# 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. ### 3C2H2 + Cu2Cl2 and more

If I am doing this right, 3C2H2 in Cu2Cl2 will give you one molecule of unreacted C2H2 and vinyl ethyne, or CH2-CH-CCH, which if you add up all the carbons and hydrogens, you get 6C and 6H. As to the second question, I don't think C6H4 exists, but it is listed as a hypothetical byproduct in...
5. ### Role of Selenium in Xerography.

This is a pretty basic answer, but I know that selenium is used as a photoconductor and also as part of the print toner that is used to reproduce images put through the copier.
6. ### 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...
7. ### 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...
8. ### 555 Astable Circuit question

I see... thanks!
9. ### 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...
10. ### 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...
11. ### Impedance and frequency-domain

what if its a circuit consisting of only a resistor and a capacitor?
12. ### 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} ...
13. ### First-order ODE

its been a really long time since I've had to solve ODEs for any class, so I'm just using the cookie cutter of an example in my old diffeq book to help. Please correct me if I am wrong in my work. (Note: I've disregarded the constants of integration for now). The original equation is...
14. ### 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?
15. ### Mayer's relation

because the units on the two sides of the equation must match in order for the equation to be valid, the units of C_p and C_v must be the same as the units for the universal gas constant R.
16. ### Electrostatics question

I don't know if its valid on such a small scale but you could try the following: You have the force. You know that F = ma. Once you find the acceleration, you could use a newtonian equation of motion. I believe there is one that relates acceleration, distance, initial and final velocity. The...
17. ### 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?
18. ### Hydrogenation of alkynes and alkenes

got it. quinoline stops reduction at the alkene stage. reacting alkyne with direct H2 and Pd gives a tetrahydrogenated alkane.
19. ### What would DNA look like?

I'm really digging our highly intellectual discussions of snot. :rofl:
20. ### Chemistry Question on Hydrated Molecules

plus, correct me if im wrong experts, but i dont think there is much of a reactivity difference with anhydrous and hydrated salts, except in cases where the water can interfere to give different products. I think theres just a difference in the reaction times? This is even more ammo for physical...
21. ### Chemistry Question on Hydrated Molecules

i'm with borek. its very annoying to classify some things especially when it could be both. on one hand, it could be a chemical change since each unit of CuSO4.xH2O is losing its water and becoming just CuSO4, and you release water vapor in the reaction. on the other hand, hydrated salts...
22. ### Preparation of Alkyl Halide from Alcohol

water can act as an acid or a base. If water is left to stand with your t-butyl chloride you can eliminate a small amount, get back your t-butanol and lose some product.
23. ### Chem reactions

Oh yeah, it won't react with the alcohol because if you protonate the alcohol O, you lose aromaticity in resonance. Since aromaticity is a strong driving force, the reaction with the alcohol O is not favored. Does that make sense?
24. ### Chem reactions

my first reaction was that it should react with the alcohol... but if your text or teacher says it doesnt then... my guess is that instead of looking at "functional groups" per se, try to understand the structure of the molecule. Both oxygens have free electrons but the ether O is farther out...
25. ### 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...
26. ### What would DNA look like?

In regards to looking like snot, I don't think there would be much difference between plant and animal DNA. Feels? Probably slimey.
27. ### Proving solution of wave equation

Sorry, completely forgot the context :redface: This is for ultrasonic imaging. The function p(x,t) is a function of position (depth) in tissue and time.
28. ### Proving solution of wave equation

Here is the work: \nabla^2 p - \frac{1}{c_0^2}\frac{\partial^2 p}{\partial t^2} = \frac{\partial^2 p}{\partial x^2} - \frac{1}{c_0^2}\frac{\partial^2 p}{\partial t^2} = 0 \frac{\partial^2 p}{\partial x^2} = A_1 \frac{\partial^2 f_1}{\partial x^2} + A_2 \frac{\partial^2 f_2}{\partial x^2}...
29. ### 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...
30. ### What would DNA look like?

To have a mole of something you need a finite number of regular molecules. 6.022*10^23 to be exact. DNA comes in long chains or little snippets, and depending on its nucleotide makeup would come in different molecular weights even if it was of uniform length. So I don't know if you can even have...