1,338 research outputs found

    Mobile Phone Power Amplifier Linearity and Efficiency Enhancement Using Digital Predistortion

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    The new generation mobile communication systems using spectrum efficient linear modulation schemes (QPSK,8PSK,QAM)need linear power amplifiers in the transmission path to have good ACPR and EVM values. Linearization methods can be used to increase the linearity of the power amplifiers (PA).However,it is not reasonable o use complicated,power consuming and high cost systems. This paper presents a digital predistortion implementation for WCDMA signals using an FPGA (Field Programmable Gate Array)as DSP and investigates the application of this system in handsets.The method applied requires minimum change in the conventional transmitter path configuration but considerable PAE improvement can be achieved

    Heroically Protecting Our Arguments: Using Superheroes to Teach Inductive and Deductive Reasoning

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    Abstract Barkl, Porter, and Ginns, (2012) explain the importance of reasoning as it relates to fluid intelligence and an individual’s capacity to broaden their understanding of knowledge. With the difficulty many students find in recognizing examples of reasoning, this teaching activity uses student descriptions of superheroes to teach inductive and deductive reasoning skills. Educators are provided with the instructions to conduct a 50-minute lesson to explain these skills, allow students to form and recognize their own examples of inductive and deductive reasoning, and variations on how to conduct this assignment in both the physical and online classroom environments

    Density Matrix Functional Calculations for Matter in Strong Magnetic Fields: I. Atomic Properties

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    We report on a numerical study of the density matrix functional introduced by Lieb, Solovej and Yngvason for the investigation of heavy atoms in high magnetic fields. This functional describes {\em exactly} the quantum mechanical ground state of atoms and ions in the limit when the nuclear charge ZZ and the electron number NN tend to infinity with N/ZN/Z fixed, and the magnetic field BB tends to infinity in such a way that B/Z4/3→∞B/Z^{4/3}\to\infty. We have calculated electronic density profiles and ground state energies for values of the parameters that prevail on neutron star surfaces and compared them with results obtained by other methods. For iron at B=1012B=10^{12} G the ground state energy differs by less than 2 \% from the Hartree-Fock value. We have also studied the maximal negative ionization of heavy atoms in this model at various field strengths. In contrast to Thomas-Fermi type theories atoms can bind excess negative charge in the density matrix model. For iron at B=1012B=10^{12} G the maximal excess charge in this model corresponds to about one electron.Comment: Revtex, 13 pages with 6 eps figures include

    OSETI with STACEE: A Search for Nanosecond Optical Transients from Nearby Stars

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    We have used the STACEE high-energy gamma-ray detector to look for fast blue-green laser pulses from the vicinity of 187 stars. The STACEE detector offers unprecedented light-collecting capability for the detection of nanosecond pulses from such lasers. We estimate STACEE's sensitivity to be approximately 10 photons per square meter at a wavelength of 420 nm. The stars have been chosen because their characteristics are such that they may harbor habitable planets and they are relatively close to Earth. Each star was observed for 10 minutes and we found no evidence for laser pulses in any of the data sets.Comment: 38 pages, 12 figures. Accepted for publication in Astrobiolog

    Absence of Persistent Magnetic Oscillations in Type-II Superconductors

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    We report on a numerical study intended to examine the possibility that magnetic oscillations persist in type II superconductors beyond the point where the pairing self-energy exceeds the normal state Landau level separation. Our work is based on the self-consistent numerical solution for model superconductors of the Bogoliubov-deGennes equations for the vortex lattice state. In the regime where the pairing self-energy is smaller than the cyclotron energy, magnetic oscillations resulting from Landau level quantization are suppressed by the broadening of quasiparticle Landau levels due to the non-uniform order parameter of the vortex lattice state, and by splittings of the quasiparticle bands. Plausible arguments that the latter effect can lead to a sign change of the fundamental harmonic of the magnetic oscillations when the pairing self-energy is comparable to the cyclotron energy are shown to be flawed. Our calculations indicate that magnetic oscillations are strongly suppressed once the pairing self-energy exceeds the Landau level separation.Comment: 7 pages, revtex, 7 postscript figure

    Quantum impurity solvers using a slave rotor representation

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    We introduce a representation of electron operators as a product of a spin-carry ing fermion and of a phase variable dual to the total charge (slave quantum rotor). Based on this representation, a new method is proposed for solving multi-orbital Anderson quantum impurity models at finite interaction strength U. It consists in a set of coupled integral equations for the auxiliary field Green's functions, which can be derived from a controlled saddle-point in the limit of a large number of field components. In contrast to some finite-U extensions of the non-crossing approximation, the new method provides a smooth interpolation between the atomic limit and the weak-coupling limit, and does not display violation of causality at low-frequency. We demonstrate that this impurity solver can be applied in the context of Dynamical Mean-Field Theory, at or close to half-filling. Good agreement with established results on the Mott transition is found, and large values of the orbital degeneracy can be investigated at low computational cost.Comment: 18 pages, 15 figure

    Stationary solutions of the one-dimensional nonlinear Schroedinger equation: I. Case of repulsive nonlinearity

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    All stationary solutions to the one-dimensional nonlinear Schroedinger equation under box and periodic boundary conditions are presented in analytic form. We consider the case of repulsive nonlinearity; in a companion paper we treat the attractive case. Our solutions take the form of stationary trains of dark or grey density-notch solitons. Real stationary states are in one-to-one correspondence with those of the linear Schr\"odinger equation. Complex stationary states are uniquely nonlinear, nodeless, and symmetry-breaking. Our solutions apply to many physical contexts, including the Bose-Einstein condensate and optical pulses in fibers.Comment: 11 pages, 7 figures -- revised versio

    A-dependence of nuclear transparency in quasielastic A(e,e'p) at high Q^2

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    The A-dependence of the quasielastic A(e,e'p) reaction has been studied at SLAC with H-2, C, Fe, and Au nuclei at momentum transfers Q^2 = 1, 3, 5, and 6.8 (GeV/c)^2. We extract the nuclear transparency T(A,Q^2), a measure of the average probability that the struck proton escapes from the nucleus A without interaction. Several calculations predict a significant increase in T with momentum transfer, a phenomenon known as Color Transparency. No significant rise within errors is seen for any of the nuclei studied.Comment: 5 pages incl. 2 figures, Caltech preprint OAP-73

    Electron Dephasing in Mesoscopic Metal Wires

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    The low-temperature behavior of the electron phase coherence time, τϕ\tau_{\phi}, in mesoscopic metal wires has been a subject of controversy recently. Whereas theory predicts that τϕ(T)\tau_{\phi}(T) in narrow wires should increase as T−2/3T^{-2/3} as the temperature TT is lowered, many samples exhibit a saturation of τϕ\tau_{\phi} below about 1 K. We review here the experiments we have performed recently to address this issue. In particular we emphasize that in sufficiently pure Ag and Au samples we observe no saturation of τϕ\tau_{\phi} down to our base temperature of 40 mK. In addition, the measured magnitude of τϕ\tau_{\phi} is in excellent quantitative agreement with the prediction of the perturbative theory of Altshuler, Aronov and Khmelnitskii. We discuss possible explanations why saturation of τϕ\tau_{\phi} is observed in many other samples measured in our laboratory and elsewhere, and answer the criticisms raised recently by Mohanty and Webb regarding our work.Comment: 14 pages, 3 figures; to appear in proceedings of conference "Fundamental Problems of Mesoscopic Physics", Granada, Spain, 6-11 September, 200
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