Showing papers by "University of Electro-Communications published in 1999"

Realization of Dynamic Walking and Running of the Quadruped Using Neural Oscillator

Abstract: In the present study we attempt to induce a quadruped robot to walk dynamically on irregular terrain and run on flat terrain by using a nervous system model. For dynamic walking on irregular terrain, we employ a control system involving a neural oscillator network, a stretch reflex and a flexor reflex. Stable dynamic walking when obstructions to swinging legs are present is made possible by the flexor reflex and the crossed extension reflex. A modification of the single driving input to the neural oscillator network makes it possible for the robot to walk up a step. For running on flat terrain, we combine a spring mechanism and the neural oscillator network. It became clear in this study that the matching of two oscillations by the spring-mass system and the neural oscillator network is important in order to keep jumping in a pronk gait. The present study also shows that entrainment between neural oscillators causes the running gait to change from pronk to bound. This finding renders running fairly easy to attain in a bound gait. It must be noticed that the flexible and robust dynamic walking on irregular terrain and the transition of the running gait are realized by the modification of a few parameters in the neural oscillator network.

Properties of Nd3+-doped and undoped tetragonal PbWO4, NaY(WO4)2, CaWO4, and undoped monoclinic ZnWO4 and CdWO4 as laser-active and stimulated raman scattering-active crystals.

Abstract: Spectroscopic, laser, and chi((3)) nonlinear optical properties of tetragonal PbWO(4), NaY(WO(4))(2), CaWO(4), and monoclinic CdWO(4) and ZnWO(4) were investigated. Particular attention was paid to Nd(3+)-doped and undoped PbWO(4) and NaY(WO(4))(2) crystals. Their absorption and luminescence intensity characteristics, including the peak cross sections of induced transitions, were determined. Pulsed and continuous-wave lasing in the two 4F(3/2)-->4I(11/2) and 4F(3/2)-->4I(13/2) channels was excited. For these five tungstates, highly efficient (greater than 50%) multiple Stokes generation and anti-Stokes picosecond generation were achieved. All the observed scattered laser components were identified. These results were analyzed and compared with spectroscopic data from spontaneous Raman scattering. A new crystalline Raman laser based on PbWO(4) was developed for the chi((3)) conversion frequency of 1-microm pump radiation to the first Stokes emission with efficiency up to 40%. We classify all the tungstates as promising media for lasers and neodymium-doped crystals for self-stimulated Raman scattering lasers.

Strong converse to the quantum channel coding theorem

Abstract: A lower bound on the probability of decoding error for a quantum communication channel is presented, from which the strong converse to the quantum channel coding theorem is immediately shown. The results and their derivations are mostly straightforward extensions of the classical counterparts which were established by Arimoto (1973), except that more careful treatment is necessary here due to the noncommutativity of operators.

Fractal analysis of ULF geomagnetic data associated with the Guam Earthquake on August 8, 1993

Abstract: This paper presents a fractal analysis of the ULF electromagnetic data obtained at Guam observatory during a strong (Ms=8.0) earthquake occurred on August 8, 1993 near the Guam island. We have already reported the presence of seismogenic ULF emissions for this quake (Hayakawa et al., GRL, 1996). The chosen period covered four months before and two months after the earthquake. It was found that the spectrum of emissions at noon exhibited a power law behavior f−β which is typical for self-organized critical dynamics. The slope of the spectrum in the noon sector fluctuates in a range from 2.5 to 0.7 with a tendency to gradually decrease during the process of the earthquake preparation. We consider this to be a candidate for a precursory signature. The similar effect was found for the night sector. We suggest that the focal zone was at the critical stage of self-organized criticality process before the quake, related to active microfracturing processes followed by the generation of ULF emissions as we detected.

Electronic states in heavily Li-doped graphite nanoclusters

Abstract: Fracture modes in a model glass–polymer coating–substrate system indented with hard spheres are investigated. The large modulus mismatch between the glass and polymer results in distinctive transverse fracture modes within the brittle coating: exaggerated circumferential (C) ring cracks that initiate at the upper coating surface well outside the contact (as opposed to the near-contact Hertzian cone fractures observed in monolithic brittle materials); median–radial (M) cracks that initiate at the lower surface (i.e., at the substrate interface) on median planes containing the contact axis. Bonding between the coating and substrate is sufficiently strong as to preclude delamination in our system. The transparency of the constituent materials usefully enables in situ identification and quantification of the two transverse fracture modes during contact. The morphologies of the cracks and the corresponding critical indentation loads for initiation are measured over a broad range of coating thicknesses (20 mm to 5.6 mm), on coatings with like surface flaw states, here ensured by a prebonding abrasion treatment. There is a well-defined, broad intermediate range where the indented coating responds more like a flexing plate than a Hertzian contact, and where the M and C cracks initiate in close correspondence with a simple critical stress criterion, i.e., when the maximum tensile stresses exceed the bulk strength of the (abraded) glass. In this intermediate range the M cracks generally form first—only when the flaws on the lower surface are removed (by etching) do the C cracks form first. Finite element modeling is used to evaluate the critical stresses at crack initiation and the surface locations of the crack origins. Departures from the critical stress condition occur at the extremes of very thick coatings (monolith limit) and very thin coatings (thin-film limit), where stress gradients over the flaw dimension are large. Implications of the results concerning practical coating systems are considered.

Fuzzy descriptor systems: stability analysis and design via LMIs

Abstract: A fuzzy descriptor system is defined Six kinds of stability conditions for the fuzzy descriptor system are derived and represented in terms of linear matrix inequalities (LMIs) The stability analysis is reduced to a problem of finding a common Lyapunov function An LMI design approach is employed to find stable feedback gains and a common Lyapunov function

Large-scale cryogenic gravitational wave telescope

Abstract: We present here the Large-scale Cryogenic Gravitational wave Telescope (LCGT) project which is aimed to improve the sensitivity of the existing gravitational wave projects by ten times. LCGT is the project constructing the km-scale gravitational wave detector in Japan succeeding the TAMA project, which adopts cryogenic mirrors with a higher power laser. We are planing to build it in an underground site in Kamioka mine. If its target sensitivity is attained, we will be able to catch a few events per month.

Optical frequency-domain imaging microprofilometry with a frequency-tunable liquid-crystal Fabry-Perot etalon device.

Abstract: An optical frequency-domain interference microscope with a liquid-crystal Fabry–Perot interferometer as an optical frequency-scan device was developed for microscopic three-dimensional shape measurements. The proposed system can perform absolute measurement of the discontinuous surface profile of a microscopic object without use of mechanically moving components such as a piezoelectric transducer or a grating spectrometer. Experimental results are presented that demonstrate the validity of the principle.

Dynamic recrystallization of copper polycrystals with different purities

Abstract: The hot deformation behaviour and associated structural changes were studied by means of compression tests and metallographic observations of polycrystalline copper with three different purities of 99.99 (4N), 99.9999 (6N) and 99.99999 (7N) mass percent of copper. The samples were strained up to 1.2 at temperatures ranged from 523 to 773 K under various true strain rates of 10−4–10−1 s−1. The deformation behaviours are characterised by multiple peaks or a single peak flow, followed by a steady state flow stress and a new grain evolution by dynamic recrystallization (DRX) at high strains. The steady state stresses and their temperature and strain rate dependencies for 6N and 7NCu are almost the same, but clearly lower and higher than those for 4NCu, respectively. The activation energy for hot deformation is affected by materials purity, i.e. about 210 kJ mol−1 for 6N or 7NCu and 245 kJ mol−1 for 4NCu. On the other hand, the DRX grain sizes, represented by a unique function of steady state flow stress, strongly depend on the solute concentration for all of samples studied. The effect of impurity atoms on the deformation and DRX grains is discussed in such high purity materials.

Finite-size effect on the raman spectra of carbon nanotubes

Abstract: Using nonresonant bond polarization theory, we have calculated the Raman intensity of a single-wall carbon nanotube of finite length. The calculations show that the Raman peaks in the intermediate frequency range $(500--1200{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1})$ have no intensity for infinite nanotubes, but do have some intensity for finite nanotubes. These intermediate frequency modes, which are sensitive to the nanotube length, correspond to vibrations along the nanotube axis. We also found an edge state of the breathing phonon mode at an open end of the carbon nanotube, which is Raman active.

Tool path generation using C-space for 5-axis control machining

Abstract: The paper deals with the method of tool path generation for 5-axis control machining using a ball end mill. 5-axis control machining has been used for aircraft parts as well as for complicated shapes such as mold and dies. However, most of the present CAM systems for 5-axis control machining have limited functions in terms of tool collision, workpiece shapes and machining methods. For that reason, in many cases the optimal cutter location (CL) data cannot be obtained or considerable time is consumed. To solve this problem, we applied a 3-dimensional configuration space (C-Space) and showed the relationship between all tool positions and postures and the existence of tool collision. The method of tool path generation devised in the study enables users to generate CL data reflecting their own machining strategy such as smooth change in tool posture and the state of machining without considering the gouging. The validity of this method was experimentally confirmed by successfully milling an impeller without tool collision occurring.

Grain Refinement under Multiple Warm Deformation in 304 Type Austenitic Stainless Steel

Abstract: The dynamic process of fine grain evolution as well as deformation behaviour under warm working conditions was studied in compression of a 304 type austenitic stainless steel. Multiple compression tests were carried out at a strain rate of 10-3 s-1 to produce high cumulative strains, with changing of the loading direction in 90o and decreasing temperature from 1223 to 873 K (0.7-0.5Tm) in each pass. The steel exhibits two types of deformation behaviours with different mechanical and structural characteristics. In the deformation region where flow stresses are below about 400 MPa, conventional dynamic recrystallization takes place accompanied mainly by bulging of serrated grain boundaries. The dynamic grain size evolved can be related to the high temperature flow stress through a power law function with a grain size exponent of -0.72. On the other hand, in the region of higher stresses above 400 MPa the flow stresses show small strain rate and temperature dependence, and so it is suggested to be in an athermal deformation region. The stress-strain curves show a steady state like flow without any strain softening, while the multiple deformation to high cumulative strains brings about the evolution of fine grained structures with grain sizes less than one micron. The relationship between the warm temperature flow stresses and the grain sizes evolved also can be expressed by a unique power law function of grain size with an exponent of -0.42. The interrelations between the mechanisms of plastic deformation and microstructure evolution at warm and high temperatures are analysed in detail and also the multiple compression method for obtaining ultra fine grained structure is discussed as a simple thermomechanical processing.

Strong converse theorems in the quantum information theory

Abstract: Strong converse theorems for two different subjects in quantum information theory are presented. First, we show a lower bound on the probability of decoding error for a quantum communication channel, from which the strong converse to the quantum channel coding theorem is obtained. Second, we give the strong converse theorem for the quantum hypothesis testing as an application of a new inequality on the error probabilities. This inequality is also used to establish the quantum Stein's lemma.

Diode-pumped high-efficiency Tm:YAG lasers

Abstract: Eye-safe solid-state lasers that operate at 2 μm wavelength have many applications in medical, remote sensing and military technologies. With a 3-W CW laser-diode pumping, we obtained 760 mW 2.01 μm Tm:YAG laser under CW operation. The slope efficiency was 44% and the optical to optical efficiency reached 36%. In the acousto-optic Q-switched operation, laser pulses with the energy of 1.2mJ and 380 ns FWHM width have been achieved.

Analytical solutions describing the phase separation driven by a free energy functional containing a long-range interaction term

Abstract: We are primarily concerned with the variational problem with long-range interaction. This functional represents the Gibbs free energy of the microphase separation of diblock copolymer melts. The critical points of this variational problem can be regarded as the thermodynamic equilibrium state of the phase separation phenomenon. Experimentally it is well-known in the diblock copolymer problem that the final equilibrium state prefers periodic structures such as lamellar, column, spherical, double-diamond geometries and so on. We are interested in the characterization of the periodic structure of the global minimizer of the functional (corresponding to the strong segregation limit). In this paper we completely determine the principal part of the asymptotic expansion of the period with respect to e (interfacial thickness), namely, we estimate the higher order error term of the period with respect to e in a mathematically rigorous way in one space dimension. Moreover, we decide clearly the dependency of the constant of proportion upon the ratio of the length of two homopolymers and upon the quench depth. In the last section, we study the time evolution of the system. We first study the linear stability of spatially homogeneous steady state and derive the most unstable wavelength, if it is unstable. This is related to spinodal decomposition. Then, we numerically investigate the time evolution equation (the gradient flow of the free energy), and see that the free energy has many local minimizers and the system have some kind of sensitivity about initial data.

Solid-State High-Resolution 1H and 2D NMR Study of the Electron Spin Density Distribution of the Hydrogen-Bonded Organic Ferromagnetic Compound 4-Hydroxyimino-TEMPO

Abstract: The electron spin density distribution at hydrogen atoms of 4-hydroxyimino-2,2,6,6-tetramethylpiperidin-1-yloxyl (4-hydroxyimino-TEMPO), which has recently been shown to act as a molecular ferromagnet at low temperature, was determined in the crystalline phase on the basis of the temperature dependence of the Fermi contact shifts in the magic angle spinning deuterium NMR spectrum to elucidate the mechanism of intermolecular magnetic interaction. There are two kinds of close contacts among neighboring radical molecules in the crystalline phase. An axial methyl hydrogen atom locates near a neighboring N−O radical group, and the hydroxyl group undergoes hydrogen bonding with another neighboring N−O radical group. The plus and minus signs of the observed hyperfine coupling constants AD of methyl deuteriums indicate that there are two different mechanisms for the electron spin density distribution. Equatorial CD3 groups show negative coupling constants (AD = −0.24 MHz) induced by an intramolecular spin polariz...

Pair Plasma Dominance in the 3C 279 Jet on Parsec Scales

Abstract: We have investigated whether a pc-scale jet of 3C 279 is dominated by a normal plasma or an electronpositron plasma. By analyzing Very Long Baseline Interferometry data between 1983 and 1990, and utilizing the theory of synchrotron self-absorption, we have derived the lower limits for the proper electron number density. Comparing the lower limit with another independent constraint for the electron density that is deduced from the kinetic luminosity, we find that the core and components C3 and C4 are likely dominated by an electron-positron plasma.

Photochemical Bissilylation of C60 with Disilane1

Abstract: The photochemical reaction of C60 with disilane 1 affords the adduct 2 as a bissilylated product. The unique redox properties of 2 are reported by means of differential pulse voltammetry. The compound 2 was characterized by NMR, IR, and UV−vis spectroscopies. Spectroscopic and theoretical investigation strongly support the 1,16-addition structure having C2 symmetry which results from addition at the 1,16 positions in C60. The results are reasonably accounted for by the generation of a silyl radical which is responsible for the formation of 2.

An estimation theoretical characterization of coherent states

Abstract: We introduce a class of quantum pure state models called the coherent models. A coherent model is an even-dimensional manifold of pure states whose tangent space is characterized by a symplectic structure. In a rigorous framework of noncommutative statistics, it is shown that a coherent model inherits and expands the original spirit of the minimum uncertainty property of coherent states.

A fast audio classification from MPEG coded data

Abstract: Audio information classification becomes a very important task for such purposes as automatic keyword spotting and other content-based audio-visual query systems. In this paper, we describe a fast and accurate audio data classification method on the MPEG coded data domain. Firstly silent segments are detected using a robust approach for different recording conditions. Then the non-silent segments are classified into three types, music, speech, and applause using temporal density, bandwidth and center frequency of subband energy. In order to be robust for a variety of audio sources as much as possible, we use Bayes discriminant function for multivariate Gaussian distribution instead of manually adjusting a threshold for each discriminator. In the experiment, every one-second of MPEG audio data is classified and about 90% of audio and speech segments have been successfully detected. As for the detection speed, less than 20% of MPEG audio decoding processing power is required.

Hydrogen at the surface and interface of metals on Si(111)

Abstract: The depth-resolved measurement of hydrogen using the resonant nuclear reaction of ${}^{1}{\mathrm{H}(}^{15}{\mathrm{N},\mathrm{\ensuremath{\alpha}}\mathrm{\ensuremath{\gamma}})}^{12}\mathrm{C}$ in the formation of (Pb, Ag, and Cu)/Si(111) interfaces is reported. It was found that Pb deposition on $\mathrm{Si}(111)1\ifmmode\times\else\texttimes\fi{}1\ensuremath{-}\mathrm{H}$ at 110 and 360 K leads to the formation of the Pb/H/Si(111) interface. Upon deposition of Ag at 110 K, however, it was found that a quarter of the monolayer of H migrates to the surface of Ag with the rest of H remaining at the Ag/Si(111) interface. The preadsorbed H atom was desorbed from the surface by deposition of Ag and Cu at 360 K, suggesting that (Ag, Cu)/H/Si(111) is a metastable structure. The relative stability of the interface H is discussed.

Task-model based human robot cooperation using vision

Abstract: In order to assist a human, the robot must recognize human motion in real time by vision, and must plan and execute the needed assistance motion based on the task purpose and the context. In this research, we tried to solve such problems. We defined the abstract task model, analyzed the human demonstration by using events and an event stack, and automatically generated the task models needed in the assistance by the robot. The robot planned and executed the appropriate assistance motions based on the task: models according to the human motions in the cooperation with the human. We implemented a 3D object recognition system and a human grasp recognition system by using trinocular stereo color cameras and a real time range finder. The effectiveness of these methods was tested through an experiment in which the human and the robotic hand assembled toy parts in cooperation.

Stability of Runge-Kutta methods for the generalized pantograph equation

Abstract: This paper deals with stability properties of Runge-Kutta (RK) methods applied to a non-autonomous delay differential equation (DDE) with a constant delay which is obtained from the so-called generalized pantograph equation, an autonomous DDE with a variable delay by a change of the independent variable. It is shown that in the case where the RK matrix is regular stability properties of the RK method for the DDE are derived from those for a difference equation, which are examined by similar techniques to those in the case of autonomous DDEs with a constant delay. As a result, it is shown that some RK methods based on classical quadrature have a superior stability property with respect to the generalized pantograph equation. Stability of algebraically stable natural RK methods is also considered.

Magnetic and Transport Properties of LaCo1-xNixO3-Comparison with La1-xSrxCoO3

Abstract: We have investigated magnetization, neutron scattering, resistivity, thermoelectric power and Hall effect in LaCo 1- x Ni x O 3 ( x =0.05 and 0.1) single crystals. At low temperatures, they show spin-glass behavior with a strong ferromagnetic correlation. Around 500 K, spin state transition from the intermediate spin state ( S =1) to the high spin state ( S =2) accompanied by an insulator-to-metal transition is observed as in undoped LaCoO 3 . These magnetic properties of LaCo 1- x Ni x O 3 are very similar to those previously reported for La 1- x Sr x CoO 3 . The low-temperature transport properties of both LaCo 1- x Ni x O 3 and La 1- x Sr x CoO 3 exhibit the characteristics of an insulator near the insulator-to-metal transition. The sign of the carrier is verified to be positive in both systems from the thermoelectric power measurement. However, the sign of the Hall coefficient of LaCo 1- x Ni x O 3 is negative. These transport properties are discussed in terms of small polaron hopping mechanism.

Spaces of polynomials with roots of bounded multiplicity

Abstract: We describe an alternative approach to some results of Vassiliev on spaces of polynomials, by using the scanning method which was used by Segal in his investigation of spaces of rational functions. We explain how these two approaches are related by the Smale-Hirsch Principle or the h-Principle of Gromov. We obtain several generalizations, which may be of interest in their own right.

Biologically-inspired adaptive dynamic walking of the quadruped on irregular terrain

Abstract: We attempt to induce a quadruped robot to walk dynamically on irregular terrain by using a neural system model. We propose the biologically-inspired control method consisting of four levels: adaptive control using a muscle stiffness model; adaptive control based on vestibular sensation; parameters adjustment based on somatic sensation and reflexes coordination based on vestibular sensation; and motion switching based on visual information. From the experiments, we show that a robot can walk on a single bump and up a slope by using such adaptive control method. We also show that the functions as a lower controller in the Drew's physiological model for leg control mechanism based on visual information are satisfied by a CPG characterized by mutual entrainment with a musculo-skeletal system, automatic interpolation, and self stabilization. These findings suggest a simple method for producing autonomous adaptive dynamic walking on terrain of high degree irregularity.