Stabilization and utilization of nonlinear phenomena based on bifurcation control for slow dynamics

Mechanical systems may experience undesirable and unexpected behavior and instability due to the effects of nonlinearity of the systems. Many kinds of control methods to decrease or eliminate the effects have been studied. In particular, bifurcation control to stabilize or utilize nonlinear phenomena is currently an active topic in the field of nonlinear dynamics. This article presents some types of bifurcation control methods with the aim of realizing vibration control and motion control for mechanical systems. It is also indicated through every control method that slowly varying components in the dynamics play important roles for the control and the utilizations of nonlinear phenomena. In the first part, we deal with stabilization control methods for nonlinear resonance which is the 1/3-order subharmonic resonance in a nonlinear spring-mass-damper system and the self-excited oscillation (hunting motion) in a railway vehicle wheelset. The second part deals with positive utilizations of nonlinear phenomena by the generation and the modification of bifurcation phenomena. We propose the amplitude control method of the cantilever probe of an atomic force microscope (AFM) by increasing the nonlinearity in the system. Also, the motion control of a two link underactuated manipulator with a free link and an active link is considered by actuating the bifurcations produced under high-frequency excitation. This article is a discussion on the bifurcation control methods presented by the author and co-researchers by focusing on the actuation of the slowly varying components included in the original dynamics.     

Simulation of micro/nanometer-scale self-organized lightwave network (SOLNET) using the finite difference time domain method

A simulator for self-organized lightwave network (SOLNET) is developed. The simulator is based on the finite difference time domain method. SOLNET enables us to construct self-aligned coupling waveguides between misaligned micro/nanometer-scale optical devices by self-focusing, which arises from an increase in refractive index induced by write beams in photo-refractive materials. The SOLNET simulator reveals that an L-shaped nanometer-scale optical waveguide of SOLNET is grown from a 0.5-μm-wide optical waveguide when write beams are introduced from the optical waveguide into photo-refractive materials, where a wavelength filter is embedded. The SOLNET simulator also reproduces coupling path construction between a 2-μm-wide optical waveguide and a 0.5-μm-wide optical waveguide having a wavelength filter on the core edge. The optical waveguides are placed with misalignment of 0.5-μm offset. By introducing write beams from the 2-μm-wide optical waveguide, the incident write beams and reflected write beams from the wavelength filter merge into one optical waveguide in the photo-refractive materials, constructing a self-aligned coupling waveguide.     

Coherent transfer of light polarization to electron spins in a semiconductor

We demonstrate that the superposition of light polarization states is coherently transferred to electron spins in a semiconductor quantum well. By using time-resolved Kerr rotation, we observe the initial phase of Larmor precession of electron spins whose coherence is transferred from light. To break the electron-hole spin entanglement, we utilized the big discrepancy between the transverse g factors of electrons and light-holes. The result encourages us to make a quantum media converter between flying photon qubits and stationary electron-spin qubits in semiconductors.     

Depth-control method for integral imaging

We present a method for controlling the depth of three-dimensional (3D) images reconstructed by integral photography. Incoherent light is reflected from 3D objects, propagates through a lens array, and is captured as the first elemental images by a capturing device. The second elemental images of the 3D images are generated by numerical processing from the first elemental images in accordance with the desired depth. The optical reconstruction of 3D images at the desired depth by the second elemental images is confirmed experimentally.     

Kaleidoscope of life: A 24-neighbourhood outer-totalistic cellular automaton

One of the challenges of cellular automaton research is finding models with a low complexity and at the same time a rich dynamics. A measure of low complexity is the number of states in the model and the number of transition rules to switch between those states. In this paper, we propose a 2-dimensional 2-state cellular automaton that-though governed by a single simple transition rule-has a sufficiently rich dynamics to be computationally universal. According to the transition rule, a cell’s state is determined by the sum of the states of the cells at orthogonal or diagonal distances one or two from the cell (distance-2 Moore neighbourhood), but not by the previous state of the cell itself. Notwithstanding its simplicity, this model is able to generate a great variety of patterns, including several types of stable configurations, oscillators and patterns that move over cellular space (gliders). We prove the computational universality of the model by constructing a universal set of logic gates (NOT and AND) from these patterns. A key element in this proof is the shifting of phases and positions of signals such that they meet the input requirements of the logic gates. Similarities of the model with classical spin systems are also discussed.     

Simplification of formulas for compression wave and oscillating flow in circular pipe

We had already obtained the analytical solutions for the compression wave and steady-state oscillating flow in a pipe with a circular cross section [Sato Y, Kanki H. Formulas for compression wave and oscillating flow in circular pipe. To be published in Appl Acoust [accepted 11 Sept. 2006]]. This work contains three key-components. The first key is to simplify the formulas using the unique mathematic technique without losing the accuracy. Simplifying the formulas is the one of the most important factors for formulas used in engineering use. The results will enable us to greatly reduce the work and computation costs. The second is to verify the flow distribution calculated by our formulas. The third is to study the possibility of application of our method to the analysis in turbulent flow region. Kawata et al. have represented the validity of one-dimensional quasi-analysis in turbulent flow region, using the method of D’Souza et al. and the shear viscosity. Therefore, in this paper the validity of the analysis in a turbulence region was verified by proving theoretically that the methods of D’Souza et al. and ours are intrinsically equivalent. The proof of equivalence was accomplished using the formulas simplified in this paper.     

Crystal structures of calcium IV and V under high pressure

High-pressure phases IV and V of calcium discovered in 2005 have the highest superconducting transition temperature of 25 K among all the elements; however, their crystal structures have not been determined. From the x-ray powder diffraction data, both Ca IV and V have been found to form unique and complex structures with a coordination number of 7. They were confirmed to be identical to the theoretical models that were recently predicted [Ishikawa, Phys. Rev. B 77 020101(R) (2008)].     

Radial breathing modes of single-walled carbon nanotubes in resonance Raman spectra at high temperature and their chiral index assignment

Radial breathing modes (RBMs) in resonance Raman spectra from single-walled carbon nanotubes (SWCNTs) on a SiO₂/Si (0 0 1) substrate are studied between 25 and 720 °C. A change in the relative intensity of each RBM peak with temperature is observed, which originates from the temperature dependence of the resonance condition of nanotubes. For 25 °C, each RBM peak is reasonably assigned on the basis of data in the literature [J. Maultzsch, H. Telg, S. Reich, F. Hennrich, C. Thomsen, Phys. Rev. B 72 (2005) 205438]. By taking into account the temperature-dependent behavior of the relative intensity of the RBM peaks, each RBM peak is successfully assigned even for 720 °C. It is found that most of the observed RBM peaks for a laser excitation energy of E_exc = 1.96 eV are from chiral SWCNTs. These results make it possible to discuss further details of the chirality-dependent growth behavior observed for in situ Raman spectroscopy.     

Source/drain engineering for MOSFETs with embedded-Si:C technology

Embedded silicon carbon alloy (e-Si:C) technology for source and drain (S/D) is expected to improve nMOSFET drive current. The distribution and activation characteristics of arsenic in Si:C film and the interfacial solid-phase reaction of the Ni/Si:C system were studied with the aim of achieving the maximum improvement of the characteristics of e-Si:C S/D. It was clarified that the active carrier concentration of Si:C decreased with increasing carbon concentration compared to the control Si. There is concern that the low doping activation in Si:C increases series resistance of e-Si:C S/D nMOSFETs and degrades the performance gain expected from the strain effect.     

Anisotropy dispersion in (CoCrPt)1−x(SiO2)x perpendicular recording media

The distribution of easy axis orientation in perpendicular media is of technological importance because it affects the value of S^* (see Fig. 1), which quantifies the switching field distribution (SFD) and hence partially determines the data density achievable on a given medium. The distribution is controlled by the crystallographic orientation of grains and factors such as intergranular exchange and dipolar coupling. Due to strong demagnetising fields in the perpendicular orientation, traditional measurements of remanence as a function of angle are difficult to interpret and have required the use of large-scale computational models. In this work we have utilised the variation of coercivity H_C with angle, which has the advantage that at H_C the global demagnetising field is zero. Additionally, since such materials follow essentially the Stoner–Wohlfarth mode of reversal, the variation of H_C with angle, H_C(θ), is much greater than that for the remanence. We find that for (CoCrPt)_1−x(SiO₂)_x, where the level of exchange coupling is controlled, the distribution of magnetic easy axes is narrower when the exchange coupling is reduced, but dipolar coupling between the grains is strong and affects the magnetisation reversal significantly.