679 research outputs found
Organic semiconductor-based photonic crystals for solar cell arrays: band gap and optical properties
Cataloged from PDF version of article.Photonic crystals (PCs) hold great potential for designing new optical devices because of the possibility of the manipulation of light with PCs. There has been an increase in research on tuning the optical properties of PCs to design devices. We design organic semiconductor-based PC structures and calculate optical properties using the plane wave expansion method and finite-difference time-domain method in an air background for a hexagonal lattice. We showed the possibility of the solar cell arrays for a 2D PC cavity on an organic semiconductor base infiltrated with a nematic liquid crystal. E7 type has been used as a nematic liquid crystal and 4,4-Bis[4-(diphenylamino) styryl]biphenyl as an organic semiconductor material
Optical properties of metamaterial-based devices modulated by a liquid crystal
Cataloged from PDF version of article.Due to the fact that it is possible to manipulate light with photonic crystals (PCs), PCs hold a great potential for designing new optical devices. There has been an increase in research on tuning the optical properties of PCs to design devices. We presented a numerical study of optical properties of metamaterial-based devices by liquid crystal infiltration. The plane wave expansion method and finite-difference time-domain method for both TE and TM modes revealed optical properties in photonic crystal structures in an air background for a square lattice. E7 type has been used as a nematic liquid crystal and SrTiO3 as a ferroelectric material. We showed the possibility of the metamaterials for a two-dimensional photonic crystal cavity on a ferroelectric base infiltrated with a nematic liquid crystal
Ferroelectric Based Photonic Crystal Cavity by Liquid Crystal Infiltration
Cataloged from PDF version of article.A novel type of two-dimensional photonic crystal is investigated for it optical properties as a core-shell-type ferroelectric nanorod infiltrated with nematic liquid crystals. Using the plane wave expansion method and finite-difference time-domain method, the photonic crystal structure, which is composed of a photonic crystal in a core-shell-type ferroelectric nanorod, is designed for the square lattice and the hexagonal lattice. It has been used 5CB as a photonic crystal core, and LiNbO3 as a ferroelectric material. The photonic crystal with a core-shell-type LiNbO3 nanorod infiltrated with nematic liquid crystals is compared with the photonic crystal with solid LiNbO3 rods and the photonic crystal with hollow LiNbO3 rods
ALTICORE: an initiative for coastal altimetry
ALTICORE (value-added ALTImetry for COastal REgions) is an international initiative whose main objective is to encourage the operational use of altimetry over coastal areas, by improving the quality and availability of coastal altimetry data. The ALTICORE proposal has recently been submitted for funding to the INTAS scheme (www.intas.be) by a consortium of partners from Italy, France, UK, Russia and Azerbaijan. ALTICORE is also meant as a contribution to the ongoing International Altimeter Service effort.
In this work we will describe the anticipated project stages, namely: 1) improvement of the most widely distributed, 1 Hz, data by analyzing the corrective terms and providing the best solutions, including those derived from appropriate local modelling; 2) development of a set of algorithms to automate quality control and gap-filling functions for the coastal regions; 3) development of testing strategies to ensure a thorough validation of the data.
The improved products will be delivered to ALTICORE users via Grid-compliant technology; this makes it easier to integrate the local data holdings, allows access from a range of services, e.g. directly into model assimilation or GIS systems and should therefore facilitate a widespread and complete assessment of the 1Hz data performance and limitations. We will also outline the design and implementation of the Grid-compliant system for efficient access to distributed archives of data; this consists of regional data centres, each having primary responsibility for regional archives, local corrections and quality control, and operating a set of web-services allowing access to the full functionality of data extraction.
We will conclude by discussing a follow-on phase of the project; this will investigate further improvements on the processing strategy, including the use of higher frequency (10 or 20 Hz) data. Phenomena happen at smaller spatial scales near the coast, so this approach is necessary to match the required resolution. The whole project will hopefully promote the 15-year sea surface height from altimetry to the rank of operational record for the coastal areas
Opening of a pseudogap in a quasi-two dimensional superconductor due to critical thermal fluctuations
We examine the role of the anisotropy of superconducting critical thermal
fluctuations in the opening of a pseudogap in a quasi-two dimensional
superconductor such as a cuprate-oxide high-temperature superconductor. When
the anisotropy between planes and their perpendicular axis is large enough and
its superconducting critical temperature T_c is high enough, the fluctuations
are much developed in its critical region so that lifetime widths of
quasiparticles are large and the energy dependence of the selfenergy deviates
from that of Landau's normal Fermi liquids. A pseudogap opens in such a
critical region because quasiparticle spectra around the chemical potential are
swept away due to the large lifetime widths. The pseudogap never smoothly
evolves into a superconducting gap; it starts to open at a temperature higher
than T_c while the superconducting gap starts to open just at T_c. When T_c is
rather low but the ratio of varepsilon_G(0)/k_BT_c, with varepsilon_G(0) the
superconducting gap at T=0K and k_B the Boltzmann constant, is much larger than
a value about 4 according to the mean-field theory, the pseudogap must be
closing as temperature T approaches to the low T_c because thermal fluctuations
become less developed as T decreases. Critical thermal fluctuations cannot
cause the opening of a prominent pseudogap in an almost isotropic three
dimensional superconductor, even if its T_c is high.Comment: 25 pages, 5 figures (14 subfigures
Energy States of Colored Particle in a Chromomagnetic Field
The unitary transformation, which diagonalizes squared Dirac equation in a
constant chromomagnetic field is found. Applying this transformation, we find
the eigenfunctions of diagonalized Hamiltonian, that describe the states with
definite value of energy and call them energy states. It is pointed out that,
the energy states are determined by the color interaction term of the particle
with the background chromofield and this term is responsible for the splitting
of the energy spectrum.
We construct supercharge operators for the diagonal Hamiltonian, that ensure
the superpartner property of the energy states.Comment: 25 pages, some calculation details have been removed, typos correcte
Structure, bonding and morphology of hydrothermally synthesised xonotlite
The authors have systematically investigated the role of synthesis conditions upon the structure and morphology of xonotlite. Starting with a mechanochemically prepared, semicrystalline phase with Ca/Si=1, the authors have prepared a series of xonotlite samples hydrothermally, at temperatures between 200 and 250 degrees C. Analysis in each case was by X-ray photoelectron spectroscopy, environmental scanning electron microscopy and X-ray diffraction. The authors’ use of a much lower water/solid ratio has indirectly confirmed the ‘through solution’ mechanism of xonotlite formation, where silicate dissolution is a key precursor of xonotlite formation. Concerning the role of temperature, too low a temperature (~200 degrees C) fails to yield xonotlite or leads to increased number of structural defects in the silicate chains of xonotlite and too high a temperature (>250 degrees C) leads to degradation of the xonotlite structure, through leaching of interchain calcium. Synthesis duration meanwhile leads to increased silicate polymerisation due to diminishing of the defects in the silicate chains and more perfect crystal morphologies
Pressure Raman effects and internal stress in network glasses
Raman scattering from binary GexSe1-x glasses under hydrostatic pressure
shows onset of a steady increase in the frequency of modes of corner-sharing
GeSe4 tetrahedral units when the external pressure P exceeds a threshold value
Pc. The threshold pressure Pc(x) decreases with x in the 0.15 < x < 0.20 range,
nearly vanishes in the 0.20 < x < 0.25 range, and then increases in the 0.25 <
x < 1/3 range. These Pc(x) trends closely track those in the non-reversing
enthalpy, DHnr(x), near glass transitions (Tgs), and in particular, both
DHnr(x) and Pc(x) vanish in the reversibility window (0.20 < x < 0.25). It is
suggested that Pc provides a measure of stress at the Raman active units; and
its vanishing in the reversibility window suggests that these units are part of
an isostatically rigid backbone. Isostaticity also accounts for the non-aging
behavior of glasses observed in the reversibility window
Highly stable defective TiO2-x with tuned exposed facets induced by fluorine: Impact of surface and bulk properties on selective UV/visible alcohol photo-oxidation
Titanium dioxide samples were prepared in the presence of different amounts of fluorine via hydrothermal method. It has been found that the presence of fluoride influenced the physico-chemical properties of TiO2 in various ways as polymorphic form stability, surface hydroxylation, generation of hydroxyl radicals under irradiation and formation of Ti3+ centers and oxygen vacancies. The generation rate of [rad]OH radicals was investigated by the photoluminescence technique in the presence of terephthalic acid. X-ray diffractometry indicated that fluorine stabilized the anatase TiO2. X-Ray photoelectron spectroscopy (XPS) revealed the presence of fluorine on the surface and the shift of the valence band edge towards less negative potentials, electron paramagnetic resonance (EPR) confirmed the formation of Ti3+ in the bulk of the photocatalysts, UV–vis spectra showed the extension of the TiO2 photo-response in the visible light region. 2-Propanol degradation and 4-methoxybenzyl alcohol partial oxidation were studied as probe reactions by using the home prepared powders as photocatalysts. Surprisingly, the photocatalytic activity resulted to be mainly affected by [rad]OH radicals formation ability under irradiation, rather than by the presence of {0 0 1} facets, although it cannot be excluded that the latter could influence the ability to form radicals under irradiation
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