Group behaviour in physical, chemical and biological systems

Groups exhibit properties that either are not perceived to exist, or perhaps cannot exist, at the individual level. Such `emergent' properties depend on how individuals interact, both among themselves and with their surroundings. The world of everyday objects consists of material entities. These are, ultimately, groups of elementary particles that organize themselves into atoms and molecules, occupy space, and so on. It turns out that an explanation of even the most commonplace features of this world requires relativistic quantum field theory and the fact that Planck's constant is discrete, not zero. Groups of molecules in solution, in particular polymers ('sols'), can form viscous clusters that behave like elastic solids ('gels'). Sol-gel transitions are examples of cooperative phenomena. Their occurrence is explained by modelling the statistics of inter-unit interactions: the likelihood of either state varies sharply as a critical parameter crosses a threshold value. Group behaviour among cells or organisms is often heritable and therefore can evolve. This permits an additional, typically biological, explanation for it in terms of reproductive advantage, whether of the individual or of the group. There is no general agreement on the appropriate explanatory framework for understanding group-level phenomena in biology.

The influence of mesoporous silica in low T-g cyclic olefin copolymer nanocomposite films: Mechanical and moisture barrier studies

In this study, mesoporous silica-cyclic olefin copolymer nanocomposite films were fabricated by solution casting. With an increase in silica loading, the stiffness of the matrix increased. The nanocomposite film shows increased strain to failure with moisture after aging by matrix plasticization. The storage modulus and loss factor for samples with silica content show better results compared with pristine polymer, as indicated by dynamic mechanical analysis. The interaction between filler-polymer chain exhibit hydrophobicity compared to the neat polymer. Water absorption studies at room temperature and near the T-g of the polymer (similar to 64 degrees C) were carried out. The nanocomposites up to 4 wt% filler reduces the water diffusion by forming hydrogen and chemical bonding. The result by calcium degradation test method for moisture permeability and Schottky structured organic device encapsulation under weathering condition confirms the effective reinforcement effect of silica particles in the matrix. (C) 2014 Elsevier Ltd. All rights reserved.

Microscopic description of the evolution of the local structure and an evaluation of the chemical pressure concept in a solid solution

Extended x-ray absorption fine-structure studies have been performed at the Zn K and Cd K edges for a series of solid solutions of wurtzite Zn1-xCdxS samples with x = 0.0, 0.1, 0.25, 0.5, 0.75, and 1.0, where the lattice parameter as a function of x evolves according to the well-known Vegard's law. In conjunction with extensive, large-scale first-principles electronic structure calculations with full geometry optimizations, these results establish that the percentage variation in the nearest-neighbor bond distances are lower by nearly an order of magnitude compared to what would be expected on the basis of lattice parameter variation, seriously undermining the chemical pressure concept. With experimental results that allow us to probe up to the third coordination shell distances, we provide a direct description of how the local structure, apparently inconsistent with the global structure, evolves very rapidly with interatomic distances to become consistent with it. We show that the basic features of this structural evolution with the composition can be visualized with nearly invariant Zn-S-4 and Cd-S-4 tetrahedral units retaining their structural integrity, while the tilts between these tetrahedral building blocks change with composition to conform to the changing lattice parameters according to the Vegard's law within a relatively short length scale. These results underline the limits of applicability of the chemical pressure concept that has been a favored tool of experimentalists to control physical properties of a large variety of condensed matter systems.

A Stochastic Chemical Dynamic Approach to Correlate Autoimmunity and Optimal Vitamin-D Range

Motivated by several recent experimental observations that vitamin-D could interact with antigen presenting cells (APCs) and T-lymphocyte cells (T-cells) to promote and to regulate different stages of immune response, we developed a coarse grained but general kinetic model in an attempt to capture the role of vitamin-D in immunomodulatory responses. Our kinetic model, developed using the ideas of chemical network theory, leads to a system of nine coupled equations that we solve both by direct and by stochastic (Gillespie) methods. Both the analyses consistently provide detail information on the dependence of immune response to the variation of critical rate parameters. We find that although vitamin-D plays a negligible role in the initial immune response, it exerts a profound influence in the long term, especially in helping the system to achieve a new, stable steady state. The study explores the role of vitamin-D in preserving an observed bistability in the phase diagram (spanned by system parameters) of immune regulation, thus allowing the response to tolerate a wide range of pathogenic stimulation which could help in resisting autoimmune diseases. We also study how vitamin-D affects the time dependent population of dendritic cells that connect between innate and adaptive immune responses. Variations in dose dependent response of anti-inflammatory and pro-inflammatory T-cell populations to vitamin-D correlate well with recent experimental results. Our kinetic model allows for an estimation of the range of optimum level of vitamin-D required for smooth functioning of the immune system and for control of both hyper-regulation and inflammation. Most importantly, the present study reveals that an overdose or toxic level of vitamin-D or any steroid analogue could give rise to too large a tolerant response, leading to an inefficacy in adaptive immune function.

Carbon nanotubes and graphene-based chemical sensors

The chemical sensing behaviour of the carbon nano-tube and graphene-based sensors for detecting various chemical analytes is presented in this article. A focus on detection mechanisms has been provided to assess their relative potential under different environmental conditions. The performance of these two carbon allotropes is compared based on their sensitivity towards various types of electron donating and accepting molecules. Although these carbon materials still have to meet crucial challenges in fabrication and optimization, continued progress in this field may lead to a sensor with superior sensitivity for a wide range of applications.

Contrasting geochemical signatures on land from the Middle and Late Permian extinction events

The end of the Palaeozoic is marked by two mass-extinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative C-13 anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new high-resolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant syn-extinction and post-extinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coal-beds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates.

Influence of source concentration on structural and optical properties of SnO2 nanoparticles prepared by chemical precipitation method

In present work, a systematic study has been carried out to understand the influence of source concentration on structural and optical properties of the SnO2 nanoparticles. SnO2 nanoparticles have been prepared by using chemical precipitation method at room temperature with aqueous ammonia as a stabilizing agent. X-ray diffraction analysis reveals that SnO2 nanoparticles exhibit tetragonal structure and the particle size is in range of 4.9-7.6 nm. High resolution transmission electron microscopic image shows that all the particles are nearly spherical in nature and particle size lies in range of 4.6-7 nm. Compositional analysis indicates the presence of Sn and O in samples. Blue shift has been observed in optical absorption spectra due to quantum confinement and the bandgap is in range of 4-4.16 eV. The origin of photoluminescence in SnO2 is found to be due to recombination of electrons in singly occupied oxygen vacancies with photo-excited holes in valance band.

Layer-by-Layer Assembly of Nafion on Surlyn with Ultrahigh Water Vapor Barrier

A layer-by-layer approach was used for the fabrication of multilayer films for ultra high gas barrier applications. The ultra high gas barrier material was designed by incorporating Nafion layer in between bilayers of poly(ethylene imine) and poly(acrylic acid) on a Surlyn substrate. When the barrier film with self-assembled Nafion is exposed to the moist environment, Nafion absorbs and desorbs water molecules simultaneously, thereby reducing the ingress of moisture in to the film. In order to study the effect of Nafion, the fabricated barrier materials with and without the presence of Nafion were tested for water vapor barrier properties. The barrier films were further used for encapsulating organic photovoltaic devices and were evaluated for their potential use in barrier applications. The devices encapsulated with the films containing Nafion exhibited better performance when subjected to accelerated aging conditions. Therefore, this study demonstrates the effectiveness of self-assembled Nafion in reducing the water vapor permeability by nearly five orders of magnitude and in increasing the lifetimes of organic devices by similar to 22 times under accelerated weathering conditions.

Chemical specificity and conformational flexibility in proteinase-inhibitor interaction: Scaffolds for promiscuous binding

One of the most important roles of proteins in cellular milieu is recognition of other biomolecules including other proteins. Protein protein complexes are involved in many essential cellular processes. Interfaces of protein protein complexes are traditionally known to be conserved in evolution and less flexible than other solvent interacting tertiary structural surface. But many examples are emerging where these features do not hold good. An understanding of inter-play between flexibility and sequence conservation is emerging, providing a fresh dimension to the paradigm of sequence structure function relationship. The functional manifestation of the inter-relation between sequence conservation and flexibility of interface is exemplified in this review using proteinase inhibitor protein complexes. (C) 2014 Elsevier Ltd. All rights reserved.

Sources of major ions and processes affecting the geochemical and isotopic signatures of subsurface waters along a tropical river, Southwestern India

Systematic monitoring of subsurface hydrogeochemistry has been carried out for a period of one year in a humid tropical region along the Nethravati-Gurupur River. The major ion and stable isotope (delta O-18 and delta H-2) compositions are used to understand the hydrogeochemistry of groundwater and its interaction with surface water. In the study, it is observed that intense weathering of source rocks is the major source of chemical elements to the surface and subsurface waters. In addition, agricultural activities and atmospheric contributions also control the major ion chemistry of water in the study area. There is a clear seasonality in the groundwater chemistry, which is related to the recharge and discharge of the hydrological system. On a temporal scale, there is a decrease in major cation concentrations during the monsoon which is a result of dilution of sources from the weathering of rock minerals, and an increase in anion concentrations which is contributed by the atmosphere, accompanied by an increase in water level during the monsoon. The stable isotope composition indicates that groundwater in the basin is of meteoric origin and recharged directly from the local precipitation during the monsoonal season. Soon after the monsoon, groundwater and surface water mix in the subsurface region. The groundwater feeds the surface water during the lean river flow season.

Simple chemical aqueous synthesis of dahlia nanoflower consisting of finger-like ZnO nanorods and observation of stable ultraviolet photoluminescence emission

In this work, we have reported the synthesis of dahlia flower-like ZnO nanostructures consisting of human finger-like nanorods by the hydrothermal method at 120 degrees C and without using any capping agent. Optical properties of the samples, including UV-vis absorption and photoluminescence (PL) emission characteristics are determined by dispersing the samples in water as well as in ethanol media. The quenching of PL emission intensity along-with the red shifting of the PL emission peak are observed when the samples are dispersed in water in comparison to those obtained after dispersing the samples in ethanol. It has been found that PL emission characteristic, particularly the spectral nature of PL emission, of the samples remains almost unaltered (except some improvement in UV PL emission) even after thermally annealing it for 2 h at the temperature of 300 degrees C. Also the synthesized powder samples, kept in a plastic container, showed a very stable PL emission even after 15 months of synthesis. Therefore, the synthesized samples might be useful for their applications in future optoelectronics devices. (C) 2014 Elsevier Ltd. All rights reserved.

Metal-organic chemical vapor-deposited cobalt oxide films as negative electrodes for thin film Li-ion battery

In this study, thin films of cobalt oxide (Co3O4) have been grown by the metal-organic chemical vapor deposition (MOCVD) technique on stainless steel substrate at two preferred temperatures (450 degrees C and 500 degrees C), using cobalt acetylacetonate dihydrate as precursor. Spherical as well as columnar microstructures of Co3O4 have been observed under controlled growth conditions. Further investigations reveal these films are phase-pure, well crystallized and carbon-free. High-resolution TEM analysis confirms that each columnar structure is a continuous stack of minute crystals. Comparative study between these Co3O4 films grown at 450 degrees C and 500 degrees C has been carried out for their application as negative electrodes in Li-ion batteries. Our method of electrode fabrication leads to a coating of active material directly on current collector without any use of external additives. A high specific capacity of 1168 micro Ah cm(-2) mu m(-1) has been measured reproducibly for the film deposited at 500 degrees C with columnar morphology. Further, high rate capability is observed when cycled at different current densities. The Co3O4 electrode with columnar structure has a specific capacity 38% higher than the electrode with spherical microstructure (grown at 450 degrees C). Impedance measurements on the Co3O4 electrode grown at 500 degrees C also carried out to study the kinetics of the electrode process. (C) 2014 Published by Elsevier B.V.

Chemical Functionalization of Graphene To Augment Stem Cell Osteogenesis and Inhibit Biofilm Formation on Polymer Composites for Orthopedic Applications

Toward designing the next generation of resorbable biomaterials for orthopedic applications, we studied poly(epsilon-caprolactone) (PCL) composites containing graphene. The role, if any, of the functionalization of graphene on mechanical properties, stem cell response, and biofilm formation was systematically evaluated. PCL composites of graphene oxide (GO), reduced GO (RGO), and amine-functionalized GO (AGO) were prepared at different filler contents (1%, 3%, and 5%). Although the addition of the nanoparticles to PCL markedly increased the storage modulus, this increase was largest for GO followed by AGO and RGO. In vitro cell studies revealed that the AGO and GO particles significantly increased human mesenchymal stem cell proliferation. AGO was most effective in augmenting stem cell osteogenesis leading to mineralization. Bacterial studies revealed that interaction with functionalized GO induced bacterial cell death because of membrane damage, which was further accentuated by amine groups in AGO. As a result, AGO composites were best at inhibiting biofilm formation. The synergistic effect of oxygen containing functional groups and amine groups on AGO imparts the optimal combination of improved modulus, favorable stem cell response, and biofilm inhibition in AGO-reinforced composites desired for orthopedic applications. This work elucidates the importance of chemical functionalization of graphene in polymer composites for biomedical applications.

Graphene on Paper: A Simple, Low-Cost Chemical Sensing Platform

Graphene layers have been transferred directly on to paper without any intermediate layers to yield G-paper. Resistive gas sensors have been fabricated using strips of G-paper. These sensors achieved a remarkable lower limit of detection of similar to 300 parts per trillion (ppt) for NO2, which is comparable to or better than those from other paper-based sensors. Ultraviolet exposure was found to dramatically reduce the recovery time and improve response times. G-paper sensors are also found to be robust against minor strain, which was also found to increase sensitivity. G-paper is expected to enable a simple and inexpensive low-cost flexible graphene platform