How can I mention errors in the data that I received in my thesis? Where to mention it?

Question: I received data for data analysis for my Bachelor-Thesis. I still got 4 weeks left to finish the 40 pages and after having gotten all my results, my supervisor and I realized that the data that I received had a conversion factor error (we don't even know about the magnitude of this factor-is it 3/4 times higher? etc). Anyways, I wanted to mention this issue in my thesis but I am not sure 1) where to mention it - methods? results? and...2)how to talk about it? Thank you all!
Comment: How do you know it's a conversion factor error if you're not sure of the magnitude?
Answer: Do not publish ANYTHING you know is untrue, or even suspect is untrue.
I am a PhD, a research scientist and former college professor.
You are just in trouble. You cannot publish conclusions that do not hold if the data is in error, you will be publishing a known falsehood.
Your best bet is to rescale the data by some amount, say a factor of 10, or convert mm to inches or vice versa, or Fahrenheit to Centigrade, and see if your same conclusions hold. If the number is arbitrary, try several, like [.25, .5, 2, 5, 10, 50].
If they all give the exact same results, you might be able to say (very early, like at the end of your introduction) that your data was found to have a scaling error of unknown magnitude, but your conclusions held when the data was rescaled by several different magnitudes [.25, .5, 2, 5, 10, 50], thus there is reason to believe the results are scale-invariant.
However, if these experiments do NOT give the same results, you should search for how big or how small the scaling factor can be to get the SAME results, and report that. Test in 10% increments; e.g. [0.10, 0.20, ..., 0.90] for how small, and in larger increments [1.25, 1.50, 2.0, 2.50, 3.0, 3.50, 4.0, 5.0, 7.0, 10.0].
Then you can say (very early) that a scaling error of unknown magnitude was discovered in the data after the completion of the study, but your results hold if the data is rescaled by a factor in [0.25, 5.0]. THAT IS AN EXAMPLE, you will have to find the upper and lower bounds yourself.
If, analytically, your reasoning is relative, (for example, saying "less than 10% of the samples met condition X" or saying "These samples were more than 3 times the magnitude of those samples") then a constant scaling factor will not change the logic of relative statements.
You should examine your paper and see which statements are relative and which are NOT. For example, if you thought temperature was in Fahrenheit and said a temperature of 20 was below freezing (for water), and then discover temperatures are in Centigrade, well 20C is 68F, nowhere near freezing, and that logic and what follows from it just has to be revised or deleted.
Comment: A bachelor's thesis in Germany (where the asker is studying) is not usually published. This is an exam. Having to deal with faulty data is common in German bachelor's theses (which often work with data from preliminary or pilot studies) and not a reason for concern. The purpose of the bachelor's thesis is for the student to show that they have learned how to do research and write papers. The finished thesis will usually be forgotten in an archive in the university until it is destroyed after ten years (the legal period for universities to keep exam documents).
Answer: It's been a while since I wrote a scientific thesis, so apologies, but this sounds like it would be discussed in "Results" section to the reasons why your data was returning bad values and what misstep in your methods you can attribute to that results.  The Methods section is listing the steps you took to get the data returned, so it should not be relevant to change, provided you acknowledge your mistake in the results section.
You should also have a conclusion section where you should right your initial conclusion and follow up with a revised conclusion based on the problematic return.  Best form is to draw all possible conclusions you can with the data that was not returned in an erroneous manner to the best you can, then acknowledge what cannot be concluded because of the bad data, and note that the modification that could correct this error in your testing.  Science is as much about proving what you know as it is acknowledging what was not proven and why.
In the event that the entire data returned invalidates any conclusion.  Start with admitting the problem, and showing what steps were not taken that lead to this situation.  You may be able to get away with discussing initial conclusions, but be mindful that this is inconclusive without the right data set.  If the conclusion is so off it is absurd, discuss the logical reasons of why this cannot be accepted as a valid possibility.
Answer: With four weeks still to go, the emphasis on your thesis has shifted from one of presentation to one of finding out what went wrong. This will lead you to three probable outcomes :
1) You discover exactly what went wrong, and it's a simple factor with no effect on the measurements. A note in the method or at the beginning of the results (eg. "Measured values in mph converted to m/s") would be sufficient.
2) You discover what went wrong, and there could have been an effect on the implications of the results (eg. "Variations in volumetric flow had not considered a change in viscosity with an increase in temperature."). If there's still time to retest (on a smaller sample if necessary) this would be the best way to go, if not your investigation should be reported - the process of discovering the problem and your resolution of it has become part of the thesis, and should be reflected in the method and results. Your conclusions might be no different, or you may have to report inconclusive results.
3) You are unable to discover or quantify what went wrong. You would now be writing a very different thesis - a report on the problems encountered rather than something leading to a demonstrable conclusion. You can still display valid scientific techniques - this has become the object of the thesis rather than what you originally planned, and your conclusions (if any) should reflect that.
The investigation into what happened is the important thing now, as the way you present your observations will depend on what you find. Whichever way it goes there is an outcome where you can present valid scientific observations, but the way you present them will be different.
[I'm also going to agree with Amadeus's suggestion of applying possible factors iteratively - if you can discover the variation, this may give you an idea of what might have caused it - for example if you keep running into the numbers 9.81 or 3.142, you could guess at SI gravitational acceleration or confusion of circumference/diameter.]
It's worth remembering that as long as a consistent and repeatable process has been followed and reported, results that are inconclusive or which appear to contradict a hypothesis are valid results.
Answer: The first thing to do is talk to your supervisor how they expect you to deal with this. A bachelor's thesis is an exam, and as such what is relevant here is what your supervisor wants.
In my bachelor's thesis I had several problems to deal with, from faulty study design (it was a pilot study designed by my supervisor, and in the course of my thesis he found out that the design didn't work, so all the results where irrelevant to the research question!) to insufficient data to draw meaningful conclusions from.
What he told me was:

Ignore all this and pretend the design and data where fine. Just write your thesis as if the data had been collected properly. In the end, this thesis is about you showing me that you can write a paper, not about this specific research.

Your supervisor may have another opinion than mine, and your thesis may actually be reworked into a published paper. So ask them.


Will a market offer trigger a new subentry?

Question: A market offer is, for example, a bid offer that takes on an outstanding ask offer at the same price and amount, and vice versa. Since the offer will get filled immediately, will the network reject the transaction if the XLM balance of the source account is not sufficient for another subentry (triggered by the new offer) and the transaction fee? In other words, will the new offer trigger a new subentry for purposes of calculating the XLM minimum balance in order to determine whether the network will let the transaction through or not?
Answer: It was an issue with the older protocol version (up to v9), addressed by CAP-0003 in protocol v10. It wasn't possible to go under the base reserve amount, but anyone could create multiple offers not backed by corresponding asset balance.
Now when a new offer is placed on Stelalr DEX, the corresponding buying/selling liabilities are reserved on the account balance in advance, so it's not possible to submit an offer that exceeds you actually available balance.

Starting in protocol version 10, it is no longer possible for an offer to be invalidated because the account owning the offer no longer has the asset for sale. Each offer contributes selling liabilities for the selling asset and buying liabilities for the buying asset, which are aggregated in the account (for lumens) or trustline (for other assets) owned by the account creating the offer. Any operation that would cause an account to be unable to satisfy its liabilities, such as sending away too much balance, will fail. This guarantees that any offer in the orderbook can be executed entirely.

The above also relates to transaction fees paid by the account. If xlm balance - (buying_liabilities + selling_liabilities) < fee, the transaction will be rejected.
Comment: Interesting question. Curios about it as well, need to check this on the testnet. Also, if you want to execute market order in the fill-or-kill fashion, it's better to use PathPayment with destination=source (so-called self PathPayment) for this purpose, as it doesn't create a new offer on DEX (and thus doesn't have balance requirements) if the taker offer hasn't been executed in full immediately after transaction execution (standard ManageOffer behavior).
Comment: Does the market offer require the 0.5 XLM reserve (required for each offer in general) such that if the XLM available balance is less than the fee plus 0.5 XLM, the transaction will be rejected?


How does auto-negotiate determine link speeds?

Question: I have two Linux hosts connected via category 6 wire. How do the LAN cards negotiate a link speed?
Essentially, I am trying to solidify if I am actually hammering a 1GbE NIC with traffic from a 10Gbe NIC or if they negotiated a 1GbE link speed.
Answer: A 10 Gb NIC connected directly to a 1 Gb either negotiates a 1 Gb connection, or it doesn't work at all. You cannot have the situation you describe unless you have something like a switch in between, where the 10 Gb NIC connects to a 10 Gb switch port.
It is very easy to search and find ethernet speed negotiation on the Internet, such as the Wikipedia article:

Auto-negotiation (formerly "NWay") is based on pulses similar to those
  used by 10BASE-T devices to detect the presence of a connection to
  another device. These connection present pulses are sent by Ethernet
  devices when they are not sending or receiving any frames. They are
  unipolar positive-only electrical pulses of a nominal duration of 100
  ns, with a maximum pulse width of 200 ns,[5] generated at a 16 ms time
  interval (with a timing variation tolerance of 8 ms). These pulses are
  called link integrity test (LIT) pulses in the 10BASE-T terminology,
  and are referred to as normal link pulses (NLP) in the
  auto-negotiation specification.
A device detects the failure of a link if neither a frame nor two of
  the LIT pulses is received for 50-150 ms. For this scheme to work,
  devices must send LIT pulses regardless of receiving any. Three bursts
  of Fast Link Pulses, used by autonegotiating devices to declare their
  capabilities.
Auto-negotiation uses similar pulses labeled as NLP. NLP are still
  unipolar, positive-only, and of the nominal duration of 100 ns; but
  each LIT is replaced by a pulse burst consisting of 17 to 33 pulses
  sent 125 µs apart. Each such pulse burst is called a fast link pulse
  (FLP) burst. The time interval between the start of each FLP burst is
  the same 16 milliseconds as between normal link pulses (variation
  tolerance of 8 ms). How a link code word (a 16 bit word) is encoded in
  a fast link pulse burst
The FLP burst consists of 17 NLP at a 125 µs time interval (with a
  tolerance of 14 µs). Between each pair of two consecutive NLP (i.e. at
  62.5 µs after first NLP of the pulse pair) an additional positive pulse may be present. The presence of this additional pulse indicates
  a logical 1, its absence a logical 0. As a result, every FLP contains
  a data word of 16 bits. This data word is called a link code word
  (LCW). The bits of the link code word are numbered from 0 to 15, where
  bit 0 corresponds to the first possible pulse in time and bit 15 to
  the last.

Edit for the dumbed-down, plain-English version from Fluke, per your comment:

In regular English, auto-negotiation is simply the method used by two
  devices to achieve the best rate possible of transmission. It allows
  them to discuss in a sense, the possible rates of transmission, then
  pick the best one that they both share. They do this by swapping
  advertisements of their own abilities using pulses called Fast Link
  Pulses (FLPs). The FLP lets one link partner know what the other is
  capable of. As they swap FLPs, the two stations detect the highest
  common denominator between them, according to the following:

1000BASE-T
100BASE-T2 Full Duplex
100BASE-TX Full Duplex
100BASE-T2
100BASE-T4
100BASE-TX
10BASE-T Full Duplex
10BASE-T

For example, if station A and B are auto-negotiating with each other,
  and A is capable of 10/100/1000 full or half duplex, but B is only
  capable of 10/100 full or half duplex, then the highest common link
  rate is 100, at full duplex. As long as both sides are negotiating,
  the link will operate at the highest possible connection rate between
  them.
Comment: Note that the auto-negotiation always selects link speed according to *advertised* capabilities. If your link has poor quality (e.g. poorly made connectors), the auto-negotiation method will not automatically select slower standard and you'll get lots of re-transmissions instead.
Answer: The auto-negotiation protocol will attempt to link at the fastest speed available on both ports.   Back in the day when there was still half-duplex, full-duplex would be preferred.
You didn't mention what operating system you were using but there will be a tool (like ethtool for Linux) to determine what capabilities each port advertises.  Generally the same tool will also tell you what link speed you ended up with.
In case you were wondering, it is not possible to have link partners running at different speeds.


Sample size for entire population to determine sub population?

Question: Let's say a bus company has 500 markets with an average of 10000 passengers each day but some markets as large as 100000 and some as small as 300. How would I determine the simple random sample size of the entire population so that with 95% confidence I could determine if demand in a given market increased by 10%?
Comment: I think you're treating all markets as the same and you shouldn't. For example, if you sample 100,000 people from the population, you may get 0 from a certain market. With that, you cannot say anything with certainty about that market where you sample nobody. You can either treat each market as different units or each market as essentially the same thing but your final results will either be in reference to the population or each specific market. Which are you attempting to answer.
Answer: Both... It looks like the government ran into a similar issue.  See page 30 in the link below. http://www.regulations.gov/#!documentDetail;D=DOT-OST-1998-4043-0070
Another secondary issue is that most of the market sizes are fairly similar in size but have very different price points (distribution is not normal) so even a large sample from a MOE standpoint doesn't result in the sample matching the population...


Why do exports include only hard products?

Question:
Looking at country lists by exports.
Diving into exports always shows things like gas turbines, computer hardware, petrolium -- all physical things.
None show things like exporting services: financial services, engineering consulting, licensing software. I would imagine that would be a considerable component in countries like UK. In some countries medical tourism might bring considerable revenue.
If traditional export metric is for hard products only is there a metric that encompasses service export as well? And is there any data on account balance (export - inport) of countries with services included?
Answer: Found a fairly nice one from OECD. It includes combined trade in goods and services as a percentage of GDP. It is also possible to drill into goods only (which seems most commonly presented in the public domain) or services only data.
Comment: So the answer to your question is that exports do include services and the question was based on a mistaken assumption?
Comment: It seems it is a fuzzy definition and normally what is meant by exports only includes hard products which is misleading.
Comment: @A.L.Verminburger Every definition of total exports I have seen includes services. As a result, this answer does seem to answer the question, and it would be best to mark the question as answered.


How can I merge two memberships in the same contact (without losing contribution info, etc)?

Question: Occasionally, we end up with a single contact that has two membership records (e.g., an old expired one and a newer current one). I would like to programmatically merge the two memberships cleanly, so that, for example, the remaining membership gets the oldest start date, the current membership type, all contributions are retained, etc. Have browsed Dedupe.php looking for a call that might do this, but to no avail. Any suggestions?
Answer: Currently there's no support for what you're describing built in to CiviCRM.  You could implement this with API calls in an extension.  If you do, please consider submitting it to the extensions directory!
Comment: You will have to create the api to merge... which will use the api to update the first membership, move all the contributions from the second to the first membership and then delete the second membership.
Comment: I would do this, but it's not clear what API calls would enable this. Looking in the API Explorer, for entity Membership, there's no option to "merge" (or anything that looks like that).
Answer: I've started to work on a patch for CiviCRM (as it's not that simple to implement this as an extension). The work-in-progress PR is available here. Comments and feedbacks are welcome ;)
Olivier;
Comment: The PR https://github.com/civicrm/civicrm-core/pull/11298 if I am reading right solves the merging of memberships between contacts, which is great! but not within a contact.


Skipping Grades Music Theory

Question: Is it possible to skip straight to Grade 5 Theory? Will be skipping to Grade 5 piano, and would like to continue to Grade 6 Piano.
Comment: Just to be clear, you should probably mention which exam board(s) you're talking about.
Comment: You can likely skip the exam, but don't skip the content.
Answer: I imagine it's what a lot of folk do. I certainly did - take grade V theory as a passport to practical VI+. It's obvious that knowledge of the previous grades' content will be more than a bit important though.
It may well be dependent on the board used. In U.K. all of the exam boards require a grade V theory pass before continuing with practical above grade V, but it may not be so in other parts of the world and other boards.
Answer: You can do that. It is not required of you to do grades from initial level up to grade 8 level, but in most cases it would be beneficial to you to do all the grades to equip yourself for the next grade. I have done grades 1 & 2 theory, years ago. I can't remember which grade I stopped at but I am continuing from next year with grades 4,5 and then 6 and perhaps up to grade 7 maybe, but I think if you go through Trinity College of London there is a entry level of grade three at least. Perhaps read the website and see what they say.
Trinity College London
Answer: Sure.  I think you can even skip straight to Grade VIII theory if you want.   There's a Grade V theory requirement for higher-grade practical exams, but none for theory exams AFAIK.

Skipping Grades Music Theory


When to create a brand style guide?

Question: Should we create the brand style guide before or after we design the touch-points (like stationery, marketing material, website, etc)? Why? Is there any rule on when it should be created? Thank you.
Comment: no rule. do what makes sense for your project.
Answer: In my opinion that is not an isolated part of the job.
You can not create a visual guide if you have not experimented designing something, let us say the business card. Then this gives you a clue of some basic elements: complementary colors, aditional fonts, some use of space, elements, that can now be part of the guide.
Then you use this aditional elements and see how they react to let us say, a letter head. And so on.
So in reality they starts to build up together.
Answer: The purpose of the brand guide is to explain the design intent and possibly rationale to a wider audience so that they can replicate it. This happens when you have many people in the loop that have different needs.
Usually a bigger organization needs a guideline as there is a much wider need for collateral. In a smallish organization its pretty easy to numerate the kind of documents you need. Perhaps you need just stationery, brochure, a webpage and a e-mail footer, that's it. This can be easily done for you. But in a bigger company you might need, a dozen of poster templates, report templates, stationery for 20 departments, 30 webpages, 20 apps, marketing collateral (pens, boxes, usb drives, shirts, jackets, caps etc.), 5 different CAD drawing frames (electronics vs mechanical etc), product packaging, product design, laser etching templates, manuals, signs for your buildings, building maps, company cars and lorries, name plates... you name it. In addition you will be rolling many separate sub brands and marketing campaign regular intervals.
Thus, it is not possible for each and every design to be done by same person, or even one person to familiarize themselves with all that has been done. So to coordinate many designers to be coherent, and look like one entity you need some help. This is where brand guides start to kick in. The more diverse you are the better guides you need (which is why googles guide is so comprehensive, otherwise you would not recognize androids as android).
So you want one when you have many persons doing separate design activities and you feel like making your work more cohesive would make you more recognizable. Remember also that there are many different levels of brand guidelines, from light versions to very comprehensive. Sky is the limit, as is how much it costs you.

When to create a brand style guide?


What would be better tags for "What is Bitcoin?"

Question: What is Bitcoin? is currently tagged with exchanges, which doesn't seem very fitting. What would be better tags for the question?
Answer: A while ago, a new tag introducing-bitcoin was created. It is aimed at collecting "questions about methods and resources used to present Bitcoin to a person without prior knowledge of Bitcoin."
I've tagged What is Bitcoin? with introducing-bitcoin which is a better fit than exchanges, although it is not a perfect match.


elementary OS flatpak repository

Question: Does elementary OS have a flatpak repository of the curated apps from its AppCenter? I'd like to be able to use some applications from the elementary OS AppCenter without having to overhaul my operating system.
Answer: Not yet.
All curated apps for AppCenter are currently built as .deb packages. There is a plan to work on moving them all to Flatpak. But this work hasn't been completed yet, mostly due to the fact that there was a team due to go and work on this in person, but it got delayed due to Covid-19.
So there's no definitive date yet of when this will be available.

elementary OS flatpak repository


Interpreting multiple correspondence analysis

Question: I am interested in exploring how different characteristics of national pension systems are related to each other. I have used MCA for a dataset in which the rows are countries and the columns are different features of pension systems. However, I am not sure how to interpret the distances between points in the SPSS Joint Plot of Category Points. Using a symmetrical normalization, do the distances between points representing categories of different variables say something about how these categories are associated? Does a shorter distance mean a higher level of association?
Comment: If you have only rows and columns (a 2-way table), then it is called simple correspondence analysis, not multiple
Answer: The standard visualisation is the biplot.  The interpretation depends on the details of the technique applied but will usually lean on some notion of inner product. But since I don't know what SPSS does when you ask for MCA then I hesitate to offer more concrete advice.  Nevertheless you'll surely find all you need to interpret them in the (free) book Biplots in Practice, specifically chapters 9-10.
However, if you're wondering how to interpret its output then you might profitably first revise your theory of correspondence analysis.  Greenacre's CA in Practice is a good applied text.  Ch. 9 covers biplots and ch. 16-20 revise the multi-way extensions of simple correspondence analysis (they are short chapters).  That should provide enough background to see what SPSS is offering you.
As @ttnphns points out, a two way table implies simple rather than multiple correspondence analysis.  Then things are indeed easier (but still see references above).


What makes Tzitzus Possul?

Question: What is the bare minimum for Tzitzus to be Kosher? I know, for example that each corner needs 8 strings (but 7 is also Kosher). What about for example the five knots?
Comment: Bare minimum what? Number of strings? Number of knots? Length?
Answer: The five knots aren't a strict halachic requirement, but rather a custom. Technically, even one winding and one knot is enough. However, this should be relied on only in emergency cases, such as where it's right before Shabbos and there is no time to fashion the tzitzis properly. (Magen Avraham, Orach Chaim 8:19)
Answer: 7 strings is only kosher if the string is cut off until the last knot. If it is snapped further up then one must determine that there are 4 thumb-widths left of the string before the hole on the beged. 6 strings is also kosher if both strings that are snapped are on the same side of the last knot provided that one kept the 4 strings on each side clearly separated when tying the tzitzis in the first place. If a string is snapped by the hole where they are attached to the beged, without 4 thumb-widths of it remaining then that tzitza is posul.
(Kitzur Shulhan Aruch)
http://he.wikisource.org/wiki/%D7%A7%D7%99%D7%A6%D7%95%D7%A8_%D7%A9%D7%95%D7%9C%D7%97%D7%9F_%D7%A2%D7%A8%D7%95%D7%9A_%D7%98#.28.D7.99.D7.92.29
Answer: When you make them:  (assuming you buy kosher tzitzit- i.e. they don't come from a sheep which was worshipped as an avoda zara)

They are required to be 4 strings folded over.
They must be at lease a tephach long, and ideally 3 tephachim when they are folded over.
They must have been tied onto the talit- they cannot have been prepared before and then attached.
Ideally it should be 1/3 knots and loops, and 2/3 loose strings. Based on the measurements given above, ideally it should be at least 1 tephach knots and loops and 2 tephachim loose strings (but to be strictly kosher, they only need to have two knots and 3 loops).

-(Shulchan Aruch O"C 11:4-14)
If, after this point, they tear:

Every string (of the original four) must be long enough to be able to tie in a knot. Therefore, if one string tears all the way down to the knot, it is still valid. If two of them tear all the way down to the knot, we are concerned that perhaps they stem from the same string (remember, each string is folded into two) and the tzitzit are invalid. If, when you tie the knots, you keep track of which strings stem from which base string, such as by keeping one side of the original 4 on the same side of the knot, then even if 4 strings tear down to the knot (on the same side of the knot), as long as the other four are long enough to be tied in a knot, they are still valid.

-(Shulchan Aruch O"C 12:1)

What makes Tzitzus Possul?


Do electrons have some volume, area or shape?

Question: I am in 8th grade now and when I was in 6th grade, my science book had diagrams of the electronic configuration of atoms. The electrons were round like spherical balls. Is it true that the electrons have some volume, area or shape and they revolve around the nucleus?
Comment: Pictures are simplifications and should not be taken as real representations of the properties of subatomic properties that are best described by quantum mathematics.
Comment: Related on Physics: [Do electrons have shape?](https://physics.stackexchange.com/q/119732/44126)
Comment: Not too say that even point particle are meaningless out of the exact domain where they are modelled in such a mathematical way. Within a molecule or atom, perhaps an electron itself has no size no shape but is surely better modeled by its wave function or the square of the latter.  These latter are quantum mechanical as well , have shapes and volumes, and are of relevance when chemistry is involved.
Answer: Quoting from the Nobel lecture of Hans G. Dehmelt (1989):

With the rise of Dirac's
  theory of the electron in the late twenties their size shrunk to mathematically
  zero. Everybody "knew" then that electron and proton were indivisible
  Dirac point particles with radius R = 0 and gyromagnetic ratio g = 2.00. The
  first hint of cuttability or at least compositeness of the proton came from
  Stern's 1933 measurement of proton magnetism in a Stern-Gerlach molecular
  beam apparatus. However this was not realized at the time. He found for
  its normalized dimensionless gyromagnetic ratio not g = 2

...

Similar later work at still higher energies found 3 quarks
  inside the "indivisible" proton. Today everybody "knows" the electron is an
  indivisible atomon, a Dirac point particle with radius R = 0 and g = 2.00....
  But is it? Like the proton, it could be a composite object. History may well
  repeat itself.

So there is no evidence that the electron is anything but a point particle, yet a non-zero size has not been ruled out either.
New Measurement of the Electron Magnetic Moment Using a One-Electron Quantum Cyclotron Phys. Rev. Lett. 97, 030801 (2006) (more-official link) shows that any radius of the electron is less than $10^{-18}$ meters.
See also the related webpage Limit on Electron Substructure
Comment: But from a QFT perspective, the electron isn't a point particle because it isn't in any one place. It's a wave that's necessarily spread out over some volume depending on its state.
Comment: @Shufflepants Strictly speaking there is a theoretical question about the effective volume of an idealized free electron, truly unaffected by interaction with the universe. But this is probably only an asymptotic scenario in the real universe.
Comment: @Ian I believe the wave function of a free electron truly unaffected by interaction with the universe slowly spreads out over time. That is as time goes on, the size of the spherical region that contains >50% of the distribution "mass" grows without bound over time. My point is that from what we know now about QFT, all indications point to them being spread out excitations in a quantum field, not little balls or little points.
Comment: @Shufflepants Well, particle/wave dualism hasn't gone anywhere. You can't say it's not a particle at all.
Answer: Atoms are composed of a positively charged nucleus and an outer shell of negatively charged electrons. When two atoms come into close proximity, their electron shells repel, preventing the atoms from sharing the same space. The "volume" of an object can generally be understood as the total measure of space that is unavailable for other objects to occupy, as the electron shells of the atoms of the two objects would repel, preventing the intruding object from entering that space.
This macroscopic conception does not apply to an electron. However, there are other measures of an electron that can be considered analogous to the dimensions of macroscopic objects. For instance, quantum mechanics states that all objects exhibit both wave-like and particle-like behavior (although, for larger objects, the wave-like behavior is insignificant). When an electron is analyzed as a wave, that wave has a wavelength, which is called the electron's "de Broglie wavelength". There is also a phenomenon called Compton scattering for which there is a characteristic length that is used in modeling the interaction between a photon and an electron. One could also ask "For what distance would putting two electrons at that distance require more energy than the mass-energy of the electrons?"
All of these, as well as other quantities, can in various sense be considered the "size" of an electron. To what extent these quantities "actually are" the electron's size is a matter of opinion. Some people consider one or more of these quantities to be the size, without any qualification, some consider them to be merely analogous to the concept of size, and others consider them to simply be quantities that are completely distinct from the macroscopic concept of size.
One thing to realize about science is that we use various words in everyday language without bothering to come up with a precise definition of what those words mean. We just have an intuitive sense of the general meaning of words. So when we start doing science, we build off of everyday language, taking everyday words as inspiration for precise terms, but we often have definitions that can be more or less precise than everyday meanings, or only loosely connected. For instance, "energy" in everyday meaning can refer to a wide array of concepts, such as "optimism", "enthusiasm", "friendliness", etc., but in physics it's much more precise. "Salt", on the other hand, in everyday meaning refers specifically to table salt, but in chemistry it is used more generally for ionic compounds. Words can have different definitions that are equivalent in everyday use, but they are distinct when we try to apply them to more exotic situations.
So while "Do electron have volume" may sound like an objective question, if we really look at it, it has to be understood as "Do electrons have a property that corresponds to the 'normal' concept of 'volume'?", and that question depends on how exactly one understand the "normal" definition of volume, how one defines that concept precisely, how one extends that concept to the microscopic realm, and what one considers to be a valid "correspondence".
It is generally accepted that physical laws are the same regardless of direction, and other than spin and some narrow symmetry breaking, electrons haven't been found to act different depending on direction. Which implies that electrons don't have a "shape" in the sense of "looking different" from different direction. So, if they are modeled as having a shape, it makes sense to have that shape be a sphere, possibly pictured with a vector representing spin.
Also, saying that they "revolve" around the nucleus is a simplification. Position and velocity are, somewhat like volume, concepts for which there are rough analogues in quantum mechanics, but they aren't quite the same. In a spherical orbital, an electron has a certain probability of being observed at each location, and this probability is the same for all points at the same distance from the nucleus. So even though the electron has a quantity that is referred to as "velocity", it is some sense not moving (in the sense that the probability of it being found in a particular location is not changing over time). Even though the electron's wavefunction is "moving", the magnitude of the wavefunction is not changing, and so it is both moving in one sense, and not moving in another. Actually explaining this clearly requires getting into quantum mechanics.
Comment: Reading this, I don't see an actual, clear, literal answer to the question, for an 8th grader. Would you mind adding "no, by our current knowledge, eletrons do not have a volume, area or shape in the sense you are probably thinking about" at the top, or something like this?
Comment: In fact in the spherical shells, the *most* likely place for the electron to be found is in the middle of the nucleus. Where the Bohr radius for that shell (the place where the simplified models pretend that the electron is orbiting at) is just the spherical shell that contains 50% of the distribution mass. That is, the chance of interaction with that electron inside or outside that shell is 50/50.
Comment: @Shufflepants : Er...  The maximum likelihood location of the electron is in the shell, slightly inside the Bohr radius.  The average location of the electron is at the center.  The average need not be particularly likely.
Comment: @EricTowers Hmmm, yeah, I guess I don't understand the difference between the distribution function and the density function. http://www.umich.edu/~chem461/QMChap7.pdf
Answer: Missing from detailed answers above, in wikipedia page on electron
https://en.wikipedia.org/wiki/Electron ,

Observation of a single electron in a Penning trap suggests the upper limit of the particle's radius to be $10^{−22}$ meters.
Comment: As a generic classical physics observation, if an electron does not have volume but has mass, isn't that implying that it has infinite density?


Routing from Raspberry WiFi interface to Ethernet

Question: I have Raspberry Pi (with osmc), turned on Tethering from WiFi to Ethernet. Raspberry is a WiFi client on my home WiFi network with IP 10.0.0.15 and gateway 10.0.0.138. I have connected MyBookWorld NAS to Raspberry Ethernet, the eth0 has IP 192.168.0.1 and NAS have 192.168.0.2. When I ssh to Raspberry over WiFi, ssh email@example.com, I can ping NAS with ping 192.168.0.2. But I can not ping NAS from my other WiFi clients like Mac with IP 10.0.0.6. Routing to 192.168.0.2 does not work, probably because WiFi subnet is 255.255.255.0.
I believe it would be a piece of cake for someone to advise me how to access NAS at 192.168.0.2 from 10.0.0.x clients through Raspberry as router. Thank you very much!
Comment: the issue is nothing to do with the network MASK of 255.255.255.0 ... how does your 10.x.x.x network "know" where to find 192.168.0.x? For a start, you need to set routing on your 10.x.x.x network to route traffic for 192.168.0.x to 10.0.0.15
Answer: I assume you are using a Raspberry Pi 3B/3B+ with Raspbian.
The problem is not the RasPi. The problem is the home WiFi router with ip address 10.0.0.138. It does not know that it has to send ip packages with ip addresses from 192.168.0.0/24 to the RasPi so that can forward it to the NAS. You have to set a static route on the home WiFi router to the RasPi with destination 192.168.0.0/24 and with the gateway/next hop 10.0.0.15.
If you do not have access to the home WiFi router or if it doesn't support setting static routes then you could use a bridge on the RasPi that would bridge interfaces wlan0 and eth0 so all devices incl. the NAS have all ip addresses from 10.0.0.0/24, means they are all connected to the same subnet. But the problem here is that the on-board chip does not support bridging of a client WiFi connection so we have to use workarounds. But they are not very easy to setup. Keywords here are NAT, port forwarding or proxy arp.
Another solution would be to invest into a USB/WiFi dongle that supports WDS/4addr, so you can bridge the WiFi client connection.
As you see, the best solution is setting a static route on the home WiFi router if possible. Tell me if you are not able to it.
Comment: Thanks very much! Configuring static route on wifi router solved the problem.
Answer: You didn't mention whether you've enabled IP forwarding on the Pi. Edit /etc/sysctl.conf, uncomment the line that has net.ipv4.ip_forward=1 commented out, and reboot.
Comment: setting forwarding on the pi won't allow devices on the 10.x.x.x network to magically know where to route traffic for 192.168.0.x
Comment: Indeed. I read the original question a bit too quickly. The WiFi router needs to have the routing established, as the answer above indicated.


Have you considered that eventually most questions will be repeat questions?

Question: Very few questions can not be answered by searching the web, and if repeat questions are not allowed. The site will slowly move from a forum to a data base. Is the site concerned about this?
Comment: Why would we be "concerned" about that? If we truly reached a point where we cannot think of a question anymore that is not a duplicate, then I'd say that is a *tremendous accomplishment*, not something to be concerned about (although I don't believe that will ever happen).
Comment: @Lambda It's hard to say it's a "negative" question -- downvotes here on Meta just mean people don't agree with the question. So, the downvotes are a sign that people don't think what you raised is a problem.
Comment: It's worth taking a look at the number of question on Stack Overflow. Of course, they have a lot of repeats, but every week still see a multitude of good *new* questions as well.
Comment: I think people like live events and interaction. The concern would be a growing silence on the question boards and the lack of interaction between the people.  But it sounds like good new questions are not in short supply so it's not an issue.  I don't understand why this is viewed as a negative question though
Comment: The Stack Exchange sites are ***not*** forums (see e.g. ) (fora?). They are think tanks (ref. ).
Comment: Related: http://meta.physics.stackexchange.com/q/7181/2451
Answer: It was never a forum to begin. The goal of the site is to provide high quality Q&A from experts in the field. If we've answered every question, then mission accomplished.
But since science progresses, we will never be able to keep up with the questions at the leading edge of it. If science stops progressing and there is nothing new in the broad areas covered by the site, then there's a lot more to worry about than the future of the site here.
In other words, I'm not concerned about it.
And maybe to clear up another point of concern -- yes, most things can be found by using your favorite search engine. But unless the first hit, with the most comprehensive and accessible approach to answer your question, is not this site, then there's still work to be done. If you can get your answer by stitching together a few Wikipedia articles and some Yahoo Ask questions, cool. But that doesn't mean that question (and the resulting researched answer) shouldn't appear here too, as a single, authoritative source.
Comment: One thing I'd add to this answer: I see the role of this site as _complementing_ existing standard resources, rather than becoming a truly comprehensive resource on its own. That is, if a question is already perfectly well explained on Wikipedia (for example), and we could give a great answer by just quoting the Wikipedia page, there's no need to have that question here. Where we come in is when somebody is confused about something in the standard resources and needs clarification beyond that, or when the standard resources don't address a question well enough.
Comment: @lambda, just to air tpg, check this mother Meta post: [Is Stack Overflow a forum?](http://meta.stackexchange.com/questions/92107/is-stack-overflow-a-forum).
Comment: Thanks for responding to my question so quickly. I'll start to think of it as a Q&A rather than a forum.
Answer: I think that a certain density of repeat questions is a good thing, and should be supported.
The reason I think this is that repeat questions encourage new answers, and the answers may not be repeats.  It's tempting to say 'but physics is a hard science, there's only ever one right answer', but I think that's not true: new answers can present and encourage new ways of thinking about an existing area, and that's a good thing.  This is why, for instance, new textbooks on old areas of physics can still be interesting.
One answer to this is 'well, you can just add new answers to old questions'.  However, if old questions already have accepted answers then any new answer is extremely unlikely to be accepted.  So anyone interested in reputation is thus going to be put off by that.  Of course, one could then argue that, well, you should not be interested in reputation: that's nice in theory but, in fact, people are interested in reputation and the whole site is predicated on that.  Thus not allowing duplicates is likely to actively suppress new answers.
So I think a certain, not too high, ratio of repeat questions should be allowed.
Of course, this is just my opinion.
Comment: Well, to get new answers, we don't need to "allow" repeat questions. We currently close them as duplicates, and people who think they have an answer that adds something over the answers given at the older question can follow that link to the duplicate and add their own answer there. I've personally done so several times and it is good to avoid duplication of effort by giving an answer to the repeat question only to discover someone wrote almost the same years ago already.
Comment: @ACuriousMind: I realised that, of course, the reputation system means that people will almost certainly be less likely to add new answers to old questions than to new ones (see edit to my answer).  I don't expect this will change your mind, of course.
Comment: @ACuriousMind I think an actual study of typical users might be informative (you being very far from such, as probably am I).


how much RAM for heavy static content serving?

Question: I want to make a server for my static content.
I need to serve some 3-10 mb files - a lot. (I will also put on this server some .js and .css and images from my websites).
I thought of nginx and G-WAN ( http://trustleap.com/ ).
What I don't know is what resources are needed for serving static content? How much RAM is used for each file transfer?
If I will go with a 256 mb (or 512 mb) VPS with good port and huge bandwhich how many hits /seconds will I be able to serve (3-10 mb files)? (I know "it depends" - but please give me a rough estimation based on experience or theory).
There are not a lot of files, just often downloaded - should I consider caching, or this will only use my memory needed for serving hits?
Comment: Question: How much RAM is needed? Answer: Enough.
Comment: As much as you can afford.
Comment: Possible duplicate of [How do you do load testing and capacity planning for web sites?](http://serverfault.com/questions/350454/how-do-you-do-load-testing-and-capacity-planning-for-web-sites)
Answer: If you're using nginx, then you're talking just a few KB of overhead per active connection. If you're using something like Apache, you'll have one thread per connection, which means hundreds of KB or even megabytes per connection.
However, nginx does not support asynchronous disk IO on Linux (because async disk IO on Linux is basically horribly broken by design). So you will have to run many nginx worker processes, as every disk read could potentially block a whole worker process. If you're using FreeBSD, this isn't a problem, and nginx will work wonders with asynchronous disk and network IO. But you might want to stick with Apache if you're using Linux for this project.
But really, the most important thing is disk cache rather than the web server you choose. You want lots of free RAM so that the OS will cache those files and make reads really fast. If the "hot set" is more than say 8 GB, consider getting less RAM and an inexpensive SSD instead, as the cost/benefit ratio will likely be better.
Finally, consider using a CDN to offload this, and getting a really cheap server. Serving static files is what they do, and they do it very fast and very cheaply. SimpleCDN has the lowest prices, but MaxCDN, Rackspace, Amazon, etc. all are big players at the low end of the CDN space.
Comment: To anyone from the future.. nginx does have thread pools https://www.nginx.com/blog/thread-pools-boost-performance-9x/
Comment: Is this info still correct 6 years later?
Comment: Unfortunately yes, async file  IO on Linux is still broken by design in 2016 (limited to uncached full block reads and writes). Useful for database servers but not much else. To my knowledge nginx has not implemented a user-space thread pool to emulate general-purpose async file IO on Linux. https://lwn.net/Articles/671649/
Comment: Thanks for all the info. So, if I chose FreeBSD or other UNIX should be ok to serve what I need (1 - 10 TB) from a vps with less memory using nginx? What about windows?
Comment: Makes me wonder what software CDN's use though it could be nginx with freebsd...anyway it appears that if you use nginx + linux, and frequently exceed the RAM disk cache (a rare case?) there is an "offload i/o to threads" module as of 1.7.11: https://www.nginx.com/blog/thread-pools-boost-performance-9x/ I agree that just getting more RAM would help as well, to keep more disk cached in the page file.
Comment: @rogerdpack: Cloudflare and MaxCDN are both known to use nginx on their edge-facing machines. Both blog about it frequently.
Answer: If the OS can cache the hot part of the content into ram, it will not use the disk and will serve things really quickly. Hundreds of request per second should be possible on a VPS, you will most likely saturate the network well before you run into CPU limits.
If the content does not fit into ram, then disk IO (seek, throughput, filesystem fragmentation) will come into play and the equation changes.
The webserver will add a memory overhead per client, but nginx can do that in a few kilobyte per connection.
Hope these pointers can help you.
Comment: Per open connection they require some memory. 10 concurrent requests (at any time there are 10 tcp connections open sending/receiving the file) will require 10 times a few kilobytes. This has nothing to do with the contents, so the 5MB does not apply here.
Comment: Thanks, but what is not clear to me is if there is memory overhead per connection: i.e. if nginx or gwan consumes memory for every hit? If I have 10 request of a 5 mb file in the same time, will this mean there will be 50mb memory used for serving it? Maybe + memory for threads (I don't know if nginx or gwan uses threads for evey connection).
Answer:
what resources are needed for serving static content?
  How much RAM is used for each file transfer?

First, for the same number of workers, G-WAN v4.7+ is using far less RAM than Nginx at startup:
> Server 'nginx' process topology:
---------------------------------------------
  6] pid:21228 Process RAM: 0.77 MB
  5] pid:21229 Process RAM: 2.44 MB
  4] pid:21230 Process RAM: 2.44 MB
  3] pid:21231 Process RAM: 2.44 MB
  2] pid:21232 Process RAM: 2.44 MB
  1] pid:21233 Process RAM: 2.44 MB
  0] pid:21234 Process RAM: 2.44 MB
---------------------------------------------
Total 'nginx' server footprint: 15.39 MB

> Server 'gwan' process topology:
---------------------------------------------
  6] pid:6054 Thread
  5] pid:6053 Thread
  4] pid:6052 Thread
  3] pid:6051 Thread
  2] pid:6050 Thread
  1] pid:6049 Thread
  0] pid:5839 Process RAM: 2.19 MB
---------------------------------------------
Total 'gwan' server footprint: 2.19 MB

G-WAN uses threads (one per core typically), Nginx uses processes (one per core typically), and processes drag more overhead, require synchronization via shared memory, etc.  Both use the "asynchronous" model of event handling.
Note that here G-WAN can automatically grow to more than 1 million of concurrent connections while Nginx is limited to its worker_connections settings (defined at only 4096 in the ab.c test above).

what is not clear to me is if there is memory overhead per connection: i.e. if nginx or gwan consumes memory for every hit?

The short story is that G-WAN v4.7+ (where in-memory caching is disabled by default) consumes much less RAM than Nginx, for all file sizes, while serving more requests per second.
The long story is that while Nginx consumes more and more memory even with new HTTP keep-alived requests, G-WAN's memory usage can stay stable for HTTP keep-alived requests, and it grows far less than for Nginx with non-keep-alived requests.
Our weighttp wrapper ab.c measures the memory consumption of the server application and of the system for the duration of the test. And it shows that Nginx puts a heavier weight on the system regarding the memory resources consumption.
This is due to the way each web server is handling requests and allocating memory.

If I have 10 request of a 5 mb file in the same time, will this mean there will be 50mb memory used for serving it? Maybe + memory for threads (I don't know if nginx or gwan uses threads for evey connection).

Both servers (Nginx and G-WAN) use sendfile() so the kernel (rather than the application) is allocating the resources for I/O.
The web servers will still allocate resources, but that's for maintaining the context of each connection rather than to buffer disk I/O.
Therefore, the momory consumption depends on the size of the file chunks sent at each sendfile() call rather than directly on the total file size.
The totfile size has an influence on the long-term for high concurrencies, but that's due to the amount of chunks that need to be cached by the kernel.
Any more question, drop us a line at G-WAN. We have heavily invested in CDN-like applications.


Photo Competition Topics

Question: The Drones and Model Aircraft Photo Competition is designed to bring the community together while having a bit of fun. Each contest will have a set topic. If you have any topics that you would like to see in an upcoming photo contest, please leave them below in an answer.
Answer: Two topics that I think would be cool are Aerial landscape (any picture of a landscape taken with a drone/model aircraft), and Custom budget build (A drone/model aircraft that you built on your own with inexpensive parts).

Photo Competition Topics


Will 0.5mm gap/play in a seatpost shim work without cracking the seatpost tube?

Question: I have a Day 6 ebike; it's a large frame--the Samson model. The seat post (the frame member) is 31.4325mm or 1.2375 inches (I.D.) at the clamp collar. The seatpost (the seat support post) is likewise on the O.D. I would like to switch to a more comfortable seat, and the seats I'm looking at require the old-school seat clamp that bolts to a 7/8 inch end post atop the seat post. With me so far? These seat posts come in 25.4mm (1 inch) and 27.2mm (1-1/16 inch) seat posts (with the 7/8 inch seat mount at top). If I switch seat posts, I will need a seatpost shim; either 25.4mm to 30.9mm or 27.2mm to 30.9mm. There is no seatpost shim for my existing Day6 size: 31.4325mm--it is an odd ball. Here is the question: using either of these shims will leave a gap of 0.5325mm (31.4325 - 30.9mm = 0.5325mm)between the shim and seat post tube inner wall. The next size up, 31.6mm, is too large to fit. So, if I use a 30.9mm shim in my 31.4325mm seatpost tube, will I be able to tighten the seatpost collar/clamp without cracking the tube frame (aluminum alloy)? Anybody have experience with this? The ebike weights 54 lbs and I weigh 195 lbs. Thank you!!
Comment: It took me 20 seconds to find multi listings for a 31.4 seat posts and another 10 for shims.  By looking (presuming he looked) for a 31.4325mm post or shim, the OP has not been able to find the products he needs. That is important
Comment: Cane Creek do a 27.2 ID-31.4mm OD shim https://www.universalcycles.com/shopping/product_details.php?id=27081, but don't use a shim, just buy a 31.4 seat post.  Dozens of 31.4OD Shims and posts listed on ebay
Comment: Is there any reason you can't simply switch the saddle and leave the correct seatpost mount in the bike  ?  99% of saddles use the same rail connection.
Comment: The engineering tolerances are completely screwed up. Seat posts are manufactured in 0.1mm increments, probably 0.05mm tolerances, certainly no more accurate than 0.01mm. Why on earth (let alone how) would you measure seat tube to 0.1 micrometer accuracy (100 time more accurate than the manufacturers would use). At these levels of precision, the temperature  the reading was taken at is important.
Comment: @mattnz So what if he reported more accuracy than need in the measurements.
Answer: To answer the question of whether you can get away with the .5mm gap, absolutely not. It probably won't be able to clamp securely, and even trying it once could destroy the seattube opening. Bikes are essentially never tolerant of this type of mismatch.
I presume you are in this spot because you want to use a seat like a double-rail Brooks or similar that requires a pipe-style seatpost, as opposed to a more common cushy seat, most of which come with a usually-superfluous clamp that can be removed in the case of a post that has its own clamp. If that's the case, I think all you need is a 27.2-31.4 shim, which is oddbal but does exist.
Answer: You're stuck looking at a small selection of seatposts because you are focused on getting one with a 7/8" top.  Presumably you think you want to attach a seat which has a clamp like this:
http://www.jensonusa.com/Velo-78-Single-Rail-Saddle-Clamp
But every standard bicycle seat made in the past several decades uses a twin-rail system with standard spacing and almost-standard rail diameter.  So don't look for 7/8" topped posts, look for any post that fits your frame, then attach any standard seat to it using the standard twin rails.


As a Spanning Tree Protocol Programmer, how will I know when the root bridge ID election is over?

Question: I am trying to implement IEEE 802.1D. I know how the root bridge id is elected.
Initially, every switch will advertise that they are the root bridge.
Next, it will check whether the bridge ID received in BPDU is lower than it's bridge ID or not. Based on which has a lower bridge Id, it will either forward or stop advertising the root bridge ID. I can implement this part in Python.
However, I am unsure when will I know when the election is over. Like, how will I know that each device knows the root bridge ID in the network? Once it is completed, I can assign ports block, forwarding based on root path cost.
Comment: That's why STP has timers for the different stages.
Comment: Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
Answer: The election is over when you say it's over.  In other words, each switch decides on its own when to start forwarding.  That decision is made when timers expire.  Depending on the circumstance, that can be Forward-delay timer, or Max-age timer plus twice forward delay.


Which Omega theme should I use with Drupal 7?

Question: I need to use the Omega theme framework. I find there is two different versions: Omega 3 and Omega 4.
Which one should I use with Drupal 7?
Answer: There are Drupal 7 versions of both, so you can choose either. As of writing the 4.x branch is actively maintained, and 3.x not so much.
The 3.x branch will hold your hand a lot more, and make a lot of decisions about how you want to work. This may be or ideal, or may be frustrating. SASS support is clunky and a bit of a pain to work with, if I'm honest. Its main 'selling point' is that you can configure most of the options it supports through the UI.
The 4.x branch is much more of a developer-focused solution. Very little UI, but it incorporates a full front-end stack of tools for development/asset management. If you're a developer, this will likely be the one for you.
This is what the docs have to say:

Whether you should use Omega 4.x or Omega 3.x depends on several considerations:

Do you rely on the user interface for building layouts, or are you comfortable defining layouts in code in a tpl.php file? Omega 4.x does not include the elaborate layout definition UI that was a hallmark of Omega 3.x
Do you want to use a theme that is under active development, or are you comfortable with a theme that is minimally maintained? Omega 3.x is minimally maintained. In all likelihood, unless a new maintainer steps up to the task, Omega 3.x will not be upgraded to Drupal 8.
Are you comfortable with or willing to learn SASS, or do you want to stick with straight CSS? Omega 4.x does NOT require use of SASS but certainly is much easier to implement if you adopt SASS.

Beyond that, the only way you'll get a satisfactory answer is to install and try both.
Edit: to add a bit of balance to the above docs (thanks @FreeRadical for the info):
The 2nd point (claim?) is hotly disputed. It has been written by the Omega 4.x team who currently holds "ownership" over the project pages. This is a bitter dispute and there are negotiations currently taking place which probably will get the project page rewritten soon.
Sounds like fun :/
Comment: @Clive, the text you quote from the project page, and in particular "Do you want to use a theme that is under active development, or are you comfortable with a theme that is minimally maintained? Omega 3.x is minimally maintained. In all likelihood, unless a new maintainer steps up to the task, Omega 3.x will not be upgraded to Drupal 8" is hotly disputed. It has been written by the Omega 4.x team who currently holds "ownership" over the project pages.  This is a bitter dispute and there are negotiations currently taking place which probably will get the project page rewritten soon.
Comment: May I customize the css in easy way either omega 3.x or omega 4.x
Comment: Yes you can customise the CSS easily in both; neither force you to use the SASS stack to the best of my knowledge. But if you're serious about responsive development it's an essential thing to learn. If you're not interested in full on SASS/Compass/Susy development, Omega 4 would make less sense IMO. But theat's _my_ opinion based on _my_ experiences. You need to give them a run out to be sure
Comment: Thanks @FreeRadical wasn't aware of that, I've quoted you in the answer so that gets some visibility
Comment: The LESS module works quite well with Omega 3, including the way it handles the sheet stacking for the breakpoints.
Answer: On Omega 3.x vs. Omega 4.x - Comparing Apples and Oranges, you can read:

Whether you should use Omega 4.x or Omega 3.x really depends on how much you want to rely on the user interface for building layouts as this is no longer included in the 4.x branch. If you are okay with a possible lack of documentation and the fact that Omega 4.x does not come with a layout builder as 3.x did then you should definitely prefer the 4.x branch.

It is really a matter of personal taste/skills and of course the form of the project. I am using Omega 3.x, and it suits my purposes perfect. I don't have any really experience with Omega 4.x, and when i got between those two for a new project, after research and testing, I stick to 3.x, since it behaves much nicer (in my eyes) with very useful theming modules like Delta. As mentioned, it is a matter of requirements and personal view.
I propose you should take a look at the comparison done in the linked page.
Answer: Both are created for Drupal 7, and both are responsive.
Due to an "disagreement" about policy and future direction within in the Omega development community, the project has - in effect - been split in two (Omega 3.x and Omega 4.x).  These two branches are maintained by two completely separate groups of maintainers, and should be regarded as two different projects.

Omega 4.x is a base theme framework aimed at themers who want to gain full control over the theme through code, rather than a user interface.
Omega 3 is best suited to those who like to build their themes through the user interface.

Omega 3 is the original version and has about 55 000 installs for Drupal 7.  It is stable and mature. It works well, but do not expect much new development.
Omega 4 is a recent development.  It only has about 6 000 installs for Drupal 7.  It is currently much more "dynamically" maintained than Omega 3.
Both are solid platforms. Which one to use depends on whether you like to do your tweaks and adjustments through a GUI (Omega 3), or interact with the code of templates and CSS or SASS (Omega 4).
Answer: At the time I am writing this, there are 3 branches for Drupal 7:

7.x-3, with a 7.x-3.1 version used from 47538 sites
7.x-4 with a 7.x-4.4 version used from 13144 sites
7.x-5 with a 7.x-5.0-alpha1 version used from 3134 sites

Despite the 7.x-4.4 version being suggested by the project maintainers, that is not the most used version, even though it was released on July 21, 2015 (3 years after the 7.x-3.1 version, released on February 19, 2012). The 7.x-5 branch will not have an official release (which means a version that is not alpha, beta, or a release candidate) before the 8.x-5 branch (whose development snapshot was last update on October 16, 2016).
So, after two years, the choose is still between branch 7.x-4 and 7.x-3, for which the most important difference is (IMO), the presence of a user interface to tweak the theme in the branch 7.x-3. If you are comfortable with editing the code of templates, CSS, and SASS files, then you can consider using branch 7.x-4, which was also updated more recently than the other branch.
If then you would be interested in updating to Drupal 8, you could consider the 7.x-5 branch, even though the 7.x-5.0-alpha1 version was released on October, 2014; it seems rather behind the 8.x-5.0-alpha7 version which was released on  July 25, 2016 (almost two years later).
IMO, at this point, it is still too early for thinking about using the Drupal 8 version of the theme.


Basic Logic: Presuming Truth

Question: Given my belief that X is false, is it still possible for me to agree that if X were true, then Y?
Comment: Could you maybe say a little more about why you think it might and/or might not be the case?
Answer: Yes, absolutely.
This is a common technique in both informal and formal logic.
In informal logic, this is called "ex hypothesi"
In more formal treatment, this is exactly how a conditional proof works. i.e, we make an assumption and then wind up with a "If this assumption is true, then ..." as our conclusion.
Answer:
Given my belief that X is false, is it still possible for me to agree that if X were true, then Y?

It would unavoidable using classical logic. ~X => (X => Y) is a tautology. You can prove it with a truth table. In fact, it corresponds to the last two lines of the truth table where X is false. It doesn't matter whether Y is true or false.
Knowing nothing about Y, not even if it is true or false, we can infer from X being false that X => Y will always be true. Y seems to come from out of nowhere and yet this is a legitimate, commonly used method of proof (the so-called Principle of Explosion -- from a falsehood, all things follow). I often use it myself.
Comment: +1 For the link to the truth table software and the statement of the proposition.
Answer: This is a part of the mathematical and philosophical proof concept of reductio ad absurdam, which consists of proving that A implies B and that B is false.
For example, the Wikipedia article uses the concept of the smallest positive rational number.  If there was one, we could divide it by 2 and still have a rational number which will be smaller than the smallest one.
Comment: RAA is given by [~A => [B & ~B]] => A.

Basic Logic: Presuming Truth


How do I find the El Al and AA equivalent booking reference for an Iberia-managed reservation?

Question: I have booked a reservation with Iberia. It is ticketed and paid for, and contains flights with El Al, BA, AA, and Iberia. The flights on IB and BA can be changed on the BA or IB sites with the booking reference or linked to my Avios. I would like to view the reservation on the El Al and AA websites to change the seating on those flights. The IB reference does not work on those sites.
Answer: Using Check My Trip.
You can use Check My Trip from Amadeus to view the record locators for other airlines, if the prime PNR record is on Amadeus. In this case Iberia uses Amadeus so (unless a travel agent issued the ticket) you can indeed use the Iberia PNR.
The website is a bit clunky. Click on the red "Login" button which takes you to the main page (you don't need to have an account). Enter your Iberia booking reference and last name. This brings up the master record.
To find the El Al locator, scroll down to an El Al flight and click View Details.
You may find that there are several record locators for the same airline, depending on the complexity of your itinerary.

Using My Flights.
If you have an iPhone or iPad the My Flights app is an essential companion for the frequent traveller. It will show a detailed breakdown of any Amadeus PNR and will alert you if the airline makes any change to your PNRs. There is also a web version at http://www.myflightsapp.com/. However, you do need to sign up.
Comment: i tried check my trip and under the Confirmation Number it says Iberia and the a 5 digit alpha-numeric. this number doesnt work on either the LY or AA sites
Comment: It gives you only an Iberia number under the LY flight's details tab? [I'm not talking about the main confirmation number that appears at the top of the PNR.] In that case you'll have to call Iberia to ask. Good luck.
Comment: Emailed them, got the locators


Should deleted old catalog after merging two old catalog into new in abode lightroom?

Question: I having problem. i have few collection of lightroom catalog from my past work.Now i want to merge all catalog's into one and delete rest of all except keeping that one fresh.
But i am confused, is it safe to deleted all catalogs and there will be no need of old catalogs anymore.. and how to do it with lightroom 5.
Answer: It's perfectly safe to do.  Lightroom is non-destructive.  All the details about changes are stored in the lrproj files.  Once you have moved the data you need out of the lrproj file, there is no reason you need to keep the old lrproj or any of the cached files around, so long as you keep the original image files on which the catalog depends.
To avoid making errors, I suggest renaming the files and folders that you think you can get rid of and then checking for missing images in your new project.  As long as everything works correctly, you then know it is safe to remove the files you renamed.
Comment: thank you, now my problem is how to merge them and delete older in lightroom 5 version?
Answer: As I began to use Lightroom for much of my photographic work, I began to hate the LR catalogs.  So here's a hybrid workflow that I think you may find better for large archives and libraries.
Simply make a new catalog for each event.  Since I shoot many hundreds of images at an event, creating one large LR catalog slows down my whole workflow.  Making one per event allows me to work quickly and keep multiple catalogs that are small and purpose built.
Comment: thank you, i will keep it in mind and i think for small work  i will make a mix catalog but for big singal collection will make different :)


Can I sacrifice an enchantment when it is going to be destroyed?

Question: My opponent had an Elvish Lyrist and activated its sacrifice to destroy my Seal of Fire. I sacrificed Seal of Fire after that. Would my Seal still do its 2 points of damage?
Answer: Yes you can sacrifice the Seal of Fire to do 2 points of damage.
When the Lyrist activates its ability, that ability doesn't happen right away, it's put on the stack. While on the stack, you have the chance to respond, and so you activate Seal of Fire, doing 2 damage.
Then Lyrist's ability tries to resolve, but since the enchantment isn't around anymore, it fizzles, but the costs stay paid (mana and sacrifice).
Comment: The process of putting the Elvish Lyrist activated ability on the stack includes paying the costs (Green Mana, Tapping the Elvish Lyrist, and Sacrifice Elvish Lyrist). It will be gone before priority shifts to the controller of Seal of Fire.
Answer: Yes. Activated (and triggered) Abilities are independent of their sources. The typical analogy is of a hand grenade: If a soldier throws a grenade, and then is shot, the grenade will still explode.
As long as you activate the seal of fire's ability before the enchantment is destroyed (such as, in response to the effect that would destroy it), the effect still triggers (and does the two damage). In addition, the Elvish lyrist's effect would be countered upon resolution (because Seal of Fire is no longer a valid target), though this is of little importance, because the elf has already been sacrificed.
This works because abilities do not resolve instantly once activated. Instead, they are put on the Stack. When an item (be it an ability, trigger, spell being cast, or most anything else) goes onto the stack, each player gets an opportunity (called priority) to respond to that item.
In this case, Elvish Lyrist's ability is activated and placed onto the stack. You (along with any other players in the game) will receive priority in turn. While you have priority, you may activate Seal of Fire's ability in response. It goes onto the stack (above Elvish Lyrist's ability). Once each player has passed priority, items on the stack resolve in the reverse of the order they were placed there (ie, First in, Last Out). Additionally, each player will receive priority after each item on the stack resolves; so a player could choose to cast a spell after seal of fire's ability deals damage, but before Elvish Lyrist's ability resolves.
Comment: While true, abilities existing independently of their sources isn't really the reason this works. It's just a matter of the stack, activating Seal of Fire in response to it being targeted. If objects had to still exist for their abilities to work, Seal of Fire wouldn't work on its own either.
Comment: Also fun to note you *can't* respond by targeting the Elvish Lyricist with the Seal of Fire (if for some reason you wanted to), since the sacrifice is a cost and not an effect, so the elf is already dead by the time you can respond.
Comment: No, but I believe that it was the source of confusion. Regardless, I have edited my post to explain exactly why this works.
Comment: I dunno about that - if you know how the stack works the question wouldn't even occur to you. You'd know that you can use Seal of Fire entirely as normal while Elvish Lyrist's ability is still waiting around on the stack. Thanks for editing, anyway.
Comment: I like the grenade analogy.


Restricting a program's access to the Windows registry

Question: Is it possible to prevent a certain program from accessing the Windows registry? I know there are ACLs to lock out a user, but what about per-executable control?
Comment: Nope, because it's the account that the program's process is running as that writes to the registry on its behalf.  Which program is it that's you're trying to block?  What registry keys are you trying to stop it writing to?  Depending on what part of the  registry you're trying to prevent writing to, you could potentially just deny everyone.  But to me, this smells like an [XY Problem](http://xyproblem.info); what's the ACTUAL problem you're trying to solve by blocking the registry writes?
Comment: In linux you can apply Mandatory Access Control mechanisms to apps via systems like SeLinux and AppArmour, but in windows everything is user based. see here for more details:  https://msdn.microsoft.com/en-us/library/windows/desktop/bb648648(v=vs.85).aspx
Comment: @Ƭᴇcʜιᴇ007 True. There is Mandatory Access Control in Windows too, and Low integrity may be helpful here.
Answer: Sorry, that's not possible, at least not to the extent you seem to want. As mentioned in the comments by Ƭᴇcʜιᴇ007, all of Windows access control is based on users. Every process has a token attached to it, which determines what user it's running as. There is no difference between you performing an action and a program running under your account performing that action, since you do literally everything through one process or another. "Programs don't attack users; users attack users."
Besides, virtually every process accesses the Registry. Even if the program itself doesn't explicitly do any Registry access, an examination with Process Monitor reveals that every GUI app starts with a boatload of Registry reads to figure out how to set up the graphical controls. Run Process Monitor on an app you think doesn't need the Registry; you'll be surprised.
But if you want to block all writes and only writes, there actually is something that may help. Windows has a concept of "integrity levels", a part of UAC. Basically, a program running at a certain integrity level can't write to objects labeled with a higher integrity level. Normal processes and normal files (and Registry keys) have the Medium integrity level, but you can manually launch processes with the Low level. Download the PsExec tool. If you wanted to create a command prompt that can't write to normal places, run this:
psexec -l -i cmd

The -l switch sets Low integrity; the -i switch makes the process interactive. The resulting command prompt can only write to places specifically marked as Low integrity.
C:\Users\Ben>reg add HKCU\Test
ERROR: Access is denied.

That command works in a normal command prompt, but not this kind of locked-down one.
Answer: Another solution is to use Sandboxie. This program can execute any process inside sandbox, so that any change to the system made by that process can be undone.
Answer:
Go to the folder that program wrote in the registry (HCU/HLM..\Run) like:
"C:\Users\aaa\AppData\Roaming\BloatInstall\Annoying.exe"

Rename that program to a new name, like:
"Annoying.exe" -> "noMoreAnnoying.exe"

Create then a folder with the former name in the same directory
"Annoying.exe" (an empty folder)

Change your shortcut so it targets the new executable file name:
"C:\Users\aaa\AppData\Roaming\BloatInstall\noMoreAnnoying.exe"

You won't need to edit the Windows Registry anymore. When that program
tries to auto-start, it won't be able to.


Controlling bot using video and image processing

Question: I am going to start a project on controlling robots using hand gestures.
Though I have used MATLAB for this purpose earlier, I realized it is extremely slow for any practical real-time system.
I am currently planning to use OpenCV for this purpose.
I want suggestions on, if OpenCV is the best alternative, are there any other alternatives and if I use OpenCV, which language should I go for, C, C++ or Python?
Comment: Do you mean "real-time system" in the sense that you're using an [RTOS](http://en.wikipedia.org/wiki/Real-time_operating_system), or is it just that MATLAB isn't processing enough frames-per-second for your application?
Comment: Reading your question again, it sounds like you're hesitating to even try MATLAB before ruling it out as "too slow".  What gesture-recognition technique do you plan to use in MATLAB that you know in advance to be too slow to be practical?
Comment: No as of now the project is not using an RTOS
Answer: Though I did not use hand gestures, I used color based object tracking for my undergrad project. I did it through MATLAB as at that point of time I had no idea about Open-CV. I am guessing you will have a laptop for image processing and send commands run-time to your robot.
Ok first thing, sending serial commands though the serial port / USB port / wifi to your robot will be damn easy (at-least in the computer part - sending). You can do your gesture recognition using low resolution say 240*240. This will be fast considering a moderately new machine. MATLAB is itself not slow. It is your implementation and algorithms used which determines slow or fast.
Now if you want to do the entire thing in a mobile platform say Android, MATLAB is out of the question. Or if you are using any embedded platform then Open-CV is the way to go. You will have to code the communication part of things too as OpenCV does not have any serial communication or related toolbox. But even with Open-CV your implementation and algorithms will determine slow or fast.
In open-CV 2.0 the new C++ interface is much better and also faster than the old openCV 1.0 functions. You also have OO with OpenCV 2.0 and using CVMat is much more related and easy like MATLAB than the native IPLImage interface.
Answer: If starting out with programming use C/C++ as most of the examples using OpenCV on the internet use that language but there are interfaces for many other languages. I.E. Java, Python, C++, C
More details: http://opencv.org/


Text analysis : What after term-document matrix?

Question: I am trying to build predictive models from text data. I built document-term matrix from the text data (unigram and bigram) and built different types of models on that (like svm, random forest, nearest neighbor etc). All the techniques gave decent results, but I want to improve the results. I tried tuning the models by changing parameters, but that doesn't seem to improve the performance much. What are the possible next steps for me?
Comment: What is your task? Classification? Summarization? Information Retrieval?
Answer: Natural language data is usually "noisy" because of the problems like synonymy (different words have the same meaning) and polysemy (the same word has different meaning). You can try to "de-noise" this data by applying dimensionality reduction techniques.
One possibility would be to apply SVD to decompose your document-term matrix as $D = U \Sigma V^T$. If you keep only $k$ largest singular values and approximate $D$ as $D \approx U_k \Sigma_k V_k^T$, what you will get is called "Latent Semantic Analysis": it discovers "latent" concepts in the data set. So you can apply this to your problem and see if it gives a better solution or not.
In scikit learn it would be something like this (code from here):
hasher = HashingVectorizer(n_features=n_features,
                           stop_words='english', non_negative=True,
                           norm=None, binary=False)
vectorizer = make_pipeline(hasher, TfidfTransformer())
X = vectorizer.fit_transform(dataset.data)

svd = TruncatedSVD(k)
lsa = make_pipeline(svd, Normalizer(copy=False))

X = lsa.fit_transform(X)

clf = MultinomialNB().fit(X, labels)

Alternatively, you can apply a different decomposition technique called "Non-Negative Matrix Factorization", which also gives an approximate solution $D \approx U V^T$, but all elements of $U$ and $V$ are non-negative.
In scikit learn (code from here):
tfidf = vectorizer.fit_transform(dataset.data)
nmf = NMF(n_components=k, random_state=1)
X = nmf.fit_transform(tfidf)

# do something with X

Comment: note that these techniques are usually applied to unigrams, I'm not sure if they're used for bigrams
Comment: Tried LSA and got better results. Are there any other NLP techniques which can be applied easily in python? Using nlkt maybe?
Comment: you can try doing some pre-processing of text data with NLKT (if you're not doing it already), e.g. remove stop words, lemmatize, etc.


Are there any related groups of satellites that are in a line of 6 or more in a row?

Question: 02/03/20 0450hrs, in Bradford, West Yorkshire, Uk. I saw a satellite going across the sky, it was not too bright and was followed by another and then 4 more they were equally spaced. I would say they were 2-4 miles apart, a third of the sky apart if that makes sense. They were travelling West to East, they were following the same trajectory and following a straight path.
Does any one know what this could have been?
Answer: Very likely you have seen Starlink Satellites. A view we all have more often in the future...
Assuming you mean 0450 local which is more or less greenwich-time which does not differ much from UTC.
Just one thing: They are around 100 km appart ;-)
Plot for 02/03/20 0450hrs, Bradford, West Yorkshire, UK. click for full size view
Comment: `+1` for the snazzy plot!
Answer: Yes, loads! You can see the StarLink trains at Heavens Abve:
Answer: Supplemental answer to

Are there any related groups of satellites that are in a line of 6 or more in a row?

Yes No, (while) the A-train is a bunch of satellites in a row, it seems that Wikipedia says there are only 5 even though the picture shows six.

The A-train (from Afternoon Train) is a satellite constellation of five Earth observation satellites of varied nationality in sun-synchronous orbit at an altitude of 705 km (438 mi) above the Earth.
The orbit, at an inclination of 98.14°, crosses the equator each day at around 1:30 pm solar time, giving the constellation its name (the "A" stands for "afternoon"[2]) and crosses the equator again on the night side of the Earth, at around 1:30 am.
They are spaced a few minutes apart from each other so their collective observations may be used to build high-definition three-dimensional images of the Earth's atmosphere and surface.

Did you see the A-train?
Ignoring the not six problem, it's still probably not, because they move in a polar orbit so would be North-South or South-North, and the highest passes would be 1:30 AM local time (the other half of the Sun-synchronous 1:30 PM orbit)


What are the recommended vaccines for travel to Thailand?

Question: I think i'll be staying in Chiang Mai, Phuket and Bangkok. I'm from the UK.
Answer: Britons can look to the NHS's Fit for Travel website, which provides detailed health recommendations for most countries.
NHS recommended immunisations for Thailand include the following:

Confirm primary courses and boosters are up to date as recommended for life in Britain - including for example, vaccines required for occupational risk of exposure, lifestyle risks and underlying medical conditions.
Courses or boosters usually advised:   Tetanus.
Other vaccines to consider:   Cholera; Diphtheria; Hepatitis B; Japanese Encephalitis; Rabies; Typhoid.

Also see the guidance on the risks of malaria, dengue, and zika, among others.
Answer: CDC has pages on this for many countries.  For Thailand, they recommend Hepatitis-A and Typhoid, in addition to the "routine ones" everybody should have.
And then, depending on where you go and what you do, they offer half a dozen others.
Answer: According to Spain's Health Ministry (link in English but recommendations in Spanish :| Spain, you know...):

Mandatory vaccines: yellow fever vaccine for those coming from places with yellow fever transmission risk. You are from the UK, so it doesn't apply to you.
Recommended vaccines: just the ones already included in the official vaccination program. Your family doctor might recommend additional vaccines depending on your health record.
Paludism: while most of Thailand is safe, there's risk of paludism transmission in the borders with Cambodia and Myanmar, so you are warned to take precautions if you are travelling to those areas. Most cities like Bangkok, Chiang Mai, islands like Phuket, etc. are safe.

Now to the personal experience: I've been to Thailand without taking any additional vaccines beyond the ones I already took 20+ years ago. It was a (wonderful!) road trip: several places, rural villages, some street food, some wilderness, etc. We had zero problems regarding diseases.
However, we did have a medical problem, because the sun in Thailand is freaking strong -- even for a Spaniard used to 40 Celsius in summer. My wife got a heat stroke! So make sure you wear sunscreen at all times, a hat, and even a long-sleeved t-shirt wouldn't hurt either.


What are limitations of Universally Composable (UC) framework?

Question: I am beginning to read some UC framework papers, and I guess it is similar to the simulation-based security analysis. I can understand the main advantage of UC is to assist us to analyze the composable protocol. But I am wondering what are the main limitations of UC? I note that it is non-trivial to transform simulation-based security (or game-based security) into UC security. But does there exist compiler to transform form simulation-based security to UC security.
Comment: One limitation is that the notational extraganza of UC leaves you drunk with jargon and unable to stand on one foot or write a straight line.
Answer: "Simulation-based security" is a very general notion. UC security is much more specific - it refers to a simulation-based security proof in the UC framework. As such, simulation-based security encompass the UC framework, which is a particular case of it, and there is no general transformation from any primitive with a simulation-style security argument to a UC secure primitive.
One of the main limitations of the UC framework is that it's strength - arbitrary composability features - also gives rise to strong impossibility results: many important cryptographic primitives are provably impossible to realize with UC-security in the plain model, hence one must rely on trusted setup assumptions, such as the common reference string model, to build protocols in the UC framework.
Arguably, a second limitation is the relative complexity of the framework, which is not so easy to understand and master in depth - although there are now countless examples of proofs in the UC model to look at, as well as simplifications of the model such as simple UC.


Can I change glass transition temperature (Tg) and impact resistance with additives?

Question: I have three different HDPE polymers with different melting index but they don't have any elasticity. Physical form of polymers is granules. Can I change glass transition temperature (Tg) and impact resistance with additives?
Comment: Welcome to chemistry.se! If you have questions about how to beautify your posts, have a look at the [help]. Do you want to know more about this site, please take the [tour].
Comment: No. Buy a suitable Polyethylene.
Answer: The glass transition temperature depends on the cooling rate and molecular weight distribution and could be influenced by additives:
Most liquid plasticizers are low molecular weight organic materials with a glass transition temperature in the range of $125-225^0\text{C}$. When this kind of additives is added to an organic polymer, the result is a weight averaging of the glass transition temperature between that of the polymer and that of the plasticiser if they are miscible. The reduction of the the glass transition temperature of a polymer by the plasticiser is usually about   $5^0\text{C}$ per weight percent of plasticiser.
Impact modifiers ( a kind of additives) can affect the impact resistance of a polymer. Impact modifiers are key additives for
increasing flexibility and impact strength
to meet physical property requirements of
rigid polymers. All impact modifiers are elastomeric or
rubbery in nature, with a lower modulus
than the host polymer. The dispersed
rubber phase acts to absorb or dissipate the
energy of impact in order to stop craze or
crack propagation.
Comment: Plasticisers don't work in PE, because they do not dissolve. You could try blending with some low Mw LDPE.


Pump suction and discharge sizes

Question: I am looking to buy a centrifugal monoblock pump for my laboratory. The suction and discharge sizes are mentioned as 12mm x 12mm. Does anybody know what does it mean? Does it mean 12mm OD, or does it mean 1/2" BSP?
Comment: Hi Abhishek, welcome to engineering.SE!  Can you add a link to the specific pump you are looking at?  The specified dimensions can vary by manufacturer, and a link will help add context for those who aren't familiar with 'centrifugal monoblock pumps'.
Answer: Centrifugal pumps typically go by nominal pipe size for the inlet and outlet connections.  The first number is typically the inlet, and the second is the outlet.  Normally the outlet is smaller (which is why you'll see 10"x8" centrifugal pumps but never 8"x10").  This is partly due to mechanical efficiency and partly to get a justifiably higher pressure. However in small sizes such as this one, both connections are the same.

Pump suction and discharge sizes


Nitrosation of benzene

Question: How does benzene react with $\ce{NaNO2/HCl}$? Will $\ce{PhNO}$ be obtained? I read that pyridine can be produced under special conditions, but what will happen in some less exotic conditions?
Comment: Afaik, $\ce{NO^+}$-cation is too weak as electrophile to react with benzene, nitrosobenzene is obtained indirectly.
Answer: As you noted, the link you provided was to a reaction run under rather exotic conditions (low-temperature plasma). Under more everyday laboratory conditions, for example, in solution, activated aromatic rings can react with $\ce{NO^+}$ as shown below.

However if there is a ring-activating amino substituent present, then the $\ce{NO^+}$ will react with the nitrogen to produce the synthetically important diazonium ion.

Nitrosation of benzene


Autoload Error: Module has been already defined

Question: This error shows up when I do the following:

DL and paste this extension under DIR>vendor>magento-japan folder m2-jplocalize
Run the following command:
composer config repositories.veriteworksartifacts artifact \vendor\magento-japan
composer require magento-japan/m2-jplocalize
php bin/magento setup:upgrade
Then this error shows up:
Module 'Veriteworks_Region' from '\vendor\magento-japan\m2-jplocalize/region' has been already defined in '/vendor/veriteworks/m2-region'.

Where did I go wrong? Is this the correct way to install this extension?
Answer: No, it's not. Skip the first step, composer already downloads the extension in step 2


Why are motherboards designed for servers generally larger than regular motherboards?

Question: Why are motherboards designed for servers generally larger than regular motherboards? Usually servers come in larger form factors, why?
Answer: You can find server boards with 2-4 CPU slots, 16 ram slots, etc. This takes extra space. I also am guessing it has something to do with many servers being in rack mount chassis instead of desktop boxes.
Comment: Also to add RAID Risers, SCSI cards and other and other stuff.
Answer: Servers require air flow adequate to how much heat they could generate. Racks do a lot to help the air flow, and if you take a look inside a server with that in mind, it'll make more sense.
Additionally, of course, what Skaughty said is correct: you can put more hardware in there, so .. You need more room.


Where Were S.H.I.E.L.D. In Iron Man 3?

Question: Why didn't The Avengers and S.H.I.E.L.D. agents show up to help Tony in what was very clearly a dire hour of need?
Comment: Just a minor nitpick, but i might be wrong anyway, but I don't think there is an *Incredible Hulk* post-credits scene. The tony stark bit takes place just before the credits, I think. I might be wrong though!
Answer: Spoilers for Captain America: The Winter Soldier, Iron Man 3, Thor, Agents of SHIELD below.
SHIELDs absence explanation:

 In Captain America: The Winter Soldier we learn that Hydra secretly infiltrated SHIELD in the early days of it's formation, and have been shaping world events ever since, including the death of Howard Stark and the assassination of JFK. They specifically mention that they have been funding terrorist groups, and as such it is safe to say that the 10 Ring Terorrist group (which turns out to be AIM) were funded by Hydra, and as such their activites were being masked from SHIELD from with in. This is further backed up by Hydra having access to Extremis in Agents of SHIELD (although at first they are at known as Centipede in early episodes).

As for The Avengers:

 Captain America, Black Widow and Hawkeye all work for SHIELD, and as such wouldn't have known this was occuring as it could have been hidden from them. Thor was off world fighting the rebellion caused by the Bifrost being destroyed in Thor. However, Bruce Banners location thoughout what is known as "Phase 2" of the Marvel films is still currently unknown.
Answer: Thaddeus's answer to another question:

 Thor lives in Asgard most of the time. Until they repair the
technology/magic which creates the Rainbow bridge, I suspect commuting
is out of the question. The Hulk: As seen in the Avenger's
movie, it is likely the Hulk spends his time as far away from other
people who know who he is as possible. An eight hour window probably
makes getting his attention challenging. Nor is he known for his
subtlety. The last thing you want is HULK SMASHING his way toward the
problem you are trying to sneak up on. Hawkeye and Black
Widow are both SHIELD operatives and could easily be on assignments
anywhere on the planet. While they might be perfect for the job, they
could just as easily be in Kazakhstan doing a secret operation.
Captain America, currently a fellow out of time, is probably being
brought up to speed and likely living in a SHIELD base while he
catches up on the last sixty years of history. He would likely be very
concerned if he knew of the kidnapping but no information had been
made public at the time, so he would not be mobilized either.

Kevin Feige, Marvel Studios President stated in an interview:
Journalist: After cell phones came out horror directors had to come up with elaborate ways to explain why people wouldn't call someone on a cell phone for help, now that all The Avengers know each other do you have to come up with excuses for why Tony Stark wouldn't reach out when he needs a hand?
Feige: It's a good question, and it's sort of half and half. I am betting that like the comics you don't have to keep – if you are reading a standalone "Iron Man" comic, they don't spend every page explaining where every other Marvel hero is. The audience kind of accepts that there are times when they're on their own and there are times when they are together. I'm betting that movie audiences will feel the same way. That being said, there is a little bit of lip service here and there to that. There is also just the very nature of Tony wants to, once he barely survives that house attack you saw today, and even you saw it in the message he left for Pepper, he's basically saying "I'm going off the grid to try to figure something out."
Comment: Downvote because you should really try to add something, not just copy Thaddeus's answer (and you've copied other answers or external sources elsewhere).

Where Were S.H.I.E.L.D. In Iron Man 3?