Investigating silicone oil emulsification in eye chamber models

The emulsification of silicone oil in intraocular liquid is an unwanted complication occurring after retinal detachment repair. The repair surgery consists of removing most of the intraocular liquid and replacing it by a tamponade fluid. Silicone oils with dynamic viscosities in the range 1-5 Pa s are often used as tamponades due to their high biocompatibility and chemical stability. Emulsification of the oil can occur during the tamponade stay in the eye chamber and the droplets can potentially lead to loss of or impairment of vision. The aim of the project is to establish the mechanisms by which the silicone oil emulsifies and understand the different factors involved in this phenomenon. Two potential emulsification mechanisms have been studied using experimental investigations. A 3D model of the eye chamber, driven by a stepper-motor reproducing the eye geometry and saccadic motion, was developed to study the first hypothesis of bulk emulsification at the interface between oil-aqueous phases. The stability of the interface was investigated over an extensive range of experimental scenarios, supported by analytical and numerical calculations. The addition of surfactant to the aqueous phase modelled the effect of surface-active molecules on the interfacial properties. Low viscosity ratio, low interfacial tension and strong inertial motion resulted in large deformation of the oil-aqueous interface but did not result in interface breakup and droplet formation. Bulk emulsification was therefore excluded as the mechanism causing the oil droplets formation. The second hypothesis concerned the stability of the three-phase contact line (TPCL) between the two liquid phases and the retinal surface. Hydrophobic silane coatings on flat solid substrates were used as a first approximation of the retina. The TPCL motion and stability was studied on uncoated and coated substrates. Above a critical substrate speed, the drag of the TPCL by the substrate led to a transition from partial to complete wetting of the liquid, leaving an oil film on the surface. The presence of printed silane features affected the dewetting of the TPCL and led to the destabilization of the oil film into shorter oil strands pinned to the feature. The shape of the oil strands depended on the surface energies and contact angles, and the oil strand length and width increased with increasing substrate velocity and feature width. However, none of the pinned droplets detached from the features under the motions accessible by the set-up and by the stepper motor device. The bulk emulsification hypothesis was reported to be the mechanism responsible in much of the literature on this topic. The experimental findings reported here indicate that surface-driven emulsification is more likely to be responsible of oil droplet formation. Confirmation of the hypothesis requires further investigation to establish which physiological and flow conditions will promote detachment of SiOil droplets from surface features

Modeling left-truncated and right-censored survival data with longitudinal covariates

There is a surge in medical follow-up studies that include longitudinal covariates in the modeling of survival data. So far, the focus has been largely on right-censored survival data. We consider survival data that are subject to both left truncation and right censoring. Left truncation is well known to produce biased sample. The sampling bias issue has been resolved in the literature for the case which involves baseline or time-varying covariates that are observable. The problem remains open, however, for the important case where longitudinal covariates are present in survival models. A joint likelihood approach has been shown in the literature to provide an effective way to overcome those difficulties for right-censored data, but this approach faces substantial additional challenges in the presence of left truncation. Here we thus propose an alternative likelihood to overcome these difficulties and show that the regression coefficient in the survival component can be estimated unbiasedly and efficiently. Issues about the bias for the longitudinal component are discussed. The new approach is illustrated numerically through simulations and data from a multi-center AIDS cohort study.Comment: Published in at http://dx.doi.org/10.1214/12-AOS996 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Wave dynamics of a six-dimensional black hole localized on a tensional three-brane

We study the quasinormal modes and the late-time tail behavior of scalar perturbation in the background of a black hole localized on a tensional three-brane in a world with two large extra dimensions. We find that finite brane tension modifies the standard results in the wave dynamics for the case of a black hole on a brane with completely negligible tension. We argue that the wave dynamics contains the imprint of the extra dimensions.Comment: revised version, 10 pages, 1 table and 2 figures. Accepted for publication in Phys. Lett.

Relating Friedmann equation to Cardy formula in universes with cosmological constant

A relation between the Friedmann equation and the Cardy formula has been found for de Sitter closed and Anti de Sitter flat universes. For the remaining (Anti) de Sitter universes the arguments fail, and we speculate whether the general philosophy of holography can be satisfied in such contents.Comment: 11 pages, Latex file, References added. New version to be published in Phys. Lett.