954 research outputs found
Rapidly convergent quasi-periodic Green functions for scattering by arrays of cylinders---including Wood anomalies
This paper presents a full-spectrum Green function methodology (which is
valid, in particular, at and around Wood-anomaly frequencies) for evaluation of
scattering by periodic arrays of cylinders of arbitrary cross section-with
application to wire gratings, particle arrays and reflectarrays and, indeed,
general arrays of conducting or dielectric bounded obstacles under both TE and
TM polarized illumination. The proposed method, which, for definiteness is
demonstrated here for arrays of perfectly conducting particles under TE
polarization, is based on use of the shifted Green-function method introduced
in the recent contribution (Bruno and Delourme, Jour. Computat. Phys. pp.
262--290 (2014)). A certain infinite term arises at Wood anomalies for the
cylinder-array problems considered here that is not present in the previous
rough-surface case. As shown in this paper, these infinite terms can be treated
via an application of ideas related to the Woodbury-Sherman-Morrison formulae.
The resulting approach, which is applicable to general arrays of obstacles even
at and around Wood-anomaly frequencies, exhibits fast convergence and high
accuracies. For example, a few hundreds of milliseconds suffice for the
proposed approach to evaluate solutions throughout the resonance region
(wavelengths comparable to the period and cylinder sizes) with full
single-precision accuracy
On the evaluation of quasi-periodic Green functions and wave-scattering at and around Rayleigh-Wood anomalies
This article presents full-spectrum, well-conditioned, Green-function methodologies for evaluation of scattering by general periodic structures, which remains applicable on a set of challenging singular configurations, usually called Rayleigh-Wood (RW) anomalies (at which the quasi-periodic Green function ceases to exist), where most existing quasi-periodic solvers break down. After reviewing a variety of existing fast-converging numerical procedures commonly used to compute the classical quasi-periodic Green-function, the present work explores the difficulties they present around RW-anomalies and introduces the concept of hybrid “spatial/spectral” representations. Such expressions allow both the modification of existing methods to obtain convergence at RW-anomalies as well as the application of a slight generalization of the Woodbury-Sherman-Morrison formulae together with a limiting procedure to bypass the singularities. (Although, for definiteness, the overall approach is applied to the scalar (acoustic) wave-scattering problem in the frequency domain, the approach can be extended in a straightforward manner to the harmonic Maxwell's and elasticity equations.) Ultimately, this thorough study of RW-anomalies yields fast and highly-accurate solvers, which are demonstrated with a variety of simulations of wave-scattering phenomena by arrays of particles, crossed impenetrable and penetrable diffraction gratings and other related structures. In particular, the methods developed in this article can be used to “upgrade” classical approaches, resulting in algorithms that are applicable throughout the spectrum, and it provides new methods for cases where previous approaches are either costly or fail altogether. In particular, it is suggested that the proposed shifted Green function approach may provide the only viable alternative for treatment of three-dimensional high-frequency configurations with either one or two directions of periodicity. A variety of computational examples are presented which demonstrate the flexibility of the overall approach
Majorana Zero Modes in Graphene
A clear demonstration of topological superconductivity (TS) and Majorana zero
modes remains one of the major pending goal in the field of topological
materials. One common strategy to generate TS is through the coupling of an
s-wave superconductor to a helical half-metallic system. Numerous proposals for
the latter have been put forward in the literature, most of them based on
semiconductors or topological insulators with strong spin-orbit coupling. Here
we demonstrate an alternative approach for the creation of TS in
graphene/superconductor junctions without the need of spin-orbit coupling. Our
prediction stems from the helicity of graphene's zero Landau level edge states
in the presence of interactions, and on the possibility, experimentally
demonstrated, to tune their magnetic properties with in-plane magnetic fields.
We show how canted antiferromagnetic ordering in the graphene bulk close to
neutrality induces TS along the junction, and gives rise to isolated,
topologically protected Majorana bound states at either end. We also discuss
possible strategies to detect their presence in graphene Josephson junctions
through Fraunhofer pattern anomalies and Andreev spectroscopy. The latter in
particular exhibits strong unambiguous signatures of the presence of the
Majorana states in the form of universal zero bias anomalies. Remarkable
progress has recently been reported in the fabrication of the proposed type of
junctions, which offers a promising outlook for Majorana physics in graphene
systems.Comment: 14 pages, 8 figures. Included simulations of Andreev spectroscopy and
mor
Phase diagram and structural properties of a simple model for one-patch particles
We study the thermodynamic and structural properties of a simple, one-patch
fluid model using the reference hypernetted-chain (RHNC) integral equation and
specialized Monte Carlo simulations. In this model, the interacting particles
are hard spheres, each of which carries a single identical,
arbitrarily-oriented, attractive circular patch on its surface; two spheres
attract via a simple square-well potential only if the two patches on the
spheres face each other within a specific angular range dictated by the size of
the patch. For a ratio of attractive to repulsive surface of 0.8, we construct
the RHNC fluid-fluid separation curve and compare with that obtained by Gibbs
ensemble and grand canonical Monte Carlo simulations. We find that RHNC
provides a quick and highly reliable estimate for the position of the
fluid-fluid critical line. In addition, it gives a detailed (though
approximate) description of all structural properties and their dependence on
patch size.Comment: 27 pages, 10 figures, J. Chem. Phys. in pres
The acceptability of HIV testing among women receiving post abortion care
Introduction: In South Sudan few women have heard about the HIV. The prevalence of HIV infection in the country is 2.6%. Post abortion care (PAC) accounts for over 50% of all gynaecological admissions at the Juba Teaching Hospital (JTH). HIV testing is not routinely offered as part of PAC services.Objective: To determine factors associated with acceptability of HIV testing among women receiving PAC at JTH.Methods: This was a cross-sectional study, conducted at the Gynaecological Unit of JTH. Three hundred and forty patients were interviewed using a structured questionnaire.Results: The mean age of the participants was 24.7 years with 50.5% aged <25years, 31.5% were employed, and 31.8% had no formal education. Acceptability of HIV testing was 70.9% and the prevalence of HIV was 2.7%. The most common reason for not accepting, was the belief, based on previous results, that they were HIV negative. Patients aged ≥25 years and those with primary and secondary education were twice as likely to accept HIV testing than those <25 years and those with no formal education, respectively. Employment status, religion and marital status were not statistically associated with acceptability of HIV testing. Patients previously tested for HIV were more likely to accept testing.Conclusion: Routine HIV testing should be integrated into PAC services with efforts to increase awareness of HIV and importance of testingKeywords: HIV, abortion, post-abortion care, South SudanSouth Sudan Medical Journal Vol 12 No 3 August 201
A scalable Computer-Aided Detection system for microcalcification cluster identification in a pan-European distributed database of mammograms
A computer-aided detection (CADe) system for microcalcification cluster
identification in mammograms has been developed in the framework of the
EU-founded MammoGrid project. The CADe software is mainly based on wavelet
transforms and artificial neural networks. It is able to identify
microcalcifications in different kinds of mammograms (i.e. acquired with
different machines and settings, digitized with different pitch and bit depth
or direct digital ones). The CADe can be remotely run from GRID-connected
acquisition and annotation stations, supporting clinicians from geographically
distant locations in the interpretation of mammographic data. We report the
FROC analyses of the CADe system performances on three different dataset of
mammograms, i.e. images of the CALMA INFN-founded database collected in the
Italian National screening program, the MIAS database and the so-far collected
MammoGrid images. The sensitivity values of 88% at a rate of 2.15 false
positive findings per image (FP/im), 88% with 2.18 FP/im and 87% with 5.7 FP/im
have been obtained on the CALMA, MIAS and MammoGrid database respectively.Comment: 6 pages, 5 figures; Proceedings of the ITBS 2005, 3rd International
Conference on Imaging Technologies in Biomedical Sciences, 25-28 September
2005, Milos Island, Greec
Effects of patch size and number within a simple model of patchy colloids
We report on a computer simulation and integral equation study of a simple
model of patchy spheres, each of whose surfaces is decorated with two opposite
attractive caps, as a function of the fraction of covered attractive
surface. The simple model explored --- the two-patch Kern-Frenkel model ---
interpolates between a square-well and a hard-sphere potential on changing the
coverage . We show that integral equation theory provides quantitative
predictions in the entire explored region of temperatures and densities from
the square-well limit down to . For smaller
, good numerical convergence of the equations is achieved only at
temperatures larger than the gas-liquid critical point, where however integral
equation theory provides a complete description of the angular dependence.
These results are contrasted with those for the one-patch case. We investigate
the remaining region of coverage via numerical simulation and show how the
gas-liquid critical point moves to smaller densities and temperatures on
decreasing . Below , crystallization prevents the
possibility of observing the evolution of the line of critical points,
providing the angular analog of the disappearance of the liquid as an
equilibrium phase on decreasing the range for spherical potentials. Finally, we
show that the stable ordered phase evolves on decreasing from a
three-dimensional crystal of interconnected planes to a two-dimensional
independent-planes structure to a one-dimensional fluid of chains when the
one-bond-per-patch limit is eventually reached.Comment: 26 pages, 11 figures, J. Chem. Phys. in pres
An Overview of Life Gratitude on Ex-Prisoner Adolescents
Adolescence is a very important and critical part of an individual's development. This is because, in the stages of adolescent development, it is often marked by an identity crisis which causes an adolescent to be very vulnerable to conduct behavior that is not following prevailing norms and rules, such as deviant behavior. Adolescents who are found guilty according to the applicable law will be placed and fostered at the Special Development Institution for Children (LPKA) and referred to as Correctional Students (Andikpas). After serving a criminal period, adolescent ex-prisoner will come out and live again in society. However, this is not easy due to environmental resistance and the difficulty of carrying out social reintegration. On the other hand, this brings its lessons for adolescent ex-prisoners so that they can be grateful by seeing life more positively. This paper will discuss the different and unique overview of life gratitude of ex-prisoner adolescents. The discussion is hoped to be able to provide knowledge related to the gratitude of life and adolescent ex-prisoners
Amblyomma parvum Aragao, 1908 (Acari: Ixodidae) : phylogeography and systematic considerations
The geographical distribution of Amblyomma parvum Arag\ue3o 1908 in the New World is disjunct, with two main clusters separated from each other by the Amazon basin. The main objectives of this study were to further investigate the systematic relationships within A. parvum, to determine whether or not populations from different geographical areas might represent cryptic species, and to reconstruct the phylogeographical evolutionary history of the species. The genetic diversity of A. parvum collected throughout its distributional range was analyzed by using 6 molecular markers: 5 mitochondrial [the small and the large ribosomal subunits 12rDNA and 16SrDNA, the cytochrome oxidase I (COI) and II (COII) and the control region or d-loop (DL)], and one nuclear (ITS2, Inter transcribed spacer 2). Phylogenetic trees were inferred by using maximum parsimony and Bayesian analyses. In addition, node dating was attempted for the main lineages identified phylogenetically. Although mitochondrial and nuclear topologies were not totally congruent, they all identified at least two main supported clusters, a Central American lineage, and a Brazilian-Argentinian lineage. Clade support and divergence values strongly suggest that the two lineages correspond to different taxonomic entities. Node dating placed the split between the Central American and the Brazilian-Argentinian lineages at approximately 5.8-4.9 Mya, just after the progressive replacement of the dry areas that occupied the northern part of South America by the Amazon Basin in the early-mid Miocene. This event might be the cause of fragmentation and putative speciation within the ancestral relatively xerophilic A. parvum population
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