2,670 research outputs found
Cu/Ag EAM Potential Optimized for Heteroepitaxial Diffusion from ab initio Data
A binary embedded-atom method (EAM) potential is optimized for Cu on Ag(111)
by fitting to ab initio data. The fitting database consists of DFT calculations
of Cu monomers and dimers on Ag(111), specifically their relative energies,
adatom heights, and dimer separations. We start from the Mishin Cu-Ag EAM
potential and first modify the Cu-Ag pair potential to match the FCC/HCP site
energy difference then include Cu-Cu pair potential optimization for the entire
database. The optimized EAM potential reproduce DFT monomer and dimer relative
energies and geometries correctly. In trimer calculations, the potential
produces the DFT relative energy between FCC and HCP trimers, though a
different ground state is predicted. We use the optimized potential to
calculate diffusion barriers for Cu monomers, dimers, and trimers. The
predicted monomer barrier is the same as DFT, while experimental barriers for
monomers and dimers are both lower than predicted here. We attribute the
difference with experiment to the overestimation of surface adsorption energies
by DFT and a simple correction is presented. Our results show that the
optimized Cu-Ag EAM can be applied in the study of larger Cu islands on
Ag(111).Comment: 15 pages, 7 figure
Analogue of cosmological particle creation in an ion trap
We study phonons in a dynamical chain of ions confined by a trap with a
time-dependent (axial) potential strength and demonstrate that they behave in
the same way as quantum fields in an expanding/contracting universe. Based on
this analogy, we present a scheme for the detection of the analogue of
cosmological particle creation which should be feasible with present-day
technology. In order to test the quantum nature of the particle creation
mechanism and to distinguish it from classical effects such as heating, we
propose to measure the two-phonon amplitude via the red side-band
and to compare it with the one-phonon amplitude ( red side-band).
PACS: 04.62.+v, 98.80.-k, 42.50.Vk, 32.80.Pj.Comment: 4 pages, 2 figure
Some Properties of Entire Functions Associated with L-entire Functions on C(I)
In this paper, let C(I) denote the Banach algebra of all continuous complex-valued functions defined on a close interval I in the set of real numbers, R. The functions having derivatives in the Lorch sense on the whole Banach algebra C(I) are considered and they are called L-entire functions [1, 3]. For each L-entire function on C(I), entire complex functions are associated and the relationship between their orders is studied. Even more, the possibility of locating the solutions of the equation F(f) = 0 from the location of zeros of the associated family of entire functions with F is analyzed too
A Topological Study of Contextuality and Modality in Quantum Mechanics
Kochen-Specker theorem rules out the non-contextual assignment of values to
physical magnitudes. Here we enrich the usual orthomodular structure of quantum
mechanical propositions with modal operators. This enlargement allows to refer
consistently to actual and possible properties of the system. By means of a
topological argument, more precisely in terms of the existence of sections of
sheaves, we give an extended version of Kochen-Specker theorem over this new
structure. This allows us to prove that contextuality remains a central feature
even in the enriched propositional system.Comment: 10 pages, no figures, submitted to I. J. Th. Phy
Quasar-galaxy and AGN-galaxy cross-correlations
We compute quasar-galaxy and AGN-galaxy cross-correlation functions for
samples taken from the \cite{VCV98} catalog of quasars and active galaxies,
using tracer galaxies taken from the Edinburgh/Durham Southern Catalog. The
sample of active galaxy targets shows positive correlation at projected
separations consistent with the usual power-law. On the
other hand, we do not find a statistically significant positive quasar-galaxy
correlation signal except in the range
where we find similar AGN-galaxy and quasar-galaxy correlation amplitudes. At
separations a strong decline of quasar-galaxy correlations
is observed, suggesting a significant local influence of quasars in galaxy
formation. In an attempt to reproduce the observed cross-correlation between
quasars and galaxies, we have performed CDM cosmological hydrodynamical
simulations and tested the viability of a scenario based on the model developed
by \cite{silkrees98}. In this scheme a fraction of the energy released by
quasars is considered to be transferred into the baryonic component of the
intergalactic medium in the form of winds. The results of the simulations
suggest that the shape of the observed quasar-galaxy cross-correlation function
could be understood in a scenario where a substantial amount of energy is
transferred to the medium at the redshift of maximum quasar activity.Comment: 11 pages, 9 figures. Accepted for publication in Ap
Accurate quantitative EDS-TEM analysis of precipitates and matrix in equilibrium (α+β) Zr–1Nb alloys with Ta addition
The (α+β) phase microstructure in Zr-1.05Nb, Zr-0.85Nb-0.20Ta and Zr-0.85Nb-0.40Ta (wt.%) alloys annealed at 570 °C for 3840 h after β-quenching were observed at different scales by optical, SEM and TEM microscopies. A quantitative study of phase chemical compositions was carried out by EDS-TEM with experimental Cliff-Lorimer factors. The α matrix was measured on thin films and the β particle on carbon extractive replicas. The Ta addition showed a continuous increase of (Nb + Ta) solubility in α-Zr and (Zr + Ta) solubility in the β-Nb phase. The increase of Ta in the nominal composition of the Zr-1(Nb, Ta) alloy causes the decrease of the mass fraction of β-Nb phase.Fil: Ferreirós, Pedro Antonio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Materiales (CAC); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Universidad Tecnológica Nacional. Facultad Regional Haedo; ArgentinaFil: Alonso, P. R.. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Materiales (CAC); Argentina. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Quirós, D. P.. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Materiales (CAC); ArgentinaFil: Zelaya, E.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Rubiolo, Gerardo Hector. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Unidad de Actividad de Materiales (CAC); Argentin
Legal aspects of memory:A report issued by the Psychology and Law Sections of the British Academy
A Galactic O-Star Catalog
We have produced a catalog of 378 Galactic O stars with accurate spectral
classifications which is complete for V<8 but includes many fainter stars. The
catalog provides cross-identifications with other sources; coordinates
(obtained in most cases from Tycho-2 data); astrometric distances for 24 of the
nearest stars; optical (Tycho-2, Johnson, and Stromgren) and NIR photometry;
group membership, runaway character, and multiplicity information; and a
web-based version with links to online services.Comment: 76 pages, 13 tables, and 3 figures. Accepted for publication in
Astrophysical Journal. Online version of the catalog available at
http://www.stsci.edu/~jmaiz/GOSmain.htm
901-25 The Paradox of Donor Stimulation of Endothelial-induced Smooth Muscle Growth
Cardiac allograft vasculopathy (CAV) is the major cause of long-term morbidity and mortality in cardiac transplant recipients. It appears to be related to immune damage to the coronary endothelial cells, resulting in intimal proliferation. In order to delineate the mechanisms by which CAY can occur, a co-culture model of human endothelial cells (EC) and smooth muscle cells (SMC) obtained from the donor at the time of organ procurement was utilized. These cells were separated by collagenase digestion, and cultured for four passages. EC and SMC were then grown to confluence in the separate chambers of a co-culture plate separated by a 0.45 micron Millipore filter. Preserved lymphocytes (LYMPH) obtained from the donor and pooled blood lymphocytes from the recipient 3-4 weeks following transplant were added to the EC well so as to cause an immunologic stimulation of the EC. None of the recipients were exposed to monoclonal or polyclonal antibodies to lymphocytes. All cultures and assays were done in triplicate. Results are as follows:Patient#% Increase in donor lymph H3thymidinep ValueDonor 1+510.04Donor 2+450.05Donor 3+1040.05Donor 4+250.01Donor 5-19NSThe donor EC/donor LYMPH co-culture stimulated SMC growth measured by H3thymidine incorporation in 4 of 5 patients. The donor EC/recipient LYMPH co-culture did not result in significant SMC H3thymidine incorporation.ConclusionThese paradoxical findings of a lack in significant SMC proliferation in the recipient stimulated donor cells continue to raise questions in relation to the effects of circulating lymphocytes on the development of cardiac allograft vasculopathy
Removing subordinate species in a biodiversity experiment to mimic observational field studies
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