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    Transfering? And I'm Lost!

    I am currently a first year graduate student in physics and am working on external fellowship applications. With most applications being due in the November - December range, I will have only been working with my current advisor for one or two months at the point where I would have to ask for a...
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    Graphene ambipolar field effect

    In graphene the fermi level can be moved into the conduction or valence bands by applying an external electric field, allowing conduction by either holes or electrons. My question is where do these new electrons come from (or go to in the p-type case)? Also, why is this special to...
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    Why so much energy?

    What is the advantage of the higher energy of the LHC for finding the Higg's when Tevatron was already operating at an energy significantly higher than the predicted Higgs mass? Is it just that higher energy collisions will result in more particles, making data collection faster?
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    Transmission Line Impedance Matching

    In the case of a complex source impedance ZS and load impedance ZL, maximum power transfer is obtained when ZS = ZL*. For a lossless transmission line terminated on one end with a purely resistive load, zero reflection is obtained when ZS=ZL. What about the case of a lossy transmission...
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    Reflection at a conducting surface

    In Griffiths Electrodynamics (page 397) electromagnetic wave reflection at a conducting surface is introduced. He says "for ohmic conductors, Jfree = sigma * E, there can be no free surface current since this would require an infinite electric field at the boundary." I don't understand why...
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    Eye floaters Fungus

    But what can you say about the picture I linked to? Are there many different biological materials that could produce such shapes or does that characteristic of something in particular?
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    Eye floaters Fungus

    Eye floaters are debris in the eye's vitreous humour, which seem to float over your vision and are extremely annoying. When using an optical microscope my floaters become extremely clear against the bright background I am viewing, and what I see looks almost exactly like this...
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    Why the rush for papers?

    As an undergrad, I understand my motivations for my group publishing papers: that my name could be on one which would help me get into grad school; similar to the motivations of an assistant professor hoping to get tenure. Everyone I meet seems in a rush to get good results and publish them...
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    Electron hole pair

    When an electron in a semiconductor is excited to a higher state, an electron hole pair is created. How does this not violate charge conservation, a charge of +e turns into a net charge of 0? Thanks for the help
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    Trying to understand the Brillouin zone

    I am having a really hard time understanding how the Brillouin zone relates to electron states and have a couple of questions that might help clear it up for me. For a band structure like this: https://wiki.fysik.dtu.dk/gpaw/_images/silicon_banddiagram.png [Broken] I know that the...
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    REU with research experience.

    I go to a big school with lots of physics research available. I started in a group at the beginning of this year, and I'm a junior and have good grades. From looking on different REU program websites it seems like a lot of them seem to want people with limited access to research at their...
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    3D Electron Gas Derivation

    But wouldn't that give 1/(2pi)^(3/2) since the x, y, and z waves each contribute 1/(2pi)^(1/2)?
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    3D Electron Gas Derivation

    Homework Statement In a solid state book I am reading the 3 dimensional electron gas is derived. It says, "An unconfined electron in free space is described by the Schrodinger equation where m is the free-electron mass. The solutions of the equation, phi(r)=1/(2pi)^3 Exp(ik.r) are plane...
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    Adding vector components

    It's problem 4.50 in griffiths quantum mechanics and here is a quote from the solution manual: We may as well choose axes so that a lies along the z axis and b is in the xz plane. Then S(1)a= S(1)z , and S(2)b = cosθ S(2)z + sinθ S(2)x . S(1)a means the spin operator of particle 1 in the...
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    Adding vector components

    What I mean was Ax Sin(theta) + Ay Cos(theta) = A where A, Ax and Ay are vectors, I don't see where this relation comes from?
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    Adding vector components

    Homework Statement I read how to solve a problem I am working on, and part of it deals with adding vector components. A is the vector, Ax is the x component, Ay the y component, and theta is the angle A makes from the y axis. Homework Equations The Attempt at a Solution The solution...
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    Expectation value of a vector?

    Homework Statement Prove that for a particle in a potential V(r) the rate of change of the expectation value of the orbital angular momentum L is equal to the expectation value of the torque: d/dt <L> = <N> Where N = r x(-del V) N, r, and L are vectors. Homework Equations...
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    Raman Spectroscopy Exposure Time

    When you are setting up a spectral acquisition with a raman microscope, what does the exposure time mean? I would expect this to mean the amount of time the sample is exposed to the laser, but it doesn't seem like that can be true if it takes around 20 minutes to acquire the spectrum with a 2...
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    Partial derivative

    Homework Statement I have a problem where x = x1 + x2, and I need to relate d/dx to d/dx1 and d/dx2 somehow. Homework Equations The Attempt at a Solution I'm guessing there is a simple way to do this that I have just forgotten, I know how to find dx, but how can I find d/dx...
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    Matrix Element of Position Operator

    I guess I was thinking of it as an expectation value which I now see is not correct. When use this same method using the momentum operator, -i hbar d/dx, I get an integral with Sin(npix/a)Cos(npix/a), which must be zero when integrated from 0 to a by integral identities, correct? What does...
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    Matrix Element of Position Operator

    Homework Statement Calculate the general matrix element of the position operator in the basis of the eigenstates of the infinite square well. Homework Equations |\psi\rangle =\sqrt{\frac{2}{a}}\sin{\frac{n \pi x}{a}}...
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    Potential of an infinite cylinder

    Homework Statement A cylindrical cable with a center rod of diameter a surrounded by a gap and a thick pipe with inner and outer radii b & c. The charge distribution on the inner rod is Rho = k cos(s Pi /(2a)), and the outer rod has a uniform charge density such that the total system is...
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    Infinite Square Well Eigenstates

    I am talking about the energy eigenstates of the infinite square well, how are these not also momentum eigenstates since p = Sqrt[(2*m*KE)]
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    Infinite Square Well Eigenstates

    Homework Statement The eigenstates of the infinite square well are not energy eigenstates and are not momentum eigenstates. Homework Equations The Attempt at a Solution I don't understand how this can be? If the eigenstates of the infinite square well are energy eigenstates...
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    Divergence in cylindrical coordinates

    Homework Statement Calculate the divergence of the vector function f = a/s^2 (s hat) where s is the radial distance from the z axis, expressed in cylindrical coordinates. Homework Equations The Attempt at a Solution Using the divergence theorem I relate the volume integral of...
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    Infinite square well, momentum space

    What happens when you only integrate from 0 to a? When I try I get a seemingly uselessly messy answer, is there some trick to use delta functions or something I am missing?
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    Undergrad Physics Research

    I can't really find much from what can't you do because I don't understand that well what is involved in physics research as I have no experience. I guess what I should have said is what else can I learn that would help me to be valuable in physics research as an undergrad?
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    Undergrad Physics Research

    As an undergrad involved in physics research, what all can you really do? I can think of three things: -Programming -Experimental measurement -Building things in the machine shop What else should be added to this list, and what other useful skills are there to have as an undergrad for...
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    Taking notes

    When taking notes out of a book I sometimes feel like I am wasting too much time mindlessly copying ideas and equations down and that this is slowing down my learning speed. Does anyone have any general advice on how to study out of a textbook and what should and should not be copied by hand...
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    Basic Labview Help

    The part that I am having trouble understanding is how do I save a value to be used later in the program without that value being changed every time the program loops? For instance, with the voltage changing, how can I save certain values of voltages to be used later if there will always be new...
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