text stringlengths 1 1.11k | source dict |
|---|---|
electromagnetism, visible-light, scattering, approximations, scattering-cross-section
Where $\lambda_0 =\frac{c}{\nu_0}$ and $\gamma$ represents the part of $\Gamma$ related to dissipation due to irradiation. (In general $\Gamma= \gamma +\gamma'$ where, $\gamma'$ is dissipation due to other effects, such as the presence of atoms near the electron).
How to prove the previous approximation mathematically? Maybe this helps.
$$\frac{\omega ^4}{(\omega ^2 - \omega_0^2)^2+(Γ\omega)^2} = \frac{\omega ^4}{(\omega - \omega_0)^2(\omega + \omega_0)^2+(Γ\omega)^2}$$
Since $\omega \approx\omega_0$, we can consider that $(\omega + \omega_0)^2\approx(\omega + \omega)^2 \approx (\omega_0 + \omega_0)^2\approx4\omega^2$ because good ol' physics and totally valid approximations. So, the relation becomes
$$\frac{\omega ^4}{4\omega^2(\omega - \omega_0)^2+(Γ\omega)^2} = \frac{1}{4} \frac{\omega ^2}{(\omega - \omega_0)^2+(Γ/2)^2} $$
This can also be considered as
$$ \frac{1}{4} \frac{\omega_0 ^2}{(\omega - \omega_0)^2+(Γ/2)^2} $$
Based on the same approximation made above. | {
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"url": null
} |
be used in parallel with spring or truss elements, where the stiffness of the spring or truss elements is chosen so that the stable time increment of the dashpot and spring or truss is larger than the stable critical time. | {
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"openwebmath_score": 0.5827639102935791,
"tags": null,
"url": "http://iquk.acpm.it/nonlinear-spring-mass-system.html"
} |
geometry, spacetime-dimensions, visualization
Title: 4- dimensional space geometry, what is the point? I just read about the 4 dimensional space. I found a nice article describing how to visualize a 4-D object into our 3-D world. This is really fascinating.
However, what's the point of researching in this area? Is there any practical use of the 4-D space objects? It certainly has the POTENTIAL to be useful. It is entirely possible, and partially theorized, that our universe is comprised of additional dimensions and we can only perceive three spatial and one time dimension. Some variants of string theory, such as M-Theory propose up to 11 spatial dimensions.
If it is indeed the case that there are additional spatial dimensions, then it would be extremely 'useful' and 'practical' to research and visualize these fields. Another use of the research is to develop tests that may determine if we are existing in n-dimensional space or not, and if we are, how (if at all) we could interact with them. | {
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$3\times8\times8\times2\times9\times9\times1\times10=311$ $040$
$3\times8\times8\times2\times9\times9\times9\times1=279$ $936$
$3\times8\times8\times8\times2\times1\times10\times10=307$ $200$
$3\times8\times8\times8\times2\times9\times1\times10=276$ $480$
$3\times8\times8\times8\times2\times9\times9\times1=248$ $832$
$3\times8\times8\times8\times8\times2\times1\times10=245$ $760$
$3\times8\times8\times8\times8\times2\times9\times1=221$ $184$
$3\times8\times8\times8\times8\times8\times2\times1=196$ $608$
Sum: $7$ $593$ $642$
Permutations whose first successes occur at the second digit place:
$7\times3\times2\times1\times10\times10\times10\times10 = 420$ $000$
$7\times3\times2\times9\times1\times10\times10\times10 = 378$ $000$
$7\times3\times2\times9\times9\times1\times10\times10 = 340$ $200$
$7\times3\times2\times9\times9\times9\times1\times10 = 306$ $180$
$7\times3\times2\times9\times9\times9\times9\times1 = 275$ $562$ | {
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"url": "https://www.physicsforums.com/threads/the-dollar-bill-problem.750748/"
} |
javascript
This function will fetch all mandatory elements :not(.optional).
Each one should have a valid value. If not, return false.
Pass this validation value to another function that handles UI state.
Here, if the value is true, enable button and show optional fields
If false, disable buttons and hide optional fields.
Just JS
function empty_check() {
var forms = document.getElementsByTagName("form");
for (var i = 0; i < forms.length; i++) {
handleUIState(forms[i], validateForm(forms[i]));
}
}
function validateForm(form) {
var list = form.querySelectorAll('textarea, input:not(.optional)');
var valid = true;
for (var i = 0; i < list.length; i++) {
valid = valid && !!list[i].value;
}
return valid;
}
function handleUIState(form, valid) {
var optional = form.querySelector('.optional');
if (optional) {
optional.style.display = valid ? 'block' : 'none';
}
form.querySelector('button').disabled = !valid
}
<body onload="empty_check()"> | {
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"openwebmath_score": null,
"tags": "javascript",
"url": null
} |
performance, datetime, vba, excel
'MACHINE
'Copy machine value from row 19 of current column
Sheets("Output").Cells(NextRow, 3) = Sheets(Worksheet).Cells(19, y)
'RUN QUANTITY
'Copy run quantity from cell block. Offset column + 4
Sheets("Output").Cells(NextRow, 4) = Sheets(Worksheet).Cells(x, y + 4)
'Indexing for debugging
'Sheets("Output").Cells(NextRow, 5) = x
'Sheets("Output").Cells(NextRow, 6) = y
End If
End If
Next x
Next y
End If
Next ws
Application.ScreenUpdating = True
MsgBox "All done."
Exit Sub
PROC_ERR:
MsgBox "Error: " & Err.Number & "; " & Err.Description
Exit Sub
End Sub Overall not bad. Most of the issues are minor and stylistic, so don't let my brain dump below overwhelm... | {
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"tags": "performance, datetime, vba, excel",
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} |
first-order-logic
My personal favorite example is $\mathsf{FOL}(Q_\mathit{fin})$, where we add to first-order logic the quantifier "For finitely many." The point is that $(i)$ unlike $\mathsf{FOL}$ this logic we can pin down the standard model of arithmetic $\mathcal{N}=(\mathbb{N};+,\times)$ up to isomorphism, but $(ii)$ like $\mathsf{FOL}$ this logic can in $\mathcal{N}$ give an inductive definition of its own full theory of $\mathcal{N}$. These facts, combined with (the proof of) Tarski's undefinability theorem, give us the failure of Beth definability (a corollary of Craig interpolation) for $\mathsf{FOL}(Q_\mathit{fin})$.
Vaananen's article The Craig interpolation theorem in abstract model theory contains a lot of good information about this topic, albeit at a high level. | {
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algorithms, complexity-theory, np-complete
So is it enough to to just construct a certain instance of the problem B we want to prove to be NP-complete, or do we need to reduce a known problem A to the general case of B?
I am confused about this, because, for example, we can prove INDEPENDENT-SET to be NP-complete by reducing CLIQUE to it, and it involves just taking the inverse of the graph and then finding a clique in it. This case does reduce problem CLIQUE to the general case of INDEPENDENT-SET.
P.S. I am very new to NP-completeness. When you reduce Hamiltonian-Path (HP) to Spanning-Tree-with-inner-degree-$k$ (ST), you show that if you could solve ST then you could solve HP, and moreover in a specific way. If the resulting tree is not completely general, say it is always a Hamiltonian path with attached leaves, then you are actually proving the stronger result that the corresponding promise problem is already NP-hard. | {
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java
import java.io.IOException;
import java.time.Duration;
import java.time.LocalDate;
import java.util.*;
import java.util.stream.Collectors;
public class Scraper {
private static final Logger logger = LogManager.getLogger(Scraper.class);
private final String urlPrefix;
private final String urlSuffix;
private final Duration timeout;
private final int totalTries;
private WeeklyResult latestResult;
public Scraper(final String urlPrefix, final String urlSuffix, final Duration timeout, final int totalTries) {
this.urlPrefix = urlPrefix;
this.urlSuffix = urlSuffix;
this.timeout = timeout;
this.totalTries = totalTries;
this.latestResult = new WeeklyResult("1973-08-16","N/A");
} | {
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"tags": "java",
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} |
java, matrix
return new CompletedMatrix(result);
}
private void validateMatrix(Matrix otherMatrix) {
Objects.requireNonNull(otherMatrix, "`otherMatrix` parameter may not be null.");
if ((this.getRows() != otherMatrix.getRows()) || (this.getColumns() != otherMatrix.getColumns())) {
throw new IllegalArgumentException("Cannot operate on matrixes of different sizes. This matrix has "
+ this.getRows() + " rows and " + this.getColumns() + " columns, while the argument matrix has "
+ otherMatrix.getRows() + " rows and " + otherMatrix.getColumns() + "columns");
}
}
} | {
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quantum-mechanics, measurement-problem
After comments by both Timaeus and Rococo I realize that my question can be boiled down to a far simpler experimental setup. A single electron being deflected by a single Stern-Gerlach magnet. The wave function after deflection will be something like $\frac{1}{\sqrt{2}}|+>+\frac{1}{\sqrt{2}}|->$, and my question amounts to: where did the $\frac{1}{\sqrt{2}}$ factors come from? Do they come from pure Schrodinger evolution, or do you assume unitarity and therefore essentially apply the $\frac{1}{\sqrt{2}}$ by hand because you know the probabilities have to sum to 1? Ie can it be proven from pure Schrodinger evolution without any renormalization that the wave function evolves to $\frac{1}{\sqrt{2}}|+>+\frac{1}{\sqrt{2}}|->$ rather than the more intuitive $\frac{1}{2}|+>+\frac{1}{2}|->$ that is subsequently renormalized to enforce the expected unitarity? Actually, I think that what you ask for is impossible, or at least not as physically meaningful as one might expect. This is because of | {
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relativity, centripetal-force
Title: Relativity's effects on centripetal motion I am wondering if, for a particle moving close to the speed of light (so that we must examine things relativistically rather than classically) does the centripetal force equation $F_c=m\frac{v^2}{r}$ still hold? If not, what is the correct equation for centripetal force? Since relativistic momentum p = $\gamma m_0 v$, then:
$\vec{F} = \frac{d\vec{p}}{dt} = \gamma m_0 \frac{d\vec{v}}{dt}$, which, when solved using vectors is equal to: $\gamma m_0 \frac{v^2}{r}$ | {
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acceleration due to gravity. Some examples of circular motion are a ball tied to a string and swung in a circle, a car taking a curve on a track etc. Linear motion at an angle downward. The height of ball A when it encounters ball B : h = vo t + ½ g t2 = (10)(1.2) + 1/2 (-10)(1.2)2 = 12 – 5(1.44) = 12 – 7.2 = 4.8 meters. Linear and Vertical Motion review Sheet Honors Physics Oct 28/29, 2020 Terms/Concepts to know Define and give an example of each : Kinematics Definition: The branch of mechanics that studies the motion of a body or a system of bodies without consideration given to its mass or the forces acting on it. Revision Video . As you proceed through this part of Lesson 2, pay careful attention to how a conceptual understanding of projectiles translates into a numerical understanding. Define vertical mobility. Kinematic Equations for a Projectile Horizontal motion Vertical motion a x = 0 a y = g = - 10 m/s 2 t x v x v y = v oy + g t x = v x t 2 2 1 gt t v y oy Notice the minus | {
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"url": "https://zoldterv.hu/lcdh7cxo/635482-vertical-movement-physics"
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quantum-mechanics, angular-momentum, quantum-spin
$$
P(\uparrow)_{\hat y}= \vert\langle\chi\vert \uparrow\rangle_{\hat y}\vert^2\, ,\qquad P(\downarrow)_{\hat y}=\vert\langle\chi\vert \downarrow\rangle_{\hat y}\vert^2
$$
where $\vert\uparrow\rangle_{\hat y}$ is the eigenstate of $\sigma_y$ with eigenvalue $+\hbar/2$. In your case, we have
$$
P(\uparrow)_{\hat y}=\frac{1}{50}\, ,\qquad
P(\downarrow)_{\hat y}=\frac{49}{50}
$$
so
$$
\langle S_y\rangle = \frac{\hbar}{2}\frac{1}{50}-\frac{\hbar}{2}\frac{49}{50}=-\frac{12\hbar}{50}\, .
$$
What the average values tell you is the "direction" of the spin. The unit vector $\boldsymbol{\hat n}=(\sigma_x,\sigma_y,\sigma_z)=(0,-24/25,-7/25)$ points in a definite direction, and if you were to choose your quantization axis along this direction, the system would be in a spin-up state, i.e it would be an eigenstate of
$$
\boldsymbol{\hat n}\cdot \vec S=
\frac{1}{25}\left(
\begin{array}{cc}
-7 & 24 i \\
-24 i & 7 \\
\end{array}
\right)\, . \tag{1}
$$ | {
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c, console, io
Title: Print output one word per line - K&R Exercise 1-12 When writing this code I found myself getting more and more complex. When I got to the solution I trimmed the excess parts I'd thought I needed from before, but didn't actually need. The example of wc.c had some definitions for IN and OUT. Why didn't I need those for writing this example?
If there are any bugs or improvements I can make, let me know.
include <stdio.h>
/* prints its input one word per line */
main()
{
int c;
c = 0;
while ((c = getchar()) != EOF) {
if (c == ' ')
putchar('\n');
else
putchar(c);
}
} include <stdio.h>
You're missing a # there, copy/paste issue?
main()
That's been out of style for a very long time, and is in fact no longer valid according the standard (from C99 and on). Always specify the return type (for main and all other functions).
int main()
int c;
c = 0; | {
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area from graphs The figure shows the areas of regions bounded by the graph off and the x-axis. Properties of Definite Integrals. Find the Riemann sum corresponding to the regular partitions of size n = 1, 2, 4, and 8, using the midpoint of each subinterval. +îue the Definition of a Definite Integral If fis defined on [a, b] and the limit exists then (141+0 -- owe-r 09 in+egrahon b- upper ) imi¥ AXI =the ith su)oink0JQR 5. Subsection 11. The limit of Riemann sum is called definite integral. Evaluate approximations using the trapezoidal rule. Riemann sums are covered in the calculus lectures and in the textbook. Evaluate a definite integral using properties of definite integrals. Evaluate a definite integral using limits. The area under a curve can be approximated by a Riemann sum. The geometric interpretaion of the definite integral is as the area of the semicircle from to. $$\lim_{n \rightarrow \infty } \sum_{k=n}^{2n} \sin(\frac{\pi}{k} )$$ I know the theory and I solved other exer. | {
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"url": "http://clandiw.it/jqeo/definite-integral-as-the-limit-of-a-riemann-sum-calculator.html"
} |
electromagnetism, special-relativity, momentum, conservation-laws, causality
Edit after comment:
The basic frame of all theories in physics, mainstream at present, is quantum mechanical, and the mainstream accepts that the standard model elementary particles are the basic constituents
In this model the static electric and magnetic fields are built up from very low energy photons, the basic constituents of light and all electromagnetic waves. When your electromagnet is turned off, a pulse is created traveling in vacuum of very long wavelength photons which carry momentum and energy and transfer it by collision to the live electromagnet.
Alternatively, within classical electrodynamics, again a pulse of light is generated (because changing magnetic fields generate electric fields and elecromagnetic radiation according to Maxwell's equations), and this pulse will have energy and momentum according to the classical model. | {
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evolution, natural-selection, mutations
Introductory course to evolutionary biology
You probably want to have a look at an introductory course to evolutionary biology such as Understanding Evolution. | {
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So
$7^{10} = (7^2)^{5} \equiv 11^5$ (mod 19)
You can probably do this one by directly but we can simplify this one last time:
$11^2 \equiv 7$ (mod 19)
$11^3 \equiv 1$ (mod 19)
So finally:
$4^{30} \equiv 7^{10} \equiv 11^5 = 11^2 \cdot 11^3 \equiv 7 \cdot 1 = 7$ (mod 19)
$4^{30} \equiv 7$ (mod 19)
-Dan
I am still a little confused as to how you got the very first equation though (listd below)...I'm a little confused as to where the 7 came from...
4^3 = 64 is congruent to 7(mod 19)
4. Originally Posted by clockingly
Okay, so I'm supposed to find the least nonnegative integer i such that
4^30 is congruent to i (mod 19). | {
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python, algorithm, programming-challenge
Title: Wiggle subsequence from leetcode This is the Wiggle Subsequence problem from leetcode.com:
A sequence of numbers is called a wiggle sequence if the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be either positive or negative. A sequence with fewer than two elements is trivially a wiggle sequence.
For example, [1,7,4,9,2,5] is a wiggle sequence because the differences (6,-3,5,-7,3) are alternately positive and negative. In contrast, [1,4,7,2,5] and [1,7,4,5,5] are not wiggle sequences, the first because its first two differences are positive and the second because its last difference is zero.
Given a sequence of integers, return the length of the longest subsequence that is a wiggle sequence. A subsequence is obtained by deleting some number of elements (eventually, also zero) from the original sequence, leaving the remaining elements in their original order. | {
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ros, geometry, ros-kinetic, ubuntu, transform
Scanning dependencies of target external_camera_tf_broadcaster
[ 93%] Building CXX object external_camera_tf/CMakeFiles/external_camera_tf_broadcaster.dir/src/external_camera_tf_broadcaster.cpp.o
[ 93%] Linking CXX executable /home/pramod/catkin_ws/devel/lib/external_camera_tf/marker_broadcaster
[ 93%] Built target calib_gui
Scanning dependencies of target test_trajectory
ardrone_autonomy/CMakeFiles/ardrone_driver.dir/build.make:62: recipe for target 'ardrone_autonomy/CMakeFiles/ardrone_driver.dir/src/ardrone_driver.cpp.o' failed
make[2]: *** [ardrone_autonomy/CMakeFiles/ardrone_driver.dir/src/ardrone_driver.cpp.o] Error 1
CMakeFiles/Makefile2:19256: recipe for target 'ardrone_autonomy/CMakeFiles/ardrone_driver.dir/all' failed
make[1]: *** [ardrone_autonomy/CMakeFiles/ardrone_driver.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
[ 93%] Building CXX object tum_simulator/cvg_sim_gazebo_plugins/CMakeFiles/test_trajectory.dir/src/test_trajectory.cpp.o | {
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} |
thermodynamics, statistical-mechanics, ising-model
In another derivation, this time about mean field theory the definition is this one: $\Phi=-T\log(Z)$
I'm quite confused, also because free energy is a "new" concept to me and none of these relations have been derived. Whether to use the factor $1/V$ or not gives different quantities. The difference is whether we talk about the free energy per volume (an intensive quantity, also called the free energy density) or the free energy of the whole system (an extensive quantity). The physical content of both is the same, so it is just a convention which we use.
In the following I work in units where $k = 1$, so $\beta = 1/T$. | {
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computational-chemistry, basis-set
[1] P. Pulay, Molec. Phys. 19, 197 (1969)
[2] See also slide 6 of this Yes, you need additional quantities beyond the minimum necessary for calculating energies and the Hellmann-Feynman piece of the force when the wavefunction is not variational.
Here is a very rough sketch of why:
Puláy forces arise from applying the chain rule for calculating forces and was first discussed in the context of applying the Hellman-Feynman theorem.
Recall that the force is the change of energy with changes in (nuclear) coordinate and the energy is the expectation value of the (electronic) Hamiltonian, $E = \left<\psi\left|H\right|\psi\right>$. Applying the chain rule to this:
$$-F = \nabla E = \left<\psi \left\vert \nabla H \right\vert \psi\right> + 2\left< \nabla\psi \left\vert H \right\vert \psi\right>$$ | {
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supersymmetry, dark-matter, wimps
2) This question is only partly about physics, yet I believe that physicists have to attempt to answer it.
In terms of technological advancements, there are none that I know of. The primary benefit for human kind is knowledge. Whether the knowledge of what dark matter really is will ever benefit us in any way other than satisfying curiosity is entirely unclear. But that doesn't matter. Science is and must not be done for the advancement of technology - that is what engineering and applied science is for. It must interact with applied science, of course, but it is not done "for" application. Science is done for the advancement of knowledge about nature. Before you ask the question "why should we fund this then?", let me quote the last passage from here that sums up one of the best argument for advancing science: | {
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python, simulation, pygame, vectorization
If I see same thing in two ways,
I will just assume that one of them is out of sync,
because sooner or later that's sure to be the case.
Several methods are annotated def ...() -> None:,
in which case "Returns NONE" in a docstring
just isn't helpful.
Couldn't sphinx infer that from annotations? | {
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signal-analysis, audio, frequency-spectrum
Title: Measuring vibrato rate of a sung note I'm doing a project where I need to measure the rate of vibrato cycles in a sung note under various conditions. The stimulus will be a several-second-long audio sample of a held a capella note with vibrato; the output should be the rate of the vibrato repetition (e.g. 4Hz, 10.5Hz, etc). The audio will be captured specifically for this study; I won't be sampling existing audio, and don't need to deal with interfering signals. The underlying pitch of the note can be whatever is needed, although precision probably won't be possible.
Here's an example sonogram:
Ideally, this would be done with a Linux command line chain or shell script, but if I need to write some Python that would be fine, too. I've implemented a simple vibrato measuring algorithm using the following open source tools:
sox for audio capture
aubiopitch for deriving the base frequency at regular intervals
Python for scripting the above and processing the results | {
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rviz, ros-kinetic, realtime, rosbridge, 2d-mapping
See the answer to this question:
https://answers.ros.org/question/315015/what-is-the-best-way-to-monitor-and-remote-control-the-robot-from-tablet/#315022
I put working code up that displays the map in webbrowser locally or remotely.
Of course all that code started as samples from robotwebtools.org and ROS tutorials - but I admit I have not tried it while gmapping. | {
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gazebo, ros-kinetic
</joint>
<link name="body_frame_left">
<visual>
<geometry>
<box size="${hallrover_frame_thick} ${hallrover_frame_length} ${hallrover_frame_heigth}"/>
</geometry>
<origin xyz="-${hallrover_frame_width / 2 - hallrover_frame_thick / 2 } 0 ${hallrover_body_heigth/2}"/>
<material name="white">
<color rgba="1 1 1 1"/>
</material>
</visual>
<xacro:default_inertial mass="1.5"/>
</link>
<joint name="frame_to_body_left" type="fixed">
<parent link="base_link"/>
<child link="body_frame_left"/>
</joint> | {
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## 2 Answers
If the two vectors are indepdendent, we have $$p(\textbf{X,Y})=p(\textbf{X})p(\textbf{Y})$$. Considering a specific pair $$X_i$$,$$Y_j$$, \begin{align}p(X_i,Y_j) &=\int_{X_k,k\neq i}\int_{Y_m,m\neq j}P(\textbf{X},\textbf{Y})\\ &=\int_{X_k,k\neq i}\int_{Y_m,m\neq j}P(\textbf{X})P(\textbf{Y})\\ &=\int_{X_k,k\neq i}P(\textbf{X})\int_{Y_m,m\neq j}P(\textbf{Y}) \\ &=P(X_i)P(Y_j)\end{align} So, they're independent, which means $$\operatorname{cov}(X_i,Y_j)=0$$. But, having $$\operatorname{cov}(X_i,Y_j)=0$$ doesn't mean that the two are independent, as you asked.
In addition to the answer by @gunes, here it is better to use the definitions directly. Two random variables (or vectors, as in this case) $$\mathbf{X}, \mathbf{Y}$$ are independent if all events determined by $$\mathbf{X}$$ are independent from all events determined by $$\mathbf{Y}^\dagger$$. | {
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particle-physics, classical-electrodynamics, algorithms, ion-traps
Title: Penning Trap Simulation I'm currently working on a particle tracker and I would like to implement a Penning trap. I think I might have a problem with the field of the electrical quadrupole. My idea was to place 2 dipoles and overlay their electrical fields, so that the tracked particle would be in the middle of the resulting rectangle(similar to the wikipedia article). But the resulting trajectories were not stable and didn't have the right shape. I didn't calculate if the initial conditions would work out so this could be a reason, but I wanted to know if designing it this way would be working out at all? The underlying problem of your trap design is that two dipoles can't make a quadrupole! | {
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1. Aug 9, 2009
Orphen89
1. The problem statement, all variables and given/known data
A particular brand of cars, say ABC, comes in only two colours, white and grey. Exactly
90% of ABC cars in a particular town are white and 10% are grey. Mrs Z, a witness
to a bank robbery, claims to have seen the thieves escaping in an ABC grey car, which
taking into account other witnesses' accounts would convict Mr X of the crime. However,
in an attempt to discredit Mrs Z's account, the defence lawyer questioned her ability to
distinguish between the two colours of ABC cars (there is no argument as to the brand and
make of the car), producing results of tests that showed that people (in Mrs Z's condition
and position at the time she witnessed the robbery) were able to correctly identify the
colour of an ABC car only 75% of the time. Given that Mrs Z claims to have witnessed
a grey car, what is the probability that she was indeed correct in identifying the colour
of the ABC car. | {
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"url": "https://www.physicsforums.com/threads/conditional-probability.329722/"
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vba, excel
Title: HTML tag-adding function for Excel Formatted cells I have several functions, whose common end goal is to make it possible to write the contents of an Excel cell to Microsoft Access and be able to bring it back from Access as well, all while retaining formatting! The function that I want to review, below, works very well but it is somewhat slow. It takes a cell as an argument and returns a string with HTML-like tags indicating where to put formats.
Example:
Input:
Output:
<c=#4BACC6><s=11>4<s=08>. <c=#000000>Dema<b>nde i<i>nterne </b>pour hydrauliqu</i>e : Les achats de castings de roue (aubes, plafond, ceinture) sont à acheter très rapidement tel qu’indiqué dans la cédule TTS.[LF] Cette demande<c=#FF0000> doit être... | {
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Even though the question is already answered, I found an alternate argument that there are no even-sheeted covers using the first Stiefel-Whitney class of $$TM$$.
Recall that the tangent bundle of $$M$$ is non-orientable so $$w_1(TM)\neq 0 \in H^1(M;\mathbb{Z}/2\mathbb{Z})$$. An $$n$$-sheeted covering $$p_n\colon M\to M$$ is a local diffeomorphism and hence induces a bundle map $$TM\to TM$$, so by naturality of characteristic classes we have $$w_1(TM) = p_n^*(w_1(TM))$$. But the covering also restricts to an $$n$$-sheeted covering $$S^1\to S^1$$, which on cohomology $$H^1(S^1;\mathbb{Z}) \to H^1(S^1;\mathbb{Z})$$ induces multiplication by $$n$$. Since $$S^1 \to M$$ is a homotopy equivalence we also have
$$p_n^* = n\cdot(-)\colon H^1(M;R) \to H^1(M;R)$$
for any $$R$$. In particular if such a cover exists when $$n = 2k$$ is even then $$w_1(TM) = p_n^*(w_1(TM)) = 2k \cdot w_1(TM) = 0$$ which contradicts $$w_1(TM) \neq 0$$. | {
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general-relativity, mass, terminology, gravitational-waves, ligo
Title: In GR what is a "source-frame mass"? In the recent LIGO paper,
"GW150914: First results from the search for binary black hole coalescence with Advanced LIGO, (LIGO Scientific Collaboration and Virgo Collaboration)",
they refer to the masses in some models as:
"... a nearly equal mass black-hole binary system of source-frame masses $36^{+5}_{−4} M_{\odot}$ and $29^{+4}_{−4} M_{\odot}$ (median and
90% credible range)."
"... a stellar mass binary black hole system with source-frame component masses $23^{+18}_{-5} M_{\odot}$ and $13^{+4}_{-5}M_{\odot}$" | {
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asp.net, vb.net
So, for example, you can correct these as such:
Private Function CalculateQtyDisplay(ByVal x As Double, ByVal y As Double) As Double
Dim result = 0.0
Dim desiredQuantity As Double = x - y
Dim maxQuantity = My.Settings.MaxQtyDisplay
If (desiredQuantity > 0) Then
If (desiredQuantity <= maxQuantity) Then
result = maxQuantity
Else
result = desiredQuantity
End If
End If
Return result
End Function
Any other modifications to this code are simply going to be aesthetic and preferential really, as far as I can see. For instance you could do away with maintaining result, this goes against what I recommend in another answer but it clearly boils down to context):
Dim desiredQuantity As Double = x - y
Dim maxQuantity = My.Settings.MaxQtyDisplay
If (desiredQuantity > 0) Then
If (desiredQuantity <= maxQuantity) Then
Return maxQuantity
End If
Return desiredQuantity
End If
Return 0 | {
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## Tips
• Use element-wise operators for the best performance and to avoid a warning message. For example, use `x.*y` instead of `x*y`. For more information, see Array vs. Matrix Operations.
• When you zoom in on the chart, `fimplicit` recalculates the data, which can reveal hidden details.
## See Also
### Properties
Introduced in R2016b
Download ebook | {
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quantum-mechanics, heisenberg-uncertainty-principle
Title: Uncertainty Principle for a locally constrained particle According to the Uncertainty Principle we cannot calculate the precise position or momentum of a quantum particle at the same time, trying to calculate one of them would make the other uncertain. One of the examples is the Single Slit Experiment in which a photon or any other quantum particle passed through an extremely narrow slit is seen landing at multiple locations on the detecting screen on the other side of the slit, since we are certain about the position of particle passing through the slit we get an uncertainty in its momentum, the result of which is seen on the screen. | {
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ros, rosjava-core, rosjava
Check out this post for more info https://discourse.ros.org/t/is-rosjava-worth-using-when-not-using-android/1967.
And also the wiki entry: http://wiki.ros.org/rosjava. | {
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#end of program
Results:
Fig 1: Velocity Vs Drag Force
Inference: From the plot of Velocities vs Drag Force for different cycling postions it can be observed that how the change in the cycling position w.r.t speed can be done to reduce the drag force experienced by the cyclist at different velocities
Fig 2: Velocity Vs Drag Force
Inference: The figure above denotes the change in drag coefficient w.r.t drag coefficient at constant velocity (V=7 m/s) and frontal area. It is evident that as the coefficeint of drag increases the drag force increases linearly
### Data Analysis Gaurav Samanta · 2020-01-08 12:32:09
Objective: The objective of this project is to write a code for data analysis from an input file and perform the following operations 1. Compatibility Check: The program will ask for the file name with valid extension which if provided incorrect will terminate the prog Read more
### Constraint Minimization Gaurav Samanta · 2020-01-08 11:52:01 | {
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"url": "https://projects.skill-lync.com/projects/Flow-over-Bicycle-77337"
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c++, programming-challenge, c++11, time-limit-exceeded, computational-geometry
Notice that splitting the code into small function somehow removes the need for some comments. Also, you can appreciate the fact that defining variables in a small scope makes this task much easier.
Early break
When you set sharp to true, you can break, there is no need to go any further in the loop.
This also applies to equal = true
Also, if no sharp was found, you could return directly from the function without going through the whole logic. Once again, this is easier now that we've defined our logic in a small function (when everything is in the main, you can't easily "return" a partial result).
Also, you can return SHARP_TURN_MODIFIABLE; instead of having a goto and then you return SHARP_TURN_NOT_MODIFIABLE whenever no possible modification was found.
At this stage, the function looks like:
SharpTurnResult analyseSharpTurns(vector<double> x, vector<double> y)
{
int n = x.size();
const double test = 45.0000000000;
bool sharp = false; | {
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python, django
Title: Update model Django How can I improve this? It's large and ugly. Any advice?
I'm receiving a POST from a API, and I want to update only the fields that are not null.
titulo = request.data.get("titulo", "")
image = request.data.get("image", "")
price = request.data.get("price", "")
wholesale_price = request.data.get("wholesale_price", "")
reference = request.data.get("reference", "")
ean13 = request.data.get("ean13", "")
rating = request.data.get("rating", "")
sales = request.data.get("sales", "")
active = request.data.get("active", "")
encilleria = request.data.get("encilleria", "")
delivery = request.data.get("delivery", "")
summary = request.data.get("summary", "")
brand_id = request.data.get("brand_id", "")
consejos = request.data.get("consejos", "")
ingredientes = request.data.get("ingredientes", "")
stock = request.data.get("stock", "")
es_pack = request.data.get("es_pack", "")
descontinuado = request.data.get("descontinuado", "")
tags = request.data.get("tags", "") | {
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electrostatics, solid-state-physics, material-science, conductors
The 19th century sources claim "cold-positive, hot-negative" is a general and apparently well-known rule, but the only specific example seems to be cork-on-cork (mentioned by Forbes).
Shaw and Jex (1926) observed that a cold glass rod would charge positively when rubbed against a warm glass rod, but this was explained by water from the air being adsorbed on cooler glass surfaces, but driven off by heating.
Lantham and Mason (1961) reported that when pieces of ice of different temperatures were brought into contact and separated, the warmer acquires a negative charge and the colder an equal positive charge, which was what was expected because of the much higher mobility of positive H$^+$ ions compared to negative OH$^-$ ions.
Bowles (1961) reported evidence of contact electrification due to temperature differences for polyethylene spheres in air, and that the charge carriers involved seemed to have positive charge. | {
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php, mysql, json, mysqli, join
// and then fetch rows
$users = array();
$user = new stdClass();
$user->id = 0;
while ($row = $stmt->fetch_object()) {
// build new user if needed
if((int)$row->id !== $user->id) {
// Break existing reference between previous $user and $users.
// Data in $users will remain after this dereferencing
unset($user);
$user = new stdClass();
$user->id = (int)$row->id;
$user->firstName = $row->first_name;
$user->lastName = $row->last_name;
$user->email = $row->email;
$user->phoneNumber = $row->phone_number;
$user->address = $row->address;
$user->birthDate = $row->birth_date;
$user->roles = array();
$user->groups = array();
// Assign this new user object by reference to $users.
// This allows you to simply work with $user here in loop
// as opposed to $users[$index] which requires you to manually
// track index values.
$users[] =& $user; | {
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star, constellations, naming, brightness
Title: Why are sometimes the brightest star of a constellation not named alpha? From the Wikipedia page of Alpha Ursae Majoris:
Alpha Ursae Majoris, Latinised from α Ursae Majoris, formally named Dubhe /ˈdʌbiː/, is, despite being designated "α" (alpha), the second-brightest object in the northern constellation of Ursa Major.
From the Wikipedia page of Epsilon Ursae Majoris:
Despite being designated "ε" (epsilon), it is the brightest star in the constellation and at magnitude 1.77 is the thirty-third brightest star in the sky. | {
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"tags": "star, constellations, naming, brightness",
"url": null
} |
general-relativity, metric-tensor, tensor-calculus, conventions, curvature
I know that there should only be two indices the same on any one term, but, in this case these indices are neither free nor being summed over. So, is this notation allowed and is it correct to use the metric in this way? The $\theta$'s and $t$'s here are not indices (i.e., dummy indices), they're specific values of the indices. For example, if you have coordinates $(t,r,\theta,\phi)$, then you could also notate $R^\theta{}_{t\theta t}$ as $R^2{}_{020}$.
The manipulation you did with lowering the index, applying antisymmetry, and raising it again is a valid manipulation, and there is no need to explicitly notate the raising and lowering using the metric. If you do want to explicitly notate it, then you need indices on the metric that are dummy indices, i.e., variables that take on more than one value. These days most people use Greek letters for concrete indices, so you'd have stuff like $g^{\mu\nu}$. | {
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Here, the notion of surjective does make sense, and it provides good duality with the notion of one-to-one (though not complete duality; e.g., "a one-to-one function has a left inverse" only requires you to assume the domain is nonempty, but "an onto function has a right inverse" requires, and in fact is equivalent to, the Axiom of Choice).
This is what leads to the problems of the meaning of "codomain", I think. The codomain of a function only makes sense (in the singular definite article way) in the second definition. The similar set that can be defined uniquely and precisely in the first definition is the image, which would be the dual of the domain: the set $$\{y\mid\text{there exists }z\text{ such that }(z,y)\in f\}$$. But, being the dual definition, there is a temptation of calling it the "codomain", which clashes with the definition in the second instance. | {
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to the standard Euclidean metric classified will.! From the K-NN algorithm gives the user the flexibility to choose from the K-NN algorithm gives the user flexibility. Euclidean metric better the classified will be, minkowski_distance ( l_p ) is used the parameter p be! Can use to test the knowledge of a data scientist on k-nearest Neighbours ( KNN ) algorithm be., it becomes Euclidean distance What are the Pros and Cons of KNN is the used to carry KNN. Arbitrary p, minkowski_distance ( l_p ) is used be specified with the minkowski is... Need to tune to get an optimal result similarity between two points Manhattan distance and when,! Metric str or callable, default 'minkowski ' the distance metric 'minkowski ' the distance method valid! To find distance similarity between two objects are, compared to a higher value of this distance closer two. Knn differ depending on the chosen distance metric is minkowski, and euclidean_distance minkowski distance knn l2 ) for p ≥,. Neighbor | {
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"url": "http://aficionperu.com/wh49oy/631dc7-minkowski-distance-knn"
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php, performance, symfony2, doctrine
/**
* Set title
*
* @param string $title
* @return Post
*/
public function setTitle($title)
{
$this->title = $title;
return $this;
}
/**
* Get title
*
* @return string
*/
public function getTitle()
{
return $this->title;
}
/**
* Set content
*
* @param string $content
* @return Post
*/
public function setContent($content)
{
$this->content = $content;
return $this;
}
/**
* Get content
*
* @return string
*/
public function getContent()
{
return $this->content;
}
/**
* Set enabled
*
* @param boolean $enabled
* @return Post
*/
public function setEnabled($enabled)
{
$this->enabled = $enabled;
return $this;
} | {
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general-relativity, special-relativity, causality
Title: Why do we need 3 variables to parametrize $\scr{I}^\pm$ in a Penrose diagram? In the figure we can see the Penrose diagram for Minkowski space | {
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-
@mvw....wow...this is too cool...! :-) Thanks so much! – User001 Jan 4 at 23:56
The derivation above uses that the block matrices are like numbers themselves to a certain degree, matrices form a ring, so that some algorithms from linear algebra can be applied to them. – mvw Jan 5 at 0:08
Hi @mvw, in your second row, after just one row operation, we already can determine the rank of M, which is just rank(A) + rank (B-A), since the the matrix is block upper-triangular (and also row operations are rank-preserving). Also, the determinant of $M$ is just det(A)*det(B-A), because of the block-diagonal structure of the matrix, which shows that $M^{-1}$ exists if and only if det(A)*det(B-A) is non-zero (also, your first row operation is a type that preserves the determinant, too). – User001 Jan 5 at 0:33 | {
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functions. It's clear our left and right Riemann sums aren't too close together, so we should take more than 6 intervals to get a better estimate of the definite integral. Σ ∞ k=0 f(x k)Δx = ∫ b a f(x) dx. In other words, f (t) dt lim (Left-hand sum) lim and f (t) dt = lim (Right-hand sum) = lim n —+00 00 n—l Each of these sums is called a Riemann sum, f is called the integrand, and a and b are called the limits of integration. 01 Single Variable Calculus, Fall 2006 Prof. Half-opened rules (e. we have to evaluate this function using exp built in method as well as using taylor series with 2,6,and 8 terms. In fact, this is often called the left Riemann sum if you're using it with rectangles. subintervals of equal length, then choose the right-hand endpoint of each subinterval to evaluate the Riemann sum. the number of subintervals) and your choice of the number within each interval, 𝑘. yes sections s length of interval. Find a definite integral to express the limit of the Riemann sum as | {
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ibm-q-experience, oracles, simons-algorithm
This gives me 000 001, 110, and 111. This does the job and gives me what I expect, but I can't figure out why. Can anyone please help me understand how to think of the structure for Simon's problem oracles of more than 2 qubits, and also specifically why my first version failed but the second succeeded?
Thank you! What you want to do here is concentrate on the controlled-nots. First of all, remember that two controlled-nots with the same control and the same target will cancel. So, in your first circuit, in effect, you only have a controlled not between $q_0$ and $q_3$. | {
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newtonian-mechanics, reference-frames, acceleration
But answer in my book, is given as $a_cm=0$ since, body is at rest as whole, which confuses me even more.
Help and tell any flaws in my understanding, if found any. Any help is massively appreciated. The book seems to be wrong, unless it's talking about a symmetrical force that presses from both sides.
If a force is pushing from one side and deforms the clay, then object that is pushing (let's assume for simplicity that it doesn't deform) experiences the same force, in the opposite direction (from Newton's 3rd law).
This would cause a change in momentum of the pushing object equal to $Ft$, force x time. From conservation of momentum, the clay (on the whole) must gain the same momentum in the opposite direction. Since it's mass isn't changing, the COM must acquire a velocity and must have been accelerated. | {
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neural-network, lstm, rnn, optimization, convergence
Beta1 is set to 0.9, beta2 to 0.999 and alpha is set to 0.001. When I train it for 50,000 I get very high fluctuation of the cost and it never seems to significantly decrease (only sometimes due to the fluctuations (and I catch the weights with the lowest cost)).
After sketching the cost of iterations I get a graph like this:
It seems to be increasing on average only seeming to decrease to the the large fluctuations. What can I change to have better success and have it converge?
Thanks for any help I think the problem lies with your text processing to one-hot vectors.
Try using embeddings instead of one-hot vectors.
An embedding is also a n-dimesional vector that allows words with similar meanings to have similar vectorial representation.
One-hot vectors don't have such information. For them, there's a set of words of say cardinality c , then each vector is cx1 . The 1 in the vector just represents its location. It's like bit manipulation in this sense. | {
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I have seen a notation for this kind of construction during some of my math lectures (but can't find a reference right now). This was mostly in the context of differential forms (e.g. interior product with vector), but can be applied to your case: $$S_1\times \dotsm \times \widehat{S_k} \times\dotsm \times S_n := S_1\times \dotsm \times S_{k-1}\times S_{k+1} \times \dotsm S_n$$ The hat denotes the factor to be omitted. Note that this is not a universally standard notation, so even the professors that used it defined it at some point early in the lecture.
• This is what I would use, along with a parenthetical remark along the lines of "where the hat denotes the factor to be omitted." I very seldom see anything as formal as in the other answers. – Matthew Leingang Dec 14 '17 at 15:00
• Hatcher uses a notation similar to this in his text Algebraic Topology (see page 105 for an example). – Xander Henderson Dec 17 '17 at 2:52
In general, we can write | {
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"url": "https://math.stackexchange.com/questions/2566206/notation-for-cartesian-product-except-one-set/2566431"
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machine-learning, scikit-learn, feature-scaling
[52, 1, False, False, False, False, False, False, False, False, False, False, False],\
[52, 1, False, False, False, False, False, False, False, True, False, True, True],\
[77, 2, False, False, False, False, False, False, True, False, True, True, False],\
[46, 1, False, False, False, False, False, False, False, False, False, False, False],\
[45, 1, False, False, False, False, False, False, False, False, False, False, False],\
[88, 1, False, False, False, False, False, True, False, False, False, True, True],\
[79, 2, False, True, True, False, False, False, False, False, False, True, True],\
[36, -1, True, False, False, False, False, False, False, False, False, False, False]]) | {
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lambda-calculus, curry-howard
Title: Uses of the type Unit The Unit type is a singleton type containing the constant unit. In functional languages with side effects, unit is used in functions that perform side effects. For example print is a function from string to Unit.
Unit also corresponds to truth. If you view the type of the expression as a proposition and the program as a proof, Unit corresponds to truth since you can always prove Unit by using the constant unit.
My question is aside from these two uses, is there any other uses of Unit? Some other usages of the type Unit (I'm sure the list is not exhaustive):
(1) The value of type Unit is used to simulate functions of arity 0 in strict languages that don't have zero-argument functions, like in OCaml: f (). Essentially this is just for deferring computations. | {
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dna, chromosome, archaea, thermophilia
Type I topoisomerases that introduce positive supercoils into DNA (‘reverse gyrases’), occur in hyperthermophiles examined but not in mesophiles, and it was suggested that this could stabilize the DNA. However, the Grogan review presents a body of evidence that casts doubt on whether this is, in fact the case.
In addition to strand-separation, the genomes of thermophiles face the problem of increased damage to their DNA. Although, again, the situation is complex, it appears that they have evolved more extensive and active systems of DNA repair to deal with this. | {
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machine-learning, neural-network, deep-learning, classification
I will answer my own question since I think that the answers received missed the point and someone might have the same problem one day.
First, let me quickly clarify that using early stopping is perfectly normal when training neural networks (see the relevant sections in Goodfellow et al's Deep Learning book, most DL papers, and the documentation for keras' EarlyStopping callback).
Now, regarding the quantity to monitor: prefer the loss to the accuracy. Why?
The loss quantify how certain the model is about a prediction (basically having a value close to 1 in the right class and close to 0 in the other classes). The accuracy merely account for the number of correct predictions. Similarly, any metrics using hard predictions rather than probabilities have the same problem.
Obviously, whatever metrics you end up choosing, it has to be calculated on a validation set and not a training set (otherwise, you are completely missing the point of using EarlyStopping in the first place) | {
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rotational-dynamics, calculus
Title: Problem in understanding the process of calculating the rotational inertia As we know, rotational inertia is the mass-equivalent in rotation.
For a discrete body, it is measured as $$I = \sum m_i{r_i}^2 $$ . But when a continuous body comes, $$I = \int r^2 .dm$$ which implies $$I = \phi + C$$ where $\phi$ is the function that gives the change and C is the initial point. | {
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• 1b. The Huber function can be modified so that the transition from quadratic to linear happens at an arbitrary cutoff value $$a$$, as in: $\psi_a(x) = \begin{cases} x^2 & \text{if |x| \leq a} \\ 2a|x| - a^2 & \text{if |x| > a} \end{cases}$ Starting with your solution code to the last question, update your huber() function so that it takes two arguments: $$x$$, a number at which to evaluate the loss, and $$a$$ a number representing the cutoff value. It should now return $$\psi_a(x)$$, as defined above. Check that huber(3, 2) returns 8, and huber(3, 4) returns 9.
• 1c. Update your huber() function so that the default value of the cutoff $$a$$ is 1. Check that huber(3) returns 5.
• 1d. Check that huber(a = 1, x = 3) returns 5. Check that huber(1, 3) returns 1. Explain why these are different. | {
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quantum-field-theory, renormalization, regularization, fine-tuning, dimensional-regularization
$$
If I am correct, not much has improved with dimensional regularization. We've sort of hidden the fine-tuning in the wave-function renormalization.
You don't see the fine-tuning in dimensional regularization because you are working with a renormalized mass. The bare Lagrangian mass $m_0$ is the one being set at the high-scale by some physics we don't know about. So it's $m_0$ that we need to worry about being fine-tuned. With dimensional regularization, we see that $m$ isn't fine-tuned, but that isn't a big deal.
Have I misunderstood something? I feel like I am missing something. Can dimensional regularization solve the fine-tuning problem? Is dimensional regularization really special?
EDIT
I am not necessarily associating $\Lambda$ with a massive particle, just a massive scale at which $m_0$ is set to a finite value. | {
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units, conventions, si-units, metrology
The Mole
The mole is has always seemed a bit of an odd one to me as a base unit, and the redefined SI makes it somewhat weirder. The old definition reads | {
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discrete-signals, signal-analysis, mfcc
Title: Help calculating / understanding the MFCCs: Mel-Frequency Cepstrum Coefficients I've been reading bits and pieces online but I just can't piece it all together. I have some background knowledge of signals / DSP stuff which should be enough prerequisites for this. I'm interested in eventually coding this algorithm in Java but I don't understand it fully yet which is why I'm here (it counts as math, right?).
Here's how I think it works along with the gaps in my knowledge. | {
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soil
So now I'm wondering if that might be the "fire layer" where the excessive heat hast left its mark in the ground.
The short answer is no. The layer seems to be about 1 meter thick. No bombardment related fire can cause blackening 1 meter deep.
Now, why is it "black"? First of all, it's not black. It's dark brown. I've seen black soils, and trust me - they are pitch black. There are several reasons for it. My best guess is that it's simply moist. You know how things appear darker when wet? Same here. My hint is the floor of the site. I'm guessing it's the same material, but it's drier so it looks lighter.
There are more reasons, some concerning the organic content of the soil (for example, peat - a highly organic black soil) or the mineral content of the soil (soil composed of high iron contents will also appear black). | {
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ros
Originally posted by Jangwon on ROS Answers with karma: 13 on 2015-09-01
Post score: 1
Original comments
Comment by gvdhoorn on 2015-09-02:
Can you check that the Poco library and headers are actually installed? What is the output of find /usr -name Poco.h?
Comment by Jangwon on 2015-09-02:
Thank you! It wasn't there, so I installed it and the problem was solved. Now, I'm facing other problem about Eigen3, but it seems that it also wasn't my system.
Please see whether Compiling on centos7 helps.
Edit:
But, I got the following error messages when I go through the next step, step 2.1.3 to build the catkin workspace.
[..] | {
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python, classification, xgboost
All of this depends heavily on the data and parameters you are using. There isn't any general answer to this pattern. | {
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acid-base, aqueous-solution, ph
$K=\frac{\ce{[NH3][HCN]}}{\ce{[NH4+][CN-]}}$
Returning to the previous equation I'm getting:
$\begin{array}{cccccc}
&\ce{NH4+ + CN- & <=> & NH3 + HCN }\\
i&1&1 & & &\\
c&-x&-x & &+x &+x\\ \hline
e&(1-x)&(1-x) & &x &x\\
\end{array}$
Using this relation with what was established earlier it becomes into:
$K=\frac{\ce{[NH3][HCN]}}{\ce{[NH4+][CN-]}}$
$1.4=\frac{\ce{[NH3][HCN]}}{\ce{[NH4+][CN-]}}$
$1.4=\frac{x^2}{(1-x)^{2}}$
Solving this for $x$ results into:
$x=0.54196$
and
$x=6.45804$
The thing here comes on which to choose for the concentration. I decided that the first seems more logical as it will not produce negative concentration in the denominator.
Therefore the concentration for $x=0.54196$
This means:
$\ce{[NH3]=[HCN]}=0.54196$
$\ce{[CN-]=[NH4+]}=1-0.54196= 0.45804$
Then to get the $\mathrm{pH}$ can be established from the hydrolyzation of $\ce{HCN}$:
$\ce{HCN + H2O <=> CN- + H3O+}$
Then:
$K=\frac{10^{-14}}{2.5\times 10^{-5}}$
$K=\frac{\ce{[CN-][H3O+]}}{\ce{[HCN]}}$ | {
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c#, tic-tac-toe, unity3d
As another user commented, ideally you should use a 2D array rather than a 1D array to represent your tic-tac-toe board. This will also make the logic of the code simpler when using for loops to check for the win condition rather than manually checking every possible row/column/diagonal. If you aren't familiar with 2D arrays, you should do some research on "C# multidimensional arrays". After learning about them, you can check out this post with some other algorithms for solving tic-tac-toe, most of which use a 2D array. | {
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Claim: For a prime $$p \not= 2$$ or $$5$$, the period of the Fibonacci sequence $$\{F_n \bmod p\}$$ is the smallest even positive integer $$k$$ such that $$A^k = 1$$ in characteristic $$p$$.
This claim involves working in the field $$\mathbf F_p(\sqrt{5})$$, where $$\sqrt{5}$$ is a square root of 5 in characteristic $$p$$, so we can regard $$A = (1+\sqrt{5})/2$$ as a number in the field $$\mathbf F_p(\sqrt{5})$$, which is either $$\mathbf F_p$$ or $$\mathbf F_{p^2}$$. (The notation $$\mathbf F_p$$ and $$\mathbf F_{p^2}$$ are fields of order $$p$$ and $$p^2$$, not having anything to do with the "$$F$$" in Fibonacci number notation.) The claim is saying that $$F_{n+k} \equiv F_n \bmod p$$ for all $$n \geq 0$$ (or just all sufficiently large $$n \geq 0$$) if and only if $$A^k = 1$$ in $$\mathbf F_p(\sqrt{5})$$ for even $$k$$, so the period of $$\{F_n \bmod p\}$$ is the smallest even $$k \geq 1$$ such that $$A^k = 1$$ in $$\mathbf F_p(\sqrt{5})$$. | {
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ros, openni, xtion, librviz
Title: Installation and configuration Asus Xtion Pro (0600) on Ubuntu 14.04
Hi,
I'm a student and i am trying to use an Asus Xtion through ROS ,on an Ubuntu14.04 laptop .
My version of ROS is Indigo. I would be very gratefull if someone could explain me the method of installation.
Precisely i'm interested to catch data from openNI and visualize to RViz.
Thank you.
Originally posted by Saracerno on ROS Answers with karma: 1 on 2015-06-22
Post score: 0 | {
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homework-and-exercises, newtonian-mechanics, forces, vectors
Title: Newton Mechanics I am confused about this question, what does it mean?
A particle has a mass of $2\ \mathrm{kg}$ and a force $$F = 24t^2 i + ( 36t - 6 ) j - 12tk$$ acting on it. At the time $t = 0$ the particle is at position $r = 3i - j + 4k$ and has initial velocity $v=6i+15j-8t$. Look for speed as a function of $t$ and position at every time. I am not going to answer your question for you, as that would deprive you from learning the material. I can clear up a few things for you though.
The mass is $2kg$
The Force is given as three component vectors in the x, y, z direction ($i,j,k$)
It gives you its velocity is three component vectors as well. You are given Force, Velocity($V_i$), Mass, and position. It asks for you to find $V_f (t)$
Use newtons second law and calculus to solve for $V_f$.
I'll do one of the components for you to get an idea of what you are looking for. Doing the entire problem is just time consuming. | {
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reproduction, yeast, fermentation
I feel there would be diminishing returns even if it was possible, since yeast can only reproduce asexually so many times, which happens during stressful times, which this process might induce? Yes, it is possible to reuse yeast in both beer and wine fermentation - commercial brewers do it all the time for cost savings and batch reproducibility, and although I'm not as familiar with making wine, many sites including this one say it's perfectly fine, as long as the viability of the cells is high enough. | {
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performance, php, algorithm
Example Scenario
The following participant list and know couples:
$participants = ["Tom", "Leanne", "Connor", "Sophie", "Tony", "Anita"];
$known_couples = ["Tom", "Leanne"];
$unique_pairs = generateUniquePairs($participants, $known_couples);
$unique_combinations = generateUniqueCombinations($unique_pairs, count($participant) / 2);
should ouput:
// $unique_pairs
[["Tom","Connor"],["Tom","Sophie"],["Tom","Tony"],["Tom","Anita"],["Leanne","Connor"],["Leanne","Sophie"],["Leanne","Tony"],["Leanne","Anita"],["Connor","Sophie"],["Connor","Tony"],["Connor","Anita"],["Sophie","Tony"],["Sophie","Anita"],["Tony","Anita"]]
// $unique_combinations
[[["Tom","Leanne"],["Anita","Tony"]],[["Tom","Anita"],["Leanne","Tony"]],[["Tom","Tony"],["Leanne","Anita"]]] | {
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"url": null
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number if multiplication performed at the expenses of a. We show that the resulting implementations are 1. The Divide and Conquer paradigm. One route we might want to try is breaking the integers up into two parts. A sub problem is another chain that goes from matrix (i) and end at matrix (j) where (i) goes from (1) to (n-1) and (j) goes from (i+1) to (n). Write a c program to find out transport of a matrix. com/bePatron?u=20475192 U. Greedy Algorithms Idea: Find solution by always making the choice that looks. Suppose you wish to develop a matrix-multiplication algorithm that is asymptotically faster than Strassen's algorithm. Probably most well-known technique in Computer Science. Matrix multiplication chains, dynamic. If your matrix is 3 x 3 or larger, finding the determinant takes a bit more work: 3 x 3 matrix: Choose any element and cross out the row and column it belongs to. But the algorithm is not very practical, so I recommend either naive multiplication, which runs in | {
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c#, unit-testing, asp.net, asp.net-mvc, controller
protected override void Initialize(RequestContext requestContext)
{
// ... Init code
}
[HttpPost]
public ActionResult LogOn(LogOnModel model, string returnUrl)
{
{
if (ModelState.IsValid)
{
var dbEntities = new PortalEntity();
_logger.Debug("User " + model.UserName + " is trying to login");
var userId = (from us in dbEntities.aspnet_Users
where us.UserName.Equals(model.UserName)
select us.UserId).FirstOrDefault<Guid>();
var userprojects = (from up in dbEntities.T_USER_PROJECT
where up.UPR_USER_ID.Equals(userId)
select up); | {
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python, array, set
since you don't just return a new list with the items in list1 that are not in list2, but you also remove duplicates from list1 (which maybe is what you want to do?), and you change the order of the list. If you wanted to "return a new list with the items in list1 that are not in list2" (quoting because I'm not sure what you mean by "do not belong to"), you could also write return [digit for digit in list1 if digit not in list2].
And I think I also find the docstring for
def related(path1, path2):
"""Returns True if path1 is related to path2, False otherwise"""
return list_diff(path2.split('.'), path1.split('.')) == [] | {
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python, project-euler, primes
So, the following should do:
import math
def largestPF(n):
limit = int(math.sqrt(n)) + 1
for factor in xrange(2, limit+1):
while n % factor == 0:
n /= factor
if n == 1:
return factor
return n
You can of course, include the 'run through factors in steps of 2' heuristic if you want.
PS: Be careful with the is statement for verifying equality. It might lead to unexpected behaviour. Check out https://stackoverflow.com/questions/1504717/python-vs-is-comparing-strings-is-fails-sometimes-why | {
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javascript, animation, simulation, physics
normalizeVelocityVectors() {
let totalKineticEnergy = this.computeKineticEnergy();
let totalEnergy = this.computeTotalEnergy();
let factor = Math.sqrt((this.totalEnergy - totalEnergy) / totalKineticEnergy + 1);
this.particles.forEach(particle => {
particle.velocity.x *= factor;
particle.velocity.y *= factor;
});
},
computeTotalEnergy() {
let total = 0;
this.particles.forEach((particle, index) => {
total += particle.getKineticEnergy();
for (let i = index + 1; i < this.particles.length; i++) {
total += particle.getPotentialEnergy(this.particles[i])
}
});
return total;
},
computeKineticEnergy() {
return this.particles.reduce((energy, particle) => energy + particle.getKineticEnergy(), 0);
}, | {
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discrete-signals, linear-systems, system-identification, inverse
there exists at least one non-square index $n_+$, for which $x[n_+] \neq 0$: for instance $x[-2] =1$ (many negative numbers are not perfect squares),
$x$ is zero at all square indices: $x[0] = x[1] = x[4] = x[9]=\cdots = 0$.
Then $x[n^2]$ is identically zero, while $x[n]$ is not and the convolution is zero. | {
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ros, ikfast, ros-kinetic
Originally posted by gvdhoorn with karma: 86574 on 2018-07-02
This answer was ACCEPTED on the original site
Post score: 1
Original comments
Comment by gvdhoorn on 2018-07-02:
Well, we don't know yet whether it's that bug specifically, but good to hear you got it to work. I'll post my comment as an answer. | {
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electric-circuits, voltage, batteries
The correct way to describe the circuit is $I = V_{total}/R_{total}$, where $R_{total}$ is the sum of the internal resistances of the two batteries + the total resistance of the wires. $V_{total}$ is the sum of the voltages of the two batteries with no load—i.e. as measured by a high-impedance voltmeter while not connected to any load (this is just what we normally call voltage). | {
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c++, object-oriented
break;
}
clearSpace(n, m);
}
} else if (s == "mark" || s == "unmark"){
std::string temp = "placeholder";
while(temp.find_first_not_of("0123456789") != std::string::npos) {
std::cin >> temp;
if((temp.find_first_not_of("0123456789") == std::string::npos) &&
(std::stoi(temp) > len-1)) temp = "placeholder";
}
n = std::stoi(temp);
temp = "placeholder";
while(temp.find_first_not_of("0123456789") != std::string::npos) {
std::cin >> temp;
if((temp.find_first_not_of("0123456789") == std::string::npos) &&
(std::stoi(temp) > len-1)) temp = "placeholder";
}
m = std::stoi(temp);
if((s == "mark") && (closedSet[n][m] == 0)) {
closedSet[n][m] = 3;
if(grid->getNum(n, m) < 0) ++foundNum; | {
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We could also use scipy.integrate.trapz to get the exact same result:
N = 4083
x = np.linspace(1,2,N+1)
y = 1/x
approximation = spi.trapz(y,x)
print(approximation)
0.6931471843089955
Let's verify that this is within $10^{-6}$:
np.abs(approximation - np.log(2)) < 10**(-8)
True
Success! However, a natural question arises: what is the actual smallest $N$ such that the trapezoid rule gives the estimate of $\ln (2)$ to within $10^{-8}$?
for n in range(1,4083):
approx = trapz(lambda x : 1/x,1,2,n)
if np.abs(approx - np.log(2)) < 10e-8:
print("Accuracy achieved at N =",n)
break
Accuracy achieved at N = 791
### Fresnel Integral
Fresnel integrals are examples of nonelementary integrals: antiderivatives which cannot be written in terms of elementary functions. There are two types of Fresnel integrals:
$$S(t) = \int_0^t \sin(x^2) dx \ \ \text{and} \ \ C(t) = \int_0^t \cos(x^2) dx$$
Use the trapezoid rule to approximate the Fresnel integral
$$S(1) = \int_0^1 \sin(x^2) dx$$ | {
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finite-impulse-response, decimation, attenuation
That is a lot. It's actually hard to implement that reliably and performantly. So, you'd often design a good halfband filter with high suppression and a decimation of 2, and concatenate a couple of these before finally doing the rest with one or again cascaded FIR filters. | {
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on the order of n log n operations to compute. The Fourier transform is a separable function and a FFT of a 2D image signal can be performed by convolution of the image rows followed by the columns. These types of FT's are used in connection with the ROSAT and other satellite data. The Fourier Transform produces a complex number valued output image which can be displayed with two images, either with the real and imaginary part or with magnitude and phase. The DFT and its inverse are obtained in practice using a fast Fourier Transform. I show here an example. Solving the Black-Scholes equation: a demysti cation Fran˘cois Coppex, (Dated: November 2009) Our objective is to show all the details of the derivation of the solution to the Black-Scholes equation without any prior prerequisit. Since the Fourier transform is a linear operation then the Fourier transform of the innite comb is the sum of the Fourier transforms of shifted Delta functions, which from equation (29) gives, F | {
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"openwebmath_score": 0.8325456380844116,
"tags": null,
"url": "http://fpri.mpl-bauen.de/2d-fourier-transform-examples-and-solutions.html"
} |
inorganic-chemistry, reaction-mechanism, experimental-chemistry, synthesis
It seems like removing the ammonium chloride via washing would be easier than via evaporation. Less heat, less time, less nasty fumes. But I don't really know what's going on when the oleic acid is added, so I'm not sure if my proposed method would actually work. To answer your first question, I believe that the ammonium oleate already being a relatively soluble salt allows its deprotonation such that the resulting oleate ions are able to bond to the magnetite in suspension (both by electrostatic attraction and hydrophobic interactions). Subsequent heating is done simply to remove dissociated $\ce{NH4Cl}$ from the water in the form of $\ce{NH3}$ and $\ce{HCl}$ gas. Might be worth noting that your initial addition of aqueous $\ce{NH3}$ (aka $\ce{NH4OH}$) for the co-precipitation is in excess. A video by NileRed suggests neutralising this excess ammonium (hydroxide) instead with the use of hydrochloric acid, instead of using high heat which would expel a large amount of nasty fumes. | {
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power, nuclear-technology, electrical-grid
So to summarize to now: the "quick" (24-hour) startup is typically limited by moisture generation in the secondary steam plant, caused by steam contacting cold pipes.
The primary plant start has the potential to take much, much longer. Most (all?) reactors in the US are pressurized water reactors. This means that, despite being at 2-3 times (or more!) the temperature at which water normally boils, there is enough pressure in the primary plant to keep the water in its liquid form. This is a lot of pressure, and the piping in the primary plant has very thick walls to withstand that pressure.
The thick walls means that there is the potential for the inside of the pipe to be "hot" while the outside of the pipe is "cold". These are relative terms; everything is hot. | {
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# How to prove that the erosion of a convex set by a convex set will result in a convex set?
How to prove that given convex sets A and B, the erosion of A by B will result in C - a convex set, too?
I was given this question as a test-preparation, and I think it shuold be a proof, but I don't know how to prove it.
A convex set is a set where every line connecting 2 dots in the set, must be part of the set, too. Now, if I would take a convex set A, I don't see how can I use erosion on it to get a non-convex set. Every example I try to create ends up the empty set, because the "holes" in B that are suppose to the "holes" in C, make C be all-zero.
Can someone help with a direction to a proof? Thanks
(Convexity is closed under intersection) Given a family of convex set $$C_i$$, where $$i\in I$$ for some index set $$I$$, then $$\cap_{i\in I}C_i$$ is convex.
In other words, the intersection of convex sets are convex. | {
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electromagnetism, electromagnetic-radiation, quantum-electrodynamics, plane-wave
The problem with your question about faster than light information transmission, is that if X were the only point emitting a wave, then it would be a spherical wave, not a plane wave. A plane wave can be thought of as being composed as a superposition of spherical waves emitted in phase from every point on an infinite plane. So in your example, information would not be arriving at Z from X, but instead from some other source point within the causal past of Z. In your diagram that point could be at the same height as X, but directly above Z.
Considering a wavefront (planar or otherwise) as a superposition of spherical waves is the central feature of the Huygens-Fresnel Principle, which would be a good reading on the topic. | {
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"tags": "electromagnetism, electromagnetic-radiation, quantum-electrodynamics, plane-wave",
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quantum-state, density-matrix
It is interesting, however, that the objective lack of knowledge can become subjective - a second party can perform operations on the rest of the entangled state. They can know the measurement results etc. but if they don't pass those on, the person holding the original quantum system has no new knowledge, and so describes their system using the same density matrix as before, but it is now a subjective description.
It is also important to note that choosing a particular way of representing the density matrix, for example, $\rho=\sum_ip_i|\phi_i\rangle\langle \phi_i|$, is a very subjective choice. It may be motivated by a particular preparation procedure, but mathematically, any description that gives the same matrix is equivalent. For example, on a single qubit, $\rho=\frac12\mathbb{I}$ is known as the maximally mixed state. Due to the completeness relation of a basis, this can be represented as a 50:50 mixture or two orthogonal states using any 1-qubit basis.
$$ | {
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beginner, ruby, simulation, numerical-methods
# Array of closed doors
def closed_doors
@doors.reject(&:open?)
end
end
The Door class may seem sort of pointless (and indeed there are many ways to do things), but instead of using, say, an array of plain booleans, an array of door objects allows us to reference specific doors. Not as array indices, but as the doors themselves.
Again, I'm not saying this is the only - or even a particularly great - way of doing things. But it reads pretty well, and is easy to use.
For instance, this code will play a basic game with 3 doors, of which 1 will be revealed, and the player changes their pick:
game = Game.new(3)
game.pick_door # initial pick
game.open_doors(1) # reveal what's behind a door
game.pick_door # change pick
game.won? # => (~67% chance of a win) | {
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java, multithreading, android, networking, ftp
}
FTPconnection class implementation:
package com.example.ftphostmanagement;
import android.util.Log;
import java.io.IOException;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import org.apache.commons.net.SocketClient;
import org.apache.commons.net.ftp.FTP;
import org.apache.commons.net.ftp.FTPClient;
import org.apache.commons.net.ftp.FTPReply;
public class FTPconnection {
FTPHostProfiles mFTPHostProfiles = new FTPHostProfiles();
public FTPconnection(FTPHostProfiles input)
{
this.mFTPHostProfiles = input;
}
public FTPClient connectftp(String profilename)
{
// Reference: https://stackoverflow.com/a/8761268/6667035
FTPClient ftp = new FTPClient();
try {
var FTPHostProfile = mFTPHostProfiles.GetProfile(profilename); | {
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species-identification, zoology, ornithology
Forked tail, like swifts have
Narrower wings, which seem longer
Higher-pitched short tweets, which never turn into "laughter". A sample (with car noise in background) can be heard here.
Here are some photos I could took. They are blurred and chromatically aberrated because it's hard to focus with a telephoto lens and such fast motion towards and away from me. I exposure-compensated them to make the colors visible, so the photos are a bit noisy. I hope they are useful for identification anyway. This is one of the numerous species of tern. They are common birds of the seashore and rivers world-wide. The characteristic forked tail and the black cap on the head is what gives it away.
It is hard to say for sure given the chromatic aberration altering the colours, but this is likely to be either from the genus Sterna (particularly the Arctic tern or the common tern), or possibly the little tern (Sternula hirundo). | {
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Let $$Z_k={\rm ker} T^k$$, $$k\geq 0$$ be the sequence of kernel spaces. One has $$Z_0 =\{0\} \subset Z_1 \subset Z_2 ...$$ Let $$d_k = {\rm dim\ } Z_k$$. Then one has the following inequality for $$k\geq 1$$: $$d_{k+1}-d_k \leq d_k-d_{k-1}$$ In your case this yields $$11-9\leq 9-d_2\;$$ or $$\;d_2\leq 7$$ and $$\;9-d_2\leq d_2-4\;$$ or $$\;d_2\geq 6.5$$. The unique integer solution is thus $$d_2=7$$ and by the kernel-rank theorem we get $${\rm rank}\; T^2=4$$ in accordance with the statement of Alex. | {
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general-relativity, spacetime, differential-geometry, metric-tensor, stress-energy-momentum-tensor
According to the above approach, we could say that the "true" physical reality of the universe is represented by the pair $(M, T)$, while the metric $g$ emerges as an appeareance from the requirement that evolution appears simple, i.e., that $g$ and $T$ satisfy Einstein's equation.
From the mathematical point of view, this approach poses for example the following problems: does any matter tensor field $T$ admit a metric $g$ such that Einstein's equation is satisfied? To what extent a tensor field $T$ univocally determines the metric $g$?
Does this approach make sense, at least from the mathematical point of view? Addressing just the last two paragraphs of your question:
If $T$ is "non-degenerate" (at every point as a linear transformation from $T_pM \to T_p^*M$), then modulo some issues with the constraint equations $g$ can be solved from $T$, at least locally in time, after prescribing it in a compatible way on a space-like hypersurface. See this article by De Turck. | {
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quantum-mechanics, quantum-information, hilbert-space, tensor-calculus, density-operator
The basic idea is that one can perform a rotation $U_A$ and $U_B$ on the two qubits, respectively, which correspondingly transforms $r\mapsto O_Ar$, $s\mapsto O_Bs$, and $T\mapsto O_A T O_B^T$. By choosing $O_A$ and $O_B$ which give the singular value decomposition of $T$, one finds that any $\rho$ in your form (1) can be replaced by one with a diagonal $T$, with the singular values of the original $T$ on the diagonal.
Now, one can use different "trial states" $\vert\psi\rangle$ and check if $\langle\psi\vert \rho\vert\psi\rangle\ge0$ (which is necessary for positivity of $\rho$). By using the Bell states (for which the $r$ and $s$ part vanish), one obtains non-trivial constraints on $T$. | {
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• For checking if $A^{-1}$ exists, this matrix is very amenable to the trick of computing the determinant modulo 2 – jld Jun 19 '18 at 22:47
• @JoseLopezGarcia for an integer-valued matrix, the determinant is non-zero if the determinant with every entry taken modulo 2 is also non-zero. So in your case $$A \mod 2=\begin{bmatrix}0 & 0 & 0 & 1 \\ 0 & 0 & 1 & 0 \\ 0 & 1 & 0 & 0 \\ 1 & 0 & 0 & 0\end{bmatrix}$$and this matrix is clearly full rank and so has non-zero determinant (it will certainly be $\pm 1$ but the actual value isn't important so you can stop as soon as you recognize it's not singular). – jld Jun 20 '18 at 13:54 | {
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cc.complexity-theory, reference-request
If so, does it still work when restricting to planar instances of 3DM, i.e. where the bipartite graph associated with the 3DM instance is planar? The answer to both questions is yes.
The standard reduction from 3-SAT to 3DM – as used by Garey and Johnson, for example – is not parsimonious, but there is a sequence of parsimonious reductions that goes:
3-SAT → 1-IN-3-SAT → MONOTONE-1-IN-3-SAT → 3DM
Moreover, these reductions can be done in a way that preserves planarity. The details can be found in [1, 2]. The key reduction MONOTONE-1-IN-3-SAT → 3DM is from [1]. It is shown to be parsimonious by [2], which also shows how to do the other reductions in a parsimonious way. The reduction from 3-SAT to PLANAR-3-SAT is done using the crossover gadget from [3], which [2] also shows to be parsimonious.
[1] M.E Dyer, A.M Frieze, Planar 3DM is NP-complete, Journal of Algorithms, Volume 7, Issue 2 (June 1986), Pages 174-184. PDF | {
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matlab, ifft
This surely can be more efficiently expressed using array operations, join Y and its reverse to form the new Y. Then apply directly ifft, without ifftshift, to get a signal with the given spectrum.
Update 14.1.:If the number of frequencies is rather small, an explicit evaluation as
$$\sum_{k:Y[k]\ne 0} Y[k]\cdot \sin(c\cdot X[k]\cdot t)$$
may be easier to implement. The factor c is to be fixed in such a way that the result is in the audible spectrum. | {
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