beta-Turn Analogues in Model a ss-Hybrid Peptides: Structural Characterization of Peptides Containing ss 2,2Ac6c and ss 3,3Ac6c Residues

The effect of gem-dialkyl substituents on the backbone conformations of beta-amino acid residues in peptides has been investigated by using four model peptides: Boc-Xxx-beta 2,2Ac6c(1-aminomethylcyclohexanecarboxylic acid)-NHMe (Xxx=Leu (1), Phe (2); Boc=tert-butyloxycarbonyl) and Boc-Xxx-beta 3,3Ac6c(1-aminocyclohexaneacetic acid)-NHMe (Xxx=Leu (3), Phe (4)). Tetrasubstituted carbon atoms restrict the ranges of stereochemically allowed conformations about flanking single bonds. The crystal structure of Boc-Leu-beta 2,2Ac6c-NHMe (1) established a C11 hydrogen-bonded turn in the a beta-hybrid sequence. The observed torsion angles (a(similar to-60 degrees, similar to-30 degrees), beta(similar to-90 degrees, similar to 60 degrees, similar to-90 degrees)) corresponded to a C11 helical turn, which was a backbone-expanded analogue of the type III beta turn in aa sequences. The crystal structure of the peptide Boc-Phe-beta 3,3Ac6c-NHMe (4) established a C11 hydrogen-bonded turn with distinctly different backbone torsion angles (a(similar to-60 degrees, similar to 120 degrees), beta(similar to 60 degrees, ?60 degrees, similar to-60 degrees)), which corresponded to a backbone-expanded analogue of the type II beta turn observed in aa sequences. In peptide 4, the two molecules in the asymmetric unit adopted backbone torsion angles of opposite signs. In one of the molecules, the Phe residue adopted an unfavorable backbone conformation, with the energetic penalty being offset by a favorable aromatic interaction between proximal molecules in the crystal. NMR spectroscopy studies provided evidence for the maintenance of folded structures in solution in these a beta-hybrid sequences.

Study of n-ZnO/p-Si (100) thin film heterojunctions by pulsed laser deposition without buffer layer

ZnO/Si heterojunctions were fabricated by growing ZnO thin films on p-type Si (100) substrate by pulsed laser deposition without buffer layers. The crystallinity of the heterojunction was analyzed by high resolution X-ray diffraction and atomic force microscopy. The optical quality of the film was analyzed by room temperature (RT) photoluminescence measurements. The high intense band to band emission confirmed the high quality of the ZnO thin films on Si. The electrical properties of the junction were studied by temperature dependent current-voltage measurements and RT capacitance-voltage (C-V) analysis. The charge carrier concentration and the barrier height (BH) were calculated, to be 5.6x10(19) cm(-3) and 0.6 eV respectively from the C-V plot. The BH and ideality factor, calculated using the thermionic emission (TE) model, were found to be highly temperature dependent. We observed a much lower value in Richardson constant, 5.19x10(-7)A/cm(2) K-2 than the theoretical value (32 A/cm(2) K-2) for ZnO. This analysis revealed the existence of a Gaussian distribution (GD) with a standard deviation of sigma(2)=0.035 V. By implementing the GD to the TE, the values of BH and Richardson constant were obtained as 1.3 eV and 39.97 A/cm(2) K-2 respectively from the modified Richardson plot. The obtained Richardson constant value is close to the theoretical value for n-ZnO. These high quality heterojunctions can be used for solar cell applications. (C) 2012 Elsevier B.V. All rights reserved.

Current transport in nonpolar a-plane InN/GaN eterostructures Schottky junction

The temperature dependent current transport properties of nonpolar a-plane (11 2 0) InN/GaN heterostructure Schottky junction were investigated. The barrier height ( b) and ideally factor (η) estimated from the thermionic emission (TE) model were found to be temperature dependent in nature. The conventional Richardson plot of the ln(I s/T 2) versus 1/kT has two regions: the first region (150-300 K) and the second region (350-500 K). The values of Richardson constant (A +) obtained from this plot are found to be lower than the theoretical value of n-type GaN. The variation in the barrier heights was explained by a double Gaussian distribution with mean barrier height values ( b ) of 1.17 and 0.69 eV with standard deviation (� s) of 0.17 and 0.098 V, respectively. The modified Richardson plot in the temperature range 350-500 K gives the Richardson constant which is close to the theoretical value of n-type GaN. Hence, the current mechanism is explained by TE by assuming the Gaussian distribution of barrier height. At low temperature 150-300 K, the absence of temperature dependent tunneling parameters indicates the tunneling assisted current transport mechanism. © 2012 American Institute of Physics.

Analysis of the temperature-dependent current-voltage characteristics and the barrier-height inhomogeneities of Au/GaN Schottky diodes

In this report, the currentvoltage (IV) characteristics of Au/GaN Schottky diodes have been carried out in the temperature range of 300510?K. The estimated values of the Schottky-barrier height (SBH) and the ideality factor of the diodes based on the thermionic emission (TE) mechanism were found to be temperature dependent. The barrier height was found to increase and the ideality factor to decrease with increasing temperature. The conventional Richardson plot of ln(Is/T2) versus 1/kT gives the SBH of 0.51?eV and Richardson constant value of 3.23?X?10-5?A?cm-2?K-2 which is much lower than the known value of 26.4?A?cm-2?K-2 for GaN. Such discrepancies of the SBH and Richardson constant value were attributed to the existence of barrier-height inhomogeneities at the Au/GaN interface. The modified Richardson plot of ln(Is/T2)q2 sigma 2/2k2T2 versus q/kT, by assuming a Gaussian distribution of barrier heights at the Au/GaN interface, provided the SBH of 1.47?eV and Richardson constant value of 38.8?A?cm-2?K-2. The temperature dependence of the barrier height is interpreted on the basis of existence of the Gaussian distribution of the barrier heights due to the barrier-height inhomogeneities at the Au/GaN interface.

Short- and long-term temporal variations in salinity and the oxygen, carbon and hydrogen isotopic compositions of the Hooghly Estuary water, India

The Hooghly River estuary provides a unique experimental site to understand the effect of monsoonal river discharge on freshwater and seawater mixing. Water samples collected bi-weekly for a duration of 17 months were analyzed for salinity, delta O-18,delta C-13(DIC), as well as delta D to investigate the differential mixing of freshwater and seawater. The differences in salinity and delta O-18 of samples collected during low and high tides on the same day are strongly correlated suggesting a well mixed water column at our sampling site. Low salinity and depleted delta O-18 during monsoon is consistent with increased river discharge as well as high rainfall. We identified different slopes in a delta O-18 versus salinity plot for the estuary water samples collected during monsoon and non-monsoon seasons. This is driven by composition of the freshwater source which is dominated by rainwater during monsoon and rivers during non-monsoon months. Selected delta D analyses of samples indicate that groundwater contributes significantly to the Hooghly Estuary during low rainfall times of the year. delta C-13(DIC) measured in the water recorded low values towards the end of monsoon indicating low productivity (i.e. increased organic respiration) while progressively increasing delta C-13(DIC) values from October till January as well as during some of the pre-monsoon months can be explained by increasing productivity. Very low delta C-13(DIC) (similar to-20%0) suggests involvement of carbon derived from anaerobic oxidation of organics and/or methane with potential contribution from increased anthropogenic water supply. An estimate of seawater incursion into the Hooghly Estuary at different times of the year is obtained by using salinity data in a two-component mixing model. Presence of seawater was found maximum (31-37%) during February till July and lowest (less than or equal to 6%) from September till November. We notice a temporal offset between Ganges River discharge farther upstream at Farakka and salinity variation at the Hooghly Estuary. We believe that this time lag is a result of the physical distance between Farakka and Kakdweep (our sampling location) and put constraints on the travel time of river water during early monsoon. (c) 2012 Published by Elsevier B.V.

Nanostructured Pd modified Ni/CeO2 catalyst for water gas shift and catalytic hydrogen combustion reaction

Nanostructured Pd-modified Ni/CeO2 catalyst was synthesized in a single step by solution combustion method and characterized by XRD, TEM, XPS, TPR and BET surface analyzer techniques. The catalytic performance of this compound was investigated by performing the water gas shift (WGS) and catalytic hydrogen combustion (CHC) reaction. The present compound is highly active and selective (100%) toward H-2 production for the WGS reaction. A lack of CO methanation activity is an important finding of present study and this is attributed to the ionic substitution of Pd and Ni species in CeO2. The creation of oxide vacancies due to ionic substitution of aliovalent ions induces dissociation of H2O that is responsible for the improved catalytic activity for WGS reaction. The combined H-2-TPR and XPS results show a synergism exists among Pd, Ni and ceria support. The redox reaction mechanism was used to correlate experimental data for the WGS reaction and a mechanism involving the interaction of adsorbed H-2 and O-2 through the hydroxyl species was proposed for CHC reaction. The parity plot shows a good correspondence between the experimental and predicted reaction rates. (c) 2012 Elsevier B.V. All rights reserved.

Performance of established native seedlings in relation to invasive Lantana camara, rainfall and species' habitat preferences in a seasonally dry tropical forest

Native species' response to the presence of invasive species is context specific. This response cannot be studied in isolation from the prevailing environmental stresses in invaded habitats such as seasonal drought. We investigated the combined effects of an invasive shrub Lantana camara L. (lantana), seasonal rainfall and species' microsite preferences on the growth and survival of 1,105 naturally established seedlings of native trees and shrubs in a seasonally dry tropical forest. Individuals were followed from April 2008 to February 2010, and growth and survival measured in relation to lantana density, seasonality of rainfall and species characteristics in a 50-ha permanent forest plot located in Mudumalai, southern India. We used a mixed effects modelling approach to examine seedling growth and generalized linear models to examine seedling survival. The overall relative height growth rate of established seedlings was found to be very low irrespective of the presence or absence of dense lantana. 22-month growth rate of dry forest species was lower under dense lantana while moist forest species were not affected by the presence of lantana thickets. 4-month growth rates of all species increased with increasing inter-census rainfall. Community results may be influenced by responses of the most abundant species, Catunaregam spinosa, whose growth rates were always lower under dense lantana. Overall seedling survival was high, increased with increasing rainfall and was higher for species with dry forest preference than for species with moist forest preference. The high survival rates of naturally established seedlings combined with their basal sprouting ability in this forest could enable the persistence of woody species in the face of invasive species.

Effects of different modes of hot cross-rolling in 7010 aluminum alloy: part II. mechanical properties anisotropy

The influence of microstructure and texture developed by different modes of hot cross-rolling on in-plane anisotropy (A (IP)) of yield strength, work hardening behavior, and anisotropy of Knoop hardness (KHN) yield locus has been investigated. The A (IP) and work hardening behavior are evaluated by tensile testing at 0 deg, 45 deg, and 90 deg to the rolling direction, while yield loci have been generated by directional KHN measurements. It has been observed that specimens especially in the peak-aged temper, in spite of having a strong, rotated Brass texture, show low A (IP). The results are discussed on the basis of Schmid factor analyses in conjunction with microstructural features, namely grain morphology and precipitation effects. For the specimen having a single-component texture, the yield strength variation as a function of orientation can be rationalized by the Schmid factor analysis of a perfectly textured material behaving as a quasi-single crystal. The work hardening behavior is significantly affected by the presence of solute in the matrix and the state of precipitation rather than texture, while yield loci derived from KHN measurements reiterate the low anisotropy of the materials. Theoretic yield loci calculated from the texture data using the visco-plastic self-consistent model and Hill's anisotropic equation are compared with that obtained experimentally.

Experimental Studies on the Mechanics of Cohesive Frictional Granular Media

The mechanical behaviour of cohesive-frictional granular materials is a combination of the strength pervading as intergranular friction (represented as an angle of internal friction - Phi), and the cohesion (C) between these particles. Most behavioral or constitutive models of this class of granular materials comprise of a cohesion and frictional component with no regard to the length scale i.e. from the micro structural models through the continuum models. An experimental study has been made on a model granular material, viz. angular sand with different weights of binding agents (varying degrees of cohesion) at multiple length scales to physically map this phenomenon. Cylindrical specimen of various diameters - 10, 20, 38, 100, 150 mm (and with an aspect ratio of 2) are reconstituted with 2, 4 and 8% by weight of a binding agent. The magnitude of this cohesion is analyzed using uniaxial compression tests and it is assumed to correspond to the peak in the normalized stress-strain plot. Increase in the cohesive strength of the material is seen with increasing size of the specimen. A possibility of ``entanglement'' occurring in larger specimens is proposed as a possible reason for deviation from a continuum framework.

Study on important diffusion parameters of binary Ni3Sn4 phase

Important diffusion parameters, such as-parabolic growth constant, integrated diffusivity, ratio of intrinsic diffusivities of species Ni and Sn, Kirkendall marker velocity and the activation energy for diffusion kinetics of binary Ni3Sn4 phase have been investigated with the help of incremental diffusion couple technique (Sn/Ni0.57Sn0.43) in the temperature range 200-150 degrees C. Low activation energy extracted from Arrhenius plot indicates grain boundary controlled diffusion process. The species Sn is three times faster than Ni at 200 degrees C. Further, the activation energy of Sn tracer diffusivity is greater than that of Ni.

Topological saliency

Topological methods have been successfully used to identify features in scalar fields and to measure their importance. In this paper, we define a notion of topological saliency that captures the relative importance of a topological feature with respect to other features in its local neighborhood. Features are identified by extreme points of an input scalar field, and their importance measured by the so-called topological persistence. Computing the topological saliency of all features for varying neighborhood sizes results in a saliency plot that serves as a summary of relative importance of all topological features. We develop a convenient tool for users to interactively select and inspect features using the saliency plot. We demonstrate the use of topological saliency together with the rich information encoded in the saliency plot in several applications, including key feature identification, scalar field simplification, and feature clustering. (C) 2013 Elsevier Ltd. All rights reserved.

Evolution of ferromagnetism from a frustrated state in LixNi(2-x)O2 (0.67 < x < 0.98)

Two-dimensional triangular-lattice antiferromagnetic systems continue to be an interesting area in condensed matter physics and LiNiO2 is one such among them. Here we present a detailed experimental magnetic study of the quasi-stoichiometric LixNi2-xO2 system (0.67plot, Kouvel-Fisher method, and critical isotherm analysis. The critical exponents match with the long-range mean-field model. The values of the critical exponents are confirmed by the Widom scaling law: delta = 1 + gamma beta(-1). Furthermore, the universality class of the scaling relations is verified, where the scaled m and scaled h collapse into two branches. Finally, based on our observations, a phase diagram is constructed.

Long-Term Environmental Correlates of Invasion by Lantana camara (Verbenaceae) in a Seasonally Dry Tropical Forest

Invasive species, local plant communities and invaded ecosystems change over space and time. Quantifying this change may lead to a better understanding of the ecology and the effective management of invasive species. We used data on density of the highly invasive shrub Lantana camara (lantana) for the period 1990-2008 from a 50 ha permanent plot in a seasonally dry tropical forest of Mudumalai in southern India. We used a cumulative link mixed-effects regression approach to model the transition of lantana from one qualitative density state to another as a function of biotic factors such as indicators of competition from local species (lantana itself, perennial grasses, invasive Chromolaena odorata, the native shrub Helicteres isora and basal area of native trees) and abiotic factors such as fire frequency, inter-annual variability of rainfall and relative soil moisture. The density of lantana increased substantially during the study period. Lantana density was negatively associated with the density of H. isora, positively associated with basal area of native trees, but not affected by the presence of grasses or other invasive species. In the absence of fire, lantana density increased with increasing rainfall. When fires occurred, transitions to higher densities occurred at low rainfall values. In drier regions, lantana changed from low to high density as rainfall increased while in wetter regions of the plot, lantana persisted in the dense category irrespective of rainfall. Lantana seems to effectively utilize resources distributed in space and time to its advantage, thus outcompeting local species and maintaining a population that is not yet self-limiting. High-risk areas and years could potentially be identified based on inferences from this study for facilitating management of lantana in tropical dry forests.

Effect of analyte concentration on the laser-induced plasma temperature and electron density in liquid matrix

In the present work, we report spectroscopic studies of laser-induced plasmas produced by focusing the second harmonic (532nm) of a Nd:YAG laser onto the laminar flow of a liquid containing chromium. The plasma temperature is determined from the coupled Saha-Boltzmann plot and the electron density is evaluated from the Stark broadening of an ionic line of chromium Cr(II)] at 267.7nm. Our results reveal a decrease in plasma temperature with an increase in Cr concentration up to a certain concentration level; after that, it becomes approximately constant, while the electron density increases with an increase in analyte (Cr) concentration in liquid matrix.

Studies on thin film based flexible gold electrode arrays for resistivity imaging in electrical impedance tomography

Practical phantoms are essential to assess the electrical impedance tomography (EIT) systems for their validation, calibration and comparison purposes. Metal surface electrodes are generally used in practical phantoms which reduce the SNR of the boundary data due to their design and development errors. Novel flexible and biocompatible gold electrode arrays of high geometric precision are proposed to improve the boundary data quality in EIT. The flexible gold electrode arrays are developed on flexible FR4 sheets using thin film technology and practical gold electrode phantoms are developed with different configurations. Injecting a constant current to the phantom boundary the surface potentials are measured by a LabVIEW based data acquisition system and the resistivity images are reconstructed in EIDORS. Boundary data profile and the resistivity images obtained from the gold electrode phantoms are compared with identical phantoms developed with stainless steel electrodes. Surface profilometry, microscopy and the impedance spectroscopy show that the gold electrode arrays are smooth, geometrically precised and less resistive. Results show that the boundary data accuracy and image quality are improved with gold electrode arrays. Results show that the diametric resistivity plot (DRP), contrast to noise ratio (CNR), percentage of contrast recovery (PCR) and coefficient of contrast (COC) of reconstructed images are improved in gold electrode phantoms. (C) 2013 Elsevier Ltd. All rights reserved.