Do word final plosives always have 'no audible release' in all languages?

Question: Making my conlang, I've found myself avoiding word-final stops (specifically p, t, and k) because I think they would be inaudible anyway. But does this phenomenon occur in all natural languages? Is this just a common trait, or is it actually impossible for humans to pronounce a plosive at the end of a word? I think Finnish marks plurals with a final t, but do they actually pronounce it or are they relying on some kind of redundancy, like how English speakers tend to pronounce vowels longer when they appear before a voiced consonant (or a voiced plosive, at least)?
Comment: Not exactly what you asked, but English speakers frequently do pronounce word-final stops.  Korean is an example where syllable-final stops are always unreleased (I hope that's the right term), but the final consonant "colors" the preceding vowel sufficiently so that you can hear the difference, just like English speakers can tell *pack* apart from *pat* even when the k/t are unreleased.
Comment: I don't think that this is even certifiably a common trait. It exists in some languages.
Answer: "Is it actually impossible for humans to pronounce a plosive at the end of a word?" No, not at all. In French, word final plosives often have audible release (I just say "often" because I only have an intermediate level of proficiency and don't want to make too absolute claims; this may be understating things).  I'm talking about words that end with a consonant in the phonology, not in the spelling. E.g. the word "tape" in French is generally pronounced [tap] with one syllable ending in a released /p/. A disyllabic pronunciation [ˈtapə] exists, but is not usual except for in poetry/singing or in southern France, so I usually see it transcribed phonologically as /tap/ (although it seems that some more abstract analyses of modern French make use of the idea of some kind of underlying final schwa in words like this).
Also, there is a difference between "no audible release" and "not pronounced". A plosive with no audible release is pronounced: the articulators make contact in the same place as for an audibly released stop. As you mentioned, the plosive is likely to affect the pronunciation of the preceding segment(s), allowing a listener to identify the place of articulation of the plosive.
This is somewhat like how some languages have geminate stops at the start or end of a word, even though gemination is not always audible in these positions (I am thinking of Swiss German in particular).
Comment: Also unreleased plosives can be released into the following word. French probably has a name for this.
Comment: These are two separate phenomena, one called "liaison" (historical end consonant re-emerging before another word that start with a consonant and is in close syntactic relationship, e.g. "les" /le/ + "années" /ane/ pronounced as /lezane/) and "enchaînment" (chaining), where word-final consonant and subsequent word-initial vowel typically form a syllable ("frère et soeur" syllabified to /fre.re.sör/).
Comment: I believe its called 'elision', at least in English. Also, I thought that most final consonants in French were silent, unless the word was followed by another word that began with a vowel, in which case the word-final consonant would end up being pronounced at the beginning of that word.
Comment: @lXBlackWolfXl: I'm talking about words that end with a consonant in the phonology, not in the spelling. E.g. the word "tape" in French is generally pronounced /tap/ with one syllable ending in a released /p/. A disyllabic pronunciation /ˈtapə/ exists, but is not usual except for in poetry/singing or in southern France.
Answer: https://www.degruyter.com/document/doi/10.1159/000028440/html
This paper mentions that French, Polish and German plosives are always produced with audible release.

There are languages which do not allow stops either word- or
utterance-finally (e.g. Italian, Tamil, Japanese), while in some other
languages that do allow final stops they are regularly produced with
audible release, i.e. a kind of vestigial vowel (e.g. French, Polish,
German).


Armature moves when switching from Edit to Object Mode

Question: The position of the bones on the arms changes when I switch modes and I cannot figure out how to fix it..
Answer: The problem is created by the IK bone pivot not align to the child bones in edit mode. Use the cursor to snap all the bone pivot to the same location. Also make sure that your bones are rotated so that it is perpendicular to the front view as much as possible - at rest.
Attached is are the bones rotated and all the IK pivots of the bone aligned properly.

Snapping the bone pivot onto the same location do the following - In edit Mode.

Select the end bone nub.
Use CtrlS choose "cursor to selected"
Select the other bones hit CtrlS choose " Selection to Cursor"
If required , go to pose mode and reset all rotation and transformation using
AltG and AltR

Below, you can see 3 spherical nub aligned. The 2 red ones and the big green one    needs to all be aligned in one spot using the "Cursor to selection" then " selection to cursor" method.
Comment: sorry I don't get step 3. Which bones do you mean? When I selected Lower_Leg.L and selection to Cursor, the bone gets dislocated. BTW Alt G sometimes doesn't seem to work after I make a lot of changes and I have to resort to Ctrl Z.
Comment: You have 3 bone at the foot that needs to be at the same xyz coordinate at it's pivots. Namely the lower leg, the foot and the IK foot bone. If you looked at my blend file I have also reposition the knee bone and the elbow bone and alter the "pole angle" of the constraint. You will also find that I have done the same to the lowerarm and the arm IK bone so that their pivot point is one the exact same spot.
Comment: As long as all your bones are aligned properly in edit mode. Hitting Alt G and Alt R will work. As all the transformation will reference back to the edit mode's bone transformation coordinate. When your IK object location do not match your child bone's nub it can cause resetting the bone in Pose mode to not behave appropriately.
Comment: You need to first do "CURSOR TO SELECTED" meaning you have to select the first target you want all bone to target to. Select the Lower leg bone nub, it's the spherical shaped object highlighted in light blue in the image. Then select the other bone nubs ... eg. the foot spherical shaped nub and the foot IK spherical shaped nub. and do "SELECTED TO CURSOR"
Comment: Don't go selecting the whole bone you only need to align the bone nub, which are the spherical ends of the bone object.
Comment: I have aligned the nubs but the bones still move in the different modes. Do the nubs need to have same rotation as well as location? Here is my blend file after adjustment. I have also rotated all the bones to face the front.[](http://blend-exchange.giantcowfilms.com/b/1005/)
Answer: The answer is sort of correct. Hawkenfox meant to say "Shift S", not "Ctrl S" while in edit mode on an IK bone. This should solve any confusion. Ctrl S is used to save the file. At least it is in Blender 2.78a.
Answer: I just had the same problem, even by applying "with automatic weights" the armature would be out of the mesh, then I realized that I hadn't applied my mesh's modifiers, such as subdivision surface, I clicked on the apply button then I went to object mode and selected my character then shift selected my armature and ctr+p then "with automatic weights" that was it.


How to obtain service packs for SQL Server 2008 R2?

Question: Where to find the information about service packs already released or planned for SQL Server 2008 R2?
Answer: SQL Update information, for all versions, all types (Service packs and the monthly cumulative updates) is published at...
http://blogs.msdn.com/b/sqlreleaseservices/
Answer: I believe that only Cumulative Updates are released for the SQL 2008 R2.
The current SQL Server 2008 SP is SP2, but it does not apply to R2.
R2 is a separate release.
Answer: If you go towards the bottom of this KB article it is updated with the latest SP/CU for each version of SQL Server as it is released. It doesn't give a link to the KB but it is a good central point to check.
New: Microsoft has created an update center that will show the latest SP/CU currently released with a link. I'm not sure how quickly they will update this though, example being that they don't show SP1 for SQL 2012 on there yet.
Answer: I'd try the Internet. Surely this is a simple thing to google?


What is the simplest device that can remote-desktop connect to various Windows PCs on a LAN?

Question: It needs to have video, audio, mouse, keyboard and network connectors and to support nothing more than connecting remotely to various Windows PCs that will have all the real resources needed. Sort of a "pure terminal" hardware device. Is there such a thing? Or do I need to look at media boxes? (But I think those typically come with Android, not Windows, these days.) Or will it always be cheaper to just get the oldest PC that can handle the desired video bandwidth and be done with it?
Comment: Research "thin clients".  As-is, this question is too broad (IMO), voting to close.
Comment: Thanks. I didn't know that term and it is indeed what I was looking for. (And yes, questions tend to be broad when someone doesn't know there's a specific name for what they're asking about.)
Answer: I'd suggest you use a Raspberry Pi.
But you will need some knowlegde for installing software on it. There are enough tutorials on the internet on how to install for example Windows 10(or 8).
If you want a relatively cheap device I'd suggest you a Thin Client from HP. They come with Windows preinstalled and you can use them directly. They do cost way more than a Raspberry Pi (Raspberry is around 30 dollar and a Thin Client around 300).
edit: Video&Audio is never a good idea over RDP, it is very slow and you will have alot quality losses. It seems you want some sort of mediastation? Why not use an old computer without the RDP?
Comment: Video and audio via RDP 8.0 is actually stellar, even over high latency, low bandwidth (relatively speaking) connections.  I can watch YouTube videos played on my home computer on a residential cable connection, via my tablet on a 3g connection somewhere else in the country, with minimal quality loss.
Comment: I said I wanted hardware video and audio connectors on the box-thing ("thin client", apparently), not that I wanted to stream movies with sound through RDP. :)
Answer: Android or Ipad tablets can run remote desktop sessions in most situations (several free and paid RDP apps are available on either platform) and you can either use on-screen keyboard/mouse or get an external keyboard (for ipad or android) and external mouse for Android (either Bluetooth or usb-otg if supported).  If you need a desktop-like system that can act as an RDP client, they exist as well.  The Dell Wyse 5212 is an example of a purpose-built client-only desktop appliance like you are describing.  You could use an Android "media client" box with keyboard, video, mouse to do the same, but it's not purpose built so user experience might suffer.


Negative imputed values

Question: I am doing multiple imputation using chained equations in Stata to deal with item-missing data. One of the variables on which I did imputation was income. However after I did imputation, the imputed values of income contain negative values though the mean and standard deviation of income after imputation are almost similar to those before imputation. I used linear regression to impute income (though the distribution of income in the study population is not normal). While using other options of imputing income such as predictive mean matching, truncated regression, Poisson regression and negative binomial regression, the imputation model fails to converge. How should I deal with such negative imputed values? May I just ignore this and continue with further analysis of my multiple-imputed data?
Comment: Are you using Royston's **ice** package do do the multiple imputation, or the in-built multiple imputation stuff that's been available in Stata since around version 11 or so?
Answer: If you are using Royston's ice package to do the multiple imputation, you can truncate the distribution of income at 0 with the interval() option. For example, if you wanted to bound income between zero and some maximum:
ice income x1 x2 x3, saving(imputed) m(5) interval(income:0 maxincome)

See help ice##interval for more details. You can also leave the upper end unbounded (not quite sure of the syntax from the documentation, but the author of ice has responded well to my inquiries in the past). ice can be found within Stata by typing: net describe ice, from("http://www.homepages.ucl.ac.uk/~ucakjpr/stata/")

If you are using Stata's (versions 11 and up) built-in mi command to do the multiple imputation, you can truncate the distribution of income at 0 using the truncreg method for income. For example, if you wanted to bound income between zero and some maximum:
 mi impute chained (truncreg) income, ll(0) ul(maxincome) (regress) x1 x2 x3

If you did not want to specify maxincome:
 mi impute chained (truncreg) income, ll(0) (regress) x1 x2 x3

See both help mi_impute and help mi_impute_truncreg for more details.
Comment: I am using Stata's in-built `mi impute chained` command. I have benefited from your elaborate answer. Thank you Alexis.
Comment: @AyalewA. Sweet! Feel free to up vote my answer and to accept it (by clicking the check mark at the top left of it) if it works best for you.
Answer: I think you just continue with your analysis. For one thing, negative income is not impossible. If you lose money (e.g. on investments) and don't make any, that would be negative income.
Comment: You raise an interesting point about measurement and interpretation. But what happens if income is measured using brackets starting at zero? Then imputed observations become special in that only they are permitted to have negative incomes.

Negative imputed values


Underextrusion after long travels

Question: I'm having problems when printing small parts over big areas.
I'm currently printing quite big casing (~180 mm x 100 mm), which has hexagonal holes on the corners. On the first layer the printer prints, in order:

Supports inside the holes,
Borders around the holes
Border of the whole casing and finally
Infill (since it is first layer, infill is solid)

When printing borders around holes, printer's head travels between all holes (so that's around 90 % of the whole bed width), what results in filament oozing and the hole borders being underextruded (sometimes to the point, that filament doesn't stick to the bed).
My setup is CReality3D Ender 3 with Ultimaker Cura 3. Most important settings:

Print speed 40 mm/s
Nozzle temperature 215 °C
Bed temperature 60 °C
Retraction on travel turned on
Retraction additional prime amount set to 0.05 mm3.
Outer walls printed after inner ones

What would help (I guess) is slowing down the print after long travels or priming more filament, but proportionally to the travel distance. There are no such settings in Ultimaker Cura though.
How can I deal with such problem?
Comment: If you have oozing on long moves, you have it on short moves too - but you don't notice. Please report what happens if you double the advance and retract settings and reprint the same gcode.
Comment: It is suggested to tune your printer for oozing, several calibration prints can be found on Thingiverse for instance.
Comment: For the next print I lowered the temperature to 205oC and it seems like it helped a little with eliminating oozing - separated small areas looks better as well. I have two more bigger prints ahead, so I'll monitor the situation.
Answer: it seems like retraction issue
i would say you should experiment with

retraction length - so it would retract more
extra extrusion after retraction - so the printer could put some material before it will start your next hole :)

unfortunately there is no good guide how much it should retract and how much it should additionally extrude as it depends on "all your printing circumstances" but here is my arbitrary list in order of importance

filament (density - type and producer)
temperature (viscosity - hotter filament flows easier)
nozzle diam (as filament escapes easier through big hole ;)
heat barrier (cooling efficiency - filament should be cool as long as possible up to (or down to) the nozzle)
extruder gearing quality (good coupling makes precise retraction and extra-extrusion)
cooling (fan and duct should cool your printing right after it sticks to the surface)

and one more thing worth to mention
usually the first layer is not cooled which makes whole system hotter (so filament flows easier)
you could experiment with it too especially for big printouts
so

overextrude first layer AND
turn on cooling first layer

it seems like there is a bunch of things you can do to master it :)
good luck - it's definitely manageable
Answer: Set retraction_min_travel to 0. The default value is 1.5 and skips retraction when moving less than 1.5 mm. This leads to serious oozing whenever your print has small travel, which seems likely between the hole walls and the supports inside the holes.
Also, the "custom start gcode" in Cura's Ender 3 configuration seriously over-primes the extruder, possibly making retraction ineffective until the pressure drops. Lowering the E15 and E30 amounts to E9 and E18 improved things a lot for me, especially with flex filament, but also with normal PLA. Printing a skirt or brim would probably be an alternative if you don't feel up to editing that part of the config.
Increasing the retraction amount could also help. You should not need extra prime after travel. It can only help if you've lost material to oozing during travel, and if you have oozing, that's a problem in itself that you need to solve, not paper over by extruding additional material.

Underextrusion after long travels


How do I see more of the command line with the KDE System Guard Process Table

Question: I often have several java programs running and I can't tell which one needs to be killed. The command section of the process table only shows java, but doesn't tell me which jar or class files it is running.
Edit: Is there a way to see more of the command call from withing KSysGuard?
Answer:
ps aux | grep java
You look for the Process ID(PID) of the process you want and then you use kill command (for how to use kill read my post here)

Also read: here and here and here
An alternative: ps -fp $(pgrep -d, -x java) or you might use htop or top and search for java
Comment: Something staying with ksysguard would be prefered.
Answer: A GUI alternative to Ksysguard is qps. It's perhaps less visually appealing that ksysguard, but it shows a lot more information, including the whole command line.
Answer: You want the wide output option "w". Using it three times will allow unlimited width.
ps auxwww

Comment: I was hoping there is a way to see more of the command within ksysguard.


Are two bimodules isomomorphic as left and right modules also isomorphic as bimodules?

Question: let R be a commutative ring, and M, N two bimodules over R, such that there exists f : M -> N an isomorphism of left R-modules, and g : M -> N an isomorphism of right R-modules. Then are M and N isomorphic as R-bimodules?
I don't see any reason why it should be true, but I can't find any situation where this is false.
Thanks a lot!
Comment: This isn't really a research level question, but you might consider a situation where $R$ is an $R$-bimodule in the standard way, vs. a situation where $R$ is a left module in the standard way but a right module in a twisted way, twisted by an involution on the ring. Think of a familiar ring or field with an involution, and you should be on your way.
Answer: As you say, there is no reason why this should be true. Consider on the one hand $R$ regarded as an $(R, R)$-bimodule in the usual way and on the other hand $R$ regarded as an $(R, R)$-bimodule where, say, the left $R$-module has been twisted by an automorphism $\varphi : R \to R$, which is to say that left multiplication now looks like
$$L_r s = \varphi(r) s.$$
Both of these bimodules are isomorphic as left modules to $R$ and as right modules to $R$, but they usually won't be isomorphic as bimodules if $\varphi$ is nontrivial. We can try to distinguish them by their centers. Recall that the center of a bimodule $_R M_R$ is
$$Z(M) = \{ m \in M : rm = mr \forall r \in R \}.$$
Then the center of the usual $R$ is the usual center $Z(R)$, but the center of the twisted $R$ is
$$\{ s \in R : \varphi(r) s = s r \forall r \in R \}$$
and this will just be different in general (as a subgroup of $R$). For example, if $R$ is commutative, then $Z(R)$ is all of $R$, but the above cannot be all of $R$ if $\varphi$ is nontrivial since, for example, it cannot include the identity.


Error when trying to remotely debug an azure website (HRESULT: 0x89710023)

Question: I'm having troubles enabling remote debugging on sharepoint online. I have 2 machines, my local machine (Windows 8.1) and my development server(Windows Server 2008 R2). On my development server I first tried remote debugging using Visual Studio 2012 Update 4, as described here: http://azure.microsoft.com/en-us/documentation/articles/web-sites-dotnet-troubleshoot-visual-studio/#remotedebug.
When this didn't work I tried doing exactly the same thing on my local machine, which has Visual Studio 2013 (Ultimate) update 1 and the latest windows azure sdk (2.3). This worked perfectly. Thinking upgrading to visual studio 2013 would solve my problem I've installed 2013 (Premium) on my dev server, next to 2010 and 2012. After installing and updating everything for 2 hours however, I came to the conclusion that I received the same error as on VS 2012.
Googling came up with a few interesting causes for this bug: sitenames longer than 20 characters or sitenames containing hyphens. This is not the case. Then I verified port settings, the dev server has no active firewall but I wanted to exclude any possibilities. And low and behold, both telnetting from my local machine as my dev server to ports 4016 and 4018 of my azurewebsites.net url worked.
Are there any other solutions for this bug? Since debugging locally is not an option (sharepoint provider hosted app for project online) this is very inconvenient.
Thanks,
UPDATE: Deploying the site as a cloud service works, and so does remote debugging them. However, we would like to stay with azure web sites for now..
I know this is a duplicate of Azure Remote Debugging: Failed to enable remote debuggingException from HRESULT: 0x89710023; but none of the solutions there or on twitter were of any use.
Comment: possible duplicate of [Azure Remote Debugging: Failed to enable remote debuggingException from HRESULT: 0x89710023](http://stackoverflow.com/questions/21188108/azure-remote-debugging-failed-to-enable-remote-debuggingexception-from-hresult)
Answer: Check out Azure Remote Debugging: Failed to enable remote debuggingException from HRESULT: 0x89710023
I think this has to do with blocked ports 4016 and 4018
Comment: I'm able to telnet to those ports, so this can't be the problem.


How to subtract a region where two solids intersect?

Question: In Autocad 2015 for Mac, I have created a cylinder with a torus wrapped around it. The torus is 2 mm thick, with 1 mm embedded inside the cylinder and 1 mm outside. I want to subtract the torus from the cylinder, so I will be left with a semicircular groove around the cylinder. I have already done this once, but I had to remake the object so I deleted the original and started again - and now when I try to subtract the torus, it simply deletes the torus and leaves the cylinder untouched. What is going wrong, and how can I fix it?
Answer: Often this sort of problem is caused by some small and non-obvious error in your drawing, for example if a point hasn't snapped to exactly where you expected to one or more lines aren't exactly in the right place. Particularly if you end up with open loops or small gaps between lines which should intersect. You can also have problems if you have several lines or points on top of each other.
Most CAD software has a tool to diagnose these sorts of problems.
Another common problem is picking/entity selection errors, these can sometimes crop up from minor conflicts with graphics processing eg some software prefers Nvidia to Radeon graphics hardware which can sometimes cause odd problems.
Probably the first thing is to look at your basic geometry and make sure that it is what it is supposed to be. The second is to look back through your workflow and make sure that you have done everything properly. It is very easy with CAD to slip into bad habits where you do things which are a bit iffy and work in some circumstances but not others. Similarly is is very easy when learning to get yourself into a wrong mode or layer or assign an unwanted property to an object.
Autocad is also well supported by online forums so it may also be worth asking your question there as well.
Answer: To be honest this came entirely from chance and I still have NO idea what caused the problem. The answer by @ChrisJohns will probably be a more likely cause of the issue, as for me I'm simply going to put it down to a bug, because this is how I fixed it:
Turn it off and on again. Make your torus/etc and put it in place, but if subtract doesn't work, undo the subtraction, save, quit, reopen and try it again, one subtraction at a time. Like I said, no idea what the cause is, so if this still doesn't work take a look at @ChrisJohns answer


Wildfire smoke : old electronic air cleaner or normal pleated filter better?

Question: The house we live in has an old electronic air cleaner attached to the furnance. It's a Honeywell F50E 1182. We have lots of wildfire smoke in the PNW right now and am wondering if using this system or putting a regular pleated insert in like they do in this video would be better at filtering out wildfire smoke. I have a 20x20x4 filter I could put in if so.
Answer: Smoke particles are on the order of 1 micron.  A "pleated" filter is good down to about 3-5 microns so NO, that will not filter out the smoke.  Some will get through.
What you need is a HEPA filter, which usually involves adding a HEPA filter unit into your system and these are effective down to about 0.3 microns.
Comment: The PM2.5 filter may help some but as I read the spec for the 1550, it's designed for a 2.5 micro particle size.  Unfortunately the smoke particles that travel the longest distances are the smallest ones and I believe you'll find the 1550 filter to be of limited usefulness.
Comment: I agree it might help but due to the increased back pressure there will be less air filtered and some furnaces will shutdown because of low flow.
Comment: I'm not necessarily looking for something to filter each and every smoke particle out. Just wondering if the filter I have (which is an MPR 1550, MERV rating ~12) is better or worse than the electronic air filter already in place. The 1550 is supposedly rated for 'smoke' on this chart (https://www.filtrete.com/3M/en_US/filtrete/about-us/the-right-filter-for-you/), but interestingly not for PM2.5, which I believe wildfire smoke is mostly comprised of. In any case, I'm looking for relative performance. In no way can I get a HEPA system installed before tomorrow.
Answer: The electrostatic filter will be your best option to filter the smoke, you may need to clean it every week until things clear up, putting a filter that has a finer particulate rating than your system is designed for can cause problems. Your best bet now is to turn the fan on all the time so your air is getting constantly cycled over the grid. If you haven't cleaned the filter hose it down now so it will be functioning at its peak performance. I have a granddaughter that has serious as a problems and the electrostatic on the furnace keeps the air inside clean enough she doesn't end up in the hospital. The last time I also closed down the make up air intake as to reduce the amount of fresh air because of the smoke load. With the electrostatic you don't want to slow the air exchanges these filters when clean are more effective at reducing smoke. A high density filter reduces the air exchanges so it is not as good even if it could take out the finer particles.
Answer: Need to look at charcoal 'after filters'...Pre filters are the metal grate looking filter that is in there...There is a spot for a after filter...That's what our manual says


Information relationship to Special Relativity

Question: How do we write mathematically that "information" cannot go faster than light?  And along a similar line of thought, how do we relate "information" with special relativity.  Lastly, what is the relationship between Special Relativity and the fact that the phase velocity of a wave packet can go faster than light (light speed here being the group velocity).  Is there a reason we cannot consider the frame of reference of a specific phase in a wave packet?
Comment: Related question: http://physics.stackexchange.com/q/34653/2451
Answer:
How do we write mathematically that "information" cannot go faster
  than light? And along a similar line of thought, how do we relate
  "information" with special relativity.

Since you are looking for an equation (you say "mathematically"), I would undoubtedly choose this:
$$\left[\hat O (x),\, \hat O' (y)\right]=0, \, \mbox{if}\; x-y \; \mbox{is spacelike}$$
where $\hat O$ and $\hat O'$ are the (linear self-adjoint) operators corresponding to two physical  observables —in particular, both may be the same observable and therefore the same operator ($\hat O=\hat O'$)—, and $x, y$ are two points in space-time. This equation summarizes the fact that information cannot  travel faster than light because it says that the results of two experiments separated by a space-like interval cannot be correlated. And this is what "information" means since one codes information with physical effects.  Please, see this Definitions: 'locality' vs 'causality' if you are interested in the different usages of the terms "causality" and "locality", which are physically more relevant or why entanglement do not imply faster than light propagation.
The previous formula assumes that the physical laws obey the principles of quantum mechanics and special relativity, and are thus quantum field theories. This is the case for the electromagnetic, the weak and the strong interactions and also likely for the case of the gravitational interaction in the weak field limit and in the sense of an effective field theory; which are the fundamental interactions that we know.

Lastly, what is the relationship between Special Relativity and the
  fact that the phase velocity of a wave packet can go faster than light
  (light speed here being the group velocity)

Sometimes defining the speed of a wave is tricky. The signal or information velocity is often the group velocity (which is the velocity of a wave packet), even though in some media (see http://en.wikipedia.org/wiki/Signal_velocity) it is not. But the phase velocity (the rate at which the phase of the wave propagates) cannot carry information (see http://en.wikipedia.org/wiki/Phase_velocity) and may be faster than $c$.

Is there a reason we cannot consider the frame of reference of a
  specific phase in a wave packet?

You may take any inertial frame provided its speed be lower than $c$. Note that according to special relativity one needs an infinite amount of energy to cross the speed of light $c$ threshold.
Edit: SMeznaric points out —and I agree with him— that space-like separated measurements may give correlated results. What is not possible is to send information one has control over, such as the choice of measurement operators.
Comment: @SMeznaric I also say that this assumes that there is not previous correlations between the (sub)systems over which one is measuring.
Comment: This statement "This equation summarizes the fact that information cannot travel faster than light because it says that the results of two experiments separated by a space-like interval cannot be correlated." is actually not true even classically. For example $\rho = \sum_k p_k |k><k|$. Spacelike separated measurements on this system will give correlated results. What is not possible is to send information one has control over, such as the choice of measurement operators.
Comment: @SMeznaric Agreed. Have you read the answer I linked?
Comment: I just checked it out now. There you also say that causality (Einstein locality) means that spacelike separated experiments are not correlated. Several of the other things you mention are very closely related, but seem good to me.
Comment: This is what you say: "Results of experiments carried out at a space-like distance are not correlated."
Comment: @SMeznaric I *also* say in the immediately following sentence: "*This* assumes that there are not previous correlations before making the experiment." Where "this" refers to the immediately previous sentence, that is, the sentence you have quoted.
Comment: OK. So basically you are saying correlations can't just arise out of the blue by themselves only through local actions. That's fine then. I missed your qualifying sentence.
Comment: @drake: Not sure if you ever read that paper I linked you, but it shows that there do not have to be previous correlations.  I also think you're confusing entanglement with Bertlemann's Socks.  Please read Bell's famous essay Bertlemann's Socks and the Nature of Reality. You can't say it's the same as placing a red ball in box1 and a blue ball in box2, separate them and send them to two friends -- when one friend finds blue, he knows the other friend has red. That's exactly what Bell showed can't work!
Comment: @user7348 I've only had the time to read it superficially. Sorry...
Answer: Information as we know it is either carried by a physical object or a field. They both must obey special relativity and thus are thus c limited.
Answer: Rather than information, it may be clearer to say that causality cannot go faster than the speed of light.  That is to say, a particle is only affected by events that happened in its backwards light cone.  This is expressed mathematically by the equations of motion for a particle not being dependent on anything outside of its light cone.  Of course, if a particle cannot be affected in any way by events outside of its light cone, it also cannot receive information about those events.
As for your second question, regarding a superluminal phase velocity, the answer is that the frame of reference of the phase would not be an inertial frame.  That is to say, your focus of attention can of course follow the wave crest but you cannot speak of an observer who is at rest relative to the wave crest.  This is because an observer cannot be moving faster than the speed of light.  There is no Lorentz transform associated with such a frame.
If neutrinos went faster than the speed of light, then all bets are off.  We would discard all the physics that was developed in the last 100 years and start from scratch.
Answer: In order to see how special relativity implies that information cannot go faster than light, one must first consider the physical properties of information. Definition of information usually used in physics is the minimum length of a message needed to encode it. For example, given prior probabilities $p_1, \ldots, p_k$ for an outcome $k$ of some random variable, the minimum length of a message needed to represent the information of which outcome occurred is given by $H({p_k}) = - \sum_k p_k \log_2(p_k)$. You can read in great detail about this as it is a well developed field known as the Shannon information theory, as a start see for example Wikipedia. This is intuitive: given $n$ equally likely outcomes, we would need $\log_2(n)$ objects with two completely distinguishable states each to represent the information on which outcome occurred, as $m$ such objects have $2^m$ possible states. If one has objects with more states, then the base of the logarithm is changed. There is no loss of generality if we use 2, and this is the typical use with the unit of information known as bit.
This brings us to physics of transmitting information. In order to actually impart information on another observer, one needs to prepare $H({p_k})$ physical objects and send them to the receiver. Since special relativity limits how fast such objects can travel to the speed of light, this then implies that the receiver will not be able to learn anything about our part of space until our objects have reached them.
However, there is another potential way that one could send a message without moving an object. This is to instantaneously (in some frame of reference) change the state of the objects already present at receiver's end so as to match our desired message. Here our understanding of physics implies that objects need to interact through a field (i.e. particles, which are physical objects). Now special relativity requires that fields cannot propagate (translation = particles cannot travel) faster than the speed of light and therefore we are back to not being able to transmit any information.
Of course there is a but coming at the end. The existence of tachyons would throw everything I said above out the window, so everything I have said you should take it in the context of the current theories and experimental evidence. Here by tachyon I mean a particle that can travel faster than the speed of light. Whether nature really works like this or not we do not know.
As an aside, quantum entanglement does not allow one to overcome this requirement. While measurements at the would-be sender's and receiver's sides are correlated, the sender cannot determine the measurement outcome of the receiver through choice of measurements or otherwise. Quantum mechanics is thus fully compliant with the requirements of special relativity.
Comment: I up-voted this answer, even though it does not answer the original OP question: "How do we write mathematically that "information" cannot go faster than light?". Nevertheless, it should be clarified that the definition of tachyion that SMeznaric uses is not the standard field theoretic definition. He means or he should mean a particle which travels faster than light in vacuum. A field-theoretic tachyon (i.e., a field with the opposite sign in the quadratic term of the Hamiltonian) does not imply faster than light propagation.
Comment: Thank you for your comment. I have updated the answer to reflect what you say.
Answer: The speed of light can be derived from Maxwell's Equations. So information carried by light cannot go faster than c. But neutrino's were briefly in the news for possibly going faster than light, and the only problem was that there should have been energy radiating from them that was not observed. So it is just a matter of no such energy being observed that we deduce that they do not go measurably faster than light.
The phase velocity can go faster than light for the same reason that you could point a laser at the Moon and observe the reflection spot travelling faster than light. There is no object there. You could use that motion as a frame of reference, but the usual published formulas make the assumption that the speed of the observer is less than c, so those formulas won't work in your example.
Comment: I'm confused what is "information" and what is not.  How do mathematically define information vs non-information?  Also, I don't understand why if certain phenomena do exhibit faster-than-light motion, we do not expect the standard odd effects to appear in that frame of reference (such as time being negative, etc...)?
Comment: The neutrinos never went faster than light, so that doesn't factor into this issue. The only thing that prompted the news was a mechanical timing error.
Comment: mcFried - what information is exactly doesn't really matter for the original question. All that matters is whether some signal can travel faster than light. Whatever form that signal takes could be used to transmit information, such as using AM or FM modulation. And yes, faster than light travel would cause big problems for causality, because it would show that objects could exist in a frame of reference where the consequences of events could be seen at a point in spacetime where it was still possible to prevent the cause. But that already exists in general relativity.
Comment: David - I mentioned neutrinos just to illustrate the process by which it was determined that is was very unlikely that they travel FTL even before the cable problem was found. It would have had a fundamental effect on our understanding of the universe, but we couldn't rule it out completely without other observations such as the lack of Cherenkov radiation.
Answer:
[...] how do we relate "information" with special relativity.

The "exchange of information" (a.k.a. "signalling") between participants is arguably a foundational and self-explanatory notion of (special as well as general) relativity:
for instance, participant Alice stated some particular indication $A_i$ (and subsequently remembered having stated it), and later Alice observed and recognized participant Bob having observed Alice's indication $A_i$, and (in coincidence)/or (subsequently) participant Eve having observed Alice's indication $A_i$, and so on;
all without providing any more specific or even quantitative characterization of the "information" thereby exchanged.

How do we write mathematically that "information" cannot go faster than light?

This question seems to consider the exchange of  "light" as being distinct from the exchange of "information" in general. However, if so, then necessarily in some more specific "mode" (perhaps "electro-dynamically", or "chromo-dynamically", or "by curvature").
Accordingly, the correct statement would be that "information exchange in some specific mode cannot go faster than information exchange in general";
or in other words, that "light cannot go faster than information".
For suitable setups and specific modes (of "light" exchange) the corresponding ratio of "(general) information speed" to "(specific mode) light speed" can be expressed as the "group speed refractive index, $n_g$"; cmp. http://en.wikipedia.org/wiki/Index_of_refraction#Group_index

Is there a reason we cannot consider the frame of reference of a specific phase in a wave packet?

A "frame of reference" is primarily considered of some specific participant (such as Alice), as a specific geometric relation to other participants (such as "Alice and Bob having been at rest to each other"). In the context of relativity (at least), the underlying though-experimental method of establishing some specific geometric relation between suitable participants is of course based on their mutual exchange of "information", as described above.
However, "a specific phase in a wave packet" may not typically be considered as engaging in the exchange of signals with other participants (and/or with any other "specific phase in a wave packet", for instance).
Therefore, the "frame of reference of a specific phase in a wave packet" may only be identified indirectly, if at all, by suitable proxy, such as the "frame of reference" of a particle moving through a medium of refractive index $n$ at $\beta = 1/n$; cmp. http://en.wikipedia.org/wiki/Cherenkov_radiation
Comment: Please note a follow-up question: http://physics.stackexchange.com/a/37641/12262
Answer: light = information
Light (EM field) codes info in the wavelength (or frequency).
Open your eyes and your brain is illuminated with information.
The sound waves bring info to your ears but ultimately from atom to atom collision the EM field is present.
The info that you obtain from the net is frequency encoded in the fibre cable and/or in the sattelite up/down path, and again it is EM field. We have electronic computers for now, slower than the photonic ones of the future.
The science is searching to see if the gravitational field (in the form of grav waves, search LISA ) also transport info. They found none effect and a much longer time will ellapse until the fundamentalists give up and make the obvious conclusion.
Every sensation (info it is) that you feel, even your tougths, are due to EM field. Well, if you fall from the roof to the ground, I hope not, it is due to the gravity field. It is my conviction that the EM field can emulate the grav field.
The two main arguments against this idea can be avoided like this:
It is true that gravity is always attractive, idem with electric dipoles. Inside the nucleons (protons and neutrons are the only experimentally confirmed emitters and receptors of gravity) can exist elect dipoles so near one from the other and in opposition of phase that the intensity of the radiated field is so faible as detected. The frequency is so high that the antennas of reception can only be of similar size of the emmiters (nucleons).


When applying to a second master's degree , can my first master compensate a low undergraduate GPA?

Question: I have a 3.31/5 GPA in mechanical engineering undergrad but got work as a software engineer, 4 years have passed since then, i have had promotions in my work as programmer and I also Will graduate in the next months from my first master degree in software engineering with a 4,6/5 GPA.I want to pursuit a second master degree in computer science, can my undergrad affect me from getting accepted?
Comment: yes it can compensate but at around the 5th master's degree it stops working.
Answer: It is impossible to predict with certainty as systems differ, but it seems unlikely. Your most recent degree normally ranks higher in the calculations and it is closer to the new field.
But I wonder why you want a second masters. There will be a fair amount of overlap. That, alone, might count against you if people in the decision process think the slot might better go to someone else. That might depend a lot on country, though. Make sure you can justify this in any application.

When applying to a second master’s degree , can my first master compensate a low undergraduate GPA?


find permutations of items in a python list, with an added complexity

Question: Please bear with me while I struggle to explain this; my math is rusty and I just started computer programming, sorry!
Say I have a list of 3 items.  I want to find all possible arrangements of the items in this list where each arrangement consists of 3 items.
Next, still using my original list, I want to find all the possible arrangements of the items of the list, except I only want the arrangements to consist of two items.
Finally, I want to do the same thing again, except arrangements only consist of one item.
So I expect 3! + 3!/1! + 3!/2!, or 15 total arrangements.
Just to be really explicit about what I want, if my list were [1, 2, 3], then the code should produce:
1, 2, 3
1, 3, 2
2, 1, 3
2, 3, 2
3, 1, 2
3, 2, 1

1, 2
1, 3
2, 1
2, 3
3, 1
3, 2

1
2
3

The code I have written below can do what I have written above, but only for lists of length 3.  I could modify the code to handle lists of greater length by adding extra 'for' loops and 'elif' statements, but I feel like there has to be a way to generalize the pattern.  What should I do so that I can get permutations of the kind described above for lists of any length?
I think my exhaustive enumeration method might be making this more complicated than it needs to be... will try to think about other methods and update if solution found.
def helperFunction(itemsList):

    fullPermutationsOutputList = []

    def fullPermutations(itemsList, iterations):

        for item1 in itemsList:
            if iterations == 2:
                if len([item1]) == len(set([item1])):
                    fullPermutationsOutputList.append((item1,))
            else:
                for item2 in itemsList:
                    if iterations == 1:
                        if len([item1, item2]) == len(set([item1, item2])):
                            fullPermutationsOutputList.append((item1, item2))
                    else:
                        for item3 in itemsList:
                            if iterations == 0:
                                if len([item1, item2, item3]) == len(set([item1, item2, item3])):
                                    fullPermutationsOutputList.append((item1, item2, item3))

        if iterations == 0:
            fullPermutations(itemsList, iterations + 1)
        elif iterations == 1:
            fullPermutations(itemsList, iterations + 1)

    fullPermutations(itemsList, 0)
    return fullPermutationsOutputList

Comment: Have you looked at the itertools module?  http://docs.python.org/library/itertools.html
Answer: Just itertools.permutations.  You can inspect its sources if you want exact algo.
Comment: Thanks to both of you guys.  This solves my problem and I can see how it's done.
Comment: @Ryan then you should accept Roman's answer.  Click on the checkbox next to it.
Answer: this will do  what u want: https://stackoverflow.com/a/10784693/1419494
def perm(list_to_perm,perm_l,items,out):
            if len(perm_l) == items:
                out +=[perm_l]
            else:
                for i in list_to_perm:
                    if i not in perm_l:
                        perm(list_to_perm,perm_l +[i],items,out)

a = [1,2,3]
for i in range(1,len(a) +1):
    out = []
    perm(a,[],i,out)
    print out


Only show the cart block if it contains items

Question: How can I set a Drupal Commerce shopping cart block to only display if it contains items? I'd like to hide the cart block when the cart is empty.
Comment: Please explain your answer so that someone in the community can understand.
Answer: Here is the solution. Add these lines in template.php file of a theme you`re using. Change THEMENAME on the name of your theme.
function THEMENAME_commerce_cart_empty_block() {
  return '';
}

Answer: For drupal8+ and commerce 2 the answer is
function mytheme_preprocess_block(&$variables) {
  if ($variables['plugin_id'] == 'commerce_cart') {
    if ($variables['content']['#count'] == 0) {
      $variables['attributes']['class'][] = 'visually-hidden';
    }
  }
}

Answer: The solution that worked for me is not just hiding this "your shopping cart is empty" but also hiding all possible long list of items.
And you can accomplish this using views:

create two fields of text links, one for view cart and another for checkout.
Add another field to display the total amount. Look for "add commerce order: order total"
I got this idea from this
Filter criteria: commerce order to >=1. This will make block disappear when the order is greater than 1.
Apply some css.


Make NewForm.aspx Viewable

Question: I want people to be able to submit information using "NewForm," but I don't want them to see any of the information that is saved in the list.
Answer: I've done this for a few pages on our site by using an html link directly to the New Item form. You can find this address by opening the New Item form in a browser and copying the URL. By changing the "source" portion of the link, you can specify the webpage that you want to load when the form is submitted, rather than have it default to the list contents.
Example:
My Link

Answer: If I understand you correctly, you want users to submit information using the form but they should be able to see the display form, edit form and the views of the list. You will have to create a list workflow to set permission on list item. Users will have contribute permission in the list. So, they will be able to submit information. Once they submit information, list workflow will be triggered and the workflow will modify permission for the list item granting only intended users access.
Comment: I want a user to be able to submit data with Newform, but I don't want them to be able to see the other data in the list beside their own.
Answer: You can set item level permission to achieve this.
Follow below steps:

Open your list
Go-to list settings
Click on advanced settings
Under the item level permissions select option that says "Read items that were created by the user"
Click OK

Done
Now users will be able to see items in the list that are created by them only and other items will not be visible to them.

Make NewForm.aspx Viewable


is Multicast programming possible in android 4.0.3?

Question: I'm developing an Android application which can communicate to the java server using multicast socket. I've developed same application successfully in java only, but i am getting problem when I'm using the same code in android.
I found a code on Google thread reporting that android doesn't support multicastSocket.
Please tell me how can we apply multicasting in android ?
Is Multicast programming possible in android ?
Please provide some useful links..
Answer: Yes it is possible in android to use multicast socket. you may refer to this class for android
http://developer.android.com/reference/java/net/MulticastSocket.html


Fading LED with different frequencies

Question: I have a potentiometer attached to one analog port of arduino (assume A0)
I'm reading the value of that using input_voltage = analogRead (A0); which is a value between 0-1023.
So I want to map this value to frequency from 1Hz to 20Hz. Then I want to fade my LED using this frequency.
Tried to doing this map using int frequency = map (input_voltage, 0, 1023, 1, 20);
But how can i apply this frequency to LED?
I mean PWM has a constant frequency (about 500Hz). How should I apply frequencies from 1 to 20 to this LED in order to fade it?
Comment: Do you want to blink or flicker instead of dimming the led ? Or does 1Hz mean you want to fade for 1 sec between ON and OFF (20 Hz = 50 ms between On and Off will be no visible difference to immediate switching)
Comment: What is your goal? Do you want to change the rate at which you flash an LED? PWM (Pulse width modulation) doesn't to vary the  frequency of the output - it varies the duty cycle (ratio of on-time to off-time) of a fixed frequency output. If you want to dim the output of your LED based on the input pot, it seems to me you should map 0-1023 to 0-255 , an use the 0-255 output to control a PWM output pin. If you want to control the flashing rate of the LED, you need to use something other than PWM.
Comment: @DuncanC Thanks for your help. What is that "something other than PWM" ? For example timers?
Answer: There is a library in which you can change the frequency
Here is my example code I did long time ago I had the same problem
Get the library from here
Go ahead and try example code there and try to understand too.
Include the library first to code
my code
void setup() {
  pinMode(13, OUTPUT);
  pinMode(8, OUTPUT);
  digitalWrite(8,LOW);
  Serial.begin(115200);
  InitTimersSafe();
}
void loop() {
  //mapping
  long x = map(analogRead(A0),0,1023,1,20);
  bool b = SetPinFrequencySafe(9,x);
  digitalWrite(13,b);
  pwmWrite(9,127);
  Serial.print(x);
  Serial.print(" Hz ");
  Serial.println(b);
  delay(100);
}

Built in led will turn on if the frequency is stetted.
By the way led will turn on in 50% on and 50% off in one cycle in pin 9.
Use only the PWM pins in Arduino 3,9,6 etc.
Now you can change the PWM frequency...
I just put a led in the female socket in for easiness + terminal in 9 and - terminal in 8 to go to ground that's why I did put pin 8 to low.
Comment: Thank you for this complete and helpful answer!
Comment: Wouldn't it be easier to modulate the duty cycle of the PWM for fading a LED? By adapting the frequency between 1Hz and 20Hz, you'll just get changing flashing rates, unless you integrate the PWM output with a (rather large) capacitor.
Comment: @imalipusram I understand but the question asked me to do this using frequency...

Fading LED with different frequencies


Proton's half life (Energy-dependent)

Question: Proton's half life has a lower estimated bound in 10^33 years aprox. This is due to the enormous mass of the X boson, predicted by some GUTs. So my question is: if the free proton is in a high energy state, it has more energy (ready to be "used") and thus it would be easier to create the X boson needed. Is this implying a energy-dependent half life? If so, has this dependence been  calculated somewhere? I'd love to have some references if possible. Sorry for my english and thanks.
Comment: There's a misconception here: it is the mass (a Lorentz-invariant quantity) which can be "used" to create particles in a decay. Alternatively you may think of it as the energy in the centre-of-momentum frame. The relation $E=mc^2$ only works at rest. More generally it is $E^2 = p^2c^2 + m^2c^4$.
Answer: All decays behave the same way, the mass of the mediating particle affects the lifetime when measured at the rest frame.
The lifetime of the muon for example is given as ~2.2μsec, this number is for a muon at rest. Energetic muons are relativistic, and so time dilation
of   a high energy muon will give a longer lifetime according to the relativistic effects.
The same would be true for the possible proton decay, except that the mass of the X, ~10^15 GeV is so huge  and the lifetime this implies (~10^33 seconds) so large  the probability of decay could not be enhanced in the existing accelerators.

Proton's half life (Energy-dependent)


Retrieving an old WhatsApp backup from Google Drive

Question: The phone was stolen and I would like to retrieve an old WhatsApp backup from Google Drive. I do not want the most recent backups offered, as these were since my phone was stolen.
I want an old one that is visible on Google Drive, but when I click it, the only options are to delete it or turn it off. I want to install it. This chat file is not visible in my WhatsApp/databases folder.
Answer: You can't access raw files of WhatsApp from Google Drive (it is a hidden folder), and you can't choose which version you want to restore from (I cannot even see versions at my account).
But, you can try to restore the last backup from Google Drive, and then manipulate
WhatsApp db files in order to delete some of your messages.
There are plenty of guides out there on how to decrypt WhatsApp db, after you decrypt it, delete the non-relevant messages and put the db back in your sd, Didn't try but it might works.


Can you use iCloud locked iPhone like an iPod touch

Question: i already have an android smartphone and an old iPod touch. I want to upgrade my iPod touch. I was wondering if I can purchase an iCloud locked iphone cheaply and use it as an iPod touch - ie all the features except the phone, as I don't want it for the phone. Or are the features disabled when it is iCloud locked?
Comment: I don't believe you can buy a locked iPhone. Not from a proper store anyway (are there seriously stores that sell this kind of stuff?). In any case, IIRC, the entire phone is locked to protect the original user's data.
Comment: I think the OP is asking about. Carrier Locked phone.
Answer: If you purchase a phone which is activation-locked via iCloud, you will not be able to use any features on it at all. This is different than a "locked" phone by carrier, which means that it can only be used on a certain carrier (such as AT&T). If that's the case, then the phone will work as a more robust iPod touch.


Email header IP address

Question: Do the IP addresses in an email header include information from the device from which the mail is being sent, or from the mail server?
Answer: Usually, each machine on which the mail transits:

adds a Received: header stating from where the email seems to come;
announces its name (which could be an IP address) to the next machine, which may or may not include that information in its own Received: header.

Here is an example in one of the 100+ spams that I daily receive:
X-Original-To: email@example.com
Delivered-To: firstname.lastname@example.com
Received: from davisandsons.net (213-238-65-230.adsl.inetia.pl [184.108.40.206])
        by arges.bolet.org (Postfix) with ESMTP id 7951068C0D4
        for <email@example.com>; Fri,  7 Oct 2011 21:49:22 +0200 (CEST)
Received: from apache by davisandsons.net with local (Exim 4.67)
        (envelope-from <email@example.com>)
        id XD1AV6-73T5L6-H9
        for <firstname.lastname@example.com>; Fri, 7 Oct 2011 20:46:35 +0100
To: <firstname.lastname@example.com>;
Subject: Re:web site
(...)

Header lines are added in "reverse order": each mail server adds its line at the beginning of the header. So here my mail server (arges.bolet.org) received a connection for a mail which, at the SMTP level, was destined to me (over the connection, the other machine sent: RCPT TO: firstname.lastname@example.com). As part of the SMTP protocol, that machine first sent an HELO command in which it claimed to be "davisandsons.net"; my mail server looked at the source IP address (188.8.131.52) and did a reverse DNS resolution on it, yielding "213-238-65-230.adsl.inetia.pl" (from an ISP in Poland). It turns out that "davisandsons.net" can be resolved to a quite different IP address, nominally from England.
This first Received: header was added by my mail server, so it is trustworthy. The next line, and all subsequent lines, however, were sent as is by that Polish machine which began the conversation by claiming it was in England, a blatant lie, thus not the greatest way to build mutual trust. That header could be completely phony. Assuming it is not bogus, it would indicate that the mail originated from the local machine, by a user called "apache". The probable scenario is then: the home PC of some poor guy in Poland is an infected zombie, which relays spam. The infection might have began through a poorly configured Apache Web server on that machine.
(Spamassassin rated that specific spam with a whooping 20.5 score, and I automatically zap incoming emails with a score of 5.0 or more.)
Answer: It is common that every mail servers in the delivery chain add a line similar to
Received: from [sender-name] ([sender-ip])
          by [server-name] ([server-ip]);
          with SMPT; Fri, 7 Oct 2011 03:15:30 +0200

The format is not specified and varies.
Exposing the previous mail server during transit is common because it helps a lot in fighting spam.
But exposing the very first sender is often undesirable for privacy and security reasons. Some mail provider therefore omit it from the header and other mail providers treat the original sender just like any other source.
As a side note: "Received" headers can be forged, so you always have to start reading them from the top and carefully validate them.
Comment: "_Exposing the previous mail server during transit is common because it helps a lot in fighting spam._" I believed it was done to prevent mail loops.
Comment: @curiousguy Loop detection usually works on comparing the own server name with the by-parts of Received headers, counting the number of Received headers, or a local message id databases. Comparing the name in the sender part only works if it is a tight loop or the next hop plays nicely. So the "by"-approach has significant advantages.
Answer: That choice is completely up to the server the device talks to. It could include a Received header that contains information to identify the device such as its IP address. But it can also include no such header at all. It is completely an implementation option.
Logically speaking, it depends on whether you consider the device or the server to have originated the email. For example, web-based services such as GMail generally consider the server to have originated the email, so no information to identify the device is included. More traditional email services accessed by IMAP and POP often do consider the end device to have originated the email.
Answer: It will include the ip address of your device (more particularly, the address of the router that forwards packets from your work station), and all the mail servers through which it is forwarded from.

Email header IP address


Create a new database with MySQL Workbench

Question: Being new to MySQL, I have installed the latest version of the MySQL Workbench (5.2.33). I would like to know how you can create a database with this application. In the Overview tab of the SQL editor there are few "MySQL Schema" displayed, are these schemas the existing databases?
Answer:
Launch MySQL Workbench.
On the left pane of the welcome window, choose a database to connect to under "Open Connection to Start Querying".
The query window will open. On its left pane, there is a section titled "Object Browser", which shows the list of databases. (Side note: The terms "schema" and "database" are synonymous in this program.)
Right-click on one of the existing databases and click "Create Schema...". This will launch a wizard that will help you create a database.

If you'd prefer to do it in SQL, enter this query into the query window:
CREATE SCHEMA Test

Press CTRL + Enter to submit it, and you should see confirmation in the output pane underneath the query window. You'll have to right-click on an existing schema in the Object panel and click "Refresh All" to see it show up, though.
Comment: I clicked on the Yellow Database with "plus" on it, which is on rollover titled "Create a new Schema in the connected server"  for Workbench 5.2.39 CE  Revision 8757 ,  this worked for me.
Comment: wadhwa94- They are different things. The database is the file, the schema is the way the file is organized. You can have several different database instances that share a schema. What Edward said ("the terms 'Schema' and 'database' are synonymous in this program") is also true. Oracle decided to use the word schema when they meant database because they hate their users and want to make us suffer.
Comment: As far as my understanding goes, Schema and Database are two different things. Here all the methods described are for Schema creation.
Please give some clarity.
Comment: This might be a little different for the newer versions of MySQL Workbench. Step 2 seems different. For Step 3, the left pane is called "Navigation" and "Schemas" are at the bottom of Navigation, except clicking the two-way arrows at the upper-right of Schemas will open only Schemas within Navigation.
Comment: MySQL Workbench really is the worst UX has to offer. But well what can you do.
Comment: I keep saying MySQL Workbench offer the worst GUI, it is just not intuitive and sometimes crashes. I got stuck with this piece of useless trash for hours until decide to uninstall the program. Some guys say it is only for professionals.. LOL
Answer: Click the database symbol with the plus sign (shown in the below picture). Enter a name and click Apply.

This worked in MySQL Workbench 6.0
Comment: "Schema" means "Database" in MySql so it means database
Comment: Super simple. GUI way is much easier. Thanks.
Comment: in workbench 6.3, this icon shows "create a new schema in the connected server". so what we create is a schema or a dababase? I believe they are different coneepts. Also this is the quesiton in the original post.
Comment: so this has nothing to do with the existing database ?
Answer: How to create database in MySQL Workbench 6.3

In tab home (1) -> Right click on Local instance banner (2)
-> Open Connection (3)

Right click on the empty space in schema window (1) -> Create schema (2)

Type name of database (1) -> Apply (2)
Answer: In MySQL Work bench 6.0 CE.

You launch MySQL Workbench.
From Menu Bar click on Database and then select "Connect to Database"
It by default showing you default settings other wise you choose you host name, user name and password. and click to ok.
As in above define that you should click write on existing database but if you don't have existing new database then you may choose the option from the icon menu that is provided on below the menu bar. Now keep the name as you want and enjoy ....
Answer: Those who are new to MySQL & Mac users; Note that, Connection is different than Database.
Steps to create a database.
Step 1: Create connection and click to go inside

Step 2: Click on database icon

Step 3: Name your database schema

Step 4: Apply query

Step 5: Your DB created, enjoy...
Answer: If the create new schema icon is disabled in the workbench, it means that your MySQL service is not running.

Please check if your MySQL service is running in the task manager.
Answer: This answer is for Ubuntu users looking for a solution without writing SQL queries.
The following is the initial screen you'll get after opening it

In the top right, where it says Administration, click in the arrow to the right

This will show Schema (instead of Administration) and it's possible to see a sys database.

Right click in the grey area after functions and click Create Schema...

This will open the following where I'm creating a table named StackOverflow_db

Clicking in the bottom right button that says "Apply",

And in this new view click in "Apply" too. In the end you'll get a database called StackOverflow_db
Answer: you can use this command :
CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name
  [create_specification] ...

create_specification:
    [DEFAULT] CHARACTER SET [=] charset_name
    | [DEFAULT] COLLATE [=] collation_name

Answer: For me there was a weird bug in Workbench where I had to click the icon multiple times until the "Apply" and "Revert" buttons showed
Answer: first, you have to create Models. default model is sakila, so you have to create one. if you already created the new one, go to Database > Forward Engineer. then, your model will exist in local instance:80
Forward engineer is to create database in your choosed host!


Is there a problem with crushed grapes?

Question: I'm making my own grape juice with grapes bought from the local supermarket. Every so often I encounter a grape that is partially crushed. Do these crushed grapes present a problem of yayin nesech?
Answer: No. The issar of yayin nesrch is touching wine not crushed grapes.
In Shulchun Aurach YD 123 seif 17  explains that after the squeezing the grapes you have what is called must, it's the mixture of grape skins, flesh, and juice. At this point it's still not considered wine. After you separate the juice from that mixture which is called המשכה -to draw away.  From this point on if a non jew touches that liquid it will be yayin nesach.
Comment: I think this is how some kosher grape jellies are made as well...
Answer: The source for this is the Gemara Avodah Zarah from the bottom of 59a to the top of 59b. Rabbi Yeimar says that a Gentile can bring grapes to the winepress even though the grapes are squashed and the juice sprays off, Rabbi Kahana clarifies that he is talking about what is allowed after the fact.
Tosfos there (sv. Mahu) clarifies what the squashing in the Gemara means. The Ri explains that the Gemara is only referring to when wine/grape juice has actually become separated from the grapes: if the wine just drips, it is not yayin nesech. As a result, Piskei Tosfos 116 says "אין לעובד כוכבים להוליך ענבים לגת שהתחיל למשוך": a gentile worker does not carry grapes to the winepress that started to pour out wine. Rosh (4:8), says the same; "לזורקו בגת בעוטה שהתחיל היין לימשך".
The Rashba concurs because it was never the intention of the gentile to create wine by putting the grapes in a container before they went in the winepress to create wine. I think there seems to be a nafka minah resulting from these Rishonim as to why Gentiles bringing grapes can be allowed: Tosfos because the wine has not separated vs. Rashba because there was no intention to produce wine. Either way, your situation is clearly allowed.
We then come to the Beis Yosef (YD 125). He agrees with all that has been said above. The rest of the difficulties in the Ran and Beis Yosef are  about putting the grapes into the winepress, not supplying the grapes like in your situation. (I'm struggling to read this Ran so if I've got it backwards please correct me!). Shulchan Aruch (YD 125:6) codifies that bringing grapes is only allowed retrospectively, but qualifies like Tosfos that this only refers to "אף על פי שיש בדרדורים יין שזב מהענבים", when wine is pouring out from the grapes and has become separated. This is much more wine coming out of the grapes than "every so often I encounter a grape that is partially crushed" as in your situation. This is made explicit in the Taz (sk.9, see Baer Hetev sk.8 for a summary), who brings the Rashba's explanation above.
So, according to all the Rishonim, as long as the intention is to provide grapes that will then be pressed, the grape juice has not become separated from the solid grapes in a large quantity, and the grapes are not put into the vat by the Gentile, these grapes are permitted both retrospectively and from the beginning.
The Maharal Zunz explains the reasoning of the Rashba and Tosfos. Avodah Berurah summarises some of what I have said above.

Is there a problem with crushed grapes?


Raspi Audio Problems When Using a Servo

Question: So I am trying to make a raspberry pi control a servo but it also needs to have speakers attached. But whenever the servo is powered there is a horrible audio output through the speakers. This will happen even when the audio out put is set to hdmi or the PWM pin either way it comes out of the audio jack and changing the volume doesn't help either. But as soon as the servo powers off it stops. To program and wire the servo I used adafruits raspi lesson 8: using a servo. Any help?
Answer: This is likely to be caused by shared noise through the power supply. There are three possible fixes:

Put the servo on its own supply (common ground, but different supply). Although it looks from that tutorial that it's already powered by batteries.
Use digital audio to another board with its own supply (I believe there are various Raspi DAC projects out there, or USB audio may work). You could even have optical isolation over TOSLINK.
Attempt to suppress the noise from the servo with chokes, decoupling capacitors, etc. Start with a few uF across the power rails near where the servo is connected.

You said you'd set audio to HDMI but were getting noise out of the audio jack. I believe if you do that you should get audio on the television or monitor used for the display, and you should disconnect the audio jack.
Comment: Agreed with the HDMI audio output, it's digital and should not be getting analog power supply noise. The audio jack is irrelevant and should not be  connected to a speaker if using HDMI
Answer: I know this is a late response but ...
use ./servod --pcm
Comment: Welcome to EE.SE, but this wouldn't rate as one of the all-time great answers. Would you care to explain (1) how to use this commend, (2) what this command does and (3) why you think it would help eliminate what appeared to be power supply noise. Put the additional info **in your answer** and not in the comments.

Raspi Audio Problems When Using a Servo


Using regex for two delimiters to extract strings

Question: The question How to delete the words between two delimiters? was really helpful to me.
So I have a string like this:
string = $blabla$blav:1085$350_X[7:0]

I am trying to remove whatever is inside the '[]' to make the whole thing be $blabla$blav:1085$350_X.
I tried all these:
re.sub('[[^]]+]', '', string)
re.sub(r'[.+?]', '', string)
re.sub('[.*?]', '', string)

Any method to do it with regex involving one step please.
Also, I need to capture that string[7:0] for later use.
Comment: please check my updated answer.
Answer: Try the regex \[([0-9]+\:[0-9]+)\]$. It matches [X:Y] where X and Y are numbers and the whole thing is at the end of a string. There is only one group in the regex that returns the two numbers X:Y without the [ and ]
Use this to replace the string:
import re
re.sub('\[([0-9]+\:[0-9]+)\]$', '', string)

You can use this \[([0-9]+)\:([0-9]+)\]$ to match the two numbers in two groups.
numbersRegex = re.search('\[([0-9]+)\:([0-9]+)\]$', string)
number1 = numbersRegex.group(1)
number2 = numbersRegex.group(2)
bothNumbers = numbersRegex.group(0)

It is important to use regex instead of just string indexes in case the numbers are two or more digits. Otherwise, it is fine to indices.
If the [X:Y] is not at the end of the string, just remove the $ from the regex.
You can use this website and paste the regex there. It provides explanation and a text field to test it.
Comment: if the string is string = $blabla$blav:1085$350_X[12:0] then it is not working ..what to do ?
Comment: Hey! there was a mistake in my regex, I've fixed it now. Should work with double and multiple digit numbers. The + sign should have been placed after the [. Please use https://regexr.com/ to check your regexes. It provides an explanation of the syntax.
Answer: You can use rsplit with maxsplit=1 to make sure it only split on last [,
string = "$blabla$blav:1085$350_X[7:0]"
s_string = string.rsplit('[', maxsplit=1)

left = s_string[0]
right = "[" + s_string[-1]
print(left)
print(right)

# output

$blabla$blav:1085$350_X
[7:0]

If you must use regex, then try positive lookahead to match last occurrence of [,
import re

string = "$blabla$blav:1085$350_X[7:0]"
regex = r'(^.*(?=\[))(.*)'
ss = re.match(regex, string)

left = ss.group(1)
right = ss.group(2)

print(left)
print(right)

# output

$blabla$blav:1085$350_X
[7:0]

Comment: Thanks but their position not always gonna be same.
Comment: @zaki, i have also added regex answer if you like
Answer: string= '$blabla$blav:1085$350_X[7:0]'

cut_string = string.split('[')[0] # = '$blabla$blav:1085$350_X'

bracket_data = string.split('[')[1].replace(']', '') # = '7:0'

Dirty, but it just werks.
Comment: What happens if there is another `[` or `]` in the string?
Comment: Check my answer then ;)
Comment: Thanks, I solved it this way too but I wanted to solve it with regex in one line preferably .


When you fill a bottle with water then liquid nitrogen then turn it upside down, why does it blast off at high speed?

Question: I saw in the YouTube video Don't Mix Coke with Liquid Nitrogen! that when you fill a bottle part way with water then pour liquid nitrogen into it then turn it upside down, it blasts off at high speed. Why does that happen? How is it possible?
Answer: I cannot figure out the answer for sure but here's my theory. According to the article Liquid Nitrogen Is Beautiful When It's Dancing Across Gasoline, liquid nitrogen is less dense than water. I'm guessing that means at first, the liquid nitrogen floats on the water. When it's turned upside down, the liquid nitrogen starts mixing with the water but surface tension limits its rate of mixing. However, the mixing still occurs to some extent which boils some of the liquid nitrogen creating thrust. Once it starts accelerating, the acceleration speeds up the mixing which in turn creates an even stronger thrust.
Comment: Suggest you add a line to say when the nitrogen boils its volume increases 1000-fold so creating large pressure on the water, and the momentum of the squirting water is consequently enough to cause a big rocket effect.
Comment: @AndrewSteane Once the bottle starts accelerting so quickly, some of the liquid mixture might be under extreme pressure and it probably doesn't expand by that large a factor anymore under extreme pressure. The higher pressure probably also raises the boiling point of the liquid nitrogen. It's probably actually the vapour pressure of the nitrogen at the temperature it's at that determines how much force it will exert, not the amount it expands. I do also realize that evaporation absorbs heat. I think the acceleration makes the surface tension become a smaller factor so the liquid nitrogen forms
Comment: very tiny droplets but the acceleration also speeds up the mixing so the liquid nitrogen ends up absorbing energy from the water very fast.
Answer: When the bottle is turned upside down, the liquid nitrogen floats to the top and absorbs heat from the water. It therefore boils, and creates pressure in the air space at what is now the top of the bottle. This pressure then blasts the water out of the narrow end at high speed, and the bottle is compelled to obey Newton's 3rd Law of Motion (i.e. for every action there is an equal but opposite reaction).
Comment: That's basically so simple and reasonable..  these are the best answers.


Should I put the name of proof reader in scientific manuscripts?

Question: Should I acknowledge the person who has proof read my scientific paper and have contributed in the improvement of quality of manuscripts.
Comment: I can't see why not.
Comment: I've appeared in the acknowledgments of several papers for pointing out typos, minor bugs and misunderstandable statements. I don't think such a mention is necessary, but I certainly enjoyed being mentioned and I see no downside. (No one, to my knowledge, has ever been told that their work is not independent enough because they thank too many people in their acknowledgments! It rather shows that the work is interesting to many people or they are well-accepted in the community.)
Answer: You should acknowledge all who made your paper possible. If that is too many to list, then you can be generic and write something along the lines of "I would like to acknowledge and thank all those who helped and contributed to my paper."
Comment: I am not convinced adding a staple text to each paper that adds zero information is helpful. On the contrary, it seems like this has a direct negative effect on the signal to noise ratio across paper contents.


How to animate a lightbulb going on and off

Question: how would I apply all ofthis into an animation? I would like to animate a lightbulb switching on and off but it seems some of the properties discussed are not available outside the compositor.
https://www.youtube.com/watch?v=-Ya-7olrPyc
Comment: You can use drivers to drive nodes input values. Right click on a slot and choose 'add driver'
Comment: how do i do that?
Answer: The principle is the following but can be more or less complex starting from the video as it will surely involve several drivers and to do it in material and compositing nodes settings.
Here the cube's color is changing depending on the position of an empty along Y (the effect is visible in rendering mode):

In this example, I add a driver to the 'fac' value of a mix shader:

Then open a view and set it to 'graph editor' (1), then set it to 'drivers' mode (2), select your object (the lamp in your case), then its material and the 'fac'. Then (4), open the right panel (N) and choose the 'drivers' tab:

Add for instance an empty. Then in the driver panel, use it as input (variable) object (1), and for example choose its Y position to drive the result. Set (2) the driver to 'scripted expression' then set the expression to (var > 0) so that the output is 1 when the empty.Y is above 0, and is 0 when it is below 0.

Doing that, the mix shader node is driven by this previous driver's output. So you can animate a lamp this way, just moving an empty.


How to get more gargoyle dust

Question: I finished the gargoyle contract in Loc Muine but I didn't farm them to get enough gargoyle dust for the Kinslayer outfit. Is there any way to get more dust? I am willing to hack save file if that's what it takes, by any, I mean any. I am playing to PC
Answer: The gargoyles stop spawning after you do the contract so you are at loss there. The only other way I know for getting the dust is by doing the quest From a Bygone Era. Where attacking the operator will spawn Gargoyles. But you need to have started the quest in Act II tho.
Comment: btw the gargoyles that get spawned in that quest are super hard, they hit like trucks.  if that's the only way left to get dust, then he's in for a world of pain.
Comment: Actually the Dark setting is pretty tough so I wanted to get the kinslayer outfit to kill the gargoyles there
Comment: @Eric Hmm i've been looking for a save game editor but the one i found only adds exp and points. And there isn't a mod on the nexus either that helps you. But maybe there is a mod that gives better armor? :p http://witcher.nexusmods.com/
Answer: You can still get them. In the quest "SECRETS OF LOC MUINE", when you decide to help Cynthia, you'll go through the second guardian (that burning Mordor eye). Then when your answer is incorrect, 3 gargoyles will spawn in there - kill em and the prize is yours.
Comment: Thanks, unfortunately I think I already cleared this quest. I may check it out, but I didn't play this game for over 6 months

How to get more gargoyle dust


How hot can Thermal Grease get?

Question: Thermal Grease is used to remove the air gaps between CPU and heatsink. However, computing aside, what would determine the max temp that the grease can handle before it burns or breaks down?
Comment: There are different kinds of thermal grease, and the temparature they can handle will vary.
Comment: Your best bet is to contact the manufacturer or consult the labeling information for your brand.
Answer: Since most thermal greases are ceramic and/or metal suspended in a silicone or organic oil, the temperature the grease remains stable at will likely primarily be determined by the properties of that oil -- either its ease of evaporation, or decomposition temperature (or, I suppose, its flashpoint, but that seems unlikely).
As Ben Norris says in the comment above, your best bet is to contact the manufacturer or check their data sheets: for common CPU uses, most manufacturers will give you stable and extreme temperature ranges which are likely to be fairly conservative (for example, here), and they may be able to help with more esoteric data if you're using it for other purposes.
Comment: I tried burning thermal grease; it catches fire pretty easily.
Comment: @kurtnelle - That's to be expected; both silicone and other organic oils are organic compounds; get them hot enough, like exposing them to a naked flame, and they'll combust just like any hydrocarbon. Most fuel gas flames burn at between 1000-1500 degrees, with some of the crazier ones like acetylene going up to 2500. That's well above the flash point of just about any organic substance, as well as a few metals.
Comment: However, without true combustion as an ignition source, very few things on the surface of the Earth can sustain those kinds of temperatures through other means. You could likely put a dollop of silicone thermal grease on a cookie sheet and stick it in the oven at 450*F for an hour and it wouldn't burn (it would likely melt). The circuitry that grease protects by conducting heat away from it would melt down at a third that temperature.

How hot can Thermal Grease get?


UVs Distored When Importing Mesh?

Question: The first image shown below is of part of my mesh in Blender, and the second is of that same part of the mesh in UE4. For whatever reason, the UVs are distorted and glitchy once imported into UE4. I've tried flipping normals, made sure no UVs are overlapping, re-importing the mesh in a bunch of different ways, and turning on full precision UVs, but nothing seems to fix it. If anybody knows how to fix this, please let me know. Thanks! :)
Comment: Is it possible you have two faces overlapping there? Not an overlap in the UV map, but two triangles in (very nearly) the same place in the 3D model? Some of these artifacts look a bit like z-fighting between close parallel surfaces — especially if they shimmer and change when you move the camera.
Comment: @DMGregory Thanks for your response! I'll try fixing that up and seeing if it makes a difference, I made this using an older method so the geometry probably isn't the best. :)
Answer: Blender and unreal engine read the meshes in a different way, I don't know the geometry of your object, but sometimes when you have n-gons, sometimes even quads, blender triangulates the mesh in a different way from unreal causing this artifacts in the UV channel. You can fix it using a triangulate modifier on blender, in this way you tell precisely how to read the mesh to unreal.
Comment: Thanks so much! That helped a bunch with fixing the distortion on the mesh. :)
Comment: You are welcome :)

UVs Distored When Importing Mesh?


Conflict between OpenCV and Boost filesystem

Question: I'm having a problem with Boost libraries, particularly filesystem when used with OpenCV. Apparently the problem is similar to the one described in Conflict between Boost, OpenCV and Eigen libraries?. In that particular case the problem was solved by preceding the "using namespace" statement with all the "#include" statements. In my case, this was done in this way from the beginning.
I'm using OpenCV 2.4.3 and Boost 1.48 (already tried with 1.52 having the same exact problem). The programming is being done in Windows 7 (64 bit) using Eclipse CPP plugin and MinGW.
When trying to build my program I get the following errors:
C:\Boost\boost_1_48_0/boost/type_traits/decay.hpp:28:66: error: 'cvflann::<anonymous enum>' is/uses anonymous type
C:\Boost\boost_1_48_0/boost/type_traits/decay.hpp:28:66: error:   trying to instantiate 'template<class T> struct boost::remove_reference'
C:\Boost\boost_1_48_0/boost/type_traits/decay.hpp:38:17: error: 'cvflann::<anonymous       enum>' is/uses anonymous type
C:\Boost\boost_1_48_0/boost/type_traits/decay.hpp:38:17: error:   trying to instantiate    'template<class T> struct boost::remove_reference'

In my case the using namespace statements are after the include statements:
#include <opencv2/opencv.hpp>
#include <iostream>
#include <fstream>
#include <stdio.h>
#include <vector>
#include <boost/filesystem.hpp>
#include <boost/multi_index_container.hpp>

using namespace std;
using namespace cv;
using namespace boost::filesystem;

Any idea in how to solve this problem will be greatly appreciated :D:D:D
Regards,
Luis
Answer: I suggest you remove the section:
using namespace std;
using namespace cv;
using namespace boost::filesystem;

and use the scope operator :: in code.
Here's an example of these 2 different modes.


The word for realizing that other people are people too, with stories and depth

Question: I remember coming across an article that said there was a word for the realization that other people are the same as you, with stories, pain, heartache, joy, etc. I believe the word starts with an 's', but I can't figure out what it is.
Answer: I believe 'sonder' is the word you're looking for; however, the word's true definition is disputable.
Here is the definition from The Dictionary of Obscure Sorrows (which is actually a blog, not a dictionary):

n. the realization that each random passerby is living a life as vivid and complex as your own—populated with their own ambitions, friends, routines, worries and inherited craziness—an epic story that continues invisibly around you like an anthill sprawling deep underground, with elaborate passageways to thousands of other lives that you'll never know existed, in which you might appear only once, as an extra sipping coffee in the background, as a blur of traffic passing on the highway, as a lighted window at dusk.
Comment: Yes! Thank you so much. Now that I know the word, I found the article I read it in - it was a this [Cracked article](http://www.cracked.com/blog/5-reasons-your-online-dating-profile-isnt-working/). Both funny and insightful!
Answer: 'sympathy' fits this idea well.


Why is there no notation for tetration similar to summation?

Question: I noticed that we use $\sum$ and $\prod$ for summation and infinite product (I don't know why it does not have a name like the other two), but we use different looking notation for tetration. Is there some sort of historical reason why not, or did no-one just do it.
Comment: So far, the uses for iterated exponentiation or tetration  in  science and mathematics have been few to none.  Usefulness is largely what drives the popularity of concepts and notations.
Comment: Tetration is not similar to sum and product, it is similar to $na$ and $a^n$, which are not uniform either, and one needs to attach $n$ to $a$ in a distinctive way. What *is* similar to sum and product is the iterated exponential, and there is analogous notation for it with $\Xi$, see [Power Towers, and Notation for Iterated Exponentiation on MathSE](https://math.stackexchange.com/a/2564088/152568). There is also a similar notation for continued fractions, but the last two are not nearly as useful or common as sums and products, hence the notations came later and are not widely known.
Comment: @Gerald Edgar but then the unreasonable popularity of tetration (well, among amateurs and in pop science works) seems to contradict your claim to some extent ;-)
Comment: @HermannGruber, ha! :)  I guess there're pop-popularity and professional-popularity, and they're not reliably the same. :)
Answer: Mostly, it comes down to usefulness.
Pick up any mathematics textbook more advanced than elementary arithmetic, and you're probably going to find summation in there somewhere (it's especially common in statistics).  Iterated multiplication is less common, having fewer real-world applications, but it's a natural counterpart to summation.
Tetration?  It's rarely seen outside of number theory and pop-science articles.
There's also the matter of age: sigma notation dates back to Euler, who first used it around 1755, and the concept itself is considerably older.  Pi notation is more elusive, but appears to date to the early-mid 1800s.  In contrast, tetration appears to date back no further than 1901, with most work being post-1950.
Answer: Knuth arrow notation can be used to notate the hyper-operations, the fourth of which is tetration and the fifth, pentation and so on. These operations were first defined by Goodstein in 1947.
Here, the number of up arrows minus two give the degree of the hyperoperation. Thus
$a \uparrow \uparrow b$ is $a$ tetrated to $b$.
That this is not common is simply these operations aren't common.
This notation could be lifted to a symbol expessing an infinite tetration. That is:
$\uparrow \uparrow a_i$
meaning
$a_0 \uparrow \uparrow a_1 \uparrow \uparrow a_2 ...$
Where left assosciatevity is assumed.
Such a lifted operation is not common - if even used.


Raster to points problem

Question: I have geoTIFF raster with cells size 5x5 m in WGS84. I would like to make a point layer with values from raster. I use ArcMap extension: raster to point, but it makes a point net with size 5x~9 m, not each cells centroids. Do you have some idea why?
Answer: You need to transform your data into a projected coordinate system. Then the resolution of the raster will be in the units of your chosen projection and the conversion from raster to point will work.

Raster to points problem


Should I be worried about my 6-month-old not yet rolling over?

Question: My little one is 6 months old, but isn't showing any sign of rolling over. However, he is sitting up on his own. I know all babies learn things at different rates, but I want to know if I should be worried if he doesn't roll over?
Comment: @jcmack - How does that clarify the question? The OP is asking if they should be concerned that their baby isn't rolling over. The answer is yes, that is a valid concern that should be brought to the attention of the baby's primary care provider. Rolling to one side might lead someone to pooh-pooh the concern and encourage the OP to wait it out. It's entirely possible (and even probable) that this is benign; after all, someone has to be in the last 10%. But that's no reason not to bring this up with the PCP.
Comment: @jcmack - Yes, that will be the first thing a *professional* will ask. My question/comment still stands.
Comment: Can your baby roll to one side?
Comment: @anongoodnurse I think it's important to clarify the statement of "6 months but isn't showing any sign of rolling over" and gives us more information on severity of the situation. Rolling to one side is not rolling over, but on the way there. I'd even more concerned if a 6 month isn't rolling to one side either. The first thing the pediatrician will ask you is can your baby roll to one side.
Comment: @jcmack  He twists his top half over like he is going to roll doesn't actually roll. It looks like he just needs to push himself over with his legs but doesn't do it.
Answer: Nelson, E. A., Yu, L. , Wong, D. , Wong, H. and Yim, L. (2004), Rolling over in infants: age, ethnicity, and cultural differences. Developmental Medicine & Child Neurology, 46: 706-709. doi:10.1111/j.1469-8749.2004.tb00985.x
This is the page and here's the pdf view.

'Roll over' in the Denver Developmental Screening Test (Frankenburg et al. 1981, 1992)
  means that the child is seen to roll from back-to-stomach or from stomach-to-back, or the parents have seen the infant roll completely over from back-to-stomach or from stomach-to-back at least twice.

In table 3 on page 708, they compared the mean ages of when infants learned to roll over from different studies. This study showed that

25% of the 4.2 month old
50% of the 5.0 month old
75% of the 5.7 month old
90% of the 6.6 month old

infants had already learned to roll over. But the studies show some variety, e. g. take the Shanghai study with quite some delay.
Taking the arithmetic means of all the studies together, I got

25% of the 3.5 month old
50% of the 4.5 month old
75% of the 5.1 month old
90% of the 6.0 month old

infants having learned to roll over. It seems that yours would be a little late.
The CDC Milestone Moments (pdf download) notes that 4-month-olds may be able to roll over from back to tummy. They expect 6-month-olds to be able to roll over and, if not,

Tell your child's doctor or nurse if you notice any of these signs of possible developmental delay for this age, and talk with someone in your community who is familiar with services for young children in your area, such as your state's public early intervention program.

Conclusion
I suggest to follow the advice of the CDC - better safe than sorry - and talk to your doctor to see if there's anything wrong with your child.