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Efficiencies of the maximum pseudolikelihood estimator and a number of related estimators for the case-cohort sampling design in the proportional hazards regression model are studied. The asymptotic information and lower bound for estimating the parametric regression parameter are calculated based on the effective score, which is obtained by determining the component of the parametric score orthogonal to the space generated by the infinite-dimensional nuisance parameter. The asymptotic distributions of the maximum pseudolikelihood and related estimators in an i.i.d. setting show that these estimators do not achieve the computed asymptotic lower bound. Simple guidelines are provided to determine in which instances such estimators are close enough to efficient for practical purposes. 相似文献
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Since the polarization structure of reactions in the collinear directions is greatly simplified, since reactions at very high energies tend to be predominantly close to collinear, and since the one-particle exchange mechanisms are more pronounced in the forward direction, tests of one-particle-exchange (OPE) mechanisms are formulated for collinear reactions. The number of amplitudes are derived for a reaction with arbitrary spins, and examples for the practically occurring cases are given. The results are applied to the reaction 1/2+1/21+1 and in particular ton+pd+ (or to its inverse). A detailed procedure is outlined for a step-by-step testing of the various OPE processes in this reaction through a series of polarization experiments. In particular, the tests can separate out theJ=0 andJ=1/2 OPE processes. 相似文献
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Lithium reductions of 7-chloronorbornadiene and of bis(7-norbornadienyl)mercury both provide (C7H7)2Li2 ( 5a ). This product is accompanied by C7H7Li2Cl ( 5c ) in the first case, and by C7H7Li ( 5b ) in the second. The theoretically anticipated properties of all three organolithiums are apparent in the consistent Cs symmetry of their hydrocarbon ligands, their protolytic destruction by 12-crown-4, and their significant J(C(7), Li) ( 5a , 7.6; 5b , 16.0; 5c 8.9 Hz). 相似文献
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Nucleophilic addition of the peroxynitrite anion, ONOO(-), to the two prototypical carbonyl compounds, acetaldehyde and acetone, was investigated in the pH interval 7.4-14. The process is initiated by fast equilibration between the reactants and the corresponding tetrahedral adduct anion, the equilibrium being strongly shifted to the reactant side. The adduct anion also undergoes fast protonation by water and added buffers. Consequently, the rate of the bimolecular reaction between ONOO(-) and the carbonyl is strongly dependent on the pH and on the concentration of the buffer. The pK(a) of the carbonyl-ONOO adduct was estimated to be approximately 11.8 and approximately 12.3 for acetone and acetaldehyde, respectively. It is shown that both the anionic and the neutral adducts suffer fast homolysis along the weak O-O bond to yield free alkoxyl and nitrogen dioxide radicals. The yield of free radicals was determined to be about 15% with both carbonyl compounds at low and high pH, while the remainder collapses to molecular products in the solvent cage. The rate constants for the homolysis of the adducts vary from ca. 3 x 10(5) to ca. 5 x 10(6) s(-1), suggesting that they cannot act as oxidants in biological systems. This small variation around a mean value of about 10(6) s(-1) suggests that the O-O bond in the adduct is rather insensitive to its protonation state and to the nature of its carbonyl precursor. An overall reaction scheme was proposed, and all the corresponding rate constants were evaluated. Finally, thermokinetic considerations were employed to argue that the formation of dioxirane as an intermediate in the reaction of ONOO(-) with acetone is an unlikely process. 相似文献
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PHOTOSENSITIZATION BY PORPHYRINS DELIVERED TO L CELL FIBROBLASTS BY HUMAN SERUM LOW DENSITY LIPOPROTEINS. A MICROSPECTROFLUOROMETRIC STUDY 总被引:1,自引:0,他引:1
P. MORLIERE E. KOHEN J. P. REYFTMANN R. Santus C. KOHEN J. C. Maziere S. Goldstein W. F. Mangel L. Dubertret 《Photochemistry and photobiology》1987,46(2):183-191
Human serum LDL were used as vehicles to deliver protoporphyrin and hematoporphyrin dimer to L cell mouse fibroblasts. Topographic analysis by microspectrofluorometry on single living cells shows that after digestion of LDL, protoporphyrin is localized in cytoplasmic areas. Protoporphyrin and hematoporphyrin dimer are readily bleached by 420 ± 60 nm radiations at the high fluence rate used. Complex bleaching kinetics are observed. Spectral studies using the same technique demonstrate that an intense fluorescent emission (λmax = 450 nm) is produced immediately after the onset of irradiation with 365 ± 2 nm or 420 ± 60 nm radiations using LDL loaded with protoporphyrin or Photofrin II. These fluorescent products have been previously identified as lipofuscin-like pigments formed by reaction of lipid photoperoxides with amino groups. The permeation of lysosomal membranes is also induced after delivery of the porphyrins by LDL. This permeation can be strongly inhibited not only by the lysosomal inhibitors chloroquine and monensin but also by a-tocopherol. On the other hand, neither α-tocopherol nor chloroquine or monensin inhibit the lipofuscin-like pigment formation. 相似文献