Has anybody tried this circuit? this circuit supposedly takes radio waves and turns them into a voltage. My questions are what are the peak voltages? and what current could i possibly hope to get if i run a 5v circuit with say a voltage regulator or a buck-boost converter
Why can energy invested in RF radiation not be harvested fully? What are the main factors that affect this? Is there any significant research nowadays that fully describes this process? I stand on the conclusion: "Energy moves from one form to another.", but in this case why can it not be harvested in that quantity to use it for powering low-power devices or store it in significant quantities in some batteries for later use? Why is it not profitable nowadays and why is it not used today like energy from water, wind and other energy sources?
What's the weight of the earth? What's the weight of the earth?  That is, what's the weight of the earth in the gravitational field of the sun? I imagine it's either   $0$, because there's no net fall toward the sun, so the downward component of acceleration is $0$ and $F=ma=0$, or $Gm_1m_2/r^2\approx7\cdot10^{-11}\cdot6\cdot10^{24}\cdot2\cdot10^{30}/(1.5\cdot10^{11})^2\approx4\cdot10^{22}$ Newtons,   but which, and why? How to programmatically create a WPF window in a WinForm application How do I get add-apt-repository to work through a proxy? I'm trying to follow the  (on my Ubuntu 10.04 VM).  The first step is:  sudo add-apt-repository ppa:linaro-maintainers/toolchain   But when I run that I get:  Error reading https://launchpad.net/api/1.0/~linaro-maintainers/+archive/toolchain: &lt;urlopen error [Errno 110] Connection timed out&gt;   I'm guessing the problem is with my configuration for my employer's proxy server, particularly for HTTPS.  When I opened  in Firefox, I got "The connection has timed out".  I then went into Firefox Preferences -> Advanced -> Network -> Settings... and set HTTP Proxy to "gateway" and Port to 8080, and checked "Use this proxy server for all protocols".  Then the page loaded.  This supports my theory.  I've tried setting the http_proxy and https_proxy environment variables (both lower and upper case):  $ set | grep -i proxy HTTPS_PROXY=https://gateway:8080 HTTP_PROXY=http://gateway:8080 http_proxy=http://gateway:8080 https_proxy=https://gateway:8080   I also tried changing them to:  $ set | grep -i proxy HTTPS_PROXY=gateway:8080 HTTP_PROXY=gateway:8080 http_proxy=gateway:8080 https_proxy=gateway:8080   And I tried adding this second line to /etc/apt/apt.conf:  Acquire::http::proxy "http://gateway:8080/"; Acquire::https::proxy "https://gateway:8080/";   But I continue to get the same error.  How do I troubleshoot this?  Update: I followed the instructions in the  to  and got further:  $ sudo add-apt-repository ppa:linaro-maintainers/toolchain Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /etc/apt/secring.gpg --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv 1DD749B890A6F66D050D985CF1FCBACA7BE1F97B gpg: requesting key 7BE1F97B from hkp server keyserver.ubuntu.com gpgkeys: HTTP fetch error 7: couldn't connect to host gpg: no valid OpenPGP data found. gpg: Total number processed: 0   I wonder if the "HTTP fetch error" means I also need to add "Defaults env_keep = http_proxy" to /etc/sudoers...  Update #2: I added:  Defaults env_keep="http_proxy" Defaults env_keep="https_proxy"   ...as in , but I still get the same "gpgkeys: HTTP fetch error 7: couldn't connect to host" error.  And this is curious:  $ sudo env | grep proxy https_proxy=https://gateway:8080   ...because http_proxy isn't there.  Any advice is appreciated.  Update #3: Since the host of my VM is a laptop, I took it home and tried there (with no proxies):  $ sudo add-apt-repository ppa:linaro-maintainers/toolchain Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --secret-keyring /etc/apt/secring.gpg --trustdb-name /etc/apt/trustdb.gpg --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyserver keyserver.ubuntu.com --recv 1DD749B890A6F66D050D985CF1FCBACA7BE1F97B gpg: requesting key 7BE1F97B from hkp server keyserver.ubuntu.com gpg: key 7BE1F97B: public key "Launchpad Linaro Overlay PPA" imported gpg: Total number processed: 1 gpg:               imported: 1  (RSA: 1)   It worked.  So problem is related to proxy configuration.  But I suppose I have a workaround. What is the command to run System Settings from a terminal? System Settings can be run from the launcher (pinned by default), the Dash, or the power cog. But what command would I enter in a terminal window if I want to run it from there? Can I use lens brand X on interchangeable lens camera brand Y? I've just received my new SSD since the old one died. This Intel 320 SSD supports TRIM. For testing purposes, my dealer put Windows on it, but I want to get rid of this and install Kubuntu on it.  It does not have to be a "secure wipe", I just need the empty the disk in the most healthy way. I believe that dd if=/dev/zero of=/dev/sda just fills the blocks with zeroes and thereby taking another write (correct me if I'm wrong).  I've seen the answer , but it looks like it's suited for clearing empty blocks, not wiping the disk.  hdparm seems to be the program to do it, but I'm not sure if it clears the disk OR cleans empty blocks. From its manual page:     --trim-sector-ranges           For  Solid State Drives (SSDs).  EXCEPTIONALLY DANGEROUS. DO NOT           USE THIS OPTION!!  Tells the drive firmware to discard  unneeded           data  sectors,  destroying  any  data that may have been present           within them.  This makes those sectors available  for  immediate           use  by  the firmware's garbage collection mechanism, to improve           scheduling for wear-leveling of the flash  media.   This  option           expects  one  or  more  sector range pairs immediately after the           option: an LBA starting address, a colon, and  a  sector  count,           with no intervening spaces.  EXCEPTIONALLY DANGEROUS. DO NOT USE           THIS OPTION!!              E.g.  hdparm --trim-sector-ranges 1000:4 7894:16 /dev/sdz   How can I make all blocks appear as empty using TRIM? How To Group Records By Value In A Specific Field? I have a List of records of type abc__c. abc__c is a custom object. The record has a field called code__c. What I am trying to accompolish is to group the records in the list based on the code__c.  For example the list might have :  Code__c     abc__c record 30       (Record 1) 40       (Record 2) 40       (Record 3) 50       (Record 4) 30       (Record 5)   I want to group these records based on Code__c in a Map. There could be any number of code__c which is populated dynamically. It is not static. how can I loop through the list and store the records as a list for a particular code__c(Id) in Map? Center figure that is wider than \textwidth I have a figure that is wider than the \textwidth of my document. (I don't want to change the \textwidth.) As a result, the leftmost part of the figure is flush with the left margin, while the rightmost part spills into the right margin too much. I'd like to center the figure, so that it will exceed the \textwidth equally on both sides. How do I make a textbox that only accepts numbers? How to increase difficulty in Dungeon World I've been GMing for a couple of sessions now and I'm still struggling at making encounters or situations more difficult. I will describe dangerous situations and encounters in fiction but the mechanics make it too easy for my players to succeed.  For instance no matter how big I describe the Troll, if the fighter of the party charges him and swing his sword, roll+2 for Hack and slash, he'll easily hit the troll. Almost 40% chance to hit without consequences. My girlfriend forgot the password for her MacBook (don't ask), so I reset it using the Utilities.  But as you may be aware, this doesn't reset the Keychain password. Her MacBook is now virtually unusable due to Keychain demands continuously provoking a request for the Keychain password.  There are lots of other people asking this around the web and they're usually pointed towards this , which doesn't apply in our situation because the support advice involves entering the old password.  We don't know the old password.  Is it possible to reset Keychain without knowing the old password? We're not bothered about what's in there and what will be lost, we just want the continuous password prompts to go away. What is a single word for a person who, as a habit, exaggerates a lot when relating information?   So for example, they relate something that happened but exaggerate so much that they are including clear falsehood and they are well known for doing that. Regular (non-moderator) users should be able to override deletions by Community user There is a question on  that got deleted by the Community user. This question isn't terrible (we have worse one's there), and I'm not complaining about this question in particular.  I wanted to vote to undelete it. However, it says "A moderator has deleted this post and it cannot be undeleted". This "moderator" is Community!  I understand if a "real" live human moderator (no offense to all non-humans out here) deleted this question that we can't override it. But this is a Robot! It sees that it got a downvote, no answer and little activity for a while and just deletes it.  Can we have "Community user" have rights to delete, but have those "deletions" subject to normal-person override? I'm looking for one word which describes what a student who missed classes needs to do in order to complete his missing.   For example if he missed biology class he needs to seat with the teacher and study this missed class together with her and then he get the mark for this missed class. Someone -who isn't native English speaker- told me that it's called "rework". But I looked for it in some dictionaries (such as ) and I didn't find such definition.   : "SCHEDULE of reworks of missed classes" If $\cos x=\cos y$ and $\sin x=\sin y$ is $x=y$ or $x=2\pi,y=0$ or $x=0,y=2\pi$? $x,y\in[0,2\pi]$ I know that if $\sin x=\sin y$ then $x=n\pi+(-1)^ny$  and $\cos x=\cos y$ implies that $x=y+2k\pi$ or $x=-y+2l\pi$. Since the latter does not fit the form above $x=y+2k\pi$ which implies that $k=0,1,-1$. Hence, we have x=y or $x=2\pi,y=0$ or $x=0,y=2\pi$. There is a 2d rotation matrix around point $(0, 0)$ with angle $\theta$.  $$ \left[ \begin{array}{ccc} \cos(\theta) &amp; -\sin(\theta) \\ \sin(\theta) &amp; \cos(\theta) \end{array} \right] $$  Next, there is a 3d rotation matrix around point $(0, 0, 0)$ and unit axis $(u_x, u_y, u_z)$ with angle $\theta$ ().  \begin{bmatrix} \cos \theta +u_x^2 \left(1-\cos \theta\right) &amp; u_x u_y \left(1-\cos \theta\right) - u_z \sin \theta &amp; u_x u_z \left(1-\cos \theta\right) + u_y \sin \theta \\ u_y u_x \left(1-\cos \theta\right) + u_z \sin \theta &amp; \cos \theta + u_y^2\left(1-\cos \theta\right) &amp; u_y u_z \left(1-\cos \theta\right) - u_x \sin \theta \\ u_z u_x \left(1-\cos \theta\right) - u_y \sin \theta &amp; u_z u_y \left(1-\cos \theta\right) + u_x \sin \theta &amp; \cos \theta + u_z^2\left(1-\cos \theta\right)  \end{bmatrix}  How it is possible to generalize rotation matrix on $N$ dimension around zero point and $N-2$ dimensional unit axis with angle $\theta$? With the following AppleScript code within a "Run AppleScript" action in a Service:  tell application "System Events"     set theSBounds to {{572, 64}, {332, 515}}     set position of window "Google Hangouts - myemailaddress@gmail.com" of application process "Google Chrome" to item 1 of theSBounds     set size of window "Google Hangouts - myemailaddress@gmail.com" of application process "Google Chrome" to item 2 of theSBounds end tell   the Service will only work if the application from which that Service has been called has been added to the list of applications under "Allow the apps below to control your computer." This list is found at System Preferences → Security &amp; Privacy → Accessibility.  Is it possible to modify the AppleScript code somehow so that adding every application on one's computer to the list is not necessary? Or, so that, one only needs to add one item to the list, as opposed to every application on one's computer?  I thought that something like this might work:  do shell script "osascript -e 'tell application \"System Events\"' -e 'set theSBounds to {{572, 64}, {332, 515}}' -e 'set position of window \"Google Hangouts - myemailaddress@gmail.com\" of application process \"Google Chrome\" to item 1 of theSBounds' -e 'set size of window \"Google Hangouts - myemailaddress@gmail.com\" of application process \"Google Chrome\" to item 2 of theSBounds' -e 'end tell'" with administrator privileges   but this code also requires that the application from which the Service is run is added to the Accessibility list.  Note: I only want to run this AppleScript as a Service, and not in an Automator-created Application, because the code receives selected text as its input (system-wide). How to prove or disprove $\forall x\in\Bbb{R}, \forall n\in\Bbb{N},n\gt 0\implies \lfloor\frac{\lfloor x\rfloor}{n}\rfloor=\lfloor\frac{x}{n}\rfloor$. How to prove or disprove $\forall x\in\Bbb{R}, \forall n\in\Bbb{N},n\gt 0\implies \left\lfloor\frac{\lfloor x\rfloor}{n}\right\rfloor=\left\lfloor\frac{x}{n}\right\rfloor$.  So we want to prove $\left\lfloor\frac{\lfloor x\rfloor}{n}\right\rfloor\ge\left\lfloor\frac{x}{n}\right\rfloor$ and $\left\lfloor\frac{\lfloor x\rfloor}{n}\right\rfloor\le\left\lfloor\frac{x}{n}\right\rfloor$  Since $\lfloor x\rfloor\le x$, we can just start from here and prove  $\left\lfloor\frac{\lfloor x\rfloor}{n}\right\rfloor\le\left\lfloor\frac{x}{n}\right\rfloor$  But for $\left\lfloor\frac{\lfloor x\rfloor}{n}\right\rfloor\ge\left\lfloor\frac{x}{n}\right\rfloor$, I have no idea how to start. How does Java's PreparedStatement work? Why do you need 2 resistors when hooking up a transistor as a switch What is the point of R2 in the following diagram:   I get that R1 controls the current to the Base, but what does R2 do?