# Search results

1. ### Cold box power problem

Hello all, I'm having a bit of a problem on a class design project. We have to design a mini-fridge for developing coutries that runs on its own power and must cost under \$100 ideally (it can go over if necessary). My group decided to use a hand-crank powered thermoelectric module and fan...
2. ### Hand crank generator

Hello all, I have to design a hand crank generator to produce power for some downstream application. The amount of power is on the order of that needed for anything between a heavy-duty flashlight to one of those desktop mini-fridges that hold one soda can. Thing is, I'm drawing a blank on...
3. ### Spring constants

Basic engineering question. For any average spring (say, in an industrial setting), is the spring constant in compression about equivalent to the spring constant in extension?
4. ### Bode Plot Plotting

Homework Statement I have to plot some data for a lab writeup. It's based on the frequency response of fluid catheter-transducer systems. Part of this writeup includes making Bode plots for the gain and phase shift. I know how to plot my data; the problem that I am having is that I want to try...
5. ### Pressure in a column of water

Homework Statement I feel like I'm doing something seriously wrong here.:uhh: How tall must a column of water be to generate a pressure of 100mmHg? Homework Equations P = pgh, I think, is the only necessary equation. The Attempt at a Solution So..... 100mmHg = 1 kg/m3 * 9.81...
6. ### 555 Astable Circuit question

Hello. I have a question about an astable oscillator made with a 555 timer IC. According to a National Instruments website, the off-duty cycle for an astable oscillator is Rb / (Ra + 2Rb) and the frequency is 1/(0.7*(Ra + 2Rb)*C), where Ra is the resistor in between pin 7 and the power...
7. ### Debris in circulation

At a high shear rate, red blood cells become elongated and oriented in one direction, facilitating smooth blood flow. However, at a high enough shear rate, the cells will become so strained that a part of the cell membrane pinches off. This often occurs in poorly designed medical devices that...
8. ### Impedance and frequency-domain

Homework Statement This is a general question regarding impedance in circuit analysis. I know that in order to find the total impedance of a circuit, you transform each element characteristic into the frequency domain, i.e., R\rightarrow Z_R = R, C\rightarrow Z_C = \frac{1}{Cs} ...
9. ### First-order ODE

Homework Statement It's been a couple years since diff. eq. Any tips/strategies on solving the first-order ODE: K\frac{dp(t)}{dt} + \frac{p(t)}{R} = Q_0 \sin{(2\pi t)} where K, R and Q_0 are constants?
10. ### Stumped by units

Of all the evil things that I could be stuck on, its not even bad arithmetic this time around. No, I have been stumped by units. Does anybody know what the si symbol 'sc' stands for? Is that even a symbol?
11. ### Hydrogenation of alkynes and alkenes

Hello. I have a question about catalytic hydrogenation reagents. I know that you can perform syn hydrogenation of alkenes with H2 and Pd catalyst, and the same goes for alkynes except for the addition of quinoline (and CaCO3 doped Pd catalyst). I was wondering if there is a reaction with...
12. ### Proving solution of wave equation

Hello everyone. I'm asked in a problem to prove that a given general solution is valid for the wave equation \nabla^2 p - \frac{1}{c_0^2} \frac{\partial^2 p}{\partial t^2} = 0 . The given solution was p(x, t) = A_1 f_1 (x - c_0 t) + A_2 f_2 (x + c_0 t). I just need a check of work here. I...
13. ### I don't have a glue

Ahem..... no pun intended. :tongue2: Actually, I need an adhesive to affix a snippet of myocardial tissue to some polyethylene tubing. Any ideas?
14. ### MATLAB Matlab: inverse Radon transform

Hopefully someone know image processing toolbox well enough to answer my question! I need to reconstruct an image from a sinogram, and I'm using the iradon(S,theta) function, where S is the sinogram image and theta is either a scalar or vector quantity of projection angles. However, we...
15. ### Maple Syrup Vandalism

Hello PF peoples! Today was a sad, sad, day.:cry: I was on my way to class and I stepped on something sticky right outside my front door. Long story short, someone thought it would be really funny to coat my car, front doorstep and patio with a generous layer of maple syrup.:mad: I know...
16. ### Average wall stress in an aneurysm

Hints, please? "An arterial aneurysm is a life threatening condition associated with a balloon like expansion of a local segment of an artery. Using a free body diagram determine the average wall stresses in a closed spherical aneurysm with wall thickness h and inner radius r_i. Ignore blood...
17. ### Check Ochem reaction please

I did this problem a little differently than my professor, so I need someone to check if it is valid. Let's start with 1-methyl-1-cyclohexanol. If I react this with HBr, I should get 1-bromo-1-methylcyclohexane. And if I then react this with EtO-/EtOH, I should get 1-methyl-1-cyclohexene...
18. ### Convolution and a diff eq

Any hints to this problem? "Assume the solution to a differential equation is given by \frac{dy(x)}{dx}+ay(x) = f(x) where y(0)=y_0 and a is a constant. Show how y(x) can be written as a convolution of f(x) and an exponential e^{ax}." The only hint we got from the prof was to multiply...
19. ### Stereoisomerism problem

How many stereocenter containing isomers of c5h10 are there where the molecule must contain one ring? I identified the cis and trans forms of 1,2-dimethylcyclopropane, but I think my TA said there was one more form containing a cyclopropane ring.... but I can't remember for sure. Is C1 on...
20. ### Ochem energy calculation - correct answer?

I think the solution manual is wrong for this problem. The problem: The naturally occurring sugar glucose exists in two isomeric cyclic forms. These are called [alpha] and [beta], and at equilibrium they are present in a ratio of approximately 64:36. Calculate the free energy difference that...
21. ### Calculators Problem with TI89

Hello. My graphing calculator's screen is degenerating. Up near the top I get blue bands which eventually fade to nothingness, and its spreading downward. Right now the top fifth of my screen is missing. I've only had this calculator for about three years now. I was wondering if anyone else...
22. ### Wheatstone bridges

Say I have two Wheatstone bridge circuits: On each of them, the top half of the diamond is formed using two fixed resistors. The bottom half of each diamond consists of a variable resistor on the left and a resistance temperature detector on the right. Now, for the first bridge circuit, the two...

Is it always true that the gradient of a function is normal to the flux coming out of the surface represented by the function?

"The temperature of space is given by \phi (x,y,z) = xy + xz . A fly is flying in space and at each point (x,y,z) of its journey it flies in the direction \mathbf{F} (x,y,z) in which the rate of increase of temperature is maximum. (a.) Calculate F(x,y,z). (b.) Find the curve along which the fly...
25. ### Matrix manipulation in c

any tips on how to implement a way to find the null space for a given matrix?
26. ### Line equation

How do you find the equation of a line between two points in three dimensional space? I sorta forgot. =\
27. ### Don't mind me

Just copying a latex image for a physics lab. firefox doesnt let you preview the latex in a post. G=\frac{V_{out}}{V_{in}}=\frac{R_{out}}{\sqrt{R_{in}^{2} + \frac{1}{\omega C}^2}}
28. ### Volume of Ellipsoid

I've been asked to derive an expression for the volume of an ellipsoid. I know what the expression is, I just don't know how to get there from the information given. All that is given is that it is defined by \frac{x^2}{a^2} +\frac{y^2}{b^2} +\frac{z^2}{c^2} \leq 1, a standard...
29. ### Acceleration where velocity is changing

How would one describe the acceleration (linear and angular) if the velocity is constant but direction is constantly changing, i.e., circular motion?
30. ### Infinite product - the shortest question

I just heard about the inifinite product, so using my knowledge of inifinite sum this is purely guessing. \Pi_{i=1}^{N} a_i = a_1 a_2 a_3 ... a_{N-2}a_{N-1}a_{N} correct?