bluuebunny/crossref_metadata_2025 huggingface dataset:
Reduction of Threading Dislocation Density in an (InAs)1(GaAs)1 Strained Short-Period Superlattice by Atomic Hydrogen Irradiation
Authors: Yokozeki Mikihiro , Yonezu Hiroo , Tsuji Takuto , Naoki Ohshima Naoki Ohshima , Kangsa Pak Kangsa Pak
Published: October 2002

The generation process of dislocations as well as the initial growth mechanism were investigated in the growth of an (InAs)1(GaAs)1 strained short-period superlattice (SSPS) on a GaAs (001) substrate under atomic hydrogen (H) irradiation. A two-dimensional (2D) growth mode was maintained even after lattice relaxation occurred for growth at 350° C. On the other hand, the growth mode changed from 2D to a three-dimensional (3D) one without atomic H irradiation. The threading dislocation density was remarkably reduced and the critical thickness was markedly increased by atomic H irradiation. Misfit dislocations propagating along the <110> and <100> directions were generated at the heterointerface. Such effects disappeared for growth at 500° C, where the atomic H atoms desorb from the growing surface. It was also found that 3D growth was more effectively suppressed in the growth of (InAs)1(GaAs)1 SSPS than in a In0.5Ga0.5As alloy which has the same average In composition as that of the SSPS.
Photoluminescence and Photoluminescence Excitation Spectra of AlAs/GaAs Disordered Superlattices with Various Disordered Lengths
Authors: Kazuyuki Uno Kazuyuki Uno , Susumu Noda Susumu Noda , Akio Sasaki Akio Sasaki
Published: October 2002

A disordered superlattice (d-SL) is a superlattice with artificial disordering. Temperature dependence of photoluminescence (PL) and PL excitation (PLE) spectra are measured for AlAs/GaAs short-period d-SLs with various disordered lengths and are compared with those of ordered superlattices (o-SLs). X-ray satellite peaks are split and PL peak energies are red-shifted with increase of the unit length of disorder. From the PLE results, radiative recombination processes in the AlAs/GaAs d-SLs are inferred to be type-II. The d-SL with a longer unit length of disorder shows more complicated variations in the PL spectrum with changing temperature. The variations are intensified with increase of the disorder lengths. These variations indicate that the localized strength which corresponds to the disorder length is different among the states induced by disordering. The dominant radiative recombination states at higher temperature would correspond to stronger localized states in the d-SLs.
Edge Effects and Scattering in Resonant Tunneling Electron Devices
Authors: Chomsik Lee Chomsik Lee
Published: October 2002

The electron transport mechanisms and the current-voltage characteristics in one- and two-dimensional structures are investigated in double-barrier heterostructure electron devices. The resonant tunneling characteristics due to the reduced size of semiconductor devices are theoretically studied. We compare our results with calculations obtained for the case of weak lateral confinement (3 dimensional to 2 dimensional tunneling when the gated resonant tunneling diode (GRTD) becomes two-dimensional in the well region). Using the Breit and Wigner formula in the case of weak lateral confinement, the elastic and inelastic scattering mechanism are studied. As scattering time τidecreases, the current-voltage characteristics substantially broaden and the peak-to-valley current ratio decreases. We observe the edge effect and negative transconductance in the current-voltage characteristic of the gated resonant tunneling diode.
Corona-Triggering Surface Discharge Switch
Authors: Hamana Nobuhiko , Miyamoto Tetsu , Teruyuki Miyazato Teruyuki Miyazato , Keiichi Takasugi Keiichi Takasugi
Published: October 2002

Several improvements on surface discharge switch were investigated. A new triggering method based on both corona discharge and field distortion was demonstrated to be more reliable and better than for that based on only the field distortion or multiple pin triggers. It was shown that optimum values, at which the switch impedance decreased without losing the features of the surface discharge switch, existed for the thickness and width of the electrodes. The effects of floating electrodes were also investigated to decrease further the switch impedance. The damage to the discharge surface was substancially reduced remarkably by decreasing the switch resistance.
Ultrashort Electromagnetic Pulse Radiation from YBCO Thin Films Excited by Femtosecond Optical Pulse
Authors: Tonouchi Masayoshi , Tani Masahiko , Wang Zhen , Sakai Kiyomi , Tomozawa Seiji , Hangyo Masanori , Murakami Yoshishige , Nakashima Shin-ichi
Published: October 2002

We have observed ultrashort electromagnetic pulse radiation from YBa2Cu3O7-δ thin-film dipole antennas. The supercurrent transient is created by the excitation of the supercarriers into quasiparticles with a femtosecond laser pulse, and freely propagated electromagnetic pulses are measured and characterized. A pulse with 0.5 ps full width at half-maximum was obtained, containing frequency components up to 2.0 THz. A femtosecond time-resolved characterization of the spectra revealed that they strongly depend on the excitation conditions, and the quasiparticle recombination time becomes longer with increase in the excitation intensity. It is also observed that the radiation power increases in proportion to the square of both the bias current and the laser power in the region of weak excitation, which is consistent with the classical theory based on a two-fluid model. In the region of strong excitation, deviation from the classical theory was observed.
Low-Noise and Low-Operation Current AlGaAs Separated-Double-Heterostructure Lasers
Authors: Narui Hironobu , Doi Masato , Kenji Sahara Kenji Sahara , Osamu Matsuda Osamu Matsuda
Published: October 2002

Low operation current of 11 mA at 3 mW was obtained using a Separated-Double-Heterostructure (SDH) laser, whose a buried heterostructure can be fabricated using single-step metalorganic chemical vapor deposition (MOCVD). The relative intensity noise (RIN) for an optical feedback ratio less than 2.0% was below -120 dB/Hz at 700 KHz, with low reflectivity facet coating. Dependence of the RIN on the thickness of the active layer was obtained. It was found that dependence was influenced by variations in the spontaneous emission factor of the laser.
Complementary Optical Bistable Operation with Integration of Two Directional Couplers on LiNbO3 Crystal
Authors: Lee Ching-Ting , Lee How-Chiang , Hsin-Hung Lai Hsin-Hung Lai , Lih-Gen Sheu Lih-Gen Sheu
Published: October 2002

Integrated optical bistable circuits consisting of two parallel reversed-Δβ-directional couplers interconnected by single-mode waveguides were fabricated on a single LiNbO3 crystal. Superior performances of the complementary and consistent types of hysteresis curves are demonstrated theoretically and experimentally. Parallel optical signal processes of different logic gate combinations are obtained.
Influence of Manganese on the Room-Temperature Resistivity of Lanthanum-Doped BaTiO3
Authors: Chen Ying-Chung , Gun-Man Lo Gun-Man Lo , Ming-Yuan Su Ming-Yuan Su
Published: October 2002

The room-temperature resistivity of La-doped BaTiO3 increases with the increased Mn content. Some of the doped Mn ions will segregate at the grain boundaries and behave as acceptor levels. Thus, Mn will exihibit a grain growth inhibition effect which results in the increase of grain boundaries. Then, the surface charge density (N
s) will be increased by the little doped Mn ions and result in a decreased effective donor concentration (N
eff) and an enhanced barrier height at the grain boundaries. Thus, the semiconductivity of La-doped BaTiO3 is decreased by Mn addition.
Simultaneous Measurement of Rotational Viscosity, Pretilt Angle, and Dielectric Anisotropy from Transient Current in Nematic Liquid Crystal Cells
Authors: Okifumi Nakagawa Okifumi Nakagawa , Masahiro Imai Masahiro Imai , Hiroyoshi Naito Hiroyoshi Naito , Akihiko Sugimura Akihiko Sugimura
Published: October 2002

A method for determination of rotational viscosity and pretilt angle in nematic liquid crystal (NLC) cells has been proposed [M. Imai et al.: Jpn. J. Appl. Phys. 33 (1994) 3482]. The method is based on analysis of the transient current in NLC cells and requires that the dielectric anisotropy Δε be determined by another measurement. It is shown that Δε can also be determined from the transient current data. The applicability of the simultaneous measurement is demonstrated using ZLI-2293 (Merck Ltd.).
Diffusion Constants of Si Adsorbates on a Si(001) Surface
Authors: Doi Takahisa , Ichikawa Masakazu , Shigeyuki Hosoki Shigeyuki Hosoki , Ken Ninomiya Ken Ninomiya
Published: October 2002

The thermal diffusion of Si adsorbates deposited on a Si(001) clean surface was investigated using reflection electron microscopy. When the Si sample was heated using direct current, denuded zones with no observable Si islands were created at the terrace edges of the surface. From the denuded zone widths, the diffusion constants of the Si adsorbates on the Si(001) surface parallel and perpendicular to the surface dimer were determined for temperatures from 500° C to 850° C.
Existence of Magnetic Well and Increase in Rotational Transform in an L=2 Helical Heliac with High Coil Period
Authors: Osabe Yukihide , Katsurai Sumio Kogoshi
Published: October 2002

The vacuum properties of an L=2 helical heliac (HH) with high coil period have been studied. The parameter regions of a magnetic well are shown. It is also shown that the rotational transform increase as the helical displacement of a double-helix helical coil increases.
Range Finding Using Frequency-Modulated Interferometry with a Monomode External-Cavity Laser Diode
Authors: Christophe Gorecki Christophe Gorecki
Published: October 2002

A compact double-integrated Mach–Zehnder interferometer is proposed for range finding with a resolution better than 10 µm. It uses a short-external-cavity laser diode which is tuned by modulating the injection current. One of the interferometers is used as a reference for systematic calibration. The other one enables the measurement of the distance. A direct comparison between the phase determined using the measuring interferometer with that given in the reference interferometer results in the increase of the measurement resolution. The results are stabilized for external air-refractive index fluctuations, and the frequency shift of the laser is reduced. The technique can be used to measure absolute distance and velocity of a target with directional discrimination.
Study on Underwater Electric Fields of a Dipole Moment in Shallow Water
Authors: Hirota Megumi , Yoko Teranishi Yoko Teranishi , Kouko Nanaura Kouko Nanaura
Published: October 2002

We studied a method for estimating electric conductivity of the seabed which was necessary for the calculation of electric dipole moment of a boat from underwater electric field. Taking a model of a single electric dipole in a conducting medium with two boundary planes of the sea surface and the seabed, we calculated electric conductivity of the seabed using the measured underwater electric field of a direct current electric dipole. The measurement was conducted with three-axis electric field sensors set on the seabed at a depth of 16.7 m. The underwater electric fields of a tugboat were measured in the same manner as that for a direct current electric dipole. The conductivity of the seabed was calculated using the underwater electric field signature of the tugboat and the result agreed with that obtained from the direct current electric dipole.
Photothermal Dielectric Effect with Liquid
Authors: Yasuo Cho Yasuo Cho , Tomoyuki Kumamaru Tomoyuki Kumamaru
Published: October 2002

A new photothermal technique for measuring the thermal characteristics of a liquid is proposed. This is based on the temperature characteristic of the dielectric constant of light-irradiated liquid. When an alternating temperature change occurs in a liquid material due to the absorption of chopped light, an alternating variation of capacitance is caused due to the temperature characteristic of dielectric coefficient of the liquid and this variation is detectable with sufficient dynamic range and sensitivity using a frequency demodulation technique. Quantitative derivations are presented for the alternating capacitance variation in terms of the optical, thermal, dielectric and geometric parameters of the system. The experimental results for ethyl alcohol are shown to be in good agreement with theoretical ones.
Asymptotic Analyses and Experiments of Sound Propagation in a Surface Duct
Authors: Ohshima Kouji , Kikuchi Toshiaki , Toyohiko Ishihara Toyohiko Ishihara
Published: October 2002

In this paper, we propose the asymptotic representations for calculating the sound field in the surface duct with the exponentially increasing sound velocity profile. We show that the problem of sound propagation in the surface duct is equivalent to that of sound propagation in the concave cylindrical boundary. Thus, utilizing the property of this equivalence, we experimented on sound propagation in the surface duct using a cylindrical water tank. In comparison with the experimental results, we have shown that ray representation is valid in the region sufficiently away from the caustic, while the uniform asymptotic representation is useful in the regions near and away from the caustic. By experiments, we have clarified that the use of the cylindrical water tank is efficient for investigating sound propagation in the surface duct.
Relationship between Acoustic Bandwidth and Characteristics of Sound Propagation in West Mediterranean Sea
Authors: Imayoshi Shinichi , Tsuchiya Toshio , Kikuchi Toshiaki , Fujimori Akio Hasegawa
Published: October 2002

Recently, ocean acoustic tomography (OAT) has been used to investigate the phenomenon of global warming and in wide-area oceanic observations. OAT can determine the sound-speed profile from measured acoustic travel times over known ray paths. The seawater temperature profile and the existence of ocean currents can be estimated using the sound-speed profile. However, the measured arrival time structure contains many pulses with different paths. Ray geometry fundamentals (i.e., numbers of turning points of rays, initial angle, etc.) must be properly identified. The sound-speed structure varies with observation area (i.e., west Mediterranean Sea, low-, mid-latitude sea area, etc.) and season. It has been shown by the Japan Marine Science and Technology Center (JAMSTEC) that a special ocean structure with sound speed increasing linearly with depth is formed in the west Mediterranean Sea. We have to understand the characteristics of sound propagation for each sea area in advance. In this paper, the characteristics of sound propagation for an ocean model for areas such as the west Mediterranean Sea have been analyzed in the time domain using Stickler's normal mode method (SNM). The effects of acoustic bandwidth (ABW) on the pattern of arrivals have been examined.
Hybrid Finite-Element Analysis of Leaky Surface Acoustic Waves in Periodic Waveguides
Authors: Koji Hasegawa Koji Hasegawa , Masanori Koshiba Masanori Koshiba
Published: October 2002

A numerical approach based on the hybrid finite-element method (HFEM) is developed for the analysis of leaky surface acoustic wave (LSAW) propagation along periodic waveguides. Only a region corresponding to one period of the waveguide is discretized, and the dispersion relation between complex propagation constants and frequencies around a stop band and the standing-wave distributions at these frequencies are calculated. Using the hybrid variational principle, the region to which HFEM is applied is divided into elements with suitable interpolation functions; the inhomogeneous region including electrodes is divided into conventional quadratic elements of the serendipity class, and the remaining homogeneous substrate region is replaced with a hybrid element with specialized interpolation functions which are derived from modal expansions and satisfy the radiation condition of LSAWs. In this method, all the effects of piezoelectric perturbation, mechanical perturbation, energy storage due to nonradiated bulk waves, and radiation loss of LSAWs are automatically taken into account. Using this method, aluminum strip gratings on an Al/ST-X quartz or a 36° Y–X LiTaO3 substrate are analyzed, and the validity of this method is confirmed.
5 GHz Range Low-Loss Wide Band Surface Acoustic Wave Filters Using Electrode Thickness Difference Type Unidirectional Transducers
Authors: Hiroyuki Odagawa Hiroyuki Odagawa , Toshiyasu Meguro Toshiyasu Meguro , Kazuhiko Yamanouchi Kazuhiko Yamanouchi
Published: October 2002

A new electrode thickness difference type single phase unidirectional surface acoustic wave (SAW) transducer (ETD-SPUDT), which has λ/4 narrow-gap electrodes is investigated. The ETD-SPUDT is fabricated by cutting part of a meander-line electrode using the shadow of the resist pattern. The theoretical and experimental results show low-loss and large directivity. A low-loss filter for use in the 2 GHz range is fabricated on 128° Y-X LiNbO3 by optical photolithography techniques and for use in the 5 GHz range is fabricated by electron beam exposure. The results show a 3.0 dB insertion loss at 2 GHz and a 4.1 dB loss at 5 GHz.
Piezoelectric Ceramic Transformer Using Piezoelectric Lateral Effect on Input and on Output
Authors: Seiji Hirose Seiji Hirose , Norio Magami Norio Magami , Sadayuki Takahashi Sadayuki Takahashi
Published: October 2002

Recently, the authors have investigated the characteristics of many piezoelectric ceramic materials for high-power use. As a result, some advanced materials suitable for high-power ultrasonic devices have been identified. Using these materials, new piezoelectric transformer designs different from Rosen's design can be utilized for high-voltage supply. In this paper, a piezoelectric transformer using piezoelectric lateral coupling on Input and on output is presented and simulated transformer characteristics are shown.
Overtone Lam \acutee-Mode Quartz Crystal Resonators Fabricated by an Etching Process
Authors: Hirofumi Kawashima Hirofumi Kawashima , Masaru Matsuyama Masaru Matsuyama
Published: October 2002

A quartz crystal resonator of Lam\acutee-mode vibrating in overtone (m=3, n=1) is very available for realization of a frequency over approximately 3 MHz because its frequency constant has a value of 360 kHz ·cm at a cut angle φ=36° and its frequency is dependent upon contour dimensions of the resonator. In this paper, relationships of frequency constant (f ·2z
0), frequency temperature coefficients α, β and a capacitance ratio r versus cut angle φ, and also frequency temperature behavior are, respectively, shown theoretically and experimentally. The calculated values agree well with the measured ones, and a quartz crystal resonator of Lam\acutee-mode vibrating in overtone (m=3, n=1) is successfully obtained with a zero temperature coefficient at room temperature, a small series resistance R
1 and a small capacitance ratio r.
Improvement of Transitional Response Characteristics of a Piezoelectric Vibratory Gyroscope
Authors: Kudo Subaru , Sumio Sugawara Sumio Sugawara , Noboru Wakatuki Noboru Wakatuki
Published: October 2002

We describe the transitional responses in piezoelectric vibratory gyroscopes used as angular rate sensors. The transitional responses for a stepped angular velocity and an external impulse force are experimentally determined. Then, it is shown that these responses are dependent on the difference between the two resonant frequencies in the gyroscope. A new gyroscope structure, in which the null signal is reduced and the responses are improved by using the active damping method, is proposed. The improved responses are presented and the design conditions are clarified.
Surface Acoustic Wave Velocity and Attenuation Dispersion Measurement by Phase Velocity Scanning of Laser Interference Fringes
Authors: Cho Hideo , Sato Harumichi , Takemoto Mikio , Sato Akinobu , Yamanaka Kazushi
Published: October 2002

We developed a noncontact, nondestructive surface acoustic waves (SAW) velocity and attenuation measurement method in the frequency range of 30–110 MHz. This method is based on the phase velocity scanning method previously proposed by the authors that uses laser interference fringes scanned at the phase velocity of SAW to generate single-mode SAW with high intensity and directivity. In order to verify the validity and accuracy of the method, we measured SAW velocity and attenuation in Al and AISI 304 steel. The error in SAW velocity measurement was less than 1% in Al. Also, the attenuation was obtained with high precision in the AISI 304 steel. Then, we applied this method to porous silicon (PS) films on Si wafers as an example of a layered medium. The SAW velocity in PS films decreased with increasing porosity. By fitting the calculated dispersion curve to the measured one, the elastic stiffness of PS films was determined with a relative accuracy of 0.2%, which is thought to be the highest using laser ultrasonic methods. The attenuation of PS films was found to be 6–80 dB/cm in the frequency range of 30–70 MHz. The frequency dependence of attenuation was obtained with high precisely.
Phase-Sensitive Optical Probe for Surface Acoustic Wave Soliton Investigation
Authors: Kavalerov Vadim , Katoh Hideki , Kasaya Naohito , Mitsuteru Inoue Mitsuteru Inoue , Toshitaka Fujii Toshitaka Fujii
Published: October 2002

A novel phase-sensitive optical probe for observation of nonlinear surface acoustic wave (SAW) has been constructed. The probe operates in the acoustic pulse mode that allows input powers as high as 20 W. Light from a solid-state laser diode is modulated at frequencies up to 1 GHz that enables a broad-band detection of SAW and its harmonics. Measurement of harmonic generation has been carried out on LiNbO3 single-crystal plates, and information on both amplitudes and phases of the harmonics has been obtained. The developed experimental technique provides a foundation for optical detection of the waveform of nonlinear SAW, and is aimed at the observation of SAW solitons.
Noncontact Ultrasonic Imaging of Subsurface Defects Using a Laser-Ultrasonic Technique
Authors: Yamawaki Hisashi , Saito Tetsuya , Fukuhara Hiroaki , Masuda Chitoshi , Yoshihisa Tanaka Yoshihisa Tanaka
Published: October 2002

Noncontact ultrasonic imaging of subsurface defects using a laser-ultrasonic technique was demonstrated. Pulsed laser irradiation was used for ultrasonic generation, and optical heterodyne interferometry was used for detection of ultrasonic vibration on the specimen surface. Bonded thin plates with character-shaped hallmarks with 1.5 mm width on bonding layer were used as specimens. Imagings in ultrasonic transmission and reflection modes were performed, and imagings using not only XY-scanning of specimens but also a laser beam scanner were demonstrated. Ultrasonic images of hallmarks located 0.2 mm below the specimen surface were obtained through the experiments.
Experimental Investigation of 3-D Blood Flow Velocity Measurement
Authors: Naotaka Nitta Naotaka Nitta , Kazuhiro Hagihara Kazuhiro Hagihara , Tsuyoshi Shiina Tsuyoshi Shiina
Published: October 2002

Ultrasonic pulse Doppler tomography is generally applied to noninvasive vascular measurement. The present method, however, measures only one component along the beam direction of a three-dimensional (3-D) velocity vector and provides useful information only if the beam direction in relation to the flow velocity vector is known. Images obtained by such systems are not only unsuitable for quantitative evaluation and but also prone to misinterpretation. On the other hand, in terms of real-time data acquisition achieved by scanning 3-D space, a two-dimensional (2-D) array probe is expected to become indispensable for future clinical applications. From this point of view, we have proposed a method of measuring a 3-D velocity vector using the 2-D array probe. In this paper, the principles of the proposed approach are introduced and experimental data obtained using a prototype system and the flow phantom are processed. Experimental results validate the usefulness of the method and its potential for practical use.
Doppler Signal Processing of Blood Flow Using a Wavelet Transform
Authors: Ayumu Matani Ayumu Matani , Osamu Oshiro Osamu Oshiro , Kunihiro Chihara Kunihiro Chihara
Published: October 2002

In medical echography, Doppler signal analysis is one of the most important diagnostic techniques. In Doppler signal analysis, time-frequency localization techniques are necessary. Many techniques have been proposed for the analysis. Short-time Fourier transform (STFT) is one of the most popular techniques. STFT has a fixed time-frequency window making it inappropriate for analysis of signals having a wide bandwidth. On the other hand, recently, wavelet transform (WT) has received much attention. WT has a flexible time-frequency window adaptable to any time-frequency range. In this paper, we describe an application of STFT and WT to Doppler signal processing. The STFT in this study had a rectangular window and required fast Fourier transform (FFT). On the other hand, the WT with the Morlet function as the mother wavelet was modified to reduce the amount of calculation. Then, we compared the suitability of STFT and WT for application to Doppler signal processing of a simulation and an actual blood flow. In the simulation, a flow having fast and slow velocity changes was assumed. The simulation revealed that the WT could reproduce the fast change of flow velocity, while the STFT could not. Then, a blood flow Doppler signal was measured at a point near the mitral valve in the left ventriculus. Only the WT was capable of reproducing the fast change of flow velocity in the heart. The WT is expected to be useful for analyzing blood flow disorders such as regurgitation.
Acoustic Properties of Surfactant Microbubbles in Relation to their Lifetime In Vitro as Determined by Diffusion
Authors: Man Chan Man Chan , Kawan Soetanto Kawan Soetanto , Motoyoshi Okujima Motoyoshi Okujima
Published: October 2002

In this study, to make microbubbles less than 10 µm and to extend their lifetime, sodium laurate is chosen as the material for the coating of microbubbles. In studies of ultrasound contrast agents, the authors are the first to report on the use of sodium laurate as the material for manufacturing the microbubble contrast agent. In addition, the method of producing microbubbles using a syringe is proposed. Using sodium laurate and the syringe method, microbubbles with diameter less than 10 µm are produced. From the result of simulation, it is found that the dissolved gas concentration in the solution surrounding microbubbles plays an important role in determining microbubble lifetime. Microbubbles without coating are calculated to have a lifetime of less than 1 min when the dissolved concentration of gas is about 90%. On the other hand, the lifetime of microbubbles made from sodium laurate is about 5 min longer than the calculated lifetime. Therefore, it is hypothesized that when the dissolved gas in the solution is above a certain level, the mechanism governing annihilation of microbubbles is the dissolution of the surfactant coating layer into the solution, instead of the diffusion of gas from the microbubbles. Since the dissolution time of surfactants is longer than the dissolution time of gas, the lifetime becomes longer.
Effect of Calcium Chloride on Sodium Alginate Microbubbles as Ultrasound Contrast Agent
Authors: Kawan Soetanto Kawan Soetanto , Man Chan Man Chan , Motoyoshi Okujima Motoyoshi Okujima
Published: October 2002

In order to stabilize microbubbles without coating layers to be used as ultrasound contrast agent, the viscosity of the liquid for storage has to be increased. Sodium alginate is a material which forms viscous liquid when its powder is dissolved in water. The viscosity may vary from 1 cP to about 100 cP when the amount of material used is increased from 0.1% to 1%. However, the viscosity is still not enough to make stable microbubbles which can be stored for over several weeks. In this paper, by adding calcium chloride to the sodium alginate solution, a gel-type solution is produced which has a high viscosity capable of holding microbubbles for a long time. By measuring the viscosity of the sodium alginate solution and the solution with calcium chloride solution added, it is known that the solution is changed from a Newtonian liquid to a non-Newtonian liquid when calcium chloride solution is added. Since the attenuation coefficient of microbubble dispersion is proportional to the number of microbubbles, the disappearance of microbubbles lowers the attenuation coefficient. Therefore, in this study, the attenuation coefficient is used as an estimating parameter for the lifetime of microbubbles.
Measurement and Analysis of Vibrations on Surface of Phantom Induced by Piezoelectric Extracorporeal Shock Wave Lithotripter
Authors: Yun-Seok Jang Yun-Seok Jang , Tetsuya Akasaka Tetsuya Akasaka , Michie Sato Michie Sato , Hiroshi Kanai Hiroshi Kanai , Noriyoshi Chubachi Noriyoshi Chubachi
Published: October 2002

We investigated the sound radiated from an object, induced by a piezoelectric extracorporeal shock wave lithotripter (ESWL). However, it was found that more direct measurement is necessary to analyze the sounds in piezoelectric ESWL. Therefore, we investigate the vibrations of a phantom, which are directly measured using laser Doppler velocimetry. The results show that the peak frequency in the power spectrum shifts as the number of shots increases from high frequency to low frequency. The previous results are confirmed by detecting the characteristic peaks obtained from the vibrations of bronze models. The bronze models are used to simulate the phantom during the breaking process. It is found that it is more difficult to make the models vibrate exactly at the focal point than above or below the focal region. These results will be applied to the monitoring of the breaking process and the choice of the optimum focal point on the calculus.
Measurement of Structural and Acoustic Intensities Using Near-Field Acoustical Holography
Authors: Kenji Saijyou Kenji Saijyou , Shigeru Yoshikawa Shigeru Yoshikawa
Published: October 2002

A non contacting method for measuring structural and acoustic intensities is proposed by developing the signal processing in near-field acoustical holography (NAH). The effectiveness of this method is illustrated by applying it to the measurement of radiation from ribbed and unribbed submerged plates. The spatial derivatives for determining the structural intensity are evaluated by a K-space filtration method newly developed by the authors. The experimental data obtained at 928 Hz and 1464 Hz are selected for specific and detailed investigation. The attached ribs have a small influence on the structural intensity flow at 928 Hz, so the vibrational mode of the ribbed plate is the same as that of the unribbed plate. However, since the attached ribs control the direction of vibrational energy flow at 1464 Hz, the vibrational mode of the unribbed plate is markedly changed.
Experimental Measurement of Transverse Velocities Using a Single Circular Planar Transducer by Doppler-Spectra
Authors: Juei Igarashi Juei Igarashi , Tomoki Yokoyama Tomoki Yokoyama , Koichi Mizutani Koichi Mizutani , Keinosuke Nagai Keinosuke Nagai
Published: October 2002

Doppler-spectra is a method for measuring velocity of an object moving across the ultrasonic beam. We verify that the bandwidth of the wave reflected from an object moving across the ultrasonic field radiated from a circular planar transducer depends on the velocity component of the object perpendicular to the axis of radiation. The equation representing the relationship between the transverse velocity and the bandwidth of the reflected wave is derived from the results of the exact calculation of the reflected wave. We have devised an experimental system that includes a circular planar transducer which radiates a burst wave and receives a reflected wave, a controller of a stage supporting a target, and a computer that transacts the received data and calculates the velocities. The results of the experiment confirm the feasibility of the discussion. Combining this method with the classical Doppler method suggests a simple two-dimensional velocity measurement system.
Computer Experiment on Collisions of Solitons with Defects in Crystals
Authors: Ozawa Satoru , Hiki Yosio
Published: October 2002

Molecular dynamics computer simulation has been performed for solitons and phonons propagating in one-dimensional anharmonic mass-spring model crystals. Lattice anharmonicity up to the fourth order in interatomic potential was taken into account. An input pulse displacement was applied to two neighboring atoms in a crystal, and the displacements and kinetic energies of all atoms in the crystal were computed. When the input pulse is small, phonon packets propagating in opposite directions are produced, whereas for a large input pulse solitons of opposite signs with tails consisting of phonons are excited. Collisions of the solitons and phonons with three kinds of lattice defect–mass, spring-constant, and anharmonicity defects–were investigated to obtain the energy transmission coefficients for the collisions and the changes in propagation velocities after the collisions. Reflection characteristics of the defects are markedly different for solitons and phonons.
Effect of Ultrasonic Irradiation on Permeability of Dialysis Membrane
Authors: Li Hui , Etsuzo Ohdaira Etsuzo Ohdaira , Masao Ide Masao Ide
Published: October 2002

The application of ultrasound for accelerating the diffusion of electrolytes through a membrane has been attempted. However, the effect of ultrasound on membrane permeability was not clarified in previous studies. we report the relationship between the time of ultrasound irradiation to membrane and permeability of the membrane, and the relationship between sound pressure and the membrane lifetime. Experiments were conducted using a cellophane membrane which had been irradiated for a certain time by ultrasound of different sound pressures at a frequency of 27.5 kHz, and the permeability of the membrane was examined with 1 wt% NaCl solution at 25° C. It was found that the membrane permeability increases with irradiation time. Furthermore, the lifetime of membrane decreases with increasing sound pressure. The degradation of the permeability by ultrasound is due to ultrasonic cavitation.
Structural and Optical Properties of Polycrystalline Silicon Thin Films Deposited by the Plasma Enhanced Chemical Vapour Deposition Method
Authors: Zhu Furong , Kohara Hajime , Takashi Fuyuki Takashi Fuyuki , Hiroyuki Matsunami Hiroyuki Matsunami
Published: October 2002

Polycrystalline silicon (Si) films have been deposited on both Si and foreign substrates by the plasma enhanced chemical vapour deposition (PECVD) method. Structural properties of Si films were characterised by X-ray diffraction (XRD) and Raman scattering measurements. These films show (110) preferred orientation. Their optical properties were measured by a spectrophotometer over the wavelength range 0.4 to 1.2 µ m. Optical constants of Si films were calculated using the optical admittance method. The crystallinity of the films prepared at different temperatures is investigated by Raman scattering measurements and the two-phase mixture approximation. Results reveal that over 90% of the Si was in a polycrystalline structure in the films when the deposition temperature was over 800° C.
Reduction of Electron Shading Damage Using Synchronous Bias in Pulsed Plasma
Authors: Hashimoto Koichi , Hikosaka Yukinobu , Akihiro Hasegawa Akihiro Hasegawa , Moritaka Nakamura Moritaka Nakamura
Published: October 2002

A novel method is proposed for reducing charging damage due to the “electron shading” effect. The concept is to selectively utilize the coolest electrons in a pulsed plasma at the end of its off period by synchronizing rf bias; thereby one should be able to reduce the negative charge build-up responsible for the damage. This concept has been examined using an inductively coupled plasma (ICP) apparatus. Exposure to a cw Ar ICP damaged most MOS capacitors with a 6-nm-thick gate oxide and connected to 105 shaded antennas. This damage was reduced only slightly even with 5-µ s- on/10-µ s- off pulse modulation when the rf bias was asynchronous (60 kHz). When the rf bias (66.7 kHz) synchronized at the expected optimal phase, the most significant reduction of the damage was observed. This effect is discussed based on the results of time-resolved probe and optical emission measurements.
Deep Trap Measurement in Hg1-xCdxTe by Isothermal Capacitance and Deep-Level Transient Spectroscopy
Authors: Sato Koji , Suno Katsuhiko , Wada Hideo , Okamoto Yoichi , Jun Morimoto Jun Morimoto , Toru Miyakawa Toru Miyakawa
Published: October 2002

Deep-level transient spectroscopy (DLTS) and isothermal capacitance transient spectroscopy (ICTS) were applied to characterize deep levels in Hg1-
x

Cd

x

Te (x=0.22). Compared with DLTS, ICTS gave more reliable results. We found a deep trap with density, activation energy and capture cross section of 1.9×1013 cm-3, 29 meV and 1.4×10-17 cm2, respectively.
A Theoretical Investigation of the Epitaxial Relationship of Al/AlAs(001)
Authors: Tomonori Ito Tomonori Ito
Published: October 2002

The epitaxial relationship between Al thin films and AlAs(001) substrate is investigated theoretically, using cohesive energy calculations based on empirical interatomic potentials. The planar energy difference between Al(001) and Al(110) is very small (estimated at 26 meV/atom) at the interface between the thin films and a substrate. Modification with a single monolayer of In at the interface dramatically stabilizes Al(001) by an energy difference of 242 meV/atom.
New Superconducting Phase in Potassium Amalgam Doped Fullerenes
Authors: Satoh Naoki , Tamuma Sei-ichi , Takenaka Hisashi , Nishizaki Terukazu , Kobayashi Norio
Published: October 2002

Structural and magnetic studies have been performed on potassium amalgam doped fullerenes ( C60). New superconducting phases of K3Hg

x

C60 (x=1, 2, 3) have been discovered by the measurement of magnetization, the transition temperatures of which are 2.7 K, 2.8 K and 3.3 K, respectively. The diamagnetic shielding fractions range from 2 to 17%. The crystal structures of the new phases are found to be face centered cubic and body centered tetragonal ones. In contrast, in the K3-
x

Hg

x

C60 (x=0.3, 0.75, 1.5, 2) samples, Hg atoms are not substitutionally intercalated with K atoms as we expected, and thus Hg atoms have little effect on the formation of a new superconducting phase.
Limit of Electron Mobility in AlGaAs/GaAs Modulation-doped Heterostructures
Authors: Saku Tadashi , Yoshiji Horikoshi Yoshiji Horikoshi , Yasuhiro Tokura Yasuhiro Tokura
Published: October 2002

We have achieved electron mobilities as high as 1.05×107 cm2/Vs at 1.5 K with an electron density of approximately 3×1011/ cm2 for modulation-doped AlGaAs/GaAs by using high purity layers with a residual acceptor concentration of 1×1013/ cm3, and relatively thick spacer layers ∼(75 nm). We found the electron scattering process caused by spatially separated ionized donors to be most important in limiting the observed low-temperature electron mobility, even in these thick-spacer-layer samples. Theoretical calculation predicts that the mobility caused by this scattering mechanism is approximately 1.6×107 cm2/Vs. The observed electron mobility exhibits an anisotropy with respect to the principal axes ([110] and [*BAR*1*BAR*10] directions) on the (001) surface. The anisotropy is such that the mobility in the [*BAR*1*BAR*10] direction is always higher than that in the [110] direction. Theoretical calculations reasonably explained this anisotropy by assuming the existence of islands at the interface which are longer in the [*BAR*1*BAR*10] direction than in the [110] direction, and revealed that the scattering caused by interface roughness was as important as that caused by ionized donors. Thus, these two major components mainly determine the observed low-temperature electron mobility. We also discuss the mobility expected for residual impurity free limit.
Magnetic Anisotropy of Co/Pt Multilayers Evaporated on NaCl(100) Substrates
Authors: Shiomi Shigeru , Okada Masanori , Yasujima Atushi , Maeda Kohji , Tadashi Kobayashi Tadashi Kobayashi , Morio Masuda Morio Masuda
Published: October 2002

Following deposition of a platinum buffer layer, Co and Pt layers were alternately deposited on a NaCl(100) substrate. Substrate temperatures during the deposition of a Pt buffer layer and Co/Pt multilayers, T
S
buf and T
S
Co/Pt, were varied from 300 to 670 K. Co/Pt multilayers as well as a Pt buffer layer was found to grow epitaxially on a NaCl(100) substrate when T
S
buf exceeded 470 K irrespective of T
S
Co/Pt. Perpendicular magnetic anisotropy K
⊥
Co was as small as -4×106 J/m3 when T
S
Co/Pt was 300 K and T
S
buf was 470 or 570 K. However, K
⊥
Co increased with increasing T
S
Co/Pt, becoming positive and almost constant at +5×105 J/m3 when T
S
Co/Pt was 670 K regardless of T
S
buf. In-plane torque curves had fourfold symmetry, giving rise to a positive cubic anisotropy constant K
1
Co exceeding 105 J/m3 which seems too large to be explained by cubic magnetocrystalline anisotropy.
High Coercivity in Co/Pt Multilayers
Authors: Jin-Hong Kim Jin-Hong Kim , Sung-Chul Shin Sung-Chul Shin
Published: October 2002

We have found that the coercivity was increased when a Co/Pt multilayer on a Si3N4 underlayer was prepared onto a rotating substrate. A more than twofold increase in the coercivity is thought to be due to the enhancement of domain wall pinning effects caused by an increase of surface roughness in the Si3N4 underlayer. According to the results of atomic force microscopy, the surface of the Si3N4 underlayer prepared onto a rotating substrate was rougher than that of an underlayer prepared onto a stationary substrate. We believe that the enhancement of surface roughness is due to the oblique incidence of sputtered materials on the rotating substrate.
Dark Current and Breakdown Analysis in In(Al)GaAs/InAlAs Superlattice Avalanche Photodiodes
Authors: Makita Kikuo , Watanabe Isao , Masayoshi Tsuji Masayoshi Tsuji , Kenko Taguchi Kenko Taguchi
Published: October 2002

We studied and compared the reverse-bias characteristics of In(Al)GaAs/InAlAs Superlattice Avalanche Photodiodes (SL-APDs) for three types of different well structures. Dark current characteristics were drastically improved in the InAlGaAs quaternary well structure application, compared with InGaAs wells. In the InAlGaAs quaternary well SL-APDs, we observed, for the first time, a linear relation between dark current and multiplication factor. A multiplied dark current of 2.0×10-4 A/cm2 was the lowest values for the SL-APDs. We also confirmed the temperature coefficient of breakdown voltage to be about 3.4×10-4 K-1. This small temperature dependence suggests a distinctive SL-APD avalanche mechanism due to the contribution of large conduction band discontinuity.
Influence of Electrochromic Damage of a KTiOPO 4 Crystal on a Phase-Locked CW Optical Parametric Oscillator
Authors: Sergey Slyusarev Sergey Slyusarev , Takeshi Ikegami Takeshi Ikegami , Shin-ichi Ohshima Shin-ichi Ohshima , Eiichi Sakuma Eiichi Sakuma
Published: October 2002

The influence of electrochromic damage on a phase-locked cw doubly resonant optical parametric oscillator (OPO) was examined for KTiOPO4(KTP) crystals grown by three different methods. The damage occurred at a relatively low E-field of ∼3 V/mm. Additional thermal feedback control was effective to reduce the E-field necessary for the phase locking for long-term operation.
High-Density Recording on a Phase-Change Optical Disk with Suppression of Material Flow and Recording-Mark Shape-Deformation
Authors: Hirotsune Akemi , Yasushi Miyauchi Yasushi Miyauchi , Motoyasu Terao Motoyasu Terao
Published: October 2002

Double-reflective-layer structure disks with recording film containing a high-melting-point component that does not melt during recording are studied. Cr–Te is chosen for the high-melting-point component to be added to Ge–Sb–Te recording film to suppress a recording film material flow. A Si–Al double-reflective-layer structure has the advantage of increasing the material flow stopping power margin. The structure is also effective in preventing deformation of the recording marks due to the difference in light absorption between the crystallized region and the amorphized recording mark. A Si–Al double-reflective-layer-structure disk with Cr–Ge–Sb–Te recording film shows very little distortion in the reproduced signal waveform even after 104 overwrites of pulse-width modulation (PWM). This makes it suitable for high density recording as a rewritable digital video disk (DVD).
Comparison of Electroluminescence and Photoluminescence Efficiencies of Organic Electroluminescent Devices Having a Bilayer Structure
Authors: Matsumura Michio , Tomonori Akai Tomonori Akai , Masayuki Saito Masayuki Saito
Published: October 2002

The recombination processes of electrons and holes injected into the tris(8-hydroxyquinolino)aluminum (ALQ) layer of organic electroluminescent (EL) devices having the ALQ/diamine biller structure were studied. From the comparison of the EL and PL (photoluminescence) emissions, the quantum efficiency of EL under the normal operational conditions was estimated to be about 0.12 times that of PL. Experimental results suggested the occurrence of nonemissive electron-hole recombination processes at the ALQ/diamine interface.
Effect of La-Doping on Fatigue in Ferroelectric Perovskite Oxides
Authors: Kaoru Miura Kaoru Miura , Masahiro Tanaka Masahiro Tanaka
Published: October 2002

We investigated the effect of La-doping on fatigue in La-doped lead zirconate titanate (PLZT), using the discrete variational Xα cluster method. Our calculations show that the energies of the La 4f states lie between those of the O 2p states and the Ti 3d states just above the Fermi level, and also that remaining electrons prefer to occupy the La 4f states rather than the Ti 3d states. Since the origin of fatigue in lead zirconate titanate (PZT) is the occupancy of Ti 3d states by remaining electrons from oxygen vacancies, we conclude that PLZT is less susceptible to fatigue than PZT because the remaining electrons occupy the La 4f states.
Analysis of Rubbed Polyimide Films by Polarized Infrared Spectroscopy: Effects of Immersion in Organic Solvents
Authors: Hasegawa Ray , Mori Yasushi , Sasaki Hideyuki , Ishibashi Mitsuru
Published: October 2002

We applied polarized infrared (IR) spectroscopy to the analysis of rubbed polyimide (PI) films and evaluated the PI orientation induced by rubbing by measuring the dichroic difference. The IR dichroic difference and liquid crystal (LC) alignment were analyzed for rubbed PI films that were immersed in various organic solvents. The solvents which reduced the dichroic difference and pretilt angle of LC molecules could be characterized in terms of their solubility parameters. When the dichroic difference of the PI films was greatly reduced by the immersion in the solvents, a correlation between the LC pretilt angle and the dichroic difference (i.e. the in-plane orientation of the PI molecules) was observed.