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1.
This paper deals with chaotic attitude motion of a magnetic rigid spacecraft in a circular orbit near the equatorial plane of the earth. The dynamical model of the problem is derived. The Melnikov analysis is carried out to prove the existence of a complicated nonwandering Cantor set. The dynamical behavior is numerically investigated by means of time history, Poincare map, power spectrum and Lyapunov exponents. Numerical simulations indicate that the onset of chaos is characterized by break of torus as the torque of the magnetic forces is increased.  相似文献   

2.
Contact interface properties are important in determining the performances of devices that are based on atomically thin two-dimensional (2D) materials, especially for those with short channels. Understanding the contact interface is therefore important to design better devices. Herein, we use scanning transmission electron microscopy, electron energy loss spectroscopy, and first-principles calculations to reveal the electronic structures within the metallic (1T′)-semiconducting (2H) MoTe2 coplanar phase boundary across a wide spectral range and correlate its properties to atomic structures. We find that the 2H-MoTe2 excitonic peaks cross the phase boundary into the 1T′ phase within a range of approximately 150 nm. The 1T′-MoTe2 crystal field can penetrate the boundary and extend into the 2H phase by approximately two unit-cells. The plasmonic oscillations exhibit strong angle dependence, that is a red-shift of π+σ (approximately 0.3–1.2 eV) occurs within 4 nm at 1T′/2H-MoTe2 boundaries with large tilt angles, but there is no shift at zero-tilted boundaries. These atomic-scale measurements reveal the structure–property relationships of the 1T′/2H-MoTe2 boundary, providing useful information for phase boundary engineering and device development based on 2D materials.  相似文献   

3.
For a general state-space model of three-dimensional (3-D) systems the characteristic polynomial (eigenvalue) control problem via state and output feedback is considered. A frequency domain approach is employed which in the scalar input case leads to a set of necessary and sufficient conditions. The multi-input problem is treated by assuming that the state or output feedback gain matrix is expressed as the dyadic product ⊙F = ⊙ ⊙fT of a column vector ⊙β and a row vector ⊙fT. This assumption leads to an equivalent scalar input problem β which is directly solved by using the scalar input results. Concerning the dynamic feedback compensator design problem, the important particular case of proportional plus integral plus derivative (PID) control is considered and treated by essentially the same algorithm, which leads to a linear algebraic system in the unknown parameters, along with some constraint equations upon the closed-loop characteristic polynomial sought.  相似文献   

4.
Having found hidden hyperchaos in a 5D self-exciting homopolar disc dynamo, we study the existence of a Hopf bifurcation, which leads to unstable limit cycles bifurcating from a stable equilibrium. Hidden chaos with only stable equilibria can be observed from the Hopf bifurcation: a typical way to enable hidden attractors to be located. We then provide a new fuzzy controller, and a fast fuzzy disturbance observer, based on terminal sliding mode control for synchronization of the hyperchaotic system. Fuzzy inference is considered to weaken the chattering phenomena. Using Lyapunov stability theory, the stability of the closed-loop system is proved. Finally, simulations of synchronization are illustrated to show the efficient performance of the designed control method via external disturbances and dynamic uncertainties.  相似文献   

5.
The equations connecting the winding current and diaphragm motion of a telephone receiver under impressed simple harmonic electromotive and mechanical forces are formulated under: (I) The Maxwell flux theory; (2) the magnetizing-winding theory; (3) the Ampèrean resistanceless fixed molecular circuit theory of permanent magnetism; and (4) a general molecular orbital theory of ferromagnetism. On the latter theory it is found that the coupling coefficients M and N in the equations in question are in general different, in counter-distinction to the other three theories as hitherto formulated. The flux theory is shown not to be inconsistent with this result when certain dynamical phase relations are introduced into the static flux-magnetomotive force formula (Ohm's Law analog) always employed in this theory. The Ampèrean rigid circuit theory is criticized as an inadequate dynamical representation of ferromagnetism. The magnetizing-winding theory (dynamical) is reproduced in slightly generalized form.  相似文献   

6.
This paper presents a second order sliding mode observer (SOSMO) design for discrete time uncertain linear multi-output system. The design procedure is effective for both matched and unmatched bounded uncertainties and/or disturbances. A second order sliding function and corresponding sliding manifold for discrete time system are defined similar to the lines of continuous time counterpart. A boundary layer concept is employed to avoid switching across the defined sliding manifold and the sliding trajectory is confined to a boundary layer once it converges to it. The condition for existence of convergent quasi-sliding mode (QSM) is derived. The observer estimation errors satisfying given stability conditions converge to an ultimate finite bound (within the specified boundary layer) with thickness O(T2)O(T2) where T is the sampling period. A relation between sliding mode gain and boundary layer is established for the existence of second order discrete sliding motion. The design strategy is very simple to apply and is demonstrated for three examples with different class of disturbances (matched and unmatched) to show the effectiveness of the design. Simulation results to show the robustness with respect to the measurement noise are given for SOSMO and the performance is compared with pseudo-linear Kalman filter (PLKF).  相似文献   

7.
高校图书馆管理的创新研究   总被引：2，自引：0，他引：2  
张永军 《情报科学》2008,26(1):29-33
混沌理论是关于非线性系统的一门新兴科学,混沌理论的兴起颠覆了经典理论的基本假设,其世界观和方法论震撼了整个学术界.管理领域受混沌理论影响,产生了许多有价值的理念和方法.本文从混沌理论的核心概念出发,并根据高校图书馆管理系统的混沌特性,探讨了混沌理论指导下的高校图书馆管理新思维.  相似文献   

8.
The reduction of the study of continuous dynamical systems to the study of point mappings was first effected by Poincaré, and later more generally by Birkhoff, in the conservative case. However, the analytical expressions of these mappings are, in most cases, rather complicated or even unknown. This paper deals with the construction of area- preserving polynomial point mappings in the plane osculating the actual one (also area preserving) to a certain degree. These mappings can be used for an approximate study of the behaviour of solutions in a neighbourhood of the origin taken as a fixed point. To illustrate this approach, some numerical examples are given.  相似文献   

9.
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10.
A class of matrices with 1, -1 and 0 entries, called the H-matrices, is introduced and properties of such matrices are investigated. It is shown that for an H-matrix K the matrix G = KDKT, where D is a diagonal matrix with nonnegative diagonal entries, has certain properties applicable to topological synthesis of networks. A technique for decomposing a particular symmetrical matrix G, called the Q-matrix, into KDKT, where K is an H-matrix and D is a diagonal matrix with positive diagonal entries, is also developed.  相似文献   

11.
Given the linear system x = Ax - bu, y = cTx, it is shown that, for a certain non-quadratic cost functional, the optimal control is given by uopt(x) = h(cTx), where the function h(y) must satisfy the conditions ky2?h(y)y>0 for y≠0, h(0) = 0 and existence of h-1 everywhere. The linear system considered must satisfy the Popov condition 1/k + (1 +?ωβ) G(?ω)>0 for all ω, G(s) being the y(s)/u(s) transfer function.  相似文献   

12.
流域地貌和水系结构对流域的水生态功能起支撑作用.本文运用地理信息系统方法,将东江流域15m空间分辨率DEM与1∶100万地貌图和1∶25万水系图等相结合,分析了东江流域上游地貌特征,提取了东江上游水系结构特征与流域面积-高程积分值,探讨了地貌特征与水系结构对生态系统的影响.结果显示,东江上游的地貌以200～500m高程、坡度＜8°的丘陵和中小起伏山地为主;本文将东江上游地区水系划分为10级结构,河网总数目33.81万条,总长度8.12万km,沟谷密度5.29km/km2,河网频度22条/km2,平均分支比为3.86;东江上游面积-高程积分值为0.23,整体地貌发育阶段处于晚年期.东江上游流域整体水土流失为轻度,但局部为中度到重度.在地势比降平坦,人口密集的新丰江水库、涮江、船塘河三个流域,河网密度和频度相对较小,水生态与水环境相对脆弱.  相似文献   

13.
What Are the New Implications of Chaos for Unpredictability?   总被引：1，自引：0，他引：1  
From the beginning of chaos research until today, the unpredictabilityof chaos has been a central theme. It is widely believed andclaimed by philosophers, mathematicians and physicists alikethat chaos has a new implication for unpredictability, meaningthat chaotic systems are unpredictable in a way that other deterministicsystems are not. Hence, one might expect that the question ‘Whatare the new implications of chaos for unpredictability?’has already been answered in a satisfactory way. However, thisis not the case. I will critically evaluate the existing answersand argue that they do not fit the bill. Then I will approachthis question by showing that chaos can be defined via mixing,which has never before been explicitly argued for. Based onthis insight, I will propose that the sought-after new implicationof chaos for unpredictability is the following: for predictingany event, all sufficiently past events are approximately probabilisticallyirrelevant.
  1. Introduction
  2. Dynamical Systems and Unpredictability
    2.1 Dynamical systems
    2.2 Natural invariant measures
    2.3Unpredictability
  3. Chaos
    3.1 Defining chaos
    3.2 Definingchaos via mixing
  4. Criticism of Answers in the Literature
    4.1 Asymptotic unpredictability?
    4.2 Unpredictability dueto rapid or exponential divergence?
    4.3 Macro-predictabilityand Micro-unpredictability?
  5. A General New Implication ofChaos for Unpredictability
    5.1Approximate probabilistic irrelevance
    5.2 Sufficiently pastevents are approximately probabilisticallyirrelevant for predictions
  6. Conclusion
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14.
The atomic force microscope system (AFM) has become a popular and useful instrument to measure the intermolecular forces with atomic resolution that can be applied in electronics, biological analysis, materials, semiconductors, etc. This paper studies the bifurcation phenomenon and complex nonlinear dynamic behavior of the probe tip between the sample and microcantilever of an atomic force microscope using the differential transformation method. The dynamic behavior of the probe tip is characterized with reference to bifurcation diagrams, phase portraits, power spectra, Poincaré maps, and maximum Lyapunov exponent plots produced using the time-series data obtained from differential transformation method. The results indicate that the probe tip behavior is significantly dependent on the magnitude of the vibrational amplitude. Specifically, the probe tip motion changes from T-periodic to 3T-periodic, then from 6T-periodic to multi-periodic, and finally to chaotic motion with windows of periodic motion as the vibrational amplitude is increased from 0 to 5.0. Furthermore, it is demonstrated that the differential transformation method is in good agreement for the considered system.  相似文献   

15.
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16.
In this paper, we study a discrete prey-predator system with harvesting of both species and Beddington-DeAngelis functional response. By using the center manifold theorem and bifurcation theory, we establish that the system undergoes flip bifurcation and Hopf bifurcation when the harvesting effort of prey population passes some critical values. Numerical simulations exhibit period-6, 10, 12, 14, 20 orbits, cascade of period-doubling bifurcation in period-2, 4, 8, 16 orbits and chaotic sets. At the same time, the numerically computed Lyapunov exponents confirm the complex dynamical behaviors. Moreover, a state delayed feedback control method, which can be implemented only by adjusting the harvesting effort for the prey population, is proposed to drive the discrete prey-predator system to a steady state.  相似文献   

17.
Implementing human-like learning and control for nonlinear dynamical systems operating in different control situations is an important and challenging issue. This paper presents a pattern-based neural network (NN) control strategy for nonlinear pure-feedback systems via deterministic learning (DL). Firstly, an appropriately designed adaptive neural dynamic surface controller is proposed to achieve the finite time tracking control. By analyzing the recurrent property of NN input signals, a partial persistent excitation (PE) condition for radial basis function (RBF) network is established, the implicit desired control dynamics under different control situations are accurately identified via DL in the case that the dimension of NN input is reduced. And a set of pattern-based experienced actual and virtual controllers is constructed using the learned knowledge. Secondly, to classify different control situations, when the system is operating in different control situations but controlled by current normal experienced controller, the dynamics of each subsystem are accurately identified via DL, n sets of dynamical estimators are constructed using the learned knowledge. Thirdly, in the recognition phase, n sets of residuals are achieved by comparing each set of estimators with the monitored system, sudden change in the control situation is rapidly recognized based on the principle of the earliest occurrence of the minimum residual. Finally, in the control phase, according to the recognition result, the correct experienced actual and virtual controllers will be selected to control the plant, guaranteed stability and superior control performance are achieved without any further re-adaptation online. Simulation studies are given to verify the proposed scheme can not only acquire and memorize knowledge like humans, but also reuse the learned knowledge to achieve rapid recognition and control of current control situation.  相似文献   

18.
The present study was designed to compare the potential of turmeric and its active principle curcumin on T3-induced oxidative stress and hyperplasia. Adult male Wistar strain rats were rendered hyperthyroid by T3 treatment (10 μg · 100 g−1 · day−1 intraperitoneal for 15 days in 0.1 mM NaOH) to induce renal hyperplasia. Another two groups were treated similarly with T3 along with either turmeric or curcumin (30 mg kg−1 body weight day−1 orally for 15 days). The results indicate that T3 induces both hypertrophy and hyperplasia in rat kidney as evidenced by increase in cell number per unit area, increased protein content, tubular dilation and interstitial edema. These changes were accompanied by increased mitochondrial lipid peroxidation and superoxide dismutase activity without any change in catalase activity and glutathione content suggesting an oxidative predominance. Both turmeric and curcumin were able to restore the level of mitochondrial lipid peroxidation and superoxide dismutase activity in the present dose schedule. T3-induced histo-pathological changes were restored with turmeric treatment whereas curcumin administration caused hypoplasia. This may be due to lower concentration of curcumin in the whole turmeric. Thus it is hypothesized that regulation of cell cycle in rat kidney by T3 is via reactive oxygen species and curcumin reveres the changes by scavenging them. Although the response trends are comparable for both turmeric and curcumin, the magnitude of alteration is more in the later. Turmeric in the current dose schedule is a safer bet than curcumin in normalizing the T3-induced hyperplasia may be due to the lower concentration of the active principle in the whole spice.  相似文献   

19.
Conditions are given for underdamped or overdamped linear dynamical systems in terms of loop matrix parameters, (√(C)R√(C)g,g)2 ? 4(√(C)L√(C)g,g) for all [boxV]g[boxV] = 1, g ∈ H. These criteria are looked upon as natural generalizations of the elementary one-loop RLC series scalar criteria (R/2L)2 ? 1/LC, when written in the more suggestive form: (√(C)R√(C))2 ? 4√(C)L√(C). A simplified test for determining dynamical systems with all complex natural modes or all real modes are presented with additional comments.  相似文献   

20.
A new method is presented for determining the stability and vibration modes of a class of parametric oscillations where the damping terms in the Mathieu-Hill type of differential equations are complex as well as periodic. The imaginary terms are converted to phase lagged terms in a set of simultaneous first-order differential equations used to express these equations with first-order derivatives treated as additional variables, thereby doubling the number of equations but allowing matrix methods to be conveniently used in a bifurcation procedure to obtain solutions and stability boundaries. The method has advantages over methods using series expansions in determining stability boundaries and vibration modes where convergence and summability become important considerations in the case of differential-difference equations with periodic damping terms. A particular example of a fluttering helicopter blade in slow forward flight is studied and stability boundaries shown to be displaced by up to 10% from those when the nature and extent of the rows of wakes below the rotor are neglected. The range of the parameters governing the stability are given for a specific numerical example. Application to an actual blade motion study shows reconciliation with previous experimental results and theory when the new method is applied. The importance of the effect of lagged arguments in simultaneous differential-difference equations is discussed with reference to two other examples in structural vibrations.  相似文献   

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