New combined polymer/chromium approach for investigating the phototransformations involved in hologram formation in dichromated poly(vinyl alcohol)

The photochemical behavior of dichromated poly(vinyl alcohol) films has been analyzed upon exposure at 365 nm in relationship with the performances of holograms recorded in such photosensitive materials. The evolution of both involved species, poly(vinyl alcohol) and chromium, has been quantified by the implementation of an innovative approach. This approach combines the monitoring of the structural modification of the polymeric matrix and the fate of the various chromium species. For the first time, it has been established that chromium(V) not only is an indicator of the hologram quality, as previously assessed, but also appears to be responsible for the crosslinking implied in the hologram formation. Actually, the crosslinking has been proved to proceed through coordination bonds around chromium(V), which acts as a bridge between the polymeric chains. The role played by the ammonium cations in the hologram quality has also been elucidated. The improvement brought by ammonium dichromate with respect to potassium dichromate involves amide groups resulting from poly(vinyl alcohol) phototransformation. These groups provide additional chelating sites for chromium(V), leading to an increase in the matrix crosslinking. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1317–1325, 2006     

A theorem of Jon F. Carlson on filtrations of modules

We give an alternative proof to a theorem of Carlson [J.F. Carlson, Cohomology and induction from elementary abelian subgroups, Quart. J. Math. 51 (2000) 169-181] which states that if G is a finite group and k is a field of characteristic p, then any kG-module is a direct summand of a module which has a filtration whose sections are induced from elementary abelian p-subgroups of G. We also prove two new theorems which are closely related to Carlson’s theorem.     

Perturbation of semi-Browder operators and stability of Browder's essential defect and approximate point spectrum

In the present paper we investigate the stability of closed densely defined semi-Browder operators under operator perturbations that belong to a perturbation class related to compact operators. Furthermore, we apply the obtained results to give a characterization and to study the stability of Browder's essential approximate point spectrum and Browder's essential defect spectrum.     

The Configuration of Naturally Occurring Iridoid Glucosides at C(6) and C(8): A Complementary Assignment Aid by 13C-NMR. Spectroscopy

Evidence is presented which demonstrates that ¹³C-NMR. spectroscopy can be used with confidence in evaluating the configuration of R¹R²CHOH centers at C(6) and C(8) of iridoid glucosides.     

The vibration and buckling of laminated non-homogeneous orthotropic conical shells subjected to external pressure

In this paper, the free vibration and buckling of laminated homogeneous and non-homogeneous orthotropic truncated conical shells under lateral and hydrostatic pressures are studied. At first, the basic relations, the modified Donnell type dynamic stability and compatibility equations have been obtained for laminated orthotropic truncated conical shells, the Young's moduli and density of which vary piecewise continuously in the thickness direction. Applying superposition and Galerkin methods to the foregoing equations, the buckling pressures and dimensionless frequency parameter of laminated homogeneous and non-homogeneous orthotropic conical shells are obtained. The appropriate formulas for single-layer and laminated cylindrical shells made of homogeneous and non-homogeneous, orthotropic and isotropic materials are found as a special case. Finally, the effects of the number and ordering of layers, the variations of conical shell characteristics, together and separately variations of the Young's moduli and densities of the materials of layers on the critical lateral and hydrostatic pressures, and frequency parameter are found for different mode numbers. The results are compared with other works.     

A de Vries (SmC*) Phase in a Novel Series of Chiral Fluorinated Organosiloxane Liquid Crystals

The synthesis and characterization of a series of five chiral fluorinated low molar mass (bifurcated tail) organosiloxane materials is presented. The mesogenic moiety is similar to that in the TSiKN65F mesogen reported by Naciri et al., which displays a de Vries-type SmA* phase. The one parameter varied across the series reported herein is the length of the alkyl chain linking the mesogen's core to the bifurcated siloxane tail. One of the five materials displays a de Vries SmC* phase upon cooling from SmA*.     

Nucleophilic,Heterocyclic, Carbene-Catalyzed,Solvent-Free,One-Pot Synthesis of Polyhydroquinolines via Multicomponent Hantzsch Reaction: An Efficient and Ecofriendly Approach

A simple, efficient, and ecofriendly one-pot method has been reported for the synthesis of polyhydroquinolines in excellent yield using nucleophilic heterocyclic carbene as catalyst. The generalized approach is the Hantzsch four-component reaction of aromatic aldehyde, ethyl acetoacetate, cyclic 1,3-diketone, and ammonium acetate.     

Improvement of cycling stability of LiMn2O4 cathode by Fe2O3 surface modification for Li-ion battery

The surface of spinel LiMn₂O₄ was modified with Fe₂O₃ (1.0, 2.0, 3.0, 4.0, and 5.0 wt%) by a simple sol-gel method to improve its electrochemical performance at room temperature. Compared with bare LiMn₂O₄, surface modification improved cycling stability of the material. Among the surface-modified cathode materials, the 3.0- and 4.0-wt% surface-modified cathodes have lesser capacity loss than the others. While the bare LiMn₂O₄ showed 25.4 % capacity loss in 70 cycles at room temperature, 3.0 and 4.0 wt% of Fe₂O₃-modified LiMn₂O₄ only exhibited the capacity loss of 2.6 and 2.3 % in 70 cycles at room temperature, respectively. The structure and phase were identified with X-ray diffractometer along with the lattice constant calculated by a Win-Metric program.