网格计算与对等计算的比较研究

对网格计算和对等计算从概念、目标、体系结构、组成团体、资源、安全需求、应用、基础架构和特征等方面进行了深入比较，总结了各自的特点，最后对二者的研究方向进行展望．     

Sn1-xFexOy: a new material with high carbon monoxide sensitivity

The preparation method and the sensing properties (sensitivity and selectivity to interfering gases) towards carbon monoxide of the new ternary compound Sn_1-xFe_xO_y deposited in the form of thin films, are presented in this paper. The metal of the VIIIB group is introduced with concentrations in the range 0<x<25 at %. Thin films are sputtered using the RGTO (rhotaxial growth and thermal oxidation) technique. This technique consists of metal deposition onto a substrate maintained at a temperature higher than the metal melting point and metal oxidation by means of an annealing cycle in pure oxygen. Particular emphasis is given to the relations between some preparation parameters of the material, namely the atomic percentage ofiron or the annealing cycle, and to the sensor sensitivity towards CO and other interfering gases like C₂H₅OH, H₂ and NO_x diluted in dry air. A sensitivity S=(G_gas-G_air)/G_air=3.5 towards 10 ppm of CO has been measured: the kinetic characteristics of the sensors are also presented, together with the working mechanism.     

PECVD-SiOxNy films for large area self-sustained grids applications

In this work we study the structural properties and mechanical stress of silicon oxynitride (SiO_xN_y) films obtained by plasma enhanced chemical vapor deposition (PECVD) technique at low temperatures (320 °C) and report the feasibility of using this material for the fabrication of large area self-sustained grids. The films were obtained at different deposition conditions, varying the gas flow ratio between the precursor gases (N₂O and SiH₄) and maintaining all the other deposition parameters constant. The films were characterized by ellipsometry, by Fourier transform infrared (FT-IR) spectroscopy and by optically levered laser technique to measure the total mechanical stress. The results demonstrate that for appropriated deposition conditions, it is possible to obtain SiO_xN_y with very low mechanical stress, a necessary condition for the fabrication of mechanically stable thick films (up to 10 μm). Since this material (SiO_xN_y) is very resistant to KOH wet chemical etching it can be utilized to fabricate, by silicon substrate bulk micromachining, very large self-sustained grids and membranes, with areas up to 1 cm² and with thickness in the 2–6 μm range. These results allied with the compatibility of the PECVD SiO_xN_y films deposition with the standard silicon based microelectronic processing technology makes this material promising for micro electro mechanical system (MEMS) fabrication.     

HAMs体系中的同态变换方法研究

HAMs体系的一个主要问题是:它的状态空间是由机器状态与环境状态共同生成的联合状态空间,而基于子过程的状态抽象方法也不能完全解决这个问题.本文对此进行了详细的分析,并从策略耦合SMDPs的观点分析与描述了HAMs模型,提出一系列基于HAMs的同态变换的形式化定义及证明了几个较为实用的定理,表明同态变换方法可以有效地解决这一问题.在此基础上,总结了应用同态变换进行状态抽象的几个重要的观点.并使用本文提出的方法对一个典型的实例进行了分析与验证.     

Exact Algorithms for Graph Homomorphisms

Graph homomorphism, also called H-coloring, is a natural generalization of graph coloring: There is a homomorphism from a graph G to a complete graph on k vertices if and only if G is k-colorable. During recent years the topic of exact (exponential-time) algorithms for NP-hard problems in general, and for graph coloring in particular, has led to extensive research. Consequently, it is natural to ask how the techniques developed for exact graph coloring algorithms can be extended to graph homomorphisms. By the celebrated result of Hell and Nesetril, for each fixed simple graph H, deciding whether a given simple graph G has a homomorphism to H is polynomial-time solvable if H is a bipartite graph, and NP-complete otherwise. The case where H is the cycle of length 5, is the first NP-hard case different from graph coloring. We show that for an odd integer , whether an input graph G with n vertices is homomorphic to the cycle of length k, can be decided in time . We extend the results obtained for cycles, which are graphs of treewidth two, to graphs of bounded treewidth as follows: if H is of treewidth at most t, then whether input graph G with n vertices is homomorphic to H can be decided in time .     

普适计算

计算技术的发展需要与之适应的计算模式，计算技术在桌面计算模式下经历的20年的飞速发展正蕴育着一种革新性的计算模式——普适计算，普适计算是信息空间与物理空间的融合，在这个融合的空间中人们可以随时随地和透明地获得数字化的服务；计算机本身将从人们的视线中消失，人们注意力的中心可以回归到要完成的任务本身，普适计算将从根本上改变人们对什么是计算的思考，也改变我们整个生活和工作的方式，该文综述了普适计算研究的现状和发展趋势，并讨论了普适计算的两个关键研究内容——觉察上下文的计算和普适计算系统软件，最后简要介绍作者在智能空间领域的研究成果。     

Homomorphisms of symbolic dynamical systems

The densities of finite blocks of symbols can be computed for points in any substitution minimal set arising from a substitution of constant length and also for points in any Sturmian minimal set. It follows from the computations that all Sturmian minimal sets and all substitution minimal sets are strictly ergodic and have topological entropy zero. It also follows that no Sturmian minimal set is the homomorphic image of a substitution minimal set. It can also be shown that no non-trivial substitution minimal set is powerfully (totally) minimal, and it follows that no non-trivial substitution minimal set is the homomorphic image of a Sturmian minimal set.Most of the results in this paper were first obtained in the author's doctoral dissertation which was presented to the Faculty of the Graduate School of Yale University in 1968.     

浅析云计算与OA系统的联系

云计算作为未来互联网、IT应用的标准模型,已经上升到国家战略的层面,各地政府纷纷出资构建云计算中心,而在应用为王的时代,OA即将成为云计算的核心应用,伴随着OA市场的需求刚性化,OA即将进入云计算时代.     

Uq(sl(2)) Satisfies a Bernstein Duality

It is well known that in some cases the functorExt_R^μ( − , R) defines a duality between module categories. In earlier papers we studied when this duality can be represented by a bimodule and have characterized when this happens. In this paper, using some computational methods of noncommutative Gröbner bases in the construction of projective resolutions of irreducible finite-dimensional representations, we show new examples of algebras satisfying this property.     

Gas-sensing property and mechanism of CaxLa1−xFeO3 ceramics

LaFEO₃ and Ca_xLa_1−xFeO₃ ceramic powders have been prepared by the coprecipitation method from La(NO₃)₃, Fe(NO₃)₃ and Ca(NO₃)₂ aqueous solutions. The orthorhombic perovskite phases of LaFeO₃ and Ca_xLa_1−xFeO₃ are characterized by X-ray diffraction patterns. The sensors fabricated with those powders have high sensitivity to alcohol. Partial substitution of La³⁺ in LaFeO₃ with Ca²⁺ can enhance the sensitivity of the materials to reducing gases. The resistance of an LaFeO₃ sensor in air, vacuum and alcohol-containing air has been measured. Complex impedance spectroscopy has been used to try and analyse the gas-sensing mechanism. According to the experimental results, it can be deduced that the surface adsorptive and lattice oxygen govern the sensing properties of LaFeO₃ and Ca_xLa_1−xFeO₃ ceramics.     

Homomorphisms between models of parallel computation

To better understand the relationships between different models of parallel computation, we introduce a new computation system formulation and develop general notions of homomorphisms and isomorphisms between computation systems. This allows us to study relations between vector addition systems, vector replacement systems, Petri nets, and generalized Petri nets. Results in this paper that may be of particular interest include a long list of properties preserved under homomorphism, and constructions that show that vector replacement systems can be simulated by vector addition systems, and that generalized Petri nets can be emulated by Petri nets.     

Nanowire structured SnOx–SWNT composites: High performance sensor for NOx detection

A nanowire structured nanocomposite of tin oxide (SnO_x) and a single-walled carbon nanotube (SWNT) are fabricated using rheotaxial growth and thermal oxidation method for gas sensor application. The morphology, gas sensing properties, as well as the chemical and electrical properties are investigated. The oxidation temperature for Sn mainly determines the stoichiometry of the SnO_x nano-beads, and consequently the electrical and gas sensing properties of the nanocomposite sensors. The gas sensing to nitrogen oxide, hydrogen, oxygen, xylene, acetone, carbon monoxide, and ammonia are also examined to determine the gas selectivity of the sensor. The high sensitivity and selectivity towards NO_x of the nanocomposite sensor is realized via the porous structure of the SWNT template. The gas sensing mechanism of the nanocomposite structure is also discussed.     

Robust p stability and performance

In this paper we study robust stability, in the _p sense, against structured perturbations of bounded _p norm. The perturbations may be either linear time-varying, nonlinear time-varying, or nonlinear time-invariant. We develop exact tests for robust stability for each case in terms of convex optimization problems. These results are extended to solve the corresponding robust performance problems, with performance measured via the induced _p norm.     

Manufacture and characterization of sol–gel V1−x−yWxSiyO2 films for uncooled thermal detectors

V_1−x−yW_xSi_yO₂ films for uncooled thermal detectors were coated on sodium-free glass slides with sol–gel process, followed by the calcination under a reducing atmosphere (Ar/H₂ 5%). The V_1−x−yW_xSi_yO₂ films as prepared inherit various phase transition temperatures ranging from 20 to 70 °C depending on the dopant concentrations and the fabrication conditions. Compared to the hysteresis loop of plain VO₂ films, a rather steep loop was obtained with the addition of tungsten components, while a relaxed hysteresis loop with the tight bandwidth was contributed by Si dopants. Furthermore, the films with switching temperature close to room temperature were fabricated to one-element bolometers to characterize their figures of merit. Results showed that the V_0.905W_0.02Si_0.075O₂ film presented a satisfactory responsivity of 2600 V/W and detectivity of 9 × 10⁶ cm  Hz^1/2/W with chopper frequencies ranging from 30 to 60 Hz at room temperature. It was proposed that with appropriate amount of silicon and tungsten dopants mixed in the VO₂, the film would characterize both a relaxed hysteresis loop and a fair TCR value, which effectively reduced the magnitude of noise equivalent power without compromising its performance in detectivity and responsivity.     

On Characteristics of Information System Homomorphisms

The notion of information system homomorphism as a powerful tool to study the relation between two information systems was introduced by J.W. Grzymala-Busse. In this work, we will present some characteristics of information system homomorphism, which reveal the interdependence of the three mappings, namely, object mapping, attribute mapping and value domain mapping. Besides, given a partition on universe, we can derive a new information system homomorphism defining a partition on universe identical with the partition given. In the mean time, some invariant characteristics of upper approximation and lower approximation under information system homomorphism are investigated. At last, we establish a surjection between rough sets of information systems under an information system homomorphism.     

Enterprise Client/Server Computing

Few companies can afford the continuously escalating costs and implementation delays associated with first-generation client/server strategies. Second-generation or enterprise strategies characterized by consolidation of key IS resources, efficient IS infrastructures, and focused application deployment hold promise for more rapid and cost-effective delivery of organizationwide benefits.