qid int64 1 4.65M | metadata listlengths 3 3 | prompt stringlengths 31 25.8k | chosen stringlengths 17 28.2k | rejected stringlengths 19 40.5k | domain stringclasses 28
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64,816 | [
"https://electronics.stackexchange.com/questions/64816",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/22254/"
] | An SR flip flop is a flip flop that has set and reset inputs like a gated SR latch. How can an SR Flip Flop be made from using a D Flip Flop and other logic gates?
I've done several searches online and nothing really explains this. I believe a latch can determine values based on inputs and/or the clock? And flip flops... | A D flip flop simply latches the value of a wire on it's D pin at the rising edge of a clock. Using three inputs (<code>S</code>, <code>R</code>, and <code>Q</code> (output of the DFF)), you need to create a small combinational circuit which mimics an SR flop:
<ul>
<li>If <code>S</code> is set, the value of <code>D</... | You are quite correct that the SR FF is more basic then the D FF. In fact, I expect you would find one or more SR flip-flops inside a D FF. For this reason, I assume doing what you request would only serve as an academic exercise.
Since the main difference here is that the D FF has an added clock, what needs to be d... | https://electronics.stackexchange.com |
588,210 | [
"https://electronics.stackexchange.com/questions/588210",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/296626/"
] | I was taking apart an older APC UPS and found a big transformer in it. The label says CLASS 130(B) NER-B82 430-0144 from Shenzhen Jingquanhua Electronics. DB-E186-3107A E208707. When I looked it up everything I could find described a transformer with some secondary tab. This doesn't have one. It has a black, red and wh... | A transformer with only three connections could be an autotransformer, this has only one tapped winding and is cheaper to make then a dual winding transformer. It does not provide isolation of the downstream circuitry from the mains but there are however places in a UPS where this is not necessary.
| A destructive way to know data about a transformer is unroll the transformer and count turns.. etc.
This is not always possible (es. potted transformers) but I made this by myself many times, obviously if you have your transformer data and cannot find an equivalent component you have to rebuild the transformer by yours... | https://electronics.stackexchange.com |
432,197 | [
"https://physics.stackexchange.com/questions/432197",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/118252/"
] | Take the most massive known star, R136a1, with a mass of <span class="math-container">$5.3 * 10^{32}$</span>kg and a raidus of <span class="math-container">$2.5*10^{10}$</span>m. Now place a <span class="math-container">$1$</span>kg metal ball <span class="math-container">$10*10^{24}$</span>m away (about a billion ly, ... | Earthy solutions suffice. Relativistic corrections only matter if the metal ball ends up moving near the speed of light. If you do the calculations for what the potential energy of the ball is at 1 billion light years away, <span class="math-container">$PE = -GMm/r$</span> with <span class="math-container">$M = 5.3 \ti... | <strong>Very near the escape speed.</strong> This is because the particle is starting from what is in effect "near infinity". To get a particle all the way to infinity requires you to give it at least the escape velocity upon launch, by definition thereof. To get it <em>near</em> infinity you thus need a velocity <em>j... | https://physics.stackexchange.com |
438,594 | [
"https://mathoverflow.net/questions/438594",
"https://mathoverflow.net",
"https://mathoverflow.net/users/12905/"
] | I've always wondered if the <em>DeMoivre method</em> to generate an algebraic number <span class="math-container">$x_p$</span>,
<span class="math-container">$$x_p = u_1^{1/p}+u_2^{1/p}$$</span>
of degree <span class="math-container">$p$</span> using only quadratic roots <span class="math-container">$u_i$</span> could b... | The following can explain the shape of the expression and also why you always get pairs (why the minimal polynomials for the two elements in a pair differ by few coefficients, I don't know).
Let <span class="math-container">$p$</span> be a prime congruent to <span class="math-container">$1$</span> mod <span class="math... | (<em>Not an answer but an addendum that addresses three issues</em>.)
<hr />
<strong>Issue 1</strong>
While a detailed answer has explained the method works for the generic cubic, numeric testing suggests <em><strong>any</strong></em> cubic <span class="math-container">$x^3+\alpha x^2+\beta x+1=0$</span> will work as l... | https://mathoverflow.net |
88,724 | [
"https://physics.stackexchange.com/questions/88724",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/21108/"
] | Many years ego, Earth was hot. Over time, it has lost energy and has become colder. Is it now in equilibrium or is its total energy changing?
| "Total energy of the Earth" is somewhat of an odd concept, but there's no reason we can't really entertain it. It brings up some genuinely difficult questions. The right way to approach this is to define the system correctly and then identify forms of energy content and flows.
Things to "count" in the Earth's energy... | The heat generated from the Earth's core is about 4x10^13 W while the Sun provides about 1.7x10^17W so although the Earth's core is slowly cooling this has very little effect on the Earth's temperature.
The Earth is in equilibrium between the energy received from the sun and the energy it emits into space. If the amou... | https://physics.stackexchange.com |
115,617 | [
"https://mathoverflow.net/questions/115617",
"https://mathoverflow.net",
"https://mathoverflow.net/users/332/"
] | Would anybody happen to know where I could obtain a scanned version of
Lectures on Morse theory - [revised and expanded version of notes of lectures delivered at Professor R. Bott's topology seminar at Harvard in February and March of 1963], taken by Richard S Palais?
As far as I am aware, these notes were never publ... | I find myself more than a little confused by this question. First, the "Lectures on K(X)" are not about Morse Theory. It is true that I gave a lecture on Morse Theory at Bott's Seminar in 1963, but I did not take and write up notes of lectures by Bott (at least not as far as I can recall---but that was half a century a... | There actually is a Morse theory book by Bott, but it's not the one you cite. Rather, it's the 1960 volume <em>Morse theory and its application to homotopy theory</em> with the attribution "Lectures by R. Bott / Notes by A. van de Ven". It's a little red book, but my copy (given to me by Bott himself!) is in a box in... | https://mathoverflow.net |
338,393 | [
"https://electronics.stackexchange.com/questions/338393",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/168063/"
] | I have a PCB that has >10 ICs intended to be powered by a 3.3V supply. Unfortunately, 12V was applied to the circuit and the board now exhibits a short circuit. The offending power supply is current limited so that now when it is attached to the damaged PCB, the supply limits itself to < 100mV.
My question is thi... | If 3.3V was the intended supply voltage, I'm guessing that you didn't have an in-line regulator to many of these ICs. I try not to design circuits without some sort of regulator for exactly this reason. Also, you can design in Zener diodes with an inline fuse, or other forms of protection to try to prevent this.
How... | Mike Barber gave some excellent suggestions. However, you may not have a thermal imaging camera available.
In that case, the decidedly-low tech technique simply uses Isopropyl alcohol. Spread a thin layer of alcohol over the entire board surface. Set your power supply to the rated supply voltage (3.3 Vdc) and set th... | https://electronics.stackexchange.com |
300,246 | [
"https://math.stackexchange.com/questions/300246",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/61834/"
] | How to find the prime numbers that divide $10^4-1$
| <strong>HINT</strong>
<ol>
<li>$x^2 - y^2 = (x+y)(x-y)$</li>
<li>$101$ is prime</li>
</ol>
| <strong>Hint:</strong> $10^4 - 1 = (100 + 1)(100 - 1) = 3^2 \times 11 \times 101$
| https://math.stackexchange.com |
371,362 | [
"https://softwareengineering.stackexchange.com/questions/371362",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/306444/"
] | A couple of readonly variables will be used. Almost all of the classes will be using those variables. Either I place all of the variables in a separate internal static class or I pass them on repeatedly in all the classes' constructor parameters. What would be the better of the 2? Performance-wise only please.
| <blockquote>
Either I place all of the variables in a separate internal static class or I pass them on repeatedly in all the classes' constructor parameters. What would be the better of the 2? Performance-wise only please.
</blockquote>
As the commenters have noted there is going to be mostly negligible differ... | <blockquote>
Performance-wise only please.
</blockquote>
You have already made the wrong decision, right there. This is called "premature optimisation" and it's frowned upon, for good reasons.
The correct question to be asking is what effect will the two approaches have on the ease of reading, testing, reasoning an... | https://softwareengineering.stackexchange.com |
3,324,958 | [
"https://math.stackexchange.com/questions/3324958",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/696098/"
] | <blockquote>
Given four touching circles and one common tangent, show that <span class="math-container">$$\angle BAD = \dfrac{1}{2}(\angle DO_1A + \angle AO_2B)$$</span>
<img src="https://i.stack.imgur.com/ytWcQ.png" alt="1]">
</blockquote>
It is done by looking at triangles <span class="math-container">$\triangle... | Hint: As you proved <span class="math-container">$$<BAD = {1\over 2}(<AO_2B+ <AO_1D)$$</span>
similary we have also: <span class="math-container">$$<BCD = {1\over 2}(<CO_3B+ <CO_4D)$$</span>
so <span class="math-container">$$<BAD +<BCD = {1\over 2}(<AO_2B+ <AO_1D)+{1\over 2}(<CO_3B+... | It will be easy to prove sum of opposite angles of quadrilateral ABCD is 180. Hence it is cyclic quadrilateral.
| https://math.stackexchange.com |
521,998 | [
"https://physics.stackexchange.com/questions/521998",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/228212/"
] | I am a little bit confused about the following equations. In the lecture we derived the following four equations for a geodesic motion of a particle in Schwarzschild geometry using the Lagrangian approach:
<span class="math-container">$(1)\hspace{10mm}\Theta = \frac{\pi}{2}$</span>
<span class="math-container">$(2)\h... | First off, when you take the <span class="math-container">$r\to \infty$</span> limit in equation (2), you're assuming that the particle can actually reach infinity. Of course this is not always true, since there exist bound orbits in the Schwarzschild geometry. But assuming this is the case, it's also not true that <sp... | Your two constants <span class="math-container">$K$</span> and <span class="math-container">$h$</span> are not constant for <em>all</em> geodesics. They are constant for a <em>particular</em> geodesic. <span class="math-container">$K$</span> and <span class="math-container">$h$</span> are the energy and angular moment... | https://physics.stackexchange.com |
18,955 | [
"https://cs.stackexchange.com/questions/18955",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/9173/"
] | Given a non-deterministic push down automata (we define "accept" here using accept states), if we assume any operation popping from the stack and checking if the top of the stack contains some symbol can succeed (i.e. "getting rid" of the stack), we get a non-deterministic finite automata.
If we convert two such PDAs,... | I think the answer is no, even if we disallow unreachable states.
Consider the language $L$ given by the grammar $S ::= \varepsilon \mid abS \mid aSb$. In this language, every word $w \in L$ has the same number of $a$'s and $b$'s, and every prefix of $w$ has at most as many $b$'s as $a$'s. Also, if $w \in L$ is not ... | I think the general answer is no, two PDAs that recognise the same language could yield NFAs that recognise different languages.
We can construct (at least) two PDAs for the empty language (i.e. that don't recognise anything), but have unreachable states. For example, the first can have states $A$ and $B$, with one tr... | https://cs.stackexchange.com |
228,694 | [
"https://physics.stackexchange.com/questions/228694",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/80634/"
] | I have done a laboratory session at my university where I had to check that the disintegration of nucleii follows a Poisson distribution
$$P(n)=\frac{\lambda^n}{n!} e^{-\lambda},$$
where $P(n)$ is the probability of the disintegration of exactly $n$ nuclei for a given time interval.
I measured the data using a compu... | If you have a Poisson distribution with a probability
$$P(n)=\frac{\lambda^n}{n!}e^{-\lambda}$$
that there will be $n$ events per bin, then $\lambda$ is the mean number of events per bin. You can get this via a direct calculation,
$$
⟨n⟩
=\sum_{n=0}^\infty nP(n)
=\sum_{n=0}^\infty n \frac{\lambda^n}{n!}e^{-\lambda}
=\l... | At its heart, Poisson is what happens in the limit to binomial as n->infinity and p ->0 p=prob of success. n=number trials. but if np->lambda we use Poisson distribution parameter lambda.
consider a recipe for raisin cookies.
n=NumberOfRaisins/Batch -> inf as BatchSize ->inf.
1/p=(cookies/Batch)... | https://physics.stackexchange.com |
337,948 | [
"https://electronics.stackexchange.com/questions/337948",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/167138/"
] | I'm planning to run 2 DC motors in parallel for a project.
Each of my motors has rated power of 250 W and a rated current draw of 14 amps at 24V (so 28 amps from 2 motors).
After researching around, it seems that a used car battery is a good solution (versatile and cheap). I would need to use 2 in series. However, a... | The car batteries are designed to supply 300 amps or so for a few seconds. They would not ordinarily be discharged more than 30% or so very often. They will not last very long if they are discharged nearly completely every time they are used. There are batteries that are very similar to car batteries, but they are desi... | <h2>Short answer - possibly.</h2>
Batteries have a wide range of capacities, typically measured in Amp-Hours (sometimes Watt-Hours) which is <em>more-or-less</em> how many hours the battery can supply 1 amp. The battery in my truck is 70Ah, so it could supply 28 amps for around 2.5 hours. Of course, this is a very rou... | https://electronics.stackexchange.com |
83,765 | [
"https://dba.stackexchange.com/questions/83765",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/770/"
] | I am getting crashes when trying to run innobackupex --apply-log. How can I find out what files it's processing at the time? I don't see a relevant option mentioned in the documentation.
| Check the version you used to backup the data is the same as the one you are trying to use to restore. This can bite.
| One easy way to do this would be by using strace, for example:
<pre><code>$ strace -e trace=open xtrabackup --prepare --target-dir=2014-11-27_06-06-49
</code></pre>
Change 2014-11-27_06-06-49 for the path to your unprepared backup location. I'm using here xtrabackup as it is the lower level tool that innobackupex use... | https://dba.stackexchange.com |
208,353 | [
"https://dba.stackexchange.com/questions/208353",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/126366/"
] | I have following table:
<pre><code>create table osoba(
id int primary key,
idNd int,
nazwim nvarchar(500),
)
</code></pre>
Data looks like below:
<pre>
id idNd nazwim
1 NULL grandpa
2 1 child1
3 1 child2
4 2 grandchild1child1
5 2 grandchild2child1
6 3 grandchild1child2
7 3 grandchild... | You add the column, in both parts of the recursive CTE.
Starting nodes have the <code>ID</code> as startingNode id.
The descendants have as starting node id, the starting node id of their parent:
<pre><code>WITH ret AS
(
SELECT id AS idStartingNode, o.*
FROM osoba o
--WHERE ID = 1
UNION ALL
... | You also need level to get a meaningful report
<pre><code>declare @t table (id int primary key, idNd int, nazwim varchar(50));
insert @t values
(1, NULL, 'grandpa'),
(2, 1, 'child1'),
(3, 1, 'child2'),
(4, 2, 'grandchild1child1'),
(5, 2, 'grandchild2child1'),
(6, 3, 'grandchild1child2'),
(7, 3, 'grandchild2child2')... | https://dba.stackexchange.com |
331,790 | [
"https://physics.stackexchange.com/questions/331790",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/103080/"
] | When considering potential wells textbooks simply say that we search for the stationary solutions of the schrodinger equation. Why do we do this? What tells us that the wavefunction will be independent of the time?
| <h2>Linearity</h2>
First let's consider the Schrödinger Equation (SE), in one dimension for a time independent potential,
$$
i\hbar\frac{\partial}{\partial t}\psi=-\frac{\hbar^2}{2m}\frac{\partial^2}{\partial x^2}\psi + V(x)\psi.
$$
A very useful property of this equation is linearity. This says that if both $\psi_1... | Remember, that the stationary solutions have a a factor of $e^{-iEt}$ factored out; in other words, the wave functions are not time independent, they just have a very simple time dependence. In a classical setting, the analog would be a standing wave on a string: it's not really standing still; it's just that every par... | https://physics.stackexchange.com |
566,137 | [
"https://electronics.stackexchange.com/questions/566137",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/286087/"
] | Is it possible to use a Smartphone audio jack as MIDI output?
My plan is to use a standard TRS to MIDI cable, like the one Arturias Beatstep uses, to connect a Smartphone/Tablet to a MIDI device.
I want to make a step-sequencing software that uses as simple of a connection as possible.
As far as I've read, MIDI needs t... | Is it <em>possible</em>? Yes, but <strong>not</strong> with a simple cable that connects a 3.5mm TRS to a MIDI DIN connector. I'm not familiar with the Arturias Beatstep, but your question suggests that it uses something like this. (Justme's comment on your question suggests that that some other manufacturers take t... | No, you can't use headset audio output for MIDI output.
The TRS connector on smartphone is meant to be connected to headsets, it has no circuitry that is compatible with MIDI.
MIDI interface is an opto-isolated 5mA current loop, and currently it is allowed to be used with 5V and 3.3V supply voltages. Traditionally a 5-... | https://electronics.stackexchange.com |
516,858 | [
"https://math.stackexchange.com/questions/516858",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | What is the general formula to find $p$ and $q$ if we have $\def\lcm{\operatorname{lcm}}\lcm (p,q)=b$ or $\gcd(p,q)$ and $p+q=a$ where ($a,b \in \mathbb N$) and $p>q$?
Example: $\lcm(p,q)=84$ and $p+q=54$ and $p>q$.
| <strong>GCD problem:</strong>
If $gcd(p,q)=b$ and $p+q=a$ the problem is relatively easy, but the solution is not unique.
In this case, there is a solution if and only if $b |a$, and this case the problem reduces to finding $p',q'$ relatively prime such that $p'+q'=\frac{a}{b}$. Then $p=p'b, q=q'b$ are the solutions.... | We have $gcd(54,84)=6$, so we may write $p=6p', q=6q'$. This satisfies $gcd(p',q')=1$, $p'+q'=9$, and $p'q'=14$. By inspection we have $\{p',q'\}=\{2,7\}$; since $p>q$ we have $p'=7, q'=2$ so $p=42, q=12$.
In answer to the posted question, I will prove that $gcd(p,q)=gcd(p+q,lcm(p,q))$. Proof by induction on the... | https://math.stackexchange.com |
441,927 | [
"https://electronics.stackexchange.com/questions/441927",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/223607/"
] | I'm trying to solder a new headphone plug - 3 pole, i.e. stereo with no mic.
There are 4 wires: copper, red, blue green. I was expecting 3.
Copper and red I understand to commonly be ground and right respectively. Blue and green are confusing me however - what could they be? Blue or green is usually left... but there a... | Experimentation with Benji007's suggestion of two grounds in mind led me to figuring it out. Turns out it was:
Copper: Left ground
Blue: Left signal
Green: Right ground
Red: Right signal
| Copper is most likely a ground and Red is most likely right speaker. I;m going to guess that Green is Left speaker and Blue is Left ground.
To test this, insert the plug into an audio source. Play audio. Hold the wires against the terminals of the plug and listen for sound.
The worst that could happen is you might... | https://electronics.stackexchange.com |
261,411 | [
"https://electronics.stackexchange.com/questions/261411",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/103599/"
] | Is there some way in VHDL to define a range as a previously defined range plus some offset? Below is an example of what I would like to do but I can't figure out the correct way of going about it. In this example the FIFO's din/dout are 47 downto 0.
<pre><code>constant X_DEPTH : integer := 8;
constant Y_DEPTH... | You can use attributes as 'right, 'left, 'low and 'high to generate one range from another :
For example :
<pre><code> subtype X_MIN_RANGE is natural range X_MAX_RANGE'low TO X_MAX_RANGE'high + X_DEPTH;
</code></pre>
For more elaborate operations, you can also define functions (with integer parameters) that will be... | I want to make this one perfectly clear, so I'll keep it short. VHDL describes hardware, so what you are asking for is a piece of hardware to run off previous values. These stored values of which you speak are memory. So to do what you want I would suggest a latch, where based on a condition, you latch a value somewher... | https://electronics.stackexchange.com |
77,634 | [
"https://stats.stackexchange.com/questions/77634",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/14188/"
] | I am teaching a basic statistics course and today I will cover the chi-squared test of independence for two categories and the test for homogeneity. These two scenarios are conceptually different, but can use the same test statistic and distribution. In a test of homogeneity, marginal totals for one of the categories a... | Depends on the details, but in general think of each autocorrelation as close to the correlation of a series and itself lagged. An outlier adds two points to the corresponding scatter plot, as the outlier appears first as itself and second as a previous value. The net result will often be difficult to detect. I wouldn'... | Outliers affect the covariance and the variance. The acf is the ratio between the covariance and the variance. Since the variance is inflated, the acf is dampened by the outliers. Effectively, the true acf is masked by the outliers. This is why simple model identification schemes are just too simple.
| https://stats.stackexchange.com |
67,090 | [
"https://softwareengineering.stackexchange.com/questions/67090",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/20636/"
] | I'm a .NET developer and mostly builds GUI's but of course also pure C# due to architecture and database level needs.
To me, developers of games in discussions often being simply referred to as "gaming developers". I find that a little too shallow and I'm curious what a "gaming developer" really stands for.
What w... | The difference between programming games as compared to business programming (client/server stuff) is that gaming is <em>real-time based</em>, whereas the other is request/response/event based.
This represents a completely different programming approach and mind set. In gaming you have a tight run-loop that needs to c... | Even within "Game Development", you'll see a range of role titles based on what the person actually does. Graphics programmer, engine programmer, gameplay programmer, etc. Each of these tends to have specific fields of focus which translate loosely between companies.
So yes... "Game Developer" is a little vague. You c... | https://softwareengineering.stackexchange.com |
243,295 | [
"https://mathoverflow.net/questions/243295",
"https://mathoverflow.net",
"https://mathoverflow.net/users/23500/"
] | It is known that no nontrivial connected cover of $\operatorname{SL}(2,\mathbb R)$ admits a faithful finite dimensional linear representation (see, for example, page 143 in Fulton-Harris and Exercise 11.9 therein). I am looking for a reference with a proof of this fact and an information who observed it first.
<strong... | See two papers by Kubota: <em>Ein arithmetischer Satz über eine Matrizengruppe</em> (1966, MR0188194) and <em>Topological Covering of SL(2) Over a Local Field</em> (1967, MR0204422). Maybe these are the first references, although in isome sense it goes back (at least) to Weil's famous Acta paper <em>Sur certains groupe... | Within the same textbook (Hilgert and Neeb) look at Example 9.5.18 which deals with the universal cover <span class="math-container">$\widetilde{SL_2(\mathbb{R})}$</span> of <span class="math-container">$SL_2(\mathbb{R})$</span> the proof follows similarly for an arbitrary cover with non-trivial kernel.
| https://mathoverflow.net |
137,313 | [
"https://security.stackexchange.com/questions/137313",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/97789/"
] | I've only got a basic idea about networking, Google is my teacher.
<ul>
<li>Router: Tenda D303</li>
<li>Location: India</li>
<li>Connection: BSNL Unlimited 1Mbps broadband.</li>
</ul>
Friends and relatives visit me often, and connect to my Wi-Fi while they're here, just for WhatsApp or emails, and nothing heavy. I te... | Four possibilities come into mind for your slow internet.
<ol>
<li>Your neighbors are using your wifi (e.g., you are using weak security on your router like WEP or are using very weak guessable passwords - wifi passwords can be broken offline so you need strong passphrases, or your router has a backdoor your neighbors... | Before you spend more time trying to fix the anomalous MAC address issue I'd suggest verifying it's the problem. Can you use wireshark to actually check that traffic is passing to/from the devices?
(I would have made this a comment but for reasons I can't comprehend you require more reputation to comment than to answe... | https://security.stackexchange.com |
410,603 | [
"https://physics.stackexchange.com/questions/410603",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/123334/"
] | I'm struggling with a concept of normalization of 4-velocity in Special Relativity (and General Relativity eventually).
Well, after a bunch of introduction to vector/tensor calculus we came up with the mathematical fact that the inner product and the metric tensor have a quite close relation in order, at least, to per... | The phrase "the metric tensor and the inner product have a close relation at least to perform calculations" makes me a bit uncomfortable since the inner product and the metric are essentially the same thing.
But anyway, suppose you have a timelike curve in spacetime $x^\mu (\lambda)$ parametrized by some parameter $\l... | Normalization help provide a “unit vector” so that determining components of tensors is made easier.
UPDATE:
Another interpretation of the normalized 4-velocity is that it represents one-tick of that observer's clock. A normalized spacelike vector orthogonal to that 4-velocity would represent a unit of length (say one... | https://physics.stackexchange.com |
53,081 | [
"https://mechanics.stackexchange.com/questions/53081",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/36635/"
] | While I was driving 20 mph, I heard a loud snap/bang noise and the car then started making noise when turning the steering wheel or driving on small bumps. Any idea what could cause this? Broken struts?
This is a 2013 Volkswagen Golf Mk6 with approximately 40K miles. I just had to change the rear brake pads because th... | It appears that the mirror is placed over the "closer than appears" warning. This would indicate that it's an aftermarket item.
Your idea of using dental floss is a good one. The adhesives on these aftermarket mirrors are a very thin foam double-sided tape. Your objective should be to slice the foam in two pieces edge... | i think the hairdryer trick isn't a bad one.
to remove residue adhesive, i have found "Goo Gone" very helpful. i'm not sure if there's a generic variant of the chemical, but i was going to recommend that once you get the adhesive backing-residue off. i have had much success in removing super-stubborn adhesive residue ... | https://mechanics.stackexchange.com |
444,071 | [
"https://stats.stackexchange.com/questions/444071",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/270529/"
] | I have tried transforming the variable (x; <em>shown below</em>) using various methods but with nothing changing as 0 is so prominent. How would I handle the variable below in multiple regression analysis as it is predominantly zeros and thus very asymmetrically distributed? Can it be transformed? Any help would be gre... | I assume x is a predictor, not the dependent variable. Fit x as quadratic with an exception that allows for a discontinuity at zero, i.e., add an indicator variable for x > 0.
| Depending on what you are trying to estimate, sometimes it is useful with imbalanced data to re-sample the data. There are various algorithms out to resample your data. You can undersample your zeros to prevent them from dominating the model. You can oversample (aka duplicate) your non-zero values to make them have a h... | https://stats.stackexchange.com |
429,939 | [
"https://math.stackexchange.com/questions/429939",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/15416/"
] | I attempted to design an exercise for my engineer students and couldn't solve it myself. Maybe here are some experts in calculus who have some better tricks than I do:
<blockquote>
The exercise would be to find the maxima of $e^{-x}(x^2-3)(y^2-3)$ on the circle $x^2+(y-1)^2=4$.
</blockquote>
Now using the Lagrange ... | Here is what we did:
The problem with the stated optimization is that it has too many critical points (for example one sees that when looking at the set of zeros of that function).
So our answer to question 2 was as follows: We moved the circle to maximize on, so that it does not meet the set of zeros of the function... | Let us parametrize the circumfererence:$x=2\cos(\phi),y=1+2\sin(\phi)$. Then the function
$$f(\phi):=e^{-2\cos(\phi)}(4\cos^2(\phi)-3)(4\sin^2(\phi)+4\sin(\phi)-2)$$ should be maximized on $[0,2\pi]$.
The equation $f'(\phi)=0$ is equivalent to
$$
32 \sin^3 ( \phi ) \cos ^2(
\phi ) -32\cos ( \phi ) \sin^3
\le... | https://math.stackexchange.com |
56,196 | [
"https://dsp.stackexchange.com/questions/56196",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/41268/"
] | While studying the Image Magnification in spatial domain, I have come across this definition of Image Magnification by Replication:
<blockquote>
Replication is a zero order hold where each pixel along a scan line is repeated once and then each scan line is repeated.
</blockquote>
And the definition for Image Magnif... | We need to assume the reader knows some basic stuff to answer that.<br>
Let's give it a try.
Lets understand the sentence - <code>Zero / First Order Hold</code>.<br>
We have the Zero / First Order and the Hold.
Zero / First Order hold means the order of the Taylor Series of the function we use to interpolate. In othe... | the terms are clearly defined, in the excerpts and comments, so I assume you are looking for origins of the terms. The word “hold” is my guess where the problem is.
my understanding is that the terms originally were used in mixed digital-analog control systems.
feedback in real time analog control systems has very l... | https://dsp.stackexchange.com |
483,001 | [
"https://electronics.stackexchange.com/questions/483001",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/235874/"
] | There are some(or most) instructions in a computer that simply cannot be executed in a single clock cycle. But there lies a problem. How does the program counter in the computer know when an instruction is completed, considering that one instruction might take 2 clock cycles vs another being 3 clock cycles. How do prog... | tl;dr version: instructions are expanded internally to multiple microcoded steps. The PC is held by microcode until the instruction sequence completes.
get-a-cuppa version:
A CPU has two types of code: <em>instructions</em> (opcodes + operands) that are fetched and executed from RAM, and the small steps that carry ou... | There are many dozens of different ways in which this is done. And many computers have variable length instructions (multiple words or bytes, odd numbers of bytes, etc.), so the logic not only has to know when but how much to increment. Some computer (superscalar, etc.) fetch more than one instruction at a time, and ... | https://electronics.stackexchange.com |
57,923 | [
"https://electronics.stackexchange.com/questions/57923",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/18963/"
] | Often I see in circuit diagrams that the circuit is connected to the ground:
<img src="https://i.stack.imgur.com/P2vWr.gif" alt="enter image description here">
I understand that this creates a reference for zero potential, but why does all of the current not simply flow right into the ground? I must have a fundament... | The current doesn't all just flow to ground because of Kirchoff's Current Law. Kirchoff's Current Law states that the sum of the currents entering and leaving a node must be equal to zero. If x amps flow from the power supply, x amps must return to the power supply.
In your schematic, before the earth connection was ... | The ground symbol:
<img src="https://i.stack.imgur.com/1zsqA.png" alt="ground symbol">
means, "this is connected with wire to all the other things connected to other instances of this symbol". Since there is only one of these in your example schematic, it means nothing at all in this respect.
It also might mean, "If... | https://electronics.stackexchange.com |
164,151 | [
"https://softwareengineering.stackexchange.com/questions/164151",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/62898/"
] | I have been going over YouTube watching videos on eMail encryption and everyone seems to explain it from a different perspective. Some do it for a CompTIA exam while others just provide a primer.
Here is what I understood:
<img src="https://i.stack.imgur.com/2Ooj8.png" alt="email encryption">
<br>
<strong>Step1</stron... | With email encryption there are two possible options (over-simplified):
<ul>
<li>End to End encryption</li>
<li>Point to Point encryption (eg TLS)</li>
</ul>
When to use each really depends on the purpose of encrypting the email. Do you want to prevent someone eavesdropping while your mail is being sent or to you wan... | Encryption and signing are two separate things. You can send a signed email that is not encrypted, and you can send an encrypted email that isn't signed.
For the most part, you are correct. But the entire email is not 'gibberish', only the contents. The header remains unaffected, with the exception that the content-ty... | https://softwareengineering.stackexchange.com |
205,496 | [
"https://physics.stackexchange.com/questions/205496",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/86781/"
] | I understand that magnetic containment structures like tokamaks generate a toroidal magnetic field in which the plasma particles move in helices around the field lines, because of the Lorentz force. A single free particle would stay inside the torus for all time.
But how do such magnetic fields generate a force that g... | Let $\chi$ be the spinor defined as follows:-
$$\chi=\begin{pmatrix} a\\b\end{pmatrix}$$
then for measuring $S_x$ we need to find the eigenspinors of $S_x$ which are
$$\chi_{+}^x=
\frac{1}{\sqrt{2}}\begin{pmatrix}
1\\
1
\end{pmatrix}
,\hspace{1cm} \chi_{-}^x=
\frac{1}{\sqrt{2}}\begin{pmatrix}
1\\
-1
\end{pmatrix... | The adjoint eigenspinor you multiplied by was the unit length eigenvector of $\sigma_z$ with positive eigenvalue.
If you you want a spin up result for the direction $(n_x,n_y,n_z)$ find a unit length eigenvector of $n_x\hat\sigma_x+n_y\hat\sigma_y+n_z\hat\sigma_z$ with positive eigenvalue. And use that instead.
If yo... | https://physics.stackexchange.com |
135,917 | [
"https://softwareengineering.stackexchange.com/questions/135917",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/6001/"
] | I am new to Entity Framework.
I know there is an option to update model from the database, but I want to know how easy and successful is this task. I may need to update my model in a few weeks but till that time many lines of code has already been pushed inside.
Is it difficult to track changes and make code work?
| Code generators are a double-edged sword. You can build lots of complex code quickly and easily but you have to be prepared to live with the code you've generated. You can't (don't want to) customize this code because your customizations will be wiped out if you ever regenerate.
In my experience, recent versions of ... | EntityFramework was originally designed with the "Model-First" approach as the preferred approach to building your Data Access layer, however many software shops still seem to live in the Dark Ages where they prefer to design the schema first and then the model to accomodate it. Okay, I may be a little unfair, if you ... | https://softwareengineering.stackexchange.com |
22,319 | [
"https://mathoverflow.net/questions/22319",
"https://mathoverflow.net",
"https://mathoverflow.net/users/5464/"
] | If $f:X \to Y$ is a flat and proper surjective morphism between smooth schemes over an algebraically closed field, and $f$ has connected fibers, does it imply that
$$f`_*\mathcal O_X = \mathcal O_Y?$$
| This follows from Zariski's main theorem if the characteristic is zero and it is false in positive characteristics: consider the the morphism $\mathbb{A}^1 \to \mathbb{A}^1$ given by $x \mapsto x^p$ where $p$ is the characteristic. The statement would also be true in char p if you assume that the general fibre is reduc... | If $X$ is smooth over $K$ and if $K$ is of characteristic $p>0$, then the relative Frobenius $F:X\rightarrow X\times_{F_X} K=:X'$ is faithfully flat $K$-morphism and finite, hence proper. Moreover it's a homeomorphism, so the fibers are connected. But it's not hard to see that $F_*\mathcal{O}_{X}$ is locally free of... | https://mathoverflow.net |
150,548 | [
"https://physics.stackexchange.com/questions/150548",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/5788/"
] | An essential part of a guitar is its hollow body. Without it, the strings wouldn't be very loud; as far as I know, the purpose of the body is to set up some sort of resonance and make the sound louder.
How does this work? How can an isolated system amplify sound? Where is the energy coming from?
| It is not amplification! The purpose of the guitar body is to impedance and mode match between the string and the surrounding air.
<h1>Intuition</h1>
When a an object vibrates it pushes on the surrounding air creating pressure waves which we hear as sound.
A string vibrating alone without the body of the instrument doe... | <strong>Simple version:</strong> When something vibrates, it puts pressure on the air molecules around it, making them vibrate. So if just 1 or 2 strings that vibrate, it won't make very many molecules vibrate because it's not touching many of them. So you can imagine that when a large flat piece of wood is vibrating a... | https://physics.stackexchange.com |
349,574 | [
"https://electronics.stackexchange.com/questions/349574",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/174495/"
] | So I've been experimenting creating thermocouples with copper and constantan wire, just by twisting them together at one end and heating the junction with a candle and using a voltmeter to measure the emf at the other end. I thought that changing the gauge of the copper wire might change the emf output, and it appears ... | Thicker wires mean you are heating the 'cold' end more (and, as in the comment) drawing more heat from the hot end. To a rough approximation the no-load voltage is proportional to the temperature difference between the ends.
A long thick wire (long enough the cold end does not heat appreciably) should not be any diff... | You may be having types of difficulty.
<ol>
<li>The voltage may be affected by the quality of the junction. Twisting the wires together is not going to make a good thermocouple junction. They should be welded together at a single point.</li>
<li>When you connect the voltmeter to the thermocouple wires, you create two ... | https://electronics.stackexchange.com |
66,439 | [
"https://math.stackexchange.com/questions/66439",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/9262/"
] | Let $S$ be a graded ring, $M$ a graded $S$-module, and $N$ a graded submodule of $M$. I'm trying to convince myself (of the well known fact) that $M/N$ is graded by $$M/N=\oplus_{i\geq0} (M_i/N\cap M_i),$$ but I can't do it.
For $x\in M/N$, I would like to see $x$ displayed as $$(m_1+N\cap M_1,m_2+N\cap M_2,...,m_r+N\... | We have as abelian groups $M = \oplus_i M_i$ and $N = \oplus_i (M_i \cap N)$ (since $N$ is graded). Now direct sums commute with quotients (this is an instance of a more general fact from category theory, that colimits commute with colimits - in the functorial approach, this is just trivial). Thus $M/N = \oplus_i M_i /... | Use the definition of $N$ being a <strong>graded</strong> submodule of $M$.
| https://math.stackexchange.com |
370,247 | [
"https://softwareengineering.stackexchange.com/questions/370247",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/295821/"
] | <strong>Quick Summary</strong>
I'm building a search micro-service that will allow searching across different types of resources in a particular system (e.g. blog posts, users etc.). The API that will be exposed will be consumed by both web applications and native mobile applications.
<strong>My Solution</strong>
Wh... | <blockquote>
Why doesn't the Dictionary class have logic to move an object to the correct bucket <em>when it detects that the object's hashcode has changed</em>?
</blockquote>
Just to be sure, we are talking about the hash of the <em>key</em> here, the hash of the value is irrelevant.
The important part of your com... | Short answer: <code>Dictionary</code> can't detect that some hashcode changed. There is no event that it can subscribe to. Getting hashcode is just a call to <code>Object.GetHashCode()</code>. That method is called once when you insert the object. For obvious performance reasons <code>Dictionary</code> can't call that ... | https://softwareengineering.stackexchange.com |
6,052 | [
"https://mathoverflow.net/questions/6052",
"https://mathoverflow.net",
"https://mathoverflow.net/users/344/"
] | I read the following fact: if $U$ is an open subset of $P_k^1$ and $f: U \to U$ is an automorphism of schemes, then $f$ extends to an automorphism of $P_k^1$. Thus I was curious: is there a general criteria for when a continuous map defined on an open subset $U \subset X$ extends to $X$ (especially in non-Hausdorff se... | Your example is in the category of schemes, but you then ask about maps of topological spaces.
Assuming you care about schemes, the condition is that the source is one dimensional and regular, and the target is proper. That you can extend in this case is essentially the valuative criterion of properness; that you can... | For the automorphism question, I think a first criterion is that X is smooth and one dimensional. Otherwise, you can take a nontrivial finite order automorphism of a higher-dimensional scheme Z, blow up a non-fixed point to get X, and delete the orbit of that point to get U.
In general, this is a question about the t... | https://mathoverflow.net |
294,382 | [
"https://dba.stackexchange.com/questions/294382",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/232854/"
] | I have an unusual situation where I have a bunch of backups of a mysql database and I am interested in selecting the distinct members of a given table from these backups (since some records might have been added or deleted). My thought is to use a cross database join, but I'm not sure if that really is what I'm looking... | The trick is to force the Optimizer to avoid evaluating both sides of <code>OR</code>.
(I do not know if there are simpler ways, but I feel pretty sure this will work.)
If <code>id</code> is the <code>PRIMARY KEY</code>:
<pre><code>SELECT *
FROM mytable
WHERE id = IF (
EXISTS( SELECT id FROM mytable W... | Try the next query (I assume that <code>mytable.idx</code> is indexed):
<pre><code>( SELECT *
FROM mytable
WHERE idx=123
LIMIT 1)
UNION ALL
( SELECT *
FROM mytable
WHERE name like '%foo%'
AND NOT EXISTS ( SELECT NULL
FROM mytable
WHERE idx=123 )
LIMIT 1)
LI... | https://dba.stackexchange.com |
1,468,861 | [
"https://math.stackexchange.com/questions/1468861",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/142720/"
] | Exercise 7.19 of Tom Apostol's <em>Mathematical Analysis</em> defines $$f(x) = \left(\int_0^x e^{-t^2}dt\right)^2,\;\; g(x) = \int_0^1 \frac{e^{-x^2(t^2+1)}}{t^2+1}dt $$ and asks to prove that $f'(x) + g'(x) = 0$ and, from that, $f(x)+g(x)=\pi/4$.
I've successfully proven that $f'(x) + g'(x) = 0$:
$$f'(x) = 2e^{-x^2}... | Consider $x=0$ and that
$$\int_0^1 \frac{dt}{t^2+1} = \frac{\pi}{4} $$
| Because $\frac{d}{dx}(f+g)=0$, we know that $f+g$ is a constant, so we need only to plug in a number. For instance $x=0$.
$f(0)=0$ and $g(0)=\frac{\pi}{4}$
| https://math.stackexchange.com |
3,672,759 | [
"https://math.stackexchange.com/questions/3672759",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/787713/"
] | can anyone help me with this limit?
<span class="math-container">$$\lim_{n\to \infty} n!\frac{e^n}{n^n}$$</span>
I know that the result is infinity but I can't find a way to prove it.
What I tried was to "split" the expression in half to have a pruduct of n/2 and n/2 fractions and then made it smaller by taking first ... | Using Stirling's approximation we have that
<span class="math-container">$$\sqrt{2\pi n} \leq \frac{n!e^n}{n^n}.$$</span>
And since you lower bound diverges you have that limit diverges.
| Suppose that <span class="math-container">$n$</span> is a positive integer. By the concavity of <span class="math-container">$\log$</span>, we have
<span class="math-container">\begin{align*}
\log n! = & \sum\limits_{k = 1}^n {\log k} \ge \sum\limits_{k = 1}^n {\int_{k - 1/2}^{k + 1/2} {\log xdx} } = \int_{1/2}^{... | https://math.stackexchange.com |
72,353 | [
"https://security.stackexchange.com/questions/72353",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/52612/"
] | At a company I worked at, I had to change my password every 90 days and I could only reuse a password after 8 iterations. This no-reusal included passwords being too similar to the old one, e.g. when I only changed one letter, that new password was not accepted.
Does that mean they were storing this password in plaint... | No, it does not mean they are storing the passwords in plain text. The question doesn't completely describe the behavior. Are they matching patterns only from your current password, or patterns from <em>all</em> 8 of your previous passwords?
If it's the first case, the answer is dead simple, and this is that they have... | A hash by definition should not allow you to find if it's similar to something else.
From wikipedia:
<ol>
<li>it is easy to compute the hash value for any given message</li>
<li>it is infeasible to generate a message that has a given hash</li>
<li>it is infeasible to modify a message without changing the hash</li>
<l... | https://security.stackexchange.com |
517,737 | [
"https://electronics.stackexchange.com/questions/517737",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/195605/"
] | I am driving an optical modulator with a <strong>driving signal</strong> with DC(2 V)+RF signal(bandpass signal from 1GHz to 2GHz, 500 mVpp). The DC and RF are combined with a bias-tee (mini-circuit, ZFBT-6G+). The passband of the RF port of this bias-tee is <strong>10 MHz to 6 GHz</strong>.
However, I would like to ad... | I suspect that much of the trouble you're having is from trying things haphazardly and/or not communicating very well here what you've tried and/or not understanding or following suggestions made here and in your previous question.
You have established that your RFID reader is communicating over its serial port by conn... | The adapter you bought has a USB UART chip with a RS232 voltage level translator inside the DE-9 connector, so the wires you cut use the USB protocol. You cannot connect USB to your Arduino, it will not work.
| https://electronics.stackexchange.com |
762,715 | [
"https://math.stackexchange.com/questions/762715",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/144615/"
] | I have a question to ask about a function.
Suppose a function $$f(x) = \frac{x^2 - x}{ x - 1},$$ we can simplify this function to be $f(x) = x$. Yet, we say that this function is discontinuous at $x = 1$ but after the simplification, we say that the function $f(x)$ is continuous.
Which one is correct? The fact that $... | The original function $$f\left(x\right)=\frac{x^{2}-x}{x-1}$$ has $\mathbb{R}\backslash\left\{ 1\right\} $
as (maximal) domain and is continuous. It is not defined on $\left\{ 1\right\} $
and consequently statements like '$f$ is (dis)continuous at $1$' don't
make sense. It can only be (dis)continuous at points that bel... | The original function has domain $x: x \neq 1$ while the second function has domain all real numbers. So they are two different functions, and they are not equal. $f$ is discontinuous at $x = 1$. Here $f(x) = \dfrac{x^2 - x}{x - 1}$
| https://math.stackexchange.com |
18,912 | [
"https://physics.stackexchange.com/questions/18912",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/6743/"
] | Personally I learned Physics in high-school and found it very interesting, I read up a lot about physics in my free time.
Personally I am also a programmer which I think is also good when it comes to Physics.
Now I want to start studying in a university and my dilemma right is mainly between Math/Computer Science/Phy... | You might do worse than go into high energy experimental physics.
A thesis would need knowledge of most theories for elementary particles, it would be on a subset of the subject not explored before, thus new and research. At the same time the experiments are huge and depend crucially on computer programming, mathemati... | If you want to combine math, computer science and quantum mechanics, try quantum computation. Of course, most current work on quantum computers are being done by researchers, but I think it would be easier for a programmer with knowledge of quantum mechanics to do something like design or analyze quantum algorithms.
| https://physics.stackexchange.com |
175,979 | [
"https://mathoverflow.net/questions/175979",
"https://mathoverflow.net",
"https://mathoverflow.net/users/26705/"
] | If $f$ and $g$ are two functions, define $f \sim g$ if they differ only finitely often on their common domain.
The following property of a large cardinal arose from a problem in model theory. I am interested in its strength. Say that a cardinal $\kappa$ has the weak tree property if the following holds:
Suppose $(b_... | I give here some upper bounds for the consistency of the weak tree property. Namely - for every successor of regular (including double successors of singulars) we can get the weak tree property by collapsing a weakly compact, and we can get the weak tree property everywhere by collapsing a strongly compact cardinal to ... | Douglas: here's Yair's argument. Assume that $P$ is $\sigma$-closed and adds a $b$ as described. First, if $p$ forces that $b|\alpha=\beta$, then there are extsnions $p'$ and $p''$ of $p$ which force $b|\beta=g',g''$ such that $g'$ and $g''$ differ. (otherwise $b$ is in $V$.) Notice that you can make $\beta$ arbitraril... | https://mathoverflow.net |
506,134 | [
"https://physics.stackexchange.com/questions/506134",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/230701/"
] | Something intuitive and fundamental as the concept of velocity (of a particle for example) in classical physics is defined as a derivative, a concept to me quite vague and strange, although i know its mathematical definition.
Why the need for defining the velocity using a derivative ? Can you explain this to me ?
| Well, I might as well put my answer in too.
First, the velocity is useful because it tells us how far we travel in some time period, or in a different way if we know our velocity we can determine how long it will take to travel some distance, etc.
Now, it is <em>very</em> easy to work with velocity and these distance... | You could define try to define velocity as the change in position over a finite time interval (what physicists would call <em>average</em> velocity). But the problem with that is the average velocity depends on the time interval chosen, so how do you choose a time interval that works for every possible motion ?
Also, ... | https://physics.stackexchange.com |
187,773 | [
"https://electronics.stackexchange.com/questions/187773",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/39136/"
] | What are the general rules of filling / pouring traces? What traces should I pour?
I assume ground is poured most often.
Should I pour other traces? Supply/Signal or something else perhaps?
What are the advantages/disadvantages of pouring?
If specifics are needed then assume an analog low-power audio circuit.
| Assuming two layer board the most common practice is to pour the ground on both sides.
There are three reasons i can think of using a pour for other then a general ground. First, in a multi layer board (4 or more layers) one inside layer is a power pour and the other is a ground pour. Second, when running very large p... | Generally for single-layer boards you'll want to pour your ground. This is to improve the signal integrity. Suppose you have a trace that carries a clock signal. It's always best to have the return path (ground) very close to the signal trace, so that it doesn't have to loop around the board to "find" its return. Havin... | https://electronics.stackexchange.com |
478,142 | [
"https://physics.stackexchange.com/questions/478142",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/220850/"
] | Imagine we have paper book. If we put this into a pan and increase its temperature, this book would not catch on fire. If on the other hand the book interacts with this heat source directly, it does catch fire. What is the difference between these two situations?
| Before answering your question, it is important to understand how ignition of a solid material occurs. For fuels that contain hydrogen and carbon like paper, Ignition is a gas phase phenomenon . It is not the solid itself that ignites. Before a solid material can be ignited, it must be partially converted into a volati... | The pan starts out at room temperature, say 20°C. The gas flame starts out around 2000°C. The ignition temperature of paper is roughly 200°C.
So the flame can immediately ignite the paper, but the pan cannot immediately do so because it must heat up. The pan <em>can</em> ignite the paper if the flame can heat up the p... | https://physics.stackexchange.com |
63,997 | [
"https://electronics.stackexchange.com/questions/63997",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/19017/"
] | This is an image from a book showing us how to solve BJT circuits via AC analysis:<br>
<img src="https://i.stack.imgur.com/GfwXP.jpg" alt="enter image description here">
So I understand that when doing AC analysis to ground all the DC voltage sources but I don't understand <em>why</em>. Can anyone explain this concept... | If you look at your top circuit you will notice that there are shorts where the input, emitter and output capacitors were - this is the first step to doing an AC analysis. The caps are assumed to pass AC without hinderance so thay are shorted. Resistors are presumed to to attenuate so these are left in.
Whether a resi... | the DC source and AC source all have a internal resistance, Rs. for a AC signal, a ideal DC source is shorted.it means that when we doing AC analysis, only consider the path of AC current, even if we could not ignore the Rs of DC source in some case, notice the common junction betweeen circuit and Rs of DC source, and ... | https://electronics.stackexchange.com |
2,426,468 | [
"https://math.stackexchange.com/questions/2426468",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/479883/"
] | Is it possible to create a cubic function with the roots $a$, $b$ and $c$, $f(x) = K(x-a)(x-b)(x-c)$, that coincides with a sine or cosine function, $g(x)$, in the interval $d \le x \le e$, $g'(d) = g'(e) = 0$?
| It is not possible, because $f^{(4)}\equiv0$, and $g^{(4)}\not\equiv0$.
| It's not possible (assuming $d\neq e$). I am not sure what the quickest way to prove this is, but using complex analysis you can just say the following: if this is true, then $f-g$ is a function that can be extended to all of $\Bbb{C}$ which is $0$ on all of $[d,e]$. Since $[d,e]$ has a limit point, this impies $f-g$ i... | https://math.stackexchange.com |
112,372 | [
"https://electronics.stackexchange.com/questions/112372",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/7624/"
] | A lot of boards with predominantly SMT components have TH connectors on them for things like headers and power connectors. Take a standard barrel power jack for example:
TH:
<img src="https://i.stack.imgur.com/SmV7A.png" alt="Through-hole power jack">
SMT:
<img src="https://i.stack.imgur.com/yWMGt.png" alt="Surface... | The choice of through-hole versus surface-mount comes down to you, the designer of the PCB. To make that choice, you have to consider things like:
<ul>
<li>Assembly and tooling. Does the company or person assembling the PCB have the necessary tooling for the desired form factor?</li>
<li>Device construction and cleara... | The shear strength of SMT pads on a frequently jarred power cord gives rise to metallurgic fatigue.
The reliability of this interface is poor unless there is significant pressure on the connector to resist strain from stress on the pad joint from mechanical torque.
Unless you can provide this extra durability prot... | https://electronics.stackexchange.com |
28,054 | [
"https://mathoverflow.net/questions/28054",
"https://mathoverflow.net",
"https://mathoverflow.net/users/1465/"
] | The group $Diff(S^n)$ ($C^\infty$-smooth diffeomorphisms of the $n$-sphere) has many interesting subgroups. But one question I've never seen explored is what are its "big" finite-dimensional subgroups?
For example, $Diff(S^n)$ contains a finite-dimensional Lie subgroup of dimension $n+2 \choose 2$, the subgroup of c... | You can make big Lie groups act effectively on small manifolds by cheating: make the group a product of groups, with each factor acting by compactly supported diffeomorphisms on a different disjoint open subset. So the additive group $\mathbb R^N$ becomes a subgroup of $Diff(S^1)$ by flowing along $N$ commuting vector ... | For 2) I think the following is an answer: Suppose $K$ is a compact Lie subgroup
of $\mathrm{Diff}(S^n)$ of dimension $\geq{n+1\choose 2}$. Being compact it is
the group of isometries of some Riemannian metric of $S^n$ and we fix one such
metric. The stabiliser of a point therefore has dimension at most $n\choose 2$
(t... | https://mathoverflow.net |
750,175 | [
"https://physics.stackexchange.com/questions/750175",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/358380/"
] | If I stretch a spring, is the spring retaining its mass?
| Answer is yes, spring will accelerate with respect to you. As you hold spring in one hand, you will act as fix support to spring. Spring also have some mass so it will become spring-mass system (Assume mass of spring acting at end of spring, after calculation it will be mass of spring/3). After giving some initial disp... | It depends on whether or not your hand is moving with constant velocity.<br />
Consider three portions of the spring, at the fixed end, in the middle, and at end you are holding.<br />
The centre of mass of the spring is located at the middle of the spring.<br />
If your hand is moving at a constant velocity of <span c... | https://physics.stackexchange.com |
172,444 | [
"https://math.stackexchange.com/questions/172444",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/20924/"
] | Let $x_0$ be an accumulation point of the set $D \subset \mathbb{R}$. We say that $y$ is a limit point of a function $f:D \rightarrow \mathbb{R}$ in $x_0$ iff there exists a sequence $(x_n)$, where $x_n \in D\setminus \{x_0\}$ for $n\in \mathbb{N}$ and $x_n \rightarrow x_0$, such that $y=\lim_{n\rightarrow \infty} f(x_... | Note: I assume you require that $x_n\to x_0$ in your definition, otherwise this lemma is false.
Suppose $y$ is a limit point of $f$ in $0$, so we have a sequence $(x_n)$ in $(0,c)$ such that $x_n\to x$ and $f(x_n)\to y$. Then
$$\liminf\limits_{n\to\infty} f(x_n)=y=\limsup\limits_{n\to\infty} f(x_n)$$
so we have that
... | The idea behind "why this lemma is morally true" is because it is trivial in the case where $f(x) \to C$ when $x \to 0$, and because if the limit $\lim_{x \to 0} f(x)$ doesn't exist, since the function is continuous, the function must be going back and forth between the sequence going towards the $\limsup$ and the othe... | https://math.stackexchange.com |
110,493 | [
"https://security.stackexchange.com/questions/110493",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/21695/"
] | A design pattern I've noticed on internet banking sites is that you get automatically logged out and sent to a warning page if/when you hit the back button on your browser, ending your session and obliging you to log in again.
I'm presuming this is due to some sort of security consideration, but I'm at a loss to figur... | A scenario such banks might want to protect you from could be this:
<ol>
<li>you visit your banking website and do your banking stuff.</li>
<li>after you are finished you log out and then navigate to some other website to look at cat pictures or whatever.</li>
<li>you leave your computer with the cat picture website o... | There's a couple of things going on here:
Bankings sites will use cache-control headers to forbid cacheing of the pages. So when you click back the browser has to reload the page from the server.
Some parts of the site may have a strict flow of pages, e.g. you enter transaction details, enter your SMS code, view tran... | https://security.stackexchange.com |
129,511 | [
"https://electronics.stackexchange.com/questions/129511",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/53382/"
] | I have a basic Verilog block that I wrote to trigger on any change in the signal.
<pre><code>always @ (trigger)
begin
data_out <= data_in;
end
</code></pre>
I expected this to trigger on the rising or falling edge of the trigger. Instead, it tied data_out to data_in. Even when the trigger was in steady s... | Not sure why it would trigger on data_in when written like that unless your synthesising it and simulating at gate level.
<code>always @(posedge clk)</code> in RTL maps to a flip-flop.
<code>always @*</code> in RTL maps to combinatorial logic.
The <code>@*</code> is an auto completed sensitivity list based on any si... | There shouldn't be an issue with simulation. There will be an issue when synthesizing, which will generate pass through behavior instead of being clocked via double edge. Most synthesizers do not support double edge clocking and those that do often require special setup and restriction. Refer to the manual and other do... | https://electronics.stackexchange.com |
250,769 | [
"https://mathoverflow.net/questions/250769",
"https://mathoverflow.net",
"https://mathoverflow.net/users/36974/"
] | Suppose $M$ is a complex $n$-dimensioanl compact Kähler manifold and $\omega$ a Kähler class. Suppose $\alpha\in H^{1,1}(M,\mathbb{R})$ is a nef class belonging to the boundary of the Kähler cone of $M$. If for some $1\leq k\leq n-1$ we have
$$\int_M\alpha^k\omega^{n-k}=0,$$
can we conclude that $\alpha^k=0\in H^{k,... | @Kevin I think the answer is 'yes'. Here is a proof: if $\alpha$ is nef, then, for every $\varepsilon >0$ the class $\alpha+\varepsilon \omega$ is Kahler, and in particular the class $(\alpha+\varepsilon\omega)^k$ contains a positive $(k,k)$-current. We let $\varepsilon$ go to $0$, and obtain in the class $\alpha^k$... | Just for fun, here is an answer in the purely algebraic setting.
So, suppose that $X$ is irreducible projective algebraic of dimension $n$, $\alpha=c_1(\mathcal O_X(D))$ is the class of a nef divisor $D$, and $\omega=c_1(\mathcal O_X(A))$ is the class of an ample divisor.
What we want to show is that if there exists... | https://mathoverflow.net |
108,091 | [
"https://biology.stackexchange.com/questions/108091",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/70410/"
] | When our teacher was talking about the gas exchange inside the alveoli, he mentioned the flow of air and the flow of blood was going in opposite directions so that there always would be a concentration difference.
Because of this the gas exchange between the alveolar space and capillary continues and reaches ~99%.
I co... | With slight adjustments to the scientific wording, what the poster states is in effect:
<blockquote>
<ol>
<li>“…to produce one molecule of glucose in photosynthesis, 18 ATP molecules are <del>used up</del> hydrolysed”</li>
</ol>
</blockquote>
and
<blockquote>
<ol start="2">
<li>“…oxidation of <del>the same</del> a gluc... | <blockquote>
Where are these extra 20 ATP molecules coming from (or in other words
extra 20 units of energy)?
</blockquote>
The sun. They are provided by high energy photons emitted by the sun. Those photons excite electrons into being in a higher energy state, and that higher energy electron state is harnessed and c... | https://biology.stackexchange.com |
235,431 | [
"https://softwareengineering.stackexchange.com/questions/235431",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/22147/"
] | I saw this in code and was wondering if there is any performance benefit to checking the item count prior to looping:
<pre><code>if (SqlParams.Count > 0)
foreach (var prm in SqlParams)
cmd.Parameters.Add(prm);
</code></pre>
I always prefer to do a <code>null</code> check instead and let the <code>forea... | Ultimately, the best answer is to actually test it. Make a method which loops over an empty array with and without checking the length first, call each 100,000 times and see which has a faster runtime.
<pre><code>public void withCheck(Integer[] array) {
for (int i = 0; i < 100000; i++) {
if (array.leng... | Not really, because if there are 0 items, the setup of the foreach loop will find that out anyway and simply not execute the body of the loop.
It's theoretically possible, in a very tight loop in which it's common for your collection to be empty, and in which finding the count is a very inexpensive operation, for ther... | https://softwareengineering.stackexchange.com |
45,512 | [
"https://mechanics.stackexchange.com/questions/45512",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/16351/"
] | We have a 2002 Honda Odyssey that has a really weak A/C.
<ul>
<li>The refrigerant is full</li>
<li>It gets a bit cooler when put into park</li>
<li>It gets a bit cooler when the rear fan is turned on</li>
</ul>
I'm guessing it could be something electrical, but it can't be a relay, as it gets a bit cool...
Any ideas... | Turns out it had lots of water in the coolant lines, which was making the system barely work, despite being properly pressurized and the pump running.
| The refrigerant is not supposed to be made "completely full" rather a charge is measured by weight. Failing that, the other accepted method is to charge, and observe the behavior of the low side and high side of the refrigeration system. That requires two gauges to do properly.
The system relies on the fact that con... | https://mechanics.stackexchange.com |
211,765 | [
"https://math.stackexchange.com/questions/211765",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/44490/"
] | I have 10 points on a 2D plane where I know the $(x,y)$ coordinates of 9 of the points. For 1 point, $p$, I do not know its location. Additionally, I have the distances from each of the known 9 points to $p$. How can I find the position of the unknown point, $p$?
Bonus: The distances to p from each of the 9 points is... | If you know the distance exactly, swinging a circle from any two of the points will give you two choices of $p$, which can be resolved using a third point. If $p$ is at $(x,y)$, one other point is $(a,b)$ at radius $r$ you have $(x-a)^2+(y-b)^2=r^2$ and the similar equation from the second point.
If the distances are... | You can't find the location of p if it happens that your nine other points happen to lie on a single line. For in that case if u,v are mirror images of each other in the line (neither being on the line) and p happened to be at either u or v, we couldn't determine which it was, u or v. This is because any point on the l... | https://math.stackexchange.com |
528,789 | [
"https://physics.stackexchange.com/questions/528789",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/253115/"
] | [<strong>NOTE to reviewers : Voting to reopen because duplicated question was posted by same user and was closed without answers. This question has been edited in the hope of removing any lack of clarity.</strong>]
I am trying to do a lab in which we are attempting to find the spring constant of a spring.
Different ... | <span class="math-container">$$T=2\pi \sqrt{\frac{m}{k}}$$</span>
Plot of <span class="math-container">$T^2(m)$</span> is <span class="math-container">$y=\frac{4\pi^2}{\sqrt{k}} x$</span> which is linear line which must cross <span class="math-container">$(0,0)$</span> point. If the motion is not harmonic, the line wou... | The graph should not necessarily pass through the origin.
If you have not confirmed that the period is zero when the load is zero then you should not use <span class="math-container">$(0, 0)$</span> as an assumed data point. Neither should you alter recorded data points in order to force the graph to pass through an ... | https://physics.stackexchange.com |
107,987 | [
"https://softwareengineering.stackexchange.com/questions/107987",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/6801/"
] | I was using Microsoft SQL Query Analyzer the other day and wrote a very simple select statement:
<pre><code>SELECT 22/7 as [PI Equiv]
</code></pre>
I was suprized that the result was 3, when I was expecting to see 3.1428571. Even if you declare the output to be <code>Numeric(18,7)</code>, you still get 3.0000000.
<p... | Most languages that supports integer arithmetic will give you 3 from the calculation <code>22/7</code>. This includes, C, C++, C#, Ada, Java, etc. The exceptions appear to be Pascal, VB and Lisp that do floating point arithmetic by default.
Languages where you have implicit typing <em>may</em> give you a floating poin... | <strong>In integer arithmetic, the remainder is ignored</strong>. This is standard behaviour in most modern languages, initially included in programming languages due to hardware limitations and performance constraints.
For historic and performance reasons, this behaviour is present in most modern languages/platforms;... | https://softwareengineering.stackexchange.com |
65,709 | [
"https://stats.stackexchange.com/questions/65709",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/11875/"
] | I apologize for all those questions on modelling. It is the very first time that I try GLM and I am really lost even after reading a lot of papers.
I have divided my covariates according to their theme e.g. topographic variables together. I was trying to first get the most parsimonious model for each set of variables.... | Here are some options and things to consider:
First, AIC is a somewhat naive variable selection method. The fact that your model is not improved (in terms of AIC) by removing any of the variables suggests that maybe you don't want to remove anything.
Second, consider the purpose of this kind of model selection. You o... | The CAIC has more stronger penalty term (then BIC, AICc), may be it useful.
| https://stats.stackexchange.com |
380,622 | [
"https://softwareengineering.stackexchange.com/questions/380622",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/107127/"
] | I am building a internal crm which has contacts which are just people with first name, last name, email, phone etc. Contacts can be one or more types e.t.c. job candidates, hiring managers, customers, workers, sub-contractors etc... and based on the types there are more fields specific fields.
I am building the softw... | <blockquote>
can one conclude that the reference type of C++, when it was originally designed, was not well thought out?
</blockquote>
What you conclude is ultimately your choice. However, I think calling C++ references "not well thought out" merely because they forbid a particular usage is wrongheaded. Tools exist ... | The C++ reference type is not immediately problematic. A reference is not an object, but only an alias of an object. Keeping this in mind immediately solves a number of misunderstandings: a container contains objects, therefore not references. Whenever you need a reference-like behavior but also need an actual object, ... | https://softwareengineering.stackexchange.com |
1,589 | [
"https://biology.stackexchange.com/questions/1589",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/6/"
] | Many DNA isolation and protein expression protocols contain instructions to use a starter culture of E. coli that is then used to inoculate the main culture.
What are the advantages of using starter cultures compared to just let the bacteria grow in the same medium for a longer time? When should one use starter cultu... | Growth can be quite slow for some species under certain conditions when the concentration of cells is too low. Log-phase growth is powerful, and so one would like to keep cells in this state for the experiment at hand. Different genes are expressed then compared to a stationary phase.
In addition, you'd like your cult... | I agree that a starter culture would out-comete a contaminant (especially if there is no antibiotic in the media).
Another advantage of inoculating with starter culture is that your results concerning plasmid preps or preparing competent cells will be easily reproducible. By inoculating with a colony, the starter numb... | https://biology.stackexchange.com |
242,774 | [
"https://security.stackexchange.com/questions/242774",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/248250/"
] | My laptop got infected with a virus. It was "cleaned" by a professional but I am now reluctant to transfer files I had on my laptop to other computers.
I have plenty of images, MP4s, Word, PowerPoint and PDF documents that I would rather not nuke from orbit. Those are the only files that I would like to save ... | If Bob is never allowed to see Alice's public key, ever, then there's no way for Alice to prove to Bob that she owns <code>A*</code>, if Bob only has access to <code>h(A)</code> and <code>h</code> is a general-purpose hash algorithm. Bob has insufficient information.
The only way to make this work is for Alice to send ... | The general idea behind such proof is that A signs some message ("challenge") created by B with its private key - and that this signature can be checked.
B creates a random challenge which is then signed by A. It is important that this challenge is not predictable in order to avoid replay attacks. A then sen... | https://security.stackexchange.com |
374,453 | [
"https://mathoverflow.net/questions/374453",
"https://mathoverflow.net",
"https://mathoverflow.net/users/166613/"
] | Let <span class="math-container">$\mathfrak{L}(\mathbb{R})$</span> be the collection of Lebesgue measurable sets and <span class="math-container">$\mathfrak{B}(\mathbb{R})$</span> be the Borel sets.
<strong>Question:</strong> Is there a nontrivial <strong>signed</strong> measure on <span class="math-container">$\mathfr... | So, promoting my answer to a comment, this is unprovable in ZFC (assuming ZFC is consistent). I claim that such a signed measure <span class="math-container">$\nu$</span> exists only if there exists a nontrivial, atomless, countably additive probability measure <span class="math-container">$\mu$</span> on the discret... | <em>a converse of Nate Eldridge's comment</em><br />
<strong>not a proof, too long for a comment</strong>
Suppose there is a real-valued measurable cardinal. We want to show
there is a measure as requested.
There is a probability measure <span class="math-container">$\mu : \mathfrak P([0,1]) \to [0,1]$</span>.
We may ... | https://mathoverflow.net |
637,663 | [
"https://physics.stackexchange.com/questions/637663",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/299923/"
] | Say there are two stars, each exerting and equal force on a point in the midde of them. For simplicity, we'll say the two stars have the same mass and are equidistant from the point. Now suppose that there are two, equally massive planets, moving at a great speed around that point. Would the two planets be able to crea... | <ol>
<li>The state of the Universe is governed by a function.
</li>
<li>Neural networks approximate functions -- it is what they are designed to do. Period.
</li>
<li>Therefore, the Universe is an approximation of some ideal and unattainable function ... wait, what? Why? Why bother? Why do we need an approximation when... | There's less to pop physics than meets the eye. The full technical content of the argument is:
<ol>
<li>Physical theories are described by sets of complicated differential equation.</li>
<li>Training a neural network can be described as a set of complicated differential equation.</li>
<li>Since you can get any differen... | https://physics.stackexchange.com |
55,991 | [
"https://datascience.stackexchange.com/questions/55991",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/74397/"
] | I found the term "training warmup steps" in some of the papers. What exactly does this term mean? Has it got anything to do with "learning rate"? If so, how does it affect it?
| This usually means that you use a very low learning rate for a set number of training steps (warmup steps). After your warmup steps you use your "regular" learning rate or learning rate scheduler. You can also gradually increase your learning rate over the number of warmup steps.
As far as I know, this has the benefit... | As the other answers already state: Warmup steps are just a few updates with low learning rate before / at the beginning of training. After this <em>warmup</em>, you use the regular learning rate (schedule) to train your model to convergence.
The idea that this helps your network to slowly adapt to the data intuitively... | https://datascience.stackexchange.com |
423,373 | [
"https://physics.stackexchange.com/questions/423373",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/204233/"
] | When we toss a ball onto a wall, upon collision, by Newton’s third law, the reaction force on the wall would cause the ball to rebound, coming back to us. This is because this force is in our direction.
However, if we roll a ball on a floor with a lot of friction, it just slows to a stop. We know that friction acts ... | Firstly, the first scenario works because the reaction force directly cuts through the centre of mass of a ball, and that the wall being a rigid body will not move. On the other hand, frictional force doesn’t do that, and merely acts on the side of the box, at most generating a torque. For instance, if we slide a box... | The real problem is not only in the direction of the friction force, but also in its dissipative nature. It removes kinetic energy from a moving body irreversibly, so when the body stops, it has no energy to move anywhere.
| https://physics.stackexchange.com |
307,101 | [
"https://physics.stackexchange.com/questions/307101",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/46869/"
] | It is conjectured that 6d (2,0) SCFT has no known description in terms of the action or the Lagrangian. However, it has many interesting compactifications for example 3d-3d correspondence which relates 3d Chern-Simons gauge theory with $\mathcal{N}=2$ 3D super Yang-Mills and many others.
<ol>
<li>If we don't know the... | In a series circuit, the current that flows through the inductor ends up having to flow in the rest of the circuit- so you will see a finite current flowing when there is (almost) no voltage. this looks like a low impedance.
When you have the parallel circuit, the current can go around the LC loop without ever flowing... | In a series RLC circuit, you need to add the impedance of the resistor, capacitor and inductor. At high frequencies the inductor's impedance is dominant and the impedance of the circuit becomes very large, whereas at low frequencies the capacitor is the dominant one which increases the total impedance. Somewhere in the... | https://physics.stackexchange.com |
16,222 | [
"https://dsp.stackexchange.com/questions/16222",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/8895/"
] | I try to find about the delay between two audio files using Cross Correlation in Java. I've already done this algorithm so far that i get a idea about how many samples is the delay.
<ul>
<li>FFT x1 -> Zero Padding to length: x1.length() + x2.length()</li>
<li>FFT x2 -> Zero Padding to length: x1.length() + x2.length(... | You can use the double difference method or you can also use the hough transform,Bounding Box method by which you can segment the document image by detecting the table in the given document image.
| Why do not use hough transform for finding lines and then finding table region?
you can use hough transform to find horizontal and vertical lines. and then extract region of lines.
| https://dsp.stackexchange.com |
402,058 | [
"https://physics.stackexchange.com/questions/402058",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/193756/"
] | If I understand correctly, a principle of physics is that information is never created or destroyed. And, unless information is defined differently in physics, according to information theory there is information whenever an event, out of more than one possible events, occurs. The typical example is a coin flip, which ... | great question, I believe you are really asking if QM and its wave function, which shows the probability distribution is really random, or is there something in the microcosm that we do not understand and we handle it random, but it is really just that we do not have enough information about the system that builds up t... | Your question can be resolved through understanding some terms better.
A coin flip does not 'contain information.' A coin flip is a stochastic process that generates a random outcome. A well-defined stochastic process is associated with a probability distribution that has a well-defined associated information-entropy.... | https://physics.stackexchange.com |
195,966 | [
"https://mathoverflow.net/questions/195966",
"https://mathoverflow.net",
"https://mathoverflow.net/users/47837/"
] | Let $a_i\gt0$ for all $1\le i\le n$. It is well known that
$$
\frac{a_1+a_2+\cdots+a_n}{n}-\frac{n}{\frac{1}{a_1}+\frac{1}{a_2}+\cdots+\frac{1}{a_n}}\ge0,
$$
with the equality when all $a_i$ are equal. Now let $a_i$ are not equal but satisfy the following condition $|a_{i+1}-a_i|\le \varepsilon$ for some $\varepsilon$... | a simple upper bound is $(\sqrt{a_{\rm max}}-\sqrt{a_{\rm min}})^2$, with $a_{\rm max}$ and $a_{\rm min}$ the largest and smallest of the $a_i$'s. So for $a_i=a_1+(i-1)\varepsilon$ this would give as upper bound $(\sqrt{a_1+(n-1)\varepsilon}-\sqrt{a_1})^2$.
see theorem 1 of <A HREF="http://www.ams.org/journals/mcom/19... | Some results for differences $A_n-G_n, G_n-H_n$ and so after summing up for $A_n-H_n$ you may find in the book: Classical and new inequalities in analysis by D. S. Mitrinovic; J. E. Pecaric; A. M. Fink on pages 25,39.
| https://mathoverflow.net |
46,551 | [
"https://stats.stackexchange.com/questions/46551",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/18111/"
] | I've been studying contingency table analysis and got to experiment a little bit with Fisher's exact test and Fisher's power test. Now I want to be able to determine the direction of the relationships.
Can anyone tell me what are the best methods to determine the direction of the relationship in 2x2 contingency table... | The easiest way to <em>describe</em> the direction is with a sentence like "The proportion of pilots among men was 0.13 <em>higher</em> than among women". You can do this descriptively even if you use Fisher or the odds ratio for the formal test. Note that Fisher is exact for the very rare situation in which both row... | Welcome to the site.
2x2 tables do not have a direction of relationships.
In any case, statistics do not reveal the direction of relationships, thought and logic and substantive knowledge does. That is, you (the researcher) figures out which direction (if any) the relationship might go in and then you use statistics ... | https://stats.stackexchange.com |
869,536 | [
"https://math.stackexchange.com/questions/869536",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/62874/"
] | Compute $\int_{a-b}^{a+b} \chi_{(-t,t)}(y)dt$.
So if I create a number line marking a-b and a+b. If that the integral above has 5 different answers depending on where (-t,t) is located on the number line.
<ul>
<li>Of course if (-t,t) if before the mark of a-b and a+b on the number line then the integral is equal to... | I'm assuming $\chi_{(-t,t)}$ is the characteristic function of $(-t,t)$, i.e.
\begin{equation}
\chi_{(-t,t)}(y) =
\begin{cases}
1, & y \in (-t,t), \\
0, & y \notin (-t,t).
\end{cases}
\end{equation}
The way you explain the cases isn't clear, though, as you state that they depend on $t$? But $t$ is the ... | Actually, you can change it a little, $\chi_{(-t,t)} (y)=\chi_{(\max(-y,y), +\infty)} (t)=\chi_{(|y|,+\infty)} (t),$ so we change the integral to $J=\int_{a-b}^{a+b} \chi_{(|y|, +\infty)} (t) dt= \mu((|y|, +\infty)\cap (a-b, a+b ))$.
When $|y| \leq a-b, J=2b.$
When $|y| \geq a+b, J=0.$
When $a-b<|y|<a+b, J=... | https://math.stackexchange.com |
143,197 | [
"https://softwareengineering.stackexchange.com/questions/143197",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/33180/"
] | I've been talking to some people at work who believe some versions of a database store their data in discrete tables. That is to say you might open up a folder and see one file for each table in the database then several other supporting files. They do not have a lot of experience with databases but I have only been wo... | Databases usually use one big file for performance reasons. The DB engine can use its own internal structure and not have to restrict itself to file system limits on block size, buffer size, or fragmentation policies. I know some systems used to (and possibly still do) provide their own block device drivers. For tho... | Many databases keep their data in one file per table. MySQL does, for example, for MyISAM tables. Whether the data is all kept in one file or not isnt very relevant. It just depends on the storage system being used.
Basically, its among the last things I'd care about when selecting a database <em>server</em>. For... | https://softwareengineering.stackexchange.com |
348,906 | [
"https://physics.stackexchange.com/questions/348906",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/157704/"
] | I understand that unitary representations arise naturally in quantum mechanics when groups act on the Hilbert space in a way that preserves probability.
I don't understand what details make unitary representations different from other representations. It seems as though physicists talk explicitly about "unitary repres... | For a compact Lie group, every representation can be made unitary.
Say you have a vector space <span class="math-container">$V$</span> and a group representation <span class="math-container">$\rho(g)$</span> which acts on <span class="math-container">$v \in V$</span>.
Now say you have some hermitian inner product <span... | Since the Hamiltonian is hermitian, and the time evolution of a system is $U(t)=e^{-itH/\hbar}$, $U(t)$ is automatically unitary. Moreover, unitary transformations play the role of rotations in 3d space, in the sense that they preserve the inner product:
$$
\langle \phi\vert \psi\rangle = \langle \phi'\vert\psi'\rangl... | https://physics.stackexchange.com |
102,958 | [
"https://stats.stackexchange.com/questions/102958",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/46523/"
] | I would like to know how to calculate the standard deviation for a measurement value $x$ when there are two separate sources of uncertainty, 1 and 2, each with known standard deviation, $\sigma_1$ and $\sigma_2$.
I’ll give a couple of examples.
<ul>
<li>I measure length with a ruler. Each measurement has an uncertain... | Your first point certainly falls under "uncertainty/error propagation" and your equation at the end will be correct for a normal distribution, and independent variables. Any uncertainty measurement guide will confirm this (ISO, EURACHEM, NPL, ...).
Your second example is trickier, since the distribution is binomial, a... | I suggest that you look at JCGM 101:2008 Evaluation of measurement data — Supplement 1 to the “Guide to the expression of uncertainty in measurement” — Propagation of distributions using a Monte Carlo method. It is freely available on the internet and discusses the use of Monte Carlo methods for error propagation.
| https://stats.stackexchange.com |
16,755 | [
"https://stats.stackexchange.com/questions/16755",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/6731/"
] | I have a very lengthy but poorly designed questionnaire, which has a very large number of questions. The questionnaire really needs to be completely rewritten, but prior to that being done, there is an organisational need to use it again in the short term.
Given the length of the questionnaire, it would be helpful to... | @Peter and @ Jonathan have some good ideas. Without repeating, I'll add two more.
<ol>
<li>If you need to shorten your survey and you won't suffer by reducing the sample size you could give different people somewhat different surveys.</li>
<li>Reanalyze old data two ways: with and without questions you suspect are le... | I've been there before! Legacy surveys: can't live with them, can't live without them...
While I agree with @Peter Flom's approach to look at correlations and reduce the number of highly correlated statements (this is a standard approach to reducing what I call "brick walls" of rating scales in surveys, and has the ad... | https://stats.stackexchange.com |
253,176 | [
"https://mathoverflow.net/questions/253176",
"https://mathoverflow.net",
"https://mathoverflow.net/users/66131/"
] | Fix $0<h_1<h_2<h_3<1$ reals. All matrices below are $3\times3$ real.
Suppose the sequence of matrices $M(n)$ are symmetric positive definite and these converge (point-wise) to a symmetric positive definite matrix $M$ (point-wise). Assume that the eigenvalues of $M(n)$ converge to that of $M$.
<blockquote... | Let $a = n^{h_3 - h_1} \to + \infty$ and $b = n^{h_1 - h_2} \to 0$.
Note that $ab = n^{h_3 - h_2} \to +\infty$, but slower than $a$.
If $$M(n) = \pmatrix{m_{11}(n) & m_{12}(n) & m_{13}(n)\cr m_{12}(n) & m_{22}(n) & m_{23}(n)\cr
m_{13}(n) & m_{23}(n) & m_{33}(n)}$$ the characteristic polynomial... | I claim that the second eigenvalues tends to $\frac{\det(M)(M^{-1})_{33}}{M_{11}}.$ Indeed, the product of eigenvalues equals $n^{2(h_3-h_2)}\det(M(n))$, the largest eigenvalue grows as $n^{2(h_3-h_1)}M_{11}$, since $n^{-2(h_3-h_1)}A(n)=M_{11}e_{11}+o(1)$, and the largest eigenvalue of $A(n)^{-1}$ grows as $n^{2(h_2-h_... | https://mathoverflow.net |
28,250 | [
"https://mathoverflow.net/questions/28250",
"https://mathoverflow.net",
"https://mathoverflow.net/users/36038/"
] | I have a specific problem, but would also like to know how to tackle the general case. I will first state the genral question. Let $M$ be an embedded submanifold of $\mathbb{R}^n$ and let $F: \mathbb{R}^n \to \mathbb{R}^n $ be a smooth map. How do I go about checking whether $F(M)$ is a smooth embedded submanifold of $... | The specific $F(M)$ is not a smooth submanifold. Here is an argument.
To simplify formulas, I renormalize the sphere: let it be the set of $(z_1,z_2)\in\mathbb C^2$ such that $|z_1|^2+|z_2^2|=2$ rather than 1. Then, as Gregory Arone pointed out, $F(M)$ is the set of $(b,c)\in\mathbb C^2$ such that the roots $z_1,z_2$ ... | If you consider the real map $(x_1, x_2)$-->$(x_1+x_2, x_1x_2)$ then the image of the
circle is not a submanifold. Infact your map is not injective: it is symmetric with respect to swapping the two coordinates, so the circle is folded once onto itself and its image is homeomorphic to a closed segment. In the complex c... | https://mathoverflow.net |
16,885 | [
"https://quant.stackexchange.com/questions/16885",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/15566/"
] | Is there such a thing as an American butterfly spread?
For a European butterfly spread simply buying 1 put with strike price X+a, 1 put with strike price X-a and shorting 2 calls with strike price X, all with the same expiration date, would give you a butterfly spread.
However if we now do the same with american optio... | When you say OTC options, I think you're talking about contracts that aren't exchange traded (non-standard), so no one knows the wide range of term sheets that have been executed. I do know that American style (early) payoffs exist in OTC term sheets.
Most OTC deals are not about speculation. They're usually about red... | I have never seen those traded. But it is an interesting research topic.
The interest of the standard European butterfly spread is the decomposition into three vanilla European options. This decomposition is not exact anymore in the case of the American butterfly spread as specified: <strong>the linear combination of t... | https://quant.stackexchange.com |
9,460 | [
"https://datascience.stackexchange.com/questions/9460",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/3024/"
] | I have a pandas DataFrame which has the following columns:
<pre><code>n_0
n_1
p_0
p_1
e_0
e_1
</code></pre>
I want to transform it to have columns and sub-columns:
<pre><code>0
n
p
e
1
n
p
e
</code></pre>
I've searched in the documentation, and I'm completely lost on how to implement this. D... | Finally, I found a solution.
You can find the example script below.
<pre><code>#!/usr/bin/env python3
import pickle
import pandas as pd
import itertools
import numpy as np
data = pd.DataFrame(np.random.randn(10, 5), columns=('0_n', '1_n', '0_p', '1_p', 'x'))
indices = set()
groups = set()
others = set()
for c in da... | <pre><code>columns=[('0', 'n'), ('0', 'p'), ('0', 'e'), ('1', 'n'), ('1', 'p'), ('1', 'e')]
df.columns = pd.MultiIndex.from_tuples(columns)
</code></pre>
| https://datascience.stackexchange.com |
75,805 | [
"https://cs.stackexchange.com/questions/75805",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/72505/"
] | I want to prove that no PSPACE-complete problem is in NL using the space hierarchy theorem. What I want to say is this :
From the time hierarchy theorem I know that for every $t(n)$ there exists a language that is decidable in $O(t(n))$ space but not in $o(t(n))$ space. Then I want to assume that there exists $A \in PS... | Use Savitch's theorem, which shows that PSPACE=NPSPACE, and the non-deterministic space hierarchy theorem.
Alternative (suggested by OP): use Savitch's theorem to show that $\mathsf{NL} \subseteq \mathsf{SPACE}(\log^2 n)$, and then the deterministic space hierarchy theorem.
| This question is currently open, since a positive answer (i.e. no complete problems for PSPACE can lie in NL) would imply $\mathsf{P}\neq\mathsf{PSPACE}$. This statement is actually equivalent to $\mathsf{P}\neq\mathsf{PSPACE}$ (as a PSPACE complete problem in NL obviously implies P=PSPACE).
Examine the equivalent sta... | https://cs.stackexchange.com |
10,905 | [
"https://stats.stackexchange.com/questions/10905",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/4559/"
] | I have searched for this online for hours but none of online posts is what I am looking for. My question is very easy to implement in SAS Proc mixed procedure but I am not sure how to do it in lme and/or lmer packages. Assume, I have a model,
$y = \mu + \alpha + \beta +\alpha\beta + e$,
where $\alpha$ is fixed but $\b... | Try this, it's a standard way to do a split plot. The notation <code>/</code> means that method is nested in day.
<pre><code>lme(level~method, random=~1|day/method, data=d)
</code></pre>
| It would help a lot if you provided a data.frame. Now it is not clear what is a grouping factor. I judge that it is $\beta$. Then in <code>lme</code> notation your model should be written as follows:
<pre><code>lme(y~a,random=~a|b, data=mydata)
</code></pre>
| https://stats.stackexchange.com |
24,852 | [
"https://stats.stackexchange.com/questions/24852",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/8790/"
] | I have some data (a set of numbers) and I want to compare them with the normal distribution using QQ-plot. The only statistical tool that I am aware of is Octave but Octave doesn't draw the reference line.
<img src="https://i.stack.imgur.com/RMTrF.png" alt="enter image description here">
As can be seen in the above p... | This is easy in R:
<pre><code>x <- rnorm(1000, 100, 10) #Creates some data; this has is normal with mean 100 sd 10
qqnorm(x) #qq
qqline(x) #adds line
</code></pre>
| Here is one possible Octave solution to your question: (largely inspired from the corresponding Matlab function)
<pre><code>randn("state",255)
x = normrnd(10, 2, 200, 1);
[q, s] = qqplot(x);
% compute the y=x line
dx = prctile(q, 75) - prctile(q, 25);
dy = prctile(s, 75) - prctile(s, 25);
b = dy./dx; ... | https://stats.stackexchange.com |
338,277 | [
"https://stats.stackexchange.com/questions/338277",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/-1/"
] | Could someone please describe, using the reproducible code sample below, how bootstrap sampling works <strong>in practice</strong>? The more detailed questions are:
<ul>
<li>What different random datasets are generated from <code>myData</code> by bootstrap sampling it?</li>
<li>How <code>myData</code> looks like after... | You have already figured out the basics in your own answer.
To specifically address your questions (and make this an on-topic programming question, and not an off-topic theoretical/tutorial one), i.e.
<blockquote>
What different random datasets are generated from <code>myData</code> by bootstrap sampling it?
H... | After some investigations and a deleted answer to my question I figured it out. <strong>Bootstrap sampling with replacement</strong> means that a data subset is created from the original data set by selecting samples that can be also the same ones as previously selected. So, there is a chance that some samples in a dat... | https://stats.stackexchange.com |
1,493,110 | [
"https://math.stackexchange.com/questions/1493110",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/282980/"
] | If $y=x-x^3+3$ find the rate of change of y with respect to $x^2$ as a function of x?
$$y=x-x^3+3$$
$$\frac{d}{dx^2}\left(y=x-x^3+3\right)$$
Is it $-3x^2$, because of the power rule?
Let say I subsititute $z$ for $x^2$
So, $\frac{d}{dx^2}\left(z-z^3+3\right)=1-3z^2$, then I substitute back $z=x^2$. So $1-3\left(x^... | <strong>Hint:</strong>
\begin{align}
\lim _{x\to k}\frac{s\cdot x^2y\cdot \sin\left(k-x\right)}{k^2-kx}&=\left(\lim_{x\to k}\frac{sx^2y}{k}\right)\left(\lim_{x\to k}\frac{\sin \left(k-x\right)}{k-x}\right)
\end{align}
Since the last two limits exist, in particular by setting $u=k-x$ we get $$\lim_{x\to k}\frac{\si... | You haven't told us what $s,y$ are. I assume they are constants, which brings up the question: Why include them?
Hint: The only thing that matters here is
$$\frac{\sin (k-x)}{k^2 - kx} = \frac{\sin (k-x)}{k(k - x)} = \frac{1}{k}\frac{\sin (k-x)}{(k - x)}.$$
As $x\to k, k-x \to 0,$ therefore _____ .
| https://math.stackexchange.com |
302,635 | [
"https://stats.stackexchange.com/questions/302635",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/167751/"
] | I am trying to prove that in multivariate linear regression $MSE = (n-2)\sigma^2 $
<strong>Here is my approach:</strong>
Under the usual notation,
$$ Y = X\beta + \epsilon \\
$$
$$ \hat Y = X\hat\beta \\
$$
$$ \hat\beta = (X'X)^{-1}X'Y \\ \\
\implies \hat\beta' = Y'X(X'X)^{-1}
$$
Now,
\begin{align}
\Sigma (... | Martijn Weterings's commnet is very useful. Your derivation of term 2 is wrong.
$\epsilon'X (\beta - \hat \beta) \\= \epsilon'X(\beta - (X'X)^{-1}X'Y) \\=\epsilon'X\left\{\beta - (X'X)^{-1}X'(X\beta+\epsilon)\right\}\\=\epsilon'X \left\{\beta-(X'X)^{-1}X'X\beta -(X'X)^{-1}X'\epsilon\right\}\\=-\epsilon'X(X'X)^{-1}X'\e... | A less computationally intensive method would be
<span class="math-container">$$
\begin{aligned}
e&=y-\hat{y}\\
\Sigma(y[k]-\hat{y}[k])^2&=e^Te\\
y-\hat{y}&=\phi\theta-\phi\hat{\theta}+\epsilon\\
&=\phi\theta-\phi(\phi^T\phi)^{-1}\phi^Ty+\epsilon\\
&=\phi\theta-\phi(\phi^T\phi)^{-1}\phi^T(\phi\theta... | https://stats.stackexchange.com |
153,836 | [
"https://electronics.stackexchange.com/questions/153836",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/66134/"
] | I wish to calculate the load inside a shopping cart and i am confused on which type of load cell/sensor should i use. Assuming weight from (0-50 kg).
This sensor is to be interfaced with Arduino.
| The emitter can never be open with respect to the base as there are internal resistors etc., so Icbo is inappropriate. Leakage can occur from the collector to base of the input transistor. That is shunted away by the series resistors so it doesn't turn the output transistor on and no significant voltage appears at the ... | <ol>
<li>As shown in section 9.2, both bases are pulled to ground. As such, the floating state is off.</li>
<li>The leakage would be from a high input to ground through all three resistors. Lower resistances would result in higher leakage.</li>
</ol>
| https://electronics.stackexchange.com |
10,848 | [
"https://engineering.stackexchange.com/questions/10848",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/-1/"
] | I understand that poles on the left hand complex plane (LHP) make a continuous linear dynamic system stable. What's so significant about imaginary poles on the LHP that make a system stable? What does it mean to have poles and zeros on the LHP verses the right hand plane (RHP)?
| Only the poles in the LHP are necessary for stability. This is because the transient response of a LTI system will consists of a linear combinations of $e^{p_i t}$. If a pole is complex, $p_i=\rho_i+i \sigma_i$, you can use Euler's formula, such that the contribution to the transient response can be written as,
$$
e^{\... | Briefly, poles in the left half plane (R < 0) symbolize ringing that dies down over time, at R = 0 ringing that stays the same, and in the right half plane (R > 0) ringing that increases in amplitude over time.
| https://engineering.stackexchange.com |
247,358 | [
"https://stats.stackexchange.com/questions/247358",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/139623/"
] | I have a few related questions:
<ol>
<li>What is the total number of fitted paramaeters in Python Support Vector Machine: sklearn.svm.SVC(kernel='linear') and sklearn.svm.SVC(kernel='rbf')?</li>
</ol>
I am trying to find out the total number of fitted parameters in linear and kernel SVM. If I understand correctly, th... | There are multiple misunderstandings in both the question and the answer posted by @mp85.
There are to sets of parameters, but one of them are called hyperparameters.
The SVM problem/formulation is
$$ \min ||w||^2 + C \sum \xi_i $$
subject to
$$ y_i(w·\phi(x_i)+b) \ge 1−\xi_i \quad \xi_i \ge 0 $$
for all data $(x_i,... | C + gamma (for kernel="rbf") or C + degree + coef0 (for kernel="poly") are usually the hyper-parameters of a SVM you want to tune with grid search (or randomized search). For the poly kernel, you don't have to tune all the coefficients by yourself, just specifify what order you want the polynomial to be.
About the slac... | https://stats.stackexchange.com |
26,547 | [
"https://electronics.stackexchange.com/questions/26547",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/8092/"
] | I'm an Electrical Engineering student and I'm studying the hardware description language known as VHDL.
I searched for it on Google looking for an IDE (I'm on a mac), but this language seems pretty dead.
So here is my question: in my future job as an electrical engineer will VHDL be useful to me? Are you using it?
UP... | I use ONLY VHDL. It is far from dead. A couple of years ago it seemed like a 50/50 split between people using VHDL or Verilog (anecdotal evidence at best), but I doubt that it has changed much since then.
The most recent version of VHDL is "VHDL-2008", which in language standard terms was just yesterday.
| If you plan on working with programmable logic (e.g. FPGAs, not MCUs), VHDL and Verilog are the two languages you'll have to know. As a student, you'll probably have to learn both, use both and be examined in both. That was certainly the case for me (and I only took a few courses in ASIC design), though it was a long t... | https://electronics.stackexchange.com |
95,791 | [
"https://electronics.stackexchange.com/questions/95791",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/7329/"
] | I have came across these SIM modules on an online electronic shop. My primary target is just to receive short text messages from other subscribers. But then this question about these three (if there is anything apart from these, those too) modules. What are the primary differences between these GSM modules?
| Basically, SIM900 is global functioning quad-mode module, while 900A is cheaper dual-mode and works only in India.
| SIM900 is a quad band modem being able to operate in 850,900,1800,1900 MHz bands and offers improved GPRS functionalities useful in web enabled applications.
SIM300 is a triband GSM modem being able to operate only in 900,1800,1900MHz band.
SIM900 and the SIM300 modem operate from 3.4V to 4.5V supply range.
Same AT com... | https://electronics.stackexchange.com |
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