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151.
152.
K. S. Matviichuk 《International Applied Mechanics》2003,39(3):356-367
Sufficient conditions of technical stability in measure are established for nonstationary automatic-control systems with variable structure and logic control laws dependent on the mismatch error and its derivatives of finite order for all admissible initial perturbations from a predefined measurable set of initial perturbations. The associated systems of differential equations contain time-dependent coefficients. The logic control laws are described by a variable jump control function of the mismatch coordinate and its derivatives of finite order that is no higher than that of the initial system of equations. Using a signal and its derivatives for control increases the quality of discontinuous control. The relationship between the eigenvalues of the quadratic forms of the corresponding Liapunov functions and the criteria of technical stability is revealed. The general results are applied to a variable-structure system of the third order 相似文献
153.
O. Peña A.B. Antunes M.N. Baibich P.N. Lisboa-Filho V. Gil C. Moure 《Journal of magnetism and magnetic materials》2007
The erbium-based manganite ErMnO3 has been partially substituted at the manganese site by the transition-metal elements Ni and Co. The perovskite orthorhombic structure is found from x(Ni)=0.2–0.5 in the nickel-based solid solution ErNixMn1−xO3, while it can be extended up to x(Co)=0.7 in the case of cobalt, provided that the synthesis is performed under oxygenation conditions to favor the presence of Co3+. Presence of different magnetic entities (i.e., Er3+, Ni2+, Co2+, Co3+, Mn3+, and Mn4+) leads to quite unusual magnetic properties, characterized by the coexistence of antiferromagnetic and ferromagnetic interactions. In ErNixMn1−xO3, a critical concentration xcrit(Ni)=1/3 separates two regimes: spin-canted AF interactions predominate at x<xcrit, while the ferromagnetic behavior is enhanced for x>xcrit. Spin reversal phenomena are present both in the nickel- and cobalt-based compounds. A phenomenological model based on two interacting sublattices, coupled by an antiferromagnetic exchange interaction, explains the inversion of the overall magnetic moment at low temperatures. In this model, the ferromagnetic transition-metal lattice, which orders at Tc, creates a strong local field at the erbium site, polarizing the Er moments in a direction opposite to the applied field. At low temperatures, when the contribution of the paramagnetic erbium sublattice, which varies as T−1, gets larger than the ferromagnetic contribution, the total magnetic moment changes its sign, leading to an overall ferrimagnetic state. The half-substituted compound ErCo0.50Mn0.50O3 was studied in detail, since the magnetization loops present two well-identified anomalies: an intersection of the magnetization branches at low fields, and magnetization jumps at high fields. The influence of the oxidizing conditions was studied in other compositions close to the 50/50=Mn/Co substitution rate. These anomalies are clearly connected to the spin inversion phenomena and to the simultaneous presence of Co2+ and Co3+ magnetic moments. Dynamical aspects should be considered to well identify the high-field anomaly, since it depends on the magnetic field sweep rate. 相似文献
154.
155.
We discuss ergodicity properties of a controlled jumps diffusion process reflected from the boundary of a bounded domain.
The control parameters act on the drift term and on a first-order-type jump density. The controlled process is generated via
a Girsanov change of probability, and a long-run average criterion is optimized. An optimal stationary feedback is constructed
by means of the Hamilton-Jacobi-Bellman equation. 相似文献
156.
We generalize some old and new results on the determination of jumps of a periodic, Lebesgue integrable function f at each point of discontinuity of first kind in terms of the partial sums of the conjugate series to the Fourier series of
f in [1], and in terms of the Abel-Poisson means in [2], to some more general linear operators which satisfy some certain conditions.
The linear operators in discussion include the Fejér means, de la Vallée-Poussin means, and Bernstein-Rogosinski sums.
Research also supported in part by NSF of China under grant number 10471130. 相似文献
157.
刘禄勤 《数学物理学报(B辑英文版)》1995,(1)
(刘禄勤)THEEQUILIBRIUMPROBLEMANDCAPACITYFORJUMPMARKOVPROCESSES¥LiuLuqin(Dept,ofMath.,WuhanUniversity,Wuhan430072,China)Abstract:... 相似文献
158.
A binary phase grating capable of shaping an incident Gaussian beam to a flattop beam in a Fourier domain is designed iteratively. It is essential in grating design to consider the phases of diffracted waves by the grating, in addition to their amplitude uniformity and diffraction efficiency. The optimized grating phase produces the in-phase diffracted waves that interfere constructively to form a uniform amplitude and phase profile. The dependence of the shaped profile on the illuminating amplitude distribution, the grating misalignment, and the lens focusing error is investigated by computer simulation and optical experiment. 相似文献
159.
We study finite partial orders which have a chain such that every element of the order either belongs to this chain or has all its covers in this chain. We show that such orders are exactly the orders being both interval orders and truncated lattices. We prove that their jump number is polynomially tractable and that their dimension is unbounded. We also show that every order admits a visibility model having such an order as host. 相似文献
160.
Buckley Crist Costas Metaxas 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2081-2091
Intrinsic true stress–true strain response was evaluated at room temperature for three linear polyethylene samples deformed in conventional tensile tests. It was observed that high crystallinity is associated with a low rate of strain hardening that results in a sharp neck and a large drop in nominal stress. The maximum and minimum deformation loads are accounted for by Considère's analysis of neck initiation and stabilization, respectively. Following stabilization, neck propagation occurs at a load or nominal stress that is lower than the yield stress. The jump analysis of Ericksen and Hutchinson/Neale predicts steady state neck propagation stresses that are in very good (ca. 10%) agreement with experiment. Although the jump analysis is done in terms of uniaxial stress, the actual value of the propagation stress is established by the triaxial stress state in the neck shoulders. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2081–2091, 2004 相似文献