Developments in high-resolution positron emission tomography at MGH

The development of high resolution PET systems is important for the wider application of this techniques. The resolution of PET is limited by a number of physical factors such as positron range, small angle deviation, and sampling frequency. The design of the detector array and its sensitivity remain critical factors; designs incorporating analog coding have proven to be useful. PCR-I, a single plane PET system, has demonstrated the concept and has produced useful images in animal studies. PCR-II will extend the concept to a two dimensional detector array resulting in a system with high resolution and high sensitivity.     

定向麦秸板制造工艺概述

阐述了生产定向麦秸板的意义,按生产工艺流程对每个工段进行了简要叙述,并对定向麦秸板生产的关键技术进行了讨论。     

木聚糖酶酶活测定方法

介绍和比较了测定木聚糖酶酶活的三种方法,详述了工作曲线法测定木聚糖酶酶活的操作方法及注意事项,并提供了实际应用。     

Switching faults and safe control of an ARCP multicell flying capacitor inverter

The auxiliary resonant commutated pole (ARCP) multicell converter is a soft-switched variant of the multicell converter. It is shown in this paper that the ARCP technique can be very efficiently used in multicell flying capacitor converters. The main properties of the resulting soft switching multicell converter are very similar to those of the hard-switched version. They are presented and validated by simulations as well as experimental results. In practice, due to the damping, the ARCP multicell converter can suffer from switching faults as in two-level ARCP inverters, but in the case of a multicell converter failures can occur in different cells. So, the main control strategies are evaluated and the switching process is discussed step by step, taking account of the main imperfections of actual control circuits. When they can occur, the switching faults are described and analyzed. Finally, an original quasisoft switching control that should give a high safety of operation is proposed. Experimental results obtained with a 900 V-100 A ARCP multicell inverter leg are given and the performances are compared with those of a hard-switched multicell inverter leg of the same rating.     

Design and Comparison of Inductors and Intercell Transformers for Filtering of PWM Inverter Output

This paper presents an original design option dedicated to output-filtered pulsewidth modulation inverters used in uninterruptible power systems, embedded networks, or motor drives operating on long cables. It is based on the coupling of interleaved inverter cells by means of intercell transformers (ICTs) and is characterized by very good dynamic behavior on load transients, which is an important issue in such applications. ICT solutions are compared with the classical interleaved solutions using separate inductors. A specific design method is developed to achieve this comparison based on toroidal core shapes. The results obtained with a 600 V, 7.5 kW inverter show the usefulness of ICT-based designs, especially when nanocrystalline magnetic material is used; high specific power and very good dynamic performances are obtained.     

Design of Intercell Transformers for High-Power Multicell Interleaved Flyback Converter

This paper presents the developments and the results of an analytic method elaborated to design isolated intercell transformers. These particular magnetic components are intended for multicell interleaved flyback converters recently proposed and well-suited to low-voltage, high-power applications. A specific 2-D model to evaluate the winding losses is included in the design process. The results, obtained for standard core shapes, allow defining the ranges of the main parameters, number of cells, and switching frequency, required for future realizations.     

Expression Reduction Systems with Patterns

We introduce a new higher-order rewriting formalism, called expression reduction systems with patterns (ERSP), where abstraction is allowed not only on variables but also on nested patterns with metavariables. These patterns are built by combining standard algebraic patterns with choice constructors denoting cases. In other words, the nondeterministic choice between different rewrite rules which is inherent to classical rewriting formalisms can be lifted here to the level of patterns. We show that confluence holds for a reasonable class of systems and terms.     

真实感图形绘制技术研究

随着虚拟现实技术的发展,对各种图形绘制技术提出了越来越高的要求。好的图形绘制技术是虚拟现实、动态仿真、实时可视化、高品质动画等越来越多的图像、图形应用技术的实现基础。本文主要介绍了基于图像的绘制技术、基于点的绘制技术,以及基于图形与图像的混合绘制技术在原理和应用。