Taiwan government has been executing the educational reform programs for more than two decades. However, the so-called between-class ability grouping which is prohibited by Taiwan government is still found in many pla...Taiwan government has been executing the educational reform programs for more than two decades. However, the so-called between-class ability grouping which is prohibited by Taiwan government is still found in many places; and Taiwan＇s cram schools are even more popular and diversified than before. The authors argue that, in addition to individual＇s socio-economic background, regional characteristics and school attributes also play important roles. Bringing these two factors back in, the causal relationships among ability grouping, cram schooling, and student academic achievement can be analyzed more accurately. Using data from Taiwan Education Panel Survey, the authors＇ empirical results show that, first of all, in more urbanized area, between-class ability grouping is less popular but cram school participation is wider spread these years. Secondly, the effects of family backgrounds on students＇ cram school participation are not as critical as they were before. Thirdly, between-class ability grouping and students＇ performance are positively associated but the internal mechanism still needs further investigation.展开更多
Three substituted α,β,β-trifluorostyrenes(TFS's),i.e.,p-thiomethyltrifluorostyrene(4), p-cyclopropyltrifluorostyrene(5)and p-t-butyltrifluorostyrene(6),have been synthesized.The rate constants(k_2)of the therma...Three substituted α,β,β-trifluorostyrenes(TFS's),i.e.,p-thiomethyltrifluorostyrene(4), p-cyclopropyltrifluorostyrene(5)and p-t-butyltrifluorostyrene(6),have been synthesized.The rate constants(k_2)of the thermal cyclodimerization of these compounds have been measured in the tem- perature range 120—160℃.The polar parameters σ_(mb) of these TFS's calculated from ^(19)F NMR chemi- cal shifts are:for p-thiomethyl,-0.18;p-cyclopropyl,-0.31 and p-t-butyl,-0.22.The spin delo- calization substituent parameters σ'_T(140°)of p-thiomethyl,cyclopropyl and t-butyl groups are 0.59, 0.27 and 0.30 respectively.Thus all of these groups act as electron-donating groups which can also effectively stabilize a spin.展开更多
文摘Taiwan government has been executing the educational reform programs for more than two decades. However, the so-called between-class ability grouping which is prohibited by Taiwan government is still found in many places; and Taiwan＇s cram schools are even more popular and diversified than before. The authors argue that, in addition to individual＇s socio-economic background, regional characteristics and school attributes also play important roles. Bringing these two factors back in, the causal relationships among ability grouping, cram schooling, and student academic achievement can be analyzed more accurately. Using data from Taiwan Education Panel Survey, the authors＇ empirical results show that, first of all, in more urbanized area, between-class ability grouping is less popular but cram school participation is wider spread these years. Secondly, the effects of family backgrounds on students＇ cram school participation are not as critical as they were before. Thirdly, between-class ability grouping and students＇ performance are positively associated but the internal mechanism still needs further investigation.
基金This work was financially supported by the National Natural Science Foundation of China.
文摘Three substituted α,β,β-trifluorostyrenes(TFS's),i.e.,p-thiomethyltrifluorostyrene(4), p-cyclopropyltrifluorostyrene(5)and p-t-butyltrifluorostyrene(6),have been synthesized.The rate constants(k_2)of the thermal cyclodimerization of these compounds have been measured in the tem- perature range 120—160℃.The polar parameters σ_(mb) of these TFS's calculated from ^(19)F NMR chemi- cal shifts are:for p-thiomethyl,-0.18;p-cyclopropyl,-0.31 and p-t-butyl,-0.22.The spin delo- calization substituent parameters σ'_T(140°)of p-thiomethyl,cyclopropyl and t-butyl groups are 0.59, 0.27 and 0.30 respectively.Thus all of these groups act as electron-donating groups which can also effectively stabilize a spin.
