28 research outputs found
Enhancement of near-cloaking. Part II: the Helmholtz equation
The aim of this paper is to extend the method of improving cloaking
structures in the conductivity to scattering problems. We construct very
effective near-cloaking structures for the scattering problem at a fixed
frequency. These new structures are, before using the transformation optics,
layered structures and are designed so that their first scattering coefficients
vanish. Inside the cloaking region, any target has near-zero scattering cross
section for a band of frequencies. We analytically show that our new
construction significantly enhances the cloaking effect for the Helmholtz
equation.Comment: 16pages, 12 fugure
Genetic variants related to nicotine dependence
Large-scale population studies have proved that genetic factors contribute to individual differences in smoking behavior. Genes responsible for nicotine's pharmacokinetics and pharmacodynamics seem mainly involved, although a significant fraction of variance remains unexplained. In this study we examined 10 SNPs from 8 candidate genes with positive previous reports of association with smoking. A total of 454 Italian unrelated subjects were genotyped by a multiplex minisequencing assay through the SNaPShot kit. Cases were chosen as current and former nicotine dependent (FTND. >. 4 and SQ. >. 15), while controls were smoking-exposed but non-dependent and never smoker individuals (FTND = 0 and SQ < 10 and FTND = 0 and SQ = 0, respectively). Preliminary results shows that the SNPs CHRNA5-rs16969968 and CHRNA3-rs1051730 could be associated with risk of developing nicotine dependence. Factors as age, sex, and exposition to smoke were also found as possible factors of risk of nicotine addiction. The identification of susceptibility loci for individual response to substance abuse is particularly motivating for medicine for the global epidemic dimension of addictions and the urgent need of effective preventive and therapeutic strategies. 2011 Elsevier Ireland Ltd
Strong magnetic response of submicron Silicon particles in the infrared
High-permittivity dielectric particles with resonant magnetic properties are
being explored as constitutive elements of new metamaterials and devices in the
microwave regime. Magnetic properties of low-loss dielectric nanoparticles in
the visible or infrared are not expected due to intrinsic low refractive index
of optical materials in these regimes. Here we analyze the dipolar electric and
magnetic response of loss-less dielectric spheres made of moderate permittivity
materials. For low material refractive index there are no sharp resonances due
to strong overlapping between different multipole contributions. However, we
find that Silicon particles with refractive index 3.5 and radius approx. 200nm
present a dipolar and strong magnetic resonant response in telecom and
near-infrared frequencies, (i.e. at wavelengths approx. 1.2-2 micrometer).
Moreover, the light scattered by these Si particles can be perfectly described
by dipolar electric and magnetic fields, quadrupolar and higher order
contributions being negligible.Comment: 10 pages, 5 figure
Transformation elastodynamics and active exterior acoustic cloaking
This chapter consists of three parts. In the first part we recall the
elastodynamic equations under coordinate transformations. The idea is to use
coordinate transformations to manipulate waves propagating in an elastic
material. Then we study the effect of transformations on a mass-spring network
model. The transformed networks can be realized with "torque springs", which
are introduced here and are springs with a force proportional to the
displacement in a direction other than the direction of the spring terminals.
Possible homogenizations of the transformed networks are presented, with
potential applications to cloaking. In the second and third parts we present
cloaking methods that are based on cancelling an incident field using active
devices which are exterior to the cloaked region and that do not generate
significant fields far away from the devices. In the second part, the exterior
cloaking problem for the Laplace equation is reformulated as the problem of
polynomial approximation of analytic functions. An explicit solution is given
that allows to cloak larger objects at a fixed distance from the cloaking
device, compared to previous explicit solutions. In the third part we consider
the active exterior cloaking problem for the Helmholtz equation in 3D. Our
method uses the Green's formula and an addition theorem for spherical outgoing
waves to design devices that mimic the effect of the single and double layer
potentials in Green's formula.Comment: Submitted as a chapter for the volume "Acoustic metamaterials:
Negative refraction, imaging, lensing and cloaking", Craster and Guenneau
ed., Springe
Extended discrete dipole approximation and its application to bianisotropic media
In this research we introduce the formalism of the extension of the discrete dipole approximation to a more general range of tensorial relative permittivity and permeability. Its performance is tested in the domain of applicability of other methods for the case of composite materials (nanoshells). Then, some early results on bianisotropic nanoparticles are presented, to show the potential of the Extended Discrete Dipole Approximation (E-DDA) as a new tool for calculating the interaction of light with bianisotropic scatterers
Small dielectric spheres with high Refractive index as new multifunctional elements for optical devices
The future of ultra-fast optical communication systems is inevitably connected with progress in optical circuits and nanoantennas. One of the key points of this progress is the creation of elementary components of optical devices with scattering diagrams tailored for redirecting the incident light in a desired manner. Here we demonstrate theoretically and experimentally that a small, simple, spatially homogeneous dielectric subwavelength sphere with a high refractive index and low losses (as some semiconductors in the visible or near infrared region) exhibits properties allowing to utilize it as a new multifunctional element for the mentioned devices. This can be achieved by taking advantage of the coherent effects between dipolar and multipolar modes, which produce anomalous scattering effects. The effects open a new way to control the directionality of the scattered light. The directional tuning can be obtained in a practical way just by a change in the frequency of the incident wave, and/or by a well-chosen diameter of the sphere. Dielectric nanoparticles with the required optical properties in the VIS-NIR may be now readily fabricated. These particles could be an efficient alternative to the widely discussed scattering units with a more complicated design.This research was partly supported by MICINN (Spanish Ministry of Science and Innovation) through
project FIS2013-45854-P and by the Ministry of Education and Science of Russian Federation through
grant 14.Z50.31.0034
Improvement of infrared single-photon detectors absorptance by integrated plasmonic structures
Plasmonic structures open novel avenues in photodetector development. Optimized illumination configurations are reported to improve p-polarized light absorptance in superconducting-nanowire single-photon detectors (SNSPDs) comprising short- and long-periodic niobium-nitride (NbN) stripe-patterns. In OC-SNSPDs consisting of ~quarter-wavelength dielectric layer closed by a gold reflector the highest absorptance is attainable at perpendicular incidence onto NbN patterns in P-orientation due to E-field concentration at the bottom of nano-cavities. In NCAI-SNSPDs integrated with nano-cavity-arrays consisting of vertical and horizontal gold segments off-axis illumination in S-orientation results in polar-angle-independent perfect absorptance via collective resonances in short-periodic design, while in long-periodic NCAI-SNSPDs grating-coupled surface waves promote EM-field transportation to the NbN stripes and result in local absorptance maxima. In NCDAI-SNSPDs integrated with nano-cavity-deflector-array consisting of longer vertical gold segments large absorptance maxima appear in 3p-periodic designs due to E-field enhancement via grating-coupled surface waves synchronized with the NbN stripes in S-orientation, which enable to compensate fill-factor-related retrogression.United States. Dept. of Energy (Frontier Research Centers