Towards a Possibilistic Logic Handling of Preferences

The classical way of encoding preferences in decision theory is by means of utility or value functions. However agents are not always able to deliver such a function directly. In this paper, we relate three different ways of specifying preferences, namely by means of a set of particular types of constraints on the utility function, by means of an ordered set of prioritized goals expressed by logical propositions, and by means of an ordered set of subsets of possible choices reaching the same level of satisfaction. These different expression modes can be handled in a weighted logical setting, here the one of possibilistic logic. The aggregation of preferences pertaining to different criteria can then be handled by fusing sets of prioritized goals. Apart from a better expressivity, the benefits of a logical representation of preferences are to put them in a suitable format for reasoning purposes, or for modifying them.     

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     

Point mutation flanking a CTL epitope ablates in vitro and in vivo recognition of a full-length viral protein

CD8+ T cells (T(CD8+)) recognize viral Ags as short peptides (epitopes) displayed at the cell surface by MHC class I molecules. Using a panel of recombinant vaccinia viruses, we show that single-point mutations flanking either side of an H-2Kd-restricted epitope, residues 147-155, within full-length influenza nucleoprotein (NP) can impact, even ablate, presentation of that epitope, while having no effect on presentation of distal epitopes. The most severe blocking mutation (Ala to Pro at position 146) did not inhibit NP(147-155) presentation in the context of a truncated minigene, implying that this peptide is not a functional processing intermediate. An amino-terminal proline replacement also significantly reduced presentation of NP(50-57) (H-2Kk restricted), while the same mutation did not affect a third NP epitope. Thus, while trends in processing specificity may exist, the epitope itself contributes to flanking sequence effects. These findings were paralleled by in vivo priming experiments in which, depending on viral dose, subtle in vitro blocking effects were absolute. Proteasome/synthetic peptide coincubation studies support a role for enhanced epitope destruction in preventing presentation, as did the effect of the peptide aldehyde, LLnL, which restored presentation of NP(147-155) from the mutated constructs. This reagent did not inhibit epitope presentation, even from wild-type NP, suggesting that its production may be proteasome independent. These results support the notion that point mutation of epitope flanking sequence can serve as a mechanism for viral immune evasion, shed light on the mechanisms involved, and suggest that in vitro assays may not be sensitive indicators of flanking sequence effects.