Why is charging from computer using USB slower than using an outlet?

Question: And what is roughly the ratio of the charging speed in USB vs charger? My phone is Samsung Galaxy S, if that matters.
Comment: Not an exact dupe but check out this question http://android.stackexchange.com/questions/1887/charging-from-power-outlet-or-computer-to-save-battery-lifetime/1888#1888
Comment: I find that charging from a powered external USB hub goes pretty fast.
Answer: A computer USB port is limited to 500 milliamperes (or 900 mA  for a USB 3.0 port). The dedicated wall charger, on the other hand, is usually able to provide 1000 mA or more.
Let's take the case where a connected phone uses 200 mA. Then, the USB port would have 300 mA left to charge the battery while the wall USB charger would have 800 mA left. A typical smart phone battery has a capacity of about 1500 mAh (milliamperes-hour) nowadays. This means that in a perfectly efficient world, a current of 1500 mA would charge the battery in 1 hour. So the same battery would then charge in 5 hours over the USB 2.0 port and in about 1h50 with the wall charger.
Of course in reality power losses would also affect charging times but these numbers are quite close to what I get with my actual phone.
Comment: As a side note, if you're plugged into an unpowered USB hub that other devices are sharing, you'll have even less available for charging the phone.
Comment: This answer is partially wrong. A computer port is NOT limited to 500 mA. The USB 2.0 specification says that a DEVICE is not allowed to consume more than 500 mA. This is a huge difference. Because of that is allowed that an PORT or HUB delivers more and most of the PCs (except of some small ultrabooks) deliver much more. The problem is that a connected phone decides to use "PC charge" and lowers the amount to 500 mA and this is to respect the USB specification. But you can charge with much more power easily. Just buy an adapter/cable with bridged data pins and it will charge with the maximum.
Comment: A computer with Charging Downstream Ports (usually with a lightning symbol next to them) can supply more than 900 mA.  Likewise USB-C ports can support 1.5 or 3.0 A, also indicated with a lightning symbol.  Unfortunately the lightning symbol is ambiguous because it doesn't say which current or which standard is being used.
Comment: Note that the device needs to comply with the post 2007 BCS spec to actually benefit from using the dedicated charger. Also the perfect charging time is not so much affected by 'power losses' but by non-linear charging when the battery is almost full.
Comment: @mgutt: NO! Exceeding the amperage rating of a USB power source can cause property damage and personal harm (fire, computer damage, and burns). How can we guarantee to the reader that their power source is actually engineered to deliver much more than its rated current?
Comment: Is there any way to see how much power a particular USB port is supplying? My mobile discharges faster than it charges when connected to my desktop USB according to Ampere. Fine on the mains based charger which charges at >1000mA
Answer: Charging from a USB port of a computer is slower than charging using a charger because the voltage and amperage provided by the computer is considerably lower than in the case of using a normal charger, so the mobile is using "slow charge mode"
I don't know which is the charging speed ration between USB and normal charger in the case of a SGS, but in my case (HTC Desire) with a normal charger I need approximately 2 to 3 hours for a full charge, but with a USB connection that time only charges 15 to 35 percent.
Comment: The voltage is actually the same (5V) its the current (amperage) that's lower.
Comment: @ChrisThompson while definitely true for now, the USB org decided to confuse people even further, and added multiple supply voltages to the USB 3.1 spec.  Only after lots of confusing negotiation, of course...
Answer: The reason your android device draws less power from your USB connection than from a wall adapter is because of the USB specification. This can be side-stepped by shorting the data wires in in the USB cable, which will switch the phone or tablet into wall mode where it can draw the full available current. The amount of current available will vary considerably from PC to PC.
The reason the specification exists in the first place is that the voltage to the computer's USB ports is usually supplied via the motherboard by a single loop connection which services all of the USB ports at once. Being only a few microns thick, this circuit is not able to deliver the same current as a dedicated charging wire. It is highly improbable that you will 'burn out your motherboard' by trying to draw the full available current through this circuit (although it is theoretically possible if your computer was a total P.O.S. to begin with). What is more likely to happen is that you will exceed the manufacturer's design specification, thereby denying sufficient power to any other USB devices you have connected, and/or other internal circuits which can cause the PC to crash. This is the very same reason it is recommended you use powered USB hubs.
Answer: A word of caution, while we all want our batteries to charge fast, be aware that the faster you charge a battery, the warmer it gets, and heat destroys battery life. A battery charge to full each time @ 0.5 amps will last longer than one charged to full each time @ 1.0 amps. I don't know enough to say this small difference is enough to be of concern for a cell phone battery, but I have found out that using an iPad charger (5.2V, 2.4amp) vs the recommended PC USB port (5V, 0.5amp) charge rate will shorten the life of a Bose noise canceling earbud battery. Happy charging.
Comment: I've heard the same story.  Did you find any references to back up the answer?
Answer: Most of the answers are incomplete so I try to answer it, too.
The USB 2.0 specification defines a minimum of 500 mA for the hub and a maximum of 500 mA for the device and the USB 3.0 spec has the same limits for 900 mA:
http://www.maxrev.de/files/2014/08/usb_3_0_english.pdf

This means a device (the phone) is not allowed to consume more than 900 mA if it is connected to a hub (the pc) but the hub is allowed to provide as much as possible!
In addition you need to know that the USB specification does not cover USB power supplies. This is covered by the power delivery specification. This means they can deliver up to 2A @ 5V and many smartphones make use of higher currents.
Now back to the PC. A PC with three USB ports is defined as a "hub" and to meet the USB specification it will deliver >500 mA per port. And because its much cheaper to use one power supply, all three ports are connected to the same one. And because of that a device can easily consume >1500 mA if it is the only connected device. But the problem is that the device "talks" to the hub (by using 100 mA) and then both arrange the higher current (500 or 900 mA depending on the USB version).
So to answer the question: Charging from the computer is slower because both devices comply to the USB specification.
But if you fool the device so it thinks its connected to a power supply it can consume its maximum from the hub. For that you need an adaptor called "fast charge adaptor" that shortens the data lines (example 1, example 2).
So a computer port is not limited to 500 or 900 mA as stated in other answers. The limitation comes from the spec.
Note: There exist exceptions. For example mobile devices like ultrabooks are allowed to share the one port minimum for all ports. And I had a HP monitor that interpreted the USB specification very strict and limited the current of one of two USB 3.0 ports to 910 mA (avoiding the usage of many USB 3.0 usb drives that consume for a short time a little bit more).
Comment: Using a USB data blocker to enable fast charging is interesting, but I'm curious if there's any risk of damage if the device being charged draws more current than the laptop can provide. [This answer](https://electronics.stackexchange.com/questions/53747/is-it-safe-or-even-possible-to-draw-more-power-from-a-usb-port-than-it-was-des#53748) suggests it's "probably safe"...
Answer: Consider that computers often have other things inside of them or connected to them that need the same charge. The power within a computer itself is always lower than direct power from a outlet from a wall. When power is distributed through a computer to your phone, that same amount of power is also being used throughout the whole computer slowing the voltage to your phone, and other things that are plugged up. Always remember, if you want direct power and a quicker charge, its always good to use to wall outlet instead of a computer or labtop.
Comment: The USB standard officially limits the current flow to 500mA. Most mainboards can supply more, but today's phones only take 500mA when they sense a PC-USB port.
Answer: USB from computer delivers only 500mA. So, a 2100mA battery will take 5 hours to charge from a computer.
The charger outlet delivers 700mA to 1A. So, the battery will charge within 3 to 3.5 Hrs.
Answer: Samsung bridges pins 2 and 3 facing the phone. If pins 2 and 3 are open, the phone limits your charging capability to about 350 mA or so.
Check it out:
http://forum.xda-developers.com/showthread.php?t=1384253
Comment: Shorting pins 2 and 3 together is the official USB charging spec, but not all phones and chargers follow it.  Sony and HP and Apple have their own proprietary connections.
Answer: Most of the answers here are very informative on the battery issue, I don't want to touch on that, though I should let you know that if you have to charge your android with your laptop or desktop, make sure it gets full before you unplug it, otherwise you will be slowly ending the long life of your battery by unplugging every time you have to leave because it kind of takes longer. I take a major precaution when it comes to charging because I changed my phones charging adapter more than thrice due to charging using my laptop. I was finally advised by my techie to use the specified charger and since then, i have no battery issues. Just a precaution.
Answer: Completely depends on your motherboard I have a beast of a PSU and top range type motherboard which lets you turn data connection off and the charge up - it charges phone in less than half the time of dedicated charger. As said though most computers will limit this so result in a slow charge


Is drinking urine safe?

Question: We've all heard stories about how people saved their lives by drinking their urine.  Is drinking urine safe when there are no other water sources available?  Can I filter it with a water purifier?
Comment: I realize this question is somewhat unusual and perhaps subjective, but it is something that we've all wondered at one point or another, and could mean the difference between life and death in a future survival situation.
Comment: Drinking urine is a bad idea. I answered this question in detail at http://outdoors.stackexchange.com/a/5101/1854.
Comment: FYI, I have read that using tums (an anti-acid of any type) makes the urine palatable...since then I keep a roll in my car...you never know when you may have to walk miles to get to your children ;)
Answer: Assuming you don't have a genitourinary tract infection, fresh urine should be sterile, the problem is that it is a waste product which, apart from making it not taste very nice, means that consuming it will increase the concentration of waste in your body which will require an increased volume of water to absorb and subsequently excrete, resulting in you being more dehydrated. You could distil urine using a solar still to overcome this problem, such as this method, however, I wouldn't expect a filter (at least those designed for outdoor activities) to remove the salts and other waste compounds found in urine.
I've also heard of using urine to moisten your lips to lessen the symptoms of dehydration.
Comment: In addition to moistening your lips, Bear Grylls demonstrated its use in cooling your body if needed, by soaking your shirt. He says it doesn't smell nice, but it works.
Comment: Urine is not sterile. http://www.popsci.com/urine-sterile-drinking-pee
Answer: Copy and paste from the answer here: Is it a good idea to drink your own urine in a survival situation (Skeptics SE)?
Summary: You can do it, as a last resort, but it's dicey.
The US Army doesn't think it's a good idea and lists it on its "Do NOT drink" list, stating in its Field Manual that it "contains harmful body wastes" and that it is "about 2 percent salt." Several other resources seem to agree, all indicating that it will increase your rate of dehydration. (Warning: the popular science link is not fun to open.)
If it's your only source of water, it's likely that the US Army's recommendations of how to purify polluted water for consumption also applies to urine:

If polluted water is your only moisture source, dig a small trough outside
the hole about 25 centimeters from the still's lip (Figure 6-8). Dig the
trough about 25 centimeters deep and 8 centimeters wide. Pour the polluted
water in the trough. Be sure you do not spill any polluted water
around the rim of the hole where the plastic sheet touches the soil. The
trough holds the polluted water and the soil filters it as the still draws it.
The water then condenses on the plastic and drains into the container.
This process works extremely well when your only water source is salt
water.

Other sources, which support my memory on the matter, indicate that it is at best a short term solution. For example, in a Slate article named The Yellow Liquid Diet, the author says that the waste might eventually "cause symptoms similar to those brought on by total kidney failure":

How long can you survive by drinking pee?
An extra day or two, at best. A healthy person's urine is about 95 percent water and sterile, so in the short term it's safe to drink and does replenish lost water. But the other 5 percent of urine comprises a diverse collection of waste products, including nitrogen, potassium, and calcium—and too much of these can cause problems. When you drink your own pee, all the stuff that your kidneys had attempted to excrete comes right back into your stomach, and much of it ends up back in your kidneys. After several days of this, your urine will become highly concentrated with dangerous waste products, and drinking it can cause symptoms similar to those brought on by total kidney failure. At that point, you're doomed either way—from dehydration on the one hand or renal meltdown on the other. (Even if one could filter out most of the unwanted products in urine, the cycle would not be sustainable for long. In addition to what he or she pees out, the average human excretes about half a quart of water a day through sweating and exhaling.)

However, drinking urine for survival has been attempted successfully before.
For example, in 2008, a Chinese man by the name of Shen Peiyun survived six days by lying still and drinking his own urine, which is solid evidence that it won't kill you at least some of the time.  While it is not necessarily fatal, it doesn't mean it isn't harmful.  For instance, in the case above, no expert has asserted that he would have died without drinking his own urine.
Comment: I had not previously thought about trying to purify urine before consumption.  This is helpful, especially with a diagram.
Comment: @DonBranson -- Assuming you have green vegetation, yes.
Comment: If you have the gear to make a solar still such as this, you can also set it up in the sun to extract moisture from green vegetation.
Answer: Urine is normally sterile (barring urinary tract infections) - so, from bacteriological stance, fresh urine isn't going to hurt.
The problem is - urine is a waste product, and so is full of stuff that your body wants to be rid of. Worse, as you get more dehydrated, your body produces more concentrated urine. That said - as a short term measure to keep hydrated, it can be drunk.
I remember my military survival training - we were instructed how to make a filter using a sock filled with dirt. It isn't the most efficient filter, and probably tastes pretty awful. If you have a ceramic filter, that might be better, but I'd imagine there's still be a flavour.
Comment: Urine is not sterile. http://www.smithsonianmag.com/smart-news/turns-out-urine-isnt-actually-sterile-180954809/
Comment: Still, in a pinch, possible later infection is preferable to imminent death by dehydration
Comment: I don't disagree; the rest if the answer is valid with or without that incorrect assertion.
Answer: Rectal infusion
I have read of a case where people survived in a life raft not by drinking their own urine, but by rectally infusing urine through a tube.
This is apparently quite a safe way to get your body to extracting the water in a fluid without absorbing all/too many of the potentially dangerous waste products.
Turns out one of the survivors was a nurse and new how to place a rectal catheter - lucky them. :P
I can't find the actual link to these survivors story, but here is an article describing rectal fluid infusion as a means to rehydrate people: Emergency rectal infusion of fluid in rural or remote settings

Is drinking urine safe?


One camera unable to focus in low light, different camera, same brand model, has no problem

Question: With a Canon T3i mounted in a camera/flash tower, the camera cannot focus in low ambient light with dark complected subjects. All the settings are preset as this is being used in a drivers license office in a booth. It works fine otherwise. I swapped out the camera tower with another (different Canon T3i, different flash tower) and had no problem in same dim light, same dark subject. Why does one camera have this issue and not the other? Same make, model, lens, settings.
Comment: Maybe relevant: https://photo.stackexchange.com/questions/103282/why-is-my-canon-70ds-liveview-autofocus-much-worse-than-the-viewfinders with all its linked questions
Answer: One possibility to check - is the AF assist light turned off or failed on the problem camera?  You say the settings are the same - have you checked all of them, including ones hidden in the setup menus (which is where the AF light on/off one is usually found) and the selected AF point/mode?
Some of the menu settings (at least on my Nikon, but I suspect Canon is the same) don't show anything in the viewfinder or top panel LCD, so it can be easy to miss changes unless you go through all the menus :)
The relevant menu on a Canon 70D, yours should be close:
Comment: Thank you. I will check that. I'm thinking that maybe the preset instructions in the drivers license program doesn't actually take that setting into account.
Answer: If you changed the flash at the same time you changed the camera, the the AF assist light in one of the flashes could be not working properly. Try using the same flash with both cameras to rule out or confirm that there is a problem with one of flashes.
Comment: I didn't swap the camera out of the tower, I just removed the mounted camera tower with another but I will take a look at that AF assist setting in the camera when I pull it out of the tower, especially since so far this is the only camera in the state that has shown this issue.  Thank you.


Can anyone suggests some basic readings for video processing?

Question: Actually, I am new to this field and would like to work on a project in Video processing. I have a little background in Image processing but would like to study further in video processing. So, If anyone could suggest some readings as pre-requisites for video processing.
Comment: [Computer vision algorithms and applications](http://szeliski.org/Book/) is a fine place to start.  It is a big field and this is a nice free survey.
Answer: I recommend Video Tracking: Theory and Practice  as comprehensive overview of what have been done in this area for last 15 years. Also, 3D Computer Vision: Efficient Methods and Applications for quick understanding useful algorithms.
This books will be a good start, but when you have enough knowledge, you should start looking into research papers, because information there is more updated than in books.


Estimation nuclear force between proton and neutron in deuteron

Question: Is there an estimation of nuclear force between proton and neutron in deuteron to say What is the strong nuclear force between them?
1N?
10N?
100N?
1000N?
Answer: It's about 10-100 times stronger than the electromagnetic repulsive force between two "nearly touching" protons because the dimensionless "strong coupling constant" is of order one while the corresponding "fine-structure constant" is $1/137.036$.
The electrostatic force is
$$ F = \frac{e^2}{4\pi\varepsilon_0\cdot (1\,{\rm fm})^2} = \frac{(1.602\cdot 10^{-19})^2}{4\pi\cdot 8.85\times 10^{-12}\cdot 10^{-30}} {\rm N} = 230\,{\rm N} $$
Amusingly enough, it's a reasonable force we know from the everyday life. The strong force could be 10,000 newtons, still reasonable – like the weight of one ton. But one must realize how extreme the force is in the proportion: the whole force doesn't act on a car but it acts on one elementary particle.
Comment: I've found an unpublished theory that would account for the strong nuclear force.
my calculation is close to your estimation
Answer: I have a formula able to calculate the binding energy of the deuteron: it needs only to apply the electric and magnetic Coulomb's laws to the deuteron. The formula is the same as above, but with the potential instead of the force, needing the empirical radius:

A better theory, e.g. electromagnetic, gives the correct result by using only the fundamental laws and constants shown in my paper:
http://www.aemjournal.org/index.php/AEM/article/view/218/


Assignment due dates

Question: Last term I taught a large undergraduate course. I had assignments (online) due a week after we finish a chapter. There were two minor problems with this. The first was that I had to deal with students who enrolled one, two or even three weeks into the term and gave them extensions of the first several assignments, which involved logging into the website, finding the student, setting his/her new deadline and answering the student email. Secondly for some of the chapters that take more time than others, some students would bombard me with requests for extensions. So I am thinking of adopting a different method next time. Specifically, I plan to divide the 12 chapters into 4 modules with 3 chapters in each. Each module has a deadline for all 3 chapter assignments. I am hoping this would give students more flexibility on their time management, and have a little more time working on those long assignments. It also saves me from handling those extension requests because of late registration or others. The potential peril I can think of is that some students may not start on the assignments until the last minutes and it would be very difficult to crash 3 assignments within a short time. I would appreciate other thoughts on the pros and cons of this method.
Comment: Don't slip on deadlines.  Tell up front that due dates are unchangeable, and stick to it.  In the rare case of death and other calamities, use the schools normal system for getting dispensations.
Comment: @GenericJam: I tried "late says" for a year and found it impossible to manage, even for classes of 35-40.  Except for the first assignment, you have to set due dates individually, depending upon how many late days have been used, or allow everyone to submit assignments late, but some won't get credit because their late days are gone.  They'll whine.  Now I say, "Due means due."  The online system will not accept assignments after the due date, and I do not accept work by email or on paper.
Comment: I took a class this semester where the prof had 'slip days' where every student had the same number of 'slip days' that they could use on any of the assignments but there was the same number for the whole course. So if you have three slip days you could spend one on the first assignment and hand it in one day late with no penalty and still have 2 more to spend on future assignments. This helped take a lot of the pressure off of a hard deadline while letting you know that it still needs to get submitted as soon as possible.
Comment: It's been a while since I attended a university, but none of my professors were so liberal with extensions. One tactic that might reduce the number of extension requests you get would be to stop granting extensions except in the most extreme cases. Students will learn that there's no point in asking for an extension unless they really need one.
Comment: @BobBrown Was thinking more of death in the family.  You may want to add a note on becoming a zombie.
Comment: @ThorbjørnRavnAndersen: I tell students I won't hold them to the deadlines if they're dead.
Answer: I would recommend not batching up assignments to a common deadline, because that makes it even more challenging for students to manage their time properly. If someone waited to the last minute on an assignment in the prior regime, now they'll be waiting until the last minute on 3 assignments and be in even worse shape -- compounded by the mental effort in prioritizing which one they should work on first. Under the original regime, they have more opportunities to engage in this cycle and get feedback on how their study skills work for them.
My response to these types of problems is to have a blanket policy of dropping a certain number of grades from consideration; for example, in my classes, there are 12 weekly online quizzes, and the lowest 3 are dropped for each student at the end of the course. There are absolutely no makeups or past-due work allowed for any reason, which massively clears out my own time (absolutely no chasing students or managing late work after my grading process is completed). Plus, the "drop N grades" is automatically supported by the Blackboard management system.
In my classes, I don't give any special allowances to students who first show up later in the semester (but this may vary for your institution). I had a student join my class in the 2nd meeting last week, and he had already missed the first quiz submission; he asked "Can I make that up?", and the answer was simply, "No", and being pointed to the syllabus for the drop allowance, which in the years I've been using it has always been accepted quite gracefully. In my opinion, it's the most efficient use of your time as an academic.
Comment: Thanks. Your comments are very helpful. I like your approach of writing the no-make-up policy into the syllabus combined with dropping some lowest scores. Believe it or not, I actually did think that it is my obligation (and to be fair) to give extension to students who join the class late because the university keeps registration open for the first several weeks and some students in the waiting list do not have chance to get in until someone withdraws.
Comment: "students who join the class 1-3 weeks into the semester (frankly, that's just crazy for a student to think that's feasible)" - the OP does not specify whether this is the case here, but especially in first semesters of admission-restricted majors, it is quite common for people to join only after the first few weeks because of the waiting list issue @sismin mentioned in their comment. I agree it is crazy, but it is rarely the student's fault in this situation, and rather that of uni administration.
Comment: @O.R.Mapper When my classes are full, I require students who cannot register but want to take the class to submit homework, just as if they were already registered. Even for students that add late, their first few homeworks count, they were still due on their original deadline, and I do not give extensions, ever. (But like Daniel, I drop each student's N lowest homework scores, for some small value of N.)
Comment: The enrollment 1-3 weeks into the semester happens in at least one of my classes (a semester) as well - particularly when I moved to graduate work. This is also due mostly to wait-lists and lab cancellations or other issues forcing class changes
Comment: I lightly edited the 3rd paragraph to account for different institutional policies on late registrations. At our institution, there's only a 1-day period for possible added and dropped classes when the semester starts. It was good for me to see these comments about wait lists possibly being used as 3 weeks in (which itself seems crazy to me), as I was unfamiliar with policies like that.
Comment: @JeffE: I see some practical obstacles as students who aren't registered yet might not have access to the online systems for homework submission. These can be worked around with some extra work by the lecturer, though. The more important issue, however, is that students are possibly on several waiting lists and probably have already started attending classes for another major/at another university until they get admitted to their first-choice major at their first-choice university. They probably cannot do homework for all classes from all majors they are on waiting lists for at a time.
Comment: @O.R.Mapper _students are possibly on several waiting lists_ --- I've never seen that happen to the extreme you're describing, but even if it does happen, I don't see how it's the instructor's problem. (If you're admitted to the major in the middle of the term, start taking those classes _next_ term.)
Comment: @JeffE: If every instructor went that route, wouldn't that mean the student cannot take *any* classes during their first semester? Also, some classes have restrictions such as "must be passed before the end of the third semester" and are offered only once a year, so not taking the class in the first semester means not studying. As that is probably not the intended result by uni administration when admitting the student, this seems like a disagreement exclusively between the instructor and uni administration. If a student who fulfils the admission requirements cannot be admitted but has to ...
Comment: ... be put on a waiting list because university resources are not sufficient to admit everyone who fulfils the requirements, I find it hard to blame the student for that. If the student is admitted with a delay due to their own failure, e.g. because they submitted their documents late, it is of course a very different case, and I would find your policy quite reasonable.
Comment: _wouldn't that mean the student cannot take any classes during their first semester?_ — Only if the university is stupid enough to require completely different classes for every major (as opposed to all STEM majors taking calculus, physics, and chemistry, for example) _and_ restrict enrollment in those required classes to current majors.
Comment: @O.R.Mapper And I'm not _blaming_ the student.  I'm setting limits—with both the student and the university—on how flexible I'm willing to be as an instructor.
Comment: @JeffE: Mathematics classes are indeed sometimes individually adapted to each single STEM major (and physics and chemistry are not part of the curriculum for most STEM majors in my place), but that may be location-specific and indeed not problematic if these classes are not admission-restricted. However, most importantly "restrict enrollment in those required classes" tells me you are referring to enrollment per class. In all of my comments here, I am referring to enrollment *into a major* as a whole. Of course, different options exist for issues about enrollment into a class, which does ...
Comment: ... does not even have to involve university administration at all. Under that changed premise, your initial suggestion seems viable.
Answer: In your case, I'd try a larger number of smaller assignments, spreading the work out rather than bunching it up.  Your grading load doesn't change, but the students can manage their time more easily.  Put "due means due" in the syllabus and set a hard cut-off in the learning management system.
No matter what you do, the poor students will wait until the last minute, turn in rushed work, and earn poor grades.  Like you, I have a desire to help such students, but I haven't found anything that works.  By having more assignments, each one is worth less, and perhaps some students will learn after the first couple of rushed assignments earn bad grades.
For students registered late, which is really a different problem, set a time from registration date by which they must be caught up, put it in the syllabus, and set the LMS to enforce it, which you can probably do easily on an individual basis.
Be sure to see my comment on "late days."  It's a comment to the original question.
Comment: Anecdote: Last semester I tried encouraging students not to procrastinate by allowing extra credit for assignments turned in six or more hours before the due date and time.  Didn't work.  The people who were going to earn grades of A anyway got the extra credit and a few others turned in hastily-completed work for which the extra credit was little help.
Answer: As a current engineering student, third year, I would be rather wary of the idea of grouping all the assignments together under a common due date. Especially if, the course in which this takes place is a first or second year course. This is because younger students often manage their time rather poorly.
As Daniel R. Collins noted, attempting 3 assignments the night before their due date can be a discouraging experience and yield dismal results. I would also add that, as a Prof, you should set the timetable and not the students. It is very annoying to see a lenient teacher extend a deadline because a student is not on time. Especially so, if said student is behind because they are not working on the assignment and is using their time for other activities. After all, part of the skills one is to develop through a bachelor degree is time management.
Lastly, you should check either with your faculty or department if they have a late work policy, if so you should reference it in the syllabus, if not get them to establish one.
Answer: I've tried both methods for our introductory classes.  To be honest, I haven't seen very much difference.  The students who will wait until the end to do all three sections are going to be the ones that will wait until the end to do each individual section.  In all cases, you're getting rushed work that they're likely to hand in late, except that they're spreading their work out (better learning, mayhaps) but sending you more e-mails, or they're cramming their work but sending you less e-mails.
To help them with time management, you could give them estimated completion times.  Even if they're much faster or slower than the estimate, they can figure the others out relatively speaking after doing one or two ("Professor said section 2 takes two hours and section 3 takes four hours.  I did section 2 in only an hour so I can probably do section 3 in two hours").
To avoid the e-mail bombardment, I'd consider instead just instituting a general late policy.  It could be one that slowly penalizes more (so that one day late = 10/20% off, two days = 20/40%), or a one-off decrease (50% off), but they key is to balance it: too punitive, and they'll still e-mail you, too easy, and they'll take too much advantage of it.  Or you could say "I will permit one module to be handed in up to X days late".
Answer: As others have already given good answers for the 1-3 week late admissions problem (dropping lowest grades and/or a blanket reduction of points for late work). I will offer another option for dealing with the problem of too many extension requests for homework assignments when dealing with online courses.
A policy which has seemed to work well during my studies was one where professors in common undergraduate requirement courses agreed on alternate due dates that mimicked the due dates of on campus courses or simply set their due dates to match on campus meetings of the same or a similar class. It seemed to help new students budget their time more effectively - keeping all the assignments from each class being due on the same day (Sunday) - and did not seem like a lenient policy as it was essentially the same amount of time to work on assignments as it would be for on campus students (may get an extra day or so depending on when one posts the assignments online).

Assignment due dates


Can the supernova remnant SN 1572 be observed by amateur astronomers?

Question: The SN 1572 remnant, also called Tycho's supernova remnant, is beautiful in X-ray images. It seems to be rather dim in visible light. Are there any amateur photographs of this object? How long are the exposure times needed to get a nice picture?
Answer: As you say, SN 1572 is not very bright in the optical.  There are some Hα regions that have been observed with world-class optical telescopes, but they do not look like the X-ray and infrared images that you normally see.  In fact, images from the Palomar Optical Sky Survey 2 (with a limiting magnitude of ~22) do not reveal any nebular emission from this object at all:

Therefore, the optical emission must be fainter than 22nd magnitude.  I do not think there are amateur photographs of an object this faint and I believe a CCD on an amateur telescope would saturate from noise before revealing any of the nebular emission.
Answer: It does not appear to be practical to photograph with amateur equipment.  According to the Wikipedia article the remnant was viewed visually with Palomar telescope.  Links to studies of the remnants were done using 2m + telescopes.  So trying to get a visible light photo would require an extremely large telescope.
This table does not list a magnitude for the remnant (B CAS) http://maps.seds.org/Const/Data/cassiopeia_tab.html  So it appears that it might be extremely faint.
And this list of deep sky objects does not list the remnant either.  http://www.dibonsmith.com/cas_con.htm
Answer: There are two faintly visible areas of nebulosity on the above image taken from the Palomar Sky Survey, that correlate with the remnants of Supernova 1572. Sidney van den Bergh imaged this object in 1970 with the Palomar 200 inch telescope, comparing this with similar images taken by Walter Baade in 1949, 1955 and 1957. His findings were published in the Astrophysical Journal (168: 37-39, 1971 August 15). Using my 32" telescope, two areas of nebulosity were recovered visually in August, 2006. These were at: 00h 25m 06.9s, +64d 11m 37s; and 00h 25m 51.4s, +64d 09m 19s.


How has Christianity influenced Hindu thought or practice?

Question: What are examples of Hindu philosophy or practice being influenced by Christian thought, tradition, or practice (e.g. the Brahmo Samaj)?
Comment: Brahmo Samaj is not inspired by Christianity. They worship Brahman as per Vedas!!!
Comment: Christian Ashram movement remains a Christian sect & not a Hindu sect. It was rather Hindu influence on Christianity and not the other way around.
Comment: While it is true that there have not been large-scale impacts on the practice of Hinduism, there are communities of practice (especially in southern India) that have syncretized Hindu and Christian practices, e.g. by adding Jesus Christ to the pantheon. There are also things like this: http://en.wikipedia.org/wiki/Christian_Ashram_Movement.
Comment: @Anirvan If I get some more time to research the topic, I will. At the moment, my understanding of the interaction between Hinduism and Christianity is too fragmentary to really be useful.
Comment: As senshin pointed, there some organizations in southern India which use the names like Ashram and Dhyan. People are mainly attracted by such names.  Actually nothing is related to Hindu culture in those organizations. They used to tell, your savior has come, join in Christianity, escape from disbelief and misdeeds. The soul purpose of these organizations is Conversion.
Comment: @senshin, thanks for your comment. Could you post that as an answer to the question?
Comment: Hindu religion is the oldest one. All other religions came out of it and with passage of time became separate religions
Answer: Hinduism was not influenced by Christianity, rather it predates it.
The 2 religions have completely incompatible world view.
There has been lots of effort put on by European Indologists to paint Vivekananda & Ramakrishna Mission to be copying Christian values of service & charity.
The Book Indra's Net proves with philosophical & historical evidence that Vivekanda's ideology of seva originated from the Upanishads & not from Christianity. The basis of Seva(service/charity) is "Tat Tvam Asi" principle which means "you are that". You are same as your neighbor. The basis for this philosophy predates Christianity.
Comment: It's not reasonable to categorically say that there are absolutely zero examples of Hindu philosophies being influenced by Christianity — in fact it's hard to make _any_ categorical statement about a religion as diverse as Hinduism!

The question itself gives the example of the Brahmo Samaj. Brahmo leaders like Keshub Chandra Sen were very explicitly influenced by Christianity.
Comment: @Akshay, it cannot be an one way road. Hinduism accepts truth can have different versions while Christianity claims exclusivity. I.e it does not accept Hindu version of truth. This is also part of the difference in the world views.  Also see my answer for another question: http://hinduism.stackexchange.com/questions/881/can-one-be-a-hindu-that-worships-through-christ/905#905
Comment: @Anirvan Perhaps what you're looking for is how Christianity has influenced modern Hindu sects or movements. The downvote isn't appropriate -- your question needs to be more refined.
Comment: Why do you say that the two religions have completely different world views? [Just recently](http://hinduism.stackexchange.com/questions/3225/can-islamic-beliefs-be-accommodated-in-the-light-of-vedantic-beliefs) there's been quite a lot of discussion on this site about how accepting Hinduism is of other religions (i.e. Hindus believe all other religions are equal paths to God). Why would you call Christianity incompatible?
Answer: There is a fundamental difference in religious styles of the West and the East.
Western religions (Islam and Christianity) have a digital view of the world. Creator and Creation.
Hinduism in its core believe the Created and Creation are one and the same.
Western religions believe in preaching. Hinduism believes in understanding and experiencing.
Western religions have this view of "Not my way, or the highway". Hinduism treats "My way", "Highway", "Some other way", "No way" as different ways.
Western religions could have been influenced by Hinduism, since the texts and scriptures existed at the time the Western religions came up. Hinduism is unlikely to have been influenced by Christianity.
Cultural influences of the West on the East, did occur, but religious influences were very limited, as the two religions have markedly different styles of approach towards God.
Comment: "Hinduism in its core believe the Created and Creation are one and the same." Not true--the complete negation of this statement is the foundation of Dvaita Vedanta.
Comment: Not exactly, Brahman could exist without the universe, but the Universe could not exist without Brahman.
Answer: Namaste
Hinduism has vast literature and every component of "universe" is explained in detail and to go through such literature, one requires many births and then to understand it many many more.
Christianity & Islam are preachings of a single person i.e. single awakened person, within a very very limited life span
To make mountain of such preachings and to talk of "entire universe" with a single book, is far fetched.   Gita is also a small book, however, the depth of sacred text mentioned in GITA is far superior to Bible and / or Islam.
Nothing in Hindu society nor practises of any hindu individuals is influenced either by Christianity or Islam.
Saint / Sage Ramanuja himself "converted" shudras to brahmin, saying there is no casteism defined in hinduism (i.e. no cultural discrimination of any type)
Comment: You should cite sources.  By the way, Ramanujacharya wasn't against the caste system.  He just thought that if you've performed Sharanagati or surrender to Vishnu, then your varna dharma or caste duties no longer apply.  But he thought that those who haven't performed Sharanagati still have to follow their varna dharmas.


Why is RSA encryption key based on modulo $\varphi(n)$ rather than modulo $n$?

Question: While calculating RSA encryption key we take modulo $\varphi(n)$ rather than modulo $n$. I can't understand why it's done this way.
Comment: The intuition that computing in the ring $Z_n$ implies exponents can be considered in that ring is misguided. $Z_{\varphi(n)}$ is a more appropriate ring for exponents. $Z_{\lambda(n)}$ with $\lambda(n)=LCM(p-1,q-1)$ also works, and is what [PKCS#1](ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.pdf) uses.
Answer: Firstly, a number theory textbook might well help here. I own An Introduction to the theory of numbers which will give you a grounding in this and many other number theory topics which crop up in crypto. It's not my favourite book notation-wise, but in terms of topics covered it is very thorough.
Now, on to what you need help with. There exists a theorem called the division theorem that says any number $n = pq + r$, with the constraints that $n > q > r \geq 0$. In plain words, any number $n$ may be represented by a quotient $q$ (possibly multiplied by a number $p$) and a remainder $r$. An example would be to say that $13 = 7 + 6$ - you recognise this in that $13/7$ could be written as "$1$ remainder $6$".
Modular arithmetic is related - let's start off with $13 \equiv 6 \mod 7$. Intuitively, modular arithmetic is often explained as "you take the remainder and that is the result" which isn't far from the truth - what we actually say is that $7$ and $13$ are part of the same congruence class - that is, $q$ and $r$ ($7$ and $6$) remain the same and the congruence class is made up of all the $n$ for all the $p$ possible. So for $p=2$, $n = 2*7 + 5 = 19$. So $19\equiv 5 \mod 7$ (feel free to check it!).
So, you're concerned with the use of $\mod \phi(n)$ in RSA - well the expression usually given is $de = 1 \mod \phi(n)$. We can re-write that in division-theorem form as $de = k\phi(n) + 1$ - where $k$ is $p$ from the previous example, but renamed so as not to be confused with the prime $p$ that forms $n$.
Now observe what you may have learnt about exponents - that $x^{a+b} = x^ax^b$ and that $x^{ab} = (x^a)^b)$ If you're not convinced, pick numeric examples. Now, a message $m$ raised to the power $de$ is $m^{de}$ - but we have a different expression for $de$ already - that is - $m^{de} = m^{k\phi(n) + 1}$. This can then be written as $(m^{\phi(n)})^k \times m^1$.
There is a very good reason for this form being desirable - namely the Euler-Fermat generalisation to Fermat's Little Theorem, which states that:
$$a^{\phi(n)} = 1 \mod n$$.
Hopefully you should see that our manipulating the algebra to get $m^{\phi(n)}$ in it is not an accident at all - since under $\mod n$, $(m^{\phi(n)})^k \times m^1$ becomes $1^k \times m^1 = m$. This is what makes RSA work the way it does.
I'd also like to address the point fgrieu has raised in his comment, since it is important. The requirement is for the private key is such that $de = 1 \mod \phi(n)$ - or $de = 1 + k\phi(n)$. Clearly, $k$ can be any number we like - any congruence class for which this relation holds will work.
The lowest common multiple of two numbers is the smallest possible number such that both these numbers divide it - for example, the lowest common multiple of $4$ and $6$ is $12$. n this case we observe $4$ divides $12$, as does $6$. Now, the lowest common multiple of $p-1, q-1$ is a number such that both $p-1$ and $q-1$ divide it - well $\phi(n)$ is one such number, for starters! However, (thanks to Poncho), we can say that it is not the smallest possible number. To explain this, consider that $p$ is an odd number and that odd numbers can all be written of the form $2k+1$ for some $k$. If we subtract one, we are left with an even number which will have at least one factor of $2$. Therefore, since $p-1$ and $q-1$ are both even and both have a factor of two, their product ($\phi(pq)$) will have two factors of $2$ at the least, which is 2x what is necessary (at the minimum). More generally, the definition of a lowest common multiple uses the fundamental theorem of arithmetic to demonstrate that the lcm is in fact equal to the product of the maximum power each prime is raised to in each number's prime expansion - eurgh, yes? Well, let's look at that. I chose $4$ and $6$ before - now the prime expansions are $4 = 2^2$ and $6=2\times 3$. Taking the maximum exponentiation of each prime, $2^2 \times 3 = 12$. However, if we did $4\times6 = 2^2 \times 2 \times 3 = 2^3 \times 3$ we see we have gained an extra, unnecessary factor of $2$.
It turns out the Euler-Fermat generalisation can be generalised again - to the Carmichael theorem which states that:
$$a^{\lambda(n)} = 1 \mod n$$
Where $\lambda(n)$ is the smallest such integer where this expression is true. A slight detour - $\phi(pq)=\phi(p)\phi(q)$ and since $\phi(p) = p-1$ that is how we end up with our definition of $\phi(pq)=(p-1)(q-1)$. Now, in the general case, it turns out that $\lambda(pq) = lcm(\lambda(p), \lambda(q)) = lcm(p-1, q-1)$.  By the same reasoning as the case with $\phi(pq)$, $de = 1 \mod \lambda(pq)$ allows us to invert $m^e$ back to $m$ under $\mod n$.
fgrieu has used the term "Rings" - if you're interested in those, I highly recommend Rings, Fields and Groups which is possibly the best Maths textbook I have ever read. It's about (abstract) algebra and also covers some of the number theoretic points, but not as many as a pure number-theory textbook does.
Comment: One note: $\phi(n)$ will never be the smallest possible number (assuming that n has at least two distinct odd prime factors, and so $lcm(p-1, q-1) < (p-1)(q-1)$ will always hold (because both (p-1) and (q-1) both have 2 as a factor).
Comment: @poncho ah of course. I'll edit that in. I was focusing too hard on my explanation and missed the obvious. Thanks :)
Answer: In RSA, the public key is $e$ and private key is $d$, if:
$ed=1 \mod{\phi (n)} $
To rearrange:
$d=e^{-1} \mod{\phi (n)}$
In an public key system, it should be the case that one cannot compute the private key from the public key. Therefore, at least one of the variables should be kept private. In the above equation, everyone knows $e$, everyone can compute inverses, and if you were to use $n$ as the modulus, that would be known as well, allowing anyone to compute $d$.
The reason $\phi (n)$ is used as the modulus is that it is assumed to be hard to compute $\phi (n)$ given only $n$, but it is easy to compute if you know $p$ and $q$ such that $n=pq$: $\phi(n)=(p-1)(q-1)$. Essentially, the easiest way to compute $\phi (n)$ is to factor $n$ into $p$ and $q$, and then compute it.
There are deeper reasons why it is specifically $\phi (n)$ but this should get you started.
Comment: It took the liberty to reverse the implication in the first statement. In the other direction, it was incorrect; check with $n=55$, $e=3$, $d=7$ which forms a valid RSA key, yet with $e\cdot d\not \equiv 1 \pmod {\phi(n)}$.
Comment: Why there is no congruence?
Comment: @user5507: $e\cdot d \equiv 1 \pmod {\phi(n)}$ is a sufficient, but not necessary condition for $(n,e,d)$ being a working RSA key. In my counterexample above, it happens not to hold. When $n$ is the product of distinct odd primes $(p,q)$, the necessary and sufficient condition for $(n,e,d)$ being a working RSA key is $e\cdot d\equiv 1 \pmod {LCM(p-1,q-1)}$, and in my counterexample this congruence $\pmod {20}$ holds.
Answer: One usually wants to get back the plain text by decrypting the cipher text obtained by encrypting the plain text.
This works for RSA only by taking $d = e^{-1} \bmod \varphi(n)$ and NOT with $d = e^{-1} \bmod n$.
Security issues don't matter if the method does not work.
Answer: Better to view $ed \equiv 1 \pmod{\varphi (N)}$ as $ed=1 + k\varphi (N)$, then when we exponent message as $m^{ed}$ it becomes $m^{1 + k\varphi (N)}$, where $k\varphi (N)$ part strips out because of Euler's theorem $a^{\varphi(n)} \equiv 1 \pmod {n}$, so we get $\space m(m^{\varphi (N)})^k \equiv m$.
So if you use $ed \equiv 1 \pmod{N}$ it will be $ed=1 + kN$ which will make Euler's theorem not applicable.
Answer: I understand the question as follows:

Why don't we compute the private key modulo $n$ instead of modulo $\varphi(n)$?

The other answers already imply this, but here in short:
As Someone's answer states, the decryption wouldn't work: $x \neq (x^e \mod n)^{e_{n}^{-1}}$, where $e_{n}^{-1}$ is the inverse of $e$ modulo $n$ (the secret key).
From Euler's theorem: $a^{\varphi(n)} \equiv 1 \mod n$ we know $a^{e\mod\varphi(n)} \equiv a^e\mod n$.
But $a^{e\mod n} \not\equiv a^e\mod n$ (generally).
Therefore, $a^{ee_{\varphi(n)}^{-1}} \equiv a \mod n$, but $a^{ee_{n}^{-1}} \not\equiv a \mod n$.


Is Bane just an agent in Talia's plan, or is he the true mastermind?

Question: At the end of the movie, it is established that Bane would die for Talia, and that she is dedicated to completing Ra's Al Ghul's plan to destroy Gotham. It seems that Bane takes point as "Gotham's reckoning" to hide Talia's involvement and true identity. He seems to listen to her, and she takes control to finish the job at the end (the other members of the League seem to recognize her authority). She is also the one that has the detonator; so, she seems to be controlling this plan overall. She seems to be the hidden hand that controls the plan, and that she was the one that wanted to complete Gotham's destruction for her father. So, is Bane just following the orders of the child he is dedicated to protecting? Or, did Bane really plan everything, and Talia is just there to be a part of her father's original plan?
Answer: The fact that she has the detonator pretty much implies that she is the one in charge (you in fact have pointed out the major key facts in your question supporting that theory). if you look at the issue Bane has nothing what so ever to do with Gotham or its reckoning he was even kicked out of the league. But for Talia it was more personal she knew Batman was responsible for her father's death and the reason to avenge him by completing Ra's Al ghul's plan in front of Batman by bringing Gotham to an end.
Bane was merely very loyal to Talia and was very much wiling to die for her plan. Her role in the plan was as much as important as Bane's was to get the confidence of Bruce wayne and Lucius Fox to get to know as much as possible about the Reactor while Bane was responsible for all the muscle work in bludgeoning Batman and Gotham to submission.
Answer: There's also one bit which should answer this question. When Talia pulls the knife out of Batman and is about to walk away with the detonator, she plainly tells Bane to hold him until the explosion goes off 'so he can feel the heat.' Bane, being someone who has no qualms about snapping someone's neck, would not have taken that order so willingly unless he was, indeed working for her.
Comment: Until she leaves the room and then he decides to kill him anyway.


where to get Tattvasiddhi Śāstra

Question: Anyone knows where I can get my hands on Tattvasiddhi Śāstra by Harivarman, also known as Satyasiddhi Śāstra also known as Prodbhūtopadeśa also known as Chengshi lun. Paper or electronic format is fine.
Answer: It's available for download here at Scribd.com.
But it looks like one must buy a subscription in order to read their books.
Comment: Thank you. The quality of the scan is not so good but it is readable.
Comment: No problem:) It's a difficult book to find. Apparently it cannot be bought anymore and no libraries seemed to have a copy of it. I hope you can get through it in its current form.

where to get Tattvasiddhi Śāstra


If Buddhas don't feel bliss, what is the purpose of attaining nirvana?

Question: If I have zero feelings won't I be a dead robot? And how would I have love and compassion for beings without feeling?
Comment: Nibbana is the end of suffering. That is the need that most practitioners seek to meet. But the attainment of nibbana also meets another need: The need to see things as they actually are. Nibbana cures the mind of the "learning disability" which is the search for bliss. Seekers of bliss are seeking a coping mechanism for suffering. This is unskillful. If you eliminate suffering, the need for a coping mechanism disappears.
Answer: From AN 9.34:

Ven: Sariputta: "Reverends, extinguishment (Nibbana) is bliss!
Ven. Udayi: "But Reverend Sāriputta, what's blissful about it, since
nothing is felt?"
Ven. Sariputta: "The fact that nothing is felt is precisely what's
blissful about it.

Sukha or happiness for an unenlightened person is experienced when encountering pleasant feelings (from the six senses, including thoughts and the intellect) or when encountering the cessation of painful feelings (from the six senses).
But for a Buddha or arahat, sukha or bliss (in this context) is experienced when encountering neutral feelings, no feelings and Nibbana.
Please see this answer for commentaries by Nyanaponika Thera. The supporting suttas are MN 44, SN 36.5 and AN 9.34.
In addition, the Buddha and arahats can experience emotions or states of mind which are not tainted with the three poisons of greed (lobha), aversion (dosa) and delusion (moha). This includes the four brahmaviharas of loving kindness (metta), compassion (karuna), empathetic joy (mudita) and equanimity (upekkha).
The brahmaviharas are considered skillful states of mind.
An enlightened person is not an emotionless person. It's simply a person who does not have cravings, does not have plans to fulfill sensual cravings, does not have plans to become something and does not become afflicted with negative states of mind that arise as a side effect of having craving. Also please see this question.
The purpose of Nirvana is permanently ending suffering - it's not about experiencing bliss.

Adding on based on a comment by Ruslan, the Buddha did have his five aggregates (form, feeling, perception, mental formations and consciousness) intact and functioning without being tainted by the three poisons, after attaining Nibbana, and could still experience pain and pleasure, but did not suffer from it. Please see this answer for details.
Comment: Iti2.17; "Here a bhikkhu is an arahant, one whose taints are destroyed, the holy life fulfilled, who has done what had to be done, laid down the burden, attained the goal, destroyed the fetters of being, completely released through final knowledge. *However, his **five sense faculties remain unimpaired**, by which **he still** experiences what is agreeable and disagreeable and **feels pleasure** and pain. It is the extinction of attachment, hate, and delusion in him that is called the Nibbana-element with residue left.*"
Comment: @Ruslan I added an additional note, pointing to another answer that tells the same.
Comment: @Ruslan Yes. You are right.
Answer: Being enlightened as ''having love and compassion'' is from the people who cling to the dichotomy hate-love. They heard that Being enlightened means having no hate, so they think that Being enlightened means being full of love.
More generally this stems from their lack of understanding that four Brahma Vihara or four sublime states [ metta (loving kindness), karuna (compassion), mudita (sympathetic joy), and upekkha (equanimity) ] is not being enlightened.
It is the jains and hindus who keep saying that having compassion means '' consider their suffering as your own is general-compassion.''
https://www.wisdomlib.org/definition/anukampa
So the buddha has anukampa, ie compassion, and he says he teaches out of anukampa. The buddha did not get enlightened because he wanted to be full of love and be compassionate. THe buddha wanted to end dukkha and the result is the ending of dukkha and he teaches out of anukampa.
Even Ananda says he answers the nuns out of anukampa.
The usual paragraph with anukampa is like this https://www.accesstoinsight.org/tipitaka/mn/mn.152.than.html

"So, Ananda, I have taught you the unexcelled development of the
faculties in the discipline of a noble one; I have taught you how one
is a person in training, someone following the way; I have taught you
how one is a noble one with developed faculties. Whatever a teacher
should do — seeking the welfare of his disciples, out of sympathy for
them — that have I done for you. Over there are the roots of trees;
over there, empty dwellings. Practice jhana, Ananda. Don't be
heedless. Don't later fall into regret. This is our message to you
all."

Mn152 also explains how enlightened people view feelings, tactile sensations and so on.
Nibanna is bliss, but not bliss with the senses, not even the bliss from the jhana. It is the other kind of bliss and you can't know it before being enlightened.
Answer: In the context of this question, eg there are differing types of concepts described by the same English words, many of the exact concepts nothaving exact English equivalents.
Nonattached kindliness & nonattached compassion, & lovingkindness are sometimes utilised more at more existential concepts and existential nuances.
Many books talk about the subject of this question, and many words written about it, however, sometimes the concept seems oversimplified because of the words. Readers often infer, and very reasonably so, the fairly standard definitions for the words, when in fact there may be specialised meanings intended to be implied.
Some 'concepts', eg some existential concepts arent'very easily described using fairly standard English words. Yet many contributions to understanding of the concepts may be assisted by descriptions of features of the concepts for which there are more well known English word equivalents, and an example of that might include the subject of the question:
One aspect of Enlightenment is that there's lack of illusion, & there 'is' Reality, & there isn't confusion or illusion or cloudiness or dukkha. There isn't illusion or cloudiness. Things are 'seen' correctly & as they really 'are', & Kindliness & compassion & niceness are without attachment! And kindliness & compassion & niceness are for benefit to other beings rather than for personal, or to go to a heaven, etc
Answer: Why ask why?
Just be compassionate and understand that people have created their own worlds, from past lives, and that they are born with mental projections as part of the karma they need to work through.  Try not to get pulled into bullshit when other people are chasing their own tails around, in a ball of confusion.  In other words, if people refuse to listen to your calm purity, don't chase them down and try to force wisdom down their throats.  They'll spit it out.
Love all sentient beings, but also your self.  Be kind to others, but also to your self.
But I realize I have not answered your specific question.  The purpose of attaining nirvana--Is this a serious question?  All people must achieve it.  It is the purpose of living.  No one is excluded from this goal of self-purification.
Comment: Why *must* everyone achieve Nirvana? How do you arrive to the conclusion that Nirvana is the purpose of living? I think that 'must' and 'can' are two different things: one might say that everyone *can* achieve Nirvana, but how do we jump from that to "all people *must* achieve Nirvana? Does the universe have a purpose? If your answer is "yes", how do you know?
Answer: I'm pretty sure I know the answer to this: no-one knows.
You can only read the metaphors about extinguished lamps etc. to get it.
See Collins' Nirvana: it is an excellent piece of scholarship -- from a Theravadin perspective.


Why do most Android applications place the navigation bar icon (hamburger menu icon) inside the search bar?

Question: Apps like Play store and several other do this. They seem deeply flawed in their design. Since the hamburger menu has nothing to do with search, why is it designed in such a way?
Answer: Well, this isn't a great reason, but the Material Design Spec considers the top app bar to be a single component. As in "all the navigation interactions" happen in that area.
And... Google wants search to be the first and primary means of navigation so they're focusing the user's interactions there first. The message is sort of, "if a search doesn't give you what you need, this other stuff is here too."
I find it interesting that there isn't a hard answer for this question though even at Google. The Play Store functions as you described, but Gmail, Google News, and Google Home don't.
Answer: Well, The reason why Hamburger menu and search are unified into a single component is that Hamburger Menu in a way is a form of simplified search grouped into categories. In case a person wants to perform a more specific search he/she could use the search bar to type in their keywords.
Hope this helps!!


About artificially induced processes that would normally cause a cell to self-destruct

Question: Are there certain biochemical processes that would normally cause a cell to self-destruct but if the cell being tested has apoptosis mechanisms that have malfunctioned or been 'turned off' the cell will not 'malfunction' because of the induced process ? Are there such biochemical processes that could indirectly indicate which cells have no functioning apoptosis mechanisms? If so would this be a possible test for cancerous cells?
Answer: In some cases yes — when there is a mutation in apoptotic regulators such as Bcl2 family of proteins. In other cases it is difficult to identify and only identification is that those cells are growing rapidly; in other words failure to undergo apoptosis is not the cause but the effect of the cancerous transformation (as in case of p53, Ras, Myc mutations etc).


Vanilla European options: Monte carlo vs BS formula

Question: I have implemented a monte carlo simulation for a plain vanilla European Option and I am trying to compare it to the analytical result obtained from the BS formula.
Assuming my monte carlo pricer is correctly implemented, am I supposed to get the very same result with both methods (Monte Carlo and BS analytical formula)?
Comment: with large amount of simulated paths (>200 000) - yes, you should have very close match.
Comment: @Vytautas. Thanks. What do you mean by close match? Up to how many decimals for instance?
Comment: You shouldn't be able to reject that the two solutions are different.
Comment: The number of iterations is just a function of what size standard errors with which you are comfortable.
Comment: Lets than 1 cent is considered good enough
Answer: Fundamentally this is no different from other simulation-based estimation---see this little experiment in R:
<code>R> set.seed(42)
R> rowMeans(replicate(200,sapply(1:6,
+>          FUN=function(x) mean(rnorm(10^x)), simplify=TRUE)))
[1] -2.47827e-02 -9.46800e-03  2.38226e-03 -1.08650e-03  9.41395e-05  1.06759e-05
R>
</code>
We are calculating the mean of a $N(0,1)$ vector for sample sizes from $10^1$ to $10^6$. That is then repeated 200 times, and we are calculating the mean of the 200 draws at the different sample sizes.
We find that by and large, the mean gets closer to zero. But even at $10^6$, repeated 200 times, we are still pretty far from 'zero'.  That is the way it goes with simulation, and it pays to get a feel for this.
So while you have perfect benchmark with your analytical Black-Scholes result, you will be hard-pressed to get the difference to vanish  completely.
Comment: Thanks! Just one last doubt remains: up to how many decimals do I need to _get the difference to vanish?_
Answer: As long as your simulations are independents, you can calculate some confidence interval thank's to the Central Limit Theorem and see if this interval is encompassing the true BS price.
Regards


How do you derive Noether's theorem when the action combines chiral, antichiral, and full superspace?

Question: How do you derive Noether's theorem when the action combines chiral, antichiral, and full superspace?
Answer: The full superspace terms are the "most general ones" but you may convert the chiral and antichiral terms to the full superspace form, too. In particular,
$$\int d^2\bar\theta = \int d^2\theta\, d^2 \bar\theta\, \theta_1\theta_2$$
and similarly for its complex conjugate. Sorry if a sign is wrong. Note that $\theta_1\theta_2$ may be written as $\epsilon^{ab}\theta_a \theta_b/2$ up to a sign if you happen to be annoyed by the explicit components.
The fact that chiral superfields only depend on $\theta$ but not $\bar\theta$ doesn't matter: it just means that it is a more constrained field. But you may still imagine that it's a function of the full superspace that just happens to have a special form.
Once you convert the action to an integral over the full superspace, you may proceed just like you would proceed for the full superspace, D-term-like terms. I am actually a bit unfamiliar with this thing - so I would convert the action to the components (no superspace at all) and proceeded just like in non-supersymmetric theories. Of course, the resulting conserved quantities wouldn't be nicely organized in supermultiplets - which they can be in a supersymmetric theory.
Answer: You can think of a generalized innerproduct, where terms get integrated over the "correct" superspace. In my view, the best way of deriving the propagators for chiral fields. It's much cleaner than lifting everything up to full superspace.
An example of this occurs in section 4.8 of Ideas and methods of supersymmetry and supergravity and probably other papers by the authors. In this section only chiral and antichiral spaces are used, but it can be generalized to include a full superspace sector.
Once you've set up your conventions for this type of innerproduct, then everything basically works as you'd expect.


Which crowd control effects cancel Nunu's ultimate?

Question: Does Nunu's ultimate get cancelled by any crowd control like slow, or only by hard CCs like a snare or stun?
Answer: Nunu's Ulti gets canceled by any hard CC, like Knock ups, knock backs, silence, suppression, stun, charm, and polymorph. This is why Banshee's Veil is a popular item on this champ. Slows have no effect on his ultimate, as they do not interrupt anything.
Note that interrupting his ultimate doesn't fully cancel it. Part of the damage will still be dealt. This damage will be between 12.5% and 87.5% of the full damage, depending on how long he was channeling.
Answer: Yes Nunu's ultimate can be canceled by stun, knock-up, suppression, silence, and knock-back effects.
Answer: Yes, Nunu ult get's canceled by any hard cc, but I want to add, that its damage isn't bigest factor in late game teamfights. It's slow and that enemies needs to use their stuns on you and not your carries.


Google search of links:mysite.com returns less links than imagined

Question: I did a Google search links: example.com and it only returns 3 results.  I know there are a lot my more back links in existence than that. Why does Google not show the other links I have to my site?
Answer: Google disabled this search command a few years back because far to many people were find to be reserve engineering other peoples links. Additionally it only contained a sample and not the full links any how. You can find some other search commands that may be useful but ultimately there is no effective way of searching links using Google search.
Google's Webmaster Tools contains a site backlinks however it is often incomplete or generally slow. Your best bet if this is important to you is too use other methods that crawl sites and adds it to their database, for example SEO Majestic, SEO Profiler and many more....
Answer: For the best answer try to submit your website to Google Webmaster Tools. You will get there all the links that Google take in count.


How to relocate the database directory for Red Hat Directory Server 9.0

Question: I am running RHDS in a VM, but would like to store the data and logs on a separate volume, that is on a SAN.  The partition is ext4fs on /sdb1 and is mounted as /data.
I tried many variations of the different approaches described here.  First, after a fresh install of RHDS, before I created any instances, I created the folders on /data and linked to them from /var, as follows:
mkdir /data/lib
mkdir /data/log
mkdir /data/lib/dirsrv
mkdir /data/log/dirsrv
rmdir /var/log/dirsrv
rmdir /var/lib/dirsrv
ln -s /data/lib/dirsrv/ /var/lib/
ln -s /data/log/dirsrv/ /var/log/

When I create an instance (named esx02vm01) of the directory, I get this error:
[02/May/2013:09:51:45 -0400] - /etc/dirsrv/slapd-esx02vm01/dse.ldif:
nsslapd-errorlog: Cannot open errorlog file
"/var/log/dirsrv/slapd-esx02vm01/errors",
errors cannot be logged.  Exiting....

I thought RHDS might be having trouble with the symbolic links.  In my second attempt, I instantiated with files in the default locations.  After confirming the directory was working, I shut it down.  Then I moved the instance folders under /var/lib and /var/log over to the /data folder and modified the dse.ldif file for that instance to point to the new folder locations, as follows:
mkdir /data/lib
mkdir /data/log
mkdir /data/lib/dirsrv
mkdir /data/log/dirsrv
cp -r --preserve=all /var/lib/dirsrv/slapd-esx02vm01 /data/lib/dirsrv/
cp -r --preserve=all /var/log/dirsrv/slapd-esx02vm01 /data/log/dirsrv/
vi /etc/dirsrv/slapd-esx02vm01/dse.ldif
* replace all /var/lib/dirsrv/slapd-esx02vm01 with /data/lib/dirsrv/slapd-esx02vm01*
:%s/\/var\/lib\/dirsrv\/slapd-esx02vm01\//\/data\/lib\/dirsrv\/slapd-esx02vm01\//g
* (6 substitutions on 6 lines)
* replace all /var/log/dirsrv/slapd-esx02vm01 with /data/log/dirsrv/slapd-esx02vm01
:%s/\/var\/log\/dirsrv\/slapd-esx02vm01\//\/data\/log\/dirsrv\/slapd-esx02vm01\//g
* (4 substitutions on 4 lines)
:qw
mv /var/lib/dirsrv/slapd-esx02vm01 /var/lib/dirsrv/old-slapd-esx02vm01
mv /var/log/dirsrv/slapd-esx02vm01 /var/log/dirsrv/old-slapd-esx02vm01
service dirsrv start

I got the same error attempting to start the directory:
Starting dirsrv:
esx02vm01...[03/May/2013:08:56:00 -0400] - /etc/dirsrv/slapd-esx02vm01/dse.ldif:
nsslapd-errorlog: Cannot open errorlog file
"/data/log/dirsrv/slapd-esx02vm01/errors",
errors cannot be logged.  Exiting....

Then, I moved the error file back to the original location, so just the database file was on /data.  These errors where logged when the directory is started:
[03/May/2013:09:17:17 -0400] - 389-Directory/188.8.131.52 B2013.100.2247 starting up
[03/May/2013:09:17:17 -0400] - mkdir_p : error -5950 (File not found.)
[03/May/2013:09:17:17 -0400] - Can't start because the database directory
"/data/lib/dirsrv/slapd-esx02vm01/db" either doesn't exist, or is not accessible
[03/May/2013:09:17:17 -0400] - start: Failed to init database, err=-1 Unknown error: -1

In each case, I confirmed that the reported directories and files exist, and that they have the same ownership and permissions as the original directories and files.  When I created the instance, I ran setup-ds-admin.pl as root, using the account rhds for the instance.  I created the rhds user with the command:
useradd -M rhds

What is the proper way to relocate the databases for an instance of Red Hat Directory Server?
-Luke
Answer: The following procedure works successfully for me with 389-ds 126.96.36.199:

create a new instance
make sure dirsrv is stopped: service dirsrv stop
move the /var/lib/dirsrv/ directory to the data partition; in my case /mnt/389ds/data/
create a symbolic link from /var/lib/dirsrv/ to /mnt/389ds/data/
move the /var/log/dirsrv/ directory to the data partition; in my case /mnt/389ds/log/
create a symbolic link from /var/log/dirsrv/ to /mnt/389ds/log/
start the server: service dirsrv start

I have installed multiple production servers this way and they are all running well!


Should progress bars show percentage

Question: In the application I am designing we are currently just displaying a circle that rotates clockwise from gray to green. Inside the circle is a number indicating where in the process it is (20, 50, 90). Is it breaking usability if we do not display to the user that it is a percentage?
Comment: you could label the top as `100` so that users are cued in to the idea that the number shown is X out of 100.
Comment: Oh, sorry...I completely misread the question. Uh, I'd suggest not showing the number at all, or show it as "90%". It probably still works OK as 90, but it really is a percentage, so should state that (do you have a reason for NOT showing the % sign?)
Comment: ...and is the percentage a percentage of time or of progress? I always get annoyed with those windows progress bars that keep forever for the last 1-10%.
Comment: Can you provide a screenshot or mock-up of the interface in question?
Comment: The donut is saying the same thing, albeit visually. It's nice to have both, but I don't see a strong argument to keep both.
Comment: Sorry, but I can't comment yet. When asking _"90 What? Elephants?"_ is ok. It might also be ok to ask "90% of what? time? files copied? loading done? local (within that step) or overall progress? of tasks done? done preparing content?.." I would agree, that adding a "%" somewhere might help. But it may raise other questions unless the context is very clear. But I also would keep it vague and remove the number or count down instead of counting up. because everybody is familiar with countdowns.... 3.. 2.. 1.. KAWOOM! I personally would not care what is counting down (%, time or just numbers) as
Answer: If you are displaying a percentage, it's best to label it as a percentage.  The <code>%</code> doesn't have to be the same size or as dark even as the main number, but is gives a lot more clarity at a low cost.  In fact, any number without units is meaningless unless it actually has no units.
Example:
Answer: Yes, always show your units. As my maths teacher used to say:
Ninety what?...Elephants?
The problem is that people are used to seeing the percentage symbol with percentages. Therefore, it is in fact conspicuous by it's absence. That makes people think and the point is to make a UI where people don't have to think - at least not where they really don't need to.
This example simply makes users think: "I'm expecting a percentage here. I mean it makes sense to be a percentage. It looks like a percentage, but there's no percentage symbol, so maybe it's not really a percentage after all. Maybe it's a mistake. I'm really not sure, so how can I tell. I guess I'll wait and see if it goes up to a hundred. OK it got to a hundred, but was that a coincidence? What will it do next time? Will it be a different number?
Avoid all these questions and include the symbol. Don't think of the symbol as an embarrassment to the design. It adds value to the communication of the value to the user, and that's what counts. Don't fall victim to form over function.
When including the percentage sign, I would include it at the same size as the font used for the numbers. It seems the percentage sign should typically be aligned with the font baseline and not extend above the ascender line of the numerals to which it relates:

As to whether you need a space between the number and the sign - that's another question, and may vary between geographical location!
Comment: Oh, all the time I saw 50 on progress bar I thought they were potatoes. And I thought "%" was a symbol of two potatoes on branch...
Comment: Just to be pedantic, a percent is not a unit, it simply means a value "out of 100". Percentages tend to be unitless because the unit is removed by division. E.g. 8 potatoes / 10 potatoes = 0.8 because the units cancel out.
Comment: In some languages they *consider it* a unit - eg French (including French Canadian), but fair point, it's not really a unit.
Answer: Yes, always mention the unit. Your design should be as clear and as unambiguous as possible. If you do not wish to "spoil" your graphics with the % symbol, you can always add a note beneath the circle '% value' or 'Percent value' or something along this line.
Answer: Consider a color-blind user. By having both number (and I agree with showing the units) and the graphic, you increase the usability of the data visualization piece.
Answer: Yes, but what about counting down from 100 to 0? That I think is something which will not be misunderstood as unbounded or arbitrary - after all, who would expect it to ever go below 0?
Comment: I see your thinking, but this would imply that there are N items left to load/process when that isn't what's happening at all. In some situations the difference may not matter, but in some it will make a difference.
Answer: If you're going to show a number, you need to add its unit. Especially in applications where it might be that a number of tasks share a progress bar. It appears we're in agreement on that.
However, my experience, I guess like that of chaiguy, is that it's impossible to be accurate in representing progress. I've you've completed 5 tasks out of 10 that doesn't mean you're halfway done: tasks #8 might take twice as long as task #3. If your application can guess that its spent 2 minutes out of an expected 4, we still can't be sure we're halfway done for that same reason. Something may come up (and always does).
So, numerical counters indicate an accuracy that isn't there. It's like in science where you can't say that 2 + 2 = 4.0 because you can't have that extra digit of accuracy. If your prediction of progress is not accurate enough to support a scale from 0 to 100, don't show percentages.
Users know to mistrust progress-bars, because they've always been wrong. Experienced users will use their own experience to create an estimate of how long it will take. Give them information that helps build this estimate. Tell them that you are moving 5 gigs of data, or that you're doing 10 tasks. But don't bluff on your accuracy for predicting progress because you don't want to show information to a user that the user knows he or she cannot trust.
Answer: I'm really surprised that all of the answers to this so far have been "yes". I have to disagree that there's a significant benefit to displaying the percentage value numerically over simply representing the progress graphically.
Let's first of all agree that the real purpose of a progress bar (in most cases) is to show the progress of an operation that takes a certain amount of time to complete, and therefore its intention is to give the user enough information to gauge roughly how much longer the operation is going to take.
Therefore, displaying the percentage of progress with numerical accuracy has no significant advantage, since the end purpose (gauging time) is still at best a rough approximation.
I would argue that it is in fact much more valuable to display a computed estimate of time remaining than to display the progress numerically. After all, does the end user really care whether an operation is 49.5 percent complete versus 50.1 percent complete? Either way it's "roughly half done".

Should progress bars show percentage


Is Jason Isaacs in John Wick?

Question: Google says he is, IMDB says he isn't. I can't see him. Anyone know for sure? Pre production news said he was joining the cast, so if he's not in the film where did he go? Did he film any scenes or was he cut before photography?
Comment: Lots of actors are mentioned in pre-production but often don't make the final film for various reasons. Scheduling conflicts mostly.
Comment: There is also some small Reddit discussion about this. Allegedly his John Wick character was named "David" . I don't remember if there is a David in the film, but if so, you may be able to figure out whom was recast.
Answer: I found this IMDb article mentioning "Jason Isaacs joins the cast of John Wick."  At the bottom of the article, it also mentions Isaacs had joined the cast of the Brad Pitt vehicle, Fury (which IMDb's cast listing confirms he was a part of.)
Now, what follows is purely supposition on my part, as I couldn't find any direct articles about it, but I do notice that both Fury and John Wick were doing principal filmography between September and December 2013, and in very different parts of the world.
For Fury:

Principal photography began on September 30, 2013, in the Oxfordshire countryside... Filming was wrapped up on November 15, 2013 in Oxfordshire.

For John Wick:

On 14 October 2013, shooting began in Mill Neck, New York, with the filming process scheduled to continue in and around New York City and greater New York area... Principal photography was confirmed to have ended on December 20, 2013

So, I suspect that Isaacs had to drop one of the movies due to scheduling conflicts, and evidently he chose to drop John Wick.  (Perhaps because Fury had already started filming before the other, but again, this is just me putting 2 + 2 together, without a direct reference.)

Is Jason Isaacs in John Wick?


what is the best way to create a top navigation based on Geographic location of the user

Question: I am trying to create a dynamic top navigation based on the users geographic location. How do can achive it? what is the best solution for that. I was wondring to use custom profile properties, is it a god option? thanks for helping me.
Answer: The best way to go about this would be to use SharePoint Audiences.  You can create an audience that is based on a user profile property.  And then you create your navigation to use the audiences when determining who to show the links for.
Alternatively you can write your own navigation provider that feeds the top navigation with whatever data you want.
Comment: thank you. "Navigation Provider" did you mean PortalSiteMapProvider?
Comment: This should get you started: http://msdn.microsoft.com/en-us/library/bb897739(v=office.14).aspx
Comment: Yes, I hava already created a customized top navigation Control by implementing PortalSiteMapProvider. But I didn't know how you get all nodes of that based on an audience or profile property. I want to hide one or two of nodes based on a profile property (audience).
Answer: You can create audiences based upon a set of user profile / AD properties. It requires some administration in Central Admin and it's not immediate. Audiences need to be compiled first. This is done automatically or you can start it manually.
You can assign an audience to a website, lists, web parts, navigation links, ...  It becomes very easy when the publishing feature is enabled on your site. In the site settings you can set the navigation options and assign an audience to each link. So depending in which audience(s) a user resides he will see different links in the navigation.
Keep in mind that audience is not security. An audience will not prevent the user accessing a site. If you have the direct link you will be see the content. You still need to configure the site permissions correctly.
Answer: Agree with John, I have just completed a similar solution which is working fine.
Note that we are referring to Global Audiences which are configured in the User Profile Service within Central Admin.


Why are lexical scopes prefered by the compilers?

Question: How does lexical scope help the compilers? Does it help in compilation or optimization?
Answer: I do think that lexical scope helps the compiler and optimization. It depends what you mean by help though.
Lexical or static scope allow the compiler to proof availability of a variable when referenced locally, that means within its lexical context. It has to be in the scope of the method referencing the variable.
To do such in dynamic scope environments, all calling contexts have to be taken into consideration, as a function knows all variables its calling context knows as well. To make sure a variable is available for reference, a recursive backtrack of all calling contexts would be necessary at compile time.
As this is very complicated, it would be omitted at compile time, throwing exceptions at runtime.
See here: In dynamic scoping, by contrast, you search in the local function first, then you search in the function that called the local function, then you search in the function that called that function, and so on, up the call stack. "Dynamic" refers to change, in that the call stack can be different every time a given function is called, and so the function might hit different variables depending on where it is called from.
Answer: Lexical (or static) scoping reduces the amount of information a compiler needs to correctly transform text into code. It can help compilation because the compiler does not need to add additional information that must be accessed at runtime (as is the case with dynamic scoping). For optimizations, the compiler does not need to consider variables that could exist in other scopes, as you can either access local variables or global variables and nothing else.
Answer: Lexical scope does not help the compiler or optimise the code.  It is a language design decision.  See this question for more explanation.
Comment: please see 48:00 of this: http://www.youtube.com/watch?v=HIJ8ly8HOUQ&feature=PlayList&p=6879A8466C44A5D5&index=19
Comment: might not get the time to watch the whole thing.  But is sounds like I need a lesson or two ;-)
Comment: like most language design decisions, it has a large effect on efficiency.
Answer: With dynamic scope, many optimizations are impossible, because you cannot guarantee the constraints that make the optimization possible.
This is especially important in dynamic languages that do not guarantee storage sizes or representations.
For example a compiler for a dynamically typed language may be able to take a linked list of boxed objects and replace it with an array of unsigned 8 bit bytes, if it can prove that the elements of the list will always be integers between 0 and 255. This sort of thing is easy to prove with static scope when you use it properly, and can cause huge increase with both space and computational efficiency.
It is also often easier to debug lexically scoped code, because dynamic variables are much harder to track down in debugging. There is kind of a spaghetti-code of where things may have been defined, similar with the problems caused by goto and overuse of global variables.
Answer: Very simply said, lexical (or static) scope helps when a language is statically typed, dynamic scope helps when a language is dynamically typed.
In dynamic scope, the scope of a variable is resolved at runtime. If a variable declared int is used in another lexical environment where a variable with the same name has type float. The only was it to consider them two different variables, which means that variables must carry type information, in most static type systems, type information does not enter the object code at all. A program will simple only compile once it can prove that no type errors will occur, and then no type information is needed any more of course.
Dynamic languages which have lexical scope often need to use a heap rather than a stack to allocate runtime information to for this reason.


Missing Dhyana/Jhana Sutras?

Question: Are there parallel texts between Pali Canon Jhana Suttas, and Mahayana equivalent? Dhyana Sutras? I now that the theme is picked up again in Tiantai texts, but I'm thinking of between the Pali canon and the Tiantai? Does Asanga touch on this topic or skip over it? Kumarajiva?
Answer: Yes some texts of the pali canon have parallels in what people call the (chinese) agamas.
The links for the agamas is here:

Where can I find the Chinese Canon Agama in English translation?

Some people compare the agamas and the nikayas:

The Fundamental Teachings of Early Buddhism --
A comparative study based on the Sutranga
portion of the Pali Sarpyutta-Nikaya
and the Chinese Sarpyuktagama
by Choong Mun-keat (Wei-keat)

... for instance, chapter 7 ...

... with the most famous one about breath mediation here:

Translations from the Taishō Tripiṭaka

bikkhu analayo is the most famous bikkhu for this kind of comparision:

Prof. Dr. Bhikkhu Analayo

Many of the Mahayana and Vajrayana sutras (chinese or tibetan), however, have no parallel in the pali suttas (i.e. they're unique to Mahayana or Vajrayana):

Chart Comparing Pali, Chinese and Tibetan Canons
Comment: Downvoiting without comment is harsh and divisive speech. Please add a comment and/or cancel your downvote
Comment: It wasn't my downvote. I edited to improve the format of the hyperlinks, and to reduce the last paragraph.
Comment: I don't know why it was downvoted. If it wasn't because the last paragraph, perhaps it's because the answer wasn't specifically about "Dhyana/Jhana Sutras" (and maybe "Asanga" and/or "Kumarajiva").
Comment: Although direct link to "jhana suttas" is not listed, the excerpt actually suffices for my purposes: Mahayana dhyana practice is identical to Pali Sutta equivalents. Divergence into separate practices is a mark of the current, decadent period. i can even find quotes in Zen of only 1000 years ago showing dhyana was still just this. Current Zen thinking about dhyana in the development of their tradition is suffering from historical revisionism.

Missing Dhyana/Jhana Sutras?