How unhealthy is arc welding?

Question: I have a few repairs to make  that would necessitate some welding. I could do it differently, for example with pop rivets, but I take this opportunity to learn welding. However I'm a bit concerned about the unhealthy part of the process, in particular breathing carcinogen fumes. Is there a way to mitigate those risks ? I'm talking specifically about: Shielded  metal arc welding, a.k.a stick welding.
Comment: Folks weld as their profession, and loads of them live long health lives. I doubt running a couple beads poses any significant heath risks (unless you do it without proper safety equipment).  Depending on where you live, breathing the air all day, every day poses a greater risk.
Comment: You need to add more information. What welding process? Stick, tig, mig (gas shielded or flux core), etc.
Comment: I would agree with Tester on this. If you were a production welder doing it for 8 hours a day you should wear a respirator. Running a couple beads in your garage....you could do that breathe all the fumes and maybe get a headache. (Except if you are welding galvanized metal. Then you should do it outdoors and stand upwind.) Just use good ventilation and you should be fine. I have never heard of any carcinogens in stick welding gases. That would be a major manufacturing health problem.
Comment: Feel free to edit the title if you want to propose a more neutral one
Answer: Breathing the vapors is not a good thing. Especially with galvanized metal. It is important to have proper ventilation. Many times when working indoors I use a small fan pointed above the work to move the fumes away and not disturb my shielding gas (wire welding & TIG). When stick welding the fan really has little affect. Breathing the "smoke" caused by welding can cause serious lung problems as it is full of vaporized metal. I work with guys my age that have been professional welders for 30+ years and other than galvanized work they never use a fan or respirator. They laugh at me for my little fan. Welding is a great skill to have and can save you thousands (or if like me you might get bigger and bigger units. On my farm I have repaired all kinds of stuff that would have been recycled if I did not know how to weld. I usually grind the paint so there are less bad things to breathe and use a small 4" fan that has a magnetic base.
Answer: Although proper ventilation is probably the most effective defense against breathing metal fumes, I believe that P100 respirator cartridges (the soft pink discs that fit onto a standard half- or full-faced respirator) will remove most of the nasty components of welding fumes, assuming you're willing to wear a respirator while welding.
Answer: Engineered controls, such as local ventilation (a unit which removes the fumes from your breathing zone and ejects them away from the area) which can move 100 lineal feet per minute across the weld space, are preferred for metals, rod, and flux that could generate hexavalent chrome fumes / particulates (think cancer) . This would be for any type of stainless steel or alloy containing chrome.
For welding involving carbon steel only, general dilution ventilation is acceptable; basically a fan pulling air from the area, allowing fresh air to enter and dilute the fumes.
A 1/2 face respirator with P100 cartridges should always be worn.
For practical purposes, and as described in the answer by @Joel Keene, the most basic and easily used control would be a respirator with P100 cartridges. Even without ventilation, a respirator would help a lot. A 1/2 face would be what you would want, to facilitate the use of your welding hood or goggles.

How unhealthy is arc welding?


English SharePoint site with mix of Chines and English file names

Question: I am trying to execute published Captivate simulations on SP. The file name is a mixture of English and Chinese characters (VF01 - 创建商业发票-SD.htm). It works correctly on my local PC. When I upload the file to SP, it will not execute. If I rename the file to all English characters (VF01 -ChineseTest-SD.htm), republish, and upload, it works fine on SP. Does the SP server need to have have a language pack installed to allow the file to correctly execute with a Chinese file name?
Answer: Yes, it should probably require Chinese Language pack installed for identifying file names in Chinese language.
You can download them here - http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=3411


Question about Ask Different account merging

Question: I've created a second account by mistake and now I'm logged into it and cannot get out to log in the correct one. Can I merge the two or delete the one that I'm now logged in? I receive emails about comments on my own question (posted with an old real account) and cannot even comment or exchange with the people trying to help me!!
Comment: It says that I'm user3116426 - that's exactly the wrong account.
On another account I go by my real name - Alexei Zoubov
Here is the link to my original question posted with the correct account:
https://apple.stackexchange.com/questions/297071/apache-errors-on-macos-sierra?noredirect=1#comment375483_297071
Answer: In general the "my account" section of the help has the procedures to register, merge and delete accounts.

https://apple.stackexchange.com/help

If you can register your current account with the same email address (or just an email address) that helps verify and merge the two or more accounts that are easy to make if you don't register initially.
In a nutshell, you can request merge in the contact us link at the bottom of any page.
If the Alexei Zoubov account is the one you want to use, but the one your browser has you logged into is something else, then you can try logging out of that and logging back in with the correct one. If you're not sure you can log in, request a merge from the old account before you log out.
To do this:

Click on the Stack Exchange menu at top left (see image below):

After clicking on it you'll get access to the Log Out option:

Select Log Out. You should see a prompt with a blue Log Out button. Above that you'll have a checkbox option for Log out on all devices which you may want to tick before logging out.
Once you're logged out, you can log in by clicking on the Log In option at the top of the page:

Now enter the email address and password of your Alexei Zoubov account and click on the blue Log In button.

You should now have access to the correct account again. Please let me know if you run into any problems.
NOTE: I did try checking both the user3116426 and user253102 accounts, but these do not seem to have been registered.


Why is it necessary to add hydrogen and delete water before protein-ligand docking?

Question: What is the reason for adding hydrogen and removing unnecessary water molecules from the protein structure before protein-ligand docking? FYI, the tools I used for docking is GOLD.
Comment: Yes, sometimes water is needed for an enzyme to function. When it is necessary to remove water is a hard question that depends on what environment are you simulating and the protein you are modelling
Comment: I think if you could add some more context it would be helpful to answer. Who said it is needed? Under which conditions are you looking for a docking? Sometimes  water is need in order to enable interaction or form stable bounds (AFAIK)
Comment: No one say that but from the software, it say "delete water IF REQUIRED". I just don't understand what it meant by "IF REQUIRED" and when it is necessary to remove water or add hydrogen. Btw, from your reply, does it meant that sometime, water is required for an enzyme to function?
Answer: My answer is mainly based on molecular dynamics,but in this context it shouldn't make much of a difference.
The main reason has to do with the force-field-water model used during the simulation. Examples of water models are SPC, TIP3P or TIP4P; same molecule (water) but different topology.
A pdb usually comes from different sources and it can contain molecules that are not standard and therefore not recognised by the model of your simulation. Usually, once the structure is loaded, your system is re-built so that it conforms to the model topology. There are exception though, for example if your water is part of a functional active site. In that case you can keep it, but its structures (topology of the water molecule) has to be recognised by the model.
Hydrogens are usually added to "saturate" and stabilise the bonds.
Comment: Totally correct for MD. However, a wee note: most ligand docking program use implicit water (except special case such as WaterDock), which means that TIP3P waters or similar are not added, but a fudge factor is used to account for the dynamic but stabilising polar properties of water.
Answer: Hydrogens
Most crystallographic structures are X-ray and the hydrogens are absent. In the case of neutron diffraction models, there may be many missing high b-factor ones (example in PDB:5MOP). As a consequence models are reprotonated. Also missing carbons and missing loop residues are added for some in silico applications too (not docking).
However, it is always good to manually tweak the protonation. In the case of enzymes with protanatable side chains in the active site, some reading is required to get the charges right: by default aspartates will be unprotonated, but they may be protonated (glutamic acid) in the active site and it is important to get it right (cf. this post about it). Some times its the ligand parameterisation may give the physiologically incorrect protonation (cf. this post).
Waters
Crystallographic waters can be important catalytically and structurally, but can be pushed out and actually it is a good thing: you have a hit that take its place. Polar bonds are stronger than hydrophobic ones and most types of π bonding.
Waters in most docking software is implicit and is modelled as a parameter in the force-fields —think of it as a ghostly watery haze. So a left behind water, not only will get in the way of the docked small molecule, it may for some programs cause issues as they will try to dock it. A notable exception is WaterDock mod for AutoDock, but the jury is out on whether it is better. Water is polarisable in reality in a very complex way (protonated (OH3+) or deprotonated (OH-) with very different charges) and most water models do not cut it and instead do not account for this.
The way implicit waters are computed differs in some applications, which is also something to look into.
Answer: The molecular docking programs usually tread the target structure as rigid. It does not know which atom belongs to the receptor and which is bulk water. So, if you keep the water in the structure the program cannot properly place the ligand there.


What's the appropriate way to debate a closed question?

Question: Recently, Pat closed a question, someone put a comment on the question, asking why it was closed (but didn't vote to reopen) and I responded to the comment saying that I agreed, but also voted to re-open.  Pat said to take the discussion to meta, but I see no obvious way of referencing that question here.  What's the recommended process for this look like?
Answer: A reasonable workflow would be:

Create a new question here in meta, entitled something like

"Why was my question closed?"
"How can I fix this question so that it is acceptable?"
Preferably not, "OMG, teh m0ds are jerks"  :)

Include a link to the question being discussed.
Post a link to the meta discussion on the closed question.

You do not need to be the person who asked the original question to ask about the closing.
Doing it in meta provides a much nicer focal point for the discussion and encourage more people to contribute thoughts.  Once a question is closed, I'm guessing that many do not look at it any further.
Comment: Bit tricky for new users who do not have the reputation needed to post in meta.  Not a nice way to welcome them.  See it from their point of view: They ask a question about board games, it gets closed, they're told to take it to meta, they don't really know what meta is but they try, they get told that they don't have the rep needed to post in meta.  I'm guessing they go and never return.
Comment: @DanBeale How often has this happened?  Using the search it is pretty easy to figure out.  My initial impression is "very little".


Is there any term for a person who has changed his name?

Question: Is there any term for a person who has changed his name? For example, there was a man who was named "Jacob" when he was born, but when he reached the age of 18 he decided to change his name to "Joseph". Is there any term for this kind of person? Or at least for this kind of practice?
Comment: The Artist Formerly Known as Prince.
Comment: @JLG - lol. Of course that was just said because he used an unpronounceable name (as a clever way to get back at a record company he was contractually obligated to).
Answer: The term is "renamed" and the practice is called "renaming" as we read in legal documents.
Answer: Well, when such changes aren't totally unexpected, (eg: a woman changing her last name upon marriage), the old name is often appended to the new one with a "nee" in the middle. Supposedly this is French for "born as", so it could reasonably be applied in any situation where a person's birth name has been changed.
Comment: [wiktionary says](http://en.wiktionary.org/wiki/nee) "When used for a man, the masculine form né should be used."
Comment: I *almost* got into that. That's the rule *in French*. However, we generally don't borrow the gender rules of words when we borrow the words in English. So in the few times you see this "in the wild" attached to a man's name in English, you will typically see both `e`s. People who know the loaner language tend to take the position that we ought to borrow the rules along with the words we borrow, so I'm not surprised to see someone arguing that.


Maximum quantity per order magento not per product

Question: I want to set maximum quantity per order not per product. I tried to set the
System->Configuration->Catalog->Inventory->Maximum Qty Allowed in Shopping Cart to 3, as per requirement only 3 item per order, The problem is when I tried to add 9 items 3 per product it is allowed. What I want is just to set 3 on whole cart regardless of item.
Does anyone know a way to achieve this? Thanks
Answer: I already found alternative on this. My scenario is i want to limit the order in 5 quantity only. I dont know if it is the right way but it is working to me.
Go to app\code\core\Mage\Checkout\controllers\OnepageController.php
in function indexAction() put below code;
<code>$count = Mage::helper('checkout/cart')->getSummaryCount();
if (abs($count) > 5) {
    Mage::getSingleton('checkout/session')->addError($this->__('You have exceed the maximum quantity for this order. Maximum quantity per order is 5.'));
    $this->_redirect('checkout/cart');
    return;
}
</code>


What is the difference between eugenics and evolution by natural selection?

Question: So with the working definition of Eugenics: "the aim to improve the human gene pool". What are key features that distinguish Eugenics from evolution by natural selection?  I mean, besides that natural selection occurs naturally.
Comment: With that definition, the major difference is that eugenics is artificial. Additionally, natural selection has no aim.
Comment: Natural selection is a descriptive theory that aims to explain the diversity of life. Eugenics was a political/ideological project for "improving the human gene pool." Obviously, these are completely different.
Comment: Eugenics is selective breeding to artificially promote certain 'desirable' genetic traits. Natural selection occurs without human interference and is due solely to the challenges of nature.
Answer: Selection is a mechanism of evolution which favours specific forms of traits over others, this can cause the spread of beneficial mutations through a population.
Natural selection is the spread of beneficial traits/genes through populations as a result of the natural variance in their effect on reproductive output (a function of life history traits like lifespan aging and reproductive rates). A classic example is that of Darwin's finches, where different variants of bill length and shape have evolved in populations based on what food resources (types of seed) are available to them and their ability to utilise those resources.
Artificial selection is selection imposed on a population by humans to deliberately affect specific traits. Examples of this would be milk yield in cattle (we want more efficient production and better quality milk), dog breeds (selection on a whole host of traits like colour, beardedness, height, length) and crops like wheat and barley (selected for higher efficiency and  quality output).
Eugenics, coming from the greek for "well-born" or "good" race, is the application of artificial selection principles to humans. Just as with cattle or crops, there is an aim, it may be to increase height, remove genetic diseases, or promote a certain set of traits like blonde hair and blue eyes. Historically we can associate with a number of radical political ideologies, such as Nazism. Even here in Sweden (people tend to think of it as a very progressive and equality driven country) there was a program of eugenics until very recently, achieved by forcibly sterilising or coercing people in to it, for various reasons (racial purity, health, and antisocial behaviour). Here's an interesting example of a girl designated as being genetically inferior because her family had a history of alcoholism (that page gives a good history of eugenics too). The social and ethical problems of eugenics are obvious.
Under normal conditions a persons reproductive output is largely determined by their own choices and actions whereas under eugenics that choice is taken away and made by someone else and specifically with the aim of "improving" the quality of the population.
So in summary:

natural selection is the result of natural variance in fitness linked to traits
artificial selection leads to a change in traits, in a specifically targeted direction, decided and imposed by another organism (usually humans, I know of no other species which does this)
eugenics is practice of artificial selection on humans enacted by humans with the specific aim of improving quality: often for social, economic, or political reasons and is generally accepted as being against human rights these days.
Answer: First, you need to recognise the difference between Natural selection and Artificial selection. As a basic definition, you can say that in natural selection, selection is done on fitness (overall, long-term success of reproduction) and is determined by the complete living environment of the species. In artificial selection, selection is done by humans on a plant or animal species for specific attributes that are desired (see any Evolutionary textbook for more on the difference). So the two processes generally try to optimize completely different things, and artificial selection has a goal which is not the case for natural selection.
Generally, Eugenics can be likened to artificial selection, done by humans on humans. The methods used (selective breeding, culling, trunkated selection, sterilization etc.) are potentially the same. The difference between eugenics and articifial selection on plants and animals other than humans is purely moral and political (and therefore off-topic for Bio-SE).
However, eugenics has also often been misguided in practice (if you ignore for a moment the usually horrible morals behind it). First, it relies on desired and undesired genotypes and phenotypes. Most people would not regard these as valid concepts, and even so, what will be desired/undesired will clearly differ between societies and over time. Second, eugenics does not appreciate the value of genetic diversity for the long-term success of a population (it will rather result in lower diversity). Third, eugenics is usually aimed for obvious physical traits and diseases, without much regard for their genetic background (e.g. heterozygious recessive carriers of disease). Fourth, eugenics usually devolve into a hunt for "weaker" groups of people, even if this has nothing to do with the gene pool of the population (for instance, many birth defects and the prevalence of Down's syndrome has almost nothing to do with the genetics of the population).
I guess you could argue that ongoing selection in humans is a form of eugenics since it is to a large extent determined by human interactions and choices (see e.g. Courtiol et al 2012 & Geary et al. 2004). However, this is definitely not a standard definition, and big difference compared to "normal" eugenics is that it is not guided by a common and explicit goal. I also know that some people label the collective outcome of individual decisions as a form of eugenics, which might be relevant for how you view Preimplantation genetic diagnosis (PGD) and prenatal screening.
Answer: In principle, eugenics is just like selective breeding of animals and plants. For example, dogs have been bred for a variety of traits to fit into several niches, and corn has been bred to produce large yields in several climates. Eugenics would attempt to do the same for humans. However, no one agrees on how to "improve" the human gene pool, and far too often eugenecists have sought to remove criminals, the disabled, the jews, or whoever they feel is inferior. And the methods used to bring about their genetic utopia include forced sterilization and/or death camps. There is no moral way to implement eugenics, and I don't think humans should be in the business of deciding which people are superior or inferior and who is allowed to reproduce, it's always dangerous.
Comment: @user125535 Preimplantation genetic diagnosis (PGD) is not done with the purpose to improve the human gene pool (which is the case for Eugenics), so I think there is a big difference. As you say, they are done with the purpose to relieve potential suffering or for the sake of the parents. However, the same methods *could* theoretically be used by an eugenics programme.
Comment: what about PGD and using it to prevent the birth of a child who would otherwise lead a life of suffering? or inevitable death?


Which books influenced the game Halo?

Question: I read this post about the Ringworld series, but am curious about the main influences. I just started reading the Forever War and am reminded a lot about Halo; also, I read once that Starship Troopers was a big influence. Did either of these influence the original Halo plot? What were the main influences?
Comment: @user14111 - I would guess because of the scope of the answer. Halo influence is going to be arguably a small group. The "end of world" is going to invite extended discussion and argument about "What about book X", and "Why not book Y", where you would have people arguing about the intent and scope of a massive amount of literature.
Comment: I'm giving this a +1 to offset the -1; it seems reasonably well-scoped and conforms sufficiently with the most recent decision I can find about "influence" questions, here: http://meta.scifi.stackexchange.com/questions/1950/shouldnt-this-question-be-closed-as-off-topic/1954#1954
Comment: @JimmyShelter So a list of stories about the end of humanity is a no-no, but a list of stories with similarities to "Halo" is a yes-yes? I'm never going to understand the Rule Against List Questions.
Comment: @JohnP has it right; this question has established that by having a definitive and authorative answer, the end-of-world question is open-ended (also note that this question was *not* "similarities" to Halo but was explicitly *influences* on Halo).
Answer: According to the wiki entry for Halo:

Ringworld (Niven) and the Culture Series (Iain Banks, particularly Consider Phlebias and Excession) gave rise to the ringworld concept
Armor (John Steakley) - Sense of hopelessness by fighting the same war again and again
The Vang (Christopher Rowley) - The engulfing alien incursion, basis for The Flood. (Possibly also influenced the name of the Master Chief)
Speculation that the SPARTAN program and design of the Covenant drones was influenced by Ender's Game (Orson Scott Card)
Bungie has acknowledged the film Aliens (James Cameron) as a cinematic influence

Also, a report by Roger Travis published in The Escapist compares the Halo series with the Latin epic Aenid by Virgil.
Answer: Biggest inspiration
StarShip Troopers:
 - Powered armor
 - A global governing body bordering on fascism (Colonial insurrection)
 - A vast military with no enemy to fight until the arrival of the Bugs/Covenant
 - Both Halo and SS had a soldier named Jenkins
 - The Bugs and the Flood

Which books influenced the game Halo?


Is there a recipe for a Kosher for Passover beer or ale?

Question: I'm looking to do a home brew of a Kosher for Passover beer. Is there a recipe I can follow?
Answer: Here's a company that's trying it:

…
According to Chabad.org, beer is '"chametz." What's chametz? According to the site, it's "any food product made from wheat, barley, rye, oats or spelt that has come into contact with water and been allowed to ferment and rise." Aka, considering it is made from wheat and barley, beer is not Passover approved. But! All hope isn't lost — there are now "beers" on the market that are permitted on the Passover table.
An Israeli brewing company called Meadan Craft Brewing has created a beer that's totally kosher for Passover. How? Well, as you know, standard beer is chametz, meaning, it's made with ingredients that need to rise which makes it against Passover law. But this special beer is made with dates. Not only that, but it's gluten-free, too.
…
— Is Beer Kosher For Passover? Here's What You Need To Know About This Popular Drink

But how you can call something made from fruit "beer", when it's obviously "wine", I don't know.
You might consider corn, since it isn't one of the proscribed grains.
But again, there's still the problem of the yeast.
And of course anyone involved in the process up until it's bottled must be a Sabbath-observing male.
Comment: Re. your last sentence; might you be confusing this with the production of **wine**?
Comment: @Oliver, yes.  I assumed that whatever is required for wine to be kosher for Passover would apply to other fermented beverages too.
Answer: A hopped apple cider that's fermented fairly dry is a great Kosher for Passover beer substitute.
Like this one - www.passoverbeer.com
And here is homebrew information:
https://byo.com/article/hopped-cider/


Augumented Dickey fuller unit root test- STATA

Question:
The attached image is my output for augumented dickey fuller unit root test from stata, I am not sure my data is stationary. if it is please explain based on what rule. because some places i see that test statistic should be less than 5% while other places i see the test statistic should be less than 1.96(Siginificant critical value)
Answer: The null hypothesis of the (augmented) Dickey Fuller unit root test is that the series being tested has a unit root (that implies nonstationarity).
The basic logic tells you to reject the null hypothesis if the test statistic is sufficiently extreme. The question could be, does it matter whether the test statistic is extremely large and positive or extremely large and negative. Here you are lucky to see which way the extremality of interest goes: 10% critical value is -1.605, 5% critical value (more extreme than 10%) is lower (more negative) at -1.950 and 1% critical value (more extreme than 5%) is even lower at -2.639. So you see that the more negative the test statistic is, the more extreme. In other words, the extremality goes into the negative direction.
Now see what the actual test statistic is: 10.134. That is less extreme than the conventional 5% value (and even the 10% value) because it is less negative than -2.639 (and even -1.605). Therefore, you do not reject the null hypothesis of unit root at any of the conventional significance levels. You data seems to be nonstationary.
This is a generic way of using tests you do not understand well. Of course, it is always better to know more to understand the intuition behind the test, but that is not always the case.


Sharepoint Online - One Drive File Sharing size limit?

Question: Under Sharepoint Online, is there a limit to the size of a file that you share via One Drive? I've found references to the max storage size based on your license, but not how large a file you can share. Any insight or first hand knowledge is appreciated!
Answer: No, you should be able to share any file that is already uploaded regardless of size.
The max file size you can upload is 2GB (see limitations and boundaries), but the file size can grow on the server above the 2GB limit. Some files, like OneNote, can get large due to versioning, but the actual file size of the current version can be small allowing the clients to sync. If the current version of the file exceeds 2GB, you may run into syncing issues that prevent you from uploading changes to the document.


Setting MySQL "lower_case_table_name" server variable

Question: Running MYSQL 5.1 on windows 7. . . how do I change the server variable for 'lower_case_table_names'.  Need to set it to 0.  I've tried to set it from the command prompt using mysqld.exe, and I've tried manually changing the my.ini file. . . no luck.
Does anyone have some sure-fire/straight-forward do-this, and then this instructions ?
Answer: Figured it out. . . couldn't change the variable w/ mysql workbench running. Closed it out, restarted the service and the changes took effect. Weird.
Answer: As far as I know this will only affect new tables, existing tables will not be affected by this property.
Comment: thats fine. . .  I can delete the existing db, and re-dump. . . my problem is when I run 'show variables' / 'lower_case_table_names' is still set to 1.


All possible electromagnetic Lorentz invariants that can be built into the electromagnetic Lagrangian?

Question: Given the electromagnetic Lagrangian density
$$
\mathcal{L}~=~-\frac{1}{4}F_{\mu\nu}F^{\mu\nu}~=~\frac{1}{2}(E^2-B^2)
$$
is a Lorentz invariant, how many other electromagnetic invariants exists that can be incorporated into the electromagnetic Lagrangian?
Comment: One can show that all local, gauge and Lorentz invariant can be constructed from only two quantities $F_{\mu\nu}F^{\mu\nu}$ and $\tilde F_{\mu\nu}F^{\mu\nu}$
Comment: What is the meaning of the symbol "~" over "F"?
Comment: $\tilde F_{\mu\nu}=\epsilon_{\mu\nu\sigma\lambda}F^{\sigma\lambda}$ and $\tilde F_{\mu\nu}F^{\mu\nu}\propto E^2-B^2$.
Comment: Oh its the dual tensor.
Comment: Related: http://physics.stackexchange.com/q/87817/2451 and links therein.
Answer: As mentioned in the comments, to find all possible terms we normally only consider local, gauge invariant, Lorentz invariant interactions. There are in fact an infinite number of these. This is easiest understood using the Lagrangian. The gauge invariant field stength tensor is given by
\begin{equation}
F _{ \mu \nu } = \partial _\mu A _\nu - \partial _\nu A _\mu
\end{equation}
The only other tensors with Lorentz indices are
\begin{equation}
\epsilon _{ \alpha \beta \gamma  ... } \quad , \quad g _{ \mu \nu }
\end{equation}
To lowest order in $ F $ the only non-zero invariants are:
\begin{equation}
F _{ \mu \nu } F ^{ \mu \nu} \quad , \quad \epsilon _{ \alpha \beta \gamma \delta } F ^{ \gamma \delta } F ^{ \alpha \beta }
\end{equation}
If we restrict ourselves to terms with mass dimension of $4$ or lower these are the only options (these terms are called renormalizable terms). However, one can also write down other invariants which have higher mass dimensions. One such example is the mass dimension six term,
\begin{equation}
\partial ^\mu F _{ \mu \nu } \partial ^\alpha F _\alpha ^{ \,\, \nu }
\end{equation}
Such terms are small at low energies and are often ignored. In general there are an infinite number of allowed (non-renormalizable) terms in the Lagrangian. Though it may not be trivial, such terms could be written in terms of the electric and magnetic fields to find the different combinations of $\bf E$ and $\bf B$ that form Lorentz invariants.
Comment: One wonders if there are people doing $f(F)$ E&M in the same way there are people doing $f(R)$ gravity.
Comment: Can one include the Lorentz gauge term into the Lagrangian?
Comment: A Lorentz gauge term, $\partial_\mu A^\mu$ is not gauge invariant. If you want to fix the gauge such that this term is zero then you can add it in. But at that point there is no use to including the term as this term is zero.


lawnmower shaft is off aligment after hitting pipe stump

Question: I have a Ariens self propelled lawnmower that I happend to hit a iron marker(pipe) with. When the blade hit the pipe, the lawnmower jolted and the engine stopped. I took a look and the blade still intact except for a nick on the edge. I replaced the flywheel key because it got broken when it hit the pipe.  the engine turns on but it vibrates in such a way the looks like the shaft might be out of aligment. is there a way to check the aligment? and if so, can it be reset? or is the mower finished?
Comment: I would try balancing the blade first.
Answer: How are you certain it is the shaft? How did you measure the runout? What was the result?
For all the times I have hit things with lawnmowers - it is the blade / blade arm that gets bent  and I have had reasonable success with straightening the blade / blade arm...
Answer: yes there is a way to straighten the crankshaft ,you will have to remove the engine from the mower, you can buy one or take it to a lawn mower repair shop if you buy one it comes with instructions


Email to case trigger change case owner

Question: I am using email-to-case which works really well, however, I want to filter the cases coming from list of spam senders(email) to go in a spam queue and those cases which are not will go to non spam queue. The trigger works for manually created cases, but from cases from email, it does not work. The owner becomes the Default case owner set in support settings.
How can I override the case owner into the queue when email-to-case if the owner becomes the default case owner?
Answer: You can follow this step, hopefully it will work.
You can find that, in the Email-to-Case setting Case Origin in set as 'Email'.
So, you could create assignment rule and add relevant condition along with the Case origin to route to a proper queue. There will be single assignment rule to be active, but it can have multiple conditions to route to a queue.
Comment: I chose to use custom settings for the records of spam emails to track some info about that spam email and also to make it easier to look for a certain email.

Email to case trigger change case owner


Why do we dimple a focaccia?

Question: When I was making a focaccia earlier today, I realised that I've never been told why we dimple them before baking. A quick Googling didn't reveal anything, so I'm asking here: why do we make dimples in a focaccia before baking? Is it strictly cosmetic, or is there another reason?
Comment: I guess an increased surface area is also nice. More area to get that brown surface.
Answer: I have read that the dimples are there to catch the olive oil that is drizzled over the top  (sometimes water may also be sprayed) before baking.  The little pools of olive oil soak in and further enhance the crust texture and flavor.
Answer: I do agree with NadjaCS's point of "olive oil that is drizzled over the top".
I know with some pastry's you add multiple dimples to stop it rising. I could see the dimples in a Focaccia being used to keep the bread flatter.
Comment: This is the reason. It's called "docking" and it's intended to ensure an even rise.
Comment: I once did a kitchen printer setup for a Turkish Bread manufacturer; it seemed that the only difference between 3 of the styles of bread that they baked was how many dimples (if at all) were in the bread... Cooking temperature, proofing times etc were all the same.
Answer: I think this is the answer, in Claire Saffitz's words: "strategically deflating some of the the air bubbles" in order to obtain a flat structure and not a "loafy thing with a big dome".
https://youtu.be/NGnMrM9qDtE?t=652
If I can add a piece of personal experience, I often make a focaccia that rises for several hours and before dimpling I also burst the bubbles that are too big as they would burn in the oven.

Why do we dimple a focaccia?


Are there any products based on Arduino that are sold by companies?

Question: Ok, Arduino is a good technology but is it used professionally? Is the quality good enough to be used for professional purposes?
Comment: Quite a few 3d printers have the circuitry of an Arduino and a special motor/heater driver shield combined to form their main circuit board.
Answer: In theory, an Arduino board could be used in some low-end professional products (i.e. where the performance and memory limitations aren't an issue). The build quality of the official boards is certainly good enough. The only issue they would potentially have is making suitably robust connections -- i.e. anything plugged into a female header would have the potential to get shaken loose.
In practice though, using an Arduino board would only make sense for extremely small-scale projects, where only a few units will be produced, and where there will be a minimum of external circuitry.
A commercial project would normally have a custom circuit board designed. That allows them to economise on space and features, eliminating unnecessary costs. Even if it only saves a small amount per board, it can make a big difference if you're doing mass-production.
With that said, a professional product could certainly use an AVR microcontroller or similar at its heart (much like the Arduino boards). Atmel was producing chips long before Arduino was around, and their products are well known and widely used. The choice really depends on the needs of the individual project.
Comment: We are doing this right now, and it's more than a few cents difference. Our prototype (Arduino, sensors, wiring) costs about $45. Our boards will cost about $5 and could be cheaper if we make a lot of them.
Comment: Just to be totally clear... that's the *retail* cost of Arduino boards and breakout boards, along with prototyping tools like breadboards and wires. The $5 is a hard price point to hit, and most of that is the Atmel chip, but that's our estimate for wholesale cost of our boards. The product itself needs a case and some documentation as well as packaging, so don't forget to add that in.
Comment: @Jasmine - Thanks for sharing some real values. I've clarified my wording so it's hopefully better now.
Answer: Yes, you can also use an Arduino for professional usage. The Arduino is actually just a prototyping device and easy to use for people at home/school. I suppose there might be products on the market which were developed using an Arduino. But the most important thing is the Atmel MCU inside the Arduino which can be used for anything. But, if you wanna know if the ATmega328P-PU which is used in the Arduino Uno is a common MCU used by professionals? The answer would be no. Everything has to be smaller and better so it'll be more likely to find the same MCU like the Arduino Leonardo, Mega etc etc.
Examples where professionals might use an Arduino for as base (The end product will only contain the MCU of the Arduino):

Kid toys like an Simon Says Game, Line following toy cars etc etc.
Small industrial products like an automated tape dispenser.
AVR programmers.
Card readers.
Answer: Yes, I work for an engineering design house and we use Arduino frequently to prototype ideas for clients.  It significantly speeds up the time to get a proof-of-concept device in the hands of the client and their potential investors.
We have found though that there is significant work to get from an Arduino-based prototype to a commercially-ready product.  Essentially you have to start again and design a completely custom printed circuit board, which is a relatively expensive exercise.
We are now developing a platform that is compatible with the Arduino IDE, but uses surface-mount modules rather than the Arduino shield system, allowing it to be manufactured in an automated surface-mount facility.  Check it out if you are interested at duinopro.cc.  We are in development stages at the moment, but already have hardware and are mainly working on our website, and designing new modules.


What is the difference between 原则 and 原理?

Question: See title. Both of these translate as "principle" and I'm struggling to see how they are different. Thanks in advance.
Answer:
原则 is principle of personal conduct

Example:
做人要有(原则) = A man has to have (principle)
工作至上是我的(原则) = My (principle) is works always come first

原理 is principle of physics

Example:
利用槓桿(原理) = Using the (principle) of leverage
利用虹吸(原理) = Using the (principle) of siphon

"I know the 原理 of something" means I know the reason why something works
"I know someone's 原则" means I know what someone would or would not do base on his principle (personal believe and conviction)

The 原则 (principle) of insurance companies is "to try their hardest to avoid paying their customers" (that's what they do as an unwritten rule)
Answer: Very few words translate one-to-one between languages, and they are usually very basic like you/me/water or simply loanwords. European language speakers often get confused on this topic after learning some other European language (which essentially shares a huge set of the same semantic fields with minuscule variations).
What is bundled together as "principle" in English (or rather, all IE languages sharing this post-Latin loanword) is not a single idea.
原则 is "principle" as in "man has his principles" - basic rules of behaviour". By choice.
原理 is "principle" in the sense "doctrine, theoretic base etc". By nature.
Answer: 原理: 理 is for the physical principles of things.
原则: 则 is for the rules of the society/human.
Answer: I thought that could be a simple distinction.
原理: theory, principles/fundamentals in science;
For example,

a cardinal principle: 根本的原理;

原则: principle, rules;
For example,

agree in principle: 原则上同意

The key is that in English the word principle can be used to denote both scientific theories and rules to regulate ourselves. Well, in Chinese, we separate it into two words: 原理 and 原则.
Hope this could help.
Good luck!
Answer: Previous answers are quite complete. I want to provide some additional information on "原则".
原则 also has a meaning close to "generally" or "usually". Means that a rule applies to most of the cases, but, importantly, it can have some exceptions.

例句:原则上,我们不接受一年级学生的转专业申请。
Example: Generally, we don't approve applications for change of major for first-year students.

This sentence means that "there can be some exceptions for first-year students".
Answer: In addition to what others have pointed out (that 原则 & 原理 both could refer to "principle" or "rule"), 原则 usually refers to concrete principles and guidelines, whereas 原理 refers to the more abstract, theoretical, and/or foundational principles. Newton's book, Philosophiæ Naturalis Principia Mathematica, for example, is "自然哲学的数学原理" in Chinese.

What is the difference between 原则 and 原理？


Why is Theodore Roosevelt's time with the Rough Riders seen so positively?

Question: As most historians have noted, Theodore Roosevelt did lead his soldiers into a trap and suffered the most causalities during the Battle of Las Guasimas and the Battle of San Juan Hill. It has been noted that he acted recklessly while leading his group into battle.
Comment: Evidence? I'll answer that with one point. Theodore Roosevelt campaigned on his time with the Rough Riders. And won re-elected. Plus when he was stumping for President William McKinley as the VP nominee he had former Rough Riders introduce him and speak on his behalf. So yes, it was seen as positive.
Comment: [Buffalo Bill](http://en.wikipedia.org/wiki/Rough_Riders#Theatrical_productions) would be Wikipedia's opinion on the matter.
Comment: Do you have some evidence that (1) his time with Rough Riders was viewed positively by the public and (2) that it had some definitive political effect?
Answer: Because they were so damn cool.
The Rough Riders were all volunteers who signed up out of a sense of adventure or patriotism. Wikipedia says that most of them were "college athletes, cowboys, and ranchers." Roosevelt was a privileged aristocrat and Assistant Secretary of the Navy. But when war broke out (a war he pushed for), Roosevelt resigned his cushy post and helped form a rag-tag group of soldiers trained for combat.
If "it has been noted that he acted recklessly" by leading the charge up Kettle Hill, it certainly wasn't by his contemporaries. Roosevelt was honored with the Medal of Honor. His citation noted that the Rough Riders calvary charge changed the entire course of the battle.

Lieutenant Colonel Theodore Roosevelt distinguished himself by acts of bravery on 1 July, 1898, near Santiago de Cuba, Republic of Cuba, while leading a daring charge up San Juan Hill. Lieutenant Colonel Roosevelt, in total disregard for his personal safety, and accompanied by only four or five men, led a desperate and gallant charge up San Juan Hill, encouraging his troops to continue the assault through withering enemy fire over open countryside. Facing the enemy's heavy fire, he displayed extraordinary bravery throughout the charge, and was the first to reach the enemy trenches, where he quickly killed one of the enemy with his pistol, allowing his men to continue the assault. His leadership and valor turned the tide in the Battle for San Juan Hill. Lieutenant Colonel Roosevelt's extraordinary heroism and devotion to duty are in keeping with the highest traditions of military service and reflect great credit upon himself, his unit, and the United States Army.

I would add that "acting recklessly" is sometimes appropriate or praiseworthy in military situations. I don't doubt that Audie Murphy acted recklessly when he ordered his men to fall back, jumped onto a burning tank destroyer, stayed there for hours, and single-handedly killed 50 or so advancing Germans. But his daring and sacrifice is seen as the exemplar of heroism, and Murphy is considered the greatest American soldier to ever live.
In conclusion, suppose that Dick Cheney had resigned his post after the Iraq War broke out and traveled to his home state of Wyoming. There, he rallied a group of Indians, ranchers, cowboys, college students, veterans, and eccentrics. His All-American Gang lands in Iraq. During the critical battle of Fallujah, Cheney personally leads a suicide charge through the streets-- on horseback!-- turning the tide of the battle and allowing America to win a crucial victory.
Hell, I'd vote for him.
Comment: *Hell, I'd vote for him.*  You mean you didn't? ;-)
Answer: Short answer(s). Because he won. That is, his side won the battle, thanks in large part to his efforts, and his country won the war. His charge of San Juan Hill was seen as one of the high points of an otherwise "dull" war.
And "history is written by the victors."


Display child terms of taxonomy term

Question: When displaying a taxonomy term, how can I also display the teasers of all the child terms of the current term?  I still want to display all the content and fields of the current node, but also display the child teasers.
Answer: The taxonomy display won't do this on its own. You could create a view to do this, then display the view below the term page.
If you call the view from a taxonomy term template you could use a "Contextual filter" to pass the term id (tid).
Comment: Thank you for the answer.  As far as I understand it now, this is only possible by overriding the taxonomy-term.tpl.php with some custom PHP.  If that's the case, why not just do it all withing the custom theme template, and skip the View?
Comment: After reading the template module source code, looking for functions that do what I want, I came up with this.

    $terms = taxonomy_get_children($term->tid, $vid);
    $a = taxonomy_term_view_multiple($terms, 'teaser');
    echo drupal_render($a);

Does that seem reasonable?

Display child terms of taxonomy term


Zigzag Line Symbol in QGIS

Question: I'm looking for a zigzag line symbol in QGIS.
I have tried creating a marker line using a simple triangle marker (^) and adjusting the size of the marker and the marker placement interval until the triangles touched each other and appeared to make a nice zigzag line. This works for straight lines but around curves there are gaps between the triangles because the triangles aren't actually connected.
Is there perhaps a way to join the markers together or another way to go about this?
I am using QGIS 2.4.0.
Comment: If someone is interested - a very dynamic solution can be found here: [drawing wavy wiggly lines in qgis](http://gis.stackexchange.com/questions/241802/drawing-wavy-wiggly-lines-in-qgis/354873#354873)
Answer: It seems like there's no way to just symbolise the line as a zigzag: unfortunately, you'll have to alter the underlying data.
You can get a reasonably good zigzag line by first splitting the original line into many equidistant line segments, and then offsetting every other point by a fixed amount.
Here's a Python script that does this, taking NathanW's answer to How can I create random points along a polyline in QGIS? as a starting point. Save the code chunk into a file called zigzag.py in your ~/.qgis/python directory (or {User Directory}\.qgis\python\ on Windows), and then import it in the QGIS Python console by typing import zigzag. Then you can select one or more lines that you want to zigzagify, and type zigzag.createZigzag(<wavelength>, <amplitude>) in the QGIS Python console, where <wavelength> and <amplitude> are the "length" and "width" of the zigzag segments, in map units.
Here's an example:

As you can see, the zigzags aren't very nice near the original line's corners, but at least the zigzag line doesn't have any breaks.
If you use James Conkling's suggestion of smoothing the line first using Chaiken's Algorithm, the result gets much nicer:

Here's the script:
from qgis.utils import iface
from qgis.core import *
import numpy as np
from cmath import rect, phase

# Function for calculating the mean of two angles.
# Based on http://rosettacode.org/wiki/Averages/Mean_angle#Python
def meanAngle(a1, a2):
    return phase((rect(1, a1) + rect(1, a2)) / 2.0)

def createZigzag(wavelength, amplitude):
    # Create a new memory layer to store the zigzag line.
    vl = QgsVectorLayer("LineString", "Zigzag", "memory")
    pr = vl.dataProvider()

    # For each selected object in the current layer
    layer = iface.mapCanvas().currentLayer()
    for feature in layer.selectedFeatures():
        geom = feature.geometry()

        # Number of zigzag segments
        length = geom.length()
        segments = np.round(length / wavelength)

        # Find equally spaced points that approximate the line
        points = [geom.interpolate(distance).asPoint() for
            distance in np.linspace(0, length, segments)]

        # Calculate the azimuths of the approximating line segments
        azimuths = np.radians(
            [points[i].azimuth(points[i + 1]) for i in range(len(points) - 1)])

        # Average consecutive azimuths and rotate 90 deg counterclockwise
        zigzagazimuths = [azimuths[0] - np.pi / 2]
        zigzagazimuths.extend([meanAngle(azimuths[i],
            azimuths[i - 1]) - np.pi / 2 for i in range(len(points) - 1)]
        )
        zigzagazimuths.append(azimuths[-1] - np.pi / 2)

        # Offset the points along the zigzagazimuths
        zigzagpoints = []
        for i in range(len(points)):
            # Alternate the sign
            dst = amplitude * (1 - 2 * np.mod(i, 2))
            zigzagpoints.append(
                QgsPoint(points[i][0] + np.sin(zigzagazimuths[i]) * dst,
                    points[i][1] + np.cos(zigzagazimuths[i]) * dst
                )
            )

        # Create new feature from the list of zigzag points
        fet = QgsFeature()
        fet.setGeometry(QgsGeometry.fromPolyline(zigzagpoints))

        pr.addFeatures([fet])
        vl.updateExtents()

    QgsMapLayerRegistry.instance().addMapLayer(vl)

Answer: I've tried to do this before and haven't had much luck.
qGIS places repeated symbols on a line based on one reference point (by default, the center, though you can set it to top/middle/bottom x left/center/right), and rotates that symbol based on the slope of the line at that point.  On a straight line, where the slope doesn't change from one symbol placement to the next, each symbol will line up perfectly with the previous.  On a curve, though, no point on one symbol will perfectly match the corresponding point on the next symbol.

So, if the red line is the line itself, repeating a symbol along that line results in gaps between symbols along the outside of a curve, and overlaps on the inside of a curve.
To completely eliminate the gaps and overlaps, every symbol square would need to be reshaped as a rhombus of varying size--similar to how stones on an arch are beveled to match the curve.  As far as I know, it's not possible to simulate something like that.  But, you can decrease the distortion by densifying and smoothing your line geometry so that the change in angle is less extreme.  The generalizer plugin can help with that (try using it with Chaiken's algorithm).

Also, breaking your symbol into smaller segments and placing each in succession, so that again you decrease the angle between each subsequent marker, would help.  E.g., break your V symbol into a \ and a /, load both on the marker line and for each, set an x-offset equal to half their width, positive for one and negative for the other.
Lastly, a slightly thicker symbol stroke with rounded ends would help mask the slight distortion.
This is still a bit of a hack--would love to hear if anyone else has a more reliable approach.
Edit:
another thought: the misalignment from one symbol to another caused by the rotation of the symbol along the curve is greatest at the top/bottom of the symbol, but less pronounced at the middle.  So a pattern that starts and terminates at the symbol center will have smaller gaps than a pattern that starts/terminates at the top/bottom.  E.g.

...still a hack--still not foolproof
Answer: I don't think that this is a feature in QGIS. However I would try to do it this way:

make two copies of the layer using the Affine tool plugin. One of the layers with a slightly larger scale and one with a slightly smaller scale.
Densify the geometry of the layers. That means add more nodes.
Go to the attribute table and name each feature node consequently 1,2,3,... in one layer and 1b,2b,3b,... in the second layer.
merge both layers and sort the attribute layer --> this should give you a zigzag line.

Maybe this works.

Zigzag Line Symbol in QGIS


Group By (Aggregate Map Reduce Functions) in MongoDB using Scala (Casbah/Rogue)

Question: Here's a specific query I'm having trouble with. I'm using Lift-mongo-
records so that i can use Rogue. I'm happy to use Rogue specific
syntax , or whatever works.
While there are good examples for using javascript strings via java noted below, I'd like to know what the best practices might be.
Imagine here that there is a table like
comments {
 _id
 topic
 title
 text
 created
}

The desired output is a list of topics and their count, for example

cats (24)
dogs (12)
mice (5)

So a user can see an list, ordered by count, of a distinct/group by
Here's some psuedo SQL:
SELECT [DISTINCT] topic, count(topic) as topic_count
FROM comments
GROUP BY topic
ORDER BY topic_count DESC
LIMIT 10
OFFSET 10

One approach is using some DBObject DSL like
val cursor  = coll.group( MongoDBObject(
"key" -> MongoDBObject( "topic" -> true ) ,
//
"initial" -> MongoDBObject( "count" ->  0 ) ,
"reduce" -> "function( obj , prev) { prev.count += obj.c; }"
 "out" -> "topic_list_result"
))

 [...].sort( MongoDBObject( "created" ->
-1 )).skip( offset ).limit( limit );

Variations of the above do not compile.
I could just ask "what am I doing wrong" but I thought I could make my
confusion more acute:

can I chain the results directly or do I need "out"?
what kind of output can I expect - I mean, do I iterate over a
cursor, or the "out" param
is "cond" required?
should I be using count() or distinct()
some examples contain a "map" param...

A recent post I found which covers the java driver implies I should
use strings instead of a DSL :
http://blog.evilmonkeylabs.com/2011/02/28/MongoDB-1_8-MR-Java/
Would this be the preferred method in either casbah or Rogue?
Update: 9/23
This fails in Scala/Casbah  (compiles but produces error {MapReduceError 'None'} )
val map = "function (){ emit({ this.topic }, { count: 1 }); }"
val reduce = "function(key, values) {  var count = 0; values.forEach(function(v) { count += v['count']; }); return {count: count}; }"
val out  = coll.mapReduce(  map ,  reduce  , MapReduceInlineOutput  )
ConfiggyObject.log.debug( out.toString() )

I settled on the above after seeing
https://github.com/mongodb/casbah/blob/master/casbah-core/src/test/scala/MapReduceSpec.scala
Guesses:

I am misunderstanding the toString method and what the out.object is?
missing finalize?
missing output specification?
https://jira.mongodb.org/browse/SCALA-43 ?

This works as desired from command line:
   map = function (){
        emit({ this.topic }, { count: 1 });
    }

    reduce = function(key, values) {  var count = 0; values.forEach(function(v) { count += v['count']; }); return {count: count}; };

    db.tweets.mapReduce( map, reduce,  { out: "results" } ); //
    db.results.ensureIndex( {count : 1});
    db.results.find().sort( {count : 1});

Update
The issue has not been filed as a bug at Mongo.
 https://jira.mongodb.org/browse/SCALA-55
Answer: The following worked for me:
val coll = MongoConnection()("comments")
val reduce = """function(obj,prev) { prev.csum += 1; }"""
val res = coll.group( MongoDBObject("topic"->true),
                       MongoDBObject(), MongoDBObject( "csum" -> 0 ), reduce)

res was an ArrayBuffer full of coll.T which can be handled in the usual ways.
Answer: Appears to be a bug - somewhere.
For now, I have a less-than-ideal workaround working now, using eval() (slower, less safe) ...
db.eval( "map = function (){ emit( { topic: this.topic } , { count: 1 }); } ; ");
db.eval( "reduce = function(key, values) { var count = 0; values.forEach(function(v) { count += v['count']; }); return {count: count}; }; ");
db.eval( " db.tweets.mapReduce( map, reduce, { out: \"tweetresults\" } ); ");
db.eval( " db.tweetresults.ensureIndex( {count : 1}); ");

Then I query the output table normally via casbah.


Aspect of verb походить

Question: According to Etymology 2 here походить is perfective. However, it also says it "is in the class of Russian abstract verbs". And here for abstract verbs in slavic grammar it says "always imperfective in aspect, even with prefixes that are normally associated with the perfective aspect". So as far as I understand this, it is a contradiction?
Comment: Probably the article for the British Wikipedia was written by Poles. Походить, побегать, поползать, поносить, потаскать, повозить, поездить, полетать, поплавать — perfective. (I'm not sure that I remembered all the combinations of ' ПО + multidirectional verb of movement')
Answer: This rule works for some prefixes, does not work for the others, and works both ways for still others.
Приходить, прилетать, привозить etc. are imperfective, just like the rule says.
Походить, полетать, повозить are perfective.
With prefixes like с-, на-, от- and some others, the verbs split their meanings.
Слетать means to "fly off" (imperfective): нитка часто слетает с катушки "the thread often flies off the bobbin"; and "fly there and back": мы слетали в отпуск в Рим "we flew to Rome for a vacation".
Налетать means to "fly into something" (imperfective): на высоких зданиях зажигают красные огни, чтобы на них не налетали самолёты "they place red lights on the tall structures so that airplanes would not crash into them"; and "fly enough for something" (perfective): я налетал сто тысяч миль и мне дали золотую карту "I have flown hundred thousand miles with them and they gave me gold membership"
It is interesting that some iterative verbs change their roots depending on the aspect, and some don't: сбега́ть/сбе́гать, съезжать/съездить, сплывать/сплавать etc.; and some don't even have a proper imperfective root, like таскать, катать.
Answer: I think it's not a contradiction, but more like an exception to the rule, because the verb is indeed perfective because it answers the question "Что сделать?" instead of "Что делать?" (it can still become imperfective though, if used in a different meaning like "to resemble"), while it is also abstract because it describes an action that is not single and completed.
One website I found states that Abstract verbs are always imperfective and then immediately provides an example which disproves their statement:

(abstract in Russian but not in Polish) I went to the post office.
(there and back, multidirectional)

Translated to Russian this sentence appears as - "Я сходил на почту". But the verb сходил is clearly perfective because it answers the question "Что сделал?", not "Что делал?". So it appears as an exception to the rule.
P.S - to be honest I think the rule that states that "all abstract verbs are always imperfective" might indeed be totally wrong as there are other cases of abstract yet perfective verbs, like the ones that were provided by Quassnoi.
Answer: There is no contradiction at all. As you already noticed, the word походить has different meanings. One of them is походить (perfective) что сделать? meaning movement.
Он встал, походил немного, потом снова сел.
But the other one is what you call abstract походить (imperfective) что делать? It means to resemble, like быть похожим.This is not an action verb, it means a state.
Повзрослев, он походил на отца. Having grown up he resembled his father.

Aspect of verb походить


When shopping for ebooks on Amazon how do I tell if they have DRM?

Question: Some books sold on Amazon have DRM and some do not.  But "DRM" is not listed anyplace on the book descriptions that I have been able to find.  How can I know before I buy an ebook from Amazon if it has DRM?
Comment: This is because Amazon does not want to admit that drm is a problem.
Answer: Books that have "Simultaneous Device Usage: Unlimited" listed under "Product Details" do not have DRM (Digital rights management). Those without this disclaimer have DRM.
Comment: Is this still true? I can't find an ebook on Amazon with this product detail.
Comment: It is still true from my experience.  For example, when looking at books from Baen, you'll find that they do not have DRM, so all of those books should that Usage Unlimited tag.  Here is an example,  "Cats in Space" edited by Bill Fawcett.

https://smile.amazon.com/Cats-Space-Other-Places-Fawcett-ebook/dp/B01M4M9FMP/ref=sr_1_2?keywords=Cats+in+Space&qid=1637524897&sr=8-2#detailBullets_feature_div


Asking another Rabbi

Question: What are the parameters and conditions of when one is allowed (and not allowed) to ask another Rabbi once he/she got a Psak from the first Rabbi?
Comment: Can we accept the answers to this question as halakhah lemaaseh, or do we have to ask a posek.  What if that posek says no, but you ask a second posek says you can pasken from mi.yodeya?
Comment: *"Mommy, can i have a cookie?" "No." "Daddy, can i have a cookie?"*
Answer: Rav Aryeh Kaplan in his Collected Writings quotes the Shach as far as the exact parameters pertaining to this question. His basic points are:

In order to ask another posek one must have real reason to doubt the correctness of the first psak.
(As Shalom stated) One must tell the second posek that he already received a psak from posek #1.
The 2nd posek must rule on whether the first posek was mistaken and disregarded (or was ignorant of) a d'var mishnah, a clearcut and easily known unanimously held halachic decision.
If posek #2 rules that posek #1 made such a mistake, then one is free to ask posek #2 for his opinion.
If posek #2 just disagrees and cannot state a case for proving that posek #1 made a mistake on a clearly stated halacha then one may not leave posek #1's position in favor of posek #2's decision even if one feels that it makes more sense.

I am writing this from memory of Rav Kaplan's book, the Shach (I looked it up at the time I read R Kaplan's essay), and the Rosh (who is probably based on the Tosafos YS is referring to) so this is possibly an incomplete guide but it has the basics as I can recall them.
If I find online links and when I get ahold of the exact sources I will bl"n put them on to this answer.
Answer: I believe the Kitzur Shulchan Aruch says you must tell Rabbi #2 that you already asked Rabbi #1 (and honestly convey both your question as posed to him, and his answer!).
The Chochmas Adam has more guidelines on dealing with poskim and psakim; hopefully I'll have more info later.
This assumes that rabbis 1 and 2 are just random rabbis you ask.
However, sometimes a rabbi is in a position of exclusive authority over a certain sphere, at which point it could be obligatory to follow his rulings vis-a-vis that sphere.  Rabbi Mordechai Willig believes that an Israeli soldier may ask his home-town rabbi a personal-only question like "what text should I use for my personal prayers?"  Any question affecting the army's performance must go to an army rabbi.  (Though Rabbi Gil Student cites a differing view here, that one may confirm with one's personal rabbi that the army rabbi's psak was within the boundaries of reason.)
Comment: The Kitzur is quoting a Tosfos in Avodah Zarah daf Zayin where the main sugyah is.
Comment: Yayasher Koach YS!
Answer: All of the dinim can be found in YD 242:31 in the Rema. The Shach there disagrees with a lot of the Rema's psakim, but the Aruch Hashulchan says we hold like the Rema over the Shach on this one (there's no Mishnah Brura since its in YD)
Comment: Welcome to Mi Yodeya, Yoni! If you would [edit] in what these poskim said, that would improve the answer. :)
Comment: I'll second @Scimonster's welcome. You might also want to [register](http://judaism.stackexchange.com/users/login) your account, which will [give you access](http://meta.stackexchange.com/questions/44557/why-should-i-register-my-account) to more of the site's features.

Asking another Rabbi


Are Christians called to forgive Unbelievers?

Question: In Matthew 18:21-22, we are asked to forgive not just seven, but "seventy times seven" (unlimited) times our brother.
However, is there any verse concerning how we are to forgive non believers ?
Answer: Mathew 18:21-22
This verse says we should forgive seven times seventy "Period!"
It doesn't say we should forgive seven times seventy,
-asterisk-
except for non- believers.
Christians are called to
(Love) even our "Enemies!"
Mathew 5:44
But i tell you, Love your enemies an pray for those who persecutes you.
(NIV)
I'm pretty sure that conveys forgiving non-believers.
Answer: However, is there any verse concerning how we are to forgive non believers ?
"Forgiveness" concerns the restoration of relationship.
If a brother in Christ asks for forgiveness, we are to grant it.
Paul gives an example of one who was disciplined by the church in Corinth and had repented and wanted to rejoin in fellowship.

2 Corinthians 2:7  So that contrariwise ye ought rather to forgive
  him, and comfort him, lest perhaps such a one should be swallowed up
  with overmuch sorrow.

As real relationship with the unsaved is not possible, there is a real limit as to what forgiveness could accomplish.

2 Corinthians 6:14-15  Be ye not unequally yoked together with
  unbelievers: for what fellowship hath righteousness with
  unrighteousness? and what communion hath light with darkness?   And
  what concord hath Christ with Belial? or what part hath he that
  believeth with an infidel?

However, we are to work as well as we can with them.

Romans 12:18  If it be possible, as much as lieth in you, live
  peaceably with all men.
Answer: I think it's as simple as the Bible states that we should not judge others.  Therefore we have no reason to forgive them as it's not our job to judge them:
Matthew 7 NIV

Judging Others 7 "Do not judge, or you too will be judged. 2 For in
  the same way you judge others, you will be judged, and with the
  measure you use, it will be measured to you.
3 "Why do you look at the speck of sawdust in your brother's eye and
  pay no attention to the plank in your own eye? 4 How can you say to
  your brother, 'Let me take the speck out of your eye,' when all the
  time there is a plank in your own eye? 5 You hypocrite, first take the
  plank out of your own eye, and then you will see clearly to remove the
  speck from your brother's eye.
6 "Do not give dogs what is sacred; do not throw your pearls to pigs.
  If you do, they may trample them under their feet, and turn and tear
  you to pieces.
Answer: In addition to the above The entire purpose of Jesus death and resurrection was to forgive the un-forgiven. You refer to them as non believers, but it must be remembered that the Gentile Nations were not believers, and yet Jesus himself sent Paul to the Gentile nations:

Acts 9:5 and 6 NKJV  And he said, "Who are You, Lord?" Then the Lord said, "I am Jesus, whom you are persecuting. It is hard for you to kick against the goads." 6  So he, trembling and astonished, said, "Lord, what do You want me to do?" Then the Lord said to him, "Arise and go into the city, and you will be told what you must do."
Acts 13:47  NKJV  For so the Lord has commanded us: 'I HAVE SET YOU AS A LIGHT TO THE GENTILES, THAT YOU SHOULD BE FOR SALVATION TO THE ENDS OF THE EARTH.' "

We also have the prophesy of Simeon at Jesus dedication:

Luke 2:25 through 35  NKJV  And behold, there was a man in Jerusalem whose name was Simeon, and this man was just and devout, waiting for the Consolation of Israel, and the Holy Spirit was upon him. 26  And it had been revealed to him by the Holy Spirit that he would not see death before he had seen the Lord's Christ. 27  So he came by the Spirit into the temple. And when the parents brought in the Child Jesus, to do for Him according to the custom of the law, 28  he took Him up in his arms and blessed God and said: 29  "Lord, now You are letting Your servant depart in peace, According to Your word; 30  For my eyes have seen Your salvation 31  Which You have prepared before the face of all peoples, 32  A light to bring revelation to the Gentiles, And the glory of Your people Israel." 33  And Joseph and His mother marveled at those things which were spoken of Him. 34  Then Simeon blessed them, and said to Mary His mother, "Behold, this Child is destined for the fall and rising of many in Israel, and for a sign which will be spoken against 35  (yes, a sword will pierce through your own soul also), that the thoughts of many hearts may be revealed."

We also have the words of Jesus himself:

John 10:14 through 16  NKJV  I am the good shepherd; and I know My sheep, and am known by My own. 15  As the Father knows Me, even so I know the Father; and I lay down My life for the sheep. 16  And other sheep I have which are not of this fold; them also I must bring, and they will hear My voice; and there will be one flock and one shepherd.
Matthew 6:9 through 15  In this manner, therefore, pray: Our Father in heaven, Hallowed be Your name. 10  Your kingdom come. Your will be done On earth as it is in heaven. 11  Give us this day our daily bread. 12  And forgive us our debts, As we forgive our debtors. 13  And do not lead us into temptation, But deliver us from the evil one. For Yours is the kingdom and the power and the glory forever. Amen. 14  "For if you forgive men their trespasses, your heavenly Father will also forgive you. 15  But if you do not forgive men their trespasses, neither will your Father forgive your trespasses.

And finally we have Jesus saying:

Matthew 5:43 through 48 NKJV  "You have heard that it was said, 'YOU SHALL LOVE YOUR NEIGHBOR and hate your enemy.' 44  But I say to you, love your enemies, bless those who curse you, do good to those who hate you, and pray for those who spitefully use you and persecute you, 45  that you may be sons of your Father in heaven; for He makes His sun rise on the evil and on the good, and sends rain on the just and on the unjust. 46  For if you love those who love you, what reward have you? Do not even the tax collectors do the same? 47  And if you greet your brethren only, what do you do more than others? Do not even the tax collectors do so? 48  Therefore you shall be perfect, just as your Father in heaven is perfect.

It is not possible to love others as yourself and not forgive them for their wrongs.
Last of all remember that Jesus said:  Therefore you shall be perfect, just as your Father in heaven is perfect. And that perfect God in his perfect love sent Jesus:

John 3:16 and 17  For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life. 17  For God did not send His Son into the world to condemn the world, but that the world through Him might be saved.

So if God loves us so much as to do that, is his asking us to forgive others that big of a thing?


What is the furthest object in the observable universe?

Question: My question is about furthest object in the observable universe except Сosmic microwave background.
Comment: Sort of hard to answer, as it changes as more and more things leave the observable universe (as everything moves away from everything else we will eventually be all alone in the galaxy)
Comment: [This is yesterday's article on Universe Today](http://www.universetoday.com/105694/taking-measure-a-new-most-distant-galaxy/) that is directly related and straight from the start discusses how short-lived is our definition of _"the furthest observable Universe"_. ;)
Answer: About 13.1 billion light years.
The z8 GND 5296 Galaxy mentioned in the article linked by TildalWave, mere 700 millions years old (after Big Bang) would be the mentioned distance from us for the light to reach us at indicated speed, considering the 13.798 bln years old universe. As we push technological barriers, we keep finding more distant objects.
The age of the universe is the hard limit in light years of distance of any observable object - there was nothing to emit light more than 13.798 bln years ago, or respectively, visible from more than 13.798 bln light years away. visible from distance that what was 13.798 bln light years 13.798 bln years ago - or, after adjusting for universe expansion over that time, currently 46.6 billion light years away.
Of course, as RhysW mentions, this limit changes over time as the universe ages and grows. The exact rate of growth is 74.2km/sec per megaparsec, or about 0.000000007% per year. I'd say, comparing to our life and current technological progress, an insignificant factor.
Comment: The first year it grows by 1/13.768 billionths the second year it grows by 1/13.768 (+1 year) billionths, the third year 1/13.768 (+2 years) billionths. Percentage wise, it grows by a smaller and smaller amount each year as the universes compounded size increases. For it to stay at 0.000000007% increase a year the rate at which light travels would have to be increasing! Just a small note I thought was worth making
Comment: @RhysW: Yes, the rate is not constant. But the rate of change of that rate (the second differential) is even smaller and even more negligible. There is another hard limit lowering the 13.798 bln by roughly 150mln. though: first stars formed roughly 150mln years after beginning of universe. There will be nothing visible to be observed earlier/further, no bodies emitting light or radiation.
Answer: There are few objects that might have even higher redshift. Googling I've found three accepted papers:

two are about a $z\approx10$ galaxy. One published in Nature and the other one in Astrophysics Journal Letters
is about a strong lensed candidate at $z\approx11$ published on Astrophysical Journal

There are also few gamma ray burst associated with objects at large redshift. This database containts:

z=8.26 GRB090423
z=9.2 GRB090429B. The redshift if photometric, which means that the error on the determination is likely large

There might be few other around


How would enabling FileVault alter my system and TM performance?

Question: What are the pros and cons, performance-wise, of enabling and using FileVault? Is there any at all, or does it slow a computer down significantly or on the contrary speed it up? Also, what effect will it have on Time Machine-backups (performance-wise)?
Comment: Are you referring to the new FileVault "2" included in OS X Lion, where the entire disk is encrypted, or the almost-completely-different earlier FileVault from a prior edition of OS X?
Comment: Updated the question, Lion-FileVault is what I'm referring to :)
Comment: An older question, unanswered: [Apple-provided software to measure or estimate the CPU load associated with Core Storage](http://apple.stackexchange.com/q/19429/8546)
Answer: CPU load
Filevault 2 supports Intel® Advanced Encryption Standard (AES). It's important to know if your Mac has an Intel processor which supports this, as it significantly reduces the CPU overhead. Search for you CPU here an look if is supports the New AES instructions.
My Macbook Pro 2011 got this feature enabled via a firmware update (Apple did not enable this with the newly shipped MBP). With AES encryption acceleration, the performance drop with Filevault 2 enabled is almost unnoticeable during normal usage. The maximum read speeds of my SSD only dropped from 510MB/s to 490MB/s.
Ars Technica, published an extended review on Filvault 2 in Lion. They say:

Apple also leverages the special-purpose AES instructions and hardware on Intel's newest CPUs, further reducing the CPU overhead. The end result is that regular users will be hard-pressed to notice any reduction in performance with encryption enabled.

As the overall CPU load is nearly unchanged, the battery life is not affected significantly.
Time Machine Backups
If you backup up wirelessly (unencrypted) or locally (encrypted, USB) the performance of Time Machine will not be affected significantly.

First, because the of the AES acceleration mentioned earlier.
Secondly because Time Machine creates local backups (snapshots). OS X Lion compensates for the potentially unavailable external disk by keeping an additional backup locally on the primary hard drive. This has its obvious advantages, since you can restore to past Time Machine backups right away from anywhere.

I've been using Filevault 2 encryption on a MBP 8,2 for three months.
Answer: (I'm assuming you are referring to FileVault 2 found in OS X Lion)
The folks at AnandTech have run some performance benchmarks on the new FileVault.  Quote:

... [described are several I/O tests with and without FileVault enabled, including some charts you might want to have a look at] ...
Overall the hit on pure I/O performance is in the 20 - 30% range. It's
  noticeable but not big enough to outweigh the benefits of full disk
  encryption. [...]

[emphasis above is mine]
So to answer your question:

FileVault slows I/O down, and it is a measurable decrease in performance.  However, I agree with the earlier quoted statement – in that the added security is beneficial, and I use FileVault on my Macbook Air.
The answer on the second question is "it depends".  The TimeMachine backup process must certainly read a lot of data from the FileVault-encrypted disk, so the reading portion of the backup will be slower.
However, whether or not the overall backup performance suffers considerably depends on where the bottleneck is in the system – e.g. is it a very fast backup drive, or a very slow backup drive? Is it connected by USB (slower), or Thunderbolt (faster)? If the write speed is terrible, that will govern the overall speed of the backup, not so much the read speed having been reduced a bit.  Ergo, it depends.
Comment: For incremental backups by Time Machine, there may be more reading of metadata than of data. I shouldn't assume that reading will be slower.
Answer: This depends to a large extent on your hardware.  Filevault essentially encompasses 2 major elements:
Encryption
CPU bound, the faster your CPU, the quicker the OS can encrypt and decrypt the data on the disk.  Filevault uses 256 bit encryption, so it's a fairly meaty process
I/O
Once stuff is encrypted (or before it can be decrypted) is needs to be read from or written to disk.  The difference between an SSD and traditional spinning platter media is enormous.  What might be a slow decryption process could be made up for using lightening fast access.
So, really it depends on all sorts of things, and how they can affect the above.  You don't list hardware, so that makes it near impossible to gauge.
Anecdotally, as it's the only measure I have to hand, I have had Lion installed on a 1.6Ghz Macbook Air with SSD both with and without Filevault.  In use it booted marginally slower, but I had to time it (I forget the timings, but it was of the 15% slower mark or so) but in use I could see no discernible difference.
Assuming you have a USB Time Machine disk, I would say the impact will be non-existant, as it's highly unlikely that any affect on performance would take it down to below your normal USB performance.


cannot download, $GOPATH not set

Question: I want to install json2csv using go get github.com/jehiah/json2csv but I receive this error:
package github.com/jehiah/json2csv: cannot download, $GOPATH not set. For more details see: go help go path

Any help on how to fix this on MacOS?
Comment: I'm having the same problem with a different package (pup).  C'mon Go maintainers, please make an (OS X) installer that finishes the job!  The OS X installer for Node is a great example.  Using Node does not require additional manual installation steps.  It just works.  I hope future versions of the Go installer will be better.
Comment: http://golang.org/doc/code.html#GOPATH
Comment: See also: http://stackoverflow.com/questions/17872223/cannot-download-gopath-not-set
Answer: [Update: as of Go 1.8, GOPATH defaults to $HOME/go, but you may still find this useful if you want to understand the GOPATH layout, customize it, etc.]
The official Go site discusses GOPATH and how to lay out a workspace directory.
export GOPATH="$HOME/your-workspace-dir/" -- run it in your shell, then add it to ~/.bashrc or equivalent so it will be set for you in the future. Go will install packages under src/, bin/, and pkg/, subdirectories there. You'll want to put your own packages somewhere under $GOPATH/src, like $GOPATH/src/github.com/myusername/ if you want to publish to GitHub. You'll also probably want export PATH=$PATH:$GOPATH/bin in your .bashrc so you can run compiled programs under $GOPATH.
Optionally, via Rob Pike, you can also set CDPATH so it's faster to cd to package dirs in bash: export CDPATH=.:$GOPATH/src/github.com:$GOPATH/src/golang.org/x means you can just type cd net/html instead of cd $GOPATH/src/golang.org/x/net/html.
Keith Rarick notes you can set GOPATH=$HOME to put Go's src/, pkg/ and bin/ directories right under your homedir. That can be nice (for instance, you might already have $HOME/bin in your path) but of course some folks use multiple workspaces, etc.
Comment: $GOPATH is set, but "cannot download, $GOPATH not set. For more details see: go help gopath" appears anyway.
Comment: @Tyguy7 chances are you didn't `export` it; run `/bin/bash -c "echo \$GOPATH"` to verify that sub-processes can see `$GOPATH`; if it echos empty, then run `export GOPATH` and then `go get ...`
Comment: In general, no, you can use one workspace whose `src/` contains e.g. `github.com/youruser/x` and `github.com/youruser/y`. That's what I do. People might have their reasons to do otherwise (company policy to keep projects apart?), but I can't speak to that.
Comment: Thanks for the info. Do you need to change your workspace for each individual project?
Comment: What platform (Windows or Linux/OS X/other Unix)? If not Windows, what does`echo $GOPATH` say? It might be worth posting as a separate question; it sounds like you're in some unusual situation, and debugging those in comments can be tricky.
Answer: This one worked
Setting up Go development environment on Ubuntu, and how to fix $GOPATH / $GOROOT
Steps
mkdir ~/go

Set $GOPATH in .bashrc,
export GOPATH=~/go
export PATH=$PATH:$GOPATH/bin

Comment: Link is dead now.
Answer: Using brew
I installed it using brew.
$ brew install go

When it was done if you run this brew command it'll show the following info:
$ brew info go
go: stable 1.4.2 (bottled), HEAD
Go programming environment
https://golang.org
/usr/local/Cellar/go/1.4.2 (4676 files, 158M) *
  Poured from bottle
From: https://github.com/Homebrew/homebrew/blob/master/Library/Formula/go.rb
==> Options
--with-cc-all
    Build with cross-compilers and runtime support for all supported platforms
--with-cc-common
    Build with cross-compilers and runtime support for darwin, linux and windows
--without-cgo
    Build without cgo
--without-godoc
    godoc will not be installed for you
--without-vet
    vet will not be installed for you
--HEAD
    Install HEAD version
==> Caveats
As of go 1.2, a valid GOPATH is required to use the `go get` command:
  https://golang.org/doc/code.html#GOPATH

You may wish to add the GOROOT-based install location to your PATH:
  export PATH=$PATH:/usr/local/opt/go/libexec/bin

The important pieces there are these lines:

/usr/local/Cellar/go/1.4.2 (4676 files, 158M) *
export PATH=$PATH:/usr/local/opt/go/libexec/bin

Setting up GO's environment
That shows where GO was installed. We need to do the following to setup GO's environment:
$ export PATH=$PATH:/usr/local/opt/go/libexec/bin
$ export GOPATH=/usr/local/opt/go/bin

You can then check using GO to see if it's configured properly:
$ go env
GOARCH="amd64"
GOBIN=""
GOCHAR="6"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/usr/local/opt/go/bin"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.4.2/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.4.2/libexec/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fno-common"
CXX="clang++"
CGO_ENABLED="1"

Setting up json2csv
Looks good, so lets install json2csv:
$ go get github.com/jehiah/json2csv
$

What just happened? It installed it. You can check like this:
$ $ ls -l $GOPATH/bin
total 5248
-rwxr-xr-x  1 sammingolelli  staff  2686320 Jun  9 12:28 json2csv

OK, so why can't I type json2csv in my shell? That's because the /bin directory under $GOPATH isn't on your $PATH.
$ type -f json2csv
-bash: type: json2csv: not found

So let's temporarily add it:
$ export PATH=$GOPATH/bin:$PATH

And re-check:
$ type -f json2csv
json2csv is hashed (/usr/local/opt/go/bin/bin/json2csv)

Now it's there:
$ json2csv --help
Usage of json2csv:
  -d=",": delimiter used for output values
  -i="": /path/to/input.json (optional; default is stdin)
  -k=[]: fields to output
  -o="": /path/to/output.json (optional; default is stdout)
  -p=false: prints header to output
  -v=false: verbose output (to stderr)
  -version=false: print version string

Add the modifications we've made to $PATH and $GOPATH to your $HOME/.bash_profile to make them persist between reboots.
Answer: Watch a Video
In general, I always recommend this official video from Go to get a quick overview on the matter:
http://www.youtube.com/watch?v=XCsL89YtqCs
It's easier to be shown than to be told.
@jwfearn paraphrased the important part of the video:

export GOPATH="${HOME}/gocode"; export PATH="${PATH}:${GOPATH}/bin"; mkdir -p "${GOPATH}"
Comment: Thanks @jwfearn - videos are for music and other entertainment; can't copy & paste from them :-)
Comment: Excellent introductory video - I always understand better when it's shown to me.
Answer: I found easier to do it like this:
export GOROOT=$HOME/go
export GOPATH=$GOROOT/bin
export PATH=$PATH:$GOPATH

Answer: For MAC this worked well for me.
sudo nano /etc/bashrc

and add the below at the end of the file
export PATH=$PATH:/usr/local/opt/go/libexec/bin
export GOPATH=/usr/local/opt/go/bin

This should fix the problem. Try opening a new terminal and echo $GOPATH you should see the correct value.
Answer: (for MAC)
I tried all these answers and, for some still unknown reason, none of them worked.
I had to "force feed" the GOPATH by setting the environment variable per every command that required it. For example:
sudo env GOPATH=$HOME/goWorkDirectory go build ...

Even glide was giving me the GOPATH not set error. Resolved it, again, by "force feeding":
    I tried all these answers and, for some still unknown reason, none of them worked.
I had to "force feed" the GOPATH by setting the environment variable per every command that required it.
sudo env GOPATH=$HOME/goWorkDirectory glide install

Hope this helps someone.
Answer: Your $GOROOT should not be set up.
You $GOPATH should be set to $HOME/go by typing export $GOPATH=$HOME/go
Please type export GOROOT="" to fix your problem.
Answer: Just do export GOPATH="/whatever/you/like/your/GOPATH/to/be".
Comment: If I'm a go noob, I don't yet know "where I'd like my GOPATH to be".  IMHO it's a drag that there is not a *default* GOPATH behavior which can be *overridden* by an environment variable.
Answer: If you run into this problem after having $GOPATH set up, it may be because you're running it with an unsupported shell. I was using fish and it did not work, launching it with bash worked fine.
Answer: You can use the "export" solution just like what other guys have suggested. I'd like to provide you with another solution for permanent convenience: you can use any path as GOPATH when running Go commands.
Firstly, you need to download a small tool named gost : https://github.com/byte16/gost/releases . If you use ubuntu, you can download the linux version(https://github.com/byte16/gost/releases/download/v0.1.0/gost_linux_amd64.tar.gz).
Then you need to run the commands below to unpack it :
$ cd /path/to/your/download/directory
$ tar -xvf gost_linux_amd64.tar.gz

You would get an executable gost.  You can move it to /usr/local/bin for convenient use:
$ sudo mv gost /usr/local/bin

Run the command below to add the path you want to use as GOPATH into the pathspace gost maintains. It is required to give the path a name which you would use later.
$ gost add foo /home/foobar/bar     # 'foo' is the name and '/home/foobar/bar' is the path

Run any Go command you want in the format:
gost goCommand [-p {pathName}] -- [goFlags...] [goArgs...]

For example, you want to run go get github.com/go-sql-driver/mysql with /home/foobar/bar as the GOPATH, just do it as below:
$ gost get -p foo -- github.com/go-sql-driver/mysql  # 'foo' is the name you give to the path above.

It would help you to set the GOPATH and run the command. But remember that you have added the path into gost's pathspace. If you are under any level of subdirectories of /home/foobar/bar, you can even just run the command below which would do the same thing for short :
$ gost get -- github.com/go-sql-driver/mysql

gost is a Simple Tool of Go which can help you to manage GOPATHs and run Go commands. For more details about how to use it to run other Go commands, you can just run gost help goCmdName. For example you want to know more about install, just type words below in:
$ gost help install

You can also find more details in the README of the project: https://github.com/byte16/gost/blob/master/README.md
Answer: Run 'go env' and see where your GOPATH is currently pointing towards. If you change to that directory, your 'go get..etc' command should work.
Answer: This problem occured to me in raspberry pi. I had logged in through VNC client
The problem persisted despite setting and exporting the GOPATH.
Then Ran the "go get" command without sudo and it worked perfectly.
Answer: I am using vim to edit my .bashrc file but you code use a gui editor such as gedit.
Steps:
Kindly subsitute /path/to/golang/projects below with your actual path location where you will store your golang projects.
Open .bashrc file in vim that is vim ~/.bashrc. Then add below lines at the end of the file.
# Setup Golang Development Environment ::
export GOROOT=/usr/local/go
export PATH=$PATH:$GOROOT/bin

# Third party go libraries will live under "~/golib" directory
export GOPATH="$HOME/golib"
export PATH="$PATH:$GOPATH/bin"

# Where your golang project code lives
export GOPATH=$GOPATH:/path/to/golang/projects

Save the file and type source ~/.bashrc to refresh your terminal session.
Now try getting a package e.g. go get github.com/pilu/fresh and check your ~/golib/bin directory it should have fresh package in it.
Navigate to your /path/to/golang/projects and create three folders in there i.e. bin,src and pkg
Now place your project folder inside /path/to/golang/projects/src  e.g. /path/to/golang/projects/src/myfancygolangprojectand you should be good to go. Put all your golang codebase in there mate.
Answer: I had to run an application as root (to open a webserver on port 80), this produced the error for me, because the sudo user has a different environment than the normal user, hence GOPATH was not set.
If someone else is having this problem, add -E to the command, this will preserve the user environment.
sudo -E go run main.go
For more infos see discussion here: Google Groups – GOPATH Problem
Comment: Not sure why this was downvoted, but fixed it for me…

cannot download, $GOPATH not set


Can I suspend Ith, High Arcanist as my commander directly from the command zone?

Question: When Ith, High Arcanist is in command zone, can I use its suspend ability?
Does the suspend activity cost increase the second time or is the additional cost is only applied to casting cost?
Comment: @doppelgreener the link toward the gatherer does not seem to work
Comment: It works for me... could you right-click the link, copy link address, and paste here where it's pointing for you?
Comment: It points to http://gatherer.wizards.com/Pages/Search/Default.aspx?name=%2b%5bIth%2c%20High%20Arcanist%5d
Comment: Looks like that link's dependent on your language used for Gatherer; I think the linker presumes you're using English.
Answer: No, you cannot.
Suspend means:

702.61. Suspend
702.61a Suspend is a keyword that represents three abilities. The first is a static ability that functions while the card with suspend is in a player's hand. The second and third are triggered abilities that function in the exile zone. "Suspend N—[cost]" means "If you could begin to cast this card by putting it onto the stack from your hand, you may pay [cost] and exile it with N time counters on it. This action doesn't use the stack," and "At the beginning of your upkeep, if this card is suspended, remove a time counter from it," and "When the last time counter is removed from this card, if it's exiled, play it without paying its mana cost if able. If you can't, it remains exiled. If you cast a creature spell this way, it gains haste until you lose control of the spell or the permanent it becomes."

You can only use Suspend from your hand. Since the Command zone is a zone different from your hand, you cannot use Suspend.
This is also summarised in the reminder text for Ith's Suspend ability, which can be read on Gatherer.
Comment: Optionally, can a suspended card be countered when it is played?
Comment: @sinsedrix You can counter a suspended spell when it's cast (after the time counters run out) and it's on the stack. Putting it into suspend-exile in the first place doesn't use the stack, so the spell isn't on the stack, so it can't be countered.
Answer: You can't use the suspend ability. From the card's Gatherer rulings:

7/1/2013: In a Commander game where this card is your commander, you cannot suspend it from the Command zone.
Comment: You attributed that ruling to magiccards.info, but in fact magiccards.info was only reproducing an official ruling found in Ith's gatherer page (it's [the last ruling on the page](http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=114903)). I've edited your post to attribute the ruling to the original and authoritative source.


what Assassin's Creed 2 Patch version?

Question: I just wanted some Information and maybe someone smart enough to get me the solution.When I run the patch it show an error message "this patch is designed for version 1.00. 1.01 was found instead". What does this thing really means I am talking about the version? What is this version of? and how can i overcome this problem. Any answers?
Comment: "1.01 was found instead" is referring to your current game version (latest patch). Meaning you are trying to update with an older patch.
Answer: As Ben pointed out, you are trying to patch v1.00 but you already have updated to v1.01.
Try updating to future versions. I think the latest version for AC2 is v1.06. uPlay should automatically try and update your game, or you can manually get the update from ubisoft or google for it.

what Assassin's Creed 2 Patch version?


How do I create a Sharepoint hosted app for office 365 in Visual Studio 2013?

Question: I've setup Visual Studio 2013 RC and a Office 365 developer site. I can create an app using Nappa and open it in VS from there. But if I create a Sharepoint hosted app project in VS and point it to the url of my developersite it get stuck on "communicating with sharepoint" for a long while and then asks if I want to set the project in "offline mode", obviously I click "no" and then visual studio hangs.
Comment: Did you ever get any answers to your question? I have the same problem :( Edit: I solved the problem. I made two changes. Not sure which one of them actually was the solution. 1. Changed the url to http**s**://mydomain.sharepoint.com.
2. Added an app catalog to my developer site. This can be done in the SharePoint admin section (mydomain-admin.sharepoint.com) right under the apps section (first option in the right hand menu). I would guess the only real problem was the https protocol but since I didnt try them out one by one I chose to post both as a possible solution.
Comment: I am facing same issue. Any solution.
I put https://
Comment: Is this a product bug, anyone know?
Comment: @asimnadeem Same here
Answer: The answer is not obvious. You need to prefix the url of the site with httpS:// and not http://.
Comment: This may be *one* answer. But I'm facing the same problem as described above and I use HTTPs. So there are other reasons for the communication to fail aswell..
Answer: You definitely need both the https and an app catalog on your office 365 (SharePoint Online) site to resolve the "Connecting to SharePoint" issue in Visual Studio.
Answer: 1 fault in the URL will give you the message.
Comment: Can you please elaborate your answer with some brief description.