62,337 research outputs found
High harmonic generation in crystals using Maximally Localized Wannier functions
In this work, the nonlinear optical response, and in particular, the high
harmonic generation of semiconductors is addressed by using the Wannier gauge.
One of the main problems in the time evolution of the Semiconductor Bloch
equations resides in the fact that the dipole couplings between different bands
can diverge and have a random phase along the reciprocal space and this leads
to numerical instability. To address this problem, we propose the use of the
Maximally Localized Wannier functions that provide a framework to map ab-initio
calculations to an effective tight-binding Hamiltonian with great accuracy. We
show that working in the Wannier gauge, the basis set in which the Bloch
functions are constructed directly from the Wannier functions, the dipole
couplings become smooth along the reciprocal space thus avoiding the problem of
random phases. High harmonic generation spectrum is computed for a 2D monolayer
of hBN as a numerical demonstration
Exploding wire initiation and electrical operation of a 40-kV system for arc-heated drivers up to 10 feet long
Exploding wire initiation and electrical operation of 40 kV system for arc heated drivers up to 10 feet lon
Arc driver operation for either efficient energy transfer or high-current generator
An investigation is made to establish predictable electric arcs along triggered paths for research purposes, the intended application being the heating of the driver gas of a 1 MJ electrically driven shock tube. Trigger conductors consisting of wires, open tubes, and tubes pressurized with different gases were investigated either on the axis of the arc chamber or spiraled along the chamber walls. Design criteria are presented for successful arc initiation with reproducible voltage-current characteristics. Results are compared with other facilities and several application areas are discussed
Simulation of Chua's Circuit by Means of Interval Analysis
The Chua's circuit is a paradigm for nonlinear scientific studies. It is
usually simulated by means of numerical methods under IEEE 754-2008 standard.
Although the error propagation problem is well known, little attention has been
given to the relationship between this error and inequalities presented in
Chua's circuit model. Taking the average of round mode towards and
, we showed a qualitative change on the dynamics of Chua's circuit.Comment: 6th International Conference on Nonlinear Science and Complexity -
S\~ao Jos\'e dos Campos, 2016, p. 1-
Influence of Refractory Periods in the Hopfield model
We study both analytically and numerically the effects of including
refractory periods in the Hopfield model for associative memory. These periods
are introduced in the dynamics of the network as thresholds that depend on the
state of the neuron at the previous time. Both the retrieval properties and the
dynamical behaviour are analyzed.Comment: Revtex, 7 pages, 7 figure
Effects of systemic and non-systemic stresses on the thermal characteristics of corn
Experiments were conducted on corn plants using a calibrated spectroradiometer under field conditions in the indium antimonide channel (InSb, 2.8 to 5.6 mm) and the mercury cadmium telluride channel (HgCdTe, 7 to 14 mm). A ground cover experiment, an experiment on nonsystemic corn plants, and an experiment on systemic-stressed corn plants were included. The average spectral radiance temperature of corn plant populations was found (1) to be statistically significantly different for four healthy corn plant populations, (2) to increase with increased blight severity, and (3) to be statistically significantly different for varying rates of nitrogen applications
Even harmonic generation in isotropic media of dissociating homonuclear molecules
Isotropic gases irradiated by long pulses of intense IR light can generate
very high harmonics of the incident field. It is generally accepted that, due
to the symmetry of the generating medium, be it an atomic or an isotropic
molecular gas, only odd harmonics of the driving field can be produced. Here we
show how the interplay of electronic and nuclear dynamics can lead to a marked
breakdown of this standard picture: a substantial part of the harmonic spectrum
can consist of even rather than odd harmonics. We demonstrate the effect using
ab-initio solutions of the time-dependent Schr\"odinger equation for
and its isotopes in full dimensionality. By means of a simple
analytical model, we identify its physical origin, which is the appearance of a
permanent dipole moment in dissociating homonuclear molecules, caused by
light-induced localization of the electric charge during dissociation. The
effect arises for sufficiently long laser pulses and the region of the spectrum
where even harmonics are produced is controlled by pulse duration. Our results
(i) show how the interplay of femtosecond nuclear and attosecond electronic
dynamics, which affects the charge flow inside the dissociating molecule, is
reflected in the nonlinear response, and (ii) force one to augment standard
selection rules found in nonlinear optics textbooks by considering
light-induced modifications of the medium during the generation process.Comment: 7 pages, 6 figure
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