Palladium-catalyzed asymmetric synthesis of axially chiral allenylsilanes and their application to SE2' chirality transfer reactions

Stepwise application of the Pd-catalyzed S(N)2' reaction and the desilylative S(E)2' reaction to the ambivalent 2-bromo-1-silyl-1,3-dienes provides a novel route to the highly enantioselective construction of tertiary and quaternary propargylic stereogenic centers via axially chiral allenylsilanes.     

Improvement of magnetic intergranular isolation and evaluation of read/write characteristics on SmCo5 perpendicular magnetic thin films

SmCo₅ alloy is a promising candidate for ultra-high-density perpendicular magnetic recording (PMR) media because of its high uniaxial magnetocrystalline anisotropy K_u of more than 1.1×10⁸ erg/cm³. Previously, we successfully achieved high K_u in a sputter-deposited SmCo₅ thin film by introducing a Cu/Ti dual underlayer. However, in order to apply the SmCo₅ films to practical PMR media, it is necessary to decrease medium noise. A granulated magnetic film comprising of small and magnetically decoupled grains is effective in reducing the medium noise. In this paper, we have proposed a new granular film that is fabricated by partial thermodiffusion of Cu between the Sm-Co continuous layer and the Cu underlayer, which is granulated using compositional segregation caused by the addition of Ta₂O₅. We have analyzed the magnetic properties, magnetic domain size, and magnetization reversal process of the proposed SmCo₅ film. The magnetic domain size decreased and the magnetization reversal process changed from the magnetic-wall-motion mode to a coherent rotation mode to some extent on isolation of magnetic grains. The read/write characteristics of granulated SmCo₅ double-layered media were also evaluated. The medium noise decreased and the signal-to-noise ratio increased for the granulated double-layered (PMR) medium.     

Hybrid textures in minimal seesaw mass matrices

In the context of the minimal seesaw framework, we discuss the implications of Dirac and Majorana mass matrices in which two properties coexist, namely, equalities among matrix elements and texture zeros. Among the large number of general possibilities, only 12 patterns are found to be consistent with the global neutrino oscillation data at the level of the most minimal number of free parameters. The predictions of the allowed textures for mass hierarchy, θ₁₃${\theta }_{13}$ and effective mass governing neutrino-less double beta decay are discussed. We also explore the possibility of having non-zero CP violation for each allowed solution. We find that only one allowed solution can accommodate both low and high energy CP violation. We discuss the prediction of this solution for leptogenesis and explore the correlation, between leptogenesis and low energy CP violation.     

Critical current densities and vortex dynamics in FeTexSe1−x single crystals

The critical current density and the normalized relaxation rate are reported in FeTe_0.59Se_0.41 single crystal. Critical current density is of order of 10⁵ A/cm², which is comparable to that in Co-doped BaFe₂As₂. In low temperature and low field region, the vortex dynamics of this system is well defined by the collective creep theory, which is quite similar to Co-doped BaFe₂As₂ reported before. We also discuss the origin of the anomaly in the field dependence of the relaxation rate.     

Photoassisted chemical solution deposition method for fabricating uniformly epitaxial VO2 films

Epitaxial VO₂ films were prepared on the TiO₂ (001) substrates by the excimer-laser-assisted metal–organic deposition (ELAMOD). The quality of the epitaxial films obtained by irradiation with a KrF laser was found to be affected by the film structure obtained after preheating at 500 or 300°C. When the films containing crystal domains, which were obtained by preheating at 500°C, were irradiated with the laser at room temperature under a base pressure of 250 Pa, epitaxial and polycrystalline VO₂ phases were simultaneously formed. In contrast, when the amorphous films containing organic components, which were obtained by preheating at 300°C, were irradiated with the laser at room temperature in air, a single phase of epitaxial VO₂ was formed. By using thermal simulations, we determined that the formation of the epitaxial phase was affected both by the temperature distribution within the film during the laser irradiation and by the laser intensity at the interface between the substrate and the film. The latter factor is considered to play a role in the nucleation of crystallization, causing the epitaxial phase to form preferentially compared to the polycrystalline phase in the amorphous matrix of the films. These results indicate that the ELAMOD process is effective for the fabrication of epitaxial VO₂ films at low temperature.     

Small Seebeck coefficient of graphite intercalation compounds containing CaC6

Calcium graphite intercalation compounds (Ca-GICs; the composition is CaC₆) and GICs containing CaC₆ are synthesized from Grafoil and PGS graphite sheets, and the Seebeck coefficients are measured. The absolute values of the Seebeck coefficient of these GICs are very small; in some cases, the values are positive. This phenomenon observed in the Seebeck coefficient of GICs containing CaC₆ is very different from that of general GICs such as alkali-metal GICs. The temperature dependence of the Seebeck coefficient of these GICs is to that of general GICs; that is, the absolute values of the Seebeck coefficient decrease with a decrease in the temperature.     

Kinetic Simulations of Reversible Chain Transfer Catalyzed Polymerization (RTCP): Guidelines to Optimum Molecular Weight Control

Kinetic simulations of reversible chain transfer catalyzed polymerization (RTCP) were performed using the program package Predici. Mimicking the RTCP of styrene in bulk at 80 °C, the full molecular weight distributions, the polydispersities of resulting polymer and the time evolutions of monomer conversion and participating species were simulated. The influence of the kinetic coefficients governing the RTCP equilibrium – specifically, the rate coefficients of activation, k_a, and deactivation, k_da – on the controlled polymerization behavior was probed in detail by varying their respective simulation input values over five orders of magnitude. It was found that optimum results for molecular weight control are obtained for K = k_a/k_da in the range 1 to 10 and with k_a and k_da being of the order of 10⁶ L · mol⁻¹ · s⁻¹ or above. The influence of degenerative chain transfer on the process was found to be significant only in poorly controlled systems, but is small in well‐controlled RTCP. Based on the finding that the catalyst is depleting during the polymerization due to cross‐termination, guidelines for obtaining high molecular weight material via repeated addition of catalyst were developed.

     

Benchmark results in vector atmospheric radiative transfer

In this paper seven vector radiative transfer codes are inter-compared for the case of underlying black surface. They include three techniques based on the discrete ordinate method (DOM), two Monte-Carlo methods, the successive orders scattering method, and a modified doubling-adding technique. It was found that all codes give very similar results. Therefore, we were able to produce benchmark results for the Stokes parameters both for reflected and transmitted light in the cases of molecular, aerosol and cloudy multiply scattering media. It was assumed that the single scattering albedo is equal to one. Benchmark results have been provided by several studies before, including Coulson et al. [22], Garcia and Siewert [7], [8], Wauben and Hovenier [10], and Natraj et al. [11] among others. However, the case of the elongated phase functions such as for a cloud and with a high angular resolution is presented here for the first time. Also in difference with other studies, we make inter-comparisons using several codes for the same input dataset, which enables us to quantify the corresponding errors more accurately.     

New sign of vacuum ultraviolet driven crystal growth in ternary oxide Zn 3 V 2 O 8 films

Ternary oxide Zn₃V₂O₈ films was successfully formed on glass substrates only by means of vacuum ultraviolet irradiation to the spin-coated metal–organic solutions. From Fourier transform infrared spectroscopy measurements, we confirmed that the crystal growth proceeded at metal–organic bond cleavage under VUV irradiation. The crystalline size of the obtained materials was estimated to be 1.5–2.5 nm. The prepared Zn₃V₂O₈ films clearly showed yellow luminescence, corresponding to a charge transfer transition in the VO₄ tetrahedra.     

Effect of Head Size in Head‐Tail‐Type Polycations on their in vitro Performances as Nonviral Gene Vectors

Three kinds of head‐tail‐type block copolymers composed of polyamidoamine (PAMAM) dendron heads and poly(L ‐lysine) (PLL) tail blocks (PAMAM dendron‐PLL), having PAMAM dendrons with different generations (G2.5‐PLL, G3.5‐PLL and G4.5‐PLL) were synthesized. Some of the dendron heads were located at polyplex surface, and G2.5‐PLL and G3.5‐PLL could form small polyplexes (less than 150 nm in size). G2.5‐PLL and G3.5‐PLL polyplexes were taken up into the cells more effectively. PAMAM dendron‐PLL that had a larger dendron head could show a more‐effective buffering effect. The in vitro performance of the PAMAM dendron‐PLL polyplexes was controlled by the balance of cellular uptake and endosomal escape by a buffering effect.