qid int64 1 4.65M | metadata listlengths 3 3 | prompt stringlengths 31 25.8k | chosen stringlengths 17 28.2k | rejected stringlengths 19 40.5k | domain stringclasses 28
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496,932 | [
"https://physics.stackexchange.com/questions/496932",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/193422/"
] | Let's assume I have a harmonic oscillator which is one dimensional. What is my plan is to work the the two electron's spin states and my requirement is that they have to be in the triplet sates.
Lets also consider that wave function which is <span class="math-container">$\Psi (r_1,r_2) \ \chi(1,2)$</span>
If the radi... | First of all, as others have pointed out, <span class="math-container">$ t=\infty$</span> should be replaced by 'as time <em>approaches</em> infinity' (<span class="math-container">$t \rightarrow \infty$</span>).
Now, the average speed will approach zero if the total distance covered doesn't approach infinity as time... | <span class="math-container">$t=\infty$</span> is a not a useful statement in this context and should be replaced by the time tends towards infinity, <span class="math-container">$t\to \infty$</span>, and then the average speed tends towards zero.<br>
So the average speed can get smaller and smaller and smaller but gi... | https://physics.stackexchange.com |
139,938 | [
"https://security.stackexchange.com/questions/139938",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/96980/"
] | Suppose I use a framework X to build a mobile game, and the website of X allows me to submit the name of app that uses X to build. But I suspect if I should submit my app name because it would let users know my app is using X. Is letting users to know which framework I am using a security issue?
| <strong>Security through obscurity is not sufficient</strong>, but can be used aggregated to other security mechanisms and practices. Always remember that system security should not depend only on the secrecy of the implementation or its components.
You can know the framework code very well, but you can't suppose it's... | I would describe it as defense in depth measure. Not something to rely on, but if you can get away with it, might be useful. If an attacker can identify any part of the stack they could start looking for known weaknesses in it, and possibly exploit it from there.
Doing this simply adds more time and effort on the ... | https://security.stackexchange.com |
145,231 | [
"https://softwareengineering.stackexchange.com/questions/145231",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/52338/"
] | If I create this method
<pre><code>public void foo()
</code></pre>
And then I create an overloaded version like this
<pre><code>public void foo( string bar )
</code></pre>
Do we say that the second functions overloads the first, or are both methods equally "overloaded"?
This would imply (I think), that there is a ... | When talking about overloads, the <em>name</em> of the function is overloaded, not the function itself. The functions overloading the name are "overloads" and overload the name, but not each other. In your example, <code>"public void foo()"</code> and <code>"public void foo( string bar )"</code> both overload the name ... | I would simply say <code>foo</code> is overloaded. There is certainly no master/slave or parent/child relationship going on here.
| https://softwareengineering.stackexchange.com |
1,906,115 | [
"https://math.stackexchange.com/questions/1906115",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/326159/"
] | Let $A$ be a closed and unbounded set of $\mathbb{R}^n$ and $f: A \to \mathbb{R}$ a continuous function such that
$$\lim_{||x|| \to \infty} f(x)=+\infty$$
Prove that $f$ reach an absolute minimum in $A$.
That's a question I've been working for so long but I couldn't solve it correctly.
First of all, I noticed that... | Hint: Let $x_0$ be any point in $A$ and set $M:=|f(x_0)|+1$. Then, exactly as you did, find $\delta$ such that $f(x)>M$ for all $|x|>\delta$.
Now consider the partition
$$A=(A\cup\{|x|>\delta\})\ \dot{\cup}\ (A\setminus\{|x|>\delta\}):=U_1\ \dot{\cup}\ U_2$$
The question for you is why can the minimum only ... | <strong>An other way</strong>
You started well. Let $z\in A$. Take $M=f(z)$ in your proof. Now, $f$ is continuous on $B:=\{\|x\|\leq \delta\}$ which is a compact set. Therefore, there is a $y\in B$ s.t. $$\|f(x)\|\geq \|f(y)\|$$
for all $x\in B$. Now, take $\min\{\|f(y)\|,\|f(z)\|\}$, and we are done.
| https://math.stackexchange.com |
419,371 | [
"https://mathoverflow.net/questions/419371",
"https://mathoverflow.net",
"https://mathoverflow.net/users/66131/"
] | Let's consider the <span class="math-container">$1$</span>-variable rational function
<span class="math-container">$$F(z):=\frac{1-z}{(z^3 - z^2 + 2z - 1)\,(z^3 + z^2 + z - 1)}.$$</span>
Numerical evidence convinces me of the truth of the following.
<blockquote>
<strong>QUESTION.</strong> Can you prove that <span class... | Let <span class="math-container">$1/(1-2z+z^2-z^3)=\sum_{n\geq 0} f(n)z^n$</span>. Then <span class="math-container">$f(0)=1$</span>,
<span class="math-container">$f(1)=2$</span>, <span class="math-container">$f(2)=3$</span>, and
<span class="math-container">$f(n+1)=2f(n)-f(n-1)+f(n-2)=f(n)+(f(n)-f(n-1))+f(n-2)$</span>... | The rational function <span class="math-container">$(1-z)/(1-2z+z^2-z^3)$</span> has positive coefficients because it's equal to
<span class="math-container">$$\frac{1}{1-z-\displaystyle\frac{z^3}{1-z}}.$$</span>
| https://mathoverflow.net |
2,426 | [
"https://mechanics.stackexchange.com/questions/2426",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/1267/"
] | I have a '05 Mazda3 with pretty much stock wheels. I have washed my car a few times, and the first thing, without fail, that gets dirty are my wheels. What is the best protectant I can use to keep them shiny?
| Unfortunately wheels will get dirty first - they are closest to the ground so will pick up everything; they also pick up brake dust, which is very sticky.
This means there is no silver bullet here - you need to wash frequently, and apply a wax if you want to slow down the build up of crud.
Use a wheel cleaner solutio... | Use Wheel wax and clean them often.
| https://mechanics.stackexchange.com |
26,537 | [
"https://mathoverflow.net/questions/26537",
"https://mathoverflow.net",
"https://mathoverflow.net/users/4002/"
] | It is fundamental to topology that $\mathbb{R}$ is a connected topological space. However, all the topology books that I have ever looked in give the same proof. (the proof I am thinking of can be seen in Munkres's topology or Lee's Introduction to topological manifolds)
This seems strange to me, because for other fun... | If you've already developed basic facts about compactness you can prove it this way:
Let $[0,1] = A \cup B$ with $A$ and $B$ closed and disjoint. Then since $A \times B$ is compact and the distance function is continuous, there is a pair $(a, b) \in A \times B$ at minimum distance. If that distance is zero, $A$ and $B... | If you want to prove that 'complete plus densely ordered' implies connected you are almost forced to use the 'standard' proof. For the real line you could also use the bisection method: if $I$ is convex and the union of two closed sets $A$ and $B$ take $a\in A$ and $b\in B$, with $a < b$, say. Now create two sequenc... | https://mathoverflow.net |
13,130 | [
"https://mathoverflow.net/questions/13130",
"https://mathoverflow.net",
"https://mathoverflow.net/users/1464/"
] | The analytic continuation and functional equation for the Riemann zeta function were proved in Riemann's 1859 memoir "On the number of primes less than a given magnitude." What is the earliest reference for the analytic continuation and functional equation of Dirichlet L-functions? Who first proposed that they might s... | Riemann was the first person who brought complex analysis into the game, but if you ask just about functional equations then he was not the first. In the 1840s, there were proofs of the functional equation for the $L$-function of the nontrivial character mod 4, relating values at $s$ and $1-s$ for real $s$ between 0 a... | To extend on Matt's comment about Euler, here is something I wrote up some years ago about Euler's discovery of the functional equation only at integral points. I hope there are no typos.
Although Euler never found a convergent analytic expression for
$\zeta(s)$ at negative numbers, in 1749 he published a method of
... | https://mathoverflow.net |
6,859 | [
"https://mechanics.stackexchange.com/questions/6859",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/24/"
] | Driving across Europe, i noticed the car was using water. I drove slowly and got to the destination. Since then, the symptoms have been getting stranger.
<ul>
<li>The water loss is caused by excess pressure in the system, no visible leaks.</li>
<li>Sometimes the radiator works (gets hot) and the engine does not heat, ... | There was a piece of instant gasket (from the water pump replacement last year) in the circuit. This was leading to pressure coming back up into the reservoir and pushing water out of the pressure release valve, which is why I was losing water. Also the radiator may have been a bit blocked but we flushed it backwards a... | The thermostat will open/close when reaching certain temperature. If it does not work properly you can see some of the symptoms you currently have. This is, usually, not an expensive part to replace.
| https://mechanics.stackexchange.com |
121,596 | [
"https://dba.stackexchange.com/questions/121596",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/80974/"
] | <h1>Questions</h1>
I put my questions first, so that it is easier to understand the question. I have two working queries at the end, but I fear they are not very efficient with data sets larger than what I have at the moment. What are my best options to create an efficient query in the below case?
<h1>Description</h1... | I ran some tests based on the suggestions I got from you guys, using the <code>MySQLdb</code> and <code>timeit</code> modules in Python. I created 5 tables: <code>test_100</code>, <code>test_500</code>, <code>test_1000</code>, <code>test_5000</code> and <code>test_10000</code>. All the databases were given a single tab... | I don't have a direct answer to your question. I do have a suggestion, depending upon what you intend to do with the query results.
If the results are staying entirely within the database server -- for example, if the query is just a subquery of an insert statement -- your "Another working solution" is what I'd intuit... | https://dba.stackexchange.com |
715,676 | [
"https://physics.stackexchange.com/questions/715676",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/317399/"
] | Problem 2.16 from Morin's Classical Mechanics:
Given a semi-infinite stick (one that goes off to infinity in one direction), determine how its density should depend on position so that it has the following property: If the stick is cut at an arbitrary location, the remaining semi-infinite piece will balance on a suppor... | When Einstein derived his equations the Newtonian limit (and it may be taken also in the present of sources) was an important check for the theory. It is also useful to understand the limits of the Newtonian theory, and sometimes helps to work out the intuition about the relativistic case.
However to solve Einstein equ... | If, in some limit, GR didn't reduce down to <span class="math-container">$\kappa \nabla ^{2}\phi = \rho$</span> for some constant kappa, (where <span class="math-container">$\phi$</span> is a gravitational potential such that <span class="math-container">${\vec g} = {\vec \nabla}\phi$</span>), then it wouldn't be a ver... | https://physics.stackexchange.com |
262,598 | [
"https://softwareengineering.stackexchange.com/questions/262598",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/144171/"
] | I know that basically, CC can be computed as number of decision + 1. In addition, every logical operator in the condition causes CC to increase by 1. But why?
Having the code <code>if(A || B || C) else...</code> the control flow graph would simply be a node with two outcomes - two branches. So I always thought branch ... | Just because the programming language abstracts the branches away into a boolean expression, doesn't mean they aren't there. If you looked at what actually gets executed, it looks like this:
<pre><code> +-----------+
|is A true? +------------------+
+----+------+ |... | In the example you use, there are four (4) possible paths of execution, and hence four (4) tests that must be performed. They may be enumerated as follows, where x denotes "don't care":
<ul>
<li>1xx: A is true, don't care about B and C - then path</li>
<li>01x: A is false, B is true, don't care about C - then path</l... | https://softwareengineering.stackexchange.com |
24,100 | [
"https://physics.stackexchange.com/questions/24100",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/8802/"
] | Can the annihilation of matter and antimatter be explained by the electro-weak interaction?
Can pair-production be explained in the same way?
| I can't fault your reasoning. I would guess station C is supposed to be at the point where the trains meet i.e. it's position is determined by the relative speeds of the trains.
| You are right here, that's the correct solution.
The question is ambiguous regarding the location of station C. It looks like they meant "midpoint" when they said "between"--which gives an answer of $100 \:\rm km$.
Or, they may have meant that its in a position such that both trains reach C at the same time--in that ... | https://physics.stackexchange.com |
239,627 | [
"https://dba.stackexchange.com/questions/239627",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/171862/"
] | Hi everyone hope you're doing well.
I'm new to oracle and I'm reading about the concept of 'Package' and 'Package body'.
I have a function as you can see below
<pre><code>CREATE OR REPLACE Function Show_description(i_Course_No
Course.Course_No%Type)
Return Varchar2 AS
V_Description Varchar2(50);
Begin
... | Well, yes - but not necessarily. As you wanted to use <code>EXEC</code> (which is SQL*Plus), then have a look how you could have done it; first, a package with a function that returns department name for a certain department number.
<pre><code>SQL> create or replace package my_first_package as
2 function show_... | OK I've found where the problem is.
I'm calling the function within the package SO I should not use the EXECUTE syntax
I have to use it with a select statement like this :
<pre><code>select my_first_package.Show_description(12)
from dual;
</code></pre>
| https://dba.stackexchange.com |
92,419 | [
"https://stats.stackexchange.com/questions/92419",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/19676/"
] | I'd like to determine the relative importance of sets of variables toward a <code>randomForest</code> classification model in R. The <code>importance</code> function provides the <code>MeanDecreaseGini</code> metric for each individual predictor--is it as simple as summing this across each predictor in a set?
For exam... | First I would like to clarify what the importance metric actually measures.
<em>MeanDecreaseGini</em> is a measure of variable importance based on the Gini impurity index used for the calculation of splits during training. A common misconception is that the variable importance metric refers to the Gini used for assert... | The function defined above as G=sum over classes[pi(1−pi)] is actually the entropy, which is another way of evaluating a split. The difference between the entropy in children nodes and the parent node is the Information Gain.
The GINI impurity function is G = 1- sum over classes[pi^2].
| https://stats.stackexchange.com |
461,491 | [
"https://electronics.stackexchange.com/questions/461491",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/213297/"
] | Well I have two electronic circuit, one is broken and the other is solid and working. While I am making Continuity test with Fluke Multimeter on working electronic circuit, the bip voice heared only once time. but broken part is giving continutiy bip voice. How can a digital multimeter give only once bip voice. what do... | A short burst of beeping from a continuity tester generally means that there is momentary current flow in the circuit from the tester until some capacitance gets charged up and the current flow stops.
On the other hand the continuous tone indicates an actual short and the current from the tester flows as long as the ... | A charging capacitance appears as a short and then an open when fully charged.
| https://electronics.stackexchange.com |
2,477 | [
"https://biology.stackexchange.com/questions/2477",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/955/"
] | After following a course in Permaculture, I realised that if I want to get serious about it, I need to be able to distinguish plants. So I am looking for an online Video course on Plant Taxonomy and Physiology. My understanding is that it is a fairly standard course in basic Botany degrees, and since there are more and... | <ol>
<li>I speak only for the U.S. regulations: the calorie labels on wrappers refer to the energy released when burned. Sometimes these are inaccurate. Many dieticians recommend calculating the calories based on weights of protein, carbohydrates and fats in the serving: 4 kcal in each gram of protein and carbohydrate ... | 1) It depends on each country and your minister. In Finland, the thing is done so that it says the energy stored in food, which will be released if burned.
2) It is the energy pushed to the bike when the bike does not take into account your pulse. If the bike is smart one, it takes into account your pulse rate, then i... | https://biology.stackexchange.com |
29,250 | [
"https://cs.stackexchange.com/questions/29250",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/20986/"
] | Comparison-based sorting algorithms does a number of different operations to accomplish the sorting, why comparisons are the dominant time consumption? While I understand the standard analyses of asymptotical behavior of number of comparison operations, I don't quite understand why other costs of other types of opera... | Yes, you can categorize your problem as in NP and is NP-complete if you have the followings:
<ul>
<li>The set of real numbers from which you draw the number from and you use as input into your procedure is countable</li>
</ul>
In this case, you can represent your input as proper input into Turing machine because you ... | No, you can not say that your problem is NP-complete.
The reason is that it is not in NP: there is no Turing machine at all (let alone a poly-time (non-deterministic) one) that can solve it because TMs can not handle real numbers.
The reduction may still go through and show that the problem is NP-hard; a subset of th... | https://cs.stackexchange.com |
209,742 | [
"https://stats.stackexchange.com/questions/209742",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/113808/"
] | If I demonstrated that there is no correlation between two random variables, does that mean that there is no cause and effect relation between them ?
| Correlation, in the usual sense, measures the <strong>linear</strong> association between two variables. One variable can cause another without there being any correlation between the two. For example, you might have a perfectly sinusoidal relationship between a variable <span class="math-container">$x$</span> and <sp... | Let $X \sim \mathcal{N}(0,1)$ follow the standard normal distribution. Let $Y = X^2$. Clearly there is an entirely deterministic relationship, but $\mathrm{Corr}(X, Y) = 0$.
| https://stats.stackexchange.com |
73,823 | [
"https://softwareengineering.stackexchange.com/questions/73823",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/6373/"
] | What are the pros and cons of outsourcing development and testing to two different companies?
<strong>EDIT:</strong> Why do you prefer outsourcing development and testing to different companies or to the same company?
| Pros:
<ol>
<li>The two teams are independent (and rivals) so there is no posibility of the testing team colluding with the development team or being "influenced" by the developers.</li>
<li>If your testing requires some specialized testing requirements that the development company does not have, a specialized testing... | Pros:
<ul>
<li>You will get honest output from both the parties as both of them will try to prove their worth (provided they both are competent)</li>
</ul>
Cons:
<ul>
<li>You will have to give understanding of the system to both the parties. </li>
<li>Additional overhead of communication through out the life cycle o... | https://softwareengineering.stackexchange.com |
11,203 | [
"https://mathoverflow.net/questions/11203",
"https://mathoverflow.net",
"https://mathoverflow.net/users/1358/"
] | In my ODE class, we proved that if <span class="math-container">$\exp(L) = \exp(L')$</span> then the eigenvalues are congruent mod <span class="math-container">$2 \pi i$</span>. Here, <span class="math-container">$L$</span> and <span class="math-container">$L'$</span> are two <span class="math-container">$n \times n$<... | No, they cannot. Note that <span class="math-container">$\exp(PAP^{-1})=P\exp(A)P^{-1}$</span>, so wlog, both are in Jordan form. Then, we can compute by exponentiating Jordan blocks, and the first will have a two by two block (or two one by one) depending on whether it is diagonal or not <span class="math-container"... | Charles deals with your final question regarding your example. The same idea of considering Jordan forms applies to your general initial question.
If $A$ is a matrix with eigenvalues $\lambda_1,\dots,\lambda_n$ (repeated according to their multiplicities), then the eigenvalues of $e^A$ are the numbers $e^{\lambda_1},... | https://mathoverflow.net |
47,827 | [
"https://chemistry.stackexchange.com/questions/47827",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/14806/"
] | Is there any difference between the two, when talking of an acid? I am a bit confused. Please help me out.
| $\mathrm{p}K_\mathrm{a}$ is the intrinsic property of an acid. It does not depend on how much acid there is in a solution<sup>‡</sup>. For example, acetic acid has a $\mathrm{p}K_\mathrm{a}$ of $4.76$. This $\mathrm{p}x$ means $-\log x,$ we can calculate $K_\mathrm{a}$ to be $10^{-4.76}$ is $1.7\times 10^{-5}$, which m... | pKa is the pH for which the protonated ($\ce{HA}$) and unprotonated species ($\ce{A^{-}}$) of the acid are equal. So $$ \ce{10^{pKa} = \dfrac{[H+][A^{-}]}{[HA]} = \dfrac{[H+]^{2}}{[HA]}} $$
| https://chemistry.stackexchange.com |
619,832 | [
"https://physics.stackexchange.com/questions/619832",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/235643/"
] | Lets say that hypothetically we have a rocket with constant mass, and an engine providing a constant force. I understand that it is unrealistic to have a rocket of constant mass with a rocket engine that ejects mass to accelerate, however this simplifies the problem.
As the rocket accelerates the force from the engine ... | As you have noted, the effect that goes into accelerating the rocket increases with time. However, when the fuel is accelerated in the direction opposite direction to give the rocket speed, the fuel has a change in specific kinetic energy <span class="math-container">$k$</span> (kinetic energy per mass unit) according ... | I have answered a similar question on NasaSpaceFlight.com years ago. The answer is that, we do not only calculate the chemical energy of the fuel, we need to include the kinetic energy the fuel carries also. Fuel on the rocket is moving at certain speed thus has certain kinetic energy. When it is ejected after burnt, t... | https://physics.stackexchange.com |
3,441,995 | [
"https://math.stackexchange.com/questions/3441995",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/671196/"
] | I wonder how to solve this. Once I saw <span class="math-container">$\int{\ln \sin}$</span> is an improper integral that only possible to integrate in certain interval. And frankly that is still far from where I'm now. I'm just curious and sought for it back then.
Then now, I got a worksheet that contains playful and ... | Because you are given some choices, you can think about it this way, (though ofcourse it only works for these kinds of given choices, but it may help)
<span class="math-container">$-1\le \sin x \le 1$</span>
<span class="math-container">$\implies 0\le \ln(2+\sin x) \le \ln 3$</span>
<span class="math-container">$\im... | The remark about a calculator being permitted suggests just evaluating the integral numerically using your calculator.
Here's a method that doesn't require using a calculator at all: Since <span class="math-container">$\sin$</span> is decreasing on the interval <span class="math-container">$[3, 5]$</span> and <span cl... | https://math.stackexchange.com |
378,771 | [
"https://softwareengineering.stackexchange.com/questions/378771",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/248528/"
] | For example, suppose I have 2 arrays:
<pre><code>let arr1=[5,2,1];
let arr2=["abcde","ab","a"];
</code></pre>
my work is simple : to check if length of strings in arr2 are larger than corresponding element with same index in arr1, so:
<pre><code>let arr1=[5,2,1];
let arr2=["abcde","ab","a"];
</code></pre>
is true,
... | Both are perfectly possible. But there are reasons why you should prefer option 1:
<ul>
<li>First, option 1 clarifies the intent: you immediately grasp the special case and understand how to handle it. With the second option an uninformed reader (or your future you?) would have to deduct from the code that there... | In my opinion, solution 1 is better than solution 2. The simple reason for that is the overall performance. Any code which reduces the number of iteration is good for any application. Solution 1 does the same as if condition returns false then it will reduce the number of iterations.
| https://softwareengineering.stackexchange.com |
161,275 | [
"https://physics.stackexchange.com/questions/161275",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/42337/"
] | I met a Hamiltonian containing the derivative of the Dirac delta potential:
<blockquote>
In order to do it we use a method described in [9]. We define a formal Hamiltonian
$$
\tag{2}\tilde{H}_{abcd}=-\frac{{\rm d}^2}{{\rm d}x^2}+a\delta\left(x\right)+b\delta'\left(x\right)+c\delta\left(x\right)\frac{{\rm d}}{{\rm ... | Take this $\delta '(x)$ and apply in an arbitrary function $f(x)$.
$$
\int_{a}^{b} \delta'(x) f(x)\ \mathrm{d}x = f(x) \delta(x) |_{a}^{b} - \int_{a}^{b} \delta(x) f'(x)\ \mathrm{d}x = -f'(0)
$$
Then $ \delta '(x) \rightarrow -\delta (x) \frac{\mathrm{d}}{\mathrm{d}x}$.
| $\delta'$ is the charge density that generates a dipole. That is, the charge density of two nearby point charges of equal and opposite magnitude in the limit as they get closer and closer to each other.
Imagine approximating the delta function with a smooth bump function, and it becomes clear what is going on.
<img sr... | https://physics.stackexchange.com |
229,398 | [
"https://softwareengineering.stackexchange.com/questions/229398",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/120333/"
] | We have had a situation with a scrum sprint where a team member went on vacation for a few days at the beginning of the sprint. This led to us being behind the ideal trend on the burndown chart at the beginning of the sprint, although we caught up later since we knew we had slightly less resource and as a result had co... | No.
First off, vacation isn't a problem, it's a reality. The burn-down chart is supposed to reflect the reality of the project's progress, and if the project progressed less during one sprint compared to another due to vacation, a proper sprint burn-down chart will reflect that.
Secondly, vacation (along with other a... | I don't think it is a good idea.
Such a story would deliver no business value to the Product Owner. It's just a hack to get your burndown chart to work.
We don't like hacks :)
Why not simply adjust your burndown chart's projected completion date by adjusting the expected velocity?
| https://softwareengineering.stackexchange.com |
1,685,931 | [
"https://math.stackexchange.com/questions/1685931",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/303655/"
] | How can I prove that a covering space which is a homotopy equivalence is a homeomorphism?From the basic property of lifting homotopies I get that there exists $h:Y \rightarrow X $ such that:
$ p \circ h = id_Y $
Where $p:X \rightarrow Y $ is a covering.
| It is not difficult to show that, given a homotopy equivalence $f:X\to Y$ with inverse $g:Y\to X$, whenever there is a path $\kappa:f(x)\leadsto f(x')$, then there is also a path $\lambda:x\leadsto x'$ such that $f\lambda\simeq\kappa$, for any points $x,x'$ in $X$. If you want to prove this, I recommend first showing t... | If it is an homotopy equivalence, in particular it induces an isomorphism in fundamental groups. Now use the classification of covering spaces in terms of subgroups of the fundamental group.
| https://math.stackexchange.com |
67,310 | [
"https://physics.stackexchange.com/questions/67310",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/23752/"
] | The following was originally given to me as a homework question at
my physics 2 course:
<blockquote>
Consider the following circuit
<img src="https://i.stack.imgur.com/KntDu.jpg" alt="enter image description here">
The difference of potentials between the point $V_{1}$and the point
$V_{2}$ is $4.4$ volts... | This is your circuit:
<img src="https://i.stack.imgur.com/TRABL.png" alt="enter image description here">
The current that comes from the source, when reaches the point that must choose it's way, <strong>sees no difference between the two paths (symmetry)</strong> , so half of it flows through one way and the other pa... | Symmetry is a powerful way to obtain a result by inspection. Here's how it works in this case.
Remove the resistor between the A & B nodes. Now, it should be easy to see by inspection that the voltage between the A & B nodes must be zero for any $V_1$ and $V_2$.
The reason is <em>symmetry</em>. The left ha... | https://physics.stackexchange.com |
543,488 | [
"https://physics.stackexchange.com/questions/543488",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/231527/"
] | I don't understand what is the difference between Scattering and reflection?
I have searched and found that in scattering, the atom absorb and re emits the photon, while reflection is due to particle nature(elastic collision). But I don't understand what factor decides, that when a photon hits an atom, weather scatter... | Reflection is a form of scattering, but it is <em>coherent</em> scattering. When scattering occurs from a lot of identical particles rigidly fixed in a plane, then all the possible ways a single photon can be scattered from the plane of particles are fixed in phase. That is coherent scattering, and it is reflection. ... | In both cases, an electron absorbs and re-emits a photon. The difference is in the structure to which the electron belongs. In Rayleigh scattering by the atmosphere, electrons belong to molecules in a random (gaseous) structure in which each molecule moves independently from other molecules. The photon is typically re-... | https://physics.stackexchange.com |
4,269,166 | [
"https://math.stackexchange.com/questions/4269166",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/976731/"
] | The integral in question is <span class="math-container">$$\int \frac{x+1}{9x^2+6x+5}dx.$$</span> I first completed the square in the denominator giving <span class="math-container">$(3x+1)^2+4$</span> and proceeded to perform a <span class="math-container">$u$</span>-substitution with <span class="math-container">$u =... | Since <span class="math-container">$u=2\tan\theta$</span>, you have<span class="math-container">$$u^2=4\tan^2\theta=4(\sec^2\theta-1).$$</span>So,<span class="math-container">$$\sec\theta=\sqrt{\frac{u^2+4}4}$$</span>and therefore<span class="math-container">$$\frac19\ln(\sec\theta)=\frac1{18}\ln\left(\frac{u^2+4}4\rig... | There is a simpler way to determine this integral: rewrite first the numerator:
<span class="math-container">$$x+1=\frac 1{18}(18x+6)+\frac 23,$$</span>
split the integral in two:
<span class="math-container">\begin{align}
\int \frac{x+1}{9x^2+6x+5}\,\mathrm dx&=\frac 1{18}\int \frac{18x+6}{9x^2+6x+5}\,\mathrm dx+\... | https://math.stackexchange.com |
26,936 | [
"https://mechanics.stackexchange.com/questions/26936",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/4906/"
] | Some people say they wash the outside car every week as it makes the paint nice etc
<strong>Are there any benefits of washing the outside of my car?</strong>
<strong>Do I really need to wash the exterior of my car every week?</strong>
<strong>Does it damage my car if I don't wash it for a month or two?</strong>
I w... | <strong>tl;dr: How much did you pay for that shirt? How often do you wash it? Why would you bother? Shirts just get dirty anyway. Can't you get another shirt?</strong>
<blockquote>
Are there any benefits of washing the outside of my car?
</blockquote>
Do you live in an area without salt, birds, tree sap, pollution,... | The reason many people wash their car every week is to keep it looking nice and from the good old days of bad paint and no rust protection.
These days, paints are significantly better and stand up to some serious abuse, and the cars are much better rust proofed (galvanised etc...).
The washing your shirt analogy is... | https://mechanics.stackexchange.com |
3,125,701 | [
"https://math.stackexchange.com/questions/3125701",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/98037/"
] | When I write a definition, e.g.
Let <span class="math-container">$f : \mathbb{R} \rightarrow \mathbb{R}$</span>
How does one pronounce the colon ':' symbol?
I would naively guess 'Let f <em>be-a-function-mapping</em> from the reals to the reals, but this seems inelegant. Is there another way to read this statement?
... | You don't :)
This is an instance where mathematical usage corresponds with actual English-writing usage. In English, a colon introduces a list or a new idea (e.g. your tasks today are: wash the horse, replace the gaskets and remember where you left your grandmother) and is not pronounced -- it just indicates that you ... | I would guess it would take the meaning of "such that" or "with the property that"
Let <span class="math-container">$f : \mathbb{R} \rightarrow \mathbb{R}$</span>
Would therefore be analogous to "The function f with the property that maps elements of the reals to elements of the reals.
Or More General
Let <span cla... | https://math.stackexchange.com |
161,099 | [
"https://softwareengineering.stackexchange.com/questions/161099",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/25953/"
] | I am always given the advice that developers need to stay up to date with the latest in technology - things like webrtc, updates on html5 and css3 and new js libraries, software methodologies like TDD, DDD, and BDD.
The question is <em>why</em>? Why do we need to constantly update ourselves? Can't we just stick with w... | New technologies surface for a reason. Usually that reason is because they are more efficient or powerful at accomplishing a particular task.
There is still value to be had in sticking with old technology for the sake of legacy systems, but when they eventually reach their end of life you'll be behind the game.
Busi... | Although it is certainly possible to build a career on a single technology stack if you get lucky<sup>1</sup>, it is a near certainty that the technology is going to change more than once during the time when you are gainfully employed. You can (and you should) get better at what you already know, but learning new thin... | https://softwareengineering.stackexchange.com |
335,065 | [
"https://softwareengineering.stackexchange.com/questions/335065",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/4485/"
] | When a modern OS loads a process, it pre-allocates a certain amount of space for stack. This means that the programmer has to be careful to avoid stack overflow by limiting call depth and/or by increasing the stack size in run-time.
At first glance, this seems unnecessarily complicated. Why doesn't the OS implement th... | Default thread stack sizes on modern desktop OSs are usually in the MB range. They'll make use of the virtual memory paging as you describe to only use physical memory as needed.
The main reason for not making this dynamically growable is because it's rarely needed. Practically, most times that a thread blows the stac... | Programs compiled to machine code with todays compilers assume the stack is contiguous (and does not move around during execution), so this would break backwards compatibility with almost all existing software.
| https://softwareengineering.stackexchange.com |
90,716 | [
"https://security.stackexchange.com/questions/90716",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/65879/"
] | I was reading an article which explained that there is a growing movement to force ISP's to store IP-assignment logs for DHCP connections for longer periods of time in order to fight cyber-crime. However, I don't understand why this is necessary. If an ISP no longer has the information associated with an IP address, wh... | It's certainly <em>possible</em> to do it that way, and indeed investigators will sometimes ask many different parties for information related to a case to piece together scattered evidence, but why would you want to obtain this information from Google when it is much easier and more reliable to obtain it directly from... | I live in the Netherlands and we had a storage requirement for 2 years (I believe).
One of the motivation for getting the law was so law enforcement can track a malicious use back from the logs of a server to the ISP, and than (through the courts) get the Name and address of the subscriber.
Asking a third party to ... | https://security.stackexchange.com |
112,792 | [
"https://security.stackexchange.com/questions/112792",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/47692/"
] | Suppose you get an error on your PC that shows up randomly, then you do a search on the internet for the error to find out how to fix it. Typically, you will get some sites that offer a solution, but some of those sites seem a bit sketchy, especially when they say to download this registry script or an executable tool... | In my experience, though it is uncommon to find malware embedded in these fix it scripts and registry keys, <em>it does happen.</em>
As such, I would highly recommend most users getting these types of patches and assistance from the vendor directly.
An experienced security professional could download the fix it scr... | <blockquote>
Do technical advice sites often link to malware?
</blockquote>
This seems very broad. How can we easily check the majority of these websites and find which advice is malicious, and which isn't? And then there's all the advertisements on the website.
They can <em>if</em> they want. Contributors can if... | https://security.stackexchange.com |
123,869 | [
"https://electronics.stackexchange.com/questions/123869",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/49326/"
] | I am trying to interface with a HC-06 module but I can't talk to the module over serial.
My VCC is connected to 5V (also tried 3.3V) of my Arduino Uno, and GND is connected to ground of it (obviously). I've connected the RXD to pin 11 and TXD to pin 10 (also tried the opposite too). The LED on the module is blinking (... | I've pulled up the KEY pin. It didn't work. But after some more trials it worked, even though key wasn't pulled up anymore. Not sure if it was the high KEY pin that triggered it to work, or if it was something else.
Note, for future reference, it was default at baud 9600, and I used 5V VCC from Arduino, not 3.3V.
| The default baud rate is 9600, 8 bit, no parity no flow control (9600,8,N,1).
The HC-06 works with 3,3V ... You can connect the HC-06-TX (output) direct to PC-RX (TTL) but the PC-TX (TTL) CAN NOT BE DIRECTLY CONNECTED to HC-06-RX (input), due to 5V, then you have to put a level converter. In this case is enought to use... | https://electronics.stackexchange.com |
10,236 | [
"https://security.stackexchange.com/questions/10236",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/628/"
] | If I'm an administrator of a corporate network, I could use an HTTP proxy to examine outgoing connections to monitor what websites my employees are going to, and terminate connections based upon policy/content rules.
Or, I put an invisible bump-in-the-wire box at the gateway to examine traffic content and terminate co... | With the HTTP proxy, user systems can have local private addresses (e.g. addresses in the 10.0.0.0/8 or 192.168.0.0/16 networks) since, at the TCP/IP level, these systems only talk to the proxy, not the Internet at large. With the "bump-in-the-wire" box, user systems must be able to contact arbitrary external sites mor... | For the purposes of monitoring users on a corporate network, the difference between on-the-wire sniffing/interception and proxies is small. In-fact, an on-the-wire box is a superior choice in most respects if all traffic is forced over it, as it will see traffic across all ports.
However, proxies are not solely instal... | https://security.stackexchange.com |
348,315 | [
"https://physics.stackexchange.com/questions/348315",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/164488/"
] | Why does sugar dissolve faster in hot water compared to cold water?
| I am going to have to respectfully disagree with Pranjal Rana.
The reason that sugar dissolves more quickly in hot water than in cold water has to do with the kinetic energy of the particles.
The faster (hotter) the water molecules are moving, the more energy they give to the sugar molecules when they collide with ... | I will explain it with the help of Le Chatelier principle. It states that the rate of reaction depends on the temperature. If the reaction is exothermic, then decrease of temperature will increase the rate to compensate the effect caused by decrease of temperature. However the rate will decrease if the temperature is i... | https://physics.stackexchange.com |
251,653 | [
"https://electronics.stackexchange.com/questions/251653",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/120329/"
] | I will try to ask as intelligibly as possible, please bear with me.<br/><br/>
I understood that <code>P = VI</code> which is the power to be transmitted, and <code>V = IR</code> is a voltage loss which must be overcome by transmitting at high voltage and low current.<br/>
Now, a transformer works on the principle that ... | I'm going to offer a slightly different tack than the other responses, as you already have enough there to work from. And perhaps a different approach might also help a little. (Or make things worse.)
You may not understand the difference between having the <em>capacity</em> to do something doesn't mean you are actual... | The real questions:
"1] How do two different rated components work from the same line? Eg a 100W bulb and a 40W fluorescent tube?"
------ House hold devices are connected in parallel. So, appliances with variable power rating (100W and 40W in your case) working at 230V would draw different currents (i.e. 100W/230V and ... | https://electronics.stackexchange.com |
103,110 | [
"https://math.stackexchange.com/questions/103110",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/8393/"
] | At time 0, a cell culture starts with one red cell. At the end of one minute, the red cell dies and is replaced by 2 red cells with probability $\frac{1}{4}$, with 1 red and 1 white cell with probability $\frac{2}{3}$, and with 2 white cells with probability $\frac{1}{12}$. Each red cell lives for one minute and gives ... | This is a two-type branching process hence bivariate generating functions are a well-adapted tool.
Call $R_n$ and $W_n$ the numbers of red cells and of white cells in generation $n$. Let $u$ denote the generating function of the number of descendants of one red cell, hence, for every $s$ and $t$ in $(0,1)$,
$$
u(s,t... | Look up "branching process". If $\phi(s)$ is the pgf of the number of red offspring of a single red cell, and $\phi'(0)$ (which is the expected number of red offspring) is greater than $1$, then the probability of the culture dying out is the least positive solution of $\phi(p)=p$.
| https://math.stackexchange.com |
73,469 | [
"https://physics.stackexchange.com/questions/73469",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/27849/"
] | I'm intending to study General Relativity on my own. The thing is, my physics background is not very strong. I know classical mechanics and I know some electromagnetism. I'm familiar with Gauss' law, Ampere's law, RLC circuits, ... but I still have problems with the intuition behind concepts like 'momentum'. I know tha... | The physics prerequisites to general relativity are really simple -- classical mechanics (Newtonian and Lagrangian), and special relativity. You need to know Newton's inverse-square law for gravity to appreciate general relativity physically, of course, but everyone knows this.
But there is still a notational math pre... | If you know freshman calculus (derivatives and integrals) and freshman physics you should be able to handle a general relativity course or self-study.
The important part is graphing the space-time effects and being able to muster the thought experiments for time dilation. The thought experiments are largely conceptual... | https://physics.stackexchange.com |
2,801,168 | [
"https://math.stackexchange.com/questions/2801168",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/565955/"
] | Find the limit: $\lim \limits_{n\to\infty}(n-\sqrt[2018]{n^{2018}-n^{2017}})$
I've been trying to find solution myself and was always stuck with $\infty$. Then I've asked Wolfram Alpha about the answer and it evalated the limit to $\frac{1}{2018}$, but still I can't understand why's that so.
| You can try the limit as $x\to0^+$ of the function, defined over (0,1),
$$
f(x)=\frac{1}{x}-\sqrt[2018]{\frac{1}{x^{2018}}\frac{1}{x^{2017}}}=
\frac{1-\sqrt[2018]{1-x}}{x}
$$
because
$$
\lim_{n\to\infty}\Bigl(n-\sqrt[2018]{n^{2018}-n^{2017}}\,\Bigr)=
\lim_{n\to\infty}f\Bigl(\frac{1}{n}\Bigr)
$$
On the other hand
$$
\l... | We have by binomial expansion
$$\sqrt[2018]{n^{2018}-n^{2017}}=n\left(1-\frac1n\right)^{\frac 1 {2018}}=n\left(1-\frac1{2018n}+o\left(\frac1n\right)\right)=n-\frac1{2018}+o\left(1\right)$$
then
$$n-\sqrt[2018]{n^{2018}-n^{2017}}=\frac1{2018}+o\left(1\right)$$
| https://math.stackexchange.com |
6,363 | [
"https://cs.stackexchange.com/questions/6363",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/3004/"
] | <img src="https://i.stack.imgur.com/2hUx4.jpg" alt="search tree">
<strong>Problem : Two players have in front of
them a single pile of objects, say a stack of 7 pennies. The first player divides the original
stack into two stacks that must be unequal. Each player alternatively thereafter does the
same to some single s... | Because - according to the rules above - each player must divide a stack into two stacks that must be unequal.
| (b) Assume two players, min and max, play nim (as described above). Min plays first.
If a terminal state in the search tree developed above is a win for min, a utility function of zero is assigned to that state. A utility function of 1 is assigned to a state if max wins the game.
Apply the minimax algorithm to the se... | https://cs.stackexchange.com |
21,593 | [
"https://cs.stackexchange.com/questions/21593",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/947/"
] | $1+3+5+...+(2n+3)=n^2+4n$
For this series using induction proof.
Base case 1,2,3,.. not working. But induction step works well.
Base case is not given in question.
| First of all, the right hand side should be $n^2+4n+4$
You can find the generalized term for the left hand side is $2n-1$. Therefore,
$1+3+5+...+(2n-1)+(2n+1)+(2n+3)=n^2+4n+4$, which gives you:
$1+3+5+...+(2n-1)=n^2$.
Then you can apply the mathematical induction to prove it holds for every positive integer $n$.
| A proof by induction requires that the base case holds and that the induction step works. If either doesn't work, then the proof is not valid.
It can definitely happen that the induction step works, but not the base case. If that never happened, we'd define induction without the base case.
Example: consider the prope... | https://cs.stackexchange.com |
15,107 | [
"https://mathoverflow.net/questions/15107",
"https://mathoverflow.net",
"https://mathoverflow.net/users/717/"
] | In Bourbaki an <em>algebra</em> over a commutative ring $k$ is defined to be a $k$-module $A$ together with a $k$-bilinear map $A \times A \rightarrow A$. We then have the obvious notion of morphisms of $k$-algebras. This terminology is nice, because e.g. Lie algebras are then a special kind of algebras and so on. But ... | If your work requires you to work mostly with unital assosiative $k$-algebras with unital morphisms, define somewhere prominent in your work 'algebra' and 'morphism of algebras' to mean precisely that, and say 'Lie algebras', 'not necessarily associative algebra', 'possibly non unital morphism of algebra', and so on i... | I will mention: most mathematicians of my acquaintance do not agree with Bourbaki's notation. As far as I'm concerned, an algebra is unital associative. In fact, I would discourage you from using the word "algebra" to mean a possibly non-associative algebra without pointing this out explicitly to your readers.
| https://mathoverflow.net |
61,005 | [
"https://dba.stackexchange.com/questions/61005",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/35606/"
] | I have a <strong>product details table</strong>, the fields in the table are *Prod_Id, Product_Name, Quantity, Slno*. Now i have created trigger for varchar data type field and implemented auto increment for Prod_Id (Primary key) and for Slno. The output will be
<strong>Prod_Id -->>> PROD0001, PROD0002</strong> and s... | This will work
<pre><code>SET NEW.Prod_id = CONCAT('PROD', LPAD(LAST_INSERT_ID(), 3, '0'));
SET NEW.Prod_id = CONCAT(SUBSTRING(NEW.Product_Name,1,2), NEW.Prod_id);
</code></pre>
Thanks
Acube.
| <ul>
<li>Store the "BO" and "1" as two columns.</li>
<li>INDEX that pair of columns so that you can find the max</li>
<li>Construct 'BO_002' when fetching the row by doing <code>CONCAT(prefix, '_', seq)</code>. (And use <code>ZEROFILL</code> instead of <code>LPAD</code>, etc).</li>
</ul>
| https://dba.stackexchange.com |
39,352 | [
"https://engineering.stackexchange.com/questions/39352",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/16275/"
] | All the notes on Thermal boundary layer(TBL) explains the growth of TBL over a heated flat plate ie cooler fluid is flowing over a hotter plate (heat is flowing from the plate to the fluid).
How does the thermal boundary layer develop over a chilled plate, where hot fluid flows over a chilled plate. Also, Can you pleas... | The definition of the thermal boundary layer is that of <strong>the distance across a boundary layer from the wall to a point where the flow temperature has essentially reached the 'free stream' temperature, <span class="math-container">$T_{0}$</span></strong>. This distance is defined normal to the wall in the y-direc... | A higher thermal conductivity ratio in the flow causes the heat diffusion to catch up with farther layers of fleeing molecules of the flowing liquid that otherwise would have washed past unaffected. If we compare k to the speed of heat diffusion, a higher k means reaching more in less time.
For example, if the k conver... | https://engineering.stackexchange.com |
337,826 | [
"https://math.stackexchange.com/questions/337826",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/32119/"
] | Let $A$ be a commutative ring with unity. If $\mathfrak p,\mathfrak q\in \operatorname{Spec} (A)$ is it true the following equality
<blockquote>
$$A_\mathfrak p\cap A_\mathfrak q= A_{\mathfrak p\cup \mathfrak q }?$$
</blockquote>
Here the symbol $A_{\mathfrak p\cup \mathfrak q }$ means the localization $S^{-1}A$, ... | I assume that $A$ is an integral domain. As @MartinBrandenburg noticed $S^{-1}A\subseteq A_{\mathfrak{p}} \cap A_{\mathfrak{q}}$. (Here $S=A-\mathfrak{p}\cup \mathfrak{q}$.)
Let $x\in A_{\mathfrak{p}} \cap A_{\mathfrak{q}}$. Then there is $s\in A-\mathfrak p$ and $t\in A-\mathfrak q$ such that $sx\in A$ and $tx\in A... | You cannot intersect two arbitrary abstract rings. They have to be subrings of a larger ring in order to do that.
If $A$ is an integral domain (which I will assume from now on), then localizations $\neq 0$ of $A$ can be embedded into the field of fractions $Q(A)$ and their intersection makes sense. (EDIT: This paragra... | https://math.stackexchange.com |
614,671 | [
"https://physics.stackexchange.com/questions/614671",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/289062/"
] | I was cooking something in the microwave and opened the door early to check on it and the microwave didn't stop. I didn't realize this for a few seconds and when I did I shut the microwave off but I'm concerned what I could have been exposed to for the few seconds that it was open.
As far as I can remember I still hear... | The very first thing you should do is stop using your oven and have it checked out by an authorized repair service.
If in fact the oven was operating with the door open, there was a failure of the door interlocks to turn the oven off and a failure of the backup system intended to permanently shut the oven off in the ev... | When reading your post, it seemed to me that the most likely explanation for your experience is that the microwave did turn off, but the ventilation did not. You may have mistaken this for the microwave not turning off.
If indeed the microwave didn't turn off, you would have felt pain and other sensations immediately. ... | https://physics.stackexchange.com |
555,537 | [
"https://physics.stackexchange.com/questions/555537",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/137767/"
] | I tried to find an answer to this but haven't yet. Going through Jackson's Electrodynamics, the following steps are used to determine the vector potential as the curl of <span class="math-container">$\mathbf{B}$</span>. The context is magnetostatics, where <span class="math-container">$\nabla \cdot \mathbf{J} = 0$</spa... | The issue here is keeping track of your derivatives - there's a big difference between differentiating with respect to <span class="math-container">$\mathbf x$</span> inside the integral and differentiating with respect to <span class="math-container">$\mathbf x'$</span> inside the integral.
In what follows, I use t... | <span class="math-container">$\nabla \left ( \frac{1}{|\mathbf{x}-\mathbf{x'}|} \right ) = \color{red}{-}\frac{\mathbf{x}-\mathbf{x'}}{|\mathbf{x}-\mathbf{x'}|^3},$</span> which fixes the minus sign.
The first term is usually taken to be zero because of the physical boundary condition of <em>localised</em> charges an... | https://physics.stackexchange.com |
435,959 | [
"https://electronics.stackexchange.com/questions/435959",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/220683/"
] | 6I am a software engineer with a small amount of experience in electrical engineering that has been tasked with designing an embedded OS for a IDMT relay (uni project).
However, I don't understand why a protection relay would ever need a delay.
If a fault is detected shouldn't the breaker activate as soon as possible... | You really need to provide more information as to what are the particulars of your system as there are many varieties of protection relays. In any case, delays are often used to prevent nuisance tripping due to transient events because many devices protected by relays can tolerate short term faults while the consequen... | Delays are often necessary to coordinate with other protective devices in the system. If you don’t have other devices that you need to coordinate with, then you can trip as quickly as possible (within reason).
| https://electronics.stackexchange.com |
229,897 | [
"https://electronics.stackexchange.com/questions/229897",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/17642/"
] | I was trying out a hobby project and I was using the IRFD120 and IRFD110 power MOSFETs to control a motor. The transistors worked pretty fine and we simply ran out of them. When I went to buy some more I found out that they are outrageously expensive for a transistor. However, I found the FQP30N06L and FQP27P06 power M... | The 100V could be a reason: high voltage MOSFET tend to be quite expensive. But I think in this case, the reason is the strange package the IRFD110 uses. This is non standard and certainly uses specific production lines.
And usually, the reason is just that: they use older technology that is more expensive to produce ... | <blockquote>
Would it be a good idea to replace the stock of IRFD110 and IRFD120
with FQP30N06L and FQP27P06 for hobby project related applications?
</blockquote>
Nobody but a fool is going to say yes to that question. It's all down to the application, the load, the power rails, the switching frequency and the dri... | https://electronics.stackexchange.com |
34,207 | [
"https://chemistry.stackexchange.com/questions/34207",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/15363/"
] | I was helping some students today, quite successfully, until I came across this problem:
$$\begin{align}
\ce{A &<=>[$k_+$][$k_-$] B + C} \\[5pt]
\ce{C + D &->[$k_1$] E}
\end{align}$$
The first equation is a fast process with forward and reverse rate constants $k_+$ and $k_-$, respectively.
The sec... | You can't write $[\ce{B}] = [\ce{C}]$ because $\ce{C}$ is consumed in the second step but $\ce{B}$ isn't. However, you were pretty much on the right track.
Since $\ce{E}$ is produced from $\ce{D}$, you can write $[\ce{E}] = [\ce{D}]_i - [\ce{D}]$ where $[\ce{X}]$ denotes the concentration of $\ce{X}$ at a certain poi... | The best first step in any kinetics problem is writing down materials balances on all relevant species.
$$\frac{dA}{dt}=-k_+ A + k_-B C$$
$$\frac{dB}{dt}=+k_+ A - k_-B C$$
$$\frac{dC}{dt}=+k_+ A - k_-B C - k_1 C D$$
$$\frac{dD}{dt}=- k_1 C D$$
$$\frac{dE}{dt}= k_1 C D$$
We want to solve for $\frac{dE}{dt}$ ... | https://chemistry.stackexchange.com |
3,262,481 | [
"https://math.stackexchange.com/questions/3262481",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/64460/"
] | I am reading Ted Shifrin's excellent book <em>Multivariable Mathematics</em>. It claims that the equality of mixed partials is "an intuitively obvious result, but the proof is quite subtle". However, I guess I must be thinking in the wrong way, because I do not see the intuition behind this result. This is how I think ... | We can use a shortcut to calculate the sum:
<ul>
<li>We know the first term in the list (13) and the last term (98). There are 18 terms in total (= (98-13)/5 + 1)</li>
<li>If you pair up the first term and the last term, and the second term and the second-to-last-term, etc. the pairs all have the same sum, 111.</li>
<... | The sum is <span class="math-container">$$\sum _2^{19} ( 5k+3) = 5\sum _2^{19} ( k) + 3(18) = 5(189)+54 =999$$</span>
Note that <span class="math-container">$$\sum _2^{19} k =\sum _1^{19} k -1 = \frac {19(20)}{2} -1=189$$</span>
| https://math.stackexchange.com |
12,854 | [
"https://datascience.stackexchange.com/questions/12854",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/21576/"
] | How do I capture $y = x_1 x_2$ using a simple neural network with commonly used activation functions? I assume that I need at least one hidden layer. What mix of commonly activation functions should I use?
So far, I have used $max(0,x)$ and $tanh$ activation for the hidden layer, but the gradient descent diverges very... | Probably you need to do one or more of:
<ul>
<li>Decrease learning rate. Diverging loss is often a symptom of learning rate too high.</li>
<li>Increase number of hidden neurons. The output function will be the combination of many "patches" each created by a neuron that has learnt a different bias. The shape and qualit... | To add onto the above answer, a simple feedforward network doesn't learn the function itself. But recently, Neural Turing Machines claim to learn the algorithm. Worth a shot!
| https://datascience.stackexchange.com |
3,622,063 | [
"https://math.stackexchange.com/questions/3622063",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/168676/"
] | prove that characteristic of <span class="math-container">$\mathbb{Z}[i]/<2+2i>$</span> is <span class="math-container">$4$</span> and it has exactly <span class="math-container">$8$</span> elements.
I need to know, is this below approach works for characteristic?
<strong>My attempt</strong>
I saw <span clas... | <span class="math-container">$\newcommand{\r}{\langle 2+2i\rangle}$</span>
You got <span class="math-container">$\frac{c+d}{4}$</span> and <span class="math-container">$\frac{d-c}{4}$</span> both belong to <span class="math-container">$\mathbb Z$</span>. From <span class="math-container">$2a-2b = c$</span> and <span cl... | Note that
<span class="math-container">$$(2+2i)(1-i)=4$$</span>
so <span class="math-container">$4\in \langle 2+2i\rangle$</span>. You also need to know that this is the smallest, meaning the characteristic is not <span class="math-container">$2$</span> or <span class="math-container">$3$</span>. So suppose
<span class... | https://math.stackexchange.com |
307,588 | [
"https://softwareengineering.stackexchange.com/questions/307588",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/100120/"
] | Based on the context, C# can generate the expression tree for a <code>LambdaExpression</code> from lambda expression syntax:
<pre class="lang-cs prettyprint-override"><code>Expression<Func<string, int>> expr1 = s => s.Length;
</code></pre>
as can VB.NET:
<pre class="lang-vb prettyprint-override"><code... | In my opinion, the main reason this feature is not available due to the language designers not being required to implement it or not seeing point in doing that since this can be already achieved with lambdas in a sane manner.
<ol>
<li>The feature is most probably technically possible, since all expressions can be writ... | We already know that the expression tree generation mechanism is able to generate an expression tree for any arbitrary expression, because it's able to generate an expression tree for any arbitrary expression within a lambda. So it's clear that technical limitations are not the problem. The most likely answer is that... | https://softwareengineering.stackexchange.com |
21,028 | [
"https://mathoverflow.net/questions/21028",
"https://mathoverflow.net",
"https://mathoverflow.net/users/4959/"
] | Apologies for the vague title - I couldn't come up with a single sentence that summarised this problem well. If you can, please edit or suggest a better one!
This question is also rather specific and contains lots of annoying technical detail. I must admit to not really expecting an answer unless there's an obvious so... | I claim that there are no bad sequences in C(ω<sub>1</sub>).
Suppose to the contrary that x<sub>α</sub> is bad. For any countable
ordinal β, there is r<sub>β</sub> in
C(ω<sub>1</sub>) such that the distance between r<sub>β</sub> and
x<sub>α</sub> for α < β is at mos... | I can partially answer the second question. If $X$ is a compact Hausdorff space whose topology has a countable base at every point [Edit: $\omega_1$ has this property but not compact], then there are no bad sequences. Moreover the following holds:
If $F\subset C(X)$ is a family such that every countable subfamily has ... | https://mathoverflow.net |
431,926 | [
"https://physics.stackexchange.com/questions/431926",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/170472/"
] | I know how to create coherence between two states if I have a pure state. For example if the system is in pure state <span class="math-container">$|1\rangle = \begin{bmatrix}1\\0 \\\end{bmatrix}$</span> then density matrix is given by <span class="math-container">$\rho_o = \begin{bmatrix}1 & 0\\0 & 0\\\end{bmat... | If you apply any unitary <span class="math-container">$U$</span> to the maximally mixed state <span class="math-container">$\rho_0$</span>, you will get out...
<span class="math-container">$$ U \rho_0 U^\dagger = U U^\dagger \rho_0 = \rho_0 $$</span>
again. <span class="math-container">$\rho_0$</span> is a multiple o... | No, this is provably impossible using unitary evolution. You expressly need some form of projective measurement (possibly followed by a unitary gate) to create such a coherence. This can be shown using the resource theory of quantum coherence.
| https://physics.stackexchange.com |
36,111 | [
"https://quant.stackexchange.com/questions/36111",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/29342/"
] | I've been working with this trader and every time he explains something to me, it sound like foreign language. There's so many things going on. I'm a graduate analyst on the bond trading desk and I don't think it's all that complicated. It's just millions of concepts flying around. Anyone have any advice or the best wa... | <ol>
<li>Don't get discouraged – this is how we all felt when we got started. This is particularly true in fixed income, where a lot of jargons are thrown around.</li>
<li>Ask your colleagues. You can potentially figure everything out by reading books, but it's much better to just consult your colleagues – it's one thi... | This is how we've all felt when we started in FI groups. Not much way around it other than just time on the job, but what is really helpful for a lot of people (myself included) is to keep a notebook nearby and just take down every question you have or anything you don't understand. Then, when things slow down from a s... | https://quant.stackexchange.com |
614,496 | [
"https://physics.stackexchange.com/questions/614496",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/264772/"
] | Often times it is stated in books that a quantum state is physically realizable only if it is square integrable. For example, in Griffiths (2018 edition) page 14 he stated
<blockquote>
Physically realizable states correspond to the
square-integrable solutions to Schrödinger’s equation.
</blockquote>
But when we have an... | If you want to use the theory of probability, a <strong>necessary</strong> condition for a wavefunction to be physically meanigful is <span class="math-container">$$\psi \in L^2(\mathbb{R}^3,d^3x)\:.$$</span> That is because, <em>as a basic postulate of QM</em>, we have that:
<span class="math-container">$\qquad\qquad\... | The problem with my question was I assumed that this below postulate of quantum mechanics (given in R. Shankar chapter 4 as 3rd postulate) to be <strong>literally</strong> true
<blockquote>
If the particle is in a state <span class="math-container">$|\psi\rangle$</span>, measurement of the variable (corresponding to) <... | https://physics.stackexchange.com |
187,799 | [
"https://softwareengineering.stackexchange.com/questions/187799",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/43961/"
] | What I know is:
<ul>
<li>A Functional test aims to test a single component (like a WebApp's Controller) from the <strong>point of view of the developer</strong>. => Did I achieve all the requirements to make it work well? </li>
<li>An Acceptance test aims to to test a group of components together and is focused on the... | yes, there can be duplication. Often with line of business type websites, you find the acceptance tests can actually substitute for developer oriented tests, because the depth of code needed to implement features is not too great. As a comparison, image recognition software may have huge depth, but at an acceptance ... | Yes, Tests should exist at multiple levels, in multiple forms and yes, you will see a lot of redundancy.
For example in a MVC you may have test in all three places that are checking on the value of an attribute. This can be seen as as a positive thing because then you can change any piece and know the effect of the... | https://softwareengineering.stackexchange.com |
429,409 | [
"https://math.stackexchange.com/questions/429409",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/83036/"
] | <blockquote>
Given <span class="math-container">$v_1, \ldots, v_k \in V$</span> and <span class="math-container">$\phi_1, \ldots, \phi_k \in V^*$</span>. If <span class="math-container">$\phi_1, \ldots, \phi_k \in V^*$</span> are linearly dependent, prove that <span class="math-container">$\det[\phi_i(v_j)] = 0.$</sp... | I think that in general this question is difficult. Sometimes the answer is negative (see Zev Chonoles' answer). In your specific example case we can conclude that the group has to be $S_4$.
The elements in the conjugacy class of $8$ elements have centralizers of order $24/8=3$. Therefore they must be of order $3$, an... | I'm afraid I don't know the answer to your specific question about $S_4$, but in general, knowing the number and sizes of the conjugacy classes is not sufficient, because any two finite abelian groups of the same cardinality $n$ will both have $n$ conjugacy classes of size $1$, but they need not be isomorphic. For an e... | https://math.stackexchange.com |
174,915 | [
"https://physics.stackexchange.com/questions/174915",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/68207/"
] | I am studying higher algebra. I have learnt that as well as for reals, trigonometric functions can also be defined for complex numbers, by means of power series. Such as:
$$\sin(z)=z-\frac{z^3}{3!}+\frac{z^5}{5!}-\frac{z^7}{7!}+...(to \infty terms)$$
Here we are taking sine of a complex number $z$, which makes me suspe... | Hmm. Well, first of all, mathematicians do what mathematicians think is interesting. Often it applies to physics. Sometimes not. I don't want to give any examples of math that I don't think has a physical application though, since I expect someone would be able to find one. Anyway. So, we use complex numbers a lot in p... | I'm not sure how relevant for your question this could be, but you might consider Wick rotations from real to imaginary times, that usually provide a formal way for passing from quantum to statistical mechanics.
For a time-independent Hamiltonian operator $H$, consider the time evolution operator
$$U(t) = e^{itH},\qqu... | https://physics.stackexchange.com |
2,285,843 | [
"https://math.stackexchange.com/questions/2285843",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/354073/"
] | If $a+b+c+d=2$, find the maximum value of $(1+a+b)(1+c+d)$
My Attempt:
$$a+b+c+d=2$$
Now,
\begin{align}(1+a+b)(1+c+d)&=1+c+d+a+ac+ad+b+bc+bd\\
&=1+(a+b+c+d)+ac+ad+bc+bd\\
&=1+2+ac+ad+bc+bd\\
&=3+ac+ad+bc+bd\end{align}
How do I proceed further?
P.S: Edit after fractal1729 comment.
| $a+b+c+d=2$
$$\implies (1+a+b)+(1+d+c)=4$$
Thus by AM-GM inequality,
$$\frac{(1+a+b)+(1+c+d)}{2}\ge\sqrt{(1+a+b)(1+c+d)}$$
Thus $$(1+a+b)(1+c+d)\le(\frac{4}{2})^2$$
Thus maximum value of $(1+a+b)(1+c+d)$ is 4. It is attained when $$a+b=c+d=1$$.
| Similar to Basti's answer, except this substitution makes it even quicker to get the range of possible values. Use $x = c+d-1$; then $$(1+a+b)(1+c+d) = (2-x)(2+x) = 4-x^2 \leq 4.$$ Furthermore, if $a,b,c,d$ are positive, $x$ ranges between $-1$ and $1$, so $x^2$ ranges between $0$ and $1$, so $4-x^2$ ranges between $... | https://math.stackexchange.com |
308,935 | [
"https://softwareengineering.stackexchange.com/questions/308935",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/144639/"
] | I have seen programs using this strategy and I have also seen posts considering this bad practice. However, the posts considering this bad practice have been written in c# or some other programming language, where there are some error handling built in. This question is about the c++. Further, the errors I am addressin... | <blockquote>
I have a question regarding the use of exceptions at the highest level of a program.
I have seen programs using this strategy and I have also seen posts considering this bad practice.
However, the posts considering this bad practice have been written in c# or some other programming language, where there ar... | Clearly in your main () function you don't have a chance to <em>handle</em> the exception in any meaningful way. If an exception reaches main (), all you know is that something went badly wrong.
You can of course decide how you want to handle the situation that "something went badly wrong". That's not at all a bad pr... | https://softwareengineering.stackexchange.com |
94,718 | [
"https://physics.stackexchange.com/questions/94718",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/37914/"
] | I was trying to understand how the wave function for a sinusoidal wave was derived, but did not understand one specific sign, the minus sign in the following formula:
$$y(x,t) = A \sin(k x – \omega t + \theta_0)$$
Can anybody explain me what does the negative sign between $k x$ and $\omega t$ means in physical and ma... | If your phase is zero $\theta_0=0$ then your wave has zero amplitude when $k x = \omega t$ or $x = c t$ where $c = \frac{\omega}{k}$ is the wave speed.
So it represents a wave moving in the $+x$ direction with speed $c$.
| First, let's let $\theta_0=0$ for simplicity.
Now, consider $y(x,0)=Asin(kx)$. That means that when $t=0$ then $y=0$ when $x=0$. That is, $y(0,0)=0$.
Now, let's follow that point $y=0$ as time increases. Consider $t=1$, then what is $x$ such that $y(x,1)=0$? Plugging in $t=1$ we see that $0=Asin(kx-w)$. Ther... | https://physics.stackexchange.com |
128,636 | [
"https://physics.stackexchange.com/questions/128636",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/43424/"
] | When I put ice cubes in a glass of water, I find that sometimes they will stick together and form a sort of "bridge" between them as they melt. There is usually a visible line where one ends and the other begins, and they break apart if pushed (but for the most part they stick together if they aren't interfered with).... | When you put the ice cubes in, the temperature of the cubes is (much) below freezing temperature. The drink in the glass is above freezing temperature. The interface between the ice and the liquid (the surface of the ice cube) is cooled by the ice cube, but heated by the liquid. The ice cube heats up in this process an... | Ice cubes are colder than the water they are in, so the water freezes the two ice cubes together forming the bridge with the ice.
| https://physics.stackexchange.com |
7,478 | [
"https://security.stackexchange.com/questions/7478",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/2742/"
] | I've often wondered why facilities do not require authentication as a default on exit. Beyond the oblivious reasons:
<ul>
<li>Fire safety policies would require a panic mechanism to override the access control. </li>
<li>Additional cost of authentication mechanisms at an exit point.</li>
</ul>
| Some places do, but most do not from the viewpoint that they are only concerned about who is getting <em>into</em> the place.
Places I've worked where authenticating those leaving was the norm included:
<ol>
<li>A manufacturing facility, who was also checking bags and pockets to detect if you were trying to stea... | Physicalities?
Truly secure locations do require authentication on exit -- a swipe card or checking bags and persons by security et al.
Most jurisdictions require that doors unlock automatically in the event of an emergency such as fire or even power outage. Again, truly secure buildings will move security personnel ... | https://security.stackexchange.com |
690,884 | [
"https://physics.stackexchange.com/questions/690884",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/318923/"
] | A ball is dropped from a certain height. The work done on the ball by the gravitational force is
<span class="math-container">$$W = F \cdot h = mgh$$</span>
and the gravitational potential energy is
<span class="math-container">$$U = -mg h$$</span>
The difference in kinetic energy is
<span class="math-container">$$\Del... | TL;DR There are few things wrong in how you understand the work-energy theorem:
<ul>
<li>the work <span class="math-container">$W$</span> does not enter the energy diagram from both sides;</li>
<li>if you include gravitational potential energy <span class="math-container">$U$</span> separately in the energy diagram, th... | You have made a fundamental mistake in writing
<em>The potential energy is: <span class="math-container">$U = - mg h$</span></em>
What you should have written is the <strong>change</strong> in potential energy is: <span class="math-container">$\Delta U = U_{\rm final} -U_{\rm initial} = - mg h$</span> and if you assume... | https://physics.stackexchange.com |
21,525 | [
"https://stats.stackexchange.com/questions/21525",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/4559/"
] | Recently, there are several estimators have been proposed to estimate the average treatment effect (ATE) in observation studies, such as IPTW, doubly-robust estimator, etc. It fully makes senses to me for using these estimators to estimate ATE when outcome variable is continuous. However, it does not make any sense to ... | You seem to be slightly misunderstanding the purpose of the weights in IPTW. You are right it would not make sense to have a fractional value for a binary outcome, but the goal of weighting here is not to get a "corrected" outcome value for each individual.
Instead, you are creating a pseudo-population the compositio... | $\hat e_i$ is I believe the propensity score; i.e., the probability of $Z_i = 1 | X_i$, so treatment patients are weighted by the inverse of the propensity score, while control patients are weighted by (1- propensity score).
| https://stats.stackexchange.com |
133,495 | [
"https://softwareengineering.stackexchange.com/questions/133495",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/46284/"
] | To my understanding, a parser creates a parse tree, and then discards it thereafter. However, it can also pop out an abstract syntax tree, which the compiler supposedly makes use of.
I'm under the impression that both the parse tree and the abstract syntax tree are created under the parsing stage. Then could someone e... | A parse tree is also known as a concrete syntax tree.
Basically, the abstract tree has less information than the concrete tree. The concrete tree contains each element in the language, whereas the abstract tree has thrown away the uninteresting pieces.
For example the expression: <code>(2 + 5) * 8</code>
The concret... | The first thing you need to understand is that nobody forces you to write a parser or compiler in a certain way. Specifically, it is not necessarily the case that the result of a parser must be a tree. It can be any data structure that is suitable to represent the input.
For example, the following language:
<pre><cod... | https://softwareengineering.stackexchange.com |
431,702 | [
"https://physics.stackexchange.com/questions/431702",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/202812/"
] | The voltage across a capacitor as a function of time is given by:
<span class="math-container">$$V=V_ie^{-t/RC}$$</span>
Therefore, increasing the resistance and capacitance increases the time it takes for the initial voltage to drop to e.g. 63% of the original value, which also means that the exponential decay graph ... | I'll answer by analogy to give a clearer picture of what's going on. In a sense, a capacitor is like a storage tank for electrons. This means that a capacitor with a larger capacitance can store more charge than a capacitor with smaller capacitance, for a fixed voltage across the capacitor leads.
The voltage across ... | A larger capacitor has more energy stored in it for a given voltage than a smaller capacitor does. Adding resistance to the circuit decreases the amount of current that flows through it. Both of these effects act to reduce the rate at which the capacitor's stored energy is dissipated, which increases the value of the c... | https://physics.stackexchange.com |
164,259 | [
"https://dba.stackexchange.com/questions/164259",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/112158/"
] | I've inherited myself a fun table with some peculiar indexes (and no primary key) on it, that looks as follows:
<pre><code>CREATE TABLE `my_wonky_table` (
`id` bigint(20) unsigned NOT NULL,
`login` varchar(127) DEFAULT NULL,
`timestamp` int(10) unsigned NOT NULL,
`ip` varchar(32) CHARACTER SET ascii DEFAULT NU... | You can have an auto-Incrementing column, as long as there is an index (key) on it, to fix this issue you need to execute those commands:
<pre><code>ALTER TABLE my_wonky_table ADD COLUMN count SMALLINT NOT NULL;
ALTER TABLE my_wonky_table ADD INDEX (count);
ALTER TABLE my_wonky_table CHANGE count count SMALLINT NOT NU... | It is not the "hidden PK" that is in the way. <code>ALTER TABLE ... ADD PRIMARY KEY(...)</code> will replace it. The problem is that the "partition key", <code>id</code> in your case, must be part of every <code>UNIQUE</code> key, and the PK is <code>UNIQUE</code>.
It is more efficient to do all <code>ALTERs</code> ... | https://dba.stackexchange.com |
116,870 | [
"https://electronics.stackexchange.com/questions/116870",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/24685/"
] | In physics, frequency is simply \$f\$.
I mean,<br>
Frequency: \$f\$ (with unit Hz = s<sup>-1</sup>)<br>
Angular frequency: \$\omega = 2\pi f\$ (with unit rad/s)
However, when I read EE textbooks, they use `frequency' for both of them.
For example, when they say something like RF, they use frequency in Hz ― so \$f\$.... | Generally, frequency is measured in Hz, or 1/second. If a variable named "f" or "F<sub>something</sub>" is used, then its unit is generally understood to be Hz.
Sometimes it is mathematically more convenient to use radians/second instead of full rotations per second. If a variable is named "ω", then its unit i... | Radians per second and Hertz are both units of frequency, much like centimeters and inches are both units of length. If you saw a geometry book using both centimeters and inches, you wouldn't say "my book uses 'length' for both of them". Same applies here. As Olin says, its sloppy (I'd say "wrong") not to say which ... | https://electronics.stackexchange.com |
574,718 | [
"https://physics.stackexchange.com/questions/574718",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/98160/"
] | Laptop upgrade tutorials advise grounding oneself to metal objects ultimately connecting to literal ground (floor, Earth), such as the laptop's metal case, or a metal door, heater, etc. Is this really necessary? Won't simply touching a charge-neutral conductor such as a spoon suffice? Naturally it has a much lesser &qu... | Suppose we have two isolated objects with capacitances <span class="math-container">$C_1$</span> and <span class="math-container">$C_2$</span>. Suppose further that <span class="math-container">$C_1$</span> is carrying a charge <span class="math-container">$Q_i$</span> (and is therefore at potential <span class="math-... | You need to ensure that both you and every object you touch is discharged to negligible potential.
Even if everything is at the same high potential, charge will gather on the high points and spark across to other components when it touches them.
So you would have to ensure that every spoon was suitably discharged in pr... | https://physics.stackexchange.com |
369,031 | [
"https://physics.stackexchange.com/questions/369031",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/68549/"
] | This problem is from <strong>Introduction to Classical Mechanics With Problems and Solutions by David Morin</strong>. The <em>solution</em> is also given in the book for this particular problem.
<blockquote>
Problem #6.6.1
A particle moves in a potential <span class="math-container">$V(r) = -V_0 \exp(-\lambda^2 x^2)$</... | Since $\frac{\partial x^\rho}{\partial y^\lambda}\frac{\partial y^\lambda}{\partial x^\nu} = \delta^\rho_\nu$, we obtain
\begin{align*}
0 &= \partial_\mu \left(\frac{\partial x^\rho}{\partial y^\lambda}\frac{\partial y^\lambda}{\partial x^\nu} \right)\\
&= \frac{\partial^2 y^\lambda}{\partial x^\mu \partial x^\... | We start from the identity:
<span class="math-container">$$\frac{\partial \mathbf{V}}{\partial Z^S} = \nabla_S V^i \mathbf{Z}_i$$</span>
where <span class="math-container">$\nabla_S V^i$</span> is the covariant derivative whose components are: <span class="math-container">$\nabla_S V^i = \frac{\partial V^i}{\partial Z^... | https://physics.stackexchange.com |
187,149 | [
"https://mathoverflow.net/questions/187149",
"https://mathoverflow.net",
"https://mathoverflow.net/users/17308/"
] | In Prop. 4.1, p. 87 of the article "Ample vector bundles on curves" (Nagoya Math. J. 43 [1971], 73--89), R. Hartshorne states the following:
<em>Let $A$ be an abelian variety [over an alg. closed field $k$, say - my assumption]. Let $X$ be a non-singular subvariety of $A$.
Assume that every curve in $X$ generates $A$... | The assertion (X) is false in any characteristic $p > 0$ for any $Y$ with genus at least 2. (It is true and easy for $Y$ of genus 1, and true and easy and uninteresting for $Y$ of genus 0.)
To see this, we may and do choose a subgroup scheme $G \subset J := {\rm{Jac}}(Y)$ of the nonzero infinitesimal Frobenius k... | Yes, this is classic. A counterexample was found by Serre, and more classes of counterexamples are in Fulton's paper Ample Vector Bundles, Chern Classes,
and Numerical Criteria (Inventiones, 1976).
| https://mathoverflow.net |
161,344 | [
"https://dba.stackexchange.com/questions/161344",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/6815/"
] | I'm trying to build a query to aggregate together multiple columns in a legacy table stored in a similar structure as below:
<pre><code>CREATE TEMPORARY TABLE foo AS
SELECT * FROM ( VALUES
(1,'Router','Networking','Sale',NULL),
(2,NULL,'Router','Networking','Sale'),
(3,NULL,NULL,'Networking','Sale'),
(4,NULL,N... | I would suggest not using a JSON array, and instead using the native SQL array syntax which is likely much faster and more efficiently stored. It's also stronger typed. The JSON array is <em>"possibly-heterogeneously-typed"</em> per the docs.
I also wouldn't do this routinely. I would alter the table's schema to have ... | This should work:
<pre><code>SELECT
id,
( SELECT json_agg(tag ORDER BY no)
FROM
( SELECT 1, tag_1 UNION ALL
SELECT 2, tag_2 UNION ALL
SELECT 3, tag_3 UNION ALL
SELECT 4, tag_4
) AS x (no, tag)
WHERE tag IS NOT NULL
) AS tags
FROM t ;
</code... | https://dba.stackexchange.com |
153,915 | [
"https://math.stackexchange.com/questions/153915",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/22516/"
] | Let $A$ and $B$ be two subsets of $\Bbb R$ of measure zero. Is it true that the Minkowski sum $A+B = \{ a + b \mid a \in A, b \in B \}$ has measure zero as well? I think so but I can't prove it. The usual trick with the convolution $\mathbf 1_A \star \mathbf 1_B$ does not seem to lead to something interesting.
| Assuming I understand Minkowski sum correctly, this is not the case. For example, if $A$ is the Cantor ternary set and $B$ the set of opposites of the Cantor ternary set, then $A+B=[-1,1]$.
| If $A$ is the set of real numbers such that in their proper binary expansion, the even terms are $0$, and $B$ the same with odd numbers, then $A$ and $B$ have measure $0$ but their sum is the whole real line.
| https://math.stackexchange.com |
103,147 | [
"https://security.stackexchange.com/questions/103147",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/6276/"
] | I'm currently thinking about a new password policy. Originally I wanted the users to choose a password that is X digits long, contains numbers, special chars, lower and upper case,... but then I did some auditing in a friends Company. There they had such a policy. I extracted the password hashes from their Active Direc... | Best password policies:
Strong, managed, and kept secure.
<strong>Strong</strong>
<ul>
<li>long(12 or more characters)</li>
<li>full character set required(upper, lower, number, symbol)</li>
<li>no complete words</li>
<li>no personal information if based on a word</li>
</ul>
<strong>managed</strong>
<ul>
<li>kept i... | On the surface it seems more secure - but I would be concerned that you might run into issues of people writing the random password down on a post-it and slapping it on the wall next to their computer. You can suggest people use a password manager, but at the end of the day 90% of them will just do what they want.
It... | https://security.stackexchange.com |
542,363 | [
"https://electronics.stackexchange.com/questions/542363",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/273758/"
] | I've built a small desktop fume extractor for soldering.
It uses a 120mm 1000RPM, 12V, 0.08A case fan. Not huge, but it does the job.
The fan is only drawing roughly 0.04A and I have been fault finding and theory checking all afternoon and I can't figure it out and I feel like such a fool now, I should know this.
The f... | The .08A is most likely just a guide to power consumption, not a spec. The fan is designed to work on 12VDC, and that's what you should give it. The current draw will depend on the load on the fan which usually won't change much. You could try upping the voltage <em>a bit</em> but it's really pot luck how far and at so... | 0.08A is probably the MAX power consumption while the fan is spinning at its rated rpm, Not normal power consumption. Fans are used in casings which decrease the airflow and make fans struggle hence they draw more amps, try covering both sides of fan with something like a cardboard or your hands and you will notice inc... | https://electronics.stackexchange.com |
594,252 | [
"https://physics.stackexchange.com/questions/594252",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/274851/"
] | I'm a high school student.
We were taking Magnetic flux in school and the formula is <span class="math-container">$\Phi=BA\cosθ$</span>.
Please Bear with me. My issue lies in the cosθ. I'm assuming here we treated the area as a vector but how can we treat the area as a vector? and how can the area decrease due to chang... | <blockquote>
I'm assuming here we treated the area as a vector but how can we treat the area as a vector?
</blockquote>
Yes, area is considered as a vector in physics. You will come across another law called Gauss Law which also considers area as vector.
<blockquote>
and how can the area decrease due to change in orien... | I am pretty sure your book explains how the vector associated with the area is defined. The direction of the vector is perpendicular to the surface of the given area. Changing the angle between the area and the magnetic field does not change the magnitude of the area. Same as when you rotate any other vector, you don't... | https://physics.stackexchange.com |
2,762 | [
"https://cs.stackexchange.com/questions/2762",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/1895/"
] | Is there any formal definition about the average height of a binary tree?
I have a tutorial question about finding the average height of a binary tree using the following two methods:
<ol>
<li>The natural solution might be to take the average length of all possible
paths from the root to a leaf, that is
$\qquad \dis... | There is no reason to believe that both definitions describe the same measure. You can write $\operatorname{avh}_1$ recursively, too:
$\qquad \displaystyle \operatorname{avh}_1(N(l,r)) = \frac{\operatorname{lv}(l)(\operatorname{avh_1}(l) + 1) + \operatorname{lv}(r)(\operatorname{avh_1}(r) + 1)}{\operatorname{lv}(l) + ... | <strong>Edit:</strong> Jeffe makes a good point in his comment above. You should probably read "correct vs incorrect" in the following answer as "convenient/consistent vs inconsistent".
It seems to be that your second calculation is incorrect.
Let the height of a subtree with a single node (i.e. a leaf) be 0. Then the... | https://cs.stackexchange.com |
221,880 | [
"https://security.stackexchange.com/questions/221880",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/58761/"
] | Since buffer overflows always let an evil hacker write outside the buffer and overwrite the return pointer to a shellcode the evil hacker can place, does it mean that successful exploitation of a stack buffer overflow always means the ability to invoke a shell if done the right way? At least in theory, if you assume th... | No, a buffer overflow might:
<ul>
<li>Be against a buffer on the heap not the stack. This might still lead to code execution but will be much more complicated to exploit.</li>
<li>Be limited in size, so not able to overwrite return pointers. (e.g. be able to only write 1 byte beyond the buffer)</li>
<li>Be restricted ... | Douglas gives a correct answer. Not all buffer overflows give code execution. However, I felt it was missing a very important caution.
Even if a buffer overflow does not allow arbitrary code execution, that does not mean that it is safe.
A write buffer overflow lets you write to data that you are not supposed to. Th... | https://security.stackexchange.com |
42,104 | [
"https://biology.stackexchange.com/questions/42104",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/15379/"
] | Is there any evidence of animals wanting to die? Specifically, animal communication which says "come and eat me".
| Trees fruit before the monsoon season to maximize seed germination and seedling recruitment. previous studies have shown that in many species, fruiting occurs just before the wet season such that seeds germinate and establish during the wet season when conditions are most favourable.
Smythe N. 1970 Relationships betwe... | <ol start="3">
<li>Evolutionarily, these tropical fruit trees would want to maximize the amount of offspring that are produced and that survive to reproduce. This would increase their fitness and ensure that their genes are passed on to the next generation. </li>
</ol>
Tropical fruit trees would "want" (they're not ac... | https://biology.stackexchange.com |
64,926 | [
"https://softwareengineering.stackexchange.com/questions/64926",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/3755/"
] | Say you are designing a Square root method sqrt. Do you prefer to validate the parameter passed is not a negative number or do you leave it up to the caller to make sure the param passed is valid. How does your answer vary if the method/API is for 3rd party consumption or if it is only going to be used for the particul... | In general, I design my APIs as follows:<br>
1. Document the methods well, and encourage the callers to pass good/valid data.<br>
2. Validate the parameters anyway! - throwing exceptions when the preconditions are not met.
I would say that parameter validation is necessary on most public-facing APIs.
Parameter vali... | If you always validate parameters then you are doing extra work that may not be needed.
Think of the situation where the input has already been validated before the call and now you are re-validating the data in the call. OK one extra validation check is OK but now extend that logic to all functions in your applicatio... | https://softwareengineering.stackexchange.com |
10,939 | [
"https://electronics.stackexchange.com/questions/10939",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/1240/"
] | After reading some answers on SuperUser, I started thinking: Can EE/E/PROM be damaged by only reading it, with no writing at all?
I've read several datasheets for EEPROMS and products that contain them and all I've ever seen were write and erase cycles. I do know that just reading few datasheets does not make me an e... | No, they can't be damaged only by reading.
But keep in mind that a simple read by a "complex" operating system could be followed automatically by one or more write (an example of this behaviour is the change of file last access time)
| Data will slowly degrade over time (we're talking many years) due to bit rot if the contents of the flash are not periodically rewritten. The memory cells cannot hold their charge indefinitely due to infinitesimally small leakages. Given enough time, bits will decay.
Reading doesn't cause this issue, or fix this issue... | https://electronics.stackexchange.com |
307,060 | [
"https://softwareengineering.stackexchange.com/questions/307060",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/186568/"
] | I have a question about storing encrypted passwords in your database to help secure them. I have a class that encrypts the password passed in and returns a string. This string has 3 parts too it, all separated by a colon. The first part is the iteration, the 2nd part of it is the salt, and the third part of it is the e... | What you do is how most are doing it, and it is perfectly fine.
The thing people say about not doing your own security is that you should not invent your own way of hashing the password. Always use a state of the art password hashing algorithm.
So store the hashed password including the individual salt and the number... | While developing an application I was using an Encryption Library that had the same format <code>{iterations}:{salt}:{PasswordHash}</code>. It had 2 main methods <code>public string GetPasswordHash (string PlainTextPassword)</code> and <code>public bool VerifyPassword(string formatedPaswordHash, string PlainTextPasswo... | https://softwareengineering.stackexchange.com |
18,304 | [
"https://quant.stackexchange.com/questions/18304",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/11678/"
] | For counterparty credit risk, in particular, for potential future exposure computation, people use the real-world probability measure to evolve the underlying risk factors. My question is that whether there is only a single real-world probability measure for the whole market, or an individual one for each individual ma... | There is only one real world! You would use the measure that best describes all the markets together. Bear in mind that for credit you are really interested in portfolio effects. What is the potential credit risk we could have to a particular name? This depends on all the contracts we have them regardless of currency a... | The quanto adjustment is required to achieve the martingale property for the discounted payoff after currency transformation. Since you do not require discounted asset values to be martingales for risk measurement you do not need a quanto adjustment. But of course you need to include the distribution of future FX-rates... | https://quant.stackexchange.com |
2,342,779 | [
"https://math.stackexchange.com/questions/2342779",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/243059/"
] | Is there a mathematical symbol for 'implies and is not implied by'?
ie.
$$\Rightarrow \land \nLeftarrow$$
Context:
To provide extra emphasis in proofs with lines such as
$$x = 1 \,\,\,\,\,(\Rightarrow \land \nLeftarrow)\,\,\,\,\, x^2 = 1$$
| flawr has created one way to say what you're trying to say, but it isn't any better than your suggestion, in that neither will be readily understood unless you pre-define what the notation means.
To be understood clearly, simply write $$(A \to B) \land \lnot (B\to A)\tag{Use for greatest clarity (1)}$$
No need to cr... | I don't think there is an own symbol, but to express $A \implies B$ and $B \,\,\,\,\,\,\not\!\!\!\!\!\implies A$ I've seen
$\renewcommand{\arraystretch}{0.1}$
$$A \begin{array}{c} \Rightarrow \\ \nLeftarrow \end{array} B$$
| https://math.stackexchange.com |
1,291,113 | [
"https://math.stackexchange.com/questions/1291113",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/175920/"
] | Let $$\sum_{n=2}^\infty \frac{1}{n\ln n!}.$$ It is equal to
$$\sum_{n=2}^\infty \frac{1}{n(\ln n + \ln(n-1) +...+ ln(2))}.$$ But now what should I do to prove that it converges? (I have tried root test and ratio test.)
| Observe that : $n! = 2\times 3 \times \cdots \times n \ge 2^{n-1}$ for all $n\ge 2$. Consequently, we have for all $n\ge 2$
$$ 0 \le \frac{1}{n\ln(n!)}\le \frac{1}{n(n-1)\ln 2}. $$
Finally, you can conclude by comparison.
| We may also use the fact that $\log x$ is a concave function on $\mathbb{R}^+$, hence:
$$ \log(n!)=\sum_{k=1}^{n}\log(k)\geq n\cdot\log\left(\frac{1}{n}\sum_{k=1}^{n}k\right) = n\cdot\log\left(\frac{n+1}{2}\right)\tag{1}$$
and:
$$0\leq \sum_{n\geq 2}\frac{1}{n\log(n!)}\leq \frac{\zeta(2)}{\log(3/2)}.\tag{2}$$
| https://math.stackexchange.com |
1,496,353 | [
"https://math.stackexchange.com/questions/1496353",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/283639/"
] | I know that an antisymmetric relation must meet the following condition: <code>If x <=y and y<=x then x=y</code>. That being said, can one consider <code>x=x</code> to be antisymmetric?
P.S.: Something tells me that the answer is right under my eyes, but I just cannot seem to wrap my head around it.
| A relation $R$ is antisymmetric if the following statement is true for all $x$ and $y$:
<blockquote>
If $xRy$ and $yRx$, then $x=y$.
</blockquote>
To test whether this is true when $R$ is $=$, you just plug in $=$ for $R$. So the question is, is the following true for all $x$ and $y$?
<blockquote>
If $x=y$ and... | Yes, yes it is.
The definition is as you put it.
Or in other words, an antisymmetic relation is one where there is no distinct pair a, b ( a$\ne$ b) where aRb and bRa. As there are no distinct pair a $\ne$ b where a = b and b = a, equality is by definition antisymmetric.
| https://math.stackexchange.com |
197,840 | [
"https://physics.stackexchange.com/questions/197840",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/87543/"
] | I read on the net that it is a general consensus that entropy in a system decreases as pressure increases and vice versa.
<ol>
<li>How can one reach such conclusion using the characteristic equation in terms of entropy?
$$dS=(1/T)dU+(p/T)dV-(μ_B/T)dn_b$$
and lets assume there is no change in molecular mass, so we use... | From a Maxwell relation we known that:
$$\left(\frac{\partial S}{\partial p}\right)_{T}=-\left(\frac{\partial V}{\partial T}\right)_{p}$$
For gases and most liquids, $\left(\frac{\partial V}{\partial T}\right)_{p}>0$, so indeed the entropy decreases as pressure increases.
<strong>Derivation:</strong> Starting with ... | You are right: further specifications i.e. constraints have to be provided in order to provide such affirmation.
Your expression of entropy as a thermodynamical potential in terms of internal energy, volume and particle number, does not provide a unique relation between two thermodynamic variables. Instead it provide... | https://physics.stackexchange.com |
449,270 | [
"https://electronics.stackexchange.com/questions/449270",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/81897/"
] | When a supercomputer is given work and all processors begin work there would be a large spike in demand. Do large supercomputers communicate with power stations to notify them of demand changes from changing workloads?
| <blockquote>
Do large supercomputers communicate with power stations to notify them
of demand changes?
</blockquote>
No. Within most countries power stations are linked together to share loading. In addition there are stations and generators on standby ready to go online as demands require. Adjustable phase shift ... | They don't need to communicate with the energy provider.
Only few companies need to do this like some aluminum producers or steel companies and other heavy duty companies. But then we're talking about 100s of GWh to few TWh power consumption per year. A super computer needs 30MW, that is not that much for the power gri... | https://electronics.stackexchange.com |
44,060 | [
"https://mathoverflow.net/questions/44060",
"https://mathoverflow.net",
"https://mathoverflow.net/users/-1/"
] | Let $(G,\cdot,T)$ and $(H,\star,S)$ be topological groups such that
<br>
$(G,T)$ is homeomorphic to $(H,S)$ and $(G,\cdot)$ is isomorphic to $(H,\star)$.
Does it follow that $(G,\cdot,T)$ and $(H,\star,S)$ are isomorphic as topological groups?
<br>
If no, what if they are both Hausdorff? What if they are both Hausdor... | The 2-adic rationals $\mathbb{Q}_2$ and the 3-adic rationals $\mathbb{Q}_3$ are homeomorphic, because each one is a countable disjoint union of Cantor sets. They are also isomorphic as groups if you assume the axiom of choice, because they are both fields of characteristic 0 and therefore vector spaces over $\mathbb{Q... | Sorry for the necromancy, but the following was too cute to resist:
Let
$A$ be $Z_4$ with the discrete topology
$B$ be $Z_4$ with the indiscrete topology
$C$ be $Z_2 \times Z_2$ with the discrete topology
$D$ be $Z_2 \times Z_2$ with the indiscrete topology.
Then $A \times D$ is not isomorphic to $B \times C$ as... | https://mathoverflow.net |
30,594 | [
"https://electronics.stackexchange.com/questions/30594",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/9419/"
] | this is more of a theoretical question, and I do not know if this is suited for this QA site at all, but at school I was asked to provide 3 examples of sensors (in the narrow sense) that are also actuators.
I cannot find any information for the life of me. The only example I can find are piezoelectric sensors, but I a... | Examples:
<ul>
<li>(As you said) a piezoelectric transducer. It can produce sounds, or work as a microphone.</li>
<li>An electromechanical speaker. The same device can act as a speaker, or as a microphone (old walkie-talkie toys use that fact).</li>
<li>Even an LED. If you apply forward current through an LED, it prod... | To add some other cases:
<ul>
<li>To some extent, a resistor is also a temperature sensor/actuator</li>
<li>Peltier cells are also temperature/electricity converters</li>
<li>Inductors convert magnetic field into electric current and vice versa</li>
<li>Batteries are also a sort of chemical/electrical transducer, and ... | https://electronics.stackexchange.com |
370,263 | [
"https://softwareengineering.stackexchange.com/questions/370263",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/304593/"
] | I've created a class called <code>Test</code> that has a constructor and one instance variable <code>String name</code>:
<pre><code>class Test {
String name;
Test(String name){
this.name = name;
}
}
</code></pre>
I instantiate it like this:
<pre><code> Test first = new Test("First");
Te... | Change your code to:
<pre><code>Test first = new Test("First");
Test second = first;
first = new Test("First");
first.name = "Change First";
System.out.println("First: " + first.name);
System.out.println("Second: " + second.name);
</code></pre>
And you'll get:
<pre><code>First: Change First
Second: First
</code></p... | <blockquote>
I'm assigning the second Object to the same memory location referenced in the first
</blockquote>
There is no "second object." <code>first</code> and <code>second</code> are not objects. They are object <em>references</em>. Your program created an object when it called <code>new Test("First")</code>,... | https://softwareengineering.stackexchange.com |
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