~$ sudo apt-get update &amp;&amp; sudo apt-get upgrade           Hit:1 http://dl.google.com/linux/chrome/deb stable InRelease           Hit:2 http://packages.microsoft.com/repos/vscode stable InRelease                         Hit:3 http://repo.mysql.com/apt/ubuntu bionic InRelease                                   Ign:4 https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.2 InRelease                Hit:5 https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.2 Release                  Hit:6 http://ppa.launchpad.net/deadsnakes/ppa/ubuntu bionic InRelease                     Hit:7 https://packages.microsoft.com/repos/ms-teams stable InRelease                      Hit:9 https://dl.yarnpkg.com/debian stable InRelease                                      Hit:10 https://deb.nodesource.com/node_12.x bionic InRelease                              Hit:11 http://ppa.launchpad.net/linuxuprising/java/ubuntu bionic InRelease                Reading package lists... Done                                  Reading package lists... Done           Building dependency tree                  Reading state information... Done           Calculating upgrade... Done           The following packages have been kept back:           mongodb-org mongodb-org-mongos mongodb-org-server mongodb-org-shell mongodb-org-tools           0 upgraded, 0 newly installed, 0 to remove and 5 not upgraded.        ~$ sudo apt-get install sqlite3           Reading package lists... Done           Building dependency tree                  Reading state information... Done           E: Unable to locate package sqlite3
There are now errors when updating and I cannot install most software due to a corrupted  /etc/apt/sources.list   file. Is there a copy I can download to replace it?  The file would be for Ubuntu 12.04 (Final Beta) in the United States.
Cardinality of a set of closed intervals What is the cardinality of the set S of all closed intervals on the real number line with rational (positive) lengths?  I believe the number of intervals with a specific fixed length but varying start points is |R|, and the number of intervals with a fixed start point but varying lengths is |Q| = |N|. I think the answer to the question would then be |S| = |R x N| = |R|? I'm not quite sure how to prove the last equality though. Would I have to define a bijective function that maps elements of (R, N) to R? How would I approach doing so? Why is saltatory conduction in myelinated axons faster than continuous conduction in unmyelinated axons? How does spacing apart sodium and potassium channels allow the action potential to travel faster down the axon? This is the reason always cited for saltatory conduction and myelination, but my mental model of conduction tells me that the density of ion gates along the axon should not affect the speed of the AP.   To illustrate, consider a myelinated axon. A wave of Na$^+$ from action potential site 1, a node of Ranvier, rushes into and quickly diffuses down the axon. (It travels in both directions, but backwards is still in the refractory period.) It diffuses through the myelinated region, its concentration always diminishing. Before it attenuates too much, however, it happens upon node of Ranvier 2, where it triggers another action potential. A new wave of Na$^+$ rushes in and the cycle repeats. This should be plain so far.  Now imagine that there is actually a node of Ranvier halfway between node 1 and 2, called node 1.5. The wave of Na$^+$, on its way to node 2, happens to trigger an action potential at node 1.5, from which a wave of Na$^+$ pours in and either boosts the original wave or replaces it by taking its momentum. Now the reinforced wave proceeds to node 2 and triggers it just as soon as, perhaps even sooner than, if node 1.5 had not existed. Repeatedly insert nodes at higher densities until the situation is simply lack of myelination, and we conclude that unmyelinated axons can transmit an action-potential-triggering wave of Na+ as fast as or faster than a myelinated one.  In short, my point of confusion is this: I cannot see how a higher density of gated channels can possibly slow down the wavefront of Na+ that triggers action potentials. If anything, the additional influxes of Na+ should speed up the all-important wavefront, assuming that new waves really "either boost the original wave or replace it by taking its momentum", and also assuming that the wavefront of Na$^+$ is really all-important for signal transmission, and also assuming that the mere presence of (voltage?) gated ion channels in the membrane does not significantly retard the wavefront.  But the usual explanation for why saltatory conduction is faster than continuous conduction (a fact I hope is empirically and unambiguously established) relies on the putative slowing effect of ion channels on the signal fore. Please explain this effect in more detail, if it is not a misconception. Flash Player works on Firefox, but not on Chromium? I want to play online games, and other online stuff that requires Flash Player on the internet. Flash Player works just fine under Firefox, but in Chromium I just get a blank page. I don't know what is the exact problem or know to fix it. How to do string formatting with placeholders in Java (like in Python)? How fast does gravity propagate? A thought experiment: Imagine the Sun is suddenly removed. We wouldn't notice a difference for 8 minutes, because that's how long light takes to get from the Sun's surface to Earth.   However, what about the Sun's gravitational effect? If gravity propagates at the speed of light, for 8 minutes the Earth will continue to follow an orbit around nothing. If however, gravity is due to a distortion of spacetime, this distortion will cease to exist as soon as the mass is removed, thus the Earth will leave through the orbit tangent, so we could observe the Sun's disappearance more quickly.  What is the state of the research around such a thought experiment? Can this be inferred from observation? Eclipse CDT - Copy static resource file to bin_dir How does sudo handle $HOME differently since 19.10? The momentum-space fermion propagator in the free Dirac theory is given by       The arrow on the fermion propagator is said to represent the flow of charge.  How can we derive this statement quantitatively from the Dirac Lagrangian?  What is the quantitative form of the charge being referred to here? Question about repeating decimal? For simple fraction, we can easily convert it to repeating decimal by calculator. Ex. $\frac 1 3 = 0.33333\ldots$, $\frac 1 7=0.(142857),\ldots$ But some fraction fraction like $10/29, 1/97,...$ The repeating part of them are too long, so it can't fully show on the calculator. So is there any algorithm  to find the repeating part for that fraction? SQL Server 2012 Page Life Expectancy resets to 0 after about 50 days I've noticed an odd behavior on a 2-server HA cluster and I was hoping someone could confirm my suspicion, or maybe offer some other explanation... Here is my setup:   A 2-server SQL 2012 SP1 installation SQL AlwaysOn HA has been enabled for a few databases CPUs are 2.4GHz, 4 cores RAM is 34 GB (it is an AWS instance, hence the odd number) Resource utilization is relatively low - each server has 14+ GB memory free, and SQL is not capped on how much memory to use Disk access time is fine - rarely going over 15ms/Read or Write Databases are not big - 1 GB, 1.5 GB, 7.5 GB SQL server process is using 16 GB Private Bytes, 15 GB Working Set   Overall, no resource issues are noted. Now for the odd part. SQL is not restarted (process has been running for almost 6 months) but it seems that every ~50 days, the Page Life Expectancy counter drops to (almost) 0. Up until that point it climbs steadily, no drops. Here is a perf graph:    When I look at the counter data (I don't have the exact number, just an hourly aggregation) it seems the PLE counter value reached about 4,295,000 sec (roughly 50 days) every time (at least every time I have data for).   My crazy theory is that the PLE number is held as milliseconds as an unsigned long int (which has a limit of 4,294,967,295) and at 49.71 days it resets, either by design, or because of a bug. This would explain the behavior of the two servers and the identical pattern they have. Or it could be something totally different and I am just not making any sense. :)  Has anyone seen anything like that, or can explain this behavior?  P.S. I saw  post, but my case seems slightly different.  P.P.S. This is a repost - I originally posted it , but was advised the audience here is more appropriate.  Thanks! Why do some tests have a (nonzero) minimum score? C: pointer to struct in the struct definition How can I have a pointer to the next struct in the definition of this struct:  typedef struct A {   int a;   int b;   A*  next; } A;   this is how I first wrote it but it does not work. How do I tell Maven to use the latest version of a dependency? How can I refinance or get out of a car loan I am upside down on? I purchased a car a little over 1 year ago a 2012 Dodge Avenger and recently went to get it refinanced and found out that because I'm so upside down that I can't get it refinanced I still owe over 15,000 and the car is only worth about 8000. I'm so bothered by this a few days ago I received a pre-approval letter from capital one bank for 35,000 so how can I go about doing this if I trade the car in I will have to put down a substantial amount of money in order to get out of this car. Can I just get the other car and turn the other one in. What should I do How to set static IP address? , to correct a misspelled library enum in an answer. Since the edit was only one character, I also had to add a superfluous sentence to get over the character limit required to edit a post.  I've hit this problem before in other edits, always in code snippets. Since the edit limit exists to prevent trivial edits, and since there are many cases where one character code edits are not trivial (= to == etc), would it make sense to have a lower edit minimum inside code snippets? options for appearance of links in hyperref Black screen after installation of Ubuntu 18.04 I did a fresh complete install of Ubuntu 18.04 on my ASUS M32CD desktop.   Everything during install went fine. At the end it said it was complete complete, and would reboot. Popped the disc out. Rebooted itself back into bios so I changed it back from CD boot as primary to HD.  When it booted up for Ubuntu screen and then everything went black and can’t do anything now! Ugh. Help I am looking at collecting spatial information from a range of stakeholders to identify opportunities within a landscape.  However, the data that we are collecting are not presently mapped and so we wish to use an interactive method to get this information onto a map.  Which online websites/methods would people recommend for circulating to a non-technical audience to try and get them to map what they know?    Where the emphasis is on ease of use by the stakeholder. How to give an image or video a TV screen effect? I thought it would be interesting to create a .blend that filters any regular video or image with vintage television look.   Edit: Although this question initially arose from my desire to create a vintage look, it has since been pointed out in a comment that all displays use arrays of RGB emitters, so it's not really an issue of vintage or not. How vintage it will end up looking is probably more a matter of the shape, size, and density of the emitters.  Reference images:       Upon examining the structure of screens, the most common seems to be rows of vertical RGB bars:    Here is another type which I believe is common in computer displays - circular dots in a hexagonal grid:    I have been thinking about how to make a screen in Blender that takes its input from an image or image sequence and for each frame converts the RGB value for a pixel (or region) and uses that to illuminate the red green and blue phosphors in the correct ratios so that when viewed from a distance an image is distinguishable.  Do you think this will require python scripting? I made some initial attempts modeling an array of phosphors then using a Light Path node and a Separate RGB node in Cycles but I haven't gotten very far. I would love to hear what you all can suggest.  Thanks!