3,342 research outputs found
Temperature and magnetization-dependent band-gap renormalization and optical many-body effects in diluted magnetic semiconductors
We calculate the Coulomb interaction induced density, temperature and
magnetization dependent many-body band-gap renormalization in a typical diluted
magnetic semiconductor GaMnAs in the optimally-doped metallic regime as a
function of carrier density and temperature. We find a large (about 0.1 eV)
band gap renormalization which is enhanced by the ferromagnetic transition. We
also calculate the impurity scattering effect on the gap narrowing. We suggest
that the temperature, magnetization, and density dependent band gap
renormalization could be used as an experimental probe to determine the valence
band or the impurity band nature of carrier ferromagnetism.Comment: Revised versio
Description of two new actinosporean types from a brook of Fuji Mountain, Honshu, and from Chitose River, Hokkaido, Japan
Actinospore infection of oligochaetes living in the mud of 3 freshwater biotopes in Japan was studied. Using the cell-well plate method, a new aurantiactinomyxon type was found in 0.77 % of the examined Tubifex tubifex oligochaete specimens from a brook near Yamanashi Prefectural Fisheries Experimental Station on Fuji Mountain. In 0.14 % of Lumbriculus variagetus collected from Chitose River, near Chitose Salmon Hatchery, a new siedleckiella type was found, while at the same time 8.1 % of the Lumbriculus spp. oligochaetes released triactinomyxons of Myxobolus arcticus. Of the examined Rhyacodrilus komarovi oligochaetes collected from the Mena River system, Hokkaido, 0.2, 0.6, 0.5 and 0.8% were infected with echinactinomyxon, neoactinomyxum and 2 types of triactinomyxon spores, respectively, and described in our previous paper. The oligochaetes released actinospores for several weeks. Actinospore infection showed high intensity in positive oligochaetes in the case of all the actinosporean types. Two of the actinospore types (aurantiactinomyxon and siedleckiella) presented here have not been previously described
Shear stress in lattice Boltzmann simulations
A thorough study of shear stress within the lattice Boltzmann method is
provided. Via standard multiscale Chapman-Enskog expansion we investigate the
dependence of the error in shear stress on grid resolution showing that the
shear stress obtained by the lattice Boltzmann method is second order accurate.
This convergence, however, is usually spoiled by the boundary conditions. It is
also investigated which value of the relaxation parameter minimizes the error.
Furthermore, for simulations using velocity boundary conditions, an artificial
mass increase is often observed. This is a consequence of the compressibility
of the lattice Boltzmann fluid. We investigate this issue and derive an
analytic expression for the time-dependence of the fluid density in terms of
the Reynolds number, Mach number and a geometric factor for the case of a
Poiseuille flow through a rectangular channel in three dimensions. Comparison
of the analytic expression with results of lattice Boltzmann simulations shows
excellent agreement.Comment: 15 pages, 4 figures, 2 table
Influence of non-local exchange on RKKY interactions in III-V diluted magnetic semiconductors
The RKKY interaction between substitutional Mn local moments in GaAs is both
spin-direction-dependent and spatially anisotropic. In this Letter we address
the strength of these anisotropies using a semi-phenomenological tight-binding
model which treats the hybridization between Mn d-orbitals and As p-orbitals
perturbatively and accounts realistically for the non-local exchange
interaction between their spins. We show that exchange non-locality,
valence-band spin-orbit coupling, and band-structure anisotropy all play a role
in determining the strength of both effects. We use these results to estimate
the degree of ground-state magnetization suppression due to frustrating
interactions between randomly located Mn ions.Comment: 4 pages RevTeX, 2 figures included, v2: replacement because of font
proble
Cotunneling and non-equilibrium magnetization in magnetic molecular monolayers
Transport and non-equilibrium magnetization in monolayers of magnetic
molecules subject to a bias voltage are considered. We apply a master-equation
approach going beyond the sequential-tunneling approximation to study the
Coulomb-blockade regime. While the current is very small in this case, the
magnetization shows changes of the order of the saturation magnetization for
small variations of the bias voltage. Inelastic cotunneling processes manifest
themselves as differential-conductance steps, which are accompanied by much
larger changes in the magnetization. In addition, the magnetization in the
Coulomb-blockade regime exhibits strong signatures of sequential tunneling
processes de-exciting molecular states populated by inelastic cotunneling. We
also consider the case of a single molecule, finding that cotunneling processes
lead to the occurrence of magnetic sidebands below the Coulomb-blockade
threshold. In the context of molecular electronics, we study how additional
spin relaxation suppresses the fine structure in transport and magnetization.Comment: 8 pages, 8 figures, version as publishe
Assessing the accuracy of δ<sup>18<\sup>O<sub>sw<?sub> estimates from corals: lessons from simple Monte Carlo simulations
EGU2008-A-04391
Paired measurements of δ18O and Sr/Ca in coral aragonite are routinely used for deriving estimates of δ18Osw and, by extension, sea surface salinity variations over the past centuries. However, in practice, the accuracy (or the error) of these estimates is often difficult to assess.
Here, we use simulated proxy data and Monte-Carlo simulations to investigate the accuracy of δ18Osw estimates from paired coral δ18O and Sr/Ca measurements. First, we estimate expected values of coral Sr/Ca and δ18O from instrumental or reanalysis data of sea surface temperature (SST) and sea surface salinity (SSS). We then add the typical analytical errors onto the expected Sr/Ca (δ18O) data as random numbers and compute δ18Osw+error from the noisy proxy data for a 1000 sample Monte Carlo. From this simple Monte Carlo simulation, the range of correlation coefficients between δ18Osw+error and expected δ18Osw is estimated. As expected, we find that this range mainly depends on the magnitude of the actual SSS variations at a given site, as well as on the slope of the δ18Osw-SSS relationship.
A comparison with real coral-based δ18Osw reconstructions from multiple sites indicates that correlations between reconstructed δ18Osw and instrumental SSS fall within the range of correlation coefficients predicted based on our Monte-Carlo simulation. Thus, our simple simulation exercise may help to assess the feasibility of δ18Osw and salinity reconstructions from corals in different climatic settings, provided that (i) some instrumental data of δ18Osw and/or SSS is available, and (ii) the slope of the
δ18Osw-SSS relationship is known
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