Magnetic measurements and microstructure studies of highly oriented Bi2Sr2Ca2Cu3O8 bulks

A highly oriented structure for Bi₂Sr₂Ca₂Cu₃O₈ bulk superconductors was successfully made by hot-forging. The J_c values were closely related to the degree of orientation. Microstructure observations and magnetization measurements revealed that the properties of the highly oriented BSCCO reflected the two-dimensionality in this layered structure material.     

Noncommutative geometry and non-Abelian Berry phase in the wave-packet dynamics of Bloch electrons

Motivated by a recent proposal on the possibility of observing a monopole in the band structure, and by an increasing interest in the role of Berry phase in spintronics, we studied the adiabatic motion of a wave packet of Bloch functions, under a perturbation varying slowly and incommensurately to the lattice structure. We show, using only the fundamental principles of quantum mechanics, that the effective wave-packet dynamics is conveniently described by a set of equations of motion (EOM) for a semiclassical particle coupled to a non-Abelian gauge field associated with a geometric Berry phase.

Our EOM can be viewed as a generalization of the standard Ehrenfest's theorem, and their derivation was asymptotically exact in the framework of linear response theory. Our analysis is entirely based on the concept of local Bloch bands, a good starting point for describing the adiabatic motion of a wave packet. One of the advantages of our approach is that the various types of gauge fields were classified into two categories by their different physical origin: (i) projection onto specific bands, (ii) time-dependent local Bloch basis. Using those gauge fields, we write our EOM in a covariant form, whereas the gauge-invariant field strength stems from the noncommutativity of covariant derivatives along different axes of the reciprocal parameter space. On the other hand, the degeneracy of Bloch bands makes the gauge fields non-Abelian.

For the purpose of applying our wave-packet dynamics to the analyses on transport phenomena in the context of Berry phase engineering, we focused on the Hall-type and polarization currents. Our formulation turned out to be useful for investigating and classifying various types of topological current on the same footing. We highlighted their symmetries, in particular, their behavior under time reversal (T) and space inversion (I). The result of these analyses was summarized as a set of cancellation rules. We also introduced the concept of parity polarization current, which may embody the physics of orbital current. Together with charge/spin Hall/polarization currents, this type of orbital current is expected to be a potential probe for detecting and controlling Berry phase.     

Synthesis of Mesoporous TiO2/SiO2 Hybrid Films as an Efficient Photocatalyst by Polymeric Micelle Assembly

Thermally stable mesoporous TiO₂/SiO₂ hybrid films with pore size of 50 nm have been synthesized by adopting the polymeric micelle‐assembly method. A triblock copolymer, poly(styrene‐b‐2‐vinyl pyridine‐b‐ethylene oxide), which serves as a template for the mesopores, was utilized to form polymeric micelles. The effective interaction of titanium tetraisopropoxide (TTIP) and tetraethyl orthosilicate (TEOS) with the polymeric micelles enabled us to fabricate stable mesoporous films. By changing the molar ratio of TEOS and TTIP, several mesoporous TiO₂/SiO₂ hybrid films with different compositions can be synthesized. The presence of amorphous SiO₂ phase effectively retards the growth of anatase TiO₂ crystal in the pore walls and retains the original mesoporous structure, even at higher temperature (650 °C). These TiO₂/SiO₂ hybrid films are of very high quality, without any cracks or voids. The addition of SiO₂ phase to mesoporous TiO₂ films not only adsorbs more organic dyes, but also significantly enhances the photocatalytic activity compared to mesoporous pure TiO₂ film without SiO₂ phase.     

Thermodynamic and transport properties of SmS under high pressure

We measured transport and thermodynamic properties of the valence-fluctuating phase of SmS up to 8.5 kbar, and found a bump structure in the temperature dependence of the electrical resistivity and a Schottky-type anomaly in the temperature dependence of the thermal expansion coefficient at a characteristic temperature T₀. We also observed that the absolute value of the Hall constant rapidly increases below T₀. From these results, we argue that the steep rise of the electrical resistivity below T₀ is inherent to golden SmS and can be ascribed to the decrease in the carrier concentration possibly due to the pseudo gap formation.     

Hierarchical distributed stabilization of power networks

Large fluctuation of electric power due to high penetration of renewable energy sources such as photovoltaic and wind power generation increases the risk to make the whole power network system unstable. The conventional frequency control called load frequency control is based on PID (proportional-integral-derivative) control or more advanced centralized and decentralized/distributed control. If we could more effectively use information on the state of the other neighbor generators, we can expect to make the whole system more robust against the large frequency fluctuation. This paper proposes a fundamental framework towards the design of hierarchical distributed stabilizing controllers for a network of power generators and loads. This novel type of distributed controller, composed of a global controller and a set of local controllers, takes into account the effect of the interaction among the generators and loads to improve robustness for the variation of locally stabilizing controllers.     

Control of emission peaks of X-ray phosphor using dye-silica nanoparticles

Simple method yielding new emission peaks to the X-ray phosphor and its mechanism were investigated using concentrated-dye-molecule-doped silica nanoparticles (dye-silica nanoparticles) and X-ray phosphors. The dye-silica nanoparticles were coated on the sheet of the X-ray phosphor using 20 wt% polyvinyl alcohol solution. The fluorescence of the dye-silica nanoparticle coated onto X-ray phosphor was successfully observed by X-ray irradiation. The fluorescent cascade from the X-ray-irradiated phosphor could be used in the excitation of the dye-silica nanoparticles by coating on the calcium tungstate (X-ray phosphor). The observed new fluorescence was based on the extent of the overlapping of wavelengths between the emission of the X-ray phosphor and the excitation of the dye-silica nanoparticles. The fluorescent peak of the calcium tungstate as the X-ray phosphor shifted from 434 to 425 nm. The dye-silica particle-calcium tungstate hybrid material showed new emission peaks from 543 to 601 nm due to the addition of fluorescein, rhodamine red-X, or cy5. The new emission peaks changed by the content of dye and the size of the silica nanoparticles. The fluorescence intensity ratio of the new fluorescence peaks at 543 nm against that of the X-ray phosphor depended on the fluorescent cascade from the X-ray-irradiated X-ray phosphor. It can closely match the overall emission of the phosphorous intensity screens to the sensitivity of the film allowing lower dose X-rays to obtain the same image clarity.     

Coacervate formation from natural glycolipid: one acetyl group on the headgroup triggers coacervate-to-vesicle transition

Coacervate (L3 phase) formation of the single component "natural" glycoliped biosurfactant, MEL-A, was observed for the first time by using an optical microscope, a confocal laser scanning microscope (CLSM), and a freeze-fracture electron microscope (FF-TEM). It was also found that only a slight decrease in spontaneous curvature resulting from the absence of one acetyl group on the headgroup induced a drastic morphological change in the 3D self-assembled structure from coacervates (L3 phase) to ordered vesicles (Lalpha phase).     

Direct observation of deuterium migration in crystalline-state reaction by single crystal neutron diffraction IV. "Hula-twist" rotation of a long alkyl radical produced by photoirradiation

When the crystal of [(R)-1,2-bis(ethoxycarbonyl)ethyl](pyridine)bis(dimethylglyoximato)cobalt(III) was exposed to a xenon lamp, the chiral 1,2-bis(ethoxycarbonyl)ethyl group was partly inverted to the opposite configuration and finally the racemic group was produced with retention of the single crystal form. To make clear the mechanism, the hydrogen atom bonded to the chiral carbon of the chiral group was exchanged with the deuterium atom and the crystal was exposed to the xenon lamp for 3 days. The crystal after irradiation was analyzed by neutron diffraction. About 33% of the (R)-isomers were inverted to the (S) isomers in a crystal. The deuterium atom in the (S)-isomer was bonded to the same chiral carbon atom. This result clearly indicates that the inversion proceeds in the three steps; (i) the Co-C bond was homolytically cleaved by photoirradiation and the 1,2-bis(ethoxycarbonyl)ethyl radical and Co(II) were produced, (ii) the radical rotated by 180 degrees directing the C-D bond to the cobalt atom and the opposite plane of the radical faced to the cobalt atom, and (iii) the radical made a bond with Co(II). Because the peripheral atoms of the long radical occupy approximately the same positions in the process of the radical rotation, the crystal was not decomposed. The above rotation is a good example of hula-twist rotation in the process of photoisomerization of polyenes such as rhodopsin.     

Stereochemical anomaly in the thermal conversion of 7,8-dioxy-7-alkenylbenzocyclobutenes to dihydronaphthalenes

[reaction: see text] The stereochemistry of the thermal conversion of alkenylbenzocyclobutenol into dihydronaphthalene was studied. Experiments on the substrates IV, in which two oxy functions are cis, often resulted in the formation of abnormal products in view of the orbital consideration.