4,135 research outputs found
Semiclassical description of resonant tunneling
We derive a semiclassical formula for the tunneling current of electrons
trapped in a potential well which can tunnel into and across a wide quantum
well. The calculations idealize an experimental situation where a strong
magnetic field tilted with respect to an electric field is used. The resulting
semiclassical expression is written as the sum over special periodic orbits
which hit both walls of the quantum well and are perpendicular to the first
wall.Comment: LaTeX, 8 page
Some boundary effects in quantum field theory
We have constructed a quantum field theory in a finite box, with periodic
boundary conditions, using the hypothesis that particles living in a finite box
are created and/or annihilated by the creation and/or annihilation operators,
respectively, of a quantum harmonic oscillator on a circle. An expression for
the effective coupling constant is obtained showing explicitly its dependence
on the dimension of the box.Comment: 12 pages, Late
Preliminary analysis of the drive system of the CTA LST Telescope and its integration in the whole PLC architecture
This work aims to present a preliminary analysis of the drive system configuration for the CTA telescopes array and more specifically a possible architecture for the sub-array of Large Size Telescopes - LSTs. The first part of this document is focused on the control command architecture of the drive system dedicated to the LST including a view on some mechanical aspects concerning the telescopes of this class. In particular the current investigation on the interfaces between the drive system and the automatic system in charge of the camera mast control system (e.g. the arch damping) is presented. In the second part of this work the issue of the integration of the telescope drive system within a global PLC (Programmable Logic Controller) architecture for the CTA array is addressed with the corresponding links to the control software layer
Improved sensitivity of H.E.S.S.-II through the fifth telescope focus system
The Imaging Atmospheric Cherenkov Telescope (IACT) works by imaging the very
short flash of Cherenkov radiation generated by the cascade of relativistic
charged particles produced when a TeV gamma ray strikes the atmosphere. This
energetic air shower is initiated at an altitude of 10-30 km depending on the
energy and the arrival direction of the primary gamma ray. Whether the best
image of the shower is obtained by focusing the telescope at infinity and
measuring the Cherenkov photon angles or focusing on the central region of the
shower is a not obvious question. This is particularly true for large size IACT
for which the depth of the field is much smaller. We address this issue in
particular with the fifth telescope (CT5) of the High Energy Stereoscopic
System (H.E.S.S.); a 28 m dish large size telescope recently entered in
operation and sensitive to an energy threshold of tens of GeVs. CT5 is equipped
with a focus system, its working principle and the expected effect of focusing
depth on the telescope sensitivity at low energies (50-200 GeV) is discussed.Comment: In Proceedings of the 33rd International Cosmic Ray Conference
(ICRC2013), Rio de Janeiro (Brazil
Origin of strong scarring of wavefunctions in quantum wells in a tilted magnetic field
The anomalously strong scarring of wavefunctions found in numerical studies
of quantum wells in a tilted magnetic field is shown to be due to special
properties of the classical dynamics of this system. A certain subset of
periodic orbits are identified which are nearly stable over a very large
interval of variation of the classical dynamics; only this subset are found to
exhibit strong scarring. Semiclassical arguments shed further light on why
these orbits dominate the experimentally observed tunneling spectra.Comment: RevTeX, 5 page
Molecules in external fields: a semiclassical analysis
We undertake a semiclassical analysis of the spectral properties (modulations
of photoabsorption spectra, energy level statistics) of a simple Rydberg
molecule in static fields within the framework of Closed-Orbit/Periodic-Orbit
theories. We conclude that in addition to the usual classically allowed orbits
one must consider classically forbidden diffractive paths. Further, the
molecule brings in a new type of 'inelastic' diffractive trajectory, different
from the usual 'elastic' diffractive orbits encountered in previous studies of
atomic and analogous systems such as billiards with point-scatterers. The
relative importance of inelastic versus elastic diffraction is quantified by
merging the usual Closed Orbit theory framework with molecular quantum defect
theory.Comment: 4 pages, 3 figure
Plantas medicinais utilizadas na medicina etnoveterinária praticada na ilha do Marajó.
bitstream/item/63225/1/Oriental-Doc380.pd
Semiclassical theory of magnetotransport through a chaotic quantum well
We develop a quantitative semiclassical formula for the resonant tunneling
current through a quantum well in a tilted magnetic field. It is shown that the
current depends only on periodic orbits within the quantum well. The theory
explains the puzzling evolution of the tunneling spectra near a tilt angle of
as arising from an exchange bifurcation of the relevant periodic
orbits.Comment: 4 pages, RevTeX, epsf, 2 PostScript Figures (1 with color
Atomic Diagnostics of X-ray Irradiated Protoplanetary Disks
We study atomic line diagnostics of the inner regions of protoplanetary disks
with our model of X-ray irradiated disk atmospheres which was previously used
to predict observable levels of the NeII and NeIII fine-structure transitions
at 12.81 and 15.55mum. We extend the X-ray ionization theory to sulfur and
calculate the fraction of sulfur in S, S+, S2+ and sulfur molecules. For the
D'Alessio generic T Tauri star disk, we find that the SI fine-structure line at
25.55mum is below the detection level of the Spitzer Infrared Spectrometer
(IRS), in large part due to X-ray ionization of atomic S at the top of the
atmosphere and to its incorporation into molecules close to the mid-plane. We
predict that observable fluxes of the SII 6718/6732AA forbidden transitions are
produced in the upper atmosphere at somewhat shallower depths and smaller radii
than the neon fine-structure lines. This and other forbidden line transitions,
such as the OI 6300/6363AA and the CI 9826/9852AA lines, serve as complementary
diagnostics of X-ray irradiated disk atmospheres. We have also analyzed the
potential role of the low-excitation fine-structure lines of CI, CII, and OI,
which should be observable by SOFIA and Herschel.Comment: Accepted by Ap
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