What are ways to exercise abdominal muscles without harming your back?

Question: I am frequently hearing of new research finding how bad sit-ups and crunches are (example). So what are safe ways to exercise the abdominal muscles? For example, are planks proven to be safe?
Comment: I removed the part about the sixpack, it might distract people from the core of your question. Getting a sixpack is primarilly a result of your diet and low body fat. Check [this answer](http://fitness.stackexchange.com/a/1974/3941) for example.
Comment: You may want to enter the [Rectus Abdominis exercises section in EXRX](http://www.exrx.net/Lists/ExList/WaistWt.html#anchor172895) and look for alternative bodyweight exercises such as [Leg Raises](http://www.exrx.net/WeightExercises/HipFlexors/BWLyingLegRaise.html). There are many [easier](http://www.exrx.net/WeightExercises/HipFlexors/BWLyingLegRaiseFloor.html) and [harder](http://www.exrx.net/WeightExercises/HipFlexors/BWHangingLegRaise.html) variations there, as well as exercises with external resistance. I prefer leg raises, but I don't know if they are safer than crunches/situps.
Comment: If it hasn't already been mentioned, then it could be argued that [these](http://www.fitnessprogrami.com/attachments/hanging-leg-raise-knee-up-jpg.263/) would be good. However, it'd be a bit of a DIY, but the linked article's main thesis is that compression along the spine degrades the spine quicker, so you could modify a spine's-width channel for this piece of exercise equipment, kinda like the "genital saving channel" shown [here](https://images.duckduckgo.com/iu/?u=https%3A%2F%2Fimages-na.ssl-images-amazon.com%2Fimages%2FI%2F41mlYPFfjaL.jpg&f=1) for Roman Chairs.
Answer: Abs can be sufficiently trained via isometric exercise. I believe the safest way to exercise the abdominals is to use them for their intended function (stabilization) under a progressively increasing load or difficulty.
For example:

The co-contraction of the abdominals with the spinal erectors that is required during heavy squats and deadlifts in order to stabilize the torso (http://startingstrength.com/articles/abs_rippetoe.pdf). As your squat and deadlift get heavier, your abs are forced to get stronger.

Stabilization during pull-ups or chin-ups. These will leave your abs sore.

In a rehabilitation setting, when trying to correct posture-related back-pain, isometric co-contraction is suggested over concentric abdominal work, as well as emphasizing the stabilizing role of the abdominals (http://portalsaudebrasil.com/artigospsb/holist006.pdf):

Exercise involving co-contraction of the abdominal and back muscles is also in line with stabilization.
A simultaneous isometric co-contraction of transversus [abdominal] and multifidus [back], while maintaining the spine in a static neutral position, should help re-educate the stabilizing role of these muscles.

Another publication supports the use of isometric abdominal exercises in a therapeutic setting (http://www.pitt.edu/~neurolab/publications/1997/BeimGM_1997_JSportRehab_Abdominal%20strengthening%20exercise-a%20comparative%20EMG%20study.pdf)

Isometric abdominal exercises [...] have also been found to improve low back pain.
Comment: Plank is an example of an isometric abdominal exercise that is designed for ab muscles and will not hurt your spine.
Comment: I'm afraid I'm not technical enough to understand your answer. So basically you're saying doing other exercises that affect your ab muscles is sufficient? I want exercises for designed for ab muscles.
Comment: @Kate Your last post is not true in general. If you're doing the plank in a wrong way you will definately feel your lower back hurting. This pain comes from the hyperlordosis and not sticking your butt in or better said: not activating your abdominals in a full manner.
Comment: @mchlfchr Correct. The quote doesn't say *all* isometric exercises. (Or, did you mean my last comment? Sure, if you do the plank incorrectly, you can hurt yourself. That's a good point.)
Comment: @Kate I meant your last comment, sorry for being unprecise. Your comment "... will not hurt your spine" sounds to me that the plank is dummy-safe, which it isn't (unfortunately).
Answer: Besides the exercises recommended in the article you cite (planks, bridges, leg-lifts, bird-dogs and "stirring the pot"), full-body exercises that rely on your core muscles are also great ways to improve abdominal fitness, and they often strengthen your back at the same time, thereby helping prevent injury instead of potentially causing it.
Some examples of those are swimming (especially dolphin, butterfly and other strokes that rely on the abdomen -- dolphin-kicking with fins on is one of my favorite ab workouts, possibly just because it's so fun), tai chi (choose a style appropriate to your fitness level), surfing (or skateboarding, or slacklining; anything where you have to balance your body) and rock-climbing (if done properly, focusing on balance and technique rather than just arm-strength).  You'll be hard-pressed to find anyone who's a regular at any of those who doesn't have a nice strong stomach.
If you're just looking for one exercise to add to a workout, I'd go with planks.  The plank and exercises built on it are incredible stomach-strengtheners -- we use those on my swim-team as daily ab-exercises and they're intense.  As with all exercises, form is crucial if you want to avoid injury, so double-check and make sure you're doing it correctly.
Answer: Try out hanging ab exercises. Click here for a video on the various techniques using the below piece of equipment:

The spine doesn't come into contact with any form of spinal compression.

By the way, these are very easy to DIY with load straps and pool noodles.


Difference among prepaid card, prepaid debit card and debit card

Question: I'm confused with prepaid card, prepaid debit card and debit card, can anyone tell me the difference among these three cards?
Answer: Prepaid card and Prepaid debit card mean the same.
One need to load money [deposit money on the card account] for a fixed sum. Say 1000.
One can then use this 1000 where ever required. One cannot use more than 1000. If say after some usage, the money left comes to around 500, one can top up / load more money on the card when ever required.
So if you loose your card or someone hacks into it; the Maximum loss is the amount of money stored on it.
Debit Card are linked to a Bank Account. So there is no need to load any money, whatever is the balance in your Bank account can be used. The moment you use the card, the balance in the Bank Account goes down. If there is additional deposit in your Bank Account, salary etc, it can be used.
So if you loose your card or someone hacks into it; the Maximun loss is the amount of money in your Bank Account.
Comment: Then why so many Americans choose to use prepaid card instead of debit card? Is there any advantage of prepaid card? Because whether it is prepaid card or debit card, you are using your own money, I see no difference here.
Comment: The key difference is Risk and limiting spend. If I want to give my child a card, i would better give him a prepaid card. If I am travelling frequently and using card in different places, I would use a prepaid card, so even if its hacked, I just loose 1000. Where as my bank account may have 100,000 and all of it could vanish.
Comment: @JianbinYin the prepaid cards can also be given as a gift card, some are re-loadable others aren't. Prepaid cards can also be tied to a specific vendor such as a coffee shop, city subway, or college campus. This limits how they can be used, that way a child won't spend your money in ways you don't want.
Answer: The difference between prepaid debit card and non-prepaid debit card is that with the case of non-prepaid card, the charge goes through to the linked bank account, while with prepaid card - the charge is deducted from the prepaid balance, and no need to link a bank account.
Prepaid card is by default a debit card, there's no other way.


Salesforce Mobile SDK & iOS 11 Compatibility?

Question: I know that iOS 11 is going to release soon. I have been searching the internet about this so that we aren't caught off guard with our iOS app that uses it but I haven't seen anything yet. Is anyone aware of potential compatibility issues?
Answer: We, MobileCaddy, have daily tests run on all Dev preview and public betas for Android and iOS. In our August Trust Update it covers the release so far, and we have not seen any issues to date. As an update to this we've also not seen any issues with the more recent betas, either.
Whist the iOS release looks OK, I'd recommend you also check your app on iOS 10/9 with Winter 18, we have seen an issue with Salesforce doing something funky if you're trying to open VF pages from within your app.
Comment: Yeah, we are SF Mobile SDK 5.0.0. I was able to download our current app iOS app from the AppStore and run it on my phone with the iOS 11 beta, and it worked fine with everything, including the plugins. It looks like it only crashed when I built it from XCode 9 Beta. So its probably its related to XCode 9 Beta and not iOS 11.
Comment: So what version of the Salesforce Mobile SDK are you using? We are currently still on 5.0 and I just got iOS 11 beta on a phone and the app crashes when I click the gear button to go to the screen to select between the Production and Sandbox logins. I can login but once I grant access to site, it also crashes. Do I just need to be on 5.2 or is this something different?
Comment: Oh right. We've not moved any client apps to SDK 5+ yet (due to various reasons). From the top of my head we have SDK3+ and 4.2.X running OK.
Comment: We are using Pods and latest salesforce sdk ios pods version is 4.3.1. Does it work properly with ios11.0?


How can I learn all the rules and exceptions about the Vowel Reduction in Russian?

Question: I've been trying to find the rules and exceptions about this subject, but I can't really find a good source. At this point, I don't know if I'm supposed to learn this in this way. Sorry, I'm kind of perfectionist person and it bothers me a little not to find what I want.
Comment: https://docviewer.yandex.ru/htmlimage?id=824h-d1ptz8of8aa97guxx2cw606hden3i6ax06qu7dyludx9a8phjhhfcc12wxlri5em7kei1xf9uqob0v0j4qs0l1lafrmezcmwca2&width=900&name=bg-0.png&uid=0
Answer: One inexpensive Russian grammar text in which you will find the vowel reduction rules for Russian is the Schaum's Outline Series Russian Grammar.  If the book is not in bookstores near you, you will find it available (in English) from either Amazon.com, Amazon.uk.com, or Amazon.de.
If you search for the Schaum's Outline grammar on any of the above Amazon websites you will actually be able to look at and study the two pages where the Russian vowel reduction rules are stated and explained.  You can then see for yourself if that is the information you are looking for in your question.
So on the Amazon website(s) if you want to "look inside" the book all you need to do is click on the graphic of the book if the "Look Inside" logo is showing.  You can then scroll down to the index page and click on and click on "The Vowels" link [to page 5].
I believe the Russian vowel reduction rules you are looking for are those stated and explained on pages 6 and 7 of the book.
Comment: While "looking inside" the book one can click on the "View" tab on the Windows menu bar to increase the text size for better resolution of the text.


Why did Gandhi give the violent "Do or Die" slogan to the Quit India movement?

Question: Mahatma Gandhi was a pacifist and anti-violence leader. Why did he adopt the slogan "Do or Die" for the Quit India movement? It sounds more like a strong, desperate phrase.
Comment: Ghandi  was not a pacifist.
Comment: Unsourced assertions
Answer: 'Do or Die' is a very common phrase in India which almost never infer violence.  Google interpret this phrase as 'persist, even if death is the result.'
Thus, what Gandhi was trying to convey millions of Indians, were to strive for complete independence, even if death is the result. It doesn't convey violent message but very basic desperation, which was the need of the hour.
Comment: Which Google product can "interpret" a phrase written in English with an English paraphrase?
Comment: @AaronBrick, sorry I wasn't being pedantic here. I should have said [Google's automatic meaning extraction via its search](https://www.google.co.in/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=do+or+die+meaning&*)
Comment: Very well explained Nilay.
Comment: https://www.google.com/search?q=do+or+die+meaning&rlz=1C1GCEU_enIN850IN850&oq=do+or+die+meaning&aqs=chrome..69i57.5407j0j4&sourceid=chrome&ie=UTF-8
Answer: Non-violent resistance doesn't mean there won't be violence (including possibly death) happening. It just means you won't be the one committing it. In fact, it is the goal to induce the oppressor to respond with violence, to draw everyone's attention to the fact that they have no authority over the situation other than brute force.
As an example, I give you the Dharasana Salt March, which I can't describe any better than today's Wikipedia entry on it:

...the march continued under the leadership of Sarojini Naidu, a woman
  poet and freedom fighter, who warned the satyagrahis, "You must not
  use any violence under any circumstances. You will be beaten, but you
  must not resist: you must not even raise a hand to ward off blows."
  Soldiers began clubbing the satyagrahis with steel tipped lathis in an
  incident that attracted international attention. United Press
  correspondent Webb Miller reported that:
Not one of the marchers even raised an arm to fend off the blows. They
  went down like ten-pins. From where I stood I heard the sickening
  whacks of the clubs on unprotected skulls. The waiting crowd of
  watchers groaned and sucked in their breaths in sympathetic pain at
  every blow. Those struck down fell sprawling, unconscious or writhing
  in pain with fractured skulls or broken shoulders. In two or three
  minutes the ground was quilted with bodies. Great patches of blood
  widened on their white clothes. The survivors without breaking ranks
  silently and doggedly marched on until struck down....Finally the
  police became enraged by the non-resistance....They commenced savagely
  kicking the seated men in the abdomen and testicles. The injured men
  writhed and squealed in agony, which seemed to inflame the fury of the
  police....The police then began dragging the sitting men by the arms
  or feet, sometimes for a hundred yards, and throwing them into
  ditches.
Vithalbhai Patel, former Speaker of the Assembly, watched the beatings
  and remarked, "All hope of reconciling India with the British Empire
  is lost forever." Miller's first attempts at telegraphing the
  story to his publisher in England were censored by the British
  telegraph operators in India. Only after threatening to expose British
  censorship was his story allowed to pass. The story appeared in 1,350
  newspapers throughout the world and was read into the official record
  of the United States Senate by Senator John J. Blaine.

This youtube clip contains a dramatization of this from the 1981 Ghandi biopic that is worth seeing (although it is far too antiseptic).
That is what is meant by "do or die". Walking willingly into harm's way rather than submit.
Comment: If this answer ventures into TL;DR territory for you, there's a nice [youtube video](https://www.youtube.com/watch?v=WW3uk95VGes) explaining the same thing as my answer using clips from the same Ghandi biopic.
Answer: It was not a desperate phrase by any means. Since the 1920's, Indians were protesting against the British for freedom. But the British showed no signs of relenting. India was the brightest jewel in the British Crown and there was no way that the British would relinquish their hold on it.
Finally, Gandhi had enough. He knew that there had to be a decisive push for freedom and no more pussyfooting this time. It was to be the ultimate showdown, with no compromise on the final objective: Independence for India and the complete ejection of the British Raj. Even if this meant total civil disobedience and death at the hands of the British.
Hence this phrase was coined. This was to tell the British that there was to be no negotiation or no compromise on the goal for Purna Swaraj (Complete and unconditional independence).
Answer: That Gandhi was an ethical pacifist is largely a romantic conceit. He was in fact a pragmatic pacifist. He knew that it would be relatively difficult to rouse the Indian people to overthrow the British with violence, and thus promoted pacifism as the best way to accomplish that goal.
Comment: Not sure this is responsive to the question.  This would also be improved by sources/ research.
Comment: Can you add any source to your answer?
Comment: The first rule of fighting [King Shark](https://en.wikipedia.org/wiki/King_Shark) is that you don't fight him in the water.


How do I theme checkout pages?

Question: how do I theme the cart and checkout pages in Drupal commerce?  I have set content, account, billing, and payment parts. Is there any --.tpl.php file to create?
Comment: If you could be more specific about which aspects of the Commerce cart and checkout you are trying to change and what you wish your end result to be, it will help others in providing you with a more helpful answer.
Comment: Dealing with a similar issue here! I was hoping to use hook_form_alter() in order to modify the markup. At best, I get a "data" field which is already rendered as a table.
One would hope it would be possible to act on the form elements before they get rendered... Still searching...
Answer: For theming cart page add page--cart.tpl.php in your theme's templates directory.
For theming checkout page add page--checkout.tpl.php in your theme's templates directory. If you want to theme only the checkout review page add page--checkout--review.tpl.php in templates directory.
After adding tpl files do not forget to clear cache.
If you want to know about more hooks do a dpm($variables) inside YOURTHEMENAME_preprocess_page function and look into the theme_hook_suggestions array.
For details read this comment http://drupal.org/node/1142800#comment-5365466
Comment: This helped me a lot but as this question is not mine I can give only one thumbs up :)
Answer: The only template files in Commerce related to the checkout module are commerce-checkout-errors-message.tpl.php and commerce-checkout-help.tpl.php. These are located in the Commerce module directory under modules/checkout/theme.
The only template file related to the Cart module is commerce-cart-block.tpl.php, which is located in the Commerce module directory under modules/cart/theme.
Answer: Actually the easiest way I think is using hook_form_FORM_ID_alter() to alter the checkout form. If all you need is only change the part inside the checkout form.
As I see, most of the checkout & checkout review page content is inside the form. First is 'commerce_checkout_form_checkout', and second is 'commerce_checkout_form_review'. If you know how to use form API & how to alter the form by using hook_form_FORM_ID_alter(). That will be very easy to alter the form content. Like reorder them or insert/remove elements.
Here is a simple example for add a notice into the checkout page:
function my_module_form_commerce_checkout_form_alter(&$form, &$form_state, $form_id) {

  //If you have Devel module, uncomment to see what is the original form data
  //kpr($form);

  //uncomment to see current form_id
  //echo $form_id;

  //check form id
  if($form_id == 'commerce_checkout_form'){
    $form['my_test_notice'] = array(
      '#markup' => '
Hello, this is a checkout test!
',
      '#weight' => -1,
    );
  }
  elseif($form_id == 'commerce_checkout_form_review'){
    $form['my_test_notice'] = array(
      '#markup' => '
Hello, this is a checkout review test!
',
      '#weight' => -1,
    );
  }
  //You can add more ...

}

Answer: You can also use the body classes (depending on what base theme you use, these are often available). This allows you to give specific values to child items of the body with class .checkout, for example. This might be enough to jig the layout a little bit.
Answer: Have you tried Theme Develper module which gives you info about which theme hooks to implements and which themplate files to adopt.
Answer: Cart page is just a view, so style it as any other view:

Go to page when you are logged in as admin, find and click "Edit view" link.
On view edit page open "Advanced" view settings and click "Theming information"
There you can see how you should name your templates (i.e. views-view--commerce-cart-summary--default.tpl.php) and also if you at template name at beginning of the row (i.e. first is "Display output" you can see default template, copy it, save with other name in your theme's template dir and modify it as you like).
Or, you can build those pages (views) on your own. http://www.drupalcommerce.org/user-guide/modifying-shopping-cart-using-views
Answer: You can make your own .tpl files, and call them with a hook_theme function:
function yourtheme_theme(&$existing, $type, $theme, $path) {
  return array(
    'commerce_cart_add_to_cart_form'=> array(
    'render element' => 'form',
    'template' => 'path/to/template/commerce_cart_add_to_cart_form',
  ),
    'commerce_checkout_form_review'=> array(
    'render element' => 'form',
    'template' => 'path/to/template/commerce_checkout_form_review',
  ),
  ...
  ...(more templates)
}

as these are forms, you then can hide the form, find what you need, and use your own markup in your template.
<?php
  hide($form);
  dpm($form);
?>

  print render($form[...]);

Or, you can leave it as it is and do stuff around it.

How do I theme checkout pages?


Custom Case Fields do not work in Drupal Views

Question: I have correctly setup views to work for civicrm fields and am also using the civicrm entity module for Drupal to expose fields. In my testing it seems like the custom fields work for certain types of civicrm components. For example, if i use a custom field for All Contact Types then it works correctly and even the dropdown shows CiviCRM:Custom - Field name. However, for a custom field for Cases it does not work and has the same issue i.e. refers to SQLSTATE[42S22]: Column not found: 1054 Unknown column 'civicrm_case.custom_3' in 'field list'. Has anyone had any success in using custom civicrm case fields in Drupal views?
Answer: I spent some time on the setup of the Views and it does actually work. However, what is missing is the relationship in the View. It is subject to the type of view you try to create and the relationships. Also remember to choose the CiviCRM Custom: [Field_name] instead of the one provided by CiviCRM Entities.


Are small air bubbles on the surface while applying wood finish normal?

Question: While finishing my door, I've noticed a lot of small air bubbles after applying the finish.  I asked a painter about it and he told me it's normal, but it doesn't seem normal to me. Is this normal or should I hire some other person?
Answer: It can be a problem when drying conditions are too fast for the finish to release the bubbles.  Here are some strategies to try.

Good quality brush, china bristle (boar) for oil
Slight thinning (up to 10%).
Drying extenders (retarders): Floetrol for latex, Penetrol for oil based paints and stains
Don't shake your finish, stir only (to prevent mixing air into finish).
"Tip off" slowly (lightly drag brush almost laying flat, no pressure) to integrate sections and even out finish.
HVLP spraying is within home user capability and pricing.
Comment: I'll add another tip: don't squeeze the brush along the rim of the can. Especially with foam brushes this can introduce a lot of air. To get excess finish off the brush just let it trip for a moment, or gently swing it against the insides of the can.
Answer: If you're using a varnish and a paintbrush it's fairly common. You can apply varnish or oil with a rag and that will cut down on the bubbles but they aren't a big issue most of the time.
Answer: I found that thinning was the key - had to experiment a little but once I got used to it the results where very good.I would go so far as to say that almost nothing can  go from the can to the project some kind of thinning or cutting back on product is essential .
Answer: I find that the bubble almost always disappear during the drying process. Don't pop them.


Mining for rpc set number of threads

Question: In the monero-wallet-cli having connected to a public node that accepts or requires payment via mining how does one adjust the number of threads used for the mining payment.
For example, when you run the help command after starting your wallet you can see:
start_mining [<number_of_threads>] [bg_mining] [ignore_battery]

But for the rpc mining there is no [] parameter:
start_mining_for_rpc

It seems that start_mining_for_rpc defaults to 1 thread. I believe server hosts may want to increase the payment and running on multiple threads would allow for that.
Is there any non-obvious way to increase the rpc mining thread count?
Answer: There is currently no way to mine with multiple threads in monero-wallet-cli for the mine-for-RPC system.

Mining for rpc set number of threads


Do speakers of languages that use gendered nouns automatically use the same gendered pronouns when referring to an animal as Mr. or Mrs.?

Question: I know this is sort of a silly question, but the other day when walking in the park, I saw a squirrel and said, "Hello, Mr. Squirrel". I know for me, my choice of Mr. over Mrs. was random, or at least influenced by factors outside of language, but it got me thinking. I wonder if in a particular language, if squirrel were feminine, would a speaker of that language automatically use "Mrs. Squirrel"?
Comment: How naturally would you say "Mr Lady beetle"?
Answer: No, not anymore so than in English.
In German, Herr Pferd and Frau Pferd both work.  Pferd is neuter, and I think that is almost the answer right there: so-called grammatical genders are just noun classes, in IE languages there are often three classes, not two, so how would a strict 1:1 mapping to two forms of address even be possible?
Bär is masculine.  Frau Bär is fine, and Frau Bärin is a bit odd, Herr Bär is of course fine.
But Herr Kuh is unnatural, not because of the grammatical gender of the noun, but because of the actual gender of a cow in real life.  Just as in English one would probably not say Mr Cow, and one would definitely not say Mrs Rooster.
It will depend on the language, but only because it depends on whether and how strictly a word specifically refers to only one gender of a species.  (That probably varies within a language too, given speakers' varied exposure to animals in nature and agriculture.)
For example, in German or Russian there are specific words for female and male cats, a bit like chicken and rooster, and note that female is the default, for an unknown individual or mixed group.  Herr Katze and Herr Kater are roughly equally frequent on the web.
There are more complications to all of this, for example in Spanish the word for cat, gato, default male, can be feminised to gata, but the word for cow, vaca, cannot be made vaco for bull, so there is señora gata, and señora gato, but there is no señor vaco.
To really make a point that grammatical genders are just arbitrary noun classes, consider that in such languages even inanimate nouns like Automobil or abstract nouns like Situation have a gender, and speakers do not even think about it.
Comment: @Mitch - One problem is that there are many "gendered" languages, and they may be very different (German has three genders, Portuguese just two, Dutch again two, but not the same two as Portuguese). It would be difficult to give a general answer unless one could have an encyclopaedical (and in-depth!) knowledge of languages. My general guess is that there is a grammatical constraint that leads people into using a given gender - not always the masculine one - when referring to given animals. But this might be a quirk of IE languages. One alternative could be a language with an "unknown" gender.
Comment: There are a lot of examples in here, but I had a hard time figuring out what the answer is. Is it 'it's arbitrary depending on the language'? or is it 'You can say Mr or Mrs as you please'? or something else short?
Answer: In Portuguese there are animals for which there are two different names, one for the male, and one for the female:

O touro (bull) - a vaca (cow)
O cavalo (horse) - a égua (mare)

Other animals are referred by just one name, but it inflects by gender:

O gato - a gata (cat)
O porco - a porca (pig)

Still others have just one name, that does not inflect by gender. Those have a fixed gender, irrespective of the sex of the animal:

A onça (jaguar)
A doninha (weasel)
O elefante (elephant)
O furão (ferret)

And then there are a few names that do not inflect, but accept articles of either gender, according to the sex of the animal:

O jabuti - a jabuti (tortoise)

The third and fourth categories are more commonly composed by names of non-domesticated animals - and the fourth is more usual among borrowings from Tupi-Guarani.
But the issue is somewhat blurred. Some would say that "elefante" does have a feminine form (and then disagree whether it is "elefanta" or "elefoa" - placing the word in the second category above - or "aliá", which would make it an instance of the first category). And definitely there are cases where there is inflection, but one of the genders is more or less automatically used when the sex of the animal is unknown - "raposa" (fox) does have a masculine form, "raposo", but the feminine is used whenever the sex of the animal isn't important.
Now, a use such as "Seu Esquilo" (Mr. Squirrel) is unusual - it is either children talk or a peculiar subset of the literary register, pertaining to fables or fairy tales. And then the rules are much laxer than in standard or colloquial register. If the animals come in couples, it would often be natural to call them "Dona Onça" and "Seu Onço", even though the latter would be weird in colloquial speech. This is however very irregular, and the use of one of the forms may sound weird even in a fable ("Seu Furão", ?"Dona Furona"; "Dona Zebra, ?"Seu Zebro"). Also in fables, the modern (and somewhat colloquial) masculine "Seu" could possibly be replaced by the archaic "Dom" - as in "Dona Baratinha e Dom Ratão").
So, in the case in point, I think the most natural thing would be to call the squirrel "Seu Esquilo", unless for some reason one would assume it is a female (the word does have a feminine form, "esquila"). If it was a fox, it would be more natural to call it "Dona Raposa" unless for some reason it was assumed to be a male.
If it was a jaguar, it would be "Dona Onça", with the alternative "Seu Onço" only if we intended to stress it was a male, if we are telling a fable; in colloquial or standard Portuguese we would call a male jaguar "onça-macho" (and use the feminine articles and adjectives - "a onça-macho estava furiosa".)
Answer: I think the previous answers missed the point by focusing on animals, which have a biological gender (apart from the gender assigned to the noun).
As a native speaker of Spanish, if I wanted to address, say, a fork, my first instinct would definitely be to say Señor Tenedor as opposed to Señora Tenedor. But if I wanted to get the attention of, say, a napkin, I would say Señora Servilleta and not Señor Servilleta.
Comment: This question was specifically about the contradiction between the grammatical gender (GG) of a noun and the biological gender of an unknown animal. It was not about inanimate objects where only GG applies.


Is it a good idea/useful to use two Anti-virus apps on Android?

Question: Is it a waste to load two anti-virus apps on your mobile? Are two AV apps more effective than one?
Comment: Put it into another perspective - running two AV's or more on Windows is counter-productive as clashes are going to occur, one flagging up malware on the other AV during scan etc in a Windows environment. Meanwhile, on Android, not alone that, AV are a con job, they really do not do anything except hog up resources regardless, and chew up battery juice! Its down to common sense, read the permissions, download from playstore only and not going to some dicey website based in China etc, you get the drift.
Answer: No. I'll even go to the extent of saying using an Antivirus is of no use if you only install apps from Google Play.
But if you install apps from third party sources (i.e APKs, etc.), using an antivirus might actually make sense. But using 2 AVs doesn't make sense in any scenario imho.
Comment: I wouldn't say that installing apps from Play only guarantees a lack of malware (always check app permissions, at the very least!), but overall I'd agree with Karan that for the average user AV is totally unnecessary, and that having two different AV products on the same device is extremely undesirable regardless of OS as they will work at cross purposes and hugely slow down a device.
Comment: @user66264 using two antivirus in any complex machine (PC, smartphone, etc.) is a waste of resources and normally leads to conflicts. Just use the one you trust the more and stick with it.
Comment: If you do install third-party APKs, wouldn't it just suffice to upload them to virustotal.com before installing them, rather than running possibly-invasive, battery-draining, etc. AV software in the background on your own device?
Comment: No, just uploading them to virustotal.com would not be sufficient.  Virus scanners can only check for known viruses, and new variants crop up all the time - hence all the updates AV software does.  So a one time check on a sideloaded app will only tell you that, *as of that date*, there are no *known* viruses associated with that app.
Comment: ^ do you really feel it's feasible to upload every APK file to an online scanner before installing? Sadly I don't and I feel many others will also agree with me on this.
Answer: A known issue with running 2 AVs is that they'll consider each other as a potential virus.
This has to do with the behaviour of these programs. They scan directories, perform root-operations (if you have installed the AV on a rooted device), and so on.
This is true on any system, not only mobile devices.
You can in most cases run an AV together with an anti-malware product.
I do say in most cases.
As mentioned by Karan, there is no real need for AV software as long as you only run Google Play / Appstore apps and you don't download any rubbish from sites you visit.
Do keep in mind that there are some dangerous apps on Google Play. I'm an Android user myself, definitly no iFanboy, and I must admit not all Play apps are safe.
So always check the permissions and intentions of an app before installing it.
I myself have Avast! Mobile Security on my tablet.
This is because I run some off-the-market apps. MS also allows me to protect some apps with a pincode, such as my email apps.
I don't think running an AV is a waste of resources, but if you handle your device with care, there is no real need for one.
Comment: Advise @ Ground Zero was super helpful! Thanks!
Answer: If you don't use much of sharing stuffs from unreliable/unknown sources and you do not visit unknown sites.
Answer is NO, you don't need a AV.
Its a waste of resources.

Q. Is it a waste to load two anti-virus apps on your mobile? Are two AV apps more effective than one?

YES it is a waste. NO two apps are not effective.
Reason is each AV has it its own heuristic engines to scan viruses, which generally detects another AV as a virus.
Comment: AV app really has access to binary of downloaded apk?


How to find expected time to reach a state in a CTMC?

Question: Given a simple CTMC with three states 0,1,2. There are three transitions $0 \rightarrow 1$ (with rate $2u$), $1 \rightarrow 2$ (with rate $u$), $1 \rightarrow 0$ (rate $v$).So $2$ is an absorbing state. Can someone please help me understand how to find the expected time to reach state-2 from state-0? Using the understanding I get, I want to do the analysis on some complex markov chains.
Comment: Did you try the standard method? That is, introduce the expected time t(x) to reach state 2 starting from state x, find a linear system which the t(x) solve, deduce every t(x), and in particular t(0), which is the expected time you are after.
Answer: Since the OP stays silent, here is an answer. As explained in a comment, the standard method is to introduce the expected time $t_x$ to reach state $2$ starting from each state $x$, to find a linear system which the vector $(t_x)_x$ solve, to deduce $(t_x)_x$, and in particular $t_0$ which is the expected time asked for.
Here, the vector is simply $(t_0,t_1)$, and $$t_0=\frac1{2u}+t_1,\qquad t_1=\frac{1}{u+v}+\frac{u}{u+v}\,0+\frac{v}{u+v}t_0,$$ hence $$t_0=\frac1{2u}+\frac1{u+v}+\frac{v}{u+v}t_0,$$ which yields finally $$t_0=\frac{3u+v}{2u^2}.$$
Answer: You do it in a similar way as you would for finding the expected first passage time for a discrete chain. If $Q = q_{ij}$ is the transition rate matrix, $P = p_{ij}$ is the transition matrix of the embedded chain, \operatorname{Boole} is the indicator function and $T[i, Q]$ is the first passage time starting at state $i$, then
$$\begin{align*}
\operatorname{\operatorname{Mean}}[FPT[i, Q]] &= \operatorname{Expectation}[FPT \mid X[0] = i]\\
&= \operatorname{Expectation}[\operatorname{SojournTime} \mid X[0] = i] +
  \sum _{j=1}^{\infty} p_{ij} \operatorname{Expectation}[FPT \mid X[0] = j]\\
&=-\frac1{q_{ii}} +
  \sum _{j=1}^{\infty} \frac{-q_{ij}}{q_{ii}} \operatorname{Boole}[j\neq i] \operatorname{Mean}[FPT[j, Q]]
\end{align*}$$
where the sojourn/holding time is, of course, exponentially distributed with parameter $-q_{ii}$.


Can I bring cut orchids from Singapore to Australia?

Question: Changi Airport has several shops that sell boxed cut orchids.  Can I import these to Australia? Or will they be confiscated by Customs?
Answer: Australian Department of Agriculture has some information, in summary, for personal use:

You must declare them on arrival so that they can be examined by customs.
They may need to be treated or destroyed depending on origin and species of flower, or if they are found to have pests or other biohazards. There is a list of allowable species here. Orchids are on it.
You can import a limited number for personal use - six items (where an item is a small box, florist package, or individual bouquet)

They have a system called BICON which you can use to check the requirements for specific species if you were thinking of bringing something other than orchids.
Comment: I've brought back & declared orchids three times now.  Every time, I'm sent to Quarantine, they do a quick inspection for bugs in a back room, and then they're declared OK and I'm waved on.
Answer: Yes you can and maybe they might.
Cut flowers of most all members of the Orchidaceae can be imported from any country into Australia.  They do not require any permits, unless they are species listed on the CITES red list.  But any cut flowers sold at Changi Airport will be from hybrids not species.
You do have to declare them upon arrival in Australia and they will be subject to inspection for disease, insects, etc.  If found wanting they will be confiscated and destroyed.  But again what is being sold in Changi has already been selected so that it is OK for travelers to take home.
So make the folks you are visiting feel great with an orchid bouquet.


How do I disable the "CD as package" source from the command line for ubuntu 12.04 LTS server?

Question: I am trying to install or update software for Ubuntu server 12.04 LTS. I get this error:
<code>W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/precise/InRelease
</code>
and other such lines.
 Another user posted that this might be a problem if the CD is still referenced as a package. How do I remove the CD from the command line on a server?
Thank you.
Mike M
Answer: You can edit the source list by editing the following file:
<code>/etc/apt/sources.list
</code>
This link may be able to help you more.


How does enchantment combining with an anvil work?

Question: I've been reading about how you can combine enchantments and put enchantments from books onto items. It seems like this could make for some very over powered things. Is there a limit to how many times an item can be combined/books used? Do enchantments stack? For example, if I have 2 pickaxes, an unbreaking II and unbreaking III would it become an unbreaking V? I've also read that some things cannot be applied at the same time, like fire and projectile resistance. Could someone go around and murder/steal from their foes, then go and steal their enchantments to make themselves more and more powerful? Is there a limit?
Comment: Did you try reading the wiki on [Enchanting](http://minecraft.gamepedia.com/Enchanting) and [Anvil](http://minecraft.gamepedia.com/Anvil)?
Comment: As for stacking enchantments: two of the same level combine to create the next level up. So 2x Unbreaking II = 1x Unbreaking III.
Answer: When combining enchantments, the enchantment caps out at a certain number. These are as follows:
Armor:

Protection IV
Fire Protection IV
Explosion/Blast Protection IV
Projectile Protection IV
Feather Falling IV
Respiration III
Aqua Affinity 1
Thorns III
Depth Strider III

Swords/Axes:

Sharpness V
Smite V
Bane of Arthropods V
Knockback II
Fire Aspect II
Looting III

Bow:

Power V
Punch II
Flame I
Infinity I

Rod:

Luck of the sea III
Lure III

Other/Most/All:

Unbreaking III
Efficiency V
Silk Touch I
Fortune III

Enchantments of the same level can be combined to get an enchantment 1 level higher; combining enchantments of different levels always yields an item with the higher of the two levels, giving no increase.
Trying to combine any enchantment that would give you past the numbers above will just give you the cap, EX: Unbreaking III and another Unbreaking III would only give you Unbreaking III, instead of Unbreaking IV
You cannot put Silk Touch and Fortune on the same tool, you cannot put more then 1 different type of Protection on the same piece of Armor, and you can not have any combination of Sharpness, Bane of Arthropods, or Smite on a weapon. All these enchantments are standalone and may override another if put on an item.
Comment: What about fire aspect? I have a sword and it originally had smite and knockback, I put on fire aspect and looting but the fire didn't work.
Comment: @Crubleigh If the sword is killing the mob you're hitting in 1 hit, the fire will not proc. Make sure that it's taking more than 1 hit and it should catch on fire.
Answer: You need 2 enchantments of the same level to get an enchantment of the next level up. There is a cap to the max level enchant you can have. Every time you combine/repair an item in the anvil, the experience cost goes up, and when that goes past 39 levels, you cannot combine with that item again.You can only combine 2 of the same items to combine enchants, except for enchanted books.
Answer: Enchanted books can be used at an anvil to combine with another item. Enchantements will apply to the right objects (for example,you can't apply Fortune on boots,except on creative mode) or combine with another book. Note that if a book has multiple enchantments,and just some of them can be applied to an object,the others will be lost,so choose carefully which enchants to get out of the book. Be careful,though,the book enchantment method is level-consuming,and the anvil has a limit of 39 levels at once! In case you ever go over the limit,you will better do the work in more sessions. Anyway,if you
combine 2 equal enchantments,say,Protection 3,you will get Protection 4,not Protection 6. You will always get the next level if you do combine 2 enchantments of a level. There are also some limits provided in the list below:

Protection 4
Fortune 3
Unbreaking 3
Efficiency 5
Sharpness 5
Power 5
Feather Falling 4
Respiration 3

Notes: These are only some of the many enchantments,see more on the wiki. As you stated,some enchantments do not stack,such as Sharpness with Smite. Also,combining enchantments of different levels will result in receiving an item with the biggest enchant of those two. (Example: Fortune 1 + Fortune 2 = Fortune 2) Also,you can oly combine the enchants of the item of the same type or an item with an enchanted book.


What is the etymology of « fut »?

Question: I was learning about how to identify the passé simple yesterday and wondered why the passé simple of « être » is « fut ». It's very dissimilar, so much so that I mistook it for « faire ».
Comment: @DogLover jiliagre meant in English, not the French translations of those words. He's pointing out that the phenomenon is very common and applies to the past tense of the English verb *to be* just as it does to French's *être*.
Comment: Do you find it easy to identify "to be" / "I am" in "I was" ?
Comment: @jlliagre Yes. "été" still has the "êt". "I will", however... C'est "serai". However, even that still has "e" in it.
Comment: @jlliagre I've always had a nagging feeling similar to OP. Not once did I make the connection to "to be" and its conjugations. This answer was perfect—thank you.
Answer: The verb être is built from a mixture of two Latin verbs, esse (to be) and stāre (to stay), moreover, the latin esse had some tenses built from proto-Indo-European roots, like precisely fuī (which shares the same root as the English to be).
This background explains the very irregular forms depending on the persons and the tenses.
You are lucky not studying Spanish, where the situation is even more complex.
See also this thesis about suppletive verbs (like être) in Romance languages.
Answer: Être is from two Latin stems, esse and stāre, but this doesn't actually cover the problem because both the être and fut forms are from only one of those two stems.
That stem, esse, was itself a combination of two Proto-Italic stems, according to Wiktionary.

The present stem is from Proto-Italic *ezom, from Proto-Indo-European *h₁ésti ("I am, I exist").
The perfect stem is from Proto-Italic *fūai, from Proto-Indo-European *bʰúHt ("to become, be").

Naturally, the first root is the source of être and probably also soi- as in soit and ser- as in sera (though if another linguist on here can verify or deny that, please do!). The second root is the source of fut (and, incidentally, is related to futur). Meanwhile, the stems beginning with ét- as in était are from that altogether different Latin root stāre.
That these separate lexemes combined to form one verb in Latin is certainly interesting. As jlliagre points out, English has this too: be and was are ultimately from different sources. (What may surprise you most is that the be is ultimately from the same root that spawned Latin esse root and was to the one that spawned fut...! That said, when we are dealing with Proto-Indo-European, we must recall that we are speculating thousands of years back and are trying to explain commonalities between languages, so this sort of extreme etymology shouldn't be relied on too heavily.)
Note that the two-stem stage and the one-stem stage are different languages, separated in usage by long periods of time. Perhaps the fusion happened as children sometimes heard the one, sometimes the other, and the meanings were so close that they ended up misreading the import. They would unconsciously reason along these lines: "Oh, Mommy says it like that when it happened yesterday and like this when it's happening today." As Chomsky and many linguists of his school have observed, the data children get about their language is so unbelievably sparse compared to the complexity of the subject matter that such things happen all the time and are only sometimes noticed and corrected by parents (and only sometimes do children respond to explicit grammatical correction!). Such silent reinterpretations are the engine of a lot of language change, such as the transition that will eventually made from the main verb "to want" to a modal indicating the future tense. Or the amusing story of how the English word "apron" ultimately comes from the French "napperon": the English phrase "a napron" was parsed as "an apron" by enough members of a few generations.
However the fusion happened, though, what can be generalized is the following observation: the most common words in a language are usually the ones with most bizarre behaviour. "To be" is an everyday word. So is "to go", where we see three roots in French: aller, ir- as in ira, and va. "Women" represents a very strangely pronunciation for the letter "o". And so on. (I could give examples from Hebrew and Spanish as well.) This is somewhat surprising given the above explanation; you'd think that the most common words would be the ones children would hear often enough not to be mistaken about them. But conversely, being heard often enough can also cement a mistake. :)
It would be fascinating to read a source giving more detail on exactly how and when those two Proto-Italic roots fused into one verb in Latin — jlliagre's sources look very promising, and are making me rethink ser- and soit — but hopefully this gives you an idea of what's involved.
Comment: @jlliagre Thanks for fixing those! This is the first time I'm reading your name correctly. v_v
Comment: Is there a relationship between _fut_ in French and _fuit_ in Latin, or is this a mistake? - meaning that the form is superficially similar, but there is in fact a different origin for _fut_?
Comment: @Frank I wish I could say definitively, but I'd bet on it, yeah. One would have to track *fui* through the years to watch its transformation, but I can't think of another explanation. (The fact that the root is *fu-*, ending in time to accommodate something else than *-t* historically, helps.) I should probably do more than skim that thesis jlliagre linked to, but here's one implied connection on p. 59: "Un quatrième radical, celui du latin *fuī*, qui sert à dénoter un déplacement au passé (cf. fr. *je fus* ou *j'ai été à l'église*)." Not unambiguous but may help...
Comment: Should I retire my answer as too simplistic then?
Comment: Sorry, my "yes" was meant to be to your first question! To the second it should have been "no" — I don't think there's a different origin.
Comment: Extremely informative! Thank you!
Answer: Isn't it the same in Latin already: sum → fui, est → fuit? I would says that's the origin of our passé simple. sum/être is a highly irregular verb, hence the radical change in form for some tenses, most probably because it is used a lot.

What is the etymology of « fut »?


What is required to achieve Nirvana in Buddhism?

Question: Nirvana is considered by many religions the pinnacle to strive for.  What do I need to do to achieve Nirvana?  Are there different perceptions of the requirements held by different sects?
Comment: sorry if i sound trite, but just practice
Answer: To answer your question let me draw an analogy. What is required to become a professor?
According to Wikipedia, "A professor is a highly accomplished and recognized academic, and the title is in most cases awarded only after decades of scholarly work to senior academics". Being a professor is not a concrete state, it is a label they put on years of hard work, culminating in professional realization.
Similarly, Nirvana is not a concrete state, it is a common name for the condition of a highly accomplished spiritual practitioner. This condition is not something you can contrive knowing the requirements, it is a result of years of personal transformation.
Nirvana can be characterized as condition of having transcended suffering & death. The requirement for this is said to be a complete cessation of Attraction (obsessing over something as desirable), Rejection (obsessing over something as undesirable), and Ignorance (mistaken understanding of how everything works). One of the key components of Ignorance is a deeply lying conviction in existence of substantial self and a tangle of reflexes that grow around that. Much of Mahayana practice is targeted at destroying this belief, not just at conceptual level, but at the level of basic day-to-day instincts.
If we could simplify the requirement for becoming a professor to "complete cessation of ignorance in the field of study one specializes in", we could perhaps make a stretch and define Nirvana as "complete cessation of ego complex, along with negative experiences and behavioral tendencies it generates". As any simplification, this is not entirely accurate: just as becoming a professor requires tons of practical skill and experience outside of the primary field of study, attaining Nirvana requires cessation of all mental and emotional obscurations, a tendency to get stuck on anything, not just on self.
Now, for the purposes of this discussion I'm equating Nirvana with Enlightenment, which depending on a school may or may not be the right thing to do. Specifically in Mahayana, Nirvana is considered a conceptual projection (a shadow of ego so to speak) that has to be transcended as part of awakening to Self-Existing Buddha Nature (=Enlightenment).
Answer: In Buddhism you need to follow the Noble Eight Fold path to attain nirvana. It is further divided into three parts for simplicity - Sila (morality), Samadhi (mental culture) and Panna ( wisdom).
The noble eight fold path is as below :
Sila (Morality): 1) right speech 2) right action 3) right livelihood
Samadhi (mental culture): 4) right awareness 5) right concentration 6) right efforts
Panna (wisdom) : 7) right resolve 8) right view
In whichever teaching the components of Noble Eight Fold path is found there you will find source of Nirvana. So you can follow any sect you prefer. But right view is what differs in Buddhism which takes you in right direction. Understanding Buddhism's (right) view of rebirth, karma and three realities of life (impermanence, no soul and suffering) and dependent origination can help understand Nirvana better.
Comment: Good and precise answer.
Answer: I am reading a book called What the Buddha Taught by Dr. Walpola Sri  Rahula.
Noble Eightfold Path
The Fourth Noble Truth is 'The Path' (Magga) leading to the cessation of Dukkha (defined in the First Noble Truth as basically anything conditioned or in other words part of dualism; things that are not everlasting)
See other answers that already list the eight divisions/categories.
Five Hinderances
Ponder these.

lustful desires (kāmacchanda)
ill-will, hatred, or anger (vyāpāda)
torpor and languor (thīna-middha)
restlessness and worry (uddhacca-kukkucca)
sceptical doubts (vicikicchā)

Seven Factors of Enlightenment
Meditate on these.

Mindfulness (sati) i.e. to be aware and mindful in all activities and movements both physical and mental.
Investigation and research into the various problems of doctrine (dhamma-vicaya). Included here are all our religious, ethical, and
  philosophical studies, reading, researches, discussions,
  conversations, even attending lectures relating to such doctrinal
  subjects.
Energy (viriya), to work with determination till the end.
Joy (pīti), the quality quite contrary to the pessimistic, gloomy, or melancholic attitude of mind.
Relaxation (passaddhi) of both body and mind. One should not be stiff physically or mentally.
Concentration (samādhi).
Equanimity (upekkhā) i.e. to be able to face life in all its vicissitudes with calm of mind, tranquillity, without disturbance.

To cultivate these qualities the most essential thing is a genuine
  wish, will, or inclination. [...] One may also meditate on such
  subjects as the Five Aggregates investigating the question "What is
  being?" or "What is it that is called I?", or on the Four Noble
  Truths. Study and investigation of those subjects constitute this
  fourth form of meditation, which leads to the realization of Ultimate
  Truth.

Excerpt about the feeling 'I AM'

It is the vague feeling 'I AM' that creates the idea of self which has
  no corresponding reality, and to see this truth is to realize Nirvāna,
  which is not very easy. In the Samyutta-nikāya there is an
  enlightening conversation on this point between a bhikkhu named
  Khemaka and a group of bhikkhus.
These bhikkhus ask Khemaka whether he sees in the Five Aggregates any
  self or anything pertaining to a self. Khemaka relies 'No'. Then the
  bhikkhus say that, if so, he should be an Arahant free from all
  impurities. But Khemaka confesses that though he does not find in the
  Five Aggregates a self, or anything pertaining to self, 'I am not an
  Arahant free from all impurities.' O friends, with regard to the Five
  Aggregates of Attachment, I have a feeling "I AM", but I do not
  clearly see "This is I AM".' Then Khemaka explains that what he calls
  'I AM' is neither matter, sensation, perception, mental formations,
  nor consciousness, nor anything without them. But he has the feeling
  'I AM' with regard to the Five Aggregates, though he could not see
  clearly 'This is I AM'.
He says it is like the smell of a flower: it is neither the smell of
  the petals, nor the color, not of the pollen, but the smell of the
  flower. Khemata further explains that even a person who has attained
  the early stages of realization still retains this feeling 'I AM'. But
  later on, when he progresses further, this feeling of 'I AM'
  altogether disappears, just as the chemical smell of a freshly washed
  cloth disappears after a time when it is kept in a box.
This discussion was so useful and enlightening to them that at the end
  of it, the text says, all of them, including Khemata himself, became
  Arahants free from all impurities, thus finally getting rid of 'I AM'.
Answer: In Theravadan tradition you need to gain Insight through Vipassana meditation in order to attain Nirvana. That's all! Everytthing else just makes the path to Enlightenment easier or has other benefits like Samatha meditation.
Answer: Nirvana is not an achievement! According to the Buddha there is no path to it because then nirvana becomes an effect of taking that particular path. Also, no practice will lead you to nirvana. Because again, nirvana becomes the effect of the practice. If nirvana is an effect it's not the end of suffering is it? Buddha's only advice was to fully investigate, understand the cause of suffering. According to him understanding of the cause is the ending of suffering. Paths and practices were introduced by monks(not the Buddha) for their survival, existence!
Answer: Not sure about many religions. I think Hinduism and Jainism have concepts of Nirvana. But they are different from the Buddhist teaching of Nibbana. Anyways, it's so simple in Buddhism. You only need to eliminate craving to attain what Buddhists mean by 'Nibbana'. Read about the "Four Noble Truths".
Comment: what is craving?
Comment: desiring/liking/wanting
Answer: Nirvana can defined as a peaceful state of mind that is free from craving, anger and mental suffering.
So answer for, What is required to achieve Nirvana is eliminate all the above things.
Answer: Nirvana is not a one-time switch... You're in Samsara - BOOM! - you're in Nirvana and for good! It's not like that.
Nirvana is a momentary experience of freedom and peace. It can ONLY be such as there is nothing else existent but this moment. To realize such peace and freedom, it's helpful to loosen up one's attachment to desirable conditions and rejection of undesirable conditions. In other words, to loosen up your dependence on conditions overall when it comes to happiness and peace.
Through meditation practice and discipline in everyday life, it will become easier and easier to let go of our expectations, assumptions and demands that life go our way. That's not to say we don't make an effort to have favorable conditions in our lives... Not at all. That would be very anti-life and against our basic nature. We all enjoy good things and rightfully so.
But when our desire for good things becomes constant craving and strong attachment to those things, we're screwed because all good things come to an end (and are replaced by "bad things" like loss, old age, sickness and - gulp! - death). There is no peace or happiness in such craving and attachment. And there's no lack of peace or unhappiness in "bad" conditions either. But our normal approach is to loop endlessly through these cycles of craving, clinging and disappointment. It's very tiring and painful.
"Nirvana" is the momentary experience of being free of this endless cycle. It's that simple. And the more you experience this freedom, the less you will care about the changing conditions of your life and be able to flow with all of it. Yet, you are never finished with developing this capacity as it goes very deep.
Answer: I believe that all Buddhist "sects" would say that there is a path to nirvana. In deed this is the "fourth noble truth", though different "sects" interpret it differently, or at least claim that other "sects" have a different understanding of it. For your purposes, maybe that's what the long history of doctrinal debate is actually about.
I believe that all Buddhists claim that meditation is a prerequisite to nirvana, though that seems to take different forms, with different "sects" vying over e.g. the terms "sudden" and "gradual", and with different instructions and communities.
I've put 'sect' in quotes because I'm going to side with what I understand from soto zen, which I think stresses that we "don't practice zazen in order to get enlightened, we practice being enlightened as we practice zazen". So the fukanzazengi by Dogen says:

The zazen I speak of is not learning meditation. It is simply the Dharma gate of repose and bliss, the practice-realization of totally culminated enlightenment. It is the manifestation of ultimate reality... If you concentrate your effort single-mindedly, that in itself is
  negotiating the Way
Comment: sorry if i'm completely off, just makes sense to me
Answer: This may seem lengthy to some, but it simply is. The comment above this one is correct. There are many approaches, this is the personal approach my mind went through to be able to achieve it. My body and mind achieved nirvana completely by accident when experimenting with meditation at age 17. This was brief, lasting somewhere between a half an hour and a few hours.  It sought it again and failed and wrote it off as a delusion until later. See, the approach was wrong, the WANT of nirvana itself distracted my body and mind from achieving it. The Buddhist obviously have temples where monks go to achieve it, but it seems to take years for them. So how did this body achieve it by accident on it's first occasion meditating? Well, under had a very good teacher for one. My mind was also under the influence of an African tree ash that aids in meditation. The concept of achieving nirvana without seeking it seems terribly difficult/backwards, but really that in itself is the lesson. I really wanted to stress that point.
But overall, you must devoid your mind of "right" and "wrong". You must take and see things as they are, without an opinion of it. You must learn to let go of all desire. To transcend your own ego. There are many ways to coin it, but it is in fact a personal journey that must be achieved personally. For some people, this takes many many years. If you have trouble, that just means to need more practice, and you may need to apply the practice into your outside life. A teacher helps with all this. For meditation in general you will receive benefits without achieving nirvana. To properly meditate is the beginning. This body has found that having a focus/focal point for concentration helps. My mind uses breathing. In through nose, deep into the abdomen, out through the mouth, again, as deeply as possible. My mind focuses on this. Relaxing as much as possible. Then a thought crosses my mind. I take that thought, acknowledge it, and complete it. That's the process. The key for me is to not judge, to not even have an opinion on it, to simply see it for what it is. This seems to work for others as well, but I don't claim to be a mind reader in the sense that I know every step they took to achieve this state. There are many religions, nay schools of thought, that can give you more details, but truly if you understand one grain of salt, you understand all of them. One can go and study these things, the internet is a wonderful tool. There is no right and wrong. There simply is. Accept this, work at it, and the road never ends, achieving nirvana isn't a stopping point. Do it all for self-improvement. Do not confuse stubbornness for patience.
Also, I remember the exact thought that was the focal point for turning my mind into proper thought. An old saying of proper thought, that I came across whilst reading the Tao of Jeet Kun Do by Bruce Lee. I don't know if it'll help you, I don't offer a cure all. But again, this is my personal journey.
"Empty your cup, so it may be filled."
Answer: In order to achieve Nirvana (the Theravadin version of Enlightenment) you need to do a lot of mindfulness meditation and have a lot of good karma. It is not possible to understand Nirvana in terms of modern psychology and philosophy, because Buddhist psychology is very very difficult to understand. Fortunately, you do not need to understand Buddhist psychology to achieve Enlightenment. These days, suffering is mostly caused by tragic adaptations to an abusive or dysfunctional family background, causing problems in self-love and finding love. I have written a book on mindfulness meditation, if you want to read about my 50 years of experience with traditional mindfulness meditation.
Answer: Recite & memorize kītāgirisutta:

"Monks, I do not say that the attainment of gnosis is all at once.
  Rather, the attainment of gnosis is after  respectively training,
  respectively action, respectively practice. And how is there the
  attainment of gnosis after respectively training, respectively action,
  respectively practice?

There is the case where, when conviction has arisen, one visits [a
  teacher].
Having visited, one request to be his attendant (see vinaya mahāvagga mahākhandhaka, and CH. III TAKING A MEDITATION SUBJECT of Visuddhimagga)
Having been attendant, one listen carefully.
Having listened carefully, one hears the Dhamma.
Having heard the Dhamma, one memorizes it (dhatā=sutadharo).
Having remembered by memorizing, one ponders the meaning of the teachings.
Having pondered the meaning, one comes to an agreement through
  pondering the teachings.
There being an agreement through pondering the teachings, wish-to-do
  arises.
When wishing-to-do has arisen, one exerts.
When one exerted (an effort), one meditates insight.
Having meditated insight, one dedicates his life.
Having dedicated his life, one realizes with the mind (discernment's body) the ultimate truth and, having penetrated,
  enlightened, it with discernment, sees it.

"Now, monks, there hasn't been that conviction, there hasn't been that
  visiting, there hasn't been that attending ... that listening
  carefully ... that hearing of the Dhamma ... that memorizing ... that
  penetration of the meaning of the teachings ... that agreement through
  pondering the teachings ... that wishing-to-do ... that effort ...
  that meditating insight ... that dedicating his life. You have lost
  the way, monks. You have gone the wrong way, monks. How far have you
  strayed, foolish men (moghapurisa), from this Dhamma & Discipline!

I have edited many part of the translated sutta follow to many pali of many sutta and commentaries. I wish the editing makes easier for the reader to connect the sequence of steps.
Comment: You should include the original author and translator's names with your quote.
Comment: @JamesJenkins I'm sorry. my English is terrible, so I don't understand what do you mean. I already included translation link above. However I'm not recommend because the tanslation have not connect the words each other inside the same Sutta enough.  Also, the original version not compatibility with other sutta and commentary. I have not a good English skill, but I can read pali and commentary. I can connect them together without cutting off.
Answer:
"The Buddha once said, let an observant person come who is honest and no deceiver, and he would teach that person the Dhamma. Those are his prerequisites for anyone who was going to practice and get results. If you're not honest with yourself, you'll start to deny things that are arising and passing away in the mind. And if you're not observant, it all goes right past you.

This means that the Dhamma is something special. The discernment of the Dhamma is something special. It's not something you can figure out by reading books and being clever. It requires good qualities of the heart, and in particular this quality of honesty, which is basic to all the other good qualities you need. So make sure that honesty enters into the mix as well. That's how the discernment becomes penetrating, as the Buddha says, leading to the right ending of suffering and stress."

~ Thanissaro Bhikkhu "Developing Discernment" https://www.dhammatalks.org/Archive/Writings/CrossIndexed/Published/Meditations9/090804_Developing_Discernment.pdf
Answer: I would believe not even one answer unless one makes the experience for oneself. Be even skeptical that Nirvana exists, for there is no real evidence unless one is experiencing it. Just because the Buddha said it "exists" doesn't make it so. All people answer as if they are enlightened or made the experience .. hell as if they are expert on this field but they are not. If nirvana really exists it must be possible to see it under a fmri. Why? If one really abandoned greed, hatred and delusion one can expose the "enlightened" person with evocative material to see whether any greed, hatred or delusion appears in the brain. I'm positive that there will.
Comment: Thanks for clarifying -- I didn't even notice that wasn't in that CBC report of an MRI test. The kind of testing which was reported seems to me more impressive (more difficult and more useful), i.e. to remain "happy" when exposed to "unpleasant sounds and images", than dispassionate towards sensual material -- an unconditioned absence of dukkha.
Comment: People tested some monks with FMRIs, years ago: http://www.cbc.ca/news2/background/meditation/
Comment: So what? They still need to get exposed with vivid evocative stimuli to see whether their brains are responding to let's say sensual material. I'm aware that scientist tested monks but it wasn't about being enlightened.


Is there a task manager in Windows Phone 8.1?

Question: In Android we have a way to view running tasks and RAM usage. Does Windows Phone have something similar? I think it is must for a smartphone.
Answer: The closest you have is in the Battery Saver app for monitoring power consumption (albeit only when not connected to external power) - the reason there is nothing more complex is that apps is that there is only ever one app running in the foreground - the others in the task switcher are suspended, and not consuming any valuable resources (they remain in memory, but the operating system will kick them out if memory pressure means the space is needed).
Apps can have background tasks which will show in battery saver, on the usage page as either "allowed" or "not allowed" - if neither shows, that app doesn't have any background tasks; you can also tap on an app to disable its background task, if you'd like - this may disable background tasks like updating your lock screen or weather forecasts on a live tile, for instance.
Comment: I've never seen an app from the store **not** recover from being suspended - app developers are used to this, and would explicitly test this to pass store certification.
Comment: @VitorCanova I'd consider that behaviour as desired, for that app - whether or not you agree with how they've chosen to recover, the app *does* recover, and doesn't crash after being suspended...
Comment: But the tasks that have been suspended won't they become unstable
Comment: @RowlandShaw Actually a lot of apps recover as a new state. For example Facebook. If I switch to it right now it will `resuming...` until it loads the lists from the top again and lot where a left. It's more like developers need to remember where the app was left and try to go there again. But in many cases online data is got again.
Answer: Actually there isn't, and theres also no need for one as on Windows Phone there can only be one app actively running in the foreground. The OS frees up memory from suspended apps when needed. You can also manually close those apps through the task switcher by holding the back button.
There are Background Tasks which you can manage through the Battery Saver app, but those only run periodically at times and with memory limits that wont disturb the app currently running in foreground.
http://msdn.microsoft.com/en-us/library/windows/apps/jj681682(v=vs.105).aspx
Answer: Hi Yes you can hold the back button, the list of the recent applications appears and next to each one a close button is available. Close the application with the close button and that's it.
Comment: I think that these are _recent_ applications, rather than _open_ ones. And they're all in a suspended state until re-activated.


Are there any Star Wars vehicles that have not yet been produced in a Lego kit?

Question: This includes all six films and the Clone Wars spin-offs.  Every vehicle I can think seems to have been produced as part of a kit at some point.  Are there any that haven't?
Comment: Did you read [Wookiepedia](http://starwars.wikia.com/wiki/Main_Page)? All of it?
Comment: Actually, there are some sets that take place using expanded universe that LEGO did make, such as the sith sorceror/warrior ship from the old republic.
Comment: @CBredlow There's [quite a few](http://brickset.com/browse/themes/?theme=Star%20Wars&subtheme=Expanded%20Universe) more then that
Comment: But, all joke aside, LEGO is likely to focus on visual Star Wars rather than obscure expanded universe reference, so I can see why you restricted your question to the films and Clone Wars.
Comment: EU sets seem to mostly be based on (Old Republic) video games
Comment: @bungeshea Ah I forgot about the Rogue Shadow! Need to buy that one. Given enough Lego, [anything in possible](http://www.fbtb.net/features/interview-erik-varszegi/).
Comment: Wikipedia has *[List of Lego Star Wars sets](https://en.wikipedia.org/wiki/List_of_Lego_Star_Wars_sets)*.
Comment: CapnRex has started a series on what's missing, and an interesting take on why those sets might be missing over at BrickSet: http://brickset.com/news/category-What-s-Missing
Answer: As far as I know, all of the most common vehicles have been produced, but I could be forgetting something. There are many obscure vehicles which have not been produced, but I don't see any reason to try to list them all. Some examples would be many of the pod racers from Episode I, many of the hundreds of vehicles shown on Coruscant, or several of the speeders seen in the Mos Eisley approach in Episode IV.
The most notable vehicle that I can think of that has not been produced to my knowledge are the Royal Cruisers from the prequels:

Update:
I had previously been mentioned the Nebulon-B Frigate featured in Episode V and VI:

The Nebulon-B has now been produced:
Comment: Not that it hasn't been [made in LEGO by fans](http://mocpages.com/moc.php/175408) - and there's a (smaller) [one on Cuusoo](http://lego.cuusoo.com/ideas/view/16795) too. But seeing the fragility of the center section (seriously, who does design spaceships that way?), I'm not sure LEGO would be willing to make an official one. It's not so much swooshable as explodable.
Comment: There hasn't been too many of the rebel cruisers (i'm lumping all of the ships larger than a fighter together) made by LEGO.  THere's that one transportish ship they take from Hoth that wasn't used.
Comment: The podracers are an obvious one, I should have thought of that.
Comment: @Joubarc, depending on the scale you're building at, I can think of a half-dozen ways of reinforcing that center section.
Answer: There are quite a few:

The Naboo silver cruisers - I think there were three in all - none produced.
Several speeders in Episode II, all seen in the city and several transporters too.
The Jedi speeders, some have been made, but not in all the colours seen in the movies.

And as for the clone wars series, the list becomes lengthy...
Answer: The ones from the original 6 movies and that should have been made:

Naboo queen silver cruiser from episode 1 (with queen handmaid fig(s)!)
Clone quadrans (if I'm naming them correctly) from episode 2 (the guns taking down a Trade Federation ship)
Rebel transport shuttle from episode 5 (escaping Hoth) and 6
Rebel medical frigate from episode 5 and 6
Mon calamari cruiser

Very optional in my opinion:

Trade Federation admiral ship
Trade Federation transport ship
Separatist cruiser from the opening scene of episode 3
The two other Naboo cruisers
A Uta Pau shuttle seen on two or three images (and natives from the planet in the set please!)
A clone tank seen on two images on a bridge under snow in the order 66 scene

Not ships, but still should have been made:

Gungan city (and, why not, one big creature carrying their shield generator and one of their catapults)
A Jedi Temple?
Kaminoans!
Geonosis arena beasts
One of the Skywalkers house?
Republic Senate with Sidious and Yoda fighting
Bizarre blue/purple creature on which clones are riding on Felucia (order 66 scene)
Mustafar locals (humanoids and lava beasts seen on one image)
Asteroid field locals sheltering Padme at the end of episode 3
Bantos... Bantas... Ban... you know the big hairy thing the Tuskens are riding in episode 4
Answer: Millions! Separatist War Ship,UT-AT, Republic Assault Ship, Umbara Military Canon, and many many ships from the Clone Wars TV show (From Arc's this season mostly)
Answer: Banthas! That to me is the largest oversight in Lego's portrayal of the original movie so far.  This is made even more baffling with the upcoming release of a "Tatooine battle pack" that comes with yet another Tusken Raider...missed opportunity there!
Answer: TPM: Trade Federation Battleship, Trade Federation Landing Ship, Naboo Royal Starship, Coruscant Air-Taxi
ATOC: H-Type Nubian Yacht
TCW: Trident Drill Assault Craft, Umbaran Starfighter
ROTS: Separatist Cruiser, The Invisible Hand
REBELS: Imperial Interdictor, Mining Guild TIE-Fighter
RO: AT-ACT, TIE Reaper, The Profundity, Hammerhead Corvette, Zeta-Class Imperial Shuttle
ANH: pretty fleshed out
TESB: GR-75 Medium Transport, Nebulon-B Frigate
ROTJ: Mon Calamari Star Cruiser
TFA: pretty fleshed out
TLJ: First Order Dreadnought, Canto-Bight Police Speeder, The Raddus, The Supremacy


Difference between "где" and "куда"?

Question: I believe, где is where? and куда is like, to where? or something like that
I am not sure D:
Answer: Откуда ты идешь? (from) - I am going from my house.
Кудаты идешь? (to) - I am going to school.
Где эта школа? (location) - The school near your home.
Answer: ГДЕ = "Where" (the location) Где яблоко? (where is the apple?—in what location
КУДА = "To where" Куда ты положил яблоко? —where (to where) did you put the apple?
In English we have only "where", which can mean (to where (the action)) and (where(the location)).
Answer: It's deeply rooted in Russian grammar. Location without movement governs the locative, while location with movement uses the accusative.
Где -> no movement, locative
Куда -> movement, accusative

Something similar goes, for instance, in German:
wo -> no movement, dative
wohin -> movement, accusative

In English movement can be expressed directly with "where to", but often is indicated by other parts of the sentence, or not at all if that's implicitely clear. In Russian you simply must know whether there is movement or not, or else you won't be able to form a proper sentence.
Beside the need to use the proper case, "where" is not the only word that has two variants. For instance, "here" ("from here" / "to here") will also be said differently according to movement.
To show how strong a meaning these adverbs carry, these two sentences are common in Russian:
Где ты? -> where are you?
Куда Ты? -> where are you going?

While in English the meaning is carried by the verb, in Russian the adverb is sufficient.
Comment: As locative case is mostly outdated nowadays "где" is used usually along the prepositional case except a dozen of words. Probably, it's not a good idea to confuse the beginner with the archaic locative.
Comment: Sorry, that's how I was taught Russian here in France a few decades ago. We were told the locative whas a subcase of the pepositional, with a few exceptions as you said. I did not know the name had fallen in disuse since then.
Comment: Well, it never has gone but has a limited recognition along with a few others. Here the most relevant topic on SE: http://russian.stackexchange.com/questions/404/what-are-the-lesser-known-russian-cases
Answer: Где means the place itself without action, and куда means direction or aim.
Not sure, I'm right, but it seems like you have to manipulate time to male this difference between где and куда in English.
Где maps simple time, and куда maps continuous and perfect:

Где эта улица? - Where is this street?
Где было молоко? - Where was the milk?
Куда ты идёшь? - Where are you going?
Куда ты положил молоко? - Where have you put the milk.

PS: There can be the other meanings of this words, I was answering only about specific case.
Comment: I would say "to where", "to what place" if I really wanted to stress the "куда" meaning in English.
Comment: there are old english words: thence, hence, thither, hither which have similar meanings to  the Russian "where(s)" with movement—отсюда, оттуда, сюда итд

Difference between "где" and "куда"?


Why are Zigbee hardware modules so expensive?

Question: The Zigbee hardware looks quite simple to produce1, why are they so expensive?
For comparison I can get a 855 Mhz wireless module for 2-3€ but I can't find Zigbee modules under 15€.
[1]
Comment: @hardillb I thought the licence is free, do you have a reference?
Answer: As comments indicate there is apparently indeed a licensing and certification process involved that might indicate where some part of the price stems from.

Though well known in the automation industry, ZigBee is expensive. The protocol is computationally intense and the memory footprint is large. The ZigBee Alliance requires all implementers to join before undergoing an expensive licensing process. Competing (simpler) protocols using identical radio hardware can be implemented in lower cost processors without sacrificing performance. Most competing protocols are license free, especially when paired with hardware modules of the same ecosystem. Many vendors provide codebases and development tools for free.

Source: sep.com blog: The Most Popular Wireless Standard You've Never Heard Of (Part I) (emphasis mine)
It's seemingly a quite rigorous cost- and time-consuming process of which you can find the gist on the Zigbee Alliance certification page. That page also includes the very helpful information, "Test specifications only available to Alliance members in our Members Area."
Each product with a Zigbee logo has to go through that process. Being "computationally intense" and having a "[large] memory footprint" doesn't help bringing the cost down either.
Comment: But why isn't there an unlicensed hardware module for hobbyist that is cheap - licences or not as long as the standard was implemented correctly no hobbyist would bother.
Answer: There are a number of 802.15.4 solutions which are not Zigbee, and cost less. See this article: "What's The Difference Between IEEE 802.15.4 And ZigBee Wireless?"
As I understand it, to use the label "Zigbee" you must comply with certain requirements and guarantee interoperability with other Zigbee devices. Otherwise it would be "Zigbee-like" or some such. It's like USB, if you use that label you must comply with USB requirements (you also must purchase VID numbers), it's similar to a block of MAC (formerly OUI numbers) from IEEE. Doing that testing, joining the Zigbee alliance, and buying a Zigbee ID number (you also need a MAC address) are not free. Hence the added cost of being officially Zigbee. If you don't want to interoperate with other Zigbee devices then you can use one of many 802.15.4 open protocols. If you do want full Zigbee functionality and only need a few modules, the extra cost is insignificant. If you want to be a Zigbee manufacturer, then you need to bite the bullet and be official.
On the one hand this seems a hassle for casual users. On the other hand, if your Zigbee network is mission critical, you don't want half-baked nodes corrupting its operation.
Answer: You can get Microchip's MRF24J40 based modules for far less than that, around $6. But it's known to be quite old and buggy. A more modern one would be Silabs MGM111 for $7-8 in small quantities.
There isn't going to be one hobbyist-friendly though because the Zigbee licensing effectively prohibits open-source stacks at least in Zigbee layer. So you are locked into silicon vendor radio stacks when implementing Zigbee, however you are free to muck about with other 802.14.5 solutions like Thread, which does have open source stacks.
There are also quite new chips out there that are 2.4Ghz multi-protocol by Nordic and TI etc that are designed to run BLE or 802.14.5 based solutions. For example, any nRF52840 based module from Nordic or it's module partners ( Rigado BMD-340, Raytac MDBT50, Laird BL654) can run Zigbee at least in theory, but you have to obtain the right SDK from Nordic with Zigbee part being closed source.
EDIT: OpenThread.io has a nice overview of relatively modern flexible 802.14.5 chipsets, all those are hacker-friendly in that they can run OpenThread, and obviously come with Zigbee as well.
Answer: I know it's pretty old thread, but still.. Have you heard about:
http://zboss.dsr-wireless.com/
or
http://www.ti.com/tool/Z-STACK
So.. it is possible to get the stack for free and to get cheap HW, e.g. CC2531..
Only problem I can see is that it is not that easy to compile (IAR license necessary) and even more complicated to grasp the whole zigbee specification and concept to be able to implement own device..


Why is increasing block size in the Bitcoin network considered to decrease security?

Question: I have been doing some research on the Bitcoin Cash hard fork and the main contention of increasing the block size appears to be the possibility of less security on the network. How does an increased block size result in a less secure network?
Answer: Generally speaking, a larger block leads to more computational resources (tx validation, bandwidth, storage, memory) required for each person who wishes to validate newly confirmed transactions.

Higher validation cost lead end-users to rely on/trust
centralised services to "validate" their transactions.
Larger blocks require more time to propagate in the network,
increasing pooling pressures for more centralized mining-pools.

The lower the validation cost, the more we can push validation to the edge (end-user) of the network, the more decentralisation we can achieve. Decentralisation is ultimately the source of security, as it is harder for an external force to attack.
Comment: That is true. A user can choose how much security he requires from a confirmed transaction before accepting it. Yet a commitment tx, even though it is valid, has not even been confirmed, which is why I mean it has less security. So a lightning payment (a new commitment tx) cannot have the same security as a confirmed tx with a confirmation depth. The entire payment channel capacity amount is in fact still "pending" confirmation.
Comment: Well - there is a security sacrifice to be 100% fair. There is no insurance against failing to respond to a cheating counter-party in payment channels. The required vigilance is an additional risk that a confirmed transaction does not have.
Comment: Also, off-chain transactions can be made for much cheaper without sacrificing security. No need to store the history of daily coffee purchases of everybody on all Bitcoin nodes in the network.
Comment: Right, thanks. It's important that it remain easy to broadcast the state of the channel at any time.
Comment: Can you explain in more detail? Also, even a confirmed transaction still has the small risk of a reorg. There are even users who choose to accept transactions before they have one confirmation (cringe).
Comment: Sorry. I meant "A user can choose how much security [he/she] requires..."


Improving badly-lit photographs of paper taken with a cellphone

Question: A lot of questions include photographs of writing on paper (equations, diagrams, etc.) that were hastily taken in poor and/or uneven lighting. Is there a straightforward way to improve them?
Answer: Yes, there is.
I have created a procedure based on ImageMagick that seems to do a good job. You can see examples here: original vs improved, and also here (original vs improved).
The process is to first crop the image to remove all extraneous stuff outside the boundaries of the paper. For example, on the second one, I used:
convert -crop 3456x2000+0+1800 XGU75.jpg XGU75_a.jpg

Then, the following command uses a blurred copy of the image to approximate the lighting with the text and diagrams removed. This copy is negated and added to the original image in order to cancel out the effects of the uneven lighting, and then the contrast is stretched (normalized):
convert XGU75_a.jpg \( +clone -blur 30x30 -negate \) -compose Plus -composite -normalize XGU75_b.jpg

Finally, in some cases, it makes sense to convert the result to a binary (black and white rather than grayscale) PNG, which greatly reduces the file size:
convert -threshold 50000 XGU75_b.jpg XGU75_b.png

YMMV. Tweak the parameters as needed.
Comment: @AlanCampbell Users who do not trust closed source software can use Gimp https://docs.gimp.org/en/gimp-tool-curves.html, which runs on most operating systems.
Comment: I really wouldn't expect moderators (user moderators or diamond ones) to put the time and effort into improving crappy questions with this method. If you do it, then that's awesome, but we really should be prompting the poster to ask a better question instead. Let the _poster_ do the work by creating a readable schematic (it is not _that_ hard to do using Circuitlab). We can compare this situation with the situation over at SO, when users are posting screenshots of their source code, instead of posting the code as formatted text. Such poor quality questions get closed and heavily down-voted.
Comment: If you have Photoshop (or similar) you can use Curves to reduce midrange tones or enhance contrast.
Comment: @Lundin: All good points. I'm addressing the edge case where a question is otherwise fairly good, except for the bad photo(s). Newbies can't be expected to know the intricacies of CircuitLab (face it, it is rather quirky) and cellphones don't generally have easily-accessible image processing tools. I happen to do image processing as part of my day job (real-time image enhancement of HD video in FPGAs), so I had a personal interest in seeing what could be done with readily-available tools.
Comment: These are similar to the process used on B/W photocopiers that maximize contrast ratio while minimizing loss of resolution with half-tones and gamma control.
Answer: I think you are going in the wrong direction here.
Since we have tools for both diagrams & equations, why not remove those pictures alltogether and replace them with the right tools?
To take it a step further, i believe we should enforce that as a rule, i do not want to decipher an equation or a diagram on a crappy picture when the site provides good tools to write very clear ones.
Besides, it is not that hard to take a decent-quality picture of a diagram.
Answer: There are many tools to enhance image to make it more readable.  The best tool is the one you learn to use well and if you have a lot, one with fast GUI interface for interactive optimization or batch processing if the optimization is identical.
In terms of theory, we might call it a transform, where by applying  Shannon's Law to optimize spectral signal/noise ratio (SNR) we can reduce the error rate in viewing the contents.  The transforms can include cropping, histogram normalization or simply applying fixed gamma, contrast and brightness values then applying sharpening values with colour contrast enhancement.
There are many software tools that are quick and easy to use, but it depends what you know how to use. I have used Picassa, Gimp, Photoshop, PSP, but for the longest time I have used Irfanview (free).  These are all windows tools but you may prefer iOS or android image edit tools which all can work if you know how to manually edit gamma, contrast and brightness.
Example of IrfanView ( which has most of the features of ImageMagick and supports all the adobe .8bf plugins, if you have them.)
Often crop and autocorrect are good enough, but edit and manual adjust can improve if you understand how.
Say, you wanted to read the characters on the Chinese Checkers.

It would take to long to show you how to automate or repeat saved settings, but this just to give you another snapshot impression of how image transformation can be done to improve readability.
From left original to right Bot.left corner going clockwise.
1) auto adjust 2) manual correct (gamma, contrast) 3) greyscale only 4) greyscale with gamma adjustment, contrast, brightness
Histogram graph of levels is inserted in some results to show the peak number of pixels at various levels from dark to light.


Software to manage Linux machines

Question: I've 4 Linux machines (1 32-bit laptop, 1 64-bit laptop, 1 64-bit desktop and 1 Raspberry Pi 2). Is there some opensource software to manage the installed packages, the configurations and the users on it? Also, it must be easy to add a 5th machine. If it requires a server, that server needs to run on a Raspberry Pi B+.
Comment: Not a full answer: I'm sitting in the same boat (64bit laptop, desktop, and multiple BananaPis). I found ClusterSSH being a big help in keeping them up-to-date (running `apt-get update && apt-get upgrade` on all of them simultaneously). A "real management tool" sounds interesting, though :)
Answer: I was using Ansible for a similar size home cloud in my experimental project (I have Raspberry Pi as well).
The base CLI functionality is open source and free, the GUI (called Tower) is for money. In case of such low number of nodes, CLI is comfortable enough. It's using YML as configuration language (which I don't really like, but it's my personal problem).
There are minimal requirements for the host:

ssh daemon running
python installed

As you see, no agent is required, you only have to set up an account (with sudo rights) on the node.
You can organize your nodes by roles, and you can set up "playbooks", which contain items for specific roles or role groups.
Say, you set up "sql server" and "web server" roles, and create a "setup" playbook. Then you can define tasks "upgrade packages" for both rules, and "assume apache2 is installed" for only the "web server" role (it installs stuff if it's not installed, and does nothing if it's already installed).
Ansible has lot of modules in several function groups, but you can write yours in Python (I haven't needed it).
Comment: It looks good, especially that it's written in Python. I'm going to try this soon…
Answer: It sounds like you need chef:

Open Source and commercial
Runs on Windows, OS-X & Linux including Raspberry Pi
Highly scaleable so adding one or more more machines is simple
Can manage versioning, upgrades, user & rights
Lots of online "recipes" for common tasks
Good online learning material
Answer: One more to consider is Puppet
https://puppet.com/
Much like Chef they have open-source and commercial models.
Having used both I would say that although less configurable in the long run, Puppet has a shallower learning curve and is easier to get started with.

Software to manage Linux machines