Necessary and sufficient conditions for parameter insensitive disturbance-rejection problems with dynamic output feedback

Email: otsuka{at}j.dendai.ac.jp Received on November 11, 2005; Accepted on December 16, 2006 In this paper, necessary and sufficient conditions for the parameterinsensitive disturbance-rejection problem with dynamic outputfeedback which was studied in Otsuka (1999) to be solvable aregiven for the structured uncertain linear systems. Further,necessary and sufficient conditions for the solvability of theproblems with static output feedback and state feedback arealso studied as special cases. The obtained results containsome extensions of the previous results to the structured uncertainlinear systems.     

Error propagation model for microscopic magnetic resonance elastography shear-wave images

Microscopic magnetic resonance elastography is a high-resolution method for visualizing shear waves and assessing the biomechanical viscoelastic properties of small biological samples. In this work, we used error propagation to develop a simple analytical model that relates the signal-to-noise ratio of MR magnitude images to the variance in shear-wave maps collected using gradient-echo and spin-echo phase-contrast pulse sequences. Our model predicts results for shear-wave images in phantoms, which match the experimentally observed phase variance within 8%. This model can be used to optimize MR pulse sequences for elastography studies, as well as other phase-difference techniques in MRI.     

Induced explode-decay dromions in the (2 + 1) dimensional nonisospectral nonlinear Schrödinger (NLS) equation

In this paper, we have identified a novel method of inducing localized solutions in the (2+1) dimensional nonisospectral nonlinear Schr?dinger (NLS) equation by utilising the freedom in the system. The new class of localized solutions includes induced dromions, lump dromions, dipole dromions etc. The amplitude of the localized solutions generated is found to explode or decay with time. We have also brought out the interaction of induced dromions.     

空间管路振动频率计算的精确传递矩阵法

考虑了流体定常压力和流速，建立了空间管系振动及声传播的传递矩阵法。该方法可计算空间管系的频率、模态及动力响应。用该方法对典型耐压管路频率计算与解析解对比表明该方法是正确的。     

Hierarchical Nacre Mimetics with Synergistic Mechanical Properties by Control of Molecular Interactions in Self‐Healing Polymers

Designing the reversible interactions of biopolymers remains a grand challenge for an integral mimicry of mechanically superior biological composites. Yet, they are the key to synergistic combinations of stiffness and toughness by providing sacrificial bonds with hidden length scales. To address this challenge, dynamic polymers were designed with low glass‐transition temperature T_g and bonded by quadruple hydrogen‐bonding motifs, and subsequently assembled with high‐aspect‐ratio synthetic nanoclays to generate nacre‐mimetic films. The high dynamics and self‐healing of the polymers render transparent films with a near‐perfectly aligned structure. Varying the polymer composition allows molecular control over the mechanical properties up to very stiff and very strong films (E≈45 GPa, σ_UTS≈270 MPa). Stable crack propagation and multiple toughening mechanisms occur in situations of balanced dynamics, enabling synergistic combinations of stiffness and toughness. Excellent gas barrier properties complement the multifunctional property profile.     

Propagation of chaos and conditional McKean-Vlasov SDEs with regime-switching

We investigate a particle system with mean field interaction living in a random environment characterized by a regime-switching process. The switching process is allowed to be dependent on the particle system. The well-posedness and various properties of the limit conditional McKean-Vlasov SDEs are studied, and the conditional propagation of chaos is established with explicit estimate of the convergence rate.     

浅海内孤立波动态传播过程中声波模态强度起伏规律

内孤立波是一种常见于浅海海域的非线性内波,具有振幅大、周期短和流速强等特点,它通过扰动水体中的温盐分布使声速剖面产生明显的距离依赖性,进而影响水下声传播特性.内波自生成后通常以1 m/s量级的速度传播,运动的内波使声传播路径上的声波模态能量在空间和时间上剧烈起伏.本文定义模态强度为模态系数模值(模态幅度)的平方,并用其衡量各阶模态所含声能量的大小.文中基于耦合简正波理论,推导了内波运动时声波模态强度起伏的表达式,将模态强度表征为振荡项和趋势项的线性叠加.以往的工作大多局限于单独从时域或频域研究内波运动时声波模态强度的时变规律,本文则结合短时傅里叶变换在时频平面上揭示了模态强度的起伏机理.理论推导和数值仿真均表明内孤立波使各阶声波模态之间发生能量交换,即模态耦合.内波的动态传播进一步引起模态干涉,这种干涉效应表现为模态强度中的振荡项并使模态强度随时间快速起伏.受模态剥离效应(不同阶模态之间衰减系数的差异)的影响,趋势项的幅度随时间不断变化,进而对模态干涉引起的振荡叠加了时变的偏置.模态强度的整体走势和振荡项中各频率分量振幅的时变特征均与模态衰减密切相关.同时,本文使用深度积分声强作为总接...     

Interplay between polarization rotation and crack propagation in PMN-PT relaxor single crystals

Investigations on the interconnection between the polarization rotation and crack propagation are performed for [110]-oriented 74Pb(Mg_1/3Nb_2/3)O₃-26PbTiO₃ relaxor ferroelectric single crystal under electric loadings along [001] direction. The crystal is of predominantly monoclinic M_A phase with scatter distributed rhombohedral (R) phase under a moderate poling field of 900 V/mm in [001] direction. With magnitude of 800 V/mm, a through thickness crack is initiated near the electrode by electric cycling. Static electric loadings is then imposed to the single crystal. As the applied static electric field increases, domain switching in the monoclinic M_A phase and phase transition from M_A to R phase occur near the crack. The results indicate that the crack features a conducting one. Whether domain switching or phase transition occurs depends on the intensity of the electric field component that is perpendicular to the applied electric field.     

Ignition and transient dynamics of sub-limit premixed flames in microchannels

We examine, via two-dimensional numerical simulation of a model system, some unsteady transient ignition scenarios and sustained oscillatory combustion modes that can occur in a single-pass, conductive channel, premixed microburner. These issues are relevant to the problem of ignition, evolution to stable combustion and the operational modes of microcombustors. First, we describe an unsteady ignition sequence that may occur when a single-pass microburner with initially cold walls has its exit walls heated and maintained at a fixed temperature. In particular, we demonstrate that as the heat from the exit walls propagates down the microburner walls, a reaction wave is driven rapidly down the channel towards the inlet via a sequence of oscillatory ignition and quenching transients. This scenario has been observed experimentally during the ignition of a single-pass microburner. Secondly, we show how an initial axial wall temperature gradient can lead to a variety of sustained combustion modes within the channel, including stable stationary flames, regimes of periodic motion involving quenching and re-ignition, regimes of regular oscillatory combustion, and regimes consisting of a combination of re-ignition/quenching events and regular oscillatory motions, all of which have been observed experimentally.     

Wave characteristics of single-walled fluid-conveying carbon nanotubes subjected to multi-physical fields

Wave propagation in single-walled carbon nanotubes (SWCNTs) conveying fluids and placed in multi-physical fields (including magnetic and temperature fields) is studied in this paper. The nanotubes are modelled as Timoshenko beams. Based on the nonlocal beam theory, the governing equations of motion are derived using Hamilton's principle, and then solved by Galerkin approach, leading to two second-order ordinary differential equations (ODEs). Numerical simulations are carried out to verify the analytical model proposed in the present study, and determine the influences of the nonlocal parameter, the fluid velocity and flow density, the temperature and magnetic field flux change, and the surrounding elastic medium on the wave behaviour of SWCNTs. The results show that the nonlocal parameter has a considerable influence on dynamic behaviour of the nanotube and the fluid flow inside it. The results also show that the magnetic and temperature fields play an important role on the wave propagation characteristics of SWCNTs.