Dimensional stability of regenerated cellulose film in relation to orientations of crystalline and noncrystalline phases

The dimensional stability of regenerated cellulose film on swelling with water is discussed in relation to the biaxial orientation of the two kinds of structural units, cellulose II crystallites and noncrystalline chain segments, and their anisotropic swelling (anisotropic absorption of water). Considerable dimensional stability in the plane of the film but enormous instability of thickness on swelling in water of some commercial cellophanes is qualitatively interpreted in terms of the planar orientation of crystal (101) planes along the film surface and the orientation of the noncrystalline chain segments parallel to the film surface. The dimensional changes on swelling from the completely dry state to 10% moisture regain were further interpreted quantitatively in terms of the degrees of biaxial orientation of the two kinds of structural units and their degrees of anisotropic swelling by modifying the Hermans monophase model for crystalline and noncrystalline biphase structures. The following degrees of anisotropic swelling of the structural units were thus obtained: q_{c, [101]} = 0.40%, q_{c, [101 ]} = ?0.33%, and q_a = 2.42%.     

Structure of thiotropocin,a new sulfur-containing 7-membered antibiotic

The structure of a new antibiotic thiotropocin is described.     

Numerical study of localization in Anderson model for disordered systems

The localization properties in the Anderson model of two dimensional square lattices are investigated numerically. Pretty large lattices composed of 10⁴ (= 100 × 100) sites are dealt with, and the overall behaviors of the eigenvectors near the band center are directly examined. Fairly sharp transition and the exponentially decaying localized states are visualized.     

A self-consistent cluster theory of amorphous materials

A cluster method for the electronic structure of amorphous materials is presented with an application to amorphous diamond. Eight-atom cluster model gives a pseudogap in the density of states.     

Control of a photoreaction by electron spin resonance (II): The effect of radical pair lifetime on the control efficiency

The magnetic-field and the microwave effects on the photoreactions of anthraquinone-2-sulfonate and anthraquinone-2-carboxylic acid with xanthene were observed in an SDS micellar solution. The reaction products were analyzed by high performance liquid chromatography. With increasing the magnetic-field strength from the residual value to 400 mT, the yield of dixanthenyl, which is an “escape product”, increased considerably. Upon irradiating the system with a microwave (9400 MHz, 1.0 kW), however, the yield decreased almost to the minimum value at around 334 mT, where the intermediate radical pair becomes resonant with the microwave field. Therefore, we can detect the ESR spectrum of the transient radical pair by the product yield (product-yield-detected ESR or PYESR). In the present study, we observed a clear reversed microwave effect at the center of the PYESR spectrum, whose cause was attributed to “spin locking” of the radical pair by an intense microwave field. The microwave effects for the two systems were, different from each other in several respects including the extent of this spin locking effect in the product yield. The PYESR spectra were calculated by using a quantum mechanical method to discuss the relation between the microwave effect and the radical pair dynamics, the latter of which was also observed in the present study by the “pulse-PYESR” method.