Defect structures in metallic photonic crystals

Cataloged from PDF version of article.We have investigated metallic photonic crystals built around a layer‐by‐layer geometry. Two different crystal structures (face‐centered‐tetragonal and tetragonal) were built and their properties were compared. We obtained rejection rates of 7–8 dB per layer from both metallic crystals. Defect modes created by removing rods resulted in high peak transmission (80%), and high quality factors (1740). Our measurements were in good agreement with theoretical simulations. © 1996 American Institute of Physic

Distribution of mast cells in lung tissues of rats exposed to biomass smoke

This study was designed to evaluate the distribution of mast cells in the lung tissues of rats exposed to biomass  smoke. Fifty six female Wistar albino adult rats were used. They were divided into two experimental groups  (control and biomass smoke-treated), each containing 28 animals. Control rats were not exposed to the  biomass smoke at any time during the experiment. Rats in the treatment group were exposed daily (one hour)  to biomass smoke for 3, 6 or 9 months. Lung tissues samples were obtained under deep anesthesia from the  randomly selected 7 animals in both groups. Lung tissues were fixed in Mota’s fixative (BLA) for 24 h and  embedded in paraffin. Sections of 6 μm thickness were cut and stained with 0.5% toluidine blue in 0.5 N  hydrochloric acid at pH 0.5 for 30 min. The numbers of mast cell in lung tissues of the animals exposed to  the biomass for 6 or 9 months were significantly (P<0.05) higher than controls. This study showed that long  term exposure to biomass smoke was associated with the increased number of mast cells in the lung.

Plasmonic enhanced terahertz time-domain spectroscopy system for identification of common explosives

In this study, we present a classification algorithm for terahertz time-domain spectroscopy systems (THz-TDS) that can be trained to identify most commonly used explosives (C4, HMX, RDX, PETN, TNT, composition-B and blackpowder) and some non-explosive samples (lactose, sucrose, PABA). Our procedure can be used in any THz-TDS system that detects either transmission or reflection spectra at room conditions. After preprocessing the signal in low THz regime (0.1-3 THz), our algorithm takes advantages of a latent space transformation based on principle component analysis in order to classify explosives with low false alarm rate. © 2017 SPIE

Planar indium tin oxide heater for improved thermal distribution for metal oxide micromachined gas sensors

Metal oxide gas sensors with integrated micro-hotplate structures are widely used in the industry and they are still being investigated and developed. Metal oxide gas sensors have the advantage of being sensitive to a wide range of organic and inorganic volatile compounds, although they lack selectivity. To introduce selectivity, the operating temperature of a single sensor is swept, and the measurements are fed to a discriminating algorithm. The efficiency of those data processing methods strongly depends on temperature uniformity across the active area of the sensor. To achieve this, hot plate structures with complex resistor geometries have been designed and additional heat-spreading structures have been introduced. In this work we designed and fabricated a metal oxide gas sensor integrated with a simple square planar indium tin oxide (ITO) heating element, by using conventional micromachining and thin-film deposition techniques. Power consumption-dependent surface temperature measurements were performed. A 420 °C working temperature was achieved at 120 mW power consumption. Temperature distribution uniformity was measured and a 17 °C difference between the hottest and the coldest points of the sensor at an operating temperature of 290 °C was achieved. Transient heat-up and cool-down cycle durations are measured as 40 ms and 20 ms, respectively. © 2016 by the authors; licensee MDPI, Basel, Switzerland

Enhanced electro-optic modulation of LiNbO3-based photonic crystal cavities with dual mode and polarization operation

A high output transmission and high quality factor, compact LiNbO3 -based Fabry-Perot-type photonic crystal cavity is reported that can be used in electro-optical modulators at optical communication wavelengths. The electro-optic effect is 123 times enhanced as compared to the bulk material as a result of the slow light effect. The transmission wavelength is found to depend linearly on the applied voltage with 1.2 nm/V modulation sensitivity. Moreover, an externally switchable dual mode regime with high quality factors and transmissions is realized. High transmissions and high quality factors are also obtained for both transverse-electric and transverse-magnetic polarizations simultaneously. © 2017 TÜBITAK

Robust flow control in data-communication networks with multiple time-delays

Robust controller design for a flow control problem where uncertain multiple time-varying time-delays exist is considered. Although primarily data-communication networks are considered, the presented approach can also be applied to other flow control problems and can even be extended to other control problems where uncertain multiple time-varying time-delays exist. Besides robustness, tracking and fairness requirements are also considered. To solve this problem, an H∞ optimization problem is set up and solved. Unlike previous approaches, where only a suboptimal solution could be found, the present approach allows to design an optimal controller. Simulation studies are carried out in order to illustrate the time-domain performance of the designed controllers. The obtained results are also compared to the results of a suboptimal controller obtained by an earlier approach. Copyright © 2009 John Wiley & Sons, Ltd

Electronic properties of Li-doped zigzag graphene nanoribbons

Zigzag graphene nanoribbons (ZGNRs) are known to exhibit metallic behavior. Depending on structural properties such as edge status, doping and width of nanoribbons, the electronic properties of these structures may vary. In this study, changes in electronic properties of crystal by doping Lithium (Li) atom to ZGNR structure are analyzed. In spin polarized calculations are made using Density Functional Theory (DFT) with generalized gradient approximation (GGA) as exchange correlation. As a result of calculations, it has been determined that Li atom affects electronic properties of ZGNR structure significantly. It is observed that ZGNR structure exhibiting metallic behavior in pure state shows half-metal and semiconductor behavior with Li atom. © 2016 Elsevier B.V

Structural analysis of an InGaN/GaN based light emitting diode by X-ray diffraction

The important structural characteristics of hexagonal GaN in an InGaN/GaN multi quantum well, which was aimed to make a light emitted diode and was grown by metalorganic chemical vapor deposition on c-plain sapphire, are determined by using nondestructive high-resolution X-ray diffraction in detail. The distorted GaN layers were described as mosaic crystals characterized by vertical and lateral coherence lengths, a mean tilt, twist, screw and edge type threading dislocation densities. The rocking curves of symmetric (00.l) reflections were used to determine the tilt angle, while the twist angle was an extrapolated grown ω-scan for an asymmetric (hk.l) Bragg reflection with an h or k nonzero. Moreover, it is an important result that the mosaic structure was analyzed from a different (10.l) crystal direction that was the angular inclined plane to the z-axis. The mosaic structure parameters were obtained in an approximately defined ratio depending on the inclination or polar angle of the sample. © 2009 Springer Science+Business Media, LLC

Poisson CNN: Convolutional neural networks for the solution of the Poisson equation on a Cartesian mesh

Abstract The Poisson equation is commonly encountered in engineering, for instance, in computational fluid dynamics (CFD) where it is needed to compute corrections to the pressure field to ensure the incompressibility of the velocity field. In the present work, we propose a novel fully convolutional neural network (CNN) architecture to infer the solution of the Poisson equation on a 2D Cartesian grid with different resolutions given the right-hand side term, arbitrary boundary conditions, and grid parameters. It provides unprecedented versatility for a CNN approach dealing with partial differential equations. The boundary conditions are handled using a novel approach by decomposing the original Poisson problem into a homogeneous Poisson problem plus four inhomogeneous Laplace subproblems. The model is trained using a novel loss function approximating the continuous ${L}^p$ norm between the prediction and the target. Even when predicting on grids denser than previously encountered, our model demonstrates encouraging capacity to reproduce the correct solution profile. The proposed model, which outperforms well-known neural network models, can be included in a CFD solver to help with solving the Poisson equation. Analytical test cases indicate that our CNN architecture is capable of predicting the correct solution of a Poisson problem with mean percentage errors below 10%, an improvement by comparison to the first step of conventional iterative methods. Predictions from our model, used as the initial guess to iterative algorithms like Multigrid, can reduce the root mean square error after a single iteration by more than 90% compared to a zero initial guess.</jats:p

Effect of substitutional As impurity on electrical and optical properties of β-Si3N4 structure

β-Si3N4 is used as the gate dielectric for surface passivation in GaN-based, high-electron mobility transistors(HEMTs). In this study, the electrical and optical characteristics of the hexagonal β-Si3N4 crystal structure were calculated using density functional theory (DFT) and local-density approximation (LDA). Calculations of the electronic band structure and the density of states (DOS) were made for the pure β-Si3N4 crystal structure and the β-Si3N4 crystal doped with an arsenic (As) impurity atom. In addition, the optical properties such as the static dielectric constant, refractive index, extinction coefficient, absorption coefficient and reflection coefficient were examined depending on the photon energy. As a result of these calculations, it was observed that the As impurity atom drastically changed the electrical and optical properties of the pure β-Si3N4 crystalline structure, and improvements are suggested for potential further studies. © 2016 Elsevier Ltd. All rights reserved