579 research outputs found
A Constitutive Equation for Cyclically Loaded Sands
A rate type constitutive equation with internal parameters is proposed for describing the behaviour of cyclically loaded sands in undrained conditions leading to liquefaction. The mathematical model is checked versus experimental data on undrained cyclic triaxial test on Monterey No. 0 sand. General trends of real sand behaviour are captured. The equation is applicable for general stress states too
C and S induces changes in the electronic and geometric structure of Pd(533) and Pd(320)
We have performed ab initio electronic structure calculations of C and S
adsorption on two vicinal surfaces of Pd with different terrace geometry and
width. We find both adsorbates to induce a significant perturbation of the
surface electronic and geometric structure of Pd(533) and Pd(320). In
particular C adsorbed at the bridge site at the edge of a Pd chain in Pd(320)
is found to penetrate the surface to form a sub-surface structure. The
adsorption energies show almost linear dependence on the number of
adsorbate-metal bonds, and lie in the ranges of 5.31eV to 8.58eV for C and
2.89eV to 5.40eV for S. A strong hybridization between adsorbate and surface
electronic states causes a large splitting of the bands leading to a drastic
decrease in the local densities of electronic states at the Fermi-level for Pd
surface atoms neighboring the adsorbate which may poison catalytic activity of
the surface. Comparison of the results for Pd(533) with those obtained earlier
for Pd(211) suggests the local character of the impact of the adsorbate on the
geometric and electronic structures of Pd surfaces.Comment: 14 pages 9 figs, Accepted J. Phys: Conden
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Novel concept of multi-channel fiber optic surface plasmon resonance sensor
A novel multi-channel fiber optic surface plasmon resonance (SPR) sensor is reported. The sensing structure consists of a single-mode optical fiber, covered with a thin gold layer, which supports a surface plasmon (SP), and a Bragg grating. The Bragg grating induces coupling between the forward-propagating fundamental core mode and the back-propagating SP-cladding mode. As the SP-cladding modes are highly sensitive to changes in the refractive index of the surrounding medium, the changes can be accurately measured by spectroscopy of these hybrid modes. Multichannel capability is achieved by employing a sequence of Bragg gratings of different periods and their reading via the wavelength division multiplexing. Theoretical analysis and optimization based on the coupled-mode theory (CMT) is carried out and performance characteristics of the sensor are determined
The effect of Coulomb interaction at ferromagnetic-paramagnetic metallic perovskite junctions
We study the effect of Coulomb interactions in transition metal oxides
junctions. In this paper we analyze charge transfer at the interface of a three
layer ferromagnetic-paramagnetic-ferromagnetic metallic oxide system. We choose
a charge model considering a few atomic planes within each layer and obtain
results for the magnetic coupling between the ferromagnetic layers. For large
number of planes in the paramagnetic spacer we find that the coupling
oscillates with the same period as in RKKY but the amplitude is sensitive to
the Coulomb energy. At small spacer thickness however, large differences may
appear as function of : the number of electrons per atom in the ferromagnetics
and paramagnetics materials, the dielectric constant at each component, and the
charge defects at the interface plane emphasizing the effects of charge
transfer.Comment: tex file and 7 figure
The loss of anisotropy in MgB2 with Sc substitution and its relationship with the critical temperature
The electrical conductivity anisotropy of the sigma-bands is calculated for
the (Mg,Sc)B2 system using a virtual crystal model. Our results reveal that
anisotropy drops with relatively little scandium content (< 30%); this
behaviour coincides with the lowering of Tc and the reduction of the Kohn
anomaly. This anisotropy loss is also found in the Al and C doped systems. In
this work it is argued that the anisotropy, or 2D character, of the sigma-bands
is an important parameter for the understanding of the high Tc found in MgB2
Cancellation of probe effects in measurements of spin polarized momentum density by electron positron annihilation
Measurements of the two dimensional angular correlation of the
electron-positron annihilation radiation have been done in the past to detect
the momentum spin density and the Fermi surface. We point out that the momentum
spin density and the Fermi Surface of ferromagnetic metals can be revealed
within great detail owing to the large cancellation of the electron-positron
matrix elements which in paramagnetic multiatomic systems plague the
interpretation of the experiments. We prove our conjecture by calculating the
momentum spin density and the Fermi surface of the half metal CrO2, who has
received large attention due to its possible applications as spintronics
material
Structure peculiarities of cementite and their influence on the magnetic characteristics
The iron carbide is studied by the first-principle density functional
theory. It is shown that the crystal structure with the carbon disposition in a
prismatic environment has the lowest total energy and the highest energy of
magnetic anisotropy as compared to the structure with carbon in an octahedron
environment. This fact explains the behavior of the coercive force upon
annealing of the plastically deformed samples. The appearance of carbon atoms
in the octahedron environment can be revealed by Mossbauer experiment.Comment: 10 pages, 3 figures, 3 tables. submitted to Phys.Rev.
Study of Bulk Damage of High Dose Gamma Irradiated p-type Silicon Diodes with Various Resistivities
The bulk damage of p-type silicon detectors caused by high doses of gamma
irradiation has been studied. The study was carried out on three types of
n-in-p silicon diodes with comparable geometries but different initial
resistivities. This allowed to determine how different initial parameters of
studied samples influence radiation-induced changes in the measured
characteristics. The diodes were irradiated by a Cobalt-60 gamma source to
total ionizing doses ranging from 0.50 up to 8.28 MGy, and annealed for 80
minutes at 60 {\deg}C. The Geant4 toolkit for simulation of the passage of
particles through matter was used to simulate the deposited energy homogeneity,
to verify the equal distribution of total deposited energies through all the
layers of irradiated samples, and to calculate the secondary electron spectra
in the irradiation box. The main goal of the study was to characterize the
gamma-radiation induced displacement damage by measuring current-voltage
characteristics (IV), and the evolution of the full depletion voltage with the
total ionizing dose, by measuring capacitance-voltage characteristics (CV). It
has been observed that the bulk leakage current increases linearly with total
ionizing dose, and the damage coefficient depends on the initial resistivity of
the silicon diode. The effective doping concentration and therefore full
depletion voltage significantly decreases with increasing total ionizing dose,
before starting to increase again at a specific dose. We assume that this
decrease is caused by the effect of acceptor removal. Another noteworthy
observation of this study is that the IV and CV measurements of the gamma
irradiated diodes do not reveal any annealing effect
Substituting the main group element in cobalt - iron based Heusler alloys: CoFeAlSi
This work reports about electronic structure calculations for the Heusler
compound CoFeAlSi. Particular emphasis was put on the role of
the main group element in this compound. The substitution of Al by Si leads to
an increase of the number of valence electrons with increasing Si content and
may be seen as electron-doping. Self-consistent electronic structure
calculations were performed to investigate the consequences of the electron
doping for the magnetic properties. The series CoFeAlSi is
found to exhibit half-metallic ferromagnetism and the magnetic moment follows
the Slater-Pauling rule. It is shown that the electron-doping stabilises the
gap in the minority states for .Comment: J. Phys. D (accepted
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