Printer Samsung ML-2165W: Installed but it won't print (13.04)

Question: I couldn't make printer Samsung ML-2165W work for Ubuntu 13.04. I had general Linux driver from Samsung installed. The installation was successful, printer didn't print a test page.
Answer: The same issue here, although I got it running under ubuntu 12.04 LTS with linux drivers from Samsung. With 13.04, however, Samsung drivers are not installing properly any more. As a workaround, you could try Samsung driver packages from the http://bchemnet.com/suldr/ repository (look at the suld-drivers-4.00.39 package specifically).
Answer: this is instructions for wifi setup on 64bit, based on these full instructions:
<code> sudo useradd --create-home --shell /bin/bash --groups lp samsung
 xhost +local:samsung #as a X app will be run
 sudo su - samsung
 wget http://downloadcenter.samsung.com/content/DR/201110/20111019151150392/PSU_1.01.tar.gz
 tar xzf PSU_1.01.tar.gz
 cd cdroot/Linux/wirelesssetup

 ldd bin64/wirelesssetup  | grep 'not found' #if it outputs something...
 # apply these fixes (find these files with `mc` and create these proper symlinks to them as shown below)
 #tar -xf libstdc++-5-x86_64.tar.gz
 ln -s libnetsnmp.so.10.0.2 libnetsnmp.so.10
 ln -s libqt-mt.so.3.0.5 libqt-mt.so.3
 ln -s libqui.so.1.0.0 libqui.so.1

 export LD_LIBRARY_PATH="`pwd`/../psu/share/lib64/"
 bin64/wirelesssetup /dev/usb/lp0 #the application will open on X

 sudo passwd -d samsung
 passwd samsung #create a proper password if you want to keep that user or
 sudo userdel --remove samsung #delete it
</code>


Do Legendary drops only come from specific bosses?

Question: From a Gearbox forum thread, legendary weapons drop from specific bosses in Borderlands 2. While this might make it easier to farm, it would be very useful to know if I can ever get legendary guns by normal, non-boss means. I have noticed extremely few legendary guns so far (two in >50 hours of gameplay, level 38 currently) so I'm wondering if I need to farm bosses or if they're maybe more common at level 50 or something.
Do legendaries still drop from chests? Do the legendary items still drop from other enemies/bosses, just with reduced chance? I'm assuming/hoping Terramorpheous can drop any legendary?
I know Mike Mamaril might give you Orange items but since I'm on PC he's insanely rare so he's not a useful weapon source.
Answer: Doing some research as I was wondering this myself. . .
This forum post at Gamefaqs suggests that:

(Most?) legendaries can drop anywhere/from anything but
The chances in most places are extremely low and
Certain bosses/mobs have significantly higher chances to spawn certain legendaries.  Does this apply to certain chests as well?  I don't know.
It seems some legendaries only drop from certain bosses (e.g. conference call).  Meant to come back and add this but forgot!

I am doing further research.
Comment: "research", right, let's call it that. Let's play hours and hours of Borderlands 2... FOR SCIENCE!
Comment: In Borderlands a few bosses had extremely high chances of dropping (usually useless) rare weapons, not legendaries...IIRC. I never farmed bosses other than Crawmerax though so I could be wrong.
Comment: For one example, the legendary shotgun Conference Call seems to only drop from The Warrior, so certain bosses do seem to spawn certain legendaries.
Comment: @Shadur that's the spirit!
Answer:
EVERY major boss can drop a Legendary weapon.  There's a relic that will enhance rare loot drops by 5% (I got my first one at level 9, it dropped from Warmong, Nasty Kerblaster)
Yes, bosses can be farmed over and over until they drop their legendary.
Much like the Pearlescent weapons from Borderlands 1, your odds of getting a legendary just by opening chests, killing enemies is extremely slight.  Remember the runs in the Knoxx Armory (sometimes you'd make that run and see 1 legendary).  That's about how the Legendary's run in BL2.  (I'm at level 19 and have 2, my other one dropped during the boss fight on the side mission "The Good, The Bad, and the Mordecai")
I know in BL1, the Siren and another class had a skill that would enhance rare loot drops as well.  If the Siren retained her skill (and you have the 5% rare loot drop by killing enemies relic) that would seem to be the #1, best combination in getting the legendaries to drop.
The BL2 guide outlines MOST legendary locations but also has "classified" beside a lot of them.  I'm guessing a lot of those are from the side missions or you'd get them by killing BL2's "Secret Final Boss".
Re:  michael.  He's usually in the following locations in Sanctuary:
*Inside Zed's clinic
*On the other side of the radio in Moxxi's
*Down in Marcus's shop
*Beside the "This Just In" booth (This is where you'll encounter him on your first trip to Sancuary
*In/near Scooter's shop
*Right at a set of stairs leading up to the main Sanctuary center

Didn't know you could get Legendary's from him, best I got was a Purple on my first meet, then all Blues.
OH!  You can also get Legendaries (citation/confirmation needed, this is 2nd hand) from the Slot Machines in Moxxi's at Sanctuary.  You must hit 3 Borderlands symbols.  This gets expensive REAL fast (it scaled based on level, at level 19, I had to pay $363 a pull, my friend was level 22, he was paying $550+).
I hope this helps, thanks!
Comment: Yeah, at level 43 I'm up to $3500 per pull. Crap gets crazy expensive in BL2, I guess they didn't want to repeat BL1 where money stopped mattering after level 50
Comment: @BenBrocka Instead they limited the quality of items from the vendors so that the slots are the only worthwhile use of your money. What's the point of spending money in other shops when the best you'll ever see in them is a green item?
Comment: True, I very rarely see purple (and never orange) in the item of the day. Not sure I've seen blue as a normal item ever, either
Answer: First off, you can get orange items from the vendors.  It is a rare occasion, yet still does happen.  Secondly, you can also get them from hitting the jackpot on the slots (located in many different locations throughout the game).  In response to the post above about levels of loot from the slots, the information there is incorrect.  If you do join a game that is lower level then yourself, sure you will pay less to play the slots.  Although the loot level is dependent upon the level of the main quest mission that the host is on.  So a level 50 joins a level 12 game, the loot from slots, as well as the price, will be set at that level.  That also goes for any loot dropped from monsters or found in chests.
Answer: I have seen for myself that any enemy with "the invincable" in their name can drop any legendary in the game BUT the chances of them dropping one are VERY low. I farmed Terrramorphis for about 14 hours and only got one legendary weapon.  The legendary orange weapon i got is called the Derp Nukem.  It usually drops off of a named spiderant called The Black Queen, found in the Dust if i am not mistaken. That said, The chances of her dropping the Nukem are supposed to be about 5% whereas Terramorphis seems closer to 0.01%.
Mike never gave me better than a purple (still, a free purple gun beats a slap in the face), and vendors do RARELY offer a legendary (i have only ever seen one and it was a granade mod in the ammo dump at terramorhous peak), and I have never been lucky enough to get a legendary from a chest anywhere.  Not saying it cannot happen, just that I have never seen it or heard any of my friends get one in that way.
If you search youtube you can typically find the legendary items much faster by farming the boss with the best chance to drop the one you are looking for.
Yoteslaya has in my opinion the best videos because he not only shows the enemy dropping the legendary, and where it is found, but he the tests it so you can get a better idea of how it functions and if it is actually worth all that struggle trying to get it.
Here is a link to his page on the Hellfire SMG, you can use this to connect to all his vids and you'll have whatever oranges you like in no time.

Answer: I have gotten 5 orange items, 3 shields one was from a quest from Lilith, one from a chubby spiderant I found behind Ellie's in the dust, and one from the bunker. A grenade I got as an item of the day and a shotgun I got from the slots. The only one I really used at all was the shield from the Lilith quest, but I got it at such a low level I can't use it anymore.
Sidenote if you want cheap slots get in a game with a lower level, the cost is based on the level of the host and the loot is based off the level of the player.
Answer: I've actually bought the legendary commando mod from Zed's item of the day - so they can have good things, just very rare.
Answer: I have personally found 3 legendary items in vendors, specifically a low level Legendary Mechromancer Mod from a Zed vendor in sanctuary, a fastball grenade mod from the Ammo vendor at the beginning of Lynchwood, and the homing fire leech from the Ammo vendor in the Arid Badlands.  Each of these were during Playthrough One.
Last night i got my first, and so far only, legendary drop from an enemy other than an items primary boss.  The item was Sledges Shotgun, and dropped off of a normal Goliath in the Eridium Blight, killed while i was doing the LotR/Geary easter egg.
Other than those instances, all of my other legendary drops have come from the items primary boss.
In summary, yes, it is definitely possible for legendarys to both show up in vendors, and to drop off normal enemies, though the odds are very low.  I do not expect to find many, or really any, more legendary items from sources other than the items primary bosses.  But i can confirm that legendary items can drop from any loot source, and that they can show up in vending machines.
Answer: There are also some interesting answers on Orcz.com:

How to get legendary loot
The best way to get orange items is to farm the bosses at the locations listed below. Drop rates for oranges are low, but after you have killed the bosses many times you will get orange loot. The average drop rate for Legendaries are about 5% at maximum (around a 1/20 chance of drop), but many have lower drop rates. For example, the Sledge's Shotgun has a drop rate of 3.5%, and the Infinity pistol (the rarest pistol in the game and quite possibly the rarest gun of all), has a 0.07% (that's less than a 1 in 1000 chance of dropping) drop rate!
The Warrior and the Invincible bosses all have a chance to drop ANY legendary item.
They can also be gained from the Slot Machine (very rare), the Vending Machines (also very rare), and treasure chests (also very rare - this player did 3 full playthroughs including both dlcs and only ever saw 1 legendary in a chest)

More over here: http://orcz.com/Borderlands_2:_Legendary_Drop_Locations


Why am I unable to see Manage External user option in my contacts detail page?

Question: I'm new to salesforce and communities,I've enabled communities in my org and created custom log in page and custom landing page. I want to test the login page.
I am uanble to see Manage external user option in my contacts details page.
Can any tell me what I have to do to see that option and how to create users for my community ?
Answer: Check if your page layout allowed this button to appear. If not just drag it on your page layout. you will be fine.


How do you use Kontakt Player with Sibelius - program?

Question: There are some questions about Sibelius 7 which have been approved, so I dare to ask this question on relationship between Kontakt player( trial version) and Sibelius 7:
How do you use Kontakt Player with Sibelius - program? I have Kontakt Player ( trial- version) and I don't get any other sound but just piano. And I'm wondering in which way you use this program. Can it playback sibelius - files?
Answer: Kontakt Player is a sample playback engine. It takes MIDI input from a sequencer and plays back from a chosen sample library. The player included with Sibelius is not meant to be used on its own--when you are using Sibelius with the included professional samples, Kontakt player is actually running in the background for playback. You won't see it unless you dig into the audio settings.
The full version of Kontakt player can be used with any sequencer program, not just Sibelius.
Answer: In Sibelius 7, to use Kontakt, you have to create and configure a custom set of playback devices (VST or AU virtual instruments or similar). Under the Play tab, select Setup, and this pulls up the Playback Devices dialog box, where you can specific Kontakt as a source if it is installed on your system.
Comment: This is good as far as it goes, but to really utilize all the features, you must create a sound set for the Kontakt Library you want to play. Here is the link to the sound set editor: [link] (http://www.sibelius.com/download/sse/main.html). You end up generating an .xml file that tell Sibelius and the sound library how to talk to each other.


Adding UITabBar

Question: I have a UINavigationBar based application - only a one navigation bar that is handling all the work with views in my app.
And I want to have a tab bar at a bottom part of every view that will take the user to whatever view he would like to go.
What is the easiest way to add a tab bar to an application?
Thank you in advance,
Ilya.
Comment: Do you wan't to create iTunes-like application or just want than tab bar will be on one of UINavigationController's view?
Answer: If you want to have a tab bar that is the same for all your views and is always visible, then you have to:

In your application delegate class, add an IBOutlet for the new UITabBarController named e.g. tabBarController
In your mainwindow.xib file, you have to add a tab bar view controller, interface builder will automatically create the tab bar for you
In interface builder, configure the tab bar settings, and the tabs, you may nest your UINavigationController in the tab bar.
bind the UITabBarController instance to the IBOutlet you created at step 1
change your applicationDidFinihedLaunching method to look like the following code.

(void)applicationDidFinishLaunching:(UIApplication *)application {
[window addSubview:tabBarController.view];
}
Answer: Be sure to add the tabBar ABOVE your navigation bar in your view hierarchy. Depending on the structure of your user flow, you may end up with multiple navigationControllers.

                         tabBarController (w/ 3 sections, in this example)
                                |
                  ------------------------------
                  |             |               |
            navController1 navController2 navController3

Each navController maintains it's own stack.

Adding UITabBar


How to fix a downloads directory in UBUNTU 18.04?

Question: I lost the downloads directory by mistake. Updates did not replace it. I do not want to reinstall UBUNTU as a solution to fix this issue. I am using UBUNTU 18.04. I get a message asking me to use blueman-services to configure a downloads directory but I couldn't. Is there a solution other than reinstalling UBUNTU?
Comment: From terminal type in `mkdir ~/Downloads`
Comment: What do you mean by 'lost'?
Comment: I read Mchid's answer and used it before I see Terrance above. Yet I did that only today, meaning Terrance was there but I did not see it.
Answer: I used information coming from others and read other's answers on how to use bluman-services. In the transfer page there was a window opening for selections about receiving "incoming files". When I clicked on it, selected "downloads", then: apply. This resulted in disappearance of the message saying that a downloads directory does not exist, but the downloads folder did not work as it did not receive incoming files. The solution came from Mchid suggestion to use the following command in Terminal:
mkdir downloads
keep it and reboot


Why did I lose power to half the house when the breakers did not trip?

Question: Using a voltage detector I determined that three breakers in the panel are not conducting voltage, yet they are fully on (not tripped).  Thinking they were bad, I replaced a double throw 15 amp and a double throw 20 amp in the box.  Flipped them on, still no power coming out of the new breakers.  What could cause this?
Comment: When you were replacing the breakers, did you happen to notice any damage to the bus bar to which they connect? **WARNING:** Do not physically touch the bus bars, visually inspect them only. Does your panel have two continuous bus bars, or is it a split bus panel? A picture of the panel with the cover off, might be helpful.
Comment: You really should have tested if there is voltage AFTER the breaker and BEFORE the breaker before replacing anything at all! If there is no voltage before the breaker refer to testers comments. If you had no voltage after the breaker then faulty breaker, replace. But if you have voltage before and after it is obvious there is a sub panel somewhere or severe damage has occurred to the supply lines (rat eating them, over loaded and melted or got cut somewhere.) **WARNING** There might be LIVE but not GND in the sockets. Use a self grounding screwdriver to test for LIVE. BE VERY CAREFUL!
Answer: First, do the easy-to-check steps:  does a device that should be on still work?  Is the "on" switch on?  Is it plugged in?  (Children are often noted for unexpectedly changing these.)  If the device is plugged in somewhere else, does it work?  Does a portable device known to work properly suddenly not work in the alleged "failed" outlet?
Next, are you sure the breakers have not tripped?  Many manufacturers build them so that they do not visibly change when tripped.  To be sure, turn the lever all the way off and then back on.
Three circuits!  There is very little in common such that only three circuits with three separate breakers are all affected.  Maybe there are more?  Are there any other circuits which are on the same bus in the breaker panel also not working?  That would indicate a bus being disconnected, probably by a loose wire inside the panel.  A visual inspection with the panel cover off might be helpful.
Also possible—maybe probable—is that some neutral wires have come loose in the panel.  Turn off the main breaker and give all the wires a wiggle, being very careful not to touch near the service wires or where they connect to the main breaker.
Maybe something changed recently?:  Electrical work, ground work, utility work.
Answer: I just had the same problem. The power company came out and discovered their line went bad underground, and only 1 of the 2 cables coming into the house had power at the meter.
Comment: Got to dig one of those up once, there was a 6" lump of clay bonded to the cable where it had been sizzling for years till it finally ate through the aluminum cable.
Comment: Happened to me just today.  Some things working, some not. Buried line just like yours.  Stayed that way for 8 hours until the other line died and I was completely out of power.  Power company came and hooked up a temp line and all was well again.
Answer: The breakers are 240 VAC double pole breakers. If you put a voltmeter on the 2 wires, do you read 220-240 VAC? If you put a voltmeter from either of the breaker wires to ground or neutral, do you get 115 VAC?
When you say no power coming out do you mean the equipment connected to that outlet doesn't work? Even if the voltage is correct?
Look at the connection between the breaker and the panel bus (how it plugs in to the bus). I recall a time when a 2-pole breaker was not contacting both panel legs (the metal bus, there are 2 of them for each side of the 240VAC, 120VAC on each bus).
Answer: I'm betting one half of your main breaker is tripped.  Have you reset your main breaker? (At the top?)


How to protect a random number seed?

Question: I'm writing an application to protect passwords from key sniffers and screen retrievers.  I have the user type in an easy-to-remember keyword or phrase (i.e, "password123", "amazon.com", "gmail") and I use that string to create a longer and stronger password which is loaded into the clipboard.  I want the application to be completely anonymous, so I don't save any information.  To generate the passwords, I use a random number generator.  I need a way for the user to carry around their seed that isn't vulnerable to key sniffers or screen retrievers.  I'm thinking a hardware token like a YubiKey, but I would like something more easier and more mainstream.  I tried using behavioral biometrics, but I managed to replicate them with a program too easily.  Any better ideas?
Answer: What you are suggesting is a more than vulnerable approach.
First of all, there are open source and proven-correct algorithms and applications for the problem you are targeting. In security questions it is never a good idea to go and develop applications for critical operations (and handling passwords is always a critical operation) on your own, especially reinventing the wheel is almost in every case an endeavor doomed to fail.
Your approach is problematic in several points:

To be anonymous the app needs to copy/paste or in-place-generate the password needed for some action. You will have a hard time avoiding screen retrievers capture that if you do not do some magic on OS level.
Using one(!) random seed to protect several passwords makes each of them weaker than it was before.
Carrying this random seed on a usb key and freely plugging it into all kinds of computers that you cannot control is a problem as each of them may be potentially malicious. The random seed could be silently retrieved, altered or deleted.

To give you some things to get paranoid about, google e.g. blue pill and you will see that the real problems dwell on another machine layer than the application you are talking about.
Instead have a look at the following approaches:

2 factor authentication (2FA) against malicious software and hardware stealing your passwords on type-in. See e.g. Google Authenticator.
Secure operating systems against such software entering your system and retrieving your passwords. See e.g. QubesOS
Read-only drives with secure / anonymous OS for usage on foreign and potentially dangerous machines even for very critical tasks such as banking. See e.g. Tails OS on a dvd (not a usb key!)
Virtual machines to capsule potentially malicious tasks. See e.g. VirtualBox
Trustable password safes like KeyPassX

In a nutshell: You can write such an application but it will most likely not be practical nor secure nor by so usable. Sorry about that.
Comment: Thanks for the detailed response.  I currently use PasswordSafe in combination with OATH/HMAC.  I was trying to come up with a way to keep my master password safe from key sniffers, since the HMAC only adds six numbers to the end of the password.  The virtual keyboard included in PasswordSafe is vulnerable to screen retrievers.  In my application, the password is never printed on the screen, it is simply loaded into the clipboard to be pasted into a password field.  The vulnerability of USB keys is why I was considering YubiKey and similar hardware tokens.
Comment: Screen retrievers are definitely a thing to be worried about. But if one is smart enough to write or even just use one of those they will also be prepared to simply read out the clipboard. This is usually routinely done in this kind of software anyway. The "official" solution to that would be 2FA or a rom os.
Comment: Is there any way to protect the clipboard?
Comment: Depends a bit, mostly on the os you are writing for. The simple way to go  is to frequently delete the c/b or to detect the successful pasting of your password to a field and then delete it from c/b. Sure this does not prevent other software from copying it in this critical time slot. If you are able to negotiate a handshake with the receiving software or form you could set up an encrypted channel (similar to https e.g.).

How to protect a random number seed?


My Baofeng radio can transmit and hit a repeater 50 miles away but it isn't receiving

Question: My radio won't receive. Help? It literally went dead and I still have the rubber duck antenna
Comment: that's a bit of a vague description. I'm afraid "won't receive" isn't a monocausal thing. Battery OK? Do leds light up? Baofeng is a company, not a single device (they have dozens), so what are we talking about? What does "literally dead" mean (aside from giving me the opportunity to say that *literally* it was never alive)?
Comment: @Nvictoro5R I voted to reject your edit to the question.  It sounds like you're having the same problem as the original poster (OP), and you're trying to revive the question.  Kudos to you for doing your homework and finding a question that applies to your situation.  The problem is that if we voted to accept your edit, then you'd be "putting words into the OP's mouth".  The thing to do is to make a new question, so please do that and then we can help you there!
Answer: If your radio can't receive unless you hold the MONI button it can mean your squelch is set too tight.  Or, it means you can't hear static unless you hold MONI.  If it is brand new out of the box I think maybe you mean the latter.
But let's take it a step at a time.
Ideally you don't want to hear static, but you do want to hear signals when they are present.
Your post is vague but I presume that if you let go of MONI then it will transmit.  That is normal behavior.
So first, check your squelch setting.  The best way to find it is to go through the menu.  On handhelds, there is a menu button and you will find it in there.  Also on handhelds it is a secondary function of the 0 (zero) button.  But my suggestion is to stick with the menu first, and get to know what all you can find in there before using the function keys (which are different by model).
Once you find squelch, try different settings - 0 should make it act as if you were holding the MONI key - no squelch.  2 or 3 should be enough to quiet it down yet allow signals through.  4 or 5 will only let strong signals through.
Set it one step above where you hear static all the time - that will allow it to be at its most sensitive yet still have the static squelch function.
Please allow me to suggest a couple of edits to your question:
Change your title to "My Baofeng UV-5R V2+ radio can't hear anything unless I hold the MONI button"
In your text, you can describe how you can hear things with MONI pressed but can't transmit unless you let go of MONI.  Mentioning that you are using the rubber duck indicates both that you have a handheld and that you might wonder if a better antenna would fix the problem, etc., etc.  Whatever you think is relevant to your question
(Of course, use the model number of your actual radio)
Then upvote my answer.
Accepting my answer is very helpful, too, if it turns out it is correct and helpful.
Please leave a comment on my answer describing how you made it work so others might find this question and get the answer more easily.
After you do that I'll check your tags to make sure it is even easier for others to find by searching.  I'll leave you a comment so you know when that is done - so you can see how to use them in the future.
Welcome to ham.stackexchange!


Is every measure-theoretic factor map between isomorphic odometers an isomorphism?

Question: There are odometers that "look different" but are isomorphic, e.g., the odometer (4, 16, 64, ...) and the odometer (2, 4, 8, ...).  In the case above, the natural factor map ends up being an isomorphism.  Is this true for every factor map between isomorphic odometers?
Answer: This is true, and follows from the property called coalescence.
In a topological setting this definition is due to Auslander [Endomorphisms of minimal sets, Duke Math. J. Volume 30, Number 4 (1963), pp. 605-614]. In order to answer your question it is enough to state Auslander's results as follows:
Let $(X,T)$ be a minimal compact dynamical system (that is, $X$ is a compact metric space and $T\colon X\to X$ is a continuous map without nonempty proper closed invariant sets). Any odometer is a minimal compact dynamical system.
A continuous onto map $\varphi\colon X\to X$ such that
$\varphi\circ T=T\circ \varphi$ is an endomorphism. An automorphism is an injective endomorphism.
A dynamical system $(X,T)$ is coalescent if every endomorphism is an automorphism of the system. Auslander proved that (see Corollary 3 in his paper) that almost periodic (that is, equicontinuous) minimal sets are coalescent. It is well known that all odometers are equicontinuous. Now assume that you have two isomorphic odometers $(X,T)$ and $(Y,S)$, and a factor map $\varphi\colon X\to Y$. Let $\psi\colon Y\to X$ be an isomorphism. Then $\psi\circ\varphi$ is an endomorphism of $X$, which by coalescence must be invertible, which in turn implies that $\varphi$ is an isomorphism.
There is a corresponding notion of coalescent measure-preserving systems, and odometers are known to be coalescent also in this sense, see F.J. Hahn, W. Parry, Some characteristic properties of dynamical systems with quasi-discrete
spectra Math. Systems Theory 2 (1968), pp. 179-190.
Answer: According to Theorem 1.3 of Survey of odometers and Toeplitz flows, the kernel of a topological group factor map from $G_{\mathbf{k}}$ to $G_{\mathbf{k'}}$ is $G_{\mathbf{k}-\mathbf{k'}}$. Here $G_{\mathbf{k}}$ is the odometer corresponding to the supernatural number $\prod_{i \in \mathbb{N}^+} \text{p}_i^{k_i}$ with exponents $\mathbf{k}=(k_1,k_2,k_3,\dots)$, i.e. it is the inverse limit of the system $\mathbb{Z}_{a_1} \leftarrow \mathbb{Z}_{a_2} \leftarrow \dots$ with $a_i | a_{i+1}$ and $\text{lcm}(a_i)=\prod_{i \in \mathbb{N}^+} \text{p}_i^{k_i}$. Moreover, two odometers are isomorphic as topological groups if and only if their associated supernatural numbers are the same.
Consequently, any topological group factor map between isomorphic odometers has trivial kernel. One can also prove this for dynamical system factor maps by turning these into topological group factor maps via rotation by the image of $\mathbf{0}$ (or, you can check Lemma 11 of this paper). It turns out that any measure-theoretic factor map between odometers (equipped with the Haar measure and the transformation $w \mapsto w + \mathbf{1}$) is equal to a dynamical system factor map on a full measure set. See Proposition 10 of this paper for a proof of this result. Thus any measure-theoretic factor map on an odometer is injective on a full measure set.


Character-level embeddings in python

Question: I'm working on an NLP task that requires the use of character level embeddings, and I've been trying to use Spacy. However, it seems that spacy uses word-level embeddings for the word vectors, and I need character-level embeddings. The only character-level embedding library I've been able to find is chars2vec which does not seem well maintained. Is there a way to get character-level embeddings with either spacy or a more popular package than chars2vec?
Comment: maybe https://github.com/flairNLP/flair or https://fasttext.cc
Answer: No - There is no way to get character level embeddings for SpaCy.
One option for character level embeddings is the flair package which implements Contextual String Embeddings for Sequence Labeling.

Character-level embeddings in python


How to say "too busy for..." in german

Question: I want to know how to say, for example " I'm too busy to practice German".
Would that be something like "ich bin zu beschäftigt zu Deutsch üben?". I would really appreciate it, sometimes I have a hard time making sense of german prepositions.
Comment: Welcome to German.SE! Since your question is about the right preposition (in German), it's interesting that you chose *too busy **for*** in the headline and *too busy **to*** in your example.
Comment: Lol, that's true! I guess I was thinking about a noun in the headline and about a verb in the example.
Answer: You can say either

Ich bin zu beschäftigt, um* Deutsch zu üben.

or

Ich bin zu beschäftigt zum Deutschüben. (Deutschüben = one word, nominalized)

The preposition is always zu. In the first alternative you don't have a mere infinitive, but an erweiterter Infinitiv beginning with um which is considered to be subclause-equivalent. In the second alternative, you have a nominalized verb (das Deutschüben), so it becomes a substantive preceeded by an article. Because the preposition zu requires the dative, the prepositional phrase originally would be zu dem Deutschüben. However, in this case zu dem always merges into zum.

*Without um, the sentence would read I'm too busy (with) learning German.
Answer: Although

Ich bin zu beschäftigt, (um) Deutsch zu üben.

is possible and sort of a more literal translation, I would say that the phrase

Ich habe zu viel zu tun, um Deutsch zu üben.

or

Ich komme nicht dazu, Deutsch zu üben.

are more idiomatic in German.
Comment: *Ich bin zu beschäftigt Deutsch zu üben* (without *um*) would more likely mean *I'm too busy **with** learning German* from my point of view.
Answer:
I'm too busy to practice German.

As already explained in other answers, both

Ich bin zu beschäftigt, um Deutsch zu üben.

and

Ich bin zu beschäftigt zum Deutschüben.

are acceptable ways to express the aforementioned statement.
However, note that both ways can be somewhat confusing because they could be interpreted differently: In both cases, the general sentence structure reflects the meaning of "in order to", that is, explaining the purpose of something. Outside of the "zu ... um zu" construction, "um zu" very uniquely means "in order to" in German.
As a native German speaker, I am regularly wary of using "zu ... um zu" for fear of being misunderstood, and generally try to circumnavigate this construction, for which there are several options:

Only to be used in writing, and even there, it sounds rather old-fashioned:

Ich bin zu beschäftigt, als dass ich Deutsch üben könnte.

More modern, and idiomatic both in written and spoken language:

Ich bin so beschäftigt, dass ich nicht/kein Deutsch üben kann.

Also acceptable in all contexts, but switches the order in which information is given around:

Ich kann nicht/kein Deutsch üben. Dazu bin ich zu beschäftigt.
Comment: I don't get your point regarding the ambiguity. What could you mistakingly understand?
Comment: @Nearoo: "I am too busy, and the purpose of my being so busy is so I cannot practice German."
Comment: Ah, I see. I'm not sure if this interpretation would make sense semantically, both in German and English. Whenever you're too , you're too  _to_ (/for)   , you can't be e.g. too small just on its own, which would be the case if you're describing the purpose with the second part of the sentence.
Comment: @Nearoo: The intention may be pretty obvious (well, to most people, at least) in the example given here, but consider this one: "The announced number of participants was too high to get the permission." Now, does this mean the permission was denied because the announced number of participants exceeded the acceptable maximum number? Or does it mean the participant count was intentionally overestimated in order to reach some minimum participant number required to get a permission? Both seem reasonable, and they will probably become clear from context, but IMHO, the fact that you need to know ...
Comment: ... the context just to tell whether a given sentence means one thing or basically the opposite thereof is a sufficient reason to avoid the construction for the sake of clarity.
Comment: This doesn't sound right to my ears. The former is clearly the case. Further, I'm pretty sure you can't express purpose for adjectives, it must be verbs. Example: "I was too tired to take a test" / "I was _being_ too tired to take a test", although it still doesn't entirely make sense, because you're still not defining _what_ you're too tired for.
Comment: @Nearoo: Good to know - then maybe it's not as ambiguous in English as I thought. I have removed the respective remark in my answer, thank you. In German, "Die angekündigte Teilnehmerzahl war zu hoch, um die Erlaubnis zu erhalten." allows for both interpretations.

How to say "too busy for..." in german


why are my hair strands coming from the bottom of my donut and not the top

Question: why are these hair strands coming from the bottom and not at the top of the icing
Answer: To fix this problem, click on the icing and go to edit mode. There, select whichever parts you want the hair/particles to be on. Go to particle settings and click assign. I would reccomend selecting the whole upperside of the icing for the particles to be there but that is your choice.


Answer key vs key answer?

Question: AFAIK, and as I do use, "answer key" is the one I always see natives using. But there are some people around me who use "key answer" and I wonder if that is also a true way of carrying the same meaning? I've to say that I'm not a native English speaker and same about them. Any help could be appreciated...
Comment: It sounds like she meant "answer key", but it would depend on the nature of the homework.
Comment: What is the context??
Comment: 'answer key' is at least a strong collocation, probably a compound noun defined in reliable dictionaries. 'Key answer' is at most a weakish collocation.
Comment: @HotLicks, my English teacher asked us (her students) to do the pieces of homework he had given us. Then said "you have two hours to do them until I send you the "key answer" (without "S")". I decided to come ask you guys to see if there is something behind it that I'm not aware of...
Answer: An answer key is a key to the answers (to a test or exercise). It's usually a copy of the test or exercise with the instructor's idea of the best possible answers written in.
A key answer is an answer that is key. That is, it's the most important of several possible answers to a question. Alternatively, it could be the answer to a question, as given in the answer key.
Comment: @AmirF, yes, at least as the term was used in California when I was in school (30 years ago).
Comment: So, in my case, if my teacher requires me to do some kind of homework assignment, and then wants to check them, there should be an answer key, not a key answer...

Answer key vs key answer?


What estimation method is best to conduct event study on unconventional monetary policy

Question: I have collected bond yield data from 01/01/2008:31/12/2019 for several euro-zone countries. I would like to conduct an event study analysis of the main Non standard measures announced by central banks, but I am not sure which model is best from a theoretical point of view. I basically have dummy variables and control variables as regressors, that are the same for each countries, except for the first lags of the dependent variable. Would you estimate the model for each country seperately via OLS, or should I use a Panel estimation method? One of the main problem I face is that, bond yields were rising because of the sovereign debt crisis and many policies were announced on a period of turbolent markets so that I get for instance positive loadings on many non standard monetary policy announcements. How would you handle this issue?
Answer: As part of your analysis, it is always a good idea to do something simple before pulling out the big guns. So, OLS by country with perhaps a handful of controls would be a good benchmark, if only to tell later if your complicated ideas don't amount to squashing a fly with a sledge hammer.
As for the panel idea, you have to think about how you'd be pooling your information. Country by country allows a maximal degree of freedom, but if you think some effects are shared or should be shared, you'd need a panel to capture this effect. The point here is that each estimator and regression equation tells a STORY. Think about it using words or pictures -- THEN, do the math.


android and flash: can android access the webcam inside an web page?

Question: I have a very stupid question: can android (I use samsung galaxy S2 mobile) can access teh webcam ?
In my flash application, I got a flash security alert that allows to autorize or deny the access to webcam.
When I run this flash, it never shows this security alert and then It does not access the webcam.
I do tests for instance with the website http://www.dialogoo.com : works fine on my PC, works fine on my galaxy s2, but since it never shows me the autorization dialog, I cannot stream my webcam.
Any idea ?
regards
Answer: Simple answer :
no that won't work


Why did the British Royal Air force not see a mass adoption of American Fighter planes and bombers?

Question: I understand the RAF made extensive use of C-47 and other support aircraft from the US, but they never seemed to adopt fighters and bombers for frontline service like the British Army so eagerly did with the m3, lee and sherman and other equipment. What was the reason for this? Where there not enough British pilots available to justify the purchase? Or was British manufacturing just better suited to producing airframes than tank hulls?
Answer: Not sure where you get your information, but the RAF extensively used P-51 Mustangs (it was designed for them originally), P-47 Thunderbolts (in the Far East and Middle East), P-40 Tomahawks (in the Far East and Middle East), and B-25 Mitchells (Europe, Middle East and Far East) throughout the war.
They ordered some P-38 Lightnings early on but specified non-counterrototating engines and no supercharging, and the performance was disappointing as you would expect, and further orders were declined.
The RAF also operated B-17s and B-24s and PBYs in Coastal Command. The Royal Navy operated Corsairs and Wildcats off carriers. It was the Royal Navy that convinced the US Navy to revisit carrier operations for the Corsair, after the Navy initially abandoned carrier ops and transferred their Corsairs to the Marine Corps for land based ops, by perfecting the curved approach path on Royal Navy carriers.
The main limitation would be available quantities restricted as the US started to prioritize its own needs
Meanwhile, the US Army operated DeHavilland Mosquitos for reconnaissance and pathfinding, as well as Spitfires.
I'm sure there are other types I missed.
My father flew C-47s in Burma, and was based at RAF Tulihal just inside India, and the base included RAF squadrons of both B-25s and P-47s that provided tactical support to the 14th Army's drive down the Irrawaddy valley to Mandalay. When I was little he told me stories of orbiting near Japanese lines in their Dakotas and watching the RAF Mitchells and Thunderbolts pound Japanese positions so they could make their drops over British Army positions.
Comment: My conjecture is that since US manufacturing is closer to the Far East theatre than UK manufacturing, but UK manufacturing was (obviously much) closer to the European theatre, the RAF would have primarily used UK planes in Europe and US planes in the Far East. Which since many British history buffs are more interested in the European Theatre gives the impression that the RAF flew mainly UK types.
Comment: Mainly it was that the Far East was a secondary priority, way lower priority as far as  Britain was concerned, and had to distribute their more limited resources a bit more carefully.  Plus the only major theatre of operations for UK was India/Burma. The RAF did send Spits to Burma in 1943 and 1944, Mark Eights I believe. The Spit could fly circles around an Oscar (Army Zero). The UK just couldn't produce enough airplanes in-house, so they supplemented their needs with US types, and in some cases like the B-24, and B-25, they were just the best design for the job.


visibility of a view based on current node field

Question: I am displaying a block of related articles in node page using views. I want to hide a view on node page if certain entity field on this node is empty. My view has contextual filter with default value node nid (relationship to entity ref. field) and relationship to entity reference field. How is it possible to do?
My aim is to show block in sidebar or mail content based on what is in the field (n/a or sidebar for example). Or is there any better way to show that block on various positions of page?
I use context module so I would create views - one for sidebar and second for main page. One would be set to show only if field is empty and the second one opposite.
Thank you.
Answer: Just add another filter on the parent node relationship for that current field.  Not sure on what field is what for you but it seems you have all the relationships added into the view based on the parent node page?
Just add another filter, select the field you want to check, add the parent node relationship and make sure its NOT EMPTY.
If you just have the contextual filter as a nid, add a relationship to that nid so you can get access to the parents fields.
Comment: It works, I would have never guessed this solution. Thank you very much,
Comment: Hi, do you mean add another contextual filter? I need to show the blocks based on field on current node not referenced nodes.
Comment: No, not a contextual filter, a regular filter.
Comment: In my case, regular filter for that field, would only filter referenced nodes (on that nodes there is not the field) The field is on current node.
Comment: Correct, add a relationship and then add the relationship to the field.  So its joining the results and providing some extra filtering based on the parent node.


How do I sum quantities in a repeating section?

Question: I have a quantity field in a repeating section.  I need to determine the total of that field outside of the section.  How do I sum up the quantity of items inside the repeating section in Cognito Forms.
Answer: I am a developer with Cognito Forms
The easiest way to total up the quantity across all items in a repeating section is to leverage a calculation field to sum up the total.
For example, if you have a repeating section called "Products" and within each item you have a number field called "Quantity", you can create a calculation field outside of the repeating section. The calculation would simply be <code>=Products.Sum(Quantity)</code>. Make sure to set the Type of the calculation field to be "Number" so that the value is formatted correctly.
I've included a screen shot a basic form that illustrates this setup.
You can also find this, and other powerful calculations in our help documentation at: http://help.cognitoforms.com/calculations-overview, check out the section on "Working with Repeating Sections".


Propeller design

Question: I see on internet, that aircraft propellers most effective blades angle only 15 degrees on every blade. Why propellers not use 45 degrees angle on propeller's blade that give more thrust on the aircraft rather than 15 degrees?
Comment: Because of the stall angle... there are many resources that explain this.
Comment: Google "virtual wind direction"
Comment: This question may be better suited to [SE Aviation](https://aviation.stackexchange.com/).
Comment: A propeller is simply a vertical wing and as such is subject to all the principles as a wing, such as stall angle. And I agree with @Fred; this is more aptly suited on the Aviation community.
Comment: Note that a "propeller" with many blades (anything from 20 up to say 100) so the air is constrained to go through the passage *between two blades*, and running inside a duct so there is no leakage at the blade tips, often *does* have a blade angle greater than 15 degrees - but such things are called *fans* not *propellers,* and as the start of this comment implies, they don't operate in the same airflow conditions as conventional propellers.
Answer: Just think of the propeller as a mean to thrust air in one direction. The higher the angle of incidence, the more the propeller is pushing the air (up to about 45°, then the force perpendicular to the rotational direction starts to take over).
Now consider the fact that air is inertial mass. So accelerating it means building up pressure behind the propeller. Now when the angle of incidence becomes too big, so it thrusts too much air, the pressure "behind" the propeller becomes to high. The energy needed for the air to flow against that pressure is extracted from the air, thus the flow starts to separate from the propeller blade and the blade begins to stall. That means that it is losing most or even all of its aerodynamic properties and no or only little air is being thrusted.
This critical angle of incidence depends on many factors, like the rotational speed, density of air, propeller profile, relative axial speed of the propeller to the air flow, etc....

Propeller design


Performing routes lookups within my Actions

Question: What I'm trying to do is build out support for CORS in my Play 2.1 application.  The premiss is that anything that comes in on a path of /admin needs to get the CORS headers in the response.  This works well enough with cut-and-paste solutions I've cobbled together through StackOverflow.  Each of my Controller actions leverage a wrapped Action that shoves the CORS headers into the response.  The problem is my naive implementation now returns 200 OK on OPTIONS requests for URLs that don't exist in my routes file!  How do I modify my naive Controller to confirm that a URL exists in my routes file and 404 Not Found if I doesn't find a route?
conf/routes
# Routes
# This file defines all application routes (Higher priority routes first)
# ~~~~

# Home page
GET     /                           controllers.Application.index
GET     /hb                         controllers.Application.hb

# Admin API
POST    /admin/sessions             controllers.admin.Sessions.session
GET     /admin/apps                 controllers.admin.Apps.index
OPTIONS /admin/*url                 controllers.admin.Admin.options(url: String)

# Map static resources from the /public folder to the /assets URL path
GET     /assets/*file               controllers.Assets.at(path="/public", file)

My Admin Controller provides the common options handling
object Admin extends Controller {
  val log = LoggerFactory.getLogger(getClass())

  def options(url: String) = CORS_Writer {
    Action {
      log.trace("options( url: {}", url);
      /*
       * I need to validate that url exists in the routes file here
       * (this doesn't compile, but conceptually is what I want).
       */
       if(routes(url)) { Ok } else { NotFound }
    }
  }
}

I expect
OPTIONS /admin/sessions HTTP/1.1
HTTP/1.1 200 OK

and
OPTIONS /admin/sessions HTTP/1.1
HTTP/1.1 200 OK

but
OPTIONS /admin/bob HTTP/1.1
HTTP/1.1 404 Not Found

I'm new to both Scala and Play and I find the Play 2.1 documentation sorely lacking regarding the details of working with routes.  Please excuse me if this question seem rather simpleton.  I'm sure this is possible, I just don't know the incantation.
Answer: Isn't common onHandlerNotFound good enough ?

How to create a custom 404 page handler

You can make additional check to response with different error for paths starting with /admin/.
Comment: I don't think that will work due to my wildcarding all OPTIONS in the routes file (OPTIONS /admin/*url controllers.admin.Admin.options(url: String).  What I've done with this wildcard is made it so there is always a handler.


Get all records from inner joined tables if second table does not have data

Question: I follow below syntax by which I achieve the result. but it takes time
IF NOT EXISTS(select * from #tblxyz)
BEGIN
INSERT INTO #tblxyz select NULL
END

Select a.*
        FROM
            tblabc a
            INNER JOIN #tblxyz b ON a.ID = ISNULL(b.ID,a.id)

If second joined table has some rows, I only want to return those joined rows only. Only if the second table has no rows, I want to return al lrows from the first table.
Answer: I think the condition ON a.ID = ISNULL(b.ID,a.id) is not the best way to do this. It may lead to inefficient plans and may return unwanted results (according to your specifications). If the tblxyz table has rows with NULL values, you'll still get all the rows from table a (and possibly multiple times).
I would write the query without using the ISNULL() function, like this:
SELECT a.*
FROM tblabc a
    INNER JOIN #tblxyz b
    ON a.ID = b.ID
    OR NOT EXISTS (SELECT * FROM #tblxyz) ;

or like this:
SELECT a.*
FROM tblabc a
    INNER JOIN #tblxyz b
    ON a.ID = b.ID

UNION ALL

SELECT a.*
FROM tblabc a
WHERE NOT EXISTS (SELECT * FROM #tblxyz) ;

Answer: The way you've done it is correct.
So the reasons for slowness will likely come down to: when is it slow (is it when the temp table has a lot of rows, or when it has few rows?), how many rows are usually in each table, what indexes exist on each table, and what data type is ID?
You can also look at your real-world execution plan for some answers.
I think you will find that you have an index on ID on the base table, it's slow when you have a lot of rows in the temp table, and if that is the case you likely just need to add an index on the temp table (otherwise the plans are built assuming 1 row).
Answer: IF OBJECT_ID(N'tempdb..#table1') IS NOT NULL drop table #table1
IF OBJECT_ID(N'tempdb..#table2') IS NOT NULL drop table #table2

create table #table1 (id int, value varchar(10))
create table #table2 (id int)

insert into #table1(id, value) VALUES (1,'value1'), (2,'value2'), (3,'value3')
--test here. Comment next line
insert into #table2(id) VALUES (1) --Comment/Uncomment

select * from #table1
select * from #table2

select #table1.*
from #table1
left JOIN #table2 on
    #table1.id = #table2.id
where (#table2.id is not null or not exists (select * from #table2))


Android Live Wallpapers with OpenGL ES 2.0?

Question: Has anyone managed to get OpenGL ES 2.0 working in a live wallpaper?  I have a class that uses OpenGL ES 2.0 and runs fine as a Renderer for a GLSurfaceView.  However, I want it to function as a live wallpaper.  I found Robert Green's GLWallpaperService, but that is based on an older version of GLSurfaceView and does not support setEGLContextClientVersion, which is needed to run OpenGL ES 2.0.
Comment: I've found an answer to my own question at https://github.com/ghisguth/blurred-lines-live/blob/master/src/cxa/lineswallpaper/Wallpaper.java
Comment: Thanks for the link, I've been looking for the same :)
Comment: @MJP: Nice! Plz answer your own question with the link.
Comment: Can you please post your solution as an answer below so we can get this off the Unanswered list?  Thank you.
Answer: I've managed to get an opengl-based LWP working by extending GLSurfaceView and then wrapping that in a wallpaper service. I haven't specifically tested if opengl es 2.0 works with this method, but I see no reason it wouldn't.
You can find the LWP specific files at https://github.com/JesusFreke/Penroser/tree/master/src/org/jf/GLWallpaper. They should be generic and usable as-is in other projects. For an example of how to use these classes, see https://github.com/JesusFreke/Penroser/blob/master/src/org/jf/Penroser/PenroserLiveWallpaper.java
Comment: @Daniel Schuler Only difference is that I implemented an ``onDestroy()`` method to GLSurfaceView which is simply written as ``void onDestroy() { super.onDetachedFromWindow() }``. Calling this will kill the underlying GL thread, otherwise it is being left in idle state in the background. Can't tell if it has anything with the problem you're facing though.
Comment: After reading GLSurfaceView source for awhile I ended up with somewhat similar implementation/idea for getting OpenGL support for WallpaperService. But the reason for commenting your answer is that I think you're losing GLThread in your GLWallpaper implementation. It's killed only once GLSurfaceView.onDetachedFromWindow() gets called (or you can call it manually in this case), onSurfaceDestroyed() puts it only in waiting state.
Comment: @harism - how did you implement it differently?
I've worked with JesusFreke's wallpaper service for a while, and it's worked very well. The only issue is when apply the wallpaper from preview mode, where GLThread sometimes throws an exception, but I can't quite figure out how to solve it.
Answer: The code at this blog post adapts Robert Green's GLWallpaperService to work with OpenGL ES 2.0. You may have some success using it, however it would probably be simpler for you to use JesusFreke's implementation.
If you are successful in improving GLWallpaperService please submit your changes back to the project so that we can all benefit.


How to make the VJET plugin fully working in eclipse for my node.js project

Question: VJET is almoust working for me, I can get code completion in the same file and for basic Node.js  modules (using NodejsTL) but for new modules(my modules) or modules installed with npm an increasing number of errors plagues my "Problems" tab in Eclipse. It is there any way to have clean "builds" and get rid of all warnings and errors?
Answer: Vjet currently doesn't understand user defined modules. There are a three solutions to fix this... (1)a type library can be added to support more modules. (2)Vjet can be extended to support npm modules there is a enhancement request open for this. (3)There is a way to disable errors and warnings as well. You can provide disable errors and warnings at the project or workspace level. See preferences -> vjet -> code compliance -> errors and warnings. Thanks for the feedback.
Here is the enhancement request you should vote for to get VJET to understand nodejs user defined modules - https://www.ebayopensource.org/jira/browse/VJET-88


When solving second order nonhomogeneous constant-coefficient linear ODE, why does particular solution + general solution = general solution?

Question: It is said that for this type of differential equations, general solution for homogeneous case + particular solution for nonhomogeneous case = general solution for nonhomogeneous case. However, I have never seen anyone prove it and explain why. I find this to be a necessary component of the learning process. Therefore, I would appreciate it if someone could please do so. Thank you.
Comment: In order to determine the one linear, I think its slope and proper translation. And Let's think solution space of ODE is a straight line.
Answer: $$
\sum_{i=0}^n a_i y^{(i)}(t) = f(t) \quad y = y_h + y_p
$$
$$
\sum_{i=0}^n a_i (y_h+y_p)^{(i)}(t) = f(t)  = \sum_{i=0}^n a_i y_h^{(i)}(t) + \sum_{i=0}^n a_i y_p^{(i)}(t) = 0+f(t)=f(t)
$$
Comment: $y^{(i)}$ indicates the i-th derivative (when $i=0$ means $y$)
Answer: Consider the general $n$-th order constant-coefficient inhomogeneous linear ODE, $$y^{(n)} + a_{n-1}y^{(n-1)} + \cdots + a_1y' + a_0y = f.$$
Suppose $y_1$ and $y_2$ are two particular solutions to this equation. Then $y_1 - y_2$ solves the homogeneous equation $$y^{(n)} + a_{n-1}y^{(n-1)} + \cdots + a_1y' + a_0y = 0.$$
The general solution to this equation depends on $n$ arbitrary constants $C_1,\ldots,C_n$. Let $y_h(t;C_1,\ldots,C_n)$ denote the solution corresponding to these constants. Then since $y_1-y_2$ solves the homogeneous equation, there exists a choice of coefficients $C_1,\ldots,C_n$ such that $y_1(t) - y_2(t) = y_h(t;C_1,\ldots,C_n)$. Then it follows that $$y_1(t) = y_2(t) + y_h(t;C_1,\ldots,C_n).$$
Thus $y_1$ is a sum of a particular solution of the inhomogeneous equation and a solution of the homogeneous equation; moreover, since $y_1$ and $y_2$ were arbitrary solutions of the inhomogeneous equation, we have shown that every pair of solutions has this property.


How to host two Github Repositories on a single domain?

Question: I am using one Github repository to host a portfolio website on the root of my domain. Now I want a separate GitHub repository to host the blog section at the subdirectory of my domain "www.example.com/blog". How do I approach this?
I am using Publii as a CMS for my blog section.
My DNS settings are managed by Cloudflare.
Answer: There is a pretty good article on this @ Github. Basically you can set new origin in the sub directory "blog".
And you have some other options like submodules and subtrees. See the answer @ Stackoverflow.


Does Daruk's Protection absorb damage?

Question: I'm really bad at deflecting attacks, so I just use Daruk's Protection to deflect them, but I noticed that when I use it to deflect guardian beams, but it didn't kill a STATIONARY guardian! (the rusted ones, not the turrets) Why? Do I need to do some kind of absurd flurry rushing/shield parrying training? Other random stuff I had: master sword, near hyrule castle, Savage lynel shield, (I forgot the bow) and had no buffs.
Comment: Also, I got all divine beasts, full stamina wheel, 15 hearts, no yellow hearts or yellow stamina
Answer: Daruk's Protection does not reflect damage, and cannot be used to kill a guardian.
To kill a guardian, you need to do one of the following:

Do a perfect parry with your shield against the guardian's laser attack. If the guardian is capable of walking around, you will need to do this multiple times. If your timing is less than perfect, this may also use up a hit on Daruk's Protection. If you're feeling brave, you can disable Daruk's Protection in the "key items" section of your inventory to prevent this from happening. However, this will make it harder to parry because Daruk will no longer be fixing your mistakes for you.

Guardians make a "beep" noise right before they shoot. If you parry right after the beep, with a little practice, you should be able to successfully parry most laser attacks.

Wield an Ancient Shield, and block the guardian's laser attack with it. It will reflect automatically, without requiring a parry. This consumes durability, unlike parrying. You can acquire an Ancient Shield from the Akkala Ancient Tech Lab in exchange for rupees and ancient parts.

This does not work with the "regular" shields you get from the combat trials and other mini-guardian enemies. You have to purchase the shield from Robbie's lab.

Shoot the guardian with an ancient arrow. Unlike all other enemies, guardians will still drop loot if killed in this manner. Ancient arrows can be found as rare loot or purchased from Robbie's lab.
Just keep shooting the guardian's eye with non-ancient arrows, or hitting it with ordinary attacks, until its HP is depleted. This takes a while and can be riskier than the other methods.
Use Urbosa's Fury to damage and stun the guardian.
Comment: Daruks protection can be used to parry attacks. If you miss the perfect parry Daruks protection will use a charge instead to parry the attack. So it's good for protecting yourself from guardian attacks. Though it can get annoying since it does this for ANY attack.
Comment: I just use the master sword to chop off all the legs, and while its stunned, kill it. I just needed this for the guardian turrets, because they can't be stunned except for an arrow to the eye.
Comment: Just a small note, on masters mode the guardians can 'hold' their beam for a split second before shooting to throw your parry timing off.
Comment: WHAT?!?!? Oh boy... Just another reason to not to try master mode... UPDATE: I just got Mipha's Grace+, and my shield parrying got better :)
Comment: Guardian swords and ancient swords are also useful for immobilizing guardian stalkers: they always sever the legs with a single strike, whereas other weapons may require multiple strikes. Ancient armor purchased from the tech lab (and some other special gear you may find) is also useful for guardian combat.
Comment: I just tested it, and daruk's protection deflects the laser right back. You can even parry inside it!                              EDIT: Do you mean that it doesn't reflect PURE damage? Because you can't deal damage except for the lynel shields.

Does Daruk's Protection absorb damage?


Optimization problems: Finding the optimal path

Question: I'm still trying to get the hang of optimization problems in calculus and I'm looking for a little help. I'm having trouble finding equations to model the following problem: I'm fairly sure I need to combine two variables into a single variable and set up a related rates problem, but I'm not sure how to get started.
The problem is as follows: Alaina wants to get to the bus stop as quickly as possible. The bus stop is across a grassy park, 2000 feet west and 600 feet north of her starting position. She can walk west along the edge of the park on the sidewalk at a speed of 6 ft/s. She can also travel through the grass in the park, but only at a rate of 4 ft/s. What path will get her to the bus stop the fastest?
Could someone help set it up for me? Thanks!
Comment: Hint: Suppose you walk some distance along the sidewalk before heading through the grass. Call that distance x. Now draw a diagram: can you get an expression for the distance through the grass in terms of x?
Comment: Please look at my answer, I think you'll understand how to solve it now.
Answer: EDIT
To solve your question:
The path you should take is a combination of both traveling on the sidewalk and through the grass.
Let's start:
$$T(x) = \frac{\text{Distance through grass}}{\text{Rate through grass}} + \frac{\text{Distance on sidewalk}}{\text{Rate on sidewalk}}$$
$$T(x) = \frac{2000-x}{6} + \frac{\text{Distance through grass}}{4}$$
And
$$600^2 + x^2 = (\text{Distance through grass})^2$$
$$\text{Distance through grass} = \sqrt{360000 + x^2}$$
$$T(x) = \frac{2000-x}{6} + \frac{\sqrt{360000 + x^2}}{4}$$
$$T'(x) = \frac{-1}{6} + \frac{x}{4\sqrt{360000 + x^2}} = 0$$
Solving, we get $x = 240\sqrt{5}$
And our distances are:
$$\text{Through Grass} = 360\sqrt{5}$$
$$\text{On sidewalk} = 2000 - 240\sqrt{5}$$
Comment if you need further explanation.
Also take a look at this, it might help.
Comment: Traveling along the hypotenuse is only faster if the speed along all sides is the same. It's not, though: traveling along the edge of the park is 1.5 times faster, so a combination of sidewalk and grass walking is optimal.
Comment: @dlev I see that now, but OP wants to know whether traveling along the legs OR through hypotenuse is optimal. Therefore, even though the optimal distance is a combination of both, I cannot say this
Comment: I don't think that's what the problem is asking. These problems appear in intro calc courses all the time, and they almost always want a combination of paths.
Comment: @dlev Well I can change my answer then
Comment: That link at the end was fantastic, much better than my math book, thanks!
Answer: Compare the travel time along the two sides of the right triangle (2000 ft+600 ft @ speed of 6 ft/s) versus the travel time along the hypotenuse of the right triangle (2088.06 ft @speed of 4 ft/s).
It is faster to travel along the edge of the park on the sidewalk, besides being grass-friendly!


Is it necessary to have both hot ends on a dual extruder printer at the same height?

Question: I'm thinking of another extruder on my printer, and I'm curious about this one....
Is it necessary to have both hot ends on same height? Why yes / why not? (if there is not)
Answer: I have a dual extruder Replicator 1 and having the nozzles at the same height is a must and albeit a bit of a struggle otherwise. At one point, I had to disassemble my extruder head and the nozzles didn't line up quite right. There after, printing with the lower one obviously didn't have any troubles, however, printing with the high extruder made it so the lower extruder would scrape the molten plastic layer. This made my surface finish horrible and almost impossible for support structures to be printed.
Instead of fighting with my stock nozzle assembly to get everything perfectly lined up, I just shimmed the one side with some stacks of paper cutouts. This brought my extruders very close to even.
Also, you'll want to make sure excess plastic is cleaned off of BOTH nozzles when printing with either nozzle. I found that some prints would fail because of a small discharge from a previous print on the other nozzle.
Answer: I don't have dual extruder printer myself, but to my understanding having both nozzles leveled at the same height is critical for getting successful prints.
For typical FDM printers, the lowest point of the end effector should always be the nozzle. If you, for instance, mount a fan lower than the tip of your nozzle, it will eventually collide with the printed object.
The effect of having unequally leveled nozzle tips for a dual extruder printer will be exactly the same: one of the nozzles will either drag against or collide with the model during print; or, one of the nozzles will be to far away from the model, giving poor layer adhesion. Either way, the result will be sub-optimal.
So, leveling both nozzles equally is probably a good idea. You might want to have a look at this question on some advice regarding how to do it.
Answer: If your printer has no way to move the heads up and down, or otherwise out of the way, and your slicer isn't able to detect collisions and account for head height differences in the produced G code, then they must be at exactly the same height from the bed.
If extruder A is hanging lower than extruder B, then when B has printed at a certain level, and A moves across that area, A will hit the material B has printed.
Unfortunately, this is further complicated for newer printers because some of them rely on digital bed leveling.  If your bed isn't parallel to your X and Y axis movement, then you have to work very hard to make sure the heads are parallel to the bed, and with some mechanisms this isn't possible without making the mechanism itself parallel to the bed, so just mounting the new head at the same height as the other head might not be sufficient if your printer isn't perfectly calibrated already.
I have not yet seen a printer or slicer that manages heads of different heights, but I suppose it's possible to manage the problem with additional intelligence.  For instance, if the printer can move the heads up and down independently, it might move one down for printing, and the other up and out of the way when it's not printing, and then the opposite when it switches.  I can't think of a good reason to do this, though.
Another option would be to develop a slicer to generate G-Code that will prevent such collisions.  The printer would necessarily be limited in what it could print depending on the location of the second head, as there are some situations where it would need to print in a certain area, but a collision prevents it from getting to that area.
At any rate, no one has developed such software or mechanisms yet, so if you had good reason to mount the heads at different heights, you'd have to account for all of these factors and develop the complete solution yourself.
Comment: I want to say that the slicer in Octopi (RaspberryPi Print Server) has options for extruder height offsets as well as the normal X-Axis offset. Don't take my word for it though...
Comment: @tbm0115 Octopi uses Cura for its slicing, perhaps you can find a reference to multiple head use at different heights in that software.
Comment: I may have mistaken the Y-Axis offset for Z. Still a useful setting and it may be different as I'm pretty sure Octopi uses a Cura framework (not full-blown Cura). I found the following screenshot:https://www.flickr.com/photos/ultimaker/9536542189/
Answer: To add to the above answers, besides the obvious point that one hotend might collide with something another hotend positioned lower than it has printed, you also want both hotends to be positioned X microns above the bed at minimum height so your filament will stick to the bed properly. Position one a bit higher than the other and what it prints won't stick to the bed very well, position one a bit lower and it will hit the bed and clog/be unable to print the first layer.
The only reason I can think of when you'd want one hotend to be higher is a situation when you're not using both hotends and don't want the second hotend to drag on and deform a layer the main hotend has printed and is still warm and deformable. If that's an issue (I doubt) then sure, move it a bit higher.
If there are other reasons for what you would like to have the hotends at different heights, please add that to your question. I can't think of one myself.


Looking for test leads for individual PCB header pins or socket pins

Question: While recently debugging a device that had a 7-pin male XLR plug, I was trying to connect to two of the pins in the plug, without touching any of the others, and I wondered if there are test leads that can be used for such debugging: essentially just slim metal cylinders that can be slipped over each pin, without touching surrounding pins, and wired to a lead. The same question arose when I was testing a 10-way header on a PCB: how to connect to, say, pins 3 and 7 only, without touching any of the others. In that case I had a 10-way socket, which I used for debugging, but it would have been very useful to have had two, slim cylindrical test leads, to slip over the two pins in question.
[Before anyone says so, I have looked on electronics supplier sites (we use oneCall, and I also checked RS): the trouble there is knowing how to phrase the online query correctly... so far I've drawn a blank.]
Comment: I normally use crimp-pins/sockets that mate with the header in question.
Answer: For experimental purposes, bare crimp type contacts for comparable diameter posts can be used individually, covered in heat shrink tubing rather than inserted into their usual housings, provided that they are the style where the contact surrounds the post sufficiently to grab it, rather than needing the plastic housing to hold the post against a single sided contact.
There are now import/discount suppliers selling ribbon cable terminated in plastic molded single male or female .100" spacing .025" post contacts, with the idea that you can manually separate the ribbon as desired, however quality/reliability seems variable, so you'll want to test any setup with those for integrity before assuming your problem is more complicated than a failed connection.
In a situation where failure or accidental shorts would not have lasting consequences, I've also been able to crudely break out an XLR using small alligator clip leads in order to take some quick measurements.
Comment: Quality is HIGHLY variable on those molded cables. I prefer the original method of crimping single contacts to wire leads. It is more expensive, but I haven't had a failure with it yet. If you don't have a crimping tool, most contacts are available with solder cup termination.
Answer: For this purpose i soldered my own jumperwire. it's pretty straight forward. This is what you need:

22 to 23 gauge wire (male connectors for breadboards or similar)
something similar to an IDE socket (tear apart for female connectors)
heat shrink tubing (i used 1mm diameter shrinked)
flexible wire for soldering

Depending on the type of jumperwires you need just solder everything together. put heat shrink tubing on the solder and debug with them. used them for a bit now and didn't have problems yet
Here is the original article that describes the process. it's in german though
Answer: While there might be a connector specific method, the simplest way is make you own. Get a 7 pin XLR female cable, cut it in half, and add some alligator clips to it.


show username in infopath form

Question: I need to show the user full name in InfoPath form. I tried the webservice and data connection for User Information list but still not getting. Can any one show me the steps he/she follow to show display name.
Comment: Can you provide a bit more detail on what exactly it is you're hoping to achieve and what you have tried so far?
Answer: To get the current user's display name, assuming you have the User Information data connection already set up, I create a rule that runs when the form loads. The rule doesn't have any conditions, just to run when the form loads. The following actions are added to the rule:

Set a field's value: select the field for User Information List-->queryFields-->Account

Select infopath's function userName() as the value

Then in the same rule I add the action to query the data connection for the User Information List.

In the field that I want to add the current user's display name to I add the default value of the User Information List-->dataFields-->Name.

At this point you don't have to use the Name field as I suggested, you can add any dataField value that you are wanting to retrieve information for the current user. Make sure that you checkmark "Refresh value when formula is recalculated" so that this value is updated each time the form is opened.

Don't be alarmed if the name that appears in the value is different from what you selected on the  user information list. What is displayed on the value portion often changes to the field's properties name that is set on sharepoint. The end result is still the same though.

show username in infopath form


Question about changing a logarithm's base

Question: I've been using the following method to derive/remember the logarithm base conversion formula: If I want to convert $\log_a(x)$ to an expression in base $b$, I say,
$$\begin{align*}a^{\log_a(x)}&=x \\[0.3cm]
\log_b(a^{\log_a(x)})&=\log_b(x) \\[0.3cm]
\log_a(x)\log_b(a)&=\log_b(x)\\[0.3cm]
\log_a(x)&=\frac{\log_b(x)}{\log_b(a)}
\end{align*}$$
It kind of feels like I'm working backwards, and I was wondering if there's a more direct way to go about it. I tried:
$$\begin{align*}\log_a(x)&=\log_a(b^{\log_b(x)})\\[0.4cm]
\log_a(x)&=\log_b(x)\log_a(b)\end{align*}$$
but couldn't rid myself of the $\log_a$ in the right-hand side of the equation. It occurred to me that if I could rewrite the "$a$" subscript as "$b^{\log_b(a)}$", I might be onto something. (Or might not.) Does the notation ever get used like that, where you perform a substitution in a subscript?
Answer: Deriving and remembering are different things. If all you want is to remember, do remember this: All logarithm functions are proportional to each other. Thus $$\log_a(x)=C\log_b(x)$$ for some constant $C$. To find out the value of $C$, insert $x=b$ and remember that $\log_b(b)=1$.
Answer: It is not common, but substitution is universal. Anywhere there is something that represents a number, you may put there anything else that represents the same number. This is at the very heart of mathematics, the fact that numbers transcend any representation there of. Oh, and I have no idea how that would help, unless you know how to extract powers from a base. (If you do, show me your powers of magic in the comments. I have been interested in logarithms recently.)
Answer: Look at the two equations you have produced:
$$\log_a(x)  =  \frac{\log_b(x)}{\log_b(a)}  =  \log_b(x) \cdot \log_a(b)  ,  $$
all of which is correct.  This suggests a couple of things.  One is the relation
$$\log_a(b)  =  \frac{1}{\log_b(a)} ,$$
so you have found one way to manipulate logarithmic values.
You also have two equivalent expressions for the "change-of-base" formula; both are taught in various texts -- I'm not sure which is more commonly used.  But this gives you a couple ways to remember the formula:
$$ \log_{\text{new base}} (x)  =  \frac{\log_{\text{old base}}(x)}{\log_\text{old base}(\text{new base})}$$
or
$$ \log_\text{new base}(\text{old base}) \cdot \log_{\text{old base}} (x)  =  \log_{\text{new base}}(x) ,$$
[this second one was obtained by relabeling, and not just by algebra]
which sort of looks like a "cancellation rule" (but we shouldn't call it that)...
Here's an example:
$$\frac{\log_e (35)}{\log_e (10)} = \log_{10} (35)  \Rightarrow  \frac{3.55535}{2.302585}  \approx  1.544068...  \approx  \log_{10}(35) $$
You can also use the relation you found to find $\log_{10} (e) = \frac{1}{\log_e (10)}  \approx  \frac{1}{2.302585}  \approx  0.434294  $ .  A calculator actually only computes natural logarithms $\log_e (x)$ or $\ln (x)$ , and uses the change-of-base formula (with the value of $\ln 10$ "hard-wired in") to calculate and display common logarithms $\log_{10} (x)$ .  If you need logarithms to a base other than $e$ or 10 , for which the calculator has no buttons, you definitely need the "change-of-base formula" (though I've seen some recent calculators that have a "$\log_{\Box} x$"  button)...


How to write an integral like this in MathJax/LaTeX?

Question: How can I write an integral with underlined characters evenly spaced between two integral signs like this in MathJax/LaTeX?
Answer: In MathJax the easiest way to type it is probably:
\mathbf{P}((X,Y) \in B) = \iint\limits_{(x,y) \in B} f_{X,Y}(x,y) \,dx \,dy

Live example on MathB.in
If you want the two integral signs as far apart as in the picture, you could use two regular \int signs and wrap them in \mathop so that you can place limits on the combined construct.
\mathbf{P}((X,Y) \in B) = \mathop{\int\int}\limits_{(x,y) \in B} f_{X,Y}(x,y) \,dx \,dy

Live example on MathB.in
Comment: Thank you!!!  This is exactly what I needed.
Comment: +1: Cool live example!
Answer: TL;DR:
\mathbf P((X,Y) \in B) = \iint\limits_{(x,y \in B)} f_{X,Y}(x,y)\ \mathrm dx\ \mathrm dy

gives

Full answer:
First of all, the symbol \iint gives what you are looking for in terms of a double-integral sign. However, when adding the limits of integration, they appear to the side, rather than directly below. Thus, we need to make use of \limits_{...subscript...}.
If you want the two integral signs to be spaced out a bit more, replace \iint with \int \int, which places two seperate integral signs.


Blackberry app version update deletes persistent store object on some devices

Question: I have a Blackberry app that stores an object in the persistent store. After updating the app, it is supposed to read the existing value from the persistent store, if any, and continue to use that value. This works on some devices, but does not work on others. I tested on several devices running OS version 7, all of which work as expected. However on a device using version 5 and another using version 6, the object is no longer readable in the persistent store.
This is the case even if I don't change anything about the app other than the version number. Same exact class/object being saved & loaded from the persistent store, and same object ID used to access it.
The process I'm following to reproduce this is:

Completely delete the app & all it's data using the command line.
Load a version of the app, by downloading a .jad file from a browser, verify that it stores data in the persistent store.
While the app is running in the background, load a later version via browser download of the .jad file.
After downloading the later version, the system asks if I want to replace the previous version, and I confirm that I do.
The system loads the new version, and prompts that I must reboot for the change to take effect. I select "Reboot".
Device reboots. The later version is running but cannot read the object from the persistent store.

A device on which I can consistently reproduce this issue is a Blackberry 9800 (Torch) running 6.0 Bundle 2647.
As mentioned above this only happens on some, not all, devices, which makes me think something other than a coding bug may be going on here.
Anyone have ideas about this issue or how to debug it further?
Answer: Peculiar case.
Are you sure the persistent storage is being committed? Something similar generally occurs for me when data has been stored in the storage but not committed. If that is the case, and you load the older version, store some data and reboot your device, the data will not be stored in persistence.
You mentioned that the app is still running in the background when you load a later version. You may want to check whether commit() gets executed or not.
Comment: Thank you for the excellent thought Abhishek. I checked this by adding a reboot of the older version and making sure it could still read the stored data after the reboot, before installing the new version. Unfortunately the new version still cannot read the value so I suspect something about the install process clears the value.


How do you test your your wireframes?

Question: Do you usually test with real users or with your internal team first?
Comment: "test them all"
Comment: sorry, UX.SE is not the place for surveys and polls, this question has no possible correct answer (or all are correct)
Answer: Depends a lot on what are you testing, what's your intended function, what stage of design are you in right now.
Usually, most designers go through some sort of understanding phase at the start of the project, continue with more concrete ideas and finish with evaluating their project empirically.
You can do usability testing and evaluation in any of these stages though (it is highly recommended).
Users you test with should have some aspects common with your target audience.  If your product is very broadly targeted though, feel free to get opinions from as many people you have time to, hallway tests are recommended. You just need to be careful about who is giving you feedback, e.g. developer might think about their app very differently than your grandma.
Answer: To me wireframes are quick doodles in a whiteboard or a paper. I use wireframes to design and demonstrate the user's path and information structure. At this stage in design is always good to meet with the front end team and the back end and have a good brainstorm session. You can talk about all your ideas and initiatives. Is a process of discovery and understanding the user journey.
Prototype
When i prototype i usually use a online tool like invision and share all my prototypes for testing with customer support, Project managers and also i organize users session. On this user sessions i give the user a few exercise to complete to see the journey and see if they can complete task.
Every process is different depends your customer or company.
Answer: Being as brief as possible:

Do you usually test with real users or with your internal team first?

Internal team will be preferable since it doesn't cost you at all and it does help to find minor errors before going big and spending money with real users. Usually from 6-8 user tests will be good enough to find these errors. Just remember that they must not be familiar with the prototype.

How do you test your your wireframes?

There are plenty of ways. Some of them are InVision, UXPin, Pixate, Balsamiq, UserTesting, Axure, Loopback, simple user tests, paper, and more. It basically depends on the level of fidelity of your mock-up and your needs. For that you and your team must ask and answer the following question: What do we want to measure?

How do you test your your wireframes?


Why are there so few Greeks and Macedonians in India?

Question: India has be entered by people of various cultures which has led to cultural diversity but considering the fact that the Seleucid empire had ies and friendship with Indian empires why aren't there that many Greeks in India?
Comment: How do you know who is of Greek ancestry? Did you do some DNA testing? Supposing you are referring to the armies of Alexander the Great, they were all men, so there will be no mitochondrial DNA for you to find.
Comment: If you mean, why is no-one speaking Greek, remember it has been quite a long time, and languages change. According to my memory of history, Alexander's armies turned round and went home, so they would not have left much behind anyway.
Comment: @RedSonja  In fact, the Bactrian kingdom showed a lot of signs of its Greek inhabitants for a long time after Alexander.
Comment: I was thinking because of the selucid empire .
Comment: Why aren't there that many Indians in the former Selucid Empire?  Likewise, there was a lot of ocean trade between India and Greece/Rome, but not much evidence (AFAIK) of permanent immigration either way.  But why would there be?
Answer: The 'Yavanas' (Greeks) did have a strong presence in North India over 2000 years ago. They also had trading links with South India. Some mercenaries and artisans appear to have settled there.
Greek influence peaked under Demetrius I who reached as far as Magadha (modern Bihar) before being repelled by the King of Kalinga. Demetrius was married to a Mauryan princess. Indeed, the Greeks were generally of mixed origin. They maintained a separate identity till the time of Saka domination after which they were absorbed into various martial castes or became indistinguishable from  the subject population. In remote mountain redoubts, some small communities claimed Greek origin. There are also various Rajput dynasties which have Greek princesses in their family tree. It is also possible that they appear in the 'Magha' (Iranian) Brahmin lineages.
Why did the Yavanas lose their separate identity? The answer ultimately comes down to the replacement of Greek by Bactrian and other 'Aryan' languages, consequent upon 'Scythian' & 'Hun' invasions, for all official and scholarly purposes. This extinguished the tradition of Greek Paideia which had attained high regard amongst local savants. Nevertheless, the legend of the technologically proficient Yavana continued to exercise a fascination for poets and writers of later, more settled, ages.


Changing advisors during coursework

Question: Can an advisor suddenly say one day - "I have decided not to advise you anymore"?
Thanks!
Comment: So many directions answers can come from, more detail is needed to clarify the situation.
Answer: Advisors can do this. (So can students.)  I would ask for some reason (money, competence, personality, etc.)  Not an interrogation or a debate (for now).  Just listen, don't argue and take notes on what he says.  Heck for all you know, his concern may be valid and may change your behavior with a subsequent advisor.
You should also go to the department chairman to discuss your options.
The situation becomes more serious the more time that you have spent with the professor.  If there has been a fair amount of time and you are at least semi-competent, his colleagues may pressure him to just work with you and get you past the goal line.  Every situation depends on the particulars (or even how the department behaves).  But alternately, if you are a "problem child", the professors may back up their colleague.
I would not expect some Roman judge standard of fairness, but I would certainly look at your options and talk to department chair, alternate advisors, and maybe even the grad school.  If you are a decent candidate and things are early, it may be simple to just move to an alternate advisor.
Answer: This depends on a lot of things (place, field, personal situations such as illness, etc), but generally, yes. Early on it a program (usually a graduate program) either party is free to change. You don't give any circumstances and there may be some situations in which it isn't appropriate (sexism, racism, etc) but generally there should be no difficulty.
However, the university needs to assure the student that a suitable advisor is available, but not necessarily a particular one.
But, even if you could "force" an advisor to keep working with you I don't see a positive outcome.
Some people get overloaded and have to reduce the load. Better to do this early, as it can become unethical if done late where a student is left hanging.
Perhaps with more background to your question, the answer would need to change, of course.

Changing advisors during coursework


How does a viscous fluid flow?

Question: In all problem involving viscosity, while applying $f=nA \frac{du}{dz}$  why do we consider velocity of the bottom layer to be zero?
Comment: Technically, the content and the title of your question do not match; your title asks how it flows whereas the content asks how it doesn't flow at the boundaries.
Answer: There is something called the "no slip condition". You can read about it here:
https://www.princeton.edu/~asmits/Bicycle_web/frictionflows.html
Basically, the atomic level interactions between the fluid [that happens to be touching the solid-surface] and the solid-surface are too attractive to allow the solid-surface touching layer of the fluid to have any velocity relative to the solid-surface.
This, by the way, also holds for Couette flow: The top layer of the fluid that is in touch with the top solid-surface [plate] still has zero velocity relative to the plate (this is why the top layer of the fluid has the upper plate's velocity in Couette flow). For this to be applicable the speed of the upper plate can't be too high and you have to be in steady state, as described here:
https://en.wikipedia.org/wiki/Viscosity

How does a viscous fluid flow?


What is the "Heavies" mode in Halo multiplayer?

Question: In the Master Chief Collection, this mode is currently a part of the action sack playlist in at least Reach. I presume that the mode is a variant of the big team battle with a higher amount of vehicles and/or increased vehicle spawns, but can't say for sure. The player health seems identical (Elite slayer has more resistant shields).
Comment: Also it says you get bonus points for "special objectives" and I haven't the slightest clue what those are. My guess is destroying vehicules? Maybe getting kills while in a vehicule?
Comment: @CoqPwner: Interesting, where the "special objectives" is exactly mentioned?
Comment: During loading, you also clearly see the scores reflecting this. People have a higher score than kills. This is in BTB Heavy, not sure about 4v4
Answer: According to my research from Halo Waypoint forum, you are right "Heavies" mode is a variant of BTB Heavy but for action sack (4vs4). So you will play with lots of vehicles as Tanks/Wraiths/Banshees ... and lots of heavy weapons as Sniper rifle/Laser/Rocket...


May arduino hang when current is changing over time?

Question: As in title. I've got quadrocopter where Li-Po is parallely connected to motors as well as to arduino. May current driftage cause arduino hangs ?
Comment: What do you mean by "hang"?
Comment: Main loop freezeout.
Answer: There really isn't any such thing as "Current driftage". If you draw too much current from your battery it will cause the voltage to drop, and if it drops too much, the Arduino will stop working.
If you have high current devices like motors being switched on the same power supply as your Arduino you should add a reservoir capacitor as close to the input of your Arduino as possible. That will even out short term drops and spikes in supply voltage as your motors switch.
If you draw too much current continuously then your supply voltage will drop and stay dropped, and a reservoir capacitor won't help. In that case you need a higher current battery (or separate power supplies for your Arduino and motors.)
Edit: From your question it's pretty clear that you don't understand voltage and current and how they relate. I suggest you read up on the subject.
In short, the amount of current that flows through a component is determined by the voltage divided by the resistance: i = v/r. (Where i = current in amps, v = voltage, and r = resistance in ohms.)
The current that will flow will be limited by the max current that the power supply can provide.
For a non-regulated supply like a battery, the voltage from the supply will drop as you draw more and more current.
For a regulated supply, the supply keeps the voltage constant up to it's maximum current limit.
Comment: I understand voltage and current. I've just been thinking of "how can voltage drops and spikes (current driftage/drifts) affect arduino". Due to parallely connected motors I may experience such things right ?
Answer: May i ask why you don't have a separate battery for the arduino? If it is because of weight, an arduino can run of CR2032 batteries, gives it its own power supply, this should solve the problem.
If you want a battery with more longevity Google "6v 2/3 battery" (2/3 the size of an AA battery), small with loads of voltage for the arduino and with some skilled programming it should last for a flight or two, and the +side, you can get it rechargable.
Comment: I have limited space + its comfortable.
Comment: Throw in 1 or 2 CR2032 they cost less than $1 and they take virtually no space at all, and it is more comfortable than loosing power mid air.


Type of investments to protect value

Question: I live in Argentina where there are a lot of inflation, between 40% and 60% a year in last years, so my question it's what kind of assets should I study to protect value? I'm beginner in investments but as far as I know for this goal I should think in long term and low volatility assets. What do you think about that? Can someone give any advice for where could I start with investments or what approach should I have for this goal?
Comment: Real estate is the standard answer for hedging against inflation.  Maybe REITs (Real Estate Investment Trusts, if they exist in Argentina) are a good idea.
Answer: First of all you should convert your money into gold because that will reduce it from the further decrease and also give you reasonable return.

Type of investments to protect value