Simulation of Fragment Impact on Multi-Layer Targets Using Contact Method

Cased explosives generate highly energetic fragments as their casing breaks up. Due to the complexity of casing fragment related behavior such as embedment, perforation and ricochet, it may be insufficient to use equivalent triangular pressure loading in fragment impact simulations. This simplified method may over- or under-predict the target response. Recently, a procedure using contact techniques has been proposed to overcome such difficulties. It has been shown that the new method has the inherent capability in modeling the multi-piece and multi-hit fragment impact problems in a more realistic way. To investigate the applicability of the proposed method to simulations involving multi-layer penetration, the selected problems of fragment impact on multi-layer targets are described in this paper. It is demonstrated that this method is capable of predicting the complicated multi-layer structural response caused by fragment impact and penetration. Modeling procedures and some technical issues are also discussed.     

Penetration of disk fragments following impact on thin plate

To investigate the ballistic resistance and failure pattern of aeroengine casing following the impact of disk fragments, and to determine the optimum case structure, the phenomena of a 1/3rd disk fragment impact on single and double-layered thin plate targets were simulated using nonlinear dynamical analysis software MSC.Dytran. Strain rate effect was introduced in a Johnson-Cook （JC） material model for the disk fragment and the plate. Impact modeling was based on the Arbitrary Lagrange-Eulerian method, and simulated using explicit finite element method （FEM）. Simulation results showed that the major failure pattern of the plate is shearing and tensile fracture with large plastic deformation. It was also concluded that the ballistic limit velocity increases with the standoffdistance when it is beyond a certain value, and that greater resistance is obtained when the front plate has either a proportionately low or high thickness. The impact resistance of a double-layered plate may exceed that of a single plate if the thicknesses and standoff distance of the two plates are set appropriately.     

Containment of high-speed rotating disk fragments

Disk burst accidents sometimes happen in aeroengines. To avoid tragic consequences, aeroengine casings must have sufficient containment capability. Experiments and simulations need to be conducted to study the impact, distortion, and perforation caused by disk burst and which may give important clues to potential failure mechanisms. This paper presents some containment tests of high-speed rotating disk fragments, in which the original disks were burst into three equal fragments within a predetermined rotating speed range. The failure modes of the containment casing varied significantly with the thickness of the containment casing. Shearing, tearing, tensile fracture, and large plastic stretching deformation occurred in a thin-walled containment casing, while a thick-walled casing could contain disk fragments and withstand large plastic deformation. Numerical simulations were carried out to study the impact process and failure modes further. Good agreement was found between the results of the simulations and the tests.     

煤及煤层气工程专业课程体系定量评价方法

本文针对目前煤及煤层气工程专业课程取舍及教学学时定性分析较多、随意性大的问题,采用多层次分析方法对煤及煤层气工程专业课程体系进行分析,建立了各课程体系评价知识模型;根据模糊综合评价方法建立了煤及煤层气工程专业课程体系的多层次模糊综合评价指标体系,最终确定出各门专业课的学时数。     

一种求解对称TSP的简单候选集方法

TSP（旅行商问题）作为一种解决组合优化问题的有效方法,在近几十年来受到了广泛的研究。理论证明它是一个典型的NP难问题,为了更快捷地求解,候选集方法在多种求解算法比如LKH算法中都有用到,一般是用于产生一个接近局部最优的初始解,较少用于寻路过程中。本文提出了一种新的简单的候选集方法,它采用一种新的距离度量,更好地符合了对称TSP的寻路规则。将其应用于最大最小蚁群算法（MMAS）的寻路过程中,实验结果表明针对对称TSP问题,该方法能比基本的MMAS取得更好的性能。这种候选集方法也可以用于其他求解对称TSP问题的进化计算。     

Computer simulation and concept development in students of genetics

Conclusion Computer simulations in genetics have the potential to complement laboratory activities and to act as an adjunct to the use of traditional sets of problems. In these roles, simulations such as CATLAB, generate qualitative changes in the learning experiences of students. For example, the simulated breeding experiment may be repeated and strategies modified without regard of the time and management constraints associated with actual laboratory experimentation; problem-solving may involve active data generation, in contrast to the style of textbook problems. This study showed that students reported a favourable attitude to CATLAB and that their use of the program lead to meaningful learning. The cognitive gains made by the student group encompassed both genetic concepts and processes. The scope for use of computer simulations as an adjunct to, or in some cases even replacement of traditional activities, and for an analysis of their impact is considerable.     

言语交际者关系管理模式新拟

针对经典礼貌理论存在的各种问题,Helen Spencer-Oatey及其合作者在现有礼貌理论等基础上建立了"关系管理模式",认为语言使用会对具有社会属性的人际关系产生影响,因而交际者会努力通过各种语用—语言方式实施人际关系的管理,主要涉及面子管理、社交权利与义务管理以及交互目标管理。本文在扼要呈现这一理论模式后,提出关于礼貌、关系管理与人际关系的新观点,剖析新模式存在的不足,并尝试提出一个改进后的模式。     

From declarative and procedural knowledge to the management of declarative and procedural knowledge

Research on domain-specific knowledge and general knowledge such as strategies has shown that information can indeed be available to a subject and still not be used. Several hypothesis have been set forth to explain this phenomenon; they as briefly exposed. An alternative, complementary hypothesis is then presented. It is assumed that most activities have several components organized in the form of a complex hierarchy. These interdependent components require monitoring because, at certain times, they are competing with one another for resources. Competition for resources and problems in component coordination may lead to a drop in performance. Several studies dealing with diverse knowledge domains are reviewed, which provide evidence for such resource problems. The same theoretical framework is then applied to explain several facts concerning teaching and learning: the impact of advance organizers; the instability of performance across repeated executions; some effects of social variables; the efficiency of tutoring and of taking into account the ‘proximal zone of development’. The limited cognitive capacity construct proves extremely useful in interpreting a large number of phenomena in a wide variety of domains.     

探究式教学模式述评

探究式教学法是指学生在学习概念和原理时,教师只是给他们一些事例和问题,让学生自己通过阅读、观察、实验、思考、讨论、听讲等途径去独立探究,自行发现并掌握相应的原理和结论的一种方法。探究式教学模式的组织过程包括探究目标或意图的生成,探究方案的策划与设计,探究行动和反思以及探究结果的分享和校正四个部分。     

几种经典活动轮廓图像分割模型综述

图像分割是将图像进行特征提取的关键技术。图像分割算法研究成果较多,活动轮廓模型是图像分割获取边缘信息的重要方法。阐述了几种经典的活动轮廓方法,通过大量仿真实验对几种方法进行比较,指出现阶段图像分割遇到的问题并展望其研究趋势。     

钢筋砼结构施工期楼层承载力的安全性复核

提出多层钢筋砼结构在施工期间,施工荷载在各相关楼层间的分配及承载力安全性复核的方法。解决了多层砼结构模板支撑系统的安装及拆除无依据、凭经验施工的问题。     

Second language learning and reading with the additional load of dyslexia

Students speaking a language at home, which is different from the instructional at home, often face serious literacy problems in their additional language. This article examines the various factors involved in these difficulties and proposes some procedures for determining whether the reading problems are primarily due to linguistic factors, sociocultural factors, or specific learning problems such as dyslexia. The discussion of linguistic factors includes a closer examination of the concept of language proficiency. Dimensions of individual differences in the ability of second language (L2) acquisition are specified. Particular emphasis is given to the role of verbal working memory in L2 acquisition and to neuropsychological aspects. A popular target for recent research has been the orthographic structure of the language, and a general assumption has been that transparent orthographies, such as Italian or Finnish, are easier for a learner to deal with than deep orthographies. The methodological problems involved in the study of this issue are discussed. Some recent large-scale comparative surveys of reading literacy have not been able to demonstrate the impact of orthographic structures, as other, more powerful explanations of achievement variations have masked the possibly small orthographic effects. These explanatory factors are to a large extent related to social and cultural conditions in homes, communities, and schools. A tentative model is proposed where the various factors involved in L2 reading are specified, providing guidelines for assessment strategies.     

Numerical Simulations of the Performance of Steel Guardrails Under Vehicle Impact

Road side barriers are constructed to protect passengers and contain vehicles when a vehicle crashes into a barrier. In general, full-scale crash testing needs to be carried out if a geometrically and structurally equivalent barrier has not previously been proven to meet the requirements of containing the vehicle and dissipating sufficient impact energy for passenger protection. As full-scale crash testing is very expensive, the number of data that can be measured in a test is usually limited, and it may not always be possible to obtain good quality measurements in such a test, a reliable and efficient numerical simulation of crash testing is therefore very useful. This paper presents finite element simulations of a 3-rail steel road traffic barrier under vehicle impact. The performance levels defined in Australian Standards AS5100 Clause 10.5 for these barriers are checked. The numerical simulations show that the barrier is able to meet low performance levels. However, the maximum deceleration is higher than the acceptable limit for passenger protection. If present, a kerb launches the vehicles into the barrier, allowing for the possibility of overriding the barrier under certain circumstances, but it redirects the vehicle and reduces the incident angle, which reduces impact force on the barrier. Further investigation into all common kerb profiles on roads should be carried out, as only one kerb profile is investigated in this study.     

Analysis of Penetration Model for Geo-Material by Rigid Projectile

Based on the cylindrical cavity expansion theory, a plastic-damage-elastic model is proposed for the penetration problem of geo-material. In the model, the unified strength criterion (Yu, 1991) is adopted as the failure criterion. The distributions of the radial stress and velocity are analyzed. According to the Newton's second law, a series results of the final penetration depth and the impedance load are obtained to different parameter b, when a rigid projectile normally impacts and penetrates a semi-infinite geo-material target with an impact velocity of 300-1200 m/s. By comparing with the test data available, it appears that the method can be used in analyzing the final depth and the impedance load of a rigid projectile penetrating into a semi-infinite target with different impact velocities.     

Modelling reality in mathematics classrooms: The case of word problems

An abundance of recent research, in many countries, has documented a very widespread tendency of children to answer school mathematics word problems with apparent disregard for the reality of the situations described by the text of these problems. Analysis of this behaviour strongly suggests that an explanation is not to be found in some cognitive deficit of the children, but rather in the culture of the classroom wherein word problems are presented in stereotyped fashion, with an implicit assumption that a solution involving the application of one or more of the basic arithmetical operations to the numbers mentioned in the text is appropriate and unproblematical. Taking such contextual influences into account, the observed behaviour of the children may be considered a reasonable response. An alternative conceptualisation of word problems, as situations calling for mathematical modelling taking into account real-world knowledge where appropriate, is proposed, with suggestions as to how it could be implemented.     

基于政治系统理论的教育考试舆情应对分析

教育考试中的舆情愈来愈多地给政府和相关教育部门带来压力,如何更好地进行舆情应对成为一个关键问题。基于政治系统理论,从输入、输出和反馈3个环节进行舆情事件应对分析发现,教育部门在舆情应对中存在应对能力不强、回应内容不明确、信息流通性差及缺乏权威引导等问题,其原因包括舆情应对存在认知偏差、维护自身利益、应对机制不完善和舆论引导经验缺乏等。据此,提出提升舆情应对意识、健全舆情应对机制、掌握舆论话语权、建设回应型政府等建议。     

Assessing Preknowledge Cheating via Innovative Measures: A Multiple-Group Analysis of Jointly Modeling Item Responses,Response Times,and Visual Fixation Counts

Many approaches have been proposed to jointly analyze item responses and response times to understand behavioral differences between normally and aberrantly behaved test-takers. Biometric information, such as data from eye trackers, can be used to better identify these deviant testing behaviors in addition to more conventional data types. Given this context, this study demonstrates the application of a new method for multiple-group analysis that concurrently models item responses, response times, and visual fixation counts collected from an eye-tracker. It is hypothesized that differences in behavioral patterns between normally behaved test-takers and those who have different levels of preknowledge about the test items will manifest in latent characteristics of the different data types. A Bayesian estimation scheme is used to fit the proposed model to experimental data and the results are discussed.     

神经网络理论在变压器继电保护中的应用(英文)

提出一种用于变压器运行和故障状态识别的神经网络方法．此方法优于传统的变压器保护原理,能正确识别变压器的内部故障、励磁涌流、外部故障及空载合于内部故障等不同状态,具有广泛的实用性和很高的容错能力．大量仿真结果证明了此方法的优越性．     

Simulation methodology development for rotating blade containment analysis

An experimental and numerical investigation on the aeroengine blade/case containment analysis is presented. Blade out containment capability analysis is an essential step in the new aeroengine design, but containment tests are time-consuming and incur significant costs; thus, developing a short-period and low-cost numerical method is warranted. Using explicit nonlinear dynamic finite element analysis software, the present study numerically investigated the high-speed impact process for simulated blade containment tests which were carried out on high-speed spin testing facility. A number of simulations were conducted using finite element models with different mesh sizes and different values of both the contact penalty factor and the friction coefficient. Detailed comparisons between the experimental and numerical results reveal that the mesh size and the friction coefficient have a considerable impact on the results produced. It is shown that a finer mesh will predict lower containment capability of the case, which is closer to the test data. A larger value of the friction coefficient also predicts lower containment capability. However, the contact penalty factor has little effect on the simulation results if it is large enough to avoid false penetration.     

Academic sell-out: how an obsession with metrics and rankings is damaging academia

Increasingly, academics have to demonstrate that their research has academic impact. Universities normally use journal rankings and journal impact factors to assess the research impact of individual academics. More recently, citation counts for individual articles and the h-index have also been used to measure the academic impact of academics. There are, however, several serious problems with relying on journal rankings, journal impact factors and citation counts. For example, articles without any impact may be published in highly ranked journals or journals with high impact factor, whereas articles with high impact could be published in lower ranked journals or journals with low impact factor. Citation counts can also be easily gamed and manipulated, and the h-index disadvantages early career academics. This paper discusses these and several other problems and suggests alternatives such as post-publication peer review and open-access journals.