Can the wrong sync frequency really destroy a CRT monitor?

Question: I've read in various places that an incorrect signal of the wrong refresh rate can cause physical damage to a CRT monitor, but I've never found an adequate explanation of why this is so. Is this true? And if it is, how?
Comment: I am surprised no one mentioned the most famous example, the PET killer poke. http://www.6502.org/users/andre/petindex/poke/index.html
Answer: Horizontal deflection circuit is intended to make linearly increasing current in the deflection coil. At the end of ray scanning from left to right, the deflection coil should be re-magnetized in a short time by applying higher reverse voltage to it. Typical schematics for the circuit looks like this: http://repairfaq.cis.upenn.edu/sam/deflfaq.htm#dsbdc .
L2 is the deflection yoke and T2 is the flyback transformer, that is also usually used to get high voltage for the CRT anode.
During the linear ray moving, the switch is open and the constant voltage supply causes the current to raise linearly in both L2 and T2. When the switch closes, the magnetizing energy in the inductance of T2 with the help of the capacitor C1 makes a short resonant high voltage spike, that remagnetizes deflection coil L2 to the initial ray-to-the-left position.
At the too low horizontal frequency, the period the switch is open becomes too long, that causes the following:
 The flyback transformer T2, that is usually made of ferrite core with a little gap, may get saturated. Once its ferrite core is saturated, it virtually disappears from the circuit, thus greatly reducing the inductance of the T2 winding. As a result, in a very short time the current gets unboundly high and it could damage the switch or the power supply.
Even if T2 is not getting saturated, still the voltage spike during switch off time may get too much (as it is determined by the energy absorbed in the inductance of T2 during the switch on time), thus breaking down the switch, the capacitor C1 or the snubber diode.
A third option is to saturate the switch (usually an NPN transistor), which would lead to emitter-collector voltage rise and then to excessive heat dissipation at the switch.
This all could happen if the controlling circuit inside the monitor allows it to operate at the inappropriate frequencies. This might happen on older (and simpler) CRT monitors.
Comment: The circuit probably doesn't FEED the coil a current ramp. It feeds it constant voltage and has a current ramp developed through the inductance. That current can climb higher than tolerable if the ramp is allowed to build up too long, no core saturation needed...
Comment: @rackandboneman: It's possible that a drive transistor might saturate before the coil does, but in either case the collector voltage on Q1 would rise even though it's supposed to be "on".  I wonder how much cost is saved by not including a circuit to detect that and force a retrace?
Comment: @lvd: A follow-option to #3 is that the transistor may melt and fail shorted, resulting in coil saturation and burn-out.
Comment: Wow, thanks! Switch saturation is also an option! [improved the answer]
Comment: For the common switched power supplies used in all but (probably) very old CRT monitors,I don't think coil burnout is an option. Usually SPS have overcurrent/shortcircuit protection. If there is no such protection, output shortcircuiting leads to its own switch(es) burnout and then the fuse finally burns.
Answer: I've witnessed a monochrome monitor (actually, two of them) fried through software.
I worked with a friend who had a weak grasp of ethics.  He worked on an IBM PC/AT clone running DOS.  It had both a regular CGA card driving a color CRT, and a Hercules card driving a monochrome CRT.  I no longer recall why he had an extra monitor; I can only guess that it was a useful setup for debugging, since he could have the program's output shown on one screen, and debugging output shown on the other.
My friend had written a small TSR  (Terminate and Stay Resident) program that would, on demand, capture the contents of a text screen to memory, and then recall that screen using a hot key.  This was like the many so-called "boss key" programs available at the time, but instead of displaying a spreadsheet or some other generic work-like content, it displayed whatever had been previously captured, and the captured screen could be freely changed at any time by pressing a hot key.  You can see how this might be an advantage for a programmer, who doesn't generally use spreadsheets, and who wishes to sometimes not work while at work.
As I recall, when the "boss key" was pressed, the program needed to save the screen contents, which might be in a graphics mode, and replace them with the saved contents, which were in text mode.  I think (this was a long time ago) the program made the mode switch without the assistance of the BIOS, by directly hitting the CGA card's I/O ports.  I think those ports had the ability to control the monitor's scan rate, as evidenced by the destruction the TSR caused.
My friend found out the hard way that when the monochrome monitor attached to the Hercules card was in use, and the "boss key" TSR was triggered, it had a bug that could program the Hercules card with incorrect frequencies.  The evidence of this was:

Triggering the TSR by hitting its "boss key."
The monochrome monitor emitting a very loud, very high-pitched squeal
The monochrome monitor's display contracting to a point
The monitor ceasing its squeal with a "pop"
A puff of smelly magic smoke escaping the monitor
The monitor's permanent removal from the set of working monitors

My friend tried to debug this, but after he fried the second such monitor, he decided it was too expensive a problem to work on and just stopped using the TSR.
My friend and I worked very closely together, so I personally witnessed both of these monitors being fried.
My friend had a lousy grasp of ethics in his youth. We stay in touch, and I can now say with certainty that he would never consider doing such a thing, and is ashamed of having once done it.
Answer: Magnetic coils (the coils that magnetically deflect the electron beam in a CRT) have an electric resistance which is a direct function of the frequency of the current flow. If that resistance is getting too low (because the coils and circuitry are operated at a different frequency they are intended for), either the circuitry that regulates the current through the coil or the coil itself can be damaged.
Comment: Great answer, I had always wondered "what" got damaged. This makes sense, it is the same principle as a induction heater.
Answer: I worked on a variety of CRT terminals and monitors (and converted the former to the latter), and never had one fry, with two exceptions: (1) IBM-PC monitors, and (2) Exact clones of IBM-PC monitors.  Everything else maybe made strange noises, but were never damaged.  So it was certainly possible to design horizontal scan circuits that didn't burn out their drive transistor when given improper signals, and most were like that.  Lots more fear, uncertainty and doubt than is really called for.  Still, this is my empirical data rather than any industry-wide truth.
Comment: Television receivers needed to be immune from damage caused by sync signals that were out of spec, since television sets would often receive signals of varying quality.  Monitors whose designs were derived from those of television sets would inherit such immunity.  If such immunity were not required, a slightly simpler design could be used, and in some cases was.
Comment: Agreed with @supercat; devices such as televisions that expect a potentially-noisy input apply an extra level of logic. There is a sync generator: it takes syncs spotted in the incoming signal as an input, and produces syncs as an output. It always produces them at a safe frequency, which will coincide with the input only if it's in the proper range. The curvy sine patterns you sometimes see when sync is bad are actually real-life simple harmonic motion because of the way that they attempt to track phase through adjustments in frequency (i.e. the derivative of phase).
Comment: @Tommy: Does a typical sync generator simply takes syncs as input and produce them as output?  My impression was that a television set's sync circuit effectively adds the sync input (which is limited to be within a certain voltage range) to a rising signal derived from the horizontal coil current, and triggers a sync when the sum gets high enough.  Even if there's no input, the horizontal coil current will eventually get high enough to trigger a sync by itself, and even if the input is at maximum it won't be able to trigger a sync until the coil current reaches a certain point.
Comment: @supercat possibly we're talking about different implementations; I was thinking specifically of flywheel synchronisation as described e.g. at http://machineryequipmentonline.com/video-equipment/television-receivers-crt-typethe-sync-separator/ : "The flywheel sync circuit maintains an average frequency of the sync pulses by monitoring and taking the average frequency of a number of incoming line pulses so that a random pulse will have very little effect on the frequency" etc.
Comment: @Tommy: An approach like you describe would probably work better at decoding dodgy signals than the approach I describe, at the expense of more circuitry.  From a "safety" perspective, though, I would think forcing a retrace when the deflection coil current starts to get too high and disabling retrace when it's too low would be better than hoping the flywheel oscillator's capture range is suitable.
Comment: It is likely that system-specific monitors did away with some protection circuits under the assumption that they are only to be connected to a system that WON'T feed them wrong signals, and that protection circuits  which aren't needed will more likely become a potential failure point than help.
Comment: The "sweep" circuits from the vacuum tube era were mostly free-running oscillators, which then had a "sync" circuit added on. This is pretty much what @supercat suggested. They would free-run but would use sync pulses when available to "influence" the point where the retrace would happen.  Same circuit in cheap oscilloscopes. You can get a feel for this if you find an analog TV--twist the vertical hold knob and at some point the picture "breaks loose" as the frequency set by that knob gets too far away from what the sync signal is suggesting. Modern ckts are "triggered"--a different design.
Answer: I fried the CRT of a friend of mine trying to setup the X11 a long time ago :(. Just a startx fried it.  That time I was using the Monkey Linux distribution.
Comment: This answers the "is this true?" but not the "how?". It's an answer, but not very useful. Do you think you could provide some details? Brand of screen, configuration of X (if you know it), what exactly "fried" is etc..
Comment: This is entirely plausible.  Before monitors got the ability to communicate their specifics (such as horiz. and vertical sync rate) to the graphics card, you had to configure them manually in the X11 configuration file.


Which types of throws can lift the heaviest weight (hip throws, shoulder throws, etc.)?

Question: I'm relatively new on the martial arts scene, but I've enjoyed learning judo, wrestling, pretty much anything involving grappling, in stand-up or on the ground. Being sort of small (5'9" and 145 lbs.) compared to the majority of 6' and up practitioners I've found in the gyms and dojos, it raises this question for me. I understand that some throws are easier if you are shorter than your opponent, but that's not quite what I'm asking. More so, I'm asking which throws or takedowns can move the heaviest opponent? So, if I tried all these throws and executed them properly, which technique could I use on the tallest, heaviest opponent?
Answer: Foot sweeps
Assuming that your objective is to put the opponent on the ground and not actually lift them, foot sweeps are the throw that will work for the greatest size disparity.
Foot sweeps work on the principle of attacking your opponent's foot at the instant they are changing weight on a foot, either lifting it up or placing it down. At this instant, there is weight over the foot, and removing the foot will cause the opponent to fall as they are unsupported. Timing the sweep for this instant is the critical element.
Slipping and falling on ice is the basic foot sweep situation. You take a step and expect to be supported but you are not because your foot is moving unexpectedly, and you fall. It does not matter how tall or massive you are; you can still slip on ice.
To throw someone with a foot sweep, you only need to generate enough force to make your opponent move their feet. This is easier than unbalancing or lifting your opponent to perform other throws, where their defense is to move their feet. The sweep itself does not require much force, but speed and timing.
Answer: Being the shorter party is an advantage when trying to preform hip throws because it's easier to get under your opponent center of mass, there are other specific throws who use the same principle but they don't all sit under one category. While it's true that foot swaps demand lass power and more timing then most throws a taller opponent will have a reach advantage over you allowing him to execute foot swaps of himself outside of your reach. If the opponent is also heavier than you timing and clean technique will compensate for your disadvantage
Answer: If the throw is executed by an experienced judoka, the weight would not be a problem. A smaller build judoka can throw a very heavy judoka using judo scientific principles: movement, balance, and leverage. Using the attackers aggression to your advantage, you should only feel the weight if you stop the throwing movement in the middle of the throw. If a throw is executed correctly, you wouldn't feel any weight, so if you are feeling the weight  when throwing uke, go back and look at your throwing technique. Rebuild your throw and practice, you will know when you have got it right.
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/87792/discussion-on-answer-by-parto-which-types-of-throws-can-lift-the-heaviest-weight).
Answer: I would say a self defense application would be to lock the person before the throw.  The real ippon seionage breaks the opponents arm and he flies over like a bird.  As you get older parlor tricks might not work on experienced bad guys.  This is the point of locking him up or disorienting the opponent first.  After that then you throw a much bigger guy.
Comment: This "the real ippon seoi nage breaks the opponent's arm" part used to be taught in Nage no kata with the throw being the result of uke *avoiding* his arm being broken, but this turned out to be a modern myth and is not taught by the Kodokan. Think about it: breaking the arm is more powerful and easier without throwing, and throwing when you broke the arm is much harder than you might think.
Comment: Ippon seoi-nage is not executed locking the arm, Uki's arm is rapped tight across Tori's chest going with the elbow joint NOT against it, Tori has there inner elbow joint tight under Uki's armpit.  Uki is rapped tight on Tori  under Uki's armpit and Uki's arm across Tori's chest so Uki's chest is tight on to Tori's back . The original Ippon seoi-nage was a self defence move in Jiu Jitsu from a over head blow not locking the arm. Check out the Kodokan Judo Kata Nage-no-Kata
Comment: If like can move that arm then the lock is not correct.  I emphasize control with the lock first and then the throw.  Uke has no choice but go over because he would already be on his tippy toes and unbalanced.  The position of ukes arm makes it that way.


What is the difference between passé simple et plus-que parfait?

Question: In French we find many tenses about the past. So when we have to use passé simple and when plus-que-parfait?
Answer: This is a common issue for learners of French. A thorough answer would need a book chapter. Here are some suggestions:

https://about-france.com/french/past-tenses.htm
https://www.lawlessfrench.com/grammar/verb-timeline/
https://www.cliffsnotes.com/study-guides/french/french-ii/french-ii-past-tenses/using-the-correct-form-of-the-past-tense

Judging from your profile I guess you are Greek. I suggest you look at:

http://brixfax.co/mf/grammaire/verbes/les-temps/
https://www.scribd.com/document/365720056/Χρόνοι-στα-γαλλικά

See also the different links inside the suggested web pages. Speaking very briefly you just need be able to recognize passé simple. It is not used orally (at least in colloquial French). Use passé composé instead.
Plus-que-parfait is like past perfect in English or Ypersyntelikos in Greek language. Hence a typical example would be

Quand je suis arrivé(e), il avait déjà mangé.

In this way plus-que-parfait expresses what is called "antériorité dans le passé".
http://revuescolaire.over-blog.com/2017/02/le-temps-ii-l-anteriorite/la-posteriorite.html
Another typical example:

Si j'avais su, j'y serais allé(e).

which can be translated in English as:

Had I known, I would have gone there.

See below for more examples and exercises:
https://www.francaisfacile.com/exercices/exercice-francais-2/exercice-francais-47893.php
Answer:
Passé simple = I did (je fis)
Plus que parfait = I had done (j'avais fait)
Passe composé = I have done (j'ai fait)
Imparfait = I was doing (je faisais)
Passé antérieur = I had done (j'eus fait)
Comment: And honestly - my English teacher told me when I was young that it was not 1:1 match - I still use this trick and it's working pretty fine since a while... hence I would advise to keep it simple as such
Comment: I am not who downvote but...I don't found that this correspondance makes sense in general. Passé simple and Passé antérieur are almost not used in spoken French. And even in written French, their usage (especially of the latter one) is limited nowadays. Kids become familiar with the Passé simple through fables, récits and the like. So for not an Anglophone, not French native speaker, passé composé renders both I have done as well done I did. Also bear in mind that the French tense will render also the continuous form of the English ones.


Is reciting darood/salawat in front of Prophet Muhammad's peace be upon him grave permissible?

Question: Is reciting daruood in front of Prophet Mohammed's peace be upon him grave or every Friday in the mosque permissible?
Answer: All Praise to Allah Subhanahu wa Taala and blessings of him be on Prophet Muhammad peace be upon him his family and companions

The Prophet (Sal Allaahu Alaiyhi wa Sallam) said:
"Send blessings upon me for your greeting will reach me no matter
  where you are." (Abu Dawood)

So no matter where ever you are as stated in above hadith,if in front of grave or masjid you could recite salawat and send blessings on Rasulullah salAllahu alayhi wasallam as it is very mustahab to do so.There is no prohibition mentioned anywhere that salawat could not be recited in front of his grave but a respectful manner should be followed.
"Undoubtedly, Allah and His Angels send blessings on the Prophet, O you who believe ! Send upon him blessings and salute him fully well in abundance" (Surah al-Ahzab,56).
"Whoever visits me after I die, it is as if he visited me when I was still alive…"(Al-Daaraqutni)

"..And if, when they wronged themselves, they had come to you, [O
  Muhammad], and asked forgiveness of Allah and the Messenger had asked
  forgiveness for them, they would have found Allah Accepting of
  repentance and Merciful.(Quran 4:64)

Under this verse some mufassir have mentioned this incident that Imam Ali Radi Allahu anhu said: "Three days after burying the Prophet (Peace Be Upon Him) The Araabi did come and did throw himself on the grave of the Prophet (Peace Be Upon Him), he took the earth and threw it on his head. He said: "Ya Rasulallah! Peace Be Upon Him You did speak and we did hear, you learned from Allah and we did learn from you. Between those things which Allah did send you, is following: (4:64) I am the one, which is a sinner and now I did came to you, so that you may ask for me." After that a call from the grave did came: "Theres no doubt, you are forgiven!" [Tafsir al-Qurtubi]
Sending salawat on fridays are highly recommended and virtuous
It was narrated from Abu Darda' that the Messenger of Allah (ﷺ) said:

"Send a great deal of blessing upon me on Fridays, for it is witnessed
  by the angels. No one sends blessing upon me but his blessing will be
  presented to me, until he finishes them." A man said: "Even after
  death?" He said: "Even after death, for Allah has forbidden the earth
  to consume the bodies of the Prophets, so the Prophet of Allah is
  alive and receives provision.'"(Ibn majah)

It was narrated that Ibn 'Abbas said:
"The Messenger of Allah (ﷺ) said: 'Whoever forgets to send peace and blessings upon me, then he has missed the road to Paradise.'"(ibn majah)
Allah Swt and His Messenger knows best.
Comment: Does your answer by any chance represent the official view of a certain madhhab? Or which madhhab(s) does it conform to?
Comment: This is the view of all the Madhahib of true Ahlus Sunnah waljamah.
Comment: I say that back because the hadiths you quoted offer testimony to the permissibly of Tawassul to passed saints, a practice that Wahhabi school denounces as shirk.
Comment: All the four fiqhi madhahib were of the same aqeeda although holding some differences in fiqh but their aqeeda was all same they all believe in Tawassul and wahabism is something newly invented which is not related to it not following any specific fiqh and their aqaid are contrary to it.


How can I see why my Riak cluster is not running the compaction phase on the machines when I expect?

Question: I have a cluster of Riak (V1.2.0) machines, each with about 50Gb of hard disk space. We have the bitcask storage configure in the following way:
<code>%% Bitcask Config
{bitcask, [
         {data_root, "/var/lib/riak/bitcask"},
         {frag_merge_trigger, 40}, %% trigger merge if framentation is > 40% default is 60%
         {dead_bytes_merge_trigger, 67108864}, %% trigger if dead bytes for keys > 64MB default is 512MB
         {frag_threshold, 20}, %% framentation >= 20% default is 40
         {dead_bytes_threshold, 67108864} %% trigger if dead bytes for data > 64MB default is 128MB
       ]},
</code>
Our software has a pattern where the values are being rewritten frequently with the same keys. IE, the set of keys remain relatively stable while the values change at least once a day.
The pattern that we are seeing is that the available disk space shrinks each day until the other services on those machines stop operating because of out-of-space errors. Sometimes a restart on the box will reclaim some space.
Is there something wrong with my config? I'm not really sure how to set it up to reclaim the space 'automatically' enough that I don't run out of disk space within about a week.
How can I check?

When the compaction algorithm determines to run or not and what it decides based on what criteria?
How a compaction was actually run
How much space was reclaimed
Answer: Add one line to your bitcask configuration
<code>{log_needs_merge, true}
</code>
Whenever there is a merge, there will be an entry in the console.log file that shows which files met which triggers


Risk-free rate in the Sharpe ratio

Question: Let's say I have data stemming from date $t_1$ to date $t_2$, I have the annualized return each day during those two dates. Therefore I know the expected return and the standard deviation of the returns between those two dates. But what should I use as risk-free rate in the calculation of the Sharpe ratio:
$$ \frac{E(r)-r_f}{\sigma}$$
It seems like to be consistent, it would be natural to use the average 1-year risk-free rate from the Treasury yield curve during dates $t_1$ and $t_2$.
Answer: The formula wants to compare the (expected) return of a risky asset with the (known) return of a risk-free alternative. You need therefore to think of $r_f$ as the return of a risk-free asset.
The easiest way to know you're doing it right is to reconstruct this asset on a spreadsheet. To consider a typical case: if you have per annum risk-free rates posted daily, the cumulative value of an initial investment of \$1 would be
$$s_0 = 1, \quad \quad s_{t+1}= s_t \times (1+i_{t+1})^{1/252}$$
where $i_t$ is the interest rate on day $t$. The return on the risk-free asset then would simply be $r_f = s_{t_2 - t_1} -1$.

Risk-free rate in the Sharpe ratio


I read computer science, I don't have any certification yet, but I want experience

Question: Everybody in my school seems to be crazy about certification. A lot are not going for their internship, but rather certification. I'm doing my intership and I'm gaining lots of experience in the Engineering aspect. But I can't go for certification yet, I don't even know which one to go for. But is it difficult to get job after school without being certified?
Answer: In my experience, certifications are what you get when you don't have experience, because they show evidence to a base skill level. Once you've got a few years of experience, your certifications are less important than what you've accomplished and what skills you've got.
I should say that I've really only worked for small companies, where getting things done is more important than impressing HR. I don't particularly care about college degrees for administrators, either.
Comment: There are probably exceptions to this for the top tier of certificates (CCIE, RHCA and the like), but for almost all others certificates are a way to get a foot in the door if you lack actual experience.

See if you can get experience helping out with your local church/charity group/whatever doing admin stuff. Plenty of them have piles of computer stuff that doesn't get done because no one knows how, and the experience will be far more useful on your CV than any cert.
Answer: Certifications and/or Internships I think can help 'get you in the door' ( get invited for a phone or live interview ).  Which you choose is probably less important than how you use them.
If you choose to get certifications,  you want to do more than just learn how to pass the test.  Try to take each concept you learn for the certification one level deeper and learn how the concepts actually work on a lower level.  Also, try to set up some sort of lap with it.  You could also blog about it as a way of studying and building something else for your resume.  If you just do certifications, you might lack the experience to answer some questions in an interview that are about how you handled a social situation at work or applied your knowledge.
If  you choose the internship route, try to get the most out of it.  Really study the choices the company has made in their IT setup, code language choice, etc.. and why they made these choices.  Again you could blog about what you learn, just be careful you are not writing about anything the company would not want you to publish it.
If you can do both, do that.  Whatever you end up doing, you will need to demonstrate technical curiosity, intelligence, and good social skills in your interview. All the internships and certifications won't get you what you are after if you don't show that. The fact that you are concerned with which route to chose shows you are probably on the right track.
Answer: If you're getting a BS in a related field, you don't really need any certifications to get a decent job unless you have a very specific target that requires one.
Good grades, some interesting side projects, and a strong understanding of the fundamentals of your industry are generally sufficient.
Answer: There's no shortcut to being good at a job, it requires knowledge, smarts and experience, ideally in equal part, you need all three to be great.
Answer: My "in" with the IT industry was an internship position, so I'm probably a little biased as a result. In a "former life" (5+ years ago) when I "worked for the man" I was involved in hiring interviews for IT support positions. I always counted real-world experience as being more valuable than and type of certification or academic credential.
Having taught classes in a "Microsoft Certification" program at a community college for nearly 7 years, I've met and interacted with a goodly number of people who were trying to enter the IT field, either as their first career or as a mid-life career change. My sample is, no doubt, influenced by who bothered to keep in touch with me, but those people who appeared to have the most success getting into the field were those people who were willing / able to jump into low-end support jobs, prove their worth and build their experience, and then aggressively "market" themselves into higher-skilled positions. Some of them finished their various Microsoft certs (MCSA, MCSE, MCP), but many others ended up going on to jobs w/o the certification.
There are some environments where academic credentials and certifications are essential pre-requisites because of the political environment, not because of the skills that you acquire when obtaining them. I'll never have a job in academia because I have a two-year college degree. I can write code as a contractor all I want, but I'll never get a "software engineer" position with a large corporation without my B.S. in CompSci. I'm not likely to be an IT manager, CIO, or CTO of any sizeable corporate venture without my MBA or a Masters in MIS. I'm okay with that, 'cuz I enjoy what I'm doing now and it fulfills my financial needs.
Answer: Certification is most important to career advancement for those without degrees, or with degrees in other fields.
Experience trumps certification most times. I would rather hire someone who has done a job, or one like it, than someone who is certified but never done it outside the classroom.
Having taken a few certifications and specialized training before, during and after getting my degree, I know that educational examples tend to be limited in scope and idealized. They rarely take into account the full life-cycle issues and headaches.
The students to hire are, of course, ones who worked helpdesk & sysadmin positions at their school, and/or ones with internship experience.
Answer: if you can show an interviewer you can intelligently relay knowledge about a particular topic, no matter how you obtained it, you will be ok.  but being able to get in there and actually do the work is what will get you the job.  if its server work, set up virtual machines and get into the nitty-gritty stuff.  if its hardware, try to get to be friends with someone in the field and ask them to advise you on how to do things and what they have seen in their experience.  mentors help alot.
Answer: In my experience certification is less important in the IT world than other fields. Especially if you know unix / linux / open source systems. In that part of IT practically no-one has a certificate. People are judged based on their skills, not a piece of paper.


Lotus Notes & Domino RADIUS Integration

Question: Does anyone know if it's possible to have Lotus Notes & Domino do external authentication via RADIUS? Specifically to integrate a 2FA solution.
Answer: No, unless RADIUS can use IBM's Lightweight Third-Party Application (LTPA) tokens.
Here's are two workarounds. I should caveat that most them will only work for web applications (Domino and XPages), native Notes client (at least in the case of R6) support is limited to single sign on (by sync Notes ID password with AD) or SmartCards.
LDAP - If RADIUS can expose it's data as LDAP you can use Lotus Domino's Directory Assistance to set this up as a 3rd party directory.
AD as a bridge - If RADIUS can communicate with AD, then you can use AD to authenticate Domino sign ons.

Lotus Notes & Domino RADIUS Integration


What, if anything, do I do to repair notched floor joists?

Question: I have been building for a long time, so I know where floor joists can be bored or notched without compromising their strength.  Unfortunately, I have a client whose floor joists were hacked at by someone who didn't know the rules.  Her floor joists were notched by someone installing electrical cabling IN THE MIDDLE OF THE SPAN ON THE BOTTOM OF THE JOIST!!!!!! I know that I can reinforce the existing joists by sistering new joists to them, but I'm curious - is there any reason a carefully installed and glued patch wouldn't do the same trick?  It's been my experience that wood glue is stronger than the wood grain around the joint - at least as far as shear values are concerned.  But the end-grain to end-grain connection is where I worry that the glue would not hold up under tension.  Does anyone have an insight as to the efficacy of a patch?
Comment: put a short sister on it and drill a proper hole for the wires. No brainer
Comment: I think the question is obviously more like "I know one way to do it right, any advice on this other way?"  And I got some very helpful responses.  Your comment on the other hand is unproductive, and, frankly, insulting.
Comment: You continue to miss the point and continue to insult.  This is getting annoying.  Are you hazing me?
Comment: Wait... Is your question "*I know how to do it right, but how can I fix it the wrong way?*"?
Comment: @Paul If you know how to do it right, do it right. Shortcuts and hacks are not the way things should be done, especially by a professional.
Answer: Gluing a patch in place like as shown below will not add much to restoring the original strength of the joist.

If you were to attach a longer piece like shown in the second picture and glue this in place for the full length of the piece a whole lot more strength will be added to the joist.

Note that if the joist has started to sag down due to the inappropriately placed holes or notches you may want to try jacking the joist back into its original position before applying the glued on pieces.
The length of the piece that you would use is going to be dependent on an number of factors including the overall span if the joist and its top to bottom height. The material could be a variety of different things including 2x4, 2x2 or even strip of 3/4 inch plywood. You could also consider gluing on a strip on both sides of the joist. When gluing make sure to clamp the pieces to the side of the joist with good pressure to make sure the wood joints are tight.
Answer: For an end grain glue joint to properly hold, the joint would have to be some sort of long scarf joint, just sawing it off and end gluing isn't enough, end-grain pulls out and yes, the glue is stronger than the end grain. You're not going to gain much with the extra work and it's probably not approved for use in this location.
Along with what @shirlockhomes says in his comment, slap some wood glue on your repair piece and sister it to the joist. The wood glue will be a stronger joint than the nails.
Comment: some wood glue and a few screws to be sure.
Answer: You want the Simpson Catalog.  They make a variety of metal splices that are just what you need.  And for the next guy who comes along here's a pocket guide to the proper way to cut a beam: NICEIC Beam Notching Guide.  The American Wood Products Association has a similar guide.
Normally it's plumbers that do this nonsense, and Simpson has a brace just for that.


How do I remove polyurethane spray foam from my hands?

Question: I should have worn gloves but sadly I didn't. Now I have yellow stuff all over my hands. I got most of the stickiness to go away by using WD-40. Is there anything that will get this off without giving me chemical burns?
Comment: Great Stuff is a sneaky marketing name.  Anyone who has had it go somewhere they didn't desire can attest to that, as you can now.  Not only do you need gloves, you need somewhere to put the can where it can safely drip (or explode) between uses.
Comment: it will naturaly come off- your hands secrease an oil all the time. Even super glue will come off after a few day. Just keep on washing with laods of soap/ mechanics grit degrease / scrubbing(not to blead).. eventually it will come off.. next time wear gloves.
Comment: @BMitch: Yep :) I have used it before but this was a messy period. I just found Great Stuff wipes that works to clean up Great Stuff messes.
Comment: We had some high school volunteers on site that helped with caulking and insulating.  Someone had the bright idea to wipe off the excess Great Stuff on our newly painted wall.  They weren't invited back.  This was also the same group that thought that wearing a fuzzy black glove while wiping away excess caulk would keep their fingers from getting cold.  Doh.
Comment: Also [Gunk covered hand(s) avoidance](http://diy.stackexchange.com/q/2915/22)
Comment: I bought a box of latex gloves just so I would never have to relive my very first Great Stuff experience.
Comment: This stuff is chemically related to superglue (and even more closely related to the original Gorilla Glue formula). It should be handled with all the same precautions.
Comment: Put on disposable gloves before using Great Stuff.
Answer: Without looking, I think most of these adhesive foams dissolve with acetone. The first thing I'd try would be nail polish remover, or possibly Goof Off.
Comment: Polyurethane **DOES NOT** dissolve with acetone, ask me how I know....
Comment: I've tried using acetone to clean off Great Stuff, and it works before it dries. After the foam dried, acetone fails.
Comment: Natural skin oils working underneath it cause it to start releasing in a day or two. No need to poison yourself trying to get it off. Urethane glue is pretty nasty stuff, foam isn't the only thing out there that's as enduring once it hits your skin.
Comment: Finger nail polish used to be sented acetone, don't know if it still is but my wife and daughters have used it for years.
Answer: Once Great Stuff foam hardens, it can only be removed via abrasive means (such as sandpaper). Water causes it to harden. Before it hardens, it can be removed with acetone. Be careful with acetone because it toxic (You can find a copy of the acetone MSDS online for details on its safety).
Answer: Wash your hands with Olive Oil! My wife had Great Stuff all over her hands and it removed easily with Olive Oil and then a quick wash with Orange Go-Jo.
Comment: I tried olive oil right away (because I love olive oil), but it didn't get rid of that sticky feeling.  Just an FYI
Comment: Sticky feeling is easy (you're almost there): use mineral spirits, then soap and water, dry hands. Repeat. Shouldn't take more than two or three times.
Answer: had cured foam on my kitchen counter. tried many, many products and the ONLY thing that removed it ALL was "GOOF OFF" Professional Strength and a fine stiff bristle brush... nothing left!  Dow website claims that nothing will remove the cured polyurethane(?) of Great Stuff, but this did!
Comment: On a counter (as long as it's not corian) Goof off is a great idea.  I have not personally tried it with Polyurethane foam, I'm skeptical because I got it stuck on my hands once and just had to wait it out.  However if anything can do it, it's probably good off. o-m-p xylene the active ingredient is good at turning any organic compound to goo.  This includes your hands.  I would avoid this one for getting it off skin.
Answer: I tried paint thinner, acetone, alcohol, mechanics hand scrub, WD-40, Goo Gone, hand sanitizer, dish soap, course hand wipes, makeup remover, etc. the only thing that got most of mine off after it had cured was soaking in hot water until hands softened, and then scrubbed with a pumice stone. It got most of it off!
Answer: Use 150 grit sand paper.
Wait till your hands are dry and sand it off. You'll go through a whole pack because skin wears down paper. It will not only remove Great Stuff but also the stains it leaves.
Comment: You sand all the way down to the **skin**?
Comment: Anything that is hard will sand nicely away from the skin. The sand-paper will not bite the skin as much because of its softness. Decades ago, women used sandpaper for hair removal.
Answer: I was wearing flimsy gloves and somehow ended up with it on my hands anyway. What worked for me was a bit of Windex (I used that on my floor when some fell there and nothing else would clean it off), then a soapy handwash in room temperature water followed by a blob (really rubbed in well into my fingers and hands) of my Anti-bacterial Deep Cleansing Hand Sanitizer from Bath & Body Works. It worked! My hands are dry as dust, but I got it off. I did all of this within 15 minutes of it happening so I don't know the results if it sets for a while.
Answer: I did the same thing I do in the wintertime to relieve my dry skin.  I slathered petroleum jelly (or Albolene facial makeup remover) on my hands and then put on white cotton gloves.  I left them on for several hours (or you could sleep in them).  The Great Stuff's stickiness was gone.
Answer: Olive oil works nicely to remove it.
Answer: Olive, pecan or other cooking oil followed with an orange based cleaner/degreaser and the scrubbing side of a dish sponge worked for me. Remember to wear gloves.
Answer: This is a harsh product but it works better than most: Lacquer thinner.  You can find it at Home Depot, Lowe's, etc. Use in a well ventilated area as this is highly flammable.
Answer: Yes, I knew better and it happened to me. If it has not cured WD-40 will work, which is what caused the problem for me. I got some on my hands took it off with WD-40, which gave me confidence I could get it off.
After it cures nothing works. It is no miracle, but it does speed the process up. If it is only a little, it will work well. Lotion, Lotion, Lotion, so much lotion your hands turn to prunes, like I said it is no miracle, but does speed it up.
Answer: After my mother picked pieces of her skin off, used olive oil method with commercial degresser, and acetone, hand sanitizer (bath and body works Stress relief!), rubbing alcohol, gasoline, and plain soap and water. She accidently came upon orange glo furniture 2 in 1 polish.....it took it off. Like a miracle, still have to pick up goof off but did well.
Answer: After foam has dried on hands, hydrate hands in warm to hot water for approximately three to five minutes (simpler done while bathing in tub) use a cheap (dollar store) disposal razor
and of course carefully shave (soap not necessary) the foam off--take note this is done by way of feel as in shaving one's face.
Answer: Old question I know, but I use the Great Stuff Pro commercial foam gun that takes the inverted cartridge cans. They sell a cleaner for the guns that you mount on the gun just like the foam and spray the cleaner through until it runs clear. The cleaner also comes with a spray cap that you can spray down the outside of the gun. Well.....this stuff literally melts the foam away. It is amazing, and works on hands or anything else. Yes, it is a harsh chemical, but just wash your hands immediately after and put on some lotion. I've done this many times and never had even the slightest bad reaction.
https://www.amazon.com/GREAT-STUFF-Dispensing-Cleaner-12oz/dp/B0002YWRG4
Comment: The [MSDS](http://www.homedepot.com/catalog/pdfImages/b3/b3f1ee33-f178-4ad9-81b0-f2b29df29451.pdf) says it's just acetone (and propane).
Answer: Naturally, like everybody else, I was not going to get any on my hands...but ended up with it on my fingers and palms on both hands.  I tried various solvents to no avail.  I was taking a shower, and I saw this gizmo (looks like a cheese grater) that I think my wife uses on corns and calluses on her feet.  I lathered up and started scraping it off.  Most of it was removed and no one would notice that I was an idiot.
Comment: Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably [take our tour](//diy.stackexchange.com/tour) so you'll know how best to contribute here.
Answer: A lot of mechanics use Orange-based hand cleaners.  Home depot has one:

Link to Homedepot.com
Answer: It says "use gloves" on the can for a reason, as most of us has found out the hard way I think :)
Don't use this on your hands, but I've had luck getting it off a linoleum/vinyl kitchen floor by using tile grout remover (a paste that comes in a tube) and a stiff plastic brush.
Answer: Unfortunately I am the type of personality that cant seem to remember that if you don't put the toilet seat up you'll probably get P on the toilet seat. Point being I have gotten the stuff on my skin, sometimes in copious amounts,probably 15 times in my life. Nothing has worked well except for the last few times: semi course  sandpaper and  soap and water worked surprisingly better compared to solvents. Your probably filling in drywall so you probably have sandpaper around. Note: when you begin to sand your skin, you're done! you have gotten most of it off.
Answer: I removed the dry great stuff by applying lots of hand soap and a wet Scotch Green Pad. Might have to rinse your hands and reapply soap few times. I tried different solvents M.E.K. acetone and others, Last 10 years I used noting but Green Pad and soap.
Answer: Get a stanley knife,,,,,,, i know this sounds dumb but hear me out!!!  When the glue, foam, anything polyuretane will harden.... so if and ONLY if it has dried then scrape it off with a stanley knife... at about 45° angle and it will start cracking off like when you scrape paint off metal.. keep going as desired but NEVER USE JUST A BLADE........ YOU WILL SERIOUSLY INJURE YOURSELF
Answer: When I first tried to get it off, I tried dawn and water but it didn't help...so I used a kleenex to stick to my skin so it would at least stop being sticky....after about 30 minutes, it was easy to peel off the parts with the tissue- like a thick bandaid.
However, the tissue didnt stick to ALL the gunk, so as advised on this site, I used 100% pure Olive oil directly on a green scrubby coarse dish scrubby thingie, and, although it took time and lots of scrub scrubbing, it took off most of the great stuff residue gunk and all of the icky sticky feel the great stuff left behind.  Finally, i used a hefty helping of Dawn to get the oil off.
Best part? My skin was never rubbed raw or red!  There is still a bit of residue left on my hands, and my hands are super dry, but lotion will fix that right up!
Conclusion:  1st, use kleenex so it sticks to the sticky parts and it will create a bandaid like substance that is easy to peel off in 30 minutes.  2nd, wait those 30 minutes, and then have fun peeling the kleenex parts off while reminiscing about middle school.  3rd, use 100% olive oil on a scrubby pad and scrub scrub scrub.  4th, use Dawn to wash off the oil.  Finally, apply your go to hand lotion until your hands feel moisturized and renewed!
Answer: I managed to get alot of great stuff on my hands. This is what works with out chemicals. First,  it was fully cured on my hands, dried with I minutes. I soaked and scrubbed hands in warm soapy water using regular hand soap. Got some of it off but it was on thick. Ran to store bought a pumice stone, two sided, course AND medium. Went home, soaked hands again and started to use pumice stone. Got some more off. Let hands dry a few minutes,  repeating process several times and almost completely removed great stuff from hand and fingers. Moisturize after or hands will dry up.
Answer: Lotion.
Like 6 pumps of lotion in my hands. Rub them together,  let it sit for an hour or so, take a shower, and it'll peel right off.
Answer: I found out the hard way. Had it over both hands; wd40 and other products didn't work. I use a Plastic blade and some home made soap to get it off. It took two days but I removed it. Will use gloves if I touch it again.
Comment: Hello, and welcome to Home Improvement. I've edited your post to make it clearer. Please [take our tour](//diy.stackexchange.com/tour) so you'll know how better to contribute here.
Answer: Get it off best you can right away . They wait 24 hrs and with cold water and a sturdy rag scrub it off . Worked for me
Comment: Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably [take our tour](//diy.stackexchange.com/tour) so you'll know how best to contribute here.
Answer: I tried most of the suggested solutions and just made my hands hurts. Decided to just let it wear off.  Took a shower and afterward used some leave-in hair conditioner and VOILA! it loosened the spray foam on my hands when I squeezed some out of the bottle to put on my hair.  Softened it and I was able to peel it right off.  Terrific.  Try it!
Answer: I tried everything on here and finally got out my orbital sander with some fine sandpaper and went at it. It took a while but it took all the stuff off. As long as you keep moving your fingers around there are no burns or cuts.
Comment: Hello, and welcome to Stack Exchange. Sounds a bit risky...


How hydrogen molecule is formed?

Question: How two hydrogen atoms come close to form a bond ? Textbooks refer to a potential energy diagram but what i cant understand is what is this potential energy if the atoms are neutral . How they come close and how when they come close they stay in an specific distance (bond length) ? From classical physics in order to not accelarate NET FORCE must be equal 0 ? is the same with hydrogen bonding and bonding in general ? also if potential energy decreases then kinetic must increase, but where does that kinetic energy goes when a molecules is formed ?
Comment: Hydrogen bonds are not formed when two hydrogens attract: they are formed when certain hydrogens attract atoms in other molecules such as oxygen. Water being the archetypal example.
Comment: Well the atoms are not exactly neutral. There is a charge seperation between the proton and the electron in a H atom. So both repulsive and attractive forces exist. At a certain point, there is an equilibrium
Answer: The potential energy comes from the charge interaction between the negative electrons and the positive nuclei. In a simplistic way, the kinetic energy is a result of the motion of the electrons around the nuclei. The closer the electrons are to the nuclei, the lower the potential energy but the higher the kinetic energy.
From a one-electron quantum mechanical view ($\ce{H_2^+}$), the system is described by Schrodinger's equation $\hat{H}\psi = E\psi$, where $\psi$ is the wavefunction for the electron, $E$ is the energy of the electron, and $\hat{H}$ is an operator that relates the two. The Hamiltonian operator has two parts: $\hat{H}\psi = \hat{T}\psi + \hat{V}\psi = E\psi$. These two parts are attributed to kinetic energy $\hat{T} \propto \frac{d^2}{dx^2} + \frac{d^2}{dy^2} + \frac{d^2}{dz^2}$, and potential energy $\hat{V}$ described by Coulomb potential. In order to be well behaved, the curvature increases as the electron wavefunction is closer to the nucleus, and since the kinetic energy is proportional to curvature, the kinetic energy is higher. The Coulomb potential is smaller when closer to the nucleus. So the equilibrium wave-function is a balance between these two potentials.
This treatment is more complicated when you add a second electron since the potential energy also includes the repulsion between the two electrons. But the concept is the same and the resulting hydrogen molecule is the configuration of nuclei and electrons that minimizes total energy based on the opposing influences of $\hat{T}$ and $\hat{V}$.

How hydrogen molecule is formed?


Will Bitcoin remember unperformed transactions?

Question: Let's say I transfer 0.05 BTC from 1 input to 1 output and don't pay a fee. If there are 6 blocks per hour, this means that my input has to be 369 hours (about 15 days) old so no fee is required. Let's also assume that the input only is 1 hour old. Does this mean that it will never be confirmed or does it mean that the money will arrive after a little more than 15 days?
Comment: related: [Why is my transaction not getting confirmed and what can I do about it?](http://bitcoin.stackexchange.com/q/9046/5406)
Answer: First of all: there's no guarantee that it will be free after 15 days. Some miners used to have a policy that made spending old coins potentially free. But miners can change those policies and will likely go for highest fee first, as that earns them the most money. If the network is busy that means there will be hardly any free transactions going in.
Second: most nodes on the network keep transactions in the memory pool for a while. But again, the exactly policies can be different for every node. I think 3 days is a common setting. But when the network is busy, 0 fee transactions are more likely to be dropped from the mempool than paying transactions.
Third: once you've broadcast the transaction, theoretically anyone that ever saw that transaction could re-introduce it to the network at any time. Even weeks or months later. For example the receiver of such transaction might keep trying to get it through. So there's never really a guarantee to you that a transaction has "timed out". The only way to be sure is to make a new transaction spending the same coin to another address (and then include a fee).
Comment: "Some miners **used to have** a policy that made spending old coins potentially free." Isn't that the case any more? Isn't there that convention of having some space in a block reserved for high-priority transactions? Different question: I just read that the network just wouldn't propagate the transaction if the fee is too low. (Electrum doesn't even let you make a transaction with a too low fee. (I tried to figure this out experimentally.)) Would the initial nodes the transaction is sent to remember it for (probably) 3 days or what do you mean by that?


Bit Extention Rule in Calculators?

Question: I have read Sign Extention Rule in Binary Numbers. I am having a problem.When I  calculate Binary from Decimal from calculator(FX-992ES PLUS), it always appends 0's to the converted number. It is against the bit extension rule. Does it follow some other format or I am just misleading about it?
Comment: Could you give an example input/output pair, and explain how you think the rule is violated?
Comment: Please correct the tag, I could not find a relevant tag for it. Thanks
Answer: It all depends on how numbers are represented. In calculators, numbers are represented as an unsigned number + sign; the first part is itself composed of a mantissa and an exponent (look up "floating point"). When a decimal is converted to binary, the unsigned part is converted without sign extension, and the sign is just copied.
Sign extension happens when numbers are stored in two's complement (where the two is replaced by the actual base). This is usually not the case for floating point numbers. It also doesn't make sense, since this is an internal representation - you, the user, should not worry about it. When converting $-1$ from decimal to binary, there's no reason for you to get $-11111111$ or even $11111111$. You just get $-1$, even though it may internally be stored differently (which is not the case for floating-point calculators, as mentioned above).

Bit Extention Rule in Calculators?


Agile Testing with no Acceptance Criteria or Documentation to refer to

Question: I have been asked to test a new software application.  The project is run Agile.  In some cases I have no Acceptance Criteria and no documentation to refer to and I am being asked to write test cases for a User Story.
Is this even possible?  Has someone had to do this before and do you have any advice?
Thanks!!
Answer: This is sadly not uncommon especially with newer Agile teams. I would take the proactive approach and write the Acceptance Criteria and then have it reviewed with the Product Owner (or whoever wrote the User Story) and Devs. I recommend writing it in the Gherkin Given-When-Then format. The example given in the agile alliance website is like this:

Given my bank account is in credit, and I made no withdrawals recently,
When I attempt to withdraw an amount less than my card's limit,
Then the withdrawal should complete without errors or warnings

You can have multiple ACs for a User Story. And these ACs can easily be used as test cases.
At the very least, you should raise this issue in Sprint Retrospective - the team needs to come to agreement on what is an acceptable User Story, be it more description and/or acceptance criteria. And at the next Backlog Grooming and Sprint Planning meetings, be sure to call out any user story that is not ready.
Answer: User Stories provide good insight into how a product should behave.  While they seldom contain explicit testing criteria, there is often much implied that can be extracted from a user story which the test can develop into more formalized testing.
I like to break each user story down in three different passes:

First pass, identify functionality and features
Second pass, identify any limits imposed by a given environment, operating conditions, etc.  This can be things like performance/throughput, duration, security.
Third pass, identify:

Interfaces (other software, files,
databases, peripherals, etc.)
Inputs and outputs (records, messages,
files, reports, objects, etc.)
Configurations (System level,
application level, hardware, network, etc.)
Usage scenarios (normal
"happy path", error handling/recovery, backup, installation,etc.)

This may not be the perfect approach for every person or every project, but it is one approach that helps in developing a somewhat nebulous concept into a more concrete form.
Answer: Talk to the developers, product owners and stakeholders. Figure out what was build and what needs testing.
If you are being assigned to a new product I would try some of the Tour heuristics:

Feature tour: Move through the application and get familiar with all the controls and features you come across.
Complexity tour: Find the five most complex things about the application.
Claims tour: Find all the information in the product that tells you what the product does. Verify every claim
Configuration tour: Attempt to find all the ways you can change settings in the product in a way that the application retains those settings.
Persona tour: Imagine five users for the product and the information they would want from the product or the major features they would be interested in.

Research Exploratory testing and figure out ways to come up with new test ideas.


postfix - rules for relayhost

Question: I'm using postfix as my smarthost(relayhost) for an exchange cluster, it works great.  But we are working on setting up encrypted email for some of our customers, so I'm trying to take email from SOME domains and direct it to another smarthost, but everyone else, deliver as normal.
Basically I'm trying to do what the transports file does but based on the FROM address, not the TO address.  Any thoughts?
Answer: you are probably looking for sender_dependent_relayhost_maps

postfix - rules for relayhost


What is the attribute used to display the username for lightdm? Is it something I can change?

Question: Right now it looks like my username is being displayed based on the sn LDAP attribute. I'd prefer it to be displayName or gecos, is that something I can configure either via lightdm or ldap.conf?
Answer: I don't think that you can, at least not in lightdm. lightdm gets the user list from Gnome's accounts-service over dbus which I assume populates the list from ldap somehow. Perhaps there's a way to configure it in ldap.conf?


What is the benefit of increasing Amiga chip memory?

Question: For example, an Amiga 500+ has 1MiB of chip memory, but it can be expanded to 2MiB. What would be the advantage?
Answer: There's two possible routes this answer can take - the first is "what is the advantage in adding memory (that happens to be chip memory)" and the second is "what is the advantage in adding chip memory as opposed to other types of memory". I'll try to answer both!

How much memory you need depends on what programs you want to run. When it comes to games, the vast majority of games will require either 512KiB (which is the basic amount of memory shipped with the Amiga 500) or 1MiB (which is what you get if you add a 512KiB expansion card to an Amiga 500 - this was a very popular configuration of Amiga). Games developed for the AGA chipset can expect a minimum of 2MiB (as there is no AGA-based machine with less than that). It's very rare for a game to need anything other than this.
For productivity software there may be an advantage in adding more memory. Most software has the same requirements as games, but adding more memory means that you can do things like run multiple programs at once, have more documents open, use the RAM disk more, and so on. More advanced productivity software, such as video processing and 3D rendering, are more likely to have higher requirements than an unexpanded Amiga.

So, what about chip memory specifically? It's most commonly understood that the Amiga has two types of memory - chip memory and fast memory. The basic difference between these two types is:

Chip memory is the only type of memory that the custom chips can access. Therefore all data that the custom chips process must be stored in chip memory. This includes video and sound data. The CPU can access chip memory, but the custom chips are always given priority: the custom chips will lock the CPU out of chip memory if they need to access memory.
Fast memory is available exclusively for use by the CPU. The custom chips cannot lock the CPU out of fast memory, therefore the CPU is able to operate without being delayed if its instructions and data are in fast memory.

So, to answer your question, "what's the advantage in adding more chip memory" is that there is more space to store all types of data. Because it's accessible to the custom chips, it can mean that you can use more colours, or higher resolutions, or multiple screens, than perhaps you had access to before. The related question, "what's the advantage in adding more fast memory" is that although the memory cannot be used for video and sound data (exception: see below), it could cause programs to run faster since the CPU isn't being held back from accessing memory.
Therefore in the ideal world, you would have enough chip memory to hold all the graphics, sound and other custom chip data, and enough fast memory to hold all the instruction code and non-custom chip data. This means that the CPU is not unnecessarily accessing chip memory (which can slow down the CPU if it's locked out) and you have enough memory for everything you want to do.
I say "most commonly understood" because there is a complication that is often overlooked. Some Amiga models can have memory expansions installed that appears to be fast memory, but is actually on the same memory bus as the chip memory. This means that although the custom chips cannot access it, they will still lock the CPU out of it if they want to lock the chip memory. Since it's neither chip memory, nor does it have the speed advantage of fast memory, earned the nickname of slow memory. (It's also occasionally referred to as ranger memory but I don't know where this name came from.) This affected the Amiga 500 (not 500 Plus) with memory in the trapdoor slot. Possibly other configurations are also affected, but I'm not currently sure. Memory fitted to the side connector of an Amiga 500, or to a Zorro slot or CPU slot inside a big-box Amiga, is connected directly to the CPU bus and is true fast memory.

About that exception: it's not true to say that fast memory can't store video and sound data - it can, but it just can't be displayed. If my memory serves me correctly, the Rombo Vidi Amiga product was said to be able to play longer videos than other products as it kept video data in fast memory, and copied the needed frames to chip memory just before they were needed to be displayed.
Comment: To clarify, slow ram is allocated to the leftover addressing space where you could have chip RAM (all Amigas max at 2MB chip).  By default A500s come with a standard non-fat Agnes chip that can only utilize 512KB of chip RAM.  So a common configuration was 512KB of on-board chip RAM and a 512KB slow RAM trap door expansion.  If the Agnes chip was upgraded to a fat 1MB version, solder jumpers on the motherboard could be changed to make that 512KB into chip RAM.  To add fast RAM you need to get outside that reserved 2MB address space by using an expansion on the CPU bus (sidecar expansion).
Comment: Thanks @mnem. To clarify the clarification :-) all A500s *do* have a Fat Agnus chip - the "fat" refers to the physical packaging of the chip, which is a different shape and has more pins (and I think those extra pins were for the purpose of enabling slow memory). Later versions of Fat Agnus can access higher chip RAM - these were informally known as "Super Agnus" and similar, although as I understand it that was not an official name.
Comment: Ah, right you are.  I had forgotten about that.  I think the 1MB Agnus was usually referred to as the "Fatter" Agnus, and the 2MB the "Super".  Either way though, most A500s shipped with the 512KB version, although I do have a later revision 6A board that shipped with a 1MB Agnus on-board but with only 512KB of chip ram enabled by default.
Comment: Jack Tramiel said no one would ever need more than 640K of chip RAM....wait, no that was Bill Gates.  And it was conventional RAM. No, wait...none of that ever happened.  I forgot what I was saying..oh well....long live the Amiga!
Comment: Wasn't the Ranger also the name of a later Amiga branded product? Does that have something to do with the kind of memory also known as "slow memory"?
Comment: @Wilson yeah Ranger was the name of a chipset that was being designed as the successor for the original chipset, but which was apparently cancelled in favor of ECS due to cost.
Comment: Is there a way to check how much slow memory the Amiga sees ?
Answer: As a start, more memory.
Benefits of having more of those programs that only reside in chipmem.
You can have higher resolutions/colours and still not run out of mem (Indivision or other scandoubler / ECS/AGA chipset might be needed to get a productive result).
Comment: There are programs that reside in chipmem?
Answer: The more Chip RAM you have, the better. This is because it's the memory used by video and audio coprocessors. These access RAM without involving the CPU, on a completely separate bus that the CPU is not even (directly) connected to.
That means the coprocessors can access it quickly, which might increase the resolution, or colour depth, the number or size of the sprites, the sample frequency of the sound, or other things that the coprocessors can do by themselves.
This page will explain more.
Comment: "The more Chip RAM you have, the better", no, not really. It's _very_ likely that adding an extra MiB to an A500 already equipped with 1 MiB of chipmem will do _nothing at all_ unless you need to work with a very specific application. No games will for example use the extra memory, and you have to open up quite a few screens for 1 MiB to be a limitation. Unless you have a specific use case in mind, it will likely just sit unused. Then you have spent money on something that just wastes power.
Comment: @pipe If money and power consumption is a concern, then I guess an Amiga 500 is not the right platform for you...


How were the first American citizens granted citizenship?

Question: When the US declared itself independent in 1776, did it simply consider all people (of a certain demographic) already living in the US citizens? Or did these people have to apply to become citizens somehow? For example, did Benjamin Franklin become a US citizen as soon as the US began existing?
Comment: What has your research shown?  What sources have you checked?
Comment: The constitution was adopted by popular referendum in each state.  Citizens were citizens of the state first; when the ninth state joined the nation, citizens of  the state became American citizens (with the exception of Rhode Island; Rhode Island was forced to join the country, at which point RI citizens became American citizens.)
Comment: I didn't find anything when I searched, just irrelevant stuff about early immigration. My sources were the early google results, same as they would be for any sane person with a quick question to ask.
Answer: Citizenship definition did not appear in US Constitution until 1868 (XIV Amendment). So for Benjamin Franklin we have to look in previous founding document, Articles of Confederation:
*Article IV.
The better to secure and perpetuate mutual friendship and intercourse among the people of the different states in this union, the free inhabitants of each of these states, paupers, vagabonds and fugitives from justice excepted, shall be entitled to all privileges and immunities of free citizens in the several states*
Theoretically, this just passed US citizenship question to the states. In practice, free Negroes were never granted citizenship rights in southern states, and the 1857 Supreme Court Dred Scott decision denied US citizenship for all Negroes regardless of the state they inhabited.
Comment: @Alone Programmer I just provided relevant facts, and pointed to most notable violation of stated definition of citizenship. Correct if something is wrong, provide your answer if you have one. My concerns are irrelevant, and you pretty naive to assume you can read them. "Negroes" is the language was used at the time, as well as by Martin Luther King; you are free to use different.
Comment: Not sure I agree.  The Constitution was never submitted to that A o C, but was approved by popular referendum.  Of course I should make that argument in an answer not a comment......
Comment: I think this answer has nothing to do with the question cause it seems your main concern in your answer is that "black people", which I'm not sure why you called them Negroes!, are not US citizens technically.
Comment: @Mark C. Wallace This was kind of abbreviated answer; I just added reference to Constitution. Regardless how A o C was approved, it was defining document for new independent country.


Problems running Ubuntu from USB drive

Question: I just bought new computer hardware and I wanted to install Ubuntu fresh. I downloaded the latest 12.04 LTS .iso file and created a bootable USB stick (4 gb). I then selected 'install ubuntu' from the grub menu and proceeded to install Ubuntu onto a different 32 Gb flash drive. I partitioned the drive into 8 gb ext4 from /, 8 gb swap area, and the remainder on to ext4 /home. I did opt to select installing proprietary drivers. After what seemed like forever (probably 3-4 hrs but I fell asleep) the installation finally completed and I selected the 'restart now' button the next morning when I woke up. In the bios, I then switched to the 32 gb stick as my primary boot device and I don't get a grub menu upon startup, I get a single line error message like problem running operating system, but I can't remember the exact error message and I don't have access to the computer at the moment. I don't think the error message was "missing operating system" though. If I boot from the 4 gb flash drive I get the same thing as I got before before installing (I get a menu option to install ubuntu). What did I do wrong? Is booting from usb stick a bad idea? Why did it take so long to install? Mainly looking for a fix to the problem.
Answer: As for the install taking long, many USB sticks are simply one thing: slow. As for 8GB swap on USB, if that's ever used for anything it'll be even slower. It's better to have no swap at all if it's a slow USB media. Also ext4 (journaling in general) may be the wrong choice for USB, it requires extra write cycles (again, slow) and may considerably reduce the lifetime of the USB stick. I'd go with ext2 even if it means a wait time in case of fsck.
Installing on and booting from USB should work fine otherwise. Maybe Grub detected a wrong drive order; the device that's used for booting will usually be the first, i.e. what Grub sees as (hd0). In such a case you might have to install Grub manually (chroot after install, adapt the device.map, grub-install /dev/yourstick). But even so, Grub should at least show up and print an error message or something when you try to boot from the stick.
If the box has a CD drive, booting from CD might help avoid confusion regarding drive order for two USB sticks. Or any other way to get rid of the installation media stick before install (BootToRam or similar - sorry I'm not up to date if current install media offer such a feature).
Comment: I do not have a cd drive or hard drive for this computer. Also, so others are aware, the exact error I have is "error loading operating system". I am understanding that usb drive may not have been the best choice for installing on this computer, but I am going with a barebones approach for this setup and I may try reinstall again with advice above. I am using a mini itx with integrated AMD APU chip and barebones everything, so I was not planning on using a hardrive or a cd drive with this build. What about a usb 3.0 stick? would this be fast?
Answer: ,If I recall right this is a message you get trying to boot a 32bit *buntu on an UEFI computer.
You can either use a 64bit *buntu or switch to Legacy mode in BIOS from UEFI.
Comment: I did not download the 32 bit ubuntu. I downloaded the 64 bit version. The hardware is brand new, just bought last week, so i assume 64 bit will run just fine.

Problems running Ubuntu from USB drive


Doors lock from fob, then unlock themselves

Question: I have a 2002 S-Type Jaguar. When I hit the door lock button on the remote, they lock, then they all open back up in a few seconds. I can't keep them locked. What is causing this? Can anyone help me? I can hear it locking them all, then it beeps beeps and they unlock.
Comment: I wouldn't know the exact cause, but it would seem to me that the body control module thinks the doors should not be locked. Like a safety feature to ensure you don't lock yourself out of the car because you left the keys in the ignition.
Answer: I've had central locking refusing to stay locked with several cars when any of the door sensors (or boot lid sensor, or even engine cover sensor) thinks its door is open - whether it's actually the case, or the sensor has jammed for some reason. This hypothesis can be checked by setting the interior lighting to the setting where it lights upon open doors. In most cases, opening and closing the culprit door/lid would solve the issue.
Comment: I will try this, thanks for getting back to me, this is a great site! sincerely, capt.j
Comment: I'm facing this issue ATM. Toggling the lights upon open doors is not practical. Is there any other workaround for this?
Answer: I had this happen on my Nissan Altima when the mechanic left the key in the ignition while working on the car and reconnected the battery with the key in the ignition. This some how confused the car and it thought the key was still in the ignition even when it wasn't and was trying to keep me from locking myself out of the car. I disconnected the battery and let it sit for a while and then reconnected it. That seemed to reset things and it worked fine after that.
Answer: Try to move like two meters away from the car, it will lock.
When you are near the door, the module senses your keyfob and unlocks the door.
Comment: Yes it has worked by standing a couple of metres, well done you , I spent over an hour trying to find out what the problem was, and all I had to do was move away from my car .
Answer: If its happening all the time, then it wouldn't be the doors/trunk/hood just being open. There are a couple of scenarios.

key fob is damaged,  button gets stuck,  or battery going out.
sensor on the doors/trunk/hood is going bad, and its sending back an open signal (prevents you from locking keys in your car).
electric lock module in doors is going bad, connector loose, or wires getting crimped.

My Honda does the same thing,  but mine is the lock module in the front passenger door.


My computer is not reading my PNY SD 1GB memory card

Question: I use a Kodak EasyShare C160 digital camera, a PNY SD 1GB memory card, and a Dell Latitude E5500 computer. I have had my camera for over a year and have always been able to transfer my pictures to my computer. Now my computer does not recognize my memory card and I get a message from the EasyShare software that says "Cannot get device information", although my computer does recognize the pictures stored on my camera's internal memory. Is there any way to access the pictures on my memory card, or are they lost forever?
Comment: Have you tried using a different computer to read the card? That's the easiest thing to check.
Answer: Buy a USB card reader and use that. It is nice and convenient to use built-in SD card readers or CF-to-PCMCIA adapters on the computer but my experience is that there are some cards which the built-in readers cannot read. But the USB readers work fine.
If you are concerned that USB readers are too slow, that depends on the technology used in the USB reader. I have an old reader from 2000 that is indeed rather slow, but it works and I don't have to sit and stare at it while it copies. I also have a newer reader purchased in 2010 that is almost as fast as a built-in USB reader.
If this works, after you have made two copies of the photos from the card, reformat the card in the camera before using it again.
If this does not work, then you have a more serious problem but you may still be able to get the pictures by trying other computers or perhaps trying a different camera and using the camera's cable to link directly to the PC.
Answer: Can you view and take new pictures on the card using the camera? If so, This proves the card is good. Your pictures are not lost. It would then possibly be a software issue (Kodak, maybe re-install) or get a card reader and pull them off directly. I personally prefer to go direct to avoid using the bloated software the manufacturers typically put out. If your camera cannot take new pictures to and read from the card... your out of luck as they say. If the pictures are extremely valuable to you, you might be able to take it to a data recovery specialist shop but I doubt that will help.


Low  frequency snake repellant

Question: Hey guys I don't know if anyone here can help me, I have been contacted to create a sound that is going to chase snakes away, it isn't in the film industry, they want to be able to play it in a field to chase the snakes away, I have read that snakes pick up vibrations at a low frequency which would chase them away. I was just asking this question wondering if you guys has any ideas on how to create a sound like this?
Comment: How did your low frequency base and predator calls turn out? I have a similar requirement.
Answer: Perhaps some voice clips of Samuel L. Jackson with aircraft engine noise in the background?
Sorry, couldn't resist.
I'm not sure if they actually work, but there are lots of ultrasonic animal deterrent products (on the other end of the frequency spectrum). Google "ultrasonic snake repeller".
Comment: whahaha will definitely mix some of his dialogue over what ever i come up with
Comment: Haha, that totally put a smile on my face ;)
Comment: Ultrasonic pest repellers are [generally useless](http://www.straightdope.com/columns/read/403/do-ultrasonic-bug-repellers-work), and in the case of snakes almost certainly useless since snakes don't have ears in the first place. They can only feel vibrations through the ground, and ultrasound can't propagate that way.
Answer: I guess this is the kind of project, where practicality through trail n error rules.
I think u need to have a snake first to start playing it different types of sounds at different intervals of time. Best way to test this out would be , when the snake is in its nocturnal sleep. As you know, most of the poisonous snakes are nocturnal. Meaning their senses like hearing & smelling is at its wake state. So when the snake generally sleeps in the daylight, would be the best time to start your experiment.
I suppose u would take at least 2 months to derive to an result. Making charts of the LF waves your passing through to see the reaction in a snake . Frankly speaking . im not even sure if they repel from LF sounds. From my understanding its a break through if you will be able to find a LF wave which will can repel snakes. Try to make patterns of LF. Various patterns having constant amplitudes. I mentioned constant amplitude because, Ultrasonic waves which many mammals, animals, reptiles repel from are of constant amplitute. Constantly giving constant amplitude of one frequency can be quite irritating for any living being, im sure u agree with that.
So good luck, try using sub-sonic woofers. And try out loads of test patterns on tat sleeping snake!
Stephen J
Acoustic Research Engineer
Answer: Never heard of this personally, but it sounds like your talking about sounds way down in the frequency spectrum. Is your client aware of the size and number of sub-woofers they might have to lug around to pull this off (and the power needs of that kind of array)? Not to mention the need to test those sounds out in a controlled environment.
Answer: I've never heard about something like this, so I can't help you directly. But if you have never done anything like this, I can't see how your client can expect you to figure it out on your own. Try calling your local university and ask to speak with a biologist. Or ask your your client where thy got the idea from - whoever told them about it hopefully know more about it. Also, wherever you read about the low frequencies it should have a source you can track down and read for yourself. If you have a starting point, it shouldn't be impossible to get a hold of somebody who knows about it.
Answer: Perhaps looking at kookaburra recordings could provide some clues?
Comment: yes have come upon the idea that I should have a low frequency base and mix some calls of snake predators over it.
Answer: From what I could find on the net, they are actually afraid of the vibrations, which they perceive as a larger creature attacking them.
People use vibrating machines to keep the snakes away. So maybe you can experiment with low frequency square waves, or percussive sounds (Like a kick drum or a click) played in quick succession.
This is the first time I am hearing about this method. Usually I can just tell snakes off because I am an Indian, we're all Slytherins. (Is it racism if I do it to myself?)

Low  frequency snake repellant


Sharepoint Designer - Layout folder?

Question: I have been told to edit this file in Sharepoint Designer:
<code>/_layouts/KWizCom_WikiPlus/CreateNew.aspx
</code>
I found it in the Windows File Explorer at:
<code>\12\TEMPLATE\LAYOUTS\KWizCom_Wikiplus
</code>
I can't seem to find it in Sharepoint Designer?
Answer: The _layouts folder is protected by SharePoint Designer because changing the OOTB files in that directory puts SharePoint into an unsupported state. For more information, see here and here.
For custom or third party files under _layouts, if you try to open them directly with a URL (http://myserver/_layouts/KWizCom_Wikiplus/CreateNew.aspx), you will receive an error: Files in the _layouts folder are not available for editing. You can open them in SharePoint Designer with an UNC path rather than a URL (\\myserver\c$\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\TEMPLATE\LAYOUTS\KWizCom_Wikiplus\CreateNew.aspx), but at this point SharePoint Designer is not any different than Visual Studio or Notepad as you will probably only have Code View available since ~/ and virtual directory URLs will not be resolved.
I have not used Wiki Plus, but note that not only will this change affect all web applications and site collections on the server, but any changes you make will be wiped out if an updated version of Wiki Plus is deployed to the server.
Answer: This file is effectively present in every site at http::/{site url}/_layouts/KWizCom_WikiPlus/CreateNew.aspx.  To change it across all of them you would edit the file from the file system.
There are many reasons why editing the file on the file system may be a very bad idea.  At minimum you might save a copy of the original and the updated file. Better still, you could put any file you're editing this way under version control.

Sharepoint Designer - Layout folder?


Normalization of basis vectors with a continuous index?

Question: I have an infinite basis which associates with each point, $x$, on the $x$-axis, a basis vector $|x\rangle$ such that the matrix of $|x\rangle$ is full of zeroes and a one by the $x^{\mathrm{th}}$ element. The book on Quantum Mechanics by Shankar says that the inner product between a basis vector and itself is not one, why not? Why can't these basis vectors be normalized to one, only to the Dirac delta function?
Comment: Related http://physics.stackexchange.com/q/64869/2451 and links therein.
Answer: Any good basis should be complete. If the set of all $|x\rangle$ is complete, any other vector $|\psi\rangle$ in the Hilbert space of your system should be writeable as $|\psi\rangle=\sum_{x} |x\rangle\langle x|\psi\rangle$. This sum does not make sense for continuous variables $x$, hence the need to redefine the completeness relation with an integral (as Jan's answer demonstrates nicely). Once you employ integrals to define a meaningful completeness relation, then the relation $\langle x|y\rangle =\delta_{x,y}$ is not correct because it gives
\begin{equation}
|y\rangle=\int \mathrm{d}x |x\rangle\langle x|y\rangle=\int \mathrm{d}x |x\rangle\delta_{x,y}=0,
\end{equation}
which is inconsistent. The way out is to define $\langle x|y\rangle=\delta(x-y)$, which correctly gives
\begin{equation}
|y\rangle =\int \mathrm{d}x |x\rangle\langle x|y\rangle=\int \mathrm{d}x |x\rangle \delta(x-y)=|y\rangle.
\end{equation}
Now $\langle x|y\rangle=\delta(x-y)$ leads to $\langle x|x\rangle=\delta(0)$, that you may not like, but this is the best one can do.
Comment: how did you do the integral?
Comment: It is similar to $\int\mathrm{d}x \delta(x-y) f(x)=f(y)$
Answer: I) We interpret OP's question (v2) as follows:

Why not normalize
  $$\tag{1} \langle x_1 | x_2\rangle~=~\delta_{x_1,x_2}~:=~\left\{ \begin{array}{ccl}
1 & \text{for} & x_1= x_2, \\
0& \text{for} & x_1\neq x_2, \end{array} \right. $$
  via a continuous Kronecker delta function rather than a Dirac delta distribution
  $$\tag{2} \langle x_1 | x_2\rangle~=~\delta(x_1-x_2)~? $$

In a nutshell, the reason is that the rhs. of eq. (1) is equal to the zero function almost everywhere wrt. the Lebesgue measure.
In this answer we would like to build intuition via Gaussian wave packets to argue that we should use a Dirac delta distribution normalization (2) (possibly modulo a conventional normalization constant) rather than a continuous Kronecker delta function normalization (1).
II) To be concrete, let us for simplicity view a ket
$$\tag{3} |\psi\rangle \quad\longleftrightarrow\quad\psi(x)$$
as a position wave function $\psi(x)\in L^2(\mathbb{R})$ in the Hilbert space
$$\tag{4} L^2(\mathbb{R})~=~{\cal L}^2(\mathbb{R})/\sim,$$
where we have modded out by an equivalence relation "$\sim$". Here ${\cal L}^2(\mathbb{R})$ is the set of square integrable functions. Two functions $\phi\sim\psi$ are equivalent iff $\phi$ and $\psi$ are equal almost everywhere (a.e.) wrt. the Lebesgue measure. See e.g. this Phys.SE post. Overlaps/inner products read
$$\tag{5} \langle \phi|\psi\rangle ~:=~ \int_{\mathbb{R}} \! \mathrm{d}x ~\phi(x)^{\ast}~\psi(x). $$
III) Now pragmatically, short of mathematically constructs such as distributions, what would represent a state localized at $x=x_1$? Let us allow the wave packet to be spread by a tiny amount $\epsilon>0$, say smaller than any experimental resolution. We can model such a wave function by an extremely narrowly peaked Gaussian function
$$\tag{6} |x_1\rangle \quad\longleftrightarrow\quad \psi_{x_1}(x)~=~ A\epsilon^{-p} \exp\left[-\left(\frac{x-x_1}{2\epsilon}\right)^2\right], $$
where $p\in\mathbb{R}$ is some fixed power and $A>0$ is a normalization constant to be determined below. The
normalization of (6) is
$$\langle x_1|x_1\rangle ~\stackrel{(5)}{=}~ \int_{\mathbb{R}} \! \mathrm{d}x ~|\psi_{x_1}(x)|^2
~\stackrel{\text{Gauss. int.}}{=}~ \sqrt{2\pi}A^2\epsilon^{1-2p} $$
$$\tag{7}\longrightarrow ~\left\{ \begin{array}{ccl}
 0 & \text{if} & p<\frac{1}{2} \\
\sqrt{2\pi}A^2& \text{if} & p=\frac{1}{2} \\
\infty& \text{if} &p>\frac{1}{2}
\end{array} \right\} \text{  for  } \epsilon~\to~ 0^{+}.  $$
To avoid that the normalization (7) disappears in the limit $\epsilon\to 0^{+}$, we must demand that the power $p\geq \frac{1}{2}$. The Kronecker normalization (1) [modulo an overall constant] corresponds to the power $p=\frac{1}{2}$.
IV) More generally, if we assume the ansatz (6), then the overlap between two such kets $|x_1\rangle$ and $|x_2\rangle$ reads in a distributional sense
$$ \langle x_1|x_2\rangle~\stackrel{(5)}{=}~\int_{\mathbb{R}} \! \mathrm{d}x ~\psi_{x_1}(x)^{\ast}~\psi_{x_2}(x)
~\stackrel{(6)}{=}~A^2\int_{\mathbb{R}} \! \mathrm{d}x ~\epsilon^{-2p}~
\exp\left[-\left(\frac{x-x_1}{2\epsilon}\right)^2-\left(\frac{x-x_2}{2\epsilon}\right)^2\right] $$
$$~\stackrel{\text{Gauss. int.}}{=}~\sqrt{2\pi}A^2\epsilon^{1-2p}\exp\left[-\frac{1}{2}\left(\frac{x_1-x_2}{2\epsilon}\right)^2\right]$$
$$\tag{8}\longrightarrow ~\left\{ \begin{array}{ccl}
 0\text{ almost everywhere} & \text{if} & p<1 \\
4\pi A^2~\delta(x_1-x_2)& \text{if} & p=1 \\
\text{too singular}& \text{if} &p>1
\end{array} \right\} \text{  for  } \epsilon~\to~ 0^{+}.$$
In the last step we used the heat kernel representation of the Dirac distribution.
The Dirac normalization (2) [modulo an overall constant] corresponds to the power $p=1$. In detail, if $f(x_1-x_2)$ is a test function, then eq. (8) states that
$$ \tag{9}\int_{\mathbb{R}}\! \mathrm{d}x_1~ f(x_1-x_2)~
\langle x_1|x_2\rangle ~\longrightarrow ~\left\{ \begin{array}{ccl}
 0 & \text{if} & p<1 \\
4\pi A^2~ f(0)& \text{if} & p=1 \\
\infty & \text{if} &p>1
\end{array} \right\} \text{  for  } \epsilon~\to~ 0^{+}.$$
V) Physically, according to the Born rule, the integral (10) of the overlap
$$ \tag{10} \left| \int_{\mathbb{R}}\! \mathrm{d}x_1~
\langle x_1|x_2\rangle\right|^2 ~=~1 $$
is supposed to denote the tautological probability that a particle located at position $x_2$ belongs to the real axis $\mathbb{R}$ with probability 100%.
Comparing eqs. (9) and (10), we are naturally lead to choose the power $p=1$, and therefore the Dirac normalization (2). Note that the power $p=1$ means that the position state $|x_1\rangle$ fails to be normalizable, and in particular, it does not belong to the Hilbert space, cf. eq. (7).
VI) A more rigorous discussion of eqs. (2) and (10) can be given by introducing momentum eigenstates. It turns out that ultimately eq. (10) is problematic, cf. e.g. this Phys.SE post.
Answer:
Why cant these basis vectors be normalized to one, only to the delta function?

Because that would make those continuously indexed vectors unsuitable for the role of a "continuous basis" for normalizable functions. Here is the explanation. Suppose some function $\psi(\mathbf r)$ is expressed as the integral
$$
\psi(\mathbf r) = \int c(k) \phi_k(\mathbf r)\,dk,
$$
where the functions $\phi_k$, $\phi_{k'}$ are orthogonal for $k\neq k'$:
$$
\int \phi_k^*(\mathbf r) \phi_{k'}(\mathbf r)\,d^3\mathbf r = 0
$$
(at least in distributive sense).
The above expression of $\psi$ can be described as "linear combination of the basis functions $\phi_k(\mathbf r)$". If the function $\psi$ is to be used to calculate probability density according to the Born rule, we have to require
$$
\int \psi^*\psi\, d^3\mathbf r = 1.
$$
This leads to
$$
\int \int c^*(k)c(k') (\phi_k, \phi_{k'}) \,dkdk' = 1,~~~(*)
$$
where $(\phi_k, \phi_{k'})$ is a scalar product of two continuously-indexed functions:
$$
(\phi_k, \phi_{k'}) = \int \phi_k^*(\mathbf r) \phi_{k'}(\mathbf r)\,d^3\mathbf r.
$$
Imagine points of plane labeled by Cartesian coordinates $k,k'$. If we had $(\phi_k, \phi_{k'}) = \delta_{kk'}$ with ordinary Kronecker delta, the scalar product would be non-zero only on the diagonal $k=k'$ which has zero area, while all over the large area where $k\neq k'$ it would vanish. The integral in (*) would then vanish too and couldn't be equal to 1 as needed.
One way to make the integral in (*) have a non-zero value is to postulate that for the above orthogonal functions, $(\phi_k, \phi_{k'})$ is to be regarded as some singular distribution of the kind Dirac introduced - to bring substantial contributions from the diagonal $k=k'$ only.
In practice we choose functions $\phi_k(\mathbf r)$ such that they obey
$$
(\phi_k, \phi_{k'})= \delta(k-k').
$$
Then the integral in (*) is
$$
\int |c(k)|^2\,dk,
$$
which can be non-zero and equal to 1 for properly normalized function $c(k)$.
In the language of kets, the kets $|x\rangle, |y\rangle$ are meant to be such that they satisfy the relation
$$
\langle x|y\rangle = \delta(x-y),
$$
because only then the relation
$$
|\psi\rangle = \int |x\rangle \langle x|\psi\rangle \, dx,
$$
which is part of the motivation behind the formalism of kets, is valid and consistent with
$$
\langle \psi|\psi\rangle = 1.
$$
The expression
$$
\langle x|x\rangle
$$
is not a valid expression and usually is not used in manipulations with the bra-ket formalism; if we used the above relation, we would get $\delta(x-x)$, which could be regarded as either positive infinity or not a meaningful number at all (since $\delta$ is not an ordinary function and does not have ordinary number-valued function values.)
Comment: But then why is it that when we use non-continuous basis we have the relation  = 1 ?
Comment: @user35687 : Because, with a discrete basis, we have the relation $\langle n|m\rangle = \delta_{nm}$. This discrete version $\delta_{nm}$ of the delta function $\delta(x-y)$, may be seen as the identity matrix, that is $\delta_{nm}=1$ if $m=n$, $\delta_{nm}=0$ if $m \neq n$


get an attachment's media tags or check if it has a media tag?

Question: Is there a way i can get media_tags assigned to an attachment (by id)? And/or check if an attachment has a media_tag?
Not sure if i'm missing something but there seems to be very little support for doing this?
any help appreciated, Dc
Answer: Use the plugin Media Tags. It has lot of useful features, including bulk administration and roles management. It is translatable or translated too.


Merge [mac] and [osx], making [mac] a synonym of [osx]

Question: We have the mac tag without any wiki and 127 questions and the osx tag with a wiki and 367 questions (and the synonym apple). IMHO we don't need both tags (I don't see anybody discussing e.g. problems with TeXLive on Linux on Apple systems).
Proposal: Make mac a synoym of osx.
Comment: What about the change in name that's gonna happen from Sierra onwards? It should still be technically `OS 10`, but `Mac OS X` will be replaced by "macOS" to fit the naming scheme of other Apple devices and platforms.
Comment: @cfr Even if we had any OSnotX questions, would it mean we need to distinguish it by a separate tag that nobody's gonna use correctly?
Comment: But what about all our Apple II users? ;)
Comment: @AndrewCashner: Show me a TeX installation on an Apple ][. :-)
Comment: @yo' If we had any Mac OS questions then, yes, we'd need to distinguish them. At least, the case for doing so would be considerably stronger than that for distinguishing Mac OS X from other BSD questions or, even, from GNU/Linux questions since those systems are much more similar than Mac OS and Mac OS X. Whether people would use it correctly is another matter, but they would hardly be the only tags nobody uses correctly. However, if we don't have any such questions, the issue is irrelevant.
Comment: Are any of the existing questions about Mac OS as opposed to Mac OS X?
Comment: @cfr: I doubt that - they would be ancient. Mac OS 9.2.2 was released in 2002.
Comment: An awful lot of places were still using Mac OS years later, though, because lots of places had software which had not been ported or substituted for OS X. Possibly, however, those people were not using TeX or not having problems with it, if they were. (I would not be terribly surprised if people are still running it in certain cases, in fact.)
Comment: I once had a PowerPC mac that was running Linux ... kinda miss those days.  –--  But as a current osx on mac user I think the merger would make sense.
Comment: @jan I still have a PPC which dual boots Debian and OS X. I believe it can also emulate Mac OS for software purposes, but it can't boot Mac OS or run in Mac OS mode operating-system wise.
Comment: @JosephWright: Would the moderators please decide about this?
Answer: I've merged the tags here, leaving mac as the 'master' (as noted, MacOS X is being replaced by Apple by 'macOS').
Answer: To help people find tags with a few letters, I feel some interest in hyphenated tags. And to avoid tag recreation, would something like apple-mac-osx suit your needs?
Comment: Ummmm no. You've got tag synonyms for this; the fulltext tag selection recognizes the master tag itself and all its synonyms.