Bayesian modeling longitudinal dyadic data with nonignorable dropout, with application to a breast cancer study

Dyadic data are common in the social and behavioral sciences, in which members of dyads are correlated due to the interdependence structure within dyads. The analysis of longitudinal dyadic data becomes complex when nonignorable dropouts occur. We propose a fully Bayesian selection-model-based approach to analyze longitudinal dyadic data with nonignorable dropouts. We model repeated measures on subjects by a transition model and account for within-dyad correlations by random effects. In the model, we allow subject's outcome to depend on his/her own characteristics and measure history, as well as those of the other member in the dyad. We further account for the nonignorable missing data mechanism using a selection model in which the probability of dropout depends on the missing outcome. We propose a Gibbs sampler algorithm to fit the model. Simulation studies show that the proposed method effectively addresses the problem of nonignorable dropouts. We illustrate our methodology using a longitudinal breast cancer study.Comment: Published in at http://dx.doi.org/10.1214/11-AOAS515 the Annals of Applied Statistics (http://www.imstat.org/aoas/) by the Institute of Mathematical Statistics (http://www.imstat.org

High Surface Area Carbon Electrodes for Bromine Reactions in H2-Br2 Fuel Cells

In a hydrogen-bromine (H2-Br2) fuel cell, the Br2 reactions don't require precious metal catalysts, hence porous carbon gas diffusion media (GDM) are widely used as electrodes. However, the specific surface areas of the commercial carbon gas diffusion electrodes (GDEs) are quite low and need to be enhanced. In order to improve the active surface area of carbon GDEs, a study was conducted to grow multi-walled carbon nanotubes (MWCNTs) directly on the carbon electrode fiber surface. Both constant and pulse current electrodeposition techniques were used to deposit Co nanoparticles to catalyze the MWCNT growth. The MWCNTs were grown in the presence of a mixture of acetylene, argon, and hydrogen gases using the chemical vapor deposition process. Based on the results obtained from SEM, TEM, and EDX analysis, MWCNT growth following the tip model was confirmed. The results from the multi-step chronoamperometry study have shown that the synthesized carbon GDEs with MWCNTs have 7 to 50 times higher active surface area than that of a plain GDE. The performance of a single layer of the best MWCNT GDE measured in a H2-Br2 fuel cell was found to be equal or slightly higher compared to that obtained using a three-layer plain carbon electrode

High Active Surface Area and Durable Multi-Wall Carbon Nanotube-Based Electrodes for the Bromine Reactions in H2-Br2 Fuel Cells

The commercially available carbon gas diffusion electrodes (GDEs) with low specific active area but high permeability are often used as Br2 electrodes in the H2-Br2 fuel cell. In order to increase the specific active surface area of the existing carbon GDEs, a study was conducted to grow multi-wall carbon nanotubes (MWCNTs) directly on the surface of carbon fibers of a commercial carbon electrode. Experimental fixtures were developed to promote the electrodeposition of cobalt and the growth of MWCNTs on the carbon GDE. The MWCNT growth across the carbon electrode was confirmed by SEM. The carbon GDE with a dense distribution of short MWCNTs evaluated in a H2-Br2 fuel cell has 29 times higher active surface area than a plain carbon electrode and was found to be highly durable at an electrolyte flow rate of 10 cc/min/cm2. The performance of the best single layer MWCNT GDE measured at 80% discharge voltage efficiency in a H2-Br2 fuel cell was found to be 16% higher compared to that obtained using three layers of plain carbon electrodes. Finally, the preliminary material cost analysis has shown that the MWCNT-based carbon electrodes offer significant cost advantages over the plain carbon electrodes

Acquired tonsillar herniation related to spontaneous intracranial hypotension: case reports

BackgroundAcquired prolapse of the cerebellar tonsils in spontaneous intracranial hypotension (SIH) patients is rare. This study aims to evaluate neuroimaging changes of acquired prolapse of the cerebellar tonsils below the foramen magnum in SIH patients due to spontaneous spinal cerebrospinal fluid leakage, which was treated by targeted epidural blood patches (EBP).MethodsWe retrospectively reviewed clinical and neuroimaging characteristics of 5 cases of SIH with acquired prolapse of the cerebellar tonsils that received targeted EBP in our institution from January 2013 to December 2016.ResultsOf these SIH patients, all of them suffered from an orthostatic headache. Initial cranial MRI demonstrated descent of the cerebellar tonsils ≥5 mm. Intrathecal gadolinium-enhanced spinal MR myelography and/or spinal MR hydrography were performed to evaluate the level of spinal cerebrospinal fluid leakage. Symptoms were alleviated in all 5 patients after two (n = 4), or three (n = 1) targeted EBP during hospitalization. Follow-up cranial MRI revealed that the descent of cerebellar tonsils was reversed after EBP treatment.ConclusionAcquired tonsillar herniation can occur in patients with SIH and spinal cerebrospinal fluid leakage. Symptoms of these patients may be resolved and radiologic findings may be reversed after EBP treatment

Semi-supervised affinity propagation based on density peaks

Zbog nezadovoljavajućeg učinka grupiranja (klasteriranja) pomoću algoritma grupiranja propagacijom afiniteta (AP - affinity propagation) u slučaju nizova podataka složene strukture, u radu se predlaže polu nadzirani algoritam grupiranja propagacije afiniteta temeljen na vršnoj gustoći (SAP-DP). Taj algoritam primjenjuje novi algoritam vršne gustoće (DP - density peaks) čija je prednost višestruko grupiranje uz polu-nadziranje, izgradnja udvojenih ograničenja zbog usklađivanja s matricom sličnosti, a zatim izvršenje grupiranja propagacijom afiniteta. Rezultati simulacijskih eksperimenata potvrdili su da je grupiranje predloženim algoritmom učinkovitije od grupiranja konvencionalnom propagacijom afiniteta (AP).In view of the unsatisfying clustering effect of affinity propagation (AP) clustering algorithm when dealing with data sets of complex structures, a semi-supervised affinity propagation clustering algorithm based on density peaks (SAP-DP) was proposed in this paper. The algorithm uses a new algorithm of density peaks (DP) which has the advantage of the manifold clustering with the idea of semi-supervised, builds pairwise constraints to adjust the similarity matrix, and then executes the AP clustering. The results of the simulation experiments validated that the proposed algorithm has better clustering performance compared with conventional AP

Acute Effects of Microcystins on the Transcription of 14 Glutathione S-Transferase Isoforms in Wistar Rat

ABSTRACT: The glutathione S-transferases (GST) play important roles in the detoxification of microcystins (MCs). For better understanding of the responses of GST isforms to MCs exposure, informations about the effects of MCs on GSTs are necessary. In this experiment, we cloned the full length cDNA of 14 GST isoforms (GST alpha, kappa, mu, omega, pi, theta, zeta, and microsomal GST) from Wistar rat. The mRNA abundance of each rat GST isoform in the liver, kidney, and testis was analyzed by real time quantitative PCR. Multiple GST isoforms were constitutively expressed in all examined organs, but some isoforms were expressed at higher level in one organ than in others. The relative changes of the mRNA abundance in the liver, kidney, and testis of Wiatar rat i.v. injected with crude MCs extract at dose of 1LD 50 were also analyzed. Generally, the expression of most GSTs in the liver and testis was suppressed while that in kidney was induced after being injected with MCs. It is suggested that the transcription of GST isoforms varied in different ways within an organ and between organs of Wistar rat exposed to MCs. # 2009 Wiley Periodicals, Inc. Environ Toxicol 26: 187-194, 2011