82 research outputs found
Plasmonic Cloaking of Cylinders: Finite Length, Oblique Illumination and Cross-Polarization Coupling
Metamaterial cloaking has been proposed and studied in recent years following
several interesting approaches. One of them, the scattering-cancellation
technique, or plasmonic cloaking, exploits the plasmonic effects of suitably
designed thin homogeneous metamaterial covers to drastically suppress the
scattering of moderately sized objects within specific frequency ranges of
interest. Besides its inherent simplicity, this technique also holds the
promise of isotropic response and weak polarization dependence. Its theory has
been applied extensively to symmetrical geometries and canonical 3D shapes, but
its application to elongated objects has not been explored with the same level
of detail. We derive here closed-form theoretical formulas for infinite
cylinders under arbitrary wave incidence, and validate their performance with
full-wave numerical simulations, also considering the effects of finite lengths
and truncation effects in cylindrical objects. In particular, we find that a
single isotropic (idealized) cloaking layer may successfully suppress the
dominant scattering coefficients of moderately thin elongated objects, even for
finite lengths comparable with the incident wavelength, providing a weak
dependence on the incidence angle. These results may pave the way for
application of plasmonic cloaking in a variety of practical scenarios of
interest.Comment: 17 pages, 11 figures, 2 table
The chiral 1:2 adduct (S)S(S)C(-)589-ethyl 2-phenylbutyl sulphide-mercury (II) chloride:(-)589[(S)S(S)C-Et(2-PhBu)S.(HgCl2)2]. Stereoselective synthesis, asymmetric oxidation, crystal and molecular structure and circular dichroism spectra
Optically active (-)589ethyl (S)-2-phenylbutyl thioether, (-)(S)C-Et(PhBu)S (I), and its new diastereoisomeric mercury (II) chloride adduct, 1:2, (-)[(S)S(S)C-Et(PhBu)S.(HgCl2)2]2, (II) were stereoselectively synthesized; the absorbance (UV) and circular dichroism (CD) spectra were measured and the crystal and molecular structure of complex (II) was determined by single-crystal X-ray diffraction. Two different Hg centres are present whose coordination environments are built by two short bonds to chloride ligands in one case, and to one chloride and one sulphur in the other one. These originate digonal units. Electroneutrality is achieved by a further chlorine, which can be considered prevalently ionic and bonded to the two Hg centres, forming square bridging systems nearly perpendicular to the digonal molecules. The coordination polyhedra can be interpreted as 2 + 4 tetragonally-compressed octahedra with the four longer contacts lying in the equatorial plane. IR spectroscopic data are consistent with the presence of one bent and one linear ClâHgâCl moiety. The absolute configurations at both stereogenic centres of the formed diastereoisomeric complex (II) are (S). The (S)S absolute configuration at the stereogenic sulphur atom bonded to the mercury(II) atom in complex (II) has been related with the negative Cotton effect assigned in its circular dichroism (CD) spectrum to a charge-transfer transition at ca. 230 nm. The stereoselective oxidation of (I) and (II) with hydrogen peroxide, induced by the stereogenic carbon atom (S)C of the enantiopure sulphide, gave (-)598ethyl (S)C-2-phenylbutyl(S)S-sulphoxide, (-)598[(S)S(S)C-Et(PhBu)SO], (III), having 18.1% de. Oxidations carried out in the presence of a 200 molar excess of mercury(II) chloride gave (-)598ethyl (S)C-2-phenylbutyl(R)S-sulphoxide, (-) 598[(R)S(S)C-Et(PhBu)SO], (IV) with 31% de, showing the cooperative influence of mercury(II) chloride on the selectivity of the oxidation reaction
Giant energy storage density in PVDF with internal stress engineered polar nanostructures
High power dielectric capacitors with high energy density are needed in order to develop modern electronic and electrical systems, including hybrid vehicles, telecommunication infrastructures and portable electronic devices. Relaxor ferroelectric polymers (RFP) are considered to be the most promising candidates for the next generation of capacitors owing to their relatively high energy storage density. However, the commercialization of RFP capacitors in power systems is hindered by their high cost and low dielectric breakdown strength. In this study, inexpensive, free-standing nano-crystalline (~3.3 nm) poly (vinylidene fluoride) (PVDF) films with high ÎČ phase content (~98%), ârelaxor-likeâ ferroelectric behaviour and high breakdown strength (880 kV/mm) were fabricated using the facile Press & Folding (P&F) technique. An internal stress dominated polarization switching model is proposed to explain the origin of the relaxor-like ferroelectric behaviour. The internal stress generated during pressing alters the intermolecular chain distance of the (200) plane of ÎČ-PVDF from 4.24 Ă
in internal stress free films to 4.54 Ă
in P&F films, corresponding to a tensile strain and residual stress of 7.11% and 142 MPa, respectively. The internal stress acts to partially reverse the polarization on reversal of the applied electric field. This, combined with preferred in-plane orientation of the crystallites, results in a polar nanostructure with high polarization reversibility at high electric fields. A giant discharged energy storage density of 39.8 J/cm3 at 880 kV/mm was achieved for P&F films, which surpasses all previously reported polymer-based materials
Thermoelectric materials: A brief historical survey from metal junctions and inorganic semiconductors to organic polymers
The use of thermoelectric technology is attractive in many potential applications, such as energy scavenging from waste heat. The basic principles for harvesting electricity from a temperature gradient were first discovered around 180 years ago, but the contemporary technology utilising inorganic semiconductors was only developed since the early 1950s. The widespread use of this platform has so far been limited by a combination of relatively low efficiency in energy conversion or by issues related to the utilisation of rare, expensive and/or toxic elements that can be difficult to process. Recently much interest has been focused on the use of organic materials in thermoelectric devices, prompted by the possibility of developing large-area, low-cost devices. Considerable research in the last 20 years has been focused on understanding and improving organic thermoelectric properties, with remarkable progress recently published for compounds such as PEDOT and others. Here we provide an overview into thermoelectricity, from the initial discoveries made by Johann Seebeck to modern practical applications including the current trends in organic thermoelectric research. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.We are grateful to the EPSRC Doctoral Training Centre in Plastic Electronics (grant number EP/G037515/1) for fundin
Hydrocarbon reservoir volume estimation using 3-D seismic and well log data over an X-field, Niger Delta Nigeria
Structure and dynamics of pentacene on SiO2: From monolayer to bulk structure
We have used confocal micro Raman spectroscopy, atomic force microscopy (AFM), and x-ray diffraction (XRD) to investigate pentacene films obtained by vacuum deposition on SiO2 substrates. These methods allow us to follow the evolution of lattice structure, vibrational dynamics, and crystal morphology during the growth from monolayer, to TF, and, finally, to bulk crystal. The Raman measurements, supported by the AFM and XRD data, indicate that the film morphology depends on the deposition rate. High deposition rates yield two-dimensional nucleation and quasi-layer-by-layer growth of the T-F form only. Low rates yield three-dimensional nucleation and growth, with phase mixing occurring in sufficiently thick films, where the T-F form is accompanied by the "high-temperature" bulk phase. Our general findings are consistent with those of previous work. However, the Raman measurements, supported by lattice dynamics calculations, provide additional insight into the nature of the TFs, showing that their characteristic spectra originate from a loss of dynamical correlation between adjacent layers
Flexible and Stretchable Self-Powered Multi-Sensors Based on the N-Type Thermoelectric Response of Polyurethane/Na-x(Ni-ett)(n) Composites
Flexible and stretchable electronic devices have a broad range of potential uses, from biomedicine, soft robotics, and health monitoring to the internetâofâthings. Unfortunately, finding a robust and reliable power source remains challenging, particularly in offâtheâgrid and maintenanceâfree applications. A soughtâafter development overcome this challenge is the development of autonomous, selfâpowered devices. A potential solution is reported exploiting a promising nâtype thermoelectric compound, poly nickelâethenetetrathiolates (Na_{x}(Niâett)_{n}). Highly stretchable nâtype composite films are obtained by combining Nax(Niâett)n with commercial polyurethane (Lycra). As high as 50 wt% Na_{x}(Niâett)_{n} content composite film can withstand deformations of â500% and show conductivities of â10^{-2} S cm^{-1} and Seebeck coefficients of approx. â40 ”V K^{-1}. These novel materials can be easily synthesized on a large scale with continuous processes. When subjected to a small temperature difference (<20 °C), the films generate sufficient thermopower to be used for sensing strain (gauge factor â20) and visible light (sensitivity factor â36% (kW m^{-2})^{-1}), independent of humidity (sensitivity factor â0.1 (%RH)^{-1}. As a proofâofâconcept, a wearable selfâpowered sensor is demonstrated by using nâtype Na_{x}(Niâett)_{n}/Lycra and PEDOT:PSS/Lycra elements, connected in series by hot pressing, without employing any metal connections, hence preserving good mechanical ductility and ease of processing
Plasmonic nanoparticle monomers and dimers: From nano-antennas to chiral metamaterials
We review the basic physics behind light interaction with plasmonic
nanoparticles. The theoretical foundations of light scattering on one metallic
particle (a plasmonic monomer) and two interacting particles (a plasmonic
dimer) are systematically investigated. Expressions for effective particle
susceptibility (polarizability) are derived, and applications of these results
to plasmonic nanoantennas are outlined. In the long-wavelength limit, the
effective macroscopic parameters of an array of plasmonic dimers are
calculated. These parameters are attributable to an effective medium
corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial
where plasmonic monomers or dimers have the function of "meta-atoms". It is
shown that planar dimers consisting of rod-like particles generally possess
elliptical dichroism and function as atoms for planar chiral metamaterials. The
fabricational simplicity of the proposed rod-dimer geometry can be used in the
design of more cost-effective chiral metamaterials in the optical domain.Comment: submitted to Appl. Phys.
Composite Films of Arabinoxylan and Fibrous Sepiolite: Morphological, Mechanical, and Barrier Properties
Absorption, Photoluminescence, and Polarized Raman Spectra of a Fourfold Alkoxy-Substituted Phthalocyanine Liquid Crystal
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