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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

    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

    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

    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

    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

    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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    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

    I don't have programming experience and I am trying to learn how to write labview programs. I want to write a program that works like this: I want to make a positively ramped signal that becomes negatively ramped once the difference between the current signal value and the initial signal...
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    Improper Integral Infinity

    Homework Statement Using the fact that the integral from -Infinity to Infinity of e^-x^2 is equal to Sqrt(Pi), find the integral from -Infinity to Infinity of x^2 * e^-x^2 Homework Equations The Attempt at a Solution I really dont know how to find this using the fact that...
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    Jacobian math homework

    Homework Statement Suppose that P, Q, and R are regions in R2, and suppose T1 : P -> Q and T2 : Q -> R are dierentiable. Use the (multivariable) Chain Rule and det(AB) = det(A)det(B) to show that the Jacobian of the composition T2 o T1 is the product of the Jacobians of T1 and T2...
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    Particle in a box

    Homework Statement A particle is in an infinte square well extending from x = 0 to x = a. Its state is a linear combination of the two lowest energy states. Psi(x, t) = A(2 Psi1(x, t) + Psi2(x, t)) a) If a measurement of energy is made what are the possible results of the measurement...
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    Emitter Follower

    Homework Statement Use a follower with base driven from a voltage divider to provide a stiff source of +5 volts from an available regulated +15 volt supply. Load current (max) = 25mA. Choose your resistor values so that the output coltage doesn't drop more than 5% under full load...
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    Fourier Transform

    Homework Statement f(x) = {-1, -pi<x<0 ; 1, 0<x<pi ; 0, |x|>pi} Find the exponential Fourier transform of the given f(x) and write f(x) as a Fourier integral. Homework Equations The Attempt at a Solution I have the equations for the Fourier transforms and I know how to find...
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    RLC Black Box

    Homework Statement A two-terminal “black box” is known to contain an inductor L, a capacitor C, and a resistor R. On connecting a 1.5 V battery, 1.5 mA flows. When an AC voltage of 1V RMS at 60 Hz is connected, 10 mA RMS flows. As the frequency increases at a fixed 1 V RMS, the current...
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    Voltage divider

    Homework Statement The problem deals with a circuit that has a voltage divider composed of an inductor L and a capacitor C in series connected to a node, one end is an open circuit with the output voltage and the other end is connected to a resistor R that is connected to ground. Find the...
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    Maximum of a triple integral

    Homework Statement Find the region E for which the triple integral: (triple integral over E) (1 - x^2 -2y^2 -3z^2) dV is a maximum. Homework Equations The Attempt at a Solution I remember in earlier math courses finding the derivative of a single variable integral, does this...
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    Circuit Multimeter

    Homework Statement In my textbook, it says "the standard VOM " (volt-ohm-milliameter) multimeter uses a meter movement that measures current (typically 50 microamperes full-scale). I am just having trouble understanding what this means, I looked up full-scale and found that it was the...
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