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230,363 | [
"https://softwareengineering.stackexchange.com/questions/230363",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/80951/"
] | Or to put it another way how to ensure that architecture or quality doesn't suffer, doing agile.
Some of the understandings in handling architecture in agile are below(generally applies to testing as well)
<strong>* Do architecture until risks fall off your radar
* minimal design up front, so that you will not pay a ... | I think that mostly you are mixing the wrong levels of abstraction and thus, you are getting stuck.
First of all, there can be requirements to change the architecture, but they do not normally make good stories. Say for example you need to improve performance by x%. This is not a user story and it might not be achieva... | Agile architecture is a running gunbattle. I try to implement it in a just-in-time methodology, but ultimately, it is in direct opposition to agile methodologies. That doesn't mean it's bad. It is very important, it's just not something that fits into the agile process.
Up front architecture and design is really ... | https://softwareengineering.stackexchange.com |
330,594 | [
"https://physics.stackexchange.com/questions/330594",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/102349/"
] | <blockquote>
A man climbs up from ground to first floor using a ladder/stair. Assume that his kinetic energy does not change appreciably. Predict the sign of work done by ladder (if any).
</blockquote>
I think the answer should be 'positive' because the negative work done by gravity has to be countered and hence som... | The ladder (or the stairs) don't do any work at all. The reason for the same is that the ladder (or stairs) applies the force on our feet only when our feet are right in contact with the ladder (or the stairs). Thus, the point of application of force doesn't move at all while the force is being applied. Thus, net work ... | There is no work being done by the ladder/stairs. The man exerts a force on the stairs but as long as the stairs don't move, there is no energy being transferred. Work equals force times distance and this case the distance is 0.
That would be different if the ladder would deform. Than energy would be put into the ladd... | https://physics.stackexchange.com |
16,440 | [
"https://engineering.stackexchange.com/questions/16440",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/12295/"
] | I'm looking into manual pellet presses and the one in mind lists a 12T clamping force and then goes on to detail that the analogue gauge goes from 0- 24,000 lbs. Are these two numbers related? When I try to convert T to lbs I usually get 26,880 lbs for 12T.
Thanks!
| Regarding the different state space formulations. First, M might not be invertible. In many cases it will be invertible, but sometimes it will not be. In your specific case, this would correspond to a gear with zero mass. Obviously that never happens in the real world as all gears would have some finite mass. But th... | For any sinusoidal motion, the $\mathbf{q}$ really represents the motion $\Re(\mathbf{q}\,e^{i \omega t})$ in the time domain. $\mathbf{q}$ is complex because in general, the different elements of the eigenvector have different phase angles.
This will be the case for your problem since your first equation seems to co... | https://engineering.stackexchange.com |
437,751 | [
"https://stats.stackexchange.com/questions/437751",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/245746/"
] | As you know increase a data samples on training is a way to preventing of over fitting.
I'm working on an UCI data set with 198 samples and 34 feature this is my data set's dimension and I wanted to know what's the meaning of increasing our data to prevent of over fitting, I mean I should make a change on selecting te... | Since you are working with a given data set, you can't increase the amount of data, so you will have to use simpler models.
How much simpler? That depends on the model. There are some rules of thumb, e.g., for linear regression you want at least 10 observations for each independent variable; for logistic regression y... | It means literally going and getting more data. As in I took a survey of 100 people, and then decided I needed more data so I surveyed 50 more.
If you’re using UCI data, increasing your sample is not possible.
| https://stats.stackexchange.com |
500,150 | [
"https://physics.stackexchange.com/questions/500150",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/182803/"
] | Generally, the group velocity <span class="math-container">$v_g = \dfrac{\partial \omega}{\partial k}$</span> of a wave is the velocity of energy transport. In "Introduction to Solid State Physics", Kittel following is stated:
<blockquote>
The transmission velocity of a wave packet is the group velocity, given as th... | This is a good question that I have also had, so I'm answering this even though it is two years old! It looks like your definitions are all fine, but I would use
<span class="math-container">\begin{equation}
\hat{\mathcal{P}}\hat{\psi}^{}_{A}\hat{\mathcal{P}}^{-1} = \sum_{B} \hat{\psi}_{B}^{\dagger}(U_{P})_{B, A}
\... | The transformation rules given are correct. We have
<span class="math-container">\begin{align}
\hat{\mathcal{C}} \hat{\mathcal{H}} \hat{\mathcal{C}}^{-1} & =
\sum_{AB} \hat{\mathcal{C}} \hat{\psi}^{\dagger}_A \hat{\mathcal{C}}^{-1} \hat{\mathcal{C}} H_{AB} \hat{\mathcal{C}}^{-1} \hat{\mathcal{C}} \hat{\psi}_B \hat... | https://physics.stackexchange.com |
155,603 | [
"https://security.stackexchange.com/questions/155603",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/134969/"
] | Let me try to sum up this question; I want to buy VPS from (vultr - I'm not promoting them), but before that I'm wondering how secure is to run VPN on this kind (or any kind) of VPS in sense that I can endanger myself by choosing wrong company, which can tap/monitor my traffic.
I'm not trying to ask how secure is KVM ... | <blockquote>
What is the risk of running VPN on VPS?
</blockquote>
The main risk is that all traffic inside the VPN can be passively sniffed by the entity hosting the server.
Basically it is similar to giving someone physical access to a physical server. Actually the risk is a bit higher, because VPS could be passi... | <blockquote>
I'm wondering how secure is to run VPN on this kind (or any kind) of VPS in sense that I can endanger myself by choosing wrong company, which can tap/monitor my traffic.
</blockquote>
Take this as a compliment to the accepted answer:
This is something I've worried about before. If a VPN provider were ... | https://security.stackexchange.com |
324,046 | [
"https://stats.stackexchange.com/questions/324046",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/67137/"
] | I have 20 items rated on 25 dimensions. Each item was rated on each dimension ~30 times. Each of ~40 participants rated 15 of the 20 items on all of the dimensions.
I had originally thought to do PCA on the item means (i.e. averaging across all ratings for that item), but realized that I will have fewer observations t... | The term "weakly identified," as Gelman is using it in your linked post, means that there is a region of parameter space that produces similar likelihood values.
If you think of the likelihood as a surface, then a weakly identified model has a "flat" likelihood around the maximum likelihood solution... | in micro,it means the instrumental variables used for identification is weakly correalted with the endogenous varibles.
as for macro,i guess it means the parameter that are weakly identified can hardly correspond to an unique data process(as shown in your question)
| https://stats.stackexchange.com |
3,891,883 | [
"https://math.stackexchange.com/questions/3891883",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/29156/"
] | Book question: The concentration of salt in a cell, <span class="math-container">$X$</span>, can be modelled by a normal distribution with mean <span class="math-container">$\mu$</span> and standard deviation <span class="math-container">$2$</span>%. Find the value of <span class="math-container">$\alpha$</span> such t... | The textbook answer is correct. There's just a misunderstanding because the concentration is always misured in %. Thus the result is 3.29 (%, obviously).
Your error is due to the fact that you transformed in % a number that originally was already expressed in %
The correct solution was
<span class="math-container">$$\m... | It means the standard deviation is <span class="math-container">$0.02 \mu$</span>. So you should be looking at <span class="math-container">$N(\mu, (0.02 \mu)^2)$</span>.
| https://math.stackexchange.com |
350,719 | [
"https://softwareengineering.stackexchange.com/questions/350719",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/233528/"
] | thanks to the .NET evolution, today we have a lot of different frameworks and technologies. I'm very confused about the differences about it.
What is the difference between:
<ul>
<li>.NET Framework </li>
<li>ASP.NET </li>
<li>.NET Core </li>
<li>ASP.NET Core </li>
<li>.NET Standard </li>
</ul>
?
| <h1>.NET Framework</h1>
is a VM, a JIT compiler, an object memory system consisting of a memory allocator and a garbage collector, a loader, a linker, and a runtime system (collectively called the <em>Common Language Runtime (CLR)</em>) which executes and supports a language called <em>Microsoft Intermediate Language ... | ASP.NET Core is a web framework, building on top of .NET Core.
.NET Core is a set of libraries and a runtime, with which you can build any type of application (and on which ASP.NET Core is built).
The two projects are related, but have different release schedules.
<hr>
.NET Core and the .NET Framework are, at this ... | https://softwareengineering.stackexchange.com |
537,509 | [
"https://electronics.stackexchange.com/questions/537509",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/87817/"
] | In a classical chip, you have a main CPU to perform general processing and it acts as the master on a some bus and other slaves (IO, Memory) usually do not send command or data autonomously. (or at least that is my basic understanding, the master knows and waits a certain amount of time for a response)
Let's say I want... | <blockquote>
If that is the case, how would I know my scheduler received the correct data and not that of which another PE overwrote due to timing and the distance between the PEs to the scheduler?
</blockquote>
Alongside the actual data signals you have some "handshake" control signals, which tell the PE and... | <blockquote>
usually do not send command or data autonomously.
</blockquote>
That's the early 1980's. In the last decades, any microcontroller, SoC, and things usually just sold as "processor" have multiple devices on-package that all have "initiative access" to a shared bus – typically, for DMA pur... | https://electronics.stackexchange.com |
143,656 | [
"https://electronics.stackexchange.com/questions/143656",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/22818/"
] | I am trying to drive a Linear Actuator (stepper motor with a lead screw) to drive until a force of 15 pounds is reached then stop. I am having trouble finding a good method to do this (I am new to stepper motors) can anyone point me in the right direction?
I am thinking of getting the motor with an encoder and adjus... | If you're going to put a encoder on the stepper motor, then you might as well not use a stepper motor. The point of a stepper is to let you know accurate position open loop. If you're going to close the loop, then you can get other motors that are cheaper, more efficient, and smaller at the same torque.
A brushless ... | You could put a load cell on the nut if you want a really accurate force shutdown. You'll probably want to put some deliberate spring factor into the system so that each step represents a certain (rough) number of newtons force (or lbf in the Imperial system).
| https://electronics.stackexchange.com |
41,369 | [
"https://mechanics.stackexchange.com/questions/41369",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/3717/"
] | I'm looking at a used hybrid Lincoln MKZ with 70k miles. The manufacturer provides an 8-yr/100k mile warranty on the hybrid system, so I believe I should still be covered until 2019.
I've read that replacing the battery pack in any hybrid can cost a minimum of $2500 + labor.
Is there some diagnostic that a mechanic c... | At least Toyota has a special hybrid battery test that only the dealership can do. If you service your car regularly at the dealership, the test is performed annually and in Finland, this extends the warranty 1 year at a time to 10 years (with 350 000 km max). I suspect the actual test is performed continuously on the ... | I spoke to two Ford dealerships and they both said the hybrid system itself performs diagnostics, and if there is no error lit up on the dash, the hybrid system is working fine. The two mechanics I spoke with at the two different dealerships said they each had only replaced one hybrid battery in the 10+ years they had... | https://mechanics.stackexchange.com |
425,550 | [
"https://physics.stackexchange.com/questions/425550",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/29616/"
] | Can we define magnetic field at a point as:
<strong>Force on a point magnetic north pole at that
point divided by its pole strength.</strong>
<em>Anything wrong in this definition?</em>
(The concept of point magnetic pole is an idealization as point magnetic poles
don’t exist in nature and also there are no magnetic mo... | Your definition is exactly that of magnetic field strength, <strong>H</strong>, on the old cgs system. The oersted was its unit, a magnetic field strength of 1 dyne per unit pole. [A unit pole was such that if two unit poles were placed 1 cm apart in vacuo, there would be a force of 1 dyne between them.]
The study of ... | Instead of magnetic North Pole, you could refer to a moving charge with a known velocity as a test particle. This avoids the issue of monopoles you mention.
| https://physics.stackexchange.com |
110,941 | [
"https://softwareengineering.stackexchange.com/questions/110941",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/35028/"
] | I am at the moment messing around with clients and servers in C# winforms and I'm trying to implement it all asynchronously. However, I'm beginning to wonder, should I use asynchronous code for everything?
Here's a list of what I'm doing asynchronously at the moment:
<ol>
<li>TcpClient.BeginConnect with TcpClient.End... | Yes, it really is more efficient to do all this stuff asynchronously. If you do it synchronously then you're constantly polling, which wastes resources and can cause you to miss events if you don't process them quickly enough.
In addition, if you tried to do all that stuff synchronously, you'll find yourself mired in... | From the question, it sounds like you have concerns about the performance of asynchronous operations in certain circumstances. Asynchronous operations are incredibly fast and efficient because under the covers .NET uses thread pools: The threads to execute the code already exist and thus there is basically no penalty f... | https://softwareengineering.stackexchange.com |
953,875 | [
"https://math.stackexchange.com/questions/953875",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/9921/"
] | If we remove the connectedness restriction, there are easy counter examples, as in: $\left(\frac{1}{2}, \frac{1}{1}\right) \cup \left(\frac{1}{4}, \frac{1}{3 }\right) \cup \left(\frac{1}{6}, \frac{1}{5}\right) \cup \cdots$ which has $0$ in the closure but is not locally euclidean there.
| No, that's not true. Imagine three open triangles in $\mathbb{R}^2$ "meeting" at a vertex (they don't actually contain the point, but it's in their common closure). The triangles are also linked by an open annulus. See this picture:
<img src="https://i.stack.imgur.com/3zZoC.png" alt="figure">
Then the point at the cen... | No: look at an open cube .
<strong>Edit (October 2, 2014)</strong><br>
To clarify matters (since the question mentioned just the word "manifold"):<br>
$\bullet $ The closure of the open cube is not a "topological manifold" but a "topological manifold with boundary"
$\bullet \bullet $ The closure of the open cu... | https://math.stackexchange.com |
320,089 | [
"https://physics.stackexchange.com/questions/320089",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/43214/"
] | Assuming a steel wire with a Young's modulus of 400 GPa, which has a 1 mm. square cross section and 10 meters in length, what would be it's spring constant?
It is understood that Young's modulus is the special case spring constant where the cross section and length are one unit each.
I'm simpler words, the question c... | For a straight wire, the stiffness is given by $$k = \frac{EA}{L}$$ where $k$ is the stiffness (Newtons/meter), $E$ is Young's modulus (Pascals), $A$ is the cross section area (square meters), and $L$ is the length (meters).
Be careful with the units! Note, Young's Modulus (Pascals, or Newtons / <strong>meter squared<... | Young's modulus $E = \dfrac{\text{tensile stress}}{\text{tensile strain}} = \dfrac{\left(\frac F A \right )}{\left (\frac lL\right )} \Rightarrow F = \dfrac {EA}{L}\,l \Rightarrow \Delta F = \dfrac {EA}{L}\, \Delta l$
This gives the spring constant $k = \dfrac{\Delta F}{\Delta A} = \dfrac {EA}{L}$
If $A= 1\,\rm m^2$ ... | https://physics.stackexchange.com |
26,613 | [
"https://dsp.stackexchange.com/questions/26613",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/17937/"
] | if we have LTI system and we know unit step response of this system(we haven't original signal)
how we can calculate impulse response?
| You can find the impulse response
Let's take the case of a discrete system.
If $s[n]$ is the unit step response of the system, we can write
$$s[n]= u[n]\ast h[n]$$
where $h[n]$ is the impulse response of the system and $u[n]$ is the unit step function.
Now using commutative property you can write $$s[n]=h[n]\ast ... | With an LTI system, the impulse response is the derivative of the step response. Because the impulse function is the derivative of the step function. Derivative in, derivative out.
| https://dsp.stackexchange.com |
580 | [
"https://cs.stackexchange.com/questions/580",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/373/"
] | I understand the theory behind Bayesian networks, and am wondering what it takes to build one in practice. Let's say for this example, that I have a Bayesian (directed) network of 100 discrete random variables; each variable can take one of up to 10 values.
Do I store all the nodes in a DAG, and for each node store it... | The "best" data structure probably depends on what particular problem you're trying to solve with it. Here's one approach that I've seen (and have used myself), which simply stores all the information and leaves it up to the algorithm what to do with it.
<ol>
<li>First you index the nodes by unique integers, 0 through... | Basically discrete CPT are hypermatrixes, and you should look at them in this way.
A quite common way to represent an hypermatrix is to use an hashtable using string index. e.g. in 2 dimensions t[1][2] would be t.get("1_2")
More memory efficient solution are possible:
If the hypermatrix is sparse, you could use speci... | https://cs.stackexchange.com |
427,293 | [
"https://physics.stackexchange.com/questions/427293",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/-1/"
] | Why is tangential acceleration of an object moving in circular motion given by $\dfrac{d \vec{v}}{dt}$
I don't know why everywhere it is writen $$\vec{a_{net}}=\dfrac{\vec{v²}}{r} + \dfrac{\vec{dv}}{dt} \ ,$$ where $a_{net}$ is the net acceleration. But $\dfrac{d \vec{v}}{dt}$ is supposed to be the net acceleration.
| You seem to be confusing vector notation and scalar notation.
In general $\vec{a}=\frac{d \vec{v}}{dt}$.
In circular motion with tangential acceleration, total acceleration is composed of tangential acceleration and radial acceleration.
$a_r=\frac{|v|^2}{r}$
$a_t=\frac{d|v|}{dt}$
The last two equation are concerne... | $A_\text{net}$ in translational motion is always defined as the time derivative of the velocity of the centre of mass.
But now in the case of circular motion, a whole new force called the centripetal force comes into existence.
This creates an acceleration , known as centripetal acceleration, which is always direct... | https://physics.stackexchange.com |
625,089 | [
"https://electronics.stackexchange.com/questions/625089",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/274143/"
] | I am trying to set res to "----" which is done in an example in my book. When I run the following code I get the message "failure1":
<pre><code> library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.NUMERIC_STD_UNSIGNED.ALL;
entity alu is
port(a,b: in STD_LOGIC_VECTOR(3 downto 0);
aluc: ... | You have a very subtle problem.
The short answer is, for this problem, do not use the package <code>ieee.numeric_std_unsigned</code>.
If you look in <code>ieee.std_logic_1164</code>, you will find that it does not overload the implicitly defined <code>=</code> operator. Hence, matching will be character based - probab... | I am pretty sure it is because it doesn't make sense to assign a Don't Care. Don't Care is a umbrella grouping that represents multiple valid, but distinct, values so it only makes sense as a comparison condition, not as a write value because you can only write one value.
It's like positive or negative numbers. Each re... | https://electronics.stackexchange.com |
11,217 | [
"https://dsp.stackexchange.com/questions/11217",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/4376/"
] | Does the entropy of a symbol represent the most optimal average number of bits that can be used to represent a symbol? For example take the example of tossing a coin:
$$
H_{source} = -p_{head} log_2 p_{head} - p_{tail} log_2 p_{tail}
$$
so if
$$
p_{head} = p_{tail} = \frac{1}{2}
$$
then H = 1 bit, but if
... | Shannon's Lossless Source Coding theorem states that the expected length of any code is lower bounded by the entropy of the probability distribution over the symbols for that code:
$$
H\left(X\right) \leq \mathbb{E}_{P_{X}}\left(l \circ f\right)
$$
where $\circ$ denotes the function composition operation, and $l$ is ... | My understanding of entropy (as it applies to a system) is that it represents the number of different states a system can have. In the case of a coin toss, there's only one bit of entropy to represent which side of the coin it lands on (Assuming it always lands flat on one side). In a series of 10 coin tosses, you woul... | https://dsp.stackexchange.com |
300,270 | [
"https://electronics.stackexchange.com/questions/300270",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/15716/"
] | I can't find a complete answer for this anywhere, and I want to fill the gap in my knowledge of MCUs.
<ul>
<li>In MCUs why do I need any other component except, maybe, a voltage regulator and an external clock?</li>
<li>Why do PCBs with embedded MCUs look so complicated?</li>
<li>If I were to design a minimal PCB with... | <blockquote>
In MCUs why do I need any other component except maybe a voltage
regulator and an external clock?
</blockquote>
Some of the extra components are actually recommended, even for a minimum complexity design:
<ul>
<li>Capacitors required by the voltage regulator for stability and load/line regulation per... | Some microcontroller indeed only require a bypass cap to operate. Others require some kind of external clock, like a crystal, resonator, R-C, or a digital signal fed in from elsewhere. Newer micros tend to have internal clocks, but these are usually only good to a few percent accuracy.
Boards with micros can be comp... | https://electronics.stackexchange.com |
954,364 | [
"https://math.stackexchange.com/questions/954364",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/177903/"
] | When I read about mathematical history I hear of breakthroughs. For example, Cartesian geometry, Newton/Leibniz Calculus, and so on. My question is this: What are some recent epoch-making breakthroughs in maths? I'm more interested in theories/new branches of maths such as cartesian geometry and calculus, rather than t... | Two things that happened after Galois and created new branches of mathematics:
<ol>
<li>Cantor's foundations of set theory. </li>
<li>The creation of functional analysis by the Polish school around Banach. </li>
</ol>
| I suggest category theory, not because of the investigations of more or less exotic categories, but because of how different theories are coupled together through functors and become comparable.
| https://math.stackexchange.com |
745,017 | [
"https://physics.stackexchange.com/questions/745017",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/355569/"
] | If a bullet strikes a block which is sitting on a table (with friction) is it correct that momentum will not be conserved because the friction is force on the system? I'm assuming that I could then use conservation of energy assuming I know the friction coefficient of the block and therefore the work done by friction. ... | When we do quantum field theory, we still are doing quantum mechanics. We don't normally work a lot with a wave function explicitly because the wavefunction (other than perhaps the vacuum state) is quite complicated (and hard to prepare in many cases).
Nevertheless, all the postulates of Quantum Mechanics still hold, ... | The problem connecting QFT and <span class="math-container">$N$</span>-body quantum mechanics isn't so much with QFT but rather with relativistic field theories. For a non-relativistic theory the connection is actually quite straight forward, if we define the one-particle momentum states by
<span class="math-container"... | https://physics.stackexchange.com |
160,993 | [
"https://physics.stackexchange.com/questions/160993",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/57434/"
] | Why never clockwise? How does it 'know' to go anticlockwise?
| The direction of the magnetic field is defined in terms of its effect on a current (or moving charge). Specifically, the magnetic field points in a direction such that the force on a current will be in the $\vec{I}\times\vec{B}$ direction. (That's just a convention; there's no fundamental reason you must define the m... | The magnetic field is not a "vector", instead it is a bi-vector (skew-symmetrical tensor). In other words, it has a plane of action not direction. Here is a quote from Hermann Weyl
"It may be justifiable on the grounds of economy of expression to replace skewsymmetrical
tensors by vectors in ordinary vector analysis, b... | https://physics.stackexchange.com |
24,820 | [
"https://dba.stackexchange.com/questions/24820",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/2275/"
] | We have a process which selects a record from a progress table, then issues an update against that record.
If we do not do the select, then the update works all day long. If we do the select, then the update times out.
The select query is pretty simple and looks like:
<pre><code>select fg."alphakey", n."first-name"... | We were executing our queries through the Progress OpenEdge ODBC drivers.
The <code>Default Isolation Level</code> was set on the driver to be <code>Read Committed</code>. We had made this choice not realizing that <code>SELECT</code>s caused some long running table locks, when all we were after was to make sure that... | If dirty reads is not an issue in this scenario, you could try the table hint readuncommitted or nolock..
<pre><code>pub.name n WITH(NOLOCK)
join pub.[family-guardian] fg WITH(NOLOCK)
</code></pre>
| https://dba.stackexchange.com |
376,595 | [
"https://physics.stackexchange.com/questions/376595",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/131341/"
] | <blockquote>
Air pressure decreases with increasing altitude. So why is
air near the surface not continuously drawn upward toward the
lower-pressure regions above?
</blockquote>
Does this have anything to do with convection currents? Or how pressure variates with temperature across the atmosphere?
I'm not bein... | For simplicity, let's just think of a perfectly spherical planet with a uniform gravitational field and an atmosphere with constant static pressure everywhere at a given altitude.
What would happen if all the air at the surface somehow began to rise? A vacuum would be created at the surface, which is intuitively unsu... | Each layer of the atmosphere is in static equilibrium, so there are is no motion of air vertically. The barometric equation is derived from this assumption of static equilibrium.
The pressure below is greater than the pressure above, so there is a net force downwards due to pressure. However, the weight of air in the ... | https://physics.stackexchange.com |
668,743 | [
"https://physics.stackexchange.com/questions/668743",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/315173/"
] | This is a question that has bothered me for quite some time but I don't have a clue where to start in researching it.
Let's say we have a string which is arbitrarily long, light enough to not take much effort to pull but rigid enough that it would not break or stretch. If I now stand at one end of the string and pull o... | First of all, you can't even imagine the force required to pull a string of length equal to or more than <span class="math-container">$3×10^8\ \text{m}$</span>. Now, imagine you have the force to pull it, but it is nearly impossible to make a string of that rigidity. It can't withstand that enormous force.<br />
Now, i... | No. When you pull really fast on one end of the string, that pull gets transmitted along its length to the other end at the <em>speed of sound waves</em> in the string. This may be several thousand feet per second, but is nowhere near the speed of light.
| https://physics.stackexchange.com |
73,450 | [
"https://mathoverflow.net/questions/73450",
"https://mathoverflow.net",
"https://mathoverflow.net/users/9947/"
] | Let $X$ be a (quasi-)projective, nonsingular, complex variety. Denote by $\mathcal{T}_X$ its tangent sheaf and by $X^{\mathrm{an}}$ its analytification. I am looking for a proof for the equality
$\displaystyle \int_X c_n(\mathcal{T}_X) = \chi(X^{\mathrm{an}})$,
i.e. the degree of the top c... | As an alternative to R. Budney's answer, one might also notice that the Gauss-Bonnet formula (the one you mention - mind that you must assume that $X$ is projective, otherwise the integral might not even make sense) is a consequence of the Hirzebruch-Riemann-Roch theorem. Indeed, the HRR theorem says
$$
\chi(V)=\int_{X... | I'll convert my comments to an answer.
Characteristic classes were originally defined as obstruction classes, going back to the work of Whitney and Stiefel. The top Chern class of a complex bundle is the obstruction to an everywhere non-zero vector field, and frequently called the Euler class.
The reason for th... | https://mathoverflow.net |
425,022 | [
"https://stats.stackexchange.com/questions/425022",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/234488/"
] | I had a non-normal distribution of my variable of interest which required log10-transformation to reduce outliers. This was then standardized, to a mean of 0 and sd of 1 (z-score?). I now want to obtain percentile values from the standardized values. For example, how do I obtain the 75th percentile of my variable given... | As long as you’re using mini-batching for both, you’ve described the same procedure in two different ways. Dividing the <span class="math-container">$M \times N$</span> shuffled samples into <span class="math-container">$M$</span> epochs is the same number of updates as all <span class="math-container">$M\times N$</spa... | The entire idea of mini batches is two fold
<ol>
<li><strong>Faster Epoch Processing Time</strong></li>
</ol>
A lower epoch processing time helps you evaluate the progress of your model, and make necessary adjustments etc
<ol start="2">
<li><strong>A more Generalized Model</strong></li>
</ol>
Since your model is fo... | https://stats.stackexchange.com |
304,362 | [
"https://softwareengineering.stackexchange.com/questions/304362",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/206604/"
] | So I'm developing an application which is using an IoC container. Now I need some helper methods for array manipulation like set, get, etc. I see two possible ways to go:
<ol>
<li>Using a class with static methods.</li>
<li>Using a class with non-static methods registered in the IoC container.</li>
</ol>
When using m... | There's nothing wrong with static methods. That's one of those things people say to sound smart and shocking, but the reality is much more subtle and can't be explained in the title of a blog post!
So why not static methods? Static methods can't be part of a contract. That means you can't implement more than one versi... | Either way works. Personally, I have written similar classes for things like array manipulation and math functions. I used static methods because those things are true functions and do not operate on any encapsulated data, so it seemed to make more conceptual sense. Plus, I didn't want to have to instantiate an obje... | https://softwareengineering.stackexchange.com |
355,513 | [
"https://physics.stackexchange.com/questions/355513",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/128737/"
] | If I have one of the following pair of qubits:
$$
\frac{1}{\sqrt{2}}(|0\rangle+i|1\rangle)\text{ , }\frac{1}{\sqrt{2}}(i|0\rangle+|1\rangle)
$$
And I measure it, I'll not be able to distinguish one from the other since they'll have the same probability on the computational basis. But I know that there is a unitary matr... | The two operators are not identical, however they approach to each other in the semiclassical limit. To show that, we can compute matrix elements of the two expressions in a complete set of states and show that the matrix elements approach each other. (Strictly speaking this is weak convergence).
I'll perform the comp... | The answer given by @David Bar Moshe is enlightening but, seems to me, not so accurate since the <span class="math-container">$x_i$</span> and <span class="math-container">$p_i$</span> are merely labels of the coherent states, not the actual quantum operators (neither in first nor in second-quantized form).<span class=... | https://physics.stackexchange.com |
152,827 | [
"https://electronics.stackexchange.com/questions/152827",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/34600/"
] | I need to emit a unidirectional infrared pattern, i.e. the emission cone should have small angle on one dimension and large angle on the other one (basically laser-like in one dimension and normal light on the other). I tried to illustrate this in the image below (alpha should be much bigger than beta, e.g. alpha = 90 ... | It's very difficult to collimate an LED output efficiently, and LED output is not coherent.
But, many laser diodes naturally emit a pattern like you drew. The reason is that the laser cavity is typically several microns across in the horizontal direction, but only a fraction of a micron tall in the vertical dimension. ... | A cylindrical lens focuses the light in only one direction. If you place it "one focal length" in front of your LED you will get the desired emission cone.
Compared to lasers, LEDs emit from a rather large surface, which limits by how much the light can be collimated.
| https://electronics.stackexchange.com |
11,007 | [
"https://softwareengineering.stackexchange.com/questions/11007",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/2210/"
] | Most of my fellow students that I've talked to claim that aiming for good grades is useless as the companies don't care about them when hiring programmers. To them, it's enough to have simply attended courses which may be important, and that's that.
Is this true? Are university grades useless when leaving campus, or d... | Incorrect. Grades are important especially if you have no or little professional programming experience. It's the bulk of your resume until you have professional experience.
| <strong>They are useful if you don't have real work experience.</strong>
If a potential employer has nothing else to go by (no work experience, open source project development, etc), then that's the only physical thing they can evaluate you by. Typically, it doesn't matter as much as you actually knowing your stuff. ... | https://softwareengineering.stackexchange.com |
349,722 | [
"https://mathoverflow.net/questions/349722",
"https://mathoverflow.net",
"https://mathoverflow.net/users/142929/"
] | I would like to ask about if you know papers containing remarkable achievements that were written by contemporary physicists concerning the distribution of prime numbers (or closely related, maybe the distribution of the zeros of the Riemann zeta function) in the spirit of the modern analytic number theory.
I am askin... | I would nominate Sir Michael Berry, FRS. According to Wikipedia, "He is known for the Berry phase, a phenomenon observed e.g. in quantum mechanics and optics, as well as Berry connection and curvature. He specialises in semiclassical physics (asymptotic physics, quantum chaos), applied to wave phenomena in quantum mec... | The <A HREF="https://en.wikipedia.org/wiki/Montgomery%27s_pair_correlation_conjecture" rel="noreferrer">connection</A> between the distribution of the Riemann zero's and the distribution of the eigenvalues of random unitary matrices was noted by the physicist <A HREF="https://en.wikipedia.org/wiki/Freeman_Dyson" rel="n... | https://mathoverflow.net |
52,004 | [
"https://electronics.stackexchange.com/questions/52004",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/2574/"
] | Most of ARM programmers come with BSL,RESET,TXD, RXD, GND and VCC pins which we need to connect with respective pins of ARM.
For ISP, We require need to ground P0.14/BSL after Reset.
As these programmers have Both BSL and RESET pins, Does programmer itself Resets controller and pulls BSL to ground OR do I need to fi... | As starblue points out, you are referring to the LPC range of microcontrollers. Mentioning this in the title and/or text of your question is advisable.
Whether the programmer pulls BSL low for you (and also whether it resets the chip for you!) depends on the programmer and the PC software you use.
FlashMagic and lpc2... | The boot loader in the controller samples the pin(s) which decide whether to enter the boot loader shortly after reset. Once it has entered the boot loader there is no timeout and you have to reset the controller again to start the application.
Note that the pin(s) used may differ depending on the specific series of ... | https://electronics.stackexchange.com |
41,883 | [
"https://softwareengineering.stackexchange.com/questions/41883",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/14491/"
] | It seems like most of common web browsers (Firefox, Chrome, Safari) are developed using C++. Whys is that so?
| Another way to ask the question is what kind of support does a browser need? The short list is:
<ul>
<li>Support for parsing (needed to make sense of [X]HTML, CSS, and [ECMA/Java]Script)</li>
<li>Tree walking/interpreting features (part of parsing and building UI)</li>
<li>Support for <em>accelerated</em> graphics</l... | I've decided to write a novel about this in hopes that people will gloss over it and upvote me. No, no, just kidding! I suffered over every word. Every word, I tell you!
<h2>Ask 'when' before 'why'</h2>
All major web browsers can trace their origins back to the 90s. Konqueror became Safari and Chrome; Netscape became... | https://softwareengineering.stackexchange.com |
61,538 | [
"https://electronics.stackexchange.com/questions/61538",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5146/"
] | I have a 10 character x 16 segment display that I'm driving using multiplexing off a PIC. The problem is, however, that with each display only being on 1/10th of the time, the display appears much dimmer than it normally would. Currently the LED's are getting their recommended voltage - 2.2 volts across each red segmen... | You can overdrive an LED with more than the rated current. The destruction of an overdriven LED is caused (mostly) by the heat generated in the junction (P=IV, and I scales exponentially with forward voltage, V, so power is a higher exponential in V). If you can contrive to keep the heat within reasonable boundaries, p... | No... upping the current is what you want to do to increase brightness. Said differently, LED brightness is a function of current passed through them. Many LEDs can handle upwards of 100mA at 10% duty cycle. So long as you control the duty cycle, that's the way to go.
| https://electronics.stackexchange.com |
297,774 | [
"https://physics.stackexchange.com/questions/297774",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/138722/"
] | My friend told me about an equation $m(v) = \dfrac{m_0}{\sqrt{1-\left(\frac{v}{c}\right)^2}}.$
I checked the internet and saw the same equation as well.
Then I was just playing around with it.
I just googled for the mass of light and they gave the answer $0$.
I thought that in the case of light the equation would b... | For any general body, the energy (in a relativistic framework) is given by,
$E=\sqrt{m_0^2c^4+p^2c^2}=m(v)c^2$
For a photon, the rest mass $m_0=0$, and it's energy $E=pc$. The relativistic mass $m(v)$ is <em>not zero</em> for the photon. Also, the momentum $p=m(v)v$, not $m_0v$, so the formulas are consistent too.
F... | For light we have <br>
$ E = hf = mc^2$<br>
so
$\dfrac{hf}{c^2} = m$<br>
we then plug $m_0$
$\dfrac{m_0}{\sqrt{1-\left(\frac{v}{c}\right)^2}} = \dfrac{hf}{c^2}$
so $m_0 = \dfrac{hf}{c^2} \sqrt{1-\frac{v^2}{c^2}}$
since light is traveling with v = c
$ m_0 = (\dfrac{hf}{c^2})\sqrt{1-\frac{c^2}{c^2}} $<br>
$ m_0 ... | https://physics.stackexchange.com |
23,028 | [
"https://mechanics.stackexchange.com/questions/23028",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/4906/"
] | I was told that I should leave my wheels straight when I park my car on flat driveway, I think this is rubbish and it doesn't matter personally
Should I leave my wheels straight when I'm parked?
What about when I stop the engine, and then turn the wheel to engage the steering lock?
| The only time you <em>really</em> need to turn your wheels when parked is when parking on a hill. Uphill you should point your wheels away from the curb. When pointing downhill you should point your wheels towards the curb. This is so if the parking mechanism should fail, the curb will hopefully stop the momentum of th... | As Paulster2 says, as far as your car is concerned, it really doesn't matter, but if your parking brake/gear fails (from being tapped by another car, e.g.) you want the curb, if there is one, to act like a chock block. If there is no curb, then you want your car to roll away from traffic.
| https://mechanics.stackexchange.com |
121,568 | [
"https://mathoverflow.net/questions/121568",
"https://mathoverflow.net",
"https://mathoverflow.net/users/10035/"
] | Given $a \in \mathbb{Z}$ with $a > 1$. Let $g(x) \in \mathbb{Z}[x]$ be a polynomial with $g(a)=\pm 1$. Let $h(x) \in \mathbb{Z}[x]$ be a polynomial with $h(a)= p$, a prime. Let $g(x)$ and $h(x)$ have not all coefficients negative nor positive. Can $g(x)h(x)$ have only positive or only negative coefficients? Is there... | $$
g(x)h(x)=(x^2-4x+5)(x^{14}+5x^{13}+16x^{12}+40x^{11}+81x^{10}+125x^9+96x^8
$$
$$
\qquad -x^7+6x^5+25x^4+71x^3+160x^2+286x+355)
$$
$$
=x^{16}+x^{!5}+x^{14}+x^{13}+x^{12}+x^{11}+x^{10}+240x^9+484x^8
$$
$$
+ x^7 + x^6 + x^5 + x^4 + x^3 + 11x^2 + 10x + 1775.
$$
$g(2)=1$, $h(2)=378919$.
In fact, it is known that e... | $\eqalign{g(x)h(x)&=(5x^3+14x^2-3x+1)(x^3-x^2+4x+1)\cr&=5x^6+9x^5+3x^4+65x^3+3x^2+x+1\cr}$
$g(-3)=1$, $h(-3)=-47$.
| https://mathoverflow.net |
3,438,947 | [
"https://math.stackexchange.com/questions/3438947",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/417020/"
] | Let <span class="math-container">$f \in C[a,b]$</span> define <span class="math-container">$\|f\| _{1} =\int_{a}^{b} |f|.$</span>
(b)Show that there is no number <span class="math-container">$l$</span> such that<span class="math-container">$\|f\|_{\max} \leq l \|f\| _{1},
\forall f \in C[a,b].$</span>
Could anyone ... | Let <span class="math-container">$f_n(x)=n(\frac 1 n-x) $</span> for <span class="math-container">$0 \leq x\leq \frac 1n$</span> and <span class="math-container">$f_n(x)=0$</span> for <span class="math-container">$x> \frac 1 n$</span>. Then the sup norm tends to <span class="math-container">$\infty$</span> but the... | Without loss of generality, let <span class="math-container">$[a,b]=[-1,1]$</span>. Consider <span class="math-container">$f_{n}(x)=-1$</span> for <span class="math-container">$-1\leq x\leq -1/n$</span> and <span class="math-container">$f_{n}(x)=x$</span> for <span class="math-container">$-1/n\leq x\leq 1/n$</span>, an... | https://math.stackexchange.com |
41,503 | [
"https://physics.stackexchange.com/questions/41503",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/14095/"
] | In my old house there are two old tube lights. Some times they don't start properly, (specially at evening time, may be it is because of low voltage), they starts flickering i.e. on and off continuously. And when my elder brother touches them, mostly at center they just goes on. Even i have tried many times, the touchi... | I've found this to be the case, too. Generally, my shop lights will flicker when turning on, especially when it is colder outside .
There are two basic phases to this kind of light bulb: a start-up phase, and an operating phase. The start-up requires more voltage, because you are initiating the plasma stream between ... | I'll throw this into the mix. If I plug in one end of my guitar cable to my amp, turn the amp on, bring up the volume a little, and touch only the center contact on the other end of the cable, I get a loud 60 Hertz buzz from my amp. I believe this is because my body is acting as an antenna - picking up some radiation f... | https://physics.stackexchange.com |
357,242 | [
"https://softwareengineering.stackexchange.com/questions/357242",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/270271/"
] | I have an array that contains over 150,000+ object pointers of over 300+ different classes, but they all inherit from the same base class. Obviously that's very inefficient when we need to search for an object.
I've thought about splitting this array <em>per-object-type</em>, which got some better performance, but not... | It seems to me that you have a lot of already implemented code, and you want to just optimize your search.
Also, it seems to me that your search cannot be entirely refactored (by changing the filter criteria).
Since you already tried a improvement of searching only within the set of the specific Type of your object, ... | Performance has two parts:
<ul>
<li>Do as little work as possible.</li>
<li>What work you do, do as quickly as possible.</li>
</ul>
Here the second part can be addressed fairly quickly: don't use <code>dynamic_cast</code>, we'll look at ways to avoid that in a minute. Don't construct the same object over and over aga... | https://softwareengineering.stackexchange.com |
302,287 | [
"https://physics.stackexchange.com/questions/302287",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/115887/"
] | I am studying Anderson Fundamentals of Aerodynamics on my own (as a physics major), and have been struggling to understand the distinction between lifting and non-lifting flow (in particular, around a cylinder) and some of the heuristics he uses.
Anderson begins by solving Laplace equation around a cylinder (i.e. $D=... | <ol>
<li>The Laplace equation for the potential has unique solutions (up to an irrelevant constant) only when boundary conditions are given <em>everywhere</em> on the boundary of the domain. In your case, such conditions were only given on the cylinder surface. In this case there is an infinite family of possible solut... | I don't have the book in front of me, but the essential point is that for must "real world" flow situations, the fluid viscosity is very relevant in formulating the boundary conditions (i.e. there is no "slip" between the tangential velocity of the boundary and a viscous fluid), but its effect on the solution in away f... | https://physics.stackexchange.com |
234,509 | [
"https://security.stackexchange.com/questions/234509",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/238197/"
] | I'm not from Information Security or any IT related area. But I want to know if there is any security reason for my digital bank to demand my phone to be on "Automatic Date & Time"?
For example, if I'm abroad, I cannot transfer some money to a friend, because a dialog box says that my date and time is inc... | One of the reasons can be the usage of the digital signature. If the time on your phone differs essentially from the actual current time, this may cause your phone to reject signatures done by the bank server, or your bank to reject signatures done by your phone.
Why is "Automatic Date & Time" important? ... | There are numerous security algorithms that limit the window of time in which something is valid.
Regardless of the security mechanism, the concept is that a code is generated that can be used to authenticate or prove an identity. But given time, any code <em>could</em> be broken. So the idea is to limit the amount of... | https://security.stackexchange.com |
35,675 | [
"https://engineering.stackexchange.com/questions/35675",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/16386/"
] | I have seen plenty of YouTube videos in which they use carbon fiber fabric to build various things. One such channel is Mike's Patey's channel where he makes amazing aircrafts from carbon fiber.
In these videos I usually see (but not always) that after they apply the resin to the fiber fabric, they put the structure i... | Solar Mike's answer is accurate.
Carbon fiber has a resin to fiber ratio which provides the optimum strength. This is typically measured by weight. The amount of resin is applied to the fiber prior to enclosing it for vacuum application.
Once the vacuum begins, all of the air is removed from the fiber, forcing the r... | There are two reasons:
One is to remove trapped air bubbles
and
two to pack the fibres as densely as possible within the structure or weave of the fibre pattern wanted.
| https://engineering.stackexchange.com |
24,751 | [
"https://electronics.stackexchange.com/questions/24751",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/7425/"
] | I'm trying to repair a bread making machine (A Tefal/Moulinex OW500530). At the start of the program (kneading), it drives the brushed DC motor (ZYT4245-23) in short pulses every second. Now and then, the motor won't start. It will start again when I help it a bit, though. A bit further into the program, the kneading i... | If I understand you correctly, I think shorting the commutator plates for the dead pole to the adjacent working one (either side should work I guess) may actually be worth trying.
With more than e.g. 3 poles it should be okay as you won't short across the input as the brushes touch both poles.<br>
Since your motor app... | If the coil between two connectors has broken (the wire has melted and become open circuit) you will need to remove all the copper wire from that coil and re-wind a new coil.
Not a simple job for the beginner - you will need to get the right grade of copper wire and wind the right number of turns.
| https://electronics.stackexchange.com |
212,993 | [
"https://physics.stackexchange.com/questions/212993",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/95773/"
] | As I understand relativity, time is relative to your velocity, meaning your watch moves slower relative to those who are stationary when moving at great speeds.
<ol>
<li>So if that's true, then when we talk about "light years", is that a distance based on year at some average Earth velocity? </li>
<li>Furthermore if ... | There are some misconceptions in your question, and you are really asking two different things.
First, remember that if you are on a spaceship moving at high speeds, Earth people will measure your watch as moving slower than theirs and you will measure their watches as moving slower than yours! Relativity works boths ... | When we talk about distances in light-years we mean the distance from the Earth to some other object in terms of the distance that light travels as measured in any inertial frame of reference. It really doesn't matter which particular inertial frame of reference you use because light always travels at the speed <em>c</... | https://physics.stackexchange.com |
325,451 | [
"https://stats.stackexchange.com/questions/325451",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/158797/"
] | I have a question and would like to hear what the community has to say. Suppose you are training a deep learning neural network. The implementation details are not relevant for my question. I know very well that if you choose a learning rate that is too big, you end up with a cost function that may becomes nan (if, for... | Well, if you get NaN values in your cost function, it means that the input is outside of the function domain. E.g. the logarithm of 0. Or it could be in the domain analytically, but due to numerical errors we get the same problem (e.g. a small value gets rounded to 0).
It has nothing to do with an inability to "settle"... | Possible reasons:
<ol>
<li>Gradient blow up</li>
<li>Your input contains nan (or unexpected values) </li>
<li>Loss function not implemented properly</li>
<li>Numerical instability in the Deep learning framework</li>
</ol>
You can check whether it always becomes nan when fed with a particular input or is it completely... | https://stats.stackexchange.com |
164,256 | [
"https://softwareengineering.stackexchange.com/questions/164256",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/29526/"
] | I typically agree with most code analysis warnings, and I try to adhere to them. However, I'm having a harder time with this one:
<blockquote>
CA1031: Do not catch general exception types
</blockquote>
I understand the rationale for this rule. But, in practice, if I want to take the same action regardless of the ex... | These rules are <strong>generally</strong> a good idea and thus should be followed.
<strong>But</strong> remember these are generic rules. They don't cover all situations. They cover the most common situations. If you have a specific situation and you can make the argument that your technique is better (and you should... | Yes, catching general exceptions is a bad thing. An exception usually means that the program cannot do what you asked it to do.
There are a few types of exceptions that you <em>could</em> handle:
<ul>
<li><em>Fatal exceptions</em>: out of memory, stack overflow, etc. Some supernatural force just messed up your univer... | https://softwareengineering.stackexchange.com |
3,321 | [
"https://dsp.stackexchange.com/questions/3321",
"https://dsp.stackexchange.com",
"https://dsp.stackexchange.com/users/1864/"
] | I'm trying to transforming an already know signal from time domain to frequency domain using <code>fft</code> function in MATLAB. And I got different values of amplitude when I change the value of length of signal $L$. I'm therefore wondering if there is a rule to choose the length of signal when calculating FFT.
I ha... | Mai,
The length of the FFT depends on what application you are doing. A very course summary follows:
<strong>Same size FFT:</strong>
<ul>
<li>Analysis: This just means you want to 'analyse' the signal - look and see what type of spectrum it has, maybe patterns in the spectrums, etc. The 'usual' default is to simply... | A longer FFT will divide up the frequency range into more "bins" between DC (0 Hz) and Fs/2. So the result bin of a particular frequency may be in a different bin number for different lengths of FFT. Depending on the FFT implementation, you may also need to divide by the length of the FFT or the square root of the le... | https://dsp.stackexchange.com |
383,547 | [
"https://mathoverflow.net/questions/383547",
"https://mathoverflow.net",
"https://mathoverflow.net/users/13441/"
] | Consider <span class="math-container">$\mathbb CP^n$</span> and let <span class="math-container">$H\subset \mathbb CP^n$</span> be a hyperplane. Suppose <span class="math-container">$\varphi: \mathbb CP^n\to H$</span> is a rational map that fixes <span class="math-container">$H$</span> pointwise. I believe that <span c... | With the additional restriction, <span class="math-container">$\varphi$</span> is indeed a linear projection.
Applying a linear change of coordinates, <span class="math-container">$H$</span> is given by <span class="math-container">$x_0=0$</span>, so <span class="math-container">$\varphi$</span> is
<span class="math-co... | Take <span class="math-container">$p_1,p_2,p_3,p_4\in\mathbb{P}^2$</span> general points and fix a line <span class="math-container">$L$</span> passing through <span class="math-container">$p_1$</span> but not containing <span class="math-container">$p_2,p_3,p_4$</span>.
Take <span class="math-container">$x\in\mathbb{P... | https://mathoverflow.net |
253,905 | [
"https://stats.stackexchange.com/questions/253905",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/108150/"
] | In Casella Berger's Statistical Inference, they define a <strong>power function</strong> of a hypothesis test with rejection region $R$ to be the function of $\theta$ define by $\beta(\theta) = P_\theta(X\in R)$ for some data $X$. Suppose that $H_0: \theta\in \Theta_0$ and $H_1: \theta \in \Theta_0^c$.
Furthermore, th... | Consider if you have a simple null, like $\mu=\mu_0$ against a two-sided alternative. Then your power function has a "hole" at $\mu_0$.
The usual definition of power function fills in the hole, making the power function defined for all possible values of $\theta$.
Sure, at that point it's not power, but calling it ... | Power is the probability that the observation is in the rejection region when some value in the parameter space of the alternative is correct (falsely rejecting the null hypothesis). But when the two distributions are identical, the rejection region for the null hypothesis also corresponds to the non-rejection region ... | https://stats.stackexchange.com |
158,114 | [
"https://stats.stackexchange.com/questions/158114",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/77950/"
] | I have a data set with 900,000 rows and 8 features. I want to look at the significance of each feature so that I can evaluate whether the features I add are viable or not.
One method I am using after doing some research is the Lasso method, which from my understanding comes up with coefficients for each variable by tr... | Lasso basically selects variables in a linear model, $Y=X\beta+e$ using a tuning parameter ($\alpha$ in your case). It utilizes a penalty term to penalize some coefficients toward zero. Notice that the main advantage of lasso is in high-dimensional data (when there are more variables than observations). The procedure i... | The coefficients displayed are the estimates for $w$ in your equation. When $|w|$ is large, a 1-unit change in the corresponding feature is estimated to have a large effect on $y$, all else being equal. That is, the usual interpretation of a linear model applies.
Features with coefficients that are $0$ are deemed to h... | https://stats.stackexchange.com |
15,168 | [
"https://stats.stackexchange.com/questions/15168",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/6096/"
] | If I have a significant correlation coefficient of r=.80 between Variable A and B, I can work out the effect size (coefficient of determination) by squaring it, which is 64%.
I want to graph this in the simplest way possibe (given my non-statistical target audience). Can I use a 100% stacked bar graph for this purpos... | I agree with the person who suggested a scatterplot. An R-square gives the proportion of variance <em>statistically</em> explained by A. It doesn't give the effect size in the way I think you mean. If you just want to illustrate a proportion, any figure would do, but very little information is conveyed. The "effect" of... | Such bar plots are almost completely devoid of content. I would instead show scatterplots of B vs each A, which will really illustrate the relationships. You can fit a surprising number of scatterplots into a small space.
| https://stats.stackexchange.com |
146,306 | [
"https://physics.stackexchange.com/questions/146306",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/-1/"
] | In deriving the power of a circuit we can do the following:
$$\text{P}=\frac{dw}{dt}=\frac{dQ}{dt}\frac{dw}{dQ}=\text{IV}$$
But this assumes that $V$ (since $w=VQ$) is a constant. Why can we assume this, this is surely not the case for a capacitor where the voltage across it does change with time?
where $Q$ is charge a... | The "derivation" you describe is valid at a particular moment in time.
$$\begin{align}\Delta E &= V \Delta Q\\
\frac{dE}{dt} &= V \frac{dQ}{dt} \\&= VI\\
P(t) &= V(t) I(t)\end{align}$$
I added the dependence on time explicitly.
To address your comments:
$W=QV$ is only true when $V$ is constant; you... | Power is an instantaneous concept. $P=IV$ gives the instantaneous power at a given instant of time, given $V$ and $I$ at that time.
| https://physics.stackexchange.com |
40,268 | [
"https://mathoverflow.net/questions/40268",
"https://mathoverflow.net",
"https://mathoverflow.net/users/9569/"
] | This is a heuristic question that I think was once asked by Serge Lang. The gaussian: $e^{-x^2}$ appears as the fixed point to the Fourier transform, in the punchline to the central limit theorem, as the solution to the heat equation, in a very nice proof of the Atiyah-Singer index theorem etc. Is this an artifact of t... | Quadratic (or bilinear) forms appear naturally throughout mathematics, for instance via inner product structures, or via dualisation of a linear transformation, or via Taylor expansion around the linearisation of a nonlinear operator. The Laplace-Beltrami operator and similar second-order operators can be viewed as di... | (The sort of obvious answer from teaching statistics several times:)
<em>The sum of two independent normal random variables is again normal</em>, i.e., the shape of the distribution is unchanged under addition except for stretching and scaling.
Moreover, the normal distribution is unique among distributions with finite... | https://mathoverflow.net |
437,416 | [
"https://physics.stackexchange.com/questions/437416",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/148508/"
] | The Sun's effective temperature is 5778K. Using Wien's law we can calculate the wavelength λmax in which we observe the maximum amount of radiation received from the black body. After doing the calculation, we see that λmax=500nm approximately.
We can find that an absorption line of Hydrogen is at 486nm. By comparing ... | The answer is no, which you can see because plenty of counterexamples exist. For example, a main-sequence star with spectral type B burns hydrogen and has an effective temperature of 10,000-30,000 K. A type-B star with an effective temperature of 15,000 K has a peak blackbody wavelength of 199 nm, which is nowhere clos... | Well your question has already been answered in great detail but lambda max and the elements burned in the core are not directly related to each other.
For example, a star could have a surface temperature of 7800 Kelvin, which makes lambda max 370 nm. But that would correspond to the absorption line of calcium, which i... | https://physics.stackexchange.com |
361,747 | [
"https://stats.stackexchange.com/questions/361747",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/217325/"
] | How do I calculate the probability of randomly picking a number in the range from 0 to 10000 where exactly two of the digits is odd. For ex 5001 or 1010 etc.. and how would I do the same calculation for a range that starts with an odd number for ex 10000 to 20000?
| Note that we can e.g. treat $5000$ as $05000$ the condition that the left one has exactly 2 odd digits is equivalent to the condition that the right one has 2 odd digits, because 0 is even.
The process of drawing a random number out of $\{0,1, ..., 10000\}$ is therefore equivalent to drawing once from a distribution ... | I've tried to solve this using R, since im not very good with mathematic notations.
<pre><code>test = 0:10000
test = data.frame(test)
length(test$test)
# 10001 different numbers are possible
# x of them fulfill the requirement of 2 odd digits.
# find x
amount_of_digits = table(nchar(as.character(test$test)))
# Base... | https://stats.stackexchange.com |
305,930 | [
"https://softwareengineering.stackexchange.com/questions/305930",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/208914/"
] | In many books and tutorials, I've heard the practice of memory management stressed and felt that some mysterious and terrible things would happen if I didn't free memory after I'm done using it.
I can't speak for other systems (although to me it's reasonable to assume that they adopt a similar practice), but at least ... | <blockquote>
If I need to use a piece of memory throughout the lifespan of my program, is it really necessary to free it right before program termination?
</blockquote>
It is not mandatory, but it can have benefits (as well as some drawbacks).
If the program allocates memory once during its execution time, and woul... | Freeing memory at the end of a programs run is just a waste of CPU time. It's like tidying a house before nuking it from orbit.
However sometimes what was a short running program can turn into part of a much longer running one. Then freeing stuff becomes necessary. If this wasn't thought about to at least some extent ... | https://softwareengineering.stackexchange.com |
110,262 | [
"https://stats.stackexchange.com/questions/110262",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/40252/"
] | I need to prove that the limiting distribution of $(n-1)S^2/\sigma^2$ is a Normal, where $S^2$ is the sample variance.
However, I have no clue on how to do it.
We know that $(n-1)S^2/\sigma^2 \sim \chi^2(n-1)$, however, I'm not even sure this fact can help me...
Any help would be appreciated
EDIT:I needed to add so... | If $X_1,X_2,\ldots$ are i.i.d. standard normal, then
$$
Y_n=\sum_{i=1}^n X_i^2\sim \chi^2(n)
$$
for all $n\geq 1$. By the CLT
$$
\frac{1}{\sqrt{n\sigma^2}}\sum_{i=1}^n (X_i^2-{\rm E}[X_i^2])\to \mathcal{N}(0,1)
$$
in distribution as $n\to\infty$, where $\sigma^2=\mathrm{Var}(X_i^2)$. Since $X_i\sim\mathcal{N}(0,1)$ thi... | We have that (since we use the biased-corrected expression for the sample variance),
$$\frac {(n-1)S^2}{\sigma^2} = \sum_{i=1}^n\left(\frac {X_i-\bar X}{\sigma}\right)^2 \equiv W_n \sim \chi^2_{n-1}$$
with
$$ E(W_n) = n-1,\;\; SD(W_n) = \sqrt {2(n-1)}$$
Since this is a <em>finite-sample</em> result we can manipulat... | https://stats.stackexchange.com |
229,766 | [
"https://security.stackexchange.com/questions/229766",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/232176/"
] | This will seem like a very basic question, but I wanted to make sure I don't miss something.
When you enter your password in a login page and you press enter, what exactly happens right after until you're "approved"? I mean in common/regular websites.
I know some websites like Password managers, secure email provider... | <ol>
<li>Can you confirm this is the regular process in 2020?</li>
</ol>
It depends on what you mean with "regular" process. <strong>It is considered state-of-the-art</strong> for most use cases and recommended by established security standards and guidelines.
This doesn't mean that everyone is following best practic... | Short answers:
1) No. In 2020 there are still many legacy systems that manage web password in an insecure way. The password management strategy depends on the quality of engineers that have developed the software and the age of software.
2) There are no such mechanism using standard HTTP/s protocol. Server components a... | https://security.stackexchange.com |
166,015 | [
"https://dba.stackexchange.com/questions/166015",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/109302/"
] | I am trying to understand a paragraph from my notes, re Users and Groups in Active Directory. The phrase is:
<blockquote>
Users and Groups Sign in, they do not login.
</blockquote>
Now, what I (think I) understand is that logins give access to SQL server, Users are given access to specific databases. But I have no... | You sign in (or log <strong>on</strong>) to SQL Server <em>using</em> a <code>login</code>. Without a <code>login</code> you don't get to connect to SQL Server.
A <code>login</code> is a SQL Server <em>principal</em> or <em>account</em>, managed by SQL Server, that is used to grant and deny access to objects.
If... | I think arguing about login vs sign-in is sematics.
Sql server allows you to log in via 2 modes.
<ol>
<li>SQL authentication: means using a user id and password which is not the same as your domain credentials. </li>
</ol>
Or.
<ol start="2">
<li>Windows authentication: This can be granted to an individual domain u... | https://dba.stackexchange.com |
2,802 | [
"https://mechanics.stackexchange.com/questions/2802",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/1351/"
] | On my 1999 Saturn SL2, there are clips that are supposed to hold the ignition/plug wires in place onto the coil pack and the bolt that goes through it may play a role in grounding the circuit. One of them is missing. There's corrosion on the pack where it's missing, so it's apparently important. What is that part ca... | <blockquote>
Why and when would one use such charger?
</blockquote>
To my mind, the major needs fall into two major categories:
<ol>
<li>You have a vehicle that does not get driven enough to keep the battery up to charge against its passive drain. Common examples would include the summer-only car or the utility ve... | E.g., driving only short distances may make it difficult for the alternator to keep up (low running-engine-time to number-of-starts ratio.) Connecting a battery charger when the car is parked can keep the battery fully charged and eliminate the need for occasional jump-starts.
| https://mechanics.stackexchange.com |
24,729 | [
"https://stats.stackexchange.com/questions/24729",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/9158/"
] | I have independent observations $Y_1, Y_2, ...., Y_n$ that take values 1 or 0 with
$$P(Y_i = 1) = \frac{1}{1 + \exp\{-(\alpha + \beta x_i)\}}$$
where $\alpha$ and $\beta$ are unknown constant and $x_1, x_2, ....,x_n$ are known, I have to show that $(\sum Y_i,\sum x_i Y_i)$is a minimal sufficient statistics for $(\al... | Write $Y=(Y_1,\dots,Y_n)$ and $y=(y_1,\dots,y_n)$. Use the notation
$$p(y_i\mid\alpha,\beta)=P\{Y_i=y_i\mid\alpha,\beta\}\, .$$
Your initial difficulty seems to be related to the fact that you fail to see that
$$Y_i\mid\alpha,\beta\sim \mathrm{Ber}\left(\frac{1}{1+e^{-(\alpha+\beta x_i)}}\right) \, .$$
Now, you have ... | I think this is a homework question. If so, you should tag it as such. Under the assumption that this is homework, I'm just going to give you enough to get you started.
We have
$P(Y_i = 1) = \frac{1}{1 + \exp\{-(\alpha + \beta x_i)\}}$
so it must be the case that
$P(Y_i = 0) = 1 - \frac{1}{1 + \exp\{-(\alpha + \bet... | https://stats.stackexchange.com |
44,928 | [
"https://stats.stackexchange.com/questions/44928",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/17035/"
] | It is possible to test for interaction in Analysis of Covariance (ANCOVA) between the independent variable and the co-variate, but isn't “the homogeneity of regression slopes” an assumption that should not be violated in ANCOVA? If this is the case, then if we have an interaction between independent variable and co-va... | +1 to @FrankHarrell. To be honest, I find a lot of terminology in statistics to be used inconsistently, confusing, or generally unhelpful. It's best to concentrate on the underlying logical structure of your situation. For example, an ANOVA isn't fundamentally different from a multiple regression model. An ANOVA is... | This is just a nomenclature problem. ANCOVA in its original incarnation often implied an additive model for which non-parallelism was feared and tested. If we used the more general name "linear model" we would avoid this connotation (or perhaps the even more general phrase "multivariable regression model").
Beside... | https://stats.stackexchange.com |
623,662 | [
"https://electronics.stackexchange.com/questions/623662",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/315769/"
] | I want to power a very large light fixture: it has 273 G4 socket light bulbs. The bulbs I found for the thing are 12 V 5 W ones, incandescent.
So the question is how to power the beast (as it is 1365 W of power), and how can I dim the whole thing?
If it were just the power I could buy some rando cheap 12 V 1.5 kW PSU, ... | <h2>DO NOT drive it AC (mains) power!</h2>
AC mains installation/implementation expert here.
<ul>
<li>AC mains power is much more dangerous and requires great care.</li>
<li>It will create a huge mess when a bulb burns out, as you now must hunt down a bad bulb in a series string. I've done this much too much, <em>and ... | No need for 12V - totally impractical. If the bulbs are already wired in parallel then someone messed it up and it has to be all redone.
You’ll be making series strings of 10 bulbs, and those strings have to be connected in parallel to 120VAC. That’s how it’s done. You can then use any suitably rated dimmer designed fo... | https://electronics.stackexchange.com |
537,413 | [
"https://electronics.stackexchange.com/questions/537413",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/271219/"
] | I am currently using two 12V car batteries connected in series connected to a 24V power supply (SMPS), so they act as a filter.
I need to do the same with a 12V power supply and I am not sure if to:
<ol>
<li>Connect the power supply directly to ONE of the batteries (the same batteries that are connected in series to th... | #3 is the sensible choice.
#1 can be done with some care — make sure that both circuits have their ground at the same point (i.e. use the "bottom" battery for your 12V circuit, not the "top" one), or else you will potentially short out a battery from innocuous things like letting a piece of 12V equi... | The simplest answer is a blanket no, do not supply a 12 V load and a 24 V load from two 12 V batteries in series.
However, for appropriate loads, and/or if you are careful to manage the batteries, it can be done.
The problem is battery balance. The 12 V load will drain one battery more than the other. This one will run... | https://electronics.stackexchange.com |
2,443,341 | [
"https://math.stackexchange.com/questions/2443341",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/452508/"
] | Prove that the no. of isosceles triangles with integer sides, no sides exceeding $n$ is $\frac{1}{4}(3n^2+1)$ or $\frac{3}{4}(n^2)$ according as n is odd or even, n is any integer.
How to do it? I found that under these conditions no. of triangles possible may be
${n\choose 2}$
| Fix the length of the two equal sides, say $k$. In how many ways can you choose the length of the base $b(k)$? Obviously $b(k) \ge 1$ and, for the triangle inequality, $b(k) < 2k$. But, since no side can exceed $n$, $b(k) \le n$. Putting these things together, we conclude that:
<ul>
<li>when $2k - 1 \le n$, that is... | <span class="math-container">${n \choose 2}$</span> is the number of triplets <span class="math-container">$(k,k, m)$</span>. But not all triplets can be triangles. To be a triangle i) <span class="math-container">$m < k + k = 2k$</span> and ii) <span class="math-container">$k < k + m$</span>. (i) is a essenti... | https://math.stackexchange.com |
246,256 | [
"https://security.stackexchange.com/questions/246256",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/252924/"
] | As a security in-charge, I just noticed that one of our production web apps was attacked by some hackers. The attacker accessed the .git/objects/ files.
I already modified .htaccess to make .git and its content inaccessible.
The attacker may get some model file which includes some data queries but not with database cr... | <blockquote>
Should I worried about it?
</blockquote>
Worried? No, of course not.
You should be <strong>absolutely terrified</strong> and have nightmares about this.
Having stolen <code>.git</code> directory means the attacker have the current and past source for the production server, all history of all code since the... | Worried? Maybe. Is your source code filled with holes? Then yes. But quiet honesty, you should have been worried BEFORE your source code leaked.
People have this idea that they're safe because "nobody will discover my horrible security hole because they don't know how it works!". This is a bad way to thi... | https://security.stackexchange.com |
6,534 | [
"https://quantumcomputing.stackexchange.com/questions/6534",
"https://quantumcomputing.stackexchange.com",
"https://quantumcomputing.stackexchange.com/users/2403/"
] | I understand that, projecting <span class="math-container">$\lvert 00\rangle$</span> on the Bell states would produce <span class="math-container">$\lvert\Phi^+\rangle$</span>. Because,
<span class="math-container">$$
CNOT(H\lvert0\rangle \otimes \lvert0\rangle) = \frac{1}{\sqrt{2}}(\lvert00\rangle + \lvert11)\rangle
... | The Hadamard gate is:
<span class="math-container">$$\frac{1}{\sqrt 2} \left(|0\rangle \langle 0 | + |0\rangle\langle 1| + |1\rangle \langle 0| - |1\rangle \langle 1|\right)$$</span>
And since <span class="math-container">$|+\rangle$</span> is <span class="math-container">$\frac{1}{\sqrt 2}\left(|0\rangle + |1\rangle... | The four Bell states are
<span class="math-container">$$
|\Phi_{\pm}\rangle=(|00\rangle\pm|11\rangle)/\sqrt{2}\qquad |\Psi_{\pm}\rangle=(|01\rangle\pm|10\rangle)/\sqrt{2}.
$$</span>
So, let's consider what happens then we try and measure in the Bell basis, i.e. project onto one of these four states. If we started with ... | https://quantumcomputing.stackexchange.com |
82,072 | [
"https://mathoverflow.net/questions/82072",
"https://mathoverflow.net",
"https://mathoverflow.net/users/16722/"
] | QUESTION RETRACTED - My original argument was fundamentally mistaken (mixing up lower and upper semi-continuity). Sorry (and thanks for the useful comments)
I need, and (unless I am seriously mistaken) can prove, the following:
<code>Let $E \subseteq F$ be an (isometric) inclusion of Banach spaces, and let $E^*_1$, ... | If I understand the claims of the OP correctly, I don't think that such a section can actually exist (if there is a misunderstanding on my part, I will happily retract this answer!).
Upon reading the question, I immediately thought of topological vector space versions of the Michael continuous selection theorem (for i... | After Phil's answer and the ensuing discussion, the remaining question can be formulated as:
Estimate $\lambda$ s.t. if $F\subset E$ and $E/F$ is finite dimensional, then every norm one linear operator $T$ from $F$ into a $C(K)$ space can be extended to an operator from $E$ into the $C(K)$ space which has norm at most... | https://mathoverflow.net |
2,342 | [
"https://dba.stackexchange.com/questions/2342",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/1562/"
] | I have read the definition of 1NF which is, "If each attribute of relation is atomic". Please tell me what is Atomic.
| 1NF requires that every attribute position in every tuple in every relation contains a single value of the appropriate type. The types can be arbitrarily complex. In fact, the types can be relations. (CJ Date's book <em>Database in depth: relational theory for practitioners</em> treats this issue in a way that's pretty... | "Atomic" refers to Codd's original notion from 1969 that each attribute in each tuple within a relation should consist of a single value and not allow multivalued structures of the kind supported in databases like the CODASYL model.
In modern SQL DBMSs atomicity isn't really an issue. SQL tables do not allow multivalu... | https://dba.stackexchange.com |
1,471,415 | [
"https://math.stackexchange.com/questions/1471415",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/219075/"
] | I am failing to understand how to compute the derivative of a few exponential functions. Let's start with this one:
$$
v = 1 - e^{-t/\tau}
$$
The derivative is
$$
\frac{dv}{dt} = \frac{1-v}{\tau}
$$
Can someone walk me through this? If this is explained somewhere else, I'd love to know where.
| $$\begin{align*}
\frac{d}{dt} (1 - e^{-t/\tau}) &= -\frac{d}{dt}e^{-t/\tau} \\
&= - (-1/\tau) e^{-t/\tau} \\
&= \frac{e^{-t/\tau}}{\tau} \\
&= \frac{1 - (1 - e^{-t/\tau})}{\tau} \\
&= \frac{1 - v}{\tau}
\end{align*}$$
| We have $$\dfrac{dv}{dt} = \frac{1}{\tau} e^{-\frac{t}{\tau}} = \frac{1-(1-e^{-\frac{t}{\tau}})}{\tau} = \frac{1-v}{\tau}$$. Is it clear?
| https://math.stackexchange.com |
135,188 | [
"https://security.stackexchange.com/questions/135188",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/103564/"
] | On my Android device, I can store up to 3 fingerprints to unlock my phone with the fingerprint scanner that is built in to the home button. On iPhones it's 5 fingerprints if I'm not mistaken. But most people have 10 fingers and I can't imagine the performance difference between checking through 10 rather than 3 hashes ... | No, theres no specific security reason to limit the number of fingerprints stored.
However, given that these fingerprint modules normally is a HSM, like a smart card, storing fingerprints, the number of, and the size of the secrets such a fingerprint module can store, is limited.
Note that a fingerprint template can ... | iOS devices (and probably Android ones as well) use a dedicated hardware security module that talks to the fingerprint reader directly and compares the fingerprints on its own. The phone's OS has no control over that - it simply gets a result whether the authentication was successful and optionally the secrets that wer... | https://security.stackexchange.com |
131,013 | [
"https://chemistry.stackexchange.com/questions/131013",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/90302/"
] | So I was doing my chemistry assignment and became stuck. Can I get some help?
a) Calculate the pH of a buffer system that contains 0.40 M of NH3(aq) and 0.50 M of NH4Cl(aq) . Note that the Kb value of NH3(aq) is 1.8×10−5.
<strong>My ans for delta pH: 9.158362492</strong>
b) Determine the change in pH if 2.50mL of 0.... | Ok, let's beat this to death with ICE tables.
<blockquote>
(a) Calculate the pH of a buffer system that contains 0.40 M of <span class="math-container">$\ce{NH3(aq)}$</span> and 0.50 M of <span class="math-container">$\ce{NH4Cl(aq)}$</span> . Note that the <span class="math-container">$K_\beta$</span> value of <span... | Your first result is OK.
But :
First,
it does not make any sense to give a result with <span class="math-container">$\ce{10}$</span> significant figures when the initial data has only <span class="math-container">$\ce{2}$</span> significant figures. When a data is given like here <span class="math-container">$\ce{1.... | https://chemistry.stackexchange.com |
22,140 | [
"https://quantumcomputing.stackexchange.com/questions/22140",
"https://quantumcomputing.stackexchange.com",
"https://quantumcomputing.stackexchange.com/users/18988/"
] | I am new to quantum computing and I want to know the following: If I have a 2 qubit system in state e.g. <span class="math-container">$\left|01\right>$</span> and I want to calculate the probability of measuring e.g. <span class="math-container">$\left<01\right|$</span> I can write it as following: <span class="m... | Yes.
In general, given two Hilbert space <span class="math-container">$H_1$</span> and <span class="math-container">$H_2$</span> with inner product <span class="math-container">$\langle \cdot |\cdot \rangle_1$</span> and <span class="math-container">$\langle \cdot | \cdot \rangle_2$</span> then for <span class="math-c... | A more general rule is called <em>the mixed-product property:</em>
<span class="math-container">$$
(A \otimes B) (C \otimes D) = AC \otimes BD,
$$</span>
which holds for any matrices <span class="math-container">$A,B,C,D$</span> of such sizes that we can form the matrix products <span class="math-container">$AC$</span>... | https://quantumcomputing.stackexchange.com |
167,447 | [
"https://mathoverflow.net/questions/167447",
"https://mathoverflow.net",
"https://mathoverflow.net/users/1345/"
] | This question is not precise, but I believe has a precise formulation.
Consider a mathematical theorem which gives an equivalency between two conditions. As an extreme example:
<blockquote>
<strong>Theorem.</strong>
A compact 3-manifold is simply-connected if and only if it is homeomorphic to the 3-sphere.
</blo... | I think that there are numerous trivial examples of this.
Take any implication $p\to q$ that is provable, but has no short proof. It follows that the equivalence $$q\leftrightarrow (p\vee q)$$
is also provable, and furthermore has a trivial proof in the forward direction, but no very short proof in the converse di... | This fits in the program of reverse mathematics. For instance: a subtree of the set of all finite binary strings has an infinite path iff it is infinite. One direction is provable in RCA $_0$ and the other is not.
| https://mathoverflow.net |
1,353,126 | [
"https://math.stackexchange.com/questions/1353126",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/203608/"
] | $$d'(x,y)= \sqrt{d_1^2(x,y)+d_2^2(x,y)}$$
The first three properties are trivially proven. The triangle inequality, not so much. I tried using the triangle inequalities that apply to $d_1$ and $d_2$, but nothing tangible came out of that. I feel the Cauchy-Schwarz inequality might be applicable to find the answer, but... | Let $x, y, z$ be given. Then, we have
$$ \begin{align}
d(x, z) &= \sqrt{ d_1^2(x,z) + d_2^2(x,z) } \\
& \le \sqrt{ (d_1(x,y)+d_1(y,z))^2 + (d_2(x,y)+d_2(y,z))^2 } \\
& \le \sqrt{ (d_1(x,y))^2 + (d_2(x,y))^2 } + \sqrt{ (d_1(y,z))^2 + (d_2(y,z))^2 } \\
&= d(x,y) + d(y,z).
\end{align}$$
| The square of a metric is a metric, the sum of two metrics is a metric, and the square root of a metric is a metric. It then immediately follows that $d'$ is a metric. The proof for each of these is a lot simpler, than directly showing $d'$ is a metric.
| https://math.stackexchange.com |
626,027 | [
"https://electronics.stackexchange.com/questions/626027",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/267100/"
] | For curiosity reasons, I want to know why engineers used the term "slew rate" for this op-amp phenomenon, I mean <strong>"slew"</strong>.
I googled it and found this: "turn or slide violently or uncontrollably".
What is the explanation?
| If "slew" is sliding violently or uncontrollably¹, the "slew rate" is the speed at which something slides violently or uncontrollably.
In an op amp, the slew rate is the maximum speed at which the output voltage can change; if you instantaneously change the input, the output voltage will "slide... | I think the term <em>slew rate</em> is derived from servo engineering which in turn acquired this from a nautical term which means to swing a gun or rigging about a vertical axis.
The Oxford English Dictionary uses as a reference for slew: <em>1962 L. A. Stockdale Servomechanisms vii. 112 The slewing time may form... | https://electronics.stackexchange.com |
168,882 | [
"https://stats.stackexchange.com/questions/168882",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/86009/"
] | I am working SLAM based problems in robotics and I want to know whether I can use Kalman filter instead of the Extended kalman filter that is predominantly used ?
If not, what is the difference?
| The Kalman filter (KF) is a method based on recursive Bayesian filtering
where the noise in your system is assumed Gaussian. The Extended Kalman Filter (EKF) is an extension of the classic Kalman Filter for non-linear systems where non-linearity are approximated using the first or second order derivative. As an example... | Both of them are state estimators, both of them involve the following steps:
<ol>
<li>predict the state ahead ( this is the so-called prior)</li>
<li>predict the covariance ahead</li>
<li>compute Kalman gain</li>
<li>update estimates with means (this is the filtering step)</li>
<li>update error covariance</li>
</ol>
th... | https://stats.stackexchange.com |
273,199 | [
"https://electronics.stackexchange.com/questions/273199",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/110214/"
] | I made a simple 0 to 9 up counter using Verilog. The output is 4 LEDs which are turned on when their corresponding bit is 1. The code synthesizes fine, but on the FPGA, only one LED lights on and off repeatedly. The other three LEDs do not light up at all.
Here is my code:
<pre><code>module counter(
input wire cloc... | There was a problem with the top module. I did not declare the wire that is used to connect the display and counter module.
Here is the revised top.v:
<pre><code>module top ( input wire clock, input wire reset, output wire [3:0] LEDs);
wire [3:0] number;
counter c1 (.clock(clock), .reset(reset), .o_number(number));
... | My guess the issue may be in using <code>cur_state</code> and <code>next_state</code> without indexes. Try
<pre><code>always @(posedge clock or posedge reset) begin
if (reset) cur_state[3:0] <= 4'b0;
else begin
cur_state[3:0] <= next_state[3:0];
end
always @(*) begin
if (cur_state[3:0] == 4'... | https://electronics.stackexchange.com |
71,615 | [
"https://stats.stackexchange.com/questions/71615",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/28377/"
] | Why may log(natural logarithm) transformation improve results of SVM prediction(<strong>regression</strong>, eps-svm)? Is SVM based on the assumption of normal distribution or something else?
update1. I use Radial basis function kernel.
| SVM doesn't assume normality. But it's still a regression that minimizes some symmetric loss function (I suppose you use symmetric kernel).
So... this is just a feeling and I'm too tired to justify/prove all this but:
<ol>
<li>Probably your output variable has highly skewed distribution;</li>
<li>And you use symmetri... | I presume that you use Support Vector Machines and for each non-zero element of each feature vector you change its weight from n to something like log(1+n). In this case your system will give more importance to the quantity of the different features, that are associated with any class, than to their weight.
For exampl... | https://stats.stackexchange.com |
329,935 | [
"https://electronics.stackexchange.com/questions/329935",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/109235/"
] | I have a question from exam that I failed to solve:
I need to build a digital logic circuit that is receiving 4 bit number and return <code>true</code> if the number is <code>0</code>, <code>7</code> or <code>14</code>.
I have only one <code>XOR</code> gate (2 inputs), one <code>NOR</code>(3 inputs), one <code>NAND</c... | I wrote an algorithm in C# that tries every possible combination of those <code>Nor 3->1</code> <code>Xor 2->1</code> <code>Nand 2->1</code> and <code>Decoder 3->8</code>.
After running it for <s>7½ million years</s> 2 hours, it returned <s>42</s> False. I believe this prooves that the question has no answ... | This is a non-answer, to discard the most obvious solution.
I will number bits by its weight: \$ b_1 \$, \$ b_2 \$, \$ b_4 \$ and \$ b_8 \$.
As bits \$ b_2 \$ and \$ b_4 \$ are equal in all the valid numbers, we could thing about implement the logic expression:
$$ ( \text{nor} ~ \{ x=0, x=3, x=6 \} ) ~ \text{nand} ... | https://electronics.stackexchange.com |
2,712,980 | [
"https://math.stackexchange.com/questions/2712980",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/424260/"
] | In the book of Silverman, the below proof is given of the above :
$$a= q_1b + r_1$$
$$b =q_2 r_1+ r_2$$
$$r_1 =q_3r_2 + r_3$$
$$\vdots$$
$$r_{n-3} = q_{n-1}r_{n-2} + r_{n-1}$$
$$r_{n-2} = q_n r_{n-1} + r_n$$
$$r_{n-1} = q_{n+1}r_n + 0$$
But why is $r_n$ the greatest common divisor of $a$ and $b$? Suppose that $d$ is... | DEFINITION: Let $a,b \in \mathbb Z$. Then $g \in \mathbb Z^+$ is the greatest common divisor of $a$ and $b$ if
$\qquad \text{$(1.) \quad g \mid a$ and $g \mid b$}$.
$\qquad \text{$(2.) \quad \forall x \in \mathbb Z, \ x\mid a$ and $x \mid b$ implies $x \mid g$}$.
Now, suppose $x \mid a$ and $x \mid b$. Then
\begin{... | Here is a slightly different proof that $r_n$ is the greatest common divisor, based more on what @dssknj remarked (still not by contradiction though).
<em>Lemma:</em> $\gcd(x,y)=gcd(x,y+rx)$ for any integers $x,y,r$.
<em>Proof:</em><br>
If $d|x$ and $d|y$ then clearly $d|y+rx$. So every common divisor of $x$ and $y$ ... | https://math.stackexchange.com |
471,886 | [
"https://physics.stackexchange.com/questions/471886",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/155230/"
] | I learned from that plasma can reflect radiations of frequency less than that of its own oscillations. If so, considering the plasma in Sun's atmosphere, it should also reflect solar radiations.
<img src="https://i.stack.imgur.com/3UpCj.jpg" alt="enter image description here">
That would mean that the radiation emitt... | <blockquote>
Note that the intensity of observable radiation coming out from stars would now mostly depend on the outermost layer.
</blockquote>
Because the material in the star is opaque, it completely depends on the outermost layer. Of course the properties of that layer (such as its temperature) are driven by th... | <h1>Yes, you are looking at the outer layer</h1>
All the heat and light from the Sun is emitted by that outermost layer, which is essentially opaque to the processes going on inside it. The solar spectrum is a very good fit for a black body, and thus a black body temperature calculation applies to the surface of the S... | https://physics.stackexchange.com |
137,860 | [
"https://physics.stackexchange.com/questions/137860",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/60107/"
] | I know these two phenomena but I want to know a little deep explanation. What type of fringes are obtained in these phenomena?
| <ol>
<li>Two separate wave fronts originating from two coherent sources
produce interference. Secondary wavelets originating from different
parts of the same wave front constitute diffraction. Thus the two
are entirely different in nature.</li>
<li>The region of minimum intensity is perfectly dark in interference.
In d... | Feynman has come from heaven to answer your question! Listen to him:
<blockquote>
No one has ever been able to define the difference between interference and diffraction satisfactorily. It is just a quest of usage, and there is no specific, important physical difference between them. The best we can do is, roughly... | https://physics.stackexchange.com |
6,917 | [
"https://cs.stackexchange.com/questions/6917",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/2980/"
] | <blockquote>
$L_1$ is a recursively enumerable language over some alphabet
$\Sigma$. An algorithm effectively enumerates its words as $w_1, w_2, ...$. <br> $L_2$ is another language over $\Sigma \cup \{\#\}$ as
$\{w_i\#w_j : w_i, w_j \in L_1, i < j\}$<br> Consider the following
assertions.
<ol>
<li>$L... | You seem to be right. But as Raphael says, be careful.
Statement 1. Note that the $L_2$ is defined using the enumerating algorithm $\cal E$ for $L_1$, not by $L_1$ itself. To decide whether $u\#v \in L_2$, decide whether both $u,v$ in $L$, and if confirmed run the enumerator $\cal E$ and see whether $u$ is output befo... | <strong>Ad 1:</strong> The statement is true, but your reasoning is not: you can not change the enumeration; the definition of $L_2$ is intimately tied to the order of elements. Here is the simple algorithm that decides $L_2$:
<pre><code>decide2(w) = {
(u,v) = split (w,#) // w = u#v
if ( decide1(u) && dec... | https://cs.stackexchange.com |
618,074 | [
"https://math.stackexchange.com/questions/618074",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/68597/"
] | Problem :
Find the range of $f(x) = \sin^{-1}x +\tan^{-1}x +\cos^{-1}x$
Solution : Since, $\sin^{-1}x + \cos^{-1}x = \frac{\pi}{2}$
Since range of $\tan^{-1}x$ is $ (\frac{-\pi}{2}, \frac{\pi}{2})$
$\therefore, \frac{-\pi}{2} \leq \tan^{-1}x \leq \frac{\pi}{2}$
= $ \frac{-\pi}{2} + \frac{\pi}{2} \leq \tan^{-1}x ... | That is correct, you can use the quadratic formula for $c = 0$. And your work is all fine.
But note, you can save yourself time by simply factoring your equaton, and noting that when once has factors $a, b$, then $$a b = 0 \;\text{ if and only if } \;a= 0 \;\text{ or }\;b = 0$$
<hr>
$$\begin{align} 2y^2 - 3\sqrt 3y ... | If the constant term is $0$, the following is better :
$$y(2y-3\sqrt 3)=0.$$
Then?
| https://math.stackexchange.com |
288,313 | [
"https://softwareengineering.stackexchange.com/questions/288313",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/111852/"
] | Taking an example of a simple Ruby on Rails application. It creates a <code>Logger</code> object during application load process:
<pre class="lang-ruby prettyprint-override"><code># in environment.rb
config.logger = Logger.new(<STDOUT | file | whatever>)
# and in our application we use this object
logger.warn "... | Here's an example that uses Java. It's been a while since I've used log4j, but from what I remember, the whole log4j logging tool would initialize from an XML file. The XML file itself could contain multiple loggers with different configurations(where you write to, what levels are written, etc). So, in this case you... | Logger.new is a factory that will take where the result will be used (name of the class/file).
In the configuration files you can then decide what level to log to not logging at all for parts of the program without having to recompile the project.
Thus you can disable all but high-level logging (errors) for release ... | https://softwareengineering.stackexchange.com |
19,684 | [
"https://mathoverflow.net/questions/19684",
"https://mathoverflow.net",
"https://mathoverflow.net/users/4291/"
] | In the study of number theory (and in other branches of mathematics) presence of Hecke Algebra and Hecke Operator is very prominent.
One of the many ways to define the Hecke Operator $T(p)$ is in terms of double coset operator corresponding to the matrix $ \begin{bmatrix} 1 & 0 \\ 0 & p \end{bmatrix}$ .
On ... | The fact that Hecke operators (double coset stuff coming from $SL_2(\mathbf{Z})$ acting on modular forms) and Hecke algebras (locally constant functions on $GL_2(\mathbf{Q}_p)$) are related has nothing really to do with the Satake isomorphism. The crucial observation is that instead of thinking of modular forms as func... | Sorry, the first edition of this answer was shamefully incoherent. We'll see if this attempt is any better.
Any double coset KgK (for G and K as given) has a unique representative in elementary divisor form $\binom{a0}{0d}$ where a and d are (possibly negative) powers of p and a/d is a p-adic integer (i.e., a positiv... | https://mathoverflow.net |
1,830,432 | [
"https://math.stackexchange.com/questions/1830432",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/76446/"
] | <blockquote>
We have <span class="math-container">$\Omega \subset \mathbb{C} $</span> open and connected.
<span class="math-container">$f : \Omega \rightarrow \mathbb{C} $</span> and <span class="math-container">$f$</span> is holomorphic in <span class="math-container">$\Omega$</span>.
<span class="math-container">$f(... | Let $g(z) = e^{i\omega t}f(z)$, where $\omega$ is chosen so that $g$ is real-valued. (This is just a little make-up, to simplify the computations.)
Write $g = u+iv$ where $u$ and $v$ are real-valued. Then $v=0$, and Cauchy-Riemann gives $u'_x = v'_y = 0$ and $u'_y = -v'_x = 0$, so $u$ is constant. Consequently $g$, an... | Hint- Open Mapping Theorem.$~~~~~~~~~~~~~~$
| https://math.stackexchange.com |
471,284 | [
"https://electronics.stackexchange.com/questions/471284",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/72429/"
] | I have searched the programmer's manual in vain.
I can configure measurements if already on-screen but cannot figure how to add measurements if not present.
Does anyone know the correct command?
| The measurements are always there behind the scenes. You can control whether they are displayed on the screen using for example:
<pre><code>MEASUrement:MEAS<x>:STATE ON|OFF
</code></pre>
And you can configure the measurements using, for example:
<pre><code>MEASUrement:MEAS<x>:TYPe FREQuency
MEASUrement:MEAS... | I'm not a Tek scope expert and probably shouldn't comment since I work for Keysight (lol), but it seems there's two options. Option 1 is to grab a measurement result for a measurement that's already been made/already on screen, and the other option is to take a new measurement. From page 64:
"
To obtain measurement re... | https://electronics.stackexchange.com |
6,644 | [
"https://electronics.stackexchange.com/questions/6644",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/206/"
] | I'm looking for a good schematic capture checklist to use when reviewing schematics. This is for the usual issues such as check that you don't have similar but different nets (e.g. GND and GROUND) that are separate and style/readability issues (e.g. no 4-way ties). Either your list or a link to an external one would ... | A list I use for Multisim:
<ul>
<li>Do all tantalum caps on rails have at least ~20% overhead? No 25V caps on 24V lines?</li>
<li>Are there bypass caps on the power rails of <em>every</em> chip? Even the ones that don't look like chips, like regulators?</li>
<li>Are there filters on <em>every</em> transistor gate/base... | Functionality:
<ol>
<li>Check symbol pinouts, especially for new symbols and parts with multiple packages.</li>
<li>Review vendors' latest data sheets and errata to see if anything has changed since you downloaded it.</li>
<li>Have the vendor's FAE review the part of the schematic that uses their part(s)</li>
<li>Labe... | https://electronics.stackexchange.com |
662,071 | [
"https://physics.stackexchange.com/questions/662071",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/280752/"
] | Imagine the two terminal of a <em>parallel-plate capacitor</em> are connected to the two terminal of a battery with electric potential difference <span class="math-container">$V$</span>. If the capacitance of the capacitor is <span class="math-container">$C$</span>, and the area of each plate is <span class="math-conta... | The individual quantities in <span class="math-container">$\frac d {\epsilon A}$</span> can freely vary as long as the overall quantity stays the same. For instance, if you double both the distance and the area, then <span class="math-container">$\frac d {\epsilon A}$</span> remains constant, and thus <span class="mat... | You have the formula in the question: <span class="math-container">$Q=CV$</span> (which holds for any capacitor, not just one with a parallel plate). There is no way to include any additional dependence on the plates' area <span class="math-container">$A$</span>, because once you know <span class="math-container">$C$... | https://physics.stackexchange.com |
35,925 | [
"https://softwareengineering.stackexchange.com/questions/35925",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/-1/"
] | I would like to know <strong>why</strong> you decided to build your own framework in your company.
<blockquote>
By framework, I don't mean few libraries you use often. I mean a specific way of building applications on top of it, with base classes, convention, etc.
</blockquote>
So <strong>why</strong> did you built... | Answer to why:
<ul>
<li>License issues</li>
<li>Company specific requirements that didn’t exist in current frameworks</li>
<li>The company wants to have control over support and maintenance of the framework</li>
<li>The architect didn't know better! He/she didn't know about that specific framework existed, so they dec... | Why build your own?
<ol>
<li>because it's never been build before (rare, but a possibility nonetheless)</li>
<li>because you want full control.</li>
<li>because you only need a little bit of functionality so that it is cheaper to build it yourself</li>
</ol>
Why not build your own?
<ol>
<li>you don't have the time t... | https://softwareengineering.stackexchange.com |
9,960 | [
"https://softwareengineering.stackexchange.com/questions/9960",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/389/"
] | When you have no clue about the question, how do you answer/act when you do not know the answer at all? Telling the truth is pretty obvious. But how could you try to transform this weakness into a strength?
| "I don't know how to do that, but if I ran into that problem in a project, here's how I'd go about figuring out how to make it work..."
| I will always say <em>"I don't know."</em> with confidence.
Here is an alternative that may play more into your favor. Like my previous idea say it with complete confidence.
<blockquote>
I am not familiar with that yet.
</blockquote>
| https://softwareengineering.stackexchange.com |
156,809 | [
"https://electronics.stackexchange.com/questions/156809",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/68509/"
] | I have made a layout using eagle then save it as PDF to print a test paper before routing.
<img src="https://i.stack.imgur.com/bmyOQ.jpg" alt="exporting layout to PDF on eagle">
I didn't design any package its all eagle's packages.
I exported PDF as shown on the image but the problem is :
the atmega16 and l293d and eve... | In order to produce scale-accurate print you need to print the drawing from Eagle. For example, in board editor go to the top menu and select File->Print.In the window that follows pick your options. Scale factor will be one by default. You can also print to PDF from there but then you'd have to be careful with PDF ren... | Thanks to All replies i found that printing shop was printing it wrongly they print PDF from adobe x ver. 10 without correcting the print setting
adobe has option under <strong>print</strong> -> <strong>size option</strong> -> check <strong>Actual size</strong>
<img src="https://i.stack.imgur.com/fqIct.jpg" alt="Adob... | https://electronics.stackexchange.com |
144,140 | [
"https://security.stackexchange.com/questions/144140",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/36050/"
] | Is it true that if an attacker has the possibility to upload any <code>.html</code> and <code>.js</code> files, then he can get a password of another user?
Please explain how to do it.
| Depends how you store passwords. If you store the passwords as plaintext the yes it is a trivial job for anyone with write access to a web server to obtain the plaintext password. If however you store the passwords via a one-way hash using a procedure such as sha3 it becomes more difficult for an attacker. They would h... | Yes, this is a huge security hole. Lets say you discovered this on <code>example.com</code>. How do you exploit it?
<ol>
<li>Upload a HTML file containing an iframe with the login page of <code>example.com</code>, and some JavaScript to read any passwords entered and send them to <code>evil.com</code>.</li>
<li>Send t... | https://security.stackexchange.com |
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