800 research outputs found
Theoretical Analysis of the No-Slip Boundary Condition Enforcement in SPH Methods
The aim of the present work is to provide an in-depth analysis of the most representative mirroring techniques used in SPH to enforce boundary conditions (BC) along solid profiles. We specifically refer to dummy particles, ghost particles, and Takeda et al. [Prog. Theor. Phys. 92 (1994), 939] boundary integrals. The analysis has been carried out by studying the convergence of the first- and second-order differential operators as the smoothing length (that is, the characteristic length on which relies the SPH interpolation) decreases. These differential operators are of fundamental importance for the computation of the viscous drag and the viscous/diffusive terms in the momentum and energy equations. It has been proved that close to the boundaries some of the mirroring techniques leads to intrinsic inaccuracies in the convergence of the differential operators. A consistent formulation has been derived starting from Takeda et al. boundary integrals (see the above reference). This original formulation allows implementing no-slip boundary conditions consistently in many practical applications as viscous flows and diffusion problems
FIBONACCI SUPERLATTICES OF NARROW-GAP III-V SEMICONDUCTORS
We report theoretical electronic structure of Fibonacci superlattices of
narrow-gap III-V semiconductors. Electron dynamics is accurately described
within the envelope-function approximation in a two-band model.
Quasiperiodicity is introduced by considering two different III-V semiconductor
layers and arranging them according to the Fibonacci series along the growth
direction. The resulting energy spectrum is then found by solving exactly the
corresponding effective-mass (Dirac-like) wave equation using tranfer-matrix
techniques. We find that a self-similar electronic spectrum can be seen in the
band structure. Electronic transport properties of samples are also studied and
related to the degree of spatial localization of electronic envelope-functions
via Landauer resistance and Lyapunov coefficient. As a working example, we
consider type II InAs/GaSb superlattices and discuss in detail our results in
this system.Comment: REVTeX 3.0, 16 pages, 8 figures available upon request. To appear in
Semiconductor Science and Technolog
Microscopic description of anisotropic low-density dipolar Bose gases in two dimensions
A microscopic description of the zero energy two-body ground state and
many-body static properties of anisotropic homogeneous gases of bosonic dipoles
in two dimensions at low densities is presented and discussed. By changing the
polarization angle with respect to the plane, we study the impact of the
anisotropy, present in the dipole--dipole interaction, on the energy per
particle, comparing the results with mean field predictions. We restrict the
analysis to the regime where the interaction is always repulsive, although the
strength of the repulsion depends on the orientation with respect to the
polarization field. We present a series expansion of the solution of the zero
energy two-body problem which allows us to find the scattering length of the
interaction and to build a suitable Jastrow factor that we use as a trial wave
function for both a variational and diffusion Monte Carlo simulation of the
infinite system. We find that the anisotropy has an almost negligible impact on
the ground state properties of the many-body system in the universal regime
where the scattering length governs the physics of the system. We also show
that scaling in the gas parameter persists in the dipolar case up to values
where other isotropic interactions with the same scattering length yield
different predictions.Comment: 9 figures, 1 tabl
Catalytic asymmetric conjugate addition of dialkylzinc reagents to alpha,beta-unsaturated sulfones
An efficient method is reported for the highly enantioselective copper-catalyzed conjugate addition of dialkylzinc reagents to α,β-unsaturated sulfones using a monodentate phosphoramidite ligand.
Spin reversal in Fe8 under fast pulsed magnetic fields
We report measurements on magnetization reversal in the Fe8 molecular magnet using fast pulsed magnetic fields of 1.5 kT s−1 and in the temperature range of 0.6–4.1 K. We observe and analyze the temperature dependence of the reversal process, which involves in some cases several resonances. Our experiments allow observation of resonant quantum tunneling of magnetization up to a temperature of ~4 K. We also observe shifts in the maxima of the relaxation within each resonance field with temperature that suggest the emergence of a thermal instability—a combination of spin reversal and self-heating that may result in a magnetic deflagration process. The results are mainly understood in the framework of thermally-activated quantum tunneling transitions in combination with emergence of a thermal instability
Spin reversal in Fe8 under fast pulsed magnetic fields
We report measurements on magnetization reversal in the Fe8 molecular magnet using fast pulsed magnetic fields of 1.5 kT s−1 and in the temperature range of 0.6–4.1 K. We observe and analyze the temperature dependence of the reversal process, which involves in some cases several resonances. Our experiments allow observation of resonant quantum tunneling of magnetization up to a temperature of ~4 K. We also observe shifts in the maxima of the relaxation within each resonance field with temperature that suggest the emergence of a thermal instability—a combination of spin reversal and self-heating that may result in a magnetic deflagration process. The results are mainly understood in the framework of thermally-activated quantum tunneling transitions in combination with emergence of a thermal instability
SISTEMA NACIONAL DE SALUD ESPAÑOL. CARACTERÍSTICAS Y ANÁLISIS.
The Health General Law 14/1986 of April 25 made possible the step from the old Social Security model to the current Health National System model. Since then it has taken place deep changes of the system which culminate in 2002 in the total decentralization of the Comunidades Autonomas health competitions. The result of the current legislative frame is the competitions decentralization and budgets management whith a possible variability of the CCAA management models, which shows us the need to monitor a follow-up that make possible to evaluate the System competitions decentralization in the next ten years.La Ley General de Sanidad 14/1986 de 25 de Abril posibilitó el tránsito del antiguo modelo de Seguridad Social al actual modelo de Sistema Nacional de Salud (SNS).Desde entonces se han producido profundos cambios en el sistema que culminaron en el año 2002 con la descentralización total de competencias en materia de salud en las Comunidades Autónomas, resultando del actual marco legislativo la descentralización de competencias y gestión de los presupuestos con una posible variabilidad en los modelos de gestión de cada CCAA, que plantea la necesidad de monitorizar un seguimiento que permita evaluar en los próximos diez años el impacto de la descentralización de competencias del Sistema.
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