First observation of a dihydrogen bond involving the Si-H group in phenol-diethylmethylsilane clusters by infrared-ultraviolet double-resonance spectroscopy

We have experimentally identified a dihydrogen bond involving the Si-H group in phenol-diethylmethylsilane (DEMS) clusters for the first time by IR-UV double-resonance spectroscopy. Vibrational shifts to lower frequency of 21-29 cm(-1) were found for the OH stretching vibration of three isomers of the phenol-DEMS clusters. Spectral simulations based on the MP2 calculations also support our observation. In addition to these clusters, dihydrogen bonds were also observed in the phenol-H(2)O-DEMS and (phenol)(2)-DEMS clusters, which exhibited much stronger interactions than the phenol-DEMS clusters.     

Photoaddition of ketones to imidazoles,thiazoles, isothiazoles and isoxazoles. Synthesis of their oxetanes

Imidazole itself did not undergo photoaddition reactions with ketones. However, irradiation of 1-acetyl and 1-benzoylimidazole, and 1,1-carbonyldiimidazole with benzophenone yielded oxetanes. On irradiation with carbonyl compounds, 1,2-dimethylimidazole and 1-benzylimidazole did not give oxetanes but a hydroxyaryl or hydroxyalkyl derivative. Thiazole itself did not yield any photoaddition product, but 2,4-dimethylthiazole afforded oxetanes on irradiation with benzophenone and with 3-benzoylpyridine. Irradiation of 2,4-dimethylthiazole with acetophenone led to the formation of a dimeric material. On irradiation with benzophenone, 4-methylisothiazole did not yield an oxetane but rather a hydroxyphenyl derivative. 3,5-Dimethylisoxazole on irradiation with benzophenone and with 3-benzoylpyridine gave oxetanes. Irradiation of 4,5-dimethylisoxazole yielded similarly an oxetane with benzophenone     

A new synthesis of amides and γ-lactones based on the conjugate addition of lithium enolate of amides to 1-chlorovinyl p-tolyl sulfoxides

Reaction of 1-chlorovinyl p-tolyl sulfoxides, which were synthesized from chloromethyl p-tolyl sulfoxide and ketones or aldehydes, with lithium enolate of N,N-dimethylacetamide gave the adducts in good to quantitative yields. The adducts were converted to several kinds of amides in high overall yields. Treatment of the adducts with trifluoroacetic anhydride in the presence of NaI resulted in the formation of γ-tolylsulfanylated γ-lactones in high yields. The scope and limitations of this method and the mechanism of the reactions are also discussed. These procedures offer a new and effective method for the synthesis of amides and γ-lactones having substituents on the β-carbon from N,N-dimethylacetamide with carbon elongation.     

Growth by self-flux method and post-annealing effect of Bi2Sr2Ca1Cu2Ox single crystals

Post-annealing effects on superconducting characteristics have been studied in Bi₂Sr₂Ca₁Cu₂O_x single crystals grown by a conventional flux method. Also, favorable growth conditions and the effect of the pre-sintering process on the starting materials for flux growth have been examined. The best superconducting behavior is obtained in post-annealed crystals grown from pre-sintered powder materials. The critical current density J_c estimated from magnetization hysteresis in annealed crystals grown with pre-sintered materials is roughly 8×10⁵ A/cm² (Hc) and 5×10⁴ A/cm² (Hc) at 4.2 K at zero field.     

Dehydrogenation of cycloalkanes over noble metal catalysts supported on active carbon

Dehydrogenation of decalin to naphthalene through tetralin and that of dicyclohexyl to biphenyl through phenylcyclohexane with Pt/C and Pd/C was investigated mainly under the liquid film state, in which the catalyst was just wet but not suspended and covered with a thin film of liquid substrate. To improve the catalytic activities, the effects of the addition of tellurium into Pd/C were investigated to reveal that the combination of tellurium, palladium and conjugated systems produced during the dehydrogenation of cycloalkames was important to the improvement of the activities.     

Direct importance estimation for covariate shift adaptation

A situation where training and test samples follow different input distributions is called covariate shift. Under covariate shift, standard learning methods such as maximum likelihood estimation are no longer consistent—weighted variants according to the ratio of test and training input densities are consistent. Therefore, accurately estimating the density ratio, called the importance, is one of the key issues in covariate shift adaptation. A naive approach to this task is to first estimate training and test input densities separately and then estimate the importance by taking the ratio of the estimated densities. However, this naive approach tends to perform poorly since density estimation is a hard task particularly in high dimensional cases. In this paper, we propose a direct importance estimation method that does not involve density estimation. Our method is equipped with a natural cross validation procedure and hence tuning parameters such as the kernel width can be objectively optimized. Furthermore, we give rigorous mathematical proofs for the convergence of the proposed algorithm. Simulations illustrate the usefulness of our approach.     

Totally Umbilic Isometric Immersions and Curves of Order Two

In this paper we study submanifolds by use of extrinsic shapes of some curves having points of proper order 2, and give a condition that they are totally umbilic. This gives an extension of Nomizu-Yano’s result in [7] on a characterization of extrinsic spheres. The second author is partially supported by Grant-in-Aid for Scientific Research (C) (No. 17540072), Ministry of Education, Science, Sports, Culture and Technology.