Does a minor software update effect rooting method?

Question: I'm a newcomer to Android, so I'm not very familiar with how rooting works on Android. In IOS minor updates such as going from 9.0 to 9.1 can sometimes result in a jailbreak method not working, I was wondering would that be the same if a Samsung S7 edge is updated with a minor security update from Samsung.
Comment: If you're rooted, you can't install an update; you'll get an error (unless you had used systemless root). Even if it's systemless root (Android 6+), you'd have to flash the old boot.img (which is automatically done by unrooting in SuperSU) inorder to successfully install the update; which ofcourse means you're unrooted and have to root again. If minor update, the same rooting method should work.
Comment: Also since it's Samsung, I recommend you search and read about "**Knox**". If it's tripped, you won't get updates I guess. Knox is tripped upon rooting (unlocking bootloader)
Comment: @GokulNC so basically like IOS I have to find a rooting method that doesnt trip **knox** for whichever particular version of the software I'm using if I'm going from Marshmallow to Nougat for instance but should be fine with any minor updates from Samsung?
Comment: Generally the rule of thumb is to never do any ota  updates while rooted unless you plan on starting from scratch. You can check out Xda forums as to whether or not there is a root for that version. I have a s7 edge as well and Samsung is a pain with updates. I wouldn't try the same root method until it has been verified with the security update. Could get you into a bootloop. Please post version/build number and carrier and I'll look into it
Answer: This ultimately depends on the manufacturer. Samsung is not at all friendly to the rooting of it's stock ROMs, and does lots of modification to it's Android ROMs, so I'd say it is a real possibility. If it were me, I would install Cynaogenmod instead if I were to root but still wanted OTA updates.
Google itself, which is where the baseline Android comes from, usually doesn't care all that much if people want to root their devices, and usually doesn't plug holes that allow rooting unless customer data is at risk as a result.
Answer: for android apps on the market, rooting is like exploit the mobile system and get root privilege. Therefore, if the system gets updated, the update patch might fix the vulnerability, same attack approach might not be working again.
Answer: Every update may contain security fixes (for ex. monthly security patches) and the security fix may address the exact exploit used by the root method.
So yes, even the smallest update may break rooting methods.
Answer: Major updates of Android may include firmware updates/bootloader updates, which can change the process of rooting!


Load firebreath plugin in Firefox extension without injecting anything in DOM

Question: Is there any way to load firebreath plugin in firefox extension.I've seen one way by injecting html related to plugin into DOM as explain here(see "http://stackoverflow.com/questions/5688904/scriptable-npapi-plugin-doesnt-work-with-firefox")
I think its better that extension will load plugin in background to avoid any security issues.
my plugin has nothing to do with drawing, its just send data to a specific port by calling a simple function.I'm new to extension development so any example will be helpful...
Comment: Fixed it by loading it in XUL file
Answer: Sounds like you figured it out, but for the sake of any who find this question with the same issue: a NPAPI-based plugin (FireBreath or otherwise) can only be loaded inside of a DOM; however, in the case of a firefox extension (or Chrome extension for that matter) it doesn't have to neccesarily be the DOM of the web page, it could also be the DOM of the extension.
In this case, you can load the plugin in the XUL file.
It's also worth checking out this thread:
Using a plugin generated with Firebreath in a Firefox Extension?


quote copy/paste keys bindings

Question: how can I copy a quote and paste it onto an emacs file? the shortcuts please?. I have tried to type the text but it is too long to write by hand.
Comment: The question seems unclear. What do you mean by *" a quote"*? A single-quote character (curly or straight)? A double-quote character (curly or straight)? Some text that you want to cite, as a quotation? The text to be copy+pasted being "*too long*" suggests that you don't mean a quote character. But please clarify. Consider providing a recipe showing what you want to act on as the input and what result you want.
Comment: Copy from where? Is Emacs running in a terminal (as implied by the tag)? If so, on what operating system, and in what terminal application if applicable?
Answer: M-w copies the selected text into the operating system clipboard, as well as into Emacs' internal storage.
C-w cuts (or "kills", a name which derives from the very oldest predecessors of Emacs) the selected text, putting it into both the operating system's clipboard as well as the internal storage. C-k kills all the text from the point to the end of the line.
C-y pastes (or "yanks", as it is generally called in Emacs) text into the document.
The internal storage forms a list of all the things you have copied or killed. C-y yanks back the text from the head of this list. If you then hit M-y, the yanked text will be removed and replaced with the text from the next entry in the list. You can keep hitting M-y to go farther and farther back in the list. When you get to the end of the list, the next M-y will wrap back around to the beginning again, so this list is called a ring. Thus in the Emacs documentation this is called the kill-ring.
In your case you want to copy the text from whatever you're viewing the quote in, and then go to Emacs and type C-y.
I recommend reading the Emacs manual for more information like this. In your case I recommend starting with chapter 12, Killing and Moving Text, which deals with all the ways to cut, copy, and paste text.
In addition to reading the manual online, you can also read it within Emacs itself. Typing C-h i will bring up the info viewer. This normally starts at an index of all the manuals installed on your computer, which should at least be the Emacs Manual and the Emacs Lisp Manual, but may include dozens or hundreds of manual from all kinds of programs you have installed (mostly this depends on the operating system that you are using). Select the Emacs Manual, then go down to the chapter you want and select it.
As an Emacs beginner, you may also find the built–in Emacs tutorial helpful. You can access it by typing C-h t.

quote copy/paste keys bindings


Is there any generic cheap RF module

Question: Recently I got cheap RF remote controlled plug points. I hacked the remote to control buttons using raspberry pi and it works great. My question is, is there any generic RF transmitter and receiver module? Receiving side, i want few GPIO pins so that we can control multiple motors or relays. I saw xbee modules, but they are very costly. Is there any such cheap RF transmitter receiver? Please help me how to go about it.
Answer: Most receivers require a microcontroller on the receiving end. The XBee already has a micro on board, so you can use it to directly turn on/off a pin on the xbee.
If you don't want to have to program some micro-controllers (e.g. arduino's), you best bet is to get some more remote-plugs.
If you don't want to use 220V, just crack them open, and reuse the board inside. You'll have to provide it with low dc-power yourself.
Instead of reusing the remote, you can use one of these modules to send the commands.  That way you are not limited to only 3/4 devices (depending on the remote you're using).

Is there any generic cheap RF module


Roadmap to reach Arithmetic Geometry for a Physics Major

Question: Hi Everybody! I am physics major but I read mathematics for myself. my main fields of interest are number theory and geometry. it seems that due to the works of A.Grothendieck, algebraic geometry must be used for studying deepest problems of number theory which culminate in the field of Arithmetic Geometry or Arithmetic Algebraic Geometry (please correct me if this isn't so). Could someone help me for more elemntary raodmap to reach the subject! I know analysis and algebra at the level of A.W.Knapp books (Volume one of every field) and number theory at the level of "A Classical Introduction to Modern Number Theory" (now at chapter 19)! I found that "Lectures on algebraic Geometry" by G.Harder have subjects of the field like tate conjecture or etale cohomology. expected volume three of these lectures will be about topics like cohomology of arithmetic groups and Langlands program! Thanks!
Comment: I must deliver some unfortunate (or maybe fortunate?) news for you. Even the subspecialty of Arithmetic Geometry is broad enough where I can't really tell from your post what you'd really like to learn. It's true that algebraic geometry is quite useful, but the sort of deep problem you're interested in can wildly alter the amount of algebraic geometry you need to master. For instance, Zhang's recent theorem on bounded gaps uses the Weil conjectures (now a deep theorem of Deligne) but it is not a prerequisite to completely understand Deligne's work in order to understand Zhang's result.
Comment: So what is it REALLY that you'd like to know about number theory?
Comment: Take a look at the book "From Number Theory to Physics". Exerpt from the blurb : "The 14 chapters of this book are extended, self-contained versions of expository lecture courses given at a school on "Number Theory and Physics" held at Les Houches for mathematicians and physicists. Most go as far as recent developments in the field. Some adapt an original pedagogical viewpoint."
Comment: For the book of Günther Harder you will need more than the (beautiful) book of Ireland and Rosen. There was already a discussion about this type of question, see http://mathoverflow.net/questions/23385/opinions-about-the-book-lectures-on-algebraic-geometry-1-sheaves-cohomology-of.
Comment: Dear stankewicz, Thanks for your attention! My long-term aims are followings 1) understanding Diophantine aspects of elliptic curves namely the problem of rational solution and integral points on the curve. specifically deep comprehension of Moredell-Weil Theorem ,Siegel Theorem ,Faltings Theorem,Weil Theorem (STW Conjecture) and Birch-Swinnerton Dyer Conjecture! 2) Arithmetic aspects of Langlands Program; 3) understanding the scheme-theoretic approach to arithmetic problems (for this I found Q.Liu's "Algebraic Geometry and Arithmetic Curves" but it was a nightmare!)
Comment: I do not want to question your freedom to use punctuation however you like it—but are you aware of the fact that your usage of exclamation marks is very uncommon? Using that many exclamation marks is commonly considered bad style, for the reader it may suggest a certain harsh tone/harsh stresses, which might not be your intention, and those occasions where an exclamation mark is actually used to emphasise a surprise get covered. Just a remark.
Answer: I recommend Silverman's The Arithmetic of Elliptic Curves. Silverman takes the highbrow approach, but writes in such a way as to make his book friendly and accessible for newcomers.
Comment: @Math-Phys Lover: "Arithmetic Geometry" the name itself suggests that there is going to be $\textbf{Algebraic Geometry}$ involved, even if you were to start from scratch. So I don't see anybody skipping Algebraic Geometry and learning Arithmetic Geometry.
Comment: The definition of "arithmetic geometry" is more or less "algebraic geometry applied to number theory". Silverman indeed uses algebraic geometry, but he gets a lot of mileage out of only a little bit of algebraic geometry, and the needed algebraic geometry is explained in two short introductory chapters.
Comment: Dear Frank Thorne: it seems that required prerequisite for this book is algebraic geometry which is beyond my knowledge!
Comment: as the title of this topic suggests I require a roadmap! so my main question is "are the next step for someone like me with basic knowledge of Algebra & Analysis to comprehend basic arithmetic geometry for my aims explained in an answer to stankewicz is to use Silverman's book? I know that I should master Algebraic Geometry!
Comment: Honestly based upon the answer you gave, Silverman's Arithmetic of Elliptic Curves is a pretty good starting point. As Frank says, the algebraic geometry prerequisites are covered in the first two chapters and he really dives into the subject in chapter 3.
Comment: I also second Frank Thorne's advice. Silverman is not very technical, he does not use all the "modern" machinery of schemes, it gives very precise bibliographical references (which is, I think, what is crucial for you) and has many many examples computed in full details. Of course, do not try to skip the first two chapters not its exercises, nor expect to be done in a couple of weeks. But then, when it will get to Elliptic curves over local and finite fields, you will need more basic arithmetic, and I agree with Joël's advice below about reading Samuel and Gouvêa.
Answer: It seems to me a superhuman task to learn any substantial part of  modern arithmetic geometry without any other guidance that a list of books. If you want to begin learning it seriously,
the less hard way is to follow a math graduate course at your university or nearby on the subject (you say your a Phys major, so I assume you are currently affiliated in a university).
Reading books by yourself is good, but will not take you very far (I don't say that to discourage you of reading books, on the contrary| I say that in order that you understand it's normal if you get discouraged in trying to read more advanced books).
That said here is a list of relatively elementary books you might trade to read:
First, if you want to advance a little bit, you will need a solid background in algebra,
more solid that you probably can get as a Physics Major Undergrad: good books are Lang's Algebra, or Jacobson's Algebra.
For algebraic number theory proper, I like
algebraic theory of numbers, by Pierre Samuel.
Gouvêa's p-adic numbers: an introduction is also interesting.
Comment: Dear Joël, Thanks for your Comments and recommendations! as I said I read The Voume 1 of A.W.Knapp Book about algebra, "Basic Algebra". the second volume is related to number theory and algebraic geometry! it would be great if you can comment about the second volume!
Answer: Learning number theory (or any thing for that matter) wouldn't be fun without solving a lot of problems. I'd recommend "Problems in analytic number theory" and "Problems in algebraic number theory" by Murty and others
Answer: "3) understanding the scheme-theoretic approach to arithmetic problems (for this I found Q.Liu's "Algebraic Geometry and Arithmetic Curves" but it was a nightmare!)"
My suggestion for making Liu's excellent book more accessible is "The Geometry of Schemes" by Eisenbud-Harris. The latter is relatively short and gives away several of the basic "secrets"; in fact, the first half of this book would probably do so as to move on to Liu.
2) For arithmetic aspect of Langlands, a nice way to start is with Bernstein-Gelbart, "An Introduction to the Langlands Program"
1) for "deep comprehension" of arithmetic on curves, it would be nice to first go through most of Liu's book to understand many of the modern techniques. Silverman's books are also standards here.


Vulkan rendering lots of objects

Question: I'm wanting to render multiple objects on a screen and in some cases several of each object. I'm not sure what the best method of doing this is and was wanting some advice. The only way I can think of doing this is having X Command Buffers for each model I want to render and store all draw requests for that model inside, then submit them when I require the draws.... Would this work or is there a better solution?
Answer: Submitting Command Buffers is not a bad thing to do in Vulkan. So long as you're submitting them in logical batches together you'll find that it's plenty fast to submit tons of commands. However if you need more speed, "geometry instancing" can be very fast for drawing lots of objects. Note that you may not need to in the first place since submitting lots of command buffers is totally fine; profile first and optimize later.
Regarding instancing here are some resources:
This reference here is for OpenGL but the principles still apply.
If you want a Vulkan specific example Sascha Willems has a code sample on Github but it doesn't have the in-depth explanation as the previous link.
Comment: These articles are very helpful, thank you, I've managed to achieve the desired effect of rendering many models by queuing up all the draw calls in a single command buffer and using a dynamic uniform buffer to pass the required model mat4 data to the shader.
Comment: Thank you very much, I will take a look at this now and see how I get on

Vulkan rendering lots of objects


What is the best layer for chlorophyte farming on terraria mobile?Is it possible on mobile?

Question: I am having trouble getting my chlorophyte farm to work.I am on mobile and an getting ready to fight plantera. I dont even know if it is possible to farm chlorophyte on mobile terraria.Im on the newest terraria update for mobile with x2.5 world size option.No farms seem to work for me for anything.Let me know some farms for other things that work on mobile.
Comment: "Chlorophyte Farms" they spawn everywhere in the jungle.
Comment: What have you already tried?
Answer: Building a farm farming isn't the fastest way to get chlorophyte. Just get some spelunker potions and mining potions and dig straight to any chlorophyte you see. Make sure you leave one ore block for every chunk of ore you mine, so it can re-grow.


Is possible to perform algebric operation with bitwise operations in PDM domain?

Question: I have to compute the some operations (say sum and subtraction) between 2 signals.
I have data in PDM domain:
x1_pdm(t)=[0101011....];
and
x2_pdm(t)=[0101011....];
What I do now is:
convert x1_pdm and x2_pdm in PCM domain (low pass filter and decimation factor M=64) and that compute the sum and difference (or any other operation). Is it possible to perform this sum and sub in PDM domani with bitwise operation ? and then compute one pdm to pcm conversion...
thank you
mattia
Comment: What on earth is meant by `x1_pdm(t)=[0101011....]; and x2_pdm(t)=[0101011....];`? Are the bits to be interpreted as a binary integer that tells us how wide the PDM pulse is?
Comment: x1_pdm(t)=[0101011....] is the pdm stream out out the sigma delta modulator.
Answer: Yes, this is sort of possible.   While PDM signals are full of high-frequency noise, at lower frequencies the "density" domain is limited to signals representing values from -1.0 thru +1.0.   This makes it difficult to implement true addition/subtraction since 1+1 exceeds the range of possible outputs, however if the output signal is scaled back into the allowable range, so averages like 1/2(A+B) and 1/2(A-B) can be calculated by multiplexing the two bitstreams into a single output stream (at twice the bitrate).
The best explanation of this I've seen was in a series of five articles titled "Signal Processing in the Density Domain" published in 2011 by Dave Van Ess in Electronic Design magazine.   The web copies of these articles exist but the equations and figures from the original versions seem corrupted by the web's evolution over time.   I'll include this link to the finale, Part V which wraps up how addition/subtraction and multiplication work.
While not easy, the missing figures can be retrieved from the internet wayback machine.


A question about Choice Functions.

Question: Assume the axioms of ZFC. Suppose that X is an infinite set of infinite (and pairwise disjoint) sets, none of which has a cardinal number greater than that of X.  Is the cardinal number of the set of all Choice Functions for X always equal to the cardinal number of the set of all mappings of X into itself?
Answer: That is one convoluted question.
If $X$ is a set of non-empty sets such that for all $y\in X$, $|y|\leq|X|$, then $|\bigcup X|=|X|$.
If all sets have at least two elements, then there are $2^{|X|}$ choice functions. Since you have added the assumption that all the sets in $X$ are infinite, we have that indeed this is $2^{|X|}$. On the other hand, there are exactly $|X|^{|X|}=2^{|X|}$ functions from $X$ to itself (because we assume the axiom of choice).
So the answer is yes.
Comment: Many thanks for your answer. It seems to me that when mathematicians talk about choice functions they are mostly interested in whether or not they exist. They do not seem much interested in the set of all choice fuctions. So I became curious about this set and wondered what its cardinal number would be.
Comment: Yes, but it's not quite surprising that when assuming the axiom of choice we have the maximal number of choice functions possible. What is nicer is that it is consistent with $\sf ZF$, for example, that there is a family of sets which admits a countable number of choice functions.
Comment: That is a very interesting fact about ZF which I didn't know. It is just one more example of the strange things that become possible when the axiom of choice is not around to keep them from occuring.
Comment: Quite. I don't think most people are aware of this. Not even people working on axiom of choice related questions. It's one of these things you notice once, and then you forget, and then you notice again, and forget again, and so on and so forth. Pretty cute detail, though.

A question about Choice Functions.


$\int\limits_{S(1,1)} (\frac{z}{z-1} )^n dz $

Question: $\int\limits_{S(1,1)} (\frac{z}{z-1} )^n dz$ where $S(c,r)$ refers to a 2-dimensional sphere with a radius(r) and a center(c). My thoughts till now are $\left(\frac{z}{z-1} \right)^n=(z^n)\left(\frac{1}{z-1} \right)^n$ and write $\frac{1}{z-1} = \sum c_{k}z^n$ as a series with center $0$ so I can use the common $z$ in the above product $(z^n)\left(\frac{1}{z-1} \right)^n=z^n\left(\sum c_{k}z^k\right)^n=\sum \left(c_{k}\right)^nz^{nk+n}$. What I got was the series $\left(\sum_k z^{k+1}\right)^n$. And then I tried integrate that. Am I taking it too far, cause I think this may be simpler.
Answer: I presume you mean the path integral $$\oint_{S(1,1)} \left(\frac{z}{z-1}\right)^n\; dz$$
where $S(c,r)$ is the circle $|z - c| = r$ in the positive (counterclockwise) direction, and $n$ is a positive integer.
It's better to use a series in powers of $z-1$.  If you take $w = z-1$, you get
$$ \int_{S(1,1)}\left(\frac{z}{z-1}\right)^n\; dz =  \int_{S(1,0)}\left(1 + \frac{1}{w}\right)^n \; dw= \sum_{j=0}^n
{n \choose j} \int_{S(1,0)} w^{-j}\; dw = \ldots$$
Comment: So I can assume that since the only anomaly-point in $S(0,1)$ is its center $0$ and only when $j=1$.  All the integrals with $j \neq 1$ are nulled since $w^{-j}$ defines a holomorphic function except $j=1$ where we have the anomaly. So we just have to calculate $(\binom n 1 )*2πι$?
Comment: $w=0$ is still a singularity of $w^{-j}$ for $j \ne 1$, but the integral is $0$ because for $j \ne 1$, $w^{-j}$ has an antiderivative $w^{1-j}/(1-j)$ that is holomorphic except at $w=0$.
Answer: You could also apply Cauchy's integral formula, assuming $n \in \mathbb{N}\setminus \{0\}$
$$f^{(n)}(a)=\frac{n!}{2\pi i} \int\limits_{S(a,r)}\frac{f(z)}{(z-a)^{n+1}}dz$$
In this case, the function is $f(z)=z^n$
$$\int\limits_{S(1,1)}\frac{z^n}{(z-1)^n}dz=\int\limits_{S(1,1)}\frac{f(z)}{(z-1)^n}dz=\frac{2\pi i}{(n-1)!}f^{(n-1)}(1)=2\pi i \frac{n!}{(n-1)!}=2\pi i \cdot n$$


Complex plane conundrum

Question: So I've been wondering about geometry on the complex plane. Points on this plane are denoted by $(a+bi)$, right?
If we have the point $(1+i)$, the horizontal distance from the complex axis is $1$, and the vertical distance from the real axis is $i$. So the distance from the origin by Pythagorean theorem would be:
$$ 1^2 + i^2$$
$$=1+(-1)$$
$$= 0?$$
But that would mean the point $(1+i)$ is on the origin which it it obviously not!
Is there an explanation or is regular geometry like Pythagorean theorem not applicable to the complex plane.
Comment: The vertical distance is just $1$ not $i$
Comment: Yes, but distance is always real. We just use the complex plane to geometrically represent complex numbers as coordinates with real parts on the $x$ axis and imaginary parts on the $y$ axis.
Comment: The tag is wrong. Despite what you may think, the term "complex geometry" is not meant to refer to this type of topic, but something more sophisticated.
Comment: How is i equal to one, isn't the vertical axis for complex numbers
Answer: As already mentioned in the comments, distance functions are typically real valued, not complex valued.
A distance function on a set $X$ is a map $X\times X\to \mathbb R$ that satisfies certain properties. Two of the properties include inequalities.
If you try to replace $\mathbb R$ with $\mathbb C$, this stops making sense because there is no ordering for $\mathbb C$ for those axioms to work with, at least, not one that is geometrically useful.  Instead, $\mathbb C$ gets its metric from its underlying metric space $\mathbb R\times\mathbb R$.

Complex plane conundrum


How Does One Go On Charging Ni-Cd Battery's

Question: Its a simple question but I can't seem to find any info on it. I have two Ni-Cd batteries (listed bellow) so i want to know how to charge them? And how to know if they are completely dead or are still alive. Each battery has 3 cells with the same type of package style as shown in the images.

Rating 3.6V 300mAh - Reading Voltage = 0.3V
Rating 3.6V 600mAh - Reading Voltage = 0V
Answer: The normal charge rate for Nickel Cadmium (NiCd) cells is 1/10th of the capacity for 14 hours.
For the ones you have there the first would require a constant 30mA with the second needed 60mA.
You could use a resistor from 12v to provide the constant current but keep monitoring the voltage and current to determine if anything unusual occurs.
The voltage should not go over ~1.5V per cell.
NiCd are not legal in new equipment so those are old (The data code on the second is 0904 probably meaning 9th week of 2004).  They have probably degraded to the point where they do not function well.
When the batteries get old not only do they have reduced capacity but they also tend to have high self-discharge so even if they do charge up they may discharge by themselves in only a few days.
As the other poster indicates cadmium is toxic so they should be disposed of in an approved manner.
You can learn more at Battery University.
Comment: I believe they say that's for a new never used NiCd.  Otherwise a 1C 1 hour charge.  In their comparison of secondary batteries the table shows 1-2hr. http://batteryuniversity.com/learn/article/secondary_batteries
Comment: Only if you have a fast charger and batteries suitable for fast charge.  These look like they are for cordless phones and are probably not designed for fast charging.  The slow charge for NiCd is usually taken as C/10 for 14 hours.
Answer: The NiCd is one of the most rugged and forgiving batteries.
You need a charger.  A NiCd charger will charge them fastest, 1-2 hours.  A NiMH charger will take 2-4 hours.
To achieve a reliable voltage signature, the charge rate must be 0.5C and higher. Slower charging produces a less defined voltage drop, especially if the cells are mismatched in which case each cell reaches full charge at a different time point. To assure reliable full-charge detection, most NDV chargers also use a voltage plateau detector that terminates the charge when the voltage remains in a steady state for a given time. These chargers also include delta temperature, absolute temperature and a time-out timer.
Fast charging improves the charge efficiency. At 1C charge rate, the efficiency of a standard NiCd is 91 percent and the charge time is about an hour (66 minutes at 91 percent). On a slow charger, the efficiency drops to 71 percent, prolonging the charge time to about 14 hours at 0.1C.
During the first 70 percent of charge, the efficiency of a NiCd is close to 100 percent. The battery absorbs almost all energy and the pack remains cool. NiCd batteries designed for fast charging can be charged with currents that are several times the C-rating without extensive heat buildup. In fact, NiCd is the only battery that can be ultra-fast charged with minimal stress. Cells made for ultra-fast charging can be charged to 70 percent in minutes.
Comment: I have a Ni-MH Charger but the thing is I don't think it would charge the cells, as one - they are in a package of 3 cells in one and the charger has a thing that if the voltage is 0 then it won't charge, I've got a http://assets.hardwaresphere.com/uploads/2012/05/energizer-smart-nimh-battery-charger.jpg
Comment: @Xios That should be fine if you can connect them somehow. Just don't reverse the polarity.  I will not charge all three.  You need to limit the charge current to 300mA.  You could try a power supply and resistor.  I'd be wearing safety goggles the first time I hooked them up to anything.


In the movie Star Trek: First Contact, could the Borg have been beamed off the Enterprise?

Question: In Star Trek: First Contact, once the Enterprise's crew found out that the Borg were on board, could they have beamed the Borg off the Enterprise out into outer space, or do the Borg have the capability to block transporter beams?
Comment: @Rebel-Scum - I disagree. This isn't (necessarily) about using it as a weapon. Also, it's specifically about the Borg rather than about more general uses.
Comment: A quick comment not worth an answer is that shields (traditionally) block transporters. Borg have been known to have personal shields, so in principle that's why they didn't try it.
Comment: @Valorum Why else would they beam the Borg off the ship!?
Comment: @Rebel-Scum - Back to their own vessel?
Comment: @Valorum I doubt even Picard would do that. If you can beam the Borg off your ship, you send them in empty space as far away as possible ;-)
Answer: In VOY: Dark Frontier, the crew stage attempt to beam some Borg off the bridge (in a simulation). This proves impossible because individual Borg are able to inhibit transport.

CHAKOTAY: Beam them out of here.
PARIS: I can't get a lock. They've adapted to our transport frequencies.
CHAKOTAY: Computer, freeze programme, both holodecks. What happened?

Moving (way) down the canon scale, in Star Trek: Online - Khitomer Crisis, a crewman is capable of beaming some Borg into the pattern buffer, then rematerialising them next to a hull breach, to be jettisoned into space. This only seems to work because the Borg are seriously malfunctioning.


Accounting of filesystem accesses

Question: Is there any way to keep track of number of times each file system is accessed through system calls? I know that the super block will contain the details about the file system. But how can we access the superblock?
Comment: There are several layers of abstraction between the user doing a file operation and that data actually touching the disk.  You'll need to be more specific about what exactly it is that you want to keep track of and what filesystems are being used.
Comment: If a file is being opened , how do we find out which file system the file belongs to?
Answer: Have a look at dtrace4linux and sysdig

Accounting of filesystem accesses


Allowing users to create an email address

Question: I am creating a website and would like to allow users to create their own email forward.
Basically, the site will allow groups to create pages on the site, each of which will be able to have its own domain name.
I would like users to be able to automatically create an email address on the site that will forward any incoming emails to their own email account.
Right now I have to manually set these up in my hosting account control panel but I'm hoping there is a way to do this automatically.
Does anyone have experience with doing something similar?
Comment: well what email system are you using? are you using cpanel? do you have whm? what OS is your server running?
Comment: As Jason asked, we will need a LOT more information.  Different Mail servers have different levels of support for this type of thing.  With the specifics we might be able to help
Comment: Do you have any sort of control or access to the mailer except through the admin panel?
Comment: This may be beyond the scope of my abilities because I don't really have any experience with email systems.  Right now this is a very early-stage project and is being hosted on Fatcow.  I don't have any access to the mailer outside of the admin panel as far as I know.  That said, I'm really not looking for a description of how to do it, but mainly just want to know if it's possible for future reference.
Comment: Try asking this question on http://serverfault.com/
Comment: @rwain - why would you move this to serverfault? What part of it is about servers?
Answer: Take a look at this service offered by Microsoft.  It just might be what you are looking for. http://explore.live.com/windows-live-admin-center
Answer: Just pipe any emails delivered to your catchall to a PHP programming (or whatever server side program you use) and then have it parse the email for the email address sent to, look it up in the database, pull out the real address of the user, and then email the contents of the email to them.
Answer: Oh boy, this really takes me back. I honestly haven't used this service in probably close to 10 years, but Everyone.net provides an MX hosting service that allows users to sign up for their own address. You just provide a link to http://{yoursite}.mail.everyone.net from your site, and visitors will be able to sign up for a free email account on your domain.
Now, since it's been such a long time, I'm not sure if this account type is still free or not, but I do remember the service was quite good. This was a time before Gmail, but their webmail interface was relatively good as well. (From what I've read, it sounds like free accounts probably won't have IMAP or POP access.)
If Everyone.net isn't to your liking, you might try other MX hosting services. Searching Google just now, I came across another one called ZapZone or something like that, but it looks super spammy, and I can't imagine their webmail interface being very good. But some of these might be alright. Or if you use Google Apps, there may be something in the Google Apps Marketplace too.


Induction for $(A_1 \cap A_2 \cap ... \cap A_n)^c = A^c_1 \cup A^c_2 \cup ... \cup A^c_n$.

Question: I need to do induction on this problem:
$(A_1 \cap A_2 \cap ... \cap A_n)^c = A^c_1 \cup A^c_2 \cup ... \cup A^c_n$.
Induction is new to me and this problem is hard to understand. The base case here I'm guessing is just that $A^c_1 = A^c_1$. Since this works we can go to the inductive hypothesis. Then I think we have to prove that $(A_1 \cap A_2 \cap ... \cap A_k)^c \cap A_{k+1} = A^c_1 \cup A^c_2 \cup ... \cup A^c_k \cup A^c_{k+1}$. I am not sure if these are the right steps and if so how to finish the proof.
Comment: Put $A_{k+1}$ inside the brackets and there you go
Comment: Also, for the future, remember this. Induction doesn't let you conclude for infinity. It does for arbitrarely large numbers, but NOT infinity. Try to think about a counterexample. Maybe you already knew this, but better safe then sorry
Answer: The base case is $(A_1\cap A_2)^c = A_1^c\cup A_2^c$. To see this, we have
\begin{align}
x \in (A_1\cap A_2)^c &\iff x\notin A_1\cap A_2\\
&\iff x\notin A_1 \vee x\notin A_2\\
&\iff x\in A_1^c \vee x\in A_2^c\\
&\iff x\in A_1^c\cup A_2^c,
\end{align}
where $\vee$ denotes logical disjunction (OR).
 For the induction step, suppose that $$\left(\bigcap_{i=1}^n A_i\right)^c = \bigcup_{i=1}^n A_i^c$$ for some $n\geqslant2$. Then
\begin{align}
\left(\bigcap_{i=1}^{n+1} A_i\right)^c &= \left(A_{n+1}\cap\bigcap_{i=1}^n A_i\right)^c\\
&= A_{n+1}^c \cup\left(\bigcap_{i=1}^n A_i\right)^c\\
&= A_{n+1}^c \cup \bigcup_{i=1}^n A_i^c\\
&= \bigcup_{i=1}^{n+1} A_i^c.
\end{align}


How are token symbols allocated and managed on the mainnet?

Question: How is the token symbols namespace managed on the mainnet? How are token symbols allocated? Are they "attached" to the smart contract? ie we can have many tokens with the same token name?
Answer: Yes, the token is attached to the smart contract, and the smart contract is attached to an account. Whenever you transfer tokens, you have to specify the account on which the smart contract for those tokens is uploaded.


How the concentration of an antibiotic is chosen for YPD medium?

Question: I need to prepare YPD plates containing hygromycin, but I don't know which concentration I can use. I'll select transformants of Hansenula polymorpha.
Comment: Presumably this will depend upon the promoter that is driving expression of the marker, and the copy number of the plasmid. Do you know anything about either of these parameters?
Comment: First I'll linearize this plasmid. because I want it to be integrated into the genome. (linearized DNA integrates to the genome in H. polymorpha). So there will be no additional copies. And tef1 promoter is present before hygromycin gene.
Answer: According to this site,
for yeast (I assume this means Saccharomyces cerevisiae) you should use 50 µg/ml to 200 µg/ml; for fungi (!) use 100 µg/ml to 300 µg/ml. The site also stresses the importance of the pH of the medium.
I think that, unless a Hansenula expert comes along,  you will have to try an initial experiment to measure the sensitivity of untransformed cells across the range indicated. Then you can try selecting resistant cells at a concentration somewhat higher than that which kills untransformed cells. Finally, you can check to see how resistant the transformants are, to enable you to decide on a useful concentration for routine selection of transformants.


bevel shader not appearing in 2.79 on Mac

Question: I have seen tutorials showing the bevel shader in Blender 2.79b. I cannot get it to show up in the shader menu even after doing a fresh install of Blender. I wonder if it is a Mac issue. I am running Mac OS high sierra 10.13.6, AmD FirePro D700 graphics cards. In the shader node editor I am going Add:Input... bevel shader should appear between Attribute and CameraData but it doesn't.
Answer: Cycles Bevel Shader is an experimental feature introduced after the release of Blender 2.79.
It is available in experimental trunk builds post release but not in official ones.
It is to be introduced to general public as a new Blender 2.8 feature as stated in the release notes.
It should also be used sparingly since it is computationally heavy and resource hungry. In most cases it is preferable to use geometry based solutions since it is cheaper to render then the shader, unless you encounter issues or glitches with complex geometry.


how to insulate attic that contains high-efficiency furnace?

Question: We have an older home with a separate high efficiency furnace for the second floor.  It sits on a floored area of the attic.  We have virtually no insulation and I've gotten various recommendations from contractors.  The concern is that the furnace need to be in a heated area.  Right now, without insulation, the attic is somewhat heated. One contractor suggests walling off the furnace area and insulating the rafters with foam to make a warmer area for the furnace.  But I'm concerned about blocking air circulation if we do this.  Is there a good solution?
Comment: how much snow do you get in winter? ... if you heat an un-insulated attic, then you will melt some of the snow on the roof. ...  the resulting runoff will re-freeze at the edges of the roof. ... an ice dam can form with water pooling behind it and the water can leak into your house.
Comment: Yeah, what are your ground snow loads like? Also, is over-roofing an option?
Comment: We're in the Chicago area so we do get snow.  The attic has been fairly un-insulated for the past 30 years and haven't has a problem with water leaking into the house. We'd be adding more insulation, not heating the attic but I need to protect the furnace from extreme cold.  I don't know what over-roofing is?  Is that adding insulation from the roof side?
Comment: @DebBrown -- yes, over-roofing would be building insulation + a new roof deck atop the existing deck
Comment: This is an old question with not even close to the amount of info needed to answer it right... voting to close.
Answer: How big is the attic?  One solution is to take 2, 3 or 4" insulation board (R13 to R25) and affix it to the rafters.  This would basically make your attic conditioned space (and thus the air between the foamboard and your ceiling will also add R-value) while also protecting your ventilation pathways.  A board with a radiant barrier on each side would be a plus and be sure to seal between the boards.  If you Google "Superattic", you'll find a better explanation.  NOTE:  On a DIY basis, it's not very expensive.  But if you hire someone and your attic is big, the cost can add up.
Comment: Note that you _cannot_ do this in a high snow load climate (ice dam zone) or else you'll get bit *hard* by ice dams due to the R-value of snow causing the temperature gradient to shift so the roof surface is above freezing
Answer: so high efficiency furnace you have pvc piping for venting and a condensate drain for furnace? if this is correct. i would frame and insulate walls for the furnace in leaving a good access, then have a opening in the plenum cut in so you can keep heat in. otherwise the condensate or worse yet the secondary heat exchanger freeze up.


Difference between android.app.Fragment and android.support.v4.app.Fragment

Question: What is the difference between android.app.Fragment and android.support.v4.app.Fragment, and what are the circumstances in which each should be used?
Answer: android.support.v4.app.Fragment is the Fragment class in the android support library, which is a compatibility package that allows you to use some of the newer features of Android on older versions of Android.
android.app.Fragment is the Fragment class in the native version of the Android SDK. It was introduced in Android 3 (API 11).
If you want to make your app use fragments, and want to target devices before API 11, you must use android.support.v4.app.Fragment. However, if you're only targeting devices running API 11 or above, you can use android.app.Fragment.
Edit: the OS-contained android.app.Fragment is now deprecated (as of API level 28), and everyone should move to using the support library implementations.
Comment: Also see "Using FragmentStatePagerAdapter WITHOUT support library": http://stackoverflow.com/questions/18512294/using-fragmentstatepageradapter-without-support-library
Comment: will be using Androidx : androidx.fragment.app.Fragment
Comment: If you override onAttach(), please see this thread to avoid it not being called under some circumstances with android.app.Fragment:   https://stackoverflow.com/questions/32083053/android-fragment-onattach-deprecated
Answer: As of 2018:
From android.app.Fragment documentation:

This class was deprecated in API level 28.
  Use the Support Library Fragment for consistent behavior across all devices and access to Lifecycle.

So support fragments (android.support.v4.app.Fragment) should be used everywhere instead of native fragments(android.app.Fragment) now.
Comment: @ergohack See it that way: for java code you can either include the bytecode inside the runtime of the device or inside the jar file of the application. Support library code will be put in your jar, and provide the same feature as the runtime-provided code, so there's no reason not to use the modern and maintained support library instead of the ageing and unmaintained code of your target phone.
Comment: @Artyom, as a noob to android development, I expected that when the `android.app.Fragment` class was deprecated, that API level 28 would have an alternate, possibly radical replacement approach.  Is there a forward approach or is this backwards compatible `android.support.v4.app.Fragment` the proper approach?
Answer: I use android.support.v4.app.Fragment exclusively.
All the apps I write need to support right back to Android 2.3 and this is the easiest way to do it.
If you're supporting 11+ then stick to android.app.Fragment.
Comment: In that case you're missing out on a lot of features that exists in the support library but only in the native one after a certain API level. getChildFragmentManager() for example is not available until level 17.

My advice is to only use the support Fragments and pretend that the native one does not exist.
Answer: If your application is targeted for API 11 or above, You can use android.app.Fragment and your APK file will be smaller.
Otherwise, add the android.support.v4.app.Fragment library to your project in order to support older android API versions (Android 3.x).
Answer: android.support.v4.app.Fragment is a library that you can use to get backwards-compatibility for older API version.
Fragments were added on API level 11 (along with other features) you should include that library to extend those function to pre-API 11 devices. That is a useful library and I suggest having a look at ActionBarSherlock, which extends the action bar to pre-API v11 devices.
Answer: If your application is targeted for API 11 or above level, You can use android.app.Fragment and it will reduce the APK size.
Otherwise use android.support.v4.app.Fragment


Logic design for FPGAs using C

Question: I am well aware about programming processors and microcontrollers in C. But can C code (not SystemC) be used for logic design for FPGAs? Are there any specific software tools for this purpose?
Comment: In the end, FPGA require some HDL language. I'm not sure how good the [language] to HDL compilers/converts are, but the thing is, that its all HDL in the end. C is a programming (software)  language. HDL is a hardware descriptive language (not software).
Answer: Yes, it is possible to do high level logic (HLL) design using C or C-like languages. Here is a list of the more popular software tools:

C-to-Hardware (Altera)
C-to-Hardware Compilation Technology (Altium)
C-to-Silicon Compiler (Cadence)
C-to-Verilog (Nadav Rotem, free and open sourced)
Cascade (CriticalBlue)
Catapult-C (Calypto)
Comrade (Hagen Gädke)
CyberWorkBench (NEC)
Daedalus (Leiden University and University of Amsterdam, free and open-source)
DIME-C (Nallatech)
DK Design Suite (Mentor Graphics)
eXCite (Y Explorations)
FpgaC (John Bass, free and open-source)
GAUT (Philippe Coussy, free and open-source)
Impulse CoDeveloper (Impulse Accelerated Technologies)
Mitrion SDK PE (Mitrionics)
NISC (University of California, free)
ROCCC (University of California, free and open-source)
SPARK (University of California)
SpecC (University of California)
Synphony (Synopsys)

Keeping track of them is made difficult by the fact that these companies regularly swallow each other whole, change names or discontinue products entirely.
It looks like for all tools, the C code needs to go through an intermediary HDL stage. So the design will be translated into Verilog or VHDL, and these tools facilitate the transition before it is finally put into hardware. But remember, Verilog and VHDL themselves are intermediary stages. Even the netlist is intermediary. The final stage will be a proprietary binary file which reconfigures the FPGA. Designing in C will have its own challenges and trade-offs. But the answer to the question is a resounding yes, logic design in C can be done.
A nice introduction to C-to-FPGA was written way back in 2005. Wikipedia has a nice list of HDLs and tools. Currently, there are also tools for languages similar to C, C++, Java, Python and Ruby. Please comment if I missed a tool and I will add it to the answer.
Answer: No, FPGA's cannot be programmed in C.  Over the years there has been various attempts at a C-Like language, but these have either not caught on failed outright.  Even for the ones that "succeeded" I would not call them real C.  You could not, for example, take a pre-existing code intended to be compiled for a processor and recompile it for an FPGA and expect it to work.
Use VHDL or Verilog, you'll be much happier.
Comment: This is incorrect, there are tools for logic design in C. Whether they are useful, or use "real" C is just opinion.
Comment: @trav1s  Opinion, maybe, but a solid opinion.  Impulse, for example, says that "Those portions that are being moved to the FPGA as dedicated hardware are constrained in the level of C that can be written..."  Both Impulse and ROCCC work on "untimed C" (no clock timing is specified in the code), and it is unclear if you can have "timed C".  It almost appears that all of the products you mentioned are geared to accelerating DSP type algorithms and not for designing generic logic.  While I have not done exhaustive research, it appears that you can't do simple logic like a UART with these tools.
Answer: If your goal is to run a system ON the FPGA running C, you might try installing a CPU core. However, this negates the purpose of the FPGA.
Using C for programming FPGAs would be a rather poor design choice, since C is designed for iterative programs, not logic arrays. Verilog and VHDL are designed such that you create a structure, not a list of instructions.
Comment: Well, as the logic gets more complicated and the FPGAs getting larger and cheaper, it is natural to use C as the programming language for FPGAs, I would not call it a poor design choice, since you can do VERY large FPGA design using C that is much neater and smaller and easier to manage than Verilog or VHDL. Of course, it has it problem as well, bad C code can create really bad HDL and FPGA implementation, but that goes with evey programming language.
Comment: C is not a language for construction. I agree that verilog is not the ideal language, but C is far worse. There is very little to gain.

C is designed for ITERATIVE programs. This means that anything you put in your FPGA will have to simulate an ITERATIVE process, rather than the ideal parallel structure that FPGAs are best at. Using C for FPGAs is a ridiculous waste of resources.

Now, a new, C-style language, designed for the needs of FPGAs, would not be so bad.

Logic design for FPGAs using C


Unused live electrical wires in kitchen

Question: I have unused live electrical wires coming out of wall in kitchen where new cabinets are going. How should I handle this?
Comment: Are the wires in a box or are they literally hanging out of a hole in the wall?  How many wires and color?
Answer: Assuming you don't want to/can't remove them completely, (i.e.- back to an existing junction box, or all the way back to the breaker box), you need to properly terminate them (capped with wire nuts) in an accessible junction box.
In other words- install a junction box in, put wire nuts on the wires, install your cabinets, with a hole where the junction box is, and put a cover plate on.
Answer: The best way to handle this is to find out where the wires are coming from and terminate them at that box.   In most cases this is just undoing a couple of nuts and taking the wire out.  If you need to open up a small section of drywall to get the wire out, better to just do it now.  Adding a junction box is a lot of work for a half ass job and potential issues and unneeded troubleshooting in the future.
If they are coming directly from your panel I suggest that you disconnect the wires from your panel (label them there - there being outside of the physical panel but in same location) and put the wires sticking out of your wall in an accessible place in your house where you might have future electrical needs (attic or basement).   Of course if you do not know how to disconnect from the panel, that is a different question on here.
Note: Another option is moving this to right above cabinet height to allow for the ability to plug in lighting with a basic receptacle - if you don't want to remove the wire.  This is $5 and 10 mins.
Comment: I'm not exactly sure what "potential issues" a properly terminated wire in an accessible junction box might cause, nor why it is a "half ass" job.  In my house, if I had a line run from my upstairs sub-panel to my kitchen, removal of the wire would necessitate a lot more than removing a "small section" of drywall- in fact it would likely involve removing a strip of drywall in 5 separate rooms, not to mention the drywall work required to re-locate the wire somewhere it might be useful in the future.
Comment: @MarkD - I mentioned he could terminate at nearest  box too.  Junctions should be a last resort.  You don't want junctions all over your house.  It makes troubleshooting electrical issues harder because it allows more options.  Just the fact of "having" a junction box in a finished space is something I would never think about because it looks bad.  Also the potential of the non-electrical inclined hurting themselves with these wires.  If this is in a kitchen I doubt that there isn't a box within 5 feet.
Comment: @DMoore- fair enough.  Though in this case, being behind where cabinets are to be installed, I don't think the eyesore bit is an issue, as the cover plate would be inside a cabinet (of course this statement is null and void if he is putting in glass front cabinets, but then he has the issue of keeping his dishes stacked nicely which I can not help ;) )
Comment: Really, I don't see any problem with a junction box there. Backs of cabinets are a great place to hide access points, for instance the back side of a tub/shower mixing valve.  Put a false panel in the back of the cabinet if it bothers you that much, as long as it can easily be lifted out, should be code legal.
Comment: @WolfHarper - I think adding another outlet right above the cabinet is a no brainer if you are going to do the junction.  At least you could keep going from there.  You are never going to remove the cabinet to add another outlet.
Comment: Sure, plus it'll let you put cabinet lighting in, which is easy these days with LED strips.

Unused live electrical wires in kitchen


Upstairs toilet leaking into ceiling

Question: My upstairs toilet is leaking into the ceiling downstairs only when the water supply is turned on. One company came out and cut a hole in the ceiling and said it is not the water pipe. Another company came out pulled the toilet and changed the ring. The toilet is still leaking. It is a slow drip like a drop every 20-30 minutes. What could cause this?
Comment: Have you checked out the shutoff valve for the toilet... the valve coming out of the wall?
Comment: When you say "only when the water supply is turned on", do you mean that with the supply stop-valve next to/behind the toilet turned off, it does not leak? Or are you shutting off more of the system, like shutting down water supply to the pipes in the wall that lead to the toilet? This is an important trouble-shooting detail...
Comment: Tank, bowl or pipes/joints are three places to check.  Slow drip, upstairs, might want to check for condensation.
Comment: Yes, the water shut off that is connected to the wall behind the toilet, that stops the water from allowing thank to fill was turned off and the leak stopped. Water can be in the tank but the leak doesn't start until the water is turned back on behind the toilet.
Comment: Sorry forgot to add it leaks in the wall not on the floor in the bathroom. Never any water on the floor of the bathroom. It runs down the pipe and intro the ceiling of the kitchen downstairs. Since there is now a hole in the ceiling you can see the drip.
Answer: Common problem, you have unfortunately been cursed with a series of maroons since fixing a leaking toilet is about the easiest handyman job there is.
My guess is you could do a better job fixing it than the buffoons.  Turn off the water, wipe up all the drips and such behind the toilet so that everything there is clean and bone dry, then turn the water back on and lay back with your head behind the toilet for 20 minutes staring at the plumbing.  Eventually you will see a little bead of water forming somewhere that is where the leak is.  My guess is it's the valve stem seal but there's plenty of other potential areas.  Feel around on the pipes with your fingers.  Water leaks like to happen behind pipes and such where you can't see them and water likes to travel down away from the actual source to make it harder to find the leak.  You can't find these leaks by just staring at pipes you have to get your fingers in there and feel around.
Comment: maroons=more ons? (morons).
Comment: indeed https://www.youtube.com/watch?v=_NYFq7ZJg4c (5 second video  Bugs Bunny)
Answer: So the copper water pipe in the ceiling has been confirmed to be not leaking.
A new wax ring ensures the toilet horn (waste line) is sealed tightly to the closet flange.
The only other possibilities are a cracked porcelain base or a dripping  shut-off valve or supply hose.
Check the base first by trying to lift one side and then the other of the toilet. It should be un-moveable in any direction. If not try pulling the threaded studs that hold it to the closet flange (floor). These should not be moveable ,too. If they are extremely loose or free the closet flange they are attached to may have broken and needs to be replaced.
If the studs are slightly loose you can try tightening the nuts slowly until they are snug. Use a level placed on the bowl rim as a guide on which nuts to tighten first.
Also, with a flashlight verify that there are no hairline cracks at the base of the toilet which could mean a leak.
Also, with your hand feel along the supply hose at both connections
for any wetness which would mean a connection needs tightening.
The nut on the bottom of the reservoir that holds the flush valve in place may be loose.

Upstairs toilet leaking into ceiling


Electrical breaker panel

Question: I have a new compressor.  It is 15 amp 240 volt.
I have an old Sylvania panel.  What are make and model
options?
Comment: Can you post photos of the labeling on the panel?  And are you trying to get a breaker for your panel, or...?
Comment: Does it have a lot of red and sky blue breakers that are quite thin?
Comment: make and model options of what?
Comment: Hello, and welcome  to Home Improvement. We'll need (a lot) more information before we  can help you; please edit it (including, say, a picture of the breaker panel, and the make/model of the compressor) into your question.
Answer: "Sylvania" had a couple of different types of breaker panel systems during their forray into that business. One of them was called "Zinsco", the other was "Bryant" panel and breaker system. The Bryant version was eventually taken over by Eaton / Cutler hammer and is now called their "BR" Series (BR for Bryant). Zinsco breakers were / are a disaster waiting to happen and in the opinions of most people, should be ripped out and replaced as they had a tendency to not work and/or catch on fire. Zinsco as a stand-alone company went bankrupt ages ago because of this and Sylvania was unable to rescue them, so they too got out of the business. There are some aftermarket companies selling redesigned versions of the Zinsco breakers, but before wasting money on them, check to make sure your homeowner's insurance policy doesn't have a rider saying that they will not cover any losses from failures of Zinsco (and Federal Pacific Stab-lok) breakers. Some do, and in some jurisdictions you cannot make any alterations or repairs to these panels, you must rip and replace.
Comment: For a while, as Sylvania struggled with the failures of Zinsco, they brand-labeled the Bryant breakers from Westinghouse before Westinghouse went belly up. So when Eaton bought Westinghouse, they inherited the Sylvania contract but Sylvania sold out to Challenger, then eventually Eaton just bought Challenger too. It was all a big mess for a while back then...
Comment: Actually, you're mixing up Bryant with Challenger :) BR was a Westinghouse thing
Comment: Ah!  That explains quite a few things, thanks!
Comment: An update:   the Sylvania panel requires bolt on breakers.  I plan to put in a 20 amp circuit.  Eaton has a bolt on breaker QBH series; the local dist  #QBH220  (SKU 622588003815) Thermal Magnetic; 2 pole; 120/240V  AC: 20A.  Is "Thermal Magnetic"  a new standard?  It is to me anyway.  The breaker is expensive $ 80 US.
Comment: Thermal-Magnetic is just the official term for a basic standard breaker, as opposed to something more exotic like an electronic trip version that would be even more expensive (although not available for these type).

Electrical breaker panel


Are there Quest dependencies?

Question: I'm wondering if I complete the next main quest (in my case, the dragon killing quest in Whiterun), are then some other quests closed? I think, maybe someone dies who offered me a quest before... or something like this :)
Comment: Lots of things can cause a quest to become unavailable. You often have to make choices between two factions, and as you suggest quest givers can die.
Answer: The main quest "dependency" is in the civil war. If you choose one side, you can't finish up then rejoin the other side.
There are two types of quests within this game, pre-scripted quests and "random" quests. For example, asking the Riverwood barkeep for work will get you a pseudo-random quest, but working through the Companions line is fairly scripted.
I have yet to see a "random" quest direct you to kill off a questgiver, though the sheer number of possibilities will make this hard to prove unless a developer confirms it.
That said, if you go on a killing spree, be prepared for the consequences of your actions.

Are there Quest dependencies?


Why is it called drift velocity and not drift speed?

Question: Why is the average rate at which electrons cover the length of a conductor called drift velocity? Wouldn't it being called drift speed be more fitting as that would remove all notions of the conductor's shape and orientation? For example, if the electrons were moving through a bent wire of uniform cross-section, the drift velocity of the electrons would be different at the points before and after the bend, whereas the drift speed would be constant.
Answer: The technical definition often given is that $j=(nq)u$ where $j$ is the current density (which is a vector) and $nq$ together make up the charge density (which is a scalar) and with $u$ will be a vector velocity. So the idea is that the drift velocity within a material varies from point to point and time to time — in the general case. However, I would say that a lot of the time it is the magnitude of the drift velocity (say in a thin wire where the current is thought of as all in the same direction down the wire) that is computed, and you could argue that this is the drift speed. I think this is a case where people say — the meaning is clear from the context. Language is not always used in a simple manner. Details of the pragmatics and context often change the details of the meaning.
Answer: You need to consider the difference between velocity and speed. Speed is a scalar quantity and can be thought of as the rate at which an object covers distance. Velocity, on the other hand, is a vector quantity and can be thought of a the rate at which an object changes its position. The magnitude of the velocity of an object is its speed.
Without an electric field present in a conductor, the thermal motion of the free electrons is random. The individual electrons cover a great deal of distance per unit time, but over time their position does not change. So their speed is great but their velocity is zero. It's like you rapidly taking the same number of steps forward and backward. Your speed is great but your velocity (rate of change in position) is zero since your position over time does not change.
With an electric field present in a conductor, superimposed on the random motion of the electrons is the collective motion, or drift, of the electrons where their position changes in time in the direction opposite that of the electric field. The rate of change in position is the drift velocity. The drift velocity of the electrons is extremely slow compared to the speed of their thermal random motions. The drift speed is the magnitude of the drift velocity.
Hope this helps.
Answer: The simple answer is that even in physics we don't use English words to always mean exactly their technical definition. That's just the way it is...
While a speed is never used to refer to a vector quantity the term velocity is sometimes used to mean the magnitude of the rate of change of the position vector. Such is the case, for example, with drift velocity or terminal velocity.
If you want to know why we use imprecise language like that it'll be a question for linguists rather than physicist. (But given that physicists typically consider themselves to be qualified to comment on any field you might get a few answers from us here too!)
Comment: And if you're wondering how we can cope with the ambiguity, it's worth considering that other languages don't distinguish between speed and velocity at all! And that even in English we often use the same term to refer to the vector quantity as well as its magnitude  Take for example 'force'...!


Why is the IMF still lending money to Argentina?

Question: Argentina has defaulted on their debt numerous times and it looks like they're refusing to implement sensible reforms to improve their economy. So why is the IMF still lending them money rather than letting Argentina go completely bankrupt?
Answer: As another answer suggests, the IMF is a bank "of last resort". Countries don't usually like to be told what to do, and the conditions the IMF imposes on loans are often what are regarded as "onerous" in that they require particular reforms of state finances and other practices, such as liberalization of the economy (opening up to trade) which can prove highly politically unpopular.
Banerjee and Dufflo, in "Good Economics for Hard Times" (Ch.3, Penguin Economics 2019) have this to say on the experience in India, for instance:

India was forced to seek help from the International Monetary Fund (IMF), an opportunity the IMF was waiting for. China, the USSR, Eastern Europe, Mexico, and Brazil, among others, had begun to take serious steps toward letting markets decide who should produce what. India at the time was the last of the big holdouts, an economy that continued to adhere to the anti-market ideology fashionable in the 1940s and 1950s.
The deal the IMF offered would change all that. India could have the funds it needed [emphasis mine], but only if it opened its economy to trade. The government had no choice. [...]

Countries that are willing to accept IMF "handouts" don't do so willingly, as there is fine print associated.
But what does the IMF gain? The IMF is not a regular bank. It is both a political tool but also a mechanism to encourage development and world trade, and hopefully stability and wellbeing typically associated with these. This is not very different from investors who throw good money after bad chasing the next unicorn, except here the unicorn is "not becoming Haiti", that is, a next-to-lost cause, and maybe "becoming a valuable trade partner".
Argentina, by the way, is not a small country, either in area, population, or productivity, particularly agricultural. It's wellbeing is important for instance for the stability of global commodities such as cereals.
Answer: IMF approved a large chunk ($57 billion) when Marci, a neoliberal, was president. He did do some reforms like float the currency (albeit they use a horribly complicated cap scheme, so there's a black market too). But then the Peronists took power. And there was a drought this summer. It looks like the favorite candidate in the immediately upcoming elections is a libertarian, so IMF is probably factoring all those in when they decided not to cut the deal before the elections. Oh, and China gave some $18 billion directly, so there's that great powers competition at play too, probably.
A couple of sources from which I much condensed the above. Blomberg, 6 Oct 2023, France24, 18 March 2022.
(I'm also aware that Milei has been called other things besides libertarian, but for economics purposes, which is what matters to the IMF, it seem a reasonable description of what he says he wants to do. Also he came in 2nd in the first round a couple of days ago, but the Guardian still concedes that "A Massa [Peronist] victory is not assured given that many of Bullrich's right-wing voters may migrate to Milei.")
Answer:
If you owe the bank $100 that's your problem. If you owe the bank $100 million, that's the bank's problem.
J. Paul Getty

Multiply those numbers by around 500 and you get an idea of the problem.  This isn't unlike what happened in Greece's crisis, more money was lent to them to allow them to make their interest payments (but the EU had way more leverage to ensure reforms however).

(note:  that 40+B$ is 30+% of the IMF's global outstanding loans)
Economist - Argentina is pushing international lending to its breaking point

On August 23rd the government persuaded the imf to release a $7.5bn tranche of its bail-out programme, its only hope of meeting dollar-debt repayments and staving off default. The imf's reluctance stemmed not from the fact Argentina is broke—lending to such countries is the fund's purpose—but from the fact that most of the cash Argentina must repay this year is promised to the fund itself. Argentina is a rare country with the imf as its biggest creditor, owing the fund a cool $40bn, roughly a third of its external debt. By providing support, the imf has delayed disaster.
The imf lends to the world's unstable economies as a "preferred creditor". If a country only has a little cash, it is the first to be repaid. It never takes a loss during debt restructuring. This lets it and other multilateral institutions, including the World Bank, hand out cheaper rescue packages.
Argentina cannot afford its bills; the imf cannot cut the debt it is owed without forfeiting its status as preferred creditor.
The cost of letting Argentina carry on is high. In the coming months, the imf will have to figure out if the cost of cutting it off is higher.

Reuters

"No matter who wins after the vote, the IMF should insist that the government either bite the bullet - or otherwise the Fund should pull the plug on its support," said Mark Sobel, a former U.S. representative at the IMF.
"Even if that means huge arrears."
...
Some IMF executive board members have complained in Argentina-related meetings that the country has received preferential treatment, three sources close to the matter said on condition of anonymity.
The lack of "evenhandedness" has come up with countries such as Zambia, Sri Lanka and Ghana facing strict requirements under IMF-led debt reworks.
...
"In some cases, a country will require a follow-on program to resolve its balance of payments problems," said Jay Shambaugh, the U.S. Treasury's undersecretary for international affairs.
"But it cannot be the policy of the IMF to roll over programs, or approve reviews, only to avoid arrears without sound policy reforms in place."

Note:  I see this as the primary reason IMF $$$ still goes to this serial debtor.  It doesn't mean I necessarily agree with it.  I tend to be more hawkish than dovish here.  As far as I am concerned, this is good money after bad, rewarding more Peronist stupidity, an opportunity cost to using IMF resources elsewhere and is unfair to other countries that don't get such sweetheart IMF deals.  But I would also be very open to solid explanations of why I might be underestimating the large scale risks from pulling the plug.
Comment: That's certainly your opinion to have, but I can't say I find it all that convincing.  They'd have to recapitalize, for one, losing 30% of their funds is *huuuge*.  "The governments" won't be lining up to do that.  And there'd be a precedent that they can be expected to take a loss.
Comment: Does the IMF really care if they make a loss? It's government money, so no one has any real skin in the game to avoid a loss.


Convergence of QZ algorithm

Question: When performing QZ iterations on matrices A and B where A is upper hessenberg to begin with and B is upper triangular, how can one tell when the algorithm has converged? I understand that if it consists of only real eigenvalues then the subdiagonal entries of A will approach zero. However, complex eigenvalues remain below the diagonal of A. Is there a way to determine when all of the values below the subdiagonal of A that are supposed to be zero are in fact zero while the ones that are supposed to remain are still there?
Answer: The QR and QZ algorithm split the task into subtasks on corresponding upper and lower diagonal blocks whenever one of the subdiagonal entries is deemed to be equal to zero. This recursion stops whenever the block size is 1 or 2.
In blocksize 2, the eigenvalues corresponding to these blocks can be computed by solving the quadratic characteristic equation, typically they should be complex conjugate pairs, but also a real pair can happen. In the latter case, the necessary rotation to diagonal form can be computed from the eigenvalues. And also in the complex case one might rotate the block into the standard matrix representation of a complex number.
See http://www.netlib.org/lapack/lawnspdf/lawn173.pdf on the QZ algorithm using implicit multishift and chasing chains of small bulge-pairs. Discussion of deflation and infinite eigenvalues  starts on p.9-10.
Comment: But how does one deem that a subdiagonal entry is supposed to go to zero? I can visually see that certain entries start shrinking to zero and others don't (those representing the complex pairs for example). But I can't put a condition saying that all subdiagonals go to zero for example because of the complex pairs. And since A is in upper hessenberg throughout the process, all of the block sizes along the diagonal are either 1 or 2.
Comment: The subdiagonal entries converge toward zero with the factor $\frac{|p(λ_{k+1})|}{|p(λ_{k})|}$ where $p$ is the polynomial collecting the current multi-shift pattern and the eigenvalues are ordered so that the sequence of the $|p(λ_{k+1})|$ is decreasing. So the subdiagonal entries will get smaller where these polynomial values are different. Only conjugate complex pairs and multiple eigenvalues will not separate. You can compare the subdiagonal entry to the neighboring diagonal entries, if the relative size is small enough, which sometimes is taken as large as  a factor of $10^{-5}$.
Comment: That makes sense. Also, I was forgetting the definition of what a quasi-triangular matrix was which means that no two consecutive elements on the subdiagonal are nonzero. As soon as these conditions are both achieved it should be in Schur form correct?

Convergence of QZ algorithm


Mac OS 13.0.1 - using Terminal cp command to preserve file attributes

Question: After reviewing old posts, I tried various arguments to the cp command in Terminal (e.g., -p, -a, -R) attempting to copy folders/files to an external drive while keep attributes like "Date Created" the same as the source. No matter what I've tried the dates are not preserved. Helpful advice would be greatly appreciated.
Comment: I'm not a big user of the command line but if I recall the command that preserves file attributes and resource forks is **ditto** rather than **cp.** Never used it myself but maybe that will point you in a helpful direction...
Comment: Thanks for the quick reply. I'll try it out.
Answer: Use ditto instead of cp. ditto copies hierarchies by default (so no need for -r) so ditto src_folder /Volumes/external_drive most likely will be enough (but check the man page for details).
PS: Ability to preserve attributes depends on the format of the target device (so if you copy to a FAT-formatted drive some attributes will be lost).
Comment: Thanks for the quick reply. You nailed it with the formatting comment. My backup external HD is formatted ExFat so I can take videos back and forth between Mac and PC. Ditto worked fine duplicating files from one Mac folder to another.


Tag merge: bridge and bridging

Question: I think bridging should be merged into bridge, since it has the same meaning.
Answer: Good catch. Merged! And a synonym since it seems a common addition. Especially since the larger tag shows up before the smaller tag when you type 'bri' in the tag line.

Tag merge: bridge and bridging


Bash as default shell for Netware user

Question: I am connecting to the Novell Netware (OES) server via ssh. It shows me default novell console. I want it to start bash automatically when I connect. How can I do this?
Answer: Unlike SSH for Linux, SSH for NetWare doesn't come with the kind of /etc/passwd or PAM-Ldap hooks needed to specify a default shell. It also doesn't assume it's running a shell or running login scripts, which makes it further unlike Linux-SSH. It is assumed that when you SSH into a NetWare server you're an admin looking to do remote administration, and therefore you need Console. It is meant as a kind of rconsole replacement.
Because of this, you have to explicitly enter bash when you SSH into a NetWare server, it won't do it for you.
Comment: This is the correct answer. Note that dmityugov's reference is to the Unix profile, which is only active when a user logs into an actual Unix-like OS such as Linux or Solaris and has no effect in Netware.
Comment: Ok. Thanks! I understood. This is very strange console. It's only rewriting the same window every time with esc-sequences. So, it's seems hard to automate this process. I mean connect to the server, execute some commands, and then analyze the output. Maybe there is another way to make such automatic checks, more efficient than common ssh connection?
Comment: Now that I think about it, you could specify that bash start at server boot (by putting "bash" into the autoexec.ncf file) and that would leave it there for you whenever you remoted in.
Answer: The user you're connecting as either has the console set as their shell (chsh), or has the console set to run in their shell startup scripts.
Comment: chsh is not working in Novell bash. Where shell startup scripts in Netware could be? I can't find out how to change user's default shell in Netware like I did it other unix (in /etc/passwd)
Comment: Weird. Then the startup scripts should be hidden in the user's home directory.
Answer: Not sure if this helps, but in ConsoleOne, in UNIX Profile tab for a user, you can specify the shell. In particular, you can set it to Bash. It seems it also possible to do this via  iManager

Bash as default shell for Netware user


Post-hoc tests for 2x2 ANOVAs (Type II & III) with interactions in R

Question: I am trying to analyze data from an experiment using R and ran across a problem regarding the use of post-hoc tests with Type II & III ANOVAs. I only know of R functions that perform post-hoc tests based on Type I SS, such as TukeyHSD and glht. Others, such as HSD.test from the agricolae package do not seem to calculate tests for interactions.
Do post-hoc tests that also test for interaction terms exist for R that enable the use of Type II & III SS ANOVAs? Alternatively, is there a way to convert Anova objects (Type II or III, car package) to aov objects in order to use them with the TukeyHSD function?
Comment: Tests are useless (and puzzling), rather use confidence intervals, and you'll not have "type" problems.
Answer: If you really mean 2x2 as in "two factors, each at two levels" there is hardly a need for post hoc anything, because there is 1 df for each main effect and 1 df for interaction. You wouldn't use Tukey HSD for this, and if you used it, it'd be the same as the regular unadjusted tests because there is only one comparison in each family. But let me know if I misunderstand something. You might want to look at the lsmeans package and see if it offers the kind of comparisons you need.
Comment: I think you are confused about the role of sums of squares types. Those have only to do with ANOVA F tests, determining which model you are comparing with which other model. They have nothing to do with estimating linear functions of regression coefficients. The full model's error structure is always the reference for obtaining the standard errors of these estimates.
Comment: Thanks. I need to use the Tukey test in order to see which combinations of factor levels are significally different in interactions. For some calculations, I need to add covariates or perform 2x2x2 analyses, so I need the Tukey test (or at least the Bonferroni or Holm test) to work with my data.
I have also tried the lsmeans package and although it works well with my data, I could not find any information on which SS type it uses (since it is used with lm objects, not Anova or aov objects whose SS type you can choose) or how this can be set.
Comment: Oh, I see. I am indeed not very familiar with the different SS types (coming from SPSS I never had to worry about that) but I read on statmethods.net/stats/anova.html (section "Multiple Comparisons") that the results of post-hoc tests are based on the fit supplied by the aov function, which would differ if I used different SS types in the ANOVA. Does what you said entail that I can use whichever post-test function I wish?
Comment: OK, well I looked at the site you mention and it does indeed say that the TukeyHSD results are based on type I SS. But I have no idea what he means by that. Maybe somebody else can set us straight. Perhaps he means that aov provides for multiple error strata, and those are computed sequentially (as are type I SS). But iF you have a mixed model, I suggest you use lmer (lme4 package) instead of aov, especially with covariates, because aov is really designed for traditional balanced experimental designs with no covariates.
Answer: I'm not a stats or R pro, so maybe someone might want to confirm this, but the lsmeans package in combination with the multcomp package indeed helped me to analyze the significant interactions of my lmer-Model (see here, if you want to have a look whether it compares to your problem):
<code>summary(glht(model, lsm(pairwise ~ factorB | factorA)))
</code>
This tells me for each level of factor A whether the levels of factor B differ significantly. According to the help page of lsmeans, it's supposed to be an S3-method.


Print-out of a html5 canvas?

Question: I have created a simple html-based web-page consisting of a form and some text, plus a canvas. I would like to print the page including the canvas on a piece of paper, the problem is - the canvas will not show in the print-out. Is it something I have missed in how to handle the canvas?
I am currently using Opera, any knowledge whether other browsers handle this better?
Comment: According to http://stackoverflow.com/questions/8031016/printing-the-contents-of-the-canvas-tag other browsers may not have this problem.
Answer: what you need to do in this case is, have a special print view, where the canvas gets replaced by an image file, which then can be printed out easily.
have a look here: Capture HTML Canvas as gif/jpg/png/pdf?
Answer: You need to use the .toDataURL() method to convert the canvas to an image, which you could place on top of the canvas itself for example, prior to printing. Maybe make a print button on the page, which does that stuff, then prints etc...

Print-out of a html5 canvas?


Is there a performance difference between Javac debug on and off?

Question: If I switch on the generating of debug info with Javac then the class files are 20-25% larger. Has this any performance effects on running the Java program? If yes on which conditions and how many. I expect a little impact on loading the classes because the files are larger but this should be minimal.
Answer: In any language, debugging information is meta information. It by its nature increases the size of the object files, thus increasing load time. During execution outside a debugger, this information is actually completely ignored. As outlined (although not clearly) in the JVM spec the debug information is stored outside the bytecode stream. This means that at execution time there is no difference in the class file. If you want to be sure though, try it out :-).
Ps. Often for debugging there is value in turning off optimization. That does have a performance impact.
Comment: Correct. Load time is affected but execution time is not.
Comment: Does javac still have -O? Last I remember it was the equivalent of -g:none.
Comment: Indeed the sun java compiler does not have an optimize flag. Optimization mainly happens in the hotspot runtime. Optimizing at compile time may actually hamper hotspots ability to optimize (using full information only available at compile time).
Comment: *How much* does it affect size and load time? Are there benchmarks that have been run that we can look at?
Answer: Turning off debugging alone should not make a difference at all. But once you turn off debugging and turn on optimization, you should see a difference, as this makes some static optimizations at compile time. This way even your hot-spot optimized code gets faster at runtime.
But so far, the tradeoff between getting meaning full stack-traces or having some more user-performance, I always voted for the stack-traces. After all, users are willing to spend 1000$ each year to get a faster machine, but are not willing to spend 15 minutes to give you  meaningful error messages to you to solve their problems.
After the years, I'm more willing to value my 15 minutes higher than the user's 1000$. :)
Answer: Please be aware that since JDK1.3 javac ignores any optimization flags, "compile-time optimization is unnecessary"


Why does two different interfaces on the same machine result in two different MAC addresses?

Question:
My machine named debian has two different MAC Addresses. One for Wireless and one for LAN. I thought a device only had a single MAC address. How is this possible?
Answer: You are right that one device has one MAC address.
Your wireless card is considered one device.
Your Ethernet card is considered one device.
Every Network Interface Card (NIC) is one device and has its own MAC address.
Answer: Each network interface, whether wired or wireless, is a unique device and as such will have a unique MAC address.
https://en.wikipedia.org/wiki/MAC_address
Answer: A MAC address is an absolute necessity for communication on the data link layer of a network segment (basically every network wired/wireless). It is a possibility to have the same MAC address on two devices but no operating system or device is created like this, and under normal conditions will cause nothing but errors, as it will compromise the overall logic of Ethernet and network traffic will have no idea where to go.
I believe the overall effect of a duplicate MAC is to put the two devices in contention with one another, and to black hole any traffic to one of the devices. However it maybe dependent on the switch/router/topology used and you "may" not experience these issues, but its is definitely not a good idea and has few tangible benefits if any.
Its bit like putting same two numbers on a street and expecting the postman to deliver correctly.
Comment: I have noticed some devices that do have the same MAC addresses on different physical interfaces, including the PS3 which uses the same MAC for its wireline ethernet and wifi interfaces, and some routers such as the Apple Airport Extreme and the Fios Quantum Gateway router, which both use the same MAC address for all three of LAN ethernet port, LAN wifi, and WAN ethernet. I guess this doesn't lead to problems because the PS3 does not allow wifi and ethernet to be active at the same time, and the WAN and LAN ports of a router are never on the same network. ...
Comment: ... Although I guess if you wanted to use wifi and wired ethernet at the same time to maximize throughput to your router, the cloned MAC addresses might confuse things? Or maybe it would be fine because either interface could grab any packet so it would actually be faster.
Answer: Several answers here say that MAC addresses logically have to be different for every physical NIC (network interface) that a host has. But that is not the case, and I have seen devices which made the design choice to give all interfaces the same MAC address. For example the Playstation 3 uses the same MAC address for its wired LAN and wifi interface. Several brands of router use the same MAC address for both LAN, WAN, and wifi interfaces.
This hopefully doesn't give rise to the problems alluded to in the other answers that you would have if MAC addresses were duplicated across different devices, because these interfaces are used by a single host, or they are never used on the same LAN.
So the real question is then, why does it make sense for a single general purpose computer to have a unique MAC address for each interface?
Well it would be no big deal for two hosts on two different LANs to have duplicate MAC addresses, just like hosts on non-addressable NAT'ed home networks often share the 192.168.0.1 IP address. But how can you guarantee those hosts won't ever find themselves on the same LAN? Two different hosts on the same LAN will interfere with each other's traffic and impact the efficiency and security of the network. With early network cards, the MAC address is burned in at the hardware level, so they couldn't be changed in software. Imagine being the admin for a computer lab, and you have to constantly swap ethernet cards from one computer to another, as upgrades and replacements happen. They need to be globally unique. So each NIC manufacturer gets a prefix, and then makes sure they never repeat a suffix.
I could also imagine uses for distinct MAC addresses even in cases where you can ensure that the interfaces stay in the same host, for example if you have to limit the amount of wifi but can accept more wired traffic.
So each network card has a unique MAC address because there's no way to guarantee they won't end up in different hosts on the same LAN. But if the redundant address bothers you, you could override one of them to match the other, and be like the PS3.


Are there any tricks for using an oscillating multitool?

Question:
I recently got myself a Ridgid JobMax and I think I love it. I did spend quite a bit of time, however, trying to get through an old (100 year old home) 2x4 (dimensional). I don't know if the wood was just really hard or if I am just not good at using the tool yet. I did watch some YouTube videos and started using more of a sweeping motion with the cutting blade and that helped. I'm just wondering if anyone else has any good tips or experience using this tool that would be helpful to me.
Comment: I would bet that part of the problem is that the old wood really is a lot stronger.  I was blown away at how quickly I would go through reciprocating saw blades when cutting through the original walls at my house (85 years old).
Comment: Agreed w/ auujay and Evil Greebo -- old wood can be almost petrified; I burn through drillbits, saw blades, etc, for a house that was ~60 years old when I bought it.  (2x4s are ~1.75"x3.75", except for two additions)
Comment: I agree with the consensus that your 100 year old 2x4 was probably hard as a rock. But it's worth keeping in mind that of all the cool things these tools can do (aside from the name I love my Rockwell SoniCrafter too), cutting quickly isn't one of them. The small-stroke oscillating motion and those tiny triangular gear teeth just can't remove material like a "real" saw blade with raked teeth and kerf.
Comment: A rocking motion seems to help.
Comment: I also have a Rockwell and love it. Don't know how I got to this point in life without it. LOL.  Old wood can be very hard and takes a while to work thru. Also be sure you are using the most aggressive blade possible. A fine blade will dull quickly and take forever.
Comment: [Related](http://diy.stackexchange.com/questions/86718/multi-cutter-blade-blunt-in-1-day-bad-blade-bad-technique): Multi-cutter blade blunt in 1 day. Bad blade? Bad Technique?
Answer: Like you, I find it more effective as a cutter through harder surfaces if you move the blade across the surface you wish to cut.  I also apply light pressure to the tool while "sawing" with it.
Although in your case, it probably was simply that the wood was very hard.


Is it required for panel data to use dummy variables?

Question: I am doing research considering seven countries and I have panel data. My question is: do I need to include dummy variables every time I use panel data in regression, or is enough to do it as a fixed effect in Stata, without dummy variables?
Comment: Do you mean dummy variables to indicate people?  (Or whatever your units of analysis are). This is what fixed effects models too, if you set them up properly. I think we need more information to know what you are doing.
Comment: Please the answer I need is that what are the commands to use to run time and country dummies in panel regressions using STATA package. Thank you.
Answer: David Fernando implies not only the panel data by his question, but also the specific method of estimating his model, namely the fixed effect estimator. David, however, did not mention what kind of model he works with.
You have to be quite specific here. Fixed effect panel data models are conditional models. They provide inference by conditioning on the average (or total) response within the panel. This usually does not limit the interpretation (although sometimes conditional models get tricky; conditional heteroskedasticity ARCH models behave very differently from the corresponding marginal models that would use a fat tailed distribution like Student $t$ for regression errors). However, you need to have this distinction in mind when working with panel data. So, the conditioning means that

In linear models, conditioning on the panel mean with a Gaussian model means subtracting the panel mean. And, by an unfortunate coincidence of the matrix algebra of linear regression, this is equivalent to introducing dummy variables. Sometimes you can hear of this implementation of the fixed effect estimator as DVLS -- dummy variable least squares.
There are two more panel data models that can afford fixed effect estimation: the binary model with the logit link, and the Poisson model with the log link. They have a sufficient statistic (total response) that can be used for conditioning. xtlogit, fe and xtpoisson, fe do just that, but they internalize these computations, and since these are iterative maximum likelihood estimators, there are no matrix algebra tricks applicable to them.
Adding dummy variables to your other estimators (e.g., Heckman) may be a good idea, but you have to realize that you cannot refer to the resulting estimators as "fixed effects". While they would still capture some sort of an individual effect, they may not produce the benefits of the fixed effects estimators such as a better control over endogeneity biases.

Generally, I would recommend looking into the black Wooldridge to get it right.
Answer: Assuming you have the aggregate data for seven countries and 10 years, running a OLS model with dummy variables is equivalent to fixed effects.
If you include dummy variables for countries (there will be six, one omitted to avoid the dummy variable trap) or dummy variables for years (if there are 10 years, then there will be nine dummies, again to avoid the dummy variable trap) then that will be one-way fixed effects.
However, if you include dummy variables for both countries as well as years, it will be two way fixed effects. You can find details here if you are using Stata.