Showing papers by "University of Electro-Communications published in 1989"

Direct Solution of the Landau-Lifshitz-Gilbert Equation for Micromagnetics

Abstract: A mathematical framework is presented for solving the Landau-Lifshitz-Gilbert equation expressed in Cartesian components of magnetization according to the backward difference method without conflicting with the constraint of constant magnetization. Test calculation shows that the method allows the use of a large time step almost independent of spatial mesh size and damping constant. The derived program is used to calculate the magnetization structure of a crosstie wall in a Permalloy film yielding calculated structures which closely resemble the electron-holography image of an actual cross-tie wall. It is also used to investigate magnetization reversal mechanisms in fine ferromagnetic particles by pursuing time dependent changes in magnetization structures. The paper gives detailed descriptions of the reversal mechanisms which differ depending on the size of the particle.

On the computational power of PP and (+)P

Abstract: Two complexity classes, PP and (+)P, are compared with PH (the polynomial-time hierarchy). The main results are as follows: (1) every set in PH is reducible in a certain sense to a set in PP, an (2) every set in PH is reducible to a set in (+)P under randomized polynomial-time reducibility with two-sided bounded error probability. It follows from these results that neither PP nor (+)P is a subset of or equivalent to PH unless PH collapses to a finite level. This is strong evidence that both classes are strictly harder than PH. >

Temperature-induced magnetism in LaCoO 3

Abstract: Polarized and unpolarized neutron measurements have been performed on ${\mathrm{LaCoO}}_{3}$ in a temperature range between 10 and 295 K. A drastic decrease in the magnetic cross section is observed below 150 K. This is the first concrete experimental evidence for the temperature-induced magnetic moment of Co ions in this oxide as proposed in the thermally populated high-spin model. The temperature dependence of the moment is in qualitative agreement with that calculated from the magnetic-susceptibility data.

An automatic calibration system for angular encoders

Abstract: An automatic calibration system for angular encoders is described. The system consists of five subsystems: a precise rotary table with an air bearing, a direct-coupling dc servo motor which rotates the table at a constant speed, a rotary magnetic scale as a reference angular standard, time interval counters to detect slight angular differences by a time-conversion method and a microcomputer system which controls the operation of measurement and the data processing. Angular encoders under test are compared with the rotary magnetic scale which is calibrated by a new self-checking method, which we called the ‘multi-reading-head method’. The results obtained are as follows: (1) slight angular differences are detected with 0.01″ resolution and their standard deviations are about 0.01″: (2) the calibration of the master scale can be carried out automatically in about 5 min without an angular standard: and (3) the calibration values of all graduations of the magnetic scale and object encoders are obtained with an accuracy of about 0.3″.

Laser cooling and trapping of Ne metastable atoms

Abstract: A neon atomic beam in the metastable state 1${s}_{5}$ has been decelerated and trapped by the spontaneous light force of a resonant laser in a quadrupole magnetic field. Trapping has been achieved on all isotopes $^{20}\mathrm{Ne}$, $^{21}\mathrm{Ne}$, and $^{22}\mathrm{Ne}$ using a sample with natural abundance. For $^{20}\mathrm{Ne}$, approximately 4\ifmmode\times\else\texttimes\fi{}${10}^{7}$ atoms are trapped.

Array illuminator using grating couplers

Abstract: An integrated-optical array illuminator is proposed, and the principle of generating multiple beamlets by using grating couplers is described. Preliminary experiments are performed to demonstrate the validity of the principle.

Theory of the two-step spin conversion induced by the cooperative molecular distortions in spin-crossover compounds.

Abstract: G\"utlich et al. [Chem. Phys. Lett. 91, 348 (1982)] observed an ``unusual'' two-step high-spin\ensuremath{\rightleftarrows}low-spin transition in the spin crossover compound [Fe(2-pic${)}_{3}$]${\mathrm{Cl}}_{2}$\ensuremath{\cdot}${\mathrm{C}}_{2}$${\mathrm{H}}_{5}$OH. Recently, Petrouleas and Tuchagues [Chem. Phys. Lett. 137, 21 (1987)] have shown that the other compound Fe[${5\mathrm{N}\mathrm{O}}_{2}$-sal-N(1,4,7,10)] exhibits a two-step spin conversion with a wider middle step. The mechanism of these unusual spin conversions are studied theoretically on the basis of the cooperative molecular distortion model [Kambara, J. Phys. Soc. Jpn. 49, 1806 (1980) and Sasaki and Kambara, J. Chem. Phys. 74, 3472 (1981)]. The couplings of the spin states of the Fe ion with a molecular distortion and a lattice strain are taken into account in the model. The spin conversion is induced by the intermolecular spin coupling mediated by the lattice vibration mode and the lattice strain. In the present model the two inequivalent sites occupied by equivalent iron complexes are assumed in a unit cell of the lattice. Molecular distortions of a pair of the two complexes occupying the two inequivalent sites couple with each other symmetrically and antisymmetrically. The origin of the two-step spin conversion (LL\ensuremath{\rightarrow}LH\ensuremath{\rightarrow}HH) comes mainly from the differences between the effects of the interpair interaction to the symmetric distortion and on the antisymmetric distortion. Various patterns of two-step spin conversions are obtained by changing the coupling strengths of the Fe ion with molecular distortion and with lattice strain and also the strength of interpair interaction. The essential features of the observed thermally induced two-step transitions and also the observed pressure effect to the transition may be reproduced by the present model.

Fine Structure of a Directly Simulated Isotropic Turbulence

Abstract: The fine structure of the isotropic turbulence, which has recently been realized in a supercomputer by the authors, is studied at its fully-developed state. The geometrical relationship between vorticity-concentrated regions and high-strain regions and a variety of mutual orientations of the velocity and vorticity vectors in these regions are illustrated. A common exponential nature and a delicate difference of the space distributions of the velocity (longitudinal and lateral) gradients, along with the magnitude of vorticity and the square-root of local dissipation, are exposed.

UV saturable absorber for short-pulse KrF laser systems.

Abstract: A derivative of the linear tricyclic compound, acridine, is shown to be useful as a saturable absorber for short-pulse KrF lasers. The saturation characteristics and absorption recovery of a methanol solution of acridine for a 20-psec KrF laser pulse are reported. We obtain a saturation fluence of 1.2 mJ/cm2 and a ratio of the primary to the excited absorption cross section of 6.25:1.

Stability of a slotted ALOHA system with capture effect

Abstract: The stability of a slotted ALOHA system with capture effect is investigated under a general communication environment where terminals are divided into two groups (low-power and high-power) and the capture effect is modeled by capture probabilities. An approximate analysis is developed using catastrophe theory in which the effects of system and user parameters on the stability are characterized by the cusp catastrophe. In particular, the authors focus on the low-power group, since it must bear the strain under the capture effect. The stability conditions of the two groups are given explicitly by bifurcation sets. >

Turning machines with few accepting computations and low sets for PP

Abstract: The authors study two different ways to restrict the power of NP. They consider languages accepted by nondeterministic polynomial-time machines with a small number of accepting paths in case of acceptance, and they investigate three subclasses of NP that are low for complexity classes not known to be in the polynomial-time hierarchy. The subclasses, UP, FewP, and Few, are all defined in terms of nondeterministic machines with a bounded number of accepting paths for every input string, but for the last two classes this number is not known beforehand and can range over a space of polynomial size. The authors prove lowness properties of the class Few and some other interesting sets that are low for the class PP. The lowness results are used to obtain positive relativizations of complexity classes. >

Postural Control of a Monoaxial Bicycle

Abstract: 本研究は, 一つの軸の両端に二輪をもち, その軸で上部構造体を支える形式の同軸二輪車の姿勢制御とその応用に関するものである. この二輪車を倒立振子と車輪によってモデル化し, フィードバック制御系を設計した. 倒立振子に対する制御モーメント, すなわち復元トルクは車輪を制御することによって発生する. 制御の遅れ時間を考慮し, Routh-Hurwitzの安定条件により比例ゲインを求めた. これらの結果を用いて実験を行い, 同軸二輪車の姿勢制御に成功した. さらに, 姿勢制御の結果を利用したゲイン変化法とサーボ指令法の二方法により, 二輪車のサーボ制御を実現した.

Computer Experiment on the Cooperative Behavior of a Network of Interacting Nonlinear Oscillators

Abstract: The cooperative behavior of a network of interacting nonlinear oscillators is investigated numerically. Such an oscillator-net serves as a phenomenological model for an endogenous circadian pacemaker in organisms. Following two types of network are examined. (1) Ordered oscillator-net: oscillators sit on the square-lattice points and interact with the nearest neighbors. (2) Random oscillator-net: each oscillator is influenced by a certain number of randomly chosen oscillators. Detailed computer experiment is made on the oscillator-net containing one hundred to one thousand oscillators. The self-entraining behavior is found to be very different in the two types of oscillator-net. The sample- and size-dependence are also studied. The relevance of the oscillator-net as a model for the circadian pacemaker is discussed.

Cluster formation by inelastically colliding particles in one-dimensional space

Abstract: Inelastically colliding particles moving in one-dimensional space are found to form clusters, each of which consists of particles with identical coordinates and velocities. There exists a critical size of a cluster, above which the cluster grows indefinitely by absorbing a colliding particle as if the collision were completely inelastic (rebound coefficient e = 0. It is experimentally found that when e = 0, the expected number of n-particle clusters is 1n, and the average number of final clusters 〈M〉 is 〈M〉 = ΣNn 11n, where N is the number of the particles in the system.

Computer Experiment on the Complex Behavior of a Two-Dimensional Cellular Automaton as a Phenomenological Model for an Ecosystem

Abstract: Numerical studies are made on the complex behavior of a cellular automaton which serves as a phenomenological model for an ecosystem. The ecosystem is assumed to contain only three populations, i.e., a population of plants, of herbivores, and of carnivores. A two-dimensional region where organisms live is divided into square cells and the population density in each cell is regarded as a discrete variable. The influence of the physical environment and the interactions between organisms are reduced to a simple rule of cellular automaton evolution. It is found that the time dependent spatial distribution of organisms is, in general, very random and complex. However, under certain conditions, the self-organization of ordered patterns such as rotating spirals or concentric circles takes place. The relevance of the cellular automaton as a model for the ecosystem is discussed.

Learning Context-Free Languages Efficiently - A Report on Recent Results in Japan

Abstract: This paper reports some of the recent results in Japan, focussing on the inductive inference of context-free languages. The paper does not intend the thorough survey on this topic, rather intend to provide extended abstracts of recent results developed in Japan. The contents of the present paper are as follows:

Thin-film waveguide with a periodic groove structure of finite extent

Abstract: A mode-matching method in the sense of least squares is used to analyze thin-film waveguides with a periodic groove structure of finite extent. Two diffraction problems are treated. The first is that of a grating coupler for plane-wave incidence and for which the Bragg condition is satisfied. In the second problem a guided mode is incident upon the periodic part through the unperturbed part of a waveguide, and the Bragg condition is satisfied. The approximate scattered fields of each region of the waveguide are described by a superposition of plane waves with band-limited spectra. These approximate wavefunctions are determined by the minimization of the mean-square boundary residual resulting in simultaneous Fredholm-type integral equations of the second kind for these spectra. Results based on the first-order approximate solutions of the integral equations are presented.

Chemical, Optical, and Infrared Properties of Quenched Carbonaceous Composites (QCCS)

Abstract: Quenched carbonaceous composite (QCC) was synthesized by quenching the plasma of methane gas. Chemical properties as well as optical and infrared spectra of the QCC and “oxidized” QCC were measured. Good agreement of the IR spectra of the QCCs to the unidentified infrared (UIR) emission bands was obtained. Correspondence of their features to molecular structures in the QCC was estimated. It is concluded that a “cross-conjugated ketone” structure (CCK) caused the 6.2, 7.7, and 8.6 μm features and “solo” H atoms on carbon are responsible for the 3.3 and 11.3 μm features.

Formation of silicon carbide layers by the ion beam technique and their electrical properties

Abstract: β-type SiC layers were fabricated by high dose implantation of carbon ions into silicon with subsequent annealing. The effect of implanting energetic Si or P ions following the carbon ion implantation on the s-SiC formation behaviour was studied by means of infrared absorption spectroscopy. The results were compared with those obtained by implantation of Ar or Ne noble gas ions which caused a reduction in the s-SiC formation temperature. The electrical properties of the s-SiC layers formed by this ion beam technique were also evaluated.

Temperature Dependence of Resistivities in TiS2 and Its Cu-Intercalate

Abstract: The electrical resistivities of a layered dichalcogenide TiS 2 and its Cu-intercalate were investigated in the temperature range 100 K to 350 K. The a -axis resistivity of the Cu-intercalate showed a linear temperature dependence rather than the T 2 -dependence reported in TiS 2 . With increasing x in Ti 1+ x S 2 and Cu x TiS 2 , both resistivities and their slopes decrease with temperature, while the carrier concentrations enlarge up to metallike orders of 10 22 cm -3 . This origin is discussed on a common basis of the slow transition from electron-electron to electron-phonon scatterings which is due to the increase of conduction electrons of the intercalated Cu metalas well as the self-intercalated Ti metal.

Present status and prospect of KrF laser physics and technology-large volume excitation and UV optics

Abstract: The physics and technology for e -beam generation, large volume excitation and the ultra-violet optics for high power KrF lasers is presented. The potential, due to the charge deposition, induces a return current in the plasma which balances the e -beam current. The local equilibrium mechanism stabilizes the large volume excitation using intense electron beams. The spatial and temporal characteristics of large aperture diodes are analyzed. Substantial progress in ultra violet optics in Japan has been achieved. The damage threshold of HR dielectric coating increases up to 11 J/cm 2 by using low absorption materials.