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61.
B. Bellini M. A. Geday N. Bennis A. Spadło X. Quintana J. M. Otón R. Dąbrowski 《Opto-Electronics Review》2006,14(4):269-273
Liquid crystal (LC) phased arrays and gratings have been employed in optical switching and routing [1]. These diffractive
optic elements are of great interest because they can be scaled up to a large number of elements and their optical properties
can be electrically addressed with a low driving voltage. LC phase gratings have been achieved either by periodic addressing
of pixels or by using periodically-modified structures. The latter approach leads to less reconfigurable devices but the addressing
is simpler.
In this paper we focus on optical phased arrays where the phase is varied either continuously or discretely and where the
periodicity is induced by electrode configuration. We first describe a possible structure based on a conductive silicon wafer.
We argue that this structure can induce either continuously or discretely varying arrays while applying single voltage to
the array. In the second part we simulate the behaviour of such arrays. We base the simulation on a LC synthesized at the
Military University of Technology, this high-birefringence nematic LC shows in a 4-μm thick cell a linear phase shift range
of more than 360° between 1.2 V and 1.8 V. We calculate the distribution of the LC molecule director and assess the performance
of the array with respect to the applied voltage. Finally, the relevance of such technology for switchable phased arrays is
discussed. 相似文献
62.
Synthesis and properties of high tilted antiferroelectric esters with partially fluorinated alkoxyalkoxy terminal chains 总被引:1,自引:1,他引:0
M. Żurowska R. Dąbrowski J. Dziaduszek K. Czupryński K. Skrzypek M. Filipowicz N. Bennis J. M. Otón 《Opto-Electronics Review》2008,16(3):251-256
Novel chiral esters with partially fluorinated alkoxyalkoxy terminal chains are described. Their phase transition temperatures,
enthalpies, and electrooptical properties are reported. A helical pitch in pure compounds and their mixtures based on selective
reflection of light is also characterized. 相似文献
63.
Modelling of liquid crystal displays is useful to predict their optical properties and dynamic behaviour. An integrated modelling system for ferroelectric liquid crystal displays has been developed. The system employs data from real FLC materials, polarizers, glasses, backlights, and colour filters, aiming to describe actual devices accurately. Optical transmission dependence on light wavelength and angle of incidence is obtained as a function of the liquid crystal director profile. This profile is in turn derived from energy minimization of bulk and glass surface conditioning contributions.The above static model has been extended to study sample switching in multiplexed displays. Usual slot times in actual displays are quite close to time response of FLC materials, hence no energy-minimized configurations are obtained upon switching. A dynamic model has been formulated to derive the director profile evolution with time, according to the employed driving scheme, and the rotational viscosity of the material.Predicted dynamic and optical results have been compared to experimental measurements on FLC test cells. It has been found that the behaviour of FLC cells depends on a large number of physical and optical parameters. Some of them may be obtained from FLC data sheets, and manufacturing conditions. Other parameters related to director profiles in relaxed states may be experimentally obtained by sample characterization through optical transmission measurements. A few little known parameters (e.g. specific elastic constants) remain; fortunately their influence on cell dynamics is low. 相似文献
64.
Enrique Otárola 《Numerical Methods for Partial Differential Equations》2020,36(2):302-328
We propose and analyze an a posteriori error estimator for a partial differential equation (PDE)-constrained optimization problem involving a nondifferentiable cost functional, fractional diffusion, and control-constraints. We realize fractional diffusion as the Dirichlet-to-Neumann map for a nonuniformly PDE and propose an equivalent optimal control problem with a local state equation. For such an equivalent problem, we design an a posteriori error estimator which can be defined as the sum of four contributions: two contributions related to the approximation of the state and adjoint equations and two contributions that account for the discretization of the control variable and its associated subgradient. The contributions related to the discretization of the state and adjoint equations rely on anisotropic error estimators in weighted Sobolev spaces. We prove that the proposed a posteriori error estimator is locally efficient and, under suitable assumptions, reliable. We design an adaptive scheme that yields, for the examples that we perform, optimal experimental rates of convergence. 相似文献
65.
Ueveton Pimentel da Silva Gabriela Milane Furlani Antônio Jacinto Demuner Otávio Luis Marques da Silva 《Natural product research》2019,33(18):2681-2684
Euphorbia heterophylla L. is regarded as a major weed worldwide. Its high aggressiveness in agricultural environment prompted us to investigate the allelopatic activity and chemical constitution of extracts from roots of this plant. Hexane extract showed low phytotoxic activity. Methanol extract at 2.0 mg mL?1 inhibited 100% of germination, root and shoot growth of the indicator plants Sorghum bicolor and Lactuca sativa. β-sitosterol, stigmasterol, and esters of lupeol, germanicol, taraxasterol, pseudotaraxasterol, α-amyrin and β-amyrin were isolated from the hexane extract and their structures elucidated on the basis of MS and 1H, 13C and DEPT-135 NMR data. GC-MS analysis of the derivatized methanol extract allowed for identifying a series of allelopathic organic acids potentially involved in allelopathic interactions of E. heterophylla. This is the first study on the allelopathic activity of extracts and identification of metabolites from roots of E. heterophylla. 相似文献
66.
Two new oxabenzochrysenones (naphthoxanthenones), representing phenylphenalenone-related natural products, were isolated from Musa acuminata and Wachendorfia thyrsiflora. 相似文献
67.
M. Artal J. Fernández J. Muñoz Embid I. Velasco S. Otín H. V. Kehiaian 《Journal of solution chemistry》1991,20(1):3-16
Molar excess enthalpies H
E
at 298.15 K and atmospheric pressure were determined for 12 binary liquid mixtures, 1-fluoropentane, 1-fluorohexane, or 1-fluorononane + a non-polar solvent (hexane, cyclohexane, benzene, or tetrachloromethane) and were interpreted by the DISQUAC group contribution model. 1-Fluoroalkane + n-alkane mixtures are characterized by two types of groups or contact surfaces, fluorine (F) and alkane (CH3, CH2), the remaining mixtures by the additional contact surfaces of the solvents (C6H12 C6H6, or CCl4). The interchange energies, entirely dispersive, of the alkane-solvent contacts were determined independently from the study of solvent-alkane mixtures. The dispersive F-alkane parameters were assumed to equal the parameters of perfluoroalkanes + n-alkanes. The shape of the H
E
curves of 1-fluorolkane + polarizable solvent (C6H6, CCl4) mixtures are best reproduced by the model when the quasi-chemical F-solvent parameters are assumed to equal zero. The quasi-chemical F-alkane (the same for n-alkanes and cyclohexane) and the dispersive F-solvent parameters were estimated in this work. The 1-fluoroalkane solutions in C6H6 or CCl4 exhibit the characteristic features of polar solute + polarizable solvent mixtures, viz., the deviations from the ideality are less positive than in alkanes and the experimental H
E
curves are strongly asymmetrical. 相似文献
68.
Isothermal vapor-liquid equilibria (VLE) have been measured for liquid bromochloromethane + heptane or cyclohexane at 25‡C
and 40‡C, and for 1-bromo-chloroethane + heptane or cyclohexane at 40‡C. These experimental results, along with our previous
ones on excess enthalpies, as well as literature data on activity coefficients at infinite dilution, are interpreted in terms
of the DISQUAC group contribution model, and are compared with UNIFAC predictions. 相似文献
69.
Tushar S. Basu Baul Khrawborlang Nongsiej Augustine Lamin Ka‐Ot Santa Ram Joshi Irn Rojas Len Herbert Hpfl 《应用有机金属化学》2019,33(7)
A series of six new Zn (II) compounds, viz., [Zn(HLASA)2(Py)2] ( 1 ), [Zn(HLMASA)2(Py)2] ( 2 ), [Zn(HLMASA)2(4‐MePy)2] ( 3 ), [Zn(HLCASA)2(4‐MePy)2] ( 4 ), [Zn(HLBASA)2(Py)2] ( 5 ), [Zn(HLBASA)2(4‐MePy)2] ( 6 ) and representative Cu (II) and Cd (II) complexes, viz., [Cu(HLASA)2(Py)2(H2O)] ( 7 ) and [Cd(HLBASA)2(Py)3] ( 8 ) [(HLXASA)? = para‐substituted 5‐[(E)‐2‐(aryl)‐1‐diazenyl]‐2‐hydroxybenzoate with X = H (ASA), Me (MASA), Cl (CASA) or Br (BASA); Py = pyridine; 4‐MePy = 4‐methylpyridine] have been synthesized and characterized by spectroscopic techniques and single‐crystal X‐ray diffraction analysis. The structural characterization of the compounds revealed distorted tetrahedral ( 1 – 6 ), square‐pyramidal ( 7 ) and pentagonal‐bipyramidal ( 8 ) coordination geometries around the metal atom, in which the aryl‐substituted diazosalicylate ligands are coordinated only through the oxygen atoms of carboxylate groups, either in an anisobidentate or isobidentate mode; meanwhile, the 2‐hydroxy groups of the monoanionic ligand (HLXASA)? are involved only in intramolecular O‐H···O hydrogen bonds with the carboxylate function. In the crystal structures of 1 – 8 , the complex molecules are assembled by π‐stacking interactions giving mostly infinite 1D strands. The intermolecular binding in the solid state structures is accomplished by diverse additional non‐covalent contacts including C‐H···O, C‐H···N, C‐H···π, C‐H···Br, O···Br, Br···π and van der Waals contacts. Although the primary and secondary ligands in the Zn (II) complex series 1 – 6 carry different substituents at the periphery (X = H, Me, Cl, Br for (HLXASA)? and R = H, Me for 4‐Py‐R), five of the crystal structures were isostructural. Additionally, the antimicrobial activity of the pro‐ligands H2LXASA and their Zn (II), Cu (II) and Cd (II) compounds were studied in a comparative manner, showing high sensitivity (IZD ≥ 20) against Bacillus subtilis. 相似文献
70.
Costa Marlo O. Barbosa Carolina R. Azevedo Hugo M. Machado Gabriel H. Rocha Fernando S. Moreira Antonio S. Rocha Otávio L. 《Journal of Thermal Analysis and Calorimetry》2021,146(5):2059-2071
Journal of Thermal Analysis and Calorimetry - A transient horizontal solidification experiment was performed to investigate the role of the thermal parameters, such as growth and cooling rates (GR... 相似文献