Experimental investigation of the LiAlSi2O6‐MgSiO3 and LiAlSi2O6‐CaMgSi2O6 isopleths at 1 atm

The phase diagrams of the LiAlSi₂O₆‐MgSiO₃ and LiAlSi₂O₆‐CaMgSi₂O₆ isopleths were experimentally investigated at 1 atm using the quenching method and differential scanning calorimetry and the phases produced were characterized with the help of X‐ray diffraction and electron probe microanalysis. With the help of thermodynamic optimization, the phase diagrams of both systems were more accurately reported. No detectable solubility of Li₂O in diopside and enstatite was found. However, both systems are not simple binary eutectic systems because their phase equilibria are somewhat complex due to the presence of some β‐spodumene solid solution. In the β‐spodumene solid solution, no notable solubility of MgO and CaO was detected; evidence of significant solubility of SiO₂ was confirmed.     

Contested Infrastructures: Tension,Inequity and Innovation in the Global Suburb

Abstract

The article explores the suburban infrastructure reality at a global scale. It does so by acknowledging both the wide diversity of suburban forms across the world and the existence of common features that warrant the apprehension of suburbs as a unified object of study. Due to their rapid growth rate and an insufficient infrastructure development response, suburbs are perceived as more severely afflicted by infrastructure tensions than other urban sectors. They thus provide an ideal object of study to identify urban infrastructure shortcomings in the present age. At the same time, by virtue of their infrastructure difficulties and ongoing expansion, suburbs can be seen as a foremost source of infrastructure innovation.     

Boolean query optimization and the 0-1 hyperbolic sum problem

An intelligent front-end or logic assistant is an interactive program devised to assist the users of an information retrieval system in the formulation of their queries. In order to provide knowledge usable in such a program, we study a problem of query optimization with an average efficiency criterion. We formulate it as a new combinatorial optimization problem, which we call 0-1 hyperbolic sum, and provide an exact branch-and-bound algorithm and two heuristics (of simulated annealing and tabu search type) to solve it. Computational experience illustrating the effectiveness of the tabu search technique is reported.This research was done in part during a visit of the first author to the Pontifical Catholic University of Rio de Janeiro in July and August 1987, sponsored by CNPq. It was also supported in part by grants 0271 and 0066 of AFOSR to Rutgers University.     

Homogeneous and Heterogeneous Hydrogenation of Nitriles in a Liquid Phase: Chemical, Mechanistic, and Catalytic Aspects

Primary or alkylated amines are important chemicals and intermedi-ates. N-Alkylamines are used without further transformation as surface-active agents. Aliphatic primary diamines polymerize with aliphatic diacids to give linear polyamides which have conquered a large place in textile and mechanical industry [11. Mono- and polyamines are produced by catalytic hydrogenation of the corresponding nitriles [2]. In particular this pathway to hexamethylenediamine has been made easier since the synthesis of adi-ponitrile by hydrocyanation of butadiene was made possible [3]. The spec-ifications for production of amines are often very drastic from the point of view of purity, in particular for the diamines used in the textile industry. Thus the stress is put on selectivity of the reaction and most of industrial processes have a yield approaching stoichiometry. It exists few reviews on reduction of nitriles [4, 51, the literature dealing with this type of reaction being mostly published in patents [6-91, and practical knowledge is at the state of “know-how” [lo]. Up to now, two types of processes have been used industrially for the     

Polarity measurements in block copolymers (polyurethaneimides) and correlation with their pervaporation features

EtOH/ETBE azeotropic mixture was separated by pervaporation through films of polyurethaneimides (PUI), i. e., alternating block copolymers varying in their structure only by their oligomeric soft blocks. Pervaporation performances strongly depend on the flexible segments: fluxes on the molecular weight and selectivity towards ethanol on the chemical structure in the decreasing order: PEG, PCL, PCD, PTMG, PPG. In order to correlate selectivity with segment polarity, a new solvatochromic polarity probe that was well soluble in PUI was synthesized. Using 13 solvents covering a wide polarity range, Vis λ^max of the photochromic indicator open form was linearly correlated with the E_T(30) polarity scale. By illumination of the dissolved dye, PUI polarity was investigated in relation to soft segment nature and size. The very high PUI polarity values and their splitting for highest size segments were assigned to preferential probe solvation by interblock urethane junctions combined with phase segregation. Polarity values consistent with the chemical structure of the flexible segments were provided by similar measurements on suitably end-capped precursors of these segments and were then linearly correlated with the related PUI pervaporation selectivity. © 1995 John Wiley & Sons, Inc.     

Structure and properties of polyurethane acrylate prepolymers based on hydroxy‐terminated polybutadiene

Precursors of polyurethane acrylate based on hydroxy‐terminated polybutadiene (HTPB) soft segments, different diisocyanate and hydroxy ethyl acrylate (HEA) as hard units, were synthesized in bulk or in solution in methyl methacrylate. During precursor synthesis (in bulk), microphase separation was observed by small‐angle X‐ray scattering (SAXS). Diffusing particles are around 50 Å in size and are assumed to be assembling of hard segments. From these morphologies, it can be deduced that some isocyanate groups were trapped/or buried in hard domains. At a larger scale, around millimeters, hard segment crystallites were observed. Properties such as molar masses, melting and glass‐transition temperatures, and viscosities were correlated with precursor structure and morphology. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 225–233, 2002     

Interconversion of light olefins—aromatics over zeolite catalysts

Improved yield in light olefins and aromatics from methanol conversion was observed on Zn and Mn loaded ZSM-5 zeolite—asbestos catalysts. The best results in terms of conversion into hydrocarbons were obtained with a Zn content not exceeding 0.6% wt/wt. The light olefins/aromatics ratio in the products varied with the Mn content in the catalyst, the cumulative light olefinic and aromatic production being kept constant at a high value.     

Unconventional Configuration Studies to Improve Mixing Times in Stirred Tanks

Dynamic perturbations and off‐centered single and dual mixing impeller configurations have been investigated to reduce mixing time with viscous fluids. Mixing times, measured with a color‐discoloration technique based on a fast acid‐base reaction, reveal the presence of both segregated and dead zones. A statistical design approach has been used to evaluate the effect of the impeller position as well as the dynamic conditions. Homogenization is significantly enhanced when a radial flow impeller is used under both off‐centered and dynamic perturbation conditions. In the case of an axial flow impeller, a combination of long clockwise times and short counter‐clockwise times give better mixing times. An enhanced homogenization is also observed when a dual impeller configuration is used.