Shin-ichiro Yanagiya

Effects of a magnetic field on the growth rate of tetragonal lysozyme crystals

The growth process of tetragonal lysozyme crystals under static and homogeneous magnetic field of 11 T was observed in situ by using an optical microscope which was specially designed and prepared. This optical system, having a spatial resolution of 0.5 μm, was used to measure the growth rate of the lysozyme crystals under 0 and 11 T. The effect of the magnetic field of 11 T was to decrease the growth rate of the crystals. The effect of a magnetic field on the dissolution process of the crystal was also investigated.

Effect of a magnetic field on the orientation of hen egg-white lysozyme crystals

Recent experiments have shown that lysozyme crystallization in a magnetic field of the order of 1 T can result in a significant degree of orientation of the crystals. We present more extensive experimental results and propose a model to account for this phenomenon. Because of the small susceptibility anisotropy of most protein molecules, the orienting effect is unimportant for smaller aggregates, even those much larger than a critical nucleus. However, during sedimentation crystals grow larger and are more likely to become aligned. The degree of orientation thus depends on crystal growth rate and container geometry, in addition to magnetic field strength, as we have confirmed experimentally.

Monte Carlo simulation of crystal-fluid coexistence states in the hard-sphere system under gravity with stepwise control

Monte Carlo (MC) simulations were performed for hard spheres (with diameter sigma and mass m) placed between well-separated upper and lower hard walls. A periodic boundary condition was imposed in the horizontal direction. The system was exposed to the gravitational field with the acceleration due to gravity g. After preparing a melt as the initial state, g was increased stepwise up to mgsigma/k(B)T(identical with g(*))=1.5 or 2.0 with an increment Deltag(*) = 0.1; k(B)T is the temperature multiplied by Boltzmanns constant. We maintained g(*) at each value for 2.0 x 10(5) MC cycles. The transition of the system into a metastable state such as a polycrystalline state due to trapping phenomena was successfully avoided. A monotonic increase and subsequent saturation were observed for the development of the crystalline region formed at the bottom of the system. The development of this region accompanied a shrinkage of the defective (or less ordered) crystalline region that was formed between the bottom region and the fluid phase. As the development of the bottom region almost saturated, the defective region grew upward again.

Waveguide-Type Optical Circuit for Recognition of Optical QPSK Coded Labels in Photonic Router

In photonic label routing networks, optical recognition of optical labels is one of the key functions. We propose a In photonic label routing networks, optical recognition of optical labels is one of the key functions. We propose a passive waveguide-type device for recognition of optical coded labels. We consider quadrature-phase-shift-keying (QPSK) coded labels. The basic module of the proposed device consists of a 3-dB directional coupler, two Y-junctions, and an asymmetric X-junction. By using interference between an optical pulse of each coded bit and a identifying bit pulse, the basic module distinguishes optical phase of the QPSK signal in a self-routing fashion of the identifying bit pulse. QPSK codes consisting of plural bits can also be recognized by connecting the basic module device in a tree structutre through a phase adjustment circuit. The performance of the proposed basic module is confirmed by simulation using beam propagation method (BPM).passive waveguide-type device for recognition of optical coded labels. We consider quadrature-phase-shift-keying (QPSK) coded labels. The basic module of the proposed device consists of a 3-dB directional coupler, two Y-junctions, and an asymmetric X-junction. By using interference between an optical pulse of each coded bit and a identifying bit pulse, the basic module distinguishes optical phase of the QPSK signal in a self-routing fashion of the identifying bit pulse. QPSK codes consisting of plural bits can also be recognized by connecting the basic module device in a tree structure through a phase adjustment circuit. The performance of the proposed basic module is confirmed by simulation using beam propagation method (BPM).

Wavelength-Insensitive Integrated-Optic Circuit Consisting of Asymmetric X-Junction Couplers for Recognition of BPSK Labels

We have proposed a label recognition integrated-optic circuits for photonic label switching using self-routing of the label pulses. Binary phase shift keying (BPSK) format is considered as the label. An identifying bit is placed ahead of the address bits in the label. The label recognition system consists of a tree-structure connection of asymmetric X-junction couplers. The system uses self-routing propagation of the identification bit controlled by the address bits. Asymmetric X-junction couplers have a feature of small dependence on wavelength. However, the wavelength dependence of optical circuits consisting of multiple asymmetric X-junction couplers depends strongly on its architecture. In this paper, we propose a wavelength insensitive architecture of the recognition circuit. The wavelength independence in the improved circuit is confirmed using finite-difference beam propagation method (FD-BPM). We numerically demonstrate that our proposed system can recognize all the binary-code labels in wavelength range of 1500-1600 nm with crosstalk less than -25 dB and -15 dB for label length three and four, respectively.

All-optical switch consisting of two-stage interferometers controlled by using saturable absorption of monolayer graphene

At routing nodes in future photonic networks, pico-second switching will be a key function. We propose an all-optical switch consisting of two-stage Mach-Zehnder interferometers, whose arms contain graphene saturable absorption films. Optical amplitudes along the interferometers are controlled to perform switching between two output ports instead of phase control used in conventional switches. Since only absorption is used for realizing complete switching, insertion loss of 10.2 dB is accompanied in switching. Picosecond response can be expected because of the fast response of saturable absorption of graphene. The switching characteristics are theoretically analyzed and numerically simulated by the finite-difference beam propagation method (FD-BPM).

Shrinking stacking fault through glide of the Shockley partial dislocation in hard-sphere crystal under gravity

Disappearance of a stacking fault in the hard-sphere crystal under gravity, such as reported by Zhuet al. [Nature 387, 883 (1997)], has successfully been demonstrated by Monte Carlo simulations. We previously found that a less ordered (or defective) crystal formed above a bottom ordered crystal under stepwise controlled gravity [Moriet al. J. Chem. Phys. 124, 174507 (2006)]. A defect in the upper defective region has been identified with a stacking fault for the (001) growth. We have looked at the shrinking of a stacking fault mediated by the motion of the Shockley partial dislocation; the Shockley partial dislocation terminating the lower end of the stacking fault glides. In addition, the presence of crystal strain, which cooperates with gravity to reduce stacking faults, has been observed.

Crystal structure of hard spheres under gravity by Monte Carlo simulation

Abstract Monte Carlo simulations were performed for hard spheres (HSs) under gravity. The gravity was increased stepwise. HSs were placed between the bottom and the top hard walls. For g*≥0.9, we observed that a ‘sediment’ was comprised of two crystalline and one fluid regions. Here, g*is defined by g*=mgσ/kBT with m being the mass of a particle, s the HS diameter, g the acceleration due to gravity, and kBT the temperature multiplied by Boltzmann’s constant. The bottom crystal was less defective or well-ordered and the crystal lay between the bottom one and the fluid phase was defective or less-ordered. In this paper, we investigate the structure of the crystals. Despite no apparent defects, the crystal has highly been distorted. That is, the fcc lattice has been contracted in the vertical direction more than in the horizontal direction. The crystal–fluid coexistence condition for the bulk HS system does, in principle, not hold for the present systems at the crystal–fluid interface. In addition, though the fine scale density profile exhibits a discontinuity apparently across the crystal–crystal interface, the interlayer separation increases linearly with the height.

All-Optical Wavelength-Selective Switch Consisting of Asymmetric X-Junction Couplers and Raman Amplifiers for Wide Wavelength Range

In this paper, we propose an all-optical integrated-optic switch to be used in wide wavelength range. Two architectures of the switch are described. One architecture is formed with two cascaded interferometers consisting of three asymmetric X-junction couplers, two Raman amplifiers, and an attenuator. The other is formed with three cascaded interferometers consisting of four asymmetric X-junction couplers and three Raman amplifiers. In both architectures, multiple signals at different wavelengths can be wavelength-selectively switched by pumping light in the waveguide-type Raman amplifiers. The wavelength range is found to be as wide as about 400 nm, which is ten times as wide as the range usable in the previously reported switch. The switching operation in the wide wavelength range is verified numerically. As a result, switching extinction ratio of larger than 20 dB is obtained for wavelength range from 1350 to 1750 nm.

Enhancement of Crystallization of Hard Spheres by Gravity: Monte Carlo Simulation

We present the effects of gravity on the growth of a hard-sphere (HS) crystal as determined by Monte Carlo simulations. HSs were confined between hard walls at the top (z=Lz) and the bottom (z=0) of the system with a periodic boundary condition in the horizontal direction. After preparing a melt state as an initial state, the gravity was suddenly switched on. The values of the gravity were mg?/kBT(?g*)=0.1,0.2,...,2.0, where m was the mass of a HS, g the acceleration of gravity, ? the HS diameter, and kBT the temperature multiplied by Boltzmanns constant. We observed the enhancement of crystallization due to gravity up to g*=0.7 and that the crystals of largest size were formed at g*=0.7?0.9. On the other hand, for g*?1.0, the top position of the HS crystal that was grown from the bottom became lower with an increase in the gravity, where crystals with various axis directions coexisted. The polycrystallization is speculated to occur due to polynucleation. These results are qualitatively consistent with those of an experimental study of the centrifugal sedimentation of colloidal crystallization.