An approach to micro-macro modeling of heterogeneous materials

 A micro-macro strategy suitable for modeling the mechanical response of heterogeneous materials at large deformations and non-linear history dependent material behaviour is presented. When using this micro-macro approach within the context of finite element implementation there is no need to specify the homogenized constitutive behaviour at the macroscopic integration points. Instead, this behaviour is determined through the detailed modeling of the microstructure. The performance of the method is illustrated by the simulation of pure bending of porous aluminum. The influence of the spatial distribution of heterogeneities on the overall macroscopic behaviour is discussed by comparing the results of micro-macro modeling for regular and random structures. Received 9 July 2000     

An improved fuzzy-AHP (IFAHP) approach to compare SECI modes

Mental models and knowledge base of an employee are two key resources of an organisation that are imperative to develop innovative products. Effective utilisation of socialisation (S), externalisation (E), combination (C) and internalisation (I) modes within any product development (PD) phase plays an important role in creating new knowledge and updating the mental models. In order to investigate the influence of SECI modes on a specific PD phase, an improved fuzzy analytical hierarchy process approach is presented. In simple fuzzy analytical hierarchy process, the numbers are either normalised or a zero value is assigned to the degree of possibility when two triangles are not intersecting with each other. This approach calculates distorted values of degree of possibility and thus very likely produces false ranking of alternatives. The article proposes to extend the triangle edges about x-axis until they intersect when the pessimistic value of one triangle is more than the optimistic value of other triangle. It allows developing a mathematical formulation to estimate the true values of degree of possibility instead of zero. An example of conceptual design phase is discussed to illustrate the applicability and usefulness of proposed framework. In order to evaluate the performance of underlying phase in terms of knowledge creation, five criteria are selected based on the literature search and discussion with subject matter experts from strategic decision areas. After stringent analysis and exhaustive experimentation, it is found that internalisation mode highly influences the conceptual design phase.     

An effective-medium approach to the optical properties of heterogeneous materials with nonlinear properties

Abstract

We have derived an analytic approach, based on the hypothesis of the effective-medium theory, to evaluate the effective dielectric magnitudes, including the effective third order nonlinear optical susceptibility α(χ⁽³⁾), of a heterogeneous two-component medium in which one of the components (the host matrix or the embedded particle respectively) presents nonlinear behaviour. Our formulation allows us to solve the full nonlinear problem in the whole range of concentrations without treating the nonlinear effects as a small perturbation to the linear behaviour. Therefore, it can be considered as an upper limit of the commonly used low-field nonlinear approximations for heterogeneous materials. Under certain conditions, these composites can exhibit a bistable regime that the present theory properly describes in wide ranges of the concentration, shape, wavelength, dielectric contants and intrinsic nonlinear optical susceptibility of the nonlinear component as well as in terms of the intensity of the external electric field. The present approach has been used to calculate the nonlinear optical response of Cu—Al₂O₃ nanocomposites.     

An empirical study of the accessibility of web references in two Chinese academic journals

To discover the current situation and characteristics of web reference accessibility, the present study examined the accessibility of 1,637 web references in two key Chinese academic journals published from 1999 to 2003. The author develops linear regression models to demonstrate the decay of web reference accessibility. The study examines the influence of high use of web references in a paper, the associations between web reference accessibility and generic domain, country domain, protocol, and resource type, respectively, and classifies inaccessible web references according to Internet Explorer feedbacks. It compares the retrieval efficacy among three kinds of retrieval methods and reports on the limitations of Internet Archive.     

An empirical investigation of supply chain strategy typologies and relationships to performance

We propose a typology of supply chain management strategies based on data from a large sample of US firms. The resulting typologies and their relationships with firm performance are tested. The result of set correlation analysis on the data revealed six distinct supply chain management typologies, and showed significant statistical relationships with performance. Additional analysis revealed that two of the typologies describe the ideas of velocity, variability, and visibility of supply chains. The paper also discusses the relationship between product life cycle and the supply chain management initiatives that comprise the strategy typologies.     

Sufficient statistics process control:An empirical Bayes approach to process control

High volume, highly automated, information intensive, short cycle manufacturing systems severely tax most conventional statistical process control techniques. To meet this new manufacturing domain's control requirements, a new approach is needed. This paper presents such a process control procedure, sufficient statistics process control (SSPC). By drawing on empirical Bayes techniques, SSPC models the time sequence of the process while simultaneously reducing to a few sufficient statistics the large volume of incoming data. As a result, it provides real time, on-line quality control. The paper discusses the conceptual and mathematical foundations for SSPC. Its operation is illustrated through an example. Finally, the paper concludes with a discussion of the limitations of SSPC.     

A multidimensional approach to academic productivity

This study represents one of the first attempts to use empirical analysis to estimate academic productivity complex and proves the thesis that academic productivity is a function of multidimensional combination of the work of academic researchers: the scientific work, education, and external relationships. Given the complexity of academic productivity, it is necessary to clarify that it is divided into scientific productivity of the first type (scientific publications); scientific productivity of the second type (awards and academic positions); productivity in terms of external relationships (or external advice); and educational productivity. This objective of this paper is achieved through a sample survey (2,738 academics responded) conducted by Italian researchers from the PIR research project. The results obtained, however (as a case of estimates obtained using the results of a sample survey), are the result of a working reality that Italian academics are flooded by a myriad of activities that are not always consistent with the primary aims of the work of a researcher with an organisational and environmental well-being at the limit of iper productivity (or hyper productivity). The overall productivity (academic productivity) is significantly correlated with the four dimensions: average annual scientific productivity of the first type, average annual scientific productivity of the second type, the productivity external advice and, lastly, teaching productivity. The estimate of the sizes for the four indicators of productivity are the result of a literature search of the primary techniques used to assess productivity in academia. By comparing the most significant indicators, we managed to select all of the technical aspects missing in the Italian system of evaluation. This process allowed for us to add additional variables characterising the various aspects of productivity and prove the validity of our theory about the multidimensionality of academic productivity.     

An empirical approach to obtaining bounds on the failure probability through stress/strength interference

This paper proposes a new empirical approach to computing the unreliability bounds based upon the subinterval probabilities of the stress and strength in the interference region. It is demonstrated by the numerical examples that in most cases the unreliability bounds so obtained not only will include the exact value but also are narrower than the existing ones. The average of the lower and the upper bound is shown to serve as a good point estimate of the unreliability. It is also shown that the approach is practical since the number of subintervals required for an acceptable accuracy is small. In some cases a rather acceptable accuracy is achieved when the number of intervals is around ten.     

An empirical assessment of the influence of quality dimensions on organizational performance

While there are several conceptual models to suggest that there exists an association between quality dimensions (customer satisfaction, employee satisfaction, employee service quality) and organizational performance, no empirical study to date has verified such claims. This paper extends the literature by collecting hard data from 165 practising managers and testing their perceptions of the association among various quality dimensions and several organizational performance measures. The relationships between these quality dimensions and the nine component items that make up organizational performance were also investigated for both manufacturing and service firms. The data were grouped into four typologies to include type of firm, size, age, and presence of formal quality department. Multiple discriminant analysis was conducted to differentiate the typology of firms in a multivariate setting. Our results indicate that practising managers in manufacturing firms tend to perceive more widely a positive correlation between quality dimensions and the component items of organizational performance than managers in service firms. Also, managers from older manufacturing firms tend not to perceive a relationship between employee service quality and five component items of organizational performance such as competitiveness and market share.

The measures used for the three quality dimensions and organizational performance are shown to be valid and reliable. However, information derived from the study shows that practising managers in the service sector do not perceive some of the claims and expected benefits of quality management activities.     

An empirical approach for the optimisation of aggregate combinations for self-compacting concrete

The fresh and hardened properties of self-compacting concrete (SCC) depend on number of factors such as paste composition, paste content, aggregate content, aggregate gradation etc. In the present investigation, the influence of the packing density of aggregates on the properties of SCC was evaluated. Experiments were conducted to measure the packing density for different combinations of aggregates precisely. A ternary packing diagram (TPD) was developed based on the packing density of measured and interpolated data. Considering the limitations in generalising the TPD and the difficulty involved in adopting mathematical models for aggregates, an attempt was made to establish a simple method for the selection of the combination of aggregates resulting in maximum packing density from the particle size distribution of aggregates (represented by the Coefficient of uniformity??C _u). Further, studies were extended to investigate the effect of aggregate packing density on fresh and hardened SCC properties. The results indicate that for a constant paste volume and paste composition, with increase in packing density of aggregates, the fresh properties and the compressive strength of SCC were improved positively. An attempt was also made to identify the influence of 10 different proportions of aggregates having the same packing density on the properties of SCC. The results indicate that at the same aggregate packing density, the fresh concrete properties were influenced significantly by the choice of the aggregate combination, while there was little or no influence on the hardened properties. Furthermore, the experimental data obtained was used for supplementary validation of the existing model (compressible packing model) for predicting the packing density and the fresh behaviour of SCC.     

Analysis of the evaluation process of the research performance: An empirical case

Summary  In this paper we analyze the objectivity of the peer review process of research performance by research groups in the scientific and technological Valencian system, over the period 1998-2002. For that purpose, we use qualitative and quantitative indicators to assess which of them are the most important to determine a research group as excellent one, based on peer review evaluation methodology. The results show that excellence appears to be driven only by publications in SCI/SSCI and the number of sexenios, and suggest that the peer review process is not as objective as we expected.     

An inverse analysis approach to determine fatigue performance of bituminous mixes

In pavement engineering, fatigue resistance is evaluated using different tests protocols and different specimen geometries. The dependency of the specimen shape geometry on fatigue performance does not allow the evolution of intrinsic material properties. This paper deals with the calibration of intrinsic fatigue damage parameters for bituminous materials. A fatigue damage model is implemented. The decrease of stiffness of the specimen during fatigue tests for different laboratory testing conditions is calculated from finite element computations. An inverse optimization technique is used in order to adjust the fatigue damage parameters on bending fatigue tests. A Levenberg-Marquardt algorithm is implemented to fit the finite element specimen global response on experimental results. An application on bending laboratory fatigue tests is presented to illustrate the applicability of the method for pavement engineering.     

一种Linux环境下优化ZFS同步写性能的方法

为了提高Linux环境下的ZFS文件系统的同步写性能,在研究分析现有Linux环境下实现的ZFS文件系统的块设备同步写性能较低,同步写负载较重时系统吞吐量明显下降的原因的基础上,提出了一种Linux环境下的ZFS同步写优化方法。该方法通过同步写合并提交策略减少日志提交所产生的I/O请求数;使用同步写全局负载均衡机制实现各盘之间同步写的负载均衡来提高同步写的吞吐量。实验结果表明:相比原来在Linux上实现的ZFS.该优化方法提高同步写性能23.9%~88.14%。     

A fresh approach to evaluating the academic ranking of world universities

The aim of this article is to present new ideas in evaluating Shanghai University’s Academic Ranking of World Universities (ARWU). One issue frequently put forth in various publications is that the Shanghai rankings are sensitive to the relative weight they attribute to each variable. As a possible remedy to this issue, the statistical I-distance method is proposed to be used. Based on a sample containing the top 100 ranked universities, the results show a significant correlation with the official ARWU list. However, some inconsistencies concerning European universities have been noticed and elaborated upon.     

An empirical investigation into the barriers to postponement

The need for postponement is significantly driven by today's business and marketing environment. However, currently its applications are still not as widespread as expected. Therefore, this paper empirically investigates what factors hinder the adoption and implementation of postponement, and whether postponement applications are expected to increase in practice. Following a literature review on how to prompt and progress postponement applications, we present our research design. Namely, a questionnaire survey was conducted (by way of both post and e-mail) among 368 British manufacturing companies across four industrial sectors to help build statistical generalizations on the barriers to postponement. Then, we provide demographic data and response rate, and assess the reliability and validity of the survey instruments. The results from our questionnaire survey indicate that most of the highest ranked barriers were related to how a company manages its external networks (suppliers or customers), while those barriers related to distributors were put towards the bottom of the list. The respondents also expected postponement to be less used in three years. Finally, we draw some conclusions, determine limitations of this research and make suggestions for future research.     

Geometric approach to the degree of polarization for arbitrary fields

Abstract

The eigenvalue decomposition of the polarization matrix is employed to find out the geometric interpretation of the traditional degree of polarization and, in particular, of the degree of polarization for arbitrary electromagnetic fields put forward recently by Setälä et al. [2002, Phys. Rev. Lett., 88, 123902]. It is shown that both measures have similar geometric meaning as a measure for the purity of the polarization state. Possible extensions to the analysis are discussed.     

An empirical examination of response time,product variety and firm performance

Response time and product variety are both important strategies that firms utilize to cope with fast changing demand and stiff competition. However, the empirical link between the two areas is not clear. The purpose of this study is to explore the link between response time, product variety and firm performance under build-to-order scenario. A multi-method approach (mainly including OTD time mapping, document examinations, interviews and plant tours) was used to collect the data at the Chinese vehicle manufacturers. Based on the objective data statistically analyzed, this study makes the contribution in three aspects: First, this study provides an empirical examination into the order-to-delivery time structure. The research results reveal that order processing time is independent from producing time. Second, this study provides the first empirical exploration into the association between product variety and response time in the automotive industry. The results show that more model variations may significantly increase order processing time while more type variations do not significantly impact on producing time. Third, the results of this study demonstrate the impacts of both product variety and response time on firm's performance. Fast response time helps increase sales in a short term while more product variety benefits higher growth rate.     

An integrated approach to the development of performance test methods and their application to evaluation and design

The paper analyses the main features of a Performance Test Method (PTM), and demonstrates that, despite the wide range of attributes for which PTMs are required, the Performance Concept sets a unified common approach for their development. The basic relations between the four factors: a human requirement, the relevant behavioral aspects of the building and its parts, the evolving performance criteria, and the associated PTMs for evaluating compliance, establish the integrated approach presented here. It is demonstrated that PTMs should yield Response Curves as a basic tool for evaluations, assessments and decisions, while prevalent test methods, which are assigned to yield only Pass/Fail results, may be misleading. A procedure for relating compliance to the form of the Response Curve is suggested, with a differentiation between “brittle”, concave and convex curves.