Cellulose–chitin hybrids: synthesis of branched amino polysaccharides by regioselective introduction of (N-acetyl-)d-glucosamine branches into cellulose

Cellulose–chitin hybrid-type branched polysaccharides, β-1,4-d-glucans having amino sugar branches at the C-6 position, have been synthesized through a series of site-specific modification reactions. Cellulose was first transformed to two kinds of acceptors having a reactive group only at C-6. Glycosylation reactions of these acceptors with an oxazoline donor derived from d-glucosamine resulted in the introduction of amino sugar branches into cellulose. An acceptor carrying the O-trimethylsilyl group at C-6 was particularly suitable for glycosylation in solution to form branched celluloses with various degrees of substitution up to about 0.5 per pyranose unit in a controlled manner. Deprotection of the product afforded the cellulose having N-acetyl-d-glucosamine or d-glucosamine branches depending on the reaction conditions. The deprotected nonnatural branched polysaccharides were readily soluble in neutral water as well as common organic solvents and would be promising as a new type of water-soluble amino polysaccharides.     

Origin and control of high-temperature ferromagnetism in semiconductors

The extensive experimental and computational search for multifunctional materials has resulted in the development of semiconductor and oxide systems, such as (Ga,Mn)N, (Zn,Cr)Te and HfO(2), which exhibit surprisingly stable ferromagnetic signatures despite having a small or nominally zero concentration of magnetic elements. Here, we show that the ferromagnetism of (Zn,Cr)Te, and the associated magnetooptical and magnetotransport functionalities, are dominated by the formation of Cr-rich (Zn,Cr)Te metallic nanocrystals embedded in the Cr-poor (Zn,Cr)Te matrix. Importantly, the formation of these nanocrystals can be controlled by manipulating the charge state of the Cr ions during the epitaxy. The findings provide insight into the origin of ferromagnetism in a broad range of semiconductors and oxides, and indicate possible functionalities of these composite systems. Furthermore, they demonstrate a bottom-up method for self-organized nanostructure fabrication that is applicable to any system in which the charge state of a constituent depends on the Fermi-level position in the host semiconductor.     

Color control of emissions from rare earth-co-doped La2O3:Bi phosphor thin films prepared by magnetron sputtering

Multicolor photoluminescence (PL) and electroluminescence (EL) were observed from developed Bi- and rare earth (RE)-co-doped La₂O₃ (La₂O₃:Bi,RE) phosphor thin films. The phosphor thin films were prepared with various contents of co-doped RE, such as Dy, Er, Eu, Tb and Tm, by a combinatorial radio frequency magnetron sputtering deposition method. The obtainable luminance in EL and PL intensities changed considerably as the kind and content of RE were varied. Color changes from blue and blue-green to various colors in PL and EL emissions, respectively, were obtained in postannealed La₂O₃:Bi,RE phosphor thin films: films prepared by co-doping Bi at a constant content with various REs at varying levels of content. However, all of the observed emission peaks in PL and EL from La₂O₃:Bi,RE phosphor thin films were assigned to either the broad emission originating from the transition in Bi³⁺ or the visible emission peaks originating from the transition in the co-doped trivalent RE ion. The difference between PL and EL characteristics in La₂O₃:Bi,RE phosphor thin films is mainly attributed to the difference in the excitation mechanism.     

Resonance analysis of 151,153Eu from neutron capture cross section measurements in the energy range from 1 to 20 eV

The neutron capture cross sections of Europium-151 and Europium-153 have been measured by the time-of-flight method in the energy range from 0.005 to 100 eV using the Kyoto University Research Reactor Institute-Linear Accelerator (KURRI-LINAC). An assembly of Bismuth Germanate (BGO) scintillators was used to detect the prompt capture of γ rays. The absolute values of the neutron capture cross sections of ¹⁵¹Eu and ¹⁵³Eu were deduced by normalizing the thermal capture cross sections in JENDL-4.0 and ENDF/B-VII.1, respectively. Then, we have obtained the resonance parameters of 20 resonances in ¹⁵¹Eu and 17 resonances in ¹⁵³Eu using the code SAMMY.

For the 3.36-eV resonance of ¹⁵¹Eu, the evaluated resonance peak area in JENDL-4.0 is about 95% smaller than the present result. For the 7.00-, 7.22-, and 7.42-eV resonance; we confirmed that there are significant differences between the measured peaks and evaluated peaks in JENDL-4.0, ENDF/B-VII.1, and JEFF-3.2. For the ¹⁵³Eu, the evaluated resonance peak areas in JENDL-4.0, ENDF/B-VII.1, and JEFF-3.2 are about 15% larger than the measured resonance peak areas at the 2.46-, 3.29-, and 3.94-eV resonances.     

Mechanical properties of fruit-cuticular membranes isolated from 27 cultivars of Diospyros kaki Thunb.

Fruit cuticular membranes (CMs) were isolated from 27 cultivars of Diospyros kaki Thunb., and relationships among their chemical compositions, densities and mechanical properties were analysed. Wide cultivar dependency was observed in both chemical compositions and mechanical properties, however, astringency did not show clear correlation with them. Densities of the CMs showed significant positive correlation with maximum stress and elastic modulus, but negative correlation with maximum strain. Positive correlations were also observed in elastic modulus-polysaccharide content and maximum strain-polysaccharide content, and negative correlation in elastic modulus-cutin content on a weight over unit area (μg/cm²) basis. The integration of densities of fruit CMs and their chemical constituents may explain the mechanical properties which are specific to each cultivar of D. kaki fruit.