Intergranular Critical Current Density in Polycrystalline (Bi-Pb)-2223 High Temperature Superconductor by ac Susceptibility Measurements

The field dependence of real () and imaginary () component of ac susceptibility of superconductors within the critical state model can conveniently be used for evaluating the critical current when field amplitude is larger than the penetration field. A method to analyze the real () and imaginary () component of fundamental ac susceptibility with the objective of extracting the temperature dependence of critical current density J _c(T) is reported. The procedure makes use of the ac susceptibility data of two polycrystalline (Bi-Pb)-2223 samples measured with different excitation amplitudes below and close to the critical temperature. The temperature dependence of J _c is extracted using the isothermal scan over and data. Results obtained from this procedure are found to be in fair agreement with J _c(T) calculated from traditional loss-maximum data.     

Synthesis and Biological Evaluation of Ferrocenylquinoline as a Potential Antileishmanial Agent

The emergence of resistance against antileishmanial drugs in current use necessitates the search for new classes of antileishmanial compounds. Herein we report the design, synthesis, and evaluation of a novel ferrocenylquinoline for activity against Leishmania donovani. 7‐Chloro‐N‐[2‐(1H‐5‐ferrocenyl‐1,2,3‐triazol‐1‐yl)ethyl]quinolin‐4‐amine ( 1 ) was generated by coupling an iron(II) ethynylferrocene species with 4‐(2‐ethylazido)amino‐7‐chloroquinoline using click chemistry. The synthesized compound 1 was tested for its antileishmanial activity using both promastigote and amastigote stages of L. donovani. Compound 1 showed promising anti‐promastigote activity, with an IC₅₀ value of 15.26 μM and no cytotoxicity toward host splenocytes. From the battery of tests conducted in this study, it appears that this compound induces parasite death by promoting oxidative stress and depolarizing the mitochondrial membrane potential, thereby triggering apoptosis. These results suggest that ferrocenylquinoline 1 is a suitable lead for the development of new antileishmanial drugs.     

Sediment Pickup on Streamwise Sloping Beds

This paper presents an experimental investigation on noncohesive sediment pickup under a unidirectional steady-uniform stream flow on streamwise steeply sloping (down slope and adverse) sedimentary beds. The characteristic parameters affecting the sediment pickup, identified based on the physical reasoning and dimensional analysis of the sediment particle movement under stream flow, are the transport-stage parameter, particle parameter, and geometric standard deviation of sediment particles. A large number of experiments (426 runs) were carried out in two long rectangular ducts (closed-conduit flow) with nine types of sediments (six uniform and three nonuniform sediments), having a variation of bed slope from ?15° (adverse slope) to 25° (down slope). In an open channel flow (laboratory flume study), the uniform flow is a difficult, if not impossible, proposition for a steeply sloping channel and is impossible to obtain in an adversely sloping channel. To avoid this problem, the tests were conducted with a closed-conduit flow. Measurements included flow discharge and sediment pickup rate. The bed shear stress for a particular run was computed considering side wall correction. The experimental data were used to determine the equation of sediment pickup function through a regression analysis. The equation is adequate to estimate sediment pickup not only on horizontal and mild slopes but also on steep and adverse slopes.     

Localized Delaunay Refinement for Sampling and Meshing

The technique of Delaunay refinement has been recognized as a versatile tool to generate Delaunay meshes of a variety of geometries. Despite its usefulness, it suffers from one lacuna that limits its application. It does not scale well with the mesh size. As the sample point set grows, the Delaunay triangulation starts stressing the available memory space which ultimately stalls any effective progress. A natural solution to the problem is to maintain the point set in clusters and run the refinement on each individual cluster. However, this needs a careful point insertion strategy and a balanced coordination among the neighboring clusters to ensure consistency across individual meshes. We design an octtree based localized Delaunay refinement method for meshing surfaces in three dimensions which meets these goals. We prove that the algorithm terminates and provide guarantees about structural properties of the output mesh. Experimental results show that the method can avoid memory thrashing while computing large meshes and thus scales much better than the standard Delaunay refinement method.     

Properties of vinyl ester resins containing methacrylated fatty acid comonomer: the effect of fatty acid chain length

This paper reports the formulation of a low‐cost vinyl ester‐based composite resin suitable for liquid molding, which has significantly lower volatile organic compound emission associated with it. Methacrylated fatty acid comonomers were used to replace the conventional yet environmentally hazardous reactive diluent, styrene. The chain length of these fatty acids played a key role in obtaining better viscosity, as it was proved to affect two interplaying factors: intermolecular friction and hydrogen bonding. The thermomechanical performance was greatly affected by the chain length of the fatty acids as well as the crosslink density of the polymer networks. A carbon number of 6 to 8 was good enough in optimizing the viscosity parameter suitable for handling; the dynamic mechanical analysis values, namely glass transition temperature and storage modulus, were in the range 66–121 °C and 0.97–2.8 GPa, respectively, as the carbon number was varied from 4 to 16, making the material suitable for various applications. Microstructures obtained from scanning electron microscopy results were correlated with polymer properties to obtain a better insight into these polymer networks. Copyright © 2007 Society of Chemical Industry     

A novel method for synthesis of α-Si3N4 nanowires by sol–gel route

Silicon nitride (Si₃ N₄) nanowires have been prepared by carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine excess carbon obtained by the decomposition of dextrose over the temperature range of 1200–1350 °C. This innovative process involves repeated evacuation followed by purging of nitrogen gas so that the interconnected nanopores of the gel are filled with nitrogen gas prior to heat treatment. During heat treatment at higher temperatures, the presence of nitrogen gas in the nanopores of the gel starts the CTRN reaction simultaneously throughout the bulk of the gel, leading to the formation of Si₃ N₄ nanowires. The in situ generated ultrafine carbon obtained by the decomposition of dextrose decreases the partial pressure of oxygen in the system to stabilize the nanowires. The nanowires synthesized by this process are of ∼500 nm diameter and ∼0.2 mm length. The product was characterized by scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX), x-ray diffraction (XRD) and infrared (IR) spectra.     

Laser flash photolysis and magnetic-field-effect studies on interaction of thymine and thymidine with menadione: role of sugar in controlling reaction pattern

The magnetic field effect (MFE) in conjunction with laser flash photolysis has been used for the study of the interaction of one of the small drug like quinone molecules, 2-methyl, 1,4-naphthoquinone, commonly known as menadione (MQ), with one of the DNA bases, thymine (THN), and its corresponding nucleoside, thymidine (THDN), in acetonitrile (ACN) and sodium dodecylsulfate (SDS) micelles. It has been observed that THN undergoes electron transfer (ET) and hydrogen (H) abstraction with MQ, while THDN undergoes only H abstraction in both the media. However, our earlier studies showed that a purine base, adenine (ADN), and its nucleoside, 2′-deoxyadenosine (ADS), undergo ET in ACN and H abstraction in SDS. Here we have attempted to explain the differences in the reactions of these DNA bases with MQ. We also reveal the crucial role of a sugar unit in altering the behavior of purine and pyrimidine bases with respect to ET and H abstraction.     

Shock deformation of coarse grain alumina above Hugoniot elastic limit

Symmetric shock experiments were conducted on a 10 μm grain size coarse alumina ceramic with a gas gun to identify its Hugoniot elastic limit (HEL). To understand the damage initiation and their subsequent growth mechanisms in coarse grain alumina subjected to shock impact at levels much above the HEL, additional asymmetric shock recovery experiments with the same gas gun were then deliberately conducted on the same alumina at shock pressure levels more than three times as high as the HEL and the fragments collected by a dedicated catcher system. Detailed characterization of the shock recovered alumina fragments by X-ray diffraction, nanoindentation, scanning electron microscopy, field emission scanning electron microscopy and transmission electron microscopy were utilized to understand the nature and process of failure initiation, incubational growth, coalescence and propagation leading to fragmentation. Based on these data a new qualitative damage model was developed to explain the deformation mechanism.     

Crystallization kinetics of Zr-33 at % Ni amorphous alloy

The amorphous to crystalline transition in Zr-33 at% Ni amorphous alloy has been found to occur by polymorphic crystallization. The product of the cyrstallization process has been identified as the equilibrium Zr₂Ni intermetallic phase. The kinetics of crystallization have been studied independently using differential scanning calorimetry (DSC) and transmission electron microscopy. The activation energy of crystallization has been evaluated by isothermal and continuous heating in DSC. The isothermal anneals have revealed that the crystallization follows the Johnson-Mehl-Avrami kinetics with an Avrami exponent close to 4. The microstructural changes accompanying crystallization have been studied for an interpretation of the Avrami exponent. The nucleation and growth rates of crystals have been estimated at different temperatures in order to determine the activation energies of the two processes. It has been found that nucleation is thermally activated and growth is interface controlled.