496 research outputs found
Pressed boride cathodes
Results of experimental studies of emission cathodes made from lanthanum, yttrium, and gadolinium hexaborides are presented. Maximum thermal emission was obtained from lanthanum hexaboride electrodes. The hexaboride cathodes operated stably under conditions of large current density power draw, at high voltages and poor vacuum. A microtron electron gun with a lanthanum hexaboride cathode is described
Elastic properties of cubic crystals: Every's versus Blackman's diagram
Blackman's diagram of two dimensionless ratios of elastic constants is
frequently used to correlate elastic properties of cubic crystals with
interatomic bondings. Every's diagram of a different set of two dimensionless
variables was used by us for classification of various properties of such
crystals. We compare these two ways of characterization of elastic properties
of cubic materials and consider the description of various groups of materials,
e.g. simple metals, oxides, and alkali halides. With exception of intermediate
valent compounds, the correlation coefficients for Every's diagrams of various
groups of materials are greater than for Blackaman's diagrams, revealing the
existence of a linear relationship between two dimensionless Every's variables.
Alignment of elements and compounds along lines of constant Poisson's ratio
, ( arbitrary perpendicular to ) is
observed. Division of the stability region in Blackman's diagram into region of
complete auxetics, auxetics and non-auxetics is introduced. Correlations of a
scaling and an acoustic anisotropy parameter are considered.Comment: 8 pages, 9 figures, presented on The Ninth International School on
Theoretical Physics "Symmetry and Structural Properties of Condensed Matter",
5 - 12 September 2007, Myczkowce, Polan
Charge and spin transport in a metal-semiconductor heterostructure with double Schottky barriers
Taking into account the available experimental results, we model the
electronic properties and current-voltage characteristics of a
ferromagnet-semiconductor junction. The Fe/GaAs interface is considered as a
Fe/(i-GaAs)/n+-GaAs/n-GaAs multilayer structure with the Schottky barrier. We
also calculate numerically the current-voltage characteristics of a
double-Schottky-barrier structure Fe/GaAs/Fe, which are in agreement with
available experimental data. For this structure, we have estimated the spin
current in the GaAs layer, which characterizes spin injection from the
ferromagnet to the semiconductor.Comment: 3 pages, 5 figures, presented on The European Conference Physics of
Magnetism 2014 (PM'14), June 23-27, 2014 Pozna\'n, POLAN
Antibacterial Activity of Gentamicin-bonded Gelatin-sealed Polyethylene Terephthalate Vascular Prostheses
AbstractObjectivesTo create an antibiotic-modified vascular prosthesis with a prolonged bactericidal activity, susceptible to endothelialisation.MethodsWe used a covalent method of gentamicin sulphate immobilisation to polyethylene terephthalate prosthesis sealed with gelatin. Antibacterial activity was assayed in Luria-Bertani medium against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa strains. Prosthesis endothelialisation was performed using bovine aorta endothelial cells (BAEC).ResultsGentamicin was bound to vascular prostheses in the amount of 12g per kg of prosthesis. Ninety-seven percent of antibiotic bound in covalent way and remained on the biomaterial for at least 30 days during shaking in PBS solution. Gentamicin-modified prostheses exerted bactericidal or bacteriostatic effect on growth of clinical and reference bacterial strains, prevented biofilm formation and were highly susceptible to endothelialisation. BAEC viability exceeded 90%, which indicated that gentamicin-vascular prostheses were not toxic for these cells.ConclusionsCovalent gentamicin immobilisation resulted in effective antibacterial protection of vascular prostheses against clinical and reference strains of S. aureus, E. coli and P. aeruginosa and allowed for a strong adherence of endothelial cells to antibiotic-modified prostheses
End-to-end beam simulations for the new muon G-2 experiment at Fermilab
The aim of the new muon g-2 experiment at Fermilab is to measure the anomalous magnetic moment of the muon with an unprecedented uncertainty of 140 ppb. A beam of positive muons required for the experiment is created by pion decay. Detailed studies of the beam dynamics and spin polarization of the muons are important to predict systematic uncertainties in the experiment. In this paper, we present the results of beam simulations and spin tracking from the pion production target to the muon storage ring. The end-to-end beam simulations are developed in Bmad and include the processes of particle decay, collimation (with accurate representation of all apertures) and spin tracking
Closed orbit correction at synchrotrons for symmetric and near-symmetric lattices
This contribution compiles the benefits of lattice symmetry in the context of
closed orbit correction. A symmetric arrangement of BPMs and correctors results
in structured orbit response matrices of Circulant or block Circulant type.
These forms of matrices provide favorable properties in terms of computational
complexity, information compression and interpretation of mathematical vector
spaces of BPMs and correctors. For broken symmetries, a nearest-Circulant
approximation is introduced and the practical advantages of symmetry
exploitation are demonstrated with the help of simulations and experiments in
the context of FAIR synchrotrons
A finite model of two-dimensional ideal hydrodynamics
A finite-dimensional su() Lie algebra equation is discussed that in the
infinite limit (giving the area preserving diffeomorphism group) tends to
the two-dimensional, inviscid vorticity equation on the torus. The equation is
numerically integrated, for various values of , and the time evolution of an
(interpolated) stream function is compared with that obtained from a simple
mode truncation of the continuum equation. The time averaged vorticity moments
and correlation functions are compared with canonical ensemble averages.Comment: (25 p., 7 figures, not included. MUTP/92/1
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