Is it bad SEO practice to link to hundreds of internal pages on one page?

Question: I have a site with 200 pages.
On each page, I would like to set up links to the rest 199 pages. I did this because I want my users to link to other pages easily.
But is this a very bad practice for SEO? Will Google hate this?
Comment: Not sure whether google would hate it, but if I was a visitor and there were links to 200 pages, I think I might find it a bit overwhelming...
Comment: Your question can be answered by answering this question. "Do my visitors need the links and they are useful or am I putting them there only for SEO reasons?"
Comment: @Steve I used JavaScript to split them into pages. But google bot would not know it :(
Answer: It is not bad for SEO to link to other pages. In fact, internal linking is good for SEO. You're making it easier for the users to find what they're looking for and Google loves this. Having said that, only link to relevant pages. 200 pages sounds a lot to me. Choose the most important to you and the users to link to. Also take a good look at your URL structure and link to pages above/below the current page. Example:
example.com/landing-page Links to example.com/landing-page/linking
example.com/landing-page/linking links to example.com/landing-page and links to example.com/landing-page/linking/internal
example.com/landing-page/linking/internal links to example.com/landing-page
Another reason not to link to too many pages is the amount of link juice you're spreading then. Decide for yourself what are the most important pages (which you want to be well ranked in Google), those pages deserve to have more links.
Answer: Is this bad for SEO? Presumably. Yes.
Any site should be organized in a hierarchical way using directories and pages including topic/category pages. If done correctly, any user should be able to navigate your site to find what they want. You can also consider linking from page to page where you feel the user may "also be interested in" the topic.
Search engines expect you to follow tradition and do what any webmaster would do. Anything else often does not work. The reason is simple. Most sites follow tradition and this expectancy is written into the SE code. Being an outlier often does not pay dividends.
Google and presumably Bing examine link patterns looking for manipulation. Google is exceptionally good at this. Linking to every page on every page would likely be seen as manipulation. You do not want this.
Years ago, I had a site with millions of pages. I found it impossible to link to each page but did link to about 100 similar pages on each page. This did not work well. If I had followed tradition, creating category pages would created 10s of thousands of low quality pages and far too cumbersome for users. Instead, I needed to create a navigation method that allowed users and Google to drill down all of my pages. I created several ways to link to "virtual" category pages using a CGI script with parameters and a noindex tag. This worked well.
I am not recommending this of course, however, the lesson learned was that too many links added to the page was bad for SEO. However, adding a few "more focused" links was good for SEO.
If your site is about 200 pages as you use in your example, you should easily be able to organize your site using traditional methods that will work well for search. I always recommend following tradition where possible.


Multiple Tags with RFID then play media from RPi

Question: I was wondering if it is at all possible for an RFID reader to read an NFC tag, then ignore that tag, while still being available for other tags which are placed in sequence?
The project is a board game I am working on. The idea is to trigger a media file when an NFC tag is detected by an RFID reader built into the gameboard. That tag remains on the gameboard. As new tags are added to the board each would play a separate media file, whilst the previous tags are still present and no longer trigger a reaction from the RFID reader.
Ideally the project would flow like this:

A tag is placed on the 'RFID reader/gameboard' which triggers a sound/video clip (from RPi/Arduino?). The tag is not removed from the RFID reader/gameboard.
A second/third/fourth...tag is placed on the RFID reader/gameboard and each different tag causes a different media file to play.
Once a tag has generated its corresponding media file to play, its signal would be 'ignored' while the RFID reader waits for next tag.

In summary: Can an RFID reader ignore a tag once detected, not react to it again while it is still within its 'field', but also be available for reading a new tag?
Answer: If the reader can handle multiple tags, then this is easily achievable in software.
Simply keep a list of what is on the board, and only play a sound when a new one is added to the list.


Connecting 12V fan and 3V LED to 9V batteries and drawing more power

Question: I tried to connect a 12V fan and a 3V LED to a 9V battery. But I did not get the required power for the fan. So I connected 2 batteries in series. When I connect the fan alone, it draws the required power. But when I connect the LED along with it, the fan turns slower than before. However, I would like to maintain the speed of the fan. This is for a project to make a unit that looks like fake flames. So I need the fan to maintain some good RPM so that the cloth that I will attach later flutters well and looks like a flame. I am new to this. Please help.
Comment: 1) A PP3 battery (I'm guessing that's what you used) won't last very long running a fan which is powerful enough to flutter cloth. You could use eight AAA cells and get a much longer running time. 2) It is important to limit the current through an LED to prevent it from burning out - what current does your LED need according to its specification?
Comment: @Vigneshwaran, the first thing to understand is that electronics is not "plug and play". You need to carefully choose and understand each part you are using or you will get failures and explosions. Explosions are fun but not the desired outcome. An LED is a component with various needs, one of which is something to act as a current limiter (normally, a resistor). You have a 9 volt battery and a 3 volt LED. As a circuit designer, you need to put something there to deal with the other 6 volts, effectively.
Comment: Thanks. I had purchased a 1Kilo Ohm resistor just in case. Will try and add that to the equation.
Answer: It seems that you are trying to connect the led directly to the 12V thereby reducing the voltage due to the internal resistance of the two batteries. That is not the way.
Remenber also that 2 batteries of 9 V can make the ventilator turning but also there the voltage will drop.
If this is the case place a resistor in series with the led. Let us say
put some 560 ohm in series with the led and try again. It is better to look for a proper 12V supply.
Comment: If your happy with my answer please upvote and accept
Comment: Thanks @Decapod. I had purchased a 1 kilo Ohm resistor just in case. Will try adding that to the equation. I dont want to use a 12V battery for the simple reason that This is for a stage production. Kids are gonna use the torch and that too as stage props. Having them carry heavy things on stage is not desirable.


Contradiction vs. contrapositive

Question: I am having trouble in understanding the difference between a contrapositive and a contradiction. For example, on one of my practice exam, there was a question that asked to prove that $n$ is even if $n$ is an integer and $n^2 + 5$ is odd using both a contrapositive and a contradiction. When I proved it, I assumed $n$ is odd and assigned it to $2k + 1$. What method am I using right now? How would the other method look like.
Comment: Note that the implication you are dealing with says $$\text{If }\;n \text{ is an integer and } n^2+5 \text{ is odd, then } n \text{ is even }$$
Comment: Contrapositive, assume $n$ is odd, and then prove $n^2 + 5$ is even.
Comment: Contradiction: Given $n$ is an integer, Assume that $n^2 + 5$ is odd and that $n$ is not even, i.e. $n$ is odd.  Using those assumptions, arrive at a contradiction. Conclude that those assumptions cannot both be true.
Answer: There are a few ways to prove a statement of the form "if $A$ then $B$":

Directly: assume $A$, then derive $B$
By Contrapositive: assume not $B$, then derive not $A$
By Contradiction: assume $A$ and not $B$, then derive a contradiction.

So the difference is that in proof by contradiction you assume $A$, while in proof by contrapositive you do not. Also the goals are different: in proof by contradiction you wish to derive a contradiction, whereas in proof by contrapositive you wish to derive not $A$.
In your case, $A$ is "$n^2+5$ is odd" and $B$ is "$n$ is even". It sounds like you were doing contrapositive, because you started by assuming not $B$, i.e., "$n$ is odd" presumably then to derive not $A$, i.e., "$n^2+5$ is even".
Answer: To prove the implication $p \rightarrow q$, one can assume $p$ to be true, then show that $q$ follows from it.
Or, one can prove the contrapositive, i.e. $\neg q \rightarrow \neg p$, by assuming $q$ to be false, then showing that $p$ being false follows from it.
Or, one can prove that $p \wedge \neg q$ is a contradiction. i.e., prove $(p \wedge \neg q) \rightarrow F$, by simultaneously assuming $p$ to be true and $q$ to be false, then showing that this leads to an impossible situation.

Contradiction vs. contrapositive


Traveling to Germany at 16 years old, without a parent/guardian but with their permission

Question: I am currently hoping to go to Germany next year with my friend, who is a few months younger than I am. I will be 16 by the time of going, but he might not be. Is there any way as a 16 yr old and 15 yr old can travel to Germany without a parent/guardian, but with parental permission?
Comment: Is this an internet 'friend' or someone you've met in person?
Answer: Sure, why not ?
It's probably a good idea to have a letter from your parents approving of the travel but there is nothing that restricts you from moving around freely. One of my sons and his friends did a Germany trip  when they were about that age (maybe 12 years ago). We didn't do anything special and there didn't run into any issues.
Comment: +1, I've traveled without such a letter to Germany at age 17 and it was fine, no one asked any questions
Answer: Generally speaking, yes.
Under German law, the legal guardians must supervise minors as appropriate for their age and maturity. That may include letting them travel to another city, or another country, on their own.

How long is the trip, and how is it organized? The best case would be if you were visiting someone in Germany, a relative or a friend of the family. The parental consent letter would name this contact, and it would also be a good idea if a separate letter gives this adult the power to handle e.g. medical emergencies.
(Or it could be a student exchange with a host family, but you don't sound as if that is what you want.)
What is your citizenship, and do you need a visa?
Even for visa-free travel, you must have the funds to cover your stay, and you probably should not take all cash. So how will you handle that?
As a minor, your ability to enter contracts is restricted. It may be necessary for your parents to book any hotels. You should read up on what you can and cannot do in this regard.
Depending on your budget, you might look at a traditional youth hostel (Jugendherberge). They do accept minors without guardian, with the right paperwork. (Depending on the location and price, you may or may not be in a dorm with other youths.)
In a commercial backpacker hostel, you would meet young adults slightly order than you. That could be problematic. A 16-year-old may buy beer in Germany, but not share it with a 15-year-old. And if either of them get drunk, there could be a cop saying let's call your parents. And you have a problem. Better mix with other youths.
The 15-year-old will need a separate letter, and you will not be the guardian of your friend even if you are older. The letters may mention that you are traveling together, merely for information.
Answer: You may need permission to leave your home country and/or for your flight/train, as you haven't mentioned which country we can only guess.
Having letters of permission of your parents should take care of that. But it does not hurt to ask before you buy the tickets.
There might be concerns about one of you kidnapping the other, so make sure both sets of parents include both your names in their letters.
Within Germany teens traveling without parents is quite common, it may be less common where you are from, if so, are you sure you can handle traveling without adults?
As a precaution make sure you have an emergency telephone number and if at all possible one in the part of Germany where you will be.


What is Delayed Hyper Combo (DHC)?

Question: In, I believe Marvel vs. Capcom 3 and Ultimate Marvel vs. Capcom 3, there is something called the DHC glitch which stands for Delayed Hyper Combo. What is it exactly?
Comment: Note that the glitch existed in MvC3, but [it was removed in UMvC3](http://www.eventhubs.com/news/2011/jul/20/early-impressions-floe-others-umvc3-dhc-glitch-gone/).
Answer: DHC itself isn't a glitch; it just involves canceling one character's Hyper move animation into a second character's Hyper by inputting the commands for the second character's hyper (for example, Quartercircle Forward + 2 Attack buttons). The first character's Hyper will abruptly be canceled into the second character's Hyper. There's a time window when you can do this, usually around before the final hit in the first Hyper combo. Note that not all Hypers DHC into eachother cleanly; some will almost always miss when chained together.
The DHC "glitch" is something different from DHC itself; a DHC is a completely intended gameplay mechanic (which is used in other games such as Skullgirls). The DHC glitch involves using a DHC move that you're sure will miss, which will end your combo/hitstun in order to reset damage scaling. I'm not sure it's really a glitch, it's just a peculiar sort of Reset used to reset damage scaling (it's been removed in Ultimate though, so maybe it was a glitch). I can't word it much better than Chacronic in this GameFAQs thread:

When you use a hyper then tag in someone else for another hyper combo aka a DHC that will deliberately miss (Think Taskmaster/Wesker's counters or Wolvies Beserker charge hyper combos) so you get a reset in damage and can start up a new combo. This will usually result in far more damage then just doing a delayed hyper combo and usually killing an opponent in a single combo string.

Here's a video of it:

Note that the DHC reset trick was removed in Ultimate Marvel vs Capcom 3 so it might have been a glitch afterall. Either way it's MVC3 only.
Comment: @NiteCyper The fact that it reset damage scaling made the technique extremely powerful and character specific, so it affected the overall balance of the game (yes, I realize that this is a strange thing to say with Marvel).
Comment: So "glitch" is a misnomer? I wonder how it came about if it was always intended. It sounds like this started out as a glitch and became an Ascended Glitch.
Comment: @NiteCyper lots of fighting game mechanics started out as glitches, it's hard to call the line where some things are glitches or are intended; the DHC reset trick was removed in Ultimate though (updated answer) so it's likely it was either a glitch or unintentionally powerful.
Comment: Ah, so missing any hit of a DHC used to break a combo as the GAME recognizes a combo and counts hits, regardless of whether or not the opponent could escape?

What is Delayed Hyper Combo (DHC)?


Which tools are most likely used to create animated video (i.e. corporate commercials)?

Question: Animated video is sometimes very well done and extremely attractive and captivating. I would like to know what tools are typically used to create this kind of video. I specifically have in mind the kind of animation typically used in corporate training or commercials. Here's an example:
Answer: I can't be really sure, but most of that can be done using After Effects and a simple screen recording. You record the screen of a phone, put that into after effects, get a picture of a hand and put that into after effects, and just move it around with the frames.
The whole of screen recording could also be made using Adobe Flash or After Effects instead of actually taking it, but it would take a while... This way you could create a minimal and simple version of your app or something, which might be more eye-pleasing and less complicated to the audience.
Answer: If you are a Mac user, Apple have a motion graphics suite called Motion 5 which is available for $49.99 USD. There are some templates that come with it and many commercial templates can be purchased and customised. In my experience, Motion excels in very short, but snazzy animations and is quite resource intensive.
After Effects is one of the most popular animation programs. It is an Adobe product that works on both Windows and Mac and can be used with a license that costs $20 USD / month.
A free alternative to both of these is a 3D software called Blender which can also make 2d animations. It is open-source software and works on Mac, Windows and Linux. It is available at https://blender.org
However, it is arguably more suited to technically minded users and may be frustrating to learn how to use. It is an incredibly powerful though and feature rich.


Explanation of confidence interval from R function boot.ci

Question: I used boot function in R to do bootstrap for 40 times and used boot.ci to get the "normal" confidence interval. The following is my R code:
1. Define the statistic used in boot function

uni_boot <-function(data,indices,vari){
  d = data[indices,]
  unifit = coxph(as.formula(paste('Surv(time, status)~', vari))
                ,data = d)
  # return hazard ratio
  summary(unifit)$coef[2]
}

2.Bootstrap

r1 <- boot(data = data, statistic = uni_boot, R = 40,
        vari = variable)
r2 <- boot.ci(boot.out = r1, type = "norm")

Then, I examine the following things
Result of r1 object:

original     bias    std. error
t1* 1.053145 0.03274176   0.1714448

Result of r2 object

Intervals :
Level      Normal
95%   ( 0.684,  1.356 )
Calculations and Intervals on Original Scale

The bootstrap sample mean would be mean(r1$t) 1.085887 which is original plus the bias. However, when I examine the the formula used to calculate the bootstrap interval. It is original-bias-V^1/2*Z(1-alpha) or original-bias-V^1/2*Z(alpha).
I followed the formula and did the calculation:

1.053145-0.03274176+1.96*0.1714448 got me the upper bound 1.356
1.053145-0.03274176-1.96*0.1714448 got me the lower bound 0.684

My understanding of the confidence interval would be the bootstrap mean in the middle of the boot CI. However, the boot CI midpoint here turns to be 1.024. Sometimes, the boot CI from boot.ci wouldn't cover the bootstrap mean mean(r1$t).
Anything I understand wrongly?
Comment: I think the difference is that in one place you are subtracting the bias but in the other you are adding it. That does not seem correct to me.
Comment: Thank you for replying me. I also got confused about this contradictory. Which way is the correct one? Theoretically, I should minus the bias. However, then the mean is different from ``mean(r1$t)``. In my opinion, ``r1$t`` is the values we got from 40 times bootstraps.
Answer: Yes, the right way to correct for bias with bootstrapping is to subtract the bias from the value obtained on the original sample. When you get stuck thinking about bootstrapping, remember the guiding principle:

The population is to the sample as the sample is to the bootstrap samples.

Your value from the original sample is 1.053; you perform bootstrap resamples from the original sample and find a mean value of 1.086. The mean from the bootstrap samples was thus 0.033 higher than the value from the original sample: a bias of +0.033.
Applying the above principle, you use that bias value to estimate that the value from the original sample is 0.033 higher than the population value. So the bias-corrected estimate of the population value is 1.02.
The CI based on bootstrapping are supposed to represent the CI in the original population, while the values from the bootstrapped samples themselves are doubly biased from the population values (once from the original sample versus the population, and then again from the bootstrapped samples versus the original sample). With bias, you thus shouldn't be alarmed that the values obtained from the bootstrapped samples are beyond the final CI estimates for the population.
Issues of confidence intervals from bootstrapping can be even trickier; the "normal" confidence intervals assume symmetry about the (bias-corrected) mean, an assumption that might not best describe the situation in practice. With bias and asymmetry some other frequently used bootstrapping-based estimates of confidence intervals can be misleading. I struggled with these issues extensively until I forced myself to apply the above guiding principle systematically.
Comment: @Nicole please turn these comments into a new question. You can point to this question as the principle to apply, then in the new question ask how to apply the principle to your situation. In your new question please say more about the number of cases and events (if this is survival analysis) and the type of modeling (e.g., nature of variable selection, is there penalization as in ridge or LASSO, criteria for evaluating the model, what you mean by the "evaluation score"). Those details will be important for suggesting how to proceed in your case.
Comment: A new question about the application of the bootstrap's rule is posted. [Evaluate the performance of a model with bootstrap](https://stats.stackexchange.com/questions/373171/evaluate-the-performance-of-a-model-with-bootstrap)


Telegram still knows my location after using a VPN

Question: I connected to a VPN and turned off location but telegram still show my country in registration form. How this is possible?
Comment: To use any app, you still must use some connection point, which identifies itself when you use the network. Every bit of information on the internet identifies FROM/TO info for normal routing, even in generalized form.
Answer: there are different methods to get the user's current location in android. If you have turned off your location  it checks your last known location from your phone
Try changing your current location in maps by using/downloading FAKE GPS from play store.
Hope this helps.
Thank you
Answer: If you are using a Smartphone with SIM card inserted and unlocked, Telegram can simply query the network operator info (which includes the country) of your SIM card.
Answer: I used a VPN(Hola) to route through Switzerland and then I changed the location using Fake GPS Location - Hola to the same area the VPN was routed to (according to Telegram's check based on my IP). I also turned off my mobile data. I assume Telegram is keeping track of when the account was used where and then they just show the last location available in their database if the sudden change in location doesn't make sense.
Here you can see they got my location wrong:

Also when sending my location in a chat they show the fake location I set. Unfortunately, when searching for friends or groups nearby this is not the case.


Blender input and shortcuts error

Question: This error just happened. I can't rotate my viewport using mmd. I have reinstalled it but nothing changed. Not only mmd, I also found that when I press S, the "insert keyframe" menu showed up. It must be shows up when we press I, right? Not obly S, but I also found errors on another, like A, Z, and much more. Can anyone fix my problem?
Answer: Just go to File menu in blender > Defaults > Load Factory Settings
This Can Work For You But if This Does Not Works then I have Another Idea for you if you are having windows operating system
you should uninstall blender first then before reinstalling it you should go to your c drive or the drive where your operating system is installed then let us suppose it is in C drive so try searching for blender in your file explorer in the c drive
now delete all the file relating to blender except your project files
also you should go to c drive > program files > Blender Foundation

Delete this folder (Blender Fondation)
  now there should not any system file related to blender and then you should re-install it again
  hope this will work !
Answer: Look (or show) your user preferences, and look, in the right side, under
input > (blender) > 3d view > object mode

find the command "insert keyframe menu"

it should be assigned to the letter I, by default (as visible above).
Do the same with other keyboard commands that do not behave as expected.
If they're different than what you experience, there could be some OS or hardware issue, but you should get the same errors in other programs too...
If you ind that the configuration is as you experience, except that is not what you had before, either something changed it, or the configuration could be screwed.
If nothing works you could try to reset default settings. Try the menu
file > "load factory settings"
and if it works, remember to save the startup file with
file > "save startup file"
see also related question: Is there a quick way to reset a .blend files windows and settings to default

Blender input and shortcuts error


Can I use taco seasoning in chicken quesadillas?

Question: When cooking the chicken for quesadillas would it be ok to use taco seasoning to give some flavor to the chicken? Would that taste weird? I have a new quesadilla maker I will be using tonight?
Comment: Unfortunately not. The Tex-Mex Seasoning Bill of 1988 specifically prohibits the interchange of seasonings between different dishes. Thanks Obama!* *may be sarcasm
Answer: Yes, yes you can.
Recipes aren't like alchemy**.  You can adjust flavorings to suit your taste.
You're correct to add it when cooking the chicken ... if you just tried to add it when assembling, the flavors won't meld, the flavors won't fully develop, and it can be a bit ... chalky ... when it's obvious that there's a powder coating.
** unless of course, you're baking ... then it is like alchemy, and what seems like alittle change can make a huge difference in the finished item or ruin it completely.
Answer: Taco Seasoning creates a  wonderful taste sensation for Chicken quesadillas.
I would recommend rubbing it into the chicken vs sprinkling it on. I find rubbing the seasoning in gives a much better flavour through out and reduces the chance of powdery residue or texture.
Word of caution Taco Seasoning doesn't blend well with poultry seasoning. Use one or the other.


Nickel vs silver vs gold flute

Question: What are the timbral (sound quality) differences between nickel, silver and gold flutes, and what is it in these materials that produce the different sound qualities? I'm a string player, so I only know that these different materials exist, but I'm unclear about what they do. Also, are there other notable western flute materials?
Comment: Does this answer your question? [How does the use of silver influence the quality of a flute?](https://music.stackexchange.com/questions/78390/how-does-the-use-of-silver-influence-the-quality-of-a-flute) It seems like a *near* duplicate even though it doesn't narrow the field to just three materials (aaaand now I now about the "carrot clarinet")
Comment: Thanks for the link! I did come across it before I asked this question, and it did give me an idea on how a flute's material affects its sound quality (although the article within was slightly convoluted). However, it wasn't very specific on the differences, and how the materials achieve this. The answer below has provided me with everything I need to know, but thanks for the suggestion!
Answer: The general opinion (highly subjective) among flute players is that denser precious metals produce an better sound. Gold is claimed to produce a warmer, darker, more complex sound, silver is claimed to be brighter and have more projection. Professional players nearly always play at least a full silver flute if not a gold one, although there are some exceptions.
One factor that must be considered is that much more care is taken in the construction of flutes using expensive materials so they will be better instruments. You'll never find a gold flute made in a factory.
Nickel, silver and gold or alloys/combinations of these are the most popular materials. Often a silver flute is upgraded by using a gold head joint. A silver head joint might have a gold 'riser' (the piece between the body of the head joint and the lip plate) or a gold lip plate. A nickel-silver flute can be upgraded by using a full silver head joint.
Sometimes other material are used:

Platinum is extremely expensive but flutes made from it are said to be even better than gold flutes.
Wood, most commonly African blackwood (grenadilla or Dalbergia melanoxylon) is still preferred by a few players.
Carbon fiber
Plastic. There are cheap, almost unplayable plastic flutes available
Brass  (silver-plated)
Glass

The reason why noble metal produce better flutes is unclear, the density of the material and its heat conductivity might be the reasons. There are scientific studies with inconclusive results
Comment: There is probably quite a bit of placebo effect -- ie the player believes one material is better than another. There is also a difference between how the player experiences the instrument as compared to how an audience would experience it. A "better" ( ? ) comparison would be for the player to be blindfolded and playing different instruments of the exact same design behind a screen and letting the audience describe the difference (the audience should probably be flute players).
Comment: My experience is that people that spend silly amounts of money on something often believe that the thing they spend silly amounts of money on is very, very, very good.
Comment: A flutist friend of mine claims the biggest sonic difference is achieved by changing the lip plate material as well as the material of the spacer between the head joint and the lip plate. Just one person's take on it.
Comment: Aside from the acoustical effects (if any), a gold lip plate would have one possible benefit: gold, at least [anecdotally](https://www.laskey.com/pages/scott-laskey-on-gold-vs-silver), seems to "wet" better, allowing a layer of water/saliva to spread evenly over the surface, which gives it a "softer" feel that some players prefer. Brass instrument mouthpieces often have gold-plated rims for the same reason.
Comment: @Dalbergia The same effect can be achieved by gold-plating the lip plate.

Nickel vs silver vs gold flute


What's the fastest way to earn mana?

Question: What's the quickest way to farm mana in dungeon defenders?
Comment: Without having completed the full game, I have noticed that runs on boss levels (if you have a strategy to take out the boss quickly) generate a huge amount of mana. I don't want to post an answer because this is hardly authoritative, but it's something you could try while you're waiting for one.
Answer: The following is the best guide I've found to get to the point where you can reliably farm the higher difficulties. I've moved most of it over to protect against link rot.
Source: Loot Progress path for dummies
Getting the Gear
Suggested heroes: Adept/Apprentice (tower focus), Initiate/monk (tower focus), huntress/ranger (tower focus)
Starting build for each char:
Class: Hero stats - skills - Tower stats - resists
Adept: 0/0/0/0 - 0/0 - 65/120/26/120 - 0/0/0/0
Initiate: 0/0/0/0 - 0/0 - 91/120/120/0 - 0/0/0/0
Huntress: 0/0/0/0 - 0/0 - 120/120/91/0 - 0/0/0/0
Start the map with initiate/monk and play during combat phase with adept/apprentice. Focus on gearing up adept the most, but don't leave initiate left behind too much. OPEN ALL CHEST EVERY TIME.
Do each map as many times as you need to get enough gear to do the next suggested map. Also note, failing for the first time on a map doesn't mean you don't have enough gear, maybe you need to refine your tactic, build order. The original thread contains a diary post showing his gear progression (Here).
Here are some alternate tactics from the same guide.
Map #1: Medium Hall of Court (Pure Strategy or Survival)
GENIE IS REQUIRED. NOT OPTIONAL.
Build from starting mana.
Build before second wave.
Note: Start on wave 8, you finish faster, and if you choose medium PS, then it should be very easy, even naked. If you don't have any gear, just pick up whatever you find during the map. Don't forget to upgrade auras when they are at low health. Some info about Genie. When you are upgrading genie, upgrade the attack!
Map #2: Insane Glitterhelm Caverns (campaign)
Build from starting mana.
Build before second wave.
Optional build with huntress.
The following video is using somewhat modified tactic, because run speed and casting speed is low to play with two chars first wave. The characters are NAKED in this video. (2x speed, so you don't fall asleep)

Note: You can level the genie up very fast here without spending millions of mana on it.
Map #3: Nightmare Endless Spires (campaign)

Note: Chests can contain 90+ upgrade weapons and 60+ upgrade armors even after the first wave. The gear can exceed even ramparts.
Note#2: You can keep farming this in HC NM MM survival mode, and progress towards Map #6 and skip #4,#5.
Map #4: Nightmare Ramparts (campaign)
Start build.
Final build.

Note: The loot of this map doesn't exceed Endless Spires, but wanted to leave it here as a possible alternative.
Map #5: Nightmare Über Lifesteram Hollow MonsterFest
cubicleninja is missing the map, so can't provide layout. Check out the vid!

Note: Can be skipped
Map #6:  Nightmare Mistmyre Forest
Idea for this as next step, and tactic by: Mirradin
Video by me:
Part 1

Part 2

As you may have guessed, the best way to get mana is to sell the numerous items that drop during each wave. Remember to pick up items to sell since there is a cap on how many items can exist on a map at a time. This mainly becomes an issue when the waves consist of over 500 monsters.
Once you can farm Nightmare Mistmyre you should be set to get 60+ million mana every 30 minutes. Here is a more detailed guide for farming mana there:
How to farm mythic gear & mana (60+mil 30 mins)
Comment: nice and detailed answer
Comment: @yx I've been using this to get up to mythic farming, but my first character was a ranger so I've had some trouble. If you ever feel playing some feel free to message me on Steam. I've mainly been grinding survival with a second controller to level.
Comment: going to give the bounty 1 day but if someone else posts an equally good answer I'll have to give out two bounties :P
Answer: The fastest mana farming I have seen (and I do on a regular basis) is the Assault mission pack. You do have to host it though.  On hard you get a 4mil mana reward for each completion. On insane it's 9mil.  I haven't beaten it on nightmare but the reward there should be even more.  If you can solo the assault mission pack on hard difficulty ot harder, try it!
Answer: Lab assault nmhc and than restart over and over
optional is adding a controller for more items at a time
Comment: Welcome to Arqade! You are answering a question asked more than two years ago which already has an accepted and extensive answer. Your answer probably isn't needed here. I recommend using the Unanswered tab at the top of the screen to find questions more current than this one that need answers.
Comment: @ken.ganong: There is nothing wrong with answering old questions, even if they already have good answers.  In fact, it is [actively](http://gaming.stackexchange.com/help/badges/17/necromancer) [encouraged](http://gaming.stackexchange.com/help/badges/198/revival) *(we don't want to become another Yahoo Answers)*.  The real question is, is this a good answer on its own?  Does it add anything that hasn't already been said?
Comment: @BlueRaja - Danny Pflughoeft yes, lab assault is the best way of getting mana. Every other answer is worse than lab. And well, hacking obviously better than lab, since so called 'ranked' has no protection from any hacks

What's the fastest way to earn mana?


how do you get a crimson biome in a corruption world?

Question: so, I have a corruption world and I want to beat the BOC in terreria.  which means I have to get something that can spread crimsion.  can u guys help me out?
Comment: Keep in mind the same character can use different worlds
Comment: Just wanted to note that in Terraria 1.4 (released May 2020), you can buy the other evil biome seeds from the Dryad in a hardmode graveyard biome, eliminating the need for creating a different world. [Wiki link](https://terraria.wiki.gg/wiki/Dryad#Tips)
Answer: If you have no issue with going between worlds, you could technically bring crimson seeds (dropped by Eye of Cthulhu in Crimson worlds) to your Corruption world, and if your Corruption world is in Hardmode then you could also bring some Crimson blocks from the other world and place them in your Corruption world, as at that point the Crimson blocks could spread to regular stone, wood, sand, etc. in the world.
Alternatively, the "Drunk world" seed; 5162020 can generate both a Crimson and a Corruption biome in the same world.


How do I seal an electrical box for a ceiling fan?

Question: We recently installed new electrical boxes and hung fans from them. We caulked around the boxes to seal off airflow into the attic. There are several small holes (and one has a medium sized hole) on the boxes. What's the proper way to seal this off to prevent the blown-in insulation from falling through the hole into the box (a fire hazard I presume)? Is caulking them appropriate or just putting a piece of electrical tape over the holes?
Answer: I believe that insulation falling in is less of a fire hazard than air escaping through the holes during a fire.  The intent is to prevent air from flowing out into the attic space during a fire, which would create a chimney effect and continue to feed the fire oxygen.
But good news, you can achieve both with the same approach.
You want to use a fire-rated expanding foam or caulk. In the gaps within and around a ceiling box, I'd use the intumescent style of either which will expand further when exposed to heat.
Be sure to clean out any foam or caulk that works its way into the electrical box. From a code perspective, it is important to keep the volume of the box the same.
While using electrical tape to seal the holes in an electrical box is likely better than nothing, I don't suspect it will survive the heat of a fire for very long given that it is not "attached" to anything over the void of the hole.  An intumescent caulk or foam will provide a much more durable blockage to prevent not only insulation from falling in, but from air escaping during a fire (which is the bigger concern IMHO).
Comment: The OP wants to seal the holes in the electrical boxes. they have already caulked round them.
Comment: Thanks Jack, I attempted to clarify how the answer addresses the OP's question.
Answer: If your boxes are metal, while the existing answers will work okay, I'd recommend first using knockout seals (sometimes called knockout covers) to fill in all the big holes, and then using caulk or foam to make it airtight.  It'll be much easier than trying to fill a big hole with only spray foam.
Here's an example of a knockout seal:

(Image source: Home Depot)
Answer: Using foam in a can, like Great Stuff http://www.homedepot.com/p/GREAT-STUFF-Big-Gap-Filler-Insulating-Foam-Sealant-16-oz-248314/100029171 can be used to fill in gaps to help prevent air leaks.
Comment: The page you linked to says it's for "gaps larger than 1 inch". That's a pretty big hole for an electrical box.
Comment: There are multiple varieties of spray foam (including from this one company) for various applications. Read the labels, pick the one that suits. Though I'd note that any other form of caulking would also work Just Fine... and that blown-in insulation is supposed to be fire retardant.


Relativistic de Broglie wavelength

Question: Suppose a particle of mass m in special relativity. Suppose the de Broglie wave-length is (non-relativistic) case:
$$\lambda=\dfrac{h}{p}=\dfrac{h}{mv}$$
In the case of RELATIVISTIC particle, the momentum is $p = \gamma m v$. Therefore a way to recast the de Broglie wavelength is:
$$\lambda_{r}=\dfrac{h\sqrt{1-v^2/c^2}}{mv}$$
Suppose now that we focus on the kinetic energy. For a free particle, we get in the nonrelativistic case, $\mathrm{KE}=T=p^2/2m$, and thus $p=\sqrt{2Tm}$, and so
$$\lambda=\dfrac{h}{\sqrt{2Tm}}$$
I have a doubt concerting to the relativistic case. The natural election for the de Broglie wave-length in the relativistic case is well known: you take $T=E-mc^2$, and from $E^2=(pc)^2+(mc^2)^2$, by simple substitution of $E=T+mc^2$, you get $(pc)^2=T^2+2Tmc^2$, $$p=\sqrt{\dfrac{T^2}{c^2}+2Tm}=\sqrt{2Tm\left(1+\dfrac{T}{2mc^2}\right)}$$
or
$$\lambda=\dfrac{h}{\sqrt{\dfrac{T^2}{c^2}+2Tm}}=\dfrac{h}{\sqrt{2Tm \left(1+\dfrac{T}{2mc^2}\right)}}$$
Well, I have seen a couple of places where the relativistic de Broglie wavelength for a kinetic colliding partice is assumed to be
$$\lambda=\dfrac{hc}{T}=\dfrac{hc}{\sqrt{(pc)^2+(mc^2)^2}-mc^2}$$
Is this last relativistic consistent in certain limit (it seems is the ultra-relativistic case) to the previous one?
Comment: What do you mean by "better" or "worse"?
Comment: Consistency...I can not guess why the author/s defined the relativistic de Broglie waveglength for colliding particles...with the P=T/c instead of $(Pc)^2=(T^2+2Tmc^2)$...
Comment: Vocabulary term of the day *"ultra-relativistic"* regime. Occasionally also seen as *"highly relativistic"* and other variants. But if you are reading at an advanced level the authors probably expect you to be able to think like a physicist and that means paying attention to scale as it applies to the problem in front of you.
Comment: OH, I see...If $T^2>>2Tmc^2$, I get the second expression. Oh, I was so dumb...However, how can it be to do the approximation and then reinsert the masses?
Answer: Thinking about this answer:
$$KE(rel)=(\gamma-1)mc^2$$
Thus, if T=KE(rel):
$$\gamma=1+T/mc^2$$
If $T>>2mc^2>mc^2$:
$$\gamma\approx T/mc^2$$
By the other hand, from the de Broglie fundamental relationship:
$$\lambda=\dfrac{h}{p}=\dfrac{hc}{pc}=\dfrac{hc}{m\gamma v c}$$
and then, with $\gamma\approx T/mc^2$, and $v\approx c$ we obtain
$$\lambda=\dfrac{h mc^3}{m T v c}=\dfrac{h c}{T}$$
From this last equation we get the above one from a simple use of the dispersion relationship. However, as the kinetic energy is much bigger than the rest mass, my doubt concerning the presence of mass remained...Until I did some numbers...

Relativistic de Broglie wavelength


Where is the data directory in Redis?

Question: After writing some data to a redis server, I could read the data from a client.
However, how can I find the data directory on the file system?
Comment: `/var/lib/redis/dump.rdb` (Ubuntu)
Answer: Quickest method: use redis-cli.
redis-cli config get dir

If you have authentication configured, you will need to pass that in using -a password Replacing "password" with your password.
Comment: This didn't work for me, it returned a completely wrong directory. I found my config at `/usr/local/etc/redis.conf`.
Comment: It gave you the config for the instance you connected to. If not, file a bug.
Comment: this command will return the application directory location based on the redis.conf file or default config (if you don't have one) not the config file location
Comment: This outputs two directories; which is correct?
Comment: Is there a response that could be consistent when running Docker? For instance when running Mongo I map volumes like so: "'./.mongo:/data/db'", pretty useful to control the location of data during local dev. I am trying to find an equivalent for Redis.
Answer: Find your Redis configuration directory, probably /etc/redis. Then look in the config file called redis.conf and find the line that starts dir.
It will look similar to this:
dir /etc/redis/database

This will do the job slowly but surely if you can't be bothered to look :-)
sudo find / -name "redis.conf" -exec grep "^dir" {} \; 2> /dev/null
dir /etc/redis

or if you want the config filename as well:
sudo find / -name "redis.conf" -exec grep -H "^dir" {} \; 2> /dev/null
/private/etc/redis/redis.conf:dir /etc/redis

Other possibilities you can check are whether Redis was started with a custom config file as its first parameter like this:
redis-server /path/to.custom/config-file

or with the dir option set on the commandline like this:
redis-server dir /path/to/data

Use
ps -aef | grep redis

to look for these options.
Answer: Because Redis config file can be located in several possible places (depending on the system or container, such as /opt/redis/ in my case), a general solution to find the currently configured location of the RDB file (as set using dir in redis.conf - if config file is used at all*) is:
$ cat $(cd / && find | grep redis.conf) | grep dir

*Note that true to its simplicity Redis by default ships without any config files (using built-in configuration which depends on the version, see docs), and this is indeed the case for the official redis:latest container.

Where is the data directory in Redis?


Projectile Velocity with Drag

Question: I'm trying to determine the velocity profile (and trajectory) of a small projectile that is fired with an initial velocity.  I'm implementing it in Mablab and my equation isn't working out and I just can't figure out what the problem is. The reduction in velocity I get in the first step is greater than the initial velocity.
I start with:
$$ma = \frac{-CAdv^2}{2}$$
where C is the drag coefficient, A is the projected area, d is the air density, and v is the velocity.  Then,
$$\frac{dv}{dt} = \frac{-CAdv^2}{2m}$$
$$v(i)-v(i-1) = \frac{-CAdv^2}{2m}dt$$
$$v(i) = v(i-1) - \frac{CAdv^2}{2m}dt$$
My initial velocity is 1000 m/s and these are 12 mm steel cubes.  This starts supersonic and drops through transonic and subsonic regimes, but I've found that C of 0.3 is an ok drag coefficient to experiment with.  A is 1.44 (10^-4) m^2, d = 1.225 kg/m^3, m = 1.4 (10^-2) kg.  I'm just leaving dt at 1 s for now.
Using this approach results in my drag loss being greater than my initial velocity (I lose -1914 m/s to drag in the first step!  That's a lot considering my starting velocity is 1000 m/s.  Can anyone please tell me what I'm missing here?  I think I've looked at it so much that I'm only capable of looking at it the same way.
Thanks in advance.
Answer: Hint :
$$dv/dt=-v^2$$
can be reformulated as
$$dv/v^2 = -dt$$
Then integrate each side etc.

Projectile Velocity with Drag


copy attachment title to description and alt text

Question: I have a blog with a lot (over 1000) images. Each image has a meaningful descriptive filename. Wordpress has title caption and description fields for images. What's the easiest way to batch process all images and copy the file name to the title alt description and caption fields. Also if I could update yoast seo fields too that would be great.
Answer: You can make a query to loop through all the attachments, and then update the attachment info for each attachment in the while loop.
Something like
<code>$args = array(
   'post_type' => 'attachments',
   'post_status' => 'any',
   'posts_per_page' => -1,
)

$query = new WP_Query($args)

if($query->have_posts()):
while($query->have_posts()): $query->the_post();

// 1. Get the attachment filename here and store it in a variable eg. $filename. See comment at the end of this answer

// 2. Update the post title
$attachment_post = array(
   'ID' => get_the_id();
   'post_title' => $filename
)
wp_update_post($attachment_post);

endwhile; wp_reset_postdata(); endif;
</code>
Did a quick search on how to get the attachment filename but couldn't find it but this should get you started. Within the loop you should also be able to update the description. You can look at wp_update_attachment_metadata and als check this post (related to the filename).
Comment: NP. It wouldn't involve making a plugin though, you can paste the code from my answer about anywhere (in a page template for example). I'm sure there's a hook for when files get uploaded that you can use.
Comment: Thanks eskimo, I ended up just writing a php file to quickly do it for me. Your solution works I'm sure, but would have involved making a plugin. Next I need to find a way to set the other attributes to filename on upload..
Answer: I ended up writing a php file to quickly solve the problem.
<code>$s_query = "SELECT ID, post_title FROM `wp_posts` WHERE NOT post_content <=> post_title AND post_type='attachment'";
    $r_result = mysql_query($s_query);

    if($r_result)
    {
        while($row = mysql_fetch_row($r_result)){
            $s_update_query = 'UPDATE `wp_posts` SET post_content="'.$row[1].'", post_excerpt="'.$row[1].'" WHERE ID="'.$row[0].'"';
            mysql_query($s_update_query);
        }
    }
</code>
Comment: That's a nice solution!
Answer: Well, I was using lightbox gallery, and I needed to have the post title for my images as the alt text.
What I did was create a query on the database to update the post_excerpt to match the post title.
<code>UPDATE wp_posts SET `post_excerpt` = `post_title` WHERE post_type = 'attachment'
</code>
This seem to work for me and the lightbox gallery.
Comment: This doesn't answer the question. The alt field is in the post meta table, not the posts table.


Is it possible to get steady photon?

Question: When light travels from low density medium to high density medium it's speed decreases according to refractive index of medium.
And light is made of moving photons .
That means photons are slow downed.
So it should be possible to reduce the speed of light to zero and we can get a steady photon.
Answer:
So it should be possible to reduce the speed of light to zero and we can get a steady photon

No, photons always move with velocity c, whether in vacuum or crossing a transparent medium
Light is not made up by an addition of photons, the way a kilo of sugar is made up of sugar particles. Light is a superposition of photons in the complex quantum mechanical space. Zillions of photons make up the classical electromagnetic wave, that is slowed within a transparent medium. The individual photons follow a quantum mechanical solution "photon scattering off transparent lattice" . The superposition of those solutions in the lattice make up the classical beam.
One can say  that the individual photons are not collinear with the classical ray direction, but can travel in longer paths in the lattice, building up by superposition the slower emergent beam of light in the lattice.
Comment: This answer glosses over a subtlely in the definition of "photon": In a medium, wthere's a choice: Treat the excitation of the medium as a "reaction" to the bare vacuum photon, or treat the whole thing collectively as a "dressed photon". Whether to include the reaction into the notion of "light in medium" or not is already classically unclear, cf. [Abraham-Minkowski controversy](https://en.wikipedia.org/wiki/Abraham%E2%80%93Minkowski_controversy). Your answer is valid for the "bare photon" view, but the bare photon is not what really "travels" in the medium.
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/81752/discussion-on-answer-by-anna-v-is-it-possible-to-get-steady-photon).
Answer: Yes there is are ways to slow down light. It falls under the broader topic of slow light and a particular technology that one may consider as an example is electrically induced transparency (EIT). One can consider this as a slow down of the photons in the sense of an effective medium.
At the microscopic level, the photons propagating through a dielectric material would be traveling from molecule to molecule, being absorbed and re-emitted all the time. However, the macroscopic effect of this rather complicated process is that the light propagates through the medium in a normal linear fashion, but slowed down by a factor given by the refractive index. One can therefore treat each photon as if it is doing the same: propagating through a linear medium at a slowed down speed.
These days there are special materials that can be manipulated by external electric fields to slow down light by EIT. In such a case, it become transparent or opaque depending on the external control. The microscopic process is still very much a quantum process that involves the interaction of photons with the atoms/molecules, but the macroscopic effect is to slow down the light (photon) so much that it effectly stops. Such materials are being considered as possible quantum memories in that they can store the quantum state of photons for some period before being released again by being allowed to propagate further.
Now, just to clear up some misconceptions, light can be expressed as quantum states in various ways depending on the nature of the light. If the light source is a laser, its quantum state is very well represented by what we call a coherent state, which is a superposition of all the different number states (Fock states). A number state has a fixed number of photons, but because the coherent state is a superposition of all the number states it does not have a well-defined number of photons. Note however that a superposition of several different single-photon states is still a single-photon states. One cannot produce multiphoton states from single photon states through a superposition. To produce a multiphoton states from single-photon states one needs to form a tensor product of the single-photon states.
Another thing, regardless of how many photons there are in a particular state, the propagation of these photons are described by the wave function of the quantum state. It is the wave function that obeys the dynamical equations. So the probability to detect a particular photon at a particular point in space and time is given by the modulus square of the wave function, which is governed by the dynamical equations.
Comment: "One can therefore treat each photon as if it is doing the same: propagating through a linear medium at a slowed down speed." This is wrong. photons always travel at speed c inbetween atoms in vacuum when measured locally. As they travel through the lattice (as waves), they interfere, and they change path, all destructive interferences will cancel out all directions except the path that the photon will follow after scattering off the atom (constructive interference). Individual photons travel longer paths (then the straight path), that is why the wavefront slows down compared to c.
Comment: @ÁrpádSzendrei: The statement was made in the context of an effective medium. Although what you explain is correct in the microscopic sense, nobody has the patience to compute it at that detail. Therefore, one can simplify the macroscopic picture in the way I explained. In view of experimental observations, it is clear that such an approach works.
Answer: There are a few things that we should clarify:

the EM wave always travels with speed c in vacuum when measured locally
photons always travel in vacuum with speed c when measured locally
classically the Em wave is built up by a herd of photons
it is the EM wavefront that slows down in media

So in your case, when light enters a media denser then vacuum, the wavefront slows down.
But the individual photons in the media always travel in the vacuum between the atoms, and these photons always travel with speed c.
So why does the wavefront slow down if the individual photons still travel at speed c? What happens is that the individual photons interact with the media's atoms and molecules, and this interaction takes time. So although the individual photons will always travel with speed c between the atoms (in vacuum), they will as a herd slow down, the wavefront will slow down.
Although the classical EM wave is built up by a herd of photons, you need QM to understand what happens at the micro level to understand why the wavefront slows down.
To understand it, let's take how you calculate the speed of light in glass. You take the time that is spent between when the wavefront enters the glass and when the wavefront exits the glass. You divide the distance (straight path) through the glass by this time. What you come up with is that the time needed for the wavefront to pass through the glass is more then what a single photon would need to pass through vacuum (in a straight path).
Now the wavefront needs more time. Why? Because as per QM, the individual photons are interacting with the media's atoms and molecules. This interaction will cause them to take path's that are longer (then the straight path). You can call this a phase shift, and because of this, the individual photons will need more time to pass through the glass.
Though, the individual photons will still travel at speed c between the atoms (in vacuum), but since the photons' path through the entire glass will be longer (then the straight path), the wavefront will slow down.
There is a very good example to see how this works, though it is not exactly the same thing. When a photon makes its way through the Sun, from the core to the surface, it will go along a not straight path, because it interacts with the dense gas in the Sun. The gas in the Sun is so dense, that it takes for the photon to pass through the gas inside the sun  100000 years to get to the surface. In this case you could even say that the speed of sound is faster then the speed of these photons in the Sun. Of course this would be a little misleading, since we are talking about individual photons in the Sun's core making their way to the surface. But this is a good example to see how a single photon's path might be altered by interacting with the dense media.

So in the case of glass the media is not so dense but still the individual photons are making their way through the glass and take longer path's. This will cause the wavefront to seem to slow down compared to the speed c.
So when you measure the speed of the EM wave passing through the glass, the distance will be the straight path, and the time will be the time needed between when the wavefront enters and exits the media. This time will be longer then in vacuum, because the time corresponds to individual photon's not straight path's. So you are dividing a straight path with a longer time (then what would be needed for the straight path) and you get a speed slower then c.
And to answer the question, there is no way to slow down the photons themselves on a straight path as they move from atom to atom, between the atoms they move with speed c (in vacuum). Even in a dense matter like the gas of the Sun they move at speed c between atoms (in vacuum) and the only thing that will seem to be slower is altogether through the dense gas if you calculate their wavefront speed (which is a little misleading here) but even that is always above 0 speed. So you can never slow down photons in vacuum. What you can say is that the wavefront seems to move slower in dense media.
Comment: When the photon takes a diverted path what causes it to exit the material in the same direction from which it entered?
Comment: I agree the photons take a longer path therefore taking longer to transmit through the glass. There is no reason to introduce a waived because the same thing would happen even with one photon.
Comment: @Lambda excellent question. It is called the refraction index. See my answer here: https://physics.stackexchange.com/a/415437/132371
Comment: @Lambda if you are asking about a single photon passing through glass, it will not do that. It will go a random way through the glass, and it will exit from that random angle based on the refraction index.  Now what you are not taking into account is the herd of photons actong on each other. Waves interfere, and they cancel each other out in any other direction then the wavefront direction. The only constructive interference direction will be the wavefront direction, which is perpendicular to the glass.
Comment: @Lambda it is like with the double slit experiment. Why do you think in the double slit experiment, the single photon (traveling as a wave) can change direction randomly? Because the particle (traveling as a wave) interferes with itself. And so it changes angle. But it always goes straight more or less, towards the screen. Now in the glass lattice, those photons (traveling as waves) interfere, and  they interfere destructively in every direction other then the wavefront direction. The only constructive interference is the wavefront direction.
Comment: @Lambda now in the glass, the wavefront continues when exiting the same angle as it entered. But inbetween, when it is inside the glass, it travels perpendicular. That is why you see that the image through glass gets a little shift, and the shift is bigger if the glass is thicker.
Comment: @ÁrpádSzendrei there is no proof that a single photon doesn't follow the rules of the index of refraction.
Comment: @BillAlsept correct, a single photon does follow the index of refraction at the boundary between two media. But inside the media, the single photon goes a random way (scattering off every single atom it interacts with), because it is missing the leading constructive and destructive interference from the other photons of the wavefront.
Comment: @ÁrpádSzendrei there's also no proof that a photon needs interference from other photons To follow an orderly trajectory. Like you I believe they do not travel straight but take a longer path. It can be calculated to match the index of refraction if a photon travels relatively straight as it weaves back-and-forth between the atoms. If it were random it wouldn't match the index.

Is it possible to get steady photon?


Scramble the data output of a stored procedure

Question: I have a stored procedure that produces data for a call center system every morning. However, the data is sent in the same order daily. Is there a way to send the day in a different order every day without having to manually change the where clause? For examples today's data is : 1,2,3 tomorrow's will be :3,2,1 the day after 2,1,3 .. Same data different order daily.
Comment: @datagod I know Brent wants people to believe that order should never be dictated inside SQL Server, but I don't know that many people agree with him. The details are scant, but the question doesn't seem to indicate that order should really change, just which row appears first.
Comment: Can you show how you change the WHERE clause manually to get a different order? Did you mean the ORDER BY clause? Seeing some code and a rough description of the table structure, data, and how you want the data ordered would be useful (I don't know what `:3,2,1` means).
Comment: Also, do you want the order to be *random*, or do you want the order to follow a specific pattern? If random, then do you need to keep track of the previous day's order to ensure you don't repeat it? "Scramble" and "change the order in this specific way" are two very different things.
Comment: Shouldn't ordering of the data be handled at the application layer?
Comment: I order inside SQL when I need to, I am not against it.  I do this when the "end app" is a report, or a batch process that I created.  I worry though that applications taking the data will re-sort the data anyway.
Comment: @datagod I don't know that it's very common that an application will re-sort the data (unless there is some kind of grid that supports the *user* opting for a different sort). I bet you the order of a Google search result is identical on the page and coming out of the database...
Answer: Assuming you want randomish ordering of your output you can just ORDER BY NEWID().  That would jumble up the ordering of the results reasonably well.  If you only need to randomize after a certain order is established then you can still use the NEWID() trick.  Below are some quick examples:
-- Fully random ordering
SELECT
    *
FROM dbo.Foo F
    INNER JOIN dbo.Bar B ON B.Id = F.FkId
WHERE
    B.ImportantFilter > @ImpressiveVariable
ORDER BY
    NEWID() ;

-- Random ordering of results but the results still preserve the order of UserId
SELECT
    *
FROM dbo.Foo F
    INNER JOIN dbo.Bar B ON B.Id = F.FkId
WHERE
    B.ImportantFilter > @ImpressiveVariable
ORDER BY
    F.UserId
    , NEWID() ;

Another way, which will not produce all possible orderings but only a limited set but can be more efficient with large tables because it doesn't use NEWID(), only a single value for @aRandomNumber which should be drawn from the range of the column that is compared against (F.UserId here) :
WITH cte AS
  ( SELECT *, 0 AS ord
    FROM dbo.Foo F
        INNER JOIN dbo.Bar B ON B.Id = F.FkId
    WHERE ( <where conditions> )
      AND F.UserId >= @aRandomNumber
    ORDER BY F.UserId
  UNION ALL
    SELECT *, 1 AS ord
    FROM dbo.Foo F
        INNER JOIN dbo.Bar B ON B.Id = F.FkId
    WHERE ( <where conditions> )
      AND F.UserId < @aRandomNumber
    ORDER BY F.UserId
  )
SELECT <list of columns except the "ord">
FROM cte
ORDER BY ord, UserId ;


Unable to get Netgear A7000 to work on 20.04 despite multiple attempts

Question: I'm new to Linux and I'm trying to set up everything on my own (with manually created partitions for the first time). The installation process was smooth but I'm struggling to get my wifi adapter to work.
I'm using a Netgear Nighthawk AC1900 Wi-Fi USB Adapter (A7000) which works fine with Windows 10 but is not detected by Ubuntu 20.04
So far I've tried following steps mentioned in three different posts and none of them has worked for me so far:

First I tried this
sudo apt-get install git dkms
git clone https://github.com/zebulon2/rtl8814au.git
sudo dkms add ./rtl8814au
sudo dkms build -m rtl8814au -v 4.3.21
sudo dkms install -m rtl8814au -v 4.3.21

Then I tried this
sudo apt install dkms build-essential git
git clone https://github.com/aircrack-ng/rtl8812au.git
cd rtl8812au
sudo ./dkms-install.sh
reboot

Finally I tried this
git clone https://github.com/aircrack-ng/rtl8812au.git
cd rtl8812au/
sudo dkms-install.sh

Am I missing something?
Also, idk if it is related in any way or if it matters but when I restart Ubuntu my screen goes completely blank and I have to force shutdown my desktop and boot again.
Looking forward to hearing from you all.
Answer: On Ubuntu 20.04, the following worked for me:
$ sudo apt-get install dkms git
$ git clone -b v18.104.22.168 https://github.com/aircrack-ng/rtl8812au.git
$ cd rtl8812au
$ sudo make dkms_install
$ sudo reboot now


How fast do ships using FTL travel in Mass Effect?

Question: I've been looking for some info on the FTL speeds of ships in Mass Effect but I have been unable to find anything. Can anyone provide a speed and sources? If not can anyone provide the time it takes to travel between two well known (in our universe) stars?
Comment: [the mass effect wikia](http://masseffect.wikia.com/wiki/FTL) has info on this, but is unsourced.
Answer: As listed in the wiki, and repeated in each of the games at one point:

FTL drives are devices which allow ships to travel at FTL speeds through space. FTL drive cores work by exposing element zero to electric currents, creating mass effect fields. It reduces the mass of an object, such as a starship, to a point where velocities faster than the speed of light are possible. With a mass effect drive, roughly a dozen light-years can be traversed in the course of a day's cruise without bending space-time and causing time dilation.

As a simple modification of e = mc^2, if you reduce mass thru magic technological implementation of element zero, you are able to travel at light speed or further (negative mass) with reasonable power requirements.
Obviously hand waved bs, but consistent with the titular Mass Effect used for basically everything in game.
Further more FTL speeds in game vary story wise based on engine size or ship type. That said, 12 light years is 7.05419978 × 10^13 miles. That's a little under 3 times the distance to the closest star to earth, Alpha Centauri. With a Mass Effect ship, you could make it there and back in less time than it takes to drive across the US.
Comment: @Hatandboots - yeah, a lot of that wiki article reads like it was lifted from the in-game codex entries.  I don't remember it word for word, but it does look correct.
Comment: It would be interesting to map out some of the jump distances seen on the galaxy map and calculate non-mass relay travel times based on the figure given by cde. The Reapers provide *quite* the incentive to use their technology/traps!
Comment: Well I don't remember hearing the speed in the games, and that was unsourced in the wiki so I wasn't sure it was accurate.
Comment: Well, replay mass effect one and you'll hear it
Answer: In Mass Effect 3, we get this Codex entry:

[...]
The Reapers' thrusters and FTL drives appear to propel them at more than twice the speed of Citadel ships. Estimates of their location in dark space suggest they can travel nearly 30 light-years in a 24-hour period.
[...]

That works out to a strict upper bound of 15 ly/day, and a rough lower bound of 10 ly/day (any slower than that and the codex would have said "three times the speed" instead of "twice the speed").  This is nicely consistent with the other answer and may be sourced to a specific in-game Codex entry (secondary codex -> The Reapers -> Reaper Capabilities).  It also tells us about the reapers (30 ly/day), which the other answer does not.
Finally, it should be noted that these are daily cruising speeds, not long-term averages.  Since ships in Mass Effect need to periodically discharge their cores, they cannot actually sustain these speeds indefinitely without stopping (except for the reapers, which the same codex entry says are apparently not subject to this limitation).  While I'm not aware of any canonical discussion of the matter, it seems like it would be difficult to reliably find rogue planets with magnetospheres in interstellar space.
Answer: After playing Mass Effect Andromeda, where the backstory is about traveling to the Andromeda constellation in about 600 years:
I was also pondering this and wanted to put the speed of traversing 2 million lightyears in 600 years.
Please do correct me when I am making a mistake in my thinking process.
A web tool helped me converting 2 million lightyears to kilometers
To put it to a format that is actually readible, we'll need to go to km/s
18921460945161600000 km/600 years/365 days/24 hours/3600 seconds = 999992651km/s /c makes 3333 times the speed of light.
Answer: 3640-5460 times the speed of light, if the earlier post about the council drives being 10-15 light years per day is correct.
Answer: did some conversions when looking up table top game speed references such as putting FTL speeds at star wars referenced megalight speeds. To sum up a Athabasca freighter can cover the breadth of our solar system from sun to Ingame Charon relay in under 7 seconds at 35 megalights. Now I found another that had sub light drive listed at 56,750 feet per second and when doing simple calculations would take nearly 45days to reach the same relay.
Comment: Hi, welcome to SF&F.  The question was asking for sourced figures; where did these numbers come from?  Also the question wanted speeds for interstellar travel, not in-system.  Please make sure you fully answer the actual question when posting an answer.


How to enable direct to agent routing from standard Einstein bot?

Question: We have a requirement to directly route the chat from Einstein bot to a specific agent linked with the Case when the user clicks on Transfer menu and Einstein bot only supports bot/queue/skill transfer.
We have tried a lot of things, including Apex class call to create/update PSR and Agentwork records but nothing seems to work. Has anybody done this? Any ideas would be much appreciated, Thanks
Answer: I'm not familiar with the specific details of how Einstein Bot handles transfers, but I can provide some general information about how you might approach this problem.
If Einstein Bot doesn't support direct routing to a specific agent, you may need to find a workaround to achieve this functionality. One approach you could try is to use a custom Apex class to create or update a "PSR" (presumably a "Primary Service Request" record) and an "Agentwork" record, which you can use to track the transfer and route the chat to the correct agent.
To do this, you would need to create a custom Apex class that contains the logic for creating or updating the PSR and Agentwork records, and then call this class from your Einstein Bot code whenever the user clicks on the Transfer menu. You would need to pass the necessary information (such as the agent's ID and the case ID) to the Apex class so that it can properly route the chat to the correct agent.Of course, this is just one possible approach, and there may be other ways to implement this functionality in Einstein Bot.
Comment: Hi Erika, Thanks for your response! We have actually tried this- called Apex class which modifies PSR/Agentwork record with PreferredUserId but the Agentwork record remains in cancelled status and the chat never reaches the Agent's Omni console


Can you add worldbuilding footnotes in your novel?

Question: Can you add worldbuilding footnotes in your novel? Most philosophy books have footnotes on them, because sometimes the text by itself is too hard to understand. Are there novels that use footnotes to explain their extremely complex worldbuilding, or it's something no one would do and no one has done? Why is it a bad idea or a good idea?
Comment: Tolkien used appendices.  **Lots** of appendices.
Comment: Look at this one as well: https://writing.stackexchange.com/questions/43466/is-it-a-bad-idea-to-use-footnotes-to-describe-new-technologies-in-a-science-fict
Comment: Anne McCaffrey used a preface to put her Worldbuilding motes in the Dragonriders of Pern books.
Comment: Terry Pratchett and Douglass Adams both used such footnotes extensively, but that was mainly for the comedy.  Not sure how well that technique would fit in with a more serious writing style.
Answer: It is rare yet has been done. I flipped through a few dozen novels and short story collections and found a few in a the book Labyrinths by Jorge Luis Borges
"1 There is an erasure in the manuscript, perhaps the name of the port had been removed." (in the short story The Immortal,)
The bad idea part is it is unusual and could put some people off.
The good idea part is it is another tool available and like any tool, if used well it can help craft a masterpiece.
Comment: This is a good example of a footnote. It's in story and I get the impression the text is a translation or an interpretation of an old manuscript and the person doing the interpretation has added a footnote. It helps show the narrative voice of the story. A bad example would probably be to infodump in the footnotes... (i.e. even the footnotes should "show, not tell"). Another (tedious) example of footnotes is in Eco's "The Name of the Rose." (Where he infodumps on Latin as I remember, and I managed about 5 pages of that...)
Comment: Didn't Terry Pratchett do this all the time in the *Discworld* novels? Of course, most of us are not writing at his level of competence...
Comment: @Erk: "A bad example would probably be to infodump in the footnotes..." - is that always the case? I can imagine very info-dumpy footnotes that, say, explain basic facts about the fantasy world the novel plays in, which IMO help to immerse myself in that world. Precisely because they are info-dumps, they convey the feeling that these are facts the characters in the novel naturally know about, that they wouldn't even consciously think about. I can't quite pinpoint any of the novels where I encountered this style of footnotes, but personally, I enjoyed it very much whenever I did.
Comment: @O.R.Mapper, yes it's always the case that it's PROBABLY a bad idea to infodump in the footnotes or anywhere else in the novel. This also means that there is a low probability that it's a good idea to infodump in the footnotes ;o) ... And sure, if you're using footnotes and would otherwise have to write several chapters to show the vital element... then maybe... but don't expect everyone to read the footnotes... most fiction readers will likely view them as optional...
Answer: I would guess that the most famous recent example of a novel with footnotes (actually, they're endnotes) is David Foster Wallace's Infinite Jest.
The novel includes 388 endnotes, some of which have footnotes of their own.
But these endnotes are not (only) included because Wallace wanted to share the details of his near-future world unobtrusively.  They are a device the author intentionally used to produce a specific effect in the reader.

In an interview with Charlie Rose, Wallace characterized the novel's heavy use of endnotes as a method of disrupting the linearity of the text while maintaining some sense of narrative cohesion.

Infinite Jest - Wikipedia
Wallace explained that the disjointed feeling of flipping back and forth between the main text and the endnotes was intended to simulate the experience of living in the late twentieth century, when competing urgent demands on our attention constantly jerk our focus from one thing to another.
The endnotes are also intended to create a narrative structure that resembles a fractal, or a Sierpiński triangle.  You can hear him discuss this idea in his interview with Michael Silverblat:
Bookworm - David Foster Wallace: Infinite Jest
Perhaps a more extreme example is Vladimir Nabokov's Pale Fire, which takes the form of a 999-line poem, followed by many pages of endnote commentary.  In this case, the entire story is found in the endnotes.

Starting with the epigraph and table of contents, Pale Fire looks like the publication of a 999-line poem in four cantos ("Pale Fire") by the fictional John Shade with a foreword, extensive commentary, and index by his self-appointed editor, Charles Kinbote. Kinbote's commentary takes the form of notes to various numbered lines of the poem. Here and in the rest of his critical apparatus, Kinbote explicates the poem very little. Focusing instead on his own concerns, he divulges what proves to be the plot piece by piece, some of which can be connected by following the many cross-references.

Pale Fire - Wikipedia
Again, the choice to include endnotes is obvious motivated by much more than a desire to include extra detail, or clarify something confusing in the main text.
The general point I'm trying to make is that using endnotes in novels can be done extremely effectively, but perhaps only when the author's choices are considerate, deliberate, and well-informed (Wallace and Nabokov, like all great writers, are also great readers).
Answer: This is done fairly regularly in "hard science fiction" -- as by authors such as Hal Clement or Jerry Pournelle, stories such as Mission of Gravity, Still River, Close to Critical, King David's Spaceship -- and quite recently Outies.
These authors sell their work in part by making it as scientifically plausible as possible (usually giving themselves a pass on one or two items without which there is no story, like a faster than light space drive in a story about the interaction of humans with a non-human intelligent species), and readers like myself often get a kick out of reading the scientific reasoning that went into some fairly bizarre situations or alien species.
This, in fact, is a situation where it may be not just permitted, but highly desirable to include worldbuilding information (from the above authors, often couched as a scientific report or research paper) as an afterword or end notes.
Answer: I would say in fiction, if you are creating a new term, it must be explained in such a way to the reader that they can understand it.  This can be anything from context clues (In Avatar: The Legend of Korra, the characters learn of something called a "Mover" from Varrick, an eccentric rich business man who supports them.  Varrick offers to demonstrate what a Mover is and begins to set up and demonstrate... what is a very early movie projector to a modern audience.   From that point on, all the characters refer to film as "Movers" because now the audience knows... in the setting of an early 20th century technological world, the characters not knowing what Movers are is expected, so it's included),  from characters inventing the word whole-cloth and describing the function (In Book 1 of Harry Potter, Albus Dumbledore's first acts of magic is to appear from nowhere and use a device to turn off all the lights on the street.  The narrator calls this device a "Put-Outer" in Book 1 but in later books, the reader learns that these simple terms describe what the Wizarding World refers to as "Apperating" and "Dilluminators" respectively.).
Or the term is used in a turn of phrase or exchange that the reader can make the substitution easily (In Star Wars, when Princess Leia calls Han a "stuck-up, half-witted, scruffy-looking Nerf Herder" and Han takes offense to "scruffy-looking" to Leia's frustration, the audience can infer that because of the nature of the combination of the three familiar insults (stuck-up, half-witted, and scruffy-looking) and her frustration at where he placed his offense, that Nerf Herding was not a desirable profession or one that was loathsome.   We need not know what the hell a Nerf is, nor do we care because of the four insults we do hear, we know three of them, and the least offensive is the one where Han balked.  It's akin to someone in the real world calling a person an "poorly dressed, cheap, illiterate whore" and the recipient of the insult taking offense at implication that she does not offer her clients a high quality service for a reasonable price.).
At either rate, your novel should show us what these details are, not footnote it, unless the fictional work is being written in an academic voice (you're writing a fictional text book, where footnotes happen).
After all, in Star Wars, the Clone Wars were discussed as a historical event in the first film,  20+ years before they were ever depicted in a film themselves.


When to use and when not to use ridge regression

Question: What are the 'indications' (i.e. when to use) and 'contra-indications' (i.e. when not to use) of ridge-regression. I tried to read up on the net and it seems to useful when multi-collinearity is there amongst the predictor variables. But what about other situations / assumptions for ridge regression? Do the predictor variables need to be normally distributed? How does it fare with small data sets? Is there a problem if categorical predictor variables are included? How many predictor variables can be included relative to number of rows, etc. Thanks for your insight.
Answer: The predictor variables don't need to be normally distributed. Instead, the noise term $\epsilon$ is normally distributed: $$y=w^{T}x+\epsilon$$ If we build the model using maximum likelihood estimates, then it's just linear regression without regularization. If we assume the weights have a Gaussian prior and use MAP estimates, then it will become ridge regression. But in either case, predictor variables need not be normally distributed.
As for when to use ridge regression, in most cases ridge regression outperforms other regularization methods (say L1-norm). You can refer to the following FAQ page by the LIBSVM author:
https://www.csie.ntu.edu.tw/~cjlin/liblinear/FAQ.html#l1_regularized_classification
Therefore I will say try ridge regression first. You may also want to try L1-regularization (LASSO) or elastic nets when:

You know some of the features you are including in your model might be zero (i.e., you know the some coefficients in the "true model" are zero)
Your features do not highly correlate with each other
You want to perform feature selection but don't want to use wrapper/filter approaches

The above reasons are exactly the nature of L1-regularization. The LASSO yields sparse output, which can be viewed as built-in feature selection. However it only selects one feature from a bunch of highly correlated features.
Answer: I refer to this pdf
In formula (3.6) you find the formula for the estimator of $\hat{\beta}$. This formula learns that one has to invert the matrix $(X^TX)$, so you may have problems with Least squares if this matrix is (almost) not invertible.  This is the case of there is multicollinearity between the independent variables (the $X$) or if you have more independent variables than observations.
For ridge regression you have to use formula (3.44) so you have to invert $(X^T X+\lambda I)$. because of the presence of $\lambda$, this matrix is invertible whenever $\lambda >0$.  So for $\lambda > 0$ the matrix is invertible, also in case of (1) multicollinearity and (2) in the case where you have more independent variables than observations.
These are the two cases where ridge has an advantage over OLS.
Ridge regression needs the same assumptions or has the same properties as OLS. Indeed, most of OLS's properties stemm from the fact that $\hat{\beta}^{(ols)}$ is a linear combination of the $y$, as can be seen from the formula (3.4).  The formula (3.44) shows that for ridge regression the $\hat{\beta}^{(ridge)}$ is also a linear combination of the $y$'s, and consequantly all properties of the OLS-estimators that were derived from this linearity will also hold for ridge regression.


What am I doing wrong with my crepe myrtle?

Question: My tree is about 10 years old, it has six main trunks and is roughly 20' tall. The trunks don't seem to get any thicker and Now that it has bloomed, the flowers have pulled the tops to the ground. What should I do?
Comment: pictures tell good stories often
Comment: I love crepe myrtle...please send picture.  Sounds as if you've got a mature crepe myrtle, why are you worrying about trunk diameter?  What the heck do you mean about the 'flowers pulling  the tops to the ground'...do you mean they are so heavy they cause the thinner branches to bend?  PICTURES!!
Answer: This is common with Crepe Myrtles, and some other shrubs. With most plants, there's an obvious feeling of "large branches = healthy/sturdy plant", but with CMs, there's too much flowering and too much foliage on larger branches. The foliage/flower weight increases at a rate greater than what its branches can support.
Crepe Myrtles require yearly pruning in the end of winter.
For the rest of this year, deal with the droop, and tend any snapped branches (go in with a trimmer/saw and lop off the snapped branch close to its parent).
Next late winter / early spring (before dormancy ends), get in there with some heavy pruning.
This seems like a good guide: http://thedailysouth.southernliving.com/2009/02/24/what-concerns-p/

Good luck.
Answer: I found that article a while back, but that's how I've always done any tree or shrub. I start with dead branches, then suckers, then I limb it up to whatever height I want it.
Even shrubs, because you need them high enough to mulch or string trim under. Then I go to crossing branches, removing the whichever one looks like it will conflict with healthy growth the most. Any branches growing to the inside pretty much have to go. If it's a shrub or tree that has multiple trunks, just pick ones that won't rub as they get larger in diameter.
Keep in mind while doing this that you shouldn't take more than 1/3rd of the plant off at one time for most plants (not all of them though, some you can cut to the ground and they're fine). Also, you need to try and imagine where the tree is going. Look at small branches and see that two will eventually cross and rub as they get larger. Save the tree the energy of growing one that you'll lop off later and take it when it's small. It's also important not to force a tree to try to grow to fit your expectations. I let it grow however it wants and remove material only to keep it healthy. If you have to turn it into a giant bonsai, then something is seriously wrong.
Lastly, keeping all of that in mind, sometimes something just has to go. For instance, we have one crepe myrtle that was planted from a 3gal pot. I've been pruning it this way one a year for 7-8 years now. It's currently about 9' tall, has several trunks and has just started to get the smooth pretty bark in the last year or two. I went to prune it this year and noticed that while 4 of the trunks had really nice growth patterns, one of them was leaning way out. It's just as tall and thick as the others, but it's just turned into a really horrible looking trunk, leaning way out to the side. It'll get worse as it gets older. I let one well positioned sucker grow off of this "trunk" and because of the fertilizer and good root system, it's now almost 5' tall and thumb thick just from a half summers growth. Next spring I'll just have to remove the one trunk and let the sucker replace it.


Understanding Google Crawl Stats

Question: I launched my website in Jan '11 and it is indexed in Google which is great - around 300 pages of content so far. I'm trying to understand what happened the Crawl Stats around the end of June and start of July. What has caused the massive climb? What does it mean going forward? Is there anything else I should be doing?
Answer: If you feel that they are over-crawling your site (perhaps even missing deeper content) you should ensure that your HTTP headers are returning good values for things like 'lastmodified' time etc. It may be that Googlebot overestimates how much your site is changing. As a bonus your site will behave better with regards to caching (be it proxy or browser based) and thus feel a little faster.
You'd do well to study what URLs are being crawled (by reviewing your server logs). If they are recrawling the same URL again and again, you definitely have a problem. A common variant on this is if you have a page that can be displayed in many different ways using request variables. Googlbot may try to crawl every possible combination of those variables.
An example I've encountered as a crawl operator was a page that had a list of twenty headings, any combination of which could be expanded. Basically, that page had 2^20 different URLs!
Make sure that Googlebot isn't stuck crawling basically the same page over and over again with trivially different parameters (I've seen it get caught up in this)
Comment: Thanks for this, I noticed today there was another 'spike' in activity so am becoming more concerned as Google's Crawl stats crawled 1,000 pages of content - I only have 300 pages! How do I check to see what pages Google is re-crawling again and again? And how do I check that my HTTP headers are returning good values - it there a test App?
Comment: Your server logs should tell you what pages Google is crawling. As for the HTTP headers, there are a number of Firefox plugins. Personally I use Firebug.
Answer: I guess Google changes crawl rate with site age, popularity (links to your site), markup and header, proper site maps, etc.
They also changed their crawler a while ago so content now can appear in search results much faster than it used to (at least 2 weeks before the change).
So when I released my blog 2 years ago it took Google months to index all the content and weeks to index new posts. Now I see the any post in search results the same day I publish it.
That simple, google doesn't like new sites but respects the elders.

Understanding Google Crawl Stats


Makecert.exe hangs

Question: I was following the steps in Scott Hanselman's blog post describing how to create a certificate authority and code signing certificate for PowerShell scripts.
Initially, I created the certificate authority and a personal certifcate and used it to sign a powershell script successfully.  All went as described in the blog post.
The problem starts (as most do) when I did something that was (probably) stupid, although it seemed reasonable at the time.
I wanted to start over and repeat the process again with a clean slate, so from the mmc certificates snap-in console, I deleted the personal certificate and the certificate authority I created previously. After that any time I try to use makecert, (just as I did the first time around), makecert either hangs or faults (which prompts to end or debug).
Did I hose something up by deleting via the certificates snap-in?  It didn't complain or warn me that it could be potentially hazardous.  Is this just coincidence and something else entirely could be hosed?
I have Event Log entries from the times when makecert crashed, which all look very similar; here is one:
<code>   Log Name:      Application
   Source:        Application Error
   Date:          8/5/2009 3:55:04 PM
   Event ID:      1000
   Task Category: (100)
   Level:         Error
   Description:
   Faulting application makecert.exe, version 6.0.6000.16384,
   time stamp 0x4545910b, faulting module ntdll.dll, version 6.0.6002.18005,
   time stamp 0x49e03821, exception code 0xc0000005, fault offset 0x00067409,
   process id 0xe58, application start time 0x01ca160efdf30625.
</code>
Anyone have any ideas as to what exactly caused this and/or what I can do to fix it.
I'm on 32-bit Vista Enterprise w/SP2.
Answer: This seems to be a bug. The exception code is 0xc0000005, which means it is an access violation. This should create a dump file on your machine. To dig further into this, load the dump file in windbg and get a stack trace. Then post the stack trace here.

Makecert.exe hangs