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Essential Idea (essential + idea)

Distribution by Scientific Domains

Engineering	60%

Selected Abstracts

Voxel-based meshing and unit-cell analysis of textile composites

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 7 2003
Hyung Joo Kim
Abstract Unit-cell homogenization techniques are frequently used together with the finite element method to compute effective mechanical properties for a wide range of different composites and heterogeneous materials systems. For systems with very complicated material arrangements, mesh generation can be a considerable obstacle to usage of these techniques. In this work, pixel-based (2D) and voxel-based (3D) meshing concepts borrowed from image processing are thus developed and employed to construct the finite element models used in computing the micro-scale stress and strain fields in the composite. The potential advantage of these techniques is that generation of unit-cell models can be automated, thus requiring far less human time than traditional finite element models. Essential ideas and algorithms for implementation of proposed techniques are presented. In addition, a new error estimator based on sensitivity of virtual strain energy to mesh refinement is presented and applied. The computational costs and rate of convergence for the proposed methods are presented for three different mesh-refinement algorithms: uniform refinement; selective refinement based on material boundary resolution; and adaptive refinement based on error estimation. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Matched interface and boundary (MIB) method for the vibration analysis of plates

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 9 2009
S. N. Yu
Abstract This paper proposes a novel approach, the matched interface and boundary (MIB) method, for the vibration analysis of rectangular plates with simply supported, clamped and free edges, and their arbitrary combinations. In previous work, the MIB method was developed for three-dimensional elliptic equations with arbitrarily complex material interfaces and geometric shapes. The present work generalizes the MIB method for eigenvalue problems in structural analysis with complex boundary conditions. The MIB method utilizes both uniform and non-uniform Cartesian grids. Fictitious values are utilized to facilitate the central finite difference schemes throughout the entire computational domain. Boundary conditions are enforced with fictitious values,a common practice used in the previous discrete singular convolution algorithm. An essential idea of the MIB method is to repeatedly use the boundary conditions to achieve arbitrarily high-order accuracy. A new feature in the proposed approach is the implementation of the cross derivatives in the free boundary conditions. The proposed method has a banded matrix. Nine different plates, particularly those with free edges and free corners, are employed to validate the proposed method. The performance of the proposed method is compared with that of other established methods. Convergence and comparison studies indicate that the proposed MIB method works very well for the vibration analysis of plates. In particular, modal bending moments and shear forces predicted by the proposed method vanish at boundaries for free edges. Copyright © 2008 John Wiley & Sons, Ltd. [source]

The monophyly of island radiations: an evaluation of niche pre-emption and some alternative explanations

JOURNAL OF ECOLOGY, Issue 4 2005
JONATHAN SILVERTOWN
Summary 1It has been argued that niche pre-emption is not the only possible explanation for monophyly among Macaronesian endemic plants because (i) interspecific competition is diffuse, not species-specific, (ii) the radiations in question may not in fact be monophyletic, and (iii) later colonists may have hybridized with earlier ones, making a small and undetected contribution to the gene pool of lineages that appear to be monophyletic. 2The niche pre-emption mechanism does not, however, require species-specific competitive interactions. It merely proposes that the clade created by adaptive radiation will occupy more niche space than the original colonist could on its own. Members of the clade will then collectively inhibit establishment by new colonists more effectively than can a colonist that has not radiated. 3The monophyly of many larger radiations in the Macaronesian flora is well established and new studies tend to confirm this pattern. 4A few later-arriving colonists may have undetectably hybridized with earlier arrivals, but this is only a genetic interpretation of the essential idea behind pre-emption, i.e. that early arrivals so outnumber later colonists that the latter cannot establish. 5We do not therefore believe that hybridization provides an alternative explanation of why groups with multiple colonization failed to radiate in Macaronesia. [source]

Debating the ,Power' of Audit

INTERNATIONAL JOURNAL OF AUDITING, Issue 1 2000
Christopher Humphrey
This paper provides a critical but constructive review of Michael Power's recent text entitled The Audit Society: Rituals of Verification (1997). The paper first summarises the essential ideas put forward by Power with regard to the scale and significance of the Audit Society. It then debates some of Power's central arguments and claims, focusing, among other things, on the causes underlying the rise of the audit society, the definition of audit, the meaning of auditability and the relationship between audit and performance measurment. The paper concludes by considering the possibilities for auditing to serve a more positive role in society than that generally portrayed by Power. [source]

Principles and applications of control in quantum systems

INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 15 2005
Hideo Mabuchi
Abstract We describe in this article some key themes that emerged during a Caltech/AFOSR Workshop on ,Principles and Applications of Control in Quantum Systems' (PRACQSYS), held 21,24 August 2004 at the California Institute of Technology. This workshop brought together engineers, physicists and applied mathematicians to construct an overview of new challenges that arise when applying constitutive methods of control theory to nanoscale systems whose behaviour is manifestly quantum. Its primary conclusions were that the number of experimentally accessible quantum control systems is steadily growing (with a variety of motivating applications), that appropriate formal perspectives enable straightforward application of the essential ideas of classical control to quantum systems, and that quantum control motivates extensive study of model classes that have previously received scant consideration. Copyright © 2005 John Wiley & Sons, Ltd. [source]