Variable Definition and 1000 Threads

Suppose we have some partial differential equation for a scalar ##f## $$Df = \rho$$ taking values in ##\mathbb{R}^n##, and further suppose that the differential equation is completely independent of the variable ##y:=x^n## so that the differential operator ##D## only contains derivatives with...

Homework Statement The question asks for resistance R of a disk with radius r and fixed width w, whose cross sectional area is variable. Unlike in the picture below, the resistor is not connected to the circuit on the flat ends, but on the cylindrical sides. Homework Equations...

This technically might not belong here, mods, put it in it's proper place if not. So I'm studying for a test on Monday. Not a big deal, we use webassign, you may commence with the horrified gasps and groans, I know. So here's my odd little situation. I get a problem like this one Integral...

I am studying an article which involves stochastic variables http://www.rmki.kfki.hu/~diosi/prints/1985pla112p288.pdf. The author defines a probability distribution of a stochastic potential V by a generator functional G[h] = \left<exp\left(i\int...

Hi, I'm currently working on my end of the year project for my studies. I have a DC motor mechanically linked to a wind turbine PMA. My aim is to control the speed of this motor (using PWM) to simulate different types of winds. My problem lies on the generator side. I need a load to...

Hey! I'm working with some regression related stuff at the moment and i'd need some help with multiple variable prediction interval. Prediction interval for a single variable can be calculated using PI = \hat{\beta_0}+\hat{\beta_1}x_i \pm t^* s_e \sqrt{1+\frac{1}{n} +...

i'm building fm radio jammer for project for my ee class in physics department. a circuit is here. http://www.circuitstoday.com/fm-radio-jammer i bought the components, soldered on PCB. it hasn't worked. an oscilloscope shows sine oscillation even if there is no L and C for tank circuit...

Hello fellow PF members, This is my first post. I am wondering if there is a mechanism that alters the gear ratio in worm gear-worm wheel setup.. Something like a variable pitch worm gear that can be used instantaneously to alter the gear ratios. If not for worm gear, is there anything in...

if x is direct, indirect or exponentially propotional to A and as well as B can we write x=kAB ? if we write the equation seperately, we have x=k1A, x=k2B when combined, x2=(k1k2)1/2 (AB)2 then x=k3(AB)1/2 to see the real complicate example EX.1 trypsinogen is converted to trypsin in...

Homework Statement Question 1: For the circuit below, determine what happens at maximum resistance when varying the 10K (decade box) variable load. Question 2:Explain the answer to the previous question, in terms of voltage compliance of the current source. Question 3:What causes detectable...

The following function acos() does not accept any variables. I have included the math.h header. For example i = 1; acos(i/2); // This should be equal to 60

Given V=xf(u) and u = \frac{y}{x} How do you show that: x^2 \frac{\partial^2V}{\partial x^2} + 2xy\frac{\partial^2V}{\partial x\partial y} + y^2 \frac{\partial^2V}{\partial y^2}= 0 My main problem is that I am not sure how to express V in terms of a total differential, because it is a...

I've been getting pretty rusty in terms of derivation in recent years. Encountered this problem which I can't derive the steps despite knowing the solution. \frac{\partial^2 u}{\partial r^2} + \frac{\partial u}{\partial r}\left(\beta + \frac{1}{r}\right)+\frac{\beta}{r}u=0 Known...

I need to solve the equation for x, where a is a known constant and . The bs are known too. What i need to do is sto find for which xs I'll have a specific value of a, eg a=0.5, i.e. solve for x and substitute the a. I believe that the result will be a group of xs and not a single...

How would I apply the change of variable technique to solve the integral $$\int x\frac{2x}{1000^2}e^{-(x/1000)^2}dx$$ w/ out the $$x$$ I used $$u=(x/1000)^2$$ , and $$du=2x/1000^2$$ Now, I am calculating $$E(x)$$, and now sure how to deal w/ the extra $$x$$. Thanks for any help!

Homework Statement for this question, my ans is pi/2 not pi/4 . can anybody please check where's the mistake? Homework Equations The Attempt at a Solution

Here's the problem: I'm having trouble using T(u,v) to figure out how to find the region that transforms into the the given region, R. Can anyone help? Thank you!

The major problem I have with hidden variable theories is this: Even if you find hidden variable solutions which would render quantum physics unnecessary, you'd still be left with the ultraviolet catastrophe problem. You can use holographic principle, alternate realities, determinism or any...

Homework Statement for this Q and t are variables, 10 and surd k are constant, is my working correct? Homework Equations The Attempt at a Solution

I'm a little confused about these. Sometimes I have seen solutions where F=d(mv)/dt=mdv/dt+vdm/dt is used and solved as a differential equation. An example is this: A water drap falls through a cloud. It has initial mass m which increases at a constant rate km as it falls. Show that it's...

Homework Statement Given 1) xy = 1 2) x(t^2)-y = (t^3)-1/t Express x in t, y in t 2. The attempt at a solutionx/t = [(tx+1)(td-1)] / [(t^2)-1] but I still can't separate t and x, driving me mad it is. Also subtracted 1) from 2) to obtain (t^2)x - (t^3) +1/t -1/x = 0 but no progress...

Hi, I have looked everywhere. Can someone please point me in the right direction for solving a system of ODEs with variable coefficients? I managed to solve such system with constant coefficients.

Am am presented with the problem: $$ h(t) = c - (d - 4t)^2 $$ At time t = 0, a ball was thrown upward from an initial height of 6 feet. Until the ball hit the ground, its height, in feet, after $$t$$ seconds was given by the function $$h$$ above, in which $$c$$ and $$d$$ are positive constants...

Homework Statement This an example from Boyce+DiPrima's text on ODEs. Original problem is to solve 2t2y''+3ty'-y=0, given that y1=1/t is a solution. But I'm stuck at the part where I'm to solve 2tv''-v'=0, v being the second unknown solution. The Attempt at a Solution In the text...

Let $$f(x,y)= \frac{x^3+y^3}{x^2-y} $$if $$x^2 $$is not equal to y and 0 otherwise. I need to find the limit when (x,y)->(0,0) I'm sure the limit exist and is equal to 0, I was unable to conclude switching to polar coordinate so I wana use "the squeeze law" I only have to evaluate $$f(x,y)=...

Homework Statement At time t=0 a dust particle of mass m_0 starts to fall from rest through a cloud. Its mass grows exponentially with the distance fallen, so that after falling through a distance x its mass is m_0exp[αx] where α is constant. Show that at time t the velocity of the particle...

Hi, what is the name of the variable star with the longest period? I know Mira variables are in general the longest, but which particular star has the longest period? Thanks.

Homework Statement I have the equation: \mathbf{F}_{2,1} = \frac{Q_1 Q_2}{4 \pi \varepsilon_0 {r_{2,1}}^2}\hat{r}_{2,1} (standard electric force equation for 2 charges) I know the value of everything except Q2 and have to find it. The vectors each have 3 components. Normally in an...

Homework Statement In calculus 1, honestly, I never understood this as it just doesn't make sense. Now in multivariable calculus, it still doesn't make sense. After all these engineering, math, and science classes, I still cannot figure these problems out, and it pisses me off! I would...

Hi, I was reading about VASIMR ,my knowledge in rocket science is very limited ,i was able to understand how plasma is produced and used for propulsion but i didn't understand how specific impulse is varied and why is it not possible for other (ion)thrusters or even chemical ones to vary the...

Homework Statement find (x,y,z) Homework Equations 3x - 4y + 7z = 0,-------------->first equation 2x - y - 2z = 0,---------------->second equation 3x3 - y3 + z3 = 18.---->third equation The Attempt at a Solution on subtracting first two equations i get x - 3y + 9z = 0 using this if i...

Hello All, I'm building a HMM for some data where there are two different time delays. Specifically, I collect data in consecutive traces, such that the time delay between each data point within a trace is approximately fixed, and the time delay between each trace is approximately fixed, but...

This problem was originally a multi objective problem but using scalarization it can be transformed to the following: Min: -p'*x + u*x'*V*x subject to 1*x=1 -u is the risk aversion index that I wish to vary from .1 to 100 -V is a (4x4) variance covariance matrix -p is the (4x1) expected...

i was looking at an e-cig and wondering how it regulates watts. would it be viable to make your own? for those of you who don't know they run off of a 18650 3.7v battery that powers a coil. the coil is in the ballpark of .3 - 3.5 ohms. how do i get 30 watts of regulated power and jam it...

Hi, I'm hoping someone can enlighten me on this as I'm a little bit fuzzy on the reasoning: Say I have a space-time dependent field B_{a} that interacts with fermions such that it affects their energy dispersion. It appears in the energies in the form...

Homework Statement |zi - 3| = Pi Homework Equations Well, it clearly has to do with a circle but I do not believe there is a general equation for what I am asking about. The Attempt at a Solution There is no general solution not trying to solve anything. I want to know exactly...

Homework Statement Let ##Y_1,...Y_n## be independent standard normal random variables. What is the distribution of ##\displaystyle\sum_{i=1}^n{Y_i}^2## ? Let ##W_n=\displaystyle\frac{1}{n}\sum_{i=1}^n {Y_i}^2##. Does ##W_n\xrightarrow{p}c## for some constant ##c##? If so, what is the...

How to transform a random variable CDF to a standard normal Given F(x) = 1- exp (-sqrt x), for x greater that 0 Thanks.

Is there a "Leibnitz theorem" for sums with variable limits? Wikipedia says that if we want to differentiate integrals where the variable is in the limit and in the integrand, we can use Leibnitz theorem: But what if I need to integrate a function defined like this:\Sigma_{I(x)}[f(x,t)]...

Coming in here with the following question, when I see what kind of stuff you normally tackle, is very embarrassing! But... I simply am too rusty for this stuff, it seems. This is NOT homework. This is something I need to do in a game I'm working on. I end up in and endless loop when trying...

Hello, My question is: how much energy is needed for changing inertia of flywheel? example: on rotary shaft we have linear actuator which is moving some object (mass). by that movement, radius of flywheel is changing. ...if there is energy input to flywheel, mass is moving away form...

Intuitively it seems more plausible that there should be a hidden variable influencing the path of particles when they travel, than having a fundamental mechanism of nature be truly random, but what do I know. I just don't understand how you can ever completely rule out a hidden variable. I know...

I am having trouble understanding how the author of the textbook "Physics for scientists and engineers" (Randall D Knight), is performing the variable change in the definite integral of the picture that I have taken a screen clipping of. Can someone please help me figure this out?

Homework Statement Guys, could you please help me solve this equation for x: 220000=\sqrt{1.4*10^{32}*\left[ln(\frac{6.17*10^{20}+x}{6.17*10^{20}})-\frac{x}{6.17*10^{20}+x}\right]*\frac{1}{x}} It's supposed to give me the radius of the Milky Way's dark matter halo. I expect to get a...

I am interested to see if there is a way of creating a metal ring which has a variable diameter, the only way I imagine that this can be done is using segments which come together to form a circle, once pulled away the diameter changes however, the problem I face is that when the segments are...

Homework Statement Ok this might be a stupid question, but: https://fbcdn-sphotos-h-a.akamaihd.net/hphotos-ak-frc3/t31/q77/s720x720/10001118_10202561443653973_1625797585_o.jpg Why is this the case? I think for all of this to be right, then the assumption of ##Y=u(X) \Leftrightarrow...

i am middle of engg project . to make an automatic irrigation system ,using plc , main problem is humidity sensor which i am using gives out put of 0-5 volt but plc require more output for better results,...can anyone suggest a voltage amplifier or any circuit using op amp

Homework Statement Let ##f: M_{n \times n} \rightarrow M_{n \times n}## with ##f(X) = X^2##, where ##M_{n \times n}## denotes the vector space of ##n \times n## matrices. Show ##f## is differentiable and find its differential. Homework Equations The Attempt at a Solution So far...

Hey all! I've tried solving this problem every way I could think of and I wanted to see if I'm doing this even remotely right. Mind helping me out? Homework Statement Problem: A mountain climber is stranded on a ledge 30 m above the ground. Rescuers on the ground want to shoot a projectile to...

I solved this many years ago, but after revisiting Trig in order to tutor my daughter, I revisited this to stimulate myself but am hitting a brick wall. Problem: A 4 inch square sits in a corner(picture x,y origin). A 12 inch ruler or line leans against the wall at an angle such that there are...