A new car-following model considering driver’s characteristics and traffic jerk

Nonlinear Dynamics - In this paper, we propose an extension of the optimal velocity car-following model to consider explicitly the timid and aggressive driving behavior as well as the traffic jerk....     

Machine learning of frustrated classical spin models (II): Kernel principal component analysis

In this work, we apply a principal component analysis (PCA) method with a kernel trick to study the classification of phases and phase transitions in classical XY models of frustrated lattices. Compared to our previous work with the linear PCA method, the kernel PCA can capture nonlinear functions. In this case, the Z₂ chiral order of the classical spins in these lattices is indeed a nonlinear function of the input spin configurations. In addition to the principal component revealed by the linear PCA, the kernel PCA can find two more principal components using the data generated by Monte Carlo simulation for various temperatures as the input. One of them is related to the strength of the U(1) order parameter, and the other directly manifests the chiral order parameter that characterizes the Z₂ symmetry breaking. For a temperature-resolved study, the temperature dependence of the principal eigenvalue associated with the Z₂ symmetry breaking clearly shows second-order phase transition behavior.     

Interaction of strong converging shock wave with SF6gas bubble

Interaction of a strong converging shock wave with an SF6 gas bubble is studied, focusing on the effects of shock intensity and shock shape on interface evolution. Experimentally, the converging shock wave is generated by shock dynamics theory and the gas bubble is created by soap film technique. The post-shock flow field is captured by a schlieren photography combined with a high-speed video camera. Besides, a three-dimensional program is adopted to provide more details of flow field. After the strong converging shock wave impact, a wide and pronged outward jet, which differs from that in planar shock or weak converging shock condition, is derived from the downstream interface pole. This specific phenomenon is considered to be closely associated with shock intensity and shock curvature. Disturbed by the gas bubble, the converging shocks approaching the convergence center have polygonal shapes, and the relationship between shock intensity and shock radius verifies the applicability of polygonal converging shock theory. Subsequently, the motion of upstream point is discussed, and a modified nonlinear theory considering rarefaction wave and high amplitude effects is proposed. In addition, the effects of shock shape on interface morphology and interface scales are elucidated. These results indicate that the shape as well as shock strength plays an important role in interface evolution.     

桁架结构重分析的一种新方法

本文依据有限元的原理，建立了杆单元基本位移的计算方法，给出了在桁架结构拓扑优化重分析中的新方法，该方法将优化计算的结构设计变量与性态参数之间的关系以显式的形式表达出来，故在结构拓扑优化过程中，不需要再反复地用有限元方法对新产生的拓扑结构进行重分析，节省了大量的计算时间，同时，由于采用了相对基础结构的基本位移修正的方法，不仅减少计算的累积误差，也避免了由于可能出现的几何可变情况而使拓扑优化计算过程中     

Magnetoelectric gyrator

The magnetoelectric (ME) gyrator is a device that can convert not only active and reactive impedances, but also current and voltage. In this work, we have carried out research on three gyrators structures based on Terfenol-D/PZT/Terfenol-D, Metglas/PZT/Metglas and Nickel/PZT/Nickel. Detailed investigations of the ME gyrator based on these trilayer composite structures have been performed at the electromechanical resonance frequency.     

First-principles study of the switching characteristics of the 15,16-dinitrile DDP/CPD-based optical molecular switch with carbon nanotube electrodes

We have studied the switching characteristics of an optical molecular switch based on the 15,16-dinitrile dihydropyrene/cyclophanediene (DDP/CPD) molecule with two single-walled carbon nanotube (SWCNT) electrodes using first-principles transport calculations. It is shown that the DDP shows an overall higher conductance than the CPD at low bias which is independently of the SWCNT chirality. Meantime, the conductance of the molecular switch can be tuned by the chirality of the SWCNT.     

Heterogeneous oxidization of graphene nanosheets damages membrane

Graphene-based materials exhibit unique properties that have been sought to utilize for various potential applications. Many studies suggest that graphene-based materials can be cytotoxic, which may be attributed to destructive effects on cell membranes.However, there still are conflicting results regarding interactions between graphene-based materials and lipid membranes. Here,through cryo-electron microscopy(Cryo-EM) and dye-leakage experiments along with in silico methods, we found that graphene oxide nanosheets induce significant membrane damage, while the effect of pristine graphene is negligible. We revealed the importance of heterogeneous oxidization of graphene-based nanosheets in damaging vesicle membranes. Moreover, that not only the oxidization degree but also the oxidization loci and membrane tension play important roles in the cytotoxicity of the graphene-based nanosheets.     

Coal Permeability Evolution and Gas Migration Under Non-equilibrium State

Laboratory test of coal permeability is generally conducted under the condition of gas adsorption equilibrium, and the results contribute to an understanding of gas migration in the original coal seams. However, gas flow under the state of non-equilibrium, accompanied by gas adsorption and desorption, is more common in coalbed methane (CBM) recovery and \(\hbox {CO}_{2}\) geological sequestration sites. Therefore, research on gas migration under the non-equilibrium state has a greater significance with regard to CBM recovery and \(\hbox {CO}_{2}\) geological sequestration. However, most permeability models, in which only one gas pressure has been considered, cannot be used to study gas flow under the non-equilibrium state. In this study, a new mathematical model, which includes both fracture gas pressure and matrix gas pressure, and couples the gas flow with the coal deformation, has been developed and verified. With the developed model, the spatial and temporal evolution of gas flow field during gas adsorption and desorption phases has been explored. The results show that the gas pressures present nonlinear distributions in the coal core, and the matrix gas pressure is generally lower than the fracture gas pressure during adsorption, but higher than the fracture gas pressure during desorption. For gas flow during adsorption, the main factor controlling permeability varies at different points. At the initial time, the permeability is dominated by the effective stress, and at the later time, the permeability in the part close to the gas inlet is mainly controlled by the matrix swelling, whereas that in the part close to the gas outlet is still dominated by the effective stress. For gas flow during desorption, from the gas inlet to the gas outlet, the permeability deceases at the initial time, and when the time is greater than 10,000 s, it shows a decreasing and then an increasing trend. The reason is that at the initial time, the permeability is dominated by the increased effective stress caused by the sharp decrease of the fracture gas pressure. Later, desorption of the adsorbed gas results in matrix shrinkage, which further leads to an increase of the permeability.     

Stability analysis of the whirl motion of a breathing cracked rotor with asymmetric rotational damping

The stability of the whirl motion of a breathing cracked rotor with the distinction of stationary damping and the asymmetric rotational damping is studied. By Lagrange’s principal, the motion equations are formed in rotational frame such that the multi-asymmetric system, i.e., asymmetric rotational damping and asymmetric time-periodic varying stiffness, is simplified to be a system with anisotropic damping and anisotropic time-periodical varying stiffness in rotational operation. Based on the multiple scales solution of the simplified whirling equation in moving frame, root locus method for stability analysis is proposed. Different from the former stability estimation method, the corresponding Campbell diagram, decay rate plot, and root locus plot of the fifth-order approach are derived to prove the effects of both crack depth and damping effects. The numerical results of the instabilizing effects of the crack depth are well agreeing with the previous studies. In addition, the destabilizing influence of the rotational damping on the breathing cracked rotor is presented for the first time.