A new method for synthesis of α,α-disubstituted carbonyl compounds from carbonyl compounds with one-carbon homologation through β-oxido carbenoid rearrangement as the key reaction

The addition reaction of carbonyl compounds with lithium α-sulfinyl carbanions of 1-chloroalkyl p-tolyl sulfoxides gave adducts, α-chloro β-hydroxy sulfoxides, in high to quantitative yields. The adducts were first treated with a base to give alkoxides, which were treated with i-PrMgCl or t-BuLi to give β-oxido carbenoids via a sulfoxide-metal exchange reaction. The β-oxido carbenoid rearrangement then took place to afford the enolates with one-carbon elongation. The enolate intermediates were found to be able to be trapped with electrophiles such as aldehydes, ethyl chloroformate, benzoyl chloride, haloalkanes to give α,α-disubstituted carbonyl compounds in moderate to good yields. This method provides a new and efficient way for synthesis of α,α-disubstituted carbonyl compounds from carbonyl compounds with one-carbon homologation in only two synthetic operations.     

Dye-sensitized TiO2 nanotube solar cells: fabrication and electronic characterization

TiO2 nanotubes (TNTs) with large aspect ratio and large specific surface area were prepared from P25 (Nippon Aerosil) and applied to dye-sensitized titanium dioxide solar cells (DSSCs). Optimization of fabrication conditions, i.e., pH of the starting paste, sintering temperature for the TiO2 electrodes, electrolyte compositions of DSSCs gave the high conversion efficiency with improved open circuit voltage (V(oc)) and fill factor (FF) when compared to DSSCs made of P25. The evaluation of dye adsorption and the photo-injected electron transport such as electron diffusion coefficient (D) and electron lifetime (tau) in TNTs electrodes revealed that the higher efficiency resulted from increase of electron density with keeping much longer tau in TNTs electrodes than in P25 electrodes.     

Quantum phase transition of the randomly diluted heisenberg antiferromagnet on a square lattice

Ground-state magnetic properties of the diluted Heisenberg antiferromagnet on a square lattice are investigated by means of the quantum Monte Carlo method with the continuous-time loop algorithm. It is found that the critical concentration of magnetic sites is independent of the spin size S, and equal to the two-dimensional percolation threshold. However, the existence of quantum fluctuations makes the critical exponents deviate from those of the classical percolation transition. Furthermore, we found that the transition is not universal, i.e., the critical exponents significantly depend on S.     

Electric field induced nuclear spin resonance mediated by oscillating electron spin domains in GaAs-based semiconductors

We demonstrate an alternative nuclear spin resonance using a radio frequency (rf) electric field [nuclear electric resonance (NER)] instead of a magnetic field. The NER is based on the electronic control of electron spins forming a domain structure. The rf electric field applied to a gate excites spatial oscillations of the domain walls and thus temporal oscillations of the hyperfine field to nuclear spins. The rf power and burst duration dependence of the NER spectrum provides insight into the interplay between nuclear spins and the oscillating domain walls.     

Conductivity and sintering property of LaNi1 − xFexO3 ceramics prepared by Pechini method

Preparation of LaNi_1 − xFe_xO₃, which is one of the candidate materials of solid oxide fuel cell cathode, current collecting layer and interconnect coating was examined with Pechini method and solid state reaction method. Single phase LaNi_1 − xFe_xO₃ with large Ni content has successfully been prepared by low temperature sintering as 750 °C with Pechini method, whereas large amount of raw materials has remained with solid state reaction method by sintering at the same temperature. It can be ascribed to more homogenous cation distribution in raw powder material prior to sintering with Pechini method. It has also been revealed that LaNi_1 − xFe_xO₃ with x lower than 0.3 is thermodynamically unstable in air above 1000 °C. LaNi_0.6Fe_0.4O₃ showed superior property as cathode material with high electrical conductivity, thermodynamic stability and appropriate sintering property.     

Experimental signature of medium modifications for rho and omega mesons in the 12 GeV p+A reactions

The invariant mass spectra of e+e- pairs produced in 12 GeV proton-induced nuclear reactions are measured at the KEK Proton Synchrotron. On the low-mass side of the meson peak, a significant enhancement over the known hadronic sources has been observed. The mass spectra, including the excess, are well reproduced by a model that takes into account the density dependence of the vector meson mass modification, as theoretically predicted.     

Classial and quantum solitons in the transverse field Ising model

We investigate the shape and the dynamics of domain walls in the one-dimensional Ising model with spin S, exchange constant J and external transverse field Γ using numerical calculations up to S = 20 and analytical approximations. For $\tfrac{\Gamma } {{JS}}$ \] we describe classical domain walls as strongly localized excitations, which have either central spin or central bond symmetry. These symmetries are identified also in the quantum case, when solitary excitations develop into energy bands. In the classical limit S → ∞ localization results from the exponential vanishing of the bandwidth for the lowest bands. We describe the relation between the spectrum of moving classical solitons and the quantum band structure.