14,385 research outputs found
Spin-orbit effects on the Larmor dispersion relation in GaAs quantum wells
We have studied the relevance of spin-orbit coupling to the dispersion 00009
relation of the Larmor resonance observed in inelastic light scattering and
electron-spin resonance experiments on GaAs quantum wells. We show that the
spin-orbit interaction, here described by a sum of Dresselhaus and
Bychkov-Rashba terms, couples Zeeman and spin-density excitations. We have
evaluated its contribution to the spin splitting as a function of the magnetic
field , and have found that in the small limit, the spin-orbit
interaction does not contribute to the spin splitting, whereas at high magnetic
fields it yields a independent contribution to the spin splitting given by
, with being the intensity of the
Bychkov-Rashba and Dresselhaus spin-orbit terms.Comment: To be published in Physical Review
Novel software techniques for automatic microwave measurements
Although many microwave measurement techniques are heavily based on special purpose software, the application of modern software techniques like object oriented programming and new programming language like C++ is seldom used. The impact of such new software solutions can drastically improve the overall design of a microwave test set. The paper presents the design and implementation of a new multiport network analyzer with particular attention to the control program architecture. The use of Object Oriented Programming techniques results in a clear and easy to maintain solution which boosts both the user interface and the overall test set organizatio
Imaging ionospheric inhomogeneities using spaceborne synthetic aperture radar
We present a technique and results of 2-D imaging of Faraday rotation and total electron content using spaceborne L band polarimetric synthetic aperture radar (PolSAR). The results are obtained by processing PolSAR data collected using the Phased Array type L-band Synthetic Aperture Radar (PALSAR) on board the Advanced Land Observation Satellite. Distinguished ionospheric inhomogeneities are captured in 2-D images from space with relatively high resolutions of hundreds of meters to a couple of kilometers in auroral-, middle-, and low-latitude regions. The observed phenomena include aurora-associated ionospheric enhancement arcs, the middle-latitude trough, traveling ionospheric disturbances, and plasma bubbles, as well as ionospheric irregularities. These demonstrate a new capability of spaceborne synthetic aperture radar that will not only provide measurements to correction of ionospheric effects in Earth science imagery but also significantly benefit ionospheric studies
Spin and density longitudinal response of quantum dots in time-dependent local-spin-density approximation
The longitudinal dipole response of a quantum dot has been calculated in the
far-infrared regime using local spin density functional theory. We have studied
the coupling between the collective spin and density modes as a function of the
magnetic field. We have found that the spin dipole mode and single particle
excitations have a sizeable overlap, and that the magnetoplasmon modes can be
excited by the dipole spin operator if the dot is spin polarized. The frequency
of the dipole spin edge mode presents an oscillation which is clearly filling
factor () related. We have found that the spin dipole mode is especially
soft for even values, becoming unstable for magnetic fields in the region
. Results for selected number of electrons and confining
potentials are discussed. An analytical model which reproduces the main
features of the microscopic spectra has been developed.Comment: We have added some new references and minor changes on the mnuscript
have been mad
Quasi-ordinary power series and their zeta functions
The main objective of this paper is to prove the monodromy conjecture for the
local Igusa zeta function of a quasi-ordinary polynomial of arbitrary dimension
defined over a number field. In order to do it, we compute the local
Denef-Loeser motivic zeta function of a quasi-ordinary
power series of arbitrary dimension over an algebraically closed field of
characteristic zero from its characteristic exponents without using embedded
resolution of singularities. This allows us to effectively represent
such that almost all the candidate poles given
by are poles. Anyway, these candidate poles give eigenvalues of the
monodromy action of the complex of nearby cycles on In particular
we prove in this case the monodromy conjecture made by Denef-Loeser for the
local motivic zeta function and the local topological zeta function. As a
consequence, if is a quasi-ordinary polynomial defined over a number field
we prove the Igusa monodromy conjecture for its local Igusa zeta function.Comment: 74 page
Quasi-ordinary singularities and Newton trees
In this paper we study some properties of the class of nu-quasi-ordinary
hypersurface singularities. They are defined by a very mild condition on its
(projected) Newton polygon. We associate with them a Newton tree and
characterize quasi-ordinary hypersurface singularities among nu-quasi-ordinary
hypersurface singularities in terms of their Newton tree. A formula to compute
the discriminant of a quasi-ordinary Weierstrass polynomial in terms of the
decorations of its Newton tree is given. This allows to compute the
discriminant avoiding the use of determinants and even for non Weierstrass
prepared polynomials. This is important for applications like algorithmic
resolutions. We compare the Newton tree of a quasi-ordinary singularity and
those of its curve transversal sections. We show that the Newton trees of the
transversal sections do not give the tree of the quasi-ordinary singularity in
general. It does if we know that the Newton tree of the quasi-ordinary
singularity has only one arrow.Comment: 32 page
Quantum Evolution of Inhomogeneities in Curved Space
We obtain the renormalized equations of motion for matter and semi-classical
gravity in an inhomogeneous space-time. We use the functional Schrodinger
picture and a simple Gaussian approximation to analyze the time evolution of
the model, and we establish the renormalizability of this
non-perturbative approximation. We also show that the energy-momentum tensor in
this approximation is finite once we consider the usual mass and coupling
constant renormalizations, without the need of further geometrical
counter-terms.Comment: 22 page
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