Precision Matrix Estimation With ROPE

It is known that the accuracy of the maximum likelihood-based covariance and precision matrix estimates can be improved by penalized log-likelihood estimation. In this article, we propose a ridge-type operator for the precision matrix estimation, ROPE for short, to maximize a penalized likelihood function where the Frobenius norm is used as the penalty function. We show that there is an explicit closed form representation of a shrinkage estimator for the precision matrix when using a penalized log-likelihood, which is analogous to ridge regression in a regression context. The performance of the proposed method is illustrated by a simulation study and real data applications. Computer code used in the example analyses as well as other supplementary materials for this article are available online.     

Photochemical and Photophysical Processes of N-Deacetyllappaconitine and Its Monohydrobromide in Aqueous Solutions

Chemistry of Natural Compounds - The photophysical and photochemical processes of N-deacetyllappaconitine (DAL) and its hydrobromide (DAL·HBr) in aqueous solutions were investigated. Their...     

Silver as a capturing material for iodine released from lead–bismuth eutectic in various conditions

Journal of Radioanalytical and Nuclear Chemistry - The usage of silver as a filtering material for removal of iodine from the gas phase of a lead–bismuth eutectic based nuclear reactor was...     

Formation of Polyhydroxyurethanes in the Reaction of Carbon Dioxide with Diepoxides and Diamines in the Presence of a Chromium Complex

Kinetics and Catalysis - Cyclic biscarbonates were synthesized from CO2 and diepoxides in the presence of a chromium(III) salen complex. The effect of the reaction conditions on the process...     

AN EXPLORATION OF STRUCTURALLY CHARACTERIZED HETERO-TRINUCLEAR [Cu(II)2Ca(II)] FLEXIBLE-BIS(SALAMO)-TYPE COMPLEX

Journal of Structural Chemistry - A new bis(salamo)-type ligand has been designed and synthesized, and its hetero-trinuclear [Cu(II)2Ca(II)] complex has been successfully prepared. It is...     

OPERANDO X-RAY DIFFRACTION ANALYSIS OF THE MnOx–ZrO2 CATALYST DURING OXIDATION OF PROPANE

Journal of Structural Chemistry - A series of MnOx–ZrO2 catalysts is prepared by coprecipitation with variation of the calcinationtemperature from 400 °C to...     

Secondary Metabolites of Mahonia bealei

Chemistry of Natural Compounds -     

A Robust Algorithm for Roots Selection and Saturation Pressure Calculation for Cubic Equations of State

Journal of Solution Chemistry - In this work, a robust and rigorous procedure for roots calculation and selection for a Cubic Equation of State is presented. Roundoff errors are detected and...