IEC class 0.5 electronic watt–hour meter implemented with first-order sigma–delta converters

This paper presents a design of a precise electronic watt–hour meter implemented with first-order sigma–delta analog-to-digital converters. An efficient digital signal-processing circuit is introduced into the design where the whole signal processing is performed directly on an oversampled signal, eliminating the necessity for a decimation filter. It is shown that Gaussian noise, added to the input signal of sigma–delta modulators, decorrelates quantization error of first-order sigma–delta modulators and thus substantially reduces measurement error at low-signal amplitudes. The effect of added noise is analyzed by extensive behavioral simulations for various input signal amplitudes and for various input noise levels. The results show that IEC accuracy class 0.5 can be achieved with first-order sigma–delta converters and digital signal processing in the sigma–delta domain.     

关于混凝土配合比的一些探讨

本文阐述了混凝土配合比的发展历程及不同高性能混凝土配合比的特点,指出目前混凝土中存在的问题和误区,并提出自己的观点,以供工程界参考使用。     

Current-Voltage Characteristics across (0001) Twist Boundaries in Zinc Oxide Bicrystals

Current-voltage ( I – V ) characteristics across (0001) twist boundaries with various misorientation angles were investigated in undoped ZnO bicrystals fabricated by a hot-joining technique. It was confirmed by high-resolution transmission electron microscopy that the boundaries were perfectly joined without intergranular phase. None of the bicrystals prepared in this study exhibited nonlinear I – V characteristics irrespective of coherency at the boundaries. Therefore, grain-boundary atomic configuration had no relation to the formation of double Schottky barriers at the (0001) twist boundaries in ZnO.     

Highly predictable execution support for critical applications with HARETICK kernel

In this paper, the problem of providing a fully predictable execution environment for critical and hard real-time applications on embedded and DSP-based platforms is studied from the viewpoint of system architecture and operation.We introduce a set of homogenous models for time, signals and tasks, which will further serve as a basis for describing the architecture and operation of a particular hard real-time kernel – “HARETICK”. The kernel provides support for concurrent operation of hard real-time tasks (the HRT execution environment), using non-preemptive scheduling algorithms, along with soft real-time tasks (the SRT environment), using classical, preemptive, priority-based scheduling algorithms.A set of applications has been developed to test the correct operation of the HARETICK kernel according to the theoretical models and to evaluate its abilities to provide high predictability of execution for critical applications. Some of the main testing results are also discussed in the paper.     

一种定向凝固高温合金的薄壁效应研究

采用定向凝固无余量精铸工艺，制造了接近于空心涡轮叶片的２和壁厚的管状薄壁试样，研究了一种定向凝固高温合金的薄壁性能，结果表明，薄壁试样的持久性能与标准试样相比没有明显的下降，说明在本试验条件下，该合金的薄壁效应不明显，从工艺因素和显微组织方面讨论了试验结果。     

应用新型Halbach阵列的PCB定子轴向磁通永磁电机性能分析

本文针对定子为印刷线路板（printed circuit board,PCB）结构的轴向磁通永磁电机的特点,将一种新型的Halbach永磁体阵列应用于该永磁电机中,并对其性能参数进行分析。通过与传统Halbach永磁体阵列的无铁心轴向磁通永磁电机相比可知:应用新型Halbach永磁体阵列的PCB定子轴向磁通永磁电机在相同尺寸及同等永磁体用量条件下,具有更高的气隙磁密及每极磁通,可获得更高的空载反电势,同时有效地降低了漏磁,使得气隙磁密更接近正弦波,电机的整体性能得到了提升。有限元分析结果和样机的对比试验证明了应用新型Halbach永磁体阵列的PCB定子轴向磁通永磁电机的合理性和有效性。为PCB定子轴向磁通永磁电机的设计提供一定的参考。