Showing papers by "University of Tokyo published in 1992"

Spatial Tessellations: Concepts and Applications of Voronoi Diagrams

Abstract: Definitions and basic properties of the Voronoi diagram generalizations of the Voronoi diagram algorithms for computing Voronoi diagrams poisson Voronoi diagrams spatial interpolation models of spatial processes point pattern analysis locational optimization through Voronoi diagrams.

Observation of the coupled exciton-photon mode splitting in a semiconductor quantum microcavity.

Abstract: The spectral response of a monolithic semiconductor quantum microcavity with quantum wells as the active medium displays mode splitting when the quantum wells and the optical cavity are in resonance. This effect can be seen as the Rabi vacuum-field splitting of the quantum-well excitons, or more classically as the normal-mode splitting of coupled oscillators, the excitons, and the electromagnetic field of the microcavity. An exciton oscillator strength of 4\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ is deduced for 76-\AA{} quantum wells.

Tobacco BY-2 Cell Line as the “HeLa” Cell in the Cell Biology of Higher Plants

Abstract: Publisher Summary This chapter highlights tobacco BY-2 (TBY-2) cell line. TBY-2 derived from the seedlings of N. tabacum L. cv. Bright Yellow 2 grows fast and multiplies 80- to 100-fold in 1 week. After the stationary phase, cells of TBY-2 are transferred to a medium containing aphidicolin for 24 hr and then released from treatment; high synchrony is obtained starting from the S phase. TBY-2 cells are propagated in the modified medium of Linsmaier and Skoog, in which KH2PO4 and thiamine HCl are increased to 370 and 1 mg/liter, respectively, and sucrose and 2,4-D are supplemented to 3% and 0.2 mg/liter, respectively. The preparation of protoplasts from TBY-2 cells, from which the isolation of organelles is easy, has been established. Using the synchrony system, the change in the cell cycle progression of TBY-2 cells successfully followed the change in cytoskeletons. Biochemical and molecular biological studies can also be done on TBY-2 cells, as mass culture of this material is readily feasible.

Proposal of Burkholderia gen. nov. and Transfer of Seven Species of the Genus Pseudomonas Homology Group II to the New Genus, with the Type Species Burkholderia cepacia (Palleroni and Holmes 1981) comb. nov.

Abstract: Based on the 16S rRNA sequences, DNA-DNA homology values, cellular lipid and fatty acid composition, and phenotypic characteristics, a new genus Burkholderia is proposed for the RNA homology group II of genus Pseudomonas. Seven species in this group were transfered to the new genus. Thus seven new combinations, Burkholderia cepacia (Palleroni and Holmes 1981), Burkholderia mallei (Zopf 1885), Burkholderia pseudomallei (Whitmore 1913), Burkholderia caryophylli (Burkholder 1942), Burkholderia gladioli (Severini 1913), Burkholderia pickettii (Ralston et al 1973) and Burkholderia solanacearum (Smith 1896) were proposed.

Liver tumor promotion by the cyanobacterial cyclic peptide toxin microcystin-LR.

Abstract: Certain waterblooms of toxic cyanobacteria (blue-green algae) are a health threat because of their production of toxic peptides, termed microcystins, which cause liver damage in wild and domesticated animals. The most widely studied microcystin is microcystin-LR, a heptapeptide containing the twol-amino acids, leucine and arginine. The inhibition of protein phosphatase type 1 and type 2A activities by microcystin-LR is similar to that of the known protein phosphatase inhibitor and tumor promoter okadaic acid. We show in this report that microcystin-LR, applied below the acute toxicity level, dose-dependently increases the number and percentage area of positive foci for the placental form of glutathioneS-transferase in rat liver, which was initiated with diethylnitrosamine. The result was obtained independently through two animal experiments. This observation indicates that microcystin-LR is a new liver tumor promoter mediated through inhibition of protein phosphatase type 1 and type 2A activities. This provides further evidence that the okadaic acid pathway is a general mechanism of tumor promotion in various organs, such as mouse skin, rat glandular stomach and rat liver.

International Quality of Life Assessment (IQOLA) Project.

Abstract: The International Quality of Life Assesment (IQOLA) Project is a 4-year project to translate and adapt the widely used MOS SF-36 Health Survey Questionnaire in up to 15 countries and validate, norm, and document the new translations as required for their use in international studies of health outcomes. In addition to the eight-scale SF-36 health profile, the project will also validate psychometrically based physical and mental health summary scores, as well as health utility indexes incorporating SF-36 scales for use in cost-utility studies.

Molecular analysis of the association of HLA-B53 and resistance to severe malaria.

Abstract: The protective association between the human leukocyte antigen HLA-B53 and severe malaria was investigated by sequencing of peptides eluted from this molecule followed by screening of candidate epitopes from pre-erythrocytic-stage antigens of Plasmodium falciparum in biochemical and cellular assays. Among malaria-immune Africans, HLA-B53-restricted cytotoxic T lymphocytes recognized a conserved nonamer peptide from liver-stage-specific antigen-1 (LSA-1), but no HLA-B53-restricted epitopes were identified in other antigens. These findings indicate a possible molecular basis for this HLA-disease association and support the candidacy of liver-stage-specific antigen-1 as a malaria vaccine component.

Projection domains of MAP2 and tau determine spacings between microtubules in dendrites and axons.

Abstract: Neurons develop a highly polarized morphology consisting of dendrites and a long axon Both axons and dendrites contain microtubules and microtubule-associated proteins (MAPs) with characteristic structures Among MAPs, MAP2 is specifically expressed in dendrites whereas MAP2C and tau are abundant in the axon But the influence of MAP2, MAP2C and tau on the organization of microtubule domains in dendrites versus axons is unknown Both MAP2 and tau induce microtubule bundle formation in fibroblasts after transfection of complementary DNAs, and a long process resembling an axon is extended in Sf9 cells infected with recombinant baculovirus expressing tau We have now expressed MAP2 and MAP2C in Sf9 cells in order to compare their morphology and the arrangement of their microtubules to that found in Sf9 cells expressing tau We report here that the spacing between microtubules depends on the MAP expressed: in cells expressing MAP2, the distance is similar to that found in dendrites, whereas the spacing between microtubules in cells expressing MAP2C or tau is similar to that found in axons

A new modelling of cavitating flows : a numerical study of unsteady cavitation on a hydrofoil section

Abstract: A new cavity model that can explain the interaction between viscous effects including vortices and cavitation bubbles is presented in this study. This model, which is named a bubble two-phase flow (BTF) model, treats the inside and outside of a cavity as one continuum by regarding the cavity as a compressible viscous fluid whose density changes greatly. Navier–Stokes equations including cavitation bubble clusters are solved in finite-difference form by a time-marching scheme, where the growth and collapse of a bubble cluster is given by a modified Rayleigh's equation. Computation was made on a two-dimensional flow field around a hydrofoil NACA0015 at angles of attack of 8° and 20°. The Reynolds number was 3 × 105. The experiments were also performed at the same Reynolds number for comparison. The computed results by the BTF cavity model can express the feature of cloud-type cavitation shed from the trailing edge of the attached cavities when the angle of attack is 8°. It shows the mechanism of cavitation cloud generation and large-scale vortices. The boundary layer separates at the cavity leading edge. Then it rolls up and produces the cavitation cloud. In other words, the instability of the shear layer may produce the cavitation cloud. When the angle of attack is 20°, the flow was fully separated from the leading edge of the hydrofoil and vortex cavitation occurs in the separated region. The BTF cavity model can also express the generation of such vortex cavitation and the effect of cavitation nuclei in the uniform flow.

Cytokine receptors and signal transduction

Abstract: Cytokines play a vital role in coordinating immune and inflammatory re­ sponses. Unlike growth factor receptors with a tyrosine kinase, cytokine receptors have no intrin sic tyrosine kinase activity. Based on their struc­ ture, cytokine receptors are classified into several groups. High affinity recep­ tors for IL-2, IL-3, IL-5, IL-6, and GM-CSF are composed of at least two distin ct subunits, C( and {3. The C( subunits are primary cytokine binding proteins, and the {3 subunits are required for for mation of high affinity

Serum IgG antibody to ganglioside GQ1b is a possible marker of Miller Fisher syndrome.

Abstract: We studied serum anti-glycolipid antibodies by enzyme-linked immunosorbent assay and thin-layer chromatography-enzyme immunoassay in six consecutive patients with typical Miller Fisher syndrome. In all six, increased activity of IgG antibody against ganglioside GQ1b was present in the early phase and reduced with time, whereas such activity was not detected in normal control subjects and disease control subjects including those with Guillain-Barre syndrome. Anti-GQ1b IgG antibody is a new possible diagnostic marker of Miller Fisher syndrome and could well be related to the disease process itself.

Salvage of infarcted myocardium by angiogenic action of basic fibroblast growth factor.

Abstract: Coronary collateral vessels reduce damage to ischemic myocardium after coronary obstruction. Factors that stimulate collateral formation are expected to have ameliorating effects on myocardial infarction. In a canine experimental myocardial infarct model, intracoronary injection of basic fibroblast growth factor (bFGF) improved cardiac systolic function and reduced infarct size. Treatment with bFGF increased the number of arterioles and capillaries in the infarct. Thus, the angiogenic action of bFGF might lead to a reduction in infarct size. The application of bFGF might bring about a therapeutic modality for the salvage of infarcted myocardium.

Controlled-valence properties of La1-xSrxFeO3 and La1-xSrxMnO3 studied by soft-x-ray absorption spectroscopy.

Abstract: The controlled-valence properties of ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{FeO}}_{3}$ and ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ are studied by means of soft-x-ray absorption spectroscopy. A comparison between the transition-metal 2p spectra and atomic-multiplet calculations is used to determine the 3d count. The O 1s spectrum is used to characterize changes in unoccupied states that contain oxygen p character. The results indicate that the holes induced by substitution for both series are located in states of mixed metal 3d--oxygen 2p character. The ground state of ${\mathrm{LaFeO}}_{3}$ is mainly 3${\mathit{d}}^{5}$ and becomes 3${\mathit{d}}^{5}$L (where L denotes a ligand hole) in the ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{FeO}}_{3}$ series for low Sr concentration. The main component of the ground state of ${\mathrm{LaMnO}}_{3}$ is 3${\mathit{d}}^{4}$ and becomes a mixture of 3${\mathit{d}}^{3}$ and 3${\mathit{d}}^{4}$L in the ${\mathrm{La}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{MnO}}_{3}$ series. The trends in controlled- valence properties of similar oxides across the transition-metal series can be rationalized within the framework of the Zaanen-Sawatzky-Allen model.

Block of Ca2+ wave and Ca2+ oscillation by antibody to the inositol 1,4,5-trisphosphate receptor in fertilized hamster eggs.

Abstract: The concentration of cytoplasmic free calcium (Ca2+) increases in various stimulated cells in a wave (Ca2+ wave) and in periodic transients (Ca2+ oscillations). These phenomena are explained by inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release (IICR) and Ca(2+)-induced Ca2+ release (CICR) from separate intracellular stores, but decisive evidence is lacking. A monoclonal antibody to the IP3 receptor inhibited both IICR and CICR upon injection of IP3 and Ca2+ into hamster eggs, respectively. The antibody completely blocked sperm-induced Ca2+ waves and Ca2+ oscillations. The results indicate that Ca2+ release in fertilized hamster eggs is mediated solely by the IP3 receptor, and Ca(2+)-sensitized IICR, but not CICR, generates Ca2+ waves and Ca2+ oscillations.

Photochromism induced in an electrolytically pretreated Mo03 thin film by visible light

Abstract: PHOTOCHROMIC materials, whose optical absorption properties change in response to light, are important for a number of technological applications. A stable, reusable photochromic thin-film could be used, for example, in optical displays and high-density memories. Thin films of some transition-metal oxides can be coloured blue by band-gap excitation using ultraviolet light1–6. For use with common semiconductor laser sources, however, photo-chromic materials are required that respond to visible light. Here we report on the preparation of visible-light-sensitive, reversibly photochromic films of MoO3. Pretreated, vacuum-evaporated MoO3 thin films were slightly blued by cathodic polarization in a non-aqueous electrolyte; subsequent irradiation with visible light in air produced a strong colour enhancement. The photochromism could be erased by anodic polarization, and the coloration–decoloration process was repeatable over at least five cycles. The behaviour of these films contrasts with those blued by band-gap irradiation, which were not responsive to visible light.

Direct Numerical Simulation of Passive Scalar Field in a Turbulent Channel Flow

Abstract: A direct numerical simulation (DNS) of the fully developed thermal field in a dimensional turbulent channel flow of air was carried out. The isoflux condition was imposed on the two walls so that the local mean temperature increased linearly in the streamwise direction. With any buoyancy effect neglected, temperature was considered as a passive scalar. The computation was executed on 1,589,248 grid points by using a spectral method. The statistics obtained were root-mean-square temperature fluctuations, turbulent heat fluxes, turbulent Prandtl number, and dissipation time scales. They agreed fairly well with existing experimental and numerical simulation data. Each term in the budget equations of temperature variance, its dissipation rate, and turbulent heat fluxes was also calculated. It was found that the temperature fluctuation [theta][prime] was closely correlated with the streamwise velocity fluctuation u[prime], particularly in the near-wall region. Hence, the distribution of budget terms for the streamwise and wall-normal heat fluxes, [bar u][prime][theta] and [bar v][prime][theta][prime], were very similar to those for the two Reynolds stress components, [bar u][prime]u[prime]and [bar u][prime]v[prime].

Induction of Cytotoxicity by Photoexcited TiO2 Particles

Abstract: Photoexcited TiO2 particles can drive various chemical reactions due to their strong oxidizing and reducing ability. To investigate the possible use of this effect for cancer treatment, the antitumor activity of photoexcited TiO2 particles was studied in vitro and in vivo. HeLa cells cultured in vitro were completely killed in the presence of TiO2 (50 micrograms/ml) with 10-min UV irradiation by a 500-W-Hg lamp. In contrast, very little cell death was observed from TiO2 treatment without UV irradiation. Photoexcited TiO2 particles also significantly suppressed the growth of HeLa cells implanted in nude mice, compared with those receiving TiO2 alone or UV irradiation alone. The cell death caused by photoexcited TiO2 particles was significantly protected in the presence of L-tryptophan and catalase. These molecules are quenchers of hydroxyl radicals and scavengers of hydrogen peroxide, respectively, suggesting that the cells were killed by the OH. and H2O2 produced from photoexcited TiO2 particles.

Long-range correlation and partial 1/fα spectrum in a noncoding DNA sequence

Abstract: Mutual information function, which is an alternative to correlation function for symbolic sequences, and a "symbolic spectrum" are calculated for a human DNA sequence containing mostly intron segments, those that do not code for proteins. It is observed that the mutual information function of this sequence decays very slowly, and the correlation length is extremely long (at least 800 bases). The symbolic spectrum of the sequence at very low frequencies can be approximated by 1/fα, where f is the frequency and α ranges from 0.5 to 0.85. It is suggested that the existence of the repetitive patterns in the sequence is mainly responsible for the observed long-range correlation. A possible connection between this long-range correlation and those in music notes is also briefly discussed.

Discovery of the spawning area for Japanese eel

Abstract: AT the beginning of this century, the Danish oceanographer Johannes Schmidt outlined the spawning area of Atlantic eels Anguilla spp. in the Sargasso Sea1,2But the spawning location of the Japanese eel A. japonicain the Pacific Ocean has eluded researchers for over 60 years. I report here the discovery of their spawning location. By measuring oceanographic conditions and collecting the transparent leaf-like eel larvae, termed leptocephali (see Fig. 1), we determined the Japanese eel spawning area to be in the North Equatorial Current west of the Mariana Islands, at a salinity front near 15° N, 140° E. This discovery shows that the key similarity between the spawning sites of Atlantic and Pacific eels is the placement of leptocephali into the major ocean currents that will return them to their juvenile rearing habitats.

Electronic structure of 3d-transition-metal compounds by analysis of the 2p core-level photoemission spectra

Abstract: The electronic structures of a wide range of transition-metal compounds, including Cu, Ni, Co, Fe, and Mn oxides and sulfides, with metal valences ranging from 2+ to 4+, have been investigated by a cluster-type configuration-interaction analysis of the core-level 2p x-ray photoemission spectra. We show that by including the d-d exchange interaction (retaining only diagonal terms) and an anisotropic metal-ligand hybridization in the model, these spectra can be well reproduced, and so can be used to deduce quantitatively values for the ligand-to-metal charge-transfer energy \ensuremath{\Delta}, the on-site d-d Coulomb repulsion energy U, and the metal-ligand transfer integrals T. Systematics for \ensuremath{\Delta} and U are generally consistent with those found from previous valence-band studies and follow expected chemical trends. By using values of \ensuremath{\Delta} and U found from this model, we show that most of the transition-metal compounds studied in this work can be classified in the charge-transfer regime of the Zaanen-Sawatzky-Allen diagram. A few exceptions to these systematics have been found. Small U values found for pyrite-type ${\mathrm{CoS}}_{2}$ and ${\mathrm{FeS}}_{2}$ and large T values for Mn perovskite oxides, as well as the neglect of other mechanisms such as exciton satellites, may indicate a limitation of the local-cluster model.

Gauge theory of the normal state of high-Tc superconductors.

Abstract: Starting with the one-band t-J model and using the slave-boson method to enforce the constraint of no double occupations, we examine fluctuations about the uniform resonating-valence-bond mean-field solution. We restrict our attention to a temperature region where the bosons are not Bose condensed. The important low-energy fluctuations are described by gauge fields that are related to fluctuations in the spin chirality. The fermions and bosons are strongly coupled to the gauge field, leading to a transport time of order \ensuremath{\Elzxh}/${\mathit{k}}_{\mathit{B}}$T, in agreement with experiment. The model also exhibits a Fermi surface with area 1-x, where x is the dopant concentration, consistent with the Luttinger Theorem, but the low-lying excitations have a decay width much larger than its energy, in violation of Landau's criterion for a Fermi-liquid state. Other experimental implications of this model and the possibility of a direct measurement of the chirality fluctuations are discussed.

Denitrification by fungi.

Abstract: Many fungi in the centre of the group of Fusarium and its teleomorphs were shown to be capable of reducing nitrite anaerobically to form nitric oxide (NO), nitrous oxide (N2O), and/or dinitrogen (N2). Several strains could reduce nitrate as well. Nitrous oxide was the major product of the reduction of nitrate or nitrite. Several fungi could also form N2. When [15]nitrite was used as substrate for the N2-forming dinitrification, 15N2O, 15NO, and 14N15N were obtained as the products. These results demonstrated that, unexpectedly, many fungi have denitrifying abilities. It was also shown that the fungal system contains a unique reaction, formation of a hybrid dinitrogen.