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141.
Traian Florin Marinca Bogdan Viorel Neamţu Ionel Chicinaş Petru Pascuta 《Journal of Thermal Analysis and Calorimetry》2014,118(2):1245-1251
Commercially, iron (α-Fe) and hematite (α-Fe2O3) powders were used for the synthesis of composite powders of Fe2O3/Fe type by mechanical milling. Several ratios of Fe2O3/Fe were chosen for the composite synthesis; the atomic percent of oxygen in the starting mixtures ranged from 21 to 46 %. The Fe2O3/Fe composite samples with various Fe/O ratios were milled for different milling times. The milled composite samples were subjected to the heat treatments in argon up to 900 °C. During the heat treatment at temperatures that do not exceed 550 °C, Fe3O4/Fe composite particles are formed by the reaction between the Fe2O3 and Fe. Further increase of the heat treatment up to 700 °C leads to the reaction of the Fe3O4/Fe composite component phases, resulting thus in the formation of FeO/Fe composite. The heat treatment up to 900 °C of the Fe2O3/Fe leads to the formation of a composite of FeO/Fe3O4/Fe independent of the milling time and Fe2O3/Fe ratios. The onset temperatures of the Fe3O4 and FeO formations decrease upon increasing the milling time. Another important aspect is that, in the case of the same milling time but with a large amount of iron into the composite powder the formations temperatures of Fe3O4 and FeO are also decreasing. The influence of the mechanical activation time, heat treatment temperature, and Fe/O ratio on the formation of the (Fe3O4, FeO)/Fe composite from Fe2O3+Fe precursor mixtures was studied by differential scanning calorimetry and X-ray diffraction techniques. 相似文献
142.
143.
Barbu C. Kestenband 《Journal of Geometry》2003,77(1-2):61-101
The polarities of Desarguesian planes have long been known. This author has undertaken to classify
the correlations of finite Desarguesian planes in general. In [6] we have presented all the correlations with identity
companion automorphism which are not polarities, of these planes. In this sequence of papers, we classify the
correlations of planes of order $ p^{2^{i}(2n+1)}, n \neq 0 $, with companion automorphism ( $p^{2^{i}t}$ ), p an odd prime, $ t \neq 0 $.
This represents a complete classification of the correlations of planes of odd nonsquare order (i = 0). Some of
the correlations of planes of odd square order ($ t \neq 0 $ ) are also covered by the present analysis.When the companion automorphism is not trivial, the problem, naturally, becomes more involved, and a great deal
begins to hinge upon the order of the plane being odd or even, and also a square or a nonsquare.The correlations of planes of order $ 2^{2^{i}(2n+1)}, n \neq 0 $, with companion automorphism $ 2^{2^{i}t}, t \neq 0 $, and especially
those of planes of order $ p^{2^{i}(2n+1)}, i \neq 0 $, with companion automorphism $ p^{2^{j}(2r+1)}, j > i $ require a substantially
different treatment, and will be the object of separate efforts. 相似文献
144.
The tunneling time asymmetry in type II semiconductor heterostructures is related to the phase difference of the reflection coefficients for the two tunneling directions. Analytical expressions and numerical simulations are given for the difference between the left-to-right and right-to-left tunneling times in asymmetric, single and multiple barrier type II heterostructures. 相似文献
145.
Best approximation in max-plus semimodules 总被引:1,自引:0,他引:1
Marianne Akian Stéphane Gaubert Viorel Ni?ic? Ivan Singer 《Linear algebra and its applications》2011,435(12):3261-3296
146.
Viorel Barbu Michael R?ckner Francesco Russo 《Probability Theory and Related Fields》2011,151(1-2):1-43
We consider a possibly degenerate porous media type equation over all of ${\mathbb R^d}$ with d =?1, with monotone discontinuous coefficients with linear growth and prove a probabilistic representation of its solution in terms of an associated microscopic diffusion. This equation is motivated by some singular behaviour arising in complex self-organized critical systems. The main idea consists in approximating the equation by equations with monotone non-degenerate coefficients and deriving some new analytical properties of the solution. 相似文献
147.
Barbu and Triggiani (Indiana Univ. Math. J. 2004; 53:1443–1494) have proposed a solution of the internal feedback stabilization problem of Navier–Stokes equations with no-slip boundary conditions. They have shown that any unstable steady-state solution can be exponentially stabilized by a finite-dimensional feedback controller with support in an arbitrary open subset of positive measure. The finite dimension of the feedback controller is minimal and is related to the largest algebraic multiplicity of the unstable eigenvalues of the linearized equation. The feedback law is obtained as a solution of a linear-quadratic control problem. In this paper, we formulate a practical algorithm implementation of the proposed stabilization approach, based on the finite element method, and demonstrate its applicability and effectiveness using an example involving the stabilization of two-dimensional Navier–Stokes equations. 相似文献
148.
Tudor Barbu 《Numerical Functional Analysis & Optimization》2013,34(5-6):591-601
In this paper, we propose a novel eigenface-based face recognition approach. First we describe a continuous model for facial feature extraction, involving the covariance operator associated with gradient of the 2-D image function. Then we provide a discretized version of this model. Face identification and verification procedures, using a supervised classification technique, are also proposed. 相似文献
149.
Sebastian Aniţa Viorel Arnăutu Răzvan Ştefănescu 《Numerical Functional Analysis & Optimization》2013,34(3-4):183-198
We investigate an optimal harvesting problem for age-structured population dynamics with logistic term and periodic vital rates. We use first-order necessary optimality conditions in order to derive an algorithm to approximate the optimal harvesting effort. We present corresponding numerical experiments. 相似文献
150.
Tudor Barbu 《Numerical Functional Analysis & Optimization》2013,34(11):1269-1279
A Gaussian noise reduction technique for grayscale images is proposed in this article. It uses a modified Gaussian filter kernel based on a hyperbolic second-order equation. The introduced mathematical model differs from the classic Gaussian model provided by the heat equations, by a localization property. Our filtering approach reduces the amount of Gaussian noise and also enhances the image contrast. Some image denoising experiments that prove the effectiveness of the proposed method are also described in this article. 相似文献