How to make people do their civic duty?

Question: Voting is important, right? And yet less than 400 people have earned the civic duty badge. Out of how many thousand? Uncool!
Comment: b-b-ut you do not have it !
Comment: There are nagging popups trying to get people to vote, but I doubt they really achieve much. Also I don't think badges are too rewarding either. Good question, hard problem to solve.
Comment: @HackToHell visited 26 days, 16 consecutive
Comment: Suffrage is at 469 and then there is Vox Populi at 148.
Comment: @CarlB: Those two are rather irrelevant in my opinion. I have Civic Duty on SU and even Electorate on MSO, but I failed to achieve Vox Populi on either.
Comment: @Dennis: It was just a note of active voters for those badges. 30 in one day for the Suffrage and 40 in one day for Vox Populi. So 148 of the xx# of active members who can/could vote utilized the max day vote.
Comment: Civic duty is now at 183. i got my silver
Comment: @Isaac You have been a member for 2 1/2 years and cast 100 votes (IMHO that is low even when being inactive). So what is your reasoning Isaac? (HackToHell, thanks for pointing this out)
Answer: If you don't want your government to be run by people you hate, go vote.
If you don't want that only 1% of all members get to decide who looks credible and who doesn't, go vote.
But it's not that simple with Stack Exchange, is it? We need voting to make people see what is quality content and what isn't. So if people don't vote, contributions become less useful because they aren't peer-reviewed.
But I refuse to handle this as a problem because there is no real solution to it and it isn't really a problem either.
We still get a good amount of voting, even though I see much higher voting participation on beta sites. And I think therein also lies the answer to the problem. Beta sites have a strong community. They want to built up their site and they're gonna put in as much work as is needed. And voting is part of that work.
95% of all visitors to Super User come from a search engine. So there's a high plausibility that they've never been to the site and that they don't care about it. They're happy to, maybe, find their answer and then they're off. So we're only really talking about 5% of all visitors that make up the active community.
Inside that 5% are people that seem to come to Super User to earn reputation, but aren't as interested in reading material from other people. It's more like a sport to them and they aren't really into spectating. And that's great, we get a lot of good contributions from professional athletes :)
Also in the 5% are the moderators and the SU-junkies that live on the site and have nothing better to do all day than click on those voting buttons anyway, we can ignore them.
So then we end up with about 3% of all visitors, who are potential voters, but don't vote or don't vote as much as they could.
I really don't see how one could improve that situation, other than trying to pull more people from the 3% into the SU-junkie sector where they will have no chance but to browse the site all day and night to search for content they haven't seen yet.
So, yeah, go out there and comment on peoples stuff, vote on it, answer it, write some great questions that people love to write an extensive answer on, get them addicted.
Comment: @IsaacRabinovitch: About 95% of all traffic comes from search engines. To my understanding, that's true for all SE sites. There are moderator-only statistics that indicate this, so, yes, those are hard numbers. My main point is that the group of people who *could* vote, but doesn't, is possibly much smaller than one would assume (given the scale of the site). We need more people who actively participate regularly, period. But, as I said, there's room for improvement, but I don't see an actual problem.
Comment: @CarlB: There are situations where you can use voting (or the absence of it) *strategically* to affect your own reputation gain. If you don't know what I'm talking about, then I'm really happy for you.
Comment: OK, non-voting is less of a problem if you ignore people who ask questions but don't write answers. But is that really 95%? Do you have hard numbers or is that just a guess?
Comment: OK, look at it this way: 1680 users have reputation of 1000 or better. We can safely consider these people serious users, committed to participation, especially in the form of answering questions. And yet only 381 (23%) have voted 300 times. So 77% of high-rep users mostly don't bother to vote.
Comment: @IsaacRabinovitch Some people don't vote because they just don't know if an answer is right or wrong. Some people don't vote because they aren't reading other peoples answers. Some people don't vote because they don't read questions other than their own. Some don't vote because it will decrease the value of their own achievements. Some people simply don't vote because they want to do other "tasks". Voting is not just voting. You also have to read the content and be able to judge it. The motives for people to use [su] are very different. If you want to change them, you can only lead by example.
Comment: @OliverSalzburg - "Some don't vote because it will decrease the value of their own achievements." Can you elaborate on this one?
Answer: A small observation on votes. It would seem that some highly voted questions and answers like What are the windows a and b drives used for that was migrated Jan 10, 2011 had high voted, high up count on comments and answers. Alot of old questions have high votes. Maybe these days those folks that have been around for a while might have been heavy voters back then and not so much now. Some points made to a question I posted Question and suggestion on votes and Rep about voteing brought great comentary and insite from slhck: (the links that he had attached did not copy over into this quote)

Why aren't posts getting votes?
While the views are from different IPs, most of them aren't even by
  registered users or users with the privilege to vote. If—quoting Jeff
  Atwood—90% of all visitors can't vote on the stuff they see, then this
  would explain the lack of votes quite easily. And I agree: It's sad to
  see good questions stick around with 0 votes.
Also note that even though new users can participate, you need at
  least 15 reputation to vote up posts (and consequently 125 for voting
  down). This is primarily to allow users to get to know the system's
  currency first before spamming everyone with their votes, bringing
  down the value of votes and reputation to zero.
Why don't we have to have a lot of votes?
We use voting as a primary means of selecting between good and bad
  posts, and if a question turns out to be neither (i.e. not
  particularly interesting or well-asked), then it might just get no
  votes at all. And if it only manages to get a few views, then I don't
  see why the poster should gain reputation for that — there's not much
  of an achievement there. Maybe the question just had a bad title that
  prevented people from viewing it at all? Or maybe it really was not
  useful and much too localized.
While this sounds a bit harsh, think about the fact that there are pop
  ups and reminders everywhere which ask users to vote more on questions
  if they haven't done so in a while. Voting on questions is even more
  encouraged by the fact that downvotes don't cost you 1 rep as the
  voter. And you can vote for 10 more questions than answers per day.
  So, if a new user happens to ask a good question, they'll get votes
  quite easily.
Popular ≠ Good
Another aspect you should take into account is the fact that there's
  an inequality between easy and popular questions and those that are
  not as easy to find for others but still excellent questions.
Bike shed questions would get an additional boost of reputation for
  views just because of their popularity, without the need to be a
  particularly good question in the first place ("Good" in the sense of
  the criteria we ask, not in the sense of "Good question! I always
  asked this myself but never bothered to do principal research").
While we try to shut these questions down pretty early, that's still
  something you might want to think about when suggesting such a
  feature. How would popularity play a role in this?
That all being said, I think your suggestion has merit, but you will
  have to take all these factors into account. Also, why not actively
  encourage voting more on the voter's side and let reputation gain for
  others be a result of this, rather than having the system
  automatically award reputation without even knowing what for, exactly?

Is there an assumed guide line that (at least) questions must be of a certain calibur, quality or some other noteable something or other to earn a vote (again, focus to question, not answer)?
I can understand reservations on voting up answers if there is an unfimiliarity or it's not a great answer and that is understandable.
Comment: Analyzing questions by year posted shows a steady decline in post scores. However, this doesn't take into account questions gathering votes over a long time (a Q posted this year had less exposure to voters than one posted in 2009), [auto-deleting unanswered 0-score or less questions after a year](http://meta.stackexchange.com/q/78048/151367), as well as the fact that the tech landscape doesn't change fast enough to give users the opportunity to ask good questions of general interest for new tech. IMO old Qs simply had it much easier to be *good questions* without being duplicates.
Comment: These numbers are SU only. I skipped 2008 as not enough of that is useful. Much migrated from SO.
Comment: All (or most) of these votes were cast after migration: http://superuser.com/posts/231273/timeline I don't remember the "nobody votes" issue being recent either. Do you have [data](http://data.stackexchange.com/superuser/query/new) to back that up?
Comment: In fact, when viewing [answer score distributions](http://i.stack.imgur.com/fCG8H.png), the situation is almost constant over the years. Note that the data is from late June 2012, so none of those 2012 answers are older than 6 months and haven't yet had time to gather votes over time (I think this should account for the 0 score spike). And let's face it, early answers to popular, early questions gained upvotes easier, similar to the questions themselves.
Comment: The answer score distribution is for just SU? Or all of stack Exchange?

How to make people do their civic duty?


Pronunciation of long e

Question: When starting to learn German from the EUP book "Teach yourself German" many years ago, I gathered that German long e was pronounced similarly to the French é. Thus, for example, sehen, to see, would be pronounced, very approximately, as English ZAY-in, IPA /ze:n/.   However, on beginning the on-line Duolingo German course recently,  I notice that the speaker pronounces the word more like ZEE-in, IPA /zi:n/.    Is this a question of local accent, perhaps, or have I been mistaken all these years?
Comment: @sumelic not only English speakers but also speakers of many other languages. It seems in German the tongue position is too high that people will easily mistakenly hear it as /i/. [How can I distinguish the short sounds \[ɪ\] and \[e\]?](https://german.stackexchange.com/q/29433/22344), [What is the difference in pronunciation of the letters E and I?](https://german.stackexchange.com/q/7872/22344), [Problem differentiating between \[i:\] and \[e:\]](https://german.stackexchange.com/q/20035/22344)
Comment: I am brazilian, speak Portuguese and our language has the /e/ phonem. I have initially expected the German /e:/ to be the exact same sound, just longer. However, as phuciv mentioned, in the pronunciation of the German /e:/ , the tongue position is a little higher than the Portuguese /e/ (also higher than the first vowel phonem in English "day") and a little lower than Portuguese /i/ (also lower than German /i:/), making a different sound which seems similar to /i:/ to a German learner. However, it is a distinct sound.
Comment: Note that *zay* implies a completely different sound from French *é*. I don't think English has the equivalent to German *ee*.
Comment: I think English speakers tend to hear German /eː/ as English /iː/, even when the German speaker actually distinguishes German /eː/ from German /iː/. The vowels are fairly similar.
Answer: You are almost right in the pronunciation that you expect. However, the vowel of the second syllable does not completely disappear, Wiktionary gives the pronunciation as [ˈzeːən]. That may have confused you, given that the difference between a long e and a long i is often difficult for English speakers to hear as previous questions show.
Comment: [ˈzeːən] is just one of at least four standard versions, and it even is wrong when talking about Austrian German. (There almost never is a [z] in standard pronunciation of Austrian German.)
Answer: We don't have an audio sample, so this is only speculation:
The standard pronunciation of 'sehen' is transcribed as [ˈzeːən], while [ˈzeːn] is known as an often occurring version. (Duden Aussprachewörterbuch)
Speakers often don't articulate the schwa sound [ə] clearly when a word ends with an -en, and then it may sound a bit like [ˈzeːɪn].
If, however, someone clearly pronounces sehen as [ˈziːn], that would be wrong in terms of standard German pronunciation.
Comment: In my answer http://german.stackexchange.com/a/31595/1487 we have audio samples. Samples from six professional speakers, male and female, from Austria, Germany and Switzerland.
Answer: Adaba
Here is the »Österreichische Aussprachedatenbank Adaba« (Austrian pronunciation database) where you can listen to the correct pronunciation of thousands of words:
http://www.adaba.at
It contains thousands of audiofiles of standard pronunciation of German word for the three standard variations of German (Austrian German, German German and Swiss German), each spoken by a female and a male speaker (red triangle = female speaker, blue = male).
I can identify the both Austrian speakers by their voices, they have been news speakers in TV some years ago, so they are professional speakers. I don't know who the other speakers are, but I guess, they are professional speakers as well. So the audio files really let you hear what standard is.
How to use it:
Enter (part of) a word in the second area titled »Suche« (search). You can search orthographic and even phonetic (if you're not sure about the correct spelling).
When you click on the magnifying glass, you get a list of hits in the first area titles »Ergebnis« (result). If you click an item of the list, the IPA-phonetics will be shown for the standard pronunciation of this word for each of the three standard variations. If there are more than one "official" pronunciations for a word, then all of them will be displayed.
sehen
Type »sehen« into the field in the Suche-window and click the glass. You get a list of about 20 words containing »sehen« in the Ergebnis-window, among them »sehen« itself. Click it!
The pronuciations are:

In Austrian Standard German: [ˈseː.ɘn] and [ˈseːn]
There almost never is a voiced alveolar fricative [z] in Austrian German, so »sehen« starts with a voiceless alveolar fricative [s] in Austrian German.
One possibility is to speak two vowels, which gives two syllables. The first is a long close-mid front unrounded vowel [eː] followed by a syllable boundary ([.]) which you can hear as a very short break and then a short close-mid central unrounded vowel [ɘ].
The other posibility is to speak it as one syllable with just one vowel. (This is not allowed in German Standard German or Swiss Standard German, only in Austrian Standard German)
In German Standard German: [ˈzeː.ən]
Starts with [z], has two syllables, and the vowel of the last syllable is a mid central vowel [ə]
In Swiss Standard German: [ˈzeː.ɘn] or [ˈzeː.ən]
One version is the same as the German version, the other just uses an other vowel in the second syllable.

Note, that this database only contains the standard pronunciations. You will not find dialect pronunciations there or pronunciations of colloquial speech. Those pronunciations can differ very much from the standard, so you sometimes might not understand dialect pronunciation. (This can be hard for German native speakers too.) But everybody who speaks German will understand you if you use any of the standard pronunciations.
Comment: Dreimal den Namen der Aussprachedatenbank gelesen, zweimal hat mein Hirn hinten ein *i* angehängt zu *Adabai* … ^^'
Comment: @Jan sagt das etwas über den Namen der Datenbank oder über dein Hirn aus?
Comment: Über mein Hirn, primär.

Pronunciation of long e


What are some of the better English reference grammars?

Question: What is your favorite English reference grammar, particularly in terms of accuracy and completeness? Please note: I am not asking for usage guides. What are the strengths and weaknesses of the best ones?
Answer: The book that taught me what little (and how little) I know about English grammar is Huddleston and Pullum's Cambridge Grammar of the English Language. You can read chapter 1 and chapter 2 (PDF) free online. Those are introductory chapters. For a taste of the meat of the book, see this answer regarding the word yesterday, which is basically just a roundup of what CGEL has to say about it.
If you like what you see there, I enthusiastically recommend buying CGEL. It's unbelievably thorough and accurate. The writing is uniformly clear and concise. Illustrative examples are everywhere. It has both a lexical index (for looking up the peculiar grammar of enough or yesterday) and a conceptual index (for looking up terms like gerund or subject-auxiliary inversion). It's engaging enough to browse as bedtime reading.
The main drawbacks are that it costs $178 and weighs about five pounds.
Comment: The second edition of *A student's introduction to English grammar* will be available soon. It costs less than $40 and weighs only 930 g. It's a précis of *CGEL*
Answer: I find Carter and McCarthy's 2006 Cambridge Grammar of English very useful. The great advantage is that it is based on an analysis of real language (the Cambridge International Corpus), which means that its insights are evidence-based, not intuition. Any reference grammars which are not based on corpus evidence are not worth buying.
Comment: @Alan It seems Huddleston wrote a scathing 18-page review of this book, [summarized here](http://english-jack.blogspot.com/2008/03/more-muddled-grammar.html).
Comment: Have you taken a look at Pullum and Huddleston? If so, how would you say they compare? (I agree that any reference grammar which makes no use of corpora is far from ideal. I doubt that many serious (i.e., written by qualified linguists) modern reference grammars would fall into that category though.)
Comment: @AlanHogue   If someone does not understand the basics of grammar I would not recommend Pullum and Huddleston.
Comment: @rogermue, which books would you recommend instead?
Answer: I used the book Understanding and Using English Grammar by Betty Schrampfer Azar when teaching English throughout the 1990s, mostly for its clear and simplified verb tense diagrams which explain when to use the present progressive, past perfect, present tense, etc.
Answer: Please don't mark this as the answer since it is horribly out of date, but just know that H.W. Fowler, The King's English (1908) is a joy to read for its humor, wit, accuracy, and prescriptive adamancy. It is very useful for going into depth of the English language but definitely not a good choice for your first grammar text. Anyone who loves the English language should have a copy of it in their bookcase. You can find it online but do get a paper copy of it, the older and mustier the better.
Comment: That would be a usage guide though.
Comment: This is not a grammar book so I'm not upvoting this, but I agree! Fowler is enjoyable to read (as are even Strunk & White and Lynne Truss, despite the ravings of the Language Log), but of course you'd be an idiot to actually follow their advice over your own good sense.


If $p$ is prime and $p > 5$, show that when $p$ is divided by 10, the remainder is 1, 3, 7, or 9

Question:
If $p$ is prime and $p > 5$, show that when $p$ is divided by 10, the remainder is 1, 3, 7, or 9.

This is a problem from Hungerford's Abstract Algebra: An Introduction. I would like some help on it, it was an example in class. Thanks.
Comment: Consider the case when the remainder is 2. Then $p = 10 q + 2$ for some integer $q$, so that $p = 2 (5 q + 1)$ is even, but cannot be 2 by the assumption $p > 5$. The other cases are entirely similar, it is useful for you to work them out yourself.
Comment: $p > 5$ prime means $p$ not divisible by $2$ or $5$.
Answer: You already have a couple of nice 'mathematical-looking' answers. In attacking a question like this, though, you might want to start with simple, familiar facts.
The remainder when $p$ is divided by $10$ is simply the last digit of $p$. If the last digit of a number $n$ is $0,2,4,6$, or $8$, what kind of number is $n$? Can it be prime if it's greater than $2$? If the last digit is $0$ or $5$, what can you say about $n$? Can it be prime and greater than $5$?
These are enough to tell you, at least informally, why the prime $p>5$ must end in $1,3,7$, or $9$, and now you can worry about explaining the reasoning in the previous paragraph a bit more formally.
Comment: Thank you for the tip, I was not sure how to best ask questions here but I'm learning and will remember that.
Answer: By the division algorithm, we can write each $p$ as
$$p = 10q + r$$
for some quotient $q$ and remainder $0\le r < 10$. As $p$ is prime, clearly $r\neq 0$. $r$ also cannot be even, otherwise $p$ is even. Finally, note that $r \neq 5$ or $5 \mid p$.
For a more brief and algebraic solution, note that $(p,\ 10) = 1$ implies that $p$ is a unit in $\mathbb{Z}/10\mathbb{Z}$. The units of the ring are precisely $1,\ 3,\ 7$ and $9$.
For completeness, you should probably show that there exists primes for each of the remaining congruence classes.
Answer: To say that a prime $p > 5$ gives a remainder of $1, 3, 7$ or $9$ when divided by $10$ is merely remarking that the prime is odd (and not $5$, since all integers ending in five are multiples thereof).
After all, the remainder when divided by $10$ is simply the unit of the number itself, and if that unit was any of $0, 2, 4, 6, 8$ we'd plainly see that it was an even number, and therefore not prime. Likewise with the five.
That said, we could come to the conclusion of your statement by, say, basing an argument on how all primes above $3$ are of the form $6n \pm 1$ (mind you, this follows from an argument akin to the above): the multiples of $6$ begin as follows:
$$6, 12, 18, 24, 30\ldots$$
From which we father that the units of such multiples are either $0, 2, 4, 6$ or $8$. Now take the '$\pm 1$' bit into consideration and we find that we have the following units possible:
$$1, 3, 5, 7, 9$$
(Remember, a remainder of $-1$ when divided by $10$ is equivalent to a remainder of $9$.)
So, much like the above, we disregard the $5$ since that certainly isn't prime, and we have $1, 3, 7, 9$ leftover, as desired.
Answer: you are looking for the unit digit of the prime.For prime $p\neq 2$, unit digit is odd which means $p\pmod {10}\in\{1,3,5,7,9\}$
Now, for any prime $p\gt 5$, unit git can't be $5$ otherwise it would be divisible by $5$ and hence won't be a prime.
Thus only possible candidates for unit digit of a prime $p\gt 5$ are $\{1,3,7,9\}$
Answer: This is clear from the Euclidean algorithm. Write the remainder $\rm\: r = (p\ mod\ 10).\:$ By Euclid
$$\rm  p\equiv r\,\ (mod\ 10)\ \Rightarrow\ gcd(p,10) = gcd(r,10)$$
In particular,  $ $ when the $ $ gcd $= 1,\, $ then: $\rm\,\ p\,$ is coprime to $10$ $\iff$ $\rm\,r\,$ is coprime to $10$
Now, by hypothesis, $\rm\, p\,$ is prime $ > 5,\,$ so $\rm\, p\,$ is coprime to $10,\ $ thus $\rm\ r\,$ is coprime to $10,\:$ so we infer that $\rm\,r\,$ is odd and coprime to $\,5,\:$ hence $\rm\:r\in \{1,3,7,9\},\,$ since the remainder $\rm\,r\in [0,9].$
Remark $\ $ Ditto if we generalize $\rm\,10\,$ to any modulus $\rm\,m\!:\ $ if prime $\rm\,p\nmid m\:$ then its remainder $\rm\, p\ mod\ m\,$ is one of the $\,\varphi(m)\,$ remainders coprime to $\rm\,m.\:$ Or, expressed in radix language:
$\quad$ in radix $\rm\,m\!:\ $ if $\rm\,n\,$ has units digits $\rm\,r,\ $ then  $\rm\ n\,$ is coprime to $\rm\, m\iff r\,$ is coprime to $\rm\,m$


The "Add User by Name" Alchemy plugin doesn't work anymore in SDL Tridion Sites 9

Question: Unfortunately the "Add User by Name" Alchemy plugin doesn't work anymore in SDL Tridion Sites 9. Is there another way to install it or an alternative? I urgently need this plugin because the standard interface to add users is getting a timeout when I try to add a users
Answer: You could create the users using theCore Service:
UserData user = client.Create(user, new ReadOptions()) as UserData;
Jan has done something similar in the past (for Tridion 2013), so you should be able to use that as a starting point:
http://sharedbyjan.blogspot.com/2014/03/i-was-at-new-project-this-week-creating.html
Answer: Isn't the problem that Alchemy itself doesn't support Sites 9 yet?
Anyway, the Tridion PowerShell Modules have an easy alternative:
New-TridionUser -Name "DOMAIN\UserName" -Description "Full Name of User"


How can Rpi read data of a heart rate sensor module, such as AD8232?

Question: may i know what is the code you used for heart rate sensor using raspberry pi? may i get explanation on how can we use raspberry to run and show output of heart rate signal? i'm just entering pi, your advise and explanation would be much helpful.
I have tried uploading code from arduino ide to raspberry pi, it prompted to enter passsword. but the root password i entered did't work. can anyone help?
Comment: Welcome to Raspberry Pi! Please take the [tour](http://raspberrypi.stackexchange.com/tour) and visit the [helpcenter](http://raspberrypi.stackexchange.com/help) to see how things work here. Note that Stackexchange tries to answer specific question instead of providing tutorials, which seems to be what you're looking for.
Answer: Question

How to use Rpi to read AD8232 heart rate signal?
How to use Arduino IDE to upload Arduino code to Rpi?

Answer

AD8232 ECG module outputs analog signal.  Rpi does not have any analog to digital pin to entertain analog signals (I feel jealous that
  Arduino has many built in ADC pins!).  So you need to use an ADC chip/module such as
  PCF8591/MCP3008/MCP3208/ADS115/HX711/ADS1256 (8 bit to 24 bit resolution) etc to do the conversion for Rpi to handle.
You cannot use Arduino to upload code to Rpi.  Rpi has its own IDE which is called Raspbian.  You might like to google newbie tutorials
  to start learning Rpi.  You may also like to read MagPi, a free
  magazine for Rpi newbies and ninjas alike.  As said earlier, Arduino might
  use its built in ADC pins to talk to AD8232.  So it is very unlikely
  that the Arduino code can be directly used by Rpi.  Of course you can
  study the Arduino code and try to translate it to Rpi python.

You may like to read the references to get a very rough idea of how Rpi controls the AD8232 ECG chip.
Warning to Rpi and electronics newbies learning the AD8232 ECG module
ECG signal is analog and often has big noise problems as mentioned in the referenced post below.  Newbies for sure find things difficult.  You may need a small team of basic Rpi hardware and software beginners to do a long term, say at least three months to one year (depending on your background) to complete a college level group project.   You also need a US$300 digital storage oscilloscope to help displaying signals (especially the nose signals).
Recommending CircuitPython for Rpi to newbies
The learning curve of Rpi Raspbian for newbies is very deep.  I did find it discouraging and depressing learning linux terminal commands when I first tried Rpi a couple of years ago.  At that time I already had 5 hobbyist years experience on Arduino but still find Rpi linux very newbie unfriendly.  Yes, Rpi GUI Desktop is much newbie friendly now.  But for those electronics newbies, trying things beyond blinking a led to reading ECG signals is still a long and winding journey.
To shorten the long journey, I would recommend CircuitPython for Rpi.  You may like to read Lady Ada's tutorials to know more.
CircuitPython overview - Lady Ada
CircuitPython for Rpi - Lady Ada
Installing CircuitPython for Rpi - Lada Ada

Tip to poor hobbyists who cannot afford AdaFruit and SparkFun stuff
I am a huge fan of both AdaFruit and SparkFun, and I am very grateful that I have been learning so many DIY stuff from them.
But I have never bought any of their products because I cannot afford.
Fortunately almost all their stuff are open source, and as SparkFun proudly and happily claims, their new open source hardware products get copied some 6 weeks after announcement.
In other words, I need only to wait for one and half months or so, to get copycat, legal, but a bit lower quality versions from TaoBao (sort of AliExpress). And I have never bought anything from eBay or Amazon, because TaoBao is often many times cheaper.  For those who are jealous that I can buy cheap things, I must point out that the minimum hourly wage (US$5) in my place is also many times lower, and what is worse, house price and rent is ridiculously many times higher.  In other words I don't have much money left to buy high class SparkFun and AdaFruit stuff :(
References
Raspberry Pi 3B+ interface with Heart Monitor AD8232 using MCP3008 and SPI pins
CircuitPython - Wikipedia

CircuitPython is an open source derivative of the MicroPython
  programming language targeted towards the student and beginner.
  Development of CircuitPython is supported by Adafruit Industries. It
  is a software implementation of the Python 3 programming language,
  written in C. It has been ported to run on several modern
  microcontrollers.
CircuitPython is a full Python compiler and runtime that runs on the
  microcontroller hardware. The user is presented with an interactive
  prompt (the REPL) to execute supported commands immediately. Included
  are a selection of core Python libraries. CircuitPython includes
  modules which give the programmer access to the low-level hardware of
  Adafruit compatible products as well as higher level libraries for
  beginners.
Comment: *"Rpi has its own IDE which is called Raspbian."* == Incorrect and misleading.
Comment: @goldilocks Ah let me see.  (1) Raspbian is an variant of Linux. (2) Linux is an OS. (3) An OS is not IDE.  (4) Therefore Raspbian is not an IDE. So if I say Rpi has an IDE called Raspbian is nonsense.  Thank you for pointing out my mistake.  Let me see how should I correct my mistake with an errata and apology in my answer.
Comment: I understand that you perhaps meant that figuratively ('Your "IDE" will be Raspbian...'), but someone asking this question could easily take that literally leading to pointless confusion.  So anyone who shows up asking about the "Raspbian IDE" I will send your way ;)
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/93853/discussion-on-answer-by-tlfong01-can-raspberry-pi-work-exactly-like-arduino-upl).


Pressure in waves on a string

Question: We know that when we speak sound waves are created. The air particles compress and rarefy and pressure is more at the nodes and less at anti-nodes.  But can we say the same thing about waves on a string,- that pressure is more at the nodes than the anti-nodes?
Answer: Waves on a string are transverse waves not longitudinal waves. They are not variations in pressure, but variations in the displacement of the string. The (average) displacement is greatest at the anti-nodes and zero at the nodes.
Answer: Roughly explaining John's answer - but visually..!
When you wiggle a sting (using a good resonator), you'd see something like this... The structure clearly reveals Transverse vibrations.

If you still don't understand, Here's a good simulation for that...

Pressure in waves on a string


What is the difference between "Kafiroon" and "Kafireen"?

Question: As far as I can see, the words "Kafiroon" and "Kafireen" is translated the same. There are also different similar words like "Muslimoon" and "Muslimeen".
What is the difference between a word ending with "oon" and the same word ending with "een"?
Answer: The answer is technical. The short answer is that, semantically, they have exactly the same meaning; it's a difference of syntax.
In Arabic, words can be three (and sometimes, four) cases: marfoo' (ending with damma), majroor (ending with kasra), and mansoob (ending with fatha). There are some more details here which are not relevant to this answer.
In this case, the word "kafiroon" (with waw, noon) is in the marfoo' form. That usually means (among other things) that it's the subject of the sentence, or the doer of the action.
Kafireen (yaa, noon) is the majroor and mansoob forms. It usually means (among other things) that it's the receipient of an action, or it's modified by a preposition -- a word like "from," "to," etc. (Harf Al-Jarr in Arabic).
Anyway, this form (using waw/noon vs. yaa/noon) applies to all masculine plurals; commonly in the Qur'an, you will see:

Muslimoon / Muslimeen
Kafiroon / Kafireen
Muttaqoon / Muttaqeen
Muhsinoon / Muhsineen
etc.
Answer: In Arabic, a noun can be in one of three cases of E'raab إعراب (which is something related to grammar and context, affects tashkeel, spelling, and pronunciation): raf' (the noun is then called marfoo'), nasb (mansoob), and jur (majroor).
Since E'raab is related to context, then it changes according to meaning. For example, according to if the noun is the subject (actor) the verb, or the object the verb. A subject of the verb is usually marfoo', while the object of the verb is usually mansoob. (The meaning of the noun itself is not changed, but the meaning of the context is changed, I'll give some examples below).
On the other hand, a noun can be in one of three count cases:

Singular: In our example it's كافر (pronounced Kafir in the silence form, which means the noun ends with neither damma, nor fatha, nor kasra, but silence). In this case, the E'raab case changes only the tashkeel and pronounciation of the noun; If the noun is marfoo' then it ends with damma كافرُ (damma is a light pronounced O); if majroor it ends with kasra كافرِ (kasra is a light pronounced E); if mansoob it ends with fatha كافرَ (fatha is a light pronounced A). In fact it's difficult to write the pronounciations in English letters here.
Dual, in this case the noun referes to two enitites, this doesn't exist in english, instead plural is used. The E'raab case mainly changes the spelling of the noun here, it attaches either Alef and Noon ان or Yaa and Noon ين to the end of the singular form of the noun. If the noun is marfoo' then Alef and Noon ان is attached, so in our example it becomes كافران (Kafiraan); if the noun is mansoob or majroor, then Yaa and Noon ين is attached, and the final letter of the singular form has a fatha, so in our exmaple it becomes كافرَين (Kafirain).
Plural, in this case the noun referes to three or more. Just like in english, plural can be either regular prular or irreular prular:

Irregular plural (called jam' Takseer جمع تكسير in Arabic) has no general rule in Arabic (like in English), an example is that Kafir كافر does has an Irregular plural form, and it's كُفّار Kuffar. Irregular plurals are treated in matter of E'raab just like singular nouns.
Regular plural can be either masculine or feminine:
Feminine regular plural جمع مؤنث سالم: it's formed by attaching Alef and Taa ات to the end of the singular noun, in our example it becomes كافرات (Kafiraat in the silence form). The E'raab case changes the tashkeel and pronounciation: if the noun is marfoo' then it ends with damma كافراتُ, if mansoob or majroor then it ends with kasra كافراتِ.
Masculine regular plural جمع مذكر سالم: THIS IS WHAT WE WANT (FINALLY :D) The E'raab case mainly changes the spelling of the noun here, it attaches either Wao and Noon ون or Yaa and Noon ين to the end of the singular form of the noun. If the noun is marfoo' then Wao and Noon ون is attached, so in our example it becomes كافرون (Kafiroon); if the noun is mansoob or majroor then Yaa and Noon ين is attached, and the last letter in the singular form has kasra, so in our example it becomes كافرِين (Kafireen).

Examples of how :

قُلْ أَطِيعُوا اللَّهَ وَالرَّسُولَ ۖ فَإِن تَوَلَّوْا فَإِنَّ اللَّهَ
  لَا يُحِبُّ الْكَافِرِينَ
Sahih International
Say, "Obey Allah and the Messenger." But if they turn away - then
  indeed, Allah does not like the disbelievers (Kafireen).
Surat 'Āli `Imrān - 32

In the above Aya, Kafireen is the object of the verb "like".

يُرِيدُونَ أَن يُطْفِئُوا نُورَ اللَّهِ بِأَفْوَاهِهِمْ وَيَأْبَى
  اللَّهُ إِلَّا أَن يُتِمَّ نُورَهُ وَلَوْ كَرِهَ الْكَافِرُونَ
Sahih International
They want to extinguish the light of Allah with their mouths, but
  Allah refuses except to perfect His light, although the disbelievers (Kafiroon)
  dislike it.
Surat At-Tawbah - 32.

In the above Aya, Kafiroon is the subject of the verb "dislike".
Hope that's clarifying enough (and sorry for writing a journal!).
Answer: It is just declension (i'rab) at work. It is the change in ending of a noun or verb by which its grammatical case is identified. Arabic heavily uses this. In English too there is declension. For example, the sentences  "I hit you" and "You hit me".  Here "I" changed to "me" to indicate it is the object of the action. Hope you get the idea.
Answer: All grammatical changes, by very definition, are meaningful. Explanations of the question at hand with reference to E'raab are fine, but remain inadequate because these normally (rather universally) fail to mention an additional important layer of meaningfulness:
Plurals with "wao-noon" ending (e.g."Kafiroon" & "Muslimoon" etc.) refer to every individual of a group, while plurals with "yaa-noon" ending (e.g. "Kafireen" & "Muslimeen" etc.) refer to the group as a whole.
Consider this example, very explicit in the aspect of meaningfulness that I have pointed out:
3:28 لَا يَتَّخِذِ الْمُؤْمِنُونَ الْكَافِرِينَ أَوْلِيَاءَ مِنْ دُونِ الْمُؤْمِنِينَ وَمَنْ يَفْعَلْ ذَلِكَ فَلَيْسَ مِنَ اللَّهِ فِي شَيْءٍ
The ayah juxtaposes الْمُؤْمِنُونَ with الْمُؤْمِنِينَ and also with الْكَافِرِينَ. It is essentially stating that "Momin" individuals should not seek patronage (/sponsorship /protection etc.) of "Kaafir" groups when the patronage of "Momin" groups is available to them. Indeed here the context clearly indicates that الْكَافِرِينَ and الْمُؤْمِنِينَ have the signification of organized sovereign groups.
4:151 أُولَئِكَ هُمُ الْكَافِرُونَ حَقًّا وَأَعْتَدْنَا لِلْكَافِرِينَ عَذَابًا مُهِينًا
This ayah juxtaposes كَافِرُونَ with كَافِرِينَ. The context of this ayah (as well as the previous ayah) makes it abundantly clear that كَافِرُونَ here is signifying individuals while كَافِرِينَ is signifying a collective.
The Quran abounds with examples. I mention just two:
3:52 قَالَ مَنْ أَنْصَارِي إِلَى اللَّهِ قَالَ الْحَوَارِيُّونَ نَحْنُ أَنْصَارُ اللَّهِ ءَامَنَّا بِاللَّهِ وَاشْهَدْ بِأَنَّا مُسْلِمُونَ
Here "Muslimoon" is clearly indicating individuals of a group;
10:84 وَقَالَ مُوسَى يَاقَوْمِ إِنْ كُنْتُمْ ءَامَنْتُمْ بِاللَّهِ فَعَلَيْهِ تَوَكَّلُوا إِنْ كُنْتُمْ مُسْلِمِينَ
and here "Muslimeen" is clearly referring to an organized group of "Muslims."
There are literally hundreds of ayahs in the Quran encompassing dozens of root-words. In my considered opinion they lead to the conclusion that I have stated above.
Indeed this literary mechanism has been very powerfully used by the Quran to express its message. To my knowledge this is the only mechanism through which the Quran differentiates between individuals of a group, and the group as an entity.
Comment: Do you have any evidence for your claims? please share it. The given examples actually don't necessarily hold for your description.
Answer: They are both Sound Plural. The Ya or Waw ending depends on the overall rhyme scheme of the Sura. It is much easier to memorize this way.


Determine the trace of a matrix in $SO(3, \mathbb{R})$

Question: let $SO(3, \mathbb{R})$ be the group of special orthogonal  3x3 matrices, i.e., $A \in SO(3, \mathbb{R})$ if $A^tA=I$ and $det(A)=1$.
I want to show $-1\leq trace(A)\leq 3$ by considering the eigenvalues of $A$, any hint for how to make a start?
Comment: I asked a similar question: http://math.stackexchange.com/questions/64378/special-orthogonal-group-and-cayley-hamilton-theorem
Answer: I know you said you want to do it by considering the eigenvalues, but it seems worth having this answer here as well nevertheless: A matrix in $SO(3,\mathbb R)$ describes a rotation through some angle $\phi$, which is conjugate to a rotation about one of the coordinate axes through that angle. Conjugate matrices have the same trace, and a matrix describing a rotation through $\phi$ about a coordinate axis has trace $1+2\cos\phi$, which ranges from $-1$ to $3$.
Answer: Since $A$ is orthonormal, all eigenvalues lie on the  unit circle. Since $A$ is real, any complex eigenvalues must occur in conjugate pairs. Since $\det A = 1$, we have $\lambda_1 \lambda_2 \lambda_3 = 1$ where $\lambda_i$ are the eigenvalues.
The trace is given by $\mathbb{tr} A = \lambda_1 + \lambda_2+\lambda_3$.
Split into two cases: (1) Some eigenvalue is not real. (2) All eigenvalues are real.
Case 1:
Some $\lambda_1$ is not real. Then one of the other eigenvalues (suppose $\lambda_2$) must be its conjugate. Then $\lambda_1 \lambda_2 \lambda_3 = \lambda_3 = 1$, and $\mathbb{tr} A = 2 \; \mathbb{re}(\lambda_1)+1 $. Since $|\mathbb{re}(\lambda_1)| \leq 1$, the result follows in this case.
Case 2: All eigenvalues are real. Then all eigenvalues are $\pm 1$. It is easy to see that $\mathbb{tr} A \leq 3$, only the other bound needs attention. Since the product of the eigenvalues is $1$, any negative eigenvalue must have even multiplicity, so at least one eigenvalue is $1$. Consequently, $\mathbb{tr} A \geq -1$.
Answer: Let $A\in SO_3(\mathbb{R})$ $A$ has $3$ eigenvalues, so it must have a real eigenvalue.
Case 1: $A$ has $3$ real eigenvalues. Since an orthogonal matrix preserves lengths and can only have $\pm1$ as eigenvalues, and $\det A=1$, we must have either all three eigenvalues equal to $1$, or two equal to $-1$ and the other equal to $1$.
Case 2: $A$ has a complex eigenvalue. Complex eigenvalues appear in conjuate pairs, and since the matrix is orthogonal we again have that the absolute value of each eigenvalue is 1. So these two eigenvalues multiply to 1, and since the product of the eigenvalues is $\det A=1$, the remaining eigenvalue equals $1$. Adding up the real parts of the eigenvalues (we can ignore the imaginary parts, since they will cancel), we see that the sum of the eigenvalues is in the desired range.


Cheap cheese is tasteless. Can I make it tastier in my mac and cheese?

Question: I used to make mac and cheese with cheddar.  Like many, I'm cutting costs due to the recession and I'm buying the cheapest cheese I can find.  The problem is, when I make macaroni with it, it's just tasteles.  Is there anything I can do to keep using the cheap cheese, but get more taste out of it?
Comment: i would re-evaluate my budget and buy better cheese or buy high quality but less in quantity. Cheap cheese is not an option.
Comment: Make proper mac & cheese out of a box, and save the good cheese for eating. :)
Comment: For general purposes, I've found that a cheap, non-sharp cheddar will turn into a decent sharp cheddar if you just leave it in the refrigerator for about a month.
Comment: @Hath, I'm too poor to re-evaluate my budget to spend more.       @Marti, mac and cheese out of the box isn't universally available.
Comment: You can buy cheese powder over the Internet. It doesn't appear to be expensive, either. Maybe you could use it to augment the real cheese.
Comment: What gives cheese its sharpness is the development of lactic acid over time. Sharp cheese has been aged longer. I haven't tried it, but I wonder if it might help to add some vinegar?
Answer: Cheap cheese is, as others have explained, cheap for a reason.
You should be able to find old/extra old (AKA "sharp"/"extra sharp") cheddar cheese in the cheap section, which makes a reasonably good starting point - this cheese does have some flavour.
Daniel says he simmers the milk; I generally start with evaporated milk, which is even more economical than regular milk and keeps in the pantry forever.  Although I would not use evaporated milk in just any recipe calling for milk, it happens to work quite well for Mac 'n Cheese.
Other common additions to help offset the lack of flavour in poorly-aged cheeses are:

Salt. Remember, salt is essentially a flavour enhancer and will bring out the natural taste of any other ingredient.
Mustard.  Prepared mustard is OK, but concentrated mustard made from dry mustard and a small amount of water is even better, so you can avoid having to add too much liquid.  This doesn't enhance the flavour of the cheese, but it does share some of the "sharpness" associated with cheddar and makes a good complement.  As a bonus, it also acts as a natural emulsifier for the sauce, helping to minimize separation and curdling.
Ground cayenne or red pepper.  Although most people probably don't associate Mac 'n Cheese with piquant, a small amount of this won't make the sauce noticeably spicy, but it will add a bit of the same "kick" you get with very old cheese.

If all else fails, my "secret weapon" for Mac 'n Cheese is - not kidding - the sauce base from Kraft Dinner (AKA Kraft Macaroni and Cheese Dinner for you Yankees), especially if you can get the "extra sharp" version.  This stuff is dirt cheap (often just 99 cents for a package) and before you dismiss this as heresy, keep in mind that the idea is not to use the whole thing.  Just a teaspoon or two to enhance your homemade sauce.  If you don't approve of such shortcuts then you shouldn't be buying cheap cheese in the first place, right?
So there you have it.  Try some or all of the above; I'm sure you'll end up with something that's at least acceptable, if not great.
Comment: Other good piquant flavors that work well with mac & cheese : jalapeno sauce (I like goya brand), or some adobe from a can of chipole peppers.  If you just want a slight touch, consider paprika (hot preferred, but sweet can give some interesting notes as well), as you can give a nice dusting for color without adding too much heat for those who can't handle it.
Comment: Salt mustard and cayenne pepper were exactly what I was going to say!
Comment: To add in, those little pots of grated parmezan tend to be very cheap and will boost cheese flavour, as will nutritional yeast.  Also with regard to the salt boost, definitely - if it really needs a kickstart, I'd actually recommend MSG.  It is cheap as anything and easy to get from chinese stores and is probably the most active component in the cheap packet mixes you buy.
Comment: A touch of Worcestershire sauce could also add some of that sharp savoury flavour that is missing from the cheap cheese.
Comment: Mustard in macaroni is nasty ppl
Answer: You would need to add other flavours; you can't add cheese flavour without adding more (or better) cheese. When I make M&C, I like to simmer the milk before adding it to the roux, and I poach a clove or two of garlic in the flavour. Adding well-rendered bacon is also nice.
Comment: I usually add a spoonful of mustard into the mix.  Also remeber to season well.
Answer: The biggest difference between expensive cheese and cheap cheese is time.
A cheap block of cheddar aged in the fridge will become more and more sharp as the bacteria continue to work in it turning lactose into lactic acid.
This takes up fridge space and time and you have to carefully remove any mold (or reapply a rind before you start). Just for the hassle it's probably not worth it.
This is a big part of why good cheese costs more. For example, the manufacturers of the inedible canned "parmesan" powder that is sold in the USA have lobbied the FDA down to 6-months of aging to save costs.
I would recommend adding non-cheese flavor additions as Daniel suggests.
Answer: You could go halfway and buy a small bit of really sharp cheese and mix it with your cheap cheese.
Do you do a crumble topping? I find that the crispy texture can add an extra something to Mac and Cheese, as well as additional flavors.
Comment: agreed on the topping -- you can change up the texture and add other interest to the dish with the inclusion of what might've otherwise been a bunch of stale crackers you'd otherwise pitch.
Answer: make your own cheese, it will be tastier and cheaper.
its pretty simple, everyones favourtie search engine will give you a good list of result on how to do it.
Comment: Making your own cheese is generally not cheaper. For one, you need unpasteurized milk for good results; unpasteurized milk _sours_, while pasteurized milk just rots. For another, you need a whole hell of a lot of it. As well as the bacterial cultures (unless they are available from the air), as well as a temperature- and humidity-controlled environment in which to age the cheese.

Obviously soft cheeses such as ricotta, paneer, even mozzarella do not need those--but none of those cheeses are particularly suited for making mac & cheese; for that you need a lower water content.
Comment: No. Pasteurized milk does _not_ sour just fine, because pasteurization kills the bacteria that makes it go _sour_.
Comment: @daniel I think you'll find most cheese in the supermarkets is made from pasteurized milk. And you don't need a whole lot of it, have you ever done it  - I have, was fine, tasty, and cheap.
Comment: That would be cheese made by cheese manufacturers, who have cultures of the necessary bacteria on hand, yes? The amount of milk needed to make a given amount of cheese is, in fact, quite high. I have made my own ricotta and my own mozzarella, yes. But as I mentioned above neither of those cheeses is appropriate for m&c you need much lower water content.
Comment: @daniel- I agree with your point. Everything you said will be true if making cheeses with specific temp/humidity/bacteria/mold requirements like swiss, blue, brie, etc. And even simple cheddar, with months of aging, is more work than it's worth unless you get a lot of cheap milk. However, making fermented cheeses does not have to be that complicated or expensive. Pasteurized milk sours just fine. Homogenized milk is not ideal but it still works. Yogurt and buttermilk can be used for thermophilic and mesophilic inoculations respectively. A fridge works fine for temp control.
Answer: I'd suggest the downsizing method I use for most things. Start with the expensive option and slowly downsize until you reach the point where you can taste the difference, then go back one step. This works for recipes and products.
You could start with your original cheese and then slowly replace this with cheap cheddar until it makes a difference.
My mac'n'cheese recipe uses half gruyere and half cheap cheddar and turns out really well at a reasonable price. :-)
Comment: Gruyere is so strong, even a small amount will counter the lack of flavour in the plastic-cheddar.
Answer: Yes, any aged cheese would be better than plain cheap cheese. I tend to make mac 'n cheese when I have a selection of cheese starting to go bad. I mix it all up in a roux, stir in the noodles, sea salt and fresh ground black pepper, a little mustard and a little cayanne or hot pepper sauce. But my secret to really yummy mac 'n cheese - the "adult" version - is a splash of white truffle oil. Sounds terribly expensive and decadent I know but I found a large bottle in Winners - or equivalent - Ross Dress for Less for about $5! It's potent, and packed with flavor and you need just a drop or two so it will go a long way. It's yummy in any noodles, on home-made pizza, etc. A breadcrumb topping is also a must if you are looking for flavor.
Answer: Ways to add flavor to Home-Made Mac and Cheese;

Add Different Types Of Chopped Pickles; Sweet, Dill Etc.
Add Different Types Of Mustard; Honey, Reg. Etc.
Add Different Types Of Ketchup; Sweet, Reg. Etc.
Add Different Types Of Hot Sauce or Hot Peppers. BBQ
Add Different Types Of Pasta Sauces, Tomato Sauces, Pesto.
Add Different - Varies Types of Vegetables, Meat, Fish or Tofu.
Add Different Types Of Herbs, Spices and Seasonings.
Answer: when I used to use a mild cheddar for economic reasons, I would add a pinch of dry mustard to the grated cheese and mix it up. It gave the cheese a sharper flavor.


Unable to mount hard drive after upgrading

Question: after upgrading to 11.04 system starts to boot and then can not find hard drive. It gives me the option to skip or manual. I am a newb and don't know how to do it manually and then set it to auto mount. any help is appreciated.
Comment: Please include the contents of `/etc/fstab` in your question.
Answer: If you have a invalid entry in your /etc/fstab it may be asking you to skip the mounting of the filesystem, or to try to mount it manually.
If this is indeed the case, you may want to edit the /etc/fstab file and either comment out, delete, or correct the line for the filesystem in question.
I normally see these kind of messages when i add a external usb hard drive to my /etc/fstab then remove the drive and forget to edit the fstab back to normal.
If this is not the case, you may want to give the full error message. and perhaps  any information from your /etc/fstab on the filesystem in question.


Are major tourist attractions and businesses in London closed on Sundays?

Question: I'll be visiting London soon and I'll have only one day (a Sunday) to see major tourist attractions. Are most attractions and businesses open on Sundays?
Answer: Most attractions are open on Sundays, but a number are just open for 6 hours, from 11:00-17:00 or 12:00-18:00, so be sure to check each one individually. A TripAdvisor discussion about this topic.
Comment: Places of Worship such as St Pauls Cathderal and Westminster Abbey are open on Sundays for services only.
Answer: If you want to enter specific attractions, be sure to visit their websites for business hours. (Google maps will include hours). I love using google to map out my destinations. Save the outdoor attractions for before and after business hours to maximize viewing time.
You can view the London Eye, the Big Ben, Westminster Abbey, the bridges (London bridge, Millennium, Tower, etc), Shakespeare's Globe within walk distance and before and after regular business hours. All these attractions are around the Thames river. These can be very lovely lit up at night. The Millennium bridge is lit up at night and leads you towards St Paul's in the distance (from the South of the Thames).
Assuming some of these are on your list, you can see how to plan your route if you're walking. You can see signs for the underground in between all areas. Leicester square was included if you like Broadway, Lego, or Nickelodeon. Piccadilly for shopping (I love Fortnum & Mason!).
A wide variety of theater, galleries, and museums are scattered between all locations. You'll have to narrow down the specifics (photography, musicals, modern galleries, history, etc).


How do you unequip a weapon?

Question: In the loadout menu, the interface makes it pretty obvious how to equip your weapons. But since having additional weapons increases your weight and power recharge time, how do you actually unequip one? I am playing the PC version if that matters at al
Answer: When you choose which weapon of a particular type you want to equip, one of the choices should be to not equip any.
Answer: On the Xbox I scroll to the left so that the weapon number indicator (X/X) reads 0/X and then hit accept.

How do you unequip a weapon?


Language and Region

Question: I am trying to set the language of my Lenovo laptop to English while keeping my region and Formats set in German. It seems I can only keep the language set with the region of the native speaking country if that makes any sense, anyone know any ways around this?
Answer: I have the same setup you're looking for. This can be changed in the System Settings app.
All Settings > Personal > Language & Region.

Language: English
Region: United States
Formats: Germany

This way I can have English language applications, a dvorak alternate keyboard layout and German date formats. Day of the week and month names are still German. To change that you'll need dconf-editor and you'll need to do some experimentation in system/locale.
Comment: Good Day Patrick,

thanks for the reply.

Ill try this set, i am not too comfortable to tinker with dconf files yet but ill most likely keep the set you mention

kind regards
Comment: Bitteschön. If you don't want to get into dconf, then these settings are as close as you can get to what you described. Cheers.

Language and Region


Is there a way for formatting my questions and answers?

Question: Other people have such beautifully formatted questions and answers, and I have to do it basic HTML. Are there any special keys you have to use in order to have a 'touched up' post? and can someone please show me all the formats?
Answer: When you ask a question, to the right side of the page there is a block that shows the basic markups to format a page; it contains also a link to the formatting help.
Answer: In addition to what Kiamlaluno gave you, you must know that this site uses Markdown.
Most tags you'll see in that page are used here. I'll give you some quick examples:

Use of > before a paragraph, to make it look like this rectangle I'm writing in.

Or <code>[link name](www.example.com)</code> to make links in comments.
Links in answers are different. When you are writing an answer, to make it the simple way, do the following:

Click the chain button;
Paste the link;
Write the "link name".

You'll see its structure and so you'll be able to edit it without making it from the start.


How to graph equation

Question: So the problem is to find all points $(x,y)$ on the real plane such that $f(x,y) = \cos^2(x+t) + 2\sin(x+t)\cos(y) - \frac{(\cos y - 1)^2}{2} - \sin(x) \lt .5$ for all real $t$. I'm not sure where to start with this, I don't think I fully understand the equation... how can the result be in terms of $f(x,y)$ when $t$ is also essentially a variable? shouldn't this be a 3 dimensional plot?
Answer: My instinct says you want to get rid of that $t$. Maybe you could find the value of $t$ that makes $f(x,y,t)$ maximum?
Answer: To help understand the question, let's make the two $t$'s into different variables.  Now we want $f(x,y) = \cos^2(x+t_1) + 2\sin(x+t_2)\cos(y) - \frac{(\cos y - 1)^2}{2} - \sin(x) \lt .5$ for all real $t_1,t_2$.  For any $x$, we can find $t_1$ to make the $\cos^2$ anything from $0$ to $1$ and we can find $t_2$ to make the $\sin$ term anything from $-1$ to $1$.  If we want the RHS to be $\lt .5$ for all $t_1,t_2$, we can set the $\cos^2(x+t_1)$ term to $1$ (as that is worst case) and the $\sin(x+t_2)$ term to $\pm 1$ to match the sign of $\cos y$.  Now we demand that $f(x,y)=1+2|\cos y| - \frac{(\cos y - 1)^2}{2} - \sin(x) \lt .5$ or $2f(x,y)-1=-\cos^2 y + \cos y +2|\cos y|-\sin x \lt 0$.  You can set $u=\sin x, v=\cos y$, with $u,v \in [-1,1]$ and see that you need $-v^2+v+2|v|-u\lt 0$, find the region in the $u,v$ unit square that satisfies this, and translate it back to the $x,y$ plane.
The image I got of this function is below.  u is vertical, v is horizontal.  The allowable region is the part away from the -u axis

Your problem is more difficult because $t_1$ and $t_2$ are correlated, in fact the same.  All the region that satisfied the uncorrelated version will satisfy yours, but there may be others.

How to graph equation


Lending and interest rates

Question: It states in my textbook that as interest rates are lowered it says lenders are the ones who gain from the decrease in interest rates. But isnt this not true? As lower interest rates imply the amount you net from lending decreases as interest decreases?
Answer: Yes. That's tricky for newcomers to figure out. The concepts to keep in mind are:
a) to buy a bond is essentially to lend to the bond issuer
and
b) bonds are tradable.
So let's say that, in 2010, you bought a 30-year bond at \$10,000 face value that was yielding a 5% rate (known as the coupon rate) and today, in 2020, a 20-year bond is being issued also at \$10,000 par value but only offers a 4% return ($400 annual coupon).
Because bonds are tradable, that means your 30-year bond with 20 years remaining and an annual coupon of \$500 should now have buyers willing to pay a bit more than the $10,000 you paid for it.
Specifically, they can pay up to around $1.135 and still get the equivalent yield to maturity as the newly issued 20-year bond, a 13.5% profit for you.
The reverse also applies. If your 2010 30-year bond had a 4% coupon and the 2020 20-year bond is yielding 5%, you would only be able to sell the 2010 today at a price lower than $10,000.
Answer: When rates decrease, lenders will also pay less to borrow the money that they lend out, so it's plausible that the differential between the rates (equating to the lender's profit) doesn't fluctuate that much when rates go either up or down. However, when rates go down the price to borrow is lower to the consumer. This causes a higher demand for borrowing money, which ultimately leads to a higher volume of loans getting closed overall.

Lending and interest rates


Double bass position for very high octave

Question: I recently saw a Punch Brothers show and Paul Kowert repeated a short lick an octave higher and higher until the pitch was higher than I ever thought a double/upright bass could go.  He was definitely off the fingerboard, and may have been playing behind the bridge, but I don't quite remember.  At any rate, are there positions after the fingerboard comes to an end and/or behind the bridge?  If so, how might I refer to them?  I unfortunately have no experience with fretless instruments and have pretty much exhausted all the search keywords I can think of.  Currently surfing YouTube in search of high bass notes via pinched strings...
Comment: Anecdote from a cellist (me): once past the fingerboard, it's possible to play non-harmonic notes just by touching the string at the right location. I suspect it's 'cause the frequency is so high that your finger acts as a hard stop.  It is possible to play notes on the wrong side of the bridge as well, tho' they tend to be dang squeaky.
Comment: Can you post the video? Is it possible that he was playing natural harmonics?
Comment: For any definitive answer, we'll need a video or at least a title of the song.
Comment: @Shevliaskovic i wish i had taken a video of it, but i don't have one
Comment: @Tim it wasn't a part of a song they've recorded.  it was in like a breakdown section they did in the middle of a song.  i don't know how different it is to play harmonics on a double bass, i'm only familiar with it on a guitar.  but i'm pretty sure he had both his hands down by the bridge.
Answer: No, there are no formal positions behind the bridge.
As a double bassist myself, what I believe you are looking for is this: (v)
The Simandl method just would describe that positon as thumb positon but the Rabbath method would describe it as 6th postion.
It is also possible however that they are using artificial harmonics to create such high notes.


Are hi fi amplifiers used in music production?

Question:
Are hi fi amplifiers used in music production?
What if I run the signal through the hi fi amplifier and record the output? It has to become wider, more volume, deeper ? Does that make sense ?
Comment: The Blue Nile issued recordings on Linn Records, and there's an anecdote in the book Nileism about how they blew up some Linn Isobarik (very high end hifi) speakers that they were trying out as studio monitors. You wonder how loud they had to crank them to get them to blow up.,,
Comment: @BrianTHOMAS - those Blue Nile recordings are still used in sound engineering schools in the "**this** is how you do it" sections. They are phenomenal recordings; with a very odd phenomenon - it doesn't matter how loud you play them back, you can still talk over them in a normal voice & be perfectly intelligible. I'm not surprised they overloaded speakers trying to get it to sound "loud".
Answer: Are they used?
Undoubtedly someone, somewhere has tried it & swears by it.
Will it make things wider, louder, deeper?
Not if it is actually HiFi.
HiFi, by definition, is designed to add as little colouration to the signal as possible.
Could you 'torture' HiFi into adding 'interest' by pushing it hard into a variety of speakers?
Sure, if you can afford it.
Would I bother?
No.
There are a myriad amp simulators available in software, with profiles from "so subtle you can't tell it's on" to "Marshall on 11". I'd just use one of those.
Answer: You might want to test your production on a Hifi amp and speakers.
You may have heard of the loudness wars where increasing levels of compression are applied to help the music punch through. E.g. to play a song on a portable radio on a building site or  in a noisy environment. Going too far can make the production sound awful on good HiFi. So producers check their work on a variety of devices before they release the song.


Glitching whilst using CSS transitions/translate on iPad when scrolling the page

Question: I've noticed whilst optimising animations for use on iPad using hardware acceleration, I seem to be coming across an issue that I haven't fully been able to resolve. If you are applying webkit transforms such as translate, although the animation runs great, if in the middle of an animation occuring the user scrolls the page, when they release it causes the animation to stutter whereby it reverts to its original position and attempts to continue its animation to it's end point.
I've been looking everywhere for resolve on this issue, having seen it occur on the iPad store as well! If you have an iPad at hand and you navigate to, for example: http://webkit.org/demos/transitions-and-transforms/ , if you select an item then before the button animation has completed drag the page(scroll) then release it, you will see the animation flicker back to its original position and then repeat until its complete.
The only way I've been able to work around this is when a touchmove event occurs, I tell the animation to just stay where at its original location, which stops it from trying to repeat the transition on release, as even attempts to just tell it where to go again cause it to revert regardless (seeing as how css transitions seem not technically able to be stopped).
Has anyone found any workarounds to this issue, I'm pretty sure this is a bug on iPad as opposed to a problem with the animation (this does not involve issues regarding preserve-3d and what have you), or if I should be reporting this as an issue.
Thanks!
Answer: Not sure if I'm reading between the lines, but I suspect you might see better results if you use touchend versus touchmove or touchstart.


Language acquisition without interactive contact with fluent speakers

Question: Children raised in a multilingual environment learn all the languages that they are exposed to with no effort. Does the same thing happen if a child has only indirect contact with a language? For example, if the child is only exposed to music, TV and radio programs in another language, is it possible to acquire a native competence in that language?
Comment: I suggest you change "contact with native speakers" to "(interactive) contact with fluent speakers". Whether the speaker is native or not is not important here, many good teachers are not native. And TV, music, radio classify as "contact", I guess what you mean is interactive contact
Comment: Anectodally, I have just been travelling in Romania most of my friends there had grown up in Bucharest without English speakers around. They insist when I ask them that they learned English from the Cartoon Network! Obviously they were also taught in school but I still find it hard to believe since their English is so good.
Comment: @Louis Thanks for the suggestion. I have edited the title accordingly.
Comment: Actually, I recall infant studies in which infants were trained in phonemic contrasts either interactively or non-interactively (via TV or tape recording), and in the non-interactive cases they did worse. I'll try to find a citation for that later. This would indicate that infants don't tend to treat non-interactive contexts the same as speech, in support of LaurenG's answer.
Answer: Another example of this might be the recent acquisition of rather good English by large numbers of people in Scandinavia. In the case in Iceland, initially Danish was taught at schools, but that didn't lead to widespread Danish fluency (at least not to the degree you see English fluency now). After independence they switched to English as the most important second language, with much the same sort of schooling and contact with foreigners (i.e. not much), there is widespread English fluency in Iceland. I suppose some of that could be attributed to children hearing English in mass media.
Answer: There was a study (Mothers' speech in three social classes) done in the 1970s where Dutch speaking children in the Netherlands were exposed to German children's television programming for several hours a day with no other German input. These children acquired no German. Likewise, deaf parents used to get their hearing children to watch spoken language programming to give them spoken language skills and these children didn't learn anything. So children can't learn a second language (or, technically, a second first language) without rich interactional input that isn't television.
Adults can learn from television or CDs as long as they're geared towards language learning. That's because adults — and older children — are already literate and have had experience constantly learning things.
Of course, children and adults can learn a second language perfectly well without native speakers — but with near native speakers as teachers. The majority of English teachers in Europe are rarely "native speakers" in a true sense of the word but still teach the language very well.
Comment: Interesting! Could you cite the study, and/or provide a link?
Comment: This paper from Rice (1983) in Developmental Review appears to challenge some of what I've said: http://www.sciencedirect.com/science/article/pii/0273229783900308 but I'll keep trying to dig up that earlier stuff!
Comment: Here we go! All that time looking on the internet and it was right there in a book (Eve Clarke's excellent "First Language Acquisition"). Here's the one on Dutch kids: C. E. Snow, et al. (1976) "Mothers' speech in three social classes" http://www.springerlink.com/content/l08h887t73753440/
Answer: I can't claim to be an authority on the subject, but believe that the answer varies with the medium.
The way that any language is learned is by establishing a common context that contains an understood meaning and then associating linguistic data with that meaning.
If the new language is only ever heard in isolation without any context, there is no way to learn it. Therefore, if the language is only ever heard on the Radio or in music, there is no way to learn it. If the Radio program is multilingual were a given sentence or speech is translated into a language that the listener already understands, that is different because you now have a context upon which to build meaning.
TV and Videos on the other hand are different. There you have a context to be able to extract a certain amount of meaning from the sounds. A movie could be entirely in a single language but you have the context of the scene etc upon which to build a shared meaning.
Answer: Just speaking from anecdotal evidence and personal experience, I have a friend who grew up in a 100% German-speaking environment, but who seems to have acquired English from American children's cartoons. So I would say that yes, it is possible.
That said, how is that contact any less 'direct' than hearing actual people speaking? Language is language, is it not?
Comment: For babies, it isn't. Small babies do not profit from teletubbies, and they do when their parents say the same things the teletubbies tried to teach them. Even though it defies our modern intuition, interaction with screen displays is an acquired art that needs a minimal age. Also, synchronisation poses lots of problem for language learning from movies. A large part of the learning clues are missing.
Comment: @rintaun: I think you need to read a little on first language acquisition. It is generally not held that children learn by passive listening and surprisingly that "motherese" is also not important. But feedback generally is believed to be important. In language a lot of our intuitions do not pan out when tested.
Answer: The situation in Malta is interesting, supposedly a lot of children learn Italian through mass media. Because of the relative size of the populations, this is different than the Dutch/German case LaurenG mentioned. However, much of the Maltese vocabulary is quite close to Italian already.
A similar situation exists in Scandinavia with English. Almost all television shows, movies and music imported from the anglosphere, and not dubbed as in other countries with larger population. Many Scandinavians find themselves very good at understanding both written and spoken English, but less proficient in writing and especially speaking it.
Comment: I have similar experiences: In Serbia almost everyone understands/speaks English well enough to communicate; in Russia almost no one does. In Serbia there are subtitles, in Russia there's dubbing. :) (on the other hand, it's probably also related to language prestige too)


Google Analytics User Explorer - name user

Question: I want to be able to give a name to specific users to display instead of their ID. Is this possible?
Answer: Is is possible to do so, if you record their name as part of a registration process. You would have to pass their name through to Google Analytics as a Custom Dimension.
However, GA's terms of service forbid the use of personally identifiable information, so it would be a violation of these terms to use names.

You will not (and will not allow any third party to) use the Service to track, collect or upload any data that personally identifies an individual (such as a name, email address or billing information), or other data which can be reasonably linked to such information by Google.

This post by Simo Ahava has some very useful instructions on passing Custom Dimensions into GA: https://www.simoahava.com/analytics/improve-data-collection-with-four-custom-dimensions/
Comment: But is it possible for me to have a personal way of identification (that I add) so I can recognise them instead of just their ID? It wouldn't necessarily have to be a real name
Comment: Do you specifically want some sort of text name that you would be able to visually recognise better, or would a randomly generated number do? UserID is the best practice for tracking users across sessions - Simo runs through implementing UserID in the blog post I linked to previously.
Answer: I will assume that your intent is to try and gain access to the account on behalf of the owner.
Below are the steps outlined by en.advertisercommunicy.com:
To initiate the process of regaining access to your Analytics account we need the following information when you fill in the Customer form
According to Google:

(You'll need an Adwords account to do so. A vacant account without
  any payment works too) :

Next Steps:

1) The UA-XXXX-Y of the account you require access to. This can be
  found the source code of the page which has the Analytics tracking
  code. If don't know how to find this just provide the website URL when
  filling in the Adwords customer form.

2) Please specify the level of access you require i.e if you require access at the account level or at the property level. (Account
  level :UA-XXXX, Property level (See link for "account level" :UA-XXXX-Y)

Customer form is the 4th item on the right side in the white box.
After this, according to GOogle Advertiser Help:

Once we have the information we will get in touch with you over email
  :   We will get in touch with the Users who have Manage and Edit
  access to the required Analytics account asking them to directly reach
  out to you within 2 business days. Per security process we can't give
  out the identity of the Administrators of the account you need access
  t

o.


Why how 'old' are you, not how 'young' are you?

Question: English (the language) always gives an impression of being positive.  For example, when little kids are making mistake, it will refer to as 'being creative' instead of 'being incorrect'.  So as my title, isn't it the opposite?  I assume asking how "old" is not very polite, so I usually avoid it and ask 'what's your age'
Comment: [here's a nice mention of the topic](http://linguistics.stackexchange.com/a/2140/2306), kudos to Snailboat [in the chat](http://chat.stackexchange.com/transcript/message/19661452#19661452).
Comment: I don't see this as something inherent in the language at all... It is a cultural thing. English can be extremely negative.
Comment: I wonder if there is a language in which "How young are you" is the construction of choice.
Comment: @CopperKettle Interesting, never heard of "marked term" but guess I learnt something new today.  Thanks!
Comment: The idea that if a child says, for example, that 2+2=5 that we should describe this answer as "creative" rather than "wrong" is at best controversial. I think most people would say it's simply silly. There's nothing inherent in the English language that dictates that everything be presented positively. There are plenty of negative words, like "wrong" and "bad" and "stupid" and "ugly". There are social conventions for politeness, and people debate the proper balance between politeness and honesty.
Answer:
English (the language) always gives an impression of being positive.

This is not really a property of the language per se as the surrounding culture in which it exists.   It is still very if not equally important to understand this if you want to effectively communicate in a given culture.  Read about political correctness.

Why how 'old' are you, not how 'young' are you?

You don't gain youth as time passes, you gain "oldness."  So the oldness is what's measured.  Measuring something you don't collect outside of a scientific context is weird.  It's similar to asking "how much air is in this cup" as you are pouring water into it - you don't really want to know how much air is in the cup, but how much water.

I assume asking how "old" is not very polite

I would say in the US at least - it isn't unless among family, people who know each other well, or authority contexts where age verification is called for, such a police offer asking the age of a teenager who is doing something they shouldn't.  If you are older than the person and taking on a mentor role, it should be OK to ask.  Another permissible context for asking age is collecting details on people registering, signing up for something, or attending an event.
But asking "how young are you" doesn't make it polite, it makes it seem like you are trying to deliberately not use the word "old".  I would avoid this if you are trying to be polite.
Answer: This may be slightly tangential, but there exists a common-enough case where elderly people, in response to questions about there age, reply "I'm 70 (for example) years young". This is purely for irony, however, and not in line with standard usage patterns.
Answer: There are many words for quantities that express "a lot" versus "a little". There's the example you give: "young", i.e. few years, versus "old", i.e. many years. There are "near" and "far", "short" and "tall", "weak" and "strong", etc. In general, we use the word for "a lot" when asking where something falls on a range. So we generally ask, "How tall are you?", not "How short are you?" We ask, "How far is it?", not "How near is it?" Etc.
We usually use the "few" word only when we want to emphasize the "few-ness" of it.
Whether this is positive or negative depends on the quantity being measured and the context. If I'm planning to run an errand, far away is probably bad. If I'm asking the distance from my home to a toxic waste dump, far away is probably good.
As an old man, I find your implication that "old" is somehow negative offensive. I think that as I get older I am gaining maturity and wisdom. :-)
But seriously, if you ask a small child how old he is, he tries to overstate it. "I'm 5 1/2". "I'm almost 6." Etc. He sees being older as a positive thing. If you ask a middle-aged woman how old she is, she tends to understate it. "I'm ever so much more than 20", as Wendy says to Peter Pan. She sees being older as a negative thing. Old milk is bad; old wine is good. It all depends.
Answer: Yes, it would be nice to ask this, isn't it? But, as a fact of life, with each passing day and year, we grow older, not younger. So, at any given time, we are older than what we were at any time before. And if we take "any time before" the starting time of our life, i.e. 0, then the current "oldness" is the years we have lived. Hence, asking "how old are you" to know our relative age from the time of birth.
On the other hand, if we ask "how young are you," it may mean "how many more years are you to live" which is not very polite.
However, for creativity's sake, or for fun, we can ask people "how young are you" just to surprise them with a smile, because they will just think that we are referring to their age as their youth.


Why MP 7000 Xeon 6 times price DP 5400 Xeon

Question: Anyone know the technical reason a MP Server 7000 series Quad core Tigerton Xeon 2.4 Ghz is approx. six times the price of same speed 5400 Series Quad Core DP Server processor.
What is so special about the MP
Thanks
Answer: The MP is artificially expensive as it supports being used in configurations with more than two sockets.  In practice, you can view the DP as simply a crippled version of the MP fiddled so it won't work in multi-socket configurations.
The MP is almost identical to the DP and almost certainly no more physically difficult to manufacture.
On the Opteron, the Hypertransport links for configurations with more than two sockets are structured slightly differently but not in any way that makes the chip more expensive to fabricate.
The pricing is purely artificial, structured to segment the market between people buying cheaper two-socket machines so they can charge a higher margin to the more well-heeled customers buying 4 and 8 socket boxes.  That's all.  You can see the behaviour in that they have fairly well defined price points for their 'latest and greatest', 'last generation' and so-on.  As they bring out a new 'latest and greatest' the previous generation drops down a price point.  This is not the marketing strategy of a company where the actual per-unit costs of the products differ significantly.
Comment: What has to be managed or managed better in a four socket system verses two sockets. Memory access, bus contention. I don't think there is L4 shared off chip cache or anyhting.  If you happen to know ?
Comment: On a two-socket Opteron system there is a single (IIRC) 16 lane Hypertransport channel between the two sockets.  On 4+ sockets the system uses three 8 lane Hypertransport channels (or something like that - I can't remember the exact details).  Anyway, the configuration of the HT bus is slightly different.  In no way does this significantly affect the fabrication costs of the chip.
Answer: While I'm sure there are feature differences, I highly doubt that there is a major "technical" answer. Production line tool-up, poor yields on a new chip, and overall fab capacity probably account for the lion's share of the costs to Intel. Having said that, I can't imagine it really costs Intel that much more to make the higher-end chip.
This doesn't look surprising to me. Intel's highest-end processors are always priced well above the middle-of-the-market processors. Back when Intel published their "iComp" benchmarks, I would often compute the "dollars to iComp" ratio to figure out roughly where the sweet-spot in price to performance was. Now that Intel doesn't publish even proprietary benchmarks (they've had a no-public-benchmark publishing policy for a long time) it's a little harder to compute price-to-performance ratios today.
Intel's marketing people know that the segment of the market that needs the higher-end gear will often pay nearly any price. The MP series processors have additional "glue" to allow more than dual-processor configurations, whereas the DP series can only be run in a dual-processor configuration. If you need more than dual-processor operation you "graduate", in Intel's mind, to the higher-end processors.
Comment: Horrible, horrible. If only I could get my mad scientist crystal growing kit to clone their top-end silicon substrate. World domination would be assured. Cheers. I cant up-vote yet
Answer: The cost of CPU's has very little to do with what it actually does and everything to do with how many of them can be crammed into a single silicon die, and how many of them are likely to be sold. Even if they are almost identical physically if Intel sell 500k 5400's vs 50k 7000's then the cost of the 7000's will have to be higher to eat up the fixed costs of managing that product line. The overall market volume for dual socket cpu's is definitely more than 10x the market for MP capable cpu's so that alone will explain a lot of the cost.
Even so the dominant reason they are more expensive is that the market for them will support a higher price. MP CPU's go into systems that cost 10x and more the price of DP Systems and the CPU vendors make a very healthy margin on those.
The same tiering applies even within CPU ranges - and in those cases there is absolutely no difference whatsoever between the CPU's - a XEON 5520 and a XEON 5570 can come off the exact same silicon die - they are separated out during testing and may even have passed precisely the same tests before being finally sorted. But since there is a bigger market for a $250 CPU's vs $2000 CPU's and the vendors make sure they have the correct distribution of each type even if that means labeling (and possibly electrically\physically limiting) a specific high spec CPU as a lower tier version.
This is sound business sense - everyone benefits by having cheaper average performing systems while those who really want the absolute max have to pay way over the odds for the privilege.
Comment: What a wonderful business world we live in. (Sarcasm, sarcasm)


Ubuntu 12.10 Installation type

Question: I am new to linux. i am trying to install ubuntu 12.10 on my parallels virtual machine on Macbook.
it is asking for the installation type where it says "Erase disk and install ubuntu" i dont understand what option i should select here.
if i select this option "Erase disc and install ubuntu" will it erase everything on the harddisk.
i just want to install it on virtual machine so that i could use both mack and ubuntu.
please help
Answer: I am unfamiliar with parallels virtual machine. Is it same type of solution like virtual machine and vmware? Do you need to create a virtual machine & disk for this installation?
If so, erase and install ubuntu will erase the virtual disc. Not the actual hard disk.

Ubuntu 12.10 Installation type


Knocking valve sound after gasket replacement

Question: I changed the intake gaskets top and bottom along with valve cover gaskets on my Ford F-150. After I finished it was hard getting started but I finally got it started and now it sounds like the valves are knocking. I changed the oil, but they still sound like they're knocking. Do you have any ideas what could be wrong?
Comment: Did you clean the hydraulic lifters?
Comment: did you put enough oil? maybe lifter tick from the engine being low on oil?
Answer: I'm not sure how the F-150 is setup but if you had to remove the injectors to remove the valve cover or intake, check that the injector seals are still on and the injectors are down tight, or this can create a knock.
Comment: Welcome to the site. Please review the [FAQ for new users](https://mechanics.meta.stackexchange.com/q/1460/675)
Answer: You've either got the valve covers on the wrong side or it's turned around backwards.
Comment: Can you expand on why valve covers positioning would make the vehicle hard to start AND cause knocking?
Comment: I don't remember which car maker it was but you could turn the valve covers around backwards and they would still bolt onto the heads. If you lay the valve covers down on something flat and level and get your eye down level and look, you'll see that the valve covers are raised slightly on one side so the rocker arms wont hit them when the pushrods open the valves. The pushrods need more clearance so they get the higher side of the valve cover. Hard to start as in Cranking Slow is Ground wire off from head to firewall Or valve covers pressing against rockers. Give me make, model, year & motor
Answer: What year Ford is it? If you did not loosen or take off any of the rockers about the only thing it could be, unless something fell in, would be the valve covers on wrong. As to the hard starting it may be a vacuum issue. With the engine running spray some carb cleaner around the fittings and throttle body. If a change in rpm occurs there's the leak.


Water level Detection using Ultrasonic Sensor and arduino

Question: I'm making a water level detector to control my motor which supplies water in water tank and for that I'm going to use ultrasonic sensor to be attached to tank lid. My question is whether the vapor arising from water inside the tank hamper the overall working of ultrasonic sensor and/or it may be damaged permanently. I can cover complete ultrasonic sensor using hot glue stick but cannot cover its diaphragm as it will block sound waves. Please suggest something.
Comment: You may be able to find a data sheet for the usual in-air transducers giving humidity limits.  You will not be able to seal them yourself without making them not work.  Sealed ones do exist for vehicle parking systems, but require different electronics.  Also beware minimum distances.
Comment: For fluid level measurement you are best off using a capacitive fluid level sensor.
Comment: I'm not sure if there is even an issue here. But you could try out different types of plastic bags, to see which are "transparent" to ultrasonic sound. Alternatively, just replacing the sensor every one or two year, wouldn't be that bad. Just make sure that your code accounts for a bad sensor (e.g. turn of the pump after 10 minutes regardless of the water level).
Comment: Plastic bag shields will not pass enough signal for the common sensors.
Comment: I am posting an answer just because I do not have enough reputation in order to comment. This is not a straight answer but more like a workaround. Have you tried using the system from a toilet water tank? also, you could put a floating magnet inside the tank (and limit its x-y movement) and a reed switch (or more) outside of the tank at the desired levels. Another idea (not sure of it works, depends on the water quantity) is to place a barometer on the bottom of the tank and measure the pressure.
Answer: Majenko, agreed.
Use some FM antenna cable, if you can find it. Insulate the lower end by dipping in molten heat glue.
Two rods, insulated with heat shrink tubing also works well.
Use LM393 dual comparator as Schmitt trigger and inverter. That will oscillate at  frequency dependant on the water level. Works well, recalibrate or clean the sensor when accuracy suffers due to being too dirty. should not be necessary more than annually.
Answer: A friend of mine worked on a liquid level monitoring project, and after many iterations finally abandoned the kinds of sensors you're talking about. Ultimately he just pointed a cheap USB webcam at the thing and used OpenCV and the edge detection algorithm to find the level of the water.  Then it's just a matter of doing some math using the dimensions of the container, to figure out how full it is.
If you are using a clear container and if you have the option of using a Raspberry Pi (or a PC, whatever) that can run OpenCV, you might find that option worth exploring.
Answer: Sensors exist for exactly your use case. Here is an example;
Maxbotix MB7589 Ultrasonic Sensor
I have used several of these to measure river levels. they are virtually indestructible and have all the features that you would expect;

Temperature compensation
Self heating to deal with humidity/condensation
serial output
1mm resolution


Authentication and encryption using a simplex communication channel

Question: Is it possible to authenticate a client with encryption on a simplex communication channel without the use of authoritative root certs?
Comment: What do you mean by "authenticate a client"? So that the responder can be certain of the sender's identity for all received (signed) messages? What out-of-band mechanisms do you have available to establish authenticity of e.g. a public key or even to transport a secret key?
Answer: Sure. For instance:

Use PKI, register client public key (or self signed certificate) on the server and consider any registered public keys as trusted. You should understand also all drawbacks that it has, like dealing with validity period (how are you going to check if some PKs are still valid / trusted or not and should you remove them from your server PK store or not?), dealing with compromized private keys (instead of revocation list of CA), etc.
Use shared secret. Again, be prepared to the drawbacks. For instance, in such case not only the user, but also you on the server side will be responsible for keeping user authentication material safe.
One time passwords.