Selective coincidence spectrometry in the nondestructive determination of nickel in geological materials with high-energy photon activation

The combined use of photon activation and γ-γ coincidence spectrometry is described for the useful and selective nondestructive determination of nickel in geological materials. This method is characterized by the utilization of the nuclide emitting β⁺ particles in its decay and γ-γ coincidence counting with two gates: one for the annihilation photopeak region and the other for the higher Compton plateau region. The practical detection limits by this method for nickel, arsenic, rubidium, sodium and scandium in silicate matrices could be set at 2.0, 1.2, 9.0, 110 and 1.4 μg, respectively.     

Structure of amorphous Fe80-P13-C7 alloy by X-ray diffraction

In the frame of a semiclassical picture a systematic approximation scheme for the hopping-conductivity is derived which provides a classification in terms of the length of correlated hopping-chains. With the aid of an integral equation for the propagation probability of carriers and a decoupling procedure for configuration averages, conductivity is expressed by the zeroth and second moments of independently averaged contributions of paths containing less than a fixed number of hops. A sum rule allows to carry out the static limit explicitly. The lowest order conductivity reduces to a simple form which is presented for later evaluations.     

Highly Asymmetrical Porphyrins with Enhanced Push–Pull Character for Dye‐Sensitized Solar Cells

A porphyrin π‐system has been modulated by enhancing the push–pull character with highly asymmetrical substitution for dye‐sensitized solar cells for the first time. Namely, both two diarylamino moieties as a strong electron‐donating group and one carboxyphenylethynyl moiety as a strong electron‐withdrawing, anchoring group were introduced into the meso‐positions of the porphyrin core in a lower symmetrical manner. As a result of the improved light‐harvesting property as well as high electron distribution in the anchoring group of LUMO, a push–pull‐enhanced, porphyrin‐sensitized solar cell exhibited more than 10 % power conversion efficiency, which exceeded that of a representative highly efficient porphyrin (i.e., YD2)‐sensitized solar cell under optimized conditions. The rational molecular design concept based on highly asymmetric, push–pull substitution will open the possibilities of further improving cell performance in organic solar cells.     

O- and N-Glycosidation of d-glycals using Ferrier rearrangement under Mitsunobu reaction conditions. Application to N-nucleoside synthesis

We have disclosed the reaction of 3-hydroxy free glycals with O- or N-nucleophiles under Mitsunobu reaction conditions proceeded to produce 2,3-unsaturated glycosides in good to high yield and moderate stereoselectivity. The reaction would take place via allyloxycarbenium ion.     

Three p‐xylene‐solvated pseudopolymorphs of bis[1,3‐bis(pentafluorophenyl)propane‐1,3‐dionato]copper(II)

The Cu²⁺ ions in the title compounds, namely bis[1,3‐bis(pentafluorophenyl)propane‐1,3‐dionato‐κ²O,O′]copper(II) p‐xylene n‐solvate, [Cu(C₁₅HF₁₀O₂)₂]·nC₈H₁₀, with n = 1, (I), n = 2, (II), and n = 4, (III), are coordinated by two 1,3‐bis(pentafluorophenyl)propane‐1,3‐dionate ligands. The coordination complexes of (I) and (II) have crystallographic inversion symmetry at the Cu atom and the p‐xylene molecule in (I) also lies across an inversion centre. The p‐xylene molecules in (I) and (II) interact with the pentafluorophenyl groups of the complex via arene–perfluoroarene interactions. In the crystal of (III), two of the p‐xylene molecules interact with the pentafluorophenyl groups via arene–perfluoroarene interactions. The other two p‐xylene molecules are located on the CuO₄ coordination plane, forming a uniform cavity produced by metal...π interactions.     

Once-holed tori embedded in Riemann surfaces

Once-holed tori are the most primitive noncompact Riemann surfaces of positive genus, and consitute a partially ordered set, the order being defined in terms of conforaml embeddings. We consider some families of once-holed tori that are conformally embedded in target Riemann surfaces of conformal mappings of a given noncompact Riemann surface of genus one, and establish an analogue of the one-quarter theorem of Koebe. We also investigate families of once-holed tori conformally embedded in a Riemann surface of positive genus.      

Photon activation analysis of carbon in glasses for fiber amplifiers by using the flow method for the rapid separation of 11C

Summary We have studied the photon activation analysis of carbon in InF₃-based fluoride, chalcogenide and tellurite glasses for fiber amplifiers, and especially the nuclear interference from a matrix produced by (γ,n), (γ,2n), (γ,p) and (n,γ) reactions and a flow method for the rapid and simple separation of ¹¹C. A chemical separation technique is indispensable for determining carbon, because seventeen radionuclides are observed in these glasses. The flow method can sequentially be undertaken, the fusion of an irradiated sample with an oxidizer, the conversion of ¹¹C into ¹¹CO₂, and the absorption of ¹¹C in ethanolamine solution. We used a mixture of Pb₃O₄ and B₂O₃ as the oxidizer. There is interference with the ¹¹C measurement because ¹⁸F and ⁶⁸Ga are produced in fluoride and chalcogenide glasses by the ¹⁹F(γ,n), ²³Na(γ,αn) and ⁶⁹Ga(γ,n) reactions, respectively, and also absorbed in ethanolamine solution. Therefore, this flow method can only be applied to tellurite glasses. The chemical yield provided by the flow method was close to 100% when determining carbon in Japanese Iron and Steel Certified Reference Materials (JSS) by using lithium carbonate as a standard sample. We determined that the carbon concentrations in four kinds of tellurite glass were 7 to 14 ppm.     

Variation of magnetic state of amorphous Fe90Zr10 and Fe91Hf9 by the charge of hydrogen

Amorphous Fe₉₀Zr₁₀ and Fe₉₁Hf₉ ribbons were charged with hydrogen by the electrochemical method up to Fe₉₀Zr₁₀H₂₆ and Fe₉₁Hf₉H₁₅, respectively, and the change in magnetic structures were analyzed by Mössbauer spectrometry. The internal magnetic field appeared by the charge of hydrogen, the degree of change being depended on amounts of hydrogen included in amorphous Fe₉₀Zr₁₀ and Fe₉₁Hf₉, although Fe₉₁Hf₉ absorbed hydrogen more slowly than Fe₉₀Zr₁₀. The differences of hydrogen inclusion and Mössbauer hyperfine structure between Fe₉₀Zr₁₀ and Fe₉₁Hf₉ were discussed based on the results of a hyperfine field distribution and the radial distribution functions of Fe?Fe obtained by EXAFS.     

Electrical resistance of Fe-Zr and Fe-Ni-Zr amorphous alloys under hydrostatic pressure

The effect of pressure on the electrical resistance of Fe₉₀Zr₁₀ and (Fe_0.96Ni_0.04)₉₀Zr₁₀ amorphous alloys has been investigated. The minimum point in the electrical resistance versus temperature curve shifts toward lower temperature range with increasing hydrostatic pressure, corresponding to the shift of the Curie temperature. The decrement of the electrical resistance below the Curie temperature T_c is about twice that above T_c, suggesting a large compressibility in the ferromagnetic state of the amorphous Invar alloys.     

Magnetorefractive effect in granular alloys with tunneling magnetoresistance

The magnetorefractive effect and optical reflectivity are studied in granular Co-Al-O, Co-Si-O, and Co-Ti-O metal-insulator alloys exhibiting tunneling magnetoresistance for compositions close to the percolation threshold. The dependences of these effects on frequency, angle of incidence, and light polarization were measured. The experimental data obtained suggest that the major MRE mechanism in these systems is spin-dependent tunneling at optical frequencies.