Question about unpacking

Question: thank for reading, i'm a beginner trying to learn Malware Analysis and Reverse Engineering, at the moment I readed the book "Learning Malware Analysis", I fully understand it, but there is just one section that i can't grasp, Unpacking, I tried to manually unpack UPX without success even if I watched tutorial and did the exact same thing (Breakpoint on the famous jump and then dump with scylla and rebuild IAT, but nothing).
I don't understand how detect the instructions that unpack the executable, can someone give me the right resources to start learning unpacking? I already have tutorials like "unpacking xxxx" but I would prefere something more general, concepts that I need to know, I hope you understand my question, tell me if I said something wrong, thank you.
Answer: Manually unpacking is an art that takes lots of practice, but you're starting off right by working on the most simple examples. You need to have a solid understanding of the tools involved in the process and the PE file format. There are quite a few resources out there, but I've had great success spinning up folks with [yates] old docs on PE files, and Lena's tutorials (the unpacking specific things) Lena's tuts are old, but for understanding some core concepts they're still pretty relevant (x86 isn't completely dead just yet). If you want to go forward with more, there are quite a few unpackme's out for different targets too. You should be able to follow along with relative ease using x64dbg instead of olly for those tutorials as well.
So for starters, I'd suggest snagging Lena's tuts. If you're use to the toolset you probably can jump right in with Part 20 & 21, part 21 has a UPX unpackme, but part 20 teaches some other core concepts.
Familiarize yourself with the PE file format, I really liked [yates] info on PE files also his Understanding Import tables article is also a great read. Finally, his Program Flow paper ties a lot of that info together well, with some really solid and simple x86/win32 asm code examples to show you how to write your own tools.
Also a decent resource on PE things is Goppit's Code Breaker article. It's rather in depth, but covers about any question you could have.
That should be enough to get you started down the right path, knowing your tools and knowing what docs to read is definitely half the battle. Good luck, you can do it. archive.org and is your friend if you can't find some of the files linked in those tuts.
Comment: Thank you very much!
Answer: learn the basics of how packers works; I haven't read the book that you mentioned, but it should discuss it;
Detect whether it uses custom packer or known (commercial) packer:

there is known sections; UPX0
tools like Detect It Easy will identify it;
if that was not the case, it's mostly custom packer;

Unpacking known packers:

usually there is pushad/popad combination that lead to OEP.
there is far jump; meaning that sample will jump from one section to another, or similar thing. jump target usually has no actual meaning unless sample reach that address. (actual instructions will be written there). push "address" ret; jump "register"; jump "address"
you will duckduckgo it and find some forums that talk about this particular packer.

if these are the case, follow: https://www.virusbulletin.com/virusbulletin/2012/04/quick-reference-manual-unpacking
Unpacking Custom Packers:

trace it's API Calls either with DBI or inline hooking; there are tools out there that do it for you. find the point that the malware starts it's actual malicious activity; put breakpoint on corresponding APIs and dump the payload.
I usually put breakpoint on VirtualAlloc, VirtualProtect, CreateProcessInternalW, WriteProcessMemory depending on sample.
Comment: Thank you very much!

Question about unpacking


Should one mention multiple, albeit somewhat unrelated research interests?

Question: As the question implies,  I have two main research interests in the natural language processing and computational genomics domains.  While I have a preference for the former,  I am also very interested in the latter.  I ask because I am not sure if it would look like I am too unfocused for a PhD. Many professors seem to have multiple areas of interests,  some of which are not too related, but nonetheless I want to make sure that mentioning multiple interests will not hurt me.
Comment: What makes you think those interests are unrelated?
Comment: @JeffE I don't think that they're entirely distinct. There's a decent amount of overlap, I'm just afraid of coming off as being unfocused.
Answer: If you can convey your enthusiasm for the overlap of these two somewhat distinct areas, you will be ahead of the game. A PhD candidate is expected to extend the limit of human knowledge, and one of the better ways to do so is to research within the overlap of two (or more) disciplines. I would tend to see having more than one area of interest as being an advantage rather than a disadvantage. Of course, as your question implies, a multiplicity of interests can backfire by causing a candidate to appear unfocused. Focus on the overlap, and make your application shine!
Answer: Your PhD should be somewhat focused, but before that, you're not in general supposed to have real scientific results. I would surely mention both, unless you feel that one of them is significantly unsignificant.
If you managed to have multiple results as a master student, that makes you a very good candidate for a PhD, because not many people have that!
Answer: The answer depends on you, the professor and when and how you communicate, .
Mention Both

Better mention both than fear. Until you handle the fear to stand for both interests it will not go away. When you are clear about what you fear you may know the answer already.
Showing that you have a broad interest means that you are open to change.
You may get angry at yourself for not having mentioned the other interest. Especially because professors know other professors to redirect to.
If you write you can make sure that it is clearly understood that you have two interest. Such as by choosing a headline for each. The professor may then choose what to focus on.
If you talk to the professor you get responses what (s)he likes most. Then you can focus on that.

Mention One

When there is not enough time for both topics it could be bad to mention both.
Mentioning both can mean that the professor does not choose you because (s)he only takes in people with one interest who can be put under more presure because they can not choose to go somewhere else.
Sometimes professors are really proud of themselves because nobody ever tells them they are wrong. You may have to adjust what you say so they do not fear your intelligence in a field they do not know.

I come from a computer science background. There may be different cultural influences in other professions.
Comment: So to summarize: Mention both unless your professor is a jerk?
Comment: I do not really know.


How do stars from far away affect Earth?

Question: I know that we obviously get light (or we wouldn't be able to see them), but are there any other ways that they affect Earth and maybe just our solar system in general?
Comment: If you believe the astrologers, they affect everything about our daily life; but from a physicist's perspective, I think the answer is "not much". Except that it helps us realize how incredibly large the universe is, how it is expanding, ... in general they help us construct the picture of Physics.
Comment: @Floris: actually, they *do* affect the decisions of people who believe to astrologers, so the effects could be remarkable. =)
Comment: @Floris I would argue that the answer is "not much" only on the short timescales we are accustomed to.  The effects across millions of years will be much greater.
Comment: nothing about the Mach principle ?
Comment: I wrote a general answer for the impact of when a star dies [here](http://physics.stackexchange.com/a/233126/59023), but otherwise I agree with @Floris that until they die they do not do much directly...
Comment: @Floris, even European and Indian astrologers don't pay much attention to stars (planets, sun, moon, even asteroids, but not stars apart from the sun). Arabian astrology does though, which left its legacy on modern astronomy in the names for so many of the stars that are visible to the naked eye having names of Arabic origin.
Comment: They're responsible for getting me home when I'm lost ;)
Comment: @Michael - completely fair point. Millions of years have a way of accumulating small effects...
Comment: @JonHanna  I didn't know that Arabian astrologers paid more attention to stars than others... Thanks!
Answer: A lot (to put it mildly) of elements are created in stars and supernovae. These elements then travel through space until they fall to Earth (or, to be exact, some microscopic portion of them reach us).  Earth itself wouldn't exist if stars hadn't generated elements which then clumped into dust, into minerals, and so on until a big ball of matter started to orbit the Sun.
Here's a short quote from Wikipedia article on Cosmic ray:

Data from the Fermi space telescope (2013) has been interpreted as
  evidence that a significant fraction of primary cosmic rays originate
  from the supernovae of massive stars. However, this is not thought
  to be their only source. Active galactic nuclei probably also produce
  cosmic rays.

So I'll stand by my claim that stars are giving us mass (i.e. non-photons) as well as photons in real-time, not just as 5-billion-year-old space dust.
Comment: @Digital Trauma The cloud chamber in the SF Exploratorium was the thing I found most exciting too.  I've seen photos taken of collisions in physics books, but to see them happening in front of one's eyes was incredible.
Comment: The way OP's question is worded "we obviously get light [from far away stars] (or we wouldn't be able to see them)" makes it seem like they are asking about stars which from our perspective have not gone supernova yet. Seems like the Sun ejects mass https://en.wikipedia.org/wiki/Coronal_mass_ejection at a rate roughly equal to the 1/10th the biomass of Earth every day (Wolfram Alpha) but that mass is spread thin by the distance, and the Sun is so much closer to us than the next closest star. Any chance we could get a source for the claim in the last sentence?
Comment: I retract my comment. If by formed in stars and fall to Earth we are talking about meteorites formed in the solar system at more-or-less the same time as the Earth, then I agree. The way it reads is that supernovae ejecta are raining down on us, which isn't true. One could then add that comets are at least still a theory for how water is delivered to Earth.
Comment: Just this weekend we did a family trip to the [SF Exploratorium](https://en.wikipedia.org/wiki/Exploratorium). I'd never seen the cloud chamber (or any other cloud chamber) before - suffice to say I found it absolutely fascinating to watch interactions of the supernovae remnants with the alcohol vapour in real time.
Comment: I think this answer should distinguish between "live" stars, and "dead" stars. "Live" stars give us light, "dead" stars give us cosmic rays, and meteorites formed from the remains of whatever star or stars went bang to give our solar system its starting mass.
Comment: @RobJeffries Do massive lumps of rock count? Some of those were formed in the same way as Earth.
Comment: Point taken. The science is that the cosmic rays are accelerated in *supernova remnants*.
Comment: @pentane I assure you that the Sun is indeed much closer to us than the next closest star.
Answer: The stars in our galactic neighbourhood do have a dynamical, gravitational effect on the inner workings of the solar system:
They built the Oort cloud
The Oort cloud is a roughly spherical cloud of icy bodies that is thought to act as a reservoir of long-period comets (and which we speculate exists to explain said comets' existence). These icy bodies formed in much the same way that Kuiper belt objects did, accreting in circular orbits on the outer edges of the solar system, but then they had gravitational interactions with the planets that scattered them into higher orbits.
What happened next is probably best explained by Hal Levison in this interesting interview with Emily Lakdawalla:

You start out with a bunch of icy guys between the planets. And they start to scatter outward. If you think about it, you do planet flybys to get velocity kicks. Spacecraft do it all the time. The planet can't put you on an orbit that doesn't cross its orbit anymore, because it's just a velocity kick, it's not a position kick. So in the early stages, when the planets are forming, they're scattering these cometary objects around in such a way that the perihelion still remains among the planets, but the semimajor axis is doing a random walk as you get scattered. So the semimajor axis is bopping around and slowly growing because it's diffusing outward, until the point where the galaxy can become important gravitationally. And that acts as a torque. What the galaxy does is it doesn't change the semimajor axis, but it does change the perihelia distance. So you get out to a few thousand AU and the galaxy can lift the perihelia away from the planetary system and then you're frozen in the Oort cloud.

The orbits of the Oort cloud objects are huge because they were boosted there by gravity assists by the planets, but as Levison notes this process can only produce very tall ellipses that still intersect the planet's orbit - at the location of the original assist, because all elliptical orbits are closed.
The galaxy, on the other hand, is too far away to lift anyone's orbit up - it cannot provide orbital energy - but what it does is circularize these long, thin elliptical orbits. This is what Levison refers to as a torque: trading radial kinetic energy into angular velocity. This makes the orbit less elliptical while keeping the semimajor axis constant (because this keeps the energy constant), and it therefore pushes the perihelion away from the 'inner' solar system (i.e. from Neptune inward) until the object can no longer meaningfully interact with any planets, at which point the size of its orbit is sealed, and the only possible change that can happen is further drift of its ellipticity induced by extra-solar stars.
That feels like enough to be getting on with to me.
Comment: Very interesting and (to me) unexpected piece of information. I would not have assumed that other stars can have such an influence. This may even have an effect on the conditions emerging (complex) life finds on earth -- repeated meteorite impacts of bodies not removed from earth's orbit may be repeatedly change the environment enough to throw complex life off the rail.
Comment: @PeterA.Schneider Yeah, I was pretty surprised myself. Also pretty topical at the moment, with all the 'planet nine' stuff from a couple of weeks ago (covered well by [Lakdawalla](http://www.planetary.org/blogs/emily-lakdawalla/2016/01200955-theoretical-evidence-for-planet-9.html)). As mentioned in the comments, these are small effects taking place over (hundreds to thousands of) millions of years, but in the outer reaches where there's not much else happening it's still a major dynamical player. And as you mention, with a definite (lack of) impact for life down here.
Answer: The other answers talk about some of the effects.  This is a complementary answer that attempts to put a number to the force behind one of the effects - gravitational attraction.
Proxima Centuri is the closest star to our solar system.  It is about 4 × 1016 m away and has a mass of 2.45 × 1029 kg.  The mass of Earth is about 5.97 × 1024 kg.  Plugging these values into the standard gravitation formula, we find the force of gravitational attraction between Earth and Proxima Centuri is:
$F = \frac{G m_1 m_2}{r^2}$
$= \frac{6.67408 × 10^{-11} × 2.45 × 10^{29} × 5.97 × 10^{24}}{ (4 × 10^{16})^2 }$
$= 6.1 × 10^{10} N$
This is larger1 than I had expected when I started this calculation.
Obviously this force is not acting on the Earth in isolation.  Pretty much all objects of any significance in our own solar system exert vastly greater gravitational forces than this on the Earth whose effects should be considered before any potential effect from Proxima Centuri.
In addition all solar system objects will have the about the same force (proportional to their mass) exerted on them by Proxima Centuri and thus the solar system will act more or less as one object with respect to Proxima Centuri in this regard.  There is certainly no expectation that the Earth (or any other solar system object) will suddenly pop out of its normal motion and zoom off in the direction of Proxima Centuri.
Some interesting comparisons have popped up in the comments;  I'm tabulating them here for the record (figures are all very approximate):

$6.6 × 10^{9} N$ - Weight (at sea level) of the largest ever ship (Seawise Giant), fully displaced.
$6.1 × 10^{10} N$ - Gravitational force of attraction between Earth and Proxima Centuri
$6 × 10^{11} N$ - Gravitational force of attraction between Earth and Pluto
$2 × 10^{20} N$ - Gravitational force of attraction between Earth and the moon

Note also that the combined mass of the binary Alpha Centuri is a bit more than 16x the mass of Proxima Centuri, and is barely (in astronomical terms) any further away.  So its force of gravitational attraction to solar system objects will be 16x greater.

1 Please comment/edit if you see an error in the calculation.
Comment: @cst1992: It's balanced by the fact that the Sun, Moon and other planets are **also** attracted by Proxima Centauri. Due to the distance between the solar system and Proxima Centauri, the gravitational field of Proxima Centauri is pretty much constant across the solar system (both in strength and direction).
Comment: just the typo for the powers 29 and 24. Nice to compare to the ~ $2 * 10^{20}$ N of the Moon
Comment: What's balancing this force out? Something has to be, or the Earth would've gotten pulled away towards Proxima Centauri. Not to mention with greater acceleration as the distance reduced. Also, we know the gravitational force of the Earth toward the Moon is getting balanced by its centrifugal force outward.
Comment: @cst1992 The pull between Alpha Centauri and the Solar System is part of what holds the galaxy together. The stars' pull on earth balances each other out as far as they are on opposite sides (superposition); what's left, because we are not in the galactic center, is holding us here as part of the galaxy. Btw, if my off-the-cuff computation is right, Alpha Centauri's pull is sufficient over billions of years to change our trajectory (if for a moment we assume it only affected earth, and no other star). But of course the effect is complicated (it may push in winter and pull in summer, etc.).
Comment: On a side note, small as this force is relative to earth's mass, the resulting minimal acceleration integrates to speeds in the order of magnitude of the earth's orbital speed over a couple hundred million years, unless I lost a few zeroes in my off-the-cuff estimate.
Comment: For comparison, this is about one-tenth the gravitational force between the Earth and Pluto. Interesting that they're that close, actually.
Comment: What matters isn't the force (as quoted) but the force *gradient*, i.e. the tidal interactions between the star and the orbiting body, and these are smaller than the force by a factor of (orbital radius) / (distance to the star). Such interactions are much too small to influence the Earth - you need to have several hundred or even thousands of AU of orbital radius for that tidal effect to matter - hence their effect on the Oort cloud but not really further inwards.
Comment: This answer is extremely disingenuous in its current form - the raw forces as quoted tell you nothing of their actual dynamical effect. Apart from being cancelled out by stars in other directions (which is extremely important), the gravitational field of Proxima Centauri acts essentially in a uniform way throughout the solar system, so the Earth will be accelerated the same as the Sun, and the dynamical effect of the force will be zero.
Comment: @PeterA.Schneider I think that if somehow P. Centauri magically only affected the Earth and not the Sun, that our orbit would gradually become more eccentric, and "point" more in the direction of P. Centauri.
Comment: The answer confuses "force" and "effect". The interactions quoted are different in many respects (particularly their spatial and temporal variations) which directly impact their effect on the dynamics. The order-of-magnitude comparison of the force from Pluto and Proxima Centauri simply serves to obscure how different (or similar) they are dynamically. I look forward to the edit, though.
Comment: @EmilioPisanty Edited.  Hopefully its just *mildly disingenuous* now.
Comment: @EmilioPisanty : if you consider Earth side only, the effects and the forces vary in the same way
Answer: I don't think that light from the stars other than Sun is of much practical use nowadays except for the classic navigation, where it's essential of course.
I guess any effect comes from the limitless reach of the gravitational force, which drops with the square of the distance but grows linearly with the mass exerting the force. A star most obviously affects planets in its system. A bunch of stars are affecting their star cluster, and so on.
Check this subchapter in the Feynman's lectures.
Comment: @Logan In that case, it's probably a good time to recommend the [Messenger Lectures](https://www.youtube.com/watch?v=j3mhkYbznBk).
Comment: Thank you for the insight! I'm currently reading Feynman's "Six Easy Pieces".
Answer: Gravitationally, there is little immediate effect on earth on a daily basis, though over very long periods of time, stars that pass near enough to the sun could disrupt the orbits of Oort cloud objects and send them towards the sun (and earth or other planets in our Solar System).
Culturally, stars have a very big impact on our species. Religion, art, science, and other areas of our culture draw inspiration and knowledge from observing the stars. As we study and understand more about the stars and their planets, we understand more about ourselves and our place in the universe. Arguably, we would not have the same culture without having the stars with us over the centuries, and we would have had a different impact on the earth than we have had. Because the stars affect us and we affect the earth, the stars indirectly affect the earth through their effects on us.
Answer:
The gravitation of the stars in our galaxy keep the solar system in it. I'm not sure whether that's important for earth or for life on earth though, but it makes for nicer night skies.
Gamma ray bursts, if close enough and (im)properly oriented, affect earth. A gamma ray event from a "soft gamma repeater", SGR 1900+14,  is known to have affected earth's atmosphere, although it was 20,000 light years away.
The stronger events are so powerful that a close one would be devastating. Luckily they are rare (a few per million years per galaxy).
Comment: I didn't know this: +1 - excellent spot. This is a SGR though - a soft gamma ray repeater.
Comment: @RobJeffries True, sloppy editing -- related but not the same.
Answer: Machs principle, that inertia is caused by the distribution of distant stars was a principle that Einstein tried to incorporate into GR, but failed.
However Barbour, quite recently incorporated an aspect of Machs principle into his theorising of time: ephemeris time

An ephemeris gives the position of celestial bodies, and duration is deduced in terms of such positions.

And

a man-made clock, a chronometer, is "a mechanism for measuring time that is nearly as possible synchronised with ephemeris time".

Overall, the thrust of Barbours paper is to show that time is an aspect of a timeless law that governs change.
Answer: The distant stars are also responsible for cosmic rays, which in turn can affect the Earth's weather


2D bouncing formula doesn't work properly

Question: I am new to Unity, and I am trying to create a bouncing ball, so I've been researching bouncing related physics and I found a formula:
Formula:
-2*(V dot N)*N + V

Where V is the velocity vector and N is the normal of the surface on which the ball will bounce
Here is my script :
using UnityEngine;

using System.Collections;

public class BallPhysics : MonoBehaviour {

    void Start () {
        rigidbody2D.velocity =new Vector2 (-1,-3);

    }

    // Update is called once per frame
    void Update () {

    }
    void OnTriggerEnter2D(Collider2D col) {

        if (col.gameObject.name == "Pong") {
            tBounce ();
                }

    }

    void tBounce(){
        RaycastHit2D hit = Physics2D.Raycast (new Vector2 (transform.position.x,transform.position.y), rigidbody2D.velocity);
        Vector2 n = hit.normal;
        Vector2 v = rigidbody2D.velocity;
        Vector2 R = -2 * (Vector2.Dot (v, n)) * n + v;
        rigidbody2D.velocity = R;
    }
}

I am giving the ball a velocity vector in the start function, i am using OnTriggerEnter2D for collision handling and raycast2D to get the normal of a surface.
The problem is that the script doesn't reflect the velocity vector called R, I think the problem is in the normal vector.
For example let's say V is a Vector2(-1,-1) so basically R should be (-1,1), but it's not. R is (3,1) !
I've successfully been able to make a ball bouncing on Horizontal/vertical surface by reversing the ball velocity but this won't work properly with arbitrary angles, that's why I am using this formula.
So what's the problem ?
Answer: normalize your normal vector n before using in in the reflect formula.
Vector2 n = hit.normal;
n.Normalize();


Patimokkha Rule On Bathing

Question: I recall having read somewhere that monks are allowed to bathe only once every 15 days. What is the actual Patimokkha rule behind this ? Also, what is the reason behind this rule and what are its possible benefits ? Is there any specific story corresponding to this rule ?
Answer: It's Pācittiya 57:

Should any bhikkhu bathe at intervals of less than half a month, except at the proper
  occasions, it is to be confessed. Here the proper occasions are these: the last month and a
  half of the hot season, the first month of the rains, these two and a half months being a
  time of heat, a time of fever; (also) a time of illness; a time of work; a time of going on a
  journey; a time of wind or rain. These are the proper occasions here.

(Thanissaro, trans)

The reason is ostensibly that bathing is an unnecessary luxury. The benefit to the rule is that monks will not become overly attached to cleanliness and that they will not become a burden on society. The story behind it is that the king was unable to bathe because the monks were bathing.
Note that the rule only applies to bathing; showering is not mentioned.
Comment: There seems to be less reason why showering should be something different, not at least because such as shower in a bathroom is even till today unknown, as well such as taking a full bath on many places.
Comment: Ven. Sir - What, in this case, can be considered to be a difference between bathing and showering ?
Comment: Bathing is getting inside a tub, a river or a lake and submerging oneself in water. Showering is just using the shower in the bathroom.
Comment: @Monk To Bathe is clean oneself in some sort of body of water, such as a tub or lake. To shower is to be sprayed with water while cleaning oneself not in a body of water. I hope that makes the distinctions clear.

Patimokkha Rule On Bathing


How dangerous can a file be with no detected malware?

Question: Let's say there is file which successfully passed all scans by all antivirus software there is on VirusTotal. Does it mean that it can't be dangerous. If no, what kind of dangers we can expect?
Comment: It can be just as dangerous. The only thing you know is that it's (much) *less likely* to be dangerous.
Answer: It is entirely possible for a file that is not detected by any scanner to still be malware. In fact, I would expect that most new malware starts out that way! Keep in mind that the bad guys have access to antivirus software too. And they will absolutely take advantage of that by making adjustments to their malware until no antivirus software detects it. (Granted, they wouldn't be able to test with Virustotal or any online scanner that would send their file to antivirus companies for analysis, but they can still go a long way testing with offline scanners.)
After the malware is released to the world and gains meaningful distribution, antivirus companies will eventually notice it and add it to their databases. But if you're unlucky enough to be among the first few people to encounter a new piece of malware, it's quite possible that no antivirus software will detect the file as malware when you first encounter it.
It gets worse. Sophisticated attackers (e.g. nation-states) often distribute malware to a very small group of select targets. By intentionally limiting distribution, it can take years or more before any antivirus company catches on. Most people will never be the target of sophisticated attacks like this, but if you happen to be one, antivirus software will be very ineffective.
In conclusion: If many antivirus programs flag a file as malware, it's a good sign that it's malware. If no scanner flags a file as malware, you cannot conclude anything.
Comment: I would add that malware authors **can** use a VirusTotal-like service, for a fee. There are services online that will scan any file you send, and don't submit the sample to security vendors.
Answer: There are many information out there on how write or transport malware in order to bypass antivirus and other security products. And since attackers and vendors of security products continuously improve their products there will always be some some malware which passes AV, i.e. there will be no AV which is able to protect against every known and unknown malware without also having an unacceptable high false positive rate (i.e. blocking everything definitely blocks all unknown malware too but is not really useful).
The risks of letting such malware through are no different from letting the detected malware through. You just need to be prepared that your network or machine will be compromised at some time and should be able to detect successful attacks early and quickly recover from these.
In general the risk depend a lot on the context where this file was received and what kind of file this is. If it was an expected file send by a trusted person the risk is comparably low though it might still be that the senders system might be compromised and embeds malware into files. If it is a file downloaded from some uncommon or even illegal site on the internet the risk is much higher since such sources are regularly used to spread malware. If this is a pure text file (plain text, no Office document) or image the risk is low since it would require some bug in the local application or OS to execute some embedded malware. If it is instead an executable file, Office document, screensaver or similar the risk is much higher again etc.
Answer: I'll add to the other good answers here that it is best practice to store exe's long term and rescan them regularly as signatures are updated.
As for the possible dangers, it might do what you are expecting it to do and nothing more. It could do what you are expecting and also be a first stage that establishes persistence in your system then phones home for more instructions. It could be destructive on it's own
Use your best judgement based on the source and the potential risk to your system/environment.
Answer: Fresh code will not be flagged as malware, at least not by signature scanning (the most common form of analysis), someone needs to add the signature. Dynamic analysis can catch it, but there are ways around that too.
Also, even old malware, with signatures on almost all antivirus, can be cloaked with the right tools. A polymorphic crypter can make malware immune to signature scanning/static analysis and there are ways around dynamic analysis/emulation.
That said, you can never be 100% sure an executable is malware or not unless you checked the source and compiled it yourself.
Comment: A polymorphic crypter is as **OBVIOUS AS WRITING ALL UPPERCASE AND BOLD!!!** Sure, an AV software may not be able to detect what kind of malware is being hidden, but any popular AV can detect that *something* is wrong.
Comment: That will depend on how aggressive the AV is. The more aggressive an AV is, the more likely it is to detect those threats, but it will also trigger more false positives, so AVs can't afford to be overly aggressive.

A polymorphic crypter using a low entropy technique and without doing weird things with the PE (Windows) can be pretty much undetectable by **static analysis**.
Comment: That would then be a universal AV bypass. If you have one, please share it with the rest of the class.
Comment: Not universal, a decent antivirus will run the program in a sandbox (**dynamic analysis**) and can detect it that way.


How to display comment meta under each comment content

Question: I'm trying to display comment meta under each comment, but I couldn't find which action should I hook in.
Answer: You will need get_comment_meta to pull that information from the database. You will need to know the metakey. If you don't have that, you will have to search the theme/plugin that generates the metadata for the occurence of add_comment_meta to find it.
Where to hook depends on how your theme is listing the comments. If it simply uses wp_list_comments there is no filter to simply attach the metadata. You will need to change the callback argument using the wp_list_comments_args filter. Then you can make a callback function that specifies which comment and meta data to display and how (learn more).
Comment: thanks for both editing and comments. I'm trying to figure that out.
Answer: As an easier alternative, you can use flexbox to reorder the comment items:
.comment-list article {
    display: flex;
    flex-wrap: wrap;
}

.comment-list .comment-meta,
.comment-list .comment-content {
    flex: 0 0 100%;
}

.comment-list .comment-meta {
    order: 2;
}


Off screen image Direct3D processing with SharpDX, pixel shader and C#

Question: I currently have a working app that can process images with a window handle. This of course makes use of the swap chain and so on... I need to process an image with pixel shader off screen without a window handle. I have not been able to successfully port this to an off screen model. Can any please help educate me on the best way to do this? I have the Device, context for both Direct3D and Direct2D available. I'm having issues with using the correct texture to image process...
Answer: First up create the DirectX device by calling New Direct3D11.Device and then you simply call DeviceContext.Flush in place of present.
Setup the device
    Dim FL As FeatureLevel() = New FeatureLevel(0) {}
    FL(0) = FeatureLevel.Level_11_1
    MainDevice = New Direct3D11.Device(Direct3D.DriverType.Hardware, DeviceCreationFlags.None, FL)

At the end of the frame
MainDevice.ImmediateContext.Flush

Texture creation
Dim ColorFormat As Format = Format.R8G8B8A8_UNorm
Dim BufferDesc As New Texture2DDescription() With {
 .ArraySize = 1,
 .BindFlags = BindFlags.RenderTarget Or BindFlags.ShaderResource,
 .CpuAccessFlags = CpuAccessFlags.None,
 .Format = ColorFormat,
 .Height = Height,
 .Width = Width,
 .MipLevels = 1,
 .OptionFlags = ResourceOptionFlags.None,
 .SampleDescription = New SampleDescription(1, 0),
 .Usage = ResourceUsage.Default
}

    Dim ColorBuffer As Texture2D = New Texture2D(MainDevice, BufferDesc)
    Dim ClorBufferRT AS RenderTargetView = New RenderTargetView(MainDevice, _buffer)

Comment: How can I create my RenderTargetView and so on without the SwapChain? Without the SwapChain I'm not sure how to get the textures that I would normally pull from SwapChain...
Comment: just set textures up the normal way. Ill update my answer.
Comment: Outstanding! Thanks for that help. Just for giggles while I have you thinking about this... I've never done any off screen like this. I'm trying to shorten the process... I have an Image to process, single frame render... I need to pass in the image... convert to texture, then apply a compensation effect via pixel shader... I'm looking for speed and ease of use... any thoughts?
Comment: Not really a faster way, what you are doing sounds about right but if you want to talk about it more we should proly turn this into a chat rather then spamming the comments
Comment: I'm new to this site. How would we turn this into a chat? I'm new to SharpDX and I'm struggling with stripping this app down to the bear bones... perhaps you know much better than me (I'm sure you do)... what is the minimum to run a pixel shader... this is OJT for me with SharpDX thrown in...
Comment: I'm hoping that if we keep using the comments here it will ask me to turn it into a chat.


How can I download apps from the App Store without using Touch ID?

Question: I can no longer install any apps from the App Store to my iPhone as the only way to now do so is via Touch ID which I cannot use on my phone. How can I download apps from the App Store without using Touch ID?
Comment: I'm really surprised it's not smart enough to just show you the passcode keypad. (:
Answer: Go to the Settings app, then to Touch ID & Passcode. Enter your passcode, then turn off Touch ID for everything.


What is delta neutral

Question: Does delta neutral portfolio mean you add up deltas of all positions and the sum should be zero? Is this true?
Also, in a FX portfolio consisting of FX calls puts and Fwds, if FWD delta is given for each how do you make the portfolio delta neutral?
Do you just add up the fwd deltas for all and depending on the sum, buy or sell a FWD to bring the sum of delta to zero? Is this the right approach?
Answer: You are right in saying that to check whether your position is $\Delta$-neutral, you have to check the $\Delta$s of its constituents. That's a general statement that applies to positions that you are not rebalancing too fast, see e.g. this recent question.
In general, each Greek measures a particular risk/exposure of your position to a market condition that may change. For example, $\Delta$ ($\Theta$, $\rho$) tells you how much your position will change if the underlying level (time, interest rate) changes given that all other things being equal. The latter condition makes it possible to express Greeks as partial derivatives of the portfolio's value with respect to relevant variables, e.g. $\Delta = \frac{\partial V}{\partial S}$. Since partial derivatives are linear, if you hold $m$ at the money calls calls and $n$ stocks
$$
  \frac\partial{\partial S}(mC + nS) = m\Delta_C + n \approx m/2 + n
$$
where $\Delta_C \approx 1/2$ is the $\Delta$ of one at the money call. In that case, to be $\Delta$-neutral, you would hold $n = -m/2$ stocks against your at the money call position.
As such, to compute exposure of your entire position, it is enough to compute separately exposures of each leg in your position. For this reason, the approach you've described in the OP is correct. Just note that $\Delta$ changes as well, and hence to stay $\Delta$ neutral you will need to do additional trades while you proceed to hold the option position. This concept is called continuous hedging. The changes of $\Delta$ are described by higher-order Greeks such as Gamma, Charm, DdelV etc.

What is delta neutral


How do I determine the maximum thrust that a Tesla powertrain (P100D for example) could produce if attached to a single propeller?

Question: I am theorizing a drone helicopter from a tesla powertrain (P100D).
Lets assume the system is theoretically maximized with an optimum propeller (this is what I am currently stuck on).  How much thrust could a Tesla powertrain produce (I understand the thrust would decrease as the battery drains and voltage decreases, just wanting to get an idea of theoretical optimal thrust)?
Comment: Try something. Put your car's accelerator pedal to the floor and hold it there continuously for an hour. You **can't.** Within 10 seconds, safe operation will oblige you to abort the experiment. Car engine design *absolutely relies* on that; they're like a starter motor, good for 5 seconds but absolutely not made to run that power continuously. Your "200hp" engine might be good for 30hp continuous. Tesla's powertrains will have the same constraint, the motor isn't sized for continuous at-rating operation.
Answer: For a propeller/rotor, net consumed power = torque * rpm. For an electric drivetrain, net power delivered = current * voltage, with current equating to torque and voltage to rpm. Tesla should have really good data analyses on the power delivery as a function of demand over time, with wheel torque and wheel rpm as parameters.
Then you only have to replace the propellant medium: slippery air instead of the stony fixed world. Torque is a measure of drag of the rotor blade, thrust is a measure of lift. Both are a function of rpm as well, usually the rpm is limited by the tip speed approaching the speed os sound and is chosen to be as close as possible to it.
So a design process might be:

Determine payload.
Determine approximate disk load by comparing with existing designs, resulting in the disk area and the blade radius.
Compute rpm so that tip speed is about Mach 0.8
Compute power, torque and thrust from data available for comparable comfigurations.

Two books that contain chapters on pre-design of helicopters are Helicopter Performance, Stability and Control by Raymond Prouty, and Helicopter Aerodynamics by J. Gordon Leishman.
But the area that will give you most headache won't be computing the thrust etc, it will be figuring out how to control the flight path. Do you plan to use a swash plate?


Can I make a pecan pie with corn syrup only?

Question: I want to make a fructose free one for my dad. I am not a fan of sugar substitutes, either. Karo doesn't have fructose but sugar does. If I left out the sugar could I use corn syrup only or would it not set up?
Answer: It would seem to me that controlling the total amount of water in the recipe will be the trick, so you'll want a crystallized or powdered replacement for the table sugar rather than a syrup.
I've not tried it myself, but you might try using dextrose in place of the table sugar.  Dextrose is the commercial name for crystalline glucose, and I found it readily available on Amazon (https://www.amazon.com/Now-Foods-Dextrose-2-Lbs/dp/B008MVJKFU/).
Normally when substituting one kind of sugar for another, assume 7 oz (by weight) per cup of sugar specified in your recipe, then weigh out that much of your alternative.  But there are multiple sources online that state dextrose is only about 70% as sweet, meaning you'd want to divide by 0.7 to adjust the quantity from sucrose to dextrose.  Here's a typical reference, though there were many others with the same information: http://www.livestrong.com/article/534691-how-to-bake-with-dextrose/
I'd love to know whether or not it works!  If you try it, leave a comment and let us know how it goes.
Comment: Or, if like many people, you find pecan pies to be overly sweet anyway, you could leave the measurements the same.
Comment: Thanks! I was googling around and someone else suggested dextrose as a replacement for table sugar in the recipe, but I wasn't quite sure how much to use. Thanks for this answer.


Is a 1099 required when one freelancer hires another?

Question: If I'm a freelancer but I need to hire another freelancer to help me on something, do I need to send the other person tax documents (W9) and report 1099 later on?
Answer: IANAL. However according to the IRS you need to file a 1099-MISC if you made any of the following payments

File this form for each person to whom you have paid during the year:

at least $10 in royalties or broker payments in lieu of dividends or tax-exempt interest;
at least $600 in rents, services (including parts and materials), prizes and awards, other income payments, medical and health care
  payments, crop insurance proceeds, cash payments for fish (or other
  aquatic life) you purchase from anyone engaged in the trade or
  business of catching fish, or, generally, the cash paid from a
  notional principal contract to an individual, partnership, or estate;
any fishing boat proceeds,
gross proceeds of $600, or more paid to an attorney during the year, or
withheld any federal income tax under the backup withholding rules regardless of the amount of the payment.

In your case, the operative one would be the $600 "cash paid from a notional principal contract to an individual" (second point above).
Note that this is cumulative, not per-payment. If you made 4 $200 payments to this person during a single tax year you would have to file.
Exemptions can be found here

You are not engaged in a trade or business.
You are engaged in a trade or business and

the payment was made to another business that is incorporated, or
the sum of all payments made to the person or unincorporated business is less than $600 in one tax year (unless the recipient is an
  attorney or law form, see specific instructions for 1099-MISC for
  further details).

In my personal opinion, if I was using Quickbooks or something similar, I'd just fill out the form anyway and send it off (with a copy to your supplier). They can decide whether or not to declare the income - but at least you are covered.
Answer: Yes, if you and they are in the US and you pay them $600 or more in one year.
You will need to file a summary report by a certain date and get the 1099 to them by a certain date. (I think January 30th)
Doing the form yourself is a MAJOR pain because, last I read, it has to be on a certain type of paper with a specific font in a certain way because a machine reads it (you couldn't just print it, I had to buy the forms at office depot then find a typewriter, that was at least 10 years ago so maybe that has changed.)
Anyhow - what I do now is use an online tax filing service, it's less than $5 to have them done and they file the summary for you plus send them to the freelancers.  The only thing I don't like about it is typing people's tax info into the Internet, but, what else are you gonna do?!
Comment: Didn't want to risk spamming, but if you are using quickbooks it can definitely [do the 1099's for you](http://quickbooks.intuit.com/prepare-1099/). And if you use it properly it can fill out most of your tax return as well.
Comment: Thanks, Good to know - I don't use QuickBooks, but I may switch to it in the future.


QuickTime for OSX 10.9.5 has no sound

Question: So I did a screen recording with QuickTime using OSX 10.9.5. I was recording a video with sound. However, when I played it over from QuickTime, the sound was gone. How do I make it that QuickTime also records the sound?
Answer: To add external audio sources, you need to make sure the correct input is assigned before you start the recording

To record "in-computer" sound, you need software that can re-route audio within the Mac itself - to make it think an output is actually an input.
This has been traditionally done using a freeware app called Soundflower - originally by Cycling 74, taken over by Rogue Amoeba but not developed or supported further. Rogue Amoeba have always had their own system for intercepting Mac audio & routing it to chosen destinations, but their app, Audio Hijack, is not free ($50)
It is extremely good, but comes at a price.
Quick tutorial on Soundflower in Quicktime from CNet

When a situation arises where you want to record the audio along with your screen recoding on your Mac, you could try raising the volume on your speakers and hope that a built-in microphone captures that audio, but that's far from elegant.
Instead, you can use Soundflower. It is a free piece of software for Mac OS X by Cycling74 that will let you route system audio within your Mac. Download and install the utility; Soundflower requires you reboot your system after installation for it to work.
After your machine reboots, open QuickTime Player and start a new screen recording. In the QuickTime Player window, click the down arrow to the right of the record button and select "Soundflower (2ch)" as your input. Then launch System Preferences and go to the Sound settings. Go to the Output tab and select the same "Soundflower (2ch)" option as you did in QuickTime Player.
What this does is route all of your system audio out to Soundflower as if the utility were speakers or headphones. That means any sound made by your Mac (including Facebook notifications or similar) will be recorded by QuickTime Player.
Now you can hit record in QuickTime Player and you'll capture both the video and audio in one recording. While this is going on, you won't be able to hear the audio to monitor what's being recorded. When you're done, change your output audio back to your original settings in System Preferences.
Comment: Ahh... I just realised my own error - you mean "in-computer" sound. That's much harder... fixing answer...
Comment: Basically, you need either Soundflower [pretty much broken & unsupported since Mountain Lion] or pay 50 bucks for Audio Hijack - though there's a time-limited trial - https://rogueamoeba.com/audiohijack/buy.php

QuickTime for OSX 10.9.5 has no sound


What is the purpose of having contra-rotating props on an aircraft?

Question: Why do planes, like the famous XF-11 and the Tu-95, have contra-rotating props? What is their purpose?

Image credit: Mike Freer / Touchdown-Aviation / Wikimedia
Comment: These are called co-axial rotors in helis
Answer: According to my experience, you have two problems with props:

Torque
Exhaust Speed

If you use contra-rotating propellers, you eliminate the torque reaction problem because you now have two contra-rotating propellers each cancelling out the opposite's torque.
Also you increase the speed of air accelerated by the propellers, thus the aircraft's efficiency at relatively high travelling speeds is increased.
Normally, the propeller can only be operated effectively at low Mach numbers and increasing the RPM above a certain point will only cause the air behind the propeller to compress but not accelerate. Using a second propeller with higher pitch angles can generate high enough airspeed without the problem of compression because the second propeller is rotating inside the airstream generated by the first propeller.
Correction
However, having a different speed and pitch WILL induce a torque effect.
Comment: This leaves out the 3rd reason: because it just looks so darn ***cool***!
Comment: Contra-rotating propellers may have higher efficiency than _equivalent_ (same diameter and same $\Delta v$) single propeller, but that is not due to increase in speed of the air.
Comment: Increasing speed of the accelerated air _decreases_ efficiency. Because higher $\Delta v$ means the air carries away more kinetic energy ($E = \frac{1}{2}mv^2$) for the same momentum ($p = mv$) and therefore you need more power ($P = \frac{E}{t}$) for the same thrust ($F = \frac{p}{t}$).
Comment: Why would torque be an issue in a 4 engine plane?
Answer: The main advantage of contra-rotating props is the increased efficiency (6 to 16% according to Wikipedia). Another advantage is that the torque is pretty much cancelled out by the contra-rotating prop, but this is much less of an issue in aircraft with an engine configuration like the Tu-95 in your post.
I would say, another advantage is the fact that this design allows for a smaller propeller diameter, allowing a smaller landing gear, etc etc.
The disadvantages may outweigh the advantages depending on the design. They are very complex. This may lead to high maintenance costs, or an unreliable design. Contra-rotating props are also extremely loud. The Tu-95 is known to be the loudest aircraft in the world. Rumors are that they can actually be heard by submarines.
The fact that there aren't many aircraft using this design is proof that it isn't very popular. As far as I know, the only reason the Tu-95 doesn't use regular turbine engines is because there were no turbine engines available that would meet the required specification during the design stage of the aircraft.
Comment: Just a nitpick (and welcome to Aviation.SE!), but the turboprops on the Tu-95 Bear _are turbine engines_. What you are talking about are _turbojets_ or _turbofans_!
Comment: The extra efficiency gain is because an isolated propellor expends some energy imparting a "swirl" velocity to the air (i.e. an angular momentum), in addition to pushing it backwards (a linear momentum) to cause thrust.  The second contra-rotating propellor operates opposite to the swirl direction of the first rotor, resulting in a low net-swirl and recovering the energy wasted in turning the flow while still contributing to the rearward momentum that causes thrust.
Comment: @vasin1987: I'm talking about a Tu-95 flying at cruise altitude.
Comment: From what i heard submarine can hear _most_ aircraft flying at low altitude anyway.
Comment: As I understand it, the TU95's noise comes not so much from contra rotating propellors, but from the prop tips going supersonic. There was a turboprop version of the F84 Thunderstreak that had a supersonic prop. So noisy, that it was nicknamed Thunderscreech.
Answer: While there are theoretical benefits in terms of efficiency, the difficulties in gearing them have kept them from practical use except when used with very high powered engines.  After a certain point, using longer blades becomes increasingly inefficient, and other strategies have to be used to increase the swept volume.  An example would be the Spitfire, which went from 3 blades in early marks, to 4, 5, then a contrarotating 3+3 in the Mark XIX as the power of the engines increased over the production run.
Also, it is worth noting that virtually all turbines have many compressor stages which turn on one shaft but have static blades (stators) between sets which provide the benefit of reducing the tangential flow without requiring high speed gearing.  This provides nearly all the efficiency increase without adding the mechanical complexity of trying to spin each stage in opposite directions at the high RPMs of a turbine.
Answer: Apart from the reasons stated above, there is another important one, specially valid for the Tu-95. The turbines of that plane are very powerful, the most powerful ever built. In order to convert that power in acceleration of a mass of air, you would need a very large and fast-spinning propeller, so large that the blade tips would surpass the velocity of sound. Thus, the only possible compromise for the giant turboprops of the Tu-95 was to fit each turbine with two large coaxial propellers, spinning in opposite directions. Even with this solution, the blade tips are supersonic, but not by much, and the propeller efficiency is good enough to propel the Tu-95 to speeds only slightly lower than its American jet-propelled counterpart, the B-52. The Tu-95, still flying today in the air forces of Russia, was a great technical success of the Soviet technicians.
Answer: Why do these planes have four sets of counter-rotating props? Not torque compensation - they have four engines and can simply zero out torque by having two turning clockwise and two anti- clockwise.
Counter-rotating props on fixed wing aircraft are a way to overcome the inherent limitations that propellors have in converting engine power into thrust. Propellor tip speed is the issue, once it reaches speed of sound a lot of engine power is required to overcome compressibility drag, and not useful in propelling the aircraft. So the disk size is limited, or the rotation speed of the blade. More blades help a bit if power is not the issue, but only a bit. More propellor disks help, but again only to a limit.
The Tu-94 had a similar operational mission to modern passenger jets: fly long range, close to the speed of sound. It first flew in 1952, a long time before high bypass turbofans existed: the jets of the time were wasteful with fuel, also a consideration in the design of the B52. While the US was working on more efficient turbofans, the USSR chose the other option: use two propellor disks. The second disk further accelerates air from the first disk.
New user Sam posts: Seems like we need to take a look at the potential better efficiency of wind turbines. Indeed a counter rotating arrangement can extract more power from a given air flow, but at what cost? Is tip speed breaking the sound barrier really an issue with wind turbines? Does the counter-rotating arrangement cost less than simply constructing another complete generator?
Comment: Contra rotating props probably wouldn't matter for windmills. Airspeed is low, and you'll get more juice by putting two props adjacent to each other running two generators, rather than two props rotating in the same space, where the first prop has already extracted a good deal of the energy in the air flow.
Comment: Indeed, my questions are self-answering. Theoretically possible but of no practical or economical value.
Comment: " Why do these planes have four sets of counter-rotating props? Not torque compensation - they have four engines and can simply zero out torque by having two turning clockwise and two anti- clockwise." because when you're dealing with an engine which can produce 15,000 shp, it imposes huge axial and torque loads on the engine mount and wing structures.  It would be nice to eliminate that torque load and I'm guessing that was the thinking at the Tupelov Bureau when they designed that thing.
Answer: Here is an explanation of a contra-rotating propeller, explained its advantage and disadvantage.
2 - Why contra rotating propellers?
As explained, each blade of an airplane propeller is essentially a rotating wing. As a result, the propeller blades are like airfoils and produce forces that create the thrust to pull, or push, the airplane through the air.
The high-speed rotation of an airplane propeller gives a corkscrew or spiraling rotation to the slipstream. The corkscrew flow of the slipstream also causes a rolling moment around the longitudinal (roll) axis. Note that this rolling moment caused by the corkscrew flow of the slipstream is to the right, while the rolling moment caused by torque reaction is to the left—in effect one may be counteracting the other. {However, these forces vary greatly and it is up to the pilot to apply proper correction action by use of the flight controls at all times. These forces must be counteracted regardless of which is the most prominent at the time.}
At high propeller speeds and low forward speed (as in the takeoffs and approaches to power on stalls), this spiraling rotation is very compact and exerts a strong side-ward force on the airplane's vertical tail surface.
When this spiraling slipstream strikes the vertical fin on the left, it causes a left turning moment about the airplane's vertical (yaw) axis. The more compact the spiral, the more prominent this force is. As the forward speed increases, however, the spiral elongates and becomes less effective.
One solution is by adding a second propeller behind the first, contra rotating and canceling the rotating moment.
Answer: Simple answer - To counteract Torque effect.
Detailed answer - Propellers usually rotate in the clockwise direciton. Now recollect Newton's 3rd law - "Every action has an equal an opposite reaction". Here the "action" is the propeller rotating clockwise and the "opposite reaction" would be the aircraft having a tendency to turn in the anticlockwise direction (that is, towards left). Now this left turning tendency is going to be a pain for the pilots as they have to apply rudder pressure to counteract it. And that's why contra-rotating propellers were introduced!
As the name suggests it's basically 2 propellers rotating in 2 opposite directions (one would be clockwise and the other - anticlockwise). This is going to cancel out the torque effect!
Answer: Regarding noise of propellers at speeds close to sound barrier, you may have a look at the F-84 'Thunderstreak', propeller version video in YouTube, https://youtu.be/UFhSzReWTgs it has contra-rotating propellers, and is probably one of the fastest airplanes with this arrangement ever, the video discusses the development and findings of a contra-rotating propeller in a fighter flying close to Mach 1; at any speed, the aim of having contra-rotating propellers I guess is reducing the effect of torque that will tend to make the airplane turn in the opposite direction as the propeller, along the propellers axis, in a centrally placed, single engine airplane, a propeller rotating in a clockwise direction, looking from behind, will indice a force making the fuselage turning in the opposite direction, also the vortex and other changes in air column induced by the propeller may have an influence on control elements, such as the rudder
Comment: i'm not sure this has anything to do with the question posed.
Comment: This airplane, F-84 propeller version, had contrarrotating propellers, and is an special experience in the field, because of the speed it flew at, some connection to contrarrotating propellers, it could be considered it has.Thanks. Salut +
Comment: it would be useful if you could [edit] your answer to include that information.


How do I know what cards or sets are legal to play with?

Question: Can I mix older Magic the Gathering cards with cards from Magic 2015? If I have mainly Magic 2015 cards can I play my friends who mainly have older decks?
Comment: You can of course play with whatever cards you want with your friends - seems like the real question is whether it'll be *fun* to play. Depending on what kind of older decks they have, there could be some power level mismatch.
Answer: It depends on what format you want to play.
Casual
You can use whatever cards you want, as long as your friends are alright with it. This is informally known as "kitchen table magic", at least in my area. Some casual formats are are so popular that they have their own rules, such as Commander. See the link at the bottom for more information.
Standard
Prior to 2016, you could only use cards from the latest two expansion blocks and any core set(s) directly succeeding them. Starting in the Spring of 2016, you can only use cards from the latest three expansion blocks. For those unaware, a "block" is a set of expansions that are released sequentially and revolve around a single story or plane. More details on this format here.
Modern
You may use cards from any set since 8th Ed. Some cards are banned.
Legacy
You may use cards from any set. Some cards are banned.
Vintage
You may use cards from any set. Some cards are banned. Others are restricted to one copy per deck.
All Constructed Formats
The following rules apply Standard, Modern, Legacy, and Vintage.

Deck must contain at least sixty cards
With the exception of basic lands, decks may not exceed four of any card
Cards with a silver or gold border only are illegal
Decks containing a mixture of Alpha and non-Alpha cards must be played with opaque sleeves
A card from an older set is legal if a card with the same name was printed in an otherwise legal set

You can learn more about these formats, as well as some that I did not cover (such as Commander), by visiting Wizards of the Coast's website.
Comment: Also, cards from sets not allowed in a format are allowed when they are reprinted in the format. For example, a Nightmare from Alpha is still legal in Standard because it is reprinted in M15
Comment: Might want to mention "floor rules 102", about mixing alpha and non-alpha cards. Even in casual play, though of course you can do anything you want, you would want to sleeve your cards with opaque sleeves if your deck mixes alpha and non-alpha.
Comment: @Gendolkari I Googled floor rules 102 and got something about Unhinged and Unglued (which I promptly tacked on to the bottom of the answer). I'm pretty sure I didn't get what you are talking about. Feel free to edit it in.
Comment: Commander/EDH may be worth mentioning, although the card pool is "Vintage minus some additional banned cards"; it's the deck construction that really makes it different.
Comment: @BrianS Added a reference to Commander under Casual (since it's technically a casual format).
Comment: @IvoBeckers Added a note about older cards cards being legal if they are reprinted.


Loading Wallet error

Question: vWhen I open the bitcoin-qt (v0.8.5 beta) app on my MacBook Pro 10.7.5 it says - loading block index, verifying blocks, loading wallet - then immediately crashes on loading wallet to give message "bit coin-qt unexpectedly quit". I know the address of my wallet, but not the private key. How can I solve this problem ??
Comment: try using a version which is not in beta.
Answer: Find Windows PC (friends, work, family)

Install fresh bitcoin-qt for Windows and run it once and then quit
Open folder: %UserProfile%\AppData\Roaming\Bitcoin\ and replace wallet.dat file from Your Mac (overwrite)
Open bitcoin-qt again and if it start OK generate private key: Help > Debug window > Console > dumpprivkey your_wallet_address

Loading Wallet error


Car "clicks" and rolls down hill in park

Question: Today I parked on a small hill that was probably about a 25% - 30% grade. I used the parking brake as always and did not have any issue when I first parked, even just leaving the car in park without parking break. When I returned to my car about 2 hours later, removed the parking brake, the car began to roll down the hill while making a "clicking" sound; almost like park wasn't working at all. What causes this? Is it something to be concerned about?
Comment: Also curb your wheels when you park.
Comment: 25-30% is a very steep hill. Is that really what you mean?  In the future on such hill, after putting in park, ease off the brake and let the car roll a few inches *slowly* until you feel it lock, then set the parking brake.
Answer:
What causes this?

Automatic transmissions use a gear-locking lever called a pawl. When you put your car in park, the pawl pushes down onto a cog looking gear and locks into place on it, preventing any movement in the transmission.
Here is an excellent explanation of the mechanics involved.
Depending on the age of the vehicle and the kind of wear that it has seen, it is possible that the sharp edge that keeps the pawl inside the grooves of the ring has worn down. I don't think this is very likely, and it may have more to do with a one-off failure (if you haven't seen the issue since this).
There is still a chance that the pawl or the spring that pushes it onto the ring is worn though, which would help explain the clicking sound you heard. As more clearly shown in the picture of the answer linked above, there are sections of the ring that separate the notches, which would make a clicking sound if the pawl was not engaging with the notches. Kind of like a skipping stone, the pawl may fall into the notch just a bit, and then be kicked up again.

Is it something to be concerned about?

It depends on whether or not this is happening regularly. If this is the first and only time that you have seen it, I would take it to a hill of a greater grade and play around with it. Try holding the car on the hill using just the park gear. Do not get out of the car with it just in park if there is any doubt it may slip. You do not want the car to roll back on you or run away down the hill.
If you have any doubt that it may fail again or just for peace of mind, take it to a transmission shop.
Answer: It sounds like your parking pin isn't fully engaging. Hopefully this is cause by an incorrectly adjusted shift cable and not a malfunction inside the transmission.


Croatian citizen traveling thru Schengen with non-Croatian spouse

Question: For the next couple years, my family and I are planning on traveling all through Europe with our camper. I am a Croatian (and US) citizen, as well as my kids. My husband is a US citizen with Croatian residency. Will the 90/180 Schengen rule apply to us? We will travel to each country in the Europe but will never stay longer than 3 months in each one.
Comment: @DavidRicherby the 90/180 rule does not apply here.  I'll post an answer in a few hours if nobody else does before then.
Comment: If the 90/180 rule applies to your case (_if_ -- I don't know), then you're only allowed to spend 90 out of 180 days anywhere in the Schengen zone: you don't get a separate 90-day allocation for each country. You wouldn't, for example, be able to spend 90 days in France and then 90 days in Germany, without leaving Schengen for 90 days between the two. Also, bear in mind that immigration officials are usually supicious of people who try to max out their entries by repeatedly staying for about 90 days, then leaving just long enough to reset the counter.
Comment: Any other thoughts on this? The EU Direct response I received  says "it seems that your husband would still have to adhere to the 90 days in any 180 days rule even if he may not need a visa as he is from a visa waiver country." Using "seem" in their reply is a strange choice.
Comment: Does your husband have an Article 10 residence permit?
Comment: He has a temporary residency permit.
Comment: @MichaelHampton it does not matter whether he has a residence card.
Comment: @phoog Would love to hear your thoughts.
Comment: @Umarlene I'm traveling at the moment so probably won't actually be able to answer until Wednesday.  You should have a look at https://travel.stackexchange.com/q/64168/19400.  The answer from Your Europe Advice could be cause for concern, but it is clearly an incorrect interpretation of the law.  I've sent them a similar question and received a similar answer, which I have not yet gotten around to challenging because I wanted to avoid an "asked and answered" response that Alex got, but I will do so next week and see what that yields.
Comment: @phoog please post an answer :)
Comment: @JonathanReez thank you for the reminder. I am again traveling this week. I've put a reminder in my calendar to post one next week, which I obviously should have done in December.
Answer:
Will the 90/180 Schengen rule apply to us?

No.  It does not apply to you because you are a Croatian citizen.  As long as you are together, it does not apply to your husband because when he is with you he is a "person enjoying the right of free movement under Union law" for the purposes of the Schengen Borders Code.  The definition is found at Article 2(5):

5. 'persons enjoying the right of free movement under Union law' means:
(a) Union citizens within the meaning of Article 20(1) TFEU, and third-country nationals who are members of the family of a Union citizen exercising his or her right to free movement to whom Directive 2004/38/EC of the European Parliament and of the Council applies;

The quotation omits point (b), which is not relevant.  Your husband falls under the second clause of point (a).
This has the interesting consequence that your husband is not a third-country national for the purposes of the Schengen Borders Code whenever he is traveling with you or to join you.  This follows from the next definition, Article 2(6):

6. 'third-country national' means any person who is not a Union citizen within the meaning of Article 20(1) TFEU and who is not covered by point 5 of this Article;

Whenever your husband is covered by point 5, that is, when he is traveling with you or to join you, he is therefore not a third-country national.
The Schengen Borders Code applies the 90/180 rule to third-country nationals.  It is mentioned in Article 6, "Entry conditions for third-country nationals."  Therefore, it does not apply to your husband.
However, the Schengen Borders Code only concerns entry and exit.  It doesn't say anything about conditions for remaining on the territory of an EU state.  For that, we have to look at the free-movement directive, 2004/38/EC.  This lays out several requirements that individual member states must implement in their national law with respect to EU citizens and their family members.  ("Family members" is fairly narrowly defined in the directive, but definitely includes spouses.)
The requirements include:

Family members traveling with or to join an EU citizen must be admitted with a valid passport (Article 5(1)) unless they pose a threat to "public policy, public security or public health" (Article 27).

Family members may be required to have a visa to enter only if the family member is a national of a country whose citizens require a visa for a short visit (Article 5(2)).  Because your husband is a US citizen, and US citizens are not required to have visas for short visits, he cannot be required to have a visa.

Close family members (including spouses) must be allowed to reside in an EU country "for a period of up to three months without any conditions or any formalities other than the requirement to hold a valid ... passport" (Article 6(2)).

Each country may limit the right of residence for more than three months to EU citizens who are workers, self employed, self sufficient, or studying and their family members (Article 7).

Family members of EU citizens in the preceding point may be required to register with a deadline of not less than three months.  A residence card must be issued in these cases (Articles (8) and (9)).

We will travel to each country in the Europe but will never stay longer than 3 months in each one.

As you can see, there is nothing about the Schengen area in any of this.  Your husband, therefore, does not violate the directive as long as you do not remain in any country for longer than three months.
Comment: Umarlene also [asked](https://expatriates.stackexchange.com/q/15626/2440) this at [Expatriates.SE], where I posted an [answer](https://expatriates.stackexchange.com/a/15627/2440) back in January.
Answer: When traveling as a Croatian citizen, the 90/180 rule does not apply

to avoid confusion, you should not travel with a US-Passport within the European Union

You husbands temporary residency permit is not a Article 10 residence permit, since you are a Croatian citizen (and not another EU-Citizen).
For a US-Citizen the 90/180 day rule applies while outside of Croatia, based on his citizenship and is a better option than an Article 10 residence permit - which only allows that person to travel with or join the EU-Citizen.

Sources:

MVEP • Granting Stay in Croatia
Comment: Many EU countries *do* grant article 10.residence cards to family members of their own citizens even if they don't have to (Spain and Italy are examples, but I don't know about Croatia).  Furthermore, all EU countries must grant article 10 residence cards to family of their own citizens if the *Surinder Singh* conditions are met.  So it is not actually possible to know whether the card is an article 10 card. But that doesn't matter, because US citizens don't require a visa if they stay for less than 3 months in each EU country under free movement.
Comment: Because the family member is traveling under free movement, the Schengen codes do not apply, and therefore the 90/180 rule does not apply.  The three-month limit of the free movement directive applies, and this is reckoned separately for each country.  I may be able to post an answer tomorrow, but it's very busy at work these days.


Electric Field support by two negative or positive charges

Question: Is it possible for negative charges to ride along the electric field lines going in to another negative electric charge? For instance say we have two negative charges of $-5C$ and $-2C$, clearly the electric field near the $-2C$ is stronger than the electric field lines near $-5C$, so when $-5C$ moves nearer to $-2C$, can $-5C$ charge ride along the stronger field lines near the $-2C$ charge?
Comment: You should look into Coulomb's law.
Answer:
Is it possible for negative charges to ride along the electric field
  lines going in to another negative electric charge?

It depends.
If both charges are point charges, all their field lines will go to infinity, i.e., there won't be any lines connecting one with the other. This is because field lines, originating on a negative charge, either terminate on a positive charge or go to infinity.
If the charges are actually too negatively charged finite size conductors (charged bodies), the situation will depend on the distance between them.
If the bodies are far away from each other, all their field lines will go to infinity - just like if they were point charges.
But, if the bodies are getting closer to each other, their charges get redistributed and their fields will change. In particular, since both bodies are negatively charged, they will push each other's negative charges to the outside surfaces (surfaces of the two bodies farther away from each other), leaving fewer negative charges on the inside surfaces (surfaces of the two bodies facing each other).
At some point, when the bodies are close enough to each other, all excessive negative charges of the $-2C$ body will migrate from the inside surface to the outside surface and, after that, negative charges leaving the inside surface will be creating excessive positive charges on the inside surface.
As soon as this happens, some of the negative field line originating at the inside surface of the $-5C$ body, will connect to the newly created positive charges on the inside surface of the $-2C$ body. Now, a negative charge could ride one of these lines, all the way from the $-5C$ body to the $-2C$ body.
Answer: Yes, but I think not in the way you imagine. The $-5\ C$ charge will "ride" along the field lines near the $-2\ C$ charge, but away from that charge. At the same time, the $-2\ C$ charge will "ride" along the field lines near the $-5\ C$ charge, also away from that charge (assuming both are in free space and are not constrained in some way from moving).
The force between electric charges is described by $F=\frac{kq_1q_2}{r^2}$. If the force $F$ is positive, because the charges are like charges (both positive or both negative), then the force is repellant, or if the charges are unlike charges, (one positive and one negative) then the force is attractive.
Similarly, the electric field strength is given by $E=\frac{kq}{r^2}$. The similarity is that the strength of the E-field and force are governed by the inverse square law.
There is one assumption in the question that is not right: that the E-field near the $-2\ C$ charge is stronger than the E-field near the $-5\ C$ charge (assuming that the distance from the charge is the same). In fact, at any given distance, the E-field near the $-5\ C$ charge will be $2.5\times$ the E-field near the $-2\ C$ charge.
The sign of the charge represents whether the charge is positive or negative, because it has implications with two charges (whether the charges are like or unlike). The magnitude of the E-field or force ($|E|$ or $|F|$), or the strength of the field, is absolute. Thus $|\frac{k(-2)}{r^2}|$ is less than $|\frac{k(-5)}{r^2}|$ just as $|\frac{k(-2)}{r^2}|$ is less than $|\frac{k(+5)}{r^2}|$, and $|\frac{k(+2)}{r^2}|$ is less than $|\frac{k(-5)}{r^2}|$.


Keeping New and Old Ipads

Question: My wife gave me a new IPad for Christmas. I want to keep the other Ipad for the use of my 6 year old daughter that has countless games on that Ipad. How I can keep applications that interest me (like QuickOffice Pro) of my old Ipad and leave the rest of the applications on the old Ipad to my daughter?
Answer: The easiest thing is to back up the old iPad to iCloud or your computer using iTunes.
Then restore the old backup onto the new iPad Air (you need to erase all content and settings to get the device clean for the restore).
When the setup asks if you have a backup, load that on the new device.

delete all apps and settings on the old iPad that should not be there.
delete all apps and settings from the new iPad that should not be there.

At that point, you can use the two separately. Look to perhaps turn off automatic downloads. At some point you can wipe the old iPad and let your daughter start buying her own apps or split things with a mix of the old Apple ID and her new Apple ID as well - you can mix purchases unlike iCloud settings.
Answer: Make sure you have a valid backup before you follow my steps.
if you have iOS 7 or any type of iOS here's what you can do, format the ipad drive : http://techchannel.radioshack.com/format-ipad-1036.html
You can also do another way to format the IPAD. Go to your General Settings. You should find a option that says "Reset Phone", tap on that and tap "Delete Everything" known as format.
Check out this blog for more help : http://www.padgadget.com/2010/06/14/ipad-quick-tip-%E2%80%93-reboot-reset-format-your-ipad/

Keeping New and Old Ipads


Does preload_replace not work in stash:embed templates?

Question: This is a fairly straight forward question... Does preload_replace not work in stash:embed templates?  In my embed templates, I tend to set a bunch of preload replace variables for things like channel name and custom field prefix so that if i ever have to change something, one change in the first couple of lines runs through the template and replaces al such instances.  But when i try that in a stash:embed template, the preload replace items just render as plain text in the template.  Is there a way to get them to work, or is this simply an unavoidable parse order issue?
Comment: I have had the same issue. I found a suitable workaround to be using Stash settings/getters in place of preload_replace, but this is not the answer to your question.
Comment: So far, I've resorted to doing effectively the same thing by passing those same values within the stash:embed itself as variables. Not perfect, but it works. I'm finding it odd, however, that performance of the page in question is reduced at the moment compared to what it was using a native EE embed.
Answer: Stash doesn't parse preload_replace. But they will work if you use process="start" with the stash embed, since that effectively includes the sub template code in the host template prior to preload_replace being parsed by EE. However, be aware that if you need to access stash vars captured in the host template then you need to use process="end" (the default) due to parse order; also process="start" templates cannot be pre-rendered (parse_stage="set") since the EE parser is not initialised at the point the template is included.
This is off-topic but addresses your comment about performance above:
By default a Stash embed works in a similar way to an EE template, and you will not see a performance gain if you are just including one or two templates in a host template. If you nest your stash templates or use them multiple times then you will notice a gain. And if you 'tune' your embeds  - by which I mean choose to pre-render and cache parts or the whole of your template and experiment with parse_depth, parse_vars etc - then you will see significant gains. You should also disable file sync ('stash_file_sync'=false) on your production environment.
The other significant advantage of a stash embed is that you can have multiple cached instances of the same template. That is possible because you can specify a file name separately from the variable name for the embed. This can be helpful for caching things like submenus which might share the same generation code but have different output for the various sections of your site.
Comment: Thanks Mark. I thought with stash embeds avoiding the full template parser they would see an uptick in performance, which is why I asked. I like your suggestion of the re-usability and portability aspect of the stashed embed - definitely helpful.


Is there any tool which can help me to import my .msg files into PDF format?

Question: I have approximately 1500 .msg files in my system, but now I'm not using Outlook as my email client and want to convert all .msg files into PDF format, because PDF is very easy to use and I can access that anywhere, any-time. Is there any software which can import my .msg file into PDF without destroying them?
Answer: THE one tool I use for such cases is MSGConvert:

it converts .msg-files into .eml-files.
this is IMHO even better than just .pdf, because the header is kept and you can still create .pdfs or anything else you want.
it is a pretty straight forward command line tool and can therefore easily be used for batch converting, scripting etc.
it does not need an installed version of MS Outlook.
it just needs Perl as dependency and is therefore cross platform available.
it does not destroy anything because the original files are only read.
it may not convert the .msg-files completely perfect, but hardly any tool (I tested) does. - thank you Microsoft!
disclaimer: if your life depends on these e-mails, I would keep the original files anyways (no matter what tool you use), because they are called "original" for a reason. - especially when converting complex proprietary binary formats (like .msg) you should consider it as lossy.
e.g. I don't know how TNEF-attachments are handled and I have no idea if/how such messages can be identified.
it is FOSS (free as in beer and speech) and therefore can be improved and extended by everyone: https://github.com/mvz/email-outlook-message-perl
Answer: I can recommend the free Convert MSG to PDF utility developed by my company. It automatically converts all MSG files in the selected folder to Adobe PDF documents.
Answer: PstViewer Pro from Encryptomatic can do this.
https://www.encryptomatic.com/pstviewer/
Comment: @RockPaperLz-MaskitorCasket I will. I did try to include a link originally but that caused the whole answer to be rejected as potential spam!
Comment: Welcome Nemo! Can you please add a link to your answer?  Thanks!
Comment: Thanks.  That's interesting to learn.  My guess is because the answer is short, and it included a link, the SE systems automatically assumed (hopefully incorrectly!) that you post was spam.  I think another factor may have been that you are new to our community.  In any case, it looks like you were now allowed to post a link.  Just to be sure, you don't have any affiliation with Encryptomatic, do you?  If you do, that's okay, but we require that you add your affiliation to your post.  Thanks, and again, welcome!
Comment: No affiliation to Encryptomatic or any other provider of software.


Why does my cauliflower plant have leaves which are damaged and full of holes?

Question: See attached picture of my cauliflower plant in my raised bed. Other plants are healthy but this one does not look as healthy. What could be the reason?
Answer: It looks as though it's been ravaged by insects.  Are you sure you don't have cabbage worms, aphids etc attacking this plant.
Sometimes I see that the weakest plant in a group of plants gets attacked by insects leaving the more healthy ones alone.  That is it becomes the honey pot limiting damage to the other plants.
Answer: You've got flea beetles.  They only last a short time but they love the brassicas and mustards.  I found that having a TRAP crop is the best way to divert these dudes from my 'cash' crops.


After update CiviCRM IATS Extension to 1.7.4, Card on file and Expiry Date fields are not showing

Question: When we create a new iATS recurring donation, we can edit the payment information, but the old iATS recurring donations cannot be updated. I have checked in extension code getting the customer code by payment_token_id. But payment_token_id  is missing in ContributionRecur API response. Only issue is in old (before update extension) iATS recurring donations.
Answer: I have upgraded the extension 1.6.2 to 1.7.4. During upgraded extension upgrade function were not ruined upgrade_1_7_002 and upgrade_1_7_003. After manually run the SQL Queries issue is resolved.
Comment: Thanks for posting your question and answering it. FWIW, the 1.7 has some db changing bits in it and that's why the upgrade steps needed to run. Before 1.7, the extension was managing the customer tokens itself, but as of 1.7 it converted to using the civi-native token api/system.
Comment: @AlanDixon Recurring payment started at January 19th, 2021.I changed the next contribution date from February 19th to February 2nd, 2021. It was working February 2nd, 2021 , March 2nd, 2021 and April 2nd, 2021. I have updated the IATS extension after upgraded it charged at May 5th, 2021 instead of May 2th, 2021.
This happened with multiple users. Is there a way to see if it is based on an iATS update?


How to secure an embedded linux image

Question: I'm building an image with openwrt sdk and i want to secure my image (by encrypting filesystem for example).. How can i do that to prevent anyone from seeing my sscripts or programs running ?
Answer: Don't give anybody physical access to a device that's running your image. If they have physical access to the device, they can read your image. Encryption wouldn't do any good since the decryption key would have to be readable.
If the device has some tamper-resistant storage such as a TPM or a smart card, this raises the bar somewhat: someone who wants to read your image would have to snoop on some data bus (which requires a bit of equipment). But still, if the device can run it, so can anyone who is physically present.
Obviously, the image should be secured during transport. But since the transport is between locations that you control (from your development machine to the physically secured device), this shouldn't be a problem.
Don't give anyone shell access to the device. You can get away with a sufficiently restricted shell access (no administrative powers), but really, on a WRT system, there's nothing to warrant that.

How to secure an embedded linux image


Why the K is silent in "know" and "knowledge"?

Question: Why is the K silent in "knowledge" and "know"? I have heard many non-natives pronounce the K but not natives. In dictionaries there is no K in the pronunciation but there is a K in spelling.
Comment: The reason we call it ***mumbling*** (with ***two*** /m/ sounds) is because /m/ is extremely easy to say. And *that's* the reason the normal word for ***female parent*** in almost all languages  usually has plenty of /m/'s *(**Mummy, Mama, Mere,...**)*. So I think this is just a characteristic of human natural languages in general, not specifically anything to do with English.
Comment: The first one [has been answered before](https://ell.stackexchange.com/a/264877/106592). The other two are different questions, you need to ask them separately.
Comment: This should be split into two questions. I don't even know how to retitle this question.
Comment: @EddieKal Sorry. I didn't know I could only ask one question. Now there are answers to the question and if I split the question into two will the answers be moved to the new question? I see that only one answer is addressing the first question so if I ask the first one separately, will the answerer move his answer? what should i do? If i ask the second question separately all the three answers have to move so i think its better to move one.?
Comment: @EddieKal I edited my question and split it
Answer: Every language has a fixed set of rules called 'Phonotactic rules' that govern the licit and illicit sequences of sounds in syllables. A sequence of sounds that is allowed in one language may not be allowed in another language, for instance, the cluster /pn-/ is phonotactically well-formed in Greek, but ill-formed in English, that's why the /p/ in pneumonia is pronounced in Greek, but dropped in English.
Over time, a language may undergo phonotactic change. The cluster /kn-/ wasn't always silent; the /k/ was pronounced in Old & Middle English. In Modern English, the tautosyllabic1 cluster /kn/ is impermissible (or rather, banned). English cannot have a word start with Plosive + Nasal sequences, the clusters /kn-/, /gn-/, /pn-/, tn-/, /dn-/, /bn-/2 etc., are therefore not allowed.
Whenever a word starts with Plosive + Nasal, the plosive is usually dropped from pronunciation.
The k in know and knowledge was pronounced up until Modern English. The cluster /kn-/ was a part of the phonemic inventory of Old & Middle English, but it ceased to be a part of Modern English probably because changing from oral to nasal in the same syllable became awkward-to-pronounce for Modern English speakers, that's why there's no /k/ in ⟨kn-⟩3 sequences. However, the k is retained in spelling.

1. 'Tautosyllabic' means within the same syllable.
2. /slashes/ represent 'sounds' (more precisely, the mental representation of sounds), not 'spelling'.
3. ⟨Angled brackets⟩ represent 'orthography' (spelling)
Comment: I've explained how consonant clusters combine in syllables in [this answer](https://ell.stackexchange.com/a/268464/106592).
Answer: Regarding "know," you will notice certain patterns in English pronunciation that allow you to make a good guess at a word's pronunciation even if you've never encountered the word before.  For example, I think the combination kn- at the beginning of a word is always pronounced as "n-" (silent K) in English words.  Examples: know, knew, knoll, knack, knave, knight, knell.  (Many of these are "old" words, not used in everyday speech anymore.)  This rule is true even when prefixes are added: unknown, foreknowledge, acknowledge -- In the word "acknowledge," there is a "k" sound from the "ac-" prefix (rhymes with "back") but the "k" is still silent. The only exceptions would be for some proper names:  For example, in the family name "Knudsen" and the name "Knut" (a Danish king who lived around 1000 AD, usually spelled "Cnut" in English), the K and N are both pronounced.
Other patterns you will notice are that "[consonant] + igh" is always pronounced as in "sigh" and "[consonant] + ight" is always pronounced as in "night."  When a consonant is followed by "-igh" or "-ight," the vowel is a "long i" and the G and H are silent.
Examples: high, nigh, thigh, right, tight, fight, sight, light, might, plight.
The reason I specified that there must be a consonant before "-igh(t)" for this rule to be guaranteed to be true is that many words with a vowel + "-igh(t)" do not follow this rule.
Examples: weigh, weight, sleigh, neighbor, straight, freight, inveigh. (These all have the same vowel as "ate.")
However, the words height and sleight do rhyme with night!  You just have to learn these ones on a case by case basis.
The combination "-ough" is notoriously variable in its pronunciation in English, so you have to memorize all of those individually.
Side note: There is a phenomenon in certain varieties of English, including my own (Chicago/Great Lakes region), that is called Canadian Raising.  One feature of this phenomenon is that the vowel in "high" is not the same as the vowel in "height."  In "height," the "long i" of "high" gets "raised" in phonetic terms because it precedes "t," a voiceless consonant.  This distinction is rather advanced and most native English speakers are probably not even consciously aware of this type of pattern.  However, I wanted to point it out for those who are interested and want to learn more about it.
Comment: That's why I specified "kn-" at the beginning of a word!  In a word like sickness, the "ck" sound is pronounced.
Comment: Discovering the patterns of English spelling and pronunciation is *si**ckn**ess*!
Answer: English is... an extremely inconsistent language! It's the result of many different languages coming together and developing over time, and we never had an official standardisation to "tidy up" the issues. US English has made some attempts to modernise spelling and make it more consistent, but it's still light-years away from something like Spanish, for example.
The short version is: sorry, you just have to learn how everything is pronounced! There are some basic rules you can learn, which work most of the time - after a while you'll notice patterns, and you'll see how words connect to other words you know, and it'll become easier.
I think most native speakers can make a good guess at how most unfamiliar words are pronounced, and that's because we just develop an unconscious understanding of the rules from being immersed in the language. But we can still get tripped up - I just learned that hough is another spelling of hock and is pronounced the same way! That was a new -ough for me, I thought I'd heard them all.
But yeah, trust the dictionary, not the spelling.
Comment: Huh.. *Hough* is with a k? I would have rhymed it with *cough*
Comment: @Eclipse don't worry about it - honestly your English is extremely good for someone who's just noticing how messed up this language is! This probably isn't the right place to talk about it though, you'd want a forum where they deal with linguistics and etymology. If you're interested in this, find a good dictionary that tells you the history of a word - which language it comes from, what the original word was, etc. It might start to make more sense, sometimes!
Comment: Thanks. I didn't know about many other languages lol. I can't vote for you answer because it has some problem
Comment: @Void yeah apparently! https://www.collinsdictionary.com/dictionary/english/hough


Can AntMiner L3+ mine any scrypt coins or just lite coin

Question: I am planning to buy ant miner l3+. Can AntMiner L3+ mine any scrypt coins or just lite coin?
Should I buy Antminer s9 or L3+?
However, I can only afford one piece of anyone.
Answer: The L3+ is the best option right now (however if you're ordering now, you won't get a new one for some time, and the second hand ones are being resold for huge profits), however this will change as more of them are made/released.
The L3+ is a Scrypt miner, so it could in theory mine any Scrypt based coins, Litecoin being the big one.
Bitmain don't appear to be shipping anything out any time soon, Avalon (http://canaan.io) or Ebit (http://miner.ebang.com.cn) also sell alternative miners, they're not as power efficient as the S9 (and slower), but cheaper, so if you're dipping your feet into the water to test the temperature, it's an alternative.