Simulator for laser photocoagulation in ophthalmology

The practice of laser photocoagulation plays a major role in the ocular therapy, but the persistence of many postoperative complications denotes genuine difficulty in mastering the technique. The authors present a device which, thanks to the use of simulation, enables actual practice to be dissociated from apprenticeship. While complying with the constraints of realism with regard to habitual conditions of laser use, the device offers access to a wide variety of clinical situations. The apparatus is built around the traditional instrument. A virtual image of the fundus is produced in real time from the sensors which detect the actual gestures used. The calculations make use of textured geometrical models. Digitized color photographs are organized to form a database which reflects the diversity of pigmentations and pathologies. A software interface has been developed to facilitate the use of the device. The prototype is operated using a PC-compatible computer; it displays the images at the rate of at least seven per second on a miniature CGA screen incorporated in the slit-lamp. It is currently being validated for clinical applications. Above and beyond apprenticeship in laser photocoagulation, its potential applications extend to the entire field of ophthalmogical symptomatology and, more broadly, to the simulation of any examination conducted with the help of binocular or endoscopic optics.     

Cancer of the breast: the return of lymphoscintigraphy?

Lymphoscintigraphy, after arousing great hope in the past in the field of breast cancer, has now been abandoned. The inability of this examination to predict the metastatic status of the nodes, and progress in therapeutic concepts have led to abandoning this technique. However, certain problems encountered by regional irradiation programmes and the work concerning sentinel node detection may bring this technique back into the spotlight. Lymphoscintigraphy may make it possible to adopt an individual approach, case by case, of the lymphatic drainage basins in breast tumors, thus enabling certain patients to benefit from regional irradiation when it would not have been traditionally recommended for this irradiation. Another aspect concerns the problem of the volumes irradiated. Work carried out with lymphoscintigraphy has enabled internal mammary chain nodes to be precisely located. Theses studies show the necessity of adapting the irradiation field to each individual case, but the clinical impact is limited, in the end, by the low recurrence rate in the internal mammary chain area. However, the new techniques of computer merging of scintigraphic and scanner images could enable the spatial position of the nodes in the upper axillary and supraclavicular regions to be determined. This would have, a priori, much wider clinical impact. Lymphoscintigraphic detection of the sentinel node is another field of major interest, but this technique is in competition with staining techniques. This procedure leads to a large reduction in morbidity of axillary surgery in 70% of patients. The use of techniques for detecting micrometastases in the sentinel node opens prospects in terms of prognosis. The qualities of differents radiotracers and different injection sites possible are also discussed.     

Bayesian estimation of motion vector fields

A stochastic approach to the estimation of 2D motion vector fields from time-varying images is presented. The formulation involves the specification of a deterministic structural model along with stochastic observation and motion field models. Two motion models are proposed: a globally smooth model based on vector Markov random fields and a piecewise smooth model derived from coupled vector-binary Markov random fields. Two estimation criteria are studied. In the maximum a posteriori probability (MAP) estimation, the a posteriori probability of motion given data is maximized, whereas in the minimum expected cost (MEC) estimation, the expectation of a certain cost function is minimized. Both algorithms generate sample fields by means of stochastic relaxation implemented via the Gibbs sampler. Two versions are developed: one for a discrete state space and the other for a continuous state space. The MAP estimation is incorporated into a hierarchical environment to deal efficiently with large displacements     

In‐depth characterization of granular starch‐graft‐polyester compositions as obtained by in situ polymerization of lactones from the starch surface

The synthesis of poly(ε‐caprolactone) (PCL)‐grafted granular starch was carried out either in bulk (without solvent) or in toluene suspension by a two‐step procedure. First step relied upon the activation of the hydroxyl groups available at the starch surface by alkylaluminum derivatives like AlEt₃ and removal of non‐surface‐grafted organo‐aluminum active species. The latter species were made free in solution by reaction with the remaining water molecules still contaminating the polymerization medium despite intensive drying of the starch granules. In the second step, ε‐caprolactone was polymerized via a coordination‐insertion ring‐opening polymerization as initiated by the surface‐grafted aluminum alkoxide species. The present contribution aims at investigating various parameters such as nature of the alkyl aluminum activator and monomer (δ‐valerolactone was studied as well), temperature, concentration, and addition of a solvent (polymerization in toluene suspension), reaction time, and also the experimental procedure used to recover the polyester chains and measure the grafting efficiency. It turns out that, under the studied conditions, dialkylaluminum alkoxides surface‐grafted onto the starch granules were more likely generated and promote a fast polymerization reaction with the formation of grafted PCL chains with a molecular weight that can be as high as 225 000 (M_n value) for polymerization carried out in toluene suspension. Copyright © 2004 Society of Chemical Industry     

Polymer/layered silicate nanocomposites by combined intercalative polymerization and melt intercalation: a masterbatch process

Poly(ε-caprolactone) (PCL) and poly(vinyl chloride) (PVC) layered silicate nanocomposites were prepared by combination of intercalative polymerization and melt intercalation. In a first step, high clay content PCL nanocomposites were prepared by in situ polymerization of ε-caprolactone intercalated between selected organo-modified silicate layers. The polymerization was catalyzed with dibutyltin dimethoxide in the presence of montmorillonites, the surface of which were previously exchanged with (functionalized) long alkyl chains ammonium cations. Then, these highly filled PCL nanocomposites were added as masterbatches in commercial PCL and PVC by melt blending. The intercalation of PCL chains within the silicate layers by in situ polymerization proved to be very efficient, leading to the formation of intercalated and/or exfoliated structures depending on the organo-clay. These masterbatches were readily dispersed into the molten PCL and PVC matrices yielding intercalated/exfoliated layered silicate nanocomposites which could not be obtained by melt blending the matrix directly with the same organo-modified clays. The formation of nanocomposites was assessed both by X-ray diffraction and transmission electronic microscopy. Interestingly, this so-called ‘masterbatch’ two-step process allowed for preparing PCL nanocomposites even with non-modified natural clay, i.e. sodium montmorillonite, which showed a material stiffness much higher than the corresponding microcomposites recovered by direct melt intercalation. The thermal stability of PCL nanocomposites as a function of clay content was investigated by thermogravimetry (TGA).     

Le pouvoir conjugal et l'évitement des conflits chez les hommes.

Three hypotheses have been advanced to explain sex differences in withdraw behavior during conflictual marital interactions: the greater physiological reactivity of men during conflict situations, the differential socialization of men and women, and the differential power assigned to men and women. The main objective of this study was to examine the hypothesis that marital power is a good predictor of husbands' withdrawal. 132 couples completed a series of questionnaires, including the Marital Adjustment Test, a communication questionnaire, and 2 measures of marital power. Results show that marital adjustment predicted 44% of husbands' withdrawal, while marital power did not account for a significant proportion of the variance. These results are discussed in the light of the suggested hypotheses accounting for the differences in husbands and wives behavior during marital conflict. (PsycINFO Database Record (c) 2010 APA, all rights reserved)