Deformation behaviour of commercially pure titanium at extreme strain rates

The evolution of microstructure and texture during room temperature compression of commercially pure Ti with four different initial orientations were studied under quasi-static and dynamic loading conditions. At a low strain rate (epsilon)over dot = 3 x 10(-4) s(-1) the different initial textures yielded the same end texture, despite different microstructural evolution in terms of twin boundaries. High strain rate deformation at (epsilon)over dot = 1.5 x 10(3) s(-1) was characterized by extensive twinning and evolution of a texture that was similar to that at low strain rate with minor differences. However, there was a significant difference in the strength of the texture for different orientations that was absent for low strain rate deformed samples at high strain rate. A viscoplastic self-consistent model with a secant approach was used to corroborate the experimental results by simulation. (C) 2011 Published by Elsevier Ltd. on behalf of Acta Materialia Inc.

Reversible and irreversible switching processes in pure and lanthanum modified lead zirconate thin films

The mechanism of field induced phase switching in antiferroelectric lead zirconate and La-modified lead zirconate thin films has been analysed in terms of reversible and irreversible switching process under weak fields as a function of donor concentration. Extension of Rayleigh law of ferromagnetic materials to the present antiferroelectric and modified antiferroelectric compositions have clearly showed that origin of small signal dielectric permittivity is due to reversible domain wall motion. Rayleigh's constant, a measure of irreversible switching process, exhibited a slight increase with lower La3+ concentrations and followed by a gradual fall for higher concentration. This clearly illustrates that donor addition to antiferroelectric thin films controls the domain switching even under weak fields. (C) 2002 Elsevier Science B.V. All rights reserved.

Probing the Allosteric Mechanism in Pyrrolysyl-tRNA Synthetase Using Energy-Weighted Network Formalism

Pyrrolysyl-tRNA synthetase (PyIRS) is an atypical enzyme responsible for charging tRNA(Pyl) with pyrrolysine, despite lacking precise tRNA anticodon recognition. This dimeric protein exhibits allosteric regulation of function, like any other tRNA synthetases. In this study we examine the paths of allosteric communication at the atomic level, through energy-weighted networks of Desulfitobacterium hafniense PyIRS (DhPyIRS) and its complexes with tRNA(Pyl) and activated pyrrolysine. We performed molecular dynamics simulations of the structures of these complexes to obtain an ensemble conformation-population perspective. Weighted graph parameters relevant to identifying key players and ties in the context of social networks such as edge/node betweenness, closeness index, and the concept of funneling are explored in identifying key residues and interactions leading to shortest paths of communication in the structure networks of DhPylRS. Further, the changes in the status of important residues and connections and the costs of communication due to ligand induced perturbations are evaluated. The optimal, suboptimal, and preexisting paths are also investigated. Many of these parameters have exhibited an enhanced asymmetry between the two subunits of the dimeric protein, especially in the pretransfer complex, leading us to conclude that encoding of function goes beyond the sequence/structure of proteins. The local and global perturbations mediated by appropriate ligands and their influence on the equilibrium ensemble of conformations also have a significant role to play in the functioning of proteins. Taking a comprehensive view of these observations, we propose that the origin of many functional aspects (allostery rand half-sites reactivity in the case of DhPyIRS) lies in subtle rearrangements of interactions and dynamics at a global level.

The ω Phase Formation during Laser Cladding and Remelting of Quasicrystal Forming AlCuFe on Pure Aluminum

We report the formation ω phase in the remelted layers during laser cladding and remelting of quasicrystal forming Al65Cu23.3Fe11.7 alloy on pure aluminum. The ω phase is absent in the clad layers. In the remelted layer, the phase nucleates at the periphery of the primary icosahedral phase particles. A large number of ω phase particles forms enveloping the icosahedral phase growing into aluminum rich melt, which solidify as α-Al solid solution. On the other side it develops an interface with aluminum. A detailed transmission electron microscopic analysis shows that ω phase exhibits orientation relationship with icosahedral phase. The composition analysis performed using energy dispersive x-ray analyzer suggests that this phase has composition higher aluminum than the icosahedral phase. The analysis of the available phase diagram information indicates that the present results represent large departure from equilibrium conditions. A possible scenario of the evolution of the ω phase has been suggested.

Study of texture evolution of Pure Magnesium during ECAE using EBSD

Commercially Pure Magnesium initially hot rolled and having a basal texture was deformed by Equal Channel Angular Extrusion (ECAE). ECAE was carried out upto 8 passes in a 90° die following routes A and Bc through a processing sequence involving two temperatures, namely 523 and 473 K. Texture and microstructure formed were studied using electron back scatter diffraction (EBSD) technique. In addition to significant reduction in grain size, strong <0002> fiber texture inclined at an angle ~ 45o from the extrusion axis formed in the material. Texture was also analyzed by orientation distribution function (ODF) and compared vis-à-vis shear texture. A significant amount of dynamic recrystallization occurred during ECAE, which apparently did not influence texture.

Enhancement of charge and energy storage in sol-gel derived pure and La-modified PbZrO3 thin films

Antiferroelectric lanthanum-modified PbZrO3 thin films with La contents between 0 and 6 at. % have been deposited on Pt(111)/Ti/SiO2/Si substrate by sol-gel route. On the extent of La-modification, maximum polarization (Pmax) and recoverable energy density (W) have been enhanced followed by their subsequent reduction. A maximum Pmax ( ∼ 0.54 C/m2 at ∼ 60 MV/m) as well as a maximum W ( ∼ 14.9 J/cc at ∼ 60 MV/m) have been achieved on 5% La modification. Both Pmax and W have been found to be strongly dependent on La-induced crystallographic orientations.

The omega phase formation during laser cladding and remelting of quasicrystal forming AlCuFe on pure aluminum

We report the formation omega phase in the remelted layers during laser cladding and remelting of quasicrystal forming Al65Cu23.3Fe11.7 alloy on pure aluminum. The omega phase is absent in the clad layers. In the remelted layer, the phase nucleates at the periphery of the primary icosahedral phase particles. A large number of omega phase particles forms enveloping the icosahedral phase growing into aluminum rich melt, which solidify as alpha-Al solid solution. On the other side it develops an interface with aluminum. A detailed transmission electron microscopic analysis shows that omega phase exhibits orientation relationship with icosahedral phase. The composition analysis performed using energy dispersive x-ray analyzer suggests that this phase has composition higher aluminum than the icosahedral phase. The analysis of the available phase diagram information indicates that the present results represent large departure from equilibrium conditions. A possible scenario of the evolution of the omega phase has been suggested.

Association rule mining activity : A general formalism

Mining association rules from a large collection of databases is based on two main tasks. One is generation of large itemsets; and the other is finding associations between the discovered large itemsets. Existing formalism for association rules are based on a single transaction database which is not sufficient to describe the association rules based on multiple database environment. In this paper, we give a general characterization of association rules and also give a framework for knowledge-based mining of multiple databases for association rules.

Size-mediated cytotoxicity of nanocrystalline titanium dioxide, pure and zinc-doped hydroxyapatite nanoparticles in human hepatoma cells

Nanoparticles are highly used in biological applications including nanomedicine. In this present study, the interaction of HepG2 hepatocellular carcinoma cells (HCC) with hydroxyapatite (HAp), zinc-doped hydroxyapatite, and titanium dioxide (TiO2) nanoparticles were investigated. Hydroxyapatite, zinc-doped hydroxyapatite and titanium dioxide nanoparticles were prepared by wet precipitation method. They were subjected to isochronal annealing at different temperatures. Particle morphology and size distribution were characterized by X-ray diffraction and transmission electron microscope. The nanoparticles were co-cultured with HepG2 cells. MTT assay was employed to evaluate the proliferation of tumor cells. The DNA damaging effect of HAp, Zn-doped HAp, and TiO2 nanoparticles in human hepatoma cells (HepG2) were evaluated using DNA fragmentation studies. The results showed that in HepG2 cells, the anti-tumor activity strongly depend on the size of nanoparticles in HCC cells. Cell cycle arrest analysis for HAp, zinc-doped HAp, and TiO2 nanoparticles revealed the influence of HAp, zinc-doped HAp, and titanium dioxide nanoparticles on the apoptosis of HepG2 cells. The results imply that the novel nano nature effect plays an important role in the biomedicinal application of nanoparticles.

Influence of ethanol/water mixture on the undrained shear strength of pure clays

The mechanical properties of clays are highly dependent not only on the stress/strain ratio to which the material is subjected but also on the chemistry of the pore fluids which in turn affects the intergranular or the effective stresses. Atterberg limits and vane shear tests were performed with different pore fluids in order to observe how the fine-grained material mechanically responded. The diffuse double layer theory has been used to interpret the data of vane shear tests in order to explain the variation of geotechnical responses with the different clays. Van der Waals forces and double layer forces were obtained and capillary forces calculated. The results show that while for kaolinite and illite the chemistry of the pore fluids has no influence on the water content and hence on the mechanical behaviour of the material, Na-smectite shows a strong correlation between the dielectric constant of the pore fluids and an increase in undrained shear strength. The data obtained extends an understanding of the influence of the dielectric constant (epsilon) of the pore fluids on the geotechnical properties of fine-grained materials.

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.

Magneto-Transport Study of Pure and Co Doped ZnO Thin Films

A detailed low temperature magneto-transport study is carried out to understand the transport mechanism in pure and Co doped ZnO thin films grown by pulsed laser deposition (PLD) technique. A negative transverse magneto-resistance (MR) (with a value similar to 4% at 4.5 K) which decreases monotonically with the increase in temperature, is observed for the undoped ZnO film. A competition between positive and negative MR is observed for the Co doped ZnO samples. In this case at higher field values negative MR contribution dominates over the positive MR, which gives rise to a slope change in the MR data. Our data for MR shows excellent agreement with the semi-empirical formula given by Khosla et al., which is originally proposed for the degenerate semiconductors. This formula incorporates the third order perturbation expansion of the s-d exchange scattering of the conduction electrons from the localised spins. We have also obtained the Hall mobility, carrier conc. and mean free path as function of temperature for the pure ZnO film.

The irradiation of pure CH3OH and 1:1 mixture of NH3:CH3OH ices at 30 K using low energy electrons

The results of an experimental investigation of 1 keV electron irradiation of ices (deposited at 30 K) of (i) pure methanol and (ii) of a 1:1 mixture of NH3:CH3OH are reported. Molecular products formed within the ice were detected and monitored using FTIR spectroscopy. The products observed were methyl formate (H3COHCO), methane (CH4), hydroxymethyl (CH2OH), formamide (HCONH2), formic acid (HCOOH), formaldehyde (H2CO), formyl radical (HCO), cyanate ion (OCN-), isocyanic acid (HNCO), carbon monoxide (CO) and carbon dioxide (CO2). The consequences of these results for prebiotic chemistry in the interstellar medium and star forming regions are discussed. Crown Copyright (C) 2012 Published by Elsevier B. V. All rights reserved.