Mathieu Crickboom en Espagne

Conference (2000, August 25)

Small-angle neutron scattering studies of low-polarity telechelic ionomer solutions. 3. Temperature dependence of the ionic association

in Macromolecules (2000), 33(17), 6473-6484

The effect of temperature on the structure and single chain conformation of associating solutions of carboxy−telechelic polystyrene ionomers has been investigated in the dilute to semidilute concentration ... [more ▼]

The effect of temperature on the structure and single chain conformation of associating solutions of carboxy−telechelic polystyrene ionomers has been investigated in the dilute to semidilute concentration regime using the technique of small-angle neutron scattering. By applying different labeling methods, the temperature dependence of both the total scattering and single chain scattering functions was obtained independently. It was observed that temperature has a significant impact on the structure of the ionomer aggregates. Increasing temperature results in dissociation of the aggregated particles and the formation of smaller size multimers. Interestingly, the extent to which the multimers dissociate at a specific temperature compared to their initial state at room temperature is independent of concentration or ionic level, which indicates that it is independent of the degree of aggregation of particles. This leads to the conclusion that the apparent degree of aggregation can be controlled independently by concentration and temperature. For all systems studied the multimers formed through the ionic association keep an extended configuration over all the temperatures investigated. The Flory−Huggins polymer−solvent interaction parameter of the ionomer solutions showed only a slight decrease with increasing temperature. Despite the significant effect of temperature on the multimer structure, temperature was not observed to influence the single chain dimensions of the ionomer solutions. It was observed that the single chain dimensions remained unchanged over the range of variables studied. On the basis of these results, it is proposed that dissociation of the multimers takes place by disruption of the configuration of only a small number of bridging chains which connect different ionic clusters without influencing the main architecture of the associating structure. [less ▲]

Aggregates formed by amphoteric diblock copolymers in water

in Macromolecules (2000), 33(17), 6378-6387

The associating behavior of a series of monodisperse poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methacrylic acid) (PDMAEMA-b-PMAA) ampholytic diblock copolymers has been studied in water in the ... [more ▼]

The associating behavior of a series of monodisperse poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methacrylic acid) (PDMAEMA-b-PMAA) ampholytic diblock copolymers has been studied in water in the dilute regime as a function of pH and salt concentration. Dynamic light scattering (DLS) has been used to monitor the association behavior and transmission electron microscopy (TEM) to visualize the morphology of the aggregates. At and around the isoelectric point (IEP) of the ampholytic diblocks, strong electrostatic interactions occur and lead to the formation of insoluble complexes between negatively and positively charged blocks. These electrostatic interactions can be screened by the addition of salt, which leads to the partial dissolution of the material, according to Debye screening. For samples containing a major PDMAEMA block, spherical micelles are observed below the IEP. These micelles consist of a PMAA core surrounded by a water-soluble protonated PDMAEMA corona. At and above the IEP, these samples are insoluble. Spherical micelles are also formed below the IEP for samples containing a minor PDMAEMA block. These copolymers are insoluble at and around the IEP, whereas solubility is observed above the IEP with formation of aggregates of remarkable morphologies, including hollow spheres and complex compartmentalized aggregates. This aggregation is most favorable at high pH, and it cannot be accounted for only by electrostatic interaction between oppositely charged blocks. Indeed, short-range hydrophobic interaction between uncharged PDMAEMA blocks seems to play a key role in the association process. This is emphasized by quaternized poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methacrylic acid) ampholytic copolymers which are carrying a permanent positive charge on the aminated monomeric units and do not form these particular aggregates. [less ▲]

Synthesis of new hydrophilic γ-substituted poly-ε-caprolactones

Conference (2000, August 20)

Etude d'abondances dans un échantillon d'étoiles de métallicité intermédiaire entre le disque et le halo galactiques

Doctoral thesis (2000)

This work is devoted to the study of abundances in mildly metal-poor stars. We have selected 21 unevolved stars with one tenth of the solar metallicity and very similar atmospheric parameters. Such a ... [more ▼]

This work is devoted to the study of abundances in mildly metal-poor stars. We have selected 21 unevolved stars with one tenth of the solar metallicity and very similar atmospheric parameters. Such a homogeneous sample has allowed us to detect, at a given metallicity, the small abundance variations which are of cosmic origin, and especially those of the neutron capture elements. [less ▲]

New system for complexation of uranyl ions from liquid wastes of low-level activity: Polypyrrole doped with complexing polyanions

in Journal of Applied Polymer Science (2000), 77(6), 1230-1239

Polymer composites consisting of polypyrrole doped by uranyl complexing polyanions [i.e., poly(2-acrylamidoglycolic acid) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid)] were electrochemically ... [more ▼]

Polymer composites consisting of polypyrrole doped by uranyl complexing polyanions [i.e., poly(2-acrylamidoglycolic acid) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid)] were electrochemically synthesized. Bulk material and thin layers strongly adhering to inert supporting electrodes were prepared. These composites were used to precipitate uranyl ions from simulated radioactive wastes. Among different experimental techniques used for the analysis of uranium immobilized in the composites, the Rutherford backscattering of cu particles proved efficient in thin layers. Leaching tests confirmed the persistence of the uranium complexation in the solid composites. [less ▲]

Localization and Controls of Aromatase in the Quail Spinal Cord

in Journal of Comparative Neurology (The) (2000), 423(4), 552-64

In adult male and female Japanese quail, aromatase-immunoreactive cells were identified in the spinal dorsal horns from the upper cervical segments to the lower caudal area. These immunoreactive cells are ... [more ▼]

In adult male and female Japanese quail, aromatase-immunoreactive cells were identified in the spinal dorsal horns from the upper cervical segments to the lower caudal area. These immunoreactive cells are located mostly in laminae I-III, with additional sparse cells being present in the medial part of lamina V and, at the cervical level exclusively, in lamina X around the central canal. Radioenzyme assays based on the measurement of tritiated water release confirmed the presence of substantial levels of aromatase activity throughout the rostrocaudal extent of the spinal cord. Contrary to what is observed in the brain, this enzyme activity and the number of aromatase-immunoreactive cells in five representative segments of the spinal cord are not different in sexually mature males or females and are not influenced in males by castration with or without testosterone treatment. The aromatase activity and the numbers of aromatase-immunoreactive cells per section are higher at the brachial and thoracic levels than in the cervical and lumbar segments. These experiments demonstrate for the first time the presence of local estrogen production in the spinal cord of a higher vertebrate. This production was localized in the sensory fields of the dorsal horn, where estrogen receptors have been identified previously in several avian and mammalian species, suggesting an implication of aromatase in the modulation of sensory (particularly nociceptive) processes. [less ▲]

The European Large Area ISO Survey - I. Goals, definition and observations

in Monthly Notices of the Royal Astronomical Society (2000), 316

We describe the European Large Area ISO Survey (ELAIS). ELAIS was the largest single Open Time project conducted by ISO, mapping an area of 12deg[SUP]2[/SUP] at 15μm with ISOCAM and at 90μm with ISOPHOT ... [more ▼]

We describe the European Large Area ISO Survey (ELAIS). ELAIS was the largest single Open Time project conducted by ISO, mapping an area of 12deg[SUP]2[/SUP] at 15μm with ISOCAM and at 90μm with ISOPHOT. Secondary surveys in other ISO bands were undertaken by the ELAIS team within the fields of the primary survey, with 6deg[SUP]2[/SUP] being covered at 6.7μm and 1deg[SUP]2[/SUP] at 175μm. This paper discusses the goals of the project and the techniques employed in its construction, as well as presenting details of the observations carried out, the data from which are now in the public domain. We outline the ELAIS `preliminary analysis' which led to the detection of over 1000 sources from the 15 and 90-μm surveys (the majority selected at 15μm with a flux limit of ~3mJy), to be fed into a ground-based follow-up campaign, as well as a programme of photometric observations of detected sources using both ISOCAM and ISOPHOT. We detail how the ELAIS survey complements other ISO surveys in terms of depth and areal coverage, and show that the extensive multi-wavelength coverage of the ELAIS fields resulting from our concerted and on-going follow-up programme has made these regions amongst the best studied areas of their size in the entire sky, and, therefore, natural targets for future surveys. This paper accompanies the release of extremely reliable subsets of the `preliminary analysis' products. Subsequent papers in this series will give further details of our data reduction techniques, reliability and completeness estimates and present the 15- and 90-μm number counts from the `preliminary analysis', while a further series of papers will discuss in detail the results from the ELAIS `final analysis', as well as from the follow-up programme. [less ▲]

Exploring the gravitationally lensed system HE 1104-1805: near-IR spectroscopy

in Astronomy and Astrophysics (2000), 360

A new technique for the spatial deconvolution of spectra is applied to near-IR (0.95-2.50 mum) NTT/SOFI spectra of the lensed, radio-quiet quasar HE 1104-1805. The continuum of the lensing galaxy is ... [more ▼]

A new technique for the spatial deconvolution of spectra is applied to near-IR (0.95-2.50 mum) NTT/SOFI spectra of the lensed, radio-quiet quasar HE 1104-1805. The continuum of the lensing galaxy is revealed between 1.5 mum and 2.5 mum. Although the spectrum does not show strong emission features, it is used in combination with previous optical and IR photometry to infer a plausible redshift in the range 0.8 < z < 1.2. Modeling of the system shows that the lens is complex, probably composed of the red galaxy seen between the quasar images and a more extended component associated with a galaxy cluster with fairly low velocity dispersion (~ 575 km s[SUP]-1[/SUP]). Unless more constrains can be put on the mass distribution of the cluster, e.g. from deep X-ray observations, HE 1104-1805 will not be a good system to determine H[SUB]0[/SUB]. We stress that multiply imaged quasars with known time delays may prove more useful as tools for detecting dark mass in distant lenses than for determining cosmological parameters. The spectra of the two lensed images of the source are of great interest. They show no trace of reddening at the redshift of the lens nor at the redshift of the source. This supports the hypothesis of an elliptical lens. Additionally, the difference between the spectrum of the brightest component and that of a scaled version of the faintest component is a featureless continuum. Broad and narrow emission lines, including the FeII features, are perfectly subtracted. The very good quality of our spectrum makes it possible to fit precisely the optical Fe II feature, taking into account the underlying continuum over a wide wavelength range. HE 1104-1805 can be classified as a weak Fe II emitter. Finally, the slope of the continuum in the brightest image is steeper than the continuum in the faintest image and supports the finding by Wisotzki et al. (1993) that the brightest image is microlensed. This is particularly interesting in view of the new source reconstruction methods from multiwavelength photometric monitoring. While HE 1104- 1805 does not seem the best target for determining cosmological parameters, it is probably the second most interesting object after Q 2237+0305 (the Einstein cross), in terms of microlensing. Based on observations collected with the ESO New Technology Telescope (program 61.B-0413) [less ▲]

The Frequency of Plasmodesmata Increases Early in the Whole Shoot Apical Meristem of Sinapis Alba L. During Floral Transition

in Planta (2000), 211(3), 370-5

The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1 ... [more ▼]

The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to flower by exposure to a single long day. This increase is observed within all cell layers (L1, L2, L3) as well as at the interfaces between these layers, and it occurs in both the central and peripheral zones of the shoot apical meristem. The extra plasmodesmata are formed only transiently, from 28 to 48 h after the start of the long day, and acropetally since they are detectable in L3 4 h before they are seen in L1 and L2. These observations indicate that (i) in the Sinapis shoot apical meristem at floral transition, there is an unfolding of a single field with increased plasmodesmatal connectivity, and (ii) this event is an early effect of the arrival at this meristem of the floral stimulus of leaf origin. Since (i) the wave of increased frequency of plasmodesmata is 12 h later than the wave of increased mitotic frequency (A. Jacqmard et al. 1998, Plant cell proliferation and its regulation in growth and development, pp. 67 78; Wiley), and (ii) the increase in frequency of plasmodesmata is observed in all cell walls, including in walls not deriving from recent divisions (periclinal walls separating the cell layers), it is concluded that the extra plasmodesmata seen at floral transition do not arise in the forming cell plate during mitosis and are thus of secondary origin. [less ▲]