Showing papers by "University of Electro-Communications published in 2001"

Structural ( n, m) determination of isolated single-wall carbon nanotubes by resonant Raman scattering.

Abstract: We show that the Raman scattering technique can give complete structural information for one-dimensional systems, such as carbon nanotubes. Resonant confocal micro-Raman spectroscopy of an (n,m) individual single-wall nanotube makes it possible to assign its chirality uniquely by measuring one radial breathing mode frequency omega(RBM) and using the theory of resonant transitions. A unique chirality assignment can be made for both metallic and semiconducting nanotubes of diameter d(t), using the parameters gamma(0) = 2.9 eV and omega(RBM) = 248/d(t). For example, the strong RBM intensity observed at 156 cm(-1) for 785 nm laser excitation is assigned to the (13,10) metallic chiral nanotube on a Si/SiO2 surface.

Probing phonon dispersion relations of graphite by double resonance Raman scattering.

Abstract: The phonon dispersion relations of graphite can be probed over a wide range of the Brillouin zone by double resonance Raman spectroscopy. The double resonance Raman process provides us with new assignments for the dispersive and nondispersive features observed in the Raman spectra of disordered graphite and carbon nanotubes, some features having been incorrectly assigned previously, or not assigned at all.

Origin of the Breit-Wigner-Fano lineshape of the tangential G-band feature of metallic carbon nanotubes

Abstract: A detailed line-shape analysis of the tangential G-band feature attributable to metallic single-walled carbon nanotubes is presented. Only two components are needed to account for the entire G-band feature for metallic nanotubes. The higher-frequency component has a Lorentzian line shape, and the lower one has a Breit-Wigner-Fano (BWF) line shape. Through comparisons of the Raman tangential G-band spectra from three different diameter distributions of carbon nanotubes, we find that both the frequency and linewidth of the BWF component are diameter dependent and show functional forms consistent with theory. The nanotube curvature is responsible for both the frequency differences between the two components of the characteristic metallic G-band spectrum and the BWF coupling of the lower-frequency component. Surface-enhanced Raman spectroscopy studies provide supporting evidence that the phonon BWF coupling is to an electronic continuum.

Model construction, rule reduction, and robust compensation for generalized form of Takagi-Sugeno fuzzy systems

Abstract: This paper presents a systematic procedure of fuzzy control system design that consists of fuzzy model construction, rule reduction, and robust compensation for nonlinear systems. The model construction part replaces the nonlinear dynamics of a system with a generalized form of Takagi-Sugeno fuzzy systems, which is newly developed by us. The generalized form has a decomposed structure for each element of A/sub i/ and B/sub i/ matrices in consequent parts. The key feature of this structure is that it is suitable for constructing IF-THEN rules and reducing the number of IF-THEN rules. The rule reduction part provides a successive procedure to reduce the number of IF-THEN rules. Furthermore, we convert the reduction error between reduced fuzzy models and a system to model uncertainties of reduced fuzzy models. The robust compensation part achieves the decay rate controller design guaranteeing robust stability for the model uncertainties. Finally, two examples demonstrate the utility of the systematic procedure developed.

Polarized absorption spectra of single-walled 4 A carbon nanotubes aligned in channels of an AlPO(4)-5 single crystal.

Abstract: We report the polarized optical absorption spectra of single-walled $4\AA{}$ carbon nanotubes arrayed in the channels of an $\mathrm{AlPO}{}_{4}\ensuremath{-}5$ single crystal. When the light electric field $(E)$ is polarized parallel to the tube direction $(c)$, the spectra display a sharp peak at 1.37 eV, with two broadbands at 2.1 and 3.1 eV. In the $E\ensuremath{\perp}c$ configuration, the tube is nearly transparent in the measured energy region 0.5--4.1 eV. The optical dipole selection rules are discussed, and the absorption bands are assigned to the dipole transitions between the Van Hove singularities. The measured absorption spectra agreed well with the ab initio calculations of band structure based on the local density function approximation.

Stable Operation of a 300-m Laser Interferometer with Sufficient Sensitivity to Detect Gravitational-Wave Events within Our Galaxy

Abstract: TAMA300, an interferometric gravitational-wave detector with 300-m baseline length, has been developed and operated with sufficient sensitivity to detect gravitational-wave events within our galaxy and sufficient stability for observations; the interferometer was operated for over 10 hours stably and continuously. With a strain-equivalent noise level of $h\sim 5 \times 10^{-21} /\sqrt{\rm Hz}$, a signal-to-noise ratio (SNR) of 30 is expected for gravitational waves generated by a coalescence of 1.4 $M_\odot$-1.4 $M_\odot$ binary neutron stars at 10 kpc distance. %In addition, almost all noise sources which limit the sensitivity and which %disturb the stable operation have been identified. We evaluated the stability of the detector sensitivity with a 2-week data-taking run, collecting 160 hours of data to be analyzed in the search for gravitational waves.

Grain refinement in copper under large strain deformation

Abstract: Structure evolution taking place in pure polycrystalline copper was studied in multiple compressions at room temperature. Rectangular samples were compressed with consequent change in the loading direction from pass to pass. The deformation behaviour at high strains of above 2 shows an apparent steadystate flow following a rapid rise in the flow stress at an early stage of deformation. The structural changes are characterized by the evolution of many mutually crossing subboundaries at low to moderate strains, finally followed by the development of very fine grains with medium- to large-angle boundaries at large strains. These new grains are concluded to be evolved by a kind of continuous reaction, that is continuous dynamic recrystallization (DRX). The grains developed under continuous DRX are much finer than expected from the extrapolation of discontinuous DRX data for hot deformation. An average grain size of about 0.2μ evolved at room temperature is roughly similar to that for subgrains develo...

Accountable-subgroup multisignatures: extended abstract

Abstract: Formal models and security proofs are especially important for multisignatures: in contrast to threshold signatures, no precise definitions were ever provided for such schemes, and some proposals were subsequently broken.In this paper, we formalize and implement a variant of multi-signature schemes, Accountable-Subgroup Multisignatures (ASM). In essence, ASM schemes enable any subgroup, S, of a given group, G, of potential signers, to sign efficiently a message M so that the signature provably reveals the identities of the signers in S to any verifier.Specifically, we provide:The first formal model of security for multisignature schemes that explicitly includes key generation (without relying on trusted third parties);A protocol, based on Schnorr's signature scheme [33], that is both provable and efficient:Only three rounds of communication are required per signature.The signing time per signer is the same as for the single-signer Schnorr scheme, regardless of the number of signers.The verification time is only slightly greater than that for the single-signer Schnorr scheme.The signature length is the same as for the single signer Schnorr scheme, regardless of the number of signers.Our proof of security relies on random oracles and the hardness of the Discrete Log Problem.

Specular Reflection of Very Slow Metastable Neon Atoms from a Solid Surface

Abstract: An ultracold narrow atomic beam of metastable neon in the ${1s}_{3}[(2s{)}^{5}3p:^{1}P_{0}]$ state is used to study specular reflection of atoms from a solid surface at extremely slow incident velocity. The reflectivity on a silicon (1,0,0) surface and a BK7 glass surface is measured at the normal incident velocity between $1\mathrm{mm}/\mathrm{s}$ and $3\mathrm{cm}/\mathrm{s}$. The reflectivity above $30%$ is observed at about $1\mathrm{mm}/\mathrm{s}$. The observed velocity dependence is explained semiquantitatively by the quantum reflection that is caused by the attractive Casimir--van der Waals potential of the atom-surface interaction.

A fuzzy Lyapunov approach to fuzzy control system design

Abstract: This paper discusses the stability of Takagi-Sugeno fuzzy models via the so-called fuzzy Lyapunov function which is a multiple Lyapunov function. The fuzzy Lyapunov function is defined by fuzzily blending quadratic Lyapunov functions. Based on a fuzzy Lyapunov approach, we gives the stability conditions for open-loop fuzzy systems. All the conditions derived here are represented in terms of linear matrix inequalities (LMIs) and contain upper bounds of the time derivative of premise membership functions as LMI variables. Hence, the treatment of the upper bounds play an important and effective role in system analysis and design. In addition, relaxed stability conditions are also derived by considering the property of the time derivative of premise membership functions. Several analysis and design examples illustrate the utility of the fuzzy Lyapunov approach.

Switching control of an R/C hovercraft: stabilization and smooth switching

Abstract: This paper presents stable switching control of an radio-controlled (R/C) hovercraft that is a nonholonomic (nonlinear) system. To exactly represent its nonlinear dynamics, more importantly, to maintain controllability of the system, we newly propose a switching fuzzy model that has locally Takagi-Sugeno (T-S) fuzzy models and switches them according to states, external variables, and/or time. A switching fuzzy controller is constructed by mirroring the rule structure of the switching fuzzy model of an R/C hovercraft. We derive linear matrix inequality (LMI) conditions for ensuring the stability of the closed-loop system consisting of a switching fuzzy model and controller. Furthermore, to guarantee smooth switching of control input at switching boundaries, we also derive a smooth switching condition represented in terms of LMIs. A stable switching fuzzy controller satisfying the smooth switching condition is designed by simultaneously solving both of the LMIs. The simulation and experimental results for the trajectory control of an R/C hovercraft show the validity of the switching fuzzy model and controller design, particularly, the smooth switching condition.

Nd3+:Y2O3 Ceramic Laser

Abstract: We have demonstrated CW one-micron laser oscillation in new ceramic laser material on the base of cubic Nd3+:Y2O3. Slope efficiency of 32% was achieved on an uncoated 1.5 at.% Nd3+:Y2O3 ceramic plate with size of 14 ×2.7 mm under laser diode end-pumping.

Joint density of electronic states for one isolated single-wall carbon nanotube studied by resonant Raman scattering

Abstract: Resonant Raman scattering (RRS) measurements made with a tunable laser provide a highly reliable technique to study the shape of the joint density of electronic states (JDOS) of isolated single-wall carbon nanotubes (SWNTs). RRS can be used to determine the energy value for the one-dimensional (1D) van Hove singularities of a SWNT with a precision better than 5 meV, thereby providing important information that could be used for subsequent measurements on this same SWNT. With RRS, the measured width of the JDOS is on the order of $\ensuremath{\sim}0.1\ensuremath{-}1.0\mathrm{meV},$ further demonstrating that SWNTs really provide a remarkably good model for 1D mesoscopic systems.

Real-time input of 3D pose and gestures of a user's hand and its applications for HCI

Abstract: Introduces a method for tracking a user's hand in 3D and recognizing the hand's gesture in real time without the use of any invasive devices attached to the hand. Our method uses multiple cameras for determining the position and orientation of a user's hand moving freely in a 3D space. In addition, the method identifies pre-determined gestures in a fast and robust manner by using a neural network which has been properly trained beforehand. This paper also describes results of user study of our proposed method and several types of applications, including 3D object handling for a desktop system and a 3D walkthrough for a large immersive display system.

Chirality-dependent G-band Raman intensity of carbon nanotubes

Abstract: The chirality-dependent G-band Raman intensity of single wall carbon nanotubes is calculated using a nonresonant theory for the Raman tensor. We obtain six or three intense Raman modes, respectively, for chiral or achiral nanotubes, whose relative intensities depend on the chiral angle of the nanotube. The longitudinal and transverse optical phonon modes in two-dimensional graphite become, respectively, transverse and longitudinal optical phonon modes in a one-dimensional nanotube. Confocal micro-Raman measurements of individual single wall carbon nanotubes show chirality-dependent spectra of the G-band intensity, as predicted by this theory.

Diameter dependence of the Raman D-band in isolated single-wall carbon nanotubes

Abstract: Raman D-band spectra are reported for several different SWNTs using two different laser energies ${(E}_{\mathrm{laser}}=1.58$ and 2.41 eV). At a fixed ${E}_{\mathrm{laser}},$ individual isolated SWNTs exhibit different diameter-dependent D-band frequencies ${\ensuremath{\omega}}_{D}$ around an average value. For both semiconducting and metallic tubes, ${\ensuremath{\omega}}_{D}$ decreases with decreasing nanotube diameter, though ${\ensuremath{\omega}}_{D}$ for isolated metallic SWNTs is higher than for isolated semiconducting SWNTs. The average D-band frequency depends linearly on ${E}_{\mathrm{laser}},$ as previously observed for SWNT bundles, suggesting that the D-band in SWNTs is activated by defects or by the finite size of the SWNTs.

Electronic transition energy E ii for an isolated ( n , m ) single-wall carbon nanotube obtained by anti-Stokes/Stokes resonant Raman intensity ratio

Abstract: A resonant Raman study of the anti-Stokes and Stokes spectra for individual isolated single-wall carbon nanotubes is presented. The observed asymmetry between the anti-Stokes and Stokes spectra is analyzed within the framework of resonant Raman scattering theory, thereby providing a method for accurately determining the transition energy between van Hove singularities ${E}_{\mathrm{ii}}$ in the electronic density of states and unambiguously assigning the $(n,m)$ nanotube indices. Furthermore, resonant Raman theory allows us to determine whether the resonance is with the incident or scattered photon, and to estimate the relative magnitudes of the matrix elements for the G-band and the radial breathing mode Raman processes.

Secure optical memory system with polarization encryption

Abstract: A novel secure holographic memory system with polarization encoding is proposed. Two-dimensional original data are encoded as a two-dimensional polarization distribution. The polarization state at each pixel is scrambled by a mask that changes the polarization state into a random state. The mask can rotate the direction of the principal axes of the elliptically polarized light and can change the phase retardation at each pixel. The light with the random polarization state is stored as a hologram that can produce the vector phase-conjugate beam. In the decryption the vector phase-conjugation readout can recover the original polarization state by use of the same mask used in the encryption. Experimental results of encryption and decryption with a bacteriorhodopsin film are presented.

Optical Properties and Raman Spectroscopy of Carbon Nanotubes

Abstract: The optical properties and the resonance Raman spectroscopy of single wall carbon nanotubes are reviewed Because of the unique van Hove singularities in the electronic density of states, resonant Raman spectroscopy has provided diameter-selective observation of carbon nanotubes from a sample containing nanotubes with different diameters The electronic and phonon structure of single wall carbon nanotubes are reviewed, based on both theoretical considerations and spectroscopic measurements

Interrelation between ELF transients and ionospheric disturbances in association with sprites and elves

Abstract: Red sprites and elves were observed in Japan during the winter of 1998/99 in Hokuriku region by the group of Tohoku Univ. [Fukunishi et al., EOS, 80(46), F217, 1999]. We analyze quantitatively the results from coordinated measurement consisting of ELF transients, VLF subionopheric disturbances and lightning discharges associated with the optical events. We find the clear straightforward relationship between charge transfer of the parent discharge calculated from ELF (f < 15 Hz) and the ionospheric disturbances regardless of the types of optical events indicating significant atmosphere-mesosphere-ionosphere coupling. Sprites tend to associate with a large ionospheric disturbance (−13 ∼ + 4.6 dB) with a large charge transfer (52 ∼ 175 C), whereas a large lightning peak current (+223 ∼ + 470 kA) (or slow-tail amplitude) leading to the strong EMP is necessary to initiate elves, but with rather small ionospheric disturbances.

Fuzzy modeling via sector nonlinearity concept

Abstract: This paper presents a new fuzzy modeling technique via the so-called sector nonlinearity concept. To fully take advantage of the sector nonlinearity concept, we propose a new type of Takagi-Sugeno fuzzy model and develop an algorithm to identify model parameters. The algorithm consists of two steps. The purpose of the first step is to determine sector coefficients from input-output data. The second part identifies membership functions from the determined sector coefficients and the input-output data. Identification examples illustrate the utility of this approach.

Magnetoresistance of Carbon Nanotubes: From Molecular to Mesoscopic Fingerprints

Abstract: A magnetoresistance study of carbon nanotubes demonstrates that, for small diameters, the location of the chemical potential and the orientation of the magnetic field are parameters that enable tuning from positive to negative magnetoresistance, a phenomenon not related with weak localization. For larger diameters $(\ensuremath{\ge}10\mathrm{nm})$, the conventional mesoscopic behavior of magnetotransport is recovered.

Electronic structure of periodic curved surfaces: Topological band structure

Abstract: The electronic band structure for electrons bound on periodic minimal surfaces is differential-geometrically formulated and numerically calculated. We focus on minimal surfaces because they are not only mathematically elegant (with the surface characterized completely in terms of ``navels'') but represent the topology of real systems such as zeolites and negative-curvature fullerenes. The band structure turns out to be primarily determined by the topology of the surface, i.e., how the wave function interferes on a multiply connected surface, so that the bands are little affected by the way in which we confine the electrons on the surface (thin-slab limit or zero thickness from the outset). Another curiosity is that different minimal surfaces connected by the Bonnet transformation (such as Schwarz's P and D surfaces) possess one-to-one correspondence in their band energies at Brillouin-zone boundaries.

First search for gravitational waves from inspiraling compact binaries using TAMA300 data

Abstract: We analyzed 6 hours of data from the TAMA300 detector by matched filtering, searching for gravitational waves from inspiraling compact binaries. We incorporated a two-step hierarchical search strategy in matched filtering. We obtained an upper limit of 0.59/hour (C.L.=90%) on the event rate of inspirals of compact binaries with mass between 0.3M_solar and 10M_solar and with signal-to-noise ratio greater than 7.2. The distance of 1.4M_solar (0.5M_solar) binaries which produce the signal-to-noise ratio 7.2 was estimated to be 6.2kpc (2.9kpc) when the position of the source on the sky and the inclination angle of the binaries were optimal.

Possible high-T c superconductivity mediated by antiferromagnetic spin fluctuations in systems with Fermi surface pockets

Abstract: We propose that if there are two small pocketlike Fermi surfaces, and the spin susceptibility is pronounced around a wave vector $\mathbf{Q}$ that bridges the two pockets, the spin-singlet superconductivity mediated by spin fluctuations may have a high transition temperature. Using the fluctuation exchange approximation, this idea is confirmed for the Hubbard on a lattice with alternating hopping integrals, for which ${T}_{c}$ is estimated to be almost an order of magnitude larger than those for systems with a large connected Fermi surface.