Showing papers by "Tokyo Institute of Technology published in 1998"

Evidence for oscillation of atmospheric neutrinos

Abstract: We present an analysis of atmospheric neutrino data from a 33.0 kton yr (535-day) exposure of the Super-Kamiokande detector. The data exhibit a zenith angle dependent deficit of muon neutrinos which is inconsistent with expectations based on calculations of the atmospheric neutrino flux. Experimental biases and uncertainties in the prediction of neutrino fluxes and cross sections are unable to explain our observation. The data are consistent, however, with two-flavor ${\ensuremath{ u}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{ u}}_{\ensuremath{\tau}}$ oscillations with ${sin}^{2}2\ensuremath{\theta}g0.82$ and $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}l\ensuremath{\Delta}{m}^{2}l6\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}3}\mathrm{eV}{}^{2}$ at 90% confidence level.

Processing and properties of hydroxyapatite-based biomaterials for use as hard tissue replacement implants

Abstract: This paper reviews the past, present, and future of the hydroxyapatite (HAp)-based biomaterials from the point of view of preparation of hard tissue replacement implants. Properties of the hard tissues are also described. The mechanical reliability of the pure HAp ceramics is low, therefore it cannot be used as artificial teeth or bones. For these reasons, various HAp-based composites have been fabricated, but only the HAp-coated titanium alloys have found wide application. Among the others, the microstructurally controlled HAp ceramics such as fibers/whiskers-reinforced HAp, fibrous HAp-reinforced polymers, or biomimetically fabricated HAp/collagen composites seem to be the most suitable ceramic materials for the future hard tissue replacement implants.

Quantum annealing in the transverse Ising model

Abstract: We introduce quantum fluctuations into the simulated annealing process of optimization problems, aiming at faster convergence to the optimal state. Quantum fluctuations cause transitions between states and thus play the same role as thermal fluctuations in the conventional approach. The idea is tested by the transverse Ising model, in which the transverse field is a function of time similar to the temperature in the conventional method. The goal is to find the ground state of the diagonal part of the Hamiltonian with high accuracy as quickly as possible. We have solved the time-dependent Schr\"odinger equation numerically for small size systems with various exchange interactions. Comparison with the results of the corresponding classical (thermal) method reveals that the quantum annealing leads to the ground state with much larger probability in almost all cases if we use the same annealing schedule.

Quantized conductance through individual rows of suspended gold atoms

Abstract: As the scale of microelectronic engineering continues to shrink, interest has focused on the nature of electron transport through essentially one-dimensional nanometre-scale channels such as quantum wires1 and carbon nanotubes2,3. Quantum point contacts (QPCs) are structures (generally metallic) in which a ‘neck’ of atoms just a few atomic diameters wide (that is, comparable to the conduction electrons' Fermi wavelength) bridges two electrical contacts. They can be prepared by contacting a metal surface witha scanning tunnelling microscope (STM)4,5,6,7 and by other methods8,9,10,11,12, and typically display a conductance quantized in steps of 2e2/h(∼13 kΩ−1)13,14, where e is the electron charge and h is Planck's constant. Here we report conductance measurements on metal QPCs prepared with an STM that we can simultaneously image using an ultrahigh-vacuum electron microscope, which allows direct observation of the relation between electron transport and structure. We observe strands of gold atoms that are about one nanometre long and one single chain of gold atoms suspended between the electrodes. We can thus verify that the conductance of a single strand of atoms is 2e2/h and that the conductance of a double strand is twice as large, showing that equipartition holds for electron transport in these quantum systems.

Ground-motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremor

Abstract: The spectral ratio between horizontal and vertical components (H/V ra- tio) of microtremors measured at the ground surface has been used to estimate fun- damental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area. mode Rayleigh waves. Mainly based on these facts, in this study, a large proportion of microtremors are thought to con- sist of surface waves, mainly of their fundamental modes. This article first deals with the peak period in the H/V ratio of microtremors and its relation to the fundamental pe- riod of the response to vertically incident S waves. Next, peak values in the H/V ratio are related to the amplification factors for the S waves. In this process, a new smoothing function is proposed for getting a better correlation between them. A simple relation between the amplification factor and the H/V ratio, which is similar to a so-called Nakamura's method, is also formulated. Finally, the periods and the am- plification factors estimated from microtremor measurement at 546 stations in Tokyo are mapped as a demonstration of practicality of the present study.

Continuous excitation of planetary free oscillations by atmospheric disturbances

Abstract: Seismology provides a powerful tool for probing planetary interiors1,2, but it has been considered inapplicable to tectonically inactive planets where earthquakes are absent. Here, however, we show that the atmospheres of solid planets are capable of exerting dynamic pressure on their surfaces, thereby exciting free oscillations with amplitudes large enough to be detected by modern broad-band seismographs. Order-of-magnitude estimates of these forces give similar amplitudes of a few nanogals for the Earth, Venus and Mars despite widely varying atmospheric and ambient conditions. The amplitudes are also predicted to have a weak frequency dependence. Our analysis of seismograms, recorded continuously from 1992 to 1993 at 13 globally distributed stations, shows strong evidence for continuously excited fundamental-mode free oscillations on the Earth. This result, together with other recent studies3,4,5, is consistent with our estimate of atmospheric forcing and we therefore propose that it may be possible to detect atmospheric excitation of free oscillations on Venus and Mars as well.

Dsif, a novel transcription elongation factor that regulates rna polymerase ii processivity, is composed of human spt4 and spt5 homologs

Abstract: We report the identification of a transcription elongation factor from HeLa cell nuclear extracts that causes pausing of RNA polymerase II (Pol II) in conjunction with the transcription inhibitor 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole (DRB). This factor, termed DRB sensitivity-inducing factor (DSIF), is also required for transcription inhibition by H8. DSIF has been purified and is composed of 160-kD (p160) and 14-kD (p14) subunits. Isolation of a cDNA encoding DSIF p160 shows it to be a homolog of the Saccharomyces cerevisiae transcription factor Spt5. Recombinant Supt4h protein, the human homolog of yeast Spt4, is functionally equivalent to DSIF p14, indicating that DSIF is composed of the human homologs of Spt4 and Spt5. In addition to its negative role in elongation, DSIF is able to stimulate the rate of elongation by RNA Pol II in a reaction containing limiting concentrations of ribonucleoside triphosphates. A role for DSIF in transcription elongation is further supported by the fact that p160 has a region homologous to the bacterial elongation factor NusG. The combination of biochemical studies on DSIF and genetic analysis of Spt4 and Spt5 in yeast, also in this issue, indicates that DSIF associates with RNA Pol II and regulates its processivity in vitro and in vivo.

Measurements of the solar neutrino flux from Super-Kamiokande's first 300 days

Abstract: The first results of the solar neutrino flux measurement from Super-Kamiokande are presented. The results shown here are obtained from data taken between 31 May 1996, and 23 June 1997. Using our measurement of recoil electrons with energies above 6.5 MeV, we infer the total flux of ${}^{8}\mathrm{B}$ solar neutrinos to be $2.42\ifmmode\pm\else\textpm\fi{}0.06(\mathrm{stat}{)}_{\ensuremath{-}0.07}^{+0.10}(\mathrm{syst})\ifmmode\times\else\texttimes\fi{}{10}^{6}\mathrm{cm}{}^{\ensuremath{-}2}{\mathrm{s}}^{\ensuremath{-}1}$. This result is consistent with the Kamiokande measurement and is 36% of the flux predicted by the BP95 solar model. The flux is also measured in 1.5 month subsets and shown to be consistent with a constant rate.

Telomerase activation by hTRT in human normal fibroblasts and hepatocellular carcinomas.

Abstract: Telomerase is a specialized type of reverse transcriptase which catalyzes the synthesis and extension of telomeric DNA (for review, see ref.1). This enzyme is highly active in most cancer cells, but is inactive in most somatic cells2. This striking observation led to the suggestion that telomerase might be important for the continued growth3 or progression4 of cancer cells. However, little is known about the molecular mechanism of telomerase activation in cancer cells. Human telomerase reverse transcriptase (hTRT) has recently been identified as a putative human telomerase catalytic subunit5,6. We transfected the gene encoding hTRT into telomerase-negative human normal fibroblast cells and demonstrated that expression of wild-type hTRT induces telomerase activity, whereas hTRT mutants containing mutations in regions conserved among other reverse transcriptases did not. Hepatocellular carcinoma (2O samples) and non-cancerous liver tissues (19 samples) were examined for telomerase activity and expression of hTRT, the human telomerase RNA component (hTR; encoded by TER)7 and the human telomerase-associated protein (HTLP1; encoded by 7EP7)8,9. A significant correlation between hTRT expression and telomerase activity was observed. These results indicate that the hTRT protein is the catalytic subunit of human telomerase, and that it plays a key role in the activation of telomerase in cancer cells.

Single-layer feed waveguide consisting of posts for plane TEM wave excitation in parallel plates

Abstract: The authors propose a novel feed structure to excite a plane TEM wave in a parallel-plate waveguide. The feed waveguide is composed of densely arrayed posts on the same layer as the parallel plate. The posts can be easily fabricated at low cost by making metalized via holes in a grounded dielectric substrate. Such a procedure results in a quite simple fabrication of the antenna. The feed waveguide is designed to obtain a uniform division, which is confirmed by measurements on a 40-GHz band model.

Abnormal maternal behaviour and growth retardation associated with loss of the imprinted gene Mest.

Abstract: Mest (also known as Peg1), an imprinted gene expressed only from the paternal allele during development, was disrupted by gene targeting in embryonic stem (ES) cells The targeted mutation is imprinted and reversibly silenced by passage through the female germ line Paternal transmission activates the targeted allele and causes embryonic growth retardation associated with reduced postnatal survival rates in mutant progeny More significantly, Mest-deficient females show abnormal maternal behaviour and impaired placentophagia, a distinctive mammalian behaviour Our results provide evidence for the involvement of an imprinted gene in the control of adult behaviour

Kinetic measurements of DNA hybridization on an oligonucleotide-immobilized 27-MHz quartz crystal microbalance.

Abstract: A highly sensitive 27-MHz quartz-crystal microbalance, on which a 10−30-mer oligonucleotide was immobilized as a probe molecule, was employed to detect hybridization of complementary oligonucleotides in aqueous solution. From frequency decreases (mass increases due to the hybridization) with passage of time, kinetic parameters such as association constants (Ka) and binding and dissociation rate constants (k1 and k-1) could be obtained, as well as binding (hybridization) amount at the nanogram level (Δm). Kinetic studies were carried out by changing various parameters: (i) the immobilization method of a probe oligonucleotide on Au electrode, (ii) number of mismatching bases in sequences of target oligonucleotides, (iii) length of both probe and target oligonucleotides, (iv) hybridization temperature, and (v) ionic strength in solution. The obtained results were compared with those obtained by a surface plasmon resonance method using a BIAcore system.

Evidence that p-tefb alleviates the negative effect of dsif on rna polymerase ii-dependent transcription in vitro

Abstract: Recently, a positive and a negative elongation factor, implicated in 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) inhibition of transcription elongation, has been identified. P-TEFb is a positive transcription elongation factor and the DRB-sensitive kinase that phosphorylates the C-terminal domain (CTD) of the largest subunit of RNA polymerase II (Pol II). PITALRE, a member of the Cdc2 family of protein kinases, is the catalytic subunit of P-TEFb. DSIF is a human homolog of the yeast Spt4-Spt5 complex and renders elongation of transcription sensitive to DRB. DRB sensitivity-inducing factor (DSIF) binds to RNA Pol II and may directly regulate elongation. Here we show a functional interaction between P-TEFb and DSIF. The reduction of P-TEFb activity induced by either DRB, antibody against PITALRE, or immunodepletion resulted in a negative effect of DSIF on transcription. DSIF acts at an early phase of elongation, and the prior action of P-TEFb makes transcription resistant to DSIF. The state of phosphorylation of CTD determines the DSIF-RNA Pol II interaction, and may provide a direct link between P-TEFb and DSIF. Taken together, this study reveals a molecular basis for DRB action and suggests that P-TEFb stimulates elongation by alleviating the negative action of DSIF.

Perpendicular Magnetic Anisotropy Caused by Interfacial Hybridization via Enhanced Orbital Moment in Co / Pt Multilayers: Magnetic Circular X-Ray Dichroism Study

Abstract: Magnetic circular x-ray dichroism (MCXD) measurements at the Co ${L}_{2,3}$ and ${M}_{2,3}$ core edges reveal a strongly enhanced perpendicular Co orbital moment ( ${m}_{\mathrm{orb}}$) in Co/Pt multilayers which show perpendicular magnetic anisotropy (PMA). MCXD signals at the Pt ${N}_{6,7}$ and ${O}_{2,3}$ edges, arising from Pt $5d\ensuremath{-}\mathrm{Co}3d$ hybridization, persist for the thinnest Co layer. The hybridization is shown to be localized at the Co/Pt interface and to cause the ${m}_{\mathrm{orb}}$ enhancement which drives PMA. Unambiguous evidence for a transition from fcc to hcp Co is presented and ${m}_{\mathrm{orb}}$ of bulk fcc Co has been determined to be $0.11{\ensuremath{\mu}}_{B}$ for the first time.

Augment-able reality: situated communication through physical and digital spaces

Abstract: Most existing augmented reality systems only provide a method for browsing information that is situated in the real world context. This paper describes a system that allows users to dynamically attach newly created digital information such as voice notes photographs to the physical environment, through wearable computers as well as normal computers. Attached data is stored with contextual tags such as location IDs and object IDs that are obtained by wearable sensors, so the same or other wearable users can notice them when they come to the same context. Similar to the role that Post-it notes play in community messaging, we expect our proposed method to be a fundamental communication platform when wearable computers become commonplace.

The HERMES Spectrometer

Abstract: The HERMES experiment is collecting data on inclusive and semi-inclusive deep inelastic scattering of polarised positrons from polarised targets of H, D, and 3 He. These data give information on the spin structure of the nucleon. This paper describes the forward angle spectrometer built for this purpose. The spectrometer includes numerous tracking chambers (micro-strip gas chambers, drift and proportional chambers) in front of and behind a 1.3 T.m magnetic field, as well as an extensive set of detectors for particle identification (a lead-glass calorimeter, a pre-shower detector, a transition radiation detector, and a threshold Cherenkov detector). Two of the main features of the spectrometer are its good acceptance and identification of both positrons and hadrons, in particular pions. These characteristics, together with the purity of the targets, are allowing HERMES to make unique contributions to the understanding of how the spins of the quarks contribute to the spin of the nucleon.

Systematic study of the electronic state in θ-type BEDT-TTF organic conductors by changing the electronic correlation

Abstract: The behavior of the phase transitions is mapped out as a function of the dihedral angle (\ensuremath{\theta}) or the transfer integral $(t)$ between donor columns for \ensuremath{\theta}-type BEDT-TTF [BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene, abbreviated as ET] salts involving the series $\ensuremath{\theta}\ensuremath{-}(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{T}\mathrm{F}{)}_{2}{\mathrm{MM}}^{\ensuremath{'}}(\mathrm{SCN}{)}_{4}$ [$M=\mathrm{T}\mathrm{l},\mathrm{R}\mathrm{b},\mathrm{C}\mathrm{s},$ ${M}^{\ensuremath{'}}=\mathrm{C}\mathrm{o},\mathrm{Z}\mathrm{n}:$ abbreviated as $\ensuremath{\theta}{\ensuremath{-}MM}^{\ensuremath{'}}$], which we have recently prepared. The electronic correlation parameter $(U/t)$ increases by increasing the dihedral angle (\ensuremath{\theta}). In the phase diagram of \ensuremath{\theta}-ET salts the ground state varies from insulating, to superconducting, to metallic with decreasing \ensuremath{\theta}, namely, $U/t.$ The series $\ensuremath{\theta}{\ensuremath{-}MM}^{\ensuremath{'}}$ is located at the center of the phase diagram where metallic, paramagnetic insulating, and singlet states are observed at low temperatures. With applied pressure, the metal-insulator transition temperature rises because the dihedral angle increases, which is related to the enhancement of the electronic correlation.

Snurportin1, an m3G-cap-specific nuclear import receptor with a novel domain structure.

Abstract: The nuclear import of the spliceosomal snRNPs U1, U2, U4 and U5, is dependent on the presence of a complex nuclear localization signal (NLS). The latter is composed of the 5'-2,2,7-terminal trimethylguanosine (m3G) cap structure of the U snRNA and the Sm core domain. Here, we describe the isolation and cDNA cloning of a 45 kDa protein, termed snurportin1, which interacts specifically with m3G-cap but not m7G-cap structures. Snurportin1 enhances the m3G-capdependent nuclear import of U snRNPs in both Xenopus laevis oocytes and digitonin-permeabilized HeLa cells, demonstrating that it functions as an snRNP-specific nuclear import receptor. Interestingly, solely the m3G-cap and not the Sm core NLS appears to be recognized by snurportin1, indicating that at least two distinct import receptors interact with the complex snRNP NLS. Snurportin1 represents a novel nuclear import receptor which contains an N-terminal importin beta binding (IBB) domain, essential for function, and a C-terminal m3G-cap-binding region with no structural similarity to the arm repeat domain of importin alpha.

Space-time structures from iib matrix model

Abstract: We derive a long distance effective action for space-time coordinates from a IIB matrix model. It provides us an effective tool to study the structures of space-time. We prove the finiteness of the theory for finite $N$ to all orders of the perturbation theory. Space-time is shown to be inseparable and its dimensionality is dynamically determined. The IIB matrix model contains a mechanism to ensure the vanishing cosmological constant which does not rely on the manifest supersymmetry. We discuss possible mechanisms to obtain realistic dimensionality and gauge groups from the IIB matrix model.

Well-posedness of feedback systems: insights into exact robustness analysis and approximate computations

Abstract: This paper establishes a framework for robust stability analysis of linear time-invariant uncertain systems, The uncertainty is assumed to belong to an arbitrary subset of complex matrices. The concept used here is well-posedness of feedback systems, leading to necessary and sufficient conditions for robust stability. Based on this concept, some insights into exact robust stability conditions are given, In particular, frequency domain and state-space conditions for well-posedness are provided in terms of Hermitian-form inequalities. It is shown that these inequalities can be interpreted as small-gain conditions with a generalized class of scalings given by linear fractional transformations (LFT). Using the LFT-scaled small-gain condition in the state-space setting, the "duality" is established between the H/sub /spl infin// norm condition with frequency-dependent scalings and the parameter-dependent Lyapunov condition. Connections to the existing results, including the structured singular value and the integral quadratic constraints, are also discussed. Finally, we show that our well-posedness conditions can be used to give a less conservative, yet computable bound on the real structured singular value. This result is illustrated by numerical examples.