Android app to track time a child spends on a tablet?

Question: Is there some kind of background process or app that a parent could install on a tablet to track the time his/her child spends on it?
Answer: I'm using Digital Wellbeing on my phone to keep track of time spent on apps, and also set the time limit on each app. I have the latest Android OS, so not sure if it will work with your tablet.
Comment: Thanks a lot! I installed it on my android phone and it works well, I'll try on the tablet now


Does QSFP+ require 4 fibers?

Question: I am currently designing a network, and there are 2 fibers between 2 switches. Can I use a 40Gbit QSFP+ module to achieve this speed or is 10Gbit SFP the best possible without adding more fibers?
Comment: You can run up to 100G on one single OS2 singlemode fiber.
Comment: You should make this an answer, @Cown, so it can be accepted and the answer can be closed.
Comment: @TeunVink thanks, i can see Zac67 made a good answer. :-)
Answer: QSFP+ is just the transceiver interface. Medium compatibility and reach is defined by the PHY used by the fitted transceiver.
While the short-range 40GBASE-SR4 PHY requires four separate multi-mode fibers per direction (OM3 or OM4), 40GBASE-LR4 (CWDM) or -FR (single-lane) use only one fiber per direction - both require single-mode fiber, however. Both will work on short MMF runs as well - unspecified though.
Beyond the official IEEE 802.3 PHYs there's a range of other types available - many from third-party vendors.

Does QSFP+ require 4 fibers?


Calculate the Time complexity

Question: $T(n)=\sqrt{2T(n-1)}$
what will be the time complexity if $T(n)$ is given as this?
I tried substitution but no result was reached.
Comment: Possible duplicate of [Solving or approximating recurrence relations for sequences of numbers](https://cs.stackexchange.com/questions/2789/solving-or-approximating-recurrence-relations-for-sequences-of-numbers)
Comment: Note that this isn't a question about time complexity: it's a question about solving recurrence relations. Perhaps the function $T$ does denote the running time of some algorithm, but that doesn't actually matter, for your question.
Comment: What have you tried? Where did you get stuck? We do not want to just hand you the solution; we want you to gain understanding. However, as it is we do not know what your underlying problem is, so we can not begin to help. See [here](http://meta.cs.stackexchange.com/q/1284/98) for tips on asking questions about exercise problems. If you are uncertain how to improve your question, why not ask around in [chat]?
Comment: The title you have chosen is not well suited to representing your question. Please take some time to improve it; we have collected some advice [here](http://meta.cs.stackexchange.com/a/815/). Thank you!
Comment: You are asking to solve a recurrence; it has nothing to do with "time complexity" beyond maybe where the recurrence came from.
Comment: I'm curious about how you get this recursive relation. Note changing the time unit would invalidate this relation.
Answer: The answer depends on the initial value. For example, if $T(0) = 2$ then you can prove by induction that $T(n) = 2$ for all $n$. More generally, let $S(n) = T(n)/2$. Then
$$
S(n) = \frac{T(n)}{2} = \frac{\sqrt{2T(n-1)}}{2} = \sqrt{\frac{T(n-1)}{2}} = \sqrt{S(n-1)}.
$$
Simple induction now shows that $S(n) = \sqrt[2^n]{S(0)}$, and so
$$ T(n) = 2 \sqrt[2^n]{\frac{T(0)}{2}}. $$
In particular, this shows that $T(n) \to 2$.
We can estimate the speed of convergence using the estimate
$$
\sqrt[2^n]{x} = \exp \frac{\log x}{2^n} = 1 + O\left(\frac{\log x}{2^n}\right).
$$
This shows that
$$ T(n) = 2 + O(2^{-n}). $$
Answer: With substitution, we will get $T(n) = \sqrt{2\sqrt{2\sqrt{\cdots\sqrt{2}}}}$ with length $n$. Now, suppose $n$ goes to $\infty $, we will have $A = \sqrt{2A}$. Therefore, $A^2-2A = 0$ and $A = 2$. Hence, $T(n)$ would be constant as $T(n)$ is increasing. And we can write $T(n) =\Theta(1)$.
Comment: While I agree with your final answer, it seems like there is a gap in the justification here.  It appears that you are implicitly assuming that there exists a constant $c$ such that $T(n) \to c$ as $n \to \infty$.  Of course, if that is true then $T(n) = \Theta(1)$.  However, while that assumption is in fact true, you never provided any evidence for that assumption.  How do you know that there isn't some possible value for $T(0)$ that makes this sequence increasing, or eventually increasing?  I think we need to prove that $T(n+1) < T(n)$ if $T(n)>2$, or something like that.

Calculate the Time complexity


backbone.paginator - update per page

Question: I'm using backbone.paginator in my project.  I have a dropdown that allows users to select the results per page.  Now all I have to do is figure out how to make it work :-)
So far if I do something like this:
this.collection.goTo(page, {
    data: {per_page: newResultsPerPage}
});

where newResultsPerPage is the number of results the user has selected from the dropdown.  The correct number of results come back from the server, but backbone.paginator doesn't correctly update the number of pages.  Is there a method I can call that will update / reset the backbone.paginator plugin?
Answer: It looks like there is a howManyPer method that I missed in the documentation.  I'll leave this question up for anyone else searching for a similar issue in the future.

backbone.paginator - update per page


How to structure a table for additional data if a particular value of an enum/lookup table is chosen?

Question: I'd like to store additional data if a particular value is chosen in the enumerated or looked-up column in a table. The obvious option is to have an extra column in the table, but this will lead to a mostly empty column and seems to be like bad approach. Is there another option/method of doing this?
Answer: Multiple tables are one option. It's similar to object-oriented code, just with your database tables. Imagine you have a fruit object and the dropdown specifies what type of fruit: banana, apple, orange, watermelon.
So your fruit table would have your ID, Weight, Color, Price, IsOrganic, etc. fields. Then Banana might also have FruitID, Length, RipenessLevel, Brand, IsBundled, etc. Apple would have FruitID, Flavor, IsBagged, IsWaxed, etc. Orange would have FruitID, IsWaxed, Flavor, IsBagged, etc. Watermelon would have FruitID, CutType, IsSeedless, etc.
Obviously you could potentially add multiple levels here since apples and oranges have some common fields and that may or may not make sense, depending on your needs. This way, when you do a lookup of the fruit data, you look across both tables to get all data or just the Fruit table to get basic data.
Answer: The cleaner approach would be to have another table containing the mapping between rows in the original table and the optional values. For example, say you are storing employee records, so you have a table with 4 columns: Id, Name, Department, and SalesQuota. Now, the SalesQuota value is filled in only for rows where Department = "Sales".
Separate the table, so that you have your employee table with Id, Name, and Department, and a sales quota table with Id and SalesQuota. You can join the two tables on id, to get the original view, but at the same time, you don't have a mostly-empty column. You can join the two tables, or operate on each separately.
Search for "database normalization" online to get lots more articles on this topic.
Comment: Your example was much less cheesier than mine. For some reason, I always resort to fruit when it comes to explaining OO or normalization. :-P


Slow down potential attackers

Question: My server occasionally get massively hit by (probably bots) on a small group of IPs.  Is there a good way (probably in iptables) to slow down or temporarily block/tarpit connections coming from an IP that has connected many times recently?
Answer: Yes, iptables supports this kind of dynamic rate limiting.
See here for details: http://codingfreak.blogspot.com/2010/01/iptables-rate-limit-incoming.html
Comment: Hmm... it seems that I cannot set a --hitcount over 20... that's not very useful in this case.  Is there a way around that?
Answer: Maybe denyhosts would be a useful tool for you.
Comment: I'm using denyhosts already for ssh traffic, yes :)
Comment: Denyhosts needs an auth log to read... These are not failures of any kind, just DNS queries.

Slow down potential attackers


Bodhisattva Precepts

Question: I've been really into the ethical and moral foundation of buddhism and stumbled onto the precepts. Would it be wrong of me to recite the bodhisattva precepts that I've found online that I identify with as a beginner to myself every morning?
Comment: Do you mean the Bodhisattva Vow? Or do you mean the Five Precepts?
Comment: I'm not sure why you might think there would be something wrong about it? It should be completely fine. If this is a question about copyright, try reading the answers to [this question.](https://buddhism.stackexchange.com/q/2847/20268)
Answer: At my last retreat, we recited the Bodhisattva vow quite frequently.

Sentient beings are numberless; I vow to save them. Desires are
inexhaustible; I vow to put an end to them. The Dharmas are boundless;
I vow to master them. The Buddha Way is unattainable; I vow to attain
it.

Not the precepts themselves, which were only recited by a preceptor when the precepts were being taken.
I would advise against regularly intoning them; it's an interesting question whether we can take them unofficially. Why not recite the nembutsu instead?
Comment: upvote so i have comment powers!

Bodhisattva Precepts


Electric field at edge of circular plate capacitor

Question: I know that the Electric field between 2 parallel oppositely charged plates is $E = \frac{\sigma}{\epsilon}$ and that this can be calculated using Gauss' law, but this only applies under the assumption you're not near the edges of the plates.
So I was wondering how one would go about calculating an expression for the electric field near the edges of the plates.
For simplicity I will assume the plates are circular, but even then I'm not sure what shape of Gaussian surface I should choose to make this problem simpler.
Any help would be much appreciated.
Comment: Due to a lack of necessary symmetry, the use of  Gauss's law will not be helpful to find the electric field in this problem.
Comment: There are a few references that may help you, for example G. T. Carlson and B. L. Illman, "The circular disk parallel plate capacitor," Am. J. Phys. 62 (12), 1099–1105 (1994). For others, check the link http://aapt.scitation.org/doi/abs/10.1119/1.1463738
Answer: What is usually easier is to calculate the potential $\phi$, whish is a scalar, and from it find the electric field $\mathbf{E} = -\nabla \phi$.
This is for a time-independet situation, for a charging capacitor then you'd have to also find the vector potential $\mathbf{A}$ which would give yuou a magnetic field $\mathbf{B} = \nabla \times \mathbf{A}$ and an electric field $\mathbf{E} = -\nabla \phi - \frac{\partial \mathbf{A}}{\partial t}$.
Formulae for $\mathbf{A}$ and $\phi$ can be found here, where the integration region $\Omega$ would be the area of the plate of the capacitor in your case.
Another way is to solve Laplace's equation $\nabla^2 \phi = 0$ in vacuo and apply the boundary condition that the potential needs to be constant across the plate, like it's done here.
Comment: This isn't quite there - the formulae you've linked to are for known charges and currents, whereas OP deals with a known constant potential at the boundary instead. However, the core message (the hard truth that there is no gaussian-surface analysis that will work in this situation) is on target.
Comment: You can still use the $\phi$ formula for a general charge density $\rho$ no? Just need to find a suitable area element $\mathrm{d}^2\mathbf{r}$ and integrate on the plate.
Comment: You can, but you don't know $\rho$ - you just know that the potential needs to be constant. It is a substantial amount of work to find out $\rho$ from the potentials, and by the time you're in a position to calculate it you already know the fields you wanted in the first place.
Comment: Oh yeah I guess the density at the edge won't be constant anymore...
Comment: Well, it depends on what you're doing. OP lucked out by specifying that the plates are charged, presumably with constant density - but having a constant charge density at the edge is incompatible with having conducting plates.
Answer: When you have circular plates you can reduce the problem to a two-dimensional one at the edge of the capacitor, by using cylindrical coordinates r,z and then consider a large r so that the problem at the edges is approximately two-dimensional. Then you can use conformal mapping to obtain the general potential solution in this fringe region of the capacitor. You have to find the complex function which describes the boundary conditions of the charged plates. The real and imaginary part of all complex functions, in the domain where they are analytic, are solutions of the Laplace equation for the electrostatic potential. Thus if you find an analytic function describing the boundary conditions of the plates, you have the potential solutions and from this by differentiation you get the correct electric field solutions between and around the plates at the fringes.
Comment: This is inaccurate as stated. Conformal mapping works as a technique for electrostatic analysis when there is translational (instead of rotational) symmetry, i.e. when the electrostatic potential obeys the Laplace equation in cartesian (not polar) two-dimensional coordinates. The result thus obtained can only be made to work for a circular-plate capacitor in an approximate way when one 'zooms in' to the edges so much that the curvature of the edge is negligible. (Fix it or don't, up to you. This is my single comment here.)
Comment: @EmilioPisanty - Typical nitpicking! It is obvious that the edges are considered. But I will improve the wording to avoid ambiguities.
Answer: Given two infinite planes, under your symbols for field inside planes $E=\frac{\sigma}{\epsilon}$. At the edge of planes, in the middle of edge-connecting line $E=\frac{\sigma}{2 \epsilon}$. To obtain that result, you consider the mirroring of the planes along that line.
If you move away from middle-point, you will get less $E$, but your result will have the member depending from dimensions. If your dimensions are ideal, you will obtain same result on all dots of line connecting the edges.


Signal to noise ratio (SNR) of a CW signal

Question: I understand the formula SNR = 6.02N+1.76 for a N-bit ADC which quantizes a modulated tone sampled at twice the BW. I am trying to understand what the same equation would be for a unmodulated CW tones with Zero BW. Any pointers/explanation would be very helpful! Thanks.
Answer: Actually, that formula is specifically for an unmodulated sine wave at full scale just prior to clipping. This SNR result provides a reference point as to what the total quantization noise power will relative to that full scale sine wave at the input to the ADC, and that noise power will be at that similar total power level relative to that full scale reference point even
as the tone is lowered in power (it doesn't go down accordingly) and in the presence of modulated signals at lower power levels.
So for example if we have a perfect 8 bit ADC with a full scale sine wave at an incommensurate rate with +10 dBm just prior to clipping, the total quantization noise spread evenly over the sampling bandwidth would be close to 50 dB down or at -40 dBm. If we then removed the sine wave and applied modulated signals (or a lower power sine wave), the total quantization noise would remain about the same. Thus, this formula and what we know about the input to the ADC gives us a good reference point as to where our quantization noise floor is.
So that formula is already what the OP is looking for precisely.
I explain this formula in more detail at this post.
Comment: Excellent Dan! Thank you. This is precisely what I was looking for.


Google Account Sync Error

Question: I have been looking through all kinds of forums.  But have not yet found a fix. am trying everything but dont want to do a factory reset. I have a samsung galaxy core prime. its about 4 months old and everything has been updated regularly.  I am not sure of the cause of this it it may have been when i accidnetally unchecked the sync button in the menu with wifi, airplane mode etc.  i re-clicked the box and thought nothing of it.otherwise maybe it was when i changed the password of a gmail account/ I cant think of anything else i did.  i dont mess with the settings much.
Basically a few days ago I noticed I wasnt getting gmail notifications.  So i tried to open the gmail app.   Nothing loaded, just a white screen.  At first other gmail accounts I use wouldload but one wouldnt.  Eventually nothing at all would load.  This coincided with play stre not opening, I just get a white screen just like with gmail.  There is the spinning wheel showing that its trying to open but nothing happens.  Also I can not load any of my google sheets docs either.
I ahve tried turing data on and off, airplane mode, clearing cache for all of the google apps.  I eventually tried to delete my google account.  then i added the account again but it wont sync.  it just says syncing and it never finishes the job.
I tried rolling back my google play store to the factory version, did not solve the problem.
As of right now none of these apps will load for any of my google accounts.  even the ones that are listed as synced. some times there is an error message that says experienceing sync errors and check back shortly.
when i currently click gmail its as if i am using it for the first time.  i try to set up email and add an address but the 'next' button does nothing when i click it.  so its as if i have no gmail accounts added but i cant add any.
I would like to delete the gmail app and start again but play store isnt working so not sure if i can. also the fact that all google apps are affected leads me to believe its not a gmail issue but a google account issue.  I guess i could delete all google accounts and try to start fresh? Any other ideas?
I am a bit afraid of losing data or some how screwing up this worse if i delete all my google accounts.  before when i tried to delete the google account that mhy phone is mainly synced with for all the apps it told me i cant because all theother apps are using that account. i cancelled the deletion after reading this warning but it seems to have been deleted anyway.  i re-added the account and it said it was successfull but it wont sync.
does anyone know anything that i can try. thanks , i appreciate any help you can provide.
Answer: i just managed to get it to work by force shut down of gmail play store and play services. and deleted all app data and cleared the caches for all of these apps and restarted the phone and then i tried to oppen google play and seuddlenlly it asked me to sign in with a new google accoun and suddenly everything was fixed.  been banging my head against the wall all day wwith this.

Google Account Sync Error


nodejs main thread and event loops, what is the difference between?

Question: When http request hit into the Nodejs application the connect first received by Nodejs main thread (which is js main thread) and passed to event loop, if my understand is correct

The event loop is what allows Nodejs to perform non-blocking I/O operations, JavaScript is single-threaded — by offloading operations to the system kernel whenever possible.

The above statement is from Nodejs official documentation, so my question where does the main thread lives?

out side the event loop or inside the event loop

is both different? Can someone give good pictures how Nodejs work internally, with graphical representation?
Answer: Main thread is the execution thread. As asked, it stays outside the event loop and will check for any events pertaining to the event loop.
If the even added to the event loop is synchronous and only needs some CPU operations, the main thread will take control directly and will execute the need.
If an asynchronous event is added to the event loop that is delegated to the worker threads available. Worker threads will perform the async operation(db/API/fs calls). Once the async part of the event is completed the event is again added to the event loop for the execution of the remaining synchronous part.
The worker threads are built over libUV and will spawn according to the main thread requirement. This reason makes Node.js more efficient while handling async calls and less preferred for CPU extensive operations.
Follow this for a more detailed explanation:What function gets put into EventLoop in NodeJs and JS


Plumbing Payment Reduction

Question: In the New Mexico, US do you have to pay someone for work if after completion you do not feel the work is worth the original amount agreed upon. For example a plumber who gives you a quote, finishes the job, but it is not done as good as you would have liked it to be or it wasn't all that you originally thought it would be or if they took longer than originally indicated, do you have to pay them the full amount or can you hold some back? If you don't pay the agreed amount what could they do?
Comment: Did the contract (quote) say when it would be completed by? Did it specify the standards that you wanted it completed to? Did they do exactly the work that was quoted (even if you "thought" it would be more)? In a very basic sense, if you didn't spell it out and in turn they didn't specify it to you in writing, then it probably isn't enforceable and you would be required to pay them the full amount that was quoted. What was on your quote/contract?
Answer: I don't know about New Mexico specifically, but in most states, the plumber could sue you in a court appropriate for the amount at issue. The plumber could also file a contractor's lien on the property.
Comment: And the court will decide whether your reasons (incomplete work, failure to complete by agreed date, or whatever) are sufficient to reduce the amount owed. Of course, if the plumber files a lien, you have to sue him to get it removed, but the same principle applies
Answer: If they have done what the contract requires them to do (plumbing) then you must do what it requires you to do (pay them).
If they have not yet fulfilled their obligations, that is, the work is not yet complete, then you do not yet owe them the money (unless the contract provides for progress payments).
If they have breached the contract in a way that causes you damage (in a legal sense) then your owe them for the work and they owe you for the damage.
If you owe them money, they can sue you. If you claim damages, you can raise a counter claim in response to their suit.
With respect to your specific examples:

"not done as good as you would have liked" - if "as you would have liked" is a term of the contract then they have breached. However, if the contract is silent then if their work is in accordance with the codes and of a "workmanlike" quality then they haven't.
"wasn't all that you originally thought it would be" - ditto although I am confused at how "plumbing" can be anything but plumbing - did you think you were getting music lessons?
"took longer than originally indicated" - unless there was a specific completion date in the contract, providing that the work was done within a reasonable time taking longer then indicated is not a breach.

Notwithstanding, in all cases, as well as proving the breach, you would need to prove the damage caused by the breach.
Comment: The agreement was to fix pipes and repair walls and landscaping. The pipes are fixed but the holes in my walls, not so much, and it's four days past the expected completion date. I can't keep taking off work to supervise these people when they are showing up four hours late then they only work for two hours before calling it quites. I want to hire someone else but I don't think the original company deserve the whole amount, especially if I need to pay someone else to do part of their work.
Comment: @MrQs You need to talk to the plumber and come to an arrangement. Right now you have no grounds to terminate the contract.

Plumbing Payment Reduction


Parallel Processing how to distribute load amonst processors. or to specify which processor will carry out a task

Question: i have to determining which processor is busy and send tasks to processor that arent as busy instead. i have to execute a program using parallel python but i also have to determind which of the servers to send the task to. does any one no what kind of conditions i should use on the parallel processing codes? and its written in python calling PP
Answer: If you have any choice in the matter (which you might not if this is a homework assignment) you might want to consider using ØMQ to handle messaging amongst the various bits of your system. On the Learn page there is an excellent (and very rapid fire) presentation by Ian Barber. It's 45 minutes and well worth watching. It fundamentally changed the way I think about messaging and multi-thread / process / processor communication. It was so information-dense I had to watch it twice and then start doing toy programs to wrap my head around just how clean the whole concept is.
Note: although the language he uses for the presentation is PHP, the code examples he shows would look almost identical in any of the over 20 languages that ØMQ supports. (Multi-process COBOL anyone? :-)


T-SQL fulltext catalog search with freetext

Question: I have a fulltext catalog for an indexed view.
Problem: I want to search with the function 'FREETEXT' all words which contains the search term. But the result doesn't return any entries... but one entry must be the word 'freightcosts'
If the search term = 'freightcosts', the result is 'freightcosts'?
Example:
SELECT [Description]
FROM dbo.vuCmsTextDe
WHERE FREETEXT ([Description], 'fre')

Answer: You need to use a wildcard for partial words, such as
SELECT [Description]
FROM dbo.vuCmsTextDe
WHERE FREETEXT ([Description], 'fre*')


Need to increase door height in bungalow

Question: I am in a  bungalow with the doors into the bathroom and 2 bedrooms all being different height. I'd like to increase the door height and shifting the header up seemed like a simple thing. however...this is what i found and i am not sure how to proceed... i was not expecting a double header. then again i know nothing about this. any thoughts are appreciated. not sure about load bearing
Answer: That's not a header, just a nailer. Some carpenters / builders like to use two so that the trim is easier to nail and looks better. You're fine removing one of them. Leave at least one though to nail the trim to after your done (moved or not)
Comment: thanks for the response and apologies for the delay. i will have to move both up because the door height is currently 79 inches. i need to make the header/nailer 83 inches i am told. which is fine...but i have to do this on 2 separate walls. the second wall is load bearing. can i just put a piece of 2*4 on the jack stud and raise the header on the load bearing wall or put a brand new one in? also , would you suggest i build a temporary support wall while doing so?
Comment: the other wall is load bearing and has the same framing as the picture? If so, something is amiss, either the wall isn't load bearing or the wall opening is improperly framed.
Comment: yes. I just removed the doors and the frames and none of the jack studs are one piece. this house is old... and the last guy clearly just did not care...what do i do? remove and reframe?
Comment: if the wall is load bearing then at least you need to add a load bearing header. Typically, the minimum is (2) 2x10 for typical situations (say something like 1 level, 20 ft or less roof span, opening at 5' or less). Personally, yes I would replace the jack studs to 'do it right'. One issue that can occur with fill-in pieces is that each joint is a location that needs to be 'compressed' before the load will be fully transferred and this can cause excessive defection and related issues


Is there a minimum reputation to post a question?

Question: Many of the homework,  on hold, proposed to close, etc questions are from posters with a reputation of 1 or double digits. The situation appears to be that someone is either in a homework / coursework panic and just bangs a question on out of desperation or the question is ill defined. Either way, would putting in a minimum reputation requirement (of >1, 101?) help save moderators time in the long run, increase participation for people to build up the reputation and save space & time in the question lists while waiting for posts to get deleted or closed?
Comment: I don't think so.... just because _many_ newbies post junkies doesn't mean _all_ newbies post nonsense questions. Some of them are pretty genuine conceptual queries and some even rock the hot question table. Moreover, there is no need to think that only mods close question (that's rare); it's the whole community who in the form of 5 users close it after being sent at the review. So, I don't deem that would be necessary; rather it might act otherwise discouraging new ones having legitimate queries.
Comment: Increasing the rep to post questions defeats the purpose of the site. This site is meant to help people in the end. Also, with this feature implemented you'd end up with poor souls who either post their questions as answers to others (NAA) or write wrong answers here and there in order to gain some rep to post their homework. This is like a self-slap from every aspect.
Comment: BTW [downvotes on meta](http://meta.chemistry.stackexchange.com/help/whats-meta) usually only reflect disagreement with a post and do not necessarily indicate post quality.
Comment: 99% of people who visit this site for the first time are those who seeks an answer to their question. Turning them down will have a great effect on this site.
Comment: I myself was a 1-rep asker not a very long time ago. :) I understand how you feel, especially after seeing lots of lousy questions, but having a rep requirement on asking would 100% have turned me away. Right now because the duties of moderation are shared by the whole community, it is not too time-consuming to close them, so it is fine.
Comment: Fair enough! I was under the misapprehension that it took a while to close off the sub-par posts, but learning that it's community driven, changes things
Comment: @Beerhunter I think we've all entertained this idea at one time or another, but MAFIA's comment is pretty spot on.  Takes little time to close and delete a question, so missing out on some great content is too big of a risk.  As mentioned downvotes don't really "count" on Meta, so have no fear :)
Answer: This is probably a really bad idea. Many new users come to this network, because they seek answers. They might stay because they get one. And while they are here they might answer questions themselves.
I would assume that in more than ninety percent of all cases one question started the chain.
If we take that away, users would only have the possibility to answer. Which will put those bad requests, which you are referring to, exactly where they do not belong. There would be a lot more to clean up.
Another reason is, that one of the principles of the network is, that you can try it without registering personal details. This would have to go over board.
Another point is, that such questions barely ever need a moderator to deal with them. They are closed by the community, they are automatically deleted by the system. And this system works very well.
Big thanks to everyone participating in the review queues.
Comment: **Big thanks to people who give big thanks to everyone participating in the review queues.**
Comment: Big thanks to people who give big thanks and the people that give... well, you get the idea :D
Answer: Stackexchange's model is:

Anyone can ask a question. Anyone can answer.

If you turn anyone into anyone with 10 rep, well … It'll be us, the core crew and no new additions whatsoever. Because how are you supposed to accumulate 10 rep without asking or answering questions? Edit suggestions …? Think about it for a second and then cringe.


Unusual idea for fish tank design. Unsure if plausible or not

Question: I looked through the stack exchange list of sites, hoping to find one more suitable for my question, but decided that this was the most likely place to get the answer I'm looking for. I'm not an engineer, but I'll try to explain myself as clearly as possible. Here's the set up: Two fifty-five gallon fish tanks, each on a metal shelf stand. Each tank has two holes (drilled or cut out, idk, and wouldn't mind having the neccessary steps for this explained) in their glass floors. There are corresponding holes drilled through the metal shelves that they sit on. Two U shaped glass tubes seem to hang under it, one bigger than the other, so the smaller one is above it. One end of each is set securely through the holes of one shelf and the holes of one tank, same on the other side (picture to better explain). The idea is that, when both tanks are filled with water, the tubes would fill, too, and the fish would be able to use them as highways, so they could swim freely from one tank to the other. I'm not sure how the tubes could be securely connecting, though I was imagining in the same way that the walls of the tanks are connected (I think it's glue, not sure, clarification welcome). Also, a friend proposed the problem of pressure from the water above being too much on the tubes. I really just want to know if this is doable. And, if doable, but there are some glaring obstacles, to have them explained. Thanks in advance and sorry for disrupting the well-versed engineer-y air of the site. (Side note -just because I'm intruding: This is actually an idea I came up with for a tank set up in a novel I'm writing. I've lived around fish tanks, but have never actually tried doing anything remotely like this with them- not sure how to put that. Anyway, thanks again.)
Answer: I see three immediate problems:

The tubes, and their joints, will experience high pressure.
If there is even a slight movement in one tank but not the other, unless the tubes are flexible, or perhaps even if they are, the tubes or the joints will break.
Gravel, dirt, etc. will accumulate in the tubes, which will be difficult to clear.

The siphon proposal sounds better, but the tube would soon accumulate air and have to be frequently refilled with water.
If you really want to put holes in your tanks (and risk destroying them), I'd suggest putting the holes an inch or so below the water line.  That would eliminate the problems of high pressure, dirt accumulation, and air in the siphon.
Your biggest concern will be how to ensure that the seals are strong and flexible.  Eventually someone (even you) will accidentally bump into a tube.  You really don't want the tube to crack or the seal to leak.

I was about to say it sounds like an interesting idea, like a Habitrail for fish, and then I googled it and found an interesting fish habitrail video

It uses the siphon suggestion.  If you look at the video you can see the air accumulation problem starting, but I think that could be mostly eliminated if you could arrange for continuous water circulation between the tanks (e.g. a common external filtration system taking water from one tank and returning it to the other).
You could make the tubes longer and have the tanks separated farther apart.
It certainly seems like a better idea than potentially destroying two tanks.
Comment: Siphons loose "siphon" pretty quickly ( one day), one needs a vent at the top with constant suction to get trapped air out.
Answer: This is possible, but the stress concentration around the holes in the tank bottoms will probably cause them to crack and fail catastrophically! Here is an easier way:
Instead of connecting the bottoms of the tanks, simply invert your bent tubes, fill them with water, and place one end of each in each tank to form a siphon. Fish can swim up into the water-filled tube, traverse the gap between tanks, and then swim down and out of the tube in the next tank over.
Comment: Hmm.. fish have internal organs ("swim bladders") that regulate their buoyancy by changing the internal gas pressure. I wonder if that system would work properly at *less* than atmospheric pressure while they were in the syphon. Otherwise, your fish might explode...
Comment: This is no trouble for fish - source: have seen it done
Comment: @niels Nielsen - it's implied that the metal shelf takes the weight, so bottom of tank shouldn't be under significant stress. I like your suggestion because it's more awesome than 'underneath tubes', but not your answer as "probably" is barely ever a good engineering answer
Comment: I used "probably" as a useful way of expression chance of success for 34 years in high tech engineering. It implies a certain amount of experience-based judgement.
Answer: Yes, you can do it by either using flex silicon sealants or some rubber compression washers like those commonly used in copper tubing.
Your supports have to be solid and offer easy access to the bottom for maintenance of the pipes. The pipes on the suspended part have to be supported by strong but flexible brackets.
Answer: It is common for tanks intended for salt water to have holes with bulkhead fittings. The bulkheads normally come with NPS threads in the US. It would be just a matter of connecting them the way you want ; clear flexible hoses would be best. Tanks would need to be ordered with the size and location of the holes specified as it is not reasonable for an amateur to cut the standard tempered glass bottoms. Apparently one would not have gravel in these tanks.


jQuery UI Datepicker and datejs

Question: I want to have a datepicker where you can also just type basically I want to have the jQuery UI Datepicker and datejs in one. I want to type "tomorrow" and I want it to select the right day. I want to be able to type "saturday" and it actually getting the date right.
Answer: If you have any experience creating jQuery plugins, the work is not too difficult. Wrap the target input with the code required to create the UI datepicker AND value testing (with date.js) on keyup/blur/whichever events you deem necessary. You'll need to ensure that you set the date on the datepicker instance when the value changes (call datepicker("setDate", date))
I've done something very similar at work; If you are interested in the code, I should be able to make it available (in its current format - lacks a bit of polish but it's clear enough).
Comment: Apologies for the delay... been on holiday. Will dig the code out at work. Might take another few days
Comment: @RobCowie I know I'm 3+ years late, but I would love to see what you put together if you still have it

jQuery UI Datepicker and datejs


Vector bundle determined by differential structures?

Question: Let $E\to M$ be a vector bundle. Is the structure of vector bundle determined by the map $E\to M$ (as morphism between manifolds)? i.e. is it possible that there are two non-isomorphic vector bundles $E_1, E_2$ such that their underlying manifolds are the same?
Comment: If you are willing to consider complex vector bundles, you can get examples more easily (although I'm sure you can also do it with only real vector bundles). For example, the tautological line bundle and its (complex) dual are isomorphic as real vector bundles and so in particular their total spaces are diffeomorphic but they are not isomorphic as complex vector bundles.
Comment: @levap Yeah. But in that case I would require the total spaces to be holomorphic equivalent. My point is, when talking about vector bundles, can we only mention the map  (in the corresponding category) $E\to M$ (and forget about the local trivialization)?
Comment: I came up with this question when I try to understand the definition of some specific vector bundles. For example in some books the definition of tautological bundles only mentions the bundle projection "in the tautological way" and does not mention the local trivializations. I know in this case the fibre itself has the linear structure so we don't have to define it, but I still want to know in general is it true that we don't need to mention the linear structure of every fibre
Answer: This answer is close, but not quite what you are asking:  Here is a countably infinite family of examples $E_i$ of distinct vector bundles over $S^4$ which are homeomorphic as abstract manifolds. I don't know if any pair of them are diffeomorphic or not.
By clutching functions, there are a $\pi_3(SO(4))\cong\mathbb{Z}\oplus\mathbb{Z}$s worth rank $4$ bundles over $S^4$.  From Milnor's exotic $7$-spheres paper, we know that a countable subfamily of these has Euler class $\pm 1$.  Let $E_i$ enumerate these.
Using the notation $SE_i$ for the sphere bundle in $E_i$, we note that $SE_i$ is an $S^3$ bundle over $S^4$ with Euler class $1$.  The Gysin sequence then shows that $SE_i$ is a homotopy $S^7$, which must then be homeomorphic to $S^7$ by the Poncare conjecture.  In particular, $SE_i$ is homeomorphic to $SE_j$.
Now, one can use the Alexander trick to extend such a homeomorphism to a homeomorphic from $E_i$ to $E_j$, so these manifolds are pairwise homeomorphic, even though they are different vector bundles.


Wind erosion of Ice

Question: I saw this video on Youtube https://www.youtube.com/watch?v=Hs5iXGJVkb8, but I really don't how answer this question:
How is it possible that wind can cause ablation of ice? I know that ice can ablate by sublimation or evaporisation, but how can we explain that wind can cause ice to ablate?
Comment: It's the material the  wind carries that performs the erosion. http://www.geo.fu-berlin.de/en/v/geolearning/mountain_building/weathering/Erosion/index.html. This is rock, not ice, but it's the same principle of carrying particles at sometimes high velocities. This is, imo, more Earth science SE than physics
Comment: The ice tag might be appropriate, but the other tags don't seem to fit the question, imo
Answer: Temperature may play little role in the ablation process in the video. The strength of the wind is such that it shears off the ice/snow. The same as you blow off dust.

Wind erosion of Ice


Why do generating sets need not contain the inverses of their elements?

Question: I recently learned about generating sets, and a common elementary example that is provided is the sets $\{1\}$ and $\{-1\}$, both of which independently generate $(\mathbb{Z},+)$. I understand why each of them in their own right is a generating set of $(\mathbb{Z},+)$ given the definition of a generating set. My question is why generating sets are defined such that they do not need to contain the inverses of their elements. That is, why aren't generating sets defined such that $\{-1,1\}$ is a generating set of $(\mathbb{Z},+)$ and $\{-1\}$ and $\{1\}$ are not?
Comment: The reason the definition of "generating set" is as it is, is precisely so that $\{1\}$ alone generates that group.
Comment: I think what you're looking for is a generating set for the **semigroup** $(\mathbb Z, +)$ rather than for the **group** $(\mathbb Z, +)$.
Comment: If $\{1\}$ doesn't generate $\Bbb Z$, then what does it generate?
Comment: An alternate definition of "generate" is that $\langle g\rangle$, for some $g$ in some group $G$ isn't directly dependent on what you can reach with arithmetic using $g$, but rather as the smallest subgroup of $G$ which contains $G$. This way there is no issue with $\langle 1\rangle =\Bbb Z$. The use of the word "generate" does get slightly more cryptic with this definition, though.
Answer: When generating an algebraic structure from a subset, you are allowed to use all operations and axioms available to generate new elements.
So of course when you talk about $\mathbb Z$ as a group, you have $1+1$ and $1+1+1$ via the operation, but you also have the existence of $-1$ from the axioms, so including it with $1$ in a generating set would be redundant.
If instead you were merely talking about a semigroup, in $\mathbb Z$ generated by $1$ and you did not have the inverses axiom, then you could only say that $1$ can generate $2, 3,\ldots$ and not $0$ or $-1$ or anything else.  You could only use the operation and elements already known to be in the semigroup.
Suppose more generally you're in a larger ring like $\mathbb Z[x]$, and you examine how it is generated as a $\mathbb Z[x]$ module by $1$.  Not only can you generate $\mathbb Z$ with $1$ (because it is an additive group) but additionally you can use the module action to generate $x=1\cdot x$, and after that, you get everything in $\mathbb Z[x]$.  There is no need to add anything else to the generating set.
So, you can see how "generating set" heavily depends on the conrtext of the algebraic object in question.
Comment: This is a very thorough explanation, thank you!
Answer: Yes, $\{1\}$ is a generating set of the group $(\mathbb Z, +, 0, -)$. You can reach all of $\mathbb Z$ from $1$ using the operations $+, 0, -$.
No, $\{1\}$ is not a generating set of the monoid $(\mathbb Z, +, 0)$ or the semigroup $(\mathbb Z, +)$.
Comment: Well, the notation that minimizes confusion will depend on the context. It's more important to be precise about the signature of the structure in universal algebra, which is the natural setting for your question.
Comment: Now that is interesting. From what I've read so far, groups are presented as a double consisting of the set and the operation (i.e. (Z,+) is presented as a group instead of a semigroup). I would think that the notation you used for a group would be more common to avoid confusion with monoids and semigroups.
Answer: Just a guess: $\left< S \right>$ is always a subgroup for any subset $S$. If you change the definition of $\left< \cdot \right>$ as you would, then this would not be the case anymore.
Edit: Another definition of $\left< S \right>$ is that it is the smallest subgroup containing $S$, i.e. $\left< S \right> = \bigcap \{H \subseteq G \space | \space S \subseteq H \wedge H \text{ subgroup}\}$. Maybe this definition is more intuitive.
Comment: I think this alternative definition is part of what is adding to my confusion. If  is the smallest subgroup containing S, and S is the generating set {1}, then it cannot possibly be the case that =({1},+), since ({1},+) does not meet the requirements of a group (closure under +, no inverses, no identity elements).
Comment: I don't understand where your confusion is :) as you say, $\left< \{ 1 \} \right>$ cannot be $\{1\}$, since it has to be closed under $+$, have inverses and an identity element. In fact, the only subgroup $H \subseteq \mathbb{Z}$ that contains $\{ 1 \}$ is $\mathbb{Z}$ and thus $\left< \{ 1 \} \right> = \mathbb{Z}$
Comment: Okay, I think we're on the same page. I think what was confusing me was the notation. I didn't understand that  refers to the subgroup *generated* by S, and doesn't refer to the group formed by the set S and some operation (e.g. (S,+)).


Do Apple Thunderbolt displays work with Ubuntu 14.04 on 11,2 Macbook Pros with Iris graphics

Question: Do Apple Thunderbolt displays work with Ubuntu 14.04 on 11,2 Macbook Pros with Iris (integrated Intel) graphics?
Answer: As of mid-2015, probably not - although I haven't personally tested it. Andreas Noever wrote the initial kernel support for Thunderbolt and his version 3 features are listed here
I have a 11,1 MacBook Pro with Iris Graphics running Ubuntu 15.04 that supports DVI monitors via a DisplayPort (DP) adapter - but this setup only uses the Thunderbolt port as a DP port i.e. there is no PCIe transmission being muxed.


Is my outside sewer cleanout a straight line from my basement drain?

Question: I'm trying to locate my sewer cleanout outside the house. Is it usually just a straight line from my basement drain hole?
Answer: 98% of the time the answer is no.  It is a straight line from the bottom of your main stack.  The drain hole is a branch off your main stack.   This can vary though but this is the norm in the US.
Comment: and I can't use a snake through the basement drain hole, because it has a u-trap?
Comment: It is probably a larger u-trap so you can probably get past that.  If your issue is in between your main stack and drain then give it a try.  If you problem is outside your house you are probably wasting your time.
Comment: My basement drain is starting to backup, and I can't find a cleanout inside or outside the house. So frustrating.
Comment: There will be a cleanout in your yard for sure.  Also you should have one in your main stack and quite possibly on your roof.


How to attribute subfigures from other sources ? / Does cropping a figure consitute a change?

Question: I am writing a review article on common failure modes for a certain technology and to illustrate the different failures, I want to include a range of images from other publications. I have either obtained the permission to use the images or am using images from open access articles with a creative commons license. Some of the images I would like to use are (in the original source) part of a part of a single figure consistining of several subfigures (e.g. I would like to put only subfigure 2e from figure 2 into my paper). Does cropping a subfigure out of a composite figure already constitute a change or an alteration? If so, how should I attribute the changes in the image caption in my paper?
Maybe this is really trivial, I nevertheless did not really find an answer anywhere.
Answer: Image manipulation becomes problematic when one can judge them as fabrication (that is, the data visualised were actually never obtained through the methods you describe) or as falsification (whereby crucial information are lost) [1].
It follows that 'beautifying' an image to make them more reader-friendly (e.g. by changing colors) or to add valuable hints (e.g. arrows), or cropping an image to its essential parts while leaving out those sections that are irrelevant to your research would not be deemed fabrications or falsifications.
If you can safely assume that cropping the figure does not lead to an omission of crucial information, then I think you are fine. I would, however, disclose the approach by adding a note that you cropped the image, and by giving a reasons as to why you did so.

[1] See also this presentation, starting at p. 19: https://www.elsevier.com/__data/assets/pdf_file/0006/1028085/Researcher-Academy-Ethics-30-June-2020.pdf
Answer: I don't see anything special.
A caption fitting the journal style but saying something like "taken from fig. 2e in ref #" seems perfect to me.
You are not cropping the subfigure.
But even in that case, and even if the figure would be data, you just add "spectrum, plot, whatever cropped" from....
Obviously what you let out should not contradict or shouldn't be much related to the point that you actually discuss.
Answer: APA guidelines state adding the phrase "Adapted from". The relevant example shows:

General Format 1 (Figure from a Book):
[Figure]
Note: Descriptive phrase that serves as title and description.
Reprinted [or adapted]
from Book Title (page number), by Author First Initial. Second Initial. Surname,
Year, Publisher. Copyright [Year] by the Name of Copyright Holder.
Reprinted [or adapted] with permission.

And for example IEEE states the following:

Always place the Image title/caption below the image
If you adapt, amend, or otherwise modify the image, indicate this at
the end of your caption

So adding that it is adapted seems like the correct thing to do here.


How could two crossed fields polarize and deflect electromagnetic radiation and/or ionizing radiation?

Question: In the 1953 science fiction novel Childhood's End by Arthur C. Clarke, characters use two crossed fields in outer space to block some of the solar radiation traveling towards earth: "Somehow, out in space, the light of the Sun had been polarized by two crossed fields so that no radiation could pass" (page 12, here's the link: https://books.google.com/books?id=duCDX5kelHsC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false) I was wondering what is meant when Clarke writes that the radiation was "polarized by two crossed fields." What are the ways that this effect could be achieved in theory (not necessarily in practice)? Also, I am studying first year college physics, and I am asking this question out of my own curiosity. Thank you very much.
Answer: I can see something here.
So, from the sun let say you have unpolarised light. This means it could be going in every direction. I have drawn a (crap) diagram to give you an idea that the light is polarised in every direction.

Normally, I think (don't quote me), in polarisers you have long thin iodine molecules which block light in every other polarisation apart from the one in which they are aligned.

Now, if we add another polariser, at 90%s to the original, we have now no light left.

Fundamentally, I suspect this will be an electric interaction with the iodine molecules. Therefore, maybe. (I like to believe anyway).
And in the real life, we have an image like this, see the polarisers are dark (letting no light through), when their axis cross.

Anyway, this is probably what he was getting at.
Comment: You are using molecules as polarizers not fields. Therefore your answer doesn't answer the question regarding crossed fields.
Comment: I did use that as an analogy, see where I mention it is a probably an electromagnetic effect from the molecules themselves - be that their very fundamental charges. In fact, it must be because the light itself is a travelling EM wave, the only way we can kill of a E&B field like that is by it interacting with another E/M field.


Can I enter Germany as a tourist without a return flight with my German husband and kids and apply for family reunion visa there?

Question: I'm from New Zealand which means I don't require a visa to stay in Germany for 90 days out of 180, and my husband and 2 daughters all hold German passports. We're currently travelling in Mexico and decided we'd like to move to be closer to the girls' grandparents. It would be much cheaper and easier to fly straight to Germany from Mexico and my husband thinks I should enter as a tourist and apply for the Family Reunion Visa [edit: Permit] when I get there, but usually you need a return ticket to enter a country as a tourist. Does anyone have experience with this? Will I need to buy a return ticket or will they accept that I'm eligible for a Family Reunion Visa [edit: Permit] even if I don't have it yet, and let me in? I do have the financial means to support myself and my family in Germany while my husband is looking for work.
Comment: "usually you need a return ticket to enter a country as a tourist": this isn't as widespread a requirement as many people think, and it is not a requirement in the Schengen area.
Comment: You will presumably take the lane for EU citizens with your family. There may be brief questions why you are in that lane (point to your family) and perhaps a friendly reminder of the 90/180 rule (say truthfully that you are fully aware of it and that your plans are not definite yet). Ask on expatriates stack exchange about extending your stay. You should start those proceedings sooner rather than later.
Comment: @MarkJohnson it is not a requirement.  I know you've read both the Schengen Visa Code and the Schengen Borders Code.  There are requirements to be able to show that you can afford your planned trip, including leaving the Schengen area before the end of your allowed stay, but there is nothing that says that you must have an air ticket in your possession.  Having enough money to buy an air ticket is acceptable, as is a plan to depart by land or sea.
Comment: @WeatherVane As a New Zealander, OP does not need a visa to enter Germany.
Comment: @phoog It is, I believe, mainly a requirement, (togeather with proof of travel insurance) of visa holders.
Comment: Thanks everyone for your advice.
Answer:
will they accept that I'm eligible for a Family Reunion Visa

Citizens of certain countries may apply for a residence permit while in Germany.
New Zealand is one of these countries.
You enter Germany as a visa free citizen.
After your arrival, you will find a place to stay and togeather with your spouse, you will then register your residence.
You can then apply for a residence permit based on §28 AufenthG.
Depending on the state, the registry office may start the application process for the residence permit directly.
Otherwise you will have to make an (online, web) appointment at the Immigration Office yourself. The date that appointment was made will be considered the date of application and should be done before the 90 days period runs out.

Exceptions for certain countries
Special privileges apply to certain countries. You can apply for any residence title in the federal territory without needing to have a right to this title.
This applies to the following countries:

Andorra ¹
Australia
Brazil ¹
Canada
El Salvador ¹
Honduras ¹
Israel
Japan
Monaco ¹
New Zealand
San Marino ¹
South Korea
United Kingdom of Great Britain and Northern Ireland
United States of America

¹ Residence titles for the purpose of economic activity are excluded. To obtain the latter, nationals of these countries must enter Germany with a national visa.

Sources:

Legal entry without visa for nationals of certain countries - Berlin.de

§41 - Vergünstigung für Angehörige bestimmter Staaten (AufenthV)

(1) Staatsangehörige von Australien, Israel, Japan, Kanada, der Republik Korea, von Neuseeland, des Vereinigten Königreichs Großbritannien und Nordirland im Sinne des § 1 Absatz 2 Nummer 6 des Freizügigkeitsgesetzes/EU und der Vereinigten Staaten von Amerika können auch für einen Aufenthalt, der kein Kurzaufenthalt ist, visumfrei in das Bundesgebiet einreisen und sich darin aufhalten. Ein erforderlicher Aufenthaltstitel kann im Bundesgebiet eingeholt werden.

(1) Nationals of Australia, Israel, Japan, Canada, the Republic of Korea, New Zealand, the United Kingdom of Great Britain and Northern Ireland within the meaning of Section 1 Paragraph 2 Number 6 of the Freedom of Movement Act/EU [right of abode] and the United States of America can also apply for a  Stay that is not a short stay, enter the federal territory without a visa and stay there.  A required residence permit can be obtained in Germany.

(2) Dasselbe gilt für Staatsangehörige von Andorra, Brasilien, El Salvador, Honduras, Monaco und San Marino, die keine Erwerbstätigkeit mit Ausnahme der in § 17 Abs. 2 genannten Tätigkeiten ausüben wollen.

(2) The same applies to nationals of Andorra, Brazil, El Salvador, Honduras, Monaco and San Marino who do not want to work with the exception of the activities referred to in Section 17 (2).

§28 - Subsequent immigration of dependants to join a German national (AufenthG)
Comment: Ah... no, I did _not_ read that correctly. I was applying the footnote to all the countries in that list, not just the ones with the [1] next to them. Never mind, carry on... :)
Comment: Thanks very much for this info.
Answer: I can add my personal experience having been in a very similar situation.
My wife and I are US citizens, and she started a job in Germany a few months ago. She applied for an EU Blue Card while still in the US and received a Visa in her passport during that process. I did not apply for anything while still in the US, but set up an appointment with the immigration office (Ausländerbehörde) in Germany for about a month after our planned arrival.
When we landed in Germany, the immigration officers at the airport asked us about the fact that my wife had a visa and I did not. I told them that I planned to apply for a residence permit in Germany and had an appointment set up already, which satisfied them.
I would advise you to try to set up an appointment with the immigration office as soon as possible. While I don't believe it's strictly necessary to have one already set up to enter the country, they are currently very hard to get, and if you wait until you arrive you may face significant delays.
Once I was within the country I successfully applied for a residence permit and received my residence card (Elektronische Aufenthaltstitel) a few months later.
Comment: Thanks, this is great advice to make an appointment with an immigration office before flying. Will definitely do that!
Answer: Probably nobody will check for the existence of your return flight, either at the airport in Mexico or at immigration in Germany. I've flown to Germany before (as a US citizen not eligible for any kind of longer-term stay) without having bought my return flight yet, and nobody cared. But, this can not be guaranteed, and, if you want to be extra-safe, you can buy a refundable ticket to somewhere outside the Schengen area to show to anybody who asks for proof of onward travel, and then refund it when it turns out you don't need it.
No one can apply for a German visa from within Germany, because a visa is only necessary to enter Germany, and you will have already done so.
However, citizens of some countries—including New Zealand—are allowed to apply for a residence permit (Aufenthaltstitel) from within Germany after entering on a short-trip visa exemption. Questions about the exact procedure for doing so are better suited for Expatriatates SE or your own research and/or lawyers, but you should be able to go through the procedure in a fairly straightforward way as a family member of a German citizen.
Comment: There is no requirement to have a return or onward flight arranged when entering the Schengen area.  Being in possession of sufficient means to arrange one's departure from the Schengen area is enough.
Comment: Thanks for the info.
Answer: Although there is no requirement to have a return flight from a legal standpoint, be aware that airlines do have their own policies and do their own checks when you check-in, and might require to see some proof that you are allowed to enter as a tourist when going with a one-way flight.
This is from first-hand experience: I am Brazilian, who is also visa-free in Schengen. I live in Schengen and go to Brazil every 1-2 years to visit family. When going back to Schengen, because that is my return flight (one-way), the airline has always asked to see proof that I have a residence card or some other supporting document — I know I do not require one, so the first times this happened I asked why they were asking, and they told me it was because it was a one-way flight which does not qualify as tourism so they need to check (or maybe they saw it was a returning flight and I came from there, something a tourist wouldn't normally do). As I have one, I end up just showing it and did not feel like pressing further.
If this happens to you it may be possible to convince them otherwise and let you board. Not saying otherwise. Just warning you to be aware that the airline is also a factor.
Comment: Thanks for sharing your experience.


Knockout checked binding issue

Question: I'm having a problem with checkbox bindings not quite working with KnockoutJS 2.0.  I have an array of objects.  One of the properties of those objects is an array of different objects.  In the child objects there are a few properties, one of which is a boolean.  I build a list for each parent object and under each parent I show the children.  For each list of children I have two views, a read only and an edit view.  In the read only I have images that represent whether or not the item is checked based on the boolean property.  This works and if I update the boolean value through the console, I'm seeing what I would expect--the image goes away or displays based on the value I assign.  In the edit view, the images are replaced with a checkbox.  I see the same behavior when I update the value through the console--it is checked when I expect it to be and not when I don't.  The problem comes in when I check or uncheck the checkbox.  Doing this doesn't change the underlying value the checkbox is bound to.
Here's the basic idea of my data.
[
    {
        "xxx": "yyy",
        "xxx": "yyy",
        ...
        "Displays": [
            {
            "xxx": "yyy",
            ...
                "Excluded": false,
            },
            {
            "xxx": "yyy",
             ...
                "Excluded": true,
            }
        ],
    }
]

Here's the binding
<input type="checkbox" data-bind="checked: !Excluded()" />

Comment: Try removing the () from the binding (checked: Excluded). It's only needed when you evaluate an expression on an observable property, and in this case, your Excluded property is not even an observable.
Comment: It is an observable, I just didn't post the code to make it into an observable.
Answer: the problem is that "checked" here is a bidirectional binding: the bound property needs to be read to generate the correct view, but needs also to be updated when you click on the checkbox. Contrast this to a binding like:

when the expression is only read, so you can use an expression (and you need to unwrap the observable).
So, you need to bind directly to the observable property, without "unwrapping" it adding '()', it will be done by knockout when needed, both for read and write:
<input type="checkbox" data-bind="checked: Excluded" />

See http://jsfiddle.net/saurus/usKwA/ for a simple example. Note how the checkbox labels are updated on change, showing that the model is updated and the rendering triggers correctly.
If you need to negate the value (so that the checkbox is checked when the value is false), you can add a writeable computed observable, as explained on http://knockoutjs.com/documentation/computedObservables.html section "Writeable computed observables", or you can negate the data in the viewmodel, doing it on the server just before sending the data, or on the client before populating the viewmodel.
hope this helps.
Comment: If I don't use the parenthesis it doesn't work at all.  The checkboxes are never checked and checking them doesn't update the observable.
Answer: I know my answer is a bit late to the game here, but I had this problem today and this was the closest thread I could find related to the problem, and it doesn't seem to have an answer that solves it. So here's my solution.
Essentially, the issue is that knockout really wants your viewModel values to be a string, not a boolean, but this isn't always practical. So, I created a binding called "isChecked" which works strictly with booleans. Note: This will only work with observable properties.
ko.bindingHandlers.isChecked = {
    getElementDeclaredValue: function (element) {
        var declaredValue = element.getAttribute("value");

        // If a value is provided, we presume it represents "true",
        // unless its explicitly "false". If no value is provided, we
        // presume that a checked state would equal "true".
        return declaredValue && Boolean.isBool(declaredValue)
            ? Boolean.parse(declaredValue)
            : true;
    },

    init: function (element, valueAccessor) {
        var updateHandler = function () {
            var declaredValue = ko.bindingHandlers.isChecked.getElementDeclaredValue(element);
            var elementValue = element.checked ? declaredValue : !declaredValue;

            var modelValue = valueAccessor();
            var currentValue = ko.utils.unwrapObservable(modelValue);

            if (elementValue === currentValue)
                return;

            if (ko.isObservable(modelValue)) {
                modelValue(elementValue);
            }
        };

        ko.utils.registerEventHandler(element, "click", updateHandler);
    },

    update: function (element, valueAccessor) {
        var elementValue = ko.bindingHandlers.isChecked.getElementDeclaredValue(element);
        element.checked = elementValue === ko.utils.unwrapObservable(valueAccessor());
    }
};

The two Boolean methods ("parse" and "isBool") are defined as follows:
Boolean.isBool = function (value) {
    return (/^(?:true|false)$/i).test(value);
};

Boolean.parse = function (value) {
    return (/^true$/i).test(value);
};

I'll ignore any comments that say I shouldn't be modifying a built-in object prototype; I'll do as I damn well please ;-).
Usage is the same as the checked binding. The "value" attribute is optional, unless you want the checked state to represent false:
<input type="radio" id="rbNewClaim" name="ClaimType" value="false" data-bind="checked: isExistingClaim" />

Hope this helps someone.
Answer: I gave up trying to get this to work with the bool values and created an array of selected objects and handled it that way.  It isn't the optimal solution, but I was tired of fighting this.

Knockout checked binding issue


Would it be possible for species to become sapient without using tools?

Question: Set in a parallel universe, in a galaxy far far away, an Earth-like planet orbiting a yellow dwarf star with the mass of 1 solar mass. And yes, indeed that planet comes with a natural satellite that seems to be tidal locked but anyhow, could a specie, most probably mammalian would develop sapient intelligence through either evolutionary or selective pressure alone without inventing tools(physical object)? To qualify a sapient at least in my world is the ability to ask irrational questions on it's own... BTW a parrot named Alex tried to cheat but was took cared of.
Comment: What exactly do you mean by "ability to ask irrational questions?". By many definitions of sapient elephants pass for example and they only use extremely crude tools.
Comment: Well, how do you know other species aren't asking questions like that if we can't understand them properly? There are only a small handful of species that we've unlocked some measure of two-way communication with that can discuss more abstract objects. What you're asking for (sounds to me like) the ability to consider things that are not immediate but ponder an abstract scenario. Again, some animals have shown signs of doing that.
Comment: You answered your own question. Being sapient means asking "who I am, who we are, were are we going in life, what's the purpose of life". Making tools is making tools.
Comment: @S.Move: actually quite many animal species would pass the test with flying colours but only a human at least myself would seriously ponder why a chicken cross the road?
Comment: You can simply look at the countless species on earth to determine the ridiculous natural feats that can accomplished without tools.
Answer: Unlikely, but Plausible
My first reaction was no, because use of tools is one of the ways we define intelligence. For example with logical thinking and knowledge of cause and effect you can reason that hitting something with a pointy stick is better than punching them. However, your question was not about using tools, but making them.
So in order for this to work you would need a species that:

Benefits from increased communication (a social or pack animal)
Benefits from logical thought
Lacks the physical capability to
manipulate the environment with enough precision to construct objects.

For example a pack of omnivorous wolves. Increases in intelligence and communication could help them hunt, and if they figured out limited farming or ranching they would have a massive benefit to their survival, but lack the physical means to actually construct tools. They would certainly use any useful objects they found in the world around them to their benefit.
The reason this is not very likely, is that any genetic variance that increased precise manipulation would become hugely beneficial and would spread throughout the population. This would have to never have happened.
Comment: I would say more ulikely, than plausible. For cultural development there should be feedback loop: when intelligence modifies environment and then adapts to that more and more artificial (with each cycle) environment. Those " sapient wolfs" (or dolphins?) would stay at primitive culture with the languge of hundred words without any possibility to develop further.
Answer: I would probably turn that question around, why would a sapient intelligent species not use tools if they have the capacity to make them.
Tools are not a necessity for intelligence (or sapiens), though it's an inevitable outcome of intelligence. Any entity with the mental capacity to shape the world around it to it's own benefit, will invariably do so eventually.
Answer: I think you should clarify whether you mean "without MAKING tools" versus "without USING tools". There are a LOT of intelligent animals that use 'found' tools including primates, birds, and even octopus.
If the question is "can you be sapient without USING tools", I think that's extremely unlikely, and would be possible with a creature that doesn't have any ability to manipulate physical objects.
If the question is "can you be sapient without MAKING tools", I think that's entirely possible and if you go on youtube and watch some of the crazy stuff octopus do, you might even argue that it's already happened.


VB .Net Windows Service Console Messages

Question: I have a .Net Console application which displays thousands of lines on the console each minute.  I want to convert it to a Windows Service, however I still need a way of viewing these messages.  There are far too many messages to write them to the event log or even a standard log file.  I was wondering if there were a way to write a systray app that could simply intercept these messages from the service and display them in a console window.  I have no need to save older messages, I only need to see current activity.
Answer: The service will need to write to shared memory of some sort in order to communicate with another program that displays the output.  I think your best bet is to output to a SQL table or something and clear out older entries so there is never more than, say, 1000 records in the table at a time.  Then ping the table a couple times a second in the viewer app and display a streaming view of the output.
Answer: Sounds like the System.Diagnostics.Trace type would be perfect for this.  Implement your changes in two phases:
For phase 1, you add a ConsoleTraceListener to your app, and convert all of your current calls to Console to write to Trace instead. This will only maintain your existing behavior, but it sets you up to easily make the change to your new output.
For phase 2, you implement a new TraceListener you can attach instead of the ConsoleTraceListener that does whatever you want with the messages. This might include listening for a connection from your proposed systray or console app.  Even better, I bet a bit of googling will show you a TraceListener that already does what you want.
As for the actual mechanism for communicating the message, my recommendation is to use the standard SysLog approach. This has the advantages of working existing software for the client, makes it more likely you'll find an existing TraceListener, and many of the existing syslog clients will bring along some automated data mining as a bonus.


Set up cron Magento 2

Question: I want to Create the cron job, but everytime I do this step crontab -u Magento file system owner user name -e I got an error: must be privileged to use -u.
The problem is I don't know what the Magento file system owner is. Where can I find this?
Answer: You can run ls -l to list the files in directory with user and group.
This will display something like this:

-rw-r--r--   1 magentouser apache    691 Aug  2 13:54 acl.xml

Where magentouser is displayed will be your magento user.
I normally use su magentouser to switch the current user to the magento user and then run crontab -e to set up cron for that user.
Answer: Instructions for Windows

First of all, find location of php.exe – Generally where Xampp is
installed, it's in Drive:\xampp\php e.g c:\xampp\php

Go to a folder
and create a file named magentocron.bat

Edit this file and paste 3 lines
shown below:
php_path\php.exe magento_root\bin\magento cron:run
php_path\php.exe magento_root\update\cron.php
php_path\php.exe magento_root\bin\magento setup:cron:run

For example, a finished version might look like this:
C:\xampp\php\php.exe C:\xampp\htdocs\magento\bin\magento cron:run
C:\xampp\php\php.exe C:\xampp\htdocs\magento\update\cron.php
C:\xampp\php\php.exe C:\xampp\htdocs\magento\bin\magento setup:cron:run

Save the file, open command prompt and enter following command:
`schtasks /create /sc minute /mo 5 /tn Magento\Cron /tr path\to\bat\file\magentocron.bat`

Now click on Start –> Control Panel –> Administrative Tools –> Task Scheduler.

Expand Task Schedule Library from the left hand column and click Magento.

Select Cron from the middle pane, click properties from the right pane under selected items.

Under Security Options, click the Change User or Group button.

Now in the current window, enter System username in the object name box and click check names. Click OK to close the User window, and OK to close the Cron properties Window, and close Task Scheduler.

Cron job setup is successful and it will run every 5 minutes.

Instructions taken from here: https://magecomp.com/blog/set-up-magento-2-cron-in-xampp-windows/
This below assumes you are on *nix
Since you are trying to edit the crontab for another user, you need to use sudo
This is assuming your magento file system owner is magento
sudo crontab -u magento -e
You can also switch to that user, then set the crontab:
su magento
then...
crontab -e
What are the permissions set as in your deployment? What is the output of ls -la /path/to/your/magento?
Do you have a magento file system user? What is the output of id magento?
If you get something like this:
| => id magento
id: magento: no such user

Then you will need to create a magento user, and then set the permissions on your magento directory accordingly.
More information here: http://devdocs.magento.com/guides/v2.0/install-gde/prereq/file-system-perms.html
Comment: When I use sudo, I got command not found
Comment: What is your OS? What stack are you using? What do you get from `ls -la /path/to/your/magento`?
Comment: Also do you have a `magento` user? What is the output of `id magento`?
Comment: I'm using Windows 10 and Putty
Comment: and I get id: magento: no such user
Comment: Sorry, I didn't know you were on Windows, you should include that in the question. Are you using XAMPP or similar? What is your stack?
Comment: I uploaded Magento on my domain (pureatheart.eu). I'm not use Xampp. Is there a sudo command for windows?
Comment: I added an example for windows, you will need to locate the PHP executable on your windows server and make a `.bat` file with your cron instructions.

Set up cron Magento 2


rechargeable battery pack wiring

Question: I have a NiMH battery pack that needs replacing in a tv terrestrial field strength meter. The pack is 6 cells and is rated at 7.2v 2500mAh. It has 2 pairs of 2 wires so 4 wires that connect to 2 plugs on the internal board. I have opened up the pack. two of the wires are on the outside of the pack and not physically connected. I'm guessing it's some sort of sensor and if so can I just remove it and add it to another pack that doesn't have one? It doesn't appear to be connected directly in any way. I have seen similar packs but they only have the usual 2 wires.
Comment: Temperature sensor. Vital for most NiMH chargers! Yes, please move it and place as similar as possible on your new pack.
Comment: If your charger doesn't monitor temp. Is it reliable?
Comment: Thanks for the replies. I thought it might be a heat(?) sensor Winny so I'm going to remove it and stick it on the new pack. Just needed confirmation I guess. Actually just to clarify, the charging is done by the unit itself not by any external means.
Answer: That is a temperature sensor. You should reattach it in the new pack, firmly pressed against the cells by the tape.
It is difficult to detect electrically when a NiMH battery is fully charged. One standard technique is to watch for a temperature rise, because once the battery is charged the input energy will be converted to heat instead of stored.
Other packs you have seen without a temperature sensor may be used with chargers which trickle charge (charging so gently that continuous overcharge does not damage the cell) or look for signs in the change of voltage over time, as described in the linked article.
Comment: (The main point here has been mentioned in comments, but nobody wrote an answer, and questions should be answered, so I did.)

rechargeable battery pack wiring


What determines the default Site Collection Administrators?

Question: This is for SharePoint 2013. Every time a new site collection is created, there are 3 user accounts that are automatically set as the Site Administrators under Site Settings > Site Collection Administrators If I check the Site Collection Administrators from Central Administration I only see 2 of the 3 users. How does SharePoint determine these users? Where and how can I change the users that are automatically created as Site Collection Administrators?
Answer: I dont think this is true. When you create the site collection during this you have to mentioned the primary and secondary Site collection administrators. Once site collection created then you will see the both account under site collection admin from site settings.
Just, I created a brand new site collection with primary site collection admin (no secondary) after that when i checked from site settings, i am seeing only one account.
Couple of things to check.

How you are creating the site collections? central admin or pwoershell? if power-shell, then what is script?
Are you know about the account name?
is their any customization?
Comment: Your're right. I should of tried a test collection. So I created a test Site Collection assigning only a primary site collection administrator and that was the only user under `Site Collection Administrators`. Perhaps my username was added to all site collections through a script from the previous admin?
Comment: Yup, there should be some script or any thing similar this can add extra admins...if the above is helpful then upvote and mark the answer.


lost 4 out of 12 recovery phrase

Question: I lost 4 out of 12 recovery phrase
I even cant remember public address
is there a way I can find them back
please help me
thanks a lot
Answer: The BIP39 English wordlist contains 2048 entries so, since words can be repeated, you need to try (corrected) 2048 ^ 4  combinations which is 117,592,186,044,416 different phrases to try. If you could test a million guesses a second, that would take up to 204 days.
The first stage of testing would be that the checksum condition is met. This ought to be fast. I imagine the second phase involves using the phrase to generate some reasonable number of HD addresses and checking against a local copy of the blockchain to see if any generated addresses appear in any transaction outputs.
Some wallets  use a different wordlist - I think Electrum is one. Obviously you need to use the right wordlist for your wallet or attempted recovery is a complete waste of time.
There are tools that can help with this, one is btcrecover. I would use this sort of tool only on a new airgapped computer that has no WiFi, Bluetooth, Ethernet or other networking capability.
Obviously you need to be extremely careful about where and how you obtain this sort of tools. There must be many fake or maliciously altered copies around that send your recovery phrase to a thief (before or after recovery).
There is the option of adding a user passphrase to the recovery phrase. If you did use that and can't remember anything about it, I doubt the wallet is recoverable.

Useful resources

BIP39 - including implementations in numerous programming languages
bip39 checksum python
Comment: There is a checksum computation thus if the last word does not fit the checksum you don't need to test this
Comment: thank you for clear guidance. however I need to try 2039*2038*2037*2036 options since 8 words are already in the phrase.  my question is when I try random phrase at https://iancoleman.io/bip39/ it say Invalid mnemonic. therefore most of these options would be invalid. how can I omit these invalid option form  this possible option. and what is the rule for being valid or invalid mnemonic??
Comment: Answer corrected/updated accordingly, thanks.
Comment: how does this checksum computation work? how can i access it or what is the structure behind it
Comment: @lookingforhope: see last link in answer
Answer: I created a python script to try exactly this. Check it out here: https://github.com/SachinMeier/MnemonicRecovery
There is certainly no guarantee that this will work, and it's definitely not optimized for speed yet, but if you're only missing four words, it might just work. Currently, it only supports P2PKH addresses. You'll also need to install a virtual environment or have the python bitarray library installed.
The python script has no network functionality, so there's no way I can steal your seed, but you should still run it offline.
Please dm me on twitter @sachinmeier if you need help. I will never ask you for the seed or any bitcoin.

lost 4 out of 12 recovery phrase


What factors should i consider when selecting a motor for a free wheeled cart-pole balancing robot?

Question: I'm developing a small scale cart-pole balancing robot consisting of two wheels driven by a single motor at the base (essentially like a unicycle, but with two wheels to constrain balance to a one dimensional problem).
I'm not sure what qualities to look for in that motor.  I think the motor should be able to accelerate quickly in directions opposite of motion as dictated by the control system.  However, i'm not sure if this rapid acceleration should correlate with higher torque motors or faster speed motors.  I think higher torque motors would be too slow to react to control commands.  In contrast, fast speed motors may not be able to overcome the momentum of the cart.
Are there any design equations or other calculations i can make based on my robot's dimensions and weight to determine the right specs needed for my robot's motor?  How can i determine the right motor specs for this application without resorting to brute-force trial & error experiments?
Comment: since rotational inertia is m* r^2, you can solve your speed issue without concern to the motors.  just increase the pole's length if your motors can't cope with the speed. :)
Answer: High acceleration from a static (balanced) configuration is only related to high torque. However, the maximum torque you can deliver decreases as function of speed. So, in the end it depends on both. In theory you could use a tiny motor with a huge gear ratio able to deliver a lot of torque, but it speeds up really quickly, meaning that it will fail coping with larger disturbances.  It is recommended to run some simulations of desired behaviour. Then calculate the required power by multiplying velocity and torque curves of the actuated joint.
Find a motor (brushed) that is able to deliver this power. Depending on a desire for efficiency or size, select a motor based on its nominal power or all the way up to near-maximum mechanical power respectively, or somewhere in between. I would recommend the former for now, as it's an easier approach. Nominal power is often given, or easily calculated by multiplying the nominal velocity and nominal torque. Maximum mechanical power is higher, and approximated by multiplying the no-load speed and stall torque divided by four.
Lastly, you will need a transmission to obtain desired torque-velocity characteristics. For instance, if your motor is able to deliver 10 mNm at 1000 rpm, whereas you need 2 Nm at 5 rpm, then use a transmission ratio of $R=2000/10=200$.
Update your simulation model by including the motor's reflected inertia $R^2\,I_{rotor}$ and mass to check whether your motor is still capable of delivering sufficient power. If not, then you have to re-iterate motor selection. Also, check your electrical power source and motor controller. Are they capable of delivering the required voltage and current?


Can I use the Trip Attack maneuver on a already prone enemy?

Question: Can a Battle Master use trip on a prone enemy? The player just wants the extra damage. Is it possible, or against the rules?
Answer: Prone is a condition, and generally a condition is redundant. Damage is cumulative and generally untied to the condition. You can't knock an unconscious person more unconscious, but you can damage them more. You can't make a poisoned character more poisoned, but you can do more poison damage.
So in the spirit of similarity, I would say that yes, you can do the damage. You just can't make them "more prone". Ignore the saving throw if you wish, but the damage of the maneuver should stand.
Answer: Yes
The text of the Trip Attack (PHB 74) is:

Trip Attack. When you hit a creature with a weapon attack, you can expend one superiority die to attempt to knock the target down. You add the superiority die to the attack's damage roll, and if the target is Large or smaller, it must make a Strength saving throw. On a failed save, you knock the target prone.

There are no preconditions to meet, and it doesn't specify that the maneuver must be used against an enemy who can be knocked prone.
So yes, you can use it against a  prone target. You're not going to knock them any more prone, but that doesn't sound like what your player is going for.
Comment: Good flavor, but the damage gets inflicted regardless if the trip attempt is successful.
Comment: I always rationalized the superiority die extra damage as part of the fall inflicted by the trip.
Comment: I rationalized the extra damage as hooking/kicking the opponent's leg as part of trying to knock them down. Even if they don't fall, a kick to the shin still hurts. :)


Forgot to add whirfloc / irish moss to wort during boil

Question: Brewing a fat tire clone, forgot to add whirfloc tablet / irish moss... I'm 5 days into primary fermentation.
What would everyone recommend? Add something, skip it, ???
Thanks
Comment: Skip it, you'll be fine. The beer might take an extra 2-3 weeks in the bottle to completely clear, but that's it.
Answer: I've hardly ever added clarifying agents (irish moss, whirlfloc, &c.) to my beers. I don't secondary, I regularly do a 2 week primary, then rack into keg. I usually pour perfectly clear beer.
Relax. Don't worry. Have a homebrew.
Answer: At this point, neither of those fining agents will work.  They both require a good, rolling boil.  If you're going for clarity, Your best bet now is to let it mature for another couple of weeks and then cold crash the beer by refrigerating it as near as to freezing as you can get it (without actually freezing it), and let it sit for a couple of weeks/months.  You can cold condition the beer in the bottles after they've carbonated, to the same effect as doing it in bulk with the carboy/bucket.
If you are kegging, you can easily add fining agents after chilling the beer such as gelatin or isinglass to help drop out chill haze as well as residual yeast and polyphenols.  If dietary concerns are a problem regarding those two agents (kosher or veganism, respectively), you may consider polyclar, just be aware you'll want to rack the beer off the polyclar before kegging.  No one likes drinking plastic.  Another option of course is to filter, but I assume you, like many home brewers do not own a filtering setup.  You may be able to employ any of these fining agents/techniques with bottling, you'll just want to add yeast back into the batch at bottling to ensure there is enough yeast to carbonate the bottles without having to wait a month or two instead of the regular 1-2 weeks.
Here is an article containing all the information you'd need to fine the beer.
Comment: I'm going to go with trying a gelatin fining on this batch and see how it turns out.
Answer: If you're not one to care too much about the clarity of your beer, then it won't matter at all . Just proceed as normal on bottling day.
If you do care about the clarity of your beer, your options are to cold crash and use gelatin finings, or just cold crash.


Johnson A419 controls

Question: I have a summit 570 kegerator which does not get cold enough. I bought the Johnson A419 - saw reviews everyone swears by it. I hooked it up, set at 32°F, the display reads 43°F and does not come on. I do not think it is bypassing the factory thermostat in the fridge - do I need to bypass it, and if so, how?
Comment: Can you please edit your question for … english?  Maybe add some periods, capitalization, &c.
Comment: Is the Johnson controller set up for "cooling" mode?  The A419s have both a "cool" and "hot" mode that's changeable only by switching a jumper after you've opened up the controller.
Comment: Yes, it is set for cooling. Shows snow flake bottom of screen. My problem is the johnson control is not taking over for the factory thermostate.I think I need to bypass factory thermostate to see if the A419 will take over
Answer: It sounds like you could be right - if the existing fridge doesn't get cold enough, then the thermostat is opening (disconnecting the circuit) above your target temperature, so the unit doesn't get cold enough. I'm assuming you've looked for some adjustment on the thermostat - most fridges have these.
So, if you have connected the A419 to the mains socket of the freezer, then the built-in thermostat still still be in play and will shut off the fridge too soon.
This thread here talks about the temp sensor being covered in ice prematurely, which is the reason they don't get cold enough. The fix was to improve the door seal, since that was letting in moisture causing ice buildup on the sensor.
This thread gives instructions on how to bypass the thermostat:

How do I bypass the Summit thermostat? There are two wires that enter
  into the fridge compartment and clip onto the thermostat. I am
  assuming one is 115 volt and the other tells the compressor what to
  do. If I splice these two wires together, will the compressor run
  continually? I can then let my Johnson Control thermostat control the
  system and hopefully get my pours down into the proper temps in the
  30's. Right now I am pouring at 45 degrees, not acceptable!

And the reply:

You are correct that connecting the 2 wires of the thermostat results
  in it running non-stop. I don't think it's 110 volts at the thermostat
  more liKely it's a relay switch at much lower voltage but when they
  are connected the switch is in the on position. Your temp. controller
  will then be needed to take over the control of the compressor. If
  your unit is healthy it should be able to get below 29 F. the temp
  beer freezes at so be careful setting the temp on your controller.

Johnson A419 controls


Do I need to replace the garage door opener or just the remotes to upgrade to rolling code technology?

Question: I have an old Craftsman Garage door system from the mid 80s.  It still works great and for my cars, we have moved to the in car remote openers. We also have a wall remote code to access the garage door. One of our older cars still has the original opener which I believe is dip switch. Question- In order to move to a rolling code technology- Do I need to replace the whole system, or just the remote(s) and or the wall opener. The police were just here as someone remotely opened my garage door and then the dog scared them away.
Answer: I'm not sure it makes sense to spend money and effort retrofitting something on a 30 year old opener. How much longer do you think it will really last? New garage door openers can be had for around $150 and in addition to the "rolling code" remotes will include several other benefits like an electric eye safety sensor, auto-reversing contact sensor, vacation lockout controls, etc. If you want to spend more you can get other bells and whistles like quiet belt drives, wifi control, number keypads, battery backup...
Comment: Note: quiet belt drives are useless, if you have a loud metal door.
Answer: What you want is a HomeLink Conversion Kit. This will replace the wireless receiver of your old garage door opener. Or wire up like a button.
If the wireless receiver is built in to your opener then you will need to find a way to disable it, otherwise someone will still be able to send the dipswitch code and activate your opener.


Why would a CD4060BE produce a copy of an input clock signal?

Question: I am making a CMOS logic clock and I have a problem with the 1Hz signal generator (see schematic below). When I connect up the CD4060BE chip to a crystal the output on Q8 of the second chip does not blink an LED at 1Hz, but rather the LED stays permanently lit (I don't have a scope to test the frequency). I connected up a 3Hz CMOS clock to the clock input on the second CD4060BE chip and Q8 blinks the LED at the same rate as the input frequency. Why would this happen? Surely the input frequency should be divided down by 2^8 and the LED blink should be extremely slow. Am I doing something wrong?
Comment: Your schematic does not show an LED. From your question it is apparently driven by Q8 of U3. Exactly how is this done?
Comment: Doh! I plugged the LED in the wrong way around. Thanks.
Comment: Your crystal connection circuit looks flaky to me. I don't think that will work very well (well, not according to the data sheets). What made you decide on that way of doing it?
Comment: @Andy aka I copied it from a YouTube video demonstration of a CD4060BE 1Hz clock circuit. Do you have a pointer to the correct way of doing it?
Comment: The device data sheet shows how you should do it.
Comment: VSS or VDD not connected perhaps.
Answer: I plugged the LED in the wrong way around to test the output on Q8. Stupid error. Thanks.