Observation of stimulated Brillouin scattering in polymer optical fiber with pump-probe technique

Stimulated Brillouin scattering (SBS) in a perfluorinated graded-index polymer optical fiber (POF) with 120 μm core diameter was experimentally observed for the first time, to the best of our knowledge, at 1.55 μm wavelength with the pump-probe technique. Compared to spontaneous Brillouin scattering previously reported, the Brillouin gain spectrum (BGS) was detected with an extremely high signal-to-noise ratio, even with a short POF (1 m) and scrambled polarization state. We also investigated the BGS dependences on probe power and temperature, which indicate that SBS in a POF measured with this technique can be utilized to develop high-accuracy temperature sensing systems.     

Application of carbon fibers to biomaterials: a new era of nano-level control of carbon fibers after 30-years of development

Carbon fibers are state-of-the-art materials with properties that include being light weight, high strength, and chemically stable, and are applied in various fields including aeronautical science and space science. Investigation of applications of carbon fibers to biomaterials was started 30 or more years ago, and various products have been developed. Because the latest technological progress has realized nano-level control of carbon fibers, applications to biomaterials have also progressed to the age of nano-size. Carbon fibers with diameters in the nano-scale (carbon nanofibers) dramatically improve the functions of conventional biomaterials and make the development of new composite materials possible. Carbon nanofibers also open possibilities for new applications in regenerative medicine and cancer treatment. The first three-dimensional constructions with carbon nanofibers have been realized, and it has been found that the materials could be used as excellent scaffolding for bone tissue regeneration. In this critical review, we summarize the history of carbon fiber application to the biomaterials and describe future perspectives in the new age of nano-level control of carbon fibers (122 references).     

F2-selective two-dimensional NMR spectroscopy for the analysis of minor components in foods

In this study, we propose F(2)-selective 2D NMR spectroscopy as an effective method to obtain high-quality spectra of minor components in complex foodstuffs. Selective excitation along the F(2) axis overcame the problems occurring in the conventional F(1)-selective 2D NMR spectroscopy. The technique was successfully applied to mango juice to provide high-quality TOCSY, DQF-COSY, and NOESY spectra of the minor components for the assignment of their signals. In addition, high-quality TOCSY spectra were obtained for the minor components of Japanese sake and honey. These results indicate that F(2)-selective 2D NMR spectroscopy will be useful for the non-destructive analysis of various foods.     

Synthesis of skeletal analogues of saxitoxin derivatives and evaluation of their inhibitory activity on sodium ion channels Na(V)1.4 and Na(V)1.5

Skeletal analogues of saxitoxin (STX) that possess a fused-type tricyclic ring system, designated FD-STX, were synthesized as candidate sodium ion channel modulators. Three kinds of FD-STX derivatives 4a-c with different substitution at C13 were synthesized, and their inhibitory activity on sodium ion channels was examined by means of cell-based assay. (-)-FD-STX (4a) and (-)-FD-dcSTX (4b), which showed moderate inhibitory activity, were further evaluated by the use of the patch-clamp method in cells that expressed Na(V)1.4 (a tetrodotoxin-sensitive sodium channel subtype) and Na(V)1.5 (a tetrodotoxin-resistant sodium channel subtype). These compounds showed moderate inhibitory activity towards Na(V)1.4, and weaker inhibitory activity towards Na(V)1.5. Uniquely, however, the inhibition of Na(V)1.5 by (-)-FD-dcSTX (4b) was "irreversible".     

Spin fluctuations and high temperature superconductivity

Theory of spin fluctuations for itinerant magnetism and its application to high temperature superconductivity are reviewed. After a brief introduction to the whole subject the developments of the self-consistent renormalization theory of spin fluctuations are summarized with particular emphasis on critical properties at the quantum phase transitions. Most of the anomalous properties in the normal state of high-T_c cuprates are understood as due to the critical behaviours for the two dimensional antiferromagnetic metals. By analysing the nuclear magnetic relaxation rate and the T-linear term of resistivity, the set of parameters to specify the spin fluctuations are determined. It is shown that by using the parameters thus obtained one can describe other quantities as well, e.g. optical conductivity. Then we proceed to the theory of superconductivity by the spin fluctuation mechanism. After some discussion on the weak coupling treatments, the strong coupling theory is reviewed. It is shown that the set of parameters determined by the normal state properties of the high-T _c cuprates just give a transition temperature of the right order of magnitude. Among the parameters, the most sensitive one for T _c is the frequency spread of the spin fluctuations. This fact enables us to present a possible unified picture of the antiferromagnetic spin fluctuation-induced superconductors, including heavy fermion superconductors and organic superconductors. This point of view may be confirmed to a certain extent by microscopic calculations based on the fluctuation exchange approximation for the two-dimensional Hubbard models representing not only the cuprates but also organic and trellis lattice compounds. The review is concluded with some discussions on future problems, e.g. the pseudo spin-gap in the under-doped region.     

Origin of flat morphology and high crystallinity of ultrathin bismuth films

We have investigated the origin of “atomically flat” and “single-crystalline” growth of Bi films on Si(1 1 1)-7 × 7 through comparative experiments using Si(1 1 1)-β-√3 × √3-Bi as a control system. On the Si(1 1 1)-7 × 7 substrate, the majority of initial nuclei stabilize with pseudocubic (PC) paired layers analogous to the black phosphorus (BP) structure, and grow in a strong two-dimensional fashion that results in a “textured” but “atomically flat” surface morphology. After the coalescence of the BP-like grains at a nominal thickness of 4 monolayers (ML), a tiny number of minority hexagonal (HEX) bulk crystal nuclei, aligned commensurately with the substrate 7 × 7 lattice, cause the “textured” BP-like PC film to transform into a “single-crystalline” bulk-like HEX film. On the Si(1 1 1)-β-√3 × √3-Bi substrate, however, the BP-like structure breaks up into a conventional bulk-like PC structure and the HEX nucleation is suppressed up to as thick as ∼6 ML. Therefore, the morphology and crystallinity of the films are simply rough and polycrystalline, respectively.     

Modulation of stimuli-responsiveness toward acid vapor between real-time and write-erase responses based on conjugated polymers containing azobenzene and Schiff base moieties

We developed three types of film-type stimuli-responsive polymers based on aza-substituted conjugated polymers involving azobenzene, N_bith, N_fluo and Schiff base moieties, C_bith. All polymer films showed bathochromic shifts in absorption spectra followed by chromic behaviors by fuming trifluoroacetic acid (TFA). In particular, we disclosed that there were three significant differences on acid detecting ability between azobenzene and Schiff base derivatives in terms of absorption wavelengths, stability, and proton holding time. The azobenzene polymers exhibited real-time responses toward vapor fuming, meanwhile write and erase chromic behaviors were reversibly accomplished with the Schiff base polymer by exposing to acid and amine vapor. Theoretical calculation revealed that red-shifted absorption bands should be induced by protonation on nitrogen atoms in the aza-substituted positions. Diverse responses through dynamic regulation of electronic properties of main-chain conjugation can be accomplished by introducing the aza-substituents in polymers.     

An Obata-type theorem on compact Einstein manifolds with boundary

Geometriae Dedicata - We show a kind of Obata-type theorem on a compact Einstein n-manifold $$(W, \bar{g})$$ with smooth boundary $$\partial W$$ . Assume that the boundary $$\partial W$$ is minimal...