Various theoretical methods for calculating diffraction profiles of perfect crystals are available in literature. Although these methods hold within certain validity ranges due to their inherent approximations, they c...
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ISBN:
(纸本)0819425737
Various theoretical methods for calculating diffraction profiles of perfect crystals are available in literature. Although these methods hold within certain validity ranges due to their inherent approximations, they constitute the current state-of-the-art of numerical computation of diffraction profiles. In this paper we summarize the theory of Zachariasen for hat crystals, the multi-lamellar approximation for bent crystals and the Penning-Polder approximation for bent Laue crystals. Some examples of their results are presented. Another method to calculate the diffraction profile consists in solving the Takagi-Taupin equations. The finite difference method, that provides a numerical solution of these equations, is briefly discussed. A new method for solving numerically these equations using the finite element method is proposed. This method is very flexible, because it can consider a crystal with an arbitrary shape and cover the case of critical regions (i.e., inhomogeneities and deformations) with fine elements. In addition, it can couple naturally the diffraction calculation with thermal or mechanical crystal deformations. These deformations are generally induced by the x-ray beam (heat load), the crystal bender (mechanical stress) or are intrinsic to the crystal (inhomogeneities, impurities, dislocations, etc.). An example of the feasibility of this method is shown.
Traditionally, the performance of a stack machine was limited by the true data dependency. A performance enhancement mechanism-Stack Operations Folding-was used in Sun Microelectronics' picojava design and it can ...
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ISBN:
(纸本)0818682272
Traditionally, the performance of a stack machine was limited by the true data dependency. A performance enhancement mechanism-Stack Operations Folding-was used in Sun Microelectronics' picojava design and it can reduce up to 60% of all stack operations. In this paper, we use the java bytecode language as the target machine language, and study its instruction folding on a proposed machine model. Three folding strategies: 2-foldable, 3-foldable and 4-foldable, were simulated and evaluated. Statistical data show that our third folding strategy eliminates 73% of all stack operations, and each strategy has an overall program speedup of 1.19, 1.25 and 1.26, respectively, as compared to a traditional stack machine. Moreover, a java machine model suitable for instruction folding, together with its pipeline stages, are presented. It seems to have the best cost/performance effectiveness of a java stack machine if six bytes decoder width and the second folding strategy-the three-foldable strategy-are adopted.
The development of Web applications is moving quickly due to an explosive increase of Internet use. However, the architectures of current Web applications reveal several constraints and limitations in terms of perform...
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ISBN:
(纸本)081868271X
The development of Web applications is moving quickly due to an explosive increase of Internet use. However, the architectures of current Web applications reveal several constraints and limitations in terms of performance, functionality, usability, etc. Several candidate technologies such as java, java RMI, Web-ORB, and Agents have been introduced. However, it has not been studied how these unit technologies can be put together to overcome the limitations of Web applications. As these newer language/technologies are based on the object-oriented paradigm, the object-oriented Web architectures based on these newcomers should be developed. Hence, we first identify the problems and limitations of current Web applications and then propose new architectures of and development strategies for next generation Web applications based on these newer unit technologies. Also three case studies based on the proposed architectures and strategies are presented.
When dealing with communication-intensive systems, hardware/software co-simulation usually either requires the communication to be simulated with a uniformly lour level of detail or it performs poorly. This problem ma...
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When dealing with communication-intensive systems, hardware/software co-simulation usually either requires the communication to be simulated with a uniformly lour level of detail or it performs poorly. This problem manifests itself even more strongly when considering geographically distributed co-simulation, where designers take advantage of proprietary component simulation models that are made available over the Internet. In such systems, much of the communication can potentially occur over the Internet, with even, more expensive and slower communication primitives. This paper presents a technique, called "selective focus", and a java based tool which allow communication to be represented at various levels of abstraction thus giving the designer the ability to dynamically optimize inter-module communications and improve the performance of the cosimulation.
Hypermedia has become an increasingly applied paradigm in applications for training, education, and complex information retrieval. To support hypermedia users in applications where unguided browsing is unproductive, a...
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Hypermedia has become an increasingly applied paradigm in applications for training, education, and complex information retrieval. To support hypermedia users in applications where unguided browsing is unproductive, adaptive hypermedia environments are needed. Currently, WWW browsers are the cornerstones of most hypermedia applications targeted at Internet users. However, for certain applications, WWW hypermedia can not meet the high requirements for adaptive user support. We propose a spatial hypermedia environment to overcome limitations in graphical layout and adaptivity of HTML-based hypermedia. A prototype browser named HyperMap illustrates a browser user interface based on spatial navigation implemented in java.
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