Speed of object falling into a black hole, below event horizon

Question: Suppose I am at rest at a great distance $r_0$ from a black hole with a mass $M$ without rotation or charge.
During my free fall in vacuum from $\tau=0$ and $r=r_0$, I will pass the event horizon in finite proper time and the increment of my proper time in Schwarzschild coordinates is $$\text{d}\tau=(2M/r-2M/r_0)^{-1/2}\,\text{d}r$$ (disregarding my destruction by tidal forces etc.)
If it is correct to view $$\frac{\text{d}r}{\text{d}\tau}=\sqrt{2M/r-2M/r_0}$$ as the locally measured speed, I would travel at $v>c=1$ shortly after passing the event horizon and before reaching $r=0$. But the locally measured speed of light is always $c=1$. This seems contradictory.
Where do I go wrong? Is it correct to say that $$\frac{\text{d}r}{\text{d}\tau}=\sqrt{2M/r-2M/r_0}$$ is the locally measured speed even within the event horizon and can this be greater than $c=1$?
I've read quite a few Q&A's in stackexchange, but I couldn't find and answer to this question.
Comment: I've removed a number of comments that were attempting to answer the question and/or responses to them. Please keep in mind that comments should be used for suggesting improvements and requesting clarification on the question, not for answering.
Answer: The problem is that in GR coordinates do not necessarily have a physical meaning. They are just a way of labelling points in spacetime. For example the Schwarzschild coordinate $r$ is not a radial distance. It's actually the circumference of the circle centred on the black hole and passing through your point divided by $2\pi$. That is, it's what the radial distance would be if space were flat.
This means that the coordinate velocity $dr/dt$ also does not have a physical significance. You can certainly calculate $dr/dt$, e.g. for the observer at infinity, and you would find the coordinate velocity for that observer is:
$$ v = \left(1 - \frac{r_s}{r}\right)\sqrt{\frac{r_s}{r}}c \tag{1} $$
giving the notorious result that the infalling object slows to a halt at the horizon.
Alternative you could ask what an observer hovering some distance $r$ (these are known as shell observers) would observe i.e. what speed would the falling object pass them. And in that case the result is:
$$ v = \sqrt{\frac{r_s}{r}}c \tag{2} $$
and now we find that the speed the falling object passes the shell observer tends to $c$ as the shell observer approaches the horizon. The difference between the two results is due to the relative time dilation between the shell observer and the observer at infinity.
More generally the shell observer and the observer at infinity will always observe different velocities. If you're interested I go into this in detail in my answer to the question Does light really travel more slowly near a massive body? As explained in that answer the coordinate velocity can be greater than $c$ even outside the horizon, and this is because the coordinate velocity is not a physically meaningful quantity.
Now you are asking about the velocity inside the horizon, but this is even harder to discuss in any meaningful way. For any observer outside the horizon no object ever passes the horizon, so there is no velocity inside to observe. And inside the horizon it's impossible to stay at fixed $r$ so we cannot have any shell observers to watch the falling object flash past them. I guess the best we could do is ask how fast the infalling observer observes the singularity to be approaching, though note that this is theoretical since no light from the singularity could ever reach the observer's eye. And the answer that the speed would indeed exceed $c$ inside the horizon, though I must emphasise again that you shouldn't assign any physical sigificance to this.
Comment: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/108905/discussion-on-answer-by-john-rennie-speed-of-object-falling-into-a-black-hole-b).
Answer: You can use Gullstrand–Painlevé coordinates to calculate the speed of an object falling into a black hole both inside and outside of the event horizon.  To be clear the speed would be that observed by a distant observer.  It involves a coordinate transform that removes the singularity in Schwarzchild metric that occurs at the event horizon.  For a "raindrop" falling in from rest at infinity:
$$\frac{dr}{dt_r} = -\sqrt{\frac{2M}{r}}$$
This is the negative of the Newtonian escape velocity FYI.  It equals the speed of light at the event horizon and is faster within it.
Just FYI I found the above on the wikipedia article about Gullstrand–Painlevé coordinates
Comment: That's not the speed measured by a distant observer, that's the speed measured by a local and stationary observer.
Comment: And there is no stationary observer inside the event horizon.
Comment: This is what would be observed by the distant observer if they could communicate with the stationary observers, if those could exist.


study roadmap for newcomer into java ee

Question: I'm the newcomer into java ee,I have studied about core java,servlet,jsp.
Could anyone give me some suggestion(some books,forums,etc) on how to promote my skills into java ee?
Thanks a lot in advance.
Answer: One good place to start is Sun's Java 6 EE Tutorial on the Sun web site.
Answer: I would recommend Server-Based Java Programming. This isn't a Java EE book per se, but it explains what a Java based server needs to do and how to do it with good example code. It will give you the foundation to understand to understand what Java EE is trying to accomplish and why things are the way they are.
In the same vein, I would recommend Expert One-on-One J2EE Development without EJB. This book is written by the founder of the Spring project and provides insight to the problems with Java EE that Spring is trying to solve. Note this was written before Spring was open sourced, so it's more a 'this is how a server framework that's not Java EE could work' book, not a 'how to use Spring' book. Even if you are using straight Java EE, it helps to know what issues you could run into (with J2EE) or what the motivations were for Java EE 5 (based on Spring & Hibernate philosophies).
I would not recommend the actual specifications from Sun. They are dense, technical and better used as a reference.
Answer: To be an effective J2EE developer, you'll have to have a few frameworks under your belt. Start boning up on Spring, JSF, Hibernate, etc.
For more details, see my answer to this question.
Spring is an excellent first choice of framework, for reasons that may not become apparent until you've used it on a large project. But the best tutorial I know for learning it is Manning's Spring In Action.

study roadmap for newcomer into java ee


Be already + V-ing

Question: could you please explain this sentence to me "The trade war is already hurting US companies in China". As I know "already" is often used with the present perfect or past perfect. Why they use it with the present continuous?
Answer: You say "already" is "often" used with the present perfect or past perfect, so you yourself already know apparently that it's not always used with those tenses. You can use "already" with other tenses; the present continuous is one of them. So is the present, I did it myself in this paragraph.
You use "already" to say that we might think Verb will only be true in the future, but no, Verb is true in the present. This is the case whether Verb is an action that was completed in the past ("I've already done my homework" -> the doing of the homework happened in the past, but we are talking about the present state of the homework being finished, when you might have thought it would only be finished in the future), or one that is currently happening (such as the trade war already hurting US industry, when we might have thought it would start hurting US industry later).

Be already + V-ing


Monitoring solution for EC2 based deployment

Question: We have some 20 or so servers in EC2, most are dynamically spawned (scaling groups).
We're looking for a solution to monitor the uptime of our application.
As an added bonus this solution could also extend to actually monitoring the servers involved so its easy to go back in time and see what happened just before a downtime or whatnot.
We're looking for a hosted solution ideally, and it should be easy to scale with it (it needs to somehow dynamically deal with servers being added/removed with no interaction from us).
Anyways, hoping for some recommendations from you guys.

A bit of background ...
We're currently using a custom Nagios setup, its been reduced to basically doing a simple http check now that the servers have become fully dynamic. We've already been using PagerDuty to deliver the pages. It does ok, but for the maintenance cost we could well be using a http check @ Server Density of Pingdom.
I've looked briefly at ServerDensity, and it does look promising, I especially like their install mechanism of just dumping their files into your AMI and it takes care of the rest.
I'd like to know what options there are tho before diving deeper into any particular solution.
Answer: We use a combination of Server Density for monitoring and PagerDuty for alerting.  The two work quite well together.


How to format an SD card directly inside Android?

Question: How can I format an SD card directly inside Android?
Answer: These steps were using an HTC EVO with HTC Sense - your menu options may be different but should be similar.
There should be a "Format SD Card" in the phone "Settings".  Open "Settings", then go to "SD & Phone Storage", then you should see "Format SD Card".  If the option is grayed out then you may need to unmount your sd card first and then format the card.  Make sure you have backed up anything you want to save with a backup app or just by copying whatever files off your card onto a computer because this will erase everything on the card.
Hope this helps
Comment: I wouldn't describe any format as "safe", since it erases all the data, but it should format the card perfectly well.  I would expect it to remove all partitions as well, though I have never partitioned my card.
Comment: Is this format safe? Does it remove also hidden partitions, if any?
Comment: I've never formatted From Android's built-in method so I can't comment about the partitions - I've always formatted through a custom recovery (Amon RA) which gave me the option to set sizes for the partitions.
Answer: Go to Settings -> Storage -> Erase
 SD Card.

Screenshot - (Click to enlarge)
Answer: In Android 7 it can be done from the "Downloads" App"
It apparently can't be done from the Settings directly anymore.
You can open it either:

directly like any other app:

top left "three line" menu
"SD card"

through settings:

"Storage & memory"
"Tap for more details"
"SD card"

With either approach, you are now at the "SD card" view of "Downloads" and finally:

top right three dot options menu
Storage settings
Format


Hand drawings in "A Walk Among the Tombstones"

Question: In the movie A Walk Among the Tombstones, what was the significance of the drawings by the young black boy that was helping Matt?
It looked like drawings appeared several times in the movie at particular moments, and seemed to be evolving towards the end of the movie.
Comment: mcguffin or at least character development for the lad.
Answer: The drawings actually serve multiple purposes in the film.
They first and foremost add to the character building of TJ. They show that he is talented and creative and has a hobby that sets him apart from the mass. It adds to his image of a street kid that is intelligent and considerate when compared to the environment he grows up in. In this way it adds to other aspects of his character, like the general smartness, the love for books and hanging around in the library (although that has other reasons, too), the  way he cares for a healthy diet. With the hand drawings there's just another layer of uniqueness to him.
But they also serve to channel the friendship between him and Scudder. It is by finding one of his hand drawings that Scudder first comes in contact with him. Later he takes the drawing that TJ leaves at the restaurant and takes it with him. TJ later finds it laying around in Scudder's apartment. This is a way of showing (both to us and to TJ) that Matt cares for the boy to some degree, since he keeps a personal item from him. They both always play cool to each other, but it's clear they are friends and Scudder cares for TJ. While there are other signs that show this, the hand drawing that Matt took with him is just another way.
Last but not least, there's another drawing at the very end of the film. When Matt returns home after all is done and solved, he finds TJ sleeping on his couch and he finds a drawing of a superhero with a sickle emblem on his chest. This relates to TJ's earlier story in the hosptial about him having sickle-cell anaemia (and his mother's explanation of his blood being "special"). So the hero is likely a representation of TJ himself. This shows us that TJ sees himself (and by extension Scudder?) as a hero for helping Matt solve the crime and save the girl. Furthermore this might mean that he has now found a purpose in life (which adds to his general interest in detective work exhibited during the film).
Answer: The drawings simply show the evolution of TJ in the movie and how he "found himself".
The first drawing was a few prototype characters with blank faces and blank costumes which represents TJ being lost in purpose or direction and possibly even hope.
The last one shows a very detailed hero with the sickle which represents his sickle cell anemia disorder. Also the hero now has a definitive costume, face etc. which represents TJ finding himself and his purpose (if only temporary).
It could also represent a reconciliation with his wounds which he suffered due to his mother abandoning him. Remember the story she told him?  That he had very special blood and could never catch malaria so it seems he found peace with that story and that peace produced this hero he drew.


Web browser usage census map?

Question: Does anyone know of a web application that will display the types/versions of browsers people use overlaid over google maps?
Answer: Well this is close: http://gs.statcounter.com/
It doesn't have a map, but it does a pretty good job of giving a broad overview of what people are browsing on.
Comment: http://gs.statcounter.com/ now has a map feature that records the top browser by region for up to the last 90 day period.

Web browser usage census map?


Power meter upgrade on 2015 Surly Long Haul Trucker

Question: I have a 2015 Surly Long Haul Trucker with a Andel RSC6 crank and Shimano UN-55 bottom bracket. Is there a crankset I could replace that with that would be compatible with a single side power meter?
Comment: are you able to source a wheel-hub power meter?  Or one of those handlebar ones?
Comment: A pedal power meter is probably the cheapest and easiest way.
Comment: @Michael At the time they asked, I think we only had one MTB pedal power meter, and that was by SRM and hence expensive. Garmin released a competitor to that (Rally, uses SPD cleats). Also, you can unofficially convert Favero Assiomas to a spd body, but you usually have to trim the tread on your shoes. That latter factoid was known at the time. You could feel free to write this as an answer.
Answer: Power meters for square taper BBs are hard to come by, and usually custom made and expensive.
However, fortunately the Surly LHT has an ordinary English threaded bottom bracket. Just swap out the UN-55 for any Hollowtech 2 compatible external BB, such as the Shimano Tiagra BB-RS500 or 105 SM-BBR60. Then, get any hollowtech 2 crank, replace the left side with a power meter, and you're good to go.
In fact, more recent models of the LHT use hollowtech-2-type crankset systems out of the factory.
I know Stages only sells power meters for 105 and above for road, so it might make sense to get a 105 BB and a 105 crankset, coupled with a 105 power meter such as the stages Gen 3 Power L, or 4iiii equivelant.
If you want more gearing range than a 105 crankset provides, you can mix and match with other cranksets that use the Hollowtech 2 interface, of which there are plenty.
Comment: I only recall one PM for a square taper BB: Power2Max offered a spider for the TA Carmina in its first generation of PMs. P2Max is now on at least generation 3. The Carmina takes either a 103mm or a 108mm JIS axle (documentation was poor and in French, but there are in fact two versions of the Carmina, and I can attest from experience), so the OP might need a BB change if they somehow found that P2M spider for sale, and in any case the Carmina crank is quite expensive and rare by itself.
Comment: @WeiwenNg, SRM made (makes?) a meter for square taper, but anything SRM is going to be $$$$
Comment: you're right, the SRM Science Road is for ST cranks.
Answer: While product recommendations are off-topic here due to their tendency to become obsolete, it's fair to say that what you're up against here is that touring triples (24-36-46 or thereabouts) of the type that LHTs come with are pretty far opposite from the type of cranks that get left-crank power meters.
But, what may exist is a 110/74 or 104/64 triple direct-mount spider for a crank of the milieu that get left power cranks made. Sometimes third party companies make such spiders. There are a lot of 104/64 double direct-mount spiders for such cranks, but I don't think there would be a way to hack them into running a triple without running into clearance problems with the crankarm and FD or the ring itself.
You can probably find an older native 104/64 crank with a power meter where you'd be able to replicate your chainring sizes, but the Q and chainline may not be right or at least may not be what you had.
Shimano has made various HT2 triple cranks with Euro trekking type chainring configurations. You could conceivably find a match between one of those and one of the XTR/XT/Saint/DXR power left cranks. HT2 mountain power crank interchangeability is kind of a maze and is again an area where things change, so it would be on you to figure that out. That would probably be the simplest off the shelf way to get something close to what you have. In other words, there are definitely 104/64 HT2 cranks that can take the same gearing as what you have and can also match with extant HT2 power cranks. I believe the stock LHT chainline might be in a bit from what you'd get if you did that though.
Comment: OPs problem isn't the gearing range, it's the BB interface. If OP had a 2020 LHT they'd have a HT2 50x39x30T crankset, and they'd be good to go with a simple replacement of the left side crank arm in 5 minutes.
Comment: @whatsisname OP's problem is they presumably want to keep their 26/36/48 and want a power crank. Surly deciding to spec later versions with something other than proper loaded touring gearing is here nor there. It's right there in the post that they're open to buying a new crank.
Comment: I don't read this as necessarily being about what the options are within square taper.


Simple equation not working?

Question: So I found this equation
$$
  e^{20}=10^{20*.43429\dots} = 10^{8.6858\dots} = 10^9 * 10*(-.3141\dots)
$$
on this webpage and I'm really confused as to why it isn't matching up whenever I try it. The first two expressions are equal to each other but the third one doesn't equal either of them. Every time I calculate $10^9 * 10*(-.3141\dots)$ I get $-3414100000$ which is different from the other two expressions which equal $485165195.41$. I'm wondering if this is a mistake and if anyone can explain why this isn't working for me.
Answer: On that webpage, the last expression has a typo. Rather than
$$
  10\wedge 9 * 10*(-.3141\dots)
$$
it should be
$$
  10\wedge 9 * 10\color{red}{\wedge}(-.3141\dots)
$$
This works out because $10^9 * 10^{-.3141}\approx 485176771.21$, which is about what you say the other ones are equal to.
Comment: Why are you using the wedge symbol?
Comment: @ericw31415 if you're writing mathematics without special formatting, you can use the wedge or carat to denote exponentation. So x^b is x to the power of b.
Comment: I'm wondering because $\wedge$ and $\mathrm{^}$ are quite different.

Simple equation not working?


Character rotates 90 degrees and changes location in edit mode

Question: I have a character that I rigged with mixamo and I want to edit the mesh. When I try to edit it, the model rotates 90 degrees and changes location. I have the character in "rest position" but If I try to rotate the character when in edit mode and then go back to "pose position" I end up with deformations and bones in the wrong locations. I want to be able to edit the character mesh without the character moving and rotating and then without it changing the location of the bones.
Answer: Try applying rotation of the mesh and the rig in object mode, this might be the issue you're facing.
(Im sorry I don't have enough reputation score to comment, so I'm posting the answer)
Comment: Unfortunately this did not work, but thank you. This just causes further deformation.


Burn Windows 8 image to a DVD using linux

Question: I dont know why, but when i try to boot Windows 8 install from flashdisk, i get stuck on logo, nothing else happens. So, i've got an idea, that will be better burn iso to a DVD. I tried to burn that with Xfburn, that i have native in my distro, but the dvd was unusable, so i write on it "Linux sux" and threw it out of the Window. Now i have only 3 more dvds left.
How can i burn on dvd windows iso using linux?
Comment: You can use brasero, it has always worked for me, even windows disks. As long as the file is an .iso it should work.
Answer: Windows 8 image has UDF filesystem.
Try using K3b to burn ISO. It has UDF support.
If you want to burn image on USB drive read this.
Answer: The filesystem is already in the image file.
So it does not matter whether UDF, ISO 9660 or something else.
Also, the pointers for the boot firmware have to be in the image.
For flash drive this would be MBR and/or GPT partition entries
which lead BIOS or UEFI to the first program in the boot chain.
You may see these by inspecting the image file by partition
editors like fdisk (for MBR) and gdisk (for GPT).
For DVD, there has to be El Torito: boot record, catalog, one
or more boot images.
You may see this by programs like isoinfo or xorriso:
imagefile=...path.to.win8.file...

isoinfo -d -i $imagefile

should report about a "Eltorito validation header".
xorriso -indev $imagefile -toc

should report about "Boot record  :", "Boot catalog :", and
"Boot image   : ...".
Now if the image has El Torito equipment it should boot from DVD.
Make sure to burn it as single preformatted image, and not as
"data composition" or "project" where you could put more than one
file onto DVD.
Command line programs for burning to DVD:
growisofs -dvd-compat -Z /dev/sr0=$imagefile

xorriso -as cdrecord -v dev=/dev/sr0 -eject $imagefile

The program growisofs is normally used by K3b.
xorriso uses the same libburn as does Xfburn.


What's the best way to leave an air flow shaft in wood chips after removing a PVC pipe?

Question: I'm going to be composting a lot of wood chips this winter, and only have one large PVC pipe. How can I remove the PVC pipe from the wood chips while leaving the air shaft in place?
Answer: If I understand the setup, the goal of the PVC is to keep the pile aerated so it will be aerobic composting.
Some alternative solutions:

Figure out a way to periodically turn the pile and keep it fluffed-up. Turning the pile has multiple benefits beyond just aerating the pile. It also helps spread the beneficial bacteria. It also moves material from the dryer and colder edges/tops into the damper and hotter middle of the pile where it will be composted.
Get some more pipe. If cost or environmental impact are issues you could try to get some used or discarded pipes. One good trick is to set up an email alert from craigslist. You can also often find good materials at a used building goods store (in some cities these are run by Habitat for Humanity or similar organizations).
Use other materials in the pile to create a structure that has air pockets, like longer branches or stalks from plants like sunflower stems or corn stalks. These materials might not all compost as quickly as the wood chips and would need therefore need to be filtered out at the end to be composted twice. However, they should hopefully help the wood chips to compost.
Comment: I'm not going to turn 200 yards by hand, when I have 6 months to compost as well as I can.
Comment: Sure, turning 200 yards by hand would be a lot of work. If you did it in chunks it could be more manageable (it's 1 cubic yard per day, for example). Or, you could try to get a skid-steer or similar machine to turn the whole pile one time.
Comment: Shopping around may help; polyethylene drainage pipe is cheaper than PVC. If you buy it perforated you can just bury it in the pile.
Answer: I believe if you remove the PVC that is creating the air shaft, you are removing the support from the chips that permit that shape to be maintained.
Consider to construct a wire mesh or steel rod assembly to fit inside the PVC pipe prior to removing the pipe. As you lift the pipe, force the mesh/rod assembly to remain. If the shape of the mesh is appropriate, you would have a chamber to allow the air to flow/escape.
If having something in the place of the PVC is unacceptable, over time, I'd expect that the chips would settle into the void.
Comment: I compost sawdust and horse poop year round. We have 2 main air pumps that we have to pull when turning the pile or they get crushed by the tractor, even with this mixture having settled for 3 to 6 months the lines were the pipes were usually collapse but the mix is loose. We have tried different methods to ariate the mix to increase the compost rate and pulling the pipes turning or mixing the pile then rebuilding over the pipes has been our best method to breakdown the sawdust in less than 2-1/2 to 3 years to be able to sell it as organic.
Comment: maybe i should try some sticks down the shaft to keep it open some


How to use the Alt + right click in edit mode in Ubuntu 17.xx?

Question: How can I use the Alt + right click shortcut in Ubuntu 17.xx and higher without installing additional software?
Comment: I don't remember how exactly solve is, but the key is disable ALT for system shortcuts. I thing somewhere in keyboard settings
Comment: I have removed every shortcuts in the keyboard settings and it still doesn't work. Before it was in the Window settings but it has disappeared from the System Settings panel: http://blender.stackexchange.com/questions/60961/how-to-use-the-alt-right-click-in-edit-mode-in-linux-mint
Answer: You could use Alt + Shift + <Right Mouse Button> instead.
(This shortcut is normally not used by the system.)
This will have the same effect, except the "Shift" key will make it add the new selection to an already existing one.
So what you should do is:
1. Press A (if needed) to remove any old selections.
2. Press Alt + Shift + RMB.


To Underestimate: Nameru vs Anadoru 舐める vs 侮る

Question: Other than one being to lick, any difference between the 2 for underestimating?
Answer: 舐める is slangy and should be avoided in very formal contexts. Its meaning is closer to "to look down" rather than "to underestimate." 舐める often also has a connotation of behaving disrespectfully/insolently to someone/something.
侮る is a relatively literary word and typically used in a set phrase "侮るなかれ" or "侮ることなかれ". It's probably safer than 舐める, but still has a connotation of making light of something/someone.
過小評価する is a neutral and politically safer word for "to underestimate," which does not imply any disrespectful attitude.
Comment: Thank you! If 舐める is slangy then you mean the official dictionary meaning is not 'to underestimate' and is just a proper word that people gave an informal meaning to over time?
Comment: @shoryuu Yes, the original meaning of 舐める is "to lick," which is safe in formal contexts. The derivative, slangy sense is "to look down", "to make light of", "to take the piss", etc., which you should use with care.


Changing the missile's flight speed

Question: I am interested in the range of velocity changes of missiles. Planes have a minimum speed set equal to the landing speed, helicopters also have a set speed - this is zero, but what about missiles? Anti-ship and anti-radar missiles have a well-defined trajectory, however, their maximum and average speeds are determined in the documentation. Which traffic sections do they correspond to? And is it possible to somehow estimate the minimum speed of missiles? Example of missile flight sections in the picture.
Comment: Using the phrase "minimum speed" without defining what this  minimum is *for*! Minimum for maneuverability?, for 1 G level flight?, for closure on a t600 kt target ?, every one of those could be different.
Comment: Dear downvoter, since user66348 is a new user, would you consider adding a comment to explain why you think this post is sub-standard? We can't expect new contributors to be perfect from the start, and without taking the time to explain how posts can be improved we can't expect the quality to magically become better either.
Comment: For users unable to read the image: it shows the typical flight trajectory of a Harpoon anti-ship missile. The flight is split into the phases "Start", "Cruise", "Target search and acquisition" and "Self guidance".
Answer: Pretty much all missiles ignite a solid-rocket motor called a booster rocket shortly after launch/deployment/firing. Typically, the missile will reach its highest velocity and energy state, shortly after burnout of this booster. After this point, it will lose velocity because of air-drag, or because it lofts its trajectory for various reasons.
Having said that, there are a lot of exceptions. For example, most cruise missiles have some sort of air-breathing motor (e.g. the Tomahawk has a turbofan motor), which will propel the missile. In that case, the booster rocket is only intended to bring the cruise missile up to sustained flying speed, such that the motor can ignite. An interesting application is that of Ramjets: These engines need a certain speed (e.g. Mach 3) to ignite. After ignition of the motor the missile will accelerate even further. A good example is the X-51 waverider experiment in which a Scramjet (a supersonic Ramjet) was tested.
Other missiles feature a sustainer rocket engine, in principle a second rocket motor which burns slower but longer, and keeps the speed of the missile up. Especially air-to-air missiles loft their trajectory directly after launch in order to fly into thinner atmosphere. When these missiles descend again, the speed can be even higher than shortly after launch.
Missiles also do have minimal speed, however this is a bit harder to define as they loose their ability to maneuver gradually with decreasing airspeed. The question is therefore not the minimum speed but rather the mininum maneuverability you are willing to accept.
Answer: First: the numbers on that picture indicate range (in kilometers) and altitude (in meters), not speed.
A missile typically does not actively regulate its speed It's turned on, and when the fuel runs out it coasts. Depending on the power of its engine, range to target, flight path, and atmospheric conditions it may or may not reach its maximum aerodynamic speed during its flight time (most will, as most will boost to that speed very rapidly).
Of course a missile, like any object, will bleed energy (thus (max attainable) speed) when turning or climbing and may gain some when diving.
I've not heard of missiles with speed brakes (the only way to actively influence a missile's speed, especially for a missile with a solid rocket motor rather than a turbojet motor like Harpoon) but they may exist (there are bombs with speed brakes to slow their fall for example).
Comment: Re : "  it may or may not reach its maximum aerodynamic speed during its flight time (most will, as most will boost to that speed very rapidly). " -- I'm not sure what this means.  Is this a statement that pertains to the specific motor installed?  Are you essentially discussing whether or not forward acceleration has dropped to zero before the end of the motor run?
Comment: @quietflyer nope, just that it may hit its target or otherwise stops to exist before its motor runs out
Answer:
is it possible to somehow estimate the minimum speed of missiles?

Yes, if one treats them like aircraft.  Weight, wing area, and coefficient of lift should yield an estimate for minimum airspeed.
However, in application, missiles are built for speed, rather than efficiency, although, as pointed out by U flow and Jim, high subsonic cruise missiles do exist.
And, of course, we have torpedoes, which essentially are underwater "airships", using bouyancy as a source of lift.
But I doubt the crew of the "Craptonesque" could stand the suspense of waiting for anything slower than high subsonic.

Changing the missile's flight speed


What happens to Girdie?

Question: In Podkayne of Mars, Clarke leaves Poddy a cryptic note stating that he was going to rescue Girdie. Poddy is unable to reach Girdie and we find out later that she is not one of the kidnapped victims. Was this a trick to lure Clarke? Was Girdie in on it too?
Answer: In chapter twelve, Clark has been missing for three nights. Poddy finds Clark's note. Girdie has been following her normal routine, leaving work only a half hour before Poddy thinks to call her. That Girdie had 'gone shopping' instead of being available for the call seemed to be more a function of cutting Poddy off from support during the climax of the story rather than suggesting sinister motives on her part.  Since everything is in Poddy's P.O.V. except the ending(s), we don't know how Clark was convinced Girdie needed rescuing.
From my reading, Girdie was totally uninvolved with the political intrigue aspect of the novel. The character's function was the world-wise older-sister role model. There was no hint she was one of the bad guys.

What happens to Girdie?


Is there a way to customize the zoom button and legend in cartodb js?

Question: I am following this tutorial, http://docs.cartodb.com/tutorials/toggle_map_view.html, and have been successful in developing an application with similar functionality, currently I am working on customizing the appearance of the application. I would to customize the the appearance of the zoom button and the legend (font, color, location) in the application. Is there any wall to do this? In the css or js?
Answer: You can do it with plain css. For example. html body .leaflet-control-container .leaflet-top .leaflet-control-zoom a.leaflet-control-zoom-in { color: red; } changes zoom in control color.
Comment: Thanks! How did you know to call on this title "leaflet-control-container .leaflet-top .leaflet-control-zoom a.leaflet-control-zoom-in" in the css to color the zoom?
Comment: Reverse engineering as usual :) In Chrome, Right click --> inspect element. Chrome Dev Tools has some utilities to help you with that task. Maybe Leaflet has something more sophisticated for a complete replacement of the control, but if CSS is good enough... Could you please mark the answer as accepted if it's been useful? That way tracking unanswered questions is easier for us, thanks :)


How to revert all graphic sizes after library update in Flash?

Question: I made a SWF with some png's, but I didn't realize that shrinking the png's would make the graphics look shotty.  I want to have straight non-pixelated lines, so I updated the png's with a smaller size.  Now, is there a quick way to revert the graphics to their original sizes?  Or do I have to create the SWF all over again?
Answer: Select the item and do Modify > Transform > Remove Transform (Command + Shift + Z).
It will restore it to the original size.
Also, if you turn on check 'Allow Smoothing' in the properties for the PNG it will not look so pixelated when you scale it down or rotate it.
Answer: I haven't used Flash for a bit - but I remember there was an "update" command available for images in the library (properties, or right-click?).  In order for that to work, though, you would have to actually overwrite the original image files with the new ones (same names).  Doing that will allow Flash to see that they have changed.  I don't know of another way, sorry!
Comment: That's actually part of the problem.  When I update, all of the images change sizes.  I shrunk all of them to say 50% (in flash), then I shrunk them 50% in photoshop, and updated them in flash.  This makes all of the images shrink by half again, because it saves the fact that I shrunk them to 50%.


bundle install leads to git clone error. Not sure what this response means

Question: Getting a strange error on bundle install..
bundle install
Fetching gem metadata from http://rubygems.org/.....
Fetching gem metadata from http://rubygems.org/..
Fetching git://github.com/maccman/gdata.git
fatal: The remote end hung up unexpectedly
Git error: command `git clone 'git://github.com/maccman/gdata.git' "/Users/elephanttrip/.rvm/gems/ruby-1.9.2-p318@shasta/cache/bundler/git/gdata-811f852468ac76e0019108d8c5320da12b6683d4" --bare --no-hardlinks` in directory /Users/elephanttrip/Sites/shasta has failed.

This wasn't happening until I installed the mysql2 gem and mysql with brew.
Any ideas what this error means?
UPDATE
Also none of the folders it is trying to clone this to exist. It's probably something to do with my bundle paths and juggling .rvm
Answer: The problem is not on your end. Trying:
git clone 'git://github.com/maccman/gdata.git' "foobar" --bare --no-hardlinks

Fails on my machine with the same error.
Interestingly a non-bare clone seems to work as expected.
resolution: Clone from the https interface: https://github.com/maccman/gdata.git instead.
Comment: Ah, amazing. Thanks for pointing that out my European comrade. I'll just comment that piece out. ;D
Comment: Well, I might not be so fast, you'll probably need the gdata API :)
Comment: I switched it to the https connection and it worked. Interesting to say the least.
Comment: This is probably something to take up to the github team.
Answer:
In your Terminal write bundle config github.https true
In your Terminal write bundle install
Answer: Add your SSH key to the github.
Or as @brice mentioned, you need to add your team to the repo.


cutting wood trim

Question: How would I go about making this: https://www.ebay.co.uk/itm/135-degree-Corner-Edge-Molding-trim-dollhouse-1pc-23/192652458710?hash=item2cdafb3ad6:g:bjsAAOSw~4BcAIqC
I.E 135 / 45 degree wooden trim, how do I make this firstly with power tools then with hand tools?
Comment: Just as an FYI, the product you linked to wouldn't be made as given in @SaSSafraS1232's great Answer but more likely milled from a solid piece. As odd as it might seem, the glued-up assembly described actually gives a stronger result if everything goes smoothly (haha, [pun intended](https://woodworking.stackexchange.com/questions/4850/not-so-obvious-disadvantages-of-butt-joints/4857#4857)).
Answer: With power tools you'll want to use a table saw.  Rip thin strips off a larger piece of stock, tilt your blade to the appropriate angle for the miter (22.5 degrees in this case), set your fence for the desired distance from the point to the edge, and rip them to width.  Since this is so small you'll probably want to set up featherboards and/or hold downs.
For hand tools you'd basically do the same thing but with a hand saw and a plane.  Joint one edge of a larger board flat, then rip a strip off and plane it to thickness.  Then joint one edge square and layout your angle on the end of the board referencing that square edge.  Use a marking gauge to mark a line on both faces based on that layout and plane to the lines.
To glue them together I'd start by cutting a few blocks at the desired total angle (135) and cover them with packing tape.  Then run a strip of blue tape along the outside of the joint, add some glue, and fold them together.  Clamp (or tape) the blocks with the tape on them every foot or so to the inside of the work piece to make sure the angle is correct, and add tape to hold the rest of the glue line together.
Comment: Hard to describe this concisely, nicely done.

cutting wood trim


Cutting windows into a premade gingerbread

Question: We have a gingerbread kit that we would like to add windows.  What is the best way to cut into the hard gingerbread without breaking?
Answer: Very, very carefully.
Although that's rather tongue in cheek, it's true: slowly and carefully is the key approach. The quicker you try to move, the rougher the shape you produce. You also significantly increase the chance of breakage.
Make an initial rough hole at the center point of your eventual window area, and then cut out to finish the edges. A serrated knife used with a slow, steady sawing motion should work.
Luckily, if you do end up with lopsided, misshapen, or unexpected results, icing and candy decoration can help hide the mistakes :)
Answer: Serrated knife is the best choice and was what I was taught to use in my baking class. What @Erica said is right, slow and steady.
If the pre-bake is too tough and dry then a possible fix is to add steam to the area you are cutting the window to both sides to soften before cutting (assuming you didn't attach the piece to something already). You can boil some water and then set the piece above it to soften or even fill a bowl with water then put the cookie above the bowl in the microwave (microwave may over cook cookie!!!!) (don't let the water touch the cookie)
Try not to use anything other than a serrated knife if possible. But if you are trying for a small window then you may have to create room for the serrated knife with a pairing knife before hand just try not to use it too much if at all. Pairing knifes often will put lots of pressure on and make it easy to crack the brittle cookie. If it does crack, fill it with thick-ish consistency royal icing (watch out if you steam it after adding royal icing it may and probably will fall apart) and let it set before trying to deal with it more (unless you wanna try to cut out the window first then glue it together with icing).
Answer: If money (and complexity) is no object, laser cutting creates the best finish. A friend of mine created a fantastic gingerbread 'mansion', all of the pieces for which were cut from large slabs of gingerbread she baked.
The difficulty in your case would be calibrating the laser to cut in the right place on your pieces.
This is obviously not a practical solution for most people, but should nevertheless be mentioned
Comment: It's certainly not a standard kitchen utensil, but upvote regardless because I totally *want* to do it this way!
Answer: I'd propose the carving approach:

With just the very tip of a pointy knife, draw the lines where the window should be
Carve a thin layer of gingerbread away from the inside of the window to the line you made.
Re-cut the outline of the window to get a sharp and straight edge
Repeat carving out the inside of the window to the edge

The reason for this approach is that sticking a knife through the gingerbread to cut out any shape first adds material to the gingerbread that is not flexible enough to accomodate the knife without breaking. By pre-cutting shallow lines and then carving the inside out you only remove material, lowering the chances of breaking your gingerbread.
Answer: I would start not with a knife, but with a cookie cutter. If you dont't have a square cookie cutter, choose something which has at least one straight side, but is smaller than the full window, maybe some kind of triangle. Cut that out, then use the tip of a knife to cut out the other straight sides.
Answer: I was faced with this problem in baking class yesterday (I forgot to cut out the windows and doors before baking off my gingerbread). Here was my solution, and it worked better/easier for me than sawing away at rock-hard gingerbread with a serrated knife:
Leave the gingerbread somewhere humid where it will soften up (a refrigerator works, but I used the muggy humidity of our commercial kitchen), then use a paring knife to very carefully and slowly cut the shape you want. Point the knife straight down vertically or at a slight angle and drag it to cut (but don't use it parallel to the table, because you don't want to introduce too much mass from the knife into the slab of gingerbread at once, or it might crack). Have the slab show-side down when you cut for the neatest results. The weight of the slab will keep crumbs from crumbling off of the show side. Then put in the oven at low temperature to dry it back out, and use a microplane or a coarse-grit nail file to sand down any uneven edges.
Answer: I rarely make gingerbread houses myself, but I have a friend who swears by her Dremel, when making them. The result looks stunning!
Also - not for windows, but for edges - use a microplane (or sandpaper) to make sure that the edges are straight.
Comment: I'm a dremel fan myself. I've used a router bit (designed to cut horizontally as opposed to a drill bit designed to make holes) to cut out the basic designs and an emery board to sand the edges straight.


Is it to possible to have parallel access of Pi's camera to take stills, when it is streaming through FFMpEG video streaming?

Question: Is it to possible to have parallel access of Pi's camera to take stills, when it is streaming through FFMpEG video streaming ?, if not, then how both ( still and streaming) can be processed at the same time, pl reply.
Answer: Only one process can access the camera module at a given time, so you couldn't have, say, raspivid feeding data to ffmpeg and simultaneously use raspistill to capture images. That said, the underlying firmware does support the concept of a "splitter" component which can be used to accomplish something similar (e.g. by connecting one port of the splitter to a video encoder, and another to an image encoder).
An example of using this from python is given in this recipe.
Answer: This can be possible if you use opencv..
Video grab funtion might help.. you can get furthur details on this link..  http://docs.opencv.org/modules/highgui/doc/reading_and_writing_images_and_video.html#videocapture-grab


Is there any way to spawn the Enderdragon in Minecraft without mods of any kind?

Question: I need a way to spawn the Enderdragon boss mob in Minecraft without mods. I cannot get mods, heck, I can't even get texture packs, and I wan't to have an epic battle between Withers and Enderdragons in Vanilla Minecraft. I don't play in a snapshot and I don't have the Horse update.
Comment: There is no way to do it without using modifications or external tools. I suggest you to buy Minecraft if that's the reason why you don't have 1.6 yet.
Comment: @MBraedley as I read it, that other one's about getting him to reappear in The End, this one's about spawning him anywhere, any time, and even seems to be looking to spawn more than one, which is quite a different thing to go about doing.
Comment: I don't think it is exactly a duplicate though...
Comment: If anyone stumbles on this question in the future, I too think it was wrongly labelled a duplicate, just of the wrong question. https://gaming.stackexchange.com/questions/348463/how-do-i-successfully-summon-the-ender-dragon-using-commands is a good resource on spawning working ember dragon(s) at-will.  Also see https://gaming.stackexchange.com/questions/220465/i-cant-find-the-end-portal and https://gaming.stackexchange.com/questions/175309/where-is-my-end-portal for info on the regular method of spawning the initial Ender Dragon.
Comment: Also, since this question has a couple of quality answers, and has the highest view count, perhaps it should be merged, not closed. Or maybe we need a meta-question about creating enderdragons in general, since there are apparently 3 ways to do so, and several more questions about corner cases.
Answer: Use commands
As of Minecraft 1.7 you can spawn in mobs using this command:
/summon <Entity-Name> <x> <y> <z> [Data-Tag]

By typing /summon EnderDragon into the Minecraft chat you would spawn in an EnderDragon at your coordinates.
As for Minecraft 1.6 and lower - there is no way to do it without using modifications or external tools.
If you are okay with a 1v1 between the EnderDragon and the Wither Boss you can just spawn in a Wither in the End.
WS WS WS    // (3 Wither Skulls)
SS SS SS    // (3 Soul Sands)
-- SS --    // (1 Soul Sand in the Middle / -- = Air)

Comment: I just haven't updated it to the horse update, but it's pretty current.
Comment: @MasterHalo937 As I said, spawning the enderdragon in versions below 1.7 is not possible without using mods or tools. The horse update is 1.6, so it's not possible there either.
Answer: The only way to spawn the enderdragon in vanilla without 1.7 is to just go to the end, but to do that you'll need to find it.
Note: if you're in survival, be sure to bring at least four soulsand and three wither skeleton heads.
If you're in survival, you'll need to gather enderpearls and blaze powder to get eyes of ender. Then you need to throw them, and follow them in that direction. (if you're in creative you can just get them out of your inventory)
Once the eyes of ender start falling, instead of going in some other direction, dig directly down where it fell. After some digging, you should find stone bricks, and directly below that will be a stronghold. In strongholds, there is usually a room designated to the ender portal, which has a silverfish spawner and lots of lava. Use (right click) on the portal frame (what's around the biggest plot of lava) with the ender eyes and when all of their buttons are up, a black portal will appear within the frame. Jump in!
There will be an enderdragon in the end. (where you just got teleported)
Use the heads you brought with you/search "wither skeleton" in your creative inventory to get wither skeleton heads, and use the soulsand with it, in this pattern: (h = wither skeleton head, s = soulsand)
hhh
sss
 s

After building this (not in a crafting table, in the world) a wither will spawn. Have fun!
Comment: Have fun **dying** (If you're in survival).


What is the best extinguishing agent when wheels catch on fire?

Question: What extinguishing agent must be used in the event of a fire involving wheels/tires? Why?
Comment: I don't see the other question as a duplicate. The answers there certainly don't address the issues presented here, such as rubber or metal fire.
Answer: You can find some discussion in this thread but what you are looking for is

Fire Service manual. Volume 2. Fire Service Operations : aircraft
incidents Home Office - London
HMSO, 12/99. Crown copyright 1999
ISBN 0-11-341192-8; 0113411928
5.4.2 Brake and wheel fires The overheating of brake and wheel assemblies usually follows excessive braking. This can happen on
  landing when a hydraulic failure reduces the ability of the pilot to
  utilise control surfaces (flaps) and he feels the aircraft may over
  run the runway or more often, on an aborted take-off. Quite often
  tyres will burst or, as the aircraft comes to a standstill, ignite by
  transference of heat from the brakes. To avoid metal failure,
  firefighters attending overheated brake and wheel assemblies should
  usually refrain from applying water and allow natural cooling. If
  there is fire however, a fine water fog applied from fore and aft of
  the undercarriage assembly is generally used.


Difference between $\implies$ and $\;\therefore\;\;$?

Question: I've seen both symbols used to mean "therefore" or logical implication. It seems like $\therefore$ is more frequently used when reaching the conclusion of an argument, while $\implies$ is for intermediate claims that imply each other. Is there any agreed upon way of using these symbols, or are they more or less interchangeable?
Comment: In particular, "$\implies$" is most often used to indicate that the conclusion follows from relatively recent statements. If you needed to prove something first for $n$ odd then for $n$ even, if each case was a relatively long proof, I don't think you'd want to write, after the two cases were proven: "$\implies$ X(n) is true for all integers $n$."  That's a case where "$\therefore$" makes more sense, even when it is not the "end" of your proof.
Comment: Yeah, I read the $\implies$ symbols in this context as "Which implies that,..." I read the "$\therefore$" as "Therefore, ...". In normal language, we'll prefer "Which implies that,..." more in the middle of an argument, and "Therefore,..." at the end or at a natural "punctuation" point in the argument.
Comment: Zilch. ${}{}{}{}$
Comment: Once difference I notice is that I haven't used $\therefore$ since secondary school (high school), while I use $\implies$ and $\iff$ these days.
Comment: I have a related question.  I once used $\implies$ in a proof for a class to say one thing implies another.  My professor said that it is not okay to use it in that case.  He said it would be okay if you are proving an if and only if argument, to indicate which direction you're proving $\Rightarrow$: and $\Leftarrow$:  Do any others of you agree with this?
Comment: I do disagree with the accepted answer: the difference between $\implies$ and $\therefore$ is decidedly **neither** about scope **nor** about intermediate claim/conclusion versus final claim/conclusion. I've upvoted all the other answers, and also posted my own.
Answer:
"It seems like $\therefore$ is more frequently used when reaching the conclusion of an argument, while $\implies$ (alternatively $\rightarrow$) is for intermediate claims that imply each other."

Your supposition is largely correct; my only concern is your description of $\implies$ being used to denote intermediate claims (in a proof or an argument, for example) that imply each other. The $\implies$ denotation, as in $p \implies q$, merely conveys that the preceding claim ($p$, if true) implies the subsequent claim $q$; i.e., it does not denote a bi-direction implication $\iff$ which reads "if and only if".
'$\implies$' or '$\rightarrow$' is often used in a "modus ponens" style (short in scope) argument: If $p\implies q$, and if it's the case that $p$, then it follows that $q$.
Typically, as you note, $\therefore$ helps to signify the conclusion of an argument: given what we know (or are assuming as given) to be true and given the intermediate implications which follow, we conclude that...
So, put briefly, $\implies$ ("which implies that") is typically shorter in scope, usually intended to link, by implication, the preceding statement and what follows from it, whereas '$\therefore$' has typically, though not always, greater scope, so to speak, linking the initial assumptions/givens, the intermediate implications, with "that which was to be shown" in, say, a proof or argument.
Added:
I found the following Wikipedia entry on the meaning/use of the symbol'$\therefore$', from which I'll quote:

To denote logical implication or entailment, various signs are used in mathematical logic: $\rightarrow, \;\implies, \;\supset$ and $\vdash$, $\models$. These symbols are then part of a mathematical formula, and are not considered to be punctuation. In contrast, the therefore sign $[\;\therefore\;]$ is traditionally used as a punctuation mark, and does not form part of a formula.

It also refers to the "complementary" of the "therefore" symbol$\;\therefore\;$, namely the symbol $\;\because\;$, which denotes "because".
Example:
$\because$ All men are mortal.
$\because$ Socrates is a man.
$\therefore$ Socrates is mortal.
Comment: Yes, I pretty much gathered that you knew what you meant. It's just that many people experience significant confusion about what is meant by an implication, so for the sake of clarity and precision, I wanted to point that out.
Comment: @Javier Perhaps this example will help: an implication, in and of itself, asserts no conclusion, save for the implication.  "If the grass is purple, then elephants can fly." It's a "valid" statement (since anything follows from a false assertion) even though if seems absurd. And certainly, elephants being able to fly has nothing to do with the color of grass, nor is "elephants can fly" *because* "grass is purple".  In contrast, $\;\therefore\;$ typically carries with it the idea that the conclusion follows *because* of the premises, (never in spite of the premises).
Comment: Yes, "imply each other" was kind of poorly worded. I meant that $\implies$ is appropiate when you have a series of logical implications from one statement to another.
Comment: As a practicing mathematician, I would never use $\because$ nor would I advise anybody to ever use it. It's both visibly difficult to parse and unhelpful to include. Really, students of mathematics are better off avoiding $\therefore$ as well—it's better to learn to write mathematics with words—but I understand that's what the OP asked about.
Answer: There are four logic symbols to get clear about:
$$\to,\quad \vdash,\quad \vDash,\quad \therefore$$

'$\to$' (or '$\supset$') is a symbol belonging to various formal languages (e.g. the language of propositional logic or the language of the first-order predicate calculus) to express [usually!] the truth-functional conditional. $A \to B$ is a single conditional proposition, which of course asserts neither $A$ nor $B$.
'$\vdash$' is an expression added to logician's English (or Spanish or whatever) -- it belongs to the metalanguage in which we talk about consequence relations between formal sentences. And e.g. $A, A \to B \vdash B$ says in augmented English that in some relevant deductive system, there is a proof from the premisses $A$ and $A \to B$ to the conclusion $B$. (If we are being really pernickety we would write '$A$', '$A \to B$' $\vdash$ '$B$' but it is always understood that $\vdash$ comes with invisible quotes.)
'$\vDash$' is another expression added to logician's English (or Spanish or whatever) -- it again belongs to the metalanguage in which we talk about consequence relations between formal sentences. And e.g. $A, A \to B \vDash B$ says that in the relevant semantics, there is no valuation which makes the premisses $A$ and $A \to B$ true and the conclusion $B$ false.
$\therefore$ is added as punctuation to some formal languages as an inference marker. Then $A, A \to B \therefore B$ is an object language expression; and (unlike the metalinguistic $A, A \to B \vdash B$), this consists in three separate assertions $A$, $A \to B$ and $B$, with a marker that is appropriately used when the third is a consequence of the first two. (But NB an inference marker should not be thought of as asserting that an inference is being made.)

As for '$\Rightarrow$', this -- like the use of 'implies' -- seems to be used informally (especially by non-logicians), in different contexts for any of the first three. So I'm afraid you just have to be careful to let context disambiguate. (And NB in the second and third uses where '$\Rightarrow$' is more appropriately read as 'implies' there's no scope difference with '$\therefore$'. In either case, we can have many wffs before the implication/inference marker.)
Comment: I'll add here that A. N. Prior's textbook *Formal Logic* has parts of it which read like the following: "Rule: Detachment ($\alpha$, D$\alpha$D$\beta$$\gamma$ $\rightarrow$ $\gamma$) and (In all cases the sole rule beside substitution is E-detachment: $\alpha$, E$\alpha$$\beta$ $\rightarrow$ $\beta$.  And in my opinion Prior's symbolism comes as clearer here than writing {E$\alpha$$\beta$, $\alpha$} $\vdash$ $\beta$, since the "$\rightarrow$" symbol suggests that one transitions from the left-hand side to the right hand side.  So, as this answer says let context disambiguate.
Answer: $\therefore$ and $\implies$ are quite different!
"Hence" and "therefore" and "as a consequence" are all synonyms.  The usage is "A, therefore B", meaning "A is true, and it follows that B is true."  Note that the truth of A is being asserted.
Latex \therefore ($\therefore$) gives the dot triangle that has long been used to mean "therefore".
"Because" is the same in reverse.  "B because A" means that B is true because A is true.  This contains the assertion that A is true.
Latex \because ($\because$) gives the inverted dot triangle that has long been used to mean "because".
"Implies" is completely different.  "A implies B" means that IF A is true, then B is also true.  It makes no statement about the truth of A.
Latex \implies ($\implies$), \Rightarrow ($\Rightarrow$), and \Longrightarrow ($\Longrightarrow$) all give the double right arrow that is often used to mean "implies".  Sometimes a single right arrow is used, which has the same meaning.
It is very common to use the \implies symbol instead of "therefore", but since "implies" and "therefore" have significantly different meanings, this is very bad writing.
Comment: Agreed!  That is indeed a big difference between 'implies' (denotes by $\Rightarrow$) and 'therefore' (denoted by $\therefore$)
Comment: @RyanG Ha ha, yes, I agree with that as well ... worst answer was upvoted the most. Oh well!
Comment: @Bram28 I wasn't actually quibbling with zaslav's first sentence (just deleted), which I in fact thought was a pertinent warning considering that the incorrect answer has numerous more upvotes and uptick than the correct ones. My above comment was just informational; apologies for any confusion caused.
Comment: @RyanG I would agree with you. I'll remove that comment.  That should never be put in a post anyway, since other people can of course always add further answers. Thanks for your note!
Answer: Contrast these:

I deny that I was planning to rob this bank.  If I had been planning to rob this bank, I would be wearing a ski mask.
I was planning to rob this bank.  Therefore I am wearing a ski mask.
Comment: I'm not sure I understand. In which case would you use each symbol?
Comment: @Javier $\quad R$: I was planning to rob this bank. $S$: I am wearing a ski mask.  Case $(1)\;$: $\lnot R.\;$ $R \implies S.\quad$ Case $(2)\;$: $R.\;$ $\;\therefore S$. (I may be wrong.)
Comment: You use the symbol that means "If . . . then . . ." in the first case and the symbol that means "Therefore" in the second case.
Comment: @JavierBadia : Your surmise is correct.
Answer:
$$A \implies B \implies C \tag{1}$$ has a different meaning and reading from $$A;\:\:\therefore B;\:\:\therefore C \tag{2} \\\text{($A$ is true; therefore $C$ is true)}.$$ Line $(2)$ asserts premise A, that $A \implies B$ and that $B \implies C,$ and concludes that $C$ is true.
Line $(1),$ on the other hand, neither specifies that sentences $A$ and $B$ are actually true, nor asserts that sentence $C$ is true. It in fact has three possible meanings, no pair of which is equivalent (convince yourself using the truth assignments $(0,0,0)$ and $(1,0,0)$): $$A \implies (B \implies C).\tag{1a}$$
$$(A \implies B) \implies C\tag{1b}$$
$$(A \implies B)\: \text{ and } \:(B \implies C)\\\text{(A being true implies that C is true)}\tag{1c}$$ The third is the most common interpretation, and can be read as "in case $A$ is true, then $C$ too is true".

If the difference between lines $(2)$ and $(1\text c)$ seems trivial or just a matter of contextually inferring the stronger meaning as necessary, then observe that  $$x>-4;\:\:\therefore\, x>4$$ tells us that $x\not\in(-\infty,4],$ whereas $$x>-4\implies x>4$$ tells us that $x\not\in(-4,4].$

Another example: \begin{align}\lvert2x\rvert=x-1&\implies x=-1 \;\text{ or }\; \frac13\end{align} is true while $$\lvert2x\rvert=x-1; \;\text{therefore, }\; x=-1 \;\text{ or }\; \frac13$$ is false (explanation here and here).

And two illustrations that overloading the $\text'{\implies}\text'$ symbol imposes a burden of disambiguation on the reader, breaking their flow of reading and skimming.

All in all, I think it is bad practice to treat $\text'{\implies}\text'$ and $\text'\therefore\text'$ as interchangeable.
Here are several articles expounding their distinction:

implication versus conclusion
"implies" versus
"therefore"
guide to writing mathematics (p. 17)
abuse of the implication
symbol


Fallback to the default if source is invalid in AUDIO tag

Question: So I have a basic audio element.  Say I have a single mp3 source.  I'm using Firefox.  The browser sees the audio tag, likes it, places the controls as directed, but doesn't like any sources, so it doesn't load any audio, but still ignores the default items that a lesser browser would have displayed.
Sadly I'd prefer the browser actually display the default items at that point (say a link to download the mp3) rather than than display the non-working audio controls.  Since there is no AudioElement.stuffThatsNotSRC, how do we do this?
So what I do is have a checkSources() that fires onLoad that looks at the networkState and if it finds the 0 or 3 it then goes to a HTML span I have around the audio control and replaces its inner HTML with the non-source stuff that was inside the audio tag.
Is there a better way to do this?
Answer: Use the source tag to define multiple file types.
<code><audio controls="true">
    <source src="demo.mp3" type="audio/mp3">
    <source src="demo.ogg" type="audio/ogg">
    <source src="demo.aac" type="audio/mp4">
    <!-- If no support at all. -->
    HTML5 audio not supported
</audio>
</code>
http://msdn.microsoft.com/en-us/library/gg589524(v=vs.85).aspx


how to remove all but one specific block

Question: I have a world and would like to remove all blocks but command blocks, how would I do this?
I have tried looking for mcedit filters but counldnt find any.
Comment: There might be mods for this; not sure though, try googling it.
Comment: Do you actually need the blocks in your entire world removed or would just a very large section accomplish this?
Answer: How I would do it would be create a spigot server with build tools and get world edit and Async world edit then do replaces.. //replace stone,dirt,cobblestone,grass air
You can also use itemid. U can replace as many as you want at once also, just do have ,  in between each.
Answer: just looked this up myself, try using a mask, a mask uses "!" followed by the name or id of the block you don't want to replace, in this case (chain) command blocks, ID 137:
//replace !137 air
for my case, I wanted to delete every block in between the bedrock (ID 7) layers, but not the bedrock itself, so I used:
//replace !7 air.
and if you are replacing all the blocks in an area except for air (ID 0) to something like stone (ID 1) for example, you would use something like this
//replace !0 1
And so on and so forth, I hope this helps you and anyone else who may stumble across this.


Can birds pass diseases to humans through contact surfaces?

Question: My friend asked me the following question. She has a pigeon nesting on her window and the pigeon often touches the window, and my friend also sometimes touches the window (e.g. open and close it). The question is does the touching of her and the pigeon in a common surface (the window) can transmit infections or disease from the pigeon to herself? Is there a risk letting the pigeon nest on her window pane?
Comment: But it's on the other side of the window?! So how is that the same surface?
Answer: Provided she washes her hands after touching surfaces that came into direct contact with the pigeon, there shouldn't be any relevant health risks from touching this surface.
And just because it sound like the pigeon somehow is nesting WITHIN her apartment: Be aware that pigeons can carry mites that could spread within the apartment and infest plants. I would advise against having wild pigeons in the apartment!
EDIT:
Knowing the pigeon is outside, it's not 100% necessary to remove the nest. It depends on whether this window is used for venting and on the direction of air pressure. (does wind go in or out at this side of the house?). Also it depends on the visual cleanliness of the nest. Bird-droppings can potentially represent a health risk, as they can spread through the air, once they dry out, while potentially containing dangerous micro-organisms. Same with feathers that lie around.
So if wind regularly comes from the side of the nest, she could remove the nest for safety reasons, especially if the window is in the kitchen. Otherwise she can't overcome that guilt by blaming health.
Comment: Thank you for your answer. The pigeon is nesting on the outer window pane and not inside the apartment. Is the risk of mites still relevant?


Can California deny concealed carry permit after the recent SCOTUS decision?

Question: After the recent SCOTUS decision regarding concealed carry, can any state, in particular CA, deny a concealed weapon carry permit to its residents, who are not disqualified from gun ownership in any way?
Answer: There isn't one simple answer. The case prohibited a showing of a "special need" for a concealed weapon to allow one to have a permit. Many California concealed carry laws have similar requirements.
But, California doesn't have just one concealed carry law. There is a default rule that applies in small, rural counties, but most larger cities and counties in California have their own specific concealed carry laws and the precise grounds for denying a concealed carry permit would matter.
In all likelihood, many provisions of existing California concealed carry laws would remain grounds to deny permission to concealed carry (e.g. age, history of drug abuse, criminal record, restraining orders in place, etc.), while others provisions would no longer constitute valid grounds for a denial.
This particular decision is about denying permits based upon lack of a particularized need for one different from other members of the general public, rather than about any possible reason that the permit applicant could be deemed untrustworthy to have a permit. The decision discusses the idea that it is problematic to have unfettered discretion in issuing permits, but doesn't really base its ultimate conclusion on that ground. So, something like a general residual "good character" requirement, while vague, wouldn't be squarely within the scope of the most recent decision.
The case also doesn't itself prohibit (nor does the case law) some reasonable fee for issuance of a concealed carry permit.
Thus, the new case does not require uniform law with "constitutional carry" for everyone permitted by federal law to own a gun. But, it does prohibit limitations related to a requirement to show a need to have a concealed carry permit.
Answer: As it stands, this has no effect on California, which was not a party to the New York lawsuit. The ruling, in its wording, is addressed to "respondent" (New York). However, the reasoning could easily apply in the case of California, where a "good cause" requirement is a requirement for a license. In an earlier ruling, a 3-judge panel of the 9th Circuit court found the law unconsitutional (Peruta v. San Diego County, 2014)
but in 2016, the full court upheld the law. The reasoning in the most recent NY ruling could easily translate into an overturning of the California "good cause" requirement.
Answer: The problem with California is that it's a big state with a surprisingly wide amount of political difference in the state's interior.  While it has a reputation as a "blue state" that's a relatively recent trend.  Between 1952 and 1992, California went for the Republican candidate in all but one Presidential Election (1964).  It helped that the ticket for almost every winning Republican in this period included a California Candidate (Nixon, a former CA Rep and Senator, and Reagan, a former CA Governor) or a California adjacent ticket (Eisenhower selected Nixon as his Vice President, Ford was Nixon's Vice President (California REALLY REALLY loved Nixon), and George H.W. Bush was Reagan's Vice President).
California boasts 4 out the top 20 largest cities in the United States (Los Angelos, San Diego, San Jose, and San Francisco), second only to Texas (5 out of the 20) and these for major population centers tend to have voting force that overpowers the more conservative rural interior parts of California these days.
Now this all does have a point:  because Califorina's permit issuing is done at local level, not state level and must be done by applying to a local level police agency.  There are 58 counties in California, and a little under half of them do vote more conservative... and several more are swing counties and aren't as reliable.  But none of the red ones are coastal counties.   In these counties farming is a big industry and there is both agriculture and ranching... both of which draw the attention of predatory animals such as numerous big cats, coyotes, and bears, which are drawn to human farming for all the meat.  Not to mention the issue of guns tends to draw flatly on the Urban/Rural divide as the former have closer proximity to emergency services and other people while the later do not... and many who live in these areas enjoy the fact that other people do not live near them.  So California's various permit issuing authorities might have different standards for issuing permits along this divide.
Likely the change will force the hand of California's coastal counties, which are typically strong holds for stricter gun rights.


Rear derailleur too far out

Question: All I did was change the rear tyre and now the rear derailleur can only access the highest 4 sprockets out of 7.
I have followed Parktool videos on adjustments (including pulling the cable probably tighter than I should) to no avail.
Adjusting the L Limit Screw at the lowest gear doesn't show any movement to the derailleur.
The great change lever won't go any further to low gears either and shows such high resistance when trying that I'm afraid of snapping the cable.
What else can I try to fix this?
Comment: If it's not shifting to the biggest sprockets it's probably insufficient cable tension. If it's not shifting to the smallest sprockets it's too much cable tension or excessive friction. Use the cable clamping bolt for coarse adjustment and the barrel adjuster for fine adjustment. Check the cable and cable housing. Is it properly seated everywhere? Bent or broken anywhere? The limit screws only really come into play for the biggest and smallest sprocket and are really only there to limit derailleur movement to prevent the chain falling off the sides.
Comment: Shift to highest gear (smallest), take wheel off, move by hand, observe, learn, remedy.
Comment: Hanger looks bent inward a bit as well.
Answer: So - the wheel was removed and reinstalled, the gearing didn't line up, so you started changing things.
Instead, it would have been better to try resolving the indexing problem straight off rather than changing things.  Now you've got extra problems to resolve.  I would have suggested

Confirm visually that all the gear wire outer segments are firmly seated in the frame-stops.  They can pop out when tension drops, same goes for brake wires.
Remove/reinstall the wheel and see if that helps.  There may be a washer that has swapped sides of the dropout.

All this is a lot easier if you can hang or suspend your bike with the rear wheel off the ground.  Rope or anything can help here.

Limit screws do exactly one thing.  They limit how far the derailleur can move and have no effect on indexing or gear/chain alignment.H is Hi and confusingly means the littlest cog, and L for Low means the biggest cog.  Set them up first and then don't touch them again.   Don't worry if the chain is a bit clattery at this point, it should move to, and not past, the respective cog.  You can manually pull any exposed gear wire to actuate shifting, while slow-pedalling with your right hand on the right pedal.
The Low limit screw should be only just allowing the chain onto the largest cog - otherwise the chain can jump over the top and make a mess of spokes.  The Hi limit screw is more forgiving.

Then set the barrel adjuster to about half-way in/out.  Approx is fine.

Set your right-hand shifter into the "second hardest" gear, meaning not the outside smallest, but the one beside it.  The chain should be on the second smallest cog too.

Without pedalling, click your shifter into the hardest gear but don't move the chain

Now loosen the pinch bolt/nut on the rear derailleur, pull through as much of the inner wire as you reasonably can and reclamp the wire.  This should get you into the right ballpark area.

Now the only place to fine-adjust is the rear derailleur's barrel adjuster. When viewed from the rear (like your photo above) then unscrewing it will lengthen the outer housing and making the derailleur shift toward the middle of the bike, or toward the easier gears.
Likewise, tightening the barrel adjuster will move the derailleur outboard, toward the smaller cogs/harder gears.

In your photo above, you'd want to tighten the barrel adjuster a turn or so, but this presumes the limit screws haven't been fiddled too hard.
You can turn the barrel adjuster with the left hand as you slowly hand-pedal with the right hand on the right pedal.  Do mind out for pinch points - there's a lot going on down that area of the bike and you can do a lot of damage to fingers and any dangling things like cuffs and hair.
When you have it perfect, run up and down the cassette using the shifter several times.  There's always some compromise.  Do be aware that shifting is subtly different when freewheeling vs when there's a load on the bike.
Answer: @Criggie has the correct protocol for setting up and indexing a rear derailleur.  I'll just add a few things.  You need to start over from the beginning so loosen the cable pinch bolt and completely disconnect the inner cable. This allows you to set the H limit without cable tension possibly holding the derailleur from it's full travel to the right. First, though, make sure that your rear wheel is fully within and centered in the drop outs.  The wheel and thus the cassette sprocket need to be in correct alignment for indexing to work properly.
You have barrel adjusters--one where the cable enters the rear derailleur and the other where the cable exits the shifter.  Begin with each of these adjusters about 2 full turns out from fully in. This will give you room to adjust cable tension both ways (increase cable tension by counter-clockwise rotation, decrease cable tension by clockwise rotation. You'll note that these adjustments will also move the derailleur's guide pulley in or out when the cable is reattached, allowing you to align the guide pulley with the correct cassette cog.  In your photo, there is a great deal of misalignment as noted by the sharp bends in the chain. A properly indexed derailleur running the chain on the correct cog will yield a straight chain between the derailleur's and from the cassette cog to the guide pulley.
In your photo, it appears the limit screws are nearly fully wound in and it's likely your derailleur is too limited and not getting far enough in either direction.  Check the wheel, disconnect the cable and begin by setting the high limit screw: proper adjustment will be when the guide pulley is right under the outside plane of the small cog.

Rear derailleur too far out


Is there a filter to edit html of user-edit.php

Question: I am looking for a filter to edit html of user-edit.php just before it is echoed. To be more specific, I need to disable selecting multiple roles in Other Roles. But this filter would be very handy for other stuff too. And for other admin pages as well.
Comment: there is no "Other Roles" in WordPress. it's certainly a plugin which add this. have you the extension "User Role Editor" e.g.
Comment: Sorry. I didn't know it's added by that plugin. I am using that exact plugin. But the question remains the same. How can i edit the HTML in admin.
Answer: instead of editing the complet content, it's quicker to find the hook to remove
e.g. for the "other role" menu, you can use that :
add_action("wp_loaded", function () {

    remove_all_actions("edit_user_profile");

});

Comment: This is not exactly what i was looking for. I don't want to remove it completely. I just want to disable the multi select of it and probably just make it standard drop down (``). Essentially what I need to be able to add another user role to each user. But I might end up using your solution and adding custom code to it.


Dark energy and virtual particles

Question: If space time is accelerating away from itself everywhere due to dark energy, could this acceleration be the cause of virtual particles, essentially Unruh radiation?
Comment: While I agree that virtual particles don't exist except on paper, I would also go with the general direction of the question... do the fields we know about couple to a quantized background that exchanges energy and momentum? I think intuitively the idea may have some merit, at least locally.
Comment: It seems that you believe that virtual particles are physical particles rather than mathematical constructs of QFT. Right? I like the question though.
Comment: Not really sure about their ontology, just spend too much time thinking and curious if there is any discussion of any connection between Unruh and them!
Answer:
If space time is accelerating away from itself everywhere due to dark energy,

In general , given asymmetric mass distributions, gravitational waves are generated from the space time distortions.

could this acceleration be the cause of virtual particles,

Assuming quantization of gravity and the reality of gravitons, the gravitons are not virtual they are real.  Graviton particle  interactions have very small probability and any virtual diagrams thought up will have a very small probability of acting on other fields. Since in terms of energy the expansion is very small it is only soft real photons that could come from such graviton  interactions.

essentially Unruh radiation?

from this link :

The Unruh effect is a surprising prediction of quantum field theory: From the point of view of an accelerating observer or detector, empty space contains a gas of particles at a temperature proportional to the acceleration. Direct experimental confirmation is difficult because the linear acceleration needed to reach a temperature $1~\rm K$ is of order $10^{20}~\mathrm{m/s^2} .$
Furthermore, the effect is necessary for consistency of the respective descriptions of observed phenomena, such as particle decay, in inertial and in accelerated reference frames; in this sense the Unruh effect does not require any verification beyond that of relativistic free field theory itself. The Unruh theory has had a major influence on our understanding of the proper relationship between mathematical formalism and (potentially) observable physics in the presence of gravitational fields, especially those near black holes.

Let us take an accelerating observer in Galaxy1 expanding from Galaxy2. If this observer measures the vacuum between the galaxies he/she should find Unruh radiation for consistency of general relativity due to the acceleration. Again the accelerating expansion is very small to allow for measurable effects, imo.

Dark energy and virtual particles


iPhone 6, charged overnight and now stuck in bootloop

Question: I left my phone charging overnight, and in the morning I woke up and the phone was stuck in bootloop.
The Apple logo came on, then the screen turned white, sometimes with 1 black horizontal line or sometimes a pixel (greenish).
Answer: While the screen is white I would try force restarting.
If that doesn't work, and you have a computer and some time, I would force it into DFU mode and restore it with iTunes.
HOWEVER, do not use DFU mode if you do not have a backup of the phone. In that case, I would take it to the nearest Apple Store and ask how they would suggest recovering your data.


Sharing name logos made with copyrighted fonts

Question: Is it legal to share name logos for free that I made using copyrighted fonts? Do I need to write which font I used?
Comment: What does the licence for the font say?
Comment: It says I can use it for personal and commercial purposes but cannot share the ttf file with others.
Answer: It depends what the license for the font says.
The license for Windows fonts, for example, allows pretty much anything including commercial use. You can freely design and distribute a logo containing Comic Sans!
Answer: united-kingdom
As far as copyright goes, such acts are explicitly allowed in the United Kingdom.

(1) It is not an infringement of copyright in an artistic work consisting of the design of a typeface—
(a) to use the typeface in the ordinary course of typing, composing text, typesetting or printing,
(b) to possess an article for the purpose of such use, or
(c) to do anything in relation to material produced by such use;
and this is so notwithstanding that an article is used which is an infringing copy of the work.

— Copyright Designs & Patents Act 1998

A licence cannot impose copyright restrictions on acts which are explicitly allowed in legislation. You are using a typeface (section 54(1)(a)) and distributing material produced (section 54(1)(c)).
The licence could regulate other acts.


Contact Cleaner VS Alcohol

Question: If I was to use contact cleaner on some connectors, Would this have a better or worst impact then using 100% alcohol?  Does contact cleaner leave Residue?
Comment: "contact cleaner" isn't a specific substance; it a marketing label. Some contact cleaners evaporate, others leave something behind, like some sort of lubricant or oleic acid.
Answer: The 100% alcohol would be considered as the ideal material to clean any electronic contacts as they evaporate quickly and leave no residue behind.
But the only problem with them is "100% pure alcohol is too expensive". (Its also one of the most explosive components.) So normally the manufacturer mix alcohol with other components (which might or might not be volatile) so that the cost and dangers can be minimized. Still alcohol is the main content of contact cleaners.
However the best solution for you would be to be reasonable with both cost and the materials used in the product that you want to buy. You can always check about the ingredient components that are used to make a cleaner. Depending on your design requirement you can purchase a specific one.
Nobody would advice you to go for 100% pure alcohol only unless you want to clean some really expensive equipment that has gold platting over the contacts.
Comment: Very rarely is alcohol cleaner really 100% pure, but it's available cheaply enough at 99% or higher, usually the remainder is pure water or something equally safe. Contact cleaners tend to leave a lubricating / corrosion inhibiting residue which may or may not be welcome on a connector as it may attract dust & dirt. I tend to clean most things with alcohol as it's pretty universally safe & effective on electronics.
Comment: Isopropyl alcohol bought at electronics shops seems to be 99.8%. It's neither expensive or particularly dangerous (it will burn if set alight). Your mention of it being "explosive" doesn't seem right to me. A lot of places recommend 70% solution ("rubbing" alcohol) but that's getting into the territory of quite a lot more water and other residues and I don't know how good that is for electrical contacts specifically.
Answer: See Kaz's answer-as-a-comment:
"contact cleaner" isn't a specific substance; it a marketing label. Some contact cleaners evaporate, others leave something behind, like some sort of lubricant or oleic acid. –  Kaz May 13 '14 at 3:29
Just now I used Isopropyl Rubbing Alcohol (70% USP) from the pharmacy, because it's what I had on hand, and it seemed to work fine--the 30% water evaporates almost instantly, which leads me to believe that any rust/oxidation it causes will be minimal. The 70% stuff seems to be more prevalent in stores.
Contact cleaners' additives are designed to keep the contacts sliding nicely. There's a sage-sounding discussion of it at the end of this article, starting at

Curiously, there is virtually no difference in contact resistance between lubricated and unlubricated contacts.

(There, the author is talking about electrical resistance, not sliding friction).

Contact Cleaner VS Alcohol


Finding the Truth

Question: I am trying to find information about my maternal great-grandmother.  We were always told that she was a full-blooded Cherokee Indian.  However, in doing a genealogy search, this is the information I found:  She was born on March 29, 1874, in Salamonia, Indiana and her parents were Augustus and Priscilla Burkey Kantner, originally of Pennsylvania, who I don't believe were Native American, but of German heritage.  Her son, my grandfather, looked very much like a Native American as do my uncle and many of my family members. She passed away when I was two years old so I have no memory of her. I do have a photograph of her and my great-grandfather.  Her hair is pulled up and she is dressed in English clothes.
Comment: Do you have specific information that you're looking for, Mary Ellen? As it stands this is a pretty broad question -- if you can narrow it down, you'll get more help (and you can always ask other questions about her later). What is the first thing you want to know? Perhaps: How can I find out if she was Cherokee?
Answer: You could try an AncestryDNA test. If you have a parent or grandparent do the test then your maternal great-grandmother's heritage would show more prominently than in your own test.

Finding the Truth


What is the "System" disk that shows up in Disk Defragmenter?

Question: When I run the "Disk Defragmenter" program that is included with Windows, two different "drives" show up. The first is, as expected, my C: drive. The second just shows up as System:

What is this System disk that shows up?
Comment: As far as I can tell, there is only one partition on that computer, but in a few hours I'll be able to confirm that from a Linux LiveCD.
Comment: It's the System partition. It's used by Windows and is not shown in Windows Explorer, neither does it have a drive letter.
Answer: It's a hidden partition used internally by Windows to store files related to the Boot Manager & Boot Configuration Database and BitLocker Drive Encryption.
More information is available at this Microsoft TechNet article:

If you install Windows 7 on a clean disk with no existing partitions,
  it creates a System Reserved partition at the beginning of the disk
  and uses the remainder of the unallocated space to create your system
  drive.That small partition isn't assigned a drive letter, so you won't
  even know it exists unless you look in the Disk Management console or
  use a low-level utility, such as Diskpart, to inspect the disk
  structure.

This "stub" of a partition, which is new in Windows 7, serves two
  functions. First, it holds the Boot Manager code and the Boot
  Configuration Database. Second, it reserves space for the startup
  files required by the BitLocker Drive Encryption feature. If you ever
  decide to encrypt your system drive using BitLocker, you won't have to
  repartition your system drive to make it possible.
If you're confident you'll never use BitLocker and prefer to do
  without the additional complexity of this System Reserved partition,
  your best bet is to make sure it's never created. For a truly clean
  installation starting from an unformatted hard drive, you must use a
  different disk-management utility, such as the setup disk available
  from many hard-disk manufacturers or a startup disk from Windows
  Vista. Create a single primary partition using all unallocated space,
  and then point the installer to the newly created partition as the
  setup location. (Note that you cannot use the graphical
  disk-management tools available from the Windows 7 DVD to perform this
  task.) After you use the alternative tool to create a partition on the
  drive, you can point the Windows 7 installer to that location and it
  will proceed.
If you're comfortable with command-line disk management tools, you
  can use the Diskpart utility from the setup program to create the
  necessary partition. At the beginning of setup, before you select the
  location where you want to install Windows:

Press Shift+F10 to open
  a Command Prompt window
Type diskpart to enter the Diskpart environment
Assuming you have a single clean hard disk, use select disk 0 and create partition primary to manually create a new partition
Proceed with the Windows 7 setup, using this new partition as the setup location
Answer: This is the System reserved partition where the Windows Bootloder is stored. Normally that partition is hidden and has no letter assigned.


Transform negative to affirmative?

Question: What is the affirmative form of the following sentence?

He is neither poor nor honest.

I tried, but couldn't transform it from negative to affirmative.
Comment: He is both poor and honest?
Answer: There is no singular "affirmative form" of the sentence.  The original sentence tells you something about what the person is not.  To make it affirmative, you would have to say something about what the person is.
It says he is not poor, but is he rich?  Middle class?
It says he is not honest, but is he a pathological liar?  A harmless rake?
"He is a rich liar" would be a simple example of how one might be able to turn it into an affirmative sentence, but that could significantly change the meaning of the text.
For example:  "It is red" tells you a great deal more about an object than "It is neither blue nor green."
Answer: Because the phrase poor but honest, well, isn't uncommon, I would read the above sentence as "He is a rich liar".
As Lynn notes, there are other, weaker, ways of reading it. And as Lynn further notes, it's usually more informative to tell someone what something is rather than what it isn't. However, there are usually pragmatic reasons for a speaker to choose a superficially less-informative phrasing.
To my ears, He is neither rich nor honest has a trace of irony to it. I'd attribute that to the use of scalar implicature. Compare, for example:
— So how did your date go last night?
— Well, she wasn't beautiful...
So what was she?
Implicatures are cancelable: That is, an utterance might suggest a meaning pretty strongly, but the speaker can always choose to say, No, that's not what I meant. For example, the litotic phrase isn't uncommon might mean is unavoidable; however, when I used it in my first sentence, I didn't mean anything beyond the surface meaning.
Answer: Not poor = lives above poverty = lives with material comforts
Not honest = dishonest

He lives above poverty and is dishonest.
He lives above poverty dishonestly.
He lives with material comforts dishonestly.
He lives with material comforts but dishonestly.
Answer:
He is both rich and dishonest.

or more simply

He is rich and dishonest.

or

He is rich, but dishonest.

Are the immediate affirmatives that comes to mind.
But the problem is that 'not poor' isn't necessarily the same as being rich. One can be rich, or one can have a modicum of wealth. There isn't a single word or phrase that expresses 'not poor' better than 'not poor'.
The affirmative for 'not honest' isn't so much of a problem, IMO. There are several words to express different levels of honesty.

Liberal with the truth.
  Known to tell lies.
  A liar.
  Dishonest

It really depends on the context, and what you're trying to say. If you're trying to say that the guy is rich, then you can use 'rich'. However if you're simply saying that he's not about to starve to death, then 'not poor' is what fits best.
For the honesty one, as I've mentioned, using an affirmative is a bit easier.
There's a poetic element to the phrase, but describing what this guy is not you paint quite a broad picture of what he could be. That might be more effective than trying to paint a specific picture, which might detract from what you're trying to say.
eg.

He was neither poor nor honest.

vs

He was both rich and dishonest.

The latter explicitly paints the subject's wealth and honesty as a key part of his personality. Whereas the former more allows the subject to act in certain ways in certain situations, without it being a key part of who he is.
Answer: The affirmative of

He is neither poor nor honest.

is

He is poor and honest.

This is not logic, but grammatical construct. Use nor to indicate a negative state, that continues after something else negative.
Neither/ nor is an example of a correlative conjunction.
If you want to retain meaning,

He is wealthy and mendacious.

Transform negative to affirmative?