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1.
T. S. Shamirzaev A. I. Toropov A. K. Bakarov K. S. Zhuravlev A. Yu. Kobitski H. P. Wagner D. R. T. Zahn 《Semiconductors》2006,40(5):527-533
The stationary and time-resolved polariton radiation in ultrahigh quality AIGaAs layers have been studied. It has been found
that elastic exciton-exciton collisions lead to the appearance of a low-energy line of polariton radiation. We show that the
rate of exciton-to-polariton transitions caused by elastic exciton-exciton collisions is determined not only by the density
of the excitonic gas, but also by its temperature; this is in accordance with existing theoretical predictions.
The text was submitted by the authors in English. 相似文献
2.
James?Eves Vassili?V.?ToropovEmail author Harvey?M.?Thompson Nik?Kapur Jian?Fan Daniel?Copley Adrian?Mincher 《Structural and Multidisciplinary Optimization》2012,45(5):739-745
Supersonic jet pumps are simple devices with no moving parts, where a high velocity (primary) flow is used to pump a second
fluid. In this paper, Computational Fluid Dynamics (CFD) is combined with an optimization framework in order to develop a
tool for the rapid generation of jet pump designs. A key feature of the problem formulation is the transformation of the jet
pump design parameters in terms of geometric ratios. This approach dramatically reduces the number of unrealistic designs
covered by the Design of Experiments. Optimal Latin Hypercubes for surrogate model building and model validation points are
constructed using a permutation genetic algorithm and design points are evaluated using CFD. Surrogate models of primary and
entrained flow rates are built using a Moving Least Squares approach. A series of optimizations for various pump sizes are
performed using a genetic algorithm and Sequential Quadratic Programming, with responses calculated from the surrogates. This
approach results in a set of optimized designs, from which pumps for a wide range of flow rates can be interpolated. 相似文献
3.
Chkhalo NI Klimov AY Rogov VV Salashchenko NN Toropov MN 《The Review of scientific instruments》2008,79(3):033107
A new type of a reference spherical wave source (SWS) based on a single mode optical fiber with a narrowed down up to the submicrometer size exit aperture is proposed. It is intended for the precision point diffraction interferometers as a source of a reference wave. Systematic experimental errors which influence the measurement accuracy of the quality of the wave fronts generated by the SWSs are considered. Experimental data on wave front deformations are given. The combined root-mean-square (rms) wave deformation for a couple of the SWSs measured in a numerical aperture of NA=0.27 reaches the value of rms=0.36 nm that corresponds to rms=0.25 nm of a single SWS or about lambda2500 for the red He-Ne laser. 相似文献
4.
In this article, a procedure for designing a lattice fuselage barrel is developed. It comprises three stages: first, topology optimization of an aircraft fuselage barrel is performed with respect to weight and structural performance to obtain the conceptual design. The interpretation of the optimal result is given to demonstrate the development of this new lattice airframe concept for the fuselage barrel. Subsequently, parametric optimization of the lattice aircraft fuselage barrel is carried out using genetic algorithms on metamodels generated with genetic programming from a 101-point optimal Latin hypercube design of experiments. The optimal design is achieved in terms of weight savings subject to stability, global stiffness and strain requirements, and then verified by the fine mesh finite element simulation of the lattice fuselage barrel. Finally, a practical design of the composite skin complying with the aircraft industry lay-up rules is presented. It is concluded that the mixed optimization method, combining topology optimization with the global metamodel-based approach, allows the problem to be solved with sufficient accuracy and provides the designers with a wealth of information on the structural behaviour of the novel anisogrid composite fuselage design. 相似文献
5.
6.
Ioanna Lykourentzou Ioannis Giannoukos Vassilis Nikolopoulos George Mpardis Vassili Loumos 《Computers & Education》2009,53(3):950-965
In this paper, a dropout prediction method for e-learning courses, based on three popular machine learning techniques and detailed student data, is proposed. The machine learning techniques used are feed-forward neural networks, support vector machines and probabilistic ensemble simplified fuzzy ARTMAP. Since a single technique may fail to accurately classify some e-learning students, whereas another may succeed, three decision schemes, which combine in different ways the results of the three machine learning techniques, were also tested. The method was examined in terms of overall accuracy, sensitivity and precision and its results were found to be significantly better than those reported in relevant literature. 相似文献
7.
Jonathan Ollar Charles Mortished Royston Jones Johann Sienz Vassili Toropov 《Structural and Multidisciplinary Optimization》2017,55(6):2029-2044
In this work a two step approach to efficiently carrying out hyper parameter optimisation, required for building kriging and gradient enhanced kriging metamodels, is presented. The suggested approach makes use of an initial line search along the hyper-diagonal of the design space in order to find a suitable starting point for a subsequent gradient based optimisation algorithm. During the optimisation an upper bound constraint is imposed on the condition number of the correlation matrix in order to keep it from being ill conditioned. Partial derivatives of both the condensed log likelihood function and the condition number are obtained using the adjoint method, the latter has been derived in this work. The approach is tested on a number of analytical examples and comparisons are made to other optimisation approaches. Finally the approach is used to construct metamodels for a finite element model of an aircraft wing box comprising of 126 thickness design variables and is then compared with a sub-set of the other optimisation approaches. 相似文献
8.
V. V. Toropov A. A. Filatov A. A. Polynkin 《Structural and Multidisciplinary Optimization》1993,6(1):7-14
A unified approach to various problems of structural optimization, based on approximation concepts, is presented. The approach is concerned with the development of the iterative technique, which uses in each iteration the information gained at several previous design points (multipoint approximations) in order to better fit constraints and/or objective functions and to reduce the total number of FE analyses needed to solve the optimization problem. In each iteration, the subregion of the initial region in the space of design variables, defined by move limits, is chosen. In this subregion, several points (designs) are selected, for which response analyses and design sensitivity analyses are carried out using FEM. The explicit expressions are formulated using the weighted least-squares method. The explicit expressions obtained then replace initial problem functions. They are used as functions of a particular mathematical programming problem. Several particular forms of the explicit expressions are considered. The basic features of the presented approximations are shown by means of classical test examples, and the method is compared with other optimization techniques.Presented at NATO ASI Optimization of Large Strucutral Systems, held in Berchtesgarden, Germany, Sept. 23 — Oct. 4, 1991 相似文献
9.
I. D. Burlakov K. O. Boltar P. V. Vlasov A. A. Lopukhin A. I. Toropov K. S. Zhuravlev V. V. Fadeev 《Journal of Communications Technology and Electronics》2017,62(3):309-313
Photoelectric characteristics of a 320 × 256-element focal plane array (FPA) with a pitch of 30 μm, whose photosensitive element is formed in the InSb epitaxial layer deposited on a heavily doped substrate, have been investigated. For a relative aperture of 1: 0.94 and an integration time of 1.46 ms, the mean value of the noise-equivalent temperature difference is 10.5 mK, the percentage of defective elements is 0.12%, and the correction time is more than 3 h. The FPA has been compared to similar commercial devices based on bulk InSb. 相似文献
10.
The electron capture parameters and photoionization cross section of the unintentional deep levels, which are responsible
for photoelectrical memory in GaAs/AlGaAs multilayer quantum-well structures, have been found from an analysis of the kinetics
of the excess current during and after optical illumination of these structures. The dependence of the photoionization cross
section on the photon energy, the capture cross section, and the energy barrier for capture of an electron from the bottom
of the conduction band indicate that the unintentional deep levels are DX centers formed by the silicon impurity. These DX centers probably appear during growth of the structures as a result of silicon diffusion from the quantum wells along as-grown
defects.
Fiz. Tekh. Poluprovodn. 32, 1213–1218 (October 1998) 相似文献