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991.
Victor Gunther Yuri Yasenchuk Timofey Chekalkin Ekaterina Marchenko Sergey Gunther Gulsharat Baigonakova Valentina Hodorenko Ji-hoon Kang Sabine Weiss Aleksei Obrosov 《Advanced Powder Technology》2019,30(4):673-680
The objective of this study was to examine the mechanism how the surface of porous TiNi compounds produced by SHS method evolves. The prepared samples were investigated using light-microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDS). The results indicated that the surface of all pores is represented by a granular stratum due to dendrite liquation by peritectic crystallization mechanism. The voids of 2–15?μm in size are formed owing to a capillary spreading of the liquid. Reaction gases with dissociated carbon, nitrogen, and oxygen are responsible for heat-and-mass transfer through the forming pores. High pressure-temperature effect of reaction gases on the melt causes the forming voids to coalesce, as well as transfers the peritectic liquid (PL) throughout the open pores catalyzing a distinctive spitted topography. It is through the chemisorption of gasiform nonmetallics by the pore surface melt, where these impurities are chemically bound, that it was formed a massive corrosion-resistant amorphous-nanocrystalline stratified shell deduced as an intermetallic oxycarbonitride layer. 相似文献
992.
A mixed numerical–analytical stable pseudo‐inversion method aimed at attaining an almost exact tracking 下载免费PDF全文
This paper considers the problem of computing the input u(t) of an internally asymptotically stable, possibly non‐minimum phase, linear, continuous time system Σ yielding a very accurate tracking of a pre‐specified desired output trajectory . The main purpose of the new approach proposed here is to alleviate some limitations that inherent the classical methods developed in the framework of the preview‐based stable inversion, which represents an important reference context for this class of control problems. In particular, the new method allows one to deal with arbitrary and possibly uncertain initial conditions and does not require a pre‐actuation. The desired output to be exactly tracked in steady state is here assumed to belong to the set of polynomials, exponential, and sinusoidal time functions. The desired transient response is specified to obtain a fast and smooth transition toward the steady‐state trajectory , without under and/or overshoot in the case of a set point reset. The transient control input ut(t) is a priori assumed to be given by a piecewise polynomial function. Once has been specified, this allows the computation of the unknown ut(t) as the approximate least squares solution of the Fredholm's integral equation corresponding to the explicit formula of the output forced response. The steady‐state input us(t) is analytically computed exploiting the steady‐state output response expressions for inputs belonging to the same set of . Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
993.
Alfio Borzì Valentina De Simone Daniela di Serafino 《Computing and Visualization in Science》2013,16(1):1-14
Algebraic multilevel preconditioners for algebraic problems arising from the discretization of a class of systems of coupled elliptic partial differential equations (PDEs) are presented. These preconditioners are based on modifications of Schwarz methods and of the smoothed aggregation technique, where the coarsening strategy and the restriction and prolongation operators are defined using a point-based approach with a primary matrix corresponding to a single PDE. The preconditioners are implemented in a parallel computing framework and are tested on two representative PDE systems. The results of the numerical experiments show the effectiveness and the scalability of the proposed methods. A convergence theory for the twolevel case is presented. 相似文献
994.
In this brief note the authors describe the studies undertaken to date regarding the dome of the Basilica of San Gaudenzio
in Novara designed by Alessandro Antonelli, with particular emphasis on the geometry and statics of the external dome. Following
a brief summary of the events and vicissitudes attendant on the construction of the dome, the structure will be examined from
the point of view of the geometry, the construction techniques, and the materials used, in order to clarify the static behaviour
and the stability of the whole set of structural and constructive elements of which the dome is composed. These studies have
allowed us to obtain the necessary information for evaluating the complex and ambitious structural achievement of a significant
element of Antonelli’s basilica. 相似文献
995.
Valentina Shevtsova Denis Melnikov Alexander Mialdun Jean Claude Legros 《Microgravity science and technology》2006,18(3-4):38-41
The future Space experiment IVIDIL is planned to study the influence of vibration stimuli on the measurements of diffusion and thermodiffusion coefficients. A binary mixture of water and isopropanol is chosen as a working liquid. The principle of the Space experiment and ground based research are outlined. In addition preparatory experiments might be performed during parabolic flights. Results of 3D numerical simulations of thermal vibrational convection in binary mixture at the conditions of the parabolic flight are presented. Heat and mass transport arising in the system with increasing of vibration actions is discussed. 相似文献
996.
We have used x-ray and metallographic layer-by-layer phase analysis to study the structure and composition of scale formed on the alloy Ni7Zr2 during its oxidation in air over a period of 1 h and 10 h in the temperature range 500-1200°C. In the scale we find NiO, the cubic and monoclinic modifications of ZrO2, and also Ni and Ni5Zr. The phase components are nonuniformly distributed over the thickness of the scale. The outer scale consists of the oxides NiO and ZrO2, while the composition of the inner scale includes Ni and Ni5Zr in addition to monoclinic ZrO2. Cubic ZrO2 is formed on the surface of the specimen in the initial stages of its oxidation at 500-700°C. For T ≥ 900°C, on the surface of the scale we find both modifications of ZrO2, while the nickel phase is itself a solid solution Ni(Zr). We note that the mechanisms for the formation of low-temperature (T ≤ 800°C) and high-temperature (T ≥ 900°C) scales are different. It is hypothesized that these differences are determined mainly by the fact that at high temperatures, diffusion of zirconium ions toward the outer boundary of the scale is superimposed on diffusion of oxygen toward the scale – alloy boundary. 相似文献
997.
Masciotti Valentina Piantanida Luca Naumenko Denys Amenitsch Heinz Fanetti Mattia Valant Matjaž Lei Dongsheng Ren Gang Lazzarino Marco 《Nano Research》2019,12(11):2900-2907
Nano Research - DNA origami is a promising technology for its reproducibility, flexibility, scalability and biocompatibility. Among the several potential applications, DNA origami has been proposed... 相似文献
998.
The Schur stability analysis of an interval polynomial family can be quickly performed through a unique, suitably defined extreme polynomial. The purpose of this article is to provide some improvements with respect to the actually existing methods based on this approach. 相似文献
999.
1000.
Paola Palmero Valentina Naglieri Jérôme Chevalier Gilbert Fantozzi Laura Montanaro 《Journal of the European Ceramic Society》2009,29(1):59-66
Doping of commercial alumina nanopowders by using aqueous solutions of metal salts was exploited to prepare alumina-based nanocomposites.The same procedure was applied to produce a composite made of immiscible phases, that is an alumina–zirconia material, by doping an α-alumina powder with a zirconium chloride solution, as well as to produce an alumina–YAG (yttrium aluminium garnet) system by doping alumina with a yttrium chloride solution and promoting YAG formation by solid-state reaction at high temperature.For this latter case, the difference in reactivity between two commercial powders, one made of transition alumina, the other of pure α-phase, was investigated in terms of phase evolution and purity.In all cases natural sintering was performed to develop dense bodies. 相似文献