7,257 research outputs found
Experimental evidence of delocalized states in random dimer superlattices
We study the electronic properties of GaAs-AlGaAs superlattices with
intentional correlated disorder by means of photoluminescence and vertical dc
resistance. The results are compared to those obtained in ordered and
uncorrelated disordered superlattices. We report the first experimental
evidence that spatial correlations inhibit localization of states in disordered
low-dimensional systems, as our previous theoretical calculations suggested, in
contrast to the earlier belief that all eigenstates are localized.Comment: 4 pages, 5 figures. Physical Review Letters (in press
The spectral-type/luminosity and the spectral type/satellite-density relations in the 2dFGRS
We examine the relative fractions of passive (Type 1), quiet-SF (Type 2) and
active-SF (Type 3+4) galaxies as a function of luminosity and number of
neighbours in several volume limited samples selected from the 2dFGRS.
Neighbours are counted within 1 Mpc projected distance, and
1000 km s depth. We apply a maximum magnitude difference criterion and
require neighbours to be fainter than the galaxy itself. We show that, whatever
the environment, passive galaxies dominate in bright samples and active-SF
galaxies in faint samples, whereas quiet-SF galaxies never dominate. We further
show that in bright samples (M -- 5 ) the fraction of passive galaxies grows steadily with fainter neighbour
density, whereas in faint samples a threshold like dependence is observed. This
suggests that the spectral-type / density ( morphology / density)
relation extends to intermediate dense environment, but only in the surrounding
of luminous galaxies and that it reflects an enhancement of the number of
satellites rather than stronger clustering among galaxies themselves. Our
analysis indicates that, in general, luminosity is a good tracer of a galaxy
halo mass and that it dominates over environment (satellite density) in setting
the spectral type mix of a population. However, minority populations exist,
such as luminous SF galaxies and faint passive galaxies, whose luminosity is an
unfair tracer of halo mass.Comment: 8 pages, 5 figur
Characterization of Escherichia coli Carrying mcr-1-Plasmids Recovered From Food Animals From Argentina
In this study, we found mcr-1.1 and mcr-1.5 genes carried by IncI2 plasmids in a subset of Escherichia coli isolates recovered from commercial broiler farms in Argentina. The comparative analysis of the sequences of these plasmids with those described in human clinical isolates suggests that this replicon-type is one of the main mcr-disseminator sources in Argentina
Electromagnetic vertex function of the pion at T > 0
The matrix element of the electromagnetic current between pion states is
calculated in quenched lattice QCD at a temperature of . The
nonperturbatively improved Sheikholeslami-Wohlert action is used together with
the corresponding improved vector current. The electromagnetic
vertex function is extracted for pion masses down to and
momentum transfers .Comment: 17 pages, 8 figure
DualSPHysics: from fluid dynamics to multiphysics problems
DualSPHysics is a weakly compressible smoothed particle hydrodynamics (SPH) Navier–Stokes solver initially conceived to deal with coastal engineering problems, especially those related to wave impact with coastal structures. Since the first release back in 2011, DualSPHysics has shown to be robust and accurate for simulating extreme wave events along with a continuous improvement in efficiency thanks to the exploitation of hardware such as graphics processing units for scientific computing or the coupling with wave propagating models such as SWASH and OceanWave3D. Numerous additional functionalities have also been included in the DualSPHysics package over the last few years which allow the simulation of fluid-driven objects. The use of the discrete element method has allowed the solver to simulate the interaction among different bodies (sliding rocks, for example), which provides a unique tool to analyse debris flows. In addition, the recent coupling with other solvers like Project Chrono or MoorDyn has been a milestone in the development of the solver. Project Chrono allows the simulation of articulated structures with joints, hinges, sliders and springs and MoorDyn allows simulating moored structures. Both functionalities make DualSPHysics especially suited for the simulation of offshore energy harvesting devices. Lately, the present state of maturity of the solver goes beyond single-phase simulations, allowing multi-phase simulations with gas–liquid and a combination of Newtonian and non-Newtonian models expanding further the capabilities and range of applications for the DualSPHysics solver. These advances and functionalities make DualSPHysics an advanced meshless solver with emphasis on free-surface flow modelling
Monitoring local well-being in environmental interventions: a consideration of practical trade-offs
Within the field of environmental management and conservation, the concept of well-being is starting to gain traction in monitoring the socio-economic and cultural impact of interventions on local people. Here we consider the practical trade-offs policy makers and practitioners must navigate when utilizing the concept of well-being in environmental interventions. We first review current concepts of well-being before considering the need to balance the complexity and practical applicability of the definition used and to consider both positive and negative components of well-being. A key determinant of how well-being is operationalized is the identity of the organization wishing to monitor it. We describe the trade-offs around the external and internal validity of different approaches to measuring well-being and the relative contributions of qualitative and quantitative information to understanding well-being. We explore how these trade-offs may be decided as a result of a power struggle between stakeholders. Well-being is a complex, multi-dimensional, dynamic concept that cannot be easily defined and measured. Local perspectives are often missed during the project design process as a result of the more powerful voices of national governments and international NGOs, so for equity and local relevance it is important to ensure these perspectives are represented at a high level in project design and implementation
Application of Tensor Neural Networks to Pricing Bermudan Swaptions
The Cheyette model is a quasi-Gaussian volatility interest rate model widely
used to price interest rate derivatives such as European and Bermudan Swaptions
for which Monte Carlo simulation has become the industry standard. In low
dimensions, these approaches provide accurate and robust prices for European
Swaptions but, even in this computationally simple setting, they are known to
underestimate the value of Bermudan Swaptions when using the state variables as
regressors. This is mainly due to the use of a finite number of predetermined
basis functions in the regression. Moreover, in high-dimensional settings,
these approaches succumb to the Curse of Dimensionality. To address these
issues, Deep-learning techniques have been used to solve the backward
Stochastic Differential Equation associated with the value process for European
and Bermudan Swaptions; however, these methods are constrained by training time
and memory. To overcome these limitations, we propose leveraging Tensor Neural
Networks as they can provide significant parameter savings while attaining the
same accuracy as classical Dense Neural Networks. In this paper we rigorously
benchmark the performance of Tensor Neural Networks and Dense Neural Networks
for pricing European and Bermudan Swaptions, and we show that Tensor Neural
Networks can be trained faster than Dense Neural Networks and provide more
accurate and robust prices than their Dense counterparts.Comment: 15 pages, 9 figures, 2 table
Microplate technique to determine hemolytic activity for routine typing of Listeria strains
Because the hemolysis produced by Listeria monocytogenes and Listeria seeligeri on blood agar is frequently difficult to interpret, we developed a microplate technique for the routine determination of hemolytic activity with erythrocyte suspensions. This microtechnique is a simple and reliable test for distinguishing clearly between hemolytic and nonhemolytic strains and could be used instead of the CAMP (Christie-Atkins-Munch-Petersen) test with Staphylococcus aureus in the routine typing of Listeria strains. Furthermore, our results suggest that the quantitation of the hemolytic activity of the Listeria strains, along with the D-xylose, L-rhamnose, and alpha-methyl-D-mannoside acidification tests, allows the differentiation of L. monocytogenes, L. seeligeri, and Listeria ivanovii. We also observed that the treatment of erythrocytes with crude exosubstances of rhodococcus equi, Pseudomonas fluorescens, Acinetobacter calcoaceticus, and S. aureus enhanced the hemolytic activity of all Listeria strains with this characteristic
CCSD(T) Study of CD3-O-CD3 and CH3-O-CD3 Far-Infrared Spectra
From a vibrationally corrected 3D potential energy surface determined with highly correlated ab initio calculations (CCSD(T)), the lowest vibrational energies of two dimethyl-ether isotopologues, 12CH3–16O–12CD3 (DME-d3) and 12CD3–16O–12CD3 (DME-d6), are computed variationally. The levels that can be populated at very low temperatures correspond to the COC-bending and the two methyl torsional modes. Molecular symmetry groups are used for the classification of levels and torsional splittings. DME-d6 belongs to the G36 group, as the most abundant isotopologue 12CH3–16O–12CH3 (DME-h6), while DME-d3 is a G18 species. Previous assignments of experimental Raman and far-infrared spectra are discussed from an effective Hamiltonian obtained after refining the ab initio parameters. Because a good agreement between calculated and experimental transition frequencies is reached, new assignments are proposed for various combination bands corresponding to the two deuterated isotopologues and for the 020 → 030 transition of DME-d6. Vibrationally corrected potential energy barriers, structural parameters, and anharmonic spectroscopic parameters are provided. For the 3N – 9 neglected vibrational modes, harmonic and anharmonic fundamental frequencies are obtained using second-order perturbation theory by means of CCSD and MP2 force fields. Fermi resonances between the COC-bending and the torsional modes modify DME-d3 intensities and the band positions of the torsional overtones
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