初始压入位置对Ni基单晶合金纳米压痕影响研究

针对Ni基单晶合金建立初始压入γ 相的γ /γ' 模型和初始压入γ'相的γ'/γ 模型, 采用分子动力学方法模拟金刚石压头压入两种模型的纳米压痕过程, 计算两种模型[001]晶向硬度. 采用中心对称参数分析两种模型(001)相界面错配位错对纳米压痕过程的影响. 结果显示: 弛豫后, 两种模型(001)相界面错配位错形式不同, 其中γ'/γ 模型(001)相界面错配位错以面角位错形式存在; 压入深度在0.930 nm 之前, 两种模型(001)相界面错配位错变化不大, 压入载荷-压入深度及硬度-压入深度曲线较符合; 压入深度在0.930 nm之后, γ'/γ 模型(001)相界面错配位错长大很多, 导致相同压入深度时γ'/γ 模型比γ /γ'模型压入载荷和硬度计算结果小; 压入深度在2.055 nm之后, γ /γ'模型(001)相界面错配位错对γ 相中位错进入γ'相有阻碍作用, 但仍有部分位错越过(001) 相界面进入γ' 相中, γ'/γ 模型(001)相界面处面角位错对γ' 相中位错进入γ 相有更明显的阻碍作用, 几乎无位错越过(001) 相界面进入γ 相中, 面角位错的强化作用更明显, 所以γ'/γ 模型比γ /γ'模型压入载荷上升速度快.     

A survey of quantum-like approaches to decision making and cognition

There has always been a steady interest in how humans make decisions amongst researchers from various fields. Based on this interest, many approaches such as rational choice theory or expected utility hypothesis have been proposed. Although these approaches provide a suitable ground for modeling the decision making process of humans, they are unable to explain the corresponding irrationalities and existing paradoxes and fallacies. Recently, a new formulation of decision theory that can correctly describe these paradoxes and possibly provide a unified and general theory of decision making has been proposed. This new formulation is founded based on the application of the mathematical structure of quantum theory to the fields of human decision making and cognition. It is shown that by applying these quantum-like models, one can better describe the uncertainty, ambiguity, emotions and risks involved in the human decision making process. Even in computational environments, an agent that follows the correct patterns of human decision making will have a better functionality in performing its role as a proxy for a real user. In this paper, we present a comprehensive survey of the researches and the corresponding recent developments. Finally, the benefits of leveraging the quantum-like modeling approaches in computational domains and the existing challenges and limitations currently facing the field are discussed.     

Dynamic output feedback fault tolerant controller design for discrete-time switched systems with actuator fault

This paper investigates the problem of dynamic output feedback fault tolerant controller design for discrete-time switched systems with actuator fault. By using reduced-order observer method and switched Lyapunov function technique, a fault estimation algorithm is achieved for the discrete-time switched system with actuator fault. Then based on the obtained online fault estimation information, a switched dynamic output feedback fault tolerant controller is employed to compensate for the effect of faults by stabilizing the closed-loop systems. Finally, an example is proposed to illustrate the obtained results.     

Quorum Sensing: Complexity in the bacterial world

We discuss the mechanisms of bacterial Quorum Sensing, the biophysical phenomenon pointing out a social behavior in bacteria, highlighting thus the very complex structure of these systems. Actually, bacterial bioluminescence is an example of a quorum sensing mediated property. We show that the distribution of the activation times of the bioluminescent emission follows the universal behavior described by the Gumbel distribution of extreme value statistics. We provide further evidence on the system size scaling of bioluminescence, showing that the relation between cell density and total number of photons radiated by bacteria is highly non-linear.     

Higher-order free vibrations of sandwich beams with a locally damaged core

The dynamical equations describing the free vibration of sandwich beams with a locally damaged core are derived using the higher-order theory approach. The nonlinear acceleration fields in the core are accounted for in the derivations, which is essential for the vibration analysis of the locally damaged sandwich beams. A local damage in the core, arbitrarily located along the length of the sandwich beam, is assumed to preclude the transition of stresses through the core between the undamaged parts of the beam. The damage is assumed to exist before the vibration starts and not to grow during oscillations. The numerical analysis based on the derived equations has been verified with the aid of the commercial finite element software ABAQUS. The numerical simulations reveal that a small local damage causes significant changes in the natural frequencies and corresponding vibration modes of the sandwich beams. An important practical consequence of the present work is that the vibration measurements can be successfully used as a nondestructive damage tool to assess local damages in sandwich beams.     

Optimal design of PZT actuators in active structural acoustic control of a cylindrical shell with a floor partition

Genetic algorithms (GAs) are employed to optimize locations of PZT actuators in an active structural acoustic control (ASAC) system comprising a cylindrical shell with an internal floor partition. The effect of PZT actuators is simulated using a bending model and an in-plane force model, respectively. The characteristics of the optimal placements of both models are discussed and compared. Numerical simulations demonstrate that for the investigated structure, the in-plane force model has a better control performance than the bending model in the low-frequency range. The underlying physics of the control results are analyzed. Considering the practical applicability of optimally designed ASAC systems, the control performance of the optimal configuration obtained at a single frequency is assessed in the low-frequency range between 100 and 500 Hz, with results showing a significant sound attenuation in the whole range of interest.     

联合极限状态下基于最大熵可靠度的易损性分析

考虑工程需求参数(EDP)的前四阶矩,提出基于最大熵可靠度理论的地震易损性分析方法.基于SAP2000建立钢筋混凝土框剪模型,选择最大层间位移角和最大层加速度衡量结构的联合性能极限状态,建立极限状态方程.不对EDP的分布进行人为假定,在不同峰值加速度(PGA)下计算两种EDP的前四阶矩,并作为约束条件,建立极限状态方程...     

On a “deterministic” explanation of the stochastic resonance phenomenon

The cantilevered carbon nanotube is a traditional model in the design of some precise nano-oscillators. The sensitivity that is denoted by the quality factor defined as the ratio of the energy stored to the energy dissipated by losses in the oscillator is an important index for the nano-oscillators. In this paper, the small mass impacting on the single-walled carbon nanotube is simplified as an impact load and the governing equation of the transverse oscillation for the nanotube is established firstly. Based on the structure-preserving idea, the generalized multi-symplectic formulations of the governing equation are constructed. The oscillation of the damping nanotube under the transverse impact load with different amplitudes is simulated after the small numerical dissipation and the good convergence of the scheme constructed is verified. From the numerical results, the effects of the induced tension and the energy dissipation are investigated. More importantly, the high precision and the feasibility of the numerical approach proposed in this paper for reproducing the energy dissipation in the carbon nanotube oscillator are illustrated, which gives a new way to investigate the properties of the carbon nanotube oscillators.