ESO & NOT photometric monitoring of the Cloverleaf quasar

in Astronomy and Astrophysics. Supplement Series (1997), 126

The Cloverleaf quasar, H1413+117, has been photometrically monitored at ESO (La Silla, Chile) and with the NOT (La Palma, Spain) during the period 1987--1994. All good quality CCD frames have been ... [more ▼]

The Cloverleaf quasar, H1413+117, has been photometrically monitored at ESO (La Silla, Chile) and with the NOT (La Palma, Spain) during the period 1987--1994. All good quality CCD frames have been successfully analysed using two independent methods (i.e. an automatic image decomposition technique and an interactive CLEAN algorithm). The photometric results from the two methods are found to be very similar, and they show that the four lensed QSO images vary significantly in brightness (by up to 0.45 mag), nearly in parallel. The lightcurve of the $D$ component presents some slight departures from the general trend which are very likely caused by micro-lensing effects. Upper limits, at the 99% confidence level, of 150 days on the absolute value for the time delays between the photometric lightcurves of this quadruply imaged variable QSO, are derived. This is unfortunately too large to constrain the lens model but there is little doubt that a better sampling of the lightcurves should allow to accurately derive these time delays. Pending a direct detection of the lensing galaxy (position and redshift), this system thus constitutes another good candidate for a direct and independent determination of the Hubble parameter. Based on observations collected at the European Southern Observatory (La Silla, Chile) and with the Nordic Optical Telescope (La Palma, Spain). Table 1. Logbook for the ESO and NOT observations together with photometric results for the Cloverleaf quasar. This long table can be accessed on the WWW at the URL address: http://vela.astro.ulg.ac.be/grav_lens/glp_homepage.html} [less ▲]

Difunctional anionic initiator based on 1.3-diisopropenylbenzene. 5. Effect of polar additives and initiator seeding on the synthesis of poly(styrene-b-butadiene-b-styrene) copolymer

in Macromolecules (1997), 30(24), 7356-7362

The initiation of butadiene and styrene polymerization by a pure hydrocarbon soluble difunctional organolithium, 1,3-bis(1-lithio-1,3,3‘-trimethylbutyl)benzene, has been studied in a hydrocarbon solvent ... [more ▼]

The initiation of butadiene and styrene polymerization by a pure hydrocarbon soluble difunctional organolithium, 1,3-bis(1-lithio-1,3,3‘-trimethylbutyl)benzene, has been studied in a hydrocarbon solvent. The initiation occurs in such a way that part of the diadduct remains unreacted. When a second monomer feed along with tetrahydrofuran (THF) is added to the living chains, the residual diadduct is activated to the point where novel chains are formed. Weakly polar additives such as lithium alkoxides and aromatic ether can prevent part of the initiator from being inactive, although these additives are not effective enough to initiate the controlled synthesis of poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymers. The seeding of the initiator which consists of butadiene oligomerization in the presence of anisole and tBuOLi in cyclohexane, has proved to be very efficient in providing SBS containing 85% 1,4-microstructure polybutadiene (PBD) and with high mechanical properties, e.g., ultimate tensile strength higher than 30 MPa and elongation at a break of 1000%. [less ▲]

Spectroscopic analysis of the Alpha Centauri system

in Astronomy and Astrophysics (1997), 328

A detailed spectroscopic analysis of the two components of the binary system alpha Centauri has been carried out on the basis of extensive high resolution and high signal-to-noise spectra. The ... [more ▼]

A detailed spectroscopic analysis of the two components of the binary system alpha Centauri has been carried out on the basis of extensive high resolution and high signal-to-noise spectra. The temperatures of the stars have been determined from the Fei excitation equilibrium and checked from the H_alpha line wings. The abundances of 17 elements have been obtained and indicate a general overabundance of 0.24 dex relative to the Sun, with no significant difference between the two stars. All elements analysed, from CNO to the iron peak, show basically the same overabundance. Only nickel seems to be significantly more overabundant, while the neutron capture elements appear less enhanced. Based on observations carried out at the European Southern Observatory (La Silla, Chile) [less ▲]

Directional solidification by appropriate chemically active single crystal seed: An alternative way of generating large superconducting 123 single domain

in Journal of Materials Research (1997), 12(12), 3199-3202

A Dy2O3 single crystal has been used as a seed for the growth of isothermally melt-textured DY-123 material. The nucleation-controlled step has been observed to be related to the heterogeneous nucleation ... [more ▼]

A Dy2O3 single crystal has been used as a seed for the growth of isothermally melt-textured DY-123 material. The nucleation-controlled step has been observed to be related to the heterogeneous nucleation of 211 particles at the surface of the dysprosium oxide single crystal. The subsequent growth mode seems to be controlled by a high concentration gradient of dysprosium in the liquid phase. This leads to a directional solidification process of the 123 phase. The size of the 211 particles seems to decrease as the distance from the dysprosium oxide single crystal increases. [less ▲]

State-of-the-art of photorefractive holographic interferometry and potentialities for space applications

in Otrio, G. (Ed.) Proceedings of CNES International Conference on Space Optics '97 (1997, December)

Morphometric Study of the Equine Navicular Bone: Comparisons between Fore and Rear Limbs

in Zentralblatt für Veterinarmedizin. Reihe A (1997), 44(9-10), 579-94

Navicular bones collected from the four limbs of 95 sound horses were studied. The anatomic bases have been laid down about morphometry of the navicular bones and their variations according to limbs ... [more ▼]

Navicular bones collected from the four limbs of 95 sound horses were studied. The anatomic bases have been laid down about morphometry of the navicular bones and their variations according to limbs, after corrections have been made for morphologic type, gender, weight, size and age. All the dimensions of the navicular bone (except for the thickness) were larger in the fore limb. This phenomenon probably reflects an attempt to compensate for the greater forces exerted upon the fore limbs during exercise and at rest. Navicular bones collected from the four limbs of 61 sound horses were studied and the anatomic bases were described for histomorphometry of the fore and rear navicular bones. Fore navicular bones possess less cortical bone at the level of the articular surface, as well as at the level of the flexor surface and proximal border, but larger amounts of cancellous bone. Articular and flexor surface cortical bone show a larger porosity in the fore navicular bones and a larger amount of mineralized cartilage. The mineralized portion for distal impar- and collateral sesamoidean ligaments are also larger for the fore navicular bones. Two distinct zones are observed for the flexor surface cortex that have never been reported in the literature before: an external zone, which is mainly composed of poorly remodelled lamellar bone, arranged in a disto-proximal oblique direction, and an internal zone, which is mainly composed of secondary bone, with a latero-medial direction of Haversian canals. Bone architecture is discussed with regard to the mechanic load, encountered by the bone during locomotion. [less ▲]

Analyse d'un programme de formation-recherche destiné à favoriser un entrée positive dans la vie professionnelle des jeunes agrégés de l'enseignement secondaire supérieur

in Puzzle (1997), 3

Trouver une place quand tout change autour de soi (2ème partie)

Article for general public (1997)

La jeunesse contemporaine entre injonctions sociales et aspirations individuelles : quels repères pour les jeunes générations, entre repli intégriste et relativisme culturel ?

Anionic polymerization of methacrylate monomers initiated by lithium dialkylamides

in Journal of Polymer Science Part A-Polymer Chemistry (1997), 35(17), 3637-3544

The anionic polymerization of methacrylate monomers has been investigated with lithium dialkylamides as initiators in THF and toluene, respectively. Theoretical arguments and previous studies of mixed ... [more ▼]

The anionic polymerization of methacrylate monomers has been investigated with lithium dialkylamides as initiators in THF and toluene, respectively. Theoretical arguments and previous studies of mixed aggregates of lithiated organic compounds support the complexity of these systems. Lithium diisopropylamide (LDA) shows the highest initiation efficiency (e.g., f = 75% in THF at -78°C). Interestingly enough, lithium chloride has a remarkable beneficial effect on the methacrylates polymerization in THF at -78°C, due to the formation of 1 : 1 mixed dimer with LDA, which promotes a well-controlled anionic polymerization (Mw/Mn = 1.05) with a high initiation efficiency (94%). The less bulky lithium-diethylamide (LDEA) is much less efficient (f = 26%), essentially as a result of some associated dormant species and side reactions on the carbonyl group of MMA. Although various types of ligands have been screened, no remarkable improvement of LDEA efficiency has been observed. Lithium bis(trimethylsilyl)amide (LTMSA) has also been used to increase the steric hindrance of the initiator. This compound is, however, unable to initiate the methacrylates polymerization, more likely because of a too low basicity and a too strong Li - N bond. © 1997 John Wiley [less ▲]

Small-angle X-ray scattering and small-angle neutron scattering studies of liquid-crystalline halato(semi)telechelic polymers

in Journal of Applied Crystallography (1997), 30(6), 1075-1083

Model liquid-crystalline ionomers have been synthesized, which consist of low molecular weight (700-49000) linear ω- and α,ω-sodium sulfonate- and carboxylato-poly(styrenes or isoprenes) selectively end ... [more ▼]

Model liquid-crystalline ionomers have been synthesized, which consist of low molecular weight (700-49000) linear ω- and α,ω-sodium sulfonate- and carboxylato-poly(styrenes or isoprenes) selectively end-capped at one or both end(s) with an ionic mesogenic group. These compounds are referred to as liquid-crystalline halato(semi)telechelic polymers [LC H(S)TPs] A combination of small-angle X-ray scattering and small-angle neutron scattering studies on these LC H(S)TPs clearly shows the usual ionic peak related to interparticle interference between the ionic aggregates and a peak which can be related to the organization of a smectic mesophase. This mesogenic peak is generally masked by the foot of the broad ionic peak. The ionic peak Bragg spacing is much larger in the LC H(S)TP than in the H(S)TP precursor; This increased interaggregate distance results from the hindrance due to the mesogenic organization and from the restricted mobility experienced by the chains closely attached to the mesogen layers. As a rule, the lower the glass transition temperature of the polymeric matrix, the better the definition of the ionic peak, The ionic peak is well defined as long as the temperature is lower than the temperature of transition from solid to smectic phase (32.3 K). At higher temperatures, the ionic peak intensity decreases with increasing temperature. [less ▲]