Installing Ubuntu 16.04 on SSD+HDD

Question: I have 256GB SSD, 2TB HDD and 16GB RAM, I want to have Ubuntu and my programs on SSD and other files like music, photos, videos, etc. on HDD. I'm new to Ubuntu and want to know how I can install this right? And how I can do this that my ssd don't worn out to quickly? Thanks.
Comment: Personally I don't worry about SSD wearing out "too quickly". I put Windows 10 on 400GB of 512GB SSD and the other 100 GB went for Ubuntu. The 1 TB HDD drive just sits there for now. As Windows games take 60GB after I buy a few, I'll move the ones not being played to the 1 TB drive.
Comment: I tend to make my partitions first; ie. 'try-Ubuntu' and using `gparted` to create my partitions in the sizes I want; then doing my install & selecting 'something else' and have it use the partitions I've created. This will let you put the partitions on any media (hdd/sdd) you like. I also use different sizes (eg. if I wanted 2x20gb I'd create one 19.5 & the other 20.5 & write it down on scrap paper...).  Don't have your swap partition on SDD if worried about wear-out, but with 16gb i'd hope you wouldn't need swap [much] anyway.
Comment: Some more info: https://askubuntu.com/questions/343268/how-to-use-manual-partitioning-during-installation & http://askubuntu.com/questions/461394/how-to-partition-ssdhdd & https://askubuntu.com/questions/343268/how-to-use-manual-partitioning-during-installation & https://askubuntu.com/questions/921778/windows-10-dual-boot-ubuntu-on-ssd-and-data-on-hdd
Answer: If you're comfortable with the terminal, you can change the default locations of the documents and media directories any time after installation with the xdg-user-dirs-update command. Assuming your HDD is mounted as /mnt/bigdrive:
xdg-user-dirs-update --force --set DESKTOP /mnt/bigdrive/Desktop
xdg-user-dirs-update --force --set DOWNLOAD /mnt/bigdrive/Downloads
xdg-user-dirs-update --force --set TEMPLATES /mnt/bigdrive/Templates
xdg-user-dirs-update --force --set PUBLICSHARE /mnt/bigdrive/Public
xdg-user-dirs-update --force --set DOCUMENTS /mnt/bigdrive/Documents
xdg-user-dirs-update --force --set MUSIC /mnt/bigdrive/Music
xdg-user-dirs-update --force --set PICTURES /mnt/bigdrive/Pictures
xdg-user-dirs-update --force --set VIDEOS /mnt/bigdrive/Videos

The --force parameter will create the new directories if you haven't already created them manually.
If you already have contents in those directories, you'll need to move them manually and you'll probably want to delete the original directories in your home directory (or replace them with links to the new directories) to clear the clutter and avoid confusion.
I like to leave DESKTOP on the SSD (in this case, leave out the --set DESKTOP command above) and keep media I'm actively working with there, so you can take advantage of SSD speed while e.g. editing a video.
You can also assign the whole /home directory tree to your HDD during installation, but then it'll slow you down ever so slightly while doing common operations that read/write from/to anywhere under the home directories like $HOME/.config/.

Installing Ubuntu 16.04 on SSD+HDD


How low can a helicopter legally fly over the water with boats below?

Question:
My friend was paddling in a big race in Dana Point, California and she said the helicopter was directly over her taking pictures to sell. It looks to be at no more than fifty feet above sea level (if that!); this flight behavior seems insanely dangerous and/or illegal, but maybe I'm wrong. Anyone have hard facts on this type of flying for photos?
Comment: Might you wish to insert the word "legally" into the title of your question?
Answer: There's no minimum altitude over open water but the pilot must stay at least 500ft away from the boats, per 14 CFR 91.119:

(c) Over other than congested areas. An altitude of 500 feet above
  the surface, except over open water or sparsely populated areas. In
  those cases, the aircraft may not be operated closer than 500 feet to
  any person, vessel, vehicle, or structure.

There's also a catch-all regulation that prohibits endangering other people, 91.13:

(a) Aircraft operations for the purpose of air navigation. No person
  may operate an aircraft in a careless or reckless manner so as to
  endanger the life or property of another.

It's very hard to tell from the photo how far the helicopter is from the boats but if your friend believes it was closer than 500ft, she can report it to the FAA.
Comment: @Trevor Yes, it's possible the F1 guys have an FAA waiver that gives them an exception under specific conditions.
Comment: I have a feeling there is an exemption in there somewhere for special events though. If you ever watch the chopper that buzzes around F1 races they come real close sometimes.
Comment: FAA waivers are common for sporting and "reality" filming.
Comment: F1 is an excellent example - was watching the Italian GP a couple of weeks ago and there were shots from a guy in a man-lift looking _down_ on the helicopter. Of course, Monza, Italy isn't covered by FAA regs, but still...
Answer: The regulation mentioned above is correct (14 CFR 91.119), but it was taken somewhat out of context. In part D, it says:

(d) Helicopters, powered parachutes, and weight-shift-control
  aircraft. If the operation is conducted without hazard to persons or
  property on the surface—
(1) A helicopter may be operated at less than the minimums prescribed
  in paragraph (b) or (c) of this section, provided each person
  operating the helicopter complies with any routes or altitudes
  specifically prescribed for helicopters by the FAA; and
(2) A powered parachute or weight-shift-control aircraft may be
  operated at less than the minimums prescribed in paragraph (c) of this
  section.

What this means in practice for most of us, is that generally speaking we'll stay at 500-1000, depending on where we're flying, but we often practice auto-rotations and inclined landings in areas off airport, so when taking off and landing, we'll be at much lower altitude. If there's fixed wing traffic, as there often is in Chicago, ATC will direct me to fly at lower than 500 (they'll generally ask me to stay below 500 when I fly along a route also used by fixed wing).
As it was explained to me, we're allowed below as long as we're not conducting ourselves with hazards for the people below, and generally it's more or less using reasoning and common sense. So I can stay relatively low to the ground, but if I started trying to fly between buildings here in Chicago, that would be considered unsafe and a violation. On the other hand, we'll practice off airport landings and maneuvers quite close to the ground, but they'll be in relatively isolated areas (fields, hills, etc.). Over the water, flying at an event like in the picture, if it's condoned/expected for you to be there, it wouldn't be considered a hazard. If you were a private pilot that hadn't requesting it beforehand, I'm guessing you'd be hearing from the FAA.


Clustered standard errors and robust standard errors

Question: I was wondering if, when running a regression on panel data, clustered standard errors are already correcting for heteroskedasticity. Actually, I have run such a regression and detected heteroskedasticity. Since I used the pooled OLS model I have to cluster the standard errors anyway. Hence, I was hoping that I can address both issues simultaneously.  Is that right?
Comment: I think so, yes, but you might want to provide more detail on how you're handling the clustering.
Answer: Answering you question: Cluster Robust is also Heteroskedastic Consistent.
I would recommend that you read the A Practitioner's Guide to Cluster-Robust Inference which is a nice piece from Colin Cameron on several aspects of clustered/heteroskedastic robust errors.
Page 20 onward should help you out.
Comment: However, what happens if I correct for heteroscedasticity by means of clustered standard errors, even though there is prove that the initial results are homoscedastic. Is that a severe problem?
Comment: If the errors are homoscedastic, Heteroskedastic consistent errors are biased. Jusha Angrist and Jorn Pischke have a nice discussion around that topic in the book Mostly Harmless Econometrics (Chapter 8)


I read that pulsar 150 have 15 lite. Fuel capacity....but I filled the tank it takes 18 lite...is this possible

Question: Tell me in detail is 18 lite petrol fit in tank of 150 pulsar
Comment: Given the answers posted by others, then the question seems sufficiently clear, does it really need to be on hold?
Answer: I too have pulsar 150 when I did from reserve it was 13 litres. I don't think reserve will be of 5 litres.
May be try one more time in different bunker for reconfirmation.
Comment: Yes, good point are they really selling you full or exact litres - the motorcycle manufacturers are usually very precise with how much the tank holds as most bikes don't have fuel gauges.
Answer: The owners manual (and everything else I've been able to find online) says full fuel capacity is 15 litres and reserve is 3.2 litres. Reserve is included in the full capacity, so you're really getting 11.8 litres until you hit reserve.
Bajaj Pulsar 150 Owners Manual
Comment: Clear and good explanation to the question.


Does anyone know any good resources for working as a sign writer / designer?

Question: I currently work for a small but very busy family sign writing business. This includes 4 family members mum, dad and two adult kids :) there are three extra employees including me. My role is the printing and design management and I do heaps of signage which includes vehicles, flags, billboards, printing and design work which includes logo,business cards and poster design. I would really like to find some good forums websites or a network of people who work in the same industry. I enjoy working in signage and just want to keep expanding my knowledge and skills and be a real asset to help there business :)
Comment: I voted to close this as "too broad". Typically "shopping list" questions, or questions which merely ask others to list things, are not favored on Stack Exchange sites.
Comment: I've made it your question into a Community Wiki since @Scott is correct that this doesn't make a good question. But it does deserve info I think as its such a specific niche.
Answer: www.signs101.com is a great resource and community for any sign related topics, from production, design, and equipment, to installations and just plain good advice.
Signweb is also another forum you should check out as well.


Masjid Al Aqsa was the first qibla, and mentioned in the quran, so why is Medina more holy

Question: I love the prophet more than anyone else, and I know that Medina is very holy and I am not trying to discredit it, and I know that Al Aqsa cannot be more holy than the Kaaba, but why is Medina considered more precious than Al Aqsa. Allah made Al Aqsa the first qibla and mentioned "blessing its surroundings" in the quran. I am trying to learn not to criticise.
Comment: I'm not sure, but I think Muslims prayed facing Aqsa initially in an attempt to build relationships with the Jews.
Answer: Assalamualaikum! The importance of Medina can be derived from the facts given below:

The first mosque of Islam was built over there
The mosque of the Prophet (Sm.) ,i.e. the Masjid al Nababi was also built there
Rasulullah (Sm.) rests in peace there.

The 3rd one is the main reason why Medina is more important than Al-Aqsa and if you want to know the facts why logically also Medinah stands with more importance, jump to this article.
A summary of this article is that the prophet has made Medinah a Holy place, a Haram place for bloodshed, and also he (Sm.) has declared that Dajjal and Plague won't enter Medinah. So, regarding that , we do not see the same to Masjid al Aqsa. and Remember, both Mekka and Medinah are places, while Al-Aqsa is a Mosque. Anyways, people love Medinah as Our Prophet (Sm.) used to love it and due to the fact that it is the Prophet's City.
Regarding to your logic that Masjid al-aqsa has been mentioned itn Al-Quran, Masjid al Quba, the first mosque of Islam situated in Medinah has also been mentioned in the Quran as following:
The virtue of Masjid Qubas is mentioned in the following Quranic verse in Surah Taubah: "…certainly a masjid founded on piety from the very first day is more deserving that you should stand in it…" [9:108]
Jazakallahu Khairun!
Answer: Because of the many supplications of the Prophet Sallallaahualaihiwasallam صلى الله عليه وسلم! He loved Madina and its people that he decided to die there! In a narration in Sahih Muslim, he said: (O Allah makes us love Madina as much as Makkah or even more!)
So it is even permissible to love Madina more than Makkah! It is the place where Islam was established!
Allah knows best


According to Catholicism, can demons force or misguide you into receiving communion?

Question: I was listening to Father Rippergers  online sermon about communion. He said, the demons force to receive  communion even when you have not repented. He also said receiving communion if you have not repented will lead to more sin and that's what the demons want. I had believed that you can take communion only when it's the will of God. The holy ghost will guide you and let you receive communion. And Jesus had said " No one can come to me unless the Father who sent me draws them, and I will raise them up at the last day".
There are many children's who take communion, have they repented? Can demons force or misguide you into receiving communion?
Comment: Would you consider placing this question under the umbrella of catholicism and I might be able to source out a response for you.
Comment: Do not think this is a truth question. Exorcists have spoken about this subject. It will take some time to find a source.
Comment: I've tagged this under catholism.
Answer: According to Catholicism, can demons force or misguide you into receiving communion?
The short answer is: They may influence someone into doing so, but they can not force one to do so.
No one (or demon for that matter) can force someone to commit sin. Sin must be freely done and not done during duress.
That said, the Devil and his satellites can influence man's thoughts in order to tempt him to sin.

The demons gather strategic intelligence as they tempt. They learn by experience, and are good students of fallen human nature. Therefore, they tempt us now in one way, now another, observing all the while until they get some result — or not. We see that Satan himself tempted Jesus three times with three distinct sins: gluttony, avarice, and pride. Like a veteran safe-cracker plying his trade, he keeps feeling us out until he makes us "crack."
That said, demons cannot make us sin. They merely exercise persuasion. For this reason, they can be said to "cause" sin only indirectly.
Besides tempting us to sin, they also prompt us to make errors in judgment that are not sinful in themselves, but could lead others into occasions of sin. For instance, if someone in a position of authority makes an error in judgment, this can adversely affect those dependent on him and cause their downfall. This is one reason we should pray for those in authority, especially the Holy Father and the bishops.
How do demons persuade? They have no access to our intellect or our free will. They simply cannot know our actual thoughts or move our volition. But our bodies, our passions (or emotions), and our internal senses — especially the sense memory and imagination — are all subject to the diabolical power.
As Satan is called not only "the tempter" (Matt. 4:3), but also "a liar and the father thereof" (John 8:44), we know that his malefice includes lying deception. This goes for his fellow demons, too. Given what has been said of their power over the sense memory and imagination, they are capable of presenting images in our brains that we later make into ideas in our minds. From these ideas, we can form judgments that are false and reasonings that are erroneous. Thus does he turn against each other those who should be allies. Thus does he stir up enmities of all sorts. Thus does he bring marriages to ruin. - The Demonic

Thus it is possible for Satan to influence someone into going to receive Holy Communion in the state of mortal sin, but he can not force someone to do it.
If in the state of grace, the last thing that the Devil wants is for such a Catholic to receive the Eucharist since this would be an occasion for that soul to increase in grace before God.
It should be known that if a possessed person received communion, the strength of the Demon is diminished until Our Lord is no longer present in the Eucharist. Satan and his allies abhor Our Lord Jesus Christ.
Comment: Is it right to receive communion, if you haven't repented ?
Comment: No, it is a sin, if in the state of mortal sin.
Answer: No one can force you to sin, including demons, because sin requires free consent of the will.
Addressing "Whether the devil is directly the cause of man's sinning?" (Summa Theologica I-II q. 80 a. 1 co.), St. Thomas Aquinas writes:

Sin is an action: so that a thing can be directly the cause of sin, in the same way as anyone is directly the cause of an action; and this can only happen by moving that action's proper principle to act. Now the proper principle of a sinful action is the will, since every sin is voluntary. Consequently nothing can be directly the cause of sin, except that which can move the will to act.

and ibid. q. 3 "Whether the devil can induce man to sin of necessity?" co.:

The devil, by his own power, unless he be restrained by God, can compel anyone to do an act which, in its genus, is a sin; but he cannot bring about the necessity of sinning.

In other words, he cannot force one to choose to sin. He can, however, make sinning appealing so that one voluntarily chooses to sin.
Answer: We see at Luke 22:3 that Satan  entered Judas Iscariot and prompted him to betray Jesus.
We later see at the Last Supper,  at John 13:26-27 :
"Jesus answered, "It is the one to whom I give this piece of bread when I have dipped it in the dish." So when he had dipped the piece of bread, he gave it to Judas son of Simon Iscariot.   After he received the piece of bread, Satan entered into him."
In sum, Satan can tempt one to sin, whether one has just received the Holy Communion or not.
Strange enough, it was Judas Iscariot who first received Holy Communion , and it was not Jesus who dwelt in him !
Comment: That's a good point, but I think Judas actually left right before the Bread of Life discourse and therefore missed communion.
Comment: We can't know, because John does not narrate the Institution of the Eucharist .


Supported solidity compiler by truffle

Question: Hello I'm working on ethereum project using truffle framework, I want to know what is the latest solidity compiler version supported by truffle.
Answer:
You may specify...

any solc-js version (using semver) listed at solc-bin. Specify the one you want and Truffle will get it for you.
"native" to use a natively compiled solc binary (you'll need to install this yourself, links to help below).
a dockerized solc tag from one of images published here.
a path to a locally available solc
"pragma" to have Truffle autodetect solc versions from your source files. This can be used to compile using multiple versions of solc.
a solc-js parser for faster docker and native compilations

Source: https://trufflesuite.com/docs/truffle/reference/configuration#solc
Answer: Any of them, but you need to change the config file for Truffle, Truffle-config.js. If you want to use 0.8.7, you must change (or add) the following
<code>compilers: {
  solc: {
    version: "0.8.7"
  }
}
</code>
next time you compile the contract, you will see that Truffle will use this version to compile the code.

Supported solidity compiler by truffle


Stochastic methods for solving very high-dimensional PDE

Question: I am looking for stochastic methods for solving a very high-dimensional PDE (with one time dimension and very large number of spatial dimensions), which would reduce it to a lower-dimensional problem, probably at the cost of carrying out a Monte Carlo simulation. Any pointers?
Answer: It seems to me this question "has not received enough attention" because of the conflation of two issues: dimensional reduction of a high-dimensional PDE and stochastic (Monte Carlo) integration of the PDE.
The socalled "curse of dimensionality" refers to the fact that the computational time required for a non-stochastic solution of a PDE grows exponentially with the number of dimensions (each dimension needs to be discretized, say with $N$ points, so the total number of points in $d$ dimensions is $N^d$). Dimensional reduction is then imperative, and one method to achieve that is principal component analysis.
The computational time for a solution of a PDE by Monte Carlo integration grows only linearly with dimension, so dimensional reduction is not needed. The accuracy of this approach is low, and this is why one tries to avoid resorting to a Monte Carlo method.
The two approaches to the solution of a high-dimensional PDE, dimensional reduction by principal component analysis and Monte Carlo integration, are compared in these lecture notes.

Upon some more search, I found one dimensional-reduction scheme with a stochastic component. It goes by the acronym RS-HDMR = Random-Sampling-High-Dimensional-Modeling-Representation and is described here. (The HDMR Wikipedia page could use some expansion...)
Comment: I added one such approach, RS-HDMR, that seems to have the generality you are looking for.
Comment: I am aware of the link between Monte Carlo and PDEs in the Black-Scholes theory. I was looking for general stochastic, dimensionality-reducing approaches one could apply to an arbitrary linear PDE.
Answer: It seems that you are interested in a "tractability problem", that is, a problem which asks whether the solution of a very high-dimensional problem can be efficiently approximated. As far as I know some research has been done in this direction, but much more for numerical integration than for PDEs. It may make sense to look for QMC methods (Quasi-Monte Carlo methods) for solving such problems (that means, using cleverly chosen deterministic points instead of random points). Look for example at the following: https://math.unibas.ch/uploads/x4epublication/53518/Preprint_1328.pdf


SP initiated url gives a blank page when added to intranet zone

Question: I have RP added to ADFS 3.0 for SSO. This is SP initiated sign-on. Whenver I add the sp initiated url to intranet zone it gives me a blank page from domain joined machines. However, it works good when I remove it from intranet zone and add it to trusted site. It doesn't promt for password and gets me directly in to the site. That is what exactly I want, user should not be prompted for password in intranet. But I am scared if I do not add it to the intranet zone, after a period of time it will start prompting me for password. I want a seamless sso in intranet.
Answer: It's the adfs host name that needs to be in intranet to do windows integrated authentication; not the sp URL. This assumes you have configured intranet zone in internet explorer to do automatic sign in.


Downgrade from 17.10 to 16.04LTS

Question: How do I downgrade from 17.10 to 16.04LTS since I can't be upgraded to 18.04 due to my 32-bit laptop?
Comment: What laptop / processor do you have?
Comment: Are you sure that you "can't be upgraded to 18.04 due to 32-bit laptop"? My understanding is that Canonical Ltd. has stopped providing 32-bit **iso images** since Ubuntu 17.10, but they still support upgrading to the next release. How are you running 17.10 in the first place? There is no 32-bit iso for 17.10 too. Try `do-release-upgrade` for a few days. Usually release upgrade path is not opened immediately after a new release.
Comment: Bought the 32-bit laptop (Panasonic Toughbook Model CF-73) with 16.10, upgraded to 17.04, then 17.10 last Fall - figuring I'd FINALLY get an LTS on it with 18.04 and settle down - then told I can't upgrade my 32-bit to 18.04...
Answer: Ubuntu Version 18.04 LTS 32bit is supported
You can upgrade to Ubuntu 18.04 with the do-release-upgrade.
I upgraded a 16.04 LTS to 18.04 using this command:
$ sudo do-release-upgrade -d

As Pomsky suggested, it's the 32bit iso that is not provided by Canonical.  The actual supported files are in the repository.
You will have to wait a few days or use the -d option and get it immediately.
This is my installation mode:
$ file /lib/systemd/systemd
/lib/systemd/systemd: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=b6190e3094045363f5cca4d20db62b82aed17e4f, stripped

Comment: I've linked this Q&A from this question just now: https://askubuntu.com/questions/1066360/upgrade-to-18-04-from-16-04-32-bits/1069582#1069582
Answer: You need to backup all your important data into a external drive or cloud service, then you need to grab a 16.04 install disk, boot of it and then reinstall. You could try changing the repository info to 16.04 instead of 17.10 and then downgrading all the packages manually but that takes a long time. Plus there's the added risk of replacing a vital componet to the os when its in use and screwing your whole computer up. Don't take the downgrading way unless you're feeling brave.
Comment: While having backups is always good, it's not a requirement for preserving it.  Installing Ubuntu will not touch personal data unless the "format" option is specified for the partition.  If the format option isn't checked (which isn't by default) the install would only delete the directory that has system files.  No user data is in any of those directories.  You might consider adding some of these details to your answer.
Comment: Not worried about 'all my data', only want to keep all the applications and settings I've installed for 18 months and not have to hunt down, reinstall, hope I get it right without another big struggle,... looks like I can't actually downgrade, only trash and install older version.

Downgrade from 17.10 to 16.04LTS


Z Steppers just hum, vibrate and don't move at all

Question: As I said in the title there is some issue with my z axis steppers. They will make a humming sound and vibrate a little but won't actually spin. I'm fairly sure this is an issue with the firmware (but I might be totally wrong) since they turn when the wires are switched with the ones for the Y axis and swapping the driver board for a spare had no impact on them. Any help would be appreciated. I am using RAMPs 1.4 and marlin firmware.
Comment: It sounds like a bad connection on one of the wires, or switched wires. Try substituting a different cable.
Comment: try to switch 2 the wires; don't forget to turn off your shield.
Comment: sounds like stepper current issue
Answer: Try connecting Y-motor to your Z ports. If Y-motor will behave like Z-motors, then there's problem with your Z ports, be it hardware or software. I'm not a RAMPS user, but have heard that there is voltage regulator for every motor port. Sounds like your motors may be underpowered.
Comment: By "voltage regulator" you probably meant to refer to the potentiometer that lets you adjust the current limit.
Comment: @TomvanderZanden, could have been any. But even better this way, potentiometer is more newbie-friendly than programmable DC regulator of some sort.
Answer: Let's tick off the factors you have already checked for.
It isn't the driver board, because the Z driver board drives the Y motors.  It could be the Z motor itself (or the cable), which you could test by plugging the Z motor into the Y driver board.  If only one of the two motor coils were being energized, it would cause vibration but generate no motion.
@ZuOverture suggests it could be the drive current setting on the motor driver board.  Possible, especially if the Z motor requires more current.
It is also possible that the output pin from the Arduino Mega board may be bad, or not connecting well.
To investigate, find the step and direction inputs to the stepper driver board.  Use a voltmeter, logic probe, or oscilloscope to verify the signal levels.  If the signals don't jiggle when moving the motor, then follow the wires and check at each point along the way.
You could also plug in a replacement Arduino, which you have programmed with the firmware, and check if that works.
If the Arduino pin is bad, you can keep it in your junk box for future projects.
Looking at the firmware angle, one would check the speed and acceleration settings for the Z axis.  When in doubt, try slower speed and lower acceleration.  Z-axis performance doesn't make much difference in the printing speed.
Answer: Hello it's seems to be the voltage regutaltor on the steppers drivers for the nema motors. Check to adjust the voltage with a multimeter connecting the red pin from the multimeter on the voltage regulator on the driver and the black pin on the GND pin on the ramps 12v connector.
Also make sure that you have connected the jumpers to setup the microstep resolution:
Full step,Half step,Quarter step,Eighth step,Sixteenth step
Best regards.
Rodrigo


Windows installed from flash drive won't boot when flash drive is NOT inserted

Question: I installed Win 10 from flash drive on C drive, and it works fine as long as there's flash drive inserted on boot. If there is none, the system won't load. I am POSITIVE that the system wasn't installed on the flash drive. Somebody suggested that MBR could be located on flash drive, but without any advice how to move it to hdd.
Is there a relatively easy way to fix it? I have live USB drive with Linux if that helps.
Answer: This is not a unheard of issue.  Unfortunately, Windows 10 doesnt do a good enough job checking if the options the users picks during installation are really what they want.  However, this is not a hard problem to fix.  Simply google "windows 10 boot repair" and you will find countless articles on how to fix this.  This article is well written.  Just skip down to the section called "Fix Windows 10 Winload.exe Using the Command Prompt."


Connectedness in Zariski topology

Question: How to show that, for example, the Zariski topology of a cyclic group ring (thus $\mathbb{Z}[\rho]/(\rho^n-1)$) is connected?
Does this still hold for an Abelian group?
Or in general, how do we determine the connected components for such spaces? (Is it by searching its smallest prime ideals? If so, can you give an explicit example?)
Note that it's not a domain, which makes it not necessarily an irreducible space.
Many thanks.
[edit: it seems that I only need to show there's no idempotent element in this group ring, is that right?]
Answer: For an Noetherian ring $R$, $X=\mathrm{spec}(R)$ is connected if and only if the only idempotent elements of $R$ are $0,1$, or equivalently, $R$ is not of the form $R_1\times R_2$ for two subring $R_1,R_2$.
For if $X$ is disconneted, it can be written as the disjoint union of two proper closed subspaces  defined by ideal $I_1, I_2$ respectively. Since $V(I_1)\cup V(I_2)= X$, We must have $I_1I_2$ is an ideal contained in the nilradical of $R$. Replacing $I_i$ by a power of $I_i$, we may assume that $I_1I_2=0$ (note that we use the Noetherian assumption here). On the other hand, $V(I_1)\cap V(I_2)=\emptyset$, so we get $I_1+I_2=R$. In particular, we get $I_1=I_1(I_1+I_2)=I_1^2$.  Since $I_1$ is finitely generated, it follows from Cayley-Hamilton that one elements $e_1\in I_1$ acts as identity on $I_1$.  In particular $e_1\cdot e_1=e_1$. We take $e_2=1-e_1$.  Let $R_1=Re_1, R_2=Re_2$, then $R$ can be written as the direct product of the two subrings.
But in general, I am afraid that I don't know ways to find idempotents except the add-hoc methods. For example, in your case, if $n=p^r$ is a prime power, then we know the fiber over $p$ is connectd (because it is spec of $\mathbb{F}_p[x]/((x-1)^q)$). If $X$ is disconnected, then we must have $e_1 \equiv 0 \mod p$ and $e_2 \equiv 1 \mod p$. But $e_1^2=e_1$, so $e_1 \equiv 0 \mod p^m$ for all $m>0$, which leads to a contradiction. But I am not sure how one generalize this to the case $n$ is arbitrary.
Edit: I see, you already got the idempotent part.
Comment: The Noetherian hypothesis can be removed. If X is disconnected, as you say there are $e_1\in I_1$ and $e_2\in I_2$ such as $e_1+e_2=1$. And also there is a number $0<n$ such as $(e_1 e_2)^n=0$. Then using the binomial formula you get $x, y\in R$ such as $1=(e_1+e_2)^{2n}=e_1^n x+e_2^n y$. The last 2 terms are idempotent.
Answer: Here's the story for arbitrary $n.$ Let $n\in \mathbb{Z}_{n>1}$ and consider the polynomial $f(X) = X^n - 1.$ Then $f$ factors in $\mathbb{Z}[X]$ as the product of cyclotomic polynomials $\displaystyle\prod_{d|n} \Phi_d.$ As $\mathbb{Z}[X]$ is UFD, it follows that the minimal primes of $\mathbb{Z}[X]$ containing $(f)$ are exactly the ideals $(\Phi_d)$ where $d|n.$ Let $d>1$ be a fixed divisor of $n$ and $p$ be a prime dividing $d.$ Write $d = pd_0.$
We claim $V(\Phi_d)\cap V(\Phi_{d_0}) \neq \emptyset.$ Assume this is not the case. Then $(\Phi_d,\Phi_{d_0}) = \mathbb{Z}[X],$ so there exist $q_1,q_2 \in \mathbb Z[X]$ such that
$$q_1(X)\Phi_d(X) + q_2(X)\Phi_{d_0}(X) = 1.$$
Choose a primitive $d$-th of unity $\zeta_d$ in $\overline{\mathbb{Q}}$ and consider $\mathbb{Z}[\zeta_d] = \mathcal{O}_{\mathbb{Q}(\zeta_d)}.$ Then $\zeta_{d_0} := \zeta_{d}^p$ is a primitive $d_0$-th root of unity. Choose a prime $\mathfrak{p}$ of $\mathbb{Z}[\zeta_d]$ dividing $(p)$. Then $\zeta_d \equiv \zeta_{d_0} \mod \mathfrak{p}.$ It follows
$$1 = q_1(\zeta_d)\Phi_d(\zeta_d) + q_2(\zeta_d)\Phi_{d_0}(\zeta_d) \in \mathfrak{p},$$
a contradiction. We conclude $V(\Phi_d)\cap V(\Phi_{d_0}) \neq \emptyset.$
We now consider the spectrum of $R := \mathbb{Z}[X]/f.$ Let $\pi:\mathbb{Z}[X] \rightarrow R$ be the quotient map and $U_1$ be the connected component of $\pi(\Phi_n)$ in $\mathbf{Spec} R.$ Then, as $U_1$ is closed $V(\pi((\Phi_n))) = \pi(V(\Phi_n)) \subset U_1.$ Let $q$ be a prime divisor of $n.$ Then as $V(\Phi_n) \cap V(\phi_{n/q}) \neq \emptyset,$ so too must $V(\pi(\Phi_n)) \cap V(\pi(\phi_{n/q})) \neq \emptyset.$ It follows $\pi(\Phi_{n/p})$ is contained in $U_1.$ Following in this way inductively we obtain that $U_1$ contains $\pi(\Phi_d)$ for each $d|n.$ But these are precisely the minimal prime ideals of $R.$ Hence we conclude,
$$\mathbf{Spec} R \supset U_1 \supset \displaystyle\bigcup_{d|n} V(\pi(\Phi_d))  = \mathbf{Spec} R$$
and $\mathbf{Spec} R$ is connected.
Comment: Take $d=6$ and $p=2$, then $\zeta_6-\zeta_6^2=\zeta_6(1-\zeta_6)$ is a unit. But you are still right in the sense that we will have $$0=\Phi_{d_0}(\zeta_{d_0})=\Phi_{d_0}(\zeta_{d}^p)\equiv \Phi_{d_0}(\zeta_{d})^p \pmod{\mathfrak{p}},$$ hence $\Phi_{d_0}(\zeta_{d}) \equiv 0 \pmod{\mathfrak{p}}$.  Very nice answer, by the way.

Connectedness in Zariski topology


Study the equivalence of these norms

Question: I have two Hilbert spaces $H_1$ and $H_2$ and I consider a set of functions $f$ which decompose as $f=g+h$ with $g\in H_1$ and $h\in H_2$. I know that this decomposition is unique.
So I define the following norm
$$\Vert f\Vert=(\Vert g\Vert_{H_1}^2+\Vert h\Vert_{H_2}^2)^{\frac{1}{2}}$$
Is this equivalent to
$$|||f|||=\Vert g\Vert_{H_1}+\Vert h\Vert_{H_2}$$?
I've followed this reasoning:
from sublinearity of square root I have
 $$\Vert f\Vert\leq|||f|||$$;
for the other direction I observe that
$$(\Vert g\Vert_{H_1}+\Vert h\Vert_{H_2})^2\leq 2(\Vert g\Vert_{H_1}^2+\Vert h\Vert_{H_2}^2)=2\Vert f\Vert^2$$
And so
 $$\Vert f\Vert\leq|||f|||\leq\sqrt{2}\Vert f\Vert$$
Is it right?
Answer: Your calculation should be right - it is just the equivalence of the $1$-norm and the $2$-norm on $\mathbb R^2$.

Study the equivalence of these norms


How to Share One Time Pad?

Question: Supposing I wanted to send a one-time pad to a friend. What would be a good way to do that, supposing that it could be intercepted? At first blush, encrypting it would seem safe, because the encryption would seem impossible to crack, given that what it encodes is random (result of unsuccessful decryption is not obviously indistinguishable from successful deception). Yet perhaps there is still a risk is if the encrypted one time pad and a message encoded with it were intercepted.
Comment: What is your motivation for sending a one-time pad to a friend vs. something like an AES key? If the answer is "protection against computationally-unbounded adversaries", sending it over a network can't work (especially since such an adversary could man-in-the-middle you).
Answer: The strength of the scheme cannot be higher than its weakest element. Using OTP can give an impression of unbreakable strength, but actually the whole strength is the same as the strength of the encryption method used to share OTP keystream (AES?). Thus, the usage of OTP in such a scheme gives not more security than using normal encryption.
To your question How to share... ? For instance, you could deliver the OTP keystream to your friend in person, or your friend picks it up in person.

How to Share One Time Pad?


LineageOS Recovery command line interface?

Question: Is there an adb shell command line interface for LineageOS recovery? Alternatively, which adb commands will work when booted into lineage recovery? I want to factory reset my device as part of an install script running on my desktop, and I can't find any documentation about which commands (if any) are supported. The only command I can find is a fastboot command; fastboot erase <partition>, however I would prefer to do it from recovery. My old device had TWRP recovery and that did have a command line interface which could be used from a shell running on the device.
Comment: is adb shell root?
Comment: @alecxs It can be yes!
Answer: you can always use core utils
find /dev/block -iname userdata
blkid /dev/block/bootdevice/by-name/userdata
mkf2fs /dev/block/bootdevice/by-name/userdata

mkf2fs is for f2fs
mke2fs is for ext4


'Between the lines' or 'read between the lines'

Question: Do there exist any circumstances where any verb other than read is used with between the lines? That is, is between the lines an independent and complete idiom, or is it incomplete and meaningless without read?
Answer: The phrase "read between the lines" is a set phrase, with a literal and metaphoric connotation. You can use it to refer to an assessment of a work in print (literal) or use it to mean the act of examining the subtext of a strategy, a speech, etc.
You very well could say, "When we attended the talk, we were listening between the lines," but this would be a nonce coinage, playing off the standard version with "read." Same with "look," "feel," etc.
Answer: One alternative - fall between the lines?
Comment: I've got to upvote this one because it's the only answer that meaningfully addresses OP's request, and doesn't just bang on about *read between the lines* which he already knows. Just to back you up, [here's one](http://books.google.co.uk/books?id=7Y8bAQAAMAAJ&q=%22fall+between+the+lines%22&dq=%22fall+between+the+lines%22&hl=en&sa=X&ei=xbcTT_2mFYnZ8AOIw7GABA&redir_esc=y) about a *department's activities that fall between the lines of the job descriptions*.
Answer: It can be used with other verbs with a meaning related to "read", but "read between the lines" is the most common. Even in extended uses there is reading or writing (or at least interpretation of some kind) happening somewhere. For example:

She read that section again. Was he trying to say something between the lines? Hinting about Sam?

from the short story Of One Mind by Shane Tourtellotte.
This is from an article The Future of Medieval Church History by John Van Engen (Church History 71(3):492-522, September 2002):

Still, between the lines it discloses a world filled with spiritual forces and human paradoxes

Here "it" is a story from the Dialogues of Gregory the Great, so the phrase is still being used in the context of reading, although not with the verb "read".
Answer: If used as an idiom, then the full phrase is "read between the lines". Of course the phrase "between the lines" could always be used literally as opposed to figuratively, but it wouldn't have the same meaning.
It's such a well-known idiom that shortening it to "between the lines" would generally be understood, even without any specific reference to reading.
Answer: But could I say:
This woman likes to tell her stories, but at the same time keeps a lot between the lines.
Comment: Welcome to EL&U. Do you have an example of this being used in a book or mainstream English language publication?


Vlocity (Communications Cloud): set product attribute programmaticaly from Apex

Question: Is there a way to properly set an attribute value on an object in Communications cloud? Assume we've got an attribute called 'Color' on the Product2 object.
As for now, I only see the option to set the JSON string value directly to the vlocity_cmt__JSONAttribute__c field, but this doesn't seem right as there are some encoded values in the JSON which I can't find the source of.
Comment: Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
Answer: In Vlocity, the attribute values linked to any object are stored as Attribute Assignment records. Whenever we link a certain attribute to some object, behind the scenes an Attribute Assignment record is created. Here's a brief overview of some of the significant fields on Attribute Assignment object.

NOTE : API names mentioned below are with respect to Vlocity CMT
package

Attribute : ID of the Vlocity Attribute assigned to the parent object. API Name of this field is vlocity_cmt__AttributeId__c. This is a Lookup field.
Assigned To Object Id : ID of the parent object to which the attribute is assigned. API Name of this field is vlocity_cmt__ObjectId__c. This is a Text field.
Assigned To Object Name : Type of sObject to which this attribute is assigned. API Name of this field is vlocity_cmt__ObjectType__c. This is a Text field.
Value : Value of this attribute. For example, attribute strength (0–5), or a text value "Jimmy". API Name of this field is vlocity_cmt__Value__c. This is Text field.
Value Data Type : Data type of this attribute such as text, number, percent or checkbox. Overrides the Value Type field on the assigned Vlocity Attribute. API Name of this field is vlocity_cmt__ValueDataType__c. This is a Picklist field.
Following is a code snippet where I am updating Attribute Assignment records for a Product record having record Id : 01t5i0000072GeQAAU in my trial org.
<code>//Fetching the Attribute Assignment records using Object Id
List<vlocity_cmt__AttributeAssignment__c> assignmentList = [SELECT Id FROM vlocity_cmt__AttributeAssignment__c WHERE vlocity_cmt__ObjectId__c = '01t5i0000072GeQAAU'];

//Iterating over Attribute Assignment records
for(vlocity_cmt__AttributeAssignment__c assignment: assignmentList){

//Updating attribute assignment value
assignment.vlocity_cmt__Value__c = 'New Value';

//Updating attribute assignment data type
assignment.vlocity_cmt__ValueDataType__c = 'Text';

}

//Updating Attribute Assignment records
update assignmentList;
</code>
For further explanation on Attribute Assignment and related objects, you can refer the following link :
https://medium.com/@rawatswapnil911/understanding-the-vlocity-attribute-data-model-743256dc27f4


Supports in 3d printing

Question: Do astronauts print 3D in space with supports? They are needed only because of gravity, which - on a space station - obviously is not a problem.
Comment: People use "in space" to mean several different things.  In this case, by "in space", I assume you mean "in free-fall", as opposed to "in a vacuum", or "unshielded from solar radiation", or "not on Earth", or ... .
Comment: One of the more interesting aspects to consider would be the *cooling* of thermally deposited prints (FDM, etc).  The general lack of convection may actually make things better, but will probably require some changes in strategy particularly fan algorithms.
Answer: Supports are not needed "just" because of gravity. They hold pieces in exact position relative to the "bed" (and so relative to the coordinate system).
With most printers the model moves during print in at least one position, whether Y or Z, and if you just suspended some pieces in midair when they are not connected to the main body during print, they would just stay in space relative to the printer main body/station, so they would effectively move against the rest of the print and ruin your day.
On the other hand "suspending" layers without any support would probably not be possible anyway, because they would stick to your nozzle (for FDM, but imho most other technologies have some similar problem).
Comment: I think this is true for supports generated for supporting elements because the connection to the main body is above the lowest point of the element, meaning that it would be floating in mid air as you say, but it probably would eliminate the need to support large overhangs.
Comment: *"if you just suspended some pieces in midair when they are not connected to the main body during print, they would just stay in space relative to the printer main body/station"* I suspect you'd find the extruded material would be pulled along after the nozzle. Viscosity effects overcome gravity here on Earth; material extruded in mid-air *sometimes* falls to the bed, but often just bundles up on the nozzle. In space I'd expect it to do so even more readily. Supports are there to give something other than the nozzle for the material to stick to as much as they are to actually hold it up.
Comment: @anaximander I hoped I covered that with the last sentence but maybe it is not understandable?
Comment: @JamesTrotter yes, the support requirements will be different, but imho not that much. Bridges do not need supporting even now, with zero-g they would just not sag at all. Overhangs can even on Earth actually curl up and supports are sometimes needed to keep them down in my experience.
Comment: I feel like if you went slow enough with sufficient cooling, you could do a 90 degree bend on an overhang in space which would have a significantly higher change of failure under earths gravity... but thats a very specific problem.
Answer: I have no links to validate this answer, but with a few years of 3D printing behind me, I can attest to the effect of gravity on 3D printing.
Micro-gravity would be a boon for earth-bound 3D printing enthusiasts. There would be no droop to the filament when bridging (spanning open areas) and no fallen models without support. The construction of each layer would be dependent on the bond to the previous layer which is how it's done on the planet, but there would be no outside force (is gravity an outside force?) causing the new layer to fall. There would be no fall, so to speak, because the entire model being printed is falling around the earth at the same rate.
There are 3D printers described as five-axis printers which rotate the model in three-space to direct the filament "downward" respective to the desired placement, but it's not really artificial gravity.
Zero-G would enable some creativity that is unavailable to mere mortals. Loops of filament could be extruded without sag, allowing for intricate latticework and rather stunning artistic creation.
Comment: This doesn't seem to be an answer @fred_dot_u.
Comment: Upvoted for the bridging realization - performance there would indeed drastically improve.  However, *curves* and *verticies* in free space will not work any more than they would in a terrestrial case where bed adhesion is lacking.
Comment: I can't help but wonder though, in the case of FDM printing, would it actually work as well as you're suggesting, or would the adherence of the filament to the nozzle cause the moving nozzle to impart momentum to the filament, making it move in other (unwanted) directions?

Supports in 3d printing


ACRU4 model run error: climate file -> "Error running display and data rules"

Question: ACRU model was running fine and producing output.
After a few runs and parameter changes, the model returns this error message
Not sure what went wrong or changed.
Does anyone know what this means or how to resolve the problem?
Answer: It could be one of two issues:
Sometimes & likely: You've run out of space on your computer (check your local drive for space)
Often & very likely: There is data in the climate file which is in the wrong place or has the wrong formatting (the solution is to recheck your climate files and run through it line by line for anything that is out of place, it's easy to miss this in between several runs and updates to a climate file)


How can I transfer tether(USDT) using omni JSON RPC API?

Question: I looked for the information but I couldn't find that. It seemed to be done as I always do for Bitcoin though.
Any idea?
Answer: So for Omni layer token you do this omni_send
https://github.com/OmniLayer/omnicore/blob/master/src/omnicore/doc/rpc-api.md#omni_send
This is what you need (at least on Kraken and Bittrex USDT is Omnilayer token). To send Omnilayer transaction you need to have some BTC on the same address for transaction fee. And you also need to know USDT propertyId which is 31 (https://omniexplorer.info/asset/31)
Just in case:
For ETH token you do eth_sendTransaction(different methods are possible like eth_sendRawTransaction) https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sendtransaction. You need to know contract address of the token and it is your parameter to, from is normal address from here is the funny part - token transaction is defined in data. Lets take an example https://etherscan.io/tx/0x6fcf7dc3f6bc2b7e8a9e6b13689d042e659b2d016a3bdf7beffd033ab9b6db1e
this is 2.55 BNB(contract address 0xB8c77482e45F1F44dE1745F52C74426C631bDD52,  parameter to) token transfer(method name encoded in data as first 10 digits 0xa9059cbb) from 0x0861d1b074eb2489dd7878a5d6d869db5896a5f0 (parameter from) to 0x4283f315788b09a357ca83b8134cd48bde8b556f (middle part of data with some padding 0000000000000000000000004283f315788b09a357ca83b8134cd48bde8b556f). Last part of data is token amount in wei. BNB has 18 decimal places and the best way to explain that IMHO is this python assertion:

assert int('0x00000000000000000000000000000000000000000000000023803234a2f38c00', 16) * 1e-18 == 2.55809979

Answer: USDT is also an ERC20 contract in Ethereum mainnet. You need to use one of Ethereum Wallet accepting RPC calls (Geth, Parity, etc.). Then find contract address (check Etherscan). Then install contract to your wallet and manage your transaction.
Comment: I saw that it was on Omni layers on their website though .
Comment: Tether is also on the omni layer (it was originally only here, ERC20 is a new addition): https://www.omniexplorer.info/address/3MbYQMMmSkC3AgWkj9FMo5LsPTW1zBTwXL
Comment: Ohh.. My bad. Ignore my answer then.


Cable head is too small

Question: when I came to change the shifting (gear) cable on my claude butler bike I found that the original cable has a slightly bigger head(nipple) than the replacement cables I have-3.9mm compared to 3.5mm and consequently will not work-wtf
The mech is shimano v brake
Comment: You have Campagnolo compatible cables. They have slightly smaller heads. How does it not work? Does the smaller head slip through?
Comment: The ones I have are the same as those that are widely available-its the original one that is slightly bigger.Yes it slips out and wont hook on
Comment: In my opinion it makes a lot of sense to make generic cables compatible with all shifters out there. Looks like Shimano figured out a way to make their shifters non-compatible with third party cables then.
Answer: Sounds to me like you've got Campagnolo-sized shifter ends.  The difference is subtle but definite.
Left is Shimano, Right is Campagnolo.
Not sure how you're measuring, using a ruler might explain the difference. The common-quoted diameters are
<code>Shimano shifter end barrel diameter: 0.173" (4.39 mm)
Campag shifter end barrel diameter:  0.159" (4.04 mm)
</code>
Generally speaking, campagnolo stuff is more expensive because it is less common, because it is more expensive (loop!)  These shouldn't cost more than a couple of dollars each.

Cable head is too small


Why are Wifi Calling and iPhone Cellular Calls Mutually Exclusive?

Question: I tried enabling "iPhone cellular calls" on my iPhone 5S, and the phone informed me that Wifi calling must be disabled to enable this feature. So it seems that the two features are not compatible with one another. Is this iPhone 5S specific? This is quite disappointing as I was hoping to have both enabled (cell service in my house isn't the best). It would be nice to know why they're mutually exclusive.
Comment: Where are you seeing the "iPhone cellular calls" setting? I have a feeling it is in reference to Handoff, and in that case, yes they would be mutually exclusive, because they are two different ways of doing the same thing.
Comment: @tubedogg The setting is located under FaceTime
Answer: In the past, the modem software for a specific carrier was responsible for that prompt as their networks weren't able to re-reount the calls on the fly. (i.e. your carrier or carrier settings needing an update was the original issue)
I believe that window of limitation is resolved for all devices and all carriers. If you get this error in 2017, I would work with Apple support to make sure your iOS is updated and then work with carrier support to make sure your phone account is set up for seamless switch between carrier and wifi calling.
Answer: The iPhone cellular calls setting allows you to have other devices signed into your Apple ID use your iPhone's cell connection when they are nearby and on the same WiFi network as your iPhone. If you don't have strong cell service at the house, it's would be the opposite of useful. WiFi calling is the feature to leave enabled.
Edit: I realized the question was why are they mutually exclusive. My guess is it would cause issues if you tried to use another device to make a call from your iPhone, but your iPhone was in turn using WiFi calling.


Require local Apache directive not working on AWS EC2 instance

Question: I have an Apache 2.4 VirtualHost on an AWS EC2 instance with the following config:
<Directory /srv/www/example.org>
    Require ip [REDACTED] # Office IP
    Require local
</Directory>

When I make a request from the redacted external office IP address it works fine, but when I make a request from the EC2 instance I get a 401 Unauthorized error. I tried replacing Require local with Require ip 127.0.0.1 to no avail.
The only way I am able to make requests from the local machine is to add its external IP address e.g Require ip 18.104.22.168.
I had a look at the access log and all requests made from the local machine are logged as having come from the external IP address rather than 127.0.0.1.
The /etc/resolv.conf file looks like this:
options timeout:2 attempts:5
; generated by /usr/sbin/dhclient-script
search eu-west-2.compute.internal
nameserver 172.31.0.2

Could this be happening because the IP/hostname is being resolved externally by another AWS service?
Can I change any server config so that Apache sees requests from the EC2 instance as being local, so I can use the Require local directive?
Answer: The IP address you see in the logs is likely the internal IP address of the ec2 machine.
As an alternative, could you change your require line to use hostname localhost. This should be correctly defined in /etc/hostname
Comment: Thanks for your answer. The IP address in the logs is actually the external, public IP address of the instance. I changed the require line to `Require host localhost` but still got the 401 error.


How can I find out what is changing my wireless encryption from AES to TKIP automatically?

Question: I have a wireless connection using WPA2-Personal as the security type, and I've set the Encryption type to TKIP. However, without my intervention, the encryption type will change from TKIP to AES, and I have no clue what is causing this. When the encryption type does change, Windows takes forever to establish a socket connection, so it's obviously very annoying to have to change the encryption type so often back to TKIP. Is there some logged activity that will show me what's changing the encryption type?
Comment: Sounds like your router's configuration is being reset.  Are you sure you save then apply the changes.  Have you tried to update the router's firmware to see if the problem goes away.
Comment: How are you detecting that the encryption has been changing? In the UI of the router or in what the client (windows) reports when you connect?
Comment: @ScottChamberlain I'm noticing this error occurring on the Windows wireless connection client
Answer: For most intents and purposes, WPA2 is AES (AES-CCMP). WPA was TKIP, but WPA2 is AES. The other differences between WPA and WPA2 are all quite minor in comparison.
Pure WPA2 is AES only, but the WPA2 spec does allow for an optional "WPA2 mixed mode", where AES is of course available and preferred, but TKIP is available for legacy devices (mostly old 802.11b devices from before 2003, or a few lame 802.11a or maybe 802.11g devices from 2002-2003) that support TKIP but not AES. Even the earliest 802.11g chipsets from 2003 contained hardware support for AES, so keeping TKIP enabled in any way is mostly for history buffs who still have decade-old devices on their networks.
If your AP (Wi-Fi router) supports WPA2, and your client supports WPA2, you should use WPA2 (AES-CCMP) in both places. It doesn't make sense to configure a client for WPA2 and then insist it use the old troublesome TKIP encryption from WPA.
Also note that 802.11n requires AES-CCMP encryption if you're going to use encryption at all. Most TKIP and WEP implementations can't keep up with the data rates of 802.11n, so the IEEE decided to require AES encryption for 802.11n networks that require encryption. So that's another possibility; if you're setting WPA2 on your client, and still trying for some reason to insist on troublesome TKIP, but then you're trying to associate to an 802.11n-capable network, it may be that your software or hardware is being smart on your behalf and upgrading you to AES instead of downgrading your data rates to A/B/G rates instead of N rates.


How to integrate TinyMCE with Sharepoint Online/SharePoint Designer

Question: Rich text fields aren't compatible with Chrome or Firefox and so I was trying to find an alternative solution to add formatting that will work with any browser. I've come across TinyMCE as a potential option but the instructions I can find apply to SharePoint 2007 and we use SharePoint Online and SharePoint Designer 2013. I've contacted Microsoft and their suggestion was to use IE because that's the browser SharePoint/InfoPath was designed for.
Answer: It can be integrated, but I am not sure for what purpose you want it for. If you want it on a page, make a custom page layout, link tiny mce assets (js / etc) in the additional head, then on your page, add a script editor and put in the required markup ( flexible version ). Less effort requires just hard-coding it while you create the page.
Comment: We have several lists with corresponding forms. When a user clicks New item it loads the infopath form which includes several text fields. We'd like to have the additional formatting for these text fields that are embedded in the form.


How do I kill players who don't fly throught hoops using elytra?

Question: I have an elytra parkour, you must fly through hoops. I want to know how do I kill the player if they do not fly through the hoops. Specifically how you can focus that player, because knowing if the player did not go through is simple. But I do not know how I then focus that player instead of a random other player.
Comment: You say "knowing if the player did not go through is simple." Can you explain how you might accomplish that?
Comment: You can put command blocks so when u start a block disappears, so water can flow in a line. But the line is filled with blocks so the water is blocked. and for every hoop you fly through a block in that line of water disappears so the water can flow further. If you fly through all the hoops the water isn't blocked and can reach the end and you can detect if the water is at the end. So a command block says 'you finished' or something.
Answer: I'm not a great Minecraft command guy, but for your problem,you can put barrier blocks around the hoops to make a wall with only the hoop as the way through, then the players who do not fly through the hoop will either die from impact or fall damage. If you want to be 100% let them die, you can put lava on the ground or cobwebs that leads to the void.
I hope this answers your question
Comment: Cobwebs are brutal! You could just constantly kill every player in a cobweb block, though. :)
Comment: Yeah I though if that too, but it will ruin the map and lag it so I got rid of that idea


Is there a way to take picture outside would encounters?

Question: I'd like to take some pictures using the Pokémon I've captured, like having a weedle in my soup or an ekans in my boot.  Is there a way to do this?
Comment: This might possibly me rolled out in later phases. But I'd rather have proper dueling and trading first. :D
Answer: This is currently not implemented.
Nor do we have any information that it will. For now, the only possibility to create a picture with a Poké on it natively is when you encounter it and try to catch it, enable AR.
Otherwise you might also screenshot them, use software like GIMP, cut them out and place them over another photo. :)


Certificate based authentication vs Username and Password authentication

Question: What are the advantages and drawbacks of the certificate based authentication over username and password authentication?
I know some, but I would appreciate a structured and detailed answer.
UPDATE
I am interested as well in knowing what attacks are they prone to, e.g. as so far mentioned brute force, while nothing is mentioned for certificates... what about XSRF? A certificate is expected to have shorter lifetime and be able to be revoked while a password would live longer before an admin policy ask to change it...
Answer: 1. Users are dumb
A password is something that fits in the memory of a user, and the user chooses it. Since authentication is about verifying the user physical identity remotely (from the point of view of the verifier), the user behavior is necessarily involved in the process -- however, passwords rely on the part of the user which is most notoriously mediocre at handling security, namely his brain. Users simply do not grasp what password entropy is about. I am not blaming them for that: this is a technical subject, a specialization, which cannot realistically become "common sense" any time soon. On the other hand, security of a physical token is much more "tangible" and average users can become quite good at it. Evolutionists would tell that humans have been positively selected for that for the last million years, because those who could not hold to their flint tools did not survive enough to have offspring.
Hollywood movies can be used as a model of how users think about passwords -- if only because those users go to movies, too. Invariably, the Arch Enemy has a short password and just loves to brag about it and distributes clues whenever he can. And, invariably, a British Secret Agent guesses the password in time to deactivate the fusion bomb which was planted under the Queen's favorite flower bed. Movies project a distorted, exaggerated reality, but they still represent the mental baseline on which average users operate: they envision passwords as providing security through being more "witty" than the attacker. And, invariably, most fail at it.
"Password strength" can be somewhat improved by mandatory rules (at least eight characters, at least two digits, at least one uppercase and one lowercase letter...) but those rules are seen as a burden by the users, and sometimes as an insufferable constraint on their innate freedom -- so the users become to fight the rules, with great creativity, beginning with the traditional writing down of password on a stick-up note. More often than not, password strengthening rules backfire that way.
On the other hand, user certificates imply a storage system, and if that system is a physical device that the user carries around with his house or car keys, then security relies (in part) on how well the average user manages the security of a physical object, and they usually do a good job at it. At least better than when it comes to choosing good password. So that's a big advantage of certificates.
2. Certificates use asymmetric cryptography
The "asymmetry" is about separating roles. With a password, whoever verifies the password knows at some point the password or a password-equivalent data (well, that's not entirely true in the case of PAKE protocols). With user certificates, the certificate is issued by a certification authority, who guarantees the link between a physical identity and a cryptographic public key. The verifier may be a distinct entity, and can verify such a link and use it to authenticate the user, without getting the ability to impersonate the user.
In a nutshell, this is the point of certificates: to separate those who define the user digital identity (i.e. the entity which does the mapping from the physical identity to the computer world) from those who authenticate users.
This opens the road to digital signatures which bring non-repudiation. This particularly interests banks which take financial orders from online customers: they need to authenticate customers (that's money we are talking about, a very serious matter) but they would love to have a convincing trace of the orders -- in the sense of: a judge would be convinced. With mere authentication, the bank gains some assurance that it is talking to the right customer, but it cannot prove it to third parties; the bank could build a fake connection transcript, so it is weaponless against a customer who claims to be framed by the bank itself. Digital signatures are not immediately available even if the user has a certificate; but if the user can use a certificate for authentication then most of the hard work has been done.
Also, passwords are inherently vulnerable to phishing attacks, whereas user certificates are not. Precisely because of asymmetry: the certificate usage never involves revealing any secret data to the peer, so an attacker impersonating the server cannot learn anything of value that way.
3. Certificates are complex
Deploying user certificates is complex, thus expensive:

Issuing and managing certificates is a full can of worm, as any PKI vendor can tell you (and, indeed, I do tell you). Especially the revocation management. PKI is about 5% cryptography and 95% procedures. It can be done, but not cheaply.
User certificates imply that users store their private key in some way, under their "exclusive access". This is done either in software (existing operating systems and/or Web browsers can do that) or using dedicated hardware, but both solutions have their own set of usability issues. The two main problems which will arise are 1) the user loses his key, and 2) an attacker obtains a copy of the key. Software storage makes key loss a plausible issue (at the mercy of a failed hard disk), and sharing the key between several systems (e.g. a desktop computer and an iPad) implies some manual operations which are unlikely to be well protected against attackers. Hardware tokens imply the whole messy business of device drivers, which may be even worse.
A user certificate implies relatively complex mathematical operations on the client side; this is not a problem for even an anemic Pentium II, but you will not be able to use certificates from some Javascript slapped within a generic Web site. Certificate requires active cooperation from client-side software, and said software tends to be, let's say, ergonomically suboptimal in that matter. Average users can normally learn to use client certificates for a HTTPS connection to a Web site, but at the cost of learning how to ignore the occasional warning popup, which makes them much more vulnerable to some attacks (e.g. active attacks where the attacker tries to feed them its own fake server certificate).

On the other hand, password-based authentication is really easy to integrate just about everywhere. It is equally easy to mess up, of course; but at least it does not necessarily involve some incompressible extra costs.
Summary
User certificates allow for a separation of roles which passwords cannot do. They do so at the expense of adding a horde of implementation and deployment issues, which make them expensive. However, passwords remain cheap by fitting in a human mind, which inherently implies low security. Security issues with passwords can be somewhat mitigated by some trickeries (up to an including PAKE protocols) and, most of all, by blaming the user in case of a problem (we know the average user cannot choose a secure password, but any mishap will still be his fault -- that's how banks do it).
Comment: "users are dumb" - no they aren't.  Users aren't dumb.  They are rationally ignorant: they have better things to do with their time than to learn the mathematics of password entropy.  There is an important difference (and a very important difference in mindset, for security folks).  Users are also rationally non-compliant: as Cormac Herley has argued, given that it is relatively rare for a user's security to be breached, the benefit to users to spending time on annoying security measures tends to be outweighed by the time it takes to do so.
Comment: @D.W. I love that term "rationally ignorant"! I see a lot of usage of it coming up...
Comment: users are users. Users are primarily interest in their tasks, some of which operate in the security domain. Security often degrades usability, and users are intentionally non-compliant in their efforts to improve their own usability. Makeing a system secure requires the cooperation of the users. To get cooperation, they need to understand why specific measures are in place. Not just 'passwords are more secure when they are longer', but typical attackers have tools that assume passwords of eight characters or less, so we made the minimum length nine. (I made up the eight character length).
Comment: "Password strength" argument is wrong. Rules like the minimum number of characters, uppercase and numbers do not actually do much for entropy, but rather simply make the passwords easier to crack as the attacker can know exactly what the passwords will be like, as well as making the password harder to remember for the users.

A password written on a sticky note is as secure as a same-length certificate, when all the attackers have no physical access to the machine.
Comment: *"Passwords are inherently vulnerable to phishing attacks, whereas user certificates are not."* Sorry, why can't someone phish me for a copy of my certificate rather than a copy of my password?
Comment: And you issue the PKI cert to ... oh yeh a "dumb user" and rely on them looking after it and not putting it somewhere like the company file share.
Comment: I signed up for stackexchange to upvote D.W.'s comment. "Rationally Ignorant"! - very nice.
Answer: Username/Password

Pro: Easy to deploy - just takes some code and a secure data store.  Depending on the security policy, can autogenerate passwords or force new users to create them.
Pro: Easy to administrate - password resets can (for some security policies) be done with automated tools
Con: For good security, passwords should be reset early and often.  User's forgetting or failing to change passwords is either a security risk or a usability hassle.
Con: Good passwords can be hard to remember, which leads to the issues of users reusing passwords or writing them down.
Con: Password data stores are a weak point - if an intruder gets the password store, he gets the motherload.
Con:  All parts of password transmission can lead to exposure - websites that store passwords locally for ease of use, internal server components that transmit in the clear, log files in COTS products that store passwords in the clear.  With the secret being part of the transmission, you're only as strong as your weakest link - it takes serious effort to prevent exposure and the requirement is on both the user and the system developer.

Certificates:

Pro:  Doesn't require the transmission of the secret.  Proof of private key contains no secret information - mitigates all sorts of storage/transmission weak points.
Pro:  Issued by a trusted party (the CA) which allows for a centralized management system for status across multiple applications.  If a cert goes bad, it can get revoked.  Fixing a password breakin must be done separately for each system unless a shared ID is used.
Pro: Non-repudiation case is stronger - in most password systems, the way the user is initially authenticated prior to account creation is pretty weak and the password reset mechanisms can offer another factor of plausible deniability.  With many forms of certificate issuance, it's far harder for a user to say it wasn't them.  Caveat - you're still only as good as your CA's issuance policies.
Pro:  Serves more purposes than just authentication - can provide integrity and confidentiality as well.
Con:  Still requires a password/pin - almost any private key pair storage mechanism is then unlocked with a PIN.  SmartCards can have tamper protection and lockout capabilities to prevent brute force, but that doesn't fix the fact the user wrote his PIN on a sticky note next to the computer where the card is docked.  Sometimes password issues reappear on a smaller scale with PKI.
Con:  Complexity of infrastructure - setting up a PKI is no easy task and generally so expensive in both deployment and maintenance that it can only be used for large/expensive systems.
Con:  Certificate Status reporting and updates are not easy - revoking a user credential that has become corrupted is onerous due to the size and complexity of the infrastructure.  Usually, a CA generates a CRL that may or may not be provisioned within an OCSP server.  Then every application should check every login for the CRL or OCSP status.  This introduces a variety of time delays into the system between the time a PKI credential is reported as compromised and the time when the systems that rely on that credential actually start denying access.  The speed of status update can be accelerated - but at a greater system complexity cost.

A couple of other notes:
A certificate is expected to have a shorter lifetime and be able to be revoked while a password would live longer before an admin policy ask to change it...
I disagree with the premise.  On the systems I've worked on that support both password and PKI, the policy for requirements of password update is MUCH shorter than the policy for issuance of certificates.  Revocation is a different can of worms - it's for the less likely event of private key compromise.  Because the private key data does not get transmitted through the system, the risk of exposure to this data is generally assumed to be much lower than the risk of password exposure.  For practical purposes, passwords are considered to have a shorter lifespan.
I am interested as well in knowing what attacks are they prone to, e.g. as so far mentioned brute force, while nothing is mentioned for certificates... what about XSRF?
You're mixing apples and oranges here.  Brute force can be a viable attack on either type of authentication credential - but XSRF is an attack on an underlying type of application that would be possible regardless of the authentication mechanism. Unless you mean that because username/password would be input with some sort of text interface, they could be prone to cross-site scripting on that interface.
In general (apologies for my lack of official terminology - I usually look the typical attack terms up but I'm short on time):

Brute force - because the keyspace of your average password is smaller than the keyspace of an asymmetric key, a password is easier to brute force.  However, a small enough key size on a certificate is also brute force-able and the ability to brute force attack keys grows with CPU capabilities forcing a rat race with key size increases.
Educated guessing - narrowing the keyspace to a reasonable set of guesses is easier with passwords, and not so obvious for most asymmetric key algorithms, although there are weak keys in the RSA algorithm, so there is some dependancy on how a big a crypto nerd the attacker is.
Social Engineering - doable either way, although with a certificate stored in hardware, you have to not only get control of the user's PIN but also the hardware that stores their key.
Inside attack - getting the credentials from inside the system and then using them to emulate a legitimate user - depends.  If passwords are stored insecurely then this is more doable for a password-based system.  But if you can get control of the CA, you can issue yourself a legitimate certificate and then it depends on how access is controlled.
Man in the middle - depends - a man in the middle can intercept a password if the password is not encrypted in transit by an encryption mechanism that bypasses him.  That's doable with SSL/TLS.  However, a man in the middle can also intercept parts of a PKI transfer, depending on how the PKI is being used.  PKI signatures with no nonce or timestamp are open to replication attacks by a man in the middle - he can resend an intercepted message so long as there no way to tell if the message is timely or unique.
Comment: I guess it does have an effect on CSRF though. It seems to defeat CSRF Login attacks, since the attacker can't insert his own credentials in the login request.
Answer:
Usernames and Passwords

It is all about what you know. You are giving a secret code word to authenticate with the service.
This means that if it is intercepted in stream, it can be used. Use of encryption makes that unlikely but still possible. Someone can do a man in the middle to get your password or take over the computer recieving authentication.
A username and password can be use on any computer at any time. This is a bad thing if security matters and a good thing if accessibility matters. For a bank... this is bad. For facebook, it really should not matter.

Certificates

Certificates are a little more sophisticated. The server sends data to the client and the client signs the data and sends it back. This means that the server does not know the private key at any time so while a man in the middle or takeover of the server will result in them getting access, they do not have your key.
Certificates are a pain to use. You can't remember them and they can be stolen.

The best system is a combination. You put a password on the key so you have two factor authentication. Something you know (password), and something you have
(key). However, the more layers of security, the more of a pain it is. That is the great tradeoff in all of security.
Answer: I agree with Stephen's points. You present a tough question to research as the issue is typically not a comparison of one over the other.  A good way to understand why both exist and are not typically rated against each other is to focus on usage.  Certificates are tied to machine level keystores and thus are great for machine to machine authentication between specific machines planned in advance.  Passwords are very well suited to people as we are mobile and tend to authenticate from numerous systems in a way that is hard to predict in advance.  So certificates are typical in designed in advance hardware based authentication and passwords are good for mobile wetware based authentication.  A smart card is a great way to add certificate based authentication to the mobile human and another factor to the process.
Comment: "Certificates are tied to machine level keystores and thus are great for machine to machine authentication between " this is an info for instance that i have forgot when i was thinking, so +1 thx!
Answer: A password can often be brute-forced and it can be socially-engineered, because, as its owner must memorize it, it is often much simpler than a secret key.
A private key (of sufficient strength - for RSA, 2048 or 4096 bits) cannot be brute-forced. The only way to authenticate to a system which requires public-key-based authentication is to obtain access to some other computer first to obtain the private key. This introduces an additional level of complexity to any attack. Social engineering to get a person to reveal his password will not help, since the password only decrypts his private key, rather than granting him access directly to the target system. Social engineering to get a person to reveal his private key together with his password is likely to be much more difficult.
Additionally, passwords are transmitted over the network from the user's machine to the system the user wishes to use. Private keys are not transmitted over the network, neither in the clear nor in encrypted format; rather only the public key is transmitted.
Comment: I caution against using the phrase "cannot be brute-forced".
Comment: I might be misunderstanding what you mean, but isn't social engineering to retrieve the password protecting a private key just as good, if not better, than obtaining a password for a specific service?
Comment: Attempting to retrieve both a password-protected private key and the password to that key will usually prove more difficult than simply retrieving a password. Yes, social engineering is a good attack in both cases, only in the case of public key authentication it is more of a challenge to pull off. A private key, for example, cannot easily be memorized (and most often is not memorized), let alone read over the phone, requiring a more extended social engineering effort to obtain it.
Comment: I see what you mean. I missed the "...first to obtain the private key" sentence entirely.
Answer: I'd like to add an option - One time password devices. I agree with what others have said about the pros and cons of certificates and passwords - OTP devices require some back-end components to operate, but can be integrated without a lot of hassle in my opinion (Active Directory is a bit different, but other systems aren't too hard).
A combination of a password and one-time password works very well. You can go with a simpler solution like a Yubikey with a password (USB or NFC connection required), or a displayed code fob.
Both options are easy to add to Linux-based operations. If you want do it in Active Directory, you'll need to buy software to handle the code and install it on every AD server. The user then enters the OTP in the start of the password field, then their usual password. It is possible to develop your own module for it, but cost-prohibitive from what I've seen.
Comment: I agree but yubikee does not offer a otp  does it? it only regurgitates the same key for ever
Answer: You seem to forget that a web page can use both certificates and passwords.
If a user with a certificate comes, the door opens.
And if he does not have a certificate, he has to login with name and password as always.
In this way, the interested users get their ccertificate, all other do it the old way.
Answer: With the advent of user awareness of what a weak password can do, users are more likely to move to use a password manager. Consider everyone uses a password manager that creates unique passwords of a reasonable or better length and quality. These have become equivalent to a PKI, just much simpler. With certificates, there is still the delicate process of key exchange. If a private key is compromised because it is transmitted using an unsecured channel, like a USB stick or some sort of cloud-based service, the private key can be breached. All in all, a truly random and long password is a jumble of bits, and a private key is a jumble of bits. Both will not be remembered or even known by the user but sit in a system (a certificate or a password manager).
What does set certificates aside is their lifetime (unless an administrator poses an expiry on passwords) and complexity.
Two things might add a bit of extra security

the certificate is issued with a passphrase
expiry date

But if 1) is social engineered out of the hands of the user, it is useless.
Complexity might give a false sense of security as a hacker might very well understand how certificate-based logon works.
I agree with @matt-carlson that adding a physical device in some sort or form to the mix probably will make authentication more secure as it might be improbable that two of these devices exist. I'm not sure if a TPM can fulfil this property
Comment: "These have become equivalent to a PKI, just much simpler" -- no, not at all. In any way.
Comment: @schroeder elaborate
Comment: That a random password generator is "equivalent" to PKI and 3rd party validations? It would be on you to explain how that is so.
Comment: @schroeder I disagree. It is up to you why it isn't
Comment: This is *your* claim that a random *generator* is equivalent to PKI. You need to back it up. Because it is *obviously* incorrect. I was hoping you overstated things, but now it looks like you really meant it.


Tweets in my Tweetbot timeline are occasionally marked as a favorite when I see them for the first time. Is that a bug or a feature?

Question: While looking through my timeline in Tweetbot, occasionally a tweet will be marked as a favorite even though I'm sure I'm seeing it for the first time.  (I can't resist taking the time to unfavorite it.)  I don't see any mention of this in http://tapbots.com/support/tweetbot/.  Is this a bug, or a "feature" (where perhaps Twitter's API is doing this)?
Answer: It's a bug with Twitter, not Tweetbot.
I've seen people ask @tweetbot about it several times now. The answer and response generally look like this exchange:

Q: @tweetbot keeps favoriting random tweets in my timeline. It's almost embarrassing.
A: Sorry, that's a Twitter bug. As you can see on Favstar, they're not real favorites.

That particular exchange happened just yesterday.
Twitter's REST API bug list has this bug still open where the API may erroneously report a tweet as favorited when in fact it is not.
Answer: I have seen this happen in the official Twitter app, so it might be a bug in the Twitter API.


Should I put UV filter to protect the lens even if I put a lens hood?

Question: That's pretty it, usually you buy a UV filter to protect the lens. My question is do I need the UV filter even if I'm using a lens hood?
Comment: UV filters for protection is always a contentious topic whenever it comes up. See discussion on meta: http://meta.photo.stackexchange.com/questions/981/filters-must-be-destroyed-must-every-uv-protection-filter-question-get-this
Comment: @mattdm thanks for the link it's funny actually but true
Answer: The hood protects the lens of physical impact from knock and obstacles. It also reduces flare and keeps image quality to what the lens is capable of.
A UV filter protects against flying dangers such as sand, salt and other elements. While doing so a UV filter is detrimental to image quality as it adds additional reflections from another glass element in the optical path.
Therefore in most cases you should ONLY use the hood. If you are in proximity of sea-water splashing or flying sand, then you should but a UV filter too. Since flare can still be a problem, it is best to do both if you can.
Answer:
A filter offers more protection than a hood alone.
I have had a filter save a lens from certain severe damage when a lens hood failed to do so.
How much UV filters affects image quality is a much debated subject. I have added a comment on this at the end - mainly pointing to some objective measurements.
Here are the test results for the best UV filter in the comparative tests which are discussed below - compared to many others, the effects of this filter are minimal - it is also one of the cheapest available. You can decide for yourself if "minimal effect" is acceptable.
Being able to clean the (removable) filter "in the field" in non ideal conditions can be a significant advantage. Much nicer to be able to clean a spattering of mud or spray from a filter than from a lens front element.

I have had a filter glass very badly smashed while carrying a camera with a filter plus a lens hood on.
 I did not feel any impact and do not know what struck it.
 It was in a business area in early evening and I was walking with friends. There was no obvious situation that would have caused this - the camera waseither on my hip or in front of me, and I MAY have swung it against a railing or some such. There is a small chance that it was done maliciously but this seems most unlikely.
The filter was very badly starred - without it the front lens element was almost certain to have been damaged beyond practical use. The filter had been struck so hard that it distorted enough to make removal very difficult. Despite this the lens was undamaged and gave good service subsequently. I was far from home (Qingdao, China) with  a minimum of lenses with me and loss of that lens would have put a severe dent in my excessive photo taking tendencies :-).
Conclusion - the hood alone does not offer full mechanical protection.
 Even completely inobvious circumstances can result in major lens damage.
  If you value your lens front element more than the quality loss caused by a filter then the filter may serve a useful protective role.

Effect of UV filters on image quality:
Doing justice to this subject requires flame shields, thick skin and much time. In lieu of these, below are some links to others efforts. Many of these came via the stack exchange thread sited by @mattdm
This extremely interesting and detailed test UV filters test by LensTip.com describes testing of 20 UV filters using a Hitachi U2900 Spectrophotometer. The test runs to 24 internet pages, mainly due to there being one detail-page per filter, but the surprising and useful results are on page 4.
Test procedures are here - a weighted score is given based on UV transmission %, visible light transmission %, Flare and vignetting. Some users will understandably find this method inadequate for their needs  - but such people would probably not use a UV filter regardless of the test results. That's obviously a legitimate but subjective personal choice.
Test results are presented here. The results all by themselves are liable to fuel endless debate.
 Buy a Hoya HMC UV-0 :-)
I will not specify brands below. Each filter detail page also has with and without comparison photos showing the image results and comparison of these comparison pairs for various filters is extremely illuminating. To reduce risk of incineration and siege I'll leave it to readers to look at the article for themselves.
As a guide, the blue light used to drive the phosphor in a typical white LED has a wavelength of about 450 nm.
Optical transmission of their worst rated filter:

Optical transmission of their best rated filter

Here is a graphic demonstration
 of what sort of front element or filter "scratching" or damage it takes to get significant image degradation which is visible as degradation rather than general loss of contrast. What sort of results would you expect from the lens below?
See above link to see.

Below is a photo taken with my smashed filter attached. At that stage I was unable to remove it by hand !. Pieces as subsequently removed with due application of ultraviolence shown as inset. Red lines on photos show some of the visible aberrations.

Somewhat larger version here
Snapshot, internal flash, self timer, smashed filter, other excuses ... :-).

Here is a very little of the material available on this subject  - much is subjective opinion.
Here
and here
and here  (stack exchange.
and here - some informal test results.
and here including some tests.

Added - new fatality - May 2012:
Data point!
I'm not intending to make a habit of this - honest :-).
 New & drastic example.
At a friends's birthday party. Two cameras. The old Minolta 5D seen below was a backup and the Minolta 17-35mm f1/2.8 is a reasonable quality lens  with a reasonable low light no-flash performance. Good for candid portraits. It wasn't getting much use and at one stage I (stupidly) left it under a table, well away (I thought) from the edge. Several days later I took it out of the bag and, oh dear !!!! I don't know what happened, or even with certainty that it was while the camera was under the table.
 The lens proper is fine. The lens front element is very domed on this lens but also probably much stronger than the filter was. Whether it would have been damaged I know not.
Comment: Those diagrams may describe the measured effect of UV filters but they only tell part of the story. The most common degradation resulting from UV filters is much more serious than the attenuation of certain wave-lengths and will completely ruin a photo even with expensive multi-coated and super-multi-coated  filters. [See this](http://photo.stackexchange.com/questions/11518/where-does-this-reflection-come-from-in-a-long-exposure-shot) for example.
Comment: [Cont'd] As soon as you have any light source in your frame it can happen. I have seen it personally dozens of times when some of my photography students keep their UV filters on (or sometimes do not know they have one) and I take it off in the middle of the shoot. The improvement is truly dramatic and is immediately visible.
Comment: Filters are *much* easier to shatter than the front elements of most lenses. Just because a filter shattered is not proof that the front element would have been destroyed by the same impact! The front element of most lenses is harder and thicker than a filter, and is also usually stronger due to its shape.
Comment: @Itai - did you look at the test pages that I linked to as I suggested? They contain actual images with and without filter in 3 situations for each filter. The visual performance differences between filters are very substantial. I'm not in any way suggesting that filters do NOT make a difference - just that the difference varies very widely between filters and specific comments need to be related to specific filters. I doubt that any filter produces a worse result than my smashed one did :-).
Comment: It's more about the circumstances than the filter from what I've seen. Even I have to sacrifice a UV filter once in a while to save a lens :) In some cases you will see little difference, on others like the question I linked to will be extreme. It *may* depend on the lens used too (actually I strongly suspect but I have not paid attention enough to confirm).
Comment: @MichaelClark re " ... is not proof ..." -> Indeed. that's why I said, 3 years ago, re my 2nd experience " ... The lens front element is very domed on this lens but also probably much stronger than the filter was. Whether it would have been damaged I know not.... " | For my first experience the impact had clearly been severe. The filter ring was distorted and required a degree of ultra-violence to remove. Damage to bare lens would not have been certain, but seems likely.
Answer: You can also purchase a NC filter (stands for neutral color) if you don't need UV protection. I have a few of these from nikon. http://www.nikonusa.com/Nikon-Products/Product/Lens-Filters/2479/52mm-Screw-On-NC-Filter.html
As long as it's a multi-coated filter, you shouldn't have to worry about reflections in the optical path.
Comment: there are also filters like Marumi DHG Lens Protect: http://www.marumi-international.com/dhg/page2.html#a02 - also very good. I have it on my telephoto lens.


Auto complete on iMac- edit list of replacements

Question: I once mis-typed my email address into the message part of an e-mail.  Now, whenever I type my correct email into the message part, it automatically corrects to the wrong version.  Is there anyway to edit the auto complete list to correct this?
Answer: You can add a shortcut that replaces a misspelling, so when you type your email address it will autocorrect to the same address (if that makes sense).
Click System Preferences > Keyboard > Text, and click the (+) button to add a new shortcut. Type your email address in the "replace" column and the same email address in the "with" column.
This will ensure you type your correct email address but then it will stay, and not autocorrect.
Comment: Thanks.  The problem has been fixed and now I only have to half type my e-mail to get the full version