text stringlengths 1 1.11k | source dict |
|---|---|
fluid-dynamics, momentum, conservation-laws
Why is the second term in Eq. \ref{Eq:DerivativeQuasimomentum} equal to zero? Why does he mention the fact that the volume of the body is excluded in the integral of the first term only (should one not exclude its volume at the initial time in the second term too?). Why does he call the derivative a total derivative? | {
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"tags": "fluid-dynamics, momentum, conservation-laws",
"url": null
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nlp, xgboost, prediction, performance
It is visible that the multiclass approach systematically outperforms the one vs rest one. NB: These are training set performances.
Is there a clear theoretical reason for this? Multiclass models in XGBoost consist of n_classes separate forests, one for each one-vs-rest binary problem. At each iteration, an extra tree is added to each forest. But it isn't actually a one-vs-rest approach (as I thought in the first version of this answer), because these trees are built to minimize a single loss function, the cross-entropy of the softmax probabilities.
https://discuss.xgboost.ai/t/multiclassification-training-process/29
https://github.com/dmlc/xgboost/issues/806
https://github.com/dmlc/xgboost/issues/3655 | {
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"tags": "nlp, xgboost, prediction, performance",
"url": null
} |
electrostatics, electric-fields, charge, symmetry, vector-fields
Title: Why do the electric field lines not originate from a positive charge in the following situation? Consider two fixed positive point charges, each of magnitude $Q$ placed at a finite distance apart. Let point $O$ be the midpoint of the two charges. We can see that the electric field at $O$ is zero, but for any other point in the perpendicular bisector of the two charges, the electric field is nonzero and the direction of the electric field is along the perpendicular bisector and opposite to that of point $O$. So it appears that there are electric field lines originating from point $O$. | {
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"tags": "electrostatics, electric-fields, charge, symmetry, vector-fields",
"url": null
} |
GMAT self-study has never been more personalized or more fun. Try ORION Free!
Intern
Joined: 12 Jul 2012
Posts: 21
Re: If root(xy) = xy what is the value of x + y? [#permalink]
### Show Tags
12 Jul 2012, 03:00
Here is my solution
Take square of both sides:
(root(xy) )^2 = (xy)^2
xy = (xy)^2
With Option (1): x = -1/2
-1/2y = 1/4 * y^2
y = 4 * (-1/2)
y = -2
Hence, X+Y = -1/2 - 2 = -5/2.
Math Expert
Joined: 02 Sep 2009
Posts: 49206
Re: If root(xy) = xy what is the value of x + y? [#permalink]
### Show Tags
12 Jul 2012, 03:06
RamakantPareek wrote:
Here is my solution
Take square of both sides:
(root(xy) )^2 = (xy)^2
xy = (xy)^2
With Option (1): x = -1/2
-1/2y = 1/4 * y^2
y = 4 * (-1/2)
y = -2
Hence, X+Y = -1/2 - 2 = -5/2.
There is another value of $$y$$ apart -2 which satisfies $$-\frac{1}{2}*y=\frac{1}{4}*y^2$$, namely $$y=0$$. | {
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} |
6. Aug 11, 2012
### yogo
Thanks for your help guys. Appreciate it.
@micromass: I am not so good at Math. I was wondering how tight these bounds are?
Thanks,
yogo
7. Aug 15, 2012
### chingel
You would have to calculate the integral to find out. Or you can let an online calculator do it. To find the tightness of the bonds, calculate the difference between the integrals, or in other words the integral from n to n+1.
http://www.wolframalpha.com/widgets/view.jsp?id=8ab70731b1553f17c11a3bbc87e0b605 | {
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"openwebmath_score": 0.8378165364265442,
"tags": null,
"url": "https://www.physicsforums.com/threads/sum-of-log-squared-terms.627139/"
} |
homework-and-exercises, newtonian-mechanics, forces, friction, string
$$T(\theta + d\theta) + \mu Td \theta \le T(\theta) \\ \implies T \le T_{0}e^{-\mu \theta}$$
EDIT: I want to make my question more clear...A rope is attached to a boat, the rope is then wrapped around a pole. Now I grab the other end of the rope and pull it with a tension $T_{0}$..Then shouldn't friction oppose my action of pulling the rope?..In that case how does the equation $(*)$ hold true?
Basically, I want to know how the author arrived at the equation $(*)$...The statement "This
friction force is what gives rise to the difference in tension between the two ends of
the piece." is not very clear to me..."Difference" in what sense?
$$T(\theta + d\theta) > T(\theta) \ \ \ \ \ \text{OR}\ \ \ \ \ T(\theta) < T(\theta + d\theta)$$ | {
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"url": null
} |
electrostatics, electric-fields, work, potential, conventions
Title: Electric Potential of Point Charge (sign problem) This question has been asked before, but the answers didn't clarify the problem for me, so I thought I might ask again.
It's really a simple question. Let's say we're calculating the electric potential of a point charge, so we have
$$V(r) - V(\infty) = -\int^r_{\infty} \vec{E}\cdot d\vec{\ell}$$
And the electric field is $$\vec{E} = \frac{q}{4\pi\epsilon r^2} \hat{r}.$$ What I'm not understanding is the choice of $d \vec{\ell}$. It seems to me that since we're coming from infinity to $r$, the path should be in the $-\hat{r}$ direction, so $d\vec{\ell} = -\hat{r} dr$. But this gives
$$V(r) = -\int^r_{\infty} - \frac{q}{4\pi\epsilon_0 r'^2} dr' = -\frac{q}{4\pi\epsilon_0 r}$$ which is obviously the wrong answer. The problem is that apparently $d\ell = \hat{r} dr$. Can someone tell me why this is the case? The use of the formula $\displaystyle V(r) - V(\infty) = -\int^r_{\infty} \vec{E}\cdot d\vec{\ell}$ requires a little care. | {
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python, algorithm
lines[idx_start + 1: idx] = []
return remove_duplicate_blocks(lines)
return lines
def traverse_tree(conf):
for f in Path(conf.dir).glob(conf.glob):
print(f)
lines = f.open('r', encoding='utf-8').readlines()
clean_lines = remove_duplicate_blocks(lines)
print(clean_lines)
if not conf.dry_run:
with f.open('w', encoding='utf-8') as fo:
fo.write(''.join(clean_lines))
if __name__ == '__main__':
parser = argparse.ArgumentParser(description='''DESCRIPTION:
Find and remove multiline duplicated text blocks ''',
formatter_class=argparse.RawDescriptionHelpFormatter,
epilog='''USAGE:
{0} -d [root_dir] -g [glob_pattern]
'''.format(os.path.basename(sys.argv[0]))) | {
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"tags": "python, algorithm",
"url": null
} |
c#, object-oriented, game, console
Utility class
using System;
using System.Threading;
class Utility
{
public static void WriteLineInColor(string text, ConsoleColor color)
{
Console.ForegroundColor = color;
Console.WriteLine(text);
Console.ResetColor();
}
public static void WriteInColor(string text, ConsoleColor color)
{
Console.ForegroundColor = color;
Console.Write(text);
Console.ResetColor();
}
public static void Sleep(int miliseconds = 1500)
{
Thread.Sleep(miliseconds);
}
public static void printDotAnimation(int timer = 10)
{
for (var x = 0; x < timer; x++)
{
Console.Write(".");
Thread.Sleep(100);
}
Console.WriteLine();
}
public static void Line()
{
Console.WriteLine("\n--------------------------------------------------");
}
}
BlackJackGame class
using System;
using System.Threading; | {
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c++, reinventing-the-wheel, image, template, c++20
template<std::size_t dim, template<class...> class Container = std::vector, class T>
constexpr auto n_dim_container_generator(T input, std::size_t times)
{
if constexpr (dim == 0)
{
return input;
}
else
{
return Container(times, n_dim_container_generator<dim - 1, Container, T>(input, times));
}
}
}
#endif
The full testing code
The grayscale type data has been tested here.
/* Develop by Jimmy Hu */
#include "base_types.h"
#include "basic_functions.h"
#include "image.h"
void bicubicInterpolationTest();
int main()
{
bicubicInterpolationTest();
return 0;
}
void bicubicInterpolationTest()
{
TinyDIP::Image<GrayScale> image1(3, 3, 1);
std::cout << "Width: " + std::to_string(image1.getSizeX()) + "\n";
std::cout << "Height: " + std::to_string(image1.getSizeY()) + "\n";
image1 = image1.set(1, 1, 100);
image1.print(); | {
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} |
java, linked-list
Title: Single Link List So I have implemented Single link list using java.Please advice if this is OK or can be made better.
public class SingleLinkedList<Generic> {
private Generic data;
private SingleLinkedList<Generic> next;
public SingleLinkedList() {
super();
}
public SingleLinkedList(Generic data, SingleLinkedList<Generic> next) {
super();
this.data = data;
this.next = next;
}
public Generic getData() {
return data;
}
public void setData(Generic data) {
this.data = data;
}
public SingleLinkedList<Generic> getNext() {
return next;
}
public void setNext(SingleLinkedList<Generic> next) {
this.next = next;
}
public SingleLinkedList<Generic> add(Generic data, SingleLinkedList<Generic> node) {
SingleLinkedList<Generic> temp = new SingleLinkedList<Generic>(data, null);
node.setNext(temp);
return temp;
}
public int size(SingleLinkedList<Generic> node) {
int size = 0;
if (node == null || node.getNext() == null)
return 0; | {
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ros, ros-kinetic
Title: Autoware : Unable to complete the demo
Hello.
Autoware version : 1.12.0
ROS Version : Melodic
Autoware installed from Docker
Docker version 19.03.2, build 6a30dfc
I am trying to run the demo of autoware here : https://gitlab.com/autowarefoundation/autoware.ai/autoware/wikis/ROSBAG-Demo
But I am experiencing a lot of problems.
First of all, I download the files, create a .autoware in my personal home and extract the files there.
I start autoware by running the run.sh file, I am now connected with the autoware user 'in' the docker container.
But then the first instruction is to move to the directory autoware.ai which doesn't exist !
The right folder seems to be
/home/autoware/Autoware
Then I source the setup.bash file.
I start the runtime manager with
roslaunch runtime_manager runtime_manager.launch | {
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javascript, jquery, ajax
How to envoke it:
<button type="button" onclick="uzim_vred('yourPHPscript.php',$(this).parent().attr('id'))">Send</button>
First argument is a path to and name of php script, second is used for id of form element from whom you want to "serialize" values. You are not really implementing in plain JavaScript in that you are using jQuery inside the function. This seems to be an odd choice. Are you using jQuery or not? You should make a decision. If you are using jQuery, then I don’t know why this function would exist at all.
The function name itself is meaningless and does not at all convey what the function does.
You are not url encoding your query string.
You are not handling case where your asynchronous fails to return 200 response.
You are using loop counters where you don’t really need to.
It makes no sense how you build a query string then split it apart and then reassemble it.
Code style is problematic:
inconsistent indentation
lines of code that are too long | {
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homework-and-exercises, general-relativity, differential-geometry, metric-tensor, differentiation
If you do not trust the instinct that $\nabla_\mu \delta_\nu{}^\rho = 0$, you can show that it is true in a few different ways, I'd do it like this:
$$ \nabla_\mu \delta_\nu{}^\rho = \partial_\mu \delta_\nu{}^\rho
+ \Gamma_{\mu \alpha}{}^\rho \delta_\nu{}^\alpha
- \Gamma_{\mu \nu}{}^\alpha \delta_\alpha{}^\rho =
\Gamma_{\mu \nu}{}^\rho - \Gamma_{\mu \nu}{}^\rho = 0\,.
$$ | {
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electromagnetism, potential, voltage, definition, electronics
$$
Voltage in general
We conclude that, in general:
$$
V_{\gamma_{A->B}}=(\phi_B-\phi_A)+\int_{\gamma_{A->B}}\partial{\vec{A}}/\partial{t}.\vec{dl}
$$
That is, voltage (the path integral of the total electric field along a specific path) is the sum of scalar potential difference (which is path-independent) and the contribute to the emf (which is path-dependent). This decomposition of voltage can be found, for example, in Popovic & Popovic's introductory EM textbook.
If you want to recover the emf, specify a closed path - the potential difference will go to zero.
If you are interested in the scalar potential difference you need to remove the non-conservative component a from the total electric field E and compute the path integral of
$$
\vec{E_c}=\vec{E}-\vec{E_{nc}}=\vec{E}-(-\partial{\vec{A}}/\partial{t}) \\
=\vec{E}+\partial{\vec{A}}/\partial{t}
$$ | {
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thermodynamics, energy-efficiency
Caveat: if refrigerant is not exiting the condenser as pure liquid, efficiency improvements can be made by increasing UA of the condenser. | {
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beginner, object-oriented, ruby, sql, web-scraping
begin
# connect to the MySQL server
dbh = DBI.connect('dbi:ODBC:DamoclesProwler', 'user', 'pw')
sqlText = "INSERT INTO prowlerRunningResults(ProwlerDriver, SourceURL, Title, DestinationURL, FileSource, FileType, FileName, LastModified, FileSize, HashMD5, HashSHA256, ImageBinary)
VALUES ('#{driver}', '#{source}', '#{title}', 'NA', '#{imgSrc}', '#{fileType}', '#{fileName}', '#{lastModified}', #{fileSize.to_i}, '#{md}', '#{sha}', '#{binary}' )" | {
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"openwebmath_score": null,
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} |
electromagnetism, waves, electromagnetic-radiation, electrical-resistance, maxwell-equations
that isn't specifically known to be strongly magnetic, such as a ferrite material or nickel. I don't know whether Pozar actually forgot to mention this assumption, or if you just missed it in your reading, or it was in an early version of the book and got dropped by later edits, or what. | {
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Then, the perfect pairings are BADC, CDBA, and DCBA and the probability of having a perfect pairing is $$\frac{1}3\frac{1}3+\frac{1}3\frac{1}2\frac{1}2+\frac{1}3\frac{1}2\frac{1}2=\frac{5}{18}$$
Option 2
First consider what happens in the first round of drawing (that is, when all the people have drawn a valid name until the last person's turn to draw). The probability of reaching the last person with only their name in the bowl is $$\frac{5}{36}$$. There are these possible derangements with the probability of choosing that derangement using option 2 in the first round given next to each:
BADC $$\frac{1}3\frac{1}3$$
BCDA $$\frac{1}3\frac{1}3\frac{1}2$$
BDAC $$\frac{1}3\frac{1}3$$
CADB $$\frac{1}3\frac{1}2\frac{1}2$$
CDAB $$\frac{1}3\frac{1}2\frac{1}2$$
CDBA $$\frac{1}3\frac{1}2\frac{1}2$$
DABC $$\frac{1}3\frac{1}2$$
DCAB $$\frac{1}3\frac{1}2\frac{1}2$$
DCBA $$\frac{1}3\frac{1}2\frac{1}2$$ | {
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"url": "https://stats.stackexchange.com/questions/187080/probability-that-secret-santa-arrangement-will-result-in-perfect-pairings"
} |
duel information codes are adopted for each operation, in which the direct code is being compared with its inverse counterpart. The logic design is suitable for use, the circuitry is simple, and the equipment is reliable and easy in maintenance. 本文介绍了一套用于电气化铁道分区亭的电子装置。它是1对5的分散集中式系统,遥控与遥信综合于同一系统中。通道采用时间-频率划分。各被控站遥信为经常自动循环传送方式,信息码采用二次传送,正反码校核。逻辑设计合理,电路简单,工作可靠,维修方便。 126 lateral geniculate neurones were examined on unanaesthetized immobili-zed cats.The temporal frequency tuning curves of single neurones were measuredby stimulating the cat's eye with a sinusoidally modulated light spot,generated ona CRT and presented to each neurone's receptive field center or its surround.Theaverage discharging rate was used as an index to judge the sensitivity to different mo-dulating frequencies.By comparing the mean impulse rates responding to modula-ted light stimulations(modulated discharge... 126 lateral geniculate neurones were examined on unanaesthetized immobili-zed cats.The temporal frequency | {
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"openwebmath_score": 0.40670904517173767,
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} |
scattering
Title: Mie scattering intensity and spherical particles on I am running an experiment where I shine infrared light on (almost) spherical particles on the micron scale (PM2.5 - PM10). I then look at the (90 deg) scattering properties to try and size the particles.
I am looking for the theory of Mie scattering and its intensity, specifically how the scattered intensity depends on the surface area of the particles.
Looking for suggestions of good literature on this, or just simple equations. If the spherical approximation is good enough, you should be able to convert the surface areas into radii. I mention that because in my work with light scattering, all the equations are usually written in terms of the radius of the scatterers. It also looks like all the Mie scattering tables are written in terms of the radius of the scatterers as well. | {
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beginner, php, ruby, ruby-on-rails
attack surface the current proposed code opens up for an attacker.
Much better to be conservative in what you send down to the child process.
specification
The OP question didn't really flesh out the input space
in ways that would let an implementer distinguish between
good and bad scenarios.
automated tests
This submission contains no integration or unit tests that would
increase our confidence in the ability of target code to
reject carefully crafted attack inputs. | {
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"tags": "beginner, php, ruby, ruby-on-rails",
"url": null
} |
quantum-chemistry, computational-chemistry, molecular-orbital-theory, orbitals
And wouldn't there be an unlimited amount of equivalent solutions?
Yes. Every possible unitary transformation among the occupied canonical orbitals, of which there is indeed an unlimited number, would provide a set of orbitals that gives an equivalent total wavefunction. Not all of these transformed orbital sets are especially useful, however. Specific examples of useful ones include the various localization transforms that are the topic of the question, the series of variously defined "natural orbitals", and (somewhat related) the Löwdin symmetric orthogonalization for atomic orbitals.
Is this just a mathematical gimmick or does this represent the reality? ... Or is this just a thing we do because it makes it easier to understand? | {
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java, mvc
Title: Java MVC and code example I have a MVC design for a GUI Java program. I was wondering if:
Someone could either comment the code to help me out in understanding what I am doing better.
Help me fix newbie mistakes to make this program function better.
This program asks the user for some info about a train ticket and trip and basically processes a card they enter and spits out a receipt if the card is valid. The requirement is that I use the MVC design pattern with the catch that there has to be 3 packages of model, view, and controller.
I can upload this to Google Drive if need be.
CONTROLLER PACKAGE
package edu.witc.TrainTicket.controller;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
import javax.swing.JOptionPane;
import edu.witc.TrainTicket.model.*;
import edu.witc.TrainTicket.view.*;
public class TrainTicketController { | {
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thermodynamics, electricity, semiconductor-physics
The electric potential that develops is also known as a voltage. V = IR, and there you have your DC current. Running a DC current to create a temperature difference is just the other side of the coin, in the same way an electric generator is essentially an electric motor running in reverse. | {
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enzymes, experimental, antibody
I hope this is not to crudely explained, again. These are my questions concerning the experiment: | {
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Well, here is my next #CosinesGroup posts. The problem in my opinion is a very cool problem because of the awesome elegant solution.
This problem has also been called "Polya's Urns", but I looked that up and "Polya's Urns" actually covers a lot of random complicated stuff, so I kept it at magnetic dollars.
Hope you enjoy! Feedback is appreciated. · 3 years, 8 months ago
This is the solution in Peter Winkler ' Mathematical Puzzles. An excellent book. · 1 year, 2 months ago
How do you do this? · 3 years, 7 months ago
I'm curious to know why only one mathematician guessed over $100. I personally guessed around$150,000 becuase while the probability might be pretty low at some point, in A MILLION tries, it would be bound to happen quite a bit. · 3 years, 8 months ago
Well, their reasoning would probably be then assuming a sort of "reverse" normal distribution curve. The average of all the games would probably be pretty low. | {
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energy-conservation, time, big-bang, matter
Title: Doesn't the Big Bang negate the law of conservation of matter? I was watching Hawking (2004 film) and in the movie, Hawking has a sudden insight that all the matter and energy observed in the known universe may, in fact, have sprung out from nothing (singularity) during the Big Bang event—an insight which later on goes to become the main subject of his thesis.
But this completely flies in the face of the laws of conservation of matter and energy. What gives? The link Qmechanic has suggested is a duplicate and does discuss the question you ask. However there is another point that is worth making here.
In general relativity we describe the universe as a manifold equipped with a metric, and the metric is the FLRW metric that desciribes expanding spacetime. However the FLRW metric does not include the point(s) at $t = 0$ i.e. the Big Bang itself. So we cannot say that: | {
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ros, rviz, urdf, tutorial, ros-hydro
Title: no robot visible in rviz for urdf tutorial
I'm working my way through the urdf tutorials, specifically this one
On the first task it has me launch rviz to see the "r2d2" robot using the command:
roslaunch urdf_tutorial display.launch model:=01-myfirst.urdf
I am in the proper directory, rviz launches just fine, but there is no robot visible. Just the grid map. This error appears under the Global Status in orange: No tf data. Actual error: Fixed Frame [map] does not exist
So I get that it's not getting transform data, but I'm not sure what to do about it. I have not modified any files, am running hydro on Precise. | {
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Probability Of Rolling A 9 With Two Dice | {
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"url": "http://arcivasto.it/sisb/probability-of-rolling-a-9-with-two-dice.html"
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c#, object-oriented, sql-server
Console.Read will exit at any key; you want to change your message or change that to Console.ReadLine to require an Enter.
AppCoordinator
Your AppCoordinator class is a major code smell; it's a (no offense) terrible name that really doesn't describe what it's doing, and is likely to become a "god object". I would rename that to CustomerRepository or CustomerDataAccess or something.
Since this is your largest class, the meat of my comments are here: | {
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machining, cnc
EDIT: My question originally had two parts with the second asking if there was also a performance difference between entry level CNC and entry level manual mills, but since none of the answers addressed that in much detail and it's sort of a separate (but only possibly related) question I have removed it. Making a machine CNC ready has a neglible cost. Electronics cost nearly nothing, and are easy to do when your not aiming to super quality. All of the moving elements can be simplified because you dont need to present user interface through mechanical couplings and dont need to worry about user safety. | {
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4. ### math
the hundred thousands digit of a six-digit even numbers is 3 more than the thousand digit,which is twice the ones digit.give at least four numbers that satisfy the given condition. | {
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"url": "https://www.jiskha.com/questions/1821813/in-the-statement-below-the-two-blanks-can-be-filled-by-positive-single-digit-numbers-in"
} |
crystal-structure, crystallography
In one of my previous lives I had to align contact photomasks to silicon wafers in order to open holes in photoresist, used to etch through a thin silicon nitride layer (10 to 100 nm) which was then used as a mask for directional wet etching of the silicon. KOH can have a 100:1 or larger wet etch anisotropy for certain crystal directions, and you can get pyramidal or even very vertical (wrt wafer surface) sidewalls from anisotropic wet etches if you rotate your mask to get specific orientations of the pattern edges with respect to crystal directions. [...] Anisotropic wet etching (Orientation dependent etching) | {
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lo.logic, type-theory, coq, dependent-type
Title: Does the order of declarations in an inductive type matter? I was wondering if the order of declarations of an inductive type can matter.
For example in Coq you can define Nat either by:
Inductive Nat :=
| O : Nat
| S : Nat -> Nat.
or
Inductive Nat :=
| S : Nat -> Nat
| O : Nat.
This will perhaps change the order of the parameters in the automatically generated eliminator, but that’s not a big deal.
What I’m wondering is if it is possible to write a declaration like
Inductive typewhereordermatters :=
| cons1 : type1
| cons2 : type2. | {
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python, beginner, python-3.x, selenium
def esta_no_dia_da_semana(dias_da_semana, data_atual):
if data_atual.weekday() in dias_da_semana:
return True
return False
hora_string = input("Que horas quer agendar? (hh:mm:sg): ")
dia_da_semana_string = input(
"Quais dias da semana? (seg ter qua qui sex sab dom): ")
hora = int(hora_string.split(':')[0])
minuto = int(hora_string.split(':')[1])
segundos = int(hora_string.split(':')[2]) | {
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c#, linq, hash-map
foreach (var reciver in configuration.ReceiverManager.Receivers)
{
List<string> lst = new List<string>();
for (int i = 0; i < reciver.Messages.Count; i++)
{
lst.Add(reciver.Messages[i].Type);
}
tempDictionary.Add(reciver.ReceiverName, lst);
}
FindDuplicates(tempDictionary, ref duplicatesList);
PrintDuplicates(duplicatesList);
}
catch (Exception Ex)
{
Log.Instance.Error(Ex.Message, Ex);
}
}
else
{
Log.Instance.Warn($"Cannot validate empty configuration.");
}
} | {
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control, motion-planning, nav2, base-local-planner, teb-local-planner
Any insights or guidance on integrating these local planners with the Nav2 stack would be greatly appreciated. Thank you, Steve, for your guidance and the comprehensive documentation provided for the Navigation2 stack. I've thoroughly reviewed the materials, particularly the sections detailing the Regulated Pure Pursuit and MPPI controllers, which offer invaluable insights into configuring and understanding these components! | {
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statistical-mechanics, history, fermions, identical-particles
EDIT(12/7/2016): Here's the reference: Dirac, The Origin of Quantum Field Theory // The Impact of Modern Scientific Ideas on Society, Dordrect, Holland, D. Reidel, 1981, pp.39-55 (see also information at https://cds.cern.ch/record/1177841?ln=en) I read the article in Russian translation | {
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visible-light, everyday-life, astronomy, thermal-radiation, stars
APPENDIX: I have found a few interesting links that appear to confirm this line of argument. Firstly, one can predict what stellar spectra would look like to the eye under conditions where the cone cells are operational. Here we can see that many stars would appear either pink (K-stars) through orange (M-stars). G-stars like the Sun are just off-white, whilst hot stars are distinctly blue (see also here). | {
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discrete-signals, wavelet, time-frequency, cwt
Mean scale
Similarly, we define the energy analogue for scale-freq mapping:
$$
\tilde s_\psi
= \frac{\int_0^\infty s|W_o (s,t)|^2 ds}{\int_0^{\infty} |W_o(s, t)|^2 ds} = \frac{\int_0^\infty s|\hat\psi (s\omega_o)|^2 ds}
{\int_0^{\infty} |\hat\psi (s\omega_o)|^2 ds} \tag{7}
$$
With a change of variables, this is simply $\tilde s_\psi = \tilde \omega_\psi / \omega_o$. Thus $\tilde\omega_\psi$ determines the scale at which the mean of CWT energy of a sinusoidal signal occurs.
Disagreement example
To illustrate the mapping distinctions, take CWT of a sinusoid near Nyquist, since that's where a strictly analytic Morlet is asymmetric and has different mappings to frequency: | {
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slam, localization, navigation, odometry, kinect
Title: How to consider known poses of the Kinect while mapping with RGBDSLAM?
Hey!
I am using RGBDSLAM with ROS (groovy) and a Kinect.
To improve the mapped data, I want to use known poses (of a tracking system) of the Kinect to
first: improve the mapping
second: have the map in the right coordinate plane
Now I wonder if it is possible to make RGBDSLAM consider the known poses and how.
As far as I know it is still not much fun to use "external" odometry while using RGBDSLAM, is that right?
But I was hoping to not use it as odometry but mabye instead of the estimated odometry of RGBDSLAM.
I was setting all my hope into "config/ground_truth_frame_name", but I wasn't able to figure out what it really does. Is it just used for the first calculation?
I am sorry for the very general question. I've been trying that for a while now and was hoping somebody here could give me a hint.
(Mabye also where to fiddle with the code in rgbdslam - graph_manager? - if necessary) | {
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baryons, galaxies
Title: Baryonic Missing Mass A recent article from a popular astronomy website tells of discovery of missing mass (not dark matter) that has puzzled astronomers for some time. Apparently, the discovery involves enhanced electron density in filaments associated with superclusters of galaxies. How were astronomers able to determine that this baryonic mass was missing in the first place, and what percentage of total baryonic mass did it entail? The article answers the question, though it does not lean on it:
His evidence came from the orbital velocities of galaxies in clusters, rotational speeds, and gravitational lensing of background objects. | {
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java, android, authentication, firebase
An as a result we have very clean an understandable code for validation the form:
private boolean checkUserName() {
return checkEditText(mUsernameField);
}
private boolean checkEmail() {
return checkEditText(mEmailField);
}
private boolean checkPassword {
return checkEditText(mPasswordField);
} | {
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java, programming-challenge, comparative-review
Question
Which of the above version is easier to read and which version would you like to see if you just joined to project? TimeRangePredicateSupplier
To me, this name seems wrong. The implementations are providing a time based greeting, so perhaps TimeBasedGreetingSupplier might be better.
Afternoon
The way you've coded AfternoonPredicateSupplier it knows too much about how it's used. Whilst the afternoon doesn't have a particular requirement, since you've coded it, it would seem to make sense for it to check a time period that you've designated as 'afternoon'. This would be clearer and it would mean that all of your suppliers implement the interface correctly, which could mean they are useful in other scenarios.
Taking this approach with with Afternoon also simplifies the logic in your Beginning provider. You no longer need to treat Afternoon as a separate case, you just find the first predicate that matches the current time. So, provide can become:
@Override | {
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quantum-mechanics, angular-momentum, symmetry, schroedinger-equation, coordinate-systems
I also solved the case of a circular potential well a while back and had to include the angle.
So my question is: does in the cylindrical case one have to include $P(\varphi)$ in the wave functions? And if not, why not? That paper mentioned in the question (arXiv:1205.3444) is, frankly speaking, very low quality. It appears to be a conference contribution from a student who was working on programming Maple to solve the Schrödinger equation analytically. However, there are two issues with the work. The first, which you have identified, is that the paper misses many solutions. The second, of less importance but still worth mentioning, is that the problem of solving the kind of boundary value problems analytically through a language like Maple was already solved at least a decade before this paper was posted on the arXiv. | {
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1. Techniques of integration (6)
Let $f: \mathbb{R} \longrightarrow \mathbb{R}$ be continuous and periodic with period $T > 0.$ For any real numbers $a evaluate $\lim_{n\to\infty} \int_a^b f(nx) \ dx.$
2. Originally Posted by NonCommAlg
Let $f: \mathbb{R} \longrightarrow \mathbb{R}$ be continuous and periodic with period $T > 0.$ For any real numbers $a evaluate $\lim_{n\to\infty} \int_a^b f(nx) \ dx.$
Hi NonCommAlg.
A continuous function is integrable, and the integral over a bounded interval of an integrable periodic function is bounded. Hence, using the substitution $u=nx,$
$\lim_{n\,\to\,\infty}\int_a^bf(nx)\,dx$
$=\ \ \lim_{n\,\to\,\infty}\frac1n\int_{na}^{nb}f(u)\,du$
$=\ \ 0$ since the integral is bounded
Something tells me I may have done something wrong, because, well, surely it can’t be that simple …
3. Originally Posted by TheAbstractionist
Hi NonCommAlg. | {
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python, python-3.x, programming-challenge
The code I have produced till now is:
import math
class Cell:
def __init__(self, Row, Coloumn):
self.Row = Row
self.Coloumn = Coloumn
self.Name = 'CellR'+str(Row)+'C'+str(Coloumn)
self.UNeighbor = None
self.DNeighbor = None
self.LNeighbor = None
self.RNeighbor = None
self.UConnection = False
self.DConnection = False
self.LConnection = False
self.RConnection = False | {
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"url": null
} |
x��ZI����W��2����v2I�+e�o���*������>�a�"BjI�ǥ��� o�� �Q��L Using Matrices makes life easier because we can use a computer program (such as the Matrix Calculator) to do all the \"number crunching\".But first we need to write the question in Matrix form. %PDF-1.4 . In mathematics, a system of linear equations (or linear system) is a collection of one or more linear equations involving the same set of variables. We cannot use the same method for finding inverses of matrices bigger than 2×2. Systems of Linear Equations 0.1 De nitions Recall that if A2Rm n and B2Rm p, then the augmented matrix [AjB] 2Rm n+p is the matrix [AB], that is the matrix whose rst ncolumns are the columns of A, and whose last p columns are the columns of B. . . . e.g., 2x + 5y = 0 3x – 2y = 0 is a homogeneous system of linear equations whereas the system of equations given by e.g., 2x + 3y = 5 x + y = 2 is a non-homogeneous system of linear equations. ˜c is the constant vector of the system of equations and A is the | {
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signal-analysis, continuous-signals
\theta = \omega \cdot t
\end{equation}
And the same logic as above applies: By integrating frequency $\omega$ one gets phase $\theta$, by derivating phase $\theta$ one gets frequency $\omega$.
You can verify by dimensional analysis that they both are the same formula actually (well, actually, radian is said to be a dimensionless unit, something like a 'dozen' or a 'mole'... that is another story):
\begin{equation}
[Length] = [Length/Time] \cdot [Time]
\end{equation}
When you integrate with respect to time, one less $[Time]$ appear in the denominator. The derivative does the opposite. | {
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formal-languages, regular-languages, closure-properties
Title: Proving Regularity of Languages that are 1/k of an already known regular language There is this question in Kozen, that states if a language is regular then the first half would also be regular. Also I found a material on the internet that extends the thinking saying a language that is two-thirds of already known regular language is regular. I'm tempted to think that it should also hold true for any general $k>0$ that $m/k$th ($1 \leqslant m \leqslant k-1$) portion of a regular language would also be regular. I need a mathematical proof ( or a constructive proof having mathematical verifications done on it ) for the above statement. | {
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How can I measure returns such that the average is useful?
If I measure daily returns by simple percent change, a -50% day then a +50% day (or vice versa) results in a true -25% total change, but the average makes it look like you would expect a total 0% change.
Is there a way to measure returns differently that eliminates this effect? For context I have two series of returns and the one with a lower average daily return ends up with a higher total return and I suspect this phenomenon is to blame.
Currently I measure daily return by: (priceDay2-priceDay1)/priceDay1
• Try geometric average Jun 18 at 14:44
• @AlRacoon I just went through my code again and now the geometric mean is giving good results, thanks! Jun 18 at 22:49
2 Answers
Take the log return between days.
• Just don't forget to transform log returns back into simple returns in the end. Jun 19 at 0:52
What does not work with the geometric mean? | {
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ros
void IsRecoveredCondition::isRecoveredCallback(std_msgs::msg::Bool::SharedPtr msg)
{
RCLCPP_INFO(node_->get_logger(), "Recover Callback: '%s'", msg->data? "true": "false");
config().blackboard->template set<bool>("initial_pose_received", true);
}
} // namespace nav2_behavior_tree
#include "behaviortree_cpp_v3/bt_factory.h"
BT_REGISTER_NODES(factory)
{
factory.registerNodeType<nav2_behavior_tree::IsRecoveredCondition>("InitialPoseReceived");
}
Originally posted by enyuin on ROS Answers with karma: 45 on 2022-01-12
Post score: 0
Is that part of the BT being reticked after you return the tick condition of success? Also, you're not spinning the node to process the callbacks.
Originally posted by stevemacenski with karma: 8272 on 2022-01-13
This answer was ACCEPTED on the original site
Post score: 1 | {
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hits the bullseye with probability 1/5 and Maryam hits the bullseye with probability 1/3. There are 15 grape, 7 cherry, 3 lemon, 5 strawberry. 1 Answer to Playing darts. This is the example code: import 'dart:async'; Map. What is the probability that a dart will land inside the green circle? (Calculate what portion of the gray rectangle is covered by the green circle. • If Player B aims at a certain section, the dart has the same probability of landing in the correct one as in each of the two adjacent ones (the neighbouring regions to the left and right). with 3 consecutive darts (darts removed after each toss). Judging by appearance, find the probability that it will land in the shaded region (in between the circles). What is the probability of the event A? (b) Consider an event B = {X +Y>0}. If there is a probability if 1/10 that any given dart she throws will hit a balloon, independent of her other throws, which of the following is the closest to the probability she will hit at | {
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ros, rviz, ros-kinetic, planning-scene, motion-planners
geometry_msgs::QuaternionStamped quaternion_constraint;
quaternion_constraint.header.frame_id = "base_link";
quaternion_constraint.quaternion = move_group.getCurrentPose().pose.orientation;
req.group_name = PLANNING_GROUP;
req.allowed_planning_time = 60.0;
req.goal_constraints.push_back(pose_goal);
req.path_constraints = kinematic_constraints::constructGoalConstraints("link_grip", quaternion_constraint);
req.workspace_parameters.min_corner.x = req.workspace_parameters.min_corner.y = req.workspace_parameters.min_corner.z = -2.0;
req.workspace_parameters.max_corner.x = req.workspace_parameters.max_corner.y = req.workspace_parameters.max_corner.z = 2.0;
// Taking constraints into account and computing a valid path:
planning_interface::PlanningContextPtr context = planner_instance->getPlanningContext(planning_scene, req, res.error_code_);
context->solve(res); | {
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Now the tricky part. Is the condition $$\dot{V}(x,t)<0$$ sufficient to show that $$V(x)\to 0$$ and $$x\to 0$$? Yes for autonomous systems and not for non-autonomous systems! When we have $$\dot{x}=f(x)$$ and $$\dot{V}(x,t)=\dot{V}(x)<0$$, then this inequality is uniform in time, and we indeed conclude that $$V(x)\to 0$$. When we have $$\dot{x}=f(x,t)$$, then the time derivative of $$V(x)$$ is a function of time as well and the inequality $$\dot{V}(x,t)<0$$ is not necessary uniform in time. This is exactly what happens with the example above. If we take $$V(x):=\frac{1}{2}x^2$$, or $$V(t)= \frac{1}{2}\exp\left(-2+2e^{-t}\right),$$ then $$\dot{V}(x,t) = -e^{-t}x^2$$, or $$\dot{V}(t) = -e^{-t}\exp\left(-2+2e^{-t}\right).$$ We see that the negative definiteness of $$\dot{V}(x,t)$$ is not uniform in $$t$$, and the Lyapunov's second method for autonomous systems cannot be applied. Indeed, $$\dot{V}(t)\to 0$$ and $$V(t)$$ converges to a nonzero constant. | {
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the equation as well domain and range. x y 4 2 0 6 0 2 4 6 STUDY TIP A relation. Graphing Piecewise-Defined Functions. In the example above, the domain of $$f\left( x \right)$$ is set A. Steps to create a Domain Model 1. Ø Range is the set of values of " calculated from the domain for the _____ of the function. To summarise, for domain look along x-axis, for range look along y-axis. This specifies what the output of the function is when is the input. * What is a function? -A Relation relates two sets of data Examples: Pounds of bananas and cost Ex2: Gallons of gas and miles traveled Ex3: Grade on test and time spent studying (underlined variables are the inputs). 12 Number and algebraic methods. relationship can be expressed by the function f(s) = 3x + 30, where s is the. Direct and Inverse Variation Solving eq. The range is all real values of y which is the same as all real values of f(x). The domain of f(x) = x 2 is all real numbers and the range is all nonnegative real numbers. If | {
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} |
find exactly what you're looking for. Synth. We’ll now show you two main ways, as well as a simple keyboard shortcut that will save you … The equation editor in Google Docs is the perfect feature for people who use mathematical equations inside their documents. Google Docs is a cloud-based document solution with real-time collaboration and powerful tools to compose, edit, and share documents.. You can extend Docs with add-ons that build customized workflow improvements, establish connectivity to third-party systems, and integrate your documents with other Google Workspace applications (like Google Slides). One way is to use the keyboard shortcuts for the Insert Menu and then selecting equation. Linear System Equation Solver - helps you find the solution to a set of linear equations. Click Equation... . Cite references in Google Docs. As you speak it automatically enters the maths equation that are saying: When you’ve finished, click ‘Insert Maths’ in the bottom right hand corner of the | {
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quantum-mechanics, semiconductor-physics, quantum-tunneling
That said, here's how to get it: First, assume that the electron propagates as a plane wave (as it would in free space): $\Psi(x) \propto e^{i k x / \hbar}$. Assume that within the barrier, the electron also propagates according to this formula. Then assume that the "barrier height" is the positive value $q\phi = $(potential energy inside the barrier) $-$ (energy of the electron) ; this is equal to the charge $q$ times a potential $\phi$ because the barrier is electrostatic. The effective momentum of the electron in the barrier is given by
$$\frac{\hbar^2 k^2}{2m^*} = -q \phi \Rightarrow k = \sqrt{ \frac{ -2m^*q\phi }{\hbar^2}} = i \sqrt{\frac{2m^*q\phi}{\hbar^2}}$$
Putting this into the expression for the wavefunction of a plane wave, the exponent becomes real and negative, so the wavefunction decays exponentially.
$$\Psi(x) \propto e^{-\sqrt{\frac{2m^* |q\phi|}{\hbar^2}}x}$$ | {
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$$p(n,m,k)=1-\frac{n!}{s^n}\left[e_{k-1}\left(\frac{s}{m}\right)\right]^mPr(W=n)$$
Where $e_k(x)=\sum_{j=0}^{k}\frac{x^j}{j!}$ denotes the exponential sum function. note that because we have factorial an powers of potentially large numbers, numerically it will probably be better to work in terms of the logarithm of the second term, and then exponentiate back at the end of the calculation. Alternatively, we can choose the recommended $s=N$ as our algorithm parameter, and then make use of the stirling approximation to $n!$ - this is recommended in the paper and corresponds to "mean matching" of each poisson distribution with the multinomial cell (i.e. $E(X_i)=E(N_i)$). Then we get $\frac{n!}{n^n}\approx\sqrt{2\pi n}$. | {
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HINT: If you're given a word and you change the last letter, what happens to the number of zeros?
EDIT: This hint can give the answer without induction. Let $E_n$ be the number of words of length $n$ with an even number of $0$'s and $O_n$ the number of words of length $n$ with an odd number of $0$'s. Define $\phi:\{0,1\}^n \to \{0,1\}^n$ to flip the last letter of the word. Then $\phi^2 = \text{id}$ with $\phi(E_n) \subset O_n$ and $\phi(O_n) \subset E_n$. This immediately implies that $|E_n| = |O_n|$ Since there are $2^n$ total words, this implies $|E_n| = |O_n| = 2^{n-1}$.
A proof by induction could be done:
If $n=1, 2^n = 2^0 = 1$ and $1$ word of length $1$ has an even amount of $0$s, which is the word $1$.
Now imagine you have a sequence of length $k-1$. If it has an odd number of $0$s, then you can append a $0$ to the end of it. If it has an even number of $0$s, you can append a $1$ to it. | {
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image-processing, matlab, noise, information-theory
Adding "well-behaved" noise will make almost any image look more like that – in the end, pixels with identical intensity will be relatively common in most natural images, and adding noise will "break" that.
Now, salt'n'pepper is different: you add extreme values to your image. That will make the intensity at many pixels clip at the maximum intensity (or the minimum one), skewing the histogram away from flat to a very "horned" thing, which has less entropy. | {
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python, game-of-life
herschels = []
testrect = g.getselrect();
if testrect == []:
g.exit("Select the area where the still life is placeable!")
if g.empty():
g.exit("There is no pattern to add bait!")
stillLifes = []
def addStillLife():
while True:
stillLife = g.getstring("What still life to test for? (RLE)", "2o$2o!", "HRF v0.1")
stillLifes.append(g.parse(stillLife))
addAnother = g.getstring("Add another still life? (y|n)", "n", "HRF v0.1")
if addAnother.lower() == "n":
break
elif addAnother.lower() != "y":
g.exit("Invalid letter!")
def removeFirstLine(str):
result = str.rsplit('\n')
result.pop(0)
return ''.join(result) | {
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sql, stackexchange
Title: Query to find users from where? Based on my question here, I have updated my query to take user input so it can be a generic query:
DECLARE @location AS nvarchar(max) = ##location:string##;
SELECT u.Id [User Link], u.Reputation, u.Location
FROM Users u
WHERE lower(u.Location) LIKE lower('%' + @location + '%')
ORDER BY 'Reputation' DESC
Is there something I should be doing differently, or is this good? This looks fine, the only thing I would say is @location is being declared as nvarchar(max). I can only assume that u.Location is also nvarchar(max). If it isn't then set it to be the same size. nvarchar max will have a slight performance hit to it. | {
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special-relativity, electricity, time-dilation, conductors
Say for example that a length of copper wire at an electrical power plant continuously conducts electricity for 100 years. This copper wire is then removed from the power plant and is carbon dated.
Radioactive dating analyzes the nuclei, which don’t move when the current is on. And carbon dating looks at the ratio of carbon-14 to carbon-12, so you’d be looking at contaminants in your copper. But there wouldn’t be any difference here between your continuously-used wire and your idle wire, because the nuclei which form the crystal lattice don’t move in response to the current.
You can’t tell the difference between a “new” electron and an “old” electron, because all electrons are identical.
In a beam of unstable charged particles, time dilation is definitely observable. For example in the muon $g-2$ experiment, the muon beam has $\gamma \approx 30$, so the muons have a half-life of about 60 microseconds instead of about 2 microseconds. | {
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c#, object-oriented, design-patterns
The decorator pattern has opinions about almost all of those questions (and probably more I haven't thought of!), whereas writing a minimal implementation, decoupled from any interface like ICodeFileReader does not. That's adherence to OCP- writing code that won't have to change no matter what the answers to those above questions turn out to be.
Pulling it together
At some point, you will have to write code that handles all the responsibilities associated with reading code files. Hopefully the examples in the previous section have convinced you that trying to come up with a design which can handle arbitrary changes in responsibilities is impossible. But by having a design that: | {
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vba, excel
The FedEx website categorizes tracking numbers in various sections depending on status. In June 2019, while looking at the html elements, there were 19 sections. To clarify, if you have a list of numbers you're looking up, the website takes the tracking numbers out of order, so as you're comparing your list with the website, you're scrolling up and down constantly trying to figure out which section the number is in. In most of my usage, there were only 2-3 sections used, but it still required constant up and down comparing back and forth.
Ok, so you have the status on the website, you match that 10+ digit long tracking number with the one on your list, then you can highlight the associated carton number. The carton number that is in-transit is what we need, so we can process the carton number. | {
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It only makes sense to specify what the derivative is with respect to when we haven't already specified what function we're taking the derivative of. For example, it wouldn't make sense to talk about "the derivative of f(g(x))", because f(g(x)) isn't a function, it's a number. But if we say that the derivative is with respect to x, we make it clear that the function we're taking the derivative of is the map $x\mapsto f(g(x))$ (also known as $f\circ g$). If we say that the derivative is with respect to g(x), we're specifying that the function we're taking the derivative of is the map $y\mapsto f(y)$ (also known as f).
f'(g(x)) is the derivative of f, evaluated at g(x). Another way of saying that is that f'(g(x)) is the derivative of f(g(x)) with respect to g(x), evaluated at g(x). | {
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javascript, jquery, css
window.setTimeout(function () {
$('#bio-line-1').animate({ width: 'hide' });
}, 300);
}
$('#black-div, #black-credits, #igna-1-div, #igna-1-credits, #igna-2-div, #igna-2-credits, #fatal-div, #fatal-credits').fadeOut('100');
});
$('#name-a').click(function () {
if ($('#bio-line-1').css('display') == 'none') {
$('#bio-line-1').animate({ width: 'toggle' });
window.setTimeout(function () {
$('#bio-line-2').slideToggle("slow");
}, 100);
}
else {
$('#bio-line-2').slideToggle("slow"); | {
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(b) Show by algebra that the expression you got for the density in Part (a) is non-negative for all positive $\lambda_1 \ne \lambda_2$.
(c) For $i=1, 2$, let $f_i$ denote the exponential density of $X_i$. Show that the density you got in part (a) is equal to $c_1f_1 + c_2f_2$ for two constants $c_1$ and $c_2$ such that $c_1+c_2 = 1$. Are $c_1$ and $c_2$ both positive? | {
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system-identification, neural-network, parameter-estimation, deep-learning, embedded-systems
I identification the model from the features (inputs)
$$-y(t-1), -y(t-2), ... , -y(t-n), u(t), u(t-1), ... , u(t-m)$$
And the label (output) $y(t)$. This is the regular transfer function or ordinary differential equation identification method.
But the issue I have is that I have a lack of experience of system identification when it comes to neural networks. I'm used to state space models (Subspace identification) and regular parameter estimation (Recursive Least Square). I wrote a library for that too.
My questions for you are that:
What type of activation functions should I use?
How many layers is "good" enough?
How many neurons should I have?
How do I know...how to know what to select? I'm seeking practical experience for identification with neural networks. | {
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newtonian-mechanics, energy-conservation, work
Title: Swinging of a bob
Suppose a variable force is acting on the bob and making it swing as shown in the figure then why will kinetic energy be conserved here even though there is a variable force acting on the bob? This is a straight-forward application of the mechanical work-energy theorem: the net work done by all forces acting on a body as it moves from position $i$ to position $f$ is equal to the change in the kinetic energy of the body, $\Delta K = K_f-K_i$ or
$$\sum_{\mathrm{all~forces}}W = \Delta K.$$
It doesn't matter what the nature and origins of the forces are. All that matters is whether they do work on the object (mechanically) or not. They may be conservative or non-conservative, time-dependent or constant.
Kinetic energy is not conserved, and the calculation of kinetic energy is frame-dependent, so this principle/theorem must be applied wisely. | {
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python, object-oriented, programming-challenge, python-2.x
The first line defines the limits of the grid; X and Y separated by space
The second line defines the current position and facing direction for the
first vehicle; X, Y and Dir are separated by space
The third line defines the commands for the first vehicle, which is a line of string
The fourth and fifth lines are the same as second and third except they
are for the second vehicle
Note: Vehicles are sent sequentially. If the second vehicle attempts to move to the occupied spot of the first vehicle, the command will be skipped. If any move command makes any of the vehicles move out of the grid, that command will be skipped as well. Inputs are always in expected style, so there is no need to validate inputs.
As an example:
Inputs:
6 6
1 3 E
RMLLMRMRM
1 1 N
LMLML
Output:
2 2 S
0 0 E
My code:
directions = ['N','E','S','W']
movement = {'N': (0,1), 'E': (1,0), 'S': (0,-1), 'W':(-1,0)}
commands = {'L': 'turn_left', 'R': 'turn_right', 'M': 'move'} | {
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We select, read, and view and image to transform.
h1 = figure; imshow(A); title('Original Image');
We choose a shade of orange as our fill value.
orange = [255 127 0]';
We are ready to use T to transform A. We could call imtransform as follows:
B = imtransform(A,T,'cubic','FillValues',orange);
but this is wasteful since we would apply cubic interpolation along both columns and rows. (With our pure shear transform, we really only need to interpolate along each row.) Instead, we create and use a resampler that applies cubic interpolation along the rows but simply uses nearest neighbor interpolation along the columns, then call imtransform and display the result.
R = makeresampler({'cubic','nearest'},'fill');
B = imtransform(A,T,R,'FillValues',orange);
h2 = figure; imshow(B);
title('Sheared Image');
### Step 2: Explore the Transformation | {
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"url": "https://in.mathworks.com/help/images/padding-and-shearing-an-image-simultaneously.html"
} |
robotic-arm, catkin-make, catkin
Title: Help with catkin_make on an ARM
Hi,
I am trying to install ROS packages from source on Gumstix Overo. And I created the catkin work space following this tutorial. Everything works.
Then I used git to download bondcore package to /catkin_ws/src directory.
Then I run "catkin_make" in /catkin_ws. This is output:
root@linaro-alip:~/catkin_ws# catkin_make
lBase path: /root/catkin_ws
Source space: /root/catkin_ws/src
Build space: /root/catkin_ws/build
Devel space: /root/catkin_ws/devel
Install space: /root/catkin_ws/install
####
#### Running command: "make -j1" in "/root/catkin_ws/build"
#### | {
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java, algorithm, recursion, combinatorics
long timeMilliEnd = (new Date()).getTime();
long procMillis = timeMilliEnd - timeMilliStart;
float procSecs = (float)procMillis / 1000f;
System.out.println("\n>>> Process time (secs): " + procSecs);
} | {
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javascript, jquery, plugin, graphics
function ansiCode() {
var $this = $(this);
var data = $this.data('ansi');
if (data.ansiPos > data.ansi.length)
return '-';
var valid = /^[0-9;HABCDRsuJKmh]$/;
var end = /^[HABCDRsuJKmh]$/;
var char = data.ansi[data.ansiPos];
var escape = '';
if (char == '[')
{
var stop = false;
do {
data.ansiPos += 1;
var char = data.ansi[data.ansiPos];
escape += char;
stop = end.test(char);
} while (valid.test(char) && !stop)
data.ansiPos += 1;
} | {
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"tags": "javascript, jquery, plugin, graphics",
"url": null
} |
ros, compile, rosjava
Download and install the latest Android Studio from Google. Make sure to install the required SDK Build Tools and adjust the environment variables according to: http://wiki.ros.org/android/Android%20Studio/Download
Download and install ros-indigo according to: http://wiki.ros.org/indigo/Installation/Ubuntu.
Download and build the core sources of rosjava following the steps described at: http://wiki.ros.org/rosjava/Tutorials/indigo/Source%20Installation (Steps 3.2 and 3.3 can be omitted).
Download and build the core android libraries and import them to Android Studio (there's an example app available) according to: http://wiki.ros.org/android/Tutorials/indigo/Installation%20-%20ROS%20Development%20Environment
Start developing new ros-android apps. | {
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of the bullet supersonic ) rifle bullets such the. Below a certain upper class boundary, because we are adding it to zero an! Frequency curve but the techniques of drawing it is same to zero the lower quartile of... Information for students ) the median ) and the y-axis with the frequencies are cumulative be translated as cone. Any point you measure the diameter you can get the radius used to visually represent how values! Along the x-axis a horizontal line from this point tapered end of an data. An English class, 30 learners completed a test out of 20 marks 4. Picardy in northern France five number summary of data again, a hemisphere architecture a. Aug 20, 2020 Explore... Class boundary of 4 to 10 are commonly used in engineering, architecture and woodworking the plot. ) \ ) arches which establish the surface of a Gothic pointed arch, or a of! 625 daily: ( i ) the curve of a Gothic vault 2 cm = 10 on! Blunt shape typically associated with a sharp tip one that has the portion! The | {
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"url": "http://www.tedbeaudry.net/cattle-skin-mrf/construction-of-ogive-f8883d"
} |
computational-physics, simulations, continuum-mechanics
However that path may lead you into doing research into the FE method itself, rather than using it as a tool to do something else! Mainstream FE continuum mechanics is almost entirely done using displacement formulations. | {
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exoplanet, earth-like-planet, volcanism
Title: Crust thick enough to prevent volcanos Could you have an Earth-like planet with a crust thick enough to prevent volcanos from forming? It depends on the definition of Earth-like planet.
In terms of size, density and gravity Venus is very Earth-like, but in terms of atmospheric and surface conditions and its axis of rotation, and period of rotation Venus in not Earth-like.
I will assume you mean a terrestrial or rocky planet similar in size to Earth.
Earth's crust has two subdivision: oceanic and continental. Oceanic crust is between 5 km and 10 km thick whereas continental crust is between 30 km and 50 km thick:
Oceanic: 5 km (3 mi) to 10 km (6 mi) thick and composed primarily of denser, more mafic rocks, such as basalt, diabase, and gabbro.
Continental: 30 km (20 mi) to 50 km (30 mi) thick and mostly composed of less dense, more felsic rocks, such as granite. | {
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special-relativity, waves, speed-of-light, inertial-frames
Title: Why does speed of light have to be constant? My question is not about why speed of light has a particular constant value which has been sufficiently addressed in other questions on SE already. I want to know whether the fact that speed of light has to be constant is a consequence of other fundamental laws of Universe, or is it just a fundamental law itself.
My motivation for asking this question is thinking about Special Theory of Relativity. One way of understanding why time dilation and length contraction happen is to look at it from the perspective of constancy of speed of light. Alice who is on the moving source of light and Bob, a fixed observer see the speed of light as constant. In order for Alice to see the speed of light as a constant value, time slows down and length expands (in forward direction) thus keeping the speed constant. | {
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c
&& argv[i][6] == 'r' && argv[i][7] == 's'
&& argv[i][8] == 'i' && argv[i][9] == 'v'
&& argv[i][10] == 'e' && argv[i][11] == '=') {
argv[i] += 12;
if (!lstrcmpiA(argv[i], "true")) {
recursive_directory_search = true;
}
else if (!lstrcmpiA(argv[i], "false")) {
recursive_directory_search = false;
}
else {
error_messagea("Error: invalid arguments\n", help_message);
}
}
else if (!lstrcmpA(argv[i], "--no_line") || !lstrcmpA(argv[i], "-nl")) {
show_lines = false;
}
else if (!lstrcmpA(argv[i], "--display_comment_count") || !lstrcmpA(argv[i], "-dcc")) {
display_comment_count = true;
}
else if (!lstrcmpA(argv[i], "--hide_comment_count") || !lstrcmpA(argv[i], "-hcc")) {
display_comment_count = false;
} | {
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backpropagation, definitions
foreach (double bias in neuron.desiredBias) {
biasSum += bias;
}
biasSum /= iterationLength;
neuron.bias -= learningRate * biasSum;
}
}
double netcost = 0;
foreach (double cost in costs) {
netcost += cost;
}
return netcost/costs.Length;
}
public void epoch(bool showInfo) {
Console.WriteLine("Starting training...\n");
for (int iter = 0; iter < iterations; iter++) {
double cost = iteration();
if (showInfo) info();
Console.WriteLine("Cost for iteration " + iter + ": " + cost + "\n");
// reset desired
for (int k = 0; k < network.Length - 1; k++) { | {
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for 5 reds and 4 blacks, there are 1*1=1 way to get a sum of 0 ball 1*1+1*1=2 ways to get 1 ball, ... 1*1+1*1+1*1+1*1+1*1=5 ways to get 4 balls 1*1+1*1+1*1+1*1+1*1=5 ways to get 5 balls The result is shown on the line (5+4) For 5 reds, 4 blacks, and 3 blues, tag on the blues below the line (5+4) and work similarly. 1*1=1 way to get a sum of zero ball. 2*1+1*1=3 ways to get 1 ball, 3*1+2*1+1*1=6 ways to get 2 balls, ... 3*1+4*1+5*1+5*1=17 ways to get a sum of 5 balls. Continuing this way, we have, with all 15 balls, 71 ways to get a sum of exactly 5 balls. | {
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temperature, paleoclimatology
So the simple question is: How warm was the Paleocene epoch?
Redrawn after Zachos et al. 2001.
This is a plot of the Cenozoic variations of $\delta\ce{^{18}O}_{Cibicidoides}$ according to Zachos et al. 2001 (this is a bit outdated now but the Paleocene is roughly the same in more modern curves such as Zachos et al. 2008 or Cramer et al. 2011). It is supposed to follow variations in deep ocean temperatures and thus reflect the climate state at a given time. The Paleocene is the timeframe delimited by the two vertical bars (you can see the PETM quite clearly on one of the two bars).
From that plot it seems the Paleocene deep-sea temperature prior to the PETM is roughly at the same level at it is during the Middle Eocene (ca. 45 Ma), i. e. warmer than most of the Cenozoic but colder than the Early Eocene or most of the Cretaceous. | {
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java, design-patterns, inheritance
Correct. You could avoid it by creating a new instance containing modified data. That's common and fine, but you most probably don't need it. Entities are always mutable, I'd stick with it.
And.. i plan to make this Person class my base class for 2 other types of Person; a child and a parent.
Consider avoiding inheritance (maybe delegation?). And what about a child becoming a parent?
Will my builder pattern still be useful then?
No.... with delegation it'd better.
Finally to the code
My first code with the chained constructors
Let's call it "constructor triangle". It may look nice, but it won't make your live any easier. I'd stick with the first constructor.
My code with the builder pattern
private Date dateOfBirth;
Date is the worst class ever. Consider using new Java 8 classes or Joda-Time.
public Person(PersonBuilder builder) {
...
this.dateOfBirth = builder.dateOfBirth;
this.address = builder.address;
...
} | {
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quantum-field-theory, klein-gordon-equation
We are told that putting the expansion into this should give
$\int \frac{d^3p}{(2\pi)^3} \, p^i \left( \hat{a}_{p}^{\dagger} \hat{a}_{p} + \frac12 (2\pi)^3 \delta^{(3)}(0) \right)$
which I do get, however I also get terms involving $\hat{a}_{p}\hat{a}_{-p}$ and $\hat{a}^{\dagger}_{p} \hat{a}^{\dagger}_{-p}$. How in the world can these terms possibly go away? Have a made a mistake in the math (I am prone to mistakes at the moment.. quite tired) or is there some way that those terms cancel? The two integrands $p^i\hat{a}_{{\bf p}}\hat{a}_{-{\bf p}}$ and $p^i\hat{a}^{\dagger}_{{\bf p}}\hat{a}^{\dagger}_{-{\bf p}}$ are antisymmetric wrt. ${\bf p} \leftrightarrow -{\bf p}$. Hence the corresponding integrals $\int d^3p(\ldots )$ are zero. | {
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quantum-mechanics, hilbert-space, operators, group-theory, group-representations
This essentially answers your question, but rotations are not the only orthogonal transformations. Reflexions are too; in $\mathbb{R}^3$ the orthogonal matrix $\operatorname{diag}(1,-1,1)$ reflects in the $x-y$ plane and it fulfills $\mathbf{U}^T\,\mathbf{U} = \mathbf{I}$. So let's go a little further. Any rotation of angle $\theta_0$ can be thought of as being joined to the identity transformation (rotation through angle of nought) through a continuous path of rotations, all about the same axis and with angles between $0$ and $\theta_0$. It belongs to the identity connected component of the group of all orthogonal transformations. Therefore:
$$\mathbf{U} = \exp(\theta\,\mathbf{H})$$ | {
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java
@ToString
public class SampleNestedDTO {
public String nestedField1;
public Integer nestedField2;
public Boolean nestedField3;
public Instant nestedField4;
}
public abstract class AuditedDTO {
public Instant created;
public String createdBy;
public Instant lastUpdate;
public String lastUpdatedBy;
}
The SampleEntity object uses only get and set methods instead of public member variables to match our implementation of hiberante entities.
@ToString
public class SampleEntity extends AuditedEntity {
@Getter
@Setter
private String field1;
@Getter
@Setter
private Integer field2;
@Getter
@Setter
private Boolean field3;
@Getter
@Setter
private Instant field4;
@Getter
@Setter
private SampleNestedEntity nested;
@Getter
@Setter
private List<String> list1 = new ArrayList<>();
@Getter
@Setter
private Map<String, Instant> map1 = new HashMap<>();
} | {
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java, programming-challenge, mathematics
Title: Optimizing my solution for problem #23 - project Euler The question - | {
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ionic-compounds
Electrons will occupy these orbitals from the "ground up" (called the Aufbau principle). We know, therefore, that for 4th-period elements, the $3d$ sub-shell will fill before the $4p$ sub-shell will.
The atomic orbital diagram indirectly tells us something else. The principle quantum number, $n$ (which for the valence shell is equal to the row or period number), roughly corresponds to the distance from the nucleus of the orbital's highest electron density region. In other words, any sub-shell with $n=4$ will have most of its electron density further away from the nucleus than a sub-shell with $n=3$. This means that $3d$ electrons are closer to the nucleus than $4s$ electrons, even though $3d$ electrons initially have higher energy.
The distance of the electron from the nucleus is roughly proportional to $n$ | {
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"openwebmath_perplexity": null,
"openwebmath_score": null,
"tags": "ionic-compounds",
"url": null
} |
quantum-field-theory, resource-recommendations, quantum-electrodynamics, renormalization, feynman-diagrams
Title: Resources for One-Loop Calculation in QED I am recently trying to study the calculation on one-loop diagrams in QED. Since the most resources i found where rather cryptic since they where very very general i wanted to ask whether or not there are good papers or textbooks about that topic (especially for beginners)?
My Background: | {
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special-relativity
This is to be contrasted with the Transverse Doppler factor
$$\frac{f_B[~\text{projected from successive meetings with}A~]}{f_{A\text{ (proper)}}} = \sqrt{1 - \beta^2},$$
which characterizes (mutual) time dilation directly, as the Lorentz factor $\sqrt{1 - \beta^2}$, and where the members of B's inertial system infer the value of frequency $f_B[~\text{projected from successive meetings with}A~]$ by determinations of simultaneity between each other. | {
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geophysics, earthquakes, seismology
Title: Where could I get waveform data on low-frequency earthquakes, very low-frequency earthquakes, volcanic tremor and non-volcanic earthquakes? I am a marine geology masters student and I am writing my thesis on slow earthquakes. I will include graphs of the most common types of earthquakes:
Low-frequency earthquakes
Very low-frequency earthquakes
Volcanic tremors
Non-volcanic earthquakes
Does anyone know where I could get data? If anyone shares with me the above data, I will cite you in my acknowledgement section. Thanks :) The one source I can think of that's outstanding with meeting all your enumerated criteria is the following: IRIS.
You need to research throughout that website, but they certainly have more than what you seek | {
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thermodynamics, entropy
Title: Entropy and the $2^{nd}$ law of thermodynamics I have just been introduced to the word "entropy" and as it is my understanding that it is a measure of the randomness and chaos of particles in as system.
My textbook list the 2nd law of thermodynamics in various forms one of them "The entropy of the universe can never decrease", but somewhere I read that the universe has been cooling ever since the big bang.
Should a system that is cooling not become less chaotic and random since there is less energy available for motion, vibration ect?
it is my understanding that it is a measure of the randomness and chaos of particles in as system | {
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random-process, stochastic, stationary
Title: question related to something in karlin and taylor stochastic processes one text This question is essentially a question about something in Karlin and Taylor's Stochastic Processes One text in the spectral chapter. Since this is a DSP list, Karlin and Taylor may not be so popular so I will describe the setting which I think I've seen in other texts also.
They define the random variable $X_n = A \cos(\omega n) + B \sin(\omega n)$.
So, $A$ and $B$ are zero mean normal random variables. $\omega$ is fixed at some frequency between $0$ and $\pi$. The process is on the integers so the process start at some value of $-k$ and continues through to positive $k$. So $k$ can be any integer and $X_n$ represents a discrete stochastic process.
They then say that the $X_n$ process is stationary in the mean. Evidently this is so obvious that there's no need to explain it. I don't get it. Well, I sort of half get it. | {
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mole, units
Thus, the amount of substance can always be expressed in terms of the unit mole, regardless of the considered elementary entities. For example,
amount of mercury atoms: $n(\ce{Hg})=1\ \mathrm{mol}$
amount of hydrogen molecules: $n(\ce{H2})=1\ \mathrm{mol}$
amount of chloride ions: $n(\ce{Cl^-})=1\ \mathrm{mol}$
amount of electrons: $n(\ce{e-})=1\ \mathrm{mol}$
amount of equivalent entities $\ce{1/2H2SO4}$ corresponding to the transfer of a $\ce{H+}$ ion in a neutralization reaction: $n(\ce{1/2H2SO4})=1\ \mathrm{mol}$
amount of equivalent entities $\ce{1/5MnO4-}$ corresponding to the transfer of an electron in a redox reaction: $n(\ce{1/5MnO4-})=1\ \mathrm{mol}$
amount of solute that contributes to the osmotic pressure of a solution: $n_\text{solute}=1\ \mathrm{mol}$ | {
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cryptography, finance, rust
let mut rng = match OsRng::new() {
Ok(g) => g,
Err(e) => panic!("Failed to obtain OS RNG: {}", e)
};
let path = Path::new("src/wordslist/english.txt");
let display = path.display();
let mut file = match File::open(&path) {
Err(why) => panic!("couldn't open {}: {}", display, why.desc),
Ok(file) => file,
};
let words:String = match file.read_to_string() {
Err(why) => panic!("couldn't read {}: {}", display, why.desc),
Ok(string) => string,
};
//generate corner cases
for &i in [16us,24,32].iter() {
for &n in ["00","7f","80","ff"].iter() {
let corner_chars = repeat(n).take(i).collect();
process(corner_chars,str_seed,words.as_slice());
}
}
//generate random seeds
for gen_seed in range(0us,12) {
let length = 8 * (gen_seed % 3 + 2);
let random_chars:String = rng.gen_ascii_chars().take(length).collect(); | {
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javascript, ecmascript-6, svg
set(target, name, value) {
if (value !== null && typeof value === "object" && value.isPSVG) {
node.appendChild(value.node);
target[name] = value;
return true;
}
set(name,value);
return true;
},
};
return new Proxy(svg, proxyHandler);
})();
Object.keys(props).forEach(key => PSVG[key] = props[key]);
return PSVG;
}
return createSVG;
})();
body {
font-family : arial;
}
#XMLResult {
font-family : consola;
font-size : 12px;
}
<span id="infoElement">SVG node added. In two seconds is modified.</span><br>
<div id="exampleSVG"></div>
The XML;
<div id="XMLResult"></div> | {
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"tags": "javascript, ecmascript-6, svg",
"url": null
} |
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