1,314 research outputs found
Quantum wells, wires and dots with finite barrier: analytical expressions for the bound states
From a careful study of the transcendental equations fulfilled by the bound
state energies of a free particle in a quantum well, cylindrical wire or
spherical dot with finite potential barrier, we have derived analytical
expressions of these energies which reproduce impressively well the numerical
solutions of the corresponding transcendental equations for all confinement
sizes and potential barriers, without any adjustable parameter. These
expressions depend on a unique dimensionless parameter which contains the
barrier height and the sphere, wire or well radius.Comment: 4 pages, 3 figure
Remarks on supersymmetry of quantum systems with position-dependent effective masses
We apply the supersymmetry approach to one-dimensional quantum systems with
spatially-dependent mass, by including their ordering ambiguities dependence.
In this way we extend the results recently reported in the literature.
Furthermore, we point out a connection between these systems and others with
constant masses. This is done through convenient transformations in the
coordinates and wavefunctions.Comment: 8 pages, 1 figur
Dirac and Klein-Gordon particles in one-dimensional periodic potentials
We evaluate the dispersion relation for massless fermions, described by the
Dirac equation, and for zero-spin bosons, described by the Klein-Gordon
equation, moving in two dimensions and in the presence of a one-dimensional
periodic potential. For massless fermions the dispersion relation shows a zero
gap for carriers with zero momentum in the direction parallel to the barriers
in agreement with the well-known "Klein paradox". Numerical results for the
energy spectrum and the density of states are presented. Those for fermions are
appropriate to graphene in which carriers behave relativistically with the
"light speed" replaced by the Fermi velocity. In addition, we evaluate the
transmission through a finite number of barriers for fermions and zero-spin
bosons and relate it with that through a superlattice.Comment: 9 pages, 12 figure
Long-term high fat feeding of rats results in increased numbers of circulating microvesicles with pro-inflammatory effects on endothelial cells
Obesity and type 2 diabetes lead to dramatically increased risks of atherosclerosis and CHD. Multiple mechanisms converge to promote atherosclerosis by increasing endothelial oxidative stress and up-regulating expression of pro-inflammatory molecules. Microvesicles (MV) are small ( < 1 μm) circulating particles that transport proteins and genetic material, through which they are able to mediate cell–cell communication and influence gene expression. Since MV are increased in plasma of obese, insulin-resistant and diabetic individuals, who often exhibit chronic vascular inflammation, and long-term feeding of a high-fat diet (HFD) to rats is a well-described model of obesity and insulin resistance, we hypothesised that this may be a useful model to study the impact of MV on endothelial inflammation. The number and cellular origin of MV from HFD-fed obese rats were characterised by flow cytometry. Total MV were significantly increased after feeding HFD compared to feeding chow (P< 0·001), with significantly elevated numbers of MV derived from leucocyte, endothelial and platelet compartments (P< 0·01 for each cell type). MV were isolated from plasma and their ability to induce reactive oxygen species (ROS) formation and vascular cell adhesion molecule (VCAM)-1 expression was measured in primary rat cardiac endothelial cells in vitro. MV from HFD-fed rats induced significant ROS (P< 0·001) and VCAM-1 expression (P= 0·0275), indicative of a pro-inflammatory MV phenotype in this model of obesity. These findings confirm that this is a useful model to further study the mechanisms by which diet can influence MV release and subsequent effects on cardio-metabolic health
Dynamics of Electrons in Graded Semiconductors
I present a theory of electron dynamics in semiconductors with slowly varying
composition. I show that the frequency-dependent conductivity, required for the
description of transport and optical properties, can be obtained from a
knowledge of the band structures and momentum matrix elements of homogeneous
semiconductor alloys. New sum rules for the electronic oscillator strengths,
which apply within a given energy band or between any two bands, are derived,
and a general expression for the width of the intraband absorption peak is
given. Finally, the low-frequency dynamics is discussed, and a correspondence
with the semiclassical motion is established.Comment: 4 pages, Revte
Coherent electrical rotations of valley states in Si quantum dots using the phase of the valley-orbit coupling
A gate electric field has a small but non-negligible effect on the phase of
the valley-orbit coupling in Si quantum dots. Finite interdot tunneling between
valley eigenstates in a double quantum dot is enabled by a small difference in
the phase of the valley-orbit coupling between the two dots, and it in turn
allows controllable rotations of two-dot valley eigenstates at a level
anticrossing. We present a comprehensive analytical discussion of this process,
with estimates for realistic structures.Comment: 10 pages, 2 figure
Choosing a basis that eliminates spurious solutions in k.p theory
A small change of basis in k.p theory yields a Kane-like Hamiltonian for the
conduction and valence bands of narrow-gap semiconductors that has no spurious
solutions, yet provides an accurate fit to all effective masses. The theory is
shown to work in superlattices by direct comparison with first-principles
density-functional calculations of the valence subband structure. A
reinterpretation of the standard data-fitting procedures used in k.p theory is
also proposed.Comment: 15 pages, 2 figures; v3: expanded with much new materia
Large variations in the hole spin splitting of quantum-wire subband edges
We study Zeeman splitting of zone-center subband edges in a cylindrical hole
wire subject to a magnetic field parallel to its axis. The g-factor turns out
to fluctuate strongly as a function of wire-subband index, assuming values that
differ substantially from those found in higher-dimensional systems. We analyze
the spin properties of hole-wire states using invariants of the spin-3/2
density matrix and find a strong correlation between g-factor value and the
profile of hole-spin polarization density. Our results suggest possibilities
for confinement engineering of hole spin splittings.Comment: 4 pages, 3 figures, RevTex4, to appear in PR
Longitudinal spin transport in diluted magnetic semiconductor superlattices: the effect of the giant Zeeman splitting
Longitudinal spin transport in diluted magnetic semiconductor superlattices
is investigated theoretically. The longitudinal magnetoconductivity (MC) in
such systems exhibits an oscillating behavior as function of an external
magnetic field. In the weak magnetic field region the giant Zeeman splitting
plays a dominant role which leads to a large negative magnetoconductivity. In
the strong magnetic field region the MC exhibits deep dips with increasing
magnetic field. The oscillating behavior is attributed to the interplay between
the discrete Landau levels and the Fermi surface. The decrease of the MC at low
magnetic field is caused by the exchange interaction between the electron
in the conduction band and the magnetic ions.Comment: 6 pages, 9 figures, submitted to Phys. Rev.
Effective-Mass Dirac Equation for Woods-Saxon Potential: Scattering, Bound States and Resonances
Approximate scattering and bound state solutions of the one-dimensional
effective-mass Dirac equation with the Woods-Saxon potential are obtained in
terms of the hypergeometric-type functions. Transmission and reflection
coefficients are calculated by using behavior of the wave functions at
infinity. The same analysis is done for the constant mass case. It is also
pointed out that our results are in agreement with those obtained in
literature. Meanwhile, an analytic expression is obtained for the transmission
resonance and observed that the expressions for bound states and resonances are
equal for the energy values .Comment: 20 pages, 6 figure
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