the ionic and in some cases it would be the other way around.
Comment: @Martin, that's why I look at it in the context of gases, which is really the only context in which it makes sense to talk about van der Waals forces as a group. In any other context, the different interactions are treated separately.
Comment: @Phillip - Sure, you could argue that. I guess it would depend on if you consider the covalent nature or the ionic nature more significant. Traditionally, it is classified as a particularly strong dipole-dipole interaction, which makes sense because we normally talk about van der Waals forces in the context of gases.
Comment: I would not consider bifluoride, ammonium, and hydronium ions to be formed through dipole interactions.
Answer: There are two definitions of a hydrogen bond in the Gold Book: hydrogen bond (1994) and hydrogen bond (1999). The later stresses both the covalent bond nature and the electrostatic interaction component, which both can make it fall outside of the van der Waals forces as of the 1994 definition.
EDIT: Answer edited following the remarks made by @tomij below. See also the interesting discussion below his answer as to the context (historical and experimental) leading to the introduction of the notion of van der Waals forces/interactions.
Comment: The later definition is not saying hydrogen bonds are covalent, it is saying that a covalent bond between H and an electronegative atom results in electrostatic interactions between the H and a _different_ electronegative atom. Also, the van der Waals definition is excluding charge interactions between _ions_, but H and the other bonding atom are not ions. It also says "The term is sometimes used loosely for the totality of nonspecific attractive or repulsive intermolecular forces," which would include hydrogen bonding. It also mentions dipole-dipole, which includes hydrogen bonding.
Comment: @thomij In the latter definition, it says "forms an additional weaker *bond*" and then "[the] energy of hydrogen bonds [...] results from the electrostatic interaction and also from the *orbital interaction* [between] the hydrogen donor [and] the hydrogen acceptor molecule." Isn't orbital interaction a feature of covalent bonds? Also, hydrogen bonds then form [dipolar bonds](https://goldbook.iupac.org/terms/view/D01752) and result from [coordination](https://goldbook.iupac.org/terms/view/C01329) which also involves covalent bonding... In acides/bases isn't the link at least partially covalent?
Comment: It is true that hydrogen bonds are partially covalent, which is why they are distinguished from other dipole-dipole interactions. However, they are also not fully covalent - which is why they are distinguished from fully covalent bonds as well. Historically van der Waals forces were any force that accounted for non-ideal gas behavior of real gases. I think it's fair to say that hydrogen bonding is one of those forces. I also think it's fair to say that because the other forces have little to no covalent character, hydrogen bonding should be thought of as different from them.
Comment: @thomij Indeed, the historical perspective is quite enlightening. I've made a limited bibliographic survey of recent publications and although some authors argue that HBs and vdW interactions are distinct, either their argument is quantitative, thus making the distinction arbitrary, or they assign a priori attributes to vdW interactions chosen so as to set them apart from HBs, but I doubt that those attributes were stated by van der Waals himself (I need to read his original work still). But so now I tend to think that HBs should actually be considered to belong to the set of vdW interactions.


Is it a requirement that jurors of a state prosecution be residents of the state that brought the legal proceedings?

Question: Would a jury of your peers preclude jury members of neighboring states from deciding on your guilt? Is there any geographical consideration of who and what is considered your peers? I'm asking specifically for state cases, I'm assuming on a federal case they could probably get jurors from all over.
Answer: For federal prosecutions, the Sixth Amendment gives defendants a right to trial "by an impartial jury of the State and district wherein the crime shall have been committed." This hasn't been applied to the states, but I believe every state in fact requires jurors be at least residents of that state (states sometimes go farther and require that jurors be from the same county).


On the Dirichlet series for $1/\zeta(s)$ for real $s$ and the zeros of zeta

Question: For $\Re(s)>1$, it is well known that
$$\frac{1}{\zeta(s)} = \sum_{n=1}^{\infty} \frac{\mu(n)}{n^s}$$ where $\mu$ denotes the Mobius function and $\zeta$ is the Riemann zeta function. I have heard that if the series on the right-hand side has an analytic continuation REAL $s_{0} \in (1/2, 1)$, then $\zeta(s)\neq 0$ for every $s$ with$\Re(s)=s_0$. But since all nontrivial zeros of the zeta function are complex, why does the analytic continuation of the said series to real values of $s$ have anything to do with the complex zeros ?
Comment: See https://en.wikipedia.org/wiki/Dirichlet_series#Abscissa_of_convergence if $\sum_{n=1}^\infty\frac{a(n)}{n^{s_0}}$ converges then $$\sum_{n=1}^\infty\frac{a(n)}{n^s}= \lim_{N\to \infty} N^{s_0-s} (\sum_{n=1}^N a(n) n^{-s_0}) + \sum_{n=1}^{N-1} (\sum_{m=1}^n a(m)m^{-s_0}) (n^{s_0-s}-(n+1)^{s_0-s})$$ converges and is analytic for $\Re(s) > \Re(s_0)$ and where it is meromorphic it has no poles on $\Re(s_0)$. The converse is very specific to $\zeta(s)$ and follows from the same Tauberian theorems as in the proof of the PNT.
Comment: where did you hear that?
Answer: The statement you have given is not quite correct, but it is close to being correct. $\frac{1}{\zeta(s)}$ is known to have an analytic continuation to the interval $(1/2,1)$, and indeed all the way up to $(-2,1)$ (up to the first trivial zero). What is true, however, is the following:

If the series
  $$\sum_{n=1}^\infty\frac{\mu(s)}{n^{s_0}}$$
  converges for some $s_0\in(1/2,1)$, then $\zeta(s)$ has no zeros on the line $\mathrm{Re}(s)=s_0$.

This follows from the general fact which can be established just like the special case covered in this answer:

If an analytic continuation of a Dirichlet series has a pole on the line $\mathrm{Re}(s)=s_0$, then the Dirichlet series does not converge at the point $s_0$.

The brief idea of the proof is that if the series were to converge, we could estimate how large the value of the Dirichlet series is at points close to the line $\mathrm{Re}(s)=s_0$, and we can show that this value grows slower than it could if there was a pole.
Comment: I think "pole" is a bit too specific in ths last phrase; the value grows more slowly than it could if the partial sums didn't converge.
Comment: @GregMartin What partial sums do you mean? The point of the argument is to *deduce* divergence of a sum from existence of a pole. Also I thought it is possible for a Dirichlet series to converge at a point and have a logarithmic singularity on the same abscissa - doesn't $\log\zeta(s)$ have that property?
Comment: Sorry, I misread—I was thinking of the general situation of Dirichlet series convergence, but you are indeed postulating an actual pole of $1/\zeta(s)$.
Answer: Let $s_0>0$. The right statement is that the  following are equivalent:

The sum $\sum_{n=1} \tfrac{\mu(n)}{n^s}$ converges for $s>s_0$.
$\zeta(s)$ has no zeroes with real part $>s_0$.
$1/\zeta(s)$ has an analytic continuation to the half space $\mathrm{Re}(s) > s_0$
$\sum_{n=1}^N \mu(n) = O(N^{s_0+\epsilon})$ for all $\epsilon >0$.

As you point out, $1/\zeta(s)$ certainly has an analytic continuation to the real interval $(0,\infty)$, since $\zeta$ doesn't vanish on the positive reals.
Comment: Do you know any reference for a proof of your first condition from either the second or the third?


does ubuntu allow extended desktop

Question: I currently have windows 7 starter which does not allow for extended desktop, meaning I cannot run dual screens.  Does ubuntu support this?
Comment: I have used multiple screens with my laptop. However, I'm not sure if there are limitations with different hardware or versions of Ubuntu.
Comment: What kind of graphics card do you have? Most support this. Just try the live CD if you have integrated graphics and it should work fine using the regular system settings.
Answer: Yes, Ubuntu does support a desktop extended across multiple monitors by default. Just today I brought in my Thinkpad with Ubuntu 13.04 (Unity) to work to try out with 2 external monitors and both were properly detected immediately. In the "Displays" settings you can configure them to your liking, as shown here:

You can get to Displays by simply searching for it in the dash, or by going to System Settings > Displays. Your mileage may vary based on your graphics chipset. For example, an Nvidia chipset may have its settings in a utility provided by Nvidia instead of being fully configurable from this interface. In my example, the chipset is an Intel HD4000. Also be aware of how the performance capabilities of your graphics card will affect overall graphical performance across an increasing number of monitors with high resolutions.
Answer: Yes Ubuntu does have multi-monitor (extended desktop) support out of the box. Although this will depend on your hardware and if it can run it comfortably.
Multi-monitor support is a feature that Microsoft left out of Windows 7 Starter.
You can see the limitations of Windows 7 Starter here.

Windows 7 Starter does not include:

Aero Glass, meaning you can only use the Windows Basic or other opaque themes. It also means you do not get Taskbar Previews or Aero
  Peek.
Personalization features for changing desktop backgrounds, window colors, or sound schemes.
The ability to switch between users without having to log off.
64 bit version
Multi-monitor support.
DVD playback.
Windows Media Center for watching recorded TV or other media.
Remote Media Streaming for streaming your music, videos, and recorded TV from your home computer.
Domain support for business customers.
XP Mode for those that want the ability to run older Windows XP programs on Windows 7.
Answer: Yes Ubuntu does allow extended desktop. To enable this go to system -> preferences -> monitors
Answer: I run the Ubuntu 18.04. Had that issue myself. The solution for me was to:

plug all monitors to my laptop
go to Settings -> Displays

having only 1 display (laptop) on and 2 monitors connected but black

turn on all displays by clicking their names (switching betwen them) and
clicking the input for that

does ubuntu allow extended desktop


How does being exposed to strong radiations effect nanosatellite electronics equipment?

Question: I'm on paper designing a nanosatellite power system. The satellite would be orbiting in LEO. And I am wondering how and what type of radiation would affect its electronics. The system has a microcontroller, a few inductors, a few transistors, capacitors and some op-amps. How does one actually shield a nanosatellite from radiation? Does the metal box of the power system help? Or should the nanosatellite be made of some particular material to protect the subsystems from radiation?
Comment: If you are really designing a satellite that will be placed in orbit at a considerable cost, you should not be " wondering" about how to protect it.  You need to seek professional guidance from experienced engineers who have already done this, not from a website.
Comment: Probably better suited to physics.SE
Comment: The term you should feed to Google is "radiation hardening"
Comment: I worked with a physicist who specializes in understanding and mitigating difficulties that plague longer mission spacecraft. Radiation isn't the only problem, perhaps not even the most difficult one. You should contact your space agency and ask to speak with a specialist about your situation. The details are continually being updated and solutions developed. So you need to get current. There are people who specialize in this. Use them. Some info may also be classified. So that may be an issue, as well.
Answer: The electronics of a satellite can be changed by radiation because   radiation can be just photon and photons can excite electrons or holes creating unwanted error.
Radiation can be electrons or positrons and if it is positrons (β+) they can annihilate with electrons or if it is electrons they can fill holes which is not good in semiconductors.
There are different type of shieldings for different type of radiation.
Just Google how to protect from different kind of radiations.
And those mentioned are just the simplest case there could be α radiation but the changes are more for the CSE.
Answer: Radiation can flip bits in registers and memory. First minimise that, with shielding, and using 'rad-hard' components. Second, minimise the effect of that, with system design.
If the flipped bit in in the program counter, then you can expect the program to run off into the weeds. Look up 'crash bars', instructions to reset peppered amongst the program proper, so that a bad PC will hopefully eventually reset the device.
Look up 'watchdog', hardware to reset the microcontroller should it fail to do something expected, like flip a bit every 100 mS or whatever you choose.
If the flipped bit is in the program flash, then it's game over, unless you're routinely checksumming flash and have a way of correcting it with FEC (forward error correction) and/or multiple copies of the program.
Look up 'redundancy', using multiple processor running the same program, and suitable hardware voting on the outputs, and resetting or otherwise repairing the 'odd processor out'.
Answer: Silicon breakdown voltage shrinks with lithography and contamination.
Radiation shield effectiveness depends on wavelength and atomic structure of metal for Xray to alpha,beta to gamma radiation.
https://www.thomasnet.com/articles/plant-facility-equipment/radiation-shielding-materials/
But consider the E field and junction size and normal breakdown to conducted voltages can be small, but large for nano wave particles as the impedance rises in the dielectric.
This contamination is R in a dielectric C reduces the gap length and causes partial discharge,PD and might sound like a Geiger counter. When mV/um is energized by photons of alpha and gamma waves it goes through metal and is harder to shield thus larger litho older technology was generally better than newer small litho. But as contaminant levels improved by processing and process, newer smaller litho became more tolerant.
Think of it like a unijunction partial discharge , PD relaxation oscillator effect but more random excitation from cosmo solar flares. So E field is important and wavelength  for radiation hardened IC's .
They do this by  Xray bombardment precap to "oblate" the contaminant particles that might be in the PPM concentration levels making it more robust, or it could make it worse if the particles fuse together and remain behind thus extremely low current HIPOT to devices might seem practical but expensive to substrate might be done now (?) which makes more expensive $$ yet verified partly. But it must be done by a reliable process of visual inspection and XRAY bombardment.
without this then you have a Monte Carlo machine. do you feel lucky? Then add redundancy with detect and correction. The takes EMI design to a much higher frequency level of physics.


Does CPU heating to 90 C cause any permanent damage?

Question: I have a MacBook Air 6,2 (2013) with an i7 (1.7 GHz normally). When I was installing Debian on it I completely forgot about the "Turbo Boost" feature — my CPU was clocked at its highest possible value, and consistently reaching 80-90 degrees. I've since clocked it back but I just wanted to make sure it didn't hurt anything.
Answer: The i7-4650u has a max operating temp of close to 100c so you were pushing it close but it should be fine.
Answer: My Macbook reached 108/109° and still works great since 2008!
Steve Jobs hate fan noise so Macbook heat a lot, is normal, no damage! When it start overheating there's an alarm that freeze temporarily Mac but I've never see it!
Comment: It might be different for a MacBook Air since it's much more tightly packed (that's what I was worried about, and it may also be different with an SSD).
Comment: probably but all MacBooks heat a lot and is all under control, when it become dangerous Mac turns off. Don't worry, a short little "overheat" due to an installation can't damage your mac!