qid int64 1 4.65M | metadata listlengths 3 3 | prompt stringlengths 31 25.8k | chosen stringlengths 17 28.2k | rejected stringlengths 19 40.5k | domain stringclasses 28
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14,927 | [
"https://security.stackexchange.com/questions/14927",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/9708/"
] | I'm sitting at a cafe, using their public Wi-Fi. I don't go on sensitive sites; I basically go to a music site and listen to a live stream, for which there's no login. I don't check my email or visit any password-protected sites. Some rare times, I visit Stack Overflow, for which I'm automatically logged in. I'm using ... | <ol>
<li>Maybe. The question is not whether there is a possibility that someone might be able to hack into your computer; the answer to that question is always yes, it might be possible. If you are connected to a network, we can't rule out the possibility that someone might be able to attack you. Rather, the right q... | I'd argue that anytime you're in a situation where someone can inject themselves into the data stream between the user (you) and any server/service provider/content provider, you incur a higher level of risk than not.
First, let's look at the attack surface of your laptop (i'm assuming you're referring to a laptop h... | https://security.stackexchange.com |
304,234 | [
"https://mathoverflow.net/questions/304234",
"https://mathoverflow.net",
"https://mathoverflow.net/users/103722/"
] | The Latex command <code>\ldots</code> is often used to denote "and so forth". For instance,
$$
\pi \approx 3.1415\ldots
$$
When a sentence ends with an <code>\ldots</code>, one is faced with the conundrum of how to properly terminate it. The "cleanest" way would of course be to add a terminating "period", thus signal... | I believe papers in English should be written in full and correct English sentences, with any mathematical formula being part of a sentence. Therefore, I believe that the correct form in this case would be
<blockquote>
we have $\pi=3.1415\ldots\;$. However,
</blockquote>
-- not
<blockquote>
we have $\pi=3.1415... | The principle mentioned by Iosif Pinelis that equations should follow the rules of grammar suggests to look at the OP in the broader context of the use of ellipsis in text: <em>is $\ldots$ to be followed by a full stop period $.$ or not ?</em>
The answer is "no" for <A HREF="https://en.wikipedia.org/wiki/Ellipsis#In_... | https://mathoverflow.net |
325,579 | [
"https://electronics.stackexchange.com/questions/325579",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/135262/"
] | I noticed that in LC tank circuit designs very often people use air coils as the L element as opposed to an axial inductor. I understand that the problem with the axial ones is that they tend to self-resonate. But I also thought that using an air core coil allows for much smaller inductance (on a scale of nH), as oppos... | All inductors are self resonant so choose an inductor that has a self resonant frequency sufficiently higher than the operating frequency of your circuit. Or, make use of the self resonance if appropriate to do so.
For a tank circuit in the collector or drain of a transistor, higher Q occurs when the inductor/capacito... | The main reason why air core inductors are used in RF is that non-air core is nonlinear, it can saturate and it does not behave uniformly over wide bandwidth. I wouldn't make an erratic conclusion like : "I see there are almost anywhere air cores inside, which means low inductance, therefore we should put big caps to h... | https://electronics.stackexchange.com |
544,733 | [
"https://electronics.stackexchange.com/questions/544733",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/273895/"
] | What are the advantages and disadvantages of using continuous or discrete systems for control? I'm going to list some that occurred to me, but would appreciate if people help complement the list. (If this question doesn't belong here, please let me know, I'll delete it).
Advantages for discrete:
<ul>
<li>Data from the ... | It is difficult to list all the pros and cons of analogue versus digital control but below are a few things I can think of:
<ol>
<li>an analogue compensation strategy, e.g. poles/zeroes placement, is fixed during the design phase and cannot be easily changed on the fly. With discrete control, you can alter the position... | Pete W already provided good insight, let me add a few important:
The use of MCU is usually cheap, easy to implement, easy to modify. They are often the way to go except in some situations.
<strong>Speed:</strong>
The big drawback of MCU based system is speed. If the control system needs to operate with a low response ... | https://electronics.stackexchange.com |
420,862 | [
"https://physics.stackexchange.com/questions/420862",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/58825/"
] | The electromagnetic field (wave) has a spin. The electromagnetic wave travels at the speed of light. Does the spin associated with the electromagnetic wave travel at the speed of light too? If so please provide the necessary equations.
| If the final pressure is the same as for the adiabatic reversible path P', and the change in entropy for this non-adiabatic irreversible process is zero, the only possibility is that, irrespective of the details of the process, the final temperature T'' must be equal to T'. What other possibility is there? After all,... | Agree with Chester, there is no other possibility irrespective of the path between the two states.
I think you can also answer this by simply using the ideal gas law.
$P_1V_1/T_1 = P_2V_2/T_2$
For the first process:
$pv/t = P’v’/T’$
If the second process has the same final volume as the first
$pv/t = P’v’/T’’$
... | https://physics.stackexchange.com |
2,672,386 | [
"https://math.stackexchange.com/questions/2672386",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/536441/"
] | I have this problem.
Suppose that 20% of the population is made of terrorists.
A company developed an alarm such that, when a terrorist goes through the alarm, the alarm always beeps. The problem is that sometimes the alarm beeps also when the person is not a terrorist.
We can improve the alarm in such a way that it... | You can't just take the expectations of $G$ and $R$ and expect the formula to hold. The definition of $E[G]$ is $\sum G\cdot P(G)$, which does not converge. As an example, let us consider a modified game with $n$ rounds. If keep succeeding and get to $n$ rounds you stop and are paid $2^{n-1}$. Now the sums are fini... | It is not true in general that $\mathbb Ef(X)=f(\mathbb EX)$ as you seem to think.
| https://math.stackexchange.com |
484,861 | [
"https://electronics.stackexchange.com/questions/484861",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/244566/"
] | A friend of mine is interested in manufacturing ICs. He wants to know whether the different form types of packages (DIP, LGA, BGA) have intellectual property obstacles to using them. If so, who owns them and how are royalties paid?
| Most of the common, industry-standard IC package types are covered by JEDEC standards. If there is an associated JEDEC standard code for the package, then the patent is held by a manufacturer who is a JEDEC member, and there are available license terms for the applicable patents.
More innovative packages might be cove... | Be aware the thermal properties of a package will strongly depend on the (epoxy-filled) distance between the paddle and the stamped leads.
Having "better" thermal performance will not be an accident. and the failure rates will be lower.
You can use the awareness as a selling point.
| https://electronics.stackexchange.com |
162,087 | [
"https://security.stackexchange.com/questions/162087",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/147494/"
] | My company rents a Debian server to the clients, that they have to connect to their own network.
The server provides various services, an administration interface, and connects to the online service of my company.
As the client has access to the computer running these services, he can read their source code on the ha... | I'm not sure why you allow untrusted users root access to server, but the only approaches I can think of is to deny such users access to the directory containing the PHP code.
This can either done by:
<ol>
<li>Encrypting the directory containing the PHP code and decrypting it on the fly with a key that is obtained fr... | zip your clean copies so a simple fopen won't work, set attributes of read-only on the folders to the libs, run your libs from behind a admin account, set pathways and an environment for each user with set memory and keep tabs on the libs space occupied. Heap allotments for all.
| https://security.stackexchange.com |
128,816 | [
"https://stats.stackexchange.com/questions/128816",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/60431/"
] | I have questions about the mixture of conjugate priors. I learned and saw the mixture of conjugate priors a couple of times when I am learning bayesian. I am wondering why this theorem is such important, how are we going to apply it when we are doing Bayesian analysis.
To be more specific, one theorem from Diaconis and... | Calculating posteriors with general/arbitrary priors directly may be a difficult task.
On the other hand, calculating posteriors with mixtures of conjugate priors is relatively simple, since a given mixture of priors becomes the same mixture of the corresponding posteriors.
[There are also many cases where some given p... | To extend @Glen_b's answer just slightly, one implication is that we can get a closed form approximation to the posterior when a non-conjugate prior is used by first approximating the non-conjugate prior with a mixture of conjugate priors and then directly solving for the posterior of the approximation.
However, in g... | https://stats.stackexchange.com |
401,544 | [
"https://physics.stackexchange.com/questions/401544",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/45557/"
] | The definition of 'Uniform motion' in a straight line says that the body covering equal distances in equal intervals of time is to be understood to be in uniform motion. However, can the speed vary within a given interval and still covering the same distance as for any other interval?
e.g. A car travels 10 m in every ... | The car is not executing a uniform motion, since it does not cover equal distances in <em>any</em> equal intervals of time. In your example you chose a particular interval of time, 10 sec, in which luckily the car covers always the same distance. But if you chose any other interval (except for 10sec multiples), you wou... | You cannot have uniform motion with varying speed. A varying speed creates an accelerated motion. The better way to describe uniform motion in a straight line is the motion at which the instantaneous velocity equals the average velocity at any time interval including that instant.
| https://physics.stackexchange.com |
196,524 | [
"https://softwareengineering.stackexchange.com/questions/196524",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/27714/"
] | <strong>Preamble</strong><br>
My aim is to create reusable code for multiple projects (and also publish it on github) to manage subscriptions. I know about stripe and recurring billing providers, but that's not what this module is aiming for. It should just be a wrapper/helper for calculating account balance, easy noti... | Unfortunately, the answer to a complicated problem is usually complicated. My advice to you would be to save only relevant information, then use a model to construct the bigger picture.
In other words, your table SubscriptionPlanChanges would have the following information for its key:
<ul>
<li>subscriber</li>
<li>p... | In addition to the above answer, I would create a table with credits, where a credit would equal the current currency. Whenever the user switches plan to a cheaper alternative, the unused balance enters as credits.
Whenever the user has something to pay, you would use the credits first and only ask for payment if the c... | https://softwareengineering.stackexchange.com |
686,398 | [
"https://physics.stackexchange.com/questions/686398",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/182222/"
] | I'm trying to find an equation for the period of oscillation of a mass under the following potential:
<span class="math-container">$U(x) = - U_0 \exp(-\frac{x^2}{2\sigma^2})$</span>
I'm trying by doing the following:
<span class="math-container">$F = -\frac{dU}{dx} = \frac{-d(-U_0 \exp(-\frac{x^2}{2\sigma^2}))}{du} = \... | First of all we assume <span class="math-container">$U_0>0$</span>. Then we get a Gaussian potential well.
We deal here with a periodical motion of particle in Gaussian potential well. The period of such a motion can be computed from energy conservation of this motion in the potential well:
<span class="math-contain... | Unless you have a restoring force which is a linear function of distance. the period will be a function of the amplitude. If you are interested in just the small amplitude period, you might use the first term in a power series expansion of the force function.
| https://physics.stackexchange.com |
293,661 | [
"https://electronics.stackexchange.com/questions/293661",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/54964/"
] | We all know its customary for a VOLUME control on any audio product should require turning CW to make it louder. In fact for user accessible rotary adjustments, clockwise almost universally means "more". This despite the fact that all plumbing faucets do the opposite. But it seems whenever I design a circuit where a tr... | It seems logical to my way of thinking that CW is "forward , up, and more" of any parameter you are adjusting such as Black Level or White level which are opposites or simply "more resistance" using pins 1 & 2.
The pins should be numbered "one TWO three " which also is to say the CW direction of wiper rotation fro... | In my opinion, in general CW should mean "adjust up" when you are checking something on the scope or have some other measurable or visible effect (by whatever human senses apply).
Sometimes though, when it's a mixing / "either or" proposition, the direction can get complicated.
| https://electronics.stackexchange.com |
629,929 | [
"https://physics.stackexchange.com/questions/629929",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/244541/"
] | Assume that I fill a floor measuring <span class="math-container">$ 2 m^2 $</span> in a room with <span class="math-container">$1 m $</span> of water, and the rest of the room is full of air.
I have used two ways of finding the pressure of the water on the floor:
First, the weight of the water can be expressed as <span... | <blockquote>
I'm pretty sure the second method is the right one but I wonder why the first one is not valid.
</blockquote>
Both methods are right, but you are calculating different things with them. The first method you are ignoring the air so you are calculating the gauge pressure. If you include the air in the first ... | In the first case you just calculate the additional pressure of the water, wich is the only interesting thing, since th additional air pressure was on the floor even without water. Usually you calculate the pressure from the water only. When you weight yourself on a scales you also do not add the air pressure.
| https://physics.stackexchange.com |
552,658 | [
"https://physics.stackexchange.com/questions/552658",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/254094/"
] | I'm in high school and wanted to get a few things cleared up.
Isothermal process is defined as a thermodynamic process where temperature remains constant.
Does this mean that temperature remains constant at every instant? Does an isothermal process have to be reversible?
The Joule expansion of an ideal gas is an ir... | Most people consider an isothermal irreversible process as one in which the system is held in contact with a constant temperature reservoir at the initial gas temperature throughout the process. This says nothing about the spatial and temporal variations in temperature interior to the system, only at its boundary with... | An isothermal process is a thermodynamic process in which if you take to measure the temperature of the system at some time in the process and then measure it again, later in the process, the measurement of would be the same, independent of what two times you decided at whim to measure.
Reversibility is a completely ... | https://physics.stackexchange.com |
522,163 | [
"https://physics.stackexchange.com/questions/522163",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/31790/"
] | Consider a harmonic oscillator defined by the coupled differential equations
<span class="math-container">\begin{align}
\begin{split}
\dot{X} &= \omega Y \\
\dot{Y} &= - \omega X \, .
\end{split} \tag{1}
\end{align}</span>
Defining new variables <span class="math-container">$a = X + i Y$</span> and <span class=... | Firstly is there a transformation on <span class="math-container">$m^2$</span>? Otherwise what happens to the second term?
Expand the variation of the Lagrangian to first order in <span class="math-container">$\alpha$</span> - Noether's theorem uses the infinitesimal form of the transformation. Then you can look for ... | There is a general formulae for the conserved current due to such translation symmetries. Indeed, assume that under the symmetry <span class="math-container">$x\mapsto x'=x+\alpha x$</span> and <span class="math-container">$\phi\mapsto \phi'$</span>, with <span class="math-container">$\phi'(x')=\phi(x)+\alpha d\phi(x)$... | https://physics.stackexchange.com |
49,497 | [
"https://stats.stackexchange.com/questions/49497",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/2817/"
] | I have a dataset I'm working on that has some co-variate shift between the training set and the test set. I'm trying to build a predictive model to predict an outcome, using the training set. So far my best model is a random forest.
How can I deal with the shifted distributions in the training vs. test set? I've co... | Take a look at the <code>twang</code> package on CRAN. It casts the problem in terms of observational studies and propensity scoring, but the application is the same. Read the primary academic article for many more details and discussion: "Propensity Score Estimation with Boosted Regression for Evaluating Adolescent ... | I don't know of any packaged functions to perform correction for co-variate shift, but here is something that might work.
You could build a random-forest classifier between the training and test set (to estimate test-set probabilities). You can then learn a random-forest on the training set by sampling according to t... | https://stats.stackexchange.com |
290,110 | [
"https://physics.stackexchange.com/questions/290110",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/8082/"
] | I am calculating the nuclear magnetic moment of aluminium-27 (Z=13). By looking at a nuclear energy diagram it can be seen that $$j=\frac{5}{2}, s=\frac{1}{2}, l=2.$$ Since there are an even number of neutrons and an odd number of protons, we are concerned with just the final odd proton, since the rest of the nucleons ... | Using the shell model (Woods-Saxon with spin-orbit correction potential) you can fill all the neutron shells up to the $1d_{5/2}$ level. You can do the same for the proton shells and it will result in a hole in the $1d_{5/2}$. The total angular moment J of the nucleus corresponds to the total angular moment of the (mis... | Here's an answer to your question:-
<ol>
<li>Remember you have taken Aluminium-27 (with z=13 i.e. odd z) so when you calculate its j value from nuclear shell model, it gives you j=5/2 and l=2, Right!</li>
<li>Now just in case you had taken an example of some other nucleus wherein you got following values:- j=3/2 ; l=2... | https://physics.stackexchange.com |
27,931 | [
"https://electronics.stackexchange.com/questions/27931",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/8396/"
] | I know what torque is but I find difficult to understand what Torque: 3kgcm means ?
I am not sure, how much weight that motor can carry, and I want to know how I can calculate that.
Please give me some hints :)
| Torque is a measure of "twisting force".<br />
Power is a measure of twisting force x speed.
Torque is usually expressed as a Force x a distance
So for the same Torque if you double the distance you halve the force to get the same answer.
So kg.cm is kg force x centimetre distance.<br />
In fact kg is a unit ... | <strong>A motor with 1 kg.cm torque is capable of holding a 1 kg weight at a radial distance of 1 cm.</strong>
Here is a diagram to explain.
<img src="https://i.stack.imgur.com/1sS7W.jpg" alt="enter image description here">
Torque is the cross-product of force and distance: \$ \tau = F \times d \$. So the same weig... | https://electronics.stackexchange.com |
420,800 | [
"https://electronics.stackexchange.com/questions/420800",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/135180/"
] | I am new to the CAN. I have came across bit stuffing which is used to ensure that all receivers nodes are synchronized to transmitter node (After 5 bits of the same polarity, CAN will add a bit stuffing bit of the opposite polarity).
I have some doubts regarding bit stuffing in CAN:
<blockquote>
Bit stuffing in not... | The first statement is wrong - the identifier field must be bit stuffed. The CAN bus uses the stuff bit for two purposes: to synchronise timing between nodes, and to signal an active error condition. If the identifier field is not stuffed, then it would not have either of these capabilities.
| From the CAN Spec:
<blockquote>
The ERROR FLAG’s form violates the law of bit stuffing (see
CODING) applied to all fields from START OF FRAME to CRC DELIMITER or destroys
the fixed form ACK FIELD or END OF FRAME field.
</blockquote>
which includes the identifier.
| https://electronics.stackexchange.com |
20,314 | [
"https://chemistry.stackexchange.com/questions/20314",
"https://chemistry.stackexchange.com",
"https://chemistry.stackexchange.com/users/10151/"
] | I have a bowl containing cheap wine and an immersible fish tank heater. The heater warms the wine to 30 deg C. The bowl is located in a large closed bucket, where it sits on a support. The bucket is sited out of doors in winter when the air temperature is Ca 1 deg C. Evaporation occurs and the vapour condenses on the i... | Yes you can do that, this technique is called 'distillation' (it requires a minimum difference of 10 degrees celsius to seperate two liquids with different boiling points, for efficiency), I don't know what temeperature the fish tank heater runs at, but you should know that ethanol i,e. what you are trying to separate ... | The answer to my principal question is that you can concentrate an aqueous ethanol solution by "room temperature distillation". I don't have the right equipment to be able to determine what variation in output quantity and strength might be obtained by varying the temperature of the source solution and the condenser su... | https://chemistry.stackexchange.com |
113,301 | [
"https://electronics.stackexchange.com/questions/113301",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/41686/"
] | I'm attempting to capture the carry out of the addition of two N bit numbers with a carry in. My code is:
<pre><code>module alu(a, b, f, cOut, z);
parameter size = 8; // how many bits is each input
parameter n = size - 1;
input a; // operand a ... | Replicators do not zero extend, they replicate. <code>{7{f[2]}}</code> means <code>{f[2],f[2],f[2],f[2],f[2],f[2],f[2]}</code>
You miss read the message. The RHS is 9 bits but is being assigned 64 bits (the LHS width). <code>a</code> and <code>b</code> are 8 bit values, are are used as the initial width to be replicat... | a is 8 bits wide
b is 8 bits wide
{n{f2}} is 8 bits wide
so a+b+{n{f2}} is also 8 bits wide
so {8{a+b+{n{f2}}}} is 64 bits wide
In cases like thin it often helps to make all the widths explicit - do everything in 9-bits and let the synthesis tool optimize stuff out - something like:
sign {cOut,sum} = {1'b0, a} + ... | https://electronics.stackexchange.com |
181,257 | [
"https://mathoverflow.net/questions/181257",
"https://mathoverflow.net",
"https://mathoverflow.net/users/4177/"
] | It is well-known that "the" stack of elliptic curves (allow me to be vague as to singular curves, compactifications etc) has a presentation by a groupoid in schemes. One of the things that needs to be proved to see this is that the sheaves of isomorphisms between two elliptic curves over a base is representable (I'm si... | In general you have a Hom scheme $\mathrm{Hom}_S(X,Y)$ for $X$ and $Y$ two schemes over $S$ whenever $S$ is noetherian, $X$ flat and projective, $Y$ quasi-projective. It decomposes into connected components depending on the Hilbert polynomial of the graph of $f$ in $X \times_S Y$. If $X$ and $Y$ are curves, this gives ... | It should be representable by an ind-scheme. You should look at the papere by Mumford "On the equations defining abelian varieties II", section 9. He calls this moduli space $\mathcal{M}_{\infty}$, it parametrizes towers of abelian varieties.
| https://mathoverflow.net |
1,742,848 | [
"https://math.stackexchange.com/questions/1742848",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/315064/"
] | According to my text the necessary and sufficient condition for a general equation of second degree i.e. $ax^2 + 2hxy + by^2 + 2gx + 2fy + c = 0$ to represent a pair of straight lines is that 1) the discriminant $abc + 2fgh - af^2 - bg^2 - cf^2 = 0$ and 2) $h^2 \ge ab, g^2 \ge ca$ and $f^2 \ge bc$. I was able to prov... | If the conic represents a pair of lines, then it can be written as $(px+qy+r)(p'x+q'y+r')$. Therefore, we get $ab = pp'qq'$ and $h = \frac{pq'+p'q}{2}$.
1) If both $pq'$ and $p'q$ are greater than equal to zero then apply AM-GM to $pq'$ and $p'q$ to get
$$\frac{pq'+ p'q}{2} \geq \sqrt{pq' \cdot p'q}$$
Squaring both... | <strong>Hint:</strong>
The classification of conics is done through the quadratic form in $\mathbf R^3 $ associated to the matrix
$$\begin{pmatrix}
a&h&g\\h&b&f\\g&f&c
\end{pmatrix}.$$
The conic splits into two lines if and only if the quadratic form has signature $(1,1)$.
| https://math.stackexchange.com |
37,785 | [
"https://stats.stackexchange.com/questions/37785",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/13684/"
] | I come from an SPSS background and am attempting to move to <code>R</code> for it's superior flexibility and data manipulation abilities. I have some concerns however as to whether the <code>lm()</code> is really using partial correlations.
I'm basically trying to run a linear regression, using something similar to th... | Another function that you might find useful is lm.sumSquares in the lmSupport package. Basically, if you have the following model:
<pre><code>mod1 <- lm(dv ~ iv1 + iv2 + iv3, data = d)
</code></pre>
Executing the following will give you the delta R squared (the semipartial correlation squared) and PRE (the partia... | R doesn't use partial correlations to determine reported p-values from lm.
Indeed, you can examine the code that computes the p-values for yourself; if you type
<pre><code>> summary.lm
</code></pre>
you will see the code of the function includes the following:
<pre><code> ans$coefficients <- cbind(est, se... | https://stats.stackexchange.com |
12,237 | [
"https://electronics.stackexchange.com/questions/12237",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/2809/"
] | I have a cell phone that has a 1500 mAh 3.7 V battery. It comes with a 700 mA charger but I've sucessfully used a 1 A charger with no problems. I'm now trying to make my own multi-device charging station and my first problem if figuring out the maximum amount of current I can use at 5V?
| If you are charging the battery through the phone then this will have the charge controller circuitry between the 5V charge supply and the battery. You CANNOT/MUST NOT just connect a battery pack to a power supply and expect it to charge without fire and or explosion.
The charge controller in the phone will limit t... | It's probably 1C, which means 1xcapacity, or 1500mA. However, there is a reason the manufacturer chose 700mA. It's best to keep to that to preserve battery lifetime and for safety. Overcharging a lipo can damage it. It may, in rare circumstances, become "puffy", or even overheat or burn. So be careful!
Never charge a ... | https://electronics.stackexchange.com |
671,991 | [
"https://physics.stackexchange.com/questions/671991",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/135464/"
] | Consider the double slit experiment in which the position of the particle is in a superposition of the 'eigenfunctions' of the position operator before they reach the detector. This process is completely determined by the Schrodinger equation and the wavefunction of the particle evolves according to it. However, we can... | The so-called collapse of the wave function seems somewhat less mysterious when you consider that quantum mechanics provides a collection of methods for modelling the behaviour of particles by finding approximate solutions to the Schrodinger equation, usually with a number of simplifying assumptions.
If you model the '... | It is an interpretation. There are many interpretations of quantum physics which don't include wave function collapse. For instance, the many worlds interpretation says that wave function collapse does not happen.
| https://physics.stackexchange.com |
440,514 | [
"https://electronics.stackexchange.com/questions/440514",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/163738/"
] | Shockley equation is non-linear but without any linearisation effort such as in BJT small signal biasing, half wave rectifier passes almost an undistorted half sine wave.
In amplifier we bring the bias to a linear region for a small signal.
What confuses me in rectification theres no such thing as linearization and... | The current and voltage waveforms ARE distorted by the diodes, but you seem to have unrealistic expectations about the expected <em>magnitude</em> of the distortion.
The forward voltage of the diode varies in a nonlinear way based on the current through it, but it's limited to a volt or two at most, depending on the c... | The current thru a silicon diode will increase 2X for a tiny 0.018 volt change across the diode. And 0.058 volts causes 10:1, and 2*0.058 volts = 0.116 volts causes 100:1
change in current.
Thus with 160 volt peak power line voltages (using a 1:1 transformer for safety), the 0.116 voltage is less than 1/1,000 distorti... | https://electronics.stackexchange.com |
634 | [
"https://cs.stackexchange.com/questions/634",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/594/"
] | In the script I am currently reading on the lambda calculus, beta equivalence is defined as this:
<blockquote>
The $\beta$-equivalence $\equiv_\beta$ is the smallest equivalence that contains $\rightarrow_\beta$.
</blockquote>
I have no idea what that means. Can someone explain it in simpler terms? Maybe with an ex... | $\to_\beta$ is the one-step relation between terms in the $\lambda$-calculus. This relation is neither reflexive, symmetric, or transitive. The equivalence relation $\equiv_\beta$ is the reflexive, symmetric, transitive closure of $\to_\beta$. This means
<ol>
<li>If $M\to_\beta M'$ then $M\equiv_\beta M'$. </... | It is elementary set theory really. You know what is a reflexive relation, what is a symmetric relation, and what is a transitive relation, right? An equivalence relation is one that satisfies all three of those properties.
You have probably heard of the "transitive closure" of a relation $R$? Well, it is nothing... | https://cs.stackexchange.com |
363,352 | [
"https://electronics.stackexchange.com/questions/363352",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/180881/"
] | I'm in the process of assembling an embedded (Raspberry Pi-based) machine that has a lot of sensors wired together via I2C. I find myself adding headers for the I2C lines to all the little tiny breakout boards on which the sensors are mounted, and I have an I2C "bus board" that I've assembled using a prototyping board ... | Advantages of solder:
<ol>
<li>Lower part usage </li>
<li>Mechanical strength </li>
<li>Part cost</li>
</ol>
Disadvantages:
<ol>
<li>Effort to replace if needed</li>
<li>Effort to assemble</li>
</ol>
There isn't much to worry about for capacitance and noise for a header + connectors vs soldering. It really boils do... | In addition to what @Passerby said, I can think of few other considerations.
<strong>1. Space limitations:</strong> Fairly obviously, headers and pin connectors require more physical space to accommodate them without pinching or stressing the wires.
<strong>2. Fail-safe needs for wire snags/ tension:</strong> Depend... | https://electronics.stackexchange.com |
459,439 | [
"https://electronics.stackexchange.com/questions/459439",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/222922/"
] | Let us say I have an LED whose brightness or luminance value is 50 Cd/m2.
If I lit 10 same type of LEDs with same conditions of current and voltage then will the brightness of these 10 LEDs will add up to 500 Cd/m2 or will it give some other value?
| It depends if the radiated light is diffused over the same area.
50Cd/m^2 = 50 nits would be a dim desktop monitor or a bright mobile.
Adding 10 in the same area with diffusion makes that 10x brighter.
But if not diffused each source would not appear to be brighter by neighbouring LEDs but the flux of radiated light... | You're comparing apples and oranges when you refer to 'brightness' and 'luminance'.<br>
'Brightness' is 'how bright is the light when I look at it', while 'luminance' is 'how will lit is the surface the light is shining on'.
Luminance is additive - if you shine more lights on the same surface, the surface gets more... | https://electronics.stackexchange.com |
337,752 | [
"https://electronics.stackexchange.com/questions/337752",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/167735/"
] | I'm having a bit of a hard time understanding how electricity is created in the practical sense. For example, when heat is explained , you have the scientific definition of what heat is , and then you have real world practical examples , (like rubbing your hands together , etc).
When it comes to electricity though , ... | To answer this question, first we must define the word "electricity." Unfortunately, there is no single definition upon which experts all agree. Therefore, asking about "electricity" can only give confusing and obscure answers. (See the tldr; down below.)
<hr>
But why?
First, the physics definition: "electricity... | Electricity is generated by getting something to make electrons want to move. A generator does this via a moving magnetic field (moving electrons generate a magnetic field and magnetic fields also make electrons move). Moving electrons generate a kind of pressure called voltage.
Batteries also generate voltage (and m... | https://electronics.stackexchange.com |
6,441 | [
"https://engineering.stackexchange.com/questions/6441",
"https://engineering.stackexchange.com",
"https://engineering.stackexchange.com/users/3781/"
] | I'm designing a little tester for a project which uses a pneumatic cylinder. The pneumatic cylinder's purpose is to apply an impact on a hard surface to test for deflection of the surface. When I looked around catalogs, the pneumatic cylinders have a theoretical force output, for example 3,016 N at 0.6 MPa with an exte... | It's not an easy problem, there are a few things going on at the same time here. Most obviously, the piston has kinetic energy from being accelerated through the bore, which gets transferred to the test item upon impact. This can be calculated from $E_{KE}=\frac{1}{2}mv^2$, as you stated. What's not as obvious is th... | In general pneumatics are quite precise when it comes to force but modeling energy in this context brings in a lot of additional unknowns which make be difficult to measure.
The most common method of impact testing is to use an impactor fixed to a pendulum as it's fairly easy to determine the kinetic energy at the lo... | https://engineering.stackexchange.com |
1,944,178 | [
"https://math.stackexchange.com/questions/1944178",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/365976/"
] | Let
$U_1 = (1, 1, 0, 0)$
$U_2 = (1, 0, 1, 0)$
$U_3 = (0, 0, 1, 1)$
Without doing any computation, explain why span$\{U_1, U_2, U_3\}$ $\neq$ $\mathbb{R}^4$.
I could reduce it to reduced row echelon form via Gaussian Elimination but that will not satisfy the condition of 'without doing any computation'. Is there ... | The space $\mathbb R^4$ has dimension four.
| 3 vectors can span 3 dimensions at most.
| https://math.stackexchange.com |
93,812 | [
"https://security.stackexchange.com/questions/93812",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/37349/"
] | We have two hosts, theoretically in the same data center. The two machines are hosted at Online.net. We're having a bit of a debate: should the traffic between the two hosts be encrypted.
The traffic we need to exchange are Redis queries. The data that will be exchange is Twitter and Facebook user IDs, a code to indic... | I'd say an explicit ACL in the Firewall permitting the traffic to and from the devices in question should be fine in this instance.
It sounds like the information being exchanged is just user IDs? If this is the case and the information isn't necessarily sensitive, I don't see an issue with just ensuring the rules are... | If the machines were on your own network (home, your company's datacenter, etc), simple IP-based restriction and/or putting the Redis-related machines on a separate VLAN should be enough.
However, in case of a hosting provider, I recommend considering their networks as hostile and equivalent to the open Internet, in w... | https://security.stackexchange.com |
145,399 | [
"https://electronics.stackexchange.com/questions/145399",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/58902/"
] | I have been studying three-phase systems for the whole course of a subject (on the first year of the university degree). I have finished now, and I know both "Y" (star) or "Delta" (triangle) connections. I have made a lot of computations with them, however I don't know the different applications they have and I would l... | The two systems have vastly different applications. Yes, there is a lot of crossover between them in some fields, but the two are more suited to certain applications.
Take motors for instance. Delta is far superior for driving motors than star. With delta you can visualize a wave circulating around the triangle, an... | Delta is great for balanced three-phase loads and has big advantages in eliminating 3rd harmonics. (You probably covered this in your course.)
One problem with delta is that there is no wye / star point so loads that require a neutral connnection can't be connected. For this reason European domestic power distributio... | https://electronics.stackexchange.com |
47,603 | [
"https://astronomy.stackexchange.com/questions/47603",
"https://astronomy.stackexchange.com",
"https://astronomy.stackexchange.com/users/37991/"
] | Saturn's apparent magnitude from Uranus is +3.228. Jupiter orbits closer to the sun than Saturn. Can we therefore expect Jupiter’s apparent magnitude from Uranus to be dimmer than Saturn's, or is it in fact brighter?
| I started Stellarium on my computer and pressed F6 to bring up the "Location" window.
Then I changed the planet to "Uranus", and marvelled at the view of the many rings and many moons from the planet's "surface"
For convenience I clicked the buttons to remove the ground and the atmosphere.... | According to James K suggestion I downloaded the astronomical program “Stellarium” unto my desktop. Fiddled around with the different settings and got it working!
"Magnitude" seems to mean "Apparent Magnitude" since Absolute Magnitude is listed separately. The figures I got was: Uranus - Saturn = +2... | https://astronomy.stackexchange.com |
138,522 | [
"https://dba.stackexchange.com/questions/138522",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/94541/"
] | What are the differences between the daily tasks/duties of a Mongo DBA compared to a RDBMS DBA?
For example, some sites claim that a MongoDB DBA would not require to do data modelling or designing the database, as that would be done by a developer or application designer.
This would mean some tasks are no longer n... | I have been in the NoSQL field since last 3 years.<br>
Being a MongoDB DBA you need to work closely with Development and Ops teams. Following are the things you need to do as day to day tasks as a MongoDB DBA.
The role can be broadly classified into three parts:
<ol>
<li>Administration:
<ul>
<li>New deployments (manu... | DBA is a small acronym but a large role. At various times I have seen a DBA look after
<ul>
<li>storage</li>
<li>network</li>
<li>VMs</li>
<li>compute nodes</li>
<li>installation and configuration of the above</li>
<li>backups, and testing restores</li>
<li>DR strategy</li>
<li>enterprise data integrity</li>
<li>ETL</... | https://dba.stackexchange.com |
146,869 | [
"https://softwareengineering.stackexchange.com/questions/146869",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/43804/"
] | According to the essay "The Object Calisthenics" by Jeff Bay in the book ThoughtWorks Anthology,
Use of Getters and Setters should be avoided as they break encapsulation and we should instead ask the object to do something for us instead of digging in to the object and getting its fields.
how about comparison of objec... | Books can be wrong or misleading. It is certainly true that having getters and setters for every field provides little more encapsulation than having those fields be public, and it's unfortunate that this kind of design is very widespread.
But it's nonsense to conclude that getters and setters should be avoided altog... | Encapsulation is hiding implementation details from outer world, in order to make implementation changes transparent. The very notion of "outer world" assumes existence of some "inner world". But where are the boundaries? They do not always have to be identical to the class boundaries. Often several classes are tightly... | https://softwareengineering.stackexchange.com |
196,617 | [
"https://physics.stackexchange.com/questions/196617",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/87021/"
] | If I’m travelling in space near the speed of light, I would like to use radar to give me advance warning of approaching hazards. However, will I have enough time to be able to react?
From a perspective on the spaceship, the radar beam travels away from me at the speed of light, so I might imagine that I would have amp... | <blockquote>
From a perspective on the spaceship, the radar beam travels away from me at the speed of light, so I might imagine that I would have ample warning of an object positioned at rest one light-hour away.
</blockquote>
One light-hour away in which frame? If that one light-hour away is from the perspective of... | Per Bort's comment, this is easier to think about from the spaceship's frame rather than the debris's frame. A rock is traveling toward your spaceship at .99 times the speed of light. You send out a pulse of light that intercepts the rock when it's one light-minute away from the ship. The pulse bounces back and arri... | https://physics.stackexchange.com |
550,985 | [
"https://electronics.stackexchange.com/questions/550985",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/278198/"
] | I have an electrical control box that needs 48v, 12v, and 5v to power stepper motors, sensors, and microcontrollers, respecitvely. All power items will be mounted on a DIN rail right next to each other. Is it better to have an AC-DC power supply for each output voltage, or one larger 48v supply and use DC-DC converters... | Both works, however, the separate AC/DC supply is a bit better.
<ul>
<li>AC/DC power supplies are dirt cheap.</li>
<li>There are plenty of AC/DC that can be rail mounted, DC/DC is more difficult to find.</li>
<li>You will have overall fewer conversion losses.</li>
</ul>
Where it is debatable is the 12V -> 5V where y... | Parallel is better because it improves the reliability. For your logic, you want that independent so you can continue to monitor systems like motor position and fluid levels even if you have a major failure that causes one of the other supplies to completely fail. This also allows you to have some sort of logic level f... | https://electronics.stackexchange.com |
16,088 | [
"https://cs.stackexchange.com/questions/16088",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/10743/"
] | So, as is known, ILP's 0-1 decision problem is NP-complete. Showing it's in NP is easy, and the original reduction was from SAT; since then, many other NP-Complete problems have been shown to have ILP formulations (which function as reductions from those problems to ILP), because ILP is very usefully general.
Reductio... | 0-1 ILP formulated as:
Does there exist a vector <span class="math-container">$\mathbf{x}$</span>, subject to constraints:
<span class="math-container">$$
\left.\begin{array}{rrrrr|rr}
a_{11} x_1 & + &a_{12} x_2 & ... + & a_{1n} x_n\le b_1 \\
a_{21} x_1 & + &a_{22} x_2 & ... + &a... | It is some sort of necro-answer to already answered and accepted question, but I want to note, that there is really easier way.
Consider you have one of inequalities like this:
<span class="math-container">$5*x_1 + 2*x_2 + 3*x_3 \leq 6$</span>
You may easily test all no-vectors for this inequality: <span class="math... | https://cs.stackexchange.com |
114,959 | [
"https://cs.stackexchange.com/questions/114959",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/109561/"
] | In my lecture we learned:
<code>If X is NPC and X in Co-NP => NP = Co-NP</code>
Would it be enough to prove <code>NP = Co-NP</code> if I reduce a problem just in one direction (from NPC to Co-NPC) in polynomial time?
Or would it be necessary to show this for both directions?
| <h1>In short</h1>
yes
<h1>Proof</h1>
Let's assume <span class="math-container">$X$</span> is NP-complete and <span class="math-container">$X$</span> is in co-NP.
We show that <span class="math-container">$NP \subseteq coNP$</span> and viceversa.
<h2>[<span class="math-container">$NP\subseteq coNP$</span>]</h2>
Because ... | Ok I think I got it know.
If I could reduce a NP-complete problem to a coNP-complete problem every problem in NP can be reduced to every coNP-complete problem and it would show that NP is a subset of coNP.
Because every problem A in coNP has a complement co_A in NP
A in coNP => co_A in NP => co_A in coNP => A in NP
... | https://cs.stackexchange.com |
3,138,545 | [
"https://math.stackexchange.com/questions/3138545",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/217910/"
] | This is from an introduction to mathematical proofs a transition to advanced mathematics.
<blockquote>
Let <span class="math-container">$g:\mathbb{N}\to A \cup \{x\}$</span> such that
<span class="math-container">$$g(n) = \begin{cases}
x \ \ &\text{if} \ \ n=1\\
f(n-1) \ \ &\text{if} \ \ n\neq 1
\end{ca... | Neither <span class="math-container">$\mathscr{A}_1$</span> nor <span class="math-container">$\mathscr{A}_2$</span> is maximal, since they are both properly contained in <span class="math-container">$\mathscr{A}_1 \cup \mathscr{A}_2$</span>, and that union isn't maximal either. On the other hand, any smooth atlas is co... | The word "larger" here is redundant with "contained in" and contributes no additional meaning. "Contained in" means literally one atlas is a subset of the other, as a set of charts. So, an atlas <span class="math-container">$A$</span> is maximal if there does not exist any other atlas <span class="math-container">$B$... | https://math.stackexchange.com |
117,611 | [
"https://datascience.stackexchange.com/questions/117611",
"https://datascience.stackexchange.com",
"https://datascience.stackexchange.com/users/144636/"
] | If I am predicting probability of a business to reach (x) milestone (classification 1), but the only data I have is live production data, how much of the production data should I use to train the model? My assumption is that if I use all the data, the probability of any business that hasn't reached the milestone alread... | You can use 100% of the data. The more data you feed to the model, the more accurate the prediction is going to be. If you have only two features - time and live production data, 30k records is not going to be a problem. Select a timepoint - somewhere between 70%-95% of the time passed, and use the data before the time... | Note that your dataset might be considered time-series. In time-series it is common to evaluate a model via back-testing rather than a single train/test split. Back-testing uses as training data all data before time T, and as test data all data after time T, and then we do this for many different values of T and averag... | https://datascience.stackexchange.com |
11,227 | [
"https://physics.stackexchange.com/questions/11227",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/3762/"
] | Consider a solid ball of radius $r$ and mass $m$ rolling without slipping in a hemispherical bowl of radius $R$ (simple back and forth motion). Now, I assume the oscillations are small and so the small angle approximation holds. I wish to find the period of oscillation and I analyze the motion in two ways, first using ... | Your first derivation, using energy, uses two different meanings for the same symbol $\omega$. In one place, you interpret it as
$$\omega = \dot{\theta}$$
the time derivative of the angle of the line from the center of the ball to the center of the bowl with the vertical.
In another place, you interpret $\omega$ as... | The answer you got in first method was wrong.
The answer in second is nearly reached, we have to take $R-r$ instead of $r$ because you have to take $r$ from centre of the sphere.
The correct answer was $2\pi\sqrt{7(R-r)/5g}$
| https://physics.stackexchange.com |
63,769 | [
"https://cs.stackexchange.com/questions/63769",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/27250/"
] | I'm reading a book at the moment about logic gates and Boolean simplification. There is a part which I can't seem to follow.
I can easily work out that $A \vee (\neg A \wedge B) \equiv A \vee B$ using a truth table as it's easy to see.
However, I can't seem to turn $A \vee (\neg A \wedge B)$ into $A \vee B$ using st... | Note that
$\qquad A \lor (B \land C) \equiv (A \lor B) \land (A \lor C)$;
you can "multiply out". Add in
$\qquad (A \lor \lnot A) \land B \equiv B$
and you are done.
| I'll write your expression as $A\lor(\neg A\land B)$. Then
$$\begin{align}
A\lor B &= A\lor((A\lor\neg A)\land B) &\text{identity}\\
&=A\lor (A\land B)\lor(\neg A\land B) &\text{distributive}\\
&=(A\lor (A\land B))\lor(\neg A\land B)\\
&= A\lor(\neg A\land B) &\text{absorption}
\end{align... | https://cs.stackexchange.com |
1,042,814 | [
"https://math.stackexchange.com/questions/1042814",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/189901/"
] | Let $K$ be a (not necessarily normal) subgroup of the group $G$ : $K < G$
A fixed element $g\in G$ can act, from the left, on all elements of $G$, thus generating a bijection of $\,G\,$ onto itself: $\,g:\,g'\rightarrow gg'\,$.
Thereby each $g\in G$ also generates a mapping ${\hat{{L}}}_g\colon g'K \rightarrow (... | I think I now know a simpler answer to my question.
Were $G$ not isomorphic to its image in the group $\operatorname{Aut_{set}}(G/K)$ of operators, the kernel $H\equiv \ker\mathbb{L}$ of the mapping $\mathbb{L}\colon G \rightarrow \operatorname{Aut_{set}}(G/K)$ would be different from $1$. This kernel, however, is a... | Let $H< K$ with $H\lhd G$. Then $G/H$ acts on $(G/H)/(K/H)$ by left multiplication. From the isomorphism theorems $(G/H)/(K/H)\approx G/K$ and the original action factors as $$\mathbb L\colon G\to G/H\to \operatorname{Aut}_{\mathbf{Set}}(G/K)$$
(because we talk about the same multiplication after all). Especially, ... | https://math.stackexchange.com |
55,059 | [
"https://mathoverflow.net/questions/55059",
"https://mathoverflow.net",
"https://mathoverflow.net/users/5094/"
] | <blockquote>
Let $\mathfrak{p}_1, \dotsc, \mathfrak{p}_k$ be relevant homogeneous primes ideals in the graded ring $R := \Bbbk[x_0, \dotsc, x_n]$, where $\Bbbk$ is a field. Prime avoidance (in Eisenbud's terminology) tells us that there exists a nonconstant homogenous polynomial $f \not\in \cup_i \mathfrak{p}_i$. I... | The answer is yes. The following is extracted from a preprint of Gabber-Liu-Lorenzini.
<blockquote>
Let $B=\oplus_{n\ge 0}B(n)$ be a graded ring. Let $I=\oplus_{n\ge 0}I(n)$ be a homogeneous ideal of $B$. Let $\mathfrak p_1,\dots,\mathfrak p_r$ be homogeneous prime ideals of $B$ not containing $B(1)$ and not contai... | EDIT: the argument below only works if each $R/\mathfrak{p}_i$ has dimension at least $2$, as pointed out by Angelo.
Suppose $\Bbbk$ is a finite field of size $q$. Let $V_{i,n}= \mathfrak{p}_i \cap R_n$, $d_n= \dim_{\Bbbk} R_n$ and $d_{i,n}=\dim_{\Bbbk}V_{i,n}$. It is enough to show that for $n$ big enough:
$$|V_n... | https://mathoverflow.net |
3,261,185 | [
"https://math.stackexchange.com/questions/3261185",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/680564/"
] | <blockquote>
Find all real numbers a for which the equation <span class="math-container">$$x^2a-2x+1=3\lvert x\rvert$$</span> has exactly <span class="math-container">$3$</span> distinct real solutions in <span class="math-container">$x$</span>.
</blockquote>
I have tried the question very much but a big doubt is ho... | <span class="math-container">$$ax^2-2x+1=3|x|\tag1$$</span>
If <span class="math-container">$a\lt 0$</span>, then the LHS of <span class="math-container">$(1)$</span> is a downward parabola and the RHS is V-shape, so <span class="math-container">$(1)$</span> cannot have three distinct real solutions.
In the following... | Hint: For <span class="math-container">$$x\geq 0$$</span> we get
<span class="math-container">$$x^2a-5x+1=0$$</span> and the case <span class="math-container">$$a=0$$</span> can not be, so we get
<span class="math-container">$$x^2-\frac{5}{a}x+\frac{1}{a}=0$$</span>
and we obtain
<span class="math-container">$$x_{1,2}=... | https://math.stackexchange.com |
696,167 | [
"https://math.stackexchange.com/questions/696167",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/71731/"
] | My logic class didn't introduce us to multiple quantifiers. I've seen a few variations that seem to have distinct meanings:
$$ \forall x, \forall y(...) $$
$$ \forall x \forall y(...) $$
$$ \left( \forall x \forall y \right) (...) $$
$$ \left( \forall x, \forall y \right) (...) $$
$$ \left( \forall x \right)\left(... | No, they are just typographical variants of the same mathematical meaning.
| Just to amplify Henning Makholm's headline answer just a bit ...
<ol>
<li>Some older texts use $(x)$ [without the rotated 'A'] for the universal quantifier, and some use $(\forall x)$ [with the rotated 'A' <em>and</em> brackets]. In those notations multiple universal quantifiers will look like $(x)(y)\varphi$ or $(\fo... | https://math.stackexchange.com |
120,121 | [
"https://mathoverflow.net/questions/120121",
"https://mathoverflow.net",
"https://mathoverflow.net/users/54780/"
] | Let $G$ be a compact topological group (feel free to add hypotheses if necessary). Is there any mean value theorem for its (normalized to 1) Haar integral?
In general, are there mean value theorems for abstract spaces with measures? (Or at least for Borel measures?)
Later edit:
After reading the first two comments, l... | Say $\mu$ is a Borel probability measure on a connected set $A$ in a topological space. Let $f : A \to \mathbb R$ be continuous. Then the mean value
$\int_A f\;d\mu$ is equal to $f(a)$ for some $a \in A$. Proof: the mean value is between the sup of all values and the inf of all values, so (by connectedness) it is a ... | In the form asked in the edit (for every $f : G \to \Bbb C$ continuous, does there exist $x \in G$ such that $\int \limits _G f(g) \ \textrm d g = f(x)$?), the question has a negative answer.
If $\chi \ne 1$ is a character on $G$ and if the statement in the question were true, there would exist $x \in G$ such that $\i... | https://mathoverflow.net |
438,729 | [
"https://mathoverflow.net/questions/438729",
"https://mathoverflow.net",
"https://mathoverflow.net/users/8106/"
] | Suppose <span class="math-container">$M$</span> and <span class="math-container">$N$</span> are complete metric spaces and <span class="math-container">$f, g: M \to N$</span> are uniformly continuous maps between them with common modulus of continuity <span class="math-container">$m$</span>. Further suppose <span class... | I think not.
If <span class="math-container">$M$</span> is compact, then <span class="math-container">$\alpha$</span> must be uniformly continuous; but even then the modulus of continuity can be impossible to preserve; there is some interpretation on what is meant here, depending on the metric you use on the product <s... | A counterexample is given by <span class="math-container">$f,g:\mathbb R\to\mathbb R$</span>, <span class="math-container">$f(x)=x$</span>,
<span class="math-container">$$
g(x) = \begin{cases} 0 & x<0 \\ x & x\ge 0 \end{cases} .
$$</span>
Then it's not possible to find a <span class="math-container">$\delta&... | https://mathoverflow.net |
59,421 | [
"https://physics.stackexchange.com/questions/59421",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/6764/"
] | I know how and why we use this form of stationary Schrödinger equation for finding $\psi$ outside the finite square potential well:
$$\frac{d^2 \psi}{dx^2}=\kappa^2 \psi$$
I Also know that the general solution to this equation is:
$$\psi = Ae^{\kappa\, x} + Be^{-\kappa\, x}.$$
But why do we use only left part $\psi... | I think you are asking for a finite well of width L that is from $ -L/2< x< L/2$. Why do we only use
$\psi(x) = A e^{+\kappa x} $ for $ x<-L/2 $
and
$\psi(x) = B e^{-\kappa x} $ for $ x>+L/2 $.
The reason is we want to be able to interpret the wavefunction as the probability density for finding the... | You need to ensure that the wavefunction is normalisable: $$\int\limits_{-\infty}^{\infty} \mathrm{d}x\, |\psi(x)|^2 = 1. $$
This ensures that the wave function yields a valid probability distribution upon application of the Born rule. If you use the normal convention of taking positive $x$ values to the right and nega... | https://physics.stackexchange.com |
15,209 | [
"https://softwareengineering.stackexchange.com/questions/15209",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/5497/"
] | <pre><code> <body>
<!-- wrapper -->
<div id="wrapper">
<!-- title -->
<div id="title"><img src="title.png" alt="" /></div>
<!-- form wrapper -->
<div id="form_wrapper">
<!-- form -->
<form action="thankyou.php" method="POST"&g... | Some times CSS class names are generic and aren't specifically named. For example, what if you had
<pre><code><!--Code before-->
<!--Column one-->
<div class="center-bold">
<!--Tons of lines-->
</div>
<!--End column-->
</code></pre>
Wouldn't it be nice to know what y... | HTML is like compiled code to me. It's optimized, has no spaces, no comments, and is as small as possible while getting the job done. I do, however, have some comments in my templates which generate the HTML files. You'll never see them though, unless you join the dev team!
Same thing goes for JavaScript. Any JS you s... | https://softwareengineering.stackexchange.com |
452,521 | [
"https://physics.stackexchange.com/questions/452521",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/146836/"
] | I know that one can derive the continuity equation:
<span class="math-container">$$\dot{\rho}=3H(\rho+P)$$</span>
from the Friedmann equations.
<span class="math-container">$H^2=\frac{8\pi{G}\rho}{3}$</span> and <span class="math-container">$\frac{\ddot{a}}{a}=\frac{4\pi{G}\rho}{3}(\rho+3P)$</span>
But what I don't... | First, you have a few typos.
<span class="math-container">$\dot{\rho}=-3H(\rho+P)$</span>
<span class="math-container">$H^2=\frac{8\pi{G}\rho}{3}$</span> and <span class="math-container">$\frac{\ddot{a}}{a}=-\frac{4\pi{G}\rho}{3}(\rho+3P)$</span>
for <span class="math-container">$c=1$</span>
Actually, we can derive ... | The components are called the ''density and pressure components'' and is in fact, a highly simplified version - it is also adiabatic, when really, this is an unfounded assumption - it can be diabatic (ie. non-conserved). First let's go through a variation of the drag coefficient, then we will get to a diabatic form of ... | https://physics.stackexchange.com |
888,778 | [
"https://math.stackexchange.com/questions/888778",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/166613/"
] | I constructed a function $f$ from $\mathbb{N}\times\mathbb{N}$ to $\mathbb{N},$ that is,
$$f(i,j)=\frac{1}{2}(i+j)\cdot(i+j+1)+\frac{1}{2}(1-(-1)^{i+j})\cdot(i+j)+(-1)^{i+j}\cdot i,$$
with which I want to prove the claim that a countable union of countable sets is countable. Here $\mathbb{N}$ denotes the set of all th... | If $i+j$ is odd, $$f(i,j)=\frac12(i+j)(i+j+1)+\frac12(1-(-1))(i+j)+(-1)i=\frac12(i+j)(i+j+1)+j.$$ So for fixed $i+j=n$, as $j$ varys from $0$ to $n$, $f(i,j)$ varys from $\frac12n(n+1)$ to $\frac12n(n+1)+n$.
If $i+j$ is even, $$f(i,j)=\frac{1}{2}(i+j)(i+j+1)+\frac{1}{2}(1-1)(i+j)+1\cdot i=\frac12(i+j)(i+j+1)+i.$$ So f... | If you want a bijection from $\mathbb N\times\mathbb N$ to $\mathbb N$, then I suggest you construct an easier function, because the one you have is really hard to understand.
Instead, it is easier to find a bijection from $\mathbb N$ to $\mathbb N\times\mathbb N$. The most intuitively understandable function is the f... | https://math.stackexchange.com |
178,413 | [
"https://stats.stackexchange.com/questions/178413",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/92964/"
] | In the context of time series, can classification be considered a sub-type of forecasting? I feel like classification is simply projecting the outcome of a certain data set onto a predefined group of outcomes, which sounds similar to forecasting.
| I believe so. After all you may forecast tomorrow's temperature as (38 degrees C), and you can also forecast tomorrow's temperature as hot (meaning >37 degrees c). Both are forecasts because they are predictions about the future.
| I don't really think this is a useful way of looking at things.
<ul>
<li>For instance, you could classify time series as "seasonal" versus "non-seasonal" - but this classification, by itself, won't tell you whether you are looking at ice cream (high sales in summer) or snow shovels (high sales in winter).</li>
<li>Eve... | https://stats.stackexchange.com |
114,810 | [
"https://stats.stackexchange.com/questions/114810",
"https://stats.stackexchange.com",
"https://stats.stackexchange.com/users/31466/"
] | $2^{5-2}$ Design
Design Generators: $D=AB\quad E=AC$
Defining Relation: $I=ABD=ACE=BCDE$
$$\text{Aliases}$$
$$A=BD=CE=ABDE$$
$$B=AD=ABCE=CDE$$
$$C=ABCD=AE=BDE$$
$$D=AB=ACDE=BCE$$
$$E=ABDE=AC=BCD$$
$$BC=ACD=ABE=DE$$
$$CD=ABC=ADE=BE$$
But the alias structure in the book <code>Design and Analysis of Experiments</co... | I think he's just not showing the 4- and 5-way interactions, for brevity and assuming people won't be too concerned about them
| Interaction of order IV or higher are not written because they are usually not significant. This principle is called "sparsity-of-effects principle" and it is explained in Design and Analysis of Experiments by Douglas C. Montgomery.
| https://stats.stackexchange.com |
70,835 | [
"https://cs.stackexchange.com/questions/70835",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/70785/"
] | Hello I'm trying to solve this recurrence with the method that says the teacher that when you get to
\begin{align*}
T\bigg(\frac{n}{2^{k}} \bigg)
\end{align*} you do
\begin{align*}
\frac{n}{2^{k}} &= 1 \qquad (\text{by definition})\\
k &= \log_{2}(n)
\end{align*}
\begin{align*}
T(n) &= 7T(n/2) + n^2 \\ ... | Some of your sums have typos, but you already have the right answer.
Here's a useful fact about logarithms:
$a^{\lg b} = 2^{(\lg a) \cdot (\lg b)} = 2^{(\lg b) \cdot (\lg a)} = b^{\lg a}$
Apply it to your answer, keeping in mind that $\lg 7 \approx 2.8 > 2$:
$O(7^{\lg n} + n^2) = O(n^{\lg 7} + n^2) = O(n^{\lg 7}... | There are indeed some typos as @Craig Gidney pointed out. Moreover you forgot the exponent for the '$7$' in the sum and the term $T(1)$...
I propose you the following solution (which is much similar to yours):
First of all let $n=2^k$ hence the initial recurrence turns into
$$T(2^k)=7\cdot T(2^{k-1})+4^k$$
Now sett... | https://cs.stackexchange.com |
18,048 | [
"https://electronics.stackexchange.com/questions/18048",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/5317/"
] | I need to build a pressure plate to go on the front of a prop to be used in Airsoft.
The idea is this plate is both an target to be shot at and a visual representation of "health".
My initial thinking is along the lines of a translucent perspex circle mounted on springs in front of micro switches. It could have RGB L... | The usual method of doing this would be to use a Piezo buzzer as an impact sensor. Something like this: <img src="https://i.stack.imgur.com/fqvSV.jpg" alt="piezo buzzer">
When struck, these buzzers will produce a voltage spike. This is exactly what they do in most electronic drum kits. What you'd do is have a heav... | If you want to use microswitches, you could buy some with lever arms and extend them by using some heat shrink tubing to attach a few inches of cable tie. Like this:
<img src="https://i.stack.imgur.com/8t4Ee.jpg" alt="extended switch">
Then you could mount the plate on springs. (btw those white bumpers on the front o... | https://electronics.stackexchange.com |
71,778 | [
"https://mathoverflow.net/questions/71778",
"https://mathoverflow.net",
"https://mathoverflow.net/users/4760/"
] | I guess the question can be asked for all manifolds. But I am particularly interested in $S^1 \times S^2$ right now. Concrete example preferrd.
| For $S^1 \times S^2$ I believe the answer is yes. It's a theorem of Hatcher's that the group of homeo/diffeomorphisms of $S^1\times S^2$ has the homotopy-type of
$$O_2 \times O_3 \times \Omega SO_3$$
(it's on his webpage)
I think it's easy enough to check that the subgroup of this which is homotopic to the identity... | The answer is yes. The very nice paper
Hass, Joel(1-CAD); Scott, Peter(1-MI)
Homotopy and isotopy in dimension three.
Comment. Math. Helv. 68 (1993), no. 3, 341–364.
57N10 (57M99)
does not prove this, because this was already known at the time, but gives extensive references.
| https://mathoverflow.net |
3,313,461 | [
"https://math.stackexchange.com/questions/3313461",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/425181/"
] | <em>I am trying to prove the following:</em>
<strong>Let <span class="math-container">$I\subset k[x_1, ..., x_n]$</span> be an ideal. Show that <span class="math-container">$V(I)$</span> consists of a finite set of points if and only if <span class="math-container">$k[x_1,..., x_n]/I$</span>, seen as k-space
vector, i... | NB: for an ideal <span class="math-container">$I\subset R$</span>, we assume <span class="math-container">$V(I)$</span> to be closed subscheme of <span class="math-container">$\operatorname{Spec} R$</span> given by the closed immersion <span class="math-container">$\operatorname{Spec} R/I \to \operatorname{Spec} R$</sp... | <strong>Note:</strong> Here I take <span class="math-container">$V(I)$</span> to simply mean the zero locus of the set of polynomials in <span class="math-container">$I$</span>.
First of all, the assertion you are trying to prove is false. Take the ideal <span class="math-container">$I = (x^2 + y^2 +1) \subset \mathbb... | https://math.stackexchange.com |
11,742 | [
"https://scicomp.stackexchange.com/questions/11742",
"https://scicomp.stackexchange.com",
"https://scicomp.stackexchange.com/users/7695/"
] | Let $\mathbf{1}\in\mathbb{R}^d$ be a vector with all elements equal to $1$. Define:
$$\mathbf{D} = \mathrm{diag}(\mathbf{1}^\top,\mathbf{1}^\top,\ldots,\mathbf{1}^\top) =
\begin{bmatrix}
1 \cdots 1 & & \\
& 1\cdots 1 & \\
& & 1\cdots 1
\end{bmatrix} \in\mathbb{R}^{d\times d^2}$$
I would... | This can be interpreted as summing over an index of a tensor when the vector $x$ is reshaped into a box of numbers instead of a list. In particular, if $X$ is the $d\text{-by-}d$ folded version of $x$, then the operation you are doing is,
\begin{align}
Dx &= \mathrm{vec}\left((I \otimes \mathbf{1})\mathrm{vec}(X)\r... | This is equivalent to computing sums of consecutive contiguous subvectors of $\mathbf{x}$. You won't do much better than simple hand-coded nested loops if you have an automatically vectorizing compiler since you will probably be memory bandwidth limited for large $d$.
| https://scicomp.stackexchange.com |
23,073 | [
"https://electronics.stackexchange.com/questions/23073",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/3240/"
] | A "standard" computer fan has two pins; one for power, one for ground. A three-pin fan adds an additional pin used for the signal from the hall-effect sensor. A speed-controlled fan generally uses a four-pin connector, and is commonly referred to as a "PWM" fan.
It is my understanding that any DC motor can be driven w... | While the statement that "any DC motor can be driven with PWM" is broadly correct* if the actual motor is PWM controlled, in a given implementation the motor proper may be hidden behind an internal controller, and this the case for the very large majority of devices that use small BLDCMs (Brushless DC motors).
Most s... | The PWM input on a typical speed-controlled computer fan expects a logic-level PWM signal, usually around 20 kHz. These sorts of fans have an on-board embedded microcontroller (or similar hardware) which controls the speed by controlling the motor sequence timing (most PC fans are brushless DC motor driven).
In my ... | https://electronics.stackexchange.com |
44,183 | [
"https://mathoverflow.net/questions/44183",
"https://mathoverflow.net",
"https://mathoverflow.net/users/4832/"
] | Let $(X,d)$ be a metric space, and let $C_u(X)$ be the Banach space of bounded <em>uniformly</em> continuous functions on $X$ (with the uniform norm). How can I characterize its dual space $C_u(X)^*$?
I would guess it can be described as some space of measures. I would even be interested in the case $X=\mathbb{R}$.
... | $C_u(\mathbb R)^*$ is essentially the space of complex measures on $\beta \mathbb Z\coprod (\beta\mathbb Z\times(0,1)).$ Here $\beta \mathbb Z$ is the Stone-Čech compactification of $\mathbb Z,$ and the $\coprod$ denotes disjoint union.
One can identify $C_u(\mathbb R)$ with $C_0(\beta \mathbb Z \coprod (\beta \mathb... | Part of $C_u(X)^*$ is well understood. Every uniformly continuous function on $X$ uniqely extends to the completion $\bar{X}$, so certainly any signed Borel measure on $\bar{X}$ is a continuous functional on $C_u(X)$. If $\bar{X}$ is compact, then you're done. Beyond that, I don't think that much can be said. For e... | https://mathoverflow.net |
289,696 | [
"https://physics.stackexchange.com/questions/289696",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/101525/"
] | Yes, I'm thinking about the 'rubber sheet' example, but in 3 dimensions. A typical animation observes the earth from slightly above the plane of the ecliptic, and the earth needs to "come up' out of it's own gravity well in order to move forward. But, if I place myself directly between the earth and the sun, head and ... | Given any small volume in velocity space, the patch near the origin will have the highest probability of having particles. But there aren't many patches near 0.
Not far from the origin, the probability is still pretty high, and there is more volume to integrate over.
Farther away, there is lots of volume to integra... | This question bothered me for a long time also, and I do not find statisfying answers elsewhere. I just leave here an explanation that I think is correct.
The reason for that the Maxwell-Boltzmann distribution <span class="math-container">$g(v)=C_1 e^{(-C_2 v^2)} 4\pi v^2$</span> seems nonintuitive comes from two aspec... | https://physics.stackexchange.com |
212,921 | [
"https://mathoverflow.net/questions/212921",
"https://mathoverflow.net",
"https://mathoverflow.net/users/39421/"
] | I am interested in examples of dual Banach spaces $X$ with the Schur property (weakly convergent sequences in $X$ are norm convergent) like $\ell_1$.
The Lorentz spaces $d(w,1)$ [Lindenstrauss and Tzafriri. Classical Banach spaces I. Sequence spaces. Section 4.3] are candidates because they admit a predual and are here... | No. The unit vector basis $(e_n)$ is unconditional and symmetric but not equivalent to the unit vector basis for $\ell_1$, hence $(e_n)$ converges weakly to zero.
| By Rosenthal's $\ell_1$ Theorem, every normalized basic sequence in $X$ either admits a subsequence equivalent to the canonical basis of $\ell_1$, or else admits a normalized 2-block basic sequence which is weakly null. If $X$ has the Schur property, it follows that every normalized basic sequence admits a subsequence... | https://mathoverflow.net |
47,054 | [
"https://mechanics.stackexchange.com/questions/47054",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/31590/"
] | Our car has only about 22k miles on it, but it's always been kept outside (in NY) and went for several months this winter with no use. This summer, we developed a low grinding sound when braking. A visual inspection shows there's still a lot of brake pad left, but the rotors are seriously scored with grooves and rather... | I know this is long ago, but people will view this thread, so I thought I'd post an answer.
Problem is your caliper needs to be rebuilt or replaced.
Internally, the caliper piston will gum up/varnish over time, and the square-cut seal becomes brittle or fatigued. As a result, the piston will start to become sluggish a... | If the pits are really deep, then grinding may not be an option - there is normally a minimum thickness specified.
I would suggest that you save up for the new pads and rotors and change them when ready. That is ONLY if the existing ones are stopping the vehicle as they should - a bit of extra noise is not an issue as... | https://mechanics.stackexchange.com |
548,418 | [
"https://physics.stackexchange.com/questions/548418",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/254101/"
] | We can find the centre of charge of a system of charges in much the same way we find the centre of mass of a system of masses
Suppose we have two charges of the same polarity and equal in magnitude that are placed at -x and +x along the x axis. The centre of charge would be at the origin.
Would this centre of charge,... | Answered:
<blockquote>
<em>... can we say that for objects with a constant charge density that their charge can be assumed to be concentrated at their geometric centres?</em>
</blockquote>
The answer is <strong>no</strong>.
A good rule of thumb in understanding these kind of things intuitively is "what you see is ... | For an external point in the space, an electric charge uniformly distributed over the surface of an object behaves like a point charge of same magnitude located at the geometric center of that object.
Example: A uniformly charged (metallic or non-metallic) sphere behaves like a point charge for all the external point... | https://physics.stackexchange.com |
139,928 | [
"https://cs.stackexchange.com/questions/139928",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/135987/"
] | Edit: I dont have CS background and I'm still studying Algorithms, so any help will count!
I met this algorithm while I was in interview, I didn't know what category it falls in, and hence I was wondering if there is a better way to solve it and which category it falls into.
<h2>Task</h2>
Consider the following recursi... | I don't see a need for any interesting algorithm. In its essence it is equivalent to the following: given an array <span class="math-container">$A$</span> of integers and an integer <span class="math-container">$x$</span>, move all instances of <span class="math-container">$x$</span> to the front of <span class="math-... | Your solution is almost correct, you just have to add an else statement to the repeater function to delete children when node.children are undefined
<pre><code> if(repeater(node.children[i], targetVal)){
node.children.unshift(...node.children.splice(i, 1))
parentFlag = true
... | https://cs.stackexchange.com |
137,244 | [
"https://softwareengineering.stackexchange.com/questions/137244",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/47328/"
] | <code>java.util.Arrays.sort(/* int[], char[], short[], byte[], boolean[] */)</code> is implemented as a 'tuned quicksort' rather than a radix sort.
I did a speed comparison a while ago, and with something like n>10000, radix sort was always faster. why?
| I would speculate that:
<ul>
<li>Array.sort is implemented as quicksort, because quicksort can sort anything in decent time given a comparator. </li>
<li>Sorting a list of 10000 entries is not so common. Accessing a data-structure of 10000 or more elements is rather common. If you need to maintain order, a balanced se... | Back2dos has said it all, I will just try to further clarify the point which I think is the most important:
Radix sort can only sort the actual primitive values that are contained within the array, based on their binary digit patterns. In actual real-world software engineering scenarios, this case is encountered almos... | https://softwareengineering.stackexchange.com |
172,306 | [
"https://security.stackexchange.com/questions/172306",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/92579/"
] | Suppose a scenario in which you have to login to a public/friends pc which has a keylogger installed. You need to login from that pc. Will it be possible to escape compromising your passwords if you know in advance that the machine is infected.
Taking into account that different keyloggers have different functionaliti... | Most OS's provide some facility to provide user input to an application. This functionality is part of what will get hooked in any decent keylogger and so any means of creating input to the program will likely end up being picked up. This is true whether you use scripts, on-screen keyboards or the physical keyboard i... | <ol>
<li>Go on your phone and change your password to a random one</li>
<li>Login on the compromised PC using the random password</li>
<li>On your phone change the random password back to your normal one</li>
</ol>
| https://security.stackexchange.com |
112,757 | [
"https://softwareengineering.stackexchange.com/questions/112757",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/17215/"
] | Hopefully a relativity simple question. I'm starting work on a new internal project to create tractability of repaired devices within the buildings.
The database is stored remotely on a webserver, and will be accessed via web API (JSON output) and protected with OAuth. The front end GUI is being done in WPF, and the b... | It depends on the size of the project
Here's the guidelines I tend to use
<ul>
<li>A small project, with a handful of pages or less, I almost always keep to a single project.</li>
<li>If the small project's Data Access layer is large or complex, I might separate that out into it's own layer, but otherwise it just sit... | I've seen the best results with one project per layer, plus a testing project per layer. I have seen few applications that cannot be accomplished in 10 or fewer projects in the solution, where the solution encompasses <em>everything</em>.
Don't fall into the trap of using projects where you really want namespacing. ... | https://softwareengineering.stackexchange.com |
241,597 | [
"https://softwareengineering.stackexchange.com/questions/241597",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/31673/"
] | How can one go about modelling highly specific business requirements, which have no precedent in the system? Take for example the following requirement:
<code>
When a purchase order contains N lines, is over X value in total and is being recorded against project Y, an email needs to be sent to persons A and B with the... | Option one seems fine if you provide some sort of configuration setting somewhere in the system so that you can change the Email addresses.
Option two seems like overkill for what appears to be a relatively straightforward business requirement. Only implement it if it appears that it will solve more problems than j... | I suggest that you take both options.
<strong>Step 1:</strong> Introduce the concept of an <code>Alertable</code> category that can be applied to projects. For each instance of <code>Alertable</code>, allow the attachment of one or more users (who have email addresses). Introduce the concept of a <code>Condition</code... | https://softwareengineering.stackexchange.com |
541,266 | [
"https://electronics.stackexchange.com/questions/541266",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/180006/"
] | I imagined the simplest AND gate in context of a small microcontroller project operating at 3.3V with two input pins and two one output pin. This is not the case in reality though, I didn't find one AND gate chip that wouldn't also have VCC and Ground pins.
I'm trying to understand better (coming from programming side ... | Power pins are required for the gate to have gain, which is necessary for fan-out, meaning that one input can drive an output that (reliably and quickly) drives many more inputs on other gates (which may have high capacitance loading or current requirements). That's where the simplified textbook examples of gates typic... | I think you’re referring to standard 74-series logic ICs such as a 74HC00 with 14 pins and four NAND gates. Given that you need power and ground pins regardless of the number of gates, and back in the day you’d fabricate a lot of circuitry by connecting logic gates together, it makes sense to have several gates in one... | https://electronics.stackexchange.com |
238,024 | [
"https://mathoverflow.net/questions/238024",
"https://mathoverflow.net",
"https://mathoverflow.net/users/47300/"
] | If $X$ is a connected algebraic variety of finite type over $k$ (with $k$ a field of positive characteristic) of dimension $d$, and if $\mathcal{F}$ and $\mathcal{G}$ are perverse sheaves on $X$ so $(\mathcal{F}\otimes\mathcal{G})[-d]$ is also a preverse sheaf?
In the same setting above if we have a unipotent connecte... | This is extremely false. Consider the skyscraper sheaf on a smooth point of a positive dimensional variety; this is always perverse (since it is Verdier self-dual). The tensor product of this with itself will be the same sheaf again, so when you shift, you mess up perversity.
| I don't really know much about perverse sheaves, but the answer for the first general question is "No", I think, even for curves.
Here is a simple example for $\bar{\mathbf{Q}}_{\ell}$-sheaves, which is the context I understand a bit. Take a Kummer sheaf on the multiplicative group over a finite field associated to ... | https://mathoverflow.net |
3,290 | [
"https://biology.stackexchange.com/questions/3290",
"https://biology.stackexchange.com",
"https://biology.stackexchange.com/users/1278/"
] | From my experience on SE sites, I believe this is the right site to ask this question under "terminology".
I've been trying to find out whether English has one-word verbs for "undergo mitosis" and "undergo meiosis". I haven't been able to find confirmation on Google, but my linguistic imagination is limited, and I may... | I'm actually not sure myself. If I were to use something, I would go with "Mitos'd" and "Meios'd".
However, you may not win over many fans, depending on the audience. If it's with students or maybe a professor, you could get away with shortening the processes. If it's in any formal setting, be as precise and descripti... | Mitosis as a process does not have a verb form. However, as a process, there is an adjective; you could describe cells that undergo mitosis as mitotic.
| https://biology.stackexchange.com |
702,960 | [
"https://physics.stackexchange.com/questions/702960",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/298433/"
] | It makes sense that intensity of light affects the photoelectric current, but what about the frequency and wavelength, given that intensity remains constant?
The formula for intensity would be I = nhf/tA (where n is the number of photons and hf the energy of one photon, t the time, and A the area).
Now, let's say that ... | We need to be really careful in our definitions - as @Stealth849 points out, it is very easy to confuse what is photon flux, and intensity.
Flux is the number of photons which strike a unit area within a given time interval.
Intensity is the amount of <em>energy</em> per unit area within a given time, and the two are r... | Your reasoning is correct. Assuming the frequency is high enough that the photon energy is greater than the work function, if the intensity is kept constant, increasing the frequency must decrease the photon flux, and thus, the photoelectric current.
| https://physics.stackexchange.com |
105,999 | [
"https://dba.stackexchange.com/questions/105999",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/64458/"
] | I am new to SQL administration and have been tasked with creating some nightly jobs that send an email with certain details contained within a spreadsheet and so far I have the following:
<pre><code>EXEC msdb.dbo.sp_send_dbmail
@profile_name = 'support',
@recipients = 'test@mail.co.uk',
@subject = 'Post Code Analysis'... | Declare a variable first - but use format 112 for this. Like this:
<pre><code>DECLARE @query_attachment_filename NVARCHAR(255) =
N'pca-test-' +
CONVERT(NCHAR(8), GETDATE(), 112) +
N'.csv';
EXEC msdb.dbo.sp_send_dbmail
@profile_name = 'support',
...
@attach_query_result_as_file = 1,
@query_attachment_fi... | In SQL Server, a stored procedure's argument can be either a string literal or a variable. It certainly cannot be a string expression, like in your attempt. To resolve your issue, you could declare a variable, assign your expression to it and then pass the variable to the <code>sp_send_dbmail</code> stored procedure:
... | https://dba.stackexchange.com |
14,212 | [
"https://electronics.stackexchange.com/questions/14212",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/4227/"
] | We purchased a number of stainless steel kiosk keyboards from a Chinese manufacturer a while back and have been seeing extraordinary failure rates (around 30%). Groups of keys just stop working. I've pulled several of them apart and traced the problem to plated through-holes / vias that have failed. I've been repair... | <strong>What's up?</strong>
First, I assume your board has two layers only (top and bottom, no internal layers).
It may be the case that there is not enough copper in the vias. Copper is applied to vias in a galvanic or electro-chemical process. Maybe the solution used in the process was old, maybe the boards were no... | Could it be that the PCB is flexing when keys are pressed, leading to gradual cracking of the via plating as the copper work-hardens?
If so, a solution might be to improve how the PCB is supported, e.g. with high density foam and a metal plate.
| https://electronics.stackexchange.com |
9,799 | [
"https://mathoverflow.net/questions/9799",
"https://mathoverflow.net",
"https://mathoverflow.net/users/1622/"
] | Hi Everyone,
Famous anecdotes of G.H. Hardy relay that his work habits consisted of working no more than four hours a day in the morning and then reserving the rest of the day for cricket and tennis. Apparently his best ideas came to him when he wasn't "doing work." Poincare also said that he solved problems after wor... | I agree that hard work and stubbornness are very important (I think we should all take after Wiles and Perelman as much as we can). But it is also important how you spend the many hours you dedicate to mathematics. For instance, choice of problems is quite important: it is important to make sure that when you work on s... | Neglecting good sleep as a way of doing mathematics is not a good idea. To do mathematics, you need to get enough rest. As to the number of hours per day, it is impossible to count this. When you think about a mathematical problem, you think about it all the time, including when you are asleep. It is true that math... | https://mathoverflow.net |
9,844 | [
"https://cs.stackexchange.com/questions/9844",
"https://cs.stackexchange.com",
"https://cs.stackexchange.com/users/6655/"
] | I have read some complexity papers in which "for infinitely many input sizes" is used.
What is the difference in the computational complexity context between "for infinitely many input sizes" and "for all input sizes"?
| "for infinitely many input sizes $n$, $P(n)$ holds" means there are input sizes $n_1$, $n_2$, $\ldots$, (infinitely many) such that $P(n_i)$ holds for all $i$. In other words, for every integer $k$, there is an input length $n \geq k$ such that $P(n)$ holds.
In contrast, "for all input sizes, $P(n)$ holds" means that ... | "For infinitely many input sizes" makes sense in many contexts. For example, when considering the running time of a TM, it may be the case that for all odd-sized inputs, the machine trivially rejects (e.g. if it's an illegal encoding of an instance). In this case, the runtime of a machine can be long only for even size... | https://cs.stackexchange.com |
142,293 | [
"https://electronics.stackexchange.com/questions/142293",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/53075/"
] | I am using a standard 741 op-amp from TI. For me to amplify any signal, I am required to set +Vs = 15 V and -Vs = -15 V.
I am now concerned as to what will happen if I connect -Vs to 0 (ground) instead of -15 V. Will the op-amp work as it does normally? How is the gain affected?
<img src="https://i.stack.imgur.com/Ubqh... | There are two problems with having the -Vs of a 741 connected to ground.
First, as others have said, the output cannot go below ground. In fact, with a 741 it can't even get very close to ground, only to within maybe 1V or 1.5V of ground. This is called the output swing and is usually rated with some kind of a load r... | The op-amp can only output voltages between the positive and the negative supply. So if your waveform goes negative and you connect the negative supply to ground, your signal will be clipped to 0 volts.
Here's an example with the negative supply to ground of a simple circuit amplifying a sine wave.
<img src="https://... | https://electronics.stackexchange.com |
180,665 | [
"https://security.stackexchange.com/questions/180665",
"https://security.stackexchange.com",
"https://security.stackexchange.com/users/118479/"
] | Recently, I found bug in an e-commerce web app and I will report it.
The bug I found can:
<ul>
<li>delete and edit the favorite products list for all users</li>
<li>delete all notifications for all users</li>
</ul>
What severity and priority of this vulnerability can I report?
| I'd actually say that sounds only moderately <em>severe</em>, because the direct harm that can be done is pretty minor. An attacker can breach a degree of confidentiality (information disclosure), can inconvenience people, can potentially deceive people, and can definitely damage the company's reputation, but can't dir... | It sounds like a very high priority. An attacker could advertise his/her product by putting it on other users' favorites list, for example.
As mentioned by @xander, it's up to the company regarding whether or not they'll fix it, but I recommend submitting as a high priority so that they can be aware.
| https://security.stackexchange.com |
228,447 | [
"https://softwareengineering.stackexchange.com/questions/228447",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/113307/"
] | My android app needs different sized versions of images for different purpose and bandwidth preservation.
Approach one:
<ul>
<li>when the user uploads their avatar or another image, my php script creates 4 versions of that image: mini_200, medium_300, big_400 and original. those paths are then taken and stored in th... | Your first two options are similar. In your second solution, since you could have two files with the same name in different folders, I would recommend using the size as a suffix in the file name such as <code>images/mini/user_image_1482823_mini.jpg</code>, <code>images/large/user_image_1482823_large.jpg</code>.
Your ... | You do not want to store static images within a GET query (i.e. a URL with a "?"), as most HTTP caches will not hold on to the results.
An improvement on option 3 would be to use custom routing so that a path like "/images/large/foo.gif" gets interpreted on the server as something like "/resize_image?size=large&na... | https://softwareengineering.stackexchange.com |
206,254 | [
"https://softwareengineering.stackexchange.com/questions/206254",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/65800/"
] | On a high level, this is my understanding of the difference between a client and server:
<ul>
<li>a server listens on a host and a port, receives requests (e.g. through a socket connection), and then sends a response to the client who initiated the socket connection.</li>
<li>The client is what sends a request to that... | The client and server are basically <strong>two</strong> parts of a <strong>distributed computing model</strong>.
In this model, a user uses a <strong>client computer which sends requests to the server</strong>.
The server then <strong>processes the request and creates the appropriate response</strong> which it sends... | A server is a computational unit dedicated to providing services to one or more clients or other servers.
A client requests services from one or more servers or other clients.
A server can act as a client requesting services from other servers.
| https://softwareengineering.stackexchange.com |
363,125 | [
"https://softwareengineering.stackexchange.com/questions/363125",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/123189/"
] | I have a question which I'm not sure how to generalize and ask properly, so I'll try with an example.
Suppose that I design a parking lot management system. In my system, I have the objects <code>Car</code> and <code>ParkingLot</code>, where <code>ParkingLot</code> holds a map from car registration number to <code>Car... | To me, it seems the validity check of a car registration number is nothing which belongs "logically to a <code>Car</code>", as you wrote, because when you only have this number, you don't have inherently a related car object in scope, and you probably won't need one for doing the validation. (Of course, it also does n... | I think there's some confusion here over whether you're trying to model a real-world domain, or implement an actual software program.
In reality, most parking lots don't "know" which car is in what spot, or even if any given car is in the lot at all. (Some places have automated image recognition of license plates, but... | https://softwareengineering.stackexchange.com |
119,877 | [
"https://softwareengineering.stackexchange.com/questions/119877",
"https://softwareengineering.stackexchange.com",
"https://softwareengineering.stackexchange.com/users/39935/"
] | For string constants its usual to use a class with <code>final String</code> values. But whats the best practice for storing string array. I want to store different categories in a constant array and everytime a category has been selected, I want to know which category it belongs to and process based on that.
Addition... | I much prefer using Enums to store system wide string constants, makes it easy to create additional functionality and I think it is generally accepted best practice.
<pre><code>public enum Cat {
A() {
@Override public void execute() {
System.out.println("A clicked");
}
}... | Your description is quite vague, so maybe I got this wrong, but it sounds as you could use a <code>Map<String,String></code> storing your category relationships. E.g. if you have
<pre><code>class Foo {
final static String[] cat1 = {"val1_1","val1_2","val1_3"};
final static String[] cat2 = {"val2_1","val2_2... | https://softwareengineering.stackexchange.com |
1,595,537 | [
"https://math.stackexchange.com/questions/1595537",
"https://math.stackexchange.com",
"https://math.stackexchange.com/users/296752/"
] | <blockquote>
Iron Golem is an action figure in Minecraft. Iron Golems are loyal to villagers, and will defend them from Hostile Mobs and siege attacks. Suppose that in a particular setting,
an Iron Golem is trapped by Mobs in a mine containing 3 doors. The first door leads to a tunnel that will take him to safety a... | Since two of the three choices lead you right back to the initial state, you can compute the expected escape time fairly easily. Letting $E$ be the expected escape time, we have $$
E=\frac13\cdot3+\frac13\cdot(5+E)+\frac13\cdot (7+E),
$$ therefore $E=15$.
| Don't bother modeling the full distribution of escape times if all you really need is the expected value. It must solve $T=\frac{3}{3}+\frac{5+T}{3}+\frac{7+T}{3}$.
| https://math.stackexchange.com |
76,428 | [
"https://mechanics.stackexchange.com/questions/76428",
"https://mechanics.stackexchange.com",
"https://mechanics.stackexchange.com/users/57044/"
] | I'm not sure if repair/maintenance questions for rust prevention/slowdown are all right. Anyhow, here it goes. I'm sure you'll tell me.
My '03 Pontiac Vibe is showing the first signs of rust ('03! I'm doing well; aren't I!?)
Both rear doors (not the back door; I have two rear doors but one back door) have rust drippi... | No. You have to remove the panel to get to the bolt. It is completely within the door structure.
Realistically, don't be so afraid of the weather sheathing. I think most people's problem with it is they try to take it off too fast. The goo which holds it to the door is meant to be pulled apart, then you can re-stick ... | No, you cannot change that bolt without taking the panel off, you'll have to bite the bullet on that one. Don't worry about the plastic, go slow and use a paint scraper or butter knife to help pry it off. If it tears duct tape is your friend.
If rust prevention is your aim you'll want that panel off in any case so yo... | https://mechanics.stackexchange.com |
441,755 | [
"https://electronics.stackexchange.com/questions/441755",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/155908/"
] | I am using HT12E, for a rf transmitter circuit. As per the datasheet HT12E is a 2¹² encoder.
Ideally such an encoder must have 2¹² inputs and 12 outputs. In addition to that all the inputs should be 1 exclusively.
When i look at the IC, I see 12 inputs A0-A7 + AD8-AD11, which go into the transmission gate circuit o... | You're conflating a couple of definitions of the word "encoder". In this case, the chip is taking 12 binary inputs and encoding them as a serial word along with some synchronization information. The resulting word has 2<sup>12</sup> different states or values.
There is a different kind of (combinatorial) circuit that ... | A chip with 2<sup>12</sup> inputs would have <span class="math-container">\$ ( {2 ^ {12}} ) ^{12} \$</span> possible combinations.
A 12-bit chip has 4096 combinations.
| https://electronics.stackexchange.com |
587,172 | [
"https://physics.stackexchange.com/questions/587172",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/210345/"
] | What I will say is not exclusively true for the KG equation, but let's take it as a simple example.
When proving the invariance of its action under a Lorentz transformation, it suffices to show that the Lagrangian density is covariant, because the absolute value of the Jacobian determinant is 1, and the integral giving... | There is more than one relevant potential difference. You must distinguish between the potential difference, <span class="math-container">$V_L$</span>, across the load (i.e. the 'user' that we are aiming to supply) and the potential difference, <span class="math-container">$V_W$</span>, across just the transmitting wir... | <blockquote>
If we decrease the current by a factor of 10 and increase potential difference by a factor of 10, the system loss (emitted heat) decreases
</blockquote>
This is incorrect. The power is given by <span class="math-container">$P=IV$</span>, so if <span class="math-container">$I$</span> decreases and <span cla... | https://physics.stackexchange.com |
55,746 | [
"https://mathoverflow.net/questions/55746",
"https://mathoverflow.net",
"https://mathoverflow.net/users/2841/"
] | Fix a universe $\mathcal{U}$. Call a category $\mathcal{U}$-complete if every diagram indexed by a $\mathcal{U}$-small category has a limit, and a functor $\mathcal{U}$-continuous if it preserves $\mathcal{U}$-small limits. Usually, when one fixes a universe, one calls this simply complete and continuous.
Now assume w... | For a martingale $M_n$ with bounded increment, then, almost surely :
<ul>
<li>either $M_n$ converges to a finite limite.</li>
<li>or $\limsup M_n=\infty$ and $\liminf M_n=-\infty$.</li>
</ul>
Sketch of the proof. One can assume that $M_0=0$. Let $T$ be the first time at which the martingale goes below $-A$. Then $M_... | For the second part of the question: it depends on the mean and variance you have.
Let $X_t=M_t+Y_t$ where $M_t$ is a martingale and $Y_t$ is predictable. Let $\mu_t=\mathbb E[X_t]=\mathbb E[Y_t]$ and $\sigma_t^2=\sum_{s\le t}\mathbb E[(M_s-M_{s-1})^2|M_1,\ldots,M_{s-1}]$. By martingale central limit theorem, $M_t$ is... | https://mathoverflow.net |
377,800 | [
"https://electronics.stackexchange.com/questions/377800",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/190456/"
] | I have a simple question. Based on Ohm's law, \$V=I\cdot R\$, by increasing the resistance, if the voltage is fixed, the current will drop. By dropping current, the consumption or the loss will drop (\$P=V\cdot I=V^2/R=R\cdot I^2\$). So, the question is: does increasing total resistance of network, result in less consu... | <blockquote>
Based on Ohm's law, \$V=I\cdot R\$, by increasing the resistance, if the voltage is fixed, the current will drop.
</blockquote>
Correct.
<blockquote>
By dropping current, the consumption or the loss will drop (\$P=V\cdot I=V^2/R=R\cdot I^2\$).
</blockquote>
Be careful with terminology.
<ul>
<li>C... | If you assume the voltage is constant, then yes, increasing resistance decreases dissipated power.
| https://electronics.stackexchange.com |
17,301 | [
"https://physics.stackexchange.com/questions/17301",
"https://physics.stackexchange.com",
"https://physics.stackexchange.com/users/6285/"
] | Perhaps an elementary questions. Given a time limited measurement situation, would it be better for one to measure more averages or more data points?
More averages will increase the SNR by $$\sqrt{n}$$ , i.e., making the data point more reliable, but more data points may make the fitting better.
Consider the model i... | For this application, I'd suggest using the actual gravitational force equation, for vector quantities:
<span class="math-container">$$\vec{F} = \frac{Gm_1m_2}{r^3}\vec{r}$$</span>
Here <span class="math-container">$\vec{r}$</span> is the vector pointing from the source object to the point where you are computing the f... | Use $F_x = -x GmM/|r|^3$, similar for $y$ and $z$. This is obtained by taking $F=GmM/|r|^2$ where the direction is $-\hat{r} = -\vec{r}/|r| = -(x,y,z)/|r|$, so the $x$-component is $-x/|r|$.
In the above, $|r| = \sqrt{x^2+y^2+z^2}$.
| https://physics.stackexchange.com |
588,250 | [
"https://electronics.stackexchange.com/questions/588250",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/290917/"
] | I am learning about resistors and may not understand something fundamental, but are there any reasons to prefer a low wattage resistor over a high wattage one? Other than space & cost, are there any basic problems using a resistor with a power rating much higher than necessary?
| You are not missing anything, except maybe undervalue the importance of size and cost.
If a circuit needs a 1/8W resistor and you use a 1/4W or even a 1/2W, there isn't really much of a difference (mostly). However, a 1000W resistor is outright massive, can be over 30cm in length and 4 cm in diameter, whereas a 1W res... | You may find that higher power resistors are not available with value tolerances as tight as lower power ones. There may also be fewer resistance values, and available values may tend to be lower. Also higher power resistors may have higher inductance. Temperature coefficient of resistance is another possible problem a... | https://electronics.stackexchange.com |
19,725 | [
"https://electronics.stackexchange.com/questions/19725",
"https://electronics.stackexchange.com",
"https://electronics.stackexchange.com/users/3757/"
] | What does it mean when somone says something like "3 and 1/2 digit" in case of accuracy of test equipments (or maybe A/D converters?) Can somone explain this a bit with some numbers as examples?
| 3 digits would be 0 through 999<br>
3 1/2 digits is 0 through 1999 (typical for DMMs)<br>
3 3/4 digits is typically 0 through 3999
Has nothing to do with binary digits, but decimal digits, or rather their representation in 7-segments displays. To display every digit you need all 7 segments, but if for the fourth dig... | My best guess with this is that it is in reference to LCD or LED displays.
Some test equipment may well have a "3½ Digit" display. That is, a display with 3 whole digits, and only half of the fourth digit (i.e., a "1").
So the full range of a 3½ digit display would be:
<blockquote>
0 to 1999
</blockquote>
All se... | https://electronics.stackexchange.com |
15,083 | [
"https://mathoverflow.net/questions/15083",
"https://mathoverflow.net",
"https://mathoverflow.net/users/1161/"
] | One example is the Hurewicz theorem which tells us that (e.g) a CW-cx with only one 0-cell has a nontrivial fundamental group if H_1 is nontrivial. What other examples are there? (The CW-complexes I have in mind always have exactly one 0-cell, but for the sake of a more wide discussion one could assume this is not gene... | Try looking up some references on rational homotopy theory. Rational homotopy theory studies the homotopy groups tensor Q, so basically you kill all torsion information. If we focus only on homotopy groups tensor Q, the question you ask becomes easier. As Steven Sam mentions in the comments, the homotopy groups of sphe... | If you don't want to make any assumptions about $\pi_1$, then I think the question is hard.
Maybe Hurewicz is most of what you can say. If assume something like simply connected, you can say a lot more. There are many things you can say rationally, some of which were pointed bout my Kevin, but even integrally or mod p ... | https://mathoverflow.net |
20,132 | [
"https://dba.stackexchange.com/questions/20132",
"https://dba.stackexchange.com",
"https://dba.stackexchange.com/users/4779/"
] | I am in the process of defining filters on a merge replication publication for our database.
The problem I am coming up against is that merge replication has these rules, I don't like to call them limitations because I can understand the purpose.
1) When creating an article filter you cannot include a subquery, or at... | I must put out a warning. We have now moved away from merge replication, and I would have to suggest that the scheme above could be a major performance issue.
The exception to that would require you to have a small publication with either small amounts of filtering and/or filters that are not multiple levels deep. Fo... | This is a complicated situation, but I think that the best solution would be to make an additional table (which I'll call UserFilters), just to hold the consolidated data from the Road, UserRegion and SyncSetting tables in a single combined row format and then to Join your Replication Filter to that table instead. Thi... | https://dba.stackexchange.com |
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