3,043 research outputs found
Many-body approach to infinite non-periodic systems: application to the surface of semi-infinite jellium
A method to implement the many-body Green function formalism in the GW
approximation for infinite non periodic systems is presented. It is suitable to
treat systems of known ``asymptotic'' properties which enter as boundary
conditions, while the effects of the lower symmetry are restricted to regions
of finite volume. For example, it can be applied to surfaces or localized
impurities. We illustrate the method with a study of the surface of
semi-infinite jellium. We report the dielectric function, the effective
potential and the electronic self-energy discussing the effects produced by the
screening and by the charge density profile near the surface.Comment: 11 pages, 4 figure
Spectral Curves and Localization in Random Non-Hermitian Tridiagonal Matrices
Eigenvalues and eigenvectors of non-Hermitian tridiagonal periodic random
matrices are studied by means of the Hatano-Nelson deformation. The deformed
spectrum is annular-shaped, with inner radius measured by the complex Thouless
formula. The inner bounding circle and the annular halo are stuctures that
correspond to the two-arc and wings observed by Hatano and Nelson in deformed
Hermitian models, and are explained in terms of localization of eigenstates via
a spectral duality and the Argument principle.Comment: 5 pages, 9 figures, typographical error corrected in reference
C3N4 for CO2 photoreduction: catalyst performance and stability in batch and continuous reactor
In this study, various C3N4 samples were
prepared and characterized. CO2 photoreduction was carried out by using C3N4 as
powder and coated on glass support in a batch reactor or embedded in a Nafion
membrane in a continuous reacto
Ab-initio self-energy corrections in systems with metallic screening
The calculation of self-energy corrections to the electron bands of a metal
requires the evaluation of the intraband contribution to the polarizability in
the small-q limit. When neglected, as in standard GW codes for semiconductors
and insulators, a spurious gap opens at the Fermi energy. Systematic methods to
include intraband contributions to the polarizability exist, but require a
computationally intensive Fermi-surface integration. We propose a numerically
cheap and stable method, based on a fit of the power expansion of the
polarizability in the small-q region. We test it on the homogeneous electron
gas and on real metals such as sodium and aluminum.Comment: revtex, 14 pages including 5 eps figures v2: few fixe
T Dependence of the Mechanical Properties on the Microstructural Parameters of WC-Co
Abstract
The effect of binder content and WC grain size on the mechanical properties is widely investigated in literature. An increase in binder amount and WC grain size leads to a decrease in hardness and an increase in fracture toughness. Actually, these correlations are related to the influence of binder content and WC grain size through the contiguity and mean binder free path, which are the microstructural parameters that affect the mechanical properties. The aim of this study is to verify the dependence of the two microstructural parameters that govern the WCCo mechanical behaviour, namely the contiguity and mean binder free path, on the mechanical properties of an extended range of WC-Co samples, which differ in terms of Co content and tungsten carbide grain size
Connecting scaling with short-range correlations
We reexamine several issues related to the physics of scaling in electron
scattering from nuclei. A basic model is presented in which an assumed form for
the momentum distribution having both long- and short-range contributions is
incorporated in the single-particle Green function. From this one can obtain
saturation of nuclear matter for an NN interaction with medium-range attraction
and short-range repulsion, and can obtain the density-density polarization
propagator and hence the electromagnetic response and scaling function. For the
latter, the shape of the scaling function and how it approaches scaling as a
function of momentum transfer are both explored.Comment: 24 pages, 15 figures. A reference has been corrected and update
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High-J CO line emission from young stellar objects: from ISO to FIRST
we present the CO pure rotational spectrum at high J (Jup14) obtained with the Long Wavelength Spectrometer (LWS) on board of the ISO satellite towards molecular outflows exciting sources in nearby star formation regions. The physical conditions, derived using an LVG model for the line emission, indicate the presence of warm and dense gas, probably shock excited. The model fits show that often the bulk of this CO emission is expected in the spectral range that will be covered by FIRST, indicating the potentiality of this satellite to trace the warm component of gas emission in young stellar objects
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