4,154 research outputs found
Twisted split-ring-resonator photonic metamaterial with huge optical activity
Coupled split-ring-resonator metamaterials have previously been shown to
exhibit large coupling effects, which are a prerequisite for obtaining large
effective optical activity. By a suitable lateral arrangement of these building
blocks, we completely eliminate linear birefringence and obtain pure optical
activity and connected circular optical dichroism. Experiments at around
100-THz frequency and corresponding modeling are in good agreement. Rotation
angles of about 30 degrees for 205nm sample thickness are derived.Comment: 6 pages, 4 figure
VADA: A transformation-based system for variable dependence analysis
Variable dependence is an analysis problem in which the aim is to determine the set of input variables that can affect the values stored in a chosen set of intermediate program variables. This paper shows the relationship between the variable dependence analysis problem and slicing and describes VADA, a system that implements variable dependence analysis. In order to cover the full range of C constructs and features, a transformation to a core language is employed Thus, the full analysis is required only for the core language, which is relatively simple. This reduces the overall effort required for dependency analysis. The transformations used need preserve only the variable dependence relation, and therefore need not be meaning preserving in the traditional sense. The paper describes how this relaxed meaning further simplifies the transformation phase of the approach. Finally, the results of an empirical study into the performance of the system are presented
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
Numerical calculations of effective elastic properties of two cellular structures
Young's moduli of regular two-dimensional truss-like and eye-shape-like
structures are simulated by using the finite element method. The structures are
the idealizations of soft polymeric materials used in the electret
applications. In the simulations size of the representative smallest units are
varied, which changes the dimensions of the cell-walls in the structures. A
power-law expression with a quadratic as the exponential term is proposed for
the effective Young's moduli of the systems as a function of the solid volume
fraction. The data is divided into three regions with respect to the volume
fraction; low, intermediate and high concentrations. The parameters of the
proposed power-law expression in each region are later represented as a
function of the structural parameters, unit-cell dimensions. The presented
expression can be used to predict structure/property relationship in materials
with similar cellular structures. It is observed that the structures with
volume fractions of solid higher than 0.15 exhibit the importance of the
cell-wall thickness contribution in the elastic properties. The cell-wall
thickness is the most significant factor to predict the effective Young's
modulus of regular cellular structures at high volume fractions of solid. At
lower concentrations of solid, eye-like structure yields lower Young's modulus
than the truss-like structure with the similar anisotropy. Comparison of the
numerical results with those of experimental data of poly(propylene) show good
aggreement regarding the influence of cell-wall thickness on elastic properties
of thin cellular films.Comment: 7 figures and 2 table
Chiral particle separation by a non-chiral micro-lattice
We conceived a model experiment for a continuous separation strategy of
chiral molecules (enantiomers) without the need of any chiral selector
structure or derivatization agents: Micro-particles that only differ by their
chirality are shown to migrate along different directions when driven by a
steady fluid flow through a square lattice of cylindrical posts. In accordance
with our numerical predictions, the transport directions of the enantiomers
depend very sensitively on the orientation of the lattice relatively to the
fluid flow
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