15,467 research outputs found
Neutrinoless double-beta decay matrix elements in large shell-model spaces with the generator-coordinate method
We use the generator-coordinate method with realistic shell-model
interactions to closely approximate full shell-model calculations of the matrix
elements for the neutrinoless double-beta decay of Ca, Ge, and
Se. We work in one major shell for the first isotope, in the
space for the second and third, and finally in two major
shells for all three. Our coordinates include not only the usual axial
deformation parameter , but also the triaxiality angle and
neutron-proton pairing amplitudes. In the smaller model spaces our matrix
elements agree well with those of full shell-model diagonalization, suggesting
that our Hamiltonian-based GCM captures most of the important valence-space
correlations. In two major shells, where exact diagonalization is not currently
possible, our matrix elements are only slightly different from those in a
single shell.Comment: 8 pages, 7 figure
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Two-phase flow dynamics in the gas diffusion layer of proton exchange membrane fuel cells: Volume of fluid modeling and comparison with experiment
This paper proposes a three-dimensional (3D) volume of fluid (VOF) study to investigate two-phase flow in the gas diffusion layer (GDL) of proton exchange membrane (PEM) fuel cells and liquid water distribution. A stochastic model was adopted to reconstruct the 3D microstructures of Toray carbon papers and incorporate the experimentally-determined varying porosity. The VOF predictions were compared with the water profiles obtained by the X-ray tomographic microscopy (XTM) and the Leverett correlation. It was found local water profiles are similar in the sample’s sub-regions under the pressure difference p = 1000 Pa between the two GDL surfaces, but may vary significantly under p = 6000 Pa. The water-air interfaces inside the GDL structure were presented to show water distribution and breakthrough
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Investigating the in-/through-plane effective diffusivities of dry and partially-saturated gas diffusion layers
In this study, the effective oxygen diffusivity in the dry or partially-saturated gas diffusion layer (GDL) is numerically investigated by an oxygen diffusion model in GDLs reconstructed by a stochastic method. The predicted effective diffusivity in dry GDLs is compared with various diffusivity models from literatures. Reasonable agreements with other models were obtained. The effect of the PTFE loading in the dry Toray carbon paper is also investigated and compared with recent experimental data. It is found that the effective diffusivity becomes lower under higher PTFE loading due to the decreased pore volume, as expected. The relative effective oxygen diffusivity in partially-saturated GDLs is calculated using the two-phase volume of fluid (VOF) model and an oxygen diffusion model. The effects of different local water profiles and porosity distribution on the effective oxygen diffusivity in both the through-plane (TP) and in-plane (IP) directions are investigated and compared with a lattice Boltzmann model and experimental data. The present results are in good agreement with other studies. It is found that local water profile has significant impacts on the effective diffusivity in partially-saturated GDLs and the diffusivity in the TP direction is more sensitive to the water distribution than the IP direction
The Green-function transform and wave propagation
Fourier methods well known in signal processing are applied to
three-dimensional wave propagation problems. The Fourier transform of the Green
function, when written explicitly in terms of a real-valued spatial frequency,
consists of homogeneous and inhomogeneous components. Both parts are necessary
to result in a pure out-going wave that satisfies causality. The homogeneous
component consists only of propagating waves, but the inhomogeneous component
contains both evanescent and propagating terms. Thus we make a distinction
between inhomogenous waves and evanescent waves. The evanescent component is
completely contained in the region of the inhomogeneous component outside the
k-space sphere. Further, propagating waves in the Weyl expansion contain both
homogeneous and inhomogeneous components. The connection between the Whittaker
and Weyl expansions is discussed. A list of relevant spherically symmetric
Fourier transforms is given
Entanglement Rate for Gaussian Continuous Variable Beams
We derive a general expression that quantifies the total entanglement
production rate in continuous variable systems, where a source emits two
entangled Gaussian beams with arbitrary correlators.This expression is
especially useful for situations where the source emits an arbitrary frequency
spectrum,e.g. when cavities are involved. To exemplify its meaning and
potential, we apply it to a four-mode optomechanical setup that enables the
simultaneous up- and down-conversion of photons from a drive laser into
entangled photon pairs. This setup is efficient in that both the drive and the
optomechanical up- and down-conversion can be fully resonant.Comment: 18 pages, 6 figure
Searching for high- isomers in the proton-rich mass region
Configuration-constrained potential-energy-surface calculations have been
performed to investigate the isomerism in the proton-rich mass
region. An abundance of high- states are predicted. These high- states
arise from two and four-quasi-particle excitations, with and
, respectively. Their excitation energies are comparatively
low, making them good candidates for long-lived isomers. Since most nuclei
under studies are prolate spheroids in their ground states, the oblate shapes
of the predicted high- states may indicate a combination of isomerism
and shape isomerism
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