112 research outputs found
Macroscopic Maxwell's equations and negative index materials
We study the linear phenomenological Maxwell's equations in the presence of a
polarizable and magnetizable medium (magnetodielectric). For a dispersive,
non-absorptive, medium with equal electric and magnetic permeabilities, the
latter can assume the value -1 (+1 is their vacuum value) for a discrete set of
frequencies, i.e., for these frequencies the medium behaves as a negative index
material (NIM). We show that such systems have a well-defined time evolution.
In particular the fields remain square integrable (and the electromagnetic
energy finite) if this is the case at some initial time. Next we turn to the
Green's function (a tensor), associated with the electric Helmholtz operator,
for a set of parallel layers filled with a material. We express it in terms of
the well-known scalar s and p ones. For a half space filled with the material
and with a single dispersive Lorentz form for both electric and magnetic
permeabilities we obtain an explicit form for the Green's function. We find the
usual behavior for negative index materials, there is no refection outside the
evanescent regime and the transmission (refraction) shows the usual NIM
behavior. We find that the Green's function has poles, which lead to a
modulation of the radiative decay probability of an excited atom. The formalism
is free from ambiguities in the sign of the refractive index.Comment: 22 pages, accepted for publication in J. Math. Phys
Semi-analytical design of antireflection gratings for photonic crystals
This article concerns the design of antireflection structures which, placed
on a photonic crystal surface, significantly diminish the fraction of energy
lost to reflected waves. After a review of the classes of these structures
proposed to date, a new method is presented in detail for the design of
antireflection gratings operating in a wide range of angles of incidence. The
proposed algorithm is illustrated by means of several examples, showing the
advantages and limitations.Comment: Submitted to Phys. Rev.
Discrete dipole approximation in time domain through the Laplace transform
We present a form of the discrete dipole approximation for electromagnetic scattering computations in time domain. We show that the introduction of complex frequencies, through the Laplace transform, significantly improves the computation time. We also show that the Laplace transform and its inverse can be combined to extract the field inside a scatterer at a real resonance frequenc
Design of metallic nanoparticles gratings for filtering properties in the visible spectrum
Plasmonic resonances in metallic nanoparticles are exploited to create
efficient optical filtering functions. A Finite Element Method is used to model
metallic nanoparticles gratings. The accuracy of this method is shown by
comparing numerical results with measurements on a two-dimensional grating of
gold nanocylinders with elliptic cross section. Then a parametric analysis is
performed in order to design efficient filters with polarization dependent
properties together with high transparency over the visible range. The behavior
of nanoparticle gratings is also modelled using the Maxwell-Garnett
homogenization theory and analyzed by comparison with the diffraction by a
single nanoparticle. The proposed structures are intended to be included in
optical systems which could find innovative applications.Comment: submitted to Applied Optic
Determination of Effective Permittivity and Permeability of Metamaterials from Reflection and Transmission Coefficients
We analyze the reflection and transmission coefficients calculated from
transfer matrix simulations on finite lenghts of electromagnetic metamaterials,
to determine the effective permittivity and permeability. We perform this
analysis on structures composed of periodic arrangements of wires, split ring
resonators (SRRs) and both wires and SRRs. We find the recovered
frequency-dependent permittivity and permeability are entirely consistent with
analytic expressions predicted by effective medium arguments. Of particular
relevance are that a wire medium exhibits a frequency region in which the real
part of permittivity is negative, and SRRs produce a frequency region in which
the real part of permeability is negative. In the combination structure, at
frequencies where both the recovered real part of permittivity and permeability
are simultaneously negative, the real part of the index-of-refraction is found
also to be unambigously negative.Comment: *.pdf file, 5 figure
Scientific Opinion on the safety and efficacy of Urea for ruminants
Urea supplementation to feed for ruminants provides non-protein nitrogen for microbial protein synthesis in the rumen and thus in part replaces other dietary protein sources. Urea supplementation of feed for ruminants at doses up to 1 % of complete feed DM (corresponding to 0.3 g/kg bw/day) is considered safe when given to animals with a well adapted ruminal microbiota and fed diets rich in easily digestible carbohydrates. Based on the metabolic fate of urea in ruminants, the use of urea in ruminant nutrition does not raise any concern for consumers\u2019 safety. Urea is considered to be non irritant to skin and eyes and its topical use suggests that it is not a dermal sensitiser. The risk of exposure by inhalation would be low. The substitution of protein by urea in well balanced feed for ruminants would not result in an increased environmental nitrogen load. Urea is an effective source of non-protein nitrogen substituting for dietary protein in ruminants
Assessment of genetically modified maize\ua04114 for food and feed uses, under Regulation (EC) No\ua01829/2003 (application EFSA-GMO-NL-2014-123)
Maize\ua04114 was developed through Agrobacterium\ua0tumefaciens-mediated transformation to provide protection against certain lepidopteran and coleopteran pests by expression of the Cry1F, Cry34Ab1 and Cry35Ab1 proteins derived from Bacillus\ua0thuringiensis, and tolerance to the herbicidal active ingredient glufosinate-ammonium by expression of the PAT protein derived from Streptomyces viridochromogenes. The molecular characterisation data did not identify issues requiring assessment for food/feed safety. None of the compositional, agronomic and phenotypic differences identified between maize\ua04114 and the non-genetically modified (GM) comparator(s) required further assessment. There were no concerns regarding the potential toxicity and allergenicity of the newly expressed proteins Cry1F, Cry34Ab1, Cry35Ab1 and PAT, and no evidence that the genetic modification might significantly change the overall allergenicity of maize 4114. The nutritional value of food/feed derived from maize 4114 is not expected to differ from that derived from non-GM maize varieties and no post-market monitoring of food/feed is considered necessary. In the case of accidental release of viable maize\ua04114 grains into the environment, maize\ua04114 would not raise environmental safety concerns. The post-market environmental monitoring plan and reporting intervals are in line with the intended uses of maize\ua04114. The genetically modified organism (GMO) Panel\ua0concludes that maize\ua04114 is as safe as the non-GM comparator(s) and non-GM reference varieties with respect to potential effects on human and animal health and the environment in the context of the scope of this application
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