Nonionic or non-ionic?

Question: which is more correct or more frequently used? Nonionic or non-ionic (polymers)? It´s for an academic presentation.
Comment: Have you checked your style guide? (It's very relevant since some style guides specify how certain expressions should be written or which dictionary you should use to help spell words.)
Comment: Even if the answer isn't in a journal style guide (seems unlikely @Laurel). just download pdf articles from the journal you wish to publish in and search them for nonionic and non-ionic. Either go with the majority or if there is a split, make your own choice, perhaps on your respect for the authors.
Comment: Similar: [Can there be a hyphen in "nonlinear"?](https://english.stackexchange.com/questions/32428)
Comment: Possible duplicate of [Can there be a hyphen in "nonlinear"?](https://english.stackexchange.com/questions/32428/can-there-be-a-hyphen-in-nonlinear)
Answer: It would appear that nonionic is more common than non-ionic according to Google's ngrams:
Comment: Interesting, and you answered the question in a way, but as a practicing and publishing scientist I would always write non-ionic (e.g. detergent) in a biological science journal. So the advice in the comment — to check the usage in your field — would seem to be more pertintent. Google ngram checks books, not scientific journals.
Answer: Merriam-Webster spells it in the closed-form nonionic.
On the other hand, Oxford spells it in the hyphenated form non-ionic, while also providing the closed-form nonionic as being US English.
So, if you go by the dictionaries (or by a style guide that says to use a regional dictionary), use nonionic for a US audience and non-ionic for a UK audience.
Having said that, although the British corpus on Google Books Ngram Viewer shows that non-ionic is slightly more common in print in general, between 1989 and 1998 (for some reason), nonionic was actually used more often.
Comment: As a scientist I would give no credence to the 89-98 results. You'd need to look at examples to find out what is causeing the obvious anomaly.

Nonionic or non-ionic?


Change the background color of a value if it has been modified

Question: So I have a SharePoint list and I implemented a flow that sends me an email if a value in a certain column has been changed. However, I have many columns and I was wondering if there is a way to change the background color of an item that has recently been edited? I just want to easily scroll through the list and be able to see in red, what values have been edited in the last 24 hours or so. is this possible?
Answer: You can implement your design through MS Flow and JSON.
Please the following steps:
Step1.Create a Choice column named "Status" in your list

Step2.Create a MS Flow for your list
a) Add a Trigger "When an item is created or modified"

b) Add an Action "Get item"

c) Add an Action "Send an email (V2)"

d) Add a Control "Condition"

<code>(Get item)Modified is greater than or equal to addDays(utcNow(),-1)</code>

If yes

Add an Action "Update item". Change Status value is "Edit in the last 24 hours"

If not

Add an Action "Update item". Change Status value is "Edit more than 24 hours"

e) Save and Test it

Step3.View Formatting
Use below JSON code to color the rows in your list:
<code>{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/row-formatting.schema.json",
  "schema": "https://developer.microsoft.com/json-schemas/sp/view-formatting.schema.json",
  "additionalRowClass": "=if([$Status] == 'No Changing','sp-css-backgroundColor-noFill',if([$Status] == 'Edit in the last 24 hours','sp-css-backgroundColor-blockingBackground50','sp-css-backgroundColor-blueBackground27'))"
}
</code>
Comment: Thanks for the answer. So the entire row changes color when it has been edited. But is there anyway instead of the whole row, I can have just the single value change color? Basically highlight the value that was changed in the row.
Comment: Hi, Mik. I'm sorry, I cannot currently implement how to highlight the value changed in the row. If there is a solution in the future, I will share with you as soon as possible. Have a nice day!


What is the general purpose of concealment algorithms introduced in…?

Question: What is the general purpose of concealment algorithms introduced in https://eprint.iacr.org/2003/050.pdf?
Comment: This is not even a question, try to actually formulate a question instead of "blah blah.. introduced in".
Answer: The purpose seems to be offering an interesting new building block for authenticated encryption.
They split a message into a long hider $h$ and a short binder $b$ with the following properties:

$h$ reveals no information about $m$
$h$ and $b$ allow recovering $m$
There is only one $h$ with which $b$ can be used to recover $m$

They use this functionality to extend an authenticated encryption scheme that works only on short messages to one on long messages. One uses the given authenticated encryption scheme $\mathcal{AE}$ to encrypt the shorter binder $b$ and gets authenticated encryption of the entire $m$ by the properties above.
Specifically,

$h$ can be public because it reveals nothing about $m$
After decrypting $\mathcal{AE}(b)$ the receiver can reconstruct $m$ using $h$
The message must be authentic because there is only one $h$ which will work with $b$

They also use it to build Remotely Keyed Authenticated Encryption.

To summarize, we show that concealments are very natural cryptographic gadgets, and can be efficiently
  built from standard assumptions. In particular, they give an efficient way to implement "long" authenticated
  encryption from a "short" one. Finally, we describe a powerful application of concealments and our ampli-
  fication technique to the problem of
  RKAE
  , which deserves a separate introduction.

This RKAE has pretty much exactly the goal they achieve, to split authenticated encryption between something like a fast PC and a slow smartcard where the key is only used on the smartcard but it only needs to encrypt small messages.


Is there any tool to make checking that referencing is correct easier?

Question: Is there any tool to make checking that referencing is correct easier?
I sometimes find that after I've written a lot of text I begin to question, whether it is possible that I've referenced wrong pages somewhere or mistyped a source or something.
Comment: How would a tool know what you intended to reference?
Comment: @JonCuster It could at least automate opening the paper and going near the pages mentioned.
Answer: If you use LaTeX, biblatex, and biber, you can identify some issues with a bibliography file using biber's --validate-datamodel option.
Better BibTeX for Zotero also can identify similar issues when you export to a bibliography file. These are written as comments in the bib file.
Both these options tend to identify issues that I don't think are actual problems, unfortunately. But they can be useful to spot some real problems. I vaguely recall once finding out that I typed in an ISBN wrong from biber, for example, as ISBNs have check digits.
I've also used a small script I wrote myself to catch some errors. For example, in Zotero if I don't know the end page of an article before I get it, I'll put eoa (short for "end of article") in as the last page. I might forget to update Zotero after I get a copy of the article. This script will identify all instances of eoa in the pages field of my bib file so I can put in the real end page. I also have some consistency checks like identifying instances of "Ph.D." so I can change them to "PhD".
These options won't determine that you have the wrong pages or anything like that. In principle, you could determine if a page range is impossible (for example, pages 115-101 is likely a typo). You might want to write your own script to catch that, though I wouldn't expect that particular problem to be common.
It also is possible to automate getting citation information from a DOI and check consistency with that. But if you use Zotero or another reference manager, this will not likely change much.
This may be more useful for most people to make sure that their bibliographies are correct: I would recommend avoiding getting citations from less-reliable sources. For example, many times now I've found that Google Scholar has the wrong or incomplete citation information. In contrast, Zotero on journal websites has worked very well in my experience. Only rarely do I need to correct the citation data.
Comment: I've also noticed that some authors seem to not cite pages at all. Perhaps due to avoiding errors in them.


What Subversion authorization scenario

Question: I need to setup & maintain easily many Subversion repositories and make each of them accessible for strictly specified list of users only.
No anyonymous checkout (no read access).
What authorization scenario should I use here
Answer: you can use subversion through ssh (svn+ssh://) with unix based access privileges.

Create users on your subversion server (adduser)
Create user groups (groupadd) and add users to groups
Create svn projects
chgrp -R accessgroup1 svnproject1, ...
chmod -R g+rwx svnproject1

Thats about it. I hope I was clear enough.

What Subversion authorization scenario


scripting: create a user input form?

Question: I havent been able to find any references that this should be possible, maybe you can assist ?
What i would like to do is to add a user interface for our designers when dealing with a specific object (box object), its like a electrical floor drawing where they will add boxes to many segments of the drawing.
The thought was to import a CSV file with a list of predefined boxes with the following format :
Name, BoxType, Color, Floor
When all has been done and they changed what they want, we do another export of the list.
1)
When adding a box object i would like to be able to pop up a form, like a small properties form, where they are able to select from a dropdown box one of the predefined box-records from the imported list.
2)
Would also like them to be able to change each of the 4 values selected, manually in a form, so ex. they can give the box its own name ( different from what it was in the imported records ) - i imagine just a form popping up ex on rightclick or hotkey where they can change the 4 values as they wish, ex. changing what floor it is located on.
Is this possible at all in any way in Illustrator using script or SDK or somekind of other method ?
Hope you can help.
Comment: it sounds scriptable, if you want to give it shot, find all about scripting here, post here if you need assistance http://www.adobe.com/devnet/illustrator/scripting.html
Answer: This is hard to find reference for in the adobe docs, at least in the short time I scanned them. However, it appears the basic idea is:
<code>var dlg = new Window("dialog{text:'yadayada'}");
dlg.show();
</code>
A more in depth example can be found on stackoverflow
Further reading, google: "illustrator dialog jsx"

scripting: create a user input form?


We show a long form & side bar for reference, Is auto-scroll good UX

Question: In our app user has to fill a long form(containing questions) and has to refer data from right-hand panel(also containing same questions). Users complain that need to scroll the right-hand side panel to view the relevant data is a problem. So shall we
a) Implement auto-scroll the right-hand panel, will it be weird?
b) Make the form itself short so that there is no need to scroll
Any other option ?
Is there a reference app which does this well?
Rough Wireframe below
Comment: What is the reason for displaying the related data in a separate scrolling section of the page? If users want to keep the related questions together, it appears that you can place them side by side and thus eliminate the second scroll bar problem.
Answer: It sounds like having the data on the right separate is causing the problem.
Personally I would make the relevant data on the right instead appear under the data on the left, kind of like this:

This way the relevant data is always close and both the code and the user don't have to do anything to keep them close.
If this makes the list too long, consider using multiple pages: Single-Page vs. Multi-Page Forms: When to Use Which
Answer: Hope you are well. If I were you I would also consider the UI with 2 coloumns instead of the drawer, and make it scroll with the forms together on the same page.
To be honest, it isn't simple to argue that placing the relevant data right below each forms is the right answer for your concern. Because at this point, I can't identify what type of relevant data it is. Is it just a few texts? Or a group of data points? Depending on the amount and the impact of the content to filling in each form, it might not be the only answer to put each of them to the right below of each text fields, as it can also be incredibly long.
For this concern, maybe we can also think about using hide/show accordion UI for the relevant data, so that a user can selectively decide to refers to that or not when they fill in each forms. Or, it might be also beneficial to consider granulate the steps for the form, if it's feasible to consider.


Voltage Drop Between Battery and Load

Question: Why is the total length of wire in a circuit used to find the voltage drop between a battery and a load? Suppose the load is a distance l away from the battery. Wouldn't the voltage drop between the battery and the load be due to a length l of wire and not 2l? I understand that the current flows through a total distance of 2l of wire, but if the load is only a distance l away, why would it "see" a voltage drop due to 2l of wire? Is it possible to explain this with ohm's law and a simple circuit diagram?
Comment: What about the voltage drop in the return wire (one end is ground, the other end is almost a ground voltage).
Answer: Let's say we have a 12 volt source and a 12 ohm load located 100 feet away from each other.
Let's further state that the wire connecting them has a resistance of 100 milliohms per foot and - since each of the wires is 100 feet long - each of the wires will have a resistance of 1 ohm.
That's a total of 2 ohms, and being in series with the load's resistance of 12 ohms, that's a total 14 ohms.
Then, from Ohm's law we have:
$$ I = \frac{E}{R} = \frac{12V}{14\Omega} = 0.857\ amperes $$
and, since:
$$ E = I R$$
the voltage drop in \$ \boldsymbol{each}\$ wire will be:
$$ E = I R = 0.857A \times 1 \Omega = 0.857 volt $$
Then, since there are two wires, each 100 feet long, connecting the supply to the load, the total drop in the wires will be twice that, or about 1.7 volts.
Comment: Yes, that makes sense. So the problem is that there would be less than 12V to power the load due to the dissipative resistance in the wires. In the example above, how much less voltage is available to the load? Or, what supply voltage does the load "see"?
Comment: Methinks that final 1.7 ohms should read 1.7 volts
Comment: @JImDearden: Heh, heh, methinks you're right. :)
Comment: @Val: Since we started with 12 volts out of the supply and lost 1.7 volts in the wires, we'd have 10.3 volts left for the load.
Comment: Thanks EM, that makes sense. Would it also be accurate to say that the resistance in the wire reduces the current in the circuit and therefore reduces the potential difference across the 12 ohm load? (Since the potential difference across the load is proportional to the current in the circuit) And it is this reduced potential difference across the load that would cause a problem if a device required the full 12 volts to operate properly?
Comment: @Val: That would be accurate.

Voltage Drop Between Battery and Load


How do I preload a program for faster start?

Question: Is it possible to "preload"(actually not preload, but kinda emulate the startup) e.g. nautilus (or firefox) startup at login, so the first time I launch it myself it launches faster? Probably to start it on another desktop and close after some seconds?
Answer: install the preload package
with a console type :
<code>sudo apt-get install preload
</code>
And that's it. THe package will preload the applications the most used applications after calculating the usage statistic.
preload an application use ram memory and behave differently than "cold" or "warm" start an application.

Preload = putting everything in memory from the hard drive. Your application is garanteed to be run as fast as possible.
Cold Start = loading from hard drive to the memory
Warm Start : reusing what's left on memory and load what's missing from hard drive to ram memory. Your application may run faster if linux didn't had to empty the corresponding cache for another app.

The Cold Start impact is due to the hard drive speed and latency. You can purchase a good SSD drive in order to speed up cold start (it has a real overall impact on the latency of the system)
Best regards.
Comment: Don't forget to look over the log file /var/log/preload.log in order to see if preload is working.
Comment: you can do this : mapprefix = /usr/;/lib;/var/cache/;/home;!/    Just make sure to correctly specify the other variables (sizes and maximums). You must have quite a lot of ram memory for what you try to achieve. You should really consider an SSD drive
Comment: there's almost no difference wheather preload is instaled or not, the "cold" start of a programm would take more time than the second time you launch it. I want to simulate the cold start of some programms so when I launch them they would start faster(cuz it would be the second time they are launched).
Comment: It makes statistics of your most used programs and then it preload them in a "cold" start or not. A browser is exactly the kind of apps that will be preloaded. you need to wait that it builds your statistic usage. Now if you don't want to wait for preload to work then I would suggest you to buy a good SSD drive. The latency that you are experiencing is due to the latency of your hard drive.
Comment: Here's the part of preload.conf: mapprefix = /usr/;/lib;/var/cache/;!/ . This means that nothing that is in the e.g. ~/.mozilla would be preloaded(caches, adblock lists, etc). Only the libs and the application itself without the configs is preloaded.


Starteam will not check-in a new file added to a project

Question: I am using Visual Studio 2005 and StarTeam 2008 (cross-platform client and VS integration). At some point, I added an 'App.config' to a project. I notice now that this file will not check-in.

The 'StarTeam Pending Checkins' window in VS reports the file 'Not in View'. Selecting it for check in and clicking 'Check In Files' causes a dialog to appear - 'Any operation... requires completing the pending renames/deletes'. I click 'Yes' to proceed and nothing happens.
The StarTeam client reports this file as 'Modified'. If I check-in from the client, I get no 'complete pending renames/deletes' dialog and the file quickly appears with a 'Current' status.
Refreshing StarTeam from VS, I still see the file as 'Not in View'.

I have tried forcing the check-in. I completely removed my working files and pulled the solution fresh in hopes that the StarTeam status ('Current') would apply in VS.
Answer: I tried deleting the file to just start over.

I deleted it from the project in VS and StarTeam client (deleting working files too).
I can partially check-in... the 'StarTeam Pending Checkins' window in VS reports the status as 'Locally deleted'
I can't find out how to complete the 'pending delete' (I'm assuming this is the requirement).

There are no traces of the file in the StarTeam client... and I can't find any pending rename/delete information. I cannot force the check-in in VS any further.
Answer: I am not specialist of StarTeam, but this behavior could be consistent with a file already managed by a Windows process, which would prevent StarTeam to do its checkin operations.
If by checkin StarTeam must temporally move the file and rewrite it, that can be a reason of conflict with the Windows process which will block any write operations on that file.
A possible check would be to close Visual Studio (and all other non-StarTeam program, just to be sure) and try then  to add this file alone.
Answer: It appears I solved this...

I had a co-worker with better credentials add the file to the same project.
He checked in successfully.
I blew away my working files and pulled the solution from Visual Studio.
I added the content to the file, saw the modified status, and checked in.

It appears that normal users do not have delete privileges (just regular delete, not permanent history erasing delete). And in some cases the pending delete cycle (is that managed by StarTeam?) doesn't execute and you can't check in files.


How to see query executed for a specific user from V$SQL

Question: I am trying to have the queries used for a specific user at the end of the day. But it seems the queries in this view  V$SQL are deleted every short time. I am not sure how much time. Also i dont know why they are deleted if i still see some records with older LAST_ACTIVE_TIME is there a way to save them before they are deleted. For that when are they deleted?or other suggestion. Hope you can help me.
Thank you!
Answer: You can query v$sqlarea, which holds sql history for a little longer than v$sql (holds info only about current running sql). Both have similar columns, but depending on the report you want to extract, you might wanna join v$sqlarea with other views. But V$sqlarea is also limited to a period of time, and if you need to go more in depth, the view is DBA_HIST_SQLTEXT. Keep in mind that for every dynamic (V$) view, there is a corresponding dba_hist table... But since dba_hist views are often maintained by AWR, you might need to be licensed for diagnostic/ tuning pack for complete reports.


Is there any need to update again on ios 7 when i have updated it one month ago using ios 7 beta version?

Question: I update my iphone 4 on ios 7 beta version one month ago. Is there any need to download ios 7 full version and update again? However in settings (software update tab) it is showed that your software is up to date.
Answer: You should update your phone to the Gold Master (GM) or restore your phone back to iOS 6 and then update to iOS7 using the public version.
If you continue to use the beta, you will not have all the latest updates/fixes from GM and may also run into issues later.
Answer: Yes, you should definitely update to the release version of iOS7. That said, when the first update comes out, be it 7.0.1 or 7.1, that update will replace the OS anyway, so maybe you could wait for that time.
Comment: Will that be true for the beta or just if you have the production version. GvM's answer suggests the former
Answer: My iPad with iOS7 beta also reported it is up to date after release of final version. But when connected it directly to iTunes via cable,  I got it updated. Perhaps it is same with iPhone.


Changing textures realtime in game engine

Question: I am looking for a way to change the texture in the game engine.
I have managed to apply 4 textures and enable/disable them usong a python script. The textures change is working, but only becomes visible when the BGE stops.
It seems that textures are not reloaded in realtime.
How can I force update the texture in realtime ?
Answer: You can use texture bind ID.
Once you have it, you can pass a image buffer into it I think.
Answer: You're probably using functions from bpy? Don't use BPY in the game engine! Thankfully, bge.texture provides this functionality. Here's a code snippet that I use quite often:
def show_picture(obj, path, mat_id=0, tex_id=0):
    '''Loads a picture into a texture'''
    # The texture has to be stored in a place associated with other game data
    # so we store it in a game property. This name inlucdes the mat ID's and
    # tex ID's so that a single object with a complex setup does not have the
    # textures overwrite each other.
    # If a bge.texture object already exists for this object/mat_id/tex_id, then
    # we retrieve that.
    prop_name = 'SHOW_PICTURE{}:{}'.format(mat_id, tex_id)
    if prop_name not in obj:
        tex = bge.texture.Texture(obj, mat_id, tex_id)
        obj[prop_name] = tex
    else:
        tex = obj[prop_name]

    # Load the image from the path
    raw = bge.texture.ImageFFmpeg(os.path.join(path))

    # Check to see that it loaded
    if raw.status == bge.texture.SOURCE_ERROR:
        # Error in loading image
        raise ValueError("Unable to load image at {}".format(path))

    # Assign the new image to the texture and update the texture.
    tex.source = raw
    tex.refresh(True)

Pass in an object, a filepath and (optionally) the material slot and texture slot.
Now, this function reloads the image from disk every time you use it, and as a result it is quite slow - don't go calling it each frame. If you want to have something change picture rapidly, you need to keep it loaded in RAM and just point the plane's material at a bunch of different textures. This can be done by using the bind id. I don't have any nice code snippets for this, but maybe this line will help:
material = obj.meshes[0].materials[0]
material.textures[slot_id].bindCode = tex.bindId

where tex is some dynamic texture (ie a bge.texture.Texture object). You may be able to do:
material1.textures[slot_id].bindCode = material2.textures[slot_id].bindCode

But I have not tested that.
Comment: Hi, How does one find the material ID and texture ID?
Comment: Most objects have a single material, so most of the time you can leave it at zero. If not you can use: https://docs.blender.org/api/blender_python_api_2_78a_release/bge.texture.html#bge.texture.materialID

It seems you use the same function for finding materials. Normally I just hard-code the values because they match the location in the material and texture slots. (ie a texture in the first texture slot has ID zero).
Comment: Thanks, I was actually able to find it out:     tex_id = bge.texture.materialID(obj, 'filename.jpg')


How did Einstein come the conclusion that nothing can travel faster than the light in vacuum?

Question: How did Einstein come the conclusion that nothing can travel faster than the light in vacuum?
Comment: Possible duplicate of [Special Relativity, 2nd Postulate -- Why?](http://physics.stackexchange.com/q/134356/)
Comment: Are you asking a historical question of how Einstein came to that conclusion, or are you asking a physocs question about why nothing can travel faster than light?
Comment: The linked question is not a duplicate.  The linked question talks about who decided that the speed of light is a universal constant and why.  This question asks, How did Einstein get from "speed of light is a universal constant" to "nothing _else_ can outrun a light signal."
Comment: Does Einstein's theory of special relativity say that nothing can travel faster than light?  I think what it really says is that only things with imaginary masses can travel faster than light.
Comment: @jameslarge Yes I wholeheartedly agree, unless there is something blindingly obvious I'm missing (thought I was going a little mad when I saw "duplicate"). You can vote to reopen, although it would be good if the OP showed a little more research. Mind you, the question is a valid one, but also vague enough that someone without key knowledge would have trouble knowing where to begin.
Comment: Related: http://physics.stackexchange.com/q/1557/2451
Comment: The following answers may be of interest http://physics.stackexchange.com/questions/248499/why-did-einstein-took-speed-of-light-unit-or-constant-in-his-equation-of-relativ/248502#248502
Answer: We reach this conclusion because we believe in causality: certain physical processes are observed to happen always in a certain  order, never otherwise. For example, I have never eaten boiled eggs in my existence on this planet without my having to cook them first.
Before I go further, the correct rendering of your statement is that  no causal link from event $A$ to event $B$ can lie outside $A$'s future lightcone, often stated "no signal can propagate faster than $c$". See my answer here where I show that certain processes can travel at faster than $c$ if there is no causal relationship between the events within the process. The travel of a material object you refer to is just a special case of a process whose events are causally linked.
Now to the rest of my answer: we postulate that the order between my cooking my eggs and my eating them is not changed when one observes these processes from relatively moving frames: there is no inertial observer moving relatively to me whose motion causes them to see me eating my eggs before I cook them. This is a crucial point once one derives the Lorentz transformation, because the Lorentz transformation shows that there is a relativity of simulteneity. Different, relatively moving observers do indeed observe different before/after time relationships between certain events. So how do we save our notions of causality?
We postulate that causal links cannot travel faster than $c$. For example, the link between my cooking my eggs and my eating them is (1) directed forwards in my time (pointing to my future) and (2) lies inside my future light cone. As long as this inside-my-future-lightcone condition is fulfilled, the basic properties of the Lorentz group guarantee that a boost cannot change the order of events linked by such relationships, even though it does change the time and space co-ordinates of those events.
There are other ways to motivate no-faster-than-light travel: for example, that the energy required to accelerate something with nonzero restmass to $c$ would be infinite. However, the upholding of causality is the overarching and most forceful motivation: there is no way to uphold the observed orders of events within a process if any pair of events on that process's worldline lie outside each others' future/past lightcone. If we believe in causality, no faster than light signalling is an inescapable conclusion.
See my answer here  and here where I show how the basic order-preservation properties of a subluminal boost follow. Also this answer discusses causality in more detail.
Comment: @PentchoValev That doesn't needfully obviously follow: you have to prove or motivate that deduction. Causality is, IMO, the most forceful way to do it.  Even then, it's not a deduction but the invoking of a further postulate to save something else in physics - causality- we believe in. Another way to understand all this, again directly from the geometry of the Lorentz group, is to understand that the identity connected component of that group holds no supraluminal boosts: no finite number of finite boosts can accelerate one to a relative motion of $c$ or greater.
Comment: I think your causality argument is an unnecessary complication. Equivalently, but much more simply and clearly, you can say: "If Einstein's 1905 constant-speed-of-light postulate is true, then faster-than-light travel is impossible."
Comment: In the example below, if the deactivation device is able to send a faster-than-light signal to the bomb, then special relativity ends up in a contradiction: the bomb explodes in the frame of the train but does not in the frame of the tunnel (that is, Einstein's 1905 constant-speed-of-light postulate is false):

http://www.people.fas.harvard.edu/~djmorin/chap11.pdf
p. 41: 11.6. "Train in a tunnel"
Comment: @PentchoValev In other words, the faster than light signal *i.e.* a causal link between device and bomb outside the device's future light cone, messes up the order of events. This is the same idea expressed in an example: the causality argument is the overarching idea, and your example a special case.
Comment: @PentchoValev I just thought of another example you may be interested in: Look up the Tolman-Einstein paradox, aka the ["Tachyonic Antitelephone" thought experiment](https://en.wikipedia.org/wiki/Tachyonic_antitelephone).
Comment: Is that concept of ether different from Newton's as he speaks of different densities of ether? According to Michelson-Morley density does not seem to vary (just set up this question at StE, accordingly, which seems to relate to answers here).
Answer: In 1905 Einstein postulated that the speed of light is constant (more precisely, independent of the speed of the light source). I haven't seen a text where he infers from his postulate that nothing can travel faster than light.
As for the postulate, Einstein took it from the ether theory, even though in 1887 (prior to FitzGerald and Lorentz advancing the ad hoc length contraction hypothesis) the Michelson-Morley experiment had unequivocally proved that the speed of light does depend on the speed of the light source:
http://books.google.com/books?id=JokgnS1JtmMC
 Banesh Hoffmann, Relativity and Its Roots, p.92: "There are various remarks to be made about this second principle. For instance, if it is so obvious, how could it turn out to be part of a revolution - especially when the first principle is also a natural one? Moreover, if light consists of particles, as Einstein had suggested in his paper submitted just thirteen weeks before this one, the second principle seems absurd: A stone thrown from a speeding train can do far more damage than one thrown from a train at rest; the speed of the particle is not independent of the motion of the object emitting it. And if we take light to consist of particles and assume that these particles obey Newton's laws, they will conform to Newtonian relativity and thus automatically account for the null result of the Michelson-Morley experiment without recourse to contracting lengths, local time, or Lorentz transformations. Yet, as we have seen, Einstein resisted the temptation to account for the null result in terms of particles of light and simple, familiar Newtonian ideas, and introduced as his second postulate something that was more or less obvious when thought of in terms of waves in an ether. If it was so obvious, though, why did he need to state it as a principle? Because, having taken from the idea of light waves in the ether the one aspect that he needed, he declared early in his paper, to quote his own words, that "the introduction of a 'luminiferous ether' will prove to be superfluous."
http://philsci-archive.pitt.edu/1743/2/Norton.pdf
 John Norton: "The Michelson-Morley experiment is fully compatible with an emission theory of light that CONTRADICTS THE LIGHT POSTULATE."
Answer: Not sure about Einstein, I'd better speak for myself!
Relativity theory says, that it's not always possible to tell which of two events occurred earlier than the other. It's counter-intuitive, but does not lead to any paradoxes.
Wait! I'll give you a paradox! Yesterday I checked my mailbox, today I am going to put a letter into it. If for someone the "put letter into mailbox" event happens before "check mailbox", he would be able to take the letter as soon as I put it into mailbox and put it back just before I check it, so effectively I'll send a letter to myself into the past! Isn't it a paradox?
This time-travel paradox happens only if it is possible to travel faster than light. If I am traveling slower than light and some event 1 happened to me before event 2, these two events would happen in this order (first event 1 than event 2) in all the systems of reference which are moving slower than speed of light.
As soon as anyone finds a way to send some information faster than a speed of light, it would become possible to send the information back in time.
Comment: The claim that time-ordering is not fixed only applies to space-like separated events. Your checking the mail box and later putting a letter in represent time-like separated events, the ordering of which is fixed.
Comment: @dmckee
You are right, ordering of space-separated events is not fixed. But that's not a problem because you can not "travel between these events"! And that's because to travel between space-separated events you need to have a speed faster than light. If someone can travel faster than light, then the events "travel start" and "travel finish" are space-separated and in some systems of reference "finish" happens before the "start". That's what I was trying to explain in my original post.


How to modify SharePoint Online home page?

Question: I want to modify SharePoint Online home page. I am trying to add the html, css and js in snnipt webpart but its not get work. I want to add the the Text, images and sliders section on the home page. I want to this using available webpart in SharePoint online.
Can anyone please help out me in this?
Comment: Are you using modern experience or classic experience? Which webpart are you using?
Answer: If you are using Code snippet web part on modern pages, it cannot be used to render code snippets but only "display code as text on your page for others to use or learn from", quoted from the document.
If you want to render custom code on the home page, take a look at the page and web part model SharePoint Framework (SPFx). Build client-side web part and perform responding actions.
Please note that customization on modern pages is restricted. See the reference here for supported customizations: Customizing "modern" site pages.


Is there any free way to have a Mac function as an AirPlay speaker?

Question: I have a stereo system hooked up to my Mac mini, but sometimes I'll play music from my laptop. Is there any way for the Mac mini to be recognized as a speaker and allow me to output sound to it (and the speakers connected to it) from my laptop without paid solutions like Airfoil?
Answer: This isn't free, but it's only $2.99 AirServer
Comment: Thanks! i ended up finding this on my own, it works **almost** perfectly, although sometimes it has latency issues which cause echos
Answer: Currently streaming from iTunes is only supported to Apple TV and Airport Express speakers. (Thanks @Jonathan)
You could try a pretty ugly hack of using home sharing to access your laptop music library from your Mac Mini and then control the playback by using vnc or some other remote desktop app to control playback on the Mini from the laptop.
Comment: Only works with aTV
Comment: @Jonathan Correct, I thought they had enabled this feature but didn't check.  Answer amended, thanks.
Answer: Try Erica Sadun's AirPlayer. That might very well work. :)
Comment: looks like it says on the page that it doesn't support music playback
Answer: There is a free utility called shairport which acts as an airport express. If your computers are on the same network, you can use it to stream music between the two, as iTunes will see the computer it is running on as airplay speakers. I recently used it to stream music from my iPod to my computer.
Answer: If music only, there are a lot free options. shairport is a great choice, open source, support almost all platforms.
If you also need mirroring, most free tools are broken since iOS9.
check this one: lonelyscreen. It is free. Only for mac and windows, no linux. And it can capture and save iOS mirroring. I don't use that much, but it is very convenient sometimes.


How does impedance analyzer input capacitance influence the measured result?

Question: I work with an impedance analyzer, measuring impedance spectra of ionic conductors. I would like to know how the obtained data can be affected by input capacitance at higher frequencies (1kHz-1MHz). A person said that I cannot properly determine dielectric properties because the high input capacitance of the meter (on the order of 100 pF) does not allow measurement of solid samples that usually exhibit lower capacitance than the input capacitance. How can I see this input capacitance influence?
Comment: Could you give us a little bit of info about your impedance analyzer, and where your input capacitance figure is coming from?
Answer: Actually the capacitors acts as an impedance which influences the circuit.
Impedance, the vector sum of reactance and resistance, describes the phase difference and the ratio
of amplitudes between sinusoidally varying voltage and sinusoidally varying current at a given frequency.
Fourier analysis allows any signal to be constructed from a spectrum of frequencies,
whence the circuit's reaction to the various frequencies may be found.
The reactance of a capacitor is given by:
$$X_c=\frac{1}{2\pi{} f C}$$
$$\pi\approx3.14$$
$$f=frequency  $$
$$C=Capacitance$$
As the frequency increases the reactance decreases.
like this capacitance influences the circuit.


Cable Colors and Purpose

Question: I've been doing some work with some big businesses and so far I've learned yellow is internet and blue is phone.
Is this a standard or is this just a personal chose? Do colors mean different tasks?
Comment: Hi Frank, the color of the cabling jacket has no industry-wide requirements; the decision about which color is local to the facility / company.  We use blue in our DC for the backup ethernet connection and white for the primary.
Comment: in my environment - depending on the floor and room, you have totally different schemes! The only thing that's standardized is the order you crimp the 4 pairs of wires....imagine if that was a free-for-all
Comment: The entire DoD uses cabling colors that match up with classification levels.  Blue - Unclassified, Red - Secret, Yellow - Top Secret, etc.
Comment: Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
Answer: Contrary to popular belief, there are cable color standards defined, just hardly anyone (myself included) follow them closely or at all.  Check local jurisdictions for variants.
ANSI/TIA/EIA-606-A Administration Standard for the Telecommunications
Infrastructure of Commercial Buildings or the updated ANSI/TIA/EIA-606-B documents these standards.  Generally, anyone who wants to following building standards should be familiar with BICSI and vendors who are BICSI certified would be familiar with these as well.
Cable colors are specified using Pantone numbers. These colors or their equivalent are to be used.

Source/PDF on generalnetworkerror.com
Other color coded references for TIA/EIA 606 and other standards can be found at Huffmanreference.com.
Comment: As with anything cable-related, the local jurisdiction has final say. We had a cable color standard, including the red for phone systems, but some local jurisdictions reserve that for lifeline services. We didn't discover it on one job until the cable had already been run.
Comment: My understanding is that the EIA color codes are only a recommendation... I am curious, do you know whether the image is licensed for reproduction?
Comment: @Mike Pennington:  The standards are optional, but exist nonetheless for those that want to use them.  I'm seeking permission for the use of the color code table from the owner.
Comment: Regarding image licensing, the image is now a self-created one.
Answer: As far as I know there is no standard for colors in twisted pair ethernet pigtails. As Mike already explained, color codes are local to the facility and different facilities could use different color codes.
Regarding optical fiber pigtails, there is a standard color code for them. SMF pigtails are yellow and MMF are blue or orange depending on its core diameter.
You have further details optical fiber cable colors in the following link: http://www.thefoa.org/tech/ColCodes.htm
Answer: The colors for RJ45 cables are not specified. You can get any color you want. In the DC we color-code length:

0,5m yellow
1,0m white
2,0m blue
...
Everything >20m white again

In the office we use black cables for all equipment as it doesn't stick out. (Bright orange/red in a snazzy conference room doesn't look too good IMHO.)
For optical cables most of the time you've got yellow for SM cables, orange for MM cables. Sometimes MM cables come in aqua when they have 50µm laser-optimized cores.
Please beware: This is not always the case. I've seen enough yellow MM cables and orange SM cables to always check the print on the cable. MM is often orange whatever the core size is.
Also, the standard colors for connectors are blue for PC/UPC (0°) and green for APC (8°) connectors on SM cables. Again, this is for most of the cables, not all of them. Better check before connecting.
More information on Wikipedia:
http://en.wikipedia.org/wiki/Optical_fiber_cable#Color_coding
Answer: The biggest thing I would use different colored cables for is to differentiate the importance of the cable.  This way crucial cables between switches, routers, and other important devices are noted to prevent accidentally causing outages in your network.  A new employee, contractor, or regular employee can quickly learn the coloring scheme.  Sometimes it does get confusing when all the cables are the same color!  If you can follow a standard provided in the other answers, that would be great.  But not everyone can change all their cables in their existing infrastructure.
Answer: Personal/local choice.
Red is typically reserved for fire alarm.
Yellow thick BANANA cables contain multiple pairs of different AWG to support access control system door locks, motion sensors, and badge readers. Purple/violet is another common color for BANANA cables.
Color uniformity degrades over time, such as when a technician only has a yellow patch cable when a blue one is the standard.  After several years you'll have as many colors in your Telco Closets, racks and Technical Equipment Rooms (TERs) as a LGBTQIA+ gay pride parade.
If you're doing Outside Plant (OSP) work for big businesses the American Public Works Association Utility Color Code Marking is

Red      electric power lines, cables, conduit, and lighting cables
Orange   telecommunication, alarm or signal lines, cables, or conduit
Yellow   natural gas, oil, steam, petroleum, or other gaseous or
flammable material
Green    sewers and drain lines
Blue drinking water
Purple   reclaimed water, irrigation, and slurry lines
Pink     temporary survey markings, unknown/unidentified facilities
White    proposed excavation limits or route

If you're an IT person you want the Orange stuff.  If your work stinks, use yellow or green.
Personally, I call Miss Utility and let the random operator at 811 chose project colors.  Her answer is as good an answer as from anybody else.

Cable Colors and Purpose


How can colliding high-energy protons form a (micro) black hole?

Question: A body's mass increases when it aquires velocity. It approaches infinity when the velocity approaches the speed of light. This will not result though in the formation of a black hole.
A micro black hole in reach for observation is speculated to exist in a theory that tries to unify the three basis forces with gravity. Extra curled up space dimensions are postulated and these dimensions can make gravity vary in a non-$\frac{1}{r^2}$ way. Because of this the mass needed to produce a micro black hole is in reach for experimental probing. See this article for more details.
One can read that two colliding protons can (according to the theory) form a micro black hole. It's obvious that two protons with a high enough relative velocity can have a mass equivalent of a micro black hole. But if the protons can't form black holes at high enough velocities, how can a black hole be formed after they have collided? How emerges a black hole spacetime in this case?
Comment: @safesphere I get you! Thanks! All momentum (although the total is zero) is conversed in energy, so...Which is also obvious from a quark perspective. Due to the collision the six valence quarks get into an excited high energy state which translates in positive curvature(?). I like the citatation of Mencken, by the way...
Answer: "A body's mass increases when it acquires velocity" is false. Velocity is relative, so any apparent increase in mass is entirely in the eyes of the observer moving relative to the body, i.e. it's an artifact of the coordinate system. That's why modern relativity textbooks generally avoid "relativistic mass" and only talk about "invariant mass" or "proper mass" (the rest mass of the object).
So a single proton moving very fast relative to you won't form a black hole, any more than you would form a black hole because you're moving very fast relative to the proton.
However, two protons moving in opposite directions do have an invariant kinetic energy associated with the whole system. That is, every observer can agree that the total system of protons has energy greater than the sum of the rest masses -- no matter what you consider to be "at rest", one or both of the protons is going to be moving.
One could imagine that if the protons collide this kinetic energy could end up concentrated in a small enough region to form a black hole. Whether this could in fact happen in the real world is another question, and probably requires a quantum theory of gravity (which we don't have!) to answer for sure. Certainly it has never been observed.
Comment: Protons do have mass, and so they do curve spacetime. And the stress-energy tensor for a system of two protons in relative motion is not the same as the stress-energy tensor for two protons at rest relative to one another. It's certainly true that the effect is complicated -- it's not as simple as plugging the "mass equivalent" of the kinetic energy into Newton's formula.
Comment: If the particles are moving relative to one another then the stress energy tensor, and hence the curvature, is objectively different than in the case where they are at rest relative to one another. See also Tolman, Ehrenfest, and Podolsky "On the Gravitational Field Produced by Light", Phys. Rev. 37, 602, wherein they show that photons propagating in the same direction have no attraction to one another, but photons propagating in opposite directions do attract.
Comment: See also [this question](https://physics.stackexchange.com/questions/627548/can-relativistic-mass-actually-change-gravitational-pull/627578)
Comment: @safesphere : The OP and I are discussing *protons*, i.e. hydrogen nuclei, not "photons". So your objections are starting from an incorrect premise.
Comment: @safesphere said "you need a collision to convert the kinetic energy to the energy of a different type whose curvature is not offset by the gravitomagnetism of momentum" which is not exactly correct. You need a collision, as Eric Smith mentioned, to get the energy into a small region, but conversion into a different form of energy is not needed. In the center of momentum frame the momentum of the two are equal and opposite. So the gravitomagnetic terms you mention are naturally canceled in a "collision" even without any conversion. Eric's argument is valid.


Seat of My Pants

Question: I was told that I live my life by the seat of my pants, and though it doesn't sound like a compliment, I'm not sure that it is an insult either.  What is the derivation of "seat of my pants"?
Comment: Have you checked any online dictionary to find out what this phrase means?
Answer: Taken from The Phrase Finder:

This is early aviation parlance. Aircraft initially had few navigation aids and flying was accomplished by means of the pilot's judgment. The term emerged in the 1930s and was first widely used in reports of Douglas Corrigan's flight from the USA to Ireland in 1938.
That flight was reported in many US newspapers of the day, including this piece, titled 'Corrigan Flies By The Seat Of His Pants', in The Edwardsville Intelligencer, 19th July 1938:
"Douglas Corrigan was described as an aviator 'who flies by the seat of his pants' today by a mechanic who helped him rejuvinate the plane which airport men have now nicknamed the 'Spirit of $69.90'. The old flying expression of 'flies by the seat of his trousers' was explained by Larry Conner, means going aloft without instruments, radio or other such luxuries."
The 'old flying expression' quoted above (although it can't have been very old in 1938) that refers to trousers rather than pants does suggest that the phrase was originally British and crossed the Atlantic prior to becoming 'by the seat of one's pants'.

Emphasis mine.

Seat of My Pants


To fight oneself?

Question: If someone has the opportunity to do something that he would like to do but he knows that he shouldn't (for example sleeping with his best friend's wife), and he suffers from this moral dilemma, can I say "he is fighting himself"? Or "fighting with himself"?
Answer: You can use the word conflict.
Conflict can be used to mean a mental struggle arising from opposing demands or impulses
Using it in a sentence :
I was conflicted; should I support the love of my life or be more pragmatic?
Comment: Yes, conflicted is exactly what I mean, and yet it's not the word that I want to use. What about "to fight (with) oneself"? Is it idiomatic? Thanks!

To fight oneself?


How do I delete my Linux Foundation account?

Question: I made a Linux Foundation account (https://linuxfoundation.org, account system on https://openprofile.dev) for some purposes last year, and now I want to delete it. However, looking around the website I don't see any way to delete my account, and searching the web hasn't been fruitful either. How do I delete my Linux Foundation account?
Answer: From Can you delete my SSO account? section on the LF - Wiki:

We can now delete login accounts, please open a ticket with the account you would like to be deleted. https://jira.linuxfoundation.org/plugins/servlet/theme/portal/4/create/255
In case you would like to remove all your personal data from LFX, please follow our Privacy Policy Process https://linuxfoundation.org/privacy-policy/


Motor control using arduino board

Question: I want to control 2 dc motors using the arduino board directly. One motor must rotate clockwise and the other counter clockwise. The directions  doesn't change only the speed of each motors. Can this be done without any shield? Them motors may need a higher voltage than the arduino can provide. If I link the arduino board to a power source of about 15 V (the board is arduino mega limits between 6 and 20 ) and I use "analog.write()" function can I output more than 5 volts(the internal voltage)?
Comment: If you post a link to the motors you are intending to drive, you might get an even simpler solution. We need to know both the voltage and the current, preferably from the motor's datasheet.
Answer: Simplest way to do this is two MOSFETs (one per motor, because you don't need to change direction), and some miscellaneous passives, and a flyback diode for each motor.
See this tutorial for wiring diagrams and details.
Comment: Great link! You saved me! But I still don't get it. What's the difference between a mosfet and a transistor? I searcher a few more pages and they said a mosfet is a transistor. Does any transistor work?
Comment: A MOSFET is a type of transistor. BJTs (bipolar junction transistors) are the other dominant type of transistor, and are not as appropriate for this application. The difference between MOSFETs and BJTs is too much to discuss here, but as far as what you should use: use a logic-level MOSFET (low Vgs(on))
Comment: @uint128_t it is syaing that link does not exist

Motor control using arduino board


About [s] being replaced by the voiceless postalveolar fricative in the US

Question: I'm recently listening this replacement a lot on youtube, it's as if the practice is on the rising. Is it?  what conditions such occurrence? Where in the US is it happening? And how did it all begin?
Answer: This retraction happens when [s] is in a consonant cluster with a following [ɹ] (as in the video you linked, "just straight up"). The reason is articulatory: the retroflex gesture of the [ɹ] is anticipated, so the [s] becomes retroflex/postalveolar too. It's an assimilation. This is pretty common in US English: I associate it with Southern and African-American speakers.
Comment: @sumelic I don't recall hearing that, but you may well be right. I wonder what the reason would be there. Of course the same happened in German (*spät* etc.)
Comment: @sumelic That applies to German but are you sure that it happens in English? This sound change in /stɹ/ > /ʃtɹ/ is something that I have noticed but never before in English.
Comment: TKR, In German /s/ became /ʃ/ before every consonant in the onset, I think. But, before that German had two *s* sounds that differed in multiple respects. The usual *s* spelled as ⟨s⟩ actually was retracted but (when voiceless) later merged with the *ß* sound that was spelled ⟨z⟩. I'd propose the explanation that it wasn't a retraction before consonants but that *s* stayed mostly unchanged before consonants and was advanced elsewhere.
Answer: Without specific examples, it's hard to say what exactly you're hearing.
Different languages (or accents) have different boundaries for what exactly counts as /s/ vs. /ʃ/, so it's possible that the speakers you are hearing do not really "replace" their /s/ with [ʃ], but just use a pronunciation that sounds more like [ʃ] to you.
But it's also possible that they really are using [ʃ] (possibly even /ʃ/) where a typical reference English accent would have /s/. It is known that English /s/ can have retracted pronunciations; I haven't personally read a lot of the literature about this topic, but there seems to be a decent amount (maybe some of the references here would be helpful?: Variability in American English s-retraction suggests a solution to the actuation problem).
Sometimes this happens in environments where the contrast is neutralized by English phonotactics; the most well-known examples I think are the word-initial consonant clusters /str/ (as TKR says) and /stj/ or /stʃ/ (the cluster at the start of "student" in a typical southern British English accent).
Glain (2013) says that /st/ followed by a vowel, as in stop and start, also has a variant pronunciation that sounds like [ʃt]. I don't know that much about this, but this indicates that s-retraction is not restricted to the context of str-, although it may have started out there and subsequently spread to certain other s-initial clusters. I haven't heard of s-retraction occurring outside of consonant clusters.
German Phonetics and Phonology: Theory and Practice (By Mary Grantham O'Brien and Sarah M. B. Fagan, 2016), says

[s-retraction] has in fact been documented in the English of speakers from the United States, Great Britain, and New Zealand (Rutter 2011:27). It appears to be spreading, not only by being characteristic of the speech of more and more speakers, but also in the environments where it occurs. Janda and Joseph (2003:212) have documented the [ʃ] pronunciation of /s/ in a number of environments other than the sequence /str/:

(6) [ʃ] in English clusters other than /str/:

a. with r preceding: under[ʃ]tand, thunder[ʃ]storm
      b. before [r] alone: di[ʃ]respect
      c. before a plosive other than /t/, with /r/ following it: [ʃ]prinkler, [ʃ]creen
      d. before a plosive, with no /r/ involved: [ʃ]till, [ʃ]chool

(p. 431)
Answer: Are you observing it in the south/ in Texas for example? I would assume that you are actually noticing a retracted [s̠] that I usually notice in a Texas accent, Dutch, European Spanish, Icelandic... It's actually an old s sound presumably the kind of s that many medieval European languages had.
Comment: @DuarteAlfonsoMartin To me his /s/ at 1:19 sounds very different from a [ʃ].
Comment: Idk where the youtubers are from, but I heard this s-sound from a Maine girl and from Stacy of the series Phineas and Ferb, with the latter not depicting Texas I think. It may not give you certainty but I found the video of a youtuber who makes this s. Check out at 1:19-1:21. https://youtu.be/OzvJVwowTLo
Comment: @DuarteAlfonsoMartin Maybe I'm just more used to it by now. *terrori[s̠]ti[s̠] mi[s̠]drijf* https://www.youtube.com/watch?v=mjwLRanrK9s&feature=youtu.be&t=37
Comment: Well, I actually didn't even notice the /str/ cluster because I was not expecting a combinatory sound change. I thought you meant /s/ before vowels.


Census Tracts entirely within another Census Tract

Question: I am working with a U.S. Census Tract layer. I am just wondering why there are tracts entirely within another tract when, in general, the territory is divided by partitioning the space into a number of simple rectangular regions, divided up by axis parallel (more or less) splits.
Comment: populated areas? looks like county seat + surrounding county to me (But that may be anit-Kansas prejudice on my part)
Comment: It totally makes sense to me. Thanks.
Answer: Census tracts must align with county boundaries - that is part of their designation. From the US Census Bureau:
"Generally, census tracts have between 2,500 and 8,000 residents and boundaries that follow visible features. When first established, census tracts are to be as homogeneous as possible with respect to population characteristics, economic status, and living conditions."
So, since all of Kansas's counties were established in the mid-1800s, before census tracts came about in 1906, the Census Bureau had to work around the established county boundaries. Many of Kansas's counties have very low populations but since the tracts can't cross county lines, those counties have to be the extent of a single tract.  To divide a mid-size county according to the Census guidelines (keeping tracts as homogeneous as possible) one solution might be to put the area around a town into one tract and the surrounding rural areas in another.
This seems to be pretty common in surrounding states with grid-like counties.


Li-Ion batteries with 3 connections

Question: If I have a Li-Ion battery with 3 terminals and do not wish to monitor the thermal pin do I need to pull it low or high. When I measure the battery from white to red I see positive volts as do I between black and red. I assume therefore that I should either leave the white wire unconnected or connect it to the black (negative) connection. Please can someone either confirm or explain what should be done.
Comment: How many cells does it have? Whats the output voltage? Many bateries with 2 cells (~7.4V) actually have a third wire between the cells for balancing, etc (same with 3, 4, cells and so on)
Comment: If you are sure it is for thermal sensing, then just leave it unconnected. Make sure you know how to charge lithium chemistry batteries. Overcharging them can cause them to become hazardous. Does the battery say what the voltage and/or capacity is on it? If so, please edit your question and add that information.
Answer: Unless you know the configuration of the battery pack I would suggest you recycle the entire battery pack in a responsible manner.  It is dangerous to connect batteries incorrectly.
It is common to extend the life of a secondary battery pack by balancing the charge between individual cells. Here is an example of passive balancing for a 2 cell battery pack:

It does not sound intuitive to drain the charge off an individual cell to extend the pack's life.  But it works.
It may be more intuitive to think about active balancing where the charge is moved from the most charged cell to the least charged cell.  However, active balancing is much more complex to implement.

Li-Ion batteries with 3 connections


Storing multiple cryptocurrencies using a usb stick as the private key

Question: currently I am using an electrum wallet on watching only mode and using a usb stick that stores my private key whenever I need to send BTC to someone. I would like to do something similar for my ether and cardano but am having trouble finding an open-source cold wallet alternative that would be compatible with a usb stick. How could I accomplish something similar? What programs can be used? Is there any open source software to do this? Thanks for any responses in advance!
Comment: Is there a reason why you don't buy a ledger nano or Trezor?
Comment: I do not think it is worth it to buy one for the amount of crypto I am storing and I think it is safer to use a usb stick with completely open source software instead of the leger nano.
Answer: USB can easily be scanned by a virus to retrieve data on your USB. Hardware wallet are better because they can't output sensitive data.
Cold wallet mean cold so better to use a full offline computer or even old phone. You can add BIP39 to it, and MyEtherWallet to sign transaction. I don't know for cardano though, you can't even generate cardano with Ian Coleman's BIP39.
Comment: I'm worried about using a hardware wallet because even that could be running malicious code. I think usb or a raspberry pi is the option I will end up using. Do you know any way to do this on a raspberry pi?


How to get the actual Gas price?

Question: Is there a way to get the lowest and average price miners are asking for gas? Some statistics sites seem to have prices but they are outdated.
Answer: EDIT: with EIP-1559 (shipped in London fork in July 2021) this is not true anymore.
I'm changing this answer to community wiki so that anyone can fix it (I don't really have time, sorry)

As explained in the Ethereum github's wiki the gas price is set by miners and the only way to guess the acceptable value is to look at the last block gas price. Then you look at the lowest and highest prices on the block and next block price should fit close to these values. Looking at more blocks in the past could give you a trend to guess if the price raises or goes down. But there is also a part of random, at least in Geth, so you can't exactly predict the gas price but only be close to the future block price. I think you can't be more accurate than geth gas price oracle.
Comment: Nice @nicolas, it your answer gave me insight. Still wondering if you know how Mist does it, they are not using the oracle, are they?
Comment: I didn't have time to look at mist code for the moment... sorry.
Answer: web3 has an async function called getGasPrice. In a geth terminal I can use:
web3.eth.getGasPrice(function(e, r) { console.log(r) })

This currently returns 20000000000 in geth on mainnet (20 Shannon). I imagine it is using the price used in the last block that was mined.
Note: The price specified by the sender is the highest price they're willing to pay. The minor will choose whether or not to process the transaction at their own discretion.
Comment: Still relevant in 2023. It has been checked on a private self-hosted network.
Answer: It's been 3 years since this question has been posted and we now have 2 public APIs that determine the optimal gas price for a new Ethereum transaction:

EthGasStation
EtherChain's Oracle

Note that Etherchain piggybacks off EthGasStation, but their json response is less verbose, hence why I included it.
You may also want to read Gas Price Recommendations.
Update Jul 2021: Etherchain has stopped accepting requests from any domain, possibly because they are not using CORS in their API implementation. You will encounter errors when trying to fetch the gas price using their API, unless you become part of their allowlist (I don't know how to do this).
Answer: https://ethstats.net provides an idea about the current gas price and the gas limit in real time.
Comment: Site is dead...
Answer: DefiSaver's Chrome plugin is quite nice and handy.
Comment: Your answer could be improved with additional supporting information. Please [edit] to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers [in the help center](/help/how-to-answer).

How to get the actual Gas price?


Changing color of columns names in query builder

Question: Does anybody know if it is possible to change the colors of the names of the columns (attributes) when writing a query in QGIS? (e.g. when selecting by expression in the attributes table).
Comment: I think you can only set the colours using the expression in the _Conditional formatting_ option and not via the attribute selection.
Comment: Do you want to change the colors of the column headers in the attribute table? Or do you want to change the color of the font used for field names in the expression builder?
Comment: Field names in the expression builder are blue if you type them without double-quotation marks. They're yellow if you type the with double-quotation marks. As far as I know that's the only control you have over that.
Answer: In the default user interface theme, the field names in the expression builder are

blue when typed without double quotation marks (fieldname)
yellow when typed with double quotation marks: ("fieldname")

If you switch to "night mapping" theme (settings > options > general > application > UI Theme), the field names will be

green when typed without double quotation marks
greenish-yellow when typed with double quotation marks

The plugin "Load QSS - UI themes" provides a way to add different user interface themes. I tried a few of the themes that come with this plugin. In the Expression Builder, they all seem to use the same color settings as the UI Theme you have set in Options.
Notes:

In QGIS 3, the expression builder allows you to type field names with or without double quotations. But field names with spaces must be put in double quotes. It's generally not a good idea to make a field name with spaces; use camel caps (no spaces, capitalize the first letter of each word, like this: FieldName) or substitute an underscore for the space (like this: field_name).
Some functions require field name input in single quotes (like this: 'fieldname'). See the Expression Builder Help section for each function.
Comment: Excellent! Thank you!


How can I query the version of the node running a stake pool?

Question: The version of the node running on the entire blockchain can be consulted in PoolTool.
I want to check the individual version of a stake pool. Thanks.
Answer: I believe PoolTool asks node operators to send them the data.
In bitcoin style nodes there is an RPC getpeerinfo and that shows peer info like major version, I dont think there is anything for cardano-node yet.
You could try looking thorough cardano-node logs and see if there is version data exchanged (I expect there is), you would then just need to manually configure mainnet-topology.json to point your node to the pool node.
Bear in mind this will only give the public relay version, not the block producer version.


Assets bundles have higher size than uncompressed sprites

Question: I've created a script that generates assets bundles by compressing sprites using LZ4 compression. I need this in order to generate smaller files that I'll download from a server at runtime but after taking a look at those bundles. I've found out that they actually have a higher size than the uncompressed sprites.
For example, I've generated a bundle from three sprites that have a size of 201KB together, but if I take a look at its generated bundle, its size is 300KB. This is only one example, there are other bundles that are 6MB but their original files are only 500KB and that doesn't make any sense to me. Can someone point me in the right direction?
Comment: What can you tell us about these assets, their source format, and the destination format/quality settings you've applied? If you can walk us through a test case that will let us reproduce the larger bundles on our own machines, we'll have an easier time investigating and testing potential solutions.
Comment: How does that script you created work? For all we know, that script could have a bug that duplicates data, or in some way creates more data than needed and adds them in the asset bundle.
Answer: Thanks for your answers, actually you guys gave me a hint of what's going on here and I've found out the solution for this.
Well, it happens that it doesn't matter if you compress your PNG files with photoshop before, Unity converts those PNGs in a unity readable format which of course have another file size based on the import settings you are using. In this case, I was testing an asset bundle I've made from a group of png assets which were ~250 KB in total (as PNGs), but  ~600KB as an asset bundle, I've tested many different texture settings with no luck, but after changing the resolution of those PNGs to something multiple of 4, I could make use of DXT5 compression which reduced the size of the asset bundle to something more normal.


What criteria determines whether stars are supernova type II candidates?

Question: I want to find supernova candidates by using the Gaia catalog in 300 parsec (near Earth). I though they must be red super giants so they are cooler than 4100 K and more luminous than 104 solar luminosity. However, there is no data for luminosity for those stars. So I need another parameter related with brightness, magnitude or luminosity etc. Any suggestions?
Comment: Calculate the absolute magnitude!
Comment: Well there are luminosities available in the Gaia DR3 catalogue, and if not, you can easily calculate them from the absolute G magnitude and an estimated bolometric correction.
Comment: However, if you are only interested in the progenitors in the supergiant phase then there are few (one?) within 300pc, and they are so bright and large that their distances will be quite uncertain.
Comment: the problem is I cannot find absolute g magnitude in DR3 with parallaxes. and yes there must be a few stars like 6 or 10
Comment: There are G magnitudes and parallaxes...
Comment: There are but not together. They are in different catalogs.
Comment: When i go the site https://gea.esac.esa.int/archive/ and search with gaiadr3.gaia_source there is no absolute G magnitude, there are only some "mean G mangitudes" or "BP-PR magnitudes"
Comment: Calculate for millions of objects??!
Answer: If you are just interested in supergiants (note that the massive progenitors of supernovae are more likely to be main sequence stars, since that is where stars spend most of their [short] lives) then the problem amounts to selecting stars in a certain portion of the observational Hertzsprung-Russell diagram (absoloute magnitude versus colour). In the case of Gaia DR3 (or EDR3) this woud be absolute G magnitude versus Bp-Rp.
I do not know what restrictions you want to place on the types of progenitor you wish to find but let's say that you wanted stars cooler than some colour and with an absolute magnitude less than -5  (the absolute magnitude of Betelgeuse is about -6).
The distance modulus at 300 pc is $5\log d -5 = 7.38$, so your candidate stars would have to be brighter than about G=2.38 (if the star was closer than 300 pc, or more luminous, then of course it would be brighter). NB: I have however ignored extinction, but this should be a small effect within 300 pc.
So you go to the Gaia catalogue and request all stars brighter than G=2.38 and with a parallax greater than 3.333 milli-arcsec. From these few stars you can choose the ones in the colour/temperature range that you want.
Unfortunately you will probably find that data for extremely bright stars (G<3) is missing from the Gaia catalogue. The stars are too bright to be recorded and measured properly.
You probably would do better by search the Yale Bright Star Catalogue for objects with V<2.38 and a colour redder than some threshold (the catalogue also has spectral types, so you could just strip out the class I luminosity sources using this). You will then have to individually search for distance information to those stars (their parallaxes will not be very good).
You might find Messineo & Brown (2019) of interest. They produce a catalogue of red supergiants using the Gaia DR2 data (which still has the bright star problem).
Comment: Thanks. But i have some questions. 5logd−5=7.38 this calculation is for at 300 pc. But i want 300 or closer ones so what am i suppose to do? When I take 1 parsec 5 * log1 - 5 = -5. So what doest it mean? Do I need to take G mag between 7.28 and -5? Also in gaia catalog there is no absolute magnitude but apparent magnitude. I guess you offer to use that variable? At last, why G=2.38 rather than G=7.38?
Comment: Any star that is closer, or is more luminous, will of course be brighter than G=2.38. The Gaia catalogue does not contain absolute magnitude because you need to calculate it yourself using whatever assumptions you need to make about what the distance is (not necessarily just the reciprocal of parallax) and what the extinction is (I assumed it was negligible in my answer). @Aegean
Comment: thanks again totally understood well
Comment: But still with g=2.38 or smaller betelgeuse isn't in the list. Why is it?
Comment: I said why in my answer. @Aegean
Comment: Ah okay, I missed that part, now I see.
Comment: @ProfRob Are there any type 1a supernova candidates that are very close to the Chandrasekhar Limit of 1.4 solar masses?  I could post a separate question ...


Why is the photon emitted in the same direction as incoming radiation in Laser?

Question: When an atom "lases" it always gives up its energy in the same direction and phase as the incoming light. Why does this happen? How can this be explained?
How does the photon generated because of stimulated emission, know which direction to take?
What are the factors leading to this?
Comment: This is a strong thing to say without any reference or any additional context. Could you clarify this part of your question: *When an atom "lases" it always gives up its energy in the same direction and phase as the incoming light*?
Comment: during the lasing action...that is when the stimulated emission takes place and the released photon comes out...why does it go in same phase and direction.
Answer: The word "stimulated" means that the emission of the photon is "encouraged" by the existence of photons in the same state as the state where the new photon may be added. The "same state" is one that has the same frequency, the same polarization, and the same direction of motion. Such a one-photon state may be described by the wave vector and the polarization vector, e.g. $|\vec k,\lambda\rangle$.
The physical reason why photons like to be emitted in the very same state as other photons is that they are bosons obeying the Bose-Einstein statistics. The probability amplitude for a new, $(N-1)$-st photon to be added into a one-photon state which already has $N$ photons in it is proportional to the matrix element of the raising operator
$$ \langle N+1| a^\dagger|N\rangle = \sqrt{N+1}$$
of the harmonic oscillator between the $N$ times and $(N+1)$ times excited levels. Because the probability amplitude scales like $\sqrt{N+1}$, the probability for the photon to be emitted into the state goes like the squared amplitude i.e. as $N+1$. Recall that $N$ is the number of photons that were already in that state.
This coefficient $N+1$ may be divided to $1$ plus $N$. The term $1$ describes the probability of a spontaneous emission – that occurs even if no other photons were present in the state to start with – while the term $N$ is the stimulated emission whose probabilities scales with the number of photons that are already present.
But in all cases, we must talk about "exactly the same one-photon state" which also means that the direction of the motion is the same. It's because quantum field theory associates one quantum harmonic oscillator with each state i.e. with each information $\vec k$ about the direction of motion and wavelength; combined with a binary information about $\lambda$, the polarization (e.g.left-handed vs right-handed).
Comment: "The word "stimulated" means that the emission of the photon is "encouraged" by the existence of photons in the same state as the state where the new photon may be added" The word stimulated means you are making it happen by stimulating it. So when u say the emission is "encouraged" by the existence of photons i agree with you.Why do u say the new photon will be added in the same state? Just because they are bosons and so tend to be in same state?
Comment: @Luboš, if I understand your point, the reason why the two photons are colinear is statistics. You need many photons to have a large probability of the same state. However, the photons should be emitted in the same direction even if there is only 1 atom and 1 photon. How do Bose statistics work for only 1 photon?
Answer: I think it's deeply related to the fact that photons are bosons, ergo they follow the Bose-Einstein Statistics, or in this case they make a Bose-Einstein Condensate.
If you are not familiar with this exciting concept, I suggest you make a look at this Wikipedia article or any other statistical mechanics textbook you have around. Anyway, the two photons making a Bose-Einstein Condensate means that the two photons will have the same phase(and obviously wavelength) and will occupy the same point in space all the time.
Hope this was helpful.
Comment: thank u..since i have done introductory BE statistics, i can understand ur answer.
Comment: So let me see if i get this right...you are saying when the photon comes out after stimulated emission, it "somehow" knows the incoming photon is in some particular dynamic state, and so it chooses to be in that dynamic state? I am not asking about the statistics or probability or anything-just that why do bosons(photons in this case) behave like this?
Comment: Particles usually know things which you do not expect!
Although, this is not the answer of your question, but this brilliant series from Feynman might shed some light on it: [QED](https://www.youtube.com/watch?v=LPDP_8X5Hug)
Comment: well yeah...i know that bit"particles knowing things". Was looking for perhaps something that i could..well...digest!
Answer: This is a great question, and I believe one that deserves very deep thought!
Let me briefly review my understanding of a laser. For a laser, typically there are two channels the atoms can decay into by emitting photons: out into free space or into a cavity. Purely from spontaneous decay, the atom is more likely to emit photons into free space. However, because the cavity stores its photons before releasing them in a beam, photons begin to build up in the cavity. Then, these excess photons can stimulate emission into the cavity and the atoms begin to emit more and more of their photons into the cavity rather than free space. When this process runs away with a large number of photons then the output light from the cavity is laser light.
Finally, understanding why the photons are identical means understanding what a cavity does. The effect of the cavity is to dramatically modify the allowed states of the electromagnetic environment, specifically limiting the possible properties of the photons it stores. In particular, it turns out that the single-mode cavities used in many lasers can only store photons that have identical properties, and because photons are bosons it is possible to have many identical particles of light (photons) in the cavity mode.
On the other hand, if an excited atom were sitting in free space and interacted with a photon, then photon emission does not generally produce two photons with identical properties. This is actually an active area of research, i.e. computing what the state after stimulation looks like.
Comment: I'm not sure if you are correct. According to Francis LeBlanc in Introduction to Stellar Astrophysics, "Theory predicts that the photon that is emitted ... travels in the same direction..." p. 133. In space there are usually no cavities, so the emitted photons having the same direction is independent of the presence of cavities I think.


Magento 2 admin users: who did what

Question: I have made a search on google but i didn't found a results.
Is there an extension that track user's actions, so we can know which user create an invoice
Comment: Magento provide the user role and permission for admin.
Comment: If you want to track the admin actions, then you need to implement any third party extension to do it.
Comment: @DhirenVasoya i need to know which admin user who created or edited a giving order/invoice
Comment: You need to do that things using third party extension.
Comment: if you just want to know which user has created an invoice or edited an order I wouldn't recommend installing an extension you can create that functionality
Comment: @MohitRane not invoices only, there's other actions
Comment: @tarekfellah have you tested the extension in my answer? I already tested it, and they even mentioned that it's 100% open source in its description.
Answer: Check this free extension: https://github.com/kiwicommerce/magento2-admin-activity It's recommended to install via composer for it to work correctly.
You'll need to enable the extension and turn on modules as you need (e.g Order) in configuration, after that, you can see the action by going to System > Admin Activity by KiwiCommerce > Admin Activity.
I tested with creating invoice and it is able to do what you need. (magento ce 2.3)
Comment: I see that tacking actions feature is not free
Comment: What do you mean? The screenshot was taken by me and I can track admin actions after install the extension, for example creating invoices. Do you need anything else?
Comment: You changed the link in the answer?
Comment: I delete the old answer and post new one because I was afraid that you wouldn't get the notification. Anyways, check the new one, I tested it and I think it's ok.
Comment: Ok i will test it, and if it's ok i will accept the answer

Magento 2 admin users: who did what


Publication List Not Showing Up In Send Definition

Question: I have two empty Publication Lists in my ET account and want to use them in Send Definitions linked to a Data Extension.  The Publication Lists are not showing up when I try to link a Publication list to a Data Extension in the Send Definition.  Please help.
Comment: Can you tell what kind of account you have (enterprise 2.0, core, etc.?)
Comment: Also, can you tell me if you have EVER seen publication lists show up in UI sends within your account?
Answer: The Publication Lists not showing up was easily solved by calling ExactTarget customer service.  While on the user side, there's no way to tell what was wrong, the Publication Lists were made visible by the tech.  Thanks!


What's the absolute path of an icon declared in a .desktop file?

Question: In a .desktop file you can declare an icon, however it's not clear how this translates to an icon on disk:
Icon=eric

Where on the filesystem can I find this icon?
Related to this question:

How do I add an icon to an app that doesn't have one?
Answer: It's dependent on the icon theme. If the icon is not given by an absolute path, following rules are used to find the icon:

The lookup is done first in the current theme, and then recursively in each of the current theme's parents, and finally in the default theme called "hicolor" (implementations may add more default themes before "hicolor", but "hicolor" must be last). As soon as there is an icon of any size that matches in a theme, the search is stopped.
[...]
The lookup inside a theme is done in three phases. First all the directories are scanned for an exact match, e.g. one where the allowed size of the icon files match what was looked up. Then all the directories are scanned for any icon that matches the name. If that fails we finally fall back on unthemed icons. If we fail to find any icon at all it is up to the application to pick a good fallback, as the correct choice depends on the context.

See the Icon Theme Specification for details.
Comment: Sounds like an "effective icon path" shell script would be useful.  ("ubuntu-which-icon eric" would return /path/to/eric.xpm as used by ubuntu unity desktop)
Comment: You can do that like described here: http://stackoverflow.com/questions/6090241/how-can-i-get-the-full-file-path-of-an-icon-name Not sure there is a simpler way to do it (like an already existing command).
Answer: You can either specify the full path of your png/xpm file or you can install your icon first using xdg.
Example:
xdg-icon-resource install /path/to/your/icon.xpm --size 64

Then you will find it in the below path:
/usr/share/icons/hicolor/64x64/apps#

With this, you will be able to specify the icon name on your .desktop file instead of the full path.


Android NDK requiring absolute include paths in source files

Question: I've been working on some C++ code that compiled on Visual Studio and with MinGW/GCC just fine.
I've been using relative include paths in all of my source files.
#include "../../../stuff.h"

However a huge problem occurs when I compile on Android NDK.
If a header file has a relative include to another header file, it seems like NDK includes it relative to the original file.
So if in "a/b/c/source.cpp"
I do #include "../../header.h"
and inside of "a/header.h" I do
#include "../hello.h"

Instead of including from "hello.h" I think it goes relative to the source.cpp file path.  It would end up looking for it in "a/b/header.h"
This is fixable by me rewriting all includes within the header files to be absolute paths, which is a huge pain.  I'm hoping there's a way to avoid this with NDK.  I'm not really even sure what the problem really is, it could be some common make file command or variable that I need to set.
Answer: You should add
LOCAL_C_INCLUDES :=" YOUR FILES DIRECTORY"

into your android.mk


check if movieclip track has segment

Question: I'd like to remove all tracks in a movieclip that don't have any segment.
Since there's no such operator, I'd like to do it in python but I can't find a way to check if a track has a segment.
I've tried things like tracks['some-track'].has_bundle or average_error but these don't certify it.
Answer: This seems to be a good check:
track = bpy.data.movieclips['some_clip'].tracking.tracks['some_track']
len(track.markers) <= 3

As I understand it, each track has one marker per tracked frame and for some reason, some tracks with no segment can still have up to 3 markers.
There might be a better solution but so far I haven't had an issue with that.

check if movieclip track has segment


How valuable are user journeys?

Question: The last time I mapped out a user journey was during a pitch process. The only reason I did a user journey was to demonstrate to the client how the user would get from point A to B without having to wireframe all the pages to show our solution. I haven't created a user journey since. I'm wondering if I'm underestimating the value of a user journey as a deliverable. Perhaps I should be using them a lot more to demonstrate my thinking?  I'm wondering in what scenarios are user journeys most effective?
Answer: I'm with @Michael Lai, and think they're a great tool to have in your bag for the right case.
What they can help you with:
Understanding the client
As a UI/UX designer you often come into new environments, sometimes very complex ones. User journeys can help you understand processes that might be way out of your field of knowledge, by allowing your client to map out the processes involved in their business.
Determining priorities
They can be incredibly helpful in the process of determining the importance of certain elements in your design. So where it might not show up at all during most of the user journey, it will feature prominently at a later stage.
Example: "Subscribe to our newsletter" might be a footer element throughout your site, but in the middle of your screen after a user has just made a purchase, when they feel best about your product.
Identifying obstacles
User journeys can help you identify obstacles, especially when doing mapping journeys for currently existing sites/applications.
For example, you might find out that after sending a message, the user ends up on a page with nothing but a "thank you" message, instead of going back to his inbox.
Streamlining
Visually mapping out all the major user journeys, you might find that there are some common routes, hubs that could be avoided or maybe even an important journey that's far too complicated.
For example, on forums, moderators might have to look up a user's post history quite often. Adding an icon next to each username that links to an overview of this user's posts, saves them from going through that user's profile page all the time.
Scale and stages
Mapping out all the major journeys can also give you a good idea of the scope of a project, and allow you to divide a project into separate stages.
A few more use-cases:

Sales tool: Properly visualized you can use a user journey to sell a project to a big client.
Test case base: Thoroughly mapping your user's journeys also makes for a solid starting point for writing test cases later on.

I found this article a good read as well.
Answer: As with many of the UX deliverables, it depends on what you believe the best way to communicate the information to your audience is. This is also a debate going around about personas and how useful they are to the design process. In my opinion, I generally try to create some sort of 'user journey' as a way of working out all the different things that a user might come across in different usage scenarios, and where they might encounter pleasant or unpleasant experiences. I then try to make sure that in the interactions we don't let them hit too many unpleasant experiences in a row, or if they do then we need some way to make those experience less unpleasant. As I said before, it is just one of the many tools you can use, and when you come across different clients, projects or UX teams you might find it useful again.
I think you should think of UX assets as something that both you and your clients can benefit from. So don't do it just because they ask for it if you also find it useful for yourself. Often we get too caught up in the wireframes and UI designs that we don't get the chance to step back and look at the bigger picture, and user journeys are great for understanding the entire flow of the user interactions. If you create user journeys for the different personas and use cases, you might come up with some great insights on the user experiences that are important and you should focus on.
The last thing I can think of is that it allows everyone on the team to share an understanding of the product because it provides a perfect complement to personas. There are also many training and marketing assets that can be developed from a well designed user journey map.
Answer: For me, the value has decreased with the popularity of customer experience,  instead I find myself referring to an Experience Map if the project permits.
I find the lines are blurred between User Journey and Experience Maps as they're similar models albeit the latter tends to be more visual.
Adaptive path have a helpful article that explains their approach to journey models and distinguishes an Experience Map from a straight forward journey map (which this thread refers to) and a more archaic service blue print.
If your project allows enough time to gather the research to identify the required insights to create an Experience Map, then consider these five steps inspired by the adaptive path article:
The Lens – Universal principles that apply across all users types.
The Journey Model – Should diagram key steps at the highest-level.
Qualitative Insight – Approaches that have worked for me have been using auxiliary verbs, like 'Does', 'Is', 'Has', which help build a structured research approach to identify what the user needs, motivations  & goals are.
Quantitative Information – Having access to analytics or sending out surveys to subscribers, ideally needs to be captured over time from a sizable sample. Data can be used as facts to back up field studies.
Takeaways – The model should identify outcomes and outstanding things to be decided upon.
Comment: Great points. User journeys and experience maps seem to be the splint and cast of ux mapping; one providing a precise fix, where the other encapsulates the entire issue.
Comment: ... that analogy might've made more sense in my head than it did in a comment, but there it is.
Answer: I have found the journey maps effective in following ways:

Time spent - I normally map timings of varous user steps. This help quantify and identify possible inefficiencies
Repeated task - I did a study of the Washington DC Metro Rail ticket purchase process, and I found that the user had to calculate the amount of money multiple times due to the gap between making selections and depositing money. Journey maps helped me identify such redundancy in the process
Unnecessary/forced tasks - Color coding varios steps of the journey also helps me identify which tasks the user cares about v/s which are required by the system

There are other context specific observations.. but overall I think it's a very effective tool.
Answer: I think, user journey map - is a must have for every project.
User journey map helps you understand not only how user moves from page to page, but how he thinks and what he feels at each point of journey.
When you know what user thinks and what user feels, it is easier to understand his general behaviour, you know how to motivate him to do the action you are calling to.
As a result, you can design better user experience.
Comment: Every project, really? Even if they have tight deadlines with not enough time to gather research required for this kind of deliverable?
Comment: I think he may have overstated his case some - but they are very useful. There are times (for whatever reason) that one cannot flesh one out on paper - but I think one needs to at least think through the process.

How valuable are user journeys?