Showing papers by "Tokyo Institute of Technology published in 1992"

Friction measurements on phase-separated thin films with a modified atomic force microscope

Abstract: THE study of chemical phase separation in multicomponent thin organic films typically involves the addition of a dye which is selectively more soluble in one of the phases, thereby making it possible to probe the domain structures by fluorescence microscopy1–4. The resolution of this approach is generally limited to tens of micrometres. The atomic force microscope, on the other hand, has recently proved useful for imaging organic thin films down to the atomic scale5–9, but this technique provides details of the overall film topography, rather than the chemical composition. Here we show that the recently developed friction force microscope10–13, which simultaneously measures both the normal and lateral forces on the scanning tip, can be used to image and identify compositional domains with a resolution of ∼5 A. Although the topography of the individual domains can be imaged with a standard atomic force microscope, it is the additional information provided by the friction measurement that allows them to be chemically differentiated.

Transformation of Lower Alkanes into Aromatic Hydrocarbons over ZSM-5 Zeolites

Abstract: Much attention has been paid to the transformation of lower alkanes such as propane and butanes into aromatic hydrocarbons from both industrial and academic points of view The aromatic hydrocarbons can be utilized as a booster for high octane number gasoline and are fundamental raw chemicals in petroleum chemistry The activation of lower alkanes is an intriguing subject In early work, Csicsery [1–5] described dehydrocyclodimerization of lower alkanes over bifunctional catalysts such as platinum on alumina and Cr2O3 on alumina

An adaptive algorithm for mel-cepstral analysis of speech

Abstract: The authors describe a mel-cepstral analysis method and its adaptive algorithm. In the proposed method, the authors apply the criterion used in the unbiased estimation of log spectrum to the spectral model represented by the mel-cepstral coefficients. To solve the nonlinear minimization problem involved in the method, they give an iterative algorithm whose convergence is guaranteed. Furthermore, they derive an adaptive algorithm for the mel-cepstral analysis by introducing an instantaneous estimate for gradient of the criterion. The adaptive mel-cepstral analysis system is implemented with an IIR adaptive filter which has an exponential transfer function, and whose stability is guaranteed. The authors also present examples of speech analysis and results of an isolated word recognition experiment. >

Formulas for the Analysis of the Surface SFG Spectrum and Transformation Coefficients of Cartesian SFG Tensor Components

Abstract: Comprehensive expressions have been presented to facilitate the analysis of the surface sum-frequency generation (SFG) spectrum. The electric field components of the SFG beam for a given experimental setup have been related via appropriately defined Fresnel coefficients to the non-linear source polarization, which in turn has been related to the electric fields of exciting visible and infrared beams through the macroscopic SFG susceptibility tensor. The coefficients of transformation have been given to relate the laboratory-fixed Cartesian components of the SFG tensor to the components described in a surface-fixed axis system. The tensor components have been further related to the components of the microscopic hyperpolarizability tensor of surface species, and the explicit expressions (in terms of the Euler angles defining molecular orientation) of the transformation coefficients are presented to describe the Cartesian tensor components described in a surface-fixed axis system by the molecule-fixed components.

Dynamic walking control of a biped robot along a potential energy conserving orbit

Abstract: To reduce the complex walking dynamics of a biped, a particular class of trajectories of an ideal biped model where the center of gravity of the body moves horizontally and the horizontal motion of the center of gravity can be expressed by a simple linear differential equation is introduced. The authors coin the phrase 'potential energy conserving orbit' to describe this class of trajectories. Based on these properties, control laws were formulated for walk initiation, walk continuation, and walk termination. The walking motion is controlled by support leg exchange. Robust realization of the walking control is also considered. An experimental walking machine was designed as a nearly ideal biped model. To make the legs lighter, four DC motors were mounted in the body, and the legs are parallel link structures. The results of the experiment describe five steps of dynamic walking including walk initiation. >

An arbitrary Lagrangian-Eulerian finite rigid element method for interaction of fluid and a rigid body

Abstract: A computational procedure is developed to solve the problems of coupled motion of a rigid body and a viscous incompressible fluid; the former is mounted on elastic springs, and the latter is surrounding the rigid body. The arbitrary Lagrangian-Eulerian method is employed to incorporate the interface conditions between the body and the fluid. The streamline upwind/Petrov-Galerkin finite element method is used for the spatial discretization of the fluid domain, and the predictor-corrector method is used for the time integration. The method is applied to evaluate the added mass and the added damping of a circular cylinder as well as to simulate the vibration of a circular cylinder induced by vortex sheddings.

Double percolation effect on the electrical conductivity of conductive particles filled polymer blends

Abstract: Electrical conductivity of carbon black (CB) filled polymer blends which are incompatible with each other was studied as a function of the polymer's blend ratio Transmission electron microscope (TEM) analysis shows that CB distributes unevenly in each component of a polymer blend TEM photographs of phase structure of solvent extracted HDPE/PMMA blend and solvent extraction experiments of PMMA/PP blend detect the blend ratio at which the structural continuity of filler rich phase is formed The electrical conductivity of polymer blends is found to be determined by two factors One is the concentration of CB in the filler rich phase and the other is the structural continuity of this phase This double percolation affects the conductivity of conductive particle filled polymer blends

Nature and origin of the 5-eV band in SiO2:GeO2 glasses

Abstract: The sources of an absorption band at \ensuremath{\sim}5 eV observed in ${\mathrm{SiO}}_{2}$:${\mathrm{GeO}}_{2}$ and ${\mathrm{GeO}}_{2}$ glasses have not been unambiguously identified. Results reported here are consistent with the source of two types of neutral oxygen vacancies. Samples of ${95\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$:${5\mathrm{G}\mathrm{e}\mathrm{O}}_{2}$ and ${90\mathrm{S}\mathrm{i}\mathrm{O}}_{2}$:${10\mathrm{G}\mathrm{e}\mathrm{O}}_{2}$ were prepared by a chemical vapor deposition soot-remelting method. Optical-absorption and electron paramagnetic resonance spectra were measured. An absorption band centered at 5 eV in as-prepared ${\mathrm{SiO}}_{2}$:${\mathrm{GeO}}_{2}$ glasses is composed of two components. One has a peak at 5.06 eV and a FWHM (full width at half maximum) of 0.38 eV. Illumination with uv light bleached this band, and generated Ge E' centers. A linear relation was found between the decrement in the intensity of the 5.06-eV component and the concentrations of uv-induced Ge E' centers. This relation is a basis for attributing the defect responsible for this component to the precursors of uv-induced Ge E' centers. We propose that the 5.06-eV band is due to neutral oxygen monovacancies (NOV's) coordinated by two Ge ions. The oscillator strength of this band was evaluated to be approximately 0.4\ifmmode\pm\else\textpm\fi{}0.1 assuming that the NOV's are converted into Ge E' centers by absorption of uv quanta. The activation energy for this conversion process was of the order of ${10}^{\mathrm{\ensuremath{-}}2}$ eV.The second component of the absorption spectra has a peak at 5.16 eV and a FWHM of 0.48 eV. This band is not bleached but emits luminescence bands at 3.2 eV (intense) and 4.3 eV (weak) when irradiated with 5-eV light. Based on other research, we assign this band to ${\mathrm{Ge}}^{2+}$ ions coordinated by two oxygens and having two lone pair electrons (neutral oxygen divacancies). The concentrations of ${\mathrm{Ge}}^{2+}$ ions were much larger than those of the NOV's and the ratio of the NOV's to ${\mathrm{Ge}}^{2+}$ ions increases with increasing ${\mathrm{GeO}}_{2}$ content. A similarity was found in the characteristics of these two types of oxygen-deficient defects to those in ${\mathrm{SiO}}_{2}$ glasses.

The RIKEN radioactive beam facility

Abstract: A radioactive beam facility based on projectile fragmentation, RIPS, has been constructed at RIKEN to enable radioactive-beam experiments. The facility is characterized by the production of high-intensity beams and spin-polarized beams. Since the beginning of 1990, experiments on exotic nuclei have been extensively performed exploiting these useful features. The characteristics and the present status of the RIPS are described.

Relocation and distinct subcellular localization of p34cdc2-cyclin B complex at meiosis reinitiation in starfish oocytes.

Abstract: M phase promoting factor (MPF) is a major element controlling entry into the M phase of the eukaryotic cell cycle. MPF is composed of two subunits, p34cdc2 and cyclin B. Using indirect immunofluorescence staining with specific antibody against starfish cyclin B, we monitored the dynamics of the subcellular distribution of MPF during meiosis reinitiation in starfish oocytes. We found that all of the cyclin B is already associated with p34cdc2 in immature oocytes arrested at the G2/M border and that this inactive complex is present exclusively in the cytoplasm. After its activation, part of the p34cdc2-cyclin B complex moves into the germinal vesicle before nuclear envelope breakdown, independently of either microtubules or actin filaments. Thereafter, some part of the complex accumulates in the nucleolus and condensed chromosomes. Another portion of the complex accumulates on meiotic asters and spindles, while the rest is still present throughout the cytoplasm. As these patterns of localization are detected in the detergent-extracted oocytes, we propose at least four distinct subcellular states of the p34cdc2-cyclin B complex: freely soluble, microtubule-associated, detergent-resistant cytoskeleton-associated and chromosome-associated. Thus, in addition to the intramolecular modification of p34cdc2-cyclin B complex, its intracellular relocation plays a key role in promoting the M phase.

Preparation of a New Class of Polyimide-Silica Hybrid Films by Sol-Gel Process

Abstract: A new class of polyimide-silica hybrid films were successfully prepared by the sol-gel reaction starting from tetraethoxysilane (TEOS) in the solution of polyamic acid in N,N-dimethylacetamide. The hybrid films were obtained by the hydrolysis-polycondensation of TEOS in the polyamic acid solution, followed by heating at 270°C. Fairly flexible films were obtained up to 70 wt% of silica content. The films containing the silica less than 8 wt% were yellow and transparent, whereas the films with higher silica content were yellow and opaque. The density of the silica in the hybrid films was estimated to be 1.65 gcm−3. The 29Si nuclear magnetic resonance spectrum indicated that the silica in the films consisted of non-hydroxy, monohydroxy, and dihydroxy siloxane structures. Silica particles with diameter of around 5 μm were observed in the hybrid films by scanning electron microscopy. The density, decomposition temperature, and modulus of the hybrid films increased with increasing the silica content, whereas the tensile strength and elongation at break of the films decreased in this order. The glass transition temperature of the hybrid films showed the minimum at 8 wt% of silica content. The linear thermal expansion coefficient of the silica in the hybrid films was estimated to be 1.3×10−5 K−1.

Swing-up Control of Inverted Pendulum Using Pseudo-State Feedback:

Abstract: Swing-up control, that is the transfer of a pendulum from a pendant state to the inverted one, is a good laboratory experiment of optimal control theory for non-linear control systems. The optimal control can be determined by the maximum principle and obtained as a function of time. Since the control is, however, determined in a feedforward fashion, the control is not robust to disturbances and uncertainties of the system, and the transfer of the state of the pendulum is not assured. In the paper, a robust swing-up control using a subspace projected from the whole state space is proposed. Based on the projected state space or pseudo-state, the control input is determined depending on the partitioning of the state as a bang-bang type control. The control algorithm is applied for a new type of pendulum (TI Tech pendulum), and the effectiveness and robustness of the proposed control are examined by experiments.

Enzymatic degradation of microbial poly(3‐hydroxybutyrate) films

Abstract: The effects of crystallinity and spherulite size on the enzymatic degradation of microbial poly(3-hydroxybutyrate) (PHB) films have been studied at 37°C and pH 7,4 in aqueous solutions of an extracellular PHB depolymerase from Alcaligenes faecalis T1. The rate of enzymatic degradation of PHB films decreases with an increase in crystallinity, but it is little influenced by the size of PHB spherulites. It was suggested that the PHB depolymerase firstly hydrolyzes the PHB chains in the amorphous state on the surface of the films and subsequently erodes the PHB chains in the crystalline state.

A modified cyclodextrin as a guest responsive colour-change indicator

Abstract: CHEMICAL indicators that change colour in response to the presence of neutral organic molecules are valuable for qualitative chemical analysis. Although some ionophores are known to exhibit colour changes on binding metal or ammonium cations1–3, however, the detection of neutral organic species in solution by this means remains problematic. We have shown recently4–7 that some fluorophore-modified cyclodextrins exhibit variations in fluorescence intensity on binding organic guests. Here we report guest-selective binding to a cyclodextrin that has been modified in such a way as to undergo a colour change on host-guest complexation. We attach the pH indicator methyl red to the wall of a β-cyclodextrin: in acidic solution, the modified cyclodextrin remains yellow owing to binding of the methyl red group inside the cavity, protecting it from protonation. When an organic guest displaces the methyl red group from the cavity, a colour change to red is observed. It should be possible to exploit the molecular recognition capability of cyclodextrins to develop a range of such 'molecular indicators'.

Memoryless stabilization of uncertain linear systems including time-varying state delays

Abstract: The problem of stabilizing a class of uncertain time-delay systems via memoryless linear feedback is examined. The systems under consideration are linear systems with time-varying state delays. They also contain uncertain parameters (possibly time-varying) whose values are known only to within a prescribed compact bounding set. The main contribution given is to enlarge the class of time-delay systems for which one can construct a stabilizing memoryless linear feedback controller. Within this framework, a novel notion of robust memoryless stabilizability is first introduced via the method of Lyapunov functionals. Then a sufficient condition for the stabilizability is proposed. It is shown that solvability of a parameterized Riccati equation can be used to determine whether the time-delay system satisfies the sufficient condition. If there exists a positive definite symmetric solution satisfying the Riccati equation, a suitable memoryless linear feedback law can be derived. >

New origin of a convective motion: Elastically induced convection in granular materials.

Abstract: Convection and fluidization in a vibrated bed of powder are reproduced in a numerical simulation. In the simulation, each particle of the powder, during a collision, has a viscoelastic interaction with the other colliding particle. Because of the discreteness of the particles, this elasticity causes convection. The critical values of fluidization and convection agree with experiments.

Analysis of a redundant free-flying spacecraft/manipulator system

Abstract: An analysis of the momentum conservation equations of a redundant free-flying spacecraft/manipulator system acting in a zero-gravity environment is presented. In order to follow a predefined end-effector path, the inverse kinematics at velocity level is considered. The redundancy is solved alternatively in terms of pseudoinverses and null-space components of the manipulator inertia matrix, the manipulator Jacobian matrix, and the generalized Jacobian matrix. A general manipulation task is defined as end-effector continuous path tracking with simultaneous attitude control of the spacecraft. Three subtasks of the general task are considered. The case of manipulator motions that yield no spacecraft attitude disturbance is analyzed in more detail and a special 'fixed-attitude-restricted' (FAR) Jacobian is defined. Through singular-value decomposition of this Jacobian, corresponding FAR dexterity measures (FAR manipulability and FAR condition number) are derived. >

Preparation and properties of novel soluble aromatic polyimides from 4,4′‐diaminotriphenylamine and aromatic tetracarboxylic dianhydrides

Abstract: New aromatic polyimides containing triphenylamine unit were prepared by two different methods, i.e., a conventional two-step method starting from 4,4′-diaminotriphenylamine and aromatic tetracarboxylic dianhydrides and the one-step thioanhydride method starting from the aromatic diamine and aromatic tetracarboxylic dithioanhydrides. Both procedures yielded high-molecular-weight polyimides with inherent viscosities of 0.47–1.17 dL/g. Some of these polymers were soluble in organic solvents such as N,N-dimethylacetamide, N-methyl-2-pyrrolidone, m-cresol, and pyridine. All the polyimides afforded transparent, flexible, and tough films, and the color varied from pale yellow to dark red, depending markedly on the tetracarboxylic acid components. The glass transition temperatures (Tgs) of these polyimides were in the range of 287–331°C and the 10% weight loss temperatures were above 520°C in air. The polyimides prepared by the one-step method exhibited better solubility in organic solvents and had somewhat lower Tgs than the polymers prepared by a conventional two-step method.

Effects of nonionic surfactant on enzymatic hydrolysis of used newspaper

Abstract: Effects of five types of nonionic surfactant having a polyoxyethylene glycol (POG) group on enzymatic hydrolysis of used newspaper were studied. The surfactants examined in this work always enhanced the saccharification. The optimum surfactant concentration was 0.05% (wt/substrate wt) in the case of POG(21) sorbitane oleic ester. Among the surfactants, POG phenyl ether types showed the highest enhancement effect, for example, with two times higher conversion at 80 h than that without surfactant. Using POG nonylphenyl ether series, the effects of surfactant were considered from the point of the HLB (hydrophile-lypophile balance) value. The GFC (gel filtration chromatography) analysis of free enzyme quantity were also done to study the effect of surfactant on enzyme adsorption onto substrate. As the HLB value increased, the free enzyme quantity and the conversion both increased. It appears that surfactants help the enzyme to desorb from the binding site on the substrate surface after the completion of saccharification at that site.

Synthetic approach to the structure and function of copper proteins

Abstract: Publisher Summary Copper is an essential component for living systems, although excess intake causes symptoms, such as Wilson's disease. Numerous copper-containing proteins are now known and can be categorized based on their functions that are as follows: (1) electron-transfer carrier: plastocyanin, azurin, and pseudoazurin, (2) dioxygen carrier: hemocyanin, (3) oxygenation: tyrosinase, dopamine β -hydroxylase, phenylalanine hydroxylase, and peptidylglycine  -amidating monooxygenase, (4) oxidation: galactose oxidase, amine oxidase, and ascorbate oxidase, (5) reduction: nitrite reductase and nitrous reductase, (6) disproportionation: superoxide dismutase, and (7) unknown: stellacyanin, umecyanin, and cucumber basic blue copper protein. Based on the spectroscopic properties, mainly electron paramagnetic resonance (EPR), the active sites of copper proteins have been classified into three groups, types I, II, and III. In this review, new nomenclature is used to classify the copper sites more precisely with respect to their structural features and spectroscopic properties along with their definitions. The synthesis, characterization, and reactivity of low-molecular-weight copper complexes with artificial ligands, designed to mimic structurally the copper sites in proteins, have been a major topic in current bioinorganic chemistry. The unusual spectroscopic properties of type I copper have been particularly fascinating to many inorganic chemists. Hemocyanin (Hc) is a widely occurring oxygen transport protein in invertebrates, arthropods, and mollusks. Hc contains type III copper that binds dioxygen reversibly as peroxide.