12,723 research outputs found
Correlation of circular differential optical absorption with geometric chirality in plasmonic meta-atoms
We report a strong correlation between the calculated broadband circular differential optical absorption (CDOA) and the geometric chirality of plasmonic meta-atoms with two-dimensional chirality. We investigate this correlation using three common gold meta-atom geometries: L-shapes, triangles, and nanorod dimers, over a broad range of geometric parameters. We show that this correlation holds for both contiguous plasmonic meta-atoms and non-contiguous structures which support plasmonic coupling effects. A potential application for this correlation is the rapid optimization of plasmonic nanostructure for maximum broadband CDOA
The incidence of fragility hip fractures in a subpopulation of South Africa
Background. Fragility hip fractures (FHFs) are associated with significant morbidity, mortality and burden on the healthcare system. European and North American literature suggests that the worldwide incidence of FHFs is increasing, but very little is known about the incidence of FHFs in Africa and South Africa (SA). Historically FHFs were believed to be uncommon in black African populations, but recent studies have shown a marked increase in the incidence compared with the early literature.
Objectives. To investigate the age-, gender-and population group-specific incidences of FHFs in a subpopulation in Eastern Cape Province, SA.
Methods. A retrospective review of all patients presenting with FHFs was performed at a tertiary hospital in the Eastern Cape over a 1-year period. Age-, gender-and population group-specific incidence rates were calculated for 5-year age intervals using the age distribution data of the western region of the Eastern Cape (WREC) as a denominator for each age group. Overall crude incidence rates were calculated by using the sum total of FHFs, divided by the study population. All incidences were calculated as number of fractures per 100 000 people annually.
Results. A total of 253 patients with FHFs were included. The crude incidence rate of low-energy hip fractures in the WREC was 19.3 per 100 000 (males 14.6, females 23.4) over the study period. Population group-specific incidences were 15.1, 18.7, 19.9 and 46.6 per 100 000 for black, coloured, Indian and white population groups, respectively. The highest number of low-energy hip fractures in females occurred in the ≥85-year (19.6%) and 70 -74-year (16.5%) age groups, with the highest number of male cases observed in the 60 -64-year group (20.2%). The highest frequency distribution of FHFs was observed in black males aged 60 -64 years (5.5%; n=14) and black females aged 70 -74 years (6.3%; n=16).
Conclusions. The local incidence of FHFs is higher than initially reported, but when compared with other countries remains on the lower end of spectrum. A large proportion of FHFs are occurring in young patients (<65 years). These findings warrant further investigation that may prompt the development of preventive strategies and optimal treatment programmes
Numerical Investigation of Light Scattering off Split-Ring Resonators
Recently, split ring-resonators (SRR's) have been realized experimentally in
the near infrared (NIR) and optical regime. In this contribution we numerically
investigate light propagation through an array of metallic SRR's in the NIR and
optical regime and compare our results to experimental results.
We find numerical solutions to the time-harmonic Maxwell's equations by using
advanced finite-element-methods (FEM). The geometry of the problem is
discretized with unstructured tetrahedral meshes. Higher order, vectorial
elements (edge elements) are used as ansatz functions. Transparent boundary
conditions and periodic boundary conditions are implemented, which allow to
treat light scattering problems off periodic structures.
This simulation tool enables us to obtain transmission and reflection spectra
of plane waves which are incident onto the SRR array under arbitrary angles of
incidence, with arbitrary polarization, and with arbitrary
wavelength-dependencies of the permittivity tensor. We compare the computed
spectra to experimental results and investigate resonances of the system.Comment: 9 pages, 8 figures (see original publication for images with a better
resolution
Combining Contrast Invariant L1 Data Fidelities with Nonlinear Spectral Image Decomposition
This paper focuses on multi-scale approaches for variational methods and
corresponding gradient flows. Recently, for convex regularization functionals
such as total variation, new theory and algorithms for nonlinear eigenvalue
problems via nonlinear spectral decompositions have been developed. Those
methods open new directions for advanced image filtering. However, for an
effective use in image segmentation and shape decomposition, a clear
interpretation of the spectral response regarding size and intensity scales is
needed but lacking in current approaches. In this context, data
fidelities are particularly helpful due to their interesting multi-scale
properties such as contrast invariance. Hence, the novelty of this work is the
combination of -based multi-scale methods with nonlinear spectral
decompositions. We compare with scale-space methods in view of
spectral image representation and decomposition. We show that the contrast
invariant multi-scale behavior of promotes sparsity in the spectral
response providing more informative decompositions. We provide a numerical
method and analyze synthetic and biomedical images at which decomposition leads
to improved segmentation.Comment: 13 pages, 7 figures, conference SSVM 201
Scaling Study and Thermodynamic Properties of the cubic Helimagnet FeGe
The critical behavior of the cubic helimagnet FeGe was obtained from
isothermal magnetization data in very close vicinity of the ordering
temperature. A thorough and consistent scaling analysis of these data revealed
the critical exponents , , and . The
anomaly in the specific heat associated with the magnetic ordering can be well
described by the critical exponent . The values of these
exponents corroborate that the magnetic phase transition in FeGe belongs to the
isotropic 3D-Heisenberg universality class. The specific heat data are well
described by ab initio phonon calculations and confirm the localized character
of the magnetic moments.Comment: 10 pages, 8 figure
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