An iteration method using artificial boundary for some elliptic boundary value problems with singularities

By using an artificial boundary an iteration method is designed to solve some elliptic boundary value problems with singularities. At each step of the iteration the standard finite element method is used to solve the problems in a domain without singularities. It is shown that the iteration method is equivalent to a Schwarz alternating method. Some numerical examples are given, which show the effectiveness of the iteration method. Copyright © 1999 John Wiley & Sons, Ltd.     

Two refined non‐conforming quadrilateral flat shell elements

Two refined quadrilateral flat shell elements named RSQ20 and RSQ24 are constructed in this paper based on the refined non‐conforming element method, and the elements can satisfy the displacement compatibility requirement at the interelement of the non‐planar elements by introducing the common displacements suggested by Chen and Cheung. A refined quadrilateral plate element RPQ4 and a plane quadrilateral isoparametric element are combined to obtain the refined quadrilateral flat shell element RSQ20, and a refined quadrilateral flat shell element RSQ24 is constructed on the basis of a RPQ4 element and a quadrilateral isoparametric element with drilling degrees of freedom. The numerical examples show that the present method can improve the accuracy of shell analysis and that the two new refined quadrilateral flat shell elements are efficient and accurate in the linear analysis of some shell structures. Copyright © 2000 John Wiley & Sons, Ltd.     

Behaviour Analysis of Distributed Systems Using the Tracta Approach

Behaviour analysis should form an integral part of the software development process. This is particularly important in the design of concurrent and distributed systems, where complex interactions can cause unexpected and undesired system behaviour. We advocate the use of a compositional approach to analysis. The software architecture of a distributed program is represented by a hierarchical composition of subsystems, with interacting processes at the leaves of the hierarchy. Compositional reachability analysis (CRA) exploits the compositional hierarchy for incrementally constructing the overall behaviour of the system from that of its subsystems. In the Tracta CRA approach, both processes and properties reflecting system specifications are modelled as state machines. Property state machines are composed into the system and violations are detected on the global reachability graph obtained. The property checking mechanism has been specifically designed to deal with compositional techniques. Tracta is supported by an automated tool compatible with our environment for the development of distributed applications.     

Methane conversion to ethane in the presence of iron‐ and manganese‐promoted sulfated zirconia

Sulfated zirconia promoted with 1.0 wt% Fe and 0.5 wt% Mn converts methane into ethane with traces of ethylene and acetylene. The initial reaction rate at 723 K and a methane partial pressure of 20 kPa was found to be about 10^-9 mol(CH ₄) (g s)^-1, and deactivation was rapid, with the reaction rate declining to half the maximum rate within an hour. This revised version was published online in July 2006 with corrections to the Cover Date.     

A pre-emphasis filter system for in-building MPEG-2 video distribution

It is becoming popular that both residential and commercial buildings in a densely populated urban city have fibre cables laid from a central office to the basement of the building. Category 5 twisted pairs are then used for in-building distribution. This paper introduces a pre-emphasis filter system to distribute MPEG-2 videos within a building using category 5 twisted pairs. A novel technique is used to identify the frequency response of a twisted pair cable to obtain the necessary preamplification at the transmitter. Simulation results are obtained for both conventional and fractional tap-line pre-emphasis filters for a 1000 ft category 5 twisted pair. The proposed system can be used by telecom companies to provide video-on-demand, internet connection and other interactive multimedia services. The system can also be utilized by hotels, hospitals, recreation centres and corporations to deploy their private intranets, VOD and multimedia information systems. © 1998 John Wiley & Sons, Ltd.     

Bandwidth-efficient pilot-symbol-aided technique formultipath-fading channels

Pilot-symbol-aided (PSA) transmission is one of the effective methods to combat multipath-fading in digital mobile communications systems. In the PSA systems, redundant bandwidth and power are required to transmit the pilot symbols. We propose a novel fading estimation technique that requires a very low bandwidth redundancy in the PSA systems. The proposed technique uses simple linear interpolation on the pilot symbols and the detected data symbols to obtain the estimates of the channel fading effects. Monte Carlo computer simulation has been carried out to study the effects of the technique on the bit error rate performance of 16-ary quadrature amplitude modulation in the flat and the frequency-selective Rayleigh-fading channels corrupted with cochannel interference and additive white Gaussian noise. Results have shown that the proposed technique can, at the expense of a little power efficiency, significantly improve the bandwidth efficiency of the PSA systems using receivers with low complexity and latency     

Impact of ESD protection device trigger transient on the reliability of ultra-thin gate oxide

Common ESD protection devices have a snapback characteristic similar to a silicon-control rectifier. The transient voltage required to trigger these devices usually is not an important design criterion as long as it is not too high. In this work, it is demonstrated that the defect generation mechanism in oxide during electrical stress remains unchanged in the sub-nanosecond stress regime. As a result, the voltage transient can create far more defects in the gate oxide than the main ESD event clamped at the holding voltage. Due to difficulty in measurement, this oxide reliability degradation can lead to chip failure but not show up in simulated ESD test.     

不同空气状况下室内氡子体未结合态份额和活度中位直径的同时测量

根据超细粒子穿透金属筛网的渗滤理论 ,提出了一种同时测定室内空气中氡子体未结合态份额 ( fp )和活度中位直径 ( AMD)的简便的双筛网方法。实验装置包括采样和测量两部分。采样装置由采样头、流量计、活性碳盒和抽气泵组成 ,采样头用两层不同目数的金属筛网和一层滤膜构成。测量装置使用多探头低本底 α计数器和 γ谱仪 ,前者用来测量筛网和滤膜上的活度 ,以确定氡子体 α潜能浓度 ;后者用来测量活性碳盒的氡子体 γ谱 ,以确定氡浓度。用此方法测定了一个普通实验室内不同空气状况下氡子体的 fp 和 AMD值 ,并计算了各种状况下气管 -支气管 ( T- B)区的有效剂量转换因子 DCF[包括以 m Sv/ WLM为单位的“剂量学转换”和以μSv/ ( a· Bq· m-3)为单位的“约定转换”]。还计算了氡子体所致的年有效剂量。     

Anchor point indexing in Web document retrieval

Traditional World Wide Web search engines, such as AltaVista.com, index and recommend individual Web pages to assist users in locating relevant documents. As the Web grows, however, the number of matching pages increases at a tremendous rate. Users are often overwhelmed by the large answer set recommended by the search engines. Also, if a matching document is a hypertext, the document structure is destroyed and the individual pages that compose the document are returned instead. The logical starting point of the hyperdocument is thus hidden among the large basket of matching pages. Users need to spend a lot of effort browsing through the pages to locate the starting point, a very time consuming process. This paper studies the anchor point indexing problem. The set of anchor points of a given user query is a small set of key pages from which the larger set of documents that are relevant to the query can be easily reached. The use of anchor points helps solve the problems of huge answer set and low precision suffered by most search engines by considering the hyperlink structures of the relevant documents, and by providing a summary view of the result set.     

Antenna pattern scattering by rectangular cylinders

The uniform geometrical theory of diffraction (UTD) and the complex source point method are combined to predict two-dimensional (2-D) scattering by rectangular cylinders for E and H-polarized beam sources. Arrays of such beam solutions are also used to model propagation of radio beams into the shadow regions of buildings for local extended sources. Direct numerical verification of the results is obtained for square cylinders of moderate width