Recent content by helenwang413

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    Graduate Differentiate an integration of a function with respect to that function itself

    Hi, I am stuck in a differentiation problem. I need to find the derivative of an integration of an unknown function with respect to the function itself, and then set the derivative to zero in order to find the form of the funtion which gives the minimum of its integration. For example, find a...
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    Undergrad Order of Integration and Differentiation: Are There Any Exceptions?

    Under what condition can we change the order of integration and differentiation? Thanks!
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    Graduate How does the cosmic microwave background (CMB) define a cosmological frame?

    Yes, the velocity explanation is accepted by most of the researchers. What is the best evidence for that? Besides, it sounds like, to me, a bit circular argument. You define a CMB rest frame, and then calculate the velocity dipole according to the Doppler effect. What if there is something...
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    Graduate How does the cosmic microwave background (CMB) define a cosmological frame?

    How to understand that the cosmic microwave background (CMB) can define a cosmological frame? Cheers!
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    Undergrad Understanding Negative Pressure: Physical Description Explained

    Hello, everybody! I find it hard in understanding negative pressure. What is the physical description of a negative pressure? Thank you!