高功率解决方案

为了促进广大中国音频技术爱好者对音频产品及最新技术的应用和了解，以及使音频产品能日臻完美与设计创新，美国国家半导体公司与其在中国大陆的代理商之一的棋港电子公司联合举办面向中国音频爱好者的2004年音频技术应用设计大赛。本次大赛于2004年7月1日全面启动。作为本次大赛的配合媒体，本刊将选登美国国家半导体公司在音频方面的产品技术文章，以飨读者。     

Enhancement, implementation, and performance of an adaptiveshort-term load forecasting algorithm

An adaptive load forecasting algorithm that was originally developed for the one-hour time period has been extensively enhanced and implemented. The major enhancement is the ability to forecast total system hourly load as far ahead as five days. The focus is on the enhancements and implementation of the algorithm. The purpose is to describe the final form of the forecasting model and the overall forecasting procedure; the procedure for utilizing minimum/maximum daily weather forecasts made by the US Weather Bureau: the offline forecasting accuracy based on four years of historical hourly load and weather data; and the implementation of the algorithm on a desktop computer     

Processing and Properties of Cellular Silica Synthesized by Foaming Sol-Gels

A novel process for fabricating lightweight, cellular ceramics from sols is presented. The process utilizes the rapid viscosity change during gelation to stabilize the structure of a foamed silica sol. Manipulation of gel viscosity and foaming agent concentration resulted in a minimum cell size of 90 μm at 31% density and minimum density of 17% with average cell size of 400 μm. The flexural strength compared favorably with space shuttle tiles and sintered hollow glass spheres. From −50° to 150°C, the dielectric constant ranged from 1.51 to 1.55 for a 20% dense foam and was slightly dispersive, whereas the dielectric loss was comparable with fused silica.     

Use of Stress To Produce Highly Oriented Tetragonal Lead Zirconate Titanate (PZT 40/60) Thin Films and Resulting Electrical Properties

Thin films of Pb(Zr_0.4Ti_O.6)O₃ produced by chemical solution deposition were used to study the effects of stress from different platinized single-crystal substrates on film orientation and resulting electrical properties. Films deposited on MgO preferred a (001) orientation due to compressive stress on the film during cooling through the Curie temperature ( T _C). Films on Al₂O₃ were under minimal stress at T _C, resulting in a mixture of orientations. Those on Si preferred a (111) orientation due to templating from the bottom electrode. Films oriented in the 〈001〉 direction demonstrated lower dielectric constants and higher P _r and − d ₃₁ values than (111) films.     

Spray Pyrolysis Synthesis and Dielectric Properties of Pb(Mg1/3Nb2/3)O3

Spray pyrolysis was used to synthesize lead magnesium niobate (PMN) by atomizing a mixture of nitrate aqueous solutions into a high-temperature furnace. This approach allows for instant removal of solvents and decomposition of metal–salts, thereby limiting phase segregation on a nanometer scale, and lowering the transformation temperature for pyrochlore-to-perovskite phase transition. As-synthesized particles were nanocrystalline pyrochlores, with an average crystallite size ∼22 nm. More than 96% perovskite phase was obtained when as-sprayed powders were subsequently calcined at 750°C for 4 h. Sintered PMN ceramics exhibited the typical frequency-dependent dielectric properties, with a peak value of dielectric constant of 18 000, and a transition temperature at −9.6°C at 100 Hz. A series of ceramics were prepared with varied grain sizes. Increasing the grain size increased the dielectric constant, probably due to the smaller fraction of the less-polarizable grain-boundary phases.     

Interaction of Ag/Pd Metallization with Lead and Bismuth Oxide-Based Fluxes in Multilayer Ceramic Capacitors

An ongoing challenge for future developments in high-performance ceramic multilayer capacitors and integrated ceramics is to reduce the internal electrode cost and thickness without sacrificing yield or reliability. Key to these developments is a thorough understanding of the interactions which occur between flux-sintered dielectrics and low-cost, Ag/Pd electrodes. In this paper we present results on the pahse equilibria of Ag/Pd electrode systems with Bi₂O₃ and PbO fluxes. The conditions under which the bismuth reaction occurs and reactions in the Pd–PbO system are reported. Results show that the equilibrium phases which form depend strongly upon the Ag/Pd ratio and temperature. These phases include PdBi₂O₄, Pd(Bi), PdPbO₂, Pd(Pb), and PbPd₃. The PdBi₂O₄ and PdPbO₂ phases decompose when PdO destabilizes, resulting in a series of reactions which result in oxygen evolution and partial melting of components. The exact phase relations of the Ag/Pd–Bi₂O₃–O₂(air) system and Ag/Pd–PbO–O₂(air) system have been established for the first time and are discussed in terms of their impact on multilayer, cofired structures.     

Comparative in vitro study of the proliferation and growth of ovine osteoblast-like cells on various alloplastic biomaterials manufactured for augmentation and reconstruction of tissue or bone defects

In this in vitro study ovine osteoblast-like cells were cultured on seven different alloplastic biomaterials used for augmentation and for reconstruction of bone defects in dental and craniomaxillofacial surgery. The aim of this study was to examine the growth behaviour (viability, cell density and morphology) of ovine osteoblast-like cells on the investigated biomaterials to get knowledge which biomaterial is qualified to act as a cell carrier system in further in vivo experiments. The biomaterials were either synthetically manufactured or of natural origin. As synthetically manufactured biomaterials Ethisorb, MakroSorb, PalacosR, and PDS film were used. As biomaterials of natural origin BeriplastP, Bio-Oss and Titanmesh were investigated. The cell proliferation and cell colonization were analyzed by a proliferation assay and scanning electron microscopy. Osteoblast-like cells proliferated and attached on all biomaterials, except on Beriplast. On Ethisorb the highest cell proliferation rate was measured followed by PalacosR. Both biomaterials offer suitable growth and proliferation conditions for ovine osteoblast-like cells. The proliferation rates of Bio-Oss, MakroSorb, PDS-film and Titanmesh were low and SEM examinations of these materials showed less spread osteoblast-like cells. The results showed that ovine osteoblast-like cells appear to be sensitive to substrate composition and topography. This in vitro study provides the basis for further in vivo studies using the sheep model to examine the biocompatibility and the long-term interaction between the test material and tissue (bone regeneration).     

Burnout among school psychologists: An exploratory investigation into its nature, extent, and correlates.

Studied 139 school psychologists who completed a survey that included the Maslach Burnout Inventory, a stress inventory, demographic questions, and questions designed to assess their job satisfaction, ideal caseloads, and intent to leave the profession. The results suggested that symptoms of burnout occur frequently among Ss, particularly feelings of emotional exhaustion and reduced personal accomplishment. Demographic factors related modestly to burnout, whereas job-related stressors (lack of resources, interpersonal conflict, crisis cases) related more substantially to burnout. Burnout was also related to Ss' perceptions of their caseloads, overall job satisfaction, supervision satisfaction, and the desire to leave the profession. Also, Ss reported using burnout coping methods that may not adequately address its antecedents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A study of the factorial invariance of the Student Engagement Instrument (SEI): Results from middle and high school students.

The construct of student engagement is increasingly prevalent in the field of education, serving as the foundation of dropout prevention and high school reform initiatives. The purpose of this study was to further examine 1 measure of student engagement, the Student Engagement Instrument (SEI), designed to measure 2 subtypes of student engagement: cognitive and affective. This research extended the initial validation work on the SEI by examining score reliability and factorial invariance across grades and gender. Students (N = 2,416) were sampled from school districts in the rural Southeast and Upper Midwest of the United States. Results indicated similar factor structure, equal score reliability, and similar latent factor relationships across all grades. Evidence supported the contention that the SEI may be used at the middle and high school levels to measure cognitive and affective subtypes of student engagement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)