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排序方式: 共有396条查询结果,搜索用时 437 毫秒
41.
Stavros Katsas Richard Dashwood Graham Todd Martin Jackson Roger Grimes 《Journal of Materials Science》2010,45(15):4188-4195
Continuous extrusion (Conform™) is a well-established technique for the production of profiles from both solid and particulate
feed stock. To the first approximation it is considered to be analogous to conventional extrusion, although there are significant
differences in the metal flow during both processes. Metal flow during conventional extrusion is characterised by relatively
low redundant work, whereas the Conform™ process requires significant redundant work to be successful. Most of the available
scientific literature to date is concerned with the simulation of the Conform™ process and not its effect on the resultant
microstructure of the product. In this paper, a detailed comparison of the microstructure, texture and superplastic properties
developed during Conform™ and conventional extrusion for a particulate Al–4Mg–1Zr alloy are presented. 相似文献
42.
Micro-Electro-Mechanical-Systems (MEMS)-based scanning probes appear as potential candidates for a wide variety of emerging nanoscale applications, including ultra-high-density data-storage and surface imaging. In this work, a spiral trajectory nanopositioning scheme is proposed as an alternative to the conventional raster positioning pattern. The resulting positioning signal has an extremely narrowband frequency content, which shifts very slowly over time. These properties enable enhanced tracking performance and offer potentially uninterrupted high-speed operation. The mathematical analysis of the spiral positioning signal as well as its properties are presented. Experimental results obtained from applying the new nanopositioning scheme on a MEMS-based scanning-probe data-storage setup for thermomechanical storage on polymer medium are illustrated. 相似文献
43.
44.
John J. Boyle Maiko Kume Matthew A. Wyczalkowski Larry A. Taber Robert B. Pless Younan Xia Guy M. Genin Stavros Thomopoulos 《Journal of the Royal Society Interface》2014,11(100)
When mechanical factors underlie growth, development, disease or healing, they often function through local regions of tissue where deformation is highly concentrated. Current optical techniques to estimate deformation can lack precision and accuracy in such regions due to challenges in distinguishing a region of concentrated deformation from an error in displacement tracking. Here, we present a simple and general technique for improving the accuracy and precision of strain estimation and an associated technique for distinguishing a concentrated deformation from a tracking error. The strain estimation technique improves accuracy relative to other state-of-the-art algorithms by directly estimating strain fields without first estimating displacements, resulting in a very simple method and low computational cost. The technique for identifying local elevation of strain enables for the first time the successful identification of the onset and consequences of local strain concentrating features such as cracks and tears in a highly strained tissue. We apply these new techniques to demonstrate a novel hypothesis in prenatal wound healing. More generally, the analytical methods we have developed provide a simple tool for quantifying the appearance and magnitude of localized deformation from a series of digital images across a broad range of disciplines. 相似文献
45.
Behzad Babaei Steven D. Abramowitch Elliot L. Elson Stavros Thomopoulos Guy M. Genin 《Journal of the Royal Society Interface》2015,12(113)
The viscoelastic behaviour of a biological material is central to its functioning and is an indicator of its health. The Fung quasi-linear viscoelastic (QLV) model, a standard tool for characterizing biological materials, provides excellent fits to most stress–relaxation data by imposing a simple form upon a material''s temporal relaxation spectrum. However, model identification is challenging because the Fung QLV model''s ‘box’-shaped relaxation spectrum, predominant in biomechanics applications, can provide an excellent fit even when it is not a reasonable representation of a material''s relaxation spectrum. Here, we present a robust and simple discrete approach for identifying a material''s temporal relaxation spectrum from stress–relaxation data in an unbiased way. Our ‘discrete QLV’ (DQLV) approach identifies ranges of time constants over which the Fung QLV model''s typical box spectrum provides an accurate representation of a particular material''s temporal relaxation spectrum, and is effective at providing a fit to this model. The DQLV spectrum also reveals when other forms or discrete time constants are more suitable than a box spectrum. After validating the approach against idealized and noisy data, we applied the methods to analyse medial collateral ligament stress–relaxation data and identify the strengths and weaknesses of an optimal Fung QLV fit. 相似文献
46.
Tuneable Singlet Exciton Fission and Triplet–Triplet Annihilation in an Orthogonal Pentacene Dimer
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Steven Lukman Andrew J. Musser Kai Chen Stavros Athanasopoulos Chaw K. Yong Zebing Zeng Qun Ye Chunyan Chi Justin M. Hodgkiss Jishan Wu Richard H. Friend Neil C. Greenham 《Advanced functional materials》2015,25(34):5452-5461
Fast and highly efficient intramolecular singlet exciton fission in a pentacene dimer, consisting of two covalently attached, nearly orthogonal pentacene units is reported. Fission to triplet excitons from this ground state geometry occurs within 1 ps in isolated molecules in solution and dispersed solid matrices. The process exhibits a sensitivity to environmental polarity and competes with geometric relaxation in the singlet state, while subsequent triplet decay is strongly dependent on conformational freedom. The near orthogonal arrangement of the pentacene units is unlike any structure currently proposed for efficient singlet exciton fission and may lead to new molecular design rules. 相似文献
47.
Objective of this paper is to provide insight in the component selection criteria of an autonomous wind-driven desalination plant. For this purpose, a suitable logistic model of such a system is developed, which simulates its steady-state operation, taking into account the power and energy equilibrium in the system. The simulation of the system operation is performed employing two alternative control strategies and a variety of different configurations with respect to the size of its main components (wind turbine, desalination plant and batteries). For each case, the annual water production is calculated and an economic assessment is performed to estimate the expected water production cost, which is the ultimate measure of the feasibility of the stand-alone system. Other important factors, such as the desalination unit start/stop operations are also calculated. Based on the simulation results, conclusions are drawn regarding the optimal sizing of the system components and its recommended operating strategy. 相似文献
48.
MF Chan A Kois EJ Verner BG Raju RS Castillo C Wu I Okun FD Stavros VN Balaji 《Canadian Metallurgical Quarterly》1998,6(12):2301-2316
The systematic modification of the ETA selective N-(5-isoxazolyl)benzene-sulfonamide endothelin antagonists to give ETB selective antagonists is reported. The reversal in selectivity was brought about by substitution of the 4-position with aryl and substituted aryl groups. Of all the aromatic substituents studied, the para-tolyl group gave rise to the most active and selective ETB antagonist. Larger substituents caused a decrease in both ETB activity and selectivity. A similar trend was observed by substitution at the 5-position of the N-(5-isoxazolyl)-2-thiophenesulfonamide ETA receptor antagonists. The para-tolyl group was again found to be optimal for the ETB activity and selectivity. The structural features that were found to be favorable for binding to the ETB receptor, that is, the presence of a linear, conjugated pi-system of definite shape and size, have been successfully incorporated into the design of ETB selective polycyclic aromatic sulfonamides antagonists. 相似文献
49.
K. Ioannou S. Kotsopoulos P. Stavroulakis 《International Journal of Communication Systems》2003,16(9):851-863
This paper presents a dynamic guard channel assignment technique based on a two‐layer cellular architecture which optimizes the blocking probability performance of high‐speed moving terminals (HSMT) and handoff calls of low‐speed moving terminals (LSMT), in a congested urban area. The lower layer of the proposed architecture is based on a microcellular solution, for absorbing the traffic loads of LSMT. The higher layer is based on a macro‐cell umbrella solution, for absorbing the traffic load of the HSMT. The results show that using the optimum number of channels and adjusting dynamically the number of guard channels in each layer, the blocking probability of the HSMT and the handoff blocking probability of LSMT is optimized having the minimum bad effect on the new call blocking probability of LSMT. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
50.