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131.
F. J. Gallego J. J. Anza 《International journal for numerical methods in engineering》1989,28(6):1249-1264
The static elastic contact problem is approached using Lagrange multipliers, leading to a mixed finite element problem. A non-linear friction law is introduced explicitly and the non-local character of the friction phenomena is implicitly assumed. In order to avoid stress oscillations near singular points, a perturbed Lagrangian functional is considered. The algorithms herein proposed do not impose nodal dependencies over the contact surfaces, allowing for the independent discretization of both bodies. The method is able to model simultaneous contact over different regions of any geometrical shape. Computer code, examples and results presented here are restricted to axisymmetrical and bidimensional cases. 相似文献
132.
J.E. Richards † 《Computer Graphics Forum》1987,6(3):211-218
Aspects of a prototype binding of GKS to the C++ programming language are presented. The binding makes use of classes and derived classes to define GKS concepts such as segments and workstations. Operator overloading is used for some GKS Functions. 相似文献
133.
Mountfield K. Mitchell P. Lee J.-W. Demczyk B. Artman J. 《IEEE transactions on magnetics》1987,23(5):2037-2039
A sequence of Co78 Cr22 films, 500 nm in thickness, was prepared by deposition on glass in a modified Varian D.C. magnetron S-gun sputtering system. The substrate temperature during deposition, Ts , was fixed at various values with an upper limit of 300°C. Specimens were examined by VSM, TM, FMR and TEM. Ms rises significantly with increasing Ts , peaking at 200°C at 370 emu/cm3. The effective volume-averaged anisotropy drops for Ts >110°C from +1.6 KOe to progressively negative values (-4.3 KOe at 300°C). From FMR we find indications of the presence, in addition to the transition and bulk layers, of a highly negative anisotropy constituent (sim-11.5 KOe anisotropy field). This resonance appears at Ts values of 150°C and above. TEM plane and cross-section views taken on a Ts = 150°C specimen show islands composed of tilted columns within the bulk. For vertical recording, specimens prepared at Ts values between 50 and 100°C are recommended. On the other hand, for longitudinal recording applications, films prepared at Ts values above 250°C would seem to be appropriate. 相似文献
134.
135.
PCR-based procedures in detection and DNA-fingerprinting of Salmonella from samples of animal origin
A. del Cerro S. M. Soto E. Landeras M. A. Gonzlez-Hevia J. A. Guijarro M. C. Mendoza 《Food microbiology》2002,19(6):567
The usefulness of selected PCR-protocols for the detection of Salmonella in 117 samples of animal origin (17 raw minced meat, 27 raw chicken meat, 8 raw sausages, and 25 egg samples, as well as 18 poultry faecal, and caecal swabs samples) and DNA-fingerprinting typing is shown. To establish an accurate PCR-procedure for Salmonella detection the following parameters were evaluated: two pre-PCR concentration procedures, centrifugation and immunomagnetic separation (IMS) using Dynabeads anti- Salmonella; the specificity and sensitivity of 10 sets of primers; and different conditions of the amplification reaction. In light of the results obtained from the use of PCR-based procedures alone or in combination with conventional methods, the following findings can be underlined: First, IMS is more efficient than centrifugation in the recovery of Salmonella. Second, the selected IMS/PCR-detection protocol is less time-consuming (45 h) than the IMS/culture procedure (90 h), and a good concordance between them was found when the Kappa coefficient was calculated (0·87). Third, PCR-ribotyping technique showed a very low discrimination power, being able to differentiate only three profiles. Fourth, RAPD technique using specific primers supports previous works in which it was proposed as a simple and useful tool for discriminating isolates between and within serotypes. Fifth, The efficiency, rapidity, and flexibility of the PCR-protocols applied were high, and they can be performed using two PCR-programs and the same basic equipment. 相似文献
136.
Coarse filters for shape matching 总被引:3,自引:0,他引:3
Corney J. Rea H. Clark D. Pritchard J. Breaks M. Macleod R. 《Computer Graphics and Applications, IEEE》2002,22(3):65-74
This article describes the coarse shape filters that support the 3D, Internet-based search engine ShapeSifter, which aims to locate parts already in production that have a shape similar to a desired new part. The search engine analyzes the target model's shape characteristics and performs a similarity match on the database's contents. Our main challenge is identifying shape metrics that produce effective characterizations of 3D models for similarity comparison. We focus on using three novel convex hull-based indices to carry out a preliminary coarse filtering of candidates prior to more detailed analysis. We also describe the crucial role played by two databases of benchmark objects. Unlike other shape-matching systems, we chose ShapeSifter's architecture (multistep query), 3D representation (triangulated mesh), and implementation (Java3D) to allow deployment online once it matures 相似文献
137.
Action calculi, which generalise process calculi such as Petri nets, π-calculusand ambient calculus, have been presented
in terms of action graphs. We here offer linear action graphs as a primitive basis for action calculi. This paper presents the category of embeddings of undirected linear
action graphs without nesting, using a novel form of graphical reasoning which simplifies some otherwise complex manipulations
in regular algebra. The results are adapted in a few lines to directed graphs. This work is part of a long-term search for
a uniform behavioural theory for process calculi.
Received October 2000 / Accepted in revised form April 2001 相似文献
138.
Paul J. Flory 《Polymer International》1985,17(2):96-102
The earliest investigations on rubber elasticity, commencing in the 19th century, were necessarily limited to phenomenological interpretations. The realisation that polymers consist of very long molecular chains. commencing c. 1930, gave impetus to the molecular theory of rubber elasticity (1932-). according to which the high deformability of an elastomer, and the elastic force generated by deformation, stem from the configurations accessible to long molecular chains. Theories of rubber elasticity put forward from 1934-1946 relied on the assumption that the junctions of the rubber network undergo displacements that are affine in macroscopic strain. The theory of James and Guth (1947) dispensed with this premise, and demonstrated instead that the mean positions of the junctions of a ‘phantom’ network consisting of Gaussian chains devoid of material properties are affine in the strain. The vital significance of the distinction between the actual distribution of chain vectors in a network and their distribution if the junctions would be fixed at their mean positions went unnoticed for nearly 30 years. Experimental investigations, commencing with the incisive work of Gee in 1946. revealed large departures from the relationship of stress to strain predicted by the theories cited. This discrepancy prompted extensive studies, theoretical and experimental, during succeeding years. Inquiry into the fundamentals of polymer networks, formed for example by interlinking very long polymer molecules, exposed the need to take account of network imperfections, typically consisting of chains attached at only one end to a network junction. Various means were advocated to make corrections for these imperfections. The cycle rank ζ of the network has been shown (1976) to be the fundamental measure of its connectivity, regardless of the junction functionality and pattern of imperfections. Often overlooked is the copious interpenetration of the chains comprising typical elastomeric networks. Theories that attempt to represent such networks on a lattice are incompatible with this universal feature. Moreover, the dense interpenetration of chains may limit the ability of junctions in real networks to accommodate the fluctuations envisaged in the theory of phantom networks. It was suggested in 1975 that departures from the form predicted for the elastic equation of state are due to constraints on the fluctuations of junctions whose effect diminishes with deformation and with dilation. Formulation of a self-consistent theory based on this suggestion required recognition of the non-affine connection between the chain vector distribution function and the macroscopic strain in a real network, which may partake of characteristics of a phantom network in some degree. Implementation of the idea was achieved through postulation of domains of constraint affecting the equilibrium distribution of fluctuations of network junctions from their mean positions. This led in due course to a theory that accounts for the relationship of stress to strain virtually throughout the ranges of strain accessible to measurement. The theory establishes connections between structure and elastic properties. This is achieved with utmost frugality in arbitrary parameters. 相似文献
139.
Nichols M.A. Siegel H.J. Dietz H.G. Quong R.W. Nation W.G. 《Parallel and Distributed Systems, IEEE Transactions on》1991,2(3):290-303
Efficient data layout is an important aspect of the compilation process. A model for the creation of perfect memory maps for large-scale parallel machines capable of user-controlled partitionable single-instruction-multiple data/single-program-multiple data (SIMD/SPMD) operation is developed. The term perfect implies that no memory fragmentation occurs and ensures that the memory map size is kept to a minimum. A major constraint on solving this problem is based on the single program nature of both the SIMD and SPMD modes of parallelism. It is assumed that all processors within the same submachine used identical addresses to access corresponding data items in each of their local memories. Necessary and sufficient conditions are derived for being able to create perfect memory maps, and results are applied to several partitionable interconnection networks 相似文献
140.