公共投资对经济增长作用的滞延性研究——以公路建设为案例

为有效揭示公共投资对经济增长作用的滞延性,本文采用基于面板数据的向量自回归方法,建立三阶滞后PVAR模型,对中国31个省级单位1994～2004年的公路投资建设与经济增长关系进行了实证分析。结果表明,公路投资与经济增长之间的作用具有显著的滞延性;同时我们发现,二者之间的作用机制是复杂的、多重的和多样的,两者间的基本关系是"非对称互动关系"。在对二者滞延性进行深入分析的基础上,本文给出了二者之间的作用机制流程图,并对政府如何更好地进行公共投资决策提出了建议。

结构滞回阻尼比计算方法的改进研究

目前计算结构滞回阻尼比常用的方法是能量比法,该方法在给定滞回模型的基础上采用滞回耗能与结构总弹性应变能的比值求得结构滞回阻尼比,但该方法是建立在简谐激励下结构稳态响应的基础之上,对于真实地震下结构滞回阻尼比计算并不完全适用。考虑到这一不足,本文提出一种新的迭代计算结构滞回阻尼比的方法,在Carlos提出的结构滞回阻尼比计算方法的基础上,考虑地震激励频率对阻尼比的影响,通过改进Carlos迭代计算方法,得到了考虑地震激励频率影响的滞回阻尼比计算公式,通过该公式分析得出了不同延性系数和周期比对滞回阻尼比的影响规律,结果表明不同延性系数的结构滞回阻尼比会随着周期比的增大先增大再减小。本研究可为结构进入非线性状态后减震结构总体阻尼比的计算提供理论依据。

低周反复荷载作用下矩形钢管混凝土柱与钢梁连接节点的受力性能

本文进行了2种矩形钢管混凝土柱与钢梁连接节点———翼缘全螺栓(BFP)连接节点与外加强环(WFP-BW)连接节点在柱端低周反复荷载作用下的抗震性能试验,分析比较了这2类节点与焊接翼缘板(WFP)连接节点在不同轴压比下的滞回性能、强度与刚度退化、延性比与耗能比、破坏机理与破坏特征,得出了一些有参考价值的结论。

Seismic performance of double- skin steel- concrete composite box piers: Part Ⅰ——Bidirectional quasi-static testing

To study the seismic performance of double-skin steelconcrete composite box（ DSCB） piers, a total of 11 DSCB pier specimens were tested under bidirectional cyclic loading. The effects of the loading pattern, the steel plate thickness, the axial load ratio, the slenderness ratio and the aspect ratio were taken into consideration. The damage evolution process and failure modes of the tested specimens are presented in detail. Test results are also discussed in terms of the hysteretic curve, skeleton curve, ductility and energy dissipation capacity of DSCB pier specimens. It can be concluded that the hysteretic performance of DSCB piers in one direction is affected and weakened by the cyclic loading in the other direction. DSCB piers under bidirectional cyclic loading exhibit good performance in terms of load carrying capacity, ductility, and energy dissipation capacity. Overall, DSCB piers can meet the basic aseismic requirements. The research results can be taken as a reference for using DSCB piers as high piers in bridges in strong earthquakeprone areas.

Seismic behaviors of steel reinforced ECC/RC composite columns under low-cyclic loading

To improve the seismic performance of columns, engineered cementitious composite （ECC） is introduced to partially substitute concrete at the base of the columns to form ECC,/reinforced concrete （ RC） composite columns. The mechanical behaviors of the ECC/RC composite columns are numerically studied under low-cyclic loading with the finite element analysis softwareof MSC. MARC. It is found that the ECC/RC composite columns can significantly enhance the load capacity, the ductility ad energy dissipation of columns. Then, the effects of the height of the ECC, the axial compression ratio and the longitudinal reinforcement ratio on the seismic behaviors of the composite columns are parametrically studied. The results show that the ECC/RC composite column with a height of the ECC layer of 0. Sh（h is the height to the cross-section） can achieve similar seismic performance of a full ECC column. The peak load of the composite column increases significantly while the ductility decreases with the increase of the axial compression ratio. Increasing the longitudinal reinforcement ratio within a certain range can improve the ductility and energy dissipation capacity and almost has no effect on load capacity. The aalysis results ae instructive and valuable for reference in designing ECC structures.

Iterative identification of discrete-time output-error model with time delay

The problem of discrete-time model identification of industrial processes with time delay was investigated.An iterative and separable method is proposed to solve this problem,that is,the rational transfer function model parameters and time delay are alternately fixed to estimate each other.The instrumental variable technique is applied to guarantee consistent estimation against measurement noise.A noteworthy merit of the proposed method is that it can handle fractional time delay estimation,compared to existing methods commonly assuming that the time delay is an integer multiple of the sampling interval.The identifiability analysis for time delay is addressed and correspondingly,some guidelines are provided for practical implementation of the proposed method.Numerical and experimental examples are presented to illustrate the effectiveness of the proposed method.

Response of harmonically and stochastically excited strongly nonlinear oscillators with delayed feedback bang-bang control

We studied the response of harmonically and stochastically excited strongly nonlinear oscillators with delayed feedback bang-bang control using the stochastic averaging method. First, the time-delayed feedback bang-bang control force is expressed approximately in terms of the system state variables without time delay. Then the averaged It6 stochastic differential equations for the system are derived using the stochastic averaging method. Finally, the response of the system is obtained by solving the Fokker-Plank-Kolmogorov （FPK） equation associated with the averaged lt6 equations. A Duffing oscillator with time-delayed feedback bang-bang control under combined harmonic and white noise excitations is taken as an example to illus- trate the proposed method. The analytical results are confirmed by digital simulation. We found that the time delay in feedback bang-bang control will deteriorate the control effectiveness and cause bifurcation of stochastic jump of Duffing oscillator.

L_2 DISTURBANCE ATTENUATION FOR A CLASS OF TIME-DELAY HAMILTONIAN SYSTEMS

This paper considers the problem of L2-disturbance attenuation for a class of time-delay port-controlled Hamiltonian systems. A v-dissipative inequality is established by using a proper control law and a storage function. Then based on the Razumikhin stability theorem, a sufficient condition is proposed for the asymptotically stability of the closed-loop system. Finally, the authors investigate the case that there are time-invariant uncertainties belonging to some convex bounded polytypic domain and an L2 disturbance attenuation control law is proposed. Study of illustrative example with simulation shows that the presented method in this paper works very well in the disturbance attenuation of time-delay Hamiltonian systems.

RATIO-DEPENDENT PREDATOR-PREY MODEL WITH STAGE STRUCTURE AND TIME DELAY

Ratio-dependent predator prey models are favored by many animal ecologists recently as more suitable ones for predator-prey interactions where predation involves searching process. In this paper, a ratio-dependent predator prey model with stage structure and time delay for prey is proposed and analyzed. In this model, we only consider the stage structure of immature and mature prey species and not consider the stage structure of predator species. We assume that the predator only feed on the mature prey and the time for prey from birth to maturity represented by a constant time delay. At first, we investigate the permanence and existence of the proposed model and sufficient conditions are derived. Then the global stability of the nonnegative equilibria are derived. We also get the sufficient criteria for stability switch of the positive equilibrium. Finally, some numerical simulations are carried out for supporting the analytic results.

Delay-induced firing behavior and transitions in adaptive neuronal networks with two types of synapses

In this paper, we study delay-induced firing behavior and transitions in adaptive Newman-Watts networks of thermosensitive neurons with electrical or chemical synapses. It is found that electrical and chemical synapse time delay-induced firing behavior and transitions differ significantly. In the case of electrical synapses, the bursts for a fixed delay involve equal number of spikes in each burst, and for certain time delays the firing can be inhibited. However, in the case of chemical synapses the bursts for a fixed delay involve different numbers of spikes in each burst, and no firing inhibition is observed. It is also shown that larger growth rates of adaptive coupling strength or larger network randomness can enhance the synchronization of bursting in the case of electrical synapses but reduce it in the case of chemical synapses. These results show that electrical and chemical synapses have different effects on delay-induced firing behavior and dynamical evolution. Compared to electrical synapses, chemical synapses might be more beneficial to the generation of firing and abundant firing transitions in adaptive and delayed neuronal networks. These findings can help to better understand different firing behaviors in neuronal networks with electrical and chemical synapses.

ON UNIFORM ASYMPTOTIC STABILITY OF INFINITE DELAY DIFFERENCE EQUATIONS

For the infinite delay difference equations of the general form, two new uniform asymptotic stability criteria are established in terms of the discrete Liapunov functionals.

MODELING GENETIC REGULATORY NETWORKS:A DELAY DISCRETE DYNAMICAL MODEL APPROACH

Modeling genetic regulatory networks is an important research topic in genomic research and computationM systems biology. This paper considers the problem of constructing a genetic regula- tory network （GRN） using the discrete dynamic system （DDS） model approach. Although considerable research has been devoted to building GRNs, many of the works did not consider the time-delay effect. Here, the authors propose a time-delay DDS model composed of linear difference equations to represent temporal interactions among significantly expressed genes. The authors also introduce interpolation scheme and re-sampling method for equalizing the non-uniformity of sampling time points. Statistical significance plays an active role in obtaining the optimal interaction matrix of GRNs. The constructed genetic network using linear multiple regression matches with the original data very well. Simulation results are given to demonstrate the effectiveness of the proposed method and model.

DELAY DIFFERENTIAL EQUATIONS UNDER NONLINEAR IMPULSIVE CONTROL AND APPLICATIONS TO NEURAL NETWORK MODELS

In this paper, a class of delay differential equations with nonlinear impulsive control is discussed. Based on the nonsmooth analysis, criteria of stability are obtained for delay differential equations with nonlinear impulses control under certain conditions. These criteria can be applied to some neural network models. At the end of the paper, two examples are provided to illustrate the feasibility and effectiveness of the proposed results.