Dynamics modelling of a flexible hub-beam system with a tip mass

This paper presents a finite-element model for a flexible hub-beam system with a tip mass. Both viscous damping and air drag force are introduced into this model. The complete coupling between the system rigid and flexible degrees of freedom is allowed since the start of the formulation and developing the system kinematic variables. Based on deformation theory and geometric constraints, a second order approximation for the displacement field is proposed and the dynamic stiffening is accounted for. Hamilton's principle is utilized in deriving the equations of motion. The corresponding dynamics models of the tip mass and damping forces are developed in a consistent manner through formulating their energy expressions and applying Hamilton's principle. The finite element method is employed for spatial discretization due to its versatility, high accuracy and convergence. Numerical simulations show that the second order term in deformation field can have significant effect on dynamics behavior of flexible multibody systems. It is also shown that the traditional linear model cannot account for dynamic stiffening and may lead to erroneous result in some high-speed systems because the deformation field commonly used in structural dynamics is straight employed in this model. In contrast, the developed model (CCM) based on the second order deformation field can predict valid results. The effects of tip mass and damping on dynamics behavior of the hub-beam system are also discussed.     

Dynamics of an extremely short pulse in a Stark medium

Effects of propagation of an extremely short (of one or several oscillation periods) electromagnetic pulse in a medium whose resonance transition is characterized by diagonal as well as nondiagonal matrix elements of the dipole moment operator have been studied numerically. The Maxwell-Bloch system of equations is employed without using the approximation of slowly varying envelopes. An analog of the McCall and Hahn area theorem is discussed as applied to the division of the initial extremely short pulse into subpulses. The solution is obtained in the form of a solitary stable bipolar signal with a nonzero pulse area (nonzero breather).     

Dynamics of periodic structures interacting with an enclosed fluid medium

A method is developed for predicting the natural modes of periodic structures coupled with an enclosed fluid medium. In this method, the structure and the fluid medium of the basic periodic unit are first modeled using the Finite Element Method (FEM). Periodic Structures (PS) theory is then applied to the dynamic matrices obtained from the finite element program, to account for the periodicity of the structure. By using the combined FEM-PS method, natural modes of the entire coupled structure-fluid system can be computed from the resulting matrix difference equation. It is shown that significant cost saving can be achieved, both in terms of computer time and memory, by using the proposed FEM-PS method. This method can be particularly effective early in design, for identifying design parameters that are important for reducing the structure-fluid response.     

The inertial mass tensor of a polaron in an isotropic medium

Owing to a funadmentally erroneous approach to calculations of the effective polaron mass (calculations that use a model without spatial dispersion of the lattice polarizability), the polaron inertial mass has never before been distinguished from the mass as a measure of kinetic energy. In this paper we derive an expression for the tensor of the inertial mass of a large polaron. The tensor is found to be fully determined by two components: the longitudinal component, corresponding to the case where the force acting on the polaron is parallel to the polaron velocity, and the transverse component, corresponding to the case where the acceleration is perpendicular to the polaron velocity. The components of the polaron inertial mass tensor depend quasirelativistically on the polaron velocity due to the quasirelativistic compression of the polarization field in the direction of motion, which constitutes the effect of spatial dispersion of the lattice polarizability. We derive a formula that approximates the dependence of the components of the polaron mass tensor on all the parameters: the frequency and dispersion of the phonons, the polaron velocity, and the effective dielectric constant. Zh. éksp. Teor. Fiz. 115, 180–186 (January 1999)     

The effect of dissipation on the resistive admittance of an elastic medium

The effect of dissipation on the real part of the admittance of an elastic half-space is typically thought to be unimportant if the loss factor ζ of the elastic medium is small. However, dissipation induces losses in the near field of the source and, provided the size of the source is small enough, this phenomenon can be more important than elastic wave radiation. Such losses give rise to a fundamental limit in the quality factor of an oscillator attached to a substrate. Near field losses associated with strains in the elastic substrate can actually be larger than intrinsic losses in the oscillator itself if the internal friction of the substrate is larger than the internal friction of the oscillator. For a uniform stress applied to a disk of radius a, a monopole source, such phenomena become significant for k(L)a<ζ, while for higher order multipole sources of order l, near field losses are important for (k(L)a)(l+1)<ζ, a far less restrictive constraint.     

Dynamics of solitons in a three-level medium with linear birefringence

The dynamics of ultrashort pulses in a three-level or degenerate two-level medium is studied in the framework of integrable systems of the Maxwell-Bloch equations for pulses with a duration much longer than or comparable with the inverse transition frequency, with allowance made for linear birefringence. Using soliton-type solutions, we study the effect of birefringence on soliton conversion for different initial populations of the levels.     

Dynamics of mass transfer caused by the photoinduced spatially inhomogeneous modulation of mobility in a multicomponent medium

The reasons behind the three-dimensional mass transfer of the inert components of a mixture in which photoinduced spatially inhomogeneous polymerization takes place are discussed. Such a mass transfer is responsible for the laser-induced formation of controllable diffraction gratings in polymer composites containing liquid crystals [R. L. Sutherland, V. P. Tondiglia, L. V. Natarajan, and T. J. Bunning, Chem. Mater. 5, 1533 (1993); R. L. Sutherland, V. P. Tondiglia, and L. V. Natarajan, Appl. Phys. Lett. 64, 1074 (1994); R. L. Sutherland, V. P. Tondiglia, L. V. Natarajan, et al., J. Nonlinear Opt. Phys. Mater. 5, 89 (1996); R. Caputo, A. V. Sukhov, and C. Umeton, Mol. Mater. 12, 192 (1999)]. The semiphenomenological model proposed in this work is based on the assumption that mass transfer results from conventional Fickian diffusion which, however, does not occur over the entire volume of the sample, but only in regions free from clusters of long polymer chains. It is shown that such a “restriction of the active volume” is responsible for the conventional diffusion of inert components of liquid crystals as well as reagents and low-molecular products (short chains), in spite of the initial spatial homogeneity of concentrations in the sample. The qualitative predictions of the model coincide with the experimental results [R. Caputo, A. V. Sukhov, and C. Umeton, Mol. Mater. 12, 192 (1999)].     

Role of an oxide interface in a resistive switch

In the present era of data-driven architectures like 5G, Internet of things (IoT), Artificial Intelligence (AI), etc, the requirement of fast-switchable memory storage is more than ever. Oxide resistive switches are considered to be a primary choice in the non-volatile memory design. In this work, we have engineered the conventional metal-insulator-metal (MIM) structure of an oxide memristor (Ag/ZnO/ITO) by inducing an additional oxide layer La_0.7Sr_0.3MnO₃ (LSMO) at the interface between the active layer (ZnO) and Ag electrode. The presence of LSMO acts as a reservoir for the oxygen vacancies, easing the conducting filament formation process in ZnO, thereby enabling drastic improvement of the switching performance and offering reliable endurance over multiple switching cycles. First-principles-based calculations suggested the role of oxygen vacancies in controlling the electronic state of ZnO and formation of vacancies in the resistive switching process, which is in agreement with the experimental observation. The current results pave ways for improving the switching performance of resistive memory circuits through simple structural engineering incorporation, which lies at the heart of oxide electronics.     

Dynamics of an elastic L-shaped ring coupled to an internal frame

Analyzed is the dynamics of an elastic L-shaped ring coupled to an elastic frame joined at discrete locations of the ring perimeter. The approximate ring model is evaluated adopting a two-dimensional model of a short shell joined to a narrow annular disk along one of its boundaries thus forming the L-shaped cross-section. Coupling the ring to an internal frame is accomplished by segmenting the ring. The frame impedance matrix relating forces and displacements at terminations is then applied at junctions of ring segments corresponding to these terminations.     

Total internal reflection at a boundary between vacuum and an optical medium with quasi-zero refractive index

It is shown that, on a surface of optical transparency of a medium with quasi-zero refractive index, surface optical waves traveling along the surface can be excited for different angles of incidence of external radiation. Expressions for the amplitudes of nonspecular reflection and transmission of light waves at an inhomogeneous boundary between two media are derived. Using these expressions, the boundary reflectance and transmittance for different angles of incidence and refraction can be calculated.     

非对称耦合两层可激发介质中的螺旋波动力学

本文采用Bär-Eiswirth模型研究了两层可激发介质中螺旋波的动力学, 两层介质采用抑制和兴奋性非对称耦合. 数值模拟结果表明: 兴奋性非对称耦合可以促进两个不同频率的螺旋波锁频, 即使初始频率相差大, 两螺旋波也能实现锁频, 这种耦合使两个螺旋波具有最强的锁频能力; 当两层介质采用抑制性非对称耦合时, 只有当两个初始螺旋波的频率差比较小才能实现锁频, 而且比一般扩散耦合的锁频范围窄, 两螺旋波锁频能力达到最低水平; 当耦合强度和控制参数适当选取时, 抑制性和兴奋性非对称耦合既可以使其中一层介质维持螺旋波态, 使另一层介质中的螺旋波演化到静息态或低频靶波态, 也可以使两层介质中的螺旋波都漫游, 或都转变成靶波, 最后这两个靶波要么消失, 要么转变成平面波状的振荡斑图, 而且两层介质振荡是反相的, 此外在模拟中还观察到两螺旋波局部间歇锁频现象, 这些结果有助于人们理解在心脏系统中出现的复杂现象.     

Dynamics of optical pulses in a dispersive chiral medium

The dynamics of frequency-modulated pulses in an isotropic nonreciprocal chiral medium is studied. It is shown that the discrepancy between the group velocities and carrier frequencies of the circular components of the pulse causes it to split up both along the fiber and in the spectral domain. The strong dependence of the material parameters on the pulse frequency may lead to the asymmetric dynamics of the electric and magnetic fields of the pulse in different frequency intervals. For both components of the wave field, envelopes moving with a supraluminal speed may arise.     

Dynamics analysis in a tumor-immune system with chemotherapy

An ordinary differential equation (ODE) model of tumor growth with the effect of tumor-immune interaction and chemotherapeutic drug is presented and studied. By analyzing the existence and stability of equilibrium points, the dynamic behavior of the system is discussed elaborately. The chaotic dynamics can be obtained in our model by equilibria analysis, which show the existence of chaos by calculating the Lyapunov exponents and the Lyapunov dimension of the system. Moreover, the action of the infusion rate of the chemotherapeutic drug on the resulting dynamics is investigated, which suggests that the application of chemotherapeutic drug can effectively control tumor growth. However, in the case of high-dose chemotherapeutic drug, chemotherapy-induced effector immune cells damage seriously, which may cause treatment failure.     

Dynamics of Wehrl entropy of a degenerate two-photon process with a nonlinear medium

This paper describes the dynamics of the Wehrl entropy and Wehrl phase distribution of a degenerate two-photon of a single mode interacting with a two-level system with a nonlinear medium. A general analytic expression for the Husimi Q function is obtained. The influence of various parameters on the Wehrl entropy and Wehrl phase distribution are explored. It is shown that features of the Wehrl entropy and Wehrl phase distribution were influenced significantly by changing the nonlinear medium, Stark shift and the detuning. For certain amounts of the nonlinear effect, superstructure of atomic Rabi oscillation and changes of the quasi-period of the entropy evolution are observed.     

Magnetoresistive Fe19Ni81/Tb-Co medium with an internal magnetic bias

The magnetization reversal and magnetoresistance of two-layer exchange-coupled Fe19Ni81/Tb-Co films are studied. Amorphous Tb _x Co_{100 − x} layers with 30 < x < 35 are found to have a uniaxial magnetic anisotropy and a rather high coercive force, which ensures magnetic biasing of the adjacent permalloy layers. In addition, the permalloy layers subjected to selective annealing exhibit a significant anisotropic magnetoresistance and a small magnetic hysteresis. These properties make it possible to consider the developed film structure as an effective magnetoresistive medium. This structure is used to form magnetic sensor samples that have an odd transfer function in the absence of external magnetic biasing.     

Dynamics of formation of superposition states of light in an absorbing medium

The process of simultaneous absorption of two photons in a medium in the presence of a weak one-photon absorption is considered. The medium is perturbed from outside in a two-photon parametric manner. The formation of a stationary even-parity superposition state of light in such a medium is shown to be possible in the region of small amplitudes of the state (weak perturbations of the system). This is associated with the fact that, in this region of interaction, the field spends considerably more time in the even superposition state than in the odd state. It is shown that a nonstationary superposition state of light with a large amplitude of the state (large photon numbers) can be obtained for interaction times that are longer than the most probable time of the first two-photon quantum jump of the field state and shorter than the most probable time of the first one-photon jump of the field state. The dynamics of formation of the quantum entropy of the field is studied by numerical simulation of quantum trajectories of the system. The Wigner functions of the state of the field are calculated. Analytical results are obtained for the density matrix of the stationary state of the system in the presence of a weak one-photon absorption.     

Vibrating rectangular plate with a free edge: The effect of a concentrated mass and an internal support

It is shown that use of a polynomial coordinate function and the Rayleigh-Schmidt method constitute a convenient approach for determining the fundamental frequency of vibration of the title system. Experimental results are presented for the case where three edges are rigidly clamped; and it is shown that the values are in good engineering agreement with the analytical predictions.