Design and analysis of a tunable liquid crystal switch/filter with metallic nano-slits

We present a tunable device with wavelength switching/filtering features using periodic metallic nano-slits integrated with a nematic liquid crystal layer. Electrical tunability is a result of the presence of nematic liquid crystal in the cavity of a device. Resonant wavelength can be fine-tuned in 94-nm intervals by controlling the bias voltage. The present study shows that the performance of the device is dependent strongly on the geometry of nano-slits. Through the optimization of parameters, 23 dB ON–OFF ratio is achieved, which is better compared to other solutions. These characteristics can be used in switching/filtering applications at near-infrared optical communication systems. In addition, the dependence of reflectance spectrum on incident angle suggests that an application is a tunable optical filter for this device.     

A new monitor model to detect damages in surface and subsurface during cup grinding process of BK7 optical glass: a new optimization model for energy damage

Journal of Thermal Analysis and Calorimetry - Grinding is known as the most widely used method of forming borosilicate optical glass (BK7). Due to the brittle nature of the BK7 glass, the...     

Estimation of mechanical properties of LDPE/LLDPE/SEBS nanocomposite reinforced with calcium carbonate nanoparticles by Ch mathematical model

Journal of Thermal Analysis and Calorimetry - Doing experiments in order to determine mechanical properties of nanocomposites costs a lot. Therefore, finding the ways by which the properties of the...     

Dynamic analysis of a novel wide-tunable microbeam resonator with a sliding free-of-charge electrode

In this paper, a MEMS-based resonator with a novel effective stiffness tunability is presented. The performance of the proposed resonator is based on the transversal vibration of the two porous cantilever microbeams with a rectangular microplate at the end of the structure. The microplate as a free-of-charge slider electrode is in contact with two other fixed substrate electrodes via the thin layer of dielectric material. Applying a constant DC voltage to the two fixed electrodes leads to the movement of free electrons in the slider and eventually to the formation of two series capacitors. As a result, the slider meets a nonlinear electrostatic force proportional to the square of the applied DC voltage. It will act as a nonlinear spring with a tunable stiffness during the oscillation of the resonator. The coupled nonlinear equations governing the longitudinal and transversal vibration of the resonator are extracted in the presence of the nonlinear voltage-sliding spring. Its steady-state solution is obtained based on a physically based learning method that makes it possible to obtain frequency response for the first harmony as well as for the higher harmonies and to predict primary and secondary resonances in different harmonies of the response. The effect of the applied tuning DC voltage, the geometrical parameters of the resonator, and the cantilever's porosity on the dynamic response of the resonator are investigated. It is shown that the tuning stiffness of this voltage-sliding spring provides a highly effective solution to realize an extreme tunable range. In the end, a modified tunable structure is introduced in which the folded beams are replaced with common ones. The modified resonator by making the nonlinear behavior of the resonator least can improve its performance significantly.

     

Synthesis,spectroscopic characterization,crystal structure and thermal analyses of two zinc(II) complexes with methanolysis of 2-pyridinecarbonitrile as a chelating ligand

Zinc(II) complexes, [Zn(MPCA)₃][ZnCl₄] (1) and [Zn(MPCA)₃][ZnBr₄] (2) (where MPCA is O-methylpyridine-2-carboximidate), were synthesized from the reaction of ZnCl₂ and ZnBr₂ with 2-pyridinecarbonitrile in methanol, respectively. Both complexes were thoroughly characterized by elemental analysis, thermogravimetric analysis, differential thermal analysis and IR, UV–Vis, ¹H NMR spectroscopy, and their structures have been determined by the single-crystal X-ray diffraction. The spectroscopic investigations and X-ray structural analysis indicated that in both complexes, the nitrile group of ligand has been methoximation in methanol solvent in the presence of zinc(II) salts. The luminescence spectra of both complexes show that the intensity of their emission bands is stronger than that of the bands for the free O-methylpyridine-2-carboximidate ligands.     

A fluorescence detection scheme for ultra large molecules after gas phase separation

A system was proposed to remove the upper mass limitation of mass spectrometry. In present study, ultra large molecules were separated in the gas phase by mass analyzer after electrospray ionization. Instead of conventional detection with electron multiplier, a laser-induced-fluorescence detection scheme was applied. The instrument sensitivity is independent of molecular weight, but related to the spectroscopic properties of the fluorophores presented by the large biomolecules.     

Multiscale Computational Study on the Adsorption and Separation of CO2/CH4 and CO2/H2 on Li+‐Doped Mixed‐Ligand Metal–Organic Framework Zn2(NDC)2(diPyNI)

The quantum mechanics (QM) method and grand canonical Monte Carlo (GCMC) simulations are used to study the effect of lithium cation doping on the adsorption and separation of CO₂, CH₄, and H₂ on a twofold interwoven metal–organic framework (MOF), Zn₂(NDC)₂(diPyNI) (NDC=2,6‐naphthalenedicarboxylate; diPyNI=N,N′‐di‐(4‐pyridyl)‐1,4,5,8‐naphthalenetetracarboxydiimide). Second‐order Moller–Plesset (MP2) calculations on the (Li⁺–diPyNI) cluster model show that the energetically most favorable lithium binding site is above the pyridine ring side at a distance of 1.817 Å from the oxygen atom. The results reveal that the adsorption capacity of Zn₂(NDC)₂(diPyNI) for carbon dioxide is higher than those of hydrogen and methane at room temperature. Furthermore, GCMC simulations on the structures obtained from QM calculations predict that the Li⁺‐doped MOF has higher adsorption capacities than the nondoped MOF, especially at low pressures. In addition, the probability density distribution plots reveal that CO₂, CH₄, and H₂ molecules accumulate close to the Li cation site. The selectivity results indicate that CO₂/H₂ selectivity values in Zn₂(NDC)₂(diPyNI) are higher than those of CO₂/CH₄. The selectivity of CO₂ over CH₄ on Li⁺‐doped Zn₂(NDC)₂(diPyNI) is improved relative to the nondoped MOF.     

Preparation of 1,2,4,5‐tetrasubstituted imidazoles over magnetic core–shell titanium dioxide nanoparticles

Magnetic core–shell titanium dioxide nanoparticles (Fe₃O₄@SiO₂@TiO₂) were applied for the efficient preparation of 1,2,4,5‐tetrasubstituted imidazole derivatives by the one‐pot multi‐component condensation of benzil with aldehydes, primary amines and ammonium acetate under solvent‐free conditions. The catalyst was synthesized and studied using several techniques including X‐ray diffraction, transmission electron microscopy, field‐emission scanning electron microscopy and energy‐dispersive X‐ray spectroscopy. Copyright © 2016 John Wiley & Sons, Ltd.     

2-D Simulation and New Structures of Heterojunction Phototransistor for Higher Optical Amplification in Optoelectronic Integrated Devices

The improvement of optical gain is an important priority for performance design in most of optoelectronic integrated devices (OEIDS). A two-dimensional simulator is developed for the rigorous analysis and optimum design of devices. With it, we analyze the characteristics of heterojunction phototransistor (HPT) which acts as a light-detector in OEID, and we propose new structures of HPT to increase the conversion gain without much increase in dark current. Then, the simulation of an OEID composed of an HPT integrated over a light-emitting diode (LED) is implemented, and it is shown that the new structures significantly improve the optical amplification for low input light power over the conventional structure.Presented at the International Commission for Optics Topical Meeting, Kyoto, 1994.