14,142 research outputs found
Reentrant nu = 1 quantum Hall state in a two-dimensional hole system
We report the observation of a reentrant quantum Hall state at the Landau
level filling factor nu = 1 in a two-dimensional hole system confined to a
35-nm-wide (001) GaAs quantum well. The reentrant behavior is characterized by
a weakening and eventual collapse of the nu = 1 quantum Hall state in the
presence of a parallel magnetic field component B||, followed by a
strengthening and reemergence as B|| is further increased. The robustness of
the nu = 1 quantum Hall state during the transition depends strongly on the
charge distribution symmetry of the quantum well, while the magnitude of B||
needed to invoke the transition increases with the total density of the system
Assessing risks and benefits of floral supplements in conservation biological control
The use of flowering field margins is often proposed as a method to support biological control in agro-ecosystems. In addition to beneficial insects, many herbivores depend on floral food as well. The indiscriminate use of flowering species in field margins can therefore lead to higher pest numbers. Based on results from field observations and laboratory experiments we assessed risks as well as benefits associated with the provision of nectar plants in field margins, using Brussels sprouts as a model system. Results show that Brussels sprouts bordered by nectar plants suitable for the cabbage white Pieris rapae L., suffered higher infestation levels by this herbivore. In contrast, nectar plants providing accessible nectar for the diamondback moth Plutella xylostella L., did not raise densities of P. xylostella larvae in the Brassica crop. Margins with Anethum graveolens L., selected on the basis of its suitability as nectar plant for parasitoids, significantly increased the number of adult Diadegma semiclausum Hellen in the crop. This didn't translate into enhanced parasitism rates, as parasitism of P. xylostella by D. semiclausum exceeded 65 % in all treatments, irrespective of the plants in the field margin. Our findings emphasize the importance of taking a multitrophic approach when choosing flowering field margin plants for biocontrol or other ecosystem service
Dynamic regimes of fluids simulated by multiparticle-collision dynamics
We investigate the hydrodynamic properties of a fluid simulated with a
mesoscopic solvent model. Two distinct regimes are identified, the `particle
regime' in which the dynamics is gas-like, and the `collective regime' where
the dynamics is fluid-like. This behavior can be characterized by the Schmidt
number, which measures the ratio between viscous and diffusive transport.
Analytical expressions for the tracer diffusion coefficient, which have been
derived on the basis of a molecular-chaos assumption, are found to describe the
simulation data very well in the particle regime, but important deviations are
found in the collective regime. These deviations are due to hydrodynamic
correlations. The model is then extended in order to investigate self-diffusion
in colloidal dispersions. We study first the transport properties of heavy
point-like particles in the mesoscopic solvent, as a function of their mass and
number density. Second, we introduce excluded-volume interactions among the
colloidal particles and determine the dependence of the diffusion coefficient
on the colloidal volume fraction for different solvent mean-free paths. In the
collective regime, the results are found to be in good agreement with previous
theoretical predictions based on Stokes hydrodynamics and the Smoluchowski
equation.Comment: 15 pages, 15 figure
Viola adunca var. bellidifolia (Greene) Harrington
https://thekeep.eiu.edu/herbarium_specimens_byname/20176/thumbnail.jp
Viola adunca var. bellidifolia (Greene) Harrington
https://thekeep.eiu.edu/herbarium_specimens_byname/20176/thumbnail.jp
Anisotropic Fermi Contour of (001) GaAs Holes in Parallel Magnetic Fields
We report a severe, spin-dependent, Fermi contour anisotropy induced by
parallel magnetic field in a high-mobility (001) GaAs two-dimensional hole
system. Employing commensurability oscillations created by a unidirectional,
surface-strain-induced, periodic potential modulation, we directly probe the
anisotropy of the two spin subband Fermi contours. Their areas are obtained
from the Fourier transform of the Shubnikov-de Haas oscillations. Our findings
are in semi-quantitative agreement with the results of parameter-free
calculations of the energy bands.Comment: 4 pages, 4 figure
Shot Noise of Spin-Decohering Transport in Spin-Orbit Coupled Nanostructures
We generalize the scattering theory of quantum shot noise to include the full
spin-density matrix of electrons injected from a spin-filtering or
ferromagnetic electrode into a quantum-coherent nanostructure governed by
various spin-dependent interactions. This formalism yields the spin-resolved
shot noise power for different experimental measurement setups--with
ferromagnetic source and ferromagnetic or normal drain electrodes--whose
evaluation for the diffusive multichannel quantum wires with the Rashba (SO)
spin-orbit coupling shows how spin decoherence and dephasing lead to
substantial enhancement of charge current fluctuations (characterized by Fano
factors ). However, these processes and the corresponding shot noise
increase are suppressed in narrow wires, so that charge transport experiments
measuring the Fano factor in a
ferromagnet/SO-coupled-wire/paramagnet setup also quantify the degree of
phase-coherence of transported spin--we predict a one-to-one correspondence
between the magnitude of the spin polarization vector and .Comment: 8 pages, 3 figure; enhanced with 2 new figure
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