Electronic Structure of InN/GaN Quantum Dots: Multimillion-Atom Tight-Binding Simulations

The theoretical calculation of the electronic structure of any constituent materials is the first step toward the interpretation and understanding of experimental data and reliable device design. This is essentially true for nanoscale devices where both the atomistic granularity of the underlying materials and the quantum-mechanical nature of charge carriers play critical roles in determining the overall device performance. In this paper, within a fully atomistic and quantum-mechanical framework, we investigate the electronic structure of wurtzite InN quantum dots (QDs) self-assembled on GaN substrates. The main objectives are threefold: 1) to explore the nature and the role of crystal atomicity, strain field, and piezoelectric and pyroelectric potentials in determining the energy spectrum and the wave functions; 2) to address the redshift in the ground state, the symmetry lowering and the nondegeneracy in the first excited state, and the strong band mixing in the overall conduction-band electronic states, which is a group of interrelated phenomena that has been revealed in recent spectroscopic analyses; and 3) to study the size dependence of the internal fields and its impact on the electronic structure as a whole. We also demonstrate the importance of 3-D atomistic material representation and the need for using realistically extended substrate and cap layers (multimillion-atom modeling) in studying the built-in structural and electric fields in these reduced dimensional QDs. The models used in this study are as follows: 1) valence-force-field Keating model for atomistic strain relaxation; 2) 20-band nearest neighbor sp ³ d ⁵ s* tight-binding model for the calculation of single-particle energy states; and 3) microscopically determined polarization constants in conjunction with an atomistic 3-D Poisson solver for the calculation of piezo- and pyroelectric contributions.     

Influence of Some Hofmeister Anions on the Krafft Temperature and Micelle Formation of Cetylpyridinium Bromide in Aqueous Solution

In this work, the effect of some Hofmeister anions on the Krafft temperature (T_K) and micelle formation of cetylpyridinium bromide (CPB) have been studied. The results show that more chaotropic anions increase, while the less chaotropic ones lower the T_K of the surfactant. More chaotropic I^? and SCN^? form contact ion pairs with the cetylpyridinium ion and reduce the electrostatic repulsion between the CPB molecules. As a result, these ions show salting‐out behavior, with a consequent increase in the T_K. In contrast, less chaotropic Cl^? and NO₃^? increase the activity of free water molecules and enhance hydration of CPB molecules, showing a decrease in the T_K. A rather unusual behavior was observed in the case of SO₄^2? and F^?. These strong kosmotropes shift from their usual position in the Hofmeister series and behave like moderate chaotropes, lowering the T_K of the surfactant. Because of the high charge density and the strong tendency for hydration these ions preferentially remain in the bulk. Rather than forming contact ion pairs, these ions stay away from the CPB molecules, decreasing the T_K of the surfactant. In term of decreasing the T_K, the ions follow the order NO₃^? > SO₄^2? > Cl^? > F^? > Br^? > SCN^? > I^?. The critical micelle concentration (CMC) of the surfactant decreases significantly in the presence of these ions due to the screening of the micelle surface charge by the excess counterions. The decreasing trend of the CMC in the presence of the salts follows the order SCN^? > I^? > SO₄^2? > NO₃^? > Br^? > Cl^? > F^?.     

An Environmentally Benign,Highly Efficient Catalytic Reduction of p‐Nitrophenol using a Nano‐Sized Nickel Catalyst Supported on Silica‐Alumina

A green and effective method is reported for the reduction of p‐nitrophenol to p‐aminophenol using a nano‐sized nickel catalyst supported on silica‐alumina in the presence of hydrazine hydrate as an alternative source of hydrogen. It was found that nickel loaded on a silica‐alumina support is a very effective catalyst in the hydrogenation of p‐nitrophenol to p‐aminophenol. Thus it attained 100% conversion in only 69 seconds instead of 260 seconds for commercial Raney nickel. In addition, the possibility to reuse it more than one time with great efficiency gives it another advantage over commercial Rainey nickel which cannot be used more than once. This economical and environmentally friendly method provides a potentially new approach for the synthesis of the intermediate product of paracetamol in industry, which overcomes the drawbacks of the known reduction methods. The prepared catalysts were fully characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X‐ray (EDX), and electron spin resonance (ESR) tehniques.     

Coplanar Waveguide Fed Printed Antenna with Compact Size for Broadband Wireless Applications

A novel and simple coplanar waveguide fed compact antenna is introduced in this paper. The antenna structure combines the advantages of CPW with those of the broadband antenna and simplifies the structure of the antenna by reducing the number of metallization level to construct uni-planar antenna. Prototype of the proposed antenna have been constructed and studied experimentally. The measured results agrees well with the simulated prediction and shows a broad bandwidth of 6 GHz ranging from 3.5 GHz to 9.5 GHz with VSWR ≤2 (return loss ≤−10 dB), which is equivalent to 92.3% impedance bandwidth centered at 6.5 GHz. The proposed antenna shows stable radiation characteristics, gain and axial ratio of less than 1 dB over the whole operating bandwidth. Furthermore, an extensive parametric study was performed to realize the relationship between the resonance frequencies of the broadband antennas and different parameters which is helpful for advancement of the antenna design.     

A new equivalent circuit for inverters and its application for the determination of coupling matrix elements of narrow RF bandpass filters

A new equivalent circuit for inverters is presented. Using this circuit, expression for the elements of the coupling matrix of narrow RF band pass filters is derived. The derivation is based on frequency independent coupling assumed in the synthesis of narrow RF band pass filters. Our expression is different from an earlier expression obtained using lumped circuit representations of different types of coupling and their analysis. It is shown that the earlier expression can be derived from our analysis if the coupling is assumed frequency‐variant. Unlike earlier work, our derivation shows how the sign of the coupling coefficient can be obtained. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2010.     

The impact of online brand community characteristics on customer engagement: An application of Stimulus-Organism-Response paradigm

The advent of interactive digital platforms has led people to progressively interact on such platforms, urging organizations to create online communities to engage customers with them and with each other to enhance brand loyalty. This study attempts to investigate what motivates customers to engage in these brand communities. Through a questionnaire survey of 430 Facebook users, this study investigates whether and how the unique characteristics (information quality, system quality, virtual interactivity, and rewards) of online brand communities affect customer engagement. The consequent effect of customer engagement on brand loyalty is also examined. This study frames and empirically validates a model for engaging customers with online brand communities on Facebook, considering the moderating role of gender. The Stimulus-Organism-Response paradigm is solicited to justify the theoretical background of this study. The data were analyzed using structure equation modelling. Results reveal that each of the characteristics positively influences customer engagement, with information quality and virtual interactivity bearing the strongest influence. Customer engagement also exhibits a strong positive impact on brand loyalty. This results further reveal that gender gap in the online environment is declining as the impact of all the four characteristics of online brand communities on customer engagement was invariable across male and female members.     

Design and synthesis of non-steroidal diclofenac derivatives as anti-inflammatory drugs

In the course of our studies directed towards the discovery of novel non-steroidal anti-inflammatory agents (NSAIDs), which are expected to have improved drug efficacy and better toxicity profile than diclofenac, we have synthesized new derivatives of diclofenac phosphonates. These phosphonate analogs were efficiently prepared from commercially available 2-hydroxymethylaniline in three steps. The 2-hydroxymethylaniline was converted to the azide in reasonable yield. Click chemistry with a variety of alkynes followed by Arbuzov reaction resulted in a series of triazole based phosphonate products. Our inhibitors are designed to reduce the gastrointestinal bleeding caused by diclofenac by substituting the carboxylic acid group with the phosphonate group and in addition replacing with the triazole ring would allow the flexibility to explore the importance of both hydrophilicity and hydrophobicity of the ring at the active site.