156 research outputs found
Electron Spin Dynamics in Semiconductors without Inversion Symmetry
We present a microscopic analysis of electron spin dynamics in the presence
of an external magnetic field for non-centrosymmetric semiconductors in which
the D'yakonov-Perel' spin-orbit interaction is the dominant spin relaxation
mechanism. We implement a fully microscopic two-step calculation, in which the
relaxation of orbital motion due to electron-bath coupling is the first step
and spin relaxation due to spin-orbit coupling is the second step. On this
basis, we derive a set of Bloch equations for spin with the relaxation times
T_1 and T_2 obtained microscopically. We show that in bulk semiconductors
without magnetic field, T_1 = T_2, whereas for a quantum well with a magnetic
field applied along the growth direction T_1 = T_2/2 for any magnetic field
strength.Comment: to appear in Proceedings of Mesoscopic Superconductivity and
Spintronics (MS+S2002
Modeling of phase volume diffractive gratings, part 1: transmitting sinusoidal uniform gratings
A detailed model of the diffraction of plane and Gaussian beams on plane uniform phase Bragg gratings based on Kogelnik\u27s theory of coupled waves is presented. The model describes transmitting gratings with arbitrary orientation in a plane-parallel plate taking into account spectral width and angular divergence of laser beams along with material dispersion of a photosensitive medium. The model results are compared with experimental data for high- efficiency Bragg gratings in a photothermorefractive (PTR) glass
Application of Probe Nanotechnologies for Memristor Structures Formation and Characterization
This chapter presents the results of experimental studies of the formation and investigation of the memristors by probe nanotechnologies. This chapter also perspectives and possibilities of application of local anodic oxidation and scratching probe nanolithography for the manufacture of memristors based on titanium oxide structures, nanocrystalline ZnO thin film, and vertically aligned carbon nanotubes. Memristive properties of vertically aligned carbon nanotubes, titanium oxide, and ZnO nanostructures were investigated by scanning probe microscopy methods. It is shown that nanocrystalline ZnO films manifest a stable memristor effect slightly dependent on its morphology. Titanium oxide nanoscale structures of different thicknesses obtained by local anodic oxidation demonstrate a memristive effect without the need to perform any additional electroforming operations. This experimentally confirmed the memristive switching of a two-electrode structure based on a vertically aligned carbon nanotube. These results can be used in the development of designs and technological processes of resistive random access memory (ReRAM) units based on the memristor devices
Electron Spin Relaxation in a Semiconductor Quantum Well
A fully microscopic theory of electron spin relaxation by the
D'yakonov-Perel' type spin-orbit coupling is developed for a semiconductor
quantum well with a magnetic field applied in the growth direction of the well.
We derive the Bloch equations for an electron spin in the well and define
microscopic expressions for the spin relaxation times. The dependencies of the
electron spin relaxation rate on the lowest quantum well subband energy,
magnetic field and temperature are analyzed.Comment: Revised version as will appear in Physical Review
Relations between parameters of fracture processes on different scale levels
© 2018, Pleiades Publishing, Ltd. Abstract: The processes of ultrasonically-assisted drilling (UAD) and the dynamic tests on split Hopkinson pressure bar (SHPB), fracture in which is implemented at various structural-scale levels, are considered. The simulation of UAD based on the Hertz contact problem and the structural−time criterion is presented. The problem of using the value of the fracture incubation time and its linear size obtained from the tests on SHPB in the simulation is considered. A principle of equal power is used for converting the strength parameters into another structural−scale level. The theoretical curve obtained in the simulation is compared with the results of experiments on conventional drilling (CD) and UAD
Low-temperature crossover in the momentum distribution of cold atomic gases in one dimension
The momentum distribution function for the two-component 1D gases of bosons
and fermions is studied in the limit of strong interatomic repulsion. A
pronounced reconstruction of the distribution is found at a temperature much
smaller than the Fermi temperature. This new temperature scale, which equals
the Fermi temperature divided by the dimensionless coupling strength, is a
feature of the two-component model and does not exist in the one-component
case. We estimate the parameters relevant for the experimental observation of
the crossover effect.Comment: 6 pages, 2 figure
Swarmodroid 1.0: A Modular Bristle-Bot Platform for Robotic Active Matter Studies
Large swarms of extremely simple robots (i.e., capable just of basic motion
activities, like propelling forward or self-rotating) are widely applied to
study collective task performance based on self-organization or local
algorithms instead of sophisticated programming and global swarm coordination.
Moreover, they represent a versatile yet affordable platform for experimental
studies in physics, particularly in active matter - non-equilibrium assemblies
of particles converting their energy to a directed motion. However, a large set
of robotics platforms is being used in different studies, while the universal
design is still lacking. Despite such platforms possess advantages in certain
application scenarios, their large number sufficiently limits further
development of results in the field, as advancing some study requires to buy or
manually produce the corresponding robots. To address this issue, we develop an
open-source Swarmodroid 1.0 platform based on bristle-bots with reconfigurable
3D-printed bodies, external control of motion velocity, and basic capabilities
of velocity profile programming. In addition, we introduce AMPy software
package in Python featuring OpenCV-based extraction of robotic swarm kinematics
accompanied by the evaluation of key physical quantities describing the
collective dynamics. We perform a detailed analysis of individual Swarmodroids'
motion characteristics and address their use cases with two examples: a cargo
transport performed by self-rotating robots and a velocity-dependent jam
formation in a bottleneck by self-propelling robots. Finally, we provide a
comparison of existing centimeter-scale robotic platforms, a review of key
quantities describing collective dynamics of many-particle systems, and a
comprehensive outlook considering potential applications as well as further
directions for fundamental studies and Swarmodroid 1.0 platform development.Comment: 18 pages, 7 figures, 1 table + Supplementary Information. Comments
are welcom
Population dynamics and demographic history of Eurasian collared lemmings.
BACKGROUND: Ancient DNA studies suggest that Late Pleistocene climatic changes had a significant effect on population dynamics in Arctic species. The Eurasian collared lemming (Dicrostonyx torquatus) is a keystone species in the Arctic ecosystem. Earlier studies have indicated that past climatic fluctuations were important drivers of past population dynamics in this species. RESULTS: Here, we analysed 59 ancient and 54 modern mitogenomes from across Eurasia, along with one modern nuclear genome. Our results suggest population growth and genetic diversification during the early Late Pleistocene, implying that collared lemmings may have experienced a genetic bottleneck during the warm Eemian interglacial. Furthermore, we find multiple temporally structured mitogenome clades during the Late Pleistocene, consistent with earlier results suggesting a dynamic late glacial population history. Finally, we identify a population in northeastern Siberia that maintained genetic diversity and a constant population size at the end of the Pleistocene, suggesting suitable conditions for collared lemmings in this region during the increasing temperatures associated with the onset of the Holocene. CONCLUSIONS: This study highlights an influence of past warming, in particular the Eemian interglacial, on the evolutionary history of the collared lemming, along with spatiotemporal population structuring throughout the Late Pleistocene
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