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
values |
|---|---|---|---|---|---|
124,848 | [
"https://mathoverflow.net/questions/124848",
"https://mathoverflow.net",
"https://mathoverflow.net/users/32296/"
] | Suppose $M$ is a complex manifold and $\Omega$ a (edit: bounded) pseudoconvex domain in $M$. Let $u:M\setminus\Omega\to\mathbb{R}$ be a pluriharmonic function. Is it true that $u$ has a pluriharmonic extension to $M$? edit: $dim_{\mathbb{C}}(M)\geq 2$.
| Your condition $\dim M>2$ does not save the situation: you can have many counterexamples
with $M=M'\times C^n$ where $\dim M'=1$ and your functions are independent of the second
variable. And in dimension $1$ you certainly have plenty of pluriharmonic (=harmonic) functions which do not extend anywhere.
| In contrast, for plurisubharmonic functions and their subextensions the situation is more difficult:
In: Fornæss, John Erik; Sibony, Nessim: Plurisubharmonic functions on ring domains. Complex analysis (University Park, Pa., 1986), 111–120, Lecture Notes in Math., 1268, Springer, Berlin, 1987 (MR0907057),
the authors ... | https://mathoverflow.net |
82,821 | [
"https://physics.stackexchange.com/questions/82821",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/31842/"
] | Current in wire + moving charge next to wire creates magnetic force in the stationary reference frame OR electric force in the moving reference frame from special relativity due to change in charge density etc.... I think I understand this and I think it's super cool. Now here's the rub...
Current in wire + <strong>st... | Suppose you start with a linear charge density $\lambda^+$ of positive charges and $-\lambda^-$ of negative charges in the wire, everything at rest.
<strong>Case 1: No current, test charge stationary</strong>
You assume you have a <em>neutral</em> wire with no current. Therefore $\lambda^- = \lambda^+$. There's no ot... | Short answer: this type of exposition, and the video in particular, gloss over some of the details that complicate the situation.
I checked with Section 12.2 of Jackson ("On the Question of Obtaining the Magnetic Field, Magnetic Force, and the Maxwell Equations from Coulomb's Law and Special Relativity"). I think t... | https://physics.stackexchange.com |
150,308 | [
"https://security.stackexchange.com/questions/150308",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/138272/"
] | My phone is able to give me an exact position of my whereabous, using Google Maps I am able to pinpoint my exact location. However, what can the phone telecom company see?
I've read many different forensics cases in my country, and none are able to see the location, only which CellID was used to make the connection. W... | The phone provider isn't specifically collecting location information, usually. They're collecting usage data about their phone masts, so they can upgrade bandwidth to heavily used ones, plan maintenance out of peak usage hours, and other technical reasons. This includes details about devices which are connecting to a ... | To expand on Matthew's answer:
<blockquote>
Why is the operator collecting [Cell ID] information?
</blockquote>
The cell phone provider needs to know where your phone is so it can route phone calls or internet packets back to your phone. So it must know which cell towers your phone is closest to. But it wouldn't re... | https://security.stackexchange.com |
1,771,348 | [
"https://math.stackexchange.com/questions/1771348",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/336939/"
] | <blockquote>
Let $0<x<y$, such that
$$x^y=y^x$$
show that
$$x+y>2e$$
</blockquote>
Since $$y\ln{x}=x\ln{y}\Longrightarrow \dfrac{\ln{y}}{y}=\dfrac{\ln{x}}{x}$$
Let
$$f(x)=\dfrac{\ln{x}}{x}\Longrightarrow f'(x)=\dfrac{1-\ln{x}}{x^2}$$
If $0<x<e$ then $f'(x)>0$, if $x>e$,then $f'(x)<0$
... | <br>We can see that <span class="math-container">$$f(x)=\frac{\ln x}{x}$$</span> is strictly increasing in <span class="math-container">$(0,e)$</span> and striclty decreasing in <span class="math-container">$(e,+\infty)$</span>.
<br><br>Thus the equality <span class="math-container">$f(x)=f(y)$</span> cannot hold for t... | As MathematicianByMistake answer,we want prove
$$g(r)=r^{\frac{1}{r-1}}+r^{\frac{r}{r-1}}=(x+1)^{\frac{1}{x}}+(x+1)^{\frac{x+1}{x}}=(x+1)^{\frac{1}{x}}(x+2),x>0$$
since
$$g'(x)=(x+1)^{\frac{1}{x}-1}\cdot\dfrac{x(x^2+2x+2)-(x^2+3x+2)\ln{(x+1)}}{x^2}$$
we only prove
$$h(x)=x(x^2+2x+2)-(x^2+3x+2)\ln{(x+1)}>0,x>0... | https://math.stackexchange.com |
521,952 | [
"https://physics.stackexchange.com/questions/521952",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/250479/"
] | I am working through <em>Nonlinear Dynamics and Chaos</em> by Steven H Strogatz. In chapter 3.5 (overdampened beads on a rotating hoop), a differential equation is converted into a dimensionless form. I am trying to work out which dimensions the initial equations had, and why the converted form is dimensionless.
Initi... | Because you take the derivative with respect to <span class="math-container">$\tau$</span>. Since <span class="math-container">$\tau$</span> is dimensionless, the derivative is too.
| You substitute <span class="math-container">$\dot{\phi} = \frac{1}{T} \frac{d\phi}{d\tau}$</span>. Now let's consider the dimensions
<span class="math-container">\begin{align}
[\dot{\phi}] &= [\frac{d\phi}{dt}] = \frac{rad}{s}\\
[\dot{\phi}] &= [\frac{1}{T} \frac{d\phi}{d\tau}] = \frac{1}{s} \cdot [\frac{d\p... | https://physics.stackexchange.com |
19,362 | [
"https://electronics.stackexchange.com/questions/19362",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/1024/"
] | I am trying to get the ECAN functionality working on a dsPIC33. I have two identical dsPIC33s, each with identical CAN transceivers connected by a short (3 inch) bus. One is transmitting, one is receiving. However, I see no messages, I just see a repeating waveform with a period of 34.5us. Does this suggest a particula... | Turns out the answer should have been obvious from the waveforms above.
When TX goes low, so does RX. But when TX goes high, RX takes more than 1us to rise again. That's more than a whole bit time! CAN cannot work under these conditions.
The reason RX lags behind TX would have been obvious with a proper oscilloscope, r... | There is nothing magic about the terminating resistors. They are absolutely required for a CAN bus. They may be called "terminating" resistors, and this is indeed part of their function when the bus is long enough to be a transmission line. However, they also cause a unloaded bus to go to the recessive state, which ... | https://electronics.stackexchange.com |
114,552 | [
"https://chemistry.stackexchange.com/questions/114552",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/60319/"
] | From what I understand about the Michaelis Menten Model
<ul>
<li>Km defines the amount of substrate required to reach half-saturation. </li>
<li>1/2 Vmax corresponds to Km on the x axis</li>
<li>Generic formula is v = Kcat [ES] [S] / (Km + [S])</li>
</ul>
<strong>Given Km and the desired velocity in terms of reactio... | What you do is write <span class="math-container">$[D]=[C]K_{CD}$</span>, <span class="math-container">$[C]=[B]K_{BC}$</span>, and <span class="math-container">$[B]=[A]K_{AB}$</span>. So, <span class="math-container">$$[C]=K_{BC}K_{AB}[A]$$</span> and <span class="math-container">$$[D]=K_{CD}K_{BC}K_{AB}[A]$$</span>So,... | One thing the exercise is lacking is the physical state of A, B, C, and D. If they are all gases or all liquids, you can calculate as shown in question and in answers. Otherwise, you would need more information to complete the exercise.
For some insight regarding part b) of the exercise, you could rewrite your equatio... | https://chemistry.stackexchange.com |
138,357 | [
"https://cs.stackexchange.com/questions/138357",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/134715/"
] | Given a regular language <span class="math-container">$L$</span> defined over <span class="math-container">$\Sigma = \{0, 1\}$</span>. We define a new language <span class="math-container">$$Perm(L) = \{w \mid \exists x \in L, w \in perm(x)\}, $$</span> where <span class="math-container">$perm(x)$</span> is the set of ... | For every symbol <span class="math-container">$\sigma_i$</span> that the PDA reads, it guesses a symbol <span class="math-container">$\tau_i$</span>. It simulates the DFA on the word <span class="math-container">$\tau_1 \ldots \tau_i$</span>, and will only accept if the DFA accepts. Using the stack, it maintains the fo... | Clearly we cannot keep both the number of <span class="math-container">$a$</span>'s and the number of <span class="math-container">$b$</span>'s on the stack, because what order should we use. The solution (I think) is to keep the difference of these numbers on the stack. Or better, the difference between the promised n... | https://cs.stackexchange.com |
249,060 | [
"https://dba.stackexchange.com/questions/249060",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/57417/"
] | Considering a simple table with id-datetime field. I want to remove all records, where datetime is smaller than some constant, but keep ids which have at least one record with bigger date.
My first effort was
<pre class="lang-sql prettyprint-override"><code>DELETE FROM journal
WHERE id IN (
SELECT
j.id
FR... | Please try this:
<pre class="lang-sql prettyprint-override"><code>DELETE FROM journal
WHERE id NOT IN (
SELECT
j.id
FROM
journal j
WHERE j.created_at >= 636742944000000000
ORDER BY j.created_at DESC
)
</code></pre>
Please make sure to create the index on <code>created_at</code> and <code>id... | I think you already are doing it the best way.
<pre><code>DELETE FROM journal
WHERE id NOT in
(SELECT id
FROM journal
GROUP BY (id)
HAVING MAX(created_at) >= 636742944000000000);
</code></pre>
| https://dba.stackexchange.com |
580,004 | [
"https://physics.stackexchange.com/questions/580004",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/274821/"
] | An electric charge experiences a force in a magnetic field only when the charge has some velocity and is moving. But velocity is always relative to a given frame of reference. It never exists on its own. If the source of the magnetic field moves, thus moving the magnetic field, and the charge is stationary wrt the eart... | I'd recommend you read Book III of the Principia by Newton. There he sets out a careful proof based on some methodological rules and observations about planetary and satellite orbit. You might also read Feynman's chapter 7 from book 1 of the Lectures on Physics. He gives a bit more of an intuitive characterization of w... | The system of the Newton laws of movement and the law of gravity forms a whole.
The second law, <span class="math-container">$F = ma$</span> can be experimentally shown, if <span class="math-container">$F$</span> is measured by the deflection of a spring. Objects with several masses can be pushed horizontally at severa... | https://physics.stackexchange.com |
252,831 | [
"https://mathoverflow.net/questions/252831",
"https://mathoverflow.net",
"https://mathoverflow.net/users/50426/"
] | Let $f : \mathbb{R} \to \mathbb{R}$ such that the $k^{\rm th}$ derivative of $f$ is strictly positive for every $x \in \mathbb{R}$. Define the forward difference operator to be:
$$\Delta(g,h) = g(x+h) - g(x),$$
and for $h_1, \ldots , h_k > 0$,
$$\Delta(g, h_1, \ldots , h_k) = \Delta( \Delta(g , h_1 , \ldots , h_... | Yes, this is true. For the function $\Delta(f,h)$ its $(k-1)$-st derivative is strictly positive, since by Lagrange theorem it equals $$f^{(k-1)}(x+h)-f^{(k-1)}(x)=hf^{(k)}(x+\theta h)>0,$$ for some $\theta\in (0,1)$. Then induct on $k$.
| No, this is not true. For instance, for function $(10(1-e^{-1/x^2})-9)+\exp(x)$ and $f(0)=2$ all the consecutive derivatives are positive at $x=0$, while the first difference is not.
For function
$f(x)=10 (1 - \exp(-1/(x + 0.1)^2)) - 9) + \exp(x)$
first 13 derivatives at zero are positive, while the first differenc... | https://mathoverflow.net |
246,069 | [
"https://stats.stackexchange.com/questions/246069",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/138575/"
] | Until now, I treated the maximal likelihood method to fit a logistic regression model always as a black box. But recently, in the paper "Categorization Based on Regularized Linear Classification methods" by T. Zhang, F.J. Oles, on on pp 10, they describe a setting that is not known to me.
Namely, they begin by conside... | In general, $P(A|B)$ is read as "probability of $A$ given $B$" or in other words, the probability of event $A$ under the assumption of $B$. If there are multiple events that we assume are given, we can simply write $P(A|B,C)$, which mean that we now assume $B$ and $C$.
From the paper:
<blockquote>
In logistic regr... | For illustration, suppose that there are n elements($x_1$ to $x_i$) determining whether or not a man gets cancer($y=0$ or $y=1$). We have some data collected before as examples. For instance $X_j$ when $x_1 = 1, x_2 = 4.1$, .. y = 1 and $X_{j+1}$ when $x_1 = 0, x_2 = 1.2$, .. and etc then $y = 0$.
We modify the li... | https://stats.stackexchange.com |
2,553,196 | [
"https://math.stackexchange.com/questions/2553196",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/442650/"
] | I've been trying to solve the following problem:
(a) Give two proofs of the binomial coefficient identity, called the convolution formula, $\sum_{j = 0}^k \binom{m}{j}\binom{n}{k - j} = \binom{m + n}{k}$.
(b) Discover and prove an analogous identity for multiset coefficients $\bigg(\binom{n}{k}\bigg)$
Part (a) is n... | Notice that the same formula is valid for the case of multiset coefficients. Thus,
$\sum_{j = 0}^k \left(\!\left({m\atop j}\right)\!\right)\left(\!\left({n\atop k - j}\right)\!\right) = \left(\!\left({m + n\atop k}\right)\!\right)$.
As you did for the case with binomial coefficients, let's assume that we have $m$ men... | Here is another proof based on generating functions. Note that
$$
\frac{1}{(1-x)^n}=(1+x+x^2+\dotsb)^n=
\sum_{x_1+x_2+\dotsb+x_n=k; \,x_i\geq0}x^{x_1+x_2+\dotsb+x_n}
=\sum_{k=0}^\infty\left(\!\!{n\choose k}\!\!\right)x^k.
$$
Then
$$
\sum_{k=0}^\infty\left(\!\!{m+n\choose k}\!\!\right)x^k=\frac{1}{(1-x)^{m+n}}=\frac{1}{... | https://math.stackexchange.com |
230,807 | [
"https://dba.stackexchange.com/questions/230807",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/173452/"
] | I'm using MariaDB 10.3.12 on Arch Linux and haven't modified any of the default settings under <code>/etc/mysql</code>. The following script takes 0.75 s to run on average using the default InnoDB engine:
<pre class="lang-sql prettyprint-override"><code>drop database if exists test_database;
create database test_datab... | <strong>TLDR;</strong> The problem turned out to be the file system. Don't use BTRFS for database storage.
<hr>
I did an analysis of MariaDB timings for different file systems using some of the data that I have to work with. Even though this is specific to my situation I thought I'd post the results anyway in case th... | Have <code>innodb_file_per_table=OFF</code> when doing this task. This will cut back on the I/O needed.
Also consider upgrading to MySQL 8.0, which has rewritten the Data Dictionary stuff.
Inserting rows is much faster if done in batches.
| https://dba.stackexchange.com |
3,508,011 | [
"https://math.stackexchange.com/questions/3508011",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/555347/"
] | Let <span class="math-container">$f$</span> be a continuous function on the interval <span class="math-container">$[a,b]$</span> such as for all x in <span class="math-container">$(a,b)$</span> :<br>
The right hand derivative equals <span class="math-container">$0$</span>.<br>
Is <span class="math-container">$f$</span>... | Yes, <span class="math-container">$f$</span> is necessarily constant.
One can proceed similarly as in the proofs of the mean value theorem and Rolle's theorem for differentiable functions.
It suffices to show that <span class="math-container">$f(c) = f(d)$</span> for <span class="math-container">$a < c < d <... | Given <span class="math-container">$\epsilon>0$</span>, we find for each <span class="math-container">$x\in[a,b)$</span>, the set
<span class="math-container">$$ A_x:=\{\,\xi\in[a,b]\mid \xi>x,\left|\tfrac{f(\xi)-f(x)}{\xi-x}\right|\le \epsilon \,\}$$</span>
contains some open interval <span class="math-container... | https://math.stackexchange.com |
1,113,709 | [
"https://math.stackexchange.com/questions/1113709",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/209524/"
] | A quick google returns the answer on the parity of zero:
Zero is an even number. In other words, its parity—the quality of an integer being even or odd—is even. The simplest way to prove that zero is even is to check that it fits the definition of "even": it is an integer multiple of 2, specifically 0 × 2.
So I know ... | Zero is even, as you argue. There's no circumstances where zero is taken to be odd, nor can it be taken to be neither odd nor even.
What is true is that $0$ is the only real number that is neither negative nor positive, alternatively the only real number $x$ such that $x = -x$.
| "So I know I've answered my own question but I still wanted to ask whether in some respects zero is the only number that is neither even nor odd?"
There <em>is</em> a respect in which $0$ is neither even nor odd; since $\mathbb{Z}$ is an integral domain, it often makes sense to study the multiplicative structure of $\... | https://math.stackexchange.com |
200,042 | [
"https://softwareengineering.stackexchange.com/questions/200042",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/52041/"
] | I'm have been doing some research into making code more testable and modular, but after reading alot about AMD based JavaScript, it doesn't appear to fit the needs of a static website. Is this assumption correct? Is AMD based development geared more toward highly interactive web applications that simple websites?
| For a truly static website, I'd try to get by with as little javascript as possible (or none -- you can do quite a bit with just HTML and CSS). Remember, some people browse with javascript disabled. You wouldn't want to limit your audience unnecessarily.
| I've never understood the appeal of AMD loaders for the client-side web in general, although they did make some sense for mobile at one point because resource files didn't cache on Android and parsing performance wasn't great.
If you attach script files in 3 categories in the following order,
<ul>
<li>General 3rd par... | https://softwareengineering.stackexchange.com |
144,088 | [
"https://security.stackexchange.com/questions/144088",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/132158/"
] | I'm on a school WiFi network, and it's school policy to record basic PC info(name, IP, etc), along with the student name when they add the computer to the WiFi network. My assumption is that it's to track us. However, what can they really see? (Assume all data is encrypted using SSL)
| This started off as a comment on Snappie's answer, but it's getting a bit long...
<blockquote>
Assume all data is encrypted using SSL
</blockquote>
But not all data is encrypted!
(in addition to IP address, and the amount of data being passed in either direction...)
They can also see the IP names of all the resou... | They may see the names, IP addresses, and possibly MAC addresses of other computers on your home network that you may communicate with, often this will be wireless printers, but may include gaming consoles or smart televisions that you have connected to in the past.
The MAC addresses your computer asks to resolve are ... | https://security.stackexchange.com |
356,528 | [
"https://physics.stackexchange.com/questions/356528",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/130091/"
] | I've read all the questions with similar titles but I couldn't find an answer.
Suppose I'm rotating with my arms extended on a frictionless surface. I have angular momentum and energy:
\begin{equation}
L_0=I_0\ \omega_0
\end{equation}
\begin{equation}
E_0=\frac{1}{2}I_0\ \omega_0^{2}
\end{equation}
Where $I_0$ is m... | You do work on your arms as you pull them in, thus your energy has increased. The correct conserved quantity is angular momentum, as you deduce. The amount of work done on your arms can either be computed directly (force times distance type approach) or by using the solution from angular momentum (final energy minus in... | The idea you sketch out in your edit will simply not work out like you imagine.
A static frictional force alone can't cause a massive object to start moving anywhere; on the contrary static friction is the force you have to overcome to set an object resting on a surface into motion. It's the static frictional force tha... | https://physics.stackexchange.com |
2,317,795 | [
"https://math.stackexchange.com/questions/2317795",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/283716/"
] | How to derive $\lim_{x\to \infty} x^{\sin{\frac{1}{x}}} $?
My first thought is l'Hôpital's rule. So $ x^{\sin{\frac{1}{x}}} =e^{\ln x\sin{\frac{1}{x}} }$. Now to compute $\lim_{x\to \infty}\ln x\sin{\frac{1}{x}} =\lim_{x\to \infty}-\ln \frac1x\sin{\frac{1}{x}} $, let $y=\frac1x,$ we get $\lim_{y\to 0}-\frac{\frac{\si... | You can apply L'Hospital's rule after some steps $$\lim _{ x\to \infty } x^{ \sin { \frac { 1 }{ x } } }=\lim _{ x\to \infty } e^{ \sin { \frac { 1 }{ x } \ln { x } } }=e^{ \lim _{ x\to \infty } \frac { \sin { \frac { 1 }{ x } } }{ \frac { 1 }{ x } } \frac { \ln { x } }{ x } }=e^{ \lim _{ x\to \infty } \fr... | <strong>Hint:</strong>
Observe that
$$\sin\frac1x\log x=\frac{\sin\frac1x}{\frac1x}\cdot\frac{\log x}x\xrightarrow[x\to\infty]{}1\cdot0=0$$
| https://math.stackexchange.com |
112,793 | [
"https://softwareengineering.stackexchange.com/questions/112793",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/37047/"
] | Let's say I am storing start and stop points per user into a database table.
For example... let's say in a chat system, a user only needs to see lines 24-293, and 500-512. (Let's say he logged off for the night, and was not present between lines 294-499).
Saving each start and stop point as a discrete row would lead ... | You're trying to denormalise separate facts into a single record, rather than storing them as individual records.
Don't.
You appear to believe that it will be easier and more efficient to do parsing of pseudo-sets yourself than to store them in the normal way. That is <em>possible</em> but unlikely unless you actuall... | First off, database are good and storing lots of rows. That is something that <strong>is</strong> ideal for a database.
If you <em>know</em> you will never need to do more with the data, and you can guarantee that the string size has a maximum, then it won't hurt, just cause some extra parsing cpu cycles. (But don't... | https://softwareengineering.stackexchange.com |
38,012 | [
"https://quant.stackexchange.com/questions/38012",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/7714/"
] | I have been tasked with writing a 25 page paper on computational complexity. The first 10 pages of this should be background an introduction to the field (which I have largely done already) and the following 15 pages should discuss some specific area or application of computational complexity (such as cryptography).
I... | You want to stay away from this as a student for a project, even if you are a doctoral student. If you want to tackle this a doctoral student, then I would love to completely consume every moment of your time working on this because I do have a problem that I want to reduce to deterministic polynomial time. Trust me,... | Caveat - I am a finance person only recently exposed to theory of computation and complexity so this will be more finance and less CS.
The computational difficulty of option pricing is relatively well understood: If you buy the assumptions of the Black, Scholes, and Merton model, then we have a closed form expression... | https://quant.stackexchange.com |
373,476 | [
"https://physics.stackexchange.com/questions/373476",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/138135/"
] | If a ball of mass $m$ falls from a height $h_1$ from rest and hits the ground after $t_1$ seconds at a velocity of $\sqrt{2gh_1}$, then the force acting on the ball will be $F=ma$ right?
Assuming that is correct, if the ball were to fall from a height $h_2$ where $h_2>h_1$, how would it be possible for the force to... | The accleration in the equation $F=ma$ is <em>not</em> the acceleration due to gravity. It is easier to think about this by turning $F=ma$ into $$F=\frac{\Delta p}{\Delta t}$$Here we see that the acceleration in the equation is in fact the change in momentum of the object as it hits the ground. This can be re-written a... | During impact with the ground, "a" is no longer the acceleration due to gravity. It is the net acceleration that the object is currently experiencing. At the point of impact it now has a massive upward acceleration which is difficult to measure and varies during the course of the impact (which of course is quite a shor... | https://physics.stackexchange.com |
30,225 | [
"https://electronics.stackexchange.com/questions/30225",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/9321/"
] | I have a system where a setpoint temperature can be set. A heater and a cooler is connected to the object. Right now both the heater and the cooler regulate on the temperature separately with separate PID controllers. This ofcourse causes them to "battle", and also I imagine they could be stuck in a position where both... | There are three common solutions to this:<ol>
<li>Set the setpoints a bit apart. Make the heater setpoint a little lower than the cooler setpoint. These need to be far enough apart so that overshoot from one doesn't trigger the other. If you can tolerate the resulting temperature range, this is the easiest thing to... | The output of your PID controller should be a signed value. A positive value means 'heat up' and a negative value means 'cool down'. so your code would be like this:
<pre><code>output = PID_Calculation();
if (output > 0)
{
Set_Heater_Power(output);
Set_Cooler_Power(0);
}
else
{
Set_Heater_Power(0);
... | https://electronics.stackexchange.com |
391,004 | [
"https://softwareengineering.stackexchange.com/questions/391004",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/334822/"
] | I am trying to plan out php class structure for an order processing project. I've used classes before but I'm still not an expert on OOP yet. I've been searching for hours and can't seem to find the answer to this particular scenario, despite it being very common.
One of the main objects will be an <code>Order</code>.... | My advice: <strong>do both</strong>. :)
The API client can decide to use the messages from your API or read each error code and create his own messages. Like:
<pre><code>{
"errorCode": "4005",
"message": "Person already registered"
}
</code></pre>
But if you need to choose one, I would choose the error code ... | Variation on the "do both" theme:
Return error codes from your API and provide an additional API for error code translations. This service could handle localization, and by keeping business specific messages on the server you avoid having to update the client when new messages are defined to handle new rules.
| https://softwareengineering.stackexchange.com |
34,728 | [
"https://quant.stackexchange.com/questions/34728",
"https://quant.stackexchange.com",
"https://quant.stackexchange.com/users/27078/"
] | Two of the conditions for an asset price to have a lognormal distribution are:
<ol>
<li>The volatility of the asset is constant.</li>
<li>The price of the asset changes smoothly with no jumps.</li>
</ol>
In practice, neither of these conditions is satisfied for an exchange rate, but I don't understand why these reaso... | There are plenty of theories but no one is 100% certain.
<strong>Theory 1:</strong>
Options which have strike prices increasingly far away from the spot price are including extreme movements in the market such as black swan events into the price. When an event like this happens there is a sharp change in price of the... | The smile is there exactly because the model is wrong.
The reason it's used though (despite being wrong) is that it provides a convenient space to look at the underlying - the vol*
The (undiscounted) value of an option is given by:
$$ \int_0^\infty \mathrm{PDF}(s) (s-K)^+ \mathrm{d}s $$
where $\mathrm{PDF}(x)$ is t... | https://quant.stackexchange.com |
15,304 | [
"https://mechanics.stackexchange.com/questions/15304",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/6820/"
] | I am experiencing delayed forward movement at take off. I apply the accelerator nothing happens until it jolts forward. When I stop it lunges forward, which leads me to believe it is the motor mounts. However, I was told they were still good. I have recently changed my transmission mount to no improvement.
I have a 19... | Sounds like you need to look at the rear bushing of the front wheel control arms. These are made of rubber on most cars and don't last beyond 100k. The thunk you feel is because a normal bushing has firm hold of the connection with the control arm, where as your control arm is probably loosely held in place by worn rub... | This would not be a motor mount issue. What you are describing seems to be an issue with the transmission. IIRC, the C230 is a rear wheel drive vehicle. Only a front wheel drive vehicle would produce anything like what you are talking about with bad motor mounts, but then it will be far less noticeable. A motor mount p... | https://mechanics.stackexchange.com |
73,450 | [
"https://security.stackexchange.com/questions/73450",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/61259/"
] | My goal is to associate (authenticate) <em>hardware devices</em> to users in the database. The access token is generated via webinterface. It is then entered into the hardware device by the user, and the device uses it to authenticate to the webserver. The token is 20 digits random hexadecimal characters and can be rev... | Without an userID attacking your system can be done a million times faster than with userID. That seems like reason enough to me.
With an userID an attacker can only attack one token at a time. Without userID he can with one try attack all 1 million at once.
| The "userID" you intend to introduce sounds like a second-factor authentication.
So in order to access your system, an adversary needs to possess the device and also needs to know the user ID associated with the device.
It adds a second layer of security, provided that the user ID is not printed on the device itself.... | https://security.stackexchange.com |
232,800 | [
"https://physics.stackexchange.com/questions/232800",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/37023/"
] | Please consider the following:
<blockquote>
A tennis ball connected to a string is spun around in a vertical, circular path at a uniform speed. The ball has a mass m = 0.165 kg and moves at v = 4.76 m/s. The circular path has a radius of R = 0.95 m.
What is the magnitude of the tension in the string when the ball is at... | Your error is putting $g = -9.8$ in your evaluation of $m\frac {v^2}{ r}+mg$ because you already have indicated the direction of the gravitational force with a negative sign in
$ \vec{F_{net}} = \vec{F_T} - \vec{F_{grav}} $
Put another way
$ \vec{F_{net}} = \vec{F_T} + \vec{F_{grav}} = \vec {F_T}+ m (-\vec g)$
| If you have
$$ \vec{F_{net}} = \vec{F_T} - \vec{F_{grav}} $$
and net force is zero in that instant, then
$$ mg = \frac{mv^2}{r} $$
so
$$ g = \frac{v^2}{r} = \vec{a_c} $$
You should be able to see here that changing the sign of $g$ will only change the sign of the centripetal acceleration $a_c$. I'm not sure how y... | https://physics.stackexchange.com |
68,599 | [
"https://physics.stackexchange.com/questions/68599",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/12436/"
] | Basically, I understand the difference between a "Theory" and a "Theorem" but I am quite confused when it comes to "Law", "Rule" and "Principle". Can you make the differences clear to me?
| A theory is a collection of concepts, laws, and equations in science that is meant to explain some particular subset of observations. It's also used for theories describing gedanken worlds that differ from ours. There is also a related word "model" that differs by a theory by being really specific while a "theory" may ... | There is no <em>consistent</em> usage of these words among scientists.
Usually, when someone says "law" or "principle", they are referring to a general idea that has been found to apply to many different situations, but not always. More speculative ideas are generally called theories, but use of the word "theory" does... | https://physics.stackexchange.com |
10,896 | [
"https://cs.stackexchange.com/questions/10896",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/6665/"
] | I am reading Computer Architecture & Organization by William Stallings to understand I/O operations. Stallings pretty well explains why Programmed I/O (CPU keeps checking the I/O module register status) & Interrupt I/O (CPU still has to over look data transfer between I/O module & memory) are not efficient ... | The DMA engine doesn't grab the bus for the duration of the whole transfer, only while specific data is being transferred. Yes, that means CPU acces to memory is hampered, but not shut off completely. The CPU can also work with data from its cache in the meantime.
| Indeed, the wording of that sentence can lead to false conclusions. "The CPU is idle" actually means that it has no part in the memory transfer and (in principle) is free todo whatever the instructionstream(s) indicate.
While this can be phrased in only a couple of words the effects are tremendous! When the CPU does n... | https://cs.stackexchange.com |
4,511,488 | [
"https://math.stackexchange.com/questions/4511488",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/-1/"
] | <blockquote>
A courier has to make 5 stops on his route, designated <span class="math-container">$A, B, C, D$</span>, and <span class="math-container">$E$</span>. How many distinct routes can he take if he must stop at <span class="math-container">$A$</span> sometime before <span class="math-container">$D$</span> ?
</b... | B,C,E has <span class="math-container">$3!$</span> arrangements.
A,D arrangements are ten
<pre><code>(1,2),(1,3)(1,4),(1,5)
(2,3),(2,4),(2,5)
(3,4),(3,5)
(4,5)
</code></pre>
60 is the answer
| As the comments have already indicated, symmetrical considerations require that the answer is
<span class="math-container">$$\frac{5!}{2} = 60.$$</span>
However, your direct approach is also feasible.
There are <span class="math-container">$~\displaystyle \binom{5}{2}~$</span> ways of selecting the two positions that w... | https://math.stackexchange.com |
316,847 | [
"https://stats.stackexchange.com/questions/316847",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/187124/"
] | Why is Binomial data called Binary Data with repetitions? This is in context of Logistic Regression, where the response variable has a binomial distribution.
| <h3>Why can you manipulate images</h3>
The only reason that dataset augmentation works in images is that we have some previous knowledge on the structure and contents of our data. For instance, I know that a picture of an 8 is still an 8 if I rotate it 5 degrees, or if I add gaussian noise. In fact, because it is an 8... | I think it is hard to say definitively what the effect of changing clinical characteristics would be, in contrast to image augmentation.
The idea behind image augmentation is that say rotating an image does not change the label. You know this, but the network does not. So it is not just making a larger dataset (you ... | https://stats.stackexchange.com |
7,058 | [
"https://dba.stackexchange.com/questions/7058",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/3428/"
] | I am running Oracle 11.1.0 on Win Server 2008. My autobackups used to go to flash_recovery_area\myDB\autobackup\*yyyy_mm_dd*. Then I added a prefix to the file name in front of %F and they started going to C:\ORACLE\PRODUCT\11.1.0\DB_1\DATABASE\ so I removed the prefix but they still don't go to the flash recovery area... | Figured out the problem. Simply changing the Autobackup Format back to the default '%F' is not viewed as the default. In order to truly have the default value you must use the clear command.
<pre><code>CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK CLEAR;
</code></pre>
RMAN behaivor returned to normal. ... | If we don't set using CLEAR,below will be output
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '%F';
If we set using clear,then output is below:
CONFIGURE CONTROLFILE AUTOBACKUP FORMAT FOR DEVICE TYPE DISK TO '%F'; # default
observer the # default keyword.
| https://dba.stackexchange.com |
553,732 | [
"https://electronics.stackexchange.com/questions/553732",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/201217/"
] | I am trying to make sure my motor which is connected to my controller circuit would not just start spinning when you first apply power to it as if the Potentiometer is left high before the battery is connected it could be dangerous. here is my code.... and it works on power up, so if the POT is if left high when you fi... | Maybe this:
<pre><code>void main(void)
{
while (ADCRead()!=0)
{
// think about putting a short sleep here
}
while (1)
{
CCPR5L= ADCRead()>>2; // Function call for PWM
if (PORTAbits.RA3)
{
commutation180anti();
}
}
}
</co... | I figured out why my MCU was resetting, this was due to the hall effect sensors to the input of the MCU. When my motor hit the current limit the noise from the motor was induced in to the hall effect sensors which are configured inside the motor, which are than connected to the inputs of my Microcontroller, this was fi... | https://electronics.stackexchange.com |
616,279 | [
"https://physics.stackexchange.com/questions/616279",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/289833/"
] | There is a rocket <span class="math-container">$R_1$</span> that is traveling with velocity <span class="math-container">$V$</span> with respect to another rocket <span class="math-container">$R_0$</span> of the same mass. <span class="math-container">$R_1$</span> has <span class="math-container">$J$</span> joules of k... | The energy is conserved in an inertial reference frame. Once you light the fuel of <span class="math-container">$R_0$</span>, it begins to accelerate, so its reference frame is no longer inertial, so you can no longer apply conservation of energy in its reference frame. If you want to apply conservation of energy here,... | <blockquote>
What mistake was made to make it seem that this scenario has violated the conservation of energy?
</blockquote>
You neglected the energy of the rocket exhaust.
| https://physics.stackexchange.com |
162,256 | [
"https://softwareengineering.stackexchange.com/questions/162256",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/61659/"
] | In C and C++, it is very easy to write the following code with a serious error.
<pre><code>char responseChar = getchar();
int confirmExit = 'y' == tolower(responseChar);
if (confirmExit = 1)
{
exit(0);
}
</code></pre>
The error is that the if statement should have been:
<pre><code>if (confirmExit == 1)
</code></... | The best technique is to increase the warning level of your compiler.
It will then warn you about potential assignment in the if conditional.
Make sure you compile your code with zero warnings (which you should be doing anyway). If you want to be pedantic then set your compiler to treat warnings as errors.
Using Yoda... | You could always do something radical like testing your software. I don't even mean automated unit tests, just the tests every single experienced developer does out of habit by running his new code twice, once confirming the exit and once not. That's the reason most programmers consider it a non-issue.
| https://softwareengineering.stackexchange.com |
12,427 | [
"https://security.stackexchange.com/questions/12427",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/7969/"
] | I am developing my site using server side sessions using redis as backend for saving the session.
Now the issue which is bothering me is of user leaving the website without logging out.
I mean user simply closes the browser which causes the cookie to be deleted.
Now session of that user still exists on the server ... | Yes, for most sites it is fine to leave a session valid for hours (say, 24 hours).
As with any security question, you start by asking: what resources am I trying to protect? What is the threat model? What am I trying to defend against?
In this case, you are worried that an attacker might be able to "steal" a sessio... | It's a tradeoff between usability and security. Internet banking will close connection after a very short time of inactivity, and the sites you mentionated (gmail, facebook, etc) will not logout because their users would be upset to login every time.
Your decision will be much more based in this security x making user... | https://security.stackexchange.com |
47,236 | [
"https://electronics.stackexchange.com/questions/47236",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/1380/"
] | There are some diffences between consumer/Hi-Fi and pro music audio equipment, besides that pro audio equipment is bigger and louder, requires cooling fans, etc. eg. Hi-Fi uses a pre-amp, pro audio uses a mixing desk.
What's the difference in terms of the electronics? Can an electric/electronic instrument (eg. electr... | Before I answer this, let me tell you a little bit about myself. I'm an EE, and I primarily work in the Pro-Audio industry-- although I have also done some work for an audiophile company. I've been using pro-audio equipment for 25 years, and designing pro audio-stuff for 14 years. I mention this so that you can judg... | HiFi is just short for "high fidelity" and there is no technical definition. I'd go as far as to say it's a marketing term alone and I didn't know anyone still used it.
| https://electronics.stackexchange.com |
470,640 | [
"https://electronics.stackexchange.com/questions/470640",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/156271/"
] | Newbie question :
I have an external power supply which gives me 10volts reference.
The machine I need to command is reading an analog order from 0V (minimum speed) to 10V (maximum speed) and I use a STM32WB55.
My solution is to add a DAC and then an op-amp.
Do you see another solution?
Thank you
| 1) PWM output and low-pass filter<br>
2) digital potentiometer.
| You can get a few DACs that will directly output 0-10V with 3V SPI or similar serial control, but they are mostly designed for process control and other high performance applications, I doubt the cost differential is worth it if you have a low end application (and even for higher end applications the cost hit is signi... | https://electronics.stackexchange.com |
60,744 | [
"https://mathoverflow.net/questions/60744",
"https://mathoverflow.net",
"https://mathoverflow.net/users/5550/"
] | In some physical problem the following differential equation appears
$\dot{x}=F(x)+f(t)$,
where the dot denotes derivative with respect to $t$. $x$ is evidently a function of $t$. I'm wondering what the theory of differential equations knows about how to solve these kind of equation. Generic solution for arbitrarily ... | Look at Lemma 2.1.3 i.v) from Grothendieck and Murre: "The Tame Fundamental Group of a Formal Neighbourhood of a divsors with Normal Crossings on a Scheme".
It says when given a tame field extension $L \supset K$, then its Galois closure will again be tame.
Here, tameness is just defined with respect to one valution ... | For the first glance
it should follow form the Abhaynkar's lemma (see "Algebraic Function Fields" by Stichtenoth, Theorem 3.9.1) and the fact the Galois closure is the composite of all the different embeddings of L over K into fixed algebraic closure of K (so each of them has the same properties of tame ramifications).... | https://mathoverflow.net |
300,775 | [
"https://physics.stackexchange.com/questions/300775",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/140205/"
] | Let there an object with determined mass which needs to be moved with a motor (lets say electrical). We have two available motors, which have exactly the same power (and other characteristics), but different torque / rated speed. Which motor will accelerate the object faster, motor with high torque, but low rated speed... | Depends on the transmission and rotating masses. With ideal transmissions and identical rotating masses, both will achieve the exact same acceleration of the "object". If there's no transmission, then the question is what the power output of the motors look like as a function of speed.
| In theory since:
$$a = {P \over mv} $$
with:
$$a = acceleration$$
$$P = power$$
$$m = mass$$
$$v = velocity$$
then only power matters and both motors would be equal.
In practice it also depends on how you apply the motors torque to the object, or practically how your transmission works. With an ideal CVT transmission ... | https://physics.stackexchange.com |
4,002 | [
"https://bioinformatics.stackexchange.com/questions/4002",
"https://bioinformatics.stackexchange.com",
"https://bioinformatics.stackexchange.com/users/1847/"
] | I'm a bit confused and would appreciate your assistance, please.
I'm trying to use the <code>pairwiseAlignment</code> function from the <code>Biostrings</code> package to align two protein sequences.
I'm not quite sure where to put my reference sequence, the sequence I want to compare to. Is it under "subject" or "pa... | Your request is easy to implement. I wouldn't use any libraries in this case. As you haven't showed your implementation, I will provide one:
<pre class="lang-python prettyprint-override"><code>def gen_cigar(ref, qry):
if len(ref) != len(qry):
raise Exception('unequal length')
cigar = []
for i in ra... | Here is what I would do in Python. There are a few extra checks I've included, and my definitions of a few cases are different than Heng Li's above, @user172818. The performance is fairly similar.
<pre><code>def create_cigar(reference, alignment):
'''Construct CIGAR from reference and alignment'''
## if refer... | https://bioinformatics.stackexchange.com |
223,415 | [
"https://softwareengineering.stackexchange.com/questions/223415",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/7209/"
] | If I'm giving an interview coding question in Java, I can specify the most of the question just by giving a method signature. (Made-up example follows.)
<pre><code>public class Table {
public String identifier;
public int seatCount;
}
public static List<String> tablesWithEnoughSeats(List<Table> table... | Mock your inputs. Say "Assume that this array consists of integers or floats or whatever". You can also annotate things with comments.
I'd write this in Python like so:
<pre><code>class Table: #identifier: string, seat_count: int
def __init__(self, identifier, seat_count):
self.identifier = identifier
... | Give them the data structure (explain namedtuple if they haven't seen it before):
<pre><code>from collections import namedtuple
Table = namedtuple('Table', 'name seats')
</code></pre>
Then show them as sample invocation:
<pre><code>>>> tables = [
... Table(name="First", seats=6),
... Table(name="Sec... | https://softwareengineering.stackexchange.com |
95,976 | [
"https://softwareengineering.stackexchange.com/questions/95976",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/16273/"
] | My team is using clear-case as the version control. The project which I am working is not started 7-8 years back. During the entire life time of the project we had several releases bug-fixes service packs etc. The issues are tracked using the bug tracking system and most of the people who work on the bug-fixes follows ... | The problem with adding the bugfix as a comment to the code is, you don't get the full story. If I see a perfectly fine piece of code tagged "this is a fix to the bug <em>blah</em>", my first reaction would be to say "so what?". The code is there, it works. The only thing I need to know to maintain the code is a commen... | Mostly bad practice. I won't say it should never be done. Occasionally you run into something like a bug in an external API which you have to work around. The work-around can look completely brain dead if you don't know about the underlying bug. In that case it may be a good idea to document the bug in the code so co-w... | https://softwareengineering.stackexchange.com |
1,383,646 | [
"https://math.stackexchange.com/questions/1383646",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/72388/"
] | I have a function $\frac{df(\mathbf{y})}{d\mathbf{y}}=\mathbf{y}g(\kappa)$ where $\kappa=||\mathbf{y}||_2$ and $g(\cdot)$ is a scalar function.
Thing is when I differentiate this function I get a scalar, whereas I am expecting a matrix:
$$
\frac{d^2f(\mathbf{y})}{d\mathbf{y}d\mathbf{y}^T}=g(\kappa)+\mathbf{y}\frac{dg(... | Not true. For example, $z = 1 \neq w = e^{2\pi i/3}$ but $z^3 = w^3 = 1$.
| Take a cube root of unity other than $1$, and call it $w$. Thus $w \neq 1$, and $w^3 = 1$. Take another complex number, $z = i$, then clearly $i \neq iw$, but $i^3 = 1\cdot i^3 = w^3\cdot i^3 = (i\cdot w)^3$
| https://math.stackexchange.com |
16,377 | [
"https://dsp.stackexchange.com/questions/16377",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/4290/"
] | I am trying to verify for myself that aliasing actually makes it impossible to distinguish the "real" and the aliased frequency. What I have done it set the sampling rate to 20 Hz and created two sine wave with 2 Hz and 18 Hz. As far as I understand the 18 Hz signal should alias to a 2 Hz signal when the sampling rate ... | Yes, there is something to it. The phase increment of each sample of the 2 Hz wave is $2\pi * 2*.05=.2\pi$. The phase increment of each sample of the 18 Hz wave is $2\pi*18*.05=1.8\pi=-.2\pi$. Thus, the 2 Hz wave is $sin(2\pi*2*t)$, and the 18 Hz wave is $sin(2\pi*-2*t)=-sin(2\pi*2*t)$. Thus, the two waves are 180 ... | I think you should plot something like:
<pre><code>t = [0:0.05:1]; %20Hz sampling
a = sin(2*pi*2*t); %2Hz sine wave
b = sin(2*pi*18*t); %18Hz sine wave
plot(t, a, 'bo');
hold on;
plot(t, b, 'ro');
T = [0:0.001:1]; %1000Hz sampling frequency
A = sin(2*pi*2*T);
B = sin(2*pi*18*T);
% plot for 1000Hz sampling... | https://dsp.stackexchange.com |
86,264 | [
"https://electronics.stackexchange.com/questions/86264",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/8903/"
] | CodeVision has a lot of nice features, among them the automatic generation of the interrupt vector.
However, now I'm working on a very small bootloader, and I can't afford any interrupts. CodeVision still happily generates the interrupt vector at the beginning of the Flash memory, and I couldn't find a way to turn it ... | The 74HCT125 is fine. Power it with 5V and it will read your 3V3 Tx and enable signal just fine because \$V_{IH}\$ is only 1.6V (2V worst case). For the 3V3 Rx use a resistive voltage divider for 'level translation' from the 74HCT125.
| You need one driver ('125) for each direction of the bus:
<ul>
<li>One with the input connected to the 5V bus, and the output connected to the 3.3V IC. For this, you could use a 74AHC125, or a 74LVC125, powered from 3.3V, as these tolerate the 5V input. 74HC125 is not okay, as it does not tolerate input above its V<su... | https://electronics.stackexchange.com |
148,203 | [
"https://security.stackexchange.com/questions/148203",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/49449/"
] | With regard to access control, is "lattice" the same as "level"? Is "Multi-level access control" just another name of "lattice-based access control"?
Are Biba and Bell-LaPadula Security Models examples of Lattice-based Access Control?
| Biba and Bell-LaPadula are generic models. One parameter of those generic models is a multi-level security policy.
A <strong>multi-level security policy</strong> is a pair (DOMS,≤) where (DOMS,≤) is a partially ordered set and DOMS is a set of security domains (this is what you refer to as level).
A <strong>lattice</... | Depends on context. Lattice is the join point of an security label, an object and a subject. At the end of the day, it's all about levels of "<em>who</em> can access <em>what</em> through <em>where</em>". It depends on what meaning you want to extract from the text you are reading, could be the same.
Those models(Biba... | https://security.stackexchange.com |
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] | I am studying the integral
<span class="math-container">$$I=\int_{-\pi/2}^{\pi/2}
\frac{28\cos^2(\theta)+10\cos(\theta)\sin(\theta)-28\sin^2(\theta)}{2\cos^4(\theta)+3\cos^2(\theta)\sin^2(\theta)+m\sin^4(\theta)}d\theta,$$</span>
where <span class="math-container">$m>0$</span>. In the problem I am working, it is ve... | <hr>
Define the function <span class="math-container">$\mathcal{I}:\mathbb{R}_{>0}\rightarrow\mathbb{R}$</span> via the trigonometric integral
<span class="math-container">$$\begin{align}
\mathcal{I}{\left(\mu\right)}
&:=\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}}\mathrm{d}\theta\,\frac{28\cos^{2}{\left(\theta\right... | This problem is "nice" in the sense that the integrand is really trig function of <span class="math-container">$2\theta$</span>
<span class="math-container">$$
I=\int_{-\pi/2}^{\pi/2}\frac{28\cos 2\theta+5\sin2\theta}{\frac12(1+\cos2\theta)^2+\frac34\sin^2 2\theta+\frac{m}4(\cos2\theta-1)^2}\,\mathrm{d}\theta
$$</span>... | https://math.stackexchange.com |
12,875 | [
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] | Coming from a programming background, I'm used to user guides telling me how to use something, rather than how it's implemented. In the world of electronics, when it comes to discretes like, say, a MOSFET, all I can usually find is inventor, history, an overview of the theory and some implementation details.
It's quit... | I don't think there is any such guide. At least if there is one, it will be limited to a few basic uses of the device.
The difference is that if you are using, e.g., a programming library, all you really need to understand is the API. The library is designed to do a few well-constrained things.
Now, a component like ... | Get a good book, like The Art of Electronics, if you want things explained properly.
| https://electronics.stackexchange.com |
46,344 | [
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] | My daughters 2012 Mazda 3 broke down, would not start. The tow people apparently tried to jump it, it would not start. As some point they apparently had trouble putting it in neutral, there was some clicking (the details are very sketchy unfortunately, I was not there). The tow people thought it was the starter.
When ... | If cooling and music was on, they can consume some significant amounts of charge. Were the lights on? If so, that's even more charge consumed.
Old batteries don't die by reduced CCA, they die by holding reduced amounts of charge. So, music and cooling (and perhaps lights) for half an hour can definitely eat up your ch... | The starter sounds fine, the clicking noise could be all sorts of things. If your starter was sticking, you'd know. The battery sounds like it is fine as well.
This just sounds like your daughter is using too much power without running the car. In the IT world we would call it "user error", I think some training woul... | https://mechanics.stackexchange.com |
152,747 | [
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] | I am trying to set SELinux contexts within a directory structure. So it is something like this:
<pre><code>/var/www/sites
/www.example.com
/html
/logs
/www.example.org
/html
/logs
</code></pre>
I want to set different contexts on all of the <code>logs</code> directories and the... | I would still like to know if this is possible using the <code>semanage fcontext</code> command directly, but I worked out a way to do this using <code>find</code>:
<pre><code>sudo find /var/www/sites -type d -regex "/var/www/sites/[^/]+/html" -exec semanage fcontext -a -t httpd_sys_rw_content_t '{}(/.*)?' \;
</code><... | Maybe a bit of documentation on the format of the regular expressions that semanage admits would be helpful, I've discovered some patterns that work only through trial and error.
These patterns have worked for me to specify multiple paths beyond the wildcard to he end:
<pre><code>semanage fcontext -a -t httpd_sys_rw_... | https://security.stackexchange.com |
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] | Our research group was trying to simulate and analyse this circuit. But it seems that the pulse transformer is creating the problem in the sense that we cannot find its models in Pspice, microcap or any other such softwares. We would be grateful if you could help replace the pulse transformer with some other circuit el... | I'm not sure how it works in Europe, but in the US, if you are buying just the module, then even though it has an FCC ID on it, you still need to get it tested in combination with your own antenna.
<em>However</em>, if you buy a module and antenna mounted together, such as this ZigBee (notice it has a prominent CE mar... | Pre-certification may apply to the module you are using, but you are still required for CE marking of the device.
Part of the process for CE marking requires you to show evidence that your DEVICE conforms to the relevant harmonized requirements that covers emission and susceptibility.
So you are still required to o... | https://electronics.stackexchange.com |
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] | I have a set of gene names in HGNC standard and I want to get all their exons (in BED format) from the UCSC browser but it seems like the browser doesn't index genes by their HGNC name. How can I do that?
| I expect there was a sequencing problem during the last base, where some of the reagents were running low on the sequencer. This won't pose any real problem, RNAseq aligners like STAR will just soft-clip the last base or two if they're mismatches.
It's common to see a bit of bias toward the 5' or 3' ends in RNAseq, mo... | I know this is an old post, but if this plot is from <em>after</em> trimming I would suggest a different explanation: some trimming tools remove poly-A sequences from reads. If that's the case then any read ending with <code>A</code> will have that removed, this leads to a 0% <code>A</code> base content in the final ba... | https://bioinformatics.stackexchange.com |
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] | I am having a tough time, trying to understand $C([0,1])$ the sup metric space. I can even prove that it is complete. However, I encountered the following question and I really really have no idea what this is asking for. OR put it in another way, I had a hard to visualize it. Anyway, I 'd appreciate if you can give me... | Here is another way: Use continuity with the appropriate function.
Let $\phi: C[0,1] \to \mathbb{R}$ be $\phi(f) = f(\frac{1}{2})$. It is straightforward to show that $\phi$ is continuous (in fact it is Lipschitz continuous with rank one).
Then the sets are a) $\phi^{-1} (\infty,6)$, and b) $\phi^{-1} (\infty,6]$. Si... | I think that by $\{ f(1/2)<6\}$ what it actually means is the set
$$ \{f\in C[0,1] \text{ s.t. } f(1/2)<6 \}.$$
You can also prove that a set is closed $A$ if you take a Cauchy sequence $(a_n)\subset A$ and prove that its limit is also in A. A set, $A$, is open if for every element $x \in A$ there is a neighborho... | https://math.stackexchange.com |
3,835,463 | [
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] | Suppose <span class="math-container">$\mathbf{u},\mathbf{v},\mathbf{w}$</span> are noncollinear points <span class="math-container">$\in\mathbb{R}^2$</span>. Let <span class="math-container">$\mathbf{x} \in \mathbb{R}^2$</span>. Show that we can write <span class="math-container">$\mathbf{x}$</span> uniquely in the for... | Note that for any <span class="math-container">$x$</span> there is a unique <span class="math-container">$c$</span> such that
<span class="math-container">$x-u = c_1 (w-u)+c_2(v-u)$</span>.
In other words,
<span class="math-container">$x = c_1 w + c_2 v + (1-c_1-c_2) u$</span>.
| You've found a representation of <span class="math-container">$\mathbf x$</span> where the coefficients of <span class="math-container">$\mathbf u, \mathbf v, \mathbf w$</span> add to <span class="math-container">$0$</span>. That doesn't do <em>everything</em> you want, but it is a good first step.
Can you find a repre... | https://math.stackexchange.com |
184,430 | [
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] | I am not DBA ,but I need to check on the size of database files .
my database log files earlier was around 32 GB but from last few days it starts increasing and finally reached to 70 GB . first I thought it was natural , but soon I realized that I was wrong .
For shrinking the size of log file ,firstly I used to det... | A full database backup won't help your log size.
Full Recovery Model means "Can restore to any point in time." - including before that new database backup was taken.
Simple Recovery Model means "Can restore to the last database backup".
So... have a think about whether you need to restore to this morning or not (b... | You can't shrink a full log, shrinking will only reclaim empty space and even then you should be very liberal in how you use the shrink feature.
The first thing I'd recommend checking is that your database is having transactional log backups taken as well as full backups. Full backups won't clear the transactional log... | https://dba.stackexchange.com |
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] | <span class="math-container">$$
2\tan ^{-1}\left(\sqrt{\frac{a}{b}}\tan \frac{x}{2}\right)=\sin ^{-1}\frac{2\sqrt{ab}\sin x}{\left(b+a\right)+\left(b-a\right)\cos x}
$$</span>
I know within inverse of trigonometric function we have the value.
How Do I solve this.
my approach for this solution was:<br />
1st:
<span clas... | This should be the next step of your attempt: <span class="math-container">$$\sin ^{-1}\dfrac{\sqrt{ab}\sin x}{b\left(\frac{1+\cos x}{2}\right)+a\left(\frac{1-\cos x}2\right)}$$</span> using half-angle formula.
The result follows immediately.
| Let <span class="math-container">$$\tan A=\sqrt{\frac{a}{b}}\tan\frac{x}{2}$$</span> and
<span class="math-container">$$\sin B=\frac{2\sqrt{ab}\sin x}{(b+a)+(b-a)\cos x}$$</span>
You wish to show <span class="math-container">$2A=B$</span>. Calculate
<span class="math-container">$$\sin 2A=2\sin A\cos A=2\frac{\tan A}{\s... | https://math.stackexchange.com |
240,988 | [
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] | Lets say you've got a list
<code>l = [0, 2..]</code>
and you want to get the <code>n</code>th number when <code>n</code> is pretty large, say <code>n=123456789</code>.
So you call <code>l !! 123456789</code>.
On my machine, this results in <code>out of memory</code>.
So why aren't Haskell capable of realizing that ... | A sufficiently smart compiler could notice that in those cases. But for nontrivial cases, finding a closed form ranges from hard to open problem to undecidable. A compiler is a compiler, not a mathematician. There is no general procedure for turning the nth element of a sequence into a simple form that doesn't compute ... | Part of the job of programming is recognizing when you have added a complication that doesn't need to exist, and removing it.
In this case, what you're doing is finding the 123456789th entry in a list where the nth entry is 2*n. Constructing the list in the first place is extra work, which we should decline to do. ... | https://softwareengineering.stackexchange.com |
7,256 | [
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] | I am working on binary classification problem. Data set is very large and highly imbalanced.<br>
Data dimensionality is also very high.
Now I want to balance data by under-sampling the majority class, and I also want to reduce data dimensionality by applying PCA, etc...
So my question is that which one should be appl... | Generally, you want your training and validation data sets be separate as much as possible. Ideally, the validation set data would have been obtained only after the model has been trained. If you perform dimensionality reduction before splitting your data to separate sets, you break this isolation between the training ... | Do the dimensionality reduction first: Your error in estimating the principal components will be smaller due to the larger sample (your Corr/Cov-matrix used in PCA has to be estimated!).
The other way around only makes sense for computational reasons.
| https://stats.stackexchange.com |
17,516 | [
"https://mathoverflow.net/questions/17516",
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] | (Warning: a student asking)
Let $E$ be an elliptic curve over $\mathbf Q$. Let $P(a,b)$ be a (nontrivial) torsion point on $E$. Is there an easy description of the ring of algebraic integers of $\mathbf Q(a,b)$? I'm curious about the answer for general elliptic curves, but I'm not sure whether such an answer is possibl... | [Comment: what follows is not really an answer, but rather a focusing of the question.]
In general, there is not such a nice description even of the number field $\mathbb{Q}(a,b)$ -- typically it will be some non-normal number field whose normal closure has Galois group $\operatorname{GL}_2(\mathbb{Z}/n\mathbb{Z})$, w... | Abelian extensions of complex quadratic number fields are generated by division points of certain elliptic functions (which I guess you can translate into the language of torsion points on elliptic curves with complex multiplication - see Pete's answer). Their rings of integers were studied in
<ul>
<li>Ph. Cassou-Nog... | https://mathoverflow.net |
737,698 | [
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] | I am doing some homework on statistical mechanics, and I'm facing something I can't seem to understand/find what I'm doing wrong.
Suppose we have a diatomic molecule, both atoms have mass <span class="math-container">$m$</span>. Suppose the molecule isn't moving, and it is in thermal equilibrium with a heat bath at a t... | Let <span class="math-container">$R$</span> be the resistive force.
Applying Newton's second law <span class="math-container">$mg-R = ma$</span> where <span class="math-container">$a$</span> is the acceleration of the ball.
Thus <span class="math-container">$a= g-\frac Rm$</span>.
Assuming that the density of the metal... | I offer a nearly-zero-mathmatics answer:
<blockquote>
The acceleration due to gravity is <span class="math-container">$g$</span>
</blockquote>
Here is your misconception. <span class="math-container">$g$</span> is the acceleration due to gravity in <em>free fall</em>. When there is air resistance or other forces involv... | https://physics.stackexchange.com |
90,708 | [
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] | Ok this is a basic question but i am not able to figure out how does this work
<b>1:</b> This is the representation of the RS Flip-Flop with the truth table given in my
book
<img src="https://i.stack.imgur.com/8bYRl.png" alt="enter image description here">
I am not able to connect the truth table to the representat... | Try starting to think from the second line.
If you put 0 to S port, it would go to 0 in the output regardless of the other input because it is an AND port. But its output is inverted since it is and NAND port, so when you put 0 in S signal, its output will necessarily goes to 1 regardless of the other NAND input.
The... | A simple circuit for flip flop can be implemented by two transistors like this:
<img src="https://i.stack.imgur.com/yxrOj.png" alt="enter image description here">
This Flip-Flop can be changed by pushing one of the buttons.
But how it works?
Think there is no push button. and we just have two transistors and four res... | https://electronics.stackexchange.com |
54,978 | [
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] | Is alternating current more dangerous than direct current?
And give me explanation for that... Assume that 230 V, 50 Hz AC voltage and 230 V DC voltage. Which is more hazardous to human life?
Which has more probability of risk?
| AC has some time period - frequency. It repeats itself and periodically touches zero. However DC remains at a constant voltage level.
Let me compare on different points:-
<ol>
<li>Due to such nature of AC, there is a "Let go" thing with AC, At a specific point it may let you go and you could be safe. However, in case ... | This is like the question, "Which is more dangerous, a pit full of spikes, or a giant swinging blade?"
You can argue about the different ways in which they may kill you, but it doesn't much matter when you are dead, does it?
| https://electronics.stackexchange.com |
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] | If we find the force for a decelerating object (let's say a car on a road), we'll see that the force is negative as in it’s in the opposite direction of the motion of the object. I wanna know what this means. I'm still finding the force from the object (because the mass and decelaration is of the car), so does this mea... | <blockquote>
If we find the force for a decelerating object (let's say a car on a road), we'll see that the force is negative as in it’s in the opposite direction of the motion of the object.
</blockquote>
Not necessarily. The sign of the force just depends on its direction; it has nothing to do with the direction of m... | There's a few pieces to this. The first is that it will be easier to understand forces if you don't think of them as "negative." Forces are vectors, which have a (positive) magnitude and a direction.
Where you can get a "negative" thing regarding vectors is when you write them down in component fo... | https://physics.stackexchange.com |
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] | I have a question that came up in a discussion with friends. If I throw a ball straight up in an enclosed train car moving with constant velocity, I believe the basic physics books say it will land in the same spot. But will it really? I think I can say that the answer is "not in the real world".
Trivially, a train... | Yes, the ball would land in exactly the same spot, whether robot or person. The air does not remember the original speed, and new air coming in does not keep its velocity, but settles down with the co-moving air. The speed it has is determined by the fan blowing it in, not by the speed of the train.
The reason is that... | I'll discuss two situation:
<ul>
<li>The experimenter is standing on a "X" in the enclosed railcar as it rolls along with velocity $v$, and throws just as she passes a "Y" painted on the ground outside the train. In this case she throws the ball "straight up" in her own frame.
She predicts that the ball lands on the ... | https://physics.stackexchange.com |
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] | I'm trying to figure out various things surrounding PostgreSQL and how backups should work together with WAL and Commvault Simpana. Simpana is telling me that everything is ok, but leaves files lying around in the WAL Archive directory.
Let the journey begin.
<h1>Environment</h1>
<h2>PostgreSQL & OS Version</h2>... | This seems to be fundamentally a question about Commvault Simpana, not PostgreSQL. As Commvault seems to be commercial software, you might have the best luck contacting their support desk.
<blockquote>
Expected Behaviour Because Simpana is performing the backup with
PostgreSQL native commands, I expect that when ... | We have the same issue with Simpana postgres backup.
The documentation states:
<blockquote>
What are all the files that get backed up as part of Log Only backups?
Only the transaction log files that are relevant to the current backup
cycle are backed up. The entire Log directory content will not be
backed up. ... | https://dba.stackexchange.com |
141,405 | [
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] | I've read that active mass of solids and pure liquids is considered unity. I'm absolutely sure there is some misunderstanding. I know that concentration of solids doesn't change during the course of reaction, but it shouldn't necessarily be unity either. Consider graphite for example. It's density is <span class="math-... | Rather, active mass of solids need not necessarily be unity, but arbitrarily is unity with advantage. You do not have to know the molar mass nor density.
The common thermodynamic expressions like <span class="math-container">$K = \frac{[C][D]}{[A][B]}$</span>
or kinetic ones like <span class="math-container">$\frac{\ma... | Let's start from the equilibrium constant, which may be defined <span class="math-container">$\ce{K=\frac{[C][D]}{[A][B]}}$</span>. Of course, activities should be introduced here instead of concentration. But it is not the point here. The main use of this constant is to calculate how the composition of the system chan... | https://chemistry.stackexchange.com |
8,164 | [
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] | Why are hand-written signatures still so commonly used? Can they actually prove anything?
Two assumptions:
<ul>
<li>If anyone wants to forge my signature I'm sure they will be able to do it. Even my own signature looks a little bit different every time I sign a document.</li>
<li>If I commit to an agreement by signin... | It pays to investigate what we really trust in hand-written signatures.
A <em>signature</em> is the physical manifestation of the will of the signer to acknowledge the contents of what is signed. Most legal systems define that a signature is yours and is binding if and only if "you really did it". This looks like a ta... | Because the legal system is very slow to catch up with the "latest" technologies (asymmetric cryptography was discovered in 1978). Also, people manifest some inertia when it comes to trust, especially for technological things.
The best we could do is to append the hash of the pdf form of the same document at the end ... | https://security.stackexchange.com |
195,770 | [
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"https://mathoverflow.net",
"https://mathoverflow.net/users/65937/"
] | I am interested in the following question. Are maps which induce the same homomorphism on homotopy and homology groups homotopic? I am sure the answer is no, however I cannot imagine how to construct counterexamples.
| Take the composition of a degree one map $f:T^3\to S^3$ with the Hopf map $g:S^3\to S^2$, where $T^3$ is the 3-torus. This composition is trivial on homotopy groups since $T^3$ is aspherical and $\pi_1S^2=0$. It is trivial on $H_i$ for $i>0$ since this is true for $g$. If $gf$ were nullhomotopic we could lift a null... | Phantom maps provide a large class of examples of maps which are not homotopic to the constant map, but which induce the zero map on both homology and homotopy groups. There are uncountably many distinct homotopy classes of phantom maps $\mathbb{C}P^\infty\to S^3$, for example.
Edit: In many cases one can determine w... | https://mathoverflow.net |
1,226,162 | [
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] | \begin{align}
x' &= -x^3 + x^5 + (x^4)(y^5)\\[.7em]
y' &= -8y^3 + y^5 - 10(y^4)(x^5)
\end{align}
$(0,0)$ is obviously a critical point of the system, and we are given that it is asymptotically stable, but have to show it.
I have tried to make a Lyapunov function $V(x,y) = ax^2 + cy^2$, with a,c > 0 bu... | For
$$V(x,y)=\frac{1}{2}(x^2+y^2)$$
we have
$$\dot{V}=-x^4-8y^4+x^6+y^6-9y^5x^5\\
\leq -(1-x^2-|xy|)x^4-8(1-(1/8)y^2-|xy|)y^4$$
Thus if we define the region (neighborhood of the origin)
$$\Omega:=\left\{(x,y)|(x^2+|xy|<1)\textrm{ and }\frac{1}{8}y^2+|xy|<1\right\}$$
we have that $$\dot{V}(x,y)<0\qquad \forall... | Hint: choose $a$ and $c$ so the terms in $x^5 y^5$ cancel. Note that for $x$ near $0$, lower powers of $x$ dominate higher powers, and similarly for $y$.
| https://math.stackexchange.com |
283,806 | [
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] | I'm a developer not a dba, but this task was given to me...
One of our databases is hit hard by a process which reads and modifies hundreds of thousands records onece or twice a day, during the time this process is running our other services who rely on this database get very slow.
What are some "common" appr... | You have two options:
<ol>
<li>redesign/tune the procedure that is doing too much disk IO (or may too much use of cpu or ram)</li>
<li>increase hardware power (more MIOps, more ram, more logic cores)</li>
</ol>
But before doing so you have to deep dive into the issue to find what is the root cause of it.
| As others have suggested, the problem you've outlined is very open-ended. However, I can offer one general solution which you may not have considered: break up the intensive operation into smaller batches. This will keep locks brief, reducing the risk of deadlocks, may reduce the amount of memory and temp space used,... | https://dba.stackexchange.com |
3,321,219 | [
"https://math.stackexchange.com/questions/3321219",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/638643/"
] | So I was doing a integral question and I stumbled upon this question.
<span class="math-container">$\displaystyle{\int\sqrt{1 + \sin\left(\frac x2\right)}\,dx}$</span>
In order to solve it I did the following:
I took <span class="math-container">$u = \frac12x$</span>
Then <span class="math-container">$\frac {du}{dx... | First, they used the double angle formula:
<span class="math-container">$$\sin u = \sin\left(2\frac{u}{2}\right) = 2\sin\frac{u}{2}\cos\frac{u}{2}.$$</span>
Then they replaced the <span class="math-container">$1$</span> with <span class="math-container">$\sin^2\frac{u}{2}+\cos^2\frac{u}{2}.$</span>
| Use <span class="math-container">$$\sqrt{1+\sin\frac{x}{2}}=\sqrt{1+\cos\left(\frac{\pi}{2}-\frac{x}{2}\right)}=\sqrt2\left|\cos\left(\frac{\pi}{4}-\frac{x}{4}\right)\right|$$</span>
| https://math.stackexchange.com |
19,298 | [
"https://physics.stackexchange.com/questions/19298",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/7054/"
] | It seems like this experiment is possible:
<ol>
<li>Fire a photon, and start a timer</li>
<li>The photon travels through the slit(s)</li>
<li>The photon strikes a plate -- the timer is stopped.</li>
</ol>
Based on where on the plate the photon struck, the time it took, and the speed of light, it seems possible to ded... | It is possible. But it doesn't change anything about the "we can't know through which slit it went and still get an interference pattern" issue. (Surprise!)
In order to do this you need photons that can be timed very precisely, i.e. $\Delta t$ needs to be small: smaller than $c/d$ where $d$ is the slit seperation. Acc... | To explain in a more simple way, to be more easily understood by non-physicists: Two waves can obviously only interfere if they arrive at the same time. If the photon wave packet (which is the interval in which the photon might be found when measured) is so narrow that the wave packets going through the left and the ri... | https://physics.stackexchange.com |
37,973 | [
"https://softwareengineering.stackexchange.com/questions/37973",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/12611/"
] | My team and I develop software that our customers will use to interact with their customers. Additionally, we also eat our own dogfood and use the software ourselves to interact with our customers.
Therefore, it can sometimes be difficult to explain use cases and scenarios, as our employees can be operators, our cust... | <blockquote>to explain use cases and scenarios</blockquote>
That's the key: use the terminology of the domain, i.e. the names of the roles. Who can play the roles is not important. Make sure that the roles are well-defined (for each scenario).
It is entirely possible for me to visit my own website and purchase my own... | To make it clear, call <strong>your customer</strong> as <strong>clients</strong>, then <strong>your customer's customers</strong> as <strong>customers</strong>. That will make it clearer isn't it?
I recommend you to rename the terms and customize your software package (a little) for each of your customer depending on... | https://softwareengineering.stackexchange.com |
335,264 | [
"https://physics.stackexchange.com/questions/335264",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/98822/"
] | Nice question for a sunny (at least here in Holland) Thursday morning. What kind of disasters would appear on our planet if we placed a huge (say, one with ten times the earth's diameter), mirror on the shadow side of the earth in space (aligned with the sun) with the capability to focus all sun rays in one little area... | What a destructive thought. :)
This will focus the sun light from evry possible corner on the <strong>focal point</strong> of the <strong><em>parabolic mirror</em></strong>.
Since normally, in outer space temperature goes beyond <strong>120°C</strong> when the sun light is scattered over the space.
And when all its ... | Yes, but you can't focus it to a city size. A 120000km mirror could wipe out life on the whole Earth, because the whole Earth would be in focus.
With a smaller, cheaper mirror you can delete a city from the map.
| https://physics.stackexchange.com |
237,387 | [
"https://softwareengineering.stackexchange.com/questions/237387",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/106793/"
] | What is the best way to handle errors that shouldn't ever happen?
My current way to do this is to throw an exception if the 'thing that shouldn't happen' <strong>does</strong> happen, like so:
<pre><code>/*
* Restoring from a saved state. This shouldn't be
* null unless someone in the future doesn't set it properl... | It's amazing how often things that should never happen do.
You should throw a RuntimeException with a descriptive error message and let the application crash. If that ever happens, then you know that something is deeply wrong.
| It is best to not handle an exception if you cannot handle it intelligently.
This gives the opportunity for something earlier in the stack to handle the exception, since it probably has more context of what is trying to be accomplished.
Alternatively, if you know that this should never happen, this is an assertion, a... | https://softwareengineering.stackexchange.com |
2,010 | [
"https://mechanics.stackexchange.com/questions/2010",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/263/"
] | When I drive my car the first few miles, I smell exhaust inside the car with the windows rolled up. It happens when I have either the AC or the heat/air on...
What's going on?
| Exhaust inside a car is bad. It can come in through your vents, through the floor, or through the firewall. No matter where it's coming from, you should get it fixed because you can pass out from carbon monoxide, and if the engine keeps running after the crash it could kill you.
It probably won't take too much to fix ... | Basically you have an exhaust leak, it's dangerous (to you in the form of carbon monoxide) and should not be ignored. An easy way to check for the leak is to pull a vacuum line off the intake and suck a small amount (1 - 2oz) of transmission fluid into the intake via that vacuum line. Make sure the vehicle is outside, ... | https://mechanics.stackexchange.com |
49,248 | [
"https://astronomy.stackexchange.com/questions/49248",
"https://astronomy.stackexchange.com",
"https://astronomy.stackexchange.com/users/26283/"
] | The standard interpretation of Hubble constant <span class="math-container">$\approx 70~\text{km/s/Mpc}$</span> means that each mega-parsec of distance adds <span class="math-container">$70~\text{km/s}$</span> to a galaxy recession velocity from us (or to a space expansion rate ). But when expressing Hubble constant in... | One exasecond <strong>is</strong> an SI unit. There is no rule that says that one is not allowed to combine the prefix exa- with second.
Thus the interpretation is straightforward: it's the number of <span class="math-container">$e$</span>-fold expansions that <em>would</em> occur over that timeframe if the expansion r... | Unless the expansion/contraction is periodic then the frequency is just the reciprocal of an expansion timescale. There isn't any evidence that the universe will contract again. However, <em>if</em> it did, then the period of oscillation would almost certainly be much longer than 13.9 billion years, and would be unrela... | https://astronomy.stackexchange.com |
246,815 | [
"https://dba.stackexchange.com/questions/246815",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/131835/"
] | I create Dump file with EXPDP command in oracle database 11gR2 with operating system Oracle Linux 6.7
<strong>EXPDP Command:</strong>
<pre><code>expdp hmis/pass directory=MY_DATA_PUMP_DIR dumpfile=12c_db.dmp logfile=12c_db.log COMPRESSION=ALL FULL=Y
</code></pre>
Now when I run IMPDP command in oracle database 12c w... | The error message is self-explanatory:
<pre><code>ORA-01918: user 'XXXXXX' does not exist
</code></pre>
Look at the log output for your <code>expdp</code> execution. If it does not contain the following:
<pre><code>Processing object type SCHEMA_EXPORT/USER
Processing object type SCHEMA_EXPORT/SYSTEM_GRANT
Processing... | You need to create the user that you imported, and if you want to change the name of your schema; set in the configuration:
<pre><code>remapremap_schema
remap_tablespace
</code></pre>
I hope those optiones are useful for you, regards!
| https://dba.stackexchange.com |
543,146 | [
"https://physics.stackexchange.com/questions/543146",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/260293/"
] | Please tell me the relation between quantum computers and quantum mechanics. Also i want to know the topics common between the both. I searched this on the internet but didn't get clear answers.
| Quantum computers use components whose behavior and performance depend on quantum mechanics. If you want to understand the components, you will need to study quantum mechanics.
On the other hand, quantum computing can be understood independently of the hardware on which it is done, just as in ordinary computing. Y... | Do you mean to build hardware, in which case yes, or do you mean to code algorithms, in which case probably not. Computing is about calculational algorithms, not understanding the physics. The one thing you do need to understand is the principle of superposition from quantum mechanics. The potential for quantum computi... | https://physics.stackexchange.com |
422,713 | [
"https://softwareengineering.stackexchange.com/questions/422713",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/225187/"
] | CI/CD options such as bitbucket pipelines and github actions make use of virtual machines called runners. Changes in source code trigger the runners, which in turn trigger a set of commands. The commands may include instructions to run a test suite. The test suite checks whether source code changes break existing funct... | If the test fails, the software is broken. So fix the software.
It sounds like you haven't even figured out which operating system your software runs on, yet. Figure that out. If you are deploying the software on Linux then you must test it on Linux. If you are deploying the software on Windows then you must test it on... | If your software runs on both Windows and Linux, then your test assertions need to work for both platforms. I would write a helper method for string comparisons that ignore line ending differences, and change your assertions to use that helper method.
| https://softwareengineering.stackexchange.com |
232,882 | [
"https://stats.stackexchange.com/questions/232882",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/60655/"
] | Imagining that the mean IQ of the population is 100, sd is 15.
If the calculated IQ of the academic is 125, a two way t-test fails to reject the hypothesis that the professor is significantly smarter than the average person in the 5% significant, 100+1.96*15 ~ 130 is the rejection margin.
Now a one way t-test however... | You don't need any significance tests. You already have the IQ of the professor in question, namely, 125, which is not equal to 100. The situation that you seem to have this situation confused with is when you have a sample of people from some population and you want to make an inference about the mean IQ of the popula... | If the professor scored significantly below average, than that would be worth reporting. Therefore you are interested in both ends of the tails and need to perform a two tailed test.
Usually you compare your p with some alpha. That alpha is agreed upon to be 0.05 just as testing is agreed to be two tailed.
These are ... | https://stats.stackexchange.com |
439,638 | [
"https://softwareengineering.stackexchange.com/questions/439638",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/269888/"
] | I am working on a project that is structured in hexagonal architecture. It is a multi module gradle project where <code>web</code> layer is a separate module that depends on the <code>domain</code> module.
Sample code related to the question:
<pre><code>class InvoiceController(val invoiceService: InvoiceService) {
@R... | The original DDD book talked in terms of a layered architecture; in particular a "user interface" layer, an "application" layer, and a "domain layer".
A controller would normally be considered part of the "user interface" layer: it happens that input data is delivered to you via ... | I think the lower coupling, the better. I get you team's point, they're trying to hide the dependecy and keeping it centralized at InvoiceService internals. I also get your point, you're anyway coupling controllers and services by using a service on the controller, but they're looking for reducing that dependency to th... | https://softwareengineering.stackexchange.com |
295,860 | [
"https://dba.stackexchange.com/questions/295860",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/192377/"
] | I am trying to create a query that selects only a set of values, but excludes other ones.
The column I am selecting it's called "Participants" and the values therein are not a single text item, but a list of items separated by commas (length and number of items vary), for example: "Alpha, Delta, Eta"... | In your query when evaluating NOT LIKE you should use AND instead of OR, because you want all of them to be met.
<pre><code>SELECT DISTINCT
Name,
Category,
CODE,
Participants
WHERE (Participants NOT LIKE '%Alpha%'
AND Participants NOT LIKE '%Beta%'
AND Participants NOT LIKE '%Gamma%')
A... | If you can put these conditions into table variables or Table Valued Parameters, the query becomes somewhat simpler:
<pre class="lang-sql prettyprint-override"><code>DECLARE @ExclFilters TABLE (Value varchar(100);
INSERT @ExclFilters (Value)
VALUES
('Alpha'),
('Beta'),
('Gamma');
DECLARE @InclFilters TABLE (Value... | https://dba.stackexchange.com |
561,967 | [
"https://physics.stackexchange.com/questions/561967",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/267796/"
] | So let's say I have some particle in some arbitrary state where its ket vector is given as a linear combination of the spin up eigenstate and the spin down eigenstate. The magnitude square of a, which is the factor in front of the spin up eigenstate, gives the probability that a measurement on the particle yields spin ... | You can use the projection operators
<span class="math-container">$$
P_\pm = \frac 12 (1+{\bf n}\cdot {\boldsymbol \sigma}).
$$</span>
Applied to any starting state they give you the eigenstates of <span class="math-container">${\bf n}\cdot {\boldsymbol \sigma}$</span> with spin <span class="math-container">$\pm$</span... | To compute the spin components along <span class="math-container">$\hat{n}$</span> consider the matrix
<span class="math-container">$$
\sigma_{n} \equiv \hat{n} \cdot \vec{\sigma}\,.
$$</span>
Diagonalize <span class="math-container">$\sigma_n$</span> and find the list of eigenvectors <span class="math-container">$|i\r... | https://physics.stackexchange.com |
86,250 | [
"https://math.stackexchange.com/questions/86250",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/17865/"
] | I am trying to find all functions f satisfying $f'(t)=f(t)+\int_a^bf(t)dt$.
This is a problem from Spivak's <em>Calculus</em> and it is the chapter about Logarithms and Exponential functions. I gave up and read the solution (which I quickly regretted, but at the same time realized that I had not carefully read one... | <ol>
<li>How do we know that $f''(x) = f'(x)$? Differentiate both sides of
$$f'(x) = f(x) + \int_a^b f(t)\,dt.$$
Remember: $\int_a^bf(t)\,dt$ is a <em>number</em> (the net signed area between the graph of $y=f(x)$, the $x$-axis, and the lines $x=a$ and $x=b$). So what is its derivative?
Why would you d... | Since $\int_a^bf(t)dt$ is a constant, we denote it as $C$， so we get $f'(t)=f(t)+C$. It is $\frac{df(t)}{dt}=f(t)+C$, i.e. $\frac{df(t)}{f(t)+C}=dt$. Integrate it, we get $ln(f(t)+C)=t+D$, where D is a constant. Thus, $f(t)=e^{t+D}-C$. Let $e^D=K$, we get $f(t)=K{e^{t}}-C$.
Now plug it into the original eqution, w... | https://math.stackexchange.com |
65,070 | [
"https://mechanics.stackexchange.com/questions/65070",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/9415/"
] | I've observed this in my car, and in the motorcycle (carburetor) that I had previously.
When I start the car in the morning for work, the engine RPM starts off a bit high than the normal (+0.3 - 0.5 RPM) RPM. But when I shift to Drive from Park, the RPM settles and goes back to normal.
This won't happen again for the r... | <blockquote>
<ol>
<li>Does that mean the flywheel (which is connected to the engine) rotates at 800 revolution per minute while in neutral?</li>
</ol>
</blockquote>
Yes. The flywheel is directly connected to the engine so it will rotate at exactly the same speed as the engine.
<blockquote>
<ol start="2">
<... | Because neutral means none of the gears (1 to 5 or 6 plus reverse) are engaged so no drive to the driving wheels...
| https://mechanics.stackexchange.com |
71,273 | [
"https://security.stackexchange.com/questions/71273",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/2075/"
] | On occasion, I hear the terms "key length" and "bit strength" used interchangeably. Are these the same things? Or are they different?
| I'd use <em>bit length</em> for the size of something, such as a key.
I'd use <em>bit strength</em> as the base 2 logarithm of the cost of an attack. i.e. it costs about 2^n basic operations to break something.
A brute force attack against an <em>n</em> bit key that simply tries to guess the key costs <em>2^(n-1)</em... | They are pretty similar but are slightly different. The key length is simply the length, in bits, of the key used for cryptographic operations. If the key is chosen randomly and the algorithm doesn't have any vulnerabilities, then the bit strength is exactly the same as the key length.
The bit strength is a measure ... | https://security.stackexchange.com |
175,313 | [
"https://dba.stackexchange.com/questions/175313",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/121322/"
] | I have 4000 records in a temp table with one column. The column is a customerid that I need to update a record for. As of right now the only thing that comes to mind is running an exec statement for all 4000 records. Is there a more efficient way to do this without the use of a cursor?
| The Principle of Least Privilege demands two things: the runtime user (or the human user logins) should not own the objects, because you cannot stop them from modifying or dropping them (on Oracle).
The same Principle also suggests you should not need to have extensive permissions for the user who wants to update appl... | Generally speaking, it's a bad idea to have a database object in general use that is owned by a user account. If the user's account is disabled or goes away, problems can arise.
I'm a SQL Server guy, so things are a little different, but I like to have a service account as the DB owner, so we know the account will not... | https://dba.stackexchange.com |
122,207 | [
"https://dba.stackexchange.com/questions/122207",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/46827/"
] | I don't know if it's a simple question but does a data warehouse have different rules when it comes to normalization forms?
At the moment I am creating some tables in a data warehouse, and they simply do not fulfill the normalization forms rule. I have tried to find a method to fulfill them, but it seems to be pointl... | Normalization is not the holy grail. Normalize as much as possible. In a data warehouse you can group some data to get better performance. Also a data warehouse is about querying data. Less on users maintaining the data.
Go for a design that will give the information in an easy and quick way. Normalize if you can but ... | Actually it is common to denormalise in a data warehouse.
For instance I will have the full address of customers with the state and the country as columns in my Customer dimension. The data will be duplicated a lot for the customers living in the same city, but I won't have to do two costly joins to retrieve the stat... | https://dba.stackexchange.com |
56,999 | [
"https://chemistry.stackexchange.com/questions/56999",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/27603/"
] | The hydrophobic interaction is thought to be driven by an entropic force. If it is, shouldn't hydrophobic interactions be stronger at higher temperatures, where states of higher entropy are favoured? Why, then, are protein hydrophobic cores denatured by heat?
| You are correct that the hydrophobic interactions are stabilized at higher temperatures. However, I believe the addition of heat mainly disrupts protein structure by breaking hydrogen bonds through increased thermal motion.
Once the secondary structure starts to go, any tertiary interactions will get scrambled, likel... | To add to the answer of Dan Burden: the interactions might be stronger, but you're still making it easier for the protein to cross the energy barriers towards unfolding if you heat the protein.
Also, one thing that helped me understand protein physics is the following: an interaction might be worth 2 kcal/mole in a v... | https://chemistry.stackexchange.com |
77,345 | [
"https://cs.stackexchange.com/questions/77345",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/50881/"
] | i am looking for an algorithm that will generate all possible combinations of words from given dictionary that satisfy given format.
Let me explain what i mean with format:
For example, if the format is "abcd" means that we are looking for one word, length of the word must be 4 and because all the letters in format ... | Answering your second question:
<ol>
<li>Find the median $m$, and partition the set into $L_1 = \{x | x \in S \wedge x < m\}$ and $L_2 = \{x | x \in S \wedge x > m\}$.</li>
<li>Find the $k$th largest element $x_k$ in $L_2$, and partition the set into $L_2' = \{x | x \in L_2 \wedge x \leq x_k\}$ and $L_3 = \{x |... | The k elements following the median can be retrieved in O(n). To get them in sorted order, an additional O(k log k) sorting step is required.
<h3>Quickselect</h3>
From a high-level perspective, the Quickselect algorithm takes an array and an integer k. It then places the k-th largest number in the correct place, smal... | https://cs.stackexchange.com |
377,125 | [
"https://physics.stackexchange.com/questions/377125",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/109812/"
] | We know that light is an electromagnetic wave, so if we are able to build a surface with help of transparent but conducting material we will be able to build a conducting solid, so there will be no electric field inside the electric field inside the solid conductor.
Now my question is how will light incident on this ... | the LC part comes about by capacitive coupling to ground that happens naturally when the wiring comes close to a piece of grounded metal, and the fact that even a straight piece of wire possesses a little bit of inductance. If the incoming AM radio signal is strong enough, even a badly-tuned LC tank circuit coupled to ... | We have a similar yet stranger phenomenon happening in our house. I recently purchased a parabolic microphone with recorder to record bird calls. I have discovered that our house is receiving an AM station which is just below normal audible hearing range. The parabolic microphone is a sound amplifier and not a receiver... | https://physics.stackexchange.com |
251,726 | [
"https://physics.stackexchange.com/questions/251726",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/98561/"
] | The book I have gives the following derivation:
Let the temperature of the atmosphere be $-\theta$ and the temperature of the water be $0$.
Consider unit cross sectional are of ice, if layer of thickness $dx$ forms in time $dt$ with $x$ thickness of ice above it,
heat released due to its formation is $dx\rho L$ where... | A bit late maybe. A few google searches reveal that the speed at which heat propagates is infinite in the thermodynamics I am studying. So, the heat is transferred instantaneously and the time taken for a layer to form is equal to the time in which this heat is transferred.
I had thought that the heat is transferred ... | The heat is continually being released to the atmosphere, and the layer is continually getting thicker. The heat has to be conducted from the water-ice interface to the ice-atmosphere interface through the layer of ice. And, as the ice gets thicker, the rate of heat being conducted slows down. And the rate of ice fo... | https://physics.stackexchange.com |
308,038 | [
"https://mathoverflow.net/questions/308038",
"https://mathoverflow.net",
"https://mathoverflow.net/users/51480/"
] | I recently completed reading the book "Stochastic Differential Equations" by Bernt Oksendal which is the first time ever I was exposed to the topic. Now I am interested in pursuing research ( Ph.D.) SDEs and its applications in finance and I would like some help finding some recent papers related to or useful when doin... | As indicated in the comments, the field is very wide, but I understand from the comment of the OP to zab's answer that there is a specific interest in the more narrow subtopic of applications of fractional Brownian motion to quantitative finance. Here are some overviews:
<ul>
<li><A HREF="https://core.ac.uk/download/p... | For basic theory: Stephen Shreve's books (Stochastic Calculus for Finance I and II) and Martingale Methods in Financial Modelling by Marek Musiela and Marek Rutkowski. Also have a look at Oksendal's book on Jump Diffusions.
For numerical treatment of SDEs: Numerical Solution of Stochastic Differential Equations by Pla... | https://mathoverflow.net |
96,716 | [
"https://chemistry.stackexchange.com/questions/96716",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/64021/"
] | Why ethanol doesn't react with NaOH ,while methanol does?
| Methanol will react a little with NaOH because it is an acid slightly stronger than ethanol. Ethoxide ion is a stronger base than methoxyde because of the induced effect due to C2H5. So ethanol is a weaker acid.
| The problem is that methanol, ethanol and water all have similar strucutres. They will have similar pKas. I know that the pKas will increase in the order water, methanol and ethanol. The pKa of ethanol is about 18.
I think an equilibrium will exist between either methanol (or ethanol) and sodium hydroxide. It will be
... | https://chemistry.stackexchange.com |
7,256 | [
"https://mechanics.stackexchange.com/questions/7256",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/3760/"
] | I have a large crack on the left rear corner of my white '05 Prius bumper from when my wife bumped into a another car in a parking lot when the temperature was around 4 below. I also have a large dent/scrape on the front left bumper from when someone took a corner too sharp pulling into an alley and my car happened to... | On most modern vehicles, the part of the bumper you see is just a facade and has no structural purpose. Often as a part it's just called "bumper cover" or similar. So I don't think the cracks should affect safety in any way.
As for replacing it yourself, the hardest parts are:
<ol>
<li>Finding all the fasteners to re... | Check for a bumper repair specialty shop in your area. They can weld the plastic cracks as long as it isn't to badly distorted. The bumper will need to be painted if it repaired or if it is new so that cost won't change. The repair may be less than a replacement part. If you decide to repair it yourself don't forget to... | https://mechanics.stackexchange.com |
306,713 | [
"https://stats.stackexchange.com/questions/306713",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/179921/"
] | I am trying to do two-sample T-test in Minitab where I have to compare average of one variable with another binary variable. I am having difficulty in choosing alternate hypothesis. So just for guessing I tried both ways H1: u1 > u2 and H1: u1 < u2. Both gave same values of t less than critical t value (that is I ca... | You did not detect a significant difference.
If you are not sure which direction to test for, then you should have used a <strong>two-tailed test</strong>. Nevertheless, since both $p$-values are insignificant, the two-tailed test will also be. Hence, you cannot conclude a significant difference.
You also mention th... | You don't choose your hypothesis from p-value, you choose whatever you require for your experiment. Once your hypothesis is chosen, you don't go back and change it just because the p-value is too high.
While you failed to reject your hypothesis with t-test. I think it's more important to check your statistical assumpt... | https://stats.stackexchange.com |
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