Should numbers be written in numerals or words?

Question: When writing numbers, should we use numerals ("5,000") or words ("five thousand")? I'm particularly interested in how easy each is to read and interpret, and whether it's an important consideration for dyslexic users.
Comment: Quite possibly so. However, what they dismiss as mostly a stylistic issue has a number of important UX/usability aspects that can be discussed here.
Comment: Related question on ELU: http://english.stackexchange.com/questions/979/why-do-english-writers-avoid-explicit-numerals
Comment: If this is asked on English.SE, it will be closed as a duplicate of the linked question.
Comment: This is typically a copywriting style guide question. Certainly copywriting is a part of UX, but likely needs to be asked over on english.SE
Comment: @Koen I agree entirely.
Answer: In most cases it's preferable to use numerals. Numerals have a number of advantages that aid readability:

It's more compact for large numbers (three thousand three hundred and thirty three).
They stand out among text, which is beneficial because numbers tend to be a key element in a text. I've got ten marbles. I've got 10 marbles. The word ten is as visible as all the other words, but if you go for numerals it's immediately obvious there are 10 of something.
They can be compared more easily. Three thousand three hundred and thirty three plus one is three thousand three hundred and thirty four. 3333 plus 1 is 3334. This is in line with my first point but also works for small numbers.
We're so used to numerals, reading and counting with numbers, most people will have to translate the words to numerals in their mind to be able to parse their meaning.
All this together makes me think numbers should be preferable for dyslexics as well. Having to deal with less text and having a much smaller and simpler string to parse should probably help them deal with numbers*.

*I had a short look for some data on how reading numbers is affected by dyslexia. Obviously there is a big chance you're going to have issues with numbers in terms of sequencing and associating meaning to symbols. See also the International Dyslexia Association on the impact on math. But it doesn't seem to always be the case. In fact, apparently we process text and Arabic numerals using mostly different and separate pathways in our brain (studies from Oxford Journals and Taylor&Francis). This would suggest that if your dyslexia affects the reading of Arabic numerals, having to deal with the simpler shorter strings of the numerals would still be preferable over numbers in words. But there is a chance that some people with dyslexia will be able to deal with Arabic numerals much easier than words.
Comment: Do we have any research papers behind this? I'm not doubting your answer; I'd just like some more robust backing when I make recommendations. Sadly, we don't do a great job with provenance in our community.
Answer: There are multiple ways of writing numerals

If you want to draw the user's attention then it's better to use number then in words (eg. use "23" than "twenty-three")
If you think the exact number is important then show the number, disclosing the exact number (eg. 5042) increases the statement's credibility.
If the number is a big number (eg. 2,000,000), it's ideal to user numerals for the significant digits and write out the magnitude as a word. (eg. 20 billion)
Answer: Personally, I find numerals easier to read, especially when there are many numbers being displayed at once. If the numbers are in a table or other context where they could be compared to other numbers, numerals are the only appropriate choice. When the number appears in a block of text, however, it can be spelled out or represented with numerals.
A common stylistic practice for displaying numbers within text is to spell out smaller numbers, eg, zero through twenty, while using numerals for larger numbers that have longer or hyphenated spellings, eg, twenty-one.
Another consideration is whether the numbers are approximate or exact. I might say ten or twenty but finally settle on 17. It is probably best though not to mix representations within the same sentence.
Answer: The AP Stylebook provides guidelines widely used across the world of journalism. Academic scholarship in the liberal arts (like English Literary Criticism) follows guidelines laid out by the MLA Handbook.
A quick reference to AP Style is published online by many universities, including this one hosted by Purdue:

"For ordinal numbers, spell out first through ninth and use figures
  for 10th and above when describing order in time or location.
  Examples: second base, 10th in a row. Some ordinal numbers, such as
  those indicating political or geographic order, should use figures in
  all cases. Examples: 3rd District Court, 9th ward.
For cardinal numbers, consult individual entries in the Associated
  Press Stylebook. If no usage is specified, spell out numbers below 10
  and use figures for numbers 10 and above. Example: The man had five
  children and 11 grandchildren.
When referring to money, use numerals. For cents or amounts of $1
  million or more, spell the words cents, million, billion, trillion
  etc. Examples: $26.52, $100,200, $8 million, 6 cents."


When does the cleansing of the Temple happen? At the beginning of Jesus's ministry or later?

Question: The gospel of John says that the cleansing of the temple was early in Jesus's ministry (John 2:14-21). The other gospels put this event after Jesus enters Jerusalem, near the time he was crucified. So when did it happen?
Comment: Related: [How should we understand the "Cleansing of the Temple"?](http://hermeneutics.stackexchange.com/questions/562/how-should-we-understand-the-cleansing-of-the-temple),  [Did Jesus have the legal authority to cleanse the temple?](http://hermeneutics.stackexchange.com/questions/591/did-jesus-have-the-legal-authority-to-cleanse-the-temple) and [Why did Jesus "cleanse" the temple?](http://hermeneutics.stackexchange.com/questions/16881/why-did-jesus-cleanse-the-temple)
Comment: He did not "cleanse" the temple. He (if he indeed existed) was written to have simply overturned a few tables and threw a road rage.
Comment: Its a generic name: "cleansing of The Temple" that refers to that event. It's like " Mary's song" , she didn't actually sing.
Comment: Note also https://hermeneutics.stackexchange.com/questions/49365/one-temple-cleansing-or-two?noredirect=1&lq=1
Answer: There are two possible explanations.
One is that the individual Gospel writers did not arrange events in a chronologic order; each one organized the events in a way that made the most sense to their audience or to best fit their theological emphasis.
The second is that Jesus did this on more than one occasion and John records the first which took place near the beginning of His public ministry. Mathew, Mark, and Luke record the second which occurred 2-3 years later.
Besides placing the event at the beginning of the ministry, there are 2 other  differences which make John unique. One is in what is missing and the other is in what is found:

Matthew/Mark/Luke: And he was teaching them and saying to them, "Is it not written, 'My house shall be called a house of prayer for all the nations'? But you have made it a den of robbers." (Mark 11:17 ESV)

these I will bring to my holy mountain, and make them joyful in my house of prayer; their burnt offerings and their sacrifices will be accepted on my altar; for my house shall be called a house of prayer for all peoples." (Isaiah 56:7 ESV)

John: And he told those who sold the pigeons, "Take these things away; do not make my Father's house a house of trade." His disciples remembered that it was written, "Zeal for your house will consume me." (John 2:16-17 ESV)

For zeal for your house has consumed me, and the reproaches of those who reproach you have fallen on me. (Psalm 69:9 ESV)

Matthew, Mark, and Luke all make reference to Jesus saying that His House is to be a House of prayer for all peoples (from Isaiah). They place the reference to what is written with Jesus. The reference is His House being a House of prayer for both the Jewish people and the Gentiles. This is missing from John.
John has something not found in the other 3. John connects clearing the Temple with Psalm 69 which is a prophetic picture of the sacrificial death of Jesus ("the reproaches of those who reproach you have fallen on me"). John also puts the reference to the written Scripture with the disciples as something they later remembered (not something Jesus spoke). The focus in John is different and it excludes the Gentiles.
John then relates the retrospective actions of the disciples:

When therefore he was raised from the dead, his disciples remembered that he had said this, and they believed the Scripture and the word that Jesus had spoken. (John 2:22 ESV)

There is good internal evidence that John is describing something not found in the other 3 accounts, as are most of the events he records.
It also requires one to believe that after this first clearing, Jesus repeated this action when He returned to Jerusalem near the end of His life. The dual clearing of the Temple is consistent with the actual history of the Temple (it was destroyed twice); it also follows the pattern of Jesus returning to earth for a final "clearing."
Comment: It does strain credulity to suppose that the cleansing only had to be done once; it is much easier to credit that once Jesus was away preaching up north that the commerce crept back in again.
Answer: In answer to the question, when did Jesus cleanse the Temple, I would suggest we consider to two Old Testament contexts, first from Lev 14:34-45 concerning the investigation of corruption in a house (leprous plague) and second from the command in Exo 12:15 to have all leaven removed from your house prior to Passover/Feast of Unleavened Bread.
In regards to the first, we know that part of Jesus' role was to inspect his Father's house - to assess the spiritual state of the leaders because the corruption there had become obvious. We see from Leviticus 14 that there is a process for dealing with corruption in a building construction, which can also be applied to a social construct.  There is an initial inspection and clearing out (Lev 14:36) and an evaluation is made, and then the building is quarantined (Lev 14:37-39). If the situation does not correct itself, then the affected parts are removed and replaced (Lev 14:40-42).  If the plague returns, then the building is torn down completely (Lev 14:43-45).  If Jesus' actions were in fulfillment of this law, then it is possible that he cleared His Father's house initially, but returned to find the corruption was still there. This also lends understanding to Jesus' later prophetic statements that the Temple was to be torn down and a new one raised in its place (Matt 26:61, Matt 27:40) as the corruption remained in it.  So it may be possible that the cleansing was not just a one time event, but two events as part of the ongoing inspection of the spiritual state of the leadership of the Temple.
In regard to the passage in John 2:13-21, the Passover reference is significant.  Throughout his gospel, John repeatedly makes note when specific events are tied to the feasts of Israel.  In regards to Passover and the Feast of Unleavened Bread which are treated as nearly the same feast, there is a command in Exodus 13:7 to remove all leaven from your house prior to the feast, so that "no leavened bread shall be seen among you, nor shall leaven be seen among you in all your quarters." Jesus repeatedly refers to the actions and teachings of the Pharisees as leavening (Matt 16:6, 11, Luke 12:1).  So in this instance, paired with the timing of Jesus action, John recognized the significance of Jesus "getting the leaven out" of His Father's house and noted it. It was just another piece of the picture of Passover falling into place.
Comment: Welcome to Stack Exchange, we are glad you are here.  When you have a chance, you may want to read up on  how this site is [a little different](http://meta.hermeneutics.stackexchange.com/questions/653/how-can-we-educate-new-users-about-our-site-distinctives#803) than other sites around the web. *This is not a comment on the quality of your answer, but rather a standard welcome message.*
Comment: Very nice reference to the two stage cleansing the house in Leviticus. Since all of the clearings took place at Passover you may want to consider if there is a similar two step or dual removal of leaven at Passover/Unleavened Bread.
Answer: First of all, there can only have been one cleansing of the Temple. If John is correct, then after the havoc that Jesus caused in the first year of his ministry, the traders and moneychangers would have been aware of Jesus and ready to apprehend him. When Jesus came into the Temple in his final visit to Jerusalem, he would not have been given the opportunity to do this again.
John 2:13 says that when the Passover was at hand, Jesus went to Jerusalem and found sitting in the temple those who sold oxen and sheep and doves, and the money changers. He drove them all out of the temple and poured out the changers' money, and overthrew the tables, saying to take those things and not make his Father's house a marketplace.  According to John, Jesus would return four times (John 5:14; 7:14;8:2;10:23) later in his mission apparently without further troubling those he had driven out this first time, nor being troubled by them. So we already have at least some grounds for doubting John's version of this event.
In the synoptic gospels, the cleansing of the Temple was the trigger for the arrest and trial of Jesus:

Mark 11:18: And the scribes and chief priests heard it, and sought how they might destroy him: for they feared him, because all the people was astonished at his doctrine.

However, John says that when Jesus raised Lazarus from the dead, it was the trigger for the arrest and trial of Jesus:

John 11:47-48: Then gathered the chief priests and the Pharisees a council, and said, What do we? for this man doeth many miracles. If we let him thus alone, all men will believe on him: and the Romans shall come and take away both our place and nation.

It would have been a clumsy narrative if the author of John's Gospel had left the now redundant cleansing of the Temple where he had found it in the synoptic gospels, but at the same time it appears he wanted to keep this dramatic narrative, so moved it to the beginning of Jesus' mission.
Nearly all New Testament scholars accept Mark to have been a source for Luke - John Dominic Crossan, in The Birth of Christianity, page 111, calls this a massive consensus - and there is now a growing consensus for Luke to have been a major source for John. Crossan does a technical analysis (ibid, page 565) to show that the author of John was also aware of Mark's Gospel.  Andrew Lincoln (Gospel According to St John: Black's New Testament Commentaries, page 29), traces the development of the consensus of John's  dependence on the synoptics. He says that there are clear signs of John's dependence on the synoptics in the resurrection narratives, the passion narratives and elsewhere in the gospel, which can not be satisfactorily explained by other means. Once again, if John was dependent on the synoptics, then any discrepancy must be resolved in favour of the synoptics.
This still leaves open the question of whether there was a cleansing of the temple at all. Robert M. Price says in The Christ Myth Theory and Its Problems, page 310, that Mark seems to have been unaware of the vast size of the temple and the fact that any such action would have brought the temple guards down on Jesus' head then and there. I think he may have been aware of these problems but chose to play them down, whereas John at least gives a hint of the scale of things when it mentions the oxen and sheep that had to be driven from the temple courtyard. Price says (ibid, page 125) for Jesus to commandeer it like this would have required a military raid - he mentions the example of  Simon bar Gioras' entry into the temple on the eve of its destruction.


Disable skip button when some action was taken

Question: I often do reviews on my tablet. When reviewing first posts or late answers it happens now and then it happens that after voting and/or flagging I  accidentally touch Skip instead of Done. Since Done is enabled not before  some action was taken, I suggest that Skip should be disabled on the same event.
Comment: I suggest there should be a prompt telling asking you if you want to skip the post similar to when asking a question and try to go back to home page. Otherwise you could be stuck on a post wondering why you can't skip it because you have voted on the page. You should also consider that sometimes a vote or flag is the only action the OP will want to do on  a post.
Comment: I haven't done it on phone, but one thing you can do is go to your review history and show the skipped reviews. You can then review those if you had a change of heart. This is ofc less than ideal, but it's better than nothing. The browser back button does work, but idk on mobile.
Answer: There are situations when it is reasonable to use Skip after acting on a post. For example, if a post shown in review is spam, I will flag it as such and then click Skip so that it stays in review and gets more spam flags from other reviewers.
Another scenario: I can see that an answer is a really bad answer (and so I downvote it) but am not sure if it qualifies for deletion via VLQ flags. So, having downvoted it, I leave it up to next reviewer to decide if it should be flagged.
As Servy wrote on this topic before,

there may certainly be cases where you see something that you can do without being able to do the thing that the review queue actually sent you there for.
Comment: If you're flagging as spam, you're not exactly skipping. Seems like a UI problem (there's probably a feature request here somewhere).
Comment: I never knew that if I click `Done` the post is removed from the queue - I always thought there's the need for three reviewers as in Triage. But given that, the scenarios you've described are indeed reasonable. Perhaps the help text for the buttons could mention these.
Comment: I also thought the post was never removed from the triqge queue until having three similar review. Three "looks ok" = correct question. Three "should be closed" = question closed. But it looks like first post review are different. Triage : https://meta.stackoverflow.com/questions/295650/is-there-a-guide-for-the-triage-queue/295674#295674 , First Post : https://meta.stackoverflow.com/questions/334257/first-post-review-options-limited
Comment: But i haven't found any help center about reviewing, how does the mechanic works? Nothing like an official help page for reviewing.
Comment: @ThomasSchremser Depends on the queue. In First Posts, one click on "Done" means the review is done. In most other queues one needs more decisions than that.
Answer: In addition to the (useful, but admittedly obscure) use-case that ol' slim mentioned, there are a couple more boring reasons why this would be inadvisable:

You may not actually be done. The review interface for First Posts (and late answers) allows you to take multiple actions on a given post. It even recognizes actions you've taken on the post prior to seeing it in review. Just because you (say) upvoted a comment under the post doesn't necessarily mean you consider your work done (or have any desire to review the post itself at all, for that matter). Even if you do intend to eventually review the post, skip lets you "save it for later" and return to it from your review history (not usually practical on Stack Overflow, but a heavily requested feature on some other sites).
It's just plain confusing. Even without the button, you could always close the tab, hit back, click another link... There's nothing actually forcing you to review a given task. Disabling "Skip" sends a weird message, like we're trying to lock you into your decision.

I kinda mentioned this above already, but... Skip doesn't actually block you from reviewing. If you hit it by mistake, just hit your browser's back button and hit the Done button (or whatever you intended to click) instead.


What is the linux equivalent to OllyDbg and Ida Pro?

Question: What is the Linux equivalent to OllyDbg and IDA Pro ? Or if there are multiple tools that do the various functions that OllyDbg and IDA Pro do, where can I find these tools? I'd like to start reversing some elf files on Linux and I'm just looking for a set of tools to get me started.
Comment: IDA Pro for Windows runs beautifully under Wine, so no problem to use it this way ... just sayin'.
Answer: Ida Pro runs on Windows, Linux and Mac OS, so i guess the Linux equivalent of Ida Pro is Ida Pro. The debugger that's used mostly seems to be gdb, possibly enhanced with a GUI.
Hopper and Radare2 run on Linux as well.
Comment: IDA includes a debugger too
Comment: Meanwhile (2018 onwards) I would also suggest to use https://github.com/radareorg/cutter.
Comment: Thank you for this answer. I had no idea that IDA Pro ran on Linux. Its been a while.
Comment: @k170 a brief example of the Debugger with Visual view of Radare2. http://radare.tv/a/71
Answer: edb is a cross platform x86/x86-64 debugger. It was inspired by Ollydbg, but aims to function on x86 and x86-64 as well as multiple OS's.
https://github.com/eteran/edb-debugger
Answer: As an (2019) addition to all the other answers:
Try Ghidra.
It is the Software Reverse Engineering (SRE) suit of the NSA and it's free and open source. It was leaked as part of Wikileaks' "Vault 7" but the NSA decided to release it and they published it as open source software. It's written in Java and is cross platform, supporting Windows, Linux and MacOS.

Official Website
Source Code
Answer: I would say radare2. It is opensource fast moving project, and it has analysis capibilites similar to that of ida, and supports many architectures like x86 and the 64bit version of x86 plus lots of other architectures you might never hear of. It has nice command line interface and everything is somehow documented.
It comes with bunch of tools for analysing binary files, patching, generating shellcodes from C, bindiffing, assemblers, and debugging all by default.
Answer: For gbd try fGs gdbinit
There is lldb, too. It's llvm debugger and it's scriptable in python
P.S. I would have commented, but that would have required registering, and earning 50 reputation.


Feedback on my demo reel

Question: Hey guys I'm still new to the field of sound design and just finished up my demo reel. I was seeing if I could get some feedback on it. http://vimeo.com/20907263
Thanks!
Comment: My first impression was good, but effects at the start and coda are good but "more" then graphics. Some sounds are lost but it covered by music and looks good but sounds like music clip where sound design is not main thing. http://socialsounddesign.com/questions/147/hmm-demo-reel-yeah-right very good advise about length and purpose of demo.
Comment: @Evgeni Unfortunately I lost the session to the first clip and couldn't take out the music. As for the effects at the beginning and end I was trying to spice up the animation since there's not much going on there. Do you think any of the clips were too long and needed to be shortened?
Comment: Its pretty good considering the fact your new to sound designing (so am I btw lol), but just wondering what SFX Libraries are you using they sound great.
Answer: it need to decide what is the purpose of this reel then it helps you to decide what part to take out. For example you want to show game producer that you can make good shoots and war athmosphere or film producer how you work with narration. Trailers it different thing than sound design of whole picture of game. In movie and games they should see that you keep attention on every detail. Trailers especially for movies it short advertising they have 10-20 sec on the TV 30 sec on radio mostly and it's also story but very short it has begining-progress-end. I suggest you to leave EA game but give it more complete form, movie "colonial kitchen" if you have moment how narration is changing ( maybe they leave this restaurant and go to pub:), and work a little bit more on animation, it little bit scretchy on my point of view, maybe it could be soft. and write what is your job exactly in all these cuts.

Feedback on my demo reel


Finitely generated field extensions

Question:
If $F=K(u_1,\ldots,u_n)$ is a finitely generated extension of $K$ and $M$ is an intermediate field, then $M$ is a finitely generated extension of $K$.

I'm not exactly sure how to start this problem. Any help at all would be a tremendous help.
Answer: Firstly, I encourage you to simply try this with the tower rule ( $[F:K] = [F:M][M:K]$ ). Remember that you can consider the transcendent degree separately. However, if that is insufficient, I direct you to this answer over at MO.
The accepted answer covers this question very nicely, including the cases for transcendence.
Comment: I've edited your answer to get rid of the entire link - in general, the format is `[link text](url)`.
Comment: @Zev: Thanks for that!
Comment: @ mixedmath thanks for the help. You offered a lot of help.
Answer: I messed up last time. What I showed was not correct, $F$ need not be finite dimensional over $K$ just because it is finitely generated, counter example would be any transcendental extension.
Let $T = \{u_1,\cdots,u_n\}$. WLOG, let $A = \{u_1,\cdots,u_m\}\subset M$ and $B = \{u_{m+1},\cdots,u_n\}\cap M = \varnothing$. That is we partition $T = A\cup B$ into two sets $A$ and $B$, where $A$ contains all $u_i\in M$ and $B$ contains the rest.
Since $M\subset K(T)$, all elements of $M$ are in the form of $f(u_1,\cdots,u_n)$, where $f\in K(x_1,\cdots,x_n)$, the field of rational functions with coefficients in $F$ with $n$ variables.
But since $M\cap B = \varnothing$, all elements of $M$ are in the form of $f(u_1,\cdots,u_m,0,\cdots,0)$ where from position $m+1$ to $n$ its all $0$. That is all elements of $M$ are the form of $f(u_1,\cdots,u_m)$ where $f\in K(x_1,\cdots,x_m)$. Thus $M\subset K(u_1,\cdots,u_m)$.
Also $M\supset K(u_1,\cdots,u_m)$ because $M\supset K$ and $M\supset A$. That is $M = K(u_1,\cdots,u_m)$.

Finitely generated field extensions


Is moderator voting anonymous?

Question: I'm just curious as to whether voting for the moderators is anonymous, or can moderators or anyone later see who has voted for whom?
Answer: In principle, moderator voting is anonymous except to Stack Exchange developers. Now let me put on my security hat.
All votes are recorded in a database on the Stack Exchange servers. Each ballot has a user ID associated with it. This lets Stack Exchange employees audit vote counts. Barring an unintended data leak, no one other than Stack Exchange developers are able to access the ballot data in the database.
After the election, the set of ballots will be published, without an indication of who cast each ballot. Even the set of voters (vs. abstainers) will not be published.
Moderators do not have any special privilege regarding access to the ballots. Moderators can see in real time the number of people who visited the election page and the number of people who voted (there may be a lag due to caching). In principle, since moderators can also see the last activity date in a user's profile, this could let them correlate last activity times and voting times and guess who cast at least one vote. This would require a lot of data acquisition (probably enough to register as a suspicious access pattern on the Stack Exchange servers), and I doubt the data would be accurate enough to be useful. So I think this data leakage is largely theoretical. In any case, this information would not reveal anything about who the voter voted for.
Answer: The only info I was able to find was in "Stack Overflow 2010 Moderator Election Results" post by Jeff Atwood on SO blog:

You can download the Stack Overflow 2010 Moderator Election ballot file and our output result and run the election yourself, if you like. (Of course the  individual votes are anonymous in the file)

This is interesting - on one hand, it shows that public voting info is 100% surely anonymous.
OTOH, it explicitly says "in the file", meaning that it does NOT say the moderators won't be able to view this info. I will assume that the voting follows the normal pattern of up/downvoting on SE sites, which is anonymous even from mods:

Like any normal user, votes are anonymous to you and you have no power to alter votes. (source: Moderator Cheat Sheet)
Answer: Moderators do not see individual votes anywhere: not on posts and not in elections. We see the same data you see: the ballot file provided at the end of the election.
In general, moderators are given information on a "need to know" basis: there's really no reason why a moderator would ever need to know who you voted for.
Answer: I suspect that if a Stack Exchange employee wanted to know, they could figure it out. Aside from everyone else, everyone, moderator, nominee, or just regular member, gets the same information. That information is a downloadable file in which you can see, without names, the first, second, and third choices of everyone who voted. Usually the winners are declared after a few days, but the results are available as soon as the election is done. See this MSO post for how the algorithm works.
If you want to see what the election results look like, take a look at the Gaming's election results. Or any other one, just go to the site, and add election/1 to look at the first one, which is all that most sites have had...
Comment: A dev with DB access could figure it out. In the last SO election the votes released didn't match up with the number voting, they figured out it was because of deleted accounts - which means the vote is tied to the account enough to remove it if the account is deleted, so a dev could probably find it.

Is moderator voting anonymous?


Can Palisade Cells Survive Independently?

Question: I have been intrigued by this question. Can palisade cells survive independently from its parent plant in a chemical environment? For example, if we were to separate a palisade cell from a plant and place it in sucrose solution, how long would it survive?
Answer: Yes they can. In 1902 Haberlandt reported single palisade cell culture from leaves in knop's salt solution. Now there are many different methods of plant tissue culture
for PLANT TISSUE CULTURE see


Technical Questions on the FCC Technician Exam?

Question: What type of technical questions are on the FCC Technician Exam? I am asking because I have been reading the FCC Rules as a study guide for the Technician Exam and I don't want there to be any surprises when I go and take the test.
Answer: If you want to know exactly what to expect from the test, you can read the test questions; they are public. You can get them directly from the source at NCVEC.org, or you can use a web site designed to help you study the test such as HamStudy.org.

The Technician question pool has several sections with technical questions, but they are mainly vocabulary/concepts rather than any sort of, say, calculation.
There are sections on electronic principles and components, which are easy if you have some familiarity with electric circuits, and study enough about RF to know the difference between an inductor and a capacitor in RF circuits.
However, there are several other areas that will require specific study unless you have a background with which you probably wouldn't be asking this question. You need to learn about radio equipment, modes and propagation, and various jargon specific to amateur operation.
Finally, the big area that you didn't mention in your question, which is neither regulatory nor exactly technical, is operating procedures and practices. Unfortunately, there is no good way to get this information without reading the question pool or a study guide; nothing else is going to contain all of the information in one place, because it covers a wide variety of topics and some of the questions can be fairly obscure.
Comment: Thanks for your answer. I do have a little background in electronics, which is why I am looking to get my Tech license. I need to transmit signals from my project that I have been working on for a while and I want to ensure that I am in compliance with big brother, and I don't want to interfere with anyone else's operations, or have them interfere with mine. What is you opinion on AARL's study guide? I am looking into purchasing that to study, I just am not sure if that is the best use of my money. As you have mentioned, it is hard to find all of the information in one place.
Comment: The ARRL study guide is thorough.  It's the best book if you want to learn the concepts as you study to pass the exam.  If you want to learn the material quickly, you're better off with the Gordon West book.  You might consider getting in touch with your local ham club; they'll have lots of advice and maybe they can let you borrow the book for free, or at least take a look at one to see if you want to buy it.
Comment: Also, there are on-line practice tests that help you through the material and the tests.  A good set is located at: http://www.qrz.com/hamtest/?op=start&t=t2014 for the Technician Test and the page for links to all tests is: http://www.qrz.com/hamtest/


have no audio with my nokia model RM 984

Question: Have no Audio with my Nokia model RM 984. While inserting battery  heard audio for a few seconds.HELP. Also turned phone, hoping if I reset internet connection, maybe this might solve the problem. But alas, it did not work. I am desperate. HELP
Comment: Can you rule out a hardware failure?
Answer: Calm-down please. Tell us what happened before we can offer a possible solution.
As @Aulis pointed....

Why did you removed the battery in first place?
Did you dropped it somewhere? (just a blind-guess: liquid inside phone)

In-short: What were you doing with you Lumia 830, just before this happened?

I would suggest you to try a Soft Reset first:

Go to Start Screen. Then Press Volume Down + Power button, until phone vibrates. (can take 10-15 seconds). Wait for it to restart.

Hope this helps!  You are welcome for more trouble-shooting.


every subset of a measurable set is measurable

Question: Is it true that every subset of a measurable set is measurable? for any measure. So if A is a measurable set then, B as a subset of A must be measurable wrt the same measure.
Comment: Since the entire space is measurable, that would mean ...
Answer: Certainly not. The set $[0,1]$ is Lebesgue measurable, but (if we assume the Axiom of Choice) it has non-measurable subsets.
If $A$ is a set of Lebesgue measure $0$, then any subset of $A$ is Lebesgue measurable.
Comment: To expand on the last line - every subset of a set of *measure zero* is measurable if and only if the measure is *complete*.
Answer: No. This hold only for sets of measure $0$ assuming the measure is complete. The whole space itself is always measurable, so it would mean every set is measurable in that space whis not true for $\mathbb R$.
Answer: The answer to that question depends on a choice of the consistent system of axioms in which we prefer to work.
For example, if we consider the question asking  whether every subset of the real axis $R$ is Lebesgue measurable, then we will get the following different  pictures:
Theorem 1 (Vitali(1903)). (ZFC)  There exists a subset of the real axis $R$ which is not measurable in the Lebesgue sense.
Theorem 2 (Mycielski-Swierczkowski(1964)). (ZF+DC+AD) Every subset of the real axis $R$ is measurable in the Lebesgue sense.
Answer: Say $(X,\mathfrak S, \mu)$ is a measure space. Measurability of any subset of a measurable set is not a property of the measure space, but rather of the measurable space $(X,\mathfrak S)$ associated to it, thus, in order to show it is false that every subset of a measurable set is measurable, it is in fact sufficient to show that $\mathfrak S$ is not closed wrt $\subset$. It should be therefore noticed that measurability is independent of the measure.
There are trivial counterexamples, e.g. any set $X$ of more than one point endowed with the trivial $\sigma$-algebra $\mathfrak S\doteq\{\varnothing, X\}$. The singleton constituted by any point $\{x\}$ in $X$ does not belong to $\mathfrak S$, making it a nonmeasurable set.
Many non-trivial counterexamples are also known for relatively well-behaved measurable spaces, such as the Vitali set, which rely on the Axiom of Choice.
As noted above, it is true that, given $(X,\mathfrak S,\mu)$ a measure space and $A\subset X$ any measurable set of measure $0$, every subset $B\subset A$ is measurable if and only if $(X,\mathfrak S,\mu)$ is a complete measure space (this may in fact be taken as a definition of complete measure space, as e.g. here).


Think my fermentation is stuck

Question: I brewed my 5th homebrew this Saturday, an all-grain American stout.  By Sunday I had very minimal bubbling.  Monday there was a bit more but far less than my previous batches.  Today there are none.  I've never had a batch bubble this little.  Typically in 24-48 hours the bubbling is pretty intense.  Not so with this batch.  I rehydrated dry yeast (Nottingham) and pitched at the manufacturers recommended temp.  Should I re-pitch more yeast?  Is my brew bad?
Comment: What are the gravity readings?
Comment: What temp is your beer currently at?
Answer: Bubbles are an inaccurate way to gauge fermentation.  Can you see if the beer is fermenting?  Have you taken a gravity reading?  It's also possible that the temp was on the high side, fermentation finished quickly and you missed it.  Look for physical signs.  And in homebrewing you can almost never go wrong by just waiting longer.
Answer: There could be a leak somewhere that allows the CO2 to escape.
I have a pale and a speciality that is fermenting next to each other; the speciality sounds like a machine gun and the pale has barely made a bubble. I had the same thoughts as you, but I simply opened the fermenter and saw a nice krausen on the beer, so I am happy, but now I know that I have a fermenter that I have to check for leaks.
Leave the beer for at least a week and then take a gravity reading. If it has not dropped at least 50% then you have a problem.
Answer: The other answers here are spot on. I have one thing to add. Danstar Nottingham can be a freaky fast fermenter. A two day ferment is not out of the question for this strain. It might just be done.
I always have Nottingham on hand in case some other strain gets stuck. That stuff is one beast of a yeast.

Think my fermentation is stuck


Translation of "Welcome back!"

Question: In English, if someone has been gone for a while and has recently returned, it's common to greet them by saying, "Welcome back!" (or "Welcome back from your trip!", etc). What is the most natural way to say this in Spanish? Bienvenido de regreso sounds a little awkward to my (non-native) ears. Is that the only option, or is there something more common people would say in these situations?
Answer: In Spain is not usual to use "Welcome back!", at least I do not use it.
In my experience, I have a friend who had gone to Scotland to live four months ago, last week he arrived to Spain and all of us said "¡Bienvenido!".
If I translate "Welcome back!" I would say "¡Bienvenido de nuevo!" interpreting more than translating it, or "¡Bienvenido otra vez!".
I think that expression, at least in Spain, has no translation from English.
Comment: I agree with you; ¡Bienvenido de nuevo! or ¡Bienvenido de regreso! are not common in Colombia either. Just ¡bienvenido! is the more common translation.
Comment: Same in Mexico, just "Bienvenido".
Comment: same in Nicaragua...bienvenido(a)...o tambien se puede usar que "que bueno verte". No he escuchado  el uso de "bienvenido de regreso". Cuando mi amiga de Oklahoma vino de vuelta, la bienvenida fue decirle "que bueno verte", "que bueno regresastes" "Bienvenida de vuelta", o solamente le decian bienvenida.
Comment: The same in cuba
Comment: *Bienvenido de vuelta* is very commmon in Perú, if ou don't want to say just *Bienvenido*
Answer: I would say:

¡Bienvenido!

or

¡Bienvenido de vuelta!

"¡Bienvenido de regreso!" is fine too, I don't know why but I prefer to use "vuelta" instead of "regreso".
Comment: So *bienvenido* by itself works even if the person isn't new to the place you're welcoming them back to (e.g. if they lived in a city for years, left for a few months, and then came back)?
Comment: "¡Bienvenido de regreso!" in Spain is awful. Cacofonico.
Comment: Yes (at least in Chile).
Answer: No, "¡Bienvenido de regreso!" is definitely not correct, as Zhen points out it is a cacophony. In all cases of translation, if you are not trying to convey spoken language (a truly hard task, as you need to know both the source and target dialect pretty well), then you should guide yourself by the use in the written language. In that same venue, "¡Bienvenido de vuelta!" isn't correct either. But, the use of the imperative verb conjugation (one of the subtle uses of the accusative case in the Spanish language), is perfectly legal and will make you sound both warm and educated: "¡Se bienvenido!", "¡Seas bienvenido!"
Answer: Usually, in a return, we would use "Que alegria que regresaras!" (It's a pleasure to have you back) or "Gracias por regresar!" (Thanks for comming back) but there's no language translation exact to Welcome Back! The exclamation point and welcome do refer to happiness about the event being expressed and because of this, I offered happy sentences that could be used in such situations.
Answer: Generalmente en paises de habla hispana no se tendría en cuenta el hecho de que el individuo ha regresado "de nuevo". Si quien pregunta sigue insistiendo en la necesidad de traducir "Welcome back" literalmente, los comentarios anteriores son algunas buenas sugerencias. Sin embargo, este tipo de discrepancias son las que hacen especiales a los idiomas, pues cada uno de ellos percibe la realidad de maneras ligeramente diferentes.
In general, people in Spanish-speaking countries wouldn't take into account the fact that the individual has "come back again." If this thread's poster still wants to translate "welcome back" literary, the above comments are some possible suggestions. However, this kind of discrepancies make languages special, for every language perceives reality in slightly different ways.
Answer: Too long, it's just an idea:

Seas bienvenido una vez más

Translation of "Welcome back!"


How can I get a work visa for US?

Question: I'm a tech engineer and want to work in the US but I am struggling to get a work visa. I don't understand which visas I would be eligible for or how to obtain them.
Comment: Welcome Samiksha. Work permits for the US are never easy but how hard depends on where you are from, how high your education, how much work experience and more details. I will move your question to our brother site for Expatriates, but you should add details like your nationality and your education and experience.
Answer: First of all,  you should have a U.S. or foreign equivalent bachelor degree.
Secondary,you need to find a sponsored employer in the U.S. who will file H1B visa on your behalf.
Once your petition got approved, you will be able to work in the U.S. up to 3 years, even immigrant based on your employment.
Luckily, your employment  type is within STEM(science,technology,engineering, and mathematics) field, you will be more likely to get your visa approved than the others.

How can I get a work visa for US?


What could cause the world to be almost completely submerged in water, naturally or man-made?

Question: I'm trying to build a world that is almost completely water, but I couldn't come up with an explanation for WHY the world was like this. The world has the same gravity and atmosphere of Earth. It also had to have basically the same land structures. What could have happened to this planet to make it this way?
Comment: This planet's 3/4 covered with water, so you're not asking for that much of a difference from what we already know.
Comment: While it isn't a rule, ["Have you thoroughly searched for an answer before asking your question? ... Tell us what you found and why it didn't meet your needs. This demonstrates that you've taken the time to try to help yourself, it saves us from reiterating obvious answers, and above all, it helps you get a more specific and relevant answer!"](https://worldbuilding.stackexchange.com/help/how-to-ask) -- there are models predicting ocean planets and even a [Wikipedia article](https://en.m.wikipedia.org/wiki/Ocean_planet#Formation) explaining how they might form.
Comment: [Open a portal from the bottom of a large body of water on another planet.](https://what-if.xkcd.com/54/)
Comment: Read *Flood* by Stephen Baxter.
Comment: This reminds me of "Water World", with Kevin Costner.
Comment: Have a planet made of softer core material that is flattened by gravity or erosion at a faster pace.  There might be a fragmented ring of dry land around the equator where the civilisation was formed due to the oblate shape of the planet.  Seasonal tides might make the land inundated with floods often maybe?
Comment: Does the OP possibly mean that most of the planet itself is composed mostly of water? Like instead of a crust and mantle there is just water with land somehow on top of or in it? The question is't very clear
Comment: At some point in the distant past people stopped listening to their mothers and start spitting everywhere.
Comment: How hard do you like your science? One of A.E. van Vogt's novels (I forget the name) takes place on a very distant future Earth, which appears to be entirely covered with water except for a couple of little sand bars. It seems that some malicious aliens started a process in the Earth's crust that breaks rock down into silt. People used to call that "Handwavium", but today we might call it by the synonymous term "nanotechnology".
Comment: dump water soluble minerals in the ocean.or freeze the world(it doesnt have to stay frozen) a temporary shift in orbit would do it. that is to say that if glacial action was violent enough, landmasses could be 'dissolved' and gravity would do the rest. of course trouble is, then when you return to a liquid water orbit you have other issues. dont think water worlds can actually be stable.
Answer: The idea of an ocean planet isn't too far-fetched. There are several moons in the Solar System - Enceladus and Europa, for instance - that have subsurface oceans. If the ice covering their surfaces melted, they'd be just what you're looking for. Extrapolating that to a larger, planetary-mass body isn't too hard.
Creating an ocean planet isn't too difficult:

It would likely have formed in the outer reaches of the planetary system (beyond the frost line), where volatiles (think molecules like water and ammonia) are plentiful. These areas are where giant planets form, as well as ice-rich bodies like comets.
The planet would then have migrated inwards, due to interactions with other planets or the protoplanetary disk. If it came close enough to the star, the icy covering it would have developed might melt, forming an ocean surrounding the planet.
Rather than a block of rock and ice, you now have a block of rock and (largely) water.

There are some things to consider, though. The atmosphere will likely be water-heavy; you're not guaranteed a nice mixture of nitrogen and carbon dioxide (followed by oxygen, if life arises to produce it - and all you need is a lot of bacteria!). Ammonia might also be present, a relic of the planet's formation farther out form the Sun. None of this precludes aquatic life, of course.
There are several excellent candidates for ocean planets:

Gliese 1214 b
Kepler-22b
Kepler-62e
Kepler-62f

It's interesting to note that two of these are in the same system, orbiting Kepler-62. Also, if you peruse this list, you'll note that they do run the gamut of Earth-mass planets. If you look at enough ocean planets, you'll almost surely find one with a surface gravity of roughly $g$, 9.8 meters per second squared. Honestly, if you don't mind some rather dull views, life on an ocean planet would be quite manageable for, say, human colonists, given the right atmosphere and the right tech.
Comment: Europa &c wouldn't be almost what the OP is looking for, but quite a bit more.  Europa's ocean (ice & liquid both) is estimated at ~100 km deep: https://en.wikipedia.org/wiki/Europa_(moon)  But the basic principle is sound: the Earthlike planet just had a bit more water in its primordial nebula - just as Mars had rather less water originally, enough to cover about a third of the surface, rather than the ~70% of Earth.
Comment: Couldn't an ocean planet have some pretty spectacular/uncomfortable weather? I would imagine you could get some pretty huge storms if they never ran into a sizeable landmass to disperse energy.
Comment: Apologies if this isn't the place for this, but I have a follow up question: What about a breathable atmosphere? Precluding aquatic life I assume the OP wants to have human characters live on the surface. If the entire planet is ocean what gives off enough air for them to breath? Would a kind of algae be enough?
Comment: @Len [Phytoplankton alone make more than half of the oxygen we breathe](https://news.nationalgeographic.com/news/2004/06/0607_040607_phytoplankton.html), and that still doesn't cover all "[algae](https://en.wikipedia.org/wiki/Algae)" as we refer to them; Yes, oxygen-breathing life would do more than fine on a world entirely covered by water.
Comment: @Len I've made an edit, but the gist of an answer to your question is that yes, you'd only need simple organisms to produce oxygen, if the right gases were already present. Cyanobacteria would suffice; you don't even need something as complex as algae.
Comment: @user3067860 Meteorological activity would depend on temperature and atmospheric composition. Large storms aren't by any means guaranteed on ocean planets.
Answer:
Low tectonic activity This would lead to few if any mountains, and few if any rifts.  The world would be remarkably flat and tidal errosion (I'm assuming an earth-like moon) would pretty much make all land beaches.
Primarily water meteors For the sake of argument, let's assume a very large asteroid made primarily of ice broke apart over the eons and happened to collide with your planet.  The resulting impacts wouldn't tear your planet apart, but it would endow it with an enormous quantity of water.
Really, it could simply "be that way"  In a National Geographic article scientists postulate that the Earth's bounty of water didn't actually come late in its formative years via meteors, but was simply part of the formation process.  In other words, when the dust orbiting Sol condensed into our world, our world's water was a part of it.  (They further postulate that all the inner planets likely had life-sustaining water early in their existence.  Curious!)  Consequently, you don't need a reason other than "because it has water."
Comment: +1 for the third point: "The reason why there's more water is just that... there is more water"
Comment: Keep in mind that the Earth has an [estimated ~1.4 *billion km^3* of water](https://en.wikipedia.org/wiki/Water_distribution_on_Earth); We are already living on a "water world".
Comment: @errantlinguist :-), never said we didn't.  Just answering the OP's question.
Answer: More water emerges from within the planet.

https://www.youtube.com/watch?v=4Dpfy3lFC9c
Massive 'ocean' discovered towards Earth's core

A reservoir of water three times the volume of all the oceans has been
  discovered deep beneath the Earth's surface. The finding could help
  explain where Earth's seas came from.
The water is hidden inside a blue rock called ringwoodite that lies
  700 kilometres underground in the mantle, the layer of hot rock
  between Earth's surface and its core.
The huge size of the reservoir throws new light on the origin of
  Earth's water. Some geologists think water arrived in comets as they
  struck the planet, but the new discovery supports an alternative idea
  that the oceans gradually oozed out of the interior of the early
  Earth.
"It's good evidence the Earth's water came from within," says Steven
  Jacobsen of Northwestern University in Evanston, Illinois. The hidden
  water could also act as a buffer for the oceans on the surface,
  explaining why they have stayed the same size for millions of years.

Some shift occurs - perhaps -  tectonic plates get out of the way, or heating occurs where it previously did not.  Maybe a relatively higher density piece of crust subsides down into this water rich region, displacing the water up.  In any case, the oceans rise and rise a lot as this water emerges.
Having heavy regions of crust subside into this region would let you dispose of mountain peaks that would otherwise be hard to cover.  The peaks go down as the water is pushed up.
Answer: If the Earth was completely smooth, then there would be ~2.6km water covering the entire surface. I guess you can imagine some event which made all the lands sink below sea level and the ocean trenches being filled up. Realistically this is extremely unlikely and has never happened to Earth as far as we know.
Comment: or just wait long enough for erosion to wear down any mountains created by early tectonic activity. Then stop tectonic processes by cooling down the mantle/thickening the crust.
Comment: @ratchetfreak I think, the other way around (first stop tectonics, then wait) works better?
Answer: It is quite possible that Earth will be like this in the far, far, future, and this would just be caused by natural processes. If the earth crust's solid, rocky material that makes up the continents (and therefore land) would be spread evenly, all land would be submerged (jus as ACAC mentioned). It is because the ocean surface is much larger than the land surface on our planet, and the oceans are deeper (on average) than the land is high (on average).
Now, there is just a natural process that spreads the earth crust: over long times (millions of years), rock is not completely solid but flows like a very viscous (slow-moving) liquid. This makes mountains slowly sag under their own weight. This causes mountain ranges to disappear in the course of dozens of millions of years. (Erosion, a different process, caused by chemistry and weather, also helps.) Over even longer stretches of time, this destruction happens to entire continents.
The reason there are still mountains and continents, after 5 billion years of earth history, is that there are also other forces at work. That is the geological activity of earth: radioactive decay keeps the earth core hot. Meanwhile the coldness of the universe as a whole (a consequence of the expansion of the universe) makes the earth surface much colder. The heat flow from core to surface causes powerful convective currents of half molten rock in the earth's mantle, and these currents cause plate tectonics: the drifting of continents, the raising of mountains, and other phenomena of earth's active geology like volcanism. The raising of mountains by active geology compensates for the mountain's natural sagging and erosion.
Now, the heat and the radioactive decay in the earth's core that powers it all, gets weaker and weaker over time. Geologists think the mantle currents and continental drift will stop in billions of years, and earth geology will become inactive. (Source: Plate tectonics just a stage in Earth's life cycle, Simulation shows crust to stop shifting in 5 billion years,
 A window for plate tectonics in terrestrial planet evolution?) Mountains will no longer be raised, but the sagging caused by their weight will continue to destroy them, together with erosion.
I am just unsure if there is enough time for the destruction of the continents to finish before the sun swells up and destroys the entire earth. (Scheduled over 5 to 8 billion years.)
Edit: Wikipedia's Future of the earth predicts: All water will evaporate over a billion years because the sun gradually gets hotter. (The hotter sun is a (somewhat paradoxical) effect of the sun slowly running out of fuel.) Ofcourse, if all water has evaporated, there are no more oceans at all, to cover the land, even if that land is spread out even.
The Wikipedia article also expects plate tectonics to end, but for different reasons: the disappearance of water will stop the lubrication neccessary for active geology.
Edit: Mountains on Mars, volcanos on Venus and craters on the Moon are still present, despite present geologic inactivity, and despite erosion. That's bad for my theory.
Still, I think no mountains and continents will form if there is no active geology (plate tectonics) even in the youth of a planet. Meteor impacts will still cause craters, but erosion can destroy them, as has happened with most craters on Earth.
Comment: Mars and the moon do not actually have much erosion compared to earth. Little wind and water mean only the light stuff is moved.
Answer: Water Under the Crust
It has been theorized that under the Earth's crust lies a vast expanse of water. This body of water lies between the crust and the core, surrounded by a blue mineral called ringwoodite. This water would be capable of filling the Earth's oceans three-times over. If a hole were somehow drilled through the crust (which is nigh impossible), this water, under extreme pressure, would gush to the surface and wouldn't stop until the pressure above and below had achieved homeostasis.
Here's a link to the source http://www.natureworldnews.com/articles/7560/20140613/vast-underwater-ocean-trapped-beneath-earths-crust.htm
Comment: That is a misreading of the linked article. The article itself links to [here](https://www.eurekalert.org/pub_releases/2014-06/nu-nef061114.php) which says that the water is not in liquid form but is in hydrates and hydroxyl groups in rocks, such as the ringwoodite you mention. So you can't just drill a hole, you need some method of chemically unbinding these water-like molecular structures from whatever they are bound to.
Answer: The all the same amount of water can take more or less volume if affected by extra conditions, and occasional change in that balance can raise waters level on planets like Earth. For example: have you seen mountain rivers, with all that whirlpools, boulders and banks? You can scoop up a full glass of water and surprisingly see how its amount decreases to half-a-glass while all the bubbles and turbulences go away.
So, we consider the following:

What if the planet occasionally got something that makes oceans to bubble and have decreasing the water density? (and increasing the waters level) Let say, volcanic gases coming from core cracks, chemical reactions with bottom-born minerals, and staff like that. In addition, such world makes one more challenge: it's much harder to sail such waters as classic ship could deliberately sunk in less-densed water. So, captains could have kind of balloons attached to the ships, like steam-punk style. Or helicopter blades, or jet-packs.
What if there are several enormous whirlpools appeared in the seas? By tectonic activities, or resonance effect of world-size currents combined together, or that trash islands that humanity produced up to the moment, your name it.
Comment: "got something that makes oceans to bubble"  please    be  more precise.   It's    not  really useful when you tell OP to have "something"    that    solves   his   problem.
Comment: @Molot, which precision do you expect here? Extra volcanic cracks may be caused by regular Earth tectonics (hello, Pompeii habitants!). The same volcanic activity could expose new minerals that could react with salt water and produce gases as a side-effect (taking into account high pressure at the bottom, they could increase bubble sizes while floating up, and surrounding waters are already lost an ability to absorb that gases due their extra amount).
Comment: Just describe, in a believable way, how can you  have so high tectonics and  yet  keep  "basically the same land structures"  we have  on Earth, and  the   same  atmosphere.   These are  requirements from  the  question.
Comment: Let wait for OP feedback


PSU direction -up or down fan

Question:
Possible Duplicate:
Does the fan go on the bottom or top of the power supply?

which way should the fan (top-big fan) face when installing a Power supply unit? to the top or down? Does it matter?
Comment: related: http://superuser.com/questions/20127/does-the-fan-go-on-the-bottom-or-top-of-the-power-supply
Answer: It all depends on what airflow you want and how much heat you are dealing with, I guess!
EDIT: Assuming the large fan takes air into the PSU and it vents out the back...
If it's a traditional top-mount PSU position in the case, fan facing into the PC case is the most usual mounting, but if you have a hot PC and not much other ventilation, you will be pulling hot air through your PSU (though if you have a good airflow through the case this won't be too much of a problem as it won't get hotter than the inside of a PSU).
If the case has a small gap above the PSU, or even better a vented area above the PSU, installing it facing up would mean you are drawing cooler air through it.
Most cases that mount the PSU in the bottom that I've seen have a vented area in the base of the case, so the intention is to mount fan-down.  Rather like the Antec P180 my old PC lives in.
If you look at any markings on the back of the PSU, and such aesthetics bother you, mount it so they are upright when the PC is in use! ;^)
Answer: Make sure that the fan is facing inwards (so down if the PSU is mounted at the top of the case) towards the open space of the case and away from the actual casing. The fan will suck hot air from the CPU/case and blow it out of the back of the case.

PSU direction -up or down fan


How is cloud computing differrent from client-server architecture?

Question: I want to know the difference between cloud computing and client server architecture. I mean how is cloud computing different from a website that provides me some services. And what is the meaning of elasticity in terms of cloud computing.
Answer: Cloud is one of those over-used terms that mean different things to different people. However, since you mentioned elasticity, what that means is the ability to scale resources depending on requirements.
Assume for a moment that there is one VM with 64MB of RAM serving a website. There are only a few people using it. Then suddenly, there is a spike in usage (due to the slashdot effect) and that one VM and 64MB of RAM obviously will not cut it.
At this point, there are different strategies to handle this.
One possibility is to dynamically increase the RAM in the VM. Some services provide a burst-able RAM configuration to do this. Another possibility is to dynamically spawn new VMs that are clones of the existing VM and balance the load over them. This is a form of elastic computing.
The advantage of having this elasticity is resource consumption. There is no need to run a VM with a 4GB of RAM all the time if all it needs is 64MB usually. The resources can be re-allocated as and when necessary. New machines can be spawned and shutdown when needed.
Comment: It's very hard to get past the marketing of the "cloud", sybreon provides a good summary of what you can get from "the cloud" you may also want to read: http://rackerhacker.com/2010/08/25/a-nerds-perspective-on-cloud-hosting/ and http://www.saiweb.co.uk/hosting/cloud-hosting-my-views
Answer: In some ways, there is little difference. I see cloud computing as very much a subset of client/server architecture; the only difference is the where and how of the server side of things - it doesn't matter if the server is in my data centre or Amazon's "cloud", it's still client/server architecture.
Answer: think cloud as it floats...yep the services also floats in cloud computing, u can use it when you want it and release it after ur work ends, by this user doesn't need any additional resource available with him to use the service, all resources were provided by the cloud. Main advantage of this uses can get things done from anywhere, with any device.
Client server is the big picture, we can also say cloud computing is a derivative of client server architecture.
Answer: Well, neither of Amazon S3's architecture nor its implementation has yet been made public. As such, it is not available for extension in order to develop the capability of creating private clouds of any size.
There are a few papers on cloud storage architecture topics. You might find them useful. Here is a paper:  CACSS: Towards a Generic Cloud Storage Service
The method by which different technologies can be combined to provide a single excellent performance, highly scalable and reliable cloud storage system is also detailed. This research serves as a knowledge source for inexperienced cloud providers, giving them the capability of swiftly setting up their own cloud storage services.
Answer: If I may attempt at defining cloud from a pseudo-technical perspective:
"A massively scalable computing system providing computing power, networking and storage facilities mostly using consolidated virtual computing and storage methodologies to provide on-demand services, resource pooling and fast provisioning (elasticity)."
Having said that it is obvious that such a system incorporates (actually any serious system must do so) both clusters and client-server services. But also note that the above definitions does not mean that a "cloud" is something super big. Actually a single server with (two) Virtual Machines is a cloud. It is scalable - you can add systems and VM's ad nauseum. it pools resources and has on-demand capabilities. The rest, clusterizing, parallelizing etc etc - are entirely optional which extend capabilities.


What is the lowest pressure at which plants can survive?

Question: What is the lowest pressure at which plants can survive? How the plants behave in a Martian-type atmosphere? Is there any plant that can survive such atmosphere?
Can a lichen grow at Martian pressure?
Comment: Are you referring to total air pressure or partial pressures of oxygen and carbon dioxide?
Comment: Lichen is not a plant though.
Answer: I like your question!
Low surface pressure on Mars (averaging 600 Pa or about 1/170 of Earth's at sea level) is only one difficulty that an organism would have to contend with. In addition, mean surface temperatures are ~210 K (- 63 °C), the surface ultraviolet flux is extremely high (no ozone layer) and an aridity comparable to the Atacama desert. On the plus side, a 95% CO2 atmosphere might promote photosynthesis.
So, higher plants are extremely unlikely to prosper on Mars. Purely in terms of pressure, experiments suggest that at 1/10 Earth atmospheric pressure vascular plant transpiration increases significantly. So much so that they enter into a drought response which often leads to plant death.
However, lichens may be another matter. These are often adapted to low precipitation/pressure environments such as high mountains. Indeed, this article addresses exactly your question (sadly it is not open access). The authors suggest that the lichen Xanthoria elegans experiences no loss in vitality after 22 days exposure to laboratory Mars-like conditions (low pressure, low temperature etc.)!
Having skimmed this article I am frankly amazed (and slightly dubious) at the result. However, it should be noted that they only ran the experiment for 22 days, applied no ionising radiation (to simulate the high UV flux) and make little mention of the precise metabolic state of the lichen. If it has entered into cryptobiosis (cessation of metabolic processes) then it can't exactly be regarded as prospering.

de Vera et al., 2010, Astrobiology, 10, 2, Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions : A Laboratory Study
Answer: Short answer : around 0.47 atm
World's highest plants discovered growing 6 km above sea level
If this Air Pressure Calculator is to be believed that should be 0.47 atm, so for plants 'the lowest pressure at which plants can survive is around 0.47 atm' seems to be your answer.
The air pressure on Mars is 0.00628 atm, so no, plants can't survive on Mars, if they could then we'd certainly find them far above 6 km on mountains on Earth.
Howsoever
It does seem that some of Earth's toughest life could survive on Mars.
The life in that article that (not only) survived (but flourished in) the environment in the chamber (which included the atmospheric pressure of Mars) where Lichens & Cyanobacteria.
Neither of those are plants though.

Cyanobacteria are bacteria.
lichens are a composite organism incorporating a fungus & algae or cyanobacteria.
Algae are plants, but it's in a lichen, not a standalone plant, it's not clear from the article any of those lichens were algal rather than ones with cyanobacteria either.

But (that bit of pedantry aside) it would seem the answer to your second question is yes.
A lichen can grow at Martian pressure.
So there are examples of life that clearly can survive lower pressures than 0.47 atm.
But actual plants don't seem to be among them.
Answer: No, the lowest pressure at which plants can survive is not around 0.47 atm.
It is 0.07 atm or less in the case of ryegrass. And it's the total pressure. Not partial pressure of one of the constituent gases.
See this article:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19860010460.pdf
Answer: ... almost 8 years later..
A newer experiment with a timespan of 1.5 years on another one lichen species suggests that there is

.. a minor resistance potential of the lichen Buellia frigida towards
  Low Earth Orbit and Mars analogue conditions effecting the survival
  potential and the resistance of the symbiotic organism

due to a DNA damage.
Source: "DNA damage of the lichen Buellia frigida after 1.5 years in space using Randomly Amplified Polymorphic DNA (RAPD) technique" Backhaus et al, 2019 Planetary and Space Science
So the answer is possibly "no" until we find some Martian lichen.
Comment: It looks like this study is mostly showing the effects of *radiation exposure* in space rather than *atmospheric pressure*.


How can I determine if some code I want to release as opensource is already licensed or proprietary?

Question: Is there a way to analyze my code I want to release as opensource to see if it is / or has parts that are already licensed or proprietary?
Comment: You can only open source the code-base if you OWN the copyright. Your problem here is that you don't know provenance!.
Comment: Please give us your example scenario, there are too many possibilities to answer this correctly.
Comment: If you are using other code libraries in your project, keep a copy of the license. It will give you a good understanding of what the restrictions are.
Answer: If you do not know where your code came from (you did not write it, or you did not buy or license it), then there is no way for you to know its heritage. As a result, you cannot then open source it.
There is no way that I know of to analyse the code, and determine it's heritage unless you have already pre-analysed the code it may have come from (i.e. you can do a 'diff', but you need the baseline to compare to).
It is important when working with any code (open or not) to keep track of where the code comes from so that you can more easily make these determinations later.
Comment: There are services out there that determine this. Companies who use open source projects in their code under GPL licenses are not attractive candidates for buyouts, so there are services that scan the entire codebase and find pieces of code from the web and reports the license for each individual piece. I'm trying to remember the name of one such service.
Comment: There are tools to search in foss code as @MadaraUchiha points, so even if it is hard to get to know if the code came from foss software, one can think it is proprietary after a thoghtful research
Comment: These comments reinforce my answer, or am I missing something? Those companies can do the diff because they have already "ingested" the baseline open source code (and attribution for the authors)... right?
Comment: I am talking about the tools to search the code if it came from a foss project, not the companies that use and contribute to projects.
Answer: I think you're under a slight misunderstanding of what a license is. A license is merely a grant of permission subject to certain conditions to use something that you otherwise couldn't, in this case under copyright law. Copyright law tells you who make grant that permission (the copyright holder, basically).
So in order to determine if you can grant permission to use the code under an open source license, you need to determine if you hold the copyright(s) to the code, or have been given permission by those who do.
If you wrote the code yourself, not based on someone else's code, and not as part of employment, then you probably own the copyright. As long as you haven't transferred the copyright to someone else (or given them an exclusive license, or otherwise agreed not to release the code), you can release it as open source.
If parts of the code were written by other people, then you probably need their permission to release the code (or to do much anything with it). If you downloaded it from somewhere, the license likely accompanied it, and may give you that permission. You will have to read its terms.
Otherwise, you need to contact all the authors and get each author's permission.
I've heard there are products that are used by large companies to scan their source code automatically, comparing portions against a large corpus of open-source code. They're intended to prevent one of their thousands of employees from copying open-source code into their proprietary apps (as that can give rise to a lot of liability for the company). But for a project with only a few developers, you can hopefully just trace all the code.
Answer: Yes, there are (paid) services such as Black Duck  or Open Logic that will audit your code, and report all of the licensed pieces of software found.
They will even find snippets in your code which are copy/pasted or too closely resemble snippets found on the internet which are shared with an unfavorable license.
Comment: And there are free and open sources tool such as https://github.com/fossology/fossology or https://github.com/nexB/scancode-toolkit
Comment: This does not help with 'borrowed' proprietary code.
Answer: I don't see how just by looking at a piece of code you can figure out what license it uses. You wouldn't see this, for example:
<code>// You'll never know the (license goes here) that I've made super secret from the world
// and is hidden in this code. No one shall ever know, unless they come here of course...
// Mua ha ha ha ha!
</code>
Concerning code, there are two ways that I see to determine the license it uses:

Find the origin of the code:

Understanding the origin of the code will allow you to trace it to its roots, thereby connecting you to the original contributors or organization who wrote it. They would likely have the answer for you.

Look at the documentation

Since documentation is code in english (at least in my eyes it is), there will likely be a mention of it there.


How can I change the modifier to open search results in a new tab in Firefox back to Alt?

Question: I've gotten used to pressing Alt + Enter to open search results in a new tab using the Firefox search bar. With the last update the modifier key changed to Ctrl. How can I change it back to Alt?
Answer: It's also possible to open search in a new tab by using Enter alone. In about:config, right-click and Toggle browser.search.openintab to true.
Answer: vWil led me to the right answer. I had browser.search.openintab set to true, which makes searches open in a new tab when pressing Enter or Ctrl+Enter, but open in the same tab when pressing Alt+Enter.
Now I toggled browser.search.openintab to false, which makes searches open in a new tab when pressing Alt+Enter, but in the same tab when pressing Ctrl+Enter or Enter, which is the behavior I want.


I need some exercises for beginning drum-bass technique

Question: I'd like to find some exercises for beginning double drum-bass.
Do you have any links to suggest?
Comment: Do you mean a kit with 2 bass-drums, or one of those double-mallet kicks? Or that enormous drum from the Sousa band? (Tell a little story of where you've already looked for this info and what misadventures befell you.)
Comment: I have a Roland TD-7 with two bass drums, but it doesn't matter if it's two bass drums or one bass drum with two mallets, the exercices should be pretty much the same.
Answer: There are lots of exercises that you can do to improve your foot technique. Tiger Bill's website has lots of good exercises that you can try if you're looking to improve on double bass technique: http://www.tigerbill.com/drumlessons/buildyourdoublebassdrumchops_part1.htm
One of the best practice exercises I've found is to practice what I'm doing with my hands using my feet. So say for example you're practicing paradiddles with your hands. Play a couple bars doing paradiddles with your hands while playing alternating strokes with your feet, and then switch and do the paradiddles with your feet and the alternating strokes up top. So essentially, something like this:

   1 e + a   2 e + a   3 e + a   4 e + a   1 e + a   2 e + a   3 e + a   4 e + a
H: R L R R | L R L L | R L R R | L R L L | R L R L | R L R L | R L R L | R L R L
F: R L R L | R L R L | R L R L | R L R L | R L R R | L R L L | R L R R | L R L L

If you're not used to playing multiple patterns at the same time between your hands and your feet, this can be a really challenging exercise! Do this with any pattern you can imagine and you'll have loads of exercises to play around with. Another thing to try which is surprisingly difficult is leading everything with your left foot. Try starting the pattern above with the left foot instead of the right (if you're a right-handed/footed player). It feels totally different, and is an area really worth exploring. It really opens up a lot of possibilities that aren't there when you lead with your right. Having the ability to play the hi-hat on the beat with the kick drum opens up a lot of avenues for neat splashes and ways to sub-divide time.
As Eimantas said, definitely practice with a metronome. If you're just trying to blaze through chops, having a metronome handy is vital. I can't tell you the number of times I thought I was solid on some patterns only to find out that my time fluctuates terribly when I sit down with the metronome. Don't get too caught up in timing though... you don't want to ruin the natural feel of the music!
I hope this helped a little bit on your quest to find some good exercises. Have fun!
Answer: Basically, whatever goes for your leading foot, should go for the other.
We're talking about technique, control, building up muscles but also balance. With only one kick drum, you get a lot of support from your other foot usually resting on the floor. With double bass drumming, if we're talking about anything faster or more complicated, both of your feet/legs are in action. This affects your balance. Balance is a very important thing here, yet often overlooked.
Learn the basics. Play the usual things just leading with the left foot. Then depending on what you want to learn, look for exercises. Few good places to start with:

Virgil Donati: Double Bass Freedom (book)
Colin Bailey: Bass Drum Control (book)
George Kollias: 16 week speed & control exercise (pages 1, 2, 3, 4, 5, 6)
Derek Roddy: Endurance exercise (YouTube)
Derek Roddy: Weak Foot Buster (YouTube)

Just remember, it's all about what you want to achieve, but one of the main things is that you're only as strong as your weaker side. Whatever goes for the right foot, goes for the left.
Answer: From my experience, best exercise is just sit down, concentrate, turn on the metronome (or the song, no matter what you prefer) and start practising, firstly get comfortable with normal tempos like 16th notes on 80-90 BPM and the move up, this takes time to build regular feet speed and consistency. After that you can play paradiddles with your feet as you do with your hands, to improve your doubles and so on, continiue on playing triplets and so on to master all this stuff. Theres no secret technique in double bass playinh
Answer: I think you should search for methods like this Joe Franco Double Bass. It's a good way to pratice !!


What is the purpose of plastic engine covers?

Question: I have a 2010 Toyota Corolla. What is the purpose of the large plastic cover that stretches over my valve cover? Does it have a particular function? Are they just for looks? Or are they designed  by the engineers to protect wiring? I believe its called an engine cover. (I bought a car that was missing this piece and I need to know if its critical)
Comment: A law was passed, I believe in the EU, that fixed a percentage of material used to build a car that was recycled or could be recycled, an engine cover never needed previously or battery cover made of recycled plastic was added to reach to the desired percentage. And then the manufacturers looked to injection mould everything else. Just had to last till the warranty expired.
Entirely new and largely pointless components were added to cars to meet an arbitrary target set with good intentions.
Answer: I believe the most common use is noise reduction. As engines got smaller they rev'd higher. The mufflers got moved to the back of the car. No more engine exhaust roar. The result is engine buzz,noise,clacks etc. The cover muffles the injector clicks,belt noise etc. It also just looks cooler to see Vortec, Turbo,SFI .
Comment: Interesting point, I hadn't thought of that. These covers do seem to cover more area that would be needed for just wire guidance and protection.
Comment: Remove one and notice how much louder the engine noise is. Also it is atypical for manufacturers to spend money for a WOW factor that is under the hood thus mostly unseen.
Comment: I agree with the 'looking cooler' reason, but I've never heard of 'noise reduction' as a reason to have one. Do you have any sources or references on the sound reduction from a plastic cover?
Comment: Yes, this is true particularly on diesel engines.  Running my 2002 TDI without the plastic engine cover in place makes it noticeably louder.  The turbocharger spool in particular (fromthe intake side) is especially noticeable when the cover isn't on.  Which is why the cover lives in my garage now.
Comment: Plastic is a really good noise insulator; I believe it's part of the reason valve covers are starting to be made out of plastic these days instead of metal. Some manufacturers also put insulation on the bottom of the engine covers to further quiet things down. Offhand I remember seeing this on an 04 Volvo XC90 and 06 Toyota Camry, but not on an 01 Nissan Pathfinder, FWIW.
Answer: OP, Here's an example of a plastic engine cover on my 2001 VW Jetta VR6:

I can't speak for your car in particular (unless you specify what it is), but in my case it has a number of non-critical functions:

Aesthetics. This looks far nicer than seeing a bunch of exhaust headers (stock ones are never pretty), oil seepage on my valve cover, fuel injection and other wiring, etc.
Routing of spark plug wires. It keeps them organized and away from any hot engine components that would melt or deteriorate them.
Keeping fluids below the cover. In a car with 150k+ miles, I usually see more oil splatter and coolant being thrown around, up on the hood, etc. If I were to take my cover off, I'm sure I'd find some oil, grease and/or dried coolant under it.

Now, if I were to remove it, I wouldn't be too concerned except for my longer than necessary spark plug wires that I'd zip tie out of the way. However, it does look nice, so if you care about that sort of thing, buy a replacement.
Comment: +1 for aesthetics and keeping fluids from getting everywhere. Not sure routing spark plug wires is a main function - not many do that like the VR6 cover, most hide them under the cover :-)
Comment: Good info, I just looked and my vehicle (2010 Corolla) routes the spark plug wires underneath were the cover would be located. So it sounds like mine is more for looks. Are they called 'engine covers' on the market?
Comment: That's all I've heard them called, and what they're referred to on forums, so I'd have to say yes.
Comment: @DavidWalz, it would be a good idea to add your specific car information to the original question.  Right now, that info is hidden here in the comments.
Comment: @Ehryk, don't you have the air filter inside the cover also?
Another reason is that it reduces the engine noise!
Comment: @EvrenYurtesen No, my air filter is in the fender on the other end of the red pipe. I'm not sure the noise reduction is very noticeable, but that possible on some cars.
Comment: @Ehryk I have 2002 vw golf mk4 1.6l 16v with BCB engine and it has the filter in there :) I also don't have the hood isolation which you seem to have, perhaps they thought the petrol engine gets hot enough :p
Answer: I have a VW Jetta 1.8T. The factory service manual produced by Bentley (for Volkswagen) specifically calls this component the upper sound absorber panel. To an extent, these are eye candy, but their primary function is for sound dampening.
That being said, I know many people remove them when they are displaying aftermarket components, or keep their valve cover looking immaculate. I had a valve cover gasket leak up until recently, so my sound absorber is best left in place :)
Answer: The covers reduce engine noise and protect the engine from dust, debris, etc, while adding a cleaner look to the engine bay.
Comment: In my experience, they simply trap more dust and grease.
Answer: the "insulation" on the underside of a hood is not for noise, its a fire blanket. Its supposed to fall down on top of the engine fire as the plastic tabs holding it in place melt. Hood paint peeling is not from engine heat, its from sun damage and neglect of car. The engine cover is entirely there for looks, no other reason. cars ran great without them for 100 years. The first thing i do is remove mine and store it. It only gets in the way and hides leaks, holds heat into engine compartment, etc...
for the guy who suggested it stay in place to keep fluids from splashing around....lol...you may want to actually be able to see those leaks early, and fix then....not use a cover to hide them?  Noise reduction? not likely. My v8 nissan cover reduces no noise at all.  They are for looks. probably one company started it and the others followed to not lose a sale to a manufacture with a "cleaner" looking engine.
Comment: Your assumption for looks is the only answer that passes the sniff test.  And you beat me to the punch about the guy who uses his engine cover to hide mechanical failures (what a moron!).
Comment: yes, i agree !!
Answer: I assumed they were for noise reduction, but I haven't noticed much difference with mine off. Since its usually warm to hot where I live I would prefer to have some airflow over the upper intake components, even if it's a small %. Of course when the weather starts to cool again I'll put it back on to make sure the engine warms fast, so as not to get a mil light for engine temp to low. Also its convenient when you working on problems to not have it on.
Answer: How about saveing money. For the mechanic working on your car...20 minutes to remove and replace those stupid and useless eye candy plastic panels before he even fixes what's wrong is costing you money. 90 bucks an hour. I want to see leaks and problems. Take them off.
Answer: The covers usually help with noise and heat.  Notice how newer cars aren't burning the paint off their hoods like cars from the mid 1980's.  But if you  take it off, you get more air cooling on the top of the engine.  Cover on: damaged wire loom.  Cover off: cleaner engine.
Answer: I have a 2018 Jeep Wrangler with a 2.0 Turbo. The engine cover is factory labelled as "engine aesthetic cover".
Answer: For your car, the covers do offer some protection to the components under them but you could theoretically remove the plastics without hurting your longevity. Engine noise will be more noticeable. In some cases it can be a lot more noticeable. At your drivers side front corner, one of the covers has an air scoop that directs fresh outside air to your air box. Removing that one might cause a slight reduction in performance but not necessarily longevity. Also, when the time comes to sell the car any of the engine compartment plastics you removed will be counted as missing parts and that can be a deal breaker. In my professional opinion, leave them on and replace any missing hardware. Most of the parts in your car are there for a reason.
Answer: The purpose of the plastic covers is to clean up the appearance of the engine bay; pull them off, and you will quickly see the maze of wire harnesses that connect injectors, ignition, and an array of sensors = Tha mo-dar shuurz purdeee thar boayy
Under hood insulation, while its true purpose is controversial, is listed as "Thermal acoustic liner" by most suppliers. Many performance cars do not use a liner, as they are not concerned with noise; such as Dodge Challenger R/T Shaker model.
Also, the "Thermal protection" will actually keep heat from escaping the engine compartment as easily, as heat remains trapped underhood; much like if you put grandmas meatloaf in foil and then wrap it in a towel, OR if you have ever been skiing, you bundle up to keep your body heat in, to keep from getting frostbite.
"Heat damage" to paint is unlikely to occur on todays automotive finishes, as they are much more durable than paint from thirty or forty years ago, when it was common for paint to fail and result in rust within just a few years.
If your car was made with a underhood pad, you can remove it to increase the mechanical sound, especially air intake sound, without causing any harm.
Answer: The main concern for me is stopping mice chewing the plastic on motor wires, pipes and the fuel pump ( had to replace that twice). So when I change my car an engine cover is a necessity!
Comment: So you don't have mice that can climb up into the engine from below?
Answer: Take if off. Engine runs cooler without the cover so your engine will be more efficient and run better giving better performance and better mpg. I know because I have run my motor with the cover on and off. Engine runs so much better without that lump of plastic restricting air-flow over the engine. Fact.
Comment: The cover only sits above the engine, not all around the engine. That means the difference in airflow is small, airflow is only restricted near the valve cover. Also, engine temperature is regulated by the cooling system, more airflow would be compensated for by the thermostat, keeping the engine internals at the same temperature with or without covers.
Comment: While I generally tend to agree with your assertion, how does this in any way answer the question of what the "plastic engine cover" is for? Please read the [help section](http://mechanics.stackexchange.com/help/how-to-answer) on how to answer questions.
Answer: The primary function of the Engine bay cover is to absorb Heat.
It reduces the amount of heat that goes on to your bonnet.
The improvement of mpg, I'm not so sure.
The primary function of the Engine bay cover is neither to absorb noise nor to make the bay look slick.
But to absorb heat.
The material used is plastic, plane plastic does not absorb sound, rather, the 'foam' on the inner side of your bonnet is used to absorb sound.
Comment: Plastic is not a great heat shield. The parts that really need it (turbocharger, for example) have metal heat shields.
Comment: Do you happen to have any citation to back that up?
Answer: A little piece of plastic isn't going to even touch the volume level of an engine. It's literally just like the engines little plastic hat. As motors were produced in the beginning, they tried hard to keep them aesthetically pleasing. That took a bit of engineering to build the motor they wanted, and still make it look smooth and sexy. It also made it hard to work on, in that the cables and components had to be hidden out of sight, either to the side of, or below the engine. With the plastic cover they made it so that an unknowing customer could look under the hood, love how pretty it was, and buy the car. Of course it helps at car shows etc. too. If you work a lot under the hood of your car, you could leave it off,especially if it's past 200,000 miles, cause you'll be taking it off a lot! It'll also help to see leaks or issues easier. However, if you're proud of your car, you may want to leave it on, because when you pop the hood, it looks better. As far as airflow goes, your car is built with a cooling system that takes care of any heating issues. It still gets plenty of air and coolant flow. If there are spark plug cables or anything that runs along the top or is attached to it, you probably want to keep it on to keep those things in place out safe. As for your question, it's hard to know it's necessity without knowing the car and the piece that came off.
Answer: I had problem with my friends 2007 camry. All the ignition coil connector broke and disintegrate (cracked). I was suspecting the cause of the damage connectors due the plastic cover on top of the valve cover. With this plastic cover heat is much higher resulting to the brittleness of the connects. So i think its better to remove them to have good circulation of air on the upper part of the cylinder head.


Adding 3d animations in a video

Question: For a project we need 3d animations to start unfolding whilst a person is walking. The video camera will be moving. Using After effects, achieve such a thing?
Also what is this called? So I can also continue my search on google.
Thanks!
Comment: I'm honestly not sure what you are asking here.  What do you mean that you need the animation to start unfolding?  What is unfolding?
Answer: The technique you're looking for is called 3D match moving, and AE is definitely capable of pulling this off for simple/short shots, but you'll need to use it in conjunction with a 3d package like blender, maya, max, c4d, etc.  Basically, you use AE's Effect->Perspective->3d Camera Tracker to extract 3d information about your physical camera's spatial orientation, and use this data to animate a camera in your 3d package.  Render your 3D animations (with separate passes for whatever info you'll need to recomp, shadows, lights, AO, reflections, alphas, etc), and then composite them with the original footage back in After Effects.  Keep in mind, this is a VERY simplistic overview of a VERY difficult process.  For more advanced tracking, you might want to look into programs like Boujou, PFTrack, or Autodesk MatchMover.
Answer: You will need motion tracking at a minimum if the camera is moving during the shot and you want to composite a 3d animation.  It will need to be able to do 3d motion tracking, which is the hardest to do.  I believe that Mocha (which comes with recent versions of After Effects) can handle this passably enough for a simple project.  I'm not entirely sure what you are trying to do with the animation though based on how you phrased the question.
Answer: After Effects CC comes with Cinema 4D Lite, so if you're on the Adobe cloud, you're in luck. (CC is the successor to CS6 and was released this week)
There are many other programs that can accomplish this, (see other answers), but you'll need particular expertise in 3D and compositing (match moving) to accomplish it. There are tutorials floating around the net, but they are program specific...
You could also build something in After Effects 3D layers, but I wouldn't recommend it unless it is really simple boxes/planes.
If you're new to 3D, I'd suggest getting into Cinema 4D Lite as it looks like there is a lot of effort by the Maxon and Adobe teams making the match-moving and import processes really easy.

Adding 3d animations in a video