2,592 research outputs found
Electron Bloch Oscillations and Electromagnetic Transparency of Semiconductor Superlattices in Multi-Frequency Electric Fields
We examine phenomenon of electromagnetic transparency in semiconductor
superlattices (having various miniband dispersion laws) in the presence of
multi-frequency periodic and non-periodic electric fields. Effects of induced
transparency and spontaneous generation of static fields are discussed. We paid
a special attention on a self-induced electromagnetic transparency and its
correlation to dynamic electron localization. Processes and mechanisms of the
transparency formation, collapse, and stabilization in the presence of external
fields are studied. In particular, we present the numerical results of the time
evolution of the superlattice current in an external biharmonic field showing
main channels of transparency collapse and its partial stabilization in the
case of low electron density superlattices
Fractional and unquantized dc voltage generation in THz-driven semiconductor superlattices
We consider the spontaneous creation of a dc voltage across a strongly
coupled semiconductor superlattice subjected to THz radiation. We show that the
dc voltage may be approximately proportional either to an integer or to a half-
integer multiple of the frequency of the applied ac field, depending on the
ratio of the characteristic scattering rates of conducting electrons. For the
case of an ac field frequency less than the characteristic scattering rates, we
demonstrate the generation of an unquantized dc voltage.Comment: 6 pages, 3 figures, RevTEX, EPSF. Revised version v3: corrected typo
Negative high-frequency differential conductivity in semiconductor superlattices
We examine the high-frequency differential conductivity response properties
of semiconductor superlattices having various miniband dispersion laws. Our
analysis shows that the anharmonicity of Bloch oscillations (beyond
tight-binding approximation) leads to the occurrence of negative high-frequency
differential conductivity at frequency multiples of the Bloch frequency. This
effect can arise even in regions of positive static differential conductivity.
The influence of strong electron scattering by optic phonons is analyzed. We
propose an optimal superlattice miniband dispersion law to achieve
high-frequency field amplification
Photoacoustic effect in micro- and nanostructures: numerical simulations of Lagrange equations
The work provides the description of theoretical and numerical modeling techniques of thermomechanical effects that take place in absorbing micro- and nanostructures of different materials under the action of pulsed laser radiation. A proposed technique of the numerical simulation is based on the solution of equations of motion of continuous media in the form of Lagrange for spatially inhomogeneous media. This model allows calculating fields of temperature, pressure, density, and velocity of the medium depending on the parameters of laser pulses and the characteristics of micro- and nanostructures.The work provides the description of theoretical and numerical modeling techniques of thermomechanical effects that take place in absorbing micro- and nanostructures of different materials under the action of pulsed laser radiation. A proposed technique of the numerical simulation is based on the solution of equations of motion of continuous media in the form of Lagrange for spatially inhomogeneous media. This model allows calculating fields of temperature, pressure, density, and velocity of the medium depending on the parameters of laser pulses and the characteristics of micro- and nanostructures
Continuous Neel to Bloch Transition as Thickness Increases: Statics and Dynamics
We analyze the properties of Neel and Bloch domain walls as a function of
film thickness h, for systems where, in addition to exchange, the dipole-dipole
interaction must be included. The Neel to Bloch phase transition is found to be
a second order transition at hc, mediated by a single unstable mode that
corresponds to oscillatory motion of the domain wall center. A uniform
out-of-plane rf-field couples strongly to this critical mode only in the Neel
phase. An analytical Landau theory shows that the critical mode frequency
varies as the square root of (hc - h) just below the transition, as found
numerically.Comment: 4 pages, 4 figure
Spin Josephson effect in ferromagnet/ferromagnet tunnel junctions
We consider the tunnel spin current between two ferromagnetic metals from a
perspective similar to the one used in superconductor/superconductor tunnel
junctions. We use fundamental arguments to derive a Josephson-like spin tunnel
current . Here the phases are
associated with the planar contribution to the magnetization,
. The crucial step in our
analysis is the fact that the -component of the spin is canonically
conjugate to the phase of the planar contribution: . This is
analogous to the commutation relation in superconductors, where
is the phase associated to the superconducting order parameter and
is the Cooper pair number operator. We briefly discuss the experimental
consequences of our theoretical analysis.Comment: LaTex, seven pages, no figures; version to appear in Europhys. Lett.;
in order to make room for a more extended microscopic analysis, the
phenomenological discussion contained in v2 was remove
Analytical and micromagnetic study of a Neel domain wall
Journals published by the American Physical Society can be found at http://journals.aps.org/For ferromagnets with exchange, dipolar interaction, and uniaxial anisotropy, by both analytic methods and micromagnetic simulations we study Neel domain walls in thin ferromagnetic strips of finite width. Comparison of the numerical results with the analytics yields parameter values that had been unspecified by the analytics, and determines the modifications needed to describe the magnetization both near the strip center and near the boundaries. With no uniaxial anisotropy, the domain wall center can be described by the same hyperbolic secant form as with uniaxial anisotropy, but the effective anisotropy constant must now be thought of as increasing with increasing film thickness and decreasing with increasing film width
Preparation for the Inspection of the Pharmacovigilance System
The processes of planning, performing, documenting, and follow-up of pharmacovigilance system inspections are regulated by the Good Pharmacovigilance Practices (GVP) and local regulations. These inspection processes apply mainly to marketing authorisation holders, developers of medicinal products for human use, and their authorised legal representatives, but they are presented from the perspective of regulatory authorities. Currently, there are no recommendations for pharmaceutical companies on how to prepare for a pharmacovigilance system inspection. The aim of the study was to develop recommendations on how pharmaceutical companies should prepare for a pharmacovigilance system inspection. The analysis of risks associated with scheduled and unscheduled inspections of pharmaceutical companies’ pharmacovigilance systems was performed with due consideration of the number of foreign marketing authorisations and the number of medicinal products under development according to the national registers of medicinal products and medical devices of the countries of the Eurasian Economic Union (EAEU), the Commonwealth of Independent States, and some European countries as of 30 June 2021. Some differences were identified in the work of Russian and foreign pharmacovigilance inspectorates, which are partially due to different numbers of EAEU-authorised medicinal products in the national markets. Based on the results obtained as well as personal experience as a pharmacovigilance officer in preparation of and participation in pharmacovigilance inspections of Russian companies by foreign regulators, implementation of corrective and preventive actions, the author of the paper has developed preliminary recommendations on how to prepare a EAEU pharmaceutical company’s pharmacovigilance system for an inspection. Effective management of pharmaceutical companies’ pharmacovigilance systems would contribute to the provision of the population with high-quality and safe medicines
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