What is the probability of QED interactions?

Question: In Feynman diagrams of QED vertices of interaction are often labelled by the amplitude sqrt(alpha) where alpha is the e.m. fine structure constant. When higher order diagrams are constructed, each time when a virtual photon is created and absorbed the probability of the interaction process gets 1/137 time lower. Is this rule also applicable to real photons, eg in the Compton scattering diagram which has two vertices, is the interaction probability then equal to alpha? And, if an electron and a positron collide emitting two photons, what is the probability of this process?
Answer: Since there are two vertices in the lowest-order diagrams for these processes, the amplitude is proportional to $\alpha$ and the probability (such as the differential cross section) is proportional to $\alpha^2$.
Answer: We use Fermi's golden rule to calculate the probability of a given interaction per unit time:
$$\Gamma_{i\to f}=\frac{2\pi}{\hbar}|\mathcal{M}_{i\to f}|^2\rho$$
In this formula, $\rho$ is a Lorentz-invariant phase space factor; the nature of this factor depends on the particular interaction configuration (i.e. is it a $1\to 2$ reaction, a $2\to 2$ reaction, a $2\to 3$ reaction, etc.). Meanwhile, all of the "real" physics happens in the matrix element $\mathcal{M}_{i\to f}$, also known as the amplitude. In QED, this is the part where you have terms that are proportional to (not in general equal to) powers of $\alpha$.
Once you have your matrix element for a particular process, to get the total probability of the interaction happening, you must sum (or integrate) over all relevant initial and final states. This is fairly involved, but most QFT textbooks include several examples of this.
For Compton scattering, your matrix element is ultimately proportional to $\alpha$, which means your actual transition probability will be proportional to $\alpha^2$.


SharePoint Online site restore after 15 days of deletion

Question: We have a scenario that we lost some data and now we want to restore the SP online site collection. I.e., we lost data on 15 days back. Due to some reason, now we want to bring back the site using Point In Time Restore. Is it possible to restore the site collection, after 15 days of deletion. MS says they will retain 14 days of daily backup. In my scenario, as per MS, 15 days crossed. So it is possible to restore?
Answer: Deleted SharePoint sites are retained for 93 days, not 15 days. After 93 days, sites and all their content and settings are permanently deleted, including lists, libraries, pages, and any subsites. About how to restore a deleted site in the new SharePoint admin center, please refer to the following URL: https://docs.microsoft.com/en-us/sharepoint/restore-deleted-site-collection
Comment: Thanks Allen. We have NOT deleted site. Only SP security groups and its assigned permission to documents are deleted. So we want to restore the site completely.
Answer: Restoring a site that belongs to a Microsoft 365 group restores the Microsoft 365 group and all its resources.

Note that the other group resources are retained for only 30 days, whereas the site is retained for 93 days.
Comment: This is not office 365 group. Its SP security groups. We have NOT deleted site. Only SP security groups and its assigned permission to documents are gone. So we want to restore the site completely. Groups deleted 15 days back.
Answer: In this case it isn't possible to restore as security groups are not retained in the site recycle bin. You would have needed to contact Microsoft prior to the 14 day time frame.
Comment: Since you don't personally have a backup, no there is no way to restore that data.
Comment: Yes, we contacted Microsft but due to some reason, it crossed 14 days. Now is there way ?


What is this white spots inside my Bialetti Moka?

Question: What is this white spots inside my Bialetti Moka, and they appear even after clean it.
Answer: I believe that is corrosion of the metal depending on what is put in that container and the chemical properties of that substance can lead to wear and tear on the metal. Test this out to see if this works mix a baking soda solution and let it soak in the pot for 30 min to an hour. Then wash the pot that should remove it.


When is the first mention of the Horn of Eld?

Question: In the Dark Tower series, when is the Horn of Eld first mentioned? I'm trying to understand how far into writing the series Stephen King planned things.
Answer: Pretty early

The gunslinger waited for the time of the drawing and dreamed his long
dreams of the Dark Tower, to which he would some day come at dusk and
approach, winding his horn, to do some unimaginable final battle.
—The Gunslinger

There is another probable reference to the Horn of Eld in the third book:

He cried out but his cry was lost in the golden blast of some
tremendous horn. It came from the top of the Tower, and seemed to fill
the world. As that note of warning held and drew out over the field
where he stood, blackness welled from the windows which girdled the
Tower.
—The Waste Lands

The first reference to the Horn as belonging to Eld is, I think, in Wolves of the Calla:

His shirt is soaked crimson to his skin. One side of his face has been
drowned in blood; the eye on that side bulges sightlessly on his
cheek. Yet he still has Roland's horn, the one which was blown by
Arthur Eld, or so the stories did say.
—Wolves of the Calla

So it would seem that King had some idea of the Horn of Eld as early as the first book.
This is not so surprising, considering the strong mythological association between Roland and his horn.
Comment: Thanks. I would have liked to have seen the scene with him leaving behind the horn earlier so that it was in the reader's mind throughout the story and then until the end. I think it would have imbued the horn with more meaning as well; I just wasn't sure why the horn was so important by the final book.
Answer: Considering the novel is heavily influenced by Robert Browning's 1885 poem "Childe Roland to the Dark Tower Came", the final couplet of which is

Dauntless the slug-horn to my lips I set,
  And blew "Childe Roland to the Dark Tower came."

I'm fairly sure that King has some notion of the place of the Horn of Eld right from the beginning.
Interestingly, Michael Moorcock, in "Stormbringer", also had his multiversal traveller Elric of Melnibone recover the Horn of Roland from a tower and blow it.


Odometer and radio cut out sometimes when I hit the brakes

Question: Why does my odometer flicker all numbers and get dim when I sometimes hit the brakes. Nothing else in the dash is affected except the radio and it's only sometimes. Is there a short behind the radio
Comment: Welcome to SE Mechanics! This is a good question, but hard to answer without more information. It would help to know how old the car is and if it is the original radio. Also, is this a new problem? If it is can you tell us about when it started and if there is anything that could correlate with it?
Comment: What do you notice in the radio?
Comment: Even if it isn't obviously relevant, it would not hurt to add the model and year of your car.
Comment: How can this be answered without Make Model and Year of Vehicle??
Answer: There are two possibilities that come to mind:

Hitting the brakes turns on the brake lights, so there might be an issue with grounds or a loose wire that could be causing other circuits to appear to loose power.
Hitting the brakes also invokes Newton's 1st law (roughly speaking, when you change the forces on things (apply the brakes), they can move) perhaps the radio (why are you suspicious of it?) or its wiring harness are moving and damage to the wires when the radio was installed are causing the flickering.

Neither are simple problems to track down. But you may be able to at least get pointed in the right direction by noting when it happens:

If the problem is due to the brake lights going on it will happen even if the car is not moving and it won't matter how hard you push on the brake pedal. All that matters is that the brake switch get's activated.
On the other hand if the problem is due to something shifting when the brakes are applied the problem will likely not occur when the brakes are applied while stopped and will be more likely to occur if the brakes are applied hard.

So you might find a safe place to do some experimentation. What you'd like to come up with is a way to reproduce the problem. If you get to the point where you can make it occur pretty reliably and you're still not sure of the cause another thing you could try would be to find and disconnect the brake light switch (it is usually somewhere near the brake pedal). If the problem is related to the brake lights going on disconnecting the switch should make it go away. Be sure to reconnect the switch before driving on the road.
Answer: Check all the fuses; perhaps there is a bit of corrosion, etc.  How old is the Chevy?  On older cars corrosion on fuses with the old tubular style fuses was common. The brake lights draw a fair amount of current, and if the fuses are corroded, it could affect anything else on the circuit.
Image cropped from https://commons.wikimedia.org/wiki/File%3ASelection_of_Fuses.JPG
Comment: That makes more sense. Can you add that to your answer?
Comment: I am curious how this answers an intermittent issue with the odometer and the radio when the brake pedal is pressed. Can you explain your answer a little better?
Comment: The brake lights draw a fair amount of current, and if the fuses are corroded, it could affect anything else on the circuit.


Can I leave the UK and come back just before my work visa expires?

Question: My work permit expires in 2 months' time, and I am planning to go abroad for 10 days.  I will return to the UK one month before my visa expiration date. Is it possible that the border agency officer won't allow me into the UK upon my arrival?
Answer: They will look at your wp and ask how long you were out of the UK, and if you are still working for the same employer, and then advise you that your wp will expire soon.
So the answer to your question is you should not expect problems re-entering if your leave is still valid.


WOT convergence implies norm-boundedness

Question: I'm trying to prove that, on a Hilbert space $H$, convergence of a sequence of bounded operators $a_n$ to $a$ w.r.t. the weak operator topology (i.e. $\langle a_n x ,y \rangle \to \langle ax,y \rangle$ for all $x,y \in H$) implies that $a_n$ is norm-bounded. I have managed to prove the analogous statement for the strong operator topology using the Uniform Boundedness Principle, but I can't quite get it to work in the weak case. Could someone provide a hint?
Answer: Fix $x$. Consider the linear functionals $f_x:y\longmapsto \overline{\langle a_nx,y\rangle}$. Because the sequence of numbers $\{\langle a_nx,y\rangle\}$ is convergent, it is bounded. That is,
$$\tag1
\sup_n|f_x(y)|=\sup_n|\langle a_nx,y\rangle|<\infty.
$$
By the Uniform Boundedness Principle, we get that
$$\tag2
\sup_n\|a_nx\|=\sup_n\sup_{\|y\|=1}|\langle a_nx,y\rangle|<\infty.
$$
As $(2)$ holds for all $x$, applying the UBP again we get
$$
\sup_n\|a_n\|<\infty
$$
Comment: Thanks for the detailed answer. Though I guess you need to put a conjugate in the first line, to make the functional really linear, instead of conjugate-linear.
Comment: Indeed. Or I could say they are conjugate-linear ;)


nofollow option for rich texts

Question: Is there a way to add an nofollow option to the rich text editor? Just like new window option.
The only thing I found is a Redactor config to make all links nofollow. But I need it optional per link.
Answer: There's nothing native in Craft that would allow you do to that.
Should be possible via a Craft and Redactor custom plugin, though, I'd guess.
Comment: OK, thank you Brad

nofollow option for rich texts


Battery life decreased drastically after upgrading to Ubuntu 18.04

Question: I had been using only Ubuntu in my laptop for nearly two years, and the battery life with Ubuntu 16.04 was pretty long. It would last for nearly 10-12 hours. But after upgrading to Ubuntu 18.04, it only lasts for about 3-4 hours (normal light use) and the percentage of the battery decreases with every passing minute. Is there any fix for it?
Comment: Do you have two graphics cards? I had the same problem, in 16.04 working good with Nvidia Optimus but it seems to have stopped working. I just disabled it in the BIOS and my battery and heat problems were resolved.
Comment: I have also witnessed a drastic drop after upgrading from 16.04 to 20.04 (I never switched to 18.04 though). I think 16.04 really was quite awesome in power management.
Answer: First read this Ubuntu Help article about Power & battery
If not enought you may want to install TLP
TLP brings you the benefits of advanced power management for Linux
without the need to understand every technical detail. TLP comes with
a default configuration already optimized for battery life, so you may
just install and forget it. Nevertheless TLP is highly customizable to
fulfil your specific requirements.
Install TLP :
<code>sudo apt install tlp tlp-rdw
sudo tlp start
</code>
Then customize suspend setting : System Settings -> Power -> Suspend & Power Button.
Comment: why was this downvoted?
Answer: I had same problem, and I finally found a solution, (but it may not be your case).
When you log in there is an option button, where you can choose from Gnome classics, Ubuntu and Ubuntu on wayland. I have been using Ubuntu on Wayland (because of some functions), and with this option the battery lasted max. 3 hours. So I changed it to Ubuntu, and now it works perfectly. I also updated the Kernel.
Hope it will work for you.


Can I freeze fresh hyssop?

Question: Is it possible to freeze fresh hyssop? Can I expect it to be as aromatic and flavorful after defrosting?
Answer: In my experience, the answer for most leafy herbs is yes, fragance and flavor is preserved. Never tryed hyssop, however Gardening Know How site says it freezes fine:

it can be dried or frozen and stored for later use. When harvesting a hyssop plant, cut it in the morning hours once any dew has dried. Hang the plants upside down in small bunches to dry in a dark, well-ventilated area. Alternatively, you can place the leaves in a plastic bag after removing them from the stems and place in the freezer until ready to use.
Answer: The aromatics diminish. I've tried this, with hyssop - because I have a bunch of bulk spices.  I've found that an airtight jar in a dark/cool cabinet is best, even for an extended period (my jar on the shelf is over a year now).
The hyssop I get is from Jordan. I also receive sumac and the blend zaatar.

Can I freeze fresh hyssop?


What essentials are needed to have a small bedroom studio to make music?

Question: What is some of the best affordable hardware and software for producing music? I just want a basic starter kit that will help me get to know the basics. I only want the absolute essentials for now.
Comment: Can you elaborate on what skills you have already, and what kinds of music you want to make? That would help for a recommendation. For example, if you play guitar, I wouldn't tell you to go out and buy a MIDI keyboard, or if you want to make techno music I might not tell you to get an MPC.
Comment: Look into a guy who runs the recording revolution channel on youtube (he also has a website with the same name). He has tons of great articles on this topic, as well as training on how to use it!
Answer: For software, check out DAWs like Tracktion and Reaper.
For hardware, take a look at the AudioBox USB audio interface.
If you're wanting to record MIDI and have a synthesiser that supports the interface, Yamaha UX16.
Comment: They fit OP's criteria of affordable and basic, and cover all bases; audio and MIDI recording, editing and mixing.
Comment: Hi Joel, welcome to sound.stackexchange. can you please elaborate on why Zack should use these specfic products?
Comment: I still use Reaper and an Akai mpk mini using mainly virtual synthesizers. You can go a long way with Reaper.


Angular frequency ($\omega$) vs regular frequency($f$)?

Question: What is difference between angular frequency ($\omega$) and regular frequency($f$)?
As far as i am able to understand is that electric power signal has $f=60Hz$ and many other cases where i see "$f$" when discussion is about frequency but where is application of $\omega$?
Answer: @Man. Hi. Measuring frequency in terms of $\omega$ (radians/second) or in terms of $f$ (cycles/second, Hz) is the same as measuring speed in miles/hour or kilometers/hour. People measure frequency in terms that are convenient for them. In algebra equations it's convenient to represent frequency in terms of $\omega$ because it's easier to write the single $\omega$ character than to write the three $2{\pi}f$ characters. People also sometimes prefer using $\omega$ because the trigonometric functions in algebra, and in most signal processing software, expect angles to be measured in radians.
In the laboratory, working engineers (I mean the guys who know which end of the soldering iron is hot) usually prefer to measure frequency in terms of Hz because their oscilloscopes, frequency counters, spectrum analyzers, and network analyzers measure frequency in Hz.
Answer: Many signals we observe are functions of time, i.e., their value changes with an independent time variable, which can be measured in seconds. Frequency is a measure of how fast a signal changes and thus measured in "per second" which is the same as Hertz: 1 Hz = 1/s.
An oscillation is an excellent example: a harmonic wave can be described as $e^{\jmath 2\pi f t}$. Here $f$ is the frequency, which tells us how many cycles the complex phasor carries out in one second. That's the frequency in Hertz, think of it as cycles per second.
Another way of thinking about the complex phasor is as $e^{\jmath \varphi(t)}$, where $\varphi(t)$ is the angle the phasor has with the positive real axis. For a harmonic wave, from above we have $\varphi(t) = 2\pi f t$, i.e., the angle increases linearly in time. Now one may wonder at what speed it is increasing. The answer is obviously its first derivative, i.e., $\frac{{\rm d}\varphi(t)}{{\rm d}t} = 2\pi f$. This is the angular frequency, often described as $\omega$. It tells us how fast the angle grows and is thus measured in radian per second [rad/s] (though of course if you prefer your angle in degrees, you could convert it to [deg/s], just as you like). This is particularly important if we care about the phase a lot. One example would be digital communications, where the phase often contains the actual information and rates of change (due to things like clock drift or Doppler) can be limiting factors.
That's one reason for using them at least. Another one could be that people are just too lazy to always write the $2\pi$ and prefer $e^{\jmath \omega t}$ over $e^{\jmath 2\pi f t}$. This will vary across disciplines a bit.
Answer: It's a matter of the units used to measure frequency as events which happen per unit of time.
For the regular frequency f, we ask: How any wavelengths pass a specific point per second?\
For the angular frequency $\omega$, we ask: How many radians are traversed per second?
The easiest way to visualise the angular frequency is by understanding the relationship between the unit circle and sine waves. This is a good video to gain that understanding. What you'll notice from the video is that a full wavelength of a sine wave traverses an angle of $2\pi$ radians, so when we say that $\omega = 2\pi f$, we are effectively saying "$f$ is the number of wavelengths that pass a point every second, and since each wavelength traverses an angle of $2\pi$, the angular frequency, the angle traversed per second, is equal to the wavelengths multiplied by $2\pi$.
I hope this helps a little!
Answer: In simple terms your regular frequency is how many times in a second, the signal goes through the same cycle. This is not restricted to a sinusoid alone (because any real world signal can be represented by sum of sinusoids). When you say regular frequency is 60Hz, the signal cycles itself 60 times in a second. Each period is 1/60s. A sinewave is a fundamental periodic signal (sinusoid) having a single frequency.
$x = sin(2\pi f*t)$
$f$ is your frequency, and $t$ is the time. As time increases you can see the value of $x$ repeat itself every $1/f$ seconds.
Now, see the term $2\pi f t$. As $t$ increases from $n/f$ to $(n+1)/f$, the term $2\pi f t$ increases from $2\pi n$ till $2\pi n+2\pi$. Corresponding value of $x$ varies from 1 and comes back towards 1 (it passes through 1 cycle). So basically what varied here is the angle of $sin()$ function. It increased by $2\pi$ in an interval of $1/f$ seconds. So what is the angular frequency? It is $2\pi /(1/f) = 2\pi f$.


Can I forward my text messages from my Android phone to a Chromebook?

Question: I am coming from an iPhone and a mac book, and I am used to the idea of being able to send and receive all my texts, calls, and face times from my laptop. After making this huge switch, I am confused how anyone can consider this better. Can someone tell me if this is possible? I am not against any sort of under the table methods of making this happen. I have a Galaxy S3 and a Samsung Chromebook 2, so if Google can't do it, I'm thinking Samsung should be able to.
Answer: MightyText: http://www.mightytext.net
and PushBullet: https://www.pushbullet.com/
are third-party apps that provide this functionality.


Use a different protocol than http or https for a submit button url redirection in Cognito Forms

Question: I am using a mobile app framework that has its own protocol for deep linking. I tried to use this protocol in the url redirection and the system denies it - it requires http or https only protocols. Can this be over-ridden?
Answer: I work for support for Cognito Forms.  We only support http or https.
Answer: Unfortunately this can not be overridden unless you take root ownership and modify the system files.


After breaking an oath in Allah's name, I mistakenly fasted for two (instead of three) days; do I need to redo these?

Question: I had an oath in Allah's name and I broke it last year. Later, I fasted for two days; since I thought that the ruling is that I must fast for two days when an oath is broken; however, I recently discovered that I should fast for three days instead. Do I have to fast one more day now in order to make up for it?
Answer: Just a reminder, a Muslim who broke an oath must either feed or clothe 10 poor people [or free a slave, but nowadays this isn't really an option]. Only when one cannot possibly do those things is when the other option of fasting acceptable. Allah (ﷻ) said:

لا يؤاخذكم الله باللغو في أيمانكم ولكن يؤاخذكم بما عقدتم الأيمان فكفارته إطعام عشرة مساكين من أوسط ما تطعمون أهليكم أو كسوتهم أو تحرير رقبة فمن لم يجد فصيام ثلاثة أيام ذلك كفارة أيمانكم إذا حلفتم واحفظوا أيمانكم كذلك يبين الله لكم آياته لعلكم تشكرون (Allah will not punish you for what is uninentional in your oaths, but He will punish you for your deliberate oaths; for its expiation (a deliberate oath) feed ten Masakin (poor persons), on a scale of the average of that with which you feed your own families; or clothe them; or manumit a slave. But whosoever cannot afford (that), then he should fast for three days.. [Qur'an (5:89)].

As for your question.. "Do i have to fast one more day now in order to make up for it" - Yes, obviously you did not fulfill the obligation and it still sits upon you. And since the scholars say that the 3 fasts must be consecutive (ie, day after day with no breaks in between), then you ought to redo them all. (The first two you already did a while back will just get counted as Nawafil fasts).
Note: Some scholars have a different opinion that the fasts don't have to be consecutive. In their view, you can just offer the 1 day left to fast and that would be sufficient. However, if I were you then I'd pray them all consecutively.. which would involve greater reward for you anyway and also would be on the safe side of both opinions.
(Scholarly reference)


Hashavas Aveida with changing forfeiture status

Question: In an instance in which an object is found prior to forfeiture by despair ( Ye'ush) the finder is obligated to return the item. However, in an instance in which despair is presumed either implicitly or explicitly, the finder can keep the item. What is the Halacha in a case where an item is found with no presumption of forfeiture thereby obligating its return, yet forfeiture from the original owner comes in between the finding of the object and its successful return. Can the finder keep the object? Or since it came to him in a predicament requiring its return, the ultimate forfeiture is irrelevant?
Comment: See Bava Metzia 26B and Shulchan Aruch 259:1 which indicates that he would be required to return it.
Comment: Welcome to MY and thanks for the question. I don't think "forfeiture" is the right translation for "Ye'ush". Cambridge English Dictionary, forfeiture = "the loss of rights, property, or money, especially as a result of breaking a legal agreement".
Comment: @AvrohomYitzchok, right it really means "despair" or something of that nature. I just lifted the term employed by an article I read on JLaw. Not sure what the etiquette is  here re using Hebrew words, etc
Comment: @user28684 https://judaism.meta.stackexchange.com/q/1606/759
Answer: It is implied in many halachos of Hashavas Aveida in Shulchan Aruch Choshen Mishpat סימן רנ"ט - רע"א, that only if ייאוש already occurred at the time of finding,  is the finder not obligated to return the item. If at the time of finding the item ייאוש didn't yet occur, the finder is obligated to return the item even if ייאוש occurred prior to the return. The only difference would be the amount of transgressions the finder transgressed if he decides not to return the item. For further information to that point see שו"ע חו"מ סימן רנ"ט סעיף א.
An explicit source to the obligation of returning an item that was found prior ייאוש and ייאוש occurred before the return of the item can be found in בבא מציעא כ"א עמוד ב:
"בדבר שיש בו סימן כולי עלמא לא פליגי דלא הוי יאוש ואף על גב דשמעיניה דמיאש לסוף לא הוי יאוש דכי אתא לידיה באיסורא הוא דאתא לידיה דלכי ידע דנפל מיניה לא מיאש מימר אמר סימנא אית לי בגויה יהבנא סימנא ושקילנא ליה
The Gemara limits the scope of the dispute. In the case of an item on which there is a distinguishing mark, everyone agrees that despair that is not conscious is not considered despair. And even though we hear that he ultimately despairs of recovering the item, it is not considered despair, as when the item came into the possession of the finder, it was in a prohibited manner that it came into his possession. It is prohibited because when the owner learns that it fell from his possession, he does not despair of its recovery immediately. Instead, he says: I have a distinguishing mark on the item; I will provide the distinguishing mark to the finder, and I will take it."
We can see from here that if the item came to the the finder in a "prohibited manner", which as Rashi explains means before ייאוש, it doesn't matter if the owner ultimately was מתייאש, the finder is still obligated to return the item.


What are the mechanics in GURPS that allow buffing

Question: I have been looking through GURPS characters and I've been unable to find any abilities that allow one to buff their allies whether it be in a way that increases their stats, gives temporary advantages, or allows them to re-roll sixes.  What I wish to ask is: are there any mechanics for a character to buff friendlies in GURPS?
Comment: What books have you searched?  I recall spells to temporarily increase ability scores in *Magic*.
Answer: You have many options, of varying degrees of realism. Not all of these will be available, as they depend on which campaign switches are turned on by the GM. Here are the more straightforward, general, and common amongst them.
Afflictions
Afflictions (B35) are a broad-umbrella system term an Advantage that allows a character to inflict conditions, Disadvantages and/or Advantages on others. It's a mechanical term, and can represent many different in-setting methods, such as magic, cinematic bardic inspiration, highly exotic technological enhancements etc.
Complimentary Skill Rolls (CSRs)
A CSR is a generalised rule about using one skill to aid in a use of another skill, usually in a mundane way, so long as the interaction makes sense. The helper and the main actor may be different characters, or the same one, depending on circumstances. The rule was written some years after the publication of the Basic Set of 4th Edition, and as a result is now often included in various books like Social Engineering, Action, Dungeon Fantasy, the Ten for Ten article of Pyramid etc. It's a very generic rule, and a rather simple one, but whether it is applicable really depends on the circumstances.
Visualisation with Blessing
An enhancement on Powers page 87. Allows granting a rather generic bonus to rolls just by 'thinking good thoughts' (but of course can also be built as a more specific power). Starts out modest (but by default very versatile), yet becomes a very powerful ability when combined with about 30-50 points worth of the right enhancements. Is something of a controversial build from a balance perspective, in fact.
Affects Others
An enhancement found on Powers page 107. Allows you to share an Advantage you have with others.
Magic Magic [sic] and Other Magical Systems
The 'standard' form of magic holds many spells that grant some sort of bonus, Advantage, or perhaps some other benefit. Even more obscurely, other forms of magic, such as the standalone Ritual Path Magic (not to be confused to the magic of Ritual Paths found in the Basic Set!).
Tactics
Martial Arts page 60 offers an optional rule on Tactics being represented by granting one's side some number of rerolls.
Ultra-Tech Drugs and Fantasy Alchemy
This isn't as direct a method of buffing as the others, but it may still be worth checking. Availability will, of course, vary wildly by setting and GM. Check B425 for the generic rule of custom design (though I haven't seen that one used often), or individual tech and/or setting books for specific samples and their stats.
Answer: The GURPS Basic Set Characters book doesn't have very many if any mechanics of the type you are referring to.
GURPS is mostly a pretty literal representational system. Things tend to happen in ways that make literal sense because of something in the game world situation. There are not many things that are only about game mechanics. And there are not many things what would realistically have the effects you mention - those are gamey conventions of other game designs that are more abstract.
How is someone in the real world going to increase their friend's strength, health, intelligence, or dexterity, or general success? They're pretty much not, except by doing specific things that help them do things (such as both shoving on the same door at once, or teaming up in other ways, or both trying something, so if one person fails, the other may succeed), not just directly making them be better.
Or if they are, it's liable to be something like magic or super powers. The GURPS Magic book has quite a few magical spells for increasing attributes and abilities of other people. There are a few such spells in the Basic Set Characters book - see Shield, Armor, Haste, Breathe Water, and No-Smell. Also see GURPS Powers for all sorts of unrealistic arbitrary super powers you could add to a character.
Other things that might have the effects you describe include drugs and potions that can alter attributes or perhaps give some advantages (often also with disadvantages - e.g. alcohol might increase your strength but decrease your dexterity and intelligence, and give you a hangover and might lead to alcoholism), or supernatural blessing effects (in the Basic Set, the GM might allow a special Enhancement to Blessed: Heroic Feats to affect others, for example, or maybe see GURPS Religion, a 3e book, for more ideas.) Another thing some other GMs and I have done is have some religious/spiritual/supernatural blessing effects where appropriate people can gain some limited "Luck" (q.v. the advantage) through blessings which can be given by holy people).
Comment: Isn't GURPS religions third edition?
Comment: It is. I added a mention of it being a 3e book, and also another idea limited to the 4e Basic Set, and a different idea I and others have used in play.


What is the difference between "in" and "within"?

Question: It seems they can be used interchangeably but I am not sure. Can somebody explain the difference of use between these two key words? Where do they become different?
Comment: Many of my high school students (I am a History teacher) like to use "within" in places where "in" would do, because they think "within" sounds more scholarly. So I get essays with titles like "Authoritarianism Within Putin's Russia" or "Communist Economic Policies Within Cuba." The use of "within" in these titles makes it sound as if authoritarianism and communist policies are physical things that somehow float around inside the borders of those respective countries. So I encourage students to use "in" whenever it makes sense. (But it's difficult to convince a young, ambitious student to use
Comment: You certainly can't use them interchangeably in all contexts - **in** can be used in many places where **within** is totally wrong. If OP is unsure, I suggest sticking to **in**, which would rarely if ever be unacceptable.
Comment: ...a small word in place of a longer word!) @Alex
Answer: Within is closer to inside - it mainly refers to something like a building where you are physically in (or inside).
In can also mean a state or an organisation, so you can be "in trouble", or "in school" but not "within trouble".
Comment: The other answer makes a good point too: You can't always substitute _in_ for _within_ (or _inside_).
Comment: @mgb What about the example sentence "the algorithm is able to detect people in/within google-earth images"? Is *within* acceptable/preferable in this case?
Comment: @halirutan, no 'within an image' wouldn't be normal, Generally always use 'in' unless you know different.
Comment: @mgb, For  vs ?
Answer: In- A limit of some sort.

i.e. "In 6 days,..."

You limit the time in the sentence exactly.

Within- Inside the said limit.

i.e. "Within 6 days,..."

You limit the time in the sentence, but inside the said time.
Answer: where ever there is a certainty we use in and in uncertainty we use within.

I will come in next week. - Use IN-
           I will come within this week - Use within

Also, if some timeframe is allocated ie : do the work in ten minutes
Then if the work is completed in 10 min then use in and if completed before 10 min then within.
Comment: *I will come in next week* does not mean (what I surmise you are trying for) "I will come in the next week".  "I will come within the week" means the latter, but the way to express your last point is "I will come in a week's time".


Why OLS perform better than LASSO?

Question: I am comparing OLS and LASSO regression for survey data. I have n>p, but I think my data is high-dimensional data as the p is 3000 and n is 48000. I am using k cross-validation. The results are quite surprising as from R-squared and MSE, the OLS performs much better than LASSO. I have read several discussions and papers previously, but still, I can't figure out why...
Comment: are you looking at in-sample or out-of-sample performance?
Comment: both. results for both samples are showing that OLS perform better
Comment: Why is it surprising? Have you considered how your OLS is estimated in the n<p. But I think I still can categorize it as high-dimensional data, correct me if I'm wrong. One that I'm aware is LASSO will perform better than linear regression in high-dimensional data through regularization/shrinkage. But I don't find it in my case.
Answer: This is one example of a "curse of dimensionality" described for LASSO in An Introduction to Statistical Learning, second edition, at the end of Chapter 6.
With a large number of potential predictors and LASSO forced to choose a comparatively small number among them, there's an increasing risk as p increases that some truly insignificant predictors might by chance have an association with outcome in a particular data sample and be included erroneously. That might also lead to omission of truly significant predictors and poor generalizability.
With OLS in this scenario, all of your potentially important predictors are available to the final model. With a 16:1 n:p ratio, that probably isn't at much risk of overfitting. For prediction, throwing away predictors (even "insignificant" ones) doesn't typically do much good unless you are overfitting. So OLS wins here.
Comment: Would you expect Ridge regression to perform better since it would not completely remove predictors from the model?
Comment: @Eli better than LASSO but maybe not better than OLS in this particular case, as you might not need any penalization at all with your fairly high `n:p` ratio. Penalization (ridge or LASSO) trades off an increase of bias for a decrease in variance when applied to new cases. If your model isn't overfitting and thus has low variance on new cases, there is no need for that tradeoff. In general, however, ridge can do better than LASSO for predictions if you don't need to cut down on the number of predictors and many are outcome-related, or than OLS when you are close to overfitting. Try it and see.

Why OLS perform better than LASSO?


How to get page view data like stackoverflow?

Question: I want to get and display how many times a page is viewed, just like stackoverflow.
How to do it by php? Thanks!
Answer:
if (file_exists('count_file.txt'))
    {
    $fil = fopen('count_file.txt', r);
    $dat = fread($fil, filesize('count_file.txt'));
    echo $dat+1;
    fclose($fil);
    $fil = fopen('count_file.txt', w);
    fwrite($fil, $dat+1);
    }

    else
    {
    $fil = fopen('count_file.txt', w);
    fwrite($fil, 1);
    echo '1';
fclose($fil);
}
?>

For any "decent" counter I would recommend to use a database (mysql, redis ) and trace IP address to have even deeper analytics (e.g how many unique visits, where they are comming from etc)
Comment: Seriously? This is how StackOverflow does it, `count_file.txt`?
Answer: You will need to store that information somewhere, which isn't really something that you can do with only PHP.
Most commonly, this is stored in a database. The simplest solution is a single database row per page that you wish to track with a column for remembering the view count. You would increment this column each time the page is loaded.
Slightly more complicated, but far more useful, would be to add a database row on each page load, noting the page, time, and any other information that you might find useful.
Another simple way to capture this information would be to install an analytics package on your site. Something like Google Analytics, which is free. But, it isn't particularly tailored to displaying page views, simply capturing them.


Why do eggs lack an endoplasmic reticulum?

Question: Trueman's Elementary Biology book I found says that the endoplasmic reticulum is absent in eggs, but no reason is given. Why is it absent?
Comment: I did not know there was no endoplasmic reticulum in the eggs. Can you please add a reference we could easily check up?
Comment: I just found in my book. It might had initially but i thing it is reduced later .But I will try to add a reference
Comment: I think there is some mistake, check [this] (http://www.sciencedirect.com/science/article/pii/S0012160699994459). It shows eggs (at least mammalian) have ER
Comment: In addition, these Calcium waves produces by ER stores are way to block another sperm entry into egg.
Comment: I THINK THE BOOK SAID ABOUT CHICKEN EGGS ..
Answer: I could find no indication that eggs are lacking an endoplasmic reticulum. On the contrary, I could find papers written on the ER in eggs of several species.
Mouse: The onset of activation responsiveness during maturation coincides with the formation of the cortical endoplasmic reticulum in oocytes of Xenopus laevis
Sea urchin: Structural changes of the endoplasmic reticulum of sea urchin eggs during fertilization
Human: The relationship between pregnancy outcome and smooth endoplasmic reticulum clusters in MII human oocytes
Frogs: The onset of activation responsiveness during maturation coincides with the formation of the cortical endoplasmic reticulum in oocytes of Xenopus laevis
However, as can be read in the sea urchin paper, the ER changes after fertilization:

We interpret these observations to indicate that in the first few minutes after fertilization, the egg's ER is fragmented

For other species, I could only find evidence that the ER reorganizes after fertilization because of changed calcium signaling needs


It is possible to create kaleidoscope images generated by php

Question: Is this possible.
My client requires kaleidoscope images to be generated on the site and used and background for butterflies. Hence making them unique.
I found this thread Kaleidoscope effect using Javascript, CSS or ImageMagick?
But was not much help. The image magic seems to be in Java?? I'm not sure.
It is possible do with PHP?
Answer: You can achieve a similar pattern with a voronoi-diagram. It's a dual from the delaunay triangulation. You can animate and paint the voronoi-diagram. You can download my class voronoi-diagram at phpclasses.org.


What is the required distance of electrical panel from a door?

Question: How close can I place a main electrical panel from an interior or exterior door? Is there a difference in distance if the panel is placed on the hinged or non-hinged side, or if it is inward or outward swinging door?
The panel would be located in an attached garage.
I am only seeing 30" x 36" and clear above working space rule for an electrical panel.
Comment: That space needs to be kept clear *at all times* not just when the inspector comes... so it is best positioned in a pathway where you need it clear to get through.
Answer: The door's swing can't infringe on the clear working space
The situation you need to watch for here is where the door's swing infringes on said 30" wide by 36" deep working space around the panel, as that creates a situation where an unfortunate electrician taking measurements on a live panel can get clobbered into the panel by the door in a most shocking fashion.  You'll also want to make sure that the panel's own door, if present (as some small panels lack one), can open 90° while the door is fully open, as not being able to open that door 90° is also a Code violation (110.26(A)(2)).
Comment: So if the panel is on the none hinged side of the door, then it can butt up against the door frame?
Comment: @WhoShock -- no, not quite -- you don't want the door to clobber an electrician working on it, even if it won't necessarily cause them to faceplant into a live panel
Comment: Makes sense to not clobber the electrician. That said, it's residential so foot traffic will not be high. As long as it is code, it should be ok right?
Comment: @WhoShock -- yeah, as long as the door doesn't infringe on the Code required working clearance (which does *not* need to be centered on the panel, FYI!), you're cool


Modifying a Shtender on Shabbos

Question: I have a Shtender and it has an option to remove the top part of it and use it as a table-top Shtender. Is doing this — removing the top part to use as a table top or putting it back to be used as a regular Shtender — allowed on Shabbos?Another aspect of the question is the height can be adjusted to make it a sitting or standing Shtender  and is adjusted by using a  screw like implement is one allowed to adjust the height (My concern is Boineh or Makeh Bpatish.)
Answer: Shulchan Shlomo 313:7 - Rabbi Shlomo Zalman Aurbach Zatzal - and Shaalos U'Teshuvos Shevet HaLevi 6:32 permit adjusting the height of a Shtender on Shabbos. Minchas Yitzchok 9:38 prohibits adjusting a Shtender on Shabbos. Thanks to RabbiKaganoff.com
Comment: Does anyone address the separating the table top Shtender and reattaching? even thought according to the guy in the Judaica store it is a very recent feature but that just may be a sales Pitch
Comment: here is the one i bought if it helps:                                                     http://www.greenfieldjudaica.com/floor-shtender---fully-adjustable-STA.html
Answer: Rivevos Ephraim 5:264 goes through this sugya,and brings opinions some which Gershon Gold already mentioned which allows adjustment on shabbas.However he brings a shittah which holds that a yeshiva shtender which is constantly adjusted is mutar,but a shtender which is used at a specific height should not be adjusted.see inside.
http://www.hebrewbooks.org/pdfpager.aspx?req=1086&st=&pgnum=220&hilite=
Answer: Rav Nissim Karelitz in Chut Shani (Shabbos 1:36) permits this based on the Chazon Ish (Orach Chaim 50:9) who permits screwing the lid of a baby bottle on, on Shabbos as the bottle is a Keli without a lid and one isn't changing anything by putting on the lid. The same applies, says the Chut Shani by a Shtender as it is usable without the top part.

Modifying a Shtender on Shabbos


The minimum of the reciprocals of some Poisson random variables

Question: Let $X_1,\dots,X_k$ denote a collection of independent samples of a Poisson random variable whose mean also happens to be equal to $k$.  Does the quantity $$k\boldsymbol{E}\min\left\{ \frac{1}{1+X_{1}},\dots,\frac{1}{1+X_{k}}\right\} $$ have a strictly positive limit as $k$ becomes large?
Comment: Yes and using a large deviation principle one can proves that this goes to 1.
Comment: @RaphaelB4 : Can you expand your comment into a formal answer? From my answer, it seems clear that, to get the value of the limit, one needs to have the asymptotics of $P(X_1>x)$ uniformly in the zone $x=O(k)$ (which will be given by a certain analytic function of $\lfloor x\rfloor$, rather than by an analytic function of $x$). On the other hand, a large deviation principle only gives the asymptotics of $\ln P(X_1>x)$ -- which is much, much less informative than the needed asymptotics of $P(X_1>x)$.
Comment: Previous comment continued: Cf. e.g. the asymptotics $\int_0^1(1-ct)^k\,dt\sim1/(ck)$ for $c\in(0,1)$ as $k\to\infty$, which of course depends on $c$, whereas $\ln(ct)\sim\ln t$ as $t\downarrow0$. So, I don't see how a large deviation principle by itself could be enough here.
Answer: Let
\begin{equation}
 Y_i:=\frac1{1+X_i}, \quad Y:=\min(Y_1,\dots,Y_k).
\end{equation}
Then
\begin{equation}
 EY=\int_0^\infty P(Y>y)\,dy=\int_0^\infty P(Y_1>y)^k\,dy.
\end{equation}
Next, for $y\in(0,\frac1{1+2k})$ and $x:=\frac1y-1>2k$, we have
\begin{equation}
 P(Y_1>y)=1-P(X_1>x),\quad P(X_1>x)\le P(X_1>2k)=P(X_1-k>k)\le1/k,
\end{equation}
by Chebyshev's inequality, whence $P(Y_1>y)\ge1-1/k$ and
\begin{equation}
 EY\ge\int_0^{1/(1+2k)} P(Y_1>y)^k\,dy\ge\int_0^{1/(1+2k)} (1-1/k)^k\,dy\sim\frac1{2ek}
\end{equation}
as $k\to\infty$. So, if the limit of $k\,EY$ exists, it must be $\ge\frac1{2e}>0$.
Answer: (To answer Losif Pinelis, this was a bit too long for a comment)
For $X$ a Poisson of mean $k$, $$\mathbb{P}(X\geq (1+\epsilon)k) =\mathbb{P}(e^{X\epsilon/4}\geq e^{(1+\epsilon)k\epsilon/4}) \\ \leq \frac{\mathbb{E}(e^{X\epsilon / 4})}{e^{(1+\epsilon)k\epsilon/4}} =\frac{\exp(k(e^{\epsilon /4}-1))}{e^{(1+\epsilon)k\epsilon/4}} \\ \approx\exp(-k \epsilon^2(\frac{1}{4}-\frac{1}{2*4^2}) $$ for small $\epsilon$. One can then finish the proof of Pinelis and get that the limit is larger than $1/(1+\epsilon)$.


Modeling customer churn - Machine learning versus hazard/survival models

Question: Is their any rational (theoretical, substantial, statistical) to opt for either machine learning or hazard models when modeling customer churn (or more general, event occurences)?
Comment: If you by *machine learning model* mean defining it as binary prediction I'd say that if you have **loads** of data and a very clear definition churn/your query is a binary query then binary is the way to go. This is usually not the case so then you want to predict a hazard. Sorry if self-promotion but I wrote this [piece](https://ragulpr.github.io/2016/12/22/WTTE-RNN-Hackless-churn-modeling/) to answer this question which I had a year ago. You can also easily make hazard models a machine learning problem so it's kind fo a false dichotomy as noted.
Comment: Professor Tibshirani is a great counter example to the idea "Machine learning and hazard models are disjoint".
Comment: The two - why do you think they are either-or?
Comment: Here is an example of machine learning and survival analysis http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=1603631 bound to be more.  IIRC there was some work done on survival analysis based on microarray data using machine learning type approaches (e.g. L1 regularization).
Comment: For example: http://blog.wikimedia.org/2011/06/28/data-competition-announcing-the-wikipedia-participation-challenge/
Answer: I think your question could be further defined. The first distinction for churn models is between creating
(1) a binary (or multi-class if there are multiple types of churn) model to estimate the probability of a customer churning within or by a certain future point (e.g. the next 3 months)
(2) a survival type model creating an estimate of the risk of attrition each period (say each month for the next year)
Which of the two is correct for your situation depends on the model use. If you really want to understand the attrition risk over time and perhaps understand how (possibly time-varying) variables interact with time then a survival model is appropriate. For a lot of customer models, I prefer to use discrete time hazard models for this purpose because time is often discrete in databases and the hazard estimate is a probability of the event. Cox regression is another popular choice but time is treated as continuous (or via adjustment for ties) but the hazard is technically not a probability.
For most churn models, where a company is interested in targeting those x% of customers most at risk and the database is scored each time a targeting campaign launches, the binary (or multi-class) option is normally what is needed.
The second choice is how to estimate the models. Do you use a traditional statistical model such as logistic regression for the binary (multi-class) model or a machine learning algorithm (e.g. random forest). The choice is based on which gives the most accurate model and what level of interpretability is required. For discrete time hazard models, a logistic regression is typically used with splines to introduce non-linear effects of time. This can also be done with neural networks and many other types of ML algorithms as the setup is simply supervised learning with a "person-period" data set. Further, cox regression can be fit with traditional algorithms like SAS proc phreg or R coxph(). Machine learning algorithm GBM also fits cox regression with a selected loss function. As has been mentioned, ML algorithms for survival analysis using random forests and other tree based methods have also been developed and there are many within R.
Comment: (+1) Though I think it depends on more things than you mention. The predicted probability of churn within 3 months can be read off a survival model, & if it's a good model that might be a better estimate than one from model fitted to just the binary outcome of churn after or before 3 months.
Comment: How can one predict a probability of churn within three months using a random forest, logistic regression or C5.0 model? Is this even possible?
Comment: @Seanosapien, you can take your churn dataset with information about when each user churned, and for each user assign 1 if they churned before 3 months, and 0 if they did not churn before 3 months. Then you can fit e.g. a logistic regression model on the binary data and assign probabilities to new users based on the fit model
Comment: @Kdawg Thanks. I have managed to figure out a way to engineer a dataset to model with churn in mind.
Answer: First of all I would clarify where exactly you make the distinction between machines learning and hazard models. From my understanding the ml literature distinguishes between parametric and non-parametric models (among others).
And second, what do you need the model for? Is it for scientific research or something else? In any event choosing the appropriate model to describe you data is first of all depended on what you need the model for.
To your question: It depends on how much you know about the data generating process.
If for example you take the famous coin flip or die roll, you have a very good idea about the process that generates the expected outcome of an experiment.
In that case you really want to use a parametric (bayesian or frequentist) estimation because they will give you a very good estimation of the unknown parameter. Furthermore these models are very well understood, which has many advantages.
If you don't know the data generating process, or you are uncertain of it, you don't have much of a choice, will need to estimate the parameters that describe the data from the data itself. If you decide for such an approach, you must accept that these models have drawbacks (depending on the specific model etc.)
From my understanding the less you know about a process, the more you will need to estimate from the data itself, which will certainly come at price.


Can anisole be nitrated only with nitric acid?

Question: Is it possible to nitrate anisole using only concentrated nitric acid? Or is it necessary to use sulfuric acid or acetic anhydride? Could you please help me with some references?
Comment: Welcome to ChemSE! Your question will likely be considered as homework and be voted down. You need to make some effort to answer the question yourself. Take a look here about homework policy. https://chemistry.meta.stackexchange.com/questions/141/how-do-i-ask-homework-questions-on-chemistry-stack-exchange.
Comment: related https://chemistry.stackexchange.com/questions/152250/why-is-the-ortho-product-major-in-the-nitration-of-anisole-with-nitric-acid-and
Answer: Yes, it is possible to nitrate anisole (methoxybenzene) using not only concentrated nitric acid $(\ce{HNO3})$, but also dilute $\ce{HNO3}$ (Ref.1). The nitration of anisole in aqueous nitric acid in the concentration range 25.18-31.38 mol% at temperatures in the range $293$-$\pu{328 K}$ has followed the pseudo-first-order kinetics and the values of rate constant and activation energy have been reported.
The mechanism for the nitration is given as follows:
$$\ce{HNO3 + H3O+ <=> NO2+ + 2H2O} \tag1$$
$$\ce{NO2+ + ArH <=> encounter pair} \tag2$$
$$\ce{encounter pair <=> benzenonium ion ->[fast] products} \tag3$$
The author has stated that the activation energy of the rate determine step decreases with increasing acid concentration. This is a good indication that the rate of nitration is faster in concentrated nitric acid. The regioselectivity of the nitration (o-, p-, and m-selectivity) using different nitrating agents has been discussed elsewhere (Ref.2).
When only the fuming nitric acid in the solvent is used, the nitration
starts due to the autoprotonation of nitric acid and generation of a
nitronium cation $\ce{NO2+}$ (Ref.3):
$$\ce{HNO3 + HNO3 <=> H2NO3+ + NO3- <=> NO2+ + + H2O + NO3-} \tag4$$
The extended details of nitration of aromatics including anisole are given in Ref.4.

References:

David J. Belson, "Kinetics of nitration of anisole in aqueous nitric acid," Ind. Eng. Chem. Res. 1991, 30(7), 1485–1488 (DOI: https://doi.org/10.1021/ie00055a013).
George A. Olah, Henry C. Lin, Judith A. Olah, and Subhash C. Narang, "Variation of isomer distribution in electrophilic nitration of toluene, anisole, and o-xylene: Independence of high regioselectivity from reactivity of reagent," Proc. Natl. Acad. Sci. U S A 1978, 75(2), 545–548 (DOI: https://doi.org/10.1073/pnas.75.2.545).
Joanna Adamiak, "Controlled nitration of anisole over $\ce{HNO3/PO4/MoO3/SiO2/solvent}$ systems," Journal of Molecular Catalysis A: Chemical 2015, 407, 81–86 (DOI: https://doi.org/10.1016/j.molcata.2015.06.025).
J. G. Hoggett, R. B. Moodie, J. R. Penton, and K. Schofield, In Nitration and Aromatic Reactivity; Cambridge University Press: London, United Kingdom, 1971 (ISBN: 0-521-08029-0; ISBN 978-0521080293).
Comment: I am a little fuzzy about the given mechanism. In water solution the electrophile could actually be molecular HNO3 or even NO+ from some acid getting reduced. See [this answer](https://chemistry.stackexchange.com/a/95849/17175) and comments to it.
Answer: Yes, it is possible to nitrate anisole with just nitric acid. Following is the excerpt from a 1948 paper:

The nitration of anisole leads to formation of a mixture of nitroanisoles and nitrophenols in proportions depending on conditions. It is here shown that nitration of anisole in dilute nitric acid solution is nitrite-catalyzed and that the nitroanisoles are probable the intermediates in the reaction.
[...]
More precisely, anisole have been found to react rapidly with 40-50% nitric acid containing a little nitrous acid, but fails during many hours to react with nitric acid containing urea. The principal products when 40% nitric acid is used is nitrophenols; when more concentrated (60% nitric acid) used, then the principal product are nitroanisoles. The quantitative results were reported in table I:

They went ahead and tried to nitrate substituted anisoles e.g. p-nitroanisole
Ref.: The Mechanism of the Nitration of Anisole, R. M. Schramm and F. H. Westheimer, Journal of the American Chemical Society 1948 70 (5), 1782-1784
DOI: 10.1021/ja01185a036


Lower kitchen sink drain pipe

Question: So I went to install a new kitchen sink that is 9 inches deep to replace the 6 inch double drain we had. The new sink hits the top of the drain vent. What is the best way to reroute the pipes? Currently the pipe is 26 or so inches from the bottom of my cabinet. It needs to come down about 4 inches atleast. My concerns are making sure it still drains fine after I shorten it. I am also changing from a 2 drain to a 1 drain sink. I am not sure if it is allowed to just lower the top pipe the vent sits on and install a new vent or not.
Comment: Just redo the drain piping so it works correctly.
Comment: I take it there's no way to get an actual line out from here to the vent stack, hence the air-admittance valve?
Comment: Yea, this is how it was done when they built it, I think because of that.
Comment: If you solve the air-admittance valve conflict, will the tailpieces fit under the drains?
Comment: Yes I believe so.
Answer: Lower everything 4", that is your best option.
If that doesn't fit, then find a shorter air admittance valve and or lower the existing one as much as possible.
If that still doesn't fit, then cap the air admittance valve. Add a Tee fitting below where the sink drain connects to the vertical drain pipe. Connect a 90 degree fitting to the Tee to make a vertical pipe, then attach the air admittance valve to the top of that. You'll have a wet vent for about 6-12", but it should work correctly.

Lower kitchen sink drain pipe


Explosive biology

Question: My organism live in planet full of water . It has only small percent of land about 5% only. It is big as gorilla. It eats metal ores and gains sustenance from it. My organism developed an powerful defence against predators .  It has power to expel caloric energy in the form of heat and light . How can my organism plausibly do this biologically  ?
Comment: Every weapon should be adapted to the target. What is your predator like?
Answer: Magnesium Sacs
Magnesium is, simply put, nasty and highly reactive. It is highly unstable and, when exposed to oxygen, will commit to a highly exothermic reaction - that is to say, ignite and put out heat and light. Normally, this is slightly tricky to pull off because even given magnesium's high reactivity, it requires a source of heat to start the reaction. However, magnesium also reacts to water, reducing it to highly flammable hydrogen gas in a reaction that also can heat up the hydrogen gas to the point of ignition. In short, dump some magnesium and water together and you have a  potent source of both heat and light.
Now, the problem is making sure that this doesn't explode within the creature and kill them, which is where the creature's metabolism comes in. Let us assume that the creatures finds stable magnesium alloys in the metal ores it eats. It's body then processes the magnesium alloys, isolates the magnesium, and then puts it out within a kind of enclosed and stable 'sack', ready to be used in the event of an emergency.
Comment: How would the water based organism get metallic magnesium in the first place? Magnesium ore is not magnesium metal. Magnesium metal/alloy will only be common if invoking "a wizard did it".
Comment: Yes, that's pretty much how I'm envisioning it. Some naturally occurring alloy that an energy intensive biological process can isolate.

Explosive biology


Reading NSWindow resize event

Question: I was wondering if anyone knows, how do I read when NSWindow is being resized?
Let's imagine I have a button in an empty window (other than the button), then user resizes the window from the bottom right corner, now I should make it so that the button also resizes when the window is being resized. I know how to resize button, and I know how to resize a window, and I know lots of stuff, but I don't know how to get notificated when ever the user resizes the window, any tips?
Comment: Also, example is always the best answer, and giving a great example will totally make your answer the correct one, I guess it has something to do with NSWindowDelegate but not sure how to use it... :S
Comment: Did you figure out how to parse the notification to get width and height?
Answer: Can you use the <code>‑windowDidResize:</code> delegate method?
Answer: in the awake from nib of your .m file write
<code>    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(screenResize) name:NSWindowDidResizeNotification object:nil];
</code>
and create a method now
<code>(void)screenResize
{
    NSRect rect = Preloader.frame;
    rect = NSMakeRect(self.view.frame.origin.x+self.view.frame.size.width/2, self.view.frame.origin.y+self.view.frame.size.height/2, Preloader.frame.size.width, Preloader.frame.size.height);
    Preloader.frame = rect;
    NSLog(@"X = %f, Y = %f, W = %f, H= %f", rect.origin.x, rect.origin.y, rect.size.width, rect.size.height);
}
</code>
and when you get out of that class write
<code>    [[NSNotificationCenter defaultCenter] removeObserver:self name:NSWindowDidResizeNotification object:nil];
</code>
Answer: On Xcode 4.3 and later, use the autolayout to add constraints to the button, you can get very complex layouts without writing any line of code  .
Comment: this isn't very helpful, and not to the point either. Sorry for downvote, but you should change your answer
Comment: I disagree; autolayout is is correct approach to resolving this issue.
Comment: they were asking about a resizing event, which is best handled in code. and in my opinion Apple still has a long way to go with their interface builder...

Reading NSWindow resize event


Chirping Flourescent Light Fixture

Question: The flourescent lights in one end my basement have not worked since I moved in last December. I prefer incandescent lighting, so I wasn't concerned about it. A few days ago, one of the fixtures started making a strange "chirping" noise. It sounds like a smoke detector battery signal, but it is definitely coming from the light fixture. There are two fixtures on one switch; the second fixture isn't making any noise.
Answer: For older types of fitting, it might be a fluorescent starter continuously attempting to start a dead tube. If so, removing the starter would stop the noise.
Answer: If you are not using the fixtures, and they are not working, turn them off. Otherwise the ballasts are constantly trying to start the tubes and wasting a lot of energy (like $20-30 a year worth per fixture). I've also seen old ballasts overheat and ooze tar all over the inside of the fixture. If the fixture is warm to the touch, it's not off.   I respectfully disagree with RedGrittyBrick; removing the starter (a metal can the size of a pill bottle, many fixtures don't have one) won't entirely shut off the ballast. Find the "off" switch.
Fluorescents are good for making a LOT of light.  One dual 40W fixture is equivalent to about 400 W of incandescent (seven 60W bulbs).  If you wonder why on earth such office-intensity lighting would exist in a home which is meant to be a comfortable and relaxing space, it's for workspace lighting, for those of us with hobbies that involve making stuff, tinkering, sewing, fixing motorcycles, etc.
You'll like fluorescents a lot more if you do two things: a) replace the ballast with a modern electronic type that is silent and doesn't flicker... and b) get some warm-white tubes (2700-3500 degree Kelvin, lower is warmer) with high CRI such as 90 or even 98.  Wonderful light.  Alternately, you could replace with LED "tubes" and bypass the ballast entirely, but those tend to be cheaply built, and the best CRI's are still found in real fluorescent tubes.

Chirping Flourescent Light Fixture


Why do I have both HTTPS and HTTP links on site, need them all secure!

Question: I am getting the security alert: "You are about to be directed to a connection that is not secure. the information you are sending to the current site might be transmitted to a non-secure site. Do you wish to continue?" when I try to login as a customer on my clients oscommerce website. I noticed the link in the status bar goes from a https prefix to a nonsecure http prefix. The site has a SSL certificate, so how do I ensure the entire store portion of the site directs to the secured site?
Answer: It is likely that some parts of the page, most often images or scripts, are loaded non-secure. You'll need to go through them in the browser's "view page source" view one by one and eliminate the reason (most often, a configuration setting pointing to http://).
Some external tools like Google Analytics that you may be embedding on your site can be included through https://, some don't. In that case, you may have to remove those tools from your secure site.
If you can't switch all the settings, try using relative paths

but the first thing is to identify the non-secure elements using the source code view of your browser.
An immediate redirection from a https:// page to a http:/ one would not result in a warning as you describe. Can you specify what's up with that?
Comment: Sure, if you go to https://balancedecosolutions.com/products//catalog/login.php and login as a customer. I have setup firstname.lastname@example.com as the user name and test123 as the password. You'll see the message (IE6) when you try to login.
Answer: Ensure that the following are included over https:

css files
js files
embedded media (images, videos)

If you're confident none of your own stuff is included over http, check things like tracking pixels and other third-party gadgets.
Edit: Now that you've linked your page, I see that your <base> tag is the problem:
<base href="http://balancedecosolutions.com/products//catalog/">

Change to:
<base href="https://balancedecosolutions.com/products//catalog/">

Comment: Thanks shark... the only reference to that that I can find is a line of code like this:
Comment: Hopefully the OSCommerce software has an option for always using `HTTPS_SERVER`. If not, try editing that line:

``
Answer: Use Fiddler and browse your site, in the listing it should become evident what is using HTTP and HTTPS.
Comment: Jon Galloway talks about this in one of his blog-posts:

http://weblogs.asp.net/jgalloway/archive/2009/10/15/did-you-know-about-protocol-relative-hyperlinks.aspx

TL;DR - pre-pend it with // rather than http(s)
Answer: If the suggestion from Pekka doesn't suit your needs you can try using relative links based on the schema (http or https):
e.g.,
I am a 100% valid link!

The only problem with this technique is that it doesn't work with CSS files in all browsers; though it does work within Javascript and inline CSS. (I could be wrong here; anyone want to check?).
e.g., the following :
<link rel="stylesheet" href="/css/mycss.css" />

...
body{
    background-image:url(//static.example.com/background.png);
}
...

...might fail.
A simple Find/Replace on your source code could be easy.
Answer: It sounds to me like the HTML form you are submitting is hardcoded to post to a non-secure page.


"Wir gehen heute Nachmittag schwimmen" or "Wir schwimmen heute Nachmittag gehen"?

Question: My textbook says "Wir gehen heute Nachmittag schwimmen" but I was wondering why we can't write "Wir schwimmen heute Nachmittag gehen". Could someone please explain why the former is correct? Thanks.
Comment: Try building the sentence with "ich" instead of "wir". Remember the (conjugated) verb must be at position 2 in German.
Comment: *Wir gehen schwimmen* means roughly the same as *Wir gehen zum Schwimmen*. Analogously, *Wir schwimmen gehen* would be equivalent to *Wir schwimmen zum Gehen* which is nonsense.
Answer: Grammatically, this sense of gehen takes a subject and an infinitive verb as an object. The English "to go" does a similar thing but with a present participle (the "-ing" form), as in "He goes swimming," or "She goes dancing." (German has a present participle as well, but it's use is limited and German often uses the infinitive instead.) There is no such sense for schwimmen, just as there is no such sense for "to swim" in English; you can't say "She swims dancing." So gehen here is the finite verb, with the subject wir and schwimmen is an infinitive. Finite verbs come second in a German sentence (not counting questions, subclauses, etc.), and that's gehen in this case. Meanwhile, infinitives and other non-finite verb forms usually come last in a sentence, which puts schwimmen at the end. Flexible word order in German would allow Heute Nachmittag gehen wir schwimmen. But I think that's the only other option here. Note, as Roland pointed out in the comments, if the subject is ich, then gehen, being the finite verb, would be conjugated as gehe.
Comment: Also correct is "Schwimmen gehen wir heute Nachmittag" and even "Schwimmen gehen heute Nachmittag wir" (und nicht ihr, denn ihr wart gestern an der Reihe).
Comment: Not to forget that "Wir schwimmen heute Nachmittag" without the "gehen" at the end would also work fine
Comment: @Carsten S: Thanks, I didn't think of putting the infinitive first, but it makes sense that you can.
Answer: The verb "gehen" in the first sentence is used like the going to future. This is why you want to use it. The second one just doesn't make sense, it implies that you swim somewhere in order to go walking there.
Comment: The verb "gehen" is not related to future tense or the English "going to".
Comment: It's definitely related, but the tempus is understood from lexical aspect.


Current taken from USB by STM32F3 Discovery board?

Question: I am trying to find out what the board draws from the USB supply at max MHz. I really don't want to cut cables if this info is available somewhere already
Answer: Current draw is a very subjective thing - it depends on so many factors. Not just the current MHz of the CPU, but also what it is actually doing at the time.  The only true way of knowing is to graph the current draw over time - you'll see it's not a flat line.
But all is not lost.  You can buy a small USB current meter easily enough. That'll give you an average current draw smoothed over a short period.  Kind of like using the ammeter setting of a DMM but without having to cut cables.  They're reasonably cheap.
Another thing you can do is, if the USB interface conforms to the standards properly, is to examine the requested maximum current parameter of the USB descriptor.  This won't be what the board is using, but will be the maximum current it requests to be allowed to use.  This may be of more use to you than the actual real-time value, since it is what the board would be allowed to draw from the USB before being shut off (by a well behaved interface).
For instance, my STM32F4 Discovery board reports:
MaxPower              100mA

How you get that data depends on the OS you are using.  I use Linux, so I run the lsusb -v -d <vid:pid> command.  In Windows I think it can be found through the device manager somewhere.  Not sure about OS X.
Comment: Not all motherboards are going to honor the USB current cap, regardless of any USB negotiations for current.
Comment: Thanks. I am trying to work out if I can power my design, based on the F3 board, solely from USB2
Comment: @ScottSeidman It also depends on the type of port you plug into - data, CDP, DCP, etc...
Comment: I suspect the USB power figure is a default, and not anything meaningful.
Answer: Obviously, the magnitude of current that the board draws will depends on what you're doing with the board.  The STM32F3 discovery board has a jumper (JP3), where you remove the short, put in an ammeter, and you know how much current the board is using.  No need to cut cables.
See page 18, http://www.st.com/web/en/resource/technical/document/user_manual/DM00063382.pdf


Are there any API to turn on DXVA in Mac OSX

Question: I wrote a video playback application based on Carbon in MAC OSX, are there any API to turn on the DXVA feature which support by Graphic Card? Does it support in QuickTime SDK or Carbon API?
Answer: DirectX is part of Windows. It doesn't exist in Mac OS X.
If you're doing hardware-accelerated video playback: Why are you worrying about it? If the hardware supports it, chances are, the APIs will use it. So just play your movie and let the library take care of doing it through the graphics card or not.
If you're doing video capture: Core Video will let you do that through the graphics card.
Answer: I believe that on very-recent hardware only, QuickTime will use hardware video acceleration for the decoding of some types of video stream.
Note that this is NOT specifically related to the capabilities of the graphics card, for example the 8800GT PureVideo feature works fine under Windows but is unused in OS X.


Does carbon dioxide preferentially accumulate in one layer of the atmosphere?

Question: Just as Ozone concentration peaks at around 20 km in the stratosphere, having a distribution around higher and lowers layers of the atmosphere, does the same happen for carbon dioxide or other greenhouse gases?
Answer: They do, but not to the extreme that $\ce{O3}$ does. For reference, there is $\ce{O3}$ near the ground, but the $\ce{O3}$ in the stratosphere is amplified by the Chapman cycle that forms it.
Generally, greenhouse gases have the highest concentration in layers where they are generated. Let's think about a few (not all) of the greenhouse gases, their sources, and some relevant processes that keep them confined to their layer.

$\ce{CO2}$ - emitted by combustion and respiration. Because $\ce{CO2}$ is a mostly stable molecule, it can probably travel pretty high into the atmosphere before it falls down due to the molecular weight. But due to where it's generated it'd still be more concentrated near the ground.

Water vapor (yes, it is a greenhouse gas) - most prominent in the surface layer, but generally decreases with height. Generally caps out due to phase transition (it becomes liquid water and ice), but some can enter into the stratosphere.

Methane - agricultural and biological sources. Like water, it is most prominent in the surface layer. However, it isn't as bound by phase transition as water vapor is.  It does interact with other chemicals in the atmosphere, such as the hydroxyl radical.
Comment: [What is the CO2 concentration by altitude and why?](https://earthscience.stackexchange.com/questions/16364/what-is-the-co2-concentration-by-altitude-and-why)


Vanishing zero point energy in harmonic oscillator

Question: In classical mechanics, adding a constant to the potential changes nothing. In quantum mechanics, this just shifts the energy and multiples the wavefunction with a phase term.
But now suppose I use the potential $$V(x)=(1/2)m \omega^2x^2 - (1/2)\hbar\omega$$ instead of $$V(x)=(1/2)m \omega^2x^2 $$ for the harmonic oscillator. Then the energy spectrum will be $$E_n=n\hbar\omega$$ instead of $$E_n=(n+1/2)\hbar\omega.$$ This would mean that the harmonic oscillator can have a vanishing ground state energy depending on the potential that we choose. But the non-vanishing ground state energy of the harmonic oscillator is the source of the zero point energy of vacuum. So does that mean adding a constant to potential changes the system in quantum mechanics?
Comment: We don't observe the absolute energy levels of a quantum system. We can only observe transitions between states i.e. energy differences. The only exception to that is general relativity and we know that it's false at the quantum level. So, yes, you can shift the absolute energy level if you wish and then you get a different false result from the case in which you don't. Which false result do you personally like better?
Answer: The right way to interpret energy in the quantum vacuum is not known. Especially, its gravitational influence is not known.
If we say that the energy $(1/2)\hbar \omega$ is in fact present in the vacuum for every field mode, then we get an enormous energy density, and this leads to predictions about cosmic expansion which are way off from the observations. Such a model predicts an expansion accelerating at rates many orders of magnitude higher than is observed. On the other hand the Casimir effect can be calculated correctly by taking the zero point energy as $(1/2)\hbar \omega$ for each mode. So there is a real puzzle here and no-one knows the answer.


Laptop connecting to only one WiFi network and not connecting to other available WiFi networks

Question: I just installed Linux Mint 19 (Tara) on my HP laptop and everything works amazing, however I can't seem to get it to connect to my WiFi network. All my other computers can get access, plus, before when the laptop has Windows XP, it could also find and connect. Is there a way to check if it's even detecting the correct network? If so, how would I set up a proper connection to the network?
Answer: First, you should try in the terminal
sudo iwlist wlan0 scan
and check if your wifi adapter sees the WIFI network you want to connect to? If you are in a congested area with multiple wifi networks, you can use iwlist wlan0 scan | grep -i ssid and look for the name of your WIFI network in this much shorter list.
wlan0 being the name of your wireless adapter. iwconfig will list the appropriate one if it is not wlan0.
If you find yourself unable to even scan for nearby networks then this will likely become a question about setting up your wireless adapter, as opposed to deciphering why you might not be able to connect to one particular WIFI network.


Is it possible to install an FM Radio application to get local frequencies?

Question: Samsung Galaxy S10 has a built-in radio application. But it catches only USA and Canada frequencies. I do not live in USA nor in Canada. So is it possible to install an FM Radio application from Google PlayStore to get locale FM radio frequencies in my country ?
Comment: There is an related question on Stackoverflow: https://stackoverflow.com/questions/8559612 I would also suggest to read this article which explains the problems: https://github.com/mikereidis/androidfm/wiki/Creating-an-Android-FM-app
Answer: That really depends on if there is an app to stream stations from your country, unless you are talking about a real FM radio receiver function in the phone.
My s10e doesn't have an FM radio function, so the only way for me to get 'FM stations' is by streaming the station over the Internet with an app. I assume yours is the same. If not, read below. Carriers like to disable the FM radio to force you to use your data.
So if some company has built an app to stream stations like 'Iheartradio' in the US, then you can use it. Also, some US stations have websites that allow you to stream their station using a web browser. You might try that.
If you are talking about an actual FM rađio receiver app that uses 88Mhz to 108Mhz and your country doesn't use those frequencies, all I can tell you is you can try to find an app for your country. But if the radio in the phone is the US format, changing the app probably won't change the frequency capability of the hardware radio inside the phone.
As far as I know, the only areas that haven't switched to the 88-108Mhz band is Japan and Eastern Europe so Samsung may not make hardware specifically for your region.


How to run a command after receiving a mail with exim4?

Question: Where can I tell exim to run a shell/php command everytime a new mail has been delivered to a virtual mailbox. It does not matter to which user the mail is delivered?
Answer: Given that you apparently have a real user to deliver to, you probably want to look into using a .forward file, or possibly procmail if you want to get a bit fancier (such as if you only want to run the command for a subset of messages delivered to the user).
Comment: Unfortunately I am having a multi user/domain system via exim4/mysql/courier-imap I meant with local user, that this user is terminated in my system. But it should be called disjunct from the user recieving the mail.
Comment: "local user" has very specific meaning with MTAs, you might want to edit your question to say "virtual mailbox" if you're running that sort of system.
Comment: thx, I have corrected the question.
Answer: You want to look at shadow_transport.
For local deliveries (only), if delivery succeeds and the Transport references another Transport in its shadow_transport option, then that second transport will also be invoked.
You'd then have that second Transport be a driver = pipe transport.
Eg:
maildir_delivery:
  driver = appendfile
  directory = ...blah blah whatever ...
  maildir_format
  # various other maildir extension options if needed
  shadow_transport = audit_delivery

audit_delivery:
  driver = pipe
  command = /some/path/to/some/command with some options
  user = audituser
  group = mail

Answer: The easyest way I found was creating a new router afterwards delivering to the local users containing:
runscript:
        driver = accept
        transport = run_script
        unseen
        no_expn
        no_verify

So, the mail is still handeld the way it should be and my script is running, with the right transport f.e.:
run_script:
        debug_print = "T: run_script for $local_part@$domain"
        driver = pipe
        path = "<path>"
        command = "<command to be run>"


Can C++.NET and J# be used to make a website?

Question: I didn't see an option to create a web site in the c++ area. Is there a way around this or am I just stuck with C# and VB.NET
Answer: A bit of googling turned this up, not sure how applicable it still is:
http://www.codeproject.com/KB/mcpp/helloworldmc.aspx
However, I'd question WHY you'd want to use C++.NET over C#, given that the languages are fairly similar at the basic level. Any perceived "speedups" would probably not be very noticable given that they both compile to the same IL, and as such are both subject to the JIT-compiler.
Comment: Minor nitpick: it's not actually an interpreter. The JIT-*compiler* generates real native code on the fly.
Comment: You are correct. I was mixing the alternate CLR implementations (micro, in particular, as well as Mono's) with the "standard one," which DO interpret occasionally. My fault, fixed.
Answer: You can probably make your website work using C++/CLI. There is no tight coupling between a .NET page (aspx or ascx) and the language of implementation. You might even get the intellisense from within the aspx/ascx files but don't quote me on that.
So to set this up you would need to create a C++/CLI project and use managed C++ to extend Page, Control, etc classes, use HttpContext etc.
Another question is whether or not there is any point doing that. You would still be targeting .NET and calling to the same API. There won't be much performance benefit if at all and you will lose the IDE support for creating controls and you wouldn't be able to use WebForms from the designer.
Edit. If you haven't done ASP.NET before you will almost definitely be firing up a normal ASP.NET project and seeing how to implement something, which classes to extend etc. So it kind of defeats the idea of using another language.
Answer: You can, in theory, use any .NET language to build ASP.NET pages.  F#, for example, is fully supported in VS 2010.  Whether all languages are fully supported in the tools is another question -- particularly for a language like J# that has been deprecated beyond VS 2005 and doesn't support the full depth of features of the other languages (such as the ability to create new attributes).
At a minimum, you will need to do things like define an appropriate build provider to get things going.


searching based on a search term and a location

Question: We want to build a search engine based on a search term and a location. Something like Skill Pages, which prompts for a skill you are looking for and the location (e.g. http://www.skillpages.com/i/Search/Browse?Location=new+york&SearchTerm=designer&SearchType=SKILLS).
This is an incereasing common way of searching and I've been wondering how it is achieved.
Do these sites use google api to return a longitude and latitude of the location the user has entered, then decide on a radius, say 50km, and search skills within that radius (still on Skill Pages example)?
With this method, how is the radius decided on? For example, if a user chooses "London", the radius would be much smaller than if a user chooses "UK"...
What's the best method to achieve this form of search?
Answer: check out how google places work. it must be very similar that you want.


General-purpose blockchains without gas fees

Question: Is it possible to create a general-purpose, turing-complete blockchain (i.e. Ethereum) that does not need gas fees? It's to my understanding that Ethereum needs gas fees due to the halting problem (in order to prevent a DOS attack). What needs to be fixed so that gas fees are no longer needed for general-purpose, turing-complete blockchains? Is taking execution off-chain the solution to removing gas fees or something else?
Comment: As you stated, the halting problem is one issue here, and that cannot be solved for a Turing-complete blockchain. But even if you gave up Turing-completeness, you'd still need an incentive for validators to actually include your transactions in a block
Answer: Maybe in theory if you could take all computations off chain and post a sufficient proof that will always be constant compute time to the chain, maybe. Generally speaking though, gas fees are needed to compensate miners/validators for the computation power they use to process your transactions. In order to develop a chain where you dont need gas fees, you would essentially need to be able to reduce every transaction to constant compute power with some proof, so that it does not vary at all. Thats a question for theoretical mathematics/computer science if its even possible for such a thing to exist.
And I would say its not just the raw problem of denial of service, its also about incentivizing miners/validators to spend more resources to properly process transaction that vary in computing cost for the members of the network.
Generally speaking though, I don't expect we will see this, and it may be mathematically impossible to design such a system in the first place. I think its less a question of blockchain technology, and more a question of a super advanced breakthrough in mathematics happening that would enable such a system.
And while like maybe you could design some system where gas fees are replaced by some other type of incentive, or maybe a chain that caps computations at a maximum size, in all likelihood the model would be inferior to just properly incentivizing efficient computations by making users pay more for high amounts of computation.


What is the answer in this one?

Question: This is a question from Brainzilla IQ test. It gives C as the correct answer but I cannot figure out why.
Answer:
 Reading left to right, top to bottom; each grid has an extra small black square. So the missing grid must have six small black squares.

 Now notice that the small black squares use the same nine positions in sequence, looping back to the when they reach the bottom right.
 (Numbering the positions 1-9 in natural order, we have:
 one square in position 1
 two squares in positions 2,3
 three squares in positions 4,5,6
 four squares in positions 7,8,9,1
 five squares in positions 2,3,4,5,6.)
 So the six squares should be in positions 7,8,9,1,2,3, which is answer C.
Answer:
 Same as above, I noticed that the count increased from 1 square to 9 as we went, but I saw it as adding the sides together, like you would on a die. 1 + 8 make a full grid, 2+7, 4+5, so we need to pick the one that adds to 3 to make a full grid, which is C!

What is the answer in this one?


How does the prophet of Islam respond to 'salat' he receives?

Question: It is said that each time you say peace be upon the prophet of Islam, this message is transmitted to him, he hears it and he respond to your Salam. If potentially, thousands of Muslims are saying this at the same time, how this process would work ?
Answer: This is not a question we have an answer for.
After death,you basically go to a completely different life.. which could not follow our mind-limited physical laws..
It's all from the knowledge of 'ghayb which we shouldn't put our noses in.
Just like asking " How can Jibreel have 600 wings ?" or " How can Allah talk to us all on the day of judgment simultaneously?"
This is a red line which you shouldnt cross.
Comment: You just went from : this is not a question we have an answer for. To this is a red line which you shouldn't cross.
Comment: Yes, you do have the right to ask questions. But it's just the fact that we have limits. We don't have the right to ask everything.                                          A man asked Imam Malik (d. 179): "How did Allah make istiwa' on the throne?" Imam Malik inclined his head and was silent until the sweat of fever covered his brow, then he looked up and said: "Istiwa' is not unknown, the modality of it is inconceivable in the mind; but belief in it is obligatory, and inquiring about it is a heretical innovation. You are an innovator." And he gave orders for him to be taken out.
Comment: I'm referencing this just so you don't think I'm exaggerating or so.. Imam Malik called him an " innovator "  So don't try finding answers for these questions because they're from the shaitan and he wants to open for you a big door of suspicion in religion... and it probably won't stop at this point if you keep going on with these thoughts.      I'm just giving advice brother :) I might have made mistakes or so but this is what I've learnt and Im just passing knowledge
Comment: Just a correction --> Being an innovator doesnt at all mean that person is going to hell.. It depends according to what that person has innovated.. like for example a lot of people (in the arab counties) celebrate the birthday of our prophet; which is clearly an innovation and its prohibited.. but that doesn't remove them from being muslims. But others could put innovations which contradict clear Quranic verses; that one is who goes to hell; as he denied the Quran using his mind philosophy ( implying he knows more than Allah ) , in that case he's a kafir.
Comment: I don't think you should ask. This question has a good comprehensive answer https://islam.stackexchange.com/a/38993/35830


Why aren't build order questions directed to specific sites specializing in them?

Question: I see "build order" questions frequently, particuarly for starcraft 2. While often the answers are good, these questions can easily be answered by a simple google search. Liquipedia has a far more comprehensive answer on build orders than anyone can post, and comes up first in search results. Why is it acceptable to ask and answer these general reference questions that are not permissible on other SE sites?
Comment: General reference is not a close reason anymore.
Answer: The Internet is a chaotic place: you can find information about almost anything if you search hard enough or synthesize data from disparate sources.
Stack Exchange, on the other hand, is intended to be a structured repository of useful information that fits the Q&A format: if there's a chance for us to provide a better answer than the rest of the Internet, even if it's been covered to death elsewhere, we're going to do it, because it makes the Internet fundamentally better.
But we're not trying to be GameFAQs or Wikia: we specialize in specific questions. While yes, you could read a whole strategy guide to find out the answer to a specific problem, we work under the premise that if one person has a specific problem that requires the synthesis of a specific, tailored answer, other people are probably asking the same thing and would benefit from seeing the tailored answer instead of getting linked to a whole guide that covers everything.
So asking questions that are so-called "general reference" is fine here, and it's fine on all but two sites on the network (English.SE and SciFi.SE). In fact, after the field trials on English.SE and SciFi.SE, the plan to roll out the "general reference" close reason to the rest of the network was scrapped due to its potential for abuse.
To that end, I highly encourage you—and anyone else who thinks closing things as general reference is a good idea—to listen to at least minutes 14:00–20:00 of Stack Exchange Podcast #20, where Joel Spolsky and Jeff Atwood (founders of Stack Exchange) discuss its benefits and drawbacks.
Now, of course, there are questions that seem like general reference, but are bad for other reasons and should be closed:

Questions that would require a whole book to answer: close as not a real question.
Example: "Can you walk me through all the levels of Super Mario World?"
Questions that don't define a problem or correctness criteria: close as not constructive.
Example: "What's the most fun StarCraft II faction?"
Questions that are easily answered by a general reference, but define a problem in such a contrived or specific way that prima facie invalidates any obvious answer and would be useful to pretty much only the asker: close as too localized.
Example: "Diablo III says it's PC/Mac only. How can I get Diablo III to run on my TI-83 calculator?"
Comment: I feel that its a waste for people to give answers of reasonable detail and quality, when even better content exists on other sites that are easily available as the first hit on a simple google search. Is it really considered the best solution to create duplicate content of specialist sites, especially when the formatting limitations of SE ensure that answers posted here can never reach the accessibility of another site, due to lack of HTML anchors and other features? I feel like a lot of answers I see are given where a link to an outside specialist site would be superior.
Comment: @Lawton Our goal isn't to duplicate other content, but to provide better, more easily accessible answers to specific questions: to be a Wikipedia of Q&A, not to duplicate Google search results. Regarding providing nothing more than a link elsewhere: what happens when the link dies?
Comment: The problem is that to me it appears many questions are being answered with worse content, because because its harder to navigate a massive wall of text on SE sites rather than a wiki containing related SC2 Zerg builds. As far as when a link dies, sites with long histories could be argued to be as reliable if not more reliable than any content located here.
Comment: @Lawton If you can provide a better answer than what's there, you're encouraged to answer yourself. But since you don't seem to see the value, I guess it just comes down to Stack Exchange is not for everyone: if you think other sites are better, more power to you to use them instead of SE.


Should homework questions that are otherwise not problematic be left open?

Question: This is a pretty uncommon scenario here, but it appears that someone has posted what looks a lot like a homework question to the site. The twist here is that the question itself is very relevant to the site, and if the OP would have put any effort into modifying the question to appear as if it was their own, we would never have noticed. Is there any issue with leaving this question open?
Answer: As the question has been copied from some APS material and they provide an answer. I do not see a place for this particular question. It seems weird to just repost material from other sites.
Comment: It might be a good question if the OP had some good reason why the existing answer was not sufficient (besides for "My ethics professor said we can't just plagiarize the APS answer") or did not apply. But as far as I can tell, the OP just didn't even bother to Google it and find the answer.
Answer: Personally, I say leave it open.

There's really no way to police this.
The question is interesting; removing it punishes ourselves.
This happens so rarely that doesn't really need a policy.

EDIT: I posted this before @ff524 found the exact question, along with answers, already online. Given that update, I'm a bit more hesitant... as @Strongbad says, we don't need to repost stuff from other sites just for the heck of it.
Comment: I edited the question to make it clear where it came from and that it is a case study.
Comment: In the abstract, it might be OK. This question, not so much.