We propose a new method for dimension reduction in regression using the first two inverse moments. We develop corresponding weighted chi-squared tests for the dimension of the regression. The proposed method considers linear combinations of Sliced In
verse Regression (SIR) and the method using a new candidate matrix which is designed to recover the entire inverse second moment subspace. The optimal combination may be selected based on the p-values derived from the dimension tests. Theoretically, the proposed method, as well as Sliced Average Variance Estimate (SAVE), are more capable of recovering the complete central dimension reduction subspace than SIR and Principle Hessian Directions (pHd). Therefore it can substitute for SIR, pHd, SAVE, or any linear combination of them at a theoretical level. Simulation study indicates that the proposed method may have consistently greater power than SIR, pHd, and SAVE.
This article concerns the dimension reduction in regression for large data set. We introduce a new method based on the sliced inverse regression approach, called cluster-based regularized sliced inverse regression. Our method not only keeps the merit
of considering both response and predictors information, but also enhances the capability of handling highly correlated variables. It is justified under certain linearity conditions. An empirical application on a macroeconomic data set shows that our method has outperformed the dynamic factor model and other shrinkage methods.
New iron-arsenide superconductors of REFeAsO1-delta (RE = Ho, Y, Dy and Tb) were successfully synthesized by a high pressure synthesizing method with a special rapid quenching process, with the onset superconducting critical temperatures at 50.3 K, 4
6.5 K, 52.2K and 48.5 K for RE = Ho, Y, Dy and Tb respectively.
Here we report the fabrication and superconductivity of the iron-based arsenic-oxide GdFeAsO1-delta compound with oxygen-deficiency, which has an onset resistivity transition temperature at 53.5 K. This material has a same crystal structure as the ne
wly discovered high-Tc ReFeAsO1-delta family (Re = rare earth metal) and a further reduced crystal lattice, while the Tc starts to decrease compared with the SmFeAsO1-delta system.
The recently discovered quaternary arsenide oxide superconductor La[O1-xFx]FeAs with the superconducting critical transition temperature (Tc) of 26 K [1], has been quickly expanded to another high-Tc superconducting system beyond copper oxides by the
replacement of La with other rare earth elements, such as Sm, Ce, and Pr etc. [2-4], and the Pr[O1-xFx]FeAs has become to be the first non-cuprate superconductor that holding a Tc above 50 K. All these arsenide (including phosphide) superconductors formed in a same tetragonal layered structure with the space group P4/nmm which has an alternant stacked Fe-As layer and RO (R = rare earth metals) layer. Here we report the discovery of another superconductor in this system, the neodymium-arsenide Nd[O1-xFx]FeAs with an resistivity onset Tc of 51.9 K, which is the second non-cuprate compound that superconducts above 50 K.
Here we report the superconductivity in the iron-based oxyarsenide Sm[O1-xFx]FeAs, with the onset resistivity transition temperature at 55.0 K and Meissner transition at 54.6 K. This compound has the same crystal structure as LaOFeAs with shrunk crys
tal lattices, and becomes the superconductor with the highest critical temperature among all materials besides copper oxides.
Here we report the superconductivity in the LaFeAsO1-xFx system prepared by high pressure synthesis. The highest onset superconducting transition temperature (Tc) in this La-based system is 41.0 K with the nominal composition of LaFeAsO1-xFx (x = 0.6
), which is higher than that reported previously by ambient pressure synthesis. The increase of Tc can be attributed to the further shrinkage of crystal lattice that causes the stronger chemical pressure on the Fe-As plane, which is induced by the increased F-doping level under high pressure synthesis.
Since the discovery of copper oxide superconductor in 1986 [1], extensive efforts have been devoted to the search of new high-Tc superconducting materials, especially high-Tc systems other than cuprates. The recently discovered quaternary superconduc
tor La[O1-xFx]FeAs with the superconducting critical transition Tc of 26 K [2], which has a much simple layered structure compared with cuprates, has attracted quick enthusiasm and is going to become a new high-Tc system [3-6]. Here we report the discovery of bulk superconductivity in the praseodymium-arsenide oxides Pr[O1-xFx]FeAs with an onset drop of resistivity as high as 52 K, and the unambiguous zero-resistivity and Meissner transition at low temperature, which will place these quaternary compounds to another high-Tc superconducting system explicitly.
