Effects of quantum confined stark effect and well thickness on optical properties of double quantum wells violet InGaN laser diodes

The effects of quantum confined stark effect (QCSE) and quantum well (QW) thickness on the optical properties of violet InGaN laser diodes (LDs) have numerically been investigated. The simulation results indicated that the QCSE greatly effects the optical properties of LDs, where QCSE relates to the QW thickness and it increases when the QW thickness is wider which leads to deteriorating of the optical proprieties of the violet InGaN LD. The polarization in the active region of the InGaN LD has been estimated by the blue shift of the wavelength and it is found that the blue shift of the wavelength depends on the QW thickness. The major simulation result has shown that the best properties of violet InGaN LD can be obtained with smaller QW thickness, where more carriers can be restricted, stayed and overlapped inside the QW which leads to a larger stimulated recombination rate and optical material gain which in turn increase the output power of the LD; while decreasing the threshold current of the LD.     

STUDIES IN CYCLODIPHOSPHAZANES. SOME REACTIONS OF HEXACHLOROCYCLO-DIPHOSPHAZANES WITH UREA AND THIOUREA DERIVATIVES

Abstract

Interaction of chlorocyclodiphosphazanes (I) with some bifunctional reagents (such as phenylurea, diphenylurea, thiourea and its phenyl derivatives) in acetonitrile furnished geminal and nongeminal aminocyclodiphosphazanes of type (II–V). The structures of the isolated products were proposed on the basis of microanalytical data, infrared, ultraviolet, ¹H n.m.r., and mass spectra. The mechanism of the nucleophilic substitution is also discussed.     

The Behavior of Certain Coumarins and Furocoumarins Toward Sulfur Reagents

The behavior of 4-hydroxycoumarin (1), 7-hydroxycoumarin (2), 4-hydroxy-bergapten (3), and 4-hydroxyisopimpinellin (4) toward sulfur reagents, namely, thionyl chloride, phosphorus pentasulfide, thiolacetic acid, and Lawesson's reagent (5), was studied. The nature of products in each case depended upon the type of reactants and reaction conditions. Possible reaction mechanisms were considered, and structural elucidations of the new products were based upon compatible elementary and spectroscopic evidences.     

Exact inversion of decomposable interval type-2 fuzzy logic systems

It has been demonstrated that type-2 fuzzy logic systems are much more powerful tools than ordinary (type-1) fuzzy logic systems to represent highly nonlinear and/or uncertain systems. As a consequence, type-2 fuzzy logic systems have been applied in various areas especially in control system design and modelling. In this study, an exact inversion methodology is developed for decomposable interval type-2 fuzzy logic system. In this context, the decomposition property is extended and generalized to interval type-2 fuzzy logic sets. Based on this property, the interval type-2 fuzzy logic system is decomposed into several interval type-2 fuzzy logic subsystems under a certain condition on the input space of the fuzzy logic system. Then, the analytical formulation of the inverse interval type-2 fuzzy logic subsystem output is explicitly driven for certain switching points of the Karnik–Mendel type reduction method. The proposed exact inversion methodology driven for the interval type-2 fuzzy logic subsystem is generalized to the overall interval type-2 fuzzy logic system via the decomposition property. In order to demonstrate the feasibility of the proposed methodology, a simulation study is given where the beneficial sides of the proposed exact inversion methodology are shown clearly.     

QbD approached comparison of reaction mechanism in microwave synthesized gold nanoparticles and their superior catalytic role against hazardous nirto‐dye

Microwave irradiation (MI) process characteristically enables extremely rapid “in‐core” heating of dipoles and ions, in comparison to conventional thermal (conductance) process of heat transfer. During the process of nanoparticles synthesis, MI both modulates functionality behaviors as well as dynamic of reaction in favorable direction. So, MI providing a facile, favorable and alternative approach during nanoparticles synthesis nanoparticles with enhanced catalytic performances. Although, conventionally used reducing and capping reagents of synthetic origin, are usually environmentally hazardous and toxic for living organism. But, in absence of suitable capping agent; stability, shelf life and catalytic activity of metallic nanoparticles adversely affected. However, polymeric templates which emerged as suitable choice of agent for both reducing and capping purposes; bearing additional advantages in terms of catalyst free one step green synthesis process with high degree of biosafety and efficiency. Another aspect of current works was to understand role of process variables in growth mechanism and catalytic performances of microwave processed metallic nanoparticles, as well as comparison of these parameters with conventional heating method. However, due to poor prediction ability with previously published architect OFAT (One factor at a time) design with these nanoparticles as well as random selection of process variables with their different levels, such comparison couldn't be possible. Hence, using gum Ghatti (Anogeissus latifolia) as a model bio‐template and under simulated reaction conditions; architect of QbD design systems were integrated in microwave processed nanoparticles to establish mechanistic role these variables. Furthermore, in comparison to conventional heating; we reported well validated mathematical modeling of process variables on characteristic of nanoparticles as well as synthesized gold nanoparticles of desired and identical dimensions, in both thermal and microwave‐based processes. Interestingly, despite of identical dimension, MI processed gold nanoparticles bearing higher efficiency (kinetic rate) against remediation of hazardous nitro dye (4‐nitrophenol), into safer amino (4‐aminophenol) analogues.     

Synthesis,spectral, DFT calculations and biological studies of solvatochromic copper(II)-ONS hydrazone derived from 2-aminochromone-3-carboxaldehyde

New ONS hydrazone ligand, 2-[(2-aminochromon-3-yl)methylidene]-N-phenylhydrazinecarbothioamide, HL , was synthesized and reacted with different salts of Cu (II) ion (OAc⁻, NO₃⁻, SO₄²⁻ and Cl⁻) in absence and presence of secondary ligands (L′); 8-hydroxyquinoline, 1,10-phenanthroline or SCN⁻; to form binary and ternary Cu(II)-chelates. The ligand and its Cu(II)-complexes were fully characterized by analytical, spectral, thermal, conductivity and magnetic susceptibility measurements. The metal chelates showed octahedral, square planar and /or distorted tetraherdal arrangements. Coats–Redfern equations used to calculate the kinetic parameters of the thermal decomposition stages (E_a, A, ΔH, ΔS and ΔG). The compounds exhibit luminescence property; promising interesting potential applications as photoactive materials. Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet and microscopic solvent polarity parameter and E_T^N correlation methods were applied on the solvatochromic shifts of emission spectra to evaluate the ground (μ_g) and excited (μ_e) states dipole moments. Excited state dipole moment is larger than the ground state which may be attributed to π-π* transition. The coordinating anions play an important role on the position and intensity of emission band. The ligand and its metal complexes showed antimicrobial activity towards Gram–positive bacteria, Gram–negative bacteria, yeast and fungus. The molecular structural parameters of HL and its Cu(II)- complexes have been calculated on the basis of DFT engaged in the Gaussian 09 program at the B3LYP/6-31G(d,p) level; the theoretical data are correlated with the experimental data.     

Unsupervised Pattern Recognition Chemometrics for Distinguishing Different Egyptian Olive Varieties Using a New Integrated Densitometric Reversed-Phase High-Performance Thin-Layer Chromatography—Image Analysis Technique

JPC – Journal of Planar Chromatography – Modern TLC - The merits of chemometrics in categorizing different Egyptian olive chemovarieties based on their compositional integrity were...     

Biochemical Properties of Tyrosinase from Aspergillus terreus and Penicillium copticola; Undecanoic Acid from Aspergillus flavus,an Endophyte of Moringa oleifera,Is a Novel Potent Tyrosinase Inhibitor

Tyrosinase is a copper-containing monooxygenase catalyzing the O-hydroxylation of tyrosine to 3,4-dihydroxyphenylalanine then to dopaquinone that is profoundly involved in melanin synthesis in eukaryotes. Overactivation of tyrosinase is correlated with hyperpigmentation that is metabolically correlated with severe pathological disorders, so, inhibition of this enzyme is the most effective approach in controlling the overproduction of melanin and its hazardous effects. Thus, searching for a powerful, selective inhibitor of human tyrosinase to limit the hyper-synthesis of melanin is a challenge. Unlike the difficulty of overexpression of human tyrosinase, using fungal tyrosinase as a model enzyme to the human one to evaluate the mechanistics of enzyme inhibition in response to various compounds is the most feasible strategy. Thus, the purification of highly catalytic-efficient fungal tyrosinase, exploring a novel inhibitor, and evaluating the mechanistics of enzyme inhibition are the main objectives of this work. Aspergillus terreus and Penicillium copticola were reported as the most potential tyrosinase producers. The biochemical properties suggest that this enzyme displays a higher structural and catalytic proximity to human tyrosinase. Upon nutritional bioprocessing by Plackett–Burman design, the yield of tyrosinase was increased by about 7.5-folds, compared to the control. The purified tyrosinase was strongly inhibited by kojic acid and A. flavus DCM extracts with IC₅₀ values of 15.1 and 12.6 µg/mL, respectively. From the spectroscopic analysis, the main anti-tyrosinase compounds of A. flavus extract was resolved, and verified as undecanoic acid. Further studies are ongoing to unravel the in vivo effect and cytotoxicity of this compound in fungi and human, that could be a novel drug to various diseases associated with hyperpigmentation by melanin.