Showing papers by "Tokyo University of Science published in 2008"

Atomic-scale in-situ observation of carbon nanotube growth from solid state iron carbide nanoparticles.

Abstract: We have first observed the nucleation and growth process of carbon nanotubes (CNTs) from iron carbide (Fe 3C) nanoparticles in chemical vapor deposition with C 2H 2 by in situ environmental transmission electron microscopy. Graphitic networks are formed on the fluctuating iron carbide nanoparticles, and subsequently CNTs are expelled from them. Our atomic scale observations suggest that carbon atoms diffuse through the bulk of iron carbide nanoparticles during the growth of CNTs.

Local positive feedback regulation determines cell shape in root hair cells.

Abstract: The specification and maintenance of growth sites are tightly regulated during cell morphogenesis in all organisms. ROOT HAIR DEFECTIVE 2 reduced nicotinamide adenine dinucleotide phosphate (RHD2 NADPH) oxidase-derived reactive oxygen species (ROS) stimulate a Ca2+ influx into the cytoplasm that is required for root hair growth in Arabidopsis thaliana. We found that Ca2+, in turn, activated the RHD2 NADPH oxidase to produce ROS at the growing point in the root hair. Together, these components could establish a means of positive feedback regulation that maintains an active growth site in expanding root hair cells. Because the location and stability of growth sites predict the ultimate form of a plant cell, our findings demonstrate how a positive feedback mechanism involving RHD2, ROS, and Ca2+ can determine cell shape.

Current Developments and Prospective of Lead-Free Piezoelectric Ceramics

Abstract: The dielectric, ferroelectric and piezoelectric properties of perovskite ferroelectric and bismuth layered-structured ferroelectric (BLSF) ceramics are described being superior candidates for lead-free piezoelectric materials to reduce environmental damage. Perovskite-type ceramics seem to be suitable for actuator and high-power applications that require a large piezoelectric constant, d33, and a high Curie temperature, Tc, or a depolarization temperature, Td (>200 °C). For BaTiO3-based solid solutions, (1-x)BaTiO3–x(Bi0.5K0.5)TiO3 (BT–BKT100x) ceramics, Tc increases with increasing amount of x. The BT–BKT20 + MnCO3 (0.1 wt %) ceramic shows a high Tc greater than 200 °C and an electromechanical coupling factor of k33 =0.35. In the case of a(Bi1/2Na1/2)TiO3–b(Bi1/2K1/2)TiO3–cBaTiO3 [BNBK (100a/100b/100c)] solid solution ceramics, d33 is 191 pC/N for BNBK (85.2/2.8/12). KNbO3 (KN)-based ceramics are also a candidate for lead-free piezoelectrics. In Mn-doped KN ceramics, a higher k33 of 0.507 is obtained for KN + MnCO3 (0.1 wt %). On the other hand, BLSF ceramics seem to be excellent candidates as piezoelectric sensors for high temperatures and ceramic resonators with a high mechanical quality factor, Qm, and a low temperature coefficient of resonance frequency, TC-f. The k33 value of the donor (Nb)-doped and grain-oriented (HF) Bi4Ti3-xNbxO12 (BITN-x) ceramic is 0.39 for x=0.08 and is able to keep the same stable value up to 350 °C. Nd(0.01) and V(0.75) co-doped Bi4Ti3O12 ceramics, BNTV(0.01, 0.75), show a relatively low TC-f. Bi3TiTaO9 (BTT)-based solid solution, Srx-1Bi4-xTi2-xTaxO9 [SBTT2(x)] (1x2), displays the high Qm value (=13500) in (p)-mode at x=1.25. For resonator applications, (Sr1-xCax)2Bi4Ti5O18 (SCBT) (0x0.5) ceramics are suitable.

βKlotho Is Required for Fibroblast Growth Factor (FGF) 21 Signaling through FGF Receptor (FGFR) 1c and FGFR3c

Abstract: Fibroblast growth factor (FGF) 21, a structural relative of FGF23 that regulates phosphate homeostasis, is a regulator of insulin-independent glucose transport in adipocytes and plays a role in the regulation of body weight. It also regulates ketogenesis and adaptive responses to starvation. We report that in a reconstituted receptor activation assay system using BaF3 cells, which do not endogenously express any type of FGF receptor (FGFR) or heparan sulfate proteoglycan, FGF21 alone does not activate FGFRs and that βKlotho is required for FGF21 to activate two specific FGFR subtypes: FGFR1c and FGFR3c. Coexpression of βKlotho and FGFR1c on BaF3 cells enabled FGF21, but not FGF23, to activate receptor signaling. Conversely, coexpression of FGFR1c and Klotho, a protein related to βKlotho, enabled FGF23 but not FGF21 to activate receptor signaling, indicating that expression of βKlotho/Klotho confers target cell specificity on FGF21/FGF23. In all of these cases, heparin enhanced the activation but was not e...

The t–J model for the oxide high-Tc superconductors

Abstract: A theoretical review is given on high temperature superconductivity in copper oxides (cuprates) by focusing on the hole doping cases based on the view that it is realized in carrier doped Mott insulators, as noted by Anderson in the initial stage. From the detailed knowledge of electronic states deduced from experiments that showed the undoped parent case is Mott insulators (charge transfer type insulators, to be precise) and that the hole doping is mainly on oxygen sites, the t?J model, as derived by Zhang and Rice, is shown to be a canonical model for hole doped cuprates and values of various parameters of the model have been assessed. Results of many different numerical methods so far obtained for this t?J model, especially the variational Monte Carlo method, have clearly indicated the stability of the -wave superconductivity at absolute zero for the parameter region of actual experimental interest and the particular doping dependences of the condensation energy of superconductivity reflecting particular features of doped Mott insulators. For finite temperatures, on the other hand, the field theoretical slave-boson approximation based on the spin (spinons) and charge (holons) separations and the gauge fields as a glue combining them predicts qualitatively particular features of the existence of characteristic crossover temperatures of the spin singlet of the resonating valence bond (RVB) state, TRVB and the onset of Bose condensation of holons, TB, triggering coherent motion of electrons as convoluted particles of spinons and holons. The considerations based on the gauge field indicate that the onset temperature of superconductivity, Tc, is the lower one of these two, i.e. either TB (overdoped cases) or TRVB (underdoped cases), respectively. These characteristic features of the 'phase diagram' at finite temperatures are in overall agreement with various experimental observations, especially with the existence of spin-gap or pseudo-gap phases. In more detailed examinations of the underdoped region, the antiferromagnetic long-range order and superconductivity show a very intricate relationship at low temperatures depending on the system; they coexist as clarified in the inner layer of Hg-1245 but spin glass states intervene between them in La2?xSrxCuO4 (LSCO). It is argued that these differences can be attributed to the different degrees of disorder. Actually, theories based on the t?J model have also predicted the coexistence of antiferromagnetism and superconductivity in the ground state of clean systems. On the other hand, interesting experimental findings of large Nernst effect and 'Fermi arc' in LSCO and impurity effects in YBCO have prompted the necessity of theoretical investigations of electronic states of lightly doped Mott insulators in the presence of strong disorder.

Role of Sn2+ in the Band Structure of SnM2O6 and Sn2M2O7(M = Nb and Ta) and Their Photocatalytic Properties

Abstract: The photocatalytic properties of metal oxides consisting of Sn2+ with a 5s2 configuration were studied to find new visible light responsive photocatalysts. The band gaps of Ca2Ta2O7, Sn2Ta2O7, and Sn2Nb2O7 were found to be 4.8, 3.0, and 2.3 eV, respectively. Density functional calculations revealed that the valence band levels formed with Sn 5s orbitals were more negative than those with O 2p orbitals. The result is that niobates and tantalates containing Sn2+ have narrow band gaps compared with typical niobates and tantalates. SnNb2O6 showed photocatalytic activity for H2 and O2 evolution from aqueous solutions containing sacrificial reagents (methanol and Ag+) under visible light irradiation (λ > 420 nm). Moreover, the photocatalytic activity of SnNb2O6 depended on the material used as the Sn source. SnNb2O6 synthesized from Sn3O2(OH)2 showed higher activity for H2 and O2 evolution than that synthesized from commercial SnO, which included a small amount of SnO2. SnNb2O6 synthesized from Sn3O2(OH)2 showe...

The thermoelectric properties of bulk crystalline n- and p-type Mg2Si prepared by the vertical Bridgman method

Abstract: Bulk Mg2Si crystals were grown using the vertical Bridgman melt growth method. The n-type and p-type dopants, bismuth (Bi) and silver (Ag), respectively, were incorporated during the growth. X-ray powder diffraction analysis revealed clear peaks of Mg2Si with no peaks associated with the metallic Mg and Si phases. Residual impurities and process induced contaminants were investigated by using glow discharge mass spectrometry (GDMS). A comparison between the results of GDMS and Hall effect measurements indicated that electrical activation of the Bi doping in the Mg2Si was sufficient, while activation of the Ag doping was relatively smaller. It was shown that an undoped n-type specimen contained a certain amount of aluminum (Al), which was due either to residual impurities in the Mg source or the incorporation of process-induced impurities. Thermoelectric properties such as the Seebeck coefficient and the electrical and thermal conductivities were measured as a function of temperature up to 850 K. The dimen...

Ferroelectric, electrical and magnetic properties of Cr, Mn, Co, Ni, Cu added polycrystalline BiFeO3 films

Abstract: Cr, Mn, Co, Ni, and Cu were added to polycrystalline BiFeO3 films, and their influence on the ferroelectric, electrical, and magnetic properties was investigated. All the additives except Ni reduced the leakage current density in the high electric field region. The addition of Cu and Co decreased the coercive field without reducing remanent polarization. The addition of Co caused spontaneous magnetization at room temperature, which exhibited a large coercive field of 16kOe at 10K. It was revealed that Co addition suppressed the leakage current density, decreased the electric coercive field, and induced spontaneous magnetization and large magnetic coercivity.

The Arabidopsis Phosphatidylinositol Phosphate 5-Kinase PIP5K3 is a key regulator of root hair tip growth

Abstract: Phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] functions as a site-specific signal on membranes to promote cytoskeletal reorganization and membrane trafficking. Localization of PtdIns(4,5)P2 to apices of growing root hairs and pollen tubes suggests that it plays an important role in tip growth. However, its regulation and mode of action remain unclear. We found that Arabidopsis thaliana PIP5K3 (for Phosphatidylinositol Phosphate 5-Kinase 3) encodes a phosphatidylinositol 4-phosphate 5-kinase, a key enzyme producing PtdIns(4,5)P2, that is preferentially expressed in growing root hairs. T-DNA insertion mutations that substantially reduced the expression of PIP5K3 caused significantly shorter root hairs than in the wild type. By contrast, overexpression caused longer root hairs and multiple protruding sites on a single trichoblast. A yellow fluorescent protein (YFP) fusion of PIP5K3, driven by the PIP5K3 promoter, complemented the short-root-hair phenotype. PIP5K3-YFP localized to the plasma membrane and cytoplasmic space of elongating root hair apices, to growing root hair bulges, and, notably, to sites about to form root hair bulges. The signal was greatest in rapidly growing root hairs and quickly disappeared when elongation ceased. These results provide evidence that PIP5K3 is involved in localizing PtdIns(4,5)P2 to the elongating root hair apex and is a key regulator of the machinery that initiates and promotes root hair tip growth.

InBr3-promoted divergent approach to polysubstituted indoles and quinolines from 2-ethynylanilines: switch from an intramolecular cyclization to an intermolecular dimerization by a type of terminal substituent group.

Abstract: Use of a 2-ethynylaniline having an alkyl or aryl group on the terminal alkyne selectively produced a variety of polyfunctionalized indole derivatives in moderate to excellent yields via indium-catalyzed intramolecular cyclization of the corresponding alkynylaniline. In contrast, employment of a substrate with a trimethylsilyl group or with no substituent group on the terminal triple bond, exclusively afforded polysubstituted quinoline derivatives in good yields via indium-promoted intermolecular dimerization of the ethynylaniline. This indium catalytic system successfully accommodated the intramolecular cyclization of other arylalkyne skeletons involving a carboxylic acid and an amide group.

Size‐ and Shape‐Controlled Conversion of Tungstate‐Based Inorganic–Organic Hybrid Belts to WO3 Nanoplates with High Specific Surface Areas

Abstract: Two-dimensional monoclinic WO(3) nanoplates with high specific surface areas are synthesized through a novel conversion process using tungstate-based inorganic-organic hybrid micro/nanobelts as precursors. The process developed involves a topochemical transformation of tungstate-based inorganic-organic hybrid belts into WO(3) nanoplates via an intermediate product of H(2)WO(4) nanoplates, utilizing the similarity of the W-O octahedral layers in both H(2)WO(4) and WO(3). The as-obtained WO(3) nanoplates show a single-crystalline nanostructure with the smallest side along the [001] direction. The WO(3) nanoplates are 200-500 nm x 200-500 nm x 10-30 nm in size, and their specific surface areas are up to 180 m(2) g(-1). Photocatalytic measurements of visible-light-driven oxidation of water for O(2) generation in the presence of Ag(+) ions indicate that the activity of the as-obtained WO(3) nanoplates is one order of magnitude higher than that of commercially available WO(3) powders.

Constraints on scalar-tensor models of dark energy from observational and local gravity tests

Abstract: We construct a family of viable scalar-tensor models of dark energy (DE) which possess a phase of late-time acceleration preceded by a standard matter era, while at the same time satisfying the local gravity constraints (LGC). The coupling $Q$ between the scalar field and the nonrelativistic matter in the Einstein frame is assumed to be constant in our scenario, which is a generalization of $f(R)$ gravity theories corresponding to the coupling $Q=\ensuremath{-}1/\sqrt{6}$. We find that these models can be made compatible with local gravity constraints even when $|Q|$ is of the order of unity through a chameleon mechanism, if the scalar-field potential is chosen to have a sufficiently large mass in the high-curvature regions. We show that these models generally lead to the divergence of the equation of state of DE, which occurs at smaller redshifts as the deviation from the $\ensuremath{\Lambda}\mathrm{CDM}$ model becomes more significant. We also study the evolution of matter density perturbations and employ them to place bounds on the coupling $|Q|$ as well as model parameters of the field potential from observations of the matter power spectrum and the cosmic microwave background (CMB) anisotropies. We find that, as long as $|Q|$ is smaller than the order of unity, there exist allowed parameter regions that are consistent with both observational and local gravity constraints.

Effects of graft densities and chain lengths on separation of bioactive compounds by nanolayered thermoresponsive Polymer brush surfaces

Abstract: We have prepared various poly(N-isopropylacrylamide) (PIPAAm)-grafted silica bead surfaces through surface-initiated atom transfer radical polymerization (ATRP) by changing graft densities and brush chain lengths. The prepared surfaces were characterized by chromatographic analysis using the modified silica beads as chromatographic stationary phases. ATRP initiator (2-(m,p-chloromethylphenyl)ethyltrichlorosilane) density on silica bead surfaces was modulated by changing the feed composition of the self-assembled monolayers (SAMs) of mixed silane coupling agents consisting of ATRP initiator and phenethyltrichlorosilane on the surfaces. IPAAm was then polymerized on SAM-modified silica bead surfaces by ATRP in 2-propanol at 25 °C. The chain length of the grafted PIPAAm was controlled by simply changing the ATRP reaction time at constant catalyst concentration. The thermoresponsive surface properties of the PIPAAm-grafted silica beads were investigated by temperature-dependent elution behavior of hydrophobic...

Two-photon probe of the Jaynes–Cummings model and controlled symmetry breaking in circuit QED

Abstract: Micrometre-scale superconducting circuits can act as quantum two-level systems, but unlike in their natural counterparts—such as atoms—the parameters of these ‘artificial qubits’ can be controlled externally. This tunability has now been used to break the symmetry of the system hamiltonian in a controlled manner. Superconducting qubits1,2 behave as artificial two-level atoms and are used to investigate fundamental quantum phenomena. In this context, the study of multiphoton excitations3,4,5,6,7 occupies an important role. Moreover, coupling superconducting qubits to onchip microwave resonators has given rise to the field of circuit quantum electrodynamics8,9,10,11,12,13,14,15 (QED). In contrast to quantum-optical cavity QED (refs 16, 17, 18, 19), circuit QED offers the tunability inherent to solid-state circuits. Here, we report on the observation of key signatures of a two-photon-driven Jaynes–Cummings model, which unveils the upconversion dynamics of a superconducting flux qubit20 coupled to an on-chip resonator. Our experiment and theoretical analysis show clear evidence for the coexistence of one- and two-photon-driven level anticrossings of the qubit–resonator system. This results from the controlled symmetry breaking of the system hamiltonian, causing parity to become a not-well-defined property21. Our study provides fundamental insight into the interplay of multiphoton processes and symmetries in a qubit–resonator system.

The Cobalt Porphyrin−Lewis Base System: A Highly Selective Catalyst for Alternating Copolymerization of CO2 and Epoxide under Mild Conditions

Abstract: The use of a cobalt porphyrin ((TPP)CoCl, 1) in combination with dimethylaminopyridine (DMAP) for the alternating copolymerization of CO2 and epoxide is described. The (TPP)CoCl (1)−DMAP system quantitatively produced the alternating copolymer from CO2 and cyclohexene oxide (CHO) under optimized conditions (50 atm, 80 °C). This calatyst system also worked satisfactorily for the alternating copolymerization of CO2 and a terminal epoxide, e.g., propylene oxide (PO), without formation of cyclic carbonate to give the polycarbonate. The alternating copolymerization of CO2 and epoxide (CHO, PO) was achieved under very mild conditions, such as at ambient temperature and under CO2 at 1 atm, by using the 1−DMAP catalyst system.

Asymmetric Diels–Alder Reactions of α,β‐Unsaturated Aldehydes Catalyzed by a Diarylprolinol Silyl Ether Salt in the Presence of Water

Abstract: The Diels–Alder reaction is a powerful synthetic method for the construction of regioand stereochemically defined cyclohexane frameworks. There are several catalytic enantioselective methods, and MacMillan and co-workers developed the first Diels–Alder reaction involving an organocatalyst, which proceeds by a LUMO-lowering activation mechanism. Since then several asymmetric Diels–Alder reactions involving organocatalysts have been reported. Our group and that of Jørgensen developed a diarylprolinol silyl ether as an effective organocatalyst in 2005, and this type of catalyst has since been employed widely in several asymmetric reactions. Recently, we found that diarylprolinol silyl ether 1 combined with CF3CO2H is an effective Diels–Alder catalyst in toluene. In contrast, water has attracted a lot of interest as a reaction medium in current organic chemistry because of its unique properties. In the Diels–Alder reaction, for instance, the reaction is accelerated “in water” (homogeneous dilute conditions) and “on water” (biphasic conditions). We reported the positive effect of water on diastereoand enantioselectivities for the asymmetric aldol reaction in the presence of water. Palomo et al. and Ma and co-workers reported the enantioselective Michael reaction catalyzed by dialkyland diphenylprolinol silyl ethers, respectively in the presence of water. Some organocatalyzed reactions are known to be affected by dissolved water, and on the basis of our interest in reactions in the presence of water, we have examined the enantioselective Diels–Alder reaction by using diarylprolinol silyl ether as an organocatalyst. Although Northrup and MacMillan and Ogilvie and co-workers reported the asymmetric Diels–Alder reaction in the presence of water, we developed a green and practical procedure that does not require an organic solvent, even for the purification step. We also observed an interesting phenomenon, namely the positive effect of water on the rate and enantioselectivity of the reaction, which is different from that of the “on water” reaction and will be described herein. First, we chose the model reaction between cinnamaldehyde and cyclopentadiene, which we had found to be promoted by a combination of 1 (Figure 1) and CF3CO2H in

Hydrothermal preparation of ZnO:CNT and TiO2:CNT composites and their photocatalytic applications

Abstract: ZnO:CNT and TiO2:CNT composites were fabricated under mild hydrothermal conditions (T = 150–240 °C) with an autogenous pressure. The as prepared composites were characterized using X-ray diffraction, Scanning electron microscopy and FTIR spectroscopy. Photocatalytic applications of the composites were investigated using indigo caramine dye. The effect of the catalyst content, pH of the medium, source and intensity of illumination on the photodegradation of the indigo caramine dye was studied and the efficiency of the composites were investigated based on different parameters like percent transmittance (%T), percent decomposition, and chemical oxygen demand of the dye solution to obtain optimum treatment conditions. The results obtained exhibit higher photocatalytic activity when compared to the reagent grade ZnO, TiO2 and hydrothermally prepared ZnO:AC and TiO2:AC composites.