1,084 research outputs found
Interaction of a surface acoustic wave with a two-dimensional electron gas
When a surface acoustic wave propagates on the surface of a GaAs
semiconductor, coupling between electrons in the two-dimensional electron gas
beneath the interface and the elastic host crystal through piezoelectric
interaction will attenuate the SAW. The coupling coefficient is calculated for
the SAW propagating along an arbitrary direction. It is found that the coupling
strength is largely dependent on the propagating direction. When the SAW
propagates along the [011] direction, the coupling becomes quite weak.Comment: 3 figure
Z decay into two massless gauge bosons in a magnetic field
An investigation of the processes Z to gluon-gluon and Z to photon-photon in
a background magnetic field is presented. For homogeneous fields corrections to
the charged fermion propagator can be calculated in leading orders of the
magnetic field. This work examines the first order contributions of the
corrected propagator to decays that are otherwise zero. Results of the decay
rates for varying field strengths are included.Comment: 14 pages, 2 figures, needs RevTeX4; typos corrected, appendix added,
references added, format changed to preprint mod
Angular Pseudomomentum Theory for the Generalized Nonlinear Schr\"{o}dinger Equation in Discrete Rotational Symmetry Media
We develop a complete mathematical theory for the symmetrical solutions of
the generalized nonlinear Schr\"odinger equation based on the new concept of
angular pseudomomentum. We consider the symmetric solitons of a generalized
nonlinear Schr\"odinger equation with a nonlinearity depending on the modulus
of the field. We provide a rigorous proof of a set of mathematical results
justifying that these solitons can be classified according to the irreducible
representations of a discrete group. Then we extend this theory to
non-stationary solutions and study the relationship between angular momentum
and pseudomomentum. We illustrate these theoretical results with numerical
examples. Finally, we explore the possibilities of the generalization of the
previous framework to the quantum limit.Comment: 18 pages; submitted to Physica
Long-Range Correlations and the Momentum Distribution in Nuclei
The influence of correlations on the momentum distribution of nucleons in
nuclei is evaluated starting from a realistic nucleon-nucleon interaction. The
calculations are performed directly for the finite nucleus \,^{16}O making
use of the Green's function approach. The emphasis is focused on the
correlations induced by the excitation modes at low energies described within a
model-space of shell-model configurations including states up to the sdg shell.
Our analysis demonstrates that these long-range correlations do not produce any
significant enhancement of the momentum distribution at high missing momenta
and low missing energies. This is in agreement with high resolution
experiments for this nucleus. We also try to simulate the corresponding effects
in large nuclei by quenching the energy-spacing between single-particle orbits.
This yields a sizable enhancement of the spectral function at large momenta and
small energy. Such behavior could explain the deviation of the momentum
distribution from the mean field prediction, which has been observed in
experiments on heavy nuclei like Pb
Factorization in integrable systems with impurity
This article is based on recent works done in collaboration with M. Mintchev,
E. Ragoucy and P. Sorba. It aims at presenting the latest developments in the
subject of factorization for integrable field theories with a reflecting and
transmitting impurity.Comment: 7 pages; contribution to the XIVth International Colloquium on
Integrable systems, Prague, June 200
Long-Range Correlations in Closed Shell Nuclei
The effects of correlations on the bulk properties of nuclei are investigated
in large model spaces including up to 21 single-particle orbits. The evaluation
of the single-particle Green function is made feasible by means of the BAGEL
approximation. The spectral function for single-nucleon pick-up and removal is
investigated for the nuclei and . Special attention is paid
to the effects produced by correlations on the calculated ground state
properties of closed shell nuclei. It is observed that correlations beyond the
Brueckner Hartree Fock approximation tend to improve the results obtained using
realistic nucleon nucleon interactions.Comment: 23 pages 4 figures not included, Report Tu-93-081
Integrable Structure of Conformal Field Theory, Quantum KdV Theory and Thermodynamic Bethe Ansatz
We construct the quantum versions of the monodromy matrices of KdV theory.
The traces of these quantum monodromy matrices, which will be called as ``-operators'', act in highest weight Virasoro modules. The -operators depend on the spectral parameter and their expansion
around generates an infinite set of commuting Hamiltonians
of the quantum KdV system. The -operators can be viewed as the
continuous field theory versions of the commuting transfer-matrices of
integrable lattice theory. In particular, we show that for the values
of the Virasoro central charge
the eigenvalues of the -operators satisfy a closed system of
functional equations sufficient for determining the spectrum. For the
ground-state eigenvalue these functional equations are equivalent to those of
massless Thermodynamic Bethe Ansatz for the minimal conformal field theory
; in general they provide a way to generalize the technique
of Thermodynamic Bethe Ansatz to the excited states. We discuss a
generalization of our approach to the cases of massive field theories obtained
by perturbing these Conformal Field Theories with the operator .
The relation of these -operators to the boundary states is also
briefly described.Comment: 24 page
Seasonal evolution of the supraglacial drainage network at Humboldt Glacier, northern Greenland, between 2016 and 2020
Supraglacial rivers and lakes are important for the routing and storage of surface meltwater during the summer melt season across the Greenland Ice Sheet (GrIS) but remain poorly mapped and quantified across the northern part of the ice sheet, which is rapidly losing mass. Here we produce, for the first time, a high-resolution record of the supraglacial drainage network (including both rivers and lakes) and its seasonal behaviour at Humboldt Glacier, a wide-outlet glacier draining a large melt-prone hydrologic catchment (13 488 km2), spanning the period 2016 to 2020 using 10 m spatial resolution Sentinel-2 imagery. Our results reveal a perennially extensive yet interannually variable supraglacial network extending from an elevation of 200 m a.s.l. to a maximum of ∼ 1440 m a.s.l. recorded in 2020, with limited development of the network observed in the low-melt years of 2017 and 2018. The supraglacial drainage network is shown to cover an area ranging between 966 km2 (2018) and 1566 km2 (2019) at its maximum seasonal extent, with spatial coverage of up to 2685 km2 recorded during the early phases of the melt season when a slush zone is most prominent. Up-glacier expansion and the development of an efficient supraglacial drainage network as surface runoff increases and the snowline retreats is clearly visible. Preconditioning of the ice surface following a high-melt year is also observed, with an extreme and long-lasting 2019 melt season and over-winter persistence of liquid lakes, followed by low snow accumulation the following spring, culminating in earlier widespread exposure of the supraglacial drainage network in 2020 compared to other years. This preconditioning is predicted to become more common with persistent warmer years into the future. Overall, this study provides evidence of a persistent, yet dynamic, supraglacial drainage network at this prominent northern GrIS outlet glacier and advances our understanding of such hydrologic processes, particularly under ongoing climatic warming and enhanced runoff
Baxterization, dynamical systems, and the symmetries of integrability
We resolve the `baxterization' problem with the help of the automorphism
group of the Yang-Baxter (resp. star-triangle, tetrahedron, \dots) equations.
This infinite group of symmetries is realized as a non-linear (birational)
Coxeter group acting on matrices, and exists as such, {\em beyond the narrow
context of strict integrability}. It yields among other things an unexpected
elliptic parametrization of the non-integrable sixteen-vertex model. It
provides us with a class of discrete dynamical systems, and we address some
related problems, such as characterizing the complexity of iterations.Comment: 25 pages, Latex file (epsf style). WARNING: Postscript figures are
BIG (600kB compressed, 4.3MB uncompressed). If necessary request hardcopy to
[email protected] and give your postal mail addres
Decay of the metastable phase in d=1 and d=2 Ising models
We calculate perturbatively the tunneling decay rate of the
metastable phase in the quantum d=1 Ising model in a skew magnetic field near
the coexistence line at T=0. It is shown that
oscillates in the magnetic field due to discreteness of the excitation
energy spectrum. After mapping of the obtained results onto the extreme
anisotropic d=2 Ising model at , we verify in the latter model the
droplet theory predictions for the free energy analytically continued to the
metastable phase. We find also evidence for the discrete-lattice corrections in
this metastable phase free energy.Comment: 4 pages, REVTe
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