text stringlengths 1 1.11k | source dict |
|---|---|
extraction, sublimation
Title: Sublimation of Iodine from Iodine Povidone Iodine povidone is a complex of iodine and the polymer povidone. I am wondering if one were to heat it enough, the iodine would sublimate and could be collected. Normally iodine boils at 184.3 °C, according to wikipedia.
A video of how the procedure might work, except iodine crystals would replaced with boiled down iodine povidone: Sublimation of Iodine Time lapse
This can be used to purify iodine, so from my understanding, you would be able to vaporize the iodine and leave the polymer behind.
Does the complex with povidone change how this would work? | {
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java, tree, integer
}
This might verify that stored value is triple the key:
for (int i = 0; i < QUERY_SIZE; ++i) {
int key = random1.nextInt(UNIVERSE_SIZE);
tree1.get(key);
}
After all the remove() calls, I was hoping you'd at least verify smaller .size().
The code following tree2 = new TreeMap<>(); is all copy-n-paste, which suggests an opportunity to break out a new benchmark(Map map) method.
That factor of six speedup for .get() is definitely impressive.
Overall, the code base is consistent and well thought out. You should be proud of it. | {
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of the linear trend and fitting secondary wave forms. Least-squares minimization applied to a curve-fitting problem. Topic: Sine Wave Least-Squares Fitting (Read 5985 times) previous topic - next topic. In chemistry, as indeed in all of the sciences, one may have a collection of data points to which he wishes to fit. Often one needs to describe experimental data with a mathematical function containing parameters that must be adjusted to give the best fit. Linear Least Squares Regression¶ Here we look at the most basic linear least squares regression. Just like you found the least squares straight line, find the least squares quadratic and plot it together with the original data. Title: Microsoft Word - LEAST SQUARES FITTING. Least squares fit synonyms, Least squares fit pronunciation, Least squares fit translation, English dictionary definition of Least squares fit. x^b and etcetera. As the fit proceeds and better values are found, the chi- square value decreases. Tutorial: | {
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electromagnetism, lagrangian-formalism, symmetry, field-theory, parity
Title: Uniqueness of Maxwell Lagrangian from first principles In Quantum field theory by M. Srednicki, we find on p. 337 the statement regarding the Maxwell Lagrangian
The action we seek should be Lorentz invariant, gauge invariant, parity and time-reversal invariant, and no more than second order in derivatives. The only candidate is $S=\int d^4x\mathcal{L}$, where $$\mathcal{L}=-\frac{1}{4}F^{\mu\nu}F_{\mu\nu}+J^\mu A_\mu.$$
Let us ignore the source term for now and expanding the field-strength tensor $F^{\mu\nu}$, we find
$$
\mathcal{L}
=
-
\frac{1}{2}
\left(\partial^\mu A^\nu\right)
\left(\partial_\mu A_\nu\right)
+
\frac{1}{2}
\left(\partial^\mu A^\nu\right)
\left(\partial_\nu A_\mu\right)
.\tag{1}
$$
How do I arrive at eq. (1) from first principles?
We know that the action of a relativistic field theory must be Lorentz-invariant scalar. We can construct Lorentz-invariant scalars by contracting Lorentz-invariant tensors. | {
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biochemistry
Glucose and other carbohydrates can help suppress disease activity, are given by vein or by mouth, and are part of initial treatment. Intravenous heme, however, is both more specific and effective than glucose and should be started if the patient’s symptoms fail to improve within 36 hours.http://www.porphyriafoundation.com/about-porphyria/types-of-porphyria/AIP [2015-05-02]
More about carbohydrates and the suppression of symptoms in porphyria http://www.porphyriafoundation.com/about-porphyria/diet-and-nutrition/the-glucose-effect-in-acute-porphyria [2015-05-02]. | {
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electromagnetism, magnetic-fields, electric-fields, maxwell-equations, electromagnetic-induction
This other equation is for so-called motional emf, which is the part of the total emf induced in a conductor when this conductor moves in external magnetic field.
In the frame of the conducting pipe, the pipe does not move, so in this frame, the formula gives motional emf equal to zero — $\mathbf v$ is zero. There is also the induced emf, due to induced electric field. In this frame, all the emf is due to induced emf, and the familiar Faraday's law formula for a stationary loop applies.
In the frame of the magnet, the pipe is moving in the field of the stationary magnet, with variable velocity. So the formula does not give zero this time. It is the familiar Faraday formula that gives zero induced emf here. So the roles of the two mechanisms of EMF get reversed.
In both frames one gets the same value for the total emf, so in a sense, it does not matter which frame is chosen. However, one frame may be better for calculations. | {
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rotational-dynamics, rigid-body-dynamics
I encourage the reader to read more about the motion properties of a rigid body
from this answer and more importantly from my full explanation of the terms twist and wrench which describe the geometry of rigid body mechanics. | {
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ros-groovy, ubuntu-precise, ubuntu
Depends: ros-groovy-rviz (= 1.9.20-0precise-20130126-0133-+0000) but it is not going to be installed
Depends: ros-groovy-navigation (= 1.10.1-s1359173385~precise) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
multiverse reps are allowed and the ros-latest.list's value is correct, with the precise repositories. So yes, I followed the steps of the installation, but it's not working | {
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vba, excel
On Error GoTo ErrorCatch
With Workbooks("VersionList.xls").Worksheets("V_List").Range("A:A")
Set rFind = .Find(ThisWorkbook.CustomDocumentProperties.Item("MC_Number").Value, LookAt:=xlWhole)
End With
If Not rFind Is Nothing Then
bListed = True
If rFind.Offset(0, 1) = ThisWorkbook.CustomDocumentProperties.Item("MC_Revision").Value Then
bRevision = True
End If
If rFind.Offset(0, 2) = ThisWorkbook.CustomDocumentProperties.Item("MC_CF_Update Number").Value Then
bUpdate = True
End If
Call CloseVL
Else
bListed = False
Call CloseVL
Call SetStatus(False, "Spreadsheet not listed")
Exit Sub
End If
If CheckPath(ThisWorkbook.Path) = True Then
bDirectory = True
End If
If ThisWorkbook.ProtectStructure Then
bProtected = True
For Each wsLoop In ThisWorkbook.Worksheets
If Not wsLoop.ProtectContents Then | {
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c#, tic-tac-toe
return true;
}
Then this method can be called repeatedly as follows:
public static bool SomeoneWins(char[][] board)
{
// Check columns
for (var x = 0; x < board.Length; x++)
{
if (AllFieldsTheSame(x, 0, board, 0, 1))
return true;
}
// Check rows
for (var y = 0; y < board.Length; y++)
if (AllFieldsTheSame(0, y, board, 1, 0))
return true;
// Check diagonals
if (AllFieldsTheSame(0, 0, board, 1, 1))
return true;
if (AllFieldsTheSame(2, 0, board, -1, 1))
return true;
}
However, I suspect you are also interested in who wins, in which case you could have both AllFieldsTheSame and SomeoneWins return a char instead of a bool.
And by the way, I'd prefer to use an enum for the possible values of each tile. A char can have the value of Q, but I don't believe you want to place a Q tile in your game. Using an enum reduces the eliminates any possible risk of invalid characters. | {
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quantum-field-theory, dirac-delta-distributions, regularization, scattering-cross-section, volume
Title: Approximation for the square of a Dirac delta function I am working in the appendix to Section II.6 in Zee's QFT book, 2nd Ed. I am trying to compute the cross section for a meson to decay to two mesons as $\varphi\to\eta+\xi$ with three respective momenta $k,p,q$. To simplify the problem, I have imposed the big box condition which quantizes the $k,p,q$. I have computed the probability amplitude
$$ \mathcal{A}\propto \big(2\pi)^4\delta^{(4)}(p+q-k) ~~, $$
where "$\propto $" means "is proportional to." Now I need to square $\mathcal{A}$ to get the probability. I substitute the integral form of the $\delta$-function so
$$ |\mathcal{A}|^2\propto \left[\big(2\pi)^4\delta^{(4)}(p+q-k)\right ]^2=\big(2\pi)^4\delta^{(4)}(p+q-k)\int\!d^4x\,e^{ix(p+q-k )}~~. $$
Zee simplifies this to
$$ |\mathcal{A}|^2\propto\big(2\pi)^4\delta^{(4)}(p+q-k)\int\!d^4x =\big(2\pi)^4\delta^{(4)}(p+q-k)VT~~,$$ | {
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beginner, c, linked-list
In the above lines, you should add test code that removes a value that occurs several times in the list. And you should add test code that tries to remove a value that the list doesn't contain.
In summary, there are many small places to improve. But the overall design of defining short functions with good descriptive names is something you did really well, and that's usually the most crucial part. When I write code, I heavily rely on the names of functions, types and variables.
So far for now. When you have updated your code (locally on your computer, not in this question), feel free to post a follow-up question with the updated code, referring to this question. There are some more things to cover, but that would have become too much for now. :) | {
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performance, beginner, strings, haskell
Title: Function that produces \$a^nb^nc^n\$ I'm trying to write a function that produces an infinite list containing strings of the form \$a^nb^nc^n\$.
My first idea was to do it using comprehensions.
f = [replicate n 'a' ++ replicate n 'b' ++ replicate n 'c' | n <-[0..]]
But this does a lot of duplicate work. I then decided it would be better to do the following
import Data.List
f = "" : (abc "")
abc s = string : (abc string)
where string = sort $ "abc" ++ s
How can I do this more efficiently without having to sort and use ++ as frequently? Would changing to ByteStrings help? Your first solution could be more elegantly written as:
f :: [String]
f = [concatMap (replicate n) "abc" | n <- [0..]]
The basic operating principle would be the same, though.
A general sorting algorithm would be O(n log n) at best, so I don't believe that sort would be a good idea. | {
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quantum-spin, visualization
I understand that the Bohr model is clearer for educational purposes. However, it can be very misleading when you get into the nooks and crannies of quantum configuration.
Thanks a lot! As you mention in the question, the $1s$, $2s$, etc orbitals can be thought of as fuzzy clouds where the density of the cloud represents the electron density. To get the total electron density of the atom you simply add together all the clouds.
This sounds complicated, but the sum of all the three $p$ orbitals or all the five $d$ orbitals, or all the seven $f$ orbitals, and so on, has spherical symmetry. The $s$ orbitals also have spherical symmetry, so for the potassium atom we have: | {
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where $$y=b$$ and $$x=a$$ (that is, we just changed letters). Why is it called "polar form"? Because the angle $$\varphi$$ is also often called the "polar angle".
Mathematically, the complex number $$z=r(\cos \varphi +i\sin \varphi)$$ is equivalent to $$z=re^{i\varphi}$$, because of the Euler's identity, which is $$e^{i \varphi}=\cos \varphi + i \sin \varphi$$, which holds for any real number $$\varphi$$.
In our case, the real number $$\varphi$$ is the angle.
In this context, we often call the phase either the term $$e^{i\varphi}$$ or simply the angle $$\varphi$$. Note that the angle $$\varphi$$ completely determines $$e^{i\varphi}$$, that is, given $$\varphi$$, we can easily retrieve $$e^{i\varphi}$$ (without any other information) by simply replacing this angle in the Euler's identity.
Can a complex number have different phases and still be considered the same complex number? | {
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• Thank you very much for your answers. Could anyone state whether they are orthogonal in PCA case? – Bober02 May 8 '12 at 13:45
• For PCA, things can always be set up such that the eigenvectors are orthogonal. On the other hand, I would recommend looking at PCA as a singular value decomposition instead of as an eigendecomposition. It's been discussed here on math.SE a number of times; search around. – J. M. ain't a mathematician May 8 '12 at 14:48
• What do you mean by "setting up"? Is there some common technique to achive a singular matrix? – Bober02 May 9 '12 at 8:12
• My understanding based on en.wikipedia.org/wiki/Principal_component_analysis is that a singular value decomposition (SVD) of $X$ results in three matrices, where the first of them is composed of the eigenvectors of $X^T X$, and is used for PCA. This matrix is always orthogonal. – Uri Jun 14 '13 at 13:04
• Beautiful answer. – Don Larynx Nov 13 '13 at 15:14 | {
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programming-languages, computer-architecture
Some people might say C is the language I'm looking for. I haven't used C before but I think it's still a high-level language, although probably faster than Java, for example. I might be wrong here. Assembly language is a way to write instructions for the computer's instruction set, in a way that's slightly more understandable to human programmers.
Different architectures have different instruction sets: the set of allowed instructions is different on each architecture. Therefore, you can't hope to have a write-once-run-everywhere assembly program. For instance, the set of instructions supported by x86 processors looks very different from the set of instructions supported by ARM processors. If you wrote an assembly program for an x86 processor, it'd have lots of instructions that are not supported on the ARM processor, and vice versa. | {
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c++, c++14, xml, stream, qt
Title: Using QXmlStreamReader to read configuration file of key-value pairs Background
The following XML snippet contains configuration parameters for our application in key-value pair manner. (Despite using INI files for such purpose may be better, I have to use XML files.)
<configuration>
<parameter id="serial_port_name">ttyS0</parameter>
<parameter id="serial_port_baud_rate">9600</parameter>
<parameter id="check_period">1000</parameter>
<parameter id="locale">hu_HU</parameter>
<!-- ... -->
</configuration> | {
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model of ZFC+V=HOD.</p> <p>In the latter part of the paper, we introduce what we view as the natural algebraic analogue of the constructible universe, namely, the implicitly constructible universe, denoted Imp, and built as follows:</p> <p><code>$$\text{Imp}_0 = \emptyset$$</code></p> <p><code>$$\text{Imp}_{\alpha + 1} = P_{imp}(\text{Imp}_\alpha)$$</code></p> <p><code>$$\text{Imp}_\lambda = \bigcup_{\alpha < \lambda} \text{Imp}_\alpha, \text{ for limit }\lambda$$</code></p> <p><code>$$\text{Imp} = \bigcup_\alpha \text{Imp}_\alpha.$$</code></p> <p><strong>Theorem.</strong> Imp is an inner model of ZF with $L\subset\text{Imp}\subset\text{HOD}$.</p> <p><strong>Theorem.</strong> It is relatively consistent with ZFC that $\text{Imp}\neq L$.</p> <p><strong>Theorem.</strong> In any set-forcing extension $L[G]$ of $L$, there is a further extension $L[G][H]$ with $\text{gImp}^{L[G][H]}=\text{Imp}^{L[G][H]}=L$.</p> <p>Open questions about Imp abound. Can $\text{Imp}^{\text{Imp}}$ differ from | {
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After a few minutes, I got a long result from which I could not read anything useful:
$\frac{\mu ^4 \left(186624 \lambda ^{16}+3825792 \lambda ^{15} \mu +35971776 \lambda ^{14} \mu ^2+205589664 \lambda ^{13} \mu ^3+798109200 \lambda ^{12} \mu ^4+2217713192 \lambda ^{11} \mu ^5+4537481548 \lambda ^{10} \mu ^6+6954729890 \lambda ^9 \mu ^7+8071898695 \lambda ^8 \mu ^8+7133161040 \lambda ^7 \mu ^9+4799247376 \lambda ^6 \mu ^{10}+2441453824 \lambda ^5 \mu ^{11}+923808416 \lambda ^4 \mu ^{12}+252053248 \lambda ^3 \mu ^{13}+46855424 \lambda ^2 \mu ^{14}+5307904 \lambda \mu ^{15}+276224 \mu ^{16}\right)}{11664 (\lambda +\mu )^5 (2 \lambda +\mu )^7 (\lambda +2 \mu )^8}$
In addition, the command FullSimplify[Probability[]] does not help.
Edit (2014-11-17): | {
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physical-chemistry
In a closed container, however, the story is different. Let's say you put a lid over your pot. Now, there is a relatively small amount of air trapped between the lid and the water's surface. Heating the pot heats the air as well, and pressure does not remain at 1 atm. That is because that small amount of air has to handle all that heat, whereas in the situation without the lid, a bigger volume (the kitchen) allowed for more heat dissipation. So now the small amount of air molecules are moving really fast. The heat is still breaking the intermolecular forces of the water, but this time, there is no (entropic) reason to move up into the gaseous state. The air molecules are moving just as fast, and therefore have just as much pressure, as water molecules that have broken bonds. | {
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function returns (for example, 10° 27' 36") and converts it to an angle formatted as a decimal value. How many degrees per second in a radian per second: If f rad/s = 1 then. The radian [rad] to second ["] conversion table and conversion steps are also listed. To convert from radians to degrees, you simply have to multiply the radian value by 180/π. Latitude and Longitude Converter - Convert between Degrees, Minutes and Seconds and Decimal Units (or vice versa) Minutes to Decimal Hours - Converting minutes to descimal hours; Radian - The radian - unit of angle - and angular velocity; Slope - Degree, Gradient and Grade Converter - Converting slopes between degrees, gradients and grades. A degree is measuring unit of angle measurement. [rad / s] is derived SI unit of. sion factor radians 180 1 to convert radians to degrees: 90 (r 1 a 8 d 0 i ° ans) 9 1 0 8 0 radians 2 radians. First off Sorry for dragging up an old subject but google seemed to think it was relevant. How to convert | {
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"openwebmath_score": 0.6850907206535339,
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rotational-dynamics
See the full book solution here.
Source: Giancoli's Physics for Scientists and Engineers. I think that your skepticism comes about because you intuitively think that the force of kinetic friction should change gradually to static friction as the ball speeds up, since the relative motion between the ball's spinning surface and the ground decreases to zero. Your textbook assumes that this transition is actually instantaneous, and that the kinetic friction force is exactly the same until there is no relative motion at all, at which point the friction is entirely static. It seems counter-intuitive, but that's actually how it is. | {
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Here the coefficient extractor enforces the range and we may continue with
$$[z^{n+1}] \frac{1}{1-z} \sum_{k\ge 0} z^{2k} \frac{1}{(1-z)^{k}} \\ = [z^{n+1}] \frac{1}{1-z} \frac{1}{1-z^2/(1-z)} \\ = [z^{n+1}] \frac{1}{1-z-z^2} = [z^{n+2}] \frac{z}{1-z-z^2} = F_{n+2}.$$
The above construction works for $$k\ge 1.$$ For $$k=0$$ we get the empty set, for a total count of one. Note however that $${n+1\choose 0} = 1$$ so the formula holds there as well.
Hint: Choose $$k$$ pairs of consecutive numbers from $$\{1, 2, \ldots, n, n+1\}$$, then choose the lowest number in each pair. | {
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transfer-function, smoothing
$$T(z)=\frac{b(1-z^{-1})}{1-(1-b)z^{-1}}L(z)\tag{3}$$
Plugging (3) into the first equation of (2), we can express $L(z)$ in terms of $X(z)$:
$$L(z)\left[1-(1-a)z^{-1}\left(1+\frac{b(1-z^{-1})}{1-(1-b)z^{-1}}\right)\right]=aX(z)$$
from which, after some algebra, you get
$$L(z)=\frac{a\left[1-(1-b)z^{-1}\right]}{1+[a(1+b)-2]z^{-1}+(1-a)z^{-2}}X(z)\tag{4}$$
Finally, plugging (3) into the last equation of (2) gives
$$Y(z)=\left[1+\frac{b(1-z^{-1})}{1-(1-b)z^{-1}}\right]L(z)=\frac{1+b-z^{-1}}{1-(1-b)z^{-1}}L(z)$$
and combining with (4) results in a relation between the output $Y(z)$ and the input $X(z)$:
$$Y(z)=\frac{a(1+b-z^{-1})}{1+[a(1+b)-2]z^{-1}+(1-a)z^{-2}}X(z)=H(z)X(z)\tag{5}$$
where $H(z)$ is the desired transfer function, which is of course a second order IIR filter. | {
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optics, refraction
It is clear that different elements absorb (and emit) light very differently at different wavelengths (Wikipedia: Absorption Spectrum). This is to my knowledge how astronomers identify the atmospheric composition of celestial bodies. Is there an analogous phenomenon for refraction? Refractive index is not the same at every wavelength. In addition, it can vary due to environmental conditions such as temperature and pressure, and even light intensity. If the index is exactly the same for two materials at some wavelength, then their refraction behavior at that wavelength will be exactly the same. If two materials have the same index at some wavelength, it's extremely unlikely that they will have the same index at any other wavelength. So in principle it is possible to distinguish materials by the way the disperse different wavelengths. It's practically impossible for two different materials to have exactly the same index behavior at all wavelengths. | {
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physiology, food, human-physiology, digestive-system, digestion
Title: Does food continue to stay sequential once it is inside my body? I may be very off on many scientific details here, but I'm always all ears.
As far as I understand, any food that is eaten goes to the stomach, gets broken down even further into smaller food molecules, and after a period goes through the intestines where nutrients are absorbed out of this chyme.
Let's say I eat food A sometime, and it's gone down and is now sitting in my stomach, waiting for the stomach to start breaking it down. After a while, I eat food B.
When digestion occurs, is it possible that the stomach only starts breaking down food A's material first before it gets to food B?
Is it possible that food B's output goes into the duodenum before food A's output? | {
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php, mvc, url-routing
Title: The Router - dispatch after parseURL I'm hoping that the more experienced devs here can help me improve these methods. I'm building a basic MVC framework for myself (as a learning project,) and I'd really appreciate your insights. Things I'm looking for specifically are:
Efficiency: can these methods be improved (particularly with the Request:parseURI() method.)?
Clarity: do these methods make sense the way they're written, or should I refactor?
I'm including two key methods of my request routing system:
RequestRouter
Request
RequestRouter::dispatch()
public function dispatch()
{
try
{
// Instantiate the requested controller class
$class = ( $this->getController() != null ) ? ucwords( $this->getController() ) . 'Controller' : BaseController::ERROR_CONTROLLER; | {
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homework-and-exercises, kinematics, projectile
Title: Velocity and theta sign I'm doing the following problem:
A castle on a cliff has a cannon 300m above sea level. The cannon can
shoot a 10kg iron ball with a velocity of 400 m/s . If the cannon is
raised to an angle 30º of above the horizon, calculate the following:
the final velocity of the cannon ball just before it strikes the water | {
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electricity, electrochemistry
Title: Why does alkaline battery is more likely to damage quartz clock? When I purchase a quartz table/wall clock, most of the time it has a sticker saying not to use alkaline battery and from this quora question. There is also mixed thought about this but in theory (I think) both alkaline and zinc-carbon battery should not have any differences because both of them have $1.5\,\text{V}$ so if there really differences, I would love to understand the physics behind them. Alkaline zinc cells use different electrochemical system than ordinary acidic zinc-carbon cells.
The 1.5 V voltage is just a nominal value. The actual open voltage largely depends on the cell type, long and short term discharging and aging history. A new cell can have up to 1.6 V, an old used cell can have down to 1.2 V.
Another case is the voltage on load. Alkaline cells have generally much lower internal resistance, so the voltage drop during providing the current is smaller. | {
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ros, imu, robot, ros-indigo
Originally posted by kesuke on ROS Answers with karma: 58 on 2018-08-03
Post score: 0
I have two suggestions:
Place your imu in a way where the sensor frame of the imu will be orientation aligned with your base_link frame (i.e., so that in your base_link -> imu_link tf, the orientation component is unit quaternion). I've found this useful for debugging localization, because you can directly compare what your orientation state estimate is with the orientation estimate provided by your imu.
Place it as far away from sources which cause soft iron interference as you can. You should calibrate the magnetometer on the imu once it's on your robot to properly capture the hard / soft iron disturbance, and I've found the soft iron calibrations are much more unreliable than hard iron.
Originally posted by stevejp with karma: 929 on 2018-08-03
This answer was ACCEPTED on the original site
Post score: 0 | {
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bash, shell
yestdayend=$(date --date="yesterday" +"%Y-%m-%d 23:59:59")
path=/path/to/dir
filelist=$(find $path -maxdepth 1 ! \( -name "*.zip" \) -type f ! -newermt "$yestdayend")
for file in $filelist
do
moddate=$(stat -c %y $file | cut -d " " -f 1)
if zip -rv $path/"logbackup-"$moddate.zip $file; then
rm $file
fi
done Saving the output of find in a variable and looping over it is not a good idea in general: filenames with white-space (space, tab, newline) will be split, so the loop will not work on them.
It would be a little bit better to use a while loop instead:
find ... | while read file
do
# ...
done
But this is still not great, as it won't protect you from newlines.
But for your use case, it might be good enough.
For a more robust solution,
see this other post.
The \( ... \) is pointless here:
find $path -maxdepth 1 ! \( -name "*.zip" \) -type f ! -newermt "$yestdayend" | {
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homework-and-exercises, thermodynamics
I am confused in the units given and I tried to solve it by comparing latent and specific heat to get $L = C\Delta T$, but unable to solve it, since I don't know what will be the temperature difference, Please tell me how to solve it. With regard to the problem with units:
Specific heat should be in units of "calories/ gram/Celsius degree";
Latent heat of vaporization should be in "calories/gram" ;
Temperature change in Latent heat should be in "calories/gram/Celsius degree"
"calories" should be spelled here with a lower-case "c". The capitalized version is $1000$ times bigger i.e $1$ Calorie is $1$ kilo-calorie.
There is a typo in the OP: the latent heat of vaporization of water at $100 ^o$ C is $540$ calories/gram. | {
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java, dynamic-programming
return longest.size() < current.size() ? current : longest;
}
Some other tips on the original code:
Avoid arrays of generic types such as ArrayList<Integer>[]
Prefer interface types in declarations and method return types, such as List instead of ArrayList
When initializing generic types, Java 7 can guess the correct type parameter, so instead of new ArrayList<Integer>() you can write new ArrayList<>() (also known as the diamond operator <>)
The indentation and formatting was inconsistent, use an IDE to format the code nicely
Instead of printing elements of LIS one by one, System.out.println(LIS) would easily produce an output that's just as readable
A more compact writing style to initialize an array: int[] array = { 7, 1, 3, 8, 11 }; | {
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asteroids, history, comets, naked-eye, chicxulub
Title: Could the dinosaurs have seen the asteroid that killed them? Wikipedia says the Chicxulub impactor is thought to have been a 10-15 km diameter object. Would it have been visible to a (human*) naked eye before impact? And if so, would it have appeared like a star that grew brighter and brighter each night?
* I know, there were no humans at the time. The answer is yes; for a few nights prior to the impact (assuming they had eyes with a similar sensitivity to our own and could look up!). It could be a bit longer than this if the body was larger than 10 km (it goes up roughly in proportion to the impactor's radius) and could be much longer if the object was a cometary body or had a very high albedo.
Details:
Impacting solar system objects would have relative closing speeds from around 11 to 72 km/s. | {
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homework-and-exercises, newtonian-mechanics, friction, perturbation-theory
Meanwhile, the friction force is $F = \mu N = \mu m g \cos\alpha$. Using $F^2 = F_x^2 + F_w^2$ we can eliminate the forces algebraically to find the answer you quoted. | {
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electromagnetism, work, magnetic-fields
Title: Work on Ferromagnetic Object Due to Solenoid I've been going through some equations and such trying to determine the work done by a solenoid on a ferromagnetic object. I have the following:
Magnetic field due to solenoid:
$\vec{B} = \langle0,0,\mu_0nI\rangle$
(Assuming coils are on xy-plane and current is counter-clockwise)
Force of magnetic field:
$ F = q\vec{v} \times \vec{B} $
Work:
$ W = \int F \cdot dl $
Work of Magnetic Field:
$ W = \int_c(q\vec{v} \times \langle0,0,\mu_onI\rangle) \cdot d\vec{r} $
For one, this seems to indicate a work of 0 if the object is not charged, which I have seen in some places but just doesn't seem right. Also, this does not take into account the properties of the object, such as relative permeability, which I guess could have some effect with the charge value. I'm trying to calculate the acceleration of a ferromagnetic object from a magnetic field, is there a better way to do this? I've thought about the following: | {
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javascript, floating-point
You have quite numerous unnecessary (in my opinion) variables,
The loop and surrounding conditional statement is completely unnecessary as well,
Variables' names could be more descriptive, especially a's,
sDec += '0' is shorter and faster than sDec = sDec.concat("0"),
Why to assign +number.toFixed(precision) to variable number, if in the very next line you just return number? Go with return +number.toFixed(precision) instead. | {
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turing-machines, reductions, halting-problem
Title: Turing machines: can a machine write to a finite number of memory cells, but not halt? I am trying to reduce the Halting problem to show another problem is undecidable. The problem involves a program that is true if a machine $M$ writes to an arbitrary amount of memory, and false if it writes to a finite amount of memory cells. I am now thinking, is writing to a finite amount of memory cells equivalent to halting, or can there be cases where a machine writes to a finite amount of memory cells without halting?
Thank you in advance! Consider a Turing machine that repeatedly moves its head right, then left, then right, then left, and so on. | {
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javascript, object-oriented, design-patterns, modules
}, 300)
$('.container').css({
position: "fixed"
}).animate({
left: 0
}, 300)
$('.content-overlay').delay(300).hide();
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homework-and-exercises, newtonian-mechanics, reference-frames, acceleration, free-body-diagram
Hint: The textbook it is in Italian language and I like not very much because in this exercise it is confusing between weight with the mass.
\begin{cases}
(F_{\text{fict}_{\text{up}}})=m_{\text{Mark}} \ g + m_{\text{Mark}}\ a & (1) \\
(F_{\text{fict}_{\text{down}}})=m_{\text{Mark}} \ g - m_{\text{Mark}}\ a
\end{cases}
Hence
$$(F_{\text{fict}_{\text{up}}})+(F_{\text{fict}_{\text{down}}})=2 m_{\text{Mark}}\ g$$
If $(F_{\text{fict}_{\text{up}}})=(m_{\text{fict}_{\text{up}}}) g$ and $(F_{\text{fict}_{\text{down}}})=(m_{\text{fict}_{\text{down}}}) g$ I found $m_{\text{Mark}}$.
Definitively from the $(1)$ for example I will have
$$a=\frac{m_{\text{fict}_{\text{up}}}g - mg}{m_{\text{Mark}}}$$
My question is: $(F_{\text{fict}_{\text{up}}})$ or $(F_{\text{fict}_{\text{down}}})$ is it always | {
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quantum-mechanics, operators, hilbert-space, observables, time-evolution
However, operators that correspond to non-observables can depend on time. $U(t)$ is not an operator corresponding to an observable (this is obvious since $U(t)$ is not Hermitian).
In the Heisenberg picture, it is states that don't evolve with time and Observable operators that do.
Hope that helps! | {
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terminology, functional-programming, semantics
a PURE is referentially transparent: it does not cause side-effects,
its value is not affected by side-effects, and it returns the same
value each time it is evaluated.
Note, however, that Peyton-Jones and Wadler mentioned shortcomings in this approach. Worth noticing, they say, is the programming language Clean that uses linear types to introduce side-effects in a safe manner (i.e. safe for the compiler). Basically, it threads the World as a variable in all I/O related functions, including the main entry point.
With that, it is possible to have a pure functional language interacting with the world and having side-effects (I/O, the OS, the Windowing system, etc), contradicting partially your wikipedia definition. One can in fact say that Haskell has Clean as one of its influencers; although it departs from linear types and uses another type-level construct (monads) to guarantee linearity, i.e. a single-reference at all times. | {
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17:26 • @zaph No worries. To pull off Wiki's page for Big O: "Note that "=" is not meant to express "is equal to" in its normal mathematical sense, but rather a more colloquial "is". So, you can read it as a property of the function. Ex: "He is a boy" :: "$f$is (has) a Big O of$n \: log(n)$". Or at least, that's how I perceive it. Critiques are welcome of course. – user46712 Jul 30 '17 at 23:04 The best way to find big-o of a function like this: $$f(n) = \sum_{i=1}^k f_i(n)$$ is to find an i where: $$\forall j \in [1,k], j\neq i \rightarrow \lim_{n->\infty} \frac{f_j(n)}{f_i(n)} =0$$ therefor big-o is $$n\log(n)$$ •$\lim_\limits{n->\infty} \frac{f_j(n)}{f_i(n)} =0$is too restictive,$\lim_\limits{n->\infty} \frac{f_j(n)}{f_i(n)} <\infty$will be sufficient, too.$\lim_\limits{n->\infty}\sup \frac{f_j(n)}{f_i(n)} <\infty$is exact. And if$f_j(n)<f_i(n)\$ this is already sufficient, you dont have to calculate the limit. So in this case I can't see why it should be the best method. | {
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quantum-mechanics, electrons, schroedinger-equation, quantum-tunneling
For the description of tunneling it is misleading to picture the electron as a particle that hit's the wall and may or may not bounce back. | {
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• We can perform algebraic operations on functions. See [link] .
• When functions are combined, the output of the first (inner) function becomes the input of the second (outer) function.
• The function produced by combining two functions is a composite function. See [link] and [link] .
• The order of function composition must be considered when interpreting the meaning of composite functions. See [link] .
• A composite function can be evaluated by evaluating the inner function using the given input value and then evaluating the outer function taking as its input the output of the inner function.
• A composite function can be evaluated from a table. See [link] .
• A composite function can be evaluated from a graph. See [link] .
• A composite function can be evaluated from a formula. See [link] . | {
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"url": "https://www.quizover.com/course/section/decomposing-a-composite-function-into-its-component-by-openstax"
} |
c#, .net, rabbitmq
public RabbitConnectionFactory(IConnectionFactory connectionFactory)
{
_connectionFactory = connectionFactory;
_lazyConnection = new Lazy<IConnection>(() =>
_connectionFactory.CreateConnection(), LazyThreadSafetyMode.ExecutionAndPublication);
_lazyChannel = new Lazy<IModel>(() =>
CurrentConnection.CreateModel(), LazyThreadSafetyMode.ExecutionAndPublication);
}
public static IRabbitConnectionFactory From<TOptions>(TOptions options) where TOptions : RabbitBaseOptions
{
ArgumentNullException.ThrowIfNull(options);
return new RabbitConnectionFactory(FromConfig(options));
}
private static IConnectionFactory FromConfig(RabbitBaseOptions baseOptions)
{
ArgumentNullException.ThrowIfNull(baseOptions); | {
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c#
I am mainly focused on cleaning up the AssembleNodes method, but any and all help is great.
public class ReportService : IReportService
{
private readonly Permissions _permissions; | {
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electromagnetism, photons, magnetic-fields, virtual-particles
Title: How do virtual-photons curve in a magetic field? From what I understand photons only move in straight lines unless reflected or refracted (other than influences from gravitational fields and their usual wavelike movement). And since they are a fundamental force carrier I am having difficulty understanding how they are "pulled" into a pole of a magnet after leaving the opposite end. How does this occur? The field lines in your drawing are not the trajectories of photons. The field lines show the direction of the force on a test magnetic dipole. The force, and therefore its direction, is mediated by virtual photons (or can be described that way) but those photons will travel in straight lines just like ordinary photons. | {
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"tags": "electromagnetism, photons, magnetic-fields, virtual-particles",
"url": null
} |
quantum-field-theory, string-theory, conformal-field-theory
Title: Different OPE channels in bootstrap Can someone quickly explain what exactly are those different channels (namely s,t,u) in OPE expansions frequently used in conformal bootstrap. Explanation with a simple example will be really helpful. Given the four point function $\langle \phi(x_1)\phi(x_2)\phi(x_3)\phi(x_4)\rangle$, the conformal block expansion depends on what operators you replace by the OPE. So if you insert the OPE for $\phi(x_1)\phi(x_2)$ and the OPE for $\phi(x_3)\phi(x_4)$ then this corresponds to the s channel---one can also call this the (12)(34) channel---.. The t channel is then the (14)(23) channel and u is the (13)(24) channel. | {
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refraction, non-linear-optics
So your eyes will be able to see this effect only if the change in refractive index causes a change in the refractive angle large enough to be detected by your eyes. As the light is entering a denser medium from a less denser one (air to glass), it will move towards the normal. Hence, the refractive angle will have to decrease, if the refractive index increases (Snell's Law: $n_1Sin\theta_1=n_2Sin\theta_2$). You can calculate how much change you need in the refractive index and find the appropiate amount of Electric field that would cause an observable change (it would be pretty high I am guessing, very difficult to produce in a lab). | {
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used in the strong law of large numbers. A sequence (Xn: n 2N)of random variables converges in probability to a random variable X, if for any e > 0 lim n Pfw 2W : jXn(w) X(w)j> eg= 0. In probability ⦠Homework Equations N/A The Attempt at a Solution On the other hand, almost-sure and mean-square convergence do not imply each other. "Almost sure convergence" always implies "convergence in probability", but the converse is NOT true. In probability theory, an event is said to happen almost surely (sometimes abbreviated as a.s.) if it happens with probability 1 (or Lebesgue measure 1). Books. Convergence in probability says that the chance of failure goes to zero as the number of usages goes to infinity. On (Ω, É, P), convergence almost surely (or convergence of order r) implies convergence in probability, and convergence in probability implies convergence weakly. )j< . Conditional Convergence in Probability Convergence in probability is the simplest form of convergence for random | {
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"url": "http://gianpaologonzalez.com/vlt5j98m/47c220-convergence-almost-surely-implies-convergence-in-probability"
} |
quantum-mechanics, operators, quantum-states
Title: What does it mean to create particles by applying creation operator This question will be a way to ask if quantum mechanics is just a mathematical framework to predict physical outcomes without talking about the 'actual', maybe even 'deterministic' phenomena, such that the equations never make the wrong predictions.
The main reason is that its language is quite mathematical, and just mathsy in the sense I can't relate it to things that I call physical processes. Recently I was reading about creation operators and vacuum states in QFT, and the book says the following (I can't find a way to use mathjax here, sorry. If you can let me know of a link for it)
There exists a vacuum state and creation operator indexed by momentum. Applying this operator to the vacuum state gives a 1 particle state with the index momentum. | {
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"tags": "quantum-mechanics, operators, quantum-states",
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} |
linear-systems, impulse-response, time-domain
Title: Impulse response (general form for linear systems as two-variables function $h(t,\tau)$) applied to Time-invariant systems If a system is linear, then the operator $S$ mapping input signals into output signals - i.e. $y(t)=S\{u(t)\}(t)$ - is the integral of the input weighted by the impulse response:
$$ y(t) = \int_{-\infty}^{+\infty} h(t,\tau) u(\tau) \mathrm{d}\tau $$
where $h(t,\tau):=S\{\delta(t-\tau)\}$, response of the system to an impulse in $\tau$, is a function of two variables: the second one $\tau$ refers to the time at which the input is applied while the first one $t$ refers to the time at which the output is observed.
If this system is also time-invariant, the system operator commutes with the time shift operator:
$$S\{u(t-T)\}(t) = S\{u(t)\}(t-T) $$
that is, time shifting the input, a time shifted version of the output is produced. | {
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"tags": "linear-systems, impulse-response, time-domain",
"url": null
} |
python, beginner, python-3.x, parsing, csv
Title: CSV file parser and compare This may seem like a lot of stuff? I just need help with 2 small parts the code works, however I have provided the rest of the info in case some one can help. USING PYTHON 3.4
Code below is responsible for comparing multiple CSV files against a
cross-reference file and creating a metadata file, information files, also a file to keep track of points that did not have a match in the cross-reference file.
it will compare files that are ordered in daily manner, each day holds 1 5min-file , 3 exc-file, 1 ala-file, 1 accu-file.
It will produce 1 file that holds the points, one file that holds points with their timestamps, and a file that holds points that have no match with the cross-reference file
The code works fine.
# cross reference file:
header1, header2, header3, header4, header5, header6
aaaaaaa1, bbbbbbb1, ccccccc1, ddddddd1, eeeeeee1, x42, trg, zxc, dfg
aaaaaaa2, bbbbbbb2, ccccccc2, ddddddd2, eeeeeee2, fffffff2, zxc, hjg | {
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} |
and be an eigenvalue of a Hermitian matrix and the corresponding eigenvector satisfying , then we have If we have a 3x3 matrix, how can we check if it represents an orthogonal matrix? For any normal matrix A, C n has an orthonormal basis consisting of eigenvectors of A. | {
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"url": "http://eurostarinc.com/misc/fo75tf/de3401-eigenvalues-of-orthogonal-matrix"
} |
python, python-3.x, markov-chain
if segment:
prevSegment = segment
# Add the ending to segmentData
if prevSegment not in segmentData[ENDING]:
segmentData[ENDING][prevSegment] = {}
endFrequencies = segmentData[ENDING][prevSegment]
if ending in endFrequencies:
endFrequencies[ending] += 1
else:
endFrequencies[ending] = 1 | {
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} |
ros, ros-hydro, rosrun, ros-package-path, pluginlib
Original comments
Comment by Mate Wolfram on 2014-01-31:
working on the same problem... "export CMAKE_PREFIX_PATH=" helps, the rosrun ambiguity is resolved. However, pluginlib still has trouble loading trajectory planner (also my own version & dry): Exception: MultiLibraryClassLoader: Could not create class of type base_local_planner::TrajectoryPlannerROS
Comment by Constantin S on 2014-01-31: | {
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"tags": "ros, ros-hydro, rosrun, ros-package-path, pluginlib",
"url": null
} |
quantum-mechanics, quantum-entanglement
What is it about quantum entanglement that cannot be explained classically?
The phenomenon of entanglement is what you get thinking about the more general phenomenon of quantum interference/superposition from the point of view of locality. When you start asking questions about what can be achieved thanks to superpositions that could not be achieved by means of local operations only, you end up studying entanglement.
But asking what about entanglement cannot be explained classically, to me, sounds like a question that goes beyond the specific point of view that is locality. Explaining entanglement is really the same as explaining quantum interference in general. Which is essentially the same as asking what about quantum mechanics cannot be explained classically. The answer to which is: any phenomenon that is not compatible with classical explanations. There's plenty, so this becomes a bit broad for a single post. | {
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"tags": "quantum-mechanics, quantum-entanglement",
"url": null
} |
biochemistry, molecular-biology, cellular-respiration
Title: Pyruvate oxidation - where did the hydrogen come from?
(source: resource12ubio at sites.google.com)
As shown in the diagram above, NAD+ is reduced and becomes NADH by gaining two electrons
Now, where did the hydrogen come from?
In the diagram, pyruvate has 3 hydrogen, but it still has 3 hydrogen in acetyl CoA. The Wikepedia page has a really good diagram of the reactions involved. The Pyruvate Dehydrogenase Complex facilitates the removal of CO2, and the addition of two hydrogen atoms to the overall reaction come from the FADH2/FAD molecule. | {
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"tags": "biochemistry, molecular-biology, cellular-respiration",
"url": null
} |
optimization, computer-architecture, compilers, cpu
Title: What happens with register usage in deeply nested functions calls (in theory)? I am far from being able to construct a meaningful test for this using godbolt or some C compilation tool. But basically I am wondering what it would look like to have deeply nested function calls, where each function had let's say a dozen temporary variables throughout. What happens to register usage? It seems like everything would have to be stored in memory and the register usage would almost be negligible. What is it like in reality? Where am I going wrong? Ignore recursion for the moment, and pretend that a recursive call is just like any other call.
Then the solution is easy: all local variables are spilled to the stack across calls, including the recursive call. So yes, if there is deep recursion going on, most of the local variables will reside on the stack most of the time. | {
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"tags": "optimization, computer-architecture, compilers, cpu",
"url": null
} |
quantum-mechanics, hilbert-space, wavefunction, schroedinger-equation
Title: How do I find the wave function in a separable Hilbert Space? I am confused as to how I would go about finding the wave function in the Hilbert Space. As I understand, a wavefunction in the Hilbert space can be represented as
$$|\Psi\rangle = \sum_{n} c_n|\psi_n\rangle$$
and the wave function can be calculated with
$$i\frac{\partial |\psi\rangle}{\partial t} = H|\psi\rangle$$
I think I should use the second equation to try and find the wave function, then find a representation for it in terms of the orthonormal basis of the Hilbert Space. But I'm not exactly sure what that process would look like.
Also, I'm new to quantum mechanics and this site. If there's anything I need to do to improve my question or other resources I should look at, I'll gladly take any advice. I agree with the comment from ZeroTheHero: The standard text book examples will help you. Yet, it is also reasonable to discuss the following (rather simple but useful) computation scheme: | {
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computer-networks, security, authentication
There are methods that allow a client to know some secret value (the “password”) and to use it to authenticate to a server without requiring the server to know this secret value. They involve mathematical functions that have different properties compared to hashes. The most straightforward is public-key authentication: the client knows a private key, and the server knows the corresponding public key. The client signs a message using the private key, containing a nonce generated by the server. When the server receives the signed message, it can verify that the signature is genuine, using only the public key. | {
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"tags": "computer-networks, security, authentication",
"url": null
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organic-chemistry, hydrocarbons
After the attack of a nucleophile (pi bond) on the electrophilic carbocation, we have:
A: joining of the two rings with a bond, and the consequent carbocation (why did it get formed on that position? why not on the adjacent ones?)
B: rearrangement of the carbocation (why did it happen?)
C: loss of a proton to form the thermodynamically most favorable product (most substituted alkene)
The double bond was formed because of the loss of the $\ce{H+}$ ion in step C, formation of a negative charge at that position, and then the delocalisation of that negative charge into the adjacent empty p-orbital (of the $\ce{C+}$ position). | {
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Simple process of finding the mean and median dispersion: range ; quartile deviation, and standard.... The elements of measures of dispersion examples good measure of dispersion the interquartile range of the data specially it fails to any. Experts in your field units of measurements their average are called coefficients as original. Highest score to give any idea about the following dataset of final math exam for! Mean deviation ; standard deviation is large then there are large differences between individual data points ; quartile,! S Q test the most common way to measure how spread out ” the elements a... Cfa® and Chartered Financial Analyst® are registered trademarks owned by CFA Institute it! By n – 1 solutions from experts in your field of dispersion and is based on the value of.. Heights in cm of a specific unit, the mean may not be representative of the measures... Out a set of data about two things: 1 Quarterback B in unit! The variation of the deviations of individual | {
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$3 \cdot 2^x = 18^{x - 1}$
$\Rightarrow 3 \cdot 2^x = \left( 3^2 \cdot 2 \right)^{x - 1}$
$\Rightarrow 3 \cdot 2^x = 3^{2x - 2} \cdot 2^{x - 1}$
$\Rightarrow 3 \cdot 2^x = \frac 1{18} 3^{2x} \cdot 2^x$ .........2^x is never zero so we can divide by it
$\Rightarrow 3 = \frac {3^{2x}}{18}$
$\Rightarrow 3^{2x} = 3 \cdot 18 = 54$
here is where i said, "Oh, darn it! I need logs!"
$\Rightarrow 2x \ln 3 = \ln 54$
$\Rightarrow x \ln 9 = \ln 54$
$\Rightarrow x = \frac {\ln 54}{\ln 9} \approx 1.82$ as angel.white said
5. Originally Posted by Jhevon
an alternate approach. (i originally thought it could be done without logs, so i tried simplifying to equate like powers, but i had to end up using them at the end)
$3 \cdot 2^x = 18^{x - 1}$
$\Rightarrow 3 \cdot 2^x = \left( 3^2 \cdot 2 \right)^{x - 1}$
$\Rightarrow 3 \cdot 2^x = 3^{2x - 2} \cdot 2^{x - 1}$
$\Rightarrow 3 \cdot 2^x = \frac 1{18} 3^{2x} \cdot 2^x$ .........2^x is never zero so we can divide by it | {
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brain, perception, psychoneuropharmacology, psychophysics
Title: Consistency of consciouness So I was wondering if consciousness is continous and I found out it might not be the case. But in that case it begs a question, what if in every frame of consciousness my old me dies and new is reborn or rather there is nothing as consciousness but its just a reaction?
What I mean is if I clone a person, the clone would think its the original and we would be unable to determinate it either (if by clone i mean literall copy on the atomic level and with exclusion of any effect of quantum mechanics). If we would annihilate original and put clone into its place noone would be able to tell and to him it would look like everything is continous and nothing happened.
So can it be just illusion in our minds that we are continous sentient beings because we have access to our memory which tells us its like that, same as a clone but as the perception lost focus we die - frame stops to exists? | {
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general-relativity, black-holes, electric-fields
The closest analysis I found in the literature is the paper [3]. That paper considers a black hole that is already almost maximally charged ($Q\lesssim M$) and shows that we cannot make the horizon disappear ($Q>M$) by adding charged matter with $q/m>1$. Intuititively, this is because if $q/m$ is large enough to make the horizon disappear, then the matter will be repelled rather than attracted; and if we give it enough of a push (enough kinetic energy) to overcome this repulsion and force it into the black hole, then we have increased its energy enough so that $q/E$ is no longer large enough to make the horizon disappear. This doesn't quite answer the question, because the question is whether or not the horizon can be made smaller, and the paper [3] only explicitly asks whether or not we can make it disappear (and the answer is no). But the analysis in [3] is relatively detailed, and they also cite a couple of similar analyses, so with some effort, maybe those analyses can be adapted | {
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homework-and-exercises, classical-mechanics, energy, reference-frames, work
Title: Work done changes between reference frames? (This is not homework; a friend shared with me this puzzler and neither of us can figure it out.) Suppose you are in a plane traveling at velocity $v_1$ relative to the ground. The flight attendent pushes a cart of mass, say, $m$, accelerating it from rest to $v_2$, relative to the plane (so relative to the ground, its velocity goes from $v_1$ to $v_1+v_2$). From your perspective, the work done is then $$W = \Delta E = \dfrac{1}{2}mv_2^2$$ but from the perspective of the ground, the work done is $$W = \Delta E = \dfrac{1}{2}m(v_1+v_2)^2 - \dfrac{1}{2}mv_1^2 = \dfrac{1}{2}mv_2^2 + mv_1v_2.$$ Why are these quantities unequal? | {
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ros, ros2, bashrc
The first answer results in your overlay always being sourced every time you open a terminal. This contradicts the ROS2 tutorial that says you shouldn't source the overlay before building it.
Why do you need to source both /opt/ros/<distro>/setup.bash and ~/catkin_ws/devel/setup.bash?
I looked at the environment variables with printenv when I sourced both of them vs. just the latter and they were the same. It seems like you only need to source ~/catkin_ws/devel/setup.bash given that you have sourced /opt/ros/<distro>/setup.bash before running catkin_make. | {
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"lm_name": null,
"lm_q1_score": null,
"lm_q1q2_score": null,
"lm_q2_score": null,
"openwebmath_perplexity": null,
"openwebmath_score": null,
"tags": "ros, ros2, bashrc",
"url": null
} |
turing-machines, simulation
\end{array}
$$
On the second go around, the first tape reads a $0$, so we write to the third tape instead:
$$
\begin{array}{lc}
\text{Tape 1:} & 10\underset{\wedge}{1}01\sqcup\sqcup\sqcup\ldots\\
\text{Tape 2:} & 1\underset{\wedge}{\sqcup}\sqcup\sqcup\sqcup\sqcup\ldots\\
\text{Tape 3:} & 1\underset{\wedge}{\sqcup}\sqcup\sqcup\sqcup\sqcup\ldots\\
\end{array}
$$
The single-tape machine simulates this by moving the underline (by using the alternate version of the characters in $\Gamma'$, and writing to the appropriate simulated tape. So after the first step, the combined tape looks like:
$$
\#1\underset{\wedge}{\underline{0}}101\#1\underline{\sqcup}\#\underline{\sqcup}\#\sqcup\sqcup\sqcup\ldots
$$
After the second step:
$$
\#10\underset{\wedge}{\underline{1}}01\#1\underline{\sqcup}\#1\underline{\sqcup}\#\sqcup\sqcup\sqcup\ldots
$$ | {
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"tags": "turing-machines, simulation",
"url": null
} |
python, beginner, python-3.x, playing-cards
if not player_stands:
deal_one_card(shoe, player)
if score(player) > 21:
break
# After loop: dealer takes cards, etc.
results()
The results can stay mostly the same. But some of your passed in variables are not needed, since you can compute them from the other data. For example, if the len(player) is 2, that's the first_hand flag. What's key is that results is outside the loop, not inside. You print the results after breaking/exiting from the loop. | {
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"tags": "python, beginner, python-3.x, playing-cards",
"url": null
} |
quantum-mechanics, electromagnetism, quantum-spin
It is helpful to divide physics up into 'classical physics' and 'quantum physics'. Quantum physics is a model which includes classical physics as a kind of subset.
According to classical physics, you can have a current which produces a magnetic field without producing any emitted radiation. An ordinary current-carrying wire is an example, if the current is constant. If the wire makes a loop then you have a loop of current and the magnetic field far from the loop has the same form as the one produced by a charged particle with spin. | {
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Shell method: Can be used for all functions, but typically for functions that are hard to be expressed explicitly. Functions can be sliced into thin cylindrical shells, like a piece of paper wrapped into a circle, that stack into each other. For example, y = x(x - 1)³(x + 5) from [-5, 0] rotated about the y-axis (hopefully a good example, because the washer method would be difficult to use).
Hope that I helped, and correct me if I'm wrong.
• When determining the volume of a shell, I'm still confused on how you are getting the bounds? Specifically in problem 3. How did you determine what a and b was in problem 3?
• To elaborate on finding the intercept point, you can set the equations equal to one another and solve for zero.
• For problem 2, I saw that the function was even and the interval was symmetrical, and decided to factor out 2 and evaluate the integral on the interval (0,1). The answer I got was 5pi/3. Why didn't this give the correct answer? | {
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"url": "https://www.khanacademy.org/math/old-ap-calculus-bc/bc-applications-definite-integrals/bc-shell-method/a/stacy-scaling-3"
} |
sdformat
(I got it from the gazebo_worlds package in ROS)
When I run $ROS_ROOT/simulator_gazebo/gazebo/gazebo/bin/gzsdf print simple_box.urdf, I get the SDF translation out:
Warning [parser.cc:382] SDF has no <sdf> element in file[/home/jamuraa/ros/simulator_gazebo/gazebo_worlds/objects/simple_box.urdf]
Warning [parser.cc:291] parse from urdf file [/home/jamuraa/ros/simulator_gazebo/gazebo_worlds/objects/simple_box.urdf].
<sdf version='1.3'>
<model name='simple_box'>
<link name='my_box'>
<pose>0.000000 0.000000 2.000000 0.000000 -0.000000 0.000000</pose>
<inertial>
<pose>1.000000 0.000000 0.000000 0.000000 -0.000000 0.000000</pose>
<mass>1.000000</mass>
<inertia>
<ixx>1.000000</ixx>
<ixy>0.000000</ixy>
<ixz>0.000000</ixz>
<iyy>100.000000</iyy>
<iyz>0.000000</iyz>
<izz>1.000000</izz>
</inertia>
</inertial>
<collision name='my_box_geom'> | {
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• Yeah the greater than proof is fishy now.. I will check it again. But norm is a non negative quantity so cannot be $-\infty$ for sure. So its in $(0,1]$ – mm-crj Dec 8 '18 at 10:09
• Yes, that's true. Basically all I am saying is that the way it is currently written, this estimate only gives $\|f\|_{X/M}\ge-\infty$, which is nothing new - as you correctly say. I left a few comments about this question in the functional analysis chatroom - maybe somebody who has an idea how to continue will notice that it was mentioned there. (Of course, you're welcome in that room, too.) – Martin Sleziak Dec 8 '18 at 10:14
• I am new to this idea of chat rooms but I will have a look .. Anyway, that kernel idea was brilliant .. #kurnis – mm-crj Dec 8 '18 at 10:17 | {
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control-engineering, control-theory, dynamics, kinematics
My goal is to simulate PID control of the planar two-link manipulator, where each joint is actuated by an independent DC motor. The input is two continuous signals $$\theta_1(t), \theta_2(t)$$
which represent the desired angle for each joint at time t.
Following this paper: Modeling a Controller for an Articulated Robotic Arm, I can obtain an expression for the voltage I need to apply to each motor to achieve a desired angle. The paper also describes the PID controller necessary to maintain the desired angle given an error signal $$e(t) = \theta_{desired}(t)-\theta_{actual}(t)$$
Since each motor is controlled independently, coupling effects among joints due to varying configurations during motion are treated as disturbance inputs. My question is: how can I model this coupling effect in order to "simulate" the error signal e(t) for system under ideal conditions? By ideal conditions I mean that the disturbance due to coupling among joints accounts for 100% of the error signal. | {
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"tags": "control-engineering, control-theory, dynamics, kinematics",
"url": null
} |
quantum-field-theory, energy, stress-energy-momentum-tensor, exotic-matter
There is a big caveat. To be sure about this one needs a theory that combines quantum field theory and general relativity, and no such theory exists at present. Conclusions about negative energy density are based on semi-classical calculations, where classical metric tensor is coupled to quantum fields/particles. Such coupling leads to violations of fundamental principles of quantum field theory and/or general relativity, and semi-classical models are therefore self-inconsistent. From Rickles's paper (p.20):"...a classical field coupled to a quantized source will violate the uncertainty principle, since one will be able to use the classical field to determine with a precision greater than that allowed by the uncertainty relations the simultaneous position and momentum of a particle. Furthermore, if we adopt a collapse interpretation of quantum theory, so that the classical field’s measurement sends the particle’s state from a superposition into a definite state, then the principle of | {
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tools used in Bayesian statistical methods." For the analysis of contingency tables, the BayesFactor package contains a function called contingencyTableBF(). I’ve rounded 15.92 to 16, because there’s not really any important difference between 15.92:1 and 16:1. For example, suppose that the likelihood of the data under the null hypothesis $$P(d|h_0)$$ is equal to 0.2, and the corresponding likelihood $$P(d|h_0)$$ under the alternative hypothesis is 0.1. In our reasonings concerning matter of fact, there are all imaginable degrees of assurance, from the highest certainty to the lowest species of moral evidence. Do you want to be an orthodox statistician, relying on sampling distributions and $$p$$-values to guide your decisions? You keep using that word. As I discussed back in Section 16.10, Type II tests for a two-way ANOVA are reasonably straightforward, but if you have forgotten that section it wouldn’t be a bad idea to read it again before continuing. Read this book using Google | {
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} |
telescope, newtonian-telescope
All the light you see comes into your eye through your pupil. The pupil of an average adult eye, when fully dark adapted, has a diameter of about 6 or so mm. That's about 28 or so square mm of light gathering area. A modest 80mm telescope (80mm being the aperture) has an area of over 5,000 square mm - over 150 times as much light gathering area. All that light is then funneled down and concentrated on your eye. This makes dim objects much brighter. Magnification helps, but it doesn't matter how big an object appears if you can't see it at all. | {
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gravity, standard-model, spacetime-dimensions, interactions, fine-tuning
that unknown physics at the Planck scale should contribute via quantum effects to the weak scale we observe. Just by naive dimensional analysis there is no obvious reason why a sum of different terms, each of which is of order the Planck scale, should cancel amongst each other to produce a much smaller scale (the weak scale we observe). | {
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c#, performance, winforms, timer
protected override void OnFormClosing(FormClosingEventArgs e)
{
ProcessTrackerIcon.Visible = false;
base.OnFormClosing(e);
}
private void ProcessTrackerIcon_MouseDoubleClick(object sender, MouseEventArgs e)
{
WindowState = FormWindowState.Normal;
ShowInTaskbar = true;
ProcessTrackerIcon.Visible = false;
}
private void ProcessTrackerIcon_MouseClick(object sender, MouseEventArgs e)
{
WindowState = FormWindowState.Normal;
ShowInTaskbar = true;
ProcessTrackerIcon.Visible = false;
} | {
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The most interesting research directions in this area is actually to bound the number of iterations to an $$\epsilon$$-approximate solution, rather than the exact solution. In analyzing the convergence rates, you will end up trying to approximate regions on the complex plane using polynomials. There's a connection to conformal maps and Christoffel-Schwarz transforms. Also, there is the functional analysis aspect once you allow $$A$$ to be a linear operator (sort of like an infinite-dimensional matrix).
To learn more on this area, I would highly recommend starting with Greenbaum's book (which is easier to read) and moving on to Saad's book (which is more comprehensive).
@book{greenbaum1997iterative,
title={Iterative methods for solving linear systems},
author={Greenbaum, Anne},
volume={17},
year={1997},
publisher={Siam}
}
title={Iterative methods for sparse linear systems},
volume={82},
year={2003},
publisher={siam}
}
I would also recommend Lecture 32 onwards from Trefethen's book. | {
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} |
human-biology, physiology, pathology
Title: What is the "lifecycle" of an average eschar and what types of cells are involved in each stage? (after some deliberation in the comments, I've decided to make the question more general)
An eschar or "dry scab" often forms at a site of injury over a large cut or sore.
It seems as though the healing scab portion binds more strongly to the other scab cells than to those of the surrounding healthy tissue initially, as evidenced by the ability to remove the scab en masse without disturbing the edges of the actual wound (in surgical debridement or when the area is "picked" at). Then, the eschar bonds then bonds more strongly with the edges of the wounds (so it's more difficult to remove), and then finally, the underlying newly formed skin seems to push it off completely. | {
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makefile, make
# "all" is the classical default target
all: main
createdir:
$(SILENCER)mkdir -p $(OBJDIR)
main: $(OBJS)
#@echo " LINK $^"
$(SILENCER)$(CC) $(CFLAGS) -o $@ $^
# put object and dependency files away from the sources
# create the dir before building into it
$(OBJDIR)/%.o: $(SRCDIR)/%.c | createdir
#@echo " CC $<"
$(SILENCER)$(CC) $(CFLAGS) -c -o $@ $<
clean:
$(SILENCER)$(RM) -f *~ core main
$(SILENCER)$(RM) -r $(OBJDIR)
.PHONY: clean all
# dependencies won't turn into a default target here
-include $(DEPS) | {
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} |
ros, python, multiarray, array, publisher
Comment by dual-swordsman on 2019-06-13:
@PeteBlackerThe3rd @gvdhoorn thank you so much for detailed explanation for my questions. Everything is clearing up now. I really appreciate both of your help. I will take the suggestion of using custom message as it is much more suitable and simpler in my project. :D
Comment by dual-swordsman on 2019-06-13:
How do I say that this question is already answered?
Comment by PeteBlackerThe3rd on 2019-06-13:
Great, glad we could help. If you click the tick mark at the top left of this answer it will mark it as accepted.
Comment by dwd394 on 2022-08-01:
Thank you! :) | {
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ros, teleop
Originally posted by gerson_n on ROS Answers with karma: 43 on 2017-08-13
Post score: 0
It looks like you have a PID controller to control the speed of each motor, but from what you describe it seems like it is always commanding maximum speed from your motor, regardless of the requested speed.
It may be that your PID controller is not working, or it could be that encoders aren't giving good feedback signals.
Since you are using a pre-built PID controller, I would check the encoders first. You should be able to see the RPM from both encoders by echoing the rpm topic, with
rostopic echo rpm
You should be able to turn your motors by hand and see the RPM values change. If you don't, I would double check that your encoder wires are hooked up, and that your arduino sketch has the correct pin settings for both encoders.
Originally posted by ahendrix with karma: 47576 on 2017-08-13
This answer was ACCEPTED on the original site
Post score: 1 | {
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} |
java, parsing, android, graph
catch (IOException e) {
return;
}
}
Node.java
public class Node {
private int ID;
private float x;
private float y;
private float z;
private ArrayList<Edge> edges = new ArrayList<Edge>();
/* Constructor */
public Node(int ID, float x, float y, float z) {
this.ID = ID;
this.x = x;
this.y = y;
this.z = z;
}
/* Helper constructor for String input */
public Node(String sID, String sX, String sY, String sZ) {
this(Integer.parseInt(sID), Float.parseFloat(sX), Float.parseFloat(sY), Float.parseFloat(sZ));
}
/* Example: [id:569, x:1294, y:1399, z:-688, nodeConnections:(568, 570, 4322)] */
public String toString() {
String s = "[id:" + ID + ", x:" + (int)x + ", y:" + (int)y + ", z:" + (int)z + ", edges:("; | {
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physical-chemistry, boiling-point, vapor-pressure, mixtures, distillation
Why does this combined vapor pressure reaching the atmospheric pressure lower the boiling point of both liquids, while these two liquids are in equilibrium with their vapor independent from each other? What kind of interaction does these two liquids has that causes this? With comparable boiling points like for water and benzene mixture at constant pressure, neither of liquids boils when sum of partial pressures of their vapors overcomes air pressure. They are just quickly evaporating, as this evaporation is pushing air and own vapors away, not being controlled by diffusion nor convection like ordinary evaporation.
In a way, it is "boiling without boiling", or "boiling from liquid surfaces" what is not real boiling as forming bubbles inside the liquid. | {
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"tags": "physical-chemistry, boiling-point, vapor-pressure, mixtures, distillation",
"url": null
} |
javascript, performance, jquery, form
$("#step2_confirm_button").click(function() {
$("#step2_confirm").dialog("destroy");
nextStep(2);
setTabOn(2);
});
$("#step2_cancel_button").click(function() {
$("#step2_confirm").dialog("destroy");
});
$(".step").hide();
$("#step1").show();
$("#step1_tab").addClass("active");
$("#step2_confirm").hide();
$("#step1_next").click(function() {
var flagFirstStepError = 0;
var flagFirstStepEmpty = 0;
var flagFirstStepEmail = 0;
$("#step1_errors").html("");
$(".required").each(function() {
if ($(this).val() == "") {
flagFirstStepError = 1;
return false
}
else {
flagFirstStepEmpty = 1;
}
}); // end each | {
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python, array, python-3.x
def get_command_params():
commands = {
"/add": lambda *value : value_list.extend(list(value)),
"/rvalue": lambda value : value_list.remove(value),
"/rindex": lambda value : value_list.pop(int(value)),
"/print": lambda : print(value_list),
"/help": cmd_help
}
while True:
input_cmd = input("Enter a command: ")
#Separate arguments
command = ""
current_args_index = -1
args = []
last_char = ""
for char in input_cmd:
#Update separator
if char == "/" or char == " ":
last_char = char
if last_char == "/":
command += char
elif last_char == "append":
args[current_args_index] += char
elif last_char == " ":
args.append("")
#To append individual characters to same index
last_char = "append"
++current_args_index | {
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"url": null
} |
forces, friction
If you make the surfaces repel each other then you remove this mechanim for dissipation of energy and you reduce the friction. There are lots of ways to do this. For example motor oils contains additives like molybdenum dithiocarbamate that bond to metal surfaces and make the surfaces repel each other - these additives are even called friction reducers. Other methods include using electrical double layers or polymers. An air bearing sort of works like this, with the pressure in the layer of air causing the metal surfaces to stay apart.
But even in examples like these where the surfaces don't touch the friction isn't reduced to zero. You get some energy dissipation in the material keeping the surfaces apart, and you also get some energy dissipation due to deformations of the bulk as the surfaces press against each other. | {
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javascript, json
.
function processResponse(data) {
if (!data.query || !data.query.users || !data.query.users[0]) return {};
var user = data.query.users[0];
return {
isInvalid: 'invalid' in user,
isMissing: 'missing' in user,
groups: user.groups || [],
editCount: ('editcount' in user) ? user.editcount : null,
registration: ('registration' in user) ? parseDate(user.registration) : null,
isBlocked: 'blockexpiry' in user,
gender: ('gender' in user && user.gender != 'unknown') ? user.gender : null,
lastEdited: (data.query.usercontrib
&& data.query.usercontribs[0]
&& data.query.usercontribs[0].timestamp)
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But where is written that the first four dice have be successful (and in the same time the four others not)? We may select four successful dices by $$_8 \mathop{C}_4 = 70$$ ways. So all successful possibilities count $$70 \cdot 4^4 \cdot 6^4$$ which gives the result $$23{.}224{.}320$$.
So the general formula for the number of desired outcomes is
$$_n {\mathop{C}}_k \cdot p^k \cdot q^{n-k}$$
Note: Please don't forget to divide it by the number of all possibilities, i. e. by $$(p + q)^n$$ to compute the probability. | {
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earth-system
Title: What is the importance of oxidation process? I am asking this question, because I don't know the importance of oxidation process at all, and this question pops into my mind because currently I've been researching why apples turn into brown color when is it exposed to air/oxygen.
And I find at that the cause of this is due to the Polyphenol Oxidase (PPO) enzymes being present inside the apple, when the enzyme is exposed to air/oxygen, it triggers a chemical reaction called Oxidation. Perhaps this is better put on the Chemistry SE page since oxidation is much more important than beyond earth sciences, but I'll give my take on it from an atmospheric sciences perspective.
If oxidation isn't allowed to take place, then the hydroxyl radical ($\ce{^*OH}$), nicknamed the detergent of the atmosphere, cannot remove pollutants from the atmosphere. I think it is evident why removing pollution is a good thing.
This is just one of many uses that oxidation has. | {
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# Find the Jordan normal form of a nilpotent matrix $N$ given the dimensions of the kernels of $N, N^2, N^3$
Let $N\in \text{Mat}(10 \times 10,\mathbb{C})$ be nilpotent. Furthermore let $\text{dim} \ker N =3$, $\text{dim} \ker N^2=6$ and $\text{dim} \ker N^3=7$. What is the Jordan Normal Form?
The only thing I know is that there have to be three blocks, since $\text{dim} \ker N = 3$.
• What does nilpotence tell you about the eigenvalues? – Travis Feb 8 '16 at 11:48
• the only eigenvalue is zero – Hans Feb 8 '16 at 11:51
This can be seen in term of partitions.
An $n \times n$ nilpotent matrix $N$ can be described via a partition $$p = (n_{1}, n_{2}, \dots, n_{k})$$ of $n$, with $n_{1} \ge n_{2} \ge \dots \ge n_{k} > 0$, which records the size of the nilpotent Jordan block in a Jordan normal form. | {
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algorithms, quantum-computing, circuits
What that in mind, you can probably find a version of the details you're looking for in Fast Modular Exponentiation Architecture for Shor's Factoring Algorithm by Pavlidis and Gizopoulos. The exact circuit layout is lengthy and complex and probably too much for an answer here. The paper has lots of diagrams though and a quick scan should should provide you with a rough feel for the circuit construction. Unsurprisingly, the circuit makes heavy use of Hadamard gates and controlled phase-shift operators both to implement the inverse QFT and the modular exponentiation circuit. | {
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python, beginner, python-3.x, tkinter
("3" , 2, 4, self.NUM_COLOR , lambda: self.press("3")),
("+" , 3, 4, self.OPERATOR_COLOR , lambda: self.press("+")),
("⌫" , 0, 5, self.NUM_COLOR , self.backspace ),
("0" , 1, 5, self.NUM_COLOR , lambda: self.press("0")),
("." , 2, 5, self.NUM_COLOR , lambda: self.press(".")),
("=" , 3, 5, "orange" , lambda: self.evaluate(self.expression)),
] | {
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} |
c++, beginner, game
}
void winBattleBoss() { //battle victory function with Boss
int xp = rand() % 10 + 10; //obtained in battle
cout << "\t\t\t\t\t\t You have won! Received:\n";
cout << "\t\t\t\t\t\t Skill points: 10\n";
cout << "\t\t\t\t\t\t Experience: " << xp << "\n";
experience += xp; //received in battle, add to the total amount
if (experience >= new_lvl_xp) {
cout << "\t\t\t\t\t\tYou've got a new level\n";
++hero_level;
experience -= new_lvl_xp;
new_lvl_xp += (new_lvl_xp / 4);
}
++boss_lvl;
if (boss_lvl == 1) {
boss_kind = "Satan";
}
else if (boss_lvl == 2) {
boss_kind = "Lucifer";
boss_hp = 2000;
boss_damage = 500;
boss_shield = 200;
}
else if (boss_lvl == 3) {
boss_kind = "Leviathan";
boss_hp = 4000;
boss_damage = 800;
boss_shield = 300;
} | {
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bioinformatics, bacteriology, transcription, binding-sites
Secondly; Since the genome for B. subtilis is available, would I be able to find out binding site motifs for all the sigma factors, and then determine which is/are contained within the promoter for the $\alpha$ subunit? I.e. if I know the TF/SF sequence, is there a way of finding out which promoters it can bind to?
Finally; the main purpose of this question is to find out how rpoA is transcribed, and I know that in general sigma factors are required in bacteria for specific transcription initiation, but could it be that rpoA transcription is non-specific, and that the sigma factor is just not involved in its transcription?
Please let me know if there is anything I can do to improve my question, I can provide references if it would be a good idea. Thanks! I don't have a definitive answer, but I can perhaps offer some insight. Given the necessary function of rpoA, I would be willing to bet that SigA is the factor responsible for its transcription, so I will focus my discussion there. | {
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"tags": "bioinformatics, bacteriology, transcription, binding-sites",
"url": null
} |
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