Confusion about Dirac notation in quantum mechanics
Understanding Dirac's notation
Why are Marketing Cloud timestamps not stored in the same timezone as Sales Cloud? How to cleanup deadlinks I was reading some answers about ruby and there are a lot of links to _why's sites.  and took all his sites with him.  Almost every introduction question about ruby will include at least one or two links to one of his sites. Examples:          With a bit more effort I could probably find more questions with a lot of deadlinks.  My suggestion for discussion was, what would be a good way to solve deadlinks in the answers/comments? Not every site _why created has resurfaced somewhere else, but some could be replaced by new links.  But I wanted the discussion to go beyond this specific problem of deadlinks in the ruby answers, an automatic solution would be to let the links be scanned in a batch and when found dead be replaced by a google cache or webarchive version of the page, and perhaps mark it so that the community can replace the link with an alternative? Why aren't these loops homotopic? Let $S^1 = \{z \in \mathbb{C} : |z| = 1\}$.  Take the loops $f,g : [0,1] \rightarrow S^1$, $f(t) = 1$, $g(t) = e^{2\pi it}$.  I know these represent different elements in $\pi_1(S^1, 1)$, but I don't see why $F(t,s) = e^{2\pi its}$ isn't a homotopy between $f$ and $g$. What can I do to increase passive HF RFID read range? I am working on a prototype, one function of which is to detect whether an object is "in range" by a few cm. Right now I'm just using an Arduino and a cheap  that operates at 13.56 MHz:    I've successfully gotten it to detect the tag, but only at a distance of about 3-4 cm when the tag is oriented parallel to the antenna.  According to my  , the HF band allows read ranges of between 10 cm and 1 m for passive tags, depending on factors like antenna size, tag size and orientation, and transceiver power.  I realize this inexpensive reader is not up to task as-is, but I'm interested in building something that achieves read ranges of 15-20 cm.  Some criteria:   No need to read multiple tags; only whether one tag is in range or not. No need to write to the tag. Cannot use an active tag.   I'm not experienced with RFID reader construction (yet) but am interested in knowing what I should pursue.  Here are some things I've considered:   Ditch the embedded antenna on the cheap RFID reader and construct my own, larger antenna. I'd need to see if the onboard  is up to the task of providing additional power. Look for a different IC around which to build a reader from scratch. Find a ready-made solution instead of trying to build one (more cost-effective?). Use something other than RFID for simple proximity detection.   I am experienced with microcontrollers and basic electronics, and have made audio and lighting projects, but this is a first with RFID. Since I don't need to read multiple tags, which RFID is suitable for, I've considered maybe some sort of magnet and hall-effect sensor, but the range does not seem adequate. I considered using an ultrasonic proximity detector, but the application calls for detecting the tagged object while ignoring untagged ones (ultrasonic would produce false positives on untagged objects). I've considered some sort of reflective surface placed on the object, and detecting reflected light, but the object orientation is not reliable enough to maintain alignment.  So, in a nutshell, What modifications can I make to my existing reader, or what alternate technology should I pursue to achieve 15-20 cm detection of a passively tagged object?  I plan on connecting whatever proximity detector is used to a microcontroller using SPI. Callback animation to begin only after ALL children have finished animating Given a fraction:  $$\frac{a}{b}$$  I now add a number $n$ to both numerator and denominator in the following fashion:  $$\frac{a+n}{b+n}$$  The basic property is that the second fraction is suppose to closer to $1$ than the first one. My question is how can we prove that?  What I have tried:  I know $\frac{n}{n} = 1$ so now adding numbers $a$ and $b$ to it would actually "move it away" from $1$. But I cannot understand why $\frac{a}{b}$ is actually farther away from $1$ than $\frac{a+n}{b+n}$.  Why is that? What does it mean to add a number to both the numerator and denominator? How to set the command prompt's color in Bash? How can I export object's field schema information to excel? How can I export the fields of an object from Salesforce into an Excel sheet? I'm only looking for the field schema information, not the objects records. Proof that there are infinitely many prime numbers starting with a given digit string To prove the following fact: given any sequence of digits in any base, eg 314159265358979323 base 10, there are infinitely many primes that start with these digits,eg when expressed in decimal they start with 314159265358979323. I think using a prime number theorem will be helpful . But I am still not getting a point of how to start the proof. I'm one of very few people at my company who does graphic work, and I do quite a lot of it. Headquarters doesn't quite get that graphics work requires different hardware than, for example, sales work, which is pretty much email/Excel/Powerpoint/web browser and that's it. So they give everybody the same low-end rental PCs to work on.  This was tolerable when we were all on XP.  Recently I got "upgraded" to a new computer, which happens every two years or so as leases expire. The catch: the new PC had the same Core 2 Duo processor that the previous one did, less RAM, it runs Windows 7 instead of XP, and all the Creative Suite applications have been upgraded from CS3 to CS5! I am the first in my office to get 7.  So now I am in a situation where I have the slowest machine in the office, yet I have to do the most demanding work. I got them to OK 2 more gigabytes of RAM, and I hoped that would solve the issues, but it just isn't helping that much at all. I actually have to reboot every day after lunch because the machine stops responding after wake if you leave it asleep for too long.  I am currently talking to Information Systems to see if I can get a capable machine, but it does not bode well for me. Can anyone share any performance optimizations for Win7 that I might be able to use?  Thank you very much in advance! SS Chapter number and chapter title in one line Permanently remove/disable Touch Keyboard in Windows 8 taskbar? Can I run the python interpreter without generating the compiled .pyc files? What's wrong now with fwupd? It was OK since May 1st, 2020 on newly installed Ubuntu 20.04 The following packages have been kept back:    fwupd  0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded. Agent Smith, in the first Matrix movie (The Matrix) talks about how the machines originally created a paradise setting and humans didn't accept it, so it went back and created a more realistic one that humans would accept.  The human bodies, as we've seen, are kept in tanks and the body is kept asleep.  But why did the Matrix need to provide any kind of simulation for the brain to experience?  Why couldn't it have just kept all humans in a medically induced coma?  Or performed something equivalent to a lobotomy on every human?  Why did the Matrix need to spend the resources to keep the humans in good mental shape? What is the point of isomorphism concept? Why doesn't "cd" work in a shell script? I just want to write a script which changes my directory.  I put the below commands in the file /home/alex/pathABC  #!/bin/sh cd /home/alex/Documents/A/B/C echo HelloWorld   I did   chmod +x pathABC   In the Terminal, while in /home/alex, I ran ./pathABC, but the output is just HelloWorld and the current directory is not changed.  So what is wrong? Does GTA V Online Network Merge Xbox 360 and PS3 players? Prove if $(a,p)=1$, then $\{a,2a,3a,...,pa\}$ is a complete residue system modulo $p$. let $p$ be a prime and let $a$ be an integer not divisible by $p$, that is $(a,p)=1$. Then $\{a,2a,3a,...,pa\}$ is a complete residue system modulo $p$.  Since $p\nmid a$, $p\nmid\{a,2a,3a,...,(p-1)a\}$ Since $p|p$, $p|\{pa\}$ which is exactly one element in the set and is therefore a complete residue system.   Wondering if this is an acceptable proof to this theorem. Modular arithmetic: division, fractions, solving linear congruences I want to ask a question about modular arithmetic. I know, that modular multiplicative inverse exists only if modulo and integer are relatively prime. I want to know, are there any ways of division in modular arithmetic, if modulo and integer aren't relatively prime? I tried to find info about that, but failed.