Measurement problems arising from the use of a recursive algorithmfor model identification of electrical systems

The use of parameter estimation techniques in practical applications requires accurate analysis of the associated measurement and computation problems. With reference to an already proposed model identification procedure, the authors deal with the experimental tests carried out in order to highlight problems and to find the most appropriate solutions. In particular, a synchronization method is described, and some suggestions concerning the optimal working conditions of all the necessary devices are reported     

大型深海AUV无动力螺旋下潜运动特性分析

为了合理地设计大型深海自主水下航行器（autonomous underwater vehicle, AUV）,针对其无动力螺旋下潜时的静力配置问题展开研究,重点分析其无动力螺旋下潜运动特性。首先,基于拉格朗日方程推导了大型深海AUV的动力学模型,并利用CFD（computational fluid dynamics,计算流体动力学）软件对其直航试验、斜航试验、悬臂水池试验和平面运动机构试验进行数值模拟,通过最小二乘线性回归法拟合得到了相应的水动力系数;同时通过对比给定推力条件下AUV的直航速度验证了动力学模型的有效性。然后,基于所构建的动力学模型,利用MATLAB/Simulink和S函数建立了大型深海AUV的六自由度运动仿真模型,分析了其净负浮力、重心纵向位移和稳心高度与无动力螺旋下潜稳态参数之间的关系。最后,设计了1∶10的大型深海AUV缩比样机,通过水池试验验证了动力学仿真结果的正确性。结果表明：净负浮力作为大型深海AUV下潜时的主要动力来源,决定了AUV的下潜速度和偏航角速度;净负浮力和重心纵向位移与稳心高度的比值越大,AUV的垂向下潜速度越快,下潜至6 000 m深度的用时越短;由于该AUV的体量较大,其纵倾角主要由重心纵向位移与稳心高度的比值决定,压载质量对重心位置和转动惯量的影响几乎可以忽略。研究结果可为大型深海AUV无动力螺旋下潜时的静力配置提供参考。     

Hazard evaluation of chemicals for bulk marine shipment

For economic reasons most chemicals used in large quantities by industry are transported in tank vessels. These chemicals range in properties from essentially harmless to highly dangerous. Although the United States and IMCO require certain minimum data before classifying a new chemical to be transported in bulk, no formal system exists to correlate these data with specific shipboard requirements such as the location of the tank within the vessel, gauging and venting systems, or cargo overfill protection.Developing guidelines for the evaluation of chemicals is a two part problem. First, the inherent hazards of a chemical (the hazards of a product when it is released, without regard to its cargo containment system) must be investigated. In the second part of the evaluation, these hazards are then correlated with specific shipboards requirements as mentioned above. This paper outlines the essential elements for developing a comprehensive system of hazard evaluation for bulk liquid chemicals.     

Use of multidimensional utility functions in hazardous shipment decisions

Recent developments in multiple-objective decision analysis are utilized to assess the applicability of the theory to decisions in hazardous material shipments. A realistic problem involving decisions related to the shipment of anhydrous ammonia by different transportation modes is formulated and solved utilizing decision theory. The results indicate that decision analysis may prove to be a useful tool in optimizing choices regarding hazardous material transportation.     

肌力协同补偿的无动力下肢外骨骼设计与分析

无动力外骨骼具有质量小、代谢能耗低、基本不改变正常步态、无需外动力源和可持续工作时间长等优点,已逐渐成为新型外骨骼领域的研究热点。为提升常规无动力下肢外骨骼对步态能量的利用效率,设计了一种肌力协同补偿的无动力下肢外骨骼。首先,通过建立人体下肢动力学模型分析了行走过程中下肢能量的变化规律,得到了步态能量的储存与释放机理;然后,结合设置代起止点的折线路径及肌力贡献度,制定了关节肌肉的肌力协同补偿路径;最后,基于踝、髋关节的刚度设计了弹性储能元件,构建了一款无动力柔性下肢外骨骼,并利用OpenSim软件分析了有无穿戴外骨骼时人体下肢相关肌肉在行走过程中的代谢能耗。结果表明,在穿戴无动力下肢外骨骼时,比目鱼肌、腓肠肌和胫骨前肌的代谢能耗分别降低了31.5%,34.7%和40.0%,股直肌、阔筋膜张肌和缝匠肌的代谢能耗分别降低了36.3%,7.0%和5.0%;单个步态周期内下肢相关肌肉的总代谢能耗降低了15.5%。研究结果可为低代谢能耗的无动力下肢外骨骼的优化设计提供一定的理论依据。     

Electric current arising from unpolarized polyvinyl formal

An appreciable electric current is observed in a system consisting of a polyvinyl formal (PVF) film in a sandwich configuration, in the temperature range 30–110°C. The maximum value of the current during first heating is found to be of the order of 10⁻¹⁰ A and its thermograms exhibit one transition (i.e. current peak) at around 60°C. The position of the current peak in thermal spectrum shifts with the heating rate. A temperature dependence of the open circuit voltage is also observed. The activation energy of the process responsible for the current is determined. The magnitude of the current is more in the case of dissimilar electrode systems. It is proposed that the electric current arising from unpolarized metal-polymer-metal system is a water activated phenomenon, which is influenced by the transitional changes of the polymer.     

Reliability and failure patterns arising from fatigue

This paper examines the cause of ‘knees’ or ‘freaks’ in the life-failure patterns resulting from some fatigue processes. A theory is developed which takes into account the extra fatigue damage associated with the non-elastic behaviour of the material. It appears to account for the knee and agrees well qualitatively with test results, though quantitative comparisons are not possible because the stochastic data required for the calculation are not available. It is shown that ‘S’-shaped curves sometimes experienced at higher loading roughness are also due to the same mechanism. The theory suggests that the undesirable features of the failure patterns, whose origin has not hitherto been fully investigated, can be eliminated by a design which is intrinsically reliable with respect to the elastic limit (or with respect to the yield strength if a small loss of reliability is acceptable). Because the knees or freaks appear to be a consequence of the fatigue process and arise with conventionally distributed mechanical properties it is suggested that this design action would be more effective than eliminating the items by quality control.     

Synchronisation of production scheduling and shipment in an assembly flowshop

This paper studies a synchronised scheduling problem of production simultaneity and shipment punctuality in a two-stage assembly flowshop system. Production simultaneity seeks to ensure all products belonging to a same customer order are simultaneously completed (at least as close as possible). Shipment punctuality attempts to satisfy orders’ individual shipment due dates. We provide two criteria, i.e. mean longest waiting duration and mean earliness and tardiness, for measuring production simultaneity and shipment punctuality, respectively. A synchronised scheduling model is developed by balancing the two criteria using linear weighted sum method. A modified genetic algorithm (GA) is then proposed for solving this model. Numerical studies demonstrate the effectiveness of the proposed approach. The results indicate that considering production simultaneity can remarkably reduce finished products inventory. A prioritised weight combination interval for production simultaneity and shipment punctuality has been suggested. Production simultaneity is affected by the production system configuration, especially in peak seasons.     

Families of distributions arising from distributions of order statistics

Consider starting from a symmetric distributionF on ℜ and generating a family of distributions from it by employing two parameters whose role is to introduce skewness and to vary tail weight. The proposal in this paper is a simple generalisation of the use of the collection of order statistic distributions associated withF for this purpose; an alternative derivation of this family of distributions is as the result of applying the inverse probability integral transformation to the beta distribution. General properties of the proposed family of distributions are explored. It is argued that two particular special cases are especially attractive because they appear to provide the most tractable instances of families with power and exponential tails; these are the skewt distribution and the logF distribution, respectively. Limited experience with fitting the distributions to data in their four-parameter form, with location and scale parameters added, is described, and hopes for their incorporation into complex modelling situations expressed. Extensions to the multivariate case and to ℜ⁺ are discussed, and links are forged between the distributions underlying the skewt and logF distributions and Tadikamalla and Johnson'sL _U family.     

无动力下肢负重外骨骼人机动力学及其储能元件刚度优化EI北大核心CSCD

为提高人体搬运效率,降低人体关节损害,提高外骨骼能量利用效率,基于人机动力学对一种无动力辅助负重下肢外骨骼的储能元件刚度进行优化。应用牛顿-欧拉动力学方程建立人机耦合动力学模型,得到各关节力矩与大小腿长度和质量、关节转角及弹簧刚度关系的数学模型。将三维动作捕捉系统采集的角度数据代入动力学方程中,通过MATLAB进行计算得到关节力矩动态变化规律。建立人机系统各部分的能量流动模型,并进行步态周期内的能量流动分析,以储能元件刚度为参数,储能元件的能量流动为约束条件,各关节平均力矩最小为目标建立优化模型,通过与AnyBody人体仿真软件获得的人体模型作对比验证优化结果的正确性。结果表明,穿戴优化后外骨骼减轻了下肢着地时对人体的冲击,有效降低了人体能耗和下肢关节转矩。     

Eye strain and stress arising from VDU usage

Operator fatigue and eyestrain arising from prolonged use of a computer or other visual display unit (VDU) can be eliminated by fitting a circular polarising filter over the screen.     

Quantifying social distancing arising from pandemic influenza.

Local epidemic curves during the 1918-1919 influenza pandemic were often characterized by multiple epidemic waves. Identifying the underlying cause(s) of such waves may help manage future pandemics. We investigate the hypothesis that these waves were caused by people avoiding potentially infectious contacts-a behaviour termed 'social distancing'. We estimate the effective disease reproduction number and from it infer the maximum degree of social distancing that occurred during the course of the multiple-wave epidemic in Sydney, Australia. We estimate that, on average across the city, people reduced their infectious contact rate by as much as 38%, and that this was sufficient to explain the multiple waves of this epidemic. The basic reproduction number, R0, was estimated to be in the range of 1.6-2.0 with a preferred estimate of 1.8, in line with other recent estimates for the 1918-1919 influenza pandemic. The data are also consistent with a high proportion (more than 90%) of the population being initially susceptible to clinical infection, and the proportion of infections that were asymptomatic (if this occurs) being no higher than approximately 9%. The observed clinical attack rate of 36.6% was substantially lower than the 59% expected based on the estimated value of R0, implying that approximately 22% of the population were spared from clinical infection. This reduction in the clinical attack rate translates to an estimated 260 per 100000 lives having been saved, and suggests that social distancing interventions could play a major role in mitigating the public health impact of future influenza pandemics.     

A classification rule arising from accelerated life test

At the research and development stage, a decision maker may wish to classify several competitive designs with respect to a control (or standard) design. The classification problem may become very difficult when the products are highly reliable, since only a few (or even no) failures can be observed under normal use condition. The accelerated life test (ALT) model resolves this difficulty by shortening the time of life testing and quickly provides life data of products. For a highly-reliable product with a Weibull distribution whose characteristics life is a log linear function of stress, the authors propose an intuitively appealing classification procedure which divides the competitive designs into two exclusive groups. A suitable sampling plan based on this classification procedure is developed. Finally, for the purpose of illustrating this classification rule and use of this sampling plan, an example is also given.     

The quantification of uncertainties in internal doses assessed from monitoring measurements

A novel method is described for the assessment of total uncertainties in intakes and internal doses assessed from in vivo and bioassay monitoring measurements. Using the information on uncertainties in intake patterns, measurements and biokinetic model parameters, the probability distribution functions for assessed intake and dose were generated using Monte-Carlo simulations. The method was implemented using software written in MS Visual Basic 6.0. Preliminary results are presented for the example of routine tritium-in-urine monitoring. It was shown that the uncertainty in the assessed dose first decreases with increasing monitoring interval, reaching a minimum at approximately 14 d, and then increases as the monitoring interval is increased beyond 14 d. The distribution describing the ratio of assessed-dose-to-true-dose becomes very asymmetric at longer monitoring intervals. In principle, this method should allow realistic uncertainties to be placed on assessed internal doses.     

The development of frames of references

Measurement of the effectiveness of science policies is analyzed as a multi-level problem. Journal-journal citations are discussed as a potential candidate for a domain beyond the control of policy-makers and authors or research groups and therefore may function as a relatively stable and easily accessible baseline for the calibration of outputs and outcomes of science policy. A method is developed, usingSCPsJCRs which is then applied to the two cases of water pollution and humanisation of labor. This method can also be used as a simple indicator for the development of journal-journal citation patterns over time.     

Changes in the time distribution of biochemical article references from 1962 to 1977

Beside the continuous growth of the number of references per biochemical article from 1962 to 1977, an equalization tendency can be observed in the R/A values of the five leading biochemical journals investigated. While from 1962 to 1969 the number of more recent references (0–5 year old) had a higher growth rate than that of the older ones (6+year old), from 1969 to 1977 the situation turned to the opposite. The number of very recent (0–1 year old) references reached a saturation near the end of the sixties.     

Proof of a conjecture of Moed and Garfield on authoritative references and extension to non-authoritative references

Summary In a recent paper [H. F. MOED, E. GARFIELD: In basic science the percentage of “authoritative”references decreases as bibliographies become shorter. Scientometrics 60 (3) (2004) 295-303] the authors show, experimentally, the validity of the statement in the title of their paper. In this paper we give a general informetric proof of it, under certain natural conditions. The proof is given both in the discrete and the continuous setting. An easy corollary of this result is that the fraction of non-authoritative references increases as bibliographies become shorter. This finding is supported by a set of data of the journal Information Processing and Management (2002 + 2003) with respect to the fraction of conference proceedings articles in reference lists.