二阶系统非一致目标跟踪混合自适应迭代学习控制

针对一类含有时变和时不变参数的二阶非线性系统,利用Backstepping方法,提出了一种新的自适应迭代学习控制方法,该方法由微分-差分型自适应律和学习控制律组成,保证对非一致目标的跟踪误差的平方在一个有限区间上的积分收敛于零,克服了传统的迭代学习控制对目标轨线的限制,可以跟踪非一致目标轨线。通过构造复合能量函数,给出了闭环系统收敛的一个充分条件。仿真结果说明了该方法的可行性和有效性。     

Effect of porosity on the interface behavior of an Al2O3-aluminum composite: A molecular dynamics study

Molecular dynamics simulations are carried out to study the effect of porosity and temperature on a ductile-brittle interface under tensile and shear loadings. Traditionally the interface is characterized by a cohesive zone model (CZM) with the traction-separation law assumed or parameterized through experiments, where the experimental determination of the shape of the CZM has proven to be difficult. In this study a traction-separation law is thus obtained for an alumina-aluminum composite system by conducting molecular dynamics simulations. A statistical approach is suggested to characterize the cohesive strength in the parameterized traction-separation law via the Weibull distribution, which consequently governs the interface behavior of the composite.     

Quasi‐static crack propagation in plane and plate structures using set‐valued traction‐separation laws

We introduce a numerical technique to model set‐valued traction‐separation laws in plate bending and also plane crack propagation problems. By using of recent developments in thin (Kirchhoff–Love) shell models and the extended finite element method, a complete and accurate algorithm for the cohesive law is presented and is used to determine the crack path. The cohesive law includes softening and unloading to origin, adhesion and contact. Pure debonding and contact are obtained as particular (degenerate) cases. A smooth root‐finding algorithm (based on the trust‐region method) is adopted. A step‐driven algorithm is described with a smoothed law which can be made arbitrarily close to the exact non‐smooth law. In the examples shown the results were found to be step‐size insensitive and accurate. In addition, the method provides the crack advance law, extracted from the cohesive law and the absence of stress singularity at the tip. Copyright © 2007 John Wiley & Sons, Ltd.     

Determining the optimal maintenance action for a deteriorating repairable system

This paper develops a decision model for risk management of the deterioration of a repairable system. When a failure occurs in a deteriorating system, an optimal maintenance decision that includes the possibility of system replacement, as compared to mere deterioration reduction, should be made. There are many uncertainties associated with deterioration, however, so the decision may require a probabilistic analysis. Here, a well-known nonhomogeneous Poisson process with a power law intensity function is used to model the uncertain behavior of the deteriorating system. A Bayesian statistical approach is adopted to allow for the uncertainty of the parameters of the power law intensity function, which imposes a conjugate prior distribution of the parameters. A power law maintenance cost function and the failure cost are analyzed to determine the magnitude of failure risk reduction by minimizing the expected cost incurred from the maintenance action and future failures. A numerical example is given.     

Dynamics of moving interface in porous media for power law fluids with yield stress

In this paper the dynamic of moving interface in a porous medium for non-Newtonian fluids of power law with yield stress is investigated. The frontal advance theory, which describes the flow of two immiscible fluids separated by a moving interface, in which the displacing fluid is of power law with yield stress and the displaced one is Newtonian, has been used to illustrate the deviation from Newtonian behaviour in oil displacement mechanism. The limitations of this theory for non-Newtonian fluids have been shown and discussed. A criterion for determining the conditions under which the viscous fingering effect is eliminated and the interface movement may be in a regular manner has also been obtained. An approximate analytical solution for determining the interface position and its velocity at any time is presented.     

Instability of dilutely voided material in uniaxial tension

A continuum mechanical study is made of the deformation and damaging of a bar in uniaxial tension. Attention is paid to instability as caused by loss of equilibrium. The material is assumed to deform due to creep and time-independent plasticity. The damage is modelled with spherical voids, which are assumed to nucleate at a rate proportional to the strain rate. The voids are assumed to undergo self-similar expansion. The damage parameter ω is defined through the Rabotnov creep law, , where is determined by continuum mechanical analysis of the voided material. A damage growth law is derived. It is then used to investigate the influence of initial damage, hardening exponent and nucleation rate on the critical stress and strain.     

Effects of a nonhomogeneous gain saturation law on predicted performance of a high-gain and a low-gain laser systems

A modified Rigrod theory that uses a nonhomogeneous gain saturation law is used to model outcoupled, total, and intracavity power from a high-gain and a low-gain cw HF chemical laser with good accuracy. The homogeneous gain saturation law is found to have significant limitations when used to model total power data over a wide range of threshold gain values. The use of a nonhomogeneous gain saturation law indicates that a gain saturation law parameter of m = 1.2 models University of Illinois at Urbana-Champaign supersonic cw HF fundamental laser data more accurately than a homogeneous gain saturation law (m = 1). A completely inhomogeneous saturation law (m = 2) models University of Illinois at Urbana-Champaign supersonic HF overtone laser data more accurately than a completely homogeneous gain saturation law.     

Experimental mechanical characterization of plastic-bonded explosives

This article deals with the characterization of the static mechanical behavior of an energetic material. Due to its constituents (crystals and a polymeric binder), the behavior is complicated to model. A specific experimental protocol has been proposed in this article. It involves uniaxial tensile and compressive tests, compression under confinement and dynamic mechanical analysis. A constitutive law has been developed. The behavior is described using a Maxwell’s model, in which all the components are influenced by an isotropic damage. The first component takes into account an elasto-plastic behavior. The yield stress evolution is described using a parabolic criterion and an isotropic hardening law. The plastic flow rule is non-associated. A linear visco-elastic behavior is used for the other components. Numerical simulations show that experimental data are quite well reproduced. The last part of the article is devoted to a discussion highlighting the future improvements.     

我国传统法律文化对建设社会主义和谐社会的影响

社会更加和谐是全面建设小康社会的目标之一。社会主义和谐社会首先应是一个法治社会，建设社会主义和谐社会必须重视传统法律文化的影响。我国传统法律文化博大精深，良莠不齐，对建设社会主义和谐社会而言，既有有利之处，也有不利的地方，必须在严格区分的基础上加以继承、批判和改造。     

Two‐dimensional transonic aeroservoelastic computations in the time domain

A computational method to perform transonic aeroelastic and aeroservoelastic calculations in the time domain is presented, and used to predict stability (flutter) boundaries of 2‐D wing sections. The aerodynamic model is a cell‐centred finite‐volume unsteady Euler solver, which uses an efficient implicit time‐stepping scheme and structured moving grids. The aerodynamic equations are coupled with the structural equations of motion, which are derived from a typical wing section model. A control law is implemented within the aeroelastic solver to investigate active means of flutter suppression via control surface motion. Comparisons of open‐ and closed‐loop calculations show that the control law can successfully suppress the flutter and results in an increase of up to 19 per cent in the allowable speed index. The effect of structural non‐linearity, in the form of hinge axis backlash is also investigated. The effect is found to be strongly destabilizing, but the control law is shown to still alleviate the destabilizing effect. Copyright © 2001 John Wiley & Sons, Ltd.     

Non-local modeling of thermal shock damage in refractory materials

A non-local damage framework has been coupled with heat transport to model transient thermo-mechanical damage (in particular thermal shock) in refractory materials. The non-locality, to be dealt with to obtain an adequate problem formulation, is introduced by terms accounting for micro-structural strain gradients induced by transient temperature gradients. The parameters figuring in the evolution law for elasticity-based damage are temperature dependent. Damage due to isotropic thermal expansion has been accounted for by proposing a new evolution law. A single variable for the total damage is obtained by combining both damage mechanisms. The influence of non-locality and transient temperature gradients within non-locality is investigated in numerical examples. The phenomenological relevance of the framework is verified by modeling of experiments, which simulate thermal shock under process conditions.     

A large-time-stepping scheme for balance equations

A well-balanced, large-time-stepping method for conservation laws with source terms is presented. The numerical method is based on a local reformulation of the balance law as a conservation law with a discontinuous flux function, and the approximate solution of this equation by a front tracking method. This yields an unconditionally stable method which is particularly well suited to calculate stationary states. The viability of this approach is demonstrated by several numerical examples. KHK has been supported in part by an Outstanding Young Investigators Award from the Research Council of Norway.     

Measurement of aqueous Henry's law constants for oxygenates and aromatics found in gasolines by the static headspace method

A simple equilibrium vessel made from a large stopcock was used in conjunction with the static headspace method to measure the aqueous Henry's law constants for methyl tert-butyl ether (MTBE) and other potential oxygenates as well as certain of the aromatics found in gasoline. The present method involves using only one aqueous solution whose concentration is not necessarily known. The only quantity that must be known is the phase ratio. Plotting a series of peak areas of the analyte in the headspace after each equilibrium change against the initial peak area of the analyte found in the headspace leads to a linear relationship whose slope is dependent on the analyte's unitless Henry's law constant and the phase ratio. This new method is found to yield unitless aqueous Henry's law constants in the range from 0.02 to 0.2, which are especially applicable to the oxygenates and aromatics found in gasolines.     

Nonlinear mode III crack stress fields for materials obeying a modified Ramberg‐Osgood law

In this paper, an analytical study is carried out on the work‐hardening, elastic‐plastic stress distributions in a cracked body under antiplane shear deformation. A modified Ramberg‐Osgood law is introduced to describe the material behaviour, and stress and strain fields are derived in closed form. Compared with the conventional Ramberg‐Osgood formulation, the new law includes the effect of a new parameter, κ, which allows the transition from the ideally elastic behaviour (low stress regime) to the power law behaviour (large stress regime) to be controlled, thus providing 1 more degree of freedom to better fit the actual behaviour of engineering materials. A discussion is carried out on the features of stresses and strains close to and far away from the crack tip.     

Power law behavior in IF model with random excitatory and inhibitory rates

A new mechanism is proposed to generate power law behavior in interspike interval (ISI) distribution when a collection of neurons group together and fire together. Employing superstatistical framework, the mechanism requires a population of neurons which is characterized by randomly distributed excitatory and inhibitory rates. The distribution of these rates is characterized by independent gamma variates. The effect of randomness in the rates exhibits power law behavior in first passage time of the integrate and fire (IF) model. Extensive Monte Carlo simulation studies of the underlying stochastic differential equation (SDE) are carried out which also depict asymptotically power law behavior for ISI distribution for an ensemble of IF neurons.     

The effect on casualties of a compulsory seat belt wearing law in South Australia

A compulsory seat belt wearing law in South Australia was preceded by a rise in the belt wearing rate and was accompanied by a further substantial rise. Casualty rates per 1000 involved vehicles, reported on a property-damage criterion, showed lower rates for 1967 and later models, which had belts compulsorily fitted, both before and after the wearing law. A before and after comparison showed reductions in the serious grades of casualties and an increase in the least serious. There was a differential effect on casualty reduction in 1967 and later models, which accounted entirely for the 7.5% overall reduction in the fatality rate. These comparisons are substantially free of effects due to concurrent changes in exposure to risk of accident and the observed reductions can be attributed to the belt wearing law.     

The probability of hertzian fracture

The indentation strength of brittle solids is traditionally characterized by Auerbach's law, which predicts a linear relationship between the load required to initiate a Hertzian cone crack and the radius of a spherical indentor. This paper reviews both the energy balance and flaw statistical explanations of Auerbach's law. It is shown that Auerbach's law in the strictest sense only applies to well-abraded specimens. A novel application of Weibull statistics is presented which allows the distribution of fracture loads to be predicted for any specimen surface condition for a given indentor size. The indentation strength of a brittle solid, for both spherical and cylindrical indentors, is shown to be influenced by both its surface flaw statistics and the degree of interfacial friction. It is observed that the indentation strength of soda-lime glass is increased by a factor of about three times that expected for frictionless contact, and that for a fully bonded indentor, conical fractures cannot occur.     

Experimental and numerical study of compression after impact of sandwich structures with metallic skins

A finite element model is proposed to determine the residual print of sandwich structures with Nomex honeycomb core and metallic skins indented by a spherical indenter and to simulate its behavior when this indented structure is subjected to lateral compressive loading (known as CAI/ Compression after impact). The particularities of this model rely on representing the honeycomb with a grid of non-linear springs which its behavior law calibrated from uniform compression test. This simple model, after integrating the cycle behavior law of honeycomb, allows predicting the geometry of residual print with a good precision. This model is then developed to propose a complete computation from indentation, residual print geometry to lateral compressive loading after indentation (CAI). This model also allows predicting numerically the residual strength of structure in CAI and the elliptical evolution of residual print geometry during CAI loading. A good correlation with test results is obtained except for the very small residual print depth.     

Three-dimensional protein shape rendering in magnetized solution with Lambert-Beer law

When monochromatic light passes through a homogeneous absorbing medium, the absorbance is proportional to the growth of concentration and thickness of the medium, which is the Lambert-Beer law. The shade selection of protein solution magnetized for a certain time from different angles makes different absorbance, which does not meet the Lambert-Beer law. Accordingly, we derive that the absorbance A is not only proportional to the concentration and thickness of the medium but also proportional to the light area S(S) of a certain direction. For the same protein solution, we can obtain the absorbance A of six directions and thus get six values for S(S) the relative ratio of which will inevitably reveal plentiful information of the protein shape. The conformation of the protein can be easily drawn out by software (MATLAB 7.0.1). We have drawn out the molecular shape of lysozyme and bovine serum albumin. In brief, we have developed the Lambert-Beer law A=K·C·b·S(s) and a new method of exploring protein spatial structure.