How do we know that the God we encountered at Sinai is the single, infinite God?

Question: How do we know that the God of the Sinai Revelation is the single God of All other God's? Is it not possible that whatever we encountered was simply a messenger of a greater force? I understand that there was a single infinite force from which the universe came forth, but how do we know that it is that force we entered into a covenant with?
Comment: And the Raavad didn't argue.
Comment: He said so. [15]
Comment: If the force is infinite, then there is no room for division. But your question is, maybe Powerful-But-Finite Being #1 spoke at Sinai, claimed to be *the* infinite being, and meanwhile Powerful Beings 2,3, and 4 just sat there and watched. ?
Comment: there is a midrash which says God opened the seven heavens and showed them in prophetic vision that there is no other.
Comment: Has there been another overwhelming revelation of power over nature itself that has been attributed to another god? If so, cite! If not, either there are other powers that are weaker that God, who cannot control nature to the extent that he can, and we needn't pay them any respect. If there are powers greater than or equal to God's, why have we not seen or heard from them? Where are they? Either they have not control over this world, and so as far as we exist, they are nothing to us and deserve nothing from us. Or they do but they don't bother to act on that power.
Comment: Whereas God has, in doing so commanding our utmost reverence and worship. When these other hypothetical powers reveal themselves, we can discuss alternatives. Until then, I trust the God that proved Himself.
Answer: This question is handled by the Rambam in the first few lines of the Yad.
As I understand it, basically we do believe there's a hierarchy - which is described as layers of angels - with the higher ones having more powers than the lower ones.
The very Highest Power - who is actually the source of everything - is the Being we treat as The God.
The first 2 commandments are:

[You must believe that] I am the One Who made everything and I am the Highest Power (lose translation of אנכי ה' א-לקיך)
You may not question this fact (based on the Rambam ibid 1:4) וכל המעלה על דעתו שיש שם אלוה אחר, חוץ מזה--עובר בלא תעשה, שנאמר "לא יהיה לך אלוהים אחרים, על פניי"

A similar concept is reworded by the Mishna in Chagiga 2:1 וכל המסתכל בארבעה דברים, רתוי לו כאילו לא בא לעולם--מה למעלן, מה למטן, מה לפנים, מה לאחור
Essentially saying that questioning what is beyond the end of the universe - is forbidden. The mere discussion of a Greater Force than God is already forbidden.
(This is obviously a summary - the Rambam is more eloquent and more thorough.)
Answer: Rabbi Yisroel Chait tackles this question and others quite effectively in his article on Torah  From Sinai.  Article can be found here.
Comment: Can you include a summary? Otherwise, this should really just be a comment.
Answer: (as doubleaa pointed out in a comment) He said He is the only God. It does not make sense that a higher force would send a liar... and that liar would command us to be truthful in His torah etc. naaahhh
Answer: Generally speaking, we believe in things that we have positive evidence for, and we do not accept skeptical questions which do not have any positive basis to them. For example, we spend our lives growing up with our parents, being cared for by them, being told that we look like them etc. etc. This all amounts to positive evidence that our parents are indeed our parents. If a skeptic were to come and ask us for ABSOLUTE PROOF that our parents are really our parents, that we weren't say adopted or switched with a similar looking baby at the hospital, we would disregard his challenge as not having any basis. We have all of our experience to rely on in not accepting his position as true, and he has no positive evidence to back himself up with. However, if he would present us with adoption papers, we might start reconsidering. If he brought pictures of our parents at the adoption agency, we may start having serious doubts, but again he would need to bring very, very strong evidence to convince us to go against our intuitive experience.
The same is true for the Sinai experience. The challenge you present is essentially a "Bring me absolute proof" challenge, which is almost impossible to be met. But that does not give us a positive REASON to accept the challenge in light of our collective intuitive experience, which said that it was indeed God who appeared at Sinai. Additionally, it would be significantly difficult to explain the motivation of aliens to create as elaborate a system of laws as the Torah, as discussed here.
Comment: "Don't ask me a question that I cannot answer" is not usually a good answer.
Comment: @DannySchoemann Depends if the question is a good question.
Comment: @DoubleAA - agreed. Here we are dealing with an elementary question that needs an answer.
Comment: @DannySchoemann I guess Jules disagrees with that assessment.
Comment: Perhaps providing all of the circumstantial evidence which leads you to that conclusion would be helpful, rather than just comparing it to a case with lots of circumstantial evidence.  Then this might be more than just a statement that you are ok with not having proof.


Electrum 2.7.9 setup never went through the password and seed setup, now I can't send coins

Question: I installed the Electrum 2.7.9 wallet and it never went through the password and seed setup. I ended up with a default standard wallet. I then uninstalled the Electrum wallet and then reinstalled it. Once again it didn't go through any password or seed setup and I had a default standard wallet on my pc. I made the dumb decision, because I am totally new at this, to go ahead and send my bitcoins from my coinbin wallet to the address associated with the standard default wallet and now I can't send anything because it wants a password. Please help!
Comment: You entered the password it asks you for when you created the wallet. If you don't remember the password, you need the seed. You were asked to write it down when creating the wallet. Do you have it?
Comment: For the future, I would really strongly recommend against putting in Bitcoin any money that you can't afford to lose.
Comment: I'm sorry but didn't you read my post? The setup of the Electrum wallet didn't ask for or walk me through the setup of password or seed. I also think your recommendation is painfully obvious. I have not technically lost the bitcoins, they are in my default wallet I just can't access them. Is there anything else I can do?
Comment: Okay I have now figured out how to setup a new Electrum wallet from my default Electrum wallet. My bitcoins are still on an address associated with my default Electrum wallet and when I try to send to my standard Electrum wallet the default wallet is asking for a password which was never setup. The default wallet doesn't have a password. What do I do?
Answer: Apparently, without either password or seed, an Electrum wallet is not recoverable.
But let's reconstruct how it happened and see what you perhaps could do:
Electrum doesn't create a new wallet during setup only when there is already an Electrum wallet on the system.
It therefore seems likely that you or another user of your computer had installed Electrum on that computer before. Perhaps you should try to figure out if the seed and/or password was recorded back then, but you had forgotten about it. Else, you should first try likely passwords.
If you cannot make any progress with that, you might want to consider getting in touch with https://walletrecoveryservices.com/. I cannot personally vouch for them, but they appear to have helped a load of people in the past. They may be able to help you recover your password, if you have any idea about what you may have used.
Thanks to #electrum on freenode for most of the above information.


How to go about pre generating css file with variables from theme options

Question: I know there have been lots of discussions on here about rendering a css file with php variables. The "no no" way of bootstrapping the wp-load.php for example.
I've been working on a theme framework for a few months now and one of the things it does is generate a css file using the parse request action.
add_action( 'parse_request', 'parse_dynamic_css_request' );
function parse_dynamic_css_request($wp) {
    if ($_GET['dynamic-css'] && $_GET['dynamic-css'] == 'css') {
    require get_stylesheet_directory() . '/library/css/dynamic.css.php';
    exit;
    }
}

While this works and does the job. I know that there must be a better way to do this as I know as much as its a massive benefit having this, its not necessarily ideal.
I have an idea how it would work really well and serve a static file on the front end.
My thinking is that since with wordpress, you can have some functional code in the themes function.php file that runs in the admin. There must be a way with php to generate the css file when the themes options are saved from the admin.
When the theme options are saved, the css.php file is processed but the results are saved to a static css file. Then when the site is loaded on the front end by users, they receive the static file that was generated when the options were saved.
I have all the logic I need to do it and the code I have will do fine from a wordpress point of view. My problem is that my php skills with file handling is scratchy as I hardly ever use it.
So, how would I go about it with php. What I would like to do is copy the generated php code into a static css file with php. I am thinking it would be using
file_get_contents();

Any ideas?
Thanks,
Comment: file_put_contents().
Answer: $ss_dir = get_stylesheet_directory(); // Shorten code, save 1 call
ob_start(); // Capture all output (output buffering)
require($ss_dir . '/library/css/dynamic.css.php'); // Generate CSS
$css = ob_get_clean(); // Get generated CSS (output buffering)
file_put_contents($ss_dir . '/library/css/static.css', $css, LOCK_EX); // Save it

Regards.
PS: You cannot be a developer with scratchy files' skills. They're not optional.


iTunes toolbar in Windows 64 taskbar

Question: How (if possible) can I get the minimized-toolbar for iTunes into my taskbar on Windows 64 bit?
Answer: Right click the toolbar and from one of the 'Toolbar' submenu, make sure 'iTunes' is selected. You also have to go into iTunes > Preferences > Advanced and make sure "Minimize iTunes to System Tray" is unselected, and maybe even "Show iTunes icon in System Tray" is unselected as well.
Then just minimise iTunes and it should pop down in your toolbar.
Answer: If you are wanting the toolbar effect, instead of the system tray, you have to right click on your task bar, select "Toolbars", and then select "iTunes". This, and the system tray option, both work on 64bit Windows Vista.

iTunes toolbar in Windows 64 taskbar


Installing Ubuntu Server through SSH

Question: Does anyone know if it is possible to install Ubuntu server headless?
I do know of the ability to output a terminal to a COM port, BUT, I was wondering if there was a way to drop a prompt, install SSH, and relaunch the setup through SSH.
Comment: If that works for you, then you should add it as an answer.
Comment: See http://serverfault.com/questions/21255/
http://serverfault.com/questions/57305/
Comment: I kind of answered my own question from this tutorial: https://help.ubuntu.com/community/Installation/NetworkConsole though I don't know if it will work the way I want. I am installing using it right now so we will see.
Answer: I used this tutorial https://help.ubuntu.com/community/Installation/NetworkConsole to setup a network console.
Answer: Yes, it is possible.
One way to do it would be to setup a debian/ubuntu livecd that boots up with an SSH server running.  Then you can ssh in manually partition and create file systems, and then run debootstrap.  This method of installation is pretty advanced, you will have to have a pretty good understanding of how to build filesystems, how to setup boot loaders and so on.
You could even skip the livecd step and netboot a linux environment that starts up an SSH server.
Another method might be to completely automate the installation by remastering alternate installer cd with a preseed file.
Answer: You want to use the same way that you can install Debian on NASes and other small systems that don't have graphics hardware -- you just have to have the network-console udeb installed into your installer environment.  This then starts up an SSH daemon that you can connect into and do what you want to do.  That appears to be what the Ubuntu wiki article you linked to does, although it does remind me why I don't use install CDs any more -- PXE booting all the way.
Also, think very carefully whether you want to stick with manual installs, or just do fully preseeded installations -- by the time you're faffing around rebuilding ISOs, you may as well just go the whole hog and preseed the entire install.  That saves you time and hassle all round.

Installing Ubuntu Server through SSH


What is the meaning behind HOMRA motto?

Question: Every time HOMRA are about to battle, they always shouting "No Blood! No Bone! No Ash!" Does it have any meaning? Somehow I can relate "ash" to their burning power. (but it's just my assumption, and I don't know about the other)
Comment: I think the idea is that when you set a person on fire, blood or bones (or ash) could be left behind. The motto, then, expresses the idea that HOMRA should burn people so thoroughly that none of those things even remain.
Answer: HOMRA (吠舞羅, homura). It's not 炎, the spelling is different.
The Arabic word "حمرة" which means "redness" must be the origin, it is the red clan after all, and the spelling is identical. (try the speaker button on Google Translate for the pronunciation)
In season 2 episode 3, Kismet is from an Arabic origin as well.
Comment: 炎 has an alternative reading of "[homura](http://jisho.org/word/%E7%82%8E)" too. And according to Google translate, the spelling for "حمرة" is "hamra", not "homra", but the pronunciation is almost indistinguishable for non-Arabic.
Answer: "No blood, no bone, no ash" is the saying that the red king's clan yell out before battle. It is to say that they will leave no blood, no bone nor any ash behind. It is related to their burning power.
Answer: The saying "No Blood! No Bone! No Ash!" can mean a few things like the power that the red clansmen have or just the sheer strength that they have, but I think  it means that they leave nothing when they pass or that they have no regrets (I have no idea if any of these are correct)
Comment: Welcome to [anime.se], a Q&A site for anime. We're a bit different than other sites that we're not a discussion forum (you can take a quick [tour] to understand how this site works). Aside from that, personal opinion is acceptable *if* it can be backed up by some sources/references or more extensive explanation (if you yourself doubt your answer, how can other readers trust it). You can always [edit] your post to improve it.

What is the meaning behind HOMRA motto?


How would a use case in health care look like, compared to the financial side of IOTA?

Question: As I only know the financial side of IOTA, I wonder how would a use case looks like in the health care world. For example if a user wants to share his health care data to different doctors. Is it like the user has the seed and every health care data (for example heart rate) was previously sent to a different address of his seed. And as the user wants to share these data he has to tell the doctor the addresses where he can find them? Or is it completely different to the financial side of IOTA?
Comment: This seems rather speculative, it would be great if you could be more specific. Currently this mainly asks for guesses.
Answer: I would not think in this scenarios with the limited tools IOTA provide today (handly managing our seeds, for instance). The value here is in being able to propagate anonymouysly our health data, maybe get paid for it, while we allow data analysis and research that could lead to find patterns and, therefore, diagnostics.
The way I see it, our medical info will be hosted in the Tangle (MAM allows this already). Each time you visit your doctor you will be able to decide whether you wanna broadcast the info to place it in some kind of data market.
This is not only awesome in terms of having medical histories digitalized with inmutability granted. It's about what all that information could teach researchers once is put together.


Can the Disqus commenting system be used as a full-blown forum?

Question: Disqus is a pretty neat little comment system.  Does it have the ability to be turned into a full-blown community forum.  Has anyone managed to successfully hack/customize Disqus in this way?
Answer: I have personally never used Disqus on a web-developer/administration level, but as a user (reading + posting) on several Blogs such as Notch's Minecraft Blog (oops he disabled commenting!), I've noticed that it tends to have some serious issues handling large amounts of users/posts. The most apparent issue is the random disappearance of comments, particularly when multiple pages of comments were involved. Also, threading comments across multiple-pages is a nightmare, especially when you're nested even just 3 deep and then have to jump to the next page - good luck following the previous train of thought! My fear is that creating a community forum based on Disqus might put you on a sinking boat sooner than later.
Other than that I can only comment on an even more personal level: I find it rather shallow, in particular that it supports more of this horrible, unrealistic circle-jerk behavior - similar to the Facebook Like button - or rather, where is the bloody dislike button?! Answer: There is none. Enjoy the ego-stroking kiddies!
Comment: Taken from Urban Dictionary: When a bunch of blowhards (=persons who brag/boast a lot) get together for a debate but usually end up agreeing with each other's viewpoints to the point of redundancy, stroking each other's egos as if they were extensions of their genitals (ergo, the mastubatory insinuation). Basically, it's what happens when the choir preaches to itself.
Comment: What is *circle-jerk behavior*?
Comment: The most clear-cut topic is the random disappearance of remarks, especially when multiple sheets of remarks were involved. Also, threading remarks over multiple-pages is a nightmare, particularly when you're nested even just 3 deep and then have to leap to the next page
Answer: We made a one at http://forum.mctraveler.eu/
It is simple visitors can create threads/posts which then will be threaded in the disqus style.
The "forum" is only made out of static files, html and javascript.
We have also hosted it on Amazon S3 in the past.
You can copy it, you will need to save the index.html and forum.js. Change the shortname and API key. Then all you need is a better design and you are ready to go.
Comment: As someone who would like to do this, I would appreciate it if you would post your html source code on stack exchange (possible by editing your post?). Unfortunately, as is the problem with web links, the website has been taken down.
Answer: I'm wondering if jfusion could do this.
Jfusion will automatically generate forum topics for new blog posts, and I believe it will also sync comments between the blog and forum.
Haven't used it for a few years though, so I'm not sure if its deprecated


gedit 3 regex search replace plugin port

Question: So i have been trying to install gEdit Regular Expression Plugin
in gEdit 3.2.1 but there seem to be some issues. I have modified the .plugin file and now it shows up in the list of plugins.  But when i try to select the plugin from the list, gEdit closes.  So i noticed that the plugin import modules from GTK+2 so i tried changing them to the GTK+3 equivalents.  Also a lot of the built in plugins code look slightly different than this plugin.  After making changes to _init_.py, when i click on the plugin from the list of plugins that is in the list, a error icon shows up next to the plugin name and it gets greyed out.  Has anyone been able to port this plugin?
Answer: I have created a fork from this plugin some time ago, and now I ported it to Gedit 3. It is versioned / distributed here.


Odd behaviour from Infopath, SP list and active directory

Question: Hi I have built a time sheet system in Sharepoint 2013 and I am getting some unexpected results for some users (not all).
Basically I have one list which is a basic sharepoint list which lists Project names and has a field "Assigned to" which is a people picker which can accept multiple people onto one project.
Secondly I have a timesheet entry list where individuals assign time against their projects. This list uses an infopath (2013) form and has a drop down which uses a data connection to the first list. This drop down is being filtered by  so that the current user will only see the projects that have been assigned to them.
In the infopath form I am using rules on form load to set the query field of the GetUserProfileByName AccountName to the AccountID of the creator of the form. So that I get hold of the person currently logged in. Then in the dropdown field for the projects,  I am filtering on where the AccountID in the Project list lookup is equal to the value of the Account field for the person logged on.
The odd behaviour I am experiencing is that this works for some staff but not all. Some people seem to be returning their projects and the projects of their managers!
Does anyone have any ideas at all?
Thanks
Comment: Are you certain the users have a User Profile?
Answer: Sorted this one myself. The GetUserProfileByName service returns all the properties from AD for that user and this includes their manager. So what was happening was that my filter was using both AccountId's of the user and their manager. Resolved by setting a field to just be the accountId of the user and then filtering on that.


Stack Exchange experimentation sandbox

Question: This is a sandbox post for users to experiment with various Stack Exchange features. This question (and all answers) is a community wiki so that the reputation required to edit is lower.
Also, the user who owns this post is set to Community, which is not a real user but a background process. So you needn't worry that some one might be notified by all your shenanigans here (do note that comments on others' answers will still notify them).
Feel free to post an answer (gibberish welcome), delete your answers as you wish, try out various formatting tricks, test out voting to close/delete, protect posts, test new privileges, whatever the hell you want (yes, really!). Of course, as always, offensive content/spam will not be tolerated.
I merely request that you do not change the title of this post or add any new arbitrary tags. If you do cast the last close/delete vote or if it is not reopened, please let a ♦ moderator know so that we can reopen/undelete it.
Feel free to modify the question below this line
Comment: @foo @bar` test comment
Answer: SoundCloud test:
http://soundcloud.com/datageist/example-7-analog-kick-drum

Stack Exchange experimentation sandbox


Why doesn't class weight resolve the imbalanced classification problem?

Question: I know that in imbalanced classification, the classifier tends to predict all the test labels as larger class label, but if we use class weight in loss function, it would be reasonable to expect the problem to be solved. So why we need some approaches like down sampling or up sampling for imbalanced classification problem?
Answer: Class weights do help with the imbalance problem ("resolve" seems too much), but upsampling has a certain advantage on it.
If you think about it, downsampling/upsampling the number of samples in each class to balance the dataset is almost exactly the same as using class weights.
For example, say you have a dataset containing 3 samples divided into 2 classes:  and you are training with an MSE loss.
You can choose to upsample the number of samples from class B, which will get you the following cost function over a single epoch:

Here is where the small difference comes into effect, if you are training in a batch gradient descend (a single weights update per epoch), the prediction for the 2 identical B1 samples will be the same, so the loss function can be written as:

Which is exactly the same as using a weighted loss function. However if you are using a mini-batch gradient descend (as most model our days), the 2 different samples may appear in different mini-batches, and so the predictions for them at the same epoch won't be the same (because one of them will pass thru a model that was already updated once).
This is a small difference but sometimes it is important. It means that with weighted classes, the effective learning rate varies between mini-batches. In some cases that can make learning unstable. So, when possible, upsampling is the better approach (practically it produces slightly better results).
The problem is that you can't always upsample/downsample without any worry. If we go back to our example but this time we have a dataset of 5 samples, divided into 2 classes:

Downsampling is problematic - which of the 3 A class samples do we ignore?
Upsampling is problematic - which of the 2 B class samples do we duplicate?
It can be solved by randomly choosing which samples to keep/ignore at each epoch, however with very big datasets, this can lead to slower processing... So the weighted classes is still a valid option.
Comment: "It can be solved by randomly choosing which samples to keep/ignore at each epoch". How is that a solution? What does randomness do for us here?
Comment: Hey @mark, you say that up-sampling produces better results in practice.  Do you have any references for that, maybe?  Any clue why that happens?
Comment: @Mark.F your description does seem to make sense. You described that for upsampling, mini-batch has different effective learning rates. But in the end, you mentioned this is the problem of weighted class. and we should choose upsampling


What is a good method for constructing dirt jumps?

Question: What is a good method for constructing dirt jumps? Not massive jumps, just something more than a simple mound of dirt for a bit of fun. It's one thing to pile up the dirt, but there seems to be a bit of an art form to getting the surface smooth.
Answer: Jumps takes time and effort to do right.   If you're going to rush or do a half-arse job then don't even bother starting.
Design is important - you need to consider run up space before and run out space afterwards.   Make the jump wide enough to give options - a metre would be a fair width unless you're making it difficult on purpose.
Bailing-out options - riders will ride around if it looks too hard, you may make the jump really wide to reduce this, or make it longer to go around.
Try to avoid digging a moat around your jump.  Source the dirt from metres further away, you want to avoid having water collect on your track, because wheels and water means erosion.
You're aiming for a smooth curve on the face, so build up your jump a few inches then stomp or compact it.  Damp soil will compact better than dry.
Deeper inside the mound you can use big rocks for bulk, but still pack the soil around them.   Trees and wood is not so good, it will rot.   Tanalised timber is okay for surfacing.
As your jump rises, keep tamping it down.  Use water to dampen it.
Remember it doesn't all have to be built in one sitting.
You can use shingle/stones to help reinforce the surface, but don't put sharp edges facing up.  Big flat river stones are okay in moderation.
The top - I'm not so sure on this.  You want to curve it back down quicker than you went up, but you must not have a lip or a sharp edge.... it won't last.   Jury is still out on timber at the top.... if you were building a jump with a wall on the far side (ie you have to get off the ground) then timber supports will be required.
The danger of timber is wear over time may create a tyre-grabbing rut right before the edge, where it's too late to stop.
Finishing - use a watering can or hose with a shower spray to smooth off the surface.  A flat spade or rake may be useful for smoothing, or you could even use a garden roller.   Also you might want to use some matting or concrete pavers to minimise erosion and to assist traction.
Final thought - do get permission to do what you want to.   Or do it on your own land.   Don't go damaging trees or wrecking other things to make your jump.

Edit: I forgot to add maintenance.   Do periodic work on your jumps, to fill erosion or ruts, or just generally clean up.  Rubbish laying about attracts other rubbish so keep it pleasant.
Comment: Don't forget to build up the "back" side as well, not everybody is going to be able to catch air off a jump so being able to go down the back side will be a big benefit.  Having the ride around is good, but many times you can't see the back side of the ramp before committing.
Comment: I've made a start on my first dirt jump in the back yard, and this guide came in very handy! I've packed a couple of large treated logs in down the bottom and am gradually building the height and smoothing the transition. So far so good!
Answer: It's important to emphasise that the soil MUST be nicely damp all the way through if you want to build an even vaguely steep transition and a good lip at the top. Where I live in Zimbabwe I don't even bother trying in the dry season. Sprinkling a little water on the top won't do it − it must be damp the whole way through, but not slushy mud.
The dampness allows you to do two important things:

build a steep slope that doesn't just collapse
compact it nicely so that you don't sink into it when you ride, and it lasts over time, even once it has dried out. You want it to roll fast, in wet and dry conditions.

Obviously the type of soil you use will determine how well it holds together when wet, and how strong it is when it dries out. Clay soils are good, sand is bad.
Make sure you pack that lip tight. You should be able to stand on the top and jump up and down without damaging it. It'll mean extra work to get enough soil up there, but it'll be well worth it in the long run. If you skimp it'll just collapse, and where I am you'd need to wait until the next rainy season to fix it.
It's fine to use rocks and solid logs and things to bulk it up, but keep these well buried in the centre. When you're doing your final shaping it's often best to build it up a bit more than you would want, and then scrape or carve it away to get a nice smooth curve. If you find yourself unearthing your rocks you'll be in trouble − you'll have to pull the whole thing out and fill the hole again. Trying to just cover it over will leave nasty bumps in the surface.
Your tools are important. Use whatever is most convenient for moving your soil around, but you'll probably find that when it comes to shaping nothing beats a nice, smooth, gently curved shovel with a long handle. Get the surface damp, throw on a thin layer of dryer soil and smack it into the surface with the back of the shovel, smoothing downwards in one motion. A square spade can also be handy for cutting nice clean edges, and don't be afraid to use your hands to pack the soil where it needs to be steepest. You'll soon find what works for you.
Have fun!
Comment: Gidday and welcome to SE Bicycles.  Thank you for your contribution, and I look forward to your future submissions.
Comment: Thanks! I don't know how regular I'll be, but I'm glad to have found it. I've enjoyed reading your submissions too.


failed ubuntu installation

Question: so i downloaded ubuntu 12.04 and i unzipped the folder. I didn't burn it on a DVD I just launched it of the download folder. I clicked on the wubi.exe icon and proceeded to fill out the items and when i clicked next the time remaining said it was 3 Hours so i canceled it. After i burnt it on a DVD and launched the wubi.exe icon it just prompt me with Demo and Full Installation and Learn More. so how do I fix this?
Answer: If you are going to install Ubuntu using Wubi,you do not need to burn anything.
Wubi will install Ubuntu inside your windows system.Installing Ubuntu from an .iso file which you burnt in a usb or a CD will install Ubuntu at another partition.
My guess is that at the download page of Ubuntu you clicked the "Download" button at the bottom instead of the "Start Download" button at the top right.
You can download Wubi (which comes in the form of a windows executable file .exe) at this link.
From this link you can download Ubuntu 12.04 LTS in an .iso file which you have to burn.
Do not know how to burn an .iso in windows?Microsoft already has a tutorial for you.
Answer: You can prefer a downloading a wubi.exe & Ubuntu-i386.tar.xz from this link and from windows just open command prompt and run  wubi.exe as,
<code>wubi.exe --dimagepath=path\to\ubuntu-12.04-wubi-i386.tar.xz
</code>
It will take very less time than installing from Ubuntu iso and wubi....

failed ubuntu installation


Tits-Kantor-Koecher construction for Jordan algebra of symmetric bilinear form

Question: Suppose $f$ is a nondegenerate, symmetric bilinear form on a vector space $V$ over a field $F$. Then $J = V + F\cdot 1$ is a unital Jordan algebra (known as the "spin factor" Jordan algebra when $F = \mathbb{R}$ and $V = \mathbb{R}^n$). We can construct the Lie algebra $TKK(J) = L = L_{-1} + L_0 + L_1$ via the Tits-Kantor-Koecher construction where $L_1 \cong L_{-1} \cong J$. I have seen several papers reference the fact that $TKK(J) \cong K(R, *)$, the Lie algebra of skew-symmetric elements in an associative algebra $R$ with involution *. Can someone direct me to a proof of this fact? In particular, I would like to know what is $R$ and I'd like a proof when $V$ is not necessarily finite dimensional.
Comment: Is $R$ the Clifford algebra of the form you start with?
Answer: This is contained in Jacobson's Blue Book (Structure and Representations of Jordan Algebras, AMS Colloquium Publications, 1968), as Exercise 1 on p. 342, for arbitrary fields, and with no assumptions on the dimension of $V$.
More precisely, let $W$ be the $3$-dimensional vector space with bilinear form $g$ given by the matrix $\left( \begin{smallmatrix} 0 & 1 & 0 \\ 1 & 0 & 0 \\ 0 & 0 & -1 \end{smallmatrix} \right)$, and consider the orthogonal sum $h := f \perp g$ on $U := V \oplus W$. Then $TKK(J)$ is isomorphic to the Lie algebra of linear transformations of $U$ that are skew w.r.t. $h$.


Overview of basic results about images and preimages

Question: Are there some good overviews of basic facts about images and inverse images of sets under functions?
Comment: This question is also asked in an effort to make search for duplicates easier, since questions like this are asked quite often. For a more detailed discussion see [meta](http://meta.math.stackexchange.com/questions/3967/would-organizer-posts-be-useful-welcome-here).
Comment: Related: http://math.stackexchange.com/questions/746123/prove-that-ff-1-fx-fx, http://math.stackexchange.com/questions/1061602
Comment: Related: http://math.stackexchange.com/questions/608707, http://math.stackexchange.com/questions/834689
Answer: I have no doubt that there are many useful online resources for these, but many such results are available here at MSE, together with their proofs.
I'll give a list of some basic results about images and preimages links to the posts, which have proofs here at MSE. I am making this CW, so feel free to add more identities and pointers to further useful questions and answers.
$\newcommand{\Map}[3]{{#1}\colon{#2}\to{#3}}\newcommand{\Img}[2]{{#1}[#2]}\newcommand{\Pre}[2]{{#1}^{-1}[#2]}$
If $\Map fXY$ is a function and $A\subseteq X$ and $B\subseteq Y$ are some set then the set
$$\Img fA=\{f(x); x\in A\}$$
is called the image of the subset $A$ and the set
$$\Pre fB=\{x; f(x)\in B\}$$
is called the preimage or inverse image of the subset $B$.
In the other words, we have
$$y\in\Img fA \Leftrightarrow (\exists x\in A)f(x)=y$$
and
$x\in\Pre fB \Leftrightarrow f(x)\in B$.
In the notation below we always assume $A,A_i\subseteq X$ and $B,B_i\subseteq Y$.

$A\subseteq \Pre f{\Img fA}$ and, if  $f$ is injective, then $A=\Pre f{\Img fA}$.

see Proving that $C$ is a subset of $f^{-1}[f(C)]$
In fact, the equality is equivalent to the fact that $f$ is injective: Show $S = f^{-1}(f(S))$ for all subsets $S$ iff $f$ is injective or Is $f^{-1}(f(A))=A$ always true? Some counterexamples to the equality can be found in answers to Why $f^{-1}(f(A)) \not= A$

$\Img f{\Pre fB}\subseteq B$ and, if $f$ is surjective, then $\Img f{\Pre fB}=B$.

For the first part see: Need help for proving that: $f(f^{-1}(A)) ⊆ A$ For the second part, see Demonstrate that if $f$ is surjective then $X = f(f^{-1}(X))$ or Prove $F(F^{-1}(B)) = B$ for onto function.

The operation of taking images and preimages preserves inclusion, i.e. $A_1\subseteq A_2$ implies $\Img f{A_1}\subseteq \Img f{A_2}$ and $B_1\subseteq B_2$ implies $\Pre f{B_1}\subseteq\Pre f{B_2}$

Image of union of two sets is the union of their images, i.e. $\Img f{A_1\cup A_2}=\Img f{A_1}\cup\Img f{A_2}$.

See, for example, Prove $f(S \cup T) = f(S) \cup f(T)$
or Functions-Set Theory Proof that $f(C \cup D) = f(C) \cup f(D)$
or How do I prove the following: $f(S\cup T) = f(S) \cup f(T)$
or Maps - question about $f(A \cup B)=f(A) \cup f(B)$ and $ f(A \cap B)=f(A) \cap f(B)$
or Unions and Functions on Sets
or The preimage of a subset

The same is true for arbitrary union: $$\Img f{\bigcup_{i\in I} A_i} = \bigcup_{i\in I} \Img f{A_i}.$$

See Show that $\bigcup_i f(A_i) = f(\bigcup_i A_i)$

In the case of intersection, we only have one inclusion: $$\Img f{A_1\cap A_2}\subseteq \Img f{A_1} \cap \Img f{A_2}.$$ But if $f$ is injective, then $\Img f{A_1\cap A_2} = \Img f{A_1} \cap \Img f{A_2}$.

See, for example Is this a valid proof of $f(S \cap T) \subseteq f(S) \cap f(T)$?
or Is this proof correct for : Does $F(A)\cap F(B)\subseteq F(A\cap B) $ for all functions $F$?
or Prove $f(S \cap T) \subseteq f(S) \cap f(T)$
or Do we have always $f(A \cap B) = f(A) \cap f(B)$?
or Maps - question about $f(A \cup B)=f(A) \cup f(B)$ and $ f(A \cap B)=f(A) \cap f(B)$
or Verifying a proposition on image and preimage: $f(A\cap B)\subseteq f(A)\cap f(B)$ and $f^{-1}(C\cap D)=f^{-1}(C)\cap f^{-1}(D)$
or How to prove this? "For all sets $A,B\subseteq D$ and functions $f:D\mapsto R$, we have $f(A\cap B)\subseteq(f(A)\cap f(B))$."
or $f(A \cap B)\subset f(A)\cap f(B)$, and otherwise?
The part about injective functions can be found in
Conditions Equivalent to Injectivity or in
Proving: $f$ is injective $\Leftrightarrow f(X \cap Y) = f(X) \cap f(Y)$
A counterexample showing that equality is not true in general can be found here: Do we have always $f(A \cap B) = f(A) \cap f(B)$?
In fact, if this equality is true for all subsets $A_1,A_2\subseteq X$, then $f$ must be injective, see To prove mapping f is injective and the other f is bijective

Again, the same claims hold for arbitrary intersection: $\Img f{\bigcap_{i\in I} A_i} \subseteq \bigcap_{i\in I} \Img f{A_i}$ and if $f$ is injective, then $\Img f{\bigcap_{i\in I} A_i} = \bigcap_{i\in I} \Img f{A_i}$.

See: Inverse image of a union equals the union of the inverse images and Proof for Image of Indexed Collection of Sets?

Preimages preserve intersection: $\Pre f{B_1\cap B_2}=\Pre f{B_1} \cap \Pre f{B_2}$.

See, for example: What are the strategies I can use to prove $f^{-1}(S \cap T) = f^{-1}(S) \cap f^{-1}(T)$?
or how to prove $f^{-1}(B_1 \cap B_2) = f^{-1}(B_1) \cap f^{-1}(B_2)$
or Verifying a proposition on image and preimage: $f(A\cap B)\subseteq f(A)\cap f(B)$ and $f^{-1}(C\cap D)=f^{-1}(C)\cap f^{-1}(D)$

The same is true for arbitrary intersections: $\Pre f{\bigcap_{i\in I}B_i} = \bigcap_{i\in I} \Pre f{B_i}$.

See: Proving set equalities

Preimages preserve union: $\Pre f{B_1\cup B_2}=\Pre f{B_1} \cup \Pre f{B_2}$.

See: Show that $f^{-1}(A \cup B) = f^{-1}(A) \cup f^{-1}(B)$

Again, this is also true for union of more than just two sets: $$\Pre f{\bigcup_{i\in I}B_i} = \bigcup_{i\in I} \Pre f{B_i}.$$

See: Union of preimages and preimage of union
We can also ask whether image and preimage preserve difference:

$\Img f{A_1}\setminus\Img f{A_2} \subseteq \Img f{A_1\setminus A_2}$, but the equality does not hold in general

See Proving $f(C) \setminus f(D) \subseteq f(C \setminus D)$ and disproving equality. Equality holds for injective functions, see If $f$ is 1-1, prove that $f(A\setminus B) = f(A)\setminus f(B)$. In fact, validity of the equality $\Img f{A_1}\setminus\Img f{A_2} = \Img f{A_1\setminus A_2}$
characterizes injectivity: Does $f(X \setminus A)\subseteq Y\setminus f(A), \forall A\subseteq X$ imply $f$ is injective ?.

$\Pre f{B_1}\setminus\Pre f{B_2}=\Pre f{B_1\setminus B_2}$

See Proof of $f^{-1}(B_{1}\setminus B_{2}) = f^{-1}(B_{1})\setminus f^{-1}(B_{2})$. As a consequence of this we get that the preimage of complement is complement of the preimage, see here: How to approach proving $f^{-1}(B\setminus C)=A\setminus f^{-1}(C)$?, Show that for any subset $C\subseteq Y$, one has $f^{-1}(Y\setminus C) = X \setminus f^{-1}(C)$ and Show $f^{-1}(A^c)=(f^{-1}(A))^c$
The image and inverse image for composition of maps can be expressed in a very simple way. For $\Map fXY$, $\Map gYZ$ and $A\subseteq X$, $C\subseteq Z$ we have

$\Img g{\Img fA}=\Img{g\circ f}A$

$\Pre f{\Pre gC}=\Pre{(g\circ f)}C$

See Show that $(g \circ f)^{-1}(C) = g^{-1}(f^{-1}(C)).$ and Prove that if $Z\subseteq Y$, then $(g\circ f)^{-1}(Z)=f^{-1}(g^{-1}(Z)).$
Comment: I love the fact almost all of this can be deduced immediately from the adjunctions $f[-]\vdash f^{-1}[-] \vdash f_{*}[-]$.
Comment: [The amount of duplicates...](http://i.huffpost.com/gen/210699/thumbs/s-THE-RENT-IS-TOO-DAMN-HIGH-JIMMY-MCMILLAN-large.jpg)
Comment: @user18921 Corrected now. Thanks to [wj32](http://math.stackexchange.com/posts/359694/revisions).
Comment: Yeeees getting this all in one place
Comment: Is there a similar list for stronger results when the map is continuous?
Comment: @plebmatician To be honest, I am not really sure what kind of properties you have in mind. In any case, I have mentioned this in [Calculus and analysis chatroom](https://chat.stackexchange.com/transcript/14150/2018/12/20), maybe somebody will notice it there.
Answer: This big list is included in Appendix A of Introduction to Topological Manifolds by John M. Lee:
Let $f:X\to Y$ and $g:W\to X$ be maps, and suppose $R\subseteq W$, $S,S'\subseteq X$, and $T,T'\subseteq Y$.

$T\supseteq f(f^{-1}(T))$.
$T\subseteq T' \Rightarrow f^{-1}(T)\subseteq f^{-1}(T')$.
$f^{-1}(T\cup T')=f^{-1}(T)\cup f^{-1}(T')$.
$f^{-1}(T\cap T')=f^{-1}(T)\cap f^{-1}(T')$.
$f^{-1}(T\setminus T')=f^{-1}(T)\setminus f^{-1}(T')$.
$S\subseteq f^{-1}(f(S))$.
$S\subseteq S' \Rightarrow f(S)\subseteq f(S')$.
$f(S\cup S')=f(S)\cup f(S')$.
$f(S\cap S')\subseteq f(S)\cap f(S')$.
$f(S\setminus S')\supseteq f(S)\setminus f(S')$.
$f(S)\cap T=f(S\cap f^{-1}(T))$.
$f(S)\cup T\supseteq f(S\cup f^{-1}(T))$.
$S\cap f^{-1}(T)\subseteq f^{-1}(f(S)\cap T)$.
$S\cup f^{-1}(T)\subseteq f^{-1}(f(S)\cup T)$.
$(f\circ g)^{-1}(T)=g^{-1}(f^{-1}(T))$.
$(f\circ g)(R)=f(g(R))$.
Comment: found this while doing a problem from Lee's book.
Comment: Very nice! There is a similar theorems-exercises on the first chapter of Tom Apostol's mathematical analysis.
Answer: The "online compendium of mathematical proofs" known as ProofWiki has most of these results -- with one or more proofs. (For the record, I am somewhat affiliated with that site.)
Most results regarding images and preimages should be in the Mapping Theory category (look under the "M").
Answer: Here's interesting application of inverse image:

Given two functions: $ f : R \times R \rightarrow R, g : R \rightarrow 2, g=([n_0..n_1] \mapsto 1)$, the composition of them gives characteristic function $ h : R \times R \rightarrow 2$.
Use equation $h(x,y)=1$ to choose $1$ from $2=\{0,1\}$.
Once chosen, use inverse image to find all $(x,y)$ -pairs: Inverse image $g^{-1}(1)$ gives whole range $[n_0..n_1]$. Inverse image $ f^{-1} ([n_0..n_1]) $ is the interesting one.
Example of how this works is simply by choosing $f = \sqrt{x^2+y^2}$ and $g=([0..5]\mapsto 1)$ to get a (filled) circle with radius 5 from inverse image, distance function f, and simple range function g.
Example2: $f=\sqrt{x^2+y^2}$ and $g=([3..5]\mapsto 1)$ gives you circle with a hole.
Example3: $f=\sqrt{x^2+y^2}$ and $g=([r..r]\mapsto 1)$ gives you solutions to equation $x^2+y^2=r^2$ (with the caveat that the characteristic function is useless)
Key information is that inverse images can give more information about subsets defined via characteristic functions.


Why did Marcus take the contract

Question: I found this question about John Wick that stated that Marcus took the contract, but out of friendship he decided to help Wick. But couldn't he refuse the contract and help Wick anyway? Why take it, help Wick, and then have Viggo come after you for not killing him?
Comment: @ibrahimmahrir so was Viggo I guess ;)
Comment: @ibrahimmahrir - but he wasn't going to get the money anyway. He took the contract to watch over him, but he could have rejected it, and still helped Wick, without Viggo ambushing him.
Comment: Because it was $2,000,000. ;-)
Comment: I was just kidding about the $2m. :)
Answer: If he refused the contract, then Viggo would have just hired other people to kill John. Marcus, wanting to protect John, chose to take the contract, thus giving Viggo some reassuring and stalling John's assassination.
Helping John was going to get him killed anyways out of revenge from Viggo, so taking the contract or not won't change that fact. He only took it to buy John some time, allowing him to focus on his mission and reducing the chances of him getting killed by another professional hit-man (who would've been hired by Viggo if Marcus had rejected the contract).
Conversation between Viggo and Marcus when they first discussed the contract:

Viggo: It's a timely matter, it has to be handled quickly.
Marcus: Consider it done.
Viggo: Thank you, Marcus. I know I can trust you. Thanks for the drink.

Another point that needs mentioning is the fact that Viggo knew about Marcus helping John from Ms. Perkins who saw them together earlier. Marcus might have planned to secretly help John and let him kill Viggo's son, then tell Viggo later that he had failed. Viggo, knowing John's skills and what type of hitman he is, would understand and spare Marcus' life (for failing not betraying him).
Comment: Problem is, Marcus asked if the contract was exclusive, and Viggo said No, it was a timely matter, or something along those lines. So Marcus wasn't the only one going after Wick, remember Perkins was notified about the contract as well. She is the one that spotted Marcus and Wick together.
Comment: @AverageJoe **1.** The contract being open or not is irrelevant, Viggo needed a pro hitman for the job, the kind of hitman that knows John's skills, the kind that won't take on an open contract. The rest of the hitmen are no match for Wick (as shown previously in the movie). Also, Viggo might have changed the contract to an exclusive one when Marcus agreed on taking it, to show respect and faith for Marcus (such change would've happened after Perkins involvement in it). **2.** Totally forgot about this. I've added another crucial point to the answer. Thanks for reminding me.
Comment: If the contract was switched to exclusive, then why did Perkins attempt to kill John at the hotel with Marcus watching? She even says Viggo will give her 4 million to break the rules, had it been exclusive she won't have been there. I think it was a matter of loyalty, Viggo was probably testing Marcus to see which side he would take and if money can change him. Perkins was obviously motivated by greed and choose Viggo over loyalty to Wick, or even respect for the Continental rules.
Comment: @AverageJoe I said _"such change would've happened after Perkins involvement in it"_. That means that Perkins was involved before Viggo asked Marcus. Also don't you think it's kind of unusual that no other hitman seemed to be interested in the $2m contract? => maybe because it went exclusive. Anyways, whether it went exclusive or not doesn't matter. No hitman will take the risk against John. Viggo had to hire a pro personally. He stopped scouting for pros after Marcus agreed, which is why Marcus agreed.

Why did Marcus take the contract


Replacement Options for T12 Four light fluorescent light fixture

Question: I have a good number of fluorescent light fixtures that are old the ballasts are going out. There are two ballasts per fixture. The ballasts are expensive when factoring in labor cost. Covering to T8 requires new ballasts as well. Can I go with three lamps per fixture and get by with one ballast.
Is there an LED option that can eliminate the fluorescents and ballasts all together.
Comment: Hello, and welcome to Stack Exchange. What's a "good number" of fixtures? What type are they (e.g. four bulb 4' T8)? A picture might also help.
Comment: I have 4-bulb T-8 ballasts in my possession, so I'm unclear where your 3-bulb assumption comes from... There are many of those available. "Direct wire T8 LED retrofit tubes" are also available.
Answer: You can go T12, T8 or LED, and 2, 3 or 4 lamps.  That is decided by which ballast you buy.
Instant, or Rapid/Programmed Start.
This is decided by the wiring of your fixture.  Each bulb end has 2 pins because there's a small filament in each end of the bulb.  Rapid or Programmed Start ballasts use both pins to preheat those filaments for an easy start and longer lamp life - so they have 2 wires to each end of each bulb.  Instant start ballasts do not, so they only have 1 wire. If you have instant-start, stay with it - otherwise you may need to replace the lamp sockets.
T12 vs T8 vs LED
You probably have inventory of T12 bulbs, but they are basically obsolete.  T8 bulbs are inexpensive, more efficient, have much better color rendition (typically starting at 80% CRI) and come in several light colors (3500K, 5100K etc.)   Edit: since I wrote this I have started fitting 90CRI T8 tubes, readily available for under  $2 each, they are marvelous.  You don't see it in the tubes, but rather, in the stuff being lit up.
LEDs come in 2 flavors: "direct wire" (rewire the fixture for 120V on the lamp ends) or "keep the ballast". (no rewiring, the smarter LED emulates a bulb). The trouble with the second kind is you must maintain the ballast, and it must be of a certain type (i.e. instant start). With direct wire, you remove the ballast entirely and wire 120V to the lamp end(s). Some "direct wire" LEDs take the 120V on one end of the lamp (the other end is a dummy) - that can be a problem in a fixture with 1-wire sockets.
2, 3 or 4 bulbs
T8 bulbs are generally brighter than T12 bulbs.  Look at the bulb rating in lumens, but multiply by the ballast factor (a percentage) - they make ballasts designed to underdrive or even overdrive the bulb's rating.  Often when lighting is carefully designed, they replace 4 bulbs with 3 or 2, because T8's are brighter and/or because they found the space was "over-lit".
LED lumens are lower, but they're worth a lot more, because they're all aimed in the right direction - unlike fluorescents which waste a lot of energy lighting the backside of a reflector.
Sourcing
Changing ballasts is rather straightforward and I pay between $12 and $30 on 1000bulbs.com or other sources.  I aim for middle to top shelf quality - my first choice is GE, and I find good deals on boxes of new ballasts on eBay. Edit: 4-lamp ballasts are readily available.  The tactic of getting 3-lamp ballasts and only fitting 3 tubes works well with T8, as they are somewhat brighter.
I have also been doing great on eBay buying new or lightly used ballasts that were pulled from newish fixtures for LED upgrades.  As low as $4 each.
I regularly see direct-wire LED replacement 4 foot "tubes" for under $10, often from 1000bulbs.com or superbrightLEDs.com.
It's pretty easy work if you don't mess with the lamp sockets - just get a big bag of "blue" wire-nuts, a stripper, and go to town.  If your fixture is hard-wired, you must install "disconnecting means" - I power down, install half the connector on the hot lines, then power up and do everything else.
When I replace lamp socket ends ("tombstones"), I pay about 60-70 cents each for those, and they are fairly standard.  But the labor gets pretty high.
Answer: Replacing t12 Flouresents with led direct wire lamps is what I do both at home and work.
I currently use a t8 size lamp rated at 20w 5000k color these provide more perceived light.  T8, 10 & 12 lamps all use the same tombstones , the only thing you have to make sure the tombstones are not shunted. A quick check with an ohm meter across the tombstone if low resistance it is shunted open or high resistance it is not. If shunted you can use double ended direct wire lamps if open you can use single ended or double ended. Wiring them in is easy using the existing wires and a few wire nuts, I remove the ballast and unused wires from the tombstones but these can be taped or capped. The tubes I purchase are DLC approved that means 5 year warranty, they are 8.99 each.


Do Flash head banner texts need to coincide with the text on the underlying HTML banner?

Question: Let's say you have a flash head banner on the page that you are trying to optimize. Let's also assume that you've incorporated an underlying HTML banner for SEO purposes. Now, do you think Google actually "reads" flash content and can penalize you for not using the same content on both headers?
Answer: Despite "Google can read" flash content, it reads everything from flash as plain text, I mean, you can't count with semantic features and the weight they brings as HTML do, like H1, H2, strong....
So, if you are really serious about optimizing give up on flash. If you really can't drop flash, use same text, with correct markup on proper elements. Also make sure you put the header content as an alternative making use of a noscript tag.


How to block ads in Android applications?

Question: Are there ways that attempt to block ads in applications? It seems that it should be theoretically possible, by blocking web requests to certain sites, for example.
Answer: The most popular method is replacing the built-in hosts files with one that forces DNS queries to well-known ad servers to result in 127.0.0.1 (localhost).  This effectively blocks most common ads, and most of the Google Ads in applications.
The downside is that applications can tell that ads are being blocked, and can either refuse to run or otherwise degrade their usefulness while the ad blocking is in effect.
Also, root access is required to replace the hosts file.
Beyond that, I haven't seen anything that can selectively block web requests for arbitrary apps.  For some programs that only use internet access for ads, you could use a firewall app to prevent them from accessing the internet or -- if your ROM supports it (like the latest CyanogenMod) -- revoke the internet access permission from the app.
Again, root access is generally required to set up a system-wide app-level firewall or replace your ROM.
Comment: Note that there are apps for this, e.g. "Ad Free Android" or "AdAway".  A search turns them up quickly.
Comment: IMO It's better to redirect to 0.0.0.0
Answer: There are two different apps, AdFree Android and AdAway that block ads, theoretically in all applications.  You must have a rooted phone in order to use these.
AdFree Android works by

...nullifying requests to known host names in the system hosts
  file.

which is essentially an automated solution of modifying the hosts file, brought up by another user here.  It appears that Adaway does the same thing.
If you do not have a rooted phone, you can, at the very least, use the Firefox Browser with the Adblock Plus AddOn (installed via Firefox).
Answer: You can use an ad-blocking DNS server such as AdGuard DNS. Unlike the HOSTS file method, you won't need to use an app, nor root your phone.
On Android 9 Pie and later, you can use ad-blocking DNS servers by configuring the Private DNS setting:

Go to Settings → "Network & internet" or "Wi-Fi & Internet" or "Connections".

Select "Advanced" or "More connection settings" → "Private DNS".

Select the "Private DNS provider hostname". Enter dns.adguard.com. (This is the AdGuard DNS hostname. If using another ad-blocking DNS, then replace it with the corresponding hostname.) Press "Save".

For versions prior to Android 9 Pie:

Go to "Settings" → "Wi-Fi".

Press and hold the name of the Wi-Fi network you are currently connected to.

Select "Modify network".

Tick the "Advanced options" checkbox.

Change "IP Settings" to "Static".

Remove the DNS addresses that may be already listed and replace with 184.108.40.206 for DNS 1 and 126.96.36.199 for DNS 2. (These are AdGuard DNS IP addresses. If using another ad-blocking DNS, then replace them with the corresponding IP addresses.)

Press "Save". You may need to disconnect from the Wi-Fi network and reconnect for the changes to take place.
Note that if the "Save" button is grayed out, manually re-enter the current values into the "IP address", "Gateway", and "Network prefix length" text fields. Then press "Save", which should become active by this point.

Aside from the DNS / IP address-based ad blockers, I'd also recommend MinMinGuard (requires a rooted phone and the Xposed Framework). It features API-based blocking, where function calls provided by the advertisement network SDK are blocked.

MinMinGuard is an Ad-remover made with Xposed Framework for Android.
MinMinGuard can completely remove both the ads inside apps and the
empty space caused by those ads. Conventional ads removing apps are
only able to block the ad content, but the space taken by the ad will
still remain unused (black). MinMinGuard successfully removes that
black space, which extends the app window and makes your
user-experience better!
Features:

Totally remove the advertisement. You can notice that
AdBlock and AdAway only stops showing the ad content, but it can not
remove the empty field that was originally taken by the ad.
MinMinGuard can totally remove the empty field!
Lightweight.
Alternative ad removing apps (AdBlock etc) constantly run a background
VPN service, which puts a heavy loading on the system. MinMinGuard
does not need to run a VPN service, so it saves system resources and,
thus, extends the battery life.
Per App Setting. MinMinGuard lets you
choose which apps you want to remove ads from. If you only want to
remove ads from several apps, MinMinGuard is your best solution.
Answer: You can also use a firewall or permissions-limiting application (DroidWall or LBE Privacy Guard, for example) to limit internet access for particular applications. These also require root.
Answer: To disable ads, you have to understand where the ads actually come from.
There are easy-to-identify ad servers, and those can be easily avoided by editing your hosts file (you can edit hosts file on a rooted phone through ES file manager, or from a terminal session be it local or from your laptop/desktop).
But when the ad servers keep having random subdomains, that can be a real chore to keep chasing those updated servers.
There are applications (previously mentioned) that help to ease that task--but it still is the same solution of getting hit with ads--and then blocking the new servers.
None of those methods work if the ip address gets hardcoded in. That is the trump card.
Another option is to enable a firewall that denies ANY traffic for a specific application.
That means: updates, ads, pushing your stats, etc...don't use your data plan and don't tie up your phone.
Avast! Mobile security (free on marketplace or Play) gives you granular control when you want it.
I have used Avast on desktops and servers, and run it on rooted Gingerbread and CyanogenMod9 (ICS).
Very good appl.
Answer: Adblock Plus is now available for Android.
Here's a snippet from Lifehacker's review:

If you love Adblock Plus on the desktop, now you can take it with you on your Android phone. Adblock Plus for Android blocks ads on sites while you browse and even suppresses ads inside of ad-supported applications. Best of all, it's completely free.
Adblock Plus for Android doesn't require root access to your phone to suppress ads, but works best if your device is rooted. If you're rooted, it'll suppress ads over 3G/4G and Wi-Fi with no additional configuration required. If you're not rooted and you're running Ice Cream Sandwich, it'll block ads over Wi-Fi but not 3G/4G. If your device is running Gingerbread or earlier, you'll have to set up Adblock's proxy manually to get it to work. Speaking of proxies, that's how Adblock Plus for Android manages to strip out all of those ads: it routes all of your traffic through their servers, and removes the ads before it gets to your phone.
Comment: The article also notes: ".. it's important to note that the only reason so many great Android apps remain free are because the ads support the developers..." If too many people block the ads in Android apps, there will be fewer high-quality _free_ apps.
Answer: Although incomplete I have a solution in place that is sufficient for me.
I have configured the dnsmasq dns server in my lan to serve 0.0.0.0 as the response to a specified set of advertising hostnames.
The pro is that I have one solution that fixes this for both my tablet and my phone without the need to root either of them.
The con is that it only works at home on my wifi.
Answer: I like the firewall approach. Recently installed the NoRoot Firewall and by trial and error found that if I block access to l[ab]-in-f[0-9]{3}\.1e100\.net (actually, the app doesn't support regex in addresses), ads don't get through.
Answer: I had similar problem before and non of the existing apps could solve my problems, furthermore I cannot root my company phone due policy. Then I realized that you can configure proxy for each and every connection (wifi and 4g) separately. So I installed a squid, configured to block most of the annoying ad sites and deployed in docker.
Long story short:
docker run -d -p 3128:3128 --name squid-adblock andrassebo/squid-adblock

Then configure the proxy on your phone to use the hosting machines IP address and 3128 as port.
If you would like to check details or simply compile your own image, the source code is available on GitHub: source and DockerHub: images
Answer: The latest Android Market app (I have 3.15 which is the first time I've noticed the option) has an option to allow you to prevent Google or AdMob ads from tracking you and personalizing the ads to your interests. If that's all you want to stop, then it's just a tickbox away.
Open the Market app, pressMenu scroll down to the Other Settings heading where you should see:

Google AdMob Ads: personalize ads based on my interests
Choose
whether to personalize ads from Google and AdMob in mobile apps on
this device. Learn more

Just remove the tick from that tickbox to:

Opt out
If you opt-out, your device identifier information will not be
used by Google for advertising going forward and you will not receive
ads based on your interests or inferred demographics.
Comment: I don't think that's to say you won't receive ads at all, just that you won't receive _targeted_ ads.
Comment: @AlEverett That is true, which is why I said "*tracking you and personalizing the ads to your interests. If that's all you want to stop*" it's also worth noting that it also only works for the Google/AdMob/Android default ad services, if an app is serving 3rd party ads that option won't do anything.
Comment: I was just adding clarity.
Answer: The answer is: theoretically yes, practically no. Several years passed since the question, but adware got even worse.
Best way to "block ads" is to "get rid of code that produces it". This is very hard to achieve, because this would require to get rid of adware roots, which are related to current world's economical model and entrepreneurship. It's like to rehabitate all people around the world, to react ads very drastically and ultimative: "either no ad, either no use of android os/devices". This could happen through children education, via seeding strong idea, like "ads is something criminal like porn/theft/deception and speculation/terrorism/narcotics"... In such way, after several human generations adware would eventually starve, because any "ad-related activity" would refer to organisation which will be considered "codnucting illegal activity" and enormous penalty tax should be applied, and person who publish ad jailed.
There exists other, faster way: It is to create a group, who would develop android alternative firmware, essentially same as android, but with licensing terms explicitly disallowing using of ads, and maybe even some banning/firewall engine, embedded into system and easily tunable by users. Good implementation would be very costly, and it would take time to put it on a very single phone. But that would definetely force android community to react.
That is some effective approaches, but any real action should involve Google, which should "change its mind and become white and fluffy" in order to really get rid of adware in android. This is very unlikely to achieve, with current world's economical model.
Comment: Sorry, but this is not helping us to fix the issue at hand immediately. We tend to avoid opinions because we are not a forum. Please consider providing a technical solution to the problem, even if it is just about installing an app and using it to block ads
Comment: @Firelord Pease Please, reread question title: there was nothing like "it is just about installing an app".  Also, "this is not helping us" - who is "us"? Are you on behalf of some organisation? Please use correct and understandible wording.
Comment: @Firelord Good answer is not about developing app, but more about "undeveloping what was developed by human error". No app would solve this ever. Correct technical solution is: to spend next century in attempt to change people mind in such a way, that people would not participate in developing/using adware. Add ad-related stuff - firmwares, os, libraries, etc - could be just abandoned. Steps could involve politics, informing, education, so on. "Would they be taken or not?" / "Easy solution or a hard one?" - these are out of discussion scope. But it IS a solution, and is ONLY correct solution.
Comment: You are right. Current world's politico-economic system which is heavily based on capitalism, is strongly tied to competition and hence advertisement. But in our case, ***"practically no"***? No. I haven't seen a single ad (if I didn't miss one) on my device for past few years. The only thing I do is DNS filtering.


What are the most common misconceptions about Esperanto?

Question: Sometimes otherwise well educated people, can say the strangest things about Esperanto and its speakers. What are the most common misconceptions, prejudice and myths that we face? Are these misconceptions varying between different parts of the world?
Comment: See also http://esperanto.stackexchange.com/questions/1114/why-do-so-many-prejudices-and-misinformation-exist-about-esperanto, which is somewhat related to this question.
Comment: Probably no one knows which of the many misconceptions about Esperanto are the most common ones.

We also have to define what "most common" means, e. g.:
- Believed by most people
or
- To be found most often in articles

Here is a list of all the misconceptions, I was able to find (in Esperanto)
[link](https://eo.wikipedia.org/wiki/Esperanto#Eraroj_kaj_mitoj_pri_Esperanto)
Comment: "Common sense is the collection of prejudices acquired by age eighteen."
-- Albert Einstein
Comment: I'd say the misconceptions themselves are opinion-based (how could they not), but which ones are the most common, isn't primarily opinion-based.
Answer: By far the most common misconception is that Esperanto is a failure (or dead). They are oversimplifying Esperanto as a goal to "Replace English", and since we still speak English (at least 1/7 of the world can understand it), they deduce Esperanto is a failure. Since it is a failure for them, it must have not speakers.
Of course, this reasoning has errors at every level.

First, Esperanto is not a goal, but a language, a tool with unique features such as being very regular and easy. Nowadays, people are learning Esperanto for varieties of reasons and they can not be generalized under the same idea of one man.
Second, considering it a "failure" means Esperanto is a thing of the past. It is not, Esperanto is a thing of the present and its numbers are growing. For my own goal of having a comfortable way to speak with people from all other the world, Esperanto was a big success where English was never as comfortable for non-native speakers.
Third, if you don't hear about something, it does not mean it does not exist or disappeared. While Esperanto has huge numbers, it is diluted all over the world, which makes the language useful for different things that people are not used to.
Answer: "Esperanto has no culture."
To this one, I say "yes and no". People often comment that one of their main reasons for learning a new language is to learn about a culture, to experience its literature, learn its history, etc. This isn't something I have any desire to argue with, as someone's reason for learning a language is entirely their business.
But is it true that Esperanto has no culture? My answer is, as I mentioned, yes and no. Clearly, Esperanto's history is different compared to many languages one might study. Our body of literature is relatively small, same goes for our music, poetry, films, etc. And all of our history begins in the 1800's, not very long ago. And there is no Esperanto country or capital city or even neighborhood, where one can go anytime for some immersion. Our population is scattered, and small compared to many of the world's more "popular" languages. Considering all of this, I can see how this would be described as Esperanto having no--or at least very little--culture, especially by someone for whom a wealth of art, tradition, history, and the ability for 24/7 immersion is the main attraction to language learning.
Before I go on to describe what I consider to be Esperanto's culture, I want to point out that the above is, well...Kind of the "point" of Esperanto, at least originally. Esperanto was supposed to be neutral. It was supposed to be nationless, historyless, cultureless--the intenton being to make it free of the historical baggage that other languages carry. Nobody's hometown has been bombed by an Esperanto speaking nation, nobody has been imprisoned and tortured by Esperantists, nobody has had their children taken away and placed in an Esperanto school. When you speak Esperanto, you are supposed to be speaking a language that has a "clean record" worldwide, a language you could call a blank slate. Infusing such a language with cultural norms and taboos would begin to undermine its concept. (Now, whether Esperanto has actually ever achieved these "goals" of neutrality or if they are important to most Esperanto speakers today, is a whole different discussion...)
So if my answer is "yes and no" then what do I mean? What is Esperanto's culture? Well, obviously, though small, we DO have a body of literature, we do have a music scene, we do have films, etc. And though short, we DO have a history. And we do, actually, have some physical locations throughout the world that could one day become hubs of Esperanto activity, Herzberg am Harz, the "Esperanto Town", being one example. I could go on at length trying to describe the quality of our literature and whatnot, but that's not really what I am getting at and I'm sure you can find the information already written up somewhere (perhaps you can start here). And we DO have taboos, we DO have social norms and biases, which are also elements of culture, for better or worse.
Here's what Esperanto culture is, in my view: it's the thoughts, actions, and beliefs of the currently living and breathing Esperanto speakers whenever they get together and create an instance of Esperantujo. Maybe that is insignificant to someone who wants to study history and books, but to me it's fascinating. Esperanto is a language who is "just starting out". We are just recently reaching the point of having enough speakers that the rules of the language are beginning to bend under our weight; the reigns have fallen out of our hands and we are along for the ride as the language evolves, and it's evolving due to all of our involvement with it. No single person can say "this is what we should do from now on"--like any culture, we now operate more like a flowing tide of ideas than one single person instigating and guiding all changes. We have a living language developing and  growing before our very eyes, and this is the result of our collective contributions, intentional or not. It's a first row seat to the first stages of the blooming of a culture from a very small seed.
Esperanto is both a "brand new" and "artficial" language and yet it can easily express the natural thought patterns that occur in the human brain structure which evolved before recorded history. It's a window into human minds across the world, skipping over our differences and focusing specifically on one of the things that uniquely connects us all as human beings, one of humanity's oldest cultural assets--language itself. Something about that is fascinating and very moving to me. Maybe other people will not be "persuaded" by this, though my intention is not really to persuade people to learn Esperanto if they don't want to, rather I just want to describe what I think also counts as culture and might be worth some interest.
Comment: I disagree with the statement that the body of literature is "relatively small". Well, it's a relative statement, of course. And I guess we need to compare ourselves to either other small languages or small countries. But look here: http://esperanto.stackexchange.com/q/1119/134
Answer: "Esperanto is a failure because I hadn't heard of it until you told me just now."
That there are no native speakers, that there is no culture, that there are no books written in Esperanto.
That you can't make jokes or curse in Esperanto.
That it is Spanish.
That a language has to be spoken somewhere to be successful.
That you need a country to go to to learn it.
That nothing happened since you heard about it thirty years ago.
That it isn't useful.
That there aren't "enough" speakers.
That learning it won't open up new opportunities and change your life.
That only crazy people learn it.
These are clearly all wrong.
Answer: Very common misconception:

Esperanto has no native speakers (usually in conjunction with ".. and therefore it's not a real/usable/working language"). Somewhat unique misconception in that while there are native speakers, their existence and influence is (unlike in a natural language) rather irrelevant.
Answer: Probably no one knows which of the many misconceptions about Esperanto are the most common ones. I don't know any research about this.
We also have to define what "most common" means, e. g.:

Believed by most people

or

Believed by most linguists

or

To be found most often in articles

or

To be found most often on the internet

Here is a list of all the misconceptions, I was able to find (in Esperanto),
Esperanto-wikipedia: Eraroj kaj mitoj pri Esperanto with all the references I found. I would be glad, if you would add more examples in case you know some more sources or more misconceptions.
Anyway, the misconceptions "no one speaks Esperanto" or "nearly no one speaks Esperanto" seems to be very common. A lot of other misconceptions are dependent of this one: If no one speaks Esperanto, then there is not language community, there are no books and there is no culture, there are no jokes in Esperanto and it's not useful...
But let us keep in mind: All these ideas are misconceptions. There is a living language community with some hundred thousand active speakers, there are about 120 books a year, there are songs and jokes and if you like to meet people from other countries, then it's very useful.
Answer: The misconception I had for quite a long time was: "People who learn Esperanto nowadays do it because they want it to be the international auxiliary language". This misconception is kinda understandable, because that was the main goal of many Esperanto speakers for a long time.
It's hard to find good statistics, but it is clear that nowadays many Esperantists aren't concerned whether Esperanto can become an IAL, and it's very likely that the motivation of a great majority of Esperantists is based on completely different reasons, such as the possibility of meeting like-minded people.
Comment: Interestingly, clearing that misconception is like stating that several misconceptions in other answers are not misconceptions.


Why did Apollo 11 land at the sea of tranquility?

Question: As we all know in 1969 Apollo 11 landing made history but, why did it land specifically at the sea of tranquility also known as Mare Tranquilitatis. Probably they would have chosen this because of flatness and smoothness of surface but are there any other technical reasons behind it? Moreover what was the temperature of the site at the time of landing? As the lit part of moon is quite hot and the dark part is much colder than normal temperature we human come across in daily life.
Answer: The set of landing sites considered for all the Apollo missions was driven by a desire to sample a wide variety of lunar geology, but the order for them was chosen to make the first landings easiest and safest from a technical standpoint.
The scientific rationale for site selection is described in detail in an appendix to the NASA historical document Where No Man Has Gone Before: A History of Apollo Lunar Exploration Missions. In summary:

The short list of landing sites for the first 10 lunar exploration missions should include:

two types of mare material, "older" or eastern and "younger" or western;
regional stratigraphic units, such as blanket (ejecta) deposits around mare basins;
various types and sizes of impact craters in the maria and in the highlands;
morphological manifestations of volcanism in the maria and in the highlands; and
areas that may give clues to the nature and extent of processes other than impact and volcanism, which may have acted on the lunar surface.

An Apollo 11 summary gives some technical criteria for landing site selection:

The original sites were located on the visible side of the Moon, within 45° east and west of the Moon's center and 5° north and south of its equator. The final site choices were based on the following factors:
Smoothness: Relatively few craters and boulders.
Approach: No large hills, high cliffs, or deep craters that could cause incorrect altitude signals to the lunar module landing radar.
Propellant Requirements: Least potential expenditure of spacecraft propellants.
Recycling: Effective launch preparation recycling if the countdown were delayed.
Free Return: Sites within reach of the spacecraft launched on a free return translunar trajectory.
Slope: Less than 2° slope in the approach path and landing area.

I believe the propellant requirements, recycling, and free return constraints all pointed to sites close to the lunar equator, where the (slow) rotation of the moon would not take the landing site too far from the ground-track of the orbiting command module. To rendezvous from a landing site at high lunar latitudes would require an expensive plane-change maneuver.
Comment: Could you explain "recycling"? I take it that means "if the launch is delayed, it wouldn't prevent us using the site", but I can't quite make the connection. Why are some sites more "recyclable" than others in the event of delay?
Comment: So, it wasn't that the name sounded good in the Tourist Brochures ?
Comment: @SteveBennett Presumably linked to the listed benefits of landing near the equator - a location was chosen such that those benefits would not substantially come and go over time, due to orbital mechanics or something else, adding timing constraints. I'm not sure of the specifics, but by analogy I'm picturing an elevator that stops and lets you on, versus an elevator that just travels up and down and you have to jump on it at precisely the right time if you want a lift. In the former case, you can "recycle" your original landing plan a few hours or days later, as it's still viable.
Comment: @Criggie:  But just about all of the lunar "seas" and "oceans" have names that would sound good in tourist brochures: https://www.bbc.co.uk/programmes/articles/5gdrKwHtXhRkcq0xHDdhqvj/section-1-the-lunar-seas  Might want to avoid Mare Crisium (Sea of Crises), though :-)
Comment: @SteveBennett Yes, as discussed [here](https://space.stackexchange.com/a/37170/195). Sun low in the east during landing kept the sun out of the crew's eyes, provided sharp shadows to help visualize the shape of the terrain, and let the commander judge altitude by the LM shadow in front of him in the last seconds of landing.
Comment: @SteveBennett, any given landing site only has a 16-hour launch window each lunar month (due to requirements for the angle of the Sun during landing).  "Recycling" was basically about having a sequence of similar landing sites one day apart so that if, for example, the July 16 launch attempt was delayed too long, a launch on the 17th, or 18th, or 19th was possible.
Comment: Oh, wow. The sun has to be at a certain angle in order to make terrain perception as easy as possible?
Answer: It's best to go directly to the team who chose the landing sites.
Selection of Apollo lunar landing sites was contracted to Bellcomm, a joint venture between AT&T Bell Labs and Western Electric.  The team was headed by Farouk El-Baz.  Their recommendations were then approved by NASA administration.  An entire issue (30.3 Mb, 176 pp., 7 appendices) of the Bell System Technical Journal was devoted to a single article entitled "Where on the Moon? An Apollo Systems Engineering Problem".
According to section 1.3 of the article, all landing sites had to meet these basic criteria:

There had to be communications with Earth during descent, surface exploration, and ascent.  This eliminated the far side of the moon.
The landing site had to be within the latitudes for which the Saturn and Apollo spacecrafts were capable.  In particular for Apollo 11, it required a free-return trajectory:

The first landing mision was flown with a requirement on the translunar trajectory such that, if the main spacecraft engine had become inoperative following translunar injection (the start of the coasting flight from Earth to Moon), the spacecraft would have swung around the Moon and returned to the Earth with acceptable re-entry conditions, requiring only minor trajectory corrections using the Command and Service Module (CSM) attitude control system. The consequence of using this type of trajectory was that the surface area accessible for landing was confined to a region close to the lunar equator, the Apollo zone (Fig. 3).

Landing sites needed adequate lighting.  You ask about temperature; it wasn't directly considered, but lighting has a major effect on that.

Another significant constraint was that associated with lunar lighting (Appendix A), which was complicated by the fact that the Moon exhibits very little color variation or contrast. The best lighting conditions occurred when the Sun was low enough on the horizon to reveal rough terrain by shadowing, but not so low that the landing area was within shadow; in addition, the Sun needed to be behind the astronauts in order to avoid glare. The net result was a requirement for landing in the early lunar morning such that any given landing site had the proper lighting only one day per month.

Once propellants were loaded, that spacecraft had to be used within 110 days.  Thus, if a launch was to be delayed, another site needed to be available within that launch window:

In addition, the lifetime of the space vehicle propulsion subsystems after initial propellant loading was about 110 days, allowing, at best, only three monthly launch periods. Thus, it was desirable to provide as many launch opportunities as possible to insure flight of the hardware during the system's lifetime. For the first lunar landing mission, multiple launch opportunities for a given month were provided by using several sites separated in longitude. Additional launch opportunities were provided for later missions by planning to launch one day early and waiting in lunar orbit, or landing a day later than nominal (tolerating a higher Sun at landing).

Terrain roughness and clearance was considered:

Another important consideration in the selection of sites was the terrain roughness at the site and along the approach path to be followed by the Lunar Module (LM) during descent to the lunar surface. Adequate terrain clearance and the interaction between the terrain and the landing radar/descent guidance system were important for safety, as well as landing accuracy. Obviously, there had to be a suficiently large, smooth area, adequate for landing, at any site selected.

Finally, the known geology of the moon was considered.  This is described in section 2.1 of the paper.

By 1965, Belcomm had established the "Apollo Zone" on the moon.  Rangers VII, VIII, and IX; Surveyors I, III, V, and VI; and Lunar Orbiters I through V photographed the lunar surface throughout the Apollo Zone.  From these photographs, Bellcomm determined 32 possible landing sites.  The next step was to score and enumerate these 32 sites by their "landability".
For the first moon landing, the list of 32 sites were narrowed down:

From the original 32 sites, eight sites that best met the above constraints were selected. In January of 1968 these were further reduced to five sites (Fig. 3). Within these five sites, target landing areas (ellipses of various sizes representing landing error probabilities) were carefully chosen to minimize the landing hazards for the LM. Approach path landmarks and terrain features within the ellipses were identified for pilot recognition. A relief model of Apollo Site 3 (in Sinus Medii, near the center of the lunar disc) was constructed at a scale of 1:2000 for use with the LM simulators to practice final approach procedures. Map packages at a scale of 1:5000 were prepared for all the sites and included photographs and geological maps of the entire ellipse.

Section 2.2.2 describes the final choice for Apollo 11.  Apollo 10's practice flight was also targeted to the same landing site.

The Apollo Site Selection Board recommended Apollo Site 2 in Mare Tranquilitatis (Sea of Tranquility) as the prime site for Apollo 11 (Fig. 3). Apollo Site 3 in Sinus Medii (Central Bay) and Site 5 in Oceanus Procelarum (Ocean of Storms) were selected as backups in case a launch hold and recycle occurred (Fig. 3). These recommendations were approved by the Associate Administrator for Manned Space Flight. In May of 1969, Apollo 10 flew a preview mission of the Apollo 11 flight, descending to within 15 kilometers of Apollo Site 2. The astronauts reported that it appeared acceptable for landing.

Note that the scale model used in the simulator (Sinus Medii) ended up being one the back-up landing sites.  The other back-up landing site ("Ocean of Storms") would have been a cool name for a landing site, too!


How to stop a text received from splitting up?

Question: I just got my first Smart phone (Galaxy S II) and it splits up texts longer than 160 characters when I receive them. I often forward these long texts. Is there something I can do?
Answer: The following may work: download an app called SMS Backup+ from Play which backs up texts to Gmail. From there, it should be simple enough to forward.
Answer: in my experience the division of texts like this has more to do with the carrier.
For instance, I am on T-Mo.. and texts I get from other T-Mo users are never split.
This is not a limitation of the device so much as it is a limitation with SimpleMessageSyntax


FileTable and Foreign Key from another table

Question: I try to use FileTable with Entity Framework (I know it is not supported directly). So I use custom Sql commands to insert and delete (no update) the data. My problem is I have a table which refers to the FileTable with a foreign key to the stream_id of the FileTable. If I insert into the FileTable, how can I get the stream_id back?
I want to use SqlBulkCopy to insert lots of files, I can bulk insert into the FileTable, but SqlBulkCopy won´t tell me the inserted stream_id values.
If I execute single insert statements with select scopeIdentity() or something similar, the performance becomes worse.
I want to insert like 5.000 files (2MB until 20MB) into the FileTable and connect them with my own Table via foreign key. Is this bad practice and I should use a simple path column and store the data directly in the filesystem? I thought FileTable is doing exactly this for me, because I need to secure the database and the files are always in sync even if I go one hour or 4 days back in the past. I cannot backup the database and the filesystem exactly at the same time so they are 100 percent synchronized.
Answer:
I want to use SqlBulkCopy to insert lots of files, I can bulk insert into the FileTable, but SqlBulkCopy won´t tell me the inserted stream_id values.

SqlBulkCopy doesn't allow to retrieve inserted identity values or any other values.
Solution 1
You can find on the web a lot of code snippets to insert into a temporary table using SqlBulkCopy. Then from the temporary table to the destination table using the OUTPUT clause to get the stream_id values.
It's a few more steps, but the performance is still very great.
Solution 2
Disclaimer: I'm the owner of the project Entity Framework Extensions
Disclaimer: I'm the owner of the project Bulk Operations
Both libraries are not free but allow to overcome SqlBulkCopy limitation more easily.
Both of them support to output identity value.
<code>// Easy to customize
var bulk = new BulkOperation<Customer>(connection);
bulk.BatchSize = 1000;
bulk.ColumnInputExpression = c => new { c.Name,  c.FirstName };
bulk.ColumnOutputExpression = c => c.CustomerID;
bulk.ColumnPrimaryKeyExpression = c => c.Code;
bulk.BulkMerge(customers);

// Easy to use
var bulk = new BulkOperation(connection);
bulk.BulkInsert(dt);
bulk.BulkUpdate(dt);
bulk.BulkDelete(dt);
bulk.BulkMerge(dt);
</code>


Correlation of Asynchronous Brownian Motion

Question: I am trying to use the closing prices of the S&P 500 and the Nikkei Index to see how they are correlated (assuming they are exactly 12 hours apart).  In order to test my method, I have generated two Brownian Motions with a known correlation of 1/2.  I then take the odd-numbered data points of the first Brownian Motion and the even-numbered data points from the second, and I test my method on these data sets.  However, nothing I do seems to work.  I have tried the naive approach of shifting one of the BM's over, I have tried to determine the correlation of the "returns" (I know the intervals are i.i.d.), I have tried a naive data-filling method (insert the midpoint of each pair of data points into the BM), and I have tried to create a new path of the midpoints of one of the two BM's and tried finding the correlation of this, and the other BM.  All of these methods consistently get values close to zero.  Does anyone have any ideas on how to go about getting the correlation from asynchronous data?  I understand that the intervals of Brownian Motions are i.i.d., so I am thinking I should use this to my advantage.
Comment: How are you choosing the correlation to simulate the paths to begin with? If you're getting them from best of options on the close price (or some other market implied way) then you already have the numbers you need, so I don't see why you need to do this.
Answer: Bram made a good point about looking at longer-term returns, but that weakens the quality of estimates.
Here are two sources that address the issue directly - a formal approach here
and one specifically in financial context here.
Answer: Closing prices should be very highly correlated, I assume you care about close to close returns instead.
Given the frequency of the data that you seem to be looking at (ie you don't seem to be looking at correlation of the futures return intraday), I assume this is for some sort of modelling/pricing over a longer horizon.
What I believe most people do here is to look at correlations for 3 or 5 day return periods. The idea here is that in that case common factors driving returns show up again, because as you noticed, on a single day basis there is a de correlation effect due to time zone differences.
Answer: Have you tried to simulate both processes together from US close -> JP close -> US close -> JP close and so on? Where the correlation is fixed, but the volatility of each step is proportional to the square root of its length. And then pick US close and JP close points to build your two series.
You will find that the correlation of the asynchronous ones is the input correlation scaled down by the non-overlap fraction. But you don't need to simulate to show that, you can do it analytically.
Which means that you can directly simulate two series with correlation scaled down appropriately.
Answer: Brownian motion should be i.i.d, as you noted.
Subsets of two correlated series are not necessarily correlated.
The correlation of a correlated series with one lagged will simply yield the autocorrelation times the initial correlation of the lagged series.


Is it possible for smart contract to link received tokens to the senders

Question: I know when my smart contract has a payable fallback function, I can record who have sent ether to the contract and how much ether each of them have sent by storing the msg.sender and msg.value data in an array or something. However I wonder if I may achieve similar function with erc20 tokens. So that when someone transfers a certain erc20 token to the smart contract address, it will record it so later I can check who have sent tokens to my contract and the amount of token each of them has sent.
Answer: No, but with a caveat...
No, you can't get called upon token transfer with just plain old ERC20.
However the extensions in ERC223 support this via the mandated check to your tokenFallback() function.
Plan B
However any ERC20 token will be required to emit a Transfer event upon processing a token transfer, so you can listen for them, rather than logging your own.
Comment: Plan B involves using external off-chain applications right, as far as I see I can only listen to the events with something like web3 or plain old JSON-RPC. I want the smart contract itself to know who have sent it erc20 tokens without the need to interact with off-chain programs, so I wonder is it possible for the smart contract itself to access the event logs? Thanks.
Comment: Well, not necessarily since if you want to just record who has sent that amount of tokens, the event log is sufficient. If you want to take action in response to a deposit of tokens, then yes, Plan B will require an off chain application.
Answer: According to this question it's not possible for your contract to listen to the ERC20 contract directly.
But it's possible to write an external application that listens for events from the ERC20 token and relays data to your contract.
Comment: relaying data back to the contract would involve a transaction and fees right?
Comment: @shivamDev31 Yes, I think that sending data to a contract would usually imply gas fees.
Answer: If the sender is using the transfer function, your contract will not get notified of the transfer, since it can not react on the Transfer event from the ERC20 contract.
If you use approve/transferFrom then you can let the sender of tokens approve your contract to initiate the transfer. When the sender calls your contract, your contract is initiating the transfer, so it will know that it took place.
Moreover, there are other token specifications, which allow sending a transfer notification to receiving contracts (->ERC-223).
I can recommend reading this blog post if you want to learn more on features/pitfalls of currently available fungible token specifications: http://blockchainers.org/index.php/2018/02/08/token-erc-comparison-for-fungible-tokens/