8,607 research outputs found
The effect of in-plane magnetic field on the spin Hall effect in Rashba-Dresselhaus system
In a two-dimensional electron gas with Rashba and Dresselhaus spin-orbit
couplings, there are two spin-split energy surfaces connected with a degenerate
point. Both the energy surfaces and the topology of the Fermi surfaces can be
varied by an in-plane magnetic field. We find that, if the chemical potential
falls between the bottom of the upper band and the degenerate point, then
simply by changing the direction of the magnetic field, the magnitude of the
spin Hall conductivity can be varied by about 100 percent. Once the chemical
potential is above the degenerate point, the spin Hall conductivity becomes the
constant , independent of the magnitude and direction of the magnetic
field. In addition, we find that the in-plane magnetic field exerts no
influence on the charge Hall conductivity.Comment: 11 pages, 3 figures, to be published on Phys. Rev.
Sum rules for spin-Hall conductivity cancelation
It has been shown recently that the universal dc spin conductivity of
two-dimensional electrons with a Rashba spin-orbit interaction is canceled by
vertex corrections in a weak scattering regime. We prove that the zero bulk
spin conductivity is an intrinsic property of the free-electron Hamiltonian and
scattering is merely a tool to reveal this property in terms of the
diagrammatic technique. When Zeeman energy is neglected, the zero dc
conductivity persists in a magnetic field. Spin conductivity increases
resonantly at the cyclotron frequency and then decays towards the universal
value.Comment: 4 pages, 1 figur
Reliability optimization on power systems network using genetic algorithm
In this study, reliability optimization of a non-linear transmission network using Genetic Algorithm (GA) based optimization approach is presented and proposed. A GA based algorithm was developed for Koko, Guinness, Nekpenekpen, Ikpoba-Dam, Switch station, Etete and GRA 33kV tertiary transmission feeders within Benin Metropolis, Nigeria and was used to determine the optimal performance of the feeders’ reliability and availability through the minimization of downtime and the Mean Time between Failure (MTBF) by the appropriate selection of the objective functions and constraints. The equality and inequality constraints for each feeder on the network were defined, thereafter, codes were written on the Matlab 2016a environment to optimize the selected parameters. The results from the study showed a reduction in downtime of 5.63%, 26.87%, 34.20%, 5.42% 8.37%, 5.18% and 10.97% and an increment increased in MTBF by 4.95%, 19.87%, 4.58%, 3.85%, 4.88%, 5.77% and 13.56% for Guinness, Etete, Nekpenekpen, GRA, Switch station and Ikpoba-Dam feeders respectively. The obtained results, therefore, yielded an average corresponding improvement on the network’s reliability and availability by 1.85% and 2.83% respectively. Conclusively, the desired result reached in this paper validates the robustness of the GA tool in reliability studies. However, conscious effort must be geared concerning the ways and manners the system is operated in order to achieve desired results
Chemical Cues for Malaria Vectors Oviposition Site Selection:\ud Challenges and Opportunities
The attractiveness of oviposition site for malaria vector mosquitoes is dependent upon a number of physical and chemical factors. Many aspects of mosquito behavior, including host location and oviposition, are mediated by volatile semiochemicals. It is anticipated that selection of oviposition site by semio-chemicals in the form of attractants or stimulants can be used in oviposition traps to monitor or possibly in combination with insecticides to control gravid mosquito populations for mass trapping. So far, volatile compounds identified as oviposition attractants for mosquitoes include phenol, 4-methyl phenol, 4-ethyl phenol, indole, skatole, and p-cresol from hay infusions; 3-carene, terpinene, copaene, cedrene, and d-cadinene released by copepods; alcohol and terpenoids including p-cresol fromplants; ethyl acetate and hydrocarbon substances, probably released by filamentous algae; 3-methyl-1-butanol identified frombacteria. Research priorities should be directed at identifying more oviposition attractants to determine the properties of these semio-chemicals for possible use in designing control tools. This would aim at luring females to lethal traps or stimulants to increase their exposure to insecticide-impregnated substrates.\ud
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Evolving localizations in reaction-diffusion cellular automata
We consider hexagonal cellular automata with immediate cell neighbourhood and
three cell-states. Every cell calculates its next state depending on the
integral representation of states in its neighbourhood, i.e. how many
neighbours are in each one state. We employ evolutionary algorithms to breed
local transition functions that support mobile localizations (gliders), and
characterize sets of the functions selected in terms of quasi-chemical systems.
Analysis of the set of functions evolved allows to speculate that mobile
localizations are likely to emerge in the quasi-chemical systems with limited
diffusion of one reagent, a small number of molecules is required for
amplification of travelling localizations, and reactions leading to stationary
localizations involve relatively equal amount of quasi-chemical species.
Techniques developed can be applied in cascading signals in nature-inspired
spatially extended computing devices, and phenomenological studies and
classification of non-linear discrete systems.Comment: Accepted for publication in Int. J. Modern Physics
Analytical treatment of the dHvA frequency combinations due to chemical potential oscillations in an idealized two-band Fermi liquid
de Haas-van Alphen oscillation spectrum is studied for an idealized
two-dimensional Fermi liquid with two parabolic bands in the case of canonical
(fixed number of quasiparticles) and grand canonical (fixed chemical potential)
ensembles. As already reported in the literature, oscillations of the chemical
potential in magnetic field yield frequency combinations that are forbidden in
the framework of the semiclassical theory. Exact analytical calculation of the
Fourier components is derived at zero temperature and an asymptotic expansion
is given for the high temperature and low magnetic field range. A good
agreement is obtained between analytical formulae and numerical computations.Comment: 10 pages, 4 figure
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Energy overview of Botswana: generation and consumption
Botswana has a basic need to explore its energy concept, this being its energy sources, generation and percentage of the population with access to electricity. At present, Botswana generates electricity from coal, which supplies about 29% (on average) of the country’s demand. The other 71% is imported mainly from South Africa (Eskom). Consequently, the dependence of Botswana on imports posses threats to the security of its energy supply. As a result, there is the need to understand the bases for a possible generation expansion that would substantiate existing documentation. In view of this need, this study investigates the existing energy sources as well as energy consumption and production levels in Botswana. The study would be further developed by making projections of the energy demand up until the year 2020. The key techniques that were used include; literature review, questionnaire survey and an empirical study. The results presented indicated that, current dependable operation capacity (i.e. 100MW) should be increased to 2,595 MW or more assuming 85% plant efficiency. This would then be able to meet the growing demand for energy use. In addition, the installed capacity would be able to support commercial and mining activities for the growth of the economy
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