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1.
Kee S. Moon M. Levy Yong K. Hong H. Bakhru S. Bakhru 《Ferroelectrics Letters Section》2003,30(3):47-57
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices. 相似文献
2.
电源设计者们仿佛正在目睹一个新的半导体技术的诞生。随之而来的新一代功率半导体器件远远优于现有的硅技术。SiC 材料可以让器件具有迄今为止设计工程师们梦寐以求却不能得到的出色特性。其最重要的优点包括以下几个方面::工作结温高达225 ℃,而相应的漏电流只有适度的增加。由于本质上不会出现热偏移thermal run-away),故可以在
很高的结温下可靠的工作。
没有正向或反向恢复,故即使在高温
下以高频工作时,也没有开关损耗。
甚至可以实现开关损耗极小、频率
高达1 M H z 的深度切换(h a rd
正向电阻具有… 相似文献
3.
4.
Fetal alcohol syndrome in twins of alcoholic mothers: concordance of diagnosis and IQ 总被引:1,自引:0,他引:1
The effects of teratogens can be modified by genetic differences in fetal susceptibility and resistance. Twins of alcoholic mothers provide a unique opportunity to study this phenomenon with respect to alcohol teratogenesis. Sixteen pairs of twins, 5 MZ and 11 DZ, all heavily exposed to alcohol prenatally, were evaluated. They represented all available twins of alcohol-abusing mothers who were on the patient rolls of the authors. The rate of concordance for diagnosis was 5/5 for MZ and 7/11 for DZ twins. In two DZ pairs, one twin had fetal alcohol syndrome (FAS), while the other had fetal alcohol effects (FAE). In 2 other DZ pairs, one twin had no diagnosis while one had FAE. IQ scores were most similar within pairs of MZ twins and least similar within pairs of DZ twins discordant for diagnosis. Despite equivalent alcohol exposure within twin pairs, alcohol teratogenesis appears to be more uniformly expressed in MZ than in DZ twins. These data are interpreted as reflecting the modulating influence of genes in the expression of the teratogenic effects of alcohol. 相似文献
5.
Twenty-six patients with an intracardiac myxoma underwent surgical resection at our institution from 1977 through 1992. Left atrial myxoma was diagnosed in 22 patients, left ventricular in 1, right atrial in 2, and right ventricular in 1. Six patients were asymptomatic; preoperative symptoms included dyspnea, arrhythmias, embolic episodes, and syncope. The diagnosis was established with transthoracic echocardiography in all cases but one. Surgery was performed in all cases with the aid of cardiopulmonary bypass with moderate hypothermia and cold crystalloid cardioplegia. One patient with a left ventricular myxoma died in a comatose state during the immediate postoperative period. Long-term clinical and echocardiographic evaluation was performed in 19 patients; results were excellent (all the patients were in New York Heart Association functional class I or II), and no recurrences were documented. The clinical characteristics, diagnostic methods, and surgical approach are presented and discussed. 相似文献
6.
7.
Xanthan gum is an exopolysaccharide secreted by the bacterium Xanthamonas campestris whose ability to make solutions viscous at low concentrations and over a pH and temperature range have generated much interest in both academic and industrial environments. Mutant Xanthamonas strains have been derived that produce xanthan gums with an altered or variant subunit chemical structure and different measured viscosities when compared with the wild type (wt) form of the polymer. Two variant gums were targeted as potentially interesting in this study, these being the nonacetylated tetramer (natet) and the acetylated tetramer (atet), which both lack a side-chain terminal mannose residue and in one case (natet) lacks an acetate group on an internal mannose residue. Solutions of these tetrameric gums possess viscosities higher (natet) and lower (atet) than the wt gum, and therefore we have attempted to determine whether these molecules possess unique conformational preferences when compared with the wt and with each other. In this manner we can initiate an understanding of how a polysaccharide's conformation contributes to its solution properties. The GEGOP software permits a sampling of the static and dynamic equilibrium states of carbohydrate molecules, and this software was employed to calculate equilibrium states of representative oligosaccharides with chemical structures representative of xanthan-like molecules. Energy minimization techniques revealed similar local minima for all three molecules. Some of these minima are comprised of elongate backbone conformations (A type) in which side chains fold onto backbone surfaces. Other minima with A backbones possessed side chains in less intimate backbone contact especially when calculations were performed with a low dielectric constant. This phenomenon was particularly pronounced in the wt molecule where an increased number of negatively charged side-chain residues experience charge repulsion resulting in reduced side-chain-backbone contact. Metropolis Monte Carlo (MMC) dynamic simulations performed with an elevated temperature factor (1000 K) allowed a better qualitative representation of conformational space than 300 K simulations. Employing a nonhierarchical cluster analysis method (population density profile: PDP) coupled with a classification scheme, it was possible to partition resulting MMC data sets into conformational families. This analysis revealed that in simulations performed with different dielectric constant values (10, 25, and infinity) all molecules possessed primarily A-type backbones. Less elongate, more open helical backbone forms (B, C, D, J, and Flat-a) did occur during the simulations but were populated to a lesser extent. In the natet molecule significantly open helical backbones existed (E, F, G, H, and I) that did not occur in the lower viscosity wt and atet molecules. PDP clustering methods and subsequent conformational classification applied to the first residue (mannose) of the side chain permitted a determination of side-chain orientation. Comparison of all three molecules indicated a larger population of side-chain conformational families in less direct backbone contact for the wt molecule than either of the variant molecules (natet/atet) suggesting that the side chains in the wt are more flexible. Thus, a major conformational difference between the high viscosity natet and the lower viscosities of the wt/atet is the increased amount of open helical backbone in the natet. In addition, the significant difference between the higher viscosity wt and the lower viscosity atet is the increase side-chain flexibility in the wt. We hypothesize that conformational differences of this kind could form a partial explanation of the observed differences in viscosity between these xanthan-like polymers. 相似文献
8.
9.
A Levy 《Canadian Metallurgical Quarterly》1996,15(2):257-260
Delusions are evasive to define: (1) Within the process of defining, one uses part of the final conclusion, which should derive from the basic definition (in other words, Circular reasoning); (2) Many, if not most, of so-called normal persons, hold delusion-like ideas; (3) Delusion becomes, usually, more understandable and less bizarre when investigated; (4) Delusions are not unique by remaining resistible to reason; (5) For every delusional content, as bizarre and remote as it may be, there is at least one cultural niche, in which the same content is considered legitimate and reasonable, (if no important and dignified). The forensic implications of these difficulties (to define delusions), will be discussed and elaborated. 相似文献
10.
MM Odinak AA Mikha?lenko EB Shustov IuS Ivanov GF Semin SA Kotel'nikov AP Kovalenko 《Canadian Metallurgical Quarterly》1996,317(11):37-45, 79
In the article the rules about etiology and pathogenesis of vegetative paroxysms are stated based on careful analysis of the publications of researches as Russian, so foreign authors, and also own experimental and clinical supervision. During experimental and clinical researches the modern methods were used, enabling to estimate from positions of the system analysis different parts of pathogenesis of vegetative paroxysms, and also to offer ways of differential diagnostics of the various forms of disease. The application of some new preparations and direction of therapy of vegetative paroxysms are substantiated, and also the various circuits of treatment of the patients with distinguishing forms of given pathology are motivated. 相似文献