Showing papers by "University of Montpellier published in 1976"

A comparative study of “gels” and oxide mixtures as starting materials for the nucleation and crystallization of silicate glasses

Abstract: Nucleation and crystallization behaviour of glasses in SiO2-La2O3, SiO2-La2O3-Al2O3 and SiO2-La2O3-ZrO2 systems were investigated using glasses prepared by the fusion of “gels” and the mixtures of oxides in solar/image furnace. Two methods for the preparation of multicomponent homogeneous non-crystalline products in the form of gels were developed. The phase separation, devitrification and micro-hardness of the above glasses were investigated in relation to the starting materials and the composition. The results show that the glasses made from gels are more homogeneous than those made from oxide mixtures. The phase separation characteristics of glasses made from gels are markedly different from those of glasses made from a mixture of oxides. The addition of Al2O3 to the binary SiO2-La2O3 glasses improves the homogeneity but reduces the micro-hardness and the devitrification tendency, whereas the addition of ZrO2 causes a considerable increase in micro-hardness and enhances the devitrification. The rates of nucleation and crystallization of glasses of different compositions made from gels are much higher than those made from the mixture of oxides. The formation of the high temperature crystal form, (Β-La2Si2O7 is more evident with the crystallization of gel-glasses. When the rate of nucleation is low, (in the case of glasses from the mixture of oxides), the curve representing the relation between the micro-hardness and the time of heat-treatment shows a distinct minimum, whereas this minimum is not obtained with the gel-glasses. With most of the gel-glasses, the micro-hardness rises very sharply with the length of heat-treatment. The curve showing the relation between the micro-hardness and the volume fraction of the dispersed crystalline phase also gives a distinct minimum which can be explained on the basis of the fracture mechanism consisting of the processes of crack nucleation and of crack propagation around the dispersed crystalline particles.

Regulation of Estrogen Receptors in Ovarian-Dependent Rat Mammary Tumors. I. Effects of Castration and Prolactin

Abstract: The ,ovarian-dependent- rat mammary umors, induced by 9,10 dimethyl-l,2-benzanthracene, were assayed for their estrogen receptor content by dextran-coated charcoal adsorption and sucrose gradient ultra-centrifugation. The estradiol receptors bound estrogens with a high affinity (KD =0.25 IIM), limited capacity and high specificity, and sediment at 8 S in a sucrose gradient. The cytosol receptors were transferred to the nucleus after binding to estrogens either in vivo or in vitro. The tumor area regressed by 70% during the first 10 days of castration while the concentration of estradiol cytosol receptors decreased from 225 to 16 fmoles/mg of protein. Three to five days afterin vivo administration of estradiol (2 µg daily) or prolactin (1 mg daily) the concentration of estrogen receptors was increased in spayed rats. In biopsy experiments, prolactin, but not estradiol, was shown to increase the estrogen receptor concentration when endogenous prolactin release was blocked by CB 154. Prolactin did not modify...

Radiometric age of early Hipparion fauna in North-west Africa

Abstract: A TUFF for which a 40Ar/39Ar date of 12.18±1.03 Myr has been obtained is located in the lower level of the Bou Hanifia continental formation (= Oued el Hammam), several metres below the famous Hipparion primigenium locality1–3. The tuff forms a continuous layer in the lower part of the continental formation and can be observed on either side of the Oued el Hammam Dam. The Hipparion fossiliferous horizon (Bou Hanifia I) lies in a second deposit of greatly weathered tuffs and has yielded a few micromammal remains. About 15 m above Bou Hanifia I, a second micromammal locality has been discovered (Bou Hanifia II)4.

Retinohypothalamic pathway in the duck (Anas platyrhynchos)

Abstract: Retinohypothalamic connections were studied in the duck after unilateral optic nerve transection using both light and electron microscopic techniques. Degenerated endings of optic fibers were found only in a circumscribed part of the anterior hypothalamic area, i.e. the ventral region of the contralateral suprachiasmatic nucleus. Images of degenerating boutons were observed in frozen sections (method according to Johnstone-Bowsher), and their presence confirmed by electron microscopic examination. These degenerating boutons make synaptic contacts with dendrites or dendritic spines of neurons of the suprachiasmatic nucleus.

The avian pineal organ. Distribution of exogenous indoleamines: A qualitative study of the rudimentary photoreceptor cells by electron microscopic radioautography

Abstract: The uptake of 5-hydroxytryptophan (3H-5-HTP) and serotonin (3H-5-HT) and their distribution have been demonstrated, at the ultrastructural level, in the secretory rudimentary photoreceptor cells (SRP cells), in the pineal organ of the parakeet and the duck. In vivo experiments. When the parakeets were injected with 3H-5-HTP alone or pretreated with drugs interfering with monoamine metabolism (e.g. R04-4602, nialamide) prior to injection of the label, the SRP cells always exhibited specific radioautographic reactions, in the regions of the dense secretory granules of the cell body and asynaptic pedicles. The labeling concentration varied quantitatively with time (interval between injection of the label and sacrifice) and drugs used. In vitro experiments. The uptake of 3H-5-HTP and 3H-5-HT in the pineal organ of the duck has also been studied, using an incubation procedure. The results with the two precursors confirmed those obtained “in vivo” with the parakeet. From these results it is suggested that the uptake of precursors in some compartments of SRP cells is qualitatively independent of: It is concluded that the SRP cell, an important step in the cytological and functional evolution of the pineal organ (Collin, 1969, 1971), is responsible for the synthesis of 5-HT. The metabolism of 5-HT seems also possible in such cells.

Light and electron microscopic evidence of hypothalamic afferences originating from the hippocampus in the pigeon

Abstract: Degenerating nervous fibres and synaptic boutons were demonstrated in the nuclei posterior medialis hypothalami after hippocampal lesions in the pigeon (light and electron microscopy).

A vestibulothalamic pathway: electrophysiological demonstration in the cat by localized cooling.

Abstract: Localized cooling was used in the search for vestibulothalamic pathways and a study was made of its effect on the activity of the thalamic neurons brought into action by stimulation of the vestibular nerve. Two cell populations were identified by their distinctive latencies in the ventral part of the posterior thalamus. Short latency responses were transmitted monosynaptically by means of a direct controlateral pathway whose course was identified. For long latency responses, the hypothesis of a polysynaptic path seems probable.

Sur les mesures différentielles de fonctions vectorielles et certains problèmes d'évolution

Abstract: Soient $X$, $Y$, $Z$ trois espaces de Banach, $\Phi: X \times Y \to Z$ bilineaire continue, $I$, intervalle reel, $x : I\to X$ et $y : I\to Y$ a variation localement bornee; on calcule la mesure differentielle de $t \mapsto \Phi( (x (t), y (t))$. Inegalites concernant le cas ou $\Phi : X \times X \to \mathbb R$ est symetrique et engendre une forme quadratique $\geqslant 0$. Application aux solutions continues a droite d'un processus de rafle.

The half-life of luteinizing hormone in intact and castrated quail during photoperiodic stimulation.

Abstract: In the Japanese quail (Coturnix coturnix japonica) the plasma concentration of luteinizing hormone (LH) depends on the physiological state of the animal. Low levels are found in sexually immature birds on short days (0.8 +/- 0.1 (n = 20) ng/ml) while after exposure to long days, sexually mature birds have a significantly higher LH level (4.4 +/- 0.4 (n = 20) ng/ml). Castration of long day males results in an even higher rise in LH concentration to 16.8 +/- 1.8 (n = 16) ng/ml. When the half-life (t1/2) of circulating LH was determined it was found to have two components: a fast t 1/2 of about 6 min and a slower component of either 20 min (determined by a radioisotope method), or 40 min (following hypophysectomy). No significant difference was observed in either of these components between birds in the three physiological states (short days, long days, castration plus long days). It would appear, therefore, that since the half-life of plasma LH remains constant, the difference in circulating LH observed under the various physiological conditions results solely from a change in the rate of LH secretion.

L' α-Glycérophosphate-déshydrogénase du moustique Culex pipiens: Génétique formelle, linkage et étude de populations

Abstract: THE α-CLYCEROPHOSPHATE-DEHYDROGENASE IN THE MOSOUITO CULEX PIPIENS: HEREDITY, LINKAGE AND POPULATION STUDIES. Culex pipiens α-glycerophosphate-dehydrogenase is coded by an autosomal locus which is shown to have a demonstrable activity in nymphs just prior to imago emergence and in adults of any age and sex. The α-Gpd locus has two codominant alleles, α-Gpd 1.00 and α-Gpd 1.30, and heterozygotes present three isozymes. The α-Gpd locus is localized on the same chromosomes as the two linked esterase loci Est-2 and Est-1, at 37.05 and 44.88 cross-over units, respectively, of these loci. Population studies seem to indicate that the α-Gpd locus has a low variability in Culex pipiens as in most other organisms.

Effects of local illumination of the hypothalamus on spontaneous and flash-induced multiunit activity recorded from the gonadotropic hypothalamic areas in quail.

Abstract: Multiple unit activity (MUA) was obtained from gonadotropic areas of the hypothalamus in quail. Pellets of radioluminous paint (RLP) were implanted unilaterally either in the nucleus tuberis or in the n. posterior medialis hypothalami. Control data were obtained from birds receiving nonluminous material (RP). Spontaneous MUA was decreased by 25% in gonadotropic arease in RLP-treated quail. Direct permanent photostimulation of hypothalamic neuronal population was not as effective in decreasing MUA as environmental photostimulation (50%). Activation in firing rates, which was constant in nonphotostimulated intact birds in response to repetitive flash-light stimulations, was completely suppressed after implantation of RLP.

A First Step Towards Zero Sound in Ionic Crystals

Abstract: Experimental studies of the ultrasonic absorption in crystals and its dependence on the frequency are important from the standpoint of further development of the theory of phonon-phonon interactions.