determine the Laplace domain of this RL circuit

Question:
I am currently learning control system design. I have a lot of confusion about the initial conditions of the inductor in the circuit. Could someone please correctly solve this by getting the differential equations and then take the Laplace transform.
Comment: You must show your attempt at constructing the differential equation. For the initial condition, assume the circuit has been connected for a long time, therefore the initial current is constant.
Answer: Using Faraday's law of induction, we can write:
$$-\text{V}\left(t\right)+\text{V}_\text{d}\left(t\right)+\text{R}\cdot\text{I}\left(t\right)=-\text{L}\cdot\text{I}'\left(t\right)\tag1$$
Where \$\text{I}\left(t\right)\$ is the input current (which is the same trough all the components because it is a series circuit).
Using Laplace transform we can write:
$$-\text{v}\left(\text{s}\right)+\text{v}_\text{d}\left(\text{s}\right)+\text{R}\cdot\text{i}\left(\text{s}\right)=-\text{L}\cdot\left(\text{s}\cdot\text{i}\left(\text{s}\right)-\text{I}\left(0\right)\right)\tag2$$
Comment: Can you explain to me the significance of the  I(0), the initial current for the inductor ? Because in some other examples I've seen they don't include that even though the Laplace of the derivative has it.
Comment: @MaizHalyym Well that is the initial condition in this circuit. So when there is an initial current trough the inductor it has to be placed there.


Kalman filter parameter estimation

Question: From what I've known about Kalman filter, it requires all the parameters of the underlying state space model. Say the state space model is:
$$\xi_{t+1} = F\xi_t + v_{t+1}$$
$$y_t = H\xi_t + w_{t}$$
where $v$ and $w$ are disturbances.
Kalman filter needs the $F$, $H$, $Q$ (the covariance matrix of $v$) and $R$ (the covariance matrix of $w$) as well as $\xi_1$ as the initial state and the corresponding $P_1$ (the mean squared error of $\xi_1$) to start the recursion.
However, these parameters generally have to be estimated by numerical methods. Assume $y_t$ is Gaussian, how can the $H$ be estimated if we don't have any external knowledge about $\xi_t$? Alternatively, if we have some external knowledge of $H$, the estimation of all the parameters can be proceeded as well. What is the general rule to determine the initial parameter values or the state vector if we don't have any external knowledge?
Comment: H is known/set/measured exactly/pre-specified, not estimated; it's part of your model. It's akin to the predictors in a regression model in that sense (and in some state space models, that's what it is).
Comment: @Glen_b Hello Glen_b, thank you for your reply. Do you mean that prior knowledge of H is a must for state space model formulation?
Comment: In the usual state space model, the only things that are to be estimated are the state and its variance-covariance matrix (and, arguably, the error terms); perhaps missing y's if you have some of those.
Comment: @Glen_b Thank you very much for the answer! I started to learn the Kalman filter without any prior experience about the state space model. Maybe I have to go it through first.
Answer: Everything you will ever need regarding estimation of parameters in a state space model is in this document:
https://cran.r-project.org/web/packages/MARSS/vignettes/EMDerivation.pdf
Kalman Filter/Smoother assumes that the parameters are known in advance so that the unobserved state can be estimated. The initial values for the state can be user supplied or a diffuse initialization approach can be used.
For this the standard reference is:
https://www.amazon.com/Time-Analysis-State-Space-Methods/dp/019964117X
For the matrix parameters and noise co-variance estimation the standard procedure is Expectation Maximization which is described in detail in the first reference, and also in
https://www.stat.pitt.edu/stoffer/tsa4/tsa4.pdf
chapter 6.
Archived version of tsa4.pdf (Time Series Analysis and Its Applications): https://web.archive.org/web/20210401070804/https://www.stat.pitt.edu/stoffer/tsa4/tsa4.pdf
Comment: Hi Cowboy Trader. Thank you for your info. I want to clarify my question a bit. I have read through the Kalman filter chapter of Hamilton (1994)'s textbook. He mentioned the estimation procedure with numerical methods (say Newton). One could firstly assign arbitrary parameter values and iterate the Kalman filter. With the obtained state vector, one then could in turn estimate the parameter values and check the corresponding likelihood. This process ends at the trivially changing parameter values.
Comment: My questions are: Do you agree with the point that Hamilton's procedure is unrealistic or won't converge in a general sense? If you do, can you explain concisely how to determine the initial values in a general sense (without any external knowledge) if there're any. (Since it is general, I believe it doesn't require too much words to explain it.) Additionally, could you clarify the 'diffuse initialization approach'?
Comment: Finally, I know EM is a fixed point finding algorithm although I don't fully understand the mathematics behind it. What is the advantage of EM compared with other numerical methods? Just without gradient if say Newton? I am curious because why didn't the classical time series textbooks, for example Hamilton's, Ender's and Lütkepohl's, introduce this particularly useful method? Besides, EM requires initial inputs as well which returns to the essential problem. $H$ and $\xi$, we have to have one of them to start the Kalman filter and estimation. Thank you very much!
Comment: @Seymour Direct maximization of likelihood works, but on small scales. If your matrices are say 2x2, 3x3. It requires calculation of gradients. EM algorithm for Gaussian models have exact analytical solutions. Therefore iteration is more robust. All parameters can be estimated including starting value of $\xi$. Diffuse initialization is using a very large variance on prior distribution of $\xi$.
Comment: So the conclusion is, either I'm using EM or Newton, the initial parameter values have to be arbitrarily assigned or set with some belief right?
Comment: @Seymour you may use both options. I usually initialize matrices to identity matrices and noise covariances to small non-zero values.
Comment: Thank you. Maybe that's what I want to confirm. Although it is always better to have a good guess.
Comment: @Seymour 1. my recommendation is to use several widely-dispersed starting points and compare. I doubt much can be said for general rules of thumb that work for many different types of models. 2. Just a heads up: Bayesian EM is slightly different than frequentist EM, and 3. I would be interested in some empirical demonstrations of when EM is more "robust." I always see this word used, but I haven't found sufficient evidence to always prefer EM.
Comment: The document linked as tsa4 is ... rather unusual.
Answer: As mentioned in other answers, you need values for the parameters in all system matrices ($F$, $H$, $Q$) in order to run the Kalman filter. However, you may have a state-space model with unknown parameters that you need to estimate.
In order to do that, you may use the Kalman filter: running the Kalman filter with arbitrary values of the parameters will produce, as a byproduct, the likelihood. You can then embed the Kalman filter in an optimizing routine which tries different values so that the likelihood is maximized. Answering to other queries I have given detailed examples using package dlm in R. (Alternatives are packages MARSS and KFAS, among others.)
Comment: @Cowboy Trader: I think it very much depends on the problem at hand (and the OM gives no details). I have used gradient-type algorithms many times with good results. EM is generally considered to be slower (and can get stuck in a local optimum, just as a surface climbing algorithm).
Comment: @Cowboy Trader: If that means 4900 parameters unrestricted, I doubt anything will work well, unless you have oodles of data. The Kalman filter itself can cope well with missing data, whichever method you use to maximize the likelihood.
Comment: Yes that's generally what I have learnt in Hamilton's book. However, is it really the case we can just assign arbitrary initial values given the non-robustness of multi-dimensional numerical search methods? I am looking for a general rule to determine the initial parameter values if there're any.
Comment: @Seymour: I do not think you can go any further than making and educated guess. And of course the model may involve restrictions that you can exploit (like non-negativity constraints for variances, etc.).  The initial values problem will exist with either gradient-climbing or EM algorithms.
Answer: In the usual state space model, the only things that are estimated are the state and its variance-covariance matrix (at each time point) - whether filtering or smoothing only changes what information you're conditioning on, but either way you end up with estimates of those things.
The $H$'s (and $F$, $Q$ and $R$ in your notation) are known/set/measured exactly/pre-specified, not estimated; it's part of your model for how observations are related to the state vector (and how state vectors evolve over time, etc).
$H$ is akin to the predictors in a regression model in that sense (i.e. that you don't estimate the $X$ matrix in regression)
Comment: "The 's (and ,  and  in your notation) are known/set/measured exactly/pre-specified, not estimated" <-  this isn't always true.
Comment: It may be that we're interpreting "Kalman Filter" differently, but as I see it, if they're unspecified, you're not dealing with the Kalman Filter algorithm, because in that they are definitely being treated as known quantities. If they were estimated, there are terms (relating to that estimation error) missing from the variance updates. The unknowns are in the state. I have no doubt that you could write a valuable answer that expands on what exceptions specifically you mean (and - terminology aside - I expect that when we both talk about the same thing we won't substantively disagree).
Answer: To address the question of initial values, I would suggest you read Time Series Analysis by Durbin and Koopman (2012) who go into great detail on the exact diffuse initialisation procedure (this is implemented in the R package KFAS). Which is probably what you want to use in the case of a non-stationary model. For a stationary model, you can easily enough solve for the steady state and initialise with that. For a mixed model, and it's a little more tricky and often overlooked - suggest you refer to Doan (2010) Practical Issues with State-Space Models with Mixed Stationary and Non-Stationary Dynamics
Answer: Other answerers mentioned EM, which is the most traditional approach. There are many others, however.

you can do direct likelihood optimization, as various others have also remarked: run filter/smoother, obtain likelihood, iterate/optimize. Gradient expressions are available, see, e.g., Bayesian filtering and smoothing by Simo Särkkä, Chapter 12. (I have implemented this in my personal little Matlab Kalman filter/smoother toolbox, I'm sure it's also available elsewhere.) Notice that in this approach, you can use arbitrary combinations of unknown parameters, exploit known structure elements if you know part of or the functional form of one of the unknown matrices, impose constraints on the optimization scheme, etc.
you can also exploit other gradient-based optimization schemes; see, e.g., Fitting a Kalman smoother to data (Barratt, Boyd; 2020) for an approach using a proximal gradient method; python toolbox available here.

The optimization problem can, in general, be non-convex. You can ignore that and hope for the best and/or use some kind of global optimization strategy, use multiple starting points, use some stochastic optimization scheme, etc. If you do have some reasonable prior guess about possible parameter values, exploiting that in the initialization and/or providing appropriate constraints can greatly help with convergence.

Kalman filter parameter estimation


How to add form fields dynamically using webform

Question: Using webform 3 module, is there a way to dynamically add more fields or do these fields have to be created in the database first?
Currently that's what I am doing and with javascript toggling the css display attribute to show or hide fields.
Answer: You can use Webform Add More module to dynamically add more fields in webform.
The project page says:

Webform Add More enables selected fieldsets to be initially hidden and
  progressively shown with an Add more button, mimicking CCK multiple
  fields. This module adds a checkbox
  setting to webform fieldset components to select which should have Add
  more functionality, as well as an advanced setting to override the
  button label per Webform
Comment: The Add more module is very poor. It doesn't dynamically add fields in the database but shows/hides instead. Also it fails to load when I style my form or use Arrange fields.
Answer: See this question and the accepted answer over at Stack Overflow:
https://stackoverflow.com/questions/13592932/drupal-6-x-add-more-module-no-end-to-adding-more
Basically, the answer is no. This issue (354381) addresses the problem. From the module's author:

[...] there is no progress on this subject. The ability to support multiple values requires a tremendous amount of re-architecting, including changes to the way CSVs are generated, analysis, the database structure, and the UI (both for administrators and users). I wouldn't expect this feature to be added any time soon.

A possible workaround is provided at the StackOverflow question linked above. In summary, you could create a content type (or, for Drupal 7, a block type using BEAN might be slightly more appropriate). And then give anon users permission to create that entity - simulating a webform.


Example sentence with 酌む

Question: I'm trying to learn the verb 酌む (to pour sake, to serve sake), but I can only find a few sentences with this verb, and in these few sentences the verb 酌む doesn't appear to express (in theory) its main meaning: to serve sake, but derivative forms of 酌む like 酌み交わす or expressions like 意を酌む. So I would like you to give me an example sentence (or some if you please) with 酌む (not 酌み交わす) meaning "to pour sake, to serve sake".
Comment: Not sure what you are looking for. Does [this](http://yourei.jp/%E9%85%8C%E3%82%80) help? Or [try this with 酌む](https://bonten.ninjal.ac.jp/bccwj/string_search)
Comment: @sundowner Thanks for the links, although what I would like the most is just an example sentence with no need to have a context to be fully understood, unlike the majority of sentences that are extracts from corpuses.
Answer: I was browsing through the corpuses, and probably the cause of your difficulty is just that 酌む is not really used in ordinary conversations.

友達と酒を酌んだ I had a drink with a friend
酒を酌みながらテレビを見た I drank sake watching TV

are not particularly weird, but normally I would say 友達と酒を飲んだ/酒を飲みながらテレビを見た.

酌み交わす may be used more frequently, but still sounds a bit dramatic.

いつか子供と酒を酌み交わしたい I want to drink with my children some day

Again, 酒を飲みたい sounds more usual to me.

On the other hand, the sense of understand/guess is usual.

事情を酌んで considering the circumstances
意図を酌む guess/estimate the intention

[Edit]

水をコップに汲む pour water into a glass

is perfectly normal. In the same way,

日本酒をコップに酌む pour sake into a glass

should be fine. In this case what happens is only pouring, so 酌む can be replaced only by そそぐ(注ぐ) or つぐ.
I said should because for some reason I don't see any uses of 酌む with explicitly mentioning where sake is being poured. There may be hidden rules for use of 酌む that makes 日本酒をコップに酌む ungrammatical, in which case 酒を酌む always means 酒を飲む.
Comment: Almost yes, except for the sense of _consider_ etc. (which is synonymous for [斟酌する](https://dictionary.goo.ne.jp/word/en/%E6%96%9F%E9%85%8C/#je-37672) ).  I say _almost_ because of the sentences I added in the edit.
Comment: Thank you so much for answering! Then, although not in an ordinary conversation, but for example in a novel, could I always replace 飲む by 酌む? Does 酌む mean "to drink (sake)"?
Comment: Ok, I see! Thank you so much for your help. :)

Example sentence with 酌む


Effect size of Spearman's rank test

Question: I know that $r$ is itself a measure of the effect size, but I would like to know if using Spearman's rank test I can argue that the relation between X and Y is significant with $r = 0.33$ and that the effect is medium, as I do with Pearson test.
Comment: @clare Interpretation of ESs generally have no mathematical/statistical justification.
Comment: @chl It is possible your remark could be misinterpreted.  I *think* you are saying that one should seek non-mathematical justification of the interpretation of a particular ES, and *not* that you are saying interpreting an ES is altogether unjustified!
Comment: @whuber Indeed, I originally meant that interpreting ESs is highly task or domain-dependent (with some general rules of thumb for e.g., Cohen's d or Fleiss' Kappa), and that a good literature review is generally welcome.
Answer: I see no obvious reason not to do so. As far as I know, we usually make a distinction between two kind of effect size (ES) measures for qualifying the strength of an observed association: ES based on $d$ (difference of means) and ES based on $r$ (correlation). The latter includes Pearson's $r$, but also Spearman's $\rho$, Kendall's $\tau$, or the multiple correlation coefficient.
As for their interpretation, I think it mainly depends on the field you are working in: A correlation of .20 would certainly not be interpreted in the same way in psychological vs. software engineering studies. Don't forget that Cohen's three-way classification--small, medium, large--was based on behavioral data, as discussed in Kraemer et al. (2003), p. 1526. In their Table 1, they made no distinction about the different types of ES measures belonging to the $r$ family. There have by no way an absolute meaning and should be interpreted with reference to established results or literature review.
I would like to add some other references that provide useful reviews of common ES measures and their interpretation.
References

Helena C. Kraemer, George A. Morgan, Nancy L. Leech, Jeffrey A. Gliner, Jerry J. Vaske, and Robert J. Harmon (2003). Measures of Clinical Significance. J Am Acad Child Adolesc Psychiatry, 42(12), 1524-1529.
Christopher J. Ferguson (2009). An Effect Size Primer: A Guide for Clinicians and Researchers. Professional Psychology: Research and Practice, 40(5), 532-538.
Edward F. Fern and Kent B. Monroe (1996). Effect-Size Estimates: Issues and Problems in Interpretation. Journal of Consumer Research, 23, 89-105.
Daniel J. Denis (2003). Alternatives to Null Hypothesis Significance Testing. Theory and Science, 4(1).
Paul D. Ellis (2010). The Essential Guide to Effect Sizes. Cambridge University Press. -- just browsed the TOC
Comment: I only have a german text-book as a reference for it, but the authors state that a) Spearman's $r_{S}$ systematically overestimates true $\rho$ for normally-distributed data, and that b) $r_{S}$ is difficult to interpret when not near 0, 1 or -1. (Büning H & Trenkler G. 1994. Nichtparametrische statistische Methoden. 2. Aufl. Berlin: de Gruyter. With regards to a), they also state that typically, Kendall's $|\tau| <$ Spearman's $|r_{S}|$.
Comment: I edited too slowly... With regards to a), B&T cite Walter (1963) and also state that $r_{S}$ is only nonparametric under independency. Walter E. 1963. Rangkorrelation und Quadrantenkorrelation. Züchter Sonderhefte 6: Die Frühdiagnose in der Züchtung und Züchtungsforschung II, 7-11.
Comment: @caracal I guess Siegel's book is also a good reference. I also know that Kendall's $\tau$ has better statistical properties (but this has already been discussed in previous Q&A). But it seems to me that the question has to do with the interpretation of an ES, and although we're not informed of the sample size, it is likely to be small. Anyway, your proposed transformation should work fine and there exist transformation for converting an $r$-based measure into a Cohen's $d$ one. But as you didn't address directly the question, I wasn't sure of where you want to go. Now, I've +1 your response.
Comment: Thanks! Actually, I deliberately tried to answer only the first part of the question (significance test of 0.33), since I wasn't sure about using $\rho$ as an ES measure.
Comment: @caracal Ok, I mostly focused on the other point. The references I gave are mainly opposing the Hypothesis Testing approach *vs.* interpretation of ES measures. I still prefer giving confidence intervals for $\hat r$ or $\hat\rho$, but anyway I hope the asker would find good directions for further investigations.
Answer: With increasing sample size $n$, $r_{z} = \sqrt{n-1} r_{S}$ is asymptotically $N(0, 1)$ distributed (standard normal distribution). In R
<code>rSz   <- sqrt(n-1) * rS
(pVal <- 1-pnorm(rSz))   # one-sided p-value, test for positive rank correlation
</code>

Effect size of Spearman's rank test


logistic regression or mantel-haenszel?

Question: For a 2x2xk table, where k are strata from repeated cross-sectional studies over the course of 10 years, would it be suitable with a Mantel-Haenszel test of common odds ratio or would a logistic regression analysis be more apropriate? The 2x2 part are purely nominal data.
Answer: With large strata they should be identical. Only subtle differences arise between the two tests, more discussion here.
I would prefer the logistic regression model because it could be extended to use fixed or random effects to account for age / period / cohort effects of study follow-up.
Comment: The link given to more discussion is no longer usable, however, the author (Dipankar Bandyopadhyay, Ph.D.) reposted it at https://people.musc.edu/~bandyopd/bmtry711.11/lecture_15.pdf

logistic regression or mantel-haenszel?


Crossing Brooklyn Ferry

Question: In the poem Crossing Brooklyn Ferry by Walt Whitman, it seems to me the narrator is crossing a passage with a ferry. But doesn't the title literally mean he is crossing the ferry itself?
Comment: It is common, in parts of the US, for a route across a body of water to be referred to as a "ferry".
Answer: Walt Whitman wrote in the 19th century, when "crossing the ferry" was a more common phrase than either "crossing by the ferry" or "crossing on the ferry".
See Ngram.
Why does this make sense? In the 19th century, ferry meant not only the boat, but also the place on the river where you crossed using the boat.
From Webster's International Dictionary, 1892:

A place, also a boat, for transporting passengers or freight over a river, etc.
Comment: @chasly from UK: done. Indeed *ferry* ***did*** mean "place along a river where a *ferryboat* operated", as you might be able to deduce by names of towns like "Harper's Ferry".
Comment: @chaslyfromUK to me it seems a perfectly logical transfer of meaning. "Ferry" the vehicle becomes "ferry" the place, as in "it's next to Fulton ferry."  The name refers to the ferry crossing itself (analogous to a bridge), not actually to the stretch of water.  Note that Fulton Street in Brooklyn is arguably an extension of its namesake in Manhattan, as they were once joined by Fulton ferry.
Comment: https://en.wiktionary.org/wiki/ferry
Comment: That's really interesting. Can you back it up with other examples from a corpus or an explanation of why it made sense? I'd be really interested. I can't see why anyone would make "ferry" mean "stretch of water". Thanks
Comment: @phoog: actually, according the the OED, *ferry* has meant both the place of crossing and the boat used to cross since the late 13th century (their citation for the place is 4 years earlier than for the boat, but they have one for *ferryman* 100 years before that, so the record really can't tell which came first). The word originally came from some Scandinavian language in which it meant the boat.
Comment: +1 Also, Locals regularly refer to a particular ferry terminal by saying *I'm at the ferry* whether or not a boat is present. Similarly one might say *I'm at the train* meaning at the train station.
Answer: OED sense 2 ("Now somewhat rare"):

A crossing over a river or other stretch of water which is served by a ferry boat. Also: a place at which a ferry boat departs or lands.

In sum, especially in older usage, ferry could refer to the stretch of water traversed by the boat (and its passengers) as well as to the boat itself.
Answer: Ferries in the old days were often not so much a boat as a raft pulled across the water by a rope attached at each end to opposite shores. In these cases, the ferry includes the rope and by extension the route travelled by the raft as it's towed along the rope. Therefore "crossing a ferry" had a meaning very similar to "crossing a bridge", i.e. "following a guided route across the water".

Crossing Brooklyn Ferry


Setup docker.io container in Webmin DNS

Question: How can I setup a domain domain.tld forward to a specific docker container listening on a specific port i.e. port 2375 (with a lamp config inside)? The server I'm using is Ubuntu 14.04 and the server management software is Webmin 1.700.
Comment: possible duplicate of [How to use DNS/Hostnames or Other ways to resolve to a specific IP:Port](http://serverfault.com/questions/74362/how-to-use-dns-hostnames-or-other-ways-to-resolve-to-a-specific-ipport)
Answer: dns doesn't know anything about ports or routing.. its just to convert a hostname into an ip. You can't say send traffic to http://domain.com to http://220.127.116.11:4531/
Docker isn't a dump in easy solution you need some smarts around it to make the magic happen
Comment: Where do you think I can proceed? Is iptables the right direction? I'm not building a production evironment, it's just to understand the implementation logic around docker.
Answer: The most you can do with DNS is point the IP to your docker host. The port redirection has to happen elsewhere. There are multiple ways to do that depending on your needs. Here are a couple.
1) Use docker run -p 80:2375 ... to map port 80 on the docker host to port 2375 on the container. This is the simplest solution but requires that nothing else will need to listen on port 80.
2) Run a proxy such as nginx on the host or in a container (again using -p or -P) to redirect traffic to your application. It's a more complicated solution but one that will work if you need to send port 80 to multiple applications on the same docker host.
Comment: Thanks, I see #2 of your answer is what I'm look for. I'm already following an Apache mod_proxy solution. In fact there are different apps listening on port 80, all of them already on the host. The general idea is to have some side projects enclosed in containers for easier deployment.

Setup docker.io container in Webmin DNS


What is going on with this XBT token?

Question: So, I have this token called XBT, Elastic Bitcoin, in my wallet. 0x64fB96d0395f6bf105F35233911e3dF2C5bf4Ce8 Is the contract address. My address is 0x9B3De9eF1AbB57750e762e8c0762BF86a2F21033. Etherscan says that I have 9 of them, each worth $741. This is surprising, because MetaMask says I have .00014 of them, worth .01107. Other wallets say other things entirely. What is going on here and what is the true value?
Comment: XBT is an elastic token and has rebase functionality (the token supply and balances change based on something) https://defiprime.com/elastic better to ask them on their telegram channel https://t.me/elasticbitcoin don't give you private key or seed to anyone
Answer: If you go to https://etherscan.io/address/0x64fB96d0395f6bf105F35233911e3dF2C5bf4Ce8#readProxyContract and enter your address at the "balanceOf", you get a reply of 14402. Because the token has 8 decimals, this is the same as .00014 which Metamask displays (well, it should display 0.0001402, but maybe it rounds the value, or you didn't copypaste all of it).
To understand how decimals in tokens are used, you can read various articles online, or have a look at my previous answer https://ethereum.stackexchange.com/a/72481/31933 .
As for the value - difficult to say what it is, since that depends on many things. Also one place may show a different value from another. The value is simply the amount someone is (or has been) willing to pay for it.

What is going on with this XBT token?


Replacing square flush mount light falling out of ceiling

Question:
Okay, so my husband and I are avid DIYers, and we have just a few things left to do on our 1977 ranch renovation. One of those is replacing the hideous ceiling light fixtures in our hallway. After I scraped the popcorn ceiling one of these square dogs of fixtures started to come loose. It looks like the original hole was cut too big. Regardless, they are awful and I would like to replace them with something simple that would not require repairing the giant 11.25 inch square hole in two places in the ceiling of my hallway. I'm hoping something like this Lithonia 12 inch light would work. Advice please?
Answer: Replacing that light seems like a solid plan, but I think you still need to repair the sheetrock and put in a standard ceiling electrical box.  The hard part of drywall repair is taping the seams and floating, texturing, etc.  The good news is that you don't need to do any of that.  Do the absolute minimum job of replacing the square of drywall and cut a new hole in the repair for the round ceiling box.  The repair needs to be strong, but it doesn't have to be pretty.
The new fixture will cover the rough repair, but you will still have a standard light installation.
Answer: It appears that the light comes in 12", 15", or 20". I know the upsizes aren't ideal, but it might be an option as well as the side view (see C dimension) shows that there is still a lip between the housing and the diffuser which could mean that the housing itself might not cover the hole.

Is there any existing electrical box holding the light up? As long as you have one, regardless of the hole, you should be golden for installing the new light. If there isn't a box, you'll need to install one.. but you don't necessarily need to patch the ceiling.
Below is the installation diagram included with your new light selection. It again doubles the "install a box if you don't have one and you should be good" answer.


Making a specific page wordpress compatable that is not index

Question: When I first created my website I overwrote the wordpress php and essentially made the website static. Now I want to make one specific page wordpress compatable (e.g. when i make posts from the dashboard they'll appear on the page), and it is not the index. Which files will I have to redownload and what do I have to do to achieve this?
Answer: Download and install a full copy of Wordpress to a sub-directory on your site. Having it in a sub-directory won't interfere with any of your static pages in the root directory, or elsewhere on the site. The sub-directory for Wordpress can be named whatever you like; you don't have to name it /blog.


How to speed up simultaneous working with PostGIS layers in QGIS?

Question: we are working on one big layer at the same time (10-20 people). Some of us use QGIS 2.8.1 and the other 2.6.
The user with 2.8 have a lot of crashes (QGIS). The 2.6 users don't have this crashes but to add a feature is incredible slow.
The Postgres 9.4 server is running on a Virtual Machine (Hyper V) with Win7.
Maybe it's the network and not QGIS? Maybe someone have an idea. Would be great :)
Comment: how much RAM is available for Postgres HyperV might need more see > Hyper-V Overhead https://technet.microsoft.com/en-us/magazine/hh750394.aspx been there and increased to 16GB
Comment: You really should upgrade to 2.8.2 - it includes lots of fixes over 2.8.1. I can't recall offhand if any would relate to crashing with postgis, but it can't hurt to try...
Comment: Does each user connect with the same login? PostGIS does perform better on Linux but I'd say it would be best to get it running on its' own workstation (server) rather than a virtual machine. There are a few PostgreSQL performance tuning tips, Google that and see what others are saying.. questions regarding the performance of PostgreSQL and tuning would be best asked on http://dba.stackexchange.com/
Comment: @MichaelMiles-Stimson yes everyone connect with the same login. Could this be a problem?
Comment: Now all of us are working with 2.6.0 and 2.6.1. No crashes anymore. We also tried it with 2.8.2 but after saving one feature Qgis crashed.
Comment: If everyone connect with the same login the tablespace can get a little cluttered and lots of objects juggling around. It is not the best but will still work. I think the best thing is to put it on its own computer (not VM) and have the data on SSD/RAID. Post a question on DBA.SE about performance tuning but make sure you Google it first, questions without research are not likely to be well received.
Comment: RAM, disk speed, processor load and network speed could all affect performance, it's hard to say without having monitoring in place to see where the bottleneck is.  One thing I have had success with is increasing the cache sizes in QGIS to allow the individual machines to store more locally and reduce load on the server.  I think the defaults were around 50MB, I've upped mine more to the 200 MB range with good results.
Comment: you should these steps to understand if there is a Postgres provider bug or local installation issue: A) test with qgis on different platforms, win, linux, mac B) look for a replicable crash C) Always share the error or log D) Check with dev version to have log enabled.... It's diffcult to help you without more informations.
Comment: One of you should post your suggestions as an answer :)
Answer: Below the answers posted in the comments :

(@Mapperz) HyperV might need more RAM memory : See Microsoft technet article (Hyper-V Overhead). Try increasing to 16GB
(@ndawson) Try to upgrade QGIS on the lastest versions
(@Michael Stimson) PostGIS does perform better on Linux, but if possible, get it running on it's on workstation (server) rather than a virtual machine. Have also a look for questions regarding the performance of PostgreSQL and tuning on Database Administrators Stack Exchange. If everyone connect with the same login the tablespace can get a little cluttered and lots of objects juggling around. It is not the best but will still work. I think the best thing is to put it on its own computer (not VM) and have the data on SSD/RAID.
(@RustProof Labs)  RAM, disk speed, processor load and network speed could all affect performance, it's hard to say without having monitoring in place to see where the bottleneck is. One thing I have had success with is increasing the cache sizes in QGIS to allow the individual machines to store more locally and reduce load on the server. I think the defaults were around 50MB, I've upped mine more to the 200 MB range with good results.
(@Luigi Pirelli)  You should follow these steps to understand if there is a Postgres provider bug or local installation issue:

A) test with qgis on different platforms, win, linux, mac
B) look for a replicable crash
C) Always share the error or log
D) Check with dev version to have log enabled....


What is this biplane from an old photo?

Question:
Can anyone identify this biplane.
Comment: Welcome to the site. It helps to add as much info as possible, good example: https://aviation.stackexchange.com/q/89796/14897 You can press Edit.
Comment: @abelenky It's a C. "A second letter indicating the aircraft's airworthiness category followed the N and preceded the identification numbers. These airworthiness indicators were; "C" for standad, "R" for restricted, "X" for experimental, and later an "L" for limited, (for example, NC1234)."https://www.faa.gov/licenses_certificates/aircraft_certification/aircraft_registry/aircraft_nnumber_history/
Comment: @mins don't forget the [5-figures ids](http://www.airhistory.org.uk/gy/reg_N26.html)
Comment: The tail number under the wing appears to read "NC12..." or "N612..." perhaps?
Comment: I'd tend to think it's a variant of the [Laird Swallow](https://lltd.dmvd.com/wp-content/uploads/2012/08/NC979-Laird-Swallow.jpg) with another engine, perhaps NC1236. Here are the [3-figure ids](http://www.airhistory.org.uk/gy/reg_N.html), and here the [4-figure ids](http://www.airhistory.org.uk/gy/reg_N3.html) starting with NC12.
Answer: From what I have seen (I put in some screen time), I'd have to agree with mins that it appears to be a variant of the Laird Swallow. There are 5 Swallows on the registration list between 1236 and 1297. The small bit of the third number makes me think that it is a 6 or a 9, and I'd probably guess a 9, which would make it NC1297, assuming, of course, that it had a 4 digit reg number. NC1297 is a Swallow, last registered to Orin Welch Aircraft Co of Indiana. Swallows were manufactured with several different engines, so the odd cowling isn't much of a concern.
Answer: Definitely NOT a Laird Swallow, which is far too early a design with to have many of the visible features.
It is instead a Great Lakes 2T-1A sports trainer - a rather well known aerobatic aircraft, of which quite a few are still registered, although most of the survivors don't have an upright inline engine (horizontally opposed replacements being a popular replacement). Their logo is even visible on the fin.
Airhistory.org lists two batches of aircraft with potentially matching registration numbers in the NC12nnn range including NC12845, NC12846, NC12847, NC12848, NC12887, NC12889, NC12890, NC12891 - all of which also match the unknown third digit - and which actually have enough digits to match the smear on the tail - which is clearly not a 3 digit serial.
I have attached an image of a similar aircraft below.

and the company's logo:

What is this biplane from an old photo?


What does "Net Depreciation in Fair Value" mean on a financial report?

Question: I was reading about a popular pension used in Texas called Teacher's Retirement Statement.  Their latest annual report had a loss of $16B on a line item called "Net Depreciation in Fair Value" (see page 4).  This is frightening news of all the poor teachers in Texas because the pension only had a net value of $104B at the beginning of the year.  Even more scary is the headline at the beginning of the report:  "TRS Pension Fund experiences strong recovery".  If a huge loss of net value is a recovery how will it hold up the economy continues to shrink?  Would should teachers do to protect themselves?
Answer: First, the annual report is just that, a snapshot that shows value at the beginning and end of the period.
Beginning = Aug 08 = $105B
End =       Aug 09 =  $89B
Newsletter date May 10 = $96B
Odd they chose end of August as it's not even a calendar quarter end. The $16B was market loss during that period. Nearly half of that seemed to be recovered by the time this newsletter came out. The balance sheet also has to show deposits and payments made to existing retirees.
I haven't looked at the S&P numbers for those dates, but my gut says this is right. The market tanked and the plan was down, but not too bad.
Protect? The PBGC guarantees pensions up to a certain limit. I believe that in general, teachers are below the limit and are not at risk of a reduced benefit. You do need to check that your plan is covered. If not, I believe the state would take over directly. I hope this helps.


Why didn't the Weasley family use their magic tent to accommodate their visitors during Bill's wedding to Fleur?

Question: We know Mr.  Weasley had the magic expandible tent as the original owner wizard Perkins didn't feel well enough to use it for camping any more.  So when they had the Delacour family,  couldn't they have shifted the younger members to the tent instead of cramming them into shared bedrooms?
Comment: I think it's hard to answer this question definitively. Perkins was using it after all? Someone else borrowed it from Perkins? It got stolen or ruined or lost during the fiasco with the Death Eaters at the QWC?
Answer: I'm not aware of canon answer.
It's possible that the tent wasn't as secure as the Burrow itself.
The wedding happened in the atmosphere of super-heightened security (just prior to the fall of the Ministry, post-Battle of Seven Potters, with Harry there).
Burrow had a lot of security wards put on it specifically to secure it... and the tent may not have been as secured as the house.
Comment: The security wards weren't just on the building, though. There was an area surrounding the house itself (including the garden) that was protected by the same spells, so there would have been room to pitch a tent within that boundary.
Answer: Perhaps Hermione had already packed the tent in her bag

HERMIONE: I've had all the essentials packed for days.
- Deathly Hallows part 1

If Hermione had been packing all the essentials for days before the wedding had even started, then it's possible that she had already packed the tent away in her beaded bag, making it unavailable for use at the wedding.
Note that this is also a likely out-of-universe reason as well; the trio needed the tent for their wanderings, so JKR had the wedding use something different.


FitNesse Test Page Runs Alone But Not in Suite

Question: I have a FitNesse test report (GroupByTest) that runs fine if you run the test by itself. It has about 500 rows of data in the table.
The test passes when run, however when I run the report in the Suite with other tests, the other tests work fine until it gets to the GroupByTest it just hangs. The test does not show up in the list of Suite tests but the page is still at work trying to run the report, but it never finishes. There are reports after this test that pass if run alone as well.
What I just can't seem to figure out is why it runs on its own but not with the Suite. I checked the box to skip the report in the Suite and it passes that report and runs all of the others as usual without problem, so I know it's just this GroupByTest. I've tried adjusting memory and the report itself with no luck in fixing the issue and the batch file that runs the FitNesse server doesn't show any errors...
Any help would be greatly appreciated as the results of the suite go out to QA and the Product Manager daily.
Thanks!
RE:
Nevermind,
I removed more rows from the test and it now runs with the Suite. I'm guessing a memory issue? Maybe it wasn't releasing memory from a prior report in the Suite in time to run my report with 500 rows.
Anyway, I hope this helps someone else if they run into this issue.
SOLVED.
Answer: Copied from question to indicate an answer was found:
"I removed more rows from the test and it now runs with the Suite. I'm guessing a memory issue? Maybe it wasn't releasing memory from a prior report in the Suite in time to run my report with 500 rows."


"Irregardless" vs. "irrespective"

Question: Why is irrespective considered a proper word but irregardless is not?
Comment: In a [recent video](http://www.merriam-webster.com/video/0037-irregardless.htm), my favorite Merriam-Webster editor warns against calling "irregardless" a non-word.
Comment: Another similar word that you can find examples of by Googling is "unlimitless"
Comment: Simple answer: one is a word, the other is not.
Answer: The "ir" in "irrespective" means "not", i.e. "not respective".  So "irregardless" would mean "not regardless", which would mean the opposite of what you probably hope it would mean.
Comment: I agree.  But the situation with irregardless is that people mean "regardless" and so we have two words, that appear to be antonyms, which are actually synonyms.  Reminds me of "inflammable" and "flammable".
Comment: I think the case of "flammable"/"inflamable" is completely different. The prefix "in-" of "inflammable" does not mean "not", but in/into". The latin prefix "in-" can have either meaning, see for example http://www.personal.kent.edu/~rlarson/words/latin/latpref.html
Comment: @Mr. Shiny and New: Yet people don't have any trouble with "inflammatory".
Comment: I have to add (because it is a reminder of one of my most ignominious defeats) that 'irregardless' has fought its way into most dictionaries. Here's M-W: - *The most frequently repeated remark about it (irregardless - bev) is that "there is no such word." There is such a word, however. It is still used primarily in speech, although it can be found from time to time in edited prose.* . Sad but true.
Comment: Furthermore, "flammable" was essentially a neologism.  Though it may have existed to some extent before, it was "invented" ca 1960 for use on trucks and rail cars in the US, to eliminate the confusion between "inflammable" and "non-flammable".  Before that time the word was rarely used, if at all.
Comment: @mmyers: Never thought of that.  Odd :)
Comment: http://atwitsendcomics.com/comics/index/3/Irregardless
Comment: While I tend to naturally agree with it (maybe due to my maths background), irregardless actually means "regardless" according to Merriam-Webster. There's other words functioning that way - irremediless ("remediless"), irresistless ("resistless") and irrelentlessly ("relentlessly).
Answer: Some people use "irregardless" for "regardless" but many people think it is incorrect. It is probably a combination of "irrespective" and "regardless" which is sometimes used humorously.
Oxford Dictionary says:

Irregardless means the same as
  regardless, but the negative prefix
  ir- merely duplicates the suffix
  -less, and is unnecessary. The word dates back to the 19th century, but is
  regarded as incorrect in standard
  English.
Comment: It is like "misunderestimate", where "misunderstand" and "underestimate" were conflated.  Only "irregardless" has become so widespread that, at some point in the future, people might not even think twice about using it.
Comment: An informal example: `The photographer always says, irregardless of how his subjects are feeling, 'Smile!'`
Comment: The [OED](http://www.oed.com/view/Entry/99668) says "In non-standard or humorous use: regardless."
Comment: *Irregardless* has been antedated to 1795: https://motivatedgrammar.wordpress.com/2009/08/31/irregardless-has-a-posse/#comment-3152
Answer: In addition to the prefix/suffix duplication, irregardless is used rarely.  A COCA query shows 11189 hits for regardless and only 36 for irregardless.  That's a reason for it to not be considered a proper word.
Comment: @ladenedge The concept of properness is ill-defined.  People who write dictionaries are faced with what words to include and what meaning to ascribe to those words.  This is particularly relevant when adding new words.  Part of this decision has to do with how commonly and consistently they are used.  In order to evaluate these factors they use a corpus.  This is also how they identify idioms, collocations, and alternate meanings.  Researchers even use special corpora based on text from learners to find typical mistakes such as using words like 'irregardless'.
Comment: I don't see how the number of appearances in COCA suggests anything about a word's properness.  'tremulant' only has two hits, while 'cromulent' has eight.  The Corpus is a measure of rarity, not correctness.
Comment: @Chris I feel like I hear this work all the time, but only in the last 3 or 4 years.
Answer: According to Merriam-Webster, irregardless is a word that means the same as regardless.

Is irregardless a word?
Yes. It may not be a word that you like, or a word that you would use
in a term paper, but irregardless certainly is a word. It has been in
use for well over 200 years, employed by a large number of people
across a wide geographic range and with a consistent meaning. That is
why we, and well-nigh every other dictionary of modern English, define
this word.
Answer: A proper word must not be redundant by mere inclusion of a prefix. In this case, both words make use of the prefix "ir-", which in most cases creates an antonym of the word without that prefix, e.g. something that is "relevant" is that complete opposite of something not pertinent to the matter at hand, or "irrelevant".
First examining the proper word "irrespective", we have "respective" when removing the "ir-" prefix. "Respective" carries a meaning much like "with regard to", reserving an importance that had been or will be established. Hence, "irrespective" should mean "without regard to", which it does quite nicely when the preposition "of" follows.
Now, we remove the prefix "ir-" from the widely-recognized though improper word "irregardless" and have "regardless", a word used to indicate contrast. Very often, "regardless" can stand alone without a preposition immediately afterward. This usage of "regardless" gives such synonyms as "nonetheless", "nevertheless", and "even so". When "regardless" is followed by "of", the writer states that something is true despite whatever may be the object of that "of".
The redundancy of and lack of purpose for "irregardless" becomes strikingly obvious as we include the prefix "ir-" once more, since we might note that there is no apparent difference in meaning between "regardless" and "irregardless". While English is not likely the most logical language, we should nevertheless see a sharp contrast between these two words, with the prefix causing "irregardless of" to mean "in light of" or "with regard to", which is not a documented usage of the word. However, this is the correct usage of "irrespective of", which does not duplicate the meaning of the word to which the prefix "ir-" is added.
Consequently, "irregardless" should never be used in any formal writing or even in formal speech, as it accomplishes nothing other than to weaken the meaning of "regardless". When "of" does not naturally follow, use "regardless" or one of the synonyms discussed. When of naturally follows, either "irrespective of" (my personal preference whenever suitable) or "regardless of" can substitute marvelously!
Comment: Regarding the word irregardless and regardless, regardless is to irregardless what respectiveless is to irrespectiveless, not respective and irrespective. Your example hinges on a comparison which is irrelevant, which might be possible to describe as relevantless or irrelevantless, in real, proper English.
Comment: *"A proper word must not be redundant by mere inclusion of a prefix."* - Proper. Must not. You say this as if English follows laws, but it does not.

"Irregardless" vs. "irrespective"


Spotlight search still searchs when not selected

Question: Why does my iPhone 5c save deleted emails and messages and displays them when spotlight search is turn on. There doesn't seem to be any way to delete them other than to reset and use backup to restore.
Answer: Mail stays in Trash until you empty it.
Did you first empty the trash?

Select Edit, then Delete all.
Comment: Yes, and also deleted imessages but as soon as spotlight is turned on they reappear


Excel Scatter Chart with Labels

Question: I have three columns of data.  Column 1 has a short description, column 2 has a benefit number and column 3 has a cost.  I can create a cost/benefit scatter chart, but what I want is to be able to have each point in the scatter chart be labeled with the description.  I don't care if you can see it on the chart or you have to roll over the point to see the description.
Comment: Ran into the same problem today. I don't believe MS didn't implement such basic and useful feature in 30 years!
Answer: You could use this addon http://www.appspro.com/Utilities/ChartLabeler.htm
Comment: In addition to this fine add-in, Excel 2013 now has an option to add labels from cells. Add any old arbitrary labels first, then format them to access this option.
Comment: +1 Looks good.  I already did it the manual way, but this add-on looks useful for when I need to do this again.
Comment: +1 Excellent link!  Wish I could up vote it more than once.  BTW, works for all chart types with labels, not just XY.
Answer: There's another free utility (and tutorial on how to create it) available for download here:
http://www.wiseowl.co.uk/blog/s130/excel-charts-data-labels-problem.htm
Comment: Could you perhaps describe this utility? Maybe include a tutorial? Generally we prefer answers involve more detail as opposed to just linking
Comment: Pictures showing how the program works is very helpful too.
Answer: I propose one tool named Funfun that can solve your problem. With this tool, you can use an external JavaScript library to plot the scatter chart with a description that meets your needs.
I wrote a function for your problem. Here's the code of the main part:
<code><script>
    var data = $internal.data; // use Funfun API to get the data
    var plot_data = [];
    for(var i=0; i<data.length; i++){ // data preprocessing to fit in Plotly.js
     var trace = {
      x: [data[i][0]],
      y: [data[i][1]],
      type: 'scatter',
      name: data[i][2]
     };
     plot_data[i] = trace;
    }
    var layout = {
      title: 'Data Labels Hover'
    };
    Plotly.newPlot('myDiv', plot_data, layout); // use Plotly.js to plot the chart
</script>
</code>
In Excel Online it's as shown below: you can write codes in the right pane. As mentioned in the code, I use plotly.js to plot the chart.

The link https://www.funfun.io/1/edit/5a3772cd45ac15144af3fe9d of this function. You can link this function to your Excel with Funfun and this URL.
Besides, Funfun also provides an online playground which shares the same database with Funfun in Excel add-in. You can also click the link above to see what it's like in website version.

P.S. I'm a developer of Funfun.
Comment: If you have written a function that answers the question, please post the function in your answer as text.  Images are pretty useless to blind people (OK, so are charts) and links tend to break.
Comment: Ok, I'll fix it as soon as I can. Thanks for your advice.
Comment: I've added the core code.
Comment: Thank you, and thank you for disclosing your association with FunFun.   But, for your information, code doesn't display properly unless every line is indented four spaces (I fixed the `` for you), and "developer" is spelled with one 'P' (I fixed it here, but I can't edit [your profile](https://superuser.com/users/831146/yi-liang)).
Answer: At first, I thought you could accomplish this with a 'bait and switch' - make a plot of the data first, then edit the series.  Doesn't work though.  This works if and only if the numbers in column 'B' are whole numbers.  The excel chart isn't really using any of the data in column B anymore.
The only way I have been able to reliably do this in the past is to make every row of data it's own data series.  Painful, but if you want to see it in action, I have an example excel file.
Comment: +1 Every row of data as it's own series does work, but you are right it is painful to build.
Answer: The wiseowl.co.uk utility worked for me. As a "tutorial" I would recommend

Downloading this Excel worksheet, from part five of this blog and enabling macros
http://www.wiseowl.co.uk/files/blogs/s130/i3.xlsm
Move the button down and out of the way of your data if you have more than
a few columns
Paste your data in on top of the film data.
Create scatter plots by selecting two column at a time and insert scatter (plot).
Clicking on the button, which will add labels.

Easy.
Thanks to the folks that made it and recommended it.

Excel Scatter Chart with Labels


Which django apps are directly usable or easily adaptable for django-nonrel?

Question: Is there a list of django apps that can be used unaltered in django-nonrel or a list of django apps that can be easily adapted to be used in django-nonrel?
Answer: I used django-dbindexer from the same guys that made django-nonrel to use django-registration without modifications.
Answer: I haven't found such a list.
For the record, I've gotten tastypie working with tiny modifications
http://eatdev.tumblr.com/post/12076483835/tastypie-on-django-nonrel-on-app-engine
django-merchant seems to be working as well.
https://github.com/agiliq/merchant
Essentially simple apps that don't require JOINs in their DB queries will most likely work.  If they use ManyToManyRelations, they're probably not going to work.
Answer: I have used 'contenttypes, auth and sessions' from 'django.contrib' without any modification, the app code wont cause any problems. However any query using JOINs result in query errors, so you need to write your queries with this limitation in mind.
Did you have a particular app in mind?


Why is subjective/argumentative a reason to close a question?

Question: Surely these type of questions encourage debate and bring more traffic to SO.
Comment: I object very strongly to the word "censorship" in this context. Censorship involves telling the *owner* of something (be it a printing press, a web site, or a mouth) how they can't use their own property. The owners of this website telling you how you can't use StackOverflow (or letting the community tell you) is not, and can not be, censorship.
Comment: this question itself seems subjective and argumentative
Comment: Because another person's opinion, no matter how hard you try, is not something you can solve.
Comment: If it's subjective it doesn't _have_ a single, correct answer. How can it warrant something it doesn't have?
Comment: To amplify my previous comment, if you want to engage in a discussion, go to a discussion site. Or set one up. Your site, *your* choice. Someone else's site, *their* choice.
Comment: Yes but discussion is healthy - I often learn things I didn't know by reading 'subjective' questions.  And you know what? Who cares if there is no single answer - maybe one of the several answers will be what someone is looking for.
Comment: @random - I like to read others opinions on matters - that's why I ask  'subjective' questions now and again.  When I'm looking for the opinions of people more experienced in certain fields than myself.
Comment: Personally I think only spammed questions should be able to be closed - if you don;t like a question then just downvote it and move on - you'll never have to look at the question again.
Comment: Generating traffic is not the goal. Generating quality questions--and quality answers to those questions--is the goal.
Answer: Because the S[OFU] sites are designed to handle specific, answerable questions. Generally, subjective and/or argumentative (they're not the same thing) questions are not answerable. In fact, by definition, anything which is truly subjective cannot have One True Answer.
Where does this guideline come from? The FAQ for all of the sites:

Avoid asking questions that are
  subjective, argumentative, or require
  extended discussion. This is not a
  discussion board, this is a place for
  questions that can be answered!

Traffic on these sites comes generally from Google juice -- other people out on the web searching for answers to the questions which have been asked here. Subjective/argumentative questions may potentially boost traffic, but according to what I've heard from those in the know on these sites, they won't boost it by a noticeable margin -- and they do reduce the overall quality of the sites.
(And yes, I recognize the irony of me answering this way, given that I do have participatory answers in subjective questions on at least two of the sister sites!)
Answer: The purpose of stackoverflow is to provide accurate, canonical answers to programming related questions (for SU and SF substitute the appropriate topic). While you are correct that argumentative questions might generate a hire rate of traffic, it is not the type of traffic the site is attempting to attract. The site is trying to attract user's who are looking find practical, helpful solutions to their programming problems (and user's to provide those solutions), not users who are "looking for a fight" or to debate what the best programming language ever is (clearly fortran).


How to make mix mono into stereo audio

Question:
I am trying to mix a mono microphone into both channels of stereo audio. The output of the microphone amp is yellow. The stereo in is red. I am using 2 schottky diodes in order to mix. Is this an imporpor way to mix audio/is there a better way?
Also, this device is low power, but I am using a lm386 to amplify the electret microphone. Are there better alternatives or am I doing it right?
Comment: I'm pretty sure this is a duplicate, but maybe not
Comment: you can't use a diode on AC signals like music. ok, well you _can_ but shouldn't
Answer: No, using diodes does not accomplish what you want.  That will partically rectify the additional signal, making it sound like a mess.
You need to actually mix the new signal onto each of the two stereo signals separately.  That might be as simple as a few resistors if the new signal is well buffered so that its impedance is low, and whatever is receiving the mixed signals can handle high input impedance, like a few 100 Ohms.
Answer: Feed the mono output from the amplified microphone signal to left and right channels with a resistor such as 1 kohm. It can also be as simple as shorting both left and right inputs electrically to the common mono signal but using a resistor is safer.
The lowest power solution would be to not use an amplifier - you may indeed get away with connecting the microphone output to left and right input channels. From your "in" node - connect it to left and right.

How to make mix mono into stereo audio


Show number of downloads in Apache directory listing

Question: I have an Apache html server running which contains the standard directory listing. Is it possible to add an extra parameter to show the number of downloads beside each file?
Answer: Mod_AutoIndex does not have any such functionality. I don't know of any module that does or way of doing this short of an external script.
You could create a quick script that counts the downloads in the logs for each file, then adds that via the AddDescription directive in a .htaccess file. This would know be able to track downloads that appear in the logs (which generally only go back several days or weeks).
Answer: You can't do the on a directory listing, what you can do is to place a simple PHP file which will list the directory content (google for "php file list directory contents") and edit it that way to show a download counter next to each file.
You can get the download count by parsing the Apache access log file.
But this setup is not recommended for a large site, with generate a lot of traffic. and will not work on a share hosting where you don't have access to the server log files.
I'm not familiar with your setup, so i can't give a more specific answer.
Answer: I'd go for a jQuery event listener on the download
link, and have it all done server side through PHP.
It may not be foolproof, but it doesn't impact on
the user as much.
If you wanted to do something like this, then you
first need to group your buttons in a way that is
accessible through jQuery; there are other ways to
select multiple elements in jQuery but the easiest is
by making them all members of a specific class.
You can then loop through the class using the
.each() function. So for initialisation of the page;
i.e. getting all the page content working; you need
to loop through every button and make a post
request to the PHP script; all that needs to be sent
to the PHP script is the id of the download. This is
done in Part 1 of the code below.
Part 2 is setting up the event listener for when a
download occurs. Once again, by just putting an
event listener on the whole class we can detect a
click on any of them; and then identify which
button it came from by accessing it's id. (Note:
For simplicity's sake; make the id in the markup
the same as the id in the database)
This then makes another post request to the php
script; but supplies an additional parameter -
"download". In reality, the value that corresponds
to download doesn't actually matter; because this
case is simple enough that the user is either
downloading it or not. So in the PHP segment of
the code (later below) we don't even check it's
value; we just check that it exists.
$(document).ready(function(){
  /* [[PART 1]]: loop through every
element in the .button class*/
  $(".button").each(function (e) {
    /* get it's ID (which is equal to the download id stored in the db */
    var id = e.target.id;
    /* Post the download id to ranking.php; then echo the returned value to an element with the id of 'count<num>'; where num is the download id. */
    $.post( 'ranking.php', { 'id' :

I suggest jQuery as it provides enough syntactical
sugar to make things pretty easy. Additionally, by
using jQuery - you're opening up the doorway to
lots of possibilities in the future if you choose.
Server Side is where the PHP takes over. All this
needs to do in reality is to check whether
download is set, and echo back the number of
downloads. (Obviously incrementing the number
with the database if the 'download' parameter is
set)
This could be achieved with something like ...
<?php
    mysql_connect(localhost,$user,$password);@mysql_select_db($database) or die
( "Unable to select database");
    if(! isset($_POST['id']) {
         //die error!
    }
    /* if $_POST['download'] isn't set, then just get the current download number and echo it back to the browser */
    if(! isset($_POST['download'] ){

The above example would work (obviously with the
database functions corrected) for simple cases, but
obviously - this probably isnt valid code as I've
literally typed it over my dinner! Naturally, it's just
to give you an idea of a possible solution. (If you
do decide to do similar, I've demonstrated bad
practice - mysql operations should preferably be
done with mysqli* functions or PDO now)
Look up the PHP My SQL documentation; hopefully
this has pointed you in the right direction.
Now alternatively, as I know you aren't too keen on
jQuery (it's great once you get in to it!) the PHP
script that you'd use with the jQuery solution can
be used on it's own. Simply changing $_POST[] to
$_GET[] and, as other answers have said, using
URLs like ranking.php?id=; however then you
need to look at getting the PHP script to pass the
file on after the database queries have finished.
It also leaves a question as to the displaying of the
download number; as without AJAX you will have
to embed some PHP in the HTML mark-up inline. I
hope I've edited this to make a bit more sense, and
given you an overview of the other option!


UX design Process Vary from designer to designer, Which design process is commonly used by designers in worldwide

Question: I interacted with different designers, they do design with their own process. their prospective are also different. some of them use different laws like (hicks law, gestalt theory and many more). so its takes time to work with a Designer as a team, in where designer having their own process.
is there any common process that's used widely ?
Comment: I have also worked with many different designers who employ many different processes but find this useful as it brings different perspectives and viewpoints giving a better finished product - I don't see this as a problem. Like my note here, this question will prompt many different opinions of what is good or bad about multiple processes and which processes are best and I think it's probably too opinion-based for this forum.
Answer: Design processes vary among designers and among organizations. I doubt you'll find any universal design processes.
A lot of us work in Agile environments, but even then, I've found that UX Design is most comfortable outside of the sprint cycle. The best UX process I've seen is when the UX team does our research and design and iteration (in collaboration with Business Analysts, etc) until the element we're working on is ready for development. Then the BAs' user stories, linked with our prototypes, are scheduled into sprints. We then evaluate and tweak as the feature is built.
Answer: If you're thinking about UX designers in particular I would say that they are well adjusted for scrum/agile processes. However, I would say the overall encompassing process is an iterative design process.


Is there a way to 'switch OR engage/disengage' power between two different rotating shafts depending on a set RPM (wind speed)?

Question: I'm a final year mechanical eng student, I'm working on designing a prototype of a 'Hybrid vertical axis wind turbine (VAWT)". This hybrid turbine consists of two types of VAWTs Savonius & Darrieus, one providing good 'starting torque' at 'low wind speed' another, needs 'high starting torque' and ' high wind speeds' but, can spin faster than Savonius turbine (no limiting drag). So I want to combine both of these to enjoy both of these turbines' advantages, thus trying to nullify each others' disadvantages. To do this I'll be needing a switching OR engage/disengage mechanism which can switch between both turbines' shafts... Savonius turbine shaft engaged with Darrieus's shaft until Savonius assists Darrieus in starting & speeding up and after reaching its drag-limiting speed, Savonius's shaft has to disengage from the Darrieus's thereby letting it spin independently with Savonius's shaft disengaged. Here the engaging & disengaging are going to happen at a wind speed of 7 m/s. Please suggest to me if there's a mechanism that can do this switching AND if there's a mechanism that doesn't use electrical power or servo motors for the switching actuation mechanism. Any suggestion is appreciated. Thanks in advance! :)
Answer: You are looking for a one-way clutch or freewheel. You will be familiar with these from a bicycle wheel chain-drive cassette. The chain drives the wheel until the wheel's rotational speed exceeds that of the driving sprocket.
Comment: Hi Transistor, thanks so much for the suggestion. IG so far from what I've researched, one-way clutches will be the best choice for the mechanism I want to achieve. I'll be researching more about it, and reverting back to you if I get stuck somewhere. If you're fine with it. If I can DM you?
Comment: All communications need to be done through the site. That way everyone benefits (if anyone benefits!). SE sites don't have a direct messaging system anyway. Meanwhile, do a search for "sprag clutch".
Comment: Oh alright! Sure everyone will benefit... at least I am! Haha
I'll read more on the sprag clutch. Thanks!


Add pdf to a website

Question: I'm building a website containing a lot of pdf files, i added those files with add media button when creating a page, my question is when i open that page, does it mean in my navigator that i charged those files ( my site will be super slow ) ? or the pdf file will be charged(downloaded) just when i click on the link ?
In case my site will be slow because of those files can i put them in a database (mysql) that i have in the same server ? if not can you suggest me any better ideas ?
Thank you very much !
Answer: Your website speed totally depends on your server speed. If you have a lot of visitors that are going to open/use those PDF links, then you are going to have a large number of requests, of course. This might result in a slower speed on a shared hosting.
The better way is to use a document hosting to host all of your PDFs and use the links provided by that service. This way you won't have to upload those files onto your server and you will be able to manage the documents easily as well!
You can use any of the following document hostings:
PDF-Archive, docdrive
Comment: Thanks a lot for replaying, i will now try PDF-Archive and docdrive it seems a great idea.

Add pdf to a website


Confirmatory Factor Analysis - Variance Parameters - Error Variance Estimates

Question: I am referring to a confirmatory factor analysis output. I am curious to know how do we  interpret the "Variance Parameters" Output containing the "error variance estimates" if the predictors are significant (p < 0.05). Do we essentially require the error variance estimates to be significant? What does that essentially mean? (2) How do we interpret the value of LM stat in the "Rank Order of the 10 largest LM Stat forPath Relations?"
Answer: It doesn't mean much for the error variance to be significant.
It's a variance. It has to be greater than zero (unless it's exactly zero, which is very unlikely), so a significance test that tells you it's significantly greater than zero (or not significantly greater than zero) doesn't tell you much interesting.
Therefore we don't care if it's significant, and we don't require it to be significant.
I'm not familiar with the Rank Order of the LM Stat.  I guess that's the lagrange multiplier, but questions about interpreting results from specific software are usually considered to be off topic on CrossValidated.
Comment: (1)I understand Confirmatory Factor Analysis (CFA) has resemblance to SEM.  Is CFA the appropriate test to use instead of Path Analysis to examine the strength of the relationships (and whether they are significant or non-significant) and directions between multiple variables in a model. My goal is to validate a model. (2) I tried using Multiple Regression Analysis and found out most of the var in the coefficient table were non-significant whereas in CFA, the same variables were significant (p < 0.05). Please advise.
Comment: CFA it's a type of sem. I don't think you can test the same things with sem and CFA.


Mutability in functional programming

Question: First I am a Haskell newbie.
I've read this:
Immutable functional objects in highly mutable domain
And my question is nearly the same -- how to efficiently write algorithms where the state is supposed to change. Let's take for example Dijkstra's algorithm. There will be new paths found and distances should be updated. And in traditional languages this is simple while in Haskell for example I can only think of creating entirely new distances which will be too slow and memory consuming. Are there something like design patterns for such cases where one should implement algorithm with mutable data structure and speed and memory usage are main concerns?
Answer: There are of course many ways functional languages address this issue.

Different data structures - many data structures can be implemented in a purely functional manner, with the same algorithmic complexity as imperative versions.  Probably the most well-known work in this area is Chris Okasaki's Purely Functional Data Structures, but there are many other resources as well.  For Dijkstra's algorithm, Martin Erwig's work on functional graphs is appropriate.  See this question as well.
Different algorithms - some algorithms have assumptions of mutability built-in, Quicksort is an example of this.  In this case an alternative algorithm can be used that's more amenable to immutability.
Mutable state - every functional language can model functional state with a State monad.  Most provide other forms of mutability as well, such as Haskell's ST monad and IORef's.
Comment: Sadly, research into data structures and algorithms best suited for lazy functional immutable languages lags behind that for strict imperative mutable languages.  :-(
Answer: The ST Monad lets you use mutable state internally, but present a pure external interface.
Answer: Creating new immutable objects isn't nearly as expense as you might think, since large amounts of structural sharing can occur because the compiler KNOWS they can't change and thus can be safely shared. That said, using highly imperative algorithms with lots of mutable state in Haskell is a bit of a code smell.
Answer: In ML derivatives (such as OCaml, SML, F#), there are "references", which can be used as mutable variables.
In Haskell, this isn't cleanly handled. State is simply not covered by the usual "purely functional" style. Pure FP languages deal with "eternal truths", and are thus not very suitable for working with "ephemeral truths" (although it can be done, definitely).
However, yes, sometimes we need mutable state. A language such as ATS incorporates linear types for handling destructive updates and safe resource manipulation.

Mutability in functional programming


How do I add my own MBean to jmx-console in mobicents SLEE? (for getting SNMP traps)

Question: I need to add a MBean to the jmx-console. This is for getting SNMP get requests and replying to them. I wrote the MBean in a usual way, but I can't find any n00b compatible material anywhere which describes how to add this MBean to the Slee system.
In the SIPRec example, there is a MBean written which is added like this;
MBeanServer mbs = SleeContainer.lookupFromJndi().getMBeanServer();
ObjectName on = null;
try {
    on = new ObjectName(PREFIX + this.name);

if (mbs.getObjectInstance(on) != null) {
    mbs.unregisterMBean(on);
}
mbs.registerMBean(this, on);

} catch (Exception e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

But I can't get my Sbb to import the SleeContainer class. What dependency / step makes this import to the project?
Can anyone show me where to look, in order to add this MBean to SLEE and route the SNMP get request using the attributes.xml in snmp adapter.
Thanks.
Answer: I got some help from a friend and he pointed out that adding SIP 11 RA to the project adds this class. The trick here is to refrain from adding it as v 2.7.0.FINAL.
The sip 11 version which correctly imports the class is v 2.6.0.FINAL.
Just change it in the eclipse dialog box which pops up when adding dependencies if you're using the plugin to add the dependencies.
This is the dependency list in my pom.xml in sbb directory
<dependencies>
    <dependency>
      <groupId>javax.slee</groupId>
      <artifactId>jain-slee</artifactId>
    </dependency>
    <dependency>
      <groupId>org.mobicents.servers.jainslee.api</groupId>
      <artifactId>jain-slee-11-ext</artifactId>
    </dependency>
    <dependency>
      <groupId>org.mobicents.resources</groupId>
      <artifactId>http-servlet-ratype</artifactId>
      <version>2.4.0.FINAL</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.mobicents.resources</groupId>
      <artifactId>sip11-ratype</artifactId>
      <version>2.6.0.FINAL</version>
      <scope>compile</scope>
    </dependency>
  </dependencies>


Puncture/Tear at base of air valve.

Question: I have replaced three flats on my new bike and found each time a tear or hole at the base of the air valve. What can cause this.
Answer:
As Kibbee suggests, the wrong size valve.
A badly-formed valve hole in the rim.  It's not that unusual to find that there is a "lip" of metal at the hole that will cut into the tube.  This requires a bit of filing with a small round file to correct.
Running the tire flat or with very low pressure.  As an under-inflated tire rolls on the ground it tends to "walk" along the rim, tugging on the valve stem.
Poor tube installation technique.  Most importantly, inflate the tube slightly before installing -- just enough that it rounds out (though it should still be limp).
Answer: The most likely cause is using a presto valve is a rim that's drilled for Schrader. Make sure you're using the correct tube for your rims. You can get a grommet to fill the hole if you want to use presto tubes on rims that are drilled for Schrader.
It might also be because the pressure was too low. This can cause the tire to be able to move around inside the tire, and would mostly occur during braking.
Check on the valve hole to make sure there aren't any rough edges, and file them down (only lightly, be careful) if the hole has any sharp edges.

Puncture/Tear at base of air valve.


How do I remove the nut off of this when it's rusted?

Question:
I'm trying to remove the nut so I can replace the freewheel cassette thing but I can't remove it since it's rusted I've tried using WD-40 but it didn't work
Comment: Get a rust dissolver like the the Rust-Oleum one.
Comment: Nobody has yet spotted that the sprocket is held on with a snap-ring. You need a little screwdriver to remove it and then the thing will slip right off. The nuts don't look too bad, you need a decent set of cone spaners if you still wish to remove the axle
Comment: @JoeK great spotting - can you make that an answer please ?
Answer: Can you remove the nut from the non-drive side? If so, you should be able to remove the entire axle and either replace it, remove the drive side nut with the axle out of the hub (out it in a vise etc), or even reinstall adjusting the non-drive side.
If the non-drive side is also seized (likely), Rust dissolver (as already suggested) does not work,  application of heat might help.
Personally I would resort sacrificing the nut fairly early - nut and axles are cheap to replace, and a lot of time and knuckle skin can be wasted getting a seized nut off. A nut splitter would be the goto tool, or drilling the nut flats and spitting with a screwdriver (refer How to remove this stripped brake bolt?, it has a lot of answers that a relevant to this situation. )
Comment: Psst: it's "seized"
Answer: I always go for plan B - oxy-acetylene - which has never ever let me down! Get the offending item nice and cherry-red, and try again with the spanner/socket. If not, plan C is to blow it off, again with oxy-acetylene. Very carefully (it's hardly a diy job) but the thread can be saved by someone who knows what they're doing.
That was the only way to remove a trailer bearing years ago abroad - luckily, the recovery left me in a knacker's yard, with o-a available, although it took hours of persuasion to let them let me use it, and seconds to do the job!
Comment: If you go this route, just make sure you thoroughly clean and re-grease the wheel's bearings afterwards.  Heating that nut to cherry-red is not going to be kind to whatever lubricant might be in those bearings.  You should probably thoroughly clean and re-grease the bearings if you use a rust dissolver or penetrating oil on the hub anyway.
Comment: @Criggie not to mention a lot more people own a heat gun than a gas ax
Comment: I understand your point, but that level of heat is one step away from destructive removal.    A useful level of heat can be attained with a hot air gun and brings less risk.   Even a hairdryer can be sufficient (though clean it before returning :))

How do I remove the nut off of this when it’s rusted?


What can I do with a Pdf upload vulnerability on a CTF server?

Question: A web server running iis 10 ,PHP (windows) allows users to upload any type of pdf (the location and filename does not change on the server ). The files uploaded go though some file extension check which I was unable to bypass(I tried adding a null byte before extension, special characters, double periods). I am wondering if there is some code execution I could do.
Answer: Just in case and if you haven't already, spoof the MIME type - some poorly coded scripts may rely on the MIME type. What you describe doesn't seem to qualify as a vulnerability though (unless you manage to get around the extension check).
For reference here is some information on the data available server-side from a file upload: POST method uploads
Play with the file name too, add some single quotes in case there is an exploitable SQL injection vulnerability. I would also try weird characters in the file name, Unicode or emojis and see how the server reacts. Extremely long file names too. Multi-line input too. Play with the HTTP headers. Examine them, then tamper with them.
Maybe the function parsing the file name to derive the extension will break with the proper stimuli?
A tool like Burp could help automate and replay the attacks.


thermal fatigue and thermal conductivity

Question: Today I argued that heating and cooling a metal many times will affect its thermal conductivity. My idea is that heating and cooling, ie. thermal fatigue, will affect longterm the the microstructure of the crystal, perhaps form some cracks, and the same piece of metal will not have the same thermal conductivity. Is this true? In what extend? I don't recall seeing metallic pots for cooking, to increase the time of cooking if they get old. Any hint?
Comment: ANYONE??????????
Answer: It's really unanswerable.   Defects in a metal do decrease its thermal
conductivity, but heat can either cause stress and create dislocations
(because application of heat causes temperature differences inside
the material) or can cause annealing (the crystal structure can
'relax' to near-perfect, and erase the dislocations).
In electrical solder, heat can also dissolve copper wire into the tin/lead
alloy, and THAT embrittles the metal considerably.   Mostly, metal pots
aren't made of such thermally-unstable stuff.
Comment: Will anyone give me some information about this phenomenon?


Distribution of the exponential of a mixture?

Question: Suppose that $X$ is distributed as a finite mixture of normals
$$\sum_{j=1}^k w_j \phi(x;\mu_j,\sigma_j^2).$$
Is $\exp(X)$ distributed as a finite mixture of log-normal distributions?
Comment: Is it a self-study question? Hint: the answer is rather obvious, if you apply the formula for a change of variable.
Comment: @Xi'an No, it is not a self-study question. I guess I am just too slow. Thanks for the hint.
Answer: When operating a change of variable from $X$ to $Y=\exp(X)$, the density gets transformed as follows:$$f_Y(y)=f_X(x\{y\})\times\left|\dfrac{\text{d}x(y)}{\text{d}y}\right|=f_X(\log\{y\})\times\left|\dfrac{\text{d}\log\{y\}}{\text{d}y}\right|=f_X(\log\{y\})=f_X(\log\{y\})\frac{1}{y}$$which translates into$$f_Y(y)=\sum_{j=1}^k w_j \frac{1}{y}\phi(\log\{y\};\mu_j,\sigma_j^2).$$This is a mixture of log-normal densities.
Answer: When formulated in the most general way, this result can be made obvious.  In full generality the mixture components could be any distributions (not even continuous ones) and the mixture need not even be finite.  This approach forces us to reason with the most basic tools available (cumulative distribution functions)--and the conclusion drops right out.  I think this gets to the essence of the matter.

Let $X$ be distributed as a mixture.  In terms of cumulative density functions (CDFs) we may write
$$F_X(x) = \sum_i \omega_i F_{i}(x)$$
for weights $(\omega_i)$ which sum to unity and CDFs $F_i$ of independent random variables $X_i$.  (More generally, the sum could be an integral.)
Suppose $f$ is a real-valued function defined on a set containing the range of $X$.  For example, $f$ might be the exponential function.  Applying the definition of a CDF, we obtain the distribution law for any of the $f(X_i)$ as
$$G_i(y) = \Pr(f(X_i)\le y).$$
With these definitions in place, the distribution law for $f(X)$ will be given by
$$G(y) = \Pr(f(X) \le y) = \sum_i \omega_i {\Pr}_i(f(X_i) \le y) = \sum_i \omega_i G_i(y).$$
This is the desired result.
When all the $F_i$ are normal distributions and $f$ is the exponential function, this says the exponential of a mixture of normals is a mixture of lognormals.


At what point does one use fugue in the Gloria of the Mass Ordinary?

Question: In setting the Mass Ordinary, what are the words that should be set in a fugue? "Cum Sancto Spiritu in gloria Dei Patris" or just "in gloria Dei Patris"? That's to say, is the entire Cum Sancto Spiritu set fugally, or just when the words "in gloria Dei Patris" arise?
Answer: I can sympathise with this question, because it is frequently difficult to determine what is required in liturgical music, and what is actually a tradition that developed by accretion. In a field as conservative as religious music can be, at times tradition can even take on the force of law...
In this particular case, and bear in mind that I am not a scholar of liturgical music, I would have to venture that only requirement for the Cum Sancto Spiritu section is that it be choral rather than solo. The Germans from about Bach on seemed to set the words "Cum Sancto Spiritu" homophonically, and reserve fugal textures for "in gloria Dei Patris". I've noticed that both Bach's B minor Mass and Haydn's C Major Mass feature this sort of structure. I wouldn't be surprised if others did the same later, given Bach's prestige.
Vivaldi, in the Gloria RV 589, however, writes fugally throughout, and, if you go back to the start of imitative writing in Masses, Josquin's Cum Sancto Spiritu from the Missa de Beata Virgine uses fugal texture from the beginning as well, and this particular piece was very much admired, "covered" and imitated - there is a nice keyboard tiento on it by Cabezón.
So, I think you have some freedom in how to tackle this if you are writing a Mass of your own.
Comment: Very good answer.  To clarify, though, by "Haydn's C major Mass" you're referring to Joseph Haydn's BVM Mass,  Hob. XXII:5 or the War Mass  Hob. XXII:9? Presumably you're not referring to Michael Haydn's Missa Hispanica. By the way, in the St. Francis Mass, Michael Haydn sets the whole phrase fugally. Bruckner's Mass in F minor is scarcely longer than a classical mass (except when Celibidache conducts), and the Incarnatus suggests he knew the St. Francis, but like a hypothetical less pagan Wagner, Bruckner concentrates on "in gloria Dei Patris" for the fugue.
Comment: @RobertSoupe, Hob. XXII:5. The War Mass, properly speaking, doesn't have a *Cum Sancto Spiritu* movement: the *Quoniam tu solus sanctus* states "Cum Sancto Spiritu in gloria Dei Patris" once homophonically, then concludes with an extended and elaborate "Amen".
Comment: Thank you very much for clarifying, and sorry if that seemed like a trick question, I'm only familiar with one mass each from Joseph and Michael.
Comment: No worries. The St. Francis Mass reinforces the point quite nicely.


The requested version of macOS is not available. HOW TO FIX IT TUTORIAL. macOS Catalina public beta

Question: I'm unable to install catalina even after enrolling to the beta. it shows you mac is already uptodate.
Answer: After wasting a day trying to install beta 05 - macOS Catalina, here is the workaround I came across.
Here's how to fix it:

Open the terminal
Run code below
sudo /usr/sbin/softwareupdate --set-catalog https://swscan.apple.com/content/catalogs/others/index-10.15beta-10.15-10.14-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog.gz

now, delete the existing file if there is any.
sudo rm /Users/Shared/.SeedEnrollment.plist

Create a file using nano.
sudo nano /Users/Shared/.SeedEnrollment.plist

paste the following code:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>SeedProgram</key>
<string>PublicSeed</string>
</dict>
</plist>

You can get away with command+c and command+v.
Press control+z and then Y to save the file.
Now, things should be sorted out - check the update settings and it should display beta version.
Comment: Thanks!  This was the solution that worked for me.
Comment: Thanks! It worked after I changed  "PublicSeed" to "DeveloperSeed".
Comment: I am getting this error for public release. Any solution.
Comment: confirming, works for me. In my case, issue gone after "step 2", `sudo /usr/sbin/softwareupdate --set-catalog https://swscan.apple.com/content/catalogs/others/index-10.15beta-10.15-10.14-10.13-10.12-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog.gz
`
Comment: Skipped Step 2, just had to do Step 4 + 5.  Just wanted the Catalina to Big Sur update.
Answer: I tried all of the other suggestions with no luck, I was still stuck on 19A487l with no way to upgrade.
These are the steps that finally worked for me:

Delete the SeedEnrollment plist entirely sudo rm /Users/Shared/.SeedEnrollment.plist
Uninstall all installed profiles, including my unrelated IKEv2 VPN profile
Apple provides 3 different DMGs to enroll in beta programs:

macOSPublicBetaAccessUtility.dmg (didn't work)
macOSCatalinaDeveloperBeta.dmg (didn't work)
macOSDeveloperBetaAccessUtility.dmg this is the only one that worked for me
https://download.developer.apple.com/WWDC_2019/macOS_10.15_Developer_Beta_Access_Utility/macOSDeveloperBetaAccessUtility.dmg

Download and install the package in the macOSDeveloperBetaAccessUtility.dmg DMG, but quit System Preferences the moment it's opened at the end.
Open the macOS App Store.app and Go to Account > Sign Out, quit and re-open the App Store, then sign back in with your developer Apple ID.
Go to https://apps.apple.com/us/app/macos-catalina-beta/id1455661060?mt=12 which should open the macOS Catalina Beta in the App Store, click Get which should then open System Preferences and allow you to start downloading it.

During the download process it may fail at the end or halfway with An error occurred while installing the selected updates., unfortunately I don't have any advice beyond that point other than to keep retrying the steps above until you get it working.  It took me a few tries and there seems to be no rhyme or reason to when it fails or works.
Comment: Thanks Nick! Step 5. did fail for me. But worked fine when I tried it again.

If it helps, the goal for this is to try to get the Catalina installer to run a full install again, not just do an update. Other Stack Overflow answers that were trying to fix the updater did not work for me.

1. Same, but no Terminal. Unenroll from Beta updates. System Preferences -> Software Update -> Details button (lower left corner) -> Restore Defaults.

3. You can also get the beta profile installer from https://developer.apple.com/download/

4. I wasn't signed in before/during/after
Answer: Your mac shows it is already participating on the beta program (message below the gear) but something is wrong and it is not receiving the beta seed.
You can safely unenroll it, and enroll it again.
To unenroll click on "details" below the gear on that window, a dialog will appear asking if you would like to restore your default update settings. Choose 'Restore Defaults'.
After it, close System Preferences .
Download the Catalina public beta utility from:
https://beta.apple.com/sp/betaprogram/redemption#macos
Install the utility and open System Preferences -> Software update.
It should work.


Radiation interactions: how is the transition from the "electric" regimen to "particle-like" regimen?

Question: When we study the interaction of the electromagnetic radiation with free electrons we can find two different approaches in the literature: for low frequency (RF, light...) a classical view is used and it is said that the electrons oscillates due to the electric field of the wave, but for high frequency radiation (X-rays, gamma), the type of interaction seems totally different (Compton effect and the like) and radiation is usually modeled as "particles". For a radiation with "intermediate" frequency such as UV or very low energy X-rays, would interactions be "electric-like" or "compton-like"?. How is the transition between both regimens?
Comment: You have to realize that the classical view emerges from underlying quantum mechanical view (particles). Nature is really in its foundations quantum mechanical but it is practical to use classical theories and models in the macro state , i.e. dimensionswhere hbar is effectively equal to zero as far as measurements go.
Comment: I already assumed that, but how does exactly the classical oscillation emerge from particle-type (Compton) collisions?
Comment: i.e., what happens in the transition region (at an intermediate wavelength)?
Comment: Have a look at how classical fields emerge from quantum/particle ones: http://motls.blogspot.com/2011/11/how-classical-fields-particles-emerge.html .you have to define intermediate region in debroglie wavelengths of the particle. Depending on the accuracy of measurement the particle/photon view will dominate of the classical em field/particle one. I think nano technology gives such orders of discrimination. watch the fuziness in these: http://www.youtube.com/watch?v=oSCX78-8-q0 . fuzziness is due to the qm uncertainties .
Comment: good question !
Answer: Wave length.
When the wavelength is many times larger as the interacting particle, you use a field. When about the same size as the particle, field approach doesn't work that well, change to particles.
Comment: Since the electron does not have a "size", the wavelength is always larger than the particle. Did you mean the wave associated to the particle?. Anyway, there should be a smooth transition between both kinds of behaviours or regimens. How is it possible taking in to account the differences between a classical oscillation an a compton collision?
Comment: there is the de Broglie wavelength for every particle: lamda=h/p , so there is always a wavelength to gauge whether it is practical to use classical or quantum em
Comment: But how do you determine the 'size' of the interacting particle? Electron itself is defined by a wave packet and uncertainty in position depends on the specific type of measurements made.
Comment: After a few years I see that the question didn't get a satisfactory answer. Perhaps I was not able to explain the doubt correctly. We all know that when the wavelength of the radiation is very short the particle description is more useful, and for long wavelength the classical description is more convenient despite being an aproximation. But the question that remains unanswered is: what happens in the middle, for intermediate wavelengths. If we could change the wavelength of the radiation in a continuous way, what would we see in the intermediate region.


Material of mesh doesn't match the render because of subdivision surface

Question:

The material of the mesh doesn't match the render because of the subdivision surface modifier. I just tried to add vertices but it doesn't work.
Answer: The subsurf modifier is designed to interpolate geometry in between existing vertices. The materials (and their borders) are interpolated as well.
You have a couple of options:
Select an edge loop and add a crease with a value of 1 (you can access the edge crease tool with Crl+E):

Or add a loop cut (Ctrl+R) and move it closer to the existing loops.
Answer: The way a subdivision surface modifier works is by dividing faces and even out the angles to result in a smoother surface. However, it doesn't know what the intention of the mapping of your materials is. More faces get added above your tiny bit of white material and it will make those white too.
You can fix this by adding a bevel modifier in front of the subdivision surface modifier. I wouldn't know what settings would work the best in your case because you didn't include a .Blend file. Therefore, you should play around with them. But I advice using something close to the highlighted areas on this image:

Good luck!