# Recent content by coelho

1. ### Why does light and gravity travel at the same speed?

I have a question, and it seems this is the most apropriate place and time to ask it. From what i remember, black holes are created when a very massive star shrinks itself to a radius smaller than the so-called Schwarzschild radius. But, from a observer far away from it (like us, for...

Ok, i'm assuming that T' means dT/dt, and that a, b, P, r and s are not functions of t. If it were the case, this is a separable DE, and can be solved by the standard way. The only problem is you will get t as a function of T, instead of T as a function of t as wished, but i'm afraid this...
3. ### ODE Approaching the expicit solution

This small hints aren't supposed to make the DE separable. They are just things i noticed when looking to the DE, things that beginners usually dont notice, and that may put him (or her) one step closer to the solution, as we aren't supposed to give straightaway answers or hints that make they...
4. ### Volume flow rate DE - Help needed

Are H and h the same variable, or related in some way?
5. ### ODE Approaching the expicit solution

There are two hints that may be useful (or not). \frac{d(tan(y))}{dy}=? \frac{d(x^2 y)}{dx}=?
6. ### Volume flow rate DE - Help needed

Could you outline how did you arrive at the expression you found after integrating?
7. ### Stability of fixed point

For me, it seems the problem lies in defining stability of a fixed point for a function that is a function of times before "n", like, in your case, "n-1" and "n-2". For a function that is a function only of the previous value of x, a fixed point a is said stable if, for a given initial...
8. ### How to express a function as a function of another function?

Indeed... but while they may have a inverse, it may be hard (or even impossible) to write down this inverse function... unless "cheating" is allowed, like using functions like Maple's RootOf( f(x) ) ...
9. ### How to scale this expression

For some reason, for me this formula resembles Statistical Mechanics, more exactly the Partition Function. If this formula didnt come directly from it, maybe you could read about it, see if it applies to your problem, and see if there is already some technique for doing what you want.
10. ### Partial Fraction

Ok... from what ive understood, you want write \frac{1}{(ax_1+1)(ax_2+1)\cdots(ax_L+1)} as \frac{c_1}{ax_1+1}+\frac{c_2}{ax_2+1}+\cdots+\frac{c_L}{ax_L+1} where the c's are constants. My question is, what is the variable the c's must be independent of? a or x?
11. ### 2011 in review

The speedy neutrinos!
12. ### Do you suffer from an affective disorder?

Well... would an attractive disorder cause suffering? :smile:
13. ### Do you suffer from an affective disorder?

I wouldnt say its insanity... but it may be a disorder too... have you ever heard about http://en.wikipedia.org/wiki/Schizoid_personality_disorder" [Broken]?
14. ### Problem with solve two differential equations.

Well... i would like to help, but there are some things i could not understand. Is y a constant, or it is a function of v, t, or some other variable? Is f(y,v,t) a given (known) function? (like f(y,v,t)=sin(y+v*t) for example) And what are the variables you are trying to solve for?
15. ### Light hitting a superconductor?

Do superconductivity alters the X-ray transparency of a material? If i remember correctly, conducting materials are opaque to EM radiation because the EM field interacts with the free electrons, losing energy during this process, and so the field gets weaker (attenuated) as it enters the...