45°功率分割正交模变换器的分析

由于45°功率分割正交模变换器结构的对称性,输出端正交的TE10和TE01模功率分配理论上是等分的。但在HFSS仿真计算时,由于输出端方口径波导简并模的影响,得到的两正交模功率分配却不相等。为了解决仿真中的功率不等分问题,我们提出对输出端方口径进行微扰的方法,并对微扰孔的位置进行了探讨;分析了加工误差对功率等分性能的影响。     

Lamb Waves for Damage Localisation in Panels

Abstract: In this study, Lamb wave propagation phenomena have been used to localise discontinuities in aluminium and composite panels. For that purpose, piezoelectric transducers have been used to excite and register Lamb waves in the panels. Excited waves that propagate and reflect from the panel edges and discontinuities were registered by piezoelectric sensors as voltage changes in time. Three different experiments have been conducted to investigate the wave propagation phenomena. In the first experiment, the attenuation and dispersion of Lamb waves in the aluminium panel has been studied. The second experiment has been oriented to localise an additional mass attached to the same panel. A dedicated signal‐processing algorithm has been developed to aid the localisation procedure that allowed to extract relevant features of the discontinuity. The algorithm has been tested on signals from the panel with and without the additional mass. The results obtained have been compared to find the position of the discontinuity. The third experiment concerned a more realistic damage scenario when piezoelectric transducers have been arranged as a clock‐like array to find a crack in a composite panel.     

录井资料解释专家系统的研制

1　系统的组成和设计思路专家系统有 5个组成部分 :知识库、综合数据库、解释子系统、推理子系统和知识获取子系统。知识库用于存放依赖于领域中具体问题的知识 ,如一些常识性知识和元知识 ,而与领域中具体问题有关的知识 (如描述问题的数据等 )则放在数据库中。综合数据库用于存放系统运行过程中所需要和产生的所有信息。在专家系统中 ,数据的表示与组织结构应尽量做到与知识的表示与组织相容 ,以便推理机制使用知识库中的知识和描述问题当前状态的数据去求解问题。解释子系统程序负责对产生的结果进行解释。知识获取子系统负责管理知识库…     

载荷识别的等效点动标定法

围绕飞机全动式平尾翼面抖振载荷的识别问题，提出一种用于识别未知作用位置的动载荷的方法——等效点动标定法。这种方法将结构在实际外载荷作用下的响应认为是在结构上某几个特定点处伪载荷作用的结果，将未知作用位置的动载荷转化为已知作用位置的动载荷进行识别，再依据作用等效原则将各伪载荷合成，达到识别外载荷的合力大小和作用位置的目的。验证试验结果表明：恰当地选取标定点，本文提出的等效点动标定法可有效地识别出作用于结构上的外载荷的合力大小和作用位置。     

扭转振动换能器中电极厚度对谐频率的影响

设计出一种由长度方向极化的方形压电晶片构成的扭转振动换能器。利用等效电路导出该换能器振子空载时，考虑与不考虑有厚度这两种情况下的谐频率方程。通过谐频率方程，从理论上讨论了该换能器的谐频率随电极厚度的变化关系，对设计的换能器的谐频率进行实测和理论计算，得到了在考虑电极厚度时，其谐频率理论值更趋近于测量值；在其他条件下不变时，随着电极厚度的增大，其谐频率呈线性下降趋势。     

Engineering metrology—a measure of progress

In 1952 Mr F. H. Rolt, one of the pioneers of engineering metrology, who had worked at NPL for over 40 years reviewed the progress in this area during the first half of the 20th century. He concluded his lecture by identifying eight topics on which progress could be expected.
This paper considers each of these areas and identifies where progress has occurred. The paper concludes with a few new predictions for the next decade or so.     

Methods and Facilities for Determining the Metrological Characteristics of Contact Heat Flow Transducers

Questions of metrological provisions for contact heat flow transducers by means of which it is possible to monitor heat losses at the surface of thermal energy objects are considered.     

一种直接式R—T转换器

介绍一种由电桥放大器和电压比较器组成的直接式R -T转换器。具有线路简单、调整方便、线性度好和灵敏度高的特点。     

Nondeterministic operations on finite relational structures

This article builds on a tutorial introduction to universal algebra for language theory (Courcelle, Theoret. Comput. Sci. 163 (1996) 1–54) and extends it in two directions. First, nondeterministic operations are considered, i.e., operations which give a set of results instead of a single one. Most of their properties concerning recognizability and equational definability carry over from the ordinary case with minor modifications. Second, inductive sets of evaluations are studied in greater detail. It seems that they are handled most naturally in the framework presented here. We consider the analogues of top-down and bottom-up tree transducers. Again, most of their closure properties are maintained. We relate them to the logical theory of finite relational structures and hypergraphs. Our central theorem says that every transduction which is definable in counting monadic second-order logic is a bottom-up transduction on term representations. Finally, several examples indicate that one cannot hope for decidable logical theories in the presence of unbounded nondeterminism.     

双时间法在脉冲型流量传感器检定中的应用

设计了一种新型的双时间法计数器 ,并成功地应用于检定脉冲型流量传感器 .试验表明 :该计数器性价比高 ,使用方便 ,工作可靠 ,可以缩短检定时间 ,在一定条件下 ,可用较小的标准容器检定较大口径的流量传感器 ,并且比常规检定方法具有更高的计数精度