1,995 research outputs found
Resistance Noise Scaling in a Dilute Two-Dimensional Hole System in GaAs
We have measured the resistance noise of a two-dimensional (2D)hole system in
a high mobility GaAs quantum well, around the 2D metal-insulator transition
(MIT) at zero magnetic field. The normalized noise power increases
strongly when the hole density p_s is decreased, increases slightly with
temperature (T) at the largest densities, and decreases strongly with T at low
p_s. The noise scales with the resistance, , as for a
second order phase transition such as a percolation transition. The p_s
dependence of the conductivity is consistent with a critical behavior for such
a transition, near a density p* which is lower than the observed MIT critical
density p_c.Comment: 4 pages, 4 figures, to be published in Phys. Rev. Let
Gravitational quasinormal modes for Anti-de Sitter black holes
Quasinormal mode spectra for gravitational perturbations of black holes in
four dimensional de Sitter and anti-de Sitter space are investigated. The
anti-de Sitter case is relevant to the ADS-CFT correspondence in superstring
theory. The ADS-CFT correspondence suggests a prefered set of boundary
conditions.Comment: 12 pages, 6 figures in ReVTe
A sublethal concentration of Sulfoxaflor has minimal impact on buff-tailed bumblebee (Bombus terrestris) locomotor behaviour under aversive conditioning
Pesticide exposure has been cited as a key threat to insect pollinators. Notably, a diverse range of potential sublethal effects have been reported in bee species, with a particular focus on effects due to exposure to neonicotinoid insecticides. Here, a purpose-built thermal–visual arena was used in a series of pilot experiments to assess the potential impact of approximate sublethal concentrations of the next generation sulfoximine insecticide sulfoxaflor (5 and 50 ppb) and the neonicotinoid insecticides thiacloprid (500 ppb) and thiamethoxam (10 ppb), on the walking trajectory, navigation and learning abilities of the buff-tailed bumblebee (Bombus terrestris audax) when subjected to an aversive conditioning task. The results suggest that only thiamethoxam prevents forager bees from improving in key training parameters (speed and distanced travelled) within the thermal visual arena. Power law analyses further revealed that a speed–curvature power law, previously reported as being present in the walking trajectories of bumblebees, is potentially disrupted under thiamethoxam (10 ppb) exposure, but not under sulfoxaflor or thiacloprid exposure. The pilot assay described provides a novel tool with which to identify subtle sublethal pesticide impacts, and their potential causes, on forager bees, that current ecotoxicological tests are not designed to assess
From Analysis Model to Software Architecture: a PIM2PIM Mapping.
To our knowledge, no current software development methodology explicitly describes how to transit from the analysis model to the software architecture of the application. This paper presents a method to derive the
software architecture of a system from its analysis model. To do this, we are going to use MDA. Both the analysis model and the architectural model are PIMs described with UML 2. The model type mapping designed consists of
several rules (expressed using OCL and natural language) that, when applied to the analysis artifacts, generate the software architecture of the application.
Specifically the rules act on elements of the UML 2 metamodel (metamodel mapping). We have developed a tool (using Smalltalk) that permits the automatic application of these rules to an analysis model defined in RoseTM to
generate the application architecture expressed in the architectural style C2
The Spread of Bluetongue Virus Serotype 8 in Great Britain and Its Control by Vaccination
Bluetongue (BT) is a viral disease of ruminants transmitted by Culicoides biting midges and has the ability to spread rapidly over large distances. In the summer of 2006, BTV serotype 8 (BTV-8) emerged for the first time in northern Europe, resulting in over 2000 infected farms by the end of the year. The virus subsequently overwintered and has since spread across much of Europe, causing tens of thousands of livestock deaths. In August 2007, BTV-8 reached Great Britain (GB), threatening the large and valuable livestock industry. A voluntary vaccination scheme was launched in GB in May 2008 and, in contrast with elsewhere in Europe, there were no reported cases in GB during 2008.Here, we use carefully parameterised mathematical models to investigate the spread of BTV in GB and its control by vaccination. In the absence of vaccination, the model predicted severe outbreaks of BTV, particularly for warmer temperatures. Vaccination was predicted to reduce the severity of epidemics, with the greatest reduction achieved for high levels (95%) of vaccine uptake. However, even at this level of uptake the model predicted some spread of BTV. The sensitivity of the predictions to vaccination parameters (time to full protection in cattle, vaccine efficacy), the shape of the transmission kernel and temperature dependence in the transmission of BTV between farms was assessed.A combination of lower temperatures and high levels of vaccine uptake (>80%) in the previously-affected areas are likely to be the major contributing factors in the control achieved in England in 2008. However, low levels of vaccination against BTV-8 or the introduction of other serotypes could result in further, potentially severe outbreaks in future
A numerical study of Bi-periodic binary diffraction gratings for solar cell applications
In this paper, a numerical study is made of simple bi-periodic binary diffraction gratings for solar cell applications. The gratings consist of hexagonal arrays of elliptical towers and wells etched directly into the solar cell substrate. The gratings are applied to two distinct solar cell technologies: a quantum dot intermediate band solar cell (QD-IBSC) and a crystalline silicon solar cell (SSC). In each case, the expected photocurrent increase due to the presence of the grating is calculated assuming AM1.5D illumination. For each technology, the grating period, well/tower depth and well/tower radii are optimised to maximise the photocurrent. The optimum parameters are presented. Results are presented for QD-IBSCs with a range of quantum dot layers and for SSCs with a range of thicknesses. For the QD-IBSC, it is found that the optimised grating leads to an absorption enhancement above that calculated for an ideally Lambertian scatterer for cells with less than 70 quantum dot layers. In a QD-IBSC with 50 quantum dot layers equipped with the optimum grating, the weak intermediate band to conduction band transition absorbs roughly half the photons in the corresponding sub-range of the AM1.5D spectrum. For the SSC, it is found that the optimised grating leads to an absorption enhancement above that calculated for an ideally Lambertian scatterer for cells with thicknesses of 10 ?m or greater. A 20um thick SSC equipped with the optimised grating leads to an absorption enhancement above that of a 200um thick SSC equipped with a planar back reflector
Quasinormal modes for the SdS black hole : an analytical approximation scheme
Quasinormal modes for scalar field perturbations of a Schwarzschild-de Sitter
(SdS) black hole are investigated. An analytical approximation is proposed for
the problem. The quasinormal modes are evaluated for this approximate model in
the limit when black hole mass is much smaller than the radius of curvature of
the spacetime. The model mirrors some striking features observed in numerical
studies of time behaviour of scalar perturbations of the SdS black hole. In
particular, it shows the presence of two sets of modes relevant at two
different time scales, proportional to the surface gravities of the black hole
and cosmological horizons respectively. These quasinormal modes are not
complete - another feature observed in numerical studies. Refinements of this
model to yield more accurate quantitative agreement with numerical studies are
discussed. Further investigations of this model are outlined, which would
provide a valuable insight into time behaviour of perturbations in the SdS
spacetime.Comment: 12 pages, revtex, refs added and discussion expanded, version to
appear in Phys. Rev.
Composite fermion theory of collective excitations in fractional quantum Hall effect
The low energy neutral excitations of incompressible fractional quantum Hall
states are called collective modes or magnetic excitons. This work develops
techniques for computing their dispersion at general filling fractions for
reasonably large systems. New structure is revealed; in particular, the
collective mode at 1/3 is found to possess several minima, with the energy of
the principal minimum significantly smaller than the earlier estimate.
\pacs{73.40.Hm, 73.20.Dx, 73.20.Mf}Comment: 4 pages, 3 postscript figure
Quasi-normal modes of Schwarzschild-de Sitter black holes
The low-laying frequencies of characteristic quasi-normal modes (QNM) of
Schwarzschild-de Sitter (SdS) black holes have been calculated for fields of
different spin using the 6th-order WKB approximation and the approximation by
the P\"{o}shl-Teller potential. The well-known asymptotic formula for large
is generalized here on a case of the Schwarzchild-de Sitter black hole. In the
limit of the near extreme term the results given by both methods are
in a very good agreement, and in this limit fields of different spin decay with
the same rate.Comment: 9 pages, 1 ancillary Mathematica(R) noteboo
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