Two-block system acceleration when applying a force in the $x$ direction

Question:
Two blocks are connected by a light-weight string that passes over a friction-less pulley (a.k.a. Atwood's machine). Block # 1 (called $m_1$) hangs from the edge of a friction-less table. Block # 2 (called $m_2$) stands on the table in a horizontal position. A force is applied in the $m_2$ block towards the positive $x$ direction and away from tension generated by $m_1$. Find a mathematical expression for the acceleration of the system.

I have been working on this kind of problems with no previous difficulty when no force is applied and the system depends only on the masses of the blocks, but as soon as a force is introduced my calculations seems not to work.
When no force is applied:
$$F_x = -T = m_2 a$$
$$F_y = T - m_1 g = m_1a$$
Adding these two equations and solving for the acceleration you get:
$$a = -\frac{m_1}{m_1 + m_2} g $$
Now, I guess if we want to add a force being applied towards the  positive $x$ direction and away from the tension generated by $m_1$:
$$F_x =  F - T = m_2 a - T = m_2 a$$
I know my mistake is when formulating above equation because I can't added to the $F_y$ equation.
How can I get the acceleration expression when a force is involved ?
Comment: I edited the post for readability with math formatting.
Answer: Intuitively, the force will be applied to the total mass of the blocks and cause an acceleration (in addition to the one of gravity) of $\frac F{m_1+m_2}$, so the total acceleration will be $\frac {F-m_1g}{m_1+m_2}$
In your solution you cannot replace $F$ with $m_2a$ because $F$ is not the whole force on $m_2$  It is correct to say $F-T=m_2a$.  You already have $T-m_1g=m_1a$  That gives you two equations in two unknowns, $a,T$


Showing Wien's Displacement Law from Wien's Law

Question: Does anyone know how I would show that $\lambda * T$ is constant, using only Wien's Law? That $\rho(\lambda,T) = 1/\lambda^5*f(\lambda T)$
I differentiated, but all I could get was $\lambda T = 5f(\lambda T)/f'(\lambda T)$, which I don't think means it's necessarily a constant.
Answer: You are essentially there. Wien's law constricts the form of the blackbody spectrum to $$\rho(\lambda,T)=\frac{f(\lambda T)}{\lambda^5},$$ while Wien's displacement law talks about the peak of the spectrum at a given temperature. Thus you are correct that you need to set $\cfrac{\partial \rho}{\partial\lambda}=0$, and that this leads to the equation
$$5 f(\lambda T)=\lambda Tf'(\lambda T).\tag 1$$
This equation will look a lot more friendly if you introduce some more notation. If you set $\mu=\lambda T$, then you can reduce (1) to an equation that's exclusively in $\mu$:
$$5 f(\mu)= \mu f'(\mu).\tag 2$$
Depending on $f$, this may have one,  many, or no solutions, and each solution will mark a peak in the blackbody spectrum. Since Wien's law does not specify $f$, we can't tell yet, but we expect that there will be a unique solution $\mu_0$ to (2). This implies that the peak wavelength $\lambda_\text{peak}$ must obey
$$\lambda_\text{peak}=\frac{\mu_0}T.$$
Note that here $\mu_0$ is a (dimensionful) constant that is determined by the final form of $f$, but we know it can't depend on anything other than fundamental constants.
It's also important to note that this fact is part of a stronger result which is what Wien's law really embodies: a change in temperature can only make a scaling transformation on the corresponding blackbody spectrum. This is beautifully explored in Using Wien's Law to show spectral distruibution function of one temperature represents all temperatures.
Answer: I think you need more info, specifically the form of $f$:
$$ f = a e^{-b/(\lambda T)} $$
(Although not defined by Wien, this form of $f$ is now conventionally understood to be part of Wien's law.)

Update:  With thanks to Emilio Pisanty and Pulsar, I see that a more general formulation is possible:   if $f$ is such that $\rho$ has a maximum at $\lambda_1$ at temperature $T_1$, the scaling argument here shows that the displacement law is valid.  The form I initially used, from Wien's approximation, is only a specific case.
Comment: I'm sorry, I downvoted without comment. The reason is that the form of $f$ is _not_ necessary to derive the result; see my answer.


How do i make my raspberry pi zero w a wifi adapter

Question: So my computer doesn't have wireless so i was wondering, is there a way my pi 0 W can share it's connection with my PC though USB
Comment: Not posting as an answer, but this might help [RPI Zero W AP Shared internet connection over WiFi?](https://www.raspberrypi.org/forums/viewtopic.php?t=228940). It's badly written, but sounds like it's what you want to do... however, i have a feeling that the process doesn't quite match the title. The last link in that article seems to make the Pi Z an access point, which isn't what you are after. As cr1ptal states, just get a wifi USB dongle. It'll certainly be easier and probably more reliable.
Answer: First you have to connect the Raspberry Pi Zero W to your PC with an USB cable and use OTG Gadget ether emulation to get the USB connection emulated as an ethernet connection. Then you should have an interface usb0 that you can use as an ethernet interface.
As you wrote you already have a WiFi uplink connection to your local internet router. So you must also have a WiFi interface, I assume its name is wlan0. Now you can use different solutions to transfer data between usb0 and wlan0. For examples to do it, have a look at: Can a Raspberry Pi Zero W be turned into an USB WiFi dongle to any USB Host like x86 PC or mini-PC?.
Answer: To my knowledge, there is no Wifi sharing on the Pi - it is a more advanced feature, simple computers don't have. A least not as standard Raspbian.
You can google if there is a software for Internet sharing over USB for the Pi, I doubt.
Moreover, it makes little sense to use a Pi for Internet-Wifi sharing. You will be better off with a Wifi device on your PC. If you want things to be simple, go for a USB dongle.
If you have a laptop, Wifi over USB it the best option.
If you have a Desktop, it could be interesting for you to learn how to plug a PCIe Wifi card into your motherboard.


What is this thing inline with my dryer vent?

Question: Just bought a condo with appliances included, and the dryer is underperforming. Went to check the vent hose and saw this:
Comment: When you power up the external unit, does it whirr like there's a blower inside? Have you pulled the elbow off to see if the unit is clogged with lint?
Answer: Acme Miami Model 9460 Dryer Vent Booster
If the vent has a long run to the external opening (up to 100 "effective" feet), this unit has a fan and a pressure sensor to automatically turn on when it senses dryer outflow to help push the exhaust air out.
When properly adjusted per instructions, the fan motor should come on when the dryer is in operation.
Comment: ...and you should replace all that crappy flex hose with solid metal dryer vent.


What can we do to promote meaningful comments on our blog?

Question: I am not so much worried about the inevitable spammers, but I would like to see more comments from people with something worthwhile to say. How can we entice them to talk?
Answer: At the end of your post ask questions like, "What do you think"? or "Did I miss anything"? Ask for opinions and other perspectives. If it is a technical post see if anyone can offer an alternative to your content. Basically, give them something to discuss.
Answer: Something no-one else seems to have picked up on is the quality of the blog postings themselves. Are they about topics anyone cares about? Are they well written, do they provoke a response?
Making posts on other blogs is a very good idea as @Osvaldo states. If you want people to come and post good comments on your blog, you going out and doing the same on other peoples blogs, helping add value to their blog is likely to reap rewards. Either in terms of the blogger themselves returning the favour, or attracting readers of said blog who enjoy your writing style/opinion.
Failing that, run a competition. Offer a 5/10 dollar amazon voucher for the best posting in a month.
Answer: If it's a blog on tech subjects (web/internet etc) you could try removing the rel="nofollow" from link to the website of the commentor and make it loud and clear on your blog that you don't use nofollow for good interesting comments.
I would be more happy to spend time adding nice and interesting comments on blogs that reward me by adding a link to my website rather than on blogs that reward me nothing!
Obviously this means that you need to review properly each single comment before approval and remove the link to the website if the comment is poor/useless/simplicistic like and idious: "Cool article, thanks for sharing!" (and obviously if the comment is just spam)
But reviewing comments should be the normal job of whoever runs a blog, the rel="nofollow" was needed because:

too many bloggers are lazy and approve any type of comments without even reading it
many non-tech guys bloggers do not know that they were giving reputation away (see it as PR) to commentors' websites by providing them a free link to their websites.
some blogs have so many followers that would be impossible to look into each comment, but still the choice of the editor could be to publish only the comment he can read and not all of them.
Answer: You should start by commenting on other blogs, specially in blogs that the author usually comments elsewhere.


Azure powershell - accessing compute emulator

Question: Can you point me to how I can use Get-AzureRole cmdlet on the Compute Emulator? I am trying to find the various values that needs to be passed while calling Set-AzureSubscription and Select-AzureSeubscription (for compute emulator) which seems to be a pre-requisite for Get-AzureRole
Answer: You can run a startup task cmd/powershell and install the cmdlet snap-in shown here:
http://blog.smarx.com/posts/windows-azure-startup-tasks-tips-tricks-and-gotchas
That will install the Cmdlets snap-in and execute your powershell script(s).
Not sure what you are trying to do though, you do have the OnStart() method you can override and add code in programatically inside a web/worker role.  Would be a lot easier to debug.
Answer: Get-AzureRole is maeant to be used agaisnt live azure.  Access to the compute emulator is through the start-azureemulator command or the csrun command line tool.
What information would you actually like to get about the role?


What does Foucault mean by non-discursive practices? Aren't his examples of non-discursive practices actually discursive?

Question: Foucault mentions that art and music are not discursive. How is it so? Foucault had interrogated the 'author' for instance, and largely historicises everything. How could art be autonomous for Foucalt, then?
Comment: Welcome to SE Philosophy! Thanks for your contribution. Please take a quick moment to take the [tour](https://philosophy.stackexchange.com/tour) or find [help](https://philosophy.stackexchange.com/help). You can perform [searches here](https://philosophy.stackexchange.com/search) or seek additional clarification at the [meta site](https://philosophy.meta.stackexchange.com/). Don't forget, when someone has answered your question, you can click on the checkmark to reward the contributor.
Comment: I think he means "discursive" in the Kantian sense, as opposed to intuitive. As in organized by putting pieces together according to a set of rules, like grammar. "Institutions, political events, economic practices and processes" are also "non-discursive practices" according to Foucault.
Comment: "The meaning and purpose of dancing is the dance" - A. Watts
Answer: Foucault is drawing on a tradition most clearly articulated (in my estimation) by American philosopher Susanne Langer's theory of symbolic meaning (Philosophy in a New Key-1942) and philosophy of art (Feeling and Form-1953). Art, unlike science and logic dealing with discursive symbolism, is a "school of life" that "the symbolism furnished by our purely sensory appreciation of forms is a non-discursive symbolism peculiarly well suited to the expression of ideas that defy linguistic "projec- tion."" (PNK,Mentor Book, Sixth Printing, 1964, 75). Aesthetic symbols are "presentational" and rooted in the power of "exhibition." In Feeling and Form she writes, "the emotion in the work is the thought in the work. Just as the content of discourse is the discursive concept, so the content of a work of art is the non-discursive concept of feeling; and it is directly expressed by the form, the appearance before us"(FF, 82). And later in her remarks against "Freud's studies of non-discursive symbolism, and Jung's consequent speculations about "archetypes," [that] were all made in the interest of tracing dream symbols to their sources," she asserts:

Non-discursive form in art has a different office, namely to
articulate knowledge that cannot be rendered discursively because it
concerns experiences that are not formally amenable to the discursive
projection. Such experiences are the rhythms of life, organic,
emotional and mental (the rhythm of attention is an interesting link
among them all), which are not simply periodic, but endlessly complex,
and sensitive to every sort of influence. All together they compose
the dynamic pattern of feeling. It is this pattern that only
non-discursive symbolic forms can present, and that is the point and
purpose of artistic construction. (FF, 240-241)

Non-discursive art forms symbolize the "loose" relations of our feelings and emotions in encountering presentational symbols.
From sculpture, music, dance, poetry, or architecture we are moved by an experience of the "interesting," that speaks a "non-literal language," exemplifying the "laws of the imagination." Discursive symbols are concerned with literal meaning and that is not the purpose or experience we have of art. The "emotional import" of the "exhibitable" and "presentable" can work wonders on us--catharsis, for example, in Aristotle's sense is overly discursive since its focus culminates with "moral" interests. We should not moralize the aesthetic, any more than we may aestheticize morality.
Answer: I've always had a problem with this idea. I tend to side more with CDA (critical discourse analysis) which views practices and actions as reciprocal and inseparable from language.
Obviously I don't need language to breathe, to feel hunger, to feel tired, but for art? Just depends on what theory you agree with I guess. What Kant viewed as the "architectonic" tendency of the mind might be part and parcel or comparable to Chomsky's universal grammar theory, but how would anyone prove this, much less go about determining the criteria for an etiological relationship between language and human biology?
I'm sure there are theories upon theories, and they all more than likely possess their own etiological criteria, as with Susanne Langer's theory.
Comment: Welcome to SE Philosophy! Thanks for your contribution. Please take a quick moment to take the [tour](https://philosophy.stackexchange.com/tour) or find [help](https://philosophy.stackexchange.com/help). You can perform [searches here](https://philosophy.stackexchange.com/search) or seek additional clarification at the [meta site](https://philosophy.meta.stackexchange.com/). Don't forget, when someone has answered your question, you can click on the arrow to reward the contributor and the checkmark to select what you feel is the best answer.
Answer: My background is in science and the arts. For me, discursive and nondiscursive are a complementary pair. Having an experience is nondiscursive, talking about it is discursive. They complement each other. The Alan Watts quote is spot on. Philosophy is discursive, but the thing that philosophy discusses is nondiscursive. Artist John Baldessari said 'Writing helped me understand what I was thinking about'. If thinking provides meaning than we can think with our bodies, through sensation, and our minds, through words. As an artist he thought nondiscursively with his body. His discursive thinking with words complemented this. But at the end of the day describing doing is not the same as doing.


How to attach existing document in sharepoint to a newly created contact

Question: I have an existing document folder that includes summaries of various clients.  I have now added a contact's list and would like to attach the existing documents to the newly created contact as an attachment. I know how to attach a document form a folder on my computer or network. I can not figure out how to attach or link the document that is already saved to my document folder on sharepoint.
Answer: Simplest would be to create a hyperlink column... then link it with the folder having the documents.
But if you want to add it as attachments, you will need to either manually do it by downloading and then attaching.
Or you can write a custom code to achieve this


What is the celebration of Yom Haatzma'ut?

Question: Do those who celebrate Israel's Independence Day as a religious holiday celebrate as commemoration of the original "miracle" that Hashem gave jurisdiction of the land to the Jewish people, regardless of whether or not we may have bungled it, or is it a celebration of the current state of affairs?
Comment: Can't it be both (assuming it hasn't yet been...bungled)?
Comment: @DoubleAA If it is only both assuming that it hasn't been bungled, then that is effectively the former.  I think these are mutually exclusive options.  If you have a third, I'm open to hearing it.
Comment: I don't understand your last comment.
Comment: Very well worth reading the peice in the book called Thinking Aloud featuring the comments made by Rav Soloveitchik regarding Yom Hatzamus. See Here: http://www.matziv.com/pictures/ravsolovetichikyomhaatzmaut.pdf
Comment: @Mefaresh, as R' Soloveitchik did not celebrate Yom Ha'atzma'ut as a particularly special day, he wouldn't have provided an answer to this question.
Comment: @IsaacMoses I'm sorry I'm not sure I understand what you mean
Comment: @Mefaresh, the question at hand is asking about the meaning of Y"H to those who celebrate it. In the chapter you linked to, RYD"S says that he does not celebrate this day in particular, so this chapter is essentially irrelevant to the question at hand.
Comment: @IsaacMoses OK now I understand. That is why I didn't paraphrase RYBS viewpoint as an answer and instead settled for a link in a comment. But thank you for your comment 😄
Answer: According to R' Mordechai Greenberg, head of Yeshivat Kerem B'Yavneh, in his essay "The Significance of Yom Ha'atzmaut", the holiday celebrates a turning point in history, inaugurating a process of redemption that continues to this day.
R' Greenberg cites R' Avraham Yitzchak Kook as explaining that the Midrashic "Three Oaths" apparently preventing the Jews from retaking control of the Land of Israel were not actual promises made by the Jews but arrangements by Divine Providence of circumstances in a way that caused the Jews to behave as if bound by an oath. Thus, for most of the past two millenia, circumstances such as the desolation of the land, its rule by nations who were against Jewish rule, and a general sense of fear in the dispersed Jewish people made it impossible for Jews to return en masse to the Land.
Then, God permitted more and more Jews to start moving back, permitted the Land to start blooming again, and arranged the geopolitical map so that the nations of the world would permit Jewish sovereignty in the Land. The climax of this shift was the Jews' decision in 1948 to declare the establishment of the State of Israel, asserting sovereignty over the Land. "With this move the "fear" was removed, despite the fact that on that very same day the war broke out."
Thus:

The significance of Yom Ha'atzmaut is that we crossed the barrier between galut1 to geulah2; we have passed the turning point. Now we are the owners of the land, and we have the possibility of establishing the kind of government that G-d wants, on that links religion with the State. Although the road it still long, we have passed the barrier and are now on the other side. Now we have the free choice to do as we will. There is much work to do, but the land is ours, and the nations recognize this.

R' Greenberg makes it clear that although the geulah process is in motion, it is not complete. However, the trend of this process has continued in a dramatically positive direction. The number of Jews in Israel has exploded: When the Vilna Gaon was encouraging his students to move to Israel in the 1700s, there were a few thousand Jews already there; now there are millions. In the early years of the State of Israel, "people were embarrassed to wear a kipah"; now, the country is full of countless yeshivot.

"This is the day Hashem has made; let us rejoice and be glad on it!" (Tehillim 118:24)

1. Exile
2. Redemption


PCA and EFA on bond returns using Stata

Question: I've got a datafile which has bond returns (30, 20, 10, 5, 1 year) and time. The bond variables are returns on the different time bonds. I need to perform PCA and EFA on the data. I tried using time as one of the factors but it returns Heywood case as the uniqueness is 0. Should I disregard time? What i don't understand is if I disregard it then my analysis will have no practical interpretation. Already I've two principal components using PCA and I'm unable to interpret them. Please help me in understanding the practical implications of the data.
Thanks in advance for your time and kind consideration...
P.S. I'm working in Stata 12.1. Solutions in SPSS will be helpful too but I won't be able to perform them as my SPSS 20 does not accept datafile from this version of stata.
Answer: Exclude time and re-run it. For each eigenvector that you're using to build the factors, plot it to get a better sense of what they mean. There is a significant literature on a PCA of bond yields (rather than bond returns since bond returns are driven by yield curve dynamics), which normally describes the first component as corresponding to the interest rate level, the second corresponding to a shift in the slope of the yield curve, and the third corresponding to a twist in the yield curve. My guess is that the factors constructed from the returns correspond to the impact on bond returns from those changes.
Answer: I agree with you regarding the dependence of bond returns on interest rates and yield curve but I think these components are not enough to answer the question as the PCA and EFA tend to give different analyses so to base both the answers on the same parameters will be a bit faulty. Other factors that might influence it are inflation, credit rating, portfolio diversification methodology etc.
Courtesy- Copeland, Weston and Shastri's "Financial theory and Corporate policy"

PCA and EFA on bond returns using Stata


Is dofollow linking from a long list of items allowed by Google?

Question: I've just finished writing a list of 190 items. I'd like to make some links of the list dofollow, but I don't know if Google still allows dofollow links and how many per article.
Answer: I have read your question several times and am confused.
Make links. If you do not trust who you are linking to, do not make a link or at least make it nofollow. Use nofollow if you do not know if you trust who you are linking to out of safety. If you trust who you are linking to then the links should be follow. Generally, it is that simple. Link to quality sites only if you are making links manually. If they are automated, then they should be nofollow.
For internal links, then the decision becomes simpler. If you want search engines to follow the link then it should be follow. If not, then nofollow. Simple.
Google is not the boss and does not run the Internet. Google has to follow the rules just like the rest of us. This means that as long as you follow the rules of the road and do not try and abuse the search engines, all should be fine.
Answer:
and I'd like to make some links of the list dofollow.

That's the default for links, and to achieve that, you can have a code fragment like this:

Here's the list

Item 1

Item 2

Item 190

Now if you want a link to not be followed, then you need to add rel=nofollow. Here's a code listing samples of links that search engines will not crawl:

Here's the bad list

Item 122

Item 12

Item 160

Google will not attempt to consider the links for indexing that are marked as nofollow unless an external site makes reference to them.
Here's googles info on nofollow: https://support.google.com/webmasters/answer/96569?hl=en

but I don't know if Google still allows dofollow backlinks and how many per article.

You will have a backlink if an external website has an active link to your site. For example:
If your site is example.com and the external site is exampleexternal.com, and exampleextenal.com has the following code fragment that is currently processed by a user's browser:

Here's info on how to run robots. Click here to find out

then you have a backlink. If you're trying to control the follow/nofollow status of such links, you'll have a very hard time doing so because if your site is extremely popular, you may have several backlinks (example: your url could be listed on 50,000 other sites).
Additionally, asking people that link to your site to not follow it (via rel="nofollow") is bad since valuable "link juice" will not be passed on to your site and therefore you might not rank high in search engines.
If on the other hand, your site is the worst in the world to the point where all people will see are pop-ups on each page with no valuable content then by all means, ask all the people linking to your site to label the links to your site as nofollow.
I did ramble on a-lot, but please see https://support.google.com/webmasters/answer/96569?hl=en and watch google's videos so you understand what backlinks and "nofollow" are.


UK Visa Bronze Premium Service

Question: How many days on average does the Bronze Premium Service take? Does it take more than 7 working days? When I pay for the service, can I just walk in?
Comment: Just walk in where?
Comment: https://www.vfsglobal.co.uk/usa/user_pay_services.html
Answer: The priority visa service for those in the US to apply for a UK visa is through VFS Global
Note that the Bronze Premium Service indicates Standard Processing: that means within the VHS offices; an appointment is not required but there is an additional fee for walk-ins, as well as additional fees for courier services to expedite turn-around times.

Bronze Premium Service Package
Price: USD 235 (+ additional fee of USD 50 if applying without appointment)
This service package is exclusively available at the VFS Premium Application Centres in Atlanta, Boston, Chicago, Houston, Los Angeles, Miami, San Francisco, Seattle, and Washington DC. For more details on the services included with this package, please click here to visit our Premium Application Centre page.
This service is available Monday-Friday, either with or without a pre-scheduled appointment (additional $50 fee applies if you do not have a pre-scheduled appointment)

The UKVI description:

This is an optional service where you can pay an extra fee to fast track your application and have your visa application processed ahead of non priority applications.
The super priority and premium visa services enable customers to receive a decision on their application within 24 hours.

UK Visa Bronze Premium Service


Is the foreign key automatically indexed in MySQL?

Question: Do we need to create an index for a foreign key while creating the table in InnoDB of MySQL?
Comment: This question was answered on: https://stackoverflow.com/questions/304317/does-mysql-index-foreign-key-columns-automatically
Answer: An index is generated for each FOREIGN KEY definition unless there is already an obviously adequate index in existence.
The index is needed to prevent a full table scan to verify that a row being inserted won't have a key linking to nowhere.
For an index to be useable, the leftmost column(s) must match the FK definition.  Selectivity is irrelevant.
Comment: @bbaird - Create two tables.  Create a FK on one table.  Then do `SHOW CREATE TABLE` for both tables.  To further test, you could add a thousand rows to each table, and do `SHOW TABLE STATUS` -- the one with the index should show growth in "Index_length".  (I'm not a fan of FKs, or else I would do this exercise.)
Comment: I guess this brings up another question - does he mean an index on the table with the FK constraint, or the table referenced?  If the latter I'll go ahead and delete my answer.
Comment: The question is unclear, not your answer.
Answer: Foreign keys are not automatically indexed in MySQL*.  If you should index, the answer is always: "It depends."
If you are going to primarily search based on that column, it's more than likely it should form the first part of that table's primary key and there would be no need for an additional index.
If the values of that column are not particularly selective, adding an index won't improve performance as a table scan will still be required.
So as always, test and validate.
*This depends on where you are expecting the foreign key to be created, on the table with the FK constraint or the table referenced by that constraint.  Most RDBMs follow the relational model, you can only create a FK reference to a primary or candidate key in another table (in practical terms an index would already exist).  MySQL does not have this restriction and will automatically create an index on the referenced column (or use an existing index if the column(s) referenced comprise(s) the start of that index).
Comment: Foreign keys are automatically indexed in MySQL: https://stackoverflow.com/questions/304317/does-mysql-index-foreign-key-columns-automatically


Why don't Bitcoin mining operations grow exponentially?

Question: I went to Bitmain's home website one day when I saw the S21 Hyd.  I ran calculations on that and found out it could pay for itself every 4 months (after power bills).  So, how come Bitcoin mining operations don't double over a specific time period e.g. every 4 months?  Assuming you have a good paying job, and you just want to get a lot of miners until a point, after only three years, you have 1023 miners, making 25,000 dollars per day.  And then in another 3 months this turns to 50k, and so on.  What controls the growth of Bitcoin mining operations?
Answer: That is exactly what is happening: Bitcoin's hashrate is growing exponentially, except that the growth is limited by the speed at which new hardware is produced and deployed. (A line with a positive slope in a logarithmic chart indicates exponential growth.)
via bitcoin.sipa.be
The network's hashrate has increased by 37% since May with 11 adjustments increasing difficulty and only three adjustments reducing difficulty.

via btc.com
As long as mining is profitable, miners invest in additional hashrate to corner a larger share of the entire mining reward. Hardware manufacturers come out with more efficient models that replaces prior models. Miners with less profitable operations go out of business or shut down their less profitable hardware.
I would be a naïve miscalculation to expect that your hardware will pay for itself in four months, though. Just as you are deploying your new hardware, so will your competitors. Your profitability will decrease significantly in the coming four months compared to today's network outlook, and you will need to adjust your expectations accordingly.
Answer:
I ran calculations on that and found out it could pay for itself every 4 months (after power bills).

I'm rather skeptical of that. My first Google result was here. As of 27 Nov 2023, it's listed as having a gross yearly income of $9,444.62, electricity costs of $5,557.25 at 0.12/kWh, and net of $3,887.37. The lowest price listed is $5,368.73, for 497 days or 16.5 months to pay back.
And this is based on spot prices. Just because the numbers at the moment work out to be profitable, doesn't mean that they will be in the long run. And 16.5 months is a somewhat long run to be depending on profit/expense numbers to be holding steady. And this website it's not available yet, so if it really is profitable, then once it does become available, the hash rate, and hence the difficulty will spike upwards. Furthermore, I suspect that there are costs that aren't being factored in. The nature of the difficulty mechanism means that absent a breakdown in basic economics, the net risk-adjusted profit is driven towards zero.


How do you create an optimized walk list given longitude and latitude coordinates?

Question: I am working on a political campaign where dozens of volunteers will be conducting door-knocking promotions over the next few weeks. Given a list with names, addresses and long/lat coordinates, what algorithms can be used to create an optimized walk list.
Comment: [Cross posting](http://stats.stackexchange.com/q/104868) seems in poor form. Why is this tagged SQL?
Comment: Solve the (approximate) travelling salesman problem (TSP)...
Comment: Beyond lat-long, what's the geography like? A gridded city? An almost tree-shaped suburb with smaller roads into cul-de-sacs? Has a MASSIVE influence.
Answer: As Steve Kallestad has said, this is a TSP problem, and there are wonderful free solvers to find approximate solutions.
It may be too much work for what you are looking for, but you may try use one of those solvers in combination with the Google Maps API, to find real walking distances beetwen your coordinates:
https://developers.google.com/maps/documentation/directions/#DirectionsRequests
(I have never used this API, so I don't know how easy or effective it would be)
Answer: People see something closely related to the Travelling Salesman Problem and think that it can't be solved.
A good deal of work has been done on this topic and not all of it indicates that a solution is not available.  Depending on the parameters and the desired solution, you may be able to find something that will work.
You may want to give a look at the OpenOpt python library.
Another resource to look at would  be the TSP Solver and Generator.
If you are using R, there is a TSP package available.
Actually implementing a solution to your problem is a little too much to cover here, but this should provide a good starting point.  Within these packages and at the documentation within the links that I provided for you, you will find that there are a fairly wide variety of algorithmic strategies available.  You have a small geographic region and a small set of "salespeople", so the computational power needed to calculate a strategy within a reasonable time frame should be available on your desktop.
In practical terms, you don't need to find the absolutely most optimal strategy.  You just need a very good one.  Pick a TSP package that looks the least overwhelming and give it a go.
Comment: I agree with Steve K that the key to tackling this is to aim for approximately optimal or just good route strategies. Many times the difference between "best" and "good enough" isn't much.
Comment: Of course the optimum can be found, it might just take longer than the age of the universe to iterate over all the possibilities. Your answer fails to mention this.
Answer: As @SpacedMan has noted in a comment, the street layout will have a massive influence on the optimization of the walk list.  You have included only "latitude and longitude" in your question's title; but solving that problem does not lead to a "walk list", but to a "as-the-crow-flies list".
Looking at your street layout as a graph, with edge weights describing distances, and trying to find the shortest traversal between all required addresses, will lead you to think of your problem as a "Shortest path problem". Dijkstra's algorithm is the best known solution (there are others); in its naive implementation it converges in O(n2), which may be acceptable if your lists of addresses are moderate in size.  Otherwise, look for optimized versions in the above links.
As for libraries and resources to start tackling the problem, since you do not specify languages or platforms, let me point to the compilation of routing solvers in the Open Street Maps wiki and in general their frameworks and libraries page.
Answer: Here's a crazy idea: talk to the volunteers who know the neighborhoods and who have done door-to-door work before.  Get their advice and ideas.  They will probably have insights that no algorithm will produce, and those modifications will be valuable to any computer-generated route list.  One example: Avoiding crossing heavily traveled streets with slow lights or no lights.  Another example: pairs of volunteers working on opposite sides of the same street will feel safer than a volunteer working that street alone.


Algorithm to compose identity from a set of permutations

Question: Given a subset P of all the possible permutations of a fixed set of elements, is there a non-exponential or optimized algorithm for computing the smallest composition of P that yields the identity permutation?
Comment: This is closely related to the [word problem](http://en.wikipedia.org/wiki/Word_problem_for_groups) for finite groups, except that you're not restricting your set of permutations to be a group and you're looking for the shortest word equivalent to the identity. (Note that there are infinite groups with finite descriptions whose word problem is undecidable but I guess you're only dealing with finite sets of permutations.)
Answer: Assuming that "smallest composition" means smallest number of permutations used in the composition, then the NP-complete Pancake Flipping Problem is a special case of your problem.
Answer: $\mathcal{PRODUCT-PARTITION}$ is strongly $\mathrm{NP}$-hard as shown by Ng et al.
If you allow the representation of a permutation over $\mathbb{Z}^{*}_p$ to be almost-unary: except for one permutation, every other is given by the multiplier $a\in\mathbb{Z}^{*}_p$ in unary. And lastly, $p$ itself is given in binary. The only one other permutation is given by its multiplier $A\in\mathbb{Z}^{*}_p$ in binary, then your problem is $\mathrm{NP}$-hard.
Now, we show that $\mathcal{PRODUCT-PARTITION}$ can be reduced to our problem $\mathcal{PERM-IDENTITY}$.
Theorem: $\mathcal{PRODUCT-PARTITION}\leq_p\mathcal{PERM-IDENTITY}$
Proof: Given an instance $\{a_1,\:a_2,\:\dots,\: a_n\}$ of $\mathcal{PRODUCT-PARTITION}$, we show how to construct an instance of $\mathcal{PERM-IDENTITY}$.
Since all the $a_i$'s are given in unary (thanks to strong hardness), we are able to, in polynomial time, construct a prime $q$ (in unary) that is bigger any prime divisor of all the $a_i$'s. By $\Pi$, we denote the product of all the $a_i$'s. We can assume $\Pi$ to be a square number and that no $a_i$ is equal to $1$. Taking the modulus to be some big enough $k$th power of $q$ such that $p=q^k>\Pi$. All the following is done modulo $p$.
Now, we transform each $a_i$ to a permutation $\pi_i$ over $\{0, 1, \dots, p-1\}$ that describes the operation of multiplying with $a_i$ over $\mathbb{Z}_p$.
Now, the produced instance of our problem is $\{\pi_1, \:\pi_2, \:\dots, \:\pi_n,\:sqrt(\Pi)^{-1}\}$ (modulo $p$) (actually, the last one should be the corresponding permutation of $sqrt(\Pi)^{-1}$, but abusing the notation a little bit may not be quite harmful here).
If the given $\mathcal{PRODUCT-PARTITION}$ instance is a $\mathrm{YES}$ instance, then by taking the set of permutations corresponding to the set of numbers in the solution to the $\mathcal{PRODUCT-PARTITION}$ instance and $sqrt(\Pi)^{-1}$, we can easily see that the produced instance is a $\mathrm{YES}$ instance of $\mathcal{PERM-IDENTITY}$.
Conversely, if the produced instance of $\mathcal{PERM-IDENTITY}$ is a $\mathrm{YES}$ instance, then note that the product of any subset of the $n$ permutations corresponding to $a_i$ is quite small to $p$ (in the magnitude of their corresponding natural numbers). So, in order for the product to be $1\:\mathrm{mod}\:p$, the last permutation corresponding to $sqrt(\Pi)^{-1}$ (which is somehow bigger than the $a_i$'s) must be taken. Then, the set of $a_i$'s corresponding to the rest of the solution to the produced instance of $\mathcal{PERM-IDENTITY}$ problem must multiply up to exactly $sqrt(\Pi)$ (which is somehow similar in magnitude to the $a_i$'s). Thus, the given $\mathcal{PRODUCT-PARTITION}$ instance is a $\mathrm{YES}$ instance.$\square$
Comment: What is *PRODUCT-PARTITION*?
Comment: Also, it's $\mathcal{REALLY\ HARD}$ to read all those script-font problem names. `\textsc{...}` (small caps) is much more legible.


Increase Flash script execution time (FlasCC)

Question: I am using FlasCC. My app works fine but takes long to load. I get a message that it has exceeded 15 seconds (Error #1502). How can I make this time longer?
Answer: If you use mxmlc for compiling swf, you can use option 'max-execution-time'
Answer: The short answer is that you can't increase the max timeout.
The long answer is that you can work around it:

If you're doing a lot of computation in your FlasCC code

You could break up your execution into smaller "chunks" that get called asynchronously.
You could use pthreads within your FlasCC C code (FP 11.5+)

You could put your FlasCC instance into a Worker thread (FP 11.4+)
Answer: You can increase the max timeout for your local testing purposes. Check out how to set the ScriptStuckTimeout variable in mms.cfg.
Note that if your program exceeds even the extended timeout that you specify, Flash player will still show a message saying "exceeded 15 seconds", even though in fact it was waiting for longer.


Bott projection as $K_1$ class

Question: Consider the Bott projection (described in Exercise 5.I of Wegge-Olsen's book $K$-theory and $C^*$-algebras) given by $b(z)=\frac{1}{1+|z|^2}\begin{pmatrix} 1 & \bar{z} \\ z & |z|^2 \end{pmatrix}$. Regarded as an element in $C_0(\mathbb{R}^2,M_2(\mathbb{C}))$ via $z=x+iy$, $b$ represents a class in $K_0(C_0(\mathbb{R}^2))$. Under the suspension isomorphism $K_1(A)\cong K_0(SA)$ for any $C^*$-algebra $A$, which tells us in particular $K_0(C_0(\mathbb{R}^2))\cong K_1(C(S^1))$, what is the class corresponding to $b$ in $K_1(C(S^1))$? I think it should be the class of the function $z\mapsto\bar{z}$ but I cannot prove it.
Answer: I don't know if it will be helpful for you, but I'll try:
I'm not sure how you see the isomorphism between $K_0(C_0(\Bbb{R}^2))$ and $K_1(C(S^1))$ by the suspension isomorphism.
However, consider the short-exact sequence $0\to C_0(\Bbb{R}^2)\to C(\Bbb{D})\to C(S^1)\to 0$ where the maps are inclusion $\phi$ and restriction $\psi$ and you identify $\Bbb{R}^2$ with $\Bbb{D}-S^1$.
It induces a six-term exact sequence (couldn't write it here, but you know what I mean). We have: $K_1(C(S^1))\cong K_0(C(S^1)) \cong K_0(C(\Bbb{D})\cong \Bbb{Z}$ ; $K_1(C(\Bbb{D}))=0$  ;and the generator of $K_0(C(S^1))$ is $[1]_0$ . Conclude that $K_0(\psi)$ is an isomorphism (because it maps generator to generator) and thus $\delta: K_1(C(S^1)) \to K_0(C_0(\Bbb{R}^2))$ , the index map, is an isomorphism!
Now, you can check what $\delta$ does to the generator of $K_1(C(S^1))$, i.e. $[f(z)=z]_1$, to determine $\delta$ in general and to find the generator of $K_0(C_0(\Bbb{R}^2))$. After some calculations I have come to a conclusion that $\delta([z]_1)=\begin{bmatrix}|z|^2&z(1-|z|^2)^{1/2}\\ \bar{z}(1-|z|^2)^{1/2}&1-|z|^2\end{bmatrix}_0-\begin{bmatrix}1&0\\0&0\end{bmatrix}_0 \in K_0(C_0(\Bbb{R}^2))$
My writing is a little bit confusing, I mean the equivalence classes of the matrices. $[\bar{z}]_1=-[z]_1$ in $K_1(C(S^1))$, so you can easily see which element of $K_0(C_0(\Bbb{R}^2))$ mapped to $[\bar{z}]_1$.
See if it helps, I'm not familiar yet with the Bott projection.

Bott projection as $K_1$ class


Difference between database vs user vs schema

Question: What is the difference (if any) between a database, a user, and a schema?
Answer: In Oracle, users and schemas are essentially the same thing. You can consider that a user is the account you use to connect to a database, and a schema is the set of objects (tables, views, etc.) that belong to that account.
See this post on Stack Overflow: difference between a User and a Schema in Oracle? for more details and extra links.
You create users with the create user statement. This also "creates" the schema (initially empty) - you cannot create a schema as such, it is tied to the user. Once the user is created, an administrator can grant privileges to the user, which will enable it to create tables, execute select queries, insert, and everything else.
The database is the thing that contains all the users you've created, and their data (and a bunch of predefined system users, tables, views, etc. that make the whole thing work). You should look at the Oracle Database Architecture documentation in the Concepts Guide (actually, that whole page is worth a read - there's a section about users and schemas higher up in that page) to get an introduction to what a database is, and what a database instance is - two important concepts.
You can create a database with the create database statement, once you've installed the Oracle software stack. But using dbca (database creation assistant) is easier to get started.
Answer: To begin to understand the difference I think we must start saying that this nomenclature was a mistake from Oracle.
I assume that if you have an ERP called TRITON you want your database to be named TRITON, or if my company it's called JENNY EXPORT I might decide my database to be called JENNYEXP or something like that, no need for any user with the same name.
In Oracle, you need to create a USER before creating the tables and weird enough this collection of TABLES is called SCHEMA.
Then you might create the actual users and grant proper permissions to work with such database as TRITON as per this example, by the way, if you connect thru SQL DEVELOPER you must NAME A CONNECTION.
I know I sound kind of frustrated but it makes more sense to me the MS SQL SERVER naming convention and I could add that I worked with Oracle earlier than SQL SERVER.
Comment: Prior to Microsoft SQL Server 2005, the behavior in SQL Server was the same. Your Oracle experience that predates SQL Server may explain your perception here. User and schema were equivalent prior to 2005 in MSSQL. I hope this helps.
Answer: Data Base.
The Data base is a collection of data,where actually data stored.
Its a physical Memory Component Connected to a Computer Installed with DBMS Software to manipulate the data in that Memory component,the computer installed with dbms software is called Server or Database Server.The both Server(Computer) and Database(memory component) are different but Most of times refered as Same based on situation.
USER and SCHEMA
The both words, user and schema, are interchangeable, that's why most people get confused on these words.
User
User is a account to connect database(Server).
we can create user by using CREATE USER  IDENTIFIED BY .
Schema
Actually Oracle Database contain logical and physical structure to process  the data. The Schema Also Logical Structure to process the data in Database(Memory Component).
It's created automatically by Oracle when user created. It contains all objects created by the user associated to that schema.For Example if i created a user with name santhosh then oracle creates a schema called santhosh, Oracle stores all objects created by user santhosh in the santhosh schema.
We can create schema by using the CREATE SCHEMA statement, but Oracle automatically creates a user for that schema.
We can drop the schema by using the DROP SCHEMA <name> RESTRICT statement, but it can not delete schema contained objects, so to drop the schema, it must be empty. here the restrict word forces you to specify that schema with out objects.
If we try to drop a user containing objects in his schema we must specify CASCADE word because Oracle does not allow you to delete a user containing objects.
DROP USER <name> CASCADE
so Oracle deletes the objects in schema and then it drops the user automatically, Objects referred to these schema objects from other schema like views and private synonyms goes to invalid state.
Comment: Users and schemas may be interchangeable in Oracle databases - but NOT in other rdbms like MS SQL Server.
Answer: According to the way the terminology is sometimes used, a USER and a SCHEMA are somewhat similar. But there is also a major difference. A USER can be called a SCHEMA if the "USER" owns any object, otherwise it will only remain a "USER". Once the USER owns at least one object then by virtue of all of your definitions above... the USER can now be called a SCHEMA.
Comment: I think what you're pointing out here is that the term 'SCHEMA' is multi-faceted.  It is a namespace for database objects on one hand.  Also, in Oracle (and others?) but not PostgreSQL, it is a database object namespace containing exactly the objects created by the user sharing the name of the schema.  From another perspective, it is the relationships and structure of objects in a database, often ignoring both ownership and namespace.
Answer: I would add that the statements above apply to Oracle's implementation but other databases including SQL Server and PostgreSQL use schema as just a namespace, i.e. a way to group objects.  For example, the Staging schema could group all object used in staging data, the Accounting schema could group all objects related to Accounting.
Answer: From my point of view some confusion regarding the terms "database", "schema" and "user" also comes from the differences between Microsoft SQL Server and Oracle.

"Inside" Oracle the difference between schema and user/login is not to be understood without further explanation. "User" is an account to log in to the database (usually without own objects like tables or views), it can be called "schema" if it "owns" objects. But this has already been explained above.
In MS SQL Server, the term "database" describes an object that is most comparable with "schema" in Oracle.  Both are a combination of objects that are "qualified" by "database/schemaowner.object", note the "." as a separator between the ""combination"" and the actual object.

BTW: Note also the different meaning of "instance" in Microsoft SQL Server and Oracle.
Comment: I believe you are confused.  In SQL Server, the hierarchy is Instance > Database > Schema > Table.  In Oracle, "instance" is not a collection of databases, but below that the schema is the same: Database > Schema > Table.


Solder very close together contacts

Question: I have contacts that are so close together I'm either bridging them, or melting the neighboring one. What am I missing?
Comment: How big is your soldering iron tip? What about the diameter of the solder?
Comment: Are you using any flux?
Comment: http://electronics.stackexchange.com/questions/tagged/soldering
Comment: Looks like I need to pick up some flux and keep practicing. I did manage to get power and 3 status pins soldered and got the status wired up to LEDs to confirm I didn't destroy the component. Thanks all.
Answer: Flux.  You're missing flux, and lots of experience.  I regularly solder with a tip that easily covers 10 or more pins at a time, but by carefully controlling how much solder is on the tip and using lots of flux I can get perfect solder joints.  When soldering a TQFP or TSSOP package here's what I do:

If the pads on the PCB are not super flat, then use some solder braid and suck up some of the solder on the pads to make them flat.
Put the part on the PCB and carefully align the part.  Don't rush this step, because if you mess this one up then nothing else will work correctly.
Put a drop or two of liquid flux on the part.  I use water soluble liquid flux, but others are successful with other liquid fluxes.
Clean the iron tip and put a little bit of solder on it.
Carefully touch a corner pad (NOT the pin itself) and let the solder wick up and tack down that pin.
Repeat 4 & 5 for 2 to 4 corner pins.  Reapply flux as required.
Put some solder on the tip and run the tip down one complete side of the chip.  Ideally you won't have bridges, but if the last 2 or 3 pins are bridged then you did good.  Ignore the bridges.
Add more flux (you can never have too much flux).
Repeat 7 and 8 for all sides of the chip.
Add flux, clean the tip on the sponge, and touch the tip to the bridge.  Solder should stick to the tip.  Repeat until bridges are gone.
In bad cases, careful use of a solder wick can help.  But be careful because it is easy to bend the pins and then you're, um, hosed.
Clean the flux off.  Some flux can be conductive, like the water soluble flux, so make sure it's clean (and dry) before powering up.

I should mention that my soldering iron has a straight, but angled tip.  It's often called a chisel tip.  This tip makes it easy to do everything from 1206's, 0402's, TQFP's, TSSOP's, etc.  It just doesn't work for BGA's, QFN's, and some of the weirder things.
Comment: thanks a ton. these tips are easy to start using and made life so much easier.
Comment: +1 - A dished (MiniWave) tip can also help with this technique.
Answer: Use less solder, lots of flux, and practice.
Consider pre-soldering the pads on the PCB. Cover the area with some flux, and use your iron to push a bead of solder over the necessary pads. It is surprising (or was to me) how little solder was necessary.  After the small amount of extra solder you have added to the pads have cooled, add a little more flux, place your device, and use just your iron to attach.
It takes practice, and it seems everybody prefers something a little different.  I learned by watching and reading some of the superb sparkfun tutorials and other random youtube videos.  I think watching other people in action is the best way to learn.
Answer: To solder an item like that you need to:

Use flux
Make sure your iron is clean and tinned
Have your soldering iron hot enough that your solder will melt as soon as you touch it to it
Use a solder diameter that is rather narrow
Heat up your trace and pad and then slide the solder into it

I think I have everything covered, am I missing anything?
Answer: Besides flux (to prevent a short in the first place): solder wick! (to remove excess solder after the fact)
Answer: You can try to wrap some steel wire around the shaft of your iron, and use that as a makeshift extension. Clamping a sewing needle to the shaft worked for me, too.
You need lots of flux, less solder.
If even that fails, and you need to solder some really tricky stuff like BGAs, I have some other tricks in the box, like stove-soldering, etc. Those tricks are likely to break your hardware, so I'm not gonna advice them before suggesting the needle-trick.
Comment: A skinny tip is actually harder to solder with.  About 2mm chisel is as fine as I would recommend.

Solder very close together contacts


Novice level - do DataURLs automatically save to a specific location?

Question: I am a complete novice, doing some work on a HTML5 drag and drop game. I am looking at coding tutorials which will save an image of the game when the user presses a button. The canvas image is saved as a DataURL. I kind of understand what this means. But my questions are: where does the image save to (as you don't seem to need to specify a location) & will an image saved to that location always have a unique URL (i.e. images saved from different games wont overwrite).
Answer: The Data Url is just a Base64 encoded string which represents an image. I'm not sure about your exact implementation, but you almost always would have to save that string at some persistent location. Try the Local Storage for instance if you want to save the image on the user's machine and not on a server.
Otherwise, you can always POST the Base64 encoded string via Ajax to your own server and save it in a file or database.


Propagate Public Folder Permissions on Exchange 2016

Question: I have Exchange 2016 with public folders in a public folder mailbox (ie: NOT legacy public folders) and I am trying to take the permissions from a parent folder and propagate them to all the child folders.  I need all the child folder permissions removed and just inherit the ones from the parent.  The "Apply changes to this public folder and all its subfolders." does not seem to do anything to the pre-existing permissions on the child folders.
Answer: I wouldn't expect it to.
You will need to run a command to remove the permissions - all the other commands do is add the permissions.
The command you need is remove-publicfolderclientpermission and is documented here:
https://technet.microsoft.com/en-us/library/bb124573(v=exchg.160).aspx
Comment: So there is no way to, like NTFS permissions, tell a sub-folder to just inherit its permissions from the parent.  There are a lot of sub-folders with a lot of users.  I will need to run a lot of separate remove-publicfolderclientpermission commands at this rate.
Comment: Only at point of creation. So if you create a folder, then set permissions on the folder, then create sub folders - the sub folders inherit the permissions.


How do Metropolitan Area Networks (MAN) interconnect?

Question: If an organization in a city (perhaps New York) has multiple offices within that city, how would they interconnect their LANs? I already understand that they will connect to an ISP, but my question is: Does a MAN travel across the internet to connect their networks where they have routers running eBGP?
Answer: There are quite a few possibilites.

They can get a dark fiber from an ISP and interconnect their network equipment, in this case they "own" the whole network and they are fully responsible for routing between different offices.
They also can get plain Internet access in each location and build a secure overlay network, like DMVPN. The branch offices of course can run BGP with ISPs.
Another option is to get some sort of L2/L3 VPN from an ISP. In case of L2VPN the offices will be directly connected in L2. In case of L3 VPN, the company's equipment usually will have to run some sort of routing protocol with ISP, who will "own" company's core network.
Comment: Dark fiber is a possible solution, but a really expensive way to go unless you require access to the glass...
Answer: Metropolitan Area Networks (MAN)  connectivity is wide range of connectivity act between LAN and WAN networks
To connect multiple offices of same organization within city , there are possible options

Can connect with point to point lease lines and Configure static routing among this site's  between two offices

Built IPsec Site to  Site VPN tunnels between two offices and Configure routing on tunnel to pass interesting traffic among tunnel .
Answer: From techopedia - It does establish it connection through an ISP so it travels the internet
Metropolitan Area Network (MAN)
Definition - What does Metropolitan Area Network (MAN) mean?
A metropolitan area network (MAN) is similar to a local area network (LAN) but spans an entire city or campus. MANs are formed by connecting multiple LANs. Thus, MANs are larger than LANs but smaller than wide area networks (WAN).
MANs are extremely efficient and provide fast communication via high-speed carriers, such as fiber optic cables.
Comment: FYI, a MAN is never considered "the internet".  Typically MAN services themselves are all layer1 or layer2, transported on [Ethernet over SONET](http://en.wikipedia.org/wiki/Ethernet_over_SDH) or some other [SONET](http://en.wikipedia.org/wiki/Synchronous_optical_networking) payload; although there is no one way to build metro access... this happens to be the one that I've seen the most.  Sometimes you see a MAN circuit terminated to an ISP for access, but that's not the same as a MAN traveling through the internet.
Comment: There are packet-switched technologies that don't connect to the internet, which is what Mike is talking about with EoS and SONET.  If you're using a SONET connection to provide a reliable OC connection to another site, it doesn't have the ability to talk to anything other than the intended, pre-provisioned destination. So no, it isn't on 'the internet', it just happens to be traversing an ISP that also provides internet access.
Comment: It is not the internet, but it goes through an ISP to interconnect LANs. And as far as I know the ISP is in the "internet" and it's a WAN. How would you then physically connect multiple LANs if it does not connect to the "internet" through an ISP.


induction of magnetic field

Question: I am interested to know about if a charge particle is at rest and the body is rotating with constant angular velocity but does not changing its position,only its symmetry changes,but the body is axially symeetric, then magnetic field will induced or not?
Because we know that $v=r\times w$
if body is moving with constant angular velocity then there is relative velocity..
can any one explain
I shall be very thankfull.
Comment: Your question is not clear - what is the body you refer to?
Comment: any neutral body roatating
w.r.t that body magnetic field will induce or not if only rotating
Comment: And where is the charge located?
Comment: @Abhijeet Melkani the charge particle is at rest any where you can consider but the body that is axially symmetric is rotating
Answer: The body is not an inertial frame of reference (as it rotates and hence its velocity is changing) and so it is not correct to apply Maxwell's laws from such a frame.
Now, if a reference frame was uniformly moving relative to the charge, then yes it would experience a magnetic field.
Comment: May be you are not considering my question
the body is rotating with axial symmetry and also it is neutral
and the charge is at rest
now I am asking whether magnetic field induced or not?

induction of magnetic field


Non-Party Request for Documents under Litigation Hold

Question: Assume that Party A has brought a civil lawsuit against Party B. Assume further that Party A has issued a document preservation demand upon Party B covering all documents in Party B's possession, custody and control pertaining to their dispute. Can Party B honor a request by a non-party to the lawsuit for production of a copy of a document covered by the preservation demand?
Answer: Based on other questions you have posted, I assume you refer to some jurisdiction in the U.S.

Can Party B honor a request by a non-party to the lawsuit for
  production of a copy of a document covered by the preservation demand?

Generally speaking, it can (absent any reasonable privacy issues, non-disclosure agreements, or judicial prohibitions), but does not have to.
One exception is where party B is an entity subject to provisions such as the Freedom Of Information Act and the records at issue are within scope of FOIA. That applies regardless of whether the records sought are in Party A's list for litigation hold.
Other than that, the non-party may sue Party B for injunctive relief so as to compel the production of documents. However, this would require the non-party to persuade the court that some entitlement to that production. The entitlement could be in equity, by law (such as FOIA if it applies to Party B), or potentially conductive to --or determining of-- other type of relief in the future.
Answer: Yes.
So long as compliance with the request by Party C does not run afoul of Party B's obligations to impose a litigation hold and prevent spoliation of evidence, it is generally free to share its documents with whomever it wants.


Charging battery with external charger while powering load

Question: I am building a device which I would like to be able to charge with several different types of external battery chargers (different Icharge within spec of battery, of course). If I understand everything correctly, I won't need an extra charge IC on my board with this setup.
Now, while this device is charging I would like to still be able to power the loadside logic.
What is the best way to do this? Should I add a source selector and only use current provided by the charger to put in my on-board DC/DC during charging? Should I add a load sharer?
Or is it sufficient to just power everything from Vbat even with the charger plugged in and pull the 20W required for the logic from the charger like that?
Either way, isn't the charger constantly detecting current draand "thinking" the battery is not full yet potentially detrimental for the battery?
Thanks!
Comment: What kind of battery? Most battery chargers provide a fixed current until the voltage reaches a certain level then a fixed voltage until the current falls to a certain level to determine end of charge.  The fixed current stage should just increase charge time but you risk over charging during the fixed voltage stage.
Comment: Will the external battery chargers be able to simultaneously provide sufficient battery charging current AND sufficient power for the load (plus a few percent more for overhead management?). If not then you have a more complex circuit I suspect.
Comment: _"...with several different types of external battery chargers"_ which different types?
Comment: @WarrenHill li-ion or lipo probably. Either way the load will have to be powered during charging and scope says charger must be external. Any ideas?
Answer: Depending on the charger and battery type it will probably work ok.
Lead-acid:
Chargers are usually very dumb and just supply a current/voltage limited output. The charger shouldn't care at all if a load is connected in parallel. Although you should note that the "float voltage" that the charger supplies is higher than the normal battery voltage. The float voltage on a "12V" lead acid battery is usually 13.8V for example.
Li-ion:
Most chargers have an output that is voltage limited to 4.2v per cell, as well as current limited. More complicated chargers have time and mAh cutoffs which could trip you up. But in practice that would just mean you have to start the charging cycle again.
NiMh:
These have complicated charging logic. The load likely would trip some threshold on the charger.
Answer: If the external power source is a battery charger then it is likely to be confused if there is a load on the battery while it is charging.
Most devices that can run from external power or battery use a simple power supply, and put the battery charger inside the device.
Comment: I know, but the scope is explicit about not puting the charger inside of the device as different chargers with various charging currents are available.


May I put my pronouns in my username?

Question: I want to include my preferred pronouns in my username. Is that allowed? Allowed but discouraged? I just want to make it easier for everyone to know, so there's no faux pas.
Comment: Usernames on Stack Exchange are explicitly meant to be display names. As such you can edit them once a month. I don't see which rules including pronouns would run afoul of, soo ....
Comment: @Vogel612'sShadow Just tried it, usernames don't allow punctuation, so the typical way of denoting pronouns (something like `Welbog (he/him)`) is not permitted.
Comment: If anyone is wondering, the reason for the significant number of downvotes was the OP's "coy" profile page, and their so-called pronoun(s) "OP", see Glorfindel's answer.
Comment: One advantage would be that it would make them immediately visible.
Answer: Yes, it is allowed, since it doesn't offend anyone.*
Whether it's a good idea, I doubt it. As I mentioned here,

One thing to note is that @-replying might be going to look awkward, e.g. if you type a comment (or chat message reply) it will autocomplete to @fredsbend(OP). The system could for these cases omit the part between parentheses but I'm sure such a feature would be abused one way or another.

It's better to put them in your profile, as it's not in an intrusive spot there. It's then possible to fetch them with a userscript; I wrote Pronoun Assistant to do exactly that. Here's how that looks like on the usercard of the other co-author of the script:

Oh, by the way, 'OP' isn't a pronoun; it's an abbreviation of a phrase consisting of an adjective and a noun. If you don't want to be referred to with one of the regular or neo-pronouns, that's fine with me and I will respect that; I use 'OP' quite frequently and will do so with you – unless it leads to confusion because you didn't write the question.
*: There might be situations where a non-offensive username concatenated with a pronoun produces a word or phrase that is offensive; I'm talking about the general practice.
Comment: OP isn't (grammatically) a pronoun, no, but it can be used in place of a proper noun (i.e. a name).
Comment: Did SE publish a list of acceptable pronouns? Are you declaring that you're unwilling to refer to this user by their pronoun?
Comment: Not trying to sound toooo picky or cynical here, but: Where does the assumption that it does not offend anyone come from? If you asked, I'm sure *somebody* would (at least claim to) be offended. You could say "It does not violate today's policies" or something like that...
Comment: I think this argument against "OP" being a pronoun can be easily recycled into an argument against "they" as a distinguished pronoun. Based on this precedent, I would say that the fact that OP has a prior meaning does not preclude one from taking it as one's pronoun.
Answer: Adding pronouns to your signature is discouraged by many (most?) of your fellow users - because you're forcing us to focus on the pronouns business, which we would really rather not (especially given recent events, and generally). You wrote:

I just want to make it easier for everyone to know

Please don't. We don't want to know. We are here to answer your questions (or comment on your posts/comments) - about software, about literature, about international travel, Christian theology, and so on. We're not here to talk about you the person. If we want to know about you, we'll visit your user profile (where you can put a link to a personal page).
If the information is relevant to your post - put it in the post itself. Example:

I need to do [something or another] , but this is complicated because I am a [woman/man/non-binary/etc.] with [other identity features], and so [explanation of how your identity affects the situation].

or

Please do not make assumptions regarding [my/somebody's] [gender/sexual orientation/etc.]

PS - To clarify - I'm referring to any user, not just to @fredsbend personally.
Comment: This point keeps being made as though it is brilliant and incisive. It is true you don't need to know someone's gender to solve an error message the question asks about. However the moment two users start discussing a third user ("did you try what X suggested?" or "but in the question X explained that Y was not possible") most people start to use pronouns. "X said he repro'd your problem" or "X said his architect forbids that solution" -- and when you get them wrong, it stings for some people. This has nothing to do with needing to know gender to answer a question, evaluate an answer, etc.
Comment: Yes, you can. I often do. NOT THE POINT. Until the new CoC, if someone referred to me as he, whether accidentally or deliberately to upset me (which wouldn't work but that's not the point) it was almost certainly not against the CoC, a mod wouldn't edit the comment to fix it, etc etc. So the CoC was changed. Was a lot of stuff mishandled after that? Oh boy, you betcha. Does that mean none of us should have pronouns, or care about them? *It does not.** Caring enough to avoid using the wrong ones (by using none) is cool. It is not the same as "pronouns don't matter here." They do.
Comment: @KateGregory: Yours is a partially valid point. It's somewhat valid because it's natural to try and use someone's pronouns like you've demonstrated. But it's also invalid because you can write, and many do: "Did you try what SomeUser suggested?" "SomeUser reports they reproduced your problem". Also, I did not self-flatter in my post, it's simply what I know to be the sentiment and opinion of many users.
Answer: There are two parts to this:
May I put my pronouns in my username?
Some users are starting to do this. Usernames can't contain ( or ) but I've noticed some users wrapping pronouns using hyphens or quotes, like someUser -she/her- or otherUser 'they/them'.
In @ replies the spaces are removed like @someUser-she/her- and replies use stub matching so if the text gets too long, users can type @someUser and it will match @someUser-she/her-.
However, it's worth mentioning that most of the examples I've seen so far appear to be attempts to troll or protest the new policies (and/or the manner they were bought in) with confusing pronoun pairs, like:

Username -he-her-

I don't want to link to or flag examples because I don't know what's in good faith and what isn't.
If you do want pronouns to be visible, this is a convention that you could follow, but be aware this is something very much in flux.
Can I use "OP" as a requested pronoun?
The policy is currently unclear as to where the line is drawn, but it looks like there's nothing stopping you.
However, I'd suggest not choosing "OP" as a pronoun because it is a widely used abbreviation of "Original Post" or "Original Poster", which will cause confusion in cases where you are not, in fact, the "Original Poster":

[Answer] You can extract the body text from that HTML by using regular expressions. There's an answer I saw that shows how, if I can find it I'll edit the link in with a quote. -[User1234]

[Comment] Please don't parse HTML using regex, it summons demons. -[fredsbend 'OP']
[Comment] @fredsbend'OP' What do you mean? I don't understand -[AnotherUser]
[Comment] @AnotherUser I think OP's referring to [this answer]{link} -[bobince]
[Comment] @bobince No I'm not. Who's Zalgo? -[User1234]
Answer: I think this would make sense in cases where the Username is something like "TheQueenOfJavascript" or "HisBrothersKeeper" or even "TheirMunchkin".
Usually a name identifies the pronouns by proxy - David is connected to "he", Monica to "her". So using a readable name that lets people infer the pronoun  should be encouraged.
I also like names that make it clear I'll have to watch my use of language to be nice. ZoeTheTransGirl is a good example. With such a name, I might look at the profile before I address the user for the first time.
I think this is one of the best ways to avoid unpleasantness all around - if you want to be addressed in a special way, advocating it with a clever username seems like a really good way to ensure that.
It makes much less sense with Usernames such as "David-she" or "TheGroundHog-xir". Tacking on a pronoun just for the sake of it being there -  that's just ugly.
Comment: Thanks for the answer. I agree your final example is ugly, but apparently the issue is big. Your answer doesn't cover how one could use their name to denote a pronoun like xir or even they.
Comment: Yes it does, in a roundabout way. "HisBrothersKeeper" implies that the person wants to be adressed by the standard "he/him/his/" set. So a possible Username might be "ZirWhoKnowsBest", which would imply the "ze/zir/zirself". It obviously doesn't work with every possible username, but that's what I meant to say - I think it's a great idea if you're creative and find a clever username, and I'd avoid it if you can't come up with something readable.

May I put my pronouns in my username?


How do I flag a tag for moderator attention?

Question: This tag recently ended up in my review queue, which I promptly rejected due to it being a verbatim copy from http://www.php.net/manual/en/faq.passwords.php without attribution.  Unfortunately other editors weren't as deligent and it was accepted.  Sorry if this has been asked before but how would one flag a tag for moderator attention, and does it really matter anyway?  The only reason I bring it up is because a rejection reason is that it is copied content, so it must matter!
Answer: You can flag any post that uses that tag for moderator attention, using the "Other" reason and explaining exactly why you are flagging.
I have rolled back the entry.
Comment: Ah right, I didn't think of that.  Thanks!
Answer: There is no option to flag any tag. Only option to flag is flagging any question tagged with that tag (not necessary but it's better) using "other" reason. But before flagging you should probably suggest a tag edit and add attribution yourself. If it is not accepted then flag a post.


Ubuntu won't boot on win10

Question: I want to switch from Windows 10 to Ubuntu but the problem is that USB won't boot up, it just skips and Windows 10 boots up. I tried USB on second PC where I have Ubuntu and it boots fine from USB. Any idea what can be wrong ?
Comment: Have you gone into setup and checked the boot order?
Comment: Does the Windows 10 machine use [UEFI](https://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface)?
Answer: Boot your first PC into the BIOS and look for the boot order settings.
If your Ubuntu set up is on a USB drive and it works on one PC and not another, then the problem may be the BIOS setting of the first PC.  The Boot device order is set in the BIOS and frequently (but not always) defaults to looking at the Hard Drive first.  You would need to change the setting to look at the USB drive first. Your second PC may already have its BIOS set to check for a boot block on USB before it checks on the Hard Drive.

Ubuntu won't boot on win10


Is it possible to implement auto-currying to the Lisp-family languages?

Question: That is, when you call a function with >1 arity with only one argument, it should, instead of displaying an error, curry that argument and return the resulting function with decreased arity. Is this possible to do using Lisp's macros?
Comment: You'd have to implement a typed language on top of Lisp (which is very easy with macros), but it would not be easy to mix this language with the rest of the Lisp.
Answer: It's possible, but not easy if you want a useful result.

If you want a language that always does simple currying, then the implementation is easy.  You just convert every application of more than one input to a nested application, and the same for functions of more than one argument.  With Racket's language facilities, this is a very simple exercise.  (In other lisps you can get a similar effect by some macro around the code where you want to use it.)
(Incidentally, I have a language on top of Racket that does just this.  It gets the full cuteness of auto-curried languages, but it's not intended to be practical.)
However, it's not too useful since it only works for functions of one argument.  You could make it useful with some hacking, for example, treat the rest of the lisp system around your language as a foreign language and provide forms to use it.  Another alternative is to provide your language with arity information about the surrounding lisp's functions.  Either of these require much more work.
Another option is to just check every application.  In other words, you turn every
(f x y z)

into code that checks the arity of f and will create a closure if there are not enough arguments.  This is not too hard in itself, but it will lead to a significant overhead price.  You could try to use a similar trick of some information about arities of functions that you'd use in the macro level to know where such closures should be created -- but that's difficult in essentially the same way.

But there is a much more serious problem, at the highlevel of what you want to do.  The thing is that variable-arity functions just don't play well with automatic currying.  For example, take an expression like:
(+ 1 2 3)
How would you decide if this should be called as is, or whether it should be translated to ((+ 1 2) 3)?  It seems like there's an easy answer here, but what about this?  (translate to your favorite lisp dialect)
(define foo (lambda xs (lambda ys (list xs ys))))

In this case you can split a (foo 1 2 3) in a number of ways.  Yet another issue is what do you do with something like:
(list +)

Here you have + as an expression, but you could decide that this is the same as applying it on zero inputs which fits +s arity, but then how do you write an expression that evaluates to the addition function?  (Sidenote: ML and Haskell "solves" this by not having nullary functions...)
Some of these issues can be resolved by deciding that each "real" application must have parens for it, so a + by itself will never be applied.  But that loses much of the cuteness of having an auto-curried language, and you still have problems to solve...
Answer: In Scheme it's possible to curry a function using the curry procedure:
(define (add x y)
  (+ x y))

(add 1 2)           ; non-curried procedure call
(curry add)         ; curried procedure, expects two arguments
((curry add) 1)     ; curried procedure, expects one argument
(((curry add) 1) 2) ; curried procedure call

From Racket's documentation:

[curry] returns a procedure that is a curried version of proc. When the resulting procedure is first applied, unless it is given the maximum number of arguments that it can accept, the result is a procedure to accept additional arguments.

You could easily implement a macro which automatically uses curry when defining new procedures, something like this:
(define-syntax define-curried
    (syntax-rules ()
      ((_ (f . a) body ...)
       (define f (curry (lambda a (begin body ...)))))))

Now the following definition of add will be curried:
(define-curried (add a b)
  (+ a b))

add
> #<procedure:curried>

(add 1)
> #<procedure:curried>

((add 1) 2)
> 3

(add 1 2)
> 3

Comment: Great answers overall but you provided that small snipplet that proved very useful so I can't accept another answer but this.
Comment: Despite of being really interesting, both snippets are not automatically curried.
Answer: The short answer is yes, though not easily.
you could implament this as a macro that wrapped every call in partial, though only in limited context. Clojure has some features that would make this rather difficult such as variable arity functions and dynamit calls. Clojure lacks a formal type system to concretely decide when the call can have no more arguments and should actually be called.
Answer: Lisp already has Functional Currying:
* (defun adder (n)
    (lambda (x) (+ x n)))
ADDER

http://cl-cookbook.sourceforge.net/functions.html
Here's what I was reading about Lisp macros: https://web.archive.org/web/20060109115926/http://www.apl.jhu.edu/~hall/Lisp-Notes/Macros.html
It's possible to implement this in pure Lisp.  It's possible to implement it using macros as well, however it seems as though macros would make it more confusing for very basic stuff.
Comment: "arity" is a common term in Prolog. There functions (*predicates*) with same name and different arities are considered different.
Answer: As noted by Alex W, the Common Lisp Cookbook does give an example of a "curry" function for Common Lisp.  The specific example is further down on that page:
(declaim (ftype (function (function &rest t) function) curry)
         (inline curry)) ;; optional
(defun curry (function &rest args)
  (lambda (&rest more-args)
    (apply function (append args more-args))))

Auto-currying shouldn't be that hard to implement, so I took a crack at it.  Note that the following isn't extensively tested, and doesn't check that there aren't too many args (the function just completes when there are that number or more):
(defun auto-curry (function num-args)
  (lambda (&rest args)
    (if (>= (length args) num-args)
        (apply function args)
        (auto-curry (apply (curry #'curry function) args)
                    (- num-args (length args))))))

Seems to work, though:
* (auto-curry #'+ 3)
#<CLOSURE (LAMBDA (&REST ARGS)) {1002F78EB9}>

* (funcall (auto-curry #'+ 3) 1)
#<CLOSURE (LAMBDA (&REST ARGS)) {1002F7A689}>

* (funcall (funcall (funcall (auto-curry #'+ 3) 1) 2) 5)
8

* (funcall (funcall (auto-curry #'+ 3) 3 4) 7)
14

A primitive (doesn't handle full lambda lists properly, just simple parameter lists) version of some macro syntax sugar over the above:
(defmacro defun-auto-curry (fn-name (&rest args) &body body)
  (let ((currying-args (gensym)))
    `(defun ,fn-name (&rest ,currying-args)
       (apply (auto-curry (lambda (,@args) ,@body)
                          ,(length args))
              ,currying-args))))

Seems to work, though the need for funcall is still annoying:
* (defun-auto-curry auto-curry-+ (x y z)
    (+ x y z))
AUTO-CURRY-+

* (funcall (auto-curry-+ 1) 2 3)
6

* (auto-curry-+ 1)
#<CLOSURE (LAMBDA (&REST ARGS)) {1002B0DE29}>

Answer: Sure, you just have to decide exact semantics for your language, and then implement your own loader which will translate your source files into the implementation language.
You could e.g. translate every user function call (f a b c ... z) into (...(((f a) b) c)... z), and every (define (f a b c ... z) ...) to (define f (lambda(a) (lambda(b) (lambda(c) (... (lambda(z) ...) ...))))) on top of a Scheme, to have an auto-currying Scheme (that would forbid varargs functions of course).
You will also need to define your own primitives, turning the varargs functions like e.g. (+) to binary, and turning their applications to using fold e.g. (+ 1 2 3 4) ==> (fold (+) (list 1 2 3 4) 0) or something - or perhaps just making such calls as (+ 1 2 3 4) illegal in your new language, expecting of its user to write fold forms by themselves.
That's what I meant by "deciding ... semantics for your language".
The loader can be as simple as wrapping the file contents into a call to a macro - which you  would then have to implement, as per your question.


How to interpret Terrain Ruggedness Index according to Wilson et al. (2007)?

Question: Is there a categorical scale used to interpret values from the Terrain Ruggedness Index as calculated by Wilson et al. (2007), which is used in the raster library in R?
Comment: It helps if you can link to cited research, saves us tracking down the articles!
Answer: The paper by Riley et al (1999) cited by the Wilson et al paper has a map with seven categories of ruggedness (and an odd colour scheme but whatever)...

They use an "equal area" basis for the breakpoints, which I guess means they were chose so that each category is the same area on the map, which seems a bit arbitrary but unless you have some idea of what "rugged" means then I guess its as good as any other...
Comment: I'm looking at these values for southern Arizona. So if I divide the range of values in my map into 10 categories, then that would give me a relative categorical scale I could use to assign to values I sample from points in the area?
Comment: That's what they do in the paper, but with 7 categories, with the breaks in the categories set so that exactly 1/7 of the area is in the "Level" category, 1/7 in "Nearly Level" and so on. For any vector of values `z` you can get the breakpoints for 7 categories with `quantile(z,seq(0,1,len=8))` - but the category definitions will be different for Arizona if you work them out for Nebraska.


Quantifying potential energy

Question: As per the definition of potential energy we kept a fixed charge, and in the presence of an electric field of the fixed charge, we release another charge of the same sign moving towards the fixed charge with some velocity, then the conservative field produced by the fixed charge will do negative work on the moving charge so its kinetic energy will decrease and the potential energy of the system will increase. In the book it is written that it doesn't matter if we keep one charge fixed or both the charges the calculation will give us the same value of the potential energy . But on the second case where both the charges (of same sign) are moving I can figure out that the force given by the one charge on the other decreases their kinetic energy . But I am unable to figure out conservative field which is doing work on the charges so that their kinetic energy is getting converted into potential energy. Is it that at each instant the force field of one charge affecting the other charge? Or there is some unified field which is doing work on both the charges?
Answer: Let start with the basics:

Same Charges repel each other and Different charges attract each other.

Potential energy of anything is the work done to move that thing against a field or physical force a particular distance away or towards the source of that force.
Kinetic energy is the motional energy an object has at a particular velocity.
In the context of a charge being fix and another being repelled by it. When a charge $Q$ placed at a distance $l$ away from a source of an electric field is repelled and thus set in motion away from the field source, potential energy at distance $l$ from field source is being transformed to kinetic energy as the $Q$ accelerate and gain velocity. So the potential is decreasing while the kinetic is increasing.
On your last question, the field of each moving charge is causing the force decelerating the particles. As the field of one charge effects on the other, the field of the other does the same.
The force on a charge in another charge's field regardless of mobility can be calculated by the coulomb inverse square law: $$F=k_e \frac {q_1 q_2}{r^2}$$ ke ≈ 9×109 $\:\rm N⋅m^2⋅C^{−2}$
Comment: I am really sorry . I have missed a word in my question initially. And that led you to this conclusion of yours which was right indeed. Now I have edited the question. Please read it again for once. I apologize my mistake
Comment: @ Rifat Safin. I edited the answer to address your main question.

Quantifying potential energy


Client Hyper-V in Windows 8 : Synthetic Ethernet Port: Failed to finish reserving resources

Question: I am unable to run any of my virtual machines with a network connection.
I get this error when I try to start them:
<code>Synthetic Ethernet Port: Failed to finish reserving resources with
Error 'Insufficient system resources exist to complete the requested service.'
(0x800705AA). (Virtual machine ID 8787....-....-....-....-........)
</code>
Does anyone know how to fix it?
This is an error from the Hyper-V Manager, in my case, in Windows 8 pro, but also possible to occur in Windows Server 2012 R2.
Answer: It turns out that my VMs somehow had two virtual ethernet adaptors, one of which was mapped to an adapter that had been removed from the "Virtual Switch Manager".
Right clicking on the settings, locating the second adaptor, then going to the right side
of the screen and clicking the Remove button below the Network Adaptor's configurat
properties list, solved the problem.
The error message could be better. Maybe it could say:
"You have two ethernet ports on this VM. Network adaptor #2, has an invalid configuration. Repair or remove the broken network adapter and try again."
Answer: The Virtual HBA on Hyper-V has 2 ports, even if you are not able to ping over FC the 2nd port you have to set zoning and presentation for. The 2nd port is used for Live Migration.
BTW: you have to create 2 Virtual SAN and assign just one fabric to one virtual SAN. Also, be careful that the definition on all cluster nodes for NPIV address are the same. Otherwise you will probably not see the presented drives.
Comment: You are talking about something completely unrelated, I think.


Stein Manifolds and Affine Varieties

Question: When is a Stein manifold a complex affine variety? I had thought that there was a theorem saying that a variety which is Stein and has finitely generated ring of regular functions implies affine, but in the comments to my answer here, Serre's counterexample was brought up.  I'm guessing that the answer is that the ring of regular functions must be nontrivial somehow, like it must separate points, but I'm curious about what the exact condition is.
Comment: I have to ask: what is "gaga"? Google did not turn up anything useful.
Comment: GAGA refers to Serre's paper "Géométrie algébrique et géométrie analytique" and more generally, the philosophy that it embodies that there is a correspondence between complex analytic geometry and complex algebraic geometry.  Serre's paper, I believe, focuses on proving that for any variety and sheaf, there is an analytic space and sheaf defined naturally to be the analytifications of what you started with, and that cohomology doesn't change.  That is, you can compute cohomology of coherent sheaves in the complex topology.
Answer: Charlie, it is funny answering this way but here it is.
The criterion you are thinking about is a criterion that is relative to an embedding. It says that if $X$ is a quasi-affine complex normal variety, whose associated analytic space $X^{an}$ is Stein, then $X$ is affine if (and only if) the algebra $\Gamma(X,\mathcal{O}_{X})$ is finitely generated. This is a theorem of Neeman.
You can reformulate the requirement of $X$ being quasi-affine as a separation of points property: for any point $x \in X$ consider the subset $S_{x} \subset X$ defined as the set of all points $y \in X$ such that all regular functions on $X$ have equal values at $x$ and $y$. Then by an old theorem of Goodman and Hartshorne $X$ is quasi-affine if $S_{x}$ is finite for all $x$. So you can say that $X$ is affine if it satisfies: 1) $X^{an}$ is Stein; 2) $S_{x}$ is finite for all $x \in X$; 3) $\Gamma(X,\mathcal{O}_{X})$ is finitely generated.
Comment: Answering this way (rather than in person) means more people get to see it!
Comment: Goodman and Hartshorne must have an implicit assumption that $X$ is separated, the result as stated is false for the line with doubled origin. (Of course, Stein implies separated, so your main answer is fine.)

Stein Manifolds and Affine Varieties


Alternative for Criminal Defense Lawyer?

Question: I used to think Devil's Advocate meant the defense lawyer, though it actually means someone who, given a certain argument, takes a position they do not necessarily agree with, for the sake of debate. My question is, does an idiomatic phrase, or euphemism exist, meaning 'Defense Lawyer'?
Answer: They're all pretty dated slang terms, but you might just still come across...

legal eagle a lawyer, especially one who is keen and astute.
mouthpiece a criminal lawyer (who speaks on behalf of the defendant).
brief (sense 10, British slang) a lawyer, esp. a barrister.
Comment: Legal eagle can refer to any lawyer. As for mouthpiece, its usage in the meaning given above is not very much.Isn't there any phrase/word which can almost always taken to mean 'defense lawyer'?
Comment: @Adil: The context will invariably make it clear whether the *legal eagle* is [your] defence lawyer, or acting for the prosecution, but to be honest I don't think that term was ever used much. In context, most Anglophones will understand ***my mouthpiece***, and most Brits will understand ***my brief***, but (unless I'm just moving in the "wrong" circles) people don't normally use any of these sort of words except facetiously. If you're being serious (as befits most *real* contexts), it's ***my lawyer***.
Comment: **brief** isn't dated in UK; you'll hear it in most current police television programmes.  "He said he's saying nothing until his brief gets here."
Comment: @jonathanjo: I think the slang *brief = lawyer* was always primarily AmE anyway. There aren't enough written BrE instances of [***his brief says***](https://books.google.com/ngrams/graph?content=his+brief+says&year_start=1930&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Chis%20brief%20says%3B%2Cc0) in Google Books to chart, but you can see a massive decline since its heyday in the context of American prohibition-fueled gangsters. Whatever - I'm far from convinced scripted TV serials reliably reflect current usage trends.
Comment: @FumbleFingers ... I do not know if it's contemporary police/legal slang in the UK, but it's at least expected to be understood by contemporary audiences in eg *Criminal Justice II, ep 1* (2009) "You're a brief, right?"; *A Very English Scandal* (2018, set in late 1970s) "I was talking to my brief", as well as The Sweeney (1970s)  "A good brief will tear it to shreds."
Answer: I am not aware of any word or phrase for "defense lawyer" other than: (a) "defense lawyer"; (b) "my lawyer", when you're the defendant; and (c) "the defense", when discussed from the viewpoint of the judge and jury. A judge will say "the defense has presented a motion to ...", but the defendant doesn't refer to his own lawyer as "the defense".
RE FumbleFingers answer, I suspect "my brief" is a British term. I have never heard it used in the U.S. In U.S. legal jargon, a "brief" is a paper that a lawyer or other interested party gives to the judge summarizing his legal argument. Maybe there's a relation between the two usages.
Comment: There's no need to "suspect" ***brief*** is BrE slang. That was specifically flagged up by the dictionary I linked to, and I included it in my text. But you're quite right that the BrE slang usage derives from OED's definition: *A summary of the facts of a case, with reference to the points of law supposed to be applicable to them, drawn up for the instruction of counsel conducting the case in court.*
Comment: _I am not aware of any word or phrase for "defense lawyer" other than "defense lawyer..."_ Well, there's always "defense attorney," too – but I'll concede that's not a very impressive synonym. :^) There's also "public defender," which is a specialized kind of defense lawyer, but it might be worth mentioning.
Comment: @FumbleFingers I meant, "EXCLUSIVELY British term". Yes, you said (or quoted someone saying) it was "British slang", I was trying to make clear that that usage is not found in the US.
Comment: @J.R. You're right, I'll grant you "defense attorney". As you concede, "public defender" is not a synonym for "defense lawyer", but a subset of defense lawyers. Just because some animals are dogs doesn't mean that "dog" is a synonym for "animal". :-)
Comment: In the UK, specifically in England and Wales: a "brief" is the formal term for the instructions the solicitor (approximately "desk based lawyer") gives to the barrister ("lawyer permitted to represent you in court").  "The solicitor gave the barrister the brief and he accepted it".  Scotland and Northern Ireland have different legal systems to England and Wales, so it's likely usage differs there.