A new type of depressed collector using a magnetic field†

A new form of depressed collector for microwave tubes has been investigated. It is shown that the use of a suitably selected transverse magnetic field in the collector leads to a smoothing of the power dissipation curve on the collector walls and to a fifty-fold reduction in the returning secondary-electron current.     

非声学公共建筑中的声品质

本文分析了在八种公共建筑类型中的声学专题研究结果, 包括火车站、商城、图书馆、开敞式办公室、足球场、游泳空间、用餐空间、及教堂, 旨在考查主观评价和客观指标之间的关系, 并且探索在非声学建筑中创造舒适的声环境的原则和框架。分析表明了声品质在这类非声学建筑中的重要性, 另外, 即使客观指标例如声压级和混响时间相同, 声舒适度亦可能完全不同。其它关键因素包括社会背景、心理调节、声音喜好、声学处理的接受程度, 声学与其他环境因素的相互作用、以及不满意的声品质可能造成的健康影响。     

Long-lived yeast as a model for ageing research

Yeast has essentially two lifespans: a replicative lifespan (the number of daughters produced by each dividing mother cell) and a chronological lifespan (the capacity of stationary (G0) cultures to maintain viability over time). There is a tendency now to label every investigation that addresses these lifespans as ageing research. It is, though, analyses of the longest lifespans that will be most informative about the determinants of longevity and yield results most relevant to ageing in more complex systems. This review addresses these issues and describes the ongoing studies that are now attempting to address ageing in yeast cells of maximal replicative or chronological longevity.     

Biochemical characterization of dextranase from Arthrobacter oxydans and its cloning and expression in Escherichia coli

Appreciably elevated levels of dextranase from Arthrobacter oxydans (AODex) isolated from sugar-cane farm soil was resulted from the culture on the Luria-Bertani (LB) medium containing 1%(w/v) soluble starch, glycerol, or dextran. The responsible gene (aodex) was cloned, its nucleotide sequence was determined, and expression of the encoded protein was achieved in Escherichia coli. An open reading frame was composed of 1,863 bp putatively encoding a 68.3 kDa protein. Recombinant A. oxydans dextranase (rAODex) was purified about 16 fold by nickel-nitrilotriacetic acid affinity column chromatography; K _m value for dextran T2000 was 0.85 mg/mL (w/v). AODex treatment of stale sugar cane juice resulted in a yield of square and light-colored sugar crystals.     

Prediction of Traffic Volume of Motor Vehicles Based on Mobile Phone Signaling Technology

Urban traffic volume detection is an essential part of traffic planning in terms of urban planning in China. To improve the statistics efficiency of road traffic volume, this thesis proposes a method for predicting motor vehicle traffic volume on urban roads in small and medium-sized cities during the traffic peak hour by using mobile signal technology. The method is verified through simulation experiments, and the limitations and the improvement methods are discussed. This research can be divided into three parts: Firstly, the traffic patterns of small and medium-sized cities are obtained through a questionnaire survey. A total of 19745 residents were surveyed in Luohe, a medium-sized city in China and five travel modes of local people were obtained. Secondly, after the characteristics of residents’ rest and working time are investigated, a method is proposed in this study for the distribution of urban residential and working places based on mobile phone signaling technology. Finally, methods for predicting traffic volume of these travel modes are proposed after the characteristics of these travel modes and methods for the distribution of urban residential and working places are analyzed. Based on the actual traffic volume data observed at offline intersections, the project team takes Luohe city as the research object and it verifies the accuracy of the prediction method by comparing the prediction data. The prediction simulation results of traffic volume show that the average error rate of traffic volume is unstable. The error rate ranges from 10% to 30%. In this thesis, simulation experiments and field investigations are adopted to analyze why these errors occur.     

A deformable model of the human iris for measuring small three-dimensional eye movements

This paper describes a deformable model of the human iris which forms part of a system for accurate off-line measurement of binocular three-dimensional eye movements, particularly cyclotorsion (torsion), from video image sequences. At least two existing systems measure torsion from infrared video images by pupil tracking followed by cross correlation using arcs of bandpass-filtered iris texture. Unfortunately, pupil expansion and contraction reduces the accuracy of this method unless drugs are used to constrict the pupil, which causes temporary blurred vision. A five-parameter deformable model of the iris is therefore developed for analysing images obtained without the use of drugs. This model can translate (horizontal and vertical eye motion), rotate (torsion) and scale both uniformly and radially (pupil changes). Torsion measurements obtained with the model are repeatable and accurate to within 0.1°; this performance is illustrated by analysing binocular torsion during fixation on a stationary target. Received: 27 August 1997 / Accepted: 15 January 1998     

Robust hyperplane design in multivariable variable structure control systems

The problem of designing a stable sliding mode giving robust performance of a variable structure control system is studied. A set of specified eigenvalues is assigned to the closed-loop feedback system during the sliding mode. The design philosophy seeks to build on the known robustness and invariance properties associated with the use of discontinuous (or continuous) non-linear controls, by assigning the eigenvectors associated with the sliding-mode eigenvalues in a manner that leads to a robust control scheme. A previously developed canonical form for the hyperplane design problem is again employed. The design technique centres on a recently published eigenvalue assignment algorithm, and is illustrated by the inclusion of an example.     

Continuous approximation of variable structure control

A straightforward modification of the theory of ‘sliding’ variable structure control systems is used to design a control law that is a continuous arbitrarily close approximation, within a predefined subspace, to the discontinuous variable structure control law. Linear combinations of eigenvectors, and certain null spaces, are used to analyse the state trajectory under the influence of the continuous control law. Comparisons are drawn and the inherent robustness properties of variable structure control systems are retained, while the undesirable chatter motion of the sliding mode is eliminated. The accuracy of the approximation to the idealized case can easily be calculated. The general results are illustrated by the simulation of a time-invariant fourth-order multivariable system with two controls