How to check the VPN setting created by an app on an iOS device?

Question: Many VPN apps would create VPN profiles on the iOS device. Unlike VPN profiles create by the user, they cannot be edited, and therefore the user cannot see the setting of said profile. With a jailbroken device, is there a way to hunt down such profile and read the setting in file?
Answer: Yes you can on a jailbroken iPhone using an app called OpenSSH.
It will allow you access to all the system files and in normally conditions you can simple change the extension to .txt and open it with textedit for example.
What you'll need:

A jailbroken iPhone/iPod Touch with Cydia installed.
OpenSSH Cydia Package.
Wi-Fi and Internet access on the device.
Mac/PC on the same Wi-Fi connection
Suitable FTP/SSH clients like Cyberduck, Transmit etc.

Here is the guide on CultofMac
Also a link to the OpenSSH Cydia Package
Basic Instructions:

install the OpenSSH package

(click, Install, Confirm, Close, Back)

open Wi-Fi from Settings
click your network's
read the "IP Address" field

(example: 192.168.1.100)

open Terminal on desktop

(open Spotlight, search for "Terminal")
Or if you're on Windows, you can use a desktop terminal application such as PuTTY(http://www.putty.org/).

run "ssh root@[insert IP Address]"

(example: ssh firstname.lastname@example.com)

wait a few minutes (just once)

(it's generating some crypto keys)

accept new computer host key

(if it doesn't ask you, that's fine)

log in with password "alpine"

(you should change this now)
Comment: This is just an instruction of the basic tool OpenSSH. How do you use OpenSSH to read VPN setting created by an app on an iOS device?
Comment: @JamesWayne That depends on the app. Once you have access to the filesystem, you can search for it. I have no idea where it is located, but you should find it on your own. If you want some help, you have to provide a lot more information (like the app and whatever you have found and the file structure). Also, even if you do find the settings, I'm sure you won't find how to parse the file and make sense of those. They may be in SQLite3, JSON, plaintext, yalm, csv ... And the files may be even encrypted! I have no idea and only the developers of the app could say (**IF** it is possible!).
Answer: You won't need to use OpenSSH at all whatsoever. The VPN settings are saved in /var/preferneces/com.apple.networkextension.plist file. Open it with a text editor. It's not encrypted. The passwords are saved in the keychain instead of inside this file. You cannot access the keychain on an iOS device and decrypt it easily but you can do it over a macbook that shares the keychain with your iOS device (if you enabled it). Type in your master password to view the saved passwords.
Comment: How do you read this folder without a jailbroken device?


ROKO bed levelling sensor

Question: I was sent my sensor (a ROKO) and I plugged it in with the pins in the wrong order, would this break my sensor? If so is there anything I could do?
Comment: Did you plug it in correctly and test if it works?
Comment: Yes I have now, it doesn't turn on, but should it still work?
Answer: I can't comment for the specific sensor you have, but in general, yes, if you plug something in backwards you have a chance of breaking it - and whatever you plug it into - permanently.
You might have gotten lucky, though - but short of testing the sensor to see whether it will work there is no way to find out.
Consider that these sensors are not made to be plugged directly into endstop connectors. The endstop connectors only provide 5V, whereas these sensors often require at least 6V to operate. Some people get lucky and have theirs work on only 5V, but it's not guaranteed to work. This might also be the cause why your sensor is not working, even if it's not broken. There are some special sensors out there that are rated to work at 5V, but you should check the operating voltage of your specific sensor.
If your sensor requires more than 5V to operate, then you should also be aware that the signal pin might output more than 5V, in which case, it should not be connected directly to the signal pin on the board (since anything over 5V might damage the board).
Finally, consider the possibility that neither orientation (backwards or not) is correct. Perhaps the order of the wires in the sensor's connector is different from that of the main board. Make sure that the pinout of your sensor matches the pinout of the connector on your board. These sensors usually have a slightly strange color coding where black is signal, blue is ground and brown is power.

ROKO bed levelling sensor


Can inductive reasoning support the beginning of the universe?

Question: Is it reasonable to use induction to conclude that the universe probably had a beginning?
Comment: Can you clarify if you mean mathematical induction or inductive reasoning? They're different.
Comment: I mean inductive reasoning
Comment: Do you require that inductive reasoning be used *alone*, or can it be used in conjunction with deductive and abductive reasoning? Because if you really restrict yourself to just inductive reasoning, you will severely limit the set of conclusions that you can reach. With no deduction, you have no mathematics; with no abduction, you have no scientific hypotheses. With no math and no science, you can barely figure out anything at all.
Comment: Umberto Eco once said that there is but one question in philosophy – to whit, "why is there something rather than nothing?" (from memory btw!) What I mean is – yes, inductive reasoning implies a chain of inferences going all the way back … a causal chain – many then say, "there must be a first cause, a prime cause, a prime mover – God", or you could accept that the first cause spontaneously sprung into existence *ex nihilo* (from nothingness itself, quite alarming) or you could deny a first cause and posit infinite regress. Them's your choices to my mind. My advice, don't think about it :)
Answer: To use inductive reasonning you need a record of experiences with a similar object than the one you are considering now.
Let's say I have a whole egg in my hand. I know that if I drop it it will break on impacting the floor.
Obviously, I never dropped this particular egg, otherwise it would be broken. But I have dropped lots of similar eggs in the past (I'm super clumsy), and based on this experience I expect this egg to break too. The fact that I have a large record of experiences and that any chicken egg is similar enough to any other makes it reasonable to draw this conclusion.
Based on this,  your question can be reformulated as "do I have enough experience of having observed the beginning of objects similar enough to the universe ?". My personal opinion is that no object can be considered similar to the universe, therefore no.
Answer: If you use induction then it's more reasonable to conclude that the universe has no  beginning. All things you see happening have causes that precede them so seen from this perspective there can no beginning be induced.
Comment: Quite so.  Since each observable universe-state is derived from the previous universe-state, a claim that there was an original one that derived from something else would not stand without a supporting argument or evidence of some kind.
Comment: @Frog Indeed. You could claim it had a beginning but then you have to state a non causal mechanism. General relativity doesnt give one. So maybe this already is a sign that its not the whole story. I mean that a cause must exist in the non GR domain.
Comment: @DescheleSchilder, it is known that GR breaks down in the very very early universe. This does not mean you must invoke a noncausal mechanism, all it means is that you must search for the correct *causal* one.


Eclipse Palette unavailable

Question: When using Eclipse on my Macbook Pro I am not able to use the Palette capability. A message appears that says "A palette is not available". if anyone could provide me with insight on this matter it would be greatly appreciated.
Answer: You should open the page in Web page editor.
Right click on the page and select Web page editor.
Answer: I know this is an old question but maybe I can help someone else.
the "A palette is not available" is only there because you haven't opened a Report/Page yet. to do so:
File -> New -> Project -> Report Project.
Then create a new page:
File -> New -> Report -> Select The Project you've just created -> Finish.
Good Luck

Eclipse Palette unavailable


How to secure user passwords for a thick client that allows login when offline?

Question: I am working on a project that composes of C# thick client and a server where users can login to the application whether the client has internet access or not. When there is access, then we can easily make a call to the server with some salted hashed challenge response scheme to authenticate the user. But when they are offline, I can't think of any way without storing the password or its hash in some form on a local database which seems quite insecure. Anyone have any suggestions on how to best handle this scenario?
Comment: The nature of the business sector we service demands that we don't let a user even open the app to see or do anything until they are authenticated unfortunately. Otherwise the suggestions about storing the userId only and then authenticating and syncing would be ideal.
Comment: See my updated answer for one possible way to deal with this need.
Answer: Maybe you should let them in to do changes and then only push those changes to the server once they authenticate?
Answer: You can look at something like DPAPI (SecureData in .Net) to allow you to protect the password until you need it. However, I'd suggest thinking about it differently, and only architect it so you ask for the password when the user is connecting. If they start in offline mode, they operate until they go online without entering the password. Once they go online, then query the user for their password.
Answer: You could simply store the offline work with the user information (the identity, not the password), and then deal with syncing once the network is restored. At that point, the user would need to authenticate the batch of changes.
You will likely need conflict resolution during the sync anyways, which will likely need human intervention at some point, so they would need to log in to resolve conflicts anyways. The user also would be able to verify that they made the changes as well.
If you need better control over letting the users use the application in offline mode, you could always store a client-side-only hash for each user that is allowed to use it offline. This way you are not storing users' actual passwords within the application but a hash of them. You would also need the same hash function built into the client, but it could be different that the one the server uses and could even use a different hash per installation if needed.
You can build in the needed sync options to update the allowed list whenever the application is connected to it's server, which would also be required to change passwords, add users, etc.
Ultimately, if you need to authenticate "for real", you need to have an accessible store of authentication pairs. In an offline scenario, the only option is to store that within the client, and at that point, the goal is to keep the important data (ie. the users' passwords) safe from prying eyes.


Using Macbook Pro is the external monitor driven by the dedicated GPU or the integrated graphics chip?

Question: I am using a 2019 Macbook Pro which has a:

AMD Radeon Pro 5300M 4 GB, and also a
Intel UHD Graphics 630 1536 MB

When I connect an external display, what graphics card drives this display? How can I find out to be sure?
Answer: Yes, from what I can gather, MBPs switch to the dedicated GPU (if present) to run external displays.
One method of telling whether the discrete GPU is in use is documented here:
https://support.apple.com/en-gb/HT202053
(Activity Monitor shows a "Requires High Perf GPU" column in Energy panel when the dGPU is active.)
It's possible there are other ways. There is an undocumented gpuswitch option for pmset. I don't know if pmset -g or pmset -g gpuswitch will show which gpu is in use.
Answer: You can also find out from the Apple menu (top left) > About this Mac.

Details can be found after clicking "System Report" and looking up "Graphics/Displays" in the sidebar.

The discrete GPU part will usually mention your external display - officially an external display will always run on that GPU but I'm not sure what to make of the DisplayLink driver software (for connecting a DP monitor via USB) telling me it's running the monitor on the integrated GPU.
At some point I came across an app called gSwitch which supposedly allows you to tell what GPU is running and switch it manually but for me it was unreliable to the point of being useless. The DisplayLink driver didn't work for me either, it had a rather substantial appetite for resources and I had crashes and other stability issues multiple times a day. But maybe it's great software that just didn't get along with my configuration.


What size wire for a cooktop and microwave oven on the same circuit?

Question: For the cook top it states amperage is 39.2 and the amperage on the micro oven combo is 30 on a 240v. The model # for GE cook top PEP9030DTBB and the Cafe oven wall CTC912P2NS1 my location is in California currently have a 10 wire for 240 v
Comment: It's generally inadvisable (or even illegal) to combine high-current appliances like that. What's your reason?
Comment: Wire size will be the easy part.  You will need a sub panel if you want one cable from the main panel to the stoves.  If this is a new circuit/you do not have a circuit already for cooking with high amps, you also need a load calculation for the extra 90 amps.
Comment: The cooking appliance/range rules are ...special. NEC220.55
Comment: @FreeMan the Lowes ad  implies United States of America.
Comment: @isherwood In general yes, but not relevant here. There are special (more permissive) rules in the NEC for stoves/ranges/cooktops.
Answer: NEC 220.55 The weird and whacky range rules. I'd personally prefer a breaker per device, having seen what won't trip a high-amp breaker...
You may also find more restrictive requirements in the manufacturer's instructions for installing the appliance. Those have the force of code, if extant.
Your cooktop is 9.408 KW (as kVA) and your oven has a nameplate KW of 7.2 (If your cooktop has a KW rating lower than 9.408 in its documentation, you can use that instead of 9.408 in the following, but that's all the information you've given us to work with.)
They are treated as equivalent to a "range" of 16.608KW for Table 220.55 according to Note 6 on table 220.55. I'm interpreting that language to mean they get treated as a single appliance at that point, not 2. That makes a significant difference, and I am not entirely happy with the clarity of the language on that point.
Note 1 on table 220.55 requires increasing the demand in column C (8KW) by 5% for each KW or major fraction over 12, so 13, 14, 15, 16, 17 = 25% or 10KW which is 41.67A (or if treated as 5% applied 5 times, 10.21KW and 42.5A)
42A or 43A breakers are not made, but 45A breakers are. A "range" circuit is required to have a 40A minimum breaker by 210.19(C) if the range is more than 8-3/4KW. 45A is larger than 40A so that's covered.  210.19(C) Exception 1 permits sizing the wiring (Tap conductors) to the 30A oven "sufficient to the load served and no longer than necessary to service the appliance" as the breaker is not more than 50A.
Answer: Ignore the listed current rating (amperage), unless there is no alternative. If there is no alternative that you can see, post the model numbers of the appliances for more help.
And now with model numbers:

Cooktop PEP9030DTBB - according to GE specs on web site: Recommended Circuit Breaker (Amps) at 240V = 40A
Oven CTC912P2NS1 - according to Cafe specs on web site: Amp Rating at 240V = 30A

which means for the cooktop - 8 AWG and for the oven 10 AWG.

Most major appliances from reputable brands will include specific information regarding circuit breaker size. Sometimes they will include a minimum and a maximum, in which case it is your choice. But if there is a minimum and a maximum then I recommend the maximum unless you already have wire capable for the minimum (but not for the maximum) in place and running new wire is a major hassle/expense.
Then size the wire to match the circuit. Check an ampacity table for details. Some typical sizes are:

30A = 10 AWG copper cable or 10 AWG copper wire or 10 AWG aluminum wire
40A = 8 AWG copper cable or 8 AWG copper wire or 8 AWG aluminum wire
50A = 6 AWG copper cable or 8 AWG copper wire or 6 AWG aluminum wire

Most jurisdictions will allow aluminum wire, but you have to make sure that the appliance (if hardwired) or receptacle (if plug/receptacle) is rated for connecting to aluminum. Copper or aluminum wires (as opposed to cables) must be inside conduit.
I highly recommend hardwiring for these types of appliances rather than plug/receptacle. If you use plug/receptacle, make sure they are modern properly grounded receptacles (e.g., NEMA 14 instead of NEMA 10).
Installing separate circuits for each appliance has some big advantages over a shared circuit:

One circuit can be turned off for servicing a hardwired appliance without affecting the other appliance
A fault in one appliance tripping the breaker (e.g., for an unknown reason that requires investigation) won't affect the other appliance
While NEC (see Ecnerwal's answer) allows for combining hardwired cooking appliances within certain constraints, separate circuits guarantees you won't have a Thanksgiving Day disaster due to everything on at once cooking for hours tripping the shared breaker.


Is Google Sitesearch better than internal search?

Question: In terms of SEO is there any benefit about using Google SiteSearch over internal search (eg. Wordpress' own search engine)?
Answer: Not directly. They both will find your content (although Wordpress will find it faster since it knows about the content immediately whereas Google has to find it and index it first) and display it to your users. And neither affect your rankings since neither affect your content.
The only possible advantage I see from using Google SiteSearch is it forces Google to crawl your site more frequently and deeply as they need to make sure they know about all of your content in order to deliver useful search results. Obviously doing this for site search means they can use the same information in their main search results which is a good thing.
Comment: Pretty sure that adding Google SiteSearch is not improving their indexing of your website. If you have an official source from Google stating otherwise, it would be nice of you to link to it. If not, then it is just not true and might mislead the OP.
Comment: I didn't say it did. I said "possible advantage" and provided my reasoning for it. If you think otherwise please state why.
Comment: You might want to include a link to http://www.google.com/support/customsearch/bin/answer.py?answer=97294 in your answer then.
Comment: You already did. :)
Answer: Google internal search will work great if 100% of your pages are indexed by Google. If for some reason you have pages that are not indexed correctly it will usually be better to use the wordpress own search engine.
Comment: Apparently, it does. http://www.google.com/support/customsearch/bin/answer.py?answer=97294
Comment: Does Google site search not crawl your site separately from regular Google indexing? Surely the paid site search entitles you to more detailed indexing than the free custom search or regular Google indexing.
Comment: That makes sense, since not every page on the web is worth indexing, but if you install a search engine for your own site, it had better include every page in the site.
Answer: I just use both with this custom addition to the theme's search.php file:

Google Search

    <iframe id="gcs" src="<?php
        $url_iframe .= 'http://www.google.com/cse?';
        $url_iframe .= 'title=Search_Results&';
        $url_iframe .= 'cx=' . $google_code_cx . '&';
        $url_iframe .= 'cof=' . $google_code_cof;
        $url_iframe .= 'q=' . urlencode( get_search_query() ) . '&';
        $url_iframe .= 'sa=Search&';
        $url_iframe .= 'siteurl=' . urlencode($_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'] ) . '&';
        $url_iframe .= 'ad=w9&num=10';
        echo htmlspecialchars( $url_iframe );
    ?>">

... add some CSS styling and some show/hide functionality with Javascript and your visitors get all the search they need (and then some).


Viral RNA to DNA

Question: I have a question concerning reverse transcriptase.
Why is it that when the viral rna is converted to viral dna( as in the case for hiv), the virus develops resistance to medicine?
Under what circumstances does reverse transcriptase causes a viral mutation?
Comment: Welcome to Biology.SE! We encourage you to do some research on your own and then ask questions informed by what you have learned (ideally with references to reliable sources). For example, the top hit I found searching with "mutation-rate reverse-transcription" was: https://www.ncbi.nlm.nih.gov/pubmed/12456349 ——— Please also take the time to go through the [tour] and the help pages starting with [Ask] questions effectively on this site. Thanks!
Answer: Via: https://en.wikipedia.org/wiki/Reverse_transcriptase#Replication_fidelity

There are three different replication systems during the life cycle of a retrovirus. First of all, the reverse transcriptase synthesizes viral DNA from viral RNA, and then from newly made complementary DNA strand. The second replication process occurs when host cellular DNA polymerase replicates the integrated viral DNA. Lastly, RNA polymerase II transcribes the proviral DNA into RNA, which will be packed into virions. Therefore, mutation can occur during one or all of these replication steps.[17]
Reverse transcriptase has a high error rate when transcribing RNA into DNA since, unlike most other DNA polymerases, it has no proofreading ability. This high error rate allows mutations to accumulate at an accelerated rate relative to proofread forms of replication. The commercially available reverse transcriptases produced by Promega are quoted by their manuals as having error rates in the range of 1 in 17,000 bases for AMV and 1 in 30,000 bases for M-MLV.[18]  (Emphasis added.)

Polymerases are proteins (enzymes) that make copies of genetic material: DNA or RNA. https://en.m.wikipedia.org/wiki/Polymerase
These enzymes have different fidelity or error rates. This means that different polymerases can make fewer or more mistakes when copying genetic information.
To accommodate errors, DNA polymerases have proofreading mechanisms that go back and fix errors. Most of the time, this works as expected.  https://en.m.wikipedia.org/wiki/Proofreading_(biology)
However, the reverse transcriptase that copies RNA into DNA does not do any proofreading, so there will be various mutations in some fraction of copies, depending on the transcriptase's fidelity rate. https://en.m.wikipedia.org/wiki/Reverse_transcriptase
For viruses, it is a pure numbers game. All they are programmed to do is make copies of themselves, and as many copies as possible, when they are in infectious, non-dormant state. https://en.wikipedia.org/wiki/Lysogenic_cycle and https://en.wikipedia.org/wiki/Lytic_cycle
Most mutations will be deleterious and the virus won't infect, integrate, and replicate successfully. A random mutation will often break a needed protein involved in the viral reproductive cycle.
Some mutations are "neutral" or "silent" and won't change how the virus copies itself. Consider that the genetic code is redundant — substitute a base here or there and you can still get the same amino acid sequence. https://en.wikipedia.org/wiki/Silent_mutation
But if you have enough virus particles copying themselves, all you need are mutations in the parts of the virus genome that allow it to keep replicating and also change the proteins it makes, just enough to evade the host's immune system.
If a mutated virus can still replicate and also change the proteins it gets the infected cell to make on its behalf, it can be more successful at copying itself. Immune cells will have to "relearn" whatever changes were made in order to trigger the usual immune response and fight back.
In the case of HIV, it also attacks the immune system directly, which is another complication.
Medications try to interfere with the different ways in which HIV works to infect immune cells and to make copies of themselves.
For example, one class of medication tries to "compete" with the part of HIV that binds to the surface of T cells. It's like a night club, where the bouncers at the doors are more likely to keep HIV from getting into the cell/club and partying.
Other classes of medication interfere with a protein called integrase that HIV makes to integrate its viral DNA into the host DNA. Integration of the HIV DNA into the host cell's DNA is a critical step for infection, so that's one way to target the virus. https://en.wikipedia.org/wiki/Integrase
Still other drugs try to inhibit the reverse transcriptase that turns HIV RNA into DNA. If the virus RNA is inhibited from being made into DNA, then that can help keep further infection in check. PrEP is a combination of two drugs (tenofovir and emtricitabine) which are RT inhibitors. https://www.cdc.gov/hiv/basics/prep.html
An overview of some of these medications is available here: https://www.webmd.com/hiv-aids/aids-hiv-medication
These medications all try to target the proteins involved in how HIV infects and replicates inside immune cells.
In turn, reverse transcriptase is sloppy enough in turning HIV RNA into DNA that it can get lucky and mutate enough to make one or another medication less effective.
Treatments are sometimes put into so-called "cocktails" of multiple drugs. A multi-drug regimen that attacks the virus by different means will give HIV a harder time in getting lucky enough to mutate in ways that it can get past a multi-pronged attack in those who are HIV+. Another good summary of such medications — many of which target reverse transcriptase activity — is available here: http://www.aidsinfonet.org/fact_sheets/view/403

Viral RNA to DNA


Why lights dim when the AC compressor switches on

Question: If two points in circuit are not connected there is supposed to unlimited resistance between them. So when the compressor is added to circuit it is either very high resistance or very low. In either case the voltage is not supposed to fluctuate but adjust according to distribution of voltage across resistance according to ohm's law. Does it mean that it sinks current flow? or what is it that happens?
Comment: The title makes sense, but the rest is gibberish.
Comment: All the outlets are connected at the fusebox or daisy chained around the room or both, so (unless you have 3ph power) every outlet is in parallel and shares the same supply which is why the lights dim when the compressor starts up, they're sharing the same supply and so any disturbance at one outlet will affect *everything* else in the house (although most appliances won't mind too much)
Answer: I can't understand the text of your question, so I'll just answer the question in the title.
While it's true that the power supplied by the utility can generally be considered a voltage source, in practice, the wiring always has a small but nonzero resistance. This, combined with the very high current drawn by a large motor at startup, creates a voltage drop that is large enough to notice on parallel loads, including light bulbs.
Answer: An AC motor has a very low resistance when it is initially connected to power. As the speed increases, the resistance increases to a higher value. That means that the current is initially very high then decreases to a lower value. The high current causes a voltage drop in the wiring between the source and the motor. The lights or anything else that shares the wiring that carry the high current experience a temporary voltage drop. The starting current of a motor can exceed the current that the circuit can carry continuously. If the load would jam, the bearings fail, or anything else prevent the motor from starting quickly, a circuit breaker or fuse would open. All of that is generally normal operation, but the dimming lights could indicate that the wire size is smaller than it should be for the distance between the source and the motor.
Comment: Actually, the resistance doesn't change at all. As the motor speeds up, the "back EMF" that it produces goes up. This reduces the net voltage across the motor's resistance, and this is why the current drops at speed.
Comment: I am assuming this is an induction motor. As such, the Steinmetz circuit is the usual model.


leave that behavior in the background

Question: Explain please the meaning of this phrase in the title. Macroeconomic models do not deal with the optimizing behavior but leave them in the background. I don't understand.
The source is the book "Macroeconomics" by Gregory Mankiw.
The context:
Yet the model does not focus on how these microeconomic decisions are made; instead, it leaves these decisions in the background. Similarly, although microeconomic decisions
underlie macroeconomic phenomena, macroeconomic models do not necessarily focus on the optimizing behavior of households and firms, but instead sometimes leave that behavior in the background.
Thanks in advance!
Answer: From the context, it simply means that the models don't focus on/highlight/ deal with this optimizing behavior.

leave that behavior in the background


Conformal invariance of Electromagnetic field action

Question: What is the significance of Conformal invariance of Electromagnetic field action? What does it lead to? And how can we break it?
Answer: Maxwell action is conformally invariant basically because of masslessness of photon, which implies that the action doesn't contain any dimensionful parameters. Such parameters would set the scale, and thus break the scaling symmetry. There is no proof that in $4D$ the scale invariance implies full conformal symmetry, but there are no counterexamples known. So the easiest way to break the conformal symmetry is to add the mass term to the Lagrangian $-m^2 A^{\mu} A_{\mu}$.
Conformal invariance allows us to obtain many new solutions to the equations of motion from the given one -- any solution obtained by acting the symmetry generator on the solution is again a solution.
Comment: Just to add to the answer: one technical consequence of conformal invariance is that, classically at least, the trace of the energy-momentum tensor vanishes.


Do Daleks Travel in Time?

Question: Do Daleks travel in time, like Timelords?  And, if so, is there any thing to show how they pick when they're going next?  Or are they a "linear" threat that got big, were defeated, and grew back later (and repeated that cycle a number of times)?
Comment: As long as there are no time-stairs ...
Answer: Yes, they do travel through time, although in most episodes in a less sophisticated way than the Time Lords (as others, like Time Agents, do).
The Daleks envied the Time Lords' superior technology, and try to gain it for themselves.  In "Remembrance of the Daleks" (7th Doctor) the Daleks try to steal the Hand of Omega, which could create a power source for (Time Lord style) time travel.
By the time of the Last Great Time War, Dalek time travel technology is perhaps as sophisticated as the Time Lords'.  In particular, in Doomsday (10th Doctor) the Daleks are able to "emergency temporal shift" without (as far as we see) any external device, suggesting that the Dalek "travel machines" (their suits) incorporate some form of time travel device.
The Daleks sometimes use devices that create "Time Corridors" for travel rather than vessels like a TARDIS, for example:

"The Evil of the Daleks" (2nd Doctor) - their device isn't very good yet, and it might not be Corridor-based, but it's similar
"Day of the Daleks" (3rd Doctor) - a device that transports people (or Daleks) - it's not clear if this was a Corridor or not, but it's similar
"Resurrection of the Daleks" (5th Doctor) - explicitly a Time Corridor
"Remembrance of the Daleks" (7th Doctor) - explicitly a Time Corridor
"Victory of the Daleks" (11th Doctor) - the Daleks escape via a Corridor

In "The Chase" (1st Doctor), the Daleks are using ships (Vicki stows away on one when she gets left behind by the Doctor) that can time travel.  Also with the 1st Doctor, in "The Daleks' Master Plan" we see the Daleks with time-travel capable ships (but not as sophisticated as the Doctor's or the Meddling Monk's).
In terms of how their choose their destination time, it differs with each of these stories.  Generally the date and location have been chosen because they offer some opportunity to further the domination of the Daleks (sometimes, as in "The Evil of the Daleks", to improve their time travel technology and prevent anyone else having it).  Presumably they have also travelled widely throughout time on occasions where the Doctor was not around to prevent it.
Answer: Well, Dalek Caan once used an Emergency Temporal Shift, so I presume they travel through time this way, or maybe they ships and other technology that allows them to travel through time, much like the Time Lords. That's probably why they're so dangerous and feared.
Comment: This doesn't really add anything that the existing (accepted) answer hasn't already mentioned.
Answer: Of course they can time travel the cult of Skaro are chasing the first doctor through time , that's why he can't steer the TARDIS in  on random-mode to shake off the dalek death squads chasing him through the vortex, the daleks as a full empire are on par with the timelords in many ways , probably not temporal engineering fully but close, and they have no morals holding them back.
The daleks and davros started to get wise shortly after Tom Baker tried to stop them being born, that was the turning point of dalek temporal engineering as they were threatened by another (more brutal?) Species and so had to prove that daleks are king badass.the time lord CIA were the main reason the daleks even knew about time travel originally, arguably they doctor but he was sent by them.
Comment: Hi, welcome to SF&F.  Is "radis" supposed to be "TARDIS?"  Note that a lot of this is covered by the accepted answer, so if you're going to post a new answer you should have new examples or new sources to cite.  You might want to read [answer] and take the [tour].

Do Daleks Travel in Time?


dvd-rw content check

Question: How can I make sure that I only burned the video/photos that were meant to be burned onto dvd-rw ? Want to check in case other files added in eror
Comment: It's safe to assume that we can't guess the operating system and sftware you're using.
Answer: The only way to do it is to load the disc into a computer and see what's on it.
If you have the files readily collected on your hard drive somewhere, you could use a diff util like WinMerge to compare the hierarchy on your hard drive to the one on disc and see if there's any extra, missing, or corrupt files.  However, it still requires loading the disc and reading the contents.
Comment: Should probably be a DIFFERENT computer, since some of the recent versions of windows can be a bit weird with disk writing through explorer...
Comment: True, it also avoids the "laser is misaligned and the only device that can read it is the one that burned it" problem.

dvd-rw content check


Windows Auth into page; App Pool user into database

Question: Is it possible, using a classic ASP application hosted in IIS 7.5, to use Windows Authentication on the page (so I can access LOGON_USER) but use the app pool identity to connect to the database?  If I turn on Anonymous Authentication and set it to run as the app pool identity, I can connect to the database, but I can't get the LOGON_USER.  If I disable Anonymous Authentication, I can get the LOGON_USER, but I can't connect to the database.
Answer: Coworker found this:  Apparently setting Physical Path Credentials under Advanced Settings on the app will also translate to the network communications with the database.  So, anonymous auth off, windows auth on, physical credentials set to service account.
Not really sure why that works, since I would have expected Physical Path Credentials to affect only interactions with disk..


Not getting daily updates of answers

Question: I've specified my email and it says it's already registered for receiving daily updates to answers received but I never get emails.  Checked my spam box / filter also.
Comment: possible duplicate of [Not receiving notifications on new answers](http://meta.stackexchange.com/questions/5673/not-receiving-notifications-on-new-answers)
Comment: @Jon: That question is over a year old, so it's possible a new bug is in the system.
Comment: @Jon: I wonder who I'm talking to?
Comment: @mmy: To Jon! No, honestly to Seigel. Always the last one in the queue ...
Comment: @Jon: What makes you think, that something was changed the last time? Please say the status-tag, so I can laugh at you.
Comment: @mmyers: That one hit me, and I'm pretty sure it *didn't* hit Jon B. Unless the reply system has been changed recently.
Comment: @Ladybug: Errrrr... I suppose I should have read the question in its entirety. I still agree with TheTXI's answer, though. Voting to close. Would you like to do the honours and roll back the `[status-completed]` tag? :)
Comment: @Jon: Lovely idea :) Done!
Comment: I don't think this feature has ever worked for me.  And I know because it already told me that email was registered and I have NEVER gotten emails even months and months ago.  I just decided today that I had enough and wanted to put this bug in.
Comment: @cof: It is widely guessed, that you do not get emails, if you have already looked at the answers (e.g. via the envelope icon). Probably email only works, if you do not visit SO at all. Otherwise the system thinks you already know the new stuff.
Comment: I do not assume that.  That's a usabilty issue then because most forums email you when you subscribe.  This feature needs to be improved to be more underderstandble and more usable.   It's useless if I have no clue how the thing works...especially when the pattern of subscribing to a thread in all other forums on the net works the same...and even if I did not view the answers I'm STILL not getting emails.  So either way it's a bug AND a usability issue..2 issues actually.
Answer: The answer is simple:
your account has no email address in it, so therefore we cannot possibly email you.
https://stackoverflow.com/users/93468/coffeeaddict
If you want emails, enter an email address.
edit: ah, I see you have a duplicate registered account, with an email, from Feb 9 2009 at
https://stackoverflow.com/users/62759
I have merged that into your main account.
Comment: /me opens `[feature-request]` for automatic email prediction :)
Comment: Ok, wtf.  Then why when I put my email into the subscribe box, it tells it's already registered?  Go figure right?  Jeff this is a usability issue, major.  Of all the other features in this forum, this is the only issue I have.  If you've got a textbox asking for an email and then a) says it's already registered  and b) there's not even an indication that it's been saved in that textbox and c) you're expected to manually go into your account to specify that same email then what's the point of this feature at all if it doesn't work intuitively?  I guarantee it's not intuitive to all.
Comment: also I'm using openID, so one would assume if you put in an email to the subscribe box that Stackoverflow is albe to at least save that for you??  I don't get it.
Comment: "/me opens [feature-request] for automatic email prediction :) ".  I have no idea what that means.
Comment: Just went to my account using the edit option.  I see an email right there!  So not sure what you're talking about Jeff??

Not getting daily updates of answers


Overriding the default views in RailsAdmin

Question: I am using Ruby on Rails 4.2.1 with RailsAdmin. The gem works excellent, but I have the requirement that the layout of the admin panel and the forms must look different than what is generated by default. For example, the navigation should be horizontal top, the forms should order the fields in two columns.
So far I haven't find a way to copy the views locally and modify them (like in Devise for example). I have tried to replicate the views manually in the respective path under my views folder by copying the original views, but I got problems with the helper methods that are part of RailsAdmin not being accessible from my views.
I dug deeper and found that there is a task copy_views, it was referred to in questions for the older versions of the gem, but if I try to use it now rake rails_admin:copy_views, it is not available anymore.
Am I doing something wrong, or is there another way to do this?
Answer: You can create folders in your app
app/views/rails_admin/main for https://github.com/sferik/rails_admin/tree/master/app/views/rails_admin/main
app/views/layouts/rails_admin/ for
https://github.com/sferik/rails_admin/tree/master/app/views/layouts/rails_admin
Put modified files there.  It can get a little messy and you will need to update the files if the gem changes.


how to enable my shortcut key as previous versions?

Question: I just want to use shortcut key as before versions i.e. when i press alt+space it gives us options like minimize, unmaximize, move etc... but they are not working with keys like 'n'  for minimize 'c' for close etc.. as our previous versions.
Comment: Could you better describe what sequence of keys you mean to type, and what actions do you want to get?
Answer: Assuming you are using Ubuntu 20, there are shortcuts for minimizing/restoring/maximizing windows: <Win>+<Up>, <Win>+<Down>, <Win>+H.
Plus other shortcuts.
I am not sure this goes exactly the way you had in mind, but it may be useful.
See


z-index issue in IE7

Question: I am trying to call one div on click of select element. there are 4 select elements two in each row. When that div is called it goes behind the succesive select element. This issue is specific to IE7. It works fine with IE8 and firefox3.
please can anybody help...
Thanks,
Comment: The div which I am trying to call is absolutely positioned.
Comment: Post some of the source code you have already written. That should make it easier for others to understand the problem and help you
Answer: You can read the following link for a detailed info
How the Z-index Attribute Works for HTML Elements
There are two work around for this.
The first is to hide the select element when the div appears. This might not be a good solution.
The other better solutions is to place an iframe at the same position as that of the div.
The iFrame must be added at the end of the page so that it appears in front of all other windowed controls (the windowed controls are stacked in the order in which they appear on the page). That takes care of covering any SELECT that may be in our way.
You can have a look at the code in the page
Bug Fix: SELECT box displayed through Dynamic DIV in Internet Explorer

z-index issue in IE7


How to persist ethtool settings through reboot

Question: I would like to turn off tcp segmentation offload on a CentOS5 server. Using ethtool the command is ethtool -K eth0 tso off However, this setting only persists for this session. How can I make it persist through reboots?
Comment: put it in a start script somewhere.
Answer: For RHEL7 in /etc/sysconfig/network-scripts/ifcfg-* you may have:
ETHTOOL_OPTS="-K ${DEVICE} gso off gro off tso off"
if more options then use like
ETHTOOL_OPTS="-K ${DEVICE} gso off;-K ${DEVICE} gro off;-K ${DEVICE} tso off"
you have to have naturally DEVICE defined in your ifcfg file.
No rc.local nor extra ifup scripts needed. Easy to you in generic deployment systems.
Answer: From this webpage:
You can enter the ethtool commands in /etc/rc.local (or your distribution's equivalent) where commands are run after the current runlevel completes, but this isn't ideal. Network services may have started during the runlevel and ethtool commands tend to interrupt network traffic. It would be more preferable to have the commands applied as the interface is brought up.
The network service in CentOS has the ability to do this. The script /etc/sysconfig/network-scripts/ifup-post checks for the existence of /sbin/ifup-local, and if it exists, runs it with the interface name as a parameter (eg: /sbin/ifup-local eth0)
We can create this file with touch /sbin/ifup-local make it executable with chmod +x /sbin/ifup-local set its SELinux context with chcon --reference /sbin/ifup /sbin/ifup-local and then open it in an editor.
A simple script to apply the same settings to all interfaces would be something like
#!/bin/bash
if [ -n "$1" ]; then
/sbin/ethtool -G $1 rx 4096 tx 4096
/sbin/ethtool -K $1 tso on gso on
fi

Keep in mind this will attempt to apply settings to ALL interfaces, even the loopback.
If we have different interfaces we want to apply different settings to, or want to skip the loopback, we can make a case statement
#!/bin/bash
case "$1" in
eth0)
/sbin/ethtool -G $1 rx 16384 tx 16384
/sbin/ethtool -K $1 gso on gro on
;;
eth1)
/sbin/ethtool -G $1 rx 64 tx 64
/sbin/ethtool -K $1 tso on gso on
/sbin/ip link set $1 txqueuelen 0
;;
esac
exit 0

Now ethtool settings are applied to interfaces as they start, all potential interruptions to network communication are done as the interface is brought up, and your server can continue to boot with full network capabilities.
Comment: also note about ETHTOOL_OPTS described here https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html-single/Deployment_Guide/#s2-networkscripts-interfaces-eth0 However by some reason it doesn't work on my machine yet http://superuser.com/questions/995200/persist-ethtool-settings-between-reboots
Answer: If you are on RHEL7 (or alike) and use Network Manager instead of /etc/init.d/network to control your interfaces the proposed answer will not work, since /sbin/ifup-local (as well as ifdown-pre-local and ifdown-local) will never get executed.
Instead put your scripts into /etc/NetworkManager/dispatcher.d/ and make sure the NetworkManager-dispatcher service is enabled
systemctl enable NetworkManager-dispatcher

Hint: The dispatcher will only kick in once NetworkManager makes changes to an interface, it doesn't need to be running or anything, so if the status reads
Active: inactive (dead)

that's completely fine!
Also make sure your script is:

executable (chmod +x)
owned by root (chown root:root)
writable by root only (chmod 755)

Now NetworkManager will pass two (2) variables to the dispatcher:

$1 being the interface (eno16777984, eth0, ppp0, etc...)
$2 holding the status (either up or down)

and it allows chaining the scripts (just like /etc/rc...) to have some control over the order in which the dispatcher will execute them:

10-first, 20-second and so on...

The order will be ascending on a connect

if [$2 = "up"] its 10-first followed by 20-second

and descending on a disconnect

if [$2 = "down"] you get 20-second followed by 10-first

and so on.
So to accomplish what OP was looking for you could put something like this:
#!/bin/bash
if [ "$1" = "eth0" ] && [ "$2" = "up" ]; then
  /sbin/ethtool --offload eth0 tso off
fi

in /etc/NetworkManager/dispatcher.d/20-ethtool
And call it a day.
Cheers
Comment: Search Google for "ifup-local" and you get this as the 6th hit. Nothing i would consider "old"
Comment: This definitely adds something in regards to CentOS 7.  No other solution worked for me in CentOS 7.
Comment: The bash script has an error, it should be: `if [ "$1" = "eth0" ] && [ "$2" = "up" ]; then`
Comment: Please note that this question is very old and that it already has an accepted answer and your answer does not really add new. Please try to avoid answering very old posts as it tends to clutter up the front page.
Comment: On other distro's, ethtool is at `/usr/bin/ethtool` instead.
Answer: I ran into problems with the accepted answer (which, I hasten to add, I found very helpful) because I was using bonded interfaces.
It took me a while to discover what was happening but I found that when bringing up a bond, or even when bringing up a bond slave individually, the ifup-local script would not be called for the slave interfaces. I assume that this is because the slave interfaces did not have any IP addresses assigned to them.
To get round this I modified my ifup-local to parse the contents of /proc/bonding/bondX for the interface which had been brought up, if it was a bond, to get the slave interface names, and then did the necessary stuff with them.
In the end my ifup-local looked like the following:
#!/bin/bash

if [ -n "$1" ]
then
  IFACE="$1"

  # If interface is physical
  if [[ $IFACE =~ ^eth[0-9]+$ ]]
  then
    # Do whatever you need for a physical interface here
    # example below
    /sbin/ethtool -K $IFACE rx off

  # Else if it's a bond
  elif [[ $IFACE =~ ^bond[0-9]+$ ]]
  then
    # Do whatever you need for the bond here
    # example below
    /sbin/ethtool -K $IFACE gso off

    # Now deal with slaves
    # Pull out slave interface names from /proc/net/bonding/bondX
    SLAVES=$(/bin/grep -oP "Slave Interface: \K(eth[0-9]+)" /proc/net/bonding/$IFACE)
    for SLAVE in $SLAVES
    do
      # Do whatever you need with the slave here
      # example below
      /sbin/ethtool -K $SLAVE tso off gso off
    done
  fi
fi

Caveat: the contents of /proc/net/bonding/bondX may be different for different versions of RedHat/Fedora/CentOS to the one I was using when I wrote the script, so the command to pull out the slave interface names may not work.
Answer: Off-topic, for Ubuntu users who came here, like me, this as a note:
On Ubuntu, the textbook way to do it is to edit the /etc/network/interfaces file which in turn is read by the init.d/pre-up -up, etc. scripts. So an /etc/network/interfaces file might look like this:
auto eth0
iface eth0 inet static
pre-up /sbin/ethtool -s eth0 speed 10 duplex full

That's what the docs say, but it does not work. Might be that the parsing logic in the pre-up and up scripts is a bit dated and they don't parse out the required settings from the interfaces file. Don't know. At least, it was not working for me.
So the hack-ish but working solution for now is still to create/edit a local /etc/rc.local file and stating the command to be exuted there (but note that this may interrupt networking for a seconds after the interface has already been brought up). So having this:

ethtool -s eth0 speed 10 duplex full autoneg on

in /etc/rc.local is the working solution to slow down an interface as intended above.
On Ubuntu 17.04 and above
More recent Ubuntus use Systemd, and thus the rc.local file isn't necessarily executed upon reaching the 'start' runlevel, for example. The "rc-local" service has to be enabled. Although it seems to be by default, for backwards compatibility reasons, probably - make sure to check its status with sudo systemctl status rc-local
Comment: The `pre-up` directive worked for me on Linux Mint 17.3 for setting the TSO flag, thanks :)
Answer: I found that setting this kind of configuration in /etc/network/interfaces actually works for Ubuntu (granted I used it for turning off large-receive-offload, but that shouldn't really matter):

auto eth1
iface eth1 inet static
    address xxx.xxx.xxx.xxx
    netmask xx
    pre-up /sbin/ethtool -K $IFACE lro off
Answer: For Ubuntu, you can do this by adding following line in /etc/network/interfaces:
auto eth0
iface eth0 inet static
[...]
post-up /sbin/ethtool -K eth0 tso off gso off gro off

post-up here will perform the given operation after bringing up the specific interface.
Answer: Yeah, it can't be done using configuration files for the moment. You can put up the command in /etc/init.d/rc.local and it should be done.
That file is executed at the last of the booting sequence and so tso would be turned off for the interface.


King + Queen vs. King + Queen - is this a draw?

Question: Black and white both have one queen and the king. Is this game a draw?
Answer: The side to move first in KQ vs KQ wins in 41.75% of the positions. That's because the side to move first gets the first check, which is often decisive in these major-piece endgames - compare how many KQQ vs KQQ positions, which ostensibly have equal material, are won by the side to move first (83%).
Caveat: "positions" here refers to all legal positions, some of which might not be realistic in practical play.
Comment: Correct answer to the wrong question
Comment: I agreed with David's comment until clicking the link and reading the article. The way this answer is worded it seemed like it was only talking about KQQ vs KQQ. Might be worth improving the answer to make that clearer by including the text from the article
Comment: @David I don't understand your commend.
Comment: @Allure This question is about KQ vs KQ, not KQQ vs KQQ
Answer: There are various positions that matter for pawn endgames. Often both sides promote to queen and then the side that moves first still wins.
This can happen right after promotion, when the king of the stronger side is close by.
Some examples:
<code>[FEN "8/1KP1q3/8/8/3k4/8/8/8 w - - 0 1"]

1.Kb8?? {Ka8 is correct} Kc5! 2.c8=Q+ Kb6 {And white can't prevent checkmate}
</code>
and
<code>[FEN "8/6p1/8/8/7k/5K2/2P5/8 w - - 0 1"]

1.Ke4! g5 2.c4 g4 3.c5 g3 4.Kf3 Kh3 5.c6 g2 6.c7 g1=Q 7.c8=Q+ {Check!} Kh4 {Otherwise Qh8#} 8.Qh8+ Kg5 9.Qg8+ {Wins the queen}
</code>
and
<code>[FEN "8/8/8/p7/k7/3K4/3P4/8 w - - 0 1"]

1.Kc4! {Locking up the black king so it has to spend an extra tempo} Ka3 2.d4 Kb2 3.d5 a4 4.d6 a3 5.d7 a2 6.d8=Q a1=Q 7.Qd2+! Kb1 (7...Ka3 8.Qb4+ Ka2 Qb3#) 8.Kb3 {White wins. }
</code>
Source: 100 Endgames You Must Know, by Jesus de la Villa.
Comment: Nice, helpful examples.
Answer: Unless there is some forced sequence that leads to mate or either side losing the queen, King+Queen vs King+Queen will be an easy draw with correct play.
Comment: "Unless there is some forced sequence that leads to mate, it will be a draw with correct play" does this statement not apply to *any* position?
Comment: From a game theory perspective, yes. But those mating/ queen-losing sequences can be simply calculated by a human in a matter of seconds.


Uses of $\infty$-categories in TCS

Question: I'm not a theoretical computer scientist. I'm a stable homotopy theorist using $\infty$-categories. I've seen applications of category theory and topos theory to theoretical computer science, and I was wondering if there was any way one could use $\infty$-categories (and preferably for me, stable homotopy theory) in theoretical computer science. I think HoTT mught be one such application, but I may very well be wrong because I know close to nothing about HoTT. (So I also don't know how HoTT is used in TCS.)
Comment: Have you taken a look at the [HoTT Book](http://homotopytypetheory.org/2013/06/20/the-hott-book/)? For example, the suspension theorem is proven in chapter 8.
Comment: You should ask this question five years from now. We don't know yet exactly how we're going to use $\infty$-categories in computer science. At the moment we have a pretty good idea about $\infty$-groupoids: they improved greatly our understanding of type theory.
Comment: @cody Yes, I've looked at it (but not in much detail); I'm not really interested in the application of HoTT to homotopy theory (or vice versa) but the application of homotopy theory and $\infty$-categories to TCS. Do you know some such applications?
Comment: Have a look at Michael Shulmans section "Expository notes and talks" at the bottom of his page http://home.sandiego.edu/~shulman/papers/index.html. Mike is a homotopy-theorist by training, so you might find his stuff more easily understandable.
Answer: Applying higher homotopy-theoretic ideas to CS is still a very nascent field! My understanding is that it's not even that old as a mathematical field.
Certainly HoTT is the central impetus for such ideas. Even there though, there only have been few applications of category theory of "dimension" higher than 2.
One nice "computer science-y" one is Homotopical Patch Theory by Anguili et al. They show that some common operations and properties inherent git like version control systems can be best understood using homotopy type theory.
Another rather unrelated train of thought is some interesting work on the relationship between (2-)Homology theory and confluence of term rewrite systems (or more complex structures such as higher algebras). Some examples are
Y. Guiraud Confluence of linear rewriting and homology of algebras .
Y. Lafont & A. Proute Church-Rosser property and homology of monoids.
Comment: Thanks, cody! I'll wait to see if there are any more answers before accepting.
Answer: Theoretical computer scientists do many things, one of which is mathematical modeling of various computer-sciency things. For instance, we like to provide mathematical models of programming languages, so that people can actually prove things about programs (such as proving that the program does what it's supposed to). In this sense it is always good to have a good supply of mathematical techniques that will give us models for various things that computer scientists come up with.
In fact theoretical computer scientists had to invent some pretty advanced mathematical models because they wanted to get a good mathematical graps of what computer scientists were doing. Often classical set theory is not good enough for our purposes, for example because we want a non-tivial complete small category or a non-trivial set $D$ satisfying $D \cong D^D$.
Recently a connection between type theory (which is a common generalization of programming languages, logic and set theory) and homotopy theory has been uncovered. It is still very early to tell what exactly will come out of it, but our understanding of type theory has certainly been advanced by the homotopy-theoretic ideas. Conversely, it is becoming clear that intensional type theory, whatever that is, is a very good formal language for describing $(\infty,1)$-categories. People suspect there ought to be "directed type theory" which would correspond to $\infty$-categories, but nobody is sure yet. This is active area of research.
The only connection between stable homotopy theory and type theory I am aware of is the work of Matthijs Vákár on linear dependent type theory. Apparently, one model of it is stable homotopy theory, but this has not been published yet, only hinted at the end of the linked paper.
Another place where you could look for applications of homotopy theory (stable or not) in computer science is computational topology. There persistent homology has recently found many uses, and people are surely looking at homotopy-theoretic applications of a similar kind. The basic idea is to use algebraic topology to study properties of large datasets.
Without a doubt there are other applications. Cody mentioned the use of homotopy theory (in the guise of homotopy type theory) to study revision control systems. There are also applications of homotopy theory to the study of parallel and cuncurrent computations, such as "Algebraic topology and concurrency". Someone more knowledgable may be kind enough to provide better references. In any case, you will notice that all these applications (with the possible exception of homotopy type theory) are fairly unsophisticated from a mathematical point of view – which does not mean they are worthless!
Answer: this attempts to sketch out more general connections. some of this program can be considered a very recent & more elaborate extension of the old Curry-Howard correspondence noted between proofs and programs. there is also a close connection with automated theorem proving (aka proof assistants). many techniques used in automated theorem proving proofs are not on entirely solid mathematical ground and homotopy theory adds firmer grounding.
this proposal by a sizeable team captures/ surveys much of the currently known connections with CS: Homotopy Type Theory:
Unified Foundations of Mathematics and Computation (MURI Proposal)
Licata from that team is esp interested in computer scientific applications of homotopy theory. some of his talks, and one by Voevodsky founder of the standout Univalence axiom:

Mathematical and Computational Applications of Homotopy Type Theory. Colloquium at University of Iowa. November, 2013. [slides]
Computer-Checked Proofs in the Logic of Homotopy Theory. Invited Talk at the Association for Symbolic Logic North American Meeting. May, 2013. [slides]
Programming and Proving in Homotopy Type Theory. Colloquium at Wesleyan, Princeton, and Cornell. Spring, 2013. [slides]
Computer Science and Homotopy Theory, 10m video lecture by Voevodsky / IAS

Uses of $\infty$-categories in TCS


Are glasses muktzeh on shabbat for Jews who can see

Question: According to the Halacha, are glasses muktzeh   on Shabbat for Jews who can see fine without them? Or no, are they not muktzeh and may they be moved on Shabbat?
Answer: See S"A Harav, 318:41 where he states that the status of muktzeh is a status that is dependent on the object and its owner, and that status propagates to all people who dwell in his home, regardless of whether the condition which would render the item muktzeh applies to them or not.
If the item has been discarded, or is otherwise being used by someone who is not staying in his home, then their personal rules apply. In that halacha, that would mean that a rich person could not consider rags to be clothes and hence they are muktzeh, while a poor person may consider them to be clothes.


Why is data science not yet widely applied to Law?

Question: Law (judiciary) contains such a huge corpus to apply NLP to, but yet there are only search engines designed for Law. Why is NLP not yet extensively applied? Is it because of dimensionality?
Comment: You may want to try to ask this question on our sister site: [Artificial Intelligence Stack Exchange](https://ai.stackexchange.com/)
Answer: Welcome to the site and thanks for the great question! I recently led an NLP project that dealt with a lot of laws. While I have to obfuscate my actual work, here's a general view:

The laws themselves may not be the best source data. It would take a massively transformed recordset in order to make most laws actionable for modeling. I'm talking about big rooms, full of lawyers providing an annotated version of laws in order to create a recordset that can actually be useful
The above assumes that the laws have been digitized in some easy to digest format. That may not always be the case. In a lot of instances, you are referring back to classic OCR approaches as part of  your data prep and I don't know anyone that likes working with OCR :-)
The human-in-the-loop requirements are very high. So you have an algorithm, now what? That's not something you can just put out on Mechanical Turk for the layman to verify. You need more lawyers to help with the verification of your approach and correct mistakes that are happening
Finally, you must get very sophisticated with your embedding layers in how you create and apply them. That's not an easy thing to do and very processor intensive - a GPU is highly recommended and not a lot of grassroot efforts are going to have this processing power

Good luck!
Comment: I would also add that it is a high-risk domain, and to use AI in such domain, the stakes aren't the same as classifying if this is a photo of a dog or a cat. So i understand that it is taking longer than other fields for it to implement AI-based solutions.
Answer: A friend (Law and CS graduate) recently wrote his PhD dissertation about the use of AI and ML approaches in law.
His conclusion is as you suggested (dimensionality), semantics, cultural concepts of justice, as well as non-binary data types (e.g. confessed but with what constraints and conditions?) will not lead to satisfying mathematical results, when it comes to the actual range of sentences.
However, NLP can help preprocessing cases to better distribute them to the person in charge of. In categorical cases (e.g. traffic delinquency) one can use NLP approaches to make the whole process more efficient.
Answer: NLP is very widely used in certain aspects of law. I worked on few use cases related to contract management. While I can't talk about specifics, general areas where NLP is applied are:

Distance analysis for paragraphs / sections of contract (v/s corpus of historical judgements)
Automation of manual reviews and validations
Automation of Business processes related to discovery
NER (Specific to Legal domain)

Some articles on this topic:

Law and Word Order: NLP in Legal tech
Contract Analysis Software Technology Fundamentals
Contract Analytics Software Using Artificial Intelligence(AI) & NLP methods


Can I filter my homebrew hard cider with a few coffee filters?

Question: I haven't seen many people filter their hard cider to get rid of bits of yeast.  what will happen if I filter?
Comment: I am thinking of doing this. I did a racking into secondary fermentation. Then bottled after a few weeks of that. Quite a bit of sediment in the last cm of each bottle. Very careful pouring seems to avoid most of it reaching the glass but wondered about filtering at the racking stage. I have a cotton filter though, not coated paper filters. Would that make a difference?
Answer: Oxidation, big time.  Imagine flavors of cardboard mixed with a decadent undertone of down-pouring rain.
If you do it, do it when you pour the beer to consume it, not to package it.  The off-flavors take weeks to develop, and if you're pouring it to consume it, I doubt you'll be taking weeks to drink it.
Answer: I think I tried to get a clear sample from the dregs of a bottling session this way once. The yeast went right through the filters.
Answer: Doing a cursory google search reveals that the pore size of coffee filters* is about 20 microns. Given that yeast are in the single digit micron range (varies depending on strain, age, etc.) the yeast will pass through the coffee filter. You may retain some clumps if they've bound together on a macro-scale, but otherwise this won't work.
*I suspect that the pore size of a coffee filter is subject to brand, but this value is a reasonable and probable benchmark.
Good flocculation is the easiest way to "filter" yeast away from your product. This can be enhanced with cooling of the product, and finning agents such as isinglass (at least in beer).
Some homebrewers employ water cartridge filters when kegging to filter yeast and other particulate out of their beer. These are often available in practical 1 - 5 micron ranges at most hardware stores.
Answer: Not sure if you're doing a secondary fermentation, but that always helps to clarify whatever your brewing, be it cider, wine, or beer. It will be much easier and produce a better result than attempting to run through filters.


ArcMap 9.3 Hangs on trying to save

Question: I am having trouble with a machine running Arc GIS 9.3. When one tries to save an mxd, ArcMap stops responding and just hangs. I have even tried with an blank new mxd but the moment one clicks save it hangs without even opening the dialogue box that allows you to navigate to the location to save. Please help
Comment: A re-install followed by contacting your ESRI support would be the best suggestion based on the comments in these threads. There's something very broken with the install.
Answer: Try using MXD Doctor - this can fix many issues with 'broken' MXDs.  I assume that this particular MXD is now always giving you problems even after a fresh re-start.
Additional tangential info
I have had a similar issue too.  In particular I have notice this happening, or sometimes a more graceful result of an error message as opposed just hanging, when I have let my machine go into extended hibernation with ArcMap open.  It used to happen in 9.3x and still happens in 10.1.  It also happens with a fresh install.
Another situation (and I don't know how Arc gets itself into this situation but I have seen it many times) is when Arc has not completely shut istelf down properly.  It looks like it has but there is still an ESRI process alive behind the scenes.  This can also impact your ability to edit files as well as save MXD documents because the locks persist.  I can't tell if this is effecting you but it worth a look if/when you get any strange locks or MXD behaviour with Arc.
Press Ctrl+Shift+Esc to open the Windows Task Manager. Since you are trying to save, you should have at least one instance of ArcMap in the applications tab. Right click on it and select 'Go To Process'.  Note how your current process is highlighted.  Now click on 'Name' to sort the processes alphabetically.  If you have another entry for ArcMap, a previous instance of ArcMap has failed to shut down correctly.  Right-click on the ArcMap entry which is NOT highlighted (i.e. the one you are NOT trying to save and which ought to be dead anyway).  Select 'End Process Tree'.  This is different to End Process and it kills all dependent process associated with the un-dead ArcMap instance.
This pre-supposes you had at least one other ArcMap instance open prior to the one you are trying to save.  I can't guarantee this is the solution to your problem but it can be a solution to many unexpected locks and errors, and is well worth a try if you really don't want to shut your machine down for some reason.
Comment: If a new installation cannot create new MXDs, then there is something fundamentally wrong either with the machine or the installation.  Assuming that the machine is not below spec, that really only leaves one sensible option, regardless of how busy your user is.  Even if you do find a work around, I wouldn't trust the stability of the install.
Comment: This is not editing an existing mxd, its a new installation and the user wants to create new mxds.
Answer: Have you tried to wait for few hours?
I have noticed similar behavior when I had broken links to network location which I used previously from ArcMap (open/save mxd). i.e. when taking laptop to new network environment.
In such case you can take your laptop to previous net environment, try to use ArcMap there and open/save data from your local HDD. Or try to wait for quite a long time (few hours).
I hope it helps you!
Comment: Waiting for 2 hours and counting...
Comment: Have you considered reinstalling ArcGIS ?
Comment: re-installing would be the last resort because the particular user is rather busy and getting his free for a bit to do the reinstall is an issue
Comment: Waiting till the next morning did the trick.
Comment: So, the problem was with broken network locations ?

ArcMap 9.3 Hangs on trying to save


Any way to enable dynamic/automatic brightness adjustment?

Question: My Lenovo ThinkPad X201 Tablet has a very bright screen (400 nits!), which is good for when objects on the screen are dark (say a night scene in a movie), but it is of course very blinding when objects are bright/white. I find myself continuously changing the brightness when watching a movie/video like this, and it is quite annoying.
Is there any utility available that will automatically change display brightness depending on if objects on screen are bright or dark? I know this is an option built into some desktop monitors (in the form of Dynamic Contrast I believe), but I have not found the same kind of thing for laptops.
To clarify, I would like a utility (or simple script, even) that turns the brightness (as in the backlight) up when the majority of stuff on screen is dark/black, and dims the brightness down when the majority of stuff on screen is bright/white, to take full advantage of this bright screen.
Any help would be greatly appreciated!
Comment: did you find some option?
Comment: @AlexandreMartinsMontebelo I don't believe I ever found a solution to this. Most existing dynamic contrast solutions actually work inverse from this (dimming backlight during dark scenes and brighter when light, for increased contrast effect).
Answer: You could have a look at WildGuppy which will adjust your brightness according to the light it gets from your webcam (not according to your screen content though).
Comment: its not working properlly
Answer: Run this command:
<code>sudo apt install brightness-controller
</code>
You will see the brightness controller:


How to test player movement speed in 1.8?

Question: I am wondering if there is a better way to track, or test, how fast a player is going, then activate command off that. So far I have: /scoreboard objective add Sprint stat.WalkOneCm Then, every tick I have that set to zero. /scoreboard players set @p Sprint 0 Then, after it resets 5 times, It tests to see if the players movement speed if in between 150 and 200 WalkOneCm score per tick. If true, then you get a speed boost. However, sometimes it fails, and tests when its at 50 or so. Is there a better measurement?
Comment: Are you using 1.8 or 1.9 version of Minecraft?
Comment: How are you doing your test?  That seems to be the important part.
Comment: I am using 1.8 Jason_
@MBraedley I am using a testfor command **/testfor @p[score_Sprint=200,score_Sprint_min=150]** and that activates every 5 ticks. Each reset is 1 tick
Comment: also, I have no idea how to highlight test, only bold and italic it. sorry about that, I would highlight commands if I knew how.
Comment: With the editor just push the button that looks like two brackets { } and it will format your code nicely for you.
Answer: I found a possible answer, but I haven't got it to work yet:
First, you build a clock (with a bit longer delay).
Then, you let a set of Command blocks be triggered at once. Theese CMD blocks should summon a circle of Armour Stands with different names around the Player.
Then, after a small delay, a CMD Block row tests the Player distance from each ArmorStand (by name). If any Player-ArmorStand distance is smaller then, let's say, 1 block, another command is executed, eg.:

/execute @e[name=ArmorStand1] ~ ~ ~ execute @a[r=1] say @p is sprinting

If summoned in this way, it gives a total of 24 CMD blocks:

_ ■ ■ ■ _
  ■ _ _ _ ■
  ■ _ P _ ■
  ■ _ _ _ ■
   _ ■ ■ ■ _

P for Player, ■ for ArmorStand, _ for nothing.


Plugin variables class versus twig functions/filters class

Question: Is there a particular school of thought on which is best to use?
They both appear to offer the same thing - exposing data and functionality to templates.
Answer: The following answer is all personal opinion of course, but here's a key quote from the docs:

Many of your template variable methods will likely be simple wrappers for your service API methods.

If you look at Craft's built-in Variables, they're all about exposing data. Personally, I like to think of Variables as template APIs.
Twig Filters, on the other hand, is all about modifying data (e.g. capitalizing strings, rounding numbers, formatting dates, sorting arrays etc). If you compare Craft's built-in Variables to its Filters, I think the distinction between the two starts to become fairly clear.
To exemplify:
Bad use of Variables:
{% set sortedEntries = craft.myPlugin.sortByAwesomeLevel( entries ) %}
{{ craft.myPlugin.makeEntryTitleAwesome( entry.title ) }}

The above template code use Variable methods to modify data already present in the template. It works, but it looks pretty convoluted and doesn't really make sense, neither from a Twig nor Craft point of view. Here, using Filters would be much more appropriate:
{% set sortedEntries = entries | sortBy( 'awesomeLevel' ) %}
{{ entry.title | makeAwesome }}

Good use of Variables:
{% set awesomeEntries = craft.myPlugin.getAwesomeEntries %}
{% set sortedAwesomeEntries = craft.myPlugin.getAwesomeEntries( { 'sortBy' : 'awesomeLevel' } ) %}

Here, MyPlugin exposes a "template API" method called getAwesomeEntries. The only thing it does, is to pull entries that are awesome, optionally taking an arguments object for sorting or the like. Obviously, this would not be feasible to implement as a Filter:
{% set awesomeEntries = entries | getAwesomeEntries %}

In short – if you need to expose data, use a Variable. If you need to modify data, use Filters.
Answer: I'd say; use twig functions/filters when the data you want to operate on comes from your template, plugin variables when you need to operate on data from your plugin/another source.
You can, to my knowledge, do the exact same things with both. But the purpose of twig filters is to manipulate data in your templates. If the filter relies on tapping into Craft to work, I'd rethink using one.
But that's just my opinion, I don't think there's been a lot of discussion about this in the community. :)


iPhoto isn't working on my 2011 MacBook Pro with OS X Lion

Question: I don't know why but my iPhoto on my dock just has a picture of some pencils and an ø through everything and it was the same thing when I looked at it in the applications. When I try to open it, it says that it is probably damaged but it worked just last week. Btw my MacBook Pro was shipped with OS X Lion so I don't have any startup disks or anything like that and I never set up Time Machine and I still don't know how to set it up, so anything involving those 2 are out of the question.
Answer: You need to reinstall:
First: make a backup. Any kind of back up. Always have an up-to-date back up of your iPhoto Library.
To re-install iPhoto

1. Put the iPhoto.app in the trash (Drag it from your Applications Folder to the trash)

2: Trash the Receipts: In the Finder use the Go menu and select Go To Folder. In the resulting window type
/private/var/db/receipts

A Finder Window will open at that location and you can remove files that you see with iPhoto on the name.

Re-install.

As you have a recent make you do this via the Purchases List at the App Store.


How to fight and control equipped motorcycle driver

Question: Unfortunately, in some situations motorcycle drivers that are equipped with helmets, boots and suits attack. Is there a way to fight back and control them with inability to attack their face, legs and upper body?
Comment: -1. This is prime example of why I want to [burninate the `self defence` tag](http://meta.martialarts.stackexchange.com/q/407/82). It is a hypothetical situation. It covers so much ground that the only possible answer is "it depends". It has no relation to any martial art whatsoever.
Comment: I would think wearing a motorcycle helmet would be a disadvantage because of weight, blind spots, and possibly the chance of it being spun around (depending on the fit).
Answer: A motorcycle driver in protective gear is similar to an armored opponent. Striking the opponent may not be effective, but you can still use grappling techniques. This striking constraint makes the situation like that in wrestling, judo, or jujutsu; except you are constrained by circumstances and not competition rules. You can still throw them, use other takedowns, apply joint locks, sweep legs, and so forth.
Answer: There are certain considerations you must take into account with this type of opponent.
The head
They have a helmet on, so regular boxing style techniques are going to have less or nil effect. Helmets are specifically designed to spread impact so you shouldn't attempt a king hit on the helmet - you will break your hand.
You could however apply mechanics. A helmet protects the skull (and maybe face) but it doesn't protect or enhance the neck and shoulder musculature. You can use this fact to exert some mechanical theory: the opponent will still be prone to head rotational and snapping movements. So an uppercut at a 45° angle through the chin area should still produce a knockout.
Boots
Boots protect the feet nicely, so there's no point attacking them. While the ankle area will still be a weak area it is augmented by the boot so will still be a hard target.
Legs
Even if padded pants are being worn the opponent will still be prone to thigh attacks and upper calf attacks (depending on the height of the boots). Some pants will have knee protection but this will be more for protecting the patella; the knee will still be vulnerable to sideways forces.
Jackets/gloves
Jackets and gloves will make it harder to exploit wrist and elbow locks and leverage that requires pinpoint control. Joints still move the same way they always do, it's just harder - for example I wouldn't attempt a koto gaeshi, but I would attempt an arm bar. This also don't stop you from using brute force against a wide area, i.e. power punches or kicks to the rib area.
Summary
The opponent will be harder to attack, but you simply need to change your approach. Use brute force techniques on exposed areas (thighs, side of knee, ribs, neck). Use techniques that leverage mechanical weaknesses in the musculoskeletal structure. Remember that due to the bulk of the clothing the opponent will be slower, so use this to your advantage. Don't forget other basics like using other opponents and/or objects like lampposts to hinder incoming attacks.


What materials to use replacing a water damaged bathroom ceiling?

Question: I had a leaky roof that caused half the bathroom ceiling to come down. The roof is now fixed. I know I have to remove the rest of the ceiling as well, and dry it out before replacing, and possibly do some mold remediation.  My question is, what do I replace the ceiling with?  Regular gypsum board or is there a special something that needs to go up since it is a bathroom?  Steps would be appreciated. :)  Thanks!
Answer: Do you want to have to replace it again if there's ever another leak? If yes, then use another inexpensive paper-and-gypsum-based product, such as drywall, green board, etc. If no, then use cementboard. Maybe overkill, but for a small bathroom the uncharge won't be more than $40 and that stuff can get wet till the cows come home and not complain about it! Once it's up, you can texture it, skim coat it, paint it, or whatever you were going to do to the drywall that you were considering.
Answer: Note that the use of most greenboard or moisture board on ceilings requires 12" OC joists according to manufacturer standards.  They for the most part are not a good material for ceilings and in my opinion offer nothing that drywall doesn't.
Your materials for above shower are concrete board or regular drywall.  Unless you are building an enclosed shower or sauna than I would stick with drywall.
For moisture purposes greenboard does not matter, in fact with minimal maintenance and prep drywall vs. concrete doesn't matter either.  In bathrooms we have at least two generous coats of an oil based primer go on the walls and ceilings.  This is far more effective at keeping out mold from drywall/whatever.  Top that with a mold resistant paint and you would only have surface mold if you did a really poor job of ventilating.
So your answer is drywall, oil, oil, paint.
Answer: A lot of people use mold-resistant drywall in bathrooms. This is normally blue or green and costs a few extra dollars at the hardware store.
Comment: The new stuff is purple. I don't put much stock in any of them though, as I've seen mold on greenboard before. Spend that money on anti-mold paint (a roof leak is an unfair contestant).
Answer: Any answers to this question will be heavily opinion-based. Here's mine.
Assuming a good roof and adequate bathroom ventilation, there's no reason to use anything other than standard drywall, properly sealed and painted. An exception would be a very low ceiling over a shower that's often splashed.


virtual terminal (getty) inaccessible?

Question: My issue is that I cannot login on a virtual terminal (getty). So CtlAltF2 does not give me a login prompt. None of the gettys does actually. Only shortly after booting up I can get a prompt but that does not let me login. Under the previous version of eOS this was not a problem. I do not know where to look to fix this, as I am unfamiliar with the systemd setup of recent years
Answer: OK, seems to have resolved itself by cycling default runlevels. Still curious then what caused it, but problem solved I guess.

virtual terminal (getty) inaccessible?


Can I repack toilet supply valve?

Question: The water supply to my toilet is copper with a valve sweated on.  The line from the valve to the tank seems to be a compression fitting.  The valve has developed a leak around the shaft which the handle is mounted on.  There seems to be a "nut" at the base of the shaft which looks like I could loosen it and repack the valve but I'm unsure.  I'd really prefer to avoid having a plumber come out to sweat on a new valve if I can.
Answer: I have repacked these valves many times using Teflon rope. I have even done it with Teflon tape but the rope is easier and last longer. Turn off the main supply and bleed the pressure remove the gland nut and back the assembly out (good time to inspect the seat and replace if deformed), I have a kit of seals I purchased years ago with 4 or 5 different sized seats, some shaft packing (Teflon rope) and some new rubber seals a good idea for any home owner to have a kit like this to repair faucets under 10$ and just add as you use up and save over a replacement.  I will usually wrap the shaft with at least 3 full turns and more if the shaft is in bad shape put the assembly back together and tighten the gland nut turn the water back on bleed any air out of the line and check for leaks. I do not back seat (fully force the valve open as this is hard on the packing) I learned this with SCUBA diving where you open the valve fully then close it 1/2 to 1 turn to extend the packing life.
Answer: Those valves (unless very old) do not have traditional packing in what would still be called the packing gland under the nut. They use tapered/beveled rubber gaskets there instead. Not really designed to be serviceable I'm afraid, more like disposable.
You can often stop the packing leak by simply back-seating the valve; that is, opening it fully till it stops. That brings the backside of the valve seat back against the valve stem hole at the bottom of the packing gland. Also try carefully tightening the packing nut if you haven't done that already.
There is a chance you could find a similar replacement rubber washer if you bring it to a good plumbing shop. You could try to use some graphite packing string, who knows, it might work...
Comment: Even if you can't get it to stop leaking, you don't need a new sweat valve. You could opt for a shark-bite valve. This is simply a push on valve. Turn the water off to the supply valve, cut the old valve off as close to the solder joint as you can get (leaving more pipe to play with). Sand it nice and smooth, push the shark-bite valve on and reconnect everything.

Can I repack toilet supply valve?


How did Dumbledore figure the way to destroy Marvolo Gaunt's Ring was Gryffindor's sword?

Question: How did Dumbledore figure the way to destroy Marvolo Gaunt's Ring was the sword of Gryffindor?
Comment: Generally speaking, the body of a question should not merely repeat the title, but add additional details that clarify the scope and meaning of a question.
Comment: I'm guessing he tried whacking it with lots of different things in his office.
Comment: @Valorum - Is this really not a duplicate of anything?
Comment: i'm guessing from all the books he lifted from the library ;)
Comment: @adamant - Dunno. I can't recall anything but then that's what the search button is for :-)
Comment: @Valorum - I checked and did not find anything....
Answer: It's not really that hard to figure out. You only need to know two things:

Basilisk venom is capable of destroying Horcruxes
Goblin forged weapons, such as the Sword of Gryffindor, take on the properties of things which strengthen them

Dumbledore had already seen several years before that Basilisk venom was capable of destroying a Horcrux, since Harry used a broken off basilisk fang to destroy the diary.
Regardless of what you think about Dumbledore, I hope we can at least all agree that he wasn't an idiot. It doesn't seem like a stretch to assume that he'd know about the unique properties of the sword, and therefore that it would have (or at least might have) assumed the power of Basilisk venom and therefore had the power to destroy a Horcrux.
Comment: First how do we know 'Basilisk venom is capable of destroying Horcruxes'.so we can assume that basilisk venom destroying tom riddle's diary was taken as a trial and error method by dumbledore ? If it destroys the ring well and good and if it doesn't then he will tru some other means.
Comment: Furthermore, Dumbledore had the library books about Horcruxes in his study. As we learn from Hermione in _Deathly Hallows_, they contain information about what can destroy a Horcrux (with the intention of telling Horcrux makers what they must protect their Horcrux against).
Answer: He is knowledgeable about magic
The sword could destroy the Horcrux, since,  being goblin-made, it could absorb useful substances, such as basilisk venom. Basilisk venom, of course, is one of the few things that can destroy Horcruxes, as seen with Riddle's diary.
Phineas Nigellus seemed to think the properties of goblin silver were obvious.

Phineas Nigellus paused again in his struggles to free his eyes and
sniggered.
"Muggle-borns," he said. "Goblin-made armor does not require cleaning,
simple girl. Goblins' silver repels mundane dirt, imbibing only that
which strengthens it."
—Harry Potter and the Deathly Hallows

Of course, that may not have been the case, if Hermione did not know, but it certainly suggests that the propensity of goblin-made silver to absorb useful properties is well-known.
As an exceedingly intelligent and knowledgeable wizard, Albus Dumbledore presumably is aware of this, and would have guessed that the sword had absorbed basilisk venom.  Even assuming he had not, he could probably have tested it to see if his hypothesis was correct.


PWA needs to access location when no wifi and no cellular

Question: My client wants a mobile-app that can run with no WiFi and no cellular network available.  I think that a PWA gives them the most cost-effective way to meet their needs, accept that the app needs to know location even when there is no network available.  To do this the PWA would need access to the true-GPS, i.e., the info gathered by the GPS chip talking to the satellites.  It's my understanding that a PWA does not yet have this access and there is no date for when we can expect it.  Could we buy or develop a native mobile app that delivered the GPS-info to my PWA?  I've seen some discussion of this using Cordova, but I would like to avoid diving into that world if I can.
Comment: FYI - I believe the browser does not get location info when in the background. So, if you want to check the location when the user is not using your PWA, it may not work.
Comment: Thanks for pointing that out, but we don't need the location info unless the user is running the PWA.  But because the user might be using the PWA far from cell towers, there might not be any cellular service.
Answer: I put my Android into airplane-mode and took it for a walk around the block. The PWA that I had installed on the Android was still able to give me the updated location. So perhaps the discussions and complaints I see on stackoverflow, etc., regarding this not working, are out-of-date. BTW: In the navigator.geolocation options I have:
<code>enableHighAccuracy: true
</code>
so hopefully the browser uses this as a hint to use the GPS-chip if available, and not care if there is no network available.


Electromagnetically induced transparency (EIT) and Stimulated Raman adiabatic passage (STIRAP)

Question: What is the connection between Electromagnetically induced transparency (EIT) and Stimulated Raman adiabatic passage (STIRAP) in case of lambda system? can we achieve STIRAP with different shapes of input pulses?
Answer: In general, Electromagnetic-Induced Transparency (EIT) refers to any phenomenon which involves the (quantum) interference between two (or more) transitions in a three (or more) level system - optical, optomechanical, electrical, etc. This is in opposition to something like the AC Stark shift where everything is usually far-off resonance and just driven by a strong intensity of the laser - i.e. a very intense laser may shift the absorption lines of the atoms (say) so that they are not resonant anymore with another beam, and hence become transparent. EIT, on the other hand, gets its transparency from $a + (-a) = 0$.
In theory, STIRAP is an example of EIT.
In pratice, though, STIRAP is an example of Coherent Population Transfer (CPT). That is, it is used to e.g. coherently move the atomic population from a state $|1\rangle$ to a state $|2\rangle$ by driving $|1\rangle \rightarrow |3\rangle$ and $|2\rangle\rightarrow |3\rangle$ transitions, that is by never actually coupling $|1\rangle$ and $|2\rangle$ directly by a single laser beam. Since you want to eliminate absorption and then spontaneous emission (which would not be coherent), you detune the two transitions, in a way that the resulting interference of the two beams gives you an effective ("dressed") dark state, i.e. one that does not actually absorb (and spontaneously emit) light.
This dark state in usually expressed as $|\text{dark}\rangle = \cos\theta |1\rangle - \sin\theta|2\rangle$, where $\tan\theta$ is the ratio of the strengths of the pump $\Omega_P$ and Stokes $\Omega_S$ beams. So, changing the powers of the beams (the "shape of the pulses" you are quoting) such that $\theta$ adiabatically goes $0$ to $\pi/2$ results in a coherent (never a spontaneous scattering event) and total (because adiabatic) population transfer. Does the exact shape of the input beams matter? Well yes, but you can compromise on the effect it has by taking care of how slow you vary them (because of adiabaticity).
Long story short, STIRAP focusses on the populations of the states, that is the diagonal elements of the density matrix
$\rho_{jj}$.
"Pure"-EIT focusses on the off-diagonal elements of the density matrix $\rho_{ij}$ with $i \neq j$. This affects the optical response of a material: for example, the (macroscopic) polarisation $P$ at the transition frequency $\omega_{12}$ is related to the (microscopic) coherence $\rho_{12}$.
Comment: nice!
how do I see the interference? https://physics.stackexchange.com/q/599089/137157
Comment: Do you have any references that go into the connection between macroscopic and microscopic polarization/coherence? If be interested in reading more, that's not a connection Ive seen in detail before


Samsung Galaxy s5 android update

Question: What is the star icon mean beside the WiFi symbol for the Samsung Galaxy s5. It appeared after I downloaded the new update.
Answer: I am assuming you have updated your mobile to lollipop.
If so the star icon basically notifies you that you will be notified of priority interruptions.
Go to sound settings and check for an option called interruptions and then select "Always Interrupt".

Samsung Galaxy s5 android update


Download manager apk

Question: I made a mistake... I incorrectly thought the "download manager" apk was a worthless Virgin Mobile stock one, so I deleted it. Well, I'm a bit wiser now, and I now know that the Google play store requires it. My question is this: is there a place where I can download the apk?
Answer: I dont think that the play store requires a download manager. However if you want to download something from a browser es explorer can provide you a download manager. So download es explorer from play store. Its a great app with tons of functionalities.
Answer: The download manager apk is different for each device as it gets compiled during the final build. I suggest you reinstall your firmware if your device manufacturer allows something like that.
Answer: You can find other expert users on here or xda who use the exactly same device you use but rooted. So they can extract that apk via titanium or root explorer and give it to you, so you can push it again in your device with root explorer.

Download manager apk