新型菲涅尔线聚焦聚光太阳电池组件研究

以聚甲基丙烯酸甲脂为材料,采用热压成型工艺加工成型线聚焦菲涅尔聚光透镜(8×),可用于空间、地面光伏系统太阳电池组件的聚光系统,并对在其聚光条件下,太阳电池的电流电压特性进行测试,结果表明,该菲涅尔线聚焦棱镜能有效提高太阳电池的单位输出功率.模具的机械加工精度和光学抛光精度低,是造成其部分聚光率损失的原因.     

Oxyanion derivatives of cuprate superconductors superconducting 123 phosphates

While YSr₂Cu₃O₇ cannot be prepared under ambient conditions, partial substitution of the phosphate group for copper, as in YSr₂Cu_2.8(PO₄)_0.2O_y, stabilizes this phase in the orthorhombic structure, but the material is not superconducting. Superconductivity in YSr₂Cu_2.8(PO₄)_0.2O_y is obtained by increasing the hole concentration through partial substitution of Y by Ca, as in Y_0.7Ca_0.3Sr₂Cu_2.8(PO₄)_0.2O_y (T_c≈40 K). By incorporating the phosphate group in orthorhombic YBaSrCu₃O ₇, a stable tetragonal derivative of the formula YBaSrCu_2.8(PO₄)_0.2O_y (T_c≈ 47 K) has been prepared; the T_c increases to 70 K by partial substitution of Y by Ca as in Y_0.7Ca_0.3BaSrCu_2.8(PO₄)_0.2O_y.     

Local control of electric current driven shell etching of multiwalled carbon nanotubes

We report on a novel method for local control of shell engineering in multiwalled carbon nanotubes (MWNTs) using Joule-heating induced electric breakdown. By modulating the heat dissipation along a nanotube, we can confine its thinning and shell breakdown to occur within localized regions of peak temperatures, which are distributed over one-half of the NT length. The modulation is achieved by using suitably designed nanomachined heat sinks with different degrees of thermal coupling at different parts of a current-carrying nanotube. The location of electric breakdown occurs precisely at the regions of high temperatures predicted by the classical finite-element model of Joule heating in the MWNT. The experiments herein provide new insight into the electric breakdown mechanism and prove unambiguously that shell removal occurs due to thermal stress, underpinning the diffusive nature of MWNTs. The method demonstrated here has the potential to be a powerful tool in realizing MWNT bearings with complex architectures for use in integrated nanoelectromechanical systems (NEMS). In addition, the breakdown current and power in the nanotubes are significantly higher than those observed in nanotubes without heat removal via additional heat sinks. This indicates future avenues for enhancing the performance of MWNTs in electrical interconnect and nanoelectronic applications. PACS  73.63.Fg; 65.80.+n     

A fourth order method for a singular two-point boundary value problem

Recently, Chawla et al. described a second order finite difference method for the class of singular two-point boundary value problems:

Facile synthesis of 9-（N-amino-4-fluoromethyl-3-pyrrolidinyl）-2- fluoro-6-aminopurine from trans-4-hydroxy-L-proline

A novel and simple procedure for synthesis of azanucleoside by Mitsunobu reaction between N-(p-nitrobenzyloxycarbonyl)- trans-4-hydroxy-D-proline methyl ester obtained from trans-4-hydroxy-L-proline after six-step reaction and 2-fluoro-6-azidopurine is described,and azanucleoside is fluorinated by new fluridizer 2,2-difluoro-1,3-dimethylimidazolidine (DFI).All reactions could be carded out under mild condition.