Sects of Hinduism

Question: One of my friend is a Vaishnavite Brahmin....but he says, has increased devotion to Lord Shiva and is much affected by Shaivism. Since he is the eldest son in home, he became responsible for pujas, havans, etc which are laid on him as responsibility. As he has became a devotee of Lord Shiva, he tried to replace the family devotee as Lord Krishna to Lord Shiva, which was opposed by his family and his caste/sub-caste society. He asked for help. He want to convert to Shaivism officially/religiously, so that his people accept this. He said he doesn't want to fight with society, but want to live with peace. What he must do? He needs help????
Comment: This question will give opinion based answers. So, please change your question to " Is there any procedure to change Kula Deva or something else?" before someone close it. Coming to your friend, my Ista Deva is Shiva and i worship Him on Mondays while we too worship our Kula Devata Ankamma. **By worshiping different aspects of Brahman, we know more about Brahman and this is beauty of our Sanatana Dharma. Try to convince your friend saying that worshiping or knowing  both will help him in understanding Brahman**. Most of people now-a-days, believe both are same and doesn't actually matter.
Answer: Being a devotee of Lord Shiva does not give him rights to alter the Kula Devata of his family.So that is not right.
Moreover, if one is a "true" devotee of any God,then he sees all Gods as same and  one with his Ista Devata.
He can worship Lord Shiva at the beginning of his daily religous duties before starting the pujas and havans that he is supposed to do for his family or community.
I can  also not understand how by worshipping Lord Krishna will lessen the devotion that he has for Lord Shiva?
Lord Krishna Himself was a earnest devotee of Lord Shiva in his lifetime.
So i don't see why and how this is such a big problem for your friend.
Comment: It is ideally wrong to force other people to believe what you believe in by making it something mandatory.Istadevata varies from person to person and can be judged from one's horoscope too.Every person is free to choose his or her own ista devata.Just because i love lord shiva does not mean i'll forcefully convert all other krishna vakts or ganapaty vakts to shaivism.That is wrong from my point of view.
Comment: But there's much difference. If there is freedom of religion then why not also freedom of religious sect? If a man is Moslem, he can convert to Christianity or Hinduism etc., but why can't he convert to other sect. If my friend wants to spread Shaivism among his people, why not, because they already are Hindus, why can't he create a new branch among his people/society/caste which believes in Shaivism rather than Vaishnavism. Many Hindus of traditional sects converted to Arya Samaj Hinduism, during British, but they didn't converted to other religion, they accepted a new form/sect of Hinduism.
Comment: I don't mean forcefully, bro!
Answer: You are mixing the two concepts of ishtadetaa and kula devtaa.

he can change his ishtdevtaa(due to "his" own freedom of religious sect), it is his individual choice.
but he can not change his kuldevtaa , just due to his own freedom of religious sect. For that all the persons in his kula/extended kula have to agree(democratically agree), as they all have their own freedom of religious sect. Freedom of choosing of choosing "kuladevtaa" is made of sum of agreement of every individual in kula right to choose kuladevtaa. And hence kuladevtaa does not change so often.

Why he needs to force his choice of ishtdevtaa as kuldevtaa on everyone?
So his right to worship does "not" mean "only my right of worship". Right of worship means "right of worship by each individual(sihtdevtaa) and also democratic right of worship by each social group(say,kula)".
And hence he can personally worship the kuldevtaa(due to overall democratic majoritarian right of kula) "and" additionally he can also worship ishtdevtaa(due to his democratic right to worship). And everybody else can worship their own ishtdevtaa and the kuldevtaa. Thats the meaning of democratic right of worship.

Sects of Hinduism


How to add wallpapers to Kindle Fire?

Question: Where do I add/delete pictures so the Kindle Fire will randomly select it as a wallpaper for the device?
Answer: Someone over at the XDA Forums already discovered how to do that. See link to the thread below.
I strongly advise to follow this guide only if you know your way around the procedures mentioned (repacking & zipaligning an APK file, file system operations with root permissions) and wouldn't mind jumping through several hoops to recover your device if the process fails.
XDA Thread - [Guide]Changing Kindle Wallpapers!
Answer: The free app, My Kindle Wallpaper does this simply and easily, no root required.  D/l & install it, and point it at a photo or a folder full (on the KF, not on the net), and get your favorite background photo or cycle through several (one per wake-up, the way the stock software does).  Works perfectly on my original KF with KF v6.3.1.
(I know it's a year later but this works, no f**ting around, nothing to break. It's literally a download and go. Kudos to the author!)
Answer: You can use QuickPic plus ES File Manager to customize the Kindle Fire wallpaper. Both are free.
The key point is actually that the Kindle Fire system will restore the default wallpaper by default. That's why ES File Manager is indispensable.
Note that the device must have been rooted.

QuickPic is an efficient picture viewer. It allows you to set any picture as wallpaper. Click here to download QuickPic.
Open QuickPic and choose a picture which you want to set as wallpaper. Tap the picture and then tap the top right corner of the window. Choose "Set as" option in the drop-down menu.
Drag the box to adjust the wallpaper size. Click "save" and it will be saved and set as wallpaper.
Until this step, you may not find anything different as these are normal operation. If you just lock the screen as you did before and want to see the new wallpaper (I mean "if", please don't lock the screen now), you'll find the new custom wallpaper doesn't work. The boring original wallpaper comes into your eyes again!
This is due to the fact the system will set the original wallpaper as new wallpaper forcedly every time you lock the screen. So we need to revoke the system's "write" permission so that it can't modify any data again.
Remember not to lock the screen before step 3!
Open ES File Explorer and navigate to this path: <code>/data/data/com.android.settings/files/</code>. You can find a file called "wallpaper". Press on it and choose "More" – "Properties".
Choose "Permission" and tap "change". Revoke the "write" permission of "Owner" and "Group" (They have write permission by default). Tap "OK" to confirm revoking.
Now the system won't modify the wallpaper any more. Lock the screen and press the power button, you'll find the custom wallpaper works!
Next time you change the wallpaper, please restore the "write" permission of "Owner" and "Group" first, then revoke it after you set wallpaper.

(Quoted from epubor)

How to add wallpapers to Kindle Fire?


How was the guided daily amount (GDA) calculated?

Question: We are constantly shown nutritional information on food packaging stating this food contains "x" amount of your guided daily amount. A linked to the values is here. How were these values calculated? How do we know that men as a recommendation must not consume more than 2500 calories, 55g of protein 300g of carbohydrate etc...
Comment: Many of those values are unfortunately probably made up, or at least meaningless due to the extreme variance in populations.
Comment: So not even an educated guess?
Comment: Probably an educated guess, I'm sure they funded it on some research... but it was probably not an excessive effort. They knew just as well as everyone that humans vary too much to postulate a general amount of nutrients everyone needs, so it was more important to get exactly what it is - a *guideline*.
Answer: The total calories are not in fact a recommended value - they are an example amount that is derived from some calorie intake that seemed reasonable to someone (I don't know the details). It does not mean that the government is recommending that you eat exactly 2000 calories per day.
The relative content is, however, a recommended value, based on presumably research. So, if you do take 2000 calories a day, then you know how much of it should be fat/carbs/proteins.
I think that there is some controversy about whether the recommended values were influenced by industry lobbying. Moreover, science is definitely not clear on what the optimal food content for a human is, which is why we keep having the different diet fads, oscillating from no-fat to no-carbs.
Answer: In the USA, they refer to this as the recommended daily values (DVs) for a variety of nutrients. All I can find regarding these recommendations is that they were calculated for adults and children over 4 years old with a daily energy intake of 2000 kilocalories (often referred to as calories in the US).


why does coffee make some people sleepy?

Question: I have tried different types of coffee, all causing sleepiness. Except the opposite affect with iced coffee which helps with wakefulness. What causes for this?
Answer: Disclaimer: I'm not a physician, so here are only guesses based on my experience.
Besides coffeine, there are other substances to be taken into account, plus some non-chemical effects:

Sugar and milk by themselves can have relaxing effects. It is a well known fact that sugar can induce sleepiness, and hot milk is often drunk before going to bed. I've started drinking black coffee (no sugar) after lunch because of this.
Milk and coffee together are particularly hard to process by the stomach. This can bring a sort of after-lunch drowsiness.
There may be a psychological effect related to the assumption of coffee, or any other drink that is associated with relax and calm in your mind.
Warmth can have a relaxing effect by itself
Comment: thank you teh answer, very true.
Answer: I don't know but I have a theory:

Caffeine effects neurotransmitters like serotonin
Too much/too little serotonin can make you alert/happy/anxious/sleepy
Different people have different base levels of the various neurotransmitters

So for some people, having caffeine might put some neurotransmitters into a level that causes sleepiness, while for others it might put them into a level that causes alertness.


Recovering data off of a dead hard drive

Question: My hard drive died in my macbook and it no longer will start up. It will not mount in an external enclosure but disk utility is still reading that the hard drive is there, and I tried to repair disk and I am getting this error: (Disk Utility can't repair this disk. Back up as many of your files as possible, reformat the disk, and restore your backed-up files.) So my question is how do I backup my files if the hard drive won't mount? The only way that I have been able to see the hard drive is through disk utility. I just want to be clear that I am using mac os x snow leapard.
Answer: You could try following this hint from Macworld. It makes use of the Terminal (0$) to execute the UNIX command dd to copy everything bit-by-bit from your harddrive to another location.
1. Determine UNIX id. of dead drive
If you decide to use this method you would first have to determine what the UNIX identifier of the attached disk is. Open up Terminal (Applications --> Utilities) and type the following:

diskutil list

This will give you a list of all connected drives and their partitions and it should look like shown here.
Probably your boot drive is under /dev/disk0 and the drive in the external enclosure is under /dev/disk1. This could be different, look this up by finding the name of the dead partition in the list. Let's assume for the rest of this answer that the dead drive is under /dev/disk1
Now if you can not find the name of the dead drive in that list, diskutil can not find your drive and the Macworld hint will not work for you. If you see it in the list, move on to the next step.
2. Define destination
This method copies the whole disk byte-by-byte. If it encounters an error it will skip it and write zeros to the destination (read the hint for full details). So, the destination should have enough hard drive space to accomodate the whole hard drive you're recovering. So if you've got a 320GB hard drive, you'll need 320GB of destination space. If you have 320GB to spare on your bootdrive proceed to step 3. Otherwise get another external drive with at least 320GB of space and then proceed to step 3.
3. Copy
The command given in the hint is:

dd bs=512 if=/dev/rXX# of=/some_dir/foo.dmg conv=noerror,sync

You should replace /dev/rXX# with /dev/rdisk1 (according to our earlier assumption) and /some_dir/foo.dmg differs depending on your destination. If you choose your bootdrive you could change that line to: /Users/**yourusernamehere**/Desktop/recover.dmg
If you choose an external disk you should write /Volumes/**Volumenamehere** instead of /some_dir/foo.dmg
To summarise, your Terminal command would look as follows if you choose your boot drive as destination:

dd bs=512 if=/dev/rdisk1 of=/Users/yourusernamehere/Desktop/recover.dmg conv=noerror,sync

Or if you choose an external disk:

dd bs=512 if=/dev/rdisk1 of=/Volumes/Volumenamehere conv=noerror,sync

Good luck
Comment: Actually using `dd_rescue` instead of `dd` is much better if the HD has bad sectors.
Comment: I am not a down voter but your first link (the "this hint" link) drives on a dead page.
Comment: @YannisDran Thanks for the heads up, I've replaced the link.
Comment: Also see GNU's ddrescue tool: http://www.gnu.org/software/ddrescue/ddrescue.html
Comment: Anyone care to comment on the down vote?
Answer: I would try to remove the hard disk and mount it in another PC.
Than you can then try to use software for data recovery from a hard disk with the Journal File System.
Some examples:

Clever Files (OS X)
JFS Recovery Software (Win)
Geeksnerds JFS Data Recovery Software (Win)
Comment: @Stephen I added an OS X App to the list
Comment: I am running mac osx snow leopard.
Comment: @Stephen ok, however I suppose you have to move you hard disk in another computer, where it is a secondary hard disk and not the primary one as it is in your MacBook. In this way that computer will be able to boat.
Comment: Yes I have done that. It is connected to a macbook pro.
Answer: I would try to recover from possible bad sectors using the non destructive $89 Spinrite software utility from GRC.
That requires opening the MacBook, unplug the harddrive, move the drive to a PC and attach it to a SATA connector on the PC motherboard.
Then start the PC using a Spinrite created bootable CD-ROM/floppy/USB stick.
When Spinrite its default level 4 (data recovery) fails, start at level 1, then run the next round on level 2, 3 and finally run spinrite at level 4.
Answer: Hard Disk Recovery or Hard Drive Recovery must be done by professional only.There are a variety of issues that can arise that can cause or lead to the malfunction of your hard drive. These problems are such that they can manifest themselves over a period of time or can happen suddenly, rendering your hard drive completely inaccessible.


How to install Arduino IDE on Raspberry Pi

Question: How do you install the Arduino IDE on the Raspberry Pi running an ARM version of Ubuntu or Raspbian? There doesn't seem to be any official ARM release. Both distros have an "arduino" package in their standard repos, but it only includes an ancient 1.0 version that's missing a lot of features.
Comment: Arduino are explicitly open source, right?  So this should be possible.  If you just want it for loading code into the arduino you might investigate whether is a separate smaller piece of software you could use for that, which would simply things.
Comment: You planning to develop for arduino on your pi?
Answer: The source code is available on the website you listed. You should be able to install the pre-requisite software, (gcc-avr, avrdude, avr-libc, and avr-evtd) and then compile the source code.
While entirely possible, this will probably take a long time. If you're using an RPi 2, make sure to take advantage of the multiple cores by using make -j8 instead of make. Even so, compilation will take a long time; be prepared to wait.


FlipFluids & Ocean modifier as displacement. Baked frames in 3D view show all movements but rendered animation not. Manual keyframe ok. Any solution?

Question: I have created a FlipFluids simulation in Blender 2.81 ( 2019-11-25 21:45) and added an Ocean modifier in displacement mode to the fluid_surface.
Then I have baked the complete sim from within FlipFluids.
When I move from keyframe to keyframe in the default timeline everything is moving as desired in the default 3D window:
Ocean modifier waves, FlipFluids waves & wake, flags, radars...
When I render the complete animation everything EXCEPT the ocean modifier waves are moving.
The ocean modifier waves remain static but the FLIPFLUIDS waves move on that surface.
I like to add that ALL modifiers and elements ARE enabled for renderings.
D-NOISE: AI Denoiser is on (switching denoiser off did not help). I run a Win 10 Pro, HP Z800 with dual Xeons, 72 GB of vRAM and a GTX 1060
If I render & save the frames manually individually by hand the ocean surface moves! But thats not something I really like to have to do on several hundred frames
As its working when rendering&saving each frame manually as image (Png) and its not giving the same result when saving out the same images (Png) when I hit render animation, I do suppose this might be a bug in 2.81.
Does anyone have an idea how to fix this, preferably without rebaking?
Answer: Turned out to be a bug in Blender 2.81.
The team of Blender will be fixing it:
https://developer.blender.org/T71908


WLC - How to disable 2.4Ghz

Question: Is there any way I can disable the 2.4Ghz and just leave 5.0Ghz channel enabled on a per WLAN (SSID) basis? Or the only way is to disable the AP's radio and leave 5Ghz enabled?
Comment: Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
Answer: Assuming a Cisco WLC... Go to "WLAN > Select the WLAN Profile > General Tab > Radio Policy"
Updating my answer to clarify a few things...

802.11a operates at a maximum of 54Mbps, only in the 5GHz bands
802.11b operates at a maximum of 11Mbps, only in the 2.4GHz bands
802.11g operates at a maximum of 54Mbps, only in the 2.4GHz bands

Keep in mind that wireless operates in unlicensed frequency spectrum, so it is a bit like the wild west... Many corporate networks choose to marginalize support for 802.11b/g where possible, due to the rampant use of the 2.4GHz frequency spectrum by consumer devices... today, 5GHz (and thus, 802.11a) tends to have much lower background noise levels, so it is more suitable for business voice and data services... however it also doesn't propagate as well due to the smaller wavelength in 5GHz signals.  Use care when you disable 802.11b/g... it might be worth checking for coverage holes, if most of the traffic formerly used 2.4G...
Comment: @generalnetworkerror, while that is true he is not asking about 802.11n... I would also mention that just because 802.11n *can* support both bands is not guarantee that a specific wireless device *does* support both bands.  In particular, 5GHz support tends to only be available on the more expensive products (which makes sense, but it's easy to forget if you don't remind yourself that 802.11n 5GHz is optional)
Comment: There is an option in the controller template launchpad to push out a template that just simply disables 2.4ghz, not specific 802.11 specifications.
Comment: Hi,Thanks for your response. I see that, but in there I can only choose 802.11a only, b only, g only, etc. However, if I choose b/g only, it will still work on 2.4Ghz and 5Ghz, right? I don't want to use 11a
Comment: the question says you want to disable 2.4G... that means using 5GHz, which is 802.11a... perhaps there is a misunderstanding?
Comment: That could be, but what if I wanted to run 5GHz on 802.1g only, would that be possible? If I choose a Radio Policy of 802.1g/only, then both 2.4 and 5Ghz would be enabled, right? Thanks for your help
Comment: I made an update to my answer that might help clarify a few things... perhaps this will help...
Comment: You might want to add that 802.11n can operate in either 2.4 or 5GHz.
Comment: Thanks guys. That was my mistake. I meant 802.11n, which supports dual-band instead of 802.11g. My bad. But here is the problem in the WLAN Route-Policy drop-down menu, I don't see 802.11n only. It is a 2504 WLC, and it does support 11n (at least I think so). If there is 802.11n, is there anyway I can only let the WLAN use 11n but only use radio on the 5GHz RF. Thanks for all the support
Comment: I only mentioned including 802.11n for completeness since you listed 802.11a on 5GHz.

WLC - How to disable 2.4Ghz


Is it really possible to re-shape a muscle?

Question: There's this long going notion that you cannot re-shape a muscle through trainig: what do you think about it?
Comment: Define "re-shape": Technically, making something bigger is re-shaping, but I have a feeling that's not what you're asking.
Comment: A sphere no matter how big is always a sphere. So, getting bigger is not what I intend.
Comment: Well then, since a lot of muscles consist of several muscle heads, if you want to reshape a muscle group, just do exercises that target one head more than the other.
Answer: No, you can't change the shape of your muscles without injury or surgery.
You can change the size, which can change the appearance, but if you have a biceps with a short muscle belly and a long tendon, (So that your bicep peak doesn't reach to the inside of your elbow), you can't change that shape, it's genetic.
Another example is your abdominals, the connective tissue that forms the "x pack" bulges is genetic. You may have 3, you might have 8, or whatever, but you can't change that.
Answer: Reshaping, or re-sculpting or chiseling the look of the muscles are done in various ways. First, reduction of fat. What looks like reshaping, is actually loss of fat and gain of muscles, but yes, when you have peaks on your bicep, that's a whole different story. In short, yes, whether chest, or arms, working out different sets of muscles with varied load, technique  and intensity would definitely reshape them.
Comment: This is 100% untrue and false. No idea how this has any up votes. You can NOT shape a muscle, you can only make it bigger or smaller.
Comment: I never said, "a muscle". What I'm talking here is about a group of muscles, where some heads get bigger than the other, making the whole set look reshaped.
Comment: Ok, then you have kind of a point. But the question is asking if you can reshape "a" muscle.


Do grungs have a written language?

Question: It is unclear. Do grungs have any written language at all? And if they do, which script do they use for it?
Answer: Yes, Grung has a written form. In the PDF file One Grung Above, which details the stats for playable Grung, it lists the following:

Languages. You can speak, read, and write Grung

Since PC Grung are capable of reading and writing Grung, it must therefore have a written form. What form that written form takes, however, is never stated in any of the official material I can find - I've looked through the Grung entries in Volo's Guide to Monsters, the entry for the Grung village in Tomb of Annihilation, and One Grung Above do not state anything about what that written form looks like.
It's possible that there might be some information on this from other sources; the introduction of One Grung Above states that they were originally from the ADnD 2e books for the Greyhawk setting, and that the author of One Grung Above (Christopher Lindsay) chose to import them into the Forgotten Realms during the writing of Volo's Guide to Monsters. However, information about the Grung of the Greyhawk setting may not necessarily apply to the Grung of the Forgotten Realms.
Comment: FWIW the AD&D Monstrous Compendium Greyhawk entry for Grungs does not mention language at all.
Comment: If you check the other answers about Grungs, [the Grung was first introduced in 1988](https://rpg.stackexchange.com/a/98122/22566) which is before 2e, but it *was* for the Greyhawk setting.  You may want to revise/edit.
Answer: Likely the Draconic Script
I haven't found anything explicitly indicating what alphabet Grungs use, but (per FRCS 3e p.85) Chultans use Draconic (as does Lantan and Maztica), so there is a good chance a written language used by Grungs would do so too.

Do grungs have a written language?


XEN Server - can it send RAID warnings or errors?

Question: I have XEN Server installed and running several VM's on a newer dell server with hardware raid.  My concern is what happens if one of the drives fails?    Can XEN server be configured to receive that error and alert someone?
Answer: Since this is a Dell server, you should install OMSA managed node on it, and use that to send email and SNMP alerts about hardware issues.
Another option is to use the alerts in the DRAC, but those don't cover storage issues iirc.
Answer: OMSA also gives you the possibility to run executables (e.g. shell-scripts) on warning or critical-type storage events.
In that script you can check whether your array is degraded (using omreport storage ...).
If that`s the case you can start further things (e.g. live-migrate to another XEN-server).
Once OMSA is installed smartd will possibly also capture harddisk-events (I did not verify this deeply).
I for myself trigger a mail to root using OMSA so a human can take action (call support and get a replacement disk) before the next disk fails, for example.
If you've got a DRAC-Card other than DRAC4 (older or newer) the DRAC itself won't alert upon hard disk failures, OMSA will however.
Answer: You may want to consider installing the Dell Edition of Xen Server - this comes with all the Dell OpenManage stuff built in, and can almost certainly do what you're asking.


Can we create tables dynamically in MySQL?

Question: Can we create tables dynamically in MySQL?  If so, how?
Dynamic means at run time....ie via procedure AND HOW????
I am using dotnet
Ans--> yes we can create...but problem is i want to change the name of table each time the procedure is called....
Comment: What exactly does "dynamically" mean? Once you can answer that question, you pretty much have the answer to your question.
Answer: If you have sufficient privileges, you only need to use the same SQL statement(s) you would use in the administrative interface to create tables.
Answer: Yes, you can build tables in MySQL at any point before, during, or after program execution.
Depending on your needs, you may want to create tables during execution as Temporary tables so that they get automatically cleaned up at the end of the session.  Note that these tables will not be visible to other sessions as each session has it's own private version of the temp table and will not be available for you to view at the end of the session. Once created, you can index and access them within your program just like any other table.  If you need data to be persistent and available across sessions, you should stick with plain old tables.
MySQL Create Table Syntax
Answer: Yes, it is possible.
Answer: Dynamically?? like if an insert, update, or delete statement is performed...I don't know if this is what you meant but you can look into triggers
Answer: Yes. It's just a simple MYSQL statement. Suppose you're using PHP.
<code>q = "CREATE TABLE..";
</code>
and you execute that statement in PHP.
This assumes you have privileges, of course.
Answer: Absolutely yes, though I might question the wisdom of doing so unless it's for some sort of actual database-management component.


What can an attacker do if he knew my database credentials?

Question: If an attacker knows my database username and password, what can he possibly do if he doesn't have access to my server? Let's say my database is using Microsoft SQL Server. Is there a way he can use those credentials to manipulate my database?
Comment: I'm kind of surprised nobody mentioned 'social engineering'.  There's not enough content in my comment to make that a full fledged answer, but be aware of it.
Answer: Assuming that

You're 100% sure that your database server only accepts local connections.
You're 100% sure that the attacker doesn't have access to the local environment from which connections are allowed.
You're 100% sure that the application that uses the database is otherwise secure.
You're 100% sure that those credentials aren't used for anything else directly or indirectly related to the system.

Then, there's no problem in them being exposed.
Of course, as you can see, those are very big assumptions. If you're willing to take the bet, then go ahead and allow the credentials to be exposed. If not (I wouldn't), then work as best as you can on your security, and keep those credentials secret.
Comment: Also, if you have reason to suspect your database credentials have been compromised, **CHANGE YOUR CREDENTIALS**.
Comment: And for good measure cycle any encryption keys that might be tied to the credential.
Answer: If he can't access the database, the credentials are meaningless. It's like having a key to a door that's inside a guarded military bunker hidden in a remote location in the Gobi desert. The key is only useful if you can get to the door.
That being said, it'd be very bad practice to let your credentials leak out like this. If you suspect that they're compromised, go change them.
Comment: Of course, your analogy works both ways. A determined enough infiltrator *could* find a way into the bunker and use that key. Doesn't matter whether or not they *would* - if it costs you almost nothing to change the lock, then why take the risk?
Comment: Admittedly that could be a big 'if' WRT cost of changing the credential -- though hopefully the system has been designed to make this a simple process.
Answer: As long as the DB server is properly secured and the credentials are properly linked to IP addresses that he doesn't have access to, then he can't do anything with them, but it removes one level of protection and if he does find a way to access the DB, then you are hosed.
This is called defense in depth.  Multiple mechanisms prevent a compromise, however if one level is suspected to be compromised, you are less secure until you fix the compromise.
Answer: In practise, almost all sql databases (MsSql, MySql, Oracle etc) have ability to execute operating system commands. So if attacker knows your DB password, he can execute OS commands on DB machine. If process which runs your db engine has high privileges then attacker can takeover your whole machine. Beyond this is limited with your imaginary. For example:

He/she can attack other computers in your network from the db machine.
If you are using virtualization, attack can be extended to VM engine and other OSes on virtual environment can be compromized.
Collect very important sensual data for future social engineering attacks.
Take user account names and passwords and try them for other information systems on your organisation. People mostly use same strong? password on multiple systems.
Listen traffic in your network and sniff important data.
Insert a trojan or backdoor for future access etc.

What you can do to protect yourself although attacker knows your db password:

You can limit db user account's privileges. Don't forget attacker can sometimes also increase his/her privileges on machine by special exploits using vulnerabilities on your OS.
Disable shell execute abilities of DB server (but mostly db user accounts have privilege to enable it again)
Limit db engine process privileges. Most of the time sql injection attacks are successfull because of wrong installation of db servers. Especially MsSql setup lets easily setting admin accounts as db process owner.
Isolate your db machine from network. Only let incoming requests. You need to do this by an outer firewallish machine. Remember attacker has access to OS so he/she can enable it if you limit it from DB Server.
Protect your users' accounts by hashing (with a salt of course) and if your CPU resource is available protect sensitive data with symmetric encryption at application level.

This is not a complete list. It can be grow larger.
Comment: "So if attacker knows your DB password, he can execute OS commands on DB machine." does not follow. The crucial middle step is that he also needs to get **access** to the DB.


Australian ETA with Reckless Driving (misdemeanor)

Question: I am planning on traveling to Australia so I applied for an ETA. The site said I wouldn't be eligible if I had a conviction with a sentence of 12 months. I was arrested in college for a DUI but was charged with reckless driving. Is this a criminal conviction? I applied and was informed that the application cannot be assessed online, thinking there would be another screen to give the details but there wasn't. Does anyone have any clues as to what to do next?
Comment: The answer will depend on where (state or province or country) the reckless driving violation occurred, because different jurisdictions prescribe different ranges of punishment, and may further depend on what sentence was actually imposed. I haven't seen the ETA application, but could imagine that the amount of time that has passed since conviction, as well as your age at conviction, might also affect the answer.
Comment: Also, the Australians will compare your record (supposedly a misdemeanor reckless driving) against their own laws, and if their laws say that the offence is serious enough, you will be refused entry.
Comment: Can you clarify the specific wording: was your ETA **denied**, or was the result that your ETA cannot be **assessed** online?
Comment: Sorry, I reread the email. And my ETA can not be assessed online. I looked at my paperwork from when I was charged and I only had a month of jail time, which was suspended. The exact wording from the ETA application is "If you have a criminal conviction and have been sentenced to a term of imprisonment of 12 months or more, you should not be applying for an ETA." If I only had a month of "jail time" I should be fine to say no right?
Comment: One month is less than 12, so...yes.
Comment: Thank you all for your comments, just making sure I don't get denied boarding upon entry. Much appreciated!
Answer: Per the Australian embassy to the US, if you have criminal convictions, you will need to apply for a Subclass 600 Visitor visa:

If you have had any criminal convictions in any country, you should
  obtain police checks and other relevant character documents then apply
  for a Visitor visa (subclass 600), rather than an ETA to be assessed
  against the character requirements.

(Note that while this is the US site, the same advice applies to all nationalities.)
Per the character requirements, it is unlikely that a reckless driving misdemeanour in college (how long ago?) would constitute a "substantial criminal record" that would prevent you from visiting, but you'll need a bunch of documentation to prove you've kept your nose clean since then.


Creating data model out of .csv file using Python

Question: I want to create a data model out of a .csv file using Python. I mean to create dependencies, for example the primary key and stuff such that I can check if the new .csv complies with the given data model. I would appreciate some suggestions regarding how to do that, the libraries, frameworks etc
Answer: In my opinion this is probably achieved fastest with a rule set. You can easily load and manipulate data via pandas. Then you just have to determine what are rules. But without any details its difficult to go more into details. Regular expressions might be a powerful tool to use but that is speculation given the sparse info you provide.
Comment: Thanks @El Burro. I am using pandas already and thought of making a rule set as well. Just wondering if there's another way to do create a data model. For instance if I want to remove all the columns which do not belong to the predefined data model, I might just have to stick with the rules.
Answer: Adding on top of @El Burro's  answer, most of the training/testing proof of concepts of model making happens on manipulating DataFrame which provides easy functionalities like chaining operations, broadcasting, filling missing values etc and pandas is one such library. It has datatype inferring too and it uses python stack numpy which is fast manipulating arrays.
Other than that, as you asked if you want to check format of incoming data that is being passed to the model. You can use pandas here like (this is just a demo that you can achieve all kinds of stuff, there might be a better way to pull this off)
>> import pandas as pd
>> df1 = pd.DataFrame({'a': [1, 2, 3], 'b': ['a', 'b', 'c']})
>> df1
   a  b
0  1  a
1  2  b
2  3  c
>> df2 = pd.DataFrame({'a': [1, 2, 3], 'b': [1.0, 2.0, 3.0]})
>> df2
   a  b
0  1  1.0
1  2  2.0
2  3  3.0
>> df1.dtypes
a     int64
b    object
dtype: object
>> df2.dtypes
a      int64
b    float64
dtype: object
>> df1.dtypes.to_dict() == df2.dtypes.to_dict()
False

Comment: Thanks for the tip @KiriteeGak. I am using pandas myself.
Answer: A loop might give you more control.
The csv package lets you read a CSV file line by line.
import csv

# Open the file in read mode. If encoding is an issue, specify the correct encoding here.
with open('my_csv_file.csv', mode='r', encoding='UTF8') as file:

    # Read CSV file. Specify the correct delimiter and how to handle quotation marks.
    lines = csv.reader(file, delimiter=',', quoting=csv.QUOTE_NONE)

    # Exctract header.
    header = next(data)
    ... # Check if the header complies to your data model.

    # Loop through body.
    for line in lines:
        ... # Check if the line complies to your data model.

For the actual checking, have a look at the assert command. For example:
x = 1.0
try:
    assert(isinstance, x, int)    # Check if x is an integer.
except AssertionError:
    x = int(x)    # Handle the error.


Stellar lumens coin missing

Question: On 20th of April I sent $154.79 worth of stellar lumens coins to external wallet without the memo. The transaction indicated completed and there was no credit to my external wallet account. Please help, how do I recover this coins
Answer: If you send a payment to an exchange that requires a memo and forget to include the memo when you do, the best thing to do is to contact the exchange's customer support.  It is likely that they will be able to help you.
Generally, exchanges that require memos have a pooled Stellar account for multiple users, and they use the memo field to map the payment to a specific user's balance in their internal database.  Often, they can work with you to find the transaction and credit it to your balance in their internal system.
For more information on how that works, check out this guide: https://medium.com/stellar-community/help-i-forgot-my-stellar-memo-d62b3cc9c2f7
Comment: Please post the relevant points of the guide here.  Answers consisting only of links are likely to be deleted.

Stellar lumens coin missing


What does it look like inside a transparent glowing gas?

Question: If you were inside of a gas that was producing its own light (for example, air at 900°C), what would it look like? Would it look foggy, or would objects that aren't the same colour as the glow still be visible?
Comment: Is this gas covering an entire planet (i.e. is it dominating the atmosphere?) or is it just a localized pocket?
Comment: Have you ever seen fire? It is glowing air. Can you see *through* the fire?
Comment: Can you give us a general light level? is it closer to glowstick dim light or more like spotlight in fog? I would imagine that the closer the light reaches the point of the ambient light of the area  the less you would be able to see.
Comment: The gas is a localized pocket, and the light would be quite dim
Comment: Can you give us any more information about the gas itself - molecular composition, opacity, etc.?
Comment: It is air that has been heated to 900°C (I'm pretty sure it would glow by thermal radiation)
Comment: this depends a lot of how much light the gas is emitting.
Answer: I agree largely with Matthew's answer; this is intended to put everything on a more quantitative footing.
The answer to your question primarily depends on three things: the mass of molecules in the gas, the density of the gas and the opacity. These will play the key roles in determining how the gas absorbs light traveling through it and how it emits light of its own.
Part 1: Absorption
What might be helpful here is a quantity called the optical depth, $\tau$. If you have an object a distance $z$ away, the optical depth is $\tau=nm\kappa z$, where $n$ is the gas number density, $m$ is the mass of a particle in the gas, and $\kappa$ is something called the opacity. A higher optical depth means more absorption and therefore less transmission of light.
If we assume that the gas is an ideal gas, we can calculate the number density through the ideal gas law. Let's assume that it's in equilibrium with the surrounding atmosphere. Then we get
$$n=\frac{P_{\text{atm}}}{k_BT}=6.26\times10^{-24}\text{ m}^{-3}$$
which is less than the number density of air, because the gas is hotter.
How about the opacity? That's harder to calculate, because we don't know much about the gas, and it's also wavelength-dependent. At visible wavelengths, Earth's atmosphere has, under decent conditions, an opacity of roughly $\kappa\approx10^{-8}\text{ m}^2\text{ g}^{-1}$. We can't really calculate the opacity for your gas because we don't know anything about it.
The final piece of information we'd need is $m$, the mean mass per particle. We also don't know this. One of the heaviest molecules in Earth's atmosphere is carbon dioxide, with a molecular mass of $m_{\text{CO}_2}=7.31\times10^{-23}\text{ g}$. We can assume that our gas will have $m=m_{\text{CO}_2}$ in a worst-case scenario. The optical depth for our source a distance $z$ away is
$$\tau(z)=(6.26\times10^{-24}\text{ m}^{-3})(7.31\times10^{-23}\text{ g})(10^{-8}\text{ m}^2\text{ g}^{-1})z$$
which is actually better than on Earth by a factor of 3, as the gas is hot and therefore not very dense.
Part 2: Emission
As Matthew wrote, we also have to consider that the gas itself is emitting radiation. By Wien's law, it has peak emission at about $2.49\;\mu$m, firmly in the infrared. This does make me doubtful that we'll see substantial emission at visible wavelengths. We can, however, calculate the volume emissivity by
$$j_{\lambda}=\kappa B_{\lambda}$$
where $B_{\lambda}$ is a form of Planck's law, and therefore the whole thing is wavelength-dependent. You can play around with this at various wavelengths, keeping in mind that $T=1173.2\text{ K}$.
Part 3: Putting it together.
As there is both absorption and emission, we can use the equation of radiative transfer to determine what a source a distance $z$ away looks like. The specific intensity ends up being
$$I(z)=I(0)e^{-\tau(z)}+B_{\lambda}\int_0^{\tau(z)}e^{-\tau(z)-\tau'}d\tau'$$
the integral can be simplified and we do get
$$I(z)=I(0)e^{-\tau(z)}+B_{\lambda}\left(1-e^{-\tau(z)}\right)$$
That will allow you to determine whether the emission or the source dominates. As $\tau$ is likely small, we can approximate $e^{-\tau}\approx1-\tau$, so we then get
$$I(z)\approx I(0)(1-\tau(z))+B_{\lambda}\tau(z)=I(0)+(B_{\lambda}-I(0))\tau(z)$$
which is maybe easier to calculate.
Answer: It would be foggy.
In fact, it would probably look somewhat like fog illuminated by a car's headlights.
I assume the reason this isn't obvious is because you're thinking that this glowing air is not as opaque as fog... and that's not an unreasonable line of thought. However, because it is also glowing, you are still getting a bunch of "stray" light from the gas that is going to tend to overpower the light from any object in the space, in much the manner that fog or haze occludes objects.
It will probably be a little different because most of the light of the object is still reaching you (probably¹), and what you're seeing is a bunch of extraneous light added, rather than light being blocked. However, I would expect that you will have the same effect of objects further away being harder to see.
For a real life example, consider the sun.
(¹ Depending on how uniform the temperature is inside your gas cloud, you may get a bunch of heat shimmer as well. This doesn't occlude light, exactly, but it will twist it around so that what you see is blurry/wavy due to refraction.)
Answer: If the gas is 100% transparent, there would be no blackbody radiation(i.e. something looking 'red hot' because of its temperature), and you would be able to see though it normally.
From Kirchoff's laws of radiation,
Emissivity(=absorbtion) + transmissivity + reflectivity = 1.
If the gas if fully transparent (transmissivity = 1), the emissivity (how much it emits blackbody radiation) = 0, i.e. no radiation is emitted.
If the emissivity was greater than 0, you would effectively be flooded by radiation from all sides if you were in it assuming the emissivity was high enough and the gas pocket large enough, so even if light from other sources wasnt absorbed by the gas it would be drowned out by the gas' emissions. (This would also be the case if the gas emitted at a wavelength that it was transparent to, like scintillators).
Comment: What if you were seeing it through a camera that did not pick up the colour of the glow, would the glow still cause an effect?
Comment: If you were looking through a camera that did not pick up the glow (the cameras spectral range was outside the range of wavelengths the gas emitted), the glow would have no effect on camera. However, the gas might have an effect on what the camera sees. If the gas was fully transparent in the cameras spectral range, to the camera it would look like the gas didn't exist. If the gas was fairly absorbing in those wavelengths, it would be like trying to look through smoke/fog
Comment: In addition, you can still have heat shimmer... Also, black body radiation is *very* broad-spectrum.
Comment: @Matthew in principle, you could have a wavelength range where the gas had a very low emissivity, and use a narrowband filter with your detector so that you dont see any of the emission. But that is kind of pushing it. Also, yep heat shimmer would probably be a big issue.


Winning meal by betting is halal or haram

Question: My question is that my two friends betting on something, loser will pay all expenses of the meal, I want to know is this meal is haram for me or not, and if it is haram and I pay my payment for meal but eat together then still is it haram?
Comment: betting is haram in islam, and the money which will come by betting that will also be haram, so stay away from this and also keep your friends away from this.
Answer: I think, If losers intention treat to meal there is no problem. But if somebody is always going to be a loser, and if his intention changes, maybe its haram.


When may a body be removed from its resting place and buried elsewhere?

Question: In what instances may a body be removed from its resting place and be interred elsewhere?
Comment: YD 363. [15cha]
Comment: Do you have some reason to think such cases exist? Do yuo have some reason to think there is any limitation on such cases?
Comment: If the only way you get around the system's not allowing questions which duplicate the title is by using synonyms, then I think you're doing it wrong.
Comment: There was a case of this in my community a few years ago, where a family wanted to move someone to be with the rest of the family.  It was quite controversial.
Comment: See mishna Sanhedrin [6, 6](http://beta.hebrewbooks.org/pdfpager.aspx?req=37945&st=&pgnum=426&hilite=) about removing only after decomposition of the body.
See S YD 363 about removing to Erets Israel or to familial property
Answer: Generally, a body may not be moved. However, see this article for details. Excerpted:

The Talmud Yerushalmi permits the removal of remains, even from a
  worthy to an unworthy place, that they may be buried with the
  ancestors of the deceased
In his code, Rabbi Joseph Karo adds other circumstances when
  exhumation may be permitted or is required:
A. It is a mitzvah for children to rebury a parent's body in Eretz
  Yisrael, even if the parent expressed objection during his lifetime to
  having his remains moved there.
B. When a burial site is unprotected from robbers or natural forces,
  it is permissible to remove bodies to locations that are not so
  compromised.
c. When a stipulation is made at the time of burial about the removal
  of the body at a later date.
D. When a body is buried in an available site, but without
  authorization from its owner, the body may he moved.
Comment: A is not accurate. The case of when parents state otherwise is only discussed in later authorities (see Pitchei Teshuva)


Is mustard lid supposed to pop when opening?

Question: I opened a jar of English mustard with a flat plastic lid and it didn't pop. It wasn't bulging or anything and contains citric acid. Is it supposed to pop? I notice French's mustard (North American style squeezable kind) doesn't pop so I think it's the same. It's just that we are so conditioned to expect jars to pop that when they don't I wonder. Mayonnaise doesn't either which I know is okay...
Answer: Plastic usually does not pop, it bends slowly under the pressure differential. Metal usually bends quickly and pops when the vacuum in a jar is relieved. Some jars use thicker metal that wont bend, so you have to listen for the rushing intake of air. Sometimes now they replace air with nitrogen before sealing. You won't get a pop or any other sound from a jar canned that way.
Answer: It can depend on the manufacturer, and on the lid. You may be associating the pop with metal lids, where you'll often see is a small circle in the middle of the lid, which is part of tamper-proofing. When the jar is sealed at the factory, it is sealed under pressure so that the circle is depressed. When you open the jar at home, the pressure equalizes, and the the circle will go back to normal, which is the pop that you hear.
The tamper-proofing aspect is that you can be sure you're the only person to have opened that jar since the factory if it has one of the circles and pops when you open it. If you can press it in the supermarket so that it clicks in and out, the jar has already been opened.
However, as your jar had a plastic lid, it won't have that same protection. You're probably just accustomed to hearing the pops from metal lids.
Note: this is in the UK, I don't know where you live, or even if this technique is widespread.


Transparency in swf file created using png image

Question: I have some text with transparent background and I imported this png image to flash. Now when I create a swf file, it doesnt show me transparency. I tried using wmode parameter as transparent in the webpage but that wont work. Stage of my flash file is of the same size as the png image with text in it. Can anybody please tell me how will I make the stage in swf transparent so that the file blends with the background showing on text and not any other color.
Comment: Can you comment about a possible solution which you may have found amongst the links that Jack offered? I'm curious.
Comment: I can say I followed all the 3 options that were mentioned. I save the image as a 32 bit png, added embed and object tag attibutes and also made the HTML as windowless in flash publish settings option.
Answer: The secret to this is it's hidden among the Publish settings.
Under HTML, set the Window Mode dropdown to "Transparent Windowless." I was going to put up some screen grabs, but there's a video that shows the exact steps here: http://kb2.adobe.com/cps/524/cpsid_52418.html#flash.
Comment: I tried doing this but it doesnt work. It still shows me the background color.
Comment: Hmm... it works in Flash CS3, 4 and 5 that I can test on here. Which version are you working with?
Comment: @appuser are you also exporting the html and using that generated html to include the swf file?
Answer: my fellow designer faced the same issue with flash i dont remember what he did but i am dead sure he did the things within Code, and if your sure that your doing everything according to track so all you have to recheck twice possibly your missing something
Please give a look to this :

Making Flash Movies Transparent
Flash OBJECT and EMBED tag
attributes
working HTML Flash (.swf) transparent

That first link helped my guy see if it can do something with your problem...
and in our project we used this code for the flash header

    <object classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=9,0,28,0" width="900" height="253">
  <param name="movie" value="flash2.swf" />
  <param name="quality" value="high" />
  <param name="wmode" value="transparent" />
  <embed src="flash2.swf" width="900" height="253" quality="high" pluginspage="http://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=ShockwaveFlash" type="application/x-shockwave-flash" wmode="transparent"></embed>
</object>

On SE site you can find the same issue

Transparent Flash

hope this will help....
Answer: It sounds like you are doing it right, but http://kb2.adobe.com/cps/128/tn_12804.html says

This image must be saved as a 32-bit images[sic], preferably PNG for best color fidelity. Import the PNG file into Flash using File> Import and the alpha channel transparency will be retained in Flash.

Have you confirmed your source image is 32 bit? Note that I am unable to save a 32bit PNG image using Photoshop even with transparency (windows reports 24bit). While Fireworks can (windows reports 32bit)
Comment: If you save the file as PNG-24 and then check transparency checkbox it adds 8 bit so in all if you view in the properties it saves it as a 32 bit png.
Comment: yes my source image is 32 bit png file. And I imported it in flash uisng File>Import but I still get the background color in the swf.
Comment: 32 bit is RGBA (8 bits each for R, G and B, plus 8 bits for alpha).
Comment: I know that BTW. The point is: for some reason windows reports the one file as 24 bit and the other as 32 bit. So there is a difference in the headers. If there is a difference, it can cause an issue. Note that the knowledge base article specifically mentions using Fireworks. I presume its marketing, but it could be for a technical reason.
Answer: I have use this code below for html and php. And it works fine for me. maybe, you can try this out.

<object classid="clsid:D27CDB6E-AE6D-11CF-96B8-444553540000" id="obj1" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=6,0,40,0" border="0" width="300" height="160">
<param name="movie" value="directory/subfolder/flashname.swf">
<param name="quality" value="High">
<embed src="/directory/subfolder/flashname.swf" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" name="obj1" width="300" height="160" wmode="transparent"></object>


Online Poker Results

Question: How do sites like sharkscope, PTR, and others access tournament results in near real time?
I'm trying to aggregate this results but can't find where or how someone would go about retrieving this data.
Comment: I don't know about these programs, but other networks (such as _ongame_) had a webpage history for any given table running. Perhaps pokerstars gives a secret XML url or something to these companies. Because OCR is downright impossible with the massive number of games, and these sites are extremely accurate for this.
Answer: maybe I can help.
I play poker, run a HUD, look at the stats and am a software developer.
I've seen a few posts on this suggesting it's done by OCR software grabbing the screen. Well, that's really difficult and processor hungry, so a programmer wouldn't choose to do that unless there were no other options.
Also, because you can open multiple windows, the poker window can be hidden or partially obscured by other things on the screen, so you couldn't guarantee to be able to capture the screen.
In short, they read the log files that are output by the poker software.
When you install your HUD like Sharkscope or Jivaro etc, than they run client software on your PC. It reads the log files and updates its own servers with every hand you play.
Most poker software is similar, but lets start with Pokerstars, as thats where I play. The Poker software outputs to local log files for every action you/it makes. It shows your cards, any opponents cards that you see plus what you do. eg. which button you have pressed, how much you/they bet etc. It posts these updates in near real time and timestamps the log file.
You can look at your own files to see this in action.
On a PC do this (not sure what you do on a Mac, but will be similar)
1. Load File Explorer
2. Select VIEW from the menu
3. Select HIDDEN ITEMS so that you can see the hidden data files
4. Goto C:\Users\Dave\AppData\Local\PokerStars.UK (you may not be called DAVE...)
5. Open the PokerStars.log.0 file in NOTEPAD
6. In Notepad, SEARCH for updateMyCard
7. It will show your card numerically
   3c for 3 of Clubs
   14d for Ace of Diamonds
You can see your opponents cards only where you saw them at the table.
Here is a few example lines from the log file.
OnTableData() round -2
:::TableViewImpl::updateMyCard() 8s (0) [2A0498]
:::TableViewImpl::updateMyCard() 13h (1) [2A0498]
:::TableViewImpl::updatePlayerCard() 7s (0) [2A0498]
:::TableViewImpl::updatePlayerCard() 14s (1) [2A0498]
[2015/12/13 12:19:34]
cheers, hope this helps
Dave
Comment: Hi Dave, Thanks for great answer. I'm a software developer myself and I figured there was a way to hook in to the client or atleast track your own stats from what ever games one was playing. Do you know if there are any API's that readily give you stats on a wider range of sites?I.E; similar to sharkscope that logs several different poker networks?
Answer: I was searching for some information on this and I think this answer explains things nicely. Give it a look.
Comment: Nice find. Could be a useful q&a for this site too.

Online Poker Results


How do animals handle light refraction in different media?

Question: For a human, when diving underwater, everything is blurry because of the water's different refractive index compared to that of air, which we are accustomed to. How do animals, like turtles, seals or penguins, handle that difference when changing the medium? Are they nearly blind at surface and can focus underwater or the other way around? Can they adapt to different refractive indexes on the fly? How?
Comment: I guess that they are optimized for one particular environment. In the other they might have to rely on other senses.
Answer: It is more complicated than this, but... I don't think it has as much to do with the refractive index of water but rather the shape of our corneas and the loss of this shape advantage under water, for if the eyes are protected by goggles, one can see quite clearly underwater (much the same as a camera can, as the shape of it's lenses are not affected). Any change in the shape of the cornea changes the way light passes through the eye, and results in a change in vision. The following is from Ch. 9 Optics of the eyes of marine animals, from Light and Life in the Sea:

This is different for penguins (and turtles): the surface of their eyes, the cornea, is not as much vaulted as for humans (it's much flatter), and the lens is much rounder (meaning the shape can change more than our relatively flat lenses can), so the difference between air and water is not so big and the light isn't refracted too strongly. Also, the ciliary muscles (not to be confused with the pupillary muscles) holding the eye's lens (behind the pupil) are stronger, increasing their accommodation, so a penguin has a sharp sight in the water. Or as stated in A Survey of Vertebrate Strategies for Vision in Air and Water

Whereas the cornea is usually the major refractive element of the terrestrial eye, it is of little or no refractive consequence to an aquatic vertebrate.

See the difference in these four vertebrae groups (the first is man, the second is fish, the third is whales (similar to penguins) and the fourth is sirenians - manatees and dugongs)1:

Penguins.info
[1] Comparative anatomy and physiology of vision in aquatic tetrapods
Comment: This answer is great and seems feasible. Thank you!!! So in a nutshell: The effect of light refraction in different media is only a problem for beings with very convex corneas an flat lenses. Does this mean that e.g. Penguins have a sharp sight inside and outside of the water because of their ability to bend their lenses much more than humans could do. Thus, making their visual system far superior. Or are there some disadvantages with a flat cornea-design?
Comment: No, you have it precisely correct. Their lens does all the work. They can see well in or our of the water because their cornea has little to do with their vision.
Comment: Nice answer.. But the refractive index does have a role and the convexity of the lens as you rightly explained corrects for it. I had read about fish's highly convex lens but was not aware of diving animals having a flexible lens.


Fourier-series odd vs even square wave?

Question: I really need to know the difference when doing a fourier seires between even and odd square waves. I've been trying to understand but I just get the same results and the same spectrums... Is the difference in the formula? If so, I can't find any formulas online that match with that my professor gave me. They're all a little different.
Comment: If you show your calculations for both kinds of waves, it'll be easier to tell if/where you might be making a mistake.
Comment: Okay here, updated
Comment: when you just **shift** a signal in time (to make it even for example) the Fourier series coefficients **magnitude** spectrum will be the same but their **phase** spectrum will change.
Answer: For a trigonometric Fourier series:
$$
\tilde{x}(t) = a_0 + \sum\limits_{n=1}^{\infty} a_n \cos(n \omega_0 t) + \sum\limits_{n=1}^{\infty} b_n \sin(n \omega_0 t)
$$
with
$$
a_0 = \frac{1}{T} \int_{-T/2}^{T/2}  x(t) \ dt
$$
$$
a_n = \frac{2}{T} \int_{-T/2}^{T/2}  x(t) \cos (n \omega_0 t) \ dt, \quad n = 1, 2, \ldots
$$
$$
b_n = \frac{2}{T} \int_{-T/2}^{T/2}  x(t) \sin (n \omega_0 t) \ dt, \quad n = 1, 2, \ldots
$$
and $ \omega_0 = \frac{2\pi}{T} $ .
the Fourier series of an odd square wave will be a sum of only sine terms, and the Fourier series of an even square wave will be a sum of only cosine terms.
This is because the product of an odd and an even function is an odd function, which when integrated over a symmetric interval (i.e. from $-T/2$ to $T/2$), will return zero. For an odd square wave, this means that all the $a_n$ will be zero, and for an even square wave, all the $b_n$ will be zero.
You can save yourself time and potential mistakes by exploiting this fact and only computing the coefficients that are nonzero.

Fourier-series odd vs even square wave?


Why oscillations in PI control?

Question: When integral control is added to proportional controller (i.e. PI control), why steady state error becomes 0 and  why oscillations appear , how actually the integrator works ?
Comment: Can you please clarify your question? Is there an existing system? What sort of process does the Automatic Control System drive? In the meantime, you might want to have a look at the PID diagram in [this page](https://en.wikipedia.org/wiki/PID_controller).
Answer: Integration has memory. When the error becomes zero, there is no guarantee that the integrator has reached to zero sum of the previous errors.
So even when there is no error at a particular time the integrator could still be under the influence of the errors from the history. That's why it continues to correct for a while more until it over/undershoots and counter signed error accumulates. If tuned badly, this actually drives things unstable. If tuned properly, counter-error doesn't accumulate as much as integral action corrects (mostly due to P correction simultaneously dragging the system back). This delay is what is often referred to as the phase lag of the integrator.
Similarly, the system might reach to an equilibrium with P action alone if the system is running away as much as P control is correcting. But if you have integral action with a similar reasoning the error starts to accumulate and at some point the control action starts to dominate the steady state error.
You can then make these statements more rigorous by putting them into proper mathematical language.
Answer: For symplicity, consider the SISO linear system
\begin{align*}
\dot x &= ax +bu\\
y &= cx
\end{align*}
with $x$,$u$ and $y$ taking values in $\mathbb R$. Assume that you want to stabilize the system by making $y$ to converge to some fixed set point $\bar y$. Then necessarely there must be a point $(\bar x,\bar u)$ such that
\begin{align*}
0 &= a\bar x+b\bar u,& \bar y=c\bar x
\end{align*}
since $\bar x$ must be an equilibrium and such that $y=\bar y$. Trivially one has $$\bar u = -\dfrac{a}{bc}\bar x$$ One can define the error variables as $\tilde x=x-\bar x$, $\tilde y=y-\bar y$ and $\tilde u=u-\bar u$ that yield the error system
\begin{align*} \dot{\tilde x} &= a\tilde x + b\tilde u,& \tilde y&=c \tilde x
\end{align*}
One can stabilize it by taking $\tilde u = k\tilde x$ such that $a+bk<0$. That in fact ensures that asymptotically $\tilde y=0$ which implies $y=\bar y$. The overall control law is
$$
u = \tilde u + \bar u = k(x-\bar x) -\dfrac{a}{bc} \bar x = kx + \dfrac{1}{c}\left(-k-\dfrac{a}{b}\right)\bar y
$$
Thus as you can se, simple proportional is not enough, you also need a feed-forward control action given by
$$
u_{ss} = \dfrac{1}{c}\left(-k-\dfrac{a}{b}\right)\bar y
$$
If you define an integrator system like $\dot\sigma = y-\bar y = C(x-\bar x)$ then also $\sigma$ will have a set point $\bar \sigma$, and with $\tilde \sigma=\sigma-\bar\sigma$, the extended error system becomes
\begin{align*}
\begin{bmatrix}\dot {\tilde x}\\\dot{\tilde\sigma}\end{bmatrix} &= \begin{bmatrix}a & 0\\c & 0\end{bmatrix}\begin{bmatrix}\tilde x\\\tilde{\sigma}\end{bmatrix} + \begin{bmatrix}b\\0\end{bmatrix}\tilde u, & \tilde y&=C\tilde x\end{align*}
Take $\tilde u=k_p \tilde x + k_i \tilde\sigma$ (proportional+integral), then the closed loop system reads
\begin{align*}
\begin{bmatrix}\dot {\tilde x}\\\dot{\tilde\sigma}\end{bmatrix} &= \begin{bmatrix}a+bk_p & bk_i\\c & 0\end{bmatrix}\begin{bmatrix}\tilde x\\\tilde \sigma\end{bmatrix}, & \tilde y&=C\tilde x\end{align*}
You can chose $k_p$ and $k_i$ to make the closed loop matrix to be Hurwitz, and thus to stabilize the error system and you don't need any feedforward action, in fact the control law is
$$
u = \tilde u + \bar u = k_p(x - \bar x) + k_i (\sigma -\bar \sigma)
$$
Then with $$ \bar \sigma = \dfrac{k_p}{k_i}\bar x$$ the control law to becomes
$$
u = k_p x + k_i \sigma \qquad\qquad (1)
$$
and that's all. Moreover without integral control you need a feed-forward action which depends on the system parameters. If you have uncertainties on the parameters for sure you wil have an error on your set-point. with the integral action your final control law (1) does not depend on the parameters! and as long as the closed-loop system is stable you have null error at the steady state. Oscillations depend on how you chose $k_p$ and $k_i$. In fact if you chose them such that the closed loop matrix has complex eigenvalues then you can have socillations. For MIMO system the reasoning extends trivially.
Comment: Thanks for the excellent answer.  I have a similar problem.  Could you provide a reference where I can learn more about this technique?
Answer: Personally speaking, the effects of the P, I and D terms can be interpreted in a much better way by taking into account a system's characteristic polynomial.
Let's consider a PI controller and a type-0 (no poles at the origin of the transfer function of the system) LTI system that has $R(s)$ as input/reference input, $E(s)$ as error, $U(s)$ as the control input and $Y(s)$ as the output. $C(s)$ is the PI controller's transfer function and $B(s)$ is the system's own transfer function.

Actually, rather than using time domain, analysing the effects in the s-domain is relatively easy.
In order to figure out what the I/integrator section of the PI controller is going to cause at the output, reducing the system blocks into just one block would be quite helpful and it will be much easier to anticipate the input's effect on the output of the system.
The system's transfer function can be;
$$B(s) = \frac{1}{s + 1}$$
On the other hand, the PI controller's transfer function is;
$$C(s) = K_{P} + {\frac{K_{I}}{s}}$$
So, the closed-loop transfer function becomes;
$$T(s) = \frac{C(s)B(s)}{1 – C(s)B(s)} = \frac{{sK_{P}} + K_{I}}{s^2 + s(K_{P} + 1) + K_{I}}$$
According to that closed-loop transfer function, the system can be represented by just one block.

Before moving onto the effect of the I section, first of all, we need to ensure that the overall system should be stable which is the most important feature that is expected from a system. We want our system to be stable i.e. to not go beyond our control.
For a second-order transfer function, in order to make the system completely stable (not marginally stable as marginal stability is actually the red line in terms of stability), all of the coefficients of the denominator should be positive.
$$K_{P} > -1$$
$$K_{I} > 0$$
Now that the stability criteria for the overall system is obtained, we can move onto analysing the effect of the integrator part of the PI controller. The characteristic polynomial for a second-order transfer function is;
$$\Phi(s) = s^2 + 2{\zeta}{\omega_{n}}s + {\omega_{n}}^2$$
where $\zeta$ is the damping ratio and $\omega_{n}$ is the undamped natural frequency of the overall system. If the denominator and the characteristic polynomial are matched, the undamped natural frequency becomes;
$$\omega_{n} = {\pm}\sqrt{K_{I}}rad/s$$
Since the angular frequency as well as the classical frequency cannot have negative sign, the undamped natural frequency becomes;
$$\omega_{n} = \sqrt{K_{I}} rad/s$$
Lastly, the damping ratio becomes;
$$\zeta = \frac{K_{P} + 1}{2{\sqrt{K_{I}}}}$$
For the values of damping ratio that satisfies $0 < \zeta < 1$ relationship, the system's output is said to be underdamped i.e. oscillations and some specific amount of overshoot occur.
Consequently, it is obvious that by increasing the value of the integrator gain $K_{I}$, the overall system's output tends to be more underdamped and oscillations start to occur.

Why oscillations in PI control?


How to render triple backticks as inline code block in Markdown?

Question: I am writing a tutorial on GitHub about Markdown using Markdown and I want to write ``` but rendered as inline code block like <code>this</code>.
Comment: So what's the answer then? I've tried ````, `````````, `\`\`\`` but nothing seems to work, (even if the 3rd one seems to work here)
Comment: Actually one backtick before and after the word should suffice. Are you really writing that markdown in a file on Github? Whats the extension of the file? How do you view it (on Github, some other tool)?
Comment: "one backtick before and after the word": So you suggest `````. This has a weird effect. It renders 4 plain backticks (i.e. not in code block) while the 5th backtick acts as an opening backtick and all the following text is inside a code block till it finds another backtick later on. The file is an `.md`. I view it on GitHub and on MDwiki which renders GFM.
Answer: The Syntax Rules are very clear about this:

To include a literal backtick character within a code span, you can use
  multiple backticks as the opening and closing delimiters:
``There is a literal backtick (`) here.``

which will produce this:

There is a literal backtick (`) here.

The backtick delimiters surrounding a code span may include spaces --
  one after the opening, one before the closing. This allows you to place
  literal backtick characters at the beginning or end of a code span:
A single backtick in a code span: `` ` ``

A backtick-delimited string in a code span: `` `foo` ``

will produce:

A single backtick in a code span: `

A backtick-delimited string in a code span: `foo`

The one thing the rules don't mention, but works in the reference implementation is that the opening and closing backtick deliminators only need to be a different number of backticks than those in the code span. So if you what to have two or more consecutive backticks in a code span, then you can delimit with one backtick to open and one backtick to close the code span. The trick is using the spaces (as explained above) when the code span starts or ends with backticks.
In fact, many implementations get this right:
foo ` ``` ` bar
</code>
becomes
<code><p>foo <code>``` bar

Apparently (as pointed out in a comment) a few implementations specifically require that the number of backticks in the deliminator be greater (not just different) than the number of backticks in the codespan. Putting that together with the whitespace rule, this should work on most implementations:
foo ```` ``` ```` bar
</code>
However, if neither method works with the Markdown implementation you are using, I would suggest filing a bug with the developers of that implementation.  In the meantime, you can use raw HTML to force it to work:
<code>foo <code>``` bar

becomes

foo ```</code> bar</p>
</code>
Comment: Thank you for this extensive answer full of useful info. Unfortunatelly, from the examples you propose only pure html `<code>```` works on GitHub but *not* on MDwiki's GFM (because it doesn't render html) and therefore I was about to file a bug. **HOWEVER**, reading your answer again and again I realised that you DID give the right answer even without fully realizing it: `the opening and closing backtick deliminators only need to be a different number of backticks than those in the code span`. So I'm gonna post it as an answer but it's only fair to tick yours as the accepted one.
Comment: Ah, interesting. Apparently in the Markdown implementation you are using, the number of backticks in the deliminator needs to be *greater* than the number of backticks in the code span. It hadn't occurred to me that some implementations might include this added restriction (most don't). I''' update my answer to include that as well.
Answer: Waylan's answer pointed me to the right direction where it says:

the opening and closing backtick deliminators only need to be a different number of backticks than those in the code span

So I've found that using 4 backticks as opening and closing deliminators does the trick:
So, this:
```` ``` ````</code>
renders as: <code>```
Answer: Looking at this page, it looks like one can render the meta code (chunk code) for RMarkdown/Knitr by prefixing each triple backtick with `r ''`.
So, in your RMarkdown document where you might want to finally render an example of how to set up a code chunk, you might type the following (notice the 4-space indent to render it as code):
    `r ''````{r mychunk, echo=TRUE, eval=TRUE}
    1+1
    `r ''````

and the output would be
```{r mychunk, echo=TRUE, eval=TRUE}
1+1
```

in your document (PDF, HTML, etc.). Notice it is not run, just printed.


Do I qualify for unemployment benefits if I forgot to file in time, but now I have found a new job?

Question: I had lost my job in June 2019 but I missed on filling my claim in time (since I was busy looking for new jobs). I found a job, but would I still get unemployment from my time that I was unemployed, even though I forgot to file while I was unemployed?
Answer: If you failed to file, such as forgetting your weekly certification, then you do not get the money. Unfortunately, that's just the way it is.
Additionally, since you got a new job and are now employed, then you are not eligible for unemployment, since you are now employed. Sorry. I know it hurts that you were unemployed and still have backdated bills to pay, but hopefully you can make do until your new employment earns enough to bring you stable again.
Also, congratulations on your new employment!
Answer: I believe that usually, you only qualify for unemployment benefits for the weeks starting with the week you filed the claim. So for example, if you qualified to file unemployment benefits 1 week after you lose your job, but you wait until 5 weeks after you lose your job to file the claim, then you only only get unemployment benefits that are for that 5th week (and 6th week and so on, assuming you remain eligible for unemployment benefits). You do not retroactively get the benefits for the first 4 weeks that you missed.
So if you filed a claim now, you would only get benefits for this week and onwards. But 1) I don't think unemployment benefits last for 11 months, and 2) you already got a job now, so you don't qualify for unemployment benefits now anyway. So you can't get any unemployment benefits now.
Comment: that's exactly what I already said in my answer.


play rtsp url via Darwin Streaming Server?

Question: I am trying to play RTSP url via Darwin streaming server . they play their own mp4 files as provided in the setup; but not any other which is specified in the /movies folder.Can you tell me how to stream my own files.
Answer: The media files must contain hinted media files – that means normal MP4, 3GB videos cannot be played in Darwin Streaming Server.
The media files are hinted using a special encoder or QuickTime Pro. After converting the media files with a hint track you can play them.
Answer: Have you tried VLC? It supports rtsp using live555 open source multimedia streaming library.
http://www.videolan.org/doc/streaming-howto/en/


How can I view vintage medium-format negatives (from about 1950)?

Question: I have been given a box of vintage negatives from my late Fathers estate. I believe they were taken in the '50s and the size is about 6 x 9.5 cm. Is there a piece of kit I could view these old negatives on and even go on to print them on my HP printer?
Comment: Thank you very much guys for taking the time to reply to my question. What a response....fantastic.
regards
Terry
Answer: In case you just want to view them, have a look at http://petapixel.com/2015/03/22/how-to-turn-an-ipad-and-iphone-into-a-negative-film-viewing-station/ for a quick solution (of course, you can use other light sources, etc., but the general idea is the same). For positives, there used to be dedicated slide viewers and slide projectors, but mostly for smaller medium format slides like 6x4.5cm or 6x6cm. I have never seen viewers or projectors for 6x9cm slides, but they do seem to exist (see, e.g., http://photo.net/medium-format-photography-forum/00SbW4 ) and you can probably find them second-hand from the usual sources.
In case you want to make (digital) prints with your printer, you need to scan the negatives first. There are three basic options:

dedicated film scanner: I don't think (affordable) dedicated medium format film scanners are readily available any more (and once they were more readily available, they usually only have covered formats up to 6x6cm or 6x7cm). However, you might be lucky getting some second-hand option (beware of compatibility problems with modern operating systems, though) or, if money is no problem, some professional grade equipment.
flatbed scanner with support for film scanning (i.e., with backlight and film carriers): There are various options available, you just need to make sure that the scanner actually supports your film format (some just provide enough backlighting for 35mm film). If you happen to already own a scanner, but without support for film scanning and you don't mind some simple crafting, here's a nice trick on how you can use it to scan film http://makezine.com/craft/how-to_turn_slides_and_negativ/
a camera: You can use a setup like http://petapixel.com/2013/03/25/digitizing-your-film-using-your-dslr/ or http://petapixel.com/2012/12/24/how-to-scan-your-film-using-a-digital-camera-and-macro-lens/ If you already own a suitable camera, this probably is the cheapest option, but will also require the most amount of manual work.

Regarding scanners, see also Medium Format Scanner. Scanners also typically come with some software for automatically converting the negatives to positives and might also have some support for image enhancing (e.g., dust removal) depending on the film type.
Of course, you can also try to get a good old enlarger (again, make sure it supports medium format film of your size) and make some actual prints, which is a lot of fun. Alternatively, as Blrfl points out in the comments, there should also be some labs around that still do prints from
Comment: There are still some labs around that print medium-format film.
Answer: I use the below scanner for my publishing business. These can be had used on eBay for about $10000.00  While it is a great scanner, larger negatives including 6cm x 7cm, negatives present a problem of not remaining flat during scanning. I bought a 6 x 7 Nikon Glass Negative Carrier and that introduced a new set of problems with Newton Rings. The only way to get around this is to do "Wet Scans" which eliminates warping and Newton Rings, it's a complicated process if you have a lot of negatives to process. However, it will yield excellent results if you want to reproduce them for printing @ 4000 dpi.
If you are just wanting to see the images and not reproduce them at their best resolution, perhaps the Flatbed Scanner would be a good option.  Also the Contact Sheet is a great idea wherein you can at least see if you want to bother with scanning for printing.
Nikon Coolscan 8000 ED
Spec's for Coolscan 8000 ED
Answer: You do not necessarily need an enlarger.
Back in the day photos were made as contact sheets.
That means the image (the positive) has the same size as the negative.
To make one, put the negative on the photographic paper and apply light.
You have to fix the exposure on the paper somehow. Please refer to the manual of the paper.
In the most simple case, all you need for that is water.
Comment: well, then you need to develop and fix the image on the paper, so a few steps beyond just exposing the paper. But to your point, you only need paper, developer (liquid) and fixative (liquid), and a dark space to control the light.
Comment: @cmason good point, I was referring to simple photographic paper that can be fixed with water and added that to my answer.


Does EU 261/2004 compensation apply if delayed by the border check?

Question: This came up in Athens airport 1-hour connection at normal walking speed and I must admit I do not know the answer. So we have a flight coming from outside Schengen and has a very tight connection to an intra Schengen flight. What if the border check is slow and you are late because of that? Or, what if you are made to go through security again for whatever reason (if I remember correctly, UK always does, and there was that time when I landed in Amsterdam coming from Budapest and we were made to go through security because Budapest security sucked even more than usual so they were under censure) and you are late because of that? Does the flight compensation "fire" only when the airline is late or also when the airport makes you late?
Comment: In my experience (earlier this month), Athens airport border controls are slow, but if you have a short connection an airline employee will escort you to the front of the line.
Comment: Are you looking for monetary compensation or that airline will transport you to destination (without additional expenses).
Comment: Monetary compensation.
Comment: If an An airline that schedules a 1 hour connection thru customs/immigration, they oughta be responsible when it blows up.
Comment: @Harper And almost without fail, they will be responsible for getting you to your destination.  However expecting them to pay for compensation due to something that is no fault of their own makes no sense - and that is the question being asked here.
Answer: EU261 does NOT apply in situations like this.
From the regulation itself, EU261 covers :

This Regulation establishes, under the conditions specified herein, minimum rights for passengers when:

(a) they are denied boarding against their will;
(b) their flight is cancelled;
(c) their flight is delayed.

Very clearly none of those cover things like Border delays.
There is however a gray area here - what happens if your flight was delayed, AND there were delays at the border, and the combination of these two factors cause you to miss a connection.  This situation is not well covered by the legislation, and normally airlines will state that it would not be covered unless the inbound delay was sufficient to cause you to miss the connection on it's own.
Comment: Re the gray area - if the first flight *landed* within the two/three/hour window specified, the regulation does not care if you are held up on the ground and miss a connecting flight - *unless* the second flight was booked jointly as a connecting flight (cd. *"final destination" means the destination on the ticket presented at the check-in counter or, in the case of directly connecting flights, the destination of the last flight; alternative connecting flights available shall not be taken into account if the original planned arrival time is respected*)
Comment: There's also the extraordinary circumstances exclusion, I'm betting the airlines invoke it as default: https://www.claimcompass.eu/blog/extraordinary-circumstances/
Comment: @OhadSchneider that site is _not_ official, do not rely on any paid service giving  you reliable information.
Comment: @chx That was just an anecdotal link - we don't need any site, official or not, to tell us that airline carriers will do whatever they can to avoid compensating us. The regulation states *"Air carriers should compensate passengers if they fail to do this, except when the cancellation occurs in extraordinary circumstances which could not have been avoided even if all reasonable measures had been taken"* and I'm betting the carriers will take us to court almost every time to argue about what was "reasonable" to do.


How to get rid of this plant

Question: This plant (or different plants?) has started to spread across my lawn. What is it and how can I get rid of it without harming the grass? If it is relevant, I live in northern Mississippi.
Answer: The top plant is a type of mustard that appears to be a variety we had as a "pot weed" in a couple of plant nurseries that I worked in. It's a relatively nasty weed because, like most if not all other mustards, the seedheads "shatter" when ripe, spraying seeds for a foot or more from the plant. It's a cool weather annual that dies after it spreads its seed.
The second weed is chickweed (Stellaria media) another cool-season weed, but this one can hang around throughout the growing season. Like the mustard, chickweed seeds heavily, but in this case the seeds fall much closer to the mother plant, meaning that you can get a large mat of plants in a small area, which can out-compete the lawngrass.
The third plant is also one I know of as chickweed, but it's a different genus and species than the other chickweed. It has similar characteristics as the previous weed.

In all three cases, control is rather difficult. The mustard is your first concern because it grows the fastest and will go to seed first. In the nursery, we always hand-pulled the plants, which is easy to do because their roots are rather weak and they do not come up from a partial root. If you have only a smallish number of these, I recommend hand-pulling them. Do NOT put the pulled plants into your compost, as mustards tend to set viable seeds even if pulled - these seeds will then infest your compost and yard in future years.
You can also hand-pull the chickweeds, but I'd recommend using a trowel to help you get the roots (some of the plants I've pulled have broken at the crown, leaving most of the crown intact, which then resprouts). If there are seedheads present on the pulled plants, I recommend not putting them into your compost unless it's a pile that gets very hot.
If you're more chemically inclined, you can also try to use a broadleaf killed like Weed-B-Gone. If you go the chemical route, read the label to ensure that the chemical you're applying does indeed kill the weeds you want killed.
Answer: The top weed is a member of the cress/mustard/cabbage family and the others are chickweeds. Both types are fairly easily removed by hand pulling and crowding them out by encouraging the grass to grow thickly and well. First action would be to get a sample of the soil and determine what type it is in the range of clay to sand and scoot along to the local garden shop to see what grass seed they have that suits your soil, and overseed to increase the population of the right grass types. Then encourage thick grass with fertilizer and persistent irrigation in dry spells.
Comment: Can persistent weeds (e.g. [this](https://en.wikipedia.org/wiki/Peperomia_pellucida)) be crowded out by appropriate grass types?

How to get rid of this plant


How to calculate bandwidth of a wire, "air" or other channels?

Question: I'm really curious of how engineers identify what is the frequency range that could be sent through "wire" as channel? Do they put wire in front of them and make test that consists of sending sinusoidal signals through it by gradually increasing frequency, till maybe wire suddenly "burns off" and they measure that as highest frequency of a "wire's bandwidth"? How do they test "air" as channel where EM waves travel?
Answer: First of all note that bandwidth may have multiple (but similar) definitions. A practically accepted one defines the bandwidth of a baseband lowpass channel (indeed a filter as an LTI system) as the frequency at which the magnitude of its frequency response falls to $1/\sqrt{2}$ of the value at the frequency $f=0$. This point is conventionally called as the $-3$ dB point, or as the cutoff frequency of the channel (filter).
A physical conducting wire can be electrically modeled (depending on the frequency of application) as an LTI system with relevant parameters of $R$, $L$, and $C$, according to its resistance, inductance and capacitance respectively. Such a model therefore will define an LTI filter with a frequency response magnitude which will have theoretical $-3$ dB point(s). In practice the bandwidth of the filter could indeed be measured by a set up similar to what you have defined.
The air as a channel means either the empty space (vacuum) or the atmosphere. The former case ideally has an infinite electromagnetic bandwidth which is practically limited by the ability to create EM waves and the physical space's intrinsinc space-time and energy-mass characterization. The latter has a much narrower bandwidth determined by the electromagnetic characterisation of atmospheric air composition and its different layers, furthermore the sperical shape of Earth and the conducting soil also affects the channel characterisation. It's well known that the channel bandwidth of atmosphere depends on frequency, especially the ionosphere layer.
Comment: Part 1
Well, if we assume that bandWIDTH intuitively means something like B=fmax-fmin, than in "standard" drawings of frequency response of filters you've mentioned like in this picture:

https://upload.wikimedia.org/wikipedia/commons/thumb/6/60/Butterworth_response.svg/512px-Butterworth_response.svg.png

P.S. See Part 2 below this answer
Comment: Part 2
Why do we choose bandwidth to be cutoff frequency - 0? Because, every frequency component above the cutoff frequency will be attenuated, and it is not usable. So, no point in considering that part. That's my opinion!
I presume that no two wires are identical, so they don't have same cutoff frequency. Hence, in practial cases do we have (use) something called "average cutoff frequency"?
Comment: Part 3
There is missing part between image and "P.S. See Part 2...":

bandwidth would mean B=Fcutoff-0=Fcutoff which basicaly means that bandwith is cutoff frequency.
Comment: yes that's true! frequencies outise the of bandwidth are useless. The wire bandwidths depend on their **length** , **diameter** and **intrinsinc conductivity**.
Comment: So, how in practise we know for every wire it's cutoff frequency? I mean, it would be a lot of job to calculate for every wire in our network it's cutoff frequency. Hence, in practial cases do we have (use) something called "average cutoff frequency" and we choose that as our reference point?
Comment: Krushe, wires are produced in factories? And they produce **identical** products of each particular type. Wires are **cat**-egorized according to their diameter, insulation, voltage, current, temperature and power ratings and packaged that way. When the user installs a specific type of wire of a given length, all members of the family will have the same characteristics (except nominal deviations due to uncertainities of  manufacturing) but only the length and layout will effect them. Hence just as every electronic gadget of the same model and brand are the **same**,  so will be the wires.
Answer: Technically, a wire is not a pipe, electrical currents  ideally flow on the wire instead of through a wire.
All of it is EM.  The differences are the boundary values imposed on the fields and the properties of the material.  A improperly terminated cable is useless regardless of the bandwidth limit of the cable.
A TE or HE wave guide have a critical frequency that a field needs to be above, not below, to propagate.  These modes are also dispersive .
In most cases there are mathematical models that are used that predict propagation behavior but models only capture first and perhaps second order effects so measurement, empiricism, and experience eliminates a lot of speculation.
Comment: The skin currents are ok but not all currents are there? Otherwise I just wonder, why do we waste the volumetric bulk of the wire instead of wrapping a thin layer of copper ower a cheaper and lighter something ?
Comment: Heat conducts as well
Comment: cannot comment on the heating in detail, but possible.


How to draw on an X11 Drawable with Cairo in Haskell

Question: I recently made my first steps in X11 programming in Haskell and now I want to draw texts using Cairo/Pango. I found some C tutorials and it seems as I need to create an Xlib surface using cairo_xlib_surface_create().
There is a Haskell wrapper for Cairo but a wrapper for this functions seems to be missing.
However, there still seems to be a way to draw directly on X11 windows with Cairo since the documentation for the surface mentions an Xlib backend.
But I can't find any further information.
Answer: The documentation says
Note the Haskell bindings do not support all the possible cairo backends because it would require bindings for the associated technology (eg X11, glitz, etc) however bindings to other backends may be implemented externally. For example, Gtk2Hs provides a binding to the backend for X11 (and win32 on Windows).
So it seems that you have to either use gtk2hs, or ffi the required binding yourself.


What is the meaning of 〜たりして?

Question: I've just come across "〜していたりして" at the end of a sentence in a post on Facebook, so it's probably very casual. Does anyone know the correct meaning and typical usage?
Answer: たりして is used to posit some event as a possibility but something you are not sure about. For example, about the future:

10年後に大金持ちになっていたりして。

From the nature of this expression meaning "not being sure", it is also used as a hedge when you want to be modest and a bit comical:

ひょっとして、さっきのことでまだ怒ってたりして。
Comment: would ひょっとして、さっきのことでまだ怒ってたりして。 translate as "Perhaps (I) might be still mad about what happened a little while ago."?
Comment: @yadokari Something like that.
Answer: I'm not sure what part you're stuck on, and we can give more relevant answers most of the time if we know the context, but here we go:
している is the present-continuous short form of the verb する (to do).
The 〜たり suffix indicates an incomplete list of one or more actions (more on that here), for example

新聞を読んだり、コーヒーを飲んだりする
  Read a newspaper, drink coffee, and so on. (or)
  Do such things as read a newspaper and drink coffee.

So the best translation I can give without the context here is:

〜していたりして
  Doing such things as ~

As for why the final する is in て-form, that would be easier to answer if we could see the full sentence.
Comment: Your syntactic analysis is right, but you are missing the most crucial aspect: the particular nuance of this expression.

What is the meaning of 〜たりして?