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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381,093 | [
"https://mathoverflow.net/questions/381093",
"https://mathoverflow.net",
"https://mathoverflow.net/users/172210/"
] | I would like to prove Chebyshev's sum inequality, which states that:
If <span class="math-container">$a_1\geq a_2\geq \cdots \geq a_n$</span> and <span class="math-container">$b_1\geq b_2\geq \cdots \geq b_n$</span>, then<br />
<span class="math-container">$$
\frac{1}{n}\sum_{k=1}^n a_kb_k\geq \left(\frac{1}{n}\sum_{k=... | Let <span class="math-container">$A$</span> be the random variable attaining the values <span class="math-container">$a_1,\dotsc,a_n$</span> with equal probabilities, and define <span class="math-container">$B$</span> similarly, subject to <span class="math-container">$\mathbb P(B=b_i|A=a_i)=1$</span>. Then <span class... | A more general inequality is
<span class="math-container">$$Ef(X)g(X)\ge Ef(X)\,Eg(X),\tag{1}$$</span>
where <span class="math-container">$f$</span> and <span class="math-container">$g$</span> are nondecreasing (say bounded) functions from <span class="math-container">$\mathbb R$</span> to <span class="math-container">... | https://mathoverflow.net |
1,749 | [
"https://mechanics.stackexchange.com/questions/1749",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/229/"
] | Going to be used for car maintenance/restoration work and around the house repairs.
| Core functionality of a multimeter:
<strong>Measures Voltage</strong> - the majority will cope here, as you typically are only dealing with 0 - 12 volts across most areas. You aren't going to need it to measure high tension things such as spark plugs, as you can check them using far simpler methods (such as a spark fr... | Ohm per volt rating the higher the better, Digital are minimum 1 M ohm per volt -Maximum 10 M ohm per volt. Analogs are in range of k ohm per volt- more loading of the circuit resulting in a lower than actual value. The frequency function probably would be worth not much as tach signal are pulses and would be read be... | https://mechanics.stackexchange.com |
11,264 | [
"https://mechanics.stackexchange.com/questions/11264",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/6339/"
] | This question is discussed all over the internet, but it seems to be just a voting procedure. I'd like to get a high-quality answer, and, since I couldn't find it on SE, I'll ask it again here.
With the manual transmission, when parking on a <em>horizontal</em> surface, should I leave my car in neutral plus the hand-b... | My suggestion is always park with the transmission in gear and the park brake on. Along with curbing the wheels. Gear selection (forward or reverse) on flat ground, I choose reverse. My reasoning is that a vehicle parked curbside is more likely to be struck from the rear. Even a nudge from a careless driver can push th... | The schools teach you to park in neutral to prevent you from causing the car to jerk forward the next time you start it and forget to step on the clutch first. So here goes:
<ol>
<li>If you don't want to have a minor accident while starting your car because you forgot to step on the clutch, leave it in neutral.</li>
<... | https://mechanics.stackexchange.com |
2,439,814 | [
"https://math.stackexchange.com/questions/2439814",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/473722/"
] | Please help review this part of the proof.
Suppose that $x\in C-(A\cup B)$. Therefore, $x\in C$ and $x\notin (A \cup B)$. Then, $x\in C \wedge (x\notin A \wedge x\notin B)$. By morgan laws we got that $x\in C \wedge x\notin A$ and $x\in C \wedge x\notin B$. By definition of set subtraction $x\in C-A \wedge x\in C-B$ B... | I don't think this is Riemann Integrable actually. It's obviously bounded, but $f$ is clearly discontinuous at almost every irrational (the exceptions being those for which $\sin^2(x) = \cos(x)$). For given an $x$ that isn't one of those exceptions, take a sequence of rationals $q_n \to x$. Then $f(q_n) \not \to f(x)$.... | A function is called Riemann integrable if and only if it is bounded and continuous almost everywhere on its domain. We also have if a function is continuous then it is Riemann integrable. So because $f$ is not continuous, then $f$ is not Riemann integrable.
| https://math.stackexchange.com |
112,198 | [
"https://mathoverflow.net/questions/112198",
"https://mathoverflow.net",
"https://mathoverflow.net/users/27962/"
] | Let $G$ be a finite group which has a cyclic maximal subgroup. Is $G$ solvable?
| Yes. Let $M$ be the cyclic maximal subgroup (actually the proof works for an Abelian maximal subgroup). We may suppose by induction that $M$ contains no non-trivial normal subgroup of $G.$ Then for each non-identity subgroup $X$ of $M,$ we have $M = N_{G}(X),$ as $M$ is maximal and $X \lhd M.$ It follows easily that $M... | I just want to mention that, if $M$ be an abelian maximal subgroup of finte group $G$ then $G$ is solvable and its drived length is at most 3.(Exercise 3.4.7 of Permutation Groups, Dixon and Mortimer)
| https://mathoverflow.net |
7,846 | [
"https://earthscience.stackexchange.com/questions/7846",
"https://earthscience.stackexchange.com",
"https://earthscience.stackexchange.com/users/5798/"
] | Snow is precipitation in the form of flakes of crystalline water ice that falls from clouds. Why is it not another colour?
| Normal ice (as in refrigerated ice cubes) mostly has uniform crystalline structure - water molecules are in a perfect hexagonal grid, which enables it to be transparent.
Not all ice is like that - for example, if you freeze water that contains tiny water bubbles due to a faucet aerator, the resulting ice would likely ... | Snow has a very high albedo. Actually, it reflects all wavelengths of the visible spectrum, whilst absorbing no particular wavelength. Hence the eye averages out the multiple reflected wavelengths as 'white' - as is the case with most fine granular solids.
| https://earthscience.stackexchange.com |
29,733 | [
"https://mechanics.stackexchange.com/questions/29733",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/11239/"
] | This morning I tried to open the passenger-side door (of my 2001 VW Eurovan) but it appears to be stuck. The door is unlocked. I can pull the handle, but apparently not far enough to operate the door mechanism. Same for both interior and exterior door handles. The other doors appear to be OK.
Lock/unlock with the r... | Don't know if this would be the best way to attack the problem, but here's what I would do.
Remove the interior door handle and fiddle with the linkage trying to get the door to open.
If that does not work, remove that passenger's seat so you have room to work. Remove the door cover. Hopefully this can be done with... | You need to find a way to open the door, slim jim or other tool.
Once the door is open you need to remove the lock cylinder to get the broken key out. Depending on the vehicle how hard or easy this is.
The cylinder may have been damaged and would need replaced and re-pinned to your key, this would require a locksmith... | https://mechanics.stackexchange.com |
375,830 | [
"https://physics.stackexchange.com/questions/375830",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/160654/"
] | The Covariant Derivative which is used in General Relativity is obtained by considering the concept of Parallel transport of a vector.
A vector is transported parallelly from one point on the manifold to the other because we cannot do algebraic operation on objects at two different points on a manifold.
My question... | A vector is a geometric object defined by the components and a coordinate basis. On a curved manifold both the components and the basis change from one point to the other. The partial derivative is not enough to describe the change of the vector as an object; hence the need to define the covariant derivative, which mea... | The geometric intuition is that parallel transport over a curved surface is different from that on a flat surface.
Draw a triangle on a flat surface and parallel transport a vector along it; when you return to your starting point you will find that it's the same vector.
Now draw a triangle on a sphere starting from... | https://physics.stackexchange.com |
514,694 | [
"https://electronics.stackexchange.com/questions/514694",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/214927/"
] | I am measuring voltage output from a device with 10 kohm output impedance with an arduino analog input pin. I see what I would expect with a multimeter, but with the arduino I get either garbage, or at best, oscillating measurements that average out to about what I would expect.
I know the impedance of the analog pins ... | The MCU in Arduino has a successive approximation ADC.
It works by briefly taking a voltage sample via a multiplexer into a small storage capacitor to handle multiple input channels with one ADC.
With a high source impedance, the sample/hold capacitor may not have time to fully charge, and thus the sample of the voltag... | The meter will have either a real capacitor or a software-simulation of one internally.
If it didn't, you'd never get a stable number to be displayed and it'd be impossible to read.
You can be sure this has nothing to do with any 'resistance mismatch'.
A little story....
When I was in college, I was taking a CMOS class... | https://electronics.stackexchange.com |
15,826 | [
"https://physics.stackexchange.com/questions/15826",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/5773/"
] | Consider two stationary charges, one positive the other negative. Their potential energy is clearly negative. So you would expect that the energy density of the associated electric field would also be negative. But it isn’t. It’s the square of the electric field and therefore positive. Why isn’t the energy density... | The electric field energy is indeed positive for the case of two opposite charges, but it is smaller than the electric field energy when the charges are separated. The difference is the potential energy of interaction of the two charges, which includes the self-energy, the field energy for a single charge, inside the m... | The field generated by the two charges $q_1$ and $q_2$ is the sum of the field generated by the first and the second charge, let's say $ \vec E_1+\vec E_2$. When you square this sum and integrate in the whole space you got
three terms. Integrating all over the space the square of $ \|\vec E_1\|^2$ and $\|\vec E_2\|^2$... | https://physics.stackexchange.com |
166,784 | [
"https://electronics.stackexchange.com/questions/166784",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/68288/"
] | I am asking if we have a voltage signal must be amplified
why we can't mount it in a resistance less than one and take the output as a current by using Ohm's law I = V/R and R is less than one ?
| You are right that <em>on constant resistance</em>, you can determine the voltage by measuring the current. But in no way, current an voltage are equivalent.
Voltage tells you how much energy is in a single electron, which can also be interpreted as a kind of pressure on the electrons. On the other hand, current tells... | You are wanting to increase voltage, so you need to look at the equation as:
<pre><code>V = I x R
</code></pre>
What happens if you keep the current constant, and make R small - notice that the voltage will get smaller?
Now if you could some how keep the current constant and <em>increase</em> the resistance, notice ... | https://electronics.stackexchange.com |
28,865 | [
"https://mathoverflow.net/questions/28865",
"https://mathoverflow.net",
"https://mathoverflow.net/users/2048/"
] | In Paul Halmos' Measure Theory book, section 53, he defines a content on a locally compact Hausdorff space to be a set function, $\lambda$ that is additive, subadditive, monotone, and $0\le\lambda(C)<\infty$ for all $C$ compact. The "Borel sets" he considers(section 52) in this book are the smallest $\sigma$-ring g... | The situation is indeed a delicate one and one needs to carefully check the conventions before transferring a result from one context to another. The situation is summarized in Royden's <em>Real Analysis</em>, though with just a few examples.
For a given space $X$, the main players are:
<ul>
<li>$\mathcal{B}a$ &mdash... | If your space X is sigma-compact (can be written as the union of a countable family of compact sets) then everything is okay, I think. This follows as X is in the Borel sigma-ring, and hence the Borel sigma-ring is a sigma-field (or sigma-algebra). If U is open, then $X\setminus U$ is closed, and so can be written as... | https://mathoverflow.net |
89,690 | [
"https://physics.stackexchange.com/questions/89690",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/23816/"
] | Yeah, I haven't quite understood, or been told, what happens to, for example an electron and its wavefunction, when you stop to measure it.
I mean, an electron has a wave function describing its position and so on in the region of space it is confined. When I measure it, I get an output, and the wavefunction collapses... | Assuming wave-function collapse is correct (which can be a relatively hefty philosophical claim in some circles), then think of measurement this way:
When you measure an observable on a system, you collapse the wave-function of the system into a Dirac delta function in the eigenbasis for that observable.
If you measu... | The electron doesn't get destroyed when you measure it (though photons usually do), but its wavefunction doesn't go back to how it was before. Instead it gets a new wavefunction, different from the old one. If you measured the position of the electron, this new wavefunction will be a delta function (a single infinitely... | https://physics.stackexchange.com |
207,454 | [
"https://electronics.stackexchange.com/questions/207454",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/95182/"
] | I've read that they are 90% efficient compared to linear regulators so given the relationship between volts and amperes and that I want to power the project off of a 12V battery that has 18Ah and is charged using a small solar cell. The project itself only needs 5V, so if I buck the voltage down to less than half the r... | You are kind of on the right track.
The amp-hour rating of the battery specifies how many hours you could pull a certain rated current from the battery.
The buck converter to 5V won't change the amp-hour rating of the battery at all. But if you were to only pull half of the current from the battery then the battery ... | Amp hours are not a great way of measuring battery capacity. Watt hours is a much better figure. If you stick a buck converter after the battery, the equivalent watt hours of the battery will decrease by the loss in the converter. However, since the converter will draw fewer amps from the battery, the equivalent amp... | https://electronics.stackexchange.com |
40,074 | [
"https://electronics.stackexchange.com/questions/40074",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5872/"
] | I am having troubles making a relatively simple FPGA design (for an Altera Cyclone IV) meet timing for logic driven by a 250 MHz clock. This makes me wonder how commercial microprocessors (such as the Intel Core i7) manage to meet timing at clock frequencies more than an order of magnitude higher.
How can commercial m... | FPGAs don't actually have "gates" per se. They typically have Look-Up Tables (LUTs). LUTs are typically implemented using SRAMs. For instance, Spartan 3 FPGAs use 16-bit SRAMs; that is, four address inputs produce one output signal. "Programming" is done by loading the SRAM with a bit pattern representing the truth... | Expanding on dwlech's comment. The processors have direct copper connections. The FPGAs are interconnected through programmable connections. Also the processors put critical stuff next to each other. The FPGAs also need room for the SRAM that holds the programming.
| https://electronics.stackexchange.com |
446,649 | [
"https://math.stackexchange.com/questions/446649",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/69976/"
] | Any suggestions for evaluating the limit $$\lim_{x\to0}(x\tan x)^x$$
I have tried writing $\tan$ as $\dfrac{\sin}{\cos}$ and then got the Taylor series of them but it didn't lead me somewhere. Thanks a lot
| Assuming the limit exists and is equal to $L$, take logs:
$$\log{L} = \lim_{x \to 0} x \log{(x \tan{x})}$$
Use $\tan{x} \sim x$ in this limit. Then use
$$\lim_{y \to 0} y \log{y} = 0$$
and the limit should come out easily:
$$\log{L} = \lim_{x \to 0} x \log{x^2} = \lim_{x \to 0} 2 x \log{x} = 0$$
Therefore, $L=1... | $$\large(x\tan x)^x=e^{\log(x\tan x)^x}=e^{x\log(x\tan x)}$$
Then $$\large\lim_{x\to 0}(x\tan x)^x=e^{\lim_{x\to 0}x\log(x\tan x)}\tag{since $\exp(x)$ is continuous}$$
Now $$\lim_{x\to 0}x\log(x\tan x)=\lim_{x\to 0}\dfrac{\log x+\log\tan x}{\dfrac{1}{x}}$$
Apply L'Hopital's rule.
| https://math.stackexchange.com |
137,206 | [
"https://dba.stackexchange.com/questions/137206",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/59794/"
] | We have a program that transfers cobol data (index files) to a database.
Until now we transferred the data to an oracle database.
In the beginning of the program I logged in with user <code>sys</code> and then I altered the current schema to <code>ink</code>. I did this in this way, because <code>ink</code> has n... | In Oracle a schema and a user is the same thing. In Postgres it isn't.
So there is no direct "mapping" on what you did in Oracle in "Postgres land". A table is <strong>always</strong> owned by the user who created it initially there is no way to change that.
If you do not want to give the user <code>ink</code> the... | <strong>Be warned</strong>: I'm relatively new to PostgreSQL and so I'm not sure if this is a good practice or not, but...
One way I can think this can be addressed is by executing a <code>REASSIGN OWNED</code> statement at the end of the process that has created all your objects in the database, like this:
<pre><cod... | https://dba.stackexchange.com |
308,576 | [
"https://physics.stackexchange.com/questions/308576",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/138682/"
] | I remember a long time ago my mum had told me not to use a wet tea towel when taking food out of the oven because you can burn your hands - lo and behold, it came time to make dinner and I did not head my mother's warning from all them years ago and my hand got burned. Why does a wet tea towel heat up more quickly when... | Water has a high heat capacity and is also a pretty good conductor of heat.
The dry towel has a lot of air pockets and doesn't have a lot of heat capacity in general.
Essentially you're bridging the air gap that was acting as an insulator. The water also provides a sink for the energy instead of just going into the ... | Missing from the currently-accepted answer is the importance of steam.
If you use a damp towel to grab a heavy metal dish out of an oven at $\rm 350^\circ F = 180^\circ C$, the heat from the pan will enter the water in the towel much more rapidly than conduction can carry it to your hand. Instead some of the water in... | https://physics.stackexchange.com |
12,204 | [
"https://security.stackexchange.com/questions/12204",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/3339/"
] | I'm writing an application which recovers statistical data about a user. I'm still pondering about what would be the best way to encrypt the data. I haven't got any experience with mobile applications. But I was thinking of hardcoding an RSA public key and encrypting it in that way before sending it over the net.
Ano... | I'd just use SSL with a hardcoded public key of the server. Nobody on the way can manipulate or read what you sent. No need to invent your own protocol.
But of course the user himself can manipulate and read the data this way, but solving that is a DRM problem and not a security problem.
I believe BouncyCastle can be... | Implementing your own ad-hoc-ish crypto solution is not a good idea. You'll probably get something wrong. (For instance, AES with a hardcoded passphrase is <em>terrible</em>. Anyone can get the passphrase by just downloading the app and extracting the passphrase. I don't know why you doubt anyone would do it.)
I r... | https://security.stackexchange.com |
108,274 | [
"https://electronics.stackexchange.com/questions/108274",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/39905/"
] | Im new to Microchip microcontrollers and I'm looking for very low cost device with I2C and SPI. I want to connect one I2C (ADC) and one SPI device (LCD).
I found this very low cost device:
<img src="https://i.stack.imgur.com/UMWNo.png" alt="enter image description here">
However it looks like I2C and SPI share same ... | I agree with @Olin's post. At the same time, there's another point of view on which I<sup>2</sup>C or SPI to implement in software and which in hardware.
I<sup>2</sup>C bus has a lower top speed than SPI. Typical I<sup>2</sup>C bus has a max data rate of 400 kbps **. Typical SPI can easily run at 4 Mbps. Some appl... | Yes, you can use this part to drive both a IIC bus and a SPI bus in the same circuit. However, you can't (reasonably) use the single MSSP module of this device to drive both busses.
My recommended solution is to use the MSSP to do IIC and do the SPI by firmware bit-banging of separate I/O pins. SPI is a <i>very</i> ... | https://electronics.stackexchange.com |
417,950 | [
"https://mathoverflow.net/questions/417950",
"https://mathoverflow.net",
"https://mathoverflow.net/users/95347/"
] | By Reflection I mean the following schema:
<strong>Reflection:</strong> <span class="math-container">$$\forall X \, (\varphi \implies \exists \alpha : \varphi^{V_\alpha})$$</span>
where <span class="math-container">$\varphi$</span> is a first order formula (defined predicates and functions allowed) in which only symbo... | The first answer took care of the case where "Reflection" was a scheme of formulas in the language of ZF. Now we consider what we now think was the intent of the questioner.
We expand the language of ZF by introducing a predicate symbol P and a function symbol F
for each formula in the language of ZF. We als... | Each instance of the scheme referred to as Reflection is provable in ZF.
Suppose <span class="math-container">$\psi$</span> holds for some <span class="math-container">$X$</span>. By the usual notion of reflection there is an ordinal <span class="math-container">$\alpha$</span> such that <span class="math-container">... | https://mathoverflow.net |
124,362 | [
"https://dba.stackexchange.com/questions/124362",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/44804/"
] | I want to trim dot (.) from a column value. Just say string is "Mr." and I need to trim the dot from the string. I am expecting "Mr"
Lets say,
I have two fields in my table
<pre><code> id | value
1 Mr.
2 Ms.
11 Mr.
12 Ms.
</code></pre>
But while running below query, not getting as i exp... | I looked at the trim function and it removes the character from the beginning or the end of the string. I'd bet that the two where it's not working have spaces after the ".". Try trimming spaces off the end first then trim the "."
<pre><code>select trim(trim(value,' '), '.') from mytable
</code></pre>
| I haven't used Postgresql any, but generally the syntax for trim follows:
TRIM( [ [{LEADING | TRAILING | BOTH}] [removal_char]
FROM ] target_string [COLLATE collation_name])
TRIM ('.' FROM 'STRING') would be more like what you'd want, think you have it reversed.
| https://dba.stackexchange.com |
21,249 | [
"https://robotics.stackexchange.com/questions/21249",
"https://robotics.stackexchange.com",
"https://robotics.stackexchange.com/users/27248/"
] | In ROS TURTLESIM, While moving the turtle in circle using the linear velocity and angular velocity , how do i track the distance so as to stop the turtle moving after one revolution ??
| write a distance function with the maximum value being the circumference, use rospy's Time function to update distance and whenever the current_distance exceeds the circumference, publish a zero velocity msg to stop the turtle.
| <pre><code>$ rosmsg show turtlesim/Pose
</code></pre>
Get the pose. How are you wanting to know if it did a complete revolution? You could check that the path length is equal to the circumference, or that the rotation angle is back to the start angle, or the horizontal x/y position is the same as the starting position.... | https://robotics.stackexchange.com |
509,227 | [
"https://physics.stackexchange.com/questions/509227",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/243046/"
] | I remember reading that the outer orbitals of atom have higher energy. If an electron is given enough energy it goes to higher energy orbitals from <span class="math-container">$n=1$</span> to <span class="math-container">$n=2,3,4...$</span>
My question is that why do the outer orbitals have higher energy? Is is beca... | I understand you are confused, because the electron's potential (EM) energy is negative. When you say becomes higher, you mean less negative.
Let's say the electron is at a stable energy level around the nucleus as per QM. This is due to certain forces:
<ol>
<li>the EM force (potential negative energy) keeps the elec... | Although this is quantum mechanical...If I explain in classical way you can think electrostatic force between nucleus and electron is directing inwards and due to this effect electron rotating around nuclear. Then due to rotation there appears a centrifugal force <span class="math-container">$\frac{m_ev^2}{r}$</span> d... | https://physics.stackexchange.com |
450,849 | [
"https://physics.stackexchange.com/questions/450849",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/214881/"
] | How does a trolley move with uniform velocity on a long board which has one of this ends raised to compensate for friction? If the trolley was given a gentle push down the long board, won't the trolley accelerate since a force was exerted on it? Because in my textbook it says " the trolley is given a gentle push down t... | To answer your title question, if an object is moving with a constant velocity then the <em>net force</em> is <span class="math-container">$0$</span>. However, this does not mean that there are no forces are acting on the object. For example (looking ahead to your example) if friction is present then a force is needed ... | <blockquote>
Does an object moving with uniform velocity require a force to maintain its motion?
</blockquote>
No. By <span class="math-container">$\vec F=m\vec a$</span> if there is no change in velocity (i.e. the velocity is uniform) then <span class="math-container">$\vec a=0$</span> and thus the net force <span... | https://physics.stackexchange.com |
46,708 | [
"https://physics.stackexchange.com/questions/46708",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/5788/"
] | We've all heard the statement that on the 21st of December, the planets in the solar system will "align" from the point of view of the Earth. I assume this means that they would all be in the same spot in the sky if we looked from here. The theory says that the alignment of the planets will somehow exert some influence... | First, Mercury "aligns" with the ecliptic plane only twice in its "year", when it comes from above to below and vice versa.
Luckily for our calculations, Pluto is not a planet any longer, because it would completely rain on our parade with its 248 Earth years of orbital period and another two points within it that it ... | All the planets except Mercury (7 degrees off) and Pluto (17 degrees off) are on the ecliptic plane. So a perfect alignment is not possible. I'm including Pluto as a planet out of habit.
| https://physics.stackexchange.com |
54,467 | [
"https://softwareengineering.stackexchange.com/questions/54467",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/19171/"
] | I took up a small CSS challenge to solve for a client and I'm going to be paid on a hourly rate.
I eventually solved it, it took 5 hours but I spent roughly 25% of the time in the wrong track, trying a CSS3 solution that only worked in recent browsers and finally discovering that no fallback is possible via JS (like I... | I often have such situations when I spend a few hours doing something, then noticing that there is an easier one-line solution, or that my first idea was too bad, etc.
In general, in those cases, I make the difference between three situations:
<ul>
<li>The newly discovered solution was not obvious and/or an average d... | I don't think you were on the wrong track. You coded a solution, tested the solution (kudos) and found it didn't work as you expected. You debugged the solution and then made your fix by going in a different direction.
IMHO, that's not the wrong track. That's regular software development.
If I were you, I'd charge ... | https://softwareengineering.stackexchange.com |
1,215 | [
"https://dsp.stackexchange.com/questions/1215",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/654/"
] | I have an image
<img src="https://i.stack.imgur.com/daRNS.png" alt="enter image description here">
Is there any way of removing the bright white spots ? <strong>Please help thanks</strong>
Edit:
After operating with gaussian and then displaying using imagesc get the following output which clearly shows the bright ... | Let's assume glare portions are the only saturated areas in the image.
Detection can be performed by thresholding the intensity (code in Mathematica):
<pre><code>saturated = Binarize[ColorConvert[img, "Grayscale"], .9]
</code></pre>
<img src="https://i.stack.imgur.com/5c3C0.png" alt="enter image description here">
... | <img src="https://i.stack.imgur.com/R3n7V.jpg" alt="enter image description here">Without lighting information, it is difficult. However, if the shape of the object in the image is known, you could setup a shape template of the white glare (gaussian) and do a sliding window to find possible detection of glare (followed... | https://dsp.stackexchange.com |
14,686 | [
"https://security.stackexchange.com/questions/14686",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/6072/"
] | I just learned that my dad fell for a online green card lottery scam. It happened over 3 years ago, the attacker took 60$ and disappeared. I am not even considering getting this money back.
On the other hand, he had his victim fill out all sorts of forms giving out private personal data. That worries me a lot more. I ... | <ol>
<li>you can't</li>
<li>you can't</li>
</ol>
There is one thing you should have done instantly:
File a complaint with the police, so <em>they</em> know there is a possibility that his personal details might be used in an identity scam.
Of course there are some standard things:
<ul>
<li>change pincodes</li>
<l... | Three years later? What prompted you to bring this up again?
If it were me, I would probably
<ul>
<li>rotate bank accounts (ask my bank for a new account, order new checks, can't be that bad)</li>
<li>review all credit card charges as they come in (should already be doing this, at least in USA, if there is a fraud ch... | https://security.stackexchange.com |
2,858,143 | [
"https://math.stackexchange.com/questions/2858143",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/33826/"
] | Let $E$ and $F$ be two Banach spaces, and let $T \in K(E,F)$. Assume $\dim E = \infty$. Prove that there exists sequence $(u_n)$ in $E$ such that $\| u_n \|_E = 1$ and $\| Tu_n\|_F \rightarrow 0.$
<strong>Comments:</strong> I'm trying to do it by contradiction.
I'm trying to show that there exists $C> 0$ such that... | Consider $\inf \{||Tu||:||u||=1\}$. If this is $0$ we are done.If it is a positive number $a$ then $||Tu||\geq a$ whenever $||u||=1$. By simple scaling this gives $||Tu||\geq a||u||$ for all $u$. If $\{x_n\}$ is any sequence in the unit ball of $E$ than $\{Tx_n\}$ has a convergent subsequence and the inequality $||Tx... | Let $G=\{Tx:x\in E\}.$ Suppose $\inf \{\|Tx\|_F: 1=\|x\|_E\}=1/k>0$. Then T is injective, and $T^{-1}:G\to E$ is a bounded (Lipschitz-continuous) linear function (with norm $ k $) from the normed vector-space $G$, into $E.$
Let $A=(g_n)_n$ be any Cauchy sequence in $G$. Since $T^{-1}$ is Lipschitz-continuous ... | https://math.stackexchange.com |
5,692 | [
"https://mechanics.stackexchange.com/questions/5692",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/2849/"
] | How is <code>Double Din</code> / <code>2 Din Audio System</code> better than <code>Single Din</code>?
What are some scenarios where the Single Din Audio will prove to be more beneficial?
Appreciate if you can also highlight the very basic differences in the two.
Thanks!
| The only difference between single and double DIN is the size of the unit.
However double DIN units often have added features like touch screens, dvd, and navigation features which require the extra space for mounting. Many double din units will use the same audio processors and DACs that the single din units of the s... | The difference is solely in size. A double-DIN gives you more space, but at the end of the day what you should be looking at is what will fit in your car, and this may be hidden behind fascia.
My dash will only fit a double DIN, but because I have a single DIN sound system, I use the other half as a storage space.
| https://mechanics.stackexchange.com |
82,973 | [
"https://softwareengineering.stackexchange.com/questions/82973",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/7217/"
] | Lots of people in the open source community say they strongly consider a candidate's Github profile when hiring.
I'm active on Github, with a few projects of my own and some contributions to others. But looking at my own profile as if I were an employer, I see a lot of noise: projects I cloned but never contributed to... | I've used GitHub profiles, twitter streams, and blogs all as indicators of quality in programming interviews/candidate screening. They all generate different signals in their own way.
9 out of 10 applicants have never submitted a single patch to a single open source project. Even updating broken documentation puts yo... | I think you can, you just need to take some extra time looking if he is actually active on github or not, by looking at his activity stream.
You can see how pushes, issues etc, which is a big indicator that he is actually active and working on something, rather than just fooling around.
If someone is looking to evalu... | https://softwareengineering.stackexchange.com |
1,966,156 | [
"https://math.stackexchange.com/questions/1966156",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/356308/"
] | Verify that
$ y(x) = Ae^{2x} + Be^{-2x} - 2\cos(x) - 5x\sin(x) $
is a solution of the ordinary differential equation
$ \dfrac{d^2y}{dx^2} - 4y = 25x\sin(x) $
for any value of the constants A and B. $\\$
I seem to have differentiated correctly, so I'm unsure of why my reasoning is incorrect. Please explain why my reaso... | You must substitute $Ae^{2x}+Be^{-2x}-2\cos x-5x\sin x$ instead of $y$ in the equation just before 'We can now verify if this is a solution'.
| Your "let $x=1$, $y=4$" part is wrong. There seems to be confusion about what is a solution to an ODE.
Consider a simpler equation.
$$
y'=2x\tag{1}
$$
Then
$
y(x)=x^2+C
$
is a solution to (1) for any constant $C$. What would happen if you arbitrarily pick $x$, $y$ and $C$, say $x=0$, $y=2016$, $C=\pi$?
<hr>
In ge... | https://math.stackexchange.com |
117,694 | [
"https://stats.stackexchange.com/questions/117694",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/56861/"
] | My question boils down to if I really have to use a multiple comparison adjustment or not, and if so, how I can do this to retain as much power as possible.
I have multiple models (say 5) that are scored on how well they match up to data over cross fold validation. Since the score that is used (area under an ROC curv... | Well, in practice, people routinely use Newman-Keuls or Tukey methods to test a family of pairwise differences of means in the parametric normal case. That seems similar to your situation-- am I mistaken? So I think a multiplicity adjustment is called for.
The Holm method does sound like a good choice; it offers "FD... | You should not use Wilcoxon test at all: it assumes random sampling, and you are doung cross-validation. Maybe you should use something like 5×2 cv F-test (see Alpaydm, E. (1999). Combined 5 × 2 cv F Test for Comparing Supervised Classification Learning Algorithms. Neural Computation, 11(8), 1885–1892).
| https://stats.stackexchange.com |
14,803 | [
"https://stats.stackexchange.com/questions/14803",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/5837/"
] | I have run 3 separate logistic regressions and would somehow like to summarize how well the model fits the data graphically.
Any suggestions?
| First I want to reiterate what others have said in the comments: this is in general a difficult problem with no easy solution.
With that in mind, <em>one</em> way of assessing model fit with logistic regression models when your <em>primary interest</em> is simply predictive power is to plot ROCs. Here's an example (wi... | A good reference for the kind of graphs you seem to want is John Fox, "Effect Displays for Multinomial and Proportional-Odds Logit Models," in Sociological Methodology (2006). See the citations to his earlier work. He implements these techniques in R and S-Plus in his book that accompanies his text on linear regression... | https://stats.stackexchange.com |
38,425 | [
"https://mechanics.stackexchange.com/questions/38425",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/23666/"
] | I do my own repairs. I'm pretty versed on things like engine building, and the importance of farming out things like alignment and having an exhaust system welded on. Just assume I'm "somewhat competent at repairing vehicles".
My question is this:
I have a 1998 Chrysler Sebring Convertible 160,000 miles on the odomet... | Uneven tire wear is typical caused by improper tire pressure, misalignment or both.
It is unusual for all the issues to be located a one specific axle. There may be a number of things going on or one major thing causing many issues. The brakes wearing unevenly is not common, but could be result of being improperly in... | You didn't mentioned if you changed your front end shock absorbers. I had a problem where both front tires were wearing out the inner tread at an abnormal rate. The pick-up truck did not veer to any direction when steering wheel was released and the visual inspection did not show any serious toe, camber, or caster al... | https://mechanics.stackexchange.com |
634,075 | [
"https://physics.stackexchange.com/questions/634075",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/50612/"
] | I have heard the terms "Newtonian mechanics" and "classical mechanics" used interchangeably, but is there a difference between them? If so, what is it?
| In advanced physics circles, "classical mechanics" always means something very specific, and it doesn't mean "Newtonian." Classical means not quantum. Newton's theory of gravity is just one example of a classical theory. Einstein's general relativity is also a classical theory. Any theory which says... | The term "Classical mechanics" sometimes describes brunch of physics or a course, which focuses on Lagrange and Hamiltonian formalism. This are a little bit advanced tools, which are widely used (Euler-Lagrange equations etc...).
Because this (mathematical) tools are a little bit harder, they are often taught... | https://physics.stackexchange.com |
8,565 | [
"https://dsp.stackexchange.com/questions/8565",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/4273/"
] | The matlab "ellip" function can be used to design the unquantised coefficient set.
<blockquote>
From matlab website:
$ [b,a]=ellip(n,Rp,Rs,Wp) , $
n: order of filter
Wp: normalized passband edge frequency
Rp: ripple in passband (db)
Rs: db down from he peak value in the passband
</blockq... | The quickest way would be
<pre><code>[b,a] = ellip(8,1.5,60,[.2 .3]);
</code></pre>
This designs a bandpass from .2 to .3 with 1.5 dB ripple and 60 db stop band attenuation. You don't get to pick the edges of the stop band since you already pre-selected the order. You can do one or the other but not both at the same... | With the new answer (indirectly) pointing out that Hilmar's filter is of order ten and not eight, one may have to reinterpret the edges of the original question. It is easy to assume that they are normalized to the sampling frequency and not the Nyquist frequency (not only based on the eight-order assumption, but also ... | https://dsp.stackexchange.com |
434,183 | [
"https://mathoverflow.net/questions/434183",
"https://mathoverflow.net",
"https://mathoverflow.net/users/146531/"
] | The following conjecture about analytic functions arose as a way to show the asymptotic growth for certain PDE solutions. As I am unfamiliar with any results of this type, I thought I'd ask here.
In some sense, this is an analytic continuation result, as it says that if measure of points close to <span class="math-cont... | Unfortunately, no, as requested:
Take any sequence <span class="math-container">$\delta_j\in(0,1)$</span> decaying to <span class="math-container">$0$</span>, choose small <span class="math-container">$\mu_j>0$</span> such that <span class="math-container">$\prod_j \delta_j^{\mu_j}=e^{-1}$</span> and put <span class... | The answer depends on <span class="math-container">$C$</span>. For example, for <span class="math-container">$C=1$</span> it is positive. Your estimate <span class="math-container">$|f^{(m)}(0)|\leq m!$</span> implies that <span class="math-container">$|f_n(z)|\leq 1/(1-|z|).$</span> Take <span class="math-container">$... | https://mathoverflow.net |
551,596 | [
"https://physics.stackexchange.com/questions/551596",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/239775/"
] | I am speaking about operators representing physical observables and am not interested in purely mathematical objects (if that's relevant to answering the question).
I know that a degenerate eigenvalue corresponds to an eigenspace with dim > 1, which means 'linearly independent' eigenkets, even orthogonal eigenkets, th... | <blockquote>
Now my question is: How, if at all, can you tell if a given operator's eigenspectrum will feature degeneracy. How do I show that 'all emerging eigenspaces' have dimension one only? Or how do I show that a given combination of observables forms a CSCO?
</blockquote>
This is an interesting question! The a... | I think you're really asking for too much here - for arbitrary classes of operators in infinite dimension, there's certainly no algorithmic way to simultaneously diagonalize them nor to prove that their simultaneous eigenspaces don't feature any degeneracy.
In the specific case of a position operator, it's quite clear... | https://physics.stackexchange.com |
106,931 | [
"https://mathoverflow.net/questions/106931",
"https://mathoverflow.net",
"https://mathoverflow.net/users/26265/"
] | Hi all<br>
I've the following non-linear PDE
$-\Delta Y + Y^3 =U$ on $\Omega \subset R^n $, open, bounded, Lipschitz boundary domain
$Y=0 , $ on $\partial\Omega$ <br>
<strong>1</strong>.Let $Y\in H_0^1 $ and as $H_0^1 \hookrightarrow \hookrightarrow L^5 $ can we define a compact operator $T:L^5 \times [0,1] \rightar... | The Leray-Schauder is a fixed point theorem in the spirit of Brouwer's. When it gives an existence result, it says nothing about uniqueness. Your problem is much better than that, because it does have a unique solution in $H^1_0(\Omega)\cap L^4(\Omega)$, whenever $U$ belongs to the dual space $X=H^{-1}(\Omega)+L^{4/3}(... | This equation has no unicity, and it has at least a second solution by using the Mountain Pass Theorem, check Evans, PDE, pp 482-486.
| https://mathoverflow.net |
1,526,613 | [
"https://math.stackexchange.com/questions/1526613",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/118056/"
] | I just began studying Lie algebras and I'm trying to prove that two Lie algebras $\frak g$ and $\frak h$ are isomorphic if and only if they have the same dimension.
If they're isomorphic, then proving that they have the same dimension goes just like for vector spaces, I guess.
Now, if $\{g_i\}_{i \in I}$ and $\{h_i\}... | It is not true. Take the set of all $6\times6$ matrices with usual bracket operation $[A,B]=AB-BA$. This is 36-dimensional Lie algebra.
Now look at upper triangular matrices of size $9\times 9$, under the 'same' operation. This is of dimension $9\times8/2=36$. They are not isomorphic. (Second one is solvable, whereas... | The minimal counterexample is of dimension $2$. Every $2$-dimensional Lie algebra over a field $K$ is either isomorphic to the abelian Lie algebra $K^2$, or to the solvable, non-abelian Lie algebra $\mathbb{r}_2(K)$, with basis $(x,y)$ and Lie bracket $[x,y]=x$. These two Lie algebras cannot be isomorphic for various r... | https://math.stackexchange.com |
88,236 | [
"https://chemistry.stackexchange.com/questions/88236",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/56916/"
] | My teacher told me that electrolysis of dil. $\ce{H2SO4}$ (concentration below $50\%$) using inert electrodes results in gradual increase of the concentration of $\ce{H2SO4}$.
I can't seem to figure out why. I know that the sulfate ions will remain in the solution, but aren't the $\ce{H+}$ ions of $\ce{H2SO4}$ reduced... | In a dilute solution of sulfuric acid, there are the following species present: $\ce {H_2O}$, $\ce {H^+}$, $\ce {OH^-}$, $ \ce {HSO_4^-}$, $\ce {SO_4^2-}$. Of course, the water molecules are present in the highest concentration, much higher than the other species, since it is a dilute solution. For simplicity, we would... | <span class="math-container">$\ce{OH-}$</span> can't be reduced. It may only be oxidized by giving an electron at the anode, while <span class="math-container">$\ce{H+}$</span> is reduced instead of <span class="math-container">$\ce{OH-}$</span>.
Secondly, the reducing property of <span class="math-container">$\ce{H2O}... | https://chemistry.stackexchange.com |
40,464 | [
"https://chemistry.stackexchange.com/questions/40464",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/22769/"
] | My textbook says that $\ce{SO2}$ dissolving in water produces sulfurous acid, but that seems to be a chemical change. But $\ce{NaCl}$ dissolving in water is not a chemical change. Please explain.
| Your book is glossing over some details.
There are three things occurring when you dissolve non-metal oxides in water (e.g., <span class="math-container">$\ce{SO2}$</span>, <span class="math-container">$\ce{CO2}$</span>, <span class="math-container">$\ce{NO2}$</span>, etc.):
<ol>
<li>The gas simply dissolves in the w... | $\ce{SO2}$ at normal pressure and temperature is a gas, and once dissolved follows an acid-base path. This is a chemical change.
NaCl is a salt and when immersed in water its crystal structure breaks and gives hydrated ions ($\ce{Na+}$ and $\ce{Cl-}$). This also is a chemical change.
The process of dissolution is alw... | https://chemistry.stackexchange.com |
107,825 | [
"https://mathoverflow.net/questions/107825",
"https://mathoverflow.net",
"https://mathoverflow.net/users/26250/"
] | The Thom class and Thom isomorphism theorem for oriented vector bundles are proven ( at least to my knowledge) by induction on the open covers and some manipulation with Mayer-Vietoris sequences.
What is the "actual reason" behind the existence of Thom class? It seems strange that such an interesting class would exist... | It is easy to understand the existence of a Thom class by considering cellular cohomology. Let the given vector bundle be $E\to B$ with fibers of dimension $n$. One can assume without significant loss of generality that $B$ is a CW complex with a single 0-cell. The Thom space $T(E)$ is the quotient $D(E)/S(E)$ of the... | One not-very technical way to think of the Thom Isomorphism Theorem is that if you have a vector bundle, $p : E \to B$, if you remove the $0$-section $Z$ of the vector bundle from the Thom space $Th(p)$, you get a contractible space. So given a homology class in $H_* Th(p)$ the obstruction to trivializing it can be ... | https://mathoverflow.net |
134,514 | [
"https://softwareengineering.stackexchange.com/questions/134514",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/10869/"
] | I just started a new job and I'm currently at the process of trying to introduce a DVCS (mercurial, but the actual DVCS is not really a matter of discussion at this point, it could also be git) to the company (big, multinational). So far I've gotten nothing but positive attention, even at managerial and directive level... | The best way is to do a pilot with one existing team and record what the issues are. In my experience, the biggest obstacle to using a DVCS in an enterprise is the lack of structure. A DVCS is more of an SCM <em>framework</em> than a full solution. You have to add a lot of glue to make it work in a large organizatio... | <blockquote>
People accidentally breaking other's builds or stepping on each others' toes while submitting code revisions
</blockquote>
This is an issue with organizational communication and programmer discipline. A DVCS is actually likely to make things worse in this situation, because individual programmers can ke... | https://softwareengineering.stackexchange.com |
121,162 | [
"https://electronics.stackexchange.com/questions/121162",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/49197/"
] | Here is my simple reasoning. We apply a potential difference across a resistor. All the electrons begin responding. Since it takes time for electrons to respond, our current is not yet fully established. In fact, immediately after we apply the voltage, the current is zero! And yet we have a non-zero V and R. So am I wr... | The only reason the current would be zero is if you have a non-zero inductance (which all circuits do). Once you factor in the inductance, you'll be able to calculate the rise time of the current after you apply a voltage. Only in the ideal world where there's no inductance or capacitance, will V=IR be true at all time... | V=IR is only valid at steady state.
You are trying to apply it outside of that condition, so it doesn't always work. Transient Responses are not modeled at all in a 1st order system.
| https://electronics.stackexchange.com |
598,257 | [
"https://physics.stackexchange.com/questions/598257",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/265836/"
] | Studying Quantum Mechanics I only thought about Spherical Harmonics <span class="math-container">$Y_{l,m}(\theta , \phi)$</span>:
<span class="math-container">$$Y_{l,m}(\theta , \phi)=N_{l,m}P_{l,m}(\theta)e^{im\phi}$$</span>
as the simultaneous eigenfunctions of <span class="math-container">$L_z$</span> and <span clas... | <blockquote>
How should we think about Spherical Harmonics?
</blockquote>
In short: <strong>In the same way that you think about plane waves.</strong>
<hr />
Spherical harmonics (just like plane waves) are basic, essential tools. As such, they are used over a <em>very</em> wide variety of contexts, and each of those co... | How familiar are you with Fourier analysis?
For instance, if you want a complete basis of functions defined on the unit square, you would pick:
<span class="math-container">$$ |n, m\rangle \equiv e^{2\pi i nx}e^{2\pi i my}$$</span>
with all <span class="math-container">$n, m \in \mathbb Z$</span>
Note that this is just... | https://physics.stackexchange.com |
310,557 | [
"https://softwareengineering.stackexchange.com/questions/310557",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/21669/"
] | In postgres, I need to store the hours a merchant is open each week. Essentially, the information you'd see posted on a sign in the merchant's door:
<pre><code>Mondays: Closed
Tuesday-Friday: 9am-1pm, 2pm-6pm
Weekends: 10am-2pm
</code></pre>
Some ideas so far:
<ol>
<li>Break down a week into 30 minute (or even 5 mi... | The simplest storage would be:
<pre><code>StoreID integer (foreign key)
DayOfTheWeek integer (range 0-6)
OpenTime time
CloseTime time
ValidFrom date (starting date when this record is in use)
ValidThru date (ending date when this record is in use, NULL for no ending date)
</code></pre>
A... | I programmed a system for working out shifts for a fast food outlet where we had the same problem.
I think you have missed the hardest problem which is timezones and daylight savings.
If you only have to print the information then the 'time without timezone' data type should be fine, but for any calculation of hours... | https://softwareengineering.stackexchange.com |
109,895 | [
"https://electronics.stackexchange.com/questions/109895",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/21913/"
] | I have a battery powered application that must occasionally use a servo motor (like the ones in model airplanes, e.g. Turnigy TR-1160A). This servo will be used in short bursts of 1~2 seconds at a time, with a resting (inactive) time of at least 10s between usages, but typically hours. The battery is large enough to op... | 2 amps for 2 seconds at 6V is 24 joules of energy and if this was provided by a capacitor the capacitance should be at least 5 times that required to meet the energy equation.
Energy in a capacitor is \$\dfrac{C\cdot V^2}{2}\$ therefore \$\dfrac{2 \cdot 24}{6^2} = C\$
C is therefore 1.333 farads but realistically it... | Supercaps and ultracaps are very good at supplying short-term energy needs. For example, a 30-50F capacitor rated at 3V would be more than enough to store the 24 Joules you need per operation.
In order to meet your other requirements, you would use a pair of switching power converters. The first one would be a buck re... | https://electronics.stackexchange.com |
29,785 | [
"https://softwareengineering.stackexchange.com/questions/29785",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/-1/"
] | Can programming become language-independent? Will we always program in English? Will we ever be able to program in our local languages? Is there any research that addresses the matter? Are there any such developments?
| There have been attempts to introduce programming language flavors translated into a local spoken language around the globe. They however never came to be more than experiments.
Some customer-oriented languages are localized like Excel macros language. But these are really end-user oriented.
Programmers will always n... | As a matter of fact, programming already is as "language independent" (I suppose you wanted to say "natural language...") as it gets. You see out of 3-4 thousand languages spoken today on Earth, it only depends on one major natural language, that is English.
Imagine what would it look like if the dozens of major prog... | https://softwareengineering.stackexchange.com |
237,689 | [
"https://physics.stackexchange.com/questions/237689",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/95753/"
] | Does the operator:
$$\int_a^b \mathrm{d}x \, |x\rangle \langle x|$$
have physical meaning acting in a Hilbert space where it does not exactly correspond to the identity operator?
Does it correspond to a measurement that can be at least in theory be performed on the system, and based on the mathematical properties of... | If $X^b_a := \int^b_a\lvert x\rangle\langle x \rvert\mathrm{d}x$ is not the identity operator, that means your Hilbert space is $L^2([c,d])$ with $c<a,b<d$ (for $c,d$ possibly infinite). $X^b_a$ is simply the projector onto $L^2([a,b])\subset L^2([c,d])$ since for any $\lvert \psi \rangle$ we have that the wavefu... | In simple terms I can write a state $|{\psi}\rangle = \alpha_1|x\in\{y|a<y<b\}(=A)\rangle (=|\alpha_1\rangle)+\alpha_2|x\notin A\rangle(=|\alpha_2\rangle)$
When you use operator $$\int_{a}^{b}|x\rangle\langle x|dx$$
Then it will get you simply $\alpha_1|\alpha_1\rangle$.
Physical meaning: You see your operato... | https://physics.stackexchange.com |
4,232 | [
"https://security.stackexchange.com/questions/4232",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/2666/"
] | Reverse proxies and NAT would seem to obscure a network behind such technologies to the point where it would be hard if not impossible to identify ports open and services running.
Given that many networks use these technologies I assume it is possible to bypass them in some capacity.
I am just wondering how that may ... | I would normally advice to deploy your IPS in non-blocking mode to start off with running the default policy, plus any other signatures\policies that specifically apply to whats running on your network.
Once that policy has been up and running for a while and you are happy with the following
<ol>
<li>The false positi... | Unless you have a performance or other problems I like to start with the largest most all inclusive policy I can. I then remove/edit rules on a case by case basis. I would recommend keeping rules that don't necessarily cover products you have, like the Frontpage Extensions ruleset, unless you have a procedure in plac... | https://security.stackexchange.com |
89,246 | [
"https://chemistry.stackexchange.com/questions/89246",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/57928/"
] | İ heard that :
Charge of a mole of electrons/charge of single electron =avagadros constant
How is this derived ?
| It is only a rule of thumb that a negative value for $\Delta G^0$ of a reaction means that a reaction is spontaneous. If you start out with pure reactants (and no products present), all reactions are spontaneous, irrespective of the $\Delta G^0$. A negative value for $\Delta G^0$ only signifies that the equilibrium c... | The change in the Gibbs free energy for a process at a constant temp. and pressure is equal to how much non-expansion work it can do.
| https://chemistry.stackexchange.com |
20,029 | [
"https://dba.stackexchange.com/questions/20029",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/6040/"
] | I have 2 schemas, lets say <strong>sch1</strong> and <strong>sch2</strong>. Each owned by different user.
I do want to grant <strong>SELECT</strong> rights on <strong>sch2.MyTable</strong> (but just this one object) to <strong>sch1</strong> procedures/views AND allow to reference <strong>sch2.MyTable</strong> in <stro... | You need to look into using certificates to sign the stored procedures. This will allow users to access anothers tables.
| Hope the following answer will help:
<pre><code>Syntax:
GRANT <PERMISSION> ON <SCHEMA>.<TABLE NAME>(<COLUMN NAME>) TO <GRANTEE> .
DENY <PERMISSION> ON <SCHEMA>.<TABLE NAME>(<COLUMN NAME>) TO <GRANTEE> .
REVOKE <PERMISSION> ON <SCHEMA>.<TABL... | https://dba.stackexchange.com |
73,028 | [
"https://stats.stackexchange.com/questions/73028",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/17670/"
] | I am confused by the special way required to use inverse method in the following problem,
Here is the problem:
<blockquote>
Consider a mixture distribution of two normal distributions, where the
desired PDF $f(x)$ is given by:
$f(x) = r\, f_a(x) + (1 − r)\, f_b(x)$,where $f_a$ and $f_b$ are
normal PDFs wit... | The "two uniforms" are not absolutely necessary when generating from a mixture, but they make the simulation easy to understand. The mixture of normal distributions,
$$rf_a(x)+(1-r)f_b(x)$$
has a probability mass of $r$ associated with the first normal and $(1-r)$ with the second normal. This means that the distributio... | Is this the problem from the STA511 class?:)
pnorm() won't give you the right result, because it's a CDF. What you are looking is an inverse of the CDF, so you have to use qnorm() to get it.
| https://stats.stackexchange.com |
49,995 | [
"https://dba.stackexchange.com/questions/49995",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/24418/"
] | <h2>Problem</h2>
<ul>
<li>I'm truncating a very large table ( 210+ million rows ). </li>
<li>It's been hours since it started and I have no idea when it will be done.</li>
<li>There're several tables like that, that I want to truncate.</li>
<li>The database is Ora9i.</li>
</ul>
<h2>Question</h2>
<ul>
<li><strong>How... | What finally solved my problem was <strong>turning archive mode off</strong>, perform the truncation, then turn archive mode back on.
With archive mode on, the truncation took too long and corrupted the database.
| I assume you are using dictionary managed tablespaces. You have to wait until all extents are deallocated. The following statement should report the number of extents that are to deallocate:
<pre><code>select extents
from dba_segments
where owner='TABLEOWNER'
and segment_name='TABLENAME'
</code></pre>
Index... | https://dba.stackexchange.com |
350,469 | [
"https://electronics.stackexchange.com/questions/350469",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/125595/"
] | I am wondering how charging circuits works; obviously there is some misunderstanding on my side. For example, a mobile phone is sold with a 1.5 A adapter. One can assume that charging and powering the phone can load up to 1.5 A. How is it possible that no malfunction occurs when a less powerful adapter/USB po... | Typically:
It just monitors the voltage of the power supply. If that drops too far (typically, for USB chargers, below 4.8 V), it reduces the current sink into the battery.
A smarter charger might "scan" the "tolerable" input voltage range and find the sweet spot where most power can be drawn from the supply, but rea... | The USB wires D+ and D- have attached resistors for coding the nominal current of the adapter - 500mA, 1.5A, .... This is detected by the charging IC that will sink just the nominal current of the adapter.
| https://electronics.stackexchange.com |
44,368 | [
"https://math.stackexchange.com/questions/44368",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/11939/"
] | I have a matrix $$
A =
\left[ {\begin{array}{cc}
1 & c \\
0 & d \\
\end{array} } \right]
$$
with $c$ and $d$ constant. I need to find $A^n$ ($n$ positive) and then need to prove that formula using induction.
I would like to check that the formula I derived is correct:
$$
A^n =
\left[ {\begin{ar... | Mathematical induction is the way to go, but first you want to have a "target." I'm not sure what you did, but I think you confused $c$ and $d$ somewhere along the line in your calculations. Let's see a first few values:
$$\begin{align*}
A&= \left(\begin{array}{cc}1&c\\0&d\end{array}\right)\\
A^2 &= ... | Letting $a_n$ be the upper right hand corner of $A^n$, and assuming it is obvious that the lower right corner of $A^n$ is $d^n$, and the left column is $[1,0]^T$, we get:
$$A^{n+1} = A^n A =
\left[ {\begin{array}{cc}
1 & a_n \\
0 & d^n \\
\end{array} } \right]
\left[ {\begin{array}{cc}
1 & c \... | https://math.stackexchange.com |
210,393 | [
"https://softwareengineering.stackexchange.com/questions/210393",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/42251/"
] | Almost in every interview for the position of web developer, they ask about stored procedures and triggers well I am aware from their definition and basic usage but the truths is I have never used any of them in any of my project. Well I have seen other developers who used them but only when they were the only solution... | <blockquote>
Well I have seen other developers who used them but only when they were the only solution.
</blockquote>
Stored procedures and queries are <em>never</em> the <em>only</em> solution. No one forces you to enforce consistency in the database. Hell, you don't even have to be using database in the first plac... | I like using stored procedures when using MSSQL, because in MSSQL, you can assign user permissions only to stored procedure. My limited experience with MySQL and Postgres show that stored procedures are still a good practice, but permissions must always be granted on tables used by procedure.
Basically, I use stored ... | https://softwareengineering.stackexchange.com |
218,452 | [
"https://stats.stackexchange.com/questions/218452",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/27307/"
] | Suppose there is a irreducible, reversible Markov chain with known states $1,\ldots,N$ and unknown transition matrix $T_{ij}$ and unknown limiting distribution $\pi_i$. I am able to repeatedly initialize the system in an arbitrary state $s$ then observe a random transition $s\rightarrow t$ where $t$ is a sample from $... | <h2>Notation / preliminaries</h2>
I use hats ($\hat \theta$) for estimates, except when I say otherwise or forget. I try to use OP's notation: $N$ states, tpm $T$, and stationary dist $\pi$.
The maximum likelihood estimate of $T_{i\rightarrow j}$ is $m_{i\rightarrow j} / m_i$, the number of $i$-to-$j$ transitions di... | This is an elaboration of Eric Kernfeld's answer. Please upvote his instead of this one.
The information gain optimization of the problem is particularly natural in a Bayesian formulation. The Bayesian formulation also avoids some of the problems with either invariant subspaces or bootstrapping the variance in the p... | https://stats.stackexchange.com |
742,434 | [
"https://physics.stackexchange.com/questions/742434",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/354151/"
] | I was reading about Fluids, where I cam came across this line:-
<pre><code>If two containers are filled to the same height, they have **equal pressures at the bottom**, even though the **forces on the bottom would be different**.
</code></pre>
So what do we exactly mean by forces are different, but the resulting pressu... | To insert one of the balls from the bottom, you have to provide <span class="math-container">$V\cdot \Delta P$</span> energy, where <span class="math-container">$V$</span> is the volume of a ball and <span class="math-container">$\Delta P$</span> is the difference between the pressure at the bottom of the tank and the ... | When the ball enters the water at the lower end it needs to displace its own volume of water to get inside. This will raise the level of the water column which takes exactly the energy it gains later by floating up.
The rest is the usual friction.
done.
| https://physics.stackexchange.com |
275,725 | [
"https://softwareengineering.stackexchange.com/questions/275725",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/139859/"
] | Given the following two snippets:
<strong>Snippet 1</strong>:
<pre><code>public void foo(Data data, AbstractNode node)
{
int originalId = data.getCurrentId;
node.execute(data);
//If node changed currentId reset it to the original.
data.setCurrentId(originalId);
}
</code></pre>
<strong>Snippet 2</str... | Your comment can be easily misinterpreted, as you see from some of the other answers. Most devs are trained to associate the word "if" with a conditional branch, but that is obviously not what you meant.
I guess this is what you <em>really</em> meant:
<pre><code>public void foo(Data data, AbstractNode node)
{
int... | I'd say that the method name is <em>actively misleading</em>. After all, it <em>always</em> sets the ID, not only if node changed it!
To method 1, I'd add a comment explaining that <code>node.execute(data)</code> can change the ID, and why it is necessary to keep the old one.
Thirdly, consider making this a method on... | https://softwareengineering.stackexchange.com |
215,691 | [
"https://dba.stackexchange.com/questions/215691",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/159153/"
] | MS-SQL 2008 R2 (Dell, 2 CPU)
This query takes two minutes to run, which is too slow.
<pre><code>SELECT *
FROM t_events WITH (NOLOCK)
WHERE order_no = 2783190
and event_no <= ( SELECT MIN(event_no)
FROM t_events WITH (NOLOCK)
WHERE order_no = 2783190 and complaint_id = 80898
... | From DDL:
<pre><code>`date_created` varchar(250) COLLATE utf8_unicode_ci DEFAULT '',
</code></pre>
First question - why? Why not DATETIME?
From query:
<pre><code>AND date_created = '2018-08-23'
</code></pre>
Second question - are you sure there are records containing <code>'2018-08-23'</code> value in this field D... | With only the date part in your query tell MySQL that you only want to compare the date portion of the column using DATE ... as in
<pre><code>WHERE entered_by = '1' AND DATE(date_created) = '2018-08-23'
</code></pre>
| https://dba.stackexchange.com |
1,509 | [
"https://mechanics.stackexchange.com/questions/1509",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/835/"
] | So I leased a 2011 Chevrolet Cruze, brand new (only 2 miles on it), last November, 2010. It was running perfectly fine for a while. Brought it in for the standard tire rotation/oil change a few months ago. I brought it to an actual Chevrolet dealer to get everything done because they gave me a card that racks up points... | Returned from dealer - this was their report:
"clicking" noise from the R/R of the vehicle when slowing down. The technician road tested the vehicle and verified the concern. Found the rear brake shoes grabbing the drum causing minor grooves in the drum, also the technician found some grease on the backing plate. Clean... | They might have bent a shield, and can really only be heard when going slow. Sometimes this happens if a tire hits them while removing them, or during installation.
| https://mechanics.stackexchange.com |
2,948,384 | [
"https://math.stackexchange.com/questions/2948384",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/517746/"
] | I wanted to prove that if <span class="math-container">$A$</span>, <span class="math-container">$B$</span>, <span class="math-container">$C$</span> are independent 2 by to 2, <span class="math-container">$A$</span> and <span class="math-container">$B\cup C$</span> are not always independent, but I failed to build a cou... | You already have such an isomorphism: it’s <span class="math-container">$$\phi: \pmatrix{x_1\\x_2}\mapsto x_1e_1+x_2e_2.$$</span> To construct a matrix for this linear map, recall that the columns of a transformation matrix are the images of the basis vectors, so it’s simply <span class="math-container">$$M = \pmatrix{... | You're looking for a map between <span class="math-container">$x\in\mathbb{R}^2$</span> and <span class="math-container">$y:=\sum_i x_i e_i\in\mathbb{R}^3$</span>. The second expression is a vector with <span class="math-container">$j$</span>th component <span class="math-container">$\sum_i x_i e_{ij}$</span>, where by... | https://math.stackexchange.com |
97,024 | [
"https://stats.stackexchange.com/questions/97024",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/45258/"
] | I have 10 models analysing pupal developmental rates (<code>DR</code>) and developmental times (<code>DT</code>) depending on a number of factors:
<pre><code>m1 <- lm(DR ~ population+sex+temperature+weight+population*temperature)
m2 <- lm(DR ~ population+sex+population*sex)
m3 <- lm(DR ~ population+sex+temper... | @Dian breathe easy, it's pretty much not too difficult. So let's work from familiar territory to false discovery rate (FDR).
First, I see that you have a bunch of outcomes, with a varying number of predictors. Someone who is more familiar with <em>multivariate</em> regression (i.e. multiple <em>dependent</em> variable... | What you're doing is a type of step-wise regression, so FDR in this context serves to guide the model selection: the <em>p</em>-value would be that of the goodness-of-fit (coefficient of determination), not of any individual explanatory variable.
| https://stats.stackexchange.com |
2,590,480 | [
"https://math.stackexchange.com/questions/2590480",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/516905/"
] | Let $X=\ell^2(\mathbb{N})$ and $C=\left\{x=(x_k) \in X: x_0+x_1+x_2=1\right\}$. I have prooved that $C$ is a non-empty, convex and closed subsect of $X$. Now I want to find the projection of the element $0=(0,0,\dots) \in \ell^2(\mathbb{N})$. Can you help me?
| You can write $C$ as
$$C=\{x\in X: x\cdot y=1\}$$
where $y=(1,1,1,0,0,\ldots)$. Therefore the point of minimum distance will be a multiple of $y$, and the only point satisfying the constraint is $(\tfrac13,\tfrac13,\tfrac13,0,0,\ldots)$.
| Since the projection in Hilbert space gives the nearest point, you are looking to minimize the quantity $x_0^2+x_1^2+x_2^2$ subject to the condition $x_0+x_1+x_2=1$, and it is not too hard to prove that the minimum occurs when $x_0=x_1=x_2=1/3$.
| https://math.stackexchange.com |
199,899 | [
"https://math.stackexchange.com/questions/199899",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/19192/"
] | I'm sure this has been asked a million times, but it's hard to google for a particular series without knowing its name.
$$\sum_{n=1}^{\infty} \frac{(-1)^n}{n^2}$$
I know this converges absolutely to $\frac{\pi^2}{6}$ and I know that it is absolutely convergent so that the terms can be rearranged.
So the sum is equa... | We can break the sum up into positive and negative terms, so
$$\sum_{n=1}^\infty \frac{(-1)^n}{n^2}=\sum_{n=1}^\infty \frac{1}{(2n)^2}-\sum_{n=1}^\infty\frac{1}{(2n+1)^2}=2\sum_{n=1}^\infty \frac{1}{(2n)^2}-\sum_{n=1}^\infty\frac{1}{n^2}=\frac{-1}{2}\sum_{n=1}^\infty\frac{1}{n^2}=-\frac{\pi^2}{12}$$
| HINT.
If you know
$$
\sum_{n=1}^\infty \frac{1}{n^2}
$$
Next you should find
$$
\sum_\text{even} \frac{1}{n^2}
$$
where you use only the even numbers.
Then some combination of these two will be the sum you want.
| https://math.stackexchange.com |
84,189 | [
"https://cs.stackexchange.com/questions/84189",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/77827/"
] | I learned in my data structures class that QuickSort can be optimized by calling the InsertionSort method when the length of the subarray is less than a certain threshold. However, when it comes to the actual time complexity calculation of the optimized version of QuickSort, I'm having trouble finding the result. The p... | The height of tree is not $log(\frac{k}{n})$ which is negative because $k<n$. We stop expanding the tree when we reach $k$, therefore we reduce the height of the original tree by $log(k)$. So the height is $log(n)-log(k)=log(\frac{n}{k})$ and the average running time will be: $$c_1nlog(\frac{n}{k})+c_2nk=c_1nlogn-c_... | For fixed k, and n ≤ k, O(n) is meaningless. O(n) requires <em>arbitrary large</em> values n. With a fixed k, sorting n ≤ k items with InsertionSort takes O(1) - but with a large constant if k is large. Here's what you do to find the best k:
Iterate for k = 2, 3, 4, 5 ... (hoping that your algorithm is clever enough no... | https://cs.stackexchange.com |
7,026 | [
"https://bioinformatics.stackexchange.com/questions/7026",
"https://bioinformatics.stackexchange.com",
"https://bioinformatics.stackexchange.com/users/3968/"
] | I am analysing my single cell RNA seq data with the Seurat package. I want to know if there is a possibilty to obtain the percentage expression of a list of genes per identity class, as actual numbers (e.g. a matrix) which I can write out to say an excel file. For example I want to be able to say gene X is expressed in... | This can be solved like this:
<pre><code>library(Seurat)
my_genes <- c("gene1", "gene2", "gene3")
exp <- FetchData(object, my_genes)
matrix <- as.matrix(colMeans(exp > 0))*100
</code></pre>
| You can get the table that is used to make the dot plot if you modify the DotPlot function to return it instead of the ggplot, and use the argument do.return=T.
To edit the function, the command is:
<pre><code>trace("DotPlot",edit=TRUE)
</code></pre>
Then replace the last line "return(p)" by "return(data.to.plot)" a... | https://bioinformatics.stackexchange.com |
248,686 | [
"https://physics.stackexchange.com/questions/248686",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/113350/"
] | I have a little conceptual doubt about the BCS theory of superconductivity. A visual model of the Cooper pair attraction has a passing electron which attracts the lattice, causing a slight ripple toward its path. Another electron passing in the opposite direction is attracted to that displacement. This constitutes a co... | To buid up a bit on Tamasger's awnser, BCS can indeed be very non-intuite at first glance. The picture where the electrons locally disturbs the lattice and in return attract another electron is a good one to understand the basic concept of pairing, but is far from being able to capture all the physics.
Remember that p... | Your confusion arises because you take the "visual model" too seriously. According to BCS theory, there is a certain kind of electron-phonon interaction, which can be shown to be an effective attraction between two electrons (that need to be on the surface of the Fermi-sea). This coupling generates a binded state in th... | https://physics.stackexchange.com |
15,681 | [
"https://stats.stackexchange.com/questions/15681",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/6353/"
] | I'm working at a company developing web applications and due to the load on our testing team that can execute and analyze A/B or multi-variate tests, we're being asked to run "before and after" tests--also called "launch and learn" tests.
With these before and after tests, if we make a change to a web page, we're bein... | This is quite invalid, but there are ways to deal with it.
First, you can just graph clicks over time. This way, you can visually account for the secular trends that you discuss. Alternatively but equivalently, you could fit some complex model that accounts for these secular trends.
Second, you can create a control g... | While I'm not 100% certain of the statistical validity, many testers do this sort of thing anyways. Problem is that external factors like promotions, etc. One way to mitigate against a false result is to repeat the test 2 or 3 times. If there is a true difference between the versions, the results should be repeatable.
| https://stats.stackexchange.com |
231,403 | [
"https://mathoverflow.net/questions/231403",
"https://mathoverflow.net",
"https://mathoverflow.net/users/-1/"
] | Let $1 \le p < \infty$. For all $\epsilon > 0$, does there exist $C = C(\epsilon, q)$ such that$$\|u\|_{L^p(0, 1)} \le \epsilon \|u'\|_{L^1(0, 1)} + C\|u\|_{L^1(0, 1)} \text{ for all }u \in W^{1, 1}(0, 1)?$$
| Of course.
For $u\in C^1$ denote $v=u-\int_0^1 u$, then $v(x_0)=0$ for some $x_0\in (0,1)$ and for all $x\in (0,1)$ we have $$|v(x)|=|v(x)-v(x_0)|=\left|\int_{x_0}^x v'(t)dt\right|\leqslant \|v'\|_{L^1(0,1)}=\|u'\|_{L^1(0,1)},$$
thus $M:=\|v\|_{L^{\infty}(0,1)}\leqslant \|u'\|_{L^1(0,1)}$. This extends to $u\in W^{1,... | Yes, this is the Sobolev injection $W^{1, 1}(]0, 1[) \to C^0([0, 1])$ (see e.g. Brezis' book on functional analysis)
$$
\|u\|_{L^\infty} \leq C \left( \|u'\|_{L^1} + \|u\|_{L^1}\right)
$$
followed by the $\epsilon$-Young inequality:
\begin{align*}
\|u\|_{L^p} & \leq \left(\|u\|_{L^1} \|u\|_{L^\infty}^{p-1}\righ... | https://mathoverflow.net |
25,046 | [
"https://softwareengineering.stackexchange.com/questions/25046",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/8474/"
] | I've read several books and learned through experience that optimizing code to the point where it is inscrutable, or coming up with an extremely fast but extremely complex solution to a problem is not desirable when working in teams, or even when you're working by yourself and have to understand your clever solution so... | <blockquote>
Does the average programmer understand recursion easily and thus one should use it with impunity, or does the average programmer not understand recursion very well and one should stay away from it for the sake of overall team productivity?
</blockquote>
I'd say that the average programmer understands re... | Some problems are naturally recursive. Coming up with an iterative solution in these cases can actually be more clunky and complex than recursive ones. A good example is any algorithm which needs to traverse a hierarchical tree structure, which is a not-uncommon task in programming.
TL;DR version: No.
| https://softwareengineering.stackexchange.com |
106,534 | [
"https://cs.stackexchange.com/questions/106534",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/102539/"
] | I am trying to model the following problem correctly as a min-cut network flow problem. I have <span class="math-container">$n$</span> books and 2 boxes. I also have books that I know must go in one of the two boxes. In addition, each book has a certain profit if I put it in the same box with another book. So for insta... | First, I assume that it doesn't matter which box a pair of books go into, e.g., the value of book 1 and 2 being in box 1 is the same as the value of book 1 and 2 being in box 2.
Now, denote <span class="math-container">$B_1, B_2$</span> as the books in boxes 1 and 2 respectively. The value of this partitioning is pre... | Make a graph with vertices <span class="math-container">$v_1, ..., v_n$</span> for the <span class="math-container">$n$</span> books. Let an edge <span class="math-container">$v_i, v_j$</span> for books <span class="math-container">$v_i$</span> and <span class="math-container">$v_j$</span> have weight <span class="mat... | https://cs.stackexchange.com |
454,338 | [
"https://physics.stackexchange.com/questions/454338",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/219861/"
] | In my physics book there is a diagram in which a block is placed on a table. The table is exerting an upward force <span class="math-container">$ F_n $</span> (normal force) on the block and there is a downward force <span class="math-container">$ F_g $</span> (gravitational force) on the block
The equation for normal... | Looks like in your calculations you are NOT using non-inertial frames of reference at all.
If I understood you correctly you frame of reference is at rest. In this frame of reference the elevator (and the body inside the elevator) are moving with some acceleration. But your frame of reference is not! You can use usual... | If you observe the elevator from the ground, you are evaluating its motion using an inertial reference frame (neglecting effect's of the earths rotation and revolution), and if these forces differ the elevator accelerates. The forces are: gravity and the force moving the elevator. If the elevator is accelerating rela... | https://physics.stackexchange.com |
173,054 | [
"https://stats.stackexchange.com/questions/173054",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/89446/"
] | I'm trying to model a simple system, with data:
<pre><code>zoom FOV
0 48.00069715
4000 30.9484929
8000 18.73417224
12000 9.690813595
16000 4.286154297
</code></pre>
Doing
<pre><code>> model.lin = lm(data = zFOV, formula = FOV ~ zoom)
> coef(model.lin)
</code></pre>
gives a reasonable
<pre... | To get what you want, you can type
<pre><code>poly(zoom, 2, raw = TRUE)
</code></pre>
Without the <code>raw = TRUE</code> option, R orthogonalizes and normalizes the basis polynomials. This has some advantages (e.g. in studying p values, numerical stability) but also, as you recognized, the disadvantage of complicate... | One easy way to do this is to define our own quadratic term and just use the lm function directly on that
<pre><code>zoom <- c(0,4000,8000,12000,16000)
FOV <- c(48.00069715,30.9484929,18.73417224,9.690813595,4.286154297)
plot(zoom,FOV)
datFr <- data.frame('FOV'=FOV,'zoom'=zoom, 'zoom2'=zoom^2)
model.lin = ... | https://stats.stackexchange.com |
105,733 | [
"https://mathoverflow.net/questions/105733",
"https://mathoverflow.net",
"https://mathoverflow.net/users/26023/"
] | As a sequence is the n^th root R(n, n)^1/n of a diagonal Ramsey number R(n, n) increasing, decreasing or neither?
As a sequence of positive real numbers is the n^th root of a diagonal Ramsey number, bounded in [sqrt(2), 4], namely
R(n, n)^1/n
also decreasing as n --> oo if infinitely many terms of R(n, n)^1/n are in... | Hi,
Yes, C(X) has very different maximal subrings. First note that the real line, say R, has uncountable many maximal subrings, see for example A. Azarang and O.A.S. Karamzadeh works about the existence of maximal subrings in Fields and Commutative Rings, Hence for any fixed maximal ideal M_x of C(X), C(X) contains ma... | Question 1 has a positive answer for general $X$. The reason for this is that $C(X)$ cannot distinguish between $X$ and its realcompactification. Hence if $X$ is not realcompact we construct $M_{x,y}$ as above with $x$ in $X$ and with $y$ in the realcompactification, but not in $X$. This is a maximal subring which do... | https://mathoverflow.net |
98,064 | [
"https://dba.stackexchange.com/questions/98064",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/36295/"
] | Three nested tables exist: user_groups, users, projects. Each user_group has many users and, in turn, each user has many projects.
Each project has an ordinal assigned, 1-5 (step_number).
I would like to provide a summary for each user group. Each user group summary should include the users' projects and their unique... | If I understand your requirements, this consists of selecting all the <em>users</em> that have a project in step 3, and using that list to select all the <em>projects</em> for <em>just those</em> users.
Something like:
<pre><code>SELECT ug.id
, STRING_AGG(DISTINCT p.step_number, ', ') AS summary
FROM user_groups u... | You may try to move your WHERE clause in the LEFT JOIN :
<pre><code>SELECT user_groups.id, STRING_AGG( DISTINCT(projects.step_number), ', ') AS summary
FROM user_groups
INNER JOIN users ON user_groups.id = users.user_group_id
LEFT JOIN projects ON users.id = projects.user_id AND step_number = 3
GROUP BY user_group.id
... | https://dba.stackexchange.com |
32,654 | [
"https://scicomp.stackexchange.com/questions/32654",
"https://scicomp.stackexchange.com",
"https://scicomp.stackexchange.com/users/31745/"
] | Based on the Navier-Stokes equations and a few parameterizations, the horizontal steady-state wind <span class="math-container">$u(z)$</span> within a forest of height H satisfies:
<span class="math-container">$$
a\left(\frac{du}{dz}\right)^2 + b\frac{du}{dz} \frac{d^2u}{dz^2} + cu +d\frac{du}{dz} + eu^2 + f= 0,\quad\... | The different specialized <code>VertexFunction</code>, <code>EdgeFunction</code>, <code>FaceFunction</code>, <code>FacetFunction</code>, <code>CellFunction</code> have indeed been deprecated and (at least) as of version 2018.2 removed. Instead, they have been merged into a general purpose <code>MeshFunction</code> whic... | If you're using the latest version of FEniCS, the meshing tools are deprecated as you've noticed. These tools are now under <code>mshr</code> module.
You can install it via terminal: <code>conda install -c conda-forge mshr</code>
Additionally, if you'd like to convert meshes, the <code>dolfin-convert</code> became dep... | https://scicomp.stackexchange.com |
205,969 | [
"https://softwareengineering.stackexchange.com/questions/205969",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/32468/"
] | For my job we have a nice RESTful webservice we've built out that we use to drive a couple websites we have. Basically the webservice lets you create and work with support tickets, and the website is responsible for the front end. Any webservice requests use an auth header which we use to validate the user and their ... | It sounds like there are two goals:
<ol>
<li>Easy for end-users to authenticate with their existing social accounts</li>
<li>Easy for developers using your webservice</li>
</ol>
Authorizing people to use resources on your site makes OAuth2 a preferred mechanism due to the popularity and availability of client librar... | <strong>How to make it extensible</strong>
First you should notice all these api's use the same mechanism for logging in. They all use OAuth for their authentication. This you need to leverage by starting with a general OAuth library. Don't use their own libraries for authentication, these will be unusable for other p... | https://softwareengineering.stackexchange.com |
233,828 | [
"https://mathoverflow.net/questions/233828",
"https://mathoverflow.net",
"https://mathoverflow.net/users/89074/"
] | The Borel--Bott--Weil Theorem is usually stated for the complete flag manifold of $SU(N)$. Does an analogue hold for the other flags, for example the Grassmannians?
More precisely, suppose $G(\mathbf C)$ is a complex reductive group, and $P(\mathbf C)$ is a parabolic subgroup. Characters $\lambda$ of $P(\mathbf C)$ g... | Kostant, <em>Lie algebra cohomology and the generalized Borel-Weil theorem</em>, Ann. Math. 74 (1961), 329-387.
W. Schmid, <em>Homogeneous complex manifolds and representations of semisimple Lie groups</em>, <strong>Proceedings of the International Congress of Mtahematicians: Helsinki 1978</strong> (ed. O. Lehto) 195-... | Lars, search for a paper of Kostant ora paper of Griffiths-Schmid,
you will find a complete answer to your question, even when \lambda is just an irreducible representation. best regards
| https://mathoverflow.net |
204,890 | [
"https://softwareengineering.stackexchange.com/questions/204890",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/-1/"
] | I am using eclipse for android programming, and every here and there i see the statement, "TODO Auto-generated method stub."
I understand that these methods were generated automatically by eclipse upon creation of classes and other trigger activities but I do not understand the need to have it mentioned everywhere.
W... | TODO is one of several default keywords which indicate tasks to perform in Eclipse. Under windows->Preferences->Java->Compiler->Task Tags, you should see these keywords. It is thought to add a comment with this keyword to automatically indicate the things that are still to complete, which is convenient if you make u... | Eclipse creates just empty methods that return null (hence "stub"). The comments are inserted to remind the developer that he'll probably want to <em>do</em> something in those methods, otherwise why should they exist? You're supposed to delete the comments when you've done that.
If you see those comments all over the... | https://softwareengineering.stackexchange.com |
1,359 | [
"https://dba.stackexchange.com/questions/1359",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/630/"
] | One of our corporate standards to is have a separate filegroup/file for user tables/indexes. This is set as the default so no need to qualify CREATE TABLE statements.
So it looks like this
<ul>
<li>fileid 1 = system tables, MDF</li>
<li>fileid 2 = t-log = LDF</li>
<li>fileid 3 = user stuff = NDF</li>
</ul>
Can anyo... | Microsoft's 70-432 training book says "The main reason not to place any of your objects on the primary file group is to provide as much isolation in the I/O as possible. The data in the system objects does not change as frequently as data in your objects. By minimizing the write activity to the primary data file, you r... | The isn't a performance gain to this, there is a recoverabily gain to be made. If file corruption happens in the system tables then the database is lost. If you keep the user data in a separate file group (or groups) then you can restore just those files keeping the rest of the database online during the restore (ass... | https://dba.stackexchange.com |
99,082 | [
"https://chemistry.stackexchange.com/questions/99082",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/28968/"
] | My instructor mentioned a reaction for preparation of benzaldehyde by chlorination of toluene in presence of sunlight to form benzal dichloride, which on hydrolysis gives benzaldehyde.
However, I'm not sure why the chlorination of side chain should stop after two chlorine atoms are added? At what step does the side c... | It doesn't stop, it just gets a lot slower the more chlorine atoms you add. From the abstract of an article titled <em>Photochemical side-chain chlorination of toluene</em><sup>[1]</sup>:
<blockquote>
Where $k_1$, $k_2$, and $k_3$ are the rate consts. for the successive reactions: $\ce{PhMe}$ → $\ce{PhCH2Cl}$ → $\ce... | It will not stop at the dichloro compound, it is a free radical halogenation reaction.
The benzyl radical is very stable so it is easy for a chlorine atom to abstract a hydrogen from the methyl grup thus forming a benzyl radical. The benzyl radical then reacts with a chlorine molecule to form a chlorine atom and a mol... | https://chemistry.stackexchange.com |
7,652 | [
"https://dba.stackexchange.com/questions/7652",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/4315/"
] | I'm a programmer, not a DBA. Be gentle :)
<strong>Overview</strong>
<ul>
<li>InnoDB, MySQL</li>
<li>mod_perl script, persistent connections</li>
<li>script called every 20 seconds by thousands of users</li>
</ul>
<strong>Problem</strong>
<ul>
<li>High Disk IO (presumably caused by updates[?]) slows everything down... | The issue was a result of not including a key in one of my OR statements in the UPDATE.
Hat tip to "dabest1" for helping me find the answer.
| As DTest pointed out, provide more information about your problem.
Regarding caching, you could possibly increase your innodb buffer pool size to allow more data and indexes to be cached in memory. If you have frequent updates, you may not benefit from the query cache and might be better off using that RAM for innodb ... | https://dba.stackexchange.com |
4,536,526 | [
"https://math.stackexchange.com/questions/4536526",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/1098674/"
] | Amy has four <strong>positive</strong> integers <strong><span class="math-container">$\mathbf{a, b, c,}$</span> and <span class="math-container">$\mathbf{d}$</span>.</strong>
After computing the values of <span class="math-container">$a + b$</span>, <span class="math-container">$a + c$</span>, <span class="math-contain... | If you think about the parities of the four integers, the only possibility is that you have three even and an odd, or three odd and an even (for instance if two were even and two odd there would only be two even totals and you are given three). In both these two cases, the even totals come from the sums in pairs of the... | Alternative approach:
As the OP (original poster) indicated, the <span class="math-container">$(4)$</span> partial sums, having an odd total, can not represent <span class="math-container">$2(a+b+c+d).$</span>
Therefore, you can assume, without loss of generality that
<span class="math-container">$(3)$</span> of the <s... | https://math.stackexchange.com |
536,594 | [
"https://math.stackexchange.com/questions/536594",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/95509/"
] | Let $a$, $b\in \Bbb R^+$ and $m \in \Bbb N$ then My conjectural closed form is $$\int _{0}^{\infty}\frac{x^{a-1}e^{-mbx}}{1-e^{-bx}}\,{\rm d}x
=
\frac{\Gamma(a)}{b^a}\left\lbrack\zeta(a)-\sum^{m-1}_{k=1}\frac{1}{k^a}\right\rbrack$$
Please tell me how to prove it.
| If you know what $\zeta(a)$ and $\Gamma(a)$ are, and moreover are able to guess such formula, it is somewhat strange that you are asking for a proof.
Note that $a$ should be actually greater than $1$ for the integral to converge. Under such assumption, we have
\begin{align}
\zeta(a)-\sum_{k=1}^{m-1}\frac{1}{k^a}&... | $\newcommand{\angles}[1]{\left\langle #1 \right\rangle}%
\newcommand{\braces}[1]{\left\lbrace #1 \right\rbrace}%
\newcommand{\bracks}[1]{\left\lbrack #1 \right\rbrack}%
\newcommand{\dd}{{\rm d}}%
\newcommand{\isdiv}{\,\left.\right\vert\,}%
\newcommand{\ds}[1]{\displaystyle{#1}}%
\newcommand{\equalby}[1]{{#1 \atop... | https://math.stackexchange.com |
304,155 | [
"https://mathoverflow.net/questions/304155",
"https://mathoverflow.net",
"https://mathoverflow.net/users/22810/"
] | <em>I'm aware that the following question is at best a refined version of at least 2 questions which are already on this site. I think it is justified however in that it is more precise and has some new content in it. If, however, anyone decides after reading this question that it is a duplicate I apologize in advance<... | Let me try: Consider $S^m_{1,0}$ and $SG^{m,0}$, where the second class of SG-symbols $SG^{m_\psi,m_e}$ is defined by the estimates
$$|\partial_x^\alpha \partial_\xi^\beta a(x,\xi)| \lesssim_{\alpha,\beta} \langle x\rangle^{m_e-|\alpha|} \langle \xi\rangle^{m_\psi-|\beta|}.$$
Clearly, $SG^{m,0}$ is a subset of $S^m_{1,... | I do not believe that the listed properties characterize the operators with symbols in $\cup_m S^m_{1,0}$. Let me first make precise the definition of $S^m_{1,0}$ for a given $m\in \mathbb R$: this is the Fréchet space of $C^\infty$ complex-valued functions on $\mathbb R^n_x \times\mathbb R^n_\xi$ such that for all
$\a... | https://mathoverflow.net |
173,938 | [
"https://dba.stackexchange.com/questions/173938",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/6096/"
] | SharePoint has a button to "Check Permissions". Here you can select a user from Active Directory, and it will magically traverse groups and show you all the access the user has on the site based on what groups they are in.
This is a long shot as I've been working with SQL Server for quite a while and have never heard ... | I was able to combine suggestions here with an old script I had lying around to come up with the following, which will show all the groups a user is in, along with the database roles they are mapped to. Note that this is not thoroughly tested, but it gave the results I needed.
<pre><code>-- SHOW PERMISSIONS FOR A USER... | <blockquote>
<blockquote>
<blockquote>
just seeing which groups the user is in that also have a login on the instance would be nice
</blockquote>
</blockquote>
</blockquote>
You can accomplish this using following code:
<pre><code>exec xp_logininfo 'dom\acc', 'all';
</code></pre>
Or you can imperso... | https://dba.stackexchange.com |
27,829 | [
"https://datascience.stackexchange.com/questions/27829",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/46288/"
] | I have a dataset consisting of approximately 2 million unique observations. It was initially a set of ID's and URLs. The goal is to cluster the ID's based on the URLs looked at. I transformed both columns to index form to simplify the data. As such, the set has 2 columns; 1. A unique ID and 2. A bag of key strings (the... | <blockquote>
At the moment I was thinking of possible filling the NAN values with the averages of the data points above and below. For example row 2 column r_person would become $3.05$.
</blockquote>
The problem here is that the missing data point isn't necessarily associated with a timestamp that is the average of ... | You could collect your time points into half-open intervals like $\dots, [20, 25), [25, 30), [30, 35), \dots$ and correlate the <em>average</em> observations for <code>r_person</code> and <code>l_person</code>.
An example with a few more data points:
<pre><code>import numpy as np
import pandas as pd
df = pd.DataFrame... | https://datascience.stackexchange.com |
9,675 | [
"https://softwareengineering.stackexchange.com/questions/9675",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/67/"
] | I have been discussing a project with a client and they want to use a single language to deploy to as many platforms as possible.
(I am not sure that it's such a good idea, because each platform offers a different user experience and UI metaphor. In some cases, screen sizes vary as well. Also, iPhone is out of the ru... | ActionScript 3 is the language. It runs on wide variety of platforms. In browser (flash player), on desktop (AIR), on mobile devices in browsers (Android) and also as native applications (Android and iOS both). Forget about flashlite.
| These are languages that have a very good deployment factors:
<h3>Javascript.</h3>
Why? It runs on browser, and most platforms you'd care about have a browser. Though, some lower end mobile phones may have severely stripped browser (or Opera Mini, which supports Javascript only on the proxy-side, and very limited clien... | https://softwareengineering.stackexchange.com |
506,892 | [
"https://stats.stackexchange.com/questions/506892",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/296197/"
] | Suppose that <span class="math-container">$X$</span> and <span class="math-container">$Y$</span> are dependent given <span class="math-container">$Z$</span>, and independent when not given <span class="math-container">$Z$</span>. Does this mean that:
<span class="math-container">$$
p(x,y) = p(x) \cdot p(y) \\
p(x,y|z) ... | There will be many examples of the form <span class="math-container">$Z = f(X, Y)$</span>, where <span class="math-container">$X$</span> and <span class="math-container">$Y$</span> are two independent random variables and <span class="math-container">$f$</span> is some function.
For example, <span class="math-container... | Yes the translation in formula is correct, up to a loose formalism.
A generic "real-world" example can be obtained when <span class="math-container">$X$</span> and <span class="math-container">$Y$</span> can
have either positive association or a negative association depending
on <span class="math-container">$... | https://stats.stackexchange.com |
44,871 | [
"https://physics.stackexchange.com/questions/44871",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/1127/"
] | In chapter III.6 of his <em>Quantum Field Theory in a Nutshell</em>, A. Zee sets out
to derive the magnetic moment of an electron in quantum electrodynamics.
He starts by replacing in the Dirac equation the derivative $\partial_\mu$ by
the covariant derivative $D_\mu = \partial_\mu - i e A_\mu$, where $A_\mu$ is a
(... | When you do the commutator you have to remember that it acts on something. That means you'll have (don't care for the convention of i and e):
$[D_\mu,D_\nu]\phi=(-[\partial_\mu,A_\nu]-[A_\mu,\partial_\nu])\phi$
Now you have to take into account the chain rule for differentiation! The first commutator evaluates to:
$... | You've forgotten that the expression $[D_{\mu},D_{\nu}]$ is an operator, so the derivatives act on <em>everything</em> to their right. It is easiest to work things out if you actually operate your expression on an arbitrary test function $f(x)$. So in your last equation, for example, the first term on the right-hand si... | https://physics.stackexchange.com |
169,341 | [
"https://physics.stackexchange.com/questions/169341",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/44881/"
] | Since the frequencies (or inversely, wavelengths) of photons are part of a continuous realm, doesn't this mean that no photon has exactly the same frequency?
Two photons might have the same apparent wavelength due to our measurement limitations, but that doesn't mean they'd be exactly the same. In a continuous realm,... | The uncertainty principle limits our ability to determine the wavelength of a particle with infinite precision. At the same time, there is no fundamental reason why any two photons (even if generated by exactly the same process) should produce <em>exactly</em> the same wavelength; however, you can be sure that there wi... | Surely you'd agree that all electrons and protons are $exactly$ the same (indistinguishable).
Now consider a regular Hydrogen-1 isotope: A proton and an electron bound together. There's definitely more than just one of these atoms in the observable universe.
Well then consider an electron floating around the $n=2$ sh... | https://physics.stackexchange.com |
691,862 | [
"https://physics.stackexchange.com/questions/691862",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/297949/"
] | Suppose a Man is running on a road which is a rough surface with friction coefficient <span class="math-container">$μ$</span>. Why will the maximum acceleration of man which he can get is <span class="math-container">$μ$</span>? Why not from himself by internal body mechanism he cant get a max acceleration greater than... | The only external force acting forward on the man is the friction force by the ground which is equal to and opposite to the force the man exerts backwards on the ground per Newton’s third law. The maximum possible static friction force before slipping occurs is <span class="math-container">$\mu_{s} mg$</span>. Where <s... | The starting point in understanding this is to remember that momentum always has to be conserved. That means that if you are standing still on the road and you then start to accelerate- that is, to increase your momentum- you need to impart an equal but opposite change of momentum to the Earth, so that overall there is... | https://physics.stackexchange.com |
102,611 | [
"https://physics.stackexchange.com/questions/102611",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/31496/"
] | I have perhaps meaningless question about Dirac spinors, but I'm at a loss.
The transformation laws for for left-handed and right-handed 2-spinors are
$$
\tag 1 \psi_{a} \to \psi_{a}' = N_{a}^{\quad b} \psi_{b} = \left(e^{\frac{1}{2}\omega^{\mu \nu}\sigma_{\mu \nu}}\right)_{a}^{\quad b}\psi_{b}, \quad \psi^{b}{'} = \p... | I think it is convention to write the conjugate Weyl fermion in,
\begin{equation}
\left( \begin{array}{c}
\phi _\alpha \\
\bar{\kappa} ^{\dot{\beta }}
\end{array} \right)
\end{equation}
(it is common to put a bar over the conjugate representation), with a raised index in order to comply with the ${} _{ \dot{\... | I suspect the origin of this might have to do with the bi-spinor notation. Given a four-vector $b_\mu$, one defines the corresponding bi-spinor, $b\!\!/_{\alpha\dot{\beta}}=b_\mu (\sigma^\mu)_{\alpha\dot{\beta}}$. In this convention, bi-spinors have both lower indices (or upper indices if one uses $(\bar{\sigma}^\mu)^{... | https://physics.stackexchange.com |
593,536 | [
"https://electronics.stackexchange.com/questions/593536",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/287145/"
] | When there are multiple schematics opened in LTspice and you run one of them, all pages (plots and schematics) will be arranged automatically in small windows on the screen. I want to see only the schematic that I run along with its plot, not any other one.
How can I get LTspice to only show the running schematic and i... | You can run multiple instances of LTspice.
| If the already accepted answer doesn't do it for you (thought it looks like it's selected) then consider that the quickest solution to your problem is to simply maximize any window inside the MDI. That will convert all of the opened windows as tabs. One click, that's all. I suppose that is what you expected? Personally... | https://electronics.stackexchange.com |
336,151 | [
"https://softwareengineering.stackexchange.com/questions/336151",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/253463/"
] | I've been reading a lot about different servlets/application servers like Tomcat, WildFly, Jetty and GlassFish. However, I don't understand if they're only used for testing server-side code during development, or can you also use them for deploying the final production code to end users (commercially)?
My understandin... | In addition to Robert's answer, you can use any of the mentioned servers in production environments. We do it often. Tomcat is one of the most used.
The point of these servers is that they are OpenSource and free. This fact makes them suitable for development because there're no constraints due to licences. Plus they ... | In general, Google, Amazon and Rackspace provide the <em>platform</em> on which you can run your Application Server Software. "Platform" is defined as that hardware and software required to allow software like Wildfly to run, generally a "machine," an operating system and various support software and utilities. The m... | https://softwareengineering.stackexchange.com |
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