Experimental investigation of flame spreading over pure methane hydrate in a laminar boundary layer

Flame spreading over pure methane hydrate in a laminar boundary layer is investigated experimentally. The free stream velocity (U_∞) was set constant at 0.4 m/s and the surface temperature of the hydrate at the ignition (T_s) was varied between ?10 and ?80 °C. Hydrate particle sizes were smaller than 0.5 mm. Two types of flame spreading were observed; “low speed flame spreading” and “high speed flame spreading”. The low speed flame spreading was observed at low temperature conditions (T_s = ?80 to ?60 °C) and temperatures in which anomalous self-preservation took place (T_s = ?30 to ?10 °C). In this case, the heat transfer from the leading flame edge to the hydrate surface plays a key role for flame spreading. The high speed flame spreading was observed when T_s = ?50 and ?40 °C. At these temperatures, the dissociation of hydrate took place and the methane gas was released from the hydrate to form a thin mixed layer of methane and air with a high concentration gradient over the hydrate. The leading flame edge spread in this premixed gas at a spread speed much higher than laminar burning velocity, mainly due to the effect of burnt gas expansion.     

Characterization of cationic diarylethene by electron spin resonance and absorption spectra-ratio of open/closed-ring isomers

Electrochemical cyclization/cycloreversion reactions of a diarylethene, 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene, are examined experimentally by electron spin resonance (ESR) and absorption spectra. To understand the ESR spectrum, the hyperfine coupling constants are calculated by the density functional theory (DFT) with the B3LYP exchange-correlation functional. The averaged values of the hyperfine coupling constants are approximated by imposing the C(2) symmetry on the structure of the diarylethene. We found that the spectral width of the ESR is significantly different between the open- and closed-ring isomers. This is due to the difference in the pi-conjugation between two isomers. The ESR spectral width analysis could, thus, be used to identify the isomerization of the radical species, which involve the change of the pi-conjugation. The experimentally observed spectrum is found to be the mixture of the open- and closed-ring isomers of the diarylethene. The excitation energies of the cationic diarylethenes are further identified by the SAC-CI calculations.     

One-pot transformation of trichloroacetamide into readily deprotectable carbamates

[Structure: see text] A trichloroacetamide group was converted to an isocyanate, which was in situ captured by a variety of alcohols in the presence of CuCl and n-BuN4Cl to afford the corresponding carbamates. The scope and limitation of this transformation are also described.     

CLV3/ESR-related (CLE) peptides as intercellular signaling molecules in plants

For many years, the plant hormones auxin, cytokinin, ethylene, gibberellin, abscisic acid, brassinosteroid, jasmonic acid, and salicylic acid have been extensively studied as key regulators of plant growth and development. However, recent biochemical and genetic analyses have revealed that secretory peptides are also responsible for intercellular signaling in plants and regulate various events including wound response, cell division control, and pollen self-incompatibility. We discovered two natural CLAVATA3 (CLV3)/ESR-related (CLE) peptides: tracheary elements differentiation inhibitory factor (TDIF) and CLV3, which are dodecapeptides with two hydroxyproline residues that regulate vascular development and meristem formation, respectively. This discovery enabled us to predict the chemical form of CLE gene products. In the Arabidopsis genome, there are 31 CLE genes that correspond to 26 CLE peptides. The application of all 26 chemically synthesized peptides to plants revealed the existence of distinctive functional groups. From these results, we discuss the functions of CLE peptides in plant development and plant-parasite interactions.     

Photochromism of a diarylethene having an azulene ring

Diarylethene derivatives incorporating an azulene ring at the ethene moiety were synthesized. One derivative having thiazole rings showed the expected coloration reaction by excitation at 313 nm (to a higher singlet state) but not when excited at 635 nm (S(0) to S(1) excitation). The system demonstrates that the cyclization reaction can be controlled by selective excitation at different wavelengths of the absorption spectrum. On the other hand, another derivative having thiophene rings did not show any photochromism. The results clearly show the importance of the coplanarity of the system for the photoisomerization.     

An iterative approach to the synthesis of thiophene-based organic dyes

We developed an iterative synthetic method for oligo-aryl compounds using an organosilicon-based palladium-catalyzed cross-coupling reaction. Aryl compounds containing a benzyloxy(diisopropyl)silyl group (masked Si group) had sufficient chemical stability, and the unmasking step proceeded in a high yield under mild conditions. Both of the key unmasking/coupling steps required no strict anhydrous or degassed conditions. The developed procedure was used for the synthesis of thiophene-based organic dyes for dye-sensitized solar cells.     

Zum thermischen Abbau von Poly-?-caprolacton

Ohne Zusammenfassung     

Vortical Structures in Rotating Uniformly Sheared Turbulence

Rotating homogeneous turbulence with and without mean uniform shear is investigated numerically. It is found that in the shearless case the two-dimensionalization process is most effective when the initial small-scale Rossby number is around unity and the resonant triad interactions play a central role in the process. The vortical structures are studied systematically by changing the relative strength of the mean shear and the system rotation as well as the sense of rotation. (The system is called cyclonic (or anti-cyclonic) when the direction of the vorticity associated with the rotation is the same as (or opposite to) that of the mean shear.) A distinct coherent structure appears in the anti-cyclonic system when the vorticities associated with the rotation and the mean shear cancel out, i.e. the absolute vorticity of the mean shear vanishes. For the linearly most unstable case in the anti-cyclonic system, the vortex tubes develop in the sheared direction, which is caused by instability of vortex layers. For linearly stable cases in both the cyclonic and the anti-cyclonic systems, there appear three typical structures, that is, the oblique vortex tubes, the pancake-like structures and the ribbon-like structures. It is interesting that the flow behaves quite differently between the cyclonic and anti-cyclonic systems even at the same Bradshaw number.