Differential Thermal Calorimetric Determination of the Thermodynamic Properties of Kaolinite

Four samples of kaolinite were investigated to determine the exothermic reaction enthalpy by differential thermal calorimetry. The measured 9 kcal/mol for the 980°C exothermic reaction enthalpy corresponds to the calculated heat of crystallization of silica at this temperature. Literature evidence discounts the crystallization of the other participating phases, mullite and silicon spinel. An NaOH extraction technique was used to remove the amorphous silica from a kaolinite fired at 850°C; this extraction removed the 980°C exotherm. It is tentatively suggested, therefore, that most of the heat release at 980°C on firing kaolinite accompanies the reaction SiO₂(amorphous) → SiO₂(β-quartz).     

Efficiency of surface modified Ti coated with copper nanoparticles to control marine bacterial adhesion under laboratory simulated conditions

Titanium (Ti) used as condenser material in nuclear power plants encounter severe biofouling in marine environment which in turn affects the efficiency of the metal. To reduce the biofouling by marine microorganisms, surface modification of the Ti was carried out by anodization process to obtain nanotubes (TiO₂-NTs). The electrolyte solution containing 1% of ammonium fluoride resulted in uniform growth of TiO₂-NTs. TiO₂-NTs were further coated with chemically synthesized copper nanoparticles (NT-CuNP) using 3-amino propyl triethoxy silane as a coupling agent. NT-CuNP was characterized by field-emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy and X-ray diffraction. The stability of the coating was determined by the amount of Cu⁺ ions released into the surrounding using AAS. The microbial adhesion on the surface of Ti, TiO₂-NTs and NT-CuNP coupons were evaluated by sea water exposure studies using total viable count method and also characterized by FE-SEM for any morphological changes. The NT-CuNP coupons show a 60% reduction in microbial adhesion when compared to control Ti coupons.     

Disturbance Attenuation and Trajectory Tracking via a Reduced-order Output Feedback Controller for Robot Manipulators

This paper presents a solution to the problem of trajectory tracking with external disturbance attenuation in robotics systems via a reduced-order output feedback controller, without velocity measurement. The proposed control law ensures both semi-global asymptotic stability of the closed-loop system and external disturbance attenuation. The approach is based on the notion of the L₂-gain and requires to solve two algebraic Riccati inequalities. The proposed controller design is illustrated by a simulation example.     

Vitreous cryo-sectioning of cells facilitated by a micromanipulator

Sectioning vitrified cells and tissues for cryo‐electron microscopy is more challenging than room‐temperature sectioning of plastic‐embedded samples. As the sample must be kept very cold (相似文献   

REGIONAL PARTNERSHIPS AND METROPOLITAN ECONOMIC DEVELOPMENT

Regional partnerships have grown popular as mechanisms to address public goods that transcend local boundaries, but we know little about their effectiveness. For example, what impact do regional economic development partnerships (REDPs), cooperative organizations of local governments, nonprofits and business organizations have on the economies of metropolitan areas? This article employs survival analysis and multilevel growth curve models to examine how the emergence of regional partnership arrangements influences patterns of economic development in U.S. metropolitan areas. The results suggest that, whereas these organizations do not make a great difference in some metro areas, in densely populated and politically fragmented metropolitan areas personal incomes, business firms, and employment grew significantly with the emergence of REDPs. Furthermore, state level factors, such as intergovernmental grant funding, are found to have positive influences. In conclusion, we discuss regional partnerships as solutions to institutional collective action problems in economic development and other policy arenas.     

Expert systems in production and operations management: research directions in assessing overall impact

The use and development of expert systems in public and private organizations continue to increase. Many of these systems are being developed for production and operations management. Unfortunately, the impacts that these systems are having in these environments have, for the most part, not been investigated. Most studies on expert systems to date centre either on the technical aspects or validation issues. No one has taken a systemic view that takes into account both the technical issues and the human issues that will have to be addressed in implementing these systems. This paper seeks to stimulate research into the overall impact of expert systems implementation in production. To this end, fourteen research propositions are developed and presented. In addition, the major variables associated with these propositions are combined into a causal model to show the relationships between them and to reveal an overall perspective of the impacts of expert systems implementation on the production process.     

YTTRIUM ALUMINATE CERAMIC FIBERS VIA PRE-CERAMIC POLYMER AND SOL-GEL ROUTES

ABSTRACT

Yttrium aluminum garnet (YAG - Y₃Al₅O₁₂) fibers have been prepared by dry spinning solutions of yttrium and aluminum carboxylate polymers (precursor route) and by dry spinning aqueous oxide sols (sol-gel route). Fibers from aqueous diphasic gels are prepared by mixing a colloidal alumina sol containing 50-nm hydrous alumina with a colloidal yttria sol containing 10-nm yttrium oxide, using polyvinylpyrrolidone as a spinning aid. Fibers by the precursor route are made from spinnable THF solutions of yttrium isobutyrate and aluminum isobutyrate or from aqueous solutions of polymeric aluminum formate and yttrium acetate.

The isobutyrate materials decompose between 200-400^°C to an amorphous residue. Crystallization occurs abruptly between 875°C and 900^°C, forming the YAG phase directly. The formate-acetate also decomposes to amorphous residues, which form YAG at 900^°C. In the diphasic gel, YAG forms gradually between 1000 and 1200^°C, with intermediate products YAP (YalO₃ perovskite) and/or YAM (Y₄Al₂O₉ monoclinic). At 1500^°C, single phase YAG is obtained as pore-free fibers with 500 nm grains.     

On joining non-singular and singular optimal control subarcs

Necessary conditions for junctions between non-singular and singular optimal control subarcs are proved for the case where the singular problem order is greater than one. the generalized Legendre-Clebsch condition (GLC) vanishes at the junction, and the derivative of the GLC expression is non-zero at the junction. The proof requires the derivation of two identities which are system properties of higher-order singular problems     

Case-based reasoning assisted explanation of genetic algorithm results

Abstract

This paper describes a system for explaining solutions generated by genetic algorithms (GAs) using tools developed for case-based reasoning (CBR). In addition, this work empirically supports the building block hypothesis (BBH) which states that genetic algorithms work by combining good sub-solutions called building blocks into complete solutions. Since the space of possible building blocks and their combinations is extremely large, solutions found by GAs are often opaque and cannot be easily explained. Ironically, much of the knowledge required to explain such solutions is implicit in the processing done by the GA. Our system extracts and processes historical information from the GA by using knowledge acquisition and analysis tools developed for case-based reasoning. If properly analysed, the resulting knowledge base can be used: to shed light on the nature of the search space; to explain how a solution evolved; to discover its building blocks; and to justify why it works. Such knowledge about the search space can be used to tune the GA in various ways. As well as being a useful explanatory tool for GA researchers, our system serves as an empirical test of the building block hypothesis. The fact that it works so well lends credence to the theory that GAs work by exploiting common genetic building blocks.     

Increasing the production rate of a just-in-time production system with variable operation times

This paper examines a just-in-time (JIT) system with kanbans with three subassembly lines feeding a final assembly station. Variability in operation times exists and variability effects are reduced by increasing work in process levels or by unbalancing the subassembly lines through assignment of work content at each station. Of the several unbalancing methods that were analysed in this study, only the high-medium-low showed a consistent improvement in the output rate of the JIT production system. The output rates with unbalanced stations were always superior to the output rate of the perfectly balanced configurations used as controls. The extent of improvement over the output rate of balanced systems increased directly with the variability in operation times in final assembly and subassembly stations and inversely with the interstage buffer capacity allowed in the system.