Tuning the magnetic ground state in LixNi(2-x)O2

The experimental determination of the magnetic ground state of triangular lattice anti-ferromagnet LiNiO2 is an intriguing problem as the system is prone to be Li deficient. We have been successful in preparing nearly stoichiometric LiNiO2 showing an anti-ferromagnetic ground state with an ordering temperature similar to 12 K. As the Li deficiency increases the sample exhibits spin glass behavior evidenced by a shift in the spin glass freezing temperature as a function of frequency in the ac susceptibility studies. As the Li deficiency crosses a critical limit, the sample becomes ferromagnetic in nature. We are able to tune the ferromagnetic transition temperature up to 240 K by varying the Li content. Finally, we have constructed a magnetic phase diagram. (C) 2012 American Institute of Physics. doi:10.1063/1.3675997]

Estimating the Hausdorff-Besicovitch dimension of boundary of basin of attraction in helicopter trim

Helicopter trim involves solution of nonlinear force equilibrium equations. As in many nonlinear dynamic systems, helicopter trim problem can show chaotic behavior. This chaotic behavior is found in the basin of attraction of the nonlinear trim equations which have to be solved to determine the main rotor control inputs given by the pilot. This study focuses on the boundary of the basin of attraction obtained for a set of control inputs. We analyze the boundary by considering it at different magnification levels. The magnified views reveal intricate geometries. It is also found that the basin boundary exhibits the characteristic of statistical self-similarity, which is an essential property of fractal geometries. These results led the authors to investigate the fractal dimension of the basin boundary. It is found that this dimension is indeed greater than the topological dimension. From all the observations, it is evident that the boundary of the basin of attraction for helicopter trim problem is fractal in nature. (C) 2012 Elsevier Inc. All rights reserved.

Enhanced J-protein interaction and compromised protein stability of mtHsp70 variants lead to mitochondrial dysfunction in Parkinsons disease

Parkinsons disease (PD) is the second most prevalent progressive neurological disorder commonly associated with impaired mitochondrial function in dopaminergic neurons. Although familial PD is multifactorial in nature, a recent genetic screen involving PD patients identified two mitochondrial Hsp70 variants (P509S and R126W) that are suggested in PD pathogenesis. However, molecular mechanisms underlying how mtHsp70 PD variants are centrally involved in PD progression is totally elusive. In this article, we provide mechanistic insights into the mitochondrial dysfunction associated with human mtHsp70 PD variants. Biochemically, the R126W variant showed severely compromised protein stability and was found highly susceptible to aggregation at physiological conditions. Strikingly, on the other hand, the P509S variant exhibits significantly enhanced interaction with J-protein cochaperones involved in folding and import machinery, thus altering the overall regulation of chaperone-mediated folding cycle and protein homeostasis. To assess the impact of mtHsp70 PD mutations at the cellular level, we developed yeast as a model system by making analogous mutations in Ssc1 ortholog. Interestingly, PD mutations in yeast (R103W and P486S) exhibit multiple in vivo phenotypes, which are associated with omitochondrial dysfunction', including compromised growth, impairment in protein translocation, reduced functional mitochondrial mass, mitochondrial DNA loss, respiratory incompetency and increased susceptibility to oxidative stress. In addition to that, R103W protein is prone to aggregate in vivo due to reduced stability, whereas P486S showed enhanced interaction with J-proteins, thus remarkably recapitulating the cellular defects that are observed in human PD variants. Taken together, our findings provide evidence in favor of direct involvement of mtHsp70 as a susceptibility factor in PD.

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.

Averting biodiversity collapse in tropical forest protected areas

The rapid disruption of tropical forests probably imperils global biodiversity more than any other contemporary phenomenon(1-3). With deforestation advancing quickly, protected areas are increasingly becoming final refuges for threatened species and natural ecosystem processes. However, many protected areas in the tropics are themselves vulnerable to human encroachment and other environmental stresses(4-9). As pressures mount, it is vital to know whether existing reserves can sustain their biodiversity. A critical constraint in addressing this question has been that data describing a broad array of biodiversity groups have been unavailable for a sufficiently large and representative sample of reserves. Here we present a uniquely comprehensive data set on changes over the past 20 to 30 years in 31 functional groups of species and 21 potential drivers of environmental change, for 60 protected areas stratified across the world's major tropical regions. Our analysis reveals great variation in reserve `health': about half of all reserves have been effective or performed passably, but the rest are experiencing an erosion of biodiversity that is often alarmingly widespread taxonomically and functionally. Habitat disruption, hunting and forest-product exploitation were the strongest predictors of declining reserve health. Crucially, environmental changes immediately outside reserves seemed nearly as important as those inside in determining their ecological fate, with changes inside reserves strongly mirroring those occurring around them. These findings suggest that tropical protected areas are often intimately linked ecologically to their surrounding habitats, and that a failure to stem broad-scale loss and degradation of such habitats could sharply increase the likelihood of serious biodiversity declines.

Nanocrystallization of TiO2 Anatase Phase in Hydrophobic BaO-TiO2-B2O3 Glass System

Transparent colorless glasses in the ternary BaOTiO2B2O3 system were fabricated via conventional melt-quenching technique. The glasses with certain molar concentrations of BaO and TiO2 on heat treatment at appropriate temperatures yielded nanocrystalline phase of TiO2 associated with the crystallite size in the 515 nm range. Nanocrystallized glasses exhibited high refractive index (n = 2.15) measured at lambda = 543 nm. These glasses were found to be hydrophobic in nature associated with the contact angle of 90 degrees. These high-index glass nanocrystal composites would be of potential interest for optical device applications.

Pressure induced structural phase transformation in TiN: a first-principles study

Titanium nitride (TiN), which is widely used for hard coatings, reportedly undergoes a pressure-induced structural phase transformation, from a NaCl to a CsCl structure, at similar to 7 GPa. In this paper, we use first-principles calculations based on density functional theory with a generalized gradient approximation of the exchange correlation energy to determine the structural stability of this transformation. Our results show that the stress required for this structural transformation is substantially lower (by more than an order of magnitude) when it is deviatoric in nature vis-a-vis that under hydrostatic pressure. Local stability of the structure is assessed with phonon dispersion determined at different pressures, and we find that CsCl structure of TiN is expected to distort after the transformation. From the electronic structure calculations, we estimate the electrical conductivity of TiN in the CsCl structure to be about 5 times of that in NaCl structure, which should be observable experimentally. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4798591]

Effect of vacuum treatment on CsI photocathode performance in UV photon detectors

CsI can be used as a photocathode material in UV photon detectors. The detection efficiency of the detector strongly depends on the photoemission property of the photocathode. CsI is very hygroscopic in nature. This limits the photoelectron yield from the photocathode when exposed to humid air even for a short duration during photocathode mounting or transfer. We report here on the improvement of photoemission properties of both thick (300 nm) and thin (30 nm) UV-sensitive CsI film exposed to humid air by the process of vacuum treatment. (C) 2013 Optical Society of America

Heat and SDS insensitive NDK dimers are largely stabilised by hydrophobic interaction to form functional hexamer in Mycobacterium smegmatis

The primary structure and function of nucleoside diphosphate kinase (NDK), a substrate non-specific enzyme involved in the maintenance of nucleotide pools is also implicated to play pivotal roles in many other cellular processes. NDK is conserved from bacteria to human and forms a homotetramer or hexamer to exhibit its biological activity. However, the nature of the functional oligomeric form of the enzyme differs among different organisms. The functional form of NDKs from many bacterial systems, including that of the human pathogen, Mycobacterium tuberculosis (MtuNDK), is a hexamer, although some bacterial NDKs are tetrameric in nature. The present study addresses the oligomeric property of MsmNDK and how a dimer, the basic subunit of a functional hexamer, is stabilized by hydrogen bonds and hydrophobic interactions. Homology modeling was generated using the three-dimensional structure of MtuNDK as a template; the residues interacting at the monomer-monomer interface of MsmNDK were mapped. Using recombinant enzymes of wild type, catalytically inactive mutant, and monomer-monomer interactive mutants of MsmNDK, the stability of the dimer was verified under heat, SDS, low pH, and methanol. The predicted residues (Gln17, Ser24 and Glu27) were engaged in dimer formation, however the mutated proteins retained the ATPase and GTPase activity even after introducing single (MsmNDK- Q17A, MsmNDK-E27A, and MsmNDK-E27Q) and double (MsmNDK-E27A/Q17A) mutation. However, the monomer monomer interaction could be abolished using methanol, indicating the stabilization of the monomer-monomer interaction by hydrophobic interaction.

Evolution of microstructure and texture in friction stir processed Al-Mg-Mn alloy

Friction stir processing was carried out on the Al-Mg-Mn alloy to achieve ultrafine grained microstructure. The evolution of microstructure and micro-texture was studied in different regions of the deformed sample, namely nugget zone, thermo-mechanically affected zone (TMAZ) and base metal. The average grain sizes of the nugget zone, TMAZ and base metal are 1.5 mu m +/- 0.5 mu m, 15 mu m +/- 8 mu m, and 80 mu m +/- 10 mu m, respectively. The TMAZ exhibits excessive deformation banding structure and sub-grain formation. The orientation gradient within the sub-grain is dependent on grain size, orientation, and distance from nugget zone. The microstructure was partitioned based on the grain orientation spread and grain size values to separate the recrystallized fraction from the deformed region in order to understand the micromechanism of grain refinement. The texture of both deformed and recrystallized regions are similar in nature. Microstructure and texture analysis suggest that the restoration processes are different in different regions of the processed sample. The transition region between nugget zone and TMAZ exhibits large elongated grains surrounded by fine equiaxed grains of different orientation which indicate the process of discontinuous dynamic recrystallization. Within the nugget zone, similar texture between deformed and recrystallized grain fraction suggests that the restoration mechanism is a continuous process.

Substrate conductivity dependent modulation of cell proliferation and differentiation in vitro

In designing and developing various biomaterials, the influence of substrate properties, like surface topography, stiffness and wettability on the cell functionality has been investigated widely. However, such study to probe into the influence of the substrate conductivity on cell fate processes is rather limited. In order to address this issue, spark plasma sintered HA-CaTiO3 (Hydroxyapatite-Calcium titanate) has been used as a model material system to showcase the effect of varying conductivity on cell functionality. Being electroactive in nature, mouse myoblast cells (C2C12) were selected as a model cell line in this study. It was inferred that myoblast adhesion/growth systematically increases with substrate conductivity due to CaTiO3 addition to HA. Importantly, parallel arrangement of myoblast cells on higher CaTiO3 containing substrates indicate that self-adjustable cell patterning can be achieved on conductive biomaterials. Furthermore, enhanced myoblast assembly and myotube formation were recorded after 5 days of serum starvation. Overall, the present study conclusively establishes the positive impact of the substrate conductivity towards cell proliferation and differentiation as well as confirms the efficacy of HA-CaTiO3 biocomposites as conductive platforms to facilitate the growth, orientation and fusion of myoblasts, even when cultured in the absence of external electric field.

Layerwise decomposition of water dynamics in reverse micelles: A simulation study of two-dimensional infrared spectrum

We present computer simulation study of two-dimensional infrared spectroscopy (2D-IR) of water confined in reverse micelles (RMs) of various sizes. The present study is motivated by the need to understand the altered dynamics of confined water by performing layerwise decomposition of water, with an aim to quantify the relative contributions of different layers water molecules to the calculated 2D-IR spectrum. The 0-1 transition spectra clearly show substantial elongation, due to in-homogeneous broadening and incomplete spectral diffusion, along the diagonal in the surface water layer of different sized RMs. Fitting of the frequency fluctuation correlation functions reveal that the motion of the surface water molecules is sub-diffusive and indicate the constrained nature of their dynamics. This is further supported by two peak nature of the angular analogue of van Hove correlation function. With increasing system size, the water molecules become more diffusive in nature and spectral diffusion almost completes in the central layer of the larger size RMs. Comparisons between experiments and simulations establish the correspondence between the spectral decomposition available in experiments with the spatial decomposition available in simulations. Simulations also allow a quantitative exploration of the relative role of water, sodium ions, and sulfonate head groups in vibrational dephasing. Interestingly, the negative cross correlation between force on oxygen and hydrogen of O-H bond in bulk water significantly decreases in the surface layer of each RM. This negative cross correlation gradually increases in the central water pool with increasing RMs size and this is found to be partly responsible for the faster relaxation rate of water in the central pool. (C) 2013 AIP Publishing LLC.

Gas Phase Oxygen Quenching Studies of Ketone Tracers for Laser-Induced Fluorescence Applications in Nitrogen Bath Gas

In this paper we report the quantitative oxygen quenching effect on laser-induced fluorescence of acetone, methyl ethyl ketone, and 3-pentanone at low pressures (approximate to 700torr) with oxygen partial pressures up to 450torr. Nitrogen was used as a bath gas in which these molecular tracers were added in different quantities according to their vapor pressure at room temperature. These tracers were excited by using a frequency-quadrupled, Q-switched, Nd:YAG laser (266nm). Stern-Volmer plots were found to be linear for all the tracers, suggesting that quenching is collisional in nature. Stern-Volmer coefficients (k(sv)) and quenching rate constants (k(q)) were calculated from Stern-Volmer plots. The effects of oxygen on the laser-induced fluorescence of acetone, methyl ethyl ketone, and 3-pentanone were compared with each other. Further, the Smoluchowski theory was used to calculate the quenching parameters and compared with the experimental results.

Stability of fluctuating and transient aggregates of amphiphilic solutes in aqueous binary mixtures: Studies of dimethylsulfoxide, ethanol, and tert-butyl alcohol

In aqueous binary mixtures, amphiphilic solutes such as dimethylsulfoxide (DMSO), ethanol, tertbutyl alcohol (TBA), etc., are known to form aggregates (or large clusters) at small to intermediate solute concentrations. These aggregates are transient in nature. Although the system remains homogeneous on macroscopic length and time scales, the microheterogeneous aggregation may profoundly affect the properties of the mixture in several distinct ways, particularly if the survival times of the aggregates are longer than density relaxation times of the binary liquid. Here we propose a theoretical scheme to quantify the lifetime and thus the stability of these microheterogeneous clusters, and apply the scheme to calculate the same for water-ethanol, water-DMSO, and water-TBA mixtures. We show that the lifetime of these clusters can range from less than a picosecond (ps) for ethanol clusters to few tens of ps for DMSO and TBA clusters. This helps explaining the absence of a strong composition dependent anomaly in water-ethanol mixtures but the presence of the same in water-DMSO and water-TBA mixtures. (C) 2013 AIP Publishing LLC.

Solid-solid collapse transition in a two dimensional model molecular system

Solid-solid collapse transition in open framework structures is ubiquitous in nature. The real difficulty in understanding detailed microscopic aspects of such transitions in molecular systems arises from the interplay between different energy and length scales involved in molecular systems, often mediated through a solvent. In this work we employ Monte-Carlo simulation to study the collapse transition in a model molecular system interacting via both isotropic as well as anisotropic interactions having different length and energy scales. The model we use is known as Mercedes-Benz (MB), which, for a specific set of parameters, sustains two solid phases: honeycomb and oblique. In order to study the temperature induced collapse transition, we start with a metastable honeycomb solid and induce transition by increasing temperature. High density oblique solid so formed has two characteristic length scales corresponding to isotropic and anisotropic parts of interaction potential. Contrary to the common belief and classical nucleation theory, interestingly, we find linear strip-like nucleating clusters having significantly different order and average coordination number than the bulk stable phase. In the early stage of growth, the cluster grows as a linear strip, followed by branched and ring-like strips. The geometry of growing cluster is a consequence of the delicate balance between two types of interactions, which enables the dominance of stabilizing energy over destabilizing surface energy. The nucleus of stable oblique phase is wetted by intermediate order particles, which minimizes the surface free energy. In the case of pressure induced transition at low temperature the collapsed state is a disordered solid. The disordered solid phase has diverse local quasi-stable structures along with oblique-solid like domains. (C) 2013 AIP Publishing LLC.