64 research outputs found
A multi-band semiclassical model for surface hopping quantum dynamics
In the paper we derive a semiclassical model for surface hopping allowing
quantum dynamical non-adiabatic transition between different potential energy
surfaces in which cases the classical Born-Oppenheimer approximation breaks
down. The model is derived using the Wigner transform and Weyl quantization,
and the central idea is to evolve the entire Wigner matrix rather than just the
diagonal entries as was done previously in the adiabatic case. The off-diagonal
entries of the Wigner matrix suitably describe the non-adiabatic transition,
such as the Berry connection, for avoided crossings. We study the numerical
approximation issues of the model, and then conduct numerical experiments to
validate the model.Comment: 29 pages, 10 figure
Semiclassical Vlasov and fluid models for an electron gas with spin effects
We derive a four-component Vlasov equation for a system composed of spin-1/2
fermions (typically electrons). The orbital part of the motion is classical,
whereas the spin degrees of freedom are treated in a completely
quantum-mechanical way. The corresponding hydrodynamic equations are derived by
taking velocity moments of the phase-space distribution function. This
hydrodynamic model is closed using a maximum entropy principle in the case of
three or four constraints on the fluid moments, both for Maxwell-Boltzmann and
Fermi-Dirac statistics.Comment: To appear in the European Physical Journal D, Topical Issue "Theory
and Applications of the Vlasov Equation
Hydrodynamic Models with Quantum Corrections
We derive a quantum-corrected hydrodynamic and drift-diffusion model for the out-of-equilibrium particle dynamics in the presence of particle collisions, modeled by a BGK collision term. The quantum mechanical corrections are obtained within the Liouville formalism and are expressed by an effective nonlinear force. The Boltzmann and Fermi-Dirac statistics are included
Changes in leaflet shape and seeds per pod modify crop growth parameters, canopy light environment, and yield components in soybean
Seed number (SN) is the component most strongly associated with yield in soybean. SN depends on pod number (PN) and seeds per pod (SPP). Whereas SPP is a relatively stable component, PN is strongly influenced by environmental and management factors. However, the environmental cues involved in PN regulation are not completely understood. The influence of increasing SPP on other yield components is controversial. Field trials were conducted in two growing seasons using two pairs of lanceolate (L) and ovate (O) near-isogenic lines, sown at low (LD) and high (HD) plant densities to evaluate the effect of leaflet shape on crop growth parameters, canopy red/far-red (R/FR) ratio, their relationships with pod initiation, PN, and yield; and the effect of increasing SPP on PN, SN, and yield. L canopies showed a higher number of pods initiated (PI) than O canopies owing to the increase of PI on branches. No association between PI and crop growth rate during the pod set period was found. PI was negatively associated with leaf area index (LAI) and light interception. In contrast, a positive association between PI and canopy R/FR ratio was found. This latter association was sustained irrespective of whether the LAI was below or above its critical value, providing experimental evidence that R/FR ratio is positively associated with pod initiation in soybean canopies. An increase in SPP produced a direct and steady increase in SN regardless of PN and plant density. A yield increase was observed for the L-LD treatment, which combined the increased SPP of L lines with the highest PN of L-LD canopies. These results have implications for crop management and breeding strategies aimed at increasing the yield potential of soybean.Fil: Bianchi, Julieta Sofia. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Departamento de Biologia. Cátedra de FisiologĂa Vegetal; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de Investigaciones en Ciencias Agrarias de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Instituto de Investigaciones en Ciencias Agrarias de Rosario; ArgentinaFil: Quijano, Alvaro. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Departamento de Biologia. Cátedra de FisiologĂa Vegetal; Argentina. Universidad Nacional de Rosario. Consejo de Investigaciones de la Universidad de Rosario; ArgentinaFil: Gosparini, Carlos Omar. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Departamento de Biologia. Cátedra de FisiologĂa Vegetal; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de Investigaciones en Ciencias Agrarias de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Instituto de Investigaciones en Ciencias Agrarias de Rosario; ArgentinaFil: Morandi, Eligio Natalio. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Departamento de Biologia. Cátedra de FisiologĂa Vegetal; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - Rosario. Instituto de Investigaciones en Ciencias Agrarias de Rosario. Universidad Nacional de Rosario. Facultad de Ciencias Agrarias. Instituto de Investigaciones en Ciencias Agrarias de Rosario; Argentin
Time-dependent model for diluted magnetic semiconductors including band structure and confinement effects
10 pagesInternational audienceA free-parameter theoretical model is developed in order to study the ultrafast dynamics in confined diluted magnetic semiconductors induced by laser. The hole-spin relaxation process is due to the Elliot-Yafet mechanism, which involves the scattering of the holes on the localized magnetic impurities. The role played by the quantum confinement and the band structure is analyzed. It is shown that the sample thickness and the background hole density strongly influences the phenomenon of demagnetization. Quantitative results are given for III-V ferromagnetic GaMnAs quantum wells of thickness 4 and 6 nm
A multiband envelope function model for quantum transport in a tunneling diode
We present a simple model for electron transport in semiconductor devices
that exhibit tunneling between the conduction and valence bands. The model is
derived within the usual Bloch-Wannier formalism by a k-expansion, and is
formulated in terms of a set of coupled equations for the electron envelope
functions. Its connection with other models present in literature is discussed.
As an application we consider the case of a Resonant Interband Tunneling Diode,
demonstrating the ability of the model to reproduce the expected behaviour of
the current as a function of the applied voltageComment: 8 pages, 4 figure
Pseudo-fermion formalism applied to nonequilibrium Kondo-type problems
8 pagesInternational audienceA straightforward limit procedure is developed for evaluating the expectation value of a generic many-particle operator defined in the Abrikosov-Coleman's pseudo fermion formalism. It can be useful for the study of nonequilibrium Kondo-type problems
Quantum-relativistic hydrodynamic model for a spin-polarized electron gas interacting with light
We develop a semirelativistic quantum fluid theory based on the expansion of the Dirac Hamiltonian to second order in 1/c. By making use of the Madelung representation of thewave function, we derive a set of hydrodynamic equations that comprises a continuity equation, an Euler equation for the mean velocity, and an evolution equation for the electron spin density. This hydrodynamic model is then applied to study the dynamics of a dense and weakly relativistic electron plasma. In particular, we investigate the impact of the quantum-relativistic spin effects on the Faraday rotation in a one-dimensional plasma slab irradiated by an x-ray laser source
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