A new philosophy for stochastic equivalent linearization

An extension, to the time-dependent situation, of what is known in static structural reliability as the ‘normal tail approximation’ is presented. This is pursued within the classical stochastic equivalent linearization scheme. Duffing and hysteretic oscillators are studied in detail.     

High-intensity multi-bunch beam generation by a photo-cathode RF gun

A multi-bunch photo-cathode RF gun system has been developed as an electron source for the production of intense quasi-monochromatic X-rays based on inverse Compton scattering. The desired multi-bunch beam is 100 bunches/pulse with a total charge of 500 nC and a bunch spacing of 2.8 ns. We modified the gun cavity of a ‘BNL-type IV’ RF gun to allow a CsTe cathode plug in the end plate. The system uses a four-dipole chicane beam line to allow the injection of laser light normal to the cathode surface. We compensate the gun cavity beam loading caused by the high-intensity multi-bunch electron beam by injecting the laser pulse before RF power has filled the cavity. We have achieved a total intensity of 220 nC in 100 bunches with a bunch-to-bunch energy spread under 1.3% (peak-to-peak). This paper concentrates on experiments to generate the high-intensity multi-bunch beam with compensation of the bunch-to-bunch energy spread due to heavy beam loading.     

Aeroballistic and impact physics research at EMI an historical overview

On the occasion of the Distinguished Scientist Award presentation at HVIS 1992, the technical and scientific promotion of the Impact Physics Division at EMI in the field of aeroballistics, free flight dynamics, terminal ballistics and impact physics is described. This development is closely related to the work of the recipients.

The activities began in the late fifties when a small pressurized ballistic range with a gas gun was built. The problems to construct a well working facility with observation stations are reported that arose, at those early times, from the lack of experience, money and suitable locations. In the mid-sixties, the experimental possibilities were extended by building a two-stage light gas gun that could also be used as a gun tunnel. These facilities have been the foundation for research in the field of free flight aerodynamics, such as the study of near and far wakes behind a blunt hypersonic body or the study of shock wave boundary layer interactions. In 1972, the division took the first step into terminal ballistics and, because of increasing interest, impact physics became the main research area. The division grew and with it the instrumentation. Today, diverse gas guns, powder guns and two-stage light gas guns are in operation. One topic of main interest during the years has been the penetration of rod shaped projectiles. Here the best-known result may be mentioned, the so-called ‘Hohler-Stilp S-shaped penetration curves’. In addition to this, many other topics have been investigated that can be summarized under the title “penetration mechanics and impact physics”. Based on a well developed launching technique and instrumentation, problems were investigated at low velocities of a few hundred m/s, at ordnance velocities and especially at hypervelocities up to 10 km/s. It has been recognized that dynamic material behavior and microstructural effects play an important role in understanding the interaction of projectiles with targets. Therefore, a VISAR, an electronic raster microscope, a Hopkinson bar and further equipment have been installed. Basing on the work of a period of more than 20 years, EMI has come into contact with national and foreign institutions and has become a partner for many cooperations.     

基于BP神经网络的舰炮武器系统综合保障性能评价

通过对舰炮武器系统的分析，建立舰炮武器系统综合保障性能评价的指标体系。把神经网络的相关知识应用到舰炮武器系统综合保障性能评价中，得到了相应的BP神经网络评价模型。通过一些舰炮武器系统的实例计算，验证了模型的正确性，为舰炮武器系统的研制和改进提供了一定的参考依据。     

On the dynamic behaviour of a long missile pipe after impact on a rigid target pipe

Two modes of deformation of a long missile pipe following an impact on a rigid target pipe of larger radius are analysed. It is assumed that the missile pipe can form either a ‘nutcracker’ type of mechanism or simply ‘wrap around’ the target pipe. The influence on the dynamic behaviour of the missile pipe of the parameters like the length, kinetic energy and the plastic moment of the missile pipe and the target pipe radius are discussed. A numerical procedure is presented to obtain the maximum force of interaction developed between the two pipes which also takes account of possible transition from a ‘nutcracker’ mode to the ‘wrap-around’ mode.     

In situ RHEED control of self-organized Ge quantum dots

In situ registration of high-energy electron diffraction patterns was used for constructing the diagram of structural and morphological states of the Ge film on the Si(100) surface. The following regions identified in the diagram: two-dimensional (2D)-growth, ‘hut’- and ‘dome’-clusters, ‘dome’-clusters with misfit dislocations at the interface. Variations in the lattice constants of the Ge film during the MBE growth on the Si(100) surface were determined. An increase in the lattice constant at the (100) surface was attributed to the elastic deformation at the stage of 2D growth and formation of ‘hut’-clusters and to the plastic relaxation for the ‘dome’-clusters. As a result, epitaxial silicon structures with germanium quantum dots of 15 nm base size at the density of 3×10¹¹ cm⁻² were synthesized. The total electron structure of the hole spectrum of Ge quantum dots in Si was established.     

A sustainable product design model

There are major challenges for the designer to now include Sustainable Development aspects into his/her design; particularly related to the social and wider economic impacts. The designer must, more than ever before, take into consideration the views and concerns of all the ‘interested parties’ – stakeholders. There are many topics – issues and concerns to consider and often they can be conflicting. The need is to examine the Sustainable Development risks and benefits associated with any particular design so improvements can be made. Both a ‘concept’ model and a Bournemouth University practical model are described which allows this risk/benefit assessment to be made in a structured manner on a wide range of topics. The assessment can examine the product, the company manufacturing the product and the manufacturing site. The major social, economic and environmental risks and benefits is tabulated or presented graphically for ease of evaluation in order to modify the design and so improve the Sustainable Development aspects.     

基于制造特征的火炮零件工艺决策技术研究

为简化结构复杂的火炮零件工艺设计流程,有效地提高工艺设计效率和可靠性,提出了一种基于制造特征的火炮零件工艺加工决策方法.采用参数化建模方法建立火炮零件模型,运用遗传算法对火炮零件工艺决策逻辑机制进行推理,并对制造特征进行识别与提取,从而快速确定火炮零件的工艺决策.以火炮炮尾为例进行了验证,结果表明,火炮零件模型可快速生成零件工艺流程,为火炮零件的加工制造提供条件.     

Treatment of nondetects in multivariate analysis of groundwater geochemistry data

Principal components analysis (PCA) is used to evaluate similarities in the trace element chemistry of groundwaters. Many of the trace elements, however, occur at concentrations below the detection limits (DL), which presents problems for statistical analyses. Since the optimal methods for dealing with the ‘

In this study, a new approach was developed to determine the best substitution methods when dealing with the ‘DL’ values for a given data set. Monte Carlo simulation experiments, using a mixture multivariate model, were performed to test the effects of substitution of the ‘

When ‘相似文献   

An appraisal of ecolabelling from a design perspective

This paper considers the design implications of the European ecolabelling scheme. The aims and procedures of this procedures of this product level market instrument are examined and appraised with regard to impact on product design. The paper concludes that ecolabelling, as presently defined, will have a limited affect on promoting widespreads design and provision of environmentally sensitive products. A ‘product selection model’ is therefore proposed that makes for more effective ecolabelling. This in turn is developed to provide an ‘ecodesign emphasis model’ to indicate design options that can shift products towards an optimum and sustainable ‘green’ target.     

Design method and scientific method

A recurring theme in recent design theory has been a desire to relate design method to scientific method: to create the ‘science of design’ or a ‘design science’. There is an inherent paradox in such a desire since design and science are clearly very dissimilar kinds of activities. Further, the concept of ‘scientific method’ now seems to be in epistemological chaos. For these reasons, attempts to model design method on scientific method seem misplaced. It is proposed that it would be more fruitful to regard design as a technology, rather than as a science. The paper seeks to establish the basis for such a view, drawing especially on the idea that both design and technology involve the application of types of knowledge other than the purely ‘scientific’ kind.     

常规兵器试验关键过程探讨

针对质量管理体系外审与内审中发现的问题,明确了常规兵器试验关键过程的内涵及控制的重要意义,探讨了常规兵器试验关键过程的识别方法、程序与控制要点,结合实例分析了火炮和火箭炮试验中的几个关键过程和控制要求,辨析了常规兵器试验中关键过程、需要确认的过程两者的区别与联系。可为常规兵器试验人员在识别与控制试验关键过程时提供借鉴与参考。     

Long-term effects of legislation and local promotion of child restraint use in motor vehicles in Sweden

The main objective is to study long-term effects of legislation and promotion of child-restraint use in motor vehicles. Subgoals are to describe the level of restraint use in cars and changes in mortality and morbidity patterns in regard to differences among age groups and geographical areas (morbidity). The study areas were; ‘The First Four’, ‘The Six Counties’, ‘The Rest of Sweden’, and ‘Sweden as a whole’, and the population were two age groups — 0–6 and 7–14 years. The incidence of restraint use comes from observations of car-seat-belt usage. Outcome evaluation was based on hospital-discharge data 1978–1996 and mortality statistics 1970–1996. The level of restraint use for children in the front seat was 97% in 1988 and was equal to 1995. Mortality data shows a decrease of 2.8% on an average per year, 76% over the study period. A significant change over time in the two intervention areas was shown (annual changes of −2.8 and −1.8%), but not in the rest of Sweden. The local authorities that started early with preventive programs, such as safety seat loan schemes and those having an organised safety-promotion program showed a much better improvement than the rest of Sweden. There is a need for appropriate information for local action on childhood injury prevention to accompany national legislation.     

Carbon fibres: structure and mechanical properties

The microstructure of six types of acrylic-based and hydrated cellulose-based carbon fibres of strengths from 1650 to 6120 MPa and elastic moduli from 97 to 228 GPa were studied by scanning electron microscopy (SEM). A ‘microcomposite’ structure of carbon fibres studied consisting of quasi-amorphous (‘matrix’) and orientated fibrillar carbon was revealed. This led to a new model of the fibre structure. The analysis of results of testing different carbon fibres defines the elastic modulus of ‘matrix’ carbon, and shows plastic drawing of fibrils. The model describes the properties of fibres and predicts ways to improve the fibre properties.     

Functional changes in cerebral and paraspinal muscle physiology of healthy women during exposure to whole-body vibration

The objective of this study was to investigate the effects of whole-body vibration on multiple tissues simultaneously in fourteen healthy women. On three separate days, participants were exposed to frequencies, 3, 4.5, or 6 Hz (at 0.9 g_r.m.s acceleration in vertical direction) per day on a simulator for 16 min. While sitting ‘with’ and ‘without’ backrest support, participants also performed handgrip contractions for 1 min. Cerebral and lumbar muscle oxygenation and blood volume responses were measured using near-infrared spectroscopy. Cardiorespiratory responses were collected using a metabolic cart. In general, cerebral and cardiorespiratory responses increased with vibration compared to without vibration, whereas in the lumbar region oxygenation and blood volume responses decreased. Greatest cerebral responses were observed at 6 Hz (P < 0.05). When compared to exposure to vibration without performing work, significant decrease in lumbar responses was observed during handgrip contractions in both conditions of sitting ‘with’ and ‘without’ a backrest (P < 0.05). Such decreases in the lumbar responses suggest postural load due to prolonged sitting combined with physical activity during vibration, might reduce vascular supply to the paraspinal muscles. This study reiterates the importance of understanding the physiological basis for various health disorders in women due to exposure to whole-body vibration.     

On the effect of sampling volume on the microscopic cleavage fracture stress

Reported observations of an experimental variation in the microscopic fracture stress for transgranular cleavage (σ^*_f) with specimen geometry and size are quantitatively examined in terms of a weakest-link statistical model for brittle fracture, wherein failure coincides with the critical propagation of a particle microcrack into the matrix. By analysing the onset of fracture in the ‘sharp-crack’ (K_Ic) specimen, the ‘rounded-notch’ (Charpy) specimen, and the uniaxial tensile specimen, it is shown that values of σ^*_f are reduced progressively in the ‘sharp-crack’, notched and unnotched geometries and with increasing specimen size, consistent with an increase in statistical sampling volume. Quantitative predictions for the magnitude of this variation are given for a low strength steel.     

The performance of precursor-based estimators for rare event frequencies

Data on accident ‘precursors’ or ‘near misses’ can help in obtaining accurate estimators of accident frequencies when actual accident data is sparse. A variety of precursor-based estimators have been proposed in the literature. This paper presents results of a simulation study to assess the statistical performance of several such estimators, to help in determining which are the most suitable for use in practice.     

Modelling the factors related to the seatbelt use by the young drivers of Athens

Road traffic accidents in Greece are one of the major problems of the public health sector and the first cause of death in the ages 18–24. However, there are no records available for defining the determinants of road accidents and seatbelt wearing rates. The main objective of this study is to determine and clarify the relationship between young drivers’ intentions (motivation to use/non use seatbelt) and their behaviour (self-reported use). Additionally, the purpose of this study is to evaluate the seatbelt wearing rates among young drivers in relation to their trip-type. The sample consisted of 200 young Greek drivers of both sexes. The statistical analysis included factor analysis and multiple regression analysis. The seatbelt use was measured in relation with seven trip-types. Through factor analysis, a seven factor scale of seatbelt use and a four factor scale of seatbelt non use were created which included Greek young drivers’ basic motivations for wearing or not wearing a seatbelt. A model, constructed by the multiple regression analysis, revealed the factors related with the seatbelt use. The factors positively related were ‘imitation’, ‘self-protection’, and ‘legality’. The factor of ‘discomfort’ is negatively associated with the seatbelt use. Furthermore, mileage was negatively related with seatbelt use. Finally, some preliminary suggestions on how prevention strategies should be implemented in Greece are discussed.