Good way to visualize (multiple-layer) within variation of panel data

Question: Now I have a panel data set that contains information of the land supply quota of Chinese cities. What I want to verify is whether the variation (of quotas) among different cities within a province is more volatile than same indicator in provincial level. In another word, the total quota of a province is more stable than which is distributed to the cities it governs. In my preceding econometric setting, I have made the city as the panel variable, so province here is an "upper group" compared to the city. The first approach comes into my mind is to calculate the within variations of cities within each province one by one, using a --foreach-- loop, and then calculate the variance of total quota in provincial level. Comparing these two numbers will give us a brief guide to my question. However, I'm not quite aware of any clear way to visualize this idea. Maybe put multiple time-series lines represented cities from the same province and one line for the province, a "xtline" style graph? Would someone give me a guidance or canned command? thank you.
Answer: You can use some of the panel data commands like xtsum and xtreg, fe to do this. This will give you a couple numbers or their ratio, so this does not quite make for a very interesting graph. One approach would be to bootstrap the ratio and plot a histogram. I show how to do all this below.
. webuse nlswork, clear
(National Longitudinal Survey.  Young Women 14-26 years of age in 1968)

. xtsum hours

Variable         |      Mean   Std. Dev.       Min        Max |    Observations
-----------------+--------------------------------------------+----------------
hours    overall |  36.55956   9.869623          1        168 |     N =   28467
         between |             7.846585          1       83.5 |     n =    4710
         within  |             7.520712  -2.154726   130.0596 | T-bar = 6.04395

As you can see from comparing the SD between women and within women, the hours worked vary almost as much within each woman as across them (7.5 versus 7.8).
You can also calculate the ratio using a fixed-effects regression:
. xtreg hours, i(idcode) fe

Fixed-effects (within) regression               Number of obs     =     28,467
Group variable: idcode                          Number of groups  =      4,710

R-sq:                                           Obs per group:
     within  = 0.0000                                         min =          1
     between = 0.0030                                         avg =        6.0
     overall =      .                                         max =         15

                                                F(0,23757)        =       0.00
corr(u_i, Xb)  =      .                         Prob > F          =          .

------------------------------------------------------------------------------
       hours |      Coef.   Std. Err.      t    P>|t|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       _cons |   36.55956   .0487928   749.28   0.000     36.46392     36.6552
-------------+----------------------------------------------------------------
     sigma_u |  7.8465853
     sigma_e |  8.2323986
         rho |  .47601892   (fraction of variance due to u_i)
------------------------------------------------------------------------------
F test that all u_i=0: F(4709, 23757) = 3.64                 Prob > F = 0.0000

This says that about half of the variation in the data is within women, which is what we saw above. Here $u$ is the fixed effect, which is average hours worked by each woman, so sigma_u is the same as the within SD above, and $e$ is the residual. $rho$  is the ratio of SD of u squared over the sum of the squared SDs, or total variance:
$$ \rho = \frac{\sigma_{u}^2}{\sigma_u^2 + \sigma_e^2} $$
You can then bootstrap the $\rho$ ratio:
. bootstrap ratio = e(rho), rep(500) seed(123) strata(idcode) saving("rhos.dta", replace): xtreg hours, i(idcode) fe
(running xtreg on estimation sample)
(note: file rhos.dta not found)

Bootstrap replications (500)
----+--- 1 ---+--- 2 ---+--- 3 ---+--- 4 ---+--- 5
..................................................    50
..................................................   100
..................................................   150
..................................................   200
..................................................   250
..................................................   300
..................................................   350
..................................................   400
..................................................   450
..................................................   500

Bootstrap results

Number of strata   =     4,710                  Number of obs     =     28,467
                                                Replications      =        500

      command:  xtreg hours, i(idcode) fe
        ratio:  e(rho)

------------------------------------------------------------------------------
             |   Observed   Bootstrap                         Normal-based
             |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
       ratio |   .4760189    .005062    94.04   0.000     .4660976    .4859402
------------------------------------------------------------------------------

The CI is pretty tight. You can also plot a histogram:
. use "rhos.dta", clear
(bootstrap: xtreg)

. tw kdensity ratio

This gives you:


Would it be constitutional for a US state or the federal government to ban all homeopathic "medications"?

Question: Would it be constitutional for a US state or the federal government to prohibit the sale of homeopathic "remedies"?
Comment: **Comments have been [moved to chat](https://chat.stackexchange.com/rooms/151666/discussion-on-question-by-someone-would-it-be-constitutional-for-a-us-state-or-t); please do not continue the discussion here.** Before posting a comment below this one, please review the [purposes of comments](/help/privileges/comment). Comments that do not request clarification or suggest improvements usually belong as an [answer](/help/how-to-answer), on [meta], or in [chat]. Comments continuing discussion may be removed.
Answer:
Would it be legal for a US state or the federal government to prohibit
the sale of homeopathic "remedies"?

Yes.
There are all sorts of medical treatments and drugs that are illegal. In general, Food and Drug Administration (FDA) approval is already required to sell drugs, and they impose a requirement that a drug be both safe, and more effective than a placebo. Homeopathic "remedies" are, by and large, safe, because they don't do much of anything, but are one of the treatments most scientifically well-established to be ineffective.
It probably wouldn't even require legislation for an FDA regulation to declare that anything labeled "homeopathic" (even without accompanying "remedy" language) is, by virtue of that label claiming to be an effective remedy, and to ban that. The barrier to doing so is political and not legal.
The U.S. Constitution does not afford you a legal right to use anything that you want as a drug.
There might be some opportunity for someone to try to claim a religious exemption, but that isn't an easy case to make, because homeopathic remedy advocates almost always claim a pseudo-scientific, rather than a religious basis for using them.
Comment: **Comments have been [moved to chat](https://chat.stackexchange.com/rooms/151673/discussion-on-answer-by-ohwilleke-would-it-be-constitutional-for-a-us-state-or-t); please do not continue the discussion here.** Before posting a comment below this one, please review the [purposes of comments](/help/privileges/comment). Comments that do not request clarification or suggest improvements usually belong as an [answer](/help/how-to-answer), on [meta], or in [chat]. Comments continuing discussion may be removed.
Answer: A state could not do this because of 21 USC 379(r) and other similar federal preemption laws.  This subsection reads:

(a)In general Except as provided in subsection (b), (c)(1), (d), (e),
or (f), no State or political subdivision of a State may establish or
continue in effect any requirement—
(1)that relates to the regulation of a drug that is not subject to the
requirements of section 353(b)(1) or 353(f)(1)(A) of this title; and
(2)that is different from or in addition to, or that is otherwise not
identical with, a requirement under this chapter, the Poison
Prevention Packaging Act of 1970 (15 U.S.C. 1471 et seq.), or the Fair
Packaging and Labeling Act (15 U.S.C. 1451 et seq.).
Answer: The US Constitution says nothing about medications or supplements. Regulation is overseen by the federal department called the Food and Drug Administration (FDA), which  was given authority by Congress in 1938  with the Federal Food, Drug, and Cosmetic Act to oversee food safety, drugs, medical devices, and cosmetics.
The FDA makes a legal distinction between drug and dietary supplement.
A drug is allowed to claim its intent to "diagnose, treat, cure or prevent any disease" after a lengthy FDA drug approval process pharmaceutical companies go through. (In addition, many healthcare providers prescribe "off-label use", but that's a whole another topic.) In contrast, a dietary supplement can carry a "Structure/Function" claim that is substantiated by the manufacturer, and must include a disclaimer that the claims have not been evaluated by the FDA and the substance is not intended to "diagnose, treat, cure or prevent any disease". For more details, here is the text at the FDA website:

Dietary Supplements
Structure/function claims have historically appeared on the labels of conventional foods and dietary supplements as well as drugs. The Dietary Supplement Health and Education Act of 1994 (DSHEA) established some special regulatory requirements and procedures for structure/function claims and two related types of dietary supplement labeling claims, claims of general well-being and claims related to a nutrient deficiency disease. Structure/function claims may describe the role of a nutrient or dietary ingredient intended to affect the normal structure or function of the human body, for example, "calcium builds strong bones." In addition, they may characterize the means by which a nutrient or dietary ingredient acts to maintain such structure or function, for example, "fiber maintains bowel regularity," or "antioxidants maintain cell integrity." General well-being claims describe general well-being from consumption of a nutrient or dietary ingredient. Nutrient deficiency disease claims describe a benefit related to a nutrient deficiency disease (like vitamin C and scurvy), but such claims are allowed only if they also say how widespread such a disease is in the United States. These three types of claims are not pre-approved by FDA, but the manufacturer must have substantiation that the claim is truthful and not misleading and must submit a notification with the text of the claim to FDA no later than 30 days after marketing the dietary supplement with the claim. If a dietary supplement label includes such a claim, it must state in a "disclaimer" that FDA has not evaluated the claim. The disclaimer must also state that the dietary supplement product is not intended to "diagnose, treat, cure or prevent any disease," because only a drug can legally make such a claim. For more information about the difference between structure/function claims and disease claims, see 21 CFR 101.93, entitled "Certain Types of Statements for Dietary Supplements," and FDA's January 6, 2000 final rule entitled "Regulations on Statements Made for Dietary Supplements Concerning the Effect of the Product on the Structure or Function of the Body" (65 Fed. Reg. 1000).

Homeopathic products are detailed on an informational FDA page.

How are homeopathic products regulated?
Under the Federal Food, Drug, and Cosmetic Act, homeopathic products
are subject to the same requirements related to approval, adulteration
and misbranding as other drug products. There are currently no
homeopathic products approved by FDA.
On December 6, 2022, FDA issued a final guidance, Homeopathic Drug
Products, that describes the agency's approach to prioritizing
regulatory actions for homeopathic products posing the greatest risk
to patients. Since homeopathic drug products have not been approved by
FDA for any use, they may not meet modern standards for safety,
effectiveness, and quality.
This guidance proposes a comprehensive, risk-based enforcement
approach to homeopathic products marketed without FDA approval.
FDA's approach will prioritize regulatory and enforcement actions
involving unapproved homeopathic products that pose the greatest risk
to patients. Many homeopathic products fall outside the risk-based
categories described in the guidance. FDA intends to focus its
enforcement authorities on the following kinds of products:

with reported safety concerns;
that contain or purport to contain ingredients associated with potentially significant safety concerns;
for routes of administration other than oral or topical, e.g. for use as an injection or taken nasally;
that claim to treat or prevent serious and/or life-threatening diseases and conditions, such as cancer;
marketed to vulnerable populations, including children, pregnant women and the elderly; or
with significant quality issues.

In 1988, the FDA issued Compliance Policy Guide (CPG) 400.400,
"Conditions Under Which Homeopathic Drugs May be Marketed," which
described the agency's enforcement policy. On October 24, 2019, FDA
withdrew CPG 400.400 because it was inconsistent with the agency's
risk-based approach to regulatory and enforcement action.
Answer: What do you mean by "Homeopathic Medications"?   If you are asking if the actual substance then the answer is that it would not be legal because you would be making water illegal.
Homeopathy is a pseudo-science.   The idea behind it it that water has a 'memory' for things it has encountered before.   You dilute the bad substance with water and shake it up.  You repeat until there is no actual amount of the bad substance left.   There is no plausible method for it to work.   Some German guy had an idea a couple of hundred years ago that this might work and started selling it.
There is no plausible scientific reason for it to work.   Any homeopathic "medicine" you might take could be replaced with any other homeopathic "medicine" (or pure water) and have the same results.  Just try to find an actual explanation of how the "medication" is prepared.  The idea behind it is 'like treats like'.   So if you get bitten by a rattlesnake, you take rattlesnake venom to cure you.   But you dilute it.
The problem is that the normal dose is diluted to 1% 30 times.  I think a good reason for math classes and how your high school math could be used in everyday life is to just think about that.   If you dilute it that much, the resulting water would have 1/10e60 molecules from the original 'bad' substance.
That is an astounding number.  Earth only has about 1.4e46 molecules of water.   While you are almost guaranteed to have molecules of water that have passed through my bladder (and Hitler's, and every person and animal that has ever lived including dinosaurs), you probably don't have any molecules of the substance you were diluting.  There is no mechanism put forward to account for any positive benefit from a harmful substance being diluted to the point of non-existence that doesn't account for everything else the water should 'remember' from where it's been before.
Given that, it is legal for the government to regulate claims of efficacy.  While what you are getting, if the 'homeopathic medicine' is prepared correctly, is 'pure' water, the government can protect its citizens by preventing you from claiming that your water will cure disease.
Answer: My understanding is that anything not addressed by the Constitution can be addressed by Federal, State and local jurisdictions. So if there is nothing in the Constitution that guarantees that a substance marked as homeopathic a homeopathic remedy can not be regulated, then the Federal, State, or local jurisdictions can pass laws to regulate them. Most OTC remedies are subject to the rules set forth by the FDA.
Comment: The 9th Amendment indicates that "The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people."   https://www.reaganlibrary.gov/constitutional-amendments-amendment-9-enumerated-rights-people


Specific Items to add logo/brand image to

Question: How do I create the actual items for my clients brand? For example  - food service client I want to present to go boxes, bags, cups with their logo - Do I need to create the blank item if its an actual item that exists? I have adobe suite - so basically packaging items for clients.
Comment: Welcome. Can you please clarify what exactly you are asking here? Is the question about visual illustrations, physical mock ups, creating artwork for print or something else?
Answer: Appreciate @Chris's request for clarification. I think I know where you are going with this. From experience (food client):

First, I mock-up visually in Photoshop and take representative samples (unprinted) or a mood board of relevant images to ID the approach and application. There are many different cups, boxes, bags and there is no point printing samples just to be told by a client that they don't like the shape, colour, material. Normally this is a simple flat plan view as in here:

From the feedback I will work second visuals up to agreement on sample / design. Here is an example of a more finished visual with a 3D perspective. Note: In order to visualise the Whisky point of sale unit in advance, I had to have the specification from the manufacturer and in this case I asked for a sample which I made up and filled with random CDs, photographed and then re-worked with my art in Photoshop.

In the meantime, I would run the concept by the supplier to check it is practical for their product /substrate and ask for any particular art / repro requirements they have - if it's film for example, they will want vector art from illustrator and prefer to avoid drop shadows and vignettes (they can be done but its more work / expense).
Dependent on the client and scale of the project I would now print a sample on stock for final sign-off (if its a national / multi-national they will expect this) OR I would go to print on a short run.

Note: if you are already passed this point and are asking how do I create these packaging items for fulfillment, then you have a little more homework to do. Packaging is a skill in itself and there is little leeway for error. On a box for example, you will require a flat template file (normally an EPS) from the manufacturer which will give you the exact sizes, folds, bleed to provide in your art. Have a look at this one for VR goggles in card I recently received.

Clearly this takes some time and effort which is why packaging is not cheap. On food packaging, when using film I might have 3 or 4 meetings with the engineer and production unit to ensure the film is outputting correctly before it is shipped to the supermarket. On this scale, we produce the actual piece with product inside before it ships and test for presentation (how to stack it on a shelf, clarity from 6ft away etc), travel - are the seams strong enough, can we make it lighter, can we fit more in a transportation box by changing the shape, can we change the substrate for something with more longevity (like rigid PVC instead of card). It's not always this convoluted (it might simple be a logo on a card cup) but it pays to go in with your eyes open to the work required in some cases, so always talk to the manufacturer early to get a handle on what you are dealing with for production.


How do I find the historical arrival procedure GOLDN6 for SJC that is no longer valid?

Question: I don't know exactly when this procedure disappeared.  It was used in 2013, but not sure how much longer.  It was used primarily by SEA to SJC flights.
Comment: And, to pre-empt objections about "resource location is off-topic," the real question here is about a method: how to go about researching retired procedures. And that's a perfectly valid question - because the answer **isn't** to go buy them from Amazon or from Sporty's or from Wal Mart or etc.
Comment: No idea how well it'd actually work, but I wonder if an old flight simulator with an "out-dated" database might have some useful info. It wouldn't be the whole plate, but you may be able to get fixes/coordinates out of it.
Comment: Welcome to Av.SE.
Answer: Understand that the numeric part of the arrival (6 in GOLDN6, for example) changes over time. Maybe the FAA adds, or removes, or changes a speed restriction at a given waypoint on the arrival. The number will go up, and the new version will be effective on a given date. Then in some number of months, something else changes, and the number increments again. When it gets to 9, the next revision goes back to 1.  (Which is okay, since the last GOLDN1 was now years in the past, and what's important is differentiating the current procedure from one that was recently superseded.)
Typically, these revisions are pretty minor, and when airspace gets revised on a large scale, the old procedure names are all retired, and all new procedures are published with all new names.
All of that to say, if you search for "GOLDN arrival SJC" (and don't let the search engine helpfully substitute 'golden' in the query), you may find a chart of the GOLDN4 or GOLDN5, which would most likely be quite similar to the one you're interested in.
I imagine that the FAA TERPS office keeps archival copies of everything that they've ever published, as (probably) would OAK Center and the NORCAL TRACON, and (almost certainly) Jeppesen, but those avenues start becoming a lengthy research project, trying to get in touch with the right person in the right office.
Hopefully this helps with the search.
Comment: Turns out that "GOLDN arrival SJC" is less useful than "Golden Gate arrival SJC" -  the first result for the latter is: https://www.fly.faa.gov/Information/west/zoa/sfo/atcCharts/SFO_STAR_00375GOLDENGATE.pdf
Comment: I am interested in revisions of GOLDN.  GOLDN6 was the last version.  I did google it and found only one link on flightaware.com to a flight about 8 years ago.  Unfortunately, corresponding  decode page was unable to display the waypoints and lat, long.  So if anyone has ideas on how to find this history it would be appreciated.  Is there a way to search archived NOTAMs?  I would appreciate very specific instructions.  Here is the one flight I found https://flightaware.com/live/flight/ASA324/history/20130718/1925ZZ/KSEA/KSJC.
Comment: If this is for research of some kind, Oakland ARTCC (located in Fremont) would probably have the answer in their Airspace and Procedures office. The A&S office keeps current procedures, but should also have access to archive data. Their main switchboard is at 510-745-3000.
Comment: The GOLDN standard terminal arrival route (STAR) was decommissioned about a year ago (I write ATC simulations for Denver ARTCC, and have to be current on stuff like this). It had transitions from the east over OAL VOR (in addition to transitions from SEA and others), and we saw it a lot here in Denver. VOR-based STARs are going the way of the dodo, however. RNAV STARs are the future.
Comment: Googling does little good if the sought after document is deleted from databases, as in the case of approach plates, and procedure documents like SIDs & STARs is done, for obvious reasons. And anyway, I'd strongly advice against "google it" -answers, as they simply are not usefull at all.
Comment: @Jpe61  There is more in the answer than simply "google it," but if that being included is worth the dv, be my guest. See also first comment, above.
Comment: Fair enough, I edited the answer to bring the usefull part to the front. Took the liberty to completely remove the obvious.


Is there some sort of macro facility for inserting repeated actions?

Question: I'm new to Final Cut Pro X. I do a lot of shooting with two cameras and sometimes I want to do split screen, and other times I want to show one view or the other. I transition from one view to another or from one view to split screen by inserting keyframes and changing the Transform and Crop values between them. But trying to get the keyframes just right for each change is tedious. Can I create some sort of "macro" when I can just click and insert a change from view 1 to split or the opposite, view 1 to view 2 or the opposite, or view 2 to split or the opposite? I'm not even sure what the terminology is.
Answer: You want to transition from 2 video feeds in one video to full screen video and back?
(Took me a while, I thought you were talking about the viewers on your monitor while editing multicam)
You can do it one time and cmd+C it. Then where you want to use it again do Shift+Cmd+V and choose which effects (in this case transform) you would like to paste. Works for other effects too.
You can also use a generator that does it, if you can find one or modify or create one in Motion 5 for a more permanent solution. But you'd need to learn how to do that first.
I know it can be tedious work. With Keyframes, I start with the end and work myself backwards. So when you start out with 2 feeds side by side, keyframe them at the begin situation, go to the frame where you want it all to be one video, that's the end situation. There you adjust it to what it should look like.
Play it through and if not perfect yet, walk backwards with a few frames at a time (arrow key) to adjust what you need to.
If the transformations and crops are the same for multiple cuts, you can also screenshot the inspector values for them and just type those in for the next cut.. so you don't need to do it by eyes anymore.
Hope it helps.. good luck!


How to solve for all real values of $x$, $y$, and $z$?

Question: $$
\begin{align}
  2z &= 1-\sqrt{x} \\
  2y &= 1-\sqrt{z} \\
  2x &= 1-\sqrt{y}
\end{align}
$$
Is there a way to solve it?
I have tried using simultaneous equations, but it ends up with 0=0.
I have tried squaring both sides and getting rid of one variable, but it just ends up with 0=0 in the end, is it that there is multiple real solutions? I'm confused because the question states to find all real solutions.
Is it a function or is there actually solutions?
Comment: Hi, welcome to Math.SE. Please indicate what you have tried and where you are stuck. (i.e. how did you get to $0=0$?) This will help people better tailor their answer to your background and situation. It will also demonstrate that you are interested in your question and not just looking for someone to do your homework for you - Math.SE is not a homework site.
Answer: Eliminate the square roots by rewriting
$$x=(1-2z)^2,\\y=(1-2x)^2,\\z=(1-2y)^2.$$
Then by substitution you obtain a nice polynomial equation,
$$x=(1-2z)^2=(1-2(1-2y)^2)^2=(1-2(1-2(1-2x)^2)^2)^2$$
that has $8$ real roots in $[0,1]$, among which $\frac14$ and $1$.

All these roots are valid solutions, as they yield positive RHS.

Better, if you set $x=\cos^2(w)$, the equation is
$$\cos(u)=1-2\cos^2(w)=-\cos(2w),\\
\cos(v)=1-2\cos^2(2w)=-\cos(4w),\\
\cos(w)=1-2\cos^2(2w)=-\cos(8w),$$
and
$$w=\pm(\pi-8w)+2k\pi.$$
For completeness, the signs must be discussed.


Can "× Int" skill ranks only be used for Int-based skills?

Question: When a character levels up they get a number of skill ranks based on their class and race. But the core rulebook says that a character gets × Int skill ranks.
Does that mean those skill ranks can only apply to skills based on Int?
Answer: No.
The Pathfinder Core Ruleboo0k has the clearest explanation, p.86:

Each level, your character gains a number of skill ranks dependent on your class plus your Intelligence modifier. You can never have more ranks in a skill than your total number of Hit Dice.

There are more words, but no additional restrictions. It also points out that humans get an extra skill rank each level, and races which take a level in a favored class may receive an additional skill rank.
Table 4-1: Skill Ranks, which shows the ranks each core class gains at each level, reinforces this by describing the base ranks gained as (for example) "4 + Int modifier."
So, there is no distinction between ranks gained from class and those gained from Intelligence, and you may freely assign the entire pool to skills however you like (subject to the Hit-Dice limit).
This is paraphrased in the "Allocate Skill Ranks" section of the character creation page of the online Pathfinder SRD. I find it slightly harder to follow there, but the meaning is identical.

There is a minor terminology discrepancy in the description of skill ranks between the skill section and the description of Intelligence on page 17 (thanks to KRyan and Hey I Can Chan for pointing it out in the comments). Under the Dungeons & Dragons 3.5 system (which was generalized in the d20 SRD, which Pathfinder was derived from) there was an additional step to this process: skill points. At each level in 3.5, you received some number of "skill points" based on class and intelligence, then bought skill ranks with those skill points, subject to some additional rules (not germane to this answer). The description of Intelligence on Pathfinder p.17 (and on the Pathfinder SRD) refers to gaining Skill Points instead of Skill Ranks. There is a similar error on Pathfinder p.30, under "Advancing Your Character," and there may be other similar issues.
"Skill Points" is almost certainly a translation error (and is certainly some sort of error). You should read it as gaining additional Skill Ranks instead, wherever it occurs.
Answer: No, you're misreading the notation.
Characters receive X + Y skill points per level, where X is the amount determined by class, and Y is your Int modifier.  The total of these two values is the total amount you can spend on skill ranks, regardless of what attributes correspond to them.
The notation is saying that you get more points based on Int, not that they are skill points only for Int-based skills.  There is actually an addition sign, not a multiplication sign.

Can “× Int” skill ranks only be used for Int-based skills?


What is the difference between Schedule and Arrange?

Question: What is the difference between "Arrange" and "Schedule"? How can I use these words in writing sentences and speaking? What are some examples of use?
Comment: To schedule is specifically time/diary related, but to arrange is not always. You can arrange a meeting in principle without there being a specific schedule.
Comment: You can also arrange the flowers on the table, the guest seating and books on the shelf.
Answer: The meanings of "Schedule" and"arrange" (as verbs) overlap, but are not identical. In some contexts they can be used interchangeably.
For example:

(1)  I scheduled a meeting for 3:00 pm tomorrow.
(2)  I arranged a meeting for 3:00 pm tomorrow.

Sentences (1) and (2) have very similar, possibly identical, meanings. However (1) could mean that the speaker has placed it on his or her own schedule, or on some official schedule, but has not yet secured agreement from other participants. Sentence (2) pretty clearly implies that agreement has been obtained, and (1) could  mean the same thing.
But "arrange" can cover making physical arrangements. In general "schedule" refers to setting a specific timer, while "arrange" may not. "arrange"  has a broader range of meaning.


How do I keep my solar panels clean?

Question: What sort of cleaning regime should I have for a solar energy system, and do PV and solar-thermal panels need to be treated differently?
Comment: Location, location, location. Many factors are involved: traffic intensity, average rain and wind, angle of the panels, height above the ground,  nearby industry,.... Do you have a specific location in mind?
Answer: I only have one anecdote and avague idea:
 An agrarian schooling center (Haus Düsse) in Germany clean their PV System once a year, and clean/dirty means a difference of 10% effectiveness. However, as this is basically a small farm with lifestock, different grain treatments, lots of diesel vehicles etc. you would expect far more dust there than at a lot of other places. 3 years ago, they were starting to systematically analyze what's the most economic cleaning regime.
Comment: The anecdotal evidence I've heard here in Montana, USA seems to confirm this.
Comment: To add another anecdote: I just visited a roof mounted PV system (>50 kW) with a very small roof pitch/slope of say 10°. The operator claimed to clean the modules each year in the springtime as the agricultural workings on the farm foul them significantly. Story 2: I am the "caretaker" of another PV system (18 kW) roof mounted, about 30° slope and we do not clean them on a regular basis as we do not see a significant drop in output power (so far), operational time 'bout five years now.
Answer: I work and attend classes at a University in Florida. Our 100kW system has been installed for more than five years without a single cleaning. I have walked the solar field several times and can confirm that no significant dust has collected. (The angle of inclination is about 27 degrees.) But, Florida rains a lot and that helps keep everything clean. I imagine desert areas with wind storms would be much worse. But a duster at best or some cotton rags and dish-soap at worst would be more than enough to keep any system clean.
Answer: I personally calculated the ratio energy to insolation for a friend's home system with shallow angle (15°) in the Netherlands after they got cleaned them for the first time in 5 years and there was no discernible improvement. The uncertainty is about 2% so the improvement must be lower than that.
Conclusion: it is extremely system and location dependent.
Answer: It depends on what is fouling the panels, if like us you have Lime trees nearby that drop a sticky residue in summer then you may need to clean the panels more often.
We see a 10-15% gain in power generated immediatley after cleaning the panels when they are dirty.
The angle of the panel in combination with the amount of rainfall will also affect how often the panels will benefit from being cleaned.
To clean the panels we sometimes just spray water on them or if they are heavily fouled we used a telescopic brush designed for cleaning cars.

How do I keep my solar panels clean?


firefox add-on vs. extensions vs. plugins

Question: I want to write scripts for firefox. It seems that firefox has different terms, like add-on, extensions, plugins. and I have a feeling they're not all the same. Can you sum up the difference between in a few words?
Comment: http://stackoverflow.com/q/2041261/632951
Comment: For similar chrome question, see https://stackoverflow.com/questions/16815389/what-are-chrome-apps-vs-plugins-vs-extensions-and-how-to-develop-them
Answer: Add-on: essentially anything that can be installed into the browser. This includes for example extensions, themes, plugins, dictionaries, language packs, search engines.
Extension: a package extending browser functionality, the extension format used by Firefox works in Gecko-based browsers only. Extensions typically use XUL and CSS for their user interface as well as JavaScript for dynamic actions. They have full access to XPCOM and can provide their own XPCOM components as well. Recently the Add-on SDK has been added as an alternative way to generate simple extensions, it uses HTML instead of XUL but limits the ways in which the browser's user interface can be extended significantly. As of Firefox 57, all extensions have to be based on the WebExtensions API.
Plugin: means NPAPI plugins that are supported by all browsers but Internet Explorer (the latter uses the proprietary ActiveX technology instead). Such plugins are binary libraries that are invoked if a website uses an <embed> or <object> tag with a type that is handled by the plugin. The plugin can either draw some content for the tag (windowed plugins) or stay in background and simply provide an API for the webpage's JavaScript code to use (windowless plugins). Typical examples are Flash or Silverlight. Support for plugins is being phased out, as of 2018 Flash is the only plugin still supported to some degree.
Answer: Augmenting the useful answer above, I found this high-level summary helpful:

Extensions differ slightly from plug-ins. Plug-ins usually have a narrow set of abilities. [..] Since plug-ins and extensions both increase the utility of the original application, Mozilla uses the term "add-on" as an inclusive category of augmentation modules that consists of plug-ins, themes, and search engines.

(from http://en.wikipedia.org/wiki/Plug-in_(computing))
Comment: Hmm, aren't plugins supposed to be more powerful than extensions? There seems to many things that cannot be done by extensions, but plugins have *no limit*.
Answer: According to Firefox:

Extensions

Extensions add new features to Firefox or modify existing ones. There are extensions that allow you to block advertisements, download videos from websites, integrate Firefox with websites like Facebook or Twitter and add features included in other browsers, such as translator.

Plugins

Plugins add support for all kinds of Internet content. These usually include patented formats like Flash that are used for video, audio, online games, presentations and more. Plugins are created and distributed by other companies.

add-ons

They are - Extensions, Plugnis, Themes, Search engines and Dictionaries & Language Packs.
Source: Firefox - https://support.mozilla.org/en-US/kb/find-and-install-add-ons-add-features-to-firefox
Answer: Extending the Augmentation above
Extension(s) is ment to extend the functionality of software
where a plug-in is ment to solve a problem of the software (to be able to do something it wasent designed to do already).
both types extends the program abilitys,
... and i guess this is why it can be so comfusing.
An Extension can be (and often are) a(n) option from the company that made the software (Usually cost money),
a plug-in can be from the company that made the software or a third party to add abilities to the software.


Comparison of k-means clustering output

Question: I am trying to compare the outputs of k-means algorithm coded by me and the outputs of R's kmeans. Since the objective of the algorithm is to minimize the total within cluster sum of squares (WCSS), I have to look at the withinss output of kmeans and my WCSS. What I'm not able to figure out is, how much of variation should I allow i.e. how close should these values be so I can say that they are close. (I know that I can also verify using the centroids, but when the data is not that well clustered, the centroids can be very different but the total WCSS can be close, and hence I'm looking at WCSS.)
Comment: There must exist an option in k-means to set initial cluster centres. Compare the 2 programs in that regime (give identical initial centres for both programs). Test many times: different data sets, vary _k_, vary the initial centres. The 2 programs should give identical results consistenly. Only then you can be sure there is no bug in both programs.
Comment: `how much of variation should I allow` To be sure that your code is all right there should be no difference in results between your implementation and a reference implementation at all. Until you reach that regularly you can't tell if the difference is due to a code bug or due to some minor algorithmic divergence.
Comment: I agree that there should be no difference. I'm using the Iris dataset and we know that there are 2 clear clusters in the data. Hence when I give k=2, the output perfect matches with R's. In fact, the output is perfect for k=3 and k=4 too (I use 'nstart' to get the best output). But for k=5 and above, the values are varying. The total WCSS for R's kmeans for k=5 was 46.4 while the same for my algorithm was 49.4. So, should I allow this as a close output since I know that the actual number of clusters are 2 and that further clustering can happen in multiple ways?
Comment: Thanks. I tried what you just said for k=5 and the outputs unfortunately, are not the same. But they are very close. Only one point has been clustered differently. I think this is because that point might be equidistant from 2 centroids, and in the 2 algorithms, this point is put into different clusters (since equidistant points would be clustered randomly). And they were consitent for other k values too. The difference in WCSS for k=5 was 0.009. I feel this close enough, but I wish I had a quantitative threshold above which I would approve it as good enough clustering.
Comment: Oops, I meant '..below which I would approve it as good enough clustering.'
Answer: As k-means on multiple runs will find different local minima, they can pretty much vary arbitrarily much. On contrary, if two values are close but not identical, I'd consider it much more likely that there is some slight error in one of the two implementations.
If there are multiple local minima, multiple runs with different seedings should give you a number of candidates so there is a high chance of actually finding the same result.
But in the end, k-means is so simple, and such a crude heuristic, what good is it to compare two results? On many data sets it still pretty much a random partitioning; optimized for a local minimum but still meaningless.
Comment: "On contrary, if two values are close but not identical, I'd consider it much more likely that there is some slight error in one of the two implementations." I disagree. If you assume a uniformly spread dataset, it is possible that the the centroids are not close but the WCSS are close.
"But in the end, k-means is so simple, and such a crude heuristic, what good is it to compare two results?" - Do you mean to say that verifying k-means is meaningless. I mean, I can look at 2 different values of total WCSS and come to a conclusion that one way of clustering is better than the other.
Comment: Yes, but uniform data does not have reasonable clusters. The clustering algorithm should reply "no clusters found".
Comment: Well, the kmeans in R clusters points irrespective of the data. The algorithm wouldn't know how many clusters are present. That might be something we would infer from the output.

Comparison of k-means clustering output


How do I install 12.10 on a Pavilion-G6 laptop with UEFI

Question: I have a brand new HP Pavilion-G6 which boots to pre-loaded Windows8 and I want to change the machine to boot up into Ubuntu 12.10 whist retaining Windows 8.  I am having difficulty booting into Ubuntu - I have done the following.

Downloaded 12.10 (64 bit) from Ubuntu site and burnt it to DVD.
Run the DVD from within Windows (failed to reboot the machine)
Installed the Boot Assistant from the DVD which allows a boot up offering Ubuntu 12.10.
Rebooted laptop (both with DVD in and out of the machine) selected Ubuntu option
Always get the same result - Black screen with white text saying C: Ubuntu\winboot\wubildr.mbr file not found.  I have checked in Windows and the file does exist.
Researched the forums and seen various forums for answers.
I noticed recommendations to reconfigure BIOS to disable Secure Boot and select 'Legacy' boot up mode.  I'd love to do this but HP have loaded their own 'Boot up management software' as the BIOS editor with no such options provided (at least I've not seen anything that looks 'safe' to click).

Surely life should not be this hard - and I cannot be the only one with problems?
Has anyone out there actually achieved an Ubuntu 12.10/Windows8 boot up on a Pavilion G-6 laptop pre-installed with Windows8?  If so, how do you do it please?
Comment: Are you wanting to install WUBI or native Ubuntu? Their installation processes are very different.
Comment: I'm after the simplest way to get 12.10 on the machine as a non-technical person - so preferably WUBI. But just to make it clear - the end result should be booting up the machine and going into 12.10 by default without opening Windows at all.  Thanks for helping me.
Comment: @Rod Smith has given a good reply. WUBI is great for experimenting with Ubuntu, but many people find it not a good long-term solution. I don't know how well WUBI has been tested with UEFI.
Answer: The last I heard, WUBI didn't work well on UEFI installations; however, I don't follow WUBI very closely, so that may not be accurate. If it is accurate, your best bet is to ignore any WUBI-style boot options and instead boot the Ubuntu CD/DVD directly using the firmware's boot manager (usually accessed by hitting a function key soon after you power on). You may see two CD/DVD device entries in the list; be sure to select the one that's marked as being for "EFI" or "UEFI" and not one that's marked as "BIOS" or "Legacy." Once the installer is booted, I recommend dropping to a shell and checking for the presence of a directory called <code>/sys/firmware/efi</code>. If it's present, you've booted into EFI mode; if not, you've probably accidentally booted into BIOS/legacy mode. Do not proceed with installation in BIOS/legacy mode. Although you can get it to work this way, you'll need to jump through some extra hoops, so it's better to go back and at least try to get the installer started in EFI mode.
Ubuntu 12.10 does support Secure Boot, but this is a brand-new feature and so it may yet be buggy on some systems. If you want to eliminate Secure Boot as a possible source of trouble, you can certainly disable it using your firmware setup utility, but the details of how to do so vary from one system to another.
FWIW, part of the problem with UEFI systems right now is that, despite a strict and detailed UEFI standard, manufacturers are introducing their own unique bugs, quirks, and idiosyncratic ways of doing things. It's like a cross between the Wild West and the Soviet Union. The point of this is: If you get a computer and it's giving you too much grief getting the Ubuntu installer to boot, return it, and make it very clear why you've done so. You might end up with something a little less mind-bendingly dysfunctional. FWIW, I've seen more problem reports about Sony and HP machines than most others, but I don't know if that's because they're worse than others or because they're more popular than others.
Comment: @ Rod I have tried what you have suggested but have failed.  Just so that we all know what I'm using here, the burned DVD is Ubuntu12.10 "Quantal Quetzal" Release i38C#.  In windows I see the following directories:  .disk ; boot; capser; dists; install; isolinux; pics; pool; presed and the following files:  autorun ; md5sum; Readme.diskdefins; Wubi  .  What concerns me is that I do not see any sys directory.  Am I using the right disk?  Whatever I try, the BIOS ignores the DVD and boots straight to Windows.
Comment: @ Rod For further information BIOS {Insyde F.12} settings:  CD-Rom boot ENABLED; Legacy Support DISABLED; Secureboot ENABLED; UEFI boot order  INternal DVD>USB>DVD>OS Boot Manager>USB Diskette>Network Adapter
Comment: The files visible in a CD or DVD are largely irrelevant for booting, since CD/DVD booting is done via El Torito, which hides the files in a separate filesystem. I recommend disabling Secure Boot, since it's possible that's interfering with your boot. If that doesn't work, try creating a bootable USB flash drive; maybe that will work better for you.
Comment: @ Rod Thank you for your continuing support.There is progress.  The DVD won't boot irrespective of Secure Boot BIOS status.  I created a bootable USB flash drive, rebooted and pressed ESC/F9. GRUB 2.00 appeared. I selected 'Install Ubuntu'.  The flash drive flashed, the screen went black and I heard the Ubuntu drums(music to my ears).  But then the screen stayed black. When I tried the check disk option in GRUB that went black too. I feel we are close.  Have you any suggestions please?  I can almost smell success. BTW - is it worth trying WUBI again from the flash drive? What do you think?
Comment: @ Rod It's a fix - I think?  I really don't understand what happened but after the black screen I booted to Windows and then rebooted to GRUB. This time I selected demo mode and the screen came to life with that wonderful Ubuntu pattern of moving dots.  Having checked that the wireless adaptor picks up my WiFi (thank goodness for that) I exited, rebooted to GRUB and selected the Install option.  It's doing its thing right now.  :-)  Once the installation is complete, I shall post another comment to let you know the result.
Comment: @ Rod.  I'm going to classify this as answered as Ubuntu has successfully installed on the machine.  It does not boot up by default (I've still got to press Esc then F9) - but that's another issue and it would be confusing to others to discuss it on this post.  [Thank you]^ 100
Comment: One final but important point - after some trial and error I found that GRUB will appear if Secure Boot is set to ENABLED.  It must be set to DISABLED.
Comment: correction - after some trial and error I found that GRUB will NOT appear if Secure Boot is set to ENABLED. It must be set to DISABLED.
Answer: This appears to be the same method I came up with independently to boot my HP DV7 Envy (essentially the same build as a DV7 Pavillion).  Here's a cut and paste I've been posting of what I came up with (trying to spread the work to other hapless HP owners ou there :))
For your reference,  this is how I achieved dual boot with vendor (HP)  installed Windows 8 / Ubuntu 12.10 on the machine that's in the linked data sheet,  with manufacturing date 08/12:
http://www.shopping.hp.com/shopping/pdf/c2h70ua.pdf
The chipset=HM77, Mobo=HP C181
In UEFI (F10 menu):
• •Disable Secure Boot. I could not achieve boot in any configuration with it on.
• •UEFI boot scheme (not Legacy BIOS). I tried Legacy mode, and can boot from disk, but not from an installation on the hard drive. UEFI flies right by it during boot every way I tried with it on.
In Ubuntu:
• •/Boot=EFI, /=EXT4, /Home=EXT4, SWAP=swap.
With this configuration I can boot with user intervention during the boot sequence:
1) During the boot sequence, select F9 to obtain Boot options in UEFI (BIOS)
2) In UEFI / BIOS, select the available Ubuntu Linux 2.6.32-21 option and proceed.
3) Ubuntu GRUB boot option screen is now available. Select preferred option and proceed.
4) I'm in.
Comment: Sorry for the delay in responding.  I'm glad you've got it working.  I hope this item has helped a few folks out there with HP laptop Christmas presents to have a slightly better 'holiday' than would otherwise have been the case.


Using real football player photo in a trivia quiz game, is it legal?

Question: I don't know whether this question was already been asked before, but my team is currently developing a trivia quiz game about football (soccer not NFL). And we want to put player's images or club emblems as part of the questions and answers. My question is, is it legal? Or should we just put text without the images? Please your help is much needed. Thank you.
Comment: It's a long read, but it may be worth it: http://www.postmatch.org/251/ronaldo-beckham-aguero-football-image-rights/
Answer: I'm not a lawyer but it is probably not legal -- minimally, the players did not agree to you using their portraits for your own purposes. Then you can assume that the photographer holds the copyright for the photo (or some third party does who acquired the copyright). In addition, there's a good chance that logos, emblems etc. are trademarked so you cannot use those either.


Reset External HDD password without losing data

Question: I set a password on my external HDD using disk utility. Now I am trying to access my HDD however, I cannot access it even if I am trying to give right password. Is there a way to reset this password without losing any data?
Answer: Highly unlikely.
The purpose of disk encryption is to make it so that someone unauthorized (that is, who doesn't know the password) can't access your data. Being able to reset the password and still get at the data defeats the purpose.
If you used that drive on a different system, and you allowed that system to save the password so it could automatically access the drive, then there is a slim chance that it could be sitting that other machine's Keychain Access secret store. (Whereby you'd open the Keychain Access app, authenticate, scan all the list of entries for the one that looked like your drive, click it, likely re-authenticate again, and it'd [in theory] show you the password to use on the first machine.)
Other than that, set the drive aside and see if the password comes to memory at some point in the future. Reformatting the drive will lose the data. Trying to get at it without the password ought to look like jumbled bits -- and you certainly don't want to alter them for fear of corrupting the underlying information.
For the future, always-always-always squirrel device access and/or recovery passwords somewhere away secure, whether on paper or in a password vault (like 1Password, LastPass, or some other similar secrets manager).
Sorry this wasn't the answer you hoped for.


Can you take food into the bathroom?

Question: Is one allowed to take food into the bathroom? I heard that the prohibition is only on the type of bathroom used years ago.
Answer: Is one allowed to take food into the bathroom?
Eating in the bathroom is forbidden,(Be'er Heitev O.C. 3:2)even if it is covered.(Lekutei Maharich page 226 (new),Yabea Omer 4:5:3,see Minchas Yitzchok 3:63 who questions the reason not to bring food into a bathroom) we do not find that the poskim expressly prohibit bringing food into a bathroom. Surely b'diavad, food, drinks, vitamins or medicines that were stored there do not become forbidden to ingest.(Minchas Yitzchak 3:63)Some poskim suggest that if possible the food should be washed off prior to eating it.( Yaskil Avdi 7:44:9:page 64, Otzros Yosef )One is permitted to keep medicines in a medicine cabinet that is in the bathroom.(Rivevos Ephraim 1:8:2, 2:6, Teshuvos V'hanhugos 1:11, Shevet Ha'kehusi 2:245)Some say one is permitted to drink water from the faucet in a bathroom (one should obviously recite the beracha outside).(Ohr L'tzyion 1:1, 2:1:9. One should nonetheless try to drink the water outside (Ohr L'tzyion 2:1:9))
What about todays Bathrooms?
There is a major dispute among the poskim whether or not today's modern day bathrooms are considered to be like the bathrooms of earlier times. Ealier style toilets did not retain waste materials and were known as "parsoy."(Gemorah Berochos 26a, Rashi d'parsoy," Shulchan Aruch 83:4.) In present day toilets the waste remains until it is flushed away. Nonetheless, many poskim say that our bathrooms are considered the same as the olden style bathrooms and one can be lenient in regard to the halachos that apply.(Minchas Yitzchok 1:60, Yechaveh Da'as 3:1, Ohr L'tyzion 1:1, 2:1:9, Shearim Metzuyanim B'Halacha 1:2:6) However, most poskim argue.(Har Tzvi O.C. 1:50, Chazzon Ish O.C. 17:4, Igros Moshe E.H. 1:114,Halichos Shlomo Tefilla 20:24, Yabea Omer 3:2) Therefore, in case of necessity one can rely on the lenient view, but l'chatchilah our bathrooms do not have the status of the bathrooms of "parsoy."(Minchas Yitzchok 1:60)
Quoted from:

http://torahsearch.com/page.cfm/293
R' Moishe Dovid Lebovits. Halachically Speaking: Halachos Regarding The Bathroom.
Comment: Just for clarification, when the gemara/poskim talk about "their" bathrooms, those were worse than ours because they retained waste.  In brachos 26a, in order to answer a question, the gemara makes an ukimta that the case at hand is refering to a Parsa'i toilet where the waste drops away (not the norm for them).  Like you said, the poskim debate if our toilets are like the Parsa'i toilets.
Comment: Its hard to forbid something not forbidden by the Torah, Neviim, Mishnah, Tosefta, Sifra, Sifrei, Mechilta, Bavli, Yerushalmi, Geonim, Rambam, Rishonim in general, Tur, and Shulchan Arukh.
Comment: @mevaqesh - if it's not forbidden by any sources you cited, what do the above poskim base their ruling on?

Can you take food into the bathroom?


Time derivative of unit velocity vector?

Question: Let's say I have some parametric curve describing the evolution of a particle $\mathbf{r}(t)$. The velocity is $\mathbf{v}(t) = d\mathbf{r}/dt$ of course. I am trying to understand what the expression for $$\frac{d}{dt}\frac{\mathbf{v}}{\Vert\mathbf{v}\Vert}$$
is. I think it should have something to do with the perpendicular acceleration to the particle's tangent vector, but I can't seem to get any meaningful expression that would tell me this. Helping hand would be appreciated here.
Comment: See [here](https://physics.stackexchange.com/a/646088/83835).
Answer: As the magnitude of a unit vector cannot change, $\dfrac {d\hat v}{dt}$ is related to the rate of change of the direction of the velocity.
Answer: The following is valid for any unit vector $q=Q/|Q|$, where $Q$ is a function $Q: \mathbb{R}\rightarrow \mathbb{R}^D$.
Therefore, $q(s)$ is a curve in $\mathbb{R}^D$ such that $|q(s)|=1$ for all values of the real parameter $s$.
Given that $|Q| =\sqrt{Q\cdot Q}$, direct calculation gives:
$$
\frac{dq}{ds}= \frac{d }{ds} \frac{Q}{\sqrt{Q\cdot Q}}
= \frac{1}{|Q|}\perp \frac{dQ}{ds} \, ,
$$
where $\perp$ is the operator that projects any vector on the $(D-1)$-dimensional  subspace orthogonal to $q$.
In index notation (using Einstein notation):
$$
\frac{dq_i}{ds}= \frac{1}{|Q|}\perp_{ij} \frac{dQ_j}{ds}
$$
where $\perp_{ij}=\delta_{ij}-q_i q_j$. This is consistent with the idea that the derivative must be orthogonal to $q$, which comes from the fact $d|q|/ds=0$. A totally analogous reasoning is used in special relativity to show that the 4-velocity and the 4-acceleration are "orthogonal" or that (as pointed out in the comments) a centripetal acceleration does not change the speed.


Is there any prohibition in a Yisraeli or Levi marrying a Bat Kohen?

Question: Is it assur for a Yisraeli or a Levi to marry a Bat Kohen? I know there are prohibitions for a Kohen when it comes to marriage but I was wondering if there are any special requirements for the husband of a Bat Kohen.
Comment: Have you never met the daughter of a kohein who is married to someone else? I'd expect that to be more common than the daughter of a kohein marrying another kohein.
Answer: The Gemara in Pesachim 49A states that an Am Haeretz (Ignoramus) should not marry a Kohenes (daughter of Kohen). If they do, the marriage won't last, as one of them will die young or they will quarrel. This is also stated in Shulchan Aruch Even Haezer 2:8. It seems from Ramah in 2:6, that it may only refer to someone who is lax in keeping the mitzvos. Pischei Teshuvah quotes Chavas Yair, that today's religious Jews are not considered Ignoramus regarding this law.
Answer: No there isn't.
Gemara in Pesachim (49a) discusses two apparently contradictory sentences of Rabbi Yochanan, one which says that if an Israel who marry a Kohen's daughter, the couple does not succeed. In the second sentence, Rabbi Yochanan says that in way to be rich, it's good to marry the daughter of a Kohen. The conclusion is that the Israel who is Am haarets is not adapted to her, but a Talmid chacham is. This is not an Halacha of Yochasim, as the mitsvot of Kohanim a dressed below.
The Tur and Shulchan Aruch (in sayif 8) quoted the conclusion of the Gemara. We already  soon that this rule is more an advise than a prohibition.
Strict laws of marriage:
Kohen women have not the same restrictions as men (e.g. regarding the prohibition to be unclean Bene Aharon and not Benot Aharon, see Rambam Isure Bia 19, 10 who uses this drasha, according to the Magid Mishne understanding, to allow chalal to marry with a divorced woman or a convert, so it is obviously true for a kohen woman not least than for a chalal to marry a convert). See in Sefer Hachinuch 266 - 268 who summarizes that special marriage rules concerning Kohanim are specific to males. In mitsva 269, it seems that the mitsva "to make him holy" is to honor kohen males only.
The Tur Even Haezer 2,  in name of Rabenu Tam who writes explicitely that there is no prohibition for a kohen-woman to marry even a man who is chalal.

ורבינו תם פירש שאין בדיקה אלא לכהונה. ... אבל אשה כהנת אינה צריכה לבדוק אחר האיש, שלא הוזהרו כשרות לינשא לפסולין; אבל ליוחסין שאין בו צד כהונה, לא בעי בדיקה, עד כאן.
Kohen women are not prohibited to marry pesulim likh'una.

The Bach is more explicit:

דאשה כהנת לא הוזהרה שלא ליקח חלל גר ומשוחרר אבל בקרא ערעור דפסול ממזרות פשיטא דאשה הוזהרה כמו האיש אדרבה פשטא דקרא לא יבא ממזר הוא שלא ישא ישראלית
A Kohen woman is not prohibited to take a Chalal, convert, or a freed slave, but the verses or prohibition to mamzerut are equivalent for men and women, the verse regarding prohibition of marrying with mamzerim is formulated as a prohibition of marriage between a man mamzer (bastard) and a kasher woman.
Comment: @YaacovDeane I appreciate all the ideas of the Sages, but the op looks for a prohibition.
Comment: The 1st two paragraphs are great but you seem to be underappreciating the idea of advice of the Sages. Not being prohibited is one level. Advising the better path, particularly in regard to marriage shouldn't be disregarded. In the blessing for the reestablishment of the Sanhedrin, we ask G-d to return our judges and our advisors. OP is asking about both even though main title mentions only prohibition.
Comment: Yes, and Pesachin 49a which you cite is making clear that the 'wealth' they discuss has two meanings. One applies to the educated person (talmid chacham) and one to the uneducated. The wealth of the educated is Torah and mitzvot. The wealth of the uneducated is cash. The idea that a Bat Kohen should restrict marriage to a non-Yisrael, generally, is because the Levi or a Kohen is traditionally going to be more acclimated to the type of value a talmid chacham possesses. This is emphasized by the 'exile' of Rav Kahana after marrying a Bat Kohen. The focus of the daf is partner compatibility.
Comment: @Yaakov Deane Right


What do the USCF crosstable result letters mean?

Question: In the crosstable for a tournament I played, I didn't play a round and it was listed as H. What does this mean?
Answer: The result codes are defined in the USCF website FAQ, under Member Services Area.

What do all the result codes in a crosstable mean?
Here's a list of the result codes currently in use:
W  A win for this player
L  A loss for this player
D  A draw for this player
U  This player was not paired in this round
B  A full point bye
H  A half-point bye
F  A forfeit loss
X  A forfeit win
Z  A forfeit draw

Special Use Codes
N  A win for this player (but not a loss for the other player)
S  A loss for this player (but not a win for the other player)
R  A draw for this player (but not a draw for the other player)
I  Game In Progess (will be used for correspondence events only)

Note: The N, S and R codes are used by TDs for unusual circumstances, resulting in the players being assigned results for ratings purposes that are not consistent with each other, such as a win for one player and a draw for the other player.


Can an Erc-20 token that I create on my Quorum be integrated with any cryptocurrency exchange (for example Coinbase)?

Question: I have setup my own quorum blockchain network. If I deploy an ERC20 token contract with a coin name (say ABC), will I be able to list the coin in exchanges ?
Answer: In theory, yes. But the chances for that to happen are next to nothing.
For an exchange to accept your coin they would have to:
1) Trust your blockchain that it's fair, valid and uncompromisable
2) Run their own node in your blockchain (they certainly don't want to trust your or somebody else's nodes even if they trust the blockchain)
3) Evaluate your coin to have enough liquidity and interest to be worth it. This is highly unlikely as it's only available in a private blockchain (yours).
Comment: I get your point. But just to clarify, all the altcoins like litecoin, ripple etc.. all exist in their own blockchain right ? So isn't my own private network similar to the blockchain they have? Havent they faced the same issues then for getting listed ?
Comment: Yes, basically all blockchains have the same starting position. On top of that there are a lot of different *kinds* of blockchains, so that affects the big picture quite much as well.


Returning a default value using AWS API Gateway

Question: I need to provide some sort of REST API backed by a S3 bucket. The requirement is simple: given a certain key, it should return the contents of the file whose name is that key. If no such file is found in the bucket, then return a default content. In both cases, the response status code should be 200, because the client should not care where the result came from.
This requirement is so simple that I was trying to accomplish this without writing any code. So I tried to put an API created by Amazon API Gateway in front of the S3 bucket. But even though in the "Integration Response" section you can map a "HTTP status regex" to a "Method response status", apparently the same "Method response status" can't appear twice. So, I cannot have a default mapping to 200 while mapping 404 responses also to 200 with a custom body mapping template.
Is it possible to do this using only API Gateway?
Answer: If the only thing limiting you is number of available responses you can use 203 (forwarding content from the origin) as another successful response. Or you can write a simple lambda function behind your API Gateway to craft the response.


mobile first responsive web design and responsive images questions

Question: I have created this sort of ecommerce website, with the aim to be visualized on a mobile phone web browser (possibly with an acceptable user experience on tablets/pcs/tvs also).
Yes, an awkward tempt of responsive web design:
http://rosposhop.herokuapp.com
As you can see, I used http://getbootstrap.com/ v. 3.x
and I apologize in advance for my enormous ignorance on CSS.
Mhh... I developed initially the site with a mobile handset in mind,
and mainly the site do pretty wath I want in portrait mode, see mokup here:

My idea is that every page is basically composed as a list of boxes = square" divs of let say 320x320 or 440x440 pixels (to be defined..):

header (square box)
list of N products
(again: each product is a square box made by a square image and some textaul info and buttons).
footer

I would like that in case of mobile phone in landscape mode, under certain conditions of a minimum pixel width, I could visualize 2 boxes as showed in image here below:

And I would like that in case of tablet/pc visualization,
the boxes (let say images with a resolution of 320x320 or 440x440) could be arranged in some porportional way, filling the viewport, as sketced here:

I presume that some CSS media queries could help.
Any idea ?
BTW, minor question
about UX of my website naif approach:
A part of my HTML/CSS superficial/erroneous approach... please overlook...
What do you think about user experience and navigation of the site above?
In my idea mobile phones apps (web or native) especially in ecommerce contexts, are generally too complexes, hitting off / adpating the "big" websites maybe originally made for PC. My approach have been different: every product must be defined in a single box, with few buttons to manage the cart.
Any suggestion welcome
thanks!
giorgio
twitter.com/solyarisoftware
Answer: UPDATE (A draft solution using CSS media queries)
<code>    /* product box (containing image) */
    .pb {
    position:relative;
    display:inline-block;
    text-align:left;
   }

    /* Smartphones (portrait) ----------- */
    @media only screen and (max-device-width : 480px) and (orientation: portrait) {
    .pb {width:100.0%;}
    }

    /* Smartphones (landscape) ----------- */
   @media only screen and (max-device-width : 480px) and (orientation: landscape) {
   .pb {width:49.718572%;}
   }
</code>


CentOS vmtoolsd usage 100%

Question: I installed CentOS 7 on VirtualBox but see the CPU usage at 100% by vmtoolsd. I tried multiple ways to bring it down e.g. by doing "lodctr /R" and removing open-vmware-tool but so far no success. I have Windows Host with 16 GB and allocated 8GB to centos vm.
Answer: open-vmware-tool is for running linux under VWMare.  As you are using VirtualBox then you don't need it.
If you remove it, then it cannot use the CPU.  However, if you simply uninstall it with yum there is the possibility of it still running as it has already loaded.
It might be worth rebooting the guest (CentOS) after you uninstall it, or alternatively kill vmtoolsd with:
$ sudo killall vmtoolsd

or if you don't use sudo on CentOS, as root with:
# killall vmtoolsd

Comment: What happens if I kill vmtoolsd? I have GNOME installed with VM so does it affect my VM in anyways?
Comment: `vmtoolsd` is only used if your VM is running on VMWare.  Yours isn't as you stated you're running the VM on VirtualBox.  If you don't want to `kill` it, then reboot the VM instead.
Comment: Yep, I killed it and now CPU is flying. Thanks a lot, I was a but reluctant in doing it.

CentOS vmtoolsd usage 100%


How do you create the rising cinematic sfx seen in most trailers?

Question: Looking for some help on how to create all types of rising sfx whether it be for action movies or horror movies.
Comment: @NAS, what do you mean by rising? Pitch, intensity, volume?
Comment: is this what you mean the sound at 1:28 from the signal trailer and the sound 1:20 from prometheus trailer ..........
http://www.youtube.com/watch?v=gwgfeR2pMuE#t=92 http://www.youtube.com/watch?v=SQgnnsqysZE#t=80
Answer: Start with taking various hits and impacts, process them with a long tailed reverberation, render, make a copy of processed sound and reverse it.
To enrich your newborn effects, add some other elements like vocals, strings, stretched animal roars or synthetic whooshes - whatever you may need. :)
Comment: Hey that's great but I'm looking for a specific sound it has that rising tension of a bunch of stretched out strings seen in a ton of movie trailers. Do you know the exact one i'm talking about?
Comment: You can look for specific patches in the Mophestra library or sound libraries from Sanple Logic (The Elements or Ambient Impact Rhythms). You'll need NI Kontakt though.


Does a VPN protect a network through which data is being transferred?

Question: It seems to be common knowledge that a VPN has the potential to protect data that is being transferred through an insecure network.  Does a VPN also protect a secure network/router from malicious website data being sent to a device using that network with a VPN?
I am new to this site so please forgive any mistakes or issues and just let me know.
Thanks
Answer: No.
A VPN provides an encrypted tunnel between an initial device A and a server B where the data is decrypted and processed, for example by forwarding onto a requested server C.  Responses from C are sent back to B, encrypted, and sent to A.  This means a man in the middle, M, can't determine what A is sending to C in a scenario where all of A's traffic goes through M.
HTTPS does something similar - A could talk to C directly, and M would only see encrypted traffic.  If C only serves data via an unencrypted connection however, such as HTTP, M would see all the raw data.  This latter scenario is what VPNs are useful for.
In any scenario though, B does not (ordinarily) do anything to the content sent back to A.  In this sense it's 'dumb'.  If the connection between A and C is ordinarily not encrypted, then B could potentially perform packet inspection and check for known exploit code etc., but in practice this is impractical most of the time.
Answer: what you are talking about is called "reverse tunnelling". It does work (sort of) and used to be used to transfer traffic between low security networks across a higher security bearer. The basic concept being that the payload traffic is encapsulated (by a device to the same security standard as the higher security bearer) and then broken out at the other boundary. As the traffic is 'random junk' while it is transiting the high security network, it cannot impact any device that processes it. This is still used by some military networks.
However, there are detailed attacks against reverse tunnelling which are different to the attacks against VPNs - the crypto boxes used by the couple of military networks that I am aware took a long time to get right. Coupled with the wide availability of low trust networks nowadays (ie the internet) the investment in these techniques has been limited to specialist applications.
Comment: @Seth in a scenario where a specially crafted TCP packet could attack a router, then yes a VPN would protect it, as the packet would not be seen in its original form by the router.
Comment: Not sure how a reverse tunnel (and I can't imagine trying to set up a VPN to do it, although it's reasonably common with regards SSH) would help protect a user from a malicious payload from somewhere else like a website
Comment: I can't see how it would - but it would protect the network being tunnelled through from being exposed to the malware.
Comment: Just to clarify, a VPN cannot protect an intermediary wifi router?
Comment: @seth from what? An intermediate router would just see encrypted traffic. See my answer.
Comment: @LTPCGO, So an intermediate router could not be infected with malware that a website may attempt to distribute?
Comment: @LTPCGO, Basically I want to know if a VPN can protect my home router from potentially harmful websites


If Stocks are given as a gift, is the cost basis preserved?

Question: When selling a gifted stock, is the entire value considered taxable income, or is the original cost basis used to calculate the difference?
Thank you
Answer: In 2022, the IRS gift limit is $16000.
If the value of the shares at the time they were given was above this threshold, then the gift is reportable to the IRS and is likely taxable (assuming the giver is not your spouse).
According to this FAQ from the IRS, the cost basis and purchase date are preserved across the transfer.  So as long as the giver owned the shares for more than a year, you will be paying long-term capital gains against the original cost basis when you sell.
Comment: It might help if you define *taxable*, since (I'll guess) 99% of the time, even gifts over $16000 do not require any tax to actually be paid.


Calculations needed to full-design a rocket

Question: Suppose I want to put a cubesat in Titan's orbit (saturn's moon). and I want to calculate what rocket power I need, how do I calculate it? Where do I begin? total mass of the probe or delta-v needed? I need to know even the costs, so I need to know the strength and distribution of the engines, how is it calculated?
Answer: You will need to know the impulse you will need.
To derive this, you need to know the mass of your probe, and the required delta-v.
To know the delta-v you need to know the route you're going to take.
Your route will also guide you as to the required thrust to weight ratio you will need at the different points of your flight, which will inform your decision about the type of engines to use and the typical mass fractions.
Then you work backwards calculating the minimum impulse required of the stage, from the weight of the payload and required delta-v for the stage then finding the vehicle that will provide that.
This gives you the payload weight for the stage before it, and you know the delta-v required from that, so that tells you the minimum impulse required for the stage.
That probably gives you the weight your 2 or 3 stage launch vehicle will need to put onto an escape trajectory, which lets you choose a launch vehicle.
The fun bit is deciding how much delta-v gets assigned to which stage, particularly the launch vehicle.


Calculating Mutual Inductance in Parallel Wires

Question: How would I calculate the mutual inductance (Lm) between parallel wires if I know the inductance per length of the wires and the separation between the wires?
Comment: You need to know the separation of the wires.
Comment: I'll update my question to include the fact that I know the separation of my wires
Answer: If you know the separation of the wires
$$ L = (\frac{\mu_o * Length}{\pi}) * \ln(\frac{separation}{radius} + SDfactor)$$
where separation is the center_to_center distance, to be greater than 2*radius
https://en.wikipedia.org/wiki/Inductance
shows derivation of these formula
As the link explains, there is a fudge factor to model skin effect. For low frequencies, where current uses the entire cross-section, add 1/4 inside the "ln" arqument. At high frequencies, add nothing.
Now lets put this equation to use. Consider a MCU SPI dataline, 1mm from the sensitive signal trace, and parallel for 40mm. What is the mutual inductance?
We need to know the radius, so assume its 1/2 * 0.25mm (10 mils = 0.25mm). Yes, I'm using a flat trace circuit, in an equation for "round wires".
$$L_{Ind} = \left(\frac{4*\pi*10^-7 \frac{H}{m} * 0.04m) }{ pi}\right)* \ln(\frac{1mm}{ 0.125mm})$$
$$L_{Ind} = 4*0.04 * 10^-7 * ln(8) $$   {ignoring the skin-effect factor}
$$L_{Ind} = 0.16 * 10^-7 * 2.08 = 0.32 * 10*-7 = 32 * 10^-9 = 32 nH$$
Suppose the dataline has 100pF Cload, with 2.5 volts/2.5nanoSeconds slewrate; the charging current \$I = C * \frac{dV}{dT} = 0.1nF * 1\frac{V}{ns} = 0.1 A\$. We'll assume the dataline current rises to 0.1 amps in 1nanoSecond, remains there for 0.5nS, and decays back to zero in 1nS.
What voltage is induced by the mutual inductance, from the dataline into signal trace?
V = L * dI/dT = 32nH * 0.1 amps/1nanoSec [knowing the nano cancel] = 3.2 volts.
NOW.....what is the benefit of separation? If we just have wires in air (no underlying planes), we see the mutual inductance (the coupling) drops very slowly because of ln(separation/radius).
Fortunately there can be underlying planes.
Comment: What constitutes as low frequencies and high frequencies? My signals are around the audible range ~1kHz - 18kHz so my thinking is that this constitutes as low frequency?
Comment: High frequency is where the skin depth is much less than the wire radius.  You can find a calculator here: http://www.rfcafe.com/references/calculators/skin-depth-calculator.htm . For 1-18 kHz, the skin depth varies from 2 mm to 0.5 mm.
Comment: For 1mm wires, does this SkinEffect lead to pulse distortion of the audio signals? Or are you signals purely sins?
Comment: The skin effect will have some effect on the audio at 18 kHz (that 0.5mm is RADIUS effect, and 1mm DIAMETER means the most you ought to expect is a decibel, when the speaker wire is long (about 4 ohms), and feeds a 4 ohm speaker.   Most of the cross sectional area is closer to the surface than 0.5mm even for thicker 2mm wires.


Is the diminished chord of the minor scale not used as much as the others?

Question: I'm wondering if the diminished diatonic chord (iio) in the minor scale functions as it does in the major scale, where it's not used as often as the other six diatonic chords?
Comment: We gotta be careful about what counts as ii° or ii°7. I've seen vii°7 mislabeled as ii°7 so many times (they share the exact same notes in 12-TET, but only vii°7 can cleanly resolve to i).
Answer: Yes it is used. Depending on what period of music you want to talk about, it's more or less common. For example, in classical pieces you wouldn't see VII that much and when it's used it's not functioning as VII, but as a point of modulation to the relative major. v is also rare as typically V is used instead to make use of the leading tone.
In general when talking about harmony the more relevant question is not how often a chord is used, but how is it used as part of a progression so the rest of this answer will focus on that.
In classical music, you may see it as a predominant used to add extra tension. When it's used you'll typically see it in first inversion to keep a tension out of the bass so you may see the progression ii6 - V7 - i. A very similar progression that takes this to the next level with chromatizim is using the Neopalitan chord which is the same progression with the root of ii lowered. This would be analyzed as N6 - V7 - i.
In jazz ii7 - V7 - IMaj7 is pretty common, when the key is minor iiø - V7 - IMaj7 (Dø G7 Cmaj7) is also common. You may also see it as part of a tritone subsititution like iiø - tt - IMaj7 (Dø Db7 Cmaj7).
In today's popular music you won't see iio, but you will see ii a lot in minor keys especially in genres that use power chords like metal and punk. When you do see as a diminished chord (or power chord with lowered 5th) it's typically  heading to i  or III and just used in passing.

This answer does not touch on the full scope of minor harmony. I highly recommend you go over the questions on the site that are geared toward that so you can start understanding minor harmony better.

Understanding minor key harmony
Minor key and its chords
Comment: Note also that when a diminished chord IS used, it very often won't be diatonic
Comment: @KotoriMinami Rock and metal rock songs tend to use ii in power chord form over any kind of diminished. The progressions tend also to be less functional so the ii chord being diminished makes it harder to fit in with that typical style. Not that it does not happen, just you'll see ii more minor than diminished likewise you are more likely to see v in rock an metal songs over V.
Comment: Really? In modern popular music ii° in minor keys is rare? I don't think that's true. I've seen ii° or iiø7 being used in minor-key pop songs quite often. And I don't think I have ever seen a minor ii chord being ussd in a minor-key pop song. The vii° or viiø7 in major keys is less common, though, but still not nonexistent.
Comment: Well in pop songs I've seen progressions like i-iv7-VII7-IIImaj7-VImaj7-iiø7-V7-i quite often, such as Orange Caramel's *A-ing*, which is a K-Pop song in B minor. The first 8 bars go Bm-Em7-A7-Dmaj7-Gmaj7-C#m7b5-F#.


Can't set Shotwell Photo Viewer as default XFCE4

Question: I installed Ubuntu Minimal and installed XFCE4 as my choice of DE. After that, I installed Shotwell Photo Manager, but I can't set the Photo Viewer as my default for images. I can right click and "open with" Shotwell Photo Viewer, but when I go into properties and attempt to set Shotwell as the default, I get the Manager instead of the viewer. Any ideas?
Answer: I have Ubuntu 13.04, with XFCE4.  Here is what I did.  I don't know why its not working, but see what I did, just to be sure.  I right click of the image, and choose Properties, and then changed the Open With to Shotwell.

If that doesn't help, then do this.  Right click on the image, choose Open With, and then Open with other Application.  Once the new screen comes up, choose Shotwell, and make sure the you click on Use as default for this kind of file.
Comment: Wow. When I looked at your screenshots, I realized I was using Nautilus (I prefer it) and that the options you just showed me are in Thunar! Fixed it, thanks!
Comment: It similar to do in Nautilus as well.
Comment: Oh sorry, just did that. And it is, but for some reason the option to choose Shotwell specifically was not showing up.


Does a build-up of CO2 in the lungs make you out of breath?

Question: I used to get out of breath when cycling, running or swimming and a friend mentioned that it is important to fully breathe out when feeling slightly out of breath, as it is due to a build up of carbon dioxide in the lungs, rather than a lack of oxygen. Is this true? I have found that her advice works and I rarely get out of breath now, but I've been trying to find scientific literature to better explain why this is.
Comment: *due to a build up of carbon dioxide in the lungs, rather than a lack of oxygen*  It's a lot more.  Do an all-out effort that blows through your body's entire [anaerobic capacity](https://www.physio-pedia.com/Anaerobic_Capacity) in less than a minute and throws your entire metabolism into a massive O2 deficit.  If you do that, you ***WILL*** be gasping for air like a fish out of water no matter how you breathe.  Heck, good luck trying to stop yourself from breathing fully out - or in for that matter - after you do that.  In that case, your body is trying to flush the byproducts of your effort
Comment: @AndrewHenle: Yes, I also think that our breathing instinct is quite optimized and efficient (at least when it comes to maximum effort) and I don't think one can "magically" improve it with some conscious effort. But I don't have any sources to support this gut feeling. On a bicycle posture (seating position) probably plays an important role.
Answer: This is a huge topic. It is true that the breathing reflex is controlled by CO2 in your body (not just in the lungs). The key is the acidity of the cerebrospinal fluid. If you reduce your CO2 level, you will not feel you need to breathe that much but that does not make you to have more oxygen for your exercise. So you will not be faster.
Divers know how to reduce the need for breathing by hyperventilation. That reduces the CO2 content in the body even if it does not raise the O2 level too much. This makes it possible to hold your breath longer. The danger is that you may actually pass out due to insufficient level of oxygen even if you are a few centimeters below the water level. If there is no one to save you, you will die.
To actually get faster, you need to get enough oxygen into your lungs and then your VO2max determines how much you are able to use for your activity. VO2max is the maximum amount of oxygen (measured in volume of O2 per kg of body mass and a unit of time - ml.kg⁻¹.min⁻¹) that your body is able to use for an aerobic activity. It determines the power your body is able to deliver aerobically - that means in a sustained effort, not in a short sprint. Top athletes have values of VO2 max reaching 90, normal people will have smaller values depending on their fitness, their age and their sex. There are many explanations on the internet and also tables of values telling you how good you are with a certain value for your age and sex.

Menaspà, Sassi, Impellizzeri (2010)  https://doi.org/10.1249/mss.0b013e3181ba99bc
Just getting rid of the CO2 will not let you produce more power. Also, quite obviously I think, if you do an effort that is hard enough, you will be out of breath no matter what you do. Just observe professional athletes after they cross their finish line.
Comment: Well as a caver I know the danger of elevated CO2 level. 5000 ppm is still quite fine but several per cent is ugly. Mainly headache or even dizziness. But the concentration of CO2 in the air you normally breathe out is even higher, about 4% (40000 ppm). Breathing deeply enough will indeed get you more the gases you need and will help you to get rid of the gases you need to remove.
Comment: To be honest, "panting" is a new word for me, I am not a native English speaker. But do not confuse fast shallow breathing and fast breathing. You can breathe very quickly and still deep enough, that will lead to hyperventilation, if you continue with it long enough. You can then reach abnormally low CO2 concentration in your body.
Comment: Can you explain what you mean by _VO2max_?
Comment: Thanks for your great answer. I have accepted it, but I was actually thinking from a slightly different perspective. I'm not at a high-end athlete level, I just enjoy doing sports. I do find that when I'm feeling a bit out of breath and I fully breathe out, I can more quickly recover than from panting. My question is more about why does fully breathing out have benefits over panting? Is it due to getting rid of the build up of CO2 more efficiently? For example atmospheric CO2 is ~420 ppm, but can build up higher in non-ventilated areas or when doing exercise, with danger level at ~5000 ppm.
Comment: https://www.fsis.usda.gov/sites/default/files/media_file/2020-08/Carbon-Dioxide.pdf
Comment: Thanks @VladimirF for your good response. I was thinking more of fast shallow breathing vs. breathing fully out. I had no idea that the air we breathe out is as high as 40000 ppm.
Answer: I'll post an alternate take on the question.
In exercise science, there are two notable ventilatory thresholds. VT 1 is the level of effort where breathing rate begins to increase noticeably. You won't be able to give a speech comfortably. You will need to talk in short bursts. I think that VT 1 in cycling onsets at about endurance pace, maybe 55-60% of your threshold power (for those not familiar, that's your maximum sustainable power, you're mainly producing aerobic energy, your blood lactate levels are about stable).
VT 2 onsets at a higher power level, when your blood lactate levels are elevated. I think that VT 2 typically onsets around threshold power. Speaking is difficult. You should be able to get a few words out at most.
I'm not sure what ventilatory threshold the OP was at, since we can't observe them directly. I'm not sure their friend's advice was correct, however. Untrained individuals will hit both ventilatory thresholds earlier than trained individuals, possibly much earlier depending on their base fitness. So, if the OP was untrained and trying to keep up with a friend, even if the friend wasn't that fit, their cycling-specific fitness might still have been a lot higher than the OP.
Exercise technique may also part of this. When I was first starting to run in my early teens, I couldn't modulate my power well. That is, I could only run hard or walk - in part beacuse my neuromuscular system was also first adapting to the movements of running. I had the same thing with swimming in my late teens, and I probably still have some of it because I don't swim often. I don't believe I experienced the same thing when I started cycling, but my base fitness was high and cycling isn't as technique intensive as swimming. In short, if this was the issue, then I think the only solution is to persist until you are used to the sport and you can modulate your power well. If you had gross errors of technique, you would want to correct those, and I think this would affect swimming more than cycling or running.


I have permission to republish articles. Do I need to use rel=canonical?

Question: I made a deal with a guy. I will give him advertising on my site for his business. He will give me permission to reprint the articles that appear on his site (he wrote them). I was looking for a lot of content quickly and this gives it to me. But now I'm reading in order to not get dinged by Google, I need to pass any SERP power off to his sit using the rel="canonical" tag in the head of each page. Is this true?
Comment: If you don't use rel=canonical then Panda algo will kick you definitely.
Comment: Possible duplicate of [What is duplicate content and how can I avoid being penalized for it on my site?](http://webmasters.stackexchange.com/questions/35652/what-is-duplicate-content-and-how-can-i-avoid-being-penalized-for-it-on-my-site)
Answer: Yes, you must use canonical URLs for this content. It is pure duplicate content which exactly is what Google does not want. So you will be required to use conical URLs if you publish this content on your site. Failing to do so will likely result in your site being considered low quality due to its lack of unique content and your whole site will suffer for it in the rankings up to and including having no content available in Google's index.
Answer: You want to ask yourself what's the purpose of having these articles on your site?
Since the articles have been authored by someone else and already published on another site, Google won't give you "credit" for them so they won't help your site build relevance or authority. Therefore, they'll be no help in driving traffic because they'll likely not appear in search results.
If you're publishing them on your site for your current visitors, or as landing page content, that's a valid use, if they offer value to the people who visit your site.
To be safe, you absolutely should use the rel=canonical tag on these. This is your way of telling Google you're not trying to claim credit for them as your original content. It's sort of like putting an image credit under a photo, so people know who actually took the picture.
You should still have your own original and useful content. If the majority of your content is duplicate (even if it's used with permission and with the canonical tagging) your site still risks a lower quality rating because it offers nothing unique or different.


Java Reactor Flux/Mono, when does doOnNext get triggered before or after element is emitted?

Question: I have this confusion, when does doOnNext is triggered before or after of element emission by Publisher (Flux/Mono).
Comment: Since `doOnNext` provides you the element flowing through the pipeline with a `Consumer`, it is after. Order is something like this: source emits item -> doOnNext lambda is triggered -> subscriber onNext is called: https://github.com/reactor/reactor-core/blob/master/reactor-core/src/main/java/reactor/core/publisher/FluxPeek.java#L167-L193
Answer: It's after the publication of the element - and it has to be after by definition, otherwise the Consumer passed to doOnNext wouldn't have access to the element emitted.
However, doOnNext() is called before the subscriber. For example:
Flux.just("first", "second")
        .doOnNext(x -> System.out.println(x + " onNext"))
        .subscribe(System.out::println);

...would output:
first onNext
first
second onNext
second

Comment: and doOnNext() is optional right? Is this like a hook?
Comment: @SatishPatro Correct.
Answer: I am afraid you haven't understood reactive properly, and that's perfectly fine :). In Rx, the subscription goes bottom-up. Consider the following code:
Flux<Integer> f = Flux.fromIterable(Arrays.asList(1,2,3));

Since there is no subscriber, nothing happens. No item would be emitted. Now consider this:
f.subscribe(System.out::println)

What happens is that the subscriber subscribes to the flux, and items are emitted.
Now consider this:
f.doOnNext(System.out::println).subscribe(System.out.println);

Remember, the subscription happens in a bottom-up manner. So over here, the subscriber subscribes to the doOnNext(), and the doOnNext() subscribes to the original flux, which then starts emitting events. doOnNext() then intercepts each event and performs some side-effect.
Comment: Prashant, I admit that I am still trying to get my head around the reactive stuff. Though the question from a requirement where I need to execute something just before publisher starts working to produce data.


Dual boot Windows 10 and Ubuntu 18.04.1 file sharing

Question: Dual boot with Windows 10 Pro and Ubuntu 18.04.1 LTS. Dell XPS came with Ubuntu native. I added the dual boot with media Microsoft sent. I was able to partition and install. When the Windows installed, it could not detect a network? Internet still works fine on Ubuntu. Need Windows for work. I have DLed the driver I think I need in Ubuntu, but have no way to get it over to Windows. Is there a way to do it in Ubuntu? I am very new to this.
Comment: One way to do this, without risking the integrity of either file system, is to copy the file to an external USB drive. But have you checked Device Manager? Windows has the drivers for most interfaces: does DM show an error for the interface? Try powering off Windows (not shutting down, which by default hibernates), then removing power and battery for 30 seconds. This makes sure that the interface starts from cold: I've occasionally needed to do this when switching between Ubuntu and Win10, which I put down to the hardware being left by one OS in a state that the other OS driver can't handle.
Comment: Which of my suggestions was the fix? Powering off, or importing via USB?
Comment: Yes. Since the partition already had Windows on it, that was the way I managed to get the appropriate driver there. Had a brief issue powering down from Windows this morning, but I managed to by removing the battery and haven't had issues since! Thank you.
Answer: Boot Windows, disable its fast startup feature. Nowit's "safe" to mount the Windows drive in Ubuntu with read/write permissions.
Reboot to Ubuntu, open the file manager and click on the Windows drive to mount it. Now you can copy/move the driver files to your Windows partition. Avoid writing or changing anything else outside your (Windows) user's space (suggestion: Copy/Move the files to your user's downloads folder in Windows).
This answer is provided for your convenience only and to solve a specific problem. Please avoid doing this routinely. If you need to shares files between Windows and Ubuntu in the same drive use a separated data partition (NTFS).


Mojave - disabling trackpad from terminal

Question: I tried to disable trackpad on my MacBook Pro 2015 my operating system is Mac OS X Mojave there is not have Accessability menu in System properties. So, how to disable it from Terminal?
Answer:
there is not have Accessability menu in System properties.

Look closer. Accessibility should be at the end of the fourth row of icons in System Preferences. If you don't have any third-party preference panes installed, this will be the bottom row.
The icon looks like this:
Answer: I found this solution Disabling the trackpad from the command line, which is suggests the following command line:
sudo kextunload /System/Library/Extensions/AppleUSBMultitouch.kext/
which successfully disables the trackpad, but also the keyboard and a few minutes later the computer crashes and restarts.
Unfortunately the "Ignore trackpad when mouse or wireless trackpad is present" no longer works on Mojave. Because of well document bug where mouse starts jumping in uncontrollable fashion with the only solution being to disable the trackpad and use mouse, I've had that option checked for a while. But after an upgrade to Mojave, even when the option is checked the trackpad still reacts and the mouse is jumpy, which makes the computer mostly unusable (most apps don't have a very fluid shortcut keys support).
Bottom line: any suggestion to disable the trackpad, permanently and forever, on Mojave, not only when a mouse is detected would be amazing! :)
Comment: "The mouse is jumpy" -- Do you mean the pointer on the screen when using a mouse, or when using the trackpad? I've not seen any problems on Mojave using Trackpad on a MacBook Pro, and a desktop Magic Trackpad. Can you link to the documented bug?
Comment: Please don't post follow-up questions as part of an answer.