Non-magnetic impurity effect on the optimally carrier doped superconductor BaFe1.87Co0.13As2 prepared at ambient pressure

We report properties of the Zn-substituted polycrystalline superconductors BaFe_1.87?xZn_xCo_0.13As₂ (x = 0, 0.04, 0.06 and 0.08) prepared at ambient pressure condition. Electrical conductivity and magnetization measurements revealed that the superconductivity is suppressed by at most 2% substitution of Zn, which shows typical behavior of an anisotropically gaped superconductivity rather than an isotropically gaped superconductivity. With increasing the amount of Zn, weak change in superconductivity was observed. It is likely impossible to obtain BaFe_1.87?xZn_xCo_0.13As₂ crystals with x > 0.04 at ambient pressure condition. On the basis of the structural and the physical properties of the present system, we discuss a possible mechanism of the superconducting pairing.     

Characteristics of Xeroderma Pigmentosum in Japan: Lessons From Two Clinical Surveys and Measures for Patient Care

Xeroderma pigmentosum (XP) is a rare autosomal recessive hereditary disease caused by deficiency in repair of DNA lesions generated by ultraviolet radiation and other compounds. Patients with XP display pigmentary change and numerous skin cancers in sun‐exposed sites, and some patients show exaggerated severe sunburns even upon minimum sun exposure as well as neurological symptoms. We conducted a nationwide survey for XP since 1980. In Japan, the frequency of the XP complementation group A is the highest, followed by the variant type; while in the Western countries, those of groups C or D are the highest. Regarding skin cancers in XP, basal cell carcinoma was the most frequent cancer that afflicted patients with XP, followed by squamous cell carcinoma, and malignant melanoma. The frequency of these skin cancers in patients with XP has decreased in these 20 years, and the age of onset of developing skin cancers is higher than those previously observed, owing to early diagnosis and education to patients and care takers on strict prevention from sunlight for patients with XP. On the other hand, the effective therapy for neurological XP has not been established yet, and this needs to be done urgently.     

Monohydride-Dichloro Rhodium(III) Complexes with Chiral Diphosphine Ligands as Catalysts for Asymmetric Hydrogenation of Olefinic Substrates

We report full details of the synthesis and characterization of monohydride-dichloro rhodium(III) complexes bearing chiral diphosphine ligands, such as (S)-BINAP, (S)-DM-SEGPHOS, and (S)-DTBM-SEGPHOS, producing cationic triply chloride bridged dinuclear rhodium(III) complexes ( 1 a : (S)-BINAP; 1 b : (S)-DM-SEGPHOS) and a neutral mononuclear monohydride-dichloro rhodium(III) complex ( 1 c : (S)-DTBM-SEGPHOS) in high yield and high purity. Their solid state structure and solution behavior were determined by crystallographic studies as well as full spectral data, including DOSY NMR spectroscopy. Among these three complexes, 1 c has a rigid pocket surrounded by two chloride atoms bound to the rhodium atom together with one tBu group of (S)-DTBM-SEGPHOS for fitting to simple olefins without any coordinating functional groups. Complex 1 c exhibited superior catalytic activity and enantioselectivity for asymmetric hydrogenation of exo-olefins and olefinic substrates. The catalytic activity of 1 c was compared with that of well-demonstrated dihydride species derived in situ from rhodium(I) precursors such as [Rh(cod)Cl]₂ and [Rh(cod)₂]⁺[BF₄]⁻ upon mixing with (S)-DTBM-SEGPHOS under dihydrogen.     

A novel analysis method for noise of perpendicular recording media

An in-field magnetic force microscopy (MFM) observation technology was introduced to study media noise in perpendicular recording medium. Magnetization reversal field (H_R) distribution of the recording medium could be mapped by this technology. We have extracted media noise signal image from recording pattern. The noise signal image was converted to a contour image, in which peak areas represented high-noise areas. To clarify the relationship between H_R distribution and the media noise, we novelly combined the contour with the H_R-map. The results show that the media noise mostly gets generated in the lower-H_R areas, which indicates the lower-H_R area is one of the important origins of the media noise. For comparison, a simulation work was also performed by introducing a model based on experimental parameters. The simulation agreed with experimental results very well.     

Conformational change of H+-ATPase beta monomer revealed on segmental isotope labeling NMR spectroscopy

F1-ATPase has been shown to be a stepwise molecular motor. Its rotation mechanism has been explained by the interaction of the gamma axis with the open and closed forms of the beta subunit. Although NMR should be a powerful method for elucidating its mechanism, its molecular size (473 amino acid residues, 52 kDa) is a major obstacle. We have applied segmental labeling based on intein ligation to the beta subunit, and succeeded in assigning 89% of the NH (402/451), 89% of the Calpha (417/473), 83% of the Cbeta (357/431), and 90% of the CO (425/473) signals of the beta subunit monomer. The secondary structures predicted from the chemical shifts of the main chain atoms and the relative orientations determined from residual dipolar couplings indicated that the subunit beta monomer takes on the open form in the absence of nucleotide. Furthermore, the chemical shift perturbation and the residual-dipolar-coupling changes induced by nucleotide binding show that conformational change from the open to the closed form takes place on nucleotide binding. The intrinsic conformational change of the beta subunit monomer induced by nucleotide binding must be one of the essential driving forces for the rotation of F1-ATPase.     

Integrable discrete time chains for the Frobenius-Stickelberger-Thiele polynomials

The notion of Frobenius-Stickelberger-Thiele (FST) polynomials is introduced. Spectral transformations for these polynomials analogous to the Christoffel and Geronimus transformations for orthogonal polynomials are constructed. They yield an integrable discrete time chain (the FST chain) related to the generalized -algorithm. Relations of the FST polynomials to the Padé interpolation problem and to general and symmetric biorthogonal rational functions are considered in detail. This work is supported in part by the Russian Foundation for Basic Research (RFBR) grant no. 06-01-00191 and the Grant-in-Aid for Scientific Research no. 15540119 from the Ministry of Education, Culture, Sports, Science and Technology, Japan.     

Green Nanocomposites from Renewable Resources: Biodegradable Plant Oil‐Silica Hybrid Coatings

Green nanocomposite coatings based on renewable plant oils have been developed. An acid‐catalyzed curing of epoxidized plant oils with 3‐glycidoxypropyltrimethoxysilane produced transparent nanocomposites. The hardness and mechanical strength improved by incorporating the silica network into the organic polymer matrix, and good flexibility was observed in the nanocomposite. The nanocomposites showed high biodegradability.

     

Epitaxial crystallization of crystalline polymers on the surface of drawn polytetrafluoroethylene

Crystallization of crystalline polymers on the surface of drawn polytetrafluoroethylene (PTFE) was studied. Further, cold-drawn polyethylene (PE) was heat treated in contact with drawn PTFE, holding their drawing axes at right angles to each other, and then the morphological change of PE at the interface was studied. Molecular orientation in the surface layer of the PE was examined by observing the molecular orientation of polycaprolactone (PCLn) crystallized on the PE surface.

It was found that PE, PCLn, and nascent nylon 6 crystallize epitaxially on drawn PTFE, which is well known as a polymer having a low energy surface. Intermolecular interaction between PTFE and the overgrown crystalline polymers was explained on the basis of their crystal structures. The molecular orientation of PE in the interfacial region changes from the drawing direction of PE to the drawing direction of PTFE during annealing. It is proposed that PE partially melts during annealing, and nuclei of PE with their c-axis parallel to the molecular axis of PTFE are formed at the interface. Consequently, PE lamellar crystals with their c-axis perpendicular to the original drawing direction grow in the interfacial region between PE and PTFE.     

Crystal structural, magnetic, and transport properties of layered cobalt oxyfluorides, Sr2CoO(3+x)F(1-x) (0 ≤ x ≤ 0.15)

The crystal structure of the layered cobalt oxyfluoride Sr(2)CoO(3)F synthesized under high-pressure and high-temperature conditions has been determined from neutron powder diffraction and synchrotron powder diffraction data collected at temperatures ranging from 320 to 3 K. This material adopts the tetragonal space group I4/mmm over the measured temperature range and the crystal structure is analogous to n = 1 Ruddlesden-Popper type layered perovskite. In contrast to related oxyhalide compounds, the present material exhibits the unique coordination environment around the Co metal center: coexistence of square pyramidal coordination around Co and anion disorder between O and F at the apical sites. Magnetic susceptibility and electrical resistivity measurements reveal that Sr(2)CoO(3)F is an antiferromagnetic insulator with the Néel temperature T(N) = 323(2) K. The magnetic structure that has been determined by neutron diffraction adopts a G-type antiferromagnetic order with the propagation vector k = (1/2 1/2 0) with an ordered cobalt moment μ = 3.18(5) μ(B) at 3 K, consistent with the high spin electron configuration for the Co(3+) ions. The antiferromagnetic and electrically insulating states remain robust even against 15%-O substation for F at the apical sites. However, applying pressure exhibits the onset of the metallic state, probably coming from change in the electronic state of square-pyramidal coordinated cobalt.     

Broadly tunable subterahertz emission from internal branches of the current-voltage characteristics of superconducting Bi2Sr2CaCu2O(8+δ) single crystals

Continuous, coherent subterahertz radiation arises when a dc voltage is applied across a stack of the many intrinsic Josephson junctions in a Bi2Sr2CaCu2O(8+δ) single crystal. The active junctions produce an equal number of I-V characteristic branches. Each branch radiates at a slightly tunable frequency obeying the Josephson relation. The overall output is broadly tunable and nearly independent of heating effects and internal cavity frequencies. Amplification by a surrounding external cavity to allow for the development of a useful high-power source is proposed.