Molecular dynamics insight to phase transition in n-alkanes with carbon nanofillers

The present work aims to investigate the phase transition, dispersion and diffusion behavior of nanocomposites of carbon nanotube (CNT) and straight chain alkanes. These materials are potential candidates for organic phase change materials(PCMs) and have attracted flurry of research recently. Accurate experimental evaluation of the mass, thermal and transport properties of such composites is both difficult as well as economically taxing. Additionally it is crucial to understand the factors that results in modification or enhancement of their characteristic at atomic or molecular level. Classical molecular dynamics approach has been extended to elucidate the same. Bulk atomistic models have been generated and subjected to rigorous multistage equilibration. To reaffirm the approach, both canonical and constant-temperature, constant-pressure ensembles were employed to simulate the models under consideration. Explicit determination of kinetic, potential, non-bond and total energy assisted in understanding the enhanced thermal and transport property of the nanocomposites from molecular point of view. Crucial parameters including mean square displacement and simulated self diffusion coefficient precisely define the balance of the thermodynamic and hydrodynamic interactions. Radial distribution function also reflected the density variation, strength and mobility of the nanocomposites. It is expected that CNT functionalization could improve the dispersion within n-alkane matrix. This would further ameliorate the mass and thermal properties of the composite. Additionally, the determined density was in good agreement with experimental data. Thus, molecular dynamics can be utilized as a high throughput technique for theoretical investigation of nanocomposites PCMs. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

Hardness Alternation in alpha,omega-Alkanedicarboxylic Acids

The variation of hardness as a function of the number of carbon atoms in alpha,omega-alkanedicarboxylic acids, CNH2N-2O4 (4 <= N <= 9), was examined by recourse to nanoindentation on the major faces of single crystals. Hardness exhibits odd-even alternation, with the odd acids being softer and the even ones harder; the differences decrease with increasing chain length. These variations are similar to those seen for other mechanical, physical, and thermal properties of these diacids. The softness of odd acids is rationalized due to strained molecular conformations in them, which facilitate easier plastic deformation. Relationships between structural features, such as interplanar spacing, interlayer separation distance, molecular chain length, and signatures of the nanoindentation responses, namely, discrete displacement bursts, were also examined. Shear sliding of molecular layers past each other during indentation is key to the mechanism for plastic deformation in these organic crystals.

Strategy for Obtaining Bimodal Bubble Size Distribution in Water Blown Polyurethane Foams

Polyurethane foams with multimodal cell distribution exhibit superior mechanical and thermal properties. A technique for generating bimodal bubble size distribution exists in the literature, but it uses supercritical conditions. In the present work, an alternative based on milder operating conditions is proposed. It is a modification of reaction injection molding (RIM), using reactants already seeded with bubbles. The number density of the seeds determines if two nucleating events can occur. A bimodal bubble size distribution is obtained when this happens A mathematical model is used to test this hypothesis by simulating water blown free rise polyurethane foams. The effects of initial concentration of bubbles, temperature of the reactants, and the weight fraction of water are studied. The study reveals that for certain concentrations of initial number of bubbles, when initial temperature and weight fraction of water are high, it is possible to obtain a second nucleation event, leading to bimodal bubble size distribution.

Structural characterization and in vitro biomedical activities of sulfated chitosan from Sepia pharaonis

A low molecular weight sulfated chitosan (SP-LMWSC) was isolated from the cuttlebone of Sepia pharaonis. Elemental analysis established the presence of C, H and N. The sulfation of SP-LMWSC was confirmed by the presence of characteristic peaks in FT-IR and FT-Raman spectra. The thermal properties of SP-LMWSC were studied by thermogravimetric analysis and differential scanning calorimetry. Electrolytic conductivity of SP-LMWSC was measured by cyclic voltammetry and the molecular weight was determined by MALDI-TOF/MS. The molecular structure and sulfation sites of SP-LMWSC were unambiguously confirmed using H-1,C-13, 2D COSY and 2D HSQC NMR spectroscopy. SP-LMWSC exhibited increased anticoagulant activity in avian blood by delaying coagulation parameters and displayed cytostatic activity by inhibiting the migration of avian leucocytes. SP-LMWSC demonstrated avian antiviral activity by binding to Newcastle disease virus receptors at a low titer value of 1/64. These findings suggested that SP-LMWSC isolated from an industrial discard holds immense potentials as carbohydrate based pharmaceuticals in future. (C) 2015 Elsevier B.V. All rights reserved.

Crystal growth, transport and magnetic properties of rare-earth manganite Pr1-xPbxMnO3

Crystal growth, electrical and magnetic properties are reported for mixed valence manganite Pr1-xPbxMnO3 (x = 0.2, 0.23, and 0.3). The crystals with x = 0.2 and 0.23 are ferromagnetic and insulating, whereas that with x = 0.3 is ferromagnetic below 200 K and shows an insulator-metal transition at 235 K. This composition shows a magnetoresistance of 90% in a field of 5 T. In the paramagnetic region, the temperature dependence of magnetic susceptibility of the crystals follows a Curie-Weiss behavior. The thermal evolution of magnetization in the ferromagnetic phase varies as T-3/2, in accordance with Bloch's law. The spin-stiffness constant D obtained from the Bloch constant is found to increase linearly with x. The magnetization does not reach complete saturation upto a field of 5 T. A possible contribution of the Pr spins to the total magnetic moment is discussed.

Thermal, magnetic and electrical properties of Tb1-xDyxMnO3 multiferroics

A series of multiferroic materials with the compositional formula, Tb1 - xDyxMnO3 (where x=0, 0.1, 0.2, 0.3 and 0.4) were prepared by the sol gel method. After characterizing the samples structurally, a systematic investigation of specific heat, magnetization and dielectric properties over the temperature range, 4-300 K, was undertaken. Based on these studies, it was found that all the samples exhibit a transition at 40 K and the observed behavior may be attributed to the ordering of Mn3+ ions. Further, all the five samples are found to exhibit a ferroelectric transition in the temperature range 20-24 K. Finally, yet another transition was also exhibited by all the samples at temperatures below 10 K and is attributed to the antiferromagnetic (AF) ordering of rare-earth ionic moments. The magnetic entropy of all the samples was also computed with the help of their heat capacity data. (C) 2015 Elsevier B.V. All rights reserved.

Steam-cured stabilised soil blocks for masonry construction

Energy-efficient, economical and durable building materials are essential for sustainable construction practices. The paper deals with production and properties of energy-efficient steam-cured stabilised soil blocks used fbr masonry construction. Problems of mixing expansive soil and lime, and production of blocks using soil-lime mixtures have been discussed briefly. Details of steam curing of stabilised soil blocks and properties of such blocks are given. A comparison of energy content of steam-cured soil blocks and burnt bricks is presented. It has been shown that energy-efficient steam cured soil blocks (consuming 35% less thermal energy compared to burnt clay bricks) having high compressive strength can be easily produced in a decentralised manner.

Giant Magnetoresistance and Related Properties of Rare Earth Manganates and Other Oxide Systems

Giant magnetoresistance (GMR), which was until recently confined to magnetic layered and granular materials, as well as doped magnetic semiconductors, occurs in manganate perovskites of the general formula Ln(1-x)A(x)MnO(3) (Ln = rare earth; A = divalent ion). These manganates are ferromagnetic at or above a certain value of x (or Mn4+ content) and become metallic at temperatures below the curie temperature, T-c. GMR is generally a maximum close to T-c or the insulator-metal (I-M) transition temperature, T-im. The T-c and %MR are markedly affected by the size of the A site cation, [r(A)], thereby affording a useful electronic phase diagram when T-c or T-im is plotted against [r(A)]. We discuss GMR and related properties of manganates in polycrystalline, thin-film, and single-crystal forms and point out certain commonalities and correlations. We also examine some unusual features in the electron-transport properties of manganates, in particular charge-ordering effects. Charge ordering is crucially dependent on [r(A)] or the e(g) band width, and the charge-ordered insulating state transforms to a metallic ferromagnetic state on the application of a magnetic field.

An investigation of structural, magnetic and dielectric properties of R2NiMnO6 (R = rare earth, Y)

We have investigated the structure, magnetic and dielectric properties of the double perovskite oxides, R2NiMnO6 (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho and Y). We could refine powder X-ray diffraction patterns of all the phases on the basis of monoclinic (P2(1)/n) double perovskite structure where Ni and Mn atoms are ordered at 2c and 2d sites, respectively. All the phases are ferromagnetic insulators exhibiting relatively low dielectric loss and dielectric constants in the range 15-25. The ferromagnetic ordering temperature of the R2NiMnO6 series seems to correlate better with the radius of R3+ atoms than with the average Ni-O-Mn angle (phi) in the double perovskite structure. These results are consistent with all samples having Mn4+ and Ni2+ With minimal antisite disorder.

Magnetic superconductors: Model theories and experimental properties of rare-earth compounds

Superconducting and magnetically long-range ordered states were believed to be mutually exclusive phenomena. The discovery of rare-earth compounds in recent years, which exhibit both superconductivity and magnetic ordering (ferromagnetic, antiferromagnetic or sinusoidal), has led to considerable theoretical and experimental work on such systems. In the present article, we give a review of various theoretical models and important experimental results. In the theoretical sections, we start with the Abrikosov-Gorkov pair breaking theory for dilute alloys and discuss its improvement in the work of Müller-Hartmann and Zittartz. Then, in the context of magnetic superconductors, various microscopic theories that have been advanced are presented. These predict re-entrant behaviour in some systems (ferromagnetic superconductors) and coexistence regions in others (particularly antiferromagnetic superconductors). Following this, phenomenological generalized Ginzburg-Landau theories for two kinds of orders (superconducting and magnetic) are presented. A section dealing with renormalization group analysis of phase diagrams in magnetic superconductors is given. In experimental sections, the properties of each rare-earth compounds (ternary as well as some tetranery) are reviewed. These involve susceptibility, heat capacity, resistivity, upper critical field, neutron scattering and magnetic resonance measurements. The anomalous behaviour of the upper critical field of antiferromagnetic superconductors near the Néel temperature is discussed both in theory sections and experimental section for various systems.

Influence of rapid thermal annealing (RTA) on the structural and electrical properties of SnS films

The performance of optoelectronic devices critically depends on the quality of active layer. An effective way to obtain a high quality layers is by creating excess of metal atoms through various heat treatments. Recently, rapid thermal annealing (RTA) has proved a versatile technique for the post-treatment of semiconductor materials as compared to other techniques due to its precise control over the resources. Thus, we carried out a set of experiments on SnS films to explore the influence of RTA treatment on their properties. From these experiments we noticed that the films treated at 400 °C for 1 min in N2 atmosphere have a low electrical resistivity of ~5 Ωcm with relatively high Hall mobility and carrier density of 99 cm2/Vs and 1.3 × 1016 cm−3, respectively. The observed results, therefore, emphasise that it is possible to obtain good quality SnS films through RTA treatment without disturbing their crystal structure.

Thermal decomposition of rare-earth trioxalatocobaltates

The thermal decomposition of rare-earth trioxalatocobaltates LnCo(C2O4)3 · x H2O, where Ln = La, Pr, Nd, has been studied in flowing atmospheres of air/oxygen, argon/ nitrogen, carbon dioxide and a vacuum. The compounds decompose through three major steps, viz. dehydration, decomposition of the oxalate to an intermediate carbonate, which further decomposes to yield rare-earth cobaltite as the final product. The formation of the final product is influenced by the surrounding gas atmosphere. Studies on the thermal decomposition of photodecomposed lanthanum trioxalatocobaltate and a mechanical mixture of lanthanum oxalate and cobalt oxalate in 1 : 2 molar ratio reveal that the decomposition behaviour of the two samples is different. The drawbacks of the decomposition scheme proposed earlier have been pointed out, and logical schemes based on results obtained by TG, DTA, DTG, supplemented by various physico-chemical techniques such as gas and chemical analyses, IR and mass spectroscopy, surface area and magnetic susceptibility measurements and X-ray powder diffraction methods, have been proposed for the decomposition in air of rare-earth trioxalatocobaltates as well as for the photoreduced lanthanum salt and a mechanical mixture of lanthanum and cobalt oxalates.

Spatial and vertical heterogeneities in aerosol properties over oceanic regions around India: Implications for radiative forcing

The influence of atmospheric aerosols on Earth's radiation budget and hence climate, though well recognized and extensively investigated in recent years, remains largely uncertain mainly because of the large spatio-temporal heterogeneity and the lack of data with adequate resolution. To characterize this diversity, a major multi-platform field campaign ICARB (Integrated Campaign for Aerosols, gases and Radiation Budget) was carried out during the pre-monsoon period of 2006 over the Indian landmass and surrounding oceans, which was the biggest such campaign ever conducted over this region. Based on the extensive and concurrent measurements of the optical and physical properties of atmospheric aerosols during ICARB, the spatial distribution of aerosol radiative forcing was estimated over the entire Bay of Bengal (BoB), northern Indian Ocean and Arabian Sea (AS) as well as large spatial variations within these regions. Besides being considerably lower than the mean values reported earlier for this region, our studies have revealed large differences in the forcing components between the BoB and the AS. While the regionally averaged aerosol-induced atmospheric forcing efficiency was 31 +/- 6 W m(-2) tau(-1) for the BoB, it was only similar to 18 +/- 7 W m(-2) tau(-1) for the AS. Airborne measurements revealed the presence of strong, elevated aerosol layers even over the oceans, leading to vertical structures in the atmospheric forcing, resulting in significant warming in the lower troposphere. These observations suggest serious climate implications and raise issues ranging from the impact of aerosols on vertical thermal structure of the atmospheric and hence cloud formation processes to monsoon circulation.

Electrical Properties of Thermal Evaporated Cd1−xMnxS Nanocrystalline Films

Thin films of Cd1−xMnxS (0<=x<=0.5) were deposited on glass substrates by thermal evaporation. All the films were deposited at 300 K and annealed at 373, 473, and 573 K for 1 h in a high vacuum in the range 10−4 Pa. The as-deposited and the annealed films were characterized for composition, structure, and microstructure by using energy-dispersive X-ray, X-ray diffraction, scanning electron microscopy, and atomic force microscopy (AFM). The electrical properties were studied by Hall effect measurement. Electrical conductivity was studied in the temperature range 190–450 K. AFM studies showed that all the films were in nanocrystalline form with grain size varying in the range between 36 and 82 nm. Grain size studies showed a definite increase with annealing temperature. All the films exhibited wurtzite structure of the host material. The lattice parameter varied linearly with composition, following Vegard's law in the entire composition range. Grain size, electrical conductivity, Hall mobility, carrier concentration, and activation energy varied, exhibiting either maxima or minima at x=0.3.

Mineralogical changes and geotechnical properties of an expansive soil interacted with caustic solution

The type and amount of clay mineral plays an important role in the behaviour of fine-grained soils. Clay minerals are the primary source and moisture is often the external agent of swelling in soils. Also soils may exhibit increased/reduced swelling due to interaction with chemicals. Alkalis used in industrial operations are one such example. Concentrations of alkali and mineral type are the key factors in such interactions. The present paper reports the changes in the properties of an expansive Black Cotton soil containing a mixed layer mineral, rectorite upon interaction with high concentration caustic solutions. X-ray diffraction studies have shown that the rectorite present in the soil undergoes changes with increase in the concentration of alkali. Saponite gets transformed to nantronite. Small amount of kaolinitic mineral present in the soil also reacts with alkali producing some changes in its mineralogy. Many hydroxides are produced. Differential thermal analysis studies have been supportive of these changes. Consequent of these changes, the soil-specific surface increases, changes its Atterberg limits and free swell volume increases. The results have been supported by the characteristics and behaviour of samples contaminated in the field with alkali from an alumina extraction plant.