2,390 research outputs found
Model of the Longitudinal Spin Seebeck Coefficient of InSb in a Magnetic Field
We develop a simple theory for the longitudinal spin Seebeck effect in
n-doped InSb in an external magnetic field. We consider spin- electrons in
the conduction band of InSb with a temperature gradient parallel to the applied
magnetic field. In the absence of spin-orbit interactions, a Boltzmann equation
approach leads to a spin current parallel to the field and proportional to the
temperature gradient. The calculated longitudinal spin Seebeck coefficients
oscillates as a function of magnetic field B; the peak positions are
approximately periodic in 1/B. The oscillations arise when the Fermi energy
crosses the bottom of a Landau band.Comment: 7 pages, 6 figure
Theory of plasmonic waves on a chain of metallic nanoparticles in a liquid crystalline host
A chain of metallic particles, of sufficiently small diameter and spacing,
allows linearly polarized plasmonic waves to propagate along the chain. In this
paper, we describes how these waves are altered when the liquid crystal host is
a nematic or a cholesteric liquid crystal (NLC or CLC) with or without an
applied magnetic field. We find that, in general, the liquid crystal host,
either NLC or CLC, alters the dispersion relations of the transverse () and
longitudinal () waves significantly from the dispersion relations for an
isotropic host. We show that by altering the director axis of the liquid
crystal relative to the long axis of the metallic chain, that the branch
can be split into two non-degenerate linearly polarized branches (NLC host) or
two non-degenerate elliptically polarized branches (CLC host). When an external
magnetic field is applied parallel to both the long axis of the metallic
particles and the director of the CLC host, we find that the dispersion
relations are odd in an exchange in sign for for the non-degenerate
elliptically polarized branches. That is, the application of an external
magnetic field leads to the realization of a one-way waveguide.Comment: 9 Pages, 3 Figures. arXiv admin note: text overlap with
arXiv:1210.150
Graphene with adatoms: tuning the magnetic moment with an applied voltage
We show that, in graphene with a small concentration of adatoms, the total
magnetic moment can be switched on and off by varying the Fermi energy
, either by applying a gate voltage or by suitable chemical doping. Our
calculation is carried out using a simple tight-binding model described
previously, combined with a mean-field treatment of the electron-electron
interaction on the adatom. The values of at which the moment is turned on
or off are controlled by the strength of the hopping between the graphene sheet
and the adatom, the on-site energy of the adatom, and the strength of the
electron-electron correlation energy U. Our result is in qualitatively
consistent with recent experiments by Nair {\it et al.} [Nat.\ Commun.\ {\bf
4}, 2010 (2013)].Comment: 4 Pages, 1 Figur
Microscopes and computers combined for analysis of chromosomes
Scanning machine CHLOE, developed for photographic use, is combined with a digital computer to obtain quantitative and statistically significant data on chromosome shapes, distribution, density, and pairing. CHLOE permits data acquisition about a chromosome complement to be obtained two times faster than by manual pairing
Enduring Extremes? Polar Vortex, Drought, and Climate Change Beliefs
This is the author accepted manuscript. The final version is available from Taylor & Francis via the DOI in this recordSome extreme weather events may be more likely to affect climate change beliefs than others, in part because schema individuals possess for different events could vary in encouraging such links. Using a representative sample of U.S. adults and geocoded National Weather Service data, we examine how a range of extreme weather event categories relate to climate change beliefs, and the degree to which individuals’ self-reported experiences are shaped by their political views across event types. For tornado, hurricane, and flood events, we find no link with beliefs. For polar vortex and drought events, we find that although self-reported experience is linked with climate beliefs, reporting of these experiences is influenced by political identity and partisan news exposure. These findings underscore a limited role for extreme weather experiences in climate beliefs, and show that events more open to interpretation, such as droughts and polar vortex disturbances, are most likely to be seen through a partisan lens.This work was supported by H2020 European Research Council [grant number 682758]
Aggregation of SiC-X Grains in Supernova Ejecta
We present a model for the formation of silicon carbide aggregates within the
expanding and cooling supernova remnant. Many SiC-X grains have been found to
be aggregates of smaller crystals which are isotopically homogenous. The
initial condensation of SiC in the ejecta occurs within a interior dense shell
of material which is created by a reverse shock which rebounds from the
core-envelope interface. A subsequent reverse shock accelerates the grains
forward, but the gas drag from the ejecta on the rapidly moving particles
limits their travel distance. By observing the effects of gas drag on the
travel distance of grains, we propose that supernova grain aggregates form from
material that condensed in a highly localized region, which satisfies the
observational evidence of isotopic homogeneity in SiC-X grains.Comment: 9 pages, 5 figures, To be published in the Astrophysical Journa
The risk of extinction for birds in Great Britain
t Over the last 20 years,species priorities for bird conservation in the UK
have been guided by ‘Birds of Conservation Concern’ – an in-depth assessment
made possible by the top-class data available on the status of the UK’s birds. For
other wildlife, priorities tend to be informed by measures of extinction risk,
generated by the IUCN Regional Red List process.We carried out the first formal
IUCN assessment for birds in Great Britain. Of the 241 species assessed, 100 (43%)
had at least one population (breeding and/or non-breeding) that qualified as
Threatened using the standard IUCN Red List criteria and categories. Of 289
separate assessments of breeding or non-breeding populations, 39% qualified as
Threatened (8% Critically Endangered, 14% Endangered, 17% Vulnerable) with a
further 10% classified as Near Threatened. Both Golden Oriole Oriolus oriolus and
Fieldfare Turdus pilaris were assessed as being Critically Endangered (Possibly
Extinct) as breeding species, in addition to seven species that are already extinct
(either Extinct or Regionally Extinct). The proportion of GB birds qualifying as
Threatened was high compared with birds elsewhere in Europe and other
taxonomic groups in GB. We believe that, if similar data were available, levels of
extinction risk would be higher for other areas/taxa than is currently estimated
Discretization of the velocity space in solution of the Boltzmann equation
We point out an equivalence between the discrete velocity method of solving
the Boltzmann equation, of which the lattice Boltzmann equation method is a
special example, and the approximations to the Boltzmann equation by a Hermite
polynomial expansion. Discretizing the Boltzmann equation with a BGK collision
term at the velocities that correspond to the nodes of a Hermite quadrature is
shown to be equivalent to truncating the Hermite expansion of the distribution
function to the corresponding order. The truncated part of the distribution has
no contribution to the moments of low orders and is negligible at small Mach
numbers. Higher order approximations to the Boltzmann equation can be achieved
by using more velocities in the quadrature
Higher-order Galilean-invariant lattice Boltzmann model for microflows: Single-component gas
We introduce a scheme which gives rise to additional degree of freedom for the same number of discrete velocities in the context of the lattice Boltzmann model. We show that an off-lattice D3Q27 model exists with correct equilibrium to recover Galilean-invariant form of Navier-Stokes equation (without any cubic error). In the first part of this work, we show that the present model can capture two important features of the microflow in a single component gas: Knudsen boundary layer and Knudsen Paradox. Finally, we present numerical results corresponding to Couette flow for two representative Knudsen numbers. We show that the off-lattice D3Q27 model exhibits better accuracy as compared to more widely used on-lattice D3Q19 or D3Q27 model. Finally, our construction of discrete velocity model shows that there is no contradiction between entropic construction and quadrature-based procedure for the construction of the lattice Boltzmann model.open252
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