When should you give up top tower for Dragon?

Question: Here's a rather deep question for those of you who play a lot of ranked. Without teleport, I have no real way of reaching my team short of physically going there from top lane. My question is this:
I have no real way of pushing my opponent out of lane or pushing hard enough so as to pressure his tower. When should I simply leave lane and help my team get Dragon at the risk of losing my top tower, assuming that my presence is needed?
Clarification Edit: I'm talking about the tier 1 tower during the laning phase.
Comment: This is NOT a forum for opinions =) but yes, you can ask for more answers.
Comment: Come on guys. Any more answers? This question is a bit more open-ended than usual. I want to hear your opinions!
Answer: Purely speaking of dragon vs tower. The dragon is a better option.

The dragon gives more gold. (750 vs 975).
What you lose from the tower will be won back once you killed the enemy tower.
The enemy team wont be killing the dragon over the next 6 minutes, you will not have to defend that dragon.
You don't need to defend that tower either.

That said, dragon is not the top lane responsibility.
It's strongly situational. If you can save both, just save the tower first and then do dragon. If the enemy or minions are killing bot or mid tower, it's easy to defend it. You probably already have 3 people at the dragon, and now you simply gank bot or mid before you go back to dragon. Or dispatch 1 and do the dragon with just 2 people.
If we're speaking of the first 3 towers, those will fall eventually anyway, and are not worth that much post laning phase. If we're talking inhibitor towers or base tower, you MUST defend those before doing dragon.
At the very least, make sure you keep the dragon warded and keep the enemy team away from it. That is a good job for the jungler and the support. If i had to choose between killing a enemy tower, or preventing my enemy from killing the dragon, i would certainly save the dragon.
Getting dragon and keeping tower is of course the best option. The responsibility for killing the dragon lies at the bot laners early game. They should push or win there lane, and then kill dragon. If any jungler is around, the route around level 6 or 7 should be either gank bot->dragon or just call bot->dragon. If it's not possible to do the dragon at this point because of enemy aggression (and map control), keep the dragon warded and prevent the enemy team from taking it instead.
Answer: Meta has changed so I figured I should add something slightly different in here.
First dragon is always worth losing your t1 tower for.  The first dragon is a very nice strong buff for your entire team.  After this you have different scenarios coming up.
1)  You have a dragon but the enemy team does not:
This is the hardest scenario for me to figure out.  On one hand, you want to stop the enemy from getting that buff, on the hand you can deny the tower and potentially  put pressure on top.  If it's the first tower, I might lean on giving it up just because as the game goes on that bonus feels better and better with items.  If you can deny them every dragon it's pretty huge.
2)  The enemy team has a dragon but you do not:
This is a bit risky.  Only do this if your team is ahead otherwise or you know enemy laners won't be able to outnumber you.  If it's a completely even fight, they will have the better chance of winning since they have that first dragon buff and your team doesn't.
3)  You both have a dragon:
If you both have a dragon, you are better off going for the tower.  Consecutive dragon's are worth that much unless it's the 5th one.  By that point though I expect everyone's t1 towers to be down unless it's a 1 sided game.
Answer: I suppose if you had already taken one or two of the enemy towers, or your tower was weak to the point of dying in one or two minion waves regardless, or if the enemy had already taken several dragons ahead of your team; it would then be imperative that your team claim a dragon to close the gap and that your lane is already advanced to the point that the first initial turret is not essential. True, turrets do win games, but there's more that needs to be done. Once your first turret falls, you have more time to attack other areas of importance and helping your team win teamfights is always important.
Answer: The first and foremost question you should be answering is; Is your enemy top-laner in your lane? If he is still in your lane and not making any moves to recall or going bot himself then there is absolutely no reason that you should be going to dragon to help. Since if the enemy top-laner is still in your lane then at max your team is fighting at least a 4v4 at dragon, if its not a 4v4 in your favor then your team shouldn't have been actively team-fighting over it. If it is a 4v4 at Dragon then you need to do some thinking.
Note: All these are thought assuming its an even 4v4 at dragon.
State of the lane
- How farmed are you? If you are already winning your lane by a huge margin it should be worthy for you to go bot and help with Dragon in order to force a 5v4, taking out some of their really farm reliant champions in the process makes it even more worth it. Vice-versa if you're really underfarmed then you shouldn't be going to help an even fight bot since your contribution will be minimal and losing the top tower may nudge the advantage in their favor. Another question you should be seeing is where your creep wave is, if your creep wave is in such a position that you can freeze the lane closer to your tower and zone/make him lose exp, you're better off staying, vice-versa if he can freeze close to his tower then you're better off going and helping dragon and try to pick up a kill. Although you can still push the lane more into his tower.
Nature of the Dragon Fight
First thing you should be asking yourself/team-mates, is whether this dragon really necessary? The trade off between a dragon and tower in terms of gold is only 225 gold(+minions), which is not a lot. You need to keep that in mind. So why are you contesting this dragon? Is your team really behind? In which case it maybe be worth you going bot if you can hope to pick some kills of it. Or are you really ahead? In which case its definitely worth it for you to go ahead and secure it and pick some kills of a contest. Of course the kill component is really dependent on your enemy, their positioning plus the state of them, for eg its worth it if the enemy team is positioned badly and you can pick them off if you overwhelm them numerically.
Enemy Top-laner The most important part, does the enemy top-laner have teleport himself? If he does and its not on Cooldown then you shouldn't be even thinking, go bottom and help your team since the enemy top can teleport in and turn the fight in their favor.
Remember: Dragon is not certain, it can be stolen
Answer: If you were getting beaten in lane, then you want the laning phase to end quickly.  In that case, falling behind a tower, actually helps and gives you time to free farm to catch back up.  One of the best examples of this is Nasus, who loses the laning phase to 75% of solo top champs.  Giving up the tower is a way to make it dangerous for their top to challenge you as they become more susceptible to ganks, unless they are nidalee, udyr who can speed through Nasus wither.  But this really allows him to free farm his Q, so definitely getting dragon is better.  If you are winning your lane however, and you cannot just take their top tower whenever you want, you do not want to lose your tower.  This allows them to roam freely and invade your jungle, and ultimately control when the laning phase ends.
Answer: In your case it is better for you to leave and help if you have already have taken their tower.  Because eventually they will get your tower anyways.  Another time you should go and help is when you are totally dominating lane. This is because you can really turn the tides of a potential contested or stolen dragon. Also, if you dont have their tower, it wont be hard for you to take it.
If top lane is equal I dont leave unless my other lanes are losing hard. This is because if a fight does break out my team has an edge even though other lanes are losing.(assuming enemy top lane is pushing your tower)
In a perfect game, if you are top you should try to work your dragon attempt around your top play.  Most tops grab flash and teleport this makes dragon attempts exceptionally easy sometimes depending if the other top player goes flash teleport as well.  As a top player, before your team wants to dragon you should push the enemy turret super hard.  At this time you can either go back and run bot then teleport top, or teleport bot then shop then run back top.  If done right you can keep your own tower and everyone on your team gets 150 gold.  Plus their top most likely wont come down, therefore if a team fight occurs 5v4 normally wins.


How to Delete Instances based on Proximity in Geometry Nodes?

Question: How do I set up the nodes so that all of the overlapping instances are deleted?  Or to put it another way, how do I delete an instance based on its proximity to another object?
PROJECT FILE
Comment: Changing from Random to Poisson Disk on the Distribute Points on Faces node doesn't work?
Comment: I think that the system cannot determine the closeness of instances, try Realise Instance first
Comment: @LuizAntonio it works better but there are still overlapping geometries
Comment: @3pointedit I watched a tutorial where someone was able to do this using the Geometry Proximity node, but I can't remember which tut it was and I can't get that node to work in my favor. Hoping someone here can enlighten me ;)
Answer: First, if you're spawning random points to spawn spheres on them, just use Poisson Disk distribution and specify the minimum distance as the diameter (two radiuses) of the sphere:

If the instances were already given to you you could use an approach like here:
How to use random cylinders inside a cube with geometric nodes?
You would need to realize instances first, and then you could decide if you want to remove only one instance of two overlapping instances, or both (e.g. if you're animating soap bubbles that are supposed to pop and disappear when they touch each-other) – in the former case you would only remove an instance if the ray hits something with a lower index. In both cases, however, as I pointed in that answer, you run into a problem that more than 2 spheres can overlap - in such case you could just put the setup into a custom node and repeat it a few times – repeating 10 times would be probably very reliable.

However, if you are given points, on which to instance, then you shouldn't instance to then remove instances. Instead use something similar like my quadratic sort, that is, create a copy of all points for each point, to e.g. find for each point the nearest other point that has a higher index, and then remove all points where some point with distance < 2 radiuses was found.
Comment: Thank you for this. Poisson disc doesn't work because my objects are pill shaped and I want some of them to be closer together than the distance diameter allows. The cylinders solution would probably work for what I'm doing but it seems a bit convoluted.  I did see a tutorial around the time 3.1 was released where this guy was scattering noise generated rocks on a landscape, and using some kind of proximity node setup to delete overlapping rocks. I tried recreating it from memory but I can't figure it out.
Comment: @GlenCandle Hmm, you used spheres in the question, so I assumed that… For pills I actually see a solution: figure out where the 2 points defining a pill are (e.g. based on instance rotation and instance origin), then check proximity of those points to the realized geometry - if you find something closer than the "pill radius", you have an overlap. You need some safety margin to not detect "self" as overlap. Then for each original point you can sample those two "pill ends" points if any has a captured `overlap=True` attribute, if so, don't spawn a pill on that point.
Comment: Thanks @MarkusvonBroady, that is interesting and I will try it.  Apologies for the confusion, my "pill" shape is actually a candy product for a client, and my question was more or less a general 'how to deal with overlap' and not particularly 'how to deal with it in these shown icospheres.'  I totally get how confusing that is, and again I apologize and I really appreciate your help ;)


How to convert P7C file to pem file using PHP7.1?

Question: I am dealing with some certificate problems.
I want to convert a p7c file to pem file.
For the safety reason, the system has disable some php functions such as "system, exec" and so on.
But the openssl extension in php is not complete implementation, so I don't how to do it.
Can somebody help me? Thanks.
Comment: Maybe you could ask this question on [servervault](https://serverfault.com/)?
Answer: The P7C indicates a PKCS#7 witch is either a signed or encrypted container that can contain almost everything - think of a ZIP file.
PEM specifies how to format encrypted or authenticated data (for electronic mail). Distilled: The base64 representation of data.
To convert the P7C/PKCS#7 to PEM format just read the bytes and write them as base64.
If this is not what you intended to do, please rephrase you question and give us some more details...
If your intend was to read certificates encapsulated in the P7C have a look at PHP's openssl_pkcs7_read method


How does one resolve the conflict between Renaissance theory of Cadences and the contradictions against it in Bach Chorales?

Question: A level pupil.
Made the mistake of learning Renaissance cadence voicing way before starting A-level harmony course. There's a conflict of interest between the cadential progressions of the renaissance (Cantizans, Altizans, Tenorizans and Bassizans) and the chordal nature of Bach's Chorales eg. Tenorizans in the Soprano line; unresolved Cantizans dropping to the fifth in the alto line; inability to cross parts. This (in my admittedly less-than-humble opinion) makes the individual voice lines clunky, while to rectify the clunkiness leaves final chords on a thin open 3rd. Are there any ways of settling this issue without just sucking up to the system?
Comment: The conflict is resolved by recognizing that Bach wasn't writing renaissance music.  By the mid baroque it was standard practice to have the melody in the soprano instead of the tenor.  This wasn't Bach's innovation; it was the hand he was dealt.  Many other composers preferred to resolve the leading tone and omit the fifth from the final chord.  But what exactly is your question?  What needs settling?
Comment: Why would one need to resolve any such conflict? Nobody in their right mind would claim that Bach's compositions are a strict implementation of Renaissance rule sets—they aren't even a strict implementation of Baroque rule sets. The rules do not have the absoluteness of formal logic rules, and Bach puts out a pretty impressive ratio of musical omelettes in relation to the number and size of eggs he breaks.
Answer: Admittedly, the consequent downward jump of the cantizans into the fifth in Bach's final cadences bothers me too, because to me this sounds so unsatisfactory that it spoils (IMO) the cadence, and it is unpleasent to sing for the affected voice. Obviously, Bach thought otherwise, or, more precisely, considered a different aspect more important: full chords.
When writing polyphonic music, often a compromise is necessary between singability and chord completeness. In Renaissance music, which was primarily vocal, singability was the priority. At Bach's time, music already was primarily instrumental, and for an instrument, singability is not an issue. Not all baroque composers treated vocal parts like instruments (e.g. the music by Fux, Charpentier, or Mondonville has much more "singable" vocal parts), but apparently Bach had singers that could deal with his approach to vocal lines.
Another possible explanation especially for the evasion of the cantizans in Bach's cadences might be that Bach was a keyboard virtuoso. On the harpsichord or on the organ, voice leading is not such an issue in chord progressions because the individual parts are almost not distinguishable, and still today in figured bass accompaniment, it is often taught that only the outer parts must follow the rules of voice leading.
To "resolve" the issue: It is due to different priorities.
Comment: Are there examples where Bach does not resolve the leading-tone into the tonic, but jumps back to the dominant, for purely vocal pieces, i.e. without any instrument? For pieces with choir and instruments, it might be that one instrument is higher than the highest choir voice, and resolves to the tonic. Note: I am more troubled by the trumpet finishing the piece on the dominant, in one of the orchestral suites if I remember well.
Comment: @jean-armand-moroni That is a good point. There are not much a capella 4 part pieces by Bach, I only am aware of three: "Lobet den Herrn alle Heiden", the final fugue of "Singet dem Herrn", and part 9 ("Gute Nacht o Wesen") from "Jesu meine Freude". I have just superficially checked these pieces and could not find an example of a leading tone jumping to the fifth. Actually in these pieces, Bach prefers "correct" voice leading over full chords: there are many cadences which end with chords without the fifth, without the third, or even in unisono.
Comment: @Jean-ArmandMoroni nearly every one of  Bach's four-voice chorales is written in five parts (soprano, alto, tenor, bass, basso continuo, with the last two usually being entirely in unison).  The assignment of instrumental doubling is not indicated in the score but is determined by examining the parts.  Nonetheless, with only s handful of exceptions there is no independent instrumental part, much less one sounding in a different octave from the vocal part it's doubling.
Comment: @Jean-ArmandMoroni This is in contrast to festive concerted movements, where treble instruments often double the alto an octave higher, or, more usually, move fluidly between the alto and soprano.  Details of voice leading therefore differ considerably.  It seems that voice leading is held to the rules within the orchestra and within the chorus separately, but you can easily find forbidden parallels across the two groups. But the soprano is often cantizans at final cadences in such movements. One example where it is not is BWV 66.1.  There, tenor and viola have ^7^5, and nobody has ^7^1.
Comment: Just a general comment on Bach's vocal lines.  I've sung Bach in many choirs for many years, and when it comes to a conflict between singability and harmonic architecture, Bach always decides in favor of the architecture.  That's part of his genius, but at the cost of easy singability.  So ist es.
Comment: @ScottWallace indeed, and the artistry required to sing these less singable lines gracefully is one of the hallmarks of good singing.  You can also see this in some of Handel's arias: big leaps in the melody, where more comfortable intervals would be possible, that seem awkward but, when well sung, are sublime.
Comment: Apparently he also liked to play viola, though.  (I'm not sure what historical sources may be behind this rumor I've heard.)  Another context in which this ^7 ^5 move is often heard is late 19th and early 20th century men's chorus writing, at least in the US collegiate context.  But of course it's always in qn inner voice, so many people wouldn't even notice it.


I have been learning traditional characters but my professors don't accept it. What do I do?

Question: I am a 20-year-old guy studying Chinese Translation at college here in Turkey. Currently I am taking preparatory Chinese classes to pass to actual ones (just started).
I have been studying Chinese for quite some time, and I loved traditional characters so chose to start with the traditional set. I learned a lot of traditional characters, and now all my professors are from PRC and no matter what they don't accept traditional characters (I must write by hand). She told me with a kinda angry voice 寫現在的字. Others say they won't accept it either.
Obviously this will affect my grades etc. and I don't want to change it. What should I do ? I thought of learning both together, writing simplified to materials they use and writing traditional to my own individual studying materials. This preparatory classes will take 1 year, 3 exams, some little tests. If I can't pass the barage they set I must get HSK 4.
We will be learning 1500-1600 words. Here they see China as only PRC, meaning my university only has connections with mainland universities so I will be going there early on until I can finish it or do something else. What should I do?
Comment: 人在矮簷下,不得不低頭. Unless you switch to a Taiwan based Chinese class, you'll have to learn simplified characters in order to pass the test. And it is not a bad thing to know both
Comment: Even in Mainland China, knowing traditional  Chinese characters in addition of simplified characters is an advantage.  Know more is always better. I have three nieces in Canada. All have English as first language. One  of them can speak but cannot write Chinese, one cannot speak nor write Chinese.  Only the oldest one can speak and write Chinese.  And she is the one who has the highest paying job among them.
Comment: Agrees with Tang Ho and others, learning both Simplified helps with traditional and vice versa.  Simplified Chinese are more used in PRC and it's more..simplified, or user friendly in terms of faster writing, but traditional helps understanding the word itself and the story behind, which is highly recommended.  For your exam just go with simplified, don't let anyone stop you from learning more.
Comment: Your "professors" are of very low 素質. Maybe they can't even read 繁體. What embarrassing examples of human beings...unfortunately I'll have to vote to close, as this is off topic. Try a forum like Reddit (/r/chineselanguage), where personal experience topics often come up. As a final note, HSK accepts 繁體 answers, although (1) their tests are all in Simplified and (2) writing 繁體, if you're not familiar with 行書, may negatively affect your time constraints.
Comment: @Tang Ho, i would quote the verse "不經一番寒澈骨.焉得梅花撲鼻香" (^ o ^)
Comment: 寫現在的字 sounds like lack of knowledge, although called traditional, but it's still being used by some native Chinese speakers, like Taiwanese. There IS reason can disallow you to write traditional characters, but not this one.
Answer: Young man drop everything to follow his heart.
Others drop his personal to do his responsibility.
Few do both.
Comment: Man! This is deep!
Answer: .traditionally, against one's mentor / tutor, is severe wrongdoing in chinese culture.
.when you enrol in the course, there must be some documentations, read the fine print, what's the language requirement.
if it's written in black & white, that traditional chinese should be used / accepted; then ask your university,why they hire "unqualified" tutor for the course.
if you can't find anything mentioning "traditional chinese", change yourself :(

She told me with à kinda angry voice 寫現在的字

i doubt that your tutor understand traditional chinese. frankly, if you need to read books printed before 1949, traditional chinese is a must. otherwise, simplified chinese is widely used in "that area".
her angry attitude would be interpreted as "you're smarted than her, cause you can read literature of yores directly"
without knowledge of traditional chinese, how can one inherit the traditional culture, history? all of these are recorded in traditional chinese.
last, an chinese verse for encouragement:

不經一番寒澈骨.焉得梅花撲鼻香

roughly "without the continuous bone-chilling cold, there can be no fragrant plum blossom"
behave carefully :)


Do we only know statements when we think of them?

Question: I once asked whether we only believe statements when we think of them. Now I am asking a similar but different question, about knowledge rather than belief. Do we only know statements when we are actively thinking of them?
Comment: I think this has the seed of a good non-opinion question if you can provide a framework regarding what you consider knowledge to be. For instance, if you were to pose the question in a little more detail regarding the framework of [justified, true belief](https://en.wikipedia.org/wiki/Belief#Justified_true_belief). The problem with your problem is that you need to provide some clarity on what constitutes knowledge and maybe your metaphysics. Are you [eliminative materialist](https://en.wikipedia.org/wiki/Eliminative_materialism), id est?
Comment: Questions, including those that are closed, can be edited to bring them within guidelines. [Keeping questions on-topic](https://philosophy.stackexchange.com/help/on-topic) Additional clarification at [the meta site](https://philosophy.meta.stackexchange.com/).
Answer: It seems that in an orthodox sense or use of 'knowledge' it is not the case that we only know statements - know that specific statements are true - when and while we are thinking of them.
On an orthdox view:

there are numberless things
   that I know, such as that there are Maoris in New Zealand, or that Plato wrote
   the Phaedo, which at any given time lie unconsidered in my memory. I have the
   knowledge, but it lies dormant, though ready for use. At any time during the
   waking day it might be brought to mind, with understanding and assent, and
   then it is no longer dormant: what was there potentially is now actualised. (Justin Gosling, 'Mad, Drunk or Asleep?: Aristotle's Akratic',  Phronesis, Vol. 38, No. 1 (1993), pp. 98-104: 98.)

It might be better to say that we do not cease to know that S is p - know the truth of that statement - when and while the statement is not present to mind but rather that our knowledge of the truth of the statement on such occasions is dormant or latent.
If we reject this, we face a problem. To hold that we cease to know when we cease to think creates the following difficulty. Suppose I know at t1 that S is p - I know the truth of this statement. Suppose also that at t2 I am asleep and am not thinking of the statement. If we say that because I am not thinking of it, I do not know it - my knowledge has passed out of existence - then how are we to explain that on waking at t3 I again know that S is p, that I know the truth of this statement? If my knowledge has passed out of existence at t2 how can it pass back into existence at t3?
Put the point like this. At t3 my knowledge has come into existence ex nihilo. This is because (a) my knowledge at t1 is irrelevant to explain, and can certainly have no causal or other continuity with, my knowledge at t3 since my knowledge at t1 has no existence; and because (b) my knowledge cannot ex hypothesi derive from t2 since this was when and while I was not thinking of the relevant statement. Ex nihilo can be rejected only if we can introduce some knowledge-creating factor that supervenes at t3. But what could this be?
On these grounds I am reluctant to accept that we know statements - know that they are true - only when we think of them.


How to zoom finely in GIMP?

Question: Is there any tool for fine zoom in GIMP?
I mean not 125% or 100% , something in between.
Thanks.
Answer: Try holding in ctrl-key and scrolling up or down on the mouse-wheel. while doing this you can move your mouse-pointer in the desired area of the canvas you want to zoom in on,
another way to more finely do this is hold ctrl-key in and hold in the scroll-wheel and move your mouse up or down on the canvas. this is probably what you are trying to do.
Answer: You can enter your own zoom ratio in the zoom indicator:

This is also doable via View>Zoom>Other...
Otherwise, with a given window size, you can use

View>Zoom>Fill window (your image is zoomed until its edges reach the edges of the window)
View>Zoom>Zoom to selection (your image is zoomed until the edges of the selection reach the edges of the window)

You can also click on the top right corner of your window, the zoom is then adjusted as the window size changes (the displayed image remains the same relative to the window):
Comment: Is there any shortcut? (Like Ctrl + mouse mid-button)
Comment: @goetz Current version (2.10.34) also has a sort-of-fine zoom with Ctrl-Space-mouse drag.
Comment: AFAIK there is no function for small zoom increments., so nothing to assign to a key or mouse event.
Comment: The next version, Gimp 3, will have smooth zoom with `Ctrl + mouse wheel`. You can try the beta or [development version](https://www.gimp.org/downloads/devel/) from the official site.

How to zoom finely in GIMP?


Can I do bachelor's, master's and PhD at different universities?

Question: Is it possible that I do undergraduation and post graduation from a university and Ph.D from other university?
Comment: When you say "post graduation" do you mean a Masters degree? If so, yes. However, if you mean "can I do my postgraduate PhD studies at one university and get a PhD awarded by a different university" the answer is usually no.
Comment: Not only is this possible, I would argue that it is generally advisable.
Comment: yes it is possible
Comment: https://academia.stackexchange.com/questions/149157/the-downsides-of-doing-undergraduate-masters-phd-at-the-same-institution
Answer: Yes, you can study for different degrees at different universities.
Comment: So I have another question, in my country cosmology is not available to study.. So I want to do Ph.D in cosmology from a university like Princeton, Standford etc, .. May you please tell me how can I achieve it?
Comment: @SawayamJha There's no need to go to Princeton or Stanford to study cosmology. Those universities are extremely competitive and you can get just as good an education at somewhere less well-known. For example, I did my PhD at the University of Portsmouth in the UK. I would guess that the uni is not at all famous globally, but the [cosmology department](http://www.icg.port.ac.uk/) *is* very well regarded. You need to look beyond the "brand name" universities. Then, you need to study hard, maintain good grades, get some research experience and apply to lots of places.
Comment: @SawayamJha this comment box is not the place for a long explanation but if you want more cosmology-specific advice, you are welcome to contact me directly (you can find my email address online easily enough).
Comment: Thanks alot for your kind support. I am sending you an email.
Answer: In the US, at least, it is very common to study at two or three universities on the way to a doctorate. Two is more common than three. Many undergraduate institutions in US don't have graduate programs or have only limited offerings. Some universities encourage their undergraduates to move on to another university just to get a variety of experience.
Again, in the US, one normally moves from undergraduate to doctoral study immediately. A masters degree might be earned along the way, but isn't always necessary. In other parts of the world a masters may be required to apply for doctoral studies. But changing institutions after each major milestone is permitted and common, though not universal.
If a student has worked very hard in a subfield and has worked with most of the faculty in that specialty, then the ability to learn from others, with different ideas, can be a plus. It can also be a plus to keep contact with the professors as you move on.
Comment: So I have another question, in my country cosmology is not available to study.. So I want to do Ph.D in cosmology from a university like Princeton, Standford etc, .. May you please tell me how can I achieve it?
Comment: Do they offer Ph.D degree if we have good research experience and good Graduation score?
Comment: The only way is to apply to an appropriate program. But applying to only the very top few universities is unlikely to result in success. There is a lot of competition. make a wider search if you want to get in somewhere. And "cosmology" can either imply a subfield of philosophy or of physics. They are very different.
Comment: Subfield of Physics ofcourse.... Like Stephen Hawking..... So okay, I should broaden my university interest... So on what basis I will get scholarship for my Ph.D from any university?
Comment: Scholarships in US are pretty rare. TA positions are the usual means of funding with some RAs available also in some places. But a TA or RA comes with both tuition forgiveness and a living (if minimal) stipend.
Answer: Speaking from the perspective of an American, it is certainly possible to obtain a bachelors degree at one institution, a masters at another, and a phd at a third, with all degrees being in the same field (or not).  Changing institutions between undergraduate and graduate work is quite common in the US.  I would even go so far as to say that it is preferable to complete one's graduate work at an institution different from one's bachelors institution.

Many colleges in the US do not offer any graduate degrees, and many of those institutions offer only masters degrees and not doctorates.  For example, most small, private liberal arts colleges in the US don't have any kind of graduate programs, and one of the largest public university systems in the country (the California State University system) does not offer doctoral programs (or, at least, there are only a very small number of doctorates available through the CSU system).  A student who completes work at any of these kinds of institutions would be required to go somewhere else for a phd.

Doctoral programs are extremely specialized.  To embark on a doctorate is to devote 5–10 years of your life exploring a tiny niche of human knowledge (this is very nicely illustrated here).  You want to make sure that you and your intended program are a good fit.  Do your research interests align with the institution?  Is there some faculty with whom you can get along?  How's the climate? and so on.  While students might find a faculty member at their undergraduate institution who is both a good mentor and studying something of interest to the student, it is more likely that you will find a good match if you cast a wider net.  Thus it makes sense for most people to go somewhere else after finishing a bachelors (or masters).

Admissions and funding can also play a role.  Any given phd program is only going to have a limited number of slots.  If you are close with a particular faculty member who wants to be your advisor, that faculty may lobby the admissions committee on your behalf, but even this is no guarantee of admission.  And even if you are admitted, there is no guarantee that the department will be able to support you—it is very hard to go to an institution where you are not admitted, or cannot afford a roof and three squares.

From a pragmatic point of view, moving from one institution to another exposes the student to a larger number of instructors, mentors, and colleagues.  This broadens the social network of the student, and makes it more likely that they will be able to find work in the future.  Faculty can both help a student locate promising positions, and provide recommendations for that student.  Fellow students may be able to open doors in the long run (e.g. a buddy from your undergraduate institution might end up in a position to offer you a job several years later, or to collaborate on a project).  The more connections you have, the easier it is to find work and research collaborators.  Thus it is beneficial (in my opinion) for students to leave their undergraduate institutions in order to pursue graduate work.

Finally, many institutions are understandably reticent to accept their own students into doctoral programs (or to offer post-doc positions to their own doctoral graduates, or to offer tenure track positions to their own graduates).  One of the major goals of the academy is to broaden the scope of human knowledge.  To do this, it is important to communicate widely with other scholars from other places.  Forcing students out of the nest is a way of spreading institutional knowledge to other places, whereas offering positions to one's own graduates can seem a little incestuous.  It is hard to explore the fringes of knowledge from an echo chamber.

So, again, it is not only possible to attend different undergraduate and graduate institutions, it is quite common in the US, and even (I would argue) advisable to do so.

Can I do bachelor’s, master’s and PhD at different universities?


Payload Capacity definition

Question: Does the payload capacity of a rocket include the satellite and the adaptator or is it just the satellite ?
Answer: Payload is normal taken to mean amount of mass the rocket can lift in default form, so any one off adapters or supporting hardware will need to be subtracted from that number.
This can result in some ambiguity in useful lift, where some systems can provide more services like cooling or power to the lifted satellite, or reduce the vibration/G-loads and therefore needed supporting structure. allowing a customer to use more of the payload for the satellite itself.
It is also worth noting that payloads are normally to specific orbits, so comparison can only be done where both target orbits are known and the same.

Payload Capacity definition


Is there a way to force a reroll on a saving throw?

Question: Is there a way in D&D 5e to force a creature to reroll a saving throw they just succeeded on?
I know there are lots of ways to impose disadvantage or other penalties, but I'm specifically looking to make them reroll a successful saving throw. My DM is always very smart with what they do/don't use legendary resistances on and I'd love a way to get through them faster since we haven't actually gotten them to use all 3 ever.
Comment: @Axoren I think that would be better suited to an answer. It's going at solving the problem, even if it doesn't stick to the presumed solution of the question.
Comment: Problem. Legendary Resistance [doesn't work that way](https://rpg.stackexchange.com/questions/172713).
Comment: @StopBeingEvil At that DM's table, it does.
Comment: @Someone_Evil Well, it's deleted now, and I don't remember what I wrote exactly. If someone wants to give that as an answer, it's theirs.
Comment: A quick aside; the DM shouldn't know what spell they are using Legendary Resistance on, and if they are, they are metagaming. You only know the effects of a spell after it has been cast, and its effects have been generated. If the DM is forcing you to announce your spells, and only using Legendary Resistance on "good" spells, your DM is "cheating."
Answer: The first ability that comes to my mind is the Chronurgy Wizard's 2nd level feature Chronal Shift:

You can magically exert limited control over the flow of time around a creature. As a reaction, after you or a creature you can see within 30 feet of you makes an attack roll, an ability check, or a saving throw, you can force the creature to reroll. You make this decision after you see whether the roll succeeds or fails. The target must use the result of the second roll.
You can use this ability twice, and you regain any expended uses when you finish a long rest.

It's a wizard subclass you can find in the Explorer's Guide to Wildemount and it's basically is designed to do exactly what you want to do.
Apart from that... there's one effect of the spell Wish:

You undo a single recent event by forcing a reroll of any roll made within the last round (including your last turn). Reality reshapes itself to accommodate the new result. For example, a wish spell could undo an opponent's successful save, a foe's critical hit, or a friend's failed save. You can force the reroll to be made with advantage or disadvantage, and you can choose whether to use the reroll or the original roll.

But that's like using a sledgehammer for cracking a nut.
But if you want to use an Atom Bomb instead... find a Deck of many Things, don't die or get devoured by an extraplanar force, draw The Fates...

Reality's fabric unravels and spins anew, allowing you to avoid or erase one event as if it never happened. You can use the card's magic as soon as you draw the card or at any other time before you die.

Okay, that's a bit of a joke, because it doesn't enforces a reroll and you probably want to use The Fates to repair some of the damage dealt by the deck. But theoretically you could one-shot-kill any enemy just by telling them that they were never born. But that's pretty much the most powerful effect in the whole game... so wasting it to overcome legendary resistance is... well... not a good idea.
Comment: You might be referring to Wish (which is already answered above) but it's only in the last round. I doubt there's something even more powerful than Wish available anywhere.
Comment: "Sledge hammer cracking a nut" is a particularly apt description.
Comment: @Erik Yapp, it was Wish... Dang, the Chronurgist is pretty powerful.
Comment: The Divination Wizard's Portent feature might also apply, as you can replace the succesful roll with a failed one
Comment: True, but OP asked for forced rerolls on saving throws. Ok, I included *The Fates* but that was not meant entirely serious.
Apart from that: Yes, *Portent* is quite similar to *Chrono Shift*
Answer: Wish, with gusto!

You undo a single recent event by forcing a reroll of any roll made within the last round (including your last turn). Reality reshapes itself to accommodate the new result. For example, a wish spell could undo an opponent's successful save, a foe's critical hit, or a friend's failed save. You can force the reroll to be made with advantage or disadvantage, and you can choose whether to use the reroll or the original roll.

With wish, you can not only force an opponent to reroll their successful save, you can force it to be rerolled with Disadvantage and choose the worst of all three results as the one they're forced to take.
If you're just trying to melt through Legendary Resistances
Monks are VERY good at eating away through legendary resistances with Stunning Strike, as in a single turn, they can force an opponent to make 3-4 saving throws in a single turn or risk being Stunned. This is available to them as early as Level 5.
Comment: Perhaps obvious to everyone already, but this incurs wish stress, so it's not a *practical* solution for normal situations, especially if it's not fight-ending.  But yes, good point that there is a spell for that.
Answer: Maybe not rerolls but there are other ways to hurt saves
We've already talked about Wish and Chronurgy Wizards in other answers.  But there are other ways to hurt enemy saving throws.  Some of these are deductions from an enemy save and some are straight disadvantage, essentially the same as forcing a reroll.
Edritch Knight's Eldritch Strike

At 10th level, you learn how to make your weapon strikes undercut a
creature's resistance to your spells. When you hit a creature with a
weapon attack, that creature has disadvantage on the next saving throw
it makes against a spell you cast before the end of your next turn.

Eloquence Bard's Unsettling Words

You can spin words laced with magic that unsettle a creature and cause
it to doubt itself. As a bonus action, you can expend one use of your
Bardic Inspiration and choose one creature you can see within 60 feet
of you. Roll the Bardic Inspiration die. The creature must subtract
the number rolled from the next saving throw it makes before the start
of your next turn.

Instrument of the Bards

You can play the instrument while casting a spell that causes any of
its targets to be charmed on a failed saving throw, thereby imposing
disadvantage on the save. This effect applies only if the spell has a
somatic or a material component.

Divination Wizard's Portent

Starting at 2nd level when you choose this school, glimpses of the
future begin to press in on your awareness. When you finish a long
rest, roll two d20s and record the numbers rolled. You can replace any
attack roll, saving throw, or ability check made by you or a creature
that you can see with one of these foretelling rolls. You must choose
to do so before the roll, and you can replace a roll in this way only
once per turn.

Arcane Trickster's Magical Ambush

Starting at 9th level, if you are hidden from a creature when you cast
a spell on it, the creature has disadvantage on any saving throw it
makes against the spell this turn.

Light Domain Cleric's Corona of Light

Starting at 17th level, you can use your action to activate an aura of
sunlight that lasts for 1 minute or until you dismiss it using another
action. You emit bright light in a 60-foot radius and dim light 30
feet beyond that. Your enemies in the bright light have disadvantage
on saving throws against any spell that deals fire or radiant damage.

Circle of Stars Druid Cosmic Omen

Woe (odd). Whenever a creature you can see within 30 feet of you is
about to make an attack roll, a saving throw, or an ability check, you
can use your reaction to roll a d6 and subtract the number rolled from
the total.

20th level Oath of the Ancients Paladin's Elder Champion

Enemy creatures within 10 feet of you have disadvantage on saving
throws against your paladin spells and Channel Divinity options.

Any Sorcerer's Heightened Spell

When you cast a spell that forces a creature to make a saving throw to
resist its effects, you can spend 3 sorcery points to give one target
of the spell disadvantage on its first saving throw made against the
spell.

Shadow Magic Sorcerer's Hound of Ill Omen

Additionally, while the hound is within 5 feet of the target, the
target has disadvantage on saving throws against any spell you cast.

Wild Magic Sorcerer's Bend Luck

Starting at 6th level, you have the ability to twist fate using your > wild magic. When another creature you can see makes an attack roll, an > ability check, or a saving throw, you can use your reaction and spend > 2 sorcery points to roll 1d4 and apply the number rolled as a bonus or > penalty (your choice) to the creature's roll. You can do so after the > creature rolls but before any effects of the roll occur.


Is CAPTCHA even relevant for mobile apps?

Question: How important is it to humanize the mobile-app registration process in order to prevent bot registrations? I was under the impression that CAPTCHA, probably the leading technology in this space, was made exclusively for computer-based web browsers because, unlike mobile apps that don't expose source code, web browsers do expose source code. Therefore, is a technology like CAPTCHA, or the general process of humanizing registrations, for mobile apps even necessary?
Comment: Those apps need to make calls to web services, right? If you don't have a captcha, it's trivial to automate
Comment: Google provides a library + service for Android apps named SafetyNet reCAPTCHA, so not all captcha target web.
Comment: @Robert To be fair, just because mitigation exists for something doesn't mean it is common enough to be worth protecting (abundance of caution and all that), but you are right that not all CAPTCHAs target webapps
Comment: What @MechMK1 said. In the end, it's just code interacting with some web service. Sure, it's not the same level of simplicity as F12 or view-source, but not much harder for someone who knows what they're doing. You should assume the attacker/bot has your source code and knows the APIs (only one device needs to be jailbroken/rooted/emulated to observe exactly what's going on). This is very hard to get right, and you'd probably need some out-of-band provisioning.
Answer: It is somewhat less efficient to create bots targeting mobile applications, however it is not something you should overlook. Many APKs, especially those written in Java, are trivial to reverse, so the source code argument doesn't hold up (it's just slightly more inconvenient for attackers, but presumably worthwhile if they're bothering to write a bot).
Also, anything can be automated, not necessarily directly through code, as you can just emulate device input (in a way similar to that of Autohotkey, or more relevantly, xdotool for Linux and X11-based devices, ie Android) exist.
So, if there is motivation for bots to be released on a mobile app, it can be done with similar ease to that of web applications, and protection is important.
Comment: Also, unless your registration flow involves some cryptographic secret that isn't transmitted over the wire directly, of you're using certificate/public key pinning, it's easy to write a bot for your mobile registration without any decompiling at all. Just use an intercepting proxy (with your own root CA cert installed on the device) to read the traffic to and from the app. It's usually trivial to learn how to imitate that traffic.
Comment: Depends how the keys are used, among other things. Intercepting is often still easy but if the key is used to sign or MAC messages then it's harder to spoof, especially if they also thought to include replay protections. On the other hand, iOS apps aren't that hard to disassemble (harder than Andoid ones but still not actually hard) and there are a few ways that somebody might get access to the binaries.
Comment: Assume the source code couldn't be decompiled (which I think is the case for iOS apps), how would an attacker then make a bot? Would they have to emulate the app onto a computer? Or could they jailbreak the phone's OS and run a bot on the phone that controls other apps?
Comment: @kidcoder Both of those are viable options, but realistically emulation is the way to go (jailbreaking iphones is getting more and more difficult).
Comment: @CBHacking the backend in my specific use case is Firebase which requires that only API calls from iOS devices are allowed, specifically those with the proper security keys in the app's bundle (the compiled exe file). I imagine that is rather difficult to intercept and sufficient to keep bots out?


How to get unanswered questions by tag on Stack Overflow app

Question: I'm trying to figure out how to just get unanswered questions by a tag in the Stack Overflow app. Is it possible right now? If not can anyone give an ETA on when this is coming out?
Comment: Works.!! But also lists answered ones, any idea why?
Comment: No idea why, a bug maybe. I searched for an example and all it returned was questions with **no answers**.
Comment: Thought there wud be a direct way to search in app
Answer: I'm not quite sure about the Android app, but with a web browser you can search
[your-tag] answers:0

which will return you with results that carry the tag [your-tag] and has no visible answers.
If you'd like to compete with existing answers, you can replace answers:0 with hasaccepted:no so questions that has no accepted answers will also show up.
The search engine is the same across platforms (see quotation below) so you can try it on the Android app.
Update The new search is now the default across the network.


Singular system of differential equations

Question: Consider the following second order liner singular system
$K x''( t ) = A x'( t )$,where $K$ is a singular matrix,$A$ is any matrix,$x(0)=\left<2, 1\right>,x'(0)=\left<0, 1\right>$.
how to solve the above system of differential equations?
Answer: If $K$ is singular, the system is no longer an ODE but a DAE, a differential-algebraic system. Since it is linear, you can solve it with the Kronecker normal form.
Or use any of the index theories. If $K$ and $A$ are sparse, you can use Pantelides/Pryce theory of the Taylor index.


What are these different Infernal Machines from the Level 12 Infernal Machine Plan?

Question: I recently found the Level 12 Infernal Machine in Reaper of Souls. What are the differences in the different machines in unlocks?
Answer: For a level 70 Hellfire Ring you can now choose which realm you want to farm.
It is because since patch 2.0 the maximum chance of getting an organ from ubers is only 50%(comparing to 100% at MP10 before). Also, before if you only had 2 organs and you needed 1 more you had to "gamble" and open portals hoping for a right one to open first.
Now you can choose which portal to open by crafting a corresponding machine
EDIT
As you asked: a source

Infernal Machine of Bones – Leoric and Maghda. Drops Leoric's Regret organ.
Infernal Machine of War – Siegebreaker and Zoltan Kulle. Drops Idol of Terror organ.
Infernal Machine of Gluttony – Rakanoth and Ghom. Drops Vial of Putridness organ.
Infernal Machine of Evil – Diablo and random Ubers. Drops Heart of Evil organ.
Comment: oh that's pretty cool. I'm sure you are correct but some sort of source would be awesome.


Job scheduling problem

Question: I'm working on an application where I need to automatically schedule jobs for members on a rotating schedule. I'm not very good at explaining rules, so here's some data to help out:
Positions: A job title, with rules such as Mondays and Wednesdays weekly.
Categories: A set of positions
Groups: Another set of positions. Positions in the same group cannot be assigned on the same day
Members: Users assigned to positions on a given date.
For each date in the month, members are assigned to positions (both in ascending order). If a member is assigned to a position in one category, the next time a position in the same category comes up, the next member alphabetically (or the beginning of the list) gets assigned eg.
Members: M1, M2, M3, M4
Positions in Category C1: P1, P2, P3
Members in Position P1: M1, M2, M3, M4
Members in Position P2: M1, M2, M3
Members in Position P2: M1, M3, M4
If M1 is assigned for P1, if P2 comes next, M2 will be assigned. An additional layer of complexity is introduced where if P3 comes next instead, M3 gets assigned. The system has to keep track of the fact that M2 was 'skipped' and assign M2 next if available, then assign M4 next, or wait until it gets to a position where M2 is available (this becomes additionally complex when there are many 'skipped' members).
A member will also be skipped if he has indicated he won't be available on that date. The system needs to place priority on skipped members, somehow identify them when they come up and then jump to the next logical person in the list. Skipping also applies to groups due to date clashes.
I already have a temporary [and messy] solution which I no longer understand even though I have a lot of comments in it explaining each step. Its weaknesses are in dealing with the skipped members.
If you were going to code this how would you go about it? I'm implementing this in PHP but pseudocode would work as well.
Comment: Are there hours for the positions that need to be considered? When you say positions in the same group cannot be assigned on the same day, do you mean they can't be assigned to anyone (i.e. only one position out of a group can be filled on a given day) or someone assigned to one position in a group cannot be assigned to any other?
Comment: I meant someone can fill two positions on the same day unless they happen to fall in the same group.
Answer: My solution:
You need a PriorityQueue (which is available in PHP under SplPriorityQueue). The PriorityQueue gives you elements with descending priority (sorted by values, the smallest
value has the highest priority).
Each member gets an assigned value. This value is an ASCII number with n digits (you could use 8 digits for convenience), filled up with zeroes to n positions. After that you append
the name. You also add to each member the available positions
So (n=5):

M1 value: 99999Albert  P1,P2,P3
M2 value: 99999Susi    P1,P2
M3 value: 99999Bob     P1,P3

This makes it easy to sort members by priority and name.
Preparation:
A sunny day. You are retrieving the assigned positions and a category for a given day. Each member is loaded on a long list. Each member who is not showing up on work is not loaded, but gets his value decreased by minus two. Bob is not here, so its new value gets 99997Bob. This means that Bob will be selected automatically the next time.
All other members get their value decreased by minus one.
The positions assigned for a specific Day are mapped (use SplObjectStorage):
P1->M1,M2,M3,M4 etc.
P2-> etc.
The map contains only the positions which must be assigned this day.
After the
Filter:
You must look up the groups and delete any positions on the map which cannot be assigned this day. Your group description is a bit unclear.
Assign:

You choose the position to assign
Get list of members which can fill the position
Remove available members from list and put them into the PriorityQueue
Assign the position by extract() from PriorityQueue (correct assignment is done
automaticially). Each member which is assigned will gets its value increased by
one (So the decrease and increase levels out if you are here and working).
If you are here and not assigned to a position for whatever reason, you get
a small penalty of one. If you not here, you get a penalty of two.
After completion, put remaining members on the list again, clear the PQueue and
continue with the next assignment.

Caveats:

You must be careful that there are always enough people for a position.
Comment: I second the weighted queue solution.  Maybe it's my lack of PHP knowledge, but I would just use an int for the priority.  Then do priority +1 when they are skipped and priority -1 when they are used.  Sort the queue by priority asc and name asc and you have your list in assignment order.  Lastly, work the list top down assigning or skipping each worker for each day.
Comment: I think the concat solution is used because php's implementation does not allow for multiple priority markers (in your case priority AND name). I'm sure it would be trivial to extend allowing for that though. See http://php.net/SplPriorityQueue.
Answer: uff.  i don't follow you description, but in similar situations i have used sql to solve this kind of problem.  if you are using php i guess you have sql available.
what i would suggest doing is finding a way of storing this information into a set of tables and then working out what sql query gives you the answer you want.  quite often it's a lot simpler to do in sql than it is in a procedural language.
for the skipped part, for example, you might have a column which records when someone was last assigned, and then order by that (so that you select the person who has not been assigned for a long time).  alternatively, you could have the number of times skipped as a column and order by that.
Answer: What I understand is there are 'm' members and 'n' positions.
Category: a group of positions -- a member who is assigned one position in the category can't have another?
Group: a group of positions -- positions in the same group must be assigned on different days.
Last thing, a Position has a list of members who can fill it.
Looking at this from a data-structure point of view, put the members in a linked list -- each member has to have an additional list of [position, day] that they are finally assigned.  Then, for each position, have a list of references to the members that can fill that position.  Implement categories as another list of references for a position as to which categories it is in.
The actual assignment: have a day counter = 0, and iterate through the positions.  For each position P, iterate through the members that can fill it.  A member M can fill the position if:

Any position he has filled P2 doesn't share a category with P.
Any position he has filled P2 with day = daycounter doesn't share a group with P.

If he can fill the position, the [position, day] pair is added to the member, and the member's node is moved to the END of the list (this is why references are necessary -- all the references are still valid even though the node moved).  This ensures that the 'skipped' members are given highest priority, and the members who weren't reached were given next highest priority.
Once a position is filled, go to the next position.  If the position shares a group with a position already assigned, skip it, iterating through all the positions until you can assign as many positions as you can on day 1. Then, increment the day counter and repeat for day 2.  This should give you a maximal assignment (not sure about maximum) for all the jobs.
Tip: when moving a member to the end of the member list, to prevent having to traverse the list, keep a reference to the end -- for the next position, you need to start from the beginning anyway, so there's no point going through the whole thing.

Job scheduling problem


Can I replace SCL and SDA into any other pins ? If possible How I write code?

Question: I want to use other pins which are not default SCL,SDA unlike code that Adfruit they wrote. How can I use pin 5,6 or others that active as pin scl sda ?
https://github.com/adafruit/Adafruit_CircuitPython_PCA9685

Thank you for watching my question.
Answer: You can create a software I2C bus on any pair of spare GPIO.  Note that you will need to add pull-ups to 3V3 on these GPIO for them to properly work as an I2C bus (1k8 resistors are suggested).
Name:   i2c-gpio
Info:   Adds support for software i2c controller on gpio pins
Load:   dtoverlay=i2c-gpio,<param>=<val>
Params: i2c_gpio_sda            GPIO used for I2C data (default "23")

        i2c_gpio_scl            GPIO used for I2C clock (default "24")

        i2c_gpio_delay_us       Clock delay in microseconds
                                (default "2" = ~100kHz)

        bus                     Set to a unique, non-zero value if wanting
                                multiple i2c-gpio busses. If set, will be used
                                as the preferred bus number (/dev/i2c-<n>). If
                                not set, the default value is 0, but the bus
                                number will be dynamically assigned - probably
                                3.

See /boot/overlays/README for details.


Too much load running through GFCI?

Question: I'm installing a circuit for two 12-amp loads that will plug into separate 15-amp outlets. These will be the only loads on a circuit with a 30 amp breaker. If the first outlet is a 15 amp GFCI and the second outlet is wired in line downstream with the GFCI and the two devices operate simultaneously, will this put too much load on the GFCI?
Comment: Bitcoin miners?
Answer: You can't do that to begin with
You can't put 15A receptacles on a 30A circuit in the first place -- NEC 210.21(B)(3) says no to that plan, and for good reason.
So, rethink your plan (this'd work fine and dandy with a 15A MWBC instead).
Comment: Or a 20 amp circuit can have 2 - 15 amp receptacles on it. But you cannot put 15 or 20 amp receptacles on a 30 amp branch circuit as TPE points out. And if you want 24 amps of load you will need two separate circuits or a Multi-Wire Branch Circuit.
Answer: Nope, nope, nope.  You cannot put a 30A breaker on common receptacle circuits, for so many reasons.
Your 20A-rated GFCI cannot handle 24A anyway (12A of its own load plus 12A passthru).  Use two GFCIs.  Since  you're using two GFCIs anyway, then as TPE says, use a MWBC.
Alternately, get 240V versions of these appliances, and wire this new circuit 240V instead of 120V, with NEMA 6-15 or 6-20 receptacles. Double the voltage means half the current, and that means you have two 6-amp devices, which is no problem for a 15A or 20A circuit.

240V NEMA 6-15 dual receptacle. Look familiar?
Alternately, install a dryer style circuit with 10/3 cable and a NEMA 14-30 receptacle, and have that feed a listed PSU.

Too much load running through GFCI?


Is Locking or putting a computer to Sleep safe with full disk encryption?

Question: I'm using Truecrypt for full-disk encryption of my computer's drives. Is it safe to Sleep or Lock my computer, or would that allow someone to bypass the disk encryption and access the data on the drives as if they weren't encrypted?
Comment: possible duplicate of [Is filesystem encryption any good if someone steals my computer while it's on?](http://superuser.com/questions/428630/is-filesystem-encryption-any-good-if-someone-steals-my-computer-while-its-on)
Answer: Full disk encryption, by necessity, needs the key in RAM to encrypt/decrypt data in real time.
So -

Firewire has a DMA like mode that basically allows one to scan the entire RAM of the system.  Full disk keys may be recovered from a target system's RAM if it's connected via Firewire to a host running the right software and the target system has a Firewire driver that supports this.  Your system is vulnerable to this if it is locked.  I'm not sure if it's possible to Firewire-read your RAM while it is asleep.
If your system is hibernating, all RAM is dumped to a hibernation file before power off.  I believe Truecrypt marks pages of its driver somehow to prevent this, but as long as you keep the hibernation file on an encrypted volume you should be safe.
DRAM takes a while to decay after power off.  Theoretically it's possible for an adversary to remove the RAM from your system,. possibly spray it with canned air to lower the temperature and lengthen the decay rate, and put it in a system or tool that scans the RAM and extracts the keys from there.  It also may be possible to power cycle your system, boot off of a live CD, and recover they keys from RAM that way.

If the RAM is powered off and has decayed sufficiently, it's not possible to get keys from it, and your encrypted data is safe in this situation.
Of course the first and third items are tinfoil-hat level stuff, but to prevent against it you should power your system down completely when you are not using it, and run Memtest86+ or your system diagnostics to clear RAM.  At least one security-focused Linux distribution does this before power off, I can't think of the name of it.
Full disk encryption does protect you against someone taking the hard drive out of the system and trying to read it in another system while it is asleep if they don't extract keys from RAM directly, which is an advanced operation.
Answer: I posted an answer to a similar question here:

While the contents of the disk are encrypted, the operating system is decrypting the content of the disk on the fly in order to access it. The screen lock does little to protect the contents of the disk while the computer is running.
All the screen lock does is prevent someone from running programs / reading your screen while you're away. As long as the computer is running and the encrypted disk mounted, your data is vulnerable. Granted most thieves would just shut the machine off / reboot it once they had it.
However, if you're paranoid about your data, the inconvenience of powering down/powering up every time you walk away for a while is a small price to pay IMHO.

The fact that most current full disk encryption methods use RAM to store the keys makes them only partly secure while the system is running. DMA access via Firewire or PCI bus is a possibility while the system is running and not quite as tinfoil hat as some might suggest. There was a great talk at Defcon 21 regarding the problem and the work being done to try and mitigate it (the slides for the presentation will probably show up on the archives soon, though).
Answer: No. as others pointed out, an adversary with physical access to the machine can do almost anything with data in ram.
When you hibernate a computer, it caches active ram out to your hard disk. since the key is in active ram, you are placing your key in a file on your hdd, that effectively never goes away. There are tools designed to break into Truecrypt volumes, which scrape ram for your key, and if your volume is not mounted, it will fall back to checking your hiberfil.sys on windows to see if it was cached to disk during the last hibernation.
FDE is a problem because your key will always be present in ram, and for that same reason, it will always get copied to hiberfill.sys on suspend/hibernate.
see this thread for examples of practical attacks and a fuller explaination:
Cracking truecrypt files in minutes? Or just truecrypt harddrives in minutes?
Comment: `FDE is a problem because your key will always be present in ram, and for that same reason, it will always get copied to hiberfill.sys on suspend/hibernate.` Okay, but isn't @LawrenceC's point that with FDE hiberfil.sys is on an encrypted drive a valid one? When you start a hibernated computer with TrueCrypt FDE, you need to provide the encryption key. Wouldn't someone have to decrypt the volume in the first place in order to read the keys from hiberfil.sys (in which case the fact that hiberfil.sys contains the keys is academic)?
Comment: BTW, I'd like to clarify that this discussion only applies to hibernate, not suspend or sleep. Putting an FDE computer in sleep (Windows) or suspend (Linux) does leave the keys exposed, but that's because it doesn't clear the RAM; nothing is written to hiberfil.sys or the swap space.
Comment: Sleep and Hibernate are different. Sleeping or locking the computer leaves the system booted, so the keys are still in ram and accessible to any evil maid: attack https://www.schneier.com/blog/archives/2009/10/evil_maid_attac.html


Stern-Gerlach experiment and the MRI machine question/s

Question: Exactly at which point does that valence electron in the silver atom
get its spin, in the SG experiment?
When it enters the magnetic field or when it hits the detector/screen or
when it's actually observed, by someone!?
How can a magnetic dipole align itself antiparallel to a magnetic
field, in the SG experiment and the MRI machine, and then stay like
that, thru any number of such SG magnets!? Unlike a compass needle.
It can't be diamagnetism or a gyro/scopic effect.
Answer: I'm afraid we cannot answer exactly when the electrons flip spin, due to the Uncertainty principle. What we can establish is an experiment which tells at that moment what is the spin. If you send spins through a Stern-Gerlach apparatus that separates into $+$ or $-$ components and then send only one of the components $+$ through an identical Stern-Gerlach apparatus you would see again only $+$ components, if you disregard external interactions.


Relationship between frequency and amplitude of mechanical waves

Question: Can two mechanical waves carry same energy whose frequencies are different?(assuming same medium but having different amplitudes
Answer: If you consider a mechanical wave in a string, that is possible as long as you keep $\omega A$ fixed.
That is because the energy of a mechanical wave is given by
$I = \frac{1}{2}\rho v\omega^2A^2$
Many textbooks would contain a proof, and http://cnx.org/content/m12793/latest/ may help as well.


Why is the fuel:air ratio of a turbojet engine not around ~1:15 (the stoichiometric ratio)?

Question: Also, what is the maximum fuel:air ratio possible in a combustion chamber of a jet engine?
Comment: Would you please provide some sources for your information?
Comment: I think this question should be rolled back, the latest edit of ditching the f/a ratio of 1/4-1/3 totally changes the question. As it stands now, this is a very good question, but it is **not** what Call Me Dosya asked originally.
Comment: If one would take a look at the %fuel/air combustible range for Jet A1 kerosene (Engineering Toolbox), it is around 0.7 to 5%.  So 1/4 to 1/3 would be way too rich.
Answer: Edit: to honor my original answer, I shall keep it as it is. The question was edited so much I think it would have constituted a whole new question. In it's original form, the Q presented jet engine f/a ratio as 1/4 - 1/3 and compared it to the stoich ratio of 1/15.
Your numbers seem way off, except for the stoichiometric fuel/air ratio (for kerosene).
Please see the following NASA article: Beginner's Guide to Propulsion and EngineSim
Fuel and Air Relationships
Activity
A quote from there:

For jet engine combustion, the important parameter is the fuel/air ratio (f/a) which is the ratio of the mass of fuel to the mass of air being burned in the engine.

The stoichiometric ratio of 1/15 can also be written as approximately 0.067
The article further elaborates on the subject:

For example, at sea level an airliner taking off at 375 mph with the throttle at 100% has an f/a of .017

This 0.017 translates into about 1/59
No matter how you look at the ratio, mass or volume, in no case will a jet engine run at f/a of 1/4~1/3. The mixture will simply be too rich to ignite and burn.
Here is a link to a Wikipedia graph about the range of typical jet engine air:fuel ratios:
Combustion stability limits of aircraft gas turbine.svg
Please note the graph displays the ratio in reverse order from what was used before in this answer, ranging from ~25/1 to ~180/1.
Answer: We have to remember air is only 20% oxygen.  When you write the stoichimetric formula for the chemical reaction (using oxygen) on a molar basis, you get the combustion ratio by converting the fuel and oxidizer from moles to mass.
To get the combustion ratio using air, you divide the oxygen mass by its fractional proportion in air.
Interestingly, the stoichimetric fuel/oxygen ratio (by mass) is around 1:3. 3 divided by 0.21 gives us around 15 for kerosene and air.
Turbojets burn fuel in combustion "cans" within the flammable fuel/air percentage limits and use the heat from that combustion to warm more air passing through the the core.
Bypass fans can make these ratios even higher.  For example, the Ge 90 has a bypass ratio of 9 to 1.  Of the 10% of the total air mass flow going through the core, its air to fuel ratio is around 33 to 1, much higher than stoichiometric.
The total air to fuel ratio (by mass) is 330 to 1!
One can see why fuel combustion "cans" were invented, and why fan jets are becoming more popular.
Comment: When calculating a/f ratio, you can not take into account the bypass air. It is the same as if one would calculate the a/f ratio of a propeller acft and count into it the air the propeller is moving
Comment: @Jpe61 that is true.  The total air moved is interesting.  Prop thrust may be more related to its lift that "air moved".  More to write about.
Comment: Lift *is* pretty much the air moved.


picture is not refreshing in my browser

Question: I am trying to upload a new picture into my webpage, but in the browser it is showing the old picture. When I check in the folder the new image is being saved, but it is not showing in the page. I have tried refreshing, but it does not help. It is still the same after shutting down the browser. I have tested in different browser and it is still old image. I need help as to what can I do now. I'm uploading picture using PHP coding with Ajax.
Comment: Which webpage? Do you have a link which we can check? If IE try Ctrl + F5 which will do a complete refresh and see what happens.
Answer: I'm not sure I fully understand what you are trying to accomplish, but obviously there is some caching of sorts going on.  If you've uploaded an image, with the same file name, and it refuses to refresh, or you simply don't want to depend on a refresh of the users cache, a simple solution would be to append a random number to the end of your image src after a question-mark. i.e.

...which will essentially make the browser believe the image is a new image (which it is), and thwart it's attempt to use the browsers cache.
Comment: Nice, but unfortunately ugly. Too bad browsers ignore standard HTTP headers.
Answer: Try pressing Ctrl-F5 in the browser. This should force a refresh of the cache.
If you are using a script to generate your pages, you could pass the no-cache http flag in the output headers for the image. The header would be:
Cache-control: no-cache

Edit: I see you are using php, is there any chance you could 'echo' the image in a separate php page? Then you could use the line
header("Cache-control: no-cache");

Answer: Are you updating the src attribute of the image tag with the new filename? o.O
Comment: yes, retrieving filename from db andd then putting into src.
eg: src="
Answer: Try renaming the picture with a different name.
Answer: Try clearing your cache THEN refresh the browser. There is the possibility that you are still seeing the cached image, despite the contents changing on the server.

picture is not refreshing in my browser


From a 44kHz audio signal, how could I extract 32 evenly spaced frequency bands?

Question: Assume I have an array of floating points that contain the last 8192 samples played. How would I convert that array to 32 frequency bins that are spaced from 0Hz - Nqyst?
Comment: Your question is underspecified in a number of ways. What sample rate do you want on each subband? What do you want their bandwidth to be? One way to channelize a signal uniformly is using the DFT.
Comment: What kind of result do you want for each bin?  32 sub-band channels of audio, or 32 level dB meters?  Or something else?
Comment: For a small calculation like this one, you can use the [DFT](http://en.wikipedia.org/wiki/Discrete_Fourier_transform) directly.
Comment: Yeah, you can, with relative ease, run the samples through a "simple" FFT algorithm to generate frequency domain data and then slice the data into your "bins".  This is fairly straight-forward and would permit, eg, assigning "levels" to each band.  And you can then, in theory, reverse the FFT to get back to time domain, though doing so with any accuracy is quite a bit more difficult.
Answer: Depends on what you want to do with it. Some possibilities:

Short Time Fourier Transform with a 64 FFT length will give you 33 bins as a function of time. These are actually 31 "normal" bins (with amplitude and phase) and 2 "half" bins that only have amplitude (DC and Nyquist) and half the bandwidth. If your input vector is complex, you can use an FFT length of 32 and you get 32 "normal" bins.
Do an FFT over the whole sequence, create any bins you want in the frequency domain and simply integrate the energy in each bin. However this will discard all phase information.
If you really need 32 bit equally spaced complex frequency bins for
a real valued input signal you can do "half bin rotation" of the
frequency sampling grid. You basically multiply your sequence with a
exp(-jw/N * (n/2)) before the FFT grid. YOur first bin would then go from 0Hz to 1378Hz instead from -689Hz to 689 Hz.

It really depends on how you want to do your frequency binning. Do you care about the location of center frequencies or the band edges? Do you need sharp edges or overlaps? Do you need amplitude and phase? Is the input real or complex? All this factors into the correct binning procedure.
Let's look at the example of calculating the A-weighted sound pressure level from a time domain microphone signal. Your input is real valued, i.e. you can ignore the negative frequencies. You care about center frequencies but you need a log spaced grid. You want some overlap between the bands so that frequencies that are close to a band edge have some contribution in both bands. However the overlap should conserve energy, so the overall energy is frequency independent. We don't care about phase, so we can simply integrate energy inside a band to get a single number.
As this example shows, frequency binning is application dependent on not as trivial as one might initially think.


Where can I find a gun as quickly as possible?

Question: I was told this game has guns. But I've been playing for hours and seen absolutely no sign of one. Where can I acquire a gun for what I had hoped to make into my badass new Wizard With A Shotgun?
Answer: There's actually a Unique Pistol available right on the very first map of the tutorial section of the game!
To find it, you'll need to have at least 1 point in Mechanics Skill after character creation. That means you'll need to be playing as a Cipher, Chanter, Rogue, or Wizard, OR, you'll need to select the Laborer, Merchant, or Scientist background. Any one of these options will give you at least one point of Mechanics.
Then, after you've been assigned a bodyguard and told to go look for berries, head for the far Southwestern corner of the map; the weird campfire, across the bridge near the stream:

Once there, take a closer look at the tent - you'll need to turn on Scouting Mode (i.e. Stealth), and move around in the area a bit - soon your character will notice something, and a new (hilit in purple when you tab hilight) container will appear:

You'll find The Disappointer! It... lives up to it's name, unfortunately:
Answer: For something a little less disappointing, when you pick up Kana from Caed Nua, he comes equipped with an Arquebus:
Comment: And to the south at Anslög's Compass, there's a Fine Pistol in a hidden cache in the Spore Cave.
Comment: @LessPop_MoreFIzz This has been changed to a fine wand in later patches
Answer: The Disappointer pistol may be enchanted with something cheap, if kept, to remove the bad attributes.
Also, in version 2.00, a Pistol can be looted from the corpse of the Backer NPC 'Sidi Exa', located in White March, near Madhmr Bridge and south of Black Meadow.
This NPC is not important, but killing him does drop your reputation with Defiance Bay by a small amount. You can circumvent this by equipping all of your party members with ranged weapons, positioning yourself just to the south of Peregund (out of her field of view), and killing Sidi from there.


Good resources to learn loopy belief propagation

Question: What are some of the good references to understand loopy belief propagation and the need for it? I am looking for both theory and applications (for instance in coding/information and learning theory).
Answer: The following tech-report (a simplified version of an earlier paper by the same authors) on general BP (not only loopy-BP), but has fantastic insights.
It's a great place to start, if you already haven't.
http://www.merl.com/publications/docs/TR2001-22.pdf
Another good place is this book:
Information, Physics, and Computation - by Mezard and Montanari.


My research work is published before me

Question: My project work which i was planning to publish somebody else published just 1 month before. what should i do? Is my total research work of 8 months going to be a waste?
I was working for a novel phytochemical and planned to publish my paper. When i submitted the journal manuscript in December, the editor replied in the month of January that some other Chinese group published paper for the same product in January. Is my whole research of 8 months going to be a wastage. What other options do i have? Please suggests.
Comment: Have you discussed it with your supervisor or senior colleague?
Comment: Perhaps the more important question is whether you can still get your degree without this publication. That may still be possible and the thesis can, perhaps, stand. In that sense it wouldn't really be wastage. Especially if you learned things about research.
Comment: Actually we submitted the manuscript then the journal editor highlighted this issue in front of my guide
Answer: This is a common problem that researchers face. The fear of being scooped partially explains the publish or perish culture in academia. This is definitely a setback for you, but there are a few options which you can consider to make at least some use of all those months of research:

You can try to build on the published paper. If required, conduct a few more experiments and move over to the next logical step in the idea.
Using your original idea as a base, try to come up with a related but new research question that allows you to use some of the old data.
Go through your paper again and see if there is any secondary finding that you might not have focused on at that point of time, but which could be developed into a new research idea.

Now that you have been scooped once, you should try to get your results out before anybody else does. Since the publication process of journals can take up a lot of time, one thing you can do to avoid getting scooped is post a pre-print or present at a conference as soon as you finish your research. Also, make sure that you do not take too long to write your manuscript. You should actually start writing certain sections, such as the methods and results section as and when you perform the experiments. That way, you will be able to save up on the writing time.
Most importantly, do not lose motivation. The fear of being scooped is part of a researcher's life and there is no foolproof system in place to avoid it. So just keep your spirits up and move on.
Comment: I'm curious, what's wrong with two independent parties publishing very similar studies at the same time? Surely it would be useful to compare similar studies, since it would indicate consistent results.
Comment: Hey Kakoli thank you so much actually even i also came up with the additional finding idea. Thanks i will start working on it and this time for sure no delay. Thanx duh
Comment: Hi, could you clarify what you mean by "scooped"? I interpret it as "somebody saw my materials or heard me discuss my idea in some details, then (usually to better funds and larger team) reached or confirmed my result before me". But what actually seems to have happened (the way I see it), is that an independent research group found the same chemical/process/something independently, not _based_ on OPs research. Which is still very uncomfortable, but not as bad (with some good connotations - e.g. somebody actually confirmed the validity of your research).
Comment: When your research is scooped, it means that somebody else who was conducting the same research without your knowledge has published it before you. The person(or group) that publishes a research first has their name associated with it. So, technically, even if you have spent a lot of time and effort on your research,  if somebody else beats you to it, your work will no longer be regarded as unique or novel. Your study would then be seen as replicating the results of the other study.
Answer: Some journals (like PLOS One) specifically accept papers like this ("scooped research") as long as it has only been a short time since the first paper came out. It is certainly not a wasted effort, because two people independently getting the same results on an important problem only increases the confidence that the solution is correct. But you should carefully go through the other paper before you try to just publish your work - you will probably find some hole or assumption or other imperfection that you can base another paper around that came from your own work.
Comment: Yes! Replication is important!

My research work is published before me


WhatsApp cannot be reinstalled

Question: I had uninstalled WhatsApp and downloaded the latest version, but after the download I can't install it. I am using a Lenovo A6000. Please tell me what I can do to reinstall the app.
Comment: What happens when you try to install. What phone? Android version? Need much more details than you have provided.
Answer: Here, try downloading this and installing it: http://www.apkmirror.com/apk/whatsapp-inc/whatsapp/whatsapp-2-12-373-android-apk-download/.
Make sure unknown sources is enabled: Settings > Security > Unknown Sources and confirm the popup. Then just click on the downloaded file and it should install.
It is officially signed so you will be able to receive updates from google play.

WhatsApp cannot be reinstalled


Join as shapes messes up mesh

Question: To sum things up, I am trying to use the "join as shapes" option, but for some reason the resulting shape key is really messed up. I made sure both meshes have the same number of vertices, and the toplogies seem to be similar enough, but am not sure why I am getting this result. Using transfer shape keys gets virtually the same result.
Here is the base mesh:

The resulting shape key:
Comment: The meshes need to have the same topology.  The same number of vertices does not mean they have the same topology.  'Similar enough' topologies don't cut it.  Here, it appears that your meshes do not have the same topology-- likely, they have a different vertex *order*.
Comment: I see, is there a way to fix that. I looked at the topologies and it looks like the area around the eyes is the only area that is different, which is what I want as a shape key.
Comment: It's not about looking the same, it's about being the same. You could add a cube to your scene, then add a plane and edit it to make an exact replica of the cube, chances are you will not have the same topology just because the Vertex indices will be different.
Answer: It's not about looking remotely the same, it's about being the same. You could add a cube to your scene, then add a plane and edit it to make an exact replica of the cube, chances are you will not have the same topology just because the Vertex indices will be different, and making a shapekey out of it will give strange results:

The normal way to do shapekeys is to either do them directly on the original objects itself (add a Basis shape, which is your original shape that you should never change, then make a new shape and edit that one), or duplicate your original object, modify the duplicate, and join that as shapekey to the original. In either cases, you should never add or remove anything from your mesh.

There might be a way to somehow recover your shape, I haven't tested that method though.
If they are visually strictly identical in topology but not in indices, maybe you can try to reassign the vertex order on both your original and shape object using this method, though it might break other things like UVs and weights, and it might still not work. I'm not sure.
Put the two objects in the exact same place, put your 3D cursor away from them using ⇧ Shift RMB, select both and switch to object mode before using the menu Mesh > Sort Elements > Cursor Distance. Then redo the shape key.
Answer: I had this issue and I applied my modifiers and this seemed to solve my issue.  Hope this helps.
Comment: Hi, thanks for the post. This site is not a regular forum, answers should be substantial, stand on their own, and thoroughly explain the solution and required steps. One liners and short tips rarely make for a good answer. If you can [edit] your post and provide some more details about the procedure and how it works, perhaps add a few [images](https://blender.meta.stackexchange.com/questions/963) illustrating some steps and final result. See [How to write a good answer?](https://blender.stackexchange.com/help/how-to-answer), otherwise it may be converted to a comment.

Join as shapes messes up mesh


Can a CSR be created in OpenSSL with SHA2?

Question: Can a CSR be created in OpenSSL with SHA2? If so, what would the command be and what does this tell the CA, if anything? If you could create a CSR using SHA2 would it "tell" the signing CA to use it on the entire cert chain?
Comment: For what it's worth, I don't remember the details, but I've had no problems going SHA-2 with my CAs. They offer SHA-1 or SHA-2 as a choice when ordering or take the hint from the CSR; and they provide a fully SHA-2 chain, by default or at least as an alternate download.
Answer: You can add, for example the <code>-sha256</code> flag to the OpenSSL command line when generating the CSR.  I don't believe any CA will change how they sign your CSR based on this, and it certainly won't affect the certificate chain.  They're not resigning the cert chain for each key, the only signature operation they do is on your CSR itself.  Any intermediate/root CAs provided will be exactly the same for all customers.
Comment: StartSSL certificates apparently respect the CSR SHA type, as I just had to resubmit a CSR but generated with `-sha256` in order to get the SHA2 cert back.
Comment: Yes, I was able to use the command openssl req -sha256 -new -key fd.key -out fd.csr to get a SHA2 CSR. If it has no bearing on how the CA signs the cert, then what are the use cases for creating a CSR with SHA2-256/384/512? I'm not clear on why its used.
Comment: No, RSA keeps your private key safe by nature. That's what it's for. :-) RSA can only sign relatively small things, so you hash the data and sign the conveniently-sized hash.
Comment: I suppose its hashed to prevent attackers from extracting the private key from it?
Comment: Not an available flag if you generate the CSR from an existing cert using `openssl x509 -x509toreq -in my.crt -signkey my.key -out my.csr`
Comment: @Snekse It's not available on `req`, but it is available on `req`. For example: `openssl x509 -x509toreq -in my.crt -signkey my.key -sha256 -out my.csr`


Where does "jump off the deep end" come from?

Question: I know "jump off the deep end" means to abruptly step into something but I'd like to know what it means in terms of actual physical jumping - because you usually "jump off" something not deep. What does a native speaker imagine when hearing the phrase?
Comment: Think about swimming pools.
Answer: The relates to jumping (or diving) into the deep end of a swimming pool.
In the deep end of the pool, the water is too deep for you to stand on the bottom, so you are forced to swim.  It's a metaphor for coping with the unfamiliar, especially when you are not properly prepared.  "Deep water" is a metaphor for the unknown, so when you jump into deep water you don't know what might happen, or what might be lurking under the surface.
A related idiom is sink or swim.  When you jump off the deep end, you have choice but to learn to swim, otherwise you're going to drown.
In addition, go (or jump) off the deep end has become synonymous with go crazy, or lose one's head:

lose one's head (v), "To behave irrationally or to lose self-control, especially in a distressing situation"

The connection here to swimming pools is less clear, although it's probably connected with the idea of deep water being (literally) unfathomable, meaning that you have no idea what someone who has "gone off the deep end" is going to do.
Comment: Similarly, in a situation that goes beyond your intent or control, you can be "in deep water" or "in over your head".
Comment: I just still don't understand the preposition "off". Doesn't "jump off" mean "jump from". "Jumping from the deep end" sounds like the opposite of what it should mean ("jumping to the deep waters/end").
Comment: @Probably I agree that it doesn't make sense.  How can you jump **off** from the deep end of a pool?  I expect that, originally, it was, "Jump off the **diving board**. *into* the deep end of the pool"  and the idiom got shortened over time.
Comment: I have always heard it as, "jump in at the deep end"


Does mysql return data on demand, or all? Why looping over the data is slower than accessing them?

Question: I was wondering when we call the perl dbi apis to query a database, are all the results return? Or do we get partially the result set and as we iterating we retrieve more and more rows from the database.
The reason I am asking is that I notice the following in a perl script.
I did a query to a database which returns a really large number of records. After getting this records I did a for loop over the results and created a hash of this data.
What I noticed is that the actual query from the database return in a reasonable amount of time (the results were a lot) but the big delay was looping over the data to create the hash.
I don't understand this. I would expect that the query would be the slow part since the for loop and the construction of the hash would be in-memory and would be cheap.
Any explanation/idea why this happens? Am I misunderstanding something basic here?
Update
I understand that MySQL caches data so when I run the same query multiple times it would be faster the second time and on. But still I would not expect the for loop over the data set in memory to be of the same (and more) time duration as the query to the MySQL DB.
Answer: Assuming you are using DBD::mysql, the default is to pull all the results from the server at once and store them in memory. This avoids tying up the server's resources and works fine for the majority of result sets as RAM is usually plentiful.
That answers your original question, but if you would like more assistance, I suggest pasting code - it's possible your hash building code is doing something wrong, or unnecessary queries are being made. See also Speeding up the DBI for tips on efficient use of the DBI API, and how to profile what DBI is doing.
Comment: I would paste the code but it is too straight forward.I mean there is *no* extra query to the DB made in the loop. I just create a an array of anonymous hashes based on the data I got from the DB


How long will someone that uses Tretonin live for?

Question: How long will someone that uses the drug Tretonin live for ?
I know that they will gain the health benifits similar to someone that is joined with a symbiote (not sure if its the same with healing) but not using a sarcophagus. Is it also the same with their lifespan ?
For example, a Tok'ra host lives for either 200 or 400 years (I forget which), so will the person that is using Tretonin live for about the same ?
Answer: We have a canonical example. In the series finale, Unending, Teal'c

 lives for fifty years on Tretonin, and doesn't look significantly older at the end.
Comment: While Teal'c does show that you can live for at least 50 years on tretonin, he never died of old age, so we don't know for sure what the life expectancy actually is. Given that tretonin is a new invention, we're unlikely to see exactly how long it lets a person live, unless that's ever covered by a future comic or book.
Answer: Tretonin originally is made from symbiotes themselves therefor providing all of the symbiotes regenerative powers and extended age. So i would say a jaffa that was using tretonin would most likly live closer to a Tok'Ra is age. Thought currently they are using a synthetic tretonin which may not offer quite the same healing and age as what an actual symbiote would offer. Tretonin does still destroy the users immune system as the drug itself becomes the immune system of the host, so you have a dependency on it for life.
Comment: Would someone like a Human/ Tauri live as long as that ?
Comment: I'm pretty sure humans that never had a symbiot cannot use it.