Determination of critical micelle concentration by hyper-Rayleigh scattering

The critical micelle concentration (CMC) of several surfactants that contain an NLO chromophore, either at the hydrocarbon tail, or at the hydrophilic headgroup, or even as a counterion, was determined by hyper-Rayleigh scattering (HRS). In all cases, the HRS signal exhibited a similar variation with surfactant concentration, wherein the CMC is inferred from a rather unprecedented drop in the signal intensity. This drop is attributed to the formation of small pre-micellar aggregates, whose concentrations become negligible above CMC. In addition, a probe molecule, which upon protonation yielded a species with significantly enhanced HRS intensity, was developed and its utility for the determination of the CIVIC of simple fatty acids was demonstrated.

Fluctuation quench and hydrophobic collapse of polymers and biopolymers in water-DMSO binary mixture at low DMSO concentration

Binary mixtures have strong influence on activities of polymers and biopolymers even at low cosolvent concentration. Among the several aqueous binary mixtures studied, water-DMSO especially stands out for its unusual behavior at certain specific concentrations of DMSO. In the present work, we study the effect of water-DMSO binary mixture on polymers and biopolymers by taking a simple linear hydrocarbon chain of intermediate length (n = 30) and the protein lysozyme, respectively. We find that at a mole fraction of 0.05 of DMSO (x(DMSO) = 0.05) in aqueous solution, the hydrocarbon chain adopts the collapsed conformation as the most stable and rigid state. In this case of 0.05 mole fraction of DMSO in bulk, the DMSO concentration in the first hydration layer around the polymer is found to be as large as 17%. Formation of such hydrophobic environment around the polymer is the reason for the collapsed state gaining so much stability. Interestingly, similar quench of conformational fluctuation is also observed for the protein investigated. It is observed that in the case of alkane polymer chains, long wavelength fluctuation gets easily quenched, the polymer being purely hydrophobic. However, in case of the protein, quench of fluctuation is prominent only at the hydrophobic surface, and quench of long wavelength fluctuation becomes insignificant for the full protein. As protein contains both hydrophobic and hydrophilic moieties, the extent of quench of conformational fluctuation with respect to that in pure water is almost half for the biopolymer complex (16.83%) than the same for pure hydrophobic polymer chain (32.43%).

UV Photodetectors Based on ZnO Nanorods: Role of Defect-Concentration

UV photodetectors based on ZnO nanorods prepared by two methods have been fabricated by a simple drop casting procedure. The detectors show good performance at 375 nm giving satisfactory values of responsivity, external quantum efficiency and photoconductive gain. The performance of ZnO nanorods prepared at low temperatures, containing a larger concentration of defects, is found to be superior. (C) 2011 The Japan Society of Applied Physics

Detection and determination of manganese concentration in water using a fiber Bragg grating coupled with nanotechnology

Through this paper we experimentally demonstrate the fabrication of a fiber Bragg grating (FBG) chemical sensor to detect and determine the manganese concentration in water and compare our results with sophisticated spectroscopic methods, such as atomic absorption spectrometry and the inductively coupled plasma method. Here we propose a simple method to develop a thin layer of gold nanoparticles above the etched grating region to enhance the sensitivity of the reflected spectrum of the FBG. By doing so, we achieve a sensitivity of 1.26 nm/parts per million in determining the trace level of Mn in water. Proper reagents are used to detect manganese in water. (C) 2011 Optical Society of America

In-situ measurements of concentration and temperature during transient solidification of aqueous solution of ammonium chloride using laser interferometry

The variation in temperature and concentration plays a crucial role in predicting the final microstructure during solidification of a binary alloy. Most of the experimental techniques used to measure concentration and temperature are intrusive in nature and affect the flow field. In this paper, the main focus is laid on in-situ, non-intrusive, transient measurement of concentration and temperature during the solidification of a binary mixture of aqueous ammonium chloride solution (a metal-analog system) in a top cooled cavity using laser based Mach-Zehnder Interferometric technique. It was found from the interferogram, that the angular deviation of fringe pattern and the total number of fringes exhibit significant sensitivity to refractive index and hence are functions of the local temperature and concentration of the NH4Cl solution inside the cavity. Using the fringe characteristics, calibration curves were established for the range of temperature and concentration levels expected during the solidification process. In the actual solidification experiment, two hypoeutectic solutions (5% and 15% NH4Cl) were chosen. The calibration curves were used to determine the temperature and concentration of the solution inside the cavity during solidification of 5% and 15% NH4Cl solution at different instants of time. The measurement was carried out at a fixed point in the cavity, and the concentration variation with time was recorded as the solid-liquid interface approached the measurement point. The measurement exhibited distinct zones of concentration distribution caused by solute rejection and Rayleigh Benard convection. Further studies involving flow visualization with laser scattering confirmed the Rayleigh Benard convection. Computational modeling was also performed, which corroborated the experimental findings. (C) 2011 Elsevier Ltd. All rights reserved.

Influence of the Methane-Zeolite A Interaction Potential on the Concentration Dependence of Self-diffusivity

Studies on the diffusion of methane in a zeolite structure type LTA (as per IZA nomenclature) have indicated that different types of methane zeolite potentials exist in the literature in which methane is treated within the united-atom model. One set of potentials, referred to as model A, has a methane oxygen diameter of 3.14 angstrom, while another set of potential parameters, model B, employs a larger value of 3.46 angstrom. Fritzsche and co-workers (1993) have shown that these two potentials lead to two distinctly different energetic barriers for the passage of methane through the eight-ring window in the cation-free form of zeolite A. Here, we compute the variation of the self-diffusivity (D) with loading (c) for these two types of potentials and show that this slight variation in the diameter changes the concentration dependence qualitatively: thus, D decreases monotonically with c for model A, while D increases and goes through a maximum before finally decreasing for model B. This effect and the surprising congruence of the diffusion coefficients for both models at high loadings is examined in detail at the molecular level. Simulations for different temperatures reveal the Arrhenius behaviour of the self-diffusion coefficient. The apparent activation energy is found to vary with the loading. We conclude that beside the cage-to-cage jumps, which are essential for the migration of the guest molecules, at high concentrations migration within the cage and guest guest interactions with other molecules become increasingly dominant influences on the diffusion coefficient and make the guest zeolite interaction less important for both model A and model B.

Cd concentration sensor based on fiber grating technology

Fiber Bragg grating (FBG) and Long Period Grating (LPG) chemical sensors are one of the most exciting developments in the field of optical fiber sensors. In this paper we have proposed a simple and effective chemical sensor based on FBG and LPG techniques for detecting the traces of cadmium (Cd) in drinking water at ppm level. The sensitiveness of these two has been compared. Also, these results have been compared with the results obtained by sophisticated spectroscopic atomic absorption and emission spectrometer instruments. For proper designing of FBG to act as a concentration sensor, the cladding region of the grating has been etched using HF solution. We have characterized the FBG concentration sensor sensitivities for different solutions of Cd concentrations varying from 0.01 ppm to 0.04 ppm and observed reflected spectrum in FBG and transmitted spectrum in LPG using Optical Spectrum Analyzer. Proper reagents have been used in the solutions for detection of the Cd species. The overall shift in wavelength is 10 nm in case of LPG and the shift of Bragg wavelength is 0.07 nm in case of FBG for 0.01-0.04 ppm concentrations. (C) 2011 Elsevier B.V. All rights reserved.

Dimethyl sulfoxide induced structural transformations and non-monotonic concentration dependence of conformational fluctuation around active site of lysozyme

Experimental studies have observed significant changes in both structure and function of lysozyme (and other proteins) on addition of a small amount of dimethyl sulfoxide (DMSO) in aqueous solution. Our atomistic molecular dynamic simulations of lysozyme in water-DMSO reveal the following sequence of changes on increasing DMSO concentration. (i) At the initial stage (around 5% DMSO concentration) protein's conformational flexibility gets markedly suppressed. From study of radial distribution functions, we attribute this to the preferential solvation of exposed protein hydrophobic residues by the methyl groups of DMSO. (ii) In the next stage (10-15% DMSO concentration range), lysozome partially unfolds accompanied by an increase both in fluctuation and in exposed protein surface area. (iii) Between 15-20% concentration ranges, both conformational fluctuation and solvent accessible protein surface area suddenly decrease again indicating the formation of an intermediate collapse state. These results are in good agreement with near-UV circular dichroism (CD) and fluorescence studies. We explain this apparently surprising behavior in terms of a structural transformation which involves clustering among the methyl groups of DMSO. (iv) Beyond 20% concentration of DMSO, the protein starts its final sojourn towards the unfolding state with further increase in conformational fluctuation and loss in native contacts. Most importantly, analysis of contact map and fluctuation near the active site reveal that both partial unfolding and conformational fluctuations are centered mostly on the hydrophobic core of active site of lysozyme. Our results could offer a general explanation and universal picture of the anomalous behavior of protein structure-function observed in the presence of cosolvents (DMSO, ethanol, tertiary butyl alcohol, dioxane) at their low concentrations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3694268]

Carrier concentration dependence of donor activation energy in n-type GaN epilayers grown on Si (111) by plasma-assisted MBE

The n-type GaN layers were grown by plasma-assisted MBE and either intentionally doped with Si or unintentionally doped. The optical characteristics of a donor level in Si-doped, GaN were studied in terms of photoluminescence (PL) spectroscopy as a function of electron concentration. Temperature dependent PL measurements allowed us to estimate the activation energy of a Si-related donor from temperature-induced decay of PL intensity. PL peak positions, full width at half maximum of PL and activation energies are found to be proportional to the cube root of carrier density. The involvement of donor levels is supported by the temperature-dependent electron concentration measurements. (C) 2012 Elsevier Ltd. All rights reserved.

Thermo-physical and structural studies of sodium zinc borovanadate glasses in the region of high concentration of modifier oxides

This paper reports investigation of Na2O and ZnO modified borovanadate glasses in the highly modified regime of compositions. These glasses have been prepared by microwave route. Ultraviolet (UV) and visible, infrared (IR), Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and Electron Paramagnetic Resonance (EPR) spectroscopies have been used to characterize the speciation in the glasses. Together with the variation of properties such as molar volume and glass transition temperatures, spectroscopic data indicate that at high levels of modification, ZnO tends to behave like network former. It is proposed that the observed variation of all the properties can be reasonably well understood with a structural model. The model considers that the modification and speciation in glasses are strongly determined by the hierarchy of group electronegativities. Further, it is proposed that the width of the transitions of glasses obtained under same condition reflects the fragility of the glasses. An empirical expression has been suggested to quantify fragility on the basis of width of the transition regions. (C) 2012 Elsevier Ltd. All rights reserved.

Effect of carrier concentration of InN on the transport behavior of InN/GaN heterostructure based Schottky junctions

We present the study involving the dependence of carrier concentration of InN films, grown on GaN templates using the plasma assisted molecular beam epitaxy system, on growth temperature. The influence of InN carrier concentration on the electrical transport behavior of InN/GaN heterostructure based Schottky junctions is also discussed. The optical absorption edge of InN film was found to be strongly dependent on carrier concentration, and was described by Kane's k.p model, with non-parabolic dispersion relation for carrier in the conduction band. The position of the Fermi-level in InN films was modulated by the carrier concentration in the InN films. The barrier height of the heterojunctions as estimated from I-V characteristic was also found to be dependent on the carrier concentration of InN. (C) 2012 Elsevier Ltd. All rights reserved.

Effect of doping concentration on the structural and optical properties of pure and tin doped zinc oxide thin films by nebulizer spray pyrolysis (NSP) technique

Pure and tin doped zinc oxide (Sn:ZnO) thin films were prepared for the first time by NSP technique using aqueous solutions of zinc acetate dehydrate, tin (IV) chloride fendahydrate and methanol. X-ray diffraction patterns confirm that the films are polycrystalline in nature exhibiting hexagonal wurtzite type, with (0 0 2) as preferred orientation. The structural parameters such as lattice constant ('a' and `c'), crystallite size, dislocation density, micro strain, stress and texture coefficient were calculated from X-ray diffraction studies. Surface morphology was found to be modified with increasing Sn doping concentration. The ZnO films have high transmittance 85% in the visible region, and the transmittance is found to be decreased with the increase of Sn doping concentration. The corresponding optical band gap decreases from 3.25 to 3.08 eV. Room temperature photoluminescence reveals the sharp emission of strong UV peak at 400 nm (3.10 eV) and a strong sharp green luminescence at 528 nm (2.34 eV) in the Sn doped ZnO films. The electrical resistivity is found to be 10(6) Omega-cm at higher temperature and 10(5) Omega-cm at lower temperature. (C) 2012 Elsevier Ltd. All rights reserved.

Multi-model climate change projections for India under representative concentration pathways

Climate projections for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) are made using the newly developed representative concentration pathways (RCPs) under the Coupled Model Inter-comparison Project 5 (CMIP5). This article provides multi-model and multi-scenario temperature and precipitation projections for India for the period 1860-2099 based on the new climate data. We find that CMIP5 ensemble mean climate is closer to observed climate than any individual model. The key findings of this study are: (i) under the business-as-usual (between RCP6.0 and RCP8.5) scenario, mean warming in India is likely to be in the range 1.7-2 degrees C by 2030s and 3.3-4.8 degrees C by 2080s relative to pre-industrial times; (ii) all-India precipitation under the business-as-usual scenario is projected to increase from 4% to 5% by 2030s and from 6% to 14% towards the end of the century (2080s) compared to the 1961-1990 baseline; (iii) while precipitation projections are generally less reliable than temperature projections, model agreement in precipitation projections increases from RCP2.6 to RCP8.5, and from short-to long-term projections, indicating that long-term precipitation projections are generally more robust than their short-term counterparts and (iv) there is a consistent positive trend in frequency of extreme precipitation days (e.g. > 40 mm/day) for decades 2060s and beyond. These new climate projections should be used in future assessment of impact of climate change and adaptation planning. There is need to consider not just the mean climate projections, but also the more important extreme projections in impact studies and as well in adaptation planning.

Effect of Li+-dopant on Photoluminescence of Gd2O3:Eu3+Nanophosphor

Li+-doped Gd2O3:Eu3+ phosphors have been studied as potential red phosphors for application to field emission displays. The Li+-doped and undoped Gd2O3:Eu3+ phosphors were synthesized by low temperature solution combustion method. The enhanced luminescence was regarded as the result of the creation of oxygen vacancies due to the Gd3+ sites occupied by Li+ ions, the alteration of the crystal field surrounding the activator Eu3+ ions owing to the incorporation of Li+ into interstial sites. The result in a remarkable increase on photoluminescence and the strong emission was observed at 612 nm by a factor of 4.1 in comparison with that of undoped sample.