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131.
132.
Trifluoromethyl aldimines reacted with trimethylsilyloxyfuran in presence of Lewis acids to provide butenolides in high yields with total diastereoselectivity (>98%). The configuration of these products is anti. The butyrolactone 4a, substituted with a 2-trifluoromethyl ethyl amine, could be converted into a trans α-trifluoromethyl piperidine derivative. 相似文献
133.
Soack Dae Yoon Yajie Chen Aria Yang Trevor L. Goodrich Xu Zuo Katherine Ziemer Carmine Vittoria Vincent G. Harris 《Journal of magnetism and magnetic materials》2007
We demonstrate a semiconducting material, TiO2−δ, with magnetism up to 880 K, without the introduction of magnetic ions. The magnetism in these films stems from the controlled introduction of anion defects from both the film–substrate interface as well as processing under a deficient oxygen atmosphere. First-principle band structure calculations indicate that the exchange between Ti cations mediated by an oxygen anion is positive, i.e., ferromagnetic, whereas the exchange between cations via a vacancy is negative, i.e., ferrimagnetic. It is likely that both the mechanisms are active in this system. This represents a new and promising approach in the search for room-temperature magnetic semiconductors. 相似文献
134.
135.
Shear properties of CaCO3-filled linear low density polyethylene have been determined over a wide range of filler loading. The viscosity rises with the filler loading especially at low shear rates and a yield value appears for CaCO3-contents larger than 5%. The decrease of the die-swell ratios of the filled samples indicates a reduction of the melt elasticity. 相似文献
136.
We study the dynamics of epidemic and reaction-diffusion processes in metapopulation models with heterogeneous connectivity patterns. In susceptible-infected-removed-like processes, along with the standard local epidemic threshold, the system exhibits a global invasion threshold. We provide an explicit expression of the threshold that sets a critical value of the diffusion/mobility rate below, which the epidemic is not able to spread to a macroscopic fraction of subpopulations. The invasion threshold is found to be affected by the topological fluctuations of the metapopulation network. The results presented provide a general framework for the understanding of the effect of travel restrictions in epidemic containment. 相似文献
137.
138.
Polystyrene-block-polybutadiene-block-poly(ϵ-caprolactone) SBC triblock copolymers with a PCL matrix exhibit microphase separation into three different phases within the spherulitic superstructures. Mixing of the PS-block can occur upon melting of the PCL-block if the molecular weight is low enough. Even though the crystallization takes place well below the PS-glass transition, a deformation of the amorphous microphases into ellipsoidal core-shell cylindrical microdomains is observed by TEM. These copolymers have mechanical properties which are dominated by the PCL (poly(ϵ-caprolactone)) matrix with an influence of the amorphous blocks. 相似文献
139.
Human hair was analysed by FTIR spectroscopy and single fibre analysis was achieved using an IR microscope, an ATR diamond cell was also found very useful in determining the cysteic acid content of hair tress samples. Several different data manipulations were also assessed. 相似文献
140.
Maria Sarno Giuliana Gorrasi Diana Sannino Andrea Sorrentino Paolo Ciambelli Vittoria Vittoria 《Macromolecular rapid communications》2004,25(23):1963-1967
Summary: Nanocomposite materials were obtained by blending multi‐wall carbon nanotubes (CN), obtained by acetylene catalytic chemical vapour deposition (CVD) on Co/Fe‐modified NaY zeolite, with syndiotactic poly(propylene) (sPP). The nanotubes, well dispersed in the polymer matrix, favour the crystallization of the sPP helical chains and significantly improve the sPP thermal stability either in nitrogen or in air. The morphology of the sPP affects the behaviour of the sPP degradation in air.