The effects of quantum wells number and the built-in polarization on the performance of quaternary AlInGaN UV laser diode

The performance of quaternary Al_0.08In_0.08Ga_0.84N multi-quantum well (MQW) laser diodes (LDs) using the simulation program of Integrated System Engineering Technical Computer Aided design (ISE TCAD) was studied. The simulation results show that the low threshold current, high output power and slope efficiency can be obtained when the quantum wells number is 4. Although, the fourth quantum well which placed in the right side (n-side) of the active region has a negative value of optical gain this means that the optical gain does not occur in this quantum well of laser structure. However, high external differential quantum efficiency (DQE) inside the active region was also observed. Optical gain and intensity were increased when the numbers of quantum wells increase reached 4. The built-in electric field effect inside the quantum well leads to the reduction of the overlap integral between the electrons and holes by separating their wave function was included. As well as, Al_0.25In_0.08Ga_0.67N electron blocking layer (EBL) employed to enhance the performance of Al_0.08In_0.08Ga_0.84N MQW LDs by increasing the optical confinement factor (OCF) inside the quantum wells.     

A Structural Study of Epoxidized Natural Rubber (ENR-50) and Its Cyclic Dithiocarbonate Derivative Using NMR Spectroscopy Techniques

A structural study of epoxidized natural rubber (ENR-50) and its cyclic dithiocarbonate derivative was carried out using NMR spectroscopy techniques. The overlapping ¹H-NMR signals of ENR-50 at δ 1.56, 1.68-1.70, 2.06, 2.15-2.17 ppm were successfully assigned. In this work, the ¹³C-NMR chemical shift assignments of ENR-50 were consistent to the previously reported work. A cyclic dithiocarbonate derivative of ENR-50 was synthesized from the reaction of purified ENR-50 with carbon disulfide (CS₂), in the presence of 4-dimethylaminopyridine (DMAP) as catalyst at reflux temperature. The cyclic dithiocarbonate formation involved the epoxide ring opening of the ENR-50. This was followed by insertion of the C-S moiety of CS₂ at the oxygen attached to the quaternary carbon and methine carbon of epoxidized isoprene unit, respectively. The bands due to the C=S and C-O were clearly observed in the FTIR spectrum while the ¹H-NMR spectrum of the derivative revealed the peak attributed to the methylene protons had split. The ¹³C-NMR spectrum of the derivative further indicates two new carbon peaks arising from the >C=S and quaternary carbon of cyclic dithiocarbonate. All other ¹H- and ¹³C-NMR chemical shifts of the derivative remain unchanged with respect to the ENR-50.     

Preparation, characterization, and theoretical studies of azelaic acid derived from oleic acid by use of a novel ozonolysis method

Environmentally friendly manufacture of organic compounds has been intensively reexamined in recent years. Many excellent methods have been devised to produce organic compounds from renewable resources. Azelaic acid has been produced by ozonolysis of oleic acid. The reaction was performed in a Bach bubbling reactor, with fine bubbles, at high temperature (150 °C) without utilizing any catalyst or any solvent. Yield of the reaction was 20% after 2 h. Production of azelaic acid was confirmed by use of FT-IR and ¹H NMR spectroscopic data and high-performance liquid chromatography of both synthesized and reference azelaic acid. A theoretical study was performed to obtain quantum chemical data for azelaic acid and to optimize the molecule’s geometry.     

Handling equality constraints in evolutionary optimization

Over the last few decades several methods have been proposed for handling functional constraints while solving optimization problems using evolutionary algorithms (EAs). However, the presence of equality constraints makes the feasible space very small compared to the entire search space. As a consequence, the handling of equality constraints has long been a difficult issue for evolutionary optimization methods. This paper presents a Hybrid Evolutionary Algorithm (HEA) for solving optimization problems with both equality and inequality constraints. In HEA, we propose a new local search technique with special emphasis on equality constraints. The basic concept of the new technique is to reach a point on the equality constraint from the current position of an individual solution, and then explore on the constraint landscape. We believe this new concept will influence the future research direction for constrained optimization using population based algorithms. The proposed algorithm is tested on a set of standard benchmark problems. The results show that the proposed technique works very well on those benchmark problems.     

Synthesis, characterization and antimicrobial investigation of mechanochemically processed silver doped ZnO nanoparticles

The application of nanomaterials has gained considerable momentum in various fields in recent years due to their high reactivity, excellent surface properties and quantum effects in the nanometer range. The properties of zinc oxide (ZnO) vary with its crystallite size or particle size and often nanocrystalline ZnO is seen to exhibit superior physical and chemical properties due to their higher surface area and modified electronic structure. ZnO nanoparticles are reported to exhibit strong bacterial inhibiting activity and silver (Ag) has been extensively used for its antimicrobial properties since ages. In this study, Ag doped ZnO nanoparticles were synthesized by mechanochemical processing in a high energy ball mill and investigated for antimicrobial activity. The nanocrystalline nature of zinc oxide was established by X-ray diffraction (XRD) studies. It is seen from the XRD data obtained from the samples, that crystallite size of the zinc oxide nanoparticles is seen to decrease with increasing Ag addition. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) data also supported the nanoparticle formation during the synthesis. The doped nanoparticles were subjected to antimicrobial investigation and found that both increase in Ag content and decrease in particle size contributed significantly towards antimicrobial efficiency. It was also observed that Ag doped ZnO nanoparticles possess enhanced antimicrobial potential than that of virgin ZnO against the studied microorganisms of Escherichia coli and Staphylococcus aureus.     

Modeling the interfacial effect on the yield strength and flow stress of thin metal films on substrates

It is shown in this paper that interfacial effects have a profound impact on the scale-dependent yield strength and strain hardening rates (flow stress) of metallic thin films on elastic substrates. This is achieved by developing a higher-order strain gradient plasticity theory based on the principle of virtual power and the laws of thermodynamics. This theory enforces microscopic boundary conditions at interfaces which relate a microtraction stress to the interfacial energy at the interface. It is shown that the film bulk length scale controls the size effect if a rigid interface is assumed whereas the interfacial length scale dominates if a compliant interface is assumed.     

Micromechanical theoretical and computational modeling of energy dissipation due to nonlinear vibration of hard ceramic coatings with microstructural recursive faults

Engine failures due to high-cycle fatigue during severe dynamic vibration have cost the US Air Force an estimated $400 million dollars per year over the past two decades. Therefore, structural materials that exhibit high damping capacities are desirable for mechanical vibration suppression and acoustic noise attenuation. Few experimental studies suggested that hard ceramic coatings, which are commonly used as thermal barrier coatings (TBCs) to protect engine components from high temperatures and corrosion, can also serve as passive dampers due to their unique microstructure which consists of several layers of splats with inter- and intra-microstructural recursive faults (micro-cracks). Therefore, the focus of this study is on the development of a fundamental understanding of the unique microstructural features and mechanisms responsible for this observed energy dissipation in ceramic coatings under nonlinear vibration through the development of a micromechanical computational framework. Inter- and intra-fatigue damage and internal friction is simulated through the development of thermodynamic-based nonlinear cohesive laws that consider interfacial degradation, debonding, plastic sliding, and Coulomb/contact friction between the interfaces of microstructural faults. Representative volume element-based micromechanical simulations are conducted in order to assess the main micromechanical mechanisms responsible for the experimentally observed nonlinear (amplitude- and frequency-dependent) damping in plasma sprayed hard ceramic coatings. It is concluded that the major part of energy dissipation is achieved through contact friction which results from sliding of the splat interfaces along the microstructural recursive faults. Energy dissipation due to progressive decohesion and evolution of new micro-cracks is not that significant as compared to energy dissipated due to increased friction from existing and new created faults. Therefore, internal friction is the main mechanism that makes TBCs effective dampers.     

Syntheses of some novel imidazolidinethiones and condensed imidazoles containing arylazo moieties starting from cyanothioformamides

Cyclocondensation of cyanothioformamides ( 1 ) with arylhydrazonomalononitriles ( 2 ) afforded the novel imidazole derivatives ( 4a–e ) in good yields. Isothiocyanatoazobenzene ( 6 ) was allowed to react with potassium cyanide and gave the new cyanothioformamide ( 7 ) which was reacted with 4‐chlorophenyl isocyanate to yield imidazolidinethione ( 8 ). Compound ( 8 ) was subjected to react with hydrochloric acid, o‐phenylenediamine, 4‐methylaniline, and hydrogen sulfide and furnished compounds ( 10 ), ( 11 ), ( 12 ), and ( 15 ), respectively. Also, the reactivity of thiohydantoin ( 15 ) toward some electrophilic reagents such as N,N‐dimethylformamide‐dimethylacetal and arylidene‐malononitriles was investigated. The structure of the synthesized compounds was established by analytical and spectral data. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:218–225, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20113     

An alkyl–palladium(II) complex with a bidentate phosphine ligand: [1,3‐bis(di­phenyl­phosphino)­propane‐P,P′]­dimethyl­palladium(II) toluene hemi­solvate

In the title compound, [Pd(CH₃)₂(C₂₇H₂₆P₂)]·0.5C₇H₈, the Pd atom is at the centre of an approximately square‐planar arrangement of two P atoms and two methyl groups. The P—Pd—P angle [93.19 (3)°] is significantly larger than that in the corresponding dichloride complex [Pd(dppp)Cl₂]. The toluene mol­ecule is disordered across an inversion centre.     

Fatty acid hydrazides in heterocyclic synthesis: Synthesis of 1,2‐diazepine and pyridazine derivatives

1,2‐Diazepinone derivatives 6a–d, 8a,b, and 10a–c were synthesized from the reaction of olefines carrying EWG as ethoxymethylene malononitrile, ethoxymethylene cyanoacetate, and tetracyanoethylene with 1a–f respectively. Also, 5‐alkyl‐6‐oxotetrahydropyridazine‐4,4‐dicarboxylate derivatives 12a–c were afforded via the reaction of 1d–f with diethyl ethoxymethylene malonate. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:259–264, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20294