At what size does a bigger solar sail stop increasing your acceleration?

Question: Is there a point where the larger solar sail would not add more thrust? What is the most thrust a solar sail can produce?
Can a solar sail be added to an ion engine and work better?
Comment: A bigger solar sail always adds thrust. The thrust/weight ratio may become a problem though, so the question is, 'at what size does a bigger solar sail stop increasing your acceleration'.
Answer: As long as other variables are held constant (such as the orientation with respect to the direction to the sun, reflectivity of the sail surface, etc.) the force produced by a solar sail is always proportional to its area—at least, until the sail size gets rediculously large, a significant fraction of the distance to the sun!—so bigger always produces more thrust. The area referenced is the area of the sail projected onto a plane perpendicular to the direction to the sun; if you turn a solar sail edge-on to the sun, you won't get much thrust!
But, as @Hobbes says, even though more area produces more force, it doesn't always produce more acceleration, which is what's important.
Solar sails have a figure of merit—a performance spec—of the amount of mass it takes to make a unit area of the sail: the areal density. Given the areal density $\rho$, the mass of a sail is $\rho \times A$, where A is the total area of the sail.
The maximum thrust a sail can produce (oriented face-on to the sun) is a function of its area, its reflectivity, and the intensity of sunlight falling on it: $$F = \frac {Io A} {r^{2}}\frac{1+R}{2}$$ where F is the thrust; Io is the force produced on a perfectly reflecting surface of unit area oriented face-on to the sun, at a distance of 1 AU; A is the total sail area (without any projection effect); r is the heliocentric distance (easiest if you use AU); and R is the sail's reflectivity, 0 for perfectly absorbing and 1 for perfectly specularly reflecting—for diffusely reflecting surfaces R is smaller than 1.
Holding everything constant except area, this reduces to $$F = k A$$ where k is a constant determined by all the other factors: $$k = \frac {Io} {r^{2}}\frac{1+R}{2}$$
The acceleration produced by a solar sail is just the force produced divided by the total mass of the spacecraft, which is the sail's mass plus the mass of everything else, call it Msc:$$Acc = \frac {k A} {\rho A + Msc}$$When the mass of the sail ($\rho$A) is roughly the same as, or smaller than, Msc, increasing the sail area increases the acceleration. But if you make the sail huge, many times Msc, then increases in the sail area barely affect the resultant acceleration. As the sail mass gets much, much larger than Msc, Msc becomes negligible, and the acceleration equation approaches $$Acc = \frac {k A} {\rho A} = \frac{k}{\rho}$$ or the force per unit area divided by the mass per unit area. This is called the characteristic acceleration of the sail, and is the quantity that sets the limits of a solar sail's performance.
This is the net result: as a sail attached to a fixed spacecraft mass is made larger, the craft's acceleration potential asymptotically approaches the characteristic acceleration, but can never meet or exceed it.
Note: solar sails oriented this way generally don't gain much energy—or any, in the case of a circular orbit. Solar sails are most effective at adding net energy when the force vector aligns with the spacecraft's velocity vector, which is almost never radially away from the sun.
Comment: https://space.stackexchange.com/questions/28386/can-a-solar-sail-be-added-to-an-ion-engine-and-work-better
Answer: As Tom Spilker showed, there comes a point where more sail adds almost nothing.  However, there's another factor: you don't just have a solar sail and a spacecraft.  In reality you need something to connect them together.  Yes, the forces are low but the lengths are long.
While the sail weight scales linearly with it's area (and thus thrust) the bigger the sail the heavier the cables become in comparison to the sail.  There will come a point where making your sail bigger lowers your acceleration.
Comment: Indeed, in my effort to keep it simple I oversimplified - thanks for the correction.
Answer: I am agree with @Loren Pechtel.
The math in @Tom Spilker answer doesn't tell about stiffness of construction materiel for solar sail. But when we scale the size of sail's structure we encounter square-cube law. (Scale Eiffel tower 10 times with all proportions - it will fall)
I am not a specialist in engineering and strength of materials, but I suppose as the sail size reaches several hundreds of meters (or, optimistically, several kilometers) - we'll have a problem that supporting constructions become too heavy.
Comment: Fortunately, almost all solar sail designs work entirely on tension, not compression, which makes things a lot more favorable.


Reference request for a proof of Ramanujan's tau conjecture

Question: In the Wikipedia article it states that Ramanujan's tau conjecture was shown to be a consequence of Riemann's hypothesis for varieties over finite fields by the efforts of
Michio Kuga, Mikio Sato, Goro Shimura, Yasutaka Ihara, and Pierre Deligne. Do their papers consist of the only published proof of this result? And is this proof of a similar level of difficulty to Deligne's proof of Riemann's hypothesis?
Comment: @commenters -- you should have left these as answers!
Comment: The proof of Weil => Ramanujan appears in Deligne's Seminaire Bourbaki 355 (incidentally the paper where he constructs the Galois representations associated to higher weight modular forms). It uses not much more than basic properties of étale cohomology.
Comment: You may find something useful in Katz, An overview of Deligne's proof of the Riemann hypothesis for varieties over finite fields, which appears in Proc Symp Pure Math XXVIII, Mathematical developments arising from Hilbert problems (1974) 275-305, MR0424822. According to the review, the author discusses applications to the Ramanujan-Petersson conjecture.
Comment: Have you tried the nice expository article "Modular forms, the Ramanujan conjecture, and the Jacquet-Langlands correspondence" by J. Rogawski, available on his web page:

http://www.math.ucla.edu/~jonr/eprints.html

?
Comment: Minor nitpick/question over wording: should "consist of" be "constitute"? http://forum.wordreference.com/showthread.php?t=1501780
Answer: Following the discussion at meta.MO, I'm going to post a good answer from the comments (made by JT) as a "community wiki" answer.  I should mention that the Rogawski article mentioned by Tommaso says almost nothing about the proof of Ramanujan's conjecture, but it seems to be a very nice introduction to Jacquet-Langlands.
Deligne reduced Ramanujan's conjecture about the growth of tau to the Weil conjectures (in particular, the Riemann hypothesis) applied to a Kuga-Sato variety, in his paper Formes modulaires et representations l-adiques, Seminaire Bourbaki 355.  I believe Jay Pottharst has made an English translation available.
Deligne then proved the Weil conjectures in his paper La conjecture de Weil. I.
As far as I know, all known proofs of this conjecture involve the use of cohomology of varieties over finite fields in an essential way.
Added by Emerton: One point to make is that the Weil conjectures (in their basic form,
saying that the eigenvalues of Frobenius on the $i$th etale cohomology of a variety over
$\mathbb F_q$ have absolute value $q^{i/2}$) apply only to smooth proper varieties.  On the other hand, the Kuga-Sato variety is the symmeteric power of the universal elliptic curve over a modular curve, which is not projective.  Thus one has to pass to a smooth compactification in order to apply the Weil conjectures, and then hope that this does not mess anything up in the rest of the argument.  A certain amount of Deligne's effort in
his Bourbaki seminar is devoted to dealing with this issue.  If you don't worry about this
(i.e. you accept that it all works out okay) then the proof is essentially just Eichler--Shimura theory (i.e. the relation between modular forms and cohomology of modular curves), but done with etale cohomology, combined with the Eichler--Shimura congruence relation that connects the $p$th Hecke operator to Frobenius mod $p$. (The latter was treated in the
following question.)


Remove correlated features before or after splitting test and training set?

Question: I want to remove highly correlated features before training my classifier. I am wondering if I should do this before or after splitting the test and training set. I don't immediately see how doing it before would leak test information into the training set, but I could very well be missing something. I'm also concerned that the split of the data will impact the analysis of correlation between features, though maybe in practice the likelihood of this is low. Anyone have any insight? Thanks!
Answer: By principle in supervised ML any decision which affects the model should be made using only the training set, in order to avoid data leakage. Following this principle requires the training/test split to always be done first.
Quite often the decision seems minor and has little chance to cause data leakage, like in your case. It's tempting to make our life easier and use the whole data for some pre-processing like this. However it's a good idea to follow this principle as strictly as possible not because the effect of data leakage would be huge, but because it would be impossible to detect it if it happens: when it happens, data leakage means that the performance on the test set is biased (overestimated), and there's simply no way to know by how much (except by collecting a new test set, of course).
Your concern that the split of the data could impact the analysis of correlation is a good example of the problem: suppose there would be a difference indeed. This means that there is data leakage, since the features are different depending directly on the test data. In this case the evaluation on the test set is likely to be biased.
Another way to explain the same idea is this: if something happens or doesn't happen in the training set by chance, then it's important to see if the model is able to focus on the real patterns and ignore the noise. The only way to obtain a reliable answer to this question is if nothing in the model depends on the test set.
Comment: Thank you this is very helpful and gives me some more insight on how to think about this question
Comment: What if how you split train/test affects the results of the preprocessing step? That is, say if you split train/test two times using two random seeds and get d/t correlation between the features? Also according to this answer https://stats.stackexchange.com/a/239390/223656 for a similar question, you do train/test splits right before you are about to build your model (step. 4 in the question) not before it. What do you think?
Comment: @xabush this is what I said in my amswer: if the train/test split affects the results, it means that there is some overfitting. It's better to know it by evaluating on a proper test set without any data leakage rather than to ignore it. I disagree strongly with this other answer, see also [here](https://datascience.stackexchange.com/questions/38395/standardscaler-before-or-after-splitting-data-which-is-better), [here](https://datascience.stackexchange.com/questions/54908/data-normalization-before-or-after-train-test-split)...
Comment: and [there](https://datascience.stackexchange.com/questions/53138/which-comes-first-multiple-imputation-splitting-into-train-test-or-standardiz/53146#53146). I could find many other sources: as I said in the answer, proper evaluation requires splitting before anything else to prevent any data leakage.


Setting a user's home directory on Mac OS X (Server) from the command line

Question: How can I set a user's home directory on Mac OS X Server using the command line?
Answer: As you asked how to do it from the command line, I take you can open a SSH session for the Mac OS X server, or you can open a terminal window directly from the server.
If this is the case, then execute the following command: sudo dscl . -change /Users/<username> NFSHomeDirectory <old-path> <new-path>; replace <username>, <old-path>, and <new-path> with, respectively, the user name, the old home directory, and the new home directory. The command -change requires the old value of the key being changed; if you don't know the old value, then you cannot do anything.
If you are not using any SSH session, or you cannot open a terminal window in the Mac OS X, but you can still access the server from another Mac, then the command is a little different.
The dot after sudo dscl is the datasource is described in the (dscl(1) Mac OS X Manual Page) as the following:

dscl operates on a datasource specified on the command line.  This may be a node name or a Mac OS X Server (10.2 or later) host specified by DNS hostname or IP address.  Node names may be absolute paths beginning with a slash ("/"), or relative domain paths beginning with a dot (".") character, which specifies the local domain, or "..", specifying the local domain's parent. If the hostname or IP address form is used then the user must specify the -u option and either the -P of -p options to specify an administrative user and password on the remote host to authenticate with to the remote host. The exception to this is if "localhost" is specified. Passing passwords on the command line is inherently insecure and can cause password exposure. For better security do not provide the password as part of the command and you will be securely prompted.

References

The manual page installed in every Mac (man dscl)
The online dscl(1) Mac OS X Manual Page.
Comment: If you have direct access to the server, then you can simply open the Accounts preference panel; selecting the user for which you need to change the home directory, and clicking with the right button, you will have access to the menu "Advanced options" that allow you to change the home directory, or select a new one. Take in consideration that, even using the preference panel, files are not moved from the old directory to the new one.
Answer: Warning: Experiment with this on an unimportant account or machine first; I have not tested this.
It can be done. Something like this:
sudo dscl . -change /Users/$USERNAME NFSHomeDirectory $OLDPATH $NEWPATH

Then, of course, to actually move their home directory folder to its new path, if you haven't done so already, use the following:
sudo mv $OLDPATH $NEWPATH

Alternatively, if you do not know the value of $OLDPATH, change by index as follows:
sudo dscl . -changei /Users/$USERNAME NFSHomeDirectory 1 $NEWPATH

Notes

dscl is the "Directory Services Command Line" utility
Don't worry that the key in question is called NFSHomeDirectory; that's a leftover from the heritage of the schema coming from LDAP

By the way, for this kind of thing, the Mac OS X Server Administration Guides (freely downloadable PDFs) are your friends, especially, in this case, the User Mangement one. It includes both the GUI and command-line ways to do many user management tasks. I believe the Open Directory Administration guide explains the schema.
Comment: Alas, links are dead.
Comment: @GrahamLeggett use web archive.org


Where to learn programming for mechatronics and overall?

Question: I have recently finished Matriculation and currently trying to build up certain skills I think will be useful. I have applied for university and one of the courses I am looking at is mechatronics. I was wondering if anyone had information on what programming languages to learn and where I could learn them (hopefully in a form that best fits a busy schedule and allows for me to pause and resume learning at my choice such as a video series on YouTube or something).
Comment: Mechatronics is a little further along in engineering course work. It's usually preceded by feedback control. This day and age, there are several, if not every, programming languages that drive mechatronic systems. That said, it's  typically some embedded language or something proprietary to a hardware manufacturer. IMO, play with an Arduino, learn C, and look up PID control examples. Matlab is also used to model/test control systems.
Comment: This is a resource finding question which isn't a good fit for the site.
Comment: Have you tried coursera.org or edx.org
Answer: Octave(free and open source) and Matlab(commercial and paid) are languages that are helpful in designing and analyzing control systems.
They both have scripting and modeling capabilities.
Also, there are several tutorials, sample scripts, and free lecture notes for them.
C++, Java or python could also be useful. But for engineering purposes, the simplicity of Matlab (or Octave) is a great advantage, compared to the learning curve of languages, i.e. visualization methods, finding and installing toolboxes etc for the programming languages.
Answer: I've taken the NI Labview Core 1,2 classes. They were very helpful. Labview also has a student version that is affordable, I believe I paid $60 USD for the license.
Arduino is another very great learning tool.
Answer: In my experience programming is something you can teach yourself from books etc very well, certainly well enough to get a good grounding in preparation for a course.
I taught myself C++ from a book designed for self learning and I found the learning curve to be not too difficult. I'm certainly not a particularly skilled programmer but it was enough to put together basic control software. I'm not sure how useful videos would be as it's not really a very visual skill. A lot of it is looking up specific ways to do specific tasks and getting familiar with the rules and  terminology of your chosen language.
As mentioned in the comments it is also sensible to look at control systems and feedback which involves some mathematics which is not especially hard but not immediately intuitive either at first and it can take a while to get a grasp of the relationship  between the theory and practical applications. Here even the most basic practical experimentation is hugely useful as being able to see the relationship between the functions and variables and the actual physical response is invaluable.
It is also worth looking at the nuts and bolts of how software and hardware communicate and interface with each other ie how you turn the output from a programme to a control signal.


Study methods for average IQ individuals, math and physics

Question: How should a person with 110 IQ approach studying? Particularly with math and physics. What are the methods (if any) that can be employed to compensate for my inherent inability to understand very advanced topics? Perhaps focusing on rote memorization in such a case? I'm looking for personal experiences and sources, if possible. Feel free to speak frankly.
Comment: An IQ of 110 doesn't seem to be average, but rather somewhere at the boundary of the upper 25% quantile of IQ distribution; see [here](https://en.wikipedia.org/wiki/Intelligence_quotient#Current_tests). Anyway, it seems like an utterly bad idea to take the result of some IQ test as a frame of reference when you try to find out how you should learn and what you are able to learn.
Comment: "my inherent inability to understand very advanced topics" That's not what IQ means.
Comment: How to study depends upon the individual, _and_ more than just their IQ. For example, if basing a study plan only upon test scores (a bad idea, but I digress) I would use working memory rather than IQ.
Comment: @JochenGlueck Regardless of the real utility of this question, while 110 might be higher than the population average, OP is comparing themselves to people who have started undergrad training.
Comment: Given you are on Stack Exchange, "smart and gets things done" should be the mantra (see Joel Spolsky). You are smart, but nobody learns anything without putting work into it.
Comment: @AzorAhai-him-: Admittedly, I'm not sure to whom precisely OP is comparing themselves - but anyway I don't think it's a good idea to explicitly formulate a sweepingly general claim, and leave the important qualification "within this or that peer group" implicit. Otherwise any fields medalist might write a question with the title "Research methods for people with average mathematical abilities like me", and if somebody complains they would add "well, average within the group of all fields medalist".
Comment: @JochenGlueck I mean sure, if you wanna go totally reductio ad absurdum. The point was why OP might have made that remark.
Comment: @AzorAhai-him- I agree with your reasoning why OP might have chosen that wording. My point was just that it would probably still be better to change the wording.
Answer: You seem to be interpreting the IQ test as an absolute unbreakable block to your understanding. It is no such thing. Don't try to excuse yourself from the need for hard work to understand deep things.
I was once told, based on a test, that I had the "ability" to do well in a junior college but would probably be frustrated if I tried to go farther than that. I later earned a PhD in mathematics.
No, rote memorization isn't going to take you terrifically far, though some of that may be needed. For the very young it probably is (6*7=42), but not later once the brain develops along with the ability to do abstract thought.
The key to success for most is to work hard but effectively. Don't just try to memorize, but try to solve problems and exercises in both math and physics. Don't read solutions, create them. But you also need feedback on what you do. A good course with a reasonable number of students and a skilled staff should provide that feedback. If they don't then you need to seek it out. Office hours. Be a pest if you need to.
You don't have an inability to understand deep topics. You have a need to develop skills. You may have some setbacks, but even those with great scores on IQ tests will also. Learn to push through those setbacks, with hard work and determination.
I don't know of any university that asks for IQ test results as part of admissions at any level.
The IQ number is just a number it isn't a locked gate.
For background see this at Wikipedia

Let me note a moderately common phenomenon. Some people, perhaps those with high IQ, seem to find early schooling easy and don't have to work very hard to succeed. It just comes naturally. But eventually most everyone will reach a point when it ain't so easy anymore and, if they haven't learned how to learn, might fail at that point having no concept of the work it takes to succeed. I was "lucky" to reach my natural limit early enough that I knew I had to work hard. My sister, who had an easier time in school and far surpassed me in grades, didn't go so far. The "natural limit" of ability (whatever that is) hit her harder.
Comment: +1, especially for *"Don't try to excuse yourself from the need for hard work to understand deep things."*
Answer: Basically like anyone else, some references I tend to refer to (and used myself to improve how I learn) are:

Make It Stick: The Science of Successful Learning  - https://www.goodreads.com/book/show/18770267-make-it-stick
Learning How To Learn (Online Course) - https://www.coursera.org/learn/learning-how-to-learn

The online course is offered for free and based on the material of the book, though I as a warning, it that it is designed for schoolkids as well and so the lectures may come across as childish. However the material they cover is still useful for improving the speed and depth with which you can obtain knowledge.
A couple of other points:

Regarding IQs, I remember coming across a study (can't remember where) which states that IQ is only correlated with job performance upto around 120 (a couple of jobs, such as theoretical physics and some mathematics see a correlation going upto 140, though note this was only theoretical physics). Beyond that other skills tended to dominate, e.g. emotional intelligence, networking, drive to perform.

Keep in mind IQ only refers to how quickly a person can in theory learn something, it doesn't say how much they will know. If you are an expert in something and we are talking about your area of expertise, you will be the expert regardless of how high my IQ is. All a high IQ means is that if we were both starting from the same background knowledge I would be able to reach your level of expertise quicker than you would. But I would still need to decide that I need to become an expert rather than simply deferring to you (there is such a thing as opportunity cost).

To back up Buffy's statement about coasting on natural ability, having a high IQ myself there was a lot of effort put into making sure I didn't think I'd just be able to rely on my natural ability but should have to learn how to study. There is such a thing as a growth mindset and average IQ plus growth mindset will probably be able to do more than a high IQ and fixed ability mindset, even if it might take longer to reach that point. I still need to remind myself every now (particularly if life is happening) and then to engage in focused learning rather then just falling back on my abilities and what I already know.

As suggested by the previous point on IQ only being useful upto a point, having a drive to contribute or interest in nature is something I'd say professors keep an eye out for, not just raw intelligence.

If you are still worried "My lack of intelligence means I don't have the mental resources to understand this topic", think of it another way. Those people with high IQ can just throw mental resources at a problem until they understand it, if you have to come up with a smarter way to think about something so that you "fit it into your mental capacity" then you have a drive to come up with simpler ways to understand a topic which the high IQ people do not. This can be an incredibly valuable contribution, and is something the high IQ people may also find quite useful themselves.

PS: Rote memorisation should never be your go to, its only useful when trying to deeply understand a more advanced topic than what you're memorising, but you should understand the less advanced topic first.
Comment: do you believe iq would ever be a barrier to what someone can learn, or would it always be a rate?


If someone is online in WhatsApp chat

Question: If someone is shown to be On-line in WhatsApp inside the actual Chat we  previously had, does that mean they've opened that particular chat OR that they're simply "Online"??
Answer: From WhatsApp FAQ - What does last seen and online mean exactly?

Online and last seen tell you if your contacts are online, or the last time they were using WhatsApp.

Online means that the contact has WhatsApp open and is connected to the internet. However, it does not necessarily mean the contact has read your chat.
Last seen refers to the last time the contact used WhatsApp.

If someone is online in WhatsApp chat


A word or phrase that defines "Preconceived opinions based on experience or reason?"

Question: If Prejudice is defined as Preconceived opinion not based on reason or experience.
then what, if any, is the word that defines "Preconceived opinions that are based on experience or reason?"
Comment: That's not the only definition of _Prejudice_; it doesn't have to be wrong, just previously decided. One can be prejudiced in favor of the truth, for instance. If you simply mean things that are taken for granted and can't be contradicted -- especially in sentences and by word usage -- the word you want is [_Presupposition_](http://www.umich.edu/~jlawler/Presuppositiontriggers.pdf).
Comment: In general, whatever *you* think is either "fact", or "opinion based on experience or reason". If anyone else thinks differently, that's "prejudice".
Comment: Informed opinion.
Answer: Anecdotal: Evidence or beliefs based on what has happened to someone personally.
(definition typically says in the form of stories that people tell - but the main point is the notion is not based on any empirical or scientific evidence).
"His conclusions are not supported by data; they are based only on anecdotal evidence."
Answer: An opinion is a conclusion reached that is not factually determined. Oxford offers these two definitions

a view or judgement formed about something, not necessarily based on fact or knowledge:
  that, in my opinion, is right
a statement of advice by an expert on a professional matter:
  if in doubt, get a second opinion

In both cases, the result of the analysis is not an exact calculus of indisputable facts, but requires some measure of decision-making by the opinion holder.
Obviously, there is a wide spectrum in the quantity and quality of information that leads to the opinion, ranging from none to a wealth of data and experience by an expert in the field.
The definition of preconceived is

(of an idea or opinion) formed before having the evidence for its truth or usefulness:
  the same set of facts can be tailored to fit any preconceived belief

The phrase preconceived opinions that are based on experience or reason seems somewhat oxymoronic. If it is preconceived, the suggestion is that it lacks evidence (experience being a form of evidence and reason the analysis of that evidence).
If facts are indisputable, the conclusion is not an opinion. If there is some room for differing opinions, it's because all the facts are not, or cannot be known, and some prejudgment (before all facts are know) is necessary.
It seems as if you are describing a circumstance where some facts are known and the opinion holder has experience and reason on her side. Rather than describing it as preconceived, you may want

informed opinion
or
educated guess
Answer: I would suggest the following two:
stereotyping and
pigeonholing
Both these terms imply a certain cognitive component
Answer: I think you are referring to bias.

3a : bent, tendency
  b : an inclination of temperament or outlook;

although this definition refers also to "prejudice."
Answer: A single word for a preconceived opinion that could be based on reason or experience is prejudgment. However, there is no single word for prejudgment based on reason or experience. The two-word phrase experiential prejudice is problematic because although literally, the word prejudice derives from prejudgment, the words do not mean the same thing: modern dictionary definitions of prejudice require that the opinion not be based on experience or reason.
Answer: If in debates, I would use bigotry for a preconceived opinions. Again, it all depends on the context of the subject and the mood of the audience.
Answer: If one has lived long enough, opinions can resemble hunches.  The evidence I've read indicates that these hunches are the result of subconscious recollection of varied past experiences, filtered by the brain to give direction in times of conscious uncertainty.
Those who have religion in their life believe these hunches to be signals from a deity.


Low disc space on /boot (Horus 7.1)

Question: I'm a tech newbie user who's just started using Horus and I'm loving it so far, but I had a warning pop up saying that I'm running out of disc space on /boot. Since I know enough to enter commands in the terminal but not to tinker with an OS, I tried this solution (Low Disk Space on boot warning) but it didn't work. I got this result: 0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
I've looked into other entries in this forum but balk at things that are over my head, like these:
Low disk space on file system
elementary OS disk space getting low
Any ideas what to do?
Update: I tried Bleachbit to free up space but still got an error message saying I have even less space on my /boot folder now, so I tried Bleachbit again. It hung up on me, though, so I aborted the operation (it was able to free up over 30 GB of space, though) and just in case it worked I tried this solution again (Low Disk Space on boot warning) and this time got this:
sudo apt-get autoremove
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up linux-firmware (20220329.git681281e4-0ubuntu3.29) ...
update-initramfs: Generating /boot/initrd.img-6.5.0-25-generic
I: The initramfs will attempt to resume from /dev/dm-2
I: (/dev/mapper/data-swap)
I: Set the RESUME variable to override this.
zstd: error 25 : Write error : No space left on device (cannot write compressed block)
E: mkinitramfs failure zstd -q -1 -T0 25
update-initramfs: failed for /boot/initrd.img-6.5.0-25-generic with 1.
dpkg: error processing package linux-firmware (--configure):
installed linux-firmware package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
linux-firmware
E: Sub-process /usr/bin/dpkg returned an error code (1)
Help, please?
Comment: Can you provide your disk partitions sizes? Also, can you use `ncdu` to find out what is taking that much space?
Answer: Did you ever get any help with this issue?
I'm in the very same boat as you and can't find any topic that has helped. Did you? Could you pass it along?

Low disc space on /boot (Horus 7.1)


Do you trust an OLS estimated coefficient when it's not statistically significant?

Question: Suppose you add a feature $x$ to an OLS model. The AIC goes down by 100 but the new feature is not statistically significant. The expanded model should be preferred overall but is the estimated coefficient on $x$ any good? According to statistical theory if it's not significant you can't reject the possibility that it's $0$.
Comment: "According to statistical theory if it's not significant it's likely 0." This is not what a p-value tells you.
Comment: It will be helping if summary output is inserted in your question.
Comment: I meant colloquially. I clarified it now.
Answer:
According to statistical theory if it's not significant it's likely 0.

That is absolutely not what the theory says.  First of all, effects of any variable are never really 0.  They may be imperceptibly small, perhaps too small for instrumentation to detect, but never actually 0.
Second of all, the theory when properly interpreted really says that when the p value is greater than 0.05 (let's call it $p$), then there is a $p$ probability that we observe effects at least as large if not larger assuming the effect was truly 0 and all of our assumptions about the data generating process associated with the test, possibly including but not limited to: Normality, independence, heterogeneity of variance, asymptotics, etc.  That is very different from what you've said.
Third of all, including or excluding  a variable has little to do with significance as I explain here.
EDIT: I see you've edited your post to clarify and instead say " According to statistical theory if it's not significant you can't reject the possibility that it's 0."
And I'm still going to challenge this and say "what if my type one error rate was different from 0.05"?
The point is, collapsing inference to a single number (namely the p value) is THE original sin of statistics.  There is so much more you can lean on to make this decision, and much of it will depend on what you're trying to do with that model.  Now, I know you're not looking for a philosophical discussion (neither am I), and I imagine you're instead looking for pragmatic instruction on what to do in these cases.  I don't think giving a set of "if/then" type rules for inference is particularly effective.  So I'll ask a question in response: What do you intend to do with this model?
Comment: I do wonder what we should make of a point estimate of $5$ but a confidence interval of $(-5, 15)$, though, especially if a value like $5$ would have practical significance.
Comment: @Dave Frank Harrell and company have an interesting thread on this [here](https://discourse.datamethods.org/t/language-for-communicating-frequentist-results-about-treatment-effects/934).  In your example, if the interval covered practically significant values then that would mean that practically significant values are consistent with the data. Additionally, a salient argument against assuming the effect is null is the classic "absence of evidence is not the absence of evidence", but this may have its own problems as has been argued [here](https://stats.stackexchange.com/a/476442/111259).
Comment: "...when the p value is greater than 0.05 (let's call it p), then there is a p probability that we observe effects ..." Not to nitpick, but isn't this statement true no matter what value p has?
Comment: I would like to estimate the effect size associated with this new variable. A statement like "by increasing the value of $x$ by 1 unit, $y$ goes up by $n$ units'. In regression $n$ would be the estimated coefficient $\beta$, but is still still valid under the conditions I describe?
Comment: @badmax absolutely. You can't reject the null in the typical sense, but hypothesis testing has no effect on estimation. You're free to make the estimates you mention. I would also construct a confidence interval and report that.
Comment: @Dave that's exactly what I'm getting at. What can you say about a variable that adds a lot to model power but the confidence interval is straddling zero?
Comment: @nope yep. I'm partially pointing out the absurdity of defining a cut off point


Can I still use match filter (eg.RCC)at rx when there is none at tx? Can it help with ISI?

Question: As the transmitter is restricted to size and power considerations, there is no way to apply a SRRC filter at tx side. Can I just put a RC(raised cosine filter) at the rx side to alleviate ISI?
Comment: That makes no sense: a *matched filter* is **defined** to be **matched to the transmit filter**, so, um, without transmit filters, no matched receive filters. Also, RC does *not* alleviate ISI – at all. Quite the contrary! Like any filter, it has the potential of *introducing* ISI.
Comment: Can you explain what size/power constraints prevent applying a filter?
Answer: The RRC filter's only purpose in the transmitter is to reduce out-of-band emissions in the transmitted spectrum.  Below shows a rectangular pulse waveform before and after using an RRC filter, where the upper plot is the time domain and the lower plot is the spectrum. Notice the significant reduction in sidelobe level and increase in spectral containment. Given our allocation of spectrum as a resource for wireless communications, this is highly desired, and in most cases required (one exception is GPS since the waveform as received as any potential interference to other receivers is already well below the spectral density of the noise floor).

If spectral containment isn't required then there is no reason for using an RRC filter. If spectral containment is required then additional filtering is needed one way or the other. Applying an RRC filter is a very efficient approach to doing this filtering and alleviates other filtering in the transmitter that would otherwise be needed. Further, when done in combination with the matched filter in the receiver as an additional RRC filter, the filtering is applied without introducing inter-symbol interference (ISI).
The purpose of the "matched filter" is to match all filtering that was applied to the transmitted waveform in order to provide an optimum correlation in the receiver. Optimum means the best signal to noise ratio after correlation in the presence of white noise (and would not be optimum under other noise conditions that are spectrally shaped).  If an RRC is used in the filter, and then an RRC in the receiver would be the "matched filter" (although other filtering/ equalization for channel distortions which also cause ISI may be needed).  If no filter is used in the transmitter (meaning we transmit rectangular pulses), then the matched filter in the receiver is itself a rectangular pulse (implemented as "integrate and dump" correlators).
For further details on how an RRC filter "eliminates ISI", please see this post.  The eliminate ISI part means introducing relatively tight filtering without introducing ISI. To get tight filtering, long impulse responses are required. If not managed properly, the impulse response from prior symbols will interfere with subsequent symbols. Two Root-Raise-Cosine (RRC) filters in cascade become a Raise-Cosine (RC) filter, which has the unique property that it's impulse response passes through zero at every symbol duration- and thus we get bandwidth restriction with zero ISI!
Putting the complete RC filter on the Rx side would result in the same received waveform under high SNR conditions but doing this would not provide the optimum receiver with a matched filter which is matched to the waveform transmitted. Further we would have none of the benefit of using the RC filter in the first place since its sole purpose is to minimize spectral sidelobes in the transmitted signal (the spectrum in this case would be contained after it is received, which is of no useful purpose).
Comment: Thank you for your professional reply, Mr Boschen.  "If spectral containment isn't required then there is no reason for using an RRC filter", in my situation, spectral containment is not of my concering. If RRC is availible at tx, the signal distortion might not be severe due to limited passband, but without RRC, in order to mitigate channel fading(underwater acoustic channel), do I have to do things like channel estimation or equalization to get a reasonable reciever performance?
Comment: @ztscotty I don't have any experience with the underwater acoustic channel but in general consideration is given to the symbol duration in comparison to the delay spread of the channel. If equalization is indeed needed then adding an RC filter in the receiver won't serve that purpose.


How long does it take for an initial charge with MBP?

Question: We unboxed a new 2017 MBP three hours ago. I wasn't expecting it to start by opening the lid. I then went through all the stuff you have to do when you startup (icloud, apple id, etc) It was at 34%. It has been charging for two hours. It's at 41%. The charger is in the port furtherest from the front. Is this normal? All of this? I have since shut down to charge (and of course have no idea what is going on now since there is no LED). How long does it take to do the full charge? And was it normal to start by lifting the lid? Brand new (well, brand new looking with wrap)
Answer: Power it off. The first 80% should charge in 2 hours. The last 20% should charge in the second 2 hours.
If the battery was deeply discharged I would repeat that test once you get the battery full and then drained.
Contact support either way to have them check the full charge capacity and review your powered down charge timings.
That protects you and gives Apple the data it needs if you feel it wasn't a great battery. In the past, Apple would ship closer to full. Now with changed airline regulations and changed chemistry in the batteries, they ship mostly empty. I wouldn't worry once you get your two tests in and contact support.
Everything you say seems perfectly normal, but for sure shut it down and do a controlled test - now is when you want to be sure it's fully operational.
Comment: Thanks. I unplugged and plugged back in. DING! And it started charging. Only took about an hour to get to 100%. Been closed sleeping for a day and just checked and at 100%. Thanks for your input, however. Glad to get a quick and reasonable response to an actual question. :-)


Independent increments and independence of natural filtration

Question: I am studying a stochastic process $(X_t)$ in continuous time which has independent increments. For $\mathscr{F}_t$ being the natural filtration I would like if
$$
\mathop{\mathbb{E}}[X_t-X_s \vert \mathscr{F}_s] = \mathop{\mathbb{E}}[X_t-X_s]
$$
whenever $s \leq t$. Is it true and do we in general have that $X_t-X_s$ is independent of $\mathscr{F}_r$ for $r \leq s \leq t$?
Answer: Yes, it is true. You can prove this by showing that $(X_t-X_s)^{-1}(A)$ is independent of $X_{r_1}^{-1}(A_1) \cap X_{r_2}^{-1}(A_2) ... \cap X_{r_N}^{-1}(A_N)$ whenever $N$ is a positive integer,  $r_1<r_2<\cdots<r_N\leq r$ and each $A_i$ is a Borel set.
Comment: Thank you. What you are hinting at here is it to use that $\mathscr{F}_r$ is generated by intersections on the form $X_{r_1}^{-1}(A_1) \cap ... \cap X_{r_N}^{-1}(A_N)$ as you write and the use that it is enough to show independence of a generator of the sigma algebra? If so, can you be a bit more explicit on how to continue the proof from here? It will be appreciated a lot.
Comment: @J.Goles One way is to use the $\pi -\lambda$ theorem. Consider $\{ F: \in \mathcal F_r: P( E\cap F)=P(E)P(F)$ where $E=(X_t-X_s)^{-1}(A)$. This is a $\lambda system and we have proved that it contains  a$\pi$ system which generates $\mathcal F_r$.
Comment: Thank you. I will look further in to that.


What's the difference between `:e foo.ext` and `:n foo.ext`

Question: As title. Sorry for being possibly a very simple question but could anyone rephrase the answer so it can be easily understood by a beginner?
Answer: You are using two different commands, :e and :n, that are thoroughly documented.
:help :edit_f says:
:e[dit] [++opt] [+cmd] {file}
                        Edit {file}.
                        This fails when changes have been made to the current
                        buffer, unless 'hidden' is set or 'autowriteall' is
                        set and the file can be written.
                        Also see |++opt| and |+cmd|.

while :help :next_f says:
Same as |:args_f|.

and :help :args_f says:
:ar[gs] [++opt] [+cmd] {arglist}            *:args_f*
                        Define {arglist} as the new argument list and edit
                        the first one.  This fails when changes have been made
                        and Vim does not want to |abandon| the current buffer.
                        Also see |++opt| and |+cmd|.

So…

:e filename edits filename,
:n filename sets the argument list to filename and edit filename.

If, in fine, both commands give you a filename buffer to edit, they have different side-effects. If you are confident those side-effects are irrelevant to you, then you can use them interchangeably. If not, use the command that does exactly what you want.
FWIW, the basics are introduced in chapter 7 of the user manual: :help usr_07.
Comment: Thank you for the detailed answer! I didn't know that `:` can still be appended after `:h`, now I learned it.
Answer: In this case (just a single filename folliwing :e and :n) they're basically identical.
You can see the definitive builtin help :h edit_f and :h next_f (just few lines below :h :e and :h :n). Use Ctrl-] to jump between helps, and Ctrl-O to jump back.


Entity Id Across Multiple Orgs

Question: I have created a package and in it I have two custom objects foo__c and bar__c. My question is can I assume that their entity id (the first 3 digits of their id) is the same across all of the Orgs that use my package?
Answer: Behavior of custom object prefix ID when using Change Sets
Knowledge Article Number: 000176809
Depending on the type of Sandbox you are using, a custom object prefix ID might change upon deploying it on a target organization. This article gives all the possible scenarios and their outcome.
Resolution
The list below assumes you are transferring a Change Set from a Sandbox to another Sandbox or a Production instance.
If you transfer a Change Set from

Developer Sandbox to Full Sandbox
Developer to Production.
Configuration to Full Sandbox
Configuration to Configuration Sandbox.
Configuration To Production.
Full Sandbox to Developer Sandbox
Full Sandbox to Configuration Sandbox.

The custom object ID Prefix will be different. Salesforce will generate a new custom object ID.
If you transfer a Change Set from

Full Sandbox to Production
Configuration to Developer sandbox.
Developer to Configuration Sandbox.
Developer to Developer Sandbox

The custom object ID Prefix will remain the same.
Comment: That is what I figured since a Production org can have multiple packages.
Answer: When a managed package is installed, the 3 digit prefix of a custom object will vary: the values are allocated perhaps on a "first custom object created" basis and so will vary from org to org.
So in your code you should not assume a fixed value but instead use e.g. DescribeSObjectResult.getKeyPrefix() or grab the first 3 characters of an ID that you know is of the correct type.
Answer: Yes!  The package runs in your context.
The first 3 digit will be same across all the organisation where your package is installed.

Entity Id Across Multiple Orgs


How to tell if an air-separator is working

Question: We have a Spirovent Air-Separator on the hydronic heating system, between the boiler and the circulator.  How to determine if it is working properly to remove dissolved air bubbles and has not been clogged by minerals in the water?
Answer: The maintenance and operation documentation, for what I think is your model, provides the following steps if service is required.

WARNING! System fluid under pressure can be very hazardous. Before removing the vent head for inspection, reduce system pressure to zero,
  or isolate the Spirovent from the system. Allow the system to cool to
  below 100°F. Failure to follow these instructions may cause serious
  bodily injury or property damage.

Using two strap wrenches, hold the body in place in the piping while
  removing the vent head, taking care not to damage the O-ring. Pipe
  wrenches may be used, but they can leave marks in the brass.
To clean the vent head, use a mild detergent and water or vinegar
  and water solution. For extremely dirty conditions, soak the head in
  mineral spirits for several hours and then clean thoroughly. The
  vent head is available as a replacement part if necessary. Use part
  number PJR000HA. Assembly includes the O-ring.
While the vent head is removed, remove the coalescing medium from
  the body and rinse thoroughly with mild detergent and water or
  vinegar and water to remove any system contaminants.
Examine O-ring before installing on the Spirovent and replace if
  necessary. Use part number PJR000RG.
Reassemble the Spirovent.
Return system to operating condition.

It's a bit of work, but I think it will be the most complete way to ensure the vent is in good condition.
Answer: My spirovent stopped working so I tried back pressure.  Held a bicycle pump against the vent until it sealed and then tried to compress the pump. Initially nothing, just pressure build up, then suddenly it compressed and I could hear air going into the system.  Works just fine again. Valve must just have been stuck.


why the background image I add not show in render?

Question: blender 2.81
I press shift+a to add image - background, and then go to render image, and the background image does not show up in the render result.
Answer: There's a great addon exactly for this.
Go to Preferences > Addons  and search for Images as Planes addon.
Check it to enable it.

Then you can easily add a new image that will appear in your render.
Add > Image > Images as Planes

Note:
The way you described is for reference images only - thy're not supposed to be visible in a render.
Comment: This add-on works as the functionality that I had expected Blender to have. I wonder why this this feature does not exist natively and users had to search the web for a solution and install an add-on for this...
Comment: Hello :). It's an official extension shipped directly with Blender. To keep the UI clean, not all Blender features are enabled by default. But you're right, this one should be.


Executing a BAT file as a domain user from a service in Windows 7

Question: Firstly a few basics:

I am running a database server application which runs as a service ServiceA.
ServiceA is installed on Server1 and Server2
ServiceA only runs on one of the two servers at any one time (they are redundant servers, if one server fails, ServiceA on the other server automatically starts)
I have no control over the code ServiceA
ServiceA logs on as the Local System account
ServiceB needs to run on both Server1 and Server2
ServiceB logs on as the Local System account
I can create configuration objects in the ServiceA database. One type of object is like a scripting language which ServiceA executes
The scripting language has functions to allow file manipulation and execution of commands on the local system - OPEN_FILE(), WRITE_FILE(), CLOSE_FILE(), and SYSTEM()
When these commands are executed, they run with the credentials of the Local System account
ServiceA generates configuration files for ServiceB using the above file manipulation commands
ServiceB needs to be shutdown before the new configuration files are created (I actually create them in a temporary folder, shutdown ServiceB, copy the files, and then start ServiceB)
Server1 and Server2 are both Windows 7 Enterprise
Server1 and Server2 are both on the same domain

I'm trying to get ServiceA to:

Shutdown ServiceB on both Server1 and Server2
Copy some files to Server1 and Server2
Start ServiceB on both Server1 and Server2

What I have done:

Created a Domain Account (DomainX/UserY) with a password (PasswordZ)
Created a share on both servers (ShareW)
Given DomainX/UserY permission to access ShareW on both servers
Used OPEN_FILE(), WRITE_FILE(), and CLOSE_FILE() to create an INSTALL.BAT file
Used SYSTEM('C:\Temp\INSTALL.BAT >> C:\Temp\INSTALL.LOG 2>&1') to run the INSTALL.BAT (run by Service A as Local System) and create a debug log

What works from within the BAT file
NET USE \\Server1\ShareW PasswordZ /USER:DomainX/UserY
NET USE \\Server2\ShareW PasswordZ /USER:DomainX/UserY
DEL /F /Q "\\Server1\ShareW\*.*
DEL /F /Q "\\Server2\ShareW\*.*
XCOPY /Y "C:\Temp\*.*" "\\Server1\ShareW\"
XCOPY /Y "C:\Temp\*.*" "\\Server2\ShareW\"
NET USE \\Server1\ShareW /DELETE
NET USE \\Server2\ShareW /DELETE

So the share and permissions are setup correctly
My problem is trying to Stop and Start Service B from within INSTALL.BAT
I have tried:
NET USE \\Server1\IPC$ PasswordZ /USER:DomainX/UserY
SC \\Server1 STOP "Service B"
NET USE \\Server1\IPC$ /DELETE
NET USE \\Server2\IPC$ PasswordZ /USER:DomainX/UserY
SC \\Server2 STOP "Service B"
NET USE \\Server2\IPC$ /DELETE

The SC command works for the local machine, but fails for the remote machine. This is the output from INSTALL.BAT running on Server2:
C:\Windows\system32>NET USE \\Server1\IPC$ PasswordZ /USER:DomainX/UserY
The command completed successfully.

C:\Windows\system32>SC \\Server1 STOP ServiceB
[SC] OpenService FAILED 5:

Access is denied.

(I've tried with ServiceA running on Server1 and Server2 - same results - Works locally, fails remotely)
If I use 'Run as different user' to run CMD.EXE as DomainX/UserY, the SC command works perfectly. So on Server2, running INSTALL.BAT from CMD.EXE as DomainX/UserY I get:
C:\Temp>NET USE \\Server1\IPC$ PasswordZ /USER:DomainX/UserY

The command completed successfully.
C:\Temp>SC \\Server1 START ServiceB

SERVICE_NAME: ServiceB
        TYPE               : 110  WIN32_OWN_PROCESS  (interactive)
        STATE              : 2  START_PENDING
                                (NOT_STOPPABLE, NOT_PAUSABLE, IGNORES_SHUTDOWN)
        WIN32_EXIT_CODE    : 0  (0x0)
        SERVICE_EXIT_CODE  : 0  (0x0)
        CHECKPOINT         : 0x1
        WAIT_HINT          : 0xbb8
        PID                : 4856
        FLAGS              :

So the DomainX/UserY has the necessary permissions to Stop and Start the service on the remote server. It appears to be some kind of blocking of privilege escalation from the Local System account.
I have read about setting LocalAccountTokenFilterPolicy in HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\ to 1 and rebooting. I've done this with no changes to the outcome.
I've tried using psservice.exe with practically identical results (output from INSTALL.BAT run by ServiceA on Server2)
C:\Windows\system32>C:\Utilities\psservice.exe \\Server1 -u DomainX/UserY -p PasswordZ -accepteula stop ServiceB

PsService v2.24 - Service information and configuration utility
Copyright (C) 2001-2010 Mark Russinovich
Sysinternals - www.sysinternals.com

Access is denied.
Access is denied.
Error querying services on Server1:
Error opening ServiceB on Server1:

I then tried to use psexec (in a rather convoluted manner to trap all the logging)
INSTALL2.BAT
C:\Utilities\psexec -accepteula -u DomainX/UserY -p PasswordZ C:\Temp\INSTALL3.BAT >> C:\Temp\INSTALL3.LOG 2>&1

INSTALL3.BAT
C:\Temp\INSTALL.BAT >> C:\Temp\INSTALL.LOG 2>&1

When I run INSTALL2.BAT from the command line (running as DomainX/UserY), everything works fine.
But run from ServiceA, In INSTALL3.LOG I get:
PsExec v2.11 - Execute processes remotely
Copyright (C) 2001-2014 Mark Russinovich
Sysinternals - www.sysinternals.com

Access is denied.

PsExec could not start C:\Temp\INSTALL3.BAT:

So I explicitly added DomainX/UserY with Full Control to the security of all three BAT files. The result was the same (Access is denied. in INSTALL3.LOG)
I've also tried turning off UAC with no perceivable impact
So I'm pretty much stuck now - How can I get a BAT file executed by a service running as Local System to impersonate another user and allow it to Stop and Start services on a remote machine?
Answer: The answer turns out to be very simple - use the -h option of psexec
The SYSTEM() command of the script run by ServiceA is now:
C:\Utilities\psexec -accepteula -h -u DomainX/UserY -p PasswordZ C:\Temp\INSTALL.BAT >> C:\Temp\INSTALL.LOG 2>&1

Works perfectly


Novel Netware 5.1 network drives for windows

Question: We have a novel netware 5.1 file server in use for several years with xp machines now we have a new win 7 machine.
I downloaded the novell network client for windows put in the tree and context info and double checked the user name and password. but can't map the network drive.
also i can't ping the server as well. Server is working just fine with xp machine. Any idea?
Answer: It could be a couple of things:

It is possible, though not likely, that the Novell Netware servers are still running pure IPX. Microsoft dropped IPX support for Windows as of Vista. If your NW servers are in this state, there isn't a thing you can do short of turning on TCP/IP for them.
It is possible, though somewhat more likely, that you're running both IPX and TCP/IP on your network. TCP name resolution isn't working for some reason, so it's falling back on IPX SAP resolution which is how it is learning about network resources. To fix this, you will need to get your SLP environment up and running.
It is more likely that your SLP environment is working just fine, but your Windows firewall doesn't have the needed rule added to it. By default, the NW client will use multicast to search for a SLP directory-agent, and the DA will reply to the client via unicast UDP to a specific port. If that port isn't allowed through the Windows firewall (port 524 from memory) name resolution won't work and you'll get the behavior you describe.

A quick test is to put the IP address of one server that holds an eDirectory replica in the "Server" field. If that works, TCP/IP is working but SLP name resolution is failing for some reason.
Comment: You might not want to admit to this much "top-of-your-head" knowledge about Netware. Might end up with consulting gig offers.
Comment: @mfinni We all have our legacy-knowledge boat-anchors to carry. At least if you've been in the industry long enough.


If we brought ancient germs to the present

Question: If germs from the past was brought to the present/future on a person (or by some other means of transportation) and we have immunity to its descendants, like the modern germs for example, would we be immune to the germs brought to the present? I have only seen conversations about people bringing germs from the modern day to the past, but what happens when we flip the tables.
Comment: @Cyn good catch! Edit made!
Comment: Welcome to Worldbuilding, yo76yo! If you have a moment, please take the [tour] and visit the [help] to learn more about the site. You may also find [meta] and [The Sandbox](https://worldbuilding.meta.stackexchange.com/questions/7183/sandbox-for-proposed-questions) useful. [Here](https://worldbuilding.meta.stackexchange.com/q/6388) is a meta post on the culture and style of Worldbuilding.SE, just to help you understand our scope and methods, and how we do things here. Have fun!
Comment: Hi yo76yo, I imagine that for the purpose of a story, anything could happen. Your will as an author has more power over the course of a virus than anything else. I would recommend removing your first line, as it tells me this is more about the needs of your story than any world building.
Comment: @Shadowzee edit has been made, thanks for the tip.
Comment: Hi welcome.  Do you mean bacteria or "germs" in general?  Because you give influenza as an example, but that's a virus, not bacteria.  And for viruses, no, we're not immune to mutations (backwards or forwards) just because we're immune to one type.
Answer: You don't know how actual your question is: link. The melting of the polar cap might actually release long dormant viruses, bacteria and funghi.

In August 2016, in a remote corner of Siberian tundra called the Yamal Peninsula in the Arctic Circle, a 12-year-old boy died and at least twenty people were hospitalised after being infected by anthrax.
The theory is that, over 75 years ago, a reindeer infected with anthrax died and its frozen carcass became trapped under a layer of frozen soil, known as permafrost. There it stayed until a heatwave in the summer of 2016, when the permafrost thawed.
This exposed the reindeer corpse and released infectious anthrax into nearby water and soil, and then into the food supply. More than 2,000 reindeer grazing nearby became infected, which then led to the small number of human cases.

About the risks

"Following our work and that of others, there is now a non-zero probability that pathogenic microbes could be revived, and infect us," says Claverie. "How likely that is is not known, but it's a possibility. It could be bacteria that are curable with antibiotics, or resistant bacteria, or a virus. If the pathogen hasn't been in contact with humans for a long time, then our immune system would not be prepared. So yes, that could be dangerous."
Answer: We tend to correlate the word "evolution" with the word "improvement", but that is a false association.  "Evolution" is more closely related to the word "change".
If at a particular moment in the past, a disease emerges to threaten the survival of a population, then the portion of that population which had previously "evolved/changed" to resist that disease would have a higher survival rate than the rest of the population.  Then for a time, that higher survival rate would give them a propagation advantage, allowing their particular genetics to pervade a larger percentage of the population.
Once the presence of that disease decreased, the propagation advantage would fade as well.  Other threats would emerge to endanger the population and other genetic changes would gain the advantage.
It is entirely possible over deep time that other genetic changes might break the historic disease immunity change in pursuit of immunity to a different threat.  It is also possible that over deep time, an immunity change (which is no longer valuable because it's disease is not present) can disperse or even vanish from a local gene pool.  Gene lines die out all the time for no reason greater than personal dating choices.
So yes, a historic disease can be a threat to a modern populace even if they had survived the disease in their distant past.  As with wisdom and un-persisted knowledge, we tend to loose what we do not use.  So if a particular version of a disease has been gone for a long enough time, we may very well be susceptible to it again.
Answer: NO, But...
This is an something that has actually been tested in the long term e-coli experiment.
 In bacteria separated by several generation older generations can outcompete there distant descendendants. It is not a given of course but the chances are not insignificant either.  This is because the population of bacteria is constantly changing as bacteria adapt to each other and their hosts but such adaptations are not immediately lost nor always useful in the long run. For example an ancestor may have produced a toxin to help kill off competing bacteria but it may completely kill off that competing strain or other bacteria may become resistant to the toxin, so later it loses the ability to produce the toxin since the toxin takes calories to make. But put the toxin producing ancestor in with its descendants and it may wipe out is later descendants as well.
There is also an effect with diseases that causes them to become less lethal, later strains of HIV are milder for instance because living hosts are more likely to spread the disease. A reintroduction of the original strain would be devastating since it would be more virulent and kill a lot of people even as it drives itself extinct. This is not uncommon, very virulent diseases are worse off evolutionarily than less virulent descendants precisely because they are much worse for the hosts, and living hosts are better at spreading disease.
Now the but, if you go back far enough the chances of catching a compatible disease are lessened, simply because there is nothing with similar biochemistry to you around. For instance go back to the carboniferous and there are no warm blooded animals around and the chances of a comparable disease are extremely low. The worst diseases tend to be from your own species or closely related species, that or you need long contact with the species like humans and livestock.


Why does increased voltage increase processor performance

Question: When you increase the voltage into a computer's CPU it increases the clock speed of the processor and can lead to better performance.  Why does the increased voltage cause the processor's clock speed to change?
Comment: "...it increases the clock speed of the processor..." [citation needed]
Comment: I think that it is the other way around. A higher clock speed needs a physically smaller IC, and a smaller IC needs a lower voltage.
Comment: You don't increase frequency when you increase power. But if you increase frequency, you have to increase power to make your CPU work. It require more "juice". But thermal dissipation get bigger, wich make it hotter, more ressitance, more heat... and so on.
Answer: A CPU is, at its root, an extremely large sequence of FETs driving each other in complex combinations. These FETs have a very large number of possible states, only some of which are valid. Each clock cycle, the processor should move from one valid state to the correct succeeding valid state. The FETs are arranged such that they begin to switch from one state to the next only on a clock edge. But if one FET drives another, that means the driving FET has to complete its transition before the load FET can even start!
This is propagation delay, and the longest chain of propagation delays in the system determines your maximum clock frequency. You have to be sure that by the time the next clock edge arrives, all FETs everywhere have completed whatever transitions are going to occur. Otherwise you end up with your chip in an invalid or incorrect state, and all bets for correct operation are off.
So the minimum clock period (and thus maximum frequency) is a function of the longest propagation path in the chip, and of how long the individual transistors in that path take to switch. You can't change the propagation path once the die is etched, but you can change the time it takes for a transistor to switch. As with any FET, the switching time is affected directly by the time it takes the gate capacitance to charge. Since the capacitance is fixed, a higher voltage through the same FET results in more current flow, and a faster rate of charge. So increasing the rail voltage of the processor can increase the switching speed.
Of course, the down-side is that at higher voltages, the switching loss of the FETs also goes up, more than the gains from faster switching times make it go down. So higher voltage results in increased operating temperature, which can also affect the switching time of the FETs, and ultimately result in damage to the chip.
Also, quantum wibbly-wobbly effects can make the chip behave unreliably.
Comment: Yup, speed increase is linear while power increase is quadratic.
Comment: "Since the capacitance is fixed, a higher voltage through the same FET results in more current flow, and a faster rate of charge". Yes, but the voltage in the "load capacitor" would also need to reach a higher threshold (to be considered a '1' for instance). Just like in a RC circuit where the constant time tau is independent of the charging voltage. Am I overlooking something?
Comment: @RogerC. I see you reasoning, and I don't have a definite answer. Best guess is that since the FETs are on "harder", their effective resistance goes down, reducing the time constant. Also, the threshold voltage of the FETs hasn't changed, so while it might take the same amount of time for them to reach their new ultimate voltage, it will take less time for them to reach the threshold voltage and start to switch.
Comment: @StephenCollings your explanation does make sense. Thanks!
Answer: Without going in to details when you design a chip you spend a lot of time doing timing analysis between all the little logical and signal paths to each cell inside the chip.   You can only run a chip as fast as it will meet this timing without getting errors.
This max speed is also affected by: process, temperature, and voltage.  So you can either by design or by trying to over clock increase the voltage to increase performance.
Raising the core voltage raises the voltage to each cell of the chip and this decreases the prop delay through that cell in effect making the paths faster.  You can then increase the clock rate separately to see if your chip still functions error free at this speed.
Of course you can break timing this way too or break your chip by damaging it with over voltage or over temp.
Your process and temp will affect things too so you could get lucky and get a chip that can already run faster than it's clocked, or unlucky and get one already running at near max speed.
In the before time people would cool down chips too to get them to run faster but now at the smaller process nodes we have temperature inversion so they run faster hotter.


Perforce auto sync

Question: I work in a large evolving code base and use perforce to manage it. The problem is that I need to update it everyday and it takes a long time to do it. I am looking for ways to automate this process.
I first thought of writing an script and make it a scheduled task. I could not do it since running "p4 sync" gives me "p4 protect" related error. I don't have, and will not get, admin rights to server so I can't add myself to the protect table.
Since I can sync through P4V - perforce UI- I guess there should be a way to achieve this through custom tools or something similar.
Can you guys please provide pointers on how to approach this problem or if there is already a solution for it.
Answer: If 'p4 sync' gets a protect error in your script, but not when you use P4V, you most likely have the wrong environment in your script. P4PORT, P4USER, and P4CLIENT need to have the exact same settings in our script as they do in your P4V connection.

Perforce auto sync


Unity: Keyboard Shortcut to Deselect Game Object

Question: How do you unselect a game Object in the 3d view using your keyboard?
Comment: I don't know a keyboard shortcut. But if you click the Hierarchy, on an empty space, everything is deselected.
Comment: maybe this could help? https://answers.unity.com/questions/639981/quicky-deselect-all-selected-object-in-editor.html
Answer: Reading through the list of Unity editor keyboard shortcuts, it doesn't look like such a shortcut exists.
We can save & load selection presets using Ctrl+(Alt/Shift)+(1-9), but you can't directly save "no selection" into any of these slots. A workaround mentioned in the link Arthur Gibraltar provided is to create a dummy object, save a selection, then delete the dummy object to end up with a saved empty selection.
Instead of this fiddly process, we can add our own Select None shortcut with an editor script placed inside a folder called "Editor":
using System.Collections.Generic;
using UnityEngine;
using UnityEditor;
using UnityEditor.SceneManagement;

public static class SelectionHelpers {

    [MenuItem("Selection/Select All (Active Scene) %a")]
    public static void SelectAll() {
        var scene = EditorSceneManager.GetActiveScene();
        var objects = scene.GetRootGameObjects();
        Selection.objects = objects;
    }

    [MenuItem("Selection/Select None %q")]
    public static void SelectNone() {
        Selection.objects = new Object[0];
    }
}

With this script we can Select All with Ctrl+A (or ⌘+A on Mac),  and Select None with Ctrl+Q (or ⌘+Q)
Answer: Extending from DMGreggory's solution, we could simplify the SelectNone function even more:
using System.Collections.Generic;
using UnityEngine;
using UnityEditor;
using UnityEditor.SceneManagement;

public static class SelectionHelpers
{

    [MenuItem("Selection/Select None %q")]
    public static void SelectNone()
    {
        Selection.objects = null;
    }
}

Where the selected objects is being reset to null as opposed to adding an empty object each time we call SelectNone(). This reduces the chances of memory leakage on heap and therefore is a safer solution.


The 行 in 大唐女儿行 or 骊歌行

Question: What does the 行 in 大唐女儿行 or 骊歌行 (those are two variants of the title of a novel / tv series) mean? My dictionary is not helping me, as isn't the web :-|
Answer: 行 stands for 歌行体, an ancient poem/folk song style, a type of yuefu(乐府) poem. Ancient poems written in this style are usually named x歌 or x行 (e.g., 琵琶行,长恨歌). Due to a looser constraint on format and length, these poems can have more narrative than many other forms of Chinese poems. The novel/tv seires you are asking about is likely using this title to invoke a sense of archaic beauty.
Answer:
ode on 骊歌(a song of farewell) or ode to 大唐女儿

ode: a poem expressing the writer's thoughts and feelings about a particular person or subject, usually written to that person or subject
Comment: In the context of 古诗, always xíng
Comment: Is that xíng or háng? 行: 古诗的一种体裁:长歌行。
Answer: I think 行 in 大唐女儿行 means journey, travel. Metaphorically, it could mean what's going on about 大唐女儿.
Not sure about 骊歌行 though.
Answer: I think 行 is the equivalent of "傳" or "記".
Here, the use of "行" in the show title is an imitation (copy-cat) of an ancient style of poem title such as "长歌行(李白)", "短歌行(陆机)", "燕歌行(曹丕)", "门有万里客行(曹植)"...etc.
.
Answer: I am sorry but their just some answers are correct. And i'm sure about it. '行'is a style of poem (a part of 樂府詩), like '長干行' of 李白, '琵琶行' of 白居易.
I had learn this at high school, Chinese teacher will tell tou a same answer
Answer: What does the 行 in 大唐女儿行 or 骊歌行 mean?
First and foremost, the word 行 has multifarious meanings, as you have no doubt found out from your rummage through the dictionaries?
As a verb, it usually means to travel, to go on a journey.
As a noun, it usually means personal behavior, conduct.
Thus, without any context marker, it could mean one of the following:-
(1)  A journey undertaken by 大唐女儿, or,
(2)  The personal behavior, conduct of 大唐女儿, as very often prepositions, semantic markers are silent in Chinese writings, especially in poetry or titles of literary works. So, the silent markers in this instance could be, (in brackets):-
大唐女儿(的)行(为)
A more contextual translation of the phrase could very well be "The antics of 大唐女儿", given that the story line of the TV play is probably of the comical genre, as modern "Sinowood" perceptions of the maidens of the Tang Dynasty era are one of coquettish, flirtatious antics.
As for 骊歌行, well, a literary translation would be like "An Ode to the Sojourner", as 骊 has something to do with a fine, handsome horse, and olden days travelers would need such a horse when going on a long, ("Romantic") journey.
Answer: I'm not sure about what "大唐女儿行" is, seems it's the name of a TV series of "骊歌行". Regarding 骊歌行, I guess it's same with 长歌行, given "行" is at the end of whole world, it should be a noun, the dictionary said it's a Poetry genre.
BTW they are all read as xíng.
Answer: All above answers are wrong
行 == Journey. period.
Comment: legend may also applies in this case,  referring to https://lyricstranslate.com/en/xi%C3%A1-k%C3%A8-x%C3%ADng-legend-knight.html

The 行 in 大唐女儿行 or 骊歌行


Why do we use the same parameters for the joint, marginal and conditional distributions in VAEs?

Question: I've noticed in several resources on variational autoencoders (for example the wikipedia article), we use the same parameters theta for the prior, likelihood, posterior, etc distributions. For example the equation $p_\theta(x) = \int_z p_\theta(x|z)p_\theta(z)dz$. Aren't $p_\theta(x)$ and  $p_\theta(z)$ two different distributions, so how can we parameterize them with the same $\theta$ params. I might be misunderstanding something about what it means to parameterize a distribution...
Answer: I think this is very confusing to many people. I had to deal with VAEs (and Bayesian neural networks) multiple times in the past, and I've seen so many inconsistent notations and unclear explanations. Here's what I know about the issue that you're raising, but I will not give you a definitive answer.
In the appendix of the VAE paper (sections C.1 and C.2), they consider the cases of

a multivariate Bernoulli decoder, and
Gaussian encoder and decoder

They write

in the case of the multivariate Bernoulli decoder, $\theta$ are the weights and biases of the neural network that outputs the Bernoulli parameters (each Bernoulli distribution has only one parameter that basically defines the probability of getting one sample rather than the other - this is not written in that section - I am just telling you this, in case you didn't know it).

in the case of the Gaussian encoder, $\phi$ (which parametrizes the variational distribution $q_\phi$) are the weights and biases of the neural network that represents the encoder (which outputs the $\mu$ and $\sigma$ of the Gaussian, which are the parameters that define the specific Gaussian - you can see this from the equations in appendix C.2)

in the case of the Gaussian decoder (appendix C.2), the weights and biases of the neural network (the decoder) are part of $\theta$ (I don't know what they mean by "part of" here, honestly).

So, in the case of the VAE (with a multivariate Bernoulli decoder, or a Gaussian encoder and decoder), which is really a neural network (or 2 neural networks - encoder and decoder) that attempts to model the random process which is represented by the graphical model in figure 1 of the VAE paper, $\phi$ and $\theta$ are the weights and biases of the neural networks that represent the encoder and decoder (partially, in the case of the Gaussian decoder, they say), respectively. $\phi$ and $\theta$ are really the learnable parameters. In fact, if you look at algorithm 1 or any implementation of the VAE (I like this simple PyTorch one), they are what we're trying to optimize.
Now, if you look at the definition of a parametric model, e.g. here, you will see that the parameters $\theta$ in $p_\theta$ actually refer to e.g. the mean and variance of the Gaussian, i.e. $\theta = \{ \mu, \sigma \}$. This is one thing that causes confusion - the subscript $\theta$ (or $\phi$) refers to different things in different articles.
HOWEVER, ultimately, what we're trying to learn are the parameters of a probability distribution, let's say it's a Gaussian, so we are trying to learn a mean and variance $\{\mu, \sigma \}$. In the VAE, we use a neural network to output the mean and variance, i.e. $\mu, \sigma = f_\phi(x)$, where $f_\phi$ is the neural network with weights $\theta$ (see the equations in appendix C) and $x$ is an input. So, $\{\mu, \sigma \}$ are defined by $\phi$.
Now, back to your actual question. Here are some possible interpretations of that notation.

If $\theta$ represented the parameters of a specific probability distribution (let's say a Gaussian), so $\theta = \{ \mu, \sigma \}$, then, as you noticed, you would have all your distributions with the same mean and variance, and I don't think this is generally the case (but could happen?) - for example, $p_\theta(x)$ and $p_\theta(z)$ would exactly be the same distribution, so that means that $x$ and $z$ follow exactly the same distribution (e.g. $\mathcal{N}(0, 1)$).

However, if you look at figure 1 of the VAE paper, both $x$ and $z$ depend on $\theta$, but is it the same $\theta$? So, even though the letter $\theta$ is used as a subscript in the likelihood, prior, marginal and posterior, do these distributions actually have the same specific values of $\theta$? If you look at section 2.1, they also use that notation you found on Wikipedia.

If $\theta$ represented the weights of neural networks, then all neural networks would be equal (this is not the case in practice - see the PyTorch implementation).

If $\theta$ were hyper-parameters, that notation could make sense (because the mean and variance of the Gaussians could still be different), but this does not seem to be consistent with the actual explanation in appendix C and the PyTorch implementation.
Comment: In most cases θ is used to indicate weights of a neural network, and with sloppy notation that could mean any NN so not necessarily the same one every time.


Open source and secure app to replace Google Keep

Question: As part of moving away from Google products I'm looking to replace Google Keep. I would love an installable client for Ubuntu but that's optional. I do need an Android app and access via browser. Should have a privacy focus and preferably be open source. I'm currently trying out Standard Notes but it lacks functionality such as uploading images and lists with checkbockes.
Comment: What does "Google Keep" do for you? What functionality do you seek?
Comment: Check boxes for lists and uploading pictures.
Answer: QOwnNotes seems to become a good replacement. May be self-hosted. Supports Markdown.
Comment: Looks good but running my own Nextcloud server is a bit above my head :(


qgis-mesh data (GRIB2) to geotiff

Question: basically i am trying to get out the direction and magnitude information of the current (flow/movement of water) information layer of a grib weather data file - which is a mesh in qgis terminology. I was following the instrucionts in Tutorial on using QGIS for marine data. the tools used there need a raster dataset for u and v components of the current. so far i have found information of how to transfer grib2 to geotiff. but the GDAL / raster analysis / translate function from Processing Toolbox doesn't seem to support mesh-data as input type. is there a straigth forward way within qgis to convert mesh into raster? or is there a way to display a u / v information from mesh as a vector field ?
Answer:
[...] is there a way to display a u / v information from mesh as a vector field ?

Not exactly within QGIS, but yes. I am working with grib2 files right now and I just found degrib, a really nice utility to extract grib information to vector files:
https://www.weather.gov/mdl/degrib_archive

I exported messages #1 and #2, which are UGRD and VGRD, for the first period of time, to point shapefiles.
Once added as layers in QGIS, I converted them to geopackage and generated a virtual layer with the information contained in both.

Then, I also exported the virtual layer to geopackage. These are the grib2 and vector layer together.

Finally, we can just rasterize the vector layer. Note that the step of merging the two vector layers would not be necessary if you want them rasterized.

This is the information contained in the u component of the wind vectors, in a raster of one band rendered in pseudocolor:
Comment: any idea how to proceed to make a mean for all winds within a month or a year? all the data i get is of 1 day forecast. https://nomads.ncep.noaa.gov/ ?
Comment: @assayag.org - speeds & directions ? ... does it make sense to mean directions? i'd suggest a count or % of the 8 main directions instead where total = number of days with wind > xy knots (or even better based on hours..)
Comment: id just wanted to know "where does the wind come from", in general, most of the time.

qgis-mesh data (GRIB2) to geotiff


How do I determine the division of cost basis for multiple NFTs minted in a single transaction?

Question: I understand (I think) how to assign cost basis (for income tax) to ordinary minted NFTs: Convert the minting price (including gas, fees, etc.) in cryptocurrency to dollars using the market rate at the time.
But when a single transaction yields multiple NFTs, how do you divide the cost basis among them?
For example, here's an Ethereum Ethereum transaction in which the originator sent 2.474 Ether (including gas) and received two Raid Party Fighter tokens and one Raid Party Hero token. The Fighter and Hero tokens had different collection sizes and radically different floor prices at the time.
Suppose the minter kept one of the tokens and sold the other two. How would we assign the total cost basis for the transaction to the three individual tokens? Do we just divide the total cost by three? Or do we try to account for the relative estimated values of the individual items?
Is there a hard and fast rule for this, or is there room for discretion?
I assume there's some non-crypto analog for this situation, for example (maybe) buying multiple non-fungible items in a single lot at auction. I would appreciate any insight whether cryptocurrency-specific or not.
Answer: In a "regular" (aka tangible) assets transaction, you'd do an appraisal of each of the assets and split the cost basis proportionally to the appraised values.


How to use Form API and and node_submit to insert taxonomy data

Question: I have a content type with a number of text fields and a field linked to a taxonomy vocabulary with about a dozen terms.
I have successfully developed code using the Form API to insert data from my custom form into my node using node_submit for the text fields.  A sniped of the code I use is for the text fields is:
<code>$node->field_s_phone[$node->language][0]['value'] = $form_state['values']['phone'];
$node->field_s_email[$node->language][0]['value'] = $form_state['values']['email'];

node_submit($node);
node_save($node);
</code>
I would like to implement a single set of checkboxes of my vocabulary terms on the custom form, then pass the values using node_submit in a similar fashion to the text fields (sort of like):
<code>$node->field_catagories[$node->language][0]['value'] = $form_state['values']['catagories'];
</code>
I would be grateful for any thoughts or insight.
Thanks,
Bill
Answer: Try this, if I completely understood you, this should help.
<code>    $i = 0;
    foreach($form_state['values']['catagories'] as $tid) {
      $node->field_catagories[$node->language][$i]['tid'] = $tid;
      $i++;
    }
</code>


how to test hosting companies's speed for our webpages / web app?

Question: Before we sign up for any hosting company to host our app or pages, i think it probably is good to find out the speed so that if it is too slow, we may as well pay a little more to find a better place to put our app.  the question is, is there a way to find out some sites that a hosting company is hosting and what is the best way to test the speed of the site? (is using "ab" command one of the best methods?)
Answer: Netcraft monitors hosting providers and can provide this type of information, but I'm not sure it's all that important.   If your testing individual sites there may be other bottle necks that may not necessarily affect you.
Comment: funny they don't list dreamhost as one of them.
Comment: yeah I didn't see my host on the list either
Answer: Check out this blog http://www.joelonsoftware.com/backIssues-2009-02.html from Joel on Software about http://www.akamai.com/
It details your packet are routed to a Akamai node and then from there go to the fast lane to the nearest Akamai exit before the end point.
I don't think that you can generally find out the speed of a site as that is a function of the route to your site and how that route is set up. If a provider has a route to Toledo before routing to the next town the speed may appear slow even if they are running the fastest type of link.


Overriding ASP.NET DropDownList width for responsive website

Question: If there's a case for using MVC for responsive websites, this is it:
I'm working on a site that is mostly ASP.NET WebForms, which is undergoing a redesign to use responsive markup. It is impractical to convert everything to MVC, so I have to make do with the existing controls.
On a particular form page, we have two combo-boxes on the same row; these have CSS classes appropriately set to specify the width at 48% of the parent element. The trouble is that since we're using the asp:DropDownList, the control is rendered with a style attribute having width:275px;, which overrides the width set in the CSS class.
In codebehind of the composite control containing these DropDownLists (particularly the RenderChildren method override), I've tried calling [control].Style.Clear(); prior to calling the base method. This has no effect; even adding:
[control].Style.Add(HtmlTextWriterStyle.Width, "inherit");

causes the element to be rendered as:
<select style="width:275px;width:inherit;" class="input-half first" id="longAndComplicated" name="longAndComplicated">

Note the two width declarations, when ideally there shouldn't be a style attribute in the first place.
I've had a poke in Reflector at the source, and couldn't find where this hard-coded width is being set; I gather that the style setters are being copied from somewhere further up the ASP.NET hierarchy.
As a lucky guess, I tried:

Setting Width to an empty string on the <asp:DropDownList> ("inherit" causes a Parse error)
Explicitly specifying Width="48%"
Setting EnableTheming="false"

None of these has had any positive effect, with the rendered style attribute still having width:275px;.
Where is this width magically being set from? How can I override this behaviour, ideally without having to create a derived class inheriting from System.Web.UI.WebControls.DropDownList?
Many thanks.
Comment: Set a breakpoint in RenderChildren and check whether the Width of the DropDownList has been set to 275px. The standard DropDownList control does not hard-code any width.
Answer: I have better Idea, fix the width and do not inherit the width, as that will inherit width from parent and over-ride the width element defined with width:275px; so that will be meaning less.
I have created a fiddle, works fine in chrome, the select tag has fixed width,
If sub element size will increase it will automatically grow.
Please check fiddle
If your question is referring to CSS class class="input-half first" then the style defined in element style is the one what is applied at last and will have high priority compare to class, better create new class, and assign it.
Hope, I have answered in right context as you have written many things with reference to ASP.net control, but I don't think that should be problem in majority cases.
Comment: Thanks, though that isn't my issue. The problem is that I don't want a `style` attribute to be set in the first place (because it overrides the width set in the `input-half` class), which is what ASP.NET is doing.
Comment: THat is not ASP.net, its CSS general precedence for style. give and example of problem. Will help to solve
Answer: Doh - I figured out what it was.
It turns out that the containing composite control defined properties along the lines of DropDown1Width and DropDown2Width. These 'cleverly' set the Width property of the underlying DropDownList controls, which were used during the DropDownList.Render() method.
Fortunately I don't have to go subclassing DropDownList, though in hindsight the lack of definitive web search results suggested the problem was likely to be somewhere in our own codebase.
I say "defined", as I have since removed these redundant properties (and their corresponding assignments in various ASPX files).


I'm new to arch linux can't connect to wifi

Question: After installation I used iwctl to connect wifi. It say me 'stat connected' and 'connected network to the wifi box'. I'm exiting and when I type ping google.com it say me Temporary failure in name resolution
Comment: First check if your WiFi card ha an IP by issuing `ip a`: under your card name there should be some ipv4 entry. Please edit your question with the output of this command if you need help on this.
Answer: The easiest way to connect to a protected WiFi network on Archlinux is to run sudo wifi-menu and follow it's instructions. Then, by issuing sudo netctl list you should see a * on the left of the active connection. Use then sudo netctl start/enable <connection_name> to either instantly start the connection or enable it at each system boot.


how to remove header from registration page?

Question: How can i remove the header,search and my home,activity,forum etc from registration page.os there any plugin to modify registration page.I am using buddypress plugin.I do not want to call color.css for my registration page.
Comment: What theme are you using?
Comment: http://wordpress.org/extend/themes/frisco-for-buddypress
Comment: Is not including color.css *all* you want to do?
Comment: yes @bungeshea i do not want to include color.css in registration page.Is there any simple way?
Comment: See [my answer](http://wordpress.stackexchange.com/a/77267/19726) below to remove color.css from registration page.
Answer: If you don't mind editing your themes files, you can remove color.css from the registration page by editing the functions.php file and change line 127 from:
wp_enqueue_style( 'frisco-color-css');

to:
if ( ! is_page( 'register' ) ) wp_enqueue_style( 'frisco-color-css');

Otherwise you can include a function in a plugin or similar:
add_action( 'init', function() {
    if ( is_page( 'register' ) )
        wp_dequeue_style( 'frisco-color-css' );
});

You will need to change register to the name, slug or ID of your registration page.
Answer: The theme you are using is a child theme of Buddypress default theme. You can override any file in the default theme by copying that file from the default theme directory (wp-content/plugins/buddypress/bp-themes/bp-default/) to your child theme directory (wp-content/themes/child-theme/) and placing it in the same sub-folder relative to bp-default.
In your case, first you need to copy register.php file located in buddypress/bp-themes/bp-default/registration/ sub-folder to your child theme (themes/frisco-for-buddypress/registration/register.php).
Next to remove the header elements of this template, create a new custom header file in your theme root directory and call it for example header-register.php. Copy the content of the header.php to the new file and remove the elements that you want to remove (the search <form> and the wp_nav_menu elements), and save the file.
Now open the register.php file that you just copied, and change the get_header('buddypress') at the top of the file to get_header('register'). This way you theme will use your custom header for the registration page.
Comment: There is no folder of registration in frisco for buddypress
Comment: @user1916876: You need to create one.
Comment: oh man! I just did it.thanxx a ton.it was very helpful.thanxx again :)
Comment: I am facing same problem for my homepage also.I have installed wordpress in www.mysite.com/user now the problem is that anybody can access the same thing which was my previous problem.my login page is at www.mysite.com/user/wp-login.php but if anyone enters in www.mysite.com/user he will be able to see all the stuff.how can i edit this?i just want to hide everything from www.mysite.com/user ? this is my /user page http://awesomescreenshot.com/004r2uj47


How to have multiple sheets automatically populate master sheet as data comes in

Question: I am trying to have multiple sheets populate into one master sheet in google sheets. I have figured out how to populate multiple sheets from the master sheet using the <code>=filter()</code> function. However I am unable to figure out how to do it the other way around. Essentially I am trying to track call bookings for our team and am using an external program to automatically populate cells when calls are booked. I have a "master sheet" with all the calls booked for the team, then individual sheets to track calls booked by each rep. I have it so the external program populates the master sheet and then the filter function populates the personal rep sheets automatically, but I cant figure out how to do it the other way around (have multiple individual sheets populate the master sheet automatically as the individual sheets get populated). Is this possible? And if so how do I do it?
Comment: Welcome to [webapps.se]. Please add more details like add a sample data of the source sheets and the expected result in the master sheet.
Answer: The setup you describe exposes you to the risk of formula results getting misaligned with manually entered data. See Lance's explanation of the row misalignment issue.
One solution is to not use multiple tabs, but have everyone edit the master sheet directly. Use filter views in the master sheet to let multiple simultaneous users sort, filter and edit the data without disturbing each other.
For additional ease of use, you can insert links in the frozen section of the sheet to easily switch between filter views, instead of having to go to Data > Filter views to switch. See the Filter views example spreadsheet for an illustration.