Showing papers by "Tokyo Institute of Technology published in 1997"

Direct observation of the rotation of F1-ATPase

Abstract: Cells employ a variety of linear motors, such as myosin, kinesin and RNA polymerase, which move along and exert force on a filamentous structure. But only one rotary motor has been investigated in detail, the bacterial flagellum (a complex of about 100 protein molecules). We now show that a single molecule of F1-ATPase acts as a rotary motor, the smallest known, by direct observation of its motion. A central rotor of radius approximately 1 nm, formed by its gamma-subunit, turns in a stator barrel of radius approximately 5nm formed by three alpha- and three beta-subunits. F1-ATPase, together with the membrane-embedded proton-conducting unit F0, forms the H+-ATP synthase that reversibly couples transmembrane proton flow to ATP synthesis/hydrolysis in respiring and photosynthetic cells. It has been suggested that the gamma-subunit of F1-ATPase rotates within the alphabeta-hexamer, a conjecture supported by structural, biochemical and spectroscopic studies. We attached a fluorescent actin filament to the gamma-subunit as a marker, which enabled us to observe this motion directly. In the presence of ATP, the filament rotated for more than 100 revolutions in an anticlockwise direction when viewed from the 'membrane' side. The rotary torque produced reached more than 40 pN nm(-1) under high load.

P-type electrical conduction in transparent thin films of CuAlO2

Abstract: Optically transparent oxides tend to be electrical insulators, by virtue of their large electronic bandgap (⩾3.1 eV). The most notable exceptions are doped versions of the oxides In2O3, SnO2 and ZnO—all n-type (electron) conductors—which are widely used as the transparent electrodes in flat-panel displays1,2. On the other hand, no transparent oxide exhibiting high p-type (hole) conductivity is known to exist, whereas such materials could open the way to a range of novel applications. For example, a combination of the two types of transparent conductor in the form of a pn junction could lead to a ‘functional’ window that transmits visible light yet generates electricity in response to the absorption of ultraviolet photons. Here we describe a strategy for identifying oxide materials that should combine p-type conductivity with good optical transparency. We illustrate the potential of this approach by reporting the properties of thin films of CuAlO2, a transparent oxide having room-temperature p-type conductivity up to 1 S cm−1. Although the conductivity of our candidate material is significantly lower than that observed for the best n-type conducting oxides, it is sufficient for some applications, and demonstrates that the development of transparent p-type conductors is not an insurmountable goal.

Paleogeographic maps of the Japanese Islands: Plate tectonic synthesis from 750 Ma to the present

Abstract: A series of paleogeographic maps of the Japanese Islands, from their birth at ca 750–700 Ma to the present, is newly compiled from the viewpoint of plate tectonics. This series consists of 20 maps that cover all of the major events in the geotectonic evolution of Japan. These include the birth of Japan at the rifted continental margin of the Yangtze craton (ca 750-700 Ma), the tectonic inversion of the continental margin from passive to active (ca 500 Ma), the Paleozoic accretionary growth incorporating fragments from seamounts and oceanic plateaux (ca 480-250 Ma), the collision between Sino-Korea and Yangtze (250–210 Ma), the Mesozoic to Cenozoic accretionary growth (210 Ma-present) including the formation of the Cretaceous paired metamorphic belts (90 Ma), and the Miocene back-arc opening of the Japan Sea that separated Japan as an island arc (25-15 Ma).

Permo-Triassic Boundary Superanoxia and Stratified Superocean: Records from Lost Deep Sea

Abstract: Pelagic cherts of Japan and British Columbia, Canada, recorded a long-term and worldwide deep-sea anoxic (oxygen-depleted) event across the Permo-Triassic (or Paleozoic and Mesozoic) boundary (251 ± 2 million years ago). The symmetry in lithostratigraphy and redox condition of the boundary sections suggest that the superocean Panthalassa became totally stratified for nearly 20 million years across the boundary. The timing of onset, climax, and termination of the oceanic stratification correspond to global biotic events including the end-Guadalupian decline, the end-Permian extinction, and mid-Triassic recovery.

Ferromagnetic order induced by photogenerated carriers in magnetic iii-v semiconductor heterostructures of (in,mn)as/gasb

Abstract: We report the inducement of a ferromagnetic order by photogenerated carriers in a novel III-V--based magnetic semiconductor heterostructure $p$-(In,Mn)As/GaSb grown by molecular beam epitaxy. At low temperatures $(l35\mathrm{K})$, samples preserve ferromagnetic order even after the light is switched off, whereas they recover their original paramagnetic condition above 35 K. The results are explained in terms of hole transfer from GaSb to InMnAs in the heterostructure, which enhances a ferromagnetic spin exchange among Mn ions in the InMnAs layer.

Ultra-thin epitaxial films of graphite and hexagonal boron nitride on solid surfaces

Abstract: In this article, we have reviewed the recent progress of the experimental studies on ultra-thin films of graphite and hexagonal boron nitride (h-BN) by using angle-resolved electron spectroscopy together with other techniques. The fundamental properties of these high-quality films are discussed on the basis of the data on dispersion relations of valence electrons, phonon dispersion etc. The interfacial orbital mixing of the -state of the monolayer graphite (MG) with the d states of the reactive substrates is the origin for the phonon softening, expansion of the nearest-neighbour C - C distance, modification of the -band, low work function, and two-dimensional plasmons with high electron density, etc. In the cases of weak mixing at the interface between the MG and relatively inert substrates, the observed properties of the MG are very close to the bulk ones. In contrast to the case for MG, the interfacial interaction between the h-BN monolayer and the substrate is weak.

Catalysis in the Production and Reactions of Dimethyl Carbonate, an Environmentally Benign Building-Block

Abstract: Dimethyl carbonate (DMC) is a unique molecule having versatile chemical reactivity. In many aspects, DMC is an environmentally benign building block. DMC is a safe substitute for dimethyl sulfate or methyl halides. These conventional methylating agents are toxic and corrosive and give a stoichiometric amount of inorganic by-products. Methylation with DMC is often very selective. The mono-methylation of phenylacetonitrile, O -methylation of phenol and N -methylation of aniline are such examples. The transesterification of DMC with phenol yields methyl phenyl carbonate, which gives diphenyl carbonate by further transesterification with DMC or the disproportionation. Diphenyl carbonate is an essential starting material for polycarbonates resins by “non-phosgene” process. DMC serves also as a methoxycarbonylation agent. The methoxycarbonylation of amines with DMC gives methyl carbamates, which can be converted into isocyanates by decomposition. DMC reacts with silica at 550–600 K to afford tetramethoxysilane. This gas-solid reaction gives a simple and convenient method to depolymerize silica. In this review, various aspects of the reactions of DMC and the catalysts involved in the reactions will be overviewed.

Unique morphology of the human eye

Abstract: Human eyes have a widely exposed white sclera surrounding the darker coloured iris, making it easy to discern the direction in which they are looking1 We compared the external morphology of primate eyes in nearly half of all primate species, and show that this feature is uniquely human Humans have the largest ratio of exposed sclera in the eye outline, which itself is elongated horizontally We suggest that these are adaptations to extend the visual field by allowing greater eye movement, especially in the horizontal direction, and to enhance the ease of detecting the gaze direction of another individual

Molecular evidence from retroposons that whales form a clade within even-toed ungulates

Abstract: The origin of whales and their transition from terrestrial life to a fully aquatic existence has been studied in depth. Palaeontological1,2, morphological3 and molecular studies4,5,6,7 suggest that the order Cetacea (whales, dolphins and porpoises) is more closely related to the order Artiodactyla (even-toed ungulates, including cows, camels and pigs) than to other ungulate orders. The traditional view that the order Artiodactyla is monophyletic has been challenged by molecular analyses of variations in mitochondrial and nuclear DNA5,6,7. We have characterized two families of short interspersed elements (SINEs) that were present exclusively in the genomes of whales, ruminants and hippopotamuses, but not in those of camels and pigs. We made an extensive survey of retropositional events that might have occurred during the divergence of whales and even-toed ungulates. We have characterized nine retropositional events of a SINE unit, each of which provides phylogenetic resolution of the relationships among whales, ruminants, hippopotamuses and pigs. Our data provide evidence that whales, ruminants and hippopotamuses form a monophyletic group.

Pacific-type orogeny revisited : Miyashiro-type orogeny proposed

Abstract: The concept of Pacific-type orogeny is revised, based on an assessment of geologic data collected from the Japanese Islands during the past 25 years. The formation of a passive continental margin after the birth of the Pacific Ocean at 600 Ma was followed by the initiation of oceanic plate subduction at 450 Ma. Since then, four episodes of Pacific-type orogeny have occurred to create an orogenic belt 400 km wide that gradually grew both oceanward and downward. The orogenic belt consists mainly of an accretionary complex tectonically interlayered with thin (<2 km thick), subhorizontal, high-P/T regional metamorphic belts. Both the accretionary complex and the high-P/T rocks were intruded by granitoids ∼100 million years after the formation of the accretionary complex. The intrusion of calc-alkaline (CA) plutons was synchronous with the exhumation of high-P/T schist belts. Ages from microfossils and K-Ar analysis suggest that the orogenic climax happened at a time of mid-oceanic ridge subduction. The orogenic climax was characterized by the formation of major subhorizontal orogenic structures, the exhumation of high-P/T schist belts by wedge extrusion and subsequent domed uplift, and the intrusion-extrusion of CA magma dominantly produced by slab melting. The orogenic climax ended soon after ridge subduction, and thereafter a new Pacific-type orogeny began. A single Pacific-type orogenic cycle may correspond to the interaction of the Asian continental margin with one major Pacific oceanic plate. Ophiolites in Japan occur as accreted material and are not of island-arc but of plume origin. They presumably formed after the birth of the southern Pacific superplume at 600 Ma, and did not modify the cordilleran-type orogeny in a major way. Microplates, fore-arc slivers, intra-oceanic arc collisions and the opening of back-arc basins clearly contributed to cordilleran orogenesis. However, they were of secondary importance and served only to modify pre-existing major orogenic components. The most important cause of cordilleran-type orogeny is the subduction of a mid-oceanic ridge, by which the volume of continental crust increases through the transfer of granitic melt from the subducting oceanic crust to an orogenic welt. Accretionary complexes are composed mainly of recycled granitic sediments with minor amounts of oceanic material, which indicate that the accretion of oceanic material, including huge oceanic plateaus, was not significant for orogenic growth. Instead, the formation and intrusion of granitoids are the keys to continental growth, which is the most important process in Pacific-type orogeny. Collision-type orogeny does not increase the volume of continental crust. The name ‘Miyashiro-type orogeny’ is proposed for this revised concept of Pacific-type or cordilleran-type orogeny, in order to commemorate Professor A. Miyashiro's many contributions to a better understanding of orogenesis.

Gold nanobridge stabilized by surface structure

Abstract: We formed gold nanowires using electron-beam irradiation in an ultrahigh vacuum electron microscope. The dimensions of these nanowires were 0.8--3 nm in thickness and 5--10 nm in length. The nanowires showed lasting stability. We propose a structure model for a nanowire with a thickness of 2 nm. The model is represented by a hexagonal prism; the surface layer of the prism has a hexagonal-close-packed (hcp) lattice, and the core of the prism has a face-centered-cubic structure. The nanowire is considered to be stabilized by the hcp lattices of the surfaces.

Photocatalytic Decomposition of Water on Spontaneously Hydrated Layered Perovskites

Abstract: A series of ion-exchangeable layered perovskite type oxides, A2-xLa2Ti3-xNbxO10 (A = K, Rb, Cs; x = 0, 0.5, 1.0), were found to be highly efficient photocatalysts for overall water splitting when a small amount of Ni was loaded. These compounds are spontaneously hydrated even in an aqueous alkaline solution and decompose intercalated H2O molecules into H2 and O2 under the bandgap irradiation.

Melting experiments on lherzolite KLB-1 under hydrous conditions and generation of high-magnesian andesitic melts

Abstract: The partial melting of natural lherzolite KLB-1 at 1 GPa was studied for both H2O undersaturated and saturated conditions. The quenched glasses obtained at 1000 and 1050 °C are andesitic in composition, having 54.4–60.3 wt% SiO2, whereas partial melts formed at temperatures above 1100 °C have basaltic compositions. This suggests that high-magnesian andesites can be formed by direct partial melting of the hydrous upper mantle only at relatively low temperatures. These andesitic melts, together with those obtained at 1100 °C, contain more than 3 wt% H2O and have compositions characteristic of hydrous melts—high SiO2 and Al2O3 and low FeO*, MgO, and CaO. The results of melting studies on KLB-1 show a strong increase in the degree of melting when H2O is added to lherzolite at a given temperature.

Strong convergence of approximated sequences for nonexpansive mappings in Banach spaces

Abstract: In this paper, we study the convergence of the sequence defined by x0 ∈ C, xn+1 = αnx + (1− αn)Txn, n = 0, 1, 2, . . . , where 0 ≤ αn ≤ 1 and T is a nonexpansive mapping from a closed convex subset of a Banach space into itself.

A new control strategy for voltage type PWM rectifiers to realise zero steady-state control error in input current

Abstract: In this paper, a new simple control strategy for AC input current of voltage-type pulsewidth modulation (PWM) rectifiers which can eliminate the steady-state control error completely is proposed. This control method requires neither the instantaneous value of the supply voltage nor any accurate circuit parameters on the AC side of the rectifier. Thus, a robust operation against the variation of the circuit parameters can be achieved. In the proposed control system, a digital resonant element implemented by a digital signal processor (DSP) is introduced as a feedback controller. The digital resonant element exhibits a function similar to an integrator for the fundamental frequency components. Thus, it can eliminate the steady-state control error of the input current completely, The principle of the proposed control method is discussed, and its effectiveness is shown theoretically. The detailed method of the implementation of the lossless digital resonant element is explained. The effects of the harmonics in the supply voltage on the AC input current waveform are clarified. To confirm the effectiveness of the proposed control method, some experimental results from two laboratory test systems are shown.

Jurassic accretion tectonics of Japan

Abstract: The Jurassic accretionary complex and coeval granites in Japan represent remnants of the Jurassic arc-trench system developed between the Asian continent and Pacific Ocean. The Jurassic accretionary complex occurs as a large-scale nappe that is tectonically sandwiched between the overlying pre-Jurassic nappes and underlying post-Jurassic nappes. By virtue of new research styles (microfossil mapping and chronometric mapping) the following new views of the Jurassic accretionary complex in Japan, that suggest those for on-land exposed ancient accretionary complexes in general, have been obtained: (i) the accretion age of the Jurassic accretionary complex ranges over ∼ 80 million years from the latest Triassic to earliest Cretaceous according to a reconstructed stratigraphy of component rocks (oceanic plate stratigraphy); (ii) the accretionary complex is subdivided into several nappe units, each characterized by unique oceanic plate stratigraphy; (iii) a tectonically downward-younging polarity is observed in the piled nappes; (iv) the Jurassic accretionary complex is composed of coherent-type and chaotic-type units, the former retaining the primary accretionary structures while the latter are characterized by collapsed and secondarily mixed materialslfabrics derived from the former; (v) the chaotic-type units predominate in volume over the coherent-type units; (vi) the accretionary complex suffered from a regional low-grade metamorphism (up to the lower greenschist facies) within ∼10–20 million years after the accretion timing; and (vii) the lateral extent of the Jurassic accretionary complex in East Asia is intermittently traced from the Koryak mountains in Russia to North Palawan in the west Philippines for ∼6000 km. Discussion focuses on (i) the low preservation ratio of the coherent-type units to the chaotic-type units with respect to frequent subduction erosion by seamount subduction; (ii) absence of the Franciscan-type melange, suggesting sedimentary mixing origin for the chaotic-type unit; (iii) a growth rate of the Jurassic accretionary complex compatible to modern analogues; and (iv) the total volume of the Jurassic accretionary complex in Japan with respect to the most likely terrigeiious elastics source along the 250 Ma continent-continent collision suture in central China (between the Sino-Korean and Yangtze blocks).

Growth of ZnO Thin Film by Laser MBE: Lasing of Exciton at Room Temperature.

Abstract: High quality ZnO thin film was grown by Laser MBE. A pure ceramic ZnO target was ablated by the KrF laser pulses (248 nm, 10 Hz, 1 J/cm2) in an ultra high vacuum to deposit ZnO film on sapphire (0001) substrate. The lateral grain size was about 50 nm for the sample with thickness of 55 nm. At room temperature, the peak of the exciton absorption and the photoluminescence have the same energy. Under high density excitation (355 nm, 35 ps, 10 Hz), an exciton–exciton collision process was observed as P2 and P lines where 2S exciton and ionized exciton remain. From the edge of the sample, a very rapid increase of the P line was observed with the increase of the excitation power. A fine structure that comes from the cavity mode was also observed. These facts suggest that the lasing of the exciton was observed at room temperature.

PRISM: a language for symbolic-statistical modeling

Abstract: We present an overview of symbolic-statistical modeling language PRISM whose programs are not only a probabilistic extension of logic programs but also able to learn from examples with the help of the EM learning algorithm. As a knowledge representation language appropriate for probabilistic reasoning, it can describe various types of symbolic-statistical modeling formalism known but unrelated so far in a single framework. We show by examples, together with learning results, that most popular probabilistic modeling formalisms, the hidden Markov model and Bayesian networks, are described by PRISM programs.

Carbon Nanotubes for Next-Generation Electronics Devices

Abstract: As electronic devices and integrated circuits get smaller and smaller, eventually quantum-mechanic effects take over. As Saito discusses in his Perspective, results reported by Collins et al. in the same issue demonstrate the use of carbon nanotubes to create nanometer-scale devices known as diodes. Rather than fighting the effects of quantum mechanics, such devices make excellent use of quantum effects on the nanometer scale.

Origin of Helix in Achiral Banana-Shaped Molecular Systems

Abstract: Helical structures were confirmed for both the SmAb and SmBlue phases of banana-shaped molecular systems from observations of the microscopic fringe pattern and the selective reflection of blue color, respectively. X-ray and optical microscopy indicate that the helical axes in the SmAb and SmBlue phases are normal and parallel to the smectic layer, respectively. In these two helical phases, 13C NMR spectra show two C=O peaks, suggesting two different configurations of ester group, whereas only one C=O peak appears in the isotropic and crystal phases. This indicates that the two C=O groups in the mesogenic core are not in the same plane but are twisted. The addition of chiral dopant makes the dichroic ratio of the right- and left-circularly polarized scattered light positive or negative in the SmBlue phase, although the wavelength (?430 nm) of the scattering peak does not change significantly. The origin of the helix will be discussed in view of the twisted molecular conformation (conformational chirality) and the escape from macroscopic polarization.

Partial melt compositions of carbonated peridotite at 3 GPa and role of CO2 in alkali‐basalt magma generation

Abstract: Partial melt compositions of natural carbonated peridotite (KLB-1 + 2.5 wt% CO2) have been determined at 3 GPa using the diamond aggregate method. Melt obtained at 1350 °C is carbonatitic, and with increasing temperature melt composition becomes silicate-rich. These melts are lower in SiO2 and Al2O3 and higher in MgO and CaO compared to dry partial melts of KLB-1 generated at the same pressure. The 1400 and 1450 °C liquids have melilititic compositions, which are in good agreement with those of natural alkali-basalts from continental regions. At higher temperatures, partial melts are richer in SiO2, and the compositions of liquids at 1475 and 1525 °C approximate nephelinite and basanite respectively. However, they deviate from natural alkaline rocks in that the CaO/(CaO+MgO) ratios are smaller, suggesting that the natural nephelinite and basanite magmas were formed at lower pressures. The compositional trend of natural alkaline rocks, melilitites-nephelinites-basanites, may reflect the effect of decreasing pressure.

Fast Hole Transport in a New Calamitic Liquid Crystal of 2-(4′-Heptyloxyphenyl)-6-Dodecylthiobenzothiazole

Abstract: The carrier transport in different phases of a new photoconductive calamitic liquid crystal, 2-(4\ensuremath{'}-heptyloxyphenyl)-6-dodecylthiobenzothiazole was studied by the time-of-flight technique: In the smectic A phase, a fast hole transient photocurrent was obtained in a nondispersive manner, in which the mobility was as high as $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\phantom{\rule{0ex}{0ex}}{\mathrm{cm}}^{2}/\mathrm{V}\mathrm{s}$ and independent of applied electric field; in the isotropic phase, however, slower carrier transport was observed, probably due to positive or negative ions, and their mobilities were as low as ${10}^{\ensuremath{-}5}\phantom{\rule{0ex}{0ex}}{\mathrm{cm}}^{2}/\mathrm{V}\mathrm{s}$. These experimental results demonstrate the importance of local molecular alignment in creating the fast electronic conduction in calamitic liquid crystals.