Influence of sintering temperature on microstructure,critical current density and pinning potential of superconducting Bi1.6Pb0.5Sr1.8Dy0.2Ca1.1Cu2.1O8+δ ceramics

The influence of sintering temperature on the microstructure, critical current density (J_C), pinning potential values (U₀) and flux pinning properties of Bi_1.6Pb_0.5Sr_1.8Dy_0.2Ca_1.1Cu_2.1O_8+δ superconductor has been investigated. The samples are prepared by the solid-state route and sintered at temperatures ranging from 846 to 860 °C. A systematic correlation between the sintering temperature, Lotgering index, J_C, U₀ and flux pinning properties has been found. The samples sintered at lower sintering temperature (846 °C) have more grain boundaries with smaller grains while those sintered at a higher temperature (856 °C) contain larger grains with good texturing. The flux pinning force (F_P) calculated from the field dependent J_C values shows that the irreversibility lines (IL) of the Dy-doped samples shift towards higher fields to different extents depending on the sintering temperature. The maximum value of F_P = 1697 kN m^?3 is obtained for the sample sintered at 846 °C and the peak position of F_P is obtained at 0.96 T as against 616 kN m^?3 and 0.52 T for the sample sintered at 856 °C. The U₀ values calculated by Anderson's function is maximum for the sample sintered at 846 °C. But the self-field J_C value of this sample is lower than that of the samples sintered at 856 °C. The samples sintered at 856 °C show best self-field J_C due to the improved microstructure. The changes in microstructure followed by very high enhancement of self-field J_C, J_C(B) characteristics, F_P and U₀ values within a narrow temperature range, are of great scientific and technological significance and the results are explained on the basis of microstructural variation with respect to sintering temperature, hole optimization and formation of point defects due to the doping of Dy atoms in Bi_1.6Pb_0.5Sr_1.8Dy_0.2Ca_1.1Cu_2.1O_8+δ system.     

Synthesis of functional hybrid silica scaffolds with controllable hierarchical porosity by dynamic templating

We report a facile one-pot synthesis of hierarchically porous scaffolds, with independent control over nanoparticle mesoporosity and scaffold macroporosity. Our technique combines the chemistry of mesoporous silica nanoparticles with the control afforded by dynamic templating of surfactant mesophases. These materials are readily functionalizable and allow controllable spatial variation in macroporosity.     

Studies on vibration of some rib-stiffened cantilever plates

An experimental study was carried out to determine the resonant mode shapes and frequencies of some rib-stiffened skew cantilever plates by holographic interferometry. The influences of varying the sweep back angle, the rib stiffness and the aspect ratio, and the effect of varying the boundary conditions at the root chord, on the frequencies and mode shapes were also investigated. Results of the above investigation and also those of a comparative study with the finite element solution obtained for some of the cases studied are presented and discussed.     

Elastic piezoelectric aerogels from isotropic and directionally ice-templated cellulose nanocrystals: comparison of structure and energy harvesting

We report the preparation of highly compressible and elastic piezoelectric aerogels of carboxylated cellulose nanocrystals (CNCs). Aqueous CNC dispersions containing polyethyleneimine and crosslinker were frozen isotropically to yield isotropic aerogels, while oriented aerogels were prepared by directional freezing. These aerogels were highly flexible and porous (~?85% void fraction), exhibiting greater than 90% recovery at 50% compressive strain even after 100 compression–decompression cycles. Since such aerogels with low bulk modulus and high anisotropy would be an ideal platform for leveraging the piezoelectric properties of CNCs, we used them to prepare piezoelectric nanogenerator devices and determined their energy transduction behavior. Anisotropic aerogels led to an enhanced open-circuit voltage of 840 mV (at ~?8 N applied force), which is over 2.6 times higher than isotropic aerogels (320 mV). The energy density of anisotropic aerogels was around 52 nW/cm², representing outstanding piezoelectric performance for cellulose-based aerogels. Such aerogels with high compressibility, elastic recovery and exceptional piezoelectric performance could have potential applications in sensors, wearable electronics, etc.

     

Synthesis and Antimicrobial Evaluation of Novel N-Substituted β-Hydroxy Benzimidazole Sulfone Fluoroquinolones by Selective Oxidation Using Ticl4-H2O2

Abstract

The synthesis of N-substituted β-hydroxy benzimidazole sulfones containing 8-methoxy fluoroquinolone has been described and they were evaluated for antimicrobial activities. The compounds of N-substituted β-hydroxy benzimidazole sulfides (4a–e) and N-substituted β-hydroxy benzimidazole sulfones (5a–e) at C-7 of fluoroquinoline exhibited superior activity in vitro. 8-Methoxy fluoroquinolone carboxylic acid (1), reaction with piperizine in acetonitrile in presence of triethylamine under reflux gives 7-piperazinyl-8-methoxyfluoroquinolone (2). The latter is reacted with epichlorohydrine in presence of NaOH in acetone yielded N-substituted epoxide (3), which on treatment with 5-substituted-2-mercaptobenzimidazoles gives N-substituted β-hydroxy benzimidazole sulfides (4). Further, 4 on treatment with TiCl₄-H₂O₂ and in DCM yielded the corresponding N-substituted β-hydroxy benzimidazole sulfone (5).     

A sector finite element for dynamic analysis of thick plates

A 24 degree of freedom sector finite element is developed for the static and dynamic analysis of thick circular plates. The element formulation is based on Reissner's thick plate theory. The convergence characteristic of the elements is first studied in a static example of an unsymmetrically loaded annular plate. The obvious advantageous effect of including the twist derivatives of deflection as degrees of freedom is shown. The elements are then used to analyze the natural frequencies of an annular plate with various ratios of inner to outer radius. The results are in good agreement with an alternative solution in which thick plate theory is used. The versatility of this finite element is finally demonstrated by performing free vibration analysis of an example of clamped sector plates with various thicknesses and different sectorial angles.     

Synthesis,Characterization, and Antimicrobial Activities of Novel N‐substituted β‐Hydroxy Amines and β‐Hydroxy Ethers that Contained 8‐Methoxy Fluoroquinolones

Synthesis of novel N‐substituted β‐hydroxy amines 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j and β‐hydroxy ethers 5a , 5b , 5c that contained 8‐methoxy fluoroquinolones has been described. 8‐Methoxy fluoroquinolone carboxylic acid 1 , reacted with piperizine in acetonitrile in the presence of triethyl amine under reflux, gave 7‐piperazine 8‐methoxyfluoroquinolone 2 . The latter is reacted with epichlorohydrine in the presence of NaOH in acetone to yield the N‐substituted epoxide 3 , which on treatment with aliphatic, aromatic, and cyclic amines gives β‐hydroxy amines 4a , 4b , 4c , 4d , 4e , 4f , 4g , 4h , 4i , 4j . On other hand, 3 on treatment with alcohols in the presence of NaOH afforded the corresponding β‐hydroxy ethers 5a , 5b , 5c . The structures of the synthesized compounds have been established on the basis of spectral and analytical data. Docking analysis was performed using Surflex‐Dock module in Sybyl X 1.0. The antimicrobial activities of newly synthesized compounds were evaluated against bacteria and fungi by using moxifloxacin as the reference. Many of the evaluated compounds exhibited remarkable activities.     

Ordering and magnetostriction in Fe alloy single crystals

Short-range and long-range ordering in α-Fe terminal solid solution phase (A2 phase with bcc structure) influences its physical, mechanical, magnetic and magnetostrictive behavior. Single crystal sample forms are ideal for examining order in these alloys using X-ray and neutron scattering techniques. Limited structural information available suggests that the lattice of A2 phase at room temperature contains a mixture of regions with local atomic environments similar to those expected in the long-range ordered structures in stable/metastable equilibrium with the A2 phase. The nature and extent of these regions are sensitive to alloy composition and the thermal history. The lattice strain modulations result from the nature of solute atom distribution (short-range ordering) in each region and impact the physical, mechanical, corrosion and magnetic behaviors. A need for a fundamental understanding of ordering in Fe and other alloys through structural evaluations of local atomic environments in alloy single crystals is suggested in this review.     

Serial and parallel simulated annealing and tabu search algorithms for the traveling salesman problem

This paper describes serial and parallel implementations of two different search techniques applied to the traveling salesman problem. A novel approach has been taken to parallelize simulated annealing and the results are compared with the traditional annealing algorithm. This approach uses abbreviated cooling schedule and achieves a superlinear speedup. Also a new search technique, called tabu search, has been adapted to execute in a parallel computing environment. Comparison between simulated annealing and tabu search indicate that tabu search consistently outperforms simulated annealing with respect to computation time while giving comparable solutions. Examples include 25, 33, 42, 50, 57, 75 and 100 city problems.