Dielectric and impedance properties of Bi(Zn2/3V1/3)O3 electronic material

A polycrystalline vanadium doped lead free dielectric material of Bi(Zn_2/3V_1/3)O₃ (BZV) has been prepared using a standard high-temperature solid state reaction technique. Its temperature and frequency dependent capacitive, conductive and resistive characteristics are outlined though experimental investigation. The formation of single phase compound of BZV material with orthorhombic crystal symmetry is identified through X-ray diffraction data analysis, and the homogeneous distribution of grains are realized through scanning electron micrograph. The acquaintance of frequency–temperature dependent electrical parameters with the obtained micrograph provides the experimental evidence of contributions of grain as well as grain boundary in its capacitive and resistive characteristics. The negative temperature coefficient of resistance behaviour of the material is revealed from impedance characteristic, and non-Debye type relaxation has been realized from the Nyquist plot. The charge carriers of this electronic compound have both long & short range order that has been validated from the complex modulus and impedance analysis. The prepared electronic material substantiate some important dielectric features which props up the material as promising component for electronic devices.     

Reduced graphene oxide supported gold nanoparticles for electrocatalytic reduction of carbon dioxide

Electrochemical reduction of carbon dioxide is one of the methods which have the capability to recycle CO₂ into valuable products for energy and industrial applications. This research article describes about a new electrocatalyst “reduced graphene oxide supported gold nanoparticles” for selective electrochemical conversion of carbon dioxide to carbon monoxide. The main aim for conversion of CO₂ to CO lies in the fact that the latter is an important component of syn gas (a mixture of hydrogen and carbon monoxide), which is then converted into liquid fuel via well-known industrial process called Fischer-Tropsch process. In this work, we have synthesized different composites of the gold nanoparticles supported on defective reduced graphene oxide to evaluate the catalytic activity of reduced graphene oxide (RGO)-supported gold nanoparticles and the role of defective RGO support towards the electrochemical reduction of CO₂. Electrochemical and impedance measurements demonstrate that higher concentration of gold nanoparticles on the graphene support led to remarkable decrease in the onset potential of 240 mV and increase in the current density for CO₂ reduction. Lower impedance and Tafel slope values also clearly support our findings for the better performance of RGOAu than bare Au for CO₂ reduction.

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Investigation of the effect of varying growth pauses on the structural and optical properties of InAs/GaAs quantum dot heterostructures

Effect of growth pause or ripening time on structural and optical properties of self-assembled InAs/GaAs quantum dot (QD) heterostructures grown by solid state molecular beam epitaxy (MBE ) technique with two different growth rates of InAs (0.032 MLs⁻¹ and 0.197 MLs⁻¹) has been investigated. The QD heterostructures were grown at 520 ^°C with InAs monolayer coverage of 2.7 ML. The results were explained on the basis of high angle annular dark field scanning transmission electron microscope (HAADF-STEM), scanning electron microscope (SEM) and photoluminescence (PL) measurements. Introduction of growth pause leads the QD system towards a thermodynamic equilibrium state which in turn makes interesting changes on the morphology of the samples. Coagulation of some smaller dots occurs because of ripening to produce evolved QDs and the dot density reduces with growth pause.     

Catalytic enantioselective conjugate addition of carbamates

Catalytic, asymmetric conjugate addition of carbamates to enoyl systems has been realized for the first time, providing a two-step access to virtually enantiopure N-protected beta-amino acids.     

The complex of apomyoglobin with the fluorescent dye coumarin 153

Understanding a protein's dielectric response requires both a theoretical model and a well-defined experimental system. The former has already been proposed by Song (J. Chem. Phys. 116, 9359 [2002]). We suggest that the latter is provided by the complex of coumarin 153 (C153) with apomyoglobin (ApoMb). C153 has been exhaustively studied and has proven to be an excellent probe of the solvation dynamics of polar solvents. Myoglobin is one of the most thoroughly studied proteins. Myoglobins from a wide range of species have been subject to X-ray structural analysis and site-directed mutagenesis. Here, we demonstrate the existence of a robust C153-apomyglobin system by means of molecular dynamics simulations, equilibrium binding studies using a Job's plot and capillary electrophoresis, circular dichroism and time-resolved fluorescence. The reorganization energy of C153 bound to ApoMb is compared with that of C153 in bulk solvent using the method of Jordanides et al. (J. Phys. Chem. B 103, 7995 [1999]).     

Regularizing Portfolio Risk Analysis: A Bayesian Approach

It is important for a portfolio manager to estimate and analyze portfolio volatility, to keep the portfolio’s risk within limit. Though the number of financial instruments in the portfolio can be very large, sometimes more than thousands, daily returns considered for analysis are only for a month or even less. In this case rank of portfolio covariance matrix is less than full, hence solution is not unique. It is typically known as the “ill-posed” problem. In this paper we discuss a Bayesian approach to regularize the problem. One of the additional advantages of this approach is to analyze the source of risk by estimating the probability of positive ‘conditional contribution to total risk’ (CCTR). Each source’s CCTR would sum up to the portfolio’s total volatility risk. Existing methods only estimate CCTR of a source, and does not estimate the probability of CCTR to be significantly greater (or less) than zero. This paper presents Bayesian methodology to do so. We propose a simple Monte Carlo (MC) approach to achieve our objective, which can be paralleled. Estimation of various risk measures, such as Value at Risk and Expected Shortfall, becomes a by-product of this Monte-Carlo approach.     

Sulfur ligand mediated electrochemistry of gold surfaces and nanoparticles: What,how, and why

Gold surfaces and gold nanoparticles are widely used. The surfaces and nanoparticles often have to be coated by sulfur-bound organic ligands, which both provide stability and participate in many desired processes. We overview here what, how, and why it is that the core Au-S surface bond offers such versatile structure and function.

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Preparations and Applications of Polysaccharide Based Green Synthesized Metal Nanoparticles: A State-of-the-Art

Green chemistry is the torch bearing field of sustainable research where without use of any toxic chemicals, environment-friendly metal nanoparticles are produced. Advantages of green nanoparticle synthesis over chemical-based synthesis are its nearly zero toxicity with wider applications. As the multidrug resistant species begin to emerge, green synthesized nanoparticles have been arisen as a potent alternative of antimicrobials along with various other applications in diverse fields. The main hindrances behind green synthesis are choice of material and its availability. Because of cheaper cost, wide availability, enhanced effectivity and fewer side effects, polysaccharides have successfully replaced the position of chemical reducing agents in nanoparticle synthesis. Our present review focuses on preparation and applications of polysaccharide based metal nanoparticles; a state-of-the-art research with special emphasis on green synthesized silver nanoparticles as a potent source of emerging antimicrobial.     

Solvation dynamics in protein environments: comparison of fluorescence upconversion measurements of coumarin 153 in monomeric hemeproteins with molecular dynamics simulations

The complexes of the fluorescence probe coumarin 153 with apomyoglobin and apoleghemoglobin are used as model systems to study solvation dynamics in proteins. Time-resolved Stokes shift experiments are compared with molecular dynamics simulations, and very good agreement is obtained. The solvation of the coumarin probe is very rapid with approximately 60% occurring within 300 fs and is attributed to interactions with water (or possibly to the protein itself). Differences in the solvation relaxation (or correlation) function C(t) for the two proteins are attributed to differences in their hemepockets.