Why both hypokinetic and hyperkinetic changes are seen in Parkinsons?

Question: In Parkinsons disorder the substanstia nigra pars compacta get affected and there is destruction of the dopaminergic neurons, which ultimately disturbs the direct and indirect pathways. Now we know indirect pathway is overall inhibitory to movement and direct pathway is overall stimulatory.
Now because both of these pathways are not working properly, can we consider this as a reason for both hypokinetic and hyperkinetic disorders seen in Parkinsons? Or there is some other explanation.
Answer: I am not highly proficient in neuroscience, but I managed to find the following  from Sonne et al. (2020) which may help while you wait for a more proficient answer. (Emphasis mine)

While most forms of Parkinson disease are due to the insidious degeneration of the substantia nigra over a lifetime or during old age, the cause of that degeneration is unknown. These forms of Parkinson disease are termed idiopathic due to their unknown cause. A great deal of research is being done to identify these causes, which can include peripheral inflammation,[15] metabolic insufficiency,[16] and various environmental toxins,[17][18][19] which have been shown to affect the substantia nigra. Several other neurological conditions exhibit parkinsonian-like signs and symptoms by affecting the dopaminergic neurons of the substantia nigra. These include drug-induced parkinsonism in which a patient is taking a pharmaceutical compound, such as antipsychotics and antihypertensive, that affects dopamine metabolism.

Brydon L, Harrison NA, Walker C, Steptoe A, Critchley HD. Peripheral inflammation is associated with altered substantia nigra activity and psychomotor slowing in humans. Biol Psychiatry. 2008 Jun 01;63(11):1022-9. [PMC free article] [PubMed]
Yang L, Wang H, Liu L, Xie A. The Role of Insulin/IGF-1/PI3K/Akt/GSK3β Signaling in Parkinson's Disease Dementia. Front Neurosci. 2018;12:73. [PMC free article] [PubMed]
Langston JW, Irwin I, Langston EB, Forno LS. 1-Methyl-4-phenylpyridinium ion (MPP+): identification of a metabolite of MPTP, a toxin selective to the substantia nigra. Neurosci Lett. 1984 Jul 13;48(1):87-92. [PubMed]
Gash DM, Rutland K, Hudson NL, Sullivan PG, Bing G, Cass WA, Pandya JD, Liu M, Choi DY, Hunter RL, Gerhardt GA, Smith CD, Slevin JT, Prince TS. Trichloroethylene: Parkinsonism and complex 1 mitochondrial neurotoxicity. Ann Neurol. 2008 Feb;63(2):184-92. [PubMed]
Tanner CM, Kamel F, Ross GW, Hoppin JA, Goldman SM, Korell M, Marras C, Bhudhikanok GS, Kasten M, Chade AR, Comyns K, Richards MB, Meng C, Priestley B, Fernandez HH, Cambi F, Umbach DM, Blair A, Sandler DP, Langston JW. Rotenone, paraquat, and Parkinson's disease. Environ Health Perspect. 2011 Jun;119(6):866-72. PMC free article PubMed

Reference
Sonne J, Reddy V, Beato MR. (2020) Neuroanatomy, Substantia Nigra. In: StatPearls. Treasure Island (FL): StatPearls Publishing. Available from: https://www.ncbi.nlm.nih.gov/books/NBK536995/
Answer: The motor system has a LOT of paralell pathways. The model you state is very old and told in med school because it looks nice, but it just doesn't fit the reality. For example, there are a lot of papers trying to come up with models of tremor generation involving corticothalamic loops and beyond.
I suggest reading Motor Control chapters of this book, which is very short and introductory, but beautiful. Neurophysiology: A Conceptual Approach by R. Carpenter, fifht edition. Or you could go with Gazzaniga and even better Kandels'.
Comment: *"The model you state is very old and told in med school because it looks nice, but it just doesn't fit the reality."* I have a problem with this as I cannot understand why they would teach this in med school if it doesn't fit reality. Can you cite some reputable sources to back this up?
Comment: Welcome to Medical Sciences. Chris is right to ask for supporting references. We work differently than most SE sites in that we have a strict policy that all answers should be [backed up with reliable references](https://medicalsciences.meta.stackexchange.com/questions/1/should-we-require-references-to-back-up-all-answers) so the answer can be independently verified. You don't have to write a doctoral thesis, just enough to back up your assertions of fact. Unreferenced claims can lead to answers being deleted.


The ability to convert your Stack Overflow's reputation into money

Question: Is it possible to convert my Stack Overflow reputation into dollars (or better in euro)? It would be nice to see a service which allows it (not to say it will encourage people to spend their time more productively).
Comment: Jon Skeet would be *set*!
Comment: I see no point in changing hard earned rep that tells us how someone is helping with questions/answers to a number that reflects how wealth someone is. -1
Answer: Step 1: Earn a reputation on Stack Overflow.
Step 2: Head over to Stack Overflow Careers.
Step 3: Get an awesome new job after showing off your skills.
Step 4: Profit!
Comment: some employers do in fact weight this fairly heavily..
Comment: Btw this worked for me. `(1)` Got 4K rep on SO `(2)` No college degree `(3)` [Headed to careers](http://careers.stackoverflow.com/giddy) `(4)` Got an awesome job that pays me more than people with college degrees. Thanks @JeffAtwood :)
Comment: @Jeff: How truly depressing.
Comment: +1 If an employer posted on SO Careers, they're even more likely than average to care about SO rep.
Comment: I know I answered this in a semi-humorous way, but I am seriously excited about Stack Overflow Careers.  I think you guys really hit the nail on the head.  And as a side note - yay, I got a comment from Jeff!  :)
Comment: Eureka!!!!!!!!!!!!
Answer: If there was such a market, people would start farming reputation. By starting with many accounts, asking bogus questions from account A, giving bogus answers from account B, upvoting question&answer from account C.
Comment: People do that already.
Comment: @SLaks But at least don't get paid.
Comment: @SLaks I think that's the joke.
Answer: There is likely a market for 10k+ accounts, but it's liable to be small.  I expect that, at a minimum, a good programmer could rep-mine an account to 10k in about 2 months with about 2 hours a day.  120 hours of a 'good' programmer's time represents a value of around $10,000, or about $1 per rep point.  The reverse isn't necessarily true (ie, 1 vote = 10 rep != $10, but the proof is left as an exercise to the reader).
However, there are likely to be very, very few people willing to pay anywhere near that amount for a 10k account.
Further, if the Stack Overflow team learned of such transactions (which, with over 100,000 users, must certainly have already taken place) then it is likely that they would consider locking the account.
Rep is meant to be a reflection of the person's stance among their peers, and transferring rep, except for bounty questions, is not part of the system for that reason.
So yes - it is possible.  It's not liable to net you anywhere near the value of the time you put in getting that rep, and should the transaction be detected you may have an angry buyer to contend with, as well as losing your account.
Comment: Getting to 10k in 2 months spending 2h/day is only possible in popular tags. Less popular tags often give only 1 or 2 upvotes per answer. And honestly, an account that doesn't reflect one's own knowledge is not very useful. Employers are still going to test each candidate.
Comment: You'll note that most of the questions occur, by definition, in the popular tags.  You're also thinking of the need to 'buy' an account to enhance one's own careers profile, whereas one might instead buy it in order to influence the direction of certain questions by obtaining mod status.
Comment: On one hand, you forgot the bogus questions @ammoQ told about, so the values are not an exact math.  On the other hand, you are right to alert that those accounts if found, will be closed. And they will be found. A guy with no experience, using a 10k account, will emit terrible answers or not answer anything at all.
Comment: http://meta.stackexchange.com/questions/122505/why-would-people-want-to-purchase-stack-overflow-accounts-versus-creating-a-new
Answer: Ask yourself this - why would anyone want to buy your reputation? It would greatly diminish the quality of answers on SO as well - a lot of people would answer questions they know nothing about hoping to get a little bit of rep here and there.
Comment: Isn't that what happens already? [ducks]
Comment: @ire_and_curses: Now that's a weird tag if ever I saw one. [quacks]
Answer: Well, if you can find anyone willing to pay for an SO account with lots of rep, then yeah.  But I don't think you'll have much luck finding a buyer.
Edit: Especially not for 443 rep.
Comment: **Z** **i** **n** **g** **!**
Answer: Put your stackoverflow userpage URL on your resume or business card, so that others can see how much you know.
Comment: I'd do that if business cards supported iframes.


"excursion over city" vs "excursion around city"

Question: Is there any difference in phrases usage? Which one is better for title of a story? The story is about tourists.
Comment: You would likely want to add an article saying "to/around/above **a** or **the** city".
Answer: One would normally take an excursion to a city, but if you were flying and never landing you could take an excursion over a city. Or you could take an excursion around a city. It's just a short trip. As NOAD says:

excursion |ikˈskər zh ən|
  noun
  1 a short journey or trip, esp. one engaged in as a leisure activity : an excursion to Mount Etna

And a further usage note under journey:

Excursion also applies to a brief pleasure trip, usually no more than a day in length, that returns to the place where it began (: an afternoon excursion to the zoo).
Answer: I agree with others in that "excursion over the city" would have to be literally over the city, most likely via flying.
"Excursion around the city" implies that the tourists will be exploring within the city, but it also suggests that they are already there ("Let's take a trip around the city.")
"Excursion into the city implies that the tourists are going into a city that they will then explore.
It really depends on the setting and context of these tourists as you set up your story.
Answer: I honestly can't think of an example where you would take an excursion over a city.
I would definitely choose around in this case. It implies that they went to the city in question, and travelled around it, taking in the sights.
An excursion over the city just seems absurd. I would fly over a city, take a flight over a city, take a trip over a city (maybe, it's very ambiguous), but I'm not sure I would ever take an excursion over a city. Perhaps that's just me, though.
Comment: if the character/s in the story had the ability to fly or jump over the city (i.e. Heroes, X-Men, Smallville), then excursion/s OVER the city might be possibly used! :)
Comment: Haha ... very good point! I hadn't considered such a fanciful explanation ;)


Is it possible to withdraw USD from an ATM in Nairobi, Kenya?

Question: While in Nairobi I might need to top up my supply of USD. Is it possible to get it directly from an ATM or will I need to go to a currency exchange?
Comment: @BenCrowell have you been to Kenya? Because I haven never experienced the problems with ATMs you are talking about.
Comment: Keep in mind that the reliability of ATMs is extremely low in East Africa, even if you're only trying to withdraw local currency. Count on trying several ATMs before you find one that works at all.
Comment: The KCB at the Village Market, near the UN Headquarters in Nairobi also offers up to 300 USD.
Comment: And what about at the airports?
Comment: Any limit on how much you can withdraw in USD?
Comment: I couldn't find any, but according to @shnozolla response there is one. Anyway you can get USD from banks or exchange offices in Nairobi.
Comment: It is possible to withdraw any currency (USD) UERO etc in Nairobi Kenya. I have done many withdraws in KCB and Banklays Bank for USD withdraws. Its really interesting.
Answer: Yes, I have successfully withdrawn USD from KCB in Nairobi a couple of times.
Here is the location I have done this: http://goo.gl/maps/fvojb
Comment: Was this with a local or an international card?
Comment: @AndrewWidgery This was using a US local bank card (I used a bank of america debit card, and a chase debit card)
Comment: @shnozolla what were the fees like?
Answer: There is rumor that there is at least one ATM with an USD cash option:

I found one KCB ATM (across from main post office in Nairobi) which gives you the choice to withdraw in KSH or US dollars.

Source: Lonely Planet
Drop a line here if you could confirm it!
Answer: So this has been an issue for quite a while. Fortunately here is a local who withdraws USDs from local ATM every week.
FYI I use a Bank of America ATM
KCB University way ATM @ Anniversary towers (1 machine)
KCB Kipande House ATM (1 machine)
KCB Kencom ATM (2 machines)

Bienividos Kenya!
Answer: Though it seems every answer is equally valid they might benefit from some organisation:
Date     User       Where                                   Notes
20121019 Dan        KCB across from main post office
20121115 shnozolla  KCB                                     US local bank card
20130416 user6326   KCB Village Market near UN Headquarters up to 300 USD
20141128 mark       the mall                                withdrawn US $1000
20150603 Danny      KCB Univerity way Anniversary towers    1 machine
                    KCB Kipande House                       1 machine
                    KCB Kencom                              2 machines
20150808 Bradley    KCB Karen Shopping centre
         Gibbs
20160302 Mark       TRM 2nd flour
20160901 Lawrence   I&M bank Gigiri near WarWick building
         Kimani     KCB Sarit Centre
                    JKIA                                    3 ATMS
                    TRM                                     1
20170209 Kelvin     KCB and Banklays Bank                   also UERO
         Jackson

Answer: There is a USD atm at the KCB Kipandi House (across the road from the post office) but when I went there on 2/8/15 it was out of order. It is the one on a the far right as you enter (ones with USD are not labelled). I cannot confirm the one at Anniversary towers as I went there on a Sunday and could not get access to the ATMS. I was told by locals there we one at kencom. I could not see one providing USD when I went there. I only checked the atms on the northern side though. There may still be something there as it is the main office for KCB.
I ended up being able to get 1000 USD from the KCB atm at Karen Shopping centre. It is the one on the right. This is the closes atm for all those starting overland tours from Karen Camp. I heard that other people could only get 300 USD from this one so it may depend on your own bank.
Also the KCB at Moyale does not give USD
Answer: Yeah! Nowadays it is possible to withdrawal dollars in Kenya ATMs, You can get these services from I&M bank at Gigiri near WarWick building, several KCB ATMS such as two in Kencom but you need to ask the soldier there to show you, 1 in Kipande house, 1 in Sarit Centre, 3 ATMS in the JKIA and 1 in TRM.
Comment: Great first answer, welcome to TSE.
Answer: I wanted to post an update since many of these answers are years old.
I tried one KCB ATM at "The Mall" at Westlands,  it did not have dollars.
I found this website has a list of I&M bank ATMs that dispense dollars: https://www.imbankgroup.com/ke/atms_category/us-dollar-dispensing-atms/
The I&M ATM at Yaya Center worked for me. It has a limit of $2000. It did not charge me any ATM fees, but maybe it has to do with an agreement with my own international bank? Not sure.
Note that your bank may have a different ATM limit that is lower. You can call them to have them temporarily raise your ATM limit for 24 hours.
Here's a photo, the ATM had signs about dispensing dollars
Answer: I have successful withdrawn US $1000 from KCB ATM at the mall in Nairobi, Kenya.
Comment: For completeness' sake do you remember which mall? How long ago was it?
Comment: There's a mall called "The Mall" in the Westlands district of Nairobi

https://goo.gl/maps/hTqGuU3GUq8QRL6z9 @JoErNanO
Answer: There is a KCB ATM at TRM 2nd flour adjacent to KCB Bank in the mall where you can withdraw USD


Can we measure complexity of web site?

Question: I am familiar with using cyclomatic complexity to measure software. However, in terms of web site, do we have a kind of metrics to measure complexity of website?
Comment: +1 for this is a good, rarely asked question.
Answer: If you count HTML tags in the displayed HTML pages, as "Operators", you can compute a Halstead number for each web page.
If you inspect the source code that produces the web pages, you can compute complexity measures (Halstead, McCabe, SLOC, ...) of those.  To do that, you need tools that can compute such metrics from the web page sources.
Our SD Source Code Search Engine (SCSE) is normally used to search across large code bases (e.g., the web site code) even if the code base is set of mixed languages (HTML, PHP, ASP.net, ...).   As a side effect, the SCSE just so happens to compute Halstead, McCabe, SLOC, comment counts, and a variety of other basic measurements, for each file it can search (has indexed).
Those metrics are exported as an XML file; see the web link above for an example.
This would give you a rough but immediate ability to compute web site complexity metrics.
Answer: Though the question was asked 6 moths ago...
If your website is 100% static site with no javascript at all, then it needs to be powered by a back-end programmed in a programming language. So indirectly, the complexity measures that afflict the back-end programming will also affect the complexity of maintaining the site.
Typicall, I've observed a corellation between the maintainability and quality (or lack thereof) of the web pages themselves to the quality (or lack thereof) exhibited, through software metrics, in the back-end programming. Don't quote me on that, and take it with a grain of salt. It is purely an observation I've made in the gigs I've worked on.
If your site - dynamic content or not - also has JavaScript in it, then this is also source code that demonstrate measurable attributes in terms of software complexity metrics. And since JavaScript is typically used for rendering HTML content, it stands as a possibility (but not as a certainty) that attrocious, hard to maintain JavaScript will render similarly attrocious, hard to maintain HTML (or be embedded in attrocious, hard to maintain markup.)
For a completely static site, you could still devise some type of metrics, though I'm not aware of any that are publisized.
Regarless, a good web site should have uniform linking.
It should provide uniform navigation.
Also, html pages shouldn't be replicated or duplicated, little to no dead links.
Links within the site should be relative (either to their current location or to the logical root '/') and not absolute.  That is, don't hard-code the domain name.
URI naming patterns should be uniform (preferably lower case.) URLs are case-insensitive, so it makes absolutely no sense to have links that mix both cases. Additionally, links might be mapping to stuff in actual filesystems that might be case-sensitive, which leads to the next.
URIs that represent phrases should be uniform (either use - or _ to separate words, but not both, and certainly no spaces). Avoid camel case (see previous comment on lower casing.)
I'm not aware of any published or advocated software-like metrics for web sites, but I would imagine that if there are, they might try to measure some of the attributes I mentioned above.
Comment: It would be nice if people were to explain with technical detail the reason for downvoting (assuming they are not puerile.)
Answer: I suppose you could consider "hub scores" to be a complexity metric since it considers how many external sites are referenced.  "Authoritative sources in a hyperlinked environment" by Jon Kleinberg discusses it.
Answer: This is a great paper on the topic.
Comment: Consider improving this answer to contain more than just a link. See http://meta.stackexchange.com/questions/8231/are-answers-that-just-contain-links-elsewhere-really-good-answers
Comment: Understanding Website Complexity:Measurements, Metrics, and Implications  Michael Butkiewicz, Harsha  Madhyastha, Vyas Sekar

Can we measure complexity of web site?


How long does it take to create a team in Dota 2

Question: I recently tried to create a team in dota 2, uploaded all banners and stuff from omij's guide, but I got nothing after a modal came up daying Creating Team with an OK button which I clicked. I'm not able to create a team with the same name again, so I think it got created, but it does not appear in My Teams. How long does it take to create a team?
Comment: I think it should be instant so either it'd a bug, either the team already exists and the creation just failed
Comment: Maybe steam / dota2 network was down. you should post into the dev forum of dota2 about this: http://dev.dota2.com/forum.php
Comment: I've created two teams, albeit with no images, but both were created instantly, when I found a name that wasn't taken.
Comment: Yeah so I created a team with a slightly different name and it was created instantly too. Now what do I do to this question?
Answer: Creating a team is instantaneous.  You should see it in My Teams after, with you as the only member.
If you don't, you need to create another team. Any issues you have with duplicates will have to be resolved unless you manage to get Valve to fix it.


How do we know that two quantum states are entangled?

Question: When two particles are entangled, is there a way of determining that a particle is entangled if one does not have access to both particles?
Answer:
is there a way of determining that a particle is entangled if one does not have access to both particles?

No, you need access to both, and you need to be able to collect statistics through repeated measurements on an ensemble of such setups that have all been prepared in the same way. Even then, it can be tough. This is called the quantum separability problem, and it's known to be intractable in a certain technical sense.
Answer: The much used term "entanglement" means that there exists a quantum mechanical wavefunction describing the particles. This means that one knows the particles participating in the interaction and the initial conditions. Then the complex conjugate squared of the wavefunction will predict the probability distribution of the decay or interaction. This means in general that the experiment has to be repeated enough times so that the statistical distributions give an accurate measurement, as the other answer states.
There is an exception of the need for statistics, when one measures conserved  quantum numbers, that  have to be conserved in an interaction. Given the existence of  two particles, the measurements of the quantum numbers of one particle gives information on the quantum numbers of the other which is not measured.
A simple example is the $π0 -> γ γ$  meson. If the input four vector is known, i.e. that the mass is that of the $π0$  then measuring the spin of one of the $γ$ informs us that the entangled one that was not detected has the negative spin, because the $π0$ has spin zero, and angular momentum is a conserved quantum number.
So it is by use of the mathematical model of the interaction that in particular cases the state of the unmeasured particle is determined also.
Answer: Having access to both particles won't help.  Given a measurement (on one particle or on the entire system), and given an outcome of that measurement, there is always some non-entangled state that yields that outcome with nonzero probability.  (In fact, there's always a non-entangled state that yields that outcome with certainty!).  So no measurement can reveal that the inital state was entangled, and you can never know that a system is entangled unless you know its history.


What is the procedure for electing a Speaker of the House by plurality vote?

Question: In 1849 and 1856, the US House of Representatives elected a speaker by plurality vote after repeated failures to elect one by majority vote (62 failed ballots in 1849, 132 in 1855-1856).  What is the procedure for switching from majority voting to plurality voting?
Answer: CBS News has published quite a good article on this.
December 1849, 31st Congress

On Dec. 19, the Whig caucus invited six Democrats and six Whigs to create a "Conference Committee," which met the next day, at which point 59 ballots had been cast with no speaker elected, according to "Fighting for the Speakership."
The "Conference Committee" decided there would be three more majority votes for speaker and if no speaker could receive a majority, it would go to a plurality vote. The rule change was brought to the House floor on Dec. 22, and it passed 113-105. The Democrats and the Whigs also decided to go back to supporting their original candidates, Cobb and Winthrop.
After no one received a majority in the next three votes, Cobb won on the 63rd ballot with a plurality, thanks to the newly enacted rule change.

February 1856, 34th Congress

On Feb. 1, 1856, Democrats decided to back pro-slavery Rep. William Aiken Jr. of South Carolina. Democratic leaders also said they would again support a proposal to elect a speaker via a plurality if nobody could win a majority in the next three ballots. On Feb. 2, the plurality resolution passed. Banks received the most votes in each of the first three ballots, but he fell short of a majority each time. Aiken then seemed poised to pick up the plurality on the fourth vote.
But Banks managed to secure 103 votes to Aiken's 100 because some of Aiken's expected votes fell through. Banks had won the speakership on the 133rd ballot, nearly two months after the first ballot had been cast.

It appears that the House can vote on a motion to allow plurality voting, and once it has done that, can elect a Speaker by that means.
I suspect that the current House would not have a majority for plurality voting at present. The Democratic candidate, Hakeem Jeffries, had a plurality on all of the first eleven votes, and none of the Republicans would be happy with him winning. McCarthy has had a plurality for the 12th and 13th votes, but the Democrats will want to make him work for the speakership.
Experience with Brexit has shown that a small group of hard-liners can make a party leadership's life very difficult for a long time.
Comment: Presumably they might switch to plurality if they can get promises from enough defectors to vote for McCarthy.  But presently it seems these 20-some-odd detractors refuse to vote for McCarthy at all, regardless of concessions or situation.  Otherwise it'd take a coalition of Repubs and Democrats to force it that way with a pick of their own.  So, yeah, break out the popcorn, this doesn't seem likely to change soon.
Comment: I have heard talk about it with the intended goal of forcing some of the hold outs to switch to McCarthy or let the Democrats pick the speaker. Though even if this does happen it would be short lived as they have the numbers to call for a vote to replace the speaker.


Game in iphone using Flash Lite

Question: Hai everyone, may I ask whether iphone can support .swf file or not? This is because I have developed a mini game using Adobe Flash Lite by using action script 2.0 and save as .fla file and export as .swf file. If can, can give me some guidances on how to import .swf to iphone. Thank a lot.:)
Answer: The iPhone and other iOS devices cannot run Flash apps (at least not without being jailbroken first). See http://www.apple.com/hotnews/thoughts-on-flash/ for Apple's official position on Flash.
Answer: Somedays the iPhone can support flash, others it can not. It all depends how Apple are feeling at the moment...
Currently the only way to run flash on iPhone is to jailbreak it first.

Game in iphone using Flash Lite


Neng [能] vs Ke yi [可以]

Question: What is the main differences between 能,and 可以? They both mean "to be able to", or simply "can", correct?
Comment: consult grammars on modal (auxiliary) verbs, search web using "Chinese auxiliary verbs"
Answer: There is a substantial difference between the following contrast pair:
a. 我能说汉语。
b. 我可以说汉语。
In a., neng 能 indicates that I have the ability to speak Chinese while in b. keyi 可以 implies that this action, my speaking Chinese can be carried out if asked or allowed.
Answer: Neng primarily means that the current CIRCUMSTANCES ALLOW you to carry out a certain action. Ke Yi has the sense of being ALLOWED (or asked) to do something. If you want to say, I have the ability to do something, as in an acquired ability such as speaking Chinese, you should definitely use this word.: 会 hui4.

Neng [能] vs Ke yi [可以]


What's the difference between elenchus and dialectic?

Question: I know that "elenchus" is often associated with Socrates and the Socratic method whereas "dialectic" is more associated with Plato. But what is their relationship? Is elenchus a part of dialectics? Or is elenchus basically the same as dialectics?
Comment: Elenchus is "destructive": a sort of refutation. Stating an assumption (hypothesis) and deriving absurd consequences in order to reject it.
Comment: See Jakob Fink (editor), The Development of Dialectic from Plato to Aristotle (Cambridge UP).
Comment: Consider that the etymology of "dialectic" is "dia-" for "two-of-" and "-lectic" from "lekta," which in Stoic logic were propositions (in modern parlance, the meanings of that-clauses). So "dialectic" would mean at base something like "two propositions," and as a process is the comparison and contrast of propositions as in Hegelian thesis-antithesis pairings (which linguistic imagery was inherited from Kant's discourse on antinomies as samples of "transcendental dialectic"). The elenchtic process, by comparison(!), would be specifically *erotetic*, of questions above/beyond just that-clauses.
Comment: And see G.Vlastos, *The Socratic Elenchus*, into [Socratic Studies (Cambridge UP, 1994)](https://www.google.it/books/edition/Socratic_Studies/bCfaayaHBXEC), page 4: "Socratic *elenchus* is a search for moral truth by question-and-answer
adversary argument in which a thesis is debated only if asserted as
the answerer's own belief and is regarded as refuted only if its negation
is deduced from his own beliefs."
Answer: Both technical terms are not synonyms.
Quoting from Richard Robinson Plato's earlier Dialectic:

The
outstanding method in Plato's earlier dialogues is the Socratic
elenchus. 'Elenchus' in the wider sense means examining a person with
regard  to a statement he has made, by putting to him questions
calling for further statements, in the hope that they will determine
the meaning and the truth-value of his first statement. Most often the
truth-value expected is falsehood; and so 'elenchus' in the narrower
sense is a form of cross-examination or refutation. In this sense it
is the most striking aspect of the behaviour of Socrates in Plato's
ealier dialogues. (p. 7)

The particular method [for attaining positive doctrine, not for
rejecting it] which Plato discusses and recommends is called by him
'the dialectical method' […] (Rp 533C) or 'the power of conversing'
[…] (Rp. 511) or 'the art concerning discussions' […] (Phd. 90B) or
the procedure of discussion' […] (Sph. 227A).  (p. 69)

Therefore 'elenchus' is used by Plato as a method of refutation in his early dialogues, while 'dialectic' is his method to obtain a positive doctrine in his middle and late dialogues.
From the dictionary: elenchus = argument of disproof, refutation; dialectic = from the verb "dialegesthai = to parley".
Comment: Let me see if I'm understanding this correctly, the basic difference is that 'elenchus' ends up with a negative result whereas 'dialectic' ends up with a positive result? Can it also be that elenchus is a part of the dialectic?
Comment: @JohnSmith Of course Plato's method of dialectic also refutes - in the sense of elenchus - certain claims discussed in the dialogues. But dialectic does not aim at refuting all statements and to end in aporia. The aim of dialectic is to obtain true doctrines.
Comment: So elenchus ends in aporia, dialectic ends in knowledge. Is that right?
Comment: @JohnSmith Concerning elenchus I agree. Concerning dialectic: E..g., Plato's dialogue Parmenides indicates some difficulties with Plato's earlier theory of forms. Hence Plato questioned and sometimes even revised some results from his earlier work - which is not unusual for sincere academic work :-)


Identifying jack socket contacts

Question: Was just trying to identify the contacts on this jack socket (datasheet: http://www.farnell.com/datasheets/2047485.pdf )
Image of schematic below.
I was thinking that 1 would be ground? Which I guess would then lead 2/3 to be right/left? This may be totally wrong however, and I'd appreciate the help of anyone who can clear this up.
Thanks.
Answer: It may help to realize that the schematic symbol for this connector is a representation of what's inside the physical connector:

Pin 1 is in contact with the sleeve of the plug, pin 2 is the tip, and pin 3 is the ring.
Answer: The tip of the jack is the left channel (2), the ring (3) is the right channel and the sleeve (1) is ground.
Like this one:
Comment: Cheers for the help.

Identifying jack socket contacts


Can I use a 55mm close-up filter on a lens with 67mm filter threads?

Question: I just bought a new camera which comes with a lens with 67mm filter threads.  I would like to use my Canon close-up filter, which has 55mm threads, on this lens.  Would it be possible with a step-down ring?
Comment: You are likely asking something about the filters that go on the front of the lens, though exactly what is still a bit unclear.  Could you describe the two lenses that you have, and the filter and the problem you are trying to solve?
Answer: Your question is pretty unclear. However, there's two possible things you could be doing and generally, they don't work too well, but can be done with the right parts.

Trying to mount a filter which is too small for the lens — this will block part of the image.
Using a lens which is too small for the camera — even if you could find an adapter to do this, the image from the smaller lens won't cover your sensor.

Either way, it's not ideal, and you're much better off just buying the correctly sized parts. Going the other way on both of those options is usually ok.
Answer: Its really a matter of the focal length of the lens and the f-stop you want to shoot at. If the lens was a longer zoom you could use a step down ring and adapt it. On a longer lens you will have a narrower field of view so you will be less likely to see the step down rings in the edges of the frame. That doesn't mean you wont get some darkening in the corners though.  You have to realize that the step down ring is now blocking out some of the lens and reducing the amount of light let in. That's why you will need to pair this with a small aperture to avoid vignette.  All that being said its really not a great plan. I would say you are better off even buying a cheapo macro filter off ebay that is the right size. This will most likely result in higher quality than using the step down ring.  Granted you would be better off yet if you got a quality macro filter that is the correct size.


What is the best way to sense if a climbing hold is being used by a climber?

Question: I am designing a climbing wall game that gets what holds are being used as inputs. I'm currently planning on using a Kinect sensor to tell where hands are relative to holds and capacitive touch sensors embedded in the hold to verify that the climbing hold is actually in use. But I'm worried that I'll get too many false negatives if someone grabs a climbing hold in an unexpected way. Any thoughts on other solutions? maybe a pressure sensor?
Comment: it kind of makes no sense that a player would only need to touch a handhold ... have the handhold spring loaded ... pulling down on the handhold closes a switch .... something like a joystick sticking out of the wall ... use microswitches for dependable sensing
Answer: You question asks for the "best way" but there's no pat answer without understanding the requirements (cost, reliability, etc).
Capacitive touch sensors seem challenging. If the "holds" are metal, you'd have to insulate them from the climbing wall. If nonmetallic, they don't work as capacitive sensors unless you embed wires/plates close to their surface. And climbing shoes might interfere with capacitive touch effects.
I would suggest you consider a pressure sensor, not to directly sense the pressure of a hand against the "hold", but of the load being carried by the hold. You can buy low-cost "force-sensitive resistors" that are easily read by an Arduino analog input. [
You could embed one like a shim between the hold and the climbing wall, putting it at the bottom edge of the hold below any fastening bolts. Calibrate them with no climbers present so you cancel out the force of the bolts fastening the holds to the climbing wall. When a climber's weight is added to the hold, the sensor will be compressed and the resistance will drop. I think this could work quite well.


Which plugin can do horizontal scrolling of RSS feeds in WordPress

Question: I need a plugin which can do horizontal scrolling of RSS feeds in wordpress, I have got a vertical scrolling RSS feeds but cannot find a horizontal one
Comment: What's the name of that widget? Maybe it is pretty easy to switch it to horizontal scrolling.
Answer: Things that present headlines in a horizontal scroll tend to be called tickers. (Probably due to there resemblance to old-school ticker tape printers.)
Anyway, try these:

http://wordpress.org/extend/plugins/news-ticker/
http://wordpress.org/extend/plugins/wordpress-news-ticker-plugin/ (may not do RSS)
http://wordpress.org/extend/plugins/accessible-news-ticker/

They should all do pretty much the same thing, but they will differ in their appearance. If you don't mind about the appearance, I would recommend the first due to the ease of management.


Find $f$ if $f(f(x))=\sqrt{1-x^2}$

Question: Find $f$ if $f(f(x))=\sqrt{1-x^2} \land [-1; 1] \subseteq Dom(f)$
$$$$Please give both real and complex functions. Can it be continuous or not (if f is real)
Comment: $f(f(f(f(x))))=|x|$, $f$ has only one fixpoint $\frac{1}{\sqrt2}$, I also tried substituting $x=sin(y)$ but no succes
Comment: OK. Help incoming.
Comment: Do they want ONE function or many?
Comment: I want (if exist) a continuous real function or just a real one. -> Thanks to Alec we already know a complex solution.
Answer: I guessed that $f$ is of the form $\sqrt{ax^2+b}$. Then, $f^2$ is $\sqrt{a^2x^2 + \frac{a^2-1}{a-1}b}$. From here on in, it is algebra:
$$
a^2 =-1 \implies a = i ~~~~\text{and}~~~~\frac{a^2-1}{a-1}b = 1 \implies b = \frac{1-i}{2}
$$
So we get $f(x) = \sqrt{ix^2 + \frac{1-i}{2}}$. I checked using Wolfram, and $f^2$ appears to be what we want.
DISCLAIMER: This is not the only solution.
Comment: What do you mean by $a^2=1 \implies a=i $?
Comment: I simply followed one solution; if you take $a=-i$ you get a $b =\frac{i+1}{2}$ and you get another one. The point of the answer was to sketch out what to do. But yes, as usual, you are right.
Answer: Consider real functions on $[0, 1].$ Notice that $\sqrt{1-x^2}$ is an involution, so think of it as a permutation of of the (infinite) set $[0, 1]$ Its cycle type is a product of disjoint transpositions. Now this permutation is supposed to be a square of some other permutation, and while a transposition is not a square of a (finitely supported) permutation, for sign reasons, a product of two disjoint transpositions is (it's a square of a four-cycle). So, break your transpositions into pairs in your favorite way, and there is your function (which is not very continuous, in general). This argument would seem to indicate that you cannot extend such a function to $[-1, 1],$ though I could be wrong.
EDIT The above, can, in fact, be completed to a function defined on $[-1, 1].$
Take $x<0.$ if $-x$ fits into a four-cycle $(-x, a, \sqrt{1-x^2}, b)$ map $x$ to $a.$
ANOTHER EDIT of course, this also answers the question of uniqueness: there are uncountably many such functions.
Comment: I was thinking about using permutations but I didn't know whether it works for continuously infinite sets as well. From this point I still don't know how to extend it to $[-1,1]$ because the fact that $f$ won't be an injective function anymore makes the approach with permutations useless but doesn't tell anything about the other possible solutions.
Comment: @user115826 I disagree. The point is that the structure of real line is only useful if you are thinking of _continuous_ functions, otherwise the real line is just a set. Since you understand the action on positive part of the set, the negative part is not so far away, see the edit.
Comment: (user115826 was me)
Ok, this gave us a real function but doesn't prove that there isn't any continuous real one.
You wants to map x and -x to the same number but this restriction which may cause the absence of a continuous function.
Can you explain why a 4 cycle makes it not continuous?
Answer: I don't know how to approach the real case, but here's a way to solve it if you allow $f$ to be complex.
Start from the guess
$f(x) = \sqrt{1-x^2}$. It almost works, and suggests trying the larger family
$$f(x) = \sqrt{a-bx^2}.$$
For what values of $a,b$ does $f(f(x)) = \sqrt{1-x^2}$?
Comment: See my answer for the real case...

Find $f$ if $f(f(x))=\sqrt{1-x^2}$


My strings keep muting

Question: I started learning guitar and I learned the correct finger positioning on the fretboard and my guitar is tuned. I don't know what I'm doing wrong.
Comment: Hi Paul, welcome to the site! Can you edit the question to add more details? Is this happening to some of the strings when you play a chord, or does it happen when you play just a single note?
Answer: There is not enough info to really help but here are a few possibilities.

If you are trying to play a chord then some of the flesh of one finger might be touching another string that needs to ring.  It takes time to get the correct posture in your muscle memory so this will happen for a while.

If it mutes when you are playing open strings then your guitar is out of adjustment and some of the strings are being damped by hitting frets.  This can happen even with chords.

Try pressing the string to the fret with less force.

My strings keep muting


How to show that $\sum_{\phi \in \hat{G}} d_{\phi}^2 \leq \vert G \vert$ for a finite group $G$?

Question: I am trying to prove that $\vert \hat{G}\vert \leq \sum_{\phi \in \hat{G}} d_{\phi}^2 \leq \vert G  \vert$ for a finite group $G$ where $\hat{G}=\{\text{inequivalent irreducible unitary representation } \phi \text{ of } G\}$. I am able to prove that $\vert \hat{G}\vert \leq \vert G \vert$. By considering the map $\alpha : \hat{G} \longrightarrow L^{2}(G)$ given by $\alpha(\phi)=\text{Trace}(\phi)$ which is well defined as trace is well defined (since similar matrices have same trace) and it is also injective by the orhogonality of the character. Let $A_{\phi}=\{\phi_{ij} : 1 \leq i,j\leq d_{\phi}\}$, and $\vert A_{\phi}\vert = d_{\phi}^2$. Now consider the map $\beta: \hat{G} \longrightarrow \cup_{\phi \in \hat{G}} A_{\phi} $ defined by $\beta(\phi)=\phi_{11}$, where $\cup_{\phi \in \hat{G}} A_{\phi}$ has finitely many elements. $\beta$ is injective by schur's orhogonality relations, but I am not able to show why $\beta$ is well defined? Is there any other map which will work? It might be a small thing but I am unable to get it. Any help in this regard would be appreciated!
Comment: What is $d_\phi$?
Comment: $d_{\phi}$ is the degree of the irreducible unitary representation  $\phi : G \longrightarrow GL(V) $ which is defined to be the dimension of the complex vector space $V$.
Comment: Okay, I'm pretty sure $\sum_{\phi\in\hat{G}}d_\phi^2=\vert G\vert$, from which the inequality is straightforward. Have you seen a proof of that? Were you looking for a more direct proof?
Comment: Actually, I am trying to prove the fact which you stated, and I need the well-definedness of the map $\beta$, to conclude the result. All the other remaining details I have verified.
Answer: The proof I've seen (in "Erdos-Ko-Rado Theorems: Algebraic Approaches" by Godsil and Meagher) is to look at the left-regular representation $\Lambda:G\rightarrow GL(L(G))$, where $L(G)$ is the set of all complex functions on $G$. The action is, for $\phi\in L(G)$ and $g,x\in G$, that
$$(\Lambda(g)\phi)(x)=\phi(g^{-1}x)$$
In other words, $\Lambda(\phi)=\phi'$, where $\phi'$ is a new function such that $\phi'(x)=\phi(g^{-1}x)$ (you can check that it's a representation).
Then we take functions $\delta_g\in L(G)$, defined as $\delta_g(g)=1$, $\delta_g(x)=0$ if $x\neq g$. These form a basis for $L(G)$, and we note that $(\Lambda(a)\delta_g)(x)=\delta_g(a^{-1}x)=\delta_{ag}$. Then if we define $\lambda(g)=Tr(\Lambda(g))$:
$$\lambda(a)=\sum_{g\in G}\langle \delta_g,\Lambda(a)\delta_g\rangle=\sum_{g\in G}\langle \delta_g,\delta_{ag}\rangle$$
And the terms in the sum are only non-zero if $ag=g$, so it's only non-zero if $a=e$. Thus we have that $\lambda(e)=\vert G\vert$, and $\lambda(x)=0$ for $x\neq e$. Using this, we can use the fact that the irreducible characters are an orthonormal basis of all characters and say that:
$$\lambda=\sum_{\phi\in\hat{G}}m_\phi \phi$$
And then to find the coefficients, use the inner product:
$$m_\phi=\langle \lambda,\phi\rangle=\frac{1}{\vert G\vert}\sum_{g\in G}\phi(g^{-1})\lambda(g)=\frac{\phi(e)}{\vert G\vert}$$
(where all but one of the terms in the sum disappeared since $\lambda(g)=0$ if $g\neq e$). This means that $\lambda=\frac{1}{\vert G\vert}\sum_{\phi\in\hat{G}}\phi(e)\phi$. Then since $\lambda(e)=1$:
$$1=\lambda(e)=\frac{1}{\vert G\vert}\sum_{\phi\in\hat{G}}\phi(e)\phi(e)$$
And $\phi(e)=d_\phi$, so that gives that $\sum_{\phi\in\hat{G}}d_\phi^2=\vert G\vert$.
Running with the method you were trying, I don't think $\beta$ is well-defined. For any irreducible representation, there is an equivalent one where I just swap any two vectors. By the orthogonality, we know that for any representation $\phi$, if $i\neq j$, then $\phi_{ii}\neq\phi_{jj}$. Then I can construct an equivalent representation $\phi'=M^{-1}\phi M$, where $M$ swaps $v_1$ and $v_j$, then $\beta(\phi)\neq\beta(\phi')$. But what stops you from simply choosing a representative of each equivalence class of irreducible representations and constructing a set $\hat{G}'$ of these? Then you can define $\beta':\hat{G}'\rightarrow \cup A_\phi$ in the same way and avoid problems of equivalence.
Comment: Why is it a contradiction that $\phi_g\neq P^{-1}\phi_g P$?
Comment: $\beta'$ uses representatives from each equivalence class, instead of the class itself (I called the set of representatives $\hat{G}'$). It's defined explicitly for each element of $\hat{G}'$, so it can't be ill-defined. There's a small issue of whether we can choose such representatives, but since $\hat{G}'$ is finite and every equivalence class is non-empty, that's no problem.
Comment: Firstly, thanks for the answer and for your valuable time Sam Jaques. In my problem, by $\hat{G} $, I meant equivalence classes of irreducible representations of $G$ which I forgot to mention about. Sorry! For that. The proof you which gave using regular representation and characters I knew it, but I was trying to prove the injectivity of $\beta$  without using characters and I wanted to show that $\vert \hat{G}\vert \leq \sum_{\phi \in \hat{G}}^{s} d_{\phi}^{2} \leq \vert G \vert$.
Comment: I was also discussing the same problem with my friend Senthil Rani and she sujjested me the following answer yesterday. $ \beta $ is well defined : Let $ \{e_1, \ldots, e_n\} $ be the standard basis for $ \mathbb{C}^n $ and $ \langle, \rangle $ be the standard inner product on $ \mathbb{C}^n $. We will show that, if $ \phi \sim \psi $ (i.e. $ \exists $ $ P \in GL_{n}(\mathbb{C}) $ such that $ \phi = P^{-1} \psi P $) then $ \phi_{11}=\psi_{11}$. On contrary, assume that $ \phi_{11} \neq \psi_{11}  \Rightarrow $ $ \exists $ $ g \in G $ such that
Comment: \begin{alignat*}{2}
                \quad && \phi_{11}(g)    & \neq \psi_{11}(11)\\ \Rightarrow  \quad && \langle \phi_{g}e_{1},e_{1} \rangle                    & \neq \langle \psi_{g}e_{1},e_{1} \rangle \\ \Rightarrow  \quad && \langle \phi_{g}e_{1},e_{1} \rangle & \neq \langle (P^{-1}\phi_{g}P) e_{1},e_{1} \rangle \\  \Rightarrow  \quad && \langle [\phi_{g}-(P^{-1}\phi_{g}P)]e_{1} ,e_{1} \rangle & \neq 0 \\
\Rightarrow  \quad && \phi_{g} - P^{-1}\phi_{g}P & \neq 0\\ \Rightarrow  \quad && \phi_{g}  & \neq P^{-1}\phi_{g} P\end{alignat*}
Comment: Which is clearly a contradiction. Hence $ \beta $ is well-defined. Note that in the above proof we might as well choose any other $ \phi_{ij} $ which is not same as $ \phi_{11} $.
Comment: Thanks! for pointing out my mistake. You are right! It is not giving any contradiction to the assumption. Could you please suggest me some way to show that $\beta$ is well defined? I would be very thankful to you!
Comment: In your answer, If I define the map $\beta' $ same as yours. Then, why can I avoid the problems of equivalence?
Comment: You are right! Thanks for the help :)


Ganglia Metric Value Decay To Zero

Question: I am sending metrics to Ganglia using Gmetric once every 5 minutes. But if the cron task that is sending the metrics is not working, I would expect the metric value on the Ganglia graph to go to zero, whereas it stays at its last updated value. Is there a way to change this behaviour?
Answer: Note that using the '-d' flag (aka DMAX) in your gmetric will make gmond/gmetad forget about the metric completely after DMAX seconds have passed without a gmetric update.
So if you're running Ganglia straight out of the box, the .rrd file and the Ganglia graph for that metric will disappear entirely.
If you'd like to preserve the .rrd history of the metric and/or you want the Ganglia graph to stay around (but have the plot drop to zero), you could edit the call to rrdtool inside /path/to/webserver/ganglia/graph.d/metric.php.
Check out the rrdtool docs for CDEF and VDEF to see how you can incorporate conditionals into rrdtool calls.  Within those statements I believe you can inspect the timestamp of the last metric inside the .rrd and then arbitrarily graph a value of zero (or any other value you want).  Alternatively you could change the color or style of the line for time periods that you don't trust, etc., etc.
rrdtool is fairly powerful, if incomprehensible.  The best man pages to peruse would be rrdgraph_data, rrdgraph_graph, and rrdgraph.  Also check out some of the other PHP scripts provided by Ganglia to see more examples of how to invoke rrdtool.
Comment: BTW, I had the same issue and i fixed it by editing the `gmond.conf` file, which has a `host_dmax` property that defaults to zero.
Answer: I believe that's a feature of rrdtool.  It will continue to show the 'last reported' value until it gets new data.  If you wanted a metric value to go to 0, you'd have to have some process which actually reported a 0 value for that metric.
Try setting the -d flag in your gmetric calls.  This indicates the maximum lifetime (in seconds) of the metric you send.  I believe gmond/gmetad will drop the metric after that amount of time has elapsed, and you won't see it graphed in the PHP app after that.
That isn't exactly what you asked for, but maybe it's an acceptable alternative?

Ganglia Metric Value Decay To Zero


How do I pipe colored diff output to less?

Question: I've been using git diff, which produces colored output. However, I now find I need to use ordinary diff for something, and it's producing a lot of output that is hard to read because of the lack of colors. How do I make diff produce a readable, colored output? Ideally while piping it to less, for easy review of large files.
Answer: diff cannot output colors, you need another program, such as colordiff for that. Colors in the terminal are printed via ANSI escape codes which less does not interpret by default. To get less to correctly show colors, you need the -r, or even better, -R switch:
colordiff -- "$file1" "$file2" | less -R

From man less:
   -R or --RAW-CONTROL-CHARS
          Like -r, but only ANSI  "color"  escape  sequences  are
          output in "raw" form.  Unlike -r, the screen appearance
          is maintained correctly in most  cases.   ANSI  "color"
          escape sequences are sequences of the form:

               ESC [ ... m

          where  the  "..."  is  zero or more color specification
          characters For the purpose of keeping track  of  screen
          appearance,  ANSI color escape sequences are assumed to
          not move the cursor.  You  can  make  less  think  that
          characters  other  than  "m"  can end ANSI color escape
          sequences by setting the environment  variable  LESSAN‐
          SIENDCHARS  to  the  list of characters which can end a
          color escape sequence.  And you  can  make  less  think
          that characters other than the standard ones may appear
          between the ESC and the m by  setting  the  environment
          variable  LESSANSIMIDCHARS  to  the  list of characters
          which can appear.

Alternatively, you can use more which will display colors correctly by default.

If you cannot install external programs, you should be able to get the same output using a more manual approach:
diff a b |
   perl -lpe 'if(/^</){$_ = "\e[1;31m$_\e[0m"}
              elsif(/^>/){$_ = "\e[1;34m$_\e[0m"}'

Comment: And if someone wants to view the percentage of the data displayed, they have to use `less -RM +Gg`: https://superuser.com/questions/64972/could-less-show-the-viewed-proportion-of-text-file#comment2180596_680555
Answer: The other answers here might be out of date. As of coreutils 3.5 diff can indeed produce colored output which is turned off by default when the stdout is not a console.
From the man page:

--color[=WHEN]
                colorize the output; WHEN can be never, always, or auto (the default)

To force color output when stdout is a pipe diff --color=always -- "$file1" "$file2" | less -R should work.
Comment: Yes. I'm using `alias diff='diff --side-by-side --left-column --color=always'`
Comment: You can also include `alias diff='diff --color=always'` in a `.bashrc` or `.zshrc` file.
Comment: I use `alias diff='/usr/bin/diff --color=always '` and `alias less='/usr/bin/less -r '` but although the diff is initially coloured on the first few pages of less but on long diffs it sometimes flips back to mono. This might be on jumps which clearly would not affect diff, since it's output is only generated once and does not have to jump, but somehow less loses track of the colours.
Answer: To pipe colored diff to less:
diff $file1 $file2 | colordiff | less -r

To make it more readable, by limiting it to a single screen:
diff -uw $file1 $file2 | colordiff | less -r

And, to cause less not to display if there is only one screens worth of content:
diff -uw $file1 $file2 | tee /dev/stderr | colordiff | less -r -F

The -F causes less to close immediately if there is less than one screens worht of content, the pipe to stderr is because when less closes you lose the output - by piping to stderr, it gets output even if less does not display.
An alternative (and, I think, better) way, is to just use -X to prevent less clearing the screen:
diff -uw $file1 $file2 | colordiff | less -r -X -F

This works well for me, but might be specific to bash. colordiff is not a built-in, but is easily installed.
Comment: The only command he needs is `less -r`
Answer: I'd use riff:
diff "$A" "$B" | riff

Or just this, which will implicitly invoke diff under the hood:
riff "$A" "$B"

Riff not only tells you which lines changed, but also what parts of the lines that changed (see screenshot below).
Riff defaults to paging the output the same way that git does, so you don't need to worry about pager integration.
On top of that, Riff integrates with git so you can get this output from git diff and its friends as well.
Get it here: https://github.com/walles/riff/releases/

Disclaimer: I wrote riff myself so of course I'm recommending it :).
Comment: Very cool! Thanks for writing that, that's a useful tool to have indeed.


Is it complicated to deploy my own CA?

Question: We want to implement a free solution to sign digitally internal documents. No legal value of this sign are requested.
We want to consider to deploy an internal CA.
Why is it always said that keeping your own CA is so much complicated? Where does that complication reside?
Comment: Try it, and you'll know. Some people might find it complicated, some might not.
Answer: Deploying internally is easy. The hard part is getting all the procedures right so that it is convincingly uneasy to obtain a fake certificate. This is the condition for signatures: a signature has any value only inasmuch as people believe in it.
Of course, if your signatures are not meant to have legal value, then things are a lot simpler. But then, why would you want to sign things ? A signature is useful only through its binding property: he who signed can be held responsible for what which was signed. The whole point of a signature is to serve as a weapon against the signer. From which we can draw two conclusions:

Nobody in his right frame of mind wants to sign things. You want other people to sign things; you accept to sign things yourself only because you are pressured to do so in a specific context.
A proof is a legal weapon. If you do not want "legal value" for your signatures, then you have made them a lot less frightening, and thus a lot less useful as well.
Let's explain things with an analogy: suppose that you have a warehouse with valuable goods in it. You fear that thieves may break into it, so you want to hire armed guards. But it takes some precautions, because you do not necessarily want to give a loaded pistol to just any guy that looked good during the hiring interview; you will want some medical certificate that says that the guy is not mad, and some legal certificate that says that he is not wanted for some crime, or anything like that. A much less risky solution is to equip the guards with water pistols -- but then, thieves are unlikely to be much deterred by the prospect of being merely soaked.

Running a CA is 5% technology, 95% procedures (access control, audit, logs,...). The 95% are what makes running a CA expensive and complicated. You have to understand all that is going on (including dreary details on certificate formats such as revocation and renewals). If you do not accept to do that part of the job, then things can be very simple (a couple of scripts around OpenSSL), but then, you no longer have actual security to your signatures. You have merely sprinkled crypto all over the place, giving a feeling of security.
Comment: "things ?"  ->  "things?"
Comment: There is no such thing as a definitive, authoritative source for English typography (contrary to, say, French typography, because the French, in all their frenchness, created an _Académie Française_ whose job is to be Right, always). Using a space before the question mark is relatively rare but not unheard of among English writers. It is often said to mimic French punctuation. The question mark itself is a relatively recent import into English (circa 1580, say some authors). Bottom-line: it is not absolutely incorrect to put a space; and I find it clearer that way.
Comment: A signature is not just a legal tool but a proof of origin for a given resource - which is the more likely utility for an intra-organization signing system.

Is it complicated to deploy my own CA?


When I say 'She teaches high school English', do I use H and S as capital? (American English)

Question: When I say 'She teaches high school English', do I use H and S as capital?  (American English)
Comment: If you think there's such a thing as "High School English" (as opposed to simply saying [*She teaches English at high school*](https://www.google.com/search?tbm=bks&q=%22teaches+english+at+high+school%22)) then you should probably capitalize it to reflect that. But personally, I think only non-native speakers would think like that.
Comment: @FumbleFingers, maybe a British/American difference.  ["She teaches high school English"](https://www.google.com/search?tbm=bks&ei=QXttXM7ZJo6jjwS-nKnYAw&q=%22teaches+high+school+English%22&oq=%22teaches+high+school+English%22&gs_l=psy-ab.3...52184.57021.0.572188.8.131.52.0.0.0.280.2118.0j10j3.13.0....0...1c.1.64.psy-ab..12.0.0....0.Cs-hDveCtQg) is fairly common here.
Comment: @Juhasz: I'm quite sure of that. At the moment there are probably far more US teenagers than UK equivalents who don't actually know English very well, so they still need to be taught *normal / correct use of the language itself* at high school (as opposed to studying English Literature, dabbling in linguistics, etc.). But to a first approximation many of those teenagers are in fact "non-native speakers".
Answer: No you do not. At least not in general.
If what you mean is that she teaches English at high school, then neither 'high school English' nor 'high school' are themselves proper nouns and so are not capitalized. "She teaches high school English." is correct. This is going to be 99% of cases.
You might use capitals if she teaches a specific course, whose formal title is "High School English".
Under more bizarre circumstances you might capitalize if she taught English at a specific school called High School (presumably in the little-known town of 'High').
Answer: If a particular place is identified in the sentence, it would be a proper noun, and therefore capitalized.
Ex. She teaches English at ABC High School.
But absent that, "high school" is a common noun and should not be capitalized.


Stationary VAR( 1) process : complex eigenvalues

Question: For a stationary Vector autoregressive process of order 1, eigenvalues of A should be smaller than one. However, I am getting some eigenvalues as a complex number after the estimation. however, the real components of the complex eigenvalues, as well as their norm both, are less than unity. Does that imply that process is stationary??
Answer: The process is stationary when all the complex eigenvalues are within the complex unit circle. This implies you are correct in checking that the norm is less than 1.
An AR process with complex eigenvalues will tend to behave a little differently than one with only real eigenvalues, but it is still stationary.
Comment: What I meant is that if you look at the PACF of AR(p) processes with real roots vesus those with complex roots, then they tend to look a bit different. It's been a while since I've looked at this area specifically, but normally I would just simulate from the different series and see how they behave.
Comment: @SudarshanKumar I don't know if I had noticed your comment on the restrictions before. I'm not sure how easy that is or not. I only know that calculating  all the eigenvalues of potentially large matrices at each iteration can significantly slow down your algorithm. You may be better off finding out what about the process is causing the eigenvalues to be non-real and seeing if you can model that.
Comment: "An AR process with complex eigenvalues will tend to behave a little differently" Would it be possible for you to elaborate on that? If its problematic for the empirical estimation, I always have the option of putting the restriction of real eigenvalue in the optimization


Can a weapon have a negative Strength requirement through upgrades?

Question: Through the use of Upgrade Scrolls, is it possible to reach a negative strength requirement? Assuming there are enough Upgrade Scrolls in the game and you don't die due to your lack of quality armour or weapon.
Comment: I will try to test this, but I doubt anyone will ever be able to. The game does not give enough Scrolls of Upgrade to make it possible.
Answer: Yes. I once got a glaive on Lvl 1 of the dungeon and I was like "This is great!" I then proceeded to put every scroll I found into it. By the Tengu I got it to +20 and it did require a minumum strength of -2 to use. I was playing an Assassin and was eventually killed by ranged attacks (Dwarf Warlock).


Is validating the results of an article important before citing such an article?

Question: During writing my academic paper, I need to cite accuracy values of cited research paper.
I have been advised that if you will cite a paper, you need to read that paper entirely. But in this case, Do i need to validate results that they achieved.
Answer: Reading yes. It is important to avoid extraction of sentences or results which can be less general than as they appear at the first glance.
Validating not at all, unless you feel you must do it because something is suspicious or you think to deal with a particular or new case.
You can't validate each statement for every cited reference, and you can't do so for several reasons.
Also a referee does not. Papers exists to be used. That is an implicit form of validation.
Answer: This depends on the situation. In some cases it is impossible to do so, not having access to all the necessary materials. If you can do so with reasonable effort, however, it is good to do this, just to satisfy yourself.
But, another consideration is the quality of the source/journal. If the journal is of high quality with a good reputation, then you can probably depend on the journals review and editorial process to give assurance to the results of the paper. It isn't a perfect process, of course, but it adds some evidence of validity at least.
But, it is poor practice to cite things without reading them, as you say. It is also poor practice to cite things that you either don't understand or believe to be incorrect. The first requires more work, and the latter may require more research and a correction.
Answer: The idea of peer review is to remove this element of research. If you had to validate all previous work you are building upon you would need to start science from scratch each time...
If the work is published in a reputable journal - then validation is absolutely not necessary. However, you should always read the work you are citing!
If the paper is not published in a reputable journal and you are dubious about the results, then either find a higher quality citation or try to replicate the results (if possible).
Answer: You should do enough work to convince yourself that the paper you cite is valid (or that it's invalid, if you're citing them to critique them). So that means:

Reading enough of the paper that you are sure you understand the part of it that you're referring to when you cite it. If you're using paragraph 4.2, make sure you know what section 4 as a whole is about for example. You don't want to be surprised if someone points out that paragraph 4.4 contains some limits on what 4.2 does.
It's probably safest to read the whole paper, but you don't have to read equally "deep" in the parts that aren't really related to what you're doing. But make sure you read the introduction, look through the related work, and the conclusions.

To convince yourself that the paper is valid, you look at several different things that can show you that there are problems or that can show that it's high quality:

Is the paper written clearly, with the normal structure you would expect for a paper in your academic field?
Are experiments clearly described? Does the methodology seem reasonable?
Are the results properly described?
Do the conclusions the paper draws make sense, given the results?
Is the paper written by someone with a good reputation, someone with experience in that field? What was their academic title when they wrote it?
Is the paper published in a journal with a good reputation/peer reviewed?
Is the paper cited by others? What do people citing the paper (in Related Work sections for example) have to say about it?
Look at the References section of the paper; who does it cite? A possible sign of a bad paper is that it doesn't refer to the normal literature for that topic. That could mean it's a crackpot working on crazy  theories and disregarding normal science in the field.

Doing these things, you can get a good impression of whether a paper could be valid or not, without having to re-do all their experiments.


Working with text fields in a UITableView

Question: I am making a search form with a number of free text fields that I would like the user to edit in line on a tableview (and not go to a seperate view for each individual item). So far I have it so when you press on the field, a text input dialog appears, here is the relevant code:
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier] autorelease];

        UILabel *label = [[UILabel alloc] initWithFrame:CGRectMake(10, 10, 130, 25)];
        label.textAlignment = UITextAlignmentRight;
        label.tag = kLabelTag;
        [cell.contentView addSubview:label];
        [label release];

        UITextField *theTextField = [[UITextField alloc] initWithFrame:CGRectMake(150, 10, 140, 25)];
        theTextField.tag = kTextFieldTag;
        theTextField.delegate = self;
        [cell.contentView addSubview:theTextField];
        [theTextField release];

This has the desired effect of allowing a user to press a row and get an edit dialog, but I have a few problems:
1) You can see I have set the text field's delegate to equal self. The class this is run in implements UITextFieldDelegate yet textFieldShouldEndEditing is not being fired.
2)How can i realisticly persist what the user puts in memory. In other words, is it possible to find out which text field the user has selected currently so i can go [myArray getObjectAtIndex:blah] and edit the actual data.
Thanks
Answer: 1) Are the other delegate methods being called?
2) You can for example set the tag attribute on each text field to identify them, and use that as an index into the array.


Store - How to Count Downloads

Question: When selling downloadable files, is there an existing way to track the number of times each user has downloaded a file after purchasing?
Comment: I was trying to do the same thing, ended up writing a custom module. Here is my question http://expressionengine.stackexchange.com/questions/13286/are-there-hooks-i-can-use-to-log-file-downloads
Answer: Not natively in Store. Similar to this question
Link Vault can track downloads per user.
Answer: Store doesn't support this natively.
There's nothing special about the way Store handles downloads, except that it provides a neat way to hide the real URL to a file and require a purchased order to visit the link. Since the files are just stored in regular EE channel fields, there is certainly no requirement that you use Store's download tag.
Therefore, if you want more advanced features or reporting, as Peter mentioned your best bet is to look to third party add-ons. Link Vault is definitely the most popular that I'm aware of.
Answer: I think, its late reply.
I developed a module "Member Downloads". One can see the documentation from here: http://www.sidd3.com/member-downloads-tracking-members-downloads/. It seems something suitable for you.
Soon, it will be available at devot:ee to purchase.

Store - How to Count Downloads


Does clearance delivery assign VOR or GPS-A approaches?

Question: I've listened to clearance delivery feeds on LiveATC. Is it possible for clearance delivery to assign VOR or GPS-A approaches instead of standard terminal arrivals (STARs)? Or would they just give you routing to a VOR or another waypoint near the arrival airport, and say "direct" afterwards to indicate that the TRACON for the arrival airport will assign the specific approach?
Answer: No.  Normally you don't know which approach you are going to be using at your destination because you can't be sure which runway will be in use.  The STARs at larger airports are to provide standard routings for all/most the of airport's approaches/runways and each STAR is based on a different arrival direction, so the STAR in your clearance will usually be based on where you're coming from and you usually include one in your filed flight plan, that you've picked because its initial waypoint links in nicely to your route.  The actual routing within the STAR you will be using, you find out when you listen in on the destination ATIS to find out the approach in use as you plan your arrival.
Once you get there, you may only fly one or two legs of the STAR before ATC gives you a heading and now you are on radar vectors to get lined up for the approach and you just do what you're told and the rest of the STAR routing goes out the window.
The key thing in IFR is accommodation of communication failures. Comm failure procedures are intended to allow you to complete your flight by following your most current clearance and observing SOPs that allow ATC to predict where you're going to go and when, with reasonable confidence, so that they can work traffic around you.  If you've declared a comm failure (7600) enroute, you would fly the STAR routing and altitudes as published and use as much common sense as possible.
For example, a lot of STAR routes kind of drop you off at a Downwind Termination Waypoint for a particular runway and indicate radar vectors beyond that.  In a comm failure situation you are expected to fly the published route to the DTW and from there you are expected to find your own way to the approach by the most logical, predictable routing that causes minimum disruption.
If the destination has no STAR, your clearance will be to the last waypoint in your route that gets you close to the airport, and that will be your clearance limit and from there you would get radar vectors to line up with whatever approach is in use.  In a case of a comm failure, you are supposed to proceed to your clearance limit, hold there if you're early, then proceed to fly the appropriate approach at the time specified in your flight plan by the most logical routing, so that ATC can predict where you're going and when.
Comment: So if the destination airport has no STARs, your clearance limit won't be the airport. And when you get to your clearance limit, they will give you radar vectors and amend your clearance limit. Why not issue you a clearance limit all the way to the arrival airport right off the bat, instead of giving it to you later?
Comment: No because you aren't going to just fly to the middle of the airport.  You're going to fly to a fix that places you in a position to proceed to an instrument approach to that airport.  When you get the initial clearance, it's gotta stop somewhere short of the airport itself because you don't know which way you're going to proceed until you are close enough to be able to plan for a particular approach to a particular runway, and when you get there, further clearance is necessary. That's the clearance limit - your legal authorization to travel to point X at the time you depart.


Ternary operator, shortcut to return checked condition if true?

Question: I am looking to see if there is an even-shorter notation for an already relatively compact notation. It seems like some piece of syntax that would exist for a fairly common pattern in code.
Here, the ternary operator returns props.initialValues.time if it is truthy, and something else if falsy:
props.initialValues.time ? props.initialValues.time : props.startTime

But why specify the checked condition twice in this case?
I found myself trying to type it this way: (maybe I have seen it somewhere else a while ago or something)
props.initialValues.time ? : props.startTime

What I mean to say is, return the checked condition if it is true otherwise return props.startTime. Does similar syntax for this purpose exist in JS, or in any other language? Checked on google with little luck, maybe I am wording my question incorrectly, or maybe it in fact does not exist.
Answer: || can be used as a shortcut - it'll evaluate to the left side if the left side is truthy, and to the right side otherwise.
props.initialValues.time || startTime

In modern syntax, it'd be preferable to use ?? if the left-hand side will specifically be undefined or null:
props.initialValues.time ?? startTime

Answer: If you're checking whether the property exists, you can use the nullish coalescing operator:
props.initialValues.time ?? props.startTime

let a = 5
let b = 6

console.log(a ?? b)
console.log(a ? a : b)
Answer: a ? a : b can be changed to a || b
a ? b : a can be changed to a && b
So for your case:
props.initialValues.time || props.startTime


What MX records to use for pointing my domain at Microsoft 365?

Question: I'm switching from Gmail to Microsoft 365/Outlook. I have my own domain. I have found some directions for getting this information using the Admin link at the Microsoft 365 website (gear icon among all the Apps icons), but that link isn't there for me. I'm guessing it's just for Microsoft 365 Business and not Microsoft 365 Home. So, does anyone know what MX records I need to use in my DNS settings (hosted at Hover.com) to point mail to Microsoft 365 instead of Google's mail servers? I may need to change the CNAME and A records, too, but I imagine all that info would normally be found in one place. I just can't find it.
Comment: "change the CNAME" no "and A records, too" no, at least not for SMTP - that's just the MX, SPF, DKIM and DMARC records.
Comment: If you can't access the admin link – how did you configure the domain in Microsoft 365? (The system needs to be set up to accept mail before you can do anything with MX.)
Comment: @user1686 I DIDN'T configure the domain in Microsoft 365. So far, I just filled in my username/password for my Gmail account when opening Outlook for the first time, so Outlook uses Gmail for sending/receiving e-mail (via IMAP, I guess). I'm trying to get Gmail out of the loop.
Answer: Much like any other type of hosting service, pointing DNS records to the new server is only the second step after that server has been configured to expect the service for that particular domain to be hosted there. If you only point MX records at M365, it will just bounce all messages as undeliverable.
Although M365 Home supports a "custom domain" feature where addresses in your domain are associated to an existing @outlook.com mailbox, it is a somewhat weird partnership with GoDaddy specifically where Outlook.com automatically configures the records – it doesn't accept other registrars – and Microsoft is planning to discontinue this feature for Personal/Family subscribers, so whatever answer you find won't be useful for long.
So you really need the Business plan for this (or another mail provider entirely).
(If I understand things correctly, M365 "Home" and "Business" are completely different things behind the scenes; the latter hosts a separate Exchange Online instance dedicated to your domain, while the Home edition is just an account in the shared Outlook.com instance, with the "custom domain" feature rather bodged on top. So it's not just the admin panel that is inaccessible – it is inaccessible because the actual features behind it are not available to you either.)
Comment: Thanks for your help. At least I won't keep spinning my wheels.


Why is the tour page example question about unicorns?

Question: I for one am thrilled to know about the corn syrup spray solution, but wouldn't that question be a better fit on the Gardening stack exchange?
https://law.stackexchange.com/tour
Comment: I want to clarify, that since the most recent answer, the question on the tour page has changed to a more suitable question for the site, and is no longer about unicorns.
Answer: The question on the tour page is a placeholder until we are able to select our own. However, it's not all that simple. There's a post on MSE with some more info. Right now, there aren't any questions that are eligible.


Explanation on Newton's second law

Question: I have asked a question on I  pushing the wall,where the force of me is not zero but as per the formula F=m.a,the force is zero and then I got the answer , it is because here the net force is acting on the body.But I a doubt that then a body of mass 5kg and moving with an acceleration 2m/s^2 will experience a force = 10N,Is in this case also the net force acting?
Or
the net force is acting only when the body doesn't move?
If this is correct then my question why?
Comment: When clearing your doubts, edit the question that you already asked.  Don't open a new question to ask the same question a different way.
Comment: You have posted this question 3 times with different formating in less than an hour. This is not only duplicating but spamming the forum. I think it is rude that even when this was been answered here you still opened the same question again, at least read the answers before you duplicate it man.
Comment: No,I am just clearing my doubts
Comment: Okk I will do that from next time onwards
Answer: In the equation for Newton's second law $F=ma$ the $F$ always represents the net force.  It's better to write the equation as $\Sigma F= ma$ or $F_{net}=ma$.
In your example of a 5 kg object experiencing an acceleration of 2 m/s^2 there might be a single 10 N force acting or, more likely, there are two or more forces acting which add to 10 N.
Comment: In case of force=zero we see a lot of force but in case of a body experiencing force we see a single force why?
Answer: Now starting from scratch, what we know from Newton's 2nd law is given below:-$$\vec{F_{net}}=m\vec{a}$$
When we push the wall the forces acting on it are:-
 1) Friction in opposite direction of your push.
 2)Your pushing force.
 3)Normal reaction from earth.
 4)Weight.
 5)Downward normal reaction from ceiling.
As,$$\vec{a_{net}}=0$$
$$\vec{f}+\vec{N_{e}}+m\vec{g}+\vec{N_{c}}+\vec{F_{you}}=0$$
 I think these two equations in itself describes the whole mechanics of the problem.
Hope this helps!
Comment: Thank you very much Unique
Answer:
I have asked a question on I pushing the wall,where the force of me is not zero but as per the formula F=m.a,the force is zero and then I got the answer , it is because here the net force is acting on the body.

The net force on a body is the sum of all the forces acting on that body. By sum I don't mean adding the intensity of each force (their absolute values), I mean vector addition.
When you push a wall you are excerting a force on it. Why it doesn't accellerate (starts moving)? because there are more forces at play. The wall is anchored to the floor, this means that when you push the wall the wall pushes on the floor in the same direction. But because of Newton's third law the floor is also pushing on the wall with the same intensity but in the opposite direction. Thus ON the wall there are two forces acting; your force acting on the wall, and the force of the floor reacting to the action of the wall (an action that was created by pure transmission of your force throught the wall to the floor). Thus the net force acting on the wall is the sum of the two forces we have described on this body. Those two forces are equally intense but opposite so they cancel each other out.
When you think of accelleration as the final change in movement of the object Newton's second law can be interpreted as the force been the net force applied on that object. Since the net force is zero the wall does remain at rest.

But I a doubt that then a body of mass 5kg and moving with an acceleration 2m/s^2 will experience a force = 10N

Why? If the body is moving with accelleration $a = 2\; m/s^2$ and the mass of the object is $m = 5\; kg$ then the force has to be $F = 10\; N$. It obeys Newton's second law and also obeys intuition. No object would start to accellerate if there is no force pushing/pulling it. The net force in this case is the same as the force applied since there is no other force at play on the $5\;kg$ body (the sum of 1 thing is just that thing).

In case of force=zero we see a lot of force but in case of a body experiencing force we see a single force why?

This is a plain contradiction. If $F = 0$ then we don't see a lot of $F$. I think you are still playing here with the difference between a force and the net force (the sum of all the forces), but if you use the same word for everything it is impossible to make sense of it. They are not the same concept, even if in the particular scenario when only one force is acting on a body it is the same as the net force logically.

TL;DR;
You seem to have a missconception on what is the difference (or you don't acknowledge that difference at all) between a force acting on an object and the resulting net force acting on an object. The second is the sum of the contributions of any number of the first ones.
You present two scenarios;
Scenario A: I push the wall but the wall doesn't move. Your question is why if $F = something$ I observe $a = nothing$ when $F = ma$ tells me that if $F = something$ then $a = something$? And the answer is that you missed the fact that your push is not the only force acting on the wall, that there is another force; the reaction of the floor (or the thing to which the wall is fixed) against the wall. The net force is thus the sum of both forces and in this scenario it turns out that they cancel each other out. So the answer is that you observe $a = nothing$ because $F = nothing$, which is in perfect concordance to $F=ma$, where $F$ is the net force.
Scenario B: An object (let's say floating in space so we don't have to think of anything else) is pushed by me and I see it accellerating at $a = 2\;m/s^2$. Then how if Newton's laws are correct there should be a net force acting on it. But the net force should be zero like before right? NO! If the object is moving according to $F = ma$ the net force is non-zero. So why this is not the same case as the wall? because the net force, the sum of all the forces acting on the object, is just the same as the only force acting on the object: your push. According to Newton's third law there is a reaction force from the object to you (the pusher), in fact in space when you push the object you would also be flown back (not only the object would be moved but also you in the opposite direction). But this is important, these two forces are acting on two different objects (the action is made by you towards the object and the reaction is applied by the object towards you).
Difference between scenarios A and B
I will repeat this: in the Scenario A this is more complex, there are 4 forces at play (your push on the wall, the wall reaction pushing you, the wall pushing the floor (or the object which is fixated to) and the floor pushing on the wall) but only 2 of these 4 forces are acting on the object "wall", the other two are acting on the floor and on you. In the Scenario B there are only 2 forces at play (you pushing the object and the object reaction on you) but only 1 of those 2 forces is applied on the object, the other is applied on you.
The net force acting on the object is not the sum of all the forces at play but only of all the forces acting on the specific object. That's why in Scenario B the object moves and in Scenario A it doesn't, in perfect confirmation of Newton's laws.
Comment: Thank you very much Swike

Explanation on Newton's second law


2/4 vs 4/4 time signature in Dixieland Jazz

Question: I'm teaching on the IB Music Diploma Programme and am looking at an examiner's markscheme for a question about the Dixieland jazz piece "Tiger Rag" (similar to this version:

) on a past listening exam paper. In the markscheme, the examiner states the first section is made up of 4 X 2-bar phrases, which makes 8 bars in total (0:00 - 0-16 in link version). However, my previous understanding of this type of piece is that it uses ragtime form, which is based on a 16-bar strain (not 8). If you look at this version with a scrolling score:

, you can see that it uses 2/4 time and the first section is indeed 16 bars (0:00-0:18). This examiner seems to be using 4/4 time, resulting in it being analysed as 8 bars instead of 16. Can this examiner's analysis also be acceptable, meaning either 2/4 or 4/4 can be used for this piece or should it always be 2/4 for this particular type of jazz piece?
Answer: From looking at lots of tangos and ragtimes from the 1890-1950 era, I find that the use of 2/4 vs 4/4 is somewhat sloppy. Sometimes a piece will really be in two, successions of two-beat patterns (some marches in general). These are usually notated in cut time or 2/4 with either the half-note or quarter-note getting one beat. Sometimes they are in either common or 4/4 time but taken in two. Some pieces have four beat counts but are notated in 2/4 with an eighth note pulse (very common) and some four-beat songs will be in 4/4 with quarter-note pulse (more common in later works.) A few cases (four-beat pulse) will just write in 2/4 and use pairs of measures (in which case, the wrong parity may be used).
You have to just play the music and see what's appropriate.
In your case, as it's now the Twenty-First Century, you can just write in 4/4 with quarter beat pulse. (Or 2/4 with two beat pulse.)
Comment: That's very helpful thanks. So if we take the latter YouTube example with scrolling score above. Could this be written in 4/4 with every 2 bars condensed into 1?
Comment: you can count it through. 4/4 will fit.


Big $\mathcal{O}$ notation

Question: I'm learning about the big $\mathcal{O}$ notation and I'm a bit confused. Why is it that we can write things like $$\displaystyle x+\frac{x^3}{3}+\frac{x^5}{5}+\mathcal{O}(x^6)$$ when there's no $x^6$ term? Wouldn't it make sense to write $$\displaystyle x+\frac{x^3}{3}+\frac{x^5}{5}+\mathcal{O}(x^7)$$ instead? This is for the $\tanh^{-1}{x}$ series if it makes a difference.
Comment: Because $O(x^7)\subset O(x^6)$, both statements are correct. Recall that the $O$-notation only states a domination, not an exact behaviour, for example $x^9=O(x^6)$ (when $x\to0$).
Answer: The estimate
$$
\frac12\log\left(\frac{1+x}{1-x}\right)=x+\frac{x^3}3+\frac{x^5}5+O\left(x^7\right)\tag{1}
$$
is only for small $x$. For $\left|x\right|\le a$, we have that $\left|x\right|^7\le a\left|x\right|^6$; therefore, $(1)$ implies
$$
\frac12\log\left(\frac{1+x}{1-x}\right)=x+\frac{x^3}3+\frac{x^5}5+O\left(x^6\right)\tag{2}
$$
However, $(1)$ gives more information (that is, a closer approximation for small $x$) than $(2)$.
Answer: You're correct in saying that it would make more sense to say $\tanh^{-1}x=x+x^3/3+x^5/5+O(x^7)$ - this would be more useful. However, it's also still the case that $\tanh^{-1}x=x+x^3/3+x^5/5+O(x^6)$, it just happens to be a weaker condition.
It's worth noting that there doesn't have to be a "term" corresponding to the function in the big-Oh notation - for example, we could write:
$$\tanh^{-1}x=x+x^3/3+x^5/5+O((\sin^7 x))   (x \to 0)$$
I wouldn't claim that this specific claim is useful, though. The point is more that big-Oh notation covers bounds/asymptotic behaviour, rather than referring specifically to some expansion.

Big $\mathcal{O}$ notation


How do Streptococcus thermophilus and Lactobacillus bulgaricus precipitate the curd of swiss cheese?

Question: I learned in my food microbiology class that Streptococcus thermophilus and Lactobacillus bulgaricus precipitate the curd of swiss cheese. However, I was wondering what type of mechanisms do these bacteria use in order to accomplish this process.
Answer: lactic acid bacteria ferment the disaccharide lactose present in high amounts in milk to the three-carbon compound lactic acid, which acidifies the milk. this causes the proteins also present in milk to denaturate and coagulate, forming curdles. other causes/methods of curdling can be application of heat, salts or by adding the enzyme chymosin (rennin).
Comment: my bad, I am quite new here. is this satisfactory?
Comment: Well, maybe *adding* a better link would strengthen it a little.
Comment: all concepts in my answer are pretty googlable. I understood from Chris' comment that just dropping Wikipedia links on everything is not the best way to answer, so yeah.


memory usage and codes in android

Question: sorry if it's a silly question. Do comments in the java or xml file effect the memory usage of the android application? has anyone tried to monitor the memory usage of his/her application with and without the comments?
Answer: No, comments do not use any memory.
It's important to understand that, in programming in C, Java, etc. what you're writing is source code which, before being run on the computer (or, specifically, your Android device) is compiled into a machine code format. The processor does not run your source code as you see it. The source code you write typically contains lots of stuff like comments (which do NOT have any effect on the actual code) or perhaps things like compiler directives (which may control how the compiler compiles sections of your code).
(I realise it's more correct to use the term byte code in the case of Java, but trying to keep the answer simple here.)
An exception to this however would be if you're talking about the case where you insert a file (e.g. XML file) as a raw resource within your Android application. But, I think this topic is an advanced one for you to learn about later.
Answer: Comments in your code are compiled out and have no effect whatsoever on memory usage in an application.

memory usage and codes in android


How to have one stylesheet for logged in users and another one for anonymous users?

Question: Anyone know how to have one CSS stylesheet for logged in users and another for anonymous users?
Comment: Can you give more information on what you want to look different for the different roles? The best solution will probably depend on what you want to change per user. For example, if it is a large amount of things it might make sense to have multiple themes but if it's only a very small amount of things it may just be using a body class to distinguish between logged in or out.
Comment: @rooby certainly. thanks for your reply. I have a 'sharing' bar on a specific node type that I've absolutely positioned on the page. However, it gets out of position if a user is logged in because of all the admin UI stuff at the top of the page. So I want this particular  to have a different value for 'top' if a user is logged in.
Answer: The template_preprocess_html() preprocess function adds a 'logged-in' or 'not-logged-in' class to the classes array.
These classes get printed in the html.tpl.php template on the body tag.
So you should be able to target anything in your css for logged in or logged out users by using those classes. For example:
<code>.sharing-block {
  top: 0px;
}
.logged-in .sharing-block {
  top: 25px;
}
</code>
Something like that should work without needing to worry about conditionally applied stylesheets or anything like that.


Embedding an Iframe inside an image

Question: I have a web page in which I have an iframe which plays various youtube videos. Now I want this iframe to be display inside an image (The image is basically an iPad Image and I want that the iframe should be embedded inside the screen area of the iPad image). Is it possible to achieve? and if so how can I do that.
Any help would be highly appreciated!
Thanks
Answer: Wrap it in a div, use background image

.frame {
    width:400px;
    height: 400px;
    background-size: 100% 100%;
    background-repeat: no-repeat;
    background-image: url(http://want2scrap.com/store/images/large/Cat%20Frame%20DC_LRG.jpg)
}

.frame iframe {
  position: relative;
  top: 165px;
  left: 100px;
  width: 250px;
  }

Answer: You will need to use styling to overlay the iframe on top of the image.  See this answer for more details.
Comment: Anyone know the exact reason for the downvote?  The two questions look similar but not exact to me.

Embedding an Iframe inside an image