I accidentally refrigerated my lens for a month. Should I be worried?

Question: When preparing for a hike, I ended up putting my whole backpack in the fridge to cool the water in the Camelbak inside of it. The hike was canceled, and I'm the kind of guy that doesn't really care that there's a backpack in my fridge for a month. Only now have I realized that I had my Sigma 35mm f/1.4 in it. I have removed it from the fridge. My backpack is no worse for wear, but I worry the lens might be damaged. Should I be concerned? The fridge is 43° F (6° C).
Comment: The real shame here is that a 35mm f1.4 went unused for a month!
Comment: Thats even above freezing point, it would be very strange if a lens won't be able to withstand that, but the datasheet for it will list storage and operation temperature ranges
Comment: Don't try to move the ring until it gets well to room temp as the greases on low temp can get rigid and may make some damage. Leave it out for a day. The other concern is condensation, but that is the second step to handle, may take a bit more to wait.
Comment: Buy some packs of desiccant - seal the desiccant and lens in a plastic bag / ziplock bag for a bit as it warms up.  I also recommend this when you are returning to your A/C after photographing outside in humid air.
Comment: @Sean not really...small backpack (Camelbak MULE) and I lived alone so my fridge was pretty bare
Comment: If you bag it while in the freezer, you don't need a desiccant as there air is cold and dry.  Just like coming inside in the winter, simply bag it first before going to the warm environment.
Comment: You must have a gargantuan fridge if you didn't mind having a hiking backpack taking up space in it for a whole month!
Answer: Storing the lens in the refrigerator for a month or even indefinitely at 43° will not harm it in any way. What could potentially damage it is removing it from that environment without taking adequate precautions.
Any time you move your camera or lens from a cold environment, such as your refrigerator, to a warmer one you should be sure to place it in a container of some kind so that the temperature change is gradual enough that moisture in the warmer air does not condense on or, more importantly, inside the lens. This can be as simple as a zip lock bag or a camera case or the backpack it was stored in when it was in the refrigerator. If you do have moisture condense inside the lens it will usually leave water spots behind. Moisture can also promote the formation of fungus inside the lens. If the moisture is extensive enough, it can even cause havoc with the electronics of the lens.
This question and the answers submitted cover how to prevent condensation when going from cold air to moist hot air:   What precautions should I take when taking a camera into humid conditions?
After the fact, you need to dry it out as best you can. See How do I dry water condensation off my camera?
Answer: I wouldn't be too worried. Many cameras are rated for use in temperatures as low as 0 degrees Celsius and some pro bodies even lower. Lenses tend to be specified in the same temperature range. As for this particular lens I couldn't find the storage and operation temperatures unfortunately. However I own many similar Sigma lenses and live in Sweden where I use them during the winters and never had any problems with the cold weather (it can be a lot colder here than in your fridge).
Your lens stayed in the fridge for a month but as the temperature there isn't below the freezing point of water (which could otherwise be a problem if condensed water freezes inside the lens) I don't think there's any danger.
Did you remove the lens from the fridge by placing it in a sealed bag? This prevents water to condense on the very cold lens elements while the lens is heating up too room temperature. If you didn't there is a change that water ended up on the lens surfaces within the lens and this can promote fungi growth. Inspect the lens surfaces and if there are spots inside the lens that don't go away consider taking it to a service center for cleaning.
I would continue to use the lens as usual and if there has been any damage time will tell. Of course malfunctioning lenses may electrically damage camera bodies, but I'd imagine that risk is slim indeed and would not worry about that either.
Answer: Keeping a lens at 43°F indefinitely does no harm.  The only issue for the camera as a whole might be the batteries, although 43°F is still pretty warm, so even those should be unscathed.
The real danger is when you remove the camera from the fridge.  It will be colder than the surroundings, so moisture in the air will condense on it.  Even that is clean (distilled) water, and as long as it doesn't pool shouldn't cause any long term effects after the camera has warmed and the coating of condensation has evaporated.
The thing to do is to remove the whole backpack from the fridge without opening it.  Put it in the corner of the sofa, throw some towels over it, go to work, and when you come back around 8 hours later everything will be fine and ready to use normally.  The point of the sofa and towels is to insulate the backpack so that the temperature of the camera inside changes only slowly.  The point of not opening the backpack is to keep condensation from happening on the camera directly.  Condensation, if any due to the slow warming, will happen on the outside of the backpack where it won't do any harm.  8 hours should be enough for the backpack and its contents to slowly warm to room temperature, and for whatever condensation that may have formed early on to evaporate.
Comment: You are correct that any condensation is pure water. But any dust present in the air will stick to the condensation much more readily than would stick to a dry surface, and be much harder to remove. Condensation inside the lens tends to dry much slower than external moisture and can cause rust in the electrical components. After photographing an eclipse on a cool, very humid night the resulting rust inside the lens disabled AF for a decent Sigma 70-300 lens.
Answer: 43°F is not a problem as such.  The problem with a fridge, however, is that it feeds air from a quite warmer room likely to contain more humidity than sustainable at fridge temperatures.  You state "I'm the kind of guy that doesn't really care that there's a backpack in my fridge for a month" but it makes quite a difference whether the fridge stays shut all that while or whether you get to see the backpack all the time because of opening and closing the door.  If it's the latter, the lens had a lot more opportunity to gather condensing humidity.  A sort-of mitigating factor is that it would have to pass through the backpack first.  That's sort-of reassuring because the backpack material tends to be a better breeding ground for fungus than the lens is on its own.
So there a number of variables in question here, and several can make a difference or not, to the degree that you are likely better off asking your lens rather than StackExchange whether you have grounds to be worried.  Either way, there is not a whole lot you can do.  Packing the lens with desiccant has been mentioned: this will halt any prospective bad processes but not revert whatever they might have done so far.


Identifying non-human voice noise in EQ

Question: Are there bands in EQ that can be safely quashed that are outside of human voice. Thinking that if noise is not human noise it must be room/background noise.
Answer: You could definitely lower the volume of all frequencies outside human vocal range, and this will help remove low and high frequency noise.
This will do nothing for noise within the human vocal range though, so you need to be aware that while this sort of filtering will help reduce noise, it is limited.
If you do have a specific frequency noise source within the human range, you could drop that frequency using a tight Q filter - this will affect and vocal elements on that frequency as well.
Answer: Note that due to formants, the harmonics of the human voice are much more complex than just the fundamentals + consonant sounds.  It is true that some amount of highpass filtering can get rid of rumble.  Another strategy for reducing perceived noise is to use a side-chain gate that opens when it detects signals that sound human.  When the gate opens, the noise will be present, but it will likely be masked by all the other sounds of the human speech.  When the gate closes, the noise is attenuated, preventing one from fixating too much on what a terrible job the audio team did in the first place by not having appropriate microphones, not placing them appropriately, and/or not recording in a properly treated acoustic environment.
Answer: You can use an equalizer to lower the noise "around" some voice such as dialog, but only to a certain extent.
In some cases equalizing or equalizing too much "around" the vocal leads to an unnatural tonal balance and unnatural voice (this happens e.g. if one removes "room noise" that one thinks is useless, when in fact it's what makes the recording sound natural), even if the other sounds sounded like "noise". That is, even if equalizing made the voice more clear, then overall recording may become unnatural sounding and then you've got another problem.
If it's a vocal that's going into a mix (i.e. there will be other sounds mixed with it), then the noise can be buried by the other sounds that are mixed into it and then the equalization may be redundant or behave differently.

Identifying non-human voice noise in EQ


Testing for nitrogen after applying blood meal?

Question: In preparation for refreshing a garden box for a winter season, I tested for nutrients and found it was very low in nitrogen.  I added more soil and amendment (for other reasons -- neither has many nutrients) as well as blood meal (to add nitrogen).  If I were to test it again for nitrogen, should I expect it to be improved?  I did test again and it showed almost no nitrogen -- much less than before.  But is that just because the nitrogen in the blood meal takes time to become available?  Or could it be I've done something wrong?
Answer: Blood meal is not a quick  fix, it's a slow release product   https://plantcaretoday.com/blood-meal-fertilizer.html, unlike some other proprietary chemical (as opposed to organic/natural) fertilizers, so testing the level is probably not going to be useful because it won't change much. There are other variables which might explain why the nitrogen level fell after application; the time gap between application of whatever other amendments you made might be a factor, as well as precisely what other materials you added. For instance, if you added some composted material which contained fresh woody pieces, and didn't retest for a couple of weeks to a month, the woody material will take up nitrogen as part of the decomposition process. Equally, other partially composted materials may take up some nitrogen (depending on composition) as they break down. High rainfall will also wash out some nutrients such as nitrogen.


How can I clear the "crawl errors" of Google webmaster tools?

Question: How can I clear the "crawl errors" of Google webmaster tools? On my webmaster tools page, there are some "Not found" crawl errors dating back two years which I cleared up a long time ago, but they are still hanging around on webmaster tools. I thought they would go away naturally once the mistaken links were fixed, but they don't seem to. Is there any way to clear old crawl errors manually?
Comment: I too am having this error, although mine date back as far as 2 years. And have not found a solution.
Comment: hey like i put ma site.. n crawl found 25 errors 404 but wat link it shows to me when i am opening it they are working well but why  it says itz a error  :S plzz tell me how to fix it
Answer: You can resolve 404 errors (and get them to stop appearing in Webmaster Tools) by implementing a 301 redirect from the old URI to a valid URI - if the links were incorrect to begin with, go ahead and redirect them to the content they were supposed to link to.
Comment: The point is that the page they say links to the page no longer links to it.
Comment: @Kinopiko - It's still a good idea to alert Googlebot to the change with a 301 redirect.
Answer: You can only "clear" the errors by fixing them. If the pages return 404 Not Found then that is still an error. It's likely that the page is being linked from somewhere else on the web.
If there is an equivalent page, add a 301 redirect to that page and the error will disappear in a few weeks.
Look at where the 404 link comes from and see if you are able to fix it. For example if it's from a blog post, the site owner may be interested in fixing it. If it's from a forum you are probably out of luck.
EDIT based on comment: if the page no longer links to you, check that google's cache of the page isn't an old one. If the link was only recently removed it will take several weeks for GWT to update.
Answer: I've  done  301 redirects  when  you  click  now  on the   404 page  it  goes  to  where  it  should  but the  error  won't  clear  from  webmaster  tools  and  its  been  more  than  a  month  almost  2  ,  additionally    a bunch  of  non existing  pages   that  where  at  some  point  on the   sitemap  but  have  since  been  removed  and   the  sitemap rebuilt  still  show  as  404 ,  this  pages  BTW   are  not  referenced on  any  external  URL and  no  longer  exist  on  the  site  coding   or  sitemaps  , sitemap crawling change  time  where    updated  to .  still  this  errors  remain  like  they  are  stuck  on   Google  cache  the  pages  BTW  they are  not indexed  on  Google   the  wrong  URLs  and  the  non existing   .
so  i've  search and  search  and   i  found  no  answer  on  how  to   get   Google  to clear  this  pages   that don't  exixt  and are  not linked  anywhere  anymore
Answer: Steps to fix 404 not found webmaster tools errors (I assume you already know how to access .htaccess file of your wordpress blog):

First and very crucial, backup your .htaccess file, by downloading it and save it in your hard drive.
Once you done the step (1) above, go to your Google webmaster tools, copy the URL which causes 404 not found webmaster tools errors one by one, if you have many.

Copy it in notepad, that's the easiest method.

Go back to your .htaccess file, add this code:

redirect 301 /2010/02/13/change-homelink-to-your-own-created-page http://www.timesnewstoday.com/change-homelink-to-your-own-created-page
The code above should be in one line. That's one of my example post that i did redirect.
Replace my URL address with yours.
What that code will do, is redirected the 404 not found webmaster tools errors URL old page to the new one.


Last combinatorics question

Question: In how many different ways can we place 8 identical rooks on a chess board so that no two of them attack each other?
Comment: Lol at your title.
Answer: HINT: The chessboard has $8$ rows; number them $1$ through $8$. Let the rook in Row $1$ be in Column $c_1$, the rook in Row $2$ in Column $c_2$, and so on. The numbers $c_1,\dots,c_8$ must all be different and can be any arrangement of the $8$ column numbers.
Answer: Hint:  Think about how many ways you can place the first rook on the board, then the second one, the third one, and so on.  Then think about how many ways you can place them (in total) if the rooks were distinguishable.
That should get you going.
Answer: Since rook in the $(i,j)$-th position can attack row $i$ and column $j$, for $i,j =  1,2,\dots,8$, it is equivalent to having the rooks on the diagonal. Since there are $8$ diagonal positions, the problem then becomes the number of ways of arranging the $8$ rooks, i.e. $8!$
Answer: You can only have one rook per column. Therefore for each column there is one rook. Call the rook in the first column $R_1$ in the second $R_2$ and so on. Therefore you must assign a row from $1$ to $8$ to each $R$ without repeating. There are $8!$ Ways to do so which is the same as $40320$.

Last combinatorics question


Is this old question about git not off-topic?

Question: I stumbled upon this question How do I edit git's history to correct an incorrect email address/name from google and was surprised to find it here on SF.
I did notice it's very old (5 years) so just out of curiosity, was it not off-topic then or is it not off-topic even now? If it is, should it be migrated to SO?
Comment: These days I generally send people who ask git questions back to SO where they will get a better audience.
Answer: I'm not sure how that escaped notice for so long, why it got so many upvotes, or why it was posted here in the first place. It's very obviously a question for Stack Overflow, and so I've closed it. (Questions older than 60 days can't be migrated.)
Comment: @kasperd Locking it would prevent anyone from editing the question or the answers. Since this has had recent edits, I don't think it _yet_ needs to be locked. The most important part is making the point that git usage questions are generally a better fit elsewhere.
Comment: The huge number of up-votes is almost certainly that they were slowly added over the last 5 years by people who found it via Google long after it fell off the front page and voted up because it was what they Googled for. He only got a handful of up votes when it was first posted; and IIRC that was long enough ago that the current level of hostility to lower skill level questions wasn't nearly as strong here as it is today.
Comment: @DanNeely The problem with the question isn't the skill or lack thereof of the person asking, it is the subject matter. While system administrators do occasionally use git, this particular task is one that is almost always done by developers in the process of managing their source code. Thus it is a better fit for [so].
Comment: Wouldn't locked as a historically significant question have been more appropriate than closed as off-topic?


Is watermarking worth it?

Question: I've recently become aware that one of my photos has been used by a national newspaper beyond its licensing terms (cc-by-sa-2.5, used without the required credit), and whilst I can pursue them for some compensation, I was wondering about how effective watermarking is as a deterrent for the future? After all, if somebody has little regard for copyright, what's to stop them cropping a watermark out?
Comment: Also, don't forget to add copyright info to the EXIF.
Comment: Here is an example of mine on how a watermark can be tasteful. As to the question of whether or not it helps, I agree with Reid.
http://cgm.technion.ac.il/Computer-Graphics-Multimedia/Undergraduate-Projects/archive/2006/Poisson_Image/MVP_Site/pie_sample2.html
Comment: @danny I always do...
Comment: [Click for a good rundown by Trey Ratcliff](https://plus.google.com/+TreyRatcliff/posts/UTKKo5Su6Rj)
Answer: I think adding your copyright info to the meta of the images is more important than a watermark. I understand both sides of the "to watermark, or not to watermark" discussion, and both have valid points.
But more important is that you should always added copyright and contact info to your file's meta data. There's really no excuse not to - it doesn't detract from the image at all, and it's fairly easy to do in a batch process with Photoshop, Bridge, or even Lightroom.
Of course, if you don't mind people using your images, well then don't bother. But if you do, there's no excuse for not having your copyright stuff in the file meta.
I'm not really sure, but I think that might even go further in a litigated case over copyright infringement, if it can be shown the violator's file has the meta there and they ignored it, that's pretty hard to fight from their side.
Comment: I guess the only caveat is that they can simply copy the pixel data and none of that meta information comes with it.
Comment: @Nick Bedford - or, use the original file while editing the meta themselves.
Comment: Good mention of contact information -- you don't know how the editor is going to get your picture (could be an FWD: FWD: FWD: type email), so including a way for the company to find you helps honest people to be able to pay/credit you.
Comment: Another point -- the more complicated your licensing terms are (how many newspaper people are going to know what cc-by-sa-2.5 is?) the easier it is for people to misunderstand the terms. I think what the creative commons people are trying to do is nice, but it still isn't as clear as "Copyright 2012, Rowland Shaw -- (xxx) xxx-xxxx"
Answer: I think probably they do deter misuse. Psychologically, using an plain image without credit is a different beast than using one with COPYRIGHT ROLAND SHAW staring you in the face (or taking active steps to remove the watermark). Also, there's more opportunities for people in the chain who might not otherwise think of it to say "hey, do we have permission for that image?", and I think there's a good chance the situation you describe is due to ignorance rather than active malice ("all images on the Internet are free, aren't they?"). And if there's no watermark, it's easier to rationalize, e.g. "we'll talk to him later" and then forget about it.
On the other hand, I've never seen a watermark that didn't look awful, detracting significantly from the image. Perhaps it can be done "tastefully and artfully", but I've never seen it. So it's a tradeoff.
Comment: +1 for mentioning awfulness. Personally I prefer my pictures without the self-abuse. License fees can always be negotiated later.
Comment: I tend to agree about working out license fees later. The thing about a watermark is that if it IS made tasteful, it usually also means it is easy to remove (anyone loathing PS5's content-aware fill, yet?)  Watermarks really only work as a deterrent when they are glaringly blatant...which mitigates 99.9% of their value in 99% of cases where they are needed.
Comment: For a large percentage of the population, an easy to remove watermark is an effective deterrent.  However, it's the small percentage that it doesn't deter whom use it in the worst ways.
Answer: I use a D90, and i took some advice from Ken Rockwell, and put a copyright notice in the camera's comment field, which is stamped into the EXIF data of every image.
Comment: This works assuming you never happen to share the body with anybody else. Not a problem for most people, but it's something to think about.
Answer: I am generally of the opinion that people with no respect for copyright will continue to ignore/subvert any deterrents that you use. If they can see it, they can steal it.
Watermarking, however, can be used as a marketing tool, and as long as it does not detract from the image itself it is completely valid.
As far as tracking down usage, there are lots of other tools, including Exif data or image tracking services like Digimarc, that you can use to discover infringement.
Comment: I agree about marketing. If you like a fantastic photo or set of photos, you'll generally be interested in more of what the photographer has to offer.
Comment: Just a note that Digimarc isn't an image tracking service that tracks based on meta-data.  Digimarc For Images (DFI) embeds digital watermarks that are not visible to the naked eye.  The watermark can survive some extent of cropping and photo resizing.  Their service tracks images based on this embedded digital watermark rather than exif data.
Answer: I think watermark, if done tastefully and artfully is worth it, perhaps not as a deterrent for copyright theft, but so if your images are seen, that it properly gets people to look you up. Yes they can crop out the watermark, but if you can prove that, then you probably can increase the damages awarded.
I also think that a well done watermark enhances an image, much like a well done image border, but that is clearly personal preference.
If you do portraits and the like, and you offer online proofs, I'd definitely put a big "PROOF" watermark across the image.
Comment: Oh god, I can't stand whole image watermarks. Makes the photo much less appealing than it could otherwise be to a prospective customer/client.
Answer: If you actually want your pictures to be printed, you drop the watermark. Editors are in a hurry and can't wait to buy a non-watermarked version.  You'll have to find out who used your image and send the bills yourself though, but that's some money after all.
Answer: I must say that watermarking when done tastefully doesn't detract from an image. I personally think the most unobtrusive way to do it is to have a simple translucent white logo in the corner, roughly 10-15% of the width of the photo.
An example (of a friend's work) would be something like this: http://www.flickr.com/photos/teddibrice/4629473858/ though you could go further and simply stick it right against the edge.
You see it but it doesn't yell at you and gets the point across that this is their photo.
Answer: The most tasteful "watermarks" (if they can be called that) that I have seen are actually more akin to the postcard-style advertizing you sometimes see from studios. What I'm thinking of is a moderately translucent stripe that goes across the photo, often at the line 60% of the way down the photo - although a vertical stripe works too. The stripe is usually at something like 20% translucent (rather than the typical "watermark" which might by 90% translucent).
I'd be interested in other opinions.

Is watermarking worth it?


Fast publishing in wordpress

Question: Wodpress editor is too slow. How to create other faster interface or how to fast publish posts. I just need fileds for author, category and subtitle. Is there any way instead of default wordpress editor ?
Comment: Subtitle? Is that some kind of custom field in your site? You can hide almost every part of the posting screen via "Screen Options" - have you tried that?
Answer: I get what you want, it will require some coding skills though.
What I did was create myself a plugin that registers a new menu page, and then I use
    wp_insert_post()
function to create a post with given parameters. You can check out my plugin here:
http://www.mediafire.com/?499tk848njaz7hq
It's for fast image posting, but I believe you can adjust it to your need.
Answer: Press This (/wp-admin/tools.php) does almost what you ask for.

Just drag the button to your bookmarks bar. Clicking it will open the following popup:

The matter is that it grabs the current browser window title and selected content. But this can be easily changed. It does not have the Author option though, nor Custom Fields.

Fast publishing in wordpress


Importance of exercises for learning mathematics

Question: For me it seem to be obvious that exercises and exercise courses are important for undergraduates to learn mathematics and skills like finding a proof or writing it down. Was there any research showing that exercises are necessary for math education (undergraduate education, math majors) or that they are very effective?
Comment: My own personal research seems to indicate that students who actually do their own homework do better in the course. Despite ethical considerations, I even have a group of placebo students, these students tell themselves they study, but, in reality they just talk to friends in study groups. Weirdly, doing math is needed for understanding math. I also have a group who has neither placebo nor actual effort, these try to survive on hope alone. It usually goes worst for the third category.
Comment: I might quibble that the usual notion of "exercise(s)" is far too stylized to serve the purposes it claims... unless success is measured exactly and only by more-of-the-same, which is usually the case. Surely what we _really_ want is (prolonged) _engagement_, and having assigned exercises is a caricature of that. I'd claim that mathematics is about phenomena, or human mock-ups of phenomena (whether "pure" or "applied" math), and our struggles to understand them. The typical contrived end-of-chapter exercises do not reliably do this (from what I've seen of myriad textbooks at many levels)...
Comment: Is there any research showing that exercises are necessary to become a plumber, an athlete, an artist… What I am trying to say is, that mathematics is "doing something" and to learn to do something you must do it.
Comment: Can you learn to ride a bike by watching someone else ride a bike?
Comment: Oh, I'd agree that "doing the thing" is important to learn how to ... do the thing. But genuine mathematics does not much resemble the exercises in textbooks.
Comment: The third reference in @BenjaminDickman's answer [here](http://matheducators.stackexchange.com/a/804/77) might be relevant.
Answer: From my own experiences as a undergrad math major, I would say that good, quality exercises are one of the best tools for teaching math to people. Paul Halmos was right: "The only way to learn mathematics is to do mathematics."
I myself, got by for a long time on just showing up to class and paying attention in college math classes (I even aced vector calculus doing that; grade was all exams, so I didn't do any of the homework). But eventually I got the point in math where that stopped working (and did rather poorly in Advanced Linear Algebra because of it; it was also a rather challenging senior-level class and that was my first year of university after having been at a community college). By my senior year, I was actually working though the homework, and I was acing all of my advanced math classes. I remember the material I actually worked on far better than the material I didn't actually work though (I don't even know vector calculus very well these days, but I can still do challenging topology proofs even though it's been 3 years since I took that class).
So what are good, quality exercises? In my opinion, the best kinds of exercises and the ones that present a problem, maybe a new thing related to what they've been learning, and then guide them in exploring that new thing via some prodding questions designed to make the student examine its relation to the things they've been learning about.
For example, suppose you were teaching algebra students about associativity and commutativity. A good, quality exercise, might be to introduce 2x2 matrices and their addition and multiplication operations (definition in problem style; as is common in advanced math texts) and then ask them to show that those operations are associative. Then ask if they are commutative and to explain their answer.
Questions like this are great for several reasons: They force the student to comprehend the definitions presented, as well as requiring them to understand the ideas they have been learning. It requires basic problem solving skills, and implicitly forces them to learn about the new object they are being introduced to (great way to stimulate curiosity in mathematics students). It forces them to work from definitions towards what they want to show, which emphasizes the necessity for justification and the reasoning behind a result.
Answer: I keep rather copious statistics on student performance in my classes, but these statistics are unpublished and not peer-reviewed. In my community college remedial algebra courses, doing the assigned homework exercises is, among 40 factors assessed, the single highest-correlated item with the test average, final exam score, and end-of-semester grade ($R^2$ = 0.20, 0.10, 0.15 respectively; N = 149 over the last year-and-a-half). This is self-reported by students (Likert 5-point scale), and despite the homework not being collected nor directly worth any points in the class.
This effect is not so pronounced in my sophomore-level statistics class ($R^2$ = 0.02, 0.02, 0.03 on the same measures; N = 208). I might guess that more competent students are able to "see" the principles and concepts immediately in class, whereas weaker students are more dependent on an extended series of rote exercises to develop the expected skills.


Where should standard deductions be mentioned on form 1040NR?

Question: I am a non-resident alien for the year 2017 as far as tax returns are concerned. I used a software to complete my 1040NR form, but I have a question regarding the document that was prepared by the software. I am a citizen of India, therefore I can claim a standard deduction of $6350 as per the US India Tax Treaty Article 21. In the form that was prepared, this value appeared on page 3 line 1 (State and local income taxes) under Schedule A - Itemized Deductions (Taxes you paid) with "US-India Income Tax Treaty, Article 21" on the dotted line. Is this the correct place to mention this standard deduction? Please help.
Answer: You calculate the standard deduction with Worksheet 5-1 in Publication 519. At the end of the worksheet, the result is entered into Line 38 of 1040NR (the "Itemized deductions" line) or Line 11 of 1040NR-EZ (the "Itemized deductions" line), and you put "Standard Deduction Allowed Under U.S.–India Income Tax Treaty" in the space to the left of the line.
If you use 1040NR, you do not need to fill out Schedule A, whose result normally goes into Line 38, because the standard deduction replaces all itemized deductions. The standard deduction doesn't just replace state and local income taxes, so it doesn't make sense to put it there. (If nothing else was entered on Schedule A, the result would be the same, though the schedule unneeded; if something else was entered on Schedule A, then you would have taken too many deductions, as you cannot take the standard deduction and some itemized deductions at the same time.)
Comment: @ayerhs7: I think you write it on the dotted line in line 38
Comment: Yes, that makes sense. So where should the standard deduction be mentioned? Line 38 states 'Itemized deductions from page 3, Schedule A, line 15'. Does that mean it should be mentioned somewhere on page 3 or just on line 38?


Why did mammals evolve to have two testes?

Question: What makes mammals tend to evolve to have two testes?
Comment: My guess would be symmetry and redundancy. :-)
Comment: And, you could probably ask the same about: ears, eyes, nipples, etc.
Comment: Two eyes and ears is to do with stereo receptivity, having two sensors of the same type in different places helps to gather much more information about distance and position (triangulation) of the source. One cool example of this is the hammerhead shark. It's believed that it has smell sensory organs in either end of its head. The further apart they are the better the sharks are at finding prey. It is also why predators have the eyes on the front of their head - so they work in tandem.

http://news.bbc.co.uk/earth/hi/earth_news/newsid_8376000/8376740.stm
Comment: I guess the same could be asked of ovaries
Comment: Mammals inherited them, testes are paired way back in fish.
Answer: EvoDevo is not my field, but I will try to give you some pointers.
Mammals as vertebrates, start out as fertilized oocytes, transform into a rapidly dividing lump of cells with eventual polarity through numerous gradients of numerous chemical messengers, and form a neural tube.
The forming body is ever more segmented through the use of gradients and thresholds (see french flag model) and (dorsoventral) axial symmetry is maintained throughout development, and as such two testes represent the default development.
Therefore, it may be more interesting to ask for singular organs which require more information, and thus maintenance throughout evolution of this information. But when considering the energy requirements, the need for synchronization, the need for a separate blood supply and thus the introduction of additional faults, it is easy to see why we only have one heart.

Wikipedia; author: Zephyris, title: "The first few weeks of embryogenesis in humans", DOR: 25/09/2012
See:

Inversion
Evolutionary developmental biology

I hope this helps as a starting point.
Comment: I might further speculate that the female reproductive system has strong axial symmetry and the testes are probably following the conservative development pattern of the female reproductive system.


How do we edit or remove a Tag from the Tags section?

Question: If a Tag has been entered by mistake, for example, the spelling is wrong, how can the Tag be changed?
Answer: Additionally to removing it from all questions as Chenmunka suggested, a moderator can fix this directly:
The tag can be merged into one of the correct spelling. Let's say somebody created prove-of-stake, and obviously it should be proof-of-stake.
When the moderator merges prove-of-stake into proof-of-stake all questions with the former get retagged to proof-of-stake.
The usual way to ask for moderator help is to a) open a ticket on meta and tag it with support, or b) to flag a question with "Needs moderator attention" and give a sufficient explanation there.
If it is only on a very small number of questions (<5), it's probably easiest to just retag all of those questions, when it's on more questions it is probably better to request moderator support, as all edited questions get bumped to the frontpage needlessly otherwise.
Synonyms
A similar effect can also be reached by suggesting synonyms:
Let's say both pos and proof-of-stake exist. Only the latter should be kept, but people will surely use the former again. You would go on the Tag Info of pos and click "suggest synonym". When other users vote to accept the synonym, pos gets replaced to proof-of-stake on all questions and whenever it is applied later.
Answer: To answer the 'remove' part of your question.
The system automatically deletes tags that have no questions.  This is done by a task that checks every now and again.  See this post on SE.Meta.
Just remove the tag from all questions and wait.
Answer: Click the 'edit' link under the question. You'll get the post input UI back, along with the tag input section at the bottom.
Comment: Though you might be able to delete the badly spelled Tag from being applied to one's own post, using this method, it does not prevent that Tag being suggested to other users, since it has already been created.


What is the diameter of a clarinet and bass clarinet mouthpiece?

Question: I'm looking for the diameter of the connection point for both the clarinet and bass clarinet. The part in red below.
Comment: Different models of clarinets have different dimensions. There is no "universal standard size" either for the tenon (the external diameter) or the bore (internal diameter).
Comment: @alephzero: Despite its brevity this should be an answer.
Answer: My research indicates that there are two standard sizes:
"The diameter of the bore is defined by the instrument (or better: its type), because the mouthpiece must have the same bore as the rest of the instrument. This is for example 15,2 mm (equals 0.598 inch) for a German style A- or B flat clarinet and it is 14,9 mm (equals 0.587 inch) for an A or B flat Boehm instrument, just below the mouthpiece."
http://www.the-clarinets.net/english/clarinet-mouthpiece.html
(It is highly likely that if you aren't in Germany, you will be using a Boehm instrument.)
Further evidence for there being a standard fitting comes from various suppliers' online shops, where a range of clarinet mouthpieces are offered with no mention of different sizes.
I will be able to consult a clarinet player on the subject later today!
Answer: As has been commented, the diameter of the mouthpiece connection point will change from brand to brand and model to model.
Comment: I'd love to view a chart of all of the brands / models of clarinets and their sizes. Or at least an average.
Comment: @ThomasReggi There is way too much variation between sizes, it would be very hard to create a chart
Answer: Laurence Payne gave the inner diameter numbers. In your image it looks like you're looking for the outer diameter.
I'm measuring my B45 (Bb clarinet) and EPE JM (Bb bass clarinet) mouthpieces with a simple ruler, so I can't give a sub-1mm accuracy. I'm reading 22mm and 30mm respectively. For comparison, the inner diameters are 15mm and 23mm.


Reinstalling Ubuntu from Ubuntu

Question: I already have Ubuntu, and I was told that if I re-install the software that it would wipe the hard drive. I clicked start download and a status bar filled up and said that the download complete but nothing happened? Is this because I did not boot from an external device? How can I reinstall? Any help?
Comment: I am assuming you downloaded the Ubuntu ISO installer? You need to burn it to a CD or install it to a USB, then boot into the CD/USB to reinstall the OS.
Answer: You've downloaded an ISO image of a CD-ROM. In order to install it, you will have to prepare a bootable medium of some sort (either burning the image to a CD with Brasero or creating a bootable USB stick with Startup Disk Creator), boot it, and install the software.
The community wiki installation page is here
Another topic I can think you might want to visit is ...
How can I keep recent files from appearing in Unity?
Answer: Based on your question, you downloaded a reinstaller. If this was Wubi, the problem would be using am .exe file, and Ubuntu cannot open those without Wine patches. Now a recommended course of action would to burn a live CD or USB based on whether or not you have a disk drive. If you have a disk drive you should burn a live CD. You should have access to a disk burning application already and if you don't, they're available in the Ubuntu Software Center. After you burn the disk you need to reboot the computer. During the boot up, hold the key that allows you to access the BIOS settings. If you are using a Mac, if I can remember correctly, you hold down the "c" key, and if not, try "Cmd+C". BIOS keystrokes vary from computer to computer, however "f2" and "f12" I've found common enough. Simply find your boot device section within the BIOS and switch from the main Hard Drive to the CD drive. Now save changes and exit. You should now come to a Live Installation of Ubuntu 12.04 LTS. Simply click install and there should be an option to erase the current drive and install Ubuntu over it. With a Mac, by holding "C" or "cmd + c" you should boot directly to yaboot (Similar to the GRUB boot manager), simply press enter, and you will enter the live install. Again there is the option to erase everything. The reinstall should wipe the disk.
Hope this was of help!

Reinstalling Ubuntu from Ubuntu


Square Wave input into Transformer

Question: Can a square wave generated using an astable NE555 be used as input of a transformer instead of AC? Say, I generate a square wave of 60Hz using NE555 and a 24V at 6A supply and feed it into a transformer with 50:1 turns ratio, will I get 0.48V at 300A out?
Comment: I think that is how most chopper circuits in switch mode power supplies work. A transformer just needs changing current to prevent saturation and to cause induction, a square wave should fit the bill.
Answer: You'll need to couple the square wave with a capacitor to the transformer because standing DC voltages will just cause heat but there is no problem feeding a transformer with a square wave in principle.
In practice, if you fed a 60Hz "power" square wave to a transformer, the higher order harmonics in the square wave would mean that a regular AC power transformer wouldn't be as efficient as being fed with a sine wave.
A 24V 6 A supply is capable of providing a power of 144 watts and your output requirement is also 144 watts so you need to be aware that you might only get 90% efficiency and expecting 144 watts from the transformer output is a little naive.
Comment: But wouldn't adding a capacitor make the square wave back to normal DC voltage?
Comment: The capacitor couples the square wave to the transformer i.e. it is in series - it removes the dc content of the square wave - it isn't connected to ground.
Comment: @AvZ it needs to be a value of several microfarads I think because you don't want to square wave to droop or become differentiated under load. Do you use a simulator (LTSpice is pretty much everyone's free-favourite)
Comment: What value should I add in series?
Comment: @AvZ are we done here now or do you still have questions on this subject?
Answer: For every action there is a reaction, and think how a transformer can buzz with AC. Now make it a square wave and you could hammer it around a bit, even more so than with sinusoidal AC. So, it depends on your frequency a bit, too, I'd say, for you to set up a noticeable or worse mechanical standing wave in your transformer itself. However, depending on the size and robust quality of the transformer it should be OK to do at your power level, at least. On the other hand, will you get square wave out? I think it won't be "as square" as the input. The windings (and their proximity to the plates, if any), also create a changing inductive environment, so it may goof with the shape of electrical wave(s) a bit. And the fact that the transformer will have those mechanical waves (manifested as vibration or sound), assumedly worsening at certain frequencies, leads me to believe that it will not pass all frequencies at the same efficiency, thereby further distorting the "squareness" of the wave. That may be saying the same thing twice in two different ways, but maybe at least for more than one reason. It may be, though, that the two are just manifestations of the same condition. Not sure at the moment. Either way, not going to be a perfect representation of the input. Also, I wonder if you are going to get EMF (or reverse EMF) effects at the points of voltage reversal, which may grossly distort the output.
Comment: First upvote  since 2014! And you just had 1 reputation score until now.
Answer: This is exactly what happens in the ignition system of older cards with points. The make-and-break of the points provided a 12 V square wave to the ignition coil (a transformer)!, which then output several thousand volts. A similar method was also used in "the olden days" to produce high voltage AC from a battery, such as in spark-gap radio transmitters.
Answer: I don't see why it would harm anything other than your efficiency, and the fact that it may saturate if the core isn't rated for the frequency and pulse width you provide until it is tuned to function.. All car audio amplifiers pretty much use pulse width modulated power supplies and they could use tiny to massive transformers in the audio section. It's the circuitry you use along with it that will aid it's output.. smoothing capacitors generally change the square wave to a sinewave under load so I think youll be just fine, however, ensure you will not be blocking lower frequencies with the cap as the cap in series is a crossover. Measure your impedance of the circuit to . Try adding a capacitor to your load and fire up a 100ohm resistor with a capacitor of say 47uF to your fgen with a square wave of the same frequency you are thinking of using, then scope it's output to see what happens.. I think you'll be pleasantly surprised. Square wave inverters have been known to work much better than the choppy, spiky and really crappy modified sinewave inverters.. In fact, I've bought several of those clunkers come to find out that the oscillator circuit could easily be swapped with a true sinewave oscillator board in some of the most standard brands out there. If you look in the circuit for the inverter, you'll see a pcb that normally plugs in vertically and they are pretty standard in China and on Ebay. 99% of the inverter and amplifier manufacturers produce these units for all of the manufacturers worldwide, so, they make it easy upon them selves so swaps can be made in the time of demand. If you are trying to invert dc to ac using this method, it's simple to change, and buy if you pull the oscillator out of the device before ordering!

Square Wave input into Transformer


How was the APL character set represented on IBM mainframes?

Question: The APL language used a unique set of characters, and additionally allowed overstriking of some characters on the terminal to form characters that were used in the language. When an APL workspace was saved, or a function with an overstrike was executed, were overstruck characters (e.g. <code>⌹</code>, matrix division) saved as a single token, or as the three-character sequence quad, backspace, divide (or the reverse)?
Answer: It's important to keep in mind, that there weren't that much symbols using overstrike in basic (IBM) APL. By using an 8 bit codeset they all could be integrated. The most common charset on the mainframe side was Page 293 which extends EBCDIC with all (at that time) legal APL codes.
With APL2 code handling became more complicated and Page 293 was replaced by a combination of an arbitrary base Page (nowadays Page 037, the EBCDIC equivalent of ISO8859-1) used for text and a separate page for APL symbols, Page 310. Page 310 holds all original APL symbols at the same encoding as Page 293, but replaces the letter blocks with 'new' APL symbols as well as making the decimals superscript. Page 310 is, despite its alike organization, not an EBCDIC page, but a strict graphical supplement, not usable on it's own. Keeping the (APL1) codes at the same place simplified loading and conversion of older programs.
Comment: @JonCuster - APL was great.  You could do most undergraduate statistics problems with simple one liners.  When I was at HMC in the 70's and living in Pitzer dorms I used to amaze Pitzer students by doing their homework that way.  Didn't help get me a single date though.  Still don't know why.
Comment: Man, I really miss the simplicity of APL for a variety of problems...
Comment: @davidbak Especially the setup for printing on the backside as well - they couldn't simply tun the  page, so two pf thes garden shed sized printers were setup in 90 degree with the output of the first feeding the second after being tuned over a 45 degree shaft. Timing was critical - it even measured the stretching o paper to adjust printing speed. One customer has **three** of these combinations - each several times the value of the controlling mainframe setup. They did replace 40 high speed chain printers. Needless to say that it was a government agency.
Comment: @JonCuster - between APL for numeric calculations and SPITBOL for text handling - you could do nearly every _ad hoc_ problem you came across ...
Comment: @davidbak - indeed. I did various parts of my thesis in APL (Fortran for some serious heavy duty calculations). Learned SNOBOL and SPITBOL in an algorithms course. Good times.
Comment: @Raffzahn - sounds fun! I remember those laser printers - especially their wicked large sharp electromechanical blade used to cut pages at terrific speeds!
Comment: @Raffzahn - oh I never saw that, wouldn't that have been neat! The mainframe room I did see back then: I was like a rube looking around! At HMC we had a nice computer room with a DEC-10 and mechanical line printer and such ... but then to see a _real_ installation!
Comment: @davidbak Around 1980 I discovered a mainframe editor that was programmable in a language much like APL, but with a standard character set. Extreme handy to program some format function but unlike anything else. Its main usage was to be able to construct forms to be printed on mainframe laser printers (these huge printing lines working from rolls of paper :)). Used as part of output formating, mundane datasets could be tuned in beautiful letters, automatically cut, folded, stacked into an envelop, stamped and bundled to be handed to Deutsche Post. It was serious fun.
Answer: IBM had several different APL mainframe implementations, and they where updated and modified over many years to support different types of hardware and I/O equipment over their life time. The source for one of the earliest APL implementations for System/360 is available from the Computer History Museum. As far as I can remember they assign unique codes to the overstrike combinations when they are identified in the input buffer, before processing by the actual interpreter. One obvious reason for this is that you do not want the encoding to depending on the order of the overstruck characters. Another reason is that different terminal types provide the characters in different ways. Some types of 3270 (APL) terminals would let the user perform a kind of overstrike operation on the keyboard, but only store and transmit the composed character from its buffer.
Answer: I was once writing an APL compiler (never finished, having figured I could single-handedly write a compiler in a 10 week undergraduate programming project), and the choice I made was to have an internal 8-bit character set where each composite symbol was a single character. This seemed an obvious choice to me, since that way you're separated from how that symbol is represented on any particular external device.
The thing was supposed to be portable, but my development system was on ICL 1906A, with an impoverished 6-bit character set, and accessed through teletypes with a standard typehead. So my pro tem external representation used two-letter abbreviations preceded by dot. I might have picked .MD for the matrix-divide operator, for example.  But only the lexical scanner needed to know about that.  If I had ever had a better terminal, I would just write an alternative lexer.
I see your title explicitly asks about IBM implementations, but I think a description of alternative system might shed a little light. Fundamentally this feels like the same solution as the IBM one -- define the character set you need, and then translate to/from the devices you've actually got (which, if you have a fancy terminal that I did not, might be done by installing extra character sets in your fancy terminal).
Comment: APL came up with a similar scheme too if you were using certain kinds of impoverished systems.  The APL-deriviative language J adopted the technique in full and never used a special character set.
Answer: This is a late answer but I hope that it might to some small extent be useful.
I've not delved into the original IBM APL to any extent other than to adapt my 2741 emulator to handle it, but have gone moderately deeply into other applications in particular derivatives of Ken Thompson's APL/11.
I can't remember whether the source of IBM APL was ever made available, my recollection was that after the Silverberg(?) brothers reconstituted it from tape nobody in IBM would authorise the release of anything other than a binary.
In the general case, I don't think an implementation saves an APL workspace etc. as the characters as entered, since this would mess up compatibility between different types of terminal (e.g. IBM printing terminals such as the 2741, and CRT-based terminals in the 3270 range).
I don't believe that an implementation saves a compound (overstruck) operation as a single character, since ultimately the number of potential compound operators comes close to exhausting the free codepoints in EBCDIC.
I don't believe that an implementation trivially tokenises. I think that in general what happens is that it reads the input into a buffer (where it can still be edited to some extent character-by-character), parses left-to-right (saving operations in numeric form, i.e. + becomes a single number, antilog becomes a single number and so on), and then evaluates right-to-left.
Finally, I agree that APL is great and can be spectacularly efficient... provided that one doesn't look too closely at storage requirements (there are plenty of stories of elegant APL programs sending a mainframe into a paroxysm of thrashing, and taking months to complete).


Are there galaxies with 2 or more super massive black holes orbiting each other?

Question: We now know that most stellar systems have 2 or more stars orbiting each other. Do we know of any galaxies which have 2 or more super massive black holes orbiting each other? Is it possible?
Answer: Yes, there are galaxies with two supermassive black holes in the center, see for instance 4C +37.11
Most likely such galaxies are formed by collision and merger of two galaxies, and their cores have not yet merged. Source
Comment: Binary black holes are always losing energy to gravitational waves and are destined to eventually merge. Someone else may know the expected timescale for supermassive black holes orbiting at galactic-scale differences.
Comment: @Mark "Simple" calculations of the SMBH merger time result in times longer than the current age of the universe. Yet it appears that SMBH mergers have occurred, so the simple calculations aren't adequate. This is known as the [final parsec problem](https://en.wikipedia.org/wiki/Binary_black_hole#Final_parsec_problem).
Comment: Are they stable or are they destined to merge? What about their axis of rotation, are they parallel, if not, what happens where the jets collide? What are the effects in the region between the 2?
Comment: I just added a link to one source with more details about the merger. I haven't read through all the papers this article refers to, but they seem interesting and relevant, and might shed some more light into question about the eventual merger and its timescales
Comment: The thought of my question was that if black holes swallow even light then 2 smbh should swallow each other and not even be able to orbit unless far apart. The fact that they can orbit but that it decays and they merge answers my question. But the effects of the jets from both smbh is still something I would like to know about.
Comment: All orbits decay over time, due to gravitational waves if nothing else. Jets would make a great question, so please take the time asking it!


What's the proper word for this type of 'porridge'?

Question:
What's called in English for this type of Chinese food? It's made of rice and water. Refer to the picture.
Comment: The dish is not common (at least in the UK), and would probably only be found in Chinese restaurants and the Chinese community. *Rice porridge* (or *porage*), and *rice congée* (if you want to be posh) sound OK (and Google knows about them). Connoisseurs of Chinese cuisine would probably know it by its Chinese name. I'm afraid I just order sweet and sour chicken, and egg-fried rice. I would avoid *rice gruel*. Gruel has negative connotations, and was a dish that only the poorest of people would eat (see Charles Dickens: *Oliver Twist*).
Comment: Are you looking for a term that would be understood by most native English speakers?
Comment: @Tᴚoɯɐuo, yes, or commonly used among most native English speakers.
Answer: The "proper" term is the Chinese name, congee.  It's a perfectly acceptable (if not widely known) borrowed food term, like sushi or spanokopita or falafel or borscht or soufflé or (the ironically named) chop suey.

Congee (n): (in Chinese cooking) broth or porridge made from rice.

"Rice porridge" would also be fine.


Can icons improve readability on a navigation?

Question: Our app has many tools and we have a navigation of about 10 tabs. Tabs can be re-arranged and this forces the user to find them by reading the label. Would icons make it more usable?
Answer: Icons can improve readability and findability in sense that users, that a familiar with interface, usually don't read the labels in common way, but search for visual markers, that help identify item.
It happens due to visual form, that we percieve before "read" — for instance, in peripheral vision we don't read, only percieve the form and colour of item, so when using only text labels it looks only as formless lines of gray (in sense of contrast) colour. Icons help to distinguish one element from another (by colour and shape), so increase the ability to read them faster.
Such perception can be simulated by using blur effect:
Comment: Excellent example of pseudo-peripheral vision; our peripheral vision's a lot worse than it seems, so simple, recognizable shapes really help
Answer: Icons would only make it more usable if the iconography was THAT obvious that it's just apparent to the user as he word itself.
TLDR - Keep the words. Yes there's more physical data there in terms of character count, but for usability stick with words! If you're really stuck for space consider having an icon which when hovered reveals the word too. If you can do that when you hover the menu even better!

download bmml source – Wireframes created with Balsamiq Mockups
EDIT:
If you are going to use icons this is worth buying - ISO/IEC 11581-5:2004
If you're looking for further reading the Texas Uni site has a great little resource by Sheng-Cheng Huang: http://www.ischool.utexas.edu/~huangsc/files/home/qualifying_paper_hsc_10312008.pdf
Answer: I don't know if an icon can improve readability as much as it might aid in the discoverability and affordance of the item. Of course this is dependent on the relation between the navigation/action and the text accompanied with it. Example. If a user is moving forward (next) or back; an icon helps convey that idea better by adding the arrow.


What are the tax consequences of transferring a house out of a trust to my two daughters?

Question: I currently have my house in a revocable living trust with my two daughters as beneficiaries.  Are there any tax consequences to transferring the house into their names now before I am deceased?
Comment: Tax and legal issues require us to know the country. Also since they are "children" we would have to know if they are minors.
Comment: The major consequence is that the house won't be yours anymore. And relationships between parents and children can change. Think about that. I'm sure your daughters love you and only want your best - but what if your best is your home? Will they still love you when they've got it?
Answer: littleadv is correct in his response, no surprise there. But, given that information, there are consequences you should be aware of.
Gifts to any non-spouse are a non-issue up to $14000/yr per person. Not enough to gift a house. You would need to tap your lifetime gift exclusion, which in 2016 is $5.45 million. More than enough to give your house away with no tax consequence. There's a form 709 that you need to file. It's just a way to track your generosity over the years, and tax you once you're above this level.
That was the easy part. The tough part comes later. Gifts' tax basis is not adjusted. In other words, you die and leave the kids a $1M house, they now have a basis of $1M and can sell with no cap gain or keep it, but pay only the gain from sale above $1M. When you gift your $1M house, you may avoid the gift tax, but your kids now have your basis. It's very possible you bought that house for $250K, never tracked any updates, and the kids will have that $250K basis for their eventual sale, and potential tax due on the $750K "gain."
On a personal note this is exactly what was done to my sister. The family house, bought in the 40's for $4000, was transferred over the years, from my grandmother, to my father, then mother, now sister. It was gifted 3 times, never inherited, which would have stepped up the basis. When she sells it (mom passed recently) she will have a $600K gain and nearly $100K tax bill due to this series of transactions.
As littleadv stated, the trust is moot. What I've answered is the second nuance of your question, the tax effect of the gift. Not upon gifting, but for the eventual sale. In my sister's case, lawyers often know just enough to be dangerous, how to transfer property titles, but not enough to advise on the future tax consequences.
Answer: The point of living trust is to avoid probate, not taxes. Usually, revocable living trust is transparent for tax purposes and from tax perspective the assets are considered your personal assets.
There may be some nuances depending on country, which  you haven't mentioned, but that's the general rule.


What do Islam say about mercy killing?

Question: i want to know what Islams says about mercy killing. Does Islam allow killing someone who is very ill, in order to stop them suffering any more pain or it is forbidden in Islam.
Answer: In Islam, life is a sacred thing that can only be taken by Allah or based on Allah's commands. The person in question (whose life it is) has no choice in the matter in either case either to keep his life or to take it. It is not his life or body to give or harm.
Suicide is specifically banned in many hadith:

The Prophet (ﷺ) said, "He who commits suicide by throttling shall keep on throttling himself in the Hell Fire (forever) and he who commits suicide by stabbing himself shall keep on stabbing himself in the Hell-Fire." (Bukhari)
--
The Prophet (ﷺ) said, "Whoever swears by a religion other than Islam, is, as he says; and whoever commits suicide with something, will be punished with the same thing in the (Hell) Fire; and cursing a believer is like murdering him; and whoever accuses a believer of disbelief, then it is as if he had killed him." (Bukhari)

Referring specifically to mercy killing, it can be likened to the situation in the following hadith:

We witnessed (the battle of) Khaibar. Allah's Messenger (ﷺ) said about one of those who were with him and who claimed to be a Muslim. "This (man) is from the dwellers of the Hell-Fire." When the battle started, that fellow fought so violently and bravely that he received plenty of wounds. Some of the people were about to doubt (the Prophet's statement), but the man, feeling the pain of his wounds, put his hand into his quiver and took out of it, some arrows with which he slaughtered himself (i.e. committed suicide). Then some men amongst the Muslims came hurriedly and said, "O Allah's Apostle! Allah has made your statement true so-and-so has committed suicide. "The Prophet (ﷺ) said, "O so-and-so! Get up and make an announcement that none but a believer will enter Paradise and that Allah may support the religion with an unchaste (evil) wicked man.(Bukhari)

The hadith makes it clear that it was seen as a great sin akin to disbelief itself to commit suicide to avoid pain. I don't believe it would make a difference if it is another person doing the actual killing.
In conclusion, mercy killing is forbidden.
Answer: No Islam does not allow killing someone who is very ill .It is forbidden in Islam because Allah create every single person and Everyone is died on their own time no one have to right to kill anyone.It is against in Islam. Eclveryone's life is in the hand of Allah.
Islam says ; killing one person is equal to killing the whole humanity.
And if the person is very ill and suffering it means his or her guilt was less in his life and after his or her death Allah forgive them and he or she entered in heaven.

What do Islam say about mercy killing?


About visual ways of teaching Math

Question: There is a concept called 'Infographics' that uses lots of colourful diagrams and graphs and artwork to visually depict some set of concepts and tries to explain the ideas through pictures. I recommend these Infographics to any person trying to learn some complicated principle in Math, say. I was wondering if there are any easy-to-comprehend infographics for hard subjects like Category theory or Topology?
Comment: People learn/understand differently. Some concepts are extremely hard to force into images. And doing so is moreover a very, very underdeveloped skill.
Answer: For complex variables, there is the famous "visual" book
Tristan Needham, Visual Complex Analysis
Comment: Tristan Needham's book is great, I have a copy. There is also one on 'Visual Group Theory' from the Math. Assoc. of America. I haven't found much else. The Infographics I mentioned would be a great 'medium' for Advanced Math.
Comment: I think many hard concepts in math or science could be explained in a MUCH simpler fashion with clever art and diagrams. Even animated gif documents on a computer that show moving surfaces or graphs could help immensly. The Wolfram math site has what they call 'cdf' documents that stands for 'calculating' document format I think. Like a larger version of an animated gif document. The cdf has many changing demonstration abilities. So why is artistic presentations and mathematics usually separate in many math books??
Answer: The slides of Dror Bar-Natan are excellent examples of such mathematical "infographics".
Answer: In addition to Needham's famous book mentioned in Gerald Edgar's answer, there is
Visual Complex Functions: An Introduction with Phase Portraits by Elias Wegert.
The book is richly illustrated with colour diagrams of complex functions, especially the "phase portraits" mentioned in the title, as can be seen on the author's website for the book.
Answer: For topology, Peter Saveliev has written:
Topology Illustrated.
A partial draft is available on the author's website, in case you would like a preview of some sections.
True to the title, it is heavily illustrated. While there is certainly plenty of explanatory text, the large number of pictures and diagrams could be seen as a form of infographics.
Answer: Traditionally (say up to the last 40, 50 years?) images were extremely expensive to produce and distribute (line graphs had to be drafted by hand, other images had to be created by expensive methods, colour meant special pages in the book), and thus used sparingly. Creating, distributing and viewing videos was much worse. As a result, people streamlined methods to make their point without images. That is hard to unlearn.

About visual ways of teaching Math


Who is the decision body for forking a blockchain ledger?

Question: Is it fair to compare the decision body responsible for forking a blockchain as 'escrow officers'? How can users of the blockchain network dare to the treat the distributed ledger as immutable as long as forking (ledger tampering) exists as a corrective measure? Who are these people and how who holds them accountable?
Answer: First of all, it is important to distinguish between multiple things, all of which are often called 'forks'.

The existence of two or more competing versions of history. These happen unintentionally in proof-of-work consensus systems when two miners produce a candidate block around the same time. These get resolved automatically.
Software projects branching off from another one. These are not generally (but could be) associated with a change to the ledger/rules.
A change in the rules about the validity of blocks (which additions to the ledger are accepted).

My view is that in a perfect world, (3) would never be necessary. We would all agree on what properties the system should have, encode those into software, and never touch those rules again. Reality is different of course, and sometimes changes to the system's rules are necessary - due to improve the technology, or to prevent against certain weaknesses or attacks. However, I do feel that cryptocurrencies (in general, as a research topic) intend to approach that goal, and are an experiment in building a system that lacks the need for human control. One of its value propositions is the prospect of creating a monetary system that is beyond control.
So how do we accomplish that? Clearly developers of node software that implements these rules have a strong influence over how it works. However, this influence is not absolute control. When you run a fully validating node, it comes with certain rules programmed in. It won't ever accept a chain of blocks that doesn't satisfy those rules. Only its operator can change that software to another version which has different rules. Developers can of course publish new versions that changes things, but they need to take into account that not everyone may update. Depending on the type of change, if significant (and not necessary large) parts of the ecosystem choose to not adopt an update, this can cause the ledger to split (where the result is 2 separate currencies, with each pre-existing coin spendable once on both sides). This risk is a strong deterrent to adopting changes, unless it is clear that those changes will be universally accepted.
So to answer your question:

Who are these people and how who holds them accountable?

You are.
Cryptocurrencies have the unique property that all of the system's rules are verifiable by everyone. By running software that implements the rules you want, you know that the system maintains those properties. Anyone who wishes to change these will at least need to convince you to change your software (this is why Bitcoin Core intentionally does not have an auto-update function, for example - it would place far too much power in whomever has control over the auto-update server).
Answer:
Is it fair to compare the decision body responsible for forking a blockchain as 'escrow officers'?

Not really. Escrow officers are generally agreed upon by all of the parties in a transaction, but there's no practical way to find someone that every blockchain user trusts.

How can users of the blockchain network dare to the treat the distributed ledger as immutable as long as forking (ledger tampering) exists as a corrective measure?

Immutable can mean two things. In a narrow technical sense, it can mean that a particular block or data structure can't be changed easily. People usually use 'immutable' in a more vague way, though. For example, the set of unspent transaction outputs in Bitcoin is not immutable, because if it was, then you wouldn't be able to send your money to someone else.
When people say that a blockchain is immutable, they usually mean that it can't be changed except through things that follow the technical rules/informal norms of the system.
Norms around how a blockchain may be changed differ between different communities. Systems with broad norms (like Ethereum) require more developer discretion than systems with narrow norms (like Bitcoin.)
If a blockchain and its community has broad norms, and you do not trust the judgement of the developers, then you can't trust the resulting blockchain, either.

Who are these people and how who holds them accountable?

It depends on the blockchain! A system based on Quorum might make decisions based on majority vote of participants. Bitcoin Core uses a do-ocracy combined with judging new contributions by the consensus of existing contributors. The Ethereum Foundation has a formal corporate identity.
It's worth noting that 'accountable' implies that there are objectively correct changes, which isn't generally true. Almost all changes are only subjectively good.


How Do You Analyse A Film or Game For It's Sound Content?

Question: I've heard and read about how recording/mixing engineers in the music business analyze each others mixes to learn the techniques used to make a certain track sound so good or what the latest trend/style is being used for them to incorporate in their work. They listen to how the track is balanced, panned and where each instrument fits in the frequency spectrum and so on, I'm guessing the same applies to a film or video game?, what else is there to look for?
Answer: light spoilers ahead for We Own the Night, Inglorious Basterds and Michael Clayton ahead
Be careful not to get too lost in the technical details. Be mindful of the overall purpose of the sound design. I brought this up in another question a couple years ago... the movie, We Own the Night, starring Joaquin Phoenix and Mark Wahlberg has a very compelling car chase sequence in the rain where the viewer gets the sense of claustrophobia as the unwilling passenger in the car that's being chased thanks to great editing and sound design.
In Inglorious Basterds, the scene where the Nazi officer gets beaten to death with a bat is pretty intense. You get this great buildup as Sgt. Donny Donowitz beats his bat against the wall of this long tunnel for an eternity... before he even appears on screen. Accompanying his entrance is this epic music that heralds the Bear Jew and just when the tension and music builds up to its highest point, the music is pulled out and all we hear are the cheers of the American Soldiers and the brutal pummeling of the twitching Nazi officer. It kind of makes for a rather dystopic experience if your sensitive to such brutality.  At the same time, the movie does not really tell you how to feel about the scene. It's pretty much determined by how you feel about the situation as it unfolded.
Lastly, there's a scene in Michael Clayton near the end where Michael's Car blows up in the background. You see his car in the distance and out of focus blow up and almost a second later you hear the explosion. Perhaps someone accidentally slipped the explosion SFX behind a second or so by accident. Or, was it done on purpose to create a surreal effect. As if to ask yourself, "Did my car just blow up?" only to get the affirmative answer a half second later with the explosion.  Or perhaps that happened as recorded because light travels faster than sound and to get that delay, Michael was far enough away from the effect to watch that delay occur (shrug)
Anyway, my point is to also consider the context or the role sound design plays in supporting or telling the story.
Comment: I had assumed the Michael Clayton thing was light traveling faster than sound...one of the few observances of that fact in film, as far as explosions go.
Comment: Ya, I'm with ya on that one, Joe. I was wondering if he was really far enough for that. Haha, perhaps Mythbusters can have fun with it.
Comment: I wonder if the sound designer had to fight to keep it in and not "fix" it?
Answer: The music engineering world is very different from a technical standpoint because the music usually stands on its own, giving the engineers, producers and artists free reign (more or less) to make choices without penalty. On the other hand, film and game sound design must work harmoniously with visual elements to tell a story (as Hubert described above). It's quite easy to get in the habit of listening to the finer details of the mix (panning, processing, reverbs, etc.), but remember that the ordinary listener appreciates sound design as a whole gesture and not as a sum of parts. Moreover, many designers strive to design that way too, trumping slight imperfections in the mix with contextual intent.
When watching films and playing games, sit back, turn off the lobe of your brain that says "whoa what's the reverb tail on that", and just enjoy the experience first. Try to listen without expectations, and then when you listen again and check out the detail you'll have a better understanding of why the designers made the decisions they did.
Answer: I found it effective to use Adobe Audition and XMind (mind mapping tool).
In Audition I am able to see both waveform and spectrum at the same time. I set markers at the in and out points of certain audio sections that I'm interested in and then use Marque Tool to listen to exact frequency range of the sound. I can reverse, de-noise, make it louder.
In XMind I have a template mindmap for this kind of task with several sections that I need to fill in, like Melody, Harmony, Rhythm, Instruments, FX, Structure, Mix, Automation, Stats etc. I tried to use simple lists and spreadsheets for this but I'm a visual person and mindmaps just work better for me.


Can you steal someone's aveirah item?

Question: In order to prevent another Jew from sinning are you allowed to steal the item he uses to sin with? For example assuming it is assur to smoke (Shu"t Tzitz Eliezer 17:21) can I steal another Jew's cigarettes to prevent him from smoking?
Comment: 'aveira items' is a slippery slope, and this may well encroach into the realm of imposing your own chumras and world-view onto others. (e.g. "a smartphone is assur so I can steal it".)
Comment: Stealing sounds like taking something for yourself. I assume you mean getting rid of it?
Comment: There is a posek who allows this ,have to find it
Comment: Dupe. http://judaism.stackexchange.com/q/1811/5
Answer: 1) Rav Sternbuch in Tshuvos V'hanhagos chelek 1:368 answers a question very similar to this one. The questioner(a Bal Tshuvah) asks if he can damage his parents television.
The Rav answers that this is a machlokes between The Ketzos and the Nesivos in Choshen Mishpat siman 3(which discusses forcing someone to keep mitzvos).The Ketzos holds that the power of forcing someone to keep the mitzvos was only given to Beis din while the Nesivos holds it is on every individual. He writes that it seems even if one holds that it is on every individual still in order to take away someones money one needs a beis din ,and in many instances if one acts alone it can push the  recipient even further away from mitzvos. He brings a gemara in berachos where someone acted in such a way and he brings the story with Rachel stealing the terafim which would imply that one can damage a sinful thing.
He ends off by saying that one should ask his Rav as every case is different,and the two proofs given the end of the story shows that maybe it shouldn't have been done.
2) The Be'er Moshe 1:60:10 towards the end writes about a case where  a son should not get his father cigarettes if his father wants them or wants him to go buy. However , he writes:
אבל לילך ולהצניע"
 או לגנבו מאביו כרי שלא יהי׳ לו הסיגארעט להעלות
 עשן, בזה אני עדיין נבוך ולא ברירא לי ויותר נראה
 שלא יעשה כן"
"but to go and hid or steal from his father in order he doesn't smoke ,it is not clear to me but it seems that it is better not to."
3)  Rav Nebontzol in his Kuntres Hanhagos writes if one is in a room with someone who has inappropriate pictures he can take them down without permission.
4) This is a very interesting case brought by Business halacha institute where a rebbi takes a mp5 player from student.
http://www.businesshalacha.com/articles/educational-damage
Comment: There is a Be'er Moshe on fathers cigarettes and Rav Nebontzol on inappropriate pictures
Comment: there is more to add,don't have time now, will try to add later
Answer: There may be permission to do this, even to B'nai Noach (non-Jews). We see (Genesis 31:19) that Rachel stole her father's (Laban's) teraphim and hid them, with some commentators explaining that this was because she did not want her father to worship idols. (A Ben No'ach is prohibited from idol worship.) I would infer that if this can be done to a Ben Noach then it can be done to a Jew as well.
Comment: @DoubleAA We just know that there were idols in Ya'akov's camp after Shimon and Levi looted all of the property in Shechem and took captives. There's no reason to think Rachel intended to worship idols; if anything, the context of the verses there suggest that she took the *t'raphim* to prevent Lavan from using them sorcerously to locate Ya'akov's party (as suggested by the Rashbam and Ramban, *B'reishis* 31:19).
Comment: She might have stolen them to worship them. We know there was idol worship in Yaakov's camp ([Gen 35:2](http://www.mechon-mamre.org/p/pt/pt0135.htm#2))
Comment: Dont some commentaries say the she was wrong in stealing them?

Can you steal someone's aveirah item?


Confusion matrix - determine the values of FP FN TP and TN

Question: After running my code ,I get the values of accuracy, precision and recall and I want t determine the values of FP FN TP and TN from these metrics. I tried to calculate it using the formula of each metric but I couldn't. Is there any way to do this?
Comment: Welcome to Data Science SE; if the answer below resolved your issue, kindly *accept* it - see [What should I do when someone answers my question?](https://datascience.stackexchange.com/help/someone-answers)
Answer: You can!
The trick is that you actually know two other critical variables: the number of positive and negative examples (P and N). You can then use them to algebraically solve for the confusion matrix:
$ recall=\frac{TP}{TP+FN}=1-\frac{FN}{P}\Rightarrow $

$ FN = P(1-recall) $

$ recall=\frac{TP}{TP+FN}\Rightarrow (recall)(TP+FN)=TP\Rightarrow TP(1-recall)=FN\Rightarrow$

$ TP=\frac{FN}{1-recall} $
or simply: $ TP=P-FN $

$ accuracy = \frac{TP+TN}{P+N}\Rightarrow (accuracy)(P+N)=TP+TN\Rightarrow $

$ TN=(accuracy)(P+N)-TP $

$ accuracy = \frac{TP+TN}{TP+TN+FP+FN}\Rightarrow (accuracy)(TP+TN+FP+FN)=TP+TN\Rightarrow $

$ FP=\frac{TP+FN}{accuracy}-TP-TN-FN $
or simply: $ FP=N-TN $
Comment: Thanks ! you saved my life
Answer: You should modify the code to produce the confusion matrix itself.  But assuming that's impossible for some reason...
A bit of linear algebra helps here.  @n1k31t4 is right that given only accuracy, precision, and recall, you can't expect to reproduce the confusion matrix: you have three equations in four unknowns, and the equations can be expressed as linear equations (in the unknowns; see below), so there are definitely infinitely many solutions (but made finite by the non-negativity requirement, and in odd cases made few or even unique by the integer requirement).
If you happen to also know the total number of samples (or perhaps some other confusion-matrix measurement), you can recover everything.  You don't need both P and N as @BenjiAlbert uses (although that produces more pleasing formulas IMO).  Below I've done it by putting everything else in terms of $TP$, but there are sure to be several routes to the answer.
From $\text{recall}=\frac{TP}{TP+FN}$, we get
$\frac{1}{\text{recall}} = 1+\frac{FN}{TP}$ and so

$FN = (\frac{1}{\text{recall}}-1)TP$.

Similarly, from $\text{precision}=\frac{TP}{TP+FP}$ we obtain

$FP = (\frac{1}{\text{precision}}-1)TP$.

Finally,

$TN = \text{accuracy}\cdot\text{count} - TP$,

so
$$\begin{align*}
\text{count} &= TP+TN+FP+FN \\
 &= \text{accuracy}\cdot\text{count} + (\frac{1}{\text{precision}}-1)TP + (\frac{1}{\text{recall}}-1)TP,
\end{align*}
$$
and now you can solve for TP:
$$TP = \frac{(1 - \text{accuracy})\cdot(\text{count})}{\frac{1}{\text{precision}}+\frac{1}{\text{recall}}-2}$$
Plugging that back into the above formulas gives the values for all the others.
Answer: As others have pointed out, you could retrospectively compute those values if you know enough about the data.
If you literally only know the accuracy, precision and recall then it wouldn't be possible. It would be like someone telling you the answer is 0.79, and asking how it was computed... there are infinitely many ways.
I would suggest looking into the code where those metrics are computed and intercept the raw predictions and labels. You could sum up the values in the confusion matrix (TP, FP, FN) during inference, then just use something like the  sklearn.metrics.precision_recall_fscore_support function from Sci-kit Learn.
Depending on what method you are using to get the metrics, there might even already be an argument to the function that will also return the full confusion matrix.
Answer: <code># Calculating FP, FN, TP, and TN using accuracy, precision, and recall
from sklearn.metrics import precision_score
from sklearn.metrics import recall_score
from sklearn.metrics import accuracy_score
from sklearn.metrics import confusion_matrix

y_true = [0, 1, 0, 0, 1, 1, 1, 1]
y_pred = [0, 0, 1, 0, 0, 1, 1, 1]

num_values = len(y_true)
print("Number of observations: {}".format(num_values))

# Calculate Precision
# The precision is the ratio tp / (tp + fp)
precision = precision_score(y_true, y_pred)
print("Precision Score: {}".format(precision))

# Calculate Recall
# The recall is the ratio tp / (tp + fn)
recall = recall_score(y_true, y_pred)
print("Recall Score: {}".format(recall))

# Calculate Accuracy
# The accuracy is the ratio (TP + TN)/(TP + TN + FP + FN)
accuracy = accuracy_score(y_true, y_pred)
print("Accuracy Score: {}".format(accuracy))

# Calculate the number of positive predictions
num_pos_preds = accuracy * num_values
num_neg_preds = num_values - num_pos_preds
print("Number of Positive Predictions: {0} \n"
      "Number of Negative Predictions: {1}".format(num_pos_preds, num_neg_preds))

# Calculate the False Negatives
FN = num_pos_preds * (1 - recall)
print("FN: {0}".format(FN))

# Calculate the True Positives
TP = num_pos_preds - FN
print("TP: {0}".format(TP))

# Calculate the True Negatives
TN = num_pos_preds - TP
print("TN: {0}".format(TN))

# Calculate the False Positives
FP = num_neg_preds - TN
print("FP: {0}".format(FP))

# Verify the results
sk_tn, sk_fp, sk_fn, sk_tp = confusion_matrix(y_true, y_pred).ravel()
print("Verify our results using Sklearn confusion matrix values\n"
      "FN: {0}\n"
      "TP: {1}\n"
      "TN: {2}\n"
      "FP: {3}".format(sk_fn, sk_tp, sk_tn, sk_fp,))
</code>
Output:
<code>Number of observations: 8
Precision Score: 0.75
Recall Score: 0.6
Accuracy Score: 0.625
Number of Positive Predictions: 5.0
Number of Negative Predictions: 3.0
FN: 2.0
TP: 3.0
TN: 2.0
FP: 1.0
Sklearn values
FN: 2
TP: 3
TN: 2
FP: 1
</code>


How do you determine the phonemes in small phonemic inventories?

Question: Languages with small phoneme inventories such as Pirahã often encourage different constructions of the phoneme system. In the case of Pirahã, it either lacks phonemic velars or phonemic nasals. Are there any metrics to measure which option is more likely?
Answer: Pirahã has a consonant phoneme that's pronounced [g] in some contexts and [n] in others.  (It has no other nasal phonemes, and arguably no other velar phonemes.)  So the question here is, "Is this Mystery Consonant really a /g/, or is it really an /n/?"
As a matter of convention, linguists tend to name consonants after their default pronunciation if there is a clear default.  According to the Wikipedia article, the Pirahã Mystery Consonant is pronounced [n] after a pause and [g] elsewhere.  That suggests that [g] is the default pronunciation, and that we should name the phoneme /g/.  And by the looks of it, that's what the linguists who work on Pirahã have done.
For what it's worth, too, it's not terribly uncommon for languages to lack nasal phonemes.  Whereas it's quite uncommon for languages to lack velar phonemes: /k/ is the most common consonant across languages.  (There are some languages without phonemic /k/, including Tahitian and maybe some varieties of Hawaiian.  But it's very, very rare.)
Comment: Kind of an aside, but for anyone that is interested, and in case you see this "out in the wild", for the commonality of features linguists will often use markedness, where a marked feature is uncommon and an unmarked feature is common.
Comment: Do you have a source for /k/ as most common consonant?  I was under the impression that the distinction belonged to /t/, with Hawai'ian being unusual precisely because it lacks /t/ after a *t > k sound change.
Comment: I'm afraid I don't have a source handy, and it's possible I've misremembered.  I should have just said that lacking /k/ is rarer than lacking /m/ or /n/ and left it at that.  (As for Hawai'ian: most varieties have /k/ but no /t/, but at least one has /t/ but no /k/.  I believe the story is that all had *k go to glottal stop, and most but not all then had *t go to /k/.)
Comment: Only a tiny number of languages lack nasal phonemes. WALS (combining features 18A and 10A) records a single language with neither nasal consonants or vowels.
Comment: Related: http://linguistics.stackexchange.com/questions/342/how-to-determine-which-phoneme-a-group-of-allophones-realize


why can't I do push up or pull up?

Question: why can't I do a push up or pull up??I am not a fat  guy but I can't do a single push up or pull up,I can lift pair  of dumbbell of 20 kg and do 3 sets of 20 but I can't do more than 5 push up or pull ups why??It has been a  month now but still I can't do it
Comment: I'm not going to write this up as an answer because its bro science, but when doing a exercise for the first time you have to get your nervous system firing to this new motion.  And are you curling these dumbbells?  More info needed
Comment: How often do you perform the push ups? And when do you do them? You shouldn't perform those exercises after bicep curls or exercises that have weakened your arms.
Comment: Thanks to anyone on here who ACTUALLY responded with suggestions for people who cant even do one. So many talked about reps, etc.. but that is so unhelpful for people who can barely hang. I know how this feels. Its hard to even tense my shoulders to hang up more.. but I can do 60 pound rows (total long bar), Lat Pulldowns at 80, etc. There's more to it than just 'do reps this way'.
Answer: The first question I would have to ask you is are you 40 kg or less?  The reason you have a hard time with these body weight exercises is because the resistance of your body is more than you are currently used to.
As you get stronger, you will be able to do more.  Before I started losing weight, I could barely get 5 push ups at 138 kg body weight, but now I can do 20 at 130 kg body weight.  I've been working at both losing weight and the pushups since the spring (it's late summer now).
Some exercises are just very difficult to do, but even more so if you are a woman.  Pull ups are very difficult for me, but I do know a number of guys who can do them well.  The number of women I know who can do pull ups I can count on one hand.  It takes a lot of dedicated work to build up the strength needed to do them.
Here's some tips that will help you:

Work on a progression.  You can start with an easier variation until you can do 4 sets of 8 with that variation.  Then change to a more strict variation and work back up.
Add more sets in the beginning.  You might only be able to do a couple repetitions at a time.  However, you get stronger by doing more, so do multiple sets of the reps when you can.
Try to increase the total repetitions over time.  When you add up all the repetitions you've done on any given day, try to add at least one rep every week.

There's several approaches that can help you, but one that I've seen help a number of people is called "ladders".  The idea is that you are working with a partner, and you only rest for the time it takes your partner to finish their set.  If you are by yourself, try to rest about the same time that you were working.  With that in mind:

The first set is just one rep.
Each set you try to add a rep.
When you can't add any more reps, start subtracting a rep each set

In the beginning you might only be able to work up to a set of 3.  But you've done 1+2+3+3+2+1 = 12 reps total that day.
If you practice it at least once or twice a week, you'll be surprised at how soon you'll be able to perform the push ups and pull ups at a level you want.
Comment: Awesome answer. I also wouldn't advise performing pushups/pullups once or twice a week, especially if you want to get better. If you can't do it everyday, do it every other day. If possible, work it into your daily routine. [This](http://www.artofmanliness.com/2008/07/08/pull-ups-fitness-routine/) helped me develop the concept of progressive increment in both pushups and pullups.
Comment: Notice, I said _at least_ once or twice a week.  Obviously, if push ups and pull ups are all you are doing then frequency is king.  If it's part of a more comprehensive strength building plan, once or twice a week is sufficient.
Answer: Bodyweight exercises depend on, well, your body weight--specifically, how much strength you have relative to the weight you are moving.
If it makes you feel better, when I started out I couldn't do more than five push-ups nor more than one pull-up.  Now I can do at least 20 push-ups in a set (I have not actually tried doing them until exhaustion) and about 10 pull-ups.
How did I make this change?  Simple:  I didn't do those exercises.  Instead, I did exercises that worked similar muscle groups but at less weight than what my body weight would require.  So for example, I did bench presses, both with dumbbells and the barbell.  Started out real light, somewhere around 60 lbs, and worked my way up.  I also did lat pulldowns with the cable machine, again starting somewhere around 60 lbs.
Bicep curls are fun but they don't hit all the required muscle groups for push-ups or pull-ups, which are primarily chest and back exercises with arm involvement in the shoulder, biceps, and triceps.
A more general point is that bodyweight exercises are great because you don't necessarily need a lot of equipment to do them, but the downside is that their difficulty level is not easily quantified as in the case with barbell, dumbbell, or cable weight exercises.  I'd encourage you to focus on compound lifts like the bench press, squats, deadlifts, and rows, rather than isolating exercises like curls.  Progression of difficulty is also an important factor.  If you are not increasing weight steadily, you won't continue to adapt and gain strength.
Comment: Great answer, but I'd like to know why you encourage to do compound lifts rather than bodyweight exercises? You seem to imply that the number one reason to do bodyweight exercises if because you don't need any equipment.
Comment: He's saying, that you can't do half a pull up, but you can take half the weight in barbells. There are some ways around it, but with weights it's easier.
Answer: A really interressing book about bodyweight exercice for strength is Naked Warrior by Pavel Tsatsouline.
In quick, if you want to be good with pullup and pushup, do lot of pullup and pushup, increase the volume for train your nervous system. Nerver train for failure, do  1 to 5 reps range of a challenging variation but do it many time by day, for more information look around about Grease the Groove.
My point of view if you want to be good with bodyweight exercices train with bodyweight forget about free weight or machine, if you can't do pushup or pullup begin with a variation you can do but challenging enougth for build strength.
Answer: I think the others have this fairly well covered (and I have my doubts as to whether you'll ever see this), but also consider making the exercise easier at first. I do not recommend doing "girl pushups" on the knees, as I feel like that's harmful to the knees, but one easy way to make pushups easier is to raise your hands higher. Put them on a chair. Or, if you have trouble with even that, push them on a wall. It may sound silly at first, but you can get exercise just pushing yourself from a bit off-vertical to vertical and it will get your body used to the proper movement. As you get better, you move closer and closer to the floor.
As regards pull-ups, the classic advice for people who can't even do one unassisted pull-up is to either do assisted pull-ups or negatives. For the former, you simply don't take your feet off of the ground. If the bar is low enough, just stand. If not, stand on a chair. Put as much of the weight on your arms as you can, but use your legs to give yourself that extra bit of lift. For negatives, it's even easier. Jump (or step off of a chair) into the position of having completed a pull-up and then lower yourself as slowly as you can. It's much the same exercise as an actual pull-up, but you're only using a fraction of the force since you're only slowing yourself, not countering gravity completely.

why can't I do push up or pull up?