Spectral analysis of transition metal-doped MgO “matched emitters” for thermophotovoltaic energy conversion

A new, thermally excited Co/Ni-doped MgO ceramic emitter for TPV energy conversion is described in this work, and termed the matched emitter because its emissive power spectrum is very efficiently matched with the portion of the electromagnetic spectrum that can be converted directly into electrical energy by infrared responding GaSb photovoltaic cells. Ligand Field Theory calculations are used to estimate the crystal field splitting energies at high temperatures for Co and Ni-doped MgO matched emitters. Experimental measurements of the high temperature (1300–1400°C) emissive power spectrums for Co and Ni-doped MgO emitters are compared with predictions obtained from ligand field calculations for what is believed to be the first time. It was found that crystal field splitting energies of 10 Dq = 9070 cm^–1 represented the best fit for the Co-doped MgO high temperature emissive power spectrum, and 10 Dq = 7950 cm^–1 for the Ni-doped MgO spectrum. These values are only slightly lower than values reported for corresponding single crystal, transition metal doped laser materials that were measured at or well below room temperature.     

Microscale elastic strain evolution following damage in Ti-SiC composites

Fiber fractures are crucial in initiating damage zones that ultimately determine the strength and lifetime of fiber-reinforced metal matrix composites. The evolution of damage in a metal matrix composite (MMC) comprised of a row of unidirectional SiC fibers (32 vol pct) surrounded by a Ti matrix was examined, for the first time, using X-ray microdiffraction. Multiple strain maps including both phases were collected in situ under applied tensile stress. The elastic axial strains were then compared to predictions from a modified shear-lag model, which, unlike other shear-lag models, considers the elastic response of both constituents. The strains showed good correlation with the model. The results confirmed, for the first time, both the need and validity of this new model specifically developed for large scale multifracture simulations of MMCs. The results also provided unprecedented insight for the model, revealing the necessity of incorporating such factors as plasticity of the matrix, residual stress in the composite, and selection of the load sharing parameter.     

Writing and revising persuasive documents: Cognitive demands.

In 2 experiments, 40 graduate and 60 undergraduate students wrote preliminary and final drafts of a persuasive document. In Exp I, the need for Ss to comply with mechanics (i.e., punctuation and spelling), to form complete sentences, and to sequence their ideas, respectively, were eliminated one at a time from preliminary-draft formats. The elimination of sentence-formation and sequence operations produced corresponding increments in persuasive argument production. In Exp II, Ss with average verbal ability (as assessed by the Scholastic Aptitude Test) benefited more from the elimination of these structure operations than did Ss with low verbal ability. When allowed to freely choose their typical preliminary-draft format, Ss with average verbal ability usually selected proposition-based formats (e.g., lists, outlines, and diagrams) that dispensed with the need for structure operations. Ss with average verbal ability also produced more sentences, more arguments per sentence, and fewer mechanical errors than did those with low verbal ability. In both experiments, comparatively few new arguments were constructed during revision. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Design of a microprogrammable computer with bit-slice devices

In this two-part series of articles the basic principles of designing a 16-bit computer made up of 4-bit bit-slice devices are discussed. The first part considers the data processing and control sections of such a system.     

冷冻成形工艺控制复杂形体陶瓷的精细结构

用冷冻铸造和冷冻干燥的观念成形高密度,基本上无裂缝复杂形体的陶瓷。含水或无水的陶瓷泥浆60％体积高固体饱和百分比。注入到紧密的模具,冷冻后零件从模具中移出。然后在真空中借助冰的升华获得近乎于模型形状尺寸一样的生坯,含水泥料的冷冻过程受到形成氢键化合物的影响,为了减小水固化过程中冰晶的尺度,在泥料中加入甘油。高固态饱和泥料中使用水结晶变性剂制备可注入的泥浆料,生产显微结构均匀的高密烧结陶瓷,本编论文纵览冷冻铸造法在复杂形体陶瓷零件成形中的发展。