Compact open topology

Question: What is the intuition behind using compact open topology for eg. in the case of Pontryagin dual ?
Comment: Wouldn't that go for any topology you put on the set of continuous maps between two spaces?
Comment: []:http://pages.bangor.ac.uk/~mas010/pdffiles/functionspaces.pdf

My paper "Function spaces and product topologies" (1964), available [here][1],  showed in the Hausdorff case that the compact-open topology allows for a non symmetric monoidal closed category of topological spaces. The non Hausddorff case was treated later by by Booth and Tillotson(Pacific J Math).
Comment: The reason I use the compact open topology is because it lets me view continuous maps between two spaces as a space. So it gives a function object in the category of spaces and that's what we need for it to be a monoidal category.
Comment: @David: About "that's what we need for it to be a monoidal category" --- You probably meant "monoidal closed".
Comment: It has to be functorial and satisfy the hom-tensor adjunction (sometimes called Currying). I don't think a random topology would do
Comment: Yep, monoidally closed
Comment: See Giving Top(X,Y) an appropriate topology for the topological and categorical background to this,
albeit without the group structure.
Answer: Given two spaces $X$ and $Y$, how to define the mapping space betweeen them, i.e. what topology should we put on the set of maps between them?
If $X$ is compact and $Y$ a metric space, this is quite easy as one can put a metric on $Map(X,Y)$: For $f,g\in Map(X,Y)$ define their distance just to be the maximum of the distances between $f(x)$ and $g(x)$ as $x$ ranging over the points in $X$.
If $Y$ is no longer metric, we have to find a replacement what it means for two maps to be close. Say, we have again two maps $f,g\in Map(X,Y)$. Let $K\subset X$ be compact and $U\subset Y$ be open such that $f(K)\subset U$. Assume now that $Y$ is Hausdorff (else, this construction might behave badly anyhow). Then $f(K)\subset Y$ is closed, so you would expect that if you move $f(K)$ a little bit, then it stays inside of $U$. So if $g$ is close to $f$, then $g(K)$ should be still inside of $U$.
Thus, it is sensible to define an open neighborhood of $f$ to be all maps $g$ such that $g(K) \subset U$. And actually, this agrees with the metric definition when $X$ is compact and $Y$ metric! Furthermore, as long as you have "enough" compact subsets in $X$ (i.e. $X$ is compactly generated) and everything is Hausdorff, then this topology has all the pleasant properties one likes.
Answer: I have a weakness for pictures. So here is one
 (source)
The above shows a function $f: \mathbb  R \to \mathbb R$, a  compact set $C$, and an open set $U$. The condition $f(C) \subseteq U$ is that the graph of $f$ passes through the shaded part shown in the picture.
Comment: I share your "weakness."
Comment: Great! This sort of justifies why compact-open topology is related to uniform continuity.
Answer: The compact open topology is essential for getting compact sets in your function space–especially a version of the Arzelà-Ascoli theorem holds for spaces of continuous functions to uniform spaces equipped with the compact open topology ($C(X,Y)$ with the compact open topology where $X$ is an appropriate topological space and $Y$ is an appropriate uniform space).
In your case (Pontryagin duality) the uniform space $Y$ is just the circle group $\mathbb{T}$ and $X$ is your group $G$. Consider a compact neighbourhood $U$ of the neutral element $e\in G$, an open neighbourhood $I:=\exp((-2\pi i\epsilon, 2\pi i\epsilon))\subset\mathbb{T}$ of 1 where $0<\epsilon<1$. Now there is a maximal set of irreducible representations $S\subset \hat{G}\subset C(G,\mathbb{T})$ such that $\forall \pi\in S\ \pi(U)\subset I$. The definition of the compact open topology guarantees that $S$ is open (it is just the definition). But $S$ is also equicontinuous: For $n\in\mathbb{N}$ define $U_0:=U$,$U_{n+1}:=\{x\in U_n\mid x+x\in U_n\}$. Clearly for $\pi\in S$ we have $\pi(U_n)\subset \exp((-2\pi i \epsilon/2^n,2\pi i \epsilon/2^n))$. It suffices to prove equicontinuity at the point $e$ (shifting does not change the situation). Now we can apply Arzelà-Ascoli: $S$ is in fact precompact and we get a compact neighbourhood $\bar{S}$ of the neutral element of $\hat{G}$ thus $\hat{G}$ is locally compact.
There is also a categorical motivation for this topology: The category of topological spaces is not cartesian closed, thus in this category (and many usual related topologies) the adjunction mentioned by David White in the comment above (currying) does not exist—it is impossible to choose the right topology. However, in the category of compactly generated spaces it works: It is cartesian closed and the topology for function spaces is the compact open topology. Again, the compact open topology guarantees that there are enough compact sets such that the topology is actually compactly generated (I guess that this is also a consequence of a version of Arzelà-Ascoli using even continuity, which does not need a uniformity, instead of equicontinuity, but I am not sure).
Answer: Firstly, it is natural to take this topology, because it's convergence is just compact convergence, or, in the case of locally compact Hausdorff spaces, locally uniform convergence. Then secondly, in the most structural proof of the Pontryagin duality using the Gelfand-Naimark theorem, you identify the Pontryagin dual with the structure space of the C*-algebra and the latter carries a natural topology, the Krull topology and it turns out that in the interpretation as function spaces this just is the compact-open topology.

Compact open topology


Why do we need a rooted phone to capture screenshots on older versions of Android?

Question: I realize in order to capture screenshots of my phone, all screenshot applications require I have a rooted phone. Why is this so? Why can't we have a simple screenshot application for Android, just like we have for Windows?
Comment: I have always found it interesting that the iPhone implements this feature out of the box while it is a major affair to enable on Android.
Comment: Note that since approximately Android 4.0, it is possible to take a screenshot by holding Volume Down+Power buttons; this is out-of-the-box functionality, no apps required (noted here for posterity and search engines)
Answer: The answer is rather simple, it's a permissions issue.
Android uses what is called a framebuffer for the video display. The framebuffer is located at /dev/graphics/fb0. this "file", which is basically a stream that the device writes to when changes in the user interface occur, contains ~2 frames of the screen display.
The permissions on the framebuffer file is rw- rw- ---. Note that the last "group" has 3 "-"'s. That basically means that if you are not the owner (which is root) you do not have permission to even read from that file.
If there was a system installed application, that could take screenshots, it would have permission to read from the framebuffer. Which, I believe, is how the Motorola Xoom is able to take screenshots. It has an application installed on the device, as a system app.
Reading the framebuffer, for a developer, is actually simple, if they have access to read it.
Comment: I think mod of o+r would be a security concern if just any market app could read the screen.
Comment: Sounds like Google should update the permissions into `r--`. This may create a security risk if any app can spy on your screen, but wouldn't it just be one of the permissions (*This app can monitor your screen*) you have to accept before installing? Either that or Google should add a built in screen capture in the menu fly-out, then no one else gets access to it. The latter my very well be the case, I mean they just now are adding print-preview to Chrome.
Comment: I think it depends. Windows OS does not prevent applications from taking its screen shoot. So far, have we heard any security issues caused by screen shoot?
Comment: Don't need to take screenshots in windows, there are far easier ways to get data off a windows machine. Mobile, i think, is a bigger concern. Just think about apps like Square, that processes credit cards. If I wrote a service that listened for when the card was swiped, I could possible do a screen grab and pull information like credit card number, name, etc.
Answer: Due to Android's security focus on separating all apps from each others' data, to prevent malicious apps from stealing or altering data in apps that you trust, they can't allow an app to take screenshots of other apps.
Think about how many of your apps are able to do things like OCR to translate pictures into text, I can think of at least four apps on my phone that can do this, prime example is Google Goggles OCRing book titles, and also OCRing and then translating blocks of text in foreign languages. Now think about how many of your apps put text on screen that you wouldn't want an untrustworthy app to see, I have a password database app on my phone with an encrypted database of my passwords for various systems, a malicious screensaver app could wait until that password app's running, take a picture of the screen with the login details on it, then OCR them and send them off. It could also do the same for everything in your Contacts list, even if you don't give the app permission to your Contacts database, or your browser history, or chat logs and so on. This is only one way that it could abuse access to your screen.
This is why for screenshotting to be universal it needs to be in the OS (which you already trust with all your data). This is why on phones that do have the screen shot function built-in it's been added as part of the system, not as a separate app.
If you root your phone and allow an app to take screenshots, then you are effectively saying that you implicitly trust that app to be able to do everything that the system can do, including accessing and interfering with other apps and their data, and that you totally trust it not to abuse that access. That's not something that Android's ever going to allow anything except the System/OS to do.
Answer: Short answer: Because 1) computers are Complicated and 2) the screenshot functionality is actually not very simple (for the programmer, not for the user).
In other words, taking a screenshot requires the screenshotting process to hook pretty deep into the OS internals, mess with them for a bit, and unhook again. Since Android tries to have a built-in security model (as opposed to the "bolted-on afterthought" seen in Windows), taking a screenshot trips on several security barriers. Those can be bypassed, but the only currently practical way (short of creating holes - and potential vulnerabilities - in the kernel) is to use the all-powerful root account, which is not subject to the limitations.
Comment: @John Isaacks, that is basically what happens with the framebuffer. see my answer as to why it still requires root.
Comment: I don't know much about computer hardware works, but I assume the GPU sends an "image" to the screen. Couldn't that image be intercepted and saved?


Wiring a ceiling fan with different wires from the ceiling

Question: I'm trying to wire a ceiling fan and light. I have 2 wires coming from the ceiling. 1 is a black, white and ground where the black is constant hot. The second wire is a black, white, ground and red and is only hot when I turn the wall switch on. There are 2 wall switches, one for the fan and one for the light but only the one wire (black, white, ground and red). How the neck do I connect it to work? Right now, I capped off the constant black and white wire and hooked up the other, black to black, white to white,, and red to blue and turn the switches on and it doesn't work.....
Comment: How was it wired before? Pictures of the switch box(s) and the ceiling box. It sounds to me that your set (sheathed cable) BWG is your live power from the breaker, and therefore needs to be wired differently to feed power to the switch(s).
Comment: Well, I don't remember how it was wired before. It was hooked up to a fan with a remote......
Comment: So should I connect the constant hot black to the other 2 blacks and the whites together?
Comment: Can you post a picture of the *inside* of the switch box?
Comment: The switch on the right controlled the light, the middle controlled the fan, and the left controls an outlet along the wall......
Comment: There is a 3 wire coming in the box and connects the the switch on the left. The 4 wire comes in from the top of the box and goes to the other 2 switches.....
Comment: I wired it, hopefully like you said and it keeps pooping the breaker. Pic above.....the constant hot black from the ceiling to the white from the switch box, the white from the ceiling to the white from the fan, the blue (black) from the switch box the the blue from the fan, and the red from the switch box to the black from the fan.....
Answer: This deal is sorely in need of some colored electrical tape.  Seriously.
There is one /3 cable (black white red) since ground is not counted as a conductor.   It is the same cable both in the fan box and the switch box.  On this cable:

Mark both ends of the white wire with black tape, to designate that it is for "always-hot".  Use of the white wire for always-hot is mandatory in this case, but also mandatory is the marking I just described.   This is the only mandatory marking; the rest a done for sanity's sake.
You see in the switch box where the white wire joins a black and red wire in a wirenut.  They are both short pigtails, also mark the red wire with black tape near each end, which will reduce confusion in that box.
The red wire exits the cable in the switch box, and hits a wirenut to connect to a red pigtail that goes to a switch.  We'll leave that all red.
The black wire exits the cable in the switch box, and hits a wirenut to connect to a red (!!!) pigtail that goes to a switch.  Annoying!  So we will:
get blue tape, and on the /3 cable, mark both ends of the black wire with blue tape.  Also mark the red pigtail with blue tape.

Ok, now counting the tape color, black = always hot, blue = switch 1, red = switch 2 and white is neutral.   This just got a whole lot easier.
Up in the fan box,  black gets nutted to black (which is the white wire remarked black, and NOT the black wire remarked blue).
Three wires remain: blue, red and white which is actual neutral.   That is what your fan needs.


How do I go about finding the bottleneck in a slow web based chat application

Question: I am working on a one-to-one chat application running in production. It uses StropheJS to connect to Ejabberd server over BOSH (using ejabberd's default connection manager). The main problem we are facing is that sometimes it takes a long time for messages to reach the other end (~30 secs or so) while otherwise they reach in no time. Something like this --
User A sends a message
User B receives instantly
---- [some more message exchange that happens instantly] -----
User A sends message
No message received by B
User A sends another message
Still no message received by B
...
...
(20-30 secs later) B receives the two messages together (not as a single message but without any noticeable time interval between them)
Apart from the chat, the other parts of the web application work fine.
I am having a hard time figuring out what is the exact bottleneck. It's running on a Ubuntu 10.04 instance (2 GB memory + 4 GB Swap).
One thing I should mention is that a single machine is used for hosting everything -- apache2, mysql, ejabberd, rabbitmq, mongodb, the message queue workers and the python web app served by apache2 using mod_wsgi. Besides, apache also serves some (very few) static files and proxies the BOSH requests to ejabberd. At any time apache has the max process count (around 40) and using 700-800 MB of memory so my guess is that it's doing most of the work. Per day, it's serves an average of 200k requests (this figure is obtained from access logs)
We have moved static files to be served from CDN (which had improved performance significantly) and had also logged slow queries and optimized by creating indexes which again resulted in overall perf gain although I plan to do the exercise tomorrow again.
Is there a systematic approach that can be followed to arrive at the bottleneck.
I am also confused as to,

whether switching to nginx will improve performance
whether it's time to move stuff to their own servers, probably they may be competing for resources on the single machine?
upgrade the memory on the machine
load balancing the http server (although I am a bit doubtful about this since New Relic shows almost negligible time spent in request queuing.)
What kind of measurements can be done on the frontend/backend to get an idea?

PS: It would also be great to have some suggestions on books to read for understanding the basics of server management/architecture/tuning.
Answer: I'd say you're putting a lot on a single box. Memory is just one metric. You could be hitting CPU bottlenecks when you get traffic, or you're limiting I/O. iostat will give an idea on the disk activity. You'll probably see the issue go away if you move services to their own servers (have your web server separate from the jabber one).


Are Wards actually useful?

Question: Is there any point to using these spells? They drain so much magicka it hard for me to believe there is an actual use for them. If there is a use can someone please tell me how and what combination of spells if any do they use with them.
Comment: There is a specific dungeon I was in with various wall traps that I could not pass without using a steadfast ward.
Comment: hmm interesting :O ty for the info +1
Comment: @GmNoob Labyrinthian by any chance? (you'll only get access during the Winterhold College quest-line but it's a massive dungeon that has all sorts of magic puzzles in it, usually one has just picked up the right spell trap. Also, there are some enemies that manage to use wards pretty well.
Comment: @ewanm89 shhhh. I try not to reveal spoilers
Comment: @GmNoob O right i remember that trap, not really the kind of traps i was thinking of...i was more thinking of physical traps(the massive swinging saws) i have really only come across that trap in the Labyrinthian.
Comment: Without reading the question,,, yes I am
Answer: It would be nice to hear from someone who does use them, but I remember looking at the math quickly and deciding against doing much with them. I'm revisiting that here with a bit more detail.
Here's how the wards break down (they add to armor and absorb magic damage):
<code>------------------------------------
Name      Cost/sec  +Armor  Absorbed
------------------------------------
Lesser         28      40        40
Steadfast      50      60        60
Grand         203      80        80
</code>
and here are fire projectiles (which all have rough equivalents in frost and shock):
<code>-----------------------------
Name           Cost   Damage
-----------------------------
Flames          12/s      8/s
Firebolt        35       25
Fire Rune      202       50
Fireball       247       40
Incinerate     255       60
Wall of Flames 101/s     50/s
</code>
and here are the mage armor spells:
<code>------------------------
Name        Cost  +Armor
------------------------
Oakflesh     90      40
Stoneflesh  170      60
Ironflesh   228      80
Ebonyflesh  292     100
</code>
So, here's my thinking: if you just want physical protection, Oakflesh costs as much as holding a Lesser Ward for 3 seconds but lasts for 20x that (while freeing up both hands), and the metrics just get more favorable from there. Plus, you can take ranks in Mage Armor to triple that. Oh, and ranks in Alteration let you take the Magic Resistance perk, which adds 10% spell resistance for each rank, and you get Atronach at 100, which lets you absorb 30% of the magicka from spells that hit you. Ward Absorb is nice, but still not enough, IMO, to focus on Restoration.
If you look at the Destruction spells, you'll notice that they can quickly break wards (no more than two spells), which has the nasty effect of staggering you. Often, I'd rather absorb an enemy mage's damage -- and elemental protection is cheap -- while backpedaling than get caught flat-footed by a warrior type. And whereas NPCs can put the ward back up immediately after a stagger and resume moving around, evading, keeping the ward up, and targeting you (made even harder by the ward's animation in first-person), I just don't have that coordination. Of course, I'd be very interested in a real strategy for using them, but I find it more effective to deal with the underlying problem -- enemies -- by dealing damage.
You could enchant equips to bring the cost down, but even then, I'd rather do that with a different school. The only exception I can see is if you have a bunch of spare magicka and a spare hand, particularly the less sneaky spellswords (I prefer shields with Elemental Protection, but to each his own). A more general use is for dealing with traps, as others have pointed out below.
So yes, I suppose that like everything it has its uses, but mostly for very specific character types.
Comment: I use wards when fighting dragons because stopping dragon breath with your hands is just plain cool :P
Comment: You just gave me the brilliant idea of using Wards to "more safely" disable Elemental Rune traps.
Comment: You could use wards and alteration spells and become a mage tank. Hell yea!
Comment: Yeah you follow roughly the same thinking as me im really interested to see if there is a ward expert out there that can actually enlighten me on why and how they use wards. +1 for a great answer confirming what i thought of wards
Comment: @RavenDreamer that's what I use them for.
Comment: traps is the only thing I use them for, and that's rare as I have good lockpick and sneak skills, it's only specific types of traps I can't avoid where I'll fire up a ward.
Answer: Wards are good for non-mage characters to help them out against magic-wielding opponents. It is not uncommon for a fighter-character specializing in melee weapons to also at least go a bit into the Restoration tree. Free healing during a fight is awesome, and there's not much else to use your magicka on before you smash your enemies' faces in.
If you have the right perks and some good timing, you can make yourself immune to most ranged spells as you close the distance to get some damage in.
Comment: +1: I only ever use this with my dual-wield warrior. I had to push stamina so hard that my health isn't high enough to soak a lot of spell damage. In this case the ward is super useful, as it gives me the time I need to close to melee against a ranged magic user. On the other hand, it's not uncommon that I just shout, knock them on their ass, and close that way, so it's not required.
Comment: hmm interesting i never really thought about fighter types using it.
Answer: I use the apprentice stone to regenerate magicka faster, but it gives me 100% weakness to magic attacks, so wards are necessary.  Plus, that 40/60/80 that it blocks doesn't stack.  When you cast your ward, notice it starts out weak, then after about 2 seconds it becomes full strength.  If someone casts a 50 damage fireball at you, your ward will block it all, then charge back up.  Basically, they have to damage you faster than your ward can recharge in order to break the ward.  You can hold your ward out and block fireball after fireball all day long if you have the mana and the opponent isn't casting with both hands seperately.  It's more useful than you think.
Comment: Hmmm interesting i have added wards as part of my arenal now your bring up some interesting points. +1
Answer: Regarding Ward vs Oakflesh:

Ward protects from spells, Oakflesh doesn't.
You can use them both.
Ward is in Restoration, which many people use.  Oakflesh is in Alteration which many people don't use.  Given high Resto skill and low Alteration skill, ward might be cost effective.

One of the big downsides of Ward is the cost.  You want a predictable situation to have the spell ready and to keep it active for as short a period as possible.  One such situation - traps.  Use Ward while running through swinging axe hallways or stepping onto a rune.
Comment: Ward and Oakflesh both add armor.  They reduce physical damage through this armor increase and do not "absorb" damage. Think of casting ward like equiping (but not blocking with) a shield.
Comment: Does ward Protect from physical damage as well? from what your it make me believe it acts like a physical shield, do you use a ward your self? +1 for raising some good points
Comment: ahh that makes sense ty for clearing that up =)
Answer: I made a pure mage character and fitted her with full daedric armor and a magicka cost reduction to destruction and restoration so instead of swinging swords I'm just throwing elements everywhere like a real battlemage should lol. Once you get to the higher end wards, magicka based attacks don't touch you at all while its out.
I stood in front of an elder dragons flame with it and it acted as an invisible wall. Pretty neat. You can also move around pretty well with it up and cast spells. You may not be able to bash with it but you can quickly switch the spell to use impact with a dual destruction spell to stun them. It also levels up your restoration when attacked just like a shield.
Wards are pretty good and saved me many times. They're not as good as shields but they're good enough in terms of melee damage reduction and frankly mages, dragon priests and daedra are much harder to kill than the melee enemies on par with em and it takes a few points in blocking to even get magic reduction on your shield or to enchant your armor or even make a potion good enough for it. also, getting the perk where you absorb magicka when a ward gets hit with a spell is cool too.
One thing that I've been trying out though is a shield on one hand and spells on the other. Melee enemies and archers are a lot easier this way then just switch to wards for mages and dragons.
Comment: Hmm yeah im pure mage to the ward seems to be fairly useless against melee damage but it is great against dragons i have yet to properly use it against a mage but im tempted to swap my conjuration/destruction to restoration/destruction.
Answer: I don't use them currently.  However, since it's possible to use fortify restoration enchants to make all spells in that school cost zero mana, you can negate the problem of the ward being too mana intensive.  If you combined fortify restoration with fortify destruction (using the extra effect perk), you could potentially channel a ward in one hand while spamming firebolts at the bad guy in your other hand.  At least, that's what the AI does to me.
Comment: lol yeah thats what i was thinking atm i am using destruction and conjuration without mana cost but im trying to work out if its worth remaking half my ebony Armour to add restoration instead of conjuration.
Answer: I use steadfast ward when I fight Dragons to absorb their fire or frost breath. I only have to hold it for a couple of seconds and then the breath stops and I can use that time to get off a couple of destruction spells. Lather, rinse, repeat basically haha. It may seem sort of tedious but after asking what their use was myself I found my answer and it's become an integral part of my Dragon-fighting.
Answer: No. I don't even use wards at all.
I carry around three double enchanted shields. They all give 20% spell resistance and 39% resistance to one of the three elemental spells. 100 enchantment rocks.
Answer: If you have 100 enchanting, wards are your best friends: with high enchanting skill, you can enchant your armor to make spells cost nothing, which will allow you to keep up wards all the time. Just keep one hand reserved for the ward, and use your other hand to do everything else.
Comment: Or your could enchant your armor to resist 85% of incoming magic and not lose the use of one hand.
Answer: I don't know if this has already been put out there, but I have items that boost my max magika, and my magika regen, and then in the other hand, I just equip a staff. If you have enough enchantments equipped, plus the increased magika regen in the restoration tree, then you can be regenerating magika faster than the ward would be draining it. the Ward Absorb is a must if you plan on using wards often. The last time I was up against an ancient dragon, I dropped it without my majika bar even showing up.
Answer: use wards in ranged fire fights with other magic users and the such. ward absorption thingy keeps your magicka replenished for the long haul so you could fire back twice as nice. you could dodge but, i deflect to absorb. oh, and i use it when im getting sprayed with conical projectiles to get all close like to other squishy mages and i give them the enchanted dagger.
Answer: Wards will completely negate certain shouts like unrelenting force and drain vitality. The former is good if you are engaging higher level draugr outdoors in an elevated location(prevents getting knocked off and falling to your death). With Dawnguard installed, it stops the Drain Vitality shout from Revered and Legendary Dragons(a fairly annoying shout since it ignores magic resistance and difficulty level). It should be noted the ward effect from daedric artifact Spell Breaker can do the same thing, but not for you if it's currently being used by a follower skilled in block. The good thing about using it versus shouts is you can hear the shout called out before it actually comes your way. You can wait to put the ward up until right before you need it and just keep it up long enough to negate the shout, thus saving magicka.
Answer: Wards negate magic damage entirely as long as you can keep it up, with even the weakest ward being enough to completely block dragonbreath from even high level dragons.
Oakflesh and Stoneflesh add armor but do not negate damage, they simply reduce it.
Wards are magicka expensive at first, but a few upgrades to magicka and perks in restoration and it can be an incredibly effective tool to provide relief from spellcasters.
As it is it takes 2 firebolts hitting in roughly half a second to break a lesser ward [the ward has 40 points of negation per second, it takes 25 from the first bolt and recharges enough to take a second in roughly a quarter-second] while a steadfast ward can take 2 fireballs in about the same time frame without breaking [60 from full down to 20 after a hit, back up to 40 half a second later]
Used effectively wards can completely disable magic attacks, especially since enemies don't tend to try and sync up their attacks to overwhelm wards making it very possible that you can take on a room of spell casting enemies with a ward in one hand and a sword in the other.

Are Wards actually useful?


How to sign hours on Logbook if doing aerial work in right seat on single pilot aeroplane?

Question: Recently I got an offer to work during the incoming summer as survey pilot, but since I do not have the required hours for insurance I can not be the PIC on left seat. So they proposed to be on the right seat until getting enough experience and then switch on. Can I sign those hours on the right if the aircraft is certify for single pilot operation? How?
Comment: @TimothyTruckle questions about regulations are on topic here, such as [What are the requirements for logging SIC time?](https://aviation.stackexchange.com/q/8969/1696) (FAA)
Comment: Also, I noticed you tagged "EASA regulations" so I assume that you don't care what the FAA has to say about the matter.  Is that correct?
Comment: Are you asking if a) you can fly from the right seat with another pilot in the left seat, or b) fly solo from the right seat?
Comment: Well, I am going to work in Europe under EASA rules, for that reasons I tagged EASA regulations. But if you got some info for FAA as well could be interesting to share some light.
Comment: This is a *legal* question. You cannot expect reliable answers for that here, only personal opinions.
Comment: The owner can name you as a pilot if he really wants you.  Not sure if that works in Europe though.
Comment: What makes you think which seat you're in changes whether you can be PIC or not?
Comment: @Pondlife a) fly from the right seat with another pilot in the left and log PICus.
Answer: I am not sure about EASA regulations but in the US you can log PIC time whenever you are the sole manipulator of the controls and properly rated to fly the aircraft.  In the US there is a distinction between the legal PIC (person legally responsible for the flight) and PIC time which is the person actually flying the airplane.  Since the plane is certified for only single pilot operations you can only log PIC time not SIC time and only when you are the sole manipulator of the controls.  The FAA regulations for logging time can be found in FAR 61.51.


What does the tty tag mean?

Question: What does the tag tty mean? It seems to be used sometimes synonymously with terminal, sometimes synonymously with console, even sometimes to mean command-line. Does it have a meaning of its own? Should we retag it away?
Comment: It can have a meaning of its own. If someone bothers to make a wiki description for it! Other than that, I don't even see much difference between [console] and [terminal].
Answer: A terminal is at the end of an electric wire, a shell is the home of a turtle, tty is a strange abbreviation and a console is […] :-)
Believe it, might, should keep on living, but with a decent wiki defining it. It could also perhaps be an idea to have a "see also: terminal, console, shell ..." and, in danger of perhaps breaking some wiki-convention, even a link to the above quoted answer/question or the like. (It is perhaps not possible in the excerpt / short-tag.)
In my experience, at least for Linux etc. users, where one usually have tty1-7 trough Ctrl+Alt+F#, and the familiar. (as in):
+-------------------------------------------------------------------- - -  -
|
| Welcome to Linux 3.10-rc1 (tty1)
|
| SERV login: _
|
. ...
|
| SERV login: john
| Password:
| Linux 3.10-rc1
| Last login: May 14 05:32:16 +0200 2013 on tty1.
| You have new mail.
|
| Blore's Razor:
|        Given a choice between two theories, take the one which is funnier.
|
| SERV@john: ~$

the light use of the word is for these access points to the system. Usually when explicitly referring to a non-X environment – as in: not terminal-emulator.
It kind of becomes a short-cut to express something in a way that hopefully is quickly recognized. I.e. "When on tty4 …", "X went nuclear so I logged into another TTY …", etc.
Whilst terminal often, but not always, is used to express virtual emulators in a GUI environment. And console get a mixed use between them all. I seldom see anyone use the phrasing tty-window, but it happens.
I do not know how the tags affect the underlying logic of e.g. search beyond direct specification. But at least for those of us frequently using "[some_tag] search term" the use of tty would perhaps have it's purpose.
Though, as a side point, I rarely use it here, but mostly on Stackoverflow for [C], [asm] etc. where it definitively is a saver.

Point of i all being how to express the tag-wiki in a way best served. Giving the possibility to re-tag if far off, and also being a source of information thus learning.

A short undecided discussion with myself and you all.
So; what does the tty tag mean? Quickly realizing that this did not became an answer, I'll leave it in hope it might give some input on how and what to do. If not I can delete.
Answer: ttys are special files (i. e. an interface provided by kernel) for terminal devices, and things directly related to it (stty, line vs character mode, etc.).
console is an actual set of devices and stuff specific to it (virtual consoles, loadkeys, setfont, framebuffer vs VGA, raw vs cooked keyboard in Linux, etc.)
Ī̲ don't know whether a useful denotation for terminal can be defined under current conditions of this site. It is so broadly used that ceased to be selective; seemingly for anything related to TUI (mostly run within emulators by modern users). Whereas specific tags (terminal-emulator, pty) are underpopulated and neglected.

What does the tty tag mean?


Can operations research be used for protein folding?

Question: I understand from this active COVID-19 question: Are there any COVID-19 (coronavirus) related optimization problems with input datasets that we can "crowd solve"?  that the protein folding problem is very important in the fight against COVID-19. When I look for OR studies about the problem, I reach the "Variable neighborhood search for graphical model energy minimization" article. "Computational Protein Design" problem is mentioned in the article. Also, there are MIP, LP and similar approaches for solving the protein design problem. The relation between folding and design is explained as "The protein folding problem has two components:  the 'direct' folding problem (i.e. folding) and the 'inverse' problem  (i.e. protein design)". I am looking for OR resources (starting point) for the problems (such as a book) and ideas about solvability of the problems from experienced researchers.
Answer: A good starting point is to look at the following Wikipedia resources:

https://en.wikipedia.org/wiki/Protein_design
https://en.wikibooks.org/wiki/Structural_Biochemistry/Proteins/Protein_Folding_Problem

The biochemistry problematic is described and the related mathematical optimization problems are discussed. Now, the state of the art on this topic can be found in this book. Note that an interesting discussion related to the topic can also be found on this forum.
Answer: Optimisation technology is practically irrelevant for protein folding because of the garbage-in garbage-out rule.
Our models for molecular interactions are simply so bad that solving Gibbs free energy models is pointless in practice (from an optimisation point of view).
Just to give you a bit more context about the state of the art, people are still struggling to model water properly (let alone very complex structures like proteins).
The underlying reason is that these models are only approximations to the interactions encoded into the Schroedinger equation, but the resulting modelling error makes de Novo based molecular design kind of pointless.
Until we can actually solve the Schroedinger equation at large scale (or somehow devise simple models that approximate it extremely well), discovery of new molecular compounds will be driven by experiments and empirical knowledge.
Answer: Protein folding calculations have been turned into QUBO (quadratic unconstrained binary optimization) in this paper where the goal was to run the calculations on a quantum annealer (in OR we are familiar with "simulated annealing", so think of quantum annealing as "real annealing" or "not just simulated" annealing).
The "objective function" for the optimization is in the first equation of the above paper: $$E({\bf s})=\sum h_is_i+\sum J_{ij}s_is_j\tag1$$ where $s_i\in\{0,1\}$ and $h_i$ and $J_{ij}$ are just real numbers: Basically you are just trying to minimize a quadratic function of binary variables, to get the lowest energy configuration of the protein.
Unfortunately there's better ways of solving the protein folding problem using molecular dynamics and other types of physics/chemistry simulations, than to convert the problem into QUBO and then solve the QUBO. This seems to be the case with all QUBO problems, as I have not yet found a case where converting problem "A" to QUBO form, then solving the QUBO, is better than just solving "A" in its original form without "forcing" yourself to use OR techniques via QUBO.


Is there a fee to be paid to reactivate a bank account of an American citizen?

Question: I'm a South African and was listed as beneficiary of a fund from an American citizen. I've received correspondence that the account which the fund was paid into has been inactive for a very long time and it must be reactivated with a fee of US$200 before the fund can get transferred.
Comment: If it's *your account* why can't you ask your bank?
Comment: Was this correspondence via email or letter?
Comment: Do you *know* an American citizen that might have listed you as a beneficiary?
Answer: This has all the hallmarks of a scam. If they really needed to charge a fee they could deduct it from the account balance. And if this fund has existed for a long time why didn't you already know about it and do something about it before?
If you have reason to think it is legitimate, e.g. you actually knew the "American citizen" the money came from and have reason to believe they left/gave you money, then you should get it sorted out by contacting them or their executors, or the bank where the money is directly
Comment: @Nathan, don't "try and get to the bottom of it" - it's a scam. Delete the messages, block the sender and move on.
Comment: Another point is that if the account had a significant amount of money in it, as would almost  certainly be the case if it's a trust fund (and if the amount isn't significant, why are they bothering?), then the bank would almost certainly be perfectly happy to let the account stay open, collecting interest.
Comment: @jamesqf the risk of false negative here is tiny given the background numbers. This probably happens legitimately (and without the $200 fee required) like once per 100,000 people a year. On the other hand attempted scams like this happen more like 1,000,000 times per 100,000 people per year (I certainly get at least one such email per month). So that's million to one odds.
Comment: Thank you I will try and get to the bottom of this. Your response is highly appreciated
Comment: @Vicky: There are instances where people have been left legacies (or distant relatives inherit if the person dies intestate), and "heir hunters" locate them, so something of this sort COULD be legitimate.
Comment: @jamesqf in many American jurisdictions, accounts not accessed for several years are turned over to the government.
Answer: If it isn't a scam, then all of the following need to be true.
The lawyer who contacts you will give their name, practise name, address and phone number.
Googling that practice name will come up with a website with the same address, and ideally the same phone number. If it is not the same phone number, calling the number on the website (not the phone number they gave you) and asking to be put through to your contact will reach them.
The lawyer will send you a physical copy of the will in the mail.
The lawyer will tell you which bank it is, which branch it is, and what the account number is.
Calling the bank's customer services department via the number on their website (not a phone number they gave you) will get through to someone who can tell you whether this is correct, and why the money needs to be paid by you instead of being deducted from the closing balance.
If any of these does not happen, it's a scam.
Comment: Also, the lawyer will be listed at the relevant bar association, and the bank will be listed by the bank supervisor. Use independent sources of verification.
Comment: I haven't seen one personally, but I image some inventive scammers have their own website that will pass the "googling" step above. Better to verify independently with other sources like the bar association.
Comment: @MSalters Yes, I tried to lean on the "verify independently" angle there.  Certainly don't trust anything!
Comment: @studog Some have done imitation websites, yes. But Google doesn't list them, or at least they're not going to come high in the search rankings. So googling for the bank is pretty reliable. Unless the bank itself is entirely fake, of course.
Comment: "practice", not "practise".
Comment: @Acccumulation Thanks! On my phone, and that one got past me. :)
Answer: In my experience, there can be "slap on the wrist" fees charged by banks for this sort of thing, so the premise is not entirely implausible. That being said:

$200 is absurdly high for an account reactivation fee - keep in mind, the bank usually wants to keep your business.
Typically, dormant account fees are automatic. In other words, you don't have to agree to pay the bank anything - they will just automatically debit your account, say, $5 a month until the funds are considered abandoned and surrendered to the state (or the account balance reaches $0). From the banks point of view, they're trying to extract a bit of income from customers who are not coming back. Requiring approval from the customer to assess the fee would make it very difficult to get any income on truly inactive accounts.
Most banks will happily waive or even refund some/all these fees for you if you ask politely. The fees are designed to generate income from balances that would otherwise be surrendered to the state - typically, you will be worth much more to the bank in the long term as an active and happy customer. Think about it from the bank's perspective: if you stand to inherit a bunch of money, the bank would love to do you as many favors as possible to increase the chance you leave the money in an account with them when all is said and done.

Listen - I can't promise with 100% certainty that this is a scam, but I'd happily give you 50-1 odds on it. It's got all the trappings of a scam (unexpected, small initial request, different country).
Answer: Scam. Scam. Super scam.
It has all the red flags of a scam pitch.
Out of the blue, you get contacted.   Didn't expect it, no advance phone calls, and you don't know the person.
... Always through some media that is extmely low cost to send out.  (as opposed to how a real executor would operate, first class mail ($1.20) or certified ($10ish).  Because they sent out a million of these, because that's how many they need to send to find a few suckers, and they'd go broke sending them certified mail.
... Because a real executor of an estate has access and authority to spend the assets of the estate itself, to pay for the costs of managing the estate, including hiring a detective to find you if need be.
You are in a fortunate situation, dear sir! A bunch of money will be coming to you Real Soon Now.
... From someone you've never heard of.  Yeah, right.  (or possibly from someone you have heard of; if you're active and public with genealogy, scammers can scrape that data and look for distant relations who have recently died.)
However, you need to put forward a little money to unlock it.
Bunk. There's no such thing as bank reopening fees. If there were, the bank would simply take the fee out of the account itself, directly: the $40,000 account would reopen with $39,800.  Or in the unlikely possibility the executor of the estate had to front that money, the executor would simply do so from other estate assets. Or go to court to get a judge to resolve the situation.
What will really happen is more roadblocks, more fees.
Scammers know what they're doing.  The $200 is a carefully calculated number based on the experience that it's an amount that many people will spend for the chance.  But here's what happens next.  The scammer tells you that it worked.  And you are thus assured the deal is legitimate, and you are relieved of that worry.  Your money will be along soon.
However, there's another issue, perfectly normal in this case. Another fee is needed; it's $500 but of course this is a pittance compared to the amount you're due to receive.  Can you go ahead and send that along please.
Now what has happened?  You've already sunk the $200.  But this thing has been proven to be legitimate, because it's working.  I'm getting contacts from other people, a thing in actual mail just showed up for me to sign (funded by your $200)... it's the real deal.  Besides, why would I start believing it's a scam? I've already sunk $200.  If I back out now, the $200 will be wasted.  This last bit is called "The fallacy of sunk costs".
So yeah, this logic will prevail someone to go deeper and deeper into the scam. And believe me, the scammer will be badgering you with all their strength to continue, and using cohorts to also try to convince you this is real.
Scammers know precisely how to game the "fallacy of sunk costs". The most effective (profitable) point is around 2.5 times the last payment.  So it won't be an accident that the next payment will be around $500, and the next around $1300 give or take.  They'll keep doubling this and-then-some until you simply run out of money and credit line.
Oh, but I'm hellbound and determined to fall for this. It's free money!
OK, then you get a lawyer in the US to find this money for you.  Here's how you get a US attorney.  First, search mainstream media news reports for something lawyer related - get the name (from the CNN news report) of an attorney firm.  Then call them up and describe your problem coarsely. They say "We don't handle that kind of case" (this is good!)  You then ask "If it was you, who would you hire for that type of job?"  You will get a candid reference to the best lawyer in town.
Now, you have a bona-fide US attorney.  Tell them what the scammer has told you about this money you're supposedly owed and who has it.
Understand the very important difference between someone who seeks you out, and someone you seek out.  The person who seeks you out, unbeknownst to you, has sent this same come-on to millions.  But when you call a lawyer's office who you have identified as bona-fide, and get a reference from them, you're not going to happen to get a scam lawyer, because scam lawyers don't get references from other lawyers.**
The lawyer you picked is going to do all the legwork on this opportunity.  Now, there are two ways to pay for this.

You can pay them for time and materials out of your own pocket.  I note that you were seriously considering sending up-front money to some scammer, so clearly, you don't have a problem with this "up-front" payment strategy.  Upside, you keep ALL the winnings. Downside, you're out the cash if it's a bogus deal, but you're already comfortable with that.
You can pay them on contingency, or typically 33% of the winnings.  However, once they hear your story, no lawyer will agree to do that, because they will recognize it as a scam, and will know there is no winning at all, and 33% of nothing is nothing.
Comment: @RonJohn international.  The scammer is not in ZA and probably not in the US either.
Comment: *first class mail ($1.20)* Where?
Answer: It's a scam!
At least, that's my initial gut feeling.  Here is a key reason why I'm inclined to think that:

the fund was paid into has been inactive for a very long time

If this were legitimate, the money is likely not in the account any more.
I recall a scene from a television series called Highlander where a person who no longer ages, and who is now hundreds of years old, withdrawals money that has been gaining interest for centuries based on a very old deposit.  Well, it's an interesting theory, but with today's financial laws used in America, the ability to do such a thing might be even less likely than an un-aging person who is a few hundred years old.
Case in point: I had some money sitting in a checking account.  This was not my primary account, and so I just ignored the money for a while.  After about 3 years and 8 months, the bank closed out my account and gave it to the state I live in.  Now, if I wish to retrieve that money, I need to contact the state.
From my brief research into doing that, I suspect the specific details vary from state to state.  In the state where I live, financial institutions are supposed to do that after 3 years of inactivity.  In my case, this happened before the 4th year.
If the letter doesn't even tell you which state laws this account is in, that would indicate that this "bank" is being vague on the details, which would be another flag of this being legitimate.
Comment: @RonJohn The fact that the term for this is "escheat" (Law French) provides a guideline for how old it is!
Comment: Sending old money to The State is at least 35 years old, not a consequence of "today's financial laws".
Comment: I meant in contrast to laws from hundreds of years ago.  I didn't mean to suggest any specific change that happened within some of our lifetimes.
Comment: @WoJ to be clear, when an account goes through escheatment in the US, the bank does not literally give the money to the state in the sense of the state taking ownership. The state simply becomes the custodian of the account (the bank no longer maintains it), the original owner retains permanent title to the account. In effect it's very similar to the process you've described, and most US states have websites that operate similarly to your example, where you can verify your identity and receive your property, no matter how old it is.
Comment: @dwizum: ah ok, thanks for the explanation. yes indeed, this looks very much like the French service Ciclade (https://ciclade.caissedesdepots.fr/)
Comment: Many financial laws have been changed in the last twenty years to fight terrorism and money laundering, so "today's financial laws" **does** have a pretty specific meaning.
Comment: *After about 3 years and 8 months, the bank closed out my account and gave it to the state* This is an interesting approach - to **give money** to the state after a short period of time :) Here in France the government wanted a few years to rationalize the management of old accounts by moving them (as it) into a centrally managed "banking institution". I had an old account (30 years old) with a few euros on and finally went to the bank to claim it. They gave me a document stating that the account was moved and I needed to apply for the money on a web site. It went surprisingly smoothly
Comment: It's very similar. For reference, here's the website for New York State: https://ouf.osc.state.ny.us/ouf/
Comment: For reference, my state's web page mentions a URL of ClaimYourCash.org which simply redirected to https://ucp.dor.wa.gov (Unclaimed Property site at Department of Revenue for Washington State's government) where it seems I can claim things free of any fees/charges.  Today when I checked, the top banner picture has the following text: "Chances are 1 in 2 that you or someone you know has unclaimed property."
Comment: I suspect they greatly exaggerate the number of people who actually *have* unclaimed property as an enticement to get you to at least *check*.
Comment: @chepner I wouldn't assume that's an exaggeration. Many states have an astounding volume of unclaimed property in their care. I just checked my state's website and out of myself and my 4 siblings, three of us have unclaimed property in the state's care right now. It's not just bank accounts - escheated property can come from uncollected insurance claims, old paychecks, refunds owed for overpayment of utility bills, unclaimed class action settlement checks, and so on.
Answer: A perfectly legal, but (IMO) sleazy variant of this scam:
In my state, California, "abandoned" bank accounts are turned over to the state after three years of inactivity, and other unclaimed monies (i.e. funds from an uncashed paycheck) can also get turned over to the state.
If the balance is high enough, it will draw the attention of lawyers who will offer to retrieve the money for a finders' fee. Or, you can just go to the California unclaimed property database and fill out the claim form yourself for free.
Other states probably have similar setups and similar people who offer to fill out free online claims forms for a fee.


Are there any miracles in the holy Quran?

Question: Are there any miracles in Quran such as fact it contains, that people at the time had no knowledge about but later they know it was the truth or it is associated with an event that can only be miracle or it is associated with something miraculous? I am not asking about the miracles mentioned in the Quran.
Comment: This is whole site is just for you....
Miracles of Qur'an - Proven and talks science that most of us don't know... http://www.speed-light.info/miracles_of_quran/
Comment: please specify you mean miracles of prophets mentioned in stories in Quran. or miracles today acceptable by non-Muslim scientists as a miracle bracking Natural laws.
Comment: I think it would be good to clarify the question a little bit. Right now it is not clear if you are talking about 1) miracles performed by our prophet and mentioned in Quran, 2) Quran itself as a miracle, 3) miracles by other prophets and mentioned in Quran.
Comment: I heard miracles like if you are in hot dessert and there is no where you can hide, quran will provide shadow for you. Or may be some thing that was told to us in Quran, the chances of it happening was close to 0 but it happened after 1300 years or so. But the question is aimed at first type of miracles but would like to know the second type as well.
Comment: 4 answers where given before muslim1 clarified question in comment and they where not changed since that and they are now not appropiate. then there were not new answers for long time. then appeared answer of Zohal. then muslim1 edited his question at Nov 20 '15 at 17:22 and its meaning is again changed. then appeared answer of ysn_akst.
Comment: "or it is associated with an event that can only be miracle or it is associated with something miraculous? I am not asking about the miracles mentioned in the Quran" - i understand here as contradiction. please edit.
Answer: They're indeed 14 miracles done by prophets which have been mentioned explicitly. You might look at their meaning and interpretations to find out the story behind them:

Al-Qamar: The Hour has come near, and the moon has split in two

Taha: And We had inspired to Moses, "Travel by night with My servants and strike for them a dry path through the sea; you will not fear being overtaken [by Pharaoh] nor be afraid [of drowning]."(77)

Taha: And draw in your hand to your side; it will come out white without disease - another sign,(22)

Al-baqarah: And [mention] when Abraham said, "My Lord, show me how You give life to the dead." [ Allah ] said, "Have you not believed?" He said, "Yes, but [I ask] only that my heart may be satisfied." [ Allah ] said, "Take four birds and commit them to yourself. Then [after slaughtering them] put on each hill a portion of them; then call them - they will come [flying] to you in haste. And know that Allah is Exalted in Might and Wise."(260)

Al-Isra': Exalted is He who took His Servant by night from al-Masjid al-Haram to al-Masjid al- Aqsa, whose surroundings We have blessed, to show him of Our signs. Indeed, He is the Hearing, the Seeing.(1)

Saba: And to Solomon [We subjected] the wind - its morning [journey was that of] a month - and its afternoon [journey was that of] a month, and We made flow for him a spring of [liquid] copper. And among the jinn were those who worked for him by the permission of his Lord. And whoever deviated among them from Our command - We will make him taste of the punishment of the Blaze.(12)

Al-anbia': They said, "Burn him and support your gods - if you are to act."(68) Allah said, "O fire, be coolness and safety upon Abraham."(69) And they intended for him harm, but We made them the greatest losers.(70)

Al-ankabut: But We saved him and the companions of the ship, and We made it a sign for the worlds.(15)

Ali imran: And [make him] a messenger to the Children of Israel, [who will say], 'Indeed I have come to you with a sign from your Lord in that I design for you from clay [that which is] like the form of a bird, then I breathe into it and it becomes a bird by permission of Allah . And I cure the blind and the leper, and I give life to the dead - by permission of Allah . And I inform you of what you eat and what you store in your houses. Indeed in that is a sign for you, if you are believers.(49)

Which includes three miracles.

Al-araf: So Moses threw his staff, and suddenly it was a serpent, manifest.(107)

Ash-shoara: Then We inspired to Moses, "Strike with your staff the sea," and it parted, and each portion was like a great towering mountain.
(63)

An-naml: And put your hand into the opening of your garment [at the breast]; it will come out white without disease. [These are] among the nine signs [you will take] to Pharaoh and his people. Indeed, they have been a people defiantly disobedient."(12)
Answer: There are many miracles told in the Qur'an, like the raising of Jesus:

بَل رَّفَعَهُ ٱللَّهُ إِلَيۡهِ‌ۚ وَكَانَ ٱللَّهُ عَزِيزًا حَكِيمً۬ا
(١٥٨)
Nay, Allah raised him up unto Himself; and Allah is Exalted in Power, Wise. (158)

Surat 4 Ayah 158
And there is the Isra'a:

سُبۡحَـٰنَ ٱلَّذِىٓ أَسۡرَىٰ بِعَبۡدِهِۦ لَيۡلاً۬ مِّنَ ٱلۡمَسۡجِدِ ٱلۡحَرَامِ إِلَى ٱلۡمَسۡجِدِ ٱلۡأَقۡصَا ٱلَّذِى بَـٰرَكۡنَا حَوۡلَهُ ۥ لِنُرِيَهُ ۥ مِنۡ ءَايَـٰتِنَآ‌ۚ إِنَّهُ ۥ هُوَ ٱلسَّمِيعُ ٱلۡبَصِيرُ (١)
mi>Glory to (Allah) Who did take His Servant for Journey by night
from the Sacred Mosque to the Farthest Mosque whose precincts We did
bless― in order that Weght show him some of Our Signs: for He is the
one Who heareth and seeth (all things). (1)

But The biggest of all miracles is the Qur'an itself.
Answer: Please read this question I asked before:
Did the stories in Quran happen as is, or are they symbolizing different and more common events?
There is a strong possibility that stories and terms in Quran are symbolizing more realistic events. Quran is not a fantasy book, it is a realistic book that brings solutions to humanity in all eras and ages. It must be pointing out the actual and realistic facts by telling us that kind of stories.
Quran is only 600+ pages. Text in its pages are not condensed. In an ordinary page of it, there is approximately 20% of text compared to any other text book. When you condense it to a standard text book format, it becomes only 100-150 pages. And, I have to add that, most of the Quran is repeating the same stories, warnings and phrases. For example, story of Musa (Moses) is told 50+ times. If you remove the duplicating parts, it becomes only about 50 pages.
Now there is a problem of condensed information.
Supposed that you are working in an information department. They wanted you to write a book, consisting of only 50 pages, or 150 pages with repeating parts, which will be a solution to the entire problems of the world, will bring a perfect system for daily life, and will be perfectly consistent inside.
And, also suppose that, you had never heard of Quran before. What would you write in your book?
Quran is a solution of this problem of condensed information. No human can solve this problem and write a similar book solving all the problems of human. A special book like that must have a special way of explaining the issues (i.e.; with those supernatural stories). Unfortunately, most people think this kind of things with a skeptic mind, it is not possible to discuss these kind of things openly.
Answer: Surah Lahab is also considered as miracle of Quran
If you notice, Allah dooms Abu Lahab to Hellfire in this surah. Now, the mufassireen (interpreters) point out an interesting point–at any time, Abu Lahab could have accepted Islam–even as a fake-out. And he could have said "Hey guys, I'm Muslim now, how come the Qur'an is claiming I'm in Hellfire?" And that would've caused great fitnah.
But he never did.
And Allah knew that he wouldn't.
And so, we see even in this small, oft-repeated surah, one of the miracles of the Qur'an. More about Surah Lahab can be read here
Answer: If your question is asking does the Qur'an mention any miracles:
The Qur'an makes mention of many miracles which took place to help the Prophets and the believers.
If your question is asking is the Qur'an a miracle:
The Qur'an is the words of Allah and sent down the the Prophet Muhammad (saw) the Angel Jibrael. Therefore it is a miracle.
If your question is asking can the Qur'an be used as a miracle:
The Qur'an can be used as a protection. The verses can be read to keep you safe. The Qur'an is a medicine. The words can cure an ill person. Reciting the Qur'an has many benefits. I have even read once in an article that it has been scientifically proven that reciting the Qur'an or even just listening to a recitation improves our memory and keeps our brains health. It also boost up our immunize system. Recting Ayat Al Kursi acts as a barrier against all evil and nothing can harm us. Even if a thief was to rob you they would lose their way be unsuccessful. These are all miracles and the blessing of Allah.
Comment: I appreciate your response which has stated from different aspects and angels. Well done. و من الله توفیق
Answer: There are miracles of prophets as Gigili mentioned. But also, The Qur'an is a miracle

But they say, "Why are not signs sent down to him from his Lord?" Say, "The signs are only with Allah, and I am only a clear warner. And is it not sufficient for them that We revealed to you the Book which is recited to them? Indeed in that is a mercy and reminder for a people who believe." [29:50-51}

You can check this book out http://www.quranmiracles.com/wp-content/uploads/2016/03/The-Quran-Unchallengeable-Miracle.pdf


To share a summary of a book, and put my name on it, is illegal?

Question: I made a summary of a book I used in class years ago in order share it with my students.
In the summary, I took whole sentences and equations from the original book, and reduce the pages from 600 to 200, my intention at that time was to give to my students a more compacted book which implemented the important information for the class.
The mistake I made was to put my name in this summarized book and shared the book with my students. My name is on the cover and in all the pages.
Back then, I did not consider this could affect me, but I realized weeks ago that the book was uploaded to the internet through Scribd and SlideShare.
I have been extremely preoccupied since then. I fear the editorial of the original book can take legal action against me.
Do this can lead to legal problems?
The summarized book has been on the internet since 2011, is there the possibility of a demand coming from the editorial or author of the original book?
Answer: The basic question is whether you "copied" the book, which is not limited to verbatim cut and paste type copying. Even with verbatim quotes and equations copied from the book, some amount of that is allowed under the fair use doctrine. There is not much (any) clarity in the law when it comes to educational-use quote-copying. However, based on your description, I would not conclude that this work counts as "fair use": but a judge or jury might decide it is, depending on the exact facts.
If you reduce a 600 page book to 200 pages, that sounds like "copying" while creating a derivative work. This would be especially the case if the structure of your book strongly resembled the structure of the original book, and what you did was omit some sentences and reword some sentences. On the other hand if you wrote an independent book on the topic, happened to reflect the original author's ideas, and even copied a small amount of text by way of illustrative quotes, then that resembles an independent creation rather than copying.
There are 4 plus factors recognized in the fair use defense, where the fact-finder would somehow "take into consideration" these factors: purpose and character (non-profit, teaching, exegesis all in your favor), nature of the work (equations implies science hence facts, being factual favors fair use), amount and substantiality (not in your favor, if you're paraphrasing a whole book), and effect on market. As a first approximation, your work might have a devastating effect if your work is good and the original is expensive plus popular – you created a free competitor. Framed in terms of your intended original use, probably not so significant, limited to the size of your class (assuming that your work was a replacement for, and not a supplement to, the original – which may be what you did). The law isn't stated in terms of your intent in creating the work, it's stated in terms of what you did. Still, the fact-finders might be influenced by innocent intent. Then finally, there is "transformativeness" as a unifying consideration, so that copying that substantially transforms a work into a new work fares better under a fair use analysis – this would appear to be a quite transformative work.
Whether or not the rights-holder is likely to go after you depends on many unknowables, especially whether there would be any point in suing you, and how much the publisher and author care.
Regardless of the relationship between the original book and your version, you have created a work that is also protected by copyright. That means that it is illegal to upload your work to Scribd, Slideshare, or anywhere else, without your permission. When someone illegally uploads a work to a server, if you learn about it, you as author can file a DMCA takedown notice. A law-abiding service will then take the work down (unless the uploader officially claims he has the right to upload it). If they do claim they have the right, you have to sue them. So even if it's all over the internet, you can play whack-a-mole with copies and get many of them taken down.
Comment: Thank you so much, you gave me some light on the problem, and I did not know about the possibility to take the documents down from the websites, I'll definitely try to communicate with the websites to asked them to remove the documents. Thank you again!
Comment: Hello, I have another quick question, I really appreciate the time you put on the answer. I have some other doubts. Is there a fixed amount of time in which the crime or illegality must be ignored even if the editorial realizes it?. The illegal derivative work was made six years ago, I've read that after ten years the offense cannot be considered for trial. Is that true?
Comment: That is a related but distinct question of independent interest, and you should ask it as a separate (preferably general) question.


Is it possible to extend the life of a star?

Question: Is it true that when a star 'runs out' of its fuel, it hasn't really used up all its hydrogen, it still has hydrogen left, but the hydrogen is not at its center where the fusion happens. If something crashed into it rearranging its content a bit, could its life be extended?
Comment: I suppose in theory you could suck the helium out of the core, but I suspect the technical difficulties would be insurmountable.
Answer:
If something crashed into it rearranging its content a bit, could its life be extended?

Yes! This is precisely what we think causes the creation of blue stragglers.
When we look at a cluster of stars, we expect them to all be of roughly the same age.  This is usually borne out by observations.  Because larger stars evolve faster, the age of a cluster can then be roughly determined by working out the mass of the most massive star still on the main sequence (i.e. still burning hydrogen in the core).  We call this the main-sequence turnoff.
But in some clusters, we see and handful of stars that are more massive, but still on the main sequence, even though all the evidence says they should have already evolved into giants and other more-evolved objects.  The consensus view is that these stars are at the very least interacting with binary companions, and many are thought to be merger products. i.e. something left over from two stars merging into one.  Either two companions in a binary have orbited so close that they've become one star, or two stars have simply collided (which is quite possible in the dense cores of clusters).  Depending on what types of star collide, you can basically get a new star where everything is mixed up again, allowing the star to be "born again".
Comment: +1 this is the only proper answer for this question.
Answer: The outer shell of the star contains still a lot of hydrogen, after running out of fuel.
Elements other than hydrogen are denser than hydrogen. This makes it difficult to get hydrogen to the core of a star, or to the region of hydrogen-burning at least, after the core has been burnt to helium or heavier elements.
But the life of a star can be extended in some way, e.g. by adding hydrogen to a white dwarf. This can trigger burning of carbon with a supernova Ia as result.
Answer: Stars actually do this on their own, to an extent.  The material inside a star (in some layers) does convect, and at certain points in the star's life, the material in the core can actually rise up and mix with the rest of the star.  This might replenish some H and He in the core, but the main effect that can be observed is that the fusion products become visible at the surface.
Also, the size and location of the convective layers depends very much on stellar size - in a red dwarf the convective zone is most of the star.  That's one reason red dwarf stars live so long - they continually "recycle" their available Hydrogen.
http://en.wikipedia.org/wiki/Star#Structure
http://en.wikipedia.org/wiki/Dredge-up
Answer: When stars transition from the main sequence core Hydrogen burning to core Helium burning they can experience Hydrogen shell burning.

However, when you burn the Hydrogen in the shell to Helium, it will fall on the core creating a hotter core where the radiation pressure from the Helium burning core will push the Hydrogen further out into the outer envelope. From here you can get a Helium flash which is the cause of Horizontal Branch stars.
If you were able to somehow force more Hydrogen to shell burn then you could possibly extend the life for a short while, though the lifetimes post main sequence are much shorter < 1 Gyr compared to the lifetimes on the main sequence.
Comment: There is no helium burning when a post main sequence star is on the red giant branch. The helium core is initially inert. The helium flash marks when that inert helium core finally ignites.