What is *Cell standby* and how can I keep it from eating my battery?

Question: Looking up my battery statistics, I almost always find Cell standby amongst the top consumers:

I never thought that "idle" would use so much energy. I saw that other people encounter similar problems:

Cell standby and Phone idle
Galaxy S3 cell standby is eating my battery

Answers on those questions just give some raw ideas. I would like to know what exactly stands behind this, an whether there are ways to keep this "standby" from eating my battery?
Comment: These percentages should not be compared from one time to another; you should only use them as a guide to relative power consumption.  Keep in mind that 100% of battery usage is not always the same.   Just for an example, assume that cell standby consumes 10mw, the display 50mw, and other miscellaneous use consumes 40mw.   In this case, your total use would be 100mw, and cell standby would be consuming 10%.  If you turn the display off without changing anything else, cell standby would still be 10mw, but would show as 20%, since your total consumption is now just 50mw.
Comment: I'm aware of that, Tom. But my "usage pattern" is rawly comparable, and at least this gives an idea. I wish they would additionally provide absolute values here, though.
Comment: I'm running into the same problem. What made you to solve this? Does Tasker app manages this automatically and solves the problem?
Answer: Cell Signal
Some backgrounds as explained by ce4 on the question Does 'poor' reception deplete the battery quicker?:

The transceiver circuit is engineered with power saving in mind and will reduce sending power as much as possible if the reception is good. This also reduces the SAR value which is a measurement for exposure of the human body to radiation.
If the reception is bad sending signal strength has to be adjusted accordingly.

So that's what's really behind it: On poor reception, the device spends a lot of power to find a better/stronger signal (or any signal at all if lost). The following screenshot1 clearly shows those times, when you take a look at the bar titled Phone signal.

"The greener the cleaner": A bright green means "good reception" (the screenshot shows this at the begin and end, that is here: morning and evening -- so at home I have good reception). Getting yellowish: "Moderate reception". This uses more energy: compare it with the graph on top of it (not in the screenshot -- but the same as in the first screenshot), and you see the bar is almost flat where the cell signal  is good -- but falls faster where it's not. See the little red spots: "no reception". And phone will power-up like crazy to find a new cell tower...
How to find out where the dead spots are?
I already showed in my answer on Does 'poor' reception deplete the battery quicker? how one can find out about those "Dead Zones" and where they are:
Apps like No Signal Alert2 and OpenSignalMaps3 monitor the cell signal in background, and record those areas, so they can show you a map of where the dead zones were. OpenSignalMaps has the plus of showing you all cell towers in reach, pointing out which you are connected to. It also offers you a "compass" giving the direction to the strongest signal.

However, my answer on how to automatically deal with those dead zones was not that detailed. So I played around a bit with different solutions -- and here's what I've found out:
How to automatically deal with those dead zones to save energy?
Apps to automatize Airplane Mode
I've reached fairly good results with two apps: Autopilot4 and NoBars Battery Saver5. Both monitor the cell signal and, when it drops to far, switch to Airplane Mode for a predefined time. The user can define how long that would be. After that timeout, Airplane Mode gets disabled, and cell monitoring takes over.

In the second graph of my question, this shows up as "gaps" in the Phone Signal bar: As the cell radio was disabled during Airplane Mode, no colors are shown; the system didn't know anything about signal strength in this time frame. And with the cell radio turned off, it also didn't use additional power (more precisely, it didn't use any power for this radio then) -- which was exactly what was intended.
With Autopilot, the only annoying side-effect was: For each signal check, it flashed on the display for about a second. Aside from that, it gives more options to be configured by the user. However, as the results of both apps where absolutely comparable, those extra options seem not really necessary, while being nice to have. Another plus of Autopilot is the log provided to the user: This way you can see the exact times of mode switches.
Apps to handle data network
I've also tested ShutUpBatterySaver6, which aims to handle the data traffic. Dropping below a certain signal strength the user can define, it disables AutoSync, and below a second definable level switches off mobile internet altogether.

It does, however, never activate (or deactivate) Airplane Mode, so the power used to get a (better) signal will still be the same. Though, with a bad signal data transfer uses more power than with a good signal, as e.g. package loss might be bigger. In the status bar I saw several times that it had AutoSync disabled7, so it seems to work. Not being a heavy data user (as the LBE stats in the same screenshot show), I could however not really tell how much help that brought: Compared to the two Airplane-Mode handling apps above, results in terms of gained battery duration were minimal (if any).
Combined solution
It would probably gain best results to join the two approaches. As I was not in the mood to check all possible combinations, I rather decided for the allmighty 6-letter-solution: T-A-S-K-E-R.
As most of you probably know, Tasker is the automation solution on Android. Guess it could even prepare coffee, if our devices had sensors to detect coffee and water. So I created some profiles for this great app -- and results were magnific!

So basically it's 3 Profiles, communicating via a common variable:

%SIGSTATE < 1: check if the signal falls below ~25%. If so, disable mobile data, set %SIGSTATE to 1.
%SIGSTATE < 2: check if the signal falls below ~15%. If so, switch to airplane mode, set %SIGSTATE to 2.
%SIGSTATE > 0: wait for 5 min, then disable airplane mode, activate mobile data, wait another 15 sec (for the signal to be restored), set %SIGSTATE to 0.

In my global Init profile (which gets executed when Tasker starts monitoring), %SIGSTATE is set to 0 (if it is unset). All 3 above profiles additionally set notifications, as the screenshot above shows9. Each state maintains one notification (which gets replaced when the same state re-occurs), the most up-to-date state is always on the bottom.
Results seemed even better than with the two airplane-mode handling apps above, but that might also be due to slightly different signal conditions. So it should at least be comparable. Using one of these 3 solutions, I came home after about 11 hours with about 20% more charge left then without applying any of them.
Having said this, I will end this answer showing the Tasker profiles I created, so you might use them with your Tasker installation:
Task "InitVars":

Variable -> Variable Set: %SIGSTATE = 0

Task "SigLow":

Net -> Mobile Data: Off
Variable -> Variable Set: %SIGSTATE = 1
Alert -> Notify Vibrate: Title "IzzySignal"; Text: "Signal Low; Mobile data disabled (Signal: %CELLSIG)"

Task "SigLost":

Variable -> Variable Set: %WLANSTATE = 0
Variable -> Variable Set: %WLANSTATE = 1 IF %Wifi ~ on
Net -> Airplane Mode: On
Net -> Wifi: On IF %WLANSTATE ~ 1
Variable -> Variable Set: %SIGSTATE = 2
Alert -> Notify Vibrate: Title "IzzySignal", Text: "Signal Lost; Entering Airplane Mode"

Task "SigReturn":

Task -> Wait: 5 Minutes
Net -> Airplane Mode: Off
Task -> Wait: 15 Seconds
(give the device some time to find a new signal!)
Net -> Mobile Data: On IF %ROAM ~ Off
(prevent bad surprise when returning from vacation abroad!)
Variable -> Variable Set: %SIGSTATE = 0
Alert -> Notify Vibrate: Title "IzzySignal", Text "Signal On; Airplane Mode disabled (Signal: %CELLSIG)"

Now for the profiles:
Profil SigLowCheck:

State -> Variable -> Variable Value: Name "%SIGSTATE", Op "Math: Less Than", Value "1"
State -> Phone -> Signal Strength: From 0 To 2
State -> Tasker -> Profile Active: "SigLost", [x] Invert
(make sure to avoid a conflict: %SIGSTATE~0 && SignalStrength~1 would match both profiles condition)
Task: SigLow

Profil SigLostCheck:

State -> Variable -> Variable Value: Name "%SIGSTATE", Op "Math: Less Than", Value "2"
State -> Phone -> Signal Strength: From 0 To 1
Task: SigLost

Profile SigReturnCheck:

State -> Variable -> Variable Value: Name "%SIGSTATE", Op "Math: Greater Than", Value "0"
Task: SigReturn

Profile Init:

Event -> Tasker -> Monitor Start
Task: InitVars

Now that's just the basic concept, and can be extended with e.g. playing sounds, vibrating, flashing the display, and more. But the energy saving stuff is already in -- and does its job as described. Hope this can help you as well!
Another remark: At least with GSM (I cannot tell for CDMA), returning from Airplane Mode by default forces you to enter the SIM PIN. This can of course be switched off -- but in that case this additional protection is also gone when switching on the phone. No idea why this is not possible selectively, as it was with my pre-Android phones.
However, for some phones there's an alternative to some items in above tasks, which remove this limitation:

In SigLost, instead of Net -> Airplane Mode: On use Phone -> Radio: Off if your phone supports this (my Droid2/Milestone2 does not, unfortunately). If you can do this, the WiFi check becomes obsolete (and your Task cleaner).
The counter-reaction in SigReturn then also needs to be changed: Instead of Net -> Airplane Mode: Off, use Phone -> Radio: On.

Please let me know in the comments if this removes the limitation of the SIM PIN, as I cannot test it (my device does not support it, as described above).
Edit by t0mm13b
The interesting thing I noticed was that there was multiple tasker icons appearing on the Status bar, which made things confusing as to regards the state that the tasker profiles was running as; I discovered that by setting the Title for the 'Notify Vibrate' in each of the above tasks to be the same, the net result is, one singular notification titled 'IzzyTasker' shows up, with the appropriate message used instead.
Comment: This must win a prize for the most thoughtful, useful, detailed answer ever.
Comment: Thank you! Took me about a week to collect all the statistics, test all the solutions, plus separating the good ones from the, hm, not so good ones ;)
Comment: Hehe -- thanks @t0mm13b for the update. Hint: The current state is always the "last one" (farther down than the others). So with different titles you get a little "log" added. But interesting discovery that the *title* is what makes a notification get replaced -- thanks for that!
Comment: As *Tasker* does not deal with dbm values directly, I didn't dig into those very deep. You could observe it for a while (or monitor it with e.g. [RF Signal Tracker](http://www.appbrain.com/app/RF-Signal-Tracker/com.hotrod.utility.rfsignaltrackereclair)) to find suitable values. From my monitoring with that app, I agree to -113dbm meaning "out", no useful signal then. So you could start with -110=SigLost, -100=SigLow, better=OK – and from there play with the values until you're satisfied. I'd appreciate to read your results (values) here then :)
Comment: The magical value seems to be -105dbm. Everything above is represented by 2 bars signal strength, -105dbm and everything below is one bar or less. This holds true for a Samsung Galaxy S2 i9100.
Comment: @Firelord So what? This answer is 3 years old. Still enough other pointers there :)
Comment: This happens even when reception is good, though, it's not due to reception problems.
Comment: Awesome research, thanks for sharing!  I'm setting up a llama profile similar to your tasker setup. Do you know what would be a good threshold value for weak and no signal? Afaik -113dbm counts as no signal, but what about weak signal strength?
Comment: I don't understand "On poor reception, the device spends a lot of power to find a better/stronger signal (or any signal at all if lost)."  How does it use energy finding a better signal? I can imagine it scans frequencies, listening for a strong one, but unless it transmits, I don't see how that takes much more power than sitting on one frequency, listening. If it transmits...why? Is it to get a handshake?  Wouldn't it be better if masts transmitted heartbeats very frequently so that phones could tell immediately if they had a good signal from one?
Comment: @Poldie, a receiver requires energy. If it already sits on a fine connection, it doesn't need to check for others. If it needs to, it must check whether "the other cell" is usable, if it can "get a lock" to the other tower (or gets refused, as it e.g. belongs to a different carrier). For that it also must transmit, of course. It might need to scan additional frequencies as well (2G/3G/LTE, each with different bands) instead of just sticking to the one it has a connection to. For a detailed technological description of this Android independent part, I cannot give an answer (I'm no engineer).
Comment: Is this still relevant with Lollipop?
Comment: @wizlog Lollipop wasn't installed on the cell towers, and neither changed the GSM/UMTS/LTE protocols – so I assume the topic remains relevant. I don't have an LP device here (and no corresponding test environment or the time to run such a test) to see whether LP handles this more efficiently, but it certainly cannot do anything to signal quality (only react on it).
Comment: @Izzy AutoPilot and ShutUpBatterySaver's link seems to be dead.
Comment: Apps suggested in the answer are no longer exist.
Comment: @Pandya look at the date. And be welcome to be more precise (e.g. mentioning which ones). Though there might not be a replacement – and I have no time to search for them.


how to set up internet wire connection on Ubuntu 12.04?

Question: I install Ubuntu 12.04 on VMWare on D drive of Window 7. Now, Window 7 have internet connection but Ubuntu have no internet connection. In window 7, I use automatically detect proxy with wired connection. It's ok on Window7. Why it doesn't on Ubuntu. Please let me know.
Answer: Simply selecting NAT in the VM's options should work for basic network access - assuming that the NAT networking was set up when VMware (whatever?) was installed. more info can be found in here
Comment: Yes, I use only NAT. Before Ubuntu, I installed Window XP on that VMware. At that time, its ok in internet connection. I didn't make any changes. I can't find it out.
Comment: which version of VMware you are using?
Comment: please refer [this](http://communities.vmware.com/thread/402577) link, it might be help you.
Comment: My VMWare version is 6.5.


Windows: How to create a shortcut for the Safely Remove Hardware dialog?

Question: I find it useful to have a handy shortcut icon for the hardware removal operation. How do I create a shortcut for the Safely Remove Hardware dialog?
Answer: RunDll32.exe shell32.dll,Control_RunDLL hotplug.dll

Source: Create a Shortcut or Hotkey for the Safely Remove Hardware Dialog
Answer: Beyond chopeen's answer, if you find your USB device does not accept a remove operation.
Read these tips for pendrives.
You might also want to keep the RemoveDrive tool handy.


Is it theoretically possible to restore the Tiger population to 100,000?

Question: The current global Tiger population is roughly 5100 according to Wikipedia. With habitat destruction and poaching continuing and no effective improvement in conservation, most likely the Tiger population will continue to decrease. I'm wondering what is the theoretical maximum population to which the Tiger species could be restored. Suppose poaching and habitat destruction stopped today and conservation efforts were increased drastically, so the only factors limiting population growth are the natural dynamics between the species and its prey. Could we then restore the global population of tigers to its pre-20th century level of 100,000?
Comment: Just FYI: to go from a population size of 5100 to a population size of 100,000 in 85 years, each female has to have on average 1.036 offsprings. This calculation assumed no stochasticity. variance in number of babies among females would bring this number up by a little bit.
Comment: Well, it is. It just makes a bunch of assumptions as it is super simplistic. As said, you can use more complicated models but you'll have to define other parameters such as the carrying capacity or the environmental change through time for examples.
Comment: $5100 * x^{85} = 100000$ and solving for `x`. Of course it also assumes constant growth. But I think that it gives a feeling that if we manage to have growing populations, then whether and threshold of is at 50000 or at 250000 does not matter so much. Of course, whether each female will keep reproducing as much depend on whether the carrying capacity is high enough, and typically a logistic model might be a better fit than this exponential model.
Comment: Yes that is not a rigorous calculation.
Comment: How did you calculate that.
Comment: Yeah that is what I meant. Anyways 1.036 offspring is low for tigers anyways, so your calculation shows that its not an unreasonable goal at least theoretically.
Comment: The question is interesting but I think there are tons of parameters involved and to answer this question one would need knowledge in a whole lot of different field. Generally, speaking I am afraid that biology (and geography and sociology as all those things are in interplay in the question) is rarely advanced enough to be able to answer this kind of question. We can make predictions about what should and should not be done, we can observe the beneficial impact of conservation efforts but we're not good enough to make the predictions you're looking for.
Comment: I think more interesting question would be what the minimum is (caused by outbred selection).
Comment: It is possible any day. Given time, their population will increase exponentially. But, we need co-operation fo people which can't be achieved easily
Answer: I don't think your core question can be answered exactly, namely "...the theoretical maximum population to which the Tiger species could be restored", since there are too many variables to consider. However, the comment from @Remi.b is apt, in the sense that it shows that population growth rate per se (or reproductive rate) should not be the limiting factor. The bottleneck will probably be some concept of carrying capacity (the number of tigers that the current tiger habitats can sustain). This number will naturally depend on many factors, for instance whether all hunting of tigers and their prey is removed from the remaining habitats.
You could arrive at a ballpark estimate of the current "theoretical" maximum population size by finding the area of suitable tiger habitat and dividing this by the average size of tiger territories. However, the size of tiger territories differ quite a bit between males and females and between areas with different prey densities, and probably also between different tiger subspecies (which will covary with average prey density to some extent - Siberian tigers generally live in habitats with lower prey densities). Looking at estimates from the Smithsonian and wikipedia, territory sizes seems to range between 20 to 510 km2, with maybe even larger male territories in Siberia (so quite a big range). The IUCN Red list assessment of tigers state that the current tiger range is to 1.185 million km2 (from Sanderson et al. 2006 as "Tiger Conservation Landscapes"). It is however unclear whether this number corresponds to the total range extent or to the actual amount of suitable habitat (probably the former though). Nevertheless, lets say that the average territory size is 265km2 (probably way to high on average), that the estimated area from IUCN is correct, and lets assume that territories never overlap (which they do; male territories overlap with several female territories and female territories can also overlap to some extent). In that case, we will arrive at an estimated theoretical popultion size of ~4500 tigers. If we instead use a more modest territory size of 40km2 we will arrive at a population size of ~30000 tigers. Since territories can overlap, these estimates should be biased low, given their other assumptions.
Sanderson et al. (2006) however also includes a summary of "Effective Potential Habitat" of tigers, which sum to 5.65 million km2. If this number is used to calculate the estimated theoretical popultion size you will arrive at ~21300 or 141000 tigers, using the same territory sizes as above. However, this completely ignores issues such as landscape connectivity, and that tigers are completely missing from large parts of their former distribution (these factors, and others, were used to define the "Tiger Conservation Landscapes"). Also note that much of the potential habitat lies in low-productivity areas (Russia and parts of China), where territory sizes are relatively large.
Another perspective would be to use the historical population size pre-20th century and the amount of decrease in tiger habitat to estimate a theoretical population size. I don't know anything about the historical population size, but let's say that your 100000 is accurate (source?). Dinerstein et al (2007) state that current tiger ranges correspond to 7% of historical ranges. Using only these numbers, you could arrive at a current theoretical population size of 7000 tigers (100000*0.07), assuming that the tiger population should directly mirror the amount of available habitat. However, the current 7% of historical ranges include range contractions due to hunting, so this estimate should be biased low (maybe strongly so) with respect to the possible population size that could be obtained if all hunting stopped.
These calculations should show that the current Tiger populations could probably be increased quite a bit with strong and effective conservation efforts (in your words: if "poaching and habitat destruction stopped today and conservation efforts were increased drastically"), but that 100000 will probably be extremely hard to obtain, given that so much of the historical range has been lost. With reintroduction programmes and a long timeframe it doesn't appear to be impossible though, but this is ignoring potential future problems such as increased tiger-human conflicts. Also note that I don't know much about Tiger biology, that these are merely rough back-of-an-envelope calculations, and an expert could certainly give you a more detailed and accurate answer.
References:

Dinerstein et al. 2007. The Fate of Wild Tigers. Bioscience 57 (6): 508-514. doi: 10.1641/B570608
Sanderson et al. 2006. Setting Priorities for the Conservation and Recovery of Wild Tigers: 2005-2015. The Technical Assessment. WCS, WWF, Smithsonian, and NFWF-STF, New York – Washington, D.C.
The Smithsonian: Tigers
Wikipedia: Tiger
IUCN Red List: Panthera tigris
Comment: What about the bottle neck effect? Increasing the population size won't increase the genetic diversity, won't it possibly lead to tigers that are not fit?
Comment: @SolarLunix For individual populations/subspecies inbreeding/genetic diversity might an issue, but for the species as a whole (if pooled) it is probably not a big problem. Overall, I don't think inbreeding is seen as a big problem in wild tiger populations at the moment. Either way, I don't think it makes much difference for this particular question, which is speculative and other factors are likely to be much more important.
Comment: but pooling the tiger population would be difficult wouldn't it? It would involve moving tigers to new habitats and hoping that that group of tigers will accept the new tiger rather than shun or kill them. According to my evolution teacher they are already going through a bottle neck effect, and if it's anything like the wolves we read about on the isolated island it could be quite detrimental to the species as a whole.
Comment: @SolarLunix My point isn't that all populations can be pooled, but that inbreeding is probably not the main factor to consider when answering this question. I agree that all populations cannot simply be pooled per se, and genetic effects might be an issue for some subpopulations. However, I doubt that inbreeding is the main problem for the survival of tigers as a species or for trying to restore tigers to much larger populations (but I might be mistaken). Also, a bottleneck is one thing (they are by definition going through one), and effects of inbreeding on population growth is another thing.


Proof that $\lim_{x\to0}\frac{\sin x}x=1$

Question: Is there any way to prove that
$$\lim_{x\to0}\frac{\sin x}x=1$$
only multiplying both numerator and denominator by some expression?
I know how to find this limit using derivatives, L'Hopital's rule, Taylor series and inequalities. The reason I tried to find it using only multiplying both numerator and denominator and then canceling out indeterminate terms is because the most other limits can be solved using this method.This is an example:
$$\begin{align}\lim_{x\to1}\frac{\sqrt{x+3}-2}{x^2-1}=&\lim_{x\to1}\frac{x+3-4}{\left(x^2-1\right)\left(\sqrt{x+3}+2\right)}\\=&\lim_{x\to1}\frac{x-1}{(x+1)(x-1)\left(\sqrt{x+3}+2\right)}\\=&\lim_{x\to1}\frac{1}{(x+1)\left(\sqrt{x+3}+2\right)}\\=&\frac{1}{(1+1)\left(\sqrt{1+3}+2\right)}\\=&\frac18\end{align}$$
It is obvious that we firtly multiplied numerator and denominator by $\sqrt{x+3}+2$ and then canceled out $x-1$. So, in this example, we can avoid indeterminate form multiplying numerator and denominator by
$$\frac{\sqrt{x+3}+2}{x-1}$$
My question is can we do the same thing with $\frac{\sin x}x$ at $x\to0$? I tried many times, but I failed every time. I searched on the internet for something like this, but the only thing I found is geometrical approach and proof using inequalities and derivatives.
Edit
I have read this question before asking my own. The reason is because in contrast of that question, I do not want to prove the limit using geometrical way or inequalities.
Comment: Using L'Hopital's rule or a McLaurin series isn't kosher, because those require knowing the derivative of sine, and proving that the derivative of sine is cosine is generally done using this limit.
Comment: "I know how to find this limit using derivatives, L'Hopital's rule, Taylor series" That's a bit suspect. One usually proves $\lim \sin x /x = 1$ first, with a bare-handed geometry argument. From that you obtain the derivatives of the trig functions. Finding $\lim \sin x /x = 1$ using L'Hopital is a bit of joke really.
Comment: You can use *L'Hopital's Rule* or use a Mclaurin Series. Trigonometric functions are not algebraic, so no special cancelling can be done, at least in the same matter as you'd like.
Comment: Possible duplicate of [How to prove that $\lim\limits_{x\to0}\frac{\sin x}x=1$?](http://math.stackexchange.com/questions/75130/how-to-prove-that-lim-limits-x-to0-frac-sin-xx-1)
Comment: @GauravRamanan. I have read that question before asking this. In that question, OP said "Best would be a geometrical solution", but I mentioned in my question that I have already proved it in geometrical way. My question is different way of proving it.
Comment: @Mathematician171 Oops sorry, missed it!
Comment: "I searched on the internet for something like this, but the only thing I found is geometrical approach and proof using inequalities and derivatives." I doubt very much you found that. Inequalities yes, derivatives no.
Comment: The problem with what you ask is the definition of $\sin$. The geometric "definition" doesn't give you a lot of wiggle room. If you use another definition, than that's a different matter.
Comment: "I do not want to prove the limit using geometrical way" So you want to prove a theorem about a geometry-defined function with no geometry. Unfortunately, I don't think there's any non-circular proof of the limit besides the famous geometry-based one. What don't you like about that proof?
Answer: If I remember correctly, it is not possible to solve this limit algebraically, as therefore the Numerator $f(x)=\sin{x}$ and the Denominator $g(x)=\frac{1}x$ must have both an existing limit, so one can use the rule
$$\lim_{x\to x_0}\frac{f(x)}{g(x)}=\frac{c}{d}$$
The right and lefthand side limits of the Denominator $g(x)=\frac{1}x$ are
$$\lim_{x\to 0+}\frac{1}x=\infty$$ and
$$\lim_{x\to 0-}\frac{1}x=-\infty$$
So you cannot solve this limit algebraically, as the limit is not defined at $x=0$.
Hope this helps!
Comment: @user164524 well thought out question.


Potential difference in a circuit of n cells = 0? How?

Question: I was supposed to find the potential difference across any one cell in an arrangement consisting of n cells of EMF E connected in series in a closed circuit and internal resistance r.
I proceeded by finding the current in the cell.
i=nE/nr=E/r
Then across any one cell potential diff. is V=E-ir=E-(E/r)r =0
This answer i.e. 0 matches with the book answer.
But if we sum up the pd across all cells in this way then pd across all cells would be 0.
This would violate my initial assumption while finding current that pd across the circuit is nE.
So where am I going wrong?
Is it a misprint in the book or am I mistaken in my fundamentals?
Comment: I see no reason as to why my question should be downvoted!A question should be downvoted not beacause it is dumb,but when it seeks to ask anything without any attempt from the asker's side.
Comment: No, we downvote questions for all sorts of reasons, related to them being low-effort or otherwise unsuitable for the site.
Answer: You are mistaken about your fundamentals.  Your initial assumption was that the potential difference across the resistors was nE, not the whole circuit.  You implicitly assumed the difference across the whole circuit was zero when you connected the components in a closed circuit.  One of Kirchhoff's laws says the sum of the voltages in a loop in zero.


Why aren't glass spoons used for eating?

Question: Why aren't glass spoons used for eating? It seems it would solve the problem of metallic taste with some foods.
Comment: Mmmm, nothing like the delicious food and glass combo of accidentally biting down too hard on your glass flatware.... also, having to replace your flatware every time you drop it.
Comment: Perhaps because there is a risk of damaging the glass when taking a bite, which might result in cutting lips and swallowing bits of glass. When drinking from a glass, we don't touch it with our teeth as much. In fact, in this day and age, plastic spoons would be the most efficient.
Answer: There has actually been some significant research into cutlery being made of the correct substance to match the food
Testing shows perceptible difference in tastes from various metals when combined with certain foods. Just as silver spoons and egg are an unpleasant experience, some metals (e.g. copper, zinc) acted as a catalyst and improved the taste experience of certain foods
We use wood and ceramic for similar reasons, often for the mouth feel of the cutlery and heat dispersion, e.g. hot soups with metal spoons can be painful
Glass would have it's place, but probably not to dissimilar to porcelain (ceramic). Glass spoons are available, but rare

Some references:
Institute of Making - Sensoaesthetic Properties of Materials
Fine Dining Lovers - Cutlery food science
Answer: There was never a need, as there was no benefit.
Spoons made from wood, nacre, horn or porcelain were widely available and don't come with the disadvantages of glass, like insufficient resistance to sudden temperature changes or shock resistance.
Borosilicate glass was invented in the late 19th century, so it wasn't available at a time where it might have had a greater influence on culture.
Porcelain spoons are cheap, with no apparent disadvantages, are widely accepted and do match with other kitchenware.


How to rename a project in the Team Foundation Server (TFS)

Question: How to rename a project in the Team Foundation Server 2008? What are khown issues?
Answer: The Team project cannot be renamed in TFS v1
You may use the following workaround (sort of workaround, because you won't really end up with renamed project with identical contents):

Create new project with desired name
Copy work items from old project to a new one (one-by-one, as there is no bulk copy option).
Move all source control folders from under old project folder to a new project folder
Sharepoint portal documents cannot be moved in bulk (as far as I know), so you do that manually
Move of source code will retain the files history, and work items will also have partial history, but overall I would say the workaround does not worth the labour (and Sharepoint docs will not have their history). At any rate, selecting right name in the beginning beats any workaround by far.

Source
Comment: Renaming a Team Project is also not supported in the latest version of TFS currently in development (TFS 2010).  Therefore probably best to just stick with the name you have unless it is really bad.
Answer: You can't rename a project name even in TFS 2010.
However, the renaming feature is often requested. Go here and vote for this feature to force Microsoft to put it in next version of TFS.
https://connect.microsoft.com/VisualStudio/feedback/details/554539/cant-rename-a-team-project-in-tfs-2010
Comment: Voting was closed: "Due to current priorities, the product team decided to postpone the resolution of this item."
Answer: I think renaming is one of the most sought after features.  Unfortunately, as mentioned above, there is no contextual menu to do a site rename.  If you don't utilize the work items or the sharepoint features, the built in move command will be your best bet.  You will, as mentioned above have to create a new team project with the desired name.
Answer: Whilst you can't rename a Project from within TFS, there are now easier ways to accomplish the whole Move files, Copy/Paste Work Items steps outlined previously:

TFS Integration Platform

If you download the release from the Visual Studio Tools Gallery this will allow you to move source control items with history, as well as work items to a new project - indeed the initial Hands On Lab included in the documentation walks you through this exact scenario.
Answer: You can now rename a team project on Visual Studio Online and in the upcoming TFS 2015 release: https://msdn.microsoft.com/library/vs/alm/tfs/administer/project-rename
Comment: That link has been moved or renamed :(


Why is a question asking about how to improve a post on main being close voted as not clear?

Question: I recently asked this question on meta about how to improve another question on main. Currently, the former question has a total score of 18 downvotes and 4 close votes. The close votes mention as a reason that the question lacks clarity. However, I fail to see how this is the case. What can I do to improve my meta question, or make it more clear?
Comment: Because the world is asynchronous. Retracting a vote would require the person who casted it to care enough to return and retract it.
Comment: And since there is no built in incentive to return and reassess a post, you're counting on folks who are either bored or have a personal revisiting policy for posts they've voted on. In general the old stuff stays and the upvotes for a fixed post will come from new visitors in the future. That can be slow. Since only the close voter can cancel the close vote, you're usually stuck with them, and hopefully no one sees reason to add more close votes.
Comment: I mean, 2 of the votes were casted before you updated your question to now ask about the now downvoted so post. Ignoring the meta effect, your question was infact quite unclear, in that there was no reason to believe your post needed to be reviewed at all.
Comment: @KevinB So the close reasons are now no longuer valid. Why were they not retracted?
Answer: It's the pile-on effect. Once you get an initial early downvote, it usually doesn't make any difference what you do to improve your question. The damage is done, and others will downvote it regardless of how good it becomes.
Instances of people coming back to remove their downvote, or even upvote, due to your edits are extremely rare.
This is just how SO works I'm afraid.
Comment: I think the pile-on effect certainly exists, though I'm not sure how significant it can be.


Size of black hole

Question: I am wondering about size of black hole. How is it possible that we have black holes of different sizes? As I know the singularity is point which is infinite small and is infinite dense. So my question is how can infinite dense and infinite small object create different size black holes. We have different big infinite singularities?
Comment: Usually when we talk about the size of the black hole we're talking about its event horizon.  You're right it doesn't make much sense to talk about the size of the singularity.  Plus, due to the extremely distorted space I'm pretty sure you can measure an arbitrarily long length inside of the black hole that's arbitrarily small outside of it.  That is, I'm pretty sure the curvature allows a black hole to be "much bigger" inside than it is outside.
Comment: @BrandonEnright: I think you might want to make that a separate question and spell out in more detail what you have in mind.
Comment: Nobody has ever seen an infinitely small and infinitely dense object. This is an example of an over-extrapolation of a theory that makes absolutely no statements about the microscopic states of dense matter. It doesn't predict the density of planets, stars or even neutron stars all by itself. We always have to add an equation of state the regulates the density as a function of pressure (and temperature) to general relativity to make these predictions. We simply do not have an equation of state for the interiors of black holes.
Answer: A black hole has two main features:

a singularity
an event horizon

The event horizon is a sphere with a certain radius. Most people visualize the singularity as a point at the center of the sphere, and although that's not quite rigorously right, it's good enough for the purposes of the present discussion.
Using a rough Newtonian analogy, the event horizon is like the surface from which the escape velocity exceeds the speed of light. In the real relativistic theory, it's boundary that no cause-and-effect relationships can cross from the inside out.
Black holes form by the gravitational collapse of massive bodies. You can think of the singularity as the place where all the in-falling matter accumulated.
When people talk about the radius of a black hole, they usually mean the radius of the event horizon.

Thank you, but what is making that diference between sizes of event horizons (we have got super massive black holes, smaller blackholes? I mean how is possible that one blackhole is smaller than the other or bigger when singularity is just infinite in size and mass ?

Different black holes have singularities containing different amounts of mass. The mass is not infinite. For example, if a star with a mass of 6 solar masses collapses to form a black hole, then the black hole is a 6-solar-mass black hole. The size of the event horizon is proportional to the mass.
Comment: Thank you, but what is making that diference between sizes of event horizons (we have got super massive black holes, smaller blackholes? I mean how is possible that one blackhole is smaller than the other or bigger when singularity is just infinite in size and mass ? When is once something infinite small and infinite dense why it doesn´t create still same big black hole ? why is that event horizon still different in size ? Or singularity is  that point in the middle and around him there is another mass which is creating size of black hole  ? Sorry for english.
Comment: Hi Ben, welcome back :-)  I made a comment above on the question suggesting the curvature inside of the black hole does strange things with "length".  Am I completely off?  Can you say more about what reference frame the radius is measured in?
Comment: @TomasKlema: I edited the answer to respond to your comment.
Answer:
So my question is how can infinite dense and infinite small object
  create different size black holes.

The singularity within a black hole is not the crucial consideration here.
If an amount of (non-spinning, non-charged) mass $M$ is contained within a volume of radius of $r_s = \frac{2GM}{c^2}$, the mass $M$ is 'hidden' within a spherical event horizon (black hole) of radius $r_s$.
Thus, the larger the mass $M$, the larger the radius $r_s$ of the black hole.
The result that the mass cannot remain static within the horizon and must collapse to a singularity is secondary to the above result.
Answer: Different black holes have different masses. For non-rotating black holes, the distance
$$r=\frac{2Gm}{c^2}$$
describes the event horizon. As you can see, the mass $m$ of the black hole enters here. This WP page on the Schwarzschild radius describes has more information.
Answer: Different sizes are formed because while infinitely small there is technically a measurable amount of mass. That mass creates a different size event horizon like event horizon is gravitational pull no return point. Like he said a 6 solar mass star becomes a black hole it will have X as its event horizon now lets say it collides with a 10 mass black hole. It will now be a 16 mass black hole whos event horizon size will now be X1+X2. The size of the black hole is dictated by first how large of a star created it PLUS whatever it collides with after
Comment: As it's currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer).

Size of black hole


iOS12 beta crashed doing update

Question: I've been running the iOS consumer beta for a few months largely without issue.  Today it offered to install the latest update.  The battery was highly charged and I had it sitting on a wireless charger and it failed in the middle of the update.  Now it just cycles with the white apple logo showing and off in a 5 second loop.  I got it to connect both to iTunes and imazing but neither could fix the problem, no doubt because they are trying to do ios11 and running into conflict with iOS12.  Help!!!
Answer: Put it into DFU mode and use iTunes to restore it. You can restore it to either iOS 11 or iOS 12 beta 9.
Here are instructions on entering DFU mode: https://www.theiphonewiki.com/wiki/DFU_Mode (Since the instructions vary between devices and you did not mention which device you have, I won't copy and paste them all to this page)
When it's connected to iTunes you should be able to press Restore. If that doesn't work, try restoring a specific IPSW file. You can download files here: https://ipsw.me
You can use the IPSW by holding option (mac) or shift (windows) when pressing the "Update" button. It will prompt you to select the IPSW.

iOS12 beta crashed doing update


Bus and System Clocks

Question: What is the difference between a Bus clock and a System Clock? Do they function the same way? I have been reading about System clocks but I can't really find anything about bus clocks in my book to compare the two.
Answer: In a simple computer architecture with a single active CPU connected to RAM and other passive peripherals by a bus, then there is a timing signal (typically produced by a quartz oscillator) that synchronises the internal operation of the CPU. This clock signal is the system clock.
There may also be a separate timing signal that synchronises the activities of writing to and reading from the bus. This is the bus clock. Because the speed at which data can be reliably transmitted across the bus may be lower than the internal speed at which the CPU runs, the bus clock signal is usually at a lower frequency than the system clock. The bus clock signal may be produced by passing the higher frequency system clock signal through a frequency divider.
In more complex architectures, where there are multiple active components (CPUs, FPUs, graphics cards, memory controllers, I/O controllers) running at different speeds, then the bus clock is often the fundamental synchronising signal, and each component then multiplies the frequency of the bus clock signal by a specific ratio to obtain its internal system clock signal.
For more details see https://anydifferencebetween.com/difference-between-system-clock-and-bus-clock/ and https://en.wikipedia.org/wiki/CPU_multiplier.

Bus and System Clocks


How can I convince the universities that I am applying to for Ph.D. program for accepting the reference letters given to me by my referees?

Question: I am in the process of applying to overseas institutions for the phd programme. For this purpose, my referees have already provided me with the reference letters as I am applying to the multiple institutions. So, they are unable to find time for filling the reference request forms. Unfortunately, most of the universities are asking for online reference request which I know my supervisors won't be able to fill it due to the time constraints. So, I fear on losing out on the applications of interest. Please guide me through this.
Comment: Does this answer your question? [How frequently can you ask for a personal reference without being disrespectful?](https://academia.stackexchange.com/questions/9757/how-frequently-can-you-ask-for-a-personal-reference-without-being-disrespectful)
Answer: There is nothing you can do but politely ask of your referees that they understand your situation and fill the online form.
There is simply no way my school will accept reference letters supplied through the applicant, and no amount of convincing will change this: there is just too much fraud with LoRs supplied by students.
Even if your referees fill the form online, expect (depending on the country) that they may be randomly contacted via their university or institutional email address to confirm the contents of the LoRs.  Again, there is just too much fraud with applicants (or sometimes their agents) creating or controlling false emails.  Be advised that our school logs the IP address of people filling out reference forms.  I suspect other schools have similar policies.
Regrettably, we have seen (international) applicants arriving under false pretences, leading to absolutely horrible situations.
Finally I would personally automatically dismiss as not fully frank any LoR that is not confidential and has been seen by the applicant.
Answer: This really depends on the country, you're not very specific. But my gut instinct is that, if your referees really wouldn't find the five minutes it takes to fill out one of these online forms, they wouldn't actually want to support you.
But my guess is that your referees will be happy to support you, you're just too shy to ask them to fill out the online forms! Can't say I don't understand you.
Comment: I am not sure I agree. Yes, it's probably only 5 minutes for one graduate school for one student. But, if the professor has 20 students applying for graduate schools, each student applies 10 schools, then the professor has to spend 20 x 10 x 5 minutes to fill out online forms. That's 1000 minutes, more than 16 hours. It's quite a lot of time for a busy professor.
Comment: @Nobody it is then incumbent to the professor not to agree to write so many letters of support.
Comment: I think it is just rude by the institutions not to provide an upload option for a fixed reference letter. That's what I am usually encountering: the possibility of filling a form or else upload my own written reference letter. The latter can be done a number of times without undue burden.


Why are bagpipes tuned using just intonation?

Question: To my knowledge, the Great Highland Bagpipes are tuned using just intonation rather than equal tempered tuning. Why is this? What is the advantage of just intonation?
Comment: They aren't tuned to either. They are tuned to a temperament of their own. Source: New Grove Dictionary of Music, volume 2, p.21. This is readily audible.
Answer: The reason doesn't seem to be a technical advantage but the favored  traditional sound of the just tuning that bagpipers describe as more colorful and warmer:
Patrick McLaurin writes in his bagpipe blog:

If bagpipers used the equal temperament scale the drones would sound out of tune for every note but the As, although B, D, and E might be close enough. C#, F#, and G would be way off; hence why we need to beauty of the just intonation scale.

In the link above he also explains the difference between the TET and the just intonation.
He explains that the bag pipe is in D major and

there are several resources for learning how to (and understanding the theory behind) tuning a bagpipe with an equal temperament tuner. Now, this sounds like an odd thing to want to do since we don't use the equal temperament scale. The reason you would want to use an equal temperament tuner to tune a just intonation instrument is simple, economics.

He also refers to Kyle Gann who compares the 2 tuning systems and tells us why he favors the traditional tuning:

I've had interesting experiences playing just-intonation music for non-music-major students. Sometimes they will identify an equal-tempered chord as "happy, upbeat," and the same chord in just intonation as "sad, gloomy." [...]
[...]
On a more subtle level, after I've been immersed in just intonation for a couple of weeks, equal temperament music begins to sound insipid, bland, colorless. [...]
[...] playing in just intonation for long periods sensitizes me to a myriad colors, and coming back to the equal tempered world is like seeing everything click back into black and white.

The two links above also explain - as does this one by Ewan Macpherson - the system of the different temperatures - and all agree that the A (pitch 460 and higher) sounds sharper than a B♭ in concert pitch.
So we can assume that the just tuning is rather a tradition and sentimental reason than a technical aspect - despite  the lower costs of equal tuning.
Comment: Note that equal temperament really only applies to keyboards, computers and fretted instruments . In any other kind of vocal, wind or string music everybody is adjusting the temperament as they go.
Comment: Every bagpipe I've ever tried to accompany has been somewhere between A and Bb. Closer to Bb.
Comment: @PiedPiper but since the bagpipe offers the player no contact with the reed, the only way to tune individual notes is with air pressure or partial occlusion of tone holes with the fingers.  With oboe, bassoon, clarinet, saxophone, and so on, the player can also use the embouchure to alter the pitch.  Also, fretted instruments can bend pitch, and older fretted instruments used tied-on frets that could be adjusted to alter the intonation.
Comment: @phoog Take fretted instruments out of the first group if you want, but that just strengthens my point: only a small subset of instruments are strongly equal tempered. The pitch of bagpipes can't be controlled is the same way as on classical woodwinds, but players aren't trying to match equal temperament, or any other temperament except their own
Answer: The drones are tuned by ear so you expect them to be tuned to just intonation.
The holes in the chanters can't be made exactly enough that you could say they're  just or equal tempered. The difference between two different chanters is probably greater than the difference between just and equal temperament.
In general for any kind of non-keyed "folk" wind instruments the whole concept of equal temperament is meaningless.
Comment: As far as I know, many standard pipers use chanters with a seventh tuned near the septimal seventh (7:4 ratio).  With A as a normal tonic, that's referring to the G.  As that's over *31 cents* lower than then ET minor seventh, I'm pretty sure chanter holes can be made to that level of precision (and, in fact, they should be able to be made to distinguish just vs. major thirds, about 14 cents difference). I know there are sometime jokes about how out-of-tune bagpipes are, but if holes varied enough for 31+-cent deviations, the result would be horrendous indeed.
Comment: @Athanasius Another answer links to the site of a bagpipe player who discourses at length on tuning, but the video of him playing sounds out of tune according to any system I've ever heard (As a wind player I know what just intonation sounds like). Maybe that's a desired effect.
Comment: I downvoted this answer. I will remove my downvote when you can provide a source that either proves or gives sufficient arguments to your statement that chanter-holes can't be made with enough precicion, or when you restrict your statement to a smaller subgroup of chanters.
The reason for that is that know counter-examples: Polyphonic  just-sounding bagpipe music exists, but wouldn't be possible if what you wrote was true.
Comment: @Quantumwhisp Do you have a link to the polyphonic bagpipe music you are talking about?
Comment: @PiedPiper: https://www.youtube.com/watch?v=awEoKT_HQb4 this is a duo for german sheppherds-pipe, they play polyphonic music (which wouldn't sound so nice if the builder wasn't able to make theese chanters within the margins of 10 cents)
Comment: @PiedPiper Since you have been talking about the GHB in particular, I found a vid of 3 pipers playing in unison here: https://www.youtube.com/watch?v=TbpHPBXla7s, which wouldn't be possible if chanter pitches were varying as mutch as you suggested either.
And here https://www.youtube.com/watch?v=27cS1pDWcQQ, the major thirds you can hear in the beginning wouldn't sound that clean either.
Comment: @Quantumwhisp Listening to those videos, even when they are playing in unison they aren't better in tune than about ±10cents
Comment: @PiedPiper you might want to check out the 78th Fraser Highlanders.
Answer: This answer will be about bag-pipes in general, not about the Great-Highland-Bagpipe in particular. As such I won't make a statement about the tuning of the GHB, but instead about the general tuning of Bag-pipes:
There is no standard on how to build a bag-pipe. Bag-pipes in general are handmande instruments, so (in principle),  with every instrument, the builder is free to choose a a tuning. It would however be unusual for a builder to not stick to a tuning of his choice, because of that instruments of a kind of one builder will (in usual cases) not have different tunings.
Examples of different tunings in case of the german shepphards-pipe I have seen featured "Just Intonation", "Kirnberger II"described here or some weird other selfnamed-intonation (I emailed the guy and got a table with how mutch cents the individual notes would differ from the equal-temperament-version),which was a mixture of just and equal temperament.
There are 2 reasons why bag pipes (including the GHB) are usually tuned in a "more just" intonation than the equal-temperament version:
Both reasons are connected with how we perceive Intervals, and that "just intervals", with more simple frequency rations, CAN be perceived as "better sounding". You probably know this, but I still want to reconcile it for the sake of the answer:
What sounds better to an ear is as well a product of what one is used to, but what one can say objectively about just intervals is that they are more stable (this
video shows that), because the frequency ratios are simpler. The intervals are also perceived as "more in tune" because of that (which doesn't necessarily mean they are "better sounding".
Now comes the reasons for a more just tuning to be choosen for bag-pipes:
Bag-Pipes, no matter wether they are played together, or solo, are drone-instruments. A Drone (which is an accompanying tone) will be audible most of the time during the piece one performs, even if it might not "fit" harmonically to the actual passage (for example because the drone-note is not present in the harmony that a melodic line is based on). You might want to play a broken D-minor chord (D F A F), while a C-Drone is constantly audible.
In general, such situations will be more pleasant sounding when all notes are justly tuned to the drone. Because the frequency ratios the notes have with the drown are more just, the drone can be perceived as a nice accompanyment, no matter what notes are played.
Another example would be the melody featuring a B, while the drone being C. The interval is a 7th, which sounds more harmonic in a just tuning, than in the equally tempered one. That is reason 1.
Reason 2 is that the drone automatically restricts the repertoire to keys close to the drone-note. A bag-pipe doesn't need to transpose wildly through all the keys possible, most keys wouldn't work with the fixed drone-note anyways. So there is no need to use equal temperament (which was invented for exactly this reason).


Why Scifi not allowing me to post a question?

Question: My last question hit HNQ, but now Scifi not allowing me to post a question:
Comment: @Valorum As far as I'm aware deleting posts actually goes against you for the rate limiting and in any case the user won't be able to delete the questions because they both have upvoted answers.
Comment: Because two of your last three questions are underwater. I'd suggest editing (or deleting) the one that's most heavily downvoted.
Comment: @TheLethalCarrot - Does disavowing them count against you?
Comment: @Valorum Disassociating the posts? No idea but it's not really something that would happen just to avoid a question block.
Comment: @TheLethalCarrot - I was thinking more because they're so heavily downvoted.
Answer: The rate limit here is put in place by the system based on a number of factors, mostly though how well all your recent questions have been received, not just your latest one.

How is the length of  time that I'm limited actually calculated?
It's based on your average question score, how long you tend to wait between asking questions, how well you participate in other ways on the site, and how often you tend to revisit and improve your posts, even the positively scored ones. We don't provide the actual formula and details, only because we want folks to focus on what the system is trying to tell them, rather than trying to find ways around it.
Rate limits vary from 1 to 7 days.
Why won't the system allow me to ask questions for several days?

The linked meta post above from SO meta has some good details about this case for you to look over, as does the relevant help page. I suggest you read over some of the more general suggestions there and then see if you can improve your questions going forward. This might just be a false positive as your last question was well received but it's worth taking a step back and seeing if there is anything you need to do moving forward.


Lowest level of a Slayer of Terramorphous Class Mod?

Question: A Slayer of Terramorphous Class Mod is a guaranteed drop (only) from Terramorphous the Invincible. I believe Terramorphous the Invincible can only be at least level 50 and thus drop at least level 50 items. Can one acquire a Slayer of Terramorphous Class Mod at any level below 50 without the use of such tools as Gibbed's Borderlands 2 Save Editor or Cheat Engine, i.e. without modifying game values from outside of the game client?
Answer: As the quest is level 50 (You.Will.Die.(Seriously.) and rewards are always tailored towards the Quest-Level I dare to say the answer is no.
Answer: Unless you enter someone else's game and they are on the quest 'You. Will. Die. (Seriously.)', then you have to wait till at least level 50. I managed to find a player nice enough to let me 'piggyback' him on his game, so to speak, and managed to get the class mod for my siren at level 5.
Comment: But is the class mod itself level 5? I suspect not.


How Scalable is the Wave Disk Generator Engine

Question: How scalable is the wave disk generator engine?  Are there fundamental limits to how large or small the engine can be and if so, what are they?  I'm not looking for answers addressing microscale issues, but rather, I want to know if the fluid dynamics inside the engine require a certain size range in order for the combustion to work properly.
Comment: Let's just say there is an optimal size of the engine that maximizes output. In that case, you could probably configure multiple engines coaxially so they are turning the same, albeit larger, generator together.
Comment: I'll leave more informed users to say otherwise, but I'm guessing that most people won't have much experience with a brand new technology. That is unless the professor or one of his students are users here.
Answer: "Let me say this about that"  (extra points to those who recognize the originator of that phrase).
First:  yeah, they've invented a cool-looking device.  But, they appear to be getting nowhere so far as either advanced funding or a fieldable model produced.
Second:  I have seen at least 5 or 6 "groundbreaking new powerful/efficient/wunderdevice" internal combustion engine designs pop up over the last 30 years (not even counting the Wankel rotary).  Not one has been able to show both minimal life testing and improved efficiency over modern piston-crankshaft engines.   I see no reason to expect this design to do so either.
For further, quite specific, counterarguments, take a look at  this review
Comment: Actually it's not that these designs aren't promising, it's that the existing supply chains are so tight that getting a new design from a new company into the chain is next to impossible, no matter what the advantages.


404 error on Google Webmaster toools

Question: I have some issues with 404´s on google web master tools.
Google is telling us this one is a 404 (is a real 404):
http://www.apartmentratings.com/VA-Midlothian-Woodlake-Village-Waterpoint.html
And that url is linked from:
http://www.apartmentratings.com/rate/VA-Midlothian-Crowne-at-Swift-Creek-Map.html
But that url, is not there, is not on the code, nothing.
I don´t know why google is saying we have a 404 there. I had to create some apache rules to avoid this, rewriting those urls with the "/rate" prefix.
Answer: click on "Mark as Fixed" under  Crawl > Crawl Errors and see if it helps

404 error on Google Webmaster toools


How to replace hex encoded string with chars?

Question: I have UTF-8 encoded HTML with id(s) and href(s) encoded as hex values like %D0%B0%D0%B1 or .D0.B0.D0.B1. Can I convert such strings into readable form using Vim?
Comment: I'm not sure I grab what is the content of the html file. What is the code you have in your file? What if you go to one of this character and hit `ga`? How they are currently displayed in Vim (a screenshot would help)? How do you want to see them?
Comment: Vim can't do that on its own out of the box, if that's what you are asking.
Comment: May be I was not clear but HTML is UTF-8; text is UTF-8 but _id_'s and _href_'s in tags are encoded as... you read.
Answer: You can convert some special codes (e.g. %80 to %FF into  0x80 to 0xFF) with the following command:
:%s/\([\x80-\xFF]\)/\='0x'.printf('%02x', char2nr(submatch(1)))/g

The following question could be worth reading.
Answer: If the file contents are really %D0%B0%D0%B1 verbatim, then vim cannot do it directly. You'll first need to convert the 3-byte string %D0 into the byte \xd0. You can do it via vivian's command , butthe other way round like
:%s/%\([A-Za-z0-9]\{2}\)/\=nr2char(str2nr(submatch(1), 16))/g

Conduct the substitution, save the file (dont forget to leave a backup), and try to open the file again.
Then if you're seeing something like ç<99>½è<80><81>, it is because you're opening the file with the wrong encoding. For example opening a file containing Chinese characters with latin1 encoding results in junk like that.
To view the contents in human-readable form,

Find out the actual encoding for the file, be it UTF8 or something else. It's not specified in the file, but you can guess. Guess with utilities like file -i or enca, and also you can guess based on where you got the file (like utf8 and cp936 are most likely for Chinese documents).
Open the file vim some-utf8.html, and change the encoding to utf8 by :e ++enc=utf8. You can check the encoding used by vim to open the file with :set fenc.
Answer: I've Vim compiled with +perl, so I made
:perldo s/[.%]([0-9a-f]{2})/chr(hex($1))/ige

and that do what I want.
But is's not clear for  me.
Comment: It's magic: pairs of octets turns into one UTF-8 char. This subst converts only byte representation. But in Vim they become ONE char. Magic.


Outlook won't open after the latest Windows 10 Pro update

Question: This morning I updated Windows 10 Pro (64-bit) to build number 19041.388. But since the update, Outlook has been refusing to start up. All the other Office applications work without error. Only Outlook is behaving problematically. It crashes almost immediately with the following message in Event Viewer:
Faulting application name: OUTLOOK.EXE, version: 16.0.13001.20384, time stamp: 0x5f05e3bb
Faulting module name: OUTLOOK.EXE, version: 16.0.13001.20384, time stamp: 0x5f05e3bb
Exception code: 0xc0000005
Fault offset: 0x000000000015c52a
Faulting process id: 0x31f8
Faulting application start time: 0x01d65acc4ccf67dc
Faulting application path: C:\Program Files\Microsoft Office\root\Office16\OUTLOOK.EXE
Faulting module path: C:\Program Files\Microsoft Office\root\Office16\OUTLOOK.EXE

I ran first the offline, and then the online, version of the repair tool that comes with Office installer. Both reported that the problem had been fixed. (The online version even seemed to download Office all over again.) But Outlook still won't open--or rather, won't stay open for more than a few seconds.
What other steps can I take?
Answer: Try to run this "%Programfiles%\Common Files\microsoft shared\ClickToRun\officec2rclient.exe" /update user updatetoversion=16.0.12827.20470
Patch causing problems today.
Answer: You need to execute this from Windows + R and copy past this
"%Programfiles%\Common Files\microsoft shared\ClickToRun\officec2rclient.exe" /update user updatetoversion=16.0.12827.20470

This will update office and fix the problem for me
Answer: I have one machine working and one machine not working.
Try reverting to a prior version on the not working machine.
First, go to Office Account and disable Updates. You may need to go into Safe Mode if Outlook won't open.
Next, open an Admin Command Prompt and enter the following command:
`"C:\Program Files\Common Files\Microsoft shared\ClickToRun\officec2rclient.exe" /update user updatetoversion=16.0.13001.20266`

Now Office did not downgrade (it might for you) but it appears that simply turning Updates OFF works. My Outlook is running normally.
Office Account, Updates, Disable Updates.
Answer: It seems that the new symptom of Outlook crashing on launch is a known issue starting on 7/15/2020. As a workaround, you could temporarily use Outlook web mail or revert to an earlier version of Outlook. Besides, please keep an eye on the update from Microsoft.
https://social.technet.microsoft.com/Forums/office/en-US/1b1f952f-cb31-43d3-bf93-221b84080a70/outlook-office365-will-not-open-after-windows-update?forum=Office2016ITPro
For more information, pelase check this similar thread.


About augmented algebra

Question: An augmented algebra is equipped with a morphism of algebras $ \epsilon: A \to \mathbb{K}$. In this case $ A \equiv \mathbb{K} \oplus \ker(\epsilon)$. May you please clarify what the meaning of $ A \equiv \mathbb{K} \oplus \ker(\epsilon)$? What is the role of augmented algebras in the case of relations between non-unital algebra and unital ones?
Comment: Should probably be $\ker(\epsilon)$. The author may be using informal/different notation, just as people sometimes talk about the "kernel of a matrix".
Comment: Right, it must be $ker(\epsilon)$. I correct that. Now what will be the meaning of augmentation ideal?
Answer: An augmentation for a unital algebra $A$ is a morphism of unital algebras $\varepsilon \colon A \rightarrow \mathbb{K}$. In particular, it satisfies $\varepsilon(1_A) = 1_{\mathbb{K}}$ and so it is non-zero and onto. Let's denote the kernel by $\overline{A} = \ker \varepsilon$. The kernel $\overline{A}$ is a two-sided ideal of $A$ calle the augmentation ideal and can be thought of as a not-necessarily unital algebra. We have a vector space (internal) direct-sum decomposition
$$ A = \mathbb{K}\cdot 1_A \oplus \overline{A}. $$
This means that an element $x \in A$ can be written uniquely as $x = c \cdot 1_A + y$ where $c\in \mathbb{K}$ and $y \in \overline{A}$. Explicitly, we have
$$ x = \varepsilon(x) \cdot 1_A + (x - \varepsilon(x) \cdot 1_A). $$

The relation between not-necessarily unital and augmented algebra is as follows. Given a not-necessarily unital algebra $I$, one can adjoin to $I$ and define
$$ I_{+} = \mathbb{K} \oplus I$$
(here, on the right side we have an external direct sum of vector spaces). The multiplication on $I_{+}$ is defined by
$$ (\lambda + a) \cdot (\mu + b) = \lambda \mu + (\lambda b + \mu a + ab) $$
where $\lambda,\mu \in \mathbb{K}$ and $a,b\in I$. This gives $I_{+}$ the structure of a unital algebra with unit $1_{\mathbb{K}} + 0_{I}$ and in addition, it has a "canonical" copy of $I$ sitting inside it. Stated differently, $I_{+}$ is not only a unital algebra but it has a natural augmentation $\varepsilon \colon I_{+} \rightarrow \mathbb{K}$ given by the projection onto the first factor and we have $\overline{I_{+}} = I$.
Hence, we have two operations:

Given an augmented unital algebra $(A,\varepsilon)$ over $\mathbb{K}$, we can get a not-necessarily unital algebra $\overline{A}$.
Given a not-necessarily unital algebra $I$, we get an augmented unital algebra $\overline{I}_{+}$.

One readily sees that the two operations are functorial and are inverses of each other (up to natural identifications) so we get an equivalence of categories between the category of unital augmented algebras and the category of not-necessarily unital algebras.
Comment: @user40491: The kernel $\ker \varepsilon = \overline{A}$ is called the augmentation ideal, I don't think I have much to add other than the name.
Comment: Thank you for your detailed answer. May I ask you to add a brief description on augmentation ideal to the above answer, because I would like to add your answer to my library.  (I want to consider that as a  quick reference for this concept).

About augmented algebra


Is upping the voltage on a multiplexed LED display an appropriate response for dimness?

Question: I have a 10 character x 16 segment display that I'm driving using multiplexing off a PIC. The problem is, however, that with each display only being on 1/10th of the time, the display appears much dimmer than it normally would. Currently the LED's are getting their recommended voltage - 2.2 volts across each red segment. Would increasing the voltage across the display be a safe way to make it brighter? Is there a way to do this in software?
Answer: To increase brightness of a multiplexed display, the current through each LED segment needs to be increased (to a limited extent), while ensuring that the average current and power ratings of each LED are not exceeded. It isn't about raising the voltage to the LEDs.
The current may be limited by either a constant-current driver, resistors on each LED, or a resistor array serving multiple LEDs. Changing this current limiting mechanism can be done, but is not for the faint of heart. Also, the display then will be unsuitable for direct (non-multiplexed) drive, as the LEDs would blow due to too much current.
Alternatively, if resistors or a resistor array have been used, the voltage source feeding these resistors could be increased, thereby increasing current through the segment.
Also, keep in mind that increasing the current through an LED significantly over the rated current, for however short a period, can have detrimental or outright destructive effect on the LEDs. See this answer for further insight into this.
Another approach that merits investigation is whether the multiplexing algorithm is optimal, as in, is it keeping individual segments lit as long as it can per cycle. If not, then software fixes can improve the brightness somewhat.
Comment: Ok thank you, I'll give those a try; I'll start by swapping out the resistors on some infrequently-used segments and seeing if they can handle the heat, as it were. I've also optimized my code, the display fairly bright now, but nowhere near it's potential. Thank you!
Answer: You can overdrive an LED with more than the rated current. The destruction of an overdriven LED is caused (mostly) by the heat generated in the junction (P=IV, and I scales exponentially with forward voltage, V, so power is a higher exponential in V). If you can contrive to keep the heat within reasonable boundaries, probably by overdriving for only short periods to allow heat to dissipate, you can put as much current though an LED as you want. @Anindo Ghosh's answer has a link describing the limits of this.
Another solution, which you can do if you have the ability to add components to the design, is to use shift register/LED driver. This means you can push the data in to a chain of ICs and have all the LEDs constantly driven at a constant current (some driver ICs also include things like dimming controls). When you have pushed in new data, you flip all the chips to the new values at once. Many driver chips have 16 outputs, which sounds like a good match for your displays.
Additionally, you only need 2 pins from your MCU for an I2C device (4 for an SPI), do you can potentially downside on the MCU. You might need another couple for things like output enable and latch strobe if this is not part of the serial protocol used, but it should still be less than the "outputs * log2(devices)" for a basic multiplexer. Also, the time taken to write out to the displays is very short (you only need a few cycles per LED to toggle the lines, and if you can use an interrupt-drive hardware module, it becomes even easier!), freeing processor cycles for other things. You can also ditch whatever multiplexers you currently have.
An example part is the Texas Instruments TLC5925, which has 16 constant-current outputs up to 45mA with analogue dimming control. You need 2 lines to clock data in, one line to en/disable the output and one line to strobe the register latches. This part costs about £1 in single-unit quantities, half that in bulk. It is an SOIC, so soldering is easy, but you can also get much more compact packages if space if limited and your hand is steady.
Comment: A display whose peak current is much higher than the allowable continuous current for a digit will be destroyed very quickly if for whatever reason a single digit or "row" gets left on.  It's possible to design circuitry to force a safety-shutdown if scanning fails, but unless you're trying to make a really big display, it may be easier to simply use shift registers to directly drive the segments.
Comment: Exactly - while you CAN overdrive LEDs like this, a single bug or debugging it using a breakpoint could fry slices of your display in a fraction of a second. Or you could be causing damage to your display that causes all the segments to fail after a few million cycles. You might not notice it during development, but the devices may start to fail one after another soon after sale/installation/shipping.
Comment: I wonder why I fairly often see expensive commercially-produced signboards with a row "stuck" on?  Guarding against all problematic drive scenarios is difficult, but there are some pretty simple approaches which should guard against a failed processor or wiring harness (e.g. if rows are driven by transistors, a capacitor and diode on the signal driving the transistor could ensure that the transistor could only turn on strongly if the signal's duty cycle was at least somewhat reasonable).
Comment: For something like a 16x10 display, using ten 16-segment-driver chips (and thus not needing row drivers) may be easier than using e.g. two 16-segment drivers and five beefy row drivers, and having to include shutdown logic on the rows; for displays with relatively-wider rows, though, I would think a simple shutdown circuit per row should be pretty cheap.
Comment: Supercat: the stuck rows could be a blown row-driver MOSFET, either from inadequate I/V rating, heat dissipation problems (i.e. not enough heatsinking, using in high temperatures or in unventilated enclosed spaces), or maybe even ESD (as I doubt many cheaply-made, but still expensive-to-buy, displays have a lot of protection built in). If the MOSFET fails-to-short, any of these could leave the row stuck on.
Comment: Most of the time when I've seen displays with stuck rows, it looked like a processor or connector failure; a blown row-driver MOSFET should leave the rest of the display working more or less fine; indeed, having other drivers scanning normally would probably protect the LEDs on the row with the stuck driver, since if those LEDs start to heat up their voltage drop would increase and more current would be diverted to the LEDs of the rows with non-damaged drivers.
Answer: No... upping the current is what you want to do to increase brightness. Said differently, LED brightness is a function of current passed through them. Many LEDs can handle upwards of 100mA at 10% duty cycle. So long as you control the duty cycle, that's the way to go.


How to lock the position of one of my bones?

Question: I want to move some of my bones without moving the entire rig. Is there a way to do this without unparenting the bones?
Answer: Maybe you should explain more precisely what is your case. But for example, you could unparent your bone in Edit mode, then in Pose mode, give it a Child Of constraint (press the Set Inverse button to keep the bone at its original position). When you'll need the child bone to be unparented, you'll simply create 2 Influence value keyframes: at frame X-1 you'll keyframe an Influence of 1, and at frame X you'll keyframe an Influence of 0.


How do I use 7-zip to backup files, but exclude some directories

Question: I would like to use 7-zip to backup a directory, but I would like it to exclude all directories named ".svn" (anywhere in the source tree). Does anybody know if this is possible and in that case how?
Answer: To exclude all .svn directories you need to add the -xr!?svn\* switch
For example the following will create a backup of the C:\Project\To\Backup directory excluding any folders that satisfy ?svn:
"C:\Program Files\7-Zip\7z.exe" a -r -tzip -y -xr!?svn\* Project.zip C:\Project\To\Backup\*

Comment: And if you stumbled here looking for general folder exclusion, note that the `?` is to match "period-svn" (`.svn`), so to to skip everything in folder `SkipMe` you would use `-xr!SkipMe\*`
Comment: Thanks ManiacD, but I can't get this to work -xr!?svn\* gives me an error and if I try -xr!.svn\* it still won't exclude .svn
Comment: you need a backslash after ?svn for it to work that signifies to exclude everything underneath the .svn directory. -xr!?svn\\*
Comment: Don't worry I had heaps of problems initially getting it work as well. The 7-zip exclude switch -x (-xr recurse directory) with ! excludes filenames based on a wildcard search.  Without the backslash it is trying to exclude filenames that match ?svn* ie. asvn.log with the \\* at the end mean don't include anything underneath a directory matching ?svn
Comment: For details on how to use wildcards have a look at the help file shipped with 7-Zip. Helped me to fix a similar task a few days ago. 7-Zip uses wildcards a bit ... different ;)
Comment: I got it to work, strange that this answer currently is the only one that hasn't been upvoted. +1 and accepted. Thanks to to all who answered my question.
Answer: Instead of using 7-Zip to exclude the .svn (or potentially _svn) folders, I would recommend using the svn export command (use svn.exe from SlikSVN) to export the working copy to a temporary folder:
svn export C:\Path\To\WC C:\Backup\Staging

Then use 7-Zip as follows:
7z.exe a "C:\Parth\To\Archive" "C:\Backup\Staging\*" -bd t7z -v2g -r

Then delete the staging folder.
This is what I do to backup my local working copies.
Comment: Thanks for the export tip. Available on TortoiseSVN menu too.
Answer: You can exclude files with 7zip using a list of files or directories:
/path/to7Zip/7z a -bd f:/backup/backup_2009-08-23_daily.zip home \
          '-xr@\path\to\backup_daily_exclude.lst'

The exclude file looks like:
home\Photos\iPod*
home\dhltd\*
BlogMatrix\Sparks\db\*.archive
home\eclipse\*
.svn

The key is the -xr and in particular the "r" which indicates apply the exclude list recursively, to each level of the directory. You may want to use 2 exclude file lists one for absolute and one for recursive exclusions. The above is from a bash script that runs in cygwin.
Answer: When I used
"C:\Program Files\7-Zip\7z.exe" a -r -ttar -xr!?git\* aufs2-util.tar aufs2-util\*

it ended up adding the .git directory which I didn't want, changing it to
"C:\Program Files\7-Zip\7z.exe" a -r -ttar -xr!?git\ aufs2-util.tar aufs2-util\*

got the desired result.
Answer: When I used
7z a "D:\codebase\w.7z" "D:\codebase\Edison\otm\Webapp" -t7z -mx0 -xr!WEB-INF\*

the WEB-INF directory was not excluded. Adding an asterisk before the dir name
7z a "D:\codebase\w.7z" "D:\codebase\Edison\otm\Webapp" -t7z -mx0 -xr!*WEB-INF\*

Got the desired result.
Comment: asterisk part is the most important. This should get more upvotes.
Answer: For me, I was trying to backup a bunch of maven code directories and wanted to exclude any directory named "target":
"C:\Program Files\7-Zip\7z.exe" a -r -tzip -y -xr!*\target\* site.zip C:\code\site\

Relevant exclude parameter was -xr!*\target\*.


Can I use wired Xbox One controller

Question: Can I use wired Xbox One controller? Googling only gave me Xbox 360 controller, and I don't think that the new Xbox One Controller can be mapped as old 360 one.
Answer: My brother just bought a xbox one controller today and it does not work.
He tried the standard xpad driver as well as the xboxdrv but they apparently do not even recognize the press of a button :(
It's a sad thing to say but no you may not use a wired or wireless Xbox one(360 works absolutely fine) controller with ubuntu RIGHT NOW:
Looking around I was able to find this commit to the Linux kernel xpad driver
https://github.com/torvalds/linux/commit/1a48ff81b3912be5fadae3fafde6c2f632246a4c
That means the work is already done and we have to wait for ubuntu to reach the kernel version that includes this controbution.
It was committed 7 days ago, that means it will probably be included in kernel version 3.18, but I'm absolutely not an expert so my prediction might be worth nothing.
If we are lucky xboxdrv(alternative to the  standard driver) will add support soon.
Comment: Looks like my patch should hit kernel 3.17 given the tags on the commit, but I don't know if/when that will hit Ubuntu 14.04.
Comment: UPDATE:

Xbox One Controller support is defenetly in 3.17 as you can read here:

Linux Kernel 3.17 Is Out With Plenty of New Features
http://www.omgubuntu.co.uk/2014/10/linux-kernel-3-17-whats-new-improved

The kernel version is not yet included with Ubuntu 14.10(the artikel on omg ubuntu covers that) but 14.10 is still in testing so I guess we can expect 3.17 to be included.
Answer: I've compiled and made debian packages for "3.16.0-rc6" kernel with the xpad xbone controller support. Havent uploaded the packages yet though. Seems to work fine with epsxe.
<code>Linux wepu 3.16.0-rc6 #2 SMP Mon Sep 22 21:16:48 BST 2014 i686 GNU/Linux

w*****h@wepu:~/Downloads/deb$ ls -l
total 373892
-rw-r--r-- 1 w*****h w*****h    966206 Sep 22 21:32 linux-firmware-image-3.16.0-rc6_3.16.0-rc6-2_i386.deb
-rw-r--r-- 1 w*****h w*****h   6536604 Sep 22 21:33 linux-headers-3.16.0-rc6_3.16.0-rc6-2_i386.deb
-rw-r--r-- 1 w*****h w*****h 342097294 Sep 22 22:06 linux-image-3.16.0-rc6_3.16.0-rc6-2_i386.deb
-rw-r--r-- 1 w*****h w*****h  32491312 Sep 22 22:10 linux-image-3.16.0-rc6-dbg_3.16.0-rc6-2_i386.deb
-rw-r--r-- 1 w*****h w*****h    765926 Sep 22 21:33 linux-libc-dev_3.16.0-rc6-2_i386.deb
</code>
Answer: hello there have you check
gamepadtool download it here
click here
and xpadneo here
click here
and install joystick via terminal
<code>$sudo apt-get install joystick -y
</code>
but I got problems with wine it doesn't recognize my controller
but I gues I'm gonna needs some workaround
Comment: If this answer doesn't work, why are you posting it as a solution?
Comment: it does works but not in wine. wine is a compatibility layer that calls dynamic links library so if my driver is setup correctly but in wine the game don't recognize it. I've make my controller works in wine so I think this is a solution just need a little bit of tinkering

Can I use wired Xbox One controller


Development setup on linux

Question: On a linux system should we install and use our development tools and setup like java ee and hadoop as a root user or as user.
Comment: Might I suggest against developing on Linux at this time if you need to ask this question? I spend all day dealing with the product of (probably) similar developers and it causes at best frustration and at worst a vulnerable system.
Answer: Don't run it as root, that's a serious security risk. Setup a new user for each if needed and make sure that they only have access to what they strictly need. If your application doesn't run without root privileges it might be a good idea to think about rewriting the parts needing it
Comment: It also helps if the installer does not require root to run,  Extract anything needing root into a script that can be run by the system admin.

Development setup on linux


Local Vol vs Stoch Vol Option Pricing

Question: This is an interview question:
Imagine you have a double knock-out barrier option: the current spot is 100, the lower barrier is 80, and upper barrier is 120. The barrier is continuous, meaning that once the spot goes out side the range of 80-120 anytime before time to maturity, you got nothing. If the spot stays within the range 80-120 the whole time before the option matures, you will get paid a fixed amount of 10 as the final payoff.
The question is, if you need to price this option, which volatility model will give a higher option price? Local vol or Stoch vol? Why?
The interviewer said it's the Stoch vol gives a higher option price, but I didn't get the reason.
Does anyone know why?
Answer: To simplify things, let's begin by considering a one touch option (that pays cash if the barrier is touched) rather than the double no touch option of the question. Also, let's assume interest rate and dividend yield are zero.
And before starting, we can remember that we are given a volatility surface at the start. Then both local and stochastic volatility models will value vanillas and digitals the same.
As dm63 pointed out, an approximate hedge for the one touch is a digital with strike equal to the barrier level, and double the notional. At the moment the barrier touches, the digital is worth around 50% of its notional, so 100% of the one touch notional. As soon as the barrier touches, the digital hedge must be unwound.
In practice, this is not a perfect hedge for two reasons. Firstly, in a log-normal world, an at-the-money digital is not worth exactly 50%. That is easily dealt with by adding a vanilla option to the hedge that exactly corrects for this.
The second and more interesting reason is that a digital option has a correction to its Black-Scholes value equal to minus its Black-Scholes vega, multiplied by the derivative of the implied volatility (at the money) with respect to strike (hereafter, the "skew").
The upshot is that the value of the one touch at touch time can be replicated from a digital and a vanilla (whose values are independent of the model) plus a constant multiplied by the expected value of the skew at touch time.
In a stochastic volatility model, the smile tends to float when spot moves, meaning the at-the-money skew stays constant. In a local volatility model, the smile tends to stick in strike space when spot moves. As the smile is convex and at-the-money is near the bottom at the outset, this means the skew increases in magnitude. If one is careful with the sign of the factor multiplying the skew term, this gives the result.
It's important to be aware this is not a mathematical proof, and I have heard of claimed counter examples. For all practical cases though, it seems to be true.
Full details of the above calculation, and of the assumptions made are in chapter 9 of the book Smile Pricing Explained.
Returning to the specific question, we have one touch plus no touch equals cash. Then as a one touch is higher in local vol, a no touch is lower in local vol and higher in stochastic vol. Deterministic interest rates and dividend yield can be included back in fairly easily.  Finally, we are asked to take on trust that the model behaviour of a double no touch is similar to a no touch. It is, and in fact, it is much more strongly model dependent than a single no touch. Even on a relatively modest FX volatility surface, a double no touch price can vary by a factor of two according to the model.
Finally it is worth mentioning that both volatility swaps and forward volatility agreements (forward starting vanilla options) are valued higher in local volatility than stochastic volatility. For the volatility swap, there is a beautiful proof (due to Dupire) in the very special case of an "instantaneous" volatility swap.
Comment: sorry I confused with below answer. The logic is: one touch <=> Call spread <=> smile skew. And for ATM skew (at hitting time), local vol > stoch vol => value of one touch (local vol) > value of one touch (stoch vol) => value of no touch (local vol) < value of no touch (stoch vol) => value of knock out  (local vol) < value of knock out  (stoch vol).
Comment: However in here: http://www.matthiasthul.com/wordpress/2015/06/26/stochastic-vs-local-volatility-barrier-options/#:~:text=Consequently%2C%20they%20also%20agree%20on,hitting%20probabilities%20that%20they%20generate. The conclusion seems contradict to yours: `Consequently, the conditional value of the European binary call (put) option upon the first hitting time is higher (lower) in the stochastic volatility model.`
Answer: I'm more of a rates person than equities, but i'll give it a shot: first of all one assumes that both models have been calibrated so that vanilla options at all strikes and maturities are aligned, otherwise the question doesn't make sense.  Since European digital options are the limit of European call spreads, it must also be true that the European digital options at all maturities are the same in both models.  For example, the price of a digi 120 call is the same in both models.  Furthermore, there is a well known result due to the reflection theorem, that the price of an American digital call is (under no drift conditions at least (r=q)), equal to twice the value of a European digital call, under any model.  Hence, the single knockout 120 call and the single knockout 80 put must be the same under both models.  So, if there is a difference in price for the double knockout option in the OP, it must be because there is a difference between the 2 models in the probability of hitting BOTH barriers.
Why should this be?  My proposed logic would be to suppose that under some path of the underlying, we have hit one of the barriers (say the 120).  Then , I claim that the probability of later hitting the 80 barrier (given that we are at 120 right now) is higher under the local vol model.  Why?  because under that path, we expect that implied volatilities have gone up (because that is the way that a local vol model explains the smile).  In contrast, in a stoch vol model, vol may have gone up or down because it is driven by a separate random variable.  So, under local vol we are more likely to hit both barriers, so the double no touch is worth less.
I did assume here that we have a typical positive smile in the underlying.  I'm happy to be corrected by a equities or fx practitioner.
EDIT:  I stand corrected by the comment of @Peter A.  I give below a link with what appears to be an explanation consistent with his comment.
http://www.matthiasthul.com/wordpress/2015/06/26/stochastic-vs-local-volatility-barrier-options/#:~:text=Consequently%2C%20they%20also%20agree%20on,hitting%20probabilities%20that%20they%20generate.
Comment: This isn't actually the correct explanation. A one touch (single barrier) is also valued higher in local vol than stoch vol. The reason is related to the forward skew and can be understood from the approximate digital hedge that you outlined. Roughly, the explanation comes from the fact that the approximate digital hedge is highly skew dependent, and the evolution of skew is diffferent in local vs stoch vol. However, it is a little more involved than this.

Local Vol vs Stoch Vol Option Pricing


Orwell: "A glimmer [is] one who watches vacant motor-cars." What does this mean?

Question: Title is a quote from Orwell's Down and Out in Paris and London. In this section he goes through a bunch of London slang terms and what they mean, but I don't understand his definition. What does it mean to watch vacant motor-cars? The only thing I can think of is someone who you pay when you park who makes sure nobody steals your car when it's gone. But how does that work? What assurance does the driver have that the person watching won't just leave or steal the car themselves?
Comment: Paying someone (unofficial) to park and look after your car was common when I lived in Sicily. The confidence came from the fact that this was how they made their living. If they didn't provide a reliable service, they would be out of work. (And there may have been "others" behind the scenes who organised this semi-legal activity.)
Comment: There seems nothing beyond 'Glimmer: one who watches vacant motor cars' available on the internet. I assume it does indeed refer to 'someone who you pay when you park your car to "make sure nobody steals it when **you**'ve  gone" '. // Your final question is not about English, but when my father used to pay kids in a certain part of Manchester for this service, it was tacitly assumed that they'd be at the match before us, but would not damage the car.
Answer: Orwell attempts the etymology of his slang, saying of glimmer

'Glimmer' (with the verb 'to glim') may have something to do with the
  old word 'glim', meaning a light, or another old word 'glim', meaning
  a glimpse;

Down and Out was published in 1933, a memoir of his time spent destitute in London in 1927 and Paris in 1928. He seems to have missed the slang word glimmers (also glims) meaning eyes, words current in London slang during the 1920s according to Partridge's A Dictionary of Slang and Unconventional English.
So a glimmer is someone who used his glimmers to (in modern parlance) keep his eye on something, in this case your car when you leave it somewhere dicey. Presumably this works in the usual way: you pay half up front and the other half when you retrieve your car undamaged. You have no assurance that the glimmer won't be satisfied with half or that he's not working for a chop shop.
Answer:
glimming n. [glim v. (2); note London cab-driver jargon, glim, to look for a cab] (UK Und.)

watching out for cabs etc. for wealthy people, in return for a tip. ...
http://www.oxfordreference.com/view/10.1093/acref/9780199829941.001.0001/acref-9780199829941-e-20048
Answer: However, in chapter XXXIII of Down and Out in London and Paris, Paddy earns a few extra shillings through glimming, which is referred to as a precarious job because it is illegal. Watching a car to ensure it isn't stolen surely isn't illegal.
Comment: Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer).


adding code for a Django admin field

Question: I have a tinymce textarea in my django admin and I need users to be able to upload images (via AJAX) that will be linked in this textarea.
That would be accomplished by adding an "Image Upload" button (it's already working) in the top of the "Content" textarea.
What's the recommended way of doing that?
I can think on 2 solutions:

extending change_form and replacing {% for fieldset in adminform %} for the actual fields... and when it's the content field, I add this value
dynamically adding this button with javascript (find out where the content field is and add a
 before it)

A better solution, if possible, would be to override just this specific field in the admin templates. Is that possible? Or are there better solutions?
PS: this field is not part of the DB (it just uploads one or more images, saves it to the storage and returns a link that will be included on the tinymce).
Answer: maybe you could  use this
formfield_overrides from the djangodocs
if not, create a subclass of modelform and overide the form of admin with ModelAdmin.form.

adding code for a Django admin field