An improved source model for aircraft interior noise studies

There is concern that advanced turboprop engines currently being developed may produce excessive aircraft cabin noise levels. This concern has stimulated renewed interest in developing aircraft interior noise reduction methods that do not significantly increase take off weight. An existing analytical model for noise transmission into aircraft cabins was utilized to investigate the behavior of an improved propeller source model for use in aircraft interior noise studies. The new source model, a virtually rotating dipole, is shown to adequately match measured fuselage sound pressure distributions, including the correct phase relationships, for published data. The virtually rotating dipole is used to study the sensitivity of synchrophasing effectiveness to the fuselage sound pressure trace velocity distribution. Results of calculations are presented which reveal the importance of correctly modeling the surface pressure phase relations in synchrophasing and other aircraft interior noise studies

Device for preventing high voltage arcing in electron beam welding Patent

Development of device to prevent high voltage arcing in electron beam weldin

X-ray edge singularity of bilayer graphene

The X-ray edge singularity of bilayer graphene is studied by generalizing the path integral approach based on local action which was employed for monolayer graphene. In sharp contrast to the case of monolayer graphene, the bilayer graphene is found to exhibit the edge singularity even at half-filling and its characteristics are determined by interlayer coupling. At finite bias the singular behaviors sensitively depend on the relative magnitude of fermi energy and applied bias, which is due to the peculiar shape of energy band at finite bias.Comment: RevTeX 4.1, 4 pages. No figur

Nonlinear photon transport in a semiconductor waveguide-cavity system containing a single quantum dot: Anharmonic cavity-QED regime

We present a semiconductor master equation technique to study the input/output characteristics of coherent photon transport in a semiconductor waveguide-cavity system containing a single quantum dot. We use this approach to investigate the effects of photon propagation and anharmonic cavity-QED for various dot-cavity interaction strengths, including weakly-coupled, intermediately-coupled, and strongly-coupled regimes. We demonstrate that for mean photon numbers much less than 0.1, the commonly adopted weak excitation (single quantum) approximation breaks down, even in the weak coupling regime. As a measure of the anharmonic multiphoton-correlations, we compute the Fano factor and the correlation error associated with making a semiclassical approximation. We also explore the role of electron--acoustic-phonon scattering and find that phonon-mediated scattering plays a qualitatively important role on the light propagation characteristics. As an application of the theory, we simulate a conditional phase gate at a phonon bath temperature of $20$K in the strong coupling regime.Comment: To appear in PR

Vibrational coherence in electron spin resonance in nanoscale oscillators

We study a scheme for electrical detection, using electron spin resonance, of coherent vibrations in a molecular single electron level trapped near a conduction channel. Both equilibrium spin-currents and non-equilibrium spin- and charge currents are investigated. Inelastic side-band anti-resonances corresponding to the vibrational modes appear in the electron spin resonance spectrum.Comment: 4 pages, 3 figures: Published versio

Polarons and Molecules in a Two-Dimensional Fermi Gas

We study an impurity atom in a two-dimensional Fermi gas using variational wave functions for (i) an impurity dressed by particle-hole excitations (polaron) and (ii) a dimer consisting of the impurity and a majority atom. In contrast to three dimensions, where similar calculations predict a sharp transition to a dimer state with increasing interspecies attraction, we show that the polaron ansatz always gives a lower energy. However, the exact solution for a heavy impurity reveals that both a two-body bound state and distortions of the Fermi sea are crucial. This reflects the importance of particle-hole pairs in lower dimensions and makes simple variational calculations unreliable. We show that the energy of an impurity gives important information about its dressing cloud, for which both ans\"atze give inaccurate results.Comment: 5 pages, 2 figures, minor change

Phonon-dressed Mollow triplet in the regime of cavity-QED

We study the resonance fluorescence spectra of a driven quantum dot placed inside a high $Q$ semiconductor cavity and interacting with an acoustic phonon bath. The dynamics is calculated using a time-convolutionless master equation obtained in the polaron frame. We demonstrate pronounced spectral broadening of the Mollow sidebands through cavity-emission which, for small cavity-coupling rates, increases quadratically with the Rabi frequency. However, for larger cavity coupling rates, this broadening dependence is found to be more complex. This field-dependent Mollow triplet broadening is primarily a consequence of the triplet peaks sampling different parts of the asymmetric phonon bath, and agrees directly with recent experiments with semiconductor micropillars. The influence from the detuned cavity photon bath and multi-photon effects is shown to play a qualitatively important role on the fluorescence spectra.Comment: 4 pages, 4 figure

Self-localized impurities embedded in a one dimensional Bose-Einstein condensate and their quantum fluctuations

We consider the self-localization of neutral impurity atoms in a Bose-Einstein condensate in a 1D model. Within the strong coupling approach, we show that the self-localized state exhibits parametric soliton behavior. The corresponding stationary states are analogous to the solitons of non-linear optics and to the solitonic solutions of the Schroedinger-Newton equation (which appears in models that consider the connection between quantum mechanics and gravitation). In addition, we present a Bogoliubov-de-Gennes formalism to describe the quantum fluctuations around the product state of the strong coupling description. Our fluctuation calculations yield the excitation spectrum and reveal considerable corrections to the strong coupling description. The knowledge of the spectrum allows a spectroscopic detection of the impurity self-localization phenomenon.Comment: 7 pages, 5 figure

Gilbert Damping in Conducting Ferromagnets II: Model Tests of the Torque-Correlation Formula

We report on a study of Gilbert damping due to particle-hole pair excitations in conducting ferromagnets. We focus on a toy two-band model and on a four-band spherical model which provides an approximate description of ferromagnetic (Ga,Mn)As. These models are sufficiently simple that disorder-ladder-sum vertex corrections to the long-wavelength spin-spin response function can be summed to all orders. An important objective of this study is to assess the reliability of practical approximate expressions which can be combined with electronic structure calculations to estimate Gilbert damping in more complex systems.Comment: 10 pages, 10 figures. Submitted to Phys. Rev.

Interplay between electron-phonon couplings and disorder strength on the transport properties of organic semiconductors

The combined effect of bulk and interface electron-phonon couplings on the transport properties is investigated in a model for organic semiconductors gated with polarizable dielectrics. While the bulk electron-phonon interaction affects the behavior of mobility in the coherent regime below room temperature, the interface coupling is dominant for the activated high $T$ contribution of localized polarons. In order to improve the description of the transport properties, the presence of disorder is needed in addition to electron-phonon couplings. The effects of a weak disorder largely enhance the activation energies of mobility and induce the small polaron formation at lower values of electron-phonon couplings in the experimentally relevant window $150 K<T<300 K$. The results are discussed in connection with experimental data of rubrene organic field-effect transistors.Comment: 4 pages, 3 figure