How does Getsuga mode works?

Question: It is said that in order to release Final Getsuga Tenshou, Ichigo has to be Getsuga himself. But, what does it mean? How this Getsuga mode worked? Is it only Zangetsu exclusive? Is it cancelable and be reused?
Comment: from what i have read Ichigo lost his powers because he used Final Getsuga Tenshou (before the Fullbringer Arc), i wouldn't really say that's reusable unless being a Fullbringer eliminates that drawback
Comment: Edited to make less 'what if'
Answer: To understand how Final Getsuga Tenshou (FGT) works, we need first to understand what happened with Ichigo when he wanted to learn it.
Ichigo and Isshin was in the Dangai (Precipice World) a tunnel that connects Living World and Soul Society. Isshin stopped Ichigo and noted that the train was not there and that while it usually is a bad thing, it was a good thing for them since because the flow of time is different in the Dangai than that in Real World or Soul Society, it is a good time for him to teach Ichigo the FGT. Isshin then told Ichigo that he can only attain the technique by asking his Zanpakutou to teach it to him. He then told Ichigo to sit crossing his legs and start communicating with his Zanpakutou, which is similar to what meditation is.
What happened with Ichigo when he entered his inner world is that he found that all the tall buildings are under water. He was surprised but then Tensa Zangetsu shows up and tell him that he can breathe just fine even under water since its just his inner world. Ichigo asked Tensa Zangetsu to teach him, but Tensa Zangetsu refused. Hollow Ichigo shows up and then fused with Tensa Zangetsu and then fight Ichigo, claiming that if he persist on trying to learn the technique, Hollow Tensa Zangetsu will kill him. They fought, but Ichigo keeps getting beaten.
Then Ichigo realized that there is something wrong with the fight. Hollow Tensa Zangetsu could have killed him from the first strike, yet he didn't do it. He then understands how he can learn the technique, that is by accepting Hollow Tensa Zangetsu's blade. Thus he let the blade pierce him. Hollow Tensa Zangetsu then told him that that is the right answer for Hollow Tensa Zangetsu is Ichigo himself. Ichigo then proceeds to fight Aizen using his newfound power.
Now what does all this means? This means that to learn (to use) Final Getsuga Tenshou, Ichigo needs to understand himself and accept it as is. That's why it was said that to use Final Getsuga Tenshou, he needs to be Getsuga itself.
How does it works? If we see how he attained it, he probably need to enter a special state of mind, which he can reach by meditation. In Zen teachings, there are some special states of mind, namely, Shoshin, Fudoushin, Mushin, and Zanshin. Mushin in sports is often called as "Zone". If you watched Kuroko no Basuke (The Basketball that Kuroko Plays) you will see that when in the "Zone", all abilities goes up drastically, which in Ichigo's case would be his reiatsu goes up so high that even Aizen no longer able to comprehend it.
Is it Zangetsu exclusive? Maybe. That question cannot be answered with exact answer. The only thing that we know is that Isshin knows about the technique, and quite possibly has used it before, and that Ichigo was able to learn it as well. If we go by how Ichigo attained it, then it is very possible that others might be able to learn similar technique although it won't be called Final Getsuga Tenshou since they only ones who has been shown to be able to use Getsuga Tenshou are Isshin and Ichigo.
Is it cancel-able and reusable? If we go by what Kise Ryouta did during the match between Kaijo and Seirin in the semi-final of the Winter Competition, then yes, it can be canceled, assuming that FGT works by entering a "Zone", and that it works the same way in Bleach universe. What we know for sure is that Isshin/Tensa Zangetsu (I forgot which one) said that once he used the technique he will lost all his powers. He will turn into a normal person. This means that it is not reusable.
Answer: Unfortunately, There are no solid answers yet, just theories. As it currently stands, it seems unlikely that we will ever find out either, as the Manga is only a few chapters from ending, Though it may make a return to defeat the final villain and we may get to learn something about it then.
Theory 1) Ichigo fused with his zanpaktou sword spirit. This one does not make much sense, since the zanpaktou is already a part of its wielders spirit, but his sword did disappear, so it has some merits.
Theory 2) It was some kind of Shinigami, Quincy, Hollow, or unique technique to the Kurosaki Family (specifically on his fathers side), a lot like what Uryu did when he fought Miyuri, since both lost their powers after the fact. Though there are several big differences depending on where you place it, we only know that Isshin could supposedly do it as well, but cross species abilities are not explored much outside of Vizards/Arrancars.
Theory 3) The most likely theory as it stands, is simply that Kubo wrote himself into a corner. He made Aizen too strong, So he had to come up with a way to make Ichigo Stronger.
Theory 4) This one is the newest, but also spoils a lot from the last Arc in the manga, Some very big plot points are revealed about Ichigo spoiled here:

 Ichigo is in some way partially all 4 of the main races, and as we find out, His quincy part suppressed his Shinigami part, and then somehow used some of its own power and the Hollows power to give him his regular powers that we all knew and loved. Eventually, Ichigo is able to fully access all of his powers, and we see his new regular strength is well beyond Yamamoto's and Aizen's, with his reatsu being visible to the naked eye in just his shikai form. This theory is simply that Ichigo used a technique that forced any limiters to be removed, and accessed his absolute power. Like Uryu again, The removal of the limiters caused damage to his Spiritual power network, and he could no longer produce more Reatsu, so he slowly drained it all away until he was human again.

Lets hope in the next few chapters we find something out, but as it stands, If we don't, we probably never will.
Comment: Thank you.. finally! I can properly 'reword my question' to fit 'community guidelines'.. and finally get a proper answer.. is a pain to reword stuff..  Now, fusing with zanpakuto, i think the best theory since there is some of that stuff referenced in OVA.. Blades, the rogue shinigami. Also, he said it himself, he is being the getsuga tenshou himself. However, in the case of Blades.. he cannot cancel it; thats why he stole ichigo power to seperate himself from zanpakuto.. though, im not sure why he wanted to stop the fuse mode..
Comment: If so, if ichigo can keep up with aizen 1:1 combat instead of just kaboom his power to 2:1 (since aizen is not dead yet but sealed xD).. he can keep his getsuga mode forevaaa and be an unsealable, immortal creature since that black hollow+shiningami bakudo didnt work for him. Plus, in non canon movie, he can fuse himself to hell guardian and get access to hell chain management.. so perfect being.. he might as well drinks tea together every day with soul king.. sad thats not happening.
Comment: His father was not a Kurosaki. He is a Kurosaki due to marriage only. His name before his marriage was Shiba Isshin. He is from the Shiba clan of Soul Society.
Comment: @AyaseEri I tried to avoid such a spoiler in the answer by saying it was on his fathers side.
Comment: @LordSacha i Suppose i should throw in the fact that OVA's, Fillers, and Movies are usually completely non canon and in actuality are only given the most basic of help from the author if anything. Using them to support Canon material, theories, or ideas is worse than using WIkipedia on a scholarly paper. Those kinds of media are not bound by continuity like the Author is, so they do whatever they want so long as it sounds plausible, even if it contradicts the story thus far.
Comment: @Ryan ok fine I'm just commenting.. Hehe

How does Getsuga mode works?


What is the best standmixer 350 wattage or higher

Question: What is the best Stand mixer with 350 or more wattage?
Comment: Sorry, we don't do "what is the best XY" questions - they are opinion-based and not a good fit for the site. Please take the [tour] and browse our [help], especially [ask] for more information.
Comment: The one w/ the features you actually want?  See http://cooking.stackexchange.com/q/17497/67
Answer: Opinion-based questions aren't a good fit, but I can at least give an answer that's a good fit!  How about some things you can use to evaluate a stand mixer?
Check the fit between the attachments and the bowl.  Does the whisk reach all the way to the bottom?  If not, you'll have trouble whipping egg whites as liquid pools up underneath where the whisk can reach.  Does the paddle reach all the way out to the sides of the bowl?  If not, you'll have trouble creaming and need to stop to scrape the sides of the bowl more often.
As for power, forget about wattage.  That just measures power usage.  A combination of horsepower (the force the motor is capable of generating) and torque (which is rotational force specifically) tells you about how powerful the mixer is.  Some mixers have high horsepower, but generate comparatively low torque due to the design of the transfer gears.  You may have to go to the manufacturer's web site for these numbers.
Check the capacity.  If you want to make double batches of dough, you'll probably want something 4.5 quarts or larger.  Most high-end mixers have a 6 or 7 quart capacity.
Look for a model with a bowl lift versus a tilt head.  That makes it easier to use the mixer without worrying about where it sits with relationship to your upper cabinets.
Hope that helps!
Comment: Hello Chris, thank you for not going into the question as asked. Still, answering a different question is not much better. If you think that this information is needed, a self-answered question is a better way to do it. In this specific case, there even is an older question where you can post your answer. This one would have been closed anyway.


minimal rights needed to write powershell scripts

Question: I got some CSOM scripts in a .Net Application, that I have to to move to the server, using the server object model/powershell. As our Sharepoint team has no time and skills, it was decided that I have to do this. My question is, how can we set up my authorization to fulfill this task? I am a site collection administrator and all the scripts refer to that site collection. Would it be enough, if I get remote login to the server? If possible I would like to avoid having any extra rights that I do not explicitly need.
Answer: The permissions to use the SSOM are highly privileged. If minimal permissions are a requirement you should stick to CSOM.
To use the SSOM you need to have shell admin permissions. See this Technet article for full details.
Comment: Indeed. Might be worth starting a new post explaining your problem to see if there are alternatives.
Comment: Moving to the server has more weight, because we have items in the backlog that require accessing objects that are not available in CSOM. That's why I am looking for an option that lets development on the server, but restricts other rights to the target site collection. But, if I read it correctly: `However, the result of running this cmdlet is that the user specified with the UserName parameter will have the dbo_owner role access on the affected databases as described above. Therefore, you should carefully plan which users are given this access.`, it looks like an all or nothing option.


Snapping feature classes together for one section of a polygon and not the whole feature where slivers are visible

Question: I have used the snapping tool to snap the vertex in 2 feature classes together where they contain slivers gaps and overlaps. This works fine however the tool executes this for the whole polygon and snaps vertex/edges and therefore can move lines where lines should not be moved and creates errors rather than fix the issue. How can I specify somehow to only snap those areas where the gaps and slivers are noticeable?
Comment: You need to select individual vertices when adjusting the polygon.  Otherwise you are moving the whole shape.  You can also look at topological editing.  There are also tools in arcgis to remove slivers from polygons.
Answer: If I understand correctly, you have a series of polygons, which have slivers and overlaps and you would like to remove them?
One way to do this would be as follows:

Create a larger polygon around the area where you want to remove the slivers and then use the "ERASE" tool in Arc / X-Tools / ET Geowizards to remove the original polygons from your larger AOI. This will leave you with some large polygons and smaller polygons where the slivers were between the original polygon features.
I am not sure how your polygon layer looks (perhaps add a picture so we can see), but from a guess you can now easily see those areas in the erased polygon which were never slivers but rather are meant to be there. IE: those areas between polygons where data is in reality not there - these can be deleted through selecting areas larger than X. Where X is an area you can decide. Once these are deleted, you will be left with just the slivers.
You can now use the "Eliminate" tool to merge the sliver polygons into the original polygon layer. If I recall you may need to start an edit session or have the sliver polygon layer selected, I can't quite recall.

Another tool to look at is the "Integrate" Tool - this tool reshapes the polygon to match the edges between the polygons - fixing the overlaps and slivers...I am not too familiar with this tool but it may help.
If you create a GDB and import your polygon layer into it, you can set up Topology Rules. These rules can be quite useful in identify those areas where you have issues with slivers and overlaps. It is a good way to check the final results of which ever method you use.


Why have I become invisible?

Question: After Brelyna in the College of Winterhold "experimented" on me, I became invisible. Now I am unable to see my character at all. Is this just a glich; is there anything I can do short of starting a new game?
Comment: Your entire character or can you see the clothes but not the person in them? (I know there is a glitch with some things you get from the college that will make you a walking pile of clothes, hehe)
Comment: I tried changing clothes to see if it would fix itself, I tried sleeping and fast traveling and etc.. Under active affects in the magic section it showed Bre's spell and I waited for it to wear off(like the first time) but nothing changed. I can still interact with the world like normal but I can't see my character, her clothes or her weapons. It's really annoying. and of course I saved since this happened so theres no going back...
Comment: If it makes any difference... when Bre turned me into a horse and then back again to myself; the horse is still in the room where this transpired. I killed the horse and nothing changed. I will probably just start a new game... f*$#!
Comment: [How to solve the Player Becomes Invisible bug?](https://www.nexusmods.com/skyrimspecialedition/articles/3821) - it's usually hair; SMP or HDT.
Answer: Edit: None of these seemed to work for the OP, but I'll leave them here as suggestions for those experiencing similar issues.
For the why, well, I have no idea (aside from "oh, Bethesda"). But I had a similar issue with a spell effect being permanently attached to my feet. It generated smoke, so my sneaky little thief looked something like Smoke from Mortal Kombat. I gamboled about until it finally resolved, I believe due to transformation into a werewolf. Your problem is due to either opacity (most likely) being set to 0 or your character model being non-existent (unlikely IMO).
There are several solutions I'll suggest:
Become Ethereal:
The Become Ethereal shout should fix any opacity issues when it ends. Here's a YouTube video from a user with a similar issue. Although it ends with the person just reloading a save and exacting revenge, the user claims that the suggestion to use Become Ethereal repaired the problem.
Become Ethereal's Words can be found in Lost Valley Redoubt, Ironbind Barrow and Ustengrav. If you can handle Hagravens and a few Forsworn, Lost Valley Redoubt's Word Wall is outside and probably the quickest.
There are also unique potions that let you become ethereal, called Philters of the Phantom. You can find them in a quest in Shroud Hearth Barrow, near Ivarstead. It's possible that an invisibility spell or potion will have the same effect, but I haven't tried that or seen it done.
Console (PC only):
Open the console (~ or whatever's above tab and left of 1) and type
player.setactoralpha 100

If that doesn't work, there's
sexchange
sexchange

It should force your character model to, uh, rebuild.
Werewolf:
Transforming to a Werewolf and back will also force rebuilding.
Comment: Nothing I tried seemed to work: drinking potions or Becoming Ethereal (I already had that shout, good suggestion tho). I didn't try to become a werewolf, so that may still be a possibility. I don't think it would have worked tho, this was a serious glitch. I ended up starting a new game today; this was my first character and now I have a better idea of where to go and what to do. Thanks everyone for the help.
Comment: The player.setactoralpha 100 worked for me. Thank you very much!
Comment: Thanks guys! I tried the Become Ethereal thing and fast traveled right away and it worked! Again thanks for your help! :)
Answer: I'm dealing with the Breylin glitch too - now my character is invisible, and I don't have a save to load.
I tried the werewolf and no dice. Instead of walking and trying to get all the shouts to become ethedral (and doing all that while invisible which sucks), I decided to try my own thing.
So first invisibility potion, then I walked in a door while still invisible. I could see my weapons but nothing else.
Then I used a appear spectral (like a ghost) and you could see him but ghostly. I walked outside, waited for potion to wear off and - boom fixed - I can now see my character again!
Answer: I did some research a while ago for my own purposes and it turns out that using Become Ethereal and then fast traveling RIGHT after using it will you turn back to normal.  This also works with the phantom potion everyone is talking about (Philter of the Phantom? Look it up).  Results can be varied though, sometimes fast traveling is not needed, sometimes it is, and sometimes just using an invisibility spell works too.  Hope this helps.
Answer: It's a longshot, but I would try drinking an invisibility potion. Maybe making yourself invisible will make the game remember to turn you visible when it wears off.
Answer: Drinking a Potion that makes you appear in a Spectral Form works, I just tried transforming into the werewolf, it did nothing, sleeping did nothing and drinking a potion of invisibility didn't do anything either. But the potion that turns you into Spectral Form does :)  you end up turning visible after you've been spectral! I have no idea where to find it though....good luck!!
Comment: Is the potion you mentioned, the [Philter of the Phantom](http://uesp.net/wiki/Skyrim:Philter_of_the_Phantom#Philter_of_the_Phantom)?
Answer: I had the same problem and I fixed it with a potion. It's called Philter of the Phantom which can be found in Shroud Hearth Barrow.

Why have I become invisible?


What does Summon Dragon do?

Question: What does the "Summon Dragon" button accomplish during the waiting period for Kairos to recharge, other than bring the Kairos Dragon back to its perch?
Answer: "Summon Dragon" (previously referred to as "Call") is a purely cosmetic behavior of the Perch of Kairos.  Once you have acquired Kairos, he will either sit on the Perch or lazily fly around the area.  If he is on the perch you'll see that "Summon Dragon" is not selectable.  If he is flying around, pressing the "Summon Dragon" button calls him to the Perch.  Within about a second he will teleport there with a time-dragony-wormhole-looking animation.
I don't believe Kairos needs to be on the Perch to use his "Activate" ability, so I see no mechanics reason to use this other than because you'd prefer Kairos stop flying around.  I have seen a few account of him getting stuck, but it's unconfirmed if this ability can "unstick" him - and I highly doubt that is its core purpose.
Answer: "Summon Dragon" allows you to call the dragon "Oddaving." I don't think that
it can be used in most situations, though.

What does Summon Dragon do?


Difference between Albedo and Surface Reflectance

Question: Can anyone tell me what is the difference between Albedo and surface reflectance? I know for sure that they are not the same. Any links / comments are most welcome.
Comment: "Albedo is defined as the fraction of incident radiation that is reflected by a surface. While reflectance is defined as this same fraction for a single incidence angle, albedo is the directional integration of reflectance over all sun-view geometries." -- [Retrieval of surface albedo from space](http://www2.hawaii.edu/~jmaurer/albedo/).
Comment: There is a good link from OSU here: http://curry.eas.gatech.edu/Courses/6140/ency/Chapter9/Ency_Atmos/Reflectance_Albedo_Surface.pdf
Comment: @whuber, that actually sounds a lot like diffuse (multiple/all angles of reflection) vs. specular (1 angle of reflection).
Comment: @GBh, what does "Surface Reflectance" mean to you in this context (providing such context will help potential answerers provide better answers).
Comment: Everyone thanks for the reply.
@blah238 -I think surface reflectance and reflectance are probably the same
Albedo is different from reflectance , I somewhat agree with whuber.
Please let me know If we can further clarify between reflectance and albedo
Regards,
GBh
Answer: Albedo is a measure of the diffuse reflectivity of a surface, as opposed to specular reflectivity such as that of glass or water.
Comment: I cannot find any reference that equates specular reflection with "surface reflectance." Could you quote an authoritative source for your answer?
Comment: I avoided making that equation because I don't know what "surface reflectance" is. AFAIK the statement is factual based on the Wikipedia links given, but a better answer would probably say something specifically about "surface reflectance" and what it means to the OP.
Comment: Please, then, consider posting a *comment* to the question asking for what the meaning of "surface reflectance" is in this context. That preliminary back-and-forth helps assure that the answers that get posted are actually relevant to the questions. :-)
Answer: Albedo is the percentage of solar energy striking a surface that is reflected away from the earth.
Surface Reflectance is ratio of the amount light not absorbed by a surface to the amount of light striking the surface.
Albedo is a measure of energy and Surface Reflectance is a property of a material.
Solar radiation times the percentage that gets through the atmosphere and strikes the surface times the Surface Reflectance ratio equals Albedo.
A perfect mirror at night produces zero Albedo.
Answer: I agree with @blah238 here is more information
Albedo is the percentage of solar radiation reflected by an
object.
Reflectivity is the capacity of an object to reflect solar radiation.
It is described as a function of radiation wavelength and is
determined by the physical composition of the object.
Relation of reflectivity to albedo
Albedo is the integrated product of incident solar radiation spectral
composition and the spectral reflectivity of the object. Outside
the atmosphere, solar radiation spectral composition is relatively
constant, peaking at about 0.5µm, decreasing rapidly at shorter
wavelengths to small amounts at 0.2µm, and decreasing less rapidly
at longer wavelengths to small amounts at about 4.0µm.
The atmosphere selectively absorbs and scatters solar radiation.
As a result, at the Earth's surface the spectral composition
of solar radiation varies significantly as a function of atmospheric
conditions (e.g. clouds, water vapor, and dust) and solar
elevation (Robinson, 1966; Dickinson, 1983). The majority of
albedo measurements have been carried out under clear-sky,
high-sun elevation conditions (Table A15). Under cloudy conditions
radiation is predominantly in the visible spectrum. This
decreases the albedos of soils and vegetation but increases snow
albedo (Miller, 1981). When atmospheric turbidity is high, or
the sun is low in the sky, the spectral distribution of solar radiation
shifts to the red and infrared portion of the spectrum. Soil
and vegetation albedos increase and snow albedo decreases
(Kondrotyev, 1973). This variability points out the need to know
both the spectral reflectivity of objects and the spectral composition
of incident radiation in order to evaluate earth albedos.


Zero amount transfer?

Question: I just want to use EOSIO as a DB of some events by sending transactions when other events fire. Is it possible to send ZERO amount transfers? The events are millions a day, and I don't know how to calculate the initial token supply if the amount of the transfers is greater than zero.
Answer: If you remove line 93 from eosio.token.cpp
        check( quantity.amount > 0, "must transfer positive quantity" );

you will be able to send zero amount transfers.
But to be honest, that doesn't sound like a good and smart idea.
If you want to use EOSIO as database without the need to execute logic that depends on the state of the blockchain that's not the right way and it doesn't seem that you need a token for whatever you are trying to build.
Answer: You can keep track of events by simply calling actions. An example of an action is a transfer, but you can make arbitrary actions using a smart contract. In this way you can have a very modular way to keep track of the events on chain.
An example way you could do this is as follows (in a smart contract):
ACTION zerotransfer(std::string const & data_to_store_on_chain){}

If you know the specific data associated with certain events, you can make this type safe:
ACTION registername(std::name const & myname){}
ACTION changenumber(double const number){}

And so on

Zero amount transfer?


Area 51 - Discussion in Commit phase

Question: I think we need to be able to discuss things in the commit phase the way we could discuss things in the definition. I mean the discussion above all the questions. That is needed to keep the community spirit in the commitment phase. Of course, the commit discussion should be separate from the define discussion.
Answer: I think by "discussion," you're really asking for the ability to comment on proposals after they are in the commit phase, which is already the topic of this post:
Please add comments to the commitment phase
Answer: I'd suggest to open the "meta" site early, for the commitment phase.
It could also be helpful to start a sense a community. And even it may allow people to organize a promotion campaign, to propose already written "promotionnal messages" that we can post on appropriate forums (I often hesitate to promote because I'm not good at "selling" things and I'm not sure I'll explain well what it Stack Exchange and why people should like it).
For instance, in "Guitars", I was looking for someone that has a high reputation in the Ultimate Guitars community. So far I contacted random people but most of them don't like the principle of creating another community in another website. Even if I explain that the aim is different some of them feel we want to steal people from their community.
That's also why I hesitate to post a promotionnal message on their forum. I'm not sure I'd be welcome.
So, I'd have been really happy to talk about it with the people that will be in my community but so far I can't easily communicate with them !
So I'd vote for a meta site as soon as the proposals are in commitment. Moreover it will give already committed people something to do in order to work for the building of the community.
Comment: A chat room would be also acceptable.
But an "advertisement" for the chat room should be present on the proposal, as most people don't know about it. Something like "Discuss about this proposal here"
Comment: I wouldn't want those in the beta and full phases. Use the chat-room.

Area 51 - Discussion in Commit phase


Traveling to the Dominican Republic with a Mexican passport/US resident card

Question: I am a teacher in the USA, taking students on a trip to the Dominican Republic. I have one student who has a Mexican passport as well as a permanent Rlresident card for the U.S. Will she be ok to travel to/from the Dominican Republic? Does she need another visa besides the tourist visa? Thanks for your help.
Answer: According to Visa policy of the Dominican Republic, citizens of Mexico do not require a visa to enter the Dominican Republic (same as for US citizens).
Your student should have no paperwork problems on the trip and of course should bring both her Mexican passport and her US Permanent Resident card.
Note also that:

As of 1 January 2018 visitors to Dominican Republic are no longer obliged to purchase a tourist card as this fee is now incorporated into airfare.


Energy momentum tensor of EM field written in symmetric form

Question: I'm reading A. Zee's book, Einstein Gravity in a Nutshell. In problem 7 of chapter IV.2, it is said that the energy momentum tensor of the electromagnetic field
\begin{align}
T^{\mu\nu}=\eta_{\lambda\sigma}F^{\mu\lambda}F^{\nu\sigma}-\frac{1}{4}\eta^{\mu\nu}F_{\sigma\rho}F^{\sigma\rho}
\end{align}
can be written in the symmetric form using the dual electromagnetic tensor defined as $\tilde{F}_{\mu\nu}=-\frac{1}{2} \epsilon_{\mu\nu\lambda\sigma}F^{\lambda\sigma}$,
\begin{align}
T^{\mu\nu}=\frac{1}{2}\eta_{\lambda\sigma}(F^{\mu\lambda}F^{\nu\sigma}+\tilde{F}^{\mu\lambda}\tilde{F}^{\nu\sigma}).
\end{align}
It is mentioned in problem 6 that the key is the identity
\begin{align}
\eta_{\lambda\sigma}(F^{\mu\lambda}F^{\nu\sigma}-\tilde{F}^{\mu\lambda}\tilde{F}^{\nu\sigma})=\frac{1}{2}\eta^{\mu\nu}F^{\rho\tau}F_{\rho\tau}
\end{align}
However, I'm stuck when proving this identity. First problem is that I can't separate a $\eta^{\mu\nu}$ from the first term in left hand side. The second problem is the second term will have something like $\epsilon^{\mu\lambda\alpha\beta}\epsilon^{\nu}_{~\lambda\gamma\eta}$ after plugging the expression of dual tensor, but I don't know how to simplify it. Any hints about proof of this identity?
Comment: What's your goal? If your goal is simply deriving a symmetric EM tensor for the EM field, then vary the EM action wrt the metric, e.g. as is done in Carroll's book in Sec 4.3.
Comment: I'm just curious how the last identity is derived since I'm going through all the problems in Zee's book. It is one of the problem so I think it won't be too complicated.
Answer: You can express the product of two $\epsilon$'s using the following: $$\epsilon^{\mu\lambda\alpha\beta} \epsilon_{\tau\lambda\gamma\eta}= \epsilon^{\lambda\mu\alpha\beta} \epsilon_{\lambda\tau\gamma\eta}=\epsilon^{\mu\alpha\beta} \epsilon_{\tau\gamma\eta}$$ $$=\delta^\mu_\tau(\delta^\alpha_\gamma \delta^\beta_\eta-\delta^\alpha_\eta \delta^\beta_\gamma)-\delta^\mu_\gamma(\delta^\alpha_\tau \delta^\beta_\eta-\delta^\alpha_\eta \delta^\beta_\tau)+\delta^\mu_\eta(\delta^\alpha_\tau \delta^\beta_\gamma-\delta^\alpha_\gamma \delta^\beta_\tau)$$
Comment: Thanks. I think this can take care of the second term to produce what we want, but any suggestions about what to do with the first term? The free indices is on two F's, and I think it's crucial to move them out on to the metric. Still can't figure out a way to do this.
Comment: Thanks, it turns out as long as the second term is simplified, it will give one term that will cancel the first term, and the reminding piece is what we want!
Answer: The first step is to solve the second problem, which is to find the product $\tilde{F}_{\mu\nu}\tilde{F}^{\mu\nu}$. To this, you will need to calculate the product
\begin{equation}
\epsilon^{\alpha\beta\gamma\delta}\epsilon_{\mu\nu\rho\sigma}=\left(
-1\right)  ^{s}\delta_{\mu\nu\rho\sigma}^{\alpha\beta\gamma\delta}
,\tag{1}\label{eq1}
\end{equation}
where $s$ is the number of negative eigenvalue of the metric [1] and $\delta_{\mu\nu\rho\sigma}^{\alpha\beta\gamma\delta}$ is the generalized Kronecker's delta, which we can to expresses as
\begin{equation}
\delta_{\mu\nu\rho\sigma}^{\alpha\beta\gamma\delta}=\delta_{\sigma}^{\delta
}\delta_{\mu\nu\rho}^{\alpha\beta\gamma}-\delta_{\sigma}^{\gamma}\delta
_{\mu\nu\rho}^{\alpha\beta\delta}+\delta_{\sigma}^{\beta}\delta_{\mu\nu\rho
}^{\alpha\gamma\delta}-\delta_{\sigma}^{\alpha}\delta_{\mu\nu\rho}
^{\beta\gamma\delta}.\tag{2}\label{eq2}
\end{equation}
You can find a general study of Kronecker's delta in [2].
Once knowing \eqref{eq1}, you will be able to calculate the product $\tilde{F}_{\mu\nu}\tilde{F}^{\mu\nu}$.
The first problem can be solved by means of a game of rising and falling indices, as long as you remember that
\begin{equation}
\eta_{\mu\rho}\eta^{\mu\rho}=\delta_{\mu}^{\mu}=4\rightarrow\dfrac{1}{4}
\eta_{\mu\rho}\eta^{\mu\rho}=1.\tag{3}\label{eq3}
\end{equation}
1 Sean Carrol, Spacetime and Geometry:An Introduction to General Relativity.
2 David Lovelock and Hanna Rund, Tensor, differential forms and variational principles, section 4.2, page 109.
Comment: Thanks. I solve this problem following you suggestion. The two identities you show here is crucial!


Common use cases for hashing functions?

Question: I'm developing my first dapp with solidity and I was wondering in which cases should I use hashing functions like keccak. I know how they work but it is not clear to me when should I use them and to do what. Thank you so much
Answer: One use case is using it for string comparisons. In Solidity, you cannot directly compare two strings:
function compareStrings() returns(bool) {
    string a = "test";
    return a == a;
}

The above code does not compile, and gives an error that states TypeError: Operator == not compatible with types string storage ref and string storage ref
The way to properly compare strings is to compare the hash of the two strings. The following returns true:
function compareStrings() returns(bool) {
    string a = "test";
    return keccak256(a) == keccak256(a);
}

Answer: They can be used to authenticate large payloads/documents stored in other places. For example, consider a large object that produces a certain hash. That hash can be stored in a contract along with details such as who stored it, when it was stored, and other application-specific details.
Later, when someone is presented with the document from some other source, they can compute the hash themselves and then consult the contract. The contract would either respond that there is no known object with that hash (inauthentic), or it would be able to respond with the recorded details.
Hope it helps.

Common use cases for hashing functions?


how to import an already deployed contract into my contract

Question:
I have two smart contracts,   the first which i intend to deploy first then after a couple of days the other will follow. my issue is how to import this contract i have already deployed and use its functions in my contract.i have tried
Coin1 _coin1 = Coin1(addressOfCoin1);
 but it doesn't work and when i use the import statement it throws error at point of deployment.
Comment: Possible duplicate of [Calling function from deployed contract](http://ethereum.stackexchange.com/questions/9733/calling-function-from-deployed-contract)
Comment: Upvoted even though I agree duplicate and added more helpful information on Sig's question, such as coderwithattitude question about specifying all arguments in the abstract contract; and an example of 3 files showing the abstract contract, the implementation, and the "caller".
Answer: in the same file define the first contract in an abstract form and within your current contract make the needed call,e.g:
 contract Coin1{
        function f() payable returns (uint);
    }

    contract Coin2{
        Coin1 coin;
        function setcoin(address addr) { coin= Coin1(addr); }
        function callcoin() { coin.f.value(10).gas(800)(); // you call the desired function here we call info with 800 gas; }
    }

you will find more detail on the official documentation about the External Function Calls
Comment: Thank you for your response but when i do this i get the following error "member not found in argument dependent lookup" do i need to specify all the arguments in the live contract in the abstract form also?
Comment: and the constructor in coin gives me error "non empty returns directive"
Comment: @coderwithattitude Yes, you need to specify all arguments in the abstract form.  Constructors don't return values so remove the returns in your constructor to fix it.
Comment: thanks for your time, this is what worked for me incase anyone needs it. https://dappsforbeginners.wordpress.com/tutorials/interactions-between-contracts/


How to search Google Drive for Docs and Sheets?

Question: I have been using Google Drive for several years. At this moment, I have a very robust folder structure there, with many files of various types, altogether more than 13 GB. Now I need to search my Drive for all .gdoc and .gsheet files. With so many files on my Drive, it is almost impossible to do it manually. I know how to search Google Drive for all "text documents" (or for all "spreadsheets") but this gives me also all .docx, .odt, .txt and so on (.xlsx, .ods and so on) files. This is not what I want, I need to filter only .gdoc and .gsheet files.
Comment: After doing some cursory testing, have you tried using a `NOT` operator in your search and exempt .xlsx, .docx, etc? For instance, `type:document` brings up Google Docs as well as .docx files. Using `type:document NOT *.doc OR *.docx` removed Word docs from the search results.
Comment: Thank you, this workaround worked. Just for amusement, I had to type these two commands: "type:spreadsheet NOT *.xlsx NOT *.xls NOT *.ods" and "type:document NOT *.docx NOT *.doc NOT *.pdf NOT *.txt NOT *.odt NOT *.bbl NOT *.blg NOT *.aux NOT *.snm NOT *.out NOT *.nav NOT *.tex NOT *.tcp NOT *.tps NOT *.ipe NOT *.svn-base NOT *.civBeyondSwordWBSave NOT *.spl NOT *.brf NOT *.vrb NOT *.pgn NOT *.ini".
Comment: Use `AND` to group things. You can also sync Drive to your computer and then you can search by extension type. It just doesn't run that way on Drive because they're not actually documents.
Answer: There's an updated version of this now. You can search by apps, so you can just put:
app:"Google Sheets"

And
app:"Google Docs"

Comment: As of december 2017 this does not seem to work.
Comment: As of January 2019, this works. Try https://drive.google.com/drive/u/0/search?q=app:%22Google%20Docs%22. Also, you can search for `app:"Google Drawings"`.
Comment: Works, and so does `type:spreadsheet`. Probably the latter will find XLSX and ODS documents as well.
Answer: You can use type:spreadsheet in your query.
Works with: spreadsheet, presentation, drawing, image, video, pdf
Answer: After some searching, I found out why app:"Google Docs" did not work for me.
You seem to have to type exactly the words it is translates to in your language. I wish to have Google in English, but since I live in the Netherlands, it automatically chooses Dutch as language.
So instead of searching for app:"Google Docs", I have to search for app:"Google Documenten" and then it finds everything.

Then you type app:"Google 'thing in your native language you want'"
So for example:

app:"Google Documenten"
app:"Google Presentaties"
app:"Google Spreadsheets"

for Dutch.


Download CS:GO server without redownloading entire game

Question: I'm trying to setup a home CS:GO server, but I want to do it without redownloading the entire game. I'm using Steamcmd to download the server and I've had a look at the files which it is downloading, they appear to be exactly the same as CS:GO which I already have installed. Is there anyway I can copy my current installation over so it can only download the files it needs for the dedicated server? My internet isn't very fast so letting it download will take a very long time.
Comment: As far as I know these are two separate entities. There might be some commonalities between the games, and Steam might automatically skip those for you.
Comment: The dedicated server appears to be 5191610831 bytes. Which is larger than the actual game. What is going on?
Comment: It's a huge server though. Is it really 5GB?
Comment: You understand that the dedicated server is ONLY used if you want to have your computer host a game for a long time, right? If your internet is slow that might not even be possible.
Comment: It is purely for LAN games.
Answer: Both, the Steam client and steamcmd create a directory called SteamApps by default. Inside there's common/Counter-Strike Global Offensive and common/Counter-Strike Global Offensive - Dedicated Server respectively. The contents should be roughly the same for the game client and the dedicated server.
Copying the contents from the client to the server's directory and calling app_update 740 validate inside steamcmd (or steamcmd +login anonymous +app_update 740 validate) should result in a minimal download time.


Fill slivers using R or SAGA GIS

Question: I have  polygon shapefile representing administrative districts. There are small spaces between polygons where the polygons should be touching. There are probably also overlapping polygons. How can I have the polygons snap together, filling the gaps or slivers and removing overlap (possibly in R, QGIS or SAGA)?
Answer: You might be able to do this in R with the rmapshaper package, more specifically the ms_simplify function.
The best tool I've actually used for this is pprepair, which is a standalone C program, gettable from github:
https://github.com/tudelft3d/pprepair
Answer: I'd use GRASS 7 for this personally, since its topologically aware. You can import with a snap distance set to remove small slivers, and then use the module v.clean in various ways to handle whatever other problems the software reports. As a last resort, you may have to hand edit a couple of points, but this should be unusual.

Fill slivers using R or SAGA GIS


What is so innovative about smart contracts?

Question: I still don't quite understand what is so innovative about smart contracts because it sounds like a general conditional statement to me.  Is it merely about automating contracts with computer programs or am I missing something?
Answer: The innovation is the fact that because of the decentralized network of nodes that the code runs on, they provide certain guarantees[1] that cannot be provided by traditional backend code.
Some examples of smart contracts that do something not possible by regular backends (with the same guarantees):

A "slot machine" contract that is provably fair (you can verify that the code that is running behind the slot machine is the same as some open-source code that can be published). The proceeds can be routed to a particular NGO, or the "players" of the slot machine can even vote on which NGO the funds should go to. Because smart contracts are immutable, the code is guaranteed not to change, or re-route the money (with the same caveats here[1]).
A social network which stores everything in encrypted form on the blockchain, in which not even the developers of the code/other infrastructure have access to your information – only "friends" that you approve using smart contracts have access.

Basically, the draw is that blockchains are decentralized, and they remove the requirement of trusting any one organization to continue operations, or at least continue them in good faith. If data is store on the blockchain, it is public, and anyone theoretically is free to build UI on top of those "interfaces".
[1] Not literally guarantees because the network can "fork" if 51% (this number differs for different blockchain implementations) of nodes go another way, but the difference is you put your trust into the unlikelihood of this happening, rather than into one centralized organization. The more nodes that are on the network, the less likely this is (in theory, at least).
Comment: I'd like to point out that an example about encrypted messages is not a very good example from decentralization's point of view. The data can't be decrypted within the network (without leaking the key).
Comment: @LauriPeltonen It's possible to encrypt messages for certain users using public-key encryption and their public key, and then put the encrypted message on the blockchain. But I agree with you that the example may be too convoluted for the purposes of this question. It's just one of my "go-to's" when explaining blockchain to laypeople, as it's something they can relate to.
Answer: Smart contracts on their own are just conditional pieces of code indeed, very simple ones often. The most similar reference are Ricardian Contracts.
The name smart contract stems from the idea that the contract's logic is the enforcer and not an external judical system.
It's when these smart contracts are put on a blockchain or DLT to be interacted with through the network that they become interesting because now they are distributed.

The contract is immutable and public (we can easily gauge expected behaviour as outsider)
There is an audit trail (every state change has to happen through a transaction)
Transactions can now be sent when conditions are mutually agreed upon and enforced by code which can't be altered by either party during the process.

On a traditional backend one has to keep logs of everything for it to be auditable. These logs are only stored on a centralized server and can be faulty (someone can change these if the changes to the logs aren't logged themselves).
Comment: Strongly agree.  Blockchain with the executable codes is innovative.


How can I tell if my cat is getting enough stimulation?

Question: I have a 13 month cat, a domestic short hair brown tab. I've seen people equip cats with wheels these days like hamsters but that seems to be mainly bengals with much more energy and need to exercise. I spend the bulk of my day at work and my cat has a small toy, and the hurricane frisbee ball toy. At night before bed I try to laser pointer it for 5-10 mins and I get a few sprints out of it. I'm not sure if this is enough though?
Comment: Maybe try looking at it the other way: are you seeing anything suggesting your cat is not getting enough stimulation? If the answer is no, then your cat is probably getting enough stimulation. Most cats can entertain themselves in my experience.
Answer: The activity level of cats varies widely. Some breeds are known for being extremely active, e.g. Bengals, but it also depends on the particular cat and their environment.
As @Beo commented, the key is to look for signs they're not being stimulated enough. This could be bringing you toys, running back and forth, playing with invisible toys, nipping or pawing at you like they would another cat, or anything else that may indicate they want more attention from you. Note that, to a cat, negative attention is still attention, so this can include deliberately misbehaving.
Generally, if you have two cats that get along, they will keep each other plenty busy. If two days don't get along, though, it's often because one has a higher energy level and the other is annoyed by it; playing with that cat to burn off some of its energy may help them get along better.
Finally, be aware that cats are evolved to have brief periods of activity separated by long periods of light sleep, up to 20 hours a day in total. So, just sleeping a lot (by human standards) doesn't mean they do or don't get enough activity; you have to examine the periods when they are actually awake.
Comment: Now that you mention It, my cat runs back and forth a lot often after ingesting a meal. I attribute it to a sudden caloric surge or joy at getting fed but could be need for more play hmmm


How do you calculate the safe working load of chains?

Question: Say for instance you have a chain that has a safe working load of 200 lbs.  If I wanted to hang an item from 4 corners, each with its own chain would I be able to hang 800 lbs?  Or is there some other variable to factor?
Answer: Another thing to consider is that the effective load on the chains is increased if the chains are not vertical, as would be the case if the chains are attached to the corners of the item, but are all attached to a single central attachment point above. Multiply the chain's working load limit by the cosine of the angle between the chain and vertical to get the adjusted limit. For example, if 1000 lb rated chains are at 45 degrees to the vertical their safe working load limit is reduced to 707 lbs.
For overhead lifting where human safety is involved you should use Grade 80 or above. You would probably have to go to a specialty dealer to find it. Proof Coil, Grade 43 (Hi-Test) and Grade 70 (Transport Grade) are not rated for overhead lifting.
Answer: The safe working load limit is generally 1/4 or 1/5 the minimum breaking strength.  So there is a buffer and safeguard already built in if you are using the safe working limit number.
However, you should confirm this with the chain's packaging or identification.  There are cheap chains at the big-box stores that will have 1/2 ratios - do not use a chain that has a breaking strength of 200lbs to lift a 200lbs object.
As for hanging over humans or expensive property - the safe thing to do is to use chain meant for overhead lifting, and give yourself plenty of additional strength.  Somethings to consider include a single chain (or attachment point) breaking which means the other 3 chains now have to support 800lbs.   Also any movement will cause the load on each corner to vary. While you might think you will mount it and never move it - you never know who will jump up and try to hang on it; or an earthquake will shake things up.
Chain is cheap; people's heads are not. If you are supporting 800lbs by 4 corners, use 1000lb working load chain with grade-8 or AN-quality attachments.
Answer: Well, there's the possibility of non-uniform loading, so probably not. And there's the pesky question of "What happens if this 800 lb. thing plummets?"
The fine print on most lifting hardware (chains, hooks, rings, etc) will state that it's not suitable for lifting or supporting loads over people; and hardware that is will be very conservatively rated, at least for that use.
Comment: The termination hardware must have the same kind of ratings as the chain and properly attached to structure that will bear the load as well. Lag screws into wood don't count. Forged eye bolts penetrating the beam and supported by a nut and washer working against a large iron plate to spread the load come to mind.
Answer: No.You always have to approach a lift as though only 2 chains are lifting.Then you need to consider the load factor angles .If its less than 30 degrees its considered a straight lift and you can lift 400.If its  above that angle then the  2 chains need to be multiplied by 1.6 or 1.8 which will give you a lower lift capacity of the chains
Comment: Welcome to DIY.SE! Can you expand upon this some more, maybe with some links to sources for your numbers? e.g., why can you only take into account 2 chains, even though there are 4 present? Where does 1.6 and 1.8 come from, and which should you use?


Should I define interfaces in Duck Typed languages?

Question: I'm just about to write my first application in a duck typed language (Groovy).
If I was to write the same application in a static typed language then I would need to define some interfaces. Obviously because of the duck typing in Groovy they are not actually required. At the moment I am thinking that it might make sense to define them anyway as documentation of the methods that need to be implemented in the various objects. Am I missing the point?
Answer: I've been reading on this recently here on SO (and I can't find the link right now, but it's one of those "why are dynamic languages good?" posts, and a big answer by S. Lott with many comments), and the answer is:
You could. In Groovy especially, you can define interfaces in Java or Groovy and implement them. However, with duck-typing (which Groovy allows but also allows explicit types) many people would say "why bother?" The source is it's own documentation, the interface is in the source, "use the source" etc.
Personally, this drives me mad -- I love the compile-time (or really, dev-time) checks Java gives me, but that's another debate. If you're using Groovy, it's because you want to write that brilliantly concise and clear code that comes from duck-typing. In that case, interfaces are to be avoided except where necessary.
Where are they necessary? Between parts of a program, and in the Public API for a program (though they can be abstract classes, too). Otherwise, I would say that you should try to avoid them in duck-typed languages. This forces you to write the docs on the classes, or write code that is so clear that it's the same thing.
I think this is terrible practice, HOWEVER this is part of the paradigm shift towards dynamic languages. And I think that if you avoid separating interface from implementation enough, you'll understand the 'why' behind it. I still do not, though it has a lot to do with not repeating code (keeping DRY).
Edit: Got some clarity away from the computer :) One of the main reasons NOT to separate interface from implementation is so that you move away from a dependence on types. In duck-typing, as you know, I don't care if it's an implementer of the Vehicle interface (for instance). I only care if it has a go method with 2 params. So the more you work with interfaces, the more you are writing Java in Groovy ("you can write Fortran in any language"). This should be avoided, as new languages open you up to new stuff.
Comment: @Martin, thank you, I've appended my answer a bit to explain better.
Answer: I'm not familiar with groovy, but in general, no, you don't need to define interfaces in loosely typed languages.

You would be repeating yourself, if you need to change a methods signature, then you need to do it in two places, not one.
Although interfaces do have some use as documentation, in a loosely typed language, most coders will not expect an interface, and therefore will not go searching for an interface if they need documentation.
Most dynamic languages have good IDE's available for them, with method completion, which further diminishes the need for a separate interface.
Methods can be bound and unbound in dynamic languages.  Therefore, you can, and probably will, end up with objects that do not adhere to the interface. Having a separate interface could end up confusing people reading your code.
Comment: @longshot what IDE/language do you use with good method completion? I use Netbeans with Ruby, and more often than not it doesn't know what methods are available, and is just completing them from a global namespace.
Comment: Squeak smalltalk has good method completion, and method browser.  AllegroCL has good autocompletion for Common Lisp.
WingIDE has good autocompletion for Python, as long as it knows what type you are referencing.
XCode has good completion for ObjC, with the same caveat that it needs to know the type you are sending a message to.
Comment: and @Sergey Mirvoda, thanks for that. Objective-C is my new problem, so I hope that XCode does that.
Answer: Defining an interface is a kind of in-code documentation. With an interface you declare explicitly what you expect from the class to satisfy your needs.
PS: groovy is not my language, so I actually don't know whether it's possible to define interfaces there at all.
Answer: In some cases yes.  I have an example where I'm creating a Groovy class that gets injected into a Java class by Spring. I created an interface using generics like this:
//interface injected to a java class
public interface SomeInterface {
    <T> T getSomething(int version, Long id);
}

Then the groovy implementation looks like this:
//Groovy impelentation
class SomeInterfaceImpl implements SomeInterface {
    def getSomething(int version, Long id) {
        //use duck typing to create similar objects based on version
    }
}

My example is that I'm using JAXB and XJC to create objects from an XML schema and using them in a Jersey restful web service.  I'm versioning the web service and the changes are enough to version, but there's still a lot of code that can be reused.  Using interfaces proved to be problematic, so I used Groovy instead and moved all the similar logic to the above mentioned Groovy class with duck typing.  The objects are mostly the same with some some changes so duck typing with an interface to inject in the Java class works perfectly.


Stop vibration fedback

Question: How can I stop my HTC m8 from vibration at the start and end of call? I turned off all vibration notifications but still I can't stop my phone from vibrating at the start and end of calls.
Answer: Open the Settings application on your device and Navigate to Sound and uncheck the option labelled Vibrate with a description of Vibration feedback for calls.

Stop vibration fedback


What element could be used on a fictional metal-poor planet for biological oxygen exchange?

Question: I'm working on a hard sf novel about humans being forced to survive on a metal-poor planet. They have to take dietary metal supplements at first but eventually a bio-engineer rigs the biochemical pathways from a native species to work in their offspring using bacterial and viral vectors. I'd like a non-metallic element to assist in oxygen gas exchange. An alternative is that they use iron but that it is recycled, somehow, within the body. So, for example, heavy blood loss would be a serious accident since the iron in the blood would be hard to replace. Any ideas would be appreciated.
Comment: You're going to need more than just a replacement for iron, you're going to need a whole new molecule that isn't hemoglobin. Hemoglobin is designed to work with iron, and its molecular structure wouldn't allow anything but a metal to be used (it's a chelated compound).

Also: The liver works very hard to recycle iron already.
Comment: @Willk This is not a duplicate. All the answers to that previous question involve metal ions, while this one is specifically asking for non-metallic options.
Comment: Hey tgrignon, I've added the tag [tag:chemistry], as it might be useful to have that specialty on-board with this question. If this goes against your wishes, feel free to remove  it.
Answer: Fluorine.
Specifically, fluorine bound into perfluorocarbon molecules. These substances can dissolve ridiculously high concentrations of oxygen--enough so that they can be used for liquid breathing. Some perfluorocarbons can even carry more oxygen and CO2 than blood can (that's by bulk measure, though, and you definitely don't want to simply replace blood entirely with perfluorocarbons to get that performance--you'd break a lot of other stuff in the process!).
Instead of normal red blood cells, your modified people would have perfluorocarbon vesicles--basically, fancy oil droplets--suspended in their bloodstream.
Of course, there are numerous disadvantages to such a system. For one, fluorine isn't exactly a common element either, so they may be better off sticking with the iron supplement anyway. For another, haemoglobin alters its binding strength according to pH, so it selectively releases oxygen in areas that need it most (i.e., tissues which are producing a lot of metabolic byproducts like CO2 or lactic acid). Oxygen-solvating vesicles would not have that kind of specific response, thus further reducing the efficiency of oxygen delivery.
Comment: @stix and fancy globs of protein encased in fat don't?
Comment: "fancy oil droplets" suspended in the bloodstream sounds like a sure recipe for an embolism to me... No thanks...
Comment: This answer surprised me. It is a gas though, right? Until it's bound into the PFC?
Comment: @tgrignon In elemental form, yes, but you wouldn't acquire it that way, just like you don't get dietary calcium or sodium in highly reactive elemental form. It would most likely enter the biosphere in the form of various fluoride salts, which are solids.
Comment: @LoganR.Kearsley Yes, actually.

PFCs have extremely high viscosity and poor CO2 removal. This is a problem in their use as a medical treatment and in liquid breathing.
Comment: @stix Separated red blood cells have pretty dang high viscosity as well. That's why I specifically noted that you *don't* want to replace the blood entirely with PFCs. You want it encased in vesicles, *exactly* like red blood cells. You are not pumping around a liquid oxygen carrier; you are pumping around *solid* oxygen carriers suspended in the liquid blood plasma, in either case.
Answer: Water
Everyone loves water for biology.  A water molecule can carry an extra oxygen and in doing so becomes hydrogen peroxide.  Our bodies generate hydrogen peroxide which circulates around and is induced to give up its oxygen via various enzymatic reactions.
https://www.ncbi.nlm.nih.gov/pubmed/23849856

Hydrogen peroxide is generated in numerous biological processes and is
  implicated as the main transmitter of redox signals. Although a strong
  oxidant, high activation energy barriers make it unreactive with most
  biological molecules.

Water is not a metal.  It can carry oxygen as the peroxide and as opposed to sulfates or borates, carries it loosely.  As the iron containing heme ring is shepherded about by the huge protein hemoglobin, so there would be a hemoglobin analogous protein which would protect one or more molecules of hydrogen peroxide, and mediate the release and reuptake of the oxygen.
Comment: For reference: the average molarity of haemoglobin in normally-saturated blood is around 2mM. Haemoglobin can carry up to 4 oxygen molecules, but most haemoglobin in arterial blood is not fully saturated, so typical oxygen molarities are around 5mM. Each peroxide molecule carries *half* an oxygen molecule, but at slightly higher oxidizing potential, so you're looking at 8-9mM concentration of hydrogen peroxide in arterial blood. That's actually not too bad. I can easily believe stabilizing protein complexes could keep that safe.


I saw an orange light in the sky which changed into flashing lights, what is this?

Question: It's Saturday 15th July 2017 and currently 00:44. I saw this strange object at around 00:35. I was looking out my window and spotted a bright orange light moving at a steady speed across the sky, it was definitely not a star, at first I thought it was maybe a plane and one of its engines was on fire but it was moving too fast to be a plane and it didn't appear to lose any speed or height as you might expect in that situation. Then I though it could be a landing plane since I live near an airport, again the same conclusion. I watched this bright orange light fly across the sky and occasionally dim as it went behind a cloud although it was still visible. It came out the first cloud and wntered the second, however when it came out of the second cloud it had changed into several dim red lights in a flat line, with the accasional bright flash of green to replace the red lights. It continued to fly over the airport and eventually got too far away to see anymore. I read up and though I could have seen a satellite but I've seen iridium flares before and they've been very different to this, this incident has left me confused and I'd love some insight as to what this might have been. Thanks :)
Comment: Sounds like a plane behind cloud most of the time.
Comment: James K - it isn't, I've already read that in an attempt to find an answer and my sighting is much different. Found no answers from the comments on that question.
Comment: What makes you think it isn't a plane besides the fact that it was "moving too fast"? Everything else you've said sounds just like a plane to me. Furthermore, what does this have to do with astronomy? Even if you couldn't identify it, it doesn't sound astronomical in nature (particularly because of the "dim red lights in a flat line").
Answer: Your description matches that of a fireball, which are typically large meteors.  As they enter the atmosphere they heat up and glow.  The colour will depend on their speed and composition.  As they get hotter, they often break up into several pieces, which follow the same trajectory.  Much the same effect arise when old satellites or space debris re-enters the atmosphere.
Comment: "It continued to fly over the airport" does sound more like a plane to me.  Likewise the "occasional bright flash of green".
Comment: Yes, but since the OP lives near the airport, my presumption was that this was something unusual.
Comment: I lived near airports all my life (grew up near one) and I can tell you there's no end of strange optical and lighting effects that look like e.g planes on fire, you name it.   The combination of sun (or moon), bright metal and flashing and non-flashing lights together with the ability of the mind to see what's not there and "fill in the gaps" just makes for some weird visuals.  IMO anyone *not* seeing some strange things near an airport is not looking. :-)
Comment: Thankyou for your answers, thing is this was not similar to the planes I'd already seen in the sky that night, or any other timeIt flew over the airport but not as if it was about to land; I will try to explain in more detail. Basically as I'm looking out my window, the airport is on my left, the runway faces the same way as my house, so any plane taking off or landing will be parallel to my house, this was not, it was going across the sky faster than a plane and was just very strange. Not to invalidate your answer, just thought I'd elaborate, thanks again
Comment: Thankyou Dr Chuck that kind of explains it, still slightly confused about it seemingly changing into a plane like object but maybe that was my eyes or the clouds playing tricks on me lol.


Multi-site User Sessions

Question: I have a client that wants to create several WordPress sites and utilize a "site switcher" at the top, sort of like ThemeForest.net. I know in WP 3 you can create multiple blogs on the same installation, but what about enabling users who login to one blog to be logged into all of the blogs in the WordPress installation? Is this possible?
Answer: Definitely. Think of it this way: wordpress.com is a big Multisite install. You're always logged into wordpress.com, regardless of which blog you're on.
Answer: @brianmcculloh As @John P Bloch said, WordPress Multisite is a perfect fit. The list of sites is what WordPress now calls a Network. Here are some resources that you might find helpful:

Creating a Network (WordPress Codex)
Installing Multiple Blogs (WordPress Codex)
How to enable Multi-Site option in WordPress 3.0 (WPBeginner.com)
WordPress 3.0 Walkthrough: Getting Started with Multisite (WebToolsCollection.com)
WordPress 3.0: Multisite Domain Mapping Tutorial (ottopress.com)
WordPress MU Domain Mapping Plugin (wordpress.org/extend/plugins)
Answer: Try the 'Multisite Switcher' plugin. I use it to switch from one site to another within the Admin of a multisite install.
I know SuperAdmin can access this feature, but you may(?) need to set capability permissions via the Role Manager plugin for lesser roles to use this feature.

Multi-site User Sessions


Nash Embedding Theorems for Pseudo-Riemannian Manifolds?

Question: Are there analogs of the Nash Embedding Theorems for Pseudo-Riemannian Manifolds?
Comment: Yes, and the proof much easier, one can explicitly can write a formula for the embedding into $\mathbb{R}^{N,N}$
Comment: @AntonPetrunin: Why not give a reference? Others might stumble upon this question through a web search and find your reference useful.
Comment: @AlexM. There is an explicit construction is called Nash twist. For the given metric $g$ it produce one parameter family of embeddings $f_t$ in $\mathbb{R}^N$ with induced metric $g+t{\cdot}h$ for some fixed metric $h$. The embedding $x\mapsto (2{\cdot}f_t(x), f_{2\cdot t}(x))$ in $\mathbb{R}^{N,N}$ is isometric. I learned it from Gromov's book on partial differential relations.
Answer: See here:
MR0262980  Reviewed Greene, Robert E. Isometric embeddings of Riemannian and pseudo-Riemannian manifolds. Memoirs of the American Mathematical Society, No. 97 American Mathematical Society, Providence, R.I. 1970 iii+63 pp. (Reviewer: W. F. Pohl)
Answer: Not clear where you are headed with your concise question,
but if you have any interest in Lorenzian manifolds as instances of pseudo-Riemannian manifolds,
then this might be of interest, especially for the theorem of Campbell:
"The embedding of General Relativity in five dimensions."
Carlos Romero, Reza Tavakol, Roustam Zalaletdinov.
General Relativity and Gravitation.
March 1996, Volume 28, Issue 3, pp 365-376. (Springer link.)

Abstract.
  We argue that General Relativistic solutions can always be locally embedded in Ricci-flat 5-dimensional spaces. This is a direct consequence of a theorem of Campbell (given here for both a timelike and spacelike extra dimension, together with a special case of this theorem) which guarantees that any $n$-dimensional Riemannian manifold can be locally embedded in an $(n+1)$-dimensional Ricci-flat Riemannian manifold. [...]

And there are many papers in some sense following, e.g.: "The embedding of space–times in five dimensions with nondegenerate Ricci tensor,"
F. Dahia and C. Romero, J. Math. Phys. 43, 3097 (2002). (AIP link.)
Comment: I see the "locally embedded" part, but surely an $S^{3}XS^{1}$ spacetime topology needs an embedding into $\mathbb{R}^{4,2}$ to yield a global vector basis (in order to describe the parallelization thereof)


What is the purpose of the "disciplined" badge?

Question: Which type of behavior is the "disciplined" badge trying to promote?
Why users who deleted their own posts, which had a score of at least three, would get a badge?
Comment: Welcome to S&M.SE.
Answer: I suppose it's for users who wrote an answer that was somewhat well-received but who later realized that their answer had some major flaw and deleted it anyway, knowing that even though they had popular support for their answer, it was wrong and so they had the "discipline" to delete the answer.
Comment: The title of the badge for someone who deletes their own entry with a minus 3 (or lower) is peer-pressured. On other stock exchange sites, that also has the effect of eliminating the impact of the down votes. Apparently it does not on this site.
Comment: The fact of deleting an answer that had a score of +3 doesn't automatically mean the answer had a major flow, and it was correct to delete it. I understand what you are saying, but it seems (to me) to make more sense to get a badge when deleting an answer with a score of -3; in that case, the negative score could be used as a measure of the answer really having a flaw. It is true that somebody would delete a question with a score of +3 if he is not really happy with his/her own answer, and one is more "brave" when deleting an answer with a score of +3 than with a score of -3.
Comment: Another oddity is that since badges, by and large, are not revoked, you can simply delete an answer and then undelete in an hour or so after you've gotten the badge.
Comment: @Tom Au: Stock exchange?  Did I detect a Freudian slip??
Comment: @drm65: No, I am better known in the "real world" for stocks than I am for the stack exchange. Specifically, for my 2004 book, "A Modern Approach to Graham and Dodd Investing," that correctly called the 1929-style stock market crash that took place in 2008-2009.
Comment: @Tom: Neat!  Though you really shouldn't have given me the title.  I am snoopy.  It doesn't take me long to get your ph# and street address from that!
Answer: I find deleting my own answers wrong especially if others have voted on it, up or down. I feel there should remain a record of what people responded to (especially if it was downvoted, then people can see what a wrong or unpopular answer is).
I can see that deleting a high voted answer takes discipline (do you lose the associated rep?), but I don't get why it is rewarded with a badge.
Comment: Sometimes we have two (and more) identical answers posted within seconds of one another. Naturally, people upvote all of them. But it makes perfect sense to leave only one of them up. (And yes, you do lose the rep, but only upon the next rep recalc.)
Comment: @Mitch: It's just a bronze badge.  Not all of them are meant to be milestones like silver badges or gold badges.  Not everyone is in a situation to get some of the bronzies.  I don't think I'll ever get Tumbleweed, for instance.
Answer: I am contemplating deleting my answer to a question on Programmers.SE because the original question has changed so much that my answer no longer applies.  I have four upvotes (some of which I have received since the question changed) so deleting my answer would earn the badge.  I have not deleted it yet because it helps show the confusion that can surround the entire topic of the question.


Difference between Saturated Liquid and Saturated Steam

Question: I have a (maybe stupid) question which is making me crazy: what is the difference between a saturated steam and saturated liquid state? I mean the physical difference not the difference on a Thermodynamic diagram (such as the greater entropy of the sat steam w/r/t the sat liquid).
Comment: Could you describe what you think a 'saturated liquid state is'? What does it comprise? (compared to the steam, which is moisture (water) vapour mixed in air above the water's boiling point wher some of that vapour will start to condense [I think])
Comment: In my mind a Saturated liquid is a "mixture" of all liquid with a as small as possible steam bubble, in the same way a Saturated Steam is a "mixture" of all steam with a as small as possible liquid drop. Is that correct?
Comment: I found a few web reference that may help, particularly about wet vs dry, vs superheated steam (which is way beyond Sauna steam ;-) http://www.tlv.com/global/UK/steam-theory/types-of-steam.html http://www.tlv.com/global/UK/steam-theory/wet-steam-dry-steam.html and https://www.quora.com/Thermodynamics-What-is-the-difference-between-wet-steam-and-dry-steam. So that's me educated at least !
Answer: The difference is just that:  one is in the liquid phase and the other is in the vapor phase.
A material like water has a certain temperature at which it boils.  This temperature changes with ambient pressure, such that a low pressure corresponds to a low boiling point temperature and a high pressure increases the boiling point temperature.
When a saturation condition is reached, the liquid phase and the vapor phase are in equilibrium with one another, i.e., both phases can exist simultaneously.  If a small amount of energy is added to saturated liquid, it turns into vapor at constant temperature.  Likewise, if a small amount of energy is removed from saturated vapor, it will condense to liquid at const. temp.
Comment: So the difference is due to the non ideal behaviour of substances, like water? If they were ideal the transition from liquid to vapor phase will be instantaneous without intermediate states?
Comment: I don't know what you mean by "intermediate states".  In the saturated condition, as long as the pressure is kept constant, the two phases remain in equilibrium with one another.  If the pressure changes, then this equilibrium will be disturbed, and you'll get either 100% liquid phase or 100% vapor phase.  Equilibrium also implies that the rate of evaporation of the liquid phase is matched by the rate of condensation of the vapor phase.
Comment: I agree with you, and by intermediate states I mean the two-phase states.
Answer: this is incredibly late, but for people still googling this question: I understand it as Hg being the vapour state with almost 0 liquid state. The quality x of this would 1. And the saturated liquid state is where the liquid is on the cusp of changing state, thus an infinitesimal amount of the liquid has vaporised, with a subsequent quality x would be 0. Denote saturated liquid state as Hf.
Answer: From "Thermodynamics: an engineering approach", by Yunus A. Çengel, Michael A. Boles:
Consider a piston–cylinder device containing liquid water at 20°C and 1 atm pressure being heated. Under these conditions, water exists in the liquid phase, and it is called a compressed liquid, meaning that it is not about to vaporize.
As more heat is transferred, the temperature keeps rising until it reaches 100°C. At this point water is still a liquid, but any heat addition will cause some of the liquid to vaporize. A liquid that is about to vaporize is called a saturated liquid.
Once boiling starts, the temperature stops rising until the liquid is completely vaporized. Any heat loss from this vapor will cause some of the vapor to condense. A vapor that is about to condense is called a saturated vapor.
If the temperature of the vapor is, let us say, 300°C; and if we transfer some heat from the vapor, the temperature may drop somewhat but no condensation will take place as long as the temperature remains above 100°C (for P = 1 atm). A vapor that is not about to condense (i.e., not a saturated vapor) is called a superheated vapor.
Answer: This is a late answer, but I see that no one has mentioned the true physical processes at work here, and so it's worth an update.  Look at the Pressure/Internal-Energy (bar vs kj/kg) diagram for steam: https://www.mathworks.com/matlabcentral/fileexchange/9817-x-steam-thermodynamic-properties-of-water-and-steam .  There, you can see that "at saturation conditions," which involve all states at the same temperature and pressure, there is a continuous change of thermodynamic state, identified by the property called "quality."  Zero quality contains all vapor (gas) and 100% quality involve all liquid.  There is a continuum between.  Thus, at the same temperature and pressure throughout, there are an infinite number of well defined states, with each having a different quality, or amount of internal energy.
With this knowledge, the answer to the question is that "steam" is in general a mixture of two phases of water, a vapor or gas phase and a liquid phase.  At one extreme there is only gas, and at the other, only liquid.  Thus, the questions isn't properly posed because of its confusion of "steam" with "vapor."  The best answer is thus, the physical difference between the "steam" state and the "liquid" state is that the "steam" state in general contains both vapor and liquid and the "liquid" state contains only liquid.  The physical difference between the vapor state and the liquid state is simply the difference between a gas and a liquid.  Yes, the vapor state of water is a true gaseous state.


Undeleted comments of deleted posts

Question: I made a comment to an answer, which resulted in a follow up comment after which I edited my question and the answer on which I commented became obsolete and was deleted.  The answerer undeleted his answer to create a new answer, and my comment, now thoroughly irrelevant, reappeared with the techiyas hameisim of the answer.  Is is possible to issue a message to the inbox of someone with a resurrected comment to allow them to re-assess it?
Answer: Comments on posts retain their "state" if the post is undeleted -- that is, if the comments were deleted before the post is deleted then they stay dead, but if the post with comments is deleted and later undeleted, the comments are undeleted too.  Often this is correct; perhaps the comments address issues in the post that haven't been corrected.  There's no way to automatically know which comments are no longer relevant.
If comments come back that are obsolete, please flag them.
Comment: Would it be possible to send a message to the inbox of someone with a resurrected comment, to allow him to reassess?
Comment: Unfortunately, even deletion or undeletion of *posts* doesn't generate an inbox notification (nor, for that matter, close/reopen), so I doubt the code supports this for comments, which are second-class citizens.
Comment: I'm kinda new here, but who has control of the code?  Not that I know how it is designed and how simple adding something like that would be.
Comment: Related: http://meta.stackexchange.com/q/80460/162102
Comment: The code is owned and maintained by Stack Exchange.  Feature requests from the community are considered, but they decide what to do.  I just linked a relevant post from MSO, the "meta of metas" site, so to speak.  You might want to read and vote on the linked question.

Undeleted comments of deleted posts


Where can I get some real life CDR/SMDR/AMA logs from asterisk or ther IP based switch?

Question: In order to develop some generic call accounting software I need some sample logs from IP based PBX. Where can I get some? - I need more than 100 records, preferably using both SIP and telephony trunks.
Answer: I would suggest downloading something like AsteriskNOW and installing it on a VM - it's relatively easy to get going with an IP phone.
The CDR's are stored in mysql for most asterisk installations (although it's not required, just the norm) and the format is relatively similar.
I'm not sure an excerpt of a random system would really allow for particularly robust development - most of the "generic" call logging systems I know of involve exporting CDR's (in whatever format they may be) to a format the generic system can read using csv/xml/etc, as the information available will vary from switch to switch and system to system depending on the type of switch, dialplan/extensions and calling contexts.


Leaflet Custom Control - changing background colour of existing control

Question: I have a Leaflet map with two custom controls on it (coverage1000Control and coverage2500Control).
coverage1000Control is defined thus:
coverage1000Control =  L.Control.extend({

  options: {
    position: 'bottomleft'
  },

  onAdd: function (map) {
    container = L.DomUtil.create('input');
    container.type = "button";
    container.title = "1,000 ft";
    container.value = "1,000 ft";
    container.style.backgroundColor = "red";
    container.style.backgroundSize = "100px 30px";
    container.style.width = "80px";
    container.style.height = "30px";

    container.onclick = function(){
      clearMap();
      setHeight(1000);
    }
    return container;
  }
});

Coverage2500Control is defined in exactly the same way with the only difference is that container.style.backgroundColor = "white";.
I'd like to change the background color of each button when the user clicks on it to indicate which button was last clicked. In other words, when the map loads the coverage1000Control button is red as it's the default. When the user clicks on the coverage2500Control button, coverage1000Control goes white and coverage2500Control goes red.
I've tried putting coverage1000Control.container.style.backgroundColor = "white" in the container.onclick but it doesn't work.
Is it possible to change the background color of an exising Leaflet control and if so, how?
Answer: In the end I figured out that I could add a unique 'id' to my container definitions and then use:
document.getElementById("1000").style.backgroundColor = "white";

to change them.  Sometimes the simplest solution can elude you until you go away, walk the dog and then come back and look at it afresh !


Where are the rules about fire damage?

Question: I have a flamethrower, which deals fire damage, but I don't know where to find the rules about it. Where in the core rule book (or any other book) can I find it?
Answer: The Flamethrower
Equipment rules for this weapon can be found on page 128 of the Star Wars: Saga Edition Core Rulebook .
Flamethrower Damage
The rules are written in the equipment description referenced above.

The flamethrower is a ranged weapon that shoots a cone of burning chemicals 6 squares long and 6 squares wide at the terminus.  Make a single attack roll and compare it to the Reflex Defense of every target within this area.  The attack deals 3d6 points of fire damage to the target; if the attack misses, the target takes half damage instead.  A target with the Evasion talent (see page 50) takes half damage from a successful attack and no damage if the attack misses.

Fire damage behaves like any other regular source of damage (energy, sonic, cold, electrical), and these names for sources of damage can be considered as "flavor text", unless some ability specifically references a special interaction with a type of damage source.
Answer: The rules for fire damage are located in the Star Wars Saga Edition Core Rulebook on page 255. It states that a character or creature that takes fire damage is set on fire until they take a full round action to put the fire out. While a character is on fire, they are subject to a 1d20+5 vs FORT attack every round that deals 1d6 damage or half damage on a miss.

Where are the rules about fire damage?


WHirlpool Super capacity 465 I hear gas at burners but will not ignite even with a match. I hear no gas in oven area

Question: I recently went to restart the Whirlpool Super Capacity 465 gas oven.  I can hear the gas and feel the gas at the burners.  No clicking and it will not light with a match.  I tried the oven, turned on the heat and hear no gas there at all.  Any ideas?
Comment: Can you see the flame being disturbed of the match when you try to light the burner?
Comment: Yes it almost blows it out
Comment: Do you *smell* the gas that's coming out?
Comment: Yes I do but it is faint
Comment: Call the gas company, they have folks that come out and fix this for free. Maintenance of the lines sometimes traps large amounts of air and it can take quite a while to flush. The gas co would rather fix this than having someone blow up there house because they don't have the testers to check if the lines are sealed after the work is done.
Answer: WARNING  WARNING*****THIS IS NOT A JOB FOR AN AMATEUR****WARNING  WARNING
I'm going to make a guess here; hopefully it can help.  I wager that somehow a large bubble of air or very low concentrate gas has gotten into the line and is giving you trouble.  If this is true here is the fix.  First ventilate the area very well; open all windows and doors to allow lots of fresh air to the immediate area.  Keep them open.  Now find a point on the gas supply line to the appliance that is accessible and has a union type fitting.  Find the appliance gas shut-off valve. It should be in the area.  Turn it off.  On the down-stream side of the service valve, break this fitting; unscrew this fitting completely. This will allow you to dump a large amount of gas in a short period of time to clear the line effectively under very controlled conditions. Now open the gas valve all the way.  Allow this gas line to vent for 15 to 20-seconds.  The gas should smell like rotten eggs and the smell should get worse as the gas concentrates.  Close the service valve.  Now leave the gas valve in the off position turn and leave the area for a good 4-minutes.  Do not turn on or off any lights in the area.  Basically don't do anything but leave the area.  After the allotted time return and reconnect the gas line tightly.  Reopen the gas service valve.  Now again try to light the appliance.  Hopefully, the results will be different.
WARNING WARNING****THIS IN NOT A JOB FOR AN AMATEUR****WARNING   WARNING
Servicing of the gas lines and gas supply is constantly going on upstream to your gas service.  It is the nature of life.  In the process of doing this, air is a times unintentionally allowed into the system. You may be experiencing one of these times. Good Luck and happy cooking. P.


What to look for when buying good quality loose black tea?

Question: What features should I look for when buying good quality loose black tea?
Comment: I'm not a tea expert, but I think you can get a better answer if you specify if you want pure tea (black? green? or another type?), aromatized tea (e. g. blended with jasmine), herbal tea, or a synthetically flavored tea (although I doubt that the last one is available as good quality loose tea).
Comment: I am looking for black tea or scented black tea (Earl grey). Thanks!
Answer: Every tea can have potentially various grades and different teas will have different qualities. I'm not sure what is available where you are, but if you're fairly new to drinking loose leaf teas, I'd for starters find a store that lets you see, smell and possibly sample various teas. Once you have a better idea of what you're looking for, then online dealers will be easier to navigate.

So, firstly, find a reputable store, one where they are knowledgeable about their product, and difference in grades.
Ask to smell the teas. Please DO NOT stick your head in the tea, waft it with your hands or the lid of the tin. If you like the aroma, it's a good starting indicator of how you'll like the tea.
Look closely, are the tea leaves fairly even in size? An unbroken leaf is generally graded higher than a leaf that is broken/crushed. Though since you're specifically asking about black teas, note that certain black teas are deliberately cut, to encourage a stronger flavour. If the leaves are torn, crushed, it may be a sign of a rough machine harvest, or poor handling. This could result in bitterness. The lower grades (small crumbs and dust) generally end up in tea bags. So, note that.
Most importantly, taste it! If the store offers a few different sampler sizes, go for that. Ask the people there, about how they'd recommend you prepare it. And try a few different kinds and grades.

Note, if you're new to loose leaf tea, it should taste different than what you're used to. Trust your taste buds and your nose first... Regardless of what it looks like and the price and what the description says, if you don't like the way it tastes & smells (which is often subjective) the rest is pretty meaningless.
Comment: Edited and added some more detail...
Comment: Thanks, I'm used to drink loose teas (Twinnings Earl Grey is one of them), but I was looking for tips on how to identify the features that make a good tea stand.
Comment: I usually buy my tea from [Le Palais des Thés](http://www.palaisdesthes.com/en/) and they have lots of choice and good quality. They mostly have physical shops in France (and a couple of other European countries), but you can buy online. If you're in the US, they also have a [US online shop](http://us.palaisdesthes.com/)
Answer: To back up what I say, I can site lots of articles that said said all sorts of things. Some that made sense, others not. Although I put it all together as such. Some black teas are premium ones (labelled Assam, Ceylon, Darjeeling, Nilgiri, Keemun, Souchong, and Yunnan). Also estate Africa blacks and good grade South/Central American ones which they also have today are good as these are generally orthodox teas. Thiland, Vietnam and Burma also produce higher quality ones. They are called flowery, tippy, golden or othodox. Most places in the world use these with the exception of North America, UK, Belgium, Egypt and some although not all or most middle Eastern countries which use CTCs a lot. Countries using orthodox though tea articles never say it directly although indicate to it if you read lots of other articles to get it -are always satisfied with their blacks.
Blended teas are not always lower quality necessarilty than single leaf estate ones. Common sense says that if you mix decent quality tea you get a decent blend. If the blend contains cheap teas you get a cheaper blend. This is common for general supermarket teas. French Breakfast tea for instance is often made of a higher quality blend. Whereas you can get good English Breakfast blends - most of them use cheaper CTC teas for the bag. This is the case today with British breakfast blends (English, Irish and Scottish) since convenience became more of an issue here. Also Earl Grey is often used in cheaper blends though one can buy expensive ones. Masala Chai blend is probably the cheapest as this is often what the dust grades are used for though they can taste quite good in it. Orange pekoe can follow suit with that although it is possible to have very good ones (flowery grade ones) which are far better than masala and most chai blends are sometimes cheapest even though they put the word specialty on it on a cheap tea set. Most in the supermarkets however are the dust grades. Orange pekoe can also refer to a leaf grade size for certain types of (often Ceylon teas) although at full is a nice flowery-bud tea. Also keep in mind that green and many herbal teas in bags are also usually these days very low quality and bland and some even below the former though I have seen it according to my observations outside
Flowery, (F) Tippy (T) and golden (G) are high end blacks. B means a broken leaf which still can be a good tea, especially if listed after the previous notations or the OP sign. If an F is listed after the B however its likely a less good tea as that means a fannings which is a lower grade. D or dust is the lowest. Flowery golden tippy are orthodox. Broken can be if not a fannings and dust. The latter two are CTC grades. They can however work well IF you want to make masala chai or some sweet iced tea, just for the sake of it. The higher end blacks are loose leaf and have more of a malty brisk flavor yet they take a couple of minutes to brew up. CTC teas brew up faster in the bag which is what people like although they never as good as an estate orthodox one


Ethereum and intermediate state tree root

Question: I'm reading about scaling in the whitepaper

In the near term, Ethereum will use two additional strategies to cope
  with this problem. First, because of the blockchain-based mining
  algorithms, at least every miner will be forced to be a full node,
  creating a lower bound on the number of full nodes. Second and more
  importantly, however, we will include an intermediate state tree root
  in the blockchain after processing each transaction. Even if block
  validation is centralized, as long as one honest verifying node
  exists, the centralization problem can be circumvented via a
  verification protocol. If a miner publishes an invalid block, that
  block must either be badly formatted, or the state S[n] is incorrect.
  Since S[0] is known to be correct, there must be some first state S[i]
  that is incorrect where S[i-1] is correct. The verifying node would
  provide the index i, along with a "proof of invalidity" consisting of
  the subset of Patricia tree nodes needing to process
  APPLY(S[i-1],TX[i]) -> S[i]. Nodes would be able to use those nodes to
  run that part of the computation, and see that the S[i] generated does
  not match the S[i] provided.

Lets say there is only one honest node, and that node could provide proof of invalidity.

Nodes would be able to use those nodes to
  run that part of the computation, and see that the S[i] generated does
  not match the S[i] provided.

If there is no other honest nodes, why would they accept that S[i] generated does not match the S[i] provided? Wouldn't they just discard that proof?
EDIT
Problem that's being addressed here in the whitepaper,

The problem with such a large blockchain size is centralization risk.
  If the blockchain size increases to, say, 100 TB, then the likely
  scenario would be that only a very small number of large businesses
  would run full nodes, with all regular users using light SPV nodes. In
  such a situation, there arises the potential concern that the full
  nodes could band together and all agree to cheat in some profitable
  fashion (eg. change the block reward, give themselves BTC). Light
  nodes would have no way of detecting this immediately. Of course, at
  least one honest full node would likely exist, and after a few hours
  information about the fraud would trickle out through channels like
  Reddit, but at that point it would be too late: it would be up to the
  ordinary users to organize an effort to blacklist the given blocks, a
  massive and likely infeasible coordination problem on a similar scale
  as that of pulling off a successful 51% attack. In the case of
  Bitcoin, this is currently a problem, but there exists a blockchain
  modification suggested by Peter Todd which will alleviate this issue.
Answer: The context of the problem is about a time when it's hard to run a full node due to the immense size of the blockchain data and only few organizations will be able to have full nodes.
As I understand, If at least one honest full node exists it will provide a proof of invalidity to other nodes (everyone including light nodes) can verify it. So if other nodes find that block is invalid they will discard that invalid block.

If there is no other honest nodes, why would they accept that S[i]
  generated does not match the S[i] provided? Wouldn't they just discard
  that proof?

What I feel is no other honest node refer to no other honest full node (may be that's what you have gotten mistakenly). But there are light nodes who will use the proof of invalidity and reject the invalid blocks.  (if what it means by no other honest node is every node including light nodes, there's no point of trying to give a proof of invalidity and it's not the problem context stated in the white paper. )


My granddaughter's Facebook account has been deleted

Question: My granddaughter's Facebook account has been deleted. She is of age. There are plenty who is not, but she is. We know who reported her due to that person being mad with my granddaughter. Facebook is how she communicates with us and the bottom line is she is of age. I can send you a list of the ones who are not tho. I would appreciate you telling me what to do, because this is unfair.
Comment: Please note that this site is not Facebook support. It's a Q&A site where volunteers offer solutions to problems using web applications. You certainly need to get in touch with Facebook directly.
Answer: Facebook usually sends an email to the ones who get their accounts disabled, with information about when and why they decided to disable it. If you disagree with the reason why the profile was disabled, I think you can send them an email explaining why do you think the profile doesn't need to be disabled. Keep in mind that they don't send emails to every disabled account, so there's a chance your granddaughter didn't get one.