Are there currents in space? Space flotsam?

Question: You know how there are some beaches in the world where tons of sea glass or other random sea trash washes up, just because the currents and the shape of the land naturally collects it all there? I was wondering if something similar could happen out in space. Certain planets or solar systems where interstellar space trash is more likely to collect into asteroid belts, planetary rings, or just fall to earth. Completely naturally though, it's not being propelled by anything, it just floats there naturally over millions of years. How would that work? Could solar winds and gravity wells have a similar effect as tides and deep-sea currents in this sense?
Comment: Would something like [Trojans](https://en.wikipedia.org/wiki/Trojan_(celestial_body)) count - objects stabilized at the $L_4$ and $L_5$ points?
Comment: There's [a very famous novel by Isaac Asimov](https://en.wikipedia.org/wiki/The_Currents_of_Space) that you should read...
Answer: Yes, absolutely.  Every planet has 5 locations around it or near its orbit where the planet's and the star's gravity cancel each other out.  These are called Lagrange Points.  L1, L2, and L3 are unstable, an object in them is only balanced in a very specific location and a slight nudge will knock it out of the Lagrange Point.  L4 and L5 however, are stable; it takes more than a slight nudge to knock them loose.
There's a lot of other situations that fit the bill a little less, but you might still count them.  For example there's a large number of bodies, including Pluto, that have ended up in a few specific orbits, guided into them by the influence of Neptune.  In short, gravity fields involving 2 or more bodies are really complicated, and you can certainly get situations that are somewhat analogous to currents.
Comment: In your second paragraph, you are talking about [orbital resonances](https://en.wikipedia.org/wiki/Orbital_resonance).
Comment: Do i remember it right that Jupiter and Mars sustain an asteroid belt between them?
Answer: Mostly no.
There are currents in liquids and winds in gases, but interplanetary space is very, very, very thin.  Interstellar space is even thinner.
So subatomic particles, atoms, molecules, and particles tend to follow ballistic trajectories in outer space.
There are some exceptions.  Stars emit "stellar winds" of particles which mostly radiate in straight lines in all directions from the stars.
If astronomical bodies like planets, moons, asteroids, comets, stars, neutron stars, black holes, nebulae, etc. have magnetic fields, those magnetic fields will alter the courses of any passing particles which are electrically charged.
Thus the Earth's magnetic field traps many charged particles in the "solar wind" and keeps them orbiting Earth in the Van Allen Belts, and similar things happen in the magnetic fields of other astronomical bodies.
And the gravity fields of various astronomical bodies can interact with passing particles or objects and bend their courses in various ways.  Thus the gravity of large astronomical bodies produces zones that are relatively free of smaller objects, because they are pulled out of those zones over time, and zones that have higher concentration of smaller objects, because they are pulled into those zones over time.
Stars sometimes emit many times as many particles as in a normal stellar wind.  The biggest such times are when a supernova explodes and expels a significant proportion of its mass, including heavy elements produced by the supernova, into space.  The particles expelled travel outwards for thousands and millions and billions of years, and many collide with interstellar dust and gas particles and push them away from the supernova.  Thus a expanding region of very thin interstellar matter is produced around the supernova.  As expelled particles and the interstellar particles they hit move outward, the interstellar matter becomes denser at the edge of the wave of matter.  And if that wave of matter density encounters another wave of matter density moving outward from another supernova, they may make a region of very dense interstellar matter that collapses under it s own gravity and forms stars and planets.
As for space flotsam ending up on space beaches, that is sort of true since there is very, very thin matter in space and every speck of space dust, asteroid, comet, moon, planet, or star can be considered a moving space beach.
Every object moving through space, be it a speck of space dust or a vast star, hits many smaller objects or particles as it moves through space.  Those smaller objects or particles either bounce off or become part of the larger object due to chemical stickiness, magnetism, or gravity.  So the object grows larger and larger over the eons as it moves through space, and leaves a tunnel of pure vacuum behind it, though that tunnel gradually becomes as dense as it was before as particles and objects pass through it.
Each day, Earth acquires many tons of space dust as it moves through space.

A micrometeorite is essentially a micrometeoroid that has survived entry through Earth's atmosphere. The size of such a particle ranges from 50 µm to 2 mm. Usually found on Earth's surface, micrometeorites differ from meteorites in that they are smaller in size, more abundant, and different in composition. They are a subset of cosmic dust, which also includes the smaller interplanetary dust particles (IDPs).1
An estimated 30,000 ± 20,000 tonnes per year (t/yr)2 of cosmic dust enters the upper atmosphere each year of which less than 10% (2700 ± 1400 t/yr) is estimated to reach the surface as particles.[14] Therefore, the mass of micrometeorites deposited is roughly 50 times higher than that estimated for meteorites, which represent approximately 50 t/yr,[15] and the huge number of particles entering the atmosphere each year (~1017 > 10 µm) suggests that large MM collections contain particles from all dust producing objects in the Solar System including asteroids, comets, and fragments from our Moon and Mars.

Micrometeorites have been found on the seafloors and on land.  Places on land to look for micrometeorites include:

Terrestrial sediments also contain micrometeorites. These have been found in samples that:
Have low sedimentation rates such as claystones[22] and hardgrounds[23][24]
Are easily dissolved such as salt deposits[25] and limestones[26]
Have been mass sorted such as heavy mineral concentrates found in deserts[27] and beach sands.[7

So a beach where you might find macroscopic terrestrial flotsam like driftwood can also be a cosmic beach where tiny micrometeorites can be found.

Amateur collectors may find micrometeorites in areas where dirt and dust from a large area has been concentrated, such as from a roof downspout.[28]

https://en.wikipedia.org/wiki/Micrometeorite1
https://www.sciencefriday.com/articles/up-on-the-roof-a-handful-of-urban-stardust/2
And of course Earth also acquires larger space rocks, up to the extremely rare asteroids and comets miles in diameter that could cause extinction events.
So space is mostly too thin a vacuum to have winds or currents in it, but there some situations vaguely resembling currents in space.  And every astronomical object functions as a sort of a cosmic beach sweeping up cosmic flotsam.
And you might as well check out Isaac Asimov's novel The Currents of Space, which has an ingenious, though now obsolete, theory for the cause of novas.
It is the second story, by internal chronology, in the "empire" series The Stars Like Dust (1951), The currents of Space (1952), and Pebble in the Sky (1950).


About Kepler's Law

Question: When Earth goes near the Sun, its velocity increases and when it goes far from the Sun its velocity decreases. Then why according to Kepler's law is the time period $T^2 \propto a^3$, where $a$ is the radius? As we know velocity has an effect on time period.
Comment: Your second sentence doesn't seem to relate to your first... but if I've interpreted correctly, you're asking why Kepler's Law states that the time period doesn't depend on the speed of the planet, when surely a faster-moving planet will have a shorter time period?
Answer: Because this radius $a$ is the semi-major axis of the elliptical orbit. It is not the instantaneous distance.
Answer: The first phenomenon you are stating is a "local" one, whilst the second is a "global" one. The radius you speak of is not the norm of the position vector from the sun to the planet, which would be a function of time, but rather the length of the semi-major axis of the ellipsis, which is a constant.
The period time is also a constant, but the planet can absolutely have a variable speed during orbits, and yet have a constant period.
Answer: Eccentricity plays no role in determining the period of a Keplerian orbit. The period is given by $T = {2 \pi}\sqrt{\frac {a^3}{G(M+m)}}$ where $T$ is the orbital period, $a$ is the semi-major axis of the orbit, $M$ is the mass of the central body, and $m$ is the mass of the orbiting body.
Eccentricity plays a definite role in determining the instantaneous velocity of an object in a Keplerian orbit. The radial distance between the central body and orbiting body ranges from $a(1-e)$ to $a(1+e)$, where once again $a$ is the semi-major axis of the orbit and $e$ is the eccentricity of the orbit. The magnitude of the instantaneous velocity at any point along the orbit is given by the vis viva equation, $v^2 = G(M+m)\left(\frac 2 r - \frac 1 a\right)$.

About Kepler's Law


Divergence free vector field

Question: How can I solve for the vector field $\vec V$, if $\mathrm{div} \vec V=0$?
I don't know the general method to find the vector function when we are given its curl or divergence.
Comment: Would [math.se] be a better home for this question?
Answer: If it is known that a vector field $\vec V$ is divergence free, that is, $\nabla \cdot \vec V = 0$ which by the fundamental theorem of vector calculus implies the field may be expressed as,
$$\vec V = \nabla \times \vec A$$
where $\vec A$ has the generic term of a vector potential, and in some cases other terminology may be used, such as in fluid dynamics it may be a stream function, for an incompressible fluid flow. This fact follows from the Helmholtz decomposition and the fact that, the divergence of a curl always vanishes. Moreover it is not unique; if $\vec A$ is a valid potential, then,
$$\vec A + \nabla f$$
is also a valid potential, with $f$ a continuously differentiable function. Finally, knowing $\nabla \cdot \vec V=0$ is not sufficient to determine $\vec V$ itself, since there are infinitely many solutions.
Comment: I'm supposed to find the radial and azimuthal velocities in cylindrical coordinates.  So I wrote down the expression of div V in cylindrical coordinates. I don't know how to proceed after that.

Divergence free vector field


Is having a delete confirmation built into the button itself an appropriate UX?

Question: This is for desktop and mobile, basically when you click the button once it changes to "Confirm" with a cancel button next to it. I got some feedback that it's not clear you have to press the button again so maybe I need to make it more clear there is a secondary action here?
Comment: Does this answer your question? [Confirmation of user input: inline button or popup/modal?](https://ux.stackexchange.com/questions/118177/confirmation-of-user-input-inline-button-or-popup-modal)
Answer: This is a little odd:

Having a button proclaim itself to be a button is not necessary. So if anything it'd be "Delete" and "Confirm delete".
Having a button change itself instead of summoning some type of pop-up-feeling dialog for the confirmation is unusual. It's a bit more ergonomic, sure, but there do exist people who double-click everything because they haven't learned yet that in the context of the web, you don't need to double-click anything. By keeping the confirm step at the same position, a double-click may be interpreted as a very fast click onto the confirm button, you may be depriving a class of users of the confirmation step who have the highest need for it.
Comment: Nice answer. I'd add this to support your second point: this is the main issue for Google's CLS algorithm and UX check. While I don't completely agree with Google's implementation or even definition of CLS (let alone User Experience), it serves as a subjective measure for many people.
Answer: It's really confusing that the button changes itself into confirmation. What I suggest is to enable a "cancel deletion" button instead. What I mean is to do this:

The delete button is working just fine.
Once the user clicks on the delete button, the button would be changed to somethings like this: "XXX deleted. Cancel deletion" and you would give some time like 5 seconds for the user to click cancel deletion in case they deleted mistakenly in the first place.
Comment: I agree with you. I was thinking exactly like you before I used some applications that have exactly the same approach as I mentioned. But after that I saw it's actually a very practical way and it also removes the need for the second tap by the user. You can see an example here:
https://www.linkedin.com/posts/sepas-haghighi_userinterface-userexperience-productdesign-activity-7147652424709705728-ltBQ?utm_source=share&utm_medium=member_desktop
Comment: While a good idea in theory, I think in practice it implies a huge cognitive load. You're actually forcing the user to decide whether their actions are right or wrong within five seconds, and with a required interaction that takes approximately one second. I think a popup dialog with no time limit would be better.


I am Chinese. Which name is my surname and which is my last name, for a flight booking?

Question: My name is Minnie Wong Qin Qing. If I put Wong as my surname, and the others as my last name, finally the full name will be:
Minnie Qin Qing Wong.
So what can I do?
Comment: If you don't have "Minnie" as a name in your passport, it's very important to NOT write it in the reservation.
Comment: surname = last name = family name. Depending on the form, if WONG is your family name / surname, you could put Qin Qing Minnie, Minnie Qin Qing or other variations by leaving off Minnie. Do you have a passport already? Then you should use the same thing that's on the passport.
Comment: Some of my colleagues would write this as Qin Qing (Minnie) WONG to make it absolutely clear that you have chosen to be called Minnie by non-Chinese speakers (assuming that is true of course).
Comment: @AndrewT. Presumably (Mandarin) Chinese _Wang/Huang Qin Qing_ and westernised _Minnie Wong_. The version given here is an odd mixture, since [_Wong_](https://en.wikipedia.org/wiki/Wong_(surname)) is the Jyutping/Yale/Hong Kong transcription (i.e., based on Cantonese pronunciation) of either 王 _wáng_ or 黄 _huáng_ (most commonly), while _Qin Qing_ is Pinyin (i.e., based on Mandarin). In Chinese, the name would be written in characters throughout, but it's not common—as far as I know—to westernise names transcribing from different languages within the same name.
Comment: Correct me if I'm wrong, but it seems you actually have 2 names: the Chinese name "Qin Qing" and [the westernized name](https://en.wikipedia.org/wiki/Chinese_name#Western_name) "Minnie Wong"?
Comment: @JanusBahsJacquet in that case look in the MRZ beginning in position 7 until the characters `<<` E.g. `PASGPWONG<<MINNIE<QIN<QING<<<<<` - here the "document type" is `PA`, the country code is `SGP`, the "official" surname for passport purposes is `WONG`, and the additional names follow.
Comment: Look in your passport. On the Photograph page there are numbered fields. Use the name in field 1 for surname and the name in field 2 for forename.
Comment: In California I've also seen it written as Minnie (Qin Qing) Wong. It's pretty much always unambiguous which are the given first names vs Western first name.
Comment: @Ben Not necessarily. As far as I can tell from the images of Singaporean passports that Google brings up, fields are not numbered, and there is only **one** field for the entire name. Tamil is one of the four official languages of the country (presumably also a significant demographic group), and Tamil people frequently have only one name; I am guessing this could be at least part of the reason why this is so.
Comment: Accord to your description… Minnie = first name, Qin Qing = Additional first names (which can be ignored), Wong = last name. It's that easy. Your password will confirm, as it also includes English wording describing the data fields like name, birth date, etc.
Comment: What type of ID are you using? And which country is it issued by?
Comment: Some western countries with centuries of Chinese fellow country men have simply hyphenated the family names. So your name would be:

"Minnie Wong-Qin-Qing " Which could be seen as a family name variation on WONG.

This isn't in line with Chinese naming traditions, as I understood them, but it's a solution.
Comment: Of course I mean beginning in position six...
Answer: In terms of booking flights, the only thing you need to consider is what your passport says. It will have fields that are also marked in English, such as "Surname" and "Given names". When you book flight tickets, input exactly what is in those fields, in the corresponding field to what your passport refers to as your "Surname", "Given names", etc.
If that happens to be wrong according to your actual name, local naming conventions, etc, then that is perhaps something the issuing authority of your passport could consider dealing with.
However, in terms of booking tickets, the only thing you personally can do is input everything exactly as it appears in your passport, in the corresponding fields. That is what airlines, governments, etc. will want to see, and the absence of it will typically cause problems.
Comment: This is the correct answer! It doesn't even matter what those words mean, just pattern match them and copy from passport into reservation.
Comment: It has two extra initials in my passport representing my Chinese name.  One of my bookings I left them out and had to get it added before the airline would issue my boarding pass.  Just look at your passport and follow it.
Comment: If your passport photograph page has numbered fields, the "official" surname is generally field 1. If it does not, you can look in the MRZ  beginning in position 7 until the characters << E.g. `PASGPWONG<<MINNIE<QIN<QING<<<<<` - here the "document type" is `PA`, the country code is `SGP`, the "official" surname for passport purposes is `WONG`, and the additional names follow. If the surname was two parts, QING WONG it would be `PASGPQING<WONG<<MINNIE<QIN<<<<<`
Comment: This is really the correct answer. I once suddenly ended up with a passport where my name was misspelled and I needed to book a flight. I put the misspelled name because this is all what mattered to get into the flight. I had all sorts of issues afterwards because of the misspelling (before it was corrected) but **from the perspective of the booking** it did not matter.
Comment: This is the correct answer, except then you get into situations like my sister, whose last name has a hyphen in her passport, but many airline booking sites call the hyphen an invalid character. It hasn't actually prevented her from flying (yet), because the ticket agents have all been capable of engaging their grey matter, but she dreads the day when it becomes all fully automated...
Comment: @Martha automated checking is already an issue with things like credit cards, but I think in practice the validation is quite loose.
Comment: Worth noting as further reading is this [list of falsehoods programmers believe about names](http://www.kalzumeus.com/2010/06/17/falsehoods-programmers-believe-about-names/).  The passport system should eliminate many of them by forcing a western-centric or even English/American system on everyone.
Comment: @ChrisH Lol, I entered to comment exactly the same thing. Take your deserved +1.
Comment: @ChrisH In particular, if the asker here is indeed Singaporean as [dda's answer surmises](https://travel.stackexchange.com/a/101312/41454), then this answer will likely be completely useless, since Singaporean passports would appear not to have anything more than [a single "Name" field](https://goo.gl/images/JFV7Cg) that does not distinguish first and last names. This lack of distinction could very likely even be the reason she asked here in the first place.
Comment: @JanusBahsJacquet I had assumed "I am Chinese" referred to nationality rather than ethnicity, but that may be a false assumption and this is an interesting point. I'll comment to OP and ask for clarification.
Comment: @Martha True! I actually have those special characters in my name myself. In the case of my language, there's a standardized way to convert them into normal letters, recognized by all airlines I have used so far.
Comment: Of course I mean beginning in position 6.
Comment: @BensaysNotoPoliticsonSO This is very useful, you could post it as an answer.
Answer: What matters is what is on your ID, but in general:
"surname" = "last name" = 姓
The phrase "last name" in English refers to your family name, regardless of whether your family name is customarily said/written first or last.
Comment: Yes, it's confusing, but that's precisely why it needs to be explained explicitly that the phrase "last name" in English means family name, not "the part of your name which is said/written last"
Comment: @choster shouldn't his *English* family name be the complete *Sánchez Cerén* then?
Comment: "Last name" is a bit confusing because in many countries or cultures (including often in China) surnames aren't last. "Surname" = "Family name"
Comment: "Family name" isn't necessarily less confusing, because multiple family names may be used, particularly in parts of the Hispano/Lusophone world, where the first surname is the father's surname and the second surname is the maternal grandfather's surname. For example, the president of El Salvador is Salvador Sánchez Cerén; Sánchez is his paternal family name, not a given name, and Cerén his maternal family name. So perhaps *patrilineal family name* is the best equivalent for the Anglophone world, although this doesn't then work for surnames which are merely patronymics.
Comment: @choster: "So perhaps *patrilineal family name* is the best equivalent for the Anglophone world" - unless the child has taken on the mother's surname, which is certainly also legally possible in some anglophone countries.
Comment: @Džuris The only way for a whole family to consistently have the same surname is for _the entire population_ to have that same surname. How else would you realistically do it? What defines a 'family'? Just two generations is enough to see that it's impossible to carry out in reality.
Comment: @Džuris The problem of trying to apply one cultural standards to a different culture. Before anyone thinks that *surname* would be better, here's the oxford dictionary's definition: "A hereditary name common to all members of a family, as distinct from a forename or given name". So no luck there either.
Comment: @Džuris It would only be common within the paternal line anyway. The Spanish convention means that all siblings share the same surname. As the name does not change after marriage, the parents already do not share a surname.
Comment: @O.R.Mapper But in such a case, there is no need to draw a distinction. I am referring only to conventions with regards to compound last names.
Comment: @Chieron That's how I usually fill out forms, yes.
Comment: @Chieron I think you are write but it sucks logically to think that neither his parents nor his children would have the same *family* name. Family name sounds to me like something that is consistent within a family...
Comment: @Chieron Spanish colleagues have had trouble in the past with a two-part surname (unhyphenated) being accepted as a single name, *including on travel bookings* (though not flights).
Comment: @ChrisH that might be the case, but is actually an oversight of the company your colleagues booked. Nobility should run into the same issue all the time, and there are other cultures with unhyphenated multi-word surnames, too.
Comment: @Chieron Just because a company gets things wrong, doesn't mean it's not the customer's problem in practice
Comment: @ChrisH true, but with that company you could run into issues when someone compares your passport and booking. I just wanted to point out that the issue is not restricted to Spanish names.
Answer: I suppose you're Singaporean? That's a current practice in Singapore. However you don't have much of a choice. Your family name is Wong, and your first names, plural, are Minnie AND Qin Qing.
Comment: There is also nothing oxymoronic about the phrase "first names" in the plural, any more than [First Nations](https://en.wikipedia.org/wiki/First_Nations) or "the first ten minutes of the game" are oxymorons. Only one entity can be first, but there is nothing oxymoronic about that entity being a group consisting of sub-entities.
Comment: @PeterCordes: "The usual phrase (in western English) is 'given names', because 'first names' (plural) is an oxymoron: only one can actually be first." - that would make the "top ten" and the "best [ones] of the best" oxymorons, as well. Avoiding the very confusion the OP is asking about seems like a likelier reason to prefer *given names* over *first names*.
Comment: @phoog I'm sure that is true. The reverse is also true in some places, that you may have as as many first and last names as you want, but only one middle name. I've also heard people claim that you can't have a middle name if you have four names. Americans saying they have multiple first or last names are common enough, too. I'm sure some do make the distinction Peter mentions, but there is far too much variation to make any kind of blanket statement on "the usual phrase (in western English)".
Comment: @PeterCordes That is not true at all, at least far from universally so. If you look them up in most dictionaries, 'first name' and 'given name' are given as synonyms, which mirrors my own personal experience exactly. You can have several first/given names, and if you normally use just one of them, then you'd also call that your first/given name. My dad has two first names but only ever uses the second one except when filling in forms; his second first name is his first name (= primary name), while his first first name is _a_ first name of his.
Comment: Terminology The usual phrase (in western English) is "given names", because "first names" (plural) is an oxymoron: only one can actually be first.  This includes first name and "middle names", but not the family name (because your parents didn't have to choose that).  (Some people use one of their given names other than the first one as their primary name, and would write their name with a first initial instead of a middle initial in a context where you don't expand all your given names.)
Comment: So OP has two separated independent first names, and I can choose one freely (*Minnie* or *Qin Qing*), but not calling both at once (*Minnie Qin Qing*)? Customarily, which one is better? And can I simply call them *Qing*?
Comment: @JanusBahsJacquet part of the problem is that these terms are not used consistently throughout the English-speaking world.  In the US, one commonly has a single first name, an arbitrary number of middle names (usually one) and a single last name.  It would not be hard to find an American who would take exception to the idea that one could have multiple first names.
Comment: OP is saying that (s)he is Chinese. But that might refer to ethnicity rather than nationality? I have asked OP to clarify.
Answer: I agree with other answers here that if this is for an airline ticket booking you should transfer what's stated in your passport to the airline ticket – that is, if this is for international travel.
First name and last name are an entirely western language concept. More generic (and culturally more sensitive) would be to use given name and family name. Since names in China and other cultures put the family name before the given name, first and last name don't make sense here anymore, though I find that many people in cultures with reversed "first name" "last name" are aware of that.
In addition to your purely Chinese name (Wong Qin Qing, seemingly a Catonese/Mandarin mix) in family name – given name order, you also have a western style name (Minnie Wong, whereby "Minnie" is probably the given name you chose) in given name – family name order. When you mix both it could lead to confusion beyond identifying you. So it would be best to be "Minnie Wong" to your western friends/colleagues or in Hong Kong, where that's more common, and be "Wong Qin Qing" or "Wang Qin Qing" in your (mainland) Chinese circle.
Answer: I am sure you are Chinese but not China residence, maybe Malaysian Chinese or Singaporean Chinese, am I right?
I face this same issue before.
Your passport printed Minnie Wong Qin Qing, am i right?
Minnie is your Christian / English name.
Wong is your family name
Qin Qing is your name.
While you make the flight booking, make in this way:
First name: Qin Qing
Last name: Winnie Wong
Only in this way, while print out your boarding pass, it will show Winnie Wong / Qin Qing, you wouldn't face any problem boarding.
This issue actually is suffering many people before, the airline also advice change the first name, last name as formal format Given name, Surname.
Remember, while flight boarding, they only recognize what word type in your passport, if your passport only write as Winnie Wong Qin Qing, don't book your flight with Winnie 黄青青!
But some country passport comes with Chinese Mandarin word and English word, they are safe with both, example Taiwan ROC.
Happy Safe Flight.
Answer: if you have a brother or sister then the commun words in your full name is the last name (last name = family name).
And the rest word or words is your first name it's also the given name par your parent to you.
Comment: This doesn't work in all languages/cultures or all situations. In some cultures children of different genders inherit different family names (which may or may not be inflected forms of the same name).  In other cases a child may be born before the parents are married, and take the mother's surname, then the parents marry, a sibling is born, but the first child's surname isn't changed.  Or many other examples
Comment: @ChrisH Or indeed the parents may simply choose to pass the mother's family name on to one child and the father's onto another, even if they are married all along.
Comment: @JanusBahsJacquet indeed.  There are many cases.  A specific example occurred to me which was why I used it.


vacuum sealed kielbasa in a hot car for 18 hours - is it still good?

Question: I bought vacuum sealed kielbasa yesterday about 6:30 pm. It must have fallen out of the bag in my very hot car and I didn't notice until about 11:45 the next day...Is it still good?
Comment: i think we need a new stack for " i left X in my car, will i die if i eat it "
Answer: Sounds like you're going to need some new kielbasa.
Kielbasa isn't fermented, and needs to be refrigerated to stay good. Vacuum sealing reduces the oxygen in the package, slowing down oxidation and inhibiting the growth of some types of bacteria when combined with refrigeration, but that kielbasa won't stand a chance in a hot car.
Answer: Of course not -- throw it out.
Answer: Time to throw it out.
Even a salted, preserved, and sealed sausage will not survive. The bacteria will begin to multiply rapidly after 30 minutes of sitting out of the fridge.
Perishable food sitting out for longer than 30 minutes is a risk to eat, even when it was frozen. Some food might last 1 hour.
I completed a food safety course with exemplary scores I might add.
Comment: seriously, 30 minutes? Some people live more than 30 minutes from the store. While I wouldn't eat the kielbasa of the question, when you give advice that all of us have routinely ignored, you increase the chances that someone will do something dangerous.
Comment: Ideally, if you're driving that far in hot weather, you pack things that are heat sensitive into a cooler.
Comment: Yeah straight from food safety course.  If it is kept hot in a warmer, that is a different story. After being cooked of course. Keep cold food cold and hot food hot.


override list view for custom object with lwc

Question: I have a custom object that I need to override the list view functionality with an LWC instead of the OOTB list view. It looks like I can only do that with a VF page (no LWC option).

Is there any other way to accomplish this?
Answer: Turns out, when you scroll down on the Tabs page in setup, there is a handy section called Lightning Component Tabs. There you can create a tab and select the LWC you want to use with it. Remember to associate the tab with the app you're want to use it in.
Answer: There is no method that is a standard override.
There is a (much) more complex route that is likely a lot of development for the benefit that you need.  That is to create a page in the lightning app builder and then create your own lwc component that repeats the custom view - perhaps using a datatable type approach.
You could consider an aura component (see https://developer.salesforce.com/docs/component-library/bundle/lightning:listView).
I think my general advice would not to go down this development route though.
Comment: Thanks @andy-nix - so I've already created a page with lightning app builder and built out the list view with LWC. I'm trying to understand how to use that view instead of the OOTB list view when clicking on the custom object tab.  The only way I've found to do it would be to create a vf page to house the LWC. Looked unnecessarily complex. I was hoping there was an easier way.


When are Accessibility Relations satisfied?

Question: We can only "measure" (quantify) counterfactuals by an accessibility relation to our own world. Therefore how can we assert something as necessarily true in all possible world's if quantification of modal relations (counterfactuals) is/are restricted to only our world?
Comment: Explain your question, what exactly do you mean by "counterfactuals," what do you mean by "quantify," is it the usual existential and universal or modal quantifier? Why are you calling modal relations "counterfactual," not all modal relations are "counterfactual" if we use the usual meaning of the term "counterfactual." Why are you saying all modal relations are restricted to only our world? what do you mean by "our world?" Are you working within a kripkean frame-work?
Comment: Counterfactuals mean what they are. A possible state of affairs. Yes, I adopt the usual meaning of "quantify" here. The rest of the questions are a matter of semantics that is well established.
Comment: Not really well established, but contextual. Are you working within a kripkean system? Do you know how QML works? I am asking so I can answer the question.
Comment: "Do you know how QML works?" I don't.
Answer: First of all I want to state that Quantification over possible worlds has some problems: both logical and philosophical. So take this as a mere exposition.
Let A be the set of all worlds accessable to A* where A* is the actual world in A.  Let C be the set of all constants {c1,c2,...,cn}. Let R be the set of all relations such that {P1^n, P^2^n,...Pm^n} n>=0. Let V be the set of all variables {x1,x2,...xn}
Model M is
M=A
D: non-empty domain of objects
R: accessability relation on W×W
V_M is a valuation funtion of the model such that
1) If cm∈C, then V(cm)∈D
2) If Pm^n∈R and n=0, then V(Pm)∈Powersetof(W)
3) If P is a predicate of power n not equal to zero, then V(Pm) is a relation from W to powerset (D1×D2×...Dm)
Let Φ be the formula you are speaking about, then to say
□Φ in all possible worlds is to say:
∀Wn∈W, □Φ is true (M) in Wn.
Answer: We can't, unless we use a modal logic in which it doesn't matter which world you're at when evaluating the truth of modal sentences:
S5 (with the additional assumption that there's only one equivalence class of worlds).
Comment: So, framing conditionals also fails too?


Is the rationality an instinct for the man?

Question: I read a post in facebook few minutes ago and the titular says something about a boy banging a dog, and then the boy broke the dog's leg because the dog bit her little sister and also the boy stabbed the dog many times. The boy was like 6 years and the girl is 2 years old. Some people said: "That is ok, the human is more important than a dog". I keep thinking on that, why we are more important? A friend answer me because we are rational. But with our rationality we are destroying the earth. I'm not a defender of animals but for being rational I dont feel more important. And when I was thinking in all these a question came to my mind: is the rationality an instinct?
Comment: Whether something is an "instinct" or not is a question of biology, not philosophy. Could you maybe rephrase to make the philsophical question more clear?
Comment: @JamesKingsbery: With the movement of philosophical anthropology (Scheler, Gehlen, Plessner et. al.) there was a whole new branch of philosophy only dealing in a philosophical way with the touching points of biology and philosophy. In there, instinct became object of philosophical thinking and by this a philosophical term. This could be taken as a hint for the OP, too *hint*
Comment: I vote for reopen. The comment of Philip convinces me that the OP deals with a question from anthropology which is a philosophical subject.
Comment: @JoWehler please see http://meta.philosophy.stackexchange.com/q/3083/2953.
Answer: It depends both of the definitions of instinct and rationality.
Taking Helmuth Plessner's work The Levels of the Organic and Man, Introduction to Philosophical Anthropology from 1928 [note: the translation is in the making], it is just the way you think:
In Chapter 6.4, he describes instinct as a certain predetermination of action that has broadness, i.e. leaves place for conciousness, difference, correction of behaviour. It is by this the frame/bounding of conciousness. This has to be discriminated from reflex, which is a direct reaction pattern with no broadness whatsoever. Therefore, instinct is left to animals (and humans, as animalic) that can conciously act towards their environment and not only react to changes in their environment (essentially, but not necessarily identical to the difference between animals with or without central nervous system).
Human rationality there could be defined as an ability that coincedentally emerges from having the ability to have distance from the self (self-conciousness, excentric positionality, Chapter 7) together with the ability to to idealize (Ideation is a term taken from Husserl), that is to make a true difference between the particular and a general concept of it. Only by this, we are enabled to be rational, i.e. not bounded by the situation and phenomena.
As rationality would in these terms be part of the specificity of our mode of conciousness and instinct is described as the frame/bounding of conciousness, rationality would in fact be instinct.
But this is only one, although in its total very convincing (only very sketchy here) way to define the terms.
Answer: Rationality is a cognitive capability. A capability which must be trained like the capability to speak.
Rationality is not an instinct:

Instinct or innate behavior is the inherent inclination of a living organism towards a particular complex behavior. The simplest example of an instinctive behavior is a fixed action pattern (Wikipedia)

Summing up the main difference: Rationality must be learned, instinct not.
Comment: If this is the answer OP is looking for, the question doesn't belong here (as James Kingsbery points out above). Please don't answer off topic questions.
Comment: Just the fact that the question mentions rationality is not enough. It should fit into one of our [seven topics](http://philosophy.stackexchange.com/help/on-topic). There are plenty of questions that contain the word "rationality" that are off topic here. Also, this is not a blog.
Comment: @Keelan Questions concerning rationality have a philosophical aspect which I consider suitable for the present blog.
Comment: @Keelan: I take it to be a poor understanding of philosophy if (philosophical!) anthropology was not taken to be a philosophical topic. And the question fits this branch just fine.
Comment: @PhilipKlöcking I agree that you can make the question fit, but not if this would be the answer.


Mistborn, Hero of Ages - The 'snapping' done by the mists reveals mistings. Of these, 1/16th burns Atium. Why 1/16th?

Question: Mistborn, Hero of Ages - The 'snapping' done by the mists reveals mistings.  Of these, 1/16th burns Atium.  Why 1/16th?  There are supposedly 16 Allomantic metals excluding Atium.  If you include Atium and Malatium, the number goes up to 18.  Should it then not be 1/18th of the affected people (mistings) that can burn Atium?  Then, would there not also be a mistborn or two that 'snapped'?  Of the 5000 plus in Elend's army that 'snapped', would there not be at least a few mistborn?  And would they not stay in bed even longer than the 16 days the Atium mistings (seers) did?  Being a mistborn means that they can burn Atium plus all the other Allomantic metals.
Comment: Yes, those were the Atium mistings, 1/16th of those who snapped. Also, mistborns seemingly requiring very pure bloodlines, I doubt we can just assume full mistborns to have equal representation compared to the other mistings, especially in a skaa army.
Comment: Assuming that Mistborns were to have a flat 1/18th chance, to follow the argument, then there should have been 277 mistborn in the 5000 troops. Also, at the end during the big fight weren't there multiple people burning the atium in the fight against the Koloss?
Comment: Atium and Malatium are not natural metals.  Atium is literally the body of a god, bound in earth and extruded over time.  After the rise of Harmony, who brings the two gods into one being, Atium no longer exists.
Answer: I've wondered about this "1/18th vs 1/16th" discrepancy too. I assume that it's one of the author's plot devices, but thought that 1/18 would have made more sense.
Regarding why there were no mistborn within the soldiers that snapped, keep in mind that even among nobles mistborn were rare, as Kelsier noted when he first revealed Vin's mistborn status. Within the trilogy, there were only three known skaa mistborn that Kelsier was aware of - his old master, Kelsier himself, and Vin. Of course, it's possible that there were others, but since noble mistborn were rare, skaa mistborn would be even harder to find.
Kar, one of the Inquisitors, noted that Vin's Allomancy was amazingly strong during the final meeting with Tevidian, the Lord Prelan:

Why, for her to have such strength, she must be of an extremely pure
  line. At least... one of her parents must have been from a very pure
  line.

Due to this fact, it's highly likely that the no members of the army had inherited enough Allomantic genes to enable mistborn to be snapped, thereby leaving only newly minted Mistings within the army.
EDIT:
In this forum, one of the members recalled a conversation had with the author about this topic:

I asked Brandon about this at his Eagle Eye Books signing during
  Dragon*Con 2010. (Although you worded it much better than I did at the
  time.)
Essentially, Brandon said that Preservation wanted the number 16 to be
  noticeable in a multitude of places. This would make it easier for
  humanity to realize that something specific / unusual / planned was
  going on. Brandon didn't say why Preservation chose 16 over 18 (or
  more, due to other atium alloys), just that Preservation wanted the
  number 16 to be noticed.

The author also has some notes regarding mistsickness in his annotations for book 3.
Answer: On the discrepancy between the known metals and the proportion of mistings in Elend's army

At the end of the original series, We know of the following metals :
Physical Metals

Iron (external)
Steel (external)
Tin (internal)
Pewter (internal)

Mental metals

Zinc (external)
Brass (external)
Copper (internal)
Bronze (internal)

Temporal metals

Gold (internal)
Electrum (internal)

Enhancement metals

Aluminum (internal)
Duralumin (internal)

God metals

Atium
Malatium
Larasium (this metal is particular and no larasium mistings would be found)

At this point, Sazed reveals to Spook that there are two metals left. Yet, when looking at other works from Brandon Sanderson, we now know that there are in fact four other metals. It is my theory that Sanderson decided to tweak his magic system a bit.
It is my opinion that, originally, Atium and Malatium were intended to be temporal metals. It all fits the allomantic structure known at the time. Atium and Malatium both let you see other people's shadows/past selves. As such, they would perfectly fit as the external temporal metals. One is also an alloy of the other, another important rule. It can probably also be assumed that one would be a pushing metal and the other a pulling one.
If you decide to classify Atium and Malatium as the missing temporal metals, Sazed is totally right in saying that there are still two metals remaining. Those would be Chromium and Nicrosil, the external enhancement metals that have effects similar to those of Aluminium and Duralumin, except applied to another allomancer (thus justifying the external classification).
This is, in my humble opinion, why there are only 1/16th of Elend's army that could burn Atium, and not 1/18th. This is either an oversight on the part of the author or a simple and forgivable act of retcon.
EDIT :
Sanderson's answers to the question unearthed by JW8 really strikes me as a justification for a retcon by giving another reason for the number 16 to popup, especially since Sazed, at the end of Hero of Ages, explicitely states that there are only two remaining metals to be discovered, not four.

On the reason behind the lack of mistborns in Elend's army

Prior to Rashek giving Larasium to his friends, there were only mistings, and no mistborns. The direct descendants of these original mistborns have a much purer bloodline, augmenting their chances of yielding allomancers.
Through interbreeding, most Skaa have some traces of allomancer blood but it's normally too diluted to be of any use. Only those with nobles as close parents have a bloodline pure enough to allow for snapping and, even then, Skaa mistborns are practically unheard of. And since, in the era described in the original trilogy, nobles seemed to be very careful about half-breed offsprings, it is highly unlikely that Vin or Kelsier's circumstances are shared by many people.
And, as the Asker mentionned, Mistborns in Elend's army would've been among the most afflicted by the snapping. They would probably have been mistaken for Atium mistings, since very few tests were done for lack of time (it was pretty much the end of the world for them).
Comment: It would indeed be very interresting to know for sure. Larasium (and it's alloys) is usable by non allomancers and should not normally be included in the regular allomantic metals since they have no power other than granting allomancy. However, the other God metal, Atium, has associated mistings. As Sansderson's magic systems are normally pretty well designed, one can only wonder... Is there a hidden meaning to this that we will uncover in later works? I'd really like FallingBullets to add a source to his claim that the Allomantic rules were changed at some point!
Comment: Sanderson has said, that while pure Larasium created Mistborn, if you cut the Larasium with another allomantic metal, it would create a misting for that metal.

I think there are just some facts that we don't have as of yet.
Comment: Indeed.  Though I'm more excited for Stormlight Archive 2 =)
Comment: I felt that the God metals (Atium, Larasium) didn't really count... but then that leaves Atium mistings as an anomaly.

Either way, we need more clarification from Sanderson.  Maybe I'll ask him on reddit and see if I get a reply.
Comment: I agree with you on this. But our current state of information remains that some facts are contradictory, like the amount of metals to be discovered at the end of "Hero of Ages", for instance. Which is why I can't wait for an official statement or more books from Sanderson ^_^
Comment: YEEESSS!!! Can't wait for that one either! So many very interresting characters!
Comment: Yes, and more importantly we're getting bigger glimpses of the Cosmere than we have through any other of his works.
Comment: This is a very reasonable answer and I think many parts of it could also apply to [this related question](https://scifi.stackexchange.com/q/139001/23386).
Answer: Regarding the '1/18' question, Brandon has confirmed that Preservation or The Lord Ruler actively changed the magic behind Allomancy, replacing the temporal metals (Cadmium and Bendalloy) with Atium and Malatium (in the Final Empire, the symbols are also used to represent numerals, and Atium and Malatium are in places 10 and 11, cadmium and bendalloy are up at 17 and 18). This meant that there were still only 16 metals, and it also allowed for the creation of atium/malatium mistings, which is where the 1/16th. I dont think it's a retcon either.
Comment: [here](http://www.theoryland.com/intvmain.php?i=428#82) you go
Comment: "Brandon has confirmed that Preservation or The Lord Ruler actively changed the magic behind Allomancy, replacing the temporal metals (Cadmium and Bendalloy) with Atium and Malatium" - Can we get a source? I'd love to see one!
Comment: as in: could a mistborn use cadmium/cerrobend in the Final Empire? or could a theoretical mistborn in Harmony's time use the god metal alloys? both I'd think, but you wont get atium/malatium mistings any more, and there were no cadmium/cerrobend mistings in the Final Empire
Comment: Nice, thanks! Reading his answer, it can make sense, as Cadmium itself is mostly found as an impurity in zinc carbonate (it is about 650 times rarer than zinc, too). And as the known uses for both cadmium and cerrobend are fairly modern, it is more than likely no one would have ever found them as allomantic materials. Now, the question that comes to my mind is "Are those metals completely gone as allomantic metals as Sazed seemed to imply or could a mistborn use them if he ever found some?"


Image quality issue

Question: I receive 3 Png file but one looks grainy when zoom in but the other looks ok. I check the resolution is the same. So what is the causes of the quality. Although there is different in document size, but when compare a smaller document size with same resolution also looks grainy. Anyone can explain the issue? Thanks.
Answer: The "grainy" PNG is in indexed color mode. The reason for this is that the creator of it likely used the "Save For Web" option in Photoshop and saved it as a PNG-8, using fewer than 256 colors.
Depending on the quality you desire, there are a few options you can ask them to do (in order from smallest file size/lowest quality to highest):

Redo "Save For Web" and increase the number of colors on the PNG-8 to 256
Redo the "Save For Web" and save as a PNG-24 instead of PNG-8
Use the regular "Save As" option and select "None" under compression

I would go with the last option, as it will provide you with the highest quality PNG.  You can worry about compressing it yourself, after you've done your work with it.

Image quality issue


What makes a origami paper popper produce loud sound?

Question: A paper popper like the one shown in this YouTube video makes a loud sound when moved quick through the air.The air pressure inside the 2 conical structures in the popper would be higher when this popper is moved fast. But how exactly is this difference in pressure converted to sound? Will having different paper types produce different frequencies?
Answer: Whilst physLads answer is correct, it is perhaps too succinct to be helpful with those unversed in gas dynamics, so I will attempt to explain what a 'blast wave' is in this case.

"My understanding currently is that the pockets created in the popper actually become high pressure pockets ( like a balloon) when moved very quickly through the air. This high pressure releases a small flap of paper suddenly when the differential pressure ( inside the pocket pressure is higher than what is just outside) is enough to push out the paper flap against frictional resistance."

This much is correct. However, as the flap of paper moves away, the high pressure gas pocket that had built up must rush in after it, pealing away layer by layer in a 'rarefaction' that means that, as the paper is moving it is followed by a moderately low pressure, but crucially very fast moving air. The paper is then brought to a very sudden halt (in the frame of reference of the persons hand), but still has a mass of fast moving air piling in towards it. This creates a 'blast wave', in this case a region of stationary high pressure air between the paper the region of fast moving low pressure air. The blast wave is the discontinuity in velocity and pressure between these two regions of air. As more air piles in across the blast wave the region of high pressure air adjacent to the paper increases in size, and the blast wave moves outwards through the air. This 'blast wave' or 'pressure discontinuity' is the loud pop heard.
Edit: you state in comments that you believe the sound to be produced by the region above the paper popper as the paper accelerates into it. It is true that this will also create a blast wave. However the acceleration of the paper is much slower than its deceleration, thus this wave will be smaller. In addition, the rarefaction caused when the paper halts will reduce the size of it yet further. Recordings of a paper popper being used may contain an ear splitting pop followed or preceeded by a much quieter one, the quieter one will be produced by this method.
Answer: Pretty much exactly off wikipedia, let me know if you have any further questions.
What happens is that air rushes in a blast wave to fill the vacuum created in the pocket that opens. The sound is described as the crack of a whip, which is an example of breaking the sound barrier, although the causes are different.
So its basically the rushing air into the newly created pocket that makes the noise.
Comment: I just read the wikipedia page and I'm pretty unconvinced by this explanation... My intuition would be that it's the paper unfolding abruptly that creates a noise. I guess trying with cloth won't make a sound, while very rigid cardboard will be harder to pop, but make a bigger sound.
Comment: cloth would also allow air to permeate through. how about trying with a sheet of plastic?
Comment: I read the wikipedia page again. I do not seem to agree or probably  not getting the language right. My understanding currently is that the pockets created in the popper actually become high pressure pockets ( like a balloon) when moved very quickly through the air. This high pressure releases a small flap of paper suddenly when the differential pressure ( inside the pocket pressure is higher than what is just outside) is enough to push out the paper flap against frictional resistance. This released flap causes the air just above the flap to suddenly compress causing the sound to be produced.
Comment: Ah really useful you compared it to a balloon actually. Read this on why balloons pop when they're burst.
Comment: When you stick a pin in the side it creates a tiny hole. The rubber around the edge of the hole isn't being pulled uniformly in all directions any more because there isn't any force exerted from the centre of the hole. So the net force pulls the rubber away from the hole, which makes it bigger and the force imbalance increases. In a fraction of a second, the entire skin of the balloon has contracted all the way back to a point on the opposite side from the pin. The high-pressure air that was inside the balloon is now free to expand and this creates a pressure wave that our ears hear as a bang.


Do I need a new collection for each component with variables and tokens in Figma?

Question: I understand there are primitives, which are raw data, and I have to reference them. But do I have to create a new collection every time for each component? And how do modes blend into it then?
Answer: If I understood your question correctly, here's some information that might help you:

Primitives collection should be used as references in semantic tokens. Apart from that it is common practice to descope/unpublish primitives collection to make sure you and your team members won't be choosing wrong properties for components. More information on how to unpublish variables in collection could be found here.
You can store different tokens inside one single collection and by specifying different names for variables (e.g. text / primary; text / secondary for different text variables) these tokens will be organized automatically according to the given name. More information regarding token's naming convention here.
Keep in mind that Figma offers variable modes which allows you to assign multiple values for one single token. It comes in handy if you're designing light/dark modes for the application. More information here.

If something's not clear, I'll update my answer according to your comment.


How do traveling far field radio waves break free from the non-traveling near field conditions at the transmitter antenna?

Question: I would like to know how far field traveling electromagnetic radio waves separate from the near field non-traveling electromagnetic fields at a radio transmitter antenna.  How is a non-traveling electromagnetic field converted into a traveling electromagnetic field?
Comment: Even the near field has "travelling" components as you put it.
Comment: Yes, but they only travel to very restricted locations near the source antenna.
Comment: I'm having a hard time getting a decent answer to this simple question from the usual sources on the internet.  Perhaps physics has no good answer at the present time.  That's why I have asked the question on this physics forum.
Comment: or perhaps it is the wrong question. (well that's what always happens to me).  Is they answer they separate because they don;t interact anyway and because they travel away from each other? If not why not.
Answer: You are confused. The near-field and far-field components are both present at all distances from the antenna. The difference is that whilst the near-field component(s) fall of in amplitude as $\sim r^{-2}$, the far-field components fall off as $r^{-1}$. In other words, they co-exist, but one can define three regions: one where the near-field dominates (at small $r$), one where the far-field dominates (at large $r$) and a third where they are of comparable magnitude and must both be considered.
There is no black & white dividing line between these regions - it depends on the purpose of your calculations/investigations. Typically one says that the far-field radiation field dominates if $r \gg \lambda/2\pi$ (where $\lambda$ is the wavelength of the far-field radiation) and if $r \gg l$, where $l$ is the dimension of the antenna. What $\gg$ means is entirely a matter for you.
Comment: Why does the amplitude of the near field fall off as r-2, while that of the far field falls off at r-1 ?
Comment: Because that is the definition of the "near field". If it fell of as $r^{-1}$ then it wouldn't be the near field @JohnPetrovic If you are asking why there is a near field and a far field, well think about the field of an accelerating charge - there will obviously be some static "Coulomb component" that varies as $r^{-2}$.
Comment: Think about this.  A single moving electron generates a magnetic field around it that moves (i.e. changes in space) with the motion of the electron.  Many moving electrons in an antenna produce a magnetic field in the vicinity of the antenna.  How does this lead to the formation of an independently traveling electromagnetic radio wave that no longer interacts with the moving electrons in the antenna?  This is what I am trying to understand.
Comment: Because a "moving" electron doesn't generate EM waves, only an accelerating electron does that. And if you are talking about a linear antenna then of course the far-field component is zero along the direction of the antenna.
Comment: Tell me how an accelerating electron produces an electromagnetic wave, that's what I want to understand.
Comment: That was not your question, which would have been a duplicate of  http://physics.stackexchange.com/questions/46946/how-em-waves-are-produced-by-accelerating-charged-particles?noredirect=1&lq=1
Answer: I read a bit the wiki article on near and far field and antennas.
To start with an electromagnetic wave always travels with velocity c , no matter how the interference patterns of continuous emissions appear.
An analogy: When one is near a lamp one can see the emitting wires or diodes, which means that it is not a plane wave of light but it has a particular structure , at a distance the light source follows the 1/r^2 law of dispersion from a point source and can be described by a spherical wave.

I would like to know how far field traveling electromagnetic radio waves separate from the near field non-traveling electromagnetic fields at a radio transmitter antenna .

It is not a matter of separating electromagnetic waves, but of diminishing importance of the interference patterns that control the near fields due to the small distance from the source  and the shape of the source, the wavelength being the gauge.

What you call "non traveling " wave is a misnomer. It is a non traveling diffraction pattern. Diffraction patterns are dependent on the continuous emission of the electromagnetic wave from the particular topology of the antenna. At a distance, as the beam opens in angle and the energy density drops these diffraction patterns disappear and a dipole pattern of energy density  dominates , if the antenna is a dipole.
Comment: This diagram is from Wikipedia near and far field waves.  But it does not answer my question.  My question is what happens at the line in the diagram that separates fresnel radiative waves from far field waves.
Comment: The diagram is for people who are not clear for far field and near field meanings. My answer states  that there is NO line, rather the line is a few wavelengths wide, of continuously fading interference. The near field interferences fade away in a few wavelengths due to the opening rays  and only the radial 1/r^2 behavior remains. Do not confuse interference patterns of em waves with the em waves.
Comment: Interference effects happen when multiple wave patterns interact with each other.  Since one radio wave is generated by each cycle of the charges moving in the antenna, where do these additional wave patterns come from?
Comment: In electromagnetism the  waves do not interact. They overlap, it is in the quantum mechanical regime, the wavefunctions are superposed, and their comlex conjugate squared show the interference patterns in the energy content of the beam. The classical wave also, but it is not an interaction, it is an overlap because by their construction the waves are in phase .
Answer: A perfect oscillator may create electric field in a capacitor, and magnetic
field in an inductor, and (being 'perfect') will not radiate.   That's not useful for a radio, so we add a component, the antenna, that has both electric and magnetic fields, but which ALSO has a loss element, a resistive component
to its impedance.
The energy loss in an antenna is intended to be radiation out into space of
an electromagnetic wave.   The OTHER parts of the energy provided to
the antenna are NOT lost, they just cycle energy from inductor/magnetic field energy
to capacitive/electric field energy, back and forth, just like an inductor and capacitor (LC tank circuit).
To evaluate an antenna design, the how-much-power-is-emitted question requires a
calculation of the fields near the antenna, due to the supplied current at the
transmitter frequency.   That is important, because nearby objects (the transmitter tower, the ground) and the shape of the antenna elements, determines beam direction.  The radiated intensity, though, in any given direction, will
only depend on the way those local fields couple to a wave-equation traveling
wave solution.   So, after solving local fields, one also finds a second part
solution, to the far field traveling wave that delivers radio to your receiver.
The calculation has two parts.   The physical situation is only ONE part,
but we can use approximations at a distance that wouldn't work up close
to the antenna (where we care about different answers, anyhow).


Obtaining Ip address loop for LG Escape 3

Question: I recently came back home from vacation and attempted to reconnect my phone to my home wifi, only to find myself in a great struggle to get my phone to loacte the IP address. It continues to insist that my connection is poor and conveys the words "avoided poor network". However I know the truth to be quite the opposite for all the other devices in my house connect without issue. But for some reason my phone refuses to obtain it. Need help to resolve this problem please!
Answer: Hey I've had this problem before forget the wifi the reconnect if that doesn't work tell me
Comment: Yes I've tried that dozens of times it doesn't work. Ive even changed the IP address several times. I'm capable of connecting to wifi other than my home wifi network, and my other devices connect without iissu so Idk where the problem lies


ipad charging problem

Question: For 5 hours it only charge 10% . How could I solve this problem.
Comment: How are you charging it?  With the charger that came with it? or plugged into a computer?
Answer: This page from Apple details how to charge an iPad.  It recommends plugging it into either the 10w Power Adaptor that comes with the iPad or a high powered USB 2 port.  Some USB2 ports are not high powered and will either not charge the ipad or only trickly charge it very slowly.
This article details how long it should take to charge the iPad with various techniques.  As you can see charging the iPad with the charger it comes with takes about 3 hours (to 80% capacity).
If you are not getting satisfactory charge times (and are using the recommended chargers), then you should book to have your iPad checked out at an authorized Apple repair centre or Apple Store.

ipad charging problem


Applied Problems in Probability which can not be modelled on Polish spaces

Question: Probabilist often work on Polish spaces. Does somebody know an ("non-exotic") example, for which it is not possible to work on a Polish space, but instead one has to work on a general measurable space? By non-exotic example I mean something like a stochastic process, which is really used in applications, and cannot be defined on a Polish space...(I posted the this question also here).
Comment: I run the risk of incurring the wrath of some hardcore probabilists here, but for problems that are *truly* applied, I doubt even measure theory is that useful. As Hamming said, "Does anyone believe that the difference between the Lebesgue and Riemann integrals can have physical significance, and that whether, say, an airplane would or would not fly could depend on this difference? If such were claimed, I should not care to fly in that plane."
Comment: @Simon: The real advantage of the Lebesgue integral is that it is meaningful for functions over other spaces than the Euclidean space, say, the symbolic space $\lbrace 0,1\rbrace^\mathbb{Z}$.
Comment: @AndyTeich In general the sample paths of a continuous-time stochastic process do not lie in a Polish space, do they ?
Comment: @Stéphane Laurent: As an example, the Skorokhod space (see wikipedia), i.e. the space of cadlag functions, is a Polish space under a certain metric...of course one could give it a metric so that it is not a Polish space, but this would be "exotic"... – Andy Teich 0 secs ago
Comment: @AndyTeich The addition is not continuous under the Skorokhod topology, isn't it ? Hence a bigger topology could be more appropriate without being so exotic.
Comment: @AndyTeich A good example is the powerful theory of empirical processes: stochastic process are considered as "random variables" in  nonseparable Banach spaces such as $\ell^\infty(\mathbb{R})$.
Answer: This answer is identical to the one I gave when the same question was posted at M.SE.:
There are a number of constructions that do not work for Polish spaces, but a certain class of probability spaces, variously known as super-atomless, saturated, nowhere countably generated and a number of other names. A nice overview can be found here.
A probability space $(\Omega,\Sigma,\mu)$ is saturated if for every two Poilsh spaces $X$ and $Y$, every probability measure
$\nu$ on $X\times Y$ and every random variable $f:\Omega\to X$ such that its distribution $\mu f^{-1}$ equals the marginal of $\nu$
on $X$, there is a random variable $g:\Omega\to Y$ such that the joint distribution of $(f,g)$ is $\nu$.
The following definition is conceptually different, but can be shown to be equivalent:
A probability space $(\Omega,\Sigma,\mu)$ is super-atomless if there is no $A\in\Sigma$ satisfying $\mu(A)>0$, such that the pseudo-metric space obtained by
endowing the trace $\sigma$-algebra on $A$ with the pseudo-metric $d(A,B)=\mu(A\triangle B)$ is separable.
Comment: I don't really see any example in these links.
Comment: I'm not sure wha you want. The paper shows that certain properties needed in applications do not hold on polish spaces. It also shows that one can do them on the space of uncountable coin-flips, a non-Polish space.


Save text on XML file or Database

Question: I'm working partime for an company and my boss ask me to make an module for PrestaShop to read/write news ( only Text ) into a XML file. But i think load text form XML will be slowly.
Anybody can tell me save text in XML file or Database, which better and why??
Thanks. :)
Comment: Is it one text at once or one million texts at once? Because if its just one, using database won't improve anything.
Answer: If the requeriments of news just involve text, i would prefer the Database Approach for storing, and XML as a way of transmitting data. The RDBMS are smart enough to handle text data.
Answer: I assume that we're talking about a small number of text entries since this is a news feed for an eCommerce site.
Given that assumption, you will probably not see a performance hit either way.
One advantage of XML is that you could format the XML as an RSS feed and then use the RSS feed for other things as well.
Answer: If you save the items to a file, there will be a lot of XML parsing and file I/O you'll need to handle yourself. If you save the individual news items in a database, the database will handle the I/O for you (probably much better than you could do yourself). If you need the news items in XML format for some reason, store them as XML in the database; most modern enterprise-class RDBMSs offer a native XML data type and some pretty good functionality for transforming the XML as needed.

Save text on XML file or Database


My DNS record can only point to an IP address. How do I make it reach for a port?

Question: I am fairly new to network administration and therefore am already excited to have successfully set up a DNS record.
Now I am a bit confused, because I would like to have this URL:
http://www.example.org:8080/fetch/characters/

be actually reached by this
http://www.example.org/fetch/characters/

So users can reach the service on port 8080 without having to explicitly set the port.
How can I do this? Do I need some special application on my server? Or any redirect stuff to be applied to requests?
Comment: Browser by default does not access port 8080. Is that a mistake in typing question?
Comment: misconception of what a dns is and what it does.
Comment: @Džuris Na it was a mistake of me thinking 8080 is the http default instead of 80
Answer: DNS records can't point to ports (with a few special case exceptions that do not apply here).
If you have a web service listen on port 8080 and want to reach it without specifying this port, you have 3 options:

Make it actually listening on port 80 (or 443 with https).
Configure whatever is already listening on port 80 to forward requests to your service on port 8080 (reverse proxy).
If you can live with a redirect, use this instead of a proxy, but then your clients will see the :8080 part in their address bars after the redirect.
Comment: What if we could use SRV records and specify ports for services... Too bad browsers don't use this.
Comment: @JacobEvans: SRV records for everything is an old dream of mine. It would make things so much easier (except for firewall admins who now can just block everything except 80 and 443)
Comment: SRV records work very well for _some_ services, like XMPP... but sadly not very many (and not HTTP for sure)
Comment: Option 4: port forward by a firewall
Answer: Web servers listen to TCP port 80 by default. If you don't want to type the port number in the URL explicitly, you have a few options:

You can reconfigure your web server to use port 80 instead of port 8080. This is recommended for web servers like nginx or Apache but not for web servers like Gunicorn. This option also is not always possible as that port might already be in use by a different web server.
Also, when your server is behind a NAT gateway, it doesn't own the public IP address and the combination of that public NAT address and port 80 might already be forwarded to a different web server.
You can put a reverse proxy server in front of your web server which accepts the traffic on TCP port 80 and sends it to your web server on TCP port 8080. This will also work if port 80 is already in use. Simply put the reverse proxy server in front of both web servers, making them both listen to ports other than 80.

In order to provide better and more detailed help on which option might be best and the limitations etc, we need to know more about your setup. Hopefully this explanation already clarified things a bit.
Comment: I already have the infos I need! I have mistaken the default web port 80 for 8080
Answer: Simple answer, related to level of question
Ignoring exotic uses of DNS, and also reverse DNS lookup (not relevant to question), almost all DNS use is of the form:

Client sends domain name (fully qualified or otherwise) to a DNS server
DNS server returns domain information from its records. Usually the key information requested is either the IP address to communicate with web/email on that domain, or the IP address of another DNS server better able to provide that information.

Once the client has contacted the server, the server itself will take over and the DNS system drops out of the picture.
What that means is, the the DNS system doesn't need to supply port information, and it almost never does so. So although the aim of the question is valid, and often done, it isn't actually the DNS system which does it. That's why you can't work it out :)
The idea is that once your client can locate the specific machine or server it's looking for, it is down to that machine to listen on any ports it chooses, and accept/deny/respond to any protocols on any ports configured.
For example, HTTP web services are usually provided on port 80. That means that once the client knows a machine IP, it can assume that sending a message to port 80 will result in that message being read/responded by that machine's web service. But it doesn't have to be that way. If the server is configured to listen for web incoming requests on port 9000, any client able to reach port 9000 will be able to reach its web service. If the server is behind a proxy/NAT/router that redirects port 10000 to port 9000, and the client sends a web request on port 10000, the server will receive it on port 9000 and respond as well.
Redirect/mapping within the web server
You asked about  redirect mapping or rewrite in a comment. These are functions a web server can do. Basically, you can configure the web server (or most/many web servers) to manage how it handles the URL it receives in a request. So it can internally modify the URL on receipt to make different URLs be handled the same way, or fix common typos (mapping), or it can actually respond to tell the client itself to ask a second time, using some different, replacement, URL (redirect).
These have their uses, and could in principle handle your use-case, but they don't sound like the "right" solution for you, for these reasons:

I don't think mapping would help at all. Mapping is almost totally internal to the web server, it says "treat this URL as if it's that URL". For example, you might use web server URL mapping to allow a user to query a forum using very-old, old and current URLs (for user convenience) using "https://example.com/index.php?area-=forum&topic=2", also "https://example.com/forum.php?topic=2" and also "https://forum.example.com?topic=2", and only handle this once, by mapping the first two of these onto the third URL internally, as the first step in handling  the query. As this targets affects the query path not the IP/port, mapping isn't much use for port management, and in your case, the client never actually queries 8080 at all.
Redirecting would work, but may not be what you want. Redirection in the web server relies upon the web server actually receiving the query (because these are web server internal functions). So the web server would have to listen on port 80 anyway to get the original query, inm order to respond with the redirect/map. It would also have to listen on port 8080. Functionally, it would need a redirect rule to have to tell any client querying port 80, to query it again using the ":8080" URL, which doesn't sound like what you want to do. The user would also see the new URL with ":8080" in it, whereas it sounds like you want it to be "transparent" and not shown.
Also redirect would only work to redirect a standard port (80 or 443) - you couldn't redirect port 2000 to 8080 say, because the client wouldn't query on 2000 by default, in the first place, so it wouldn't ever get to the web server, even if it was listening on 2000. This might not be a problem for you though.

However if you want "intelligent" redirection, where only certain queries are rerouted to 8080, this might be the way to go, because redirect can include logic to decide which URLs should be redirected, whereas port mapping (below) would map everything.
How to correctly do it
The answer to your question is, you want the web server to respond to web requests which the client sends to the default port (80/443), but which the server actually receives on port 8080.
That means, as you can see, you need something in between that maps the ports between client and server. That way, the client sends on port 80 (default port used by web browsers), but it's actually received on port 8080 by the web server. Of course you will have to configure the web server to listen on port 8080, as this isn't standard, but it's easy and any web server should be able to have its listening ports specified.
The most usual way to do this would be within the router/firewall, via port mapping.
In simple terms, to do this, the router is given a rule, that anything received which has a destination IP of  and destination port = 80, should be passed into the LAN with the destination port changed to 8080 instead. Neither the web server nor the client will be aware of the change (it's 100% handled by the router), so it will be 100% transparent to both of them. The client won't have ":8080" in its URL and won't need to redirect anything, since it queries port 80, and the web server can ignore port 80 and listen on 8080 only, since it never gets queries on port 80.
If you want a simple, straightforward way, similar to what a "DNS for ports" would do, this is probably the closest equivalent to what you're asking for in your question.
Comment: I often hear about redirect mapping or rewrite? are these solutions as well?
Comment: Those are modifiers that kick in _within_ the web server, in processing the client's command. So if the web server supports it, you **could** automatically respond to any inquiry on port 80, with an HTTP redirect to the same URL on port 8080 - after all, HTTP/80 -> HTTPS/443 redirect is much the same thing. But it has to be able to receive the query first, so it wouldn't work on ports it wasn't configured to listen to, and the client probably sees the :8080 modified URL. Doing it via port mapping makes it 100% invisible to the client, as they only ever use port 80 (8080 is 100% internal only)
Comment: I've added a section _"Redirect/mapping within the web server"_ and expanded the last section, to cover your question in more detail. I hope they help!
Answer: You can't.
I mean, technically this could be done.  DNS is famous for being able to submit a domain name and getting an IP address.  However, I've studied the DNS protocol a bit, and really DNS is technically capable of acting as a query/response mechanism for far more than just domain names and IP addresses.  One possible approach would be to use a DNS resource record that isn't the typical A or AAAA type, such as a TXT record (which is technically just text, and could be used for anything) or perhaps an SRV record, or any other newer resource record type you choose.
If you're making up your own software (both client and server), there may be no technical reason to not do such a thing, except do know that some people use DNS hosting companies and limit them to using only certain record types.  That's unfortunate, as people who run their own DNS servers certainly have enough flexibility for such things.
However, if you aren't making up your own networking protocol (for example, if you want to use HTTP), you are likely to encounter a major problem, which is that existing software won't use your custom solution, unless you use solutions that are already established.  That's going to be the barrier.  Not a technical impossibility.  A social barrier: Can you convince everybody to do things your way?
Now that I've explained why you can't do that, though, I may have a solution for what you're after.  First, let's take a look at why we even have IP addresses and ports.
IP addresses and ports do different things.  The purpose of the IP address is to fulfill the goals of Layers 2 and 3 of the OSI Model of network communications.  The purpose of the IP address is to identify which computer the traffic is supposed to go to.  The fact that we might use a port number for that purpose, by having firewalls/routers investigate port numbers in order to perform NAPT (Network Address Port-based Translation, also sometimes called PNAT or just NAT), is a newer technique which utilizes a resource (information), but was not part of the original design.  If we step away from this "abuse" of the port numbers for a minute, and consider the original design, we may be able to find an easier solution.  By the design of the Internet, machines were meant to be found using IP addresses.
The point of a "port number", used by TCP and UDP and some alternatives, is to be able to keep track of individual conversations.  This helps to line up communication with running programs.  So, if a machine receives traffic on TCP port 80, the machine will know that network traffic is meant to be used by the program that is the web server.  If a web browser downloads multiple graphics simultaneously, combinations of "source port" numbers and "destination port" numbers can keep track of which data is meant for which graphic, so those simultaneous conversations can occur without mixing up the data.
Now, my guess is that you have access to a DNS server, and it seems to you like you think that DNS administration would be convenient to be able to handle some of the traffic routing a bit more.  But DNS doesn't seem to be able to help you get a port number.  What can you do?
Consider IPv6.  IPv6 enables you to have way more IP addresses.  Furthermore, unlike some implementations of IPv4, devices that use IPv6 can typically easily support multiple active IPv6 addresses at the same time.  So, if you want to have three different network protocols on one computer, you could assign at least three different IPv6 addresses to the same computer.  And then you can do whatever routing shenanigans you like with those IPv6 addresses.
Then, you can use the AAAA resource record type to assign a name to that IPv6 address, which your network design can treat as being effectively dedicated to the specific service on the specific computer you want.
Wallah, you now have DNS effectively pointing to the piece of software, and accomplished that goal without needing to try to rely on making DNS point to a port number, which doesn't work well simply because that functionality just so happens to not be commonly supported.
Possible objection:
And if you feel stuck with IPv4 and think that IPv6 is somehow not supported, I would encourage you to try to tackle that problem.  That problem will probably be easier to fix (perhaps using some sort of tunneling), and will probably end up being a more rewarding fix once you have it implemented.
Comment: IPv6 is always good to support, but won't help if for some reason you are now allowed to use port 80 (or 443).
Comment: This is true, but if DNS managed to convey a port number, that also wouldn't work around a firewall that blocks traffic on a specific port number.  Besides that, my explanation of how to use IPv6 was really only a part of the answer, and I do believe the earlier parts of my answer address the question.
Answer: This should be possible with srv records.
https://en.wikipedia.org/wiki/SRV_record
Comment: Browsers don't use the SRV record. And this is already mentioned indirectly in the accepted answer.
Comment: This answer should be deleted.
Comment: Except there is upcoming SVCB/HTTPS records which *is* the kind of SRV for HTTP


What is a method with a star icon in eclipse?

Question: I often see a yellow start near the methods, and some percentage in Eclipse Luna's intelligent code completion:

What does this star and the percentage mean?
Answer: Both the star and the percentage are added by the Intelligent Code Completion.
These suggestions are based on context and code analysis (data mined) of similar situations. The percentage is presumably an indication for the confidence of that suggestion.

Protected methods (which was the explanation suggested by Ted Hopp) are in fact indicated by a yellow diamond with rounded corners, similar to the icon in the outline view.
Answer: From the Eclipse Luna documentation, it appears to mean that it is a protected method.
Comment: @Victor2748 The percentage is answered in this SO [Answer](http://stackoverflow.com/a/11438594/3857942)
Comment: Ok, thank you anyways (even though you are wrong with a 'protected method')
Comment: What is the percentage then?
Answer: A number of code completion engines come equipped with Eclipse Mars edition onwards.  They are provided by by eclipse.org Code Recommenders.
Normally eclipse orders members alphabetically.  However, Code recommender engines will override the alphabetical listing and place commonly used icons near the top.  For example println() would be presented near the top with a yellow star after you type  System.out. and toString() would appear near the top with a yellow star after typing String obj.
The starred items will be followed by an alphabetical list of members which either could not be identified by the engines or identified as being unlikely to be applicable.
Percentages indicate the likelihood of the suggestion being applicable based upon code from other users who have used your components in their code.
The yellow star indicates that the suggestion has been provided from code recommenders based upon mined data.


What would be the boosters on SLS Block 2?

Question: The SLS block 2 is planned to have advanced boosters. What type of boosters are these and how much thrust will those produce?
Comment: I'm voting to reopen--though the OP could've done a better job, [the planned SRBs for SLS Block 2 are the BOLE upgrade, as seen in this Space SE answer](https://space.stackexchange.com/a/60391/11262). You have to drill a little to realize it, but I think the question's actually 100% unambiguous, and the details requested aren't actually present in the answer I linked to.
Comment: Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer.
Answer: The SLS Block 2 booster upgrade is the Booster Obsolescence and Life Extension (BOLE) for Space Launch System (SLS) (Tobias, Griffin, McMillin, Haws, Fuller, 2019), which

introduces new composite casings
upgrades the propellant to HTPB from PBAN
changes the nozzle and insulation for these upgrades
electric thrust vector control
a simplified systems tunnel, among other structural simplifications like combining the nosecone and frustum

Per section 6 of the linked document, the BOLE upgrade is predicted to add three metric tons of additional TLI performance. Unfortunately, the thrust profile in that document is limited to a badly-compressed graph with poorly-labeled axes they use as their Figure 4.

This since-404'd SLS Overview from NASA indicates a vehicle takeoff thrust of 9.5 million lbf; it's a little unclear to me how much of that is provided by the RS-25s in the core stage, but it seems likely to be either the 109% or 113% power levels as summarized by Wikipedia.  For the sake of approximation we'll use the 109% power level (420,000 lbf) times four engines:
$$
(9.5*10^6 \text{lbf}- 4*4.2*10^5 \text{lbf}) / 2 \approx 3.9*10^6 \text{lbf per booster}
$$
That result compares favorably to the 3.28 million lbf sea-level thrust per current SLS booster quoted by Wikipedia, though I don't see that figure in any of the nearby sources.
Being SRBs, there's significant variation in thrust through the burn profile (see the figure reproduced from the first link) so it's not clear to me what the maximum thrust from the BOLE SRBs will be, or if that's actually intended to occur post-liftoff (I can't imagine why that would be! the stack is heaviest at liftoff!), but that's at least a preliminary number to work from.


What would be a good lens for indoor team photography and individual

Question: I have a Canon T3i and am just venturing in to new lenses..I have been asked to do indoor team and individual soccer pictures..they will be taken on a gray backdrop with white umbrella studio lights..what would be a good lens to purchase or rent?
Comment: What lens or lenses do you already have? Why do you think the lenses you already have are not sufficient?
Comment: Can you provide details of how you plan to be shooting? Is the team 15players or 300players? Are you going to be able to get back 3m or 300m?
Comment: Since OP mentions soccer I would assume 11 players + a coach, perhaps an assistant. 15 people max.
Comment: Can you tell us more about the lighting setup?
Comment: One player per photo or photos of the whole team?
Answer: Your camera probably came with an 18 to something lens, possibly the EF-S 18-55mm f/3.5-5.6 IS II. That lens should certainly serve you well for what you want to do; use it at 55 mm for the individual portraits. It's slow at the long end, but that's okay when using flash, and an ultra-narrow depth of field is arguably not really appropriate for football player portraits anyway.
That said, if you plan to take more portraits in the future, you may want to buy a dedicated fast prime lens. Both 50 and 85 mm are good focal lengths for portraits on APS-C. Which one is better depends on the type of portrait you want to take (head only, head and shoulders, full body), how far away from the person you can stand, and your personal taste. You can perhaps use your zoom lens to find out what focal length you prefer. The EF 85mm f/1.8 USM is an excellent lens, and so are the 50 mm f/1.8 lenses Canon has made over the years. These are all popular lenses that have been around for years, so you will be able to buy them used for reasonable prices.
For the group shots, try not to go too wide, certainly not wider than 18 mm. It would distort the players at the edges of the image. Rather, position yourself as far away from the team as possible and use a relatively long focal length. Again, an 18 to something kit lens should serve you well.
Answer: I am using a Canon 28-300 and a 7D Mark 2.  The 70-300 has good detail throughout the lens.  Personally, I wouldn't use a backdrop.  I would use the environment, the green of the turf with the lines in the background.  Foot on a ball kind of pose.  And then while you are that get some action shots too.  Get all the standard shots like a coach coaching, kids kicking, goalie defending a shot.  Above all else try to define your style.  The last thing I want to hear about is how someone else used to do it.
Get a test subject and get your settings dialed in and then tell them when you are ready to start taking the money shots.


The reward for the creation of spiritual benefits (Pirkei Avot)

Question: I am reading the wonderful collection of sichos of the Rebbe זי"ע called Torah Studies edited by Rav Jonathan Sacks ז״ל. In the lecture on the parashah of Chayei Sara, the Rebbe says "the reward for the creation of spiritual benefits is ascribed to the deceased", and the note refers us to Pirkei Avot, 5:8. But unfortunately, there is no mention of this issue in the quoted passage of the Pirkei Avot. Does someone know where to locate the place in the Pirkei Avot where this issue is discussed?
Thank you very much for your help in advance.
Comment: Can you show us a sicha that mentions this concept, ideally the one that refers this mishna? thank you
Comment: Did you look in the sichah of  לקוטי שיחות - ה ? - https://hebrewbooks.org/pdfpager.aspx?sits=1&req=14928&st=%d7%90%d7%91%d7%95%d7%aa&_rnd=0.11456688818725103
Comment: The sicha I am referring to is [Chayei Sara](https://www.chabad.org/therebbe/article_cdo/aid/110321/jewish/Torah-Studies-Chayei-Sarah.htm). The passage I quoted is towards the end of paragrpah 7.
Comment: @Shmuel Dear Shmuel, unfortunately my knowledge of Hebrew is still quite elementary, and I cannot read the original text of the לקוטי שיחות.
Answer: It's a misprint in the original sicha (footnote 40). It should be Avot 5:18:

Moses was righteous and caused the multitudes to be righteous, [therefore] the righteousness of the multitudes is hung on him
Comment: Thank you very very ... much @shmosel for having kindly answered my question!


Asp.net GridView - how to access datasource before data is bound?

Question: I'm trying to access datasource before I bind it to grid. How do I do that? My guess I should look in one of the events like Grid.DataBinding
Answer: Yes, the GridView.DataBinding event will be raised prior to the control being bound. You can access the DataSource control in that event and make modifications if you so desire (for example, modifying parameters).
<code>protected void Grid_DataBinding(object sender, EventArgs e)
{
  mySqlDataSource.SelectCommand = "Select * from Stars";
}
</code>
Answer: One way would be to not define the datasource on the grid itself. In the page_load, create and populate your datasource and then dynamically bind it to your datagrid. That way you would be able to access it.
Hope it helps!


Ground state electron configuration of chromium

Question: What is the ground state electron configuration of chromium?
Is it $\ce{[Ar]}4s^23d^4$ or
Is it $\ce{[Ar]}4s^13d^5$
Comment: @Googleuser Hmm, sorry then. What textbook are you using? Usually it is a rather well known thing that chromium has $\ce{[Ar] 4s^1 3d^5}$. Maybe you should consider using a different textbook.
Comment: At worst, your chances are 50:50. If you remember the rules concerning half-filled and filled _d_ orbitals, they are much better ;)
Comment: @Philipp my textbook says the answer is
[Ar]4s2 3d4

But when i googled it, the answer was opposite.
So i am confused..
Comment: See http://chemistry.stackexchange.com/questions/151/why-do-elements-in-columns-6-and-11-assume-abnormal-electron-configurations
Answer: WebElements page about chromium (and a number of resources) agree with the comment by @Philipp:

The ground state electron configuration of ground state gaseous neutral chromium is  $\ce{[Ar]}3d^54s^1$

Which in some resources is written as $\ce{[Ar]}4s^13d^5$

Based on the Royal Society of Chemistry article The trouble with the aufbau principle:

it appears that the most stable configuration for atoms of chromium, copper, niobium, molybdenum, ruthenium, rhodium, silver, platinum and gold involves only moving one electron into an $s$ orbital.

Chromium is one of a handful of Transition elements that share this electron configuration.
Answer: Chromium and copper are examples of elements with "anomalous" electron configurations, meaning that they don't follow the normal rules we use for populating the configurations of other elements.
The commonly given reason for this is that the energy of a shell is minimized when the number of electrons with the same spin is maximized (Hund's rule). As a result, when the energy levels of two successively filled sub-shells are already close together (as they are with 4s and 3d sub-shells), the slightly favored half-filled configuration can "win" over the energy increase needed to move an electron to an even-more-slightly higher energy level. In the case of chromium, this means that one of the 4s electrons will go to the 3d orbital, resulting in two half-filled sub-shells where all electrons within each sub-shell have the same spin.
In the case of copper, a similar thing happens. The difference is that the 4s electron moves into an almost-filled 3d shell in order to completely fill it. You get a slight energy decrease when all electrons are paired within a sub-shell. This, in combination with the decrease obtained from achieving a half-filled s orbital, ends up being enough to overcome the increase in energy required to move that electron to the 3d orbital in the first place.
It would be nice if these empirical rules were consistent across the entire table, but unfortunately they are not. If you look up the actual electron configuration for other d- and f-block elements, you will see there are some patterns, and similar things happen for other elements, but because they are so dependent on the delicate balance between energy levels, it is not possible to reliably predict them with simple rules for all elements. In "real life" we use spectroscopy and quantum mechanical calculations to find the actual electron configurations.
However, since chromium and copper are common enough and reliably predictable with simple rules, we tend to use those as classroom examples to demonstrate that the reality of electron configurations is more complex than the simple rules we give you in school.