Include Recent Post in Category

Question: I use a free WordPress Theme called DefautMag, It has a front page with 3 columns, In the front page settings, I could choose any category to display in any of these columns, But I want to display recent posts in one of them. However, recent post is a widget and not a category. Is there any way that I can add recent posts to the categories so as to select it.
A slight problem here is, I am not a php programmer and I don't want to break my site, just in case I have to edit the theme to replace one of the columns with recent posts.
I have searched extensively for days now. Any help will be much appreciated.
Answer: My initial thought would be to simply add a Category "Recent posts" or "Blog" or something similar and just put all of your posts in the category.
Can you please provide a link to the site in question if that's something you don't want to do?
Comment: sure www.iobservers.com       Recent post shows up in the sidebar, but that's way down under the several categories
Answer: I figured a way to solve this and I thought be might help someone someday, so here;
I created a category called Recent Posts, and then I made it a parent category to all the major categories on the site. Then I selected it as a category to be placed in one of the sections. This pulled the most recent posts from the children categories and lined them up right under. Problem solved.

Include Recent Post in Category


How different, has closed VS has been closed?

Question:
The cafe has closed
The cafe has been closed

Two of the sentences have same meaning?
Comment: You would more frequently see usage 2 with a time qualifier: "The cafe has been closed **since 5 PM**," or "The cafe has been closed **all weekend**."
Answer: While they both can been the same thing, there can be differences in both in grammar and interpretation.

The cafe has closed.

Grammar: This is a simple statement of fact about the current state of the cafe.
Interpretation: Generally, it would be interpreted as meaning that the cafe has closed for the day.

The cafe has been closed.

Grammar: Most often, this would represent the fact that the cafe has been closed by somebody. As opposed to the other sentence, it's not just a simple description but an indication of an action on somebody's part.It could also be considered not as an indication of action, but as way of expressing that it was closed at some point in the past (generally, for an extended period of time) and may or may not have reopened since.
Interpretation: In addition to the interpretations possible from the grammar, it could also be taken to mean that the cafe has gone out of business.

Context is important in each of these sentences. While they could mean the same thing, they don't have to—and different interpretations are possible.


An upper bound for a continuous and positive function

Question: Let $f \colon \mathbb{R}^{n} \to \mathbb{R}_{\geq 0}$ be a continuous function with $f(x) \to + \infty$ as $| x | \to +\infty$. Let $a \in \mathbb{R}^{n}$, a compact set $A \subset \mathbb{R}^{n}$ and $b_{i} := \frac{1}{i}$ for all $i \in \mathbb{N}$ be given. Let $f_{i}(x) := f(x + a b_{i})$ for all $x \in \mathbb{R}^{n}$ and $i \in \mathbb{N}$. My question is:
Does there exist some integrable (in the sense of Lebesgue integration) function $g \colon \mathbb{R}^{n} \to \mathbb{R}_{\geq 0}$ such that for all $x \in A$ and for all $i \in \mathbb{N}$, the following holds
$$
f_{i}(x) \leq g(x) ?
$$
If so, how can we prove this claim?
Thanks.
Comment: I don't understand a thing, surely I am wrong. If $f$ is continuous and infinite at infinity, then surely it isn't Lebesgue integrable. Therefore its translates $f_i$ cannot be Lebesgue integrable either. But then, $g$ cannot be Lebesgue integrable.
Comment: Can't we define $g(x)=\max\{f(x+ab_i):i\in\mathbb{N}\}$?
Comment: It seems like you should be able to do something with the supremum of $f(x)$ in a closed disk centered at the origin. I haven't the time to think about it right now, but maybe this will give you an idea.
Comment: Thanks guys for the helpful answers. I didn't explain the problem correctly. Actually the integration in on a subset of "R^{n}" on which "f" has finite values.
Answer: The answer seems to be trivial. For each point $x \in A$ and each index $i \in \mathbb{N}$ there exists a point $y\in A+B$ such that $f_i(x)=f(y)$, where $B$ is a ball centered at the zero of the space $\mathbb R^n$ with radius $\|a\|$. Since the set $A+B$ is compact and the function $f$ is continuous, the function $f$ is bounded on the set $A+B$. So $f_i(x)\le g(x)$, where we can take as $g$ an arbitrary constant function $g(x)=c$ such that $c\ge\max\{f(y):y\in A+B\}$.


Is there a word for person who is obsessed with scores

Question: Is there a word for a person who is very eager to earn points or scores? Not only in some academic field but everywhere, like sports or even if they join Stack Exchange, they start concentrating on getting reputation rather than on helping people.
Comment: I'd like to downvote this question because it doesn't interest me, but I can't bear to lose a rep point when I'm *so* close to reaching 100K! :)
Comment: ... FumbleFingers?
Comment: Isn't the point of reputation systems to encourage such (point-whores)? to help people?
Comment: @DigitalChris Competitive is some one who wants more point in comparison of others. I am looking for someone who just want to score. Like i gave example of rep in Stack Exchange, there one is not being competitive, while wants have more points.
Comment: @FumbleFingers you only lose rep for downvoting answers, not questions. ;)
Comment: In academia it is called 'grade-grubbing', but that doesn't translate to outside.
Answer: The most accurate term is point-whore. This is a term common to tabletop gaming and computer gaming. This type of person only plays in order to get the most points or highest score in the game. Often this type of player even sabotages the game in order to end up with more points than the others.
Answer: Pathologically competitive would be my description of such a person, but that is two words and you asked for "a word."
As far as "not being competitive while wants to have more points" -- more points than whom? If he is  not competing, the points wouldn't mean anything. It's obviously a competition in his mind.
Answer: I am thinking of a term called: score keeper
Comment: A score-keeper is normally one who keeps a record of the score for others (during a game, for instance), not someone who obsesses about *his own* score. But I suppose it might be used as an extension of its usual sense.
Answer: In cricket such a person is known as a statistician.
This is a common species, obsessed with the scores of everyone in every team, throughout history.
A true cricket statistician can recite the top ten scores by a number nine on a Saturday in Yorkshire since 1872.  They are often found around the ground recording every ball's delivery and stroke.  Then in a pub later discussing their favourite numbers.
And of course, they all worship at the altar of the great Bill Frindall.  A legend amongst cricketers everywhere.
Comment: That's not what the question asks for.


PC Algorithm Causal Inference

Question: What are some reasons why the PC algorithm might generate zero edges for a certain dataset? How and why could this happen?
Answer: The PC algorithm starts with a complete graph (all nodes have edges to all remaining nodes). In the first step all node pairs are tested for conditional independence with conditional independence tests, suspect to a certain threshold. If those tests suggest conditional independence between pairs of nodes the edges are deleted from the complete graph. As far as I am concerned all remaining steps are concerned with directing the edges between nodes.
Therefore, the only (theoretical) solution to your question is that all your variables in the dataset are conditionally independent with respect to the threshold of your CI-test (reasonable/default values of that threshold should lie between 0 and 0.05).
Comment: Let's say I run PC algorithm on 10/15 total variables and I get edges. I then run PC algorithm again on the total data set of 15 variables and the algorithm gives me 0 edges. Why would this happen? Why does adding new variables remove previous association?
Comment: The base version of PC is not order dependent. Maybe your variable order and therefore the order in which the conditional independences are checked for are responsible for you not getting any edges. You could try changing the variable order and see if you get edges this way.
Comment: I'm using the stable pc algorithm, which takes care of the order issue. Wondering why I'm still getting no edges in some cases.
Answer: As @ReelSaemon's answer points out, if the data is suggesting complete independence, you get a completely disconnected graph (no edges).
You asked in the comments to @ReelSaemon's answer, how it can be that adding nodes could turn a graph with edges into an edge-free graph. In general, if $G$ is a Bayesian network and $M$ is a marginalization of $G$, then if $M$ has edges, $G$ must have edges, too. If there is an edge in $M$ between two nodes $x_1$ and $x_2$, there must be an open path between $x_1$ and $x_2$ in $G$.
So there is definitely a contradiction in your results which is due to the probabilistic nature of the problem. Lots of things can go wrong, especially if the independency relations are not very clear and there is not a sufficient amount of data. And since PC is a nontrivial algorithm, it is difficult to investigate its numerical stability.
Having said that, I just want to point out one way in which this phenomenon of "edge removal" in the larger graph $G$ could happen. Let's say there is an edge in the marginalization $M$ between $x_1$ and $x_2$ and when switching to the original graph $G$, this edge becomes a collection of several connections, as shown in this figure:

Now, imagine that for each of those nodes $y_i$, the edges of the path from $x_1$ to $x_2$ via $y_i$ describe only weak dependencies, too weak to be recognized by PC. But in the marginalization $M$, only the combined strength of all the paths is measured. And this combination can get you a strong enough dependence in $G$ between $x_1$ and $x_2$. E.g., the variables $y_i$ could be a collection of weak predictors that, when boosted, get you a strong prediction of both $x_1$ and $x_2$.
The PC algorithm working on $G$ will also recognize the strong connection between $x_1$ and $x_2$ e.g. when testing the unconditional independence between $x_1$ and $x_2$ and it probably rejects independence there, too. But the edge between $x_1$ and $x_2$ will be removed when testing the independence $x_1\perp\kern-5pt\perp x_2\;| (y_1,y_2,y_3,y_4)$.

PC Algorithm Causal Inference


Is there a difference between 杀害 and 杀死?

Question: I have tried browsing examples, but the only potential difference I see is that you can say "它也会杀死庄稼", but I am not sure if 杀害 also refers to plants.
Answer: 害 in 杀害 (kill; murder) means 'victimize'. You can only victimize creatures that have emotion, capable of feeling pain. '杀害' mostly refer to murder of human; And only killing of human can be deemed 'murder'
Note: only human intentionally killing other human is called 'murder' . A tiger killing a human is not a murder, but a killing
杀死 (kill someone/ something dead) can apply to any living organism, from single cell bacteria to human
Answer: For most case, the 杀害 emphasizes on the purpose(the intention of killing), and the 杀死 emphasizes on the result:

In 杀害, the 杀 and 害 are both verb, and both meaning to kill, they almost have same meaning, just the 害 is more like make it suffer, so 杀害 shouldn't refers to plants, unless it's personified to suffer.
And in 杀死, it means kill something dead, the 杀 is the kill part and 死 is the dead part, so it can refers to anything that is alive and can die, like plants in your case.
Comment: Thanks for the nice explanation, and welcome to the community :-)
Answer: Just share some of my own understandings here.
杀死 and 杀害 are all verbs. 杀死了 and 杀害了 show results.
杀死 is just a statement of fact, but 杀害 is accompanied by human's emotions.(Most are pity and compassion emotions)
For example, a good leader is murdered by terrorists or a loyal minister is assassinated by  traitor. If you use 杀害, more expressive of your regret for the dead. If you use 杀死,just statements a fact without human emotions.
Answer: 杀害 implies killer has bad intention while 杀死 just means to kill


what's the difference between *zoom and zoom?

Question: in the reset part of bootstrap there is a
<code>.clearfix {
*zoom: 1;
}
</code>
may I ask what's the difference here between *zoom and  zoom?
I appreciate any answer.
Answer: it's a css hack, which means it's only apply to ie7 and below.
you could get the detail refer here:http://www.webdevout.net/css-hacks#unrecommended-asterisk_prefix
Answer: http://en.wikipedia.org/wiki/CSS_filter#Star_hack
I think this is here to fix IE.


Chain rub on chainstay when in smallest front crank and highest gear

Question: I've just bought my son a 2nd hand Orbea MX 27 (thought it was an MX40 but the groupset is consistent with the tech specs of the 2020 27). It was hardly used so doesn't appear to be age / mileage related and I have the same problem. It looks like the smallest crank and the highest gear at the back are incompatible with the bike. A previous post on something similar seems to have also highlighted that the chain length might be wrong. This might be the same for this bike. Specs of the bike here: https://www.nrgcycles.co.uk/kids-bikes/kids-mountain-bikes/2020-orbea-mx-27-xs-dirt__73958
Comment: It appears the chain has a sticky link, which might account for the lock up problem mentioned. Otherwise with a chainring that small, there's not a lot that can be done short of a radically configured chainstay.
Answer: Based on the photo, the front derailleur is a long way from the chainring.
I originally thought the chainring was rather small given the height to the front derailleur.  So I guessed that someone had changed crankset or chainrings to smaller ones.  Also I knew the older versions of this had a triple crankset, but if this is 2020 year or newer, it did come with a double.   Apologies. but my initial idea doesn't apply.
You could change to larger chainrings to minimise this scraping.   Here's a 2019 Orbea with larger chainrings - notice the space under the chain but that same downslope to the chainstay.

The other cheaper option is don't ride in small:small combo.  Tell the rider to stay on the large chainring unless there's a long uphill climb coming and only then drop to the smaller chainring.    Small-big abd big-small combos shouldn't have the same ability to rub.
Comment: Cheers Criggie. Yes i originally thought that the original supplier of the bike had put lesser components on it as most of the searches on the internet show the bike shipped with 8 speed groupset, however the link i posted with the bike does show it with the Tourney rear / Alivo front derailleur setup. I have to say in the big crank the front trim is required between the high half / low half gearing because of inner / outer chain rub. Seems like a fudge for the components used. Great frame, but poor choice of groupset. I've tried educating my 12 year old adsd kid in the art of gear selection!
Comment: @RobertW Somethig like "prefer to stay in the big ring unless you're going up a hill AND run out of low gears" might work
Answer: As a quick answer for now, I don't think it's a problem because you wouldn't normally use this combination of gears.
In fact I was taught as a kid to never even try this because of the strain it puts on the chain and derailleur. This may be apparent if you look at the chain "in the plane of the chain", i.e. top down or from behind the bike.
As a rule of thumb:
The low gear at the front (small chain wheel) should only be used with the lower gears at the back (that half of them with big cogs).
The high gear at the front (big chain wheel) should only be used with the higher gears at the back (that half of them with small cogs.
That's not to say that your chain is or isn't the correct length, that's something that would need to be checked separately.
Comment: I agree with that however we are talking about my 12 year old son who doesn't have that kind of sense! :-)
However I have never seen a bike where the chain practically lies on top of the chainstay before
Answer: Assuming the bike is in original spec you might actually be right that this gear combination is incompatible by design and that has just been accepted as limitation when building it because nobody rides like that.
In essence, the small (22t) chainring is too small for the chain to (reliably) run above the chainstay, you could only opt for larger chainrings to mitigate that, depending on groupset compatibility and required gearing for your son's typical rides.
I don't think the problem here is chain length here because the top of the chain is under tension (especially under load), the slack would typically appear on the bottom if the rear derailleur can't extend, anymore. It doesn't look like there is too much slack in the chain, if it shifts and runs well in "usual" gear combinations, that's probably OK.
In a practical sense, I think you have two main options

Tell your son to avoid this gear combination, the rubbing will give him a good acoustic cue :)
If he is only riding in the flat and the range of the cassette alone is sufficient, somehow blocking the front derailleur for a "false 1x build" could be an option to safe the frame. I'm not sure what the best approach would be, perhaps turning the inner limit screw in to the extreme, experimenting with cable tension so that he can't shift down. A full 1x conversion would be a much cleaner solution but probably too expensive, maybe taking off the derailleur and adding a chain-catcher? It probably depends how creative you want to get to avoid him destroying the frame unintentionally.

I wouldn't be as strict regarding "cross-chaining" as the other reply, it increases chain wear but doing it for short period of time might be legit depending on the riding situation. Not even road cycling pros always follow the small ring - large cogs, big ring, small cogs rule all the time. :)
Answer: Add a chainstay protector.
You'll have to find one that will work around the cable guides on the underside of the chainstay, but a decent chaninstay protector will protect the frame.
Buy several, check its condition periodically, and replace it if it starts getting worn through.
Comment: Locking up and chain rub can be different problems, your question (as it stands) doesn't mention it locked up.
Comment: Trouble is he's said it locked up on him last time he was out on it which suggests its dangerous. Appreciate all the comments where you shouldn't cross chain...totally understand that, and yes, you can visibly hear it but if he's riding along and in the highest gear and accidentally drops the crank he could end up going over the handlebars. I've personally never had a bike that had the potential to throw him out the saddle in such a way


Features for blink detection in real-time single channel EEG

Question: I am looking to detect blink events in real-time single channel EEG. Classification of a moving window of samples to determine whether a blink artifact exists requires feature extraction (except when using deep learning, I am not experienced enough for this). What features would be useful to extract from a window of approx. 50-200 samples of time series data for detecting a blink event. The blink event can be easily seen in the below picture:
Answer: I would try a combination of the following:

A rolling-window variance to detect unusually large deflections
Bollinger bands to detect the spikes
Autocorrelation to detect the 'up down up' pattern


Window unit AC get outlet and plug hot

Question: How come when I use an extension cord to run my ac the outlet and the plug of the extension cord gets hot it's on a 15 AMP breaker and the AC states it is pull 12 Amps and there is nothing else running on that breaker
Comment: How many BTUs is the air conditioner?  How old is it?
Answer: Most AC units say specifically NOT to use extension cords.  The reason for overheating is voltage drop caused by the possible smaller gauge of wire and length of the extension cord.  An appliance rated at 12amps probably has a 14 or 12 gauge cord. If your extension is a smaller gauge, it may be too small for the current and heating up like an old fashion fuse.
Comment: If you absolutely must use an extension cord, use a heavy-duty one intended for air conditioners and similar large appliances. They cost a bit more. Not burning down the building is worth it.
Answer: Large appliances like that need extremely burly extension cords which, not surprisingly, cost a lot more money than normal extension cords.  Their ends are "fragile" in the sense that it's easy for them to take damage which results in them heating up, at which point the cord needs to be replaced.
But even these cords are not intended (nor legal) for permanent all-summer usage.
Because so many consumers mess this up, the air conditioner manufacturers' lawyers say "Do not use extension cords at all."  This means it's all on you to select and watchdog an extension cord which does not have the above problems or any other.
In my experience, extension cord sockets are more troublesome than plugs.  When a socket gives out, I'll lop it off and feed the cord (with listed strain relief) into a steel 4" junction box holding the $4 duplex outlets.  Mount that on a piece of lumber milled to hold the box and protect the cord exit.
Answer: I think you are saying that the heat is being generated at the wall outlet where the male end of the extension cord is plugged in.
If this is so, the heat is generated by high resistance at some of the metal-to-metal contacts inside the outlet device, which is caused by the contact areas being too small.
Problematic metal-to-metal contacts would be at the backstab connectors (if the device is that style) and where the plug prongs meet the slip connectors. Also possible but much less likely are a nicked or nearly broken wire, or an improperly tightened screw connection.
You should replace the outlet device with the most robust one you can afford. Higher quality outlets have more than just thicker metal parts, there are design differences too; e.g. a cheap outlet may contact each plug prong only on one side, while a better device will grab the prong on both sides. Pay special attention to all the connections when replacing the outlet. If it has backstabs, don't use them - use the screw connectors. Examine all the wires for cuts, corrosion, or other damage.
Don't go wild and install a 20A outlet, though. That has got to be some kind of illegal.
Of course also make sure (as others here have said) you are using a proper rated extension cord.
Comment: Of course replace it if there is any since of smoke or discoloration too. It may be work having a look inside for evidence of soot or arcing.
Answer: Heavy Duty Indoor 9' Extension Cord (14 gauge)

(source)
Answer: My experiance is in the UK but I doubt this differs much.
First off how hot is hot? a bit warm is generally ok, too hot to touch is generally a bad sign. Evidence of charring/burning is definately bad.
What tends to happen is you get a poor contact, maybe due to corrosion from age, maybe due to weak springs, maybe due to crap design in the first place. The contacts get very hot which causes further corrosion and can weaken the springs leading to worse contact and more heat.
If a plug/socket pair is overheating I would adise replacing both the plug and the socket. Replace them with good quality parts.
You should also ensure that the cable is thick enough to avoid undue voltage drop. While resistive loads will draw less current at lower voltages motor-driven and electronic loads can draw more.
Personally for high current loads I would make my own extension leads. That way I can get the exact length I need and can chose an appripriate cable size.

Window unit AC get outlet and plug hot


Soul vide without the bag

Question: I am experimenting with the sous vide style of cooking with fairly great results. I am wondering if I can cook poultry, (a turkey),without the bag, just submerging it into the water. I know it will float, but I could place a vacuum bag on top of it and weigh it down with a can or two.  And, if that's possible, instead of just water, could I cook it in a brine?  Quite often I will poach chicken breasts so I don't see much of a difference.  Has anyone tried this?
Comment: Sounds like you plan to make a stock...
Comment: Worth noting that *sous vide* means 'under vacuum'; this may well be a good cooking method but it's probably best described as very precise poaching.
Comment: Or low-temperature braising/pot-roasting.
Answer: The benefit of low temperature cooking (also now known as sous vide, though technically "sous vide" translates as under vacuum), is that you can maintain a low temperature over a long time, both keeping proteins safe, and achieving textural results you can't otherwise.  If you have the old school-type of immersion circulator (the kind that looks like lab equipment), you can probably get away with this.  In the early days of sous vide, some folks were experimenting with cooking directly in oil heated by a circulator.  These days, as @Sneftel points out, most of these devices are designed to work with water only.  Other liquids, or particles of food can really mess things up.  Beyond that, I see a couple of other potential problems.  Floating items means poor heat transfer.  You can account for this by weighing items down, as you suggest, but if you are poaching a whole turkey, for example, if there is an air pocket in the cavity, that could be a potential safety risk, as the heat transfer in the air space will be quite different from the rest of the bird.  Finally, specifically in the case of poultry, dark and white meat are best at different temperatures, so you would have to factor that in.  I do like to cook turkey breast sous vide, then finish in the oven.  So there is merit to your approach.  However, without containing your food, you create some challenges that you need to overcome.
Comment: Interesting information about the oil. Sort of a forced-convection confit, and wouldn't leach away flavor like water would. I am intrigued.
Comment: @Sneftel I don't think many folks did it (I know Dave Arnold experimented, but he plays with everything).  Obviously it did not have much staying power.
Answer: The sous vide "wands" I'm familiar with do not want to be immersed in anything but water. Protein could build up on the impeller and the heating element during cooking and damage them, and salt in the water could lead to pitting. And in any case, it could be quite  difficult to clean them afterwards. Check your sous vide device's manual about this.
Beyond that, the plan sounds fine.
EDIT: incidentally, I'll mention that eggs (in the shell) are often cooked directly in the water. Not the case you were interested in, but an example of sous vide without bagging.
Comment: Thanks for all the great advice.  I'm glad you brought it to my attention regarding cooking it in the brine, wasn't thinking about all the particles, (spices, sugar, salt), floating in the water.  Aside from that, I think I'll give it a try and then crisp it up in the oven!  Never cooked a Turkey in my cooler before!!
Answer: Not exactly what you're asking, but in case you're wondering because you can't find a bag or container big enough.  I've done it before like this:

I closed the lid as best I could, but it did steam up the room a little.
I put removed the wings and legs and did them in zip locs.  The body I put in a Reynolds baking bag. I added some chicken stock this.  You can remove most of the air this way.

After sous-viding overnight, we put it in the fridge for while in the morning.  Later in the day, right before dinner, broiled for 30 minutes or so, it was delicious.

Sorry I can't remember all the details to get it to the right temperature at serve time.
But some ideas...

Soul vide without the bag


When I google a ticker like XLE or something, I see a price which updates frequently (about every second or so), where can I find this for options?

Question: Is there an options ticker I can google to get this equivalent? Or any free place where I can see the quotes updating more regularly? I know the bats order book sh
Comment: -1 / Vote to close as offtopic: if you need second-level accuracy you're probably not doing personal finance anymore; you're doing amateur or semiprofessional day-trading.
Answer: you can try CME DataSuite.
Your broker gives you real time options quotes. If you do not have one you can open a scottrade account with just $500 deposit. When I moved my money from scottrade to ameritrade they did not close my account even till this day I can access my scottrade account and see real time quotes and the same research they offered me before. You can try withdrawing your deposit and see if it stays open like mine did.
Answer: You probably will not find to many places if any that give you live quotes on options because for the general public there is not that high of a demand. Most people do not even know what stock options are.
You can get update on some sites like CNBC, but you will have refresh constantly to get the latest option prices.
You can also try an online broker, most of whom will let you have access to their tools and quotes if you sign up for an account. Some require a deposit before you can access those tools and some don't. Personally, I use TD Ameritrade and I do not believe they require a deposit to use their tools, but don't quote me on that.


What problems may occur if clutch is not used?

Question: I was curious about what problems may arise if clutch is not used when shifting gears. Are the problems similar for both cars and bikes?
Answer: If you match revs correctly you should be able to change gear with no ill effects at all. The challenge is of course to match revs. This is pretty easy when accelerating, but when decelerating you'll need to use the accelerator to bump the engine revs up to match. Google for heel-and-toe (this also helps make for faster downshifts when using the clutch)
Getting started into first is tricky though. If your clutch does fail, parking on a down hill can help with this:-)
Comment: you should probably point out that on a synchro gearbox, you might think you're matching speeds really well when, in fact, you're making the synchros do the speed matching.
Comment: @bobcross - very true. Most people don't get to practice on a box without a synchro but should be able to learn the difference in feel and noise.
Comment: In my first car I tried to learn to shift without using the clutch and instead just rev-matching...  I eventually gave up, it was just too often likely to fail and, well, I have a clutch that prevents the need.  It was nice to learn to do it, in case I ever had a clutch failure, but saving the clutch at the expense of the gearbox and in particular the synchros seems like a bad trade-off.  One of my current cars has 200K on the original clutch, so what exactly am I hoping to save?
Comment: @Sean - not really a save of a clutch at the expense of something else. If you do it right nothing will wear. I learned it for racing, as some gearboxes in use don't have synchromesh so you need to get the revs right anyway. Don't really use it much on the road, but heel-and-toe-ing techniques learned from those days mean I get very smooth clutch/gearbox action.
Comment: In my experience, it's so hard to get right that it is at the expense of the gears.  If you can do it perfectly every time, my hat's off to you, but I never felt like I was making progress beyond a certain point.  I'd get it right around 10% of the time.  If you practice 20 hours a week or something at the track because you don't have synchros on the track car, yeah, you'll probably get good at it.  And knowing how to rev match before engaging the clutch when downshifting is a good skill to have.
Answer: Excessive wear on the gears and a complete breakdown of the gearbox will be very likely to occur soon. Also the crankshaft and it's bearings will suffer a beating everytime you shift gears which will cause (fatal) damage to the engine.
The results will be similar (but definitely not the same) on a bike. If you keep pedaling while shifting gears you'll keep tension on the chain. This will momentarily put excessive sideways forces on the sprockets which will cause bent teeth and broken chain links.
If you must drive a bit when your clutch breaks down, for example on a railroad crossing, you can use emergency propulsion. You leave the car in gear and use the starter to drive the car for a few meters. Park the car at a safe location and call a tow truck.
Comment: I'm pretty sure the OP meant "motorcycle" when he was referring to "bikes".  Also, the last time I rode my bike (admittedly, it's been awhile) I'm pretty sure I *wasn't* able to change gears *without* pedaling the bike.  You need to keep pedaling so that the chain can move and be guided onto the new gear.  At least, that's how it is on your typical mountain bike.
Comment: +1 - Definitely use the clutch.  Don't risk the rest of your car by forcing it to do things it wasn't designed to do.
Comment: @Iszi @Alex right, there's no clutch in mountain bike :-)
Comment: Note that on most cars you can't use the starter to drive the car because there's a switch on the clutch pedal that prevents the starter from engaging unless the pedal is depressed. It's easily bypassed (unplug the terminal from the switch and jamming a paperclip in it usually works) and this is a good modification to make in advance in case you're ever in a situation where you need to drive the car with the starter.
Answer: There are synchro rings that match the speed of the gears when you push the stick. Synchro rings are not designed to accelerate/decelare the engine / whole car and will wear out quickly if you don't use the clucth.
...unless you are a real ninja with the gas pedal and match the gear speeds manually.
Answer: In a car with a conventional manual transmission, this will rapidly wear out the synchros unless you are able to match engine RPM to target gear RPM every time you change (possible, but not easy). Stopping and starting would be impossible to do smoothly without the clutch.
Many motorcycles use a sequential gearbox which allows shifting up and down without the use of the clutch (but you can only shift to the next gear in each direction). You still need to use the clutch for stopping and starting.


Why Earth does not have rings?

Question: Why does the Earth not have rings like Saturn or Uranus?
Answer: A moon is held together by its own gravity, and pulled apart by the tidal action of a planet. If a moon comes too close to a planet it will be ripped apart by the planet's gravity and become a ring. The closest a moon can come to a planet is known as the Roche limit, and it is dependent on the mass and density of the planet and moon.
A large planet, such as as Saturn, has a large Roche limit, and has collected many moons over its history, some of which have been ripped apart to make rings.
The Roche limit for the Earth-moon system is at a radius of about 10000 km, which is very close to the surface of the earth (about 6400km). And unlike the gas giants, terrestrial planets don't have many moons. If any rings did form at one time (such as from the matter resulting from the "giant impact" that formed the moon), they would be short-lived features. They would be cleared from orbit in a few thousand years by perturbations and drag from the outer parts of the atmosphere.
So with few moons, and small Roche limits, the opportunities for ring formation are rare. That said, Phobos, one of the satellites of Mars, is now so close to Mars, that it is held together as much by its rigidity as by gravity, and is slowly getting closer to Mars. Within 50 million years it will be ripped apart and form a (small) ring around Mars
Comment: Just thought I'd add that when you say "very close to the surface of the earth" we're still talking about a distance that is beyond Low Earth Orbit (LEO)--it's just very close to Earth's surface compared to the distance of the Moon.
Comment: 1) Another interesting question here (that I should be able to find out with a little research) is why Jupiter doesn't have more massive rings than Saturn (large magnetic field?). 2) I propose that if mankind makes it through the current global warming/ over population/ etc. crisis that there may be rings around the earth in another millennia.
Comment: @JackR.Woods   Rings form under specific circumstances.   Saturn's outer E ring seems to be fed by enormous jets and volcanism from Enceladus but that doesn't explain the inner rings.  A disintegrated moon is perhaps likely what formed the more densely concentrated inner rings.   If Io drifts inside Jupiter's Roche limit, it could break apart and give Jupiter glorious rings, even bigger than Saturns, but I have no time-table on when or if that might happen.  The 4 moon system in orbital resonance might be long-term stable.
Comment: @James K . Prometheus, moon of saturn have orbit inside F-ring of saturn, so why isnt it ripped off and converted to ring?
Answer: Earth does have rings!  Not icy ones like Saturn, but ones made up mostly of solid masses a few meters across. A relatively sharp ring is centred on geostationary orbit. A rather more diffuse one (although probably with higher total mass) reaches up to altitudes of a few hundred km from the surface. The second one is constantly losing mass back to the planet due to friction from the atmosphere, but is replenished by a complex biological process.
Comment: -1 for talking in vague terms. A 'beginner' in astronomy wouldn't understand this.
Comment: I see what you did there.:) And I guess Jack Woods may have also been alluding to artificial rings.

Why Earth does not have rings?


Synchronized Data Extensions in Customer Journey

Question: I'm facing several issues working on Marketing Cloud because of the lacking documentation about Marketing Cloud available on Salesforce portal.
I have connected Service CLoud with Marketing Cloud and now I have to configure some Customer Journey with Salesforce data (updated in real time).
So, in order to achieve that, I created synchronized data extensions for the Service Cloud object I need to use.
The question is: Could I use these DEs to feed the Customer Journey? Could I use these DEs for AMP script in the emails?
Thanks for your feedback.
Alessia
Answer:
You can use the synchronized DE's in SQL and in AMPscript - you just have to refer to them with ent."DE Name" (e.g. ent.Contact_Salesforce) to pull information from them. SQL is used if you want to create a specific audience and throw them into a journey or send a campaign to them.

Use "Salesforce Data" as the entry event source in your journeys, in case you want to inject people into the journey at the time the data changes inside salesforce. Be aware that you need to be syncing the object in order for this to work. E.g. to trigger a journey when a contact becomes a customer, you must first synchronize the contact object

Hope this clarifies


Message ID and Real IP of the email sender

Question: How I get Real IP of an  email sender using  Message ID   of the said mail?
Comment: There is no sure way to do that. Some email routines use the name or IP of the source computer when generating the message id, some don't. And those which do, don't necessarily do that in Ryde same manner. That being said, are you talking about specific message ids?
Answer: The Message-ID header can be chosen arbitrarily by the client, so you cannot reliably expect to find the client IP address (if any) encoded in it.
This page lists known behaviour of many email sending softwares; some (e.g. mutt) will encode the full name of the sending machine in the Message-ID, but this is the name as the machine knows it, so it can be "localhost", which is not very informative. Moreover, even if the sending software encoded its known IP address in the header, it would often be a local-only address such as 192.168.1.100 because of the high prevalence of NAT. Finally, many emails nowadays are sent through big Webmail platforms like Gmail, so if you find an IP address in it, it will be the address of a Gmail server, not the address of the client.


Load an entire application server from SAN

Question: We have always traditionally used SAN as a backend storage for our databases. But recently our SAN vendor threw in an idea that we can even load our Application Servers (JBoss) directly from SAN.
I was suprised, but the concept is to install the application server on the SAN LUN and then run it from there. The SAN vendor mentioned about ease of DR replication of AppServer configuration, etc.
Is this a viable strategy for production systems? What are the risks, drawbacks?
Answer: If you are on most Linux or UNIX. You can even boot your whole system from san, and even mount / from SAN.
The draw back is that your kernel must present LUN at an earlier stage. Which is an easy task in Linux/UNIX. Other than that, money matters.
Answer: They might be talking about Boot from SAN. This is possible with both FC SAN Cards, and iSCSI cards, and to a lesser extent iSCSI SW only.
My suggestion is if you pursue this you setup a BOOT volume separate from your data volume from you application. If you leverage and DR or Snapshot technology the biggest issue is what level of consistency you need for you DATA. Does it know how to recover if there is a unclean shutdown, or do you need to script the application to quiesce the data so that it is in a consistent state when it returns. Windows apps that participate in VSS can quiesce via the VSS service tied into the SAN vendor, other apps need to be scripted between the SAN and your Application.
Hope that helps.
Answer: Your vendor is talking about 'BOOT FROM SAN'. It is quite a viable strategy. Many Datacentre customers are starting to adapt to this. There are 2 option in SAN loading - FC and iSCSI. Your SAN LUN can be used as a boot partition and all your applications essentially run from there.
FC: Its better to use FC SAN boot, since it has a very higher speed and bandwidth, but requires a SAN network (FC adapters, FC cables, switches).
iSCSI: Its slower still much easier than FC, since you can use your LAN network to carry your SAN traffic.
It really comes down to you choice. Good luck !


Using Cheesecloth for Pancetta

Question: I am making pancetta for the first time and I've just taken it out of the cure to dry.  I have rolled it and am ready to hang it.  Before I hang it, what are the pros and cons of wrapping it in cheesecloth while it dries?  The recipe I am using says to cover it in cheesecloth when laying flat to dry, but nothing about wrapping it in cheesecloth to hang it.
Answer: I've made pancetta many times.  When rolling, I just tie with a string. Traditionally, it is just tied off.  Personally, I prefer the results when I just hang it without rolling...poke a hole, loop a string, hang...but that is just personal preference.  The only downside I can see to the cheese cloth, is that it might slightly slow the drying process.  Other than that, as long as you are working clean, I can't see a problem with it, but I am not sure it really helps you in any significant way.  Perhaps you could get a tighter roll with a sheet of cheesecloth?
Answer: Cheese cloth would actually be great as it will inhibit some bugs getting to the meat while still being porous enough as to not let the meat sweat.
If your hanging in the summer it is a good thing to cover the meat with something. You just need a substance that lets the meat breath. If it is just a regular bag the meat can sweat and this could open the door for spoilage bacteria to enter.

Using Cheesecloth for Pancetta


Use skybox texture as world texture

Question: I have skybox texture which is a cubemap. Something like this:

Is there is any way to use such texture as world texture? It I just use this texture for world I get bad result:
Answer: Skyboxes are used on cubes tracking your camera's position. Then, with a little compositing, you render your scene and superimpose it over the skybox image. That's how you make it a world texture.
Attached is a way I work with skyboxes. I make the cube really small, barely larger than the camera. If I'm working on the scene in Render view, I hide the skybox by unchecking its eye in the Outliner panel. If I want to see the scene in context with the skybox, I scale up the skybox to surround most of the scene.
The thing is: it doesn't matter what size the skybox is, because if you check out the compositor, the scene and the skybox are rendered separately, and scale doesn't change the camera's perspective of the skybox.
To fly around the scene, select the skybox and scale it encompass the  4 objects in this scene. Then select the camera and go into camera view. Select Render view, and hit shift-F. You're now in fly mode. Use your mouse to turn and your WASD keys to move (shift to accelerate). The box moves with the camera, but doesn't rotate with the camera (check out the constraints).

Use skybox texture as world texture


11 wives of Prophet Muhammad (saw)

Question: As Allah has given men a choice to have 4 wives at a time so does that mean Prophet Muhammad (saw) disobeyed Allah because He (saw) had 11?
Answer: Prophet Muhammad SAWW and any other Prophet (peace be upon them) never disobeyed ALLAH azawajal. Disobedience is when you go against someone's specific orders.
Some Prophets ( peace be upon them) did make minor mistakes but they were in no way disobedience (I am saying this because maybe they are the reason you thought Prophets could disobey the CREATOR.)
Those mistakes, for example, when Prophet Yunus (peace be upon him) left His people before the Order from the CREATOR came. Prophets (peace be upon them) can never disobey the Creator, there is no evidence otherwise.
Now back to first part of the question:

Polygamy was allowed initially without any limit on how many wives one could keep.
Islam actually limited it to 4 wives, when verse 4:3 of the Qur'an was revealed, including the part: "marry those that please you of [other] women, two or three or four." Exact dates are difficult, but scholars put this revelation at 3-5 years after the migration to Madinah
At the time, he was married to more than 4 wives. Those whom he was already married to remained married to him, but he did not engage in any further marriages after that time.
The Prophet (pbuh) was allowed to keep all his previous wives because no one was allowed to marry the Prophet's wives (ra) after they were divorced or widowed as they were UMMUL-MOMINEEN (MOTHER OF THE BELIEVERS).

In Surah Ahzab chapter 33 verse 52:

"It is not lawful for thee (to marry more) women after this, nor to
  change them for (other) wives, even though their beauty attract thee,
  except any thy right hand should possess (as hand maidens) and Allah
  doth watch over all things ". [Al-Qur'an 33:52]

Also there are certain things specific for the Prophet saww only.

Your friend (Muhammad) was not astray, nor was he deceived. Nor was he
  speaking out of a personal desire. It was divine inspiration. Dictated
  by the Most Powerful. (The Holy Quran Al-Najm 53:2-5)

E.g. Tahajudd (Night Salah) was obligatory upon the Prophet SAWW while voluntary for the Ummah.

And during a part of the night, pray Tahajjud beyond what is incumbent
  on you; maybe your Lord will raise you to a position of great glory.
  (The Holy Quran Al-Isra 17:79)
Comment: best approach so far
Comment: Oh, yeah, the presented answer looks nice and relatively detailed, especially pointing out the verses of the holy Quran, particularly  [Al-Qur'an 33:52] and (The Holy Quran Al-Najm 53:2-5) (From my viewpoint)
Answer: According to Quran you can have up 4 official wife (life time marriage) [just in case of justice between them and you need the your first wife permission to do other marriages] and unlimited short marriage (sigheh)
Why Muhammad had 11 wives?
Because some of them was due to politics for example a girl was the daughter of the king of some country and in that country only when peace happens if the king of other country marry their daughter.
Or for example some women who their husband died in wars and needed to be supported by a man in these case a man can sigheh (marriage with time limit for example for 1 year) women then give her Mahr and life support this have 2 affects:

bad men won't abuse that woman because they know she has a husband.
the poor woman don't need to do Zinah for her sexual needs or as for making money food dress

and consider after wars lots of men dies how human begin should be populated  with lots of women and lack of men?? How future soldiers should be born?
Comment: This answer barely answers the question: *does that mean Prophet Muhammad (saw) disobeyed Allah because He (saw) had 11?*
Comment: @BleedingFingers It is required.
Comment: [Engaging in permanent marriage with another woman while being married doesn't require the permission of the current wife/wives.](http://islam.stackexchange.com/q/10941/3487). On the other hand man is required to take permission in case of temporary marriage.

11 wives of Prophet Muhammad (saw)


Is the Lightning Network sufficiently secure and well tested for wumbo channels?

Question: Has the Lightning Network reached a level of security and maturity where I can open wumbo channels (channels over the previous 0.1677 BTC limit) and be reasonably confident that I won't lose funds or have my funds locked up for long periods?
Comment: I think this is an interesting post, beyond just wumbo channels. Opening a larger value channel makes the security/reliability consideration more pertinent, but it is still a consideration in any case. Which is to say, I think editing the question to be generalized to *all* lightning channels might be worthwhile, but I'll leave that to OP's consideration.
Answer:
Lightning is great but one can't say it is battle-tested. If script
kids would be interested, they could take down those shiny new 5 BTC
wumbo channels with negligible cost and no effort at all.
The underlying issue is that a channel cannot hold more than 483 HTLCs
at a time, regardless of the channel capacity. Sending 483
micro-payments to yourself and holding on to the HTLCs is enough to
incapacitate a channel for up to two weeks.
By utilizing the max route length to add loops, each payment can
consume up to 9 HTLC slots on the target channel. If the script kid is
lucky, they only need to send 54 payments to get it done. A single
tiny channel takes double-digit amounts of Bitcoin out of business.
Below is me locking up approximately 5,800,000 satoshis with a
refundable 18 satoshi payment looping five times through three mainnet
channels owned by Bitfinex and OpenNode. For basically as long as I
want. This happened today.

Wanting to become the world's payment system sounds good but we can't
have trivially exploitable vulnerabilities like this. Walk the talk.
Therefore I started a new project called Circuit Breaker: a
firewall for Lightning nodes. The primary goal is to encourage
thinking about this problem with the potential to grow into a
full-fledged Lightning protection system.

This question was answered by Joost Jager on Twitter.


Which algorithm does CryptGenRandom use on my laptop?

Question: I have an Ideapad Gaming laptop by Lenovo, with an Intel(R) Core(TM) i5-10300H processor. On this laptop I have Windows 10 installed. To generate random numbers, I use the CryptGenRandom function. However, I found out that this function has been updated through the years. For example, in the past the algorithm used RC4 (see Wikipedia), but that algorithm contained a bug. The algorithm has been revised since then, but it has never been published. Does it still use an RC4 algorithm, or has it another name now? Is it the same on my laptop as on all other modern Windows laptops?
Answer: First of all, this API is deprecated, so this is not used on your modern laptop except for if you have legacy software, the manual for the modern API is here. It is 100% up to the programs that use the API on what cipher modes or the exact stream they pull out of, so I can't answer what the modern API uses.
To answer the question about the deprecated API, it depends on what version of Windows the API is on.

In Windows Vista with Service Pack 1 (SP1) and later, an implementation of the AES counter-mode based PRNG specified in NIST Special Publication 800-90 is used. In Windows Vista, Windows Storage Server 2003, and Windows XP, the PRNG specified in Federal Information Processing Standard (FIPS) 186-2 is used.
Comment: I think I will just ask that in a new question.
Comment: 'so this is not used on your modern laptop except for if you have legacy software': the Python secrets module and Python random module and os.urandom use this algorithm to generate random numbers. So i think that this API is used a lot by popular modern software.
Comment: I recently found this out, see this question: https://crypto.stackexchange.com/questions/107190/is-python-secrets-module-using-a-unsafe-rng-on-windows
Comment: @Riemann My point wasn't to say that modern software couldn't use it per se, but that the Microsoft developers intend for all modern software to go to their new shiny API.
Comment: I searched the NIST special publication and it doesn't mention RC4. Now the question remains whether the Secure Key Technology is used in my case. I think that this is not explained in the NIST publication, since it only contains recommendations.


How to enable External Objects in Salesforce Developer Edition

Question: I want to enable External Objects in my developer edition.
How to do it, i was not able to see any settings ?
Comment: Shaik, can you give some more details on what you are after ? what exactly you mean by external objects, and whats your complete requirement / use case ?
Comment: He it looking for that feature https://www.youtube.com/watch?v=67KIFdKshfs - I am not sure exactly, if it parts of it are still in pilot or beta.
Comment: It's hard to find hard evidence, since google brings not up very much about "Salesforce External Objects". I heard about that feature in a breakout session during a Partner Forum in London. As a matter of fact, the setup section does not exist in summer'14 but it does exist in winter'15
Answer: Option A) Use Winter'15 release
This feature is not available in Summer'14 by default. However it is available in my Preview-Org running Winter'15 release.

So you need to register a prerelease Org here https://www.salesforce.com/form/signup/prerelease-winter15.jsp
Option B) On Summer'14 you may try to log a case and ask Salesforce to enable it
as @RobinDeBondt says in his comment it worked for him, but I haven't verified this.
Comment: I've had it enabled before in one of my orgs (Spring '14), simply by logging a case and asking for the feature activation.


Multiplying the voltage output

Question: I'm working on a project where my arduino is receiving a voltage 0-5V, I need the output to be 10V always. Is there a way to do that?
Comment: You get a power supply that gives 10V and switch it using the Arduino (just like you would with a relay or a motor). Or if you need analog between 0-10V you amplify it (again with a 10V or higher power supply) with an op-amp.
Comment: Hello and welcome. Could you please be more specific about your task? Unfortunately there are multiple interpretations of what you wrote so far. Is your input signal analog (0 to 5 V) or digital (just high and low)? If analog how is your intended relation of the output to the input (multiplication implies an analog relation, i.e. in 0V - out 0V, in 2V - out 4V, in 5V - out 10V) or do you mean that if the input is low (or if analog below a certain threshold) the output should be 0V and if the input is high (analog above threshold) the output should be 10V? [...]
Comment: [...] Do you want to drive a certain load with that 10V? If recommending a specific setup (i.e. transistor circuit) that might make a difference.
Answer: Assuming the 0-5 Volts is supposed to switch the output, in which case you want a program to control your output, then you will want to use a digital output pin to either switch a relay or a transistor that controls the 10 Volts put out to whatever it is that you are controlling.
Perhaps you want PWM which indicates a transistor circuit.  Hard to tell what you want from the way this is worded.
Taking your words literaly, "I need the output to be 10V always" then that simply means hard-wiring to a 10V power supply.   ;-)

Multiplying the voltage output


Is it ok to install vinyl windows from several different manufacturers?

Question: We are looking at replacing all of the windows in our home which are original aluminum from 1963. We were going to go with all Milgard retrofit (aluminum out of budget) but unfortunately they don't carry three windows/sliding glass doors that are large enough. The only window manufacturer who does retrofit that would fit the size is Jeld-Wen. Would you recommend mixing the two brands (large windows/door in Jeld-Wen and all other windows Milgard---do they look enough alike it will not look terrible?) or go with all Jeld-Wen windows/doors? I cannot tell from the Jeld-Wen website alone if they would match and there is no showroom near us. I should mention that we already have two Milgard Tuscany sliding doors and one window that will not be replaced from a previous kitchen renovation. We live in SoCal so weather not an issue. Thank you!
Comment: If everything is basically the same color, I can't see how this would matter much at all. Navy blue for some and orange for others - no. White for all - yes, whites vary a bit but really doesn't matter. "Off white" for all - probably OK, though then it gets to what direction the "off" goes - gray vs. beige.
Comment: When my house was appraised the appraiser noted I had different brand windows. I don't know if or how much that affected the appraisal.
Comment: Thank you for the info! Would be white on all windows.
Answer: I had similar questions on a new building project. I couldn't see enough difference in the frame designs to worry about, so the primary concern was keeping the same color of windows throughout the home. The window companies were glad to give small color samples for comparisons.  My research taught me that there were primarily 2 colors of vinyl windows on the market: white and almond, with very limited variations. The reason for the limited choice has to do with thermal expansion, as color tinted vinyl windows result in too many warranty claims. (Wouldn't it be nice get brown, or wood-toned vinyl windows?)
I went with 3 different window manufactures, got the function I wanted and saved over a thousand dollars. I chose frames that all had a similar exterior reveal (similar frame widths). I also stayed with the same mullion pattern for every window.  Most of the interior sides of the windows were covered with curtains or blinds. After installation, I never gave any thought to the minor differences in the window constructions. Nor did I ever hear any comments about the window manufacture mix, just comments on the nice light.
Comment: Thank you very much. I appreciate it!
Answer: The questions you probably should ask yourself are:
Why am I replacing them?
How long will I be living there?
If you are thinking more than 10 years and if you live in are that has cold winters or is windy then the answer would have to be buy a better window.
Average windows leak air and have cold glass and frames
With the right window you will be more comfortable your utility bill will be lower and it will be a selling point when you decide to move.
Spend some time online and search for European style windows.  You will be surprised what you will find.
Roofing, cladding and windows are long term purchases.
Good Luck
Comment: We will look into the European style- we live in SoCal so weather not an issue here thankfully. Thank you very much for the information!


Do users like getting form 'we received your message' emails?

Question: I'm wondering if there has been research into whether users actually enjoy receiving those 'We got your email' type of responses from support requests or feedback forms. I find it irritating personally, but I realize I could be in the minority.
Comment: Probably the best way to implement it would be a checkbox so users can choose whether or not they got a confirm email.
Comment: I like it because it gives me a record of what a message that I sent which would otherwise have to remember myself. Why is that important? Because I can flag the thing in my inbox to denote that I did communicate something and am still waiting for the actual response. It is sort of the same as an order confirmation which I would flag to denote that I am still waiting for the goods to arrive.
Answer: This type of system behaviour is an implementation of a Feedback Loop, which is key for interaction design.
In Seductive Interaction Design, Stephen Anderson summarises:

We like to know that our actions are influencing the world in some way, that our actions cause reaction - cause and effect.

In this specific case, you can argue that a sufficient feedback loop would be to display an on-screen message saying: "We have recorded your request and will get back to you in due course."
However, confirmation emails have some additional benefits:

They serve as a receipt (or a proof), including date and ideally the content of the request. These can be highly useful for further communication with the business. For instance, I don't have an email showing when did I ask my power company to join my electricity and gas bills - despite this happening some 6 months ago; so every time I call I have to approximate the time, which reduces my credibility.
It assures the user that the email address they have provided is correct.
The email is used by some as a follow-up reminder.
In the strict development sense, many customer-service/fault-tracking packages send emails with a unique ID in the subject, facilitating further communication with the business via email exchange.

You can make an analogy here to a launderette receipt - would you prefer the owner to just tell you "It's alright Sir - I've got your name and telephone in my books; no need for a receipt. Just come back on Wednesday"?

Having said that, none of this may apply in your situation, and the benefit of such emails may outweigh the cost (of users having to deal with these emails).
Like receipts, if your reckon there may be too many too frequently, offer your users the option to opt out. Doing so would also answer your question - as you will have analytics regarding how many people, like you, find it unnecessary.
Answer: As confirmation emails are an overhead that people have to spend time and resources dealing with, the potential for annoyance is high.
When they function as feedback to an action then they are problematic because they are neither close in time to the action, nor close in location (you have to be logged in to your email account to check for, or be alerted to, the confirmation email).
When they function as receipts (i.e. in the types of processes that typically require receipts) they are more suitable. Consider though that when they serve primarily a "peace of mind" or "insurance" function (where they are only needed in the case of a breakdown of the process) they will cause the user to spend time and resources dealing with an email that is unnecessary the vast majority of the time.
So an analysis of the task and process is needed to determine their suitability.
Comment: While I don't disagree, I feel the following is worth mentioning: While the proximity of the feedback is a criterion to its effectiveness, this is also context dependent. In the case of personal email boxes - these are external to the system; an acceptable system behaviour in this case would be to send the email promptly so it is in the inbox next time the user checks or refreshes the inbox. Your personal email is in your control and rightly so, and nowadays people are able to get next to instant notifications using their mobile devices.
Comment: You wouldn't consider the postmen ringing your bell every morning as acceptable despite shortening the feedback time. Nor would you wish a system like the one the OP describes to send you an instant SMS notification - which many will consider intrusive.
Comment: Good addition. I always start from a position of don't give the user more work (especially not more work that is remote in time from the task/process). Email confirmation requires work reading, evaluating, and acting on the email (e.g. keeping/deleting) at some future time, and should be used only if it serves a vital function, and can't be achieved using more efficient methods (e.g.instant feedback that your action succeeded) that have no future work overheads. In the end the process/task demands will determine that suitability.


Open Ms Word document inside iPad Application

Question: I need to open Ms Word document inside my iPad application. Actually I need a Ms Word viewer control on my iPad application.
Thanks
Answer: Have a look at http://libopc.codeplex.com/
Answer: one problem I ran into is that the library is armv6, and that is being deprecated.  I've had a hard time locating a MS Office-sdk for iphone.  I wanted to try and render a word document in a container other than UIWebView or QuickLookPreview.  I have found that while some documents render just fine, there are word documents that don't render correctly, where the right most margin is sliced off, and if the document has useful info on the right side of the document, then it becomes useless to the end user.


Remove null values from whole data in Power BI

Question: I have 20+ tables and also there are a lot more columns so it's is not possible to filter out null values one by one for each column, Is there any alternative to remove null values from whole data in one go.
Answer: filter all null values for multiple columns at one time with the M Query below
<code>#"Filtered Rows" = Table.SelectRows(#"Changed Type", each List.Contains(Record.ToList(_),null)=false)
</code>
This will help.
Answer: or an easy easy way is using the Transforamation
you can see the columns and untick the nulls too
that is also easy but you need to do it 20 times
might be painfull but that wil make you familiar with the data in the columns


How to center text on slanted triangular face?

Question: I am trying to model my own 20 sided die and to add the numbers on each face. I am having trouble getting them centered on each triangular face. Any suggestions on how to achieve this?
Answer:
Here is the script to do that
import bpy
import bmesh

def addText(text, location, rotation, mat, fact = .2, extrude = .005):
    myFont = bpy.data.curves.new(type="FONT", name="myFont")
    fontOb = bpy.data.objects.new(fontObjName, myFont)
    fontOb.data.body = text
    bpy.context.scene.objects.link(fontOb)
    bpy.context.scene.update()
    fontOb.select = True
    bpy.context.scene.objects.active = fontOb
    fontOb.dimensions = (fontOb.dimensions[0] * fact, fontOb.dimensions[1] * fact, fontOb.dimensions[2] * fact)
    fontOb.data.extrude = extrude
    bpy.ops.object.origin_set(type='ORIGIN_GEOMETRY')
    fontOb.location = location
    fontOb.rotation_mode = 'QUATERNION'
    fontOb.active_material = mat
    fontOb.rotation_quaternion = rotation.to_track_quat('Z','Y')
    fontOb.select = False
    return fontOb

def labelObjFaces(obj, mat):
    bpy.ops.object.mode_set(mode = 'EDIT', toggle = False)
    bm = bmesh.from_edit_mesh(obj.data).copy()
    bpy.ops.object.mode_set(mode = 'OBJECT', toggle = False)
    for f in bm.faces:
        fontOb = addText(str(f.index), f.calc_center_median(), f.normal, mat)
        fontOb.parent = obj

fontObjName = "__fontObj123"
matName = '__labelMat123'
deleteOldFs = [fObj for fObj in bpy.data.objects if fObj.name.startswith(fontObjName)]

#clean-up
for delF in deleteOldFs:
    bpy.data.objects.remove(delF)
if(matName in bpy.data.materials):
    bpy.data.materials.remove(bpy.data.materials[matName])

mat = bpy.data.materials.new(matName)
mat.diffuse_color = (0.3731134057044983, 0.59569658041000366, 0.3000000715255737)

labelObjFaces(bpy.context.object, mat)

To execute the script.

open the blend file that has your object
switch to script view
click new button
paste the code
deselect all the objects (move the mouse to 3d view and press a)
select the object on which you want to put the labels by right clicking on it
click the 'Run Script' button
Comment: Thanks this is exactly what I want! However I am really new to blender how to I apply this script so I can use it?
Comment: Glad that it's of use to you. I have updated the answer.
Comment: Sorry I do have one more question, I can only run this script once. After I run it for the first time there is an error on line 31 (mat = bpy.data.materials...). How do I fix this so I can run this script over and over?
Comment: Actually I forgot to test that condition :) I have fixed it now. Also the labels are parented to the object, so if you move/rotate/scale the object the labels undergo the same transformation. You can change the color by setting different value of mat.diffuse_color. Make sure you select the object (and nothing else) before running the script. The fact value will change the size of the label. If you want the size to be different based on the face size, you will have to calculate face area and make the factor dependent on it. You can play with the other settings. Please let me know if any issues.
Answer: UV mapping.
As an alternative to using 20 font objects, I propose this can also be done with a UV map and an image editor.  Here is a very quick run down on how this can be achieved.

For a 20 sided dice like above can add a single division icosphere. Check generate UVs

Here is the generated UV map. For whatever reason drawing on this map comes out A about T, so select all and scale -1 in X to mirror. A S X - 1
Choose the menu Image Editor > UV > Export Layout to File  choose a filename, then open in your fave image editor.

Add the numbers to the triangles.


git cloning behind proxy -- different behavior, same command

Question: I researched for this problem but didn't find anything helpful. What I don't understand is that the error keeps changing. I am trying to clone a repository using
git clone http://git.osmocom.org/gr-osmosdr gr-osmosdr

and I get two different errors at different times:

Complains too many open files. (error: unable to ope object pack directory. fatal: failed to read object XXXXXXX: too many open files)
couldn't connect to proxy (couldn't connect proxy at mycompanyproxy (curl_result=7, http_code=0, sha1 = YYYYYYYY)

I did set the environment variable
http_proxy="mycompanyproxy:1080"

and
git config --global http.proxy mycompanyproxy:1080

I did verify values of the variables too.
Any help is appreciated.
Comment: assuming your company uses proxy authentication (I hope they do), you should change second line to `git config --global http.proxy http://DOMAIN\\username:password@mycompanyproxy:1080`
Answer: Try setting only environment variable or git config settings.
you can see both approaches set in "Only use a proxy for certain git urls/domains?"
set http_proxy=http://username:password@proxydomain:port
set https_proxy=http://username:password@proxydomain:port

Make sure to not use quotes, and don't forget the no_proxy one:
set no_proxy=localhost,.my.company


How to get the category title in a post in Wordpress?

Question: Say I have a post called Hello World in Wordpress and I'm directly viewing this page, how would I go about finding the category of "Hello World" and displaying it?
Answer: Use get_the_category() like this:
<?php
foreach((get_the_category()) as $category) {
    echo $category->cat_name . ' ';
}
?>

It returns a list because a post can have more than one category.
The documentation also explains how to do this from outside the loop.
Answer: You can use
<?php the_category(', '); ?>

which would output them in a comma separated list.
You can also do the same for tags as well:
<?php the_tags(':', ', ', ''); ?>

Answer: To find the category id, category link and category name in wordpress using php, you can use below code:
$cat_id = get_cat_ID('Category Name');

$category_link = get_category_link($cat_id);

$category_name = get_cat_name($cat_id);

echo $category_name; // It will print your category name


Do constructs like "going to do" and "ir a hacer" share a common origin?

Question: I'm curious about the linguistic background between these phrases because they don't make sense word-for-word in either language, but they work almost identically. Wikipedia says that a similar form also exists in French and some other languages, and gives some (uncited) background on how the meaning of "going to" changed over time. I wonder if this is a case of calque (possibly from French to Middle English?) or simply an interesting case of convergent evolution? Are the etymologies of these phrases even known?
Comment: Don't they make sense literally? If you're going somewhere, you're on your way there, moving from your current position to a new one. If you're going to do something, you're on your way towards doing it, moving from your current state (not doing it) to a new state (doing it). I don't actually know offhand if this is a calque or not, but even if it isn't, it's a perfectly logical and reasonable extension of the literal meaning. The fact that there's such a dense cluster of it around central-western Europe (western Romance + Dutch + British Isles) does support calquing, though.
Comment: They don't make sense word for word because generally speaking translation is not a word for word thing.  ir a [do something] is  not always going to [do something].
Comment: @Lambie not sure if you're responding to me or Janus but my point is that they are both non-literal uses of the word "go"/"ir", or at least secondary senses which only work in specific constructions, which I would classify as an "idiom". I simply find it curious that multiple languages have very similar idioms.
Comment: The wikipedia thing says the going to construction. What about the wanting to construction? There is no way historically that these are calques. The English form and Romance language forms have different roots....
Answer: It is quite possible that the parallel constructions have a common origin, but it is hard to prove.
Language features can cross language boundaries due to language contact, this is the basis of the formation of a Spachbund. On the other hand, semantic bleaching of a phrase like going to do something from a more literally meaning like "leaving the house to do something" to "near future tense" or even "future tense" is quite natural and has occurred independently in very different and unconnected languages. As far as I can tell, the historical data on English, French, and Spanish do not allow the conclusion that the construction is borrowed from one of the languages to another.


Replacing a ceiling fan (with a pull chain light) with a 6 bulb chandelier

Question: Once connected the lights will not turn on or off with the wall switch. In fact, the chandelier stays on regardless. Please help.
Comment: We need a lot more info.  We need to know how the wires were connected (pictures for preference), whether there's 1 or 2 (or more) switches, and possibly more.
Comment: Sorry, but I do not have any pictures. There is one wall switch. To control the ceiling fan with pull chain light, the wall switch was turned on and then you could turn the light on/off with the pull chain. Also, the speed of the ceiling fan could be controlled by its pull chain. I hope this helps.
Answer: You hooked the new light up to the 'always-hot' wire (probably red) which ran the ceiling fan.
Use the other 'switched-hot' wire (probably black) instead.
Comment: I checked to wires used for the ceiling fan and there are only 3 wires - black, white, and copper (ground). Which wire do I connect to?
Comment: What is the bulb type is in this fixture? ordinary screw base?
Answer: What is the bulb type is in this fixture? ordinary screw base? What s the type
of wire in the fixture which connects in the box? Is it lamp cord with one smooth wire and one ribbed or otherwise marked? If so, the smooth wire is to be connected to the switched hot, and the ribbed wire is to be connected to the neutral.
If the lights stay on, then you must examine the connections in the switch box. The switch is supposed to have a line hot on one side (black) and the switched hot (black) on the other. The incoming white (neutral) should be connected to the white (neutral) going to the ceiling box.


What causes the crown of the bread to crack during baking?

Question: What causes the crown of a bread loaf to crack as it bakes? I would like to prevent it.
Answer: Disclaimer: I'm not too familiar with the english technical terms, but I'll try and explain what's happening without them.
Watch a shaped bread during the final rise:

Right after shaping, the interior is still dense because the co2 bubbles from the yeast haven't developed yet. The surface is firm and the shape round(-ish), if you poke gently with a finger, the indentation springs back instantly.
If you'd bake the bread now, it would be dense, heavy and probably a bit soggy. This is called "under-proofed". Your top will most likely not crack as the bread won't expand much in the oven, but the results are far from optimal.
After while, your bread will have risen, expanded and the interior texture is filled wit small bubbles. The surface has become a bit softer and the loaf might have flattened a bit in comparison to height. If you poke the loaf, the indentation slowly fills back until almost to the top. The yeast will still be active and could expand the loaf more if the loaf is left to rise.
If you bake the bread now, it has the potential for a maximum of "oven spring", which is an increase in volume during baking. Steam in the oven or baking in a dutch oven will allow your bread to do so even better. Your bread is basically guaranteed to crack unless you direct the expansion via controlled weaknesses in the outer layer, either by slashing the loaf or by having already (during final shaping) folded your loaf with a seam for ripping and then baking with the seam up.
If you continue to proof your bread, it will reach a point from which it will start do deflate again. If poked, the indentation remains. During baking, it will not rise (much) more and will tend to "flow" outwards and collapse. If you puncture or slash your over-proofed loaf, you will make this worse, rather like a punctured balloon.

If your goal is to get a non-cracked bread, you can put the loaf in the oven once it's fully proofed, just before over-proofed. This requires a lot of practise as you will basically have to monitor the bread towards the end of the final rising. You will also need to make sure that the loaf remains humid and pliable, you want as little of a dried skin as possible to allow for expansion without cracking. Poke the loaf all over with a chopstick or a paring knife to catch larger air bubbles that may cause the crown to burst locally and brush the bread with water before placing it in the oven.
Much easier is to bake at the second stage and plan for the expansion. There is a post here that discusses the influence of different cut patterns on the final shape and a bit more on the reasons for slashing here. Rule of thumb: the closer you are to "fully proofed" and the less oven spring you expect, the shallower your cuts should be. For a lot of oven spring, you need deeper cuts, usually made almost horizontally up to an inch in depth.

Should you be talking about a different kind of cracking, namely lots of small cracks that resemble the cracks on some glazed pottery and that appear during cooling: That is considered a sign of quality for some recipes.
Comment: Edits that fill in the technical terms would be very welcome if they increase understandability, but please keep in mind that not all readers will know them.
Answer: The crown is the first thing that sets when you put the bread in the oven. Then, as the center of the loaf heats up, it rises and cracks the top, which has already set. I don't think you can prevent it completely, unless you change your recipe to a denser kind of bread that doesn't rise very much while baking. Otherwise, I find that you can minimise cracking by baking the bread at a slightly lower temperature, and placing a bowl of water in the over to add some moisture. Be warned though, both of these actions will change the final texture of the bread, making it denser.
Answer: What you are describing is the result of 'oven spring'. When a properly proofed piece of dough is placed in a hot oven it will begin to expand or spring. If the the oven is dry or the skin is not sliced it will set rather quickly, resulting in cracks.
There are two things that affect how quickly the skin sets:

Steam
Slicing the skin

Steam allows the crust to remain moist during the first part of baking so that it may stretch and expand.

Boil an inch or two of water on the stove, then place it in the oven when you put the bread in. If there is still water in the pot in the last 15 minutes of baking, remove it.
Spritz your loaf and the inside of the oven with a water spray bottle right when you add the loaf to the oven. Watch out for the steam!!

Slicing the top of the loaf with a razor blade allows the loaf to expand further because it reduces how the crust constrains the loaf. A couple of diagonal slices is popular on long loafs. A cross is popular on round loafs.
Comment: Please see my comment under my answer. Please explain how scoring can help in better expansion
Answer: If you increase the volume of a closed container which can't expand anymore, it will cause the container to break because there is no more space to expand unless the container gives way. This is what happens with bread. The top becomes fixed in shape as it looses moisture and looses its ability to expand. When the inside part expands, the lack of space will cause increased tension on the surface and at one point the surface will crack i.e. give way.
You can minimize random cracking by intentionally scoring the bread. This will help the gas which evolves to escape without causing expansion of the bread, thus preventing any cracks forming.
However you should be aware that this will decrease the volume of air inside bread thus the bread will be denser.
Comment: Just because the loaf is expanding doesn't mean that the bubbles are popping and releasing gas. If that were the case the loaf would fall or collapse. The reason the loaf "springs" in the oven is because the gasses expand and the loaf keeps it contained like a balloon. Another common misconception is that slicing the loaf is done to allow steam to collapse.
Comment: (cont.) The outer layer or the "crown" recieves most heat and sets first, loosing the flexibility, but the cuts remain soft/weak, allowing the inner parts of the dough to press outward, "opening" the slits. @CRags: Does that answer your question? If you want to see the sponge-like texture, cut your dough in two after the first rise: you should see many small bubbles through and through. And: over-proofing means not only that the yeast is "done", but also that the gluten network has weakened and can't "hold" the gas any more.
Comment: Actually, scoring the bread won't make the bread denser, it just controls the direction of expansion which would otherwise result in random cracks. If it does, you have over-proofed your loaf.
Comment: During kneading, gluten develops. You can think of the gluten strands as an elastic network that traps the gas even while the loaf is unbaked. During baking, the dough simply firms up and stabilizes his shape around the expanded bubbles. (Physically not totally precise, but close enough.) So when you slash the loaf, you are not letting the gas out, because you are opening only very few gas bubbles compared to the total amount. But as you dough is still flexible, it can "move" due to the expanding gas inside.(cont.)
Comment: Agreed. Scoring allows better expansion resulting in a less dense crumb.
Comment: @Stephie can you please explain why? If during expansion there is more gas evolving which escapes because of scoring, will it not make the bread denser? I mean, the expansion is reduced as the gas escapes (that's how I understand the process, sorry if it's wrong), is it not?


Why is the electric field inside a charged conductor zero?

Question: When a neutral conductor is positively  charged , the excess charges move to the boundary. Initially, inside the conductor there exist  a field due to these excess charges which as per my reading results in the rearrangement of mobile  electrons to cancel the initial field. My doubt is how exactly the electrons are redistributed without leading to another electric field inside the conductor.
Comment: Also here, if you feel that one of these answers has answered your question, you can consider accepting it. If not, you can consider leaving a comment asking for clarification. If you ask too many questions without accepting answers, people may notice and decide not to answer. It's just a suggestion, but in general people usually do take time to see to this before moving on.
Answer: The "NET" Electric field inside a "conductor" is always zero as you have said.This is basically due to the presence of a lot of free electrons in the conductor.
Let us consider a conducting plate kept in a uniform electric field perpendicular to the plane of the conductor as shown.

The electric field exerts a force F=-eE on the the free electrons of the conductor pulling the electrons to the left side ( to the direction opposite to the electric field) of the conductor creating negative charge accumulation on that side. This in-turn creates a positive charge accumulation on the other side of the conductor. This accumulation starts to create an electric field opposite in direction to the existing electric field ( that is the new electric field opposes the already existing one). This accumulation increases and so do the opposing electric field. This continues until both the electric field become equal in magnitude. So the new opposing electric field completely cancels out the already existing on (only inside the conductor). So the net electric field in inside the conductor becomes 0. All this happens basically in nano seconds. So, the conductor isn't affected by any new electric field coming across it as it is cancelled out instantly.

So, Getting to your question, the excess charges creates an electric field inside the conductor.Now,the mobile electrons rearranges as you have said to create another electric field which will totally cancel out the existing electric field inside the conductor. Its the "net electric field" that will be zero inside a conductor.
Answer: In this case, the conductor is positively charged, meaning that the freely moving electrons rush towards the center of the conductor to fill in the positively charged gaps. Looking at this process in slow motion (because it's all happening very fast), we'll see that all the gaps will gradually be filled, Leaving a positive charge density on under the boundary of the conductor. The electric field due to this positive charge density on the boundary will be zero everywhere inside the conductor (Gauss'law), below the boundary.
So, on the boundary, a positive shell will form. If we consider a conductor with finite spatial dimensions, then the electric field produced outside the conductor will approach that of a positive point charge (with a charge depending on the number of holes inside the conductor) if we move to infinity (inversely proportional to the squared distance to the point). If the conductor has two finite and one infinite spatial dimension, the field produced outside the conductor will approach that of a positively charged line (inversely proportional to the distance to the line). And when the conductor has one finite and two infinite spatial dimensions the electric field outside the conductor will approach a field produced by a positively charged infinite plane (independent of the distance to the plate).
Answer: I'm new to this subject, and I'm here because I was having the same question myself, which I will consider to be about a spherical charged conductor, and without reference to an exogenous electric field.
It is obvious that if all excess charge is distributed uniformly around the surface, the field at the center will be zero. But I was concerned that at interior points very close to the surface the field couldn't be uniformly zero, because if it was zero at some point, p, at some tiny distance from some point on the surface, s, it couldn't also be zero at the point, h, half-way between p and s, because s would exert a (4x) stronger force at h than it did on p, while other points on the surface would have only marginally different influences on p and h, leading to an imbalance of forces. However, it occurs to me that my concern is unfounded in a 3-D world.
This is because in the limit locally, the surface of a sphere becomes a plane, and it is a theorem that the electric field exerted by a plane does NOT depend on the distance between the test charge and the plane. So in fact, s (or a small fixed 2-D neighborhood around it) exerts the same force on both p and h, and so the net force at p and h can be the same.
Notice, though that this argument seems to show that the field will not be zero everywhere for a 2-D or 1-D sphere, where the force does in fact increase as a test charge  approaches the "surface", ( a line in the case of a 2-D "sphere" or a point for a 1-D "sphere".)
Extra Credit Thought Question: What happens in the case of a 4-D sphere?


Lorentz transformations: Distance vs "retarded distance"

Question: Suppose I have a charge situated at rest in one inertial coordinate system. The field of that drops inversely with the square of the distance. If I perform a Lorentz boost where $$v^2« c^2$$ (not necessarily $v«c$), should I expect the magnetic field to vary with the inverse square of the distance calculated in the first frame, or should I expect it to vary inversely with the square of the "retarded distance" in the second frame? The "retarded" distance depends on the velocity of the charge and the radial vector to the charge and the dependency is of order $\frac vc$. So at some points, the charge should appear closer due to retardation of the field, while at other points towards the "antipode", the charge should appear farther due to retardation of the field. This would be in addition to the length contraction which makes the charge appear closer at both ends, but that effect is of order $$\frac{v^2}{ c^2}$$ which we could neglect here.
Comment: This is a very standard calculation done in just about every undergrad E&M text... have you seen it and do you have a more specific question about it? Because yes at one level a distance is calculated in the stationary frame to find an expression for the scalar and vector potentials; but no at another level we are evaluating position and time derivatives of those potentials along the time and space axes in the moving frame to find the fields.
Comment: I'm not sure how your "yes" and "no" map to my question. So yes to, "If I perform a Lorentz boost where v^2«c^2 (not necessarily v«c), should I expect the magnetic field to vary with the inverse square of the distance caculated in the first frame" and no to, "should I expect it to vary inversely with the square of the 'retarded distance' in the second frame" ? Whether fields or potentials, they will be retarded. So my thought was "no" to the first one and "yes" to the second one. I've seen low velocity approximations where v«c such that the first one is "yes". But here my focus is on v^2«c^2.
Comment: Let's suppose for the first n observers in the first frame where the charge is at rest that they are positioned equidistant from the charge at rest. They have synchronized clocks. Now consider a "flock" of n observers whose trajectory through space-time intersects these first observers' trajectories, where the first observers each report encountering a member of the "flock" at time t moving at velocity v, with the n(n-1) messages of these n events being recieved at different times between the first observers. The messages include info by the "flock" of what they saw at each point of encounter.
Answer: A moving point charge $q$ with velocity $c~\vec \beta$ at position $\vec r = r~\hat r,$ $\|\hat r\| = 1,$ a time $t=0$ is known to have relativistic fields at the spacetime origin of (SI units)
$$
\vec E = -\frac{q~\vec r}{4\pi \epsilon_0 r^3}~\frac{\gamma}{\big(1 + (\gamma~\vec \beta \cdot \hat r)^2\big)^{3/2}},\\
\vec B = \frac{1}{c^2} \vec u \times \vec E,
$$where $\gamma=1/\sqrt{1 - \beta^2}$. See for example Richard Fitzpatrick's derivation although this is a staple of most undergrad electromagnetism textbook, as they all want to eventually excite their students with relativistic calculations.
The field points directly at the charge but is attenuated by this strange $\alpha = \gamma ~\vec \beta \cdot \hat r$ term which can certainly be merged into the $r^3$ term to be a field strength going like $\gamma r/(r')^3$ where $r'$ is the proper distance between the charged particle's world line and the field point at the spacetime origin.
It is not immediately clear to me what connection this has to the delayed distance $\ell_-.$ In cylindrical coordinates the position $\vec r$ can be treated as being at some $(\rho\cos\theta,\rho\sin\theta,z)$ position and choosing the $z$-direction parallel to $\vec \beta$ the delayed distance should be the positive solution of
$$\ell_-^2 = \rho^2 +(z + \beta ~\ell_-)^2,$$or,$$(1-\beta^2)\ell_-^2 - 2\beta z\ell_- - \rho^2 - z^2 = 0,$$ so $$\ell_- = \gamma^2\beta z + \gamma^2\sqrt{\beta^2z^2 + (\rho^2 + z^2)(1-\beta^2)}.$$
With a bit more manipulation then, we have $\rho^2 + z^2 = r^2$ while $\beta z=\vec \beta \cdot \vec r$ and this looks like $$\ell_- = \gamma~r~\left(\gamma \vec \beta \cdot \hat r + \sqrt{1 + (\gamma ~\vec \beta\cdot \hat r)^2}\right).
$$
This connection between the term I above called $\alpha$ and $\ell_-$ can be written, in other words, as $$\ell_-/(\gamma~r) = \alpha + \sqrt{1 + \alpha^2}$$
which we could even solve for $ \alpha$. Haphazardly working through it, I think I get that $$\vec E = -\frac{q~\vec r}{4\pi\epsilon_0 r^3}~\frac{\gamma}{\left(\frac{\ell_-}{2\gamma r} + \frac{\gamma r}{2 \ell_-}\right)^3},$$ which seems simple enough but it is not really "obvious" in any way that I think you are hoping it would be obvious.


Show that 2S = S for all infinite sets

Question: I am a little ashamed to ask such a simple question here, but how can I prove that for any infinite set, 2S (two copies of the same set) has the same cardinality as S? I can do this for the naturals and reals but do not know how to extend this to higher cardinalities.
Comment: By the way, Si Chen, there's nothing to be ashamed for in this question. It's a nontrivial question from the naive point of view.
Comment: What is your definition of an "infinite set"?
Comment: A set with infinitely many members? Is there something else I should have considered?
Comment: @MichaelHoppe, it depends. You could define a finite set to be a set which can be put into bijection with $\{1, \ldots n\}$ for some $n \in \mathbb N$. Then an infinite set would be a set that is not finite. I suppose you could also define an infinite set to be one that can be put into bijection with a proper subset of itself. You could also probably get away with defining an infinite set to be one that surjects onto $\mathbb N$. I'm sure Asaf can be more helpful here.
Comment: @Dylan: You can also define an infinite set as a set which satisfy many many other axioms about self injections, self surjections, or injections or surjection with $\Bbb N$. If we assume the axiom of [countable] choice, then all these become equivalent whereas if we don't assume it then they might be different.
Answer: In order to prove this is true for all infinite sets you have to use the axiom of choice in one way or another (or at least a fragment of it). And indeed we cannot prove that in naive set theory.
If you wish to prove that for "known" infinite sets, e.g. $\Bbb R$, then this can be done without the axiom of choice indeed.
Using the axiom of choice, $S$ can be put in bijection with an ordinal $\delta$ - which we will only require to be a limit ordinal. Now we can easily define the map from $2\times\delta$ into $\delta$ by the following injection, for $\beta$ limit ordinal, $n\in\omega$ and $i\in\{0,1\}$ we define $$(i,\beta+n)\mapsto\beta+2n+i.$$ This is an injection, since given $(i,\beta+n)$ and $(i',\beta'+n')$ if $i\neq i'$ then clearly the results differ, if $i=i'$ and $n\neq n'$ the result must again differ, and similarly for $\beta\neq\beta'$. So two pairs are mapped to two different pairs.
The above map is in fact a bijection (given $\gamma<\delta$ we can "decode" the pair that was mapped to it), but if one finds the proof of surjectivity any less than immediate, then we can define an injection from $\delta$ into $2\times\delta$ simply by $\alpha\mapsto(0,\alpha)$. Using the Cantor-Bernstein theorem we have that $|\delta|=2|\delta|$, and since $\delta$ and $S$ have the same cardinality we finish.
Comment: I don't understand your first injection---is there a typo perhaps?  Anyway I think it would be easier to do this by applying the usual bijection $\omega \cong 2 \times \omega$ to each interval $[\lambda, \lambda + \omega) \subset \delta$ where $\lambda < \delta$ is limit.
Comment: Trevor, it's a mental typo. :-)
Comment: I think your map is still wrong.  For example, now $(0,3n+1)$ and $(1,n)$ both map to $3n+1$.  If you just make it $\beta + 2n + i$ will be a bijection and you won't need Cantor-Bernstein.
Comment: Trevor, you're right again.

Show that 2S = S for all infinite sets