Variable Selection in Accelerated Failure Time (AFT) Frailty Models: An Application of Penalized Quasi-Likelihood

Variable selection is one of the standard ways of selecting models in large scale datasets. It has applications in many fields of research study, especially in large multi-center clinical trials. One of the prominent methods in variable selection is the penalized likelihood, which is both consistent and efficient. However, the penalized selection is significantly challenging under the influence of random (frailty) covariates. It is even more complicated when there is involvement of censoring as it may not have a closed-form solution for the marginal log-likelihood. Therefore, we applied the penalized quasi-likelihood (PQL) approach that approximates the solution for such a likelihood. In addition, we introduce an adaptive penalty function that makes the selection on both fixed and frailty effects in a left-censored dataset for a parametric AFT frailty model. We also compared our penalty function with other established procedures via their performance on accurately choosing the significant coefficients and shrinking the non-significant coefficients to zero

Chelates of Co(III) & Cu(II) with I-(2'-Pyridylazo)-2-phenanthrol (PAPL) & I-(2i-Pyridylazo)-2-naphthol (PAN)

681-68

Polarographic Studies of Cd(II) & Pb(II) Complexes with 2,3-Dihydroxypyridine

913-91

Polarographic Studies on Mixed Ligand Complexes Involving Amino Acids : Ternary Systems, Cd-ɑ-Alanine-Oxalate & Cd-β-Alanine-Oxalate

752-75

Cu(II) Complexes of the Oximes of 2-Hydroxy-5-methyl-acetophenone, -propiophenone & -butyrophenone

44

Magnetic Properties of Ru(III) Complexes of 1-(2-Pyridylazo)-2-naphthol & 1-(2-Pyridylazo)-2-phenanthrol

907-90

2,2′-[Naphthalene-1,5-diylbis(nitrilo­methanylyl­idene)]diphenol

The title compound, C24H18N2O2, lies about an inversion centre and the asymmetric unit contains one half-mol­ecule. An intra­molecular O—H⋯N hydrogen bond generates a six-membered ring, producing an S(6) ring motif. The crystal packing exhibits inter­molecular π–π stacking inter­actions between the aromatic rings with a centroid–centroid distance of 3.851 (2) Å

Layer-resolved electronic behavior in a Kondo lattice system, CeAgAs2

We investigate the electronic structure of an antiferromagnetic Kondo lattice system CeAgAs2 employing hard x-ray photoemission spectroscopy. CeAgAs2, an orthorhombic variant of HfCuSi2 structure, exhibits antiferromagnetic ground state, Kondo like resistivity upturn and compensation of magnetic moments at low temperatures. The photoemission spectra obtained at different photon energies suggest termination of the cleaved surface at cis-trans-As layers. The depth-resolved data show significant surface-bulk differences in the As and Ce core level spectra. The As 2p bulk spectrum shows distinct two peaks corresponding to two different As layers. The peak at higher binding energy correspond to cis-trans-As layers and is weakly hybridized with the adjacent Ce layers. The As layers between Ce and Ag-layers possess close to trivalent configuration due to strong hybridization with the neighboring atoms and the corresponding feature appear at lower binding energy. Ce 3d core level spectra show multiple features reflecting strong Ce-As hybridization and strong correlation. Intense f0 peak is observed in the surface spectrum while it is insignificant in the bulk. In addition, we observe a features at binding energy lower than the well-screened feature indicating the presence of additional interactions. This feature becomes more intense in the bulk spectra suggesting it to be a bulk property. Increase in temperature leads to a spectral weight transfer to higher binding energies in the core level spectra and a depletion of spectral intensity at the Fermi level as expected in a Kondo material. These results reveal interesting surface-bulk differences, complex interplay of intra- and inter-layer covalency, and electron correlation in the electronic structure of this novel Kondo lattice system