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991.
J. Janovec A. Vyrostková M. Svoboda A. Kroupa H. J. Grabke 《Metallurgical and Materials Transactions A》2004,35(3):751-759
The influence of both bulk vanadium content and aging conditions on the evolution of secondary phases in Cr-V low-alloy steels
was studied. Three 0.1C-0.9Cr-V steels with different vanadium contents (0, 0.258, and 0.512 wt pct) were aged for 100 to
5,000 hours at 773, 853, 953, and 993 K. In the investigation, a limited experimental program (transmission electron microscopy
(TEM)) was combined with credible thermodynamic predictions (ThermoCalc). Going out from the good agreement between the predicted
and experimental results, behavior of the iron-rich M7C3 carbide in time-temperature scale was characterized. The influence of bulk vanadium content was determined on appearance
of the M3C carbide in equilibrium, temperature of the M7C3 carbide precipitation, metal compositions of M3C or M7C3 carbides, and vanadium portion in the metallic part of the MX phase. 相似文献
992.
G. Kovács A.A. Groenwold K. Jármai J. Farkas 《Structural and Multidisciplinary Optimization》2004,28(2-3):170-179
The optimal design of a carbon-fibre-reinforced plastic (CFRP) sandwich-like structure with aluminium (Al) webs is addressed. The material parameters are determined using tensile tests, whereafter the results of an analytical model, a numerical model and an experimental setup are compared. The analytical and numerical approximations are then used to optimize the structure in a multi-algorithm approach for minimum cost and maximum stiffness. The selected algorithm and approximation are motivated by their accuracy and computational efficiency. The CFRP plates are optimized with respect to ply arrangement, while the complete sandwich-like structure is optimized with respect to the combination of manufacturing and material cost. Design constraints on maximum deflection of the total structure, buckling of the CFRP composite plates, buckling of the Al webs, stress in the composite plates and stress in the Al stiffeners are included in the formulation. For the different phases in the optimization process, we use the recently proposed particle swarm optimization algorithm, a dynamic search technique and a continuous-discrete optimization technique . 相似文献
993.
Quattor: Tools and Techniques for the Configuration,Installation and Management of Large-Scale Grid Computing Fabrics 总被引:1,自引:0,他引:1
R. García Leiva M. Barroso López G. Cancio Meliá B. Chardi Marco L. Cons P. Poznański A. Washbrook E. Ferro A. Holt 《Journal of Grid Computing》2004,2(4):313-322
This paper describes the quattor tool suite, a new system for the installation, configuration, and management of operating systems and application software for computing fabrics. At present Unix derivatives such as Linux and Solaris are supported. Quattor is a powerful, portable and modular open source solution that has been shown to scale to thousands of computing nodes and offers a significant reduction in management costs for large computing fabrics. The quattor tool suite includes innovations compared to existing solutions which make it very useful for computing fabrics integrated into grid environments. Evaluations of the tool suite in current large scale computing environments are presented. 相似文献
994.
Outlier Detection and Data Cleaning in Multivariate Non-Normal Samples: The PAELLA Algorithm 总被引:1,自引:0,他引:1
Manuel Castejón Limas Joaquín B. Ordieres Meré Francisco J. Martínez de Pisón Ascacibar Eliseo P. Vergara González 《Data mining and knowledge discovery》2004,9(2):171-187
A new method of outlier detection and data cleaning for both normal and non-normal multivariate data sets is proposed. It is based on an iterated local fit without a priori metric assumptions. We propose a new approach supported by finite mixture clustering which provides good results with large data sets. A multi-step structure, consisting of three phases, is developed. The importance of outlier detection in industrial modeling for open-loop control prediction is also described. The described algorithm gives good results both in simulations runs with artificial data sets and with experimental data sets recorded in a rubber factory. Finally, some discussion about this methodology is exposed. 相似文献
995.
P. González A. Godoy F. Gámiz J. A. Carrillo 《Journal of Computational Electronics》2004,3(3-4):235-238
In this work some variants of a deterministic simulation of p-n junctions are considered. From a mathematical point of view, this will be done by means of the numerical resolution of the corresponding Boltzmann transport’s equations (BTE’s): one for the electrons and another one for the holes, coupled by the Poisson equation for the potential, from which the electric field is calculated. In order to improve the efficiency of the Finite-Difference Weighted Essentially Non-Oscillatory (FD-WENO) code, we will consider the two transport equations in the depletion zone and only the corresponding BTE equation for the majority carrier in each one of the neutral zones, instead of solving the two BTE’s in the entire length of the device. 相似文献
996.
P. Dollfus J. E. VeláZquez A. Bournel S. Galdin-Retailleau 《Journal of Computational Electronics》2004,3(3-4):311-315
A preliminary study of velocity fluctuations in simple devices using an atomistic model for the ionized impurity scattering is presented. The velocity fluctuations are responsible for thermal noise in semiconductor devices. In this paper the influence on the spectral density of velocity fluctuations of the boundary conditions, the doping level, the length of the resistors and the excess/default of impurities has been addressed. 相似文献
997.
Mechanical alloying (MA) and rapid solidification (RS) are two important routes to obtain amorphous alloys. An Fe-Ni based metal-metalloid alloy (Fe50Ni30P14Si6) prepared by these two different processing routes was studied by differential scanning calorimetry, scanning electron microscopy with microanalysis, inductive coupled plasma, X-ray diffraction (XRD) and transmission Mössbauer spectroscopy (TMS). The results were compared with that obtained from other Fe-Ni based alloys of similar compositions. The structural analyses show that the materials obtained by mechanical alloying are not completely disordered after 40 h of milling whereas fully amorphous alloys were obtained by rapid solidification. TMS analyses show that, independent of the composition, after milling for 40 h, about 7% of the Fe remains unreacted. Furthermore, the thermal stability of mechanically alloyed samples is lower than that of the analogous material prepared by rapid solidification. In the MA alloys, a broad exothermic process associated to structural relaxation begins at low temperature. XRD patterns of crystallized alloys indicate that the crystallization products are bcc(Fe,Ni), fcc(Ni,Fe), and (Fe,Ni)-phosphides and -silicides. 相似文献
998.
Martina Bečvářová 《NTM》2004,12(1):40-48
The paper describes the Czech project in the history of mathematics which was initiated at the Faculty of Mathematics and
Physics of Charles University in Prague at the end of the eighties of the 20th century. Its main aim is to map the development
of mathematical research in the Czech lands in the second half of the nineteenth and the first half of the twentieth century.
The main result of this project is the production of monographs. These chart out the life and work of some prominent Czech
personalities-mathematicians who have had substantial influence on the development of Czech mathematics. The aim of the project,
the structure of the monographs and the general method are discussed in the paper. 相似文献
999.
R. Černý J. Poděbradská M. Totová J. Toman J. Drchalová P. Rovnaníková P. Bayer 《Materials and Structures》2004,37(9):597-607
The effect of elevated temperatures on basic hygric and thermal properties of three types of glass fiber reinforced cement
composites (GFRC) is analyzed in the paper. The main difference in the composition of particular GFRC is the use of wollastonite
and vermiculite in two of them instead of usual sand aggregates. The composites containing wollastonite and vermiculite are
found to have about four times lower thermal conductivity and two to three times lower thermal diffusivity in room temperature
conditions. After heating the samples to 800°C and subsequent cooling, a decrease in room-temperature thermal conductivity
as high as 50% and an increase in moisture diffusivity in the range of one to two orders of magnitude are observed for all
types of studied materials. The application of wollastonite and vermiculite exhibits a positive effect on the high temperature
linear thermal expansion coefficient. On the other hand, for temperatures higher than 450°C the thermal diffusivity of materials
with wollastonite and vermiculite is higher than of common GFRC with sand aggregates.
Résumé L'effet des températures élevées sur les principales propriétés hygriques et thermiques de trois types de matériaux composites à base de ciment renforcés par des fibres de verre (GFRC) est analysé dans cet article. La différence majeure de composition de ces matériaux est l'utilisation de wollastonite et de vermiculite dans deux d'entre eux au lieu des granulats de sable habituels. Les matériaux composites contenant de la wollastonite et de la vermiculie s'avèrent posséder une conductivité thermique environ quatre fois inférieure et une diffusivité thermique deux à trois fois inférieure en conditions de température ambiante. Après avoir chauffé les échantillons à 800°C puis les avoir refroidis, on observe pour tous les types de matériaux étudiés une diminution de la conductivité thermique à température ambiante, à hauteur de 50%, et une augmentation de la diffusivité d'humidité, d'environ un à deux ordres de grandeur. L'application de la wollastonite et de la vermiculite montre un effet positif sur le coefficient linéaire à haute température de dilatation thermique. D'autre part, pour les températures supérieures à 450°C, la diffusivité thermique des matériaux contenant de la wollastonite et de la vermiculite est plus élevée que celle des GFRC communs avec des granulats de sable.相似文献
1000.
E. E. Shalyguina I. Škorvánek P. Švec V. V. Molokanov V. A. Mel’nikov 《Technical Physics Letters》2004,30(7):591-594
Inverted hysteresis loops were observed for the first time in the near-surface layers of heterogeneous (nanocrystalline/amorphous) Fe81Nb7B12 alloys. In particular, a negative residual magnetization is retained when a positive magnetic field applied in the sample plane is decreased to zero. The inverted hysteresis is qualitatively explained within the framework of a two-phase model, according to which the heterogeneous alloys contain two dissimilar phases exhibiting uniaxial magnetic anisotropy and featuring antiferromagnetic exchange interaction. 相似文献