Do cells phones put out a signal when charged through data out?

Question: Do cells phones put out a signal when fully charged through data out? I am wondering this because there is a competition to see who can build the best and most efficient portable cell phone battery backup
Answer: Typically, no. The USB charging standard has the Data Pins tied to ground or each other through resistors to indicate what type/capacity charger the phone is plugged into, to let the phone know how much current it can pull. While connecting the phone to a regular USB Host also does not have that information by default (phones using non-standard drivers other than USB Storage might have it, varies by manufacturer).
While phones have charging circuits that are already built for efficiency by switching into trickle charge mode once done charging, you can either passively or actively sense this. One way would be to have your charger measure the current draw, to figure out when the phone went from high speed charging to trickle charge mode. Another is to use bluetooth (preferably Bluetooth 4.0 Low Energy) with a custom app/service that signals the charger when the phone is fully charged.
Both options would, IMHO, require that the phone be unplugged and replugged in (or a button pressed on the charger, or on the app for bluetooth) to start charging again, so that means it would discharge as if it were unplugged. Hope that helps.
Comment: Measuring the current draw is probably the way to go.
Answer: Mobile phones use Lithium based batteries. Mostly Li-Ion. They are voltage limiting battery. For more on such batteries pl. see http://www.cellphoneshop.net/usbdacaforsa59.html
Since we understand that is the voltage that needs to be sensed for perfect charging do see some voltage sensing circuits.
Mobiles, such as old Nokia 100, would give a "fully charged" indication on screen. There is no "data out" as the circuit for data is not connected to charging.
If you see the basic USB connection links pins are 1:Vcc 2: Data+ 3: Data- 4: Ground.
Data is isolated from charging points Vcc and gnd to maintain data integrity.
However, for your purpose you may take up the software aspect which indicated that the display "battery full" and use data ports to display it outside the phone. For this understanding of the cell phone model, the battery specifications and the OS running on it are necessary.
More on phone battery here
Answer: If you mean do they put out a radio signal ie connecting to the mobile network when charging via USB, then the answer depends on whether it is switched on or not. When the phone if switched off and is being charged there should be no communication with the network. If you want to make doubly sure, switch it into airplane mode before switching off and charging.
Answer: It sounds like what you're building is a power bank, or external recharger battery pack for a (smart)phone.  These usually consist of a USB input jack, battery charger, lithium-ion or lithium-polymer battery, battery-to-5VDC regulator, and USB output jack.  The phone then gets powered from 5.0VDC on the USB output jack of the power bank, and since the phone acts the same whether this 5V supply comes from wall adapter, laptop, power bank, etc., there is no way to optimize how anything inside the phone performs.  The charge time or power supply efficiency inside the phone is completely unaffected by the power bank design.  This is assuming the pack isn't underpowered and can put out as much current as the phone would like to have as input.
Presumably what you're trying to optimize is the efficiency of the power regulators inside the power bank.  At the least, this would entail choosing switching regulators over linear or LDO regulators for the battery charger and battery-to-5V regulator.  From there you could work on optimizing the regulators for the (known) input & output voltage ranges to try to get the converter efficiency as high as you can.  You may also need to optimize any battery protection circuitry in the pack so that it wastes as little energy as possible.
As to other features making it "better," you don't specify what this means, but we could guess some possibilities.  First would be what size battery you wish to use in the power bank - you might want to design the electronics to work over a broad range of battery sizes, or be highly optimized for one specific size.  For the battery itself you can trade off between capacity, power capability, cycle life, size, weight, cost - what chemistry or flavor of lithium-ion do you choose and which cell manufacturer.
Other features might be adding protection against ESD or a short circuit on the output pins.  Multiple output USB jacks with individual protection on each.  Multiple power input sources such as adding a wall adapter input.  How beautiful is the case.  In a real product these would be traded off against the price you believe the consumer would be willing to pay.


In applications for academic jobs that ask for a "copy of transcript", is a "copy of transcript" an unofficial or official copy?

Question: I am confused in a lot of applications for academic jobs, such as assistant professor, lecturer, instructor, at academic institutions. Many of them ask for a "copy of transcript," but I am unsure about what this means. Does this mean I need to get my official sealed transcript, open it, and copy it, or does it mean I can use the unofficial transcript?
Answer: To know for sure, the easiest thing is to email the application contact person for a given job and ask.
My impression is that in many cases, the committee reviewing the transcripts does not really care whether they are official or unofficial, photocopied or not, whatever.  All contain the same information.  If you reach a later stage of the application process, they may require an official transcript to satisfy bureaucratic requirements.
As W88's answer says, every printed version of your transcript is "a copy of your transcript".  "A copy of your transcript" doesn't necessarily mean a photocopy, it just means "a piece of paper with your transcript printed on it".  If you receive a sealed transcript from your school, that is "a copy of your transcript" and you can send it in as-is.
Answer: May I ask what you mean when you say official and unofficial?
If it helps, the copies issued from the institution where you graduated are all considered official. The original document you receive is also a copy called the original copy. You can also have multiple original copies.
So when they ask for an official copy of your transcript, as long as it has the signature of your registrar or equivalent, it is official; whether it is the original or the photocopy is a different matter.
Comment: I've often encountered simple photocopies of unofficial transcripts in applications.  If we're sufficiently interested in a candidate to invite them to interview, we'd ask the candidate to have official transcripts (with the university seal, etc.) sent before interviewing on campus or making an offer.
Comment: An official transcript comes sealed with official signatures. The unofficial transcript is a copy that I can access online without signatures, and since I can print it out, is not sealed.
Comment: The lack of clarity in the applications is that some ask for a "copy of a transcript," not worded as "copy of official transcript." Some applications specifically say a "copy of official transcript," or "copy of unofficial transcript," so in these cases, it is clear.
Comment: If I were in your place, I would have copies of my official transcript prepared; unofficial copies are always available so it would be a non-issue for me. My next step would be to ask the employers for clarification whether they need an official copy or not. In short, the best course of action may be to just ask the ones who posted the job offerings.


can't collect a weapon in fallout shelter

Question: I just crafted a weapon in Fallout Shelter, but it says I can't collect it because my inventory is full.  Just built a storage room, but still can't collect.  Any help?
Answer: If you just built your first storage room, then perhaps you still don't have space.
You can open your storage from the Pip-Boy menu. It's the icon that looks like one box stacked on two others.
Once you open your storage, look at the "Storage Space" at the bottom. Mine says 90/145. This means I can hold 145 items, and I currently have 90, so I have room for 55 more. If the number on the left is not smaller than the one on the left, you'll need more space.
You can get more space by selling things in your inventory or building more storage. You can extend your storage room, build another storage room, or upgrade it.


Omnichannel skill based routing, not assigning case to service agent

Question: I followed all the steps mentioned here to setup skill based routing

Enable Omni-Channel
Enable Skills-Based Routing Enable skill-based routing in your org.
Create Skills for Skills-Based Routing Skills identify your agents' areas of
expertise.
Create Service Resources for Agents Service resources
represent individual agents. Create a service resource for each
agent.
Assign Skills to Service Resources Assign skills to your
agents to track their areas of experience and their level of
proficiency for each skill.
Route Work Items
Using Skills To route non-Chat work items using skills, create a
PendingServiceRouting object and the associated SkillRequirement
objects. The PendingServiceRouting object is a standard Salesforce
object that represents the work item that is going to be routed. The
SkillRequirement object is a standard Salesforce object that
represents the skill and the proficiency level.

My apex class works fine to assign skills to work item but still the case is not routed to an agent.
I am new to salesforce. There is no point mentioned to route a case to agent so I was expecting omnichannel to handle it but it does not seem to work.
I have added permission set to add statuses to service agent for them to be online to receive a case.
I tested with a service agent online but unable to route the case.
Please let me know if I am missing a step here or something i need to configure.
Any help is appreciated.
Thanks
Khyati
Comment: Basically when i run my apex class by providing the case id, case gets added to Pendingservicerouting but it is not routing to an agent who is online and available.
Answer: Similar problem i faced in my project initially. What i did to solve it go to user record and check the Service cloud user check box.
After checking the checking box, log out from salesforce and again make yourself available in omnichannel.
Hope it helps!!
Answer: This is a little old, but my issue was that my user needed to be added to a presence configuration.  You can do this by going to setup > presence configuration and adding yourself.


How can I change the text colour and font of the username and password in Lion login

Question: I would like to change the text you type your username and password in with on the Lion login screen. I have a Command and conquer login screen and I would like to change the colour of the username and password Green and change the font. Is this Possible and how would i do it ?
Answer: Apple's ideology is mostly to not let the user tweak the design because, in many cases, the user may choose inferior fonts, colors, etc, and thus make Apple production look bad.
Instead of forcing design choices on user, as proudly does Linux and often does Windows, OS X contains settings that Apple considers "best" for everyone.
Of course, some people complain about certain decisions but it's much like MySpace vs Facebook. You can't change fonts and colors on a Facebook page, but frankly, imagine what a mess it would be if anyone could.
Presumably for this reasons, you can't customize how the text looks in input fields, including the login screen.
Comment: I have been coming up against this problem a lot but I have found work arounds for the back ground, the apple symbol, the login noise, the dock, the icons, the strip at the top, widgets (from geektool) and the screen saver.
Comment: Why not just use Linux? :-) I mean, that's where you really get to change everything, with no need to look for workarounds.


Where to keep ICO tokens?

Question: I want to buy some ico tokens from other users. However I don't have a wallet for that specific type of token(e.g. BasicAttentionToken).
Can I do that?
Comment: If you have your private key you can use MyEtherWallet to interact with an arbitrary contract.
Comment: I'd suggest buying from reputable exchanges, rather than other users.
Answer: Any token built on the Ethereum platform can be kept on any generic Ethereum wallet. Ethereum-based tokens are regular Ethereum smart contracts so you control them with your Ethereum account by sending Ethereum transactions.
Comment: This would be a much more useful answer if it included links to instructions on how to do this. I would upvote it, if it had some pointers. One pointer to how to do it in Mist and another on how to do it in Parity would be helpful.
Answer: It is pretty simple, a wallet like metamask for instance has a token section. You can simply define the token you want to add inserting the contract address and other few information required by the form and that's all. Metamask will show the balance for all the tokens you own and watch.
Metamask is a simple Ethereum wallet that comes as Chrome extension, but other wallets provide pretty much the same functions.
See Metamask https://metamask.io/

Where to keep ICO tokens?


Flash messages not working for Rails3 + Haml + RefineryCMS + Devise

Question: I'm unable to use flash in my haml and erb views. I can however use session[:flash], except in one case: after an unsuccessful login with devise, I want to show flash[:alert] or even session[:flash][:alert], but neither work. Both return nil and my page explodes. I can see in the session dump that flash[:alert] is set by devise. Why in the world can't I access it? I'm using Rails3 + Haml + RefineryCMS + Devise. Thanks!
Answer: It is possible RefineryCMS is already outputting the flash before you are trying to access it and therefore Rails is removing it?


Master page for user profile pages, how that works?

Question: I am building a SharePoint intranet branding solution, I have built 2 master page for site and system. Planning to build another master page for users but noticed each user has a different site collection and publishing features are also not enabled, How usually profile master pages are built? Can I use only one site collection for all users? Do I need to copy master pages and other stuf in each site collection?
Answer: You cannot use 1 site collection for all. Each profile has its own site collection.
You need to have MySite specific solution where you have a Web scoped feature that adds the masterpage to the masterpage gallery and sets the masterpage for the site collection through the FeatureActivated eventreceiver.
Answer: You'd need feature stapling to brand all the personal My Sites. The process remains similar to 2010.
Answer: You can change the master page directly using a httpmodule .
The PreRequestHandlerExecute method fires just before ASP.NET starts executing a page. In the context_PreRequestHandlerExecute method, you can get the current executing page by accessing the CurrentHandler object.
PS:
http://www.codeproject.com/Articles/43377/SharePoint-Dynamically-Change-Master-Page
If each and every profile needs a different master page better do it using css changes .


What is the best approach vector for orbital capture by an outer solar system body?

Question: I usually see the approach leg before an orbital injection trajectory around a body lying outside Earth's orbit drawn as catching up to it (moving in the same general direction/speed as the body's orbital vector) and approaching the far side of the planet/moon/etc. Does it ever make sense to approach the body from the near side, ahead of it, and still end up in orbit around the body? Can such a trajectory be accomplished without totally blowing your delta-v budget? If feasible and practicable, has any probe taken this approach vector?
Answer: In the frame of reference of the Sun, it is the outer solar system body (Mars, Jupiter, etc.) that catches up with the vehicle from Earth, not the other way around.  The energy of the vehicle from Earth is lower than the destination body, so that body is going faster around the Sun than the vehicle.
In the frame of reference of the destination body, the approach velocity of the vehicle is a vector fixed by the trajectory from Earth, and defines a plane, called the B-plane, through the body that is perpendicular to that approach velocity vector.  The vehicle can choose any point in the B plane to target, which will determine the closest approach distance to the body and a clock angle somewhere around the body.  Doing an orbit insertion burn at the closest approach point will result in an orbit that is prograde, retrograde, polar one way or the other, or somewhere in between depending on that clock angle, as you like.  Though the orbit is limited to an inclination no less than the declination of the approach vector.  So you can't go into an equatorial orbit with one maneuver.
Comment: There is no difference in $\Delta V$ for the target point clock angle.  The only difference for the single maneuver is the resulting periapsis or apoapsis given the closest approach distance.
Comment: Any significant difference in delta-v budget for prograde, retrograde, or polar, or are they all in about the same range?


Why can we flag/vote a question on Meta as duplicate of another question which has no accepted/upvoted answers?

Question: When we flag/vote-to-close a question as a duplicate on Stack Overflow, and that potential duplicate doesn't have any upvoted or accepted answers, we are alerted that we can't use that question as a duplicate and can't continue. This same check does however not seem to apply to Meta questions. Why not?
Comment: It may have something to do with the fact when something goes wrong, everyone in the Stack Exchange network feels the need to post a meta post about it at once, so this way they can consolidate all those into a single post to track until they can fix the issue and post a response. I suppose this applies to feature requests as well, not just bugs or support questions.
Comment: @rptwsthi I've made a bit of a drastic edit there. I think it's fine, but could you please check that it still says what you wanted to say? If not, feel free to roll it back.
Comment: Thanks Bart, Sure it still does.
Answer: Bug reports/support questions/feature requests don't have to be answered to be duplicates. Unlike the main site, where multiple questions being open might help at least one of them find answers (I still don't really like that you can't close them, but whatever), on Meta sites often feature requests/bug reports might not have an answer yet, but they're clearly a duplicate. And sometimes features/bugs get fixed/implemented without an answer. It'd really slow down the system on Meta if we could only close questions of answered questions, especially as Rachel notes: every time a major bug happens we usually get 3+ meta bug reports about it within minutes.
Comment: @Bart [status-tim-stoned]
Comment: I was tempted to answer with " ['cause I said so](http://meta.stackoverflow.com/posts/comments/484878) ", but this is better. :P
Comment: @TimStone Shall we propose a new [status-tim-stone]?


Why is John Carter considered a flop?

Question: According to Box Office Mojo John Carter grossed $284 million with a production budget of $250 million. I know that many things are not included in the production budget, possibly advertising and distribution. Do those things account for so much money that grossing $34 million over the production budget just doesn't cut it?
Comment: Theaters get a smaller cut of the BO than I think you imagine (it varies) and sometimes they make more money from the candy, soda, and popcorn. They pay a lot to get the rights to display the film. I worked at a theater in my younger days and saw many instances of the only worthwhile profit being from popcorn and soda, which both have **immense** mark-ups. Especially with second-run showings.
Comment: @MeatTrademark - Not too long ago the three largest theater chains in the US [refused to sell](http://www.businessinsider.com/theater-chains-not-selling-man-3-tickets-2013-4) 'Iron Man3' tickets because Disney was asking for _60-65%_ of the ticket revenue (which would mean only 35-40% for the theaters). -  Another source: [How much money does a movie need to make to be profitable?](http://io9.com/5747305/how-much-money-does-a-movie-need-to-make-to-be-profitable)
Comment: People often forget that theaters get a cut of the box office money. After all it does cost money to run a theater, and they obviously want to make a profit too. - Usually the theaters get about 50 percent of the ticket revenue.
Comment: As well as the cinema/theatre cut of the revenue, the estimate for the marketing budget for John Carter was in excess of $100m.  I've seen break even estimates for John Carter stated at $600m worldwide - that seems high - but I don't know enough about movie economics to challenge it.
Answer: It was considered a flop because it was supposed to be a bigger hit and a tent-pole to a new franchise. The production budget, like you opined, does not always cover advertising and distribution. When you spend $250 million, you expect your Domestic Total Gross to be well over $73 million. That is a flop. Even with world-wide BO it only made a small profit (not figuring in DVD sales). Put it another way: this $250 million movie is ranked 853rd in Domestic Box Office. That is  not what they were hoping for.
Comment: Whilst I agree with your answer, Production Budget *does* include [marketing and distribution](http://en.wikipedia.org/wiki/Production_budget). It is the encapsulating terminology for the total cost of the project in its entirity.
Comment: It doesn't always. Sorry, sometimes it does. That depends on the production company and their contracts. There are deals for distribution and other factors that are not necessarily in the production budget. Production Budget can mean anything from primary production to completion depending on what companies and distributions deals are worked out ahead of time, *if* they are worked out ahead of time. The Production Budget on independent films often only includes principal and editing. Not all movies are the same.
Comment: I added the italicized word *always* after the word "not" to try to fix this discrepancy.
Comment: Keep in mind that some movies only get distribution rights (and money) after being shopped around at film fests after production is completed and the film is screened in a "mostly" complete state, even if not a "locked-down" state.
Comment: +1 - And in addition: You always expect great things from Disney, and with the success of Pirates of the Caribbean, everyone expected John Carter to do better than it did. Wasn't even close to Pirates' BO, and if they still want to go ahead making a franchise out of it (despite the lack of interest in the first movie) they'll have a much harder time getting people to go see the sequel. In the end, Total Gross - Expectations = Result
Comment: Too bad the franchise failed, though. I would have watched another one. While it was far from original it was still quite entertaining.
Answer: It was a flop because it cost $307M and only grossed $284M. A substantial loss.
http://www.forbes.com/sites/csylt/2014/10/22/revealed-the-307-million-cost-of-disneys-john-carter/
Comment: Can you elaborate a little on your answer to flesh it out a bit more? There are many films that cost more than $307M and were no flops. How is that a reason for being a flop? And what does that linked article actually say, does it provide a better answer? Link-only answers are rather discouraged.
Comment: Especially when the link is apparently paywalled.

Why is John Carter considered a flop?


How do the open loop voltage gain and closed loop voltage gain differ?

Question: The closed-loop gain of op-amp is calculated by the ratio of Vout/Vin. What about the open-loop gain? How does the value of open-loop gain and closed-loop gain affect the performance of op-amp ? What is the relationship between open-loop and closed-loop gain of op-amp?
Answer: Closed loop gain is the gain that results when we apply negative feedback to "tame" the open loop gain. The closed loop gain can be calculated if we know the open loop gain and the amount of feedback (what fraction of the output voltage is negatively fed back to the input).
The formula is this:
$$ A_{closed} = \frac{A_{open}}{1 + A_{open} \cdot Feedback} $$
The open-loop gain affects the performance generally like this. Firstly, look at the above formula. If the open loop is huge, like 100,000, then the 1 + does not matter. \$A_{open} \cdot Feedback\$ is a large number, and it doesn't matter whether or not we add 1 to this large number: it is like a drop in a bucket.  Thus the formula reduces to:
$$ \begin{align}
  A_{closed} &= \frac{A_{open}}{A_{open} \cdot Feedback} \\
             &= \frac{1}{Feedback}\\
\end{align}
$$
So, with a huge open-loop gain, we can easily get the closed loop gain if all we know is the negative feedback: if it just the reciprocal. If the feedback is 100% (i.e. 1) then the gain is 1, or unity gain.  If the negative feedback is 10%, then the gain is 10. With a huge open-loop gain, we can precisely set up gains: as precisely as we care to design and build our feedback circuit. With open-loop gain which is not that large, we may not be able to ignore that 1 +. All the more so if \$Feedback\$ is small.
Okay, so far that's more of an issue of clean math and design convenience. Big open loop gain: closed loop gain is simple.  But, practically speaking, small open-loop gains means that you must use less negative feedback to achieve a given gain. If the open loop-gain is a hundred thousand, then we can use 10% feedback to get a gain of 10.  If the open loop gain is only 50, then we must use much less negative feedback to get a gain of 10. (You can work that out with the formula.)
We generally want to be able to use as much negative feedback as possible, because this stabilizes the amplifier: it makes the amplifier more linear, gives it a higher input impedance and lower output impedance and so on. From this perspective, amplifiers with huge open loop gains are good.  It is usually better to achieve some necessary closed loop gain with an amplifier that has huge open loop gain, and lots of negative feedback, than to use a lower gain amplifier and less negative feedback (or even just an amplifier with no negative feedback which happens to have that gain open loop). The amp with the most negative feedback will be stable, more linear, and so on.
Also note that we don't even have to care how huge the open loop gain is. Is it 100,000 or is it 200,000? It doesn't matter: after a certain gain, the simplified approximate formula applies. Amplifiers based on high gain and negative feedback are therefore very gain-stable. The gain depends only on the feedback, not on the specific open-loop gain of the amplifier. The open loop gain can vary wildly (as long as it stays huge).  For instance, suppose that the open loop gain is different at different temperatures. That does not matter. As long as the feedback circuit is not affected by temperature, the closed-loop gain will be the same.
Comment: The open loop is indeed determined by the IC inside an op-amp. Although op-amps do not have many stages, they use active loads instead of passive load resistors to achieve great gains, which multiply to large numbers over just a few stages. The simple resistor calculations only work accurately because op-amps have such high gains. They are linked to the 1/feedback formula. The terminology you're using for the resistors suggests that you're visualizing an inverting op-amp configuration. This is a little tricky because the input and feedback mix to the same *virtual ground* at the - terminal.
Comment: You might want to start new questions for these instead of going through comments. The inverting configuration has a different input impedance also. Common-mode gain is a non-ideal behavior of real op-amps.  If we send the same input to both + and -, there is some amplification, although smaller than the differential gain. In an ideal op-amp, there would be no common mode gain. This is what the CMRR (common-mode rejection ratio) is all about.  http://en.wikipedia.org/wiki/Common-mode_rejection_ratio
Comment: Take a look at noninverting stages first. They are simple. Input and feedback are totally separate. Input goes to +, feedback goes to -.  The feedback fraction is given trivially by the voltage divider: the output is dropped over two resistors, R1 and R2. The feedback is the ratio between R2 / (R1 + R2). Since gain is 1/feedback, the gain must be (R1 + R2) / R2, or 1 + R1/R2.
Comment: the open loop gain is determined by the IC inside the op-amp, is it?
we just can determine the closed-loop gain by using Vout/Vin where it is determined by the input resistor and feedback resistor, is it?
Comment: what the inverting stages?
Comment: I meant to say, noninverting amplifier configurations of op-amps, sorry. Not "stages".
Comment: sorry. I have to correct my question. what about the inverting amplifier configuration in terms of determining the closed-loop gain for negative feedback ? what is the difference of the inverting and on-inverting amplifier configuration except for its output states?
Comment: A_closed = A_open / A_open * Feedback

         = 1 / Feedback
What is the relationship between common-mode gain and differential gain with closed-loop and open-loop gain ?
Comment: The answer contains the sentence "We generally want to be able to use as much negative feedback as possible, because this stabilizes the amplifier". This is NOT TRUE. It is misleading because it concerns the STATIC stability (of the dc operating point) only. In contrast, negative feedback DECREASES the most important stability aspect: The DYNAMIC stability against ringing (step response) and oscillations. The stability margin always reduces for increasing feedback. That is one of the most important (and sometimes overlooked) consequence of negative feedback.
Comment: @nee (what the inverting stages?): See my detailed answer (EDIT) from yesterday.
Answer: My answer covers the non-inverting as well as the inverting opamp-based amplifier.
Symbols:

\$A_{OL}\$ (ope-loop gain of the opamp)
\$A_{CL}\$ (closed-loop gain with feedback)
\$H_{IN}\$ (input damping factor)-
\$H_{FB}\$ (feedback factor).

For resistive feedback: \$H_{FB} = \dfrac{R1}{R1+R2}\$
A) Non-inverting
Because the input voltage is directly applied to the summing junction (differential input) the classical feedback formula from H. Black applies:
\$A_{CL} = \dfrac{A_{OL}}{1+H_{FB} \cdot A_{OL}} = \dfrac{1}{\dfrac{1}{A_{OL}} +H_{FB}} \$
For \$ A_{OL} >> H_{FB}\$ we have
\$ A_{CL} = \dfrac{1}{H_{FB}} = 1+ \dfrac{R2}{R1} \$
B) Inverting
Because now the input voltage is NOT applied directly to the summing junction (diff. input pair) but through a resistive voltage divider to the inverting terminal the input voltage is correspondingly reduced before the formula for Acl may be applied. Because of the superposition rule we set (assuming \$V_{OUT} =0\$)
\$H_{IN} = \dfrac{-R2}{R1+R2}\$
Hence we have:
\$A_{CL} = \dfrac{H_{IN} \cdot A_{OL}}{1+H_{FB} \cdot A_{OL}} = \dfrac{H_{IN}}{\dfrac{1}{A_{OL}} +H_{FB}}\$
For \$A_{OL} >> H_{FB} \$ we have
\$A_{CL} = \dfrac{H_{IN}}{H_{FB}} = - \dfrac{\dfrac{R2}{R1+R2}}{\dfrac{R1}{R1+R2}} =- \dfrac{R2}{R1} \$
C) Final remark: Taking into account that the feedback factor acts back to the negative (inverting) opamp input the product \$ -H_{FB} \cdot A_{OL}\$ is defined as the loop gain.
EDIT: "How does the value of open-loop gain and closed-loop gain affect the performance of op-amp ? "
D) The following answer concerns the availabel bandwidth for the non-inverting amplifier as a function of the open-loop bandwidth Aol (real opamp):
In most cases, we can use a first order lowpass function for the real frequency dependence of the open-loop gain:
Aol(s)=Ao/[1+s/wo]
Thus, based on the expression for Acl (given under A) we can write
Acl(s)=1/[(1/Ao)+(s/woAo)+Hfb]
With 1/Ao<< Hfb and 1/Hfb=(1+R2/R1) we arrive (after suitable re-arranging) at
Acl(s)=(1+R2/R1)[1/(1+s/woAoHfb)]
The expression in brackets is a first order lowpass function having the corner frequency
w1=woAoHfb
Hence, the due to negative feedback the bandwidth wo (open-loop gain) is enlarged by the factor AoHfb.
More than that, we can write
woAo=(w1/Hfb)=w1(1+R2/R1)
This is the classical constant "Gain-Bandwidth" product (GBW) which can be written also as
w1/wo=Ao/Acl(ideal) .
Answer: It can be helpful to think of this in terms of excess gain, that being the difference between open loop and closed loop gains. For example, if the open-loop gain is 100,000 and the closed-loop gain is 10, the difference is 99,990 or nearly 100 dB. (Read this essay if it is not clear how I converted gain to dB.) If the closed-loop gain is 1,000 instead, that barely reduces excess gain, because the difference is still very large. You have to get within a factor of 10 difference in this case to reduce the difference to below 99 dB.
The open-loop gain of this example amplifier is so high that we can just call the excess gain 100 dB for all practical purposes.
This excess gain contributes to an improvement in performance parameters.  As an example, if the offset voltage of the amplifier is 30 mV and you have an excess gain of 60 dB, the offset voltage of the closed loop system would be improved by a factor of 1000 to 30 µV.  But one must take into account the frequency of operation, as the open loop gain has difference dominant poles and zeros, so if you are operating significantly close to those the explanation becomes less simple.
Also, the concept of open loop gain only applies to voltage feedback, voltage mode amplifiers.  Norton amplifiers, current feedback amplifiers, and OTA based op-amps (like CCI and CCII class amplifiers) have different nuances to their limitations.
Answer: Open loop gain is determined by the gain characteristics of the internal devices and the internal circuit, and for an OP amp can be in the hundreds of thousands. Closed loop gain is determined by the external circuit, trivially the ratio of the input and feedback resistors.
Answer: open loop voltage gain of an operational amplifier is the gain obtained when no feed back is used in the circuit. open loop voltage gain usually exceedingly high.infact an applied an operational amplifier has infinite open loop volage gain.


Why is RPi called 'Embedded Linux'?

Question: I cannot remember where but I recall seeing something somewhere calling the Pi an 'Embedded Linux'. What does that mean? Because I believe it can run other OSes other than Linux such as the Windows 10 IOT core even though Linux is the most common. Did they have the facts wrong or am I just confused?
Comment: Simple answer, The RPi is not called embedded linux ... an embedded linux would be called embedded linux, a raspberry pi is a single board computer
Answer: The Pi isn't really a "linux" anything, it just so happens that GNU/Linux, more specifically Raspbian, which is more-or-less Debian with some tweaks (and also a few pieces of pi specific software -- the Foundation seems to have a dev that puts some work into adding stuff to the GUI, etc, as demonstrated by some recent additions -- but there are some independent things as well, such as omxplayer) has come to predominate amongst the userbase, with the encouragement of the designers/manufacturers.
There are a number of reasons this worked out that way:

GNU/Linux is open source, meaning both freely adaptable and redistributable by third parties (in fact, all the binary distros are from third parties such as Debian -- "GNU" and "Linux" are very separate organizations).
The linux kernel has probably been adapted to a wider range of contexts than any OS kernel in history, and would have required relatively little work to get going on the Pi's SoC ("relative" to writing something brand new, which would be infeasible -- I've seen cost estimates about how much it might cost to develop the kernel from scratch and it is into the billions of dollars).  I think there are some other potential candidates, but not with the same amount of playtesting, including the long paired userland (the "GNU" half of things).

However, while I am sure the Pi designers were aware of linux, I think it would be pushing things a bit to say it was actually designed for it.
Embedded...
Simply refers to a computer system dedicated to a special purpose, where the computer is not really a defining focal point of the "thing" as a whole (although it is probably essential to it functioning).  This covers everything from your set-top cable box to the electronic brains in cars, military weapons systems, etc.  They may be small and simple or large and complex. The linux kernel (as distinct from the aforementioned userland paired with it in general purpose systems) had a well established place in parts of this realm already (including those set-top boxes, and home routers, and no doubt all kinds of other things like POS systems, etc.).
The Pi all by itself isn't really an "embedded" device in this sense, as it has a general purpose set of peripheral interfaces and was not designed with any specific purpose in mind.  But its small form factor and low power and cost make it a good candidate for all sorts of embedded scenarios.  This is why a more appropriate categorization is "dev(elopment) board".  It is an ideal platform for prototyping small scale embedded systems.

Why is RPi called 'Embedded Linux'?


What is the correct visa for a spouse?

Question: I was refused for my standard visitor visa, to join my husband in the UK. We want to re-apply as a spouse but, when I try to create my application online, there is no spouse category. It asks reason for visit, type of visa, subtype of visa. Where do I find the right visa application?
Comment: @GayotFow Yes, your answer is quite helpful regardless
Comment: You want to live with your husband permanently? If so, that's a question for [expatriates.stackexchange](https://expatriates.stackexchange.com/); we only do short-term travel here. You'll want to tell them whether he's a UK citizen or what immigration status he has in the UK. Why did you apply for a _visitor_ visa if you weren't planning on just a short visit?
Comment: @ZachLipton the reverse situation may be topical for us,  see the paragraph beginning with "Conversely..." below :)
Answer: I can see the problem...
There are two portals to apply for a UK visa.  You have found the one for visitors and other types of visas that are issued for 6 months or less.
There is another portal for settlement visas, you can find it by following the links starting at Visa4UK and creating an account.  You will know you have reached the right portal when you see a screen like this...

After the email confirmation is complete, you will eventually see some drop-downs, which you can select just like this...

After that, the program knows what to do.
Note that even though the drop-down label says "Reason for visit" and the correct response for you is "Settlement", which is not a visit category, this is an artefact from an earlier era and you can safely ignore it (it is not a trick question and the form is free from trick questions).

Conversely, people who have located the settlement portal and want to reach the VISITOR portal should follow the links from Apply for a UK Visa.

They may harmonise the two portals at some point making this answer obsolete but I doubt it. Having two portals that do not link to each other makes the process more baroque, and they like that. So do not expect to see harmonisation soon.
Comment: Plus, it may involve different offices for approval in the backend - and, well, we all know how government loves efficiency :-)
Comment: Thank you very much for the quick response. It really a great help for us. So i will apply for settlement.. settlement..wife, which ive found it in the category. Thank you very much.

What is the correct visa for a spouse?


How to make a mobius strip?

Question: I am very new to Blender, so perhaps my question is so elementary.
My background is mathematics and so as my first experimentation I would like to make a Mobius Strip. In mathematics we start with a square (rectangle ) and rotate one edge and attach it to its opposite edge. I tried to do the same (by merging the vertices) in Blender and I noticed that Blender respects the orientation (or maybe I am wrong), that is it defers between front and back sides of a plane.
So I was wondering if there is another way to start from a plane and make a Mobius Strip?
Comment: https://blender.stackexchange.com/questions/14822/how-can-i-create-a-mobius-ring/14825#14825
Comment: [How can I create a Mobius ring?](https://blender.stackexchange.com/q/14822/2217) and [How to bridge edge loops with a twist of .5?](https://blender.stackexchange.com/q/32024/2217)
Comment: @cegaton Mobius Strip is a 2D object, but Mobius Ring is 3D. I am not sure making a Mobius Ring is the same as Mobius Strip. In fact, I am trying  to change the orientation of a surface . And I was wondering if it is possible in Blender.
Answer: I tried to use Bob's script on Blender 2.80, but since a lot of stuff in the Python API changed the script doesn't work anymore.
I adapted it to the new version, you may check it here:
https://github.com/ArthurHDRodrigues/collection_blender_script/blob/master/mobius.py
'''
This is a adaptation(to run in Blender 2.80) of Bob's
script to generate a mobius strip

You may find the original one here:
https://blender.stackexchange.com/questions/82480/how-to-make-a-mobius-strip
'''
import bpy
from math import *
from mathutils import *

def mobius_mesh(resolution, major_radius, minor_radius, thick):

    verts = []
    faces = []

    for i in range(resolution):

        theta = 2*pi * i/resolution
        phi = pi * i/resolution

        rot1 = Matrix.Rotation(phi, 3, [0,1,0])
        rot2 = Matrix.Rotation(theta, 3, [0,0,1])
        c1 = Vector([major_radius, 0, 0])

        V_0 = Vector((-thick / 2, 0, minor_radius)) @ rot1[0]
        print(V_0)
        v1 = apply(rot2,c1 +  apply(rot1,Vector((-thick / 2, 0, minor_radius))))
        v2 = apply(rot2,(c1 + apply(rot1,Vector((thick / 2, 0, minor_radius)))))
        v3 = apply(rot2,(c1 + apply(rot1,Vector((thick / 2, 0, -minor_radius)))))
        v4 = apply(rot2,(c1 + apply(rot1,Vector((-thick / 2, 0, -minor_radius)))))

        i1 = len(verts)
        verts.extend([v1,v2,v3,v4])

        if i+1<resolution:
            ia = i1+4
            ib = i1+5
            ic = i1+6
            id = i1+7
        else:
            ia = 2
            ib = 3
            ic = 0
            id = 1

        # faces.append( [i1+j for j in range(4) ])
        faces.append( [i1,i1+1,ib,ia])
        faces.append( [i1+1,i1+2,ic,ib])
        faces.append( [i1+2,i1+3,id,ic])
        faces.append( [i1+3,i1,ia,id])

    mesh = bpy.data.meshes.new("mobius")
    mesh.from_pydata(verts, [], faces)

    for p in mesh.polygons:
        p.use_smooth=True

    return mesh

def apply(matrix,vector):
    '''
    matrix,vector -> vector

    this function receives a matrix and a vector and returns
    the vector obtained by multipling both of them
    '''
    V_0 = vector @ matrix[0]
    V_1 = vector @ matrix[1]
    V_2 = vector @ matrix[2]

    return Vector((V_0,V_1,V_2))

def mission1(scn, resolution, major_radius, minor_radius, thick):

    me = mobius_mesh(resolution, major_radius, minor_radius, thick)

    ob = bpy.data.objects.new("Mesh", me)

    #me.from_pydata(vertex_list, edge_list, [])
    #me.update()
    bpy.context.collection.objects.link(ob)

mission1(bpy.context.scene, 36, 5, 3, 0.1)

Comment: This works nice, but I get some weird artifacts on it.
Comment: Hi, can you post the parameters that resulted the artifacts, please? Or maybe a screenshot? So I can see the artifects.
Answer: The Mobius strip as a 2D object will run into the conflict with normals, and while it can be achieved geometry it will restrict usage. In the example below the solidify modifier 'breaks' at the connection.

Depending on what your final output is, it seems it is more flexible to have a ring, essentially creating an inner and outer surface.

In the comments to your original post there are some examples as to how to create both rings and strips, but for simplicity I have added another which involves rotating one split edge 180 degrees with proportional editing set to connected.
Comment: From your answer, I understand that we can merge two vertices only if their normals have the same direction. In other words, two vertices with opposite direction can't be merged. Is this a valid conclusion? So, mathematically speaking, we can only produce orientable 2D manifolds in Blender.
Comment: As far as I know a vertex cannot be bi-directional. Vertices can be merged, but only one direction is chosen.
Answer: Since I like blender's embedded python interpreter I use python code to construct any mathematical thing I dream up.
For a möbius strip I wrote http://web.purplefrog.com/~thoth/blender/python-cookbook/mobius-strip.html which I include here (for version 2.79):
import bpy
from math import *
from mathutils import *

def mobius_mesh(resolution, major_radius, minor_radius, thick):

    verts = []
    faces = []

    for i in range(resolution):

        theta = 2*pi * i/resolution
        phi = pi * i/resolution

        rot1 = Matrix.Rotation(phi, 3, [0,1,0])
        rot2 = Matrix.Rotation(theta, 3, [0,0,1])
        c1 = Vector([major_radius, 0, 0])
        v1 = rot2*(c1 + rot1 * Vector([-thick / 2, 0, minor_radius]) )
        v2 = rot2*(c1 + rot1 * Vector([thick / 2, 0, minor_radius]) )
        v3 = rot2*(c1 + rot1 * Vector([thick / 2, 0, -minor_radius]) )
        v4 = rot2*(c1 + rot1 * Vector([-thick / 2, 0, -minor_radius]) )

        i1 = len(verts)
        verts.extend([v1,v2,v3,v4])

        if i+1<resolution:
            ia = i1+4
            ib = i1+5
            ic = i1+6
            id = i1+7
        else:
            ia = 2
            ib = 3
            ic = 0
            id = 1

        # faces.append( [i1+j for j in range(4) ])
        faces.append( [i1,i1+1,ib,ia])
        faces.append( [i1+1,i1+2,ic,ib])
        faces.append( [i1+2,i1+3,id,ic])
        faces.append( [i1+3,i1,ia,id])

    #print (verts)
    #print (faces)
    mesh = bpy.data.meshes.new("mobius")
    mesh.from_pydata(verts, [], faces)
    mesh.validate(True)

    for p in mesh.polygons:
        p.use_smooth=True

    return mesh

def mission1(scn, resolution, major_radius, minor_radius, thick):

    mesh = mobius_mesh(resolution, major_radius, minor_radius, thick)

    obj = bpy.data.objects.new("mobius strip", mesh)
    scn.objects.link(obj)

    mod = obj.modifiers.new("edge split", 'EDGE_SPLIT')

mission1(bpy.context.scene, 36, 5, 1, 0.1)

For blender 2.8 you will have to replace scn.objects.link with scn.collection.objects.link.  For blender 2.9 you will have to replace the rotn * with rotn @ because of (TypeError: Element-wise multiplication: not supported between 'Matrix' and 'Vector')
You will notice that the special case where ! (i+1<resolution) which binds the end of the strip to the start has a little twist to cope with the möbiusness.  This twist would not be necessary for a torus.

With some practice you can write python to construct any mesh you like out of whatever mathematical structure you want.
Comment: For some reason I´m getting an error in line 21. I´m using the latest Blender version.
Answer: This is an old question-- which makes it pretty surprising that during this time nobody ever gave a curve-based solution?
I think that curves are the easiest way to do this:

Careful: that's not a cyclic curve.  That's a non-cylic curve with 5 different control points, two of which have the exact same location (and handles), but which have a twist that is offset by 180 degrees.  That lets us interpolate the curve smoothly across the entire structure.  In order, the tilts of the controls are 0, 45, 90, 135, 180 degrees.
I've added a weld modifier to the curve to join the end and the beginning.  And I'm showing it with face orientation overlay so that you can see the normals are all pointing outwards (after giving the curve object a bevel and extrusion.)
The simplest way to make this particular object: make a bezier circle.  Enter edit.  Change all handles to free.  Duplicate one segment of the curve.  Toggle cyclic on the curve.  Fill the hole created by toggling cyclic with the duplicated segment: rotate as needed; connect two coincident controls; dissolve the segment between those coincident controls.  Enter tilts manually for all controls.  Edit curve geometry settings as desired.
This is not a one-sided 'thin' mesh.  The bevel property, generated by curve, makes it a solidified mesh, solidified about the center of the curve.  Just as there is no such thing as a one-sided surface in reality (even a paper moebius strip is a volume, not a surface), one-sided surfaces in Blender or almost any other rendering engine are going to give you undesirable results (but if you want, just disable the bevel on the curve and play with it!)

How to make a mobius strip?


Analyzing hot spots using point attributes?

Question: I'm interested in looking at where hot and cold spots of certain social indicators (such as poverty, housing characteristics, urban sprawl, etc...) are in coastal communities along the East Coast. I have point and polygon features containing the same attribute information. My point data are centroids of the polygons.
My first thought was to use the Hot Spot Analysis tool in arcgis but, because I'm looking at coastal communities, my polygons don't have many neighbors (some don't have any) so I don't think my results would be very accurate. So I thought there must be a hot spot analysis that  I can do using my centroid points that have the same attribute information but the only analyses I can find have to do with spatial clustering of points- not of their attributes. Does anyone know of an analysis I can do to solve my problem?
Comment: Right after reading your question the term "spatial aggregation" came to my mind. Before running to the nearest patent bureau I searched for this term and found that it's "in labs" today. :)
Answer: If your data density is so low that it is non-contiguous, the obvious alternative, which is frequency hotspot analysis using raster surfaces, won't be so good either. Also raster surfaces are not good near coastlines due to weighting issues (some cells have large chunks of sea, then you have to fiddle with weighted corrections - which requires dense paragraphs of mumbo jumbo in the report and is not so convincing to an audience).
If the data density is low enough that the resulting map won't be crowded, why not go for a bubble map? They are straightforward and easy to interpret, and you can make bubbles of your individual attributes or else indexed distributions (bubbles that represent a combination of factors).


Why does light bend after travelling half of the lens?

Question:
As light enters a denser medium from a rarer medium, it bends towards the normal. Why does the light bend after passing through point F & not E?
Comment: it doesn't, it's a simplification
Comment: Similar earlier question on [physics.se]: [Why doesn't a light ray bend again when emerging from a lens?](https://physics.stackexchange.com/questions/659006/why-doesnt-a-light-ray-bend-again-when-emerging-from-a-lens)
Comment: This is a 'thin lens' approximation. As the lens is 'thin', it doesn't really matter whether the refraction takes place at the two faces of the lens (which is what actually happens) (see NMech's diagram), or the centre of the lens (which is a close enough simplification). Optics is hard enough for most students to grasp, so it's made easier for them by just having one deflection point, to make diagrams easier to draw.
Comment: Refraction depends on the index of refraction. While that may be affected by density, density itself does not cause refraction (unless you mean optical density, in which case saying just "density" is misleading).
Answer: It changes on both E and the exit point of the beam (see image below).

source
My understanding is that refraction occurs at any boundary that there is a change of the wave propagation velocity.
The image in the original post is a simplification which is used either as an introductory image or to describe other aspects where what happens inside the lens is not important.
Comment: Your image is also a simplification... Optics is a weird rabbithole of ever complicating simplifications, all of which refuses to make sense untill you start reading some QM, at which point the world you realize that the universe refuses to make sense, in general.
Comment: More to the point, OP's diagram is commonly used when introducing and illustrating the assumptions of the [thin lens approximation](https://en.wikipedia.org/wiki/Thin_lens).
Comment: @StianYttervik I agree. I can't argue with what you are saying.
Comment: Yes you are right. My eyesight is not what it used to be. I'll correct it.
Comment: Should be E and the exit point (unlabelled), not E and F
Comment: "Focal point" is not unique ... It is a "function" of the "height" of incident ray.
Answer: You are right, rays refract at both the entry and the exit points. That drawing is just a simplified diagram, frequently used in textbooks about geometrical optics. It helps to illustrate concepts like parallel rays, focal point, object distance, image distance etc. where we do not really care what happens inside the lens.


What is Cushing's disease?

Question: I have been told that if you catch a dog drinking their urine it's a sign that they might have Cushing's disease. What is Cushing's disease and why would it cause dogs to drink their urine?
Answer: Cushing's Disease (or Syndrome, which is the symptoms) is also known as Hyperadrenocorticism which, according to Merck is a illness that is either a result of:

Enlargement of the pituitary gland as a result of a benign tumor and this results in excessive production of adrenocorticotropic hormone.
Cancer of the adrenal glands.

Symptoms, in either case, commonly include:

Excessive thirst
Excessive urine output
Increased hunger or appetite
Heat intolerance
Enlarged belly
Panting
Lethargy
Repeated urinary tract infections

So, why might it be a sign of Cushing's Disease when a dog drinks it's own urine? That would be a consequence of the first symptom I mentioned: extreme thirst. A dog that is extremely thirsty and has insufficient water resources may resort to drinking its own urine to help rehydrate.
Treatments are available, though they're not something you would administer at home. The actual treatment really depends on the source of the syndrome, but may include surgical intervention or radiation therapy.
Comment: Treatments can be administered at home. I had a dog with
Cushing's who was treated with Trilostane, though we did go in for monthly vet visits to adjust his medication and check his levels.  Cushing's Disease is very commonly associated with dachshunds.
Comment: @JoshDM - Benign tumor I would guess? Cancerous growth would normally be very medical.

What is Cushing's disease?


What to do if your husband is muktzeh

Question: My husband is muktzeh (he was born in the eighth month and is now nineteen). Our marriage is going well. However, sometimes on the three-day Yom Tov it becomes difficult that neither I nor anyone else can p̶a̶s̶s̶ ̶h̶i̶m̶ ̶t̶h̶i̶n̶g̶s̶  pass him to things at the table. Is there any solution for this?

This question is Purim Torah and is not intended to be taken completely seriously. See the Purim Torah policy.
Comment: @SAH You can touch muktza if you don't move it (eg. a very big heavy item)
Comment: I think this is misrepresenting the Halacha. Because he's muktzeh you can't move him, but you still may pass him items without physically moving his hand. In PTIJ, everything but the subject of the joke should be accurate. Perhaps it's your three year old who's muktzeh and likes to tantrum ; )
Comment: ask him to pass to you
Comment: 3 days of no passing seems not too bad compared to Niddah...
Comment: @DoubleAA Right but it's not only me! No one can pass anything to him! He sits alone.
Comment: @LN6595 Aren't we not supposed to touch muktzeh? anyway Shabbos is a good time to be machmir
Answer: From RaMBa"M's Hilchot Milah - Chapter 1
Halacha 13

Nevertheless, if such an infant remains alive for thirty days, he is considered to be a child who will live and is governed by all the same rules as other infants.

From this, I gather that since your husband is muktzeh, he must be younger than 30 days old (your question says he's 19, so I'm assuming you mean 19 days old).  Since you are implying that you are not muktzeh you must be older than 30 days old, but I will assume that you are also somewhere close to this age range so that things aren't as creepy.
As it turns out, since your husband is so young, you can't really be married after all. While the kiddushin can happen at a very young age, the minimum age for a marriage to take effect is 13 for boys and 12 for girls.  So simply don't worry about it.  Go play with your mommy and daddy for a few more years and then you can safely marry your husband when he turns 13 without any concern for him being muktzeh.
Comment: Rashi: "It is necessary to wait twenty years in order to determine that the person is fit to live and that he is not a Nefel, a stillborn."
Comment: (Trust me, if there were any doubt about it, my husband would be circumcised by now.)
Comment: a girl can be mikudeshes under 12 years old
Comment: @hazoriz Yes, note what I said in the answer. You can do kiddushin at a very young age, but she is not considered married until the age of 12. At that time, she has the option of selecting _mi'un_ and the marriage is retroactively annulled.
Comment: If someone that is not her husband has relations with her (I guess after she is 3) does he not get killed? (But if she was not married then he does not)
Comment: her husband is permitted to have relations with her before she is 12? (Do we not learn that when she has relations at age 11 she can use contraption)
Comment: What you are saying is only by a second marriage but if her father married her off the first time then she needs a get see http://www.jewishencyclopedia.com/articles/10888-mi-un
Answer: As someone who was born on the 9th day of the eighth month of the seventh year (of this century) of the sixth millenium (9 Cheshvan, 5707) I can understand your problem. Even if your husband is muktzah you do not have a problem.
First, being muktzah just means that you would not be allowed to move him from one place to another. Thus, you would not be allowed to pick him up and pass him to someone else. You would be allowed to pass to him other items at the table or to put something down next to him so that he can pick it up.
Second, since the two of you are married, he is a Kli shemelachto l'heter. Thus it is mutar to move him letzoraech gufo or letzorech mekomo. You would also be allowed to move him letzorech mitzvah. Thus oneg shabbos or oneg yom tov would also be allowed. This allows any of the things that are part of the oneg including those actions that require you to move or touch him.
Comment: is not a Kli shemelachto l'heter permitted to be moved for any tzoraech?
Comment: @hazoriz What other tzorech is there?
Comment: (Letzorech gufo and mekomo is by kli shemelachto **l'isur**) an example would be to move it so that it should not get ruined (gufo meens to use it)

What to do if your husband is muktzeh


What are the security disadvantages of rooting an Android phone?

Question: I know there was a discussion previously BUT they didn't talk about security. E.g.: if I root my phone will all my apps run with root permission?

Related: Are there any risks to rooting a device?
Answer: If you root your phone, then only the applications that you explicitly grant root access to will have root access.  This does make things fairly safe, as that extra step should be enough to make you stop and think "Why does this app need root?".
If you only grant root access to apps that need root for a good reason, are from trusted developers, and which you acquired from a trusted source then you should be ok.
Bear in mind what apps with root access can do though - from a previous answer on the subject:

On a rooted phone, an app which has been granted root access can do pretty much anything  that is possible in the hardware. Apps that have root permissions can write on non-read-only storage media (including modifying the bootloader), modify other programs' private data, modify system settings, modify system files, etc. A rooted app can also hide itself from the system, and pretend to be uninstalled while being perfectly well and alive.

I'll let you imagine what the worst-case scenario security implications are for a nefarious app being granted root access on your phone; be careful out there.
Answer: The answer is no: not all application will have root permission.
Not all the apps require root and the apps requiring root will not have it unless you give them permission to do so.
At least that's what I can tell after using z4root and superoneclick to root a few phones.
You get a superuser app that will get requests from apps needing the root account and you'll have the option to enable that or not.
Risks connected to rooting a device are, more or less, the risks connected to using an administrative user on any kind of Unix-like system.
Ever tried a rm -R (a command to delete all files) on GNU/Linux?
It's like putting in the recycle bin your Windows folder and empty it just because you're a root user and you can do it.
Superpowers always involve super responsibilities and super attentions :)
Said that I have to say that in my everyday use (with a little brain turned on) I can't see a real way to get any kind of harm.
But if you install strange scripts coming from al quaeda and tons of pirated apps and poor not certified code...
Well. Bad things could happen.
Install a recovery and do a nandroid backup.
After that play happily with your phone :)
Comment: to be more precise, if you do `rm -r`, it's more like burning the folder to ash; if you simply put it into the trash can, you will still be able to restore it relatively easily; but if you do `rm -r` in any unix-like system (including Linux and Android), you may have to do dark voodoo to recover the files and you may not necessarily recover the file intact.
Comment: Don't you mean `rm -rf`?
Comment: The `-r` flag (also `-R` for compatibility with some older Unix systems) means recursive, `-f` means forceful, i.e., you won't get a prompt asking you whether you really want to delete every single file in the (recursive) file and directory list.
Answer: The newest versions of SuperUser (3.x) support using a PIN to approve root access for apps.  In other words, whenever an app requests root you need to enter your PIN before root access is granted.  This is more or less foolproof; no app should be able to get root access on its own or through you clicking the wrong button without it exploiting some bug in SuperUser or the system, and if it's doing that you might be screwed even without root.
Comment: How can we be sure that the SuperUser app is not the one that is malicious? (Not refering to a special app, just asking in general.)
Comment: @MarcoW SuperUser is released by Chainfire [here](http://androidsu.com/superuser/); coupled with that official release you should be able to analyze any root method and do it yourself, at least if they've made the details available.  That really is the crux of security issues, though: You have to trust someone else in order to gain anything from them. Nothing we can do about that.
Comment: sry for asking, but what the hell is a "superuser 3.x" - is it binded to an Android version?
Comment: @LanceBaynes It's a version of the SuperUser application, which comes with its own su binary that screens requests for root access - you must approve the access before the app gets root.
Comment: @MarcoW. You can't, just like you can't be sure that the binary isn't malicious or that the browser isn't malicious or that every last but of Android is Google trying to steal your secrets :P.  If you don't trust your source, don't trust the software you get from that source.
Comment: This is the problem. The sources for rooted Android are always normal forums with users who made them independently. So how can you be sure to get a non-malicious package? You can't.


Win7 64-bit to Win8 Pro upgrade

Question: I bought Windows 8 Pro on Microsoft's promotion. I used upgrade assistant while installing and it got to 90% and stayed there for an hour and a half until I cancelled it. It didn't respond, so I ended the task and retried. It did the same thing, and then it wouldn't start, so I sought help. $150 later and after the deletion of anti-virus and anti-spyware it is now installed, but a majority of my apps don't work properly. So I went back to tech support only to determine that I had a 32-bit version; I was already using Windows 7 64-bit so how do I now go to 64-bit?
Answer: You need to clean install the 64-bit version. You cannot upgrade from 32 to 64-bit. The Upgrade Assistant will also not download the 64-bit version if you run it from within a 32-bit OS (or vice versa).
I suggest you get the 64-bit version on a 64-bit PC, then use the option to create install media on USB/DVD (ISO). Use that to boot from, format, reinstall the OS and all your apps and finally copy your personal data back from a backup (I know it's a lengthy process, but the best thing to do is start afresh from a clean slate).
Edit: On a second read, your post seems to imply that the Upgrade Assistant downloaded and installed Windows 8 32-bit onto Windows 7 64-bit? That is just not possible.

Win7 64-bit to Win8 Pro upgrade


Paint bubbling and peeling on a steel door

Question: I have a steel front door, behind a solid glass storm door. It gets so hot that paint bubbles and peels. Any suggestions?
Answer: I'd bet on "poor preparation/paint job" (given that preparation is 90% of a good paint job.)
If you wanted to, you could use a high-temperature paint such as engine enamel (typically good to 450F or more) (no need to go for the exhaust-manifold paints unless your doorframe is charring, I think.) I strongly suspect that's not really needed; you could put a magnet on a thermometer and stick it to the door to get a reading for what the temperature actually is some sunny day.
Answer: Depending on the glass door, you can buy vent kits to install in your outer door. What color is the door? Maybe you could paint it a lighter color.  Maybe you could plant a tree that could provide some shade in front of it.
Comment: Good ideas, but there's a chance it was just a poor paint job to begin with.
Answer: I was able to find some vents that I can install in the bottom and top of the storm door. Hopefully this will help some, and it will will be an easy option to try, before more expensive options such as a complete main door/storm door replacement.


Best way to show the image is zoomable?

Question: I have a design where an image can be zoomed in in a lightbox. What is the best way to do it on mobile (should you allow it on mobile at all) and desktop?
Answer: There are a few ways you can do this. I'm not sure if there's a clear 'best way' to do it. That might be opinion based.
Here's a few things I thought of.

Have an icon in the corner that indicates zoom.
Have a percentage in the bottom corner (like a lot of editing tools have)
Show a touch-to-zoom text/overlay when the user hovers the image.
Have a +/- button in the corner of the image.

I would consider not using zoom on mobile. Imagine if a user is scrolling through a website using touch and he accidentally hits the photo while scrolling, it will zoom. This can confuse the user.
There's also a great article by Nielsen Norman Group about lightboxes and overlays. Check it out here.

Summary: Poorly implemented overlays and lightboxes are not only
  frustrating for users, but can also be disastrous for conversion and
  task completion. Use the five W's – Who, What, When, Where, and Why –
  to determine whether an overlay is truly the most appropriate design
  solution, and how you should implement it.

I always liked this one (personal preference). It's an overlay with zoom icon.

Best way to show the image is zoomable?


Go end game scoring question

Question: I'm trying to learn Go and I'm very confused by how end of game scoring works. I've played a game against an AI player, and I don't understand the scoring that the computer came up with once the game was over. In the screenshot I've included, I don't understand why the points marked 1 and 2 are counted for white and not black. Can someone help me understand this?
Comment: As the best answer says, your programme does not manage this well. A good place to get information is Sensei's Library, especially [the beginners' pages](https://senseis.xmp.net/?PagesForBeginners). Actually I think that if both the White (foolishly) and Black passed here (two passes end the game), 1 and 2 should be scored for Black, who currently controls these points. Did the computer really say the game was over, or did you assume that? Anyway, it has given you a prediction based on optimal play.
Comment: @PJTraill Yes, this is after both I and the AI passed and the game finished (sorry, I fixed the language).
Comment: "the points marked 1 and 2 and white and not black" -- did you mean "... are white ..." or (better) "... count for white ..." .
Answer: @TimK and @KMR are correct -- the game is not quite finished yet, because the stone in atari (that you labeled "2") needs to be resolved.
Having said that, it's worth mentioning that many computer programs are not good at figuring out ambiguous positions (like an unresolved ko that remains after a player has passed prematurely, for example).  Some computer programs are very good at figuring that out; some are not.
From the screenshot, I don't recognize the software you're using; but what should have happened was (assuming you were playing as Black and the computer was playing as White), after you passed, the computer should have played at 2 (thereby capturing the stone you labeled "1") and waited for you to move.  You don't have any significant ko threats, so you would pass again (or play a ko threat that doesn't work); and the computer next should have filled the ko by playing at "1".
Answer: This game isn't really finished. The stone at 2 is in Atari, so black needs to connect at 1. Then there won't be any points in those two locations.
Answer: The spaces at 1 and 2 will be counted for white if white was to make the next play, and area scoring is in use.
This is due to Ko.
White is able to capture the black stone at by playing into space 1, but black may not respond by playing space 2, as it would return the board to its previous state.
Once white has played space 1 they can follow up on their next turn playing space 2, to take their stone in space 1 out of Atari.
Answer: This is not due to the rules of go, but to the fact that an AI is scoring the game all on its own, and tasked with the responsibility of deciding which stones are dead and which stones are alive. The situation you've shown is somewhat unresolved, so the AI is struggling.
The AI is scoring the game and does something not done in real-life, which is to automatically decide which groups are "dead". For instance, the AI found that the two black stones on the southwest are dead.
But the AI got confused by the black stone left in atari, which can either live, if black plays first and connects it, or die, if white plays first and captures it. The AI somewhat arbitrarily marked it as dead (because white could capture it).
Even if the black stone dies, the extra point of territory marked for white doesn't make sense. I am guessing this game was played on BadukPop, so the game should be scored according to Korean rules, and there is no reason why the point marked "1" should be counted as White's territory. This is most likely a bug of the AI and scoring algorithms not really being designed to score properly a game where a stone is left in atari like that.
How scoring would have worked out without the AI
If the game had been played by two humans, rather than a human against an AI, the game would end in either of these two ways:

the humans will not notice that the black stone can be captured; they will leave it on the board and count one point of territory for black; or
the humans will notice that the black stone's situation is unresolved; they will resume the game, and either the black stone would be captured by white or connected by black, depending on who gets to play first.

The second possibility is the most likely.

Go end game scoring question


What would be the ideal plane specs that minimizes consumption for 1000 kg of cargo payload (slow speed, wing span, whatever..)?

Question: Speaking of electric planes, I wonder what'd be the optimal specs if the only variable that we'd try to optimize was consumption (assuming a 1000 kg payload and 600 mile legs, unrestricted runway)?
Comment: Welcome to Aviation Stack Exchange! I did my best to answer your question, but it's a broad topic you are asking about. I think you'd get better answers if you asked more specifically how parts of a plane affect flight performance.
Answer: The most fuel-efficient configuration would be one having a very high L/D. The best examples are modern sailplanes, aerodynamically clean, and with very long, slender wings.
Answer: To truly answer this question you would have to outline all the theories of aerospace engineering and explain how they interact with each other.
Everything on an aircraft is a trading game, you want more speed, you're probably going to have an aircraft that's hard to control at low speeds since the control surfaces can't be very large when facing extreme wind speeds..
However there are only 4 basic forces of flight. Thrust, Lift, Drag, and Weight. All the crazy designs we come up with in aviation is us trying to manipulate those 4 forces in a way that fits the desired results.
In almost all cases the idea is to maximize Thrust & Lift while reducing Drag and Weight.
You've already kind of locked in "Weight" at 1000KG. However 2 things also add to the weight. The structural weight of the aircraft, and the counter lift weight the real tail wing produces.
So our best airplane would be made out of some super space material that is as light as possible to avoid adding structural weight.
Also on most planes the tail wing produces downward force to stabilize the aircraft and provide stall recovery. However this isn't a requirement, with modern computers powering on the fly adjustments people have made flying wings.
This is really the best aerodynamic shape we have at maximizing lift/thrust ratios. The longer the span of a wing, the more efficient it is.
So basically your plane would be made out of space age composites, have a wing span as long as physically possible and a computer powered control system to keep it all aerodynamically stable without a tailwing.


Will prices really be different for cash and cards?

Question: I heard Clark Howard on the radio this morning saying that due to a court settlement stores will be able to charge different rates for different tender types.  How soon will this take effect and what kind of changes can I expect to see?
Comment: dup: http://money.stackexchange.com/questions/3196/can-a-merchant-charge-you-more-if-you-want-to-use-a-credit-card
Comment: @Michael I'm asking about recent changes, I'm not sure it's a dupe.  We should update your question at least.
Answer: I think the question relates to the discussion here:
http://clarkhoward.com/liveweb/shownotes/2010/10/05/19449/
It was always the case that merchants could discount purchases made with cash.  What wasn't allowed is allowing the merchant to charge extra for credit card transactions (presumably to cover the fees the merchants pay).  These fees usually carry a flat fee per transaction, plus around 2% of the purchase price.  What also wasn't allowed was them to refuse any credit transactions.  People could charge a pack of gum, even if the fees put that transaction in the red.
What's allowed according to this new development is different levels of discounting for different credit cards.
Somewhat related to this discussion is another development that happened this summer: merchants now have the ability to refuse credit card transactions of less than $10.
Here's my feeling on all of this.  I think we'll see merchants imposing minimum credit transaction amounts before we see them monkeying at the 1-2% level on pricing for different types of credit cards.  My feeling is that they'd be wise not to change anything, even though they can.  Refusing transactions (or charging more for others) is going to come as a unpleasant shock to enough people that they may take their business elsewhere.
Answer: There are many gas stations where I live that already have different prices if you pay for cash vs. credit.  In addition, some small businesses are doing this as well.  My wife bought a birthday cake from a bakery.  If you paid with cash, you saved 5%.
Answer: I would say minimal price differences.  Stores will need to remain competative, and the difference (if any) will likely be to cover the cost of the transaction that Visa and other card companies charge them.
Answer: My guess would be for small merchants there could be a small difference.
For large merchants, the cash is also at a cost equivalent to the card fees.
Check for my other answer at
How do credit card companies make profit?


Why the ARP entry of the router recover so quickly after ARP poisoning?

Question: I use Cain to ARP spoof my host and the router. Then I use arp -an to show the ARP entries on my host.  For a second or two, I can see the router's MAC address is changed to the address of the attacker, but it recovers to the router's valid MAC address immediately.  Both Linux and Windows 7 are installed on my host, both have the same phenomenon. I use wireshark to sniffer the packets, there's no packets sending from the router.  How to explain this?
Answer: Every time a host wants to communicate with another host on a local area network segment it must somehow determine its physical address (this is what a MAC address is, after all).
The process of physical address resolution occurs with the ARP protocol. This process consists of an exchange of ethernet frames in order to map logical addresses to physical addresses (most commonly, IP addresses to MAC addresses).
Now if this process happened every time 2 hosts wanted to exchange data on network segment, this would negatively impact the network performance -especially in cases where there is a large number of hosts that constantly communicate with each other.
To solve this problem, networked systems cache the physical address entries locally for a certain period of time. This way, each time a system wants to interact with another system on the local network, it looks up the physical-to-logical address mapping in a table stored in its memory. This is much, much faster than the address resolution process mentioned earlier.
The entries in the ARP cache are not permanent, though. They have a certain lifetime and once it expires they are refreshed again through a new ARP lookup. This method minimizes the global number of ARP lookups required for communication and at the same time keeps the logical-to-physical address mappings up-to-date.
In order to "preserve" an ARP Man-In-The-Middle situation, you need to constantly spoof the MAC addresses in order to keep them in the ARP caches of the targeted systems for the duration of the attack.
The lifetimes of ARP cache entries are implementation-dependent and vary from operating system to operating system.
You mentioned that you didn't see any "packets" in Wireshark, therefore I assume you were capturing IP traffic. The ARP look-ups occur on a lower level (Layer 2) and it uses ethernet frames and not IP packets for data exchange.
Answer: I'll go ahead and preface this with the obligatory "I'm not a networking expert" statement, but if I remember correctly, this behavior has to do with resolution of IP address conflicts.  Essentially, the router is broadcasting an ARP announcement in an attempt to determine if there are any other hosts on the network with its IP address.  When the connected hosts receive the ARP announcement, their ARP cache is updated with the MAC and current IP of the router.
Comment: Thanks. But I didn't see any ARP broadcast from the router.  I'll re-check this.
Comment: This thread gives me some hints http://stackoverflow.com/questions/15372011/configuring-arp-age-timeout


"I'm new here and would appreciate your guidance"

Question: I'm a Hong Kong English learner. There's a Chinese phrase usually used when introducing yourself to a new group, that means "I'm new here and would appreciate your guidance." Would it sound strange to your ears? Thank you!
Answer: You might be asking about this greeting:

请多关照 Trad. 請多關照
  qǐng duō guān zhào
  please treat me kindly (conventional greeting on first meeting)
- yabla

English greetings don't normally carry such formalities / courtesies, and asking for open-ended guidance from newly introduced strangers might be considered self-deprecating. For the host, having a visitor ask to be treated kindly might prompt them (the host) to ask when they acquired a reputation for not being kind.
Idiomatic greetings sometimes sound odd in translation. For example, the Chinese sometimes use "Have you eaten?" as a greeting; that might elicit the reply "No, are you offering (lunch)?". I suppose the formal English greeting, "How do you do?" sounds just as odd in other languages, especially when the expected answer is to repeat the same phrase. (Then again, the Chinese "ni hao" follows a similar protocol.)
Another point to note is that while English might be a common language, each cultural group can have its own idiosyncracies. In Australia, it's common to greet each other with "How's it goin' (going)?", where "it" is left unspecified, not to mention where or even how "it" went. It's very easy to commit a faux pas when crossing cultures.
If you're joining a group for the first time, it's quite safe to just say "Hi, I'm Omega (assuming that's your name). This is my first time here."

“I'm new here and would appreciate your guidance”


How to use own REST API in web front end?

Question: I have implemented a JSON-based REST API for a simple blog. The API allows for the creation, viewing, deletion and modification of user info, blogs, blog posts, comments, 'likes', etc. Some of these operations, such as deleting a blog post, require authentication. This is done using basic access authentication.
Now I need to implement a web front-end for the blog. The front end needs to be able to do all the same things as the JSON API, so it would make sense to use the API for the front end. The JSON API and the web front end are served by the same process on the same machine.
How should I use my JSON API for the front end? Should I use it at all? The options that I can think of are:

The server recieves the request for e.g. a certain blog post. The server does a HTTP request to the JSON API, and passes the results straight to the template renderer, which returns the rendered page to the client. This would require storing the user's password in plain text for the duration of the session, so that the operations requiring authentication can be completed.
An AJAX call is used to request the JSON, which is then rendered to the page. If the user has logged in successfully, the username is already associated with the session, so no password is required for calling the JSON API.
Both the web front end and the JSON api use common code to manipulate the database, and each are responsible for using it correctly. This would require some refactoring.
The JSON API and the web front end are totally separate, meaning that everything has to be implemented twice and maintained separately.
Answer: You have many options:

Basic authentication over SSL
https://thoughtfulsoftware.wordpress.com/2014/06/30/pre-emptive-http-basic-authentication-with-jquery/
Create a UI with the ability to log-in, create, view and delete blog posts
JQuery has JSON and AJAX capabilities built-in

You just have to explore and decide which libraries to use and what to write yourself and integrate it all together with tests.


How to bulk convert ISO8859 text in Text columns to UTF8 in nvarchar(max) columns?

Question: I've been struggling for days with a problem on a MS SQL database. Here is the situation: I have an old Open Source PHP application (Limesurvey version 1.92) running on a Windows 2008R2 server, with SQL2008R2 as RDBMS. I need to migrate the surveys in the application to a new instance, running on Linux with MySQL. The new instance is version 3, and database structure between both versions is different. The scenario I tried to use is upgrading the old version on the old server, and then exporting the surveys as export files, which I can import into the new application. It works well. Except that I'm stuck because of a problem of character encoding. The old application (web application) uses UTF-8. But the database uses only VARCHAR and TEXT columns. Therefore UTF-8 characters are stored using several bytes in these columns : é is stored as é for example. When I upgrade the application, the upgrade script changes the structure of the tables: TEXT columns become NVARCHAR(MAX), but the content in the column is not converted to UTF-8. So I'm searching for a way to change the content in the NVARCHAR(MAX) columns from ISO8859 to UTF-8. The database has approx 200 tables and is 600MB.
Answer: SQL Server 2008r2 dopes not support UTF8 (such support does not arrive until the upcoming 2019 release) it only supports UCS2 (essentially a subset of UTF16). Because of this there is unlikely to be a practical solution in SQL Server itself.
You may have to code up a tool to pull the data out, convert it, and update the DB with the newly converted values.
On rereading the question, I notice you mention mysql as the target database, though your tags do not mention that. The types you mention (NVARCHAR etc.) are not mysql types. You may need to clarify the question and update the tags.
Answer: The question is a little unclear due to indicating the need to migrate to MySQL yet only mentioning SQL Server datatypes. Are you meaning to say that the "upgrade" process is converting everything within SQL Server first, and then you will export the data and import it into MySQL? Depending on the specifics of the situation, it sounds like you have at least a couple of options:

If the app really did store the UTF-8 bytes such that you have é instead of é, you can probably export the data from the VARCHAR / TEXT columns into a text file using the code page of the collation of the columns. You can find this using the following query:
SELECT col.[name],
       col.[collation_name],
       COLLATIONPROPERTY(col.[collation_name], 'CodePage') AS [CodePage]
FROM   sys.columns col
WHERE  col.[object_id] = OBJECT_ID(N'dbo.InfoSchemaBug')
AND    col.[collation_name] IS NOT NULL;

Using the same code page will ensure that the bytes written to the file are what is already in the columns, and the bytes (not the characters) in the columns are correct.
Once the data is exported, simply import into MySQL, but this time tell the import process that the file is actually encoded as UTF-8. Since the bytes were UTF-8 to begin with, it is still UTF-8 data (as long as the bytes didn't change during export).
Since internal UTF-8 support doesn't start until SQL Server 2019, you can still convert the data in-place into Unicode (UTF-16) such that it can be exported to a "Unicode" (i.e. UTF-16 Little Endian) file that should still be importable into MySQL as long as you indicate that the file is encoded as UTF-16 LE. You can try the following which uses a conversion to XML (from VARCHAR, but is written to handle if you run against the already converted to NVARCHAR column) to handle the conversion:
CREATE TABLE #UTF8bytes
(
  [Data] NVARCHAR(MAX)
);

INSERT INTO #UTF8bytes ([Data]) VALUES (N'é&');

SELECT *,
       CONVERT(NVARCHAR(MAX),
               CONVERT(XML,
                   '<?xml version="1.0" encoding="utf-8" standalone="yes" ?>'
                      )
              ) AS [Converted]
FROM   #UTF8bytes tmp;
/*
Data    Converted
é&
*/

UPDATE tmp
SET    tmp.[Data] = CONVERT(NVARCHAR(MAX),
               CONVERT(XML,
                   '<?xml version="1.0" encoding="utf-8" standalone="yes" ?>'
                      )
              )
FROM   #UTF8bytes tmp;

SELECT *
FROM   #UTF8bytes tmp;
--

After that you just need to remove the  at the end of each value. Those were included to force the existing data to be XML comments, which accepts XML-special characters such as <, ", and &. This should work as long as the data does not already include either the  in it. And, you could likely add a SUBSTRING or two to the UPDATE statement such that those two values are removed in the same operation as the conversion.


How do different styles of beer affect malt vinegar

Question: Is there a preferred beer style for making malt vinegars?  Has anybody experimented with using different styles of beer to make vinegar and what types of results were experienced.
Answer: To my knowledge there is no preferred beer style that is preferred for making malt vinegar - it is just that it can be brewed from malt. No hops are added to malt solutions used for fermenting, for example so it would be difficult to call the base liquor a "beer". Traditionally beer per se is not usually used for making vinegar. "Vin gar" bad wine is usually the traditional source of making vinegar (eg balsamico) although I accept ciders and fruit brews are also frequently used.
The modern practice is to infect a sterile sugar solution with yeast and then acetobacter and let it ferment to make acetic acid. That is distilled out to make more concentrated acetic acid which is diluted and flavoured in various ways. Modern "Malt" vinegar is usually flavoured and coloured with caramel. It can certainly be made or flavoured with malt extract (as the name suggests) but it isn't the usual method. Except perhaps its accidental use by home-brewers desperate to find a use for another spoilt brew! :0) Malt has largely been replaced with corn/maize sugar due to lower cost.
Comment: I have heard comments that hop flavoured vinegar is not to everyone's taste as it can be bitter. The hops can also act as a natural antibiotic meaning the fermentation by acetobacter may not proceed as planned.

It would be an interesting experiment to "dry hop" some commercial malt vinegar  and see how the taste was changed. One might get a hop flavoured/aroma vinegar in the fashion of balsamico.If one wanted to start with a beer base then one might try a lambic - naturally malty and brewed slightly sour by using natural yeast and wild bacteria.
Comment: I think you meant add a mixed culture of yeast and acetobacter to a sugar solution, Acetobacter will oxidise ethanol to acetic acid, but can't metabolise sugars. There's a thread on the subject here http://www.homebrewtalk.com/showthread.php?t=464480. I like the suggestion of making malt vinegar from the spent wort of a yeast starter.
Comment: I agree yeast is added. An important but missing detail. Edited answer to include the yeast addition.
Comment: Accepted, but only because there is a lack of information/research generally available on this topic. There are people starting to experiment with different beer types (malt styles, w/ and w/o hops), but limited published results. One addition, hops don't appear to be present in malt vinegars. And, most mainstream commercial processes are very different than how a homebrewer might approach them as indicated above.
Answer: I own and operate a vinegar company:
Beer style certainly effects the process and outcome of fermented vinegar. Vinegar bacteria is as unique as your environment, some strains being more aggressive or tolerable than others.
Preference with style is only dependent on how much home-brew you may mess up or what your desired end-flavor may be. Lighter beers ferment out with lower acidity due to their generally lower alcohol levels. Reds, browns and doubles can ferment out to be your average dry vinegar with great acidity. Strong ales or boozy beers can ferment out with acidity with residual sugars to balance the flavor.
Its best to understand vinegar fermentation as if you were fermenting wort. But when using aceto-bacter (AB), your fuel is alcohol, not sugar. Try fermenting a 5 Gallon LME to 4 gallons water with some basic 001. Let it go for 2 weeks, transfer to a vessel that allows breathing but is covered with cheese cloth. You will need a proven AB inoculation. 3 months later you'll have vinegar (assuming 65 to 90 degrees). Keep in mind lots of off flavors are produced through the process but it ultimately cleans out to great aroma.
Vinegar is like a college student, it loves: dark, warmth, alcohol and air
Stay SOUR!


Correct way to perform backup of Cassandra/Scylladb

Question: What's the correct(advisable) method to backup a cassandra or scylladb so that we can restore it on development environment with ease?
Answer: For Scylla, please look at the following official documentation:

Backup your Data

Full Backup Snapshots are taken using nodetool snapshot.
Enabling the incremental backup (disabled by default) will create a hard-link from each SSTable, right after it is flushed, to a backups directory.
  For a complete point in time backup you need: a snapshot plus incremental backups and commit logs since that time of the snapshot. Make sure to clean unnecessary incremental backup, Scylla will not do it for you.

Restore from a Backup and Incremental Backup

Restoring a keyspace from backup requires all snapshot files of the tables, and incremental backup files taken after the snapshot - if available. Before restoring from backup, you should truncate the table data, making sure existing data will not override the restored one.

See the linked documentation for detailed instructions.
Answer: In Cassandra we can take full backup from below command.
nodetool snapshot
A snapshot first flushes all in-memory writes to disk, then makes a hard link of the SSTable files for each keyspace. You must have enough free disk space on the node to accommodate making snapshots of your data files. A single snapshot requires little disk space. However, snapshots can cause your disk usage to grow more quickly over time because a snapshot prevents old obsolete data files from being deleted. After the snapshot is complete, you can move the backup files to another location if needed, or you can leave them in place.
We can also take snapshot for keysapce and table as well. Apart full backup we can enable incremental backup(incremental_backups) on cassandra.yaml also by default it is false.
You can refer below link for more details.
https://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsBackupTakesSnapshot.html
To restore snpashot is cassandra is very easy.however in cassandra multiple scenario for restoration. To restore a node from snapshot just copy the all sstables from snapshot folder to actual data folder after clearing the data and take restart cassandra services. it will restore the data to previous version of data.you can copy also incremental sstable also to actual data folder if require point in time recovery.
Please refer more details on below link.
https://docs.datastax.com/en/cassandra/3.0/cassandra/operations/opsBackupIncremental.html


Optical Density conversion to cfu / ml

Question: I am having troubles understanding the correlation between OD measurements and CFU/ml. What is the conversion factor between the two units, and does this conversion factor somehow compensate for dead cells OD might be reading? (Also lets say the OD is set at the standard 600nm).
Answer: The optical density measurement is the quantity of living and non-living cells in a sample. The colony forming unit measures only the viable cells in a sample. An OD 600nm is equivalent to approximately 8 x 10^8 CFU/ml. However, this is only an approximation and cannot fully take into account the dead cells the OD may be reading, it also depends on the microorganism that is being researched. A standard curve can be calculated from data, but it is quite difficult to attain an exact result.
A very useful article on the correlation between the two measurements can be found here (from the Brazilian Journal of Microbiology).
Comment: Welcome to biology SE - links to external material that allow further reading or offer support to content are strongly encouraged here

Optical Density conversion to cfu / ml