Infiltration-Growth Processing of NdBa2Cu3O7-delta Superconductor

NdBa₂Cu₃O_7-delta (Nd-123) superconductor has been processed to obtain a highly textured microstructure with micrometer-sized spherical Nd₄Ba₂Cu₂O₁₀ (Nd-422) inclusions through a process that involves the infiltration of liquid phases into a shaped preform followed by its slow cooling through the peritectic formation temperature of Nd-123. The process was carried out in high-purity argon (maximum of 4 ppm of oxygen) to reduce the formation of low- T _c solid solutions. A major advantage of the process is that it minimizes the possibility of Nd-422 coarsening in the liquid. The result is a very uniform distribution of nearly spherical Nd-422 inclusions with 80% of the particles having a diameter less than 1 µm, in the highly textured Nd-123 matrix. Since the present process eliminates shrinkage and large hollows within the interior of the samples, it can enable the fabrication of 3-dimensional complex-shaped objects with good dimensional tolerance and high J _c for applications. The critical current densities in the Nd-123/Nd-422 composites have been measured and the values obtained are discussed in the context of the microstructure of the material.     

Stability characteristics of a biochemical reactor with predator-prey relationship. A substrate inhibition case

The present work characterizes static behaviour of a CSTBR with existing food chain relationship, for a case when base carbon and energy source exhibits toxic influence on enzymatic pathways of all microorganisms. Some bifurcation diagrams for representative process parameters are presented, together with characteristic phase plane plots. Conditions leading to induction of persistent oscillations of substrate and cell concentration are derived, and ways to avoid them are also given herein.     

Alkylene oxide poylmerizations: identification of side reactions and by-products

In this study microwave-assisted anionic ring opening polymerization (ROP) of alkylene oxides is reported. Low molar mass polymers of propylene oxide (PO), butylene oxide (BO) and hexylene oxide (HO) are synthesized by anionic ring opening using various monohydric alcohols as initiators. The monohydric alcohols and lower molar masses allowed for monitoring of different types of possible unwanted by-products and their sources. Liquid chromatography at critical conditions (LCCC) and liquid adsorption chromatography (LAC) are used to determine the presence of oligomers other than targeted. Finally, MALDI-TOF MS of the products have clearly shown the trends and extents of different types of side reactions that are possible in anionic ring opening of alkylene oxides. Propylene oxide is most vulnerable to chain transfer reactions compared to higher alkylene oxide.     

NITROGEN REAGENTS IN METAL ION SEPARATION. PART IX. EXTRACTION OF COBALT AND NICKEL USING IMIDAZOLE DERIVATIVES

ABSTRACT

The extraction capability of derivatives of imidazole towards Co(II) and Ni(II) has been investigated in dilute acid medium in the presence of each of chloride, perchlorate and thiocyanate ions. The influence of the stereochemistry of the substituted imidazole on the extraction behaviour has been investigated. Two-phase potentiometric titrations were employed to determine the nature of the metal species extracted into the organic phases. The electronic spectra of the extracted metal species have been employed to provide information of the nature of such species.     

A generalized methodology for optimal configurations of hybrid distillation-pervaporation processes

The aim of this work is to illustrate the structural and parametric optimization of continuous hybrid distillation-pervaporation process with different configurations such as series, parallel, and series-parallel arrangement of pervaporation modules in the pervaporation network, and to propose a generalized methodology for difficult separations. A superstructure representation of hybrid process is considered and the process is modeled and optimized using an MINLP approach. The optimization strategy is to obtain the desired degree of either the retentate or the distillate purity without violating the composition constraints of products and heat exchange policy which minimizes the required membrane area by increasing the flux through the membrane. The structural and operating parameters such as number of trays required, feed tray location, reflux ratio, retentate recycle location, permeate recycle location, membrane feed location, number of pervaporation modules required, target composition (which is directly related to membrane area), and membrane selectivity are optimized for each configuration by minimizing the total annual cost (TAC) for the separation system. The optimization studies have been carried out with General Algebraic Modeling System software (GAMS/SBB/CONOPT) and the results of different configurations have been compared on the basis of TAC required for the separation. A total of three industrial case studies have been dealt with. The separation of isopropanol-water as an azeotropic mixture, propylene-propane as a close boiling mixture (system with a low relative volatility) and acetone-water as a tangent pinch mixture have been studied as representative examples.     

The influence of electrospinning parameters on the structural morphology and diameter of electrospun nanofibers

Electrospinning is a simple method of producing nanofibers by introducing electric field into the polymer solutions. We report an experimental investigation on the influence of processing parameters and solution properties on the structural morphology and average fiber diameter of electrospun poly ethylene oxide (PEO) polymer solution. Experimental trials have been conducted to investigate the effect of solution parameters, such as concentration, molecular weight, addition of polyelectrolyte in PEO solution, solvent effect, as well as governing parameter, such as applied voltage. The concentration of the aqueous PEO solution has shown noteworthy influence on the fiber diameter and structural morphology of electrospun nanofibers. At lower concentrations of PEO polymer solution, the fibers showed irregular morphology with large variations in fiber diameter, whereas at higher concentrations, the nanofibers with regular morphology and on average uniform fiber diameter were obtained. We find that the addition of polyelectrolytes, such as sodium salt of Poly acrylic acid (PAA) and Poly allylamine hydrochloride (PAH), increases the conductivity of PEO solutions and thereby decreases the bead formation in electrospun nanofibers. The increase in applied voltage has been found to affect the structural morphology of nanofiber while the addition of ethanol in PEO solution diminishes the bead defects. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A review of molecular interactions in organic binary mixtures

The intention of this review article is to review the knowledge about interactions in organic binary liquid mixtures. Molecular interactions in organic binary liquid mixtures are interesting due to their extensive use in many fields of solution chemistry. The thermodynamics of component molecules present in various systems interacting are particularly interesting because they display fantastic results. Studies of different organic liquid mixtures represent the different modes of interactions prevailing in the component molecules. The number of parameters required describing the properties of a given class of mixtures increases sharply with the number of segment types involved. In recent years, the theoretical and experimental investigations of interactions between unlike molecules have been conveniently carried out using excess thermodynamic functions. The properties of liquid mixtures depend on the forces between molecules and on the nature and volume of these molecules, and change with the composition of the mixtures. This change, in turn, is reflected in the thermodynamic properties of the mixtures. The influence of significant contributions of a chemical, physical and geometrical nature that change excess thermodynamic properties is considered and explained in detail.     

Multiple binding modes for the receptor-bound conformations of cyclic AII agonists

Angiotensin II, Asp-Arg-Val-Tyr-His-Pro-Phe, binds its receptor with a postulated turn centered at residue four. Analogs of angiotensin II which contain a disulfide bridge between the side chains of residues 3 and 5 retain significant activity consistent with this hypothesis. Incorporation of 4-mercaptoproline residues, a hybrid, or chimeric amino acid which combines the properties of proline and homocysteine, into either of these positions with analogous disulfide bridges allows retention of high affinity for the receptor. These more highly constrained bicyclic systems give new insight into the details of molecular recognition of residues 3-5 of angiotensin by the receptor. Retention of activity by the antiparallel dimer of [Sar1,Cys3,5]-AII in which the peptide backbone is held in an extended conformation was unexpected. Analysis of the conformational constraints imposed in these active analogs suggests that AII agonists bind to their receptor with different backbone conformations in the region of the central tyrosine residue.     

Cross-Buoyancy Mixed Convection Around a Confined Triangular Bluff Body

Two-dimensional numerical simulations are carried out to understand the effects of cross-buoyancy on the confined flow and heat transfer characteristics over an equilateral triangular bluff body at low and intermediate Reynolds numbers (Re). For a fixed Richardson number (Ri), an average cylinder Nusselt number increases with increasing Re. However, the average Nusselt number shows a soft response toward increasing Ri. The critical Re for the onset of periodic unsteady flow increases with increasing cross-buoyancy (Ri). A simple heat transfer correlation is also obtained to relate the values of average cylinder Nusselt number, Re, and Ri.