Is there a way to block wget from crawling and downloading my website?

Question: I do not want ANY of my alleged website to be crawled and downloaded (css, images, html, etc). Is there a way to block wget completely?
Answer: Yes and No. Let me explain.
Any user can change the User Agent string that Wget uses. If the string is not changed, then Wget can easily be captured using the following in your .htaccess file.
<code>RewriteCond %{HTTP_USER_AGENT} wget.* [NC]
RewriteRule .* - [F,L]
</code>
However, if the User Agent string is changed, then you may never know that it is Wget.
That being said, one thing is clear to any web master who has been around for a while - the log file must be examined often for abusive activity. It is possible to block bad actors as they come along and yet impossible to block them ahead of time though you can get a lot of them.
You will be able to stop most all abuses if you watch your site access logs often enough and know how to use .htaccess and regular expressions. It is not a difficult process and should be well understood by any web master.
While some will argue purely from a philosophical point of view, the fact is that Wget should be blocked in most cases. In all the years I have dealt with the web (and that is a lot more than almost anyone), Wget has no purpose to a user except to scrape resources from a website. While some sites do open themselves up to this form of activity and actually invite it, all accesses I have experienced with Wget have been a form of abuse or theft.
Comment: Thank you. So as I understand it, it's possible to an extent as long as I watch the logs like a hawk but impossible to prevent it before it even happens?
Comment: @ECHELON I was talking about bad bots in general at that point. It is impossible to say when and what bad bot will visit your site, but you can get a feel for what to expect for your site by watching your log files. Like a hawk might be overkill ;-) but daily or near daily to see what kind of activity you get makes sense. Traffic changes all the time, however, you will eventually learn how to block most abuse against your site. You can also simply use something like ModeSecurity which will help a lot!!
Answer: Most bots don't use wget but rather a crawler, and you can advise them to go away by publishing in your site a robots.txt file. There are some rogue bots that won't honor your robots.txt and these will have to be explicitly blocked. You can identify those by reviewing your web server's logs, but also by applying publicly available blacklists.


Is there a difference between "co-redeemer" and "co-redemptrix"?

Question: Did Pope Francis throw cold water on any hope for a 5th Marian dogma or is there a fundamental difference between "co-redeemer" and "co-redemptrix" that leaves the door slightly ajar?
Comment: I'd suspect it's a matter of the translator. redeemer is gender-neutral but redemptrix is explicitly feminine (and more Latinate)
Comment: Hot questions right now: Christianity: Is there a difference between "co-redeemer" and "co-redemptrix"? RPG: Is there a difference between "damage taken" and "damage dealt"?
Comment: Just my three cents: 1) Found a [good article](https://udayton.edu/imri/mary/c/co-redemptrix-as-dogma.php) giving a history as well as documenting progress (or lack of progress) made in recent times with both terms mentioned; 2) Surprised that the [wikipedia article](https://en.wikipedia.org/wiki/Co-Redemptrix) has already been updated with Pope Francis's address; 3) I for one, welcomed this new development since otherwise it will make it much harder for Protestants to convert.
Comment: @GratefulDisciple that's what they said in the 1950's and 1850's with the last two pronouncements of Marian dogmas.  The argument against that "makes Protestants harder to convert" argument was, and is, that the supernatural graces will surpass any apprehensions.
Comment: @PeterTurner Pope Francis was inspired to focus more on Ecumenism and Fraternal Charity, and his approach was "faith is propose not impose". The wisdom behind not pushing the Co-redeemer or Co-redemptrix title is, to allow Christian & Non-Christian to encounter Mary's role inside the Church, it's journeying together that our Christian bros. will accept Mary's role as Co-redeemer & Co-redemptrix. Pope Francis may not be the destined to Pope to proclaim the 5th Dogma, his inspiration is charity & journeying together to encounter Christ & Mary's role in the Church.
Answer: Is there a difference between "co-redeemer" and "co-redemptrix"?
Technically co-redeemer is masculine and co-redeemptrix is female.

Definition of co-redemptrix
A woman whose participation is believed by some Roman Catholics to be essential for the redemption of humanity
Specifically: Virgin Mary

The title of co-redeemer is occasionally applied the the Virgin Mary:

Mary's title of Co-Redemptrix or Co-Redeemer can assist in magnifying our understanding of God's humility. - Teachings Not Yet Declared Dogmas
Co-Redemptrix or Co-Redeemer

Yes, it seems Pope Francis did throw cold water on any hope for a 5th Marian dogma!

At his weekly public audience on March 24, 2021, Pope Francis rejected the claim that the Virgin Mary should be honored as "co-redemptrix," saying that she should be honored, "but as a mother, not as a goddess, not as co-redeemer." Noting that he was speaking on the eve of the Annunciation feast day, he pointed out that in Christian iconography, the depiction of Mary is "always in relation to her Son and in connection with Him.. she always points out the center: Jesus." - Catholic News Headlines

Although Pope Francis was not speaking ex cathedra, he definitively makes a point that he does not favour such a dogma.

Christ is the Mediator, Christ is the bridge that we cross to turn to the Father (see Catechism of the Catholic Church, 2674). He is the only Redeemer: there are no co-redeemers with Christ. He is the only one. He is the Mediator par excellence. He is the Mediator. Each prayer we raise to God is through Christ, with Christ and in Christ and it is fulfilled thanks to his intercession. The Holy Spirit extends Christ's mediation through every time and every place: there is no other name by which we can be saved: Jesus Christ, the only Mediator between God and humanity (see Acts 4:12).
Due to Christ's one mediation, other references Christians find for their prayer and devotion take on meaning, first among them being the Virgin Mary, the Mother of Jesus.
She occupies a privileged place in the lives of Christians, and therefore, in their prayer as well, because she is the Mother of Jesus. The Eastern Churches have often depicted her as the Odigitria, the one who "shows the way"; and the way is her Son, Jesus Christ. The beautiful, ancient painting of the Odigitria in the Cathedral of Bari comes to my mind. It is simple. The Madonna who shows Jesus, naked; then they put a shirt on him to cover his nakedness, but the truth is that Jesus is naked, he himself, man, born of Mary, is the Mediator. And she indicates the Mediator: she is the Odigitria. Her presence is everywhere in Christian iconography, sometimes very prominently, but always in relation to her Son and in connection with Him. Her hands, her eyes, her behavior are a living "catechism", always indicating the hinge, she always points out the center: Jesus. Mary is completely directed toward Him (see CCC, 2674) to such an extent that we can say she is more disciple than Mother. The directions she gave at the wedding at Cana: "He: do whatever he will tell you". She always refers to Christ. She is the first disciple.
This is the role Mary fulfilled throughout her entire earthly life and which she forever retains: to be the humble handmaid of the Lord, nothing more. At a certain point in the Gospels she almost seems to disappear; but then she reappears in the more crucial moments, such as at Cana, when her Son, thanks to her caring intervention, performs his first "sign" (see Jn 2:1-12), and then on Golgotha at the foot of the cross. - General Audience, 24.03.2021

Wikipedia has the following to say about the title of co-redemptrix:

According to those who use the term, Co-Redemptrix refers to a subordinate but essential participation by the Blessed Virgin Mary in redemption, notably that she gave free consent to give life to the Redeemer, which meant sharing his life, suffering, and death, which were redemptive for the world. Related to this belief is the concept of Mary as Mediatrix, which is a separate concept but regularly included by Catholics who use the title Co-Redemptrix. A Fifth Marian Dogma has been proposed including both Mediatrix and Co-Redemptrix.
The term Co-Redemptress was used by Pope Leo XIII in 1894. "For in the Rosary all the part that Mary took as our co-Redemptress comes to us..."
The concept was especially common in the late Middle Ages, when it was promoted heavily among the Franciscans, and often resisted by the Dominicans. By the early 16th century the hopes of the concept becoming Catholic doctrine had receded, and have never seriously revived. In more recent times, the title has received some support from the Catholic Magisterium though it is not included in the concluding chapter of the apostolic constitution Lumen gentium of the Second Vatican Council, which chapter many theologians hold to be a comprehensive summary of Roman Catholic Mariology. Some, in particular the adherents of the Amsterdam visions, have petitioned for a dogmatic definition, along with Mediatrix, and the process for further theological clarification and eventual dogmatic definition is ongoing. Pope John Paul II was the most favorable of recent Popes. As a Cardinal, Pope Benedict XVI suggested that the Marian title caused confusion and did not sufficiently reflect scripture. Pope Francis has repeatedly suggested the title not be used. - Co-Redemptrix
Comment: "Mary is completely directed toward Him (see CCC, 2674) to such an extent that we can say she is more disciple than Mother."  Thank you Pope Francis!
Answer: There is no difference; Redemptor (Redeemer) and Redemtrix (Redemptress) are simply the Latin for Redeemer in the masculine and feminine forms.
The Council of Trent (a Council as yet unrivaled in terms of authority) authoritatively taught that Christ is quote, "alone our Redemmer and Saviour" (Session XXV, emphasis mine; note that this doesn't preclude 'co-redeemers in the sense described below).
One can admit and accept the doctrine that Mary is 'co-redemptrix' if and when one understands it to be identical with the doctrine - the clearly and indisputably apostolic doctrine - that Mary is the new Eve. Even indisputably and uniquely and markedly co-operated in our damnation, and Mary indisputably and uniquely amd markdely in our Redemption from said.
As noted in Ken Graham's answer, Pope Francis does very explicitly reject the doctrine by that name. However, what he says is not (and may not be) opposed to the apostolic and dogmatic idea that Mary is the new Eve, and as such plays the most importantly co-operative role with the Saviour in Redemption just as Eve played the most important role next to the Damnator with regard to the Fall.
Comment: If Eve had brought Adam forth I would perhaps begin to understand this idea however the fall of Mankind in Adam is predicated upon the facts that Adam came first and that the Prohibition was given to Adam prior to Eve being created from him.  Thus it is said that the woman was deceived but the man was not (1 Tim 2:14) and thus it is that sin entered the world through one man.  Eve became a transgressor but nowhere in Scripture does she share culpability for the entrance of sin into the world.  Therefore even if Mary is considered the new Eve there is nothing for her to reverse.
Comment: Typology doesn't work like that. There is never a 1:1 direct correspondence between the two, only of theme. Christ, after all, didn't cause the Fall. He did the opposite. The Man and Woman who begin creation are Adam and Eve; the Man and Woman who begin the New Creation are Jesus and Mary. Adam and Eve were created from one flesh, as Mary and Jesus.There is the "no" of Eve to reverse. There is the key role in the Redemption instead of the key role in the Fall. The Fathers are absolutely unanimous on this, there is no room for dissent here unless you advocate 'me and my Bible under a tree'-ism.
Comment: What is the "no" of Eve?
Comment: @MikeBorden The parallelism was, Satan a cherub impregnated Eve's heart with a "false wisdom" deceving her, saying she could bear thru "human love or carnal" that led to her defiled virginity while Angel Gabriel also a cherub clarifies the impregnation as "Divine Love", Her virginity will remain and She will bear the "Eternal Wisdom". Eve was deceived by a cherub, the cause of Adam's fall, and Mary the New Eve was enlighten by a cherub, the cause of man's salvation.
Comment: @jongricafort Where, in the Genesis account, is there any mention of Eve being tempted to "bear carnally" or of her "virginity being defiled", please?
Comment: @Mike Borden Satan promised Eve that if she eat the fruit she will gain "wisdom", while Mary also gain "wisdom" thru bearing a child, the "Eternal Wisdom".. The secret is the word "Wisdom". Eve desires to have "wisdom", the "wisdom promised by Satan"  and Mary the New Eve bear Jesus the "Wisdom of God". The fruit of Mary the Tree of Life was Jesus. Who is the fruit of Eve? It was Cain.
Comment: @MikeBorden The 'no' of Eve is her rejecting the command of God, when prompted by Satan. It resulted, ultimately in the Fall, through the first Adam. Mary said, "I am the handmaid of the Lord: let it be done unto me as you have said," when prompted by Gabriel with the gospel of bringing Christ the Saviour into the world, resulting ultimately in the Redemption, through Christ, "the last Adam." The parallels don't end there, even, but even two or three, combined with the explicit reference to Jesus as a new Adam would suffice - and that's on top of the unanimous interpretation of the Fathers.
Comment: Eve was "in the transgression" through being deceived but Adam caused the Fall by disobedience:  It was Adam's "no".  I can appreciate that Mary was "in the redemption" in the same sense...although she didn't understand how these things might be she chose to trust God but it is Christ who redeems.  Christ had to be born of someone.  Like Esau, the first Adam despised his inheritance.  In this way Jacob is a type of Christ but, like all types they cannot really be pressed very far without disintegrating.  The Fathers appear to hold the type but they don't press it very far.
Answer: "Redemptrix" (English: "redemptress") is the feminine version of the masculine "redeemer".
The Redeemer is Jesus Christ. The Co-Redemptrix is His Blessed Virgin Mother:

A title of the Blessed Virgin as co-operator with Christ in the work of human redemption. It may be considered an aspect of Mary's mediation in not only consenting to become the Mother of God but in freely consenting in his labors, sufferings, and death for the salvation of the human race. As Co-Redemptrix, she is in no sense equal to Christ in his redemptive activity, since she herself required redemption and in fact was redeemed by her Son. He alone merited man's salvation. Mary effectively interceded to obtain subjective application of Christ's merits to those whom the Savior had objectively redeemed.

Yes, there is only one Mediator (1 Tim. 2:5), but that does not mean there aren't other mediators subjected to Him. Think about who brought you to Christ. You didn't do it alone. Saints and angels in heaven plus people on earth can help you through their prayers and actions. These people are your mediators, being subject to the one Mediator.
The Blessed Virgin Mother of God is Mediatrix because without her "Be it done to me according to thy word" (Luke 1:38)—her fiat—there would be no Christ, no Church, and thus no salvation. She brings us to Christ and Christ to us in a most supreme way than any other creature can.
last 2 ¶ taken from this answer to "Are Angels more accessible than Jesus?"
Answer: Is there a difference between "co-redeemer" and "co-redemptrix"?
The clear answer is none.The meaning or role as Co-redeemer & Co-redemptrix means cooperation by either male or female, but the meaning and action is basically the same.
Did Pope Francis throw cold water on any hope for a 5th Marian dogma or is there a fundamental difference between "co-redeemer" and "co-redemptrix" that leaves the door slightly ajar?
Did Pope Francis throw cold water? On the surface, the answer is Yes, but a deeper understanding must be reflected on Pope Francis inspiration in proclaiming the Catholic faith, as he said;

"Faith is propose and not impose."- Pope Francis

Pope Francis advocacy is "journeying together" with Christian and Non-Christian, and the Church mission is for the People of God including Jews, Muslims, Buddhist, Hindus, etc. is to encounter Jesus Christ and Mary's role in the Church thru their own personal encounter.
Pope Francis inspired mission is unity & fraternity, and Our Lady like St.Therese of Liseux said, "She is more Mother than Queen".
Our Lady embraced Motherhood of Christ the Redeemer first and Pope Francis cited Mary's own humble admission of Herself being the "handmaid of the Lord", and not seeking any titles because She is the humblest creature of all, eventhough She deserves all the title. But the Magnificat, saying "all generations shall call Her blessed" means, She will be crown with many titles, and the Fifth Dogma is a fitting title for Mary's role. But Pope Francis was not yet inspired by the Holy Spirit to focus on Marys's role as Co-redeemer or Co-redemptrix, the clear inspiration and direction of the Church is towards unity of all Christian and Non Christian thru fraternal charity as evident in Pope Francis latest teachings on "Fratelli Tutti" calling all the People of God as "All Brothers". Like Pope Francis signing with our Muslims brothers the fraternal agreement and add to that his recent visit to Iraq.

APOSTOLIC JOURNEY OF HIS HOLINESS POPE FRANCIS
TO THE UNITED ARAB EMIRATES
(3-5 FEBRUARY 2019)
A DOCUMENT ON HUMAN FRATERNITY
FOR WORLD PEACE AND LIVING TOGETHER http://www.vatican.va/content/francesco/en/travels/2019/outside/documents/papa-francesco_20190204_documento-fratellanza-umana.html

ENCYCLICAL LETTER
FRATELLI TUTTI
OF THE HOLY FATHER
FRANCIS
ON FRATERNITY AND SOCIAL FRIENDSHIP
http://www.vatican.va/content/francesco/en/encyclicals/documents/papa-francesco_20201003_enciclica-fratelli-tutti.html

In closing the wisdom behind Pope Francis not focusing more on Mary's other titles and simply focus on Her Motherhood role as evident in his elevation of Mary's title as "Mother of the Church" into a feast celebration. The 5th Dogma has Catholic foundation, but accepting Mary's role as Co-Redemptrix, Advocate and Mediatrix must be accepted not only by Catholic but also by the People of God that includes Protestant, Christian,Jews, Muslims, Buddhist, Hindus, etc. It is more wise to proclaim the 5th Dogma having the support of Christians and Non Christian thru their own personal encounter of the role of Mary played in the salvation of man. And this can only be realize not by imposing the Catholic faith on Mary's role but by proposing it along the Christain journey of all our brothers in Christ shining the teachings in Fratelli Tutti, Muslims Fraternal Agreement, and affirming "Ecumenism and Nostra Aetate" a teachings in the Vatican II Council.
Our Lady will wait for the perfect time, and in God's perfect time to proclaim the 5th Marian Dogma, after all the People of God had achieved unity thru fraternal charity inside the Church founded by Christ to fulfill the desires of the Father in John17:20-22.
IMPORTANT NOTE : My conclusuon and personal views was in harmony with the answer of Father Stefano de Fiores, professor of Mariology at the Pontifical Gregorian University in Rome . Here's the source of his interview explaining the primary reason was "Ecumenism & Fraternal charity" and not a theological one, as unity and fraternity must be the focus first like what Pope Francis is doing now, and it is the Christian and Non-Christian participation in imploring Mary's role that will bring about the perfect timing in proclaiming the 5th Marian Dogma.
https://udayton.edu/imri/mary/c/co-redemptrix-as-dogma.php

https://www.tandfonline.com/doi/abs/10.1080/0458063X.2018.1413279?journalCode=ultg20
Comment: With the exception of the first sentence which clearly answers one part of the question, the rest seems a vague mix of speculation which attempts to conclude "yes but not really" to the other part of the question. It's not clear what in fact co-redemptrix would actually amount to nor what Pope Francis or any theologian has said which would reconcile the possibilities.
Comment: @eques It takes wisdom to understand the great mind of Pope Francis, a schismatic heart cannot fathom Pope Francis profound wisdom.
Comment: And you have that wisdom? Please elaborate where the Church has taught that a schismatic completely lacks the ability to have wisdom.


Website's navbar on top vs navbar fixed at bottom for mobile size?

Question: For mobile size I usually add burger menu icon on top of the page (or menu links if just couple) with option to open and display all menu links in overlay, but more and more I see approach where the navbar is added to bottom as fixed, where thumb reaches it better. What type of menu would be better to use? People are used to menus on top, but I think this is starting to change.
Answer: I think you answered your own question. The discussion is more of: should I follow trends or usability practices?
I argue usability is more important then trends. Like you mentioned, bottom menus are more reachable to the thumb, therefore it is more usable and beneficial for the user.
Trends might dictate using hamburger menus on the top right corner for both desktop and mobile. Maybe it looks good, but it is the worst placement in terms of usability. On desktop, it violates the F browsing pattern and hides all the navigation. On mobile, it is hard to reach. So your choice depends on what you subscribe to: Aesthetics or Usability.
Answer: In my opinion, the fixed navbar at the bottom seems far more convenient to use and like you said ensures easy thumb movement, eg: Instagram does a great job in that. But having said that, the burger menu at the top has its own advantages and truly it depends on the user base and the App itself. As a designer you should create both alternatives in design and carry out a/b testing with a few potential users for a better understanding.


Ik bones in makehuman models

Question: I am using makehuman 1.1.0 and blender 2.77a. I am able to use rigged human models as mhx2 file exported from makehuman. In makehuman I am using the default rig. The models however dont have the Ik bones. Would it be possible for makehuman to generate rigged model with Ik bones and thus easy controls ?
Comment: I am not 100% sure, but i suppose there is no such way. As long as the model does not already have an IK contraint in make human, it is more as unlikely that in blender it should got one. and even if it has ik in make human (im not very familiar with make human) there is no guarantee that it will export to blender.
Comment: But you can easily add your own ik contraints to the exportet rig. it is really not that hard. just watch some tutorials.
Comment: Thanks Demons. As it turns out that makhuman does support ik bones. But to load them, you need to override exported data with proper options while importing mhx2 files.
Answer: Yes, I did find solution. It was under my nose all this time. While in pose mode Under tools section we have an option to switch to IK bones. Ik bones does help making things easy.
Comment: Several days I was searching that !

Ik bones in makehuman models


How do I full-screen QuickTime Player on an external monitor in Lion?

Question: I am trying to play a QuickTime video in Lion on an external monitor. How do I get it to play full screen on the external monitor, not on the laptop screen?
Answer: Install QT 7 from http://support.apple.com/kb/dl923 and open your movie with QT7. Then open Preferences and select Fullscreen tab and click on your second display.
Update:
Movist is a great player. You can get it from here: http://code.google.com/p/movist/
Comment: Ah! I didn't think of that. I will try it out and let you know!
Answer: Move the non-fullscreen QuickTime window to the external monitor, then click the fullscreen button.
Sorry, just tested and that doesn't work. It used to, not sure when that changed.
It's not a proper solution, but using VLC would be a workable stopgap measure - it doesn't use the built-in Lion fullscreen functionality, and thus can be put wherever you like, and doesn't blank the other screens at the same time.
Comment: Thanks for the answer, but it still doesn't fix QT player.
Comment: That _does work_ in Mountain Lion.
Answer: The only way I can see fullscreen playing on a non-primary display (without editing System Preferences or adding additional software) is this:

select movie file in Finder
activate Quick Look (click the eye button or press space bar)
move the Quick Look window over to the target display
click the "expand to fullscreen" arrows button in its top right corner.

QuickTime Player Version 10.1 (501.8) on Lion - the Quick Look hack only works on non-streamed content so it is kind of a bummer. I seriously hope that Apple fixes this in a software update soon :-/
Comment: *No*, dear sales people, it will not trick me into buying and carrying around an AppleTV :-/


If I'm running a full node and wallet on my local network can someone get my wallet information?

Question: If someone connected to my WIFI could they get information about my wallet or steal from me?
Answer: Just getting connection to your WIFI would not instantly allow someone to see your wallet information, gaining access to your WIFI is only allowing first and foremost access to your internet connection.
However, someone with access to your WIFI could essential hyjack your information, if a few other things fall into place first.

If your WIFI router is set up as a Home/Work Network and Network sharing is turned on, then a hyjacker, could potentially view any files/ documents shared on your network. Your computer would have to also be set-up, to share files with the Home/Work Network, therefore, if for whatever reason you stored your wallet information on a non-encrypted file, then the hyjacker would aslo be able to access this information.
Another method to gain access to your wallet data is through: packet-data sniffing; if a hyjacker has gained access to your WIFI, and they have hacking knowledge (pretty basic hacking knowledge in all honesty) then it is possible for the hacker to "sniff packets" of data that you send over your WIFI, if at any point you send your private wallet data over the WIFI, then it is highly likely that the hacker will be able to see your private wallet information that you have sent through the WIFI.

To ensure your WIFI is secure:

Ensure your router has a Strong and Unique WIFI password.
Ensure your router firmware is upto date.
Enable WIFI encryption WPA2 if your router is newer than 2006, else WPA should be adequate but less secure
Change your WIFI SSID (Name) to make it less easy for the hacker to directly relate the network to yourself and/or allow the user to identify the brand of router that your network uses.
Answer: Getting access to your router is the first step towards your computer so use a strong WPA2 password. Also use a different admin pass and a different log in pass. The main concern with someone accessing your router is packet sniffing, which means that person could follow your non https traffic. This does not affect your wallet.
Once someone is in your router, however it is easier to exploit your computer if you have vulnerabilities such as not up to date and patched OS. Regarding your Monero wallet, if you have a strong password for your wallet/s, even if someone accesses your computer, they will not be able to open your wallet (to spend or see balance). However, if they do manage to access your computer, they could install a keylogger and grap your password when you open your wallet.
So, I suggest you use Linux Os as it is much less vulnerable than Windoze and way fewer malware. You also need root to install anything which adds an extra layer for you. Then make sure you have a strong password for your router and strong password for your wallet (all different obviously), and you should be fine under normal circumstances. Oh, and make sure you haven't labeled any parts of your computer for local sharing.


How to choose right PWM frequency for LED?

Question: I want to control LED's brightness with PWM (via BJT transistor). What frequency of PWM should I choose?
Comment: @starblue _"Between 70 and 200 Hz."_ - 70Hz produces visible flicker to many people, and very visible flicker to virtually everyone if the led (or the observer) moves. Please, use a higher frequency than that. I'd recommend 200Hz as a _minimum_.
Comment: @marcelm Yes, it is probably a better idea to go as high as practical, to get the most pleasant light. I'm now using 1kHz for an RGB light, a hobby project. Even then you can see the PWM as stripes when you quickly move the eye, but IMHO that's not really a problem.
Comment: Between 70 and 200 Hz.
Answer: For a question like this, you will probably get as many answers as there are people interested in answering. Here is my answer: It depends.
Here are some of the limiting factors, first the lower limits:

Persistence of vision:

Different people are differently sensitive to flicker in a light source. Some would notice flicker even at 100 Hz, others perhaps not  even at as low as 10 Hz.
Motion of light source relative to the eye makes flicker more discernible, scaling up with speed of the motion.
Human vision sensitivity at low intensity of light - both ambient and source intensity. At very low intensity, the eye is much more sensitive to any change in intensity. So an LED operated at low duty cycle / low current and in a dark environment would require a higher minimum PWM frequency.

Now the upper limits:

LED turn-on characteristics: An LED cannot be toggled at arbitrarily high frequency, once the pulse duration approaches the turn-on time, the LED never really turns on fully, hence linearity of PWM control is lost to begin with, and at higher frequency / shorter pulses, eventually the LED just stays dim or off.
PWM provider capabilities: Your microcontroller would have its own maximum PWM rate, which sets a hard limit.
Switching losses: Any switching system, MOSFET based, BJT based, or other, suffers switching losses of power as switching rate increases. At one point this become significant both in terms of heating of switching device, and efficiency of illumination.

Thus, depending on these parameters, and any others affecting your specific requirement, the correct answer could be anywhere in the 50 Hz to few dozen KHz range.
Comment: @Passerby No, there are several conditions which do not count as blindness but which cause flicker threshold reduction. The common cold is one such. I have been part of a human vision study where flicker thresholds down to 10 Hz were found in several participants.
Comment: @Passerby: our eyes don't work like monitors. Not only does the response time differ between cones and rods, but it differs between different areas of the retina and between varying light levels, and then to add to it, we ultimately don't see with our eyes but with our brains.
Comment: Human Vision "refreshes" (the Flicker fusion threshold) at minimum 50hz to 60hz. Flashing 10hz would be visible to anyone short of the blind...
Comment: I doubt your assertion that some people cannot discern flicker down to 10 Hz.  They would have a serious vision impairment if they cannot even detect 25 Hz motion flicker in cinema. Enhanced Peripheral flicker detection is useful when driving a car to detect and avoid collisions starting from the side ( kids running towards street) or cavemen seeing attacking animals for self-preservation reasons.  @AnindoGhosh  Did you want to back this up with a reference? or personal experience?  I suggest 1kHz minimum >3kHz is better. Your answer neglects peripheral enhancement of perception. N.B.
Comment: I am currently experimenting with dimmable LED lights installed in a living/eating area indoors. Setup right now is a LED dimmer Leviton and dimmable LemonBest 4W LED spot light. At lower dimmer settings there is a bad flicker. It's at 120 Hz (2 zeros per wavelength) and it generates a stroboscope effect. (You can see the flakes of grated cheese falling on food; not very nice believe me).
Answer: It depends entirely on the application and human eye natural sensitivity to flicker when the light is moving or when  your eye is moving with peripheral sensitivity improved to flicker, while steady-state peripheral vision declines.
Cadillac was one of the, if not THE first car to introduce LED brake lights and we as Engineers wonder how this missed this major detail.
People would say why is that car brake light flickering as it was driving past our view? It was so irritating to some with Seizure sensitive to flicker, that it could trigger an "episode".
Since we have house LEDs stationary we, don't often care yet we know something is irritating to some people. This is often because Engineers don't know much about Biomedical responses and think 150 Hz is OK, because they can't tell anything staring at it. That's because it requires motion artifact to detect the flicker or moving images across the retina peripheral.
The range of frequency I would suggest is 300 Hz minimum for stationary and 1kHz minimum for moving flicker-free.  Although the industry has been slack with 300 Hz and peripheral eye motion flicker-sensitivity still exists at this flicker rate in moving tail lights.
White LED phosphor responds much much faster than TV tube phosphor.

If you don't care about my concerns, feel free to follow the others' advice at lower frequencies.

I looked for references to back up my experience. This is just one example.  http://www.thenakedscientists.com/forum/index.php?topic=45126.0
Answer: As I've seen, almost all of the PWM dimmer diagrams with LM555, have the oscillating circuit formed by a 0u1 capacitor and a 1k resistor. That means something about 2 kHz with slight variations at low and high widths. I think this frequency offers enough switching speed in order to not see bad flickers on moving and, on the other hand, slowly enough to turn on the LED al low width. I wanna try higher frequencies to see what happens (5...10 kHz)
Answer: Agree with those above on the low end, but on the higher end of frequency spectrum, you can sometimes hear an audible switching if you are in the 1k-15k range.  You'll want to stay out of the audible range or you can potentially hear a high pitched noise at your PWM frequency.
Answer: There is research that suggest the majority cannot distinguish past 500Hz, and some other research that suggest a minority can see flicker up to 1500Hz. I have a housemate who is very sensitive to flicker - 1Khz caused them problems but had no further problems once my lighting system as set with a 4kHz PWM frequency.
(apologies I read it some time ago and cannot find the reference now)
Note my application was soft lighting for the whole room, so peripheral visions would definitely be an issue.
The limiting factor is really the rise and fall time/resistance of your mosfets as this will dictate switching losses in relatively high current applications. Fast low resistance fets are worthwhile in this application.
Answer: If you put a capacitor parallel to the led you should be able to avoid the flickering and instead get a slight declining wave, or ripple. The higher the frequency, as well as longer 'on' pulse width will give the most consistent light.
Choice of frequency now depends more on how many different widths you wish be able to squeeze into a cycle, or intended dimming resolution so to speak.
Comment: Reducing the forward current through an LED is ineffective and certainly not the "ideal" way over PWM. Most LEDs characteristics are rated at full forward current, and these will drift out of specification as the forward current drops. For example, in high-power white LEDs the color temperature will change as the forward current drops. This is why most LED manufacturers recommend PWM as the method of dimming, the LED stays in it's ideal region of operation.
Comment: Wouldn't the cap act to smooth the pwm signal? Instead of the LED being fully-on and fully-off, it would be continuously on with a lower forward current.. as if pwm wasn't be used at all? My understanding was one benefit of the pwm approach was to maximize LED efficiency by avoiding just such a situation. Or is the situation different if you use a sufficiently small cap?
Comment: Yes you are right, it'd smooth the signal, "ideally" as if there was no pwm used at all. The reason I suggested it is that I would want to avoid the on/off flickering since it sometimes affects concentration. I did not reflect on maximizing efficiency .
Comment: Pardon the n00b question here, but would one be able to use a capacitor in parallel to an entire strip of LED to achieve the same result? How does one determine the size of said capacitor?
Comment: I have the problem that I get audio noise from the power supply coil at hearable frequencies (like 10kHz). I changed the frequency to the full 31.25 kHz of Timer0 from a AtTiny85 at 8MHz, but I'm not sure what the maximum supported PWM frequency for a 5050 SMD LED is. It seems to work, but I'm not sure if it's in the safe specs of the LEDs.


Does a recruiter expect you to be employed or to have a job in the relevant field?

Question: If a recruiter contacts you and inquires about your current employment status, does one have an advantage in saying that he is currently employed as opposed to unemployed? Moreover, does the recruiter expect you to have a job in the field for which he/she is recruiting? Does it really matter at all?
Answer: Do you have an advantage if you're currently employed?  Generally, yes.  Employers generally prefer hiring people that are currently employed and those that are currently employed generally have more leverage in negotiations.
Does the recruiter expect that you have a job in the field?  If you're employed, generally yes.  It is possible, of course, that the best candidate for a job is someone that is switching fields.  But it is generally much harder to place a candidate that is changing fields since it is often hard for an employer to understand exactly what skills transfer from one field to another.
Answer:
does one have an advantage in saying that he is currently employed as
  opposed to unemployed?

Often, the answer is Yes.
Being employed means (by definition) that you are employable. It means that you passed the interviews for some other company, and thus might have a better chance of passing upcoming interviews.
Rightly or wrongly, many recruiters and hiring managers value being employed - either consciously or unconsciously.
Some recruiters and hiring managers (fortunately not all), believe that the best workers are seldom unemployed, and are very seldom unemployed for a long time.

Moreover, does the recruiter expect you to have a job in the field for
  which he/she is recruiting?

That almost always depends on the specifics and requirements of the job.
An entry-level job by definition wouldn't expect a candidate to have a job in the field.
Some jobs can be filled by candidates who don't work in the specific field.
Others (for example, more senior positions) expect current job experience in a particular field.

Does it really matter at all?

Everything matters. Sometimes it's critical. Other times not as much.


Search engine of Italian buses

Question: Is there one search engine of scheduled buses in Italy, where I can search timetables of any bus company? Or, if not all of them, at least significant number of companies.
Comment: Local, long-distance, or both?
Comment: The best would be both, or long distance (between eg. major cities)
Answer: Every city has its own local bus company with timetables and lines:

Milan local buses: Milano ATM
Rome local buses: Roma ATAC
Florence local buses: Firenze ATAF
Bologna local buses: Bologna ATC

Take the train could be a good choice to travel across Italy:

Trenitalia - national train company
Italo - new company with a lot of offers but less destinations

Last but not least, consider Google Maps search. It supports public transit in its "Got Directions" pretty well.
Enjoy your trip!
Comment: You can post the links as text, and a high-rep user will take care of this.
Comment: P.S. I had to ask you to google since I don't have (yet) the reputation to post more than 2 hyperlinks. Sorry for that!
Comment: lol, don't trust Google Maps: coverage is very very spotty. [This is certainly one way to go from Milan to Bergamo](http://i.imgur.com/2W2Kw.png), for example, but I wouldn't recommend it to my worst enemy.
Answer: The accepted answer concerns local buses and recommends trains for long-distance journeys. However especially for travel to the south of Italy, this is not always the most convenient option.
To the best of my knowledge there is no search engine that covers all long-distance bus lines of Italy. Typically I proceed as:

Search on iBus
Search with Rome2Rio
Google for further direct bus links using "autobus/bus/pullman departure city destination city", e.g. "pullman Roma Matera". It is recommended to use Italian city names here, as not all services may be advertised in English.
Maybe you are lucky and your departure or destination city has a bus terminal that lists departures/arrivals, this could give a good overview of existing lines. Search for "stazione pullman city".
If you know someone from the area (especially students), you could ask them how they typically travel - I discovered some bus lines this way that I was not aware of.

Then take the best result you get from these searches and proceed to booking either via the search engines above or from the bus company directly (often slightly cheaper).
Answer: Italy is also covered by Google transit. I don't know how good it is for Italy, but for my home town it is quite good.
Comment: Coverage is exceptional, or in other words it is the exception rather than the rule. I wish I could change this :(

Search engine of Italian buses


Altering colors for the background theme for better contrast

Question: On StackOverflow jobs, the colors make it difficult to view the name of the company. Very poor contrast, as shown in the image below (the blue text). Hope it could be improved.
Comment: I agree that monitor brightness plays a role, but using better contrasting colors is necessary. This is part of the basics of graphic design. Ask any interaction designer. You just have to turn on the dark theme in StackOverflow's preferences and visit the jobs page.
Comment: It seems fine to me, but one could say it's a matter of opinion. I noticed that putting your screen on super low brightness does affect it a little, but it's still okay, not that bad. Also, can you please provide a link to that page? So we can view it as well.
Comment: I have dark theme on, and I don't really find the need to change it. However, it does have a status-planned, so maybe it;s just me.
Answer: Thank you for bringing this to our attention. This is a bug where old CSS colors are overriding our dark-theme colors. I've added this to our bug board and hope to get it fixed as soon as possible.
Update
Thank you again. We ended up finding multiple accounts of CSS overriding our dark-theme anchor style, so /jobs should be a bit easier to navigate in dark mode now!
For those curious, some areas affected were company page ads, saved searches, edit job preference link, and downloading resume on job applications.
Comment: Glad to hear this. Hope the improved dark theme could be extended to all StackExchange websites too. It's a relief from the bright white backgrounds.


Adding a garage subpanel

Question: Currently I have a 200-amp main panel located in the basement. I would like to install a subpanel in the garage. I will use to power my electrical tools, heater, and PC. The garage is part of the house.
Most likely I will need a 100-amp 2-2-2-4 wire to run from the main panel to the new sub-panel. Couple double pole breaker of 100-amp.
I would like to have at least 4 breakers for the tools, one breaker for the heater, one breaker for the PC to start.
Does the 100-AMP sub-panel will be enough?
Do I need to install an additional ground rod?
Any suggestion and advice will be appreciated.
Respectfully,
Bernard
Comment: Hi welcome to the site.  This is a very popular project on the site. Use the search bar to see numerous very similar questions with even more good answers. I feel sure you will find one that matches your project perfectly.
Comment: Are we talking about an attached or a detached garage here?
Comment: @ThreePhaseEel  The OP says it's part of the house so I'm guessing it's attached.
Answer: Go big, Big, BIG on the subpanel
Especially if your main panel is getting full, and having double-stuff breakers in it definitely counts as "getting full".
We have so many questions on here of "My panel is full. What can I do?" And our answers are expensive and regretful.   But that we could go back in time, to when that panel was being bought, and say "Spend a couple lattes on a bigger panel".  So, we say it now.  Go big.  Really big.
You're at 7 breakers so far (2 for the heater) + a foreseeable dust collector and EVSE, so 10. I like to finish with all full-size breakers and >50% of spaces unused, so a 20-24 space panel. Disregard "x circuits" as that calls for double-stuff breakers which are no longer viable due to Code changes. (they don't mention that in the marketing materials :b)
Don't let panel bus rating hold you back: An "R" rated tire is only rated for 85 mph, would you put that on your car? Not willingly!  So it's not a win to get a panel with 100A busing. So don't think twice about a main-lug breaker that's 225A/24 space if you can find a happy price on it.
The main breaker doesn't buy you anything (sometimes main-breaker panels come bundled with some bonus breakers, so that can be a savings), but the main breaker per se is irrelevant. You can't make the more convenient breaker trip first, because of main vs branch trip curves and Murphy's Law.  Even if you needed a main disconnect switch, the trip value is irrelevant; feel free to feed a 225A subpanel from a 30A feed breaker.  Totally legit.
Your feeder wire
2/2/2/4 is an unnecessary size, but I understand why it seems correct.
First, if it's convenient to run conduit from the main to subpanel, and  you want to do that, use THHN/THWN-2 individual wires inside the conduit.
Don't bother with copper unless it's like a 10 foot run or something.  The lugs the subpanel will be aluminum anyway because aluminum lugs play nicely with both.  So why create a dissimilar metal "problem"?  (isn't actually much of a problem on these fat feeders).  But if you do go copper, #3 will suffice and #8 Cu ground is all you need.
If you go aluminum (most of us would), you need #1 AWG.
Loads
You're in very good shape.  Your PC and tools will chomp only 15A of your 100A. Electric garage heaters range from 15A to 50A, but you're definitely covered, even with a 60A sub. But stay at 100A.
Here's why I don't think 100A in a garage is overkill.  The automotive world is changing so very fast. "Range anxiety" which used to stop the electric car industry dead in its tracks, is being alleviated from both ends: First, consumers are becoming much more aware of their actual driving patterns. And second, Tesla and others are making is making enroute recharging look stupid-easy. I do lots of transcon trips, and Tesla is at the point where I could recharge in the time I already stop for gas, bathroom, and meals. So EVs are happening, so having 50-80A of headroom in a garage panel is great, and can only help resale value.
Comment: Use conduit even if somewhat inconvenient (imho) and contemplate heat pump to get so much more heat for the same electricity (at higher initial cost, yes.)
Answer: Without knowing your existing loads on the house , let's look at your new sub panel.
First you will need a double pole 100 amp breaker in your main , your wire size is based on the 60 degree table per 110.14.C.1.A (100 amp or less /  14-1awg require the 60 degree table. So you are at #1 copper or 1/0 aluminum (aluminum is much cheaper and aluminum feeders pose no risk like branch circuit wiring did in the past).
You want 4 circuits not a problem
We would need the size of the heater electric heat will gobble up a lot of power but a 30a 240v heater will warm a well insulated garage.
A branch circuit for lighting 120v
3 ea branch circuits for receptacles 120v
If you install 20 amp in each of these with the 30 amp heater you are not even using 70 amps so you still have enough room for a 30 amp 240 v welder or air compressor . And a few 15 or 20 amp circuits more with a 100 amp panel and wiring. I would get at least a 125a panel with a main breaker.
You do not need a ground rod since the garage is attached but you will need a 4 wire feed as you had identified.
With the 2017 code all receptacles will require GFCI Protection (even ceiling mounted lights or garage door opener) . Hard wired lights do not require GFCI protection.  Get a larger panel than you think you will ever need , you said 4 and the heater , I would not get less than a 12 full sized space panel and 20 space will probably be the same price or have more choices thus cheaper for larger.
Hope this helps , note look at the table again and if you go to a 125 panel the #1 wire will you to use all of it because now you can use the 75 degree table.
So there are many advantages to going larger (you could put a 150 amp panel or larger but at this point #1 wire will only support a load of 130a  but finding a breaker bigger than 125 for your main panel may be difficult depending on the brand.
Comment: You beat me to it. I agree with the 125 amp panel. + Stay safe out there.

Adding a garage subpanel


Arduino reads hc-05 device connecting status

Question: Hello I want to get an arduino get status of bluetooth hc 05 if connect with device or not . I'm trying by myself and search on internet website but I can't find useful things.
Comment: Can you show us the code you have written so far?
Comment: if (Serial1.available()) {   Serial1.print("AT+BIND");  Serial.println(Serial1.print("AT+BIND"));  }
Comment: This's one code of codes who I tryed .  The other codes mybe the same but with some differents order...
Answer: In hc05 there is led that shows you Bluetooth is paired or not. In datasheet it says that connected the PIO9 pin. You can connect this pin to arduino's digitial input pin. After that you can understand is it paired or not.
AT+BIND? gives you which device you currently paired.
Comment: Ok I edited the post check it again
Comment: If I connect PIO9 pin maybe it's get write in serial.read()  if it's connect or not ...?
Comment: No its not like that. When you paired this led turns on so if you make a little bit solder and you can get a wire from there and put this wire to arduino's digitial input pin. When Bluetooth paired this pin goes HIGH and if its not connected this pin goes LOW
Answer: Different Bluetooth adapters (using the HC-05 module) provide different signals, besides its Rx and Tx. Most bring out a "key" input that puts the module into command mode where serial communication is between the external pins and the module itself - 'AT' commands & queries to the module's firmware. When the module is not in command mode, the firmware just passes serial data through the Bluetooth radio, ignoring the content. Some provide an LED- or State signal that you can read (or observe on an LED) to know whether the devices is paired (communicating) or unpaired (in command mode).
On some, this is a simple logic signal; on others it is a square wave of 1/2 to 1 Hz which means your code has to track the signal to know whether it is static (typically High when paired) or toggling (for unpaired/waiting to pair).
You need to read your module's datasheet to find out the behavior of this signal on your particular module. If you connect an LED to this signal, or your module has one on the board, you can often make a good enough guess by observing it with a stopwatch. Either way, you then need an Arduino function that samples the LED periodically, remembering what state it saw and for how long, to decide whether the LED is blinking or is steady.


Peak season for Thunderstorms

Question: What causes different locations to get their peak season for thunderstorms at different times of the year like some locations get the most thunderstorms in a July some in June and some in August and some get the most thunderstorms in September. What causes the peak season for thunderstorms to be different in different locations?
Comment: Ryan, weather is very complex but follows some general rules.  You might get better answers is you ask about two specific locations and why they are different.  Each location has different factors driving its weather patterns.
Comment: you need to be a bit more spesific in your question like comparing two different places,paris vs london or moscow vs new york.
Answer: What you are really asking is why the weather varies from place to place, sometimes in places which are only a few miles apart (in the hills of the Dhofar region of S.Oman, you have a transition from monsoon scrub and grassland to arid desert in the space of only 2 or 3 hundred metres!). Weather is such a complex thing it is impossible to enumerate all the factors which cause local variation, except to say that the presence of hills and mountains often has something to do with it.
Matter is made up of sub-atomic particles containing positive and negative charges. They are usually evenly distributed, every positively charged particle  being balanced by a negatively charged particle, which means these charges cancel each other out.  Nearly everything we see around us is therefore electrically neutral. This disguises the enormous power of the electromagnetic force, which is trillions of times more powerful than the gravitational force, so even a very slight imbalance between positive and negative charges, such as occurs in thunderstorms, can produce dramatic results.
These electrical imbalances can be produced by air turbulence such as takes place in rising plumes of hot air called thermals, of which the strongest happen in summer. Particles of dust or moisture in the rising air currents rub against each other and cause separation of charge.  The condensing raincloud becomes negatively charged, while the ground below becomes positively charged. Positive and negative charges hate to be separated, as they have a very strong attraction for each other.
The positive charges on the ground are pulled along by the negatively charged cloud, and tend to build up on church steeples and similar pointed objects that reach into the sky. When the two masses of separated charge become sufficiently strong, and especially if they pass over a tall, pointed object, they cannot resist the urge to recombine and an electrical discharge takes place. Why one place should have more of these events in August and another in September is a complex question which cannot be answered without knowing all the many variables which influence the weather in both of these places.

Peak season for Thunderstorms


Why resolution of photolithography evolved gradually?

Question: Moore's law states that no of transistors on a given area doubles every 18 months. Electronic components are typically made by photolithography. So,  Moores law basically limits the resolution of photolithography. Why resolution of photolithography evolved gradually and not abruptly?
Comment: Isn't it "the resolution of photolithography limits Moore's law"...
Answer: There's a adage: you have to crawl before you can walk.
You may as well ask why supersonic aircraft weren't developed first, before people started experimenting with gliders, the Wright brothers developing the first powered aircraft, followed by propeller powered biplanes, then monoplanes, then jet aircraft and finally supersonic jet aircraft. All this over the course of some five to six decades.
Every technology has its limits, then someone develops a better way and improvements are made and the technology advances. The same applies to photolithographic techniques that are used to make electronic chips. The technology used to develop the first chips couldn't make the chips of today & the engineers of the day didn't know how to develop techniques to make the chips that are made now.
Comment: ...or why did a human first get launched to orbit before suborbital flights? ;-)
Answer: The component density on chips made by photo lithography is directly dependant on the wavelength of the light source used and as shorter wavelengths equate to higher photon energies you need to develop practical sources for ever increasing frequencies and the masks and dyes to go with them,
Equally you need more and more precise and clean manufacturing plant. Once you get to UV lithography a stray hair or skin cell is like hitting your machines with a big hammer.
Part of this is the investment required to manufacture and develop the tooling required for example you need to be able to create very hard vacuums and incredible precise mirrors.
Answer: Moore's law is not a scientific law, it is only a business model (a roadmap).
It has become very famous because of its accuracy especially during the time when microelectronics was making its first steps.
When you are a business man and you manage to predict accurately how technology will develop you will have a much better chance to also estimate how markets will develop.
Also since ~2009 the resolution of photolithography is not linked Moore's law anymore.

Here is a simplified chronology:

When microelectronics was making its first steps the most successful business men investing in microelectronics were those who followed this estimation from Moore on how microelectronics would develop.
Following the success this estimation became widely known and got a name: the Moore's law. This law then started to also drive the investments and would serve as a kind of expectation/agreement between the companies and investors.
there was several attempt to push the technology faster, especially as the microelectronic markets were continuously growing up. If someone could bring a technology a little faster there was a possibility to make a lot of money. All of these attempts somehow failed or nearly did. There was a small acceleration with the nodes 90nm->45nm but the technology limits then catched up, together with the Financial crisis of 2007–2008.
Since the technology node 45nm (or 32nm depending on the opinions) the density of devices per area is not anymore linked with the patterning resolution but with the patterning technique. You can add to this a small set of submicron effects in the devices taking more importance: It is now more the investments that drive the technology than the other way around.

Nowaday, a new technology has become very expensive to bring on the market, and is therefore only possible for the richest companies and the smaller investors are looking toward a some end point for this advance. But no worry, In the meanwhile they created the 'More-than-Moore' to drive new investments.


What are the differences between "know", "know about", and "know of"?

Question: I am confused about the differences between know, know about, and know of. Why do they use different prepositions?
Answer: Level of knowledge.

I know the C language. I can write programs in it proficiently. I know the caveats and problems.
I know about Python. Basics of syntax, general structure. Given some time and references I might write some simple programs in it, but saying "I know Python" would be too much.
I know of Haskell. There is such a language and it's a functional language. That's about all I know of it.
Answer: Even the unqualified verb "know" is weak: depending on your proficiency, use verbs phrases like "am proficient in", "have use on several development projects...". in the field of programming "know" is an vague verb: I know the grammar of C, but have I developed in C?


Patent Invalidation in part or totally

Question: If a Patent claims more than one "Item", say Item A, Item B, Item C etc...
and if it can be proved that say Item A, has been offered and sold to a commercial entity,
can the Patent be invalidated in its totality, or only Item A is invalidated?
Comment: AFAIK individual "independent" claims can be invalidated without invalidating the entire patent - i.e. it lives on with the remainder of the claims. To squash a patent, every claim would have to be defeated. But I'm sure someone will have a better answer.
Answer: Ron's answer is basically correct. The part of a patent that might or might not be infringed is a claim. It is also a claim that might or might not be found invalid. As an example, a patent could have 20 or more claims, most of which are narrowed versions of a small handful of key, independent claims. One of the reasons for having a claim set with increasingly narrow claims is that the broader the claim the more susceptible to being found invalid due to something coming to light after the patent was granted. From the inventors point of view, the narrow claims stake out a fall-back position.
The only quibble with Ron's answer is that both independent and dependent claims can be invalidated, possibly leaving other independent and/or dependent claims still enforceable.

Patent Invalidation in part or totally


What are good starter outdoor cameras?

Question: My husband writes for an outdoor magazine and we go backpacking/canoeing/kayaking/etc a lot for his stories. I would love to learn real photography (and maybe one day take pictures to go along with his articles). I had a few photography classes in college so I have a rough grasp of the basics. I would love a recommendation of what type of camera would help me to really learn about all the art that goes into photography, take good pictures and is semi-professional (but I imagine I will upgrade when I get better) and will not cost my entire life savings. The pictures I would take are of wildlife at a distance and landscapes.
Comment: Backpacking/canoeing/kayaking without breaking the bank OR wildlife at a distance. You're going to have to choose one or the other.
Comment: Hello Mary-Ann, welcome to Photography.SE. If you are looking for a DSLR, your question is probably a duplicate of http://photo.stackexchange.com/questions/2876/what-should-i-look-for-when-shopping-for-my-first-dslr or http://photo.stackexchange.com/questions/5883/are-there-disadvantages-to-a-prosumer-camera-for-a-beginner-aside-from-cost
Answer: The focus on outdoors use and specifically the combination of backpacking and canoeing/kayaking make this a difficult recommendation, I think, if you are focused on learning photography instead of just "taking pictures."
For backpacking, I'm not excited about the notion of taking a full-frame DSLR along. Back in the day I carried a film SLR a few times and it wasn't fun and proved cumbersome. The small size of the smallest DSLR may be an option, but I suspect a mirrorless camera would be a better choice -- giving you full control over a scene with a large-ish sensor and aperture that will let you control depth of field.
For canoeing in calm conditions, a Pelican case will keep the camera safe (when closed) and canoes are plenty stable to pull the camera out whenever you like without much fear of water damage. In a kayak, fitting a Pelican case (and keeping it secure) could prove very difficult, depending upon the type/size of your kayak; in other words, water damage could be a much greater concern, even in calm conditions. In rougher conditions, in either a canoe or kayak, you'll need a waterproof shoot-through case or a waterproof camera. However, with a waterproof camera you are giving up significant quality and control compared to the mirrorless or DSLR.
In other words, you've got a difficult decision here, and one camera may not suit your needs adequately.
Answer: The good news is that digital cameras handle outdoor photography the easiest. There tends to be plenty of light and subjects rarely move fast.
Any modern DSLR will do and something in the mid-range will allow you to learn photographic controls to exercise your creativity. There are also several weather-sealed models which will allow you to do outdoor photography in the rain or snow. This is particularly important for professionals as you may have to get images even if the weather is bad.
Something like Nikon D610 is great to start with and is relatively cheap for a full-frame. You can easily do with an APS-C camera which will cost less and make your lenses have a longer reach. In this case, I would recommend a Pentax K-3 (Original or II) which is freezeproof too.
Do not forget to allocated enough budget for lenses, at least the same value as the camera in general. It is also necessary to buy weatherproof lenses if you want the camera as a hole to be weatherproof. Start with at least too lenses, a general zoom for landscape (say a 16-50 or 17-55 on APS-C or 24-70 on full-frame) plus a long one for wildlife (something that reaches at least 300 or 400mm). Third party makers like Sigma make good ones for less than those of the camera manufacturer.
EDIT: Just a note why I did not recommend a mirrorless. While they do save weight, it is really not much when you consider the weight of a lens to reach distant wildlife. You will notice that mirrorless systems have almost no long telephoto lenses, usually maxing out at 300mm or less, depending on the system which means you will need a DSLR lens and adapter. Most of those have limitations too.
Answer: Learning photography is much less about the equipment and much more about pushing yourself to learn. You can learn the basics of photography on essentially anything that allows for manual control of shutter speed, aperture, and ISO. Other aspects such as different focal length lenses, flash photography, and so on can be additional topics that one can learn once exposure is well understood.
If your husband works for an outdoor magazine, see if one of his coworkers has a used DSLR, advanced compact, or mirrorless camera that they could sell you inexpensively or even gift to you. That is where I would start, with equipment that is less then perfect and costs little to no money. If that doesn't work out, reach out to your own network. I can almost guarantee you know a photographer or two with used equipment collecting dust that they would love to pass on to an eager new photographer.
Once you have some equipment to start with, you will be challenged to learn how to use it despite its potential shortcomings or the fact that it is a few years old. You can focus on books , experiments, and the basics of photography vs 4k video, in camera HDR, and back button AF (all things that modern DSLRs provide but are not about learning photography for a beginner).
Answer: The problem here is that once you threw in "wildlife at a distance", you pretty much nixed most everything else except for dSLRs as well as the "starter" part of the equation.
Wildlife, especially fast-moving wildlife, is a very specialized and equipment-demanding type of shooting that causes some of us to blow thousands of bucks on a lens and a higher-end body just to get the fast tracking AF necessary to get a subject in focus and framed so it's not tiny.  This is not by any stretch of the imagination a starter subject, and one you should probably work your way up to.  [Sports would be the other similar subject]. So, if you give up National Geographic wildlife ambitions, then your question makes more sense.
I got fascinated with bird photography and most specifically bird-in-flight photography. I eventually came to realize my little 75-300 consumer-grade telephoto zoom wasn't going to cut it either on reach or AF speed, and blew $1100 on an EF 400mm f/5.6L USM lens. And eventually upgraded my entry-level dRebel for a prosumer XXD model (50D). I now jones for the 7DMkII.  But that's a lot of money and outlay as a newb. And a lot of weight to haul around in a backpack.
So you have to weigh the drawbacks, and figure out which ones you're more or less willing to put up with. dSLR can do fast action and have the long lenses for wildlife shooting, but are big heavy beasts, and the long lenses are $1000+.  Mirrorless cameras and lense are small and light, but there isn't yet a good array of wildlife lenses or the AF systems to capture them. Advanced fixed-lens compacts are smaller and lighter yet (and are cheaper because they're self-contained--you're not buying any more parts of the system), but have the limitations of the single lens.
See also: What do I need to consider to choose between dSLR, mirrorless, or a compact as my first "serious" camera?
Answer: This is sort of a trite answer, but the best camera is the one you have with you, that you are most likely to use and/or have handy. There are all sorts of amazing photo essays and very artistic shots done completely on mobile phones, or with outdoors point-and-shoots.
I won't recommend specific models or even brands, but considering your outdoor activity, weight & volume are probably important factors. With that in mind, you might want to consider mirrorless cameras. They have all the control over exposure that DSLRs have, the same control that you probably covered in your photography classes, but have reduced weight and volume by eliminating the optical viewfinder, pentaprism, and mirror that SLRs have.
There are interchangeable lenses for these mirrorless camera systems, and because the mirrorless cameras have a smaller flange distance (the distance from the lens bayonet mount to the sensor) than DSLRs, you can use an adapter to mount just about any DSLR lens to many mirrorless cameras. (Note that you might not get autofocus or aperture control of the lens, depending on which lens is under consideration, and which specific adapter is chosen).
Some of these mirrorless cameras are every bit as good as more "professional" DSLRs, for certain shooting styles or intended targets. The ones you mention, wildlife and landscape (especially landscape), are excellent use cases for mirrorless systems.
(I am not shilling for mirrorless cameras. I don't own one. But I have shot with them, and I really like what they have to offer)
Comment: General wildlife, maybe. But *wildlife at a distance* needs the fast, long lenses that render the size/weight difference between a mirrorless and DSLR camera pretty much moot and the best current sports/wildlife AF systems are in DSLR bodies.
Comment: Agreed. But I get the impression the point of the question is photographing the adventure and the wildlife inhabitants they encounter, as opposed to adventuring in support of the photography. A subtle distinction, to be sure. But it's the difference between "given that I'm kayaking/canoeing/backpacking, what kit should I get?" and "I'm willing to kayak/canoe/backpack to get the shot I want."
Comment: I guess that all depends on whether the husband's articles are primarily about going kayaking/canoeing/backpacking or are about things, such as landscapes and wildlife, that can best be reached by going kayaking/canoeing/backpacking. The question isn't really specific as to whether they are adventuring to write stories about adventuring or if they are adventuring in support of stories about the locations/wildlife that can be reached that way.
Answer: Your requirements are contradictory in every respect.
A ruggedized compact sports and active lifestyle camera will not have interchangeable lenses and will have a small sensor, even if you can get good optics.
But that's what I had on me when the "good stuff" gets sealed up in the storm bag, under Niagara Falls. I bought it for my in-laws to use and have a weather-proof (submersible, shock-proof) camera in the party.
I currently use both a mirrorless and a dSLR. Since you are interested in learning to really drive it, I recommend a dSLR. Specifically a APS-C ("crop") body that's cheaper to buy into and lighter than full frame; automatically more tele-photo (what you want) and you are not interested so much in full-frame's specific strength of low-light performance.
New low-end have the image quality of yesterday's mid-grade, but lose features like rapid burst shooting.  You want one with two dials, so you can adjust both aperture and shutter easily: if looking low-end, check for that.
Get a major brand that has a mature and common selection of lenses. That is, Canon (EF/EF-S) or Nikon (not familiar with the lens types). You can retain the lenses as you upgrade, find uses lenses, and rent lenses.
For a specific recommendation of something I'm familiar with, look for a used Canon 60D.  (When I sold mine, I found lots of them listed on eBay etc. probably for the same reason: upgrades to 70D for better video.  So the "used" price is depressed but they are still good cameras.  N.B. Michael Clark points out that the weather sealing isn't as good as other choices in the tier.)  Future readers: the point is that at any given time there may be some less-than-current model available for an especially low price.
Also important: plan a way to carry it. A strap to keep it from swinging on your chest while hiking, and cover it against splashes and sudden light rain.
When you see something you like, check dpreview for details on how easily the settings can be manipulated and how it performs, as well as weight.
Comment: Due to the differences in construction re: weather sealing and durability I would recommend the 50D or 7D/70D over the 60D, which was a step back in some respects. Especially for a camera intended to be taken kayaking/canoeing/backpacking as its primary purpose. It also lacks AFMA which is critical with long lenses used to shoot wildlife from long distances.
Comment: What is AFMA?  Google doesn't help with anything photo related.  I was thinking 60D because it's "still good" and less expensive used (and I have experience with that one).
Comment: @JDługosz AFMA = AutoFocus Micro-Adjust. Re: weather sealing, there's always the [Olympus EM-1](https://www.youtube.com/watch?v=cia2dRP9cww), but until that m.Zuiko ED 300/4 comes out...
Comment: Is auto-focus calibration really necessary for (1)non-Macro and (2)Canon-brand lens?  My 70D is the first body I've had that features it, and I've never lacked for it.

What are good starter outdoor cameras?


Finding all duplicates in a library

Question: Is there a way, probably with Search, where you can find all the documents that have duplicates? I know search will show any document that has been duplicated. Is there any search page, scope, function, etc. that I can leverage that feature to show all duplicates in a library?
Answer: You could add the file size to the view then group by file size.  The odds of multiple documents being the exact same size is rather small so anywhere you have a grouping of more than 1 is worth checking into to see if there is a duplicated file.
Answer: You want to be checking the content hash of the documents, this will show you the duplicates.
Search store these hashes, so you could look for a way of looking for duplicates of them, you could somehow use the search api to generate a list of all documents, then run an algorithm to look for duplicate hashes.
Not as a server so i can't think how the code would look.

Finding all duplicates in a library


Why a Unitary Matrix in Quantum Cryptography?

Question: I've read that in Quantum circuits the matrix that encodes the transformation has to be unitary. I understand that it must preserve the norm of the resulting qubit, but what is the intuition behind it?
Comment: A qubit encodes a "probability distribution" on $\{0,1\}$. By applying a unitary transformation to a qubit, one maps it to a different probability distribution. Since this operation is reversible, the quantum computer is too.
Answer: Short (unhelpful?) answer: the transformation are unitary, because quantum physics says all transformations on quantum states are unitary. So your question boils down to "Why are unitaries the only allowed transformations?".
For two reasons:

Quantum mechanics restricts the allowed transformation on quantum states to  be linear, transforming the vector $|ψ\rangle$ to $V|ψ\rangle$, where V is a matrix. I have no obvious intuition on why the transformation have to be linear$^\dagger$, except that

it gives an elegant and simple mathematical theory;
attempts at constructing nonlinear quantum mechanics have all lead to problematic consequences, e.g. in causality.

Once you accept the linearity of the transformation $V$, the unitarity comes from the conservation of the norm of  $|φ\rangle$, since this norm corresponds to the sum of probabilities of the different measurement results, which is therefore $1$. We have then, for all $|φ\rangle$,
\begin{align*}
\langle φ|φ \rangle &=1 & \langle φ|V^\dagger V|φ\rangle=1.
\end{align*}
Since it is true for all $|φ\rangle$, it implies that the eigenvalues of the Hermitian operator $V^\dagger V$ are all $1$, that is $ V^\dagger V=\mathbb I$: in words, $V$ is unitary. Another (maybe mor intuitive) explanation of this is that unitaries are the only matrices preserving the the scalar products $\langle φ|ψ\rangle$, which measures the distinguisability of states $|φ\rangle$ and $|\psi\rangle$.

$\dagger$: if anyone knows an intuitive explanation of the linearity of QM, I'd love to read it!
Answer: I am not a physicist, but I did take a quantum mechanics elective many decades ago.
The following question and its answers from Physics Stack Exchange illustrate the significance of unitary evolution of states in Quantum Mechanics.
Intutitively, until we make a measurement (at the very end of the computation) and the wavefunction collapses, all the other quantum evolutions are unitary. See especially the references to Wigner's and Kadison's theorems.
Quantum circuits are governed by Quantum Mechanics.


Steam Voice Chat Problem - Sound Bar Moving, No Sound

Question: I have a weird problem with voice chat in Steam that nobody else seems to have. I've read a lot of posts on Steam voice chat problems that start to sound like this one but end up being something else by the time I finish reading. So the problem is I'm not getting sound to come through in voice chat but I'm sure that Steam is receiving the sound because the bar is moving next the speaker icon but I just can't figure out where the sound is being sent to because I can't hear it in my speakers or headphones. All my friends can hear me too. The problem is on my end on my computer for sure, we've pinned it down. (I should also note I'm using a USB mic and normal headphones together, not a headset. This COULD be the problem but I can't figure out why it would be an issue.) I'm trying to look for settings in Steam on where to send the sound but it looks like there are just mic settings, nothing to help fix this problem.
Comment: Click Start Menu > Control Panel > System > Device Manager and check that under sound you don't have any missing drivers. Furthermore check if you've got all the bus drivers downloaded.
Answer: Since you said nothing about it, first check Audio devices.
Right click you Volume icon (looks like Dynamic) in system tray -> Playback Devices
Here you will see what device is currently used by default. Steam obeys these settings.
If you have more than one active device, Headphones should be "Set as Default Communication Device".
Then right click on Headphones and "Test".


Is there a punishment for breaking the vow of celibacy? If yes, what are the ways to clear the sin?

Question: What if a person broke the vow of brahmacharya by indulging in sexual activity like masturbation? Is there a punishment? Something a person would do to clear the sexual sins?
Comment: Why this is off-topic
Comment: @KeshavSrinivasan why??
Comment: @keshavSrinivasan,@brahmajijnasa please reopen it,it has been reworded.if it is too personal for u leave it ,so that people who are comfortable with this question may answer it.
Comment: The Brahma Sutras verses 3.4.40-43 says what expiation is needed for one who transgresses brahmachari. It depends upon whether one is a Nasthika Brahmacharin (lifelong) or an ordinary Brahmacharin. The Brahma Sutras are available here - https://www.wisdomlib.org/hinduism/book/brahma-sutras/d/doc62753.html
Answer: First of all what i will be posting will apply only to a Dvija Brahmachari whose being initiated into Veda study.
For a Brahmachari wasting manhood is an offence to start with, whether its voluntary or otherwise.

Manu Smriti 2.180. Let him always sleep alone, let him never waste his manhood; for he who voluntarily wastes his manhood, breaks his vow.

If its involuntary then the prayaschitta (atonement) is rather simple.

Manu Smriti 2.181. A twice-born student, who has involuntarily wasted his manly strength during sleep, must bathe, worship the sun, and afterwards
  thrice mutter the Rik-verse (which begins), 'Again let my strength
  return to me.'

Also, breaking a vow falls under UpapAtakas or minor sins that lead to jAtibhrahmsa or loss of caste.

Manu Smriti 11.61. Defiling a damsel, usury, breaking a vow, selling a tank, a garden, one's wife, or child,.. (are all) minor offences, causing loss
  of caste (Upapataka).

Atonement for voluntary discharge of seminal fluid for a Brahmachari is as given below:

Manu Smriti 11.117. Twice-born men who have committed (other) minor offences (Upapataka), except a student who has broken his vow (Avakirnin), may
  perform, in order to purify themselves, the same penance or also a
  lunar penance.
Manu Smriti 11.118. But a student who has broken his vow shall offer at night on a crossway to Nirriti a one-eyed ass, according to the rule of the
  Pakayagnas.

Nirrti is a demonness, who also is one the 10 Dikpalas (guardians of directions) and she guards the southwest direction.
And, the punishment for discharging semen by a householder, other than in intercourse, is as follows:

If a householder willingly causes the discharge of his virile seed otherwise than in sexual intercourse, he should recite the Gayathri
  verse one thousand times, and should perform three Pranayamas. (ParAshara Smriti 12-63)

Note that the above verse is not related to a Brahmachari (student) but is applicable to a householder, but since its related to masturbation, i included it in my answer.
Another general atonement measure for all sins is the recitation of the Gayatri mantra. So if you have got the Gayatri mantra upadesam you can easily use this method to your benefit.

One, by reciting the Gayatri, for ten thousand times, is freed from
  all sins
Usana Smriti's last chapter

NOTE - All the prayaschitta measures mentioned above can be performed only by those who have been initiated into VEda study. That is by those who have Gayatri mantra initiation. The only prayaschitta that can be performed without Vedic initiation is the pranayama (without using mantra).
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](http://chat.stackexchange.com/rooms/73235/discussion-on-answer-by-rickross-is-there-a-punishment-for-breaking-the-vow-of-c).
Comment: By the way I don't have usana smriti. It will be good if you quote the verse from usana smriti which says so. Because not sure whether minor sins or major sins.
Comment: All sins it says... it's stated elsewhere (Sankha Smriti) too that Gayatri japa is the best penance.. so don't worry about what has already happened.. just do the japa..@Parikshitha


What triggers solar flares?

Question: The sun is a big ball of hot plasma which contains free electrons. However, how does the absence of metallic elements in the sun generate the magnetic field to orchestrate these free electrons to display such beautiful solar phenomenon?
Answer: Magnetic fields are generated by currents - i.e. by the motion of charged particles. As you say, the Sun is full of freely moving charged particles, and these generate currents which in turn generate magnetic fields. No metals required.
Most of the magnetic field generation is thought to occur at the interface between the radiative interior of the Sun and an outer convective envelope. This region, called the tachocline, is subject to large shearing motions which are able to take small magnetic fields and amplify them. The stronger magnetic fields are then buoyant, because magnetic fields in a plasma exert a pressure. They therefore emerge at the solar surface in the form of loops of magnetic field.
These loops are strongly coupled to the plasma in the Sun. As the plasma moves around turbulently, driven by convective motions and differential rotation on the Sun's surface, the footpoints of the loops are sheared and twisted. There comes a point where the loop will snap back into a configuration with lower magnetic potential energy through a process called reconnection. The reconnection process has a side effect of accelerating particles within the magnetic loops. These relativistic particles smash into the photosphere (actually, they are mainly stopped in the chromosphere which sits above the photosphere), where they release their energy, heating plasma to millions of degrees, which evaporates into the corona. This is a solar flare.
Answer: The Sun has a very powerful magnetic field. But the rotation of the Sun on its axis is uneven. The velocity of rotation is higher at the equator and lower at the poles. Due to the large difference in the velocities, the magnetic field lines gets twisted and turned that causes some of them to come really close. The instability causes an outburst seen as solar flares.

What triggers solar flares?


Is chalking a snooker/pool stick a recent habit?

Question: I was watching this video from 1987, so I wonder if chalking the stick is a recent discovery that they didn't know about back then? Jimmy  is drinking beer and frustrated but John is shooting very good shots and I didn't see him chalk once (I don't know anything about snooker but his shots seem good to me)
Comment: Within one minute from start you can see them both chalking (about 40 sec and 52 sec into the video). And they have probably been doing so since childhood. Chalking is essential to getting spin / other effects on the ball.
Hm, I probably saw this one live on TV. First Jimmy White shot is typical for him to try.
Answer: I believe not, I have watched snooker since the early 1980's and believe it's a very old part of the game.
This is supported by wikipedia on snooker given that the inventor lived in the late 19th and early 20th centuries.
Answer: Like many sports, new discoveries/tactics are being found as the sport has evolved. It is very likely that nobody has thought about the fact that chalking might grant an advantage to the player.


How much more secure is encryption if the program requires random input from the user?

Question: I know there are existing questions about how Truecrypt uses mouse input to increase entropy. My question is, how much of a difference does it make? I don't know of any other encryption utilities that do this, so does this mean the rest of them (like 7-zip) are unsafe? To my knowledge the typical way of doing this is to use the computer time as the seed to the random number generator, which in a sense is the same as user input as an attack doesn't know (to the millisecond) when the user presses the button. How much more secure is encryption if it uses user input like moving the mouse or random keyboard strokes?
Answer: TL;DR:
None, really. Modern computers generate high-quality entropy ("randomness", essentially) fast enough that you wiggling your mouse is irrelevant.
More detail:
Programs like Truecrypt (and possibly older versions of things like ssh-keygen, gpg, and so on) that tell you to do stuff during key generation are operating on the assumption that the OS may not have very fast entropy sources other than user interaction and/or a very small entropy pool for its cryptographically secure pseudo-random number generator (CSPRNG). On old computers, especially without Internet connections or enough resources to run a lot of background processes, this was probably true at least some of the time.
Modern computers are pretty good at entropy generation and have relatively large entropy pools that can easily cough up enough pits to generate a key. Additionally, these days it is common to use CSPRNGs that support stretching entropy (on *nix OSes, this would be the difference between /dev/random, which pulls from the entropy pool directly, and /dev/urandom which can take a small amount of entropy from the pool and use it to generate a large number of slightly-less-random bits; /dev/urandom is, on modern OSes, still generally good enough for key generation). It's still theoretically possible to end up with machines that have predictable kernel entropy pools (a bunch of identical VMs running on identical headless machines running identical software versions started at the same time, etc. may sometimes have the same kernel entropy initially), but it's not easy. This kind of thing is why modern VM hosts have ways to feed some entropy to the VM guests based on the hardware states, etc. that are usually used in kernel entropy generation these days.
Most modern CPUs even have what amount to hardware RNGs based on things like the thermal state of the different parts of the CPU chip, which vary rapidly depending on things like exactly what instructions have been run recently and whether they caused cache misses or not, miniscule variations in voltage from the power supply, air movement in the room, and other stuff like that; the differences are slight, but taken together there's a lot of entropy there and the CPU has dedicated hardware for harvesting it and new opcodes for providing it to the OS. Many OSes mix this into their kernel entropy pool, along with other inputs, making it very hard to exhaust entropy under normal "user" workloads on a modern PC.
IMPORTANT:
There is no CSRPNG in the world that is seeded to any significant degree off of the system clock! The reason why is simple. You seem to think that "to the millisecond" timing is sufficiently random for crypto, but you're quite wrong about that. Let's take something like generating a GPG key pair as an example. Those generally have a validity period on their public keys, which tells me (I have your public key, it is after all public) when the key was generated, to the day. There are 86400000 ms in a day (ignoring the fact that I can probably narrow that down a lot by considering hours when a person is likely to be awake). Log2(86400000) is 26.36 bits. Your supposedly super-secure 4096-bit RSA key pair actually has less entropy than a decent-quality password! Brute-forcing 86400000 different possible key pairs to find the corresponding private key will take a while, but a hell of a lot less time than trying to factor a 4096-bit RSA public key. In fact, there aren't enough milliseconds since the dawn of electronic computing to produce a fully-random DES key (56 bits) by choosing from among them, and we can brute-force DES in under a day using off-the-shelf hardware (yes, RSA key generation takes a lot more work than just taking 56 bits and computing their parity for DES key generation, but it's still fast enough for this purpose).
Instead, any crypto program that isn't purely worthless garbage (and quite a few that are) use a CSPRNG (such as /dev/urandom on Unix-like systems, or CryptGenRandom() on Windows) for key generation. Similarly, most programming language standard libraries include at least two PRNGs: a fast but insecure one for stuff where it doesn't actually matter if somebody could theoretically predict the output (in Java, this is java.util.Random), and a cryptographically-secure one, usually either seeded by or directly just returning the output of the OS CSPRNG, for stuff like crypto (in Java, this is java.security.SecureRandom). No PRNG seeded by the current time, regardless of algorithm it uses, could ever be considered cryptographically secure; the search space is just too small.
Comment: `time` is the system clock function I mentioned above, yes, and is used by default to seed many of the insecure forms of PRNG such as libc's `rand` (which should not be used for anything more sensitive than shuffling a deck of cards, and not even that if there's money riding on the game). One should certainly never use it for any kind of crypto. CSPRNGs need to be indistinguishable from true randomness even if somebody is trying really hard, while insecure PRNGs are not intended for use in scenarios where such adversaries exist, and need only casually resemble true randomness.
Comment: Upvoted your answer for mentioning part of the question I missed — seeding from the system clock.
Comment: I didn't mean the time on the clock, I meant the `time()` function which returns the milliseconds from Unix time. Isn't this still used? http://www.cplusplus.com/reference/ctime/time/
Comment: timing info _can_ be a really unpredictable source of entropy, if it's done correctly. `randomize timer` is not correctly; you need multiple samples an indeterminate amount of time apart. For example, the ESP8266's 32b CPU clock rolls over in 30 seconds, so `time % 2^24` is basically "new" each time it's called. If you use a slow clock like network events, human typing, etc, to know when to sample the fast one, outputs will be unpredictable. If i asked you to drive across the country and back, you might be able to guess the # of miles, but could you guess the # of inches % 256  any > 1/256?
Comment: @dandavis: You still only get a fairly small amount of entropy out of every sample If you take enough samples, and if there's no bias to those samples (which, given that mice sample at regular and predictable rates, there would be), you can get usable entropy this way - such hardware interrupts *are* used to feed kernel entropy pools on most systems - but it's not going to happen fast enough that wiggling your mouse during key generation vs. not doing that is going to have a meaningful impact.
Comment: I think that in some cases (such as truecrypt?), the underlying assumtption is not that the OS has too little entropy in its standard RNG, but some paranoia that "They" might have tampered with it
Answer: Basically zero.
Operating systems already integrate every source of potential randomness that they can get their hands on in order to seed their randomness APIs (examples being CryptGenRandom() on Windows, /dev/urandom on POSIX variants, getrandom(2) on Linux, and getentropy(2) on FreeBSD). These sources include mouse movements, disk timings, and other unpredictable events.
The thing is, once you reach a certain point — say 256 bits of collected entropy, which takes less than a few seconds in practice — the operating system can generate an effectively unlimited stream of unpredictably random numbers for the remaining lifetime of the system. Many operating systems even save this internal state upon reboots, preventing the need to reinitialize the system random number generator from scratch ever again. More entropy at that point doesn't really get you more unpredictability, and collecting mouse movements is already done as part of this process anyway.
Additional entropy does allow for the operating system to recover from theoretical exposure or tainting of its internal random state, but this is very unlikely to occur in practice on a non-compromised machine.

To my knowledge the typical way of doing this is to use the computer time as the seed to the random number generator…

No cryptographically-secure RNG uses the system clock for this purpose. As @CBHacking points out, this is an exceedingly weak source of random numbers, since "what time is it" is highly predictable (and sometimes easily influenced by outside sources). Microsecond-level timings of human input can also be semi-predictable, but collecting and mixing this data repeatedly can very quickly yield a good source of entropy. Modern RNG mixing functions are very good at extracting and combining even small amounts of entropy.