Étude viscosimétrique de solutions de polyélectrolytes par dilution isoionique. Effet de la densité de charge sur la conformation du polyion

The reduced viscosity η_sp/c of dilute solutions of carboxymethylcelluloses (CMC) was studied, keeping the total ionic strength of the solution constant; the variation of η_sp/c with concentration is often linear and the Huggins constant k′ increases with decreasing ionic strength. So it is possible to obtain the intrinsic viscosity [η]_{I = 0} at zero ionic strength I and to calculate the corresponding molecular dimensions. The variation of [η]_{I = 0} with the degree of substitution of CMC is explained by a progressive change from a zig-zag conformation to a rod when the linear charge of the polyion increases.     

Adaptation de l’irradiation à l’activité tumorale en radiothérapie conformationnelle avec modulation d’intensité pour les cancers tête et cou. Étude préliminaire sur fantômes

The aim of this study was to index delivered doses of irradiation to tumor activity and not only to tumor geometry. The elaboration of a new highly precise treatment protocol, based on tumor activity required a specific configuration in order to use this type of irradiation. Using a Treatment Planning System and two head and neck phantoms specially created, we have performed system characterization according to different treatment plans. Two models were created and used: a simplistic and an anatomical model. Our results showed that high-precision radiotherapy in limited zones is possible with intensity modulated radiation therapy when several conditions are met such as location, number of organs at risk, distance between Planning Target Volume and organs at risk, presence, volume and location of the tumor activity, number of fields. In order to use this irradiation method adapted to the tumor activity, a precise geometry will be necessary. However such high total and fractionated doses should be carefully evaluated before being prescribed clinically.     

Étude par IRMf des processus phonologiques impliqués dans la lecture de mots et de pseudo-mots

The aim of the present study is to elaborate a paradigm associating methods of cognitive psychology and functional magnetic resonance imaging (fMRI) in order to assess anatomical regions of the two procedures of reading described in the dual route cognitive models (i.e., lexical and sublexical pathway). Elaboration of this paradigm allows, in one part, to identify the cerebral areas activated during the learning of reading and, in second part, to understand the origin of learning of reading deficits, such as the developmental dyslexia. In this order, 24 adults perform in reading task of words and pseudo-words and a naming pictures task using fMRI paradigm. Statistical analysis of pictures–words contrast have shown that activations were located in temporoparietal, frontal and occipital regions. Besides involving bilateral occipital cortex, the results of pseudo-words/words contrast indicate that the left inferior frontal gyrus is specially engaged in the graphophonological conversion processing. Than, our cerebral activation paradigm having being validated with adults, we used the very same with 12 dyslexic children and 12 good readers children having the same chronological age and 12 other children having the same lexical age. These data in course of analysis must help us to determine the cerebral areas activated during the learning of reading and investigate the cerebral dysfunctions in dyslexia..     

Étude de la polymérisation du styrène en émulsion inverse

The polymerization of reversed emulsions water in styrene prepared with polystyrene-polyethyleneoxide block copolymers (Cop PS-POE) has been studied. The kinetics of this polymerization has been studied as a function of the parameters: type and concentration of initiator, phase ratio water/styrene, concentration of Cop PS-POE, molecular characteristics of Cop PS-POE. The type of the emulsion can be regulated by the characteristics of the Cop PS-POE and by the phase ratio water/styrene. The initiation of the polymerizations can be achieved by water soluble initiators (K₂S₂O₈). Correlations could be established between the rate of polymerization and the initiator concentration, the amount of water in the reversed emulsions and the concentration of Cop PS-POE. It was shown furthermore that the rate of polymerization increases with the POE content of two-block copolymers and that three-block copolymers are more appropriate for the polymerization in reversed emulsions. Finally the main influence of the water/styrene interface was demonstrated which regulates the transfer of radicals from the aqueous into the organic phase.     

Étude de la stabilité à la lumière du poly(chlorure de vinyle) chloré

The light-stability of chlorinated poly(vinyl chloride) (PVCC) is investigated and the quantum yields of the major process involved are determined. By UV exposure, PVCC undergoes a fast dehydrochlorination process which develops ten times more efficiently than with poly(vinyl chloride) (PVC), leading to long chlorinated polyene sequences which are responsible for the rapid coloration of the irradiated polymer. Chain scission and crosslinking occur simultaneously, both in the presence and in the absence of oxygen, indicating that UV radiations are able to cleave the polymer chains. By reaction with polyenyl radicals, oxygen reduces slightly the efficiency of the dehydrochlorination, while promoting at the same time the formation of carbonyl and hydroperoxide groups in the polymer chain. The reasons of the high instability of PVCC against UV light are discussed and an overall reaction scheme is suggested to account for the various processes observed and their relative efficiencies.     

Analyse d’un incident de la chaîne transfusionnelle et gestion du retour d’expérience

Analysing adverse events is part of the medical practice in so far as the part it plays is outstanding in terms of feedback and improved healthcare safety. The integrated implementation of this practice is based on a four-dimensional system: strategic (corporate policies), cultural (safety-oriented cultural mindset), structural (dedicated organization and resources) and technical (methodologies and utilities). Two case studies illustrate the sequencing process from selecting the to-be-analyzed event down to figuring out the appropriate action plan. Beyond the visible and obvious origin, thanks to the implemented methods such as causal tree or ALARM method, far-fetched analysis elements and identified factors likely to explain events can be discovered. Comments on the role and terms of feedback are also hereto expressed.     

Évaluation sur un an de l’utilisation d’un dépôt de sang d’urgence vitale immédiate

ObjectivesEvaluation of a blood storage of six concentrates red blood cells of groupe O RH:-1KEL:-1 in a surgical emergency treatment center.Patients and methodsAll patients transfused with this concentrates; main points of utilisation are analysed.ConclusionThe concentrates, used by the anaesthesiologists, are part of the treatment strategy care in case of severe bleeding.     

Détection automatique des opacités dans les mammographies par la méthode de minimisation de la somme de l'inertie

In this paper a new algorithm for detection of suspicious mass area from mammographic images is presented. It uses histogram modification enhancement technique and a segmentation method based on minimization of inertia sum. The histogram modification filter is designed so as to be able to enhance disease patterns of suspected masses by cleaning up unrelated background clutters. Segmentation is then performed on the enhanced-image to localize the suspected mass areas using minimisation of inertia sum of images intensity classes. The proposed algorithm was tested on a database of 32 mammogramms provided by Gynaeco-obstetric and pediatric hospital of Yaoundé on which masses had previously been localised by experienced radiologists. Results show that the algorithm is able to identify masses in all cases presented with a sensibility of 94% approximately. In addition, we found out that sizes and edges of masses detected are similar to those marked by radiologists. Furthermore in some cases, we could detect some hidden masses that the radiologists were not able to mark out.     

Segmentation automatique d’échographies trans-abdominales de prostate pour le recalage d''images

This article presents a method for automatic segmentation of prostate from abdominal freehand ultrasound images. A statistical model of prostate is estimated from a manually delineated images. The segmentation starts by smoothing the image to enhance edges by applying a morphological and adaptive filter which detects individual speckles and remove them, while it preserves valuable details. Then the boundary is initialised starting from the model and the final form is estimated by a simulated annealing optimisation algorithm. The performances of the algorithm were compared with manual segmentation by an expert, the average distance was 3.7 pixels and an overlap surface of 93%.     

Évaluation des méthodes d’aide à la détermination du poids sec des patients hémodialysés par bio-impédance

We have measured extracellular (V_E) and total water (V_T) volumes in 17 dialysed patients for a total of 46 runs by impedance using a Xitron Hydra 4200 device and the bio-impedance spectroscopy method (BIS). These volumes were used to test two methods of patient dry weight determination by impedance, that of Chamney et al., based on Ve/W ratio and that of Lopot et al. Based on V_E /V_T ratio where W denotes body weight. We recommend the 2^nd method, but using a new equation that we have proposed for calculating V_T, which is more reliable than that of the Xitron.     

Étude cinétique de la polymérisation anionique du styrène en présence d'un contre-ion baryum

The anionic polymerization of styrene in tetrahydrofuran initiated by a bifunctional organo-barium derivative shows a remarkable property: for a given temperature the propagation rate does not depend on carbanion concentration in the range from 3.10^?5 to 5.10^?3 mol/l. This corresponds to a linear relationship between the rate constant of propagation k_p and the reciprocal of active sites concentration. The activation energy of propagation is equal to 4,1 kcal/mol (17,1±1,3 kJ/mol). Our experimental results were interpreted assuming that “living” polymer molecules form rings, their two anionic ends being associated through a divalent cation, and that they constitute aggregates with a “rosace” type structure. The validity of this assumption is supported by spectral and viscosimetric studies of living polymer solutions.     

Contribution à l'étude de la sorption de dioxanne-1,4 par un film amorphe de poly(téréphtalate d'éthylène glycol) et des modifications physiques du polymère engendrées par cette sorption, 1. Étude de la sorption du dioxanne-1,4 dans le polymère amorphe

The radiochemical methods used allow the study of the penetration of 1,4-dioxane into an amorphous poly(ethylene terephthalate), (PETP), film, by estimation of solvent uptake and penetration depth into the polymeric sample. They also contribute to the study of the desorption of the 1P-dioxane retained by the polymer under different drying conditions, or by exchange with another solvent, the sorption of which allows the characterization of the morphological changes which occurred during the drying of the 1,4-dioxane pretreated film. The kinetics of the liquid 1,4-dioxane sorption being very fast, a gravimetric study of 1,4-dioxane vapours sorption pointed out the plasticizing effect of this solvent as well as the existence of a reject phenomenon of solvent consequently to a crystallization induced by the plasticizing of the PETP. The 1,4-dioxane sorption is strongly exothermal and polymer-solvent interactions can occur involving the fixation of 1,4-dioxane into the polymer.     

Étude par spectroscopie ESR de la photodégradation de la poly(vinyl-2 pyridine) et des copolymères vinyl-2 pyridine/méthacrylate de méthyle

Irradiation of films of poly(2-vinylpyridine), (poly[1-(2-pyridyl)ethylene]), and poly(4-vinylpyridine), (poly[1-(4-pyridyl)ethylene]) at wavelengths λ > 300 nm gives rise to the corresponding vinylpyridinyl and azabenzyl radicals, the concentrations of which do not exceed 10¹⁵ spins/g. Introduction of naphthyl substituents into the polymer chain enhances appreciably the rate of radical formation from the copolymer. Irradiation at 254 nm of poly(methyl methacrylate), (PMMA) and its copolymers containing various amounts of 2-vinylpyridine monomeric units shows that the presence of pyridyl groups along the chain of PMMA reduces the rate of accumulation of radicals. This result is ascribed to the screening effect of pyridine. The photoprotection by the pyridyl ring is likewise observed in the phenanthrene sensitized photolysis at λ > 300 nm of the various 2-vinylpyridine/methyl methacrylate copolymers and its mechanism is discussed.     

Conception d’un système PC-compatible d’acquisition et de traitement des images en médecine nucléaire

We achieved a PC-compatible interface with a gamma-camera detection head. The objective was to propose a system that enabled the acquisition and the treatment of the signals emitted by the detection head by integrating some recent approaches and original solutions without making this product more expensive. This system is composed of two parts. The first block, which was for analog treatment, was conceived for the pulse shaping, the detection, and conversion of useful information. The second block, which was for digital treatment, was designed around a digital single processor (DSP) and was permitted to run the acquisition, to process the data (spectrometry, linearity and uniformity corrections, the event position calculation, etc.), and to communicate with a PC. On this PC-compatible interface, software was installed by allowing to fix the acquisition parameters, to choose the correction methods, to display, to process and to store the images. This system has properly insured the required task with performances comparable to the ones proposed by the constructors.     

Cristallisation du poly(oxyéthylène) dans des copolymères séquencés, 2. Étude de la structure et de la texture

The lamellar structure of a series of two-block poly(oxyethylene)/poly(ethyl methacrylate) and poly(oxyethylene)/polystyrene copolymers was studied by low-angle X-ray diffraction, as a function of the temperatures of crystallization and annealing. The thickness of the lamellae increases with temperature; the number of folds of the crystalline polymer chains varies, apparently, in a continuous way. The discontinuous increase of the thickness observed at 40°C in the annealing experiments was interpreted in terms of the glass transition temperature of the amorphous blocks. The spherulithic texture of the samples was examined by microscopy with polarized light.     

Étude de la microstructure de polyéthylènes de basse densité chlorés en solution et en suspension

High resolution NMR analysis of polyethylenes of low density chlorinated in suspension or in solution shows a fundamental difference of the microstructure between these two kinds of products. The products prepared in suspension with up to 65% chlorine can schematically be considered as semicrystalline copolymers with polyethylene-poly(vinyl chloride) sequences and beyond 65% chlorine as amorphous copolymers of vinyl chloride, 1,1-dichloroethylene, 1,2-dichloroethylene, and 1,2,3-trichloroethylene. The products prepared in solution are practically chlorinated statistically and become very quickly amorphous. At the beginning of their chlorination the formation of dichloromethylene groups dominates. At higher chlorine contents vinyl chloride sequences appear which become predominant at 60% chlorine. Beyond 60% chlorine 1,2-dichloroethylene units appear.     

Étude de la copolymérisation de monomères acryliques fluorés avec le méthacrylate de morpholinoéthyle

The copolymerization of 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl acrylate (AC8), methacrylate (MAC8) and α-acetoxyacrylate (αAC8) with morpholinoethyl methacrylate (MEMA) is presented. For these three systems, the values of the reactivity ratios (r_i) of both comonomers were determined by means of four methods (Jaacks, Macret, Fineman-Ross and Tidwell-Mortimer) usually used, and these results were compared. In each case, the copolymer obtained exhibits a structure with a higher content of the fluorinated base unit. A reactivity scale in the radical copolymerization with MEMA is proposed and shows that αAC8 and MAC8 are more reactive than AC8, contrary to their homopolymerization behaviour. An explanation of such a tendency was suggested taking into account the Q-e scheme of Alfrey and Price of hydrocarbon homologues.     

Évaluation par PIXE dans des coupes minces de la migration de certains éléments relargués par des implants métalliques

Migration evaluation in thin samples by PIXE of some metallic elements displaced from prosthesis.The metallic prosthesis used in orthopaedic surgery undergo degradations some years after their implantation. This phenomenon induces metallic element transfers in surrounding tissues. From an anatomical body, we have taken out implanted hip prosthesis and the surrounding tissues; we have determined the composition of the implanted prosthesis by spark spectrometry. Using a protocol adapted for each sample, we manufacture slides parallel to the femur axis. We determine the concentration of the displaced metallic elements versus depth. We have used the so-called PIXE method (Particle Induced X-rays Emission), based on the X-rays spectroscopy, to analyse our samples. The inducing particles were 3 MeV proton, the beam was 50 μm in diameter and had an intensity of 3 nA. Preliminary results show the migration of metallic elements from prosthesis to soft tissues.