Showing papers by "Tokyo Institute of Technology published in 2002"

Three-Dimensional Interaction between a Planet and an Isothermal Gaseous Disk. I. Corotation and Lindblad Torques and Planet Migration

Abstract: Gravitational interaction between a planet and a three-dimensional isothermal gaseous disk is studied. In the present paper we mainly examine the torque on a planet and the resultant radial migration of the planet. A planet excites density waves at Lindblad and corotation resonances and experiences a negative torque by the density waves, which causes a rapid inward migration of the planet during its formation in a protoplanetary disk. We formulate the linear wave excitation in three-dimensional isothermal disks and calculate the torques of Lindblad resonances and corotation resonances. For corotation resonances, a general torque formula is newly derived, which is also applicable to two-dimensional disks. The new formula succeeds in reproducing numerical results on the corotation torques, which do not agree with the previously well-known formula. The net torque of the inner and the outer Lindblad resonances (i.e., the differential Lindblad torque) is caused by asymmetry such as the radial pressure gradient and the scale height variation. In three-dimensional disks, the differential Lindblad torques are generally smaller than those in two-dimensional disks. Especially, the effect of a pressure gradient becomes weak. The scale height variation, which is a purely three-dimensional effect, makes the differential Lindblad torque decrease. As a result, the migration time of a planet is obtained as of the order of 106 yr for an Earth-size planet at 5 AU for a typical disk model, which is longer than the result of two-dimensional calculation by the factor of 2 or 3. The reflected waves from disk edges, which are neglected in the torque calculation, can further weaken the disk-planet interaction.

Japanese evaluated nuclear data library version 3 revision-3: JENDL-3.3

Abstract: The revision work of JENDL-3 has been made by considering feedback information of various benchmark tests. The main revised quantities are the resonance parameters, capture and inelastic scattering cross sections, and fission spectra of main actinide nuclides, the total and inelastic scattering cross sections of structural materials, the resonance parameters the capture and inelastic scattering cross sections of fission products, and the γ-ray production data. The revised data were released as JENDL-3.2 in June 1994. The preliminary benchmark tests indicate that JENDL-3.2 predicts various reactor characteristics more successfully than the previous version of JENDL-3.1.

Measurement of the negative muon anomalous magnetic moment to 0.7 ppm

Abstract: We present the first results of the Fermilab National Accelerator Laboratory (FNAL) Muon g-2 Experiment for the positive muon magnetic anomaly a_{μ}≡(g_{μ}-2)/2. The anomaly is determined from the precision measurements of two angular frequencies. Intensity variation of high-energy positrons from muon decays directly encodes the difference frequency ω_{a} between the spin-precession and cyclotron frequencies for polarized muons in a magnetic storage ring. The storage ring magnetic field is measured using nuclear magnetic resonance probes calibrated in terms of the equivalent proton spin precession frequency ω[over ˜]_{p}^{'} in a spherical water sample at 34.7 °C. The ratio ω_{a}/ω[over ˜]_{p}^{'}, together with known fundamental constants, determines a_{μ}(FNAL)=116 592 040(54)×10^{-11} (0.46 ppm). The result is 3.3 standard deviations greater than the standard model prediction and is in excellent agreement with the previous Brookhaven National Laboratory (BNL) E821 measurement. After combination with previous measurements of both μ^{+} and μ^{-}, the new experimental average of a_{μ}(Exp)=116 592 061(41)×10^{-11} (0.35 ppm) increases the tension between experiment and theory to 4.2 standard deviations.

Oxysulfide Sm2Ti2S2O5 as a Stable Photocatalyst for Water Oxidation and Reduction under Visible Light Irradiation (λ ≤ 650 nm)

Abstract: A Ti-based oxysulfide, Sm(2)Ti(2)S(2)O(5), was studied as a visible light-driven photocatalyst. Under visible light (440 nm < or = lambda < or = 650 nm) irradiation, Sm(2)Ti(2)S(2)O(5) with a band gap of approximately 2 eV evolved H(2) or O(2) from aqueous solutions containing a sacrificial electron donor (Na(2)S-Na(2)SO(3) or methanol) or acceptor (Ag(+)) without any noticeable degradation. This oxysulfide is, therefore, a stable photocatalyst with strong reduction and oxidation abilities under visible-light irradiation. The electronic band structure of Sm(2)Ti(2)S(2)O(5) was calculated using the plane-wave-based density functional theory (DFT) program. It was elucidated that the S3p orbitals constitute the upper part of the valence band and these orbitals make an essential contribution to the small band gap energy. The conduction and valence bands' positions of Sm(2)Ti(2)S(2)O(5) were also determined by electrochemical measurements. It indicated that conduction and valence bands were found to have satisfactory potentials for the reduction of H(+) to H(2) and the oxidation of H(2)O to O(2) at pH = 8. This is consistent with the results of the photocatalytic reactions.

M-TRAN: self-reconfigurable modular robotic system

Abstract: In this paper, a novel robotic system called modular transformer (M-TRAN) is proposed. M-TRAN is a distributed, self-reconfigurable system composed of homogeneous robotic modules. The system can change its configuration by changing each module's position and connection. Each module is equipped with an onboard microprocessor, actuators, intermodule communication/power transmission devices and intermodule connection mechanisms. The special design of M-TRAN module realizes both reliable and quick self-reconfiguration and versatile robotic motion. For instance, M-TRAN is able to metamorphose into robotic configurations such as a legged machine and hereby generate coordinated walking motion without any human intervention. An actual system with ten modules was built and basic operations of self-reconfiguration and motion generation were examined through experiments. A series of software programs has also been developed to drive M-TRAN hardware, including a simulator of M-TRAN kinematics, a user interface to design appropriate configurations and motion sequences for given tasks, and an automatic motion planner for a regular cluster of M-TRAN modules. These software programs are integrated into the M-TRAN system supervised by a host computer. Several demonstrations have proven its capability as a self-reconfigurable robot.

Observation of B̄0 → D(*)0 pp̄

Abstract: The B meson decay modes B → Dpp and B → D*pp have been studied using 29.4 fb - 1 of data collected with the Belle detector at KEKB. The B 0 → D 0 pp and B 0 → D* 0 pp decays have been observed for the first time with branching fractions B(B 0 → D 0 pp) = (1.18 ′ 0.15 ′ 0.16) X 10 - 4 and B(B 0 → D* 0 pp) = (1.20 + 0 . 3 3 - 0 . 2 9 ′ 0.21) X 10 - 4 . No signal has been found for the B + → D + pp and B + → D* + pp decay modes, and the corresponding upper limits at 90% C.L. are presented.

Formation of Protoplanet Systems and Diversity of Planetary Systems

Abstract: We investigate the formation of protoplanet systems from planetesimal disks by global (N = 5000 and 10,000 and 0.5 AU 2. The growth timescale increases with a but decreases with Σ1. Based on the oligarchic growth model and the conventional Jovian planet formation scenario, we discuss the diversity of planetary systems. Jovian planets can form in the disk range where the contraction timescale of planetary atmosphere and the growth timescale of protoplanets (cores) are shorter than the lifetime of the gas disk. We find that for the disk lifetime ~108 yr, several Jovian planets would form from massive disks with Σ1 30 with Uranian planets outside the Jovian planets. Only terrestrial and Uranian planets would form from light disks with Σ1 3. Solar system-like planetary systems would form from medium disks with Σ1 10.

Erasing genomic imprinting memory in mouse clone embryos produced from day 11.5 primordial germ cells.

Abstract: Genomic imprinting is an epigenetic mechanism that causes functional differences between paternal and maternal genomes, and plays an essential role in mammalian development. Stage-specific changes in the DNA methylation patterns of imprinted genes suggest that their imprints are erased some time during the primordial germ cell (PGC) stage, before their gametic patterns are re-established during gametogenesis according to the sex of individuals. To define the exact timing and pattern of the erasure process, we have analyzed parental-origin-specific expression of imprinted genes and DNA methylation patterns of differentially methylated regions (DMRs) in embryos, each derived from a single day 11.5 to day 13.5 PGC by nuclear transfer. Cloned embryos produced from day 12.5 to day 13.5 PGCs showed growth retardation and early embryonic lethality around day 9.5. Imprinted genes lost their parental-origin-specific expression patterns completely and became biallelic or silenced. We confirmed that clones derived from both male and female PGCs gave the same result, demonstrating the existence of a common default state of genomic imprinting to male and female germlines. When we produced clone embryos from day 11.5 PGCs, their development was significantly improved, allowing them to survive until at least the day 11.5 embryonic stage. Interestingly, several intermediate states of genomic imprinting between somatic cell states and the default states were seen in these embryos. Loss of the monoallelic expression of imprinted genes proceeded in a step-wise manner coordinated specifically for each imprinted gene. DNA demethylation of the DMRs of the imprinted genes in exact accordance with the loss of their imprinted monoallelic expression was also observed. Analysis of DNA methylation in day 10.5 to day 12.5 PGCs demonstrated that PGC clones represented the DNA methylation status of donor PGCs well. These findings provide strong evidence that the erasure process of genomic imprinting memory proceeds in the day 10.5 to day 11.5 PGCs, with the timing precisely controlled for each imprinted gene. The nuclear transfer technique enabled us to analyze the imprinting status of each PGC and clearly demonstrated a close relationship between expression and DNA methylation patterns and the ability of imprinted genes to support development.

Light-induced conversion of an insulating refractory oxide into a persistent electronic conductor.

Abstract: Materials that are good electrical conductors are not in general optically transparent, yet a combination of high conductivity and transparency is desirable for many emerging opto-electronic applications1,2,3,4,5,6. To this end, various transparent oxides composed of transition or post-transition metals (such as indium tin oxide) are rendered electrically conducting by ion doping1,2,3,4,5,6. But such an approach does not work for the abundant transparent oxides of the main-group metals. Here we demonstrate a process by which the transparent insulating oxide 12CaO·7Al2O3 (refs 7–13) can be converted into an electrical conductor. H- ions are incorporated into the subnanometre-sized cages of the oxide by a thermal treatment in a hydrogen atmosphere; subsequent irradiation of the material with ultraviolet light results in a conductive state that persists after irradiation ceases. The photo-activated material exhibits moderate electrical conductivity (∼0.3 S cm-1) at room temperature, with visible light absorption losses of only one per cent for 200-nm-thick films. We suggest that this concept can be applied to other main-group metal oxides, for the direct optical writing of conducting wires in insulating transparent media and the formation of a high-density optical memory.

Structure of the cell-puncturing device of bacteriophage T4

Abstract: Bacteriophage T4 has a very efficient mechanism for infecting cells1. The key component of this process is the baseplate, located at the end of the phage tail, which regulates the interaction of the tail fibres and the DNA ejection machine2. A complex of gene product (gp) 5 (63K) and gp27 (44K), the central part of the baseplate, is required to penetrate the outer cell membrane of Escherichia coli and to disrupt the intermembrane peptidoglycan layer, promoting subsequent entry of phage DNA into the host. We present here a crystal structure of the (gp5–gp27)3 321K complex, determined to 2.9 A resolution and fitted into a cryo-electron microscopy map at 17 A resolution of the baseplate-tail tube assembly. The carboxy-terminal domain of gp5 is a triple-stranded β-helix that forms an equilateral triangular prism, which acts as a membrane-puncturing needle. The middle lysozyme domain of gp5, situated on the periphery of the prism, serves to digest the peptidoglycan layer. The amino-terminal, antiparallel β-barrel domain of gp5 is inserted into a cylinder formed by three gp27 monomers, which may serve as a channel for DNA ejection.

Control and performance of a doubly-fed induction machine intended for a flywheel energy storage system

Abstract: A large-capacity low-speed flywheel energy storage system based on a doubly-fed induction machine basically consists of a wound-rotor induction machine, and a cycloconverter or a voltage-source pulse width modulation (PWM) rectifier-inverter which is used as an AC exciter. Adjusting the rotor speed makes the machine either release the kinetic energy to the power system or absorb it from the utility grid. Thus, the machine has the capability of achieving not only reactive-power control, but also active-power control based on the flywheel effect of the rotating parts. This paper proposes a new control strategy for a doubly-fed induction machine intended as a flywheel energy storage system, which is characterized by the combination of vector control and decoupling control. The control strategy enables the induction machine to perform active-power control independent of reactive-power control even in transient states. The validity of the theory developed in this paper, along with the effectiveness and viability of the control strategy, is confirmed by computer simulation. In addition, this paper discusses a transient behavior of a magnetizing current in the induction machine.

Large remanent polarization of (Bi, Nd)4Ti3O12 epitaxial thin films grown by metalorganic chemical vapor deposition

Abstract: (104)-oriented Bi4Ti3O12, La-substituted Bi4Ti3O12[(Bi3.44La0.56)Ti3O12] and Nd-substituted Bi4Ti3O12[(Bi3.54Nd0.46)Ti3O12] films were epitaxially grown on (111)SrRuO3//(111)SrTiO3 substrates at 700 °C by metalorganic chemical vapor deposition. All deposited films showed strong (104) orientations. The values of the remanent polarization (Pr) and coercive field (Ec) of the (104)-oriented epitaxial (Bi3.54Nd0.46)Ti3O12 thin film were 25 μC/cm2 and 135 kV/cm, respectively. This Pr value was larger than that of the (104)-oriented (Bi3.44La0.56)Ti3O12 film: Pr and Ec values of the (Bi3.44La0.56)Ti3O12 were 17 μC/cm2 and 145 kV/cm, respectively. These good ferroelectric properties of (Bi3.54Nd0.46)Ti3O12 films can be explained by a large tilting of TiO6 octahedra induced by the substitution of Nd3+, the ionic radius of which is smaller than that of La3+. Moreover, this Pr value is almost equal to that of commercially used lead zirconate titanate (PZT) films for nonvolatile ferroelectric random access memory (Fe...

Phase transitions in pyrolitic mantle around 670‐km depth: Implications for upwelling of plumes from the lower mantle

Abstract: [1] Phase relations in the natural pyrolitic mantle composition (KLB-1) around 670-km depth have been determined at 1600–2200°C by high-pressure experiments using multianvil apparatus. A phase transition between majorite garnet and Al-bearing Mg-rich perovskite occurs at depths similar to the postspinel phase transition. The seismic discontinuity observed at this depth could be caused by a combination of both transitions. The majorite-perovskite transition boundary has a positive Clausius-Clapeyron slope (+0.0013 GPa/°C for majorite-out curve), in contrast to the negative slope of the postspinel phase boundary (−0.0028 GPa/°C). Both transition boundaries cross each other at 1700–1800°C. Below this temperature, formation of Mg-perovskite starts at the majorite-perovskite or akimotoite-perovskite transition coexisting with ringwoodite but is predominantly formed by the postspinel phase transition at higher pressures. On the other hand, the stability of majorite significantly expands relative to Mg-perovskite at higher temperatures. Majorite becomes a dominant postspinel phase, and a majority of Mg-perovskite is formed by the majorite-perovskite transition with a positive Clapeyron slope. Phase transition within high-temperature plumes (>1800°C at 670-km depth) assists their upwelling from the lower mantle through the 670-km boundary. The depth of the 670-km seismic discontinuity becomes much less temperature-sensitive and is greater in such a higher temperature region.

Faithful expression of imprinted genes in cloned mice.

Abstract: Phenotypic anomalies have been observed among animals cloned from somatic cells, putatively caused by epigenetic alterations, especially those of imprinted genes ([1][1]). However, the complexity of potentially contributory technical factors associated with nuclear transfer (NT) experiments could

Nanophotonics: design, fabrication, and operation of nanometric devices using optical near fields

Abstract: This paper reviews progress in nanophotonics, a novel optical nanotechnology, utilizing local electromagnetic interactions between a few nanometric elements and an optical near field. A prototype of a nanophotonic integrated circuit (IC) is presented, in which the optical near field is used as a carrier to transmit a signal from one nanometric dot to another. Each section of this paper reviews theoretical and experimental studies carried out to assess the possibility of designing, fabricating, and operating each nanophotonic IC device. A key device, the nanophotonic switch, is proposed based on optical near-field energy transfer between quantum dots (QDs). The optical near-field interaction is expressed as the sum of the Yukawa function, and the oscillation period of the nutation of cubic CuCl QDs is estimated to be less than 100 ps. To guarantee one-directional (i.e., irreversible) energy transfer between two resonant levels of QDs, intrasublevel transitions due to phonon coupling are examined by considering a simple two-QD plus phonon heat bath system. As a result, the state-filling time is estimated as 22 ps for CuCl QDs. This time is almost independent of the temperature in the Born-Markov approximation. Using cubic CuCl QDs in a NaCl matrix as a test sample, the optical near-field energy transfer was experimentally verified by near-field optical spectroscopy with a spatial resolution smaller than 50 nm in the near-UV region at 15 K. This transfer occurs from the lowest state of excitons in 4.6-nm QDs to the first dipole-forbidden excited state of excitons in 6.3-nm QDs. To fabricate nanophotonic devices and ICs, chemical vapor deposition using an optical near field is proposed; this is sufficiently precise in controlling the size and position of the deposited material. A novel deposition scheme under nonresonant conditions is also demonstrated and its origin is discussed. In order to confirm the possibility of using a nanometric ZnO dot as a light emitter in a nanophotonic IC, spatially and spectrally resolved photoluminescence imaging of individual ZnO nanocrystallites was carried out with a spatial resolution as high as 55 nm, using a UV fiber probe, and the spectral shift due to the quantum size effect was found. To connect the nanophotonic IC to external photonic devices, a nanometer-scale waveguide was developed using a metal-coated silicon wedge structure. Illumination (wavelength: 830 nm) of the metal-coated silicon wedge (width: 150 nm) excites a TM plasmon mode with a beam width of 150 nm and propagation length of 2.5 /spl mu/m. A key device for nanophotonics, an optical near-field probe with an extremely high throughput, was developed by introducing a pyramidal silicon structure with localized surface plasmon resonance at the metallized probe tip. A throughput as high as 2.3% was achieved. Finally, as an application of nanophotonics to, a high-density, high-speed optical memory system, a novel contact slider with a pyramidal silicon probe array was developed. This slider was used for phase-change recording and reading, and a mark length as short as 110 nm was demonstrated.

The acceleration of cosmic-ray protons in the supernova remnant RX J1713.7–3946

Abstract: Protons with energies up to ∼1015 eV are the main component1 of cosmic rays, but evidence for the specific locations where they could have been accelerated to these energies has been lacking2. Electrons are known to be accelerated to cosmic-ray energies in supernova remnants3,4, and the shock waves associated with such remnants, when they hit the surrounding interstellar medium, could also provide the energy to accelerate protons. The signature of such a process would be the decay of pions (π0), which are generated when the protons collide with atoms and molecules in an interstellar cloud: pion decay results in γ-rays with a particular spectral-energy distribution5,6. Here we report the observation of cascade showers of optical photons resulting from γ-rays at energies of ∼1012 eV hitting Earth's upper atmosphere, in the direction of the supernova remnant RX J1713.7–3946. The spectrum is a good match to that predicted by pion decay, and cannot be explained by other mechanisms.

Vortex lattice formation in a rotating Bose-Einstein condensate

Abstract: We study the dynamics of vortex lattice formation of a rotating trapped Bose-Einstein condensate by numerically solving the two-dimensional Gross-Pitaevskii equation, and find that the condensate undergoes elliptic deformation, followed by unstable surface-mode excitations before forming a quantized vortex lattice. The origin of the peculiar surface-mode excitations is identified to be phase fluctuations at the low-density surface regime. The obtained dependence of a distortion parameter on time and that on the driving frequency agree with the recent experiments by Madison et al. [Phys. Rev. Lett. 86, 4443 (2001)].

Investigation of the Physical Properties of Protoplanetary Disks around T Tauri Stars by a 1 Arcsecond Imaging Survey: Evolution and Diversity of the Disks in Their Accretion Stage*

Abstract: We present the results of an imaging survey of protoplanetary disks around single T Tauri stars in Taurus. Thermal emission at 2 mm from dust in the disks has been imaged with a maximum spatial resolution of 1'' by using the Nobeyama Millimeter Array. Disk images have been successfully obtained under almost uniform conditions for 13 T Tauri stars, two of which are thought to be embedded. We have derived the disk properties of outer radius, surface density distribution, mass, temperature distribution, and dust opacity coefficient, by analyzing both our images and the spectral energy distributions on the basis of two disk models: the usual power-law model and the standard model for viscous accretion disks. By examining correlations between the disk properties and disk clocks, we have found radial expansion of the disks with decreasing H? line luminosity, a measure of disk evolution. This expansion can be interpreted as radial expansion of accretion disks due to outward transport of angular momentum with evolution. The increasing rate of the disk radius suggests that the viscosity has weak dependence on radius r and ? ~ 0.01 for the ? parameterization of the viscosity. The power-law index p of the surface density distribution [?(r) = ?0(r/r0)-p] is 0-1 in most cases, which is smaller than 1.5 adopted in the Hayashi model for the origin of our solar system, while the surface density at 100 AU is 0.1-10 g cm-2, which is consistent with the extrapolated value in the Hayashi model. These facts may imply that in the disks of our sample it is very difficult to make planets like ours without redistribution of solids, if such low values for p hold even in the innermost regions.

Control and performance of a fully-digital-controlled shunt active filter for installation on a power distribution system

Abstract: This paper presents a fully-digital-controlled shunt active filter for harmonic termination of a power distribution system. The main purpose of the active filter based on voltage detection is not to compensate for current harmonics but to damp out harmonic propagation caused by line inductors and shunt capacitors for power factor correction. However, time and phase delays inherent in digital controllers might lead to unsatisfactory harmonic-damping performance although digital controllers are preferable to analog controllers. This paper deals with the design and implementation of a digital controller for a shunt active filter based on voltage detection. Experimental results obtained from a laboratory system developed in this paper verify the viability and effectiveness of the fully-digital-controlled active filter.