291 research outputs found
Electronic States in Diffused Quantum Wells
In the present study we calculate the energy values and the spatial
distributions of the bound electronic states in some diffused quantum wells.
The calculations are performed within the virtual crystal approximation, spin dependent empirical tight-binding model and the surface Green
function matching method. A good agreement is found between our results and
experimental data obtained for AlGaAs/GaAs quantum wells with thermally induced
changes in the profile at the interfaces. Our calculations show that for
diffusion lengths {\AA} the transition (C3-HH3) is not
sensitive to the diffusion length, but the transitions (C1-HH1), (C1-LH1),
(C2-HH2) and (C2-LH2) display large "blue shifts" as L_{D} increases. For
diffusion lengths {\AA} the transitions (C1-HH1) and (C1-LH1)
are less sensitive to the L_{D} changes than the (C3-HH3) transition. The
observed dependence is explained in terms of the bound states spatial
distributions.Comment: ReVTeX file, 7pp., no macros, 4 figures available on the reques
Curvature singularity of the distributional BTZ black hole geometry
For the non-rotating BTZ black hole, the distributional curvature tensor
field is found. It is shown to have singular parts proportional to a
-distribution with support at the origin. This singularity is related,
through Einstein field equations, to a point source. Coordinate invariance and
independence on the choice of differentiable structure of the results are
addressed.Comment: Latex, 7 page
Plastic deformation at high temperatures of pure and Mn-doped GaSb
In this work the plastic behavior of GaSb and Mn-doped GaSb at high temperature has been analyzed. Several experiments at different constant load and temperatures around 500 °C were carried out. The parameters used in the Haasen model have been obtained experimentally and compared with the ones obtained from simulations
Quark propagator and vertex: systematic corrections of hypercubic artifacts from lattice simulations
This is the first part of a study of the quark propagator and the vertex
function of the vector current on the lattice in the Landau gauge and using
both Wilson-clover and overlap actions. In order to be able to identify lattice
artifacts and to reach large momenta we use a range of lattice spacings. The
lattice artifacts turn out to be exceedingly large in this study. We present a
new and very efficient method to eliminate the hypercubic (anisotropy)
artifacts based on a systematic expansion on hypercubic invariants which are
not SO(4) invariant. A simpler version of this method has been used in previous
works. This method is shown to be significantly more efficient than the popular
``democratic'' methods. It can of course be applied to the lattice simulations
of many other physical quantities. The analysis indicates a hierarchy in the
size of hypercubic artifacts: overlap larger than clover and propagator larger
than vertex function. This pleads for the combined study of propagators and
vertex functions via Ward identities.Comment: 14 pags., 9 fig
Muon Track Reconstruction and Data Selection Techniques in AMANDA
The Antarctic Muon And Neutrino Detector Array (AMANDA) is a high-energy
neutrino telescope operating at the geographic South Pole. It is a lattice of
photo-multiplier tubes buried deep in the polar ice between 1500m and 2000m.
The primary goal of this detector is to discover astrophysical sources of high
energy neutrinos. A high-energy muon neutrino coming through the earth from the
Northern Hemisphere can be identified by the secondary muon moving upward
through the detector. The muon tracks are reconstructed with a maximum
likelihood method. It models the arrival times and amplitudes of Cherenkov
photons registered by the photo-multipliers. This paper describes the different
methods of reconstruction, which have been successfully implemented within
AMANDA. Strategies for optimizing the reconstruction performance and rejecting
background are presented. For a typical analysis procedure the direction of
tracks are reconstructed with about 2 degree accuracy.Comment: 40 pages, 16 Postscript figures, uses elsart.st
Crystal structure of sinhalite MgAlBO4 under high pressure
This document is the Accepted Manuscript version of a Published Work that appeared in final form in
Journal of Physical Chemistry C, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/jp512131eWe report on high-pressure angle-dispersive X-ray diffraction data up to 27 GPa for natural MgAlBO4 sinhalite mineral and ab initio total energy calculations. The experimental bulk modulus of sinhalite is B-0 = 171(3) GPa with a first-pressure derivative of B-0' = 4.2(3). A comparison with other olivine-type compounds shows that the value for B0 is 27% larger than that of Mg2SiO4 forsterite and 29% smaller than that of Al2BeO4 chrysoberyl. These differences are interpreted, on the basis of our ab initio calculations, in terms of the relative incompressibility of Al-O bonds in AlO6 octahedra (with a calculated bulk modulus of 250(1) GPa) as compared to Mg-O bonds in MgO6 octahedra (with a calculated bulk modulus of 130(1) GPa). The spatial cation distribution in the Pbnm orthorhombic unit cell and different polyhedral compressibilities entails a strong anisotropic compression comparable to that of forsterite. The axial compressibilities are 1.06(2) x 10(-3), 2.17(2) x 10(-3), and 1.30(3) x 10(-3) GPa(-1) for a, b, and c axes, respectively. The crystal chemistry of sinhalite under compression is compared to that of other olivine-like compounds. Compressibility trends and possible high-pressure phases are discussed.This study was supported by the Spanish government MEC under Grants No: MAT2010-21270-C04-01/03/04, MAT2013-46649-C4-1/2/3-P, and CTQ2009-14596-C02-01, by the Comunidad de Madrid and European Social Fund (S2009/PPQ1551 4161893), by MALTA Consolider Ingenio 2010 project (CSD2007-00045), and by Generalitat Valenciana (GVA-ACOMP-2013-1012 and GVA-ACOMP-2014-243). Experiments were performed at MSPD beamline at ALBA Synchrotron Light Facility with the collaboration of ALBA staff A.M. and P.R-H. acknowledge computing time provided by Red Espanola de Supercomputacion (RES) and MALTA-Cluster. J.A.S. acknowledges financial support through the Juan de la Cierva fellowship. We are particularly grateful to Angel Vegas for stimulating discussions and critical reading of this manuscript.Santamaría Pérez, D.; Errandonea, D.; Gomis, O.; Sans Tresserras, JÁ.; Pereira, ALJ.; Manjón Herrera, FJ.; Popescu, C.... (2015). Crystal structure of sinhalite MgAlBO4 under high pressure. Journal of Physical Chemistry C. 119(12):6777-6784. https://doi.org/10.1021/jp512131eS677767841191
Overview of biologically digested leachate treatment using adsorption
Biological process is effective in treating most biodegradable organic matter present in leachate; however, a significant amount of ammonia, metals and refractory organic compounds may still remain in this biologically digested leachate. This effluent cannot be released to receiving bodies until the discharge limit is met. Several physical/chemical processes have been practiced as post-treatment to remove the remaining pollutants including coagulation–flocculation, oxidation and adsorption. Adsorption is often applied in leachate treatment as it enhances removal of refractory organic compounds. This chapter will focus on works related to adsorption as one of the commonly used methods to treat biologically digested leachate further down to acceptable discharge limit
Overview of biologically digested leachate treatment using adsorption
Biological process is effective in treating most biodegradable organic matter present in leachate; however, a significant amount of ammonia, metals and refractory organic compounds may still remain in this biologically digested leachate. This effluent cannot be released to receiving bodies until the discharge limit is met. Several physical/chemical processes have been practiced as post-treatment to remove the remaining pollutants including coagulation–flocculation, oxidation and adsorption. Adsorption is often applied in leachate treatment as it enhances removal of refractory organic compounds. This chapter will focus on works related to adsorption as one of the commonly used methods to treat biologically digested leachate further down to acceptable discharge limit
Search for Supernova Neutrino-Bursts with the AMANDA Detector
The core collapse of a massive star in the Milky Way will produce a neutrino
burst, intense enough to be detected by existing underground detectors. The
AMANDA neutrino telescope located deep in the South Pole ice can detect MeV
neutrinos by a collective rate increase in all photo-multipliers on top of dark
noise. The main source of light comes from positrons produced in the
CC-reaction of anti-electron neutrinos on free protons \antinue + p \to e^+ +
n. This paper describes the first supernova search performed on the full sets
of data taken during 1997 and 1998 (215 days of live time) with 302 of the
detector's optical modules. No candidate events resulted from this search. The
performance of the detector is calculated, yielding a 70% coverage of the
Galaxy with one background fake per year with 90% efficiency for the detector
configuration under study. An upper limit at the 90% c.l. on the rate of
stellar collapses in the Milky Way is derived, yielding 4.3 events per year. A
trigger algorithm is presented and its performance estimated. Possible
improvements of the detector hardware are reviewed.Comment: 20 pages, 14 figures. Submitted to Astroparticle Physic
- …