Showing papers by "Nagoya Institute of Technology published in 1999"

Hidden Markov models based on multi-space probability distribution for pitch pattern modeling

Abstract: This paper discusses a hidden Markov model (HMM) based on multi-space probability distribution (MSD). The HMMs are widely-used statistical models to characterize the sequence of speech spectra and have successfully been applied to speech recognition systems. From these facts, it is considered that the HMM is useful for modeling pitch patterns of speech. However, we cannot apply the conventional discrete or continuous HMMs to pitch pattern modeling since the observation sequence of the pitch pattern is composed of one-dimensional continuous values and a discrete symbol which represents "unvoiced". MSD-HMM includes discrete HMMs and continuous mixture HMMs as special cases, and further can model the sequence of observation vectors with variable dimension including zero-dimensional observations, i.e., discrete symbols. As a result, MSD-HMMs can model pitch patterns without heuristic assumption. We derive a reestimation algorithm for the extended HMM and show that it can find a critical point of the likelihood function.

FDTD computation of temperature rise in the human head for portable telephones

Abstract: Temperature rises in the human head for portable telephones were computed with an anatomically based head model at 900 MHz and 1.5 GHz. The specific absorption rate (SAR) in the human head was determined using the finite-difference time-domain (FDTD) method, while a bioheat equation was numerically solved also using the FDTD method. The portable telephone was modeled by a quarter-wavelength monopole antenna on a dielectric covered metal box. The source geometries considered were the telephone barely touching the ear and the telephone pressing the ear, both having a vertical alignment at the side of the head. The antenna output power was set to be consistent with the portable telephones of today: 0.6 W at 900 MHz and 0.27 W at 1.5 GHz. Computed results show that a phone time of 6-7 min yields a temperature rise of approximately 90% of the steady-state value. Application of the ANSZ/IEEE safety guidelines restricting the 1-g-averaged spatial peak SAR to 1.6 W/kg results in the maximum temperature rise in the brain of 0.06/spl deg/C, and application of the ICNIRP/Japan safety guidelines restricting the 10-g-averaged spatial peak SAR to 2 W/kg results in the maximum temperature rise in the brain of 0.11/spl deg/C, both at 900 MHz and 1.5 GHz.

The effect of rare-earth (La, Sm, Dy, Ho and Er) and Mg on the microstructure in BaTiO3

Abstract: The effect of rare-earth elements, La, Sm, Dy, Ho and Er, on the microstructure in BaTiO3(BT)–MgO–rare-earth oxide based system was studied. Larger amount of MgO was required to suppress the grain growth for the larger ionic radius rare-earth ion (La, Sm)-doped samples than for the smaller ion (Dy, Ho, Er)-doped samples. Also, substitution modes of rare-earth elements and Mg in BT lattice were investigated. The solubility of rare-earth ions in BT lattice and the substitution ratio of rare-earth ions into Ba-site decreased as ionic radius decreases. This suggests that the formation of core-shell structures in BT–MgO–rare-earth oxide based system is dependent on the substitution ratio of rare-earth ions into Ba-site.

GaN on Si Substrate with AlGaN/AlN Intermediate Layer

Abstract: A single crystal GaN thin film was successfully grown on a Si (111) substrate by means of atmospheric pressure metalorganic chemical vapor deposition. Though there is a large difference in thermal expansion coefficients between GaN and Si, an intermediate layer consisting of AlN and AlGaN improved the quality of GaN on Si and reduced meltback etching during growth. Pits and cracks were not observed on the substrate and a mirror-like surface was obtained. The full-width at half maximum (FWHM) of the double-crystal X-ray rocking curve for GaN(0004) was 600 arcsec. Photoluminescence measurement at room temperature for a Si-doped film revealed a sharp band-edge emission with a FWHM of 62.5 meV, which is the narrowest value reported to date.

Remarkable Influence of Silver Islands on the Enhancement of Fluorescence from Eu3+ Ion-Doped Silica Gels

Abstract: A simple methodology has been developed to enable a greater enhancement of fluorescence from europium (Eu3+)-doped silica gels containing adsorbed silver (Ag) islands. The procedure involves the preparation of Eu3+-doped silica gels by a sol−gel method and then immersion in a Ag sol for ca. 48 h to allow the adsorption of Ag islands on the pore surfaces of silica gels. UV−vis spectra show the characteristic surface plasmon resonance of the Ag at around 390 nm, and transmission electron microscopy (TEM) presents Ag islandlike particles on the surface of silica gels. The photoluminescence studies reveal the fact that the enhanced fluorescence originates from the local field enhancement around Eu3+ ions, caused by the electronic plasmon resonance of the Ag islands.

Enhanced fluorescence from Eu3+ owing to surface plasma oscillation of silver particles in glass

Abstract: We describe the increase of europium ion (Eu3+) fluorescence owing to resonant plasma oscillation of silver (Ag) particles in silica (SiO2) glass, which were precipitated by annealing in a reducing atmosphere sol–gel derived SiO2 glass containing Ag+ and Eu3+ ions. Nanometer size effects of Ag particles on the increase were also investigated as a function of the reduction time. The mean particle size and the volume fraction of silver particles in glass were estimated from absorption spectra using the Mie–Drude theory modified by the electron mean free path model. The fluorescence from Eu3+ ions when the excitation was a N2 laser increased in the presence of silver particles of ∼4.3 nm size. From comparison of the radiative damping time of the plasma oscillation with the lifetime of Eu3+ fluorescence we, tentatively, concluded that the induced surface plasma oscillation by incidence and the interaction between Eu3+ and Ag particles occurred simultaneously.

Threshold proxy signatures

Abstract: A (t, n) threshold proxy signature scheme allows t or more proxy signers from a designated group of n proxy signers to sign messages on behalf of an original signer. The authors review both Zhang's threshold proxy signature scheme and Kim's threshold proxy signature scheme. They show that Zhang's scheme suffers from some weaknesses and Kim's scheme suffers from a disadvantage. Based on Zhang's scheme, they propose a new threshold proxy signature scheme to defeat the weaknesses of Zhang's scheme and the disadvantage of Kim's scheme.

Block Copolymer Mediated Synthesis of Gold Quantum Dots and Novel Gold−Polypyrrole Nanocomposites

Abstract: Polystyrene-block-poly(2-vinylpyridine) with different block lengths, viz., 190−190 and 800−860 monomer units, have been employed in order to obtain monodisperse Au nanoparticles, dispersed in a polypyrrole (PPY) matrix. In consonance with optical absorption spectra, the formation of a nanodispersion of Au has been corroborated by Mie−Drude theory. The annealing process yields a single Au nanocluster (core) in each micelle, covered by a PPY shell, forming unique core−shell particles. By variation of the block length of the polymer, different sizes of Au nanoclusters, ranging from 7 to 13 nm, covered by a PPY shell within the spherical microdomains of the block copolymer, have been prepared. Different shapes of Au particles, viz., spherical, cubic, tetrahedral, and octahedral, have been observed, with a little nudge in the preparative strategies. Furthermore, we have also observed elegant dendritic nanostructures of Au−PPY in another different approach, by employing vapor phase polymerization of pyrrole on...

High Proton Conductivity in Porous P2O5−SiO2 Glasses

Abstract: High proton conducting P2O5−SiO2 glasses were prepared using the sol−gel method, the electrical conductivities of which were studied in relation to the pore structure and the adsorbed water. The pore properties of SiO2 and P2O5−SiO2 glasses were controlled by addition of formamide during the gel synthesis, the specific surface areas of which were changed from 200 to 900 m2/g-glass. These glasses absorb water molecules on exposure to a humid atmosphere. The conductivity increased with increasing logarithm of water concentration and reached a saturated value above the water vapor pressure of 0.8. The highest conductivity, 2 × 10-2 S/cm at room temperature, was achieved by 5P2O5−95SiO2 glass heated at 700 °C and absorbing the water molecules.

Calcium phosphate invert glasses with soda and titania

Abstract: Calcium phosphate glasses in the pyrophosphate region were obtained by addition of Na2O and TiO2. The glasses with CaO content of ⩾55 mol% contain pyrophosphate and orthophosphate groups without metaphosphate by Raman and NMR observation. Crystalline phases with bioactivity such as β-Ca3(PO4)2 and/or β-Ca2P2O7 were precipitated in the glasses at 850°C. Some of the glasses can be sintered at 850°C, resulting in glass-ceramics containing significant amounts of bioactive phases.

Incremental learning methods with retrieving of interfered patterns

Abstract: There are many cases when a neural-network-based system must memorize some new patterns incrementally. However, if the network learns the new patterns only by referring to them, it probably forgets old memorized patterns, since parameters in the network usually correlate not only to the old memories but also to the new patterns. A certain way to avoid the loss of memories is to learn the new patterns with all memorized patterns. It needs, however, a large computational power. To solve this problem, we propose incremental learning methods with retrieval of interfered patterns (ILRI). In these methods, the system employs a modified version of a resource allocating network (RAN) which is one variation of a generalized radial basis function (GRBF). In ILRI, the RAN learns new patterns with a relearning of a few number of retrieved past patterns that are interfered with the incremental learning. We construct ILRI in two steps. In the first step, we construct a system which searches the interfered patterns from past input patterns stored in a database. In the second step, we improve the first system in such a way that the system does not need the database. In this case, the system regenerates the input patterns approximately in a random manner. The simulation results show that these two systems have almost the same ability, and the generalization ability is higher than other similar systems using neural networks and k-nearest neighbors.

Electrical and elastic properties of conductor-polymer composites

Abstract: Several series of conductor-polymer composites were prepared from metal, graphite and conducting ceramics as filler materials, and epoxy, silicone rubber, polyethylene and polypropylene as polymer matrix. Their percolation curves, pressure dependence of resistivity, and Young's modulus were examined for applications such as a pressure sensor.

Effect of retained austenite on the microstructure and mechanical properties of martensitic precipitation hardening stainless steel

Abstract: The effect of retained austenite (γ) on the microstructure and mechanical properties of a martensitic precipitation hardening stainless steel was experimentally investigated, whose chemical composition was Fe-1.8Cu-15.9Cr-7.3Ni-1.2Mo-0.08Nb-low C, N (mass %). The microstructures of all specimens consist of a typical lath martensite with interlath films of the retained γ, which is not reverted with aging. Cu-rich precipitates which may contribute to precipitation hardening can not clearly be observed. The tensile properties and Charpy absorbed energy are linearly approximated to the amount of retained γ as follows: 0.2% Y.S. (MPa) = 1192.3 − 13.6 × γ%, T.S. (MPa) = 1250.1 − 9.3 × γ%, El. (%) = 12.16 + 0.43 × γ%, R.A. (%) = 64.25 + 0.14 × γ%, and A.E. (J) = 72.5 + 0.8 × γ%. The introduction of retained γ is not beneficial to the fatigue limit. An excellent combinations of strength, ductility and toughness obtained in the present work is attributed to the introduction of retained γ and also to the chemical composition of the specimen used.

Preparation of novel hollow fiber silica using collagen fibers as a template

Abstract: A novel fibrous silica with a gnarled surface structure and an inner tube with bundle-replicated stripes was prepared by sol-gel polymerization of tetraethoxysilane using collagen fibers as a template.

Probe measurements and global model of inductively coupled Ar/CF4 discharges

Abstract: The electron energy distribution function (EEDF) is measured with a Langmuir probe in an inductively-coupled radio frequency (RF, 13.56 MHz) Ar/CF4 discharge over a pressure range 3-30 mTorr by changing the CF4 content from 0 to 20%, while keeping the power injected into the plasma at about 50 W. EEDFs measured at a pressure lower than 10 mTorr are bi-Maxwellian distributions over the measured CF4 content, while those at a pressure of 30 mTorr are Druyvesteyn ones in the presence of a small amount of CF4. The average electron energy slightly increases with CF4 content, while the electron density decreases. The decrease in the electron density with addition of CF4 is more prominent as the total pressure increases. Dependences of the electron density and the averaged electron energy on CF4 content are predicted in the global model.

High-Quality GaN on Si Substrate Using AlGaN/AlN Intermediate Layer

Abstract: A single crystal GaN thin film was successfully grown on a Si(111) substrate by means of atmospheric-pressure metalorganic chemical vapor deposition. An intermediate layer consisting of AlN and AlGaN improved the quality of GaN on Si with a mirror-like surface and reduced the pits and cracks over the surface. The full width at half maximum (FWHM) of the double-crystal X-ray rocking curve for GaN(0004) was 600 arcsec. Photoluminescence measurement at 4.2 K for a nondoped film revealed a sharp band-edge emission with a FWHM of 8.8 meV, which is the narrowest value reported to date. GaInN multi-quantum-well structure was grown on this structure and showed a strong blue emission peaking at 470 nm. The results suggest GaN on Si with an AlGaN/AlN intermediate layer provides reliable light emitting devices on Si substrate.

Randomized initialization protocols for packet radio networks

Abstract: The main contribution of this work is to propose efficient randomized leader election and initialization protocols for Packet Radio Networks (PRN, for short). As a result of the initialization protocol, the n stations of a PRN are assigned distinct integer IDs from 1 to n. The results include protocols to: (1) initialize the single-channel PRN with the collision detection (CD) capability in O(n) rounds with probability at least 1-1/(2/sup n/); (2) initialize the k-channel PRN with CD capability in O(n/k) rounds with probability at least 1-1/n, whenever k/spl les/n/3 log n; (3) elect a leader on the single-channel PRN with no CD in O((log n)/sup 2/) broadcast rounds with probability at least 1-1/n; (4) initialize the single-channel PRN with no CD in O(n) rounds with probability at least 1-1/(2/spl radic/n); (5) initialize the k-channel PRN with no CD in O(n/k) broadcast rounds with probability at least 1-1/n, whenever k/spl les/n/(4(log n)/sup 2/).

Synthesis of α–Al2O3 platelets using sodium sulfate flux

Abstract: When powder mixtures of {Al2(SO4)3 + Na2SO4}or {γ–Al2O3 [obtained by heating Al2(SO4)3 at 900 °C for 3 h] + Na2SO4} were heated in an alumina crucible at 1100 °C for 1 h, α–Al2O3 platelets were formed. The powder mixture of {Al2(SO4)3 + 2Na2SO4} yielded aggregations of platelets that were less than 5 μm in size. The size of the aggregations increased in proportion to the amount of Na2SO4, and aggregations of 120 μm were obtained using a mixture of {Al2(SO4)3 + 6Na2SO4}. The powder mixture of {γ–Al2O3 + 2Na2SO4 yielded hexagonal platelets having an average diameter of 3.7 μm and an average thickness of 0.3 μm. In addition to aggregation size, the size of the hexagonal platelets also increased in proportion to the amount of Na2SO4, and platelets having an average diameter of 5 μm were obtained using a mixture of {γ–Al2O3 + 6Na2SO4}.

Design of discrete-time repetitive control system for pole placement and application

Abstract: A new repetitive control system is proposed from the viewpoint of pole placement. First, the proposed repetitive controller can assign all poles of the closed-loop system on a disk with a given radius and the center at the origin. As a result, faster convergence of the controlled error to zero than the previous ones is obtained. Next, the proposed controller is obtained explicitly, and the design method does not require an equation to be solved. The design effort is independent of the period of the repetitive signals to be tracked or rejected. In other words, the design effort is very small, even if the period is very large. Then, the robustness of the control system is improved by introducing a low-pass finite-duration impulse-response filter in the controller. Finally, the proposed scheme is applied to a DC servomotor system, and the effectiveness is demonstrated by both simulations and experiments.