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81.
Kartavya Jain Carl Wu Sundar V. Atre Goran Jovanovic Vinod Narayanan Shoichi Kimura Vincent Sprenkle Nathan Canfield Sukumar Roy 《International Journal of Applied Ceramic Technology》2009,6(3):410-419
Microreactors as a novel concept in chemical technology enable the introduction of new reaction procedures in chemistry, pharmaceutical industry, and molecular biology. These miniaturized reaction systems offer many exceptional technical advantages for a large number of applications. One major application is in the bulk synthesis of nanoparticles. Despite the availability of a plethora of nanoparticle synthesis processes, there exist many difficulties in controlling the shape, size, and purity of nanoparticles in large quantities in a safe and cost-effective manner. These difficulties have been the principal factors adversely limiting the applications of ceramic nanoparticles. Recent experiments have shown that to study the process of growth and formation of nanoparticles, a reactor having much smaller dimensions, namely a microreactor is more appropriate. These studies have also shown that a microchannel reactor provides control over the mean residence time and hence over the nanoparticle size and shape. This paper deals with the design, fabrication, and testing issues related to a high temperature, ceramic microreactor by investigating the use of reactive gas streams in arrays of microchannel reactors. These innovations offer the potential to overcome the barriers associated with synthesis of ceramic nanoparticles in large quantities. 相似文献
82.
Ockwig NW Delgado-Friedrichs O O'Keeffe M Yaghi OM 《Accounts of chemical research》2005,38(3):176-182
The structures of all 1127 three-periodic extended metal-organic frameworks (MOFs) reported in the Cambridge Structure Database have been analyzed, and their underlying topology has been determined. It is remarkable that among the almost infinite number of net topologies that are available for MOFs to adopt, only a handful of nets are actually observed. The discovery of this inversion between expected and observed nets led us to deduce a system of classification "taxonomy" for interpreting and rationalizing known MOF structures, as well as those that will be made in future. The origin of this inversion is attributed to the different modes with which MOF synthesis has been approached. Specifically, three levels of complexity are defined that embody rules "grammar" for the design of MOFs and other extended structures. This system accounts for the present proliferation of MOF structures of high symmetry nets, but more importantly, it provides the basis for designing a building block that "codes" for a specific structure and, indeed, only that structure. 相似文献
83.
The weak-link approach (WLA) to supramolecular assemblies allows for the design of multimetallic two- and three-dimensional arrays, host-guest architectures, sensors, catalysts, switches, and signal amplification devices. This Account describes the course of our investigations in this area beginning with the development of a chemical tool kit of building blocks consisting of multiple metals and ligands. These building blocks can be rationally mixed and matched to provide structures with a wide range of properties that have been used to develop functional supramolecular architectures, including chemical sensors and allosteric catalysts. 相似文献
84.
Taranjot Kaur Justin Nussbaum Sanboh Lee Kevin Rodriguez Nathan B. Crane Julie Harmon 《Polymer Engineering and Science》2021,61(1):221-233
Large area projection sintering (LAPS) promises to be a new method in the field of additive manufacturing. Developed in the Mechanical Engineering Department, University of South Florida, LAPS uses long exposure times over a broad area of powder to fuse into dense, reproducible materials. In contrast, LS, a common powder-based additive manufacturing, uses a focused beam of light scanned quickly over the material. Local regions of concentrated high-energy bursts of light lead to higher peak temperatures and differing cooling dynamics and overall crystallinity. The mechanical properties of laser sintered specimens suffer because of uneven particle fusion. LAPS offers the capacity to fine-tune fusion properties through enhanced thermodynamic control of the heating and cooling profiles for sintering. Further research is required to identify the relationship between LAPS build settings and part properties to enable the fabrication of custom parts with desired properties. This study examines the influence of LAPS sintering parameters on chemical structures, crystallinity, mechanical, and thermal properties of polyamide-12 specimens using powder X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, small-angle X-ray scattering, scanning electron microscopy, and microhardness testing. It was observed that higher crystallinity was imparted to specimens that were sintered for a shorter time and vice versa. 相似文献
85.
Jianlin Li Zhijia Du Rose E. Ruther Seong Jin AN Lamuel Abraham David Kevin Hays Marissa Wood Nathan D. Phillip Yangping Sheng Chengyu Mao Sergiy Kalnaus Claus Daniel David L. WoodIII 《JOM Journal of the Minerals, Metals and Materials Society》2017,69(9):1484-1496
Reducing cost and increasing energy density are two barriers for widespread application of lithium-ion batteries in electric vehicles. Although the cost of electric vehicle batteries has been reduced by ~70% from 2008 to 2015, the current battery pack cost ($268/kWh in 2015) is still >2 times what the USABC targets ($125/kWh). Even though many advancements in cell chemistry have been realized since the lithium-ion battery was first commercialized in 1991, few major breakthroughs have occurred in the past decade. Therefore, future cost reduction will rely on cell manufacturing and broader market acceptance. This article discusses three major aspects for cost reduction: (1) quality control to minimize scrap rate in cell manufacturing; (2) novel electrode processing and engineering to reduce processing cost and increase energy density and throughputs; and (3) material development and optimization for lithium-ion batteries with high-energy density. Insights on increasing energy and power densities of lithium-ion batteries are also addressed. 相似文献
86.
Weon-Pil Tai Tadahiko Watanabe Nathan S. Jacobson 《Journal of the American Ceramic Society》1999,82(1):245-248
The high-temperature stability of alumina (Al2 O3 ) in argon and argon/water-vapor (Ar/H2 O) environments has been investigated. Samples were exposed at temperatures of 1300°C–1700°C for 10 h. The microstructure, flexural strength, and volume all showed significant changes in the Ar/H2 O environment at 1700°C. Samples also became whiter, because of the oxidation of graphite impurities that had diffused from the hot-processing dies. In the Ar/H2 O environment at 1700°C, grain-boundary etching occurred and was much more severe than in the pure-argon environment, which was very likely caused by the enhanced formation of gaseous Al(OH)3 and Al(OH)2 along grain boundaries. In addition, in the Ar/H2 O environment, substantial grain growth occurred in the surface vicinity. This grain growth, together with grain-boundary etching, led to a decrease in flexural strength. 相似文献
87.
Burkard Alan W.; Pruitt Nathan T.; Medler Barbara R.; Stark-Booth Ann M. 《Canadian Metallurgical Quarterly》2009,3(1):37
In this paper, the authors report on the development and initial psychometric evaluation of the Lesbian, Gay, and Bisexual Working Alliance Self-Efficacy Scales (LGB-WASES) with data collected from two studies and 534 counseling trainees. Exploratory factor analysis results yielded a 32-item scale with a three-factor model (a) Emotional Bond, (b) Establishing Tasks, and (c) Setting Goals. LGB-WASES scores were internally consistent and remained stable over a 3-week period. Construct validity evidence suggests the LGB-WASES scores were (a) positively related to general perceptions of counseling self-efficacy and multicultural counseling competency, (b) negatively related to attitudes toward lesbians and gay men, and (d) unrelated to social desirability. Recommendations for future research are also discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
88.
A model is introduced that utilizes geographic information systems (GIS) to predict relative reductions in crop yield due to salinity and waterlogging at a field-scale by incorporating spatially and temporally variable crop, climatic, and irrigation data to simulate crop yields. This model utilizes soil and water data commonly collected in field-scale studies. The model’s algorithms are integrated into a GIS (ARCVIEW 3.2) as an extension. The result is a model that does not require extraordinary data collection but will provide practical insight into the spatial effects of salinity and waterlogging on crop yields. 相似文献
89.
John Mellor-Crummey Robert J. Fowler Gabriel Marin Nathan Tallent 《The Journal of supercomputing》2002,23(1):81-104
It is increasingly difficult for complex scientific programs to attain a significant fraction of peak performance on systems that are based on microprocessors with substantial instruction-level parallelism and deep memory hierarchies. Despite this trend, performance analysis and tuning tools are still not used regularly by algorithm and application designers. To a large extent, existing performance tools fail to meet many user needs and are cumbersome to use. To address these issues, we developed HPCVIEW—a toolkit for combining multiple sets of program profile data, correlating the data with source code, and generating a database that can be analyzed anywhere with a commodity Web browser. We argue that HPCVIEW addresses many of the issues that have limited the usability and the utility of most existing tools. We originally built HPCVIEW to facilitate our own work on data layout and optimizing compilers. Now, in addition to daily use within our group, HPCVIEW is being used by several code development teams in DoD and DoE laboratories as well as at NCSA. 相似文献
90.
Synthetic clinkers, similar to high-silica Portland Cement clinkers, were prepared from raw material containing at times more than 50% oil shale from Har-Tuv area (central Israel) to which phosphate rock and laboratory grade CaCO3 and SiO2 were added. Although some clinkers contained more than 3% P2O5, their mineralogical composition was satisfactory (50 to 60% C3S). This result was obtained by taking into account in the SM formula the P2O5 concentrations. The resultant relatively high silica concentrations raise the melting point of the raw meal, causing a non-equilibrium state which allows the formation of C3S and its preservation. 相似文献