53,088 research outputs found
Near field pressure fluctuations in a circular jet
The vortical structures in shear layers govern many dynamic aspects of the jet, including entrainment of mass, transfer of momentum and noise generation. These structures develop from instability waves and undergo a merging process. Vortex merging reduces the time scale and increases the length scale of the shear layer. At the same time pressure fluctuations are induced by the unsteady motion. These pressure perturbations can exert high level dynamic loading on nearby structures, and radiate to the far field as noise. In this study, the generation mechanism of the pressure fluctuations and the radiation process are examined
Charged lepton mixing and oscillations from neutrino mixing in the early Universe
Charged lepton mixing as a consequence of neutrino mixing is studied for two
generations in the temperature regime in the
early Universe. We state the general criteria for charged lepton mixing,
critically reexamine aspects of neutrino equilibration and provide arguments to
suggest that neutrinos may equilibrate as mass eigenstates in the temperature
regime \emph{prior} to flavor equalization. We assume this to be the case, and
that neutrino mass eigenstates are in equilibrium with different chemical
potentials. Charged lepton self-energies are obtained to leading order in the
electromagnetic and weak interactions. The upper bounds on the neutrino
asymmetry parameters from CMB and BBN without oscillations, combined with the
fit to the solar and KamLAND data for the neutrino mixing angle, suggest that
for the two generation case there is resonant \emph{charged lepton} mixing in
the temperature range . In this range the charged lepton
oscillation frequency is of the same order as the electromagnetic damping rate.Comment: 17 pages, 2 figs, same results with more discussions on quantum Zeno
effect. To appear in Astroparticle Physic
Two-dimensional gases of generalized statistics in a uniform magnetic field
We study the low temperature properties of two-dimensional ideal gases of
generalized statistics in a uniform magnetic field. The generalized statistics
considered here are the parafermion statistics and the exclusion statistics.
Similarity in the behaviours of the parafermion gas of finite order and the
gas with exclusion coefficient at very low temperatures is noted. These
two systems become exactly equivalent at . Qumtum Hall effect with these
particles as charge carriers is briefly discussed.Comment: Latex file, 14 pages, 5 figures available on reques
Models for the integer quantum Hall effect: the network model, the Dirac equation, and a tight-binding Hamiltonian
We consider models for the plateau transition in the integer quantum Hall
effect. Starting from the network model, we construct a mapping to the Dirac
Hamiltonian in two dimensions. In the general case, the Dirac Hamiltonian has
randomness in the mass, the scalar potential, and the vector potential.
Separately, we show that the network model can also be associated with a
nearest neighbour, tight-binding Hamiltonian.Comment: Revtex, 15 pages, 7 figures; submitted to Phys. Rev.
Noncommutative D-Brane in Non-Constant NS-NS B Field Background
We show that when the field strength H of the NS-NS B field does not vanish,
the coordinates X and momenta P of an open string endpoints satisfy a set of
mixed commutation relations among themselves. Identifying X and P with the
coordinates and derivatives of the D-brane world volume, we find a new type of
noncommutative spaces which is very different from those associated with a
constant B field background.Comment: 11 pages, Latex, minor modification
Detection of changes in the characteristics of a Gauss-Markov process
Sequential detection of changes in Gauss-Markov process achieved through probability ratio tes
Transthoracic three-dimensional echocardiography for the assessment of straddling tricuspid or mitral valves
Background The advent of 3D echocardiography has provided a technique which, potentially, could afford significant additional information over conventional cross-sectional echocardiography in the assessment of patients with straddling atrioventricular valves prior to surgical correction. Methods Eight patients, aged from 1 month to 9˙2 years, were examined with 3D echocardiography. All but three had discordant ventriculoarterial connections or double outlet right ventricle. Data suitable for reconstruction was acquired with transthoracic scanning. Right and left ventricular volumes were calculated in the 3D dataset. Results 3D echocardiography proved capable of defining the exact degree of straddling by imaging theproportion of tension apparatus attached to either side of the ventricular septum. It was able also to display the atrioventricular junction “en face”, thus permitting identification of the precise site of insertion of the muscular ventricular septum relative to the atrioventricular junction. This made it possiblefirst, to calculate the degree of valvar override, and second, to predict the location of the penetrating atrioventricular bundle. End-diastolic volume of the right ventricle in those with straddling tricuspid valves was 73 (61–83)% of normal, and, of the left ventricle in those with mitral valvar straddling 71 (40‐97)% of normal. Conclusions 3D echocardiography can aid in planning the optimal surgical procedure in patients with straddling or overrriding atrioventricular valves, as it provides diagnostic information superiorto standard crosssectional techniques. It also allows for exact measurement of the volumes of the respective ventricles
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