Recent content by ddoctor

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    Old guy going 'back to the future'

    Here is my situation: I am currently a physician now for the last 20 years. I'm 51. I have a B.A. in Astronomy which is my passion. I want to go back to graduate studies in physics/astronomy. I tested this out several years back and took a graduate astronomy course at our local university. I was...
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    Physics Physics vs Medical field

    Do what you love. Forget about things like tedium and money. You can't take the money with you. Believe me. I'm an orthopedic surgeon now and after 20 years I am planning to return to graduate studies in physics and/or astronomy (I have a B.A. in astronomy) because astronomy is my passion. Sure...
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    Derivation of Kepler's laws- differential equation question

    Hi group, Could someone 'remind me' why the equation u" + u = km/L^2 has the solution of the form u(theta) = km/L^2 + C cos(theta - theta(o)). Any references would be appreciated. Thanks Dave
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    Question on stellar absorption spectra

    So basically what you are saying is that C, N, O are not present in the photosphere in sufficient quantities under the right temperature conditions in relation to their respective binding energies to produce significant absorption spectra? However there are a couple of spectral types where you...
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    Question on stellar absorption spectra

    Why don't stellar spectra show absorption lines for carbon, oxygen or nitrogen if they are such abundant elements. Is there a 'spectral type' that does? Thanks Dave
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    Simplifying radicals containing polynomial fractions

    ok. thanks! so then i get [(x+1)^2 - (x-1)^2/ (x+1)^2] . after that i expanded the polynomial expressions in the numerator and combined them. that simplifies to sqrt [(4x)/ (x+1)^2] or 2 * sqrt (x)/ (x+1). easy enough.
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    Simplifying radicals containing polynomial fractions

    no idea how to simplify this one: sqrt [1- [(x-1)^2/(x+1)^2]] thanks dave
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    Ideal gas law problems: Pascals vs Atms?

    Hi group, Simple arithmetic problems using PV = nRT or NkT. How do you know when to use pressure units in atmospheres or pascals? For example, in 1 particular problem they give you a pressure in units of Torr, volume in cubic cm and temp in Kelvin and ask for the number of molecules. Couldn't...