2,442 research outputs found
A critical review of noise production models for turbulent, gas-fueled burners
The combustion noise literature for the period between 1952 and early 1984 is critically reviewed. Primary emphasis is placed on past theoretical and semi-empirical attempts to predict or explain observed direct combustion noise characteristics of turbulent, gas-fueled burners; works involving liquid-fueled burners are reviewed only when ideas equally applicable to gas-fueled burners are pesented. The historical development of the most important contemporary direct combustion noise theories is traced, and the theories themselves are compared and criticized. While most theories explain combustion noise production by turbulent flames in terms of randomly distributed acoustic monopoles produced by turbulent mixing of products and reactants, none is able to predict the sound pressure in the acoustic farfield of a practical burner because of the lack of a proven model which relates the combustion noise source strenght at a given frequency to the design and operating parameters of the burner. Recommendations are given for establishing a benchmark-quality data base needed to support the development of such a model
Experimental study of the thermal-acoustic efficiency in a long turbulent diffusion-flame burner
An acoustic source/propagation model is used to interpret measured noise spectra from a long turbulent burner. The acoustic model is based on the perturbation solution of the equations describing the unsteady one-dimensional flow of an inviscid ideal gas with a distributed heat source. The model assumes that the measured noise spectra are due uniquely to the unsteady component of combustion heat release. The model was applied to a long cylindrical hydrogen burner operating over a range of power levels between 4.5 kW and 22.3 kW. Acoustic impedances at the inlet to the burner and at the exit of the tube downstream of the burner were measured and are used as boundary conditions for the model. These measured impedances are also presented
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
Eigenstate thermalization within isolated spin-chain systems
The thermalization phenomenon and many-body quantum statistical properties
are studied on the example of several observables in isolated spin-chain
systems, both integrable and generic non-integrable ones. While diagonal matrix
elements for non-integrable models comply with the eigenstate thermalization
hypothesis (ETH), the integrable systems show evident deviations and similarity
to properties of noninteracting many-fermion models. The finite-size scaling
reveals that the crossover between two regimes is given by a scale closely
related to the scattering length. Low-frequency off-diagonal matrix elements
related to d.c. transport quantities in a generic system also follow the
behavior analogous to the ETH, however unrelated to the one of diagonal
elements
Transient thermal modeling of the nonscanning ERBE detector
A numerical model to predict the transient thermal response of the ERBE nonscanning wide field of view total radiometer channel was developed. The model, which uses Monte Carlo techniques to characterize the radiative component of heat transfer, is described and a listing of the computer program is provided. Application of the model to simulate the actual blackbody calibration procedure is discussed. The use of the model to establish a real time flight data interpretation strategy is recommended. Modification of the model to include a simulated Earth radiation source field and a filter dome is indicated
Finite momentum condensation in a pumped microcavity
We calculate the absorption spectra of a semiconductor microcavity into which
a non-equilibrium exciton population has been pumped. We predict strong peaks
in the spectrum corresponding to collective modes analogous to the Cooper modes
in superconductors and fermionic atomic gases. These modes can become unstable,
leading to the formation of off-equilibrium quantum condensates. We calculate a
phase diagram for condensation, and show that the dominant instabilities can be
at a finite momentum. Thus we predict the formation of inhomogeneous
condensates, similar to Fulde-Ferrel-Larkin-Ovchinnikov states.Comment: 7 pages, 4 figures, updated to accepted versio
Quantum mechanical picture of the coupling between interlayer electronic excitations and infrared active phonons in bilayer cuprate superconductors
The formula frequently used to describe the c-axis infrared response of the
coupled electron-phonon system of bilayer cuprate superconductors and providing
important insights into the physics of these materials has been originally
obtained at the level of the phenomenological multilayer model. Here we derive
it using diagrammatic perturbation theory
Thermoelectric effects in a strongly correlated model for NaCoO
Thermal response functions of strongly correlated electron systems are of
appreciable interest to the larger scientific community both theoretically and
technologically. Here we focus on the infinitely correlated t-J model on a
geometrically frustrated two-dimensional triangular lattice.
Using exact diagonalization on a finite sized system we calculate the
dynamical thermal response functions in order to determine the thermopower,
Lorenz number, and dimensionless figure of merit. The dynamical thermal
response functions is compared to the infinite frequency limit and shown to be
very weak functions of frequency, hence, establishing the validity of the high
frequency formalism recently proposed by Shastry for the thermopower, Lorenz
number, and the dimensionless figure of merit. Further, the thermopower is
demonstrated to have a low to mid temperature enhancement when the sign of the
hopping parameter is switched from positive to negative for the
geometrically frustrated lattice considered.Comment: 16 pages, 10 figures, color version available at
http://physics.ucsc.edu/~peterson/mrpeterson-condmat-NCO.pdf. V.2 has fixed
minor typos in Eq. 11, 19, 25, and 26. V.3 is a color versio
Polarons in semiconductor quantum-dots and their role in the quantum kinetics of carrier relaxation
While time-dependent perturbation theory shows inefficient carrier-phonon
scattering in semiconductor quantum dots, we demonstrate that a quantum kinetic
description of carrier-phonon interaction predicts fast carrier capture and
relaxation. The considered processes do not fulfill energy conservation in
terms of free-carrier energies because polar coupling of localized quantum-dot
states strongly modifies this picture.Comment: 6 pages, 6 figures, accepted for publication in Phys.Rev.
Spin Current and Shot Noise in Single-Molecule Quantum Dots with a Phonon Mode
In this paper we investigate the spin-current and its shot-noise spectrum in
a single-molecule quantum dot coupled with a local phonon mode. We pay special
attention on the effect of phonon on the quantum transport property. The
spin-polarization dependent current is generated by a rotating magnetic filed
applied in the quantum dot. Our results show the remarkable influence of phonon
mode on the zero-frequency shot noise. The electron-phonon interaction leads to
sideband peaks which are located exactly on the integer number of the phonon
frequency and moreover the peak-height is sensitive to the electron-phonon
coupling.Comment: 17 pages,5 figure
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